Secondary batteries, battery packs, and vehicles

Abstract

To provide a secondary battery whose output performance is high and whose high temperature durability is high, a battery pack including the secondary battery, and a vehicle including the battery pack.SOLUTION: According to an embodiment, a secondary battery is provided that includes a cathode, an anode, and a non-aqueous electrolyte. The cathode includes a cathode mixture layer containing a cathode active material and a sulfur atom. The mass of sulfur atom per unit volume of the cathode mixture layer is 430 g / m3 or less. The non-aqueous electrolyte contains propane sultone and lithium difluorophosphate. The concentration of propane sultone in the non-aqueous electrolyte is 0.5 mass% or greater. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass% or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments 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. 2014 / 129823 [Patent Document 2] Japanese Patent Publication No. 2021-144819 [Patent Document 3] Japanese Patent Publication No. 2021-150215 [Overview of the project] [Problems that the invention aims to solve]

[0004] The embodiment aims to provide a secondary battery with high output performance and high high-temperature durability, a battery pack including the secondary battery, and a vehicle including the battery pack. [Means for solving the problem]

[0005] According to one embodiment, a secondary battery is provided which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode active material and a positive electrode composite layer containing sulfur atoms. The positive electrode active material includes manganese dioxide, iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium manganese cobalt composite oxide, Li x Mn 2-y Ni y O 4 A lithium manganese nickel composite oxide having a spinel structure represented by 0 < x ≦ 1, 0 < y < 2, a lithium phosphate having an olivine structure, iron sulfate, vanadium oxide, LiNix Co y M z O 2 (where x + y + z = 1, x ≧ 0.8, and M consists of Mn and Al), and at least one selected from the group consisting of lithium nickel cobalt manganese composite oxides represented by Li x Ni 1-y-z Co y Mn z O 2 satisfying 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, and y + z < 1. The mass of sulfur atoms per unit volume of the positive electrode composite layer is 430 g / m 3 The following is the case. The non-aqueous electrolyte contains propane sultone and lithium difluorophosphate. The concentration of propane sultone in the non-aqueous electrolyte is 0.5% by mass or more. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2% by mass or more.

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

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

Brief Description of the Drawings

[0008]

Figure 1

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Figure 11

[0009] (First Embodiment) According to the first embodiment, a secondary battery is provided comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive electrode active material and a positive electrode composite layer comprising sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode composite layer is 430 g / m³. 3 The following conditions apply: The non-aqueous electrolyte contains propanesultone and lithium difluorophosphate. The concentration of propanesultone in the non-aqueous electrolyte is 0.5% by mass or higher. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2% by mass or higher.

[0010] As a result of diligent research, the inventors have discovered that the high-temperature durability of secondary batteries can be improved by adding propanesultone (PS; 1,3-propanesultone) to a non-aqueous electrolyte. The mechanism is presumed to be as follows.

[0011] At high temperatures, especially under conditions where the state of charge (SOC) is high, when a non-aqueous electrolyte comes into contact with the positive electrode active material in the positive electrode, oxidative decomposition of the non-aqueous electrolyte occurs, generating gas.

[0012] The secondary battery according to this embodiment contains propanesultone in the non-aqueous electrolyte. When propanesultone reacts with the positive electrode active material, it decomposes to form a sulfur-containing phase containing sulfur atoms. Therefore, the positive electrode composite layer contains sulfur atoms in addition to the positive electrode active material. The mass of sulfur atoms per unit volume of the positive electrode composite layer is 430 g / m³. 3 The following means that there is not too much sulfur-containing phase relative to the positive electrode composite layer. Therefore, resistance increase can be suppressed, and the output performance of the positive electrode can be kept high.

[0013] When propanesultone is present in a non-aqueous electrolyte, the reaction of propanesultone with the positive electrode active material proceeds more readily than the reaction of other components in the non-aqueous electrolyte with the positive electrode active material. Furthermore, no gas is generated during the decomposition reaction of propanesultone. In other words, propanesultone is decomposed preferentially over other components of the non-aqueous electrolyte as a sacrificial material, thereby suppressing gas generation due to oxidative decomposition of the non-aqueous electrolyte. Therefore, even at high temperatures, oxidative decomposition of the non-aqueous electrolyte and gas generation can be suppressed. Consequently, the formation of bubbles within the positive electrode and the resulting increase in resistance can be suppressed. Therefore, output performance and high-temperature durability can be improved.

[0014] For propanesultone to function as a sacrificial material, it must be present in the non-aqueous electrolyte. However, even if propanesultone is added during the preparation of the non-aqueous electrolyte, it is easily decomposed during the initial charge and discharge of the secondary battery. Therefore, it is difficult to maintain the presence of propanesultone in the non-aqueous electrolyte after the initial charge and discharge, for example, during storage or charge-discharge cycles.

[0015] The non-aqueous electrolyte in the secondary battery according to this embodiment contains lithium difluorophosphate (DFP: Lithium difluorophosphate, LiPO2F2) in addition to propanesultone. In the non-aqueous electrolyte, the reaction that consumes lithium difluorophosphate proceeds more readily than the reaction between the positive electrode active material and propanesultone. Therefore, the inclusion of lithium difluorophosphate in the non-aqueous electrolyte can suppress the decomposition of propanesultone.

[0016] The non-aqueous electrolyte contained in the secondary battery according to this embodiment has a lithium difluorophosphate concentration of 0.2% by mass or more, which makes it easier to suppress the decomposition of propanesultone. Therefore, even after the initial charge and discharge of the secondary battery, it is easier to maintain the presence of propanesultone in the non-aqueous electrolyte.

[0017] The non-aqueous electrolyte contained in the secondary battery according to this embodiment has a propane-sultone concentration of 0.5% by mass or more. In other words, propane-sultone is present in the non-aqueous electrolyte to a degree that allows it to function sufficiently as a sacrificial material. As a result, gas generation due to oxidative decomposition of the non-aqueous electrolyte can be suppressed.

[0018] Therefore, according to this embodiment, a secondary battery with high output performance and high high-temperature durability can be provided.

[0019] A secondary battery according to this embodiment will be described in more detail with reference to the drawings.

[0020] The secondary battery in question 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).

[0021] The lower limit of the mass of sulfur atoms per unit volume in the positive electrode composite layer is, for example, 20 g / m³. 3 This can be achieved. The mass of sulfur atoms per unit volume of the positive electrode composite layer is 100 g / m³. 3 More than 420g / m 3 Preferably, it should be within the following range: 350 g / m² 3 More than 410g / m 3 It is more preferable that the mass of sulfur atoms per unit volume of the positive electrode composite layer be, for example, 390 g / m³. 3 The above is also acceptable. If there is a large amount of sulfur-containing phase relative to the positive electrode composite layer, the mass of sulfur atoms per unit volume of the positive electrode composite layer may increase. Therefore, if the mass of sulfur atoms per unit volume of the positive electrode composite layer is high, contact between the positive electrode composite layer and the non-aqueous electrolyte is difficult, and thus gas generation can be suppressed.

[0022] The negative electrode of the secondary battery according to this embodiment may include a negative electrode composite layer. Preferably, the negative electrode composite layer further contains sulfur atoms in addition to the negative electrode active material.

[0023] Propanesultone can form a sulfur-containing phase even when reacting with the negative electrode active material. Therefore, the negative electrode composite layer may contain sulfur atoms in addition to the negative electrode active material.

[0024] In electrodes containing a sulfur-containing phase, contact between the non-aqueous electrolyte and the active material in the electrode may be difficult. Generally, water (H2O) can be introduced as an unavoidable impurity during the assembly of secondary batteries. Water introduced into a secondary battery can react with the non-aqueous electrolyte to produce hydrofluoric acid (hydrogen fluoride, HF) in the non-aqueous electrolyte. Contact between hydrofluoric acid in the non-aqueous electrolyte and the electrode is undesirable because it can degrade the active material.

[0025] Therefore, when the negative electrode composite layer contains sulfur atoms in addition to the negative electrode active material, contact between the negative electrode active material and the non-aqueous electrolyte is less likely, which suppresses the deterioration of the negative electrode active material and is therefore preferable.

[0026] The mass of sulfur atoms per unit volume in the negative electrode composite layer is 430 g / m³. 3 The following is preferable. Being within the above numerical range means that there is not too much sulfur-containing phase relative to the negative electrode composite layer. Therefore, resistance increase can be suppressed, and the output performance of the negative electrode can be kept high.

[0027] The lower limit of the mass of sulfur atoms per unit volume in the negative electrode composite layer is, for example, 20 g / m³. 3 This can be achieved. The mass of sulfur atoms per unit volume of the negative electrode composite layer is 100 g / m³. 3 More than 420g / m 3 Preferably, it should be within the following range: 350 g / m² 3 More than 410g / m 3 It is more preferable that the mass of sulfur atoms per unit volume of the negative electrode composite layer be, for example, 380 g / m³. 3 The above is also acceptable. If there is a large amount of sulfur-containing phase relative to the negative electrode composite layer, the mass of sulfur atoms per unit volume of the negative electrode composite layer may increase. Therefore, if there are many sulfur atoms per unit volume of the negative electrode composite layer, it becomes more difficult for the negative electrode active material and the non-aqueous electrolyte to come into contact, thereby suppressing the degradation of the negative electrode active material.

[0028] As a result of the decomposition of propanesultone, the positive electrode composite layer contained in the positive electrode and the negative electrode composite layer that may be contained in the negative electrode (electrode composite layers) may contain a sulfur-containing phase containing sulfur atoms. The sulfur atoms may originate from the decomposition products of the non-aqueous electrolyte. Alternatively, the sulfur atoms may originate from the decomposition products of propanesultone contained in the non-aqueous electrolyte. The sulfur-containing phase may be formed on the active material within the electrode composite layer. The sulfur-containing phase may be a layer formed on the active material, or it may be a film that covers at least a part of the surface of the active material particles. In addition to sulfur atoms (S), the sulfur-containing phase may contain other types of atoms. Examples of other types of atoms include oxygen atoms (O) and carbon atoms (C).

[0029] The electrode composite layer may include an active material-containing layer containing an active material and a sulfur-containing phase formed on at least a portion of the active material. Here, the active material-containing layer refers to the layer of the electrode composite layer that is formed on the current collector and contains the active material. The sulfur-containing phase may be formed on at least a portion of the active material-containing layer, or on at least a portion of the surface of the active material-containing layer. The sulfur-containing phases that the positive electrode composite layer and the negative electrode composite layer may contain may be referred to as the positive electrode sulfur-containing phase and the negative electrode sulfur-containing phase, respectively.

[0030] The upper limit of the propanesultone concentration in the non-aqueous electrolyte can be 5% by mass, but it can also be, for example, 5.0% by mass. The propanesultone concentration is preferably in the range of 0.55% by mass or more and 4.8% by mass or less, and more preferably in the range of 0.6% by mass or more and 4.6% by mass or less. The propanesultone concentration in the non-aqueous electrolyte can also be, for example, 4.50% by mass or less. An excessively high concentration of propanesultone is undesirable because it can lead to the excessive formation of propanesultone decomposition products in the electrode composite layer, which can cause an increase in resistance.

[0031] The concentration of propanesultone in the non-aqueous electrolyte may be 0.50% by mass or higher.

[0032] The upper limit of the concentration of lithium difluorophosphate in the non-aqueous electrolyte can be 5% by mass, but it can also be, for example, 5.0% by mass. The concentration of lithium difluorophosphate is preferably in the range of 0.55% by mass or more and 4.8% by mass or less, and more preferably in the range of 0.6% by mass or more and 4.6% by mass or less. The concentration of lithium difluorophosphate in the non-aqueous electrolyte can also be, for example, 4.50% by mass or less. An excessively high concentration of lithium difluorophosphate is undesirable because it may precipitate in the non-aqueous electrolyte.

[0033] The concentration of lithium difluorophosphate in the non-aqueous electrolyte may be 0.20% by mass or higher.

[0034] Figures 1 and 2 show an example of a secondary battery using a laminate film exterior component.

[0035] 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.

[0036] 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.

[0037] Figures 3 and 4 show an example of a secondary battery using a metal container.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The exterior component 12 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] First, the positive electrode 3 and the negative electrode 4 are fabricated.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 performed at a temperature above room temperature. Through the first charge-discharge and aging, a reaction occurs between propanesultone and the positive electrode active material, and as a result, sulfur atoms are incorporated into the positive electrode active material-containing layer. Specifically, decomposition products of a non-aqueous electrolyte containing propanesultone may be formed on the surface of the positive electrode active material contained in the positive electrode active material-containing layer. As a result, a layered sulfur-containing phase may be formed on the surface of the positive electrode active material. In this way, a positive electrode composite layer 3b containing sulfur atoms can be obtained. At this time, sulfur atoms may also be incorporated into the negative electrode active material-containing layer. As a result, a negative electrode composite layer 4b containing sulfur atoms can be obtained.

[0054] 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.

[0055] Next, the end portion 24 along the cutting line 22 is sealed under reduced pressure (e.g., -90kPa).

[0056] By adjusting the manufacturing conditions of the manufacturing method described above, the mass of sulfur atoms per unit volume of the positive electrode composite layer, and the concentrations of propanesultone and lithium difluorophosphate in the non-aqueous electrolyte can be set within the desired range. This yields the secondary battery 31 of the embodiment.

[0057] Details of the manufacturing conditions are described below.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Furthermore, while lithium difluorophosphate can capture moisture introduced into secondary batteries, it is consumed in the process. Therefore, if a large amount of moisture is introduced into the secondary battery, lithium difluorophosphate is consumed more easily, which may reduce the effectiveness of lithium difluorophosphate in suppressing the decomposition of propanesultones.

[0062] Therefore, it is preferable that the positive and negative electrodes used in the preparation of the electrode group are dry, as this can suppress side reactions and allow lithium difluorophosphate and propanesultone to remain in the non-aqueous electrolyte, thereby suppressing gas generation in the secondary battery of the embodiment.

[0063] 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.

[0064] 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.

[0065] The higher the aging temperature and the longer the aging time, the easier it is to promote the gas generation reaction during aging.

[0066] The lower the aging temperature, the more the decomposition and consumption of propanesultone during aging can be suppressed, thus increasing the amount of propanesultone remaining in the non-aqueous electrolyte of the secondary battery 31 in the embodiment.

[0067] The aging temperature is preferably set to a low temperature of 25°C to 50°C. Furthermore, the aging time is preferably set to a long duration of 30 to 48 hours.

[0068] In order to retain propanesultone in the secondary battery 31 of the embodiment and to suppress gas generation within the secondary battery 31 of the embodiment, it is preferable to perform the aging process at a low temperature and for a long period of time.

[0069] 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.

[0070] 1) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode composite material layer. The positive electrode composite material layer can be formed on one or both sides of the positive electrode current collector. The positive electrode composite material layer can include a positive electrode active material, sulfur atoms, and optionally a conductive agent and a binder. The positive electrode composite material layer can include the positive electrode sulfur-containing phase described above. The sulfur atoms can be included in the positive electrode sulfur-containing phase. The positive electrode sulfur-containing phase may be present on at least a part of the positive electrode surface, or may cover at least a part of the surface of the positive electrode active material particles. The positive electrode sulfur-containing phase may be in the form of a film or a layer.

[0071] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain one type of compound alone or a combination of two or more types of compounds as the positive electrode active material. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and desorbed.

[0072] 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 [[ID=1ó]]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 Mny PO4; 0 < x ≤ 1, 0 < y ≤ 1, Li x CoPO4; 0 < x ≤ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., 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 z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) is included.

[0073] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≤ 1, Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≤ 1, Li[[ID=​​​​​​​​​​​​​​​​​​If the active material contains sulfur atoms in its composition, sulfur atoms originating from the active material may be present in the extract in the ICP emission spectrometry described later. That is, the mass of sulfur atoms per unit volume of the electrode composite layer identified in the ICP emission spectrometry may include the mass of sulfur atoms originating from the active material. In this case as well, the mass of sulfur atoms per unit volume of the positive electrode composite layer is 430 g / m³. 3 The following applies:

[0075] The positive electrode active material may be in particulate form. Preferably, the primary particle size of the positive electrode active material is between 100 nm and 1 μm. Positive electrode active materials with a primary particle size of 100 nm or more are easy to handle in industrial production. Positive electrode active materials with a primary particle size of 1 μm or less allow for smooth diffusion of lithium ions within the solid.

[0076] The specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g or more 10m 2 It is preferable that it is less than or equal to / g. 0.1m 2 A positive electrode active material with a specific surface area of ​​10m or more can adequately secure sites for Li ion intercalation and release. 2 Positive 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.

[0077] 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.

[0078] 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.

[0079] In the positive electrode composite 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.

[0080] 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.

[0081] 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.

[0082] 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 electrolyte can be reduced. This lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0083] 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.

[0084] 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.

[0085] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode composite layer is not formed. These portions can function as positive electrode current collector tabs.

[0086] 2) Negative electrode The negative electrode may include a current collector and a negative electrode composite layer. The negative electrode composite layer may be formed on one or both sides of the current collector. The negative electrode composite layer may include a negative electrode active material and optionally a conductive agent and a binder. The negative electrode composite layer preferably contains sulfur atoms. The negative electrode composite layer may include the negative electrode sulfur-containing phase described above. Sulfur atoms may be contained in the negative electrode sulfur-containing phase. The negative electrode sulfur-containing phase may be present on at least a portion of the negative electrode surface, or it may cover at least a portion of the surface of the negative electrode active material particles. The negative electrode sulfur-containing phase may be in the form of a film or a layer.

[0087] The negative electrode active material is not particularly limited as long as it can intercept and deintercept lithium or lithium ions. The type of negative electrode active material used can be one or more types. Examples of negative electrode active materials include titanium-containing oxides, niobium-containing oxides, and carbon materials.

[0088] Examples of titanium-containing oxides include lithium titanium-containing oxides and titanium oxides. Examples of niobium-containing oxides include niobium titanium oxides, niobium tungsten-containing oxides, and niobium titanium molybdenum-containing oxides.

[0089] Examples of titanium-containing oxides include lithium titanate (e.g., Li) which has a ramsdellite structure. 2+y Li3O7 (0≦y≦3), lithium titanate having a spinel structure (e.g., Li 4+xTi5O 12 (where 0 ≦ x ≦ 3), monoclinic titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, hollandite-type titanium composite oxide, orthorhombic titanium composite oxide. The lithium ion intercalation and deintercalation potential of the titanium-containing oxide is 0.4 V (vs. Li / Li + ).

[0090] Examples of the orthorhombic titanium-containing composite oxide include Li 2+a M I 2-b Ti 6-c M II d O 14+σ compounds represented by. Here, M I is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M II is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. Each subscript in the composition formula satisfies 0 ≦ a ≦ 6, 0 ≦ b < 2, 0 ≦ c < 6, 0 ≦ d < 6, -0.5 ≦ σ ≦ 0.5. Specific examples of the orthorhombic titanium-containing composite oxide include Li 2+a Na2Ti6O 14 (0 ≦ a ≦ 6).

[0091] Examples of the niobium-containing oxide include niobium oxide, niobium titanium oxide, niobium tungsten-containing oxide, niobium titanium molybdenum-containing oxide.

[0092] Examples of the niobium titanium oxide include monoclinic niobium titanium oxide. Examples of the monoclinic niobium titanium oxide include Li x Ti 1-y M1 y Nb 2-z M2​​​Compounds represented by the following formula are included. 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. As a specific example of the monoclinic niobium titanate, Li x Nb2TiO7 (0 ≦ x ≦ 5) can be mentioned.

[0093] As other examples of the monoclinic niobium titanate, compounds represented by Li x Ti 1-y M3 y+z Nb 2-z O 7-δ are included. 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.

[0094] Examples of the carbon material include graphite, hard carbon, etc. When a carbon material is used for the negative electrode, a copper foil is used for the negative electrode current collector.

[0095] Among the negative electrode active materials, the monoclinic niobium titanate can moderately cause the decomposition reaction of propanesultone because the lithium ion intercalation / deintercalation potential is around 1.0 V (vs. Li / Li + ). Note that the lithium ion intercalation / deintercalation potential of lithium titanate is around 1.4 V (vs. Li / Li + ), and the lithium ion intercalation / deintercalation potential of the carbon material is around 0 V (vs. Li / Li + ).

[0096] The negative electrode active material can be in a particulate shape.

[0097] 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.

[0098] 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.

[0099] As an example, the preferred blending ratios of the negative electrode active material, conductive agent, and binder in the negative electrode composite 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 composite layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient bonding between the negative electrode composite 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.

[0100] 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.

[0101] Furthermore, the current collector may include portions on its surface where the negative electrode composite layer is not formed. These portions can function as negative electrode current collector tabs.

[0102] 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, an organic solvent capable of dissolving the electrolyte salt, propanesultone (1,3-propanesultone), and lithium difluorophosphate. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0103] Propanesultone and lithium difluorophosphate may or may not function as an electrolyte salt or an organic solvent. Propanesultone and lithium difluorophosphate may also function as both an electrolyte salt and an organic solvent.

[0104] The composition of the non-aqueous electrolyte contained in the secondary battery of the embodiment, particularly the concentration of propanesultone and the concentration of lithium difluorophosphate, may have changed 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, propanesultone and lithium difluorophosphate may be consumed during the first charge-discharge, aging, etc.

[0105] In other words, it is preferable that the non-aqueous electrolyte be prepared such that, in the secondary battery of the embodiment after the initial charge-discharge and aging, the concentration of propane sultone in the non-aqueous electrolyte is 0.5% by mass or more, and the concentration of lithium difluorophosphate is 0.2% by mass or more.

[0106] Specifically, it is preferable to prepare the non-aqueous electrolyte such that the concentration of propanesultone in the non-aqueous electrolyte immediately after preparation (initial concentration) is in the range of 0.7% by mass or more and 5% by mass or less. The initial concentration of propanesultone may be 1.0% by mass or more.

[0107] The higher the initial concentration of propanesultone, the more likely it is that propanesultone will remain in the non-aqueous electrolyte after the initial charge and discharge.

[0108] The lower the initial concentration of propanesultone, the fewer decomposition products are generated when propanesultone reacts with the electrode active material, thus suppressing the increase in electrode resistance.

[0109] In this embodiment, the secondary battery contains lithium difluorophosphate in addition to propanesultone in the non-aqueous electrolyte. Therefore, even if the initial concentration of propanesultone is low, propanesultone tends to remain in the non-aqueous electrolyte after the first charge and discharge. This makes it possible to suppress both the increase in electrode resistance and the decomposition of the non-aqueous electrolyte.

[0110] Preparing the non-aqueous electrolyte so that the concentration of lithium difluorophosphate in the non-aqueous electrolyte immediately after preparation (initial concentration) is high makes it easier to obtain the effect of suppressing the decomposition of propanesultone. The initial concentration of lithium difluorophosphate is preferably 0.3% by mass or higher, and more preferably 0.5% by mass or higher. If the initial concentration of lithium difluorophosphate is low, the precipitation of lithium difluorophosphate in the non-aqueous electrolyte can be suppressed. The initial concentration of lithium difluorophosphate is preferably 5% by mass or lower, and more preferably 3% by mass or lower.

[0111] The non-aqueous electrolyte is preferably prepared such that the initial concentration of propanesultone to the initial concentration of lithium difluorophosphate (PS:DFP initial concentration ratio) is between 1:9 and 10:1. In other words, it is preferable to prepare the electrolyte so that the initial concentration of lithium difluorophosphate is between 0.1 and 9 times the initial concentration of propanesultone. Within this range, the decomposition inhibitory effect of lithium difluorophosphate on propanesultone is easily obtained, and the initial concentration of propanesultone can be kept low. Therefore, the increase in resistance can be suppressed.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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:

[0117] 5) Exterior components For example, the outer packaging material can be a container made of laminate film or a metal container.

[0118] The thickness of the laminating film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] <Measurement method> Mass of sulfur atoms per unit volume of the positive electrode composite layer or negative electrode composite layer (g / m³) 3 The following describes how to measure the concentration (mass%) of propanesultone and the concentration (mass%) of lithium difluorophosphate in non-aqueous electrolytes.

[0124] (Preparation of the sample for measurement) Open the outer casing of a secondary battery with a State of Charge (SOC) of 50% and remove the electrode group. Remove the jig (tape, etc.) that bundles the electrode group together, and if the outermost layer is a separator, peel back the separator to remove the first layer electrode (e.g., negative electrode). Peel back the separator again to remove the first layer electrode (e.g., positive electrode). Repeat the process of peeling back the separator and removing the electrodes until all positive and negative electrodes constituting the electrode group are removed. Centrifuge the removed electrodes and separators to extract the non-aqueous electrolyte and separate the electrodes from the separators.

[0125] (ICP emission spectrometry) Mass of sulfur atoms per unit volume of the positive electrode composite layer or negative electrode composite layer (g / m³) 3The ) is measured by inductively coupled plasma (ICP) emission spectrometry. Each electrode separated by the centrifuge described above is washed with methyl ethyl carbonate (MEC) and vacuum dried. Each electrode is then placed over a fixed area (2 × 2 cm²). 2 The material is punched out, a certain amount of pure water (10cc) is added, and ultrasonic irradiation is performed for 30 minutes or more. The extracted solution is analyzed by ICP and the mass of sulfur atoms in the extract is measured to obtain the mass of sulfur atoms per unit volume of each electrode composite layer.

[0126] (GC-MS) The non-aqueous electrolyte extracted using the method described above 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 below, the concentration (mass%) of propane sultone in the non-aqueous electrolyte can be determined.

[0127] [Table 1]

[0128] (Capillary electrophoresis) The non-aqueous electrolyte extracted using the method described above can be diluted 20 times in volume with acetonitrile and subjected to capillary electrophoresis (CE) under the following measurement conditions to determine the concentration (mass%) of lithium difluorophosphate in the non-aqueous electrolyte.

[0129] Capillary tube: inner diameter 50 μm, length 72 cm Applied voltage -30kV Temperature 10℃ Electrophoresis buffer: Agilent Technologies inorganic anion analysis buffer Detection wavelength Signal=350(±80) nm, Ref=245(±10) nm Measurement time: 20 min According to the first embodiment described above, a secondary battery is provided comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive electrode active material and a positive electrode composite layer comprising sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode composite layer is 430 g / m³. 3 The following conditions apply: The non-aqueous electrolyte contains propanesultone and lithium difluorophosphate. The concentration of propanesultone in the non-aqueous electrolyte is 0.5% by mass or higher. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2% by mass or higher. Therefore, a secondary battery with high output performance and high high-temperature durability can be realized.

[0130] (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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] The battery pack of the second embodiment described above includes the secondary battery of the embodiment. Therefore, it can achieve excellent output performance and excellent high-temperature durability.

[0145] (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.

[0146] 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.

[0147] Figure 10 shows an example of an automobile equipped with a battery pack according to one embodiment.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] The vehicle of the embodiment includes a battery pack containing a secondary battery according to the embodiment. Since the battery pack (for example, battery packs 312a, 312b, and 312c) has excellent output performance and high-temperature durability, a vehicle with excellent charge / discharge performance and high reliability can be obtained. Furthermore, since each battery pack is inexpensive and highly safe, the cost of the vehicle can be reduced and safety can be enhanced. [Examples]

[0167] A secondary battery was fabricated using the following procedure.

[0168] (Example 1) <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.

[0169] <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. 2The 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.

[0170] <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.

[0171] <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.

[0172] <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. 1,3-propanesultone (PS) was added and dissolved to achieve an initial concentration of 1.0 mass% in the non-aqueous electrolyte. Lithium difluorophosphate (DFP) was then added and dissolved to achieve an initial concentration of 1.0 mass%. That is, the non-aqueous electrolyte was prepared so that the initial concentration of PS to the initial concentration of DFP (PS:DFP initial concentration ratio) was 1:1. 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.

[0173] <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.

[0174] <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.

[0175] <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.

[0176] <Post-processing> 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 3V. Then, the first sealed battery was charged with a constant voltage (CV) of 3V 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 100%. This first sealed battery was then subjected to aging. Aging was carried out by holding it in a constant temperature bath at 35°C for 35 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.

[0177] (Examples 2-6) A secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material was changed as shown in Table 2.

[0178] (Examples 7, 9, 10) A secondary battery was fabricated in the same manner as in Example 1, except that the negative electrode active material was changed as shown in Table 2.

[0179] (Example 8) The negative electrode active material was changed to C (graphite) as shown in Table 2. Graphite powder and polyvinylidene fluoride (PVdF) were mixed in a ratio of 90% by mass and 10% by mass, and the resulting mixture was kneaded in the presence of an organic solvent (N-methylpyrrolidone) to prepare a slurry. The obtained slurry was applied to a current collector made of copper foil with a thickness of 15 μm, dried, and pressed to obtain the negative electrode. Furthermore, when using a negative electrode containing graphite, a secondary battery was fabricated by carrying out the following steps from initial charging to post-processing.

[0180] <First charge> 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 4.15V. Next, the first sealed battery was charged with a constant voltage (CV) of 4.15V. Constant voltage charging was terminated when the total time of constant current charging and constant voltage charging reached 10 hours.

[0181] <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 2V.

[0182] <Post-processing> 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 4.15V. Then, the first sealed battery was charged with a constant voltage (CV) of 4.15V 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 100%. This first sealed battery was subjected to aging. Aging was carried out by holding it in a constant temperature bath at 35°C for 35 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 8 was manufactured.

[0183] (Example 11) A secondary battery was prepared in the same manner as in Example 1, except that a mixed solvent of propylene carbonate (PC) and methyl ethyl carbonate (MEC) (volume ratio 1:2) was prepared as the solvent for the liquid non-aqueous electrolyte.

[0184] (Example 12) A secondary battery was prepared in the same manner as in Example 1, except that a mixed solvent of propylene carbonate (PC) and dimethyl carbonate (DMC) (volume ratio 1:2) was prepared as the solvent for the liquid non-aqueous electrolyte.

[0185] (Example 13) A secondary battery was prepared in the same manner as in Example 1, except that a mixed solvent of propylene carbonate (PC) and ethyl propionate (EP) (volume ratio 1:4) was prepared as the solvent for the liquid non-aqueous electrolyte.

[0186] (Examples 14-18) In the preparation of the liquid non-aqueous electrolyte, the initial concentrations of 1,3-propanesultone (PS) and lithium difluorophosphate (DFP) were set to the values ​​shown in Tables 2 and 3, respectively. The initial PS:DFP ratio (PS:DFP initial concentration ratio) in the non-aqueous electrolyte for each example is shown in Tables 2 and 3.

[0187] Furthermore, the aging temperature and time during post-processing were set as described in Tables 5 and 6.

[0188] Aside from the above, a secondary battery was fabricated in the same manner as in Example 1.

[0189] (Examples 19-21) A secondary battery was fabricated in the same manner as in Example 1, except that the aging temperature during post-processing was as shown in Table 6.

[0190] (Examples 22-24) A secondary battery was fabricated in the same manner as in Example 1, except that the aging time in the post-processing was as shown in Table 6.

[0191] (Examples 25-27) In the preparation of the liquid non-aqueous electrolyte, the initial concentrations of 1,3-propanesultone (PS) and lithium difluorophosphate (DFP) were set to the values ​​shown in Table 3. The initial PS concentration and DFP concentration in the non-aqueous electrolyte for each example are shown in Table 3.

[0192] Furthermore, the aging temperature and time during post-processing were as shown in Table 6.

[0193] Aside from the above, a secondary battery was fabricated in the same manner as in Example 1.

[0194] (Example 28) A secondary battery was fabricated in the same manner as in Example 1, except that the positive and negative electrodes were vacuum-dried at 80°C during the preparation of the electrode group.

[0195] (Example 29) A secondary battery was fabricated in the same manner as in Example 1, except that vacuum drying of the positive and negative electrodes was not performed during the preparation of the electrode group. Since vacuum drying was not performed, the electrode drying temperatures in Table 6 are indicated with "-".

[0196] (Comparative Example 1) A secondary battery was prepared in the same manner as in Example 1, except that 1,3-propanesultone (PS) was not added in the preparation of the liquid non-aqueous electrolyte.

[0197] (Comparative Example 2) A secondary battery was prepared in the same manner as in Example 1, except that lithium difluorophosphate (DFP) was not added in the preparation of the liquid non-aqueous electrolyte.

[0198] (Comparative Examples 3-4) A secondary battery was fabricated in the same manner as in Example 1, except that the aging temperature and time in the post-processing were as shown in Table 7.

[0199] (Comparative Examples 5-6) In preparing the liquid non-aqueous electrolyte, the initial concentrations of 1,3-propanesultone (PS) and lithium difluorophosphate (DFP) were set to the values ​​shown in Table 4. The initial PS:DFP concentration ratio in the non-aqueous electrolyte is shown in Table 4.

[0200] Furthermore, the aging temperature and time during post-processing were as shown in Table 7.

[0201] Aside from the above, a secondary battery was fabricated in the same manner as in Example 1.

[0202] (Comparative Example 7) In the preparation of the liquid non-aqueous electrolyte, the initial concentrations of 1,3-propanesultone (PS) and lithium difluorophosphate (DFP) were set to the values ​​shown in Table 4. The initial concentrations of PS and DFP in the non-aqueous electrolyte are shown in Table 4.

[0203] Aside from the above, a secondary battery was fabricated in the same manner as in Example 1.

[0204] <Measurement of the mass of sulfur atoms per unit volume of the asphalt mixture layer> For each example and comparative example of secondary battery, the mass of sulfur atoms per unit volume of the positive electrode composite layer (amount of S per positive electrode composite layer) and the mass of sulfur atoms per unit volume of the positive electrode composite layer (amount of S per negative electrode composite layer) were measured by ICP emission spectrometry as described above. The measurement results are shown in Tables 8 to 10.

[0205] <Measurement of non-aqueous electrolytes> After post-treatment, the concentration of propanesultone (PS concentration in the non-aqueous electrolyte) and the concentration of lithium difluorophosphate (DFP concentration in the non-aqueous electrolyte) in the liquid non-aqueous electrolyte of the secondary batteries of each example and comparative example were measured using the method described above. The measurement results are shown in Tables 8 to 10.

[0206] <Storage Test> Storage tests were conducted on the secondary batteries of each example and comparative example as follows.

[0207] A secondary battery was charged with a constant current (CC) of 0.2C until it reached a voltage of 3V. Then, the battery was charged with a constant voltage (CV) of 3V until the current was 1 / 20C. In other words, the battery was subjected to constant current constant voltage (CCCV) charging until its state of charge (SOC) reached 100%. This charged battery was placed in a 55°C constant temperature bath. Every 10 days, the battery was removed from the 55°C bath, cooled to 25°C, and then subjected to 3V CCCV charging again before being placed back into the 55°C bath. This process was repeated until the battery, stored in the constant temperature bath for 90 days, was cooled to 25°C. After cooling, its volume was measured, and the difference between the volume before and after the test was defined as the gas generation amount (ml). The gas generation amount serves as an indicator of high-temperature endurance.

[0208] <Direct Current (DC) resistance measurement> Before conducting the storage test, the DC resistance of the secondary batteries in each example and comparative example was measured as follows: The battery was discharged with a constant current (CC) of 0.2C until the voltage reached 1.5V. Then, the battery was charged with a constant current (CC) of 0.2C until the voltage reached 2.25V. Next, the battery was charged with a constant voltage (CV) of 2.25V until the current value became 1 / 20C, thereby bringing the battery's state of charge (SOC) to 50%. The battery adjusted to SOC 50% was discharged with a constant current (CC) of 10C for 10ms, and the DC resistance (mΩ) was determined from the difference between the voltage and current values ​​at this time.

[0209] Furthermore, DC resistance measurements were performed on the secondary batteries after the storage test, in the same manner as described above, and the DC resistance (mΩ) was determined.

[0210] Let R1 be the DC resistance before the storage test, and R2 be the DC resistance after the storage test. The resistance increase was calculated by dividing R2 by R1.

[0211] Tables 2 to 4 show the types of positive electrode active materials and negative electrode active materials, the types of solvents and electrolyte salts used in the preparation of the liquid non-aqueous electrolyte, the initial PS concentration, the initial DFP concentration, and the PS:DFP initial concentration ratio for each example and comparative example.

[0212] Tables 5 to 7 show the electrode drying temperature, electrode drying time in the production of the electrode group, aging temperature, and aging time in the post-treatment for each of the examples and comparative examples.

[0213] Tables 8 to 10 show the amount of S per positive electrode composite layer, the amount of S per negative electrode composite layer, the concentration of PS in the non-aqueous electrolyte, the concentration of DFP in the non-aqueous electrolyte, the gas generation amount (ml), and the resistance increase value in the secondary battery after the post-treatment for each of the examples and comparative examples.

[0214]

Table 2

[0215]

Table 3

[0216] [[ID=2)5]]

Table 4

[0217]

Table 5

[0218]

Table 6

[0219]

Table 7

[0220]

Table 8

[0223] From Tables 2 to 10, the following became clear.

[0224] The positive electrodes of the secondary batteries in Examples 1 to 29 contained a positive electrode composite layer containing sulfur atoms. This is thought to be because a reaction occurred between propanesultone and the positive electrode active material after the initial charge-discharge and aging, resulting in sulfur atoms being incorporated into the positive electrode active material layer.

[0225] Comparative Example 1 was the same as Example 1 except that the non-aqueous electrolyte did not contain propanesultone. In Comparative Example 1, neither the positive electrode composite layer nor the negative electrode composite layer contained sulfur atoms. Furthermore, the resistance increase was high and the amount of gas generated was large. This is thought to be because the non-aqueous electrolyte did not contain propanesultone, so gas generation due to the decomposition of the non-aqueous electrolyte was not suppressed.

[0226] Comparative Example 2, which was the same as Example 1 except that the non-aqueous electrolyte did not contain lithium difluorophosphate, had a high amount of sulfur per cathode composite layer and a low concentration of polysulfide (PS) in the non-aqueous electrolyte. Furthermore, it generated a large amount of gas. This is thought to be because the decomposition of propanesultone was not suppressed during the initial charge-discharge and aging phases. As a result, high-temperature durability was reduced.

[0227] Comparative Example 3, which was prepared in the same manner as Example 1 except for the increased aging temperature, produced a large amount of gas. This was because the aging was performed at a high temperature of 60°C, which caused excessive decomposition of propanesultone during aging, resulting in a sulfur content of 430 g / m² per cathode composite layer. 3 This is thought to be due to the fact that the value became larger than the given value, and the PS concentration in the non-aqueous electrolyte became less than 0.5% by mass.

[0228] Comparative Example 4, which was prepared in the same manner as Example 1 except that the aging time was extended, had a higher resistance increase value and a larger gas generation amount than Example 1. This is because the decomposition of propane sultone proceeded excessively during aging due to the long aging time, resulting in an S amount per positive electrode composite material layer greater than 430 g / m 3 and a PS concentration in the non-aqueous electrolyte less than 0.5 mass%, which is considered to be the cause.

[0229] Comparative Example 5, in which the S amount per positive electrode composite material layer and the S amount per negative electrode composite material layer were both greater than 430 g / m 3 had a high resistance increase value. This is presumably because, as a result of the decomposition of propane sultone, a sulfur-containing phase was excessively formed on the surface of the active material, which became a factor in the increase in resistance.

[0230] Comparative Example 6, in which the PS concentration in the non-aqueous electrolyte was less than 0.5 mass%, had a large gas generation amount. This is thought to be because propane sultone, which can function as a sacrificial material, did not sufficiently remain in the non-aqueous electrolyte contained in the secondary battery after post-treatment, so the reaction in which the non-aqueous electrolyte decomposes and generates gas was not suppressed.

[0231] Comparative Example 7, in which the DFP concentration in the non-aqueous electrolyte was less than 0.2 mass%, also had a PS concentration in the non-aqueous electrolyte less than 0.5 mass% and a large gas generation amount. This is because lithium difluorophosphate was not sufficiently present in the non-aqueous electrolyte, so the consumption of propane sultone during the first charge / discharge and aging was not suppressed. As a result, propane sultone, which can function as a sacrificial material, did not sufficiently remain in the non-aqueous electrolyte contained in the secondary battery after post-treatment.

[0232] As shown in Examples 1 to 6, even if the positive electrode active material is changed to one different from that of Example 1, for example, a lithium nickel cobalt manganese composite oxide with different ratios of Ni, Co, and Mn, a lithium manganese composite oxide, a lithium phosphate oxide having an olivine structure, etc., the effects of suppressing gas generation and resistance increase can be obtained.

[0233] As shown in Examples 7 to 10, even when the negative electrode active material is changed to something different from that in Example 1, such as lithium titanate having a spinel structure, carbon material, orthorhombic titanium composite oxide, or monoclinic titanium dioxide, the effect of suppressing gas generation and resistance increase can be obtained.

[0234] As shown in Examples 11-13, even if the non-aqueous solvent of the non-aqueous electrolyte is changed to one different from that in Example 1, for example, a solvent containing methyl ethyl carbonate, dimethyl carbonate, or ethyl propionate, the effect of suppressing gas generation and resistance increase can be obtained.

[0235] As shown in Examples 14-18, the effect of suppressing gas generation and resistance increase can be obtained even when the initial concentration of PS and the initial concentration of DFP in the non-aqueous electrolyte are varied.

[0236] Comparing Examples 1, 19-21 and Comparative Example 3, there was a tendency for the amount of sulfur (S) per cathode composite layer to decrease as aging was performed at lower temperatures. The amount of sulfur per cathode composite layer was 430 g / m³. 3 Examples 1, 19-21, and Comparative Example 3 showed lower gas generation than Comparative Example 3. Furthermore, comparing Examples 1, 19, 20, and Comparative Example 3, there was a tendency for the amount of PS in the non-aqueous electrolyte to decrease as the aging temperature increased.

[0237] Comparing Examples 1, 22-24, and Comparative Example 4, there was a tendency for the amount of sulfur (S) per cathode composite layer to decrease with shorter aging times. The amount of sulfur per cathode composite layer was 430 g / m². 3 Examples 1, 22-24, described below, produced lower gas emissions than Comparative Example 4.

[0238] Comparing Examples 25-26, the amount of sulfur per negative electrode composite layer was 430 g / m². 3 Example 25, described below, has a sulfur content of 430 g / m² per negative electrode composite layer. 3 The amount of gas generated tended to be lower than in the larger example 26.

[0239] Comparing Examples 1 and 15 with Comparative Examples 1 and 6, there was a tendency for the amount of gas generated to be lower as the PS concentration in the non-aqueous electrolyte increased.

[0240] Comparing Examples 1, 28, and 29, Examples 1 and 28, in which the electrodes were vacuum-dried, tended to have lower resistance increases and less gas generation than Example 29, in which the electrodes were not vacuum-dried. Furthermore, Example 1, in which the electrodes were vacuum-dried at 120°C, tended to have even lower resistance increases and less gas generation than Example 28, in which the electrodes were vacuum-dried at 80°C. This is thought to be due to the fact that the higher the temperature and the longer the drying time, the less moisture remains in the electrodes. It is thought that the less moisture there is in the electrodes, the less propane sultone and lithium difluorophosphate in the non-aqueous electrolyte are consumed, making it easier to obtain the propane sultone consumption suppression effect by lithium difluorophosphate and the gas generation suppression effect by propane sultone even after the initial charge and discharge.

[0241] According to at least one embodiment or example, a secondary battery is provided comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive electrode active material and a positive electrode composite layer comprising sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode composite layer is 430 g / m³. 3 The following applies: The non-aqueous electrolyte contains propanesultone and lithium difluorophosphate. The concentration of propanesultone in the non-aqueous electrolyte is 0.5% by mass or more. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2% by mass or more. Therefore, it is possible to suppress gas generation and resistance increase at high temperatures, and to provide a secondary battery that can achieve excellent lifespan performance even at high temperatures.

[0242] 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 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 variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. The invention described in the claims of the present application at the time of filing is appended below. [1] A secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, where the positive electrode includes a positive electrode composite material layer containing a positive electrode active material and sulfur atoms, the mass of the sulfur atoms per unit volume of the positive electrode composite material layer is 430 g / m 3 or less, the non-aqueous electrolyte includes propanesultone and lithium difluorophosphate, the concentration of propanesultone in the non-aqueous electrolyte is 0.5 mass% or more, the concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass% or more. [2] The secondary battery according to [1], wherein the negative electrode includes a negative electrode composite material layer containing a negative electrode active material and sulfur atoms. [3] The mass of the sulfur atoms per unit volume of the negative electrode composite material layer is 430 g / m 3 or less, The secondary battery according to [2]. [4] A battery pack including the secondary battery according to any one of [1] to [3]. [5] An external terminal for energization and a protection circuit The battery pack according to [4], further including. [6] The battery pack according to [4], including a plurality of the secondary batteries, where the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. [7] A vehicle including the battery pack according to [4]. [8] The vehicle according to [7], including a mechanism for converting the kinetic energy of the vehicle into regenerative energy. [Explanation of symbols]

[0243] 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.

Claims

1. It includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive electrode active material and a positive electrode composite layer containing sulfur atoms. The positive electrode active material includes at least one selected from the group consisting of manganese dioxide, iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium manganese cobalt composite oxide, lithium manganese nickel composite oxide having a spinel structure represented as Li x Mn 2-y Ni y O 4 satisfying 0 < x ≤ 1 and 0 < y < 2, lithium phosphorus oxide having an olivine structure, iron sulfate, vanadium oxide, LiNi x Co y M z O 2 (satisfying x + y + z = 1 and x ≥ 0.8, where M consists of Mn and Al), and lithium nickel cobalt manganese composite oxide represented as Li x Ni 1-yz Co y Mn z O 2 satisfying 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1. The mass of sulfur atoms per unit volume of the positive electrode composite layer is 430 g / m³. ３ The following: The non-aqueous electrolyte comprises propanesultone and lithium difluorophosphate. The concentration of the propanesultone in the non-aqueous electrolyte is 0.5% by mass or more. A secondary battery in which the concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2% by mass or more.

2. The secondary battery according to claim 1, wherein the negative electrode comprises a negative electrode active material and a negative electrode composite layer containing sulfur atoms.

3. The mass of sulfur atoms per unit volume of the negative electrode composite layer is 430 g / m³. ３ The following is: The secondary battery according to claim 2.

4. A battery pack including a secondary battery according to any one of claims 1 to 3.

5. External terminals for power supply, Protection circuit and The battery pack according to claim 4, further comprising:

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

7. A vehicle comprising the battery pack described in claim 4.

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

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