Active material, electrode material, electrode, secondary battery, battery pack, and method for recycling electrode

Abstract

To provide an active material, an electrode material, and an electrode capable of achieving a secondary battery excellent in rate performance, a secondary battery and a battery pack excellent in rate performance, and a recycling method of an electrode capable of improving a recycling rate of the electrode.SOLUTION: According to one embodiment, an active material including oxide particles containing a monoclinic niobium titanium oxide phase is provided. The X-ray diffraction spectrum includes a maximum peak P1 appearing in a range of 23.6 ° or more and 24.3 ° or less and a plurality of peaks appearing in a range of 25.8 ° or more and 26.6 ° or less. I2 / I4 is 5 or more and 26 or less when the peak intensities of three peaks having the largest peak intensity among the peaks appearing in the range of 25.8 ° or more and 26.6 ° or less are respectively I2, I3, and I4 in descending order.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to an active material, an electrode material, an electrode, a secondary battery, a battery pack, and a method for recycling an electrode. [Background technology]

[0002] Development of secondary batteries with electrodes containing niobium-titanium-containing oxide is underway. There is a demand for improving the high-current performance of secondary batteries. There is also a demand for increasing the recycle rate in the manufacturing process of secondary batteries, thereby reducing manufacturing costs. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-92417 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-348782 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-84321 [Patent Document 4] Special Publication No. 2022-545753 [Non-patent literature]

[0004] [Non-Patent Document 1] "Practice of Powder X-ray Analysis" First Edition (2002) Edited by the X-ray Analysis Research Forum of the Japan Society for Analytical Chemistry, edited by Izumi Nakai and Fujio Izumi (Asakura Shoten) [Non-patent document 2] Chem. Mater. 2022, 34, 10311-10319 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved is to provide an active material, an electrode material, and an electrode that can realize a secondary battery and a battery pack with excellent rate performance, a secondary battery and a battery pack with excellent rate performance, and an electrode recycling method that can improve the recycling rate of the electrodes. [Means for solving the problem]

[0006] According to an embodiment, an active material is provided that includes oxide particles containing a monoclinic niobium titanium oxide phase. The X-ray diffraction spectrum of the oxide particles includes a maximum peak P1 appearing in the range of 23.6° to 24.3° and multiple peaks appearing in the range of 25.8° to 26.6°. When the peak intensities of the three peaks with the highest peak intensities among the peaks appearing in the range of 25.8° to 26.6° are I2, I3, and I4, respectively, the ratio I2 / I4 is 5 to 26.

[0007] According to an embodiment, there is provided an electrode material comprising the above-mentioned active material, wherein the electrode material further comprises a carbon material on oxide particles.

[0008] According to an embodiment, an electrode including the above electrode material is provided.

[0009] According to an embodiment, there is provided a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode is the electrode described above.

[0010] According to an embodiment, a battery pack including the above secondary battery is provided.

[0011] According to an embodiment, a method for recycling electrodes is provided, comprising the steps of: heat-treating a target electrode comprising a first current collector and an active material-containing layer supported on the first current collector and containing an active material, a binder, and a conductor, to decompose the binder to obtain a heat-treated product; separating the first current collector from the heat-treated product to obtain a mixture containing the active material and the conductor; and manufacturing an electrode using the mixture. The active material includes monoclinic niobium titanium oxide. The target electrode is heat-treated at a temperature below the melting point of the first current collector in an environment with a lower oxygen concentration than air. [Brief explanation of the drawings]

[0012] [Figure 1] X-ray diffraction spectrum showing the reduction of TiNb2O7. [Figure 2] FIG. 2 is a plan view showing an example of an electrode according to the embodiment. [Figure 3] 3 is a cross-sectional view of the electrode shown in FIG. 2 taken along line III-III. [Figure 4] 4 is a cross-sectional view of the electrode shown in FIG. 2 taken along line IV-IV. [Figure 5] FIG. 1 is a partially cutaway perspective view showing an example of a battery according to an embodiment. [Figure 6] FIG. 6 is an enlarged cross-sectional view of part A in FIG. 5. [Figure 7] FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. [Figure 8] FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. [Figure 9] FIG. 9 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 8. [Figure 10] 1 is a flowchart showing an example of the flow of a recycling method according to an embodiment. [Figure 11] 10 is a flowchart showing another example of the flow of a recycling method according to the embodiment. [Figure 12] 1 is a flowchart showing an example of the flow of an electrode manufacturing method in a recycling method according to an embodiment. [Figure 13]FIG. 1 shows an example of measurement results obtained by evolved gas analysis-mass spectrometry (EGA-MS). [Figure 14] FIG. 1 is a diagram showing an example of measurement results by thermogravimetry (TG). [Figure 15] 3 is a flowchart showing an example of the flow of a battery manufacturing method according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) According to a first embodiment, an active material is provided. The active material includes oxide particles containing a monoclinic niobium titanium oxide phase. The X-ray diffraction spectrum of the oxide particles includes a peak P1 having the maximum intensity among peaks appearing in the range of 23.6° to 24.3° and multiple peaks appearing in the range of 25.8° to 26.6°. Among the multiple peaks appearing in the range of 25.8° to 26.6°, the three peaks with the highest peak intensities are designated as peaks P2, P3, and P4, respectively. The peak intensities of these peaks P2, P3, and P4 are designated as I2, I3, and I4, respectively, in descending order. In this active material, the I2 / I4 ratio is 5 to 26.

[0014] Furthermore, according to the first embodiment, an electrode material is provided. The electrode material includes the above-described active material and further includes a carbon material on oxide particles. The carbon material may be, for example, particulate, such as carbon black, attached to the surface of the oxide particles. Alternatively, the carbon material may be fibrous, such as carbon nanotubes, entangled on the surface of the oxide particles. The carbon material on the oxide particles can function as a conductor. Alternatively, the oxide particles and the carbon material may be integrated together.

[0015] Such active materials include oxide particles having a monoclinic niobium titanium oxide phase as the main phase. In a specific example of the active material, the main phase of the oxide particles is the TiNb2O7 phase. The oxide particles include, in addition to the TiNb2O7 phase, a phase formed by the reduction of TiNb2O7. In one example, this reduced phase can be TiNb2O6. When monoclinic niobium titanium oxide is reduced, defects (e.g., oxygen vacancies) occur and tetravalent Nb (Nb 4+ ) is formed, the conductivity is significantly increased. For example, TiNb2O6 exhibits higher conductivity than TiNb2O7. Therefore, oxide particles containing mainly the TiNb2O7 phase and TiNb2O6 have higher conductivity than oxide particles consisting purely of TiNb2O7, and can improve the rate performance of batteries containing the oxide particles as an active material. Note that TiNb2O6 may have, for example, a tetragonal crystal structure, more specifically, a rutile crystal structure.

[0016] In the spectrum of oxide particles measured by X-ray diffraction (XRD) using Cu-Kα radiation, the highest intensity peak P1 in the range of 23.6° to 24.3° appears in samples containing only unreduced monoclinic niobium titanium oxide (e.g., TiNb2O7), only reduced niobium titanium oxide (e.g., rutile TiNb2O6), and both. Among peaks P2, P3, and P4 appearing in the range of 25.8° to 26.6°, peaks P2 and P3 appear in samples containing only monoclinic niobium titanium oxide, only reduced niobium titanium oxide, and both. On the other hand, peak P4 is not seen in the spectrum of a sample containing only monoclinic niobium titanium oxide, but appears in samples containing at least a portion of reduced niobium titanium oxide. In other words, peak P4 is attributed to reduced niobium titanium oxide, such as TiNb2O6. Therefore, among the intensities of multiple peaks appearing in the range of 25.8° or more and 26.6° or less, the ratio I2 / I4 of the largest peak intensity I2 to the third largest peak intensity I4 is an index representing the content ratio of monoclinic niobium titanium oxide and reduced niobium titanium oxide in the oxide particle.

[0017] An active material having an I2 / I4 ratio of 5 or more and 26 or less contains an appropriate proportion of reduced niobium titanium oxide (e.g., rutile TiNb2O6) in oxide particles having a monoclinic niobium titanium oxide (e.g., TiNb2O7) as the main phase. Therefore, a battery containing this active material can exhibit excellent rate performance for the reasons described above, and can also exhibit excellent energy density derived from the monoclinic niobium titanium oxide. In an active material having an I2 / I4 ratio of less than 5, the proportion of monoclinic niobium titanium oxide is low, resulting in a reduced capacity. In an active material having an I2 / I4 ratio of more than 26, the amount of reduced niobium titanium oxide is low, so the conductivity does not increase significantly, and the effect of improving the rate performance described above cannot be expected.

[0018] Note that, for both the non-reduced monoclinic niobium titanate (such as TiNb2O7) and the reduced niobium titanate (such as rutile-type TiNb2O6), in the XRD spectrum obtained in the state of a single substance, the intensity I1 of peak P1 is smaller than the intensity I2 of peak P2, that is, I1 < I2. Therefore, for the oxide particles containing both phases, I1 < I2.

[0019] In addition to the particles of niobium titanate that are partially reduced and have improved conductivity as described above, the electrode material according to the embodiment contains a carbon material on the oxide particles. Since the carbon material functions as a conductor, it can exhibit further improved rate performance.

[0020] The above active material and electrode material can be manufactured as follows.

[0021] By mixing precursor particles containing non-reduced monoclinic niobium titanate (for example, TiNb2O7 particles) and a carbon material, and subjecting the obtained mixture to low-temperature firing under low-oxygen conditions, particles containing partially reduced niobium titanate can be obtained. In addition, at least a part of the carbon material can remain on the oxide particles after firing, and an electrode material containing the oxide particles and the carbon material thereon can be obtained.

[0022] For the precursor particles, particles containing at least monoclinic niobium titanate (for example, TiNb2O7) are used. As a specific example of the precursor particles, single-phase TiNb2O7 particles can be mentioned.

[0023] Examples of the monoclinic niobium titanate include unsubstituted monoclinic niobium-containing oxides such as TiNb2O7, and substituted niobium titanate composite oxides in which at least a part of Nb and / or Ti is substituted with a different element. Examples of the substitution element are Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, and Al, etc. The substituted niobium titanate composite oxide may contain one type of substitution element or may contain two or more types of substitution elements.

[0024] Examples of niobium titanium oxides with monoclinic structure include Nb2TiO7, Nb2Ti2O9, and Nb 10 Ti2O 29 , Nb 14 TiO 37 , Nb 24 TiO 62 Examples of monoclinic niobium titanium-containing oxides include 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. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. Another example of a monoclinic niobium titanium oxide is Li x Examples include TiNb2O7 (0≦x≦5).

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

[0026] The carbon material can be, for example, one or more selected from carbon fiber (e.g., vapor-grown carbon fiber (VGCF)), carbon nanotubes, carbon black such as acetylene black, and graphite. Carbon nanotubes tend to entangle with the surface of precursor particles. Carbon black such as acetylene black also tends to adhere to the surface of precursor particles. Therefore, carbon nanotubes and carbon black can increase the contact area with the precursor particles, and tend to remain on the oxide particles after calcination and become conductive.

[0027] The calcination is carried out under conditions with low oxygen content. More specifically, the calcination is carried out in an environment with an oxygen concentration lower than that of air. The term "air" used here refers to the dry air equivalent to that found at sea level, which has an oxygen concentration of approximately 21%. The calcination atmosphere may be, for example, an environment with an oxygen concentration of less than 19%. A practical approach is to place a mixture containing precursor particles and a carbon material in a container and at least partially cover the opening of the container to reduce the supply of external air. By calcining under conditions with a low air supply, the oxygen in the container is burned. This naturally reduces the oxygen concentration in the calcination environment.

[0028] The firing time can be, for example, 30 minutes to 2 hours. The firing temperature can be, for example, 300°C to 650°C. A heat treatment temperature in the range of 400°C to 450°C is more preferable. The higher the firing temperature, the more easily the reduction of the monoclinic niobium titanium oxide contained in the precursor particles progresses, and the intensity I4 of peak P4 in the XRD spectrum of the obtained active material tends to be greater.

[0029] By firing under low-oxygen conditions, the portions of the precursor particles in contact with the carbon material are reduced, thereby obtaining oxide particles containing unreduced monoclinic niobium titanium oxide as a main phase with reduced niobium titanium oxide distributed mainly on the particle surface, and an electrode material containing the oxide particles and a carbon material (conductor) thereon.

[0030] The reduction of precursor particles by calcination is shown in the XRD spectrum in Figure 1. Here, we show an example using TiNb2O7 particles as precursor particles. In the figure, the dotted line (Ref) shows the spectrum obtained by measuring uncalcined TiNb2O7, the dashed line (calcined at 450°C for 1 hour) shows the spectrum obtained by measuring oxide particles after calcining a mixture of TiNb2O7 and carbon material at 450°C for 1 hour, and the solid line (calcined at 650°C for 1 hour) shows the spectrum obtained by measuring oxide particles after calcining the mixture at 650°C for 1 hour.

[0031] As shown, for particles at all stages, peak P1 appears within the 23.6° ≤ 2θ ≤ 24.3° range, and at least two peaks appear within the 25.8° ≤ 2θ ≤ 26.6° range. For unsintered TiNb2O7, there were only two peaks within the 25.8° ≤ 2θ ≤ 26.6° range; therefore, the peak with the highest intensity was designated P2 and the peak with the lowest intensity was designated P3. For the samples sintered at 450°C and 650°C for 1 hour, respectively, three peaks appeared within the 25.8° ≤ 2θ ≤ 26.6° range, designated P2, P3, and P4 in descending order of intensity. The positions of peaks P2 and P3 for unsintered TiNb2O7 correspond to those of peaks P2 and P3 after sintering. Therefore, compared to the spectra after sintering, the spectrum for unsintered TiNb2O7 lacks peak P4.

[0032] As mentioned above, peak P4 is attributed to the reduced form of niobium titanium oxide. Therefore, peak P4 does not appear in the spectrum of unreduced, uncalcined TiNb2O7. Peak P4 (41) in the spectrum of oxide particles after sintering at 650°C for 1 hour has a higher intensity than peak P4 (42) in the spectrum after sintering at 450°C for 1 hour, indicating that reduction is promoted by increasing the sintering temperature. In both spectra, the intensity I1 of peak P1 is smaller than the intensity I2 of peak P2.

[0033] The following describes how to verify the active material. The crystalline structure and elemental composition of the active material can be confirmed by powder X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy. Of course, the presence or absence of the above-mentioned peaks P1 to P4 and their intensities I1 to I4 can be confirmed in the XRD spectrum.

[0034] First, when the electrode to be measured is incorporated in a battery, the electrode to be measured is taken out of the battery as follows. First, the battery incorporating the electrode is disassembled in a glove box filled with argon. The electrode to be measured is taken out from the disassembled battery. This electrode is washed with an appropriate solvent. As the solvent used for washing, for example, methyl ethyl carbonate can be used. The washed electrode is dried under vacuum.

[0035] Next, a composite material containing an active material is collected from the electrode. The electrode may have, for example, a current collector and an active material-containing layer supported on its surface. The active material-containing layer can be peeled off from the current collector to obtain a sample containing the active material. The active material-containing layer may be physically peeled off, but it is easier to peel off by applying ultrasonic waves in a solvent. When ultrasonic treatment is performed to peel off the active material-containing layer from the current collector, the electrode composite powder (including the active material and the conductive agent, or the electrode material containing the active material and the conductor, and the binder) can be recovered by volatilizing the solvent. If necessary, the peeled active material-containing layer is pulverized in a mortar or the like to obtain the electrode composite powder. Thus, a measurement sample containing the active material is obtained.

[0036] <XRD Measurement Method> The crystal structure of the active material can be determined, for example, as follows by powder X-ray diffraction measurement.

[0037] First, the active material is pulverized as necessary to prepare a sample with an average particle size of less than about 5 μm. The average particle size can be determined by the laser diffraction method. The obtained sample is filled into a holder portion with a depth of 0.2 mm formed on a glass sample plate. Next, another glass plate is pressed from the outside to flatten the surface of the filled sample. Care is taken to fill an appropriate amount of the sample so that no cracks, voids, unevenness, etc. occur in the filled sample. Also, pay attention to pressing the glass plate with sufficient pressure. Next, the glass plate filled with the sample is installed in a powder X-ray diffractometer, and an XRD pattern is obtained using Cu-Kα rays.

[0038] The measurement of the average particle diameter by the laser diffraction method is performed, for example, by the following method. The measurement of the average particle diameter is carried out using a laser diffraction type particle size distribution measuring device (Shimadzu SALD-300 manufactured by Shimadzu Corporation or a device having an equivalent function). After adding about 0.1 g of the sample, a surfactant, and 1 mL to 2 mL of distilled water to a beaker and sufficiently stirring, this is poured into a stirring water tank, the light intensity distribution is measured 64 times at intervals of 2 seconds, and the average particle diameter obtained from the obtained particle size distribution data is obtained.

[0039] The conditions for the above powder X-ray diffraction measurement are set to conditions under which an XRD pattern applicable to the Rietveld analysis can be obtained. Specifically, to collect data for the Rietveld analysis, the step width is set to 1 / 3 - 1 / 5 of the minimum half-value width of the diffraction peak, and the measurement time or X-ray intensity is appropriately adjusted so that the intensity at the peak position of the strongest reflection is 5000 cps or more. Specifically, for example, the following measurement conditions are used: measurement angle range: 2θ = 10° to 900°; sampling width: 0.0500°; scan speed: 2° / min. For example, the Rietveld analysis can be performed based on the method described in detail in Non-Patent Document 1 ("Practice of Powder X-ray Analysis" First Edition (2002), edited by the X-ray Analysis Research Symposium of the Japanese Society for Analytical Chemistry, edited by Izumi Nakai and Fujio Izumi (Asakura Shoten)).

[0040] By the above method, information regarding the crystal structure of the active material to be measured can be obtained. Furthermore, the crystallinity and symmetry of the crystal structure of the measurement target, such as monoclinic system, can be examined.

[0041] In the obtained XRD pattern, the XRD pattern is corrected so that the intensities at 2θ = 22° and 2θ = 28° match, and the peak intensity is measured in the corrected XRD pattern.

[0042] <ICP Method> The composition of the niobium-titanium-containing oxide phase in the active material can be analyzed using inductively coupled plasma atomic emission spectroscopy, for example, as follows. A powder containing the active material obtained by the procedure described above can be dissolved in acid to prepare a liquid sample containing the active material. The acid used in this analysis can be hydrochloric acid, nitric acid, sulfuric acid, hydrogen fluoride, or the like. By subjecting this liquid sample to ICP atomic emission spectroscopy, the components in the active material, such as the composition of the niobium-titanium oxide phase, can be determined.

[0043] The active material according to the first embodiment includes oxide particles containing a monoclinic niobium titanium oxide phase. Among the peaks appearing in the X-ray diffraction spectrum of the oxide particles within the angle range of 25.8° to 26.6°, the largest peak intensity I2 and the third largest peak intensity I4 satisfy the relationship 5≦I2 / I4≦26. This active material is used as an electrode material, for example, with a conductor containing a carbon material present on the oxide particles. This active material and electrode material can realize secondary batteries exhibiting excellent rate performance.

[0044] (Second embodiment) According to a second embodiment, an electrode is provided.

[0045] The electrode according to the second embodiment includes the active material according to the first embodiment. This electrode can be a battery electrode containing the active material according to the first embodiment as a battery active material. The electrode as a battery electrode can be, for example, a negative electrode containing the active material according to the first embodiment as a negative electrode active material.

[0046] Such an electrode may include a current collector and an active material-containing layer. The active material-containing layer may be formed on one or both sides of the current collector. The active material-containing layer may include an active material and, optionally, a conductive agent and a binder.

[0047] The active material-containing layer may contain a single active material according to the first embodiment, or may contain two or more types of active materials according to the first embodiment, or may contain a mixture of one or more types of active materials according to the first embodiment and one or more types of other active materials.

[0048] For example, when the active material according to the first embodiment is contained as a negative electrode active material, examples of other active materials include lithium titanate having a ramsdellite structure (e.g., Li 2+y Ti3O7, 0≦y≦3), lithium titanates with spinel structure (e.g., Li 4+x Ti5O 12 , 0≦x≦3), titanium dioxide (TiO2), anatase type titanium dioxide, rutile type titanium dioxide, niobium pentoxide (Nb2O5), hollandite type titanium composite oxide, and orthorhombic titanium composite oxide.

[0049] As an example of the above orthorhombic titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O 14+σ In this case, M I is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb and K. II is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+a Na2Ti6O 14 (0≦a≦6).

[0050] The conductive agent is blended to improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. One of these may be used as the conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surfaces of the active material particles may be coated with carbon or an electronically conductive inorganic material. Furthermore, in the electrode material described in the first embodiment, the carbon material (conductor) on the oxide particles can also be considered as the conductive agent.

[0051] The binder is blended to fill gaps between the dispersed active materials and to bind the active materials and the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. These may be used alone or in combination.

[0052] The blending ratios of the active material, conductive agent, and binder in the active material-containing layer can be appropriately changed depending on the application of the electrode. For example, when the electrode is used as the negative electrode of a secondary battery, the active material (negative electrode active material), conductive agent, and binder are preferably blended in proportions of 68% by mass to 96% by mass, 2% by mass to 30% by mass, and 2% by mass to 30% by mass, respectively. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the active material-containing layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient binding between the active material-containing layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amount of conductive agent and binder to 30% by mass or less, respectively, in order to achieve high capacity.

[0053] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and extracted from the active material. For example, when the active material is used as a negative electrode active material, the current collector is preferably made of copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

[0054] The current collector may also include a portion on the surface of which the negative electrode active material-containing layer is not formed, and this portion can function as a negative electrode current collecting tab.

[0055] Examples of electrodes are shown in Figures 2 to 4. In Figures 2 to 4, the long side direction of electrode 1 is the y-axis direction. The short side direction of electrode 1 is the x-axis direction. The thickness direction of electrode 1 is the z-axis direction. Electrode 1 includes current collector 2 and active material-containing layer 3 containing an active material, a binder, and a conductor. Current collector 2 is, for example, a conductive sheet-like material. The surfaces of the sheet-like material parallel to the xy plane are quadrangular. In Figure 2, it is rectangular. In Figures 2 to 4, active material-containing layer 3 is supported on two surfaces of current collector 2 parallel to the xy plane, but this is not limited thereto. For example, active material-containing layer 3 may be supported on only one surface of current collector 2 parallel to the xy plane. In Figures 2 to 4, active material-containing layer 3 is supported on both surfaces of current collector 2 except for both ends in the short side direction, but this is not limited thereto. The active material-containing layer 3 may be supported on both surfaces of the current collector 2 except for one end portion in the short side direction, or may be supported on the entire surfaces of both surfaces of the current collector 2. The portion of the current collector 2 on which the active material-containing layer 3 is not supported can function as a current collecting tab.

[0056] The electrode can be fabricated, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. The electrode material described in the first embodiment may be used instead of the active material or the active material and the conductive agent. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of an active material-containing layer and a current collector. After that, this laminate is pressed. In this manner, an electrode is fabricated.

[0057] Alternatively, the electrode may be fabricated by the following method. First, an active material, a conductive agent, and a binder are mixed to obtain a mixture. The electrode material described in the first embodiment may be used instead of the active material or the active material and the conductive agent. Next, this mixture is formed into pellets. These pellets are then placed on a current collector to obtain an electrode.

[0058] The electrode according to the second embodiment contains the active material or electrode material according to the first embodiment, and therefore, such an electrode can realize a secondary battery with excellent rate performance.

[0059] (Third embodiment) According to a third embodiment, a secondary battery including a negative electrode, a positive electrode, and an electrolyte is provided. This secondary battery includes, as the negative electrode, the electrode according to the second embodiment. That is, the secondary battery according to the third embodiment includes, as the negative electrode, an electrode including, as a battery active material, the active material according to the first embodiment, or an electrode including, as a negative electrode, the electrode material according to the first embodiment.

[0060] The secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, the positive electrode, and the separator may constitute an electrode assembly. The electrolyte may be held in the electrode assembly.

[0061] Moreover, such a secondary battery can further include an exterior member that houses the electrode group and the electrolyte.

[0062] Furthermore, such a secondary battery may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

[0063] Such a secondary battery may be, for example, a lithium secondary battery. The secondary battery also includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0064] The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal will be described in detail below.

[0065] 1) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode current collector and the negative electrode active material-containing layer may be the current collector and the active material-containing layer, respectively, that can be included in the electrode according to the second embodiment. The negative electrode active material-containing layer contains the active material according to the first embodiment as the negative electrode active material.

[0066] Details of the negative electrode that overlap with those described in the second embodiment will be omitted.

[0067] The density of the negative electrode active material-containing layer (excluding the current collector) is 1.8 g / cm 3 or more and 2.8 g / cm 3 or less, which is preferable. A negative electrode with the density of the negative electrode active material-containing layer within this range is excellent in energy density and electrolyte retention. The density of the negative electrode active material-containing layer is more preferably 2.1 g / cm 3 or more and 2.6 g / cm 3 or less.

[0068] The negative electrode can be manufactured, for example, by the same method as the electrode according to the second embodiment. Further, the negative electrode can also be manufactured by the recycling method of the electrode according to the sixth embodiment described later.

[0069] 2) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer can be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer can include a positive electrode active material, and optionally a conductive agent and a binder.

[0070] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain one kind of compound alone or a combination of two or more kinds of compounds as the positive electrode active material. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and desorbed.

[0071] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (for example, Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (for example, Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (for example, Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (for example, Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (for example, Lix Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), a lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), a lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≤ 1, Li x Fe 1-y Mn y PO4; 0 < x ≤ 1, 0 < y ≤ 1, Li x CoPO4; 0 < x ≤ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) is included.

[0072] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (e.g., Li x Mn2O4; 0 < x ≤ 1), lithium nickel composite oxides (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxides (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxides (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxides having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium manganese cobalt composite oxides (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; 0 < x ≤ 1), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-zCo y Mn z O2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1 are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0073] When a room-temperature molten salt is used as the electrolyte of the battery, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li x VPO4F (0 ≤ x ≤ 1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. Since these compounds have low reactivity with the room-temperature molten salt, the cycle life can be improved. Details of the room-temperature molten salt will be described later.

[0074] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle size of 1 μm or less can allow smooth solid-state diffusion of lithium ions.

[0075] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material with a specific surface area of 0.1 m 2 / g or more can sufficiently secure the Li-ion intercalation and deintercalation sites. A positive electrode active material with a specific surface area of 10 m 2 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0076] The binder is blended to fill gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0077] The conductive agent is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination as the conductive agent. The conductive agent may also be omitted.

[0078] In the positive electrode active material-containing layer, the positive electrode active material and the binder are preferably mixed in proportions of 80% by mass to 98% by mass and 2% by mass to 20% by mass, respectively.

[0079] By using a binder amount of 2% by mass or more, sufficient electrode strength can be obtained. Furthermore, the binder can function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

[0080] When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably mixed in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

[0081] By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.

[0082] The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0083] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0084] The positive electrode current collector may also include a portion on the surface of which the positive electrode active material-containing layer is not formed, and this portion can function as a positive electrode current collecting tab.

[0085] The positive electrode can be produced, for example, using a positive electrode active material by the same method as that for the electrode according to the second embodiment.

[0086] 3) Electrolytes The electrolyte may be, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte. The liquid nonaqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0087] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoride (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bistrifluoromethylsulfonylimide (LiN(CFSO)), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and LiPF is most preferred.

[0088] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or in combination.

[0089] The gel-like non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymeric material, such as polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0090] Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, and the like may be used as the nonaqueous electrolyte.

[0091] Room-temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C to 25°C). Room-temperature molten salts include those that exist as a liquid on their own, those that become liquid when mixed with an electrolyte salt, and those that become liquid when dissolved in an organic solvent, as well as mixtures of these. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or below. Furthermore, organic cations generally have a quaternary ammonium skeleton.

[0092] The solid polymer electrolyte is prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

[0093] The inorganic solid electrolyte is a solid substance that has Li-ion conductivity. Here, "having Li-ion conductivity" means that the Li-ion conductivity is 1×10 at 25°C. -6 This refers to a material that exhibits a lithium ion conductivity of 1000 S / cm or more. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows:

[0094] The oxide-based solid electrolyte has a NASICON (Sodium (Na) Super Ionic Conductor) type structure and is represented by the general formula Li 1+xIt is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. In the above general formula, Mα is, for example, one or more selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is within the range of 0≦x≦2.

[0095] 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; compounds represented by 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; compounds represented by Li 1+x Al x Ge 2-x (PO4)3 with 0≦x≦2; and compounds represented by Li 1+x Al x Zr 2-x (PO4)3 with 0≦x≦2; compounds represented by Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 where Mγ is one or more selected from the group consisting of Ti and Ge and 0<x≦2, 0≦y<3; compounds represented by Li 1+2x Zr 1-x Ca x (PO4)3 with 0≦x<1 can be mentioned.

[0096] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, there is also an amorphous LIPON compound represented by Li x PO y N z 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);La with garnet structure 5+x A x La 3-x MδO 12 A is at least one selected from the group consisting of Ca, Sr, and Ba, Mδ is at least one selected from the group consisting of Nb and Ta, and 0≦x≦0.5; Li3Mδ 2-x L2O 12 wherein Mδ is at least one 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 and 0≦x≦0.5; Li 5+x La3Mδ 2-x Zr x O 12 where Mδ is at least one selected from the group consisting of Nb and Ta, and 0≦x≦2. LLZ compounds (e.g., Li7La3Zr2O 12 ); and La 2 / 3-x Li x Examples include compounds represented by TiO3 where x is 0.3≦x≦0.7.

[0097] One or more of the above compounds can be used as the solid electrolyte, and two or more of the above solid electrolytes can also be used.

[0098] 4) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene, because these porous films melt at a certain temperature and can interrupt current.

[0099] 5) Exterior materials The exterior member may be, for example, a container made of a laminate film or a metal container.

[0100] The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[0101] The laminate film is a multilayer film containing multiple resin layers and metal layers interposed between the resin layers. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it by heat fusion.

[0102] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0103] The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably 100 mass ppm or less.

[0104] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected depending on the battery dimensions and the intended use of the battery.

[0105] 6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the Li absorption / desorption potential of the above-mentioned negative electrode active material and has electrical conductivity. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferably used as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0106] 7) Positive terminal The positive electrode terminal has a potential range of 3V to 4.5V relative to the redox potential of lithium (vs. Li / Li + ) and can be formed from a material that is electrically stable and conductive. Examples of materials for the positive electrode terminal include aluminum and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0107] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0108] Examples of secondary batteries are shown in Figures 5 and 6. Figure 5 is a partially cutaway perspective view showing a nonaqueous electrolyte secondary battery, which is an example of a secondary battery. Figure 6 is an enlarged cross-sectional view of part A of the nonaqueous electrolyte secondary battery shown in Figure 5. As shown in Figure 5, a nonaqueous electrolyte battery 20 includes a bottomed rectangular cylindrical metal container 21, a flat electrode group 22, a metal sealing plate 23, a negative electrode terminal 24, and a positive electrode terminal 25. The flat electrode group 22 is housed in the metal container 21.

[0109] The flat electrode group 22 includes a negative electrode 26, a positive electrode 27, and a separator 28. The electrode group 22 has a structure in which the negative electrode 26 and the positive electrode 27 are spirally wound with the separator 28 interposed therebetween to form a flat shape. Note that although a wound electrode group is described here, the electrode group may also be a stacked electrode group in which a plurality of negative electrodes 26, separators 28, and positive electrodes 27 are stacked. As shown in FIG. 6, the negative electrode 26 includes a negative electrode current collector 26a and a negative electrode active material-containing layer 26b supported on the negative electrode current collector 26a. As shown in FIG. 6, the positive electrode 27 includes a positive electrode current collector 27a and a positive electrode active material-containing layer 27b supported on the positive electrode current collector 27a. An electrolyte (not shown) is held in the electrode group 22. The opening of the metal container 21 is sealed with a metal sealing plate 23. The metal container 21 and the sealing plate 23 constitute an exterior member.

[0110] As shown in Fig. 6, a negative electrode terminal 24 is provided on the metal sealing plate 23. A negative electrode current collector tab 29 is electrically connected to the negative electrode terminal 24. The negative electrode current collector tab 29 is electrically connected to a negative electrode current collector 26a of the negative electrode 26. In addition, a positive electrode terminal 25 is fixed to the metal sealing plate 23 via an insulating member 30. A positive electrode current collector tab 31 is electrically connected to the positive electrode terminal 25. The positive electrode current collector tab 31 is electrically connected to a positive electrode current collector 27a of the positive electrode 27.

[0111] Such secondary batteries are suitable for use in applications requiring excellent cycle performance when drawing large current. Specifically, they are used as power sources for digital cameras, or as vehicle batteries or stationary batteries for, for example, two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, and railroad vehicles (e.g., electric trains). In particular, they are suitable for use as automotive batteries installed in vehicles.

[0112] The secondary battery according to the third embodiment contains in the negative electrode the active material or electrode material according to the first embodiment, and therefore, the secondary battery can exhibit excellent rate performance.

[0113] (Fourth embodiment) According to a fourth embodiment, there is provided a battery pack, which includes a plurality of secondary batteries according to the third embodiment.

[0114] In such a battery pack, the individual cells may be electrically connected in series or in parallel, or may be connected in a combination of series and parallel.

[0115] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0116] Fig. 7 is a perspective view schematically showing an example of a battery pack. The battery pack 200 shown in Fig. 7 includes five cells 100a to 100e, four bus bars 221, a positive electrode lead 222, and a negative electrode lead 223. Each of the five cells 100a to 100e is a secondary battery according to the third embodiment.

[0117] The bus bar 221 connects, for example, the negative terminal 24 of one cell 100a to the positive terminal 25 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four bus bars 221. That is, the battery pack 200 in FIG. 7 is a five-series battery pack. Although an example is not shown, in a battery pack including a plurality of cells electrically connected in parallel, the plurality of cells can be electrically connected by, for example, connecting the negative terminals of the cells together by a bus bar and connecting the positive terminals of the cells together by a bus bar.

[0118] The positive electrode terminal 25 of at least one of the five cells 100a to 100e is electrically connected to a positive electrode lead 222 for external connection. Also, the negative electrode terminal 24 of at least one of the five cells 100a to 100e is electrically connected to a negative electrode lead 223 for external connection.

[0119] The battery pack according to the fourth embodiment includes the secondary battery according to the third embodiment, and therefore can exhibit excellent rate performance.

[0120] (Fifth embodiment) According to a fifth embodiment, there is provided a battery pack. This battery pack includes the battery assembly according to the fourth embodiment. This battery pack may include a single secondary battery according to the third embodiment instead of the battery assembly according to the fourth embodiment.

[0121] Such a battery pack may further include a protection circuit. The protection circuit has a function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device 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.

[0122] The battery pack may further include external terminals for current flow. The external terminals for current flow are for outputting current from the secondary battery to the outside and / or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for current flow. When the battery pack is charged, charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminals for current flow.

[0123] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0124] Fig. 8 is an exploded perspective view schematically showing an example of a battery pack, and Fig. 9 is a block diagram showing an example of an electric circuit of the battery pack shown in Fig. 8.

[0125] The battery pack 300 shown in FIGS. 8 and 9 includes a container 310, a lid 320, a protective sheet 330, a battery pack 200, a printed wiring board 340, wiring 351, and an insulating plate (not shown).

[0126] 8 is a bottomed, square container having a rectangular bottom. The container 310 is configured to be able to accommodate a protective sheet 330, the battery pack 200, a printed wiring board 340, and wiring 351. The lid 320 has a rectangular shape. The lid 320 covers the container 310 to accommodate the battery pack 200 and other components. Although not shown, the container 310 and the lid 320 are provided with openings or connection terminals for connection to external devices and the like.

[0127] The battery pack 200 includes a plurality of cells 100 , a positive electrode lead 222 , a negative electrode lead 223 , and an adhesive tape 240 .

[0128] At least one of the plurality of cells 100 is a secondary battery according to the third embodiment. The plurality of cells 100 are electrically connected in series as shown in FIG. 9. The plurality of cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the plurality of cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0129] The adhesive tape 240 fastens the plurality of cells 100 together. Heat-shrinkable tape may be used to secure the plurality of cells 100 together instead of the adhesive tape 240. In this case, protective sheets 330 are placed on both side surfaces of the battery pack 200, and the heat-shrinkable tape is wrapped around the cells 100, and the heat-shrinkable tape is then thermally shrunk to bind the plurality of cells 100 together.

[0130] One end of the positive electrode lead 222 is connected to the battery pack 200. One end of the positive electrode lead 222 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 223 is connected to the battery pack 200. One end of the negative electrode lead 223 is electrically connected to the negative electrode of one or more cells 100.

[0131] The printed wiring board 340 is installed along one of the shorter sides of the inner surface of the container 310. The printed wiring board 340 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for supplying current, a positive wiring (positive wiring) 348a, and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 340 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 340 and the battery pack 200.

[0132] The other end 222a of the positive electrode lead 222 is electrically connected to the positive electrode connector 342. The other end 223a of the negative electrode lead 223 is electrically connected to the negative electrode connector 343.

[0133] The thermistor 345 is fixed to one main surface of the printed wiring board 340. The thermistor 345 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 346.

[0134] The external terminals 350 for applying current are fixed to the other main surface of the printed wiring board 340. The external terminals 350 for applying current are electrically connected to devices located outside the battery pack 300. The external terminals 350 for applying current include a positive terminal 352 and a negative terminal 353.

[0135] The protection circuit 346 is fixed to the other main surface of the printed wiring board 340. The protection circuit 346 is connected to the positive terminal 352 via a positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via a negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via a wiring 343a. The protection circuit 346 is also electrically connected to each of the plurality of single cells 100 via wiring 351.

[0136] The protective sheet 330 is disposed on both inner surfaces of the long sides of the container 310 and on the inner surface of the short side that faces the printed wiring board 340 across the battery pack 200. The protective sheet 330 is made of, for example, resin or rubber.

[0137] The protection circuit 346 controls charging and discharging of the plurality of cells 100. Furthermore, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to an external device, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from each cell 100 or the battery pack 200.

[0138] An example of the detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of the cell 100 is equal to or higher than a predetermined temperature. An example of the detection signal transmitted from each cell 100 or the battery pack 200 is a signal indicating that overcharge, overdischarge, or overcurrent of the cell 100 is detected. When detecting overcharge or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

[0139] The protection circuit 346 may be a circuit included in a device (such as an electronic device or an automobile) that uses the battery pack 300 as a power source.

[0140] As described above, the battery pack 300 is also provided with the external terminals 350 for current application. Therefore, the battery pack 300 can output current from the battery assembly 200 to an external device and input current from the external device to the battery assembly 200 via the external terminals 350 for current application. In other words, when the battery pack 300 is used as a power source, the current from the battery assembly 200 is supplied to the external device via the external terminals 350 for current application. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 via the external terminals 350 for current application. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as the charging current from the external device.

[0141] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 340 and the wiring 351 may be omitted. In this case, the positive electrode lead 222 and the negative electrode lead 223 may be used as the positive terminal 352 and the negative terminal 353, respectively, of the external terminal 350 for supplying current.

[0142] Such a battery pack is used in applications requiring excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

[0143] The battery pack according to the fifth embodiment includes the secondary battery according to the third embodiment or the battery pack according to the fourth embodiment, and therefore, the battery pack can exhibit excellent rate performance.

[0144] (Sixth embodiment) According to a sixth embodiment, a method for recycling electrodes is provided. The electrode recycling method according to the sixth embodiment will be described below with reference to the drawings. In the sixth embodiment, a new electrode is produced using a target electrode. The target electrode includes a first current collector and an active material-containing layer supported on (or formed on) the first current collector and containing an active material, a binder, and a conductor. The target electrode does not retain an electrolyte. The target electrode is, for example, a discarded electrode that may be generated during the electrode or battery manufacturing process. The target electrode is also called a waste material or a discarded electrode. One example of a target electrode is an off-spec electrode that may be generated during the electrode or battery manufacturing process. Another example of a target electrode is an electrode that has been stored unused. Another example of a target electrode is an electrode fragment such as a scrap resulting from cutting. When the target electrode is a discarded electrode generated during the manufacturing process, the composition of the active material-containing layer is usually known. Furthermore, since the target electrode is unused, e.g., has not been charged or discharged, the active material is hardly degraded. Therefore, by using the active material and conductor separated from the target electrode, it is possible to easily regenerate an electrode having an active material-containing layer having the same composition as the active material-containing layer of the target electrode.

[0145] 10 to 12 are flow charts showing a method according to the sixth embodiment. An electrode recycling method I, which is one example of the method according to the sixth embodiment, includes, for example, steps S1 to S3 shown in Fig. 10. Each step will be described below.

[0146] <Process S1> The binder is thermally decomposed from the target electrode by heat treatment to obtain a heat-treated product.

[0147] The target electrode may have a structure similar to that of the electrode according to the second embodiment. The target electrode includes at least monoclinic niobium titanium oxide as an active material. An example of the target electrode may have a structure similar to that of the electrode described with reference to FIGS. 2 to 4. Here, the current collector included in the target electrode is referred to as a first current collector.

[0148] When the target electrode is heat-treated at a temperature below the melting point of the first current collector, the first current collector is heat-treated but not melted, and can maintain almost its original state (e.g., shape) before the heat treatment. As a result, it becomes easy to separate the heat-treated first current collector from the entire heat-treated product. One example of heat treatment is calcination. For calcination, a furnace or the like can be used as a heat treatment means. Therefore, calcination allows for a simple heat treatment method.

[0149] The first current collector may be electrically conductive. An example of the first current collector is the current collector described in the second embodiment. Therefore, the first current collector may contain at least one of aluminum and an aluminum alloy. The melting point of the first current collector containing at least one of aluminum and an aluminum alloy may be around 660°C. The temperature below the melting point of the first current collector may be set to, for example, 660°C or lower, preferably below 660°C.

[0150] The conductor is not particularly limited, but may include a carbon material. When a conductor containing a carbon material is used, decomposition (thermal decomposition) of the conductor can be suppressed by setting the heat treatment temperature to 660°C or less. By suppressing the loss of the conductor, the conductive paths between the active materials in the regenerated electrode can be maintained. Examples of carbon materials include carbon fiber (e.g., vapor-grown carbon fiber (VGCF)), carbon nanotubes, carbon black such as acetylene black, and graphite. One of these may be used as the conductor, or two or more may be combined. The conductor may exist independently of the active material or may be supported on the surface of the active material particles. A conductor containing carbon nanotubes easily entangles with the surface of the active material particles. Furthermore, a conductor containing carbon black such as acetylene black easily adheres to the surface of the active material particles. A conductor containing at least one of carbon nanotubes and carbon black can increase the contact area with the active material particles. Therefore, it is easy to maintain a good conductive path between the active material particles in the regenerated electrode.

[0151] The heat treatment temperature can be set to be at least 20°C lower than the melting point of the first current collector. This further suppresses melting of the first current collector. It also suppresses loss of the conductor due to heat. The heat treatment temperature can be set to, for example, 640°C or lower, more preferably below 640°C.

[0152] The decomposition of the binder may be, for example, thermal decomposition. The decomposition (thermal decomposition) of the binder may occur in at least a portion of the binder contained in the target electrode. This is because partial decomposition of the binder can reduce the binding strength between the active material or conductor and the first current collector. This facilitates the separation of the active material and conductor from the first current collector. To promote the decomposition reaction of the binder, the lower limit of the heat treatment temperature can be set to the decomposition temperature of the binder or higher. Here, when multiple types of binders are used, it is desirable to set the maximum decomposition temperature (or the higher decomposition temperature in the case of two types) as the lower limit of the heat treatment temperature. The decomposition temperature of the binder will be described in detail later. The binder is not particularly limited, but may include an organic substance. The binder is preferably a hydrophilic binder that is water-soluble or water-dispersible, such as an emulsion. The hydrophilic binder may be an organic hydrophilic binder. Examples of organic hydrophilic binders include polyacrylic acid compounds, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and salts of CMC. These may be used alone or in combination.

[0153] The heat treatment temperature can be, for example, 300°C or higher and 650°C or lower. By setting the heat treatment temperature to 300°C or higher, the decomposition reaction of the binder can be promoted. Furthermore, by setting the heat treatment temperature to 650°C or lower, melting of the first current collector can be suppressed. Furthermore, loss of the conductor can be suppressed. A heat treatment temperature in the range of 400°C or higher and 450°C or lower is more preferable.

[0154] The atmosphere in which the heat treatment is performed is an oxygen-poor environment. More specifically, the heat treatment is performed in an environment with an oxygen concentration lower than that of air. Here, air refers to the same as the dry air in the atmosphere at sea level, which has an oxygen concentration of approximately 21%. The atmosphere in which the heat treatment is performed can be, for example, an environment with an oxygen concentration of less than 19%. A practical approach is to place the target electrode in a container and at least partially cover the opening of the container to reduce the supply of outside air. By performing the heat treatment with a reduced air supply, the oxygen in the container is consumed (combusted). This naturally reduces the oxygen concentration in the atmosphere in which the target electrode is placed.

[0155] The heat treatment time is adjusted depending on the heat treatment temperature, the composition of the target electrode, and other factors. For example, the heat treatment time can be 30 minutes or more and 2 hours or less. The heat treatment temperature and time can be set so that the organic components contained in the target electrode are reduced by 10% to 90% of their total weight. The target electrode does not contain an electrolyte. Examples of organic components include carbon materials as conductors and organic substances as binders. By setting the weight of the organic components reduced by the heat treatment to 10% or more of the total weight of the organic components, the amount of decomposition of the binder is sufficient, making it easy to separate the first current collector from the active material and conductor. By setting the weight of the organic components reduced by the heat treatment to 90% or less of the total weight of the organic components, loss of conductors due to the heat treatment can be suppressed.

[0156] The active material is, for example, a lithium ion (Li + ) is capable of absorbing and releasing. An example of the active material is an active material that does not substantially contain Li. The active material that does not substantially contain Li is, for example, an active material that does not contain Li, or an active material that does not contain Li at the time of synthesis but contains lithium ions (Li +Examples of such active materials include those in which Li remains due to the absorption / desorption reaction of Li or the irreversible reaction that occurs during charge / discharge reactions. Active materials that are substantially free of Li can suppress the reaction that would produce lithium carbonate (Li2CO3) by reacting with moisture in the atmosphere, for example. This can prevent the active material from deteriorating when the target electrode is heat-treated in air.

[0157] The active material includes at least monoclinic niobium titanium oxide (e.g., TiNb2O7). The active material may be the active material according to the first embodiment, but the active material included in the target electrode is not limited to the active material according to the first embodiment. The target electrode includes at least monoclinic niobium titanium oxide as the active material, and may further include other active materials.

[0158] Examples of monoclinic niobium titanium oxides include unsubstituted monoclinic niobium titanium-containing oxides such as TiNbO, and substituted niobium titanium composite oxides in which at least a portion of Nb and / or Ti is substituted with a different element. Examples of the substituting 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 substituting element, or may contain two or more types of substituting elements.

[0159] Monoclinic niobium titanium-containing oxides are characterized by high stability of the crystal structure, excellent resistance to water, acid and alkali, and high density. Examples of monoclinic niobium titanium-containing oxides include Nb2TiO7, Nb2Ti2O9, and Nb 10 Ti2O 29 , Nb 14 TiO 37 , Nb 24 TiO 62 Examples of monoclinic niobium titanium-containing oxides include Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δHere, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. Another example of a monoclinic niobium titanium oxide is Li x Examples include Nb2TiO7 (0≦x≦5). x The density of Nb2TiO7 (0≦x≦5) is 4.34g / cm 3 is.

[0160] Another example of a monoclinic niobium-titanium-containing oxide is Li x Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

[0161] Examples of other active materials include silicon, carbonaceous materials, and oxides. Each material can absorb and release lithium ions. Each material may also be an active material that is substantially free of lithium.

[0162] Examples of carbonaceous materials include graphite, carbon fiber, coke, and non-graphitizable carbon.

[0163] Examples of the oxide include titanium-containing oxides and niobium-containing oxides. Examples of the titanium-containing oxide include lithium titanium oxide, monoclinic titanium dioxide (TiO2(B)), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, and orthorhombic titanium composite oxide. Examples of the niobium-containing oxide include niobium oxide, niobium-tungsten-containing oxide, and niobium-titanium-molybdenum-containing oxide.

[0164] Niobium-containing oxides may have lower electronic conductivity than carbonaceous materials. By adding a conductor to the mixture obtained in step S2 together with the active material containing the niobium-containing oxide, it becomes easier to maintain contact between the active material and the conductor in the regenerated electrode. Therefore, an electrode with good electronic conductivity can be regenerated.

[0165] Examples of niobium oxides include Nb2O5.

[0166] Examples of niobium-tungsten-containing oxides include Nb 14 W3O 44 , Nb 16 W5O 55 ,Nb 18 W8O 69 Examples include:

[0167] Examples of niobium titanium molybdenum-containing oxides include those represented by the general formula Li a Ti b Nb 2-2d Mo c+2d O 2b+5+3c (wherein the subscripts a, b, c, and d are preferably within the ranges of 0≦a≦b+4+3c, 0.3≦b≦1.6, 0.3≦c<1.6, and 0≦d<0.4, respectively), and a tetragonal titanium-niobium-molybdenum composite oxide represented by the general formula Li a M b NbMo c O d where M is one or more selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y, and Si, and includes composite oxides satisfying 0≦a≦b+2+3c, 0≦b≦1.4, 0≦c≦0.5, and 2.33≦d / (1+b+c)≦2.50.

[0168] The niobium titanium-containing oxide may contain unavoidable impurities, examples of which include K, Na, Si, and P.

[0169] <Process S2> The first current collector is separated from the heat-treated product to obtain a mixture containing the active material and the conductor.

[0170] In the heat-treated product obtained in step S1, at least a portion of the binder has disappeared due to decomposition. Furthermore, although the first current collector has been heat-treated, melting has been suppressed, and the current collector is not a molten product. The conductor and active material have been heat-treated. Furthermore, at least a portion of the active material is in contact with the conductor. In the heat-treated product, the bonding strength of the conductor and active material to the first current collector has decreased, allowing the first current collector to be easily separated from the conductor and active material.

[0171] Separation can be performed by peeling, lifting, suction, centrifugation, sieving, or the like, of the heat-treated first current collector from the heat-treated product. The heat-treated product may be crushed or subjected to ultrasonic vibration before separation, but this is not necessary. The heat-treated first current collector can be easily separated from the heat-treated product without crushing or subjecting the heat-treated product to ultrasonic vibration. This prevents damage such as impact to the active material and conductor. Furthermore, the heat-treated first current collector can be maintained at approximately its original size without being crushed, allowing for easy removal of the heat-treated first current collector.

[0172] <Process S3> The mixture containing the active material and the conductor is used to manufacture the electrode.

[0173] The active material and the conductor are heat-treated at a temperature below the melting point of the first current collector, which reduces the effects of the heat treatment. The active material and the conductor are contained in the mixture, which makes it easier to maintain conductive paths between the active materials in an electrode manufactured using the mixture, thereby suppressing active material degradation and improving battery performance.

[0174] When the conductor contains a carbon material, the carbon material content of the mixture can be 0.1% by mass or more and 10% by mass or less. By setting the carbon material content of the mixture to 0.1% by mass or more, an electrode with a good conductive path between the active materials can be obtained. Furthermore, by setting the carbon material content of the mixture to 10% by mass or less, an electrode with a practical capacity can be obtained.

[0175] In addition, because the heat treatment is performed under low-oxygen conditions, when the conductor contains a carbon material, the monoclinic niobium titanium oxide contained in the active material is reduced by the carbon material. That is, the heat treatment conditions match the firing conditions in the production of the active material described in the first embodiment. Therefore, an electrode containing the active material according to the first embodiment and having excellent rate performance can be obtained.

[0176] The mixture is allowed to contain a binder to the extent that it does not interfere with the separation in step S2.

[0177] As another example of the method of the sixth embodiment, an electrode recycling method II comprising the steps described below will be described with reference to Fig. 11. The electrode recycling method II comprises steps S1 to S3 in the electrode recycling method I described with reference to Fig. 10. The electrode recycling method II comprises the following steps after step S2: a step of measuring the content of the conductor in the mixture obtained in step S2 (hereinafter referred to as step S2A); A step of determining the composition of the electrode to be manufactured based on the content of the conductor (hereinafter referred to as step S2B).

[0178] In electrode recycling method II, step S2B is followed by step S3, which is a step (referred to as step S3A) of producing an electrode having the determined composition using the mixture.

[0179] Next, steps S2A and S2B will be described in detail.

[0180] <Process S2A> The content of the conductor in the mixture obtained in step S2 is measured.

[0181] Details of the method for measuring the conductor content of the mixture will be described later. Monoclinic niobium titanium oxide and other niobium-containing oxides have higher thermal stability than conductors containing carbon materials. Therefore, when a niobium-containing oxide is used as the active material, the conductor is more affected by the heat treatment than the active material. By measuring the conductor content of the mixture and comparing the measured value with the composition of the active material-containing layer of the electrode to be recycled, the amount of composition change due to the heat treatment can be determined.

[0182] The mixture may contain a binder to the extent that the separation in step S2 is not hindered.

[0183] <Process S2B> The composition of the electrode to be manufactured, specifically the composition of the active material-containing layer of the electrode to be manufactured, is determined based on the content of the conductor in the mixture. An example of the determination method is described below. The content of the conductor in the mixture is compared with the content (initial content) of the conductor in the active material-containing layer of the electrode to be recycled. If, as a result of the comparison, for example, the content of the conductor in the mixture is approximately equal to the initial content, the amount of active material can also be considered to be approximately the same as the initial value. The composition of the active material-containing layer of the electrode to be manufactured is determined based on the comparison result. In the slurry preparation in step S11 described below, other components other than the active material and conductor (e.g., binder), and at least one of the active material and conductor, as necessary, are added to the mixture to achieve the determined composition.

[0184] In the determined composition, the carbon material content of the mixture is preferably 0.1% by mass or more and 10% by mass or less. By setting the carbon material content of the mixture to 0.1% by mass or more and 10% by mass or less, it is possible to ensure a practical capacity while improving the conductive paths between the active materials.

[0185] <Process S3A> An electrode having the determined composition is fabricated using the mixture.

[0186] The electrode recycling method II described above includes a step of measuring the conductor content of the mixture and a step of determining the composition of the electrode to be produced based on the conductor content. As a result, the variation in the composition of the produced electrodes can be reduced, thereby ensuring the stability of the quality of the recycled electrodes.

[0187] The electrode can be manufactured (step S3 of recycling method I and step S3A of recycling method II) by a method including steps S11 to S15 illustrated in Fig. 12. Steps S11 to S15 will be described below.

[0188] <Process S11> A slurry is prepared using the mixture containing the active material and the conductor obtained in step S2. The amounts of the active material and the conductor remain almost unchanged from their initial values ​​even after step S2. Therefore, the amounts of the active material and the conductor in the mixture can be estimated based on the composition of the active material-containing layer of the target electrode. A binder and a solvent are added to the mixture containing the active material and the conductor to achieve the target composition. If necessary, an active material and / or a conductor may be added. After the addition, these are mixed to prepare a slurry. An example of the solvent is water. The composition of the slurry may be the same as or different from the composition of the active material-containing layer of the target electrode. For example, the type of binder in the slurry may be different from the type of binder contained in the target electrode.

[0189] Alternatively, the slurry may be prepared by measuring the amounts of the active material and conductor in the mixture, adding the active material, conductor, binder, and solvent to the mixture based on the measured amounts, and mixing them.

[0190] Before preparing the slurry, the mixture containing the active material and the conductor may be pulverized, which allows the particle size of the mixture to be set within a desired range.

[0191] <Process S12> The slurry is applied to a second current collector.

[0192] The coating is performed on at least a portion of the second current collector. For example, the slurry can be coated on one or both main surfaces of the second current collector. The main surface of the second current collector is, for example, a surface that defines the thickness of the second current collector or a surface that intersects with the thickness direction of the second current collector.

[0193] The second current collector may be the first current collector separated from the target electrode, or may be an unused current collector, or may be a current collector different from the first current collector.

[0194] <Process S13> The coated slurry is dried to form an active material-containing layer on the second current collector. The active material, conductor, and binder in the active material-containing layer may be mixed in proportions of 68% by mass to 96% by mass, 2% by mass to 30% by mass, and 2% by mass to 30% by mass, respectively, for example.

[0195] <Process S14> The second current collector carrying the active material-containing layer is pressed to obtain an electrode. The electrode may be cut as shown in step S15 to obtain a predetermined shape or size.

[0196] The active material and conductor are mixed once during the production of the target electrode, so the surface properties (hydrophilicity, hydrophobicity, etc.) are maintained stably. As a result, the newly produced electrode has strong adhesion between the active material-containing layer and the second current collector, and also has excellent charge / discharge efficiency.

[0197] <Process S15> The electrode is cut to set it to a predetermined shape or size. If the electrode after pressing has the desired shape or size, step S15 can be omitted.

[0198] The manufactured electrode may have a structure similar to that of the electrode according to the second embodiment. The manufactured electrode may also have a structure similar to that of the target electrode. The details of the structure are as described with reference to FIGS. 2 to 4.

[0199] Note that instead of steps S11 to S15, the following method may be performed. To a mixture containing an active material and a conductor, an active material, a conductor, and a binder are added so as to achieve a target composition, and these are mixed. Next, the resulting mixture is formed into pellets. Thereafter, the pellets may be placed on a current collector to obtain an electrode.

[0200] Hereinafter, a method for measuring the decomposition temperature of the binder, thermogravimetry, a method for measuring the content of the conductor in the mixture, and a method for confirming the positive and negative electrode active materials will be described.

[0201] First, if the electrode to be measured (positive electrode or negative electrode) is incorporated in a battery, the electrode to be measured is removed from the battery in the same manner as described in the first embodiment, thus obtaining a measurement electrode.

[0202] <Method for measuring the decomposition temperature of the binder> The decomposition temperature of the binder is measured, for example, by evolved gas analysis (EGA-MS). Evolved gas analysis measures the temperature profile of gas evolved from a sample. Detection is performed by mass spectrometry (MS). Approximately 1 mg of the active material-containing layer (electrode composite) of the measurement electrode extracted by the above method is weighed into a sample cup for EGA-MS analysis. The measurement is performed, for example, at a temperature rise rate of 10°C / min. The measurement conditions are described in detail below.

[0203] For the pyrolyzer, the heating temperature is maintained at 40°C for 4 minutes, and then the temperature is increased to 600°C at a rate of 10°C / min. The sample weight is approximately 1 mg.

[0204] For GC (gas chromatography), the injection port temperature was 300°C, and the column was an Ultra Alloy DTM 2.5 m 0.15 mm id. The temperature was maintained at 300°C. The split ratio was 1:50. The He flow rate was 1.0 mL / min. For MS, the mass range was 10-600 m / z. The ionization method was EI (EI stands for electron impact or electron ionization).

[0205] An example of the measurement results is shown in FIG. 13. The horizontal axis in FIG. 13 is temperature. The vertical axis is the intensity (arbitrary units) of the obtained mass ions. In the case of FIG. 13, there is a peak in the range of 350°C to 450°C. Therefore, it can be said that the decomposition temperature of the binder is approximately 350°C to 450°C. In the case of FIG. 13, the temperature at which the peak shows maximum intensity is approximately 420°C. By setting the heat treatment temperature (e.g., the firing temperature) in step S1 to the temperature at which the peak shows maximum intensity (e.g., approximately 420°C), it is possible to promote the decomposition of the binder. As a result, it is possible to almost completely eliminate the binder.

[0206] <Qualitative analysis of binder> The organic components contained in the target electrode can be identified by pyrolysis-gas chromatography-mass spectrometry (Pyro-GC-MS). Pyrolysis-gas chromatography-mass spectrometry is a flash pyrolysis method in which a sample is thermally decomposed at a set pyrolysis temperature, and the flash pyrolyzed material is then analyzed by gas chromatography-mass spectrometry (GC-MS). The analysis conditions are described below.

[0207] Approximately 1 mg of the active material-containing layer (electrode mixture) of the measurement electrode is weighed out and placed in a sample cup for EGA-MS analysis. <Pyrolyzer> The heating temperature is set to 400°C to 700°C. The sample amount is approximately 1 mg. <gc> The injection port temperature is set to 300°C. The column used is a UA-5 (HT / MS) 30 m, 0.25 mm id. The temperature is maintained at 40°C for 2 minutes, and then increased to 320°C at a rate of 10°C / min. The split ratio is 1:50. The He flow rate is set to 1.0 mL / min. The mass range is 10 m / z to 600 m / z. The ionization method is EI (EI stands for Electron Impact or Electron Ionization).

[0208] <Thermogravimetry: Method for measuring the content of conductors in a mixture> The relationship between the heat treatment temperature and the weight loss of the organic components during heat treatment of the target electrode, as well as the content of the conductor in the mixture, can be measured, for example, by thermogravimetry (TG). The thermogravimetric analysis conditions are as follows: Air is used at a flow rate of 100 mL / min. The temperature is increased from 40°C to 900°C at a rate of 10°C / min. An example of the thermogravimetric analysis results is shown in Figure 14. The horizontal axis in Figure 14 represents time (minutes) corresponding to the heat treatment temperature. The vertical axis represents weight (mg). First, the active material-containing layer of the target electrode is heated from 40°C to approximately 900°C, and the weight of the total organic components is calculated from the weight obtained when all the organic materials contained in the target electrode are decomposed. The weight of the total organic components obtained is considered to be the weight of the carbon material acting as the conductor. Furthermore, the active material-containing layer of the target electrode is maintained at 40°C for the first 5 minutes, as shown in Figure 14. The temperature is then increased from 40°C to 450°C at a rate of 10°C / min. The temperature increase takes 47 minutes. After holding the electrode at 450°C for 33 minutes, weight loss is observed, as shown in Figure 14. The weight loss from 47 to 80 minutes is approximately 0.05 mg. If the total amount of organic components is 0.5 mg, the weight loss of the organic components due to the heat treatment at 450°C accounts for 10% of the total weight. Therefore, by subjecting the target electrode to heat treatment at 450°C for 33 minutes, an amount equivalent to 10% by weight of the organic components contained in the target electrode can be eliminated through decomposition.

[0209] The measurement object described with reference to Figure 14 is a target electrode. Instead of the target electrode, the mixture obtained in step S2 is heated to 900°C under the above-mentioned conditions, and the weight loss is measured to obtain the weight of the carbon material as a conductor contained in the mixture. The content of the conductor in the mixture is calculated from the obtained weight and the weight of the entire mixture.

[0210] <Cathode active material> The crystal structure and elemental composition of the positive electrode active material can be confirmed by powder X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy.

[0211] <Negative electrode active material> The crystal structure and elemental composition of the negative electrode active material can be confirmed by powder X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy.

[0212] Whether or not the mixture obtained in step S2 contains a conductor can be confirmed, for example, by the following method. First, the mixture is pulverized to prepare a sample having an average particle size of less than about 5 μm. The average particle size can be determined by laser diffraction. The conditions for the laser diffraction method are as described in the first embodiment. An XRD pattern is obtained for the obtained sample under the conditions described above.

[0213] The electrode recycling method of the sixth embodiment described above includes the steps of: heat-treating a target electrode, which includes a first current collector and an active material-containing layer containing an active material containing monoclinic niobium titanium oxide, a binder, and a conductor, at a temperature below the melting point of the first current collector in an environment with a lower oxygen concentration than air to decompose the binder and obtain a heat-treated product; separating the first current collector from the heat-treated product to obtain a mixture containing the active material and the conductor; and manufacturing an electrode using the mixture. According to the method of the embodiment, the binder in the target electrode can be reduced by decomposition, making it easy to separate the first current collector from the heat-treated product without pulverizing it. Furthermore, since the mixture obtained by separation contains a conductor, a newly manufactured electrode using the mixture can easily form a conductive path between the active material, thereby suppressing degradation of the active material and improving electrode performance. Furthermore, using electrodes discarded during the manufacturing process as the target electrode can increase the recycling rate during the manufacturing process. In addition, the heat treatment in the step of obtaining a heat-treated product included in this recycling method corresponds to the firing in the active material manufacturing method described in the first embodiment, and therefore the active material contained in the newly manufactured electrode corresponds to the active material according to the first embodiment, so that an electrode that can realize a secondary battery with excellent rate performance can be obtained.

[0214] (Seventh embodiment) The seventh embodiment is a method for manufacturing a battery using the electrode manufactured in the sixth embodiment. The seventh embodiment includes manufacturing an electrode by the method of the sixth embodiment, manufacturing an electrode assembly including the manufactured electrode as a negative electrode, housing the electrode assembly in a housing member, holding an electrolyte in the electrode assembly housed in the housing member, and sealing the housing member. The electrode assembly can include a positive electrode in addition to a negative electrode. The electrode assembly may also include a separator.

[0215] FIG. 15 is a flowchart illustrating an example of the flow of the battery manufacturing method according to the seventh embodiment. First, a waste electrode 11 is prepared as a target electrode. The waste electrode 11 may be, for example, a non-standard electrode, an electrode stored unused, or an electrode fragment such as a scrap resulting from cutting. The waste electrode 11 may also be an electrode removed from a non-filled waste battery 12 that may be generated during the battery manufacturing process. The non-filled waste battery 12 is a battery that contains necessary components such as electrodes in a container but has not been filled with electrolyte due to reasons such as being non-standard. An example of a method for removing the waste electrode 11 from a battery will be described later. In either case, the waste electrode 11 does not retain any electrolyte. The composition of the active material-containing layer of the waste electrode 11 is known. Furthermore, because the waste electrode 11 has not been charged or discharged, there is little deterioration of the active material. Rather, an active material with improved conductivity equivalent to that of the active material according to the first embodiment can be obtained. Therefore, by using the active material and conductor separated from the waste electrode 11, it is possible to easily obtain an electrode that can realize a battery that exhibits better rate performance than a battery using an electrode having an active material-containing layer with the same composition as the active material-containing layer of the waste electrode 11.

[0216] A mixture containing an active material and a conductor is obtained from waste electrodes 11 through steps S1 and S2. Details of steps S1 and S2 are as described in the sixth embodiment. Steps S2A and S2B may be performed after steps S1 and S2. Details of steps S2A and S2B are as described in the sixth embodiment.

[0217] Next, the electrode is manufactured according to step S3 or step S3 A. The electrode is manufactured according to steps S3 and S3 A, for example, according to steps S11 to S15, respectively.

[0218] First, dispersion is performed in step S11, that is, a slurry is prepared using the mixture. Details of step S11 are as described in the sixth embodiment.

[0219] Next, the electrodes are manufactured by carrying out the coating, drying, pressing and cutting steps S12 to S15 in this order. The details of steps S12 to S15 are as explained in the sixth embodiment.

[0220] Next, as the assembly step S21, after manufacturing an electrode group including the manufactured electrode as a negative electrode, the electrode group is housed in an exterior member. The electrode group is manufactured, for example, by providing a separator between a positive electrode and a negative electrode. The shape of the electrode group is not particularly limited, and for example, those in which a positive electrode, a separator, and a negative electrode are laminated, those in which a positive electrode, a separator, and a negative electrode are wound in a flat or cylindrical shape, those in which a positive electrode, a separator, and a negative electrode are folded into a ninety-nine shape, etc. can be used.

[0221] Subsequently, as the electrolyte injection step S22, after allowing the electrode group housed in the exterior member to hold an electrolyte, the exterior member is sealed.

[0222] Thereafter, as the processing step S23 for productization, initial charging, aging, etc. are performed to obtain a battery.

[0223] Examples of the positive electrode, separator, electrolyte, and exterior member used in the above steps will be described. In addition to the following examples, for example, corresponding members and materials described in the third embodiment can be used instead or in combination.

[0224] <Positive electrode> The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer carried on one side (one main surface) or both surfaces of the current collector and containing a positive electrode active material. The positive electrode active material-containing layer contains a positive electrode active material. The positive electrode active material-containing layer may contain a binder, a conductor, or both.

[0225] 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 (e.g., LixNi 1-a Co a O2, 0 < x ≦ 1, 0 < a ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2, 0 < x ≦ 1), lithium nickel manganese cobalt composite oxide (e.g., 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 (e.g., Li x Mn 1-a Co a O2, 0 < x ≦ 1, 0 < a < 1), spinel - type lithium manganese nickel composite oxide (e.g., Li x Mn 2-a Ni a O4, 0 < x ≦ 1, 0 < a < 2), iron fluoride 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.

[0226] The positive electrode active material - containing layer may contain a conductor. Examples of the conductor include acetylene black, carbon black, graphite, etc. The type of the conductor can be one type or two or more types.

[0227] The positive electrode active material-containing layer may contain a binder. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, and acrylic materials. The type of binder may be one or more types.

[0228] The positive electrode current collector may contain at least one of aluminum and an aluminum alloy, and may be, for example, an aluminum foil or an aluminum alloy foil.

[0229] The compounding ratio of the positive electrode active material, conductor, and binder is preferably in the range of 80% to 95% by mass of the positive electrode active material, 3% to 19% by mass of the conductor, and 1% to 7% by mass of the binder.

[0230] The positive electrode can be produced, for example, by suspending a positive electrode active material, a conductor, and a binder in a suitable solvent, applying the suspension to a positive electrode current collector, drying, and pressing. Alternatively, the positive electrode can be produced by the following method: First, the active material, the conductor, and the binder are mixed to obtain a mixture. Then, the mixture is formed into pellets. Then, the pellets are placed on a current collector to obtain an electrode.

[0231] <separator> The separator may be, for example, a porous film, a nonwoven fabric made of synthetic resin, or a solid electrolyte layer.

[0232] <Electrolytes> The electrolyte may be, for example, an aqueous electrolyte or a non-aqueous electrolyte. Examples of non-aqueous electrolytes include non-aqueous electrolyte solutions prepared by dissolving an electrolyte salt such as a lithium salt in an organic solvent. Examples of aqueous electrolytes include aqueous electrolyte solutions prepared by dissolving an electrolyte salt such as a lithium salt in an aqueous solvent. Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoride (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bistrifluoromethylsulfonylimide (LiN(CFSO)).

[0233] <Exterior materials> The exterior member may be, for example, a container made of a laminate film or a metal container. Details of the exterior member are the same as those described in the third embodiment, so detailed description will be omitted.

[0234] The battery manufactured according to the embodiment is not particularly limited. Examples of the battery include a battery with an aqueous electrolyte and a battery with a non-aqueous electrolyte. The battery may be a single battery (single cell), a battery pack, or a battery pack.

[0235] Here, an example of a method for removing electrodes from the non-injected waste battery 12 will be described. The non-injected waste battery 12 is, for example, a substandard battery that may be generated before the injection step S22 in battery manufacturing. First, the exterior member is separated from the non-injected waste battery 12. Next, the positive electrode and negative electrode contained in the battery from which the exterior member has been removed are separated. Each step will be described in detail below.

[0236] <Exterior separation> The non-injected waste battery 12 is disassembled to separate the exterior member. The exterior separation may be performed using an exterior separation device.

[0237] The exterior separation device may be housed in a chamber together with the positive and negative electrode separation device. The chamber is preferably in a low-oxygen atmosphere, such as a nitrogen atmosphere. This prevents the electrolyte and other components from coming into contact with air when the battery is disassembled, thereby improving work safety. The exterior separation device is used to open the battery's exterior member by cutting it, for example, and remove the electrode group inside the exterior member. For example, a cutter, a cutting machine, or a cutter can be used as the exterior separation device. The electrode group is removed from the battery by separating the exterior. Next, the positive and negative electrodes contained in the electrode group are separated.

[0238] <Positive and negative electrode separation> The positive electrode and the negative electrode included in the electrode group are separated. The positive electrode and the negative electrode may be separated using a positive / negative electrode separator.

[0239] The positive and negative electrode separator is used to separate the electrode assembly into a positive electrode, a separator, and a negative electrode. The electrode assembly can be obtained as a stack in which positive and negative electrodes are stacked with a separator between them (i.e., positive electrode, separator, negative electrode, separator, positive electrode), or as a wound assembly in which a positive electrode, a separator, and a negative electrode are wound. For example, in the case of an electrode assembly using a continuous separator, a device having a separator winding mechanism is used as the positive and negative electrode separator. In this way, the positive and negative electrodes can be separated on the front and back sides of the separator. By separating the positive and negative electrodes in advance in this way, the components constituting the positive and negative electrodes do not mix, allowing for effective recycling. The separator may be divided into a packaging separator and a positive and negative electrode separator as described above, or it may be a device that combines the functions of packaging separation and positive and negative electrode separation.

[0240] The electrode (eg, negative electrode) separated from the non-filled waste battery 12 by the above-described separation of the packaging and separation of the positive and negative electrodes is subjected to a recycling process according to a method including steps S1 to S3.

[0241] According to the seventh embodiment, a battery is manufactured using the electrodes regenerated by the method of the sixth embodiment, which makes it possible to manufacture batteries with a high recycling rate. Furthermore, the regenerated electrodes have excellent electronic conductivity and can suppress the deterioration of the active material, making it possible to realize a battery that is not only excellent in rate performance but also in durability.

[0242] A specific example of an electrode recycling method according to an embodiment will be described below. First, the target electrode is removed from the non-filled waste battery. When the exterior member of the non-filled waste battery is a metal can, the target electrode is removed by the method described below. The non-filled waste battery is placed in a packaging separator installed in a chamber set to a nitrogen atmosphere, and the exterior member (can) is cut to remove the electrode group. This electrode group is then placed in a positive / negative electrode separator installed in the chamber, where it is separated into a positive electrode, a separator, and a negative electrode. For example, a negative electrode is used as the target electrode. A positive electrode can also be used instead of the negative electrode.

[0243] This negative electrode includes a negative electrode active material-containing layer containing 80% by mass of niobium titanium oxide particles (Nb2TiO7) as the negative electrode active material, 5% by mass of acetylene black as a conductor, 5% by mass of carbon nanotubes, and 10% by mass of CMC as a binder, and a first current collector made of aluminum foil. The negative electrode is baked at 450°C for approximately 30 minutes in a low-oxygen environment to decompose the binder and obtain a baked product. The decomposition temperature of the binder, CMC, is approximately 350°C. The baking temperature of 450°C is also 210°C lower than the melting point of the first current collector (approximately 660°C). Baking reduces the weight of the organic components contained in the negative electrode by approximately 10% of their total weight. The organic components here are the conductor and binder.

[0244] The fired product of the first current collector is separated from the resulting fired product by sieving. This yields a mixture containing a negative electrode active material and a conductor. The conductor content of the mixture can vary depending on factors such as temperature variations during firing and the placement of the negative electrode in the firing furnace. The conductor content of the mixture is up to 10% by mass. CMC and water are added to the mixture to achieve the target composition of the negative electrode active material-containing layer, and the mixture is then crushed to a predetermined particle size. SBR is then added to the mixture and stirred to prepare a slurry. SBR can enhance the binding strength of the active material-containing layer. The resulting slurry is applied to a second current collector made of aluminum foil, dried, and pressed to produce an electrode. In the resulting electrode, carbon nanotubes are present, entangled on the surface of niobium titanium oxide particles. Acetylene black is also present on the surface of the niobium titanium oxide particles. This results in the formation of good conductive paths between the niobium titanium oxide particles, resulting in an electrode with excellent electronic conductivity. In addition, firing under low-oxygen conditions in the presence of carbon nanotubes and acetylene black, which are carbon materials, reduces a portion of the niobium titanium oxide Nb2TiO7 to form Nb2TiO6. The formation of particles containing Nb2TiO6 along with Nb2TiO7 improves the electrical conductivity of the niobium titanium oxide particles. Furthermore, because niobium titanium oxide is resistant to degradation by moisture, firing in air hardly degrades the niobium titanium oxide. This allows for the production of electrodes with long life. Furthermore, electrodes can be regenerated from waste materials generated during the manufacturing process, reducing the amount of waste material discarded. This increases the electrode recycling rate and also reduces manufacturing costs. [Example]

[0245] Examples will be described below.

[0246] Example 1 Niobium titanium oxide particles (Nb2TiO7) were mixed at 80% by mass with 5% by mass of acetylene black. The resulting mixture was placed in an alumina crucible, and the crucible was covered with a lid, leaving a small gap. The covered crucible was then transferred to a firing furnace and fired at 650°C for approximately two hours with the air flow rate set to 1 L / min to obtain a fired product.

[0247] In this way, an electrode material containing active material particles and a carbon material (conductor) on the particles was obtained. The active material particles (oxide particles) contained in the obtained electrode material were subjected to XRD measurement using the method described above. The magnitude relationship between the intensities of peaks P1 and P2 in the obtained XRD spectrum and the relationship between peaks P2 and P4 (P2 / P4) were calculated. The calculated results are shown in Table 1 below.

[0248] To the obtained electrode material, 6% by mass of CMC and 4% by mass of SBR as binders and water as a solvent were added, and the mixture was stirred to prepare a slurry. The obtained slurry was applied to an aluminum foil current collector, dried, and pressed to prepare the electrode of Example 1.

[0249] A non-aqueous electrolyte was prepared as follows. An electrolyte salt was dissolved in an organic solvent to obtain a liquid non-aqueous electrolyte. LiPF6 was used as the electrolyte salt. The molar concentration of LiPF6 in the non-aqueous electrolyte was 1 mol / L. A mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used as the organic solvent. The volume ratio of EC to DEC was 1:2.

[0250] A three-electrode beaker cell was fabricated using the fabricated electrode as a working electrode, metallic lithium foil as a counter electrode and a reference electrode, and the prepared non-aqueous electrolyte.

[0251] The discharge rate performance of the fabricated cells was evaluated as follows. The evaluation temperature was 25°C, and the potential range was the lower limit potential of 0.7 V (vs. Li / Li) from the lithium reference potential. + ), upper limit potential 3.0V (vs. Li / Li + ) was charged and discharged. After charging at a current value of 1C, the battery was discharged at a discharge current value of 1C, and the discharge capacity was measured. In addition, after charging at a current value of 1C, the battery was discharged at a discharge current value of 10C, and the discharge capacity was measured. The discharge capacities measured at each discharge rate are shown in Table 1 below.

[0252] (Examples 2 to 3) An electrode material was obtained in the same manner as in Example 1, except that the firing temperature of the mixture of niobium titanium oxide particles and acetylene black was changed as shown in Table 1 below. The obtained electrode material was subjected to the same XRD measurement. A beaker cell was produced using the electrode material in the same manner as in Example 1, and the discharge rate performance was evaluated. The results of the XRD measurement and the evaluation of the discharge rate performance are summarized in Table 1 below.

[0253] (Comparative Examples 1 to 4) An electrode material was obtained in the same manner as in Example 1, except that the firing conditions for the mixture of niobium titanium oxide particles and acetylene black were changed as shown in Table 1 below. Note that, for Comparative Example 4, firing was not performed. The obtained electrode material was subjected to the same XRD measurement. A beaker cell was produced using the electrode material in the same manner as in Example 1, and the discharge rate performance was evaluated. The results of the XRD measurement and the evaluation of the discharge rate performance are summarized in Table 1 below.

[0254] [Table 1]

[0255] As shown in Table 1, for the electrode materials obtained in Examples 1 to 3, the ratio I2 / I4, which represents the intensity relationship between peaks P2 and P4 in the XRD spectrum, was within the range of 5 to 26. This indicates that active materials containing oxide particles in which a moderate portion of the TiNb2O7 added as a raw material was reduced were obtained. In contrast, for the electrode materials obtained in Comparative Examples 1 to 4, the ratio I2 / I4 was less than 5 or greater than 26, indicating insufficient or excessive reduction of TiNb2O7. Note that for Comparative Example 4, peak P4 was not observed in the spectrum, so the peak intensity I4 was zero and the ratio I2 / I4 was "infinite." The beaker cells using the electrode materials of Examples 1 to 3 exhibited improved discharge capacities at a 10C rate compared to the beaker cells using the electrode materials of Comparative Examples 1 to 4. That is, the active material contained in the electrode materials of Examples 1 to 3 contained an appropriate amount of reduced TiNb2O7 phase (TiNb2O6 phase), which improved the conductive performance of the active material and enabled it to exhibit better rate performance.

[0256] The active material according to at least one of the above-described embodiments or examples includes oxide particles containing a monoclinic niobium titanium oxide phase, and when the peak intensities of the three peaks with the highest intensities among those peaks appearing in the range of 25.8° to 26.6° in an X-ray diffraction spectrum of the oxide particles are designated I2, I3, and I4, in descending order of intensity, I2 / I4 is 5 to 26. This active material can realize a secondary battery and a battery pack with excellent rate performance.

[0257] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0258] The invention according to the embodiment will be described below. <1> comprising oxide particles containing a monoclinic niobium titanium oxide phase, The X-ray diffraction spectrum of the oxide particles includes a maximum peak P1 appearing in the range of 23.6° or more and 24.3° or less and a plurality of peaks appearing in the range of 25.8° or more and 26.6° or less, and when the peak intensities of the three peaks with the highest peak intensities among the peaks appearing in the range of 25.8° or more and 26.6° or less are I2, I3, and I4, respectively, in descending order, I2 / I4 is an active material in which I2 / I4 is 5 or more and 26 or less. <2> The peak intensity I1 of the peak P1 is smaller than the peak intensity I2. <1> The active material according to claim 1. <3> <1> or <2> The active material according to Further comprising a carbon material on the oxide particles. electrode material. <4> <1> or <2> An electrode comprising the active material according to claim 1. <5> <3> An electrode comprising the electrode material according to claim 1. <6> A positive electrode and a negative electrode; Electrolytes and A secondary battery comprising: The negative electrode is <4> or <5> A secondary battery comprising the electrode according to claim 1. <7> <6> A battery pack comprising the secondary battery according to claim 1. <8> An external terminal for applying current; Protection circuit and Further provided with <7> The battery pack according to claim 1. <9> A battery includes a plurality of the secondary batteries, The secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. <7> or <8> The battery pack according to claim 1. <10> a step of heat-treating a target electrode comprising a first current collector and an active material-containing layer supported on the first current collector and including an active material containing monoclinic niobium titanium oxide, a binder, and a conductor, at a temperature below the melting point of the first current collector in an environment with a lower oxygen concentration than air to decompose the binder, thereby obtaining a heat-treated product; a step of separating the first current collector from the heat-treated product to obtain a mixture containing the active material and the conductor; manufacturing an electrode using the mixture; A method for recycling electrodes, comprising: <11> the conductor comprises a carbon material; <10> A method for recycling the electrode described in claim 1. <12> The carbon material includes carbon nanotubes. <11> A method for recycling the electrode described in claim 1. <13> The content of the carbon material in the mixture is 0.1% by mass or more and 10% by mass or less. <11> or <12> A method for recycling the electrode described in claim 1. <14> the heat treatment temperature is lower by 20°C or more than the melting point of the first current collector; <10> ~ <13> 10. The method for recycling an electrode according to claim 9, wherein the electrode is a molten metal. <15> The heat treatment temperature is equal to or higher than the decomposition temperature of the binder. <10> ~ <14> 10. The method for recycling an electrode according to claim 9, wherein the electrode is a molten metal. <16> The active material is substantially free of Li. <10> ~ <15> 10. The method for recycling an electrode according to claim 9, wherein the electrode is a molten metal. <17> the heat treatment is carried out so that the weight of the organic component contained in the target electrode is reduced by 10% to 90% of the weight of the organic component; <10> ~ <16> 10. The method for recycling an electrode according to claim 9, wherein the electrode is a molten metal. <18> The manufacturing of the electrode includes a step of preparing a slurry using the mixture and a step of applying the slurry to a second current collector. <10> ~ <17> 10. The method for recycling an electrode according to claim 9, wherein the electrode is a molten metal. <19> measuring the content of the conductor in the mixture obtained; and determining a composition of the electrode to be manufactured based on the content of the conductor, wherein manufacturing the electrode using the mixture is performed by manufacturing an electrode having the determined composition using the mixture. <10> ~ <18> 10. The method for recycling an electrode according to claim 9, wherein the electrode is a molten metal. [Explanation of symbols]

[0259] 1...electrode, 2...current collector, 3...active material-containing layer, 11...waste electrode, 12...unfilled waste battery, 20...nonaqueous electrolyte battery, 21...metallic container, 22...electrode group, 23...metallic sealing plate, 24...negative electrode terminal, 25...positive electrode terminal, 26...negative electrode, 26a...negative electrode current collector, 26b...negative electrode active material-containing layer, 27...positive electrode, 27a...positive electrode current collector, 27b...positive electrode active material-containing layer, 28...separator, 29...negative electrode current collector tab, 30...insulating member, 31...positive electrode current collector tab, 100...secondary battery, 200...battery assembly, 221...bus bar, 222...positive electrode side lead, 222a...other end, 223...negative electrode side lead, 223a...other end, 240...adhesive tape, 300...electrical Pond pack, 310...container, 320...lid, 330...protective sheet, 340...printed wiring board, 342...positive electrode connector, 343...negative electrode connector, 345...thermistor, 346...protective circuit, 342a...wiring, 343a...wiring, 348a...positive electrode wiring, 348b...negative electrode wiring, 350...external terminal for energizing, 351...wiring, 352...positive terminal, 353...negative terminal, S1...heat treatment of target electrode, S2...separation of first current collector, S3...electrode production, S11...slurry preparation (dispersion), S12...coating, S13...drying, S14...pressing, S15...cutting, S21...assembly, S22...pouring, S23...product. < / gc>

Claims

1. comprising oxide particles containing a monoclinic niobium titanium oxide phase, an X-ray diffraction spectrum of the oxide particles includes a maximum peak P1 appearing in the range of 23.6° or more and 24.3° or less and a plurality of peaks appearing in the range of 25.8° or more and 26.6° or less, and when the peak intensities of the three peaks with the highest peak intensities among the peaks appearing in the range of 25.8° or more and 26.6° or less are I2, I3, and I4, respectively, in descending order, I2 / I4 is 5 or more and 26 or less.

2. The active material according to claim 1 , wherein the peak intensity I1 of the maximum peak P1 is smaller than the peak intensity I2.

3. The active material according to claim 1 or 2, Further comprising a carbon material on the oxide particles. electrode material.

4. An electrode comprising the electrode material of claim 3 .

5. A positive electrode and a negative electrode; Electrolytes and A secondary battery comprising: The secondary battery according to claim 4 , wherein the negative electrode is the electrode.

6. A battery pack comprising the secondary battery according to claim 5 .

7. An external terminal for applying current; Protection circuit and The battery pack according to claim 6 , further comprising:

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

9. a step of heat-treating a target electrode comprising a first current collector and an active material-containing layer supported on the first current collector and including an active material containing monoclinic niobium titanium oxide, a binder, and a conductor, at a temperature below the melting point of the first current collector in an environment with a lower oxygen concentration than air to decompose the binder, thereby obtaining a heat-treated product; a step of separating the first current collector from the heat-treated product to obtain a mixture containing the active material and the conductor; manufacturing an electrode using the mixture; A method for recycling electrodes, comprising:

10. The method for recycling electrodes according to claim 9 , wherein the conductor comprises a carbon material.

11. The method for recycling electrodes according to claim 10 , wherein the carbon material comprises carbon nanotubes.

12. The method for recycling electrodes according to claim 10 , wherein the content of the carbon material in the mixture is 0.1% by mass or more and 10% by mass or less.

13. The method for recycling an electrode according to claim 9 , wherein the heat treatment temperature is lower by 20° C. or more than the melting point of the first current collector.

14. The electrode recycling method according to claim 9 , wherein the heat treatment temperature is equal to or higher than the decomposition temperature of the binder.

15. The method for recycling an electrode according to claim 9 , wherein the active material is substantially free of Li.

16. 10. The method for recycling electrodes according to claim 9, wherein the heat treatment is carried out so as to reduce the weight of the organic components contained in the target electrode by 10% to 90% of the weight of the organic components.

17. The electrode recycling method according to claim 9 , wherein the manufacturing of the electrode includes the steps of preparing a slurry using the mixture and applying the slurry to a second current collector.

18. measuring the content of the conductor in the mixture obtained; 10. The electrode recycling method according to claim 9, further comprising a step of determining a composition of the electrode to be manufactured based on the content of the conductor, wherein manufacturing the electrode using the mixture is performed by manufacturing an electrode having the determined composition using the mixture.

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