Secondary batteries, battery packs, and vehicles

Abstract

The objective is to provide a secondary battery that generates little gas, a battery pack containing the secondary battery, and a vehicle containing the battery pack. [Solution] According to the embodiment, a secondary battery is provided. The secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The surface of the negative electrode is SO x Includes a group and a CS bond. x The ratio B / A, where A is the number of sulfur atoms in the group and B is the number of sulfur atoms in the CS bond, is 0.25 or greater.

Description

[Technical Field]

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

[0002] Secondary batteries containing non-aqueous electrolytes have issues with output performance and high-temperature durability. One reason for this is that gas is generated when the non-aqueous electrolyte reacts with the electrodes. When gas is generated, bubbles form inside the electrodes, making the active material more prone to detachment, increasing resistance, and potentially reducing output performance. Secondary batteries containing non-aqueous electrolytes are particularly susceptible to gas generation in high-temperature environments. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. WO2015 / 136688 [Patent Document 2] Special Publication No. 2015-522209 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The embodiment aims to provide a secondary battery that generates little gas, a battery pack containing the secondary battery, and a vehicle containing the battery pack. [Means for solving the problem]

[0005] According to the embodiment, a secondary battery is provided. The secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The surface of the negative electrode is SO x Includes a group (x is 3 or 4) and a CS bond. SO x The ratio B / A, where A is the number of sulfur atoms in the group and B is the number of sulfur atoms in the CS bond, is 0.25 or greater.

[0006] According to another embodiment, a battery pack including a secondary battery of the embodiment is provided.

[0007] According to other embodiments, a vehicle including the battery pack of the embodiment is provided. [Brief explanation of the drawing]

[0008] [Figure 1] A cross-sectional view of the secondary battery of the embodiment, cut in a direction perpendicular to the terminal extension direction. [Figure 2] Enlarged cross-sectional view of section A in Figure 1. [Figure 3] A partially cutaway cross-sectional view of a secondary battery according to an embodiment. [Figure 4] Figure 3 is a side view of the battery. [Figure 5] A partially cutaway perspective view schematically showing another example of the secondary battery of the embodiment. [Figure 6] Figure 5 shows an enlarged cross-sectional view of section B of the secondary battery. [Figure 7] A schematic plan view showing an example of a manufacturing method for a secondary battery according to the embodiment. [Figure 8] An exploded perspective view of the battery pack of the embodiment. [Figure 9] A block diagram showing the electrical circuit of the battery pack in Figure 8. [Figure 10] A schematic diagram showing an example of a vehicle equipped with a secondary battery according to the embodiment. [Figure 11] A schematic diagram showing another example of a vehicle according to the embodiment. [Figure 12] This figure shows an example of a hard X-ray photoelectron spectroscopy spectrum of the surface of the negative electrode contained in a secondary battery. [Modes for carrying out the invention]

[0009] (First embodiment) According to the first embodiment, a secondary battery is provided. The secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The surface of the negative electrode is SO x Includes a group (x is 3 or 4) and a CS bond. SO xThe ratio B / A, where A is the number of sulfur atoms in the group and B is the number of sulfur atoms in the CS bond, is 0.25 or greater.

[0010] When a non-aqueous electrolyte comes into contact with the negative electrode, reductive decomposition of the non-aqueous electrolyte is likely to occur, generating gas.

[0011] The inventors have discovered that gas generation in a secondary battery can be suppressed by incorporating sulfur atoms into the surface of the negative electrode. Furthermore, they have found that this gas generation suppression effect can be changed depending on the bonding state of the sulfur atoms contained on the surface of the negative electrode.

[0012] Specifically, SO x When the number of sulfur atoms B in the CS bond is greater than the number of sulfur atoms A in the group, the reductive decomposition of the non-aqueous electrolyte can be suppressed, which is preferable.

[0013] The secondary battery according to this embodiment is SO x The ratio of the number of sulfur atoms in the CS bond to the number of sulfur atoms in the base (A) is 0.25 or higher (B / A). Therefore, a secondary battery with low gas generation can be provided.

[0014] The secondary battery according to this embodiment will be described further.

[0015] The secondary battery according to this embodiment may be, for example, a secondary battery that uses alkali metal ions as carrier ions. For example, it may be a lithium battery (lithium-ion battery).

[0016] At least a portion of the surface of the negative electrode may include a coating. x Groups and CS bonds may be contained in the coating. The coating may contain an inorganic coating, an organic coating, or both an inorganic and an organic coating. When the coating contains both an inorganic and an organic coating, the inorganic and organic coatings may be contained in the coating in a mixed state. A higher relative amount of the organic coating to the amount of the inorganic coating is preferable because it can enhance the inhibitory effect on the decomposition reaction of non-aqueous electrolytes.

[0017] "SO x group (where x is 3 or 4)" means that the subscript x of O is 3 or 4. SO x group can be a SO3 group when x = 3 and a SO4 group when x = 4. SO x group can be included in the inorganic film among the films. Therefore, SO x a large amount of group may mean that the surface of the negative electrode contains a large amount of inorganic film.

[0018] In the C-S bond, the carbon atom (C) and the sulfur atom (S) can be, for example, in a single-bonded state. The C-S bond can be included in the organic film among the films. Therefore, a large amount of C-S bond may mean that the surface of the negative electrode contains a large amount of organic film.

[0019] The non-aqueous electrolyte preferably contains a sulfur-containing substance containing a sulfur atom in its composition. In this case, sulfur atoms are likely to be contained on the surface of the negative electrode. For example, when a non-aqueous electrolyte containing a sulfur-containing substance decomposes on the surface of the negative electrode, sulfur atoms can be contained on the surface of the negative electrode. Specifically, when a non-aqueous electrolyte containing a sulfur-containing substance decomposes on the surface of the negative electrode, a film containing sulfur atoms can be formed on at least a part of the surface of the negative electrode.

[0020] The sulfur-containing substance preferably contains a sultone compound. When a non-aqueous electrolyte not containing a sultone compound reacts with the negative electrode and decomposes, the amount of hydrofluoric acid (HF) liberated in the non-aqueous electrolyte can increase. As a result, lithium fluoride (LiF) is likely to be generated on the surface of the negative electrode. Lithium fluoride can be a resistance to the insertion and desorption of lithium in the negative electrode. On the other hand, when a sultone compound is present in the non-aqueous electrolyte, the reaction in which the sultone compound reacts with the negative electrode and decomposes proceeds more easily than the reaction in which components other than the sultone compound in the non-aqueous electrolyte react with the negative electrode. Also, no gas is generated in the decomposition reaction of the sultone compound. That is, by the sultone compound being preferentially decomposed as a sacrificial material over other non-aqueous electrolyte components, gas generation due to the reductive decomposition of the non-aqueous electrolyte can be suppressed. Also, since the generation of lithium fluoride can be suppressed, the resistance can be kept low, contributing to an improvement in output performance.

[0021] On the surface of the negative electrode, SO x To facilitate obtaining a secondary battery in which the ratio B / A (the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the base) is 0.25 or greater, it is preferable to use a sultone compound as the sulfur-containing substance.

[0022] By containing sultone compounds, SO x The following mechanism is thought to be responsible for the ease with which secondary batteries can be obtained in which the ratio B / A (the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the group) is 0.25 or greater. Sulton compounds may contain sulfur atoms in the molecule that are single-bonded to carbon atoms and bonded to multiple oxygen atoms (typically three). In such slton compounds, when the single bond between the carbon atom and the sulfur atom is broken, SO₂ is formed on the surface of the negative electrode. x It can form a substrate. For example, SO₂ on the surface of the negative electrode. x It can form an inorganic film containing the group. Furthermore, the sultone compound can form CS bonds on the surface of the negative electrode by the detachment of multiple oxygen atoms bonded to a sulfur atom from the sulfur atom. For example, it can form an organic film containing CS bonds on the surface of the negative electrode. Of the reactions described above, the reaction that forms CS bonds proceeds relatively more easily, so on the surface of the negative electrode, SO x It is thought that the ratio B / A, which is the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the group, tends to be 0.25 or higher.

[0023] Specific examples of sultone compounds include 1-propene-1,3-sultone (PES) and 1,3-propanesultone (PS). The number of sultone compounds can be one or more.

[0024] The sultone compound preferably contains PES. When PES is reduced and decomposed, it readily forms an organic film on the surface of the negative electrode. In other words, when the sultone compound contains PES, SO xThe ratio B / A, which is the number of sulfur atoms in the CS bond relative to the number of sulfur atoms A in the group, tends to be higher.

[0025] The sultone compound more preferably contains PES and PS. In this case, the decomposition reaction of PES proceeds more readily than the decomposition reaction of PS. Therefore, PS tends to remain in the non-aqueous electrolyte. In other words, since PES decomposes first and sulfur atoms can be incorporated into the surface of the negative electrode, the decomposition of the non-aqueous electrolyte can be made less likely to proceed. In addition, the presence of PS in the non-aqueous electrolyte can further suppress gas generation due to the decomposition of the non-aqueous electrolyte. Furthermore, PS is more effective in suppressing the formation of hydrofluoric acid, thus further improving output performance.

[0026] The negative electrode preferably contains at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides. Titanium-containing oxides and niobium-containing oxides are compounds that can intercept and deintercept lithium ions at relatively high potentials. When a negative electrode containing such compounds is used, the non-aqueous electrolyte is easily decomposed on the surface of the negative electrode.

[0027] More specifically, sulfur-containing substances that may be present in the non-aqueous electrolyte can be decomposed at the lithium ion intercalation and release potential of titanium-containing oxides and niobium-containing oxides, forming a film on the negative electrode surface. Therefore, using a negative electrode containing at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides is preferable because it makes it easier to obtain a negative electrode containing sulfur atoms on its surface.

[0028] When the non-aqueous electrolyte contains a sultone compound and the negative electrode contains at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides, SO4 is present on the surface of the negative electrode. x This is preferable because it makes it easier to obtain a secondary battery in which the ratio B / A of the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the base is 0.25 or higher.

[0029] A secondary battery according to this embodiment will be described in more detail with reference to the drawings.

[0030] Figures 1 and 2 show an example of a secondary battery using a laminate film exterior component.

[0031] As shown in Figures 1 and 2, the electrode group 1 is a flat wound electrode group. The wound electrode group 1 is housed in a bag-shaped outer casing member 12 made of a laminate film with a metal layer interposed between two resin films. The flat wound electrode group 1 is formed by stacking a laminate in the order of negative electrode 4, separator 5, positive electrode 3, and separator 5 from the outside, winding the laminate in a spiral shape around an axis parallel to the short side direction, and then press-molding this laminate. The outermost negative electrode 4 has a configuration in which a negative electrode layer (negative electrode composite layer) 4b containing negative electrode active material is formed on one side of the inner surface of the negative electrode current collector 4a, as shown in Figure 2, while the other negative electrodes 4 are configured by forming negative electrode layers 4b on both sides of the negative electrode current collector 4a. The positive electrode 3 is configured by forming positive electrode layers (positive electrode composite layers) 3b on both sides of the positive electrode current collector 3a.

[0032] Near the outer edge of the wound electrode group 1, the negative electrode terminal 13 is connected to the negative electrode current collector 4a of the outermost negative electrode 4, and the positive electrode terminal 14 is connected to the positive electrode current collector 3a of the inner positive electrode 3. These negative electrode terminals 13 and positive electrode terminals 14 extend outward from the opening of the bag-shaped outer casing member 12. The wound electrode group 1 is sealed by heat sealing the opening of the bag-shaped outer casing member 12. When heat sealing, the negative electrode terminals 13 and positive electrode terminals 14 are sandwiched by the bag-shaped outer casing member 12 at this opening.

[0033] Figures 3 and 4 show an example of a secondary battery using a metal container.

[0034] The electrode group 1 is housed in a rectangular cylindrical metal container 2. The electrode group 1 is formed, for example, by winding a positive electrode 3 and a negative electrode 4 in a flat spiral shape around an axis parallel to their short sides, with a separator 5 interposed between them. As shown in Figure 4, multiple strip-shaped positive electrode leads 6 are electrically connected to each of the multiple points on the end of the positive electrode 3 located on the end face of the electrode group 1 intersecting the stacking direction of the electrodes. Similarly, multiple strip-shaped negative electrode leads 7 are electrically connected to each of the multiple points on the end of the negative electrode 4 located on this end face. These multiple positive electrode leads 6 are bundled together and electrically connected to a positive electrode current collector tab 8. The positive electrode terminal is formed from the positive electrode leads 6 and the positive electrode current collector tab 8. The negative electrode leads 7 are bundled together and connected to a negative electrode current collector tab 9. The negative electrode terminal is formed from the negative electrode leads 7 and the negative electrode current collector tab 9. A metal sealing plate 10 is fixed to the opening of the metal container 2 by welding or the like. The positive electrode current collector tab 8 and the negative electrode current collector tab 9 are each led out to the outside through outlet holes provided in the sealing plate 10. The inner circumferential surface of each outlet hole in the sealing plate 10 is covered with an insulating member 11 to prevent short circuits caused by contact with the positive electrode current collector tab 8 and the negative electrode current collector tab 9.

[0035] The secondary battery according to this embodiment is not limited to the secondary battery with the configuration shown in Figures 1 and 2, or the secondary battery with the configuration shown in Figures 3 and 4, but may also be a battery with the configuration shown in Figures 5 and 6, for example.

[0036] Figure 5 is a schematic partially cutaway perspective view showing another example of a secondary battery. Figure 6 is an enlarged cross-sectional view of section B of the secondary battery shown in Figure 5.

[0037] The secondary battery shown in Figures 5 and 6 comprises an electrode group 1 shown in Figures 5 and 6, an outer casing member 12 shown in Figure 5, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the outer casing member 12. The electrolyte is held within the electrode group 1.

[0038] The exterior component 12 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0039] As shown in Figure 6, electrode group 1 is a stacked electrode group. The stacked electrode group 1 has a structure in which negative electrodes 4 and positive electrodes 3 are alternately stacked with separators 5 interposed between them.

[0040] The electrode group 1 includes a plurality of negative electrodes 4. Each of the plurality of negative electrodes 4 comprises a negative electrode current collector 4a and a negative electrode active material-containing layer 4b supported on both sides of the negative electrode current collector 4a. The electrode group 1 also includes a plurality of positive electrodes 3. Each of the plurality of positive electrodes 3 comprises a positive electrode current collector 3a and a positive electrode active material-containing layer 3b supported on both sides of the positive electrode current collector 3a.

[0041] Each negative electrode 4's negative electrode current collector 4a includes a portion on one side where the negative electrode active material-containing layer 4b is not supported on any surface. This portion functions as a negative electrode current collector tab 4c. As shown in Figure 6, the negative electrode current collector tab 4c does not overlap with the positive electrode 3. Furthermore, multiple negative electrode current collector tabs 4c are electrically connected to a strip-shaped negative electrode terminal 13. The tip of the strip-shaped negative electrode terminal 13 is extended to the outside of the outer casing member 12.

[0042] Although not shown in the diagram, the positive electrode current collector 3a of each positive electrode 3 includes a portion on one side where the positive electrode active material-containing layer 3b is not supported on any surface. This portion functions as a positive electrode current collector tab. The positive electrode current collector tab, like the negative electrode current collector tab 4c, does not overlap with the negative electrode 4. Furthermore, the positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab 4c. The positive electrode current collector tab is electrically connected to the strip-shaped positive electrode terminal 14. The tip of the strip-shaped positive electrode terminal 14 is located on the opposite side from the negative electrode terminal 13 and is extended to the outside of the outer casing member 12.

[0043] As an example of a secondary battery according to the embodiment, a secondary battery equipped with a wound electrode group will be described with reference to Figure 7, detailing its manufacturing method. Figure 7 is a schematic diagram showing the general method of manufacturing a secondary battery using a bag-shaped outer casing made of laminate film.

[0044] First, the positive electrode 3 and the negative electrode 4 are fabricated.

[0045] The positive electrode can be manufactured by, for example, preparing a slurry by suspending a positive electrode active material, a conductive agent, and a binder in a solvent. This slurry is then applied to one or both sides of a current collector. The applied slurry is then dried to obtain a laminate of a positive electrode active material-containing layer and a current collector. After that, this laminate is pressed. In this way, a positive electrode is manufactured. Alternatively, the positive electrode may be manufactured by the following method: First, the active material, conductive agent, and binder are mixed to obtain a mixture. Then, this mixture is formed into pellets. Then, these pellets are placed on a current collector to obtain a positive electrode.

[0046] The negative electrode can be manufactured, for example, by the following method. First, a slurry is prepared by suspending the negative electrode active material, a conductive agent, and a binder in a solvent. This slurry is applied to one or both sides of the current collector. Next, the applied slurry is dried to obtain a laminate of the negative electrode active material-containing layer and the current collector. Then, this laminate is pressed. In this way, the negative electrode is manufactured. Alternatively, the negative electrode may be manufactured by the following method. First, the negative electrode active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, these pellets are placed on the current collector to obtain the negative electrode.

[0047] An electrode group 1 is fabricated by placing a separator 5 between the positive electrode 3 and the negative electrode 4. The positive electrode terminal 14 is electrically connected to the positive electrode 3 of electrode group 1, and the negative electrode terminal 13 is electrically connected to the negative electrode 4 of electrode group 1.

[0048] The electrode group 1, having positive and negative electrode terminals 13 and 14, is housed in a bag-shaped outer casing member 12 made of laminate film, and then the other ends 21b, excluding the first end 21a, are sealed by heat fusion. Next, a non-aqueous electrolyte is injected into the bag-shaped outer casing member 12 from the first end 21a, and the first end 21a is sealed by heat fusion. Heat fusion may be performed under reduced pressure. This gives rise to a secondary battery 30 with the first sealing completed.

[0049] Next, the first-sealed secondary battery 30 is subjected to its first charge-discharge at room temperature (e.g., 25°C), and then aging is carried out at a temperature above room temperature. Through the first charge-discharge and aging, a reaction occurs between the non-aqueous electrolyte and the negative electrode, and as a result, sulfur atoms may be contained on the surface of the negative electrode. For example, sulfur-containing substances that the non-aqueous electrolyte may contain may decompose, and a film containing sulfur atoms may be formed on the surface of the negative electrode active material-containing layer.

[0050] In this way, SO on the surface x A negative electrode 4 can be obtained in which the ratio B / A of the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the base is 0.25 or greater.

[0051] After aging, the temperature of the secondary battery 30 is returned to room temperature. Then, in an argon atmosphere, the bag-shaped outer casing member 12 is cut along the unsealed cutting line 22 inside the first end 21a to open it and release the gas inside the bag-shaped outer casing member 12 to the outside. The portion cut out from the bag-shaped outer casing member 12 along the cutting line 22 is indicated by reference numeral 23.

[0052] Next, the end portion 24 along the cutting line 22 is sealed under reduced pressure (e.g., -90kPa).

[0053] By adjusting the manufacturing conditions of the manufacturing method described above, the SO2 on the negative electrode surface can be improved. x The ratio B / A, which is the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the base, can be made 0.25 or greater. This yields the secondary battery 31 of the embodiment.

[0054] Details of the manufacturing conditions are described below.

[0055] It is preferable to pre-dry the positive and negative electrodes used in the fabrication of the electrode group before the electrode group is fabricated. The higher the temperature and the longer the drying time, the less moisture can be left in the electrodes. From the viewpoint of reducing moisture in the electrodes, it is preferable to dry under reduced pressure. For example, it is preferable to vacuum dry at 120°C for 24 hours.

[0056] When the positive and negative electrodes are manufactured by applying a slurry to one or both sides of a current collector and then drying the slurry coating, it is preferable to perform the above-mentioned drying process after the coating drying step.

[0057] If the positive and negative electrodes used in the fabrication of the electrode group are dry, the amount of moisture introduced into the secondary battery can be reduced. When moisture is introduced into a secondary battery, the water itself can be electrolyzed and produce gas, and side reactions are more likely to occur at the negative electrode. Therefore, in the battery reaction, lithium ions released from the positive electrode are consumed in the side reactions at the negative electrode, making it difficult for lithium ions to be absorbed into the negative electrode. As a result, a state of charge shift may occur, or the positive electrode potential may shift to a higher potential. If the positive electrode potential becomes too high and exceeds the potential range in which the non-aqueous electrolyte can stably exist, decomposition of the non-aqueous electrolyte is more likely to occur at the positive electrode, which can cause gas generation. In addition, when moisture is introduced into a secondary battery, the non-aqueous electrolyte and water can react to produce hydrofluoric acid, which can degrade the electrodes.

[0058] Therefore, it is preferable that the positive and negative electrodes used in the manufacture of the electrode group are dry, as this can suppress gas generation in the secondary battery of the embodiment.

[0059] As explained with reference to Figure 7, when the first charge-discharge and aging are performed on the first sealed secondary battery 30, gas is generated within the first sealed secondary battery 30. Gas generation reactions include, for example, the decomposition of water introduced into the secondary battery 30, and the decomposition of non-aqueous electrolytes under high-temperature conditions, which generates gas.

[0060] As explained with reference to Figure 7, the gas generated during the initial charge-discharge and aging is released to the outside after aging. Therefore, by actively promoting the gas generation reaction during aging, the amount of residual substances that cause gas generation in the secondary battery 31 of the embodiment obtained after aging can be reduced. Thus, gas generation in the secondary battery 31 of the embodiment can be suppressed.

[0061] The higher the aging temperature and the longer the aging time, the easier it is for the gas generation reaction to proceed during aging. Furthermore, increasing the State of Charge (SOC) during aging can also facilitate the gas generation reaction.

[0062] SO x To increase the ratio B / A (the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the base), it is preferable to lower the aging temperature and shorten the aging time. It is also preferable to lower the state of charge (SOC) during aging.

[0063] The aging temperature is preferably set to a low temperature of 30°C to 60°C, and the aging time is preferably set to a short time of 3 hours to 12 hours. Furthermore, the SOC during aging is preferably set to 50% to 70%. When the non-aqueous electrolyte contains PES and PS as sulfur-containing substances, setting the aging conditions within the above numerical range makes it easier to retain PS in the non-aqueous electrolyte. Therefore, gas generation can be further suppressed, which is even more preferable.

[0064] The positive electrode, negative electrode, and non-aqueous electrolyte will be described below. Separators and casing components that the secondary battery of this embodiment may include in addition to these components will also be described below.

[0065] 1) Positive electrode The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may optionally include a positive electrode active material and a conductive agent 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, as the positive electrode active material, one type of compound alone, or may contain a combination of two or more types of compounds. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and desorbed.

[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), LiNi x Co y M z O2 (x + y + z = 1, x ≧ 0.8, M consists of Mn and Al), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn zO2; 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; where 0 < x ≤ 1, Li x Mn 2-y Ni y O4; where 0 < x ≤ 1, 0 < y < 2), lithium nickel cobalt manganese composite oxides (Li x Ni 1-y-z Co y Mn z O2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1), lithium phosphate oxides having an olivine structure (e.g., Li x FePO4; where 0 < x ≤ 1, Li x Fe 1-y Mn y PO4; where 0 < x ≤ 1, 0 < y ≤ 1, Li x CoPO4; where 0 < x ≤ 1) are included. Using these compounds as the positive electrode active material can increase the battery voltage. In Li x Ni 1-y-z Co y Mn z O2 represented by the lithium nickel cobalt manganese composite oxide, those with y and z such that 0 < y + z ≤ 0.2 can achieve a high energy density.

[0069] The positive electrode active material can be in the form of particles. The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle size of 1 μm or less can allow the solid-state diffusion of lithium ions to proceed smoothly.

[0070] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material having a specific surface area of 0.1 m 2 / g or more can sufficiently secure the sites for lithium ion absorption and release. A specific surface area of 10 m 2Positive electrode active materials with a specific surface area of ​​less than / g are easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0071] A binder is added to fill the gaps between dispersed positive electrode active materials and to bond the positive electrode active materials to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, imide compounds, carboxymethylcellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0072] Conductive agents are added to enhance current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as a conductive agent, or two or more may be used in combination. Conductive agents may also be omitted.

[0073] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0074] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, reducing the binder amount to 20% by mass or less reduces the amount of insulator contained in the electrode, thereby reducing internal resistance.

[0075] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0076] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the non-aqueous electrolyte can be reduced. This lower proportion reduces the decomposition of the non-aqueous electrolyte under high-temperature storage conditions.

[0077] 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.

[0078] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0079] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode active material-containing layer is not formed. These portions can function as positive electrode current collector tabs.

[0080] 2) Negative electrode The negative electrode may include a 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 current collector. The negative electrode active material-containing layer may include the negative electrode active material and optionally a conductive agent and a binder. The negative electrode active material may be in particulate form.

[0081] The surface of the negative electrode is SO x It contains groups and CS bonds. Specifically, the surface of the negative electrode active material containing layer is SO x It may contain groups and CS bonds. More specifically, the surface of the negative electrode active material containing layer is SO x The coating may include a group and a CS bond. The coating may be present on at least a portion of the surface of the negative electrode active material-containing layer, or it may cover at least a portion of the surface of the negative electrode active material particles. The coating may be in the form of a film or in the form of layers.

[0082] The titanium-containing oxides and niobium-containing oxides described above can be included in the negative electrode as negative electrode active materials. Preferably, the negative electrode active material contains at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides.

[0083] Examples of titanium-containing oxides include lithium titanium-containing oxides, titanium oxides, and niobium titanium oxides. Examples of niobium-containing oxides include niobium oxides, niobium titanium oxides, niobium tungsten-containing oxides, and niobium titanium molybdenum-containing oxides.

[0084] A more specific example of a titanium-containing oxide is lithium titanate (e.g., Li) which has a ramsdelite structure. 2+y Li3O7 (0≦y≦3), lithium titanate having a spinel structure (e.g., Li 4+x Ti5O 12 Examples include monoclinic titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, and orthorhombic titanium composite oxide. The lithium ion intercalation / deintercalation potential of titanium-containing oxides is 0.4V (vs. Li / Li). + That's all.

[0085] As an example of the above orthorhombic titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O 14+σ Examples of compounds represented by are given. Here, M I It is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. IIis at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. Each subscript in the composition formula satisfies 0 ≦ a ≦ 6, 0 ≦ b < 2, 0 ≦ c < 6, 0 ≦ d < 6, and -0.5 ≦ σ ≦ 0.5. Specific examples of the orthorhombic titanium-containing composite oxide include Li 2+a Na2Ti6O 14 (0 ≦ a ≦ 6).

[0086] Examples of niobium titanium oxides include monoclinic niobium titanium oxides. Examples of monoclinic niobium titanium oxides include Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ The compounds represented by. Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. Each subscript in the composition formula satisfies 0 ≦ x ≦ 5, 0 ≦ y < 1, 0 ≦ z < 2, and -0.3 ≦ δ ≦ 0.3. Specific examples of monoclinic niobium titanium oxides include Li x Nb2TiO7(0 ≦ x ≦ 5).

[0087] Other examples of monoclinic niobium titanium oxides include Li x Ti 1-y M3 y+z Nb 2-z O 7-δ The compounds represented by. Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula satisfies 0 ≦ x ≦ 5, 0 ≦ y < 1, 0 ≦ z < 2, and -0.3 ≦ δ ≦ 0.3.

[0088] The negative electrode active material may contain one or more other compounds other than titanium-containing oxides and niobium-containing oxides.

[0089] Other negative electrode active materials are not particularly limited as long as they can intercept and deintercept lithium or lithium ions, but carbon materials are examples. Examples of carbon materials include graphite and hard carbon. When a carbon material is used for the negative electrode, copper foil is used as the negative electrode current collector.

[0090] The negative electrode potential is 0.9 (vs. Li / Li + ) or more 1.6 (vs.Li / Li + It is preferable that the potential is within the following range. At such a potential, SO₂ is present on the surface of the negative electrode. x The ratio B / A, which is the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the group, tends to be 0.25 or higher.

[0091] Titanium-containing oxides and niobium-containing oxides have a lithium ion intercalation / deintercalation potential of 1.0V (vs. Li / Li). + ) or more 1.5V (vs.Li / Li + ) is relatively high. Therefore, a negative electrode containing at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides is preferable because the potential tends to fall within the above range.

[0092] More specifically, monoclinic niobium titanium oxide has a lithium ion intercalation / deintercalation potential of 1.0V (vs. Li / Li + Near ) the lithium ion intercalation / deintercalation potential of lithium titanate is 1.4V (vs.Li / Li + It is around ). Note that the intercalation and deintercalation potential of lithium ions in carbon materials is 0V (vs.Li / Li). + It is near ).

[0093] From the viewpoint of keeping the negative electrode potential within the above-mentioned range, it is preferable that the negative electrode active material contains 50% by mass or more of at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides. The upper limit of the proportion of titanium-containing oxides or niobium-containing oxides in the negative electrode active material can be, for example, 100% by mass. The type and proportion of the negative electrode active material can be measured, for example, by inductively coupled plasma (ICP) analysis.

[0094] Conductive agents are added to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon nanotubes, carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as a conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with a carbon coating or an electronically conductive inorganic material coating.

[0095] A binder is added to fill the gaps between dispersed active materials and to bond the active materials to the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0096] As an example, the preferred blending ratios of the negative electrode active material, conductive agent, and binder in the negative electrode active material-containing layer are 68% to 96% by mass, 2% to 30% by mass, and 2% to 30% by mass, respectively. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient bonding between the negative electrode active material-containing layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amount of conductive agent and binder to 30% by mass or less, respectively, in order to achieve high capacity.

[0097] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and removed from the negative electrode active material. The negative electrode active material has a lithium ion intercalation / deintercalation potential of 0.4V (vs.Li / Li). + Examples of current collectors used when the above are employed include copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm to 20 μm. A current collector with such a thickness can balance electrode strength and weight reduction.

[0098] Furthermore, the current collector may include portions on its surface where the negative electrode active material-containing layer is not formed. These portions can function as negative electrode current collector tabs.

[0099] 3) Non-aqueous electrolytes As the non-aqueous electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used. The liquid non-aqueous electrolyte contains an electrolyte salt and an organic solvent capable of dissolving the electrolyte salt. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0100] The non-aqueous electrolyte may further contain the sulfur-containing substance described above. The sulfur-containing substance may or may not function as an electrolyte salt or an organic solvent. The sulfur-containing substance may also function as both an electrolyte salt and an organic solvent.

[0101] The composition of the non-aqueous electrolyte contained in the secondary battery of the embodiment, in particular, the concentration of sulfur-containing substances that the non-aqueous electrolyte may contain, may change from the composition of the non-aqueous electrolyte immediately after preparation (initial composition). This is because, for example, after assembling a secondary battery that has been first sealed using the non-aqueous electrolyte immediately after preparation, the non-aqueous electrolyte may decompose during the first charge-discharge, aging, etc. Therefore, even when a secondary battery that has been first sealed is assembled using a non-aqueous electrolyte containing sulfur-containing substances, the sulfur-containing substances may not remain in the secondary battery of the embodiment. The concentration of sulfur-containing substances in the non-aqueous electrolyte in the secondary battery of the embodiment may be in the range of 0% by mass or more and 10% by mass or less.

[0102] The higher the concentration of sulfur-containing substances in the non-aqueous electrolyte immediately after preparation (initial concentration), the more likely the sulfur-containing substances are to remain in the non-aqueous electrolyte after the first charge and discharge. A low initial concentration of sulfur-containing substances can suppress the excessive formation of a film on the negative electrode surface, thereby suppressing the increase in electrode resistance.

[0103] When using a sultone compound as the sulfur-containing substance, it is preferable to prepare the non-aqueous electrolyte so that the concentration of the sultone compound in the non-aqueous electrolyte immediately after preparation (initial concentration) is in the range of 0.5% by mass to 10% by mass. The initial concentration of the sultone compound may be 1.0% by mass or higher. The non-aqueous electrolyte preferably contains PES in an amount of 0.5% by mass to 5.0% by mass among the sultone compounds. Among the sultone compounds, PES is easily decomposed during the initial charge-discharge, aging, etc., of the secondary battery. Therefore, even when a secondary battery is made using a non-aqueous electrolyte containing PES, PES may not be detected in the non-aqueous electrolyte contained in the secondary battery of the embodiment.

[0104] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; Lithium bis(trifluoromethanesulfonyl)imide, LiN(CF3SO2)2), and lithium bis(fluorosulfonyl)imide (LiFSI; Lithium Bis(fluorosulfonyl)imide, LiN(FSO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0105] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); and γ-butyrolactone (GBL), acetonitrile (AN), ethyl propionate (EP), and sulfolane (SL). These organic solvents can be used individually or as mixed solvents.

[0106] Gel-like non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0107] Alternatively, in addition to liquid nonaqueous electrolytes and gel-type nonaqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymer solid electrolytes, and inorganic solid electrolytes may be used as nonaqueous electrolytes. 4) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a nonwoven fabric made of synthetic resin. From a safety standpoint, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and interrupt the electric current.

[0108] An electrolyte layer containing an inorganic solid electrolyte may be used as a separator. Examples of lithium-ion conductive inorganic solid electrolytes include lithium-ion conductive oxide-based solid electrolytes and lithium-ion conductive sulfide-based solid electrolytes. Examples of lithium-ion conductive oxide-based solid electrolytes include lithium phosphate solid electrolytes with a NASICON-type structure and amorphous LIPON(Li 2.9 PO 3.3 N 0.46 ), or LLZ(Li7La3Zr2O) with a garnet-type structure 12 Examples include:

[0109] 5) Exterior components For example, the outer packaging material can be a container made of laminate film or a metal container.

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

[0111] As the laminate film, a multilayer film is used that includes multiple resin layers and a metal layer interposed between these resin layers. The resin layers include polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be molded into the shape of an exterior component by sealing it by heat fusion.

[0112] The thickness of the metal container wall is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0113] Metal containers are made from, for example, aluminum or aluminum alloys. Aluminum alloys preferably contain elements such as magnesium, zinc, and silicon. If aluminum alloys contain transition metals such as iron, copper, nickel, and chromium, their content is preferably 100 ppm by mass or less.

[0114] The shape of the exterior components is not particularly limited. For example, the exterior components may be flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior components can be appropriately selected according to the battery dimensions and intended use.

[0115] (Measurement method) The following describes the method for analyzing the negative electrode using hard X-ray photoelectron spectroscopy (HAXPES) and for identifying sulfur-containing substances.

[0116] First, if the electrode to be measured (positive or negative electrode) is incorporated into a battery, remove the electrode from the battery as follows: First, disassemble the battery containing the electrode in a glove box filled with argon. Remove the electrode to be measured from the disassembled battery. Wash this electrode with a suitable solvent. For example, methyl ethyl carbonate can be used as the solvent for washing. Vacuum dry the washed electrode. Thus, obtain the electrode for measurement.

[0117] <haxpes> The electrode (e.g., negative electrode) extracted using the method described above is attached to the HAXPES sample folder with carbon tape in a glove box filled with argon. The sample folder is placed in a transfer vessel, sealed, and the vessel is removed from the glove box and attached to the sample inlet of the HAXPES instrument. By transferring the sample folder within the instrument, the electrode sample is introduced into the instrument without exposure to air. The HAXPES analysis is performed as follows: The energy is calibrated with Au4f7 / 2 (5870 eV) before measurement. The excitation energy is set to 5947.51 eV. The beam size is 20 μm vertically × 30 μm horizontally. The electron analyzer (Scienta Omicron R4000 L1) is set to 12 keV. The photoelectron detection angle is set to an oblique incidence configuration of approximately 89°. Charge neutralization is not used.

[0118] Next, the Nb2p1 / 2 spectrum is obtained by performing HAXPES analysis on the electrode not immersed in the electrolyte (unimmersed electrode) in the same manner as above. Since the unimmersed electrode has not undergone lithium absorption, it is considered to contain no sulfur atoms. The Nb2p1 / 2 spectrum obtained for the unimmersed electrode is used as the background and subtracted from the S1s spectrum obtained by HAXPES analysis of the electrode being measured. Then, assuming a linear background, peak fitting is performed.

[0119] An example of a chart obtained after peak fitting is shown in Figure 12. In Figure 12, the chart obtained for the surface of the negative electrode of an example secondary battery according to the embodiment is shown as S1. The chart obtained for the surface of the negative electrode of a secondary battery according to another example is shown as S2. The horizontal axis of the chart shows the binding energy (unit: eV), and the vertical axis shows the normalized intensity.

[0120] From the obtained spectrum, SO x The integrated intensity of the peak component attributed to the base and the integrated intensity of the peak component attributed to the CS bond are measured, respectively. x The integrated intensity of the peak component attributed to the base is SO x The integral intensity of the peak component attributed to the CS bond correlates with the number of sulfur atoms A in the group, and the integral intensity of the peak component attributed to the CS bond correlates with the number of sulfur atoms B in the CS bond. Therefore, (integral intensity of the peak component attributed to the CS bond) / (SO x The integral intensity of the peak component attributed to the base is SO x It can be calculated as the ratio B / A of the number of sulfur atoms in the CS bond to the number of sulfur atoms A in the group.

[0121] Specifically, peaks with their peak centers in the range of 2469 eV to less than 2475 eV may be peaks attributed to CS binding. Peaks with their peak centers in the range of 2475 eV to 2483 eV may be SO x It could be a peak attributed to the base.

[0122] As shown in Figure 12, comparing the integrated intensity of the peak component attributed to CS bonding in chart S1 and chart S2, the integrated intensity of the peak component attributed to CS bonding in chart S2 is smaller. As a result, on the surface of the negative electrode included in the example of the secondary battery according to the embodiment, (integral intensity of the peak component attributed to CS bonding) / (SO x Although the integrated intensity of the peak component attributed to the base satisfies 0.25 or higher, it can be seen that this is not the case on the surface of the negative electrode included in secondary batteries related to other examples. Note that in Figure 12, the peaks whose peak centers are in the range of 2464 eV to less than 2469 eV are Nb2p 1 / 2 This could be a peak attributed to [a specific group / system].

[0123] <How to identify sulfur-containing substances> A non-aqueous electrolyte (e.g., a non-aqueous electrolyte solution) is diluted 20 times with acetonitrile to prepare the sample for measurement. By performing gas chromatography-mass spectrometry (GC-MS) on the sample under the conditions shown in Table 1, the type and concentration (mass %) of sultone compounds in the non-aqueous electrolyte can be determined.

[0124] According to the first embodiment, a secondary battery is provided. The secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The surface of the negative electrode is SO x Includes a group (x is 3 or 4) and a CS bond. SO x The ratio B / A, where A is the number of sulfur atoms in the group and B is the number of sulfur atoms in the CS bond, is 0.25 or higher. Therefore, a secondary battery with low gas generation can be provided.

[0125] (Second embodiment) The battery pack according to the second embodiment may comprise one or more of the secondary batteries (single cells) according to the embodiment. Multiple secondary batteries may be electrically connected in series, parallel, or a combination of series and parallel to form a battery pack. The battery pack according to the embodiment may include multiple battery packs.

[0126] The battery pack according to this embodiment may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) can be used as the protection circuit for the battery pack.

[0127] Furthermore, the battery pack according to this embodiment may also be further equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and for inputting current to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of a vehicle such as an automobile) is supplied to the battery pack through the external terminals.

[0128] Figures 8 and 9 show an example of a battery pack 50. This battery pack 50 includes a plurality of flat-type batteries having the structure shown in Figure 8. Figure 8 is an exploded perspective view of the battery pack 50, and Figure 9 is a block diagram showing the electrical circuit of the battery pack 50 in Figure 8.

[0129] Multiple individual cells 51 are stacked so that their outwardly extending negative terminals 13 and positive terminals 14 are aligned in the same direction, and then fastened together with adhesive tape 52 to form a battery pack 53. These individual cells 51 are electrically connected in series, as shown in Figure 9.

[0130] The printed circuit board 54 is positioned opposite the side of the single cell 51 from which the negative terminal 13 and positive terminal 14 extend. As shown in Figure 9, the printed circuit board 54 is equipped with a thermistor 55, a protective circuit 56, and an external terminal 57 for supplying power to an external device. An insulating plate (not shown) is attached to the side of the printed circuit board 54 that faces the battery pack 53 to avoid unnecessary connections with the wiring of the battery pack 53.

[0131] The positive lead 58 is connected to the positive terminal 14 located at the bottom layer of the battery pack 53, and its tip is inserted into the positive connector 59 of the printed circuit board 54 for electrical connection. The negative lead 60 is connected to the negative terminal 13 located at the top layer of the battery pack 53, and its tip is inserted into the negative connector 61 of the printed circuit board 54 for electrical connection. These connectors 59 and 61 are connected to the protection circuit 56 through wiring 62 and 63 formed on the printed circuit board 54.

[0132] The thermistor 55 detects the temperature of the single cell 51, and the detection signal is transmitted to the protection circuit 56. The protection circuit 56 can, under predetermined conditions, disconnect the positive side wiring 64a and the negative side wiring 64b between the protection circuit 56 and the terminal 57 for supplying power to an external device, which serves as an external terminal for power supply. The predetermined conditions are, for example, when the temperature detected by the thermistor 55 exceeds a predetermined temperature. Another predetermined condition is when overcharging, over-discharging, overcurrent, etc., of the single cell 51 is detected. This detection of overcharging, etc., is performed for each individual single cell 51 or for the single cell 51 as a whole. When detecting individual single cells 51, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each single cell 51. In Figures 8 and 9, wiring 65 for voltage detection is connected to each single cell 51, and the detection signal is transmitted to the protection circuit 56 through these wirings 65.

[0133] Protective sheets 66 made of rubber or resin are placed on three sides of the battery pack 53, excluding the side from which the positive terminal 14 and negative terminal 13 protrude.

[0134] The battery pack 53 is housed in a storage container 67 along with each protective sheet 66 and printed circuit board 54. Specifically, protective sheets 66 are placed on both inner surfaces in the long direction and on each inner surface in the short direction of the storage container 67, and the printed circuit board 54 is placed on the inner surface opposite to the short direction. The battery pack 53 is located in the space enclosed by the protective sheets 66 and the printed circuit board 54. The lid 68 is attached to the top surface of the storage container 67.

[0135] Alternatively, heat-shrinkable tape may be used instead of adhesive tape 52 to secure the battery pack 53. In this case, protective sheets are placed on both sides of the battery pack, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to secure the battery pack.

[0136] Figures 8 and 9 show a configuration in which the single cells 51 are connected in series, but they may be connected in parallel to increase the battery capacity. Alternatively, a combination of series and parallel connections may be used. The assembled battery pack can also be further connected in series or parallel.

[0137] Furthermore, although the battery packs shown in Figures 8 and 9 have one battery pack, the battery pack according to this embodiment may have multiple battery packs. Multiple battery packs are electrically connected by series connection, parallel connection, or a combination of series and parallel connection.

[0138] Furthermore, the configuration of the battery pack can be appropriately changed depending on the application. The battery pack according to this embodiment is suitably used in applications where excellent cycle performance is required when drawing a large current. Specifically, it can be used as a power source for digital cameras, or as a vehicle battery for, for example, two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, electric assist bicycles, or railway vehicles (e.g., electric trains), or as a stationary battery. In particular, it is suitably used as an on-board battery installed in a vehicle.

[0139] The battery pack of the second embodiment described above includes the secondary battery of the embodiment. Therefore, it is possible to realize a battery pack that generates less gas.

[0140] (Third embodiment) The vehicle of the third embodiment includes one or more secondary batteries of the embodiment, or includes a battery pack of the embodiment.

[0141] In a vehicle such as an automobile equipped with a battery pack according to the third embodiment, the battery pack may, for example, recover regenerative energy from the vehicle's power. The vehicle may also include a mechanism that converts the vehicle's kinetic energy into regenerative energy.

[0142] Figure 10 shows an example of an automobile equipped with a battery pack according to one embodiment.

[0143] The automobile 71 shown in Figure 10 has an example battery pack 72 according to the embodiment mounted in the engine compartment at the front of the vehicle body. The mounting location of the battery pack in an automobile is not limited to the engine compartment. For example, the battery pack can also be mounted in the rear of the automobile body or under the seats.

[0144] Figure 11 is a schematic diagram showing the configuration of an example of a vehicle according to the embodiment. The vehicle 300 shown in Figure 11 is an electric vehicle.

[0145] The vehicle 300 shown in Figure 11 includes a vehicle power supply 301, a vehicle ECU (ECU: Electric Control Unit) 380 which is a higher-level control means for the vehicle power supply 301, an external terminal 370, an inverter 340, and a drive motor 345.

[0146] Vehicle 300 has its vehicle power supply 301 mounted, for example, in the engine compartment, at the rear of the vehicle body, or under the seats. However, Figure 11 shows the locations of the secondary battery mounted on vehicle 300 in a schematic manner.

[0147] The vehicle power supply 301 comprises a plurality (for example, three) of battery packs 312a, 312b, and 312c, a battery management unit (BMU) 311, and a communication bus 310.

[0148] The three battery packs 312a, 312b, and 312c are electrically connected in series. Battery pack 312a includes a battery pack 314a and a battery pack monitoring device (VTM: Voltage Temperature Monitoring) 313a. Battery pack 312b includes a battery pack 314b and a battery pack monitoring device 313b. Battery pack 312c includes a battery pack 314c and a battery pack monitoring device 313c. Battery packs 312a, 312b, and 312c can each be independently removed and replaced with other battery packs.

[0149] Each of the battery packs 314a to 314c comprises multiple secondary batteries connected in series. Each secondary battery is a secondary battery according to the embodiment. Each of the battery packs 314a to 314c is charged and discharged through the positive terminal 316 and the negative terminal 317, respectively.

[0150] The battery management device 311 collects information regarding the maintenance of the vehicle power supply 301 by communicating with battery monitoring devices 313a to 313c to collect information such as the voltage and temperature of the secondary batteries in the battery packs 314a to 314c included in the vehicle power supply 301.

[0151] A communication bus 310 is connected between the battery management device 311 and the battery pack monitoring devices 313a to 313c. The communication bus 310 is configured to share one set of communication lines among multiple nodes (the battery management device and one or more battery pack monitoring devices). The communication bus 310 is a communication bus configured, for example, based on the CAN (Control Area Network) standard.

[0152] The battery pack monitoring devices 313a to 313c measure the voltage and temperature of each secondary battery constituting the battery pack 314a to 314c based on commands communicated from the battery management device 311. However, the temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all secondary batteries.

[0153] The vehicle power supply 301 may also have an electromagnetic contactor (for example, a switch device 333 shown in Figure 11) for switching the connection between the positive and negative terminals. The switch device 333 includes a precharge switch (not shown) that turns on when charging is performed on the battery packs 314a to 314c, and a main switch (not shown) that turns on when the battery output is supplied to the load. The precharge switch and the main switch include a relay circuit (not shown) that is turned on and off by a signal supplied to a coil located near the switch element.

[0154] The inverter 340 converts the input DC voltage into a high voltage three-phase alternating current (AC) for motor drive. The output voltage of the inverter 340 is controlled based on control signals from the battery management device 311 or the vehicle ECU 380 for controlling the overall operation of the vehicle. The three-phase output terminals of the inverter 340 are connected to the three-phase input terminals of the drive motor 345.

[0155] The drive motor 345 rotates using power supplied from the inverter 340, and transmits this rotation to the axle and drive wheels W, for example, via a differential gear unit.

[0156] Although not shown in the diagram, vehicle 300 is also equipped with a regenerative braking mechanism that rotates the drive motor 345 when the vehicle 300 is braked, converting kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 340 and converted into a DC current. The DC current is input to the vehicle power supply 301.

[0157] One terminal of connection line L1 is connected to the negative terminal 317 of the vehicle power supply 301 via a current detection unit (not shown) in the battery management device 311. The other terminal of connection line L1 is connected to the negative input terminal of the inverter 340.

[0158] One terminal of connection line L2 is connected to the positive terminal 316 of the vehicle power supply 301 via a switch device 333. The other terminal of connection line L2 is connected to the positive input terminal of inverter 340.

[0159] The external terminal 370 is connected to the battery management device 311. The external terminal 370 can be connected to, for example, an external power supply.

[0160] The vehicle ECU 380 controls the battery management device 311 in coordination with other devices in response to operational inputs from the driver or other users, thereby managing the entire vehicle. Data related to the maintenance of the vehicle power supply 301, such as the remaining capacity of the vehicle power supply 301, is transferred between the battery management device 311 and the vehicle ECU 380 via a communication line.

[0161] The vehicle of the embodiment includes a battery pack containing a secondary battery according to the embodiment, and since the battery pack (for example, battery packs 312a, 312b, and 312c) generates little gas, a highly reliable vehicle can be obtained.

[0162] (Examples) The present invention will be further explained with the following examples, but the present invention is not limited to the embodiments listed below unless it exceeds the spirit of the invention.

[0163] (Example 1) A secondary battery was fabricated using the following procedure.

[0164] <Fabrication of the positive electrode> As the positive electrode active material, lithium nickel cobalt manganese composite oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2 powder was prepared. Acetylene black was prepared as a conductive agent. Polyvinylidene fluoride (PVdF) was prepared as a binder. Next, the positive electrode active material, conductive agent, and binder were added to N-methylpyrrolidone (NMP) as a solvent in a ratio of 82% by mass, 9% by mass, and 9% by mass, and mixed to prepare a positive electrode slurry. This positive electrode slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm. Then, the coating was dried in a constant temperature bath at 120°C to form a positive electrode active material-containing layer, and the positive electrode active material-containing layer was pressed to obtain the positive electrode.

[0165] <Fabrication of the negative electrode> Niobium titanium oxide (Nb2TiO7) powder was prepared as the negative electrode active material. The average secondary particle size of the niobium titanium oxide was 7.5 μm. The specific surface area of ​​the niobium titanium oxide was 4.0 m². 2 The concentration was / g. Acetylene black was prepared as the conductive agent, and polyvinylidene fluoride (PVdF) was prepared as the binder. Next, the negative electrode active material, conductive agent, and binder were added to N-methylpyrrolidone (NMP) as a solvent in a ratio of 82% by mass, 9% by mass, and 9% by mass, and mixed to prepare a negative electrode slurry. This negative electrode slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm. Then, the coating film was dried in a constant temperature bath at 120°C to form a negative electrode active material-containing layer, and the negative electrode active material-containing layer was pressed to obtain the negative electrode.

[0166] <Fabrication of electrode groups> The positive and negative electrodes were vacuum-dried at 120°C for 24 hours. Two nonwoven polyethylene fabrics with a thickness of 25 μm were prepared as separators. Next, the positive electrode, separator, negative electrode, and separator were stacked in this order to obtain a laminate. Then, this laminate was wound into a spiral shape. A flattened electrode group was fabricated by heating and pressing this at 80°C. The positive electrode terminal was electrically connected to the positive electrode of the electrode group. The negative electrode terminal was also electrically connected to the negative electrode of the electrode group.

[0167] <Storage of electrode groups> A container was prepared from a laminate film with a three-layer structure of nylon, aluminum, and polyethylene, and a thickness of 0.1 mm. The electrode group prepared as described above was placed inside this container. Next, with a portion of the periphery of the container left open, the inside of the container was dried in a vacuum at 80°C for 16 hours.

[0168] <Preparation of liquid non-aqueous electrolytes> A mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio 1:2) was prepared as the solvent. LiPF6 was dissolved in the solvent at a concentration of 1 mol / L as the electrolyte salt. Then, 1,3-propanesultone (PS) and 1-propene-1,3-sultone (PES) were added as sultone compounds so that their initial concentrations in the non-aqueous electrolyte were each 1.0 mass%, and then dissolved. Thus, a liquid non-aqueous electrolyte (non-aqueous electrolyte solution) was obtained. The preparation of the liquid non-aqueous electrolyte was carried out in an argon box.

[0169] <Battery manufacturing> A non-aqueous electrolyte was injected into a container housing the electrode group. Next, the open portion of the container's periphery was heat-sealed to seal the container. This resulted in a battery with external dimensions of 11 cm × 8 cm × 0.3 cm (excluding the positive and negative electrode terminals, also called positive and negative electrode tabs) and internal dimensions (dimensions of the sealed portion) of 9 cm × 7 cm × 0.25 cm. This battery is referred to as the first sealed battery.

[0170] <First charge> The initial charge and discharge cycle was performed by carrying out the following initial charge and discharge procedures. The first sealed battery was subjected to initial charging in a 25°C environment using the following procedure. First, the first sealed battery was charged with a constant current (CC) of 0.2C until it reached a voltage of 3V. Next, the first sealed battery was charged with a constant voltage (CV) of 3V. Constant voltage charging was terminated when the total time of constant current charging and constant voltage charging reached 10 hours.

[0171] <Initial discharge> Next, the first sealed battery was discharged at a constant current (CC) of 0.2C in a 25°C environment until the voltage reached 1.5V.

[0172] <Aging> Next, the first sealed battery, after its initial charge and discharge, was charged with a constant current (CC) of 0.2C at 25°C until it reached a voltage of 2.4V. Then, the first sealed battery was charged with a constant voltage (CV) of 2.4V until the current value became 1 / 20C. In other words, the first sealed battery was subjected to constant current constant voltage (CCCV) charging. As a result, the state of charge (SOC) of the first sealed battery was 60%. This first sealed battery was subjected to aging. Aging was carried out by holding it in a constant temperature bath at 40°C for 6 hours. After that, the first sealed battery was placed in an argon box, and one part of the sealing portion of the outer casing was cut to release the gas inside the outer casing. The end that was opened by the cut was sealed with a heat seal. In this way, a secondary battery according to Example 1 was manufactured.

[0173] (Examples 2-5) A secondary battery was fabricated in the same manner as in Example 1, except that the type of negative electrode active material was changed as shown in Table 1.

[0174] (Example 6) A secondary battery was prepared in the same manner as in Example 1, except that the amount of PS used in the preparation of the non-aqueous electrolyte was changed as shown in Table 1.

[0175] (Examples 7, 8) In the preparation of the non-aqueous electrolyte, the amounts of PES and PS were changed as shown in Table 1. The aging conditions were also changed as described in Table 1. Except for the above, the secondary battery was prepared in the same manner as in Example 1.

[0176] (Examples 9-14) A secondary battery was fabricated in the same manner as in Example 1, except that the aging conditions were changed as shown in Table 1.

[0177] (Comparative Example 1) A secondary battery was prepared in the same manner as in Example 1, except that PES was not included in the preparation of the non-aqueous electrolyte.

[0178] (Comparative Examples 2-4) A secondary battery was fabricated in the same manner as in Example 1, except that the aging conditions were changed as shown in Table 1.

[0179] (Measurement of B / A ratio) The B / A value of the negative electrode in each example and comparative example of the secondary battery was measured using the HAXPES method described above.

[0180] (Gas generation test) The amount of gas generated when the secondary batteries of each example and comparative example were subjected to the following charge-discharge cycles was measured.

[0181] First, the volume of the secondary battery before being subjected to the charge-discharge cycle was measured using the Archimedes method. Then, the secondary battery was charged at a constant current (CC) of 0.2C in an environment of 70°C until it reached a voltage of 3V. Next, the secondary battery was charged at a constant voltage (CV) of 3V until the current value became 1 / 20C. In other words, the secondary battery was subjected to constant current constant voltage (CCCV) charging to bring its state of charge (SOC) to 100%. After that, it was discharged at a constant current (CC) of 1C. One cycle consisted of the above constant current constant voltage (CCCV) charging and constant current (CC) discharge, and this was repeated 600 times. After 600 charge-discharge cycles, the volume of the secondary battery was measured again using the Archimedes method. The difference between the volume of the secondary battery after 600 cycles and the volume of the secondary battery before being subjected to the charge-discharge cycle was defined as the amount of gas generated (cc).

[0182] Table 1 shows the manufacturing conditions, B / A ratio, and gas generation amount for the secondary battery. The manufacturing conditions for the secondary battery include the type of negative electrode active material, the proportions of PES and PS used in the preparation of the non-aqueous electrolyte, the state of charge (SOC) during aging, the aging temperature, and the aging time.

[0183] [Table 1]

[0184] The secondary batteries in Examples 1 to 14 all produced less gas compared to the secondary batteries in Comparative Examples 1 to 4.

[0185] Examples 1 to 5 demonstrate that gas generation can be suppressed even when the type of negative electrode active material is changed in various ways.

[0186] Furthermore, from Examples 1, 6-8 and Comparative Example 1, it became clear that the B / A value changes when the formulation of the non-aqueous electrolyte is varied. It also became clear that even when the formulation of the non-aqueous electrolyte is varied, gas generation can be suppressed if the B / A is 0.25 or higher.

[0187] Examples 1, 9-14 and Comparative Examples 2-4 clearly show that the B / A value changes even when the aging conditions are varied. Furthermore, it was found that even when the aging conditions are varied, gas generation can be suppressed if the B / A value is 0.25 or higher.

[0188] Comparative Example 2, Comparative Example 3, and Comparative Example 4, which had a higher SOC during aging, a higher aging temperature, and a longer aging time, all showed a B / A ratio of less than 0.25. This is thought to be because increasing the SOC during aging, increasing the aging temperature, or extending the aging time makes the decomposition of PS among the non-aqueous electrolytes more likely to proceed. Comparing PES and PS, the decomposition reaction of PS is relatively more likely to form an inorganic film on the surface of the negative electrode. Therefore, it is thought that the B / A ratio was lower for these three.

[0189] The reaction in which an organic film is formed on the surface of the negative electrode due to the decomposition reaction of PES is thought to proceed more readily when the state of charge (SOC) during aging is lowered, the temperature during aging is lowered, or the aging time is shortened.

[0190] A secondary battery is provided according to at least one embodiment or example described above. The secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The surface of the negative electrode is SO x Includes a group (x is 3 or 4) and a CS bond. SO x The ratio B / A, where A is the number of sulfur atoms in the base and B is the number of sulfur atoms in the CS bond, is 0.25 or higher. Therefore, a secondary battery with low gas generation can be realized.

[0191] The invention according to the embodiment is described below.

[0192] [1] comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, The surface of the negative electrode is SO x It includes a group (x is 3 or 4) and a CS bond, The SO x A secondary battery in which the ratio B / A, where A is the number of sulfur atoms contained in the base and B is the number of sulfur atoms contained in the CS bond, is 0.25 or greater.

[0193] [2] The secondary battery according to [1], wherein the nonaqueous electrolyte comprises a sultone compound.

[0194] [3] The secondary battery according to [2], comprising the sultone compound 1-propene-1,3-sultone.

[0195] [4] The secondary battery according to any one of [1] to [3], wherein the negative electrode comprises at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides.

[0196] [5] A battery pack containing a rechargeable battery as described in any one of the items [1] to [4].

[0197] [6] The battery pack described in [5] further comprising an external terminal for power supply and a protection circuit.

[0198] [7] comprising a plurality of the aforementioned secondary batteries, The battery pack described in [5] or [6], wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

[0199] A vehicle equipped with a battery pack as described in any one of the items [8] [5] to [7].

[0200] [9] The vehicle according to [8], which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

[0201] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0202] 1...Electrode group, 2...Container (outer casing), 3...Positive electrode, 3a...Positive electrode current collector, 3b...Positive electrode composite layer, 4...Negative electrode, 4a...Negative electrode current collector, 4b...Negative electrode composite layer, 5...Separator, 6...Positive electrode lead, 7...Negative electrode lead, 8...Positive electrode current collector tab, 9...Negative electrode current collector tab, 10...Sealing plate, 11...Insulating material, 12...Outer casing, 13...Negative electrode terminal, 14...Positive electrode terminal, 30...Secondary battery with first sealing, 31...Secondary battery, 50...Battery pack, 51...Unit cell, 53...Battery pack, 54...Print Wiring board, 55...Thermistor, 56...Protection circuit, 57...External terminal for power supply, 71...Automobile, 72...Battery pack, 300...Vehicle, 301...Vehicle power supply, 310...Communication bus, 311...Battery management device, 312a~c...Battery pack, 313a~c...Battery pack monitoring device, 314a~c...Battery pack, 316...Positive terminal, 317...Negative terminal, 340...Inverter, 345...Drive motor, 370...External terminal, 380...Vehicle ECU, L1, L2...Connection lines, W...Drive wheel.< / haxpes>

Claims

1. It includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The surface of the negative electrode is SO ｘ It includes a group (x is 3 or 4) and a C-S bond, The aforementioned SO ｘ A secondary battery in which the ratio B / A, where A is the number of sulfur atoms contained in the base and B is the number of sulfur atoms contained in the C-S bond, is 0.25 or greater.

2. The secondary battery according to claim 1, wherein the non-aqueous electrolyte contains a sultone compound.

3. The secondary battery according to claim 2, wherein the sultone compound comprises 1-propene-1,3-sultone.

4. The secondary battery according to claim 1, wherein the negative electrode includes at least one selected from the group consisting of titanium-containing oxides and niobium-containing oxides.

5. A battery pack comprising a secondary battery according to any one of claims 1 to 4.

6. The battery pack according to claim 5, further comprising an external terminal for power supply and a protection circuit.

7. The device comprises multiple secondary batteries, The battery pack according to claim 5, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

8. A vehicle equipped with the battery pack described in claim 5.

9. The vehicle according to claim 8, which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

Images