Secondary battery, battery pack, and vehicle

Abstract

The embodiment relates to a secondary battery, a battery pack and a vehicle. The present invention provides a secondary battery having high output performance and high high-temperature durability, a battery pack including the secondary battery, and a vehicle including the battery pack. According to one embodiment, there is provided a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode composite layer containing 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 / m3 or less. The nonaqueous electrolyte contains propane sultone and lithium difluorophosphate. The concentration of propane sultone in the nonaqueous electrolyte is 0.5 mass% or more. The concentration of the lithium difluorophosphate in the nonaqueous electrolyte is 0.2 mass% or more.

Description

Technical Field

[0001] Embodiments relate to a secondary battery, a battery pack, and a vehicle. Background Art

[0002] Secondary batteries containing non-aqueous electrolytes have problems in output performance and high temperature durability. As a reason for this, gas is generated due to the reaction between the non-aqueous electrolyte and the electrode. If gas is generated, bubbles are generated inside the electrode, whereby the active material becomes easy to peel off, the resistance increases, and the output performance decreases. Secondary batteries containing non-aqueous electrolytes are particularly prone to gas generation in high temperature environments. Summary of the invention

[0003] An object of the present invention is to provide a secondary battery having high output performance and high high-temperature durability, a battery pack including the secondary battery, and a vehicle including the battery pack.

[0004] 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 composite material layer containing a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode composite material 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 mass % or more. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass % or more.

[0005] According to another embodiment, there is provided a battery pack including the secondary battery of the embodiment.

[0006] According to other embodiments, a vehicle including the battery pack of the embodiments is provided.

[0007] According to the secondary battery having the above configuration, the output performance and high-temperature durability can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a cross-sectional view of the secondary battery according to the embodiment cut in a direction perpendicular to the terminal extending direction.

[0009] Figure 2 yes Figure 1 An enlarged cross-sectional view of section A.

[0010] Figure 3 It is a partially cutaway cross-sectional view of a secondary battery according to an embodiment.

[0011] Figure 4 yes Figure 3 Side view of a battery.

[0012] Figure 5It is a partially cutaway perspective view schematically showing another example of the secondary battery according to the embodiment.

[0013] Figure 6 yes Figure 5 An enlarged cross-sectional view of portion B of the secondary battery shown.

[0014] Figure 7 It is a schematic plan view showing an example of a method for manufacturing a secondary battery according to an embodiment.

[0015] Figure 8 It is an exploded perspective view of the battery pack according to the embodiment.

[0016] Fig. 9 Yes means Figure 8 Block diagram of the battery pack circuit.

[0017] Fig.10 It is a schematic diagram showing an example of a vehicle equipped with the secondary battery according to the embodiment.

[0018] Fig.11 It is a diagram schematically showing another example of the vehicle according to the embodiment.

[0019] (Explanation of symbols)

[0020] 1-electrode group, 2-container (outer packaging member), 3-positive electrode, 3a-positive electrode collector, 3b-positive electrode composite material layer, 4-negative electrode, 4a-negative electrode collector, 4b-negative electrode composite material layer, 5-diaphragm, 6-positive electrode lead, 7-negative electrode lead, 8-positive electrode collector ear, 9-negative electrode collector ear, 10-sealing plate, 11-insulating member, 12-outer packaging member, 13-negative electrode terminal, 14-positive electrode terminal, 30-secondary battery after completing the first sealing, 31-secondary battery, 50-battery pack, 51-unit battery, 53-group battery, 54-printed circuit board Wiring substrate, 55 - thermistor, 56 - protection circuit, 57 - external terminal for power supply, 71 - automobile, 72 - battery pack, 300 - vehicle, 301 - vehicle power supply, 310 - communication bus, 311 - battery management device, 312a~312c - battery pack, 313a~313c - battery pack monitoring device, 314a~314c - battery pack, 316 - positive terminal, 317 - negative terminal, 340 - inverter, 345 - drive motor, 370 - external terminal, 380 - vehicle ECU, L1, L2 - connecting wires, W - drive wheel. DETAILED DESCRIPTION

[0021] (First embodiment)

[0022] According to a 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 composite material layer including a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode composite material 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 mass % or more. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass % or more.

[0023] The present inventors have conducted intensive studies and found that the high-temperature durability of a secondary battery can be improved by adding propane sultone (PS: 1,3-propane sultone) to a non-aqueous electrolyte. The mechanism is presumed to be as follows.

[0024] At high temperatures, especially under high SOC (state of charge) conditions, if the nonaqueous electrolyte comes into contact with the positive electrode active material in the positive electrode, oxidative decomposition of the nonaqueous electrolyte occurs, thereby generating gas.

[0025] The secondary battery involved in the embodiment contains propane sultone in the non-aqueous electrolyte. When propane sultone reacts with the positive electrode active material, it decomposes to form a sulfur-containing phase containing sulfur atoms. Therefore, the positive electrode composite material layer contains sulfur atoms in addition to the positive electrode active material. The mass of sulfur atoms per unit volume of the positive electrode composite material layer is 430 g / m 3 This means that the sulfur-containing phase should not be excessive relative to the positive electrode composite material layer. Therefore, the resistance increase can be suppressed, and thus the output performance of the positive electrode can be maintained at a high level.

[0026] If propane sultone is present in the non-aqueous electrolyte, propane sultone is likely to react with the positive electrode active material in the positive electrode to undergo a decomposition reaction compared to the reaction between the components other than propane sultone in the non-aqueous electrolyte and the positive electrode active material. In addition, no gas is produced in the decomposition reaction of propane sultone. In other words, propane sultone can suppress the generation of gas caused by the oxidative decomposition of the non-aqueous electrolyte by being preferentially decomposed as a sacrificial material over other non-aqueous electrolyte components. Therefore, even at high temperatures, the generation of gas due to the oxidative decomposition of the non-aqueous electrolyte can be suppressed. Therefore, the increase in resistance due to the generation of bubbles in the positive electrode can be suppressed. Therefore, the output performance and high temperature durability can be improved.

[0027] In order for propane sultone to function as a sacrificial material, propane sultone needs to be present in the non-aqueous electrolyte. However, even if propane sultone is added when preparing the non-aqueous electrolyte, propane sultone is easily decomposed during the initial charge and discharge of the secondary battery. Therefore, it is difficult to maintain the presence of propane sultone in the non-aqueous electrolyte after the initial charge and discharge, for example, during storage and charge and discharge cycles.

[0028] The non-aqueous electrolyte contained in the secondary battery according to the embodiment contains lithium difluorophosphate (DFP: Lithium difluorophosphate, LiPO2F2) in addition to propane sultone. In the non-aqueous electrolyte, the reaction that consumes lithium difluorophosphate is more likely to proceed than the reaction between the positive electrode active material and propane sultone. Therefore, the non-aqueous electrolyte containing lithium difluorophosphate can suppress the decomposition of propane sultone.

[0029] Since the concentration of lithium difluorophosphate in the nonaqueous electrolyte of the secondary battery according to the embodiment is 0.2 mass % or more, the decomposition of propane sultone can be easily suppressed. Therefore, even after the initial charge and discharge of the secondary battery, the propane sultone can be easily maintained in the nonaqueous electrolyte.

[0030] In the non-aqueous electrolyte contained in the secondary battery according to the embodiment, the concentration of propane sultone is 0.5 mass % or more. That is, propane sultone is present in the non-aqueous electrolyte to such an extent that it can fully function as a sacrificial material. As a result, the generation of gas caused by oxidative decomposition of the non-aqueous electrolyte can be suppressed.

[0031] Therefore, according to the embodiment, a secondary battery having high output performance and high high-temperature durability can be provided.

[0032] The secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0033] The secondary battery may be, for example, a secondary battery using alkali metal ions as carrier ions, such as a lithium battery (lithium ion battery).

[0034] The lower limit of the mass of sulfur atoms per unit volume of the positive electrode composite material layer can be set to, for example, 20 g / m 3 The mass of sulfur atoms per unit volume of the positive electrode composite material layer is preferably 100 g / m 3 Above and 420g / m 3 The following range, more preferably 350g / m 3 Above and 410g / m 3 The mass of sulfur atoms per unit volume of the positive electrode composite material layer may be, for example, 390 g / m 3If the sulfur-containing phase is large in the positive electrode composite material layer, the mass of sulfur atoms per unit volume of the positive electrode composite material layer can be large. Therefore, if the mass of sulfur atoms per unit volume of the positive electrode composite material layer is large, the positive electrode composite material layer and the non-aqueous electrolyte are difficult to contact, so gas generation can be suppressed.

[0035] The negative electrode included in the secondary battery according to the embodiment may include a negative electrode composite material layer. Preferably, the negative electrode composite material layer further contains sulfur atoms in addition to the negative electrode active material.

[0036] Propane sultone can also form a sulfur-containing phase when reacting with the negative electrode active material. Therefore, the negative electrode composite material layer can also contain sulfur atoms in addition to the negative electrode active material.

[0037] In an electrode containing a sulfur-containing phase, the non-aqueous electrolyte and the active material contained in the electrode become difficult to contact. Generally speaking, when assembling a secondary battery, water (H2O) may be brought in as an unavoidable impurity. The water brought into the secondary battery reacts 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 contacts the electrode, the active material may deteriorate, so it is not preferred.

[0038] Therefore, when the negative electrode composite material layer contains sulfur atoms in addition to the negative electrode active material, the negative electrode active material and the non-aqueous electrolyte are unlikely to come into contact with each other, thereby being able to suppress deterioration of the negative electrode active material, which is preferred.

[0039] The mass of sulfur atoms per unit volume of the negative electrode composite material layer is preferably 430 g / m 3 The above numerical range means that the sulfur-containing phase is not excessive relative to the negative electrode composite material layer. Therefore, the resistance increase can be suppressed, and thus the output performance of the negative electrode can be maintained at a high level.

[0040] The lower limit of the mass of sulfur atoms per unit volume of the negative electrode composite material layer can be set to, for example, 20 g / m 3 The mass of sulfur atoms per unit volume of the negative electrode composite material layer is preferably 100 g / m 3 Above and 420g / m 3 The following range, more preferably 350g / m 3 Above and 410g / m 3 The mass of sulfur atoms per unit volume of the negative electrode composite material layer may be, for example, 380 g / m 3If the sulfur-containing phase is more relative to the negative electrode composite material layer, the mass of sulfur atoms per unit volume of the negative electrode composite material layer can be increased. Therefore, if the sulfur atoms per unit volume of the negative electrode composite material layer are more, the negative electrode active material and the non-aqueous electrolyte may be difficult to contact, thereby suppressing the degradation of the negative electrode active material.

[0041] The decomposition results of propane sultone show that the positive electrode composite material layer contained in the positive electrode and the negative electrode composite material layer (electrode composite material layer) contained in the negative electrode can respectively contain a sulfur-containing phase containing sulfur atoms. The sulfur atoms can be derived from the decomposition products of the non-aqueous electrolyte. In addition, the sulfur atoms can also be derived from the decomposition products of propane sultone contained in the non-aqueous electrolyte. The sulfur-containing phase can be formed on the active material in the electrode composite material layer. The sulfur-containing phase can also be a layer formed on the active material, or it can be a film that covers at least a portion of the surface of the active material particles. The sulfur-containing phase can also contain other types of atoms in addition to sulfur atoms (S). As examples of other types of atoms, oxygen atoms (O), carbon atoms (C), etc. can be listed.

[0042] The electrode composite material layer may also include an active material-containing layer containing an active material and a sulfur-containing phase formed on at least a portion of the active material. Among them, the active material-containing layer refers to a layer containing an active material formed on the current collector in the electrode composite material layer. The sulfur-containing phase may also be formed on at least a portion of the active material-containing layer, or may be formed on at least a portion of the surface of the active material-containing layer. Sometimes the sulfur-containing phase that may be contained in the positive composite material layer and the negative composite material layer is recorded as a positive sulfur-containing phase and a negative sulfur-containing phase, respectively.

[0043] The upper limit of the concentration of propane sultone in the non-aqueous electrolyte can be set to 5 mass %, and the upper limit can also be set to 5.0 mass %, for example. The concentration of propane sultone is preferably in the range of more than 0.55 mass % and less than 4.8 mass %, more preferably in the range of more than 0.6 mass % and less than 4.6 mass %. The concentration of propane sultone in the non-aqueous electrolyte can also be set to, for example, less than 4.50 mass %. If the concentration of propane sultone is excessively high, the decomposition product of propane sultone is excessively formed in the electrode composite material layer, which can be the main cause of resistance increase, and is therefore not preferred.

[0044] The concentration of propane sultone in the non-aqueous electrolyte may be 0.50 mass % or more.

[0045] The upper limit of the concentration of the lithium difluorophosphate in the non-aqueous electrolyte can be set to 5 mass %, and the upper limit can also be set to 5.0 mass %, for example. The concentration of lithium difluorophosphate is preferably in the range of more than 0.55 mass % and less than 4.8 mass %, more preferably in the range of more than 0.6 mass % and less than 4.6 mass %. The concentration of the lithium difluorophosphate in the non-aqueous electrolyte can also be set to, for example, less than 4.50 mass %. If the concentration of lithium difluorophosphate is excessively high, lithium difluorophosphate can be precipitated in the non-aqueous electrolyte, so it is not preferred.

[0046] The concentration of lithium difluorophosphate in the non-aqueous electrolyte may be 0.20 mass % or more.

[0047] Figure 1 and Figure 2 An example of a secondary battery using an outer packaging member made of a laminated film is shown in FIG.

[0048] like Figure 1 and Figure 2 As shown in FIG. 1 , the electrode group 1 is a flat wound electrode group. The wound electrode group 1 is housed in a bag-shaped outer packaging member 12 composed of a laminate film in which a metal layer is sandwiched between two resin films. The flat wound electrode group 1 can be formed by winding a stack formed by stacking a negative electrode 4, a separator 5, a positive electrode 3, and a separator 5 in this order from the outside into a spiral shape around an axis parallel to the short side direction, and then press-forming the stack. The outermost negative electrode 4 is as shown in FIG. Figure 2 As shown in the figure, a negative electrode layer (negative electrode composite material layer) 4b containing a negative electrode active material is formed on one side of the inner side of the negative electrode collector 4a, and the other negative electrode 4 is formed by forming the negative electrode layer 4b on both sides of the negative electrode collector 4a. The positive electrode 3 is formed by forming a positive electrode layer (positive electrode composite material layer) 3b on both sides of the positive electrode collector 3a.

[0049] Near the outer peripheral end of the wound electrode group 1, the negative terminal 13 is connected to the negative electrode collector 4a of the outermost negative electrode 4, and the positive terminal 14 is connected to the positive electrode collector 3a of the inner positive electrode 3. These negative terminal 13 and positive terminal 14 extend to the outside from the opening of the bag-like outer packaging member 12. The wound electrode group 1 is sealed by heat-sealing the opening of the bag-like outer packaging member 12. During heat sealing, the negative terminal 13 and the positive terminal 14 are sandwiched by the bag-like outer packaging member 12 at the opening.

[0050] Figure 3 and Figure 4 An example of a secondary battery using a metal container is shown in FIG.

[0051] The electrode group 1 is housed in a rectangular cylindrical metal container 2. The electrode group 1 can be formed, for example, by winding a separator 5 between a positive electrode 3 and a negative electrode 4 into a flat spiral shape around an axis parallel to the short side direction of the positive electrode 3 and the negative electrode 4. Figure 4 As shown, a strip-shaped positive electrode lead 6 is electrically connected to multiple locations of the end of the positive electrode 3 on the end face of the electrode group 1 intersecting the stacking direction of the electrodes. In addition, a strip-shaped negative electrode lead 7 is electrically connected to multiple locations of the end of the negative electrode 4 on the end face. The multiple positive electrode leads 6 are electrically connected to the positive electrode collector tab 8 in a bundled state. The positive electrode lead 6 and the positive electrode collector tab 8 constitute a positive terminal. In addition, the negative electrode lead 7 is connected to the negative electrode collector tab 9 in a bundled state. The negative electrode lead 7 and the negative electrode collector tab 9 constitute a negative terminal. A metal sealing plate 10 is fixed to the opening of the metal container 2 by welding or the like. The positive electrode collector tab 8 and the negative electrode collector tab 9 are respectively led out to the outside from the extraction holes provided on the sealing plate 10. The inner peripheral surface of each extraction hole of the sealing plate 10 is covered with an insulating member 11 in order to avoid a short circuit caused by contact with the positive electrode collector tab 8 and the negative electrode collector tab 9 .

[0052] The secondary battery according to the embodiment is not limited to Figure 1 and Figure 2 The secondary battery having the structure shown and Figure 3 and Figure 4 The secondary battery of the structure shown may also be Figure 5 and Figure 6 A battery having the structure shown.

[0053] Figure 5 It is a partially cutaway perspective view schematically showing another example of a secondary battery. Figure 6 yes Figure 5 An enlarged cross-sectional view of portion B of the secondary battery shown.

[0054] Figure 5 and Figure 6 The secondary battery shown has: Figure 5 and Figure 6 The electrode group 1 shown, Figure 5 The outer packaging member 12 is shown, and the electrolyte is not shown. The electrode group 1 and the electrolyte are accommodated in the outer packaging member 12. The electrolyte is retained in the electrode group 1.

[0055] The outer packaging member 12 is composed of a laminate film including two resin layers and a metal layer sandwiched therebetween.

[0056] Electrode group 1 Figure 6The stacked electrode group 1 has a structure in which negative electrodes 4 and positive electrodes 3 are alternately stacked with separators 5 interposed between the negative electrodes 4 and the positive electrodes 3 .

[0057] 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 surfaces of the negative electrode current collector 4a. In addition, the electrode group 1 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 surfaces of the positive electrode current collector 3a.

[0058] The negative electrode current collector 4a of each negative electrode 4 includes a portion on one side thereof which does not carry the negative electrode active material layer 4b on any surface. This portion functions as a negative electrode current collector tab 4c. Figure 6 As shown, the negative electrode collector tab 4c does not overlap with the positive electrode 3. In addition, the plurality of negative electrode collector tabs 4c are electrically connected to a strip-shaped negative electrode terminal 13. The front end of the strip-shaped negative electrode terminal 13 is led out of the outer packaging member 12.

[0059] In addition, although not shown, the positive electrode current collector 3a of each positive electrode 3 also includes a portion on one side thereof that does not carry the positive electrode active material layer 3b on any surface. This portion functions as a positive electrode collector ear. The positive electrode collector ear and the negative electrode collector ear 4c do not overlap with the negative electrode 4. In addition, the positive electrode collector ear is located on the opposite side of the electrode group 1 relative to the negative electrode collector ear 4c. The positive electrode collector ear is electrically connected to the strip-shaped positive terminal 14. The front end of the strip-shaped positive terminal 14 is located on the opposite side of the negative terminal 13 and is led to the outside of the outer packaging member 12.

[0060] As an example of a secondary battery of the embodiment, refer to Figure 7 A method for producing a secondary battery having a wound electrode group will be described. Figure 7 This is a schematic diagram showing a method for manufacturing a secondary battery using a bag-shaped outer packaging member formed of a laminate film.

[0061] First, the positive electrode 3 and the negative electrode 4 are prepared.

[0062] The positive electrode can be made, for example, by the following method. First, a positive electrode active material, a conductive agent and a binder are suspended in a solvent to prepare a slurry. The slurry is applied to one or both surfaces of a current collector. Next, the applied slurry is dried to obtain a stack containing a positive electrode active material layer and a current collector. Then, the stack is pressurized. In this way, a positive electrode is made. Alternatively, the positive electrode can also be made by the following method. First, an active material, a conductive agent and a binder are mixed to obtain a mixture. Then, the mixture is formed into particles. Then, these particles are arranged on a current collector, thereby obtaining a positive electrode.

[0063] The negative electrode can be made, 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. The slurry is applied on one or both surfaces of a current collector. Next, the applied slurry is dried to obtain a stack containing a negative electrode active material layer and a current collector. Then, the stack is pressurized. In this way, a negative electrode is made. Alternatively, the negative electrode can also be made by the following method. First, a negative electrode active material, a conductive agent and a binder are mixed to obtain a mixture. Next, the mixture is formed into particles. Then, these particles are arranged on a current collector, thereby obtaining a negative electrode.

[0064] The electrode group 1 is prepared by placing a separator 5 between the positive electrode 3 and the negative electrode 4. The positive electrode 3 of the electrode group 1 is electrically connected to the positive electrode terminal 14, and the negative electrode 4 of the electrode group 1 is electrically connected to the negative electrode terminal 13.

[0065] After the electrode group 1 having the positive and negative terminals 13 and 14 is housed in a bag-shaped outer packaging member 12 formed of a laminated film, the end 21b other than the first end 21a is sealed by thermal fusion bonding. Next, a non-aqueous electrolyte is injected into the bag-shaped outer packaging member 12 from the first end 21a, and the first end 21a is sealed by thermal fusion bonding. The thermal fusion bonding can also be performed under reduced pressure. Thus, a secondary battery 30 with the first seal completed is obtained.

[0066] Next, the secondary battery 30 that has completed the first sealing is charged and discharged for the first time at room temperature (for example, 25°C), and then aged at a temperature above room temperature. After the initial charge and discharge and aging, propane sultone reacts with the positive electrode active material, resulting in sulfur atoms being contained in the layer containing the positive electrode active material. Specifically, a decomposition product of a non-aqueous electrolyte containing propane sultone can be formed on the surface of the positive electrode active material contained in the layer containing the positive electrode active material. As a result, a layered sulfur-containing phase can be formed on the surface of the positive electrode active material. In this way, a positive electrode composite material layer 3b containing sulfur atoms can be obtained. At this time, sulfur atoms can also be contained in the layer containing the negative electrode active material. As a result, a negative electrode composite material layer 4b containing sulfur atoms can be obtained.

[0067] After aging, the temperature of the secondary battery 30 is returned to room temperature, and then the bag-like outer packaging member 12 is cut and opened along the unsealed cutting line 22 at the inner side of the first end 21a in an argon atmosphere, and the gas in the bag-like outer packaging member 12 is released to the outside. In addition, the portion cut from the bag-like outer packaging member 12 along the cutting line 22 is indicated by the reference numeral 23.

[0068] Next, the end portion 24 along the cutting line 22 is sealed under reduced pressure (eg, −90 kPa).

[0069] 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 nonaqueous electrolyte can be set within target ranges.

[0070] The details of the production conditions are described below.

[0071] The positive electrode and negative electrode used in the preparation of the electrode group are preferably dried in advance before the preparation of the electrode group. The higher the temperature at which the drying is performed and the longer the drying is performed, the more the residual moisture in the electrode can be reduced. From the viewpoint of reducing the moisture in the electrode, it is preferred that the drying is performed under reduced pressure. For example, it is preferred to vacuum dry at 120°C for 24 hours.

[0072] When the positive electrode and the negative electrode are produced by applying the slurry on one or both surfaces of the current collector and then drying the applied slurry coating, it is preferred that the above-mentioned drying is further performed after the coating drying step.

[0073] If the positive electrode and negative electrode used in the production of the electrode group are dry, the amount of water brought into the secondary battery can be reduced. If moisture is brought into the secondary battery, the water itself is electrolyzed, which can not only cause gas generation, but also make it easy for side reactions in the negative electrode to occur. Therefore, in the battery reaction, the lithium ions released by the positive electrode are consumed by the side reactions in the negative electrode, so it is difficult for the lithium ions to be embedded in the negative electrode. As a result, SOC fluctuations or the positive electrode potential moves 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, it becomes easy to produce decomposition of the non-aqueous electrolyte in the positive electrode, which becomes the main cause of gas generation. In addition, if moisture is brought into the secondary battery, the non-aqueous electrolyte reacts with water to generate hydrofluoric acid, thereby degrading the electrode.

[0074] In addition, lithium difluorophosphate can capture moisture brought into the secondary battery, but lithium difluorophosphate is consumed at this time. Therefore, if the amount of moisture brought into the secondary battery is large, lithium difluorophosphate is easily consumed, and it may be difficult to obtain the effect of suppressing the decomposition of propane sultone by lithium difluorophosphate.

[0075] Therefore, if the positive electrode and the negative electrode used in the preparation of the electrode group are dried, side reactions can be suppressed and lithium difluorophosphate and propane sultone can easily remain in the non-aqueous electrolyte. As a result, gas generation in the secondary battery of the embodiment can be suppressed, which is preferred.

[0076] As reference Figure 7As described above, when the first sealed secondary battery 30 is subjected to initial charge and discharge and aging, gas is generated in the first sealed secondary battery 30. Examples of the gas generation reaction include a reaction in which water brought into the secondary battery 30 decomposes.

[0077] The gases generated during initial charge and discharge and aging are as shown in the reference Figure 7 As described above, the gas will be released to the outside after aging. Therefore, by actively performing the gas generation reaction during aging, the remaining amount of the substance that is the main cause of gas generation in the secondary battery 31 of the embodiment obtained after aging can be reduced. Therefore, the gas generation in the secondary battery 31 of the embodiment can be suppressed.

[0078] The higher the aging temperature and the longer the aging time, the easier it is for the gas to react during aging.

[0079] The lower the aging temperature, the more it is possible to suppress the propane sultone from being decomposed and consumed during aging, so that the amount of propane sultone remaining in the non-aqueous electrolyte of the secondary battery 31 of the embodiment can be increased.

[0080] The aging temperature is preferably set to a low temperature of 25° C. to 50° C. In addition, the aging time is preferably set to a long time of 30 hours to 48 hours.

[0081] In order to allow propane sultone to remain in the secondary battery 31 of the embodiment and suppress the generation of gas in the secondary battery 31 of the embodiment, it is preferable to perform aging at a low temperature and for a long time.

[0082] Hereinafter, the positive electrode, the negative electrode, and the non-aqueous electrolyte will be described. In addition to these components, the separator and the outer casing member that the secondary battery of the embodiment may include will be described below.

[0083] 1) Positive electrode

[0084] The positive electrode can include a positive electrode collector and a positive electrode composite material layer. The positive electrode composite material layer can be formed on one side or both sides of the positive electrode collector. The positive electrode composite material layer can include a positive electrode active material, sulfur atoms, and any conductive agent and binder. The positive electrode composite material layer can include the positive electrode sulfur-containing phase described above. The sulfur atoms can be contained in the positive electrode sulfur-containing phase. The positive electrode sulfur-containing phase can also exist in at least a portion of the positive electrode surface, and can also cover at least a portion of the surface of the positive electrode active material particles. The positive electrode sulfur-containing phase can be film-like or layer-like.

[0085] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode can contain one compound alone as the positive electrode active material, or can also contain two or more compounds in combination. As examples of oxides and sulfides, compounds that can embed and de-embed Li or Li ions can be cited.

[0086] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2: 0<x≤1), lithium nickel composite oxide (such as Li x NiO2, 0<x≤1), lithium cobalt composite oxide (such as Li x CoO2, 0<x≤1), lithium nickel cobalt composite oxide (such as Li x Ni 1-y Co y O2, 0<x≤1, 0<y<1), lithium manganese cobalt composite oxide (such as Li x Mn y Co 1-y O2, 0<x≤1, 0<y<1), lithium manganese nickel composite oxide with spinel structure (such as Li x Mn 2-y Ni y O4, 0<x≤1, 0<y<2), lithium phosphate with olivine structure (such as Li x FePO4, 0<x≤1, Li x Fe 1-y Mn y PO4, 0<x≤1, 0<y≤1, Li x CoPO4, 0<x≤1), iron sulfate (Fe2(SO4)3), vanadium oxide (such as V2O5), LiNi x Co y M z O2 (x+y+z=1, x≥0.8, M includes 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).

[0087] Among the above, examples of more preferred compounds as positive electrode active materials include: lithium manganese composite oxides having a spinel structure (e.g., Li x Mn2O4, 0<x≤1, Li x Mn 2-y Ni yO4, 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 with olivine structure (such as 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). If these compounds are used in the positive electrode active material, the battery voltage can be increased. x Ni 1-y-z Co y Mn z In the lithium nickel cobalt manganese composite oxide represented by O2, a high energy density can be achieved when y and z are 0<y+z≤0.2.

[0088] When the active material contains sulfur atoms in the composition, the sulfur atoms derived from the active material may be contained in the extract in the ICP emission analysis described later. That is, the mass of sulfur atoms per unit volume of the electrode composite material layer specified in the ICP emission analysis 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 composite material layer is 430 g / m 3 the following.

[0089] The positive electrode active material may be in the form of particles. The primary particle size of the positive electrode active material is preferably greater than 100 nm and less than 1 μm. Positive electrode active materials with a primary particle size of greater than 100 nm are easy to handle in industrial production. Positive electrode active materials with a primary particle size of less than 1 μm can smoothly perform solid diffusion of lithium ions.

[0090] The specific surface area of ​​the positive electrode active material is preferably 0.1 m 2 / g or more and 10m 2 / g or less. With 0.1m 2 / g or more of the positive electrode active material can fully ensure the insertion and extraction sites of Li ions. 2 A positive electrode active material having a specific surface area of ​​1000 Å or less is easy to handle in industrial production and can ensure good charge and discharge cycle performance.

[0091] The binder is used to fill the gaps between the dispersed positive electrode active materials and to bind the positive electrode active materials to the positive electrode collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC) and salts of CMC. One of these can be used as a binder, or two or more of these can be used in combination as a binder.

[0092] The conductive agent is formulated to improve the current collection performance and suppress the contact resistance between the positive electrode active material and the positive electrode collector. Examples of conductive agents include carbon black such as vapor grown carbon fiber (VGCF), acetylene black, and carbonaceous materials such as graphite. One of them can be used as a conductive agent, or two or more of them can be combined and used as a conductive agent. In addition, the conductive agent can also be omitted.

[0093] In the positive electrode composite material layer, the positive electrode active material and the binder are preferably blended in a ratio of 80 mass % to 98 mass % and 2 mass % to 20 mass %, respectively.

[0094] By making the amount of the binder more than 2% by mass, sufficient electrode strength can be obtained. In addition, the binder can function as an insulator. Therefore, if the amount of the binder is less than 20% by mass, the amount of the insulator contained in the electrode is reduced, so the internal resistance can be reduced.

[0095] When adding a conductive agent, the positive electrode active material, the binder and the conductive agent are preferably blended in a ratio of 77 mass % to 95 mass %, 2 mass % to 20 mass % and 3 mass % to 15 mass %, respectively.

[0096] By making the amount of the conductive agent more than 3% by mass, the above-mentioned effect can be exerted. In addition, by making the amount of the conductive agent less than 15% by mass, the proportion of the conductive agent in contact with the electrolyte can be reduced. If this proportion is low, the decomposition of the electrolyte can be reduced under high temperature storage.

[0097] The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from the group consisting of Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0098] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0099] Furthermore, the positive electrode current collector may include a portion on the surface of which the positive electrode composite material layer is not formed, and this portion may function as a positive electrode current collector tab.

[0100] 2) Negative electrode

[0101] The negative electrode can include a current collector and a negative electrode composite material layer. The negative electrode composite material layer can be formed on one or both sides of the current collector. The negative electrode composite material layer can include a negative electrode active material and any conductive agent and binder. Preferably, the negative electrode composite material layer includes sulfur atoms. The negative electrode composite material layer can include the negative electrode sulfur-containing phase described above. Sulfur atoms can be contained in the negative electrode sulfur-containing phase. The negative electrode sulfur-containing phase can also exist in at least a portion of the negative electrode surface, and can also cover at least a portion of the surface of the negative electrode active material particles. The negative electrode sulfur-containing phase can be in a film-like or layered form.

[0102] The negative electrode active material is not particularly limited as long as it can insert and remove lithium or lithium ions. The type of negative electrode active material used can also be specified as one or more than two. Examples of negative electrode active materials include titanium-containing oxides, niobium-containing oxides, and carbon materials.

[0103] Examples of titanium-containing oxides include lithium-containing titanium oxides and titanium oxides. Examples of niobium-containing oxides include niobium-titanium oxides, niobium-containing tungsten oxides, and niobium-containing titanium-molybdenum oxides.

[0104] Examples of titanium-containing oxides include lithium titanate (e.g., Li 2+y Ti3O7, 0≤y≤3), lithium titanate with spinel structure (such as Li 4+x Ti5O 12 , 0≤x≤3), monoclinic titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, alkali-hard manganese ore titanium composite oxide and orthorhombic titanium composite oxide. The lithium ion insertion and deinsertion potential of titanium oxide is 0.4V (vs.Li / Li + )above.

[0105] Examples of orthorhombic titanium-containing composite oxides include Li 2+a M I 2-b Ti 6-c M II d O 14+σ The compound represented by I It is at least one selected from Sr, Ba, Ca, Mg, Na, Cs, Rb and K. M IIAt least one selected from 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, -0.5≤σ≤0.5. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+ a Na2Ti6O 14 (0≤a≤6).

[0106] Examples of the niobium-containing oxide include niobium oxide, niobium-titanium oxide, niobium-containing tungsten oxide, and niobium-containing titanium-molybdenum oxide.

[0107] Examples of niobium titanium oxides include monoclinic niobium titanium oxides. Examples of monoclinic niobium titanium oxides include Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ A compound represented by wherein M1 is at least one selected from Zr, Si and Sn. M2 is at least one selected from V, Ta and Bi. Each subscript in the composition formula is 0≤x≤5, 0≤y<1, 0≤z<2, -0.3≤δ≤0.3. As specific examples of monoclinic niobium titanium oxide, Li x Nb2TiO7(0≤x≤5).

[0108] As another example of monoclinic niobium titanium oxide, Li x Ti 1-y M3 y+z Nb 2-z O 7-δ A compound represented by wherein M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta and Mo. Each subscript in the composition formula is 0≤x≤5, 0≤y<1, 0≤z<2, -0.3≤δ≤0.3.

[0109] Examples of the carbon material include graphite, hard carbon, etc. When the carbon material is used in the negative electrode, copper foil can be used as the negative electrode current collector.

[0110] In the negative electrode active material, the lithium ion insertion and deinsertion potential of monoclinic niobium titanium oxide is 1.0V (vs. Li / Li + ), so the decomposition reaction of propane sultone can be moderately generated. In addition, the insertion and deinsertion potential of lithium ions in lithium titanate is 1.4V (vs. Li / Li + ) near the carbon material, the lithium ion insertion and deinsertion potential is 0V (vs.Li / Li+ )nearby.

[0111] The negative electrode active material may be in the form of particles.

[0112] Conductive agents are formulated to improve current collection performance and suppress the contact resistance between the active material and the current collector. Examples of conductive agents include carbon black such as vapor grown carbon fiber (VGCF), carbon nanotubes, acetylene black, and carbonaceous materials such as graphite. One of them can be used as a conductive agent, or two or more can be combined and used as a conductive agent. Alternatively, instead of using a conductive agent, the surface of the active material particles can be coated with carbon or an electronically conductive inorganic material.

[0113] The binder is used to fill the gaps between the dispersed active materials and to bind the active materials to the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC) and salts of CMC. One of these can be used as a binder, or two or more of them can be used in combination as a binder.

[0114] As an example, the proportion of the negative electrode active material, the conductive agent and the binder in the negative electrode composite material layer is preferably matched with the negative electrode active material, the conductive agent and the binder in a ratio of 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. By setting the amount of the conductive agent to more than 2% by mass, the current collection performance of the negative electrode composite material layer can be improved. In addition, by setting the amount of the binder to more than 2% by mass, the bonding properties of the negative electrode composite material layer and the collector become sufficient, and excellent cycle performance can be expected. On the other hand, it is preferred to make the conductive agent and the binder less than 30% by mass in order to achieve high capacity.

[0115] The current collector can be made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted and released in the active material. The negative electrode active material uses a lithium ion insertion and release potential of 0.4V (vs. Li / Li + An example of a current collector when the material is copper, nickel, stainless steel or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector with such a thickness can achieve a balance between electrode strength and lightness.

[0116] Furthermore, the current collector may include a portion on the surface of which the negative electrode composite material layer is not formed, and this portion may function as a negative electrode collector tab.

[0117] 3) Non-aqueous electrolyte

[0118] As the non-aqueous electrolyte, for example, a liquid non-aqueous electrolyte or a gel non-aqueous electrolyte can be used. The liquid non-aqueous electrolyte includes an electrolyte salt, an organic solvent that can dissolve the electrolyte salt, and 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.

[0119] Propane sultone and lithium difluorophosphate may or may not function as an electrolyte salt or an organic solvent, respectively. Propane sultone and lithium difluorophosphate may also function as an electrolyte salt or an organic solvent.

[0120] The composition of the non-aqueous electrolyte contained in the secondary battery of the embodiment, in particular, the concentration of propane sultone and the concentration of lithium difluorophosphate may be changed compared to the composition of the non-aqueous electrolyte just after preparation (initial composition). This is because, for example, after the secondary battery after the first sealing is assembled using the non-aqueous electrolyte just after preparation, propane sultone and lithium difluorophosphate may be consumed during the initial charge and discharge, aging, etc.

[0121] That is, the nonaqueous electrolyte is preferably prepared so that the concentration of propane sultone in the nonaqueous electrolyte is 0.5 mass % or more and the concentration of lithium difluorophosphate is 0.2 mass % or more in the secondary battery of the embodiment after initial charge / discharge and aging.

[0122] Specifically, the nonaqueous electrolyte is preferably prepared so that the concentration of propane sultone in the nonaqueous electrolyte immediately after preparation (initial concentration) is in the range of 0.7 mass % to 5 mass %. The initial concentration of propane sultone may be 1.0 mass % or more.

[0123] The higher the initial concentration of propane sultone is, the easier it is for propane sultone to remain in the non-aqueous electrolyte after the initial charge and discharge.

[0124] The lower the initial concentration of propane sultone is, the less decomposition products generated by the reaction of propane sultone with the electrode active material can be generated, and thus an increase in electrode resistance can be suppressed.

[0125] The secondary battery according to the embodiment contains lithium difluorophosphate in addition to propane sultone in the non-aqueous electrolyte, so even if the initial concentration of propane sultone is reduced, propane sultone is likely to remain in the non-aqueous electrolyte after the initial charge and discharge. Therefore, it is possible to achieve both suppression of electrode resistance increase and suppression of non-aqueous electrolyte decomposition.

[0126] If the nonaqueous electrolyte is modulated in a manner that the concentration (initial concentration) of the lithium difluorophosphate in the nonaqueous electrolyte just after modulation is increased, it becomes easy to obtain the effect of suppressing the decomposition of propane sultone. The initial concentration of lithium difluorophosphate is preferably more than 0.3 mass %, more preferably more than 0.5 mass %. If the initial concentration of lithium difluorophosphate is low, the precipitation of lithium difluorophosphate in the nonaqueous electrolyte can be suppressed. The initial concentration of lithium difluorophosphate is preferably less than 5 mass %, more preferably less than 3 mass %.

[0127] The non-aqueous electrolyte is preferably modulated in such a manner that the initial concentration of propane sultone: 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 modulated in such a manner 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. If it is within the above range, it is easy to obtain the effect of suppressing the decomposition of propane sultone by lithium difluorophosphate, and the initial concentration of propane sultone can be reduced. Therefore, the resistance increase can be suppressed.

[0128] Examples of electrolyte salts 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: Lithium bis(trifluoro methanesulfonyl)imide, LiN(CF3SO2)2), and lithium bis(fluorosulfonyl)imide (LiFSI: Lithium Bis(fluorosulfonyl)imide, 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.

[0129] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (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 as a mixed solvent.

[0130] The gel non-aqueous electrolyte can be prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0131] Alternatively, as the nonaqueous electrolyte, besides a liquid nonaqueous electrolyte and a gel nonaqueous electrolyte, a room-temperature molten salt (ionic melt) containing lithium ions, a polymer solid electrolyte, an inorganic solid electrolyte, or the like may be used.

[0132] 4) Diaphragm

[0133] The separator can be formed of, for example, a porous film or a synthetic resin nonwoven fabric containing polyethylene (PE), polypropylene (PP), cellulose or polyvinylidene fluoride (PVdF). From the perspective of safety, a porous film formed of polyethylene or polypropylene is preferably used. This is because these porous films melt at a certain temperature and can cut off the current.

[0134] As the separator, an electrolyte layer containing an inorganic solid electrolyte may also be used. Examples of lithium ion conductive inorganic solid electrolytes include lithium ion conductive oxide-based solid electrolytes and lithium ion conductive sulfide-based solid electrolytes. Examples of lithium ion conductive oxide-based solid electrolytes include NASICON-type lithium phosphate solid electrolytes, amorphous LIPON (Li 2.9 PO 3.3 N 0.46 ), or garnet-type LLZ (Li7La3Zr2O 12 )wait.

[0135] 5) Outer packaging components

[0136] As the outer packaging member, for example, a container formed of a laminated film or a metal container can be used.

[0137] The thickness of the laminate film is, for example, 0.5 mm or less, or preferably 0.2 mm or less.

[0138] As the laminated film, a multilayer film including a plurality of resin layers and a metal layer sandwiched between the resin layers can be used. The resin layer contains, for example, a polymer material such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably formed of aluminum foil or aluminum alloy foil for light weight. The laminated film can be sealed by hot melt bonding and formed into the shape of an outer packaging member.

[0139] The thickness of the metal container is, for example, preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0140] The metal container can be made of, for example, aluminum or an aluminum alloy. Preferably, the aluminum alloy contains elements such as magnesium, zinc, and silicon. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content thereof is preferably 100 mass ppm or less.

[0141] The shape of the outer packaging member is not particularly limited. The shape of the outer packaging member may be, for example, flat (thin), square, cylindrical, coin-shaped, or button-shaped. The outer packaging member may be appropriately selected according to the battery size and the purpose of the battery.

[0142] <Measurement method>

[0143] The mass of sulfur atoms per unit volume (g / m 3 ), a method for measuring the concentration (mass %) of propane sultone and the concentration (mass %) of lithium difluorophosphate in the non-aqueous electrolyte is described.

[0144] (Preparation of Samples for Measurement)

[0145] Unseal the outer packaging of a secondary battery with a state of charge (SOC) of 50% and take out the electrode group. Remove the clamp (tape, etc.) that binds the electrode group together. If the outermost layer is a separator, peel off the separator and take out the electrode of the first layer (e.g., the negative electrode). Also peel off the separator and take out the electrode of the first layer (e.g., the positive electrode). By repeating the operation of peeling off the separator and taking out the electrodes, all the positive and negative electrodes that constitute the electrode group are taken out. Place the taken out electrodes and separator in a centrifuge to extract the non-aqueous electrolyte and separate the electrodes from the separator.

[0146] (ICP luminescence analysis)

[0147] The mass of sulfur atoms per unit volume of the positive electrode composite material layer or the negative electrode composite material layer (g / m 3 ) can be measured by inductively coupled plasma (ICP: Inductively Coupled Plasma) emission analysis. Each electrode separated by the above centrifugal separator was cleaned with methyl ethyl carbonate (MEC) and vacuum dried. Each electrode was punched into a fixed area (2×2 cm 2 ), add a certain amount of pure water (10cc) and irradiate with ultrasound for more than 30 minutes. The extract is analyzed by ICP to measure the mass of sulfur atoms in the extract, thereby obtaining the mass of sulfur atoms per unit volume of each electrode composite material layer.

[0148] (GC-MS)

[0149] The non-aqueous electrolyte extracted by the above method was diluted with acetonitrile to a volume 20 times that of the sample to be measured. The concentration (mass %) of propane sultone in the non-aqueous electrolyte can be determined by subjecting the sample to gas chromatography-mass spectrometry (GC-MS) under the conditions shown in Table 1 below.

[0150] Table 1

[0151]

[0152] (Capillary Electrophoresis)

[0153] The nonaqueous electrolyte extracted by the above method is diluted with acetonitrile to a volume 20 times that of the nonaqueous electrolyte. The diluted sample is used as a measurement sample, and the sample is subjected to capillary electrophoresis (CE) under the following measurement conditions to identify the concentration (mass %) of lithium difluorophosphate in the nonaqueous electrolyte.

[0154]

[0155] According to the first embodiment described above, a secondary battery including a positive electrode, a negative electrode and a non-aqueous electrolyte can be provided. The positive electrode includes a positive electrode composite material layer containing a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode composite material 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 mass % or more. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass % or more. Therefore, a secondary battery with high output performance and high high temperature durability can be realized.

[0156] (Second embodiment)

[0157] The battery pack according to the second embodiment may include one or more secondary batteries (single batteries) according to the embodiment. A plurality of secondary batteries may 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 also include a plurality of battery packs.

[0158] The battery pack according to the embodiment may further include a protection circuit. The protection circuit has the function of controlling the charge and discharge of the secondary battery. Alternatively, a circuit in a device (such as an electronic device, a car, etc.) that uses the battery pack as a power source may be used as a protection circuit for the battery pack.

[0159] In addition, the battery pack involved in the embodiment can further include an external terminal for power supply. The external terminal for power supply is used to output current from the secondary battery to the outside and input current to the secondary battery. In other words, when the battery pack is used as a power source, the current is supplied to the outside through the external terminal for power supply. In addition, when charging the battery pack, the charging current (including the regenerative energy of the power of a vehicle such as a car) is supplied to the battery pack through the external terminal for power supply.

[0160] Figure 8 and Fig. 9 An example of a battery pack 50 is shown in FIG. The battery pack 50 includes a plurality of Figure 8 A flat battery with the structure shown. Figure 8 is an exploded perspective view of the battery pack 50. Fig. 9 Yes means Figure 8 A block diagram of the circuit of the battery pack 50 is shown.

[0161] A plurality of cells 51 are stacked so that the negative electrode terminals 13 and the positive electrode terminals 14 extending outward face the same direction, and are fastened with adhesive tape 52 to form a battery pack 53. Fig. 9 are electrically connected in series as shown.

[0162] The printed wiring board 54 is arranged opposite to the side surface of the cell 51 from which the negative electrode terminal 13 and the positive electrode terminal 14 extend. Fig. 9 As shown, a thermistor 55, a protective circuit 56, and an external terminal 57 for supplying power to an external device are mounted on the printed wiring board 54. In addition, an insulating plate (not shown) is mounted on the surface of the printed wiring board 54 facing the battery pack 53 to avoid unnecessary connection with the wiring of the battery pack 53.

[0163] The positive electrode side lead 58 is connected to the positive electrode terminal 14 located at the bottom layer of the battery assembly 53, and its front end is inserted into the positive electrode side connector 59 of the printed circuit wiring substrate 54 to make an electrical connection. The negative electrode side lead 60 is connected to the negative electrode terminal 13 located at the top layer of the battery assembly 53, and its front end is inserted into the negative electrode side connector 61 of the printed circuit wiring substrate 54 to make an electrical connection. These connectors 59 and 61 are connected to the protection circuit 56 through wirings 62 and 63 formed on the printed circuit wiring substrate 54.

[0164] The thermistor 55 detects the temperature of the single cell 51 and sends its detection signal 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 the power supply terminal 57 for external equipment as an external terminal for power supply under specified conditions. The so-called specified conditions refer to, for example, when the detection temperature of the thermistor 55 reaches or exceeds the specified temperature. In addition, the so-called specified conditions refer to, for example, when overcharging, overdischarging, overcurrent, etc. of the single cell 51 are detected. The detection of overcharging, etc. is performed on each single cell 51 or the single cell 51 as a whole. When detecting each single cell 51, the battery voltage can be detected, and the positive electrode potential or the negative electrode potential can also be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each single cell 51. Figure 8 and Fig. 9 In the case of , wirings 65 for voltage detection are connected to the cells 51 , respectively. Detection signals are sent to the protection circuit 56 through these wirings 65 .

[0165] Protective sheets 66 made of rubber or resin are disposed on three side surfaces of the assembled battery 53 except for the side surfaces from which the positive electrode terminal 14 and the negative electrode terminal 16 protrude.

[0166] The battery pack 53 is stored in the storage container 67 together with the protective sheets 66 and the printed circuit wiring substrate 54. That is, the protective sheets 66 are respectively arranged on the two inner side surfaces in the long-side direction and the inner side surface in the short-side direction of the storage container 67, and the printed circuit wiring substrate 54 is arranged on the inner side surface on the opposite side in the short-side direction. The battery pack 53 is located in the space surrounded by the protective sheets 66 and the printed circuit wiring substrate 54. The cover 68 is mounted on the upper surface of the storage container 67.

[0167] In addition, heat shrink tape may be used to fix the battery module 53 instead of the adhesive tape 52. In this case, protective sheets are placed on both sides of the battery module, and after the heat shrink tape is wrapped around the battery module, the heat shrink tape is thermally shrunk to bundle the battery module.

[0168] Figure 8 , Fig. 9 The single cells 51 are connected in series, but they can also be connected in parallel to increase the battery capacity. Alternatively, they can be connected in a combination of series connection and parallel connection. The assembled battery packs can also be connected in series or in parallel.

[0169] also, Figure 8 and Fig. 9 The battery pack shown in the figure includes one assembled battery, but the battery pack according to the embodiment may include a plurality of assembled batteries. The plurality of assembled batteries may be electrically connected in series, in parallel, or in a combination of series connection and parallel connection.

[0170] In addition, the shape of the battery pack can be changed appropriately according to the purpose. The battery pack involved in the embodiment is suitable for use in applications that require excellent cycle performance when taking out a large current. Specifically, it can be used as a power source for a digital camera, or as a vehicle battery or a fixed battery for, for example, a two-wheeled to four-wheeled hybrid electric vehicle, a two-wheeled to four-wheeled electric vehicle, a power-assisted bicycle, or a railway vehicle (such as a tram). It is particularly suitable for use as a vehicle-mounted battery mounted in a vehicle.

[0171] 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.

[0172] (Third embodiment)

[0173] The vehicle according to the third embodiment includes one or two or more secondary batteries according to the embodiment or the battery pack according to the embodiment.

[0174] In a vehicle such as an automobile equipped with the battery pack according to the third embodiment, the battery pack can recover, for example, regenerative energy of the vehicle's power. In addition, the vehicle may include a mechanism that converts the vehicle's kinetic energy into regenerative energy.

[0175] Fig.10 An example of a vehicle including a battery pack according to an example of the embodiment is shown in FIG.

[0176] Fig.10 The illustrated automobile 71 has a battery pack 72 of one example of the embodiment mounted in the engine room in front of the vehicle body. The mounting position of the battery pack in the automobile is not limited to the engine room. For example, the battery pack can also be mounted behind the vehicle body or under the seat.

[0177] Fig.11 It is a diagram schematically showing the structure of an example of a vehicle according to the embodiment. Fig.11 The illustrated vehicle 300 is an electric vehicle.

[0178] Fig.11 The illustrated vehicle 300 includes a vehicle power supply 301 , a vehicle ECU (Electric Control Unit) 380 which is a higher-level control mechanism of the vehicle power supply 301 , an external terminal 370 , an inverter 340 , and a drive motor 345 .

[0179] The vehicle 300 has a vehicle power supply 301 mounted in, for example, the engine room, the rear of the vehicle body, or under the seat. Fig.11 2 schematically shows the mounting position of the secondary battery in the vehicle 300 .

[0180] 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: Battery Management Unit) 311 , and a communication bus 310 .

[0181] The three battery packs 312a, 312b, and 312c are electrically connected in series. The battery pack 312a includes a battery pack 314a and a battery pack monitoring device (VTM: Voltage Temperature Monitoring) 313a. The battery pack 312b includes a battery pack 314b and a battery pack monitoring device 313b. The battery pack 312c includes a battery pack 314c and a battery pack monitoring device 313c. The battery packs 312a, 312b, and 312c can be independently removed and exchanged with other battery packs.

[0182] Each of the assembled batteries 314a to 314c includes a plurality of secondary batteries connected in series. Each of the secondary batteries is a secondary battery according to the embodiment. Each of the assembled batteries 314a to 314c is charged and discharged through a positive electrode terminal 316 and a negative electrode terminal 317.

[0183] The battery management device 311 communicates with the assembled battery monitoring devices 313 a to 313 c to collect information on maintenance of the vehicle power supply 301 , and collects information such as voltage and temperature of the secondary batteries of the assembled batteries 314 a to 314 c included in the vehicle power supply 301 .

[0184] The battery management device 311 and the assembled battery monitoring devices 313a to 313c are connected by a communication bus 310. The communication bus 310 is configured so that a plurality of nodes (battery management devices and one or more assembled battery monitoring devices) share a single communication line. The communication bus 310 is, for example, a communication bus configured based on the CAN (Control Area Network) standard.

[0185] The assembled battery monitoring devices 313a to 313c measure the voltage and temperature of each secondary battery constituting the assembled batteries 314a to 314c based on the communication command from the battery management device 311. However, the temperature may be measured at only a few locations in one assembled battery, and the temperature of all the secondary batteries need not be measured.

[0186] The vehicle power supply 301 may further include an electromagnetic contactor (eg, Fig.11 The switch device 333 is shown in FIG. 333. The switch device 333 includes a pre-charge switch (not shown) that is turned on when charging the assembled batteries 314a to 314c and a main switch (not shown) that is turned on when the battery output is supplied to the load. The pre-charge switch and the main switch each include a relay circuit (not shown) that is turned on and off based on a signal sent to a coil disposed near the switch element.

[0187] The inverter 340 converts the input DC voltage into a three-phase AC high voltage for motor driving. The inverter 340 controls the output voltage based on a control signal from the vehicle ECU 380 that controls the battery management device 311 or the overall operation of the vehicle. The three-phase output terminals of the inverter 340 are connected to the three-phase input terminals of the drive motor 345.

[0188] The driving motor 345 is rotated by the electric power supplied from the inverter 340. The rotation is transmitted to the axle and the driving wheel W via, for example, a differential gear unit.

[0189] Although not shown, the vehicle 300 is provided with a regenerative braking mechanism that rotates the drive motor 345 and converts kinetic energy into regenerative energy as electrical energy when braking the vehicle 300. 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.

[0190] One terminal of the 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 .

[0191] One terminal of the connection line L2 is connected to the positive terminal 316 of the vehicle power supply 301 via the switch device 333 . The other terminal of the connection line L2 is connected to the positive input terminal of the inverter 340 .

[0192] The external terminal 370 is connected to the battery management device 311. The external terminal 370 can be connected to an external power source, for example.

[0193] The vehicle ECU 380 responds to the operation input of the driver, etc., and coordinates with other devices to control the battery management device 311 to manage the entire vehicle. The battery management device 311 and the vehicle ECU 380 transmit data related to the maintenance of the vehicle power supply 301, such as the remaining capacity of the vehicle power supply 301, through the communication line.

[0194] The vehicle of the embodiment includes a battery pack including the secondary battery of the embodiment, and the battery pack (e.g., the battery packs 312a, 312b, and 312c) has excellent output performance and high temperature durability, and can obtain a vehicle with excellent charge and discharge performance and high reliability. In addition, each battery pack is inexpensive and highly safe, so the cost of the vehicle can be suppressed and the safety can be improved.

[0195] Example

[0196] A secondary battery was manufactured according to the following steps.

[0197] (Example 1)

[0198] <Production of positive electrode>

[0199] As the positive electrode active material, lithium nickel cobalt manganese composite oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2) powder. Acetylene black is prepared as a conductive agent. Polyvinylidene fluoride (PVdF) is prepared as a binder. Next, the positive electrode active material, the conductive agent and the binder are added to N-methylpyrrolidone (NMP) as a solvent in a ratio of 82 mass%, 9 mass% and 9 mass% and mixed to prepare a positive electrode slurry. The positive electrode slurry is applied on both sides of a collector consisting of an aluminum foil with a thickness of 15 μm. Next, the coating is dried in a thermostatic bath at 120°C to form a layer containing a positive electrode active material, and the layer containing a positive electrode active material is pressurized to obtain a positive electrode.

[0200] <Production of negative electrode>

[0201] Niobium titanium oxide (Nb2TiO7) powder was prepared as the negative electrode active material. The average secondary particle size of the niobium titanium oxide was 7.5 μm. The specific surface area of ​​the niobium titanium oxide was 4.0 m 2 / g. In addition, acetylene black is prepared as a conductive agent, and polyvinylidene fluoride (PVdF) is prepared as a binder. Next, the negative electrode active material, the conductive agent and the binder are 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. The negative electrode slurry is applied on both sides of a collector formed of an aluminum foil with a thickness of 15 μm. Next, the coating is dried in a thermostatic bath at 120°C to form a layer containing a negative electrode active material, and the layer containing a negative electrode active material is pressurized to obtain a negative electrode.

[0202] <Production of Electrode Group>

[0203] The positive electrode and the negative electrode were vacuum dried at 120°C for 24 hours. As a separator, two non-woven fabrics made of polyethylene with a thickness of 25 μm were prepared. Then, the positive electrode, the separator, the negative electrode and the separator were stacked in this order to obtain a laminate. Then, the laminate was wound into a spiral shape. A flat electrode group was made by heating and pressing it at 80°C. The positive terminal was electrically connected to the positive electrode of the electrode group. In addition, the negative terminal was electrically connected to the negative electrode of the electrode group.

[0204] <Storage of Electrode Group>

[0205] A container formed of a laminated film having a three-layer structure of nylon layer / aluminum layer / polyethylene layer and a thickness of 0.1 mm was prepared. The electrode group prepared above was placed in the container. Next, the inside of the container was vacuum dried at 80° C. for 16 hours with a portion of the peripheral portion of the container open.

[0206] <Preparation of Liquid Non-aqueous Electrolyte>

[0207] A mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio of 1:2) is prepared as a solvent. LiPF6 is dissolved in the solvent at a concentration of 1 mol / L as an electrolyte salt. Among them, 1,3-propane sultone (PS) is added and dissolved in a manner such that the initial concentration in the non-aqueous electrolyte becomes 1.0 mass %. In addition, lithium difluorophosphate (DFP) is added and dissolved in a manner such that the initial concentration becomes 1.0 mass %. In other words, the non-aqueous electrolyte is prepared in a manner such that the initial concentration of PS: the initial concentration of DFP (PS: DFP initial concentration ratio) becomes 1:1. In this way, a liquid non-aqueous electrolyte (non-aqueous electrolyte solution) is obtained. The preparation of the liquid non-aqueous electrolyte is carried out in an argon box.

[0208] <Battery Production>

[0209] Inject a non-aqueous electrolyte into the container containing the electrode group. Next, heat seal the open part of the container's periphery to make the container airtight. Thus, a battery with an outer dimension of 11 cm × 8 cm × 0.3 cm excluding the positive and negative terminals (also called positive and negative electrode tabs) and an inner dimension (the dimension of the sealed portion) of 9 cm × 7 cm × 0.25 cm is obtained. This battery is called a battery that has completed the first seal.

[0210] <First time charging>

[0211] The initial charge and discharge are performed by performing the following initial charge and initial discharge. In an environment of 25°C, the battery that has completed the first seal is subjected to the initial charge according to the following steps. First, the battery that has completed the first seal is charged at a constant current (CC) of 0.2C to a voltage of 3V. Next, the battery that has completed the first seal is charged at a constant voltage (CV) of 3V. Constant voltage charging is terminated when the total time of constant current charging and constant voltage charging reaches 10 hours.

[0212] <First Discharge>

[0213] Next, the battery after the first sealing was discharged at a constant current (CC) of 0.2C until the voltage reached 1.5V in an environment of 25°C.

[0214] <Post-processing>

[0215] Next, in an environment of 25°C, the battery that has completed the first seal after the initial charge and discharge is charged to a voltage of 3V at a constant current (CC) of 0.2C. Next, the battery that has completed the first seal is charged at a constant voltage (CV) of 3V until the current value becomes 1 / 20C. That is, the battery that has completed the first seal is charged with constant current and constant voltage (CCCV). As a result, the SOC of the battery that has completed the first seal is (100%). The battery that has completed the first seal is subjected to aging. Aging is performed by keeping it at 35°C in a constant temperature chamber for 35 hours. Then, the battery that has completed the first seal is placed in an argon box, and one of the sealing portions of the outer packaging member is cut off to discharge the gas in the outer packaging member. The end opened by cutting is sealed by heat sealing. In this way, the secondary battery of Example 1 is manufactured.

[0216] (Examples 2 to 6)

[0217] A secondary battery was prepared in the same manner as in Example 1 except that the positive electrode active material was changed as described in Table 2.

[0218] (Examples 7, 9, 10)

[0219] A secondary battery was prepared in the same manner as in Example 1 except that the negative electrode active material was changed as described in Table 2.

[0220] (Example 8)

[0221] The negative electrode active material was changed to C (graphite) as described in Table 2. Graphite powder and polyvinylidene fluoride (PVdF) were mixed in a ratio of 90% by mass and 10% by mass, and the resulting mixture was kneaded in the presence of an organic solvent (N-methylpyrrolidone) to prepare a slurry. The resulting slurry was applied to a collector formed of a copper foil having a thickness of 15 μm and dried, and then pressurized to obtain a negative electrode. In addition, when a negative electrode comprising graphite is used, the process from initial charge to post-treatment is implemented as follows to prepare a secondary battery.

[0222] <First time charging>

[0223] In an environment of 25°C, the first sealed battery was charged for the first time according to the following steps. First, the first sealed battery was charged at a constant current (CC) of 0.2C to a voltage of 4.15V. Next, the first sealed battery was charged at a constant voltage (CV) of 4.15V. The constant voltage charging was terminated when the total time of the constant current charging and the constant voltage charging reached 10 hours.

[0224] <First Discharge>

[0225] Next, the battery after the first sealing was discharged at a constant current (CC) of 0.2C until the voltage reached 2V in an environment of 25°C.

[0226] <Post-processing>

[0227] Next, in an environment of 25°C, the battery that has completed the first seal after the initial charge and discharge is charged to a voltage of 4.15V at a constant current (CC) of 0.2C. Next, the battery that has completed the first seal is charged to a current value of 1 / 20C at a constant voltage (CV) of 4.15V. That is, the battery that has completed the first seal is charged with constant current constant voltage (CCCV). As a result, the SOC of the battery that has completed the first seal is (100%). The battery that has completed the first seal is subjected to aging. Aging is carried out by keeping it at 35°C in a constant temperature bath for 35 hours. Then, the battery that has completed the first seal is placed in an argon box, and one of the sealing portions of the outer packaging member is cut off to discharge the gas in the outer packaging member. The end opened by cutting is sealed by heat sealing. In this way, the secondary battery of Example 8 is manufactured.

[0228] (Example 11)

[0229] A secondary battery was produced in the same manner as in Example 1 except that a mixed solvent of propylene carbonate (PC) and methyl ethyl carbonate (MEC) (volume ratio of 1:2) was prepared as a solvent in the preparation of the liquid nonaqueous electrolyte.

[0230] (Example 12)

[0231] A secondary battery was produced in the same manner as in Example 1 except that a mixed solvent of propylene carbonate (PC) and dimethyl carbonate (DMC) (volume ratio 1:2) was prepared as a solvent in the preparation of the liquid nonaqueous electrolyte.

[0232] (Example 13)

[0233] A secondary battery was produced in the same manner as in Example 1 except that a mixed solvent of propylene carbonate (PC) and ethyl propionate (EP) (volume ratio 1:4) was prepared as a solvent in the preparation of the liquid nonaqueous electrolyte.

[0234] (Examples 14 to 18)

[0235] In the preparation of the liquid non-aqueous electrolyte, the initial concentration of 1,3-propane sultone (PS) and the initial concentration of lithium difluorophosphate (DFP) were set to the values ​​shown in Table 2 and Table 3, respectively. The initial concentration of PS: the initial concentration of DFP (PS: DFP initial concentration ratio) in the non-aqueous electrolyte of each example is shown in Table 2 and Table 3.

[0236] In addition, the temperature and time of aging in the post-treatment are described in Tables 5 and 6.

[0237] A secondary battery was produced in the same manner as in Example 1 except for the above matters.

[0238] (Examples 19 to 21)

[0239] A secondary battery was prepared in the same manner as in Example 1 except that the temperature of aging in the post-treatment was as described in Table 6.

[0240] (Examples 22 to 24)

[0241] A secondary battery was prepared in the same manner as in Example 1 except that the aging time in the post-treatment was as described in Table 6.

[0242] (Examples 25 to 27)

[0243] In the preparation of the liquid nonaqueous electrolyte, the initial concentrations of 1,3-propane sultone (PS) and lithium difluorophosphate (DFP) were set to the values ​​shown in Table 3. Table 3 shows the initial concentrations of PS and DFP in the nonaqueous electrolyte of each example.

[0244] In addition, the temperature and time of aging in the post-treatment are described in Table 6.

[0245] A secondary battery was produced in the same manner as in Example 1 except for the above-mentioned matters.

[0246] (Example 28)

[0247] A secondary battery was produced in the same manner as in Example 1, except that the positive electrode and the negative electrode were vacuum dried at 80° C. during the production of the electrode group.

[0248] (Example 29)

[0249] A secondary battery was produced in the same manner as in Example 1, except that vacuum drying of the positive electrode and the negative electrode was not performed in the production of the electrode group. Since vacuum drying was not performed, the electrode drying temperature in Table 6 is indicated by "-".

[0250] (Comparative Example 1)

[0251] 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.

[0252] (Comparative Example 2)

[0253] 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.

[0254] (Comparative Examples 3 to 4)

[0255] A secondary battery was prepared in the same manner as in Example 1 except that the temperature and time of aging in the post-treatment were as described in Table 7.

[0256] (Comparative Examples 5 to 6)

[0257] In the preparation of the liquid nonaqueous electrolyte, the initial concentrations of 1,3-propane sultone (PS) and lithium difluorophosphate (DFP) were set to the values ​​shown in Table 4. Table 4 shows the initial concentration ratio of PS:DFP in the nonaqueous electrolyte.

[0258] In addition, the temperature and time of aging in the post-treatment are described in Table 7.

[0259] A secondary battery was produced in the same manner as in Example 1 except for the above matters.

[0260] (Comparative Example 7)

[0261] In the preparation of the liquid nonaqueous electrolyte, the initial concentrations of 1,3-propane sultone (PS) and lithium difluorophosphate (DFP) were set to the values ​​shown in Table 4. Table 4 shows the initial concentrations of PS and DFP in the nonaqueous electrolyte.

[0262] A secondary battery was produced in the same manner as in Example 1 except for the above matters.

[0263] <Measurement of the Mass of Sulfur Atoms per Unit Volume of Composite Material Layer>

[0264] For the secondary batteries of each embodiment and comparative example, the mass of sulfur atoms per unit volume of the positive electrode composite material layer (the amount of S per unit positive electrode composite material layer) and the mass of sulfur atoms per unit volume of the positive electrode composite material layer (the amount of S per unit negative electrode composite material layer) were measured by ICP emission analysis as described above. The measurement results are shown in Tables 8 to 10.

[0265] <Determination of non-aqueous electrolyte>

[0266] The concentration of propane sultone in the non-aqueous electrolyte (PS concentration in the non-aqueous electrolyte) and the concentration of lithium difluorophosphate (DFP concentration in the non-aqueous electrolyte) were measured for the liquid non-aqueous electrolyte contained in the secondary battery of each embodiment and comparative example after post-treatment according to the method described above. The measurement results are shown in Tables 8 to 10.

[0267] <Storage test>

[0268] The secondary batteries of the respective examples and comparative examples were subjected to a storage test as follows.

[0269] The secondary battery is charged at a constant current (CC) of 0.2C to a voltage of 3V. Next, the battery is charged at a constant voltage (CV) of 3V until the current value becomes 1 / 20C. In other words, the battery is charged by constant current constant voltage (CCCV) to a SOC of 100%. The battery in this charged state is placed in a constant temperature bath at 55°C. The battery is taken out from the constant temperature bath at 55°C every 10 days, and after cooling to 25°C, it is charged again by CCCV at 3V, and then placed in a constant temperature bath at 55°C. The operation is repeated, and the battery that has been stored in the constant temperature bath for 90 days is cooled to 25°C, and the volume is measured, and the difference with the volume before the test is taken as the gas generation (ml). The gas generation is an indicator of high temperature durability.

[0270] <DC (Direct Current) Resistance Measurement>

[0271] For the secondary batteries of each embodiment and comparative example, the DC resistance was measured as follows before the storage test. The battery was discharged at a constant current (CC) of 0.2C until the voltage reached 1.5V. Then, the battery was charged at a constant current (CC) of 0.2C until the voltage reached 2.25V. Next, the battery was charged at a constant voltage (CV) of 2.25V until the current value became 1 / 20C, so that the battery's state of charge was SOC50%. The battery adjusted to SOC50% was discharged at a constant current (CC) of 10C for 10ms, and the DC resistance (mΩ) was calculated from the difference between the voltage value and the current value at this time.

[0272] In addition, the DC resistance of the secondary battery after the storage test was measured in the same manner as above to obtain the DC resistance (mΩ).

[0273] The DC resistance before the storage test was performed was defined as R1, and the DC resistance after the storage test was defined as R2. The resistance increase value was obtained by dividing R2 by R1.

[0274] Tables 2 to 4 show the types of positive electrode active materials and negative electrode active materials, the types of solvents and electrolyte salts used in the preparation of liquid nonaqueous electrolytes, the PS initial concentration, the DFP initial concentration, and the PS:DFP initial concentration ratio of each example and comparative example.

[0275] Tables 5 to 7 show the electrode drying temperature and electrode drying time in the preparation of the electrode groups of the respective Examples and Comparative Examples, and the aging temperature and aging time in the post-treatment.

[0276] Tables 8 to 10 show the S content per positive electrode composite material layer, the S content per negative electrode composite material layer, the PS concentration in the non-aqueous electrolyte, the DFP concentration in the non-aqueous electrolyte, the gas generation amount (ml), and the resistance increase value in the secondary battery after post-treatment of each embodiment and comparative example.

[0277]

[0278]

[0279]

[0280]

[0281]

[0282]

[0283]

[0284]

[0285]

[0286] The following can be seen from Tables 2 to 10.

[0287] The positive electrodes included in the secondary batteries of Examples 1 to 29 have positive electrode composite material layers containing sulfur atoms. This is considered to be because propane sultone and the positive electrode active material reacted during initial charge and discharge and aging, resulting in sulfur atoms being contained in the positive electrode active material layer.

[0288] 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 composite material layer nor the negative electrode composite material layer contains sulfur atoms. In addition, the resistance increase value is high and the amount of gas generated is large. This is considered to be because the non-aqueous electrolyte does not contain propane sultone, and thus the gas generation caused by the decomposition of the non-aqueous electrolyte cannot be suppressed.

[0289] In Comparative Example 2, which is the same as Example 1 except that the non-aqueous electrolyte does not contain lithium difluorophosphate, the amount of S per unit positive electrode composite material layer is large, and the PS concentration in the non-aqueous electrolyte is low. In addition, the amount of gas generated is also large. It is believed that this is because the decomposition of propane sultone cannot be suppressed during the initial charge and discharge and aging. As a result, the high-temperature durability is reduced.

[0290] In Comparative Example 3, which was prepared in the same manner as Example 1 except that the aging temperature was increased, the amount of gas generated was relatively large. This is believed to be because the aging was performed at a high temperature of 60°C, which caused the decomposition of propane sultone to proceed excessively during the aging process, causing the S content per unit positive electrode composite material layer to exceed 430 g / m 3 , and the PS concentration in the non-aqueous electrolyte is less than 0.5 mass %.

[0291] In Comparative Example 4, which was prepared in the same manner as Example 1 except that the aging time was prolonged, the resistance increase value was higher and the amount of gas generated was greater than that in Example 1. This is believed to be because the decomposition of propane sultone was excessively advanced during the aging due to the long-term aging, so that the S content per unit positive electrode composite material layer exceeded 430 g / m 3 , and the PS concentration in the non-aqueous electrolyte is less than 0.5 mass %.

[0292] The S content per unit positive electrode composite material layer and the S content per unit negative electrode composite material layer are both greater than 430 g / m 3 In Comparative Example 5, the resistance increase value was high. This is considered to be because propane sultone was decomposed, and as a result, a sulfur-containing phase was excessively formed on the surface of the active material, which became a major factor of the resistance increase.

[0293] In Comparative Example 6, where the PS concentration in the non-aqueous electrolyte was less than 0.5 mass %, a large amount of gas was generated. This is considered to be because propane sultone that can function as a sacrificial material does not remain sufficiently in the non-aqueous electrolyte contained in the secondary battery after post-treatment, and thus the reaction of generating gas by decomposition of the non-aqueous electrolyte cannot be suppressed.

[0294] In Comparative Example 7, in which the DFP concentration in the non-aqueous electrolyte was less than 0.2 mass %, the PS concentration in the non-aqueous electrolyte was also less than 0.5 mass %, and the amount of gas generated was large. This is believed to be because lithium difluorophosphate was not sufficiently present in the non-aqueous electrolyte, and thus the consumption of propane sultone during initial charge and discharge and aging could not be suppressed, resulting in insufficient propane sultone remaining in the non-aqueous electrolyte contained in the secondary battery after post-treatment that could function as a sacrificial material.

[0295] As shown in Examples 1 to 6, even if the positive electrode active material is changed to a material different from that in Example 1, such as a lithium nickel cobalt manganese composite oxide but with a different ratio of Ni, Co, and Mn, a lithium manganese composite oxide, a lithium phosphate with an olivine structure, etc., the effect of suppressing gas generation and suppressing resistance increase can be obtained.

[0296] As shown in Examples 7 to 10, even if the negative electrode active material is changed to something different from that in Example 1, such as lithium titanate with a spinel structure, carbon material, orthorhombic titanium composite oxide, monoclinic titanium dioxide, etc., the effect of suppressing gas generation and suppressing resistance increase can be obtained.

[0297] As shown in Examples 11 to 13, even if the non-aqueous solvent of the non-aqueous electrolyte is changed to a solvent different from that in Example 1, such as ethyl methyl carbonate, dimethyl carbonate, ethyl propionate, etc., the effect of suppressing gas generation and suppressing resistance increase can be obtained.

[0298] As shown in Examples 14 to 18, even when the initial concentration of PS and the initial concentration of DFP in the nonaqueous electrolyte were changed to various values, the effects of suppressing gas generation and suppressing resistance increase were obtained.

[0299] By comparing Examples 1, 19 to 21, and Comparative Example 3, it is found that the S content per positive electrode composite material layer tends to decrease as the aging is performed at a lower temperature. The S content per positive electrode composite material layer is 430 g / m 3 The following Examples 1, 19 to 21 have lower gas generation amounts than Comparative Example 3. In addition, by comparing Examples 1, 19, 20 and Comparative Example 3, it is found that the PS in the nonaqueous electrolyte tends to decrease as the aging temperature increases.

[0300] By comparing Examples 1, 22 to 24, and Comparative Example 4, it is found that the shorter the aging time, the lower the S content per positive electrode composite material layer. The S content per positive electrode composite material layer is 430 g / m 3 Compared with Comparative Example 4, the following Examples 1 and 22 to 24 have lower gas generation amounts.

[0301] By comparing Examples 25 to 26, it can be seen that the amount of S per unit negative electrode composite material layer is 430 g / m 3 The following Example 25 and the S content per unit negative electrode composite material layer are greater than 430 g / m 3 Compared with Example 26, there is a tendency for lower gas generation.

[0302] Comparison between Examples 1 and 15 and Comparative Examples 1 and 6 revealed that the amount of gas generated tends to decrease as the PS concentration in the nonaqueous electrolyte increases.

[0303] By comparing Example 1, Example 28 and Example 29, it is known that Example 1 and Example 28, which vacuum dried the electrode, have a tendency to have a lower resistance increase value and a smaller amount of gas generation than Example 29, which did not vacuum dry the electrode. In addition, Example 1, which vacuum dried the electrode at 120°C, has a tendency to have a lower resistance increase value and a smaller amount of gas generation than Example 28, which vacuum dried the electrode at 80°C. It is believed that this is because: the higher the temperature and the longer the drying condition of the electrode, the less water remains in the electrode. Because the less water in the electrode, the more difficult it is to consume propane sultone and lithium difluorophosphate in the non-aqueous electrolyte, so after the initial charge and discharge, it is easy to obtain the effect of suppressing the consumption of propane sultone by lithium difluorophosphate and the effect of suppressing gas generation by propane sultone.

[0304] According to at least one of these embodiments or examples, a secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte can be provided. The positive electrode includes a positive electrode composite material layer containing a positive electrode active material and sulfur atoms. The mass of sulfur atoms per unit volume of the positive electrode composite material 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 mass % or more. The concentration of lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass % or more. Therefore, it is possible to provide a secondary battery that can suppress the amount of gas generated at high temperature and the increase in resistance and can achieve excellent life performance even at high temperature.

[0305] Furthermore, the above-mentioned implementation modes can be summarized as the following technical solutions.

[0306] (Technical Solution 1)

[0307] A secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,

[0308] The positive electrode comprises a positive electrode composite material layer containing a positive electrode active material and sulfur atoms.

[0309] The mass of the sulfur atoms per unit volume of the positive electrode composite material layer is 430 g / m 3 the following,

[0310] The non-aqueous electrolyte contains propane sultone and lithium difluorophosphate.

[0311] The concentration of the propane sultone in the non-aqueous electrolyte is 0.5 mass % or more,

[0312] The concentration of the lithium difluorophosphate in the non-aqueous electrolyte is 0.2 mass % or more.

[0313] (Technical Solution 2)

[0314] The secondary battery according to claim 1, wherein the negative electrode includes a negative electrode composite material layer containing a negative electrode active material and sulfur atoms.

[0315] (Technical Solution 3)

[0316] According to the secondary battery of technical solution 2, the mass of the sulfur atoms per unit volume of the negative electrode composite material layer is 430 g / m 3 the following.

[0317] (Technical Solution 4)

[0318] A battery pack comprises the secondary battery according to any one of technical solutions 1 to 3.

[0319] (Technical Solution 5)

[0320] The battery pack according to technical solution 4 further comprises:

[0321] External terminals for electrical connection; and

[0322] Protection circuit.

[0323] (Technical Solution 6)

[0324] The battery pack according to claim 4 or 5, wherein the battery pack comprises a plurality of the secondary batteries.

[0325] The secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

[0326] (Technical Solution 7)

[0327] A vehicle comprises the battery pack according to any one of technical solutions 4 to 6.

[0328] (Technical Solution 8)

[0329] The vehicle according to Technical Solution 7 includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

[0330] In addition, several embodiments of the present invention have been described, but 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 ways, and various omissions, substitutions, and changes can be made without departing from the scope of the subject matter of the invention. These embodiments and their variations are included in the scope and subject matter of the invention, and are also included in the invention described in the claims and their equivalents.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, The positive electrode comprises a positive electrode composite material layer containing a positive electrode active material and sulfur atoms. The mass of the sulfur atoms per unit volume of the positive electrode composite material layer is 430 g / m 3 the following, 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 composite material layer containing a negative electrode active material and sulfur atoms.

3. The secondary battery according to claim 2, wherein: The mass of the sulfur atoms per unit volume of the negative electrode composite material layer is 430 g / m 3 the following. 4 . A battery pack comprising the secondary battery according to claim 1 .

5. The battery pack according to claim 4, wherein: Further including: External terminals for electrical connection; and Protection circuit.

6. The battery pack according to claim 4 or 5, wherein: A plurality of the secondary batteries are provided, 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 according to claim 4 .

8. The vehicle according to claim 7, wherein: A mechanism is included for converting the kinetic energy of the vehicle into regenerative energy.

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