Secondary battery, battery pack, vehicle, and method of manufacturing secondary battery

Abstract

To provide a secondary battery that has excellent high-temperature storage performance and input / output characteristics and that suppresses self-discharge, a battery pack including this secondary battery, and a vehicle including this battery pack.SOLUTION: A secondary battery 100 according to an embodiment includes an electrode group 1 including a positive electrode 5, a negative electrode 3, and a separator 4, and an electrolyte. The positive electrode 5 includes a positive electrode active material and a carbon material. The carbon material includes Co atoms at a concentration of 100 mass ppm or more and 1500 mass ppm or less. The separator 4 includes a base material 4a and a site 4b including Co atoms present in the base material. From among the region in which the separator 4 is disposed between the positive electrode 5 and the negative electrode 3, the outermost layer located at the outermost layer in the electrode group 1 includes sites including Co atoms at a rate of 200 atoms / m2 or more and 10000 atoms / m2 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Secondary batteries such as lithium ion secondary batteries have a problem of increasing self-discharge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-158643 A [Non-patent literature]

[0004] [Non-Patent Document 1] B. Ravel and M. Newville, ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT, Journal of Synchrotron Radiation 12, 537-541 (2005) Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide a secondary battery that has excellent high-temperature storage performance and input / output characteristics and suppressed self-discharge, a battery pack including this secondary battery, a vehicle including this battery pack, and a method for manufacturing this secondary battery. [Means for solving the problem]

[0006] According to an embodiment, a secondary battery is provided. The secondary battery includes an electrode group including a positive electrode, a negative electrode, and a separator, and an electrolyte. The positive electrode includes a positive electrode active material and a carbon material. The carbon material contains Co atoms at a concentration of 100 mass ppm to 1500 mass ppm. The separator includes a substrate and a site containing Co atoms present in the substrate. In a region where the separator is disposed between the positive electrode and the negative electrode, the outermost layer that is the outermost layer in the electrode group has 200 sites containing Co atoms / m 2 More than 10000 pieces / m 2 Contains the following percentages:

[0007] According to another embodiment, a battery pack including a secondary battery according to the embodiment is provided.

[0008] According to another embodiment, a vehicle is provided that includes a battery pack according to an embodiment. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a secondary battery according to an embodiment. [Diagram 2] 2 is an enlarged cross-sectional view of a portion A of the secondary battery shown in FIG. 1. [Diagram 3] 2 is an enlarged cross-sectional view of a portion C of the secondary battery shown in FIG. 1. [Figure 4] FIG. 2 is a diagram illustrating an example of a separator included in the secondary battery according to the embodiment. [Diagram 5] FIG. 2 is a cross-sectional view illustrating the vicinity of the outermost layer of a separator included in the secondary battery according to the embodiment. [Figure 6] FIG. 4 is a partially cutaway perspective view illustrating a schematic diagram of another example of a secondary battery according to an embodiment. [Figure 7] FIG. 7 is an enlarged cross-sectional view of a portion B of the secondary battery shown in FIG. 6. [Figure 8] FIG. 1 is a perspective view illustrating an example of a battery pack according to an embodiment. [Figure 9] FIG. 1 is an exploded perspective view illustrating an example of a battery pack according to an embodiment. [Figure 10] 10 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 9. [Figure 11] FIG. 1 is a partially see-through view illustrating an example of a vehicle according to an embodiment. [Figure 12] 1 is a diagram illustrating an example of a control system for an electrical system in a vehicle according to an embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (First embodiment) The present inventors conducted a detailed analysis of the self-discharge of secondary batteries and found that cobalt (Co) atoms are one of the causes of increased self-discharge. Co atoms can be brought into secondary batteries, for example, as impurities in the carbon material contained in the positive electrode. Co atoms can be contained in the carbon material, for example, as a Co component such as a simple Co metal or a compound in which Co is bonded with another element.

[0011] The mechanism by which Co atoms increase self-discharge is thought to be as follows. Co atoms contained in the positive electrode can dissolve in the electrolyte and release Co ions. For example, when the negative electrode potential drops during charging, Co ions can precipitate on the negative electrode and form crystal nuclei. Further precipitation on these crystal nuclei can cause coarse metal crystals to form on the negative electrode. When the metal crystals penetrate the separator and come into electrical contact with the positive electrode, an internal short circuit occurs with the metal crystals as the short-circuit point, increasing self-discharge.

[0012] Furthermore, when a secondary battery is stored at high temperature, an internal short circuit may occur due to deposition of Co on the negative electrode, which may result in a decrease in the capacity of the secondary battery after high-temperature storage.

[0013] The present inventors conducted extensive research based on the above analysis results and achieved the secondary battery according to the first embodiment.

[0014] According to an embodiment, a secondary battery is provided. The secondary battery includes an electrode group including a positive electrode, a negative electrode, and a separator, and an electrolyte. The positive electrode includes a positive electrode active material and a carbon material. The carbon material contains Co atoms at a concentration of 100 mass ppm to 1500 mass ppm. The separator includes a substrate and a site containing Co atoms present in the substrate. In a region where the separator is disposed between the positive electrode and the negative electrode, the outermost layer that is the outermost layer in the electrode group has 200 sites containing Co atoms / m 2 More than 10000 pieces / m 2 Contains the following percentages:

[0015] The positive electrode contains a carbon material, so that the electronic conductivity can be increased. Since the carbon material contains 100 ppm by mass or more of Co atoms, the electronic conductivity of the entire positive electrode can be improved by the electronic conduction of Co. Therefore, the input / output characteristics can be improved. In addition, the concentration of Co atoms in the carbon material is 1500 ppm by mass or less. Therefore, for example, during the charge / discharge cycle, it is possible to suppress the dissolution and precipitation of Co atoms to form a short circuit point. Therefore, it is possible to suppress self-discharge. In addition, it is possible to suppress the dissolution and precipitation of Co atoms and the formation of a short circuit point during high-temperature storage. Therefore, it is possible to improve high-temperature storage performance.

[0016] The separator includes a substrate and a portion containing Co atoms present in the substrate. The portion may be, for example, a portion where a substance containing Co atoms formed by depositing Co atoms dissolved in an electrolyte on a negative electrode contacts the substrate of the separator. Therefore, the region of the separator disposed between the positive electrode and the negative electrode includes the portion.

[0017] The outermost layer of the electrode group is 200 pieces / m 2 The above is included. Therefore, the secondary battery can be in a state where the Co atoms dissolved in the electrolyte are sufficiently precipitated. Therefore, when the secondary battery is stored at high temperature, the Co atoms dissolved in the electrolyte can be prevented from further precipitating. Therefore, it is possible to prevent the part from growing coarsely and short-circuiting, and thus to suppress self-discharge.

[0018] In addition, when Co atoms are dissolved from the carbon material into the electrolyte, the sites can function as precipitation sites for Co atoms. The more sites the separator contains, the greater the number of precipitation sites that can be provided. When the number of precipitation sites is small, Co atoms dissolved in the electrolyte can concentrate and precipitate on a small number of precipitation sites. As a result, each site can grow coarsely and form a short circuit point. As a result, there is a risk of increased self-discharge. When the number of precipitation sites is large, Co atoms dissolved in the electrolyte can be dispersed over a large number of precipitation sites. Therefore, even if Co atoms precipitate on each site as a precipitation site, the sites are less likely to grow coarsely. The number of sites per unit area in the outermost layer is 200 / m 2 If the amount is more than this, the number of precipitation sites can be increased, so that the growth of the sites can be suppressed and the formation of short-circuit points can be suppressed.

[0019] By not increasing the density of the regions too much, the growth of the regions can be suppressed. In the secondary battery, the number of regions per unit area in the outermost layer is 10,000 / m 2 Since the thickness is less than or equal to the thickness of the insulating film, the growth of the portion can be suppressed, and self-discharge can be suppressed.

[0020] Therefore, according to the embodiment, a secondary battery having excellent high-temperature storage performance and input / output characteristics and suppressed self-discharge can be provided.

[0021] The secondary battery according to the embodiment will be further described.

[0022] The average working potential of the negative electrode is 1.0 V (vs. Li / Li + ) or more. In such a negative electrode, for example, the negative electrode potential does not become too low during charging, so that excessive deposition of Co on the negative electrode can be suppressed. Therefore, short circuit can be suppressed. The method for measuring the average working potential of the negative electrode will be described later.

[0023] The more the number of sites contained in the outermost layer, the more the secondary battery tends to separate out the Co atoms (Co ions) dissolved in the electrolyte. Since the Co ions in the electrolyte may originate from the carbon material contained in the positive electrode, the more the number of sites, the lower the Co concentration of the carbon material. If the Co concentration of the carbon material is low, dissolution and precipitation of the Co atoms remaining in the positive electrode may be suppressed during high-temperature storage.

[0024] The larger the diameter of the portion included in the outermost layer, the more the secondary battery tends to fully precipitate Co atoms (Co ions) dissolved in the electrolyte. Therefore, even after charge / discharge cycles, the Co atoms in the electrolyte tend not to precipitate, so that short circuits can be effectively suppressed. However, if the diameter of the portion is excessively large, the portion may break through the separator and cause a short circuit. The smaller the diameter of the portion, the more likely it is that a short circuit caused by the portion breaking through the separator can be suppressed. The diameter of the portion is preferably 0.1 mm or more and 0.5 mm or less. The diameter of the portion can also be within the range of 0.10 mm or more and 0.50 mm or less.

[0025] The electrolyte contained in the secondary battery may contain fluorine atoms. When an electrolyte containing fluorine atoms is used, hydrofluoric acid (hydrogen fluoride, HF) may be generated in the secondary battery, for example, at high temperatures. The hydrofluoric acid may oxidize and dissolve Co atoms contained in the carbon material, releasing Co ions into the electrolyte. The electrolyte may be a non-aqueous electrolyte containing fluorine atoms. In the manufacturing process of a non-aqueous electrolyte secondary battery, water is likely to be mixed in as an unavoidable impurity. When a side reaction occurs between water and the non-aqueous electrolyte, hydrofluoric acid may be generated as a decomposition product of the non-aqueous electrolyte. Details of the electrolyte will be described later.

[0026] The carbon material may contain at least one of metallic Co and cobalt oxide. Examples of cobalt oxide include cobalt (II) oxide (CoO) and tricobalt tetroxide (Co3O4). At least one of metallic Co and cobalt oxide may be included in the carbon material as, for example, a Co component.

[0027] The ratio A of Co atoms present as metal Co in the carbon material Co and the ratio A of Co atoms present as CoO CoO and the ratio A of Co atoms present as Co3O4 Co3O4 A using and Co / (A Co +A CoO +A Co3O4 The value of A indicates the reduction state of the Co atoms contained in the carbon material. Co / (A Co +A CoO +A Co3O4 ) is high, it can be determined that the reduction state of the Co atoms in the carbon material is high, that is, the Co atoms in the carbon material are more reduced. Co , A CoO , A Co3O4 The values ​​of can be measured by X-ray absorption spectroscopy (XAS). The method of X-ray absorption spectroscopy will be described later.

[0028] It is preferable that the carbon material contains many Co atoms existing as metallic Co. In other words, it is preferable that the reduction state of the Co atoms in the carbon material described above is high. The reason for this will be explained below.

[0029] In this embodiment, a carbon material containing Co atoms is contained in the positive electrode. The dissolution and deposition potential of Co is 2.76 V vs. Li / Li + Generally, the working potential of the positive electrode is 2.76V vs. Li / Li + Not to fall below.

[0030] However, in order for the Co atoms contained in the cobalt oxide to dissolve in the electrolyte, it is necessary to break the Co-O bond in the cobalt oxide. Therefore, the positive electrode potential must be 2.76 V vs. Li / Li, which is the dissolution and deposition potential of Co. + Even if the concentration of Co exceeds 100%, the Co atoms contained in the cobalt oxide are difficult to dissolve in the electrolyte.

[0031] Therefore, when the ratio of Co atoms present as cobalt oxide among the Co contained in the carbon material is high, that is, when the oxidation number of Co contained in the carbon material is high, for example, the Co atoms in the carbon material are difficult to dissolve in the electrolyte during the initial charge. Therefore, when the reduction state of the Co atoms in the carbon material is low, the Co atoms tend to remain in the carbon material in excess. For example, when hydrofluoric acid is generated in the battery at high temperatures, the Co atoms remaining in the carbon material in excess react with the hydrofluoric acid to dissolve in the electrolyte, generating Co ions, which can cause self-discharge.

[0032] Among the Co atoms in the carbon material, the Co atoms present as metallic Co are easily dissolved when the positive electrode potential is swept to a potential on the noble side of the dissolution and deposition potential of Co. Therefore, the Co atoms can be easily dissolved in the electrolyte during the initial charge described below. Therefore, the concentration of Co atoms in the carbon material can be easily set within the range of 100 ppm by mass to 1500 ppm by mass.

[0033] Therefore, the A of the carbon material Co / (A Co +A CoO +A Co3O4 It is preferable that the value of A is 0.6 or more. Co / (A Co +A CoO +A Co3O4 ) may be, for example, in the range of 0.60 to 0.95.

[0034] Hereinafter, a secondary battery according to an embodiment will be described in detail with reference to the drawings.

[0035] The secondary battery is, for example, a secondary battery that uses alkali metal ions as carrier ions. For example, it may be a lithium battery (lithium ion battery).

[0036] Such a secondary battery may further include an exterior member that houses the electrode group and the electrolyte.

[0037] 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.

[0038] Fig. 1 is a cross-sectional view showing an example of a secondary battery, and Fig. 2 is an enlarged cross-sectional view of part A of the secondary battery shown in Fig. 1.

[0039] The secondary battery 100 shown in Figures 1 and 2 includes a bag-shaped exterior member 2 shown in Figure 1, an electrode group 1 shown in Figures 1 and 2, and an electrolyte (not shown). The electrode group 1 and the electrolyte are stored in the bag-shaped exterior member 2. The electrolyte (not shown) is held in the electrode group 1.

[0040] The bag-shaped exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0041] As shown in Fig. 1, the electrode group 1 is a flat wound-type electrode group. As shown in Fig. 2, the flat wound-type electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

[0042] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. In the negative electrode 3, in a portion located at the outermost shell of the wound-type electrode group 1, the negative electrode active material-containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a as shown in Fig. 2. In the other portions of the negative electrode 3, the negative electrode active material-containing layer 3b is formed on both sides of the negative electrode current collector 3a.

[0043] The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b formed on both sides of the positive electrode current collector 5a.

[0044] As shown in FIG. 1, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer peripheral end of the wound electrode group 1. The negative electrode terminal 6 is connected to a portion located at the outermost shell of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to a portion located at the outermost shell of the positive electrode current collector 5a. The negative electrode terminal 6 and the positive electrode terminal 7 extend to the outside from an opening of the bag-shaped exterior member 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and the opening is closed by heat sealing.

[0045] The electrode group shown in FIG. 1 has a structure in which a positive electrode, a separator, a negative electrode, and a separator (not shown) are stacked in this order and wound so that the negative electrode is located outside the positive electrode. Each of the positive electrode, the negative electrode, and the separator may be in a strip shape having a long side direction and a short side direction. In the electrode group shown in FIG. 1, the long side directions of the positive electrode, the negative electrode, and the separator are wound. FIG. 3 is an enlarged cross-sectional view of part C of the secondary battery shown in FIG. 1. In the example shown in FIG. 1 and FIG. 3, for example, at the outer peripheral end (winding end) of the electrode group 1, the end of the positive electrode 5 protrudes beyond the end of the negative electrode 3, and the end 18 of the separator 4 protrudes beyond the end of the positive electrode 5.

[0046] The separator has a region 11. The region 11 is a portion located between the negative electrode 3 and the positive electrode 5. The end of the region 11 is defined by an end of the negative electrode 3 or the positive electrode 5 that intersects with the long side direction. For example, the end of the region 11 may be a portion corresponding to the end of the negative electrode 3 located at the outer peripheral end (winding end) of the electrode group 1 shown in FIG. 1 and FIG. 3. The portion corresponding to the end of the negative electrode 3 may be, for example, a portion where the separator contacts the end of the negative electrode 3. When the end of the negative electrode 3 protrudes more than the end of the positive electrode 5 at the winding end of the electrode group 1, the end of the region 11 may be a portion corresponding to the end of the positive electrode 5 located at the winding end. Note that, of the separator 4 shown in FIG. 2, a portion located between the exterior member 2 and the negative electrode current collector 3a is not located between the negative electrode 3 and the positive electrode 5. That is, the portion is not included in the region 11.

[0047] The separator 4 has a surface in contact with the negative electrode 3. At least a portion of the surface in contact with the negative electrode 3 is present within region 11. Furthermore, the surface in contact with the negative electrode 3 may be present outside region 11. At least a portion of the surface in contact with the negative electrode 3 is included in region 11.

[0048] The region 11 includes an outermost layer 12. One end 16 of the outermost layer 12 may be the end of the region 11. In the electrode group 1 shown in Figs. 1 and 3, the other end 17 of the outermost layer 12 is located at a position corresponding to the one end 16 of the outermost layer, on the inner side of the circumference of the outermost layer 12. In Figs. 1 and 3, the one end 16 of the outermost layer 12 and its extension are shown by a two-dot chain line. The position corresponding to the one end 16 of the outermost layer is, for example, the position where the two-dot chain line intersects with the separator 4 on the inner side of the outermost layer 12 in the electrode group 1.

[0049] The portion of the region 11 excluding the outermost layer 12 is the inner layer 13. The other end 17 of the outermost layer also serves as one end of the inner layer 13.

[0050] FIG. 4 is a schematic diagram showing an example of a separator having an outermost layer 12 and an inner layer 13, which is included in the wound electrode group shown in FIGS. 1 to 3. The separator is included in the wound electrode group in a state where the long side direction of the strip shape is wound, but FIG. 4 illustrates a state where the long side direction of the separator is stretched and the strip shape is developed along a plane. In FIG. 4, the x-axis direction is a direction along the short side direction of the strip separator. The y-axis direction is a direction perpendicular to the x-axis direction and along the long side direction of the strip separator. The z-axis direction is a direction perpendicular to the x-axis direction and y-axis direction and along the thickness direction of the strip separator. One end 16 of the outermost layer, the other end 17 of the outermost layer, and the end 18 of the separator 4 each intersect with the long side of the separator. The separator illustrated in FIG. 4 includes a portion other than the region 11, but the separator may be composed of the region 11.

[0051] FIG. 5 is a cross-sectional view that shows the vicinity of the outermost layer of the separator included in the secondary battery according to the embodiment. FIG. 5 shows an enlarged view of the vicinity of the outermost layer of the separator in a cross-sectional view of the secondary battery along the thickness direction of the separator. The negative electrode 3 and the separator 4, and the separator 4 and the positive electrode 5 are in contact with each other. In the example shown in FIG. 5, a substance 14 containing Co atoms is formed on the negative electrode 3. The substance 14 containing Co atoms may be formed, for example, by the negative electrode potential decreasing during charging, so that the negative electrode potential becomes lower than the dissolution and deposition potential of Co, and Co ions in the electrolyte are precipitated on the negative electrode. The portion where the substrate 4a of the separator is in contact with the substance 14 containing Co atoms may be the portion 4b. In this way, the portion 4b is present in the substrate 4a. Therefore, the portion 4b may be included in the surface of the separator 4 that faces the negative electrode 3.

[0052] The secondary battery according to the embodiment is not limited to the secondary battery having the configuration shown in FIGS. 1 to 3, and may be a battery having the configuration shown in FIGS.

[0053] Fig. 6 is a partially cutaway perspective view showing a schematic diagram of another example of the secondary battery, and Fig. 7 is an enlarged cross-sectional view of part B of the secondary battery shown in Fig. 6.

[0054] The secondary battery 100 shown in Figures 6 and 7 includes an electrode group 1 shown in Figures 6 and 7, an exterior member 2 shown in Figure 6, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte is held in the electrode group 1.

[0055] The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0056] The electrode group 1 is a laminated type electrode group, as shown in Fig. 7. The laminated type electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately laminated with separators 4 interposed therebetween.

[0057] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a. The electrode group 1 includes a plurality of separators 4. When the electrode group includes a plurality of separators, at least one of the plurality of separators may include a region disposed between the positive electrode and the negative electrode, and all of the plurality of separators may include the region. These forms can be expressed as the separator including the region.

[0058] The negative electrode current collector 3a of each negative electrode 3 includes a portion on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion serves as a negative electrode current collector tab 3c. As shown in FIG. 7, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. The negative electrode current collector tabs 3c are electrically connected to a belt-shaped negative electrode terminal 6. The tip of the belt-shaped negative electrode terminal 6 is pulled out to the outside of the exterior member 2.

[0059] Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion serves as a positive electrode current collector tab. The positive electrode current collector tab does not overlap with the negative electrode 3, similar to the negative electrode current collector tab 3c. The positive electrode current collector tab is located on the opposite side of the electrode group 1 to the negative electrode current collector tab 3c. The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side of the negative electrode terminal 6 and is drawn out to the outside of the exterior member 2.

[0060] The separator includes a region 11 located between the negative electrode 3 and the positive electrode 5. The separator also has a surface in contact with the negative electrode 3. At least a part of the surface in contact with the negative electrode 3 is present in the region 11. Furthermore, the surface in contact with the negative electrode 3 may be present outside the region 11. At least a part of the surface in contact with the negative electrode 3 is included in the region 11. However, in the stacked electrode group 1 shown in FIG. 6 and FIG. 7, the separator located in the uppermost layer and the separator located in the lowermost layer are not located between the negative electrode 3 and the positive electrode 5. Therefore, these separators do not include the region 11.

[0061] As shown in Fig. 7, a positive electrode 5 is in contact with the uppermost separator 4. This positive electrode is the outermost (upper) positive electrode of the electrode group. A negative electrode 3 is in contact with the lowermost separator 4. This negative electrode is the outermost (lower) negative electrode of the electrode group.

[0062] The laminated electrode group 1 includes two outermost layers 12. One outermost layer 12 is located at the top and one at the bottom in FIG. 7. The upper outermost layer 12 is a region of the separator in contact with the outermost (upper) positive electrode of the electrode group, which is disposed between the positive electrode and the negative electrode 3. The lower outermost layer 12 is a region of the separator in contact with the outermost (lower) negative electrode of the electrode group, which is disposed between the negative electrode and the positive electrode 5.

[0063] Of the separator located on the inside in the stacking direction of the electrode group from the two outermost layers 12 described above, the region disposed between the positive electrode and the negative electrode is the inner layer 13. In other words, of the region 11 disposed between the positive electrode and the negative electrode, the portion excluding the outermost layer 12 is the inner layer 13.

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

[0065] 1) 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, a carbon material, and a binder.

[0066] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain a single compound as the positive electrode active material, or may contain a combination of two or more compounds. Examples of the oxide and the sulfide can include compounds into which Li or Li ions can be inserted and desorbed.

[0067] Examples of such compounds include, for example, 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, Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (for example, Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (for example, 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 (for example, V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni1-y-z Co y Mn z O2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1 is included.

[0068] 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 oxides (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1 is included. Using these compounds as the positive electrode active material can increase the positive electrode potential.

[0069] When using a room temperature molten salt 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), a lithium manganese composite oxide, a lithium nickel composite oxide, a 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.

[0070] 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 smoothly diffuse lithium ions in the solid.

[0071] The specific surface area of ​​the positive electrode active material is 0.1 m 2 / g or more 10m 2 / g or less. 2 A positive electrode active material having a specific surface area of ​​10m / g or more can secure sufficient sites for absorbing and releasing Li ions. 2 A positive electrode active material having a specific surface area of ​​100 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0072] The binder is blended to fill the gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0073] The positive electrode conductive agent is blended to improve current collecting performance and suppress contact resistance between the positive electrode active material and the positive electrode current collector. The carbon material can function as the positive electrode conductive agent. The positive electrode conductive agent may contain a carbon material alone, or may contain a mixture of a carbon material and one or more other conductive agents.

[0074] The carbon material may be a carbonaceous material containing Co atoms at a concentration of 100 ppm by mass or more and 1500 ppm by mass or less. Examples of the carbonaceous material include vapor grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. The type of carbonaceous material may be one or more. When two or more types of carbonaceous materials are mixed and used, the Co atom concentration may vary depending on the type of carbonaceous material, and a carbonaceous material that does not contain Co atoms may be included. When a mixture of two or more types of carbonaceous materials is used as the carbon material, the Co atom concentration of the mixture is in the range of 100 ppm by mass or more and 1500 ppm by mass or less. Such a mixture can also be said to be a carbonaceous material containing Co atoms at a concentration of 100 ppm by mass or more and 1500 ppm by mass or less. The positive electrode conductive agent containing the carbon material can improve the electronic conductivity of the entire positive electrode by the electronic conduction of Co atoms, and can suppress self-discharge.

[0075] The positive electrode active material, binder, and positive electrode conductive agent are preferably mixed in ratios of 77 to 95 parts by mass, 2 to 20 parts by mass, and 3 to 15 parts by mass, respectively.

[0076] By making the amount of the binder 2 parts by mass or more, sufficient electrode strength can be obtained. In addition, the binder can function as an insulator. Therefore, by making the amount of the binder 20 parts by mass or less, the amount of insulator contained in the electrode is reduced, and the internal resistance can be reduced.

[0077] By making the amount of the positive electrode conductive agent 3 parts by mass or more, the current collection performance of the positive electrode active material-containing layer can be improved. Also, by making the amount of the positive electrode conductive agent 15 parts by mass or less, the ratio of the positive electrode conductive agent in contact with the electrolyte can be reduced. If this ratio is low, decomposition of the electrolyte during high-temperature storage can be reduced.

[0078] 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.

[0079] 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 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 mass% or less.

[0080] 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.

[0081] 2) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be formed on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer may include a negative electrode active material, and optionally a negative electrode conductive agent and a binder.

[0082] Examples of the negative electrode active material include carbonaceous materials, lithium alloy materials, metal oxides, and metal sulfides. Examples of the carbonaceous material include graphite materials. Carbonaceous materials are materials that have an average operating potential of the negative electrode of 1.0 V (vs. Li / Li + Metal oxides and metal sulfides can provide a negative electrode with an average operating potential of less than 1.0 V (vs. Li / Li) based on the lithium potential. + ) or more is preferable.

[0083] The average working potential of the negative electrode is 1.0V vs. Li / Li + An example of the negative electrode active material is 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, orthorhombic titanium composite oxide, and monoclinic type niobium titanium oxide.

[0084] As an example of the above-mentioned orthorhombic titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O 14+σ In this case, the compound represented by 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).

[0085] As an example of the monoclinic niobium titanium oxide, 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. Specific examples of monoclinic niobium titanium oxide include Li x Examples include Nb2TiO7 (0≦x≦5).

[0086] Another example of monoclinic niobium titanium oxide is Li x Ti 1-y M3y+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.

[0087] The average working potential of the negative electrode is 1.0V vs. Li / Li + The negative electrode active material having the above structure is preferably contained in a ratio of 50% by mass or more relative to the mass of the negative electrode active material-containing layer. A negative electrode containing the above negative electrode active material is unlikely to cause deposition of lithium metal on the negative electrode surface, for example, when charged with a large current and when charged at a low temperature of 25° C. or less. Therefore, short circuit can be suppressed, and self-discharge can be reduced.

[0088] The negative electrode conductive agent is blended to improve current collection performance and reduce contact resistance between the negative electrode active material and the negative electrode current collector. Examples of the negative electrode conductive agent 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 negative electrode conductive agent, or two or more may be used in combination as the negative electrode conductive agent. Alternatively, instead of using the negative electrode conductive agent, a carbon coat or an electronically conductive inorganic material coat may be applied to the surface of the negative electrode active material particles.

[0089] The binder is blended to fill the gaps between the dispersed negative electrode active material and to bind the negative electrode active material and the negative electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0090] The negative electrode active material, the negative electrode conductive agent, and the binder are preferably mixed in a ratio of 68 parts by mass or more to 96 parts by mass or less, 2 parts by mass or more to 30 parts by mass or less, and 2 parts by mass or more to 30 parts by mass or less, respectively. By making the amount of the negative electrode conductive agent 2 parts by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. In addition, by making the amount of the binder 2 parts by mass or more, the binding property between the negative electrode active material-containing layer and the negative electrode current collector becomes sufficient, and excellent cycle performance can be expected. On the other hand, it is preferable to make the amount of the negative electrode conductive agent and the binder 30 parts by mass or less each in order to achieve high capacity.

[0091] The negative electrode current collector is made of a material that is electrochemically stable at a potential at which lithium (Li) is inserted into and removed from the negative electrode active material. The negative electrode current collector is preferably made of, for example, copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the negative electrode current collector is preferably 5 μm or more and 20 μm or less. A negative electrode current collector having such a thickness can balance the strength and weight reduction of the negative electrode.

[0092] The negative electrode 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.

[0093] 3) Electrolyte The electrolyte may be, for example, a liquid non-aqueous electrolyte or a gel non-aqueous electrolyte, or may be an aqueous electrolyte.

[0094] 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.

[0095] The non-aqueous electrolyte may contain fluorine atoms. Examples of the non-aqueous electrolyte containing fluorine atoms include non-aqueous electrolytes containing an electrolyte salt containing fluorine atoms.

[0096] Examples of the electrolyte salt include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potential, and LiPF6 is the most preferable. Among the above, examples of the electrolyte salt containing a fluorine atom include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2). The type of electrolyte salt can be one or more types.

[0097] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as a mixed solvent.

[0098] The gelled 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.

[0099] Alternatively, as the nonaqueous electrolyte, in addition to the liquid nonaqueous electrolyte and the gel nonaqueous electrolyte, a room temperature molten salt containing lithium ions (ionic melt) may be used. The type of nonaqueous electrolyte may be one or more types.

[0100] Room temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C or higher and 25°C or lower). Room temperature molten salts include room temperature molten salts that exist as a liquid by themselves, room temperature molten salts that become liquid when mixed with an electrolyte salt, room temperature molten salts that become liquid when dissolved in an organic solvent, and mixtures of these. In general, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. In addition, organic cations generally have a quaternary ammonium skeleton.

[0101] The aqueous electrolyte contains an aqueous solvent and an electrolyte salt. As the aqueous solvent, a solution containing water can be used. The solution containing water may be pure water, or a mixed solution or mixed solvent of water and a substance other than water.

[0102] The aqueous electrolyte is, for example, an aqueous solution prepared by dissolving an electrolyte salt in an aqueous solvent. The aqueous electrolyte may be a gel-like aqueous electrolyte prepared by compounding the aqueous solution with a polymer material. Examples of the polymer material include polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0103] The aqueous solution preferably contains 1 mol or more of an aqueous solvent per mol of an electrolyte salt as a solute, and more preferably contains 3.5 mol or more of an aqueous solvent per mol of an electrolyte salt.

[0104] The presence of water in aqueous electrolytes can be confirmed by GC-MS (Gas Chromatography - Mass Spectrometry) measurements. The salt concentration and water content in aqueous electrolytes can be calculated, for example, by ICP (Inductively Coupled Plasma) emission spectrometry. The molar concentration (mol / L) can be calculated by weighing a specified amount of aqueous electrolyte and calculating the salt concentration. The number of moles of solute and solvent can also be calculated by measuring the specific gravity of the aqueous electrolyte.

[0105] Examples of the electrolyte salt include lithium salts such as LiCl, LiBr, LiOH, Li2SO4, LiNO3, LiN(SO2CF3)2 (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide), LiN(SO2F)2 (LiFSI: lithium bis(fluorosulfonyl)imide), and LiB[(OCO)2]2 (LiBOB: lithium bis(oxalatoborate). The type of lithium salt used may be one type or two or more types.

[0106] The electrolyte may contain Co ions. The Co ions may be, for example, Co atoms in a carbon material contained in the positive electrode that are oxidized and released.

[0107] 4) Separator The separator includes a substrate and a portion containing a Co atom present in the substrate. The separator may include the portion containing a Co atom, for example, on the surface in contact with the negative electrode.

[0108] The separator may be, for example, in the form of a sheet-like substrate having two main surfaces, with the site present. Therefore, the separator may be in the form of a sheet having two main surfaces. The surface in contact with the negative electrode may be present on at least one of the main surfaces of the separator. The surface in contact with the negative electrode may be present on both main surfaces of the separator, but it is preferable that the portion of the separator having the surface in contact with the negative electrode on one main surface does not contact the negative electrode on the other main surface.

[0109] As described above, the separator includes a region disposed between the positive electrode and the negative electrode. At least a portion of the surface that contacts the negative electrode is present within the region. Furthermore, the surface that contacts the negative electrode may be present outside the region.

[0110] The substrate of the separator may include a porous body containing at least one material selected from the group consisting of polyolefin, cellulose, and polyvinylidene fluoride (PVdF). Examples of the porous body include, for example, a porous film and a nonwoven fabric. Examples of the polyolefin include, for example, polyethylene (PE) and polypropylene (PP). From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of cutting off electric current.

[0111] The site containing Co atoms is included in the surface of the separator that contacts the negative electrode. The site may be included in the surface of the separator that contacts the positive electrode, or may be present penetrating the separator in the thickness direction. The site may also be present across the negative electrode and the separator.

[0112] The site includes a substance containing a Co atom. The substance containing a Co atom may be at least one of metallic Co, cobalt oxide, and cobalt fluoride. Examples of cobalt oxide include CoO and Co3O4, and examples of cobalt fluoride include CoF2 and CoF3. The site may include one of the above, or may include two or more of the above.

[0113] Metal Co may be, for example, a product of the carbon material contained in the positive electrode being dissolved in the electrolyte, and then reduced and precipitated on the negative electrode. Cobalt oxide may be produced by oxidizing the metal Co precipitated as described above. Cobalt fluoride may be produced, for example, by reacting the metal Co precipitated as described above with hydrogen fluoride.

[0114] The portion may be formed by depositing at least one selected from the group consisting of a metal, a metal oxide, and a metal fluoride in a layer shape. The shape of the portion may be any shape, such as a granular shape, a striped shape, or the like.

[0115] The site can be detected by X-ray fluorescence analysis mapping, which will be described later. In X-ray fluorescence analysis mapping, the site can be detected as being approximately circular or approximately elliptical.

[0116] The part preferably has an average diameter of 0.1 mm or more and 0.5 mm or less. If the average diameter of the part is small, even if the part penetrates the separator, the contact interface with the positive electrode is unlikely to become dense. In addition, the positive electrode surface has a high potential. Therefore, the Co atoms contained in the part can be oxidized and ionized on the surface of the separator that contacts the positive electrode, and can dissolve in the electrolyte. If the average diameter of the part is small, the dissolution of the part tends to proceed more favorably than the growth. Therefore, the part is unlikely to come into contact with the positive electrode. Therefore, even if the part penetrates the separator, internal short circuit is unlikely to occur, and self-discharge can be suppressed.

[0117] The portion may be conductive or non-conductive, although from the viewpoint of preventing internal short circuits, it is preferable that the portion not be conductive.

[0118] 5) Exterior materials As the exterior member, for example, a container made of a laminate film or a metal container can be used.

[0119] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0120] The laminate film is a multi-layer film including a plurality of resin layers and a metal layer interposed between the resin layers. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be molded into the shape of the exterior member by sealing it by heat fusion.

[0121] 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.

[0122] 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. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of the transition metals is preferably 100 ppm by mass or less.

[0123] 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, or button. The exterior member can be appropriately selected depending on the battery dimensions and the application of the battery.

[0124] 6) Negative terminal The negative electrode terminal has a potential range of 1V to 3V with respect to the redox potential of lithium (vs. Li / Li + ) and can be formed from a material that is electrically stable and conductive. Specifically, the material of 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. The material of the negative electrode terminal is preferably aluminum or an aluminum alloy. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce the contact resistance with the negative electrode current collector.

[0125] 7) Positive terminal The positive electrode terminal has a potential range of 3V to 4.5V with respect to the redox potential of lithium (vs. Li / Li +) and can be formed from a material that is electrically stable and conductive. Examples of the material for the positive electrode terminal include aluminum and an aluminum alloy 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 the contact resistance with the positive electrode current collector.

[0126] <Manufacturing method> A manufacturing method of a secondary battery according to the embodiment may include, for example, a step of preparing a first battery including a first electrode group including a first positive electrode containing a Co atom-containing carbon material, a first negative electrode, and a first separator not including a portion, and an electrolyte, and a step of obtaining a secondary battery by applying a constant current under predetermined conditions to the first battery.

[0127] In other words, the secondary battery according to the embodiment may be a first battery before the constant current is applied. The electrode group included in the secondary battery according to the embodiment may be a first electrode group before the constant current is applied. The positive electrode, negative electrode, and separator included in the electrode group may be a first positive electrode, a first negative electrode, and a first separator included in the first electrode group, respectively, before the constant current is applied. The carbon material included in the positive electrode may be a Co atom-containing carbon substance included in the first positive electrode before the constant current is applied.

[0128] The steps of preparing the first battery and obtaining a secondary battery by applying a constant current to the first battery under predetermined conditions will be described in detail below. As an example of the secondary battery of the embodiment, a method for producing a secondary battery including a wound electrode group will be described below.

[0129] (Preparing the first battery) The first battery can be prepared by preparing a first positive electrode, a first negative electrode, and a first separator, fabricating a first electrode group including the first positive electrode, the first negative electrode, and the first separator, housing the first electrode group in an exterior member, injecting an electrolyte into the exterior member, and then sealing the exterior member.

[0130] (First positive electrode) The first positive electrode containing a Co atom-containing carbon material can be produced, for example, as follows.

[0131] First, a positive electrode active material, a positive electrode conductive agent, and a binder are suspended in a solvent to prepare a positive electrode slurry. However, the positive electrode conductive agent contains a Co atom-containing carbon material instead of a carbon material. The details of the Co atom-containing carbon material will be described later. The positive electrode active material and the binder can be the same as those described for the positive electrode included in the secondary battery according to the embodiment. The blending of each material can be the same as that described for the positive electrode included in the secondary battery according to the embodiment, except that a Co atom-containing carbon material is blended instead of the carbon material.

[0132] The positive electrode slurry is applied to one or both sides of the positive electrode current collector. If necessary, the positive electrode current collector may be coated except for a part thereof. The uncoated part of the positive electrode current collector may be used as a positive electrode current collector tab. The positive electrode current collector may be the same as that described for the positive electrode. Next, the applied positive electrode slurry is dried to obtain a laminate of the coating film and the positive electrode current collector. Then, the laminate is pressed. In this manner, the first positive electrode is produced. Alternatively, the first positive electrode may be produced by the following method. First, a positive electrode active material, a binder, and a positive electrode conductive agent containing a Co atom-containing carbon material instead of a carbon material are mixed to obtain a mixture. Next, the mixture is formed into a pellet shape. Next, these pellets are placed on the positive electrode current collector to obtain the first positive electrode. Of the first positive electrode, the coating film or pellets may correspond to the positive electrode active material-containing layer in the positive electrode.

[0133] The Co atom-containing carbon material to be contained in the first positive electrode can be prepared as follows.

[0134] As the Co atom-containing carbon substance, a carbonaceous material containing Co atoms can be used. Examples of the carbonaceous material include vapor grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. The type of carbonaceous material can be one or more types.

[0135] When the amount of Co atoms contained in the carbonaceous material is large, the amount of Co atoms contained in the carbon material tends to be large in the secondary battery obtained after production. The carbonaceous material containing Co atoms preferably contains Co atoms in the range of 100 mass ppm to 6000 mass ppm. When two or more kinds of carbonaceous materials are mixed and used, the Co atom concentration may vary depending on the type of carbonaceous material, and may contain a carbonaceous material that does not contain Co atoms. When a mixture of two or more kinds of carbonaceous materials is used as a Co atom-containing carbon material, the Co atom concentration of the mixture is in the range of 100 mass ppm to 6000 mass ppm. Such a mixture can also be said to be a carbonaceous material containing Co atoms at a concentration of 100 mass ppm to 6000 mass ppm. The concentration of Co atoms contained in the carbonaceous material containing Co atoms may be, for example, 200 mass ppm or more and 3000 mass ppm or less.

[0136] The Co atom-containing carbonaceous material preferably contains a second carbonaceous material obtained by heat-treating the first carbonaceous material in a reducing atmosphere. Co / (A Co +A CoO +A Co3O4 The value of A) can be 0.6 or more. When such a Co atom-containing carbon material is used, the above-mentioned Co / (A Co +A CoO +A Co3O4 ) value of 0.6 or more can be obtained.

[0137] The first carbon substance may be the carbonaceous material containing Co atoms described above. Since Co atoms are easily oxidized, the Co atoms contained in the first carbon substance may be in an oxidized state.

[0138] The second carbon substance is obtained by heat-treating the first carbon substance in a reducing atmosphere. The Co atoms contained in the second carbon substance may be in a more reduced state than the Co atoms contained in the first carbon substance. Co / (A Co +A CoO +A Co3O4 ) can be high. Co / (A Co +A CoO +A Co3O4 ) may be, for example, 0.6 or greater.

[0139] The heat treatment in a reducing atmosphere can be carried out, for example, by putting the first carbon material into a reducing gas and holding it at a predetermined treatment temperature. By adjusting the conditions such as the Co concentration of the first carbon material to be subjected to the heat treatment, the type of reducing gas, the treatment temperature of the heat treatment, and the holding time, the above-mentioned A Co / (A Co +A CoO +A Co3O4 ) value of 0.6 or more can be obtained.

[0140] The reducing gas may be any gas that can function as a reducing agent for cobalt oxide at the treatment temperature, such as hydrogen gas (H2), ammonia (NH3), or carbon monoxide gas (CO).

[0141] The temperature of the heat treatment can be, for example, in the range of 600° C. to 1100° C. If the treatment temperature is too low, the reduction of the Co atoms may be insufficient, and the reduction state of the Co atoms contained in the obtained second carbon material may be low. If the treatment temperature is too high, it may become necessary to use a highly heat-resistant material for the reactor in the device used for the reduction treatment.

[0142] The holding time of the heat treatment can be, for example, 10 minutes or more and 120 minutes or less. If the holding time is too short, the reduction of the Co atoms is insufficient, so that the reduction state of the Co atoms contained in the obtained second carbon material may be low. If the holding time is too long, the production efficiency may be low.

[0143] The above heat treatment can be carried out before preparing the first positive electrode.

[0144] (First negative electrode) The first negative electrode can be prepared, for example, by the following method. First, the negative electrode active material, the negative electrode conductive agent, and the binder are suspended in a solvent to prepare a negative electrode slurry. The blending of each material can be the same as that described for the negative electrode included in the secondary battery according to the embodiment. The negative electrode slurry is applied to one side or both sides of the negative electrode current collector. If necessary, the negative electrode current collector may be coated except for a part thereof. The uncoated part of the negative electrode current collector can be used as a negative electrode current collector tab. Next, the applied negative electrode slurry is dried to obtain a laminate of the coating film and the negative electrode current collector. Then, the laminate is pressed. In this way, the first negative electrode is prepared. Alternatively, the first negative electrode may be prepared by the following method. First, the negative electrode active material, the negative electrode conductive agent, and the binder are mixed to obtain a mixture. Then, the mixture is formed into pellets. Then, these pellets are placed on the negative electrode current collector to obtain the first negative electrode. In the first negative electrode, the coating film or pellet may correspond to the negative electrode active material-containing layer in the negative electrode.

[0145] (First separator) The first separator includes the base material described above. The first separator may include the portion described above. The first separator may not include the portion, and may be made of the base material described above. Here, "not including the portion" refers to, for example, that the ratio of Co atoms is less than 60 mass% over the entire surfaces of the two main surfaces of the first separator in fluorescent X-ray analysis mapping. Other than the above, the separator may be the same as that described for the separator included in the secondary battery according to the embodiment.

[0146] A laminate in which a first negative electrode, a first separator, a first positive electrode, and a first separator are stacked in this order is wound in a spiral shape around an axis parallel to the short side direction to produce a wound-type first electrode group.

[0147] The structure of the first electrode group can be the same as the structure of the electrode group 1 previously described with reference to Figures 1 to 3. Specifically, a first electrode group having a structure similar to that of the electrode group 1 can be produced by disposing a first positive electrode, a first negative electrode, and a first separator at the positions of the positive electrode 5, the negative electrode 3, and the separator 4 shown in Figure 1, respectively. A positive electrode terminal is electrically connected to the first positive electrode of the first electrode group, and a negative electrode terminal is electrically connected to the first negative electrode of the first electrode group.

[0148] The first electrode group is housed in a bag-shaped exterior member made of a laminate film, and then an electrolyte is injected into the bag-shaped exterior member, which is then sealed to obtain a first battery.

[0149] (Constant current application step) The first battery prepared as described above is subjected to constant current charging. The constant current charging can be performed, for example, by applying a constant current for 10 to 30 seconds to the first battery having a state of charge (SOC) of 90% to 95% at a temperature of -5°C to 25°C. Before the constant current charging, it is preferable to adjust the SOC of the first battery to within the above range. When a capacity confirmation test is performed, the SOC can be adjusted after the capacity confirmation test and before the constant current charging.

[0150] It is preferable that the SOC of the first battery during constant current charging is 90% or more because the potential of the negative electrode can be lowered to facilitate deposition of Co. It is preferable that the SOC is 95% or less because the potential of the negative electrode during constant current charging does not become too low, thereby suppressing deterioration of the negative electrode.

[0151] If the temperature during constant current charging is -5°C or higher, excessive precipitation of metallic cobalt in a dendrite shape can be suppressed. It is more preferable that the temperature during constant current charging is 0°C or higher. By keeping the temperature at 25°C or lower, excessive growth of metallic cobalt crystals on the part can be suppressed. Therefore, it is possible to suppress the metallic cobalt crystals from breaking through the first separator, causing a short circuit.

[0152] When the current value of the constant current charge is high, Co deposited on the negative electrode is likely to deposit and grow in a dendrite shape. Therefore, the portion containing Co atoms is likely to grow along a direction perpendicular to the surface direction of the separator rather than along the surface direction of the separator. Therefore, the diameter of the portion containing Co atoms may be small. As a result, the proportion (density) of the area occupied by the portion on the separator surface tends to be small. When the current value of the constant current charge is low, the crystals of Co deposited on the negative electrode are likely to grow in the surface direction and become island-like. Therefore, the portion containing Co atoms is likely to grow along the surface direction of the separator. Therefore, the diameter of the portion containing Co atoms may be large. Therefore, the proportion of the area occupied by the portion on the separator surface tends to be large.

[0153] The current value of the constant current charging is 1 cm 2 It is preferable to perform the measurement so that the current value per unit time is within the range of 0.4x to 1.3x. Here, for example, 0.4x is a value obtained by multiplying 0.4 by x. x is a value calculated by the following formula. In the following formula, A 10C is the current value at which the battery capacity of the obtained secondary battery is discharged in 1 hour at a current value of 10C, and the opposing area S is the area of ​​the portion of the first positive electrode that faces the first negative electrode.

[0154] (Number 1) x=A 10C [A] / S[cm 2 ] In other words, x is the area of ​​1 cm when a current equivalent to 10C is applied to the secondary battery. 2 is the amount of current applied per

[0155] When the constant current charging time is increased, the amount of Co deposited on the negative electrode increases, and the average diameter of the portion tends to increase. When the constant current charging time is decreased, the amount of Co deposited on the negative electrode decreases, and the average diameter of the portion tends to decrease. Therefore, the constant current charging time can be set within a range of 10 seconds to 30 seconds.

[0156] Furthermore, by charging the first battery at a constant current, the potential of the first negative electrode drops. Therefore, Co atoms (Co ions) in the electrolyte may be reduced and precipitated. As a result, a substance containing Co may be formed on the first negative electrode. When the substance comes into contact with the first separator, a separator including a base material and a portion containing Co atoms present in the base material can be obtained.

[0157] By going through the above steps, the secondary battery according to the embodiment can be obtained from the first battery.

[0158] Before the constant current charging, for example, a capacity confirmation test, an initial charge and an initial discharge (initial charge and discharge) or aging may be performed. The capacity confirmation test, the initial charge and discharge, and aging may be performed by a known method.

[0159] By performing the initial charge, the potential of the first positive electrode can be increased. Therefore, the Co atoms contained in the Co atom-containing carbon material in the first positive electrode can be oxidized and dissolved, and Co ions can be released into the electrolyte. As a result, a positive electrode containing a carbon material containing Co atoms at a concentration of 100 mass ppm to 1500 mass ppm can be obtained.

[0160] After the constant current charging, constant voltage charging may be performed. The constant voltage charging may be performed, for example, by charging the secondary battery after the constant current charging at a constant voltage of about 3V. The constant voltage charging may be performed, for example, until the charging current reaches a current value equivalent to 1 / 20C. By performing the constant voltage charging, the negative electrode can be kept in a state in which Co atoms are easily precipitated. Therefore, the number of sites containing Co atoms can be increased. In addition, the average diameter of the sites can be increased. Therefore, when the constant voltage charging is performed, even if the voltage during the constant current charging is lowered, the number of sites containing Co atoms can be increased or the average diameter of the sites can be increased. Therefore, the deterioration of the secondary battery caused by the voltage during the constant current charging becoming too high can be suppressed. Therefore, even if the resistance of the secondary battery is relatively high, the deterioration of the secondary battery can be suppressed.

[0161] The above describes an example of a method for manufacturing a secondary battery including a wound-type electrode group. In manufacturing the first electrode group, the structure of the first electrode group may be the same as the structure of electrode group 1 described above with reference to Figures 6 to 7. A secondary battery including a stacked electrode group can be manufactured in the same manner as the manufacturing method described above except for this.

[0162] <Measurement method> (Measurement of the concentration of Co atoms contained in carbon materials) The concentration of Co atoms contained in the carbon material can be measured by disassembling the secondary battery to remove the positive electrode, separating the carbon material from the positive electrode, and using ICP (inductively coupled plasma).

[0163] First, adjust the SOC of the secondary battery to 0% and disassemble it to remove the positive electrode. The positive electrode is immersed in NMP and ultrasonically dispersed. This allows the positive electrode active material-containing layer and the positive electrode current collector to be separated.

[0164] Next, the dispersion liquid after removing the positive electrode current collector is centrifuged to separate the positive electrode active material and the carbon material. For example, if the specific gravity of the positive electrode active material is larger than that of the carbon material, the positive electrode active material having a larger specific gravity will settle after centrifugation, and the carbon material having a smaller specific gravity will be contained in the supernatant. Centrifugation is performed at 2000 rpm for 10 minutes.

[0165] First, the dispersion is centrifuged and the supernatant is taken out. This operation is called the first centrifugation. The supernatant obtained from the first centrifugation is further centrifuged. This operation is called the second centrifugation. The supernatant obtained from the second centrifugation is taken out.

[0166] The centrifugation operation is repeated five times in the same manner. The supernatant obtained from the fifth centrifugation is filtered to separate the liquid and solid components in the supernatant. The solid components are dried to obtain a powder of the carbon material. The mass of the obtained powder is measured.

[0167] The obtained powder is placed in aqua regia and stirred overnight. In this way, the Co in the carbon material powder is eluted. The eluate is subjected to ICP (inductively coupled plasma) measurement to measure the Co content in the eluate. The Co concentration of the carbon material is calculated from the measured Co content and a calibration curve of Co concentration created using the standard solution.

[0168] (X-ray absorption spectroscopy) The reduction state of the Co atoms contained in the carbon material can be identified using X-ray absorption spectroscopy.

[0169] First, a carbon material is sandwiched between plastic tapes to prepare a measurement sample, or the carbon material may be formed into pellets to prepare a measurement sample.

[0170] In the beamline, the measurement sample is irradiated with X-rays including the energy band between 7700 eV and 7760 eV, which is the absorption edge of Co. For example, a large synchrotron radiation facility can be used as the beamline. From the X-ray intensity before and after X-ray irradiation, an X-ray absorption spectrum can be obtained, with the X-ray energy (eV) on the horizontal axis and the amount of X-ray absorption on the vertical axis.

[0171] Of the X-ray absorption spectra obtained by the above method, the range from 7700 eV to 7760 eV is the X-ray absorption edge of Co. The spectrum in this range is subjected to linear combination fitting as follows.

[0172] First, three types of reference samples are prepared: metallic Co foil, CoO, and Co3O4. For each of the reference samples, an X-ray absorption spectrum is obtained in the same manner as above. The X-ray absorption spectrum of the measurement sample is linearly combined and fitted to each of the X-ray absorption spectra of the three reference samples. By linearly combining and fitting the X-ray absorption spectrum of the metallic Co foil, the ratio A of Co atoms present as metallic Co in the carbon material is obtained. Co By linear combination fitting of the X-ray absorption spectrum for CoO, the ratio A of Co atoms existing as CoO in the carbon material can be obtained. CoO By linear combination fitting of the X-ray absorption spectrum for Co3O4, the ratio A of Co atoms existing as Co3O4 in the carbon material can be obtained. Co3O4 The linear combination fitting can be performed using, for example, Athena described in Non-Patent Document 1.

[0173] In order to prevent the Co component contained in the carbon material in the positive electrode, for example, metallic cobalt, from reacting with oxygen gas in the air and changing the reduction state of the Co atom, it is preferable that the series of operations from disassembly of the secondary battery to X-ray absorption spectroscopy measurement be performed quickly or in an inert atmosphere of argon, nitrogen gas, or the like.

[0174] (X-ray fluorescence analysis mapping) The composition analysis of the parts, the measurement of the average diameter of the parts, and the measurement of the number of parts per unit area can be performed by X-ray fluorescence analysis (XRF) mapping of the outermost separator. Specifically, the following procedure can be used.

[0175] First, after the secondary battery is completely discharged, the secondary battery is disassembled in a glove box filled with argon, and the separator is taken out. The surface of the separator facing the negative electrode is used for measurement. If necessary, the part of the separator to be observed is cut out. For example, the outermost layer of the separator is cut out. The obtained separator is soaked in ethanol and ultrasonically cleaned for 5 minutes. After cleaning, the separator is dried in the air. If any electrode pieces are attached to the separator, they are removed by high-pressure air or wiping. In this manner, a sample for observation is obtained.

[0176] The observation sample is subjected to XRF analysis under the following conditions.

[0177] Tube voltage: 50kV Tube current: 1000μA Collimator: 1.2×1.2mm Field of view: 30mm x 50mm range (276x494 pixels) If the measurement field of view is insufficient, measurements are performed in multiple fields of view and the entire area of ​​the observation sample is analyzed. When acquiring images of multiple fields of view, it is preferable to acquire images at 0.1 mm / 1 pixel or less in order to obtain sufficient accuracy for extracting boundaries during image analysis. If it is greater than 0.1 mm / 1 pixel, there is a concern that the size and boundaries of the area to be detected will become unclear.

[0178] The composition of the region is qualitatively analyzed from the elemental mapping data obtained by XRF. From the results of the qualitative analysis, the region where the ratio of Co atoms is 60 mass% or more can be defined as the region.

[0179] Next, the XRF mapping image data is binarized using Image J (version 1.52a). In the binarization, for example, areas where the proportion of Co atoms is less than 60% by mass can be expressed as white, and areas where the proportion of Co atoms is 60% by mass or more can be expressed as black.

[0180] For the obtained binarized image, the average diameter of the regions and the number of regions per unit area are measured. In the binarized image binarized by the above-mentioned method, the regions expressed as black are the regions.

[0181] The number of particles per unit area of ​​the part can be calculated by the particle counting process (Analyze particle) in Image J. The particle detection conditions are size 0-infinity and circularity 0-1, and analysis is performed. This makes it possible to count all black regions with boundaries in the binarized image, that is, regions where the proportion of Co atoms is 60% by mass or more.

[0182] The average diameter of a region can be calculated as follows. The number of pixels in the binarized image is matched to the actual scale in advance. The Feret's diameter is measured for each region in this binarized image using Image J. The Feret's diameter of the actual region is calculated from the number of pixels in the measurement result. This value is regarded as the diameter of each region. In this way, the diameter of each region is obtained, and the average of these can be calculated as the average diameter of the region.

[0183] If a site is formed on the surface facing the negative electrode out of the two surfaces of the separator, it can be confirmed that a substance containing Co atoms is formed on the negative electrode.

[0184] (Measurement of the average working potential of the negative electrode using a three-electrode cell) The average working potential of the negative electrode can be measured as follows. A three-electrode cell is prepared with the negative electrode to be measured as the working electrode, and metallic lithium foil as the counter electrode and reference electrode. For this three-electrode cell, the natural potential (Open Circuit Voltage: OCV) is reduced by 0.6 V vs. Li / Li at 25°C.+ Charge the battery at a constant current and constant voltage of 0.1C until the battery reaches a discharge current of 1 / 20C. Then discharge the battery at a constant current and constant voltage of 0.1C until the discharge current reaches 1 / 20C. The average potential (vs. Li / Li + ) is measured.

[0185] According to a first embodiment, a secondary battery is provided. The secondary battery includes an electrode group including a positive electrode, a negative electrode, and a separator, and an electrolyte. The positive electrode includes a positive electrode active material and a carbon material. The carbon material contains Co atoms at a concentration of 100 mass ppm to 1500 mass ppm. The separator includes a substrate and a site containing Co atoms present in the substrate. In a region where the separator is disposed between the positive electrode and the negative electrode, the outermost layer that is the outermost layer in the electrode group contains 200 sites containing Co atoms / m 2 More than 10000 pieces / m 2 The content is as follows: As a result, it is possible to provide a secondary battery that is excellent in high-temperature storage performance and input / output characteristics, and in which self-discharge is suppressed.

[0186] Second embodiment According to a second embodiment, there is provided a battery pack including a plurality of secondary batteries according to the first embodiment.

[0187] In such a battery pack, the individual cells may be electrically connected in series or parallel, or may be arranged in a combination of series and parallel connections.

[0188] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0189] Fig. 8 is a perspective view showing an example of a battery pack. The battery pack 200 shown in Fig. 8 includes five cells 100a to 100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five cells 100a to 100e is a secondary battery according to the first embodiment.

[0190] The bus bar 21 connects, for example, the negative electrode terminal 6 of one cell 100a and the positive electrode terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by the four bus bars 21. That is, the battery pack 200 in FIG. 8 is a five-series battery pack. Although no example is shown, in a battery pack including a plurality of cells electrically connected in parallel, for example, the plurality of negative electrode terminals are connected to each other by a bus bar and the plurality of positive electrode terminals are connected to each other by a bus bar, thereby electrically connecting the plurality of cells.

[0191] The positive electrode terminal 7 of at least one of the five cells 100a to 100e is electrically connected to a positive electrode lead 22 for external connection. Also, the negative electrode terminal 6 of at least one of the five cells 100a to 100e is electrically connected to a negative electrode lead 23 for external connection.

[0192] The battery pack according to the second embodiment includes the secondary battery according to the first embodiment, and therefore it is possible to provide a battery pack that is excellent in high-temperature storage performance and input / output characteristics, and in which self-discharge is suppressed.

[0193] (Third embodiment) According to a third embodiment, a battery pack is provided. The battery pack includes the battery assembly according to the second embodiment. The battery pack may include a single secondary battery according to the first embodiment, instead of the battery assembly according to the second embodiment.

[0194] Such a battery pack may further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the secondary battery. Alternatively, a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack as a power source may be used as the protection circuit for the battery pack.

[0195] The battery pack may further include an external terminal for current flow. The external terminal for current flow is for outputting current from the secondary battery to the outside and / or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for current flow. When the battery pack is charged, a charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminal for current flow.

[0196] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0197] Fig. 9 is an exploded perspective view showing an example of a battery pack, and Fig. 10 is a block diagram showing an example of an electric circuit of the battery pack shown in Fig. 9.

[0198] The battery pack 300 shown in Figs. 9 and 10 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

[0199] 9 is a bottomed, square container having a rectangular bottom. The container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31 to accommodate the battery pack 200 and the like. Although not shown, the container 31 and the lid 32 are provided with openings or connection terminals for connection to an external device or the like.

[0200] The battery pack 200 includes a plurality of cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0201] At least one of the plurality of unit cells 100 is the secondary battery according to the first embodiment. Each of the plurality of unit cells 100 is electrically connected in series as shown in FIG. 10. The plurality of unit cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the plurality of unit cells 100 are connected in parallel, the battery capacity is increased compared to when they are connected in series.

[0202] The adhesive tape 24 fastens the plurality of unit cells 100. The plurality of unit cells 100 may be fixed using heat shrink tape instead of the adhesive tape 24. In this case, the protective sheets 33 are disposed on both side surfaces of the battery pack 200, the heat shrink tape is wrapped around the battery pack 200, and the heat shrink tape is then thermally shrunk to bind the plurality of unit cells 100 together.

[0203] One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100.

[0204] The printed wiring board 34 is disposed along one of the short side surfaces of the inner surface of the container 31. The printed wiring board 34 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 electricity, a positive wiring (positive wiring) 348a, and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

[0205] The other end 22a of the positive electrode lead 22 is electrically connected to the positive electrode connector 342. The other end 23a of the negative electrode lead 23 is electrically connected to the negative electrode connector 343.

[0206] The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each of the cells 100, and transmits a detection signal to the protection circuit 346.

[0207] The external terminal 350 for current supply is fixed to the other main surface of the printed wiring board 34. The external terminal 350 for current supply is electrically connected to a device present outside the battery pack 300. The external terminal 350 for current supply includes a positive terminal 352 and a negative terminal 353.

[0208] The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via 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 electrode connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative electrode connector 343 via a wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the plurality of single cells 100 via the wiring 35.

[0209] The protective sheet 33 is disposed on both inner surfaces in the long side direction of the container 31 and on the inner surface in the short side direction that faces the printed wiring board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0210] The protection circuit 346 controls charging and discharging of the multiple cells 100. In addition, the protection circuit 346 cuts off 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 of the cells 100 or the battery pack 200.

[0211] An example of the detection signal transmitted from the thermistor 345 is a signal that detects 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 that detects overcharging, overdischarging, and overcurrent of the cell 100. When detecting overcharging 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.

[0212] 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.

[0213] As described above, the battery pack 300 includes the external terminal 350 for current supply. Therefore, the battery pack 300 can output a current from the assembled battery 200 to an external device and input a current from the external device to the assembled battery 200 via the external terminal 350 for current supply. In other words, when the battery pack 300 is used as a power source, the current from the assembled battery 200 is supplied to the external device through the external terminal 350 for current supply. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 through the external terminal 350 for current supply. When the battery pack 300 is used as an in-vehicle battery, regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0214] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive electrode lead 22 and the negative electrode lead 23 may be used as a positive terminal 352 and a negative terminal 353, respectively, of the external terminal 350 for current supply.

[0215] Such a battery pack is used in applications that require excellent cycle performance, for example, when a large current is drawn. Specifically, the battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. An example of the electronic device is a digital camera. The battery pack is particularly suitable for use as an on-board battery.

[0216] The battery pack according to the third embodiment includes the secondary battery according to the first embodiment or the battery pack according to the second embodiment, and therefore has excellent high-temperature storage performance and input / output characteristics, and can suppress self-discharge.

[0217] (Fourth embodiment) According to a fourth embodiment, a vehicle is provided. The vehicle is equipped with the battery pack according to the third embodiment.

[0218] In such a vehicle, the battery pack, for example, recovers regenerative energy of the vehicle's motive power. The vehicle may include a mechanism (regenerator) that converts the kinetic energy of the vehicle into regenerative energy.

[0219] Examples of vehicles include, for example, two to four wheel hybrid electric vehicles, two to four wheel electric vehicles, power assisted bicycles, and rail vehicles.

[0220] The mounting position of the battery pack in the vehicle is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

[0221] The vehicle may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. For example, when each battery pack includes a battery pack, the battery packs may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. Alternatively, when each battery pack includes a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections.

[0222] Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

[0223] FIG. 11 is a partially see-through view that diagrammatically illustrates an example of a vehicle.

[0224] A vehicle 400 shown in Fig. 11 includes a vehicle body 40 and a battery pack 300 according to the third embodiment. In the example shown in Fig. 11, the vehicle 400 is a four-wheeled automobile.

[0225] The vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the batteries (e.g., single cells or assembled batteries) included in the battery pack 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

[0226] 11 illustrates an example in which the battery pack 300 is mounted in an engine room located in the front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, in the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for the motive power of the vehicle 400.

[0227] Next, an embodiment of a vehicle according to the present embodiment will be described with reference to FIG.

[0228] Fig. 12 is a diagram illustrating an example of a control system for an electrical system in a vehicle. The vehicle 400 illustrated in Fig. 12 is an electric vehicle.

[0229] The vehicle 400 shown in FIG. 12 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a higher-level control device of the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

[0230] The vehicle 400 has a vehicle power supply 41 mounted, for example, in an engine compartment, the rear of the vehicle body, or under a seat. Note that in the vehicle 400 shown in Fig. 12, the mounting location of the vehicle power supply 41 is shown diagrammatically.

[0231] The vehicle power supply 41 includes a plurality of (eg, three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0232] The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (for example, VTM: Voltage Temperature Monitoring). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. The battery packs 300a to 300c are battery packs similar to the above-mentioned battery pack 300, and the assembled batteries 200a to 200c are assembled batteries similar to the above-mentioned battery pack 200. The assembled batteries 200a to 200c are electrically connected in series. The battery packs 300a, 300b, and 300c can be removed independently and replaced with another battery pack 300.

[0233] Each of the assembled batteries 200a to 200c includes a plurality of unit cells connected in series. At least one of the plurality of unit cells is the secondary battery according to the first embodiment. Each of the assembled batteries 200a to 200c is charged and discharged via a positive terminal 413 and a negative terminal 414.

[0234] The battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c, and collects information on the voltage, temperature, and the like of each of the cells 100 included in the assembled batteries 200a to 200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information on the maintenance of the vehicle power supply 41.

[0235] The battery management unit 411 and the assembled battery monitoring units 301a to 301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by a plurality of nodes (the battery management unit 411 and one or more assembled battery monitoring units 301a to 301c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

[0236] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each of the cells constituting the battery packs 200a to 200c based on commands communicated from the battery management device 411. However, the temperature can be measured at only a few points per battery pack, and it is not necessary to measure the temperatures of all the cells.

[0237] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in FIG. 12) that switches between the presence and absence of an electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that is turned on when the assembled batteries 200a to 200c are charged, and a main switch (not shown) that is turned on when the output from the assembled batteries 200a to 200c is supplied to a load. Each of the pre-charge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil disposed near the switch element. The electromagnetic contactor such as the switch device 415 is controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0238] The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

[0239] The drive motor 45 rotates by electric power supplied from the inverter 44. A driving force generated by the rotation of the drive motor 45 is transmitted to the axles and drive wheels W via, for example, a differential gear unit.

[0240] Although not shown, the vehicle 400 is also equipped with a regenerative braking mechanism (regenerator). The regenerative braking mechanism rotates the drive motor 45 when the vehicle 400 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into a direct current. The converted direct current is input to the vehicle power source 41.

[0241] One terminal of a connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of the connection line L1 is connected to a negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 in the battery management device 411 is provided between the negative terminal 414 and the negative input terminal 417 on the connection line L1.

[0242] One terminal of a connection line L2 is connected to the positive electrode terminal 413 of the vehicle power supply 41. The other terminal of the connection line L2 is connected to a positive electrode input terminal 418 of the inverter 44. A switch device 415 is provided in the connection line L2 between the positive electrode terminal 413 and the positive electrode input terminal 418.

[0243] The external terminal 43 is connected to the battery management unit 411. The external terminal 43 can be connected to, for example, an external power source.

[0244] In response to operational inputs from the driver or the like, the vehicle ECU 42 coordinates with other management devices and control devices including the battery management device 411 to control the vehicle power supply 41, the switch device 415, the inverter 44, etc. Through the coordinated control of the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, and the entire vehicle 400 is managed. Data relating to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

[0245] The vehicle according to the fourth embodiment is equipped with the battery pack according to the third embodiment. Therefore, according to this embodiment, it is possible to provide a vehicle including a battery pack that is excellent in high-temperature storage performance and input / output characteristics and can suppress self-discharge. EXAMPLES

[0246] Examples will be described below, but the embodiments are not limited to the examples described below.

[0247] Example 1 <Preparation of the first negative electrode> Nb2O5 particles and TiO2 particles were mixed in a molar ratio of 1:1. The obtained powder was placed in an alumina crucible and heated at 800°C for 10 hours. Then, the mixture was crushed and mixed, and pre-fired again at 800°C for 10 hours to obtain precursor particles. The obtained precursor particles were then fired at 1100°C for 5 hours to obtain Nb2TiO7(TNO) powder.

[0248] The above-mentioned Nb2TiO7 (TNO) powder was prepared as the negative electrode active material, acetylene black (AB) and multi-walled carbon nanotubes (MWCNT) as the negative electrode conductive agent, carboxymethylcellulose (CMC) sodium salt powder as the binder, and styrene butadiene rubber (SBR) dispersion as the binder. These materials were mixed in pure water as a solvent in a ratio of 86 parts by mass of TNO powder, 5 parts by mass of AB, 5 parts by mass of MWCNT, 2 parts by mass of CMC sodium salt powder, and 2 parts by mass of SBR. The mixing was performed in the following order while stirring the pure water. After dissolving the CMC sodium salt in the pure water, the SBR dispersion was further mixed to obtain a dispersion. AB and MWCNT were dispersed in this dispersion, and finally the TNO powder was dispersed. Thus, a negative electrode slurry was obtained. This negative electrode slurry was applied to both sides of a negative electrode current collector made of aluminum foil with a thickness of 12 μm. The negative electrode slurry was then dried and pressed to obtain a first negative electrode. The first negative electrode was cut into a rectangle so that one side of the rectangle had a portion on the negative electrode current collector where the coating film was not formed. This portion was used as the negative electrode current collector tab.

[0249] <Preparation of the first positive electrode> First, reduced multi-walled carbon nanotubes (reduced MWCNTs) were prepared as follows.

[0250] In the tubular furnace, 100 g of multi-walled carbon nanotubes (MWCNTs) containing 5000 mass ppm of Co atoms were placed as the first carbon material, and 5% hydrogen gas was passed through at 50 mL / min for 30 min at room temperature. As the 5% hydrogen gas, a gas in which H2 and Ar were mixed so that the volume percentages were 5% and 95%, respectively, was used. Thereafter, while passing 5% hydrogen gas through the tubular furnace, the temperature of the tubular furnace was raised at 10°C / min. After holding at 800°C, which is the reduction treatment temperature, for 1 hour, the furnace was allowed to cool under the flow of 5% hydrogen gas. In this manner, reduced MWCNTs were obtained as the second carbon material.

[0251] As the positive electrode active material, LiNi 0.8 Co 0.1 Mn 0.1 3 g of O2 (NCM) was prepared. A Co atom-containing carbon material was prepared as a positive electrode conductive material. As the Co atom-containing carbon material, acetylene black (AB) and the above-mentioned reduced MWCNT were mixed in a mass ratio of 1:1 and used. The Co atom-containing carbon material had a Co concentration of 2170 mass ppm. In addition, a PVdF dispersion was prepared. As the PVdF dispersion, a dispersion in which PVdF as a binder was dispersed in N-methyl-2-pyrrolidone (NMP) at a solid content of 8% was used.

[0252] The above materials were mixed in a ratio of 90 parts by mass of NCM, 5 parts by mass of carbon material containing Co atoms, and 5 parts by mass of PVdF so as to be dispersed in NMP as a solvent to prepare a positive electrode slurry. This positive electrode slurry was applied to both sides of a positive electrode current collector made of aluminum foil having a thickness of 12 μm. The positive electrode slurry was then dried and pressed to obtain a first positive electrode. When cutting the first positive electrode into a rectangle, it was cut so that one side of the rectangle had a portion on the positive electrode current collector where no coating film was formed. This portion was used as a positive electrode current collector tab.

[0253] <Preparation of the first electrode group> A cellulose separator having a thickness of 15 μm was prepared as the first separator. The first positive electrode, the first separator, the first negative electrode, and the first separator were stacked in this order, and then wound in a spiral shape to prepare a flat wound electrode group. Thus, the first electrode group was prepared.

[0254] <Electrolyte adjustment> Propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a volume ratio of PC:DEC = 1:2 to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF6) was dissolved at 1.0 M in the mixed solvent to prepare a liquid nonaqueous electrolyte.

[0255] <Assembly of the first battery> The first electrode group was housed in a pack made of a laminate film composed of aluminum foil and polypropylene layers formed on both sides of the aluminum foil. A liquid nonaqueous electrolyte was then injected into the laminate film pack containing the first electrode group. The laminate film pack was completely sealed by heat sealing to produce a first battery.

[0256] <Secondary battery manufacturing> After the first battery was assembled, it was charged and discharged for the first time. Then, the first battery was adjusted to SOC 90% and was charged at a constant current of 0°C for 15 seconds. The current value of the constant current at this time was 1 cm2 for the area (opposing area) of the part of the first positive electrode facing the first negative electrode. 2 The value was set so that the current value per A is 1.0x. x can be calculated using the following formula. 10C is the current value at which the battery capacity of the obtained secondary battery is discharged in 1 hour at a current value of 10 C, and S is the area of ​​the portion of the first positive electrode facing the first negative electrode. Thus, a secondary battery was obtained. (Number 1) x=A 10C [A] / S[cm 2 ]

[0257] Example 2 Li4Ti5O as negative electrode active material 12(TLO) powder was prepared. Acetylene black (AB) was prepared as a negative electrode conductive agent. PVdF was prepared as a binder. When preparing the negative electrode slurry, each material was mixed in the pure water solvent in a ratio of 20 parts by mass of TLO, 1 part by mass of AB, and 1 part by mass of PVdF. A secondary battery was manufactured in the same manner as in Example 1 except for the above.

[0258] Example 3 A secondary battery was produced in the same manner as in Example 1, except that a Co atom-containing carbon material containing 300 ppm by mass of Co atoms was used in the preparation of the first positive electrode.

[0259] Example 4 A secondary battery was produced in the same manner as in Example 1, except that a Co atom-containing carbon material containing 2920 ppm by mass of Co atoms was used in the preparation of the first positive electrode.

[0260] Example 5 A secondary battery was produced in the same manner as in Example 1, except that the reduction treatment temperature was set to 1000° C. in the preparation of the first positive electrode.

[0261] Example 6 A secondary battery was produced in the same manner as in Example 1, except that the reduction treatment temperature was set to 600° C. in the preparation of the first positive electrode.

[0262] Example 7 A secondary battery was produced in the same manner as in Example 1, except that in the constant current charging of the first battery, the time for applying the constant current was changed to 10 seconds.

[0263] Example 8 A secondary battery was produced in the same manner as in Example 1, except that in the constant current charging of the first battery, the time for applying the constant current was changed to 30 seconds.

[0264] Example 9 A secondary battery was produced in the same manner as in Example 1, except that the temperature during the constant current charging of the first battery was set to -5°C.

[0265] Example 10 A secondary battery was produced in the same manner as in Example 1, except that the temperature during the constant current charging of the first battery was set to 25°C.

[0266] Comparative Example 1 In the preparation of the first negative electrode, graphite, which is a carbonaceous material, was prepared as the negative electrode active material. CMC and SBR were prepared as binders. Graphite, CMC, and SBR were mixed in a mixing ratio of 96 parts by mass: 2 parts by mass: 2 parts by mass into pure water as a solvent and stirred to obtain a negative electrode slurry. In addition, a liquid nonaqueous electrolyte was used as the electrolyte, in which 1.0 M of lithium hexafluorophosphate (LiPF6) was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of EC:DEC = 1:2. A secondary battery was manufactured in the same manner as in Example 1 except for the above.

[0267] Comparative Example 2 A secondary battery was produced in the same manner as in Example 1, except that in the production of the first positive electrode, multi-walled carbon nanotubes containing 5000 ppm by mass of Co atoms that had not been reduced were used instead of the reduced MWCNTs.

[0268] Comparative Example 3 A secondary battery was produced in the same manner as in Example 1, except that the reduction treatment temperature was 400° C. in the preparation of the first positive electrode.

[0269] Comparative Example 4 A secondary battery was produced in the same manner as in Example 1, except that a Co atom-containing carbon material containing 5.2 ppm by mass of Co atoms was used in the preparation of the first positive electrode.

[0270] Comparative Example 5 A secondary battery was produced in the same manner as in Example 1, except that a Co atom-containing carbon material containing 4200 ppm by mass of Co atoms was used in the preparation of the first positive electrode.

[0271] Comparative Example 6 A secondary battery was produced in the same manner as in Example 1, except that in the constant current charging of the first battery, the time for applying the constant current was changed to 3 seconds.

[0272] Comparative Example 7 A secondary battery was produced in the same manner as in Example 1, except that in the constant current charging of the first battery, the time for applying the constant current was changed to 50 seconds.

[0273] Comparative Example 8 A secondary battery was produced in the same manner as in Example 1, except that the first battery was not subjected to constant current charging.

[0274] Comparative Example 9 A secondary battery was produced in the same manner as in Example 1, except that the temperature during constant current charging of the first battery was set to -15°C.

[0275] Comparative Example 10 A secondary battery was produced in the same manner as in Example 1, except that the temperature during the constant current charging of the first battery was set to 45°C.

[0276] <Secondary battery measurement> For the secondary battery manufactured by the above method, the Co concentration [ppm by mass] of the carbon material contained in the positive electrode and the reduction state of the Co atoms were measured by the method described above. Co / (A Co +A CoO +A Co3O4 In addition, the number of particles per unit area [pieces / m2] of the portion of the outermost layer of the separator included in the secondary battery produced by the above method was calculated. 2 ] and the mean diameter [mm] of the site were measured as described above.

[0277] <Self-discharge test for secondary batteries> The secondary battery manufactured by the above method was adjusted to a state of charge (SOC) of 50% at 25°C and left for 1 hour. After that, the cell voltage was measured with a voltmeter. The cell voltage at this time was taken as the cell voltage (V0) on the 0th day of storage. Next, this secondary battery was left for 20 days at 25°C without applying current. After that, the cell voltage was measured with a voltmeter. The cell voltage at this time was taken as V20, and V0-V20 was calculated. V0-V20 is a value indicating the amount of self-discharge, and a low value is an indicator that self-discharge is suppressed.

[0278] <10 second resistance measurement> The state of charge (SOC) of the secondary battery manufactured by the above method was adjusted to 50%, and then discharged for 10 seconds at a constant current of 3C rate (converted into negative electrode active material). The difference between the voltage before discharge and the voltage after discharge was taken as ΔV, and the 10-second resistance [mΩ] was calculated from the following formula. In the formula, I represents the current value. The 10-second resistance value is an index for evaluating the input / output characteristics. (Number 2) (10 seconds resistance [mΩ])=ΔV / I

[0279] <High temperature storage test> The secondary battery was charged to SOC100% at a constant current of 1C in a temperature environment of 25°C, and after a rest period of 10 minutes, it was discharged to SOC0% at a constant current of 1C. The capacity at this time was taken as the initial capacity C0 (mAh). After that, the secondary battery was charged to SOC100% and placed in a thermostatic chamber at 60°C. After 10 days, the secondary battery was removed, charged to SOC100% at a constant current of 1C at 25°C, and after a rest period of 10 minutes, it was discharged to SOC0% at a constant current of 1C. The capacity at this time was taken as C20 (mAh). The value of C20 / C0 was calculated and taken as the capacity retention rate when stored at 60°C. The capacity retention rate when stored at 60°C is an index of high-temperature storage performance.

[0280] The manufacturing conditions of the secondary batteries of each Example and Comparative Example are shown in Tables 1 to 4. The manufacturing conditions include the type of negative electrode active material and positive electrode active material, reduction treatment temperature [°C], Co concentration [ppm by mass] of the Co atom-containing carbon material, constant current charging temperature [°C], current value equivalent to 10 C [A], facing area [cm 2 ], current value per unit area in constant current charging [A / cm 2 ], and constant current charging time [s]. Current value per unit area during constant current charging [A / cm 2 ] indicates the A of the secondary battery. 10C [A] / S[cm 2 The values ​​of [°C] are shown in the column for reduction treatment temperature [°C] for Comparative Example 2 in which reduction treatment was not performed in the preparation of the first positive electrode, and the columns for constant-current charging temperature [°C], constant-current charging current value [A], and constant-current charging time [s] for Comparative Example 8 in which constant-current charging was not performed, are indicated with "-".

[0281] The configuration of the secondary batteries of each Example and Comparative Example is shown in Tables 5 and 6. The configuration of the secondary batteries includes the Co concentration [ppm by mass] of the carbon material contained in the positive electrode, the reduction state of Co atoms, and the number of Co atoms per unit area in the outermost layer of the separator [atoms / m 2 ] and the average diameter of the site [mm]. The reduction state of Co atoms is Co / (A Co +A CoO +A Co3O4 ) is shown. In addition, for Comparative Example 4, the concentration of Co atoms contained in the carbon material was so small that the reduction state of the Co atoms could not be measured. Therefore, the corresponding column in Table 4 is indicated with "-".

[0282] The performance of each Example and Comparative Example is shown in Tables 7 and 8. The performance of the secondary battery is shown as the self-discharge amount, the 10 second resistance [mΩ], and the capacity maintenance rate when stored at 60° C. The self-discharge amount is shown as the V0-V20 value.

[0283] [Table 1]

[0284] [Table 2]

[0285] [Table 3]

[0286] [Table 4]

[0287] [Table 5]

[0288] [Table 6]

[0289] [Table 7]

[0290] [Table 8]

[0291] In all of the secondary batteries of the examples, the Co atom concentration in the carbon material contained in the positive electrode was in the range of 100 mass ppm to 1500 mass ppm with respect to the mass of the carbon material. 2 More than 10000 pieces / m 2 The ratio of the positive electrode carbon material was as follows. In contrast, among Comparative Examples 2, 3, 5, 8, and 9 in which the Co atom concentration of the carbon material contained in the positive electrode was higher than 1500 mass ppm, Comparative Examples 2, 5, 8, and 9 had lower capacity retention rates during storage at 60°C than the Examples. Comparative Example 3 had a high 10-second resistance. In addition, among Comparative Examples 4, 7, and 10 in which the Co atom concentration of the carbon material contained in the positive electrode was less than 100 mass ppm, Comparative Example 4 had a high 10-second resistance. Comparative Examples 7 and 10 had a high self-discharge amount.

[0292] The number of sites containing Co atoms in the outermost layer of the separator is 10,000 / m 2 Comparative Example 1, in which the number of sites containing Co atoms in the outermost layer of the separator was 200 / m 2 Among Comparative Examples 4, 6, and 8, which had a resistance of less than 10 seconds, Comparative Example 4 had a high 10-second resistance. Comparative Examples 6 and 8 had a low capacity retention rate when stored at 60°C.

[0293] Therefore, it was clear that the secondary batteries of the examples were excellent in high-temperature storage performance and input / output characteristics, and self-discharge was suppressed.

[0294] Comparative Example 1 is a secondary battery using graphite as the negative electrode active material. In Comparative Example 1, the number of particles per unit area in the portion of the outermost layer of the separator is 10,000 particles / m 2 This is because the negative electrode containing the carbonaceous material as the negative electrode active material has an average operating potential of 1.0 V (vs. Li / Li + This is believed to be due to the fact that the amount of Co deposited on the negative electrode increases when the potential is low, resulting in a larger number of Co particles per unit area.

[0295] In contrast, the negative electrodes included in the secondary batteries of Examples 1 and 3 to 10 contain TNO as a negative electrode active material. The negative electrode included in the secondary battery of Example 2 contains TLO as a negative electrode active material. The negative electrodes of Examples 1 to 10 containing such metal oxides all have an average operating potential of 1.0 V (vs. Li / Li + In Examples 1 to 10 including such a negative electrode, the number of sites included in the outermost layer of the separator was smaller than that of Comparative Example 1, and was 200 sites / m 2 More than 10000 pieces / m 2 It was within the following range.

[0296] Examples 1, 3, and 4 and Comparative Examples 4 and 5 are secondary batteries produced by varying the Co concentration of the Co atom-containing carbonaceous material in the production of the first positive electrode. These measurement results reveal that the higher the Co concentration of the Co atom-containing carbonaceous material contained in the first positive electrode, the higher the Co concentration of the carbonaceous material contained in the secondary battery. It also reveals that the higher the Co concentration of the Co atom-containing carbonaceous material, the higher the number of Co atoms per unit area of ​​the portion.

[0297] Examples 1, 5, 6, and Comparative Example 3 are secondary batteries fabricated in the same manner, except that the reduction temperature was changed in the fabrication of the first positive electrode. From these measurement results, it became clear that the higher the reduction temperature, the higher the reduction state of the Co atoms in the carbon material and the lower the Co concentration of the carbon material. This is considered to be because, when the reduction temperature is high, the Co atoms in the carbon material are reduced to metal Co that is easily dissolved in the electrolyte, and as a result, the Co atoms in the carbon material are dissolved in the electrolyte, and the number of Co atoms remaining in the carbon material is reduced. In addition, in Comparative Example 2, in which the reduction treatment of MWCNTs was not performed in the fabrication of the first positive electrode, the reduction state of the Co atoms in the carbon material was lower and the Co concentration of the carbon material was higher than in Comparative Example 3, in which the reduction temperature was a low temperature of 400°C. From the measurement results of these Examples and Comparative Examples, it was found that the Co atoms in the carbon material were sufficiently reduced to A Co / (A Co +A CoO +A Co3O4 It was revealed that when the value of 0.6 or more, there is a tendency for the input / output characteristics and high-temperature storage performance to be improved.

[0298] Examples 1, 7, and 8 and Comparative Examples 6 and 7 are secondary batteries fabricated in the same manner, except that the constant current charging time for the first battery was changed. These measurement results reveal that the average diameter of the portion tends to increase when the constant current charging time for the first battery is increased.

[0299] Examples 1, 9, and 10 and Comparative Examples 9 and 10 are secondary batteries fabricated in the same manner, except that the temperature during constant current charging of the first battery was changed. These measurement results reveal that the average diameter of the portion tends to increase when the temperature during constant current charging of the first battery is increased.

[0300] In Comparative Example 8, in which the first battery was not subjected to constant current charging, the average diameter of the portion was small.

[0301] In addition, when comparing Examples 1, and 5 to 8, which have the same type of negative electrode active material, Co concentration of the Co atom-containing carbon material, and constant current charging temperature conditions, it was found that the greater the number per unit area of ​​the site, the lower the Co concentration of the carbon material tends to be, and the higher the capacity retention rate when stored at 60°C tends to be.

[0302] This is believed to be due to the following reasons. In the manufacturing stage of the secondary battery of the embodiment, the Co atoms contained in the Co atom-containing carbon material contained in the first positive electrode can dissolve in the electrolyte. The Co atoms dissolved in the electrolyte can precipitate on the negative electrode during constant current charging to form a site. Therefore, it is believed that the greater the number of sites per unit area, the lower the Co concentration of the carbon material. In addition, it is believed that the low Co concentration of the carbon material could suppress the dissolution and precipitation of the Co atoms remaining in the positive electrode during high-temperature storage. It is believed that this suppressed the formation of short-circuit points, thereby increasing the capacity retention rate during storage at 60°C.

[0303] According to at least one of the embodiments described above, a secondary battery is provided. The secondary battery includes an electrode group including a positive electrode, a negative electrode, and a separator, and an electrolyte. The positive electrode includes a positive electrode active material and a carbon material. The carbon material contains Co atoms at a concentration of 100 mass ppm to 1500 mass ppm. The separator includes a substrate and a site containing Co atoms present in the substrate. In the region where the separator is disposed between the positive electrode and the negative electrode, the outermost layer that is the outermost layer in the electrode group has 200 sites containing Co atoms / m. 2 More than 10000 pieces / m 2The content is as follows: Therefore, the secondary battery is excellent in high-temperature storage performance and input / output characteristics, and can suppress self-discharge.

[0304] The invention according to the embodiment will be described below.

[0305] [1] A battery comprising an electrode group including a positive electrode, a negative electrode, and a separator, and an electrolyte; the positive electrode includes a positive electrode active material and a carbon material, the carbon material includes Co atoms at a concentration of 100 ppm by mass or more and 1500 ppm by mass or less, The separator includes a substrate and a portion including a Co atom present in the substrate, In the region where the separator is disposed between the positive electrode and the negative electrode, the outermost layer located at the outermost layer in the electrode group has a Co atom-containing site of 200 / m 2 More than 10000 pieces / m 2 Secondary batteries, including the following percentages:

[0306] [2] The negative electrode has an average operating potential of 1.0 V vs. Li / Li + The secondary battery according to [1] above.

[0307] [3] The secondary battery according to [1], wherein the average diameter of the portion is 0.1 mm or more and 0.5 mm or less.

[0308] [4] The secondary battery according to [1], wherein the electrolyte contains fluorine atoms.

[0309] [5] The secondary battery according to [1], wherein the carbon material contains at least one of metallic Co or cobalt oxide.

[0310] [6] The X-ray absorption spectrum of the carbon material in the range of 7700 eV to 7750 eV is The ratio A of the Co atoms present as metallic Co obtained by linear combination fitting with the X-ray absorption spectrum of metallic Co Co and, The ratio A of the Co atoms present as CoO obtained by linear combination fitting with the X-ray absorption spectrum for CoO CoO and, The ratio A of the Co atoms present as Co3O4 obtained by linear combination fitting with the X-ray absorption spectrum for Co3O4 Co3O4 But, A Co / (A Co +A CoO +A Co3O4 ) ≧ 0.6.

[0311] [7] The secondary battery according to [1], wherein the substrate includes a porous body containing at least one selected from the group consisting of polyolefin, cellulose, and polyvinylidene fluoride.

[0312] [8] A battery pack including the secondary battery described in any one of [1] to [7].

[0313] [9] An external terminal for supplying current; Protection circuit and The battery pack according to [8], further comprising:

[0314]

[10] A storage battery comprising a plurality of the secondary batteries, The battery pack according to [8], wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

[0315]

[11] A vehicle including a battery pack as described in [8].

[0316]

[12] A vehicle as described in

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

[0317]

[13] Preparing a first battery including a first electrode group including a first positive electrode including a Co atom-containing carbon material, a first negative electrode, and a first separator not including the site, and an electrolyte; The first battery is charged to a state of charge of 90% or more and 95% or less at a temperature of -5°C or more and 25°C or less, and the first positive electrode is charged to a state of charge of 1 cm2 or less of the area of ​​the portion of the first positive electrode facing the first negative electrode. 2 and applying a constant current having a current value of 0.4x or more and 1.3x or less per charge for 10 seconds or more and 30 seconds or less to manufacture the secondary battery according to claim 1, The x is calculated by the following formula: (Number 1) x=A 10C [A] / S[cm 2 ] The above A 10C is a current value that results in 10C when the current value at which the battery capacity of the secondary battery is discharged in 1 hour is 1C, and S is an area of ​​a portion of the first positive electrode that faces the first negative electrode.

[0318]

[14] The method according to

[13] , wherein the Co atom-containing carbonaceous material is heat-treated in a reducing atmosphere before being contained in the first positive electrode.

[0319] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0320] 1...electrode group, 2...exterior member, 3...negative electrode, 3a...negative electrode current collector, 3b...negative electrode active material-containing layer, 3c...negative electrode current collector tab, 4...separator, 5...positive electrode, 5a...positive electrode current collector, 5b...positive electrode active material-containing layer, 6...negative electrode terminal, 7...positive electrode terminal, 21...bus bar, 22...positive electrode side lead, 22a...other end, 23...negative electrode side lead, 23a...other end, 24...adhesive tape, 31...container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 41...vehicle power source, 42...electrical control device, 43...external terminal, 44...inverter, 45...driving motor, 100...secondary battery, 200...battery pack, 200a...battery pack, 200b...battery pack, 200c...battery pack, 300...battery pack, 30 0a...battery pack, 300b...battery pack, 300c...battery pack, 301a...assembled battery monitoring device, 301b...assembled battery monitoring device, 301c...assembled battery monitoring device, 342...positive connector, 343...negative connector, 345...thermistor, 346...protection circuit, 342a...wiring, 343a...wiring, 350...external terminal for energization, 352...positive terminal, 353...negative terminal, 348a...positive wiring, 348b...negative wiring, 400...vehicle, 411...battery management device, 412...communication bus, 413...positive terminal, 414...negative terminal, 415...switch device, 416...current detection unit, 417...negative input terminal, 418...positive input terminal, L1...connection line, L2...connection line, W...drive wheel.

Claims

1. An electrode group including a positive electrode, a negative electrode, and a separator, and an electrolyte; The positive electrode includes a positive electrode active material and a carbon material, and the carbon material includes Co atoms at a concentration of 100 ppm by mass or more and 1500 ppm by mass or less. The separator includes a substrate and a portion including a Co atom present in the substrate, In the region where the separator is disposed between the positive electrode and the negative electrode, the outermost layer located at the outermost layer in the electrode group has 200 Co atom-containing sites / m ２ More than 10,000 pieces / m ２ Secondary batteries, containing the following percentages:

2. The negative electrode has an average operating potential of 1.0 V vs. Li / Li ＋ The secondary battery according to claim 1 .

3. 2. The secondary battery in accordance with claim 1, wherein the average diameter of said portion is 0.1 mm or more and 0.5 mm or less.

4. The secondary battery according to claim 1 , wherein the electrolyte contains fluorine atoms.

5. The secondary battery according to claim 1 , wherein the carbon material contains at least one of metallic Co and cobalt oxide.

6. The X-ray absorption spectrum of the carbon material in the range of 7700 eV to 7750 eV is The ratio A of the Co atoms present as metallic Co obtained by linear combination fitting with the X-ray absorption spectrum of metallic Co Ｃｏ and, The ratio A of the Co atoms present as CoO obtained by linear combination fitting with the X-ray absorption spectrum for CoO ＣｏＯ and, Co ３ O ４ The linear combination fitting of the X-ray absorption spectrum of Co ３ O ４ The ratio A of the Co atoms present as Ｃｏ３Ｏ４ But, A Ｃｏ / (A Ｃｏ +A ＣｏＯ +A Ｃｏ３Ｏ４ 2. The secondary battery according to claim 1 , wherein the ratio of the ratio ...

7. 2. The secondary battery in accordance with claim 1, wherein the substrate comprises a porous body containing at least one material selected from the group consisting of polyolefin, cellulose, and polyvinylidene fluoride.

8. A battery pack comprising the secondary battery according to any one of claims 1 to 7.

9. An external terminal for supplying electricity; Protection circuit and The battery pack of claim 8 further comprising:

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

11. A vehicle including the battery pack of claim 8.

12. The vehicle of claim 11, further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.

13. preparing a first battery including a first electrode group including a first positive electrode including a Co atom-containing carbon material, a first negative electrode, and a first separator not including the site, and an electrolyte; The first battery is charged to a state of charge of 90% or more and 95% or less at a temperature of -5°C or more and 25°C or less, and the first positive electrode is charged to a state of charge of 1 cm2 or less of a surface area of ​​the portion of the first positive electrode facing the first negative electrode. ２ and applying a constant current having a current value of 0.4x or more and 1.3x or less per charge for 10 seconds or more and 30 seconds or less to manufacture the secondary battery according to claim 1, The x is calculated by the following formula: (Equation 1) x=A １０Ｃ [A] / S[cm ２ ] The above A １０Ｃ is a current value that results in 10 C when a current value at which the battery capacity of the secondary battery is discharged in one hour is 1 C, and S is an area of ​​a portion of the first positive electrode that faces the first negative electrode.

14. The method according to claim 13 , wherein the Co atom-containing carbonaceous material is heat-treated in a reducing atmosphere before being contained in the first positive electrode.

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