Secondary battery, battery pack, and vehicle

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 problems with output performance and high-temperature durability. The reason for this is that the non-aqueous electrolyte reacts with the electrodes to generate gas. When gas is generated, bubbles are generated inside the electrodes, which makes the active material more likely to peel off, increasing resistance and decreasing output performance. Secondary batteries containing non-aqueous electrolytes are particularly prone to gas generation in high-temperature environments. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2014 / 129823 [Patent Document 2] JP 2021-144819 A [Patent Document 3] JP 2021-150215 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the embodiments is to provide a secondary battery having high output performance and high durability at high temperatures, a battery pack including the secondary battery, and a vehicle including the battery pack. [Means for solving the problem]

[0005] According to an embodiment, a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. The positive electrode includes a positive electrode mixture layer including a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode mixture layer is 430 g / m. 3The non-aqueous electrolyte contains propane sultone and lithium difluorophosphate. The concentration of the propane sultone in the non-aqueous electrolyte is 0.5% by mass or more. The concentration of the 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 a battery pack of the embodiment is provided. [Brief description of the drawings]

[0008] [Figure 1] 2 is a cross-sectional view of the secondary battery according to the embodiment, taken in a direction perpendicular to the terminal extending direction. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of part A in FIG. 1 . [Diagram 3] FIG. 2 is a partially cutaway cross-sectional view of a secondary battery according to the embodiment. [Figure 4] FIG. 4 is a side view of the battery of FIG. 3 . [Diagram 5] FIG. 4 is a partially cutaway perspective view illustrating a secondary battery according to another embodiment of the present invention; [Figure 6] 6 is an enlarged cross-sectional view of a portion B of the secondary battery shown in FIG. 5. [Figure 7] 3A to 3C are schematic plan views showing an example of a method for manufacturing a secondary battery according to an embodiment. [Figure 8] FIG. 2 is an exploded perspective view of the battery pack according to the embodiment. [Figure 9] FIG. 9 is a block diagram showing an electrical circuit of the battery pack of FIG. 8. [Figure 10] 1 is a schematic diagram showing an example of a vehicle equipped with a secondary battery according to an embodiment; [Figure 11] FIG. 13 is a diagram illustrating another example of a vehicle according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (First embodiment) According to the first embodiment, a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. The positive electrode includes a positive electrode mixture layer including a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode mixture layer is 430 g / m. 3 The non-aqueous electrolyte contains propane sultone and lithium difluorophosphate. The concentration of the propane sultone in the non-aqueous electrolyte is 0.5% by mass or more. The concentration of the lithium difluorophosphate in the non-aqueous electrolyte is 0.2% by mass or more.

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

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

[0012] The secondary battery according to the embodiment contains propane sultone in the non-aqueous electrolyte. When the propane sultone reacts with the positive electrode active material, it decomposes to form a sulfur-containing phase containing sulfur atoms. Therefore, the positive electrode mixture layer contains sulfur atoms in addition to the positive electrode active material. When the mass of sulfur atoms per unit volume of the positive electrode mixture layer is 430 g / m 3 or less means that the amount of the sulfur-containing phase is not too large relative to the positive electrode mixture layer, and therefore the increase in resistance can be suppressed, so that the output performance of the positive electrode can be maintained high.

[0013] When propane sultone is present in the non-aqueous electrolyte, the reaction of propane sultone reacting with the positive electrode active material in the positive electrode and decomposing is more likely to proceed than the reaction of the positive electrode active material with components other than propane sultone in the non-aqueous electrolyte. In addition, gas is not generated in the decomposition reaction of propane sultone. In other words, gas generation due to oxidative decomposition of the non-aqueous electrolyte can be suppressed by propane sultone being decomposed preferentially as a sacrificial material over other non-aqueous electrolyte components. Therefore, even at high temperatures, the oxidative decomposition of the non-aqueous electrolyte and the generation of gas can be suppressed. Therefore, the generation of bubbles in the positive electrode and the increase in resistance can be suppressed. Therefore, the output performance and high temperature durability can be improved.

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

[0015] The non-aqueous electrolyte contained in the secondary battery according to the embodiment contains lithium difluorophosphate (DFP: LiPO2F2) in addition to propane sultone. In the non-aqueous electrolyte, a reaction in which lithium difluorophosphate is consumed proceeds more easily than a reaction between the positive electrode active material and propane sultone. Therefore, by including lithium difluorophosphate in the non-aqueous electrolyte, decomposition of propane sultone can be suppressed.

[0016] The non-aqueous electrolyte in the secondary battery according to the embodiment has a lithium difluorophosphate concentration of 0.2 mass % or more, which makes it easy to suppress the decomposition of propane sultone, and therefore makes it easy to maintain the presence of propane sultone in the non-aqueous electrolyte even after the initial charge / discharge of the secondary battery.

[0017] The non-aqueous electrolyte contained in the secondary battery according to the embodiment has a propane sultone concentration of 0.5 mass % or more. In other words, the propane sultone is present in the non-aqueous electrolyte to an extent that it can function 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 the embodiment, a secondary battery having high output performance and high durability at high temperatures can be provided.

[0019] The secondary battery according to the embodiment will be described in further detail with reference to the drawings.

[0020] The secondary battery may be, for example, a secondary battery that uses alkali metal ions as carrier ions, such as a lithium battery (lithium ion battery).

[0021] The lower limit of the mass of sulfur atoms per unit volume of the positive electrode mixture layer is, for example, 20 g / m 3 The mass of sulfur atoms per unit volume of the positive electrode mixture layer can be 100 g / m 3 More than 420g / m 3 It is preferable that the thickness is within the range of 350 g / m 3 More than 410g / m 3 It is more preferable that the mass of sulfur atoms per unit volume of the positive electrode mixture layer is within the following range: 3 If the sulfur-containing phase is more abundant than the positive electrode mixture layer, the mass of sulfur atoms per unit volume of the positive electrode mixture layer may be large. Therefore, if the mass of sulfur atoms per unit volume of the positive electrode mixture layer is large, the positive electrode mixture layer and the non-aqueous electrolyte are less likely to come into contact with each other, and gas generation can be suppressed.

[0022] The negative electrode included in the secondary battery according to the embodiment may include a negative electrode mixture layer. The negative electrode mixture layer preferably further includes sulfur atoms in addition to the negative electrode active material.

[0023] Propane sultone can also form a sulfur-containing phase when it reacts with the negative electrode active material, so that the negative electrode mixture layer can contain sulfur atoms in addition to the negative electrode active material.

[0024] In an electrode containing a sulfur-containing phase, the non-aqueous electrolyte may be less likely to come into contact with the active material contained in the electrode. In general, water (H2O) may be brought in as an inevitable impurity when assembling a secondary battery. The water brought into the secondary battery may react with the non-aqueous electrolyte to generate hydrofluoric acid (hydrogen fluoride, HF) in the non-aqueous electrolyte. If the hydrofluoric acid in the non-aqueous electrolyte comes into contact with the electrode, the active material may deteriorate, which is undesirable.

[0025] Therefore, when the negative electrode mixture layer contains sulfur atoms in addition to the negative electrode active material, the negative electrode active material is less likely to come into contact with the non-aqueous electrolyte, which makes it possible to suppress deterioration of the negative electrode active material, which is preferable.

[0026] The mass of sulfur atoms per unit volume of the negative electrode mixture layer is 430 g / m 3 It is preferable that the sulfur content is within the above range. The sulfur content is not too high in the negative electrode mixture layer. Therefore, the increase in resistance can be suppressed, and the output performance of the negative electrode can be maintained high.

[0027] The lower limit of the mass of sulfur atoms per unit volume of the negative electrode mixture layer is, for example, 20 g / m 3 The mass of sulfur atoms per unit volume of the negative electrode mixture layer can be 100 g / m 3 More than 420g / m 3 It is preferable that the thickness is within the range of 350 g / m 3 More than 410g / m 3 The mass of sulfur atoms per unit volume of the negative electrode mixture layer is more preferably within the following range: 3 If the sulfur-containing phase is more than the negative electrode mixture layer, the mass of sulfur atoms per unit volume of the negative electrode mixture layer may be large. Therefore, if the sulfur atoms per unit volume of the negative electrode mixture layer are large, the negative electrode active material and the nonaqueous electrolyte are less likely to come into contact with each other, and deterioration of the negative electrode active material can be suppressed.

[0028] As a result of the decomposition of propane sultone, each of the positive electrode mixture layer contained in the positive electrode and the negative electrode mixture layer that may be contained in the negative electrode (electrode mixture layer) may contain a sulfur-containing phase containing sulfur atoms. The sulfur atoms may be derived from a decomposition product of the non-aqueous electrolyte. The sulfur atoms may also be derived from a decomposition product of the propane sultone contained in the non-aqueous electrolyte. The sulfur-containing phase may be formed on the active material of the electrode mixture layer. The sulfur-containing phase may be a layer formed on the active material, or may be a film that covers at least a part of the surface of the active material particles. The sulfur-containing phase may contain other types of atoms in addition to sulfur atoms (S). Examples of other types of atoms include oxygen atoms (O) and carbon atoms (C).

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

[0030] The upper limit of the propane sultone concentration in the non-aqueous electrolyte can be 5% by mass, but the upper limit can also be, for example, 5.0% by mass. The propane sultone concentration is preferably in the range of 0.55% by mass to 4.8% by mass, more preferably in the range of 0.6% by mass to 4.6% by mass. The propane sultone concentration in the non-aqueous electrolyte can also be, for example, 4.50% by mass or less. If the propane sultone concentration is excessively high, decomposition products of propane sultone are excessively formed in the electrode mixture layer, which can cause an increase in resistance, and is therefore undesirable.

[0031] The concentration of propane sultone in the non-aqueous electrolyte may be 0.50 mass % or more.

[0032] The upper limit of the lithium difluorophosphate concentration in the non-aqueous electrolyte can be 5% by mass, but the upper limit can also be, for example, 5.0% by mass. The lithium difluorophosphate concentration is preferably in the range of 0.55% by mass to 4.8% by mass, more preferably in the range of 0.6% by mass to 4.6% by mass. The lithium difluorophosphate concentration in the non-aqueous electrolyte can also be, for example, 4.50% by mass or less. If the lithium difluorophosphate concentration is excessively high, lithium difluorophosphate may precipitate in the non-aqueous electrolyte, which is not preferable.

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

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

[0035] As shown in FIG. 1 and FIG. 2, the electrode group 1 is a flat wound electrode group. The wound electrode group 1 is stored in a bag-shaped exterior member 12 made of a laminate film in which a metal layer is interposed between two resin films. The flat wound electrode group 1 is formed by spirally winding a laminate in which a negative electrode 4, a separator 5, a positive electrode 3, and a separator 5 are stacked in this order from the outside around an axis parallel to the short side direction, and press-molding the laminate. The outermost negative electrode 4 has a configuration in which a negative electrode layer (negative electrode composite layer) 4b containing a negative electrode active material is formed on one side of the inner surface side of a negative electrode collector 4a as shown in FIG. 2, and the other negative electrodes 4 are configured by forming a negative electrode layer 4b on both sides of the negative electrode collector 4a. The positive electrode 3 is configured by forming a positive electrode layer (positive electrode composite layer) 3b on both sides of a positive electrode collector 3a.

[0036] Near the outer peripheral end 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 terminal 13 and positive electrode terminal 14 extend outward from an opening of the bag-shaped exterior member 12. The opening of the bag-shaped exterior member 12 is heat-sealed to seal the wound electrode group 1. When heat-sealing, the negative electrode terminal 13 and positive electrode terminal 14 are sandwiched by the bag-shaped exterior member 12 at this opening.

[0037] 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 the short side direction with a separator 5 interposed between them. As shown in FIG. 4, a strip-shaped positive electrode lead 6 is electrically connected to each of a plurality of points on the end of the positive electrode 3 located on the end face of the electrode group 1 intersecting with the stacking direction of the electrodes. In addition, a strip-shaped negative electrode lead 7 is electrically connected to each of a plurality of points on the end of the negative electrode 4 located on this end face. The plurality of positive electrode leads 6 are electrically connected to a positive electrode current collector tab 8 in a bundled state. The positive electrode lead 6 and the positive electrode current collector tab 8 constitute a positive electrode terminal. In addition, the negative electrode lead 7 is connected to a negative electrode current collector tab 9 in a bundled state. The negative electrode lead 7 and the negative electrode current collector tab 9 constitute a negative electrode terminal. A metal sealing plate 10 is fixed to the opening of the metal container 2 by welding or the like. The positive electrode current collecting tab 8 and the negative electrode current collecting tab 9 are each pulled out to the outside through an extraction hole provided in a sealing plate 10. The inner circumferential surface of each extraction hole in the sealing plate 10 is covered with an insulating member 11 to prevent a short circuit due to contact with the positive electrode current collecting tab 8 and the negative electrode current collecting tab 9.

[0039] The secondary battery according to the embodiment is not limited to the secondary battery having the configuration shown in FIGS. 1 and 2 and the secondary battery having the configuration shown in FIGS. 3 and 4, but may be, for example, a battery having the configuration shown in FIGS. 5 and 6.

[0040] Fig. 5 is a partially cutaway perspective view showing a schematic diagram of another example of the secondary battery, and Fig. 6 is an enlarged cross-sectional view of part B of the secondary battery shown in Fig. 5.

[0041] The secondary battery shown in Figures 5 and 6 includes an electrode group 1 shown in Figures 5 and 6, an exterior member 12 shown in Figure 5, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 12. The electrolyte is held in the electrode group 1.

[0042] The exterior member 12 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0043] The electrode group 1 is a laminated type electrode group, as shown in Fig. 6. The laminated type electrode group 1 has a structure in which negative electrodes 4 and positive electrodes 3 are alternately laminated with separators 5 interposed therebetween.

[0044] The electrode group 1 includes a plurality of negative electrodes 4. Each of the plurality of negative electrodes 4 includes 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 includes 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] The negative electrode current collector 4a of each negative electrode 4 includes a portion on one side where the negative electrode active material-containing layer 4b is not supported on any surface. This portion serves as a negative electrode current collector tab 4c. As shown in FIG. 6, the negative electrode current collector tab 4c does not overlap with the positive electrode 3. The negative electrode current collector tabs 4c are electrically connected to a belt-shaped negative electrode terminal 13. The tip of the belt-shaped negative electrode terminal 13 is pulled out to the outside of the exterior member 12.

[0046] Although not shown, 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 serves as a positive electrode current collector tab. The positive electrode current collector tab does not overlap with the negative electrode 4, similar to the negative electrode current collector tab 4c. The positive electrode current collector tab is located on the opposite side of the electrode group 1 to the negative electrode current collector tab 4c. The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 14. The tip of the strip-shaped positive electrode terminal 14 is located on the opposite side to the negative electrode terminal 13 and is drawn out to the outside of the exterior member 12.

[0047] As an example of the secondary battery of the embodiment, a method for manufacturing a secondary battery including a wound electrode group will be described with reference to Fig. 7. Fig. 7 is a schematic diagram showing an outline of a method for manufacturing a secondary battery using a bag-shaped exterior member made of a laminate film.

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

[0049] For example, the positive electrode is prepared by suspending a positive electrode active material, a conductive agent, and a binder in a solvent to prepare a slurry. The 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. Then, the laminate is pressed. In this manner, the positive electrode is produced. Alternatively, the positive electrode may be produced by the following method. First, the active material, the conductive agent, and the binder are mixed to obtain a mixture. Then, the mixture is formed into pellets. Then, the pellets are placed on the current collector to obtain a positive electrode.

[0050] The negative electrode can be produced, for example, by the following method. First, a negative electrode active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of a negative electrode active material-containing layer and a current collector. Then, this laminate is pressed. In this way, a negative electrode is produced. Alternatively, the negative electrode may be produced by the following method. First, a negative electrode active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into a pellet shape. Next, these pellets are placed on a current collector to obtain a negative electrode.

[0051] An electrode group 1 is prepared by disposing a separator 5 between a positive electrode 3 and a negative electrode 4. A positive electrode terminal 14 is electrically connected to the positive electrode 3 of the electrode group 1, and a negative electrode terminal 13 is electrically connected to the negative electrode 4 of the electrode group 1.

[0052] The electrode group 1 having the positive and negative electrode terminals 13, 14 is housed in a bag-shaped exterior member 12 made of a laminate film, and the other end 21b except for the first end 21a is sealed by heat fusion. Next, a non-aqueous electrolyte is injected into the bag-shaped exterior member 12 from the first end 21a, and the first end 21a is sealed by heat fusion. The heat fusion may be performed under reduced pressure. In this way, a secondary battery 30 having undergone the first seal is obtained.

[0053] Next, the secondary battery 30 after the first sealing is subjected to an initial charge and discharge at room temperature (for example, 25°C), and then aging is performed at a temperature equal to or higher than room temperature. Through the initial charge and discharge and aging, a reaction occurs between the propane sultone and the positive electrode active material, and as a result, sulfur atoms are contained in the positive electrode active material-containing layer. Specifically, a decomposition product of the non-aqueous electrolyte containing propane sultone 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 mixture layer 3b containing sulfur atoms can be obtained. At this time, sulfur atoms may also be contained in the negative electrode active material-containing layer. As a result, a negative electrode mixture layer 4b containing sulfur atoms can be obtained.

[0054] After aging, the temperature of the secondary battery 30 is returned to room temperature, and then in an argon atmosphere, the bag-shaped exterior member 12 is cut and opened along the unsealed cutting line 22 inside the first end portion 21a, and the gas inside the bag-shaped exterior member 12 is released to the outside. The portion cut out from the bag-shaped exterior member 12 along the cutting line 22 is indicated by reference numeral 23.

[0055] The ends 24 along the cut lines 22 are then sealed under reduced pressure (eg, -90 kPa).

[0056] By adjusting the manufacturing conditions of the manufacturing method described above, the mass of sulfur atoms per unit volume of the positive electrode mixture layer, and the concentrations of propane sultone and lithium difluorophosphate in the non-aqueous electrolyte can be set within the target range, thereby obtaining the secondary battery 31 of the embodiment.

[0057] The production conditions are described in detail below.

[0058] The positive and negative electrodes used in the preparation of the electrode assembly are preferably dried beforehand before the preparation of the electrode assembly. The higher the temperature at which the drying is performed and the longer the time, the less water remains in the electrodes. From the viewpoint of reducing the water content in the electrodes, the drying is preferably performed under reduced pressure. For example, it is preferable to perform vacuum drying at 120°C for 24 hours.

[0059] When the positive electrode and the negative electrode are produced through a process of applying the slurry to one or both sides of a current collector and then drying the applied coating of the slurry, it is preferable to further carry out the above-mentioned drying after the coating drying process.

[0060] If the positive and negative electrodes used to prepare the electrode group are dry, the amount of moisture brought into the secondary battery can be reduced. If moisture is brought into the secondary battery, the water itself may be electrolyzed to generate gas, and side reactions at the negative electrode may occur easily. Therefore, in the battery reaction, the lithium ions released by the positive electrode are consumed in the side reactions at the negative electrode, making it difficult for the lithium ions to be absorbed by the negative electrode. As a result, SOC deviation may occur, and the positive electrode potential may shift to the high potential side. If the positive electrode potential becomes too high and deviates from the potential range in which the non-aqueous electrolyte can exist stably, the non-aqueous electrolyte may easily decompose at the positive electrode, which may cause gas generation. In addition, if moisture is brought into the secondary battery, the non-aqueous electrolyte may react with water to generate hydrofluoric acid, which may deteriorate the electrodes.

[0061] In addition, lithium difluorophosphate can capture moisture brought into the secondary battery, but lithium difluorophosphate is consumed in the process. Therefore, if a large amount of moisture is brought into the secondary battery, lithium difluorophosphate is likely to be consumed, and it may become difficult to obtain the effect of suppressing the decomposition of propane sultone by lithium difluorophosphate.

[0062] Therefore, if the positive electrode and the negative electrode used in preparing the electrode group are dry, side reactions can be suppressed and lithium difluorophosphate and propane sultone can be more likely to remain in the non-aqueous electrolyte, which is preferable because gas generation in the secondary battery of the embodiment can be suppressed.

[0063] 7, when the first sealed secondary battery 30 is subjected to initial charge / discharge and aging, gas is generated in the first sealed secondary battery 30. The gas generating reaction may be, for example, a reaction in which water brought into the secondary battery 30 is decomposed.

[0064] The gas generated during the initial charge / discharge and aging is released to the outside after aging, as described with reference to Fig. 7. Therefore, by actively promoting the gas generation reaction during aging, the amount of the substance that causes gas generation remaining in the secondary battery 31 of the embodiment obtained after aging can be reduced. Therefore, 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 more easily the gas generating reaction during aging can proceed.

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

[0067] The aging temperature is preferably a low temperature of 25° C. or more and 50° C. or less, and the aging time is preferably a long time of 30 hours or more and 48 hours or less.

[0068] In order to allow the propane sultone to remain in the secondary battery 31 of the embodiment and to suppress gas generation in the secondary battery 31 of the embodiment, it is preferable that the aging be performed at a low temperature for a long period of time.

[0069] The positive electrode, the negative electrode, and the non-aqueous electrolyte will be described below, along with a separator and an exterior member that the secondary battery of the embodiment may include in addition to these components.

[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 a single compound as the positive electrode active material, or may contain a combination of two or more compounds. Examples of the oxide and the sulfide 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 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 x Fe 1-y Mn y PO4; 0 < x ≤ 1, 0 < y ≤ 1, Li x CoPO4; 0 < x ≤ 1) is included. When these compounds are used as the positive electrode active material, the battery voltage can be increased. Li x Ni 1-y-z Co y Mn z In the lithium nickel cobalt manganese composite oxide represented by LiNiCoMnO2, those with 0 < y + z ≤ 0.2 can achieve a high energy density.

[0074] When the active material contains sulfur atoms in its composition, sulfur atoms derived from the active material may be included in the extract in the ICP emission spectrometry described below. That is, the mass of sulfur atoms per unit volume of the electrode mixture layer determined in the ICP emission spectrometry may include the mass of sulfur atoms derived from the active material. In this case, the mass of sulfur atoms per unit volume of the positive electrode mixture layer is 430 g / m 3 The following is the result.

[0075] The positive electrode active material may be in a particle shape. The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material having a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material having a primary particle size of 1 μm or less can smoothly promote diffusion of lithium ions in a solid.

[0076] The specific surface area of ​​the positive electrode active material is 0.1 m 2 / g or more 10m 2 / g or less. 2 A positive electrode active material having a specific surface area of ​​10m / g or more can secure sufficient sites for absorbing and releasing Li ions. 2 A positive electrode active material having a specific surface area of ​​100 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0077] The binder is blended to fill the gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, polyacrylic acid compounds, imide compounds, carboxymethylcellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0078] The conductive agent is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of the conductive agent include vapor grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be combined and used as the conductive agent. The conductive agent may also be omitted.

[0079] In the positive electrode mixture layer, the positive electrode active material and the binder are preferably mixed in proportions of 80% by mass to 98% by mass and 2% by mass to 20% by mass, respectively.

[0080] By making the amount of binder 2% by mass or more, sufficient electrode strength can be obtained. In addition, the binder can function as an insulator. Therefore, by making the amount of binder 20% by mass or less, the amount of insulator contained in the electrode is reduced, and the internal resistance can be reduced.

[0081] When a conductive agent is added, the positive electrode active material, the binder, and the conductive agent are preferably mixed in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

[0082] By setting the amount of the conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Also, by setting the amount of the conductive agent to 15% by mass or less, the ratio of the conductive agent in contact with the electrolyte can be reduced. If this ratio is low, decomposition of the electrolyte during high-temperature storage can be reduced.

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

[0085] The positive electrode current collector may also include a portion on the surface of which no positive electrode mixture layer is formed, and this portion may function as a positive electrode current collecting tab.

[0086] 2) Negative electrode The negative electrode may include a current collector and a negative electrode mixture layer. The negative electrode mixture layer may be formed on one or both sides of the current collector. The negative electrode mixture layer may include a negative electrode active material, and optionally a conductive agent and a binder. The negative electrode mixture layer preferably includes sulfur atoms. The negative electrode mixture layer may include the negative electrode sulfur-containing phase described above. The sulfur atoms may be included in the negative electrode sulfur-containing phase. The negative electrode sulfur-containing phase may be present on at least a part of the negative electrode surface, or may cover at least a part 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 absorb and release lithium or lithium ions. The type of the negative electrode active material used can be one or more. Examples of the negative electrode active material include titanium-containing oxides, niobium-containing oxides, and carbon materials.

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

[0089] Examples of titanium-containing oxides include lithium titanate having the ramsdellite structure (e.g., Li 2+y Ti3O7, 0≦y≦3), lithium titanates with spinel structure (e.g., Li 4+xTi5O 12 , 0≦x≦3), monoclinic titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, and orthorhombic titanium composite oxide. The lithium ion absorption and desorption potential of titanium-containing oxides is 0.4V (vs. Li / Li + )That's all.

[0090] As an example of the above-mentioned orthorhombic titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O 14+σ In this case, the compound represented by M I is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb and K. II is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+a Na2Ti6O 14 (0≦a≦6).

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

[0092] An example of the niobium titanium oxide is a monoclinic niobium titanium oxide. An example of the monoclinic niobium titanium oxide is Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δHere, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. Specific examples of monoclinic niobium titanium oxide include Li x Examples include Nb2TiO7 (0≦x≦5).

[0093] Another example of monoclinic niobium titanium oxide is Li x Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3.

[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, monoclinic niobium titanium oxide has a lithium ion absorption / release potential of 1.0V (vs. Li / Li + ), which allows the decomposition reaction of propane sultone to occur moderately. The lithium ion absorption and desorption potential of lithium titanate is 1.4V (vs. Li / Li + ), and the lithium ion absorption / release potential of the carbon material is around 0V (vs. Li / Li + ) near the

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

[0097] The conductive agent is blended to improve the current collecting performance and to reduce the contact resistance between the active material and the current collector. Examples of the conductive agent 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 the conductive agent, or two or more may be used in combination as the conductive agent. Alternatively, instead of using a conductive agent, a carbon coating or an electronically conductive inorganic material coating may be applied to the surface of the active material particles.

[0098] The binder is blended to fill the gaps between the dispersed active materials and to bind the active materials and the current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0099] As an example, the mixing ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode mixture layer is preferably 68% by mass or more and 96% by mass or less, 2% by mass or more and 30% by mass or less, and 2% by mass or more and 30% by mass or less, respectively. By making the amount of the conductive agent 2% by mass or more, the current collection performance of the negative electrode mixture layer can be improved. Also, by making the amount of the binder 2% by mass or more, the binding property between the negative electrode mixture layer and the current collector becomes sufficient, and excellent cycle performance can be expected. On the other hand, it is preferable to make the conductive agent and the binder 30% by mass or less, respectively, in order to increase the capacity.

[0100] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted and extracted from the negative electrode active material. +) or more is used, examples of the current collector are copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

[0101] The current collector may also include a portion on the surface of which the negative electrode mixture layer is not formed, and this portion can function as a negative electrode current collecting tab.

[0102] 3) Nonaqueous electrolyte The non-aqueous electrolyte may be, for example, a liquid non-aqueous electrolyte or a gel non-aqueous electrolyte. The liquid non-aqueous electrolyte contains an electrolyte salt, an organic solvent capable of dissolving the electrolyte salt, propane sultone (1,3-propane sultone), 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] Propane sultone and lithium difluorophosphate may or may not function as an electrolyte salt or an organic solvent. Propane sultone and lithium difluorophosphate may also function as an electrolyte salt or an organic solvent.

[0104] The composition of the non-aqueous electrolyte contained in the secondary battery of the embodiment, particularly the concentration of propane sultone and the concentration of lithium difluorophosphate, may have changed from the composition (initial composition) of the non-aqueous electrolyte immediately after preparation. This is because, for example, after a secondary battery in which the first sealing is performed is assembled using the non-aqueous electrolyte immediately after preparation, propane sultone and lithium difluorophosphate may be consumed during initial charge / discharge, aging, and the like.

[0105] That is, the non-aqueous electrolyte is preferably prepared so 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 mass % or more and the concentration of lithium difluorophosphate is 0.2 mass % or more.

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

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

[0108] The lower the initial concentration of propane sultone, the less decomposition products are generated by the reaction of propane sultone with the electrode active material, and therefore the more the increase in electrode resistance can be suppressed.

[0109] Since the secondary battery according to the embodiment contains lithium difluorophosphate in addition to propane sultone in the non-aqueous electrolyte, even if the initial concentration of propane sultone is low, the propane sultone is likely to remain in the non-aqueous electrolyte after the first charge / discharge. Therefore, it is possible to suppress both the increase in electrode resistance and the decomposition of the non-aqueous electrolyte.

[0110] When the non-aqueous electrolyte is prepared so that the concentration (initial concentration) of lithium difluorophosphate in the non-aqueous electrolyte immediately after preparation is high, the effect of suppressing the decomposition of propane sultone is easily obtained. The initial concentration of lithium difluorophosphate is preferably 0.3% by mass or more, and more preferably 0.5% by mass or more. When 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 less, and more preferably 3% by mass or less.

[0111] The non-aqueous electrolyte is preferably prepared so that the ratio of the initial concentration of propane sultone to the initial concentration of lithium difluorophosphate (PS:DFP initial concentration ratio) is 1:9 or more and 10:1 or less. In other words, it is preferably prepared so that the initial concentration of lithium difluorophosphate is 0.1 times or more and 9 times or less relative to the initial concentration of propane sultone. Within the above range, the effect of suppressing the decomposition of propane sultone by lithium difluorophosphate is easily obtained, and the initial concentration of propane sultone can be reduced. Therefore, the increase in resistance can be suppressed.

[0112] Examples of the electrolyte salt include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, LiN(CF3SO2)2), and lithium bis(fluorosulfonyl)imide (LiFSI, LiN(FSO2)2), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and LiPF6 is most preferred.

[0113] Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), ethyl propionate (EP), and sulfolane (SL). These organic solvents can be used alone or in combination.

[0114] The gelled non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymeric material, such as polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0115] Alternatively, as the nonaqueous electrolyte, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, and the like may be used. 4) Separator The separator is formed, for example, from a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of cutting off electric current.

[0116] An electrolyte layer containing an inorganic solid electrolyte may be used as the separator. Examples of the lithium ion conductive inorganic solid electrolyte include a lithium ion conductive oxide-based solid electrolyte and a lithium ion conductive sulfide-based solid electrolyte. Examples of the lithium ion conductive oxide-based solid electrolyte include a NASICON-type lithium phosphate solid electrolyte and an amorphous LIPON (Li 2.9 PO 3.3 N 0.46 ), or garnet-type structure LLZ (Li7La3Zr2O 12 ) etc.

[0117] 5) Exterior materials As the exterior member, for example, a container made of a laminate film or a metal container can be used.

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

[0119] The laminate film is a multi-layer film including a plurality of resin layers and a metal layer interposed between the resin layers. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be molded into the shape of the exterior member by sealing it by heat fusion.

[0120] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0121] The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of the transition metals is preferably 100 ppm by mass or less.

[0122] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin, or button. The exterior member can be appropriately selected depending on the battery dimensions and the application of the battery.

[0123] <Measurement method> Mass of sulfur atoms per unit volume of the positive electrode mixture layer or the negative electrode mixture layer (g / m 3 The methods for measuring the concentration (% by mass) of the propane sultone and the concentration (% by mass) of the lithium difluorophosphate in the non-aqueous electrolyte are described below.

[0124] (Preparation of sample for measurement) The exterior materials of a secondary battery with a state of charge (SOC) of 50% are opened and the electrode group is removed. The jig (such as tape) binding the electrode group together is removed, and if the outermost layer is a separator, the separator is flipped over and the first layer of electrode (e.g., negative electrode) is removed. The separator is then flipped over again and the first layer of electrode (e.g., positive electrode) is removed. The process of flipping over the separator and removing the electrodes is repeated until all the positive and negative electrodes that make up the electrode group are removed. The removed electrodes and separator are put into a centrifuge to extract the non-aqueous electrolyte and separate the electrodes from the separator.

[0125] (ICP optical emission spectrometry) Mass of sulfur atoms per unit volume of the positive electrode mixture layer or the negative electrode mixture layer (g / m 3) is measured by inductively coupled plasma (ICP) emission spectrometry. Each electrode separated by the centrifuge is washed with methyl ethyl carbonate (MEC) and dried in vacuum. Each electrode is cut into a certain area (2 × 2 cm 2 ) and add a certain amount of pure water (10cc) and irradiate with ultrasound for 30 minutes or more. The extracted solution is analyzed by ICP to measure the mass of sulfur atoms in the extracted solution, thereby obtaining the mass of sulfur atoms per unit volume of each electrode composite layer.

[0126] (GC-MS) The non-aqueous electrolyte extracted by the above method is diluted with acetonitrile to a volume 20 times that of the original volume to prepare a measurement sample. The measurement sample is subjected to gas chromatography mass spectrometry (GC-MS) measurement under the conditions shown in Table 1 below to determine the concentration (mass%) of propane sultone in the non-aqueous electrolyte.

[0127] [Table 1]

[0128] (Capillary Electrophoresis) The non-aqueous electrolyte extracted by the above method can be diluted with acetonitrile to a volume 20 times that of the original volume, and the diluted solution is used as a measurement sample for capillary electrophoresis (CE) under the measurement conditions described below, thereby determining the concentration (mass %) of lithium difluorophosphate in the non-aqueous electrolyte.

[0129] Capillary: inner diameter 50 μm, length 72 cm Applied voltage -30kV Temperature 10℃ Running solution 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 including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. The positive electrode includes a positive electrode mixture layer including a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode mixture layer is 430 g / m. 3 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. Therefore, a secondary battery having high output performance and high high-temperature durability can be realized.

[0130] Second embodiment The battery pack according to the second embodiment can include one or more secondary batteries (single cells) according to the embodiment. The secondary batteries can be electrically connected in series, in parallel, or in a combination of series and parallel to form a battery pack. The battery pack according to the embodiment may include a plurality of battery packs.

[0131] The battery pack according to the embodiment may further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the secondary battery. Alternatively, a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack as a power source may be used as the protection circuit for the battery pack.

[0132] The battery pack according to the embodiment may further include an external terminal for current flow. The external terminal for current flow is for outputting current from the secondary battery to the outside and 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 terminal for current flow. When charging the battery pack, a charging current (including regenerative energy of the power of a vehicle such as an automobile) is supplied to the battery pack through the external terminal for current flow.

[0133] Figures 8 and 9 show an example of a battery pack 50. This battery pack 50 includes a plurality of flat 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 of Figure 8.

[0134] A plurality of unit cells 51 are stacked so that the negative electrode terminals 13 and positive electrode terminals 14 extending outward are aligned in the same direction, and are fastened together with adhesive tape 52 to form a battery pack 53. These unit cells 51 are electrically connected in series as shown in FIG.

[0135] The printed wiring board 54 is disposed facing the side surface of the battery cell 51 from which the negative electrode terminal 13 and the positive electrode terminal 14 extend. A thermistor 55, a protective circuit 56, and an external terminal 57 for supplying electricity to an external device as an external terminal for supplying electricity are mounted on the printed wiring board 54 as shown in Fig. 9. An insulating plate (not shown) is attached to the surface of the printed wiring board 54 facing the assembled battery 53 to prevent unnecessary connection with the wiring of the assembled battery 53.

[0136] The positive electrode lead 58 is connected to the positive electrode terminal 14 located in the bottom layer of the battery pack 53, and its tip is inserted into and electrically connected to a positive electrode connector 59 of the printed wiring board 54. The negative electrode lead 60 is connected to the negative electrode terminal 13 located in the top layer of the battery pack 53, and its tip is inserted into and electrically connected to a negative electrode connector 61 of the printed wiring board 54. These connectors 59, 61 are connected to the protection circuit 56 through wires 62, 63 formed on the printed wiring board 54.

[0137] The thermistor 55 detects the temperature of the cell 51, and the detection signal is sent to the protection circuit 56. The protection circuit 56 can cut off the positive side wiring 64a and the negative side wiring 64b between the protection circuit 56 and a terminal 57 for supplying electricity to an external device as an external terminal for supplying electricity under a predetermined condition. The predetermined condition is, for example, when the temperature detected by the thermistor 55 becomes equal to or higher than a predetermined temperature. The predetermined condition is also when overcharging, overdischarging, overcurrent, etc. of the cell 51 is detected. This detection of overcharging, etc. is performed for each cell 51 or for all the cells 51. When detecting each cell 51, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 51. In the case of FIG. 8 and FIG. 9, wiring 65 for voltage detection is connected to each cell 51, and a detection signal is transmitted to the protection circuit 56 through these wirings 65.

[0138] Protective sheets 66 made of rubber or resin are disposed on the three side surfaces of the battery pack 53 excluding the side surfaces from which the positive electrode terminal 14 and the negative electrode terminal 13 protrude.

[0139] The battery pack 53 is stored in a storage container 67 together with the protective sheets 66 and the printed wiring board 54. That is, the protective sheets 66 are arranged on both inner surfaces in the long side direction and on the inner surface in the short side direction of the storage container 67, and the printed wiring board 54 is arranged on the inner surface on the opposite side in the short side direction. The battery pack 53 is located in a space surrounded by the protective sheets 66 and the printed wiring board 54. A lid 68 is attached to the top surface of the storage container 67.

[0140] Note that heat shrink tape may be used to secure the battery pack 53, instead of the adhesive tape 52. In this case, protective sheets are placed on both sides of the battery pack, the heat shrink tape is wrapped around it, and then the heat shrink tape is thermally shrunk to bind the battery pack.

[0141] 8 and 9 show a configuration in which the 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 may be further connected in series or parallel.

[0142] 8 and 9 includes one battery pack, the battery pack according to the embodiment may include multiple battery packs. The multiple battery packs are electrically connected in series, in parallel, or in a combination of series and parallel connections.

[0143] The battery pack may be modified as appropriate depending on the application. The battery pack according to the embodiment is suitable for use in applications that require excellent cycle performance when a large current is drawn. Specifically, the battery pack is used as a power source for digital cameras, or as a vehicle battery for, for example, two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, or railroad vehicles (e.g., trains), or as a stationary battery. In particular, the battery pack is suitable for use as an on-board battery mounted on a vehicle.

[0144] The battery pack of the second embodiment described above includes the secondary battery of the embodiment, and therefore 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 the battery pack according to the third embodiment, the battery pack may, for example, recover regenerative energy of the vehicle's motive power. The vehicle may also include a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

[0147] FIG. 10 shows an example of a car equipped with a battery pack according to an embodiment.

[0148] An automobile 71 shown in Fig. 10 is equipped with a battery pack 72 according to an embodiment in an engine compartment at the front of the vehicle. The location of the battery pack in the automobile is not limited to the engine compartment. For example, the battery pack can be equipped at the rear of the automobile or under the seat.

[0149] Fig. 11 is a diagram illustrating a schematic configuration of an example of a vehicle according to an embodiment. A vehicle 300 illustrated in Fig. 11 is an electric vehicle.

[0150] The vehicle 300 shown in FIG. 11 includes a vehicle power supply 301, a vehicle 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] The vehicle 300 has a vehicle power supply 301 mounted, for example, in the engine compartment, the rear of the vehicle body, or under a seat. However, in Fig. 11, the mounting location of the secondary battery in the vehicle 300 is shown only diagrammatically.

[0152] The vehicle power supply 301 includes a plurality of (eg, three) battery packs 312 a , 312 b , and 312 c , 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. The battery pack 312a includes an assembled battery 314a and an assembled battery monitoring device (VTM: Voltage Temperature Monitoring) 313a. The battery pack 312b includes an assembled battery 314b and an assembled battery monitoring device 313b. The battery pack 312c includes an assembled battery 314c and an assembled battery monitoring device 313c. The battery packs 312a, 312b, and 312c can be removed independently and replaced with different battery packs.

[0154] Each of the assembled batteries 314a to 314c includes a plurality of secondary batteries connected in series. Each secondary battery is a secondary battery according to the embodiment. Each of the assembled batteries 314a to 314c is charged and discharged via a positive terminal 316 and a negative terminal 317.

[0155] In order to collect information related to the maintenance of the vehicle power supply 301, the battery management device 311 communicates with the assembled battery monitoring devices 313a to 313c to collect information such as the voltage and temperature of the secondary batteries of the assembled batteries 314a to 314c included in the vehicle power supply 301.

[0156] A communication bus 310 is connected between the battery management unit 311 and the assembled battery monitoring units 313a to 313c. The communication bus 310 is configured so that one set of communication lines is shared by a plurality of nodes (the battery management unit and one or more assembled battery monitoring units). The communication bus 310 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

[0157] The assembled battery monitoring devices 313a to 313c measure the voltage and temperature of each of the secondary batteries constituting the assembled batteries 314a to 314c based on commands communicated from the battery management device 311. However, the temperature can be measured at only a few points per assembled battery, and it is not necessary to measure the temperatures of all of the secondary batteries.

[0158] Vehicle power supply 301 may also have an electromagnetic contactor (for example, switch device 333 shown in FIG. 11) for connecting and disconnecting the positive and negative terminals. Switch device 333 includes a pre-charge switch (not shown) that is turned on when battery packs 314a-314c are charged, and a main switch (not shown) that is turned on when battery output is supplied to a load. The pre-charge switch and main switch include relay circuits (not shown) that are turned on and off by a signal supplied to a coil arranged near the switch element.

[0159] Inverter 340 converts the input DC voltage into a three-phase AC high voltage for driving a motor. The output voltage of inverter 340 is controlled based on a control signal from battery management device 311 or vehicle ECU 380 for controlling the overall operation of the vehicle. The three-phase output terminals of inverter 340 are connected to the three-phase input terminals of drive motor 345.

[0160] The drive motor 345 rotates by the electric power supplied from the inverter 340, and transmits the rotation to the axles and drive wheels W via, for example, a differential gear unit.

[0161] Although not shown, the vehicle 300 is equipped with a regenerative braking mechanism that rotates the drive motor 345 when the vehicle 300 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 340 and converted into a direct current. The direct current is input to the vehicle power supply 301.

[0162] One terminal of a 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 the connection line L1 is connected to the negative input terminal of the inverter 340.

[0163] One terminal of a connection line L2 is connected to a positive terminal 316 of the vehicle power supply 301 via a switch device 333. The other terminal of the connection line L2 is connected to a positive input terminal of an inverter 340.

[0164] The external terminal 370 is connected to the battery management unit 311. The external terminal 370 can be connected to, for example, an external power source.

[0165] Vehicle ECU 380 responds to operational inputs from the driver or the like and controls battery management device 311 in cooperation with other devices to manage the entire vehicle. Data relating to the maintenance of vehicle power supply 301, such as the remaining capacity of vehicle power supply 301, is transferred between battery management device 311 and vehicle ECU 380 via a communication line.

[0166] The vehicle of the embodiment includes a battery pack including the secondary battery of the embodiment, and the battery pack (e.g., battery packs 312a, 312b, and 312c) has excellent output performance and high temperature durability, so that a vehicle with excellent charge / discharge performance and high reliability can be obtained. Furthermore, each battery pack is inexpensive and highly safe, so that the cost of the vehicle can be reduced and the safety can be improved. EXAMPLES

[0167] A secondary battery was fabricated in the following manner.

[0168] Example 1 <Preparation of positive electrode> The positive electrode active material is 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 proportions of 82 mass%, 9 mass%, and 9 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. Next, the coating was dried in a thermostatic chamber at 120 ° C. to form a positive electrode active material-containing layer, and the positive electrode active material-containing layer was pressed to obtain a positive electrode.

[0169] <Preparation of negative electrode> Niobium titanium oxide (Nb2TiO7) powder was prepared as the negative electrode active material. The average secondary particle diameter of the niobium titanium oxide was 7.5 μm. The specific surface area of ​​the niobium titanium oxide was 4.0 m 2 / g. In addition, acetylene black was prepared as a conductive agent, and polyvinylidene fluoride (PVdF) was prepared as a binder. Next, the negative electrode active material, the conductive agent, and the binder were added to N-methylpyrrolidone (NMP) as a solvent in a ratio of 82 mass%, 9 mass%, and 9 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. Next, the coating was dried in a thermostatic chamber at 120 ° C. to form a negative electrode active material-containing layer, and the negative electrode active material-containing layer was pressed to obtain a negative electrode.

[0170] <Preparation of electrode groups> The positive electrode and the negative electrode were vacuum dried at 120°C for 24 hours. Two sheets of polyethylene nonwoven fabric having a thickness of 25 μm were prepared as separators. Next, the positive electrode, the separator, the negative electrode, and the separator were laminated in this order to obtain a laminate. Next, this laminate was spirally wound. This was hot-pressed at 80°C to produce a flat electrode group. A positive electrode terminal was electrically connected to the positive electrode of the electrode group. In addition, a negative electrode terminal was electrically connected to the negative electrode of the electrode group.

[0171] <Storage of electrode group> A container was prepared, which was made of a laminate film having a three-layer structure of nylon layer / aluminum layer / polyethylene layer and a thickness of 0.1 mm. The electrode group prepared as described above was placed in this container. Next, with a part 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 Electrolyte> As a solvent, a mixed solvent (volume ratio 1:2) of propylene carbonate (PC) and diethyl carbonate (DEC) was prepared. LiPF6 was dissolved in the solvent as an electrolyte salt at a concentration of 1 mol / L. 1,3-propane sultone (PS) was added and dissolved therein so that the initial concentration in the non-aqueous electrolyte was 1.0 mass%. Furthermore, lithium difluorophosphate (DFP) was added and dissolved therein so that the initial concentration was 1.0 mass%. That is, the non-aqueous electrolyte was prepared so that the initial concentration of PS: the initial concentration of DFP (PS:DFP initial concentration ratio) was 1:1. Thus, a liquid non-aqueous electrolyte (nonaqueous electrolyte) was obtained. The preparation of the liquid non-aqueous electrolyte was carried out in an argon box.

[0173] <Battery Construction> A non-aqueous electrolyte was poured into the container housing the electrode group. Next, the open peripheral portion of the container was heat sealed to hermetically seal the container. This resulted in a battery having outer dimensions of 11 cm x 8 cm x 0.3 cm, excluding the positive and negative electrode terminals (also called positive and negative electrode tabs), and inner dimensions (dimensions of the sealed portion) of 9 cm x 7 cm x 0.25 cm. This battery is referred to as the first sealed battery.

[0174] <First charge> The initial charge and discharge were carried out by carrying out the following initial charge and initial discharge. The first sealed battery was subjected to the initial charge in an environment of 25°C according to the following procedure. First, the first sealed battery was charged at a constant current (CC) of 0.2 C until a voltage of 3 V was reached. Next, the first sealed battery was charged at a constant voltage (CV) of 3 V. The constant voltage charge was terminated when the total time of the constant current charge and constant voltage charge reached 10 hours.

[0175] <First discharge> Next, the first sealed battery was discharged at a constant current (CC) of 0.2 C in an environment of 25° C. until the voltage reached 1.5 V.

[0176] <Post-processing> Next, the first sealed battery after the initial charge and discharge was charged at a constant current (CC) of 0.2C until the voltage reached 3V in an environment of 25°C. Next, the first sealed battery was charged at a constant voltage (CV) of 3V until the current value became 1 / 20C. That is, the first sealed battery was subjected to constant current constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). This first sealed battery was subjected to aging. The aging was performed by holding it in a thermostatic chamber at 35°C for 35 hours. Thereafter, the first sealed battery was placed in an argon box, and one part of the sealed part of the exterior member was cut to release the gas in the exterior member. The end opened by cutting was sealed by heat sealing. In this way, a secondary battery according to Example 1 was produced.

[0177] (Examples 2 to 6) A secondary battery was produced 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, and 10) A secondary battery was produced 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 mass% and 10 mass%, and the resulting mixture was kneaded in the presence of an organic solvent (N-methylpyrrolidone) to prepare a slurry. The resulting slurry was applied to a current collector made of copper foil with a thickness of 15 μm, dried, and pressed to obtain a negative electrode. In addition, when a negative electrode containing graphite was used, the steps from initial charging to post-treatment were carried out as follows to prepare a secondary battery.

[0180] <First charge> The first sealed battery was subjected to initial charging in an environment of 25° C. according to the following procedure. First, the first sealed battery was charged at a constant current (CC) of 0.2 C until a voltage of 4.15 V was reached. Next, the first sealed battery was charged at a constant voltage (CV) of 4.15 V. The constant voltage charging was terminated when the total time of the constant current charging and constant voltage charging reached 10 hours.

[0181] <First discharge> Next, the first sealed battery was discharged at a constant current (CC) of 0.2 C in an environment of 25° C. until the voltage reached 2 V.

[0182] <Post-processing> Next, the first sealed battery after the initial charge and discharge was charged at a constant current (CC) of 0.2C until the voltage reached 4.15V in an environment of 25°C. Next, the first sealed battery was charged at a constant voltage (CV) of 4.15V until the current value became 1 / 20C. That is, the first sealed battery was subjected to constant current constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). This first sealed battery was subjected to aging. The aging was performed by holding it in a thermostatic chamber at 35°C for 35 hours. Thereafter, the first sealed battery was placed in an argon box, and one part of the sealed part of the exterior member was cut to release the gas in the exterior member. The end opened by cutting was sealed by heat sealing. In this way, a secondary battery according to Example 8 was produced.

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

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

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

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

[0187] The aging temperature and time in the post-treatment were as shown in Tables 5 and 6.

[0188] A secondary battery was produced in the same manner as in Example 1 except for the above.

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

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

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

[0192] The aging temperature and time in the post-treatment were as shown in Table 6.

[0193] A secondary battery was produced in the same manner as in Example 1 except for the above.

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

[0195] (Example 29) Except for not carrying out vacuum drying of the positive electrode and the negative electrode in the preparation of the electrode group, a secondary battery was prepared in the same manner as in Example 1. Since vacuum drying was not carried out, the electrode drying temperature in Table 6 is indicated by "-".

[0196] Comparative Example 1 A secondary battery was produced in the same manner as in Example 1, except that 1,3-propane sultone (PS) was not added in the preparation of the liquid nonaqueous electrolyte.

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

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

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

[0200] The aging temperature and time in the post-treatment were as shown in Table 7.

[0201] A secondary battery was produced in the same manner as in Example 1 except for the above.

[0202] Comparative Example 7 In preparing the liquid non-aqueous electrolyte, the initial concentrations of 1,3-propane sultone (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] A secondary battery was produced in the same manner as in Example 1 except for the above.

[0204] <Measurement of the mass of sulfur atoms per unit volume of the composite layer> For the secondary batteries of each Example and Comparative Example, the mass of sulfur atoms per unit volume of the positive electrode mixture layer (amount of S per positive electrode mixture layer) and the mass of sulfur atoms per unit volume of the positive electrode mixture layer (amount of S per negative electrode mixture 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> The liquid non-aqueous electrolytes contained in the secondary batteries of each of the Examples and Comparative Examples after the post-treatment were measured for the propane sultone concentration (PS concentration in the non-aqueous electrolyte) and the lithium difluorophosphate concentration (DFP concentration in the non-aqueous electrolyte) in the non-aqueous electrolyte by the method described above. The measurement results are shown in Tables 8 to 10.

[0206] <Storage test> A storage test was carried out on the secondary batteries of each of the Examples and Comparative Examples as follows.

[0207] The secondary battery was charged at a constant current (CC) of 0.2C until the voltage reached 3V. The battery was then charged at a constant voltage (CV) of 3V until the current value reached 1 / 20C. That is, the battery was subjected to constant current constant voltage (CCCV) charging to make its SOC 100%. The battery in this charged state was placed in a thermostatic chamber at 55°C. Every 10 days, the battery was removed from the thermostatic chamber at 55°C, cooled to 25°C, and then subjected to CCCV charging at 3V again and placed in the thermostatic chamber at 55°C. This was repeated, and the battery was stored in the thermostatic chamber for 90 days, cooled to 25°C, and then its volume was measured, and the difference from the volume before the test was taken as the amount of gas generated (ml). The amount of gas generated is an index of high-temperature durability.

[0208] <Direct Current (DC) resistance measurement> Before carrying out the storage test, the secondary batteries of each Example and Comparative Example were subjected to DC resistance measurement as follows. The battery was discharged at a constant current (CC) of 0.2 C until the voltage reached 1.5 V. Thereafter, the battery was charged at a constant current (CC) of 0.2 C until the voltage reached 2.25 V. Next, the battery was charged at a constant voltage (CV) of 2.25 V until the current value reached 1 / 20 C, thereby setting the battery state of charge to SOC50%. The battery adjusted to SOC50% was discharged for 10 ms at a constant current (CC) of 10 C, and the DC resistance (mΩ) was calculated from the difference between the voltage value and the current value at this time.

[0209] Furthermore, the DC resistance of the secondary battery after the storage test was measured in the same manner as above to determine the DC resistance (mΩ).

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

[0211] Tables 2 to 4 show the types of positive and negative electrode active materials, the types of solvents and electrolyte salts used in preparing the liquid nonaqueous electrolytes, the initial PS concentration, the initial DFP concentration, and the initial PS:DFP concentration ratio for each of the Examples and Comparative Examples.

[0212] Tables 5 to 7 show the electrode drying temperature and electrode drying time in the preparation of the electrode group, and the 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 PS concentration in the non-aqueous electrolyte, the DFP concentration in the non-aqueous electrolyte, the amount of gas generated (ml), and the resistance increase value for the secondary batteries after post-treatment in each of the Examples and Comparative Examples.

[0214] [Table 2]

[0215] [Table 3]

[0216] [Table 4]

[0217] [Table 5]

[0218] [Table 6]

[0219] [Table 7]

[0220] [Table 8]

[0221] [Table 9]

[0222] [Table 10]

[0223] The following became clear from Tables 2 to 10.

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

[0225] In Comparative Example 1, which is the same as Example 1 except that the non-aqueous electrolyte does not contain propane sultone, neither the positive electrode mixture layer nor the negative electrode mixture layer contained sulfur atoms. In addition, the resistance increase value was high and the amount of gas generated was large. This is considered to be because the non-aqueous electrolyte does not contain propane sultone, and therefore gas generation due to decomposition of the non-aqueous electrolyte was not suppressed.

[0226] Comparative Example 2, which is the same as Example 1 except that the non-aqueous electrolyte does not contain lithium difluorophosphate, had a large amount of S per positive electrode mixture layer and a low PS concentration in the non-aqueous electrolyte. In addition, the amount of gas generated was large. This is considered to be because the decomposition of propane sultone was not suppressed during the initial charge / discharge and aging. As a result, the high temperature durability was considered to have decreased.

[0227] Comparative Example 3, which was prepared in the same manner as in Example 1 except that the aging temperature was increased, showed a large amount of gas generation. This is because the aging was performed at a high temperature of 60°C, which caused the decomposition of propane sultone to proceed excessively during aging, resulting in an S amount of 430 g / m per positive electrode mixture layer. 3 This is believed to be due to the fact that the PS concentration in the non-aqueous electrolyte became smaller than 0.5 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 amount of gas generated than Example 1. This is because the decomposition of propane sultone proceeded excessively during aging due to the long aging time, and the amount of S per positive electrode mixture layer was 430 g / m 3 This is believed to be due to the fact that the PS concentration in the non-aqueous electrolyte became smaller than 0.5 mass %.

[0229] The amount of S per positive electrode mixture layer and the amount of S per negative electrode mixture layer are both 430 g / m 3 The resistance increase was high in Comparative Example 5, which had a larger value than that of Comparative Example 5. This is considered to be because the decomposition of propane sultone resulted in the excessive formation of a sulfur-containing phase on the active material surface, which was the cause of the increase in resistance.

[0230] In Comparative Example 6, in which the PS concentration in the nonaqueous electrolyte was less than 0.5 mass%, a large amount of gas was generated. This is believed to be because the nonaqueous electrolyte contained in the secondary battery after the post-treatment did not contain a sufficient amount of propane sultone capable of functioning as a sacrificial material, and therefore the reaction of the nonaqueous electrolyte decomposing to generate gas was not suppressed.

[0231] In Comparative Example 7, in which the DFP concentration in the non-aqueous electrolyte was less than 0.2% by mass, the PS concentration in the non-aqueous electrolyte was also less than 0.5% by mass, and the amount of gas generated was large. This is considered to be because the consumption of propane sultone during the initial charge / discharge and aging was not suppressed due to the insufficient presence of lithium difluorophosphate in the non-aqueous electrolyte, and as a result, the non-aqueous electrolyte in the secondary battery after post-treatment contained insufficient propane sultone capable of functioning as a sacrificial material.

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

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

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

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

[0236] Comparing Examples 1, 19 to 21 and Comparative Example 3, there was a tendency that the amount of S per positive electrode mixture layer decreased as the aging temperature decreased. 3 The following Examples 1, 19 to 21 had lower gas generation amounts than Comparative Example 3. In addition, when Examples 1, 19, and 20 and Comparative Example 3 are compared, there was a tendency that the PS in the non-aqueous electrolyte decreased as the aging temperature increased.

[0237] Comparing Examples 1, 22 to 24, and Comparative Example 4, there was a tendency that the shorter the aging time, the lower the amount of S per positive electrode mixture layer. 3 The following Examples 1 and 22 to 24 had lower gas generation amounts than Comparative Example 4.

[0238] Comparing Examples 25 and 26, the amount of S per negative electrode mixture layer was 430 g / m 3 In the following Example 25, the amount of S per negative electrode mixture layer is 430 g / m 3 The amount of gas generated tended to be lower than that of Example 26, which had a larger amount.

[0239] Comparing Examples 1 and 15 with Comparative Examples 1 and 6, there was a tendency that the amount of gas generated decreased as the PS concentration in the nonaqueous electrolyte increased.

[0240] Comparing Example 1, Example 28 and Example 29, Example 1 and Example 28 in which the electrode was vacuum dried tended to have a lower resistance increase value and a smaller amount of gas generation than Example 29 in which the electrode was not vacuum dried. Furthermore, Example 1 in which the electrode was vacuum dried at 120°C tended to have a lower resistance increase value and a smaller amount of gas generation than Example 28 in which the electrode was vacuum dried at 80°C. This is considered to be due to the fact that the higher the temperature and the longer the drying conditions for the electrode, the less moisture remains in the electrode. The less moisture there is in the electrode, the less likely it is that the propane sultone and lithium difluorophosphate in the non-aqueous electrolyte are consumed, so that even after the initial charge and discharge, the propane sultone consumption suppression effect by lithium difluorophosphate and the gas generation suppression effect by propane sultone are easily obtained.

[0241] According to at least one of these embodiments or examples, a secondary battery is provided that includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode mixture layer that includes a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode mixture layer is 430 g / m. 3 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. Therefore, it is possible to provide a secondary battery that can suppress the amount of gas generation and the increase in resistance at high temperatures and achieve excellent life performance even at high temperatures.

[0242] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0243] Reference Signs List 1...electrode group, 2...container (exterior member), 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 member, 12...exterior member, 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 assembly, 54...print Wiring board, 55... thermistor, 56... protection circuit, 57... external terminal for current supply, 71... automobile, 72... battery pack, 300... vehicle, 301... vehicle power supply, 310... communication bus, 311... battery management device, 312a-c... battery packs, 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 wheels.

Claims

1. A positive electrode, a negative electrode, and a non-aqueous electrolyte, The positive electrode includes a positive electrode mixture layer including a positive electrode active material and a sulfur atom, The mass of the sulfur atoms per unit volume of the positive electrode mixture layer is 430 g / m ３ is as follows: the non-aqueous electrolyte contains propane sultone and lithium difluorophosphate; The concentration of the propane sultone in the non-aqueous electrolyte is 0.5 mass% or more, The concentration of the lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass % or more.

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

3. The mass of the sulfur atoms per unit volume of the negative electrode mixture layer is 430 g / m ３ The secondary battery according to claim 2 , wherein:

4. A battery pack comprising the secondary battery according to any one of claims 1 to 3.

5. An external terminal for supplying electricity; Protection circuit and The battery pack of claim 4 further comprising:

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

7. A vehicle comprising the battery pack of claim 4.

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

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