Method for manufacturing secondary battery

Abstract

The present invention realizes a manufacturing method for improving the performance of a secondary battery. The manufacturing method includes: a negative electrode forming step of forming a negative electrode including a negative electrode active material and a first electrolyte solution; a positive electrode forming step of forming a positive electrode containing a positive electrode active material and a second electrolyte solution; a cell forming step of forming a cell in which a separator is positioned between the negative electrode and the positive electrode; and a pre-charging step of pre-charging the battery cell. The composition ratio of the components of the first electrolyte solution and the composition ratio of the components of the second electrolyte solution are different from each other.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a secondary battery. Background Art

[0002] In Patent Document 1, an electric storage device is disclosed, which includes: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a first non-aqueous electrolyte in contact with the positive electrode active material; a second non-aqueous electrolyte in contact with the negative electrode active material; and a solid electrolyte membrane. In this electric storage device, the first non-aqueous electrolyte and the second non-aqueous electrolyte are separated by the solid electrolyte membrane. Further, the composition of the first non-aqueous electrolyte and the composition of the second non-aqueous electrolyte are different from each other.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-21677. Summary of the Invention

[0006] A method for manufacturing a secondary battery according to one aspect of the present invention includes: a negative electrode forming step of forming a negative electrode containing a negative electrode active material and a first electrolyte; a positive electrode forming step of forming a positive electrode containing a positive electrode active material and a second electrolyte; a battery cell forming step of forming a battery cell having a separator through which the first electrolyte and the second electrolyte can penetrate, between the negative electrode and the positive electrode; and a pre-charging step of pre-charging the battery cell. The composition ratio of the components contained in the first electrolyte is different from the composition ratio of the components contained in the second electrolyte.

[0007] In addition, a method for manufacturing a secondary battery according to one aspect of the present invention includes: a battery cell forming step of forming a battery cell having a separator through which a first electrolyte and a second electrolyte can penetrate, between a negative electrode and a positive electrode; a first electrolyte injection step of injecting the first electrolyte into the negative electrode; a second electrolyte injection step of injecting the second electrolyte into the positive electrode; and a pre-charging step of pre-charging the battery cell. The composition ratio of the components contained in the first electrolyte is different from the composition ratio of the components contained in the second electrolyte. Brief Description of the Drawings

[0008] Figure 1 is a perspective view showing the appearance of the secondary battery of the present invention.

[0009] Figure 2 is a perspective view showing the appearance of the battery cell of the present invention.

[0010] Figure 3 is for Figure 1The model diagram shown by decomposing the cross-section at the III-III line.

[0011] Figure 4 is a decomposition of Figure 1 The model diagram shown by decomposing the cross-section at the IV-IV line.

[0012] Figure 5 It is a cross-sectional view showing the specific structure of the electrode body.

[0013] Figure 6 It is a flowchart showing the manufacturing method of the secondary battery according to Embodiment 1 of the present invention.

[0014] Figure 7 It is a schematic diagram showing the manufacturing method of the secondary battery according to Embodiment 2 of the present invention. Detailed Embodiments

[0015] [Embodiment 1]

[0016] (Configuration of the secondary battery)

[0017] Figure 1 It is a perspective view showing the appearance of the secondary battery 1. The secondary battery 1 is a battery that can be charged or discharged by being electrically connected to an external terminal. For example, at least one secondary battery 1 can be mounted on a power storage device for residential use, base station use, vehicle use, robots such as drones, and medical instruments. The secondary battery 1 may include a battery cell 10, connection terminals 21 and 22, and a second housing 50. The configuration of the battery cell 10 will be described later.

[0018] The second housing 50 can accommodate the battery cell 10. The second housing 50 can be formed of, for example, an aluminum plastic film or a laminated film having a metal foil layer such as stainless steel or nickel. The aluminum plastic film can be a film obtained by vapor-depositing aluminum on a film or a film obtained by laminating an aluminum foil and a film. The material of the film can be, for example, polypropylene, polyethylene, nylon, or polyethylene terephthalate. The thickness of the second housing 50 can be 50 μm or more and 300 μm or less, and can be 200 μm, for example.

[0019] When the second housing 50 is an aluminum plastic film, the second housing 50 can have a structure in which two aluminum plastic films are located on both sides in the stacking direction (Z-axis direction) of the battery cell 10. In addition, when the second housing 50 is an aluminum plastic film, the second housing 50 can have a structure in which one aluminum plastic film is folded in half and the battery cell 10 is disposed inside.

[0020] Since the connection terminals 21 and 22 extract power from the secondary battery 1 or supply power to the secondary battery 1, they can be terminals connected to external terminals. The connection terminals 21 and 22 can protrude from the inside of the second housing 50 to the outside. The material of the connection terminals 21 and 22 can be, for example, copper, aluminum, or nickel. The thickness of the connection terminals 21 and 22 can be 50 μm or more and 500 μm or less, and can be, for example, 200 μm. In addition, surface treatment for improving the adhesiveness with an adhesive member (not shown) can be performed on the connection terminals 21 and 22. In order to determine the positions of the connection terminals 21 and 22 relative to the second housing 50, the adhesive member bonds the connection terminals 21 and 22 to the second housing 50, and the second housing 50 is located above and below the connection terminals 21 and 22.

[0021] Figure 2 FIG. is a perspective view showing the appearance of the battery cell 10. As Figure 2 shown, the battery cell 10 can have an electrode body 14 and a first housing 15. The electrode body 14 can have a sheet-like shape. The sheet-like electrode body 14 can have a negative electrode 11 and a positive electrode 12.

[0022] The first housing 15 can accommodate the electrode body 14. When a plurality of first housings 15 accommodating the electrode body 14 are stacked, the plurality of first housings 15 can be bonded to each other through an adhesive layer (not shown). The material of the first housing 15 can be, for example, a film-like PET (Polyethylene terephthalate) or nylon. More specifically, for example, two first housings 15 can have a structure located on both sides in the stacking direction (Z-axis direction) of the battery cell 10. The thickness of the base material of the first housing 15 can be 10 μm or more and 40 μm or less, and can be, for example, 25 μm. The material of the adhesive layer can be, for example, polypropylene or polyethylene.

[0023] The first housing 15 can be transparent, for example. Figure 2 FIG. is a view showing that by using the transparent first housing 15 in the battery cell 10, the state of the electrode body 14 can be confirmed through the first housing 15.

[0024] The negative electrode 11 can have an exposed portion 11e exposed from the first housing 15. The positive electrode 12 can have an exposed portion 12e exposed from the first housing 15. The connection terminals 21 and 22 can be electrically connected to the exposed portions 11e and 12e, respectively, by ultrasonic welding, laser welding, or resistance welding. Details of the negative electrode 11 and the positive electrode 12 will be described later.

[0025] The secondary battery 1 may have a structure in which the battery cell 10 is further accommodated in the second container 50, and the battery cell 10 accommodates the negative electrode 11 and the positive electrode 12 in the first container 15. By having this structure, since the electrode body 14 is doubly accommodated, the safety of the secondary battery 1 can be improved. In addition, the second container 50 may be accommodated in another container. However, the secondary battery 1 only needs to be a battery having a negative electrode 11 and a positive electrode 12, and only needs to be accommodated in at least one container.

[0026] In Embodiment 1, the secondary battery 1 has a structure in which a plurality of battery cells 10 are stacked. For example, it has a structure in which 10 layers of battery cells 10 are stacked. However, the secondary battery 1 of the present invention may have a plurality of layers of battery cells 10 different from 10 layers, or may have only 1 layer. When the secondary battery 1 has a plurality of layers of battery cells 10, those battery cells 10 may be stacked. In a plan view Figure 1 In the case of the secondary battery 1 shown, the portion where the connection terminals 21 and 22 are removed may be substantially rectangular, or may have a different shape. In addition, in a plan view Figure 2 In the case of the battery cell 10 shown, the portion where the exposed portions 11e and 12e are removed may be substantially rectangular, or may have a different shape.

[0027] Figure 3 is a model diagram showing a cross-section taken along line III-III of Figure 1 decomposed. Figure 4 is a model diagram showing a cross-section taken along line IV-IV of Figure 1 decomposed. For simplicity, the second container 50 is omitted in Figure 3 and Figure 4 . In addition, Figure 3 and Figure 4 are diagrams mainly showing the positional relationship of each component. Therefore, the size relationship of the thickness of each component is not necessarily as shown in Figure 3 and Figure 4 .

[0028] In addition, as shown in Figure 3 and Figure 4 , the negative electrode 11 may have an electrode conductor 11a and a negative electrode active material layer 11b. The positive electrode 12 may have an electrode conductor 12a and a positive electrode active material layer 12b.

[0029] The electrode conductor 11a may be, for example, a copper foil. The thickness of the electrode conductor 11a may be 5 μm or more and 25 μm or less, and may be 10 μm, for example. The electrode conductor 12a may be, for example, an aluminum foil. The thickness of the electrode conductor 12a may be 5 μm or more and 25 μm or less, and may be 10 μm, for example.

[0030] Figure 5 It is a cross-sectional view showing the specific structure of the electrode body 14. Figure 5 The shown cross-sectional view is a view of the electrode body 14 just manufactured. As Figure 5 shown, the negative electrode active material layer 11b can be a layer of a positive electrode material, and the positive electrode material is a mixture of a negative electrode active material 11c, a conductive assistant 11d, and a first electrolyte 11f. In addition, the positive electrode active material layer 12b can be a layer of a negative electrode material, and the negative electrode material is a mixture of a positive electrode active material 12c, a conductive assistant 12d, and a second electrolyte 12f. The negative electrode active material 11c, for example, can be graphite, silicon, or lithium titanate. The positive electrode active material 12c, for example, can be lithium cobaltate, lithium nickelate, lithium iron phosphate, or lithium manganate. The conductive assistants 11d and 12d, for example, can be carbon black or acetylene black. However, the negative electrode active material 11c, the positive electrode active material 12c, the conductive assistants 11d, and 12d are not limited to these. In addition, for the conductive assistants 11d, 12d, they are sometimes omitted in the following description.

[0031] The first electrolyte and the second electrolyte can be electrolytes in which an Li salt and an additive are dissolved in a solvent. The specific components and composition ratios of the first electrolyte and the second electrolyte will be described later.

[0032] The negative electrode material can have a clay-like property of mixing the first electrolyte into the mixture composed of the negative electrode active material 11c and the conductive assistant 11d. The positive electrode material can have a clay-like property of mixing the second electrolyte into the mixture composed of the negative electrode active material 12c and the conductive assistant 13d. The negative electrode 11 can be an electrode in which the negative electrode material is coated on the electrode conductor 11a. The positive electrode 12 can be an electrode in which the positive electrode material is coated on the electrode conductor 12a.

[0033] In addition, the electrode body 14 can further have a separator 13. The negative electrode 11, the positive electrode 12, and the separator 13 can have a positional relationship such that the negative electrode active material layer 11b and the positive electrode active material layer 12b are in contact with the separator 13. That is, the battery cell 10 can have a structure in which the negative electrode 11 and the positive electrode 12 are laminated via the separator 13. The separator 13 can function as an insulating member that insulates the negative electrode 11 and the positive electrode 12. In the separator 13, for example, a sheet-like non-woven fabric or a porous material can be used. Therefore, the first electrolyte and the second electrolyte can penetrate into the separator 13.

[0034] At the moment when the electrode body 14 is just manufactured, with respect to the spacer 13, only the first electrolyte exists on the negative electrode 11 side, and only the second electrolyte exists on the positive electrode 12 side. However, the first electrolyte can permeate from the negative electrode 11 side to the spacer 13 and move toward the positive electrode 12 side. In addition, the second electrolyte can permeate from the positive electrode 12 side to the spacer 13 and move toward the negative electrode 11 side. Therefore, after the electrode body 14 is manufactured, with respect to the spacer 13, both the negative electrode 11 side and the positive electrode 12 side will be in a state where an electrolyte in which the first electrolyte and the second electrolyte are mixed exists. After a sufficiently long time has passed after the electrode body 14 is manufactured, with respect to the spacer 13, the difference in the composition ratio of the components of the electrolyte disappears on the negative electrode 11 side and the positive electrode 12 side. In the following description, the electrolyte in which the first electrolyte and the second electrolyte are mixed is referred to as the mixed electrolyte.

[0035] In the case of using a porous material as the spacer 13, specifically, a porous membrane made of a thermoplastic resin having a melting point of about 80°C to 140°C can be used. As the thermoplastic resin, for example, polyolefin-based polymers such as polypropylene and polyethylene, or polyethylene terephthalate can be used. In addition, as the spacer 13, a spacer in which a porous ceramic layer is coated on a porous membrane formed of a thermoplastic resin can be used.

[0036] In the case of using a negative electrode material and a positive electrode material having a clay-like property, an adhesive can be used between the negative electrode 11 and the positive electrode 12 and the spacer. In addition, before the electrode forming of the negative electrode 11 and the positive electrode 12, an electrolyte is mixed into the negative electrode material and the positive electrode material. Therefore, the performance of the negative electrode 11 and the positive electrode 12 can be improved. By mixing the electrolyte into the negative electrode material and the positive electrode material, the number of processes in the electrode forming of the negative electrode 11 and the positive electrode 12 can be reduced compared with the case of using a negative electrode material and a positive electrode material into which no electrolyte is mixed. In addition, in the manufacturing process of the secondary battery, the process of injecting the electrolyte can be reduced. Further, compared with the case of using a negative electrode material and a positive electrode material into which no electrolyte is mixed, the negative electrode material and the positive electrode material can be thickly coated on the electrode conductor. Therefore, when realizing a secondary battery having a specified storage capacity, the number of electrode conductors and spacers used can be reduced compared with the case of using a negative electrode material and a positive electrode material having no clay-like property. Therefore, the component cost can be reduced and the energy density can be improved.

[0037] The negative electrode material and the positive electrode material may not have a clay-like property. In this case, the electrolytic solution may not be mixed into the negative electrode active material 11c and the positive electrode active material 12c. For example, the negative electrode material is a negative electrode paste composed of a mixture of the negative electrode active material 11c and the conductive assistant 11d, a binder, and a solvent. The negative electrode paste may be applied to the electrode conductor 11a and dried to form the negative electrode active material layer 11b. The solvent of the negative electrode paste may be water, for example. In addition, the positive electrode material is a positive electrode paste composed of a mixture of the positive electrode active material 12c and the conductive assistant 12d, a binder, and a solvent. The positive electrode paste may be applied to the electrode conductor 12a and dried to form the positive electrode active material layer 12b. The binder may be polyvinylidene fluoride (PVDF) or polyethylene oxide (PEO), etc. The solvent of the positive electrode paste may be an organic solvent such as N-methyl-2-pyrrolidone (NMP), for example. In addition, in this case, the electrolytic solution is filled inside the battery cell 10, and the electrolytic solution may be impregnated and held in the spacer 13.

[0038] (Method for manufacturing a secondary battery)

[0039] Figure 6 It is a flowchart showing the manufacturing method of the secondary battery 1 of Embodiment 1. The manufacturing method of the secondary battery 1 is as follows. First, a negative electrode 11 containing the negative electrode active material 11c and the first electrolytic solution is formed (S1, negative electrode forming step). Specifically, the above-mentioned clay-like negative electrode material may be applied to the electrode conductor 11a. Next, a positive electrode 12 containing the positive electrode active material 12c and the second electrolytic solution is formed (S2, positive electrode forming step). Specifically, the above-mentioned clay-like positive electrode material may be applied to the electrode conductor 12a.

[0040] Furthermore, a battery cell 10 is formed in which the spacer 13 is located between the formed negative electrode 11 and positive electrode 12 (S3, battery cell forming step). Specifically, on one surface of the spacer 13, the negative electrode 11 may be laminated such that the negative electrode active material layer 11b side is in contact with the spacer 13. Further, the positive electrode 12 may be laminated on the other surface of the spacer 13 such that the positive electrode active material layer 12b side is in contact with the spacer 13. Then, the battery cell 10 is pre-charged (S4 pre-charging step). By setting the pre-charged battery cells 10 in a stacked state in plural, the secondary battery 1 can be manufactured. In addition, the battery cell 10 in a pre-stacked state may also be pre-charged.

[0041] In the pre-charging step, relative to the spacer 13, by decomposing the mixed electrolyte on the negative electrode 11 side, a SEI (Solid Electrolyte Interface) film is formed on the surface of the negative electrode active material 11c. In addition, in the pre-charging step, relative to the spacer 13, by decomposing the mixed electrolyte on the positive electrode 12 side, a CEI (Cathode Electrolyte Interface) film is formed on the surface of the positive electrode active material 12c. The SEI film and the CEI film are films that exhibit conductivity through the movement of Li + ions and do not exhibit conductivity through the movement of electrons. In other words, the SEI film and the CEI film have the function of inserting and removing Li + ions in the negative electrode active material 11c and the positive electrode active material 12c.

[0042] In addition, if the mixed electrolyte is decomposed, the amount of Li + decreases, and the performance of the secondary battery 1 deteriorates. The SEI film and the CEI film have the function of reducing the further decomposition of the mixed electrolyte after the formation of the SEI film and the CEI film. Therefore, the SEI film and the CEI film are necessary films for reducing the decomposition of the mixed electrolyte. However, if the SEI film and the CEI film are too thick, the resistance increases, which has an adverse effect on the performance of the secondary battery 1. As specific examples of the performance of the secondary battery 1, the capacity retention rate and the area specific impedance after repeating a specified number of charge and discharge cycles can be cited.

[0043] In order to improve the performance of the secondary battery 1, it is sufficient to form a good SEI film on the negative electrode active material 11c and a good CEI film on the positive electrode active material 12c. Specifically, if the thickness is 100 nm or less, 50 nm or less, and further 30 nm or less and the deviation of the thickness is small, it can be called a good SEI film or CEI film. A good SEI film or CEI film can be further stable, have no electron conductivity, and have high Li ion conductivity.

[0044] (Electrolyte)

[0045] As described above, the first electrolyte and the second electrolyte are electrolytes in which a Li salt and an additive are dissolved in a solvent. The composition ratios of the components contained in the first electrolyte in the negative electrode formation step and the second electrolyte in the positive electrode formation step are different from each other.

[0046] As described above, after the battery cell 10 is manufactured, after a sufficiently long time, the difference in the composition ratio of the components of the mixed electrolyte disappears on the negative electrode 11 side and the positive electrode 12 side with respect to the separator 13. However, after the battery cell 10 is manufactured and before a sufficiently long time has passed, there is a difference in the composition ratio of the components of the mixed electrolyte on the negative electrode 11 side and the positive electrode 12 side. The pre-charging step is performed after the battery cell 10 is manufactured and before a sufficiently long time has passed. Therefore, in the pre-charging step, the pre-charging is performed in a state where there is a difference in the composition ratio of the components of the mixed electrolyte on the negative electrode 11 side and the positive electrode 12 side.

[0047] In the electrolyte, the components that contribute to the formation of a good SEI film on the surface of the negative electrode active material 11c and the components that contribute to the formation of a good CEI film on the surface of the positive electrode active material 12c are different from each other. In a secondary battery having a solid electrolyte membrane, although the types of ions contained in the electrolyte permeate through the solid electrolyte membrane, since organic solvent molecules do not permeate through the solid electrolyte membrane, there has conventionally been a secondary battery in which the composition ratio of the components of the electrolyte on the negative electrode side and the positive electrode side is different, as disclosed in Patent Document 1 and the like. In contrast, in a secondary battery having a porous separator, since the electrolyte can penetrate, a single electrolyte has conventionally been used on both the negative electrode side and the positive electrode side. Therefore, in an existing secondary battery having a porous separator, one or both of the SEI formed on the surface of the negative electrode active material and the CEI formed on the surface of the positive electrode active material are not good, resulting in a decrease in the performance of the secondary battery.

[0048] As a result of intensive research by the inventors of the present invention, the following knowledge was obtained. That is, the SEI film and the CEI film formed in a state where there is a difference in the composition ratio of the components contained in the mixed electrolyte on the negative electrode 11 side and the positive electrode 12 side have an impact on the performance of the secondary battery 1 even after the difference in the composition ratio of the components contained in the mixed electrolyte on the negative electrode 11 side and the positive electrode 12 side disappears. Based on this knowledge, the inventors of the present invention completed the manufacturing method of the secondary battery 1 of the present invention by making the composition ratio of the components contained in the first electrolyte different from the composition ratio of the components contained in the second electrolyte, thereby forming a good SEI film and CEI film. According to this manufacturing method, there is no need to use a separator formed of a solid material having a high resistivity, and the performance of the secondary battery 1 using a separator such as a porous material having a low resistivity can be improved.

[0049] In addition, among the components of the electrolytic solution, there are components that do not have a beneficial effect or have an adverse effect on the performance of the secondary battery 1 at the moment of forming the SEI film and the CEI film, but have a beneficial effect on the performance of the secondary battery 1 after the formation of the SEI film and the CEI film. By making the composition ratios of such components in the first electrolytic solution and the second electrolytic solution different, the performance of the secondary battery 1 can also be improved.

[0050] (Solvent)

[0051] The first electrolytic solution contains a first solvent as the solvent, and the first solvent forms a good SEI film on the surface of the negative electrode active material 11c in the pre-charging step. The volume% concentration of the first solvent contained in the first electrolytic solution can be higher than the volume% concentration of the first solvent contained in the second electrolytic solution. In other words, the second electrolytic solution can contain the first solvent at a volume% concentration lower than the volume% concentration of the first solvent contained in the first electrolytic solution. In addition, the second electrolytic solution may not contain the first solvent.

[0052] The first solvent can be ethylene carbonate. For ethylene carbonate, in the pre-charging step, the higher the volume% concentration contained in the mixed electrolytic solution on the negative electrode 11 side, the better the SEI film formed on the surface of the negative electrode active material 11c. Therefore, by making the volume% concentration of ethylene carbonate contained in the first electrolytic solution higher than the volume% concentration of ethylene carbonate contained in the second electrolytic solution, a good SEI film can be formed on the surface of the negative electrode active material 11c.

[0053] In addition, the second electrolytic solution can contain a second solvent as the solvent, and the second solvent causes an adverse situation due to its presence on the negative electrode 11 side in the pre-charging step. Examples of the second solvent include propylene carbonate or γ-butyrolactone. The volume% concentration of the second solvent contained in the second electrolytic solution can be higher than the volume% concentration of the second solvent contained in the first electrolytic solution. In other words, the first electrolytic solution can also contain the second solvent at a volume% concentration lower than the volume% concentration of the second solvent contained in the second electrolytic solution. In addition, the first electrolytic solution may not contain the second solvent.

[0054] For propylene carbonate, in the pre-charging step, there is an adverse situation that a good SEI film cannot be formed on the surface of the negative electrode active material 11c. In addition, for γ-butyrolactone, in the pre-charging step, there is an adverse situation that a film with a high resistivity is formed on the surface of the negative electrode active material 11c. However, after the formation of the SEI film, compared with before the formation of the SEI film, by making propylene carbonate and γ-butyrolactone present on the negative electrode 11 side, the above-mentioned adverse situation is reduced. On the other hand, since the freezing points of propylene carbonate and γ-butyrolactone are lower than that of ethylene carbonate, it has a beneficial effect on the performance of the secondary battery 1 in a low-temperature environment.

[0055] By setting the volume % concentration of the second solvent contained in the second electrolyte to be higher than the volume % concentration of the second solvent contained in the first electrolyte, the second solvent moves from the positive electrode 12 side to the negative electrode 11 side over time after the pre-charging step. Thereby, after the formation of the SEI film, the concentration of the second solvent on the negative electrode 11 side increases, and the performance of the secondary battery 1 in a low-temperature environment is improved.

[0056] In addition, for the second solvent, in addition to propylene carbonate or γ-butyrolactone, a nitrile / sulfone-based solvent may also be contained. These solvents have high oxidation resistance and low reduction resistance. Therefore, in the pre-charging step, these solvents are preferably contained more near the surface of the positive electrode active material 12c than near the surface of the negative electrode active material 11c.

[0057] (Additive)

[0058] The first electrolyte and the second electrolyte may contain additives. The composition of the additives contained in the first electrolyte and the composition of the additives contained in the second electrolyte may be different from each other.

[0059] The additives contained in the first electrolyte and the second electrolyte include a first additive that forms a good SEI film on the surface of the negative electrode active material 11c in the pre-charging step. The mass % concentration of the first additive contained in the first electrolyte may be higher than the mass % concentration of the first additive contained in the second electrolyte. In other words, the second electrolyte may contain the first additive at a mass % concentration lower than the mass % concentration of the first additive contained in the first electrolyte. In addition, the second electrolyte may not contain the first additive.

[0060] The first additive, for example, may contain one or more of vinylene carbonate, fluoroethylene carbonate, succinic anhydride, maleic anhydride, 1,3-propane sultone, ethylene sulfite, ethylenesulfite, lithium bis(oxalate)borate, and lithium difluoro(oxalate)borate. Vinylene carbonate, fluoroethylene carbonate, maleic anhydride, 1,3-propane sultone, ethylene sulfite, ethylenesulfite, lithium bis(oxalate)borate, and lithium difluoro(oxalate)borate are reduced at a potential lower than that of the solvent of the first electrolyte. By using such an additive as the first additive, a good SEI film can be formed on the surface of the negative electrode active material 11c.

[0061] In addition, for the first electrolyte, as the first additive, for example, it may contain more methyl benzoate, succinic anhydride, succinimide, dialkyl pyrocarbonate, etc. than the second electrolyte. Although these additives themselves are not reduced, the solvent reacts with the reduced intermediate or product, and a good SEI film can be formed on the surface of the negative electrode active material 11c.

[0062] The additives contained in the first electrolyte and the second electrolyte contain a second additive, and the second additive forms a good CEI film on the surface of the positive electrode active material 12c during the pre-charging step. The mass% concentration of the second additive contained in the second electrolyte can be higher than the mass% concentration of the second additive contained in the first electrolyte. In other words, the first electrolyte can contain the second additive at a mass% concentration lower than the mass% concentration of the second additive contained in the second electrolyte. Additionally, the first electrolyte may not contain the second additive.

[0063] The second additive can contain, for example, one or more of vinylene carbonate, fluoroethylene carbonate, ethylene sulfite, adiponitrile, biphenyl, and lithium difluorophosphate (LiPO2F2). For example, vinylene carbonate and biphenyl are oxidized and polymerized on the surface of the positive electrode active material 12c to form a CEI film. Fluoroethylene carbonate and lithium difluorophosphate (LiPO2F2) form a stable CEI film such as LiF or Li3PO4 through oxidative decomposition. Dinitrile compounds such as adiponitrile coordinate on the surface of the positive electrode active material 12c through functional groups to form a CEI film that blocks the active sites on the surface of the positive electrode active material 12c. Ethylene sulfite forms a CEI film that inactivates the active sites of the positive electrode active material 12c by adsorbing on the surface of the positive electrode active material 12c, thereby reducing the generation of CO2 and making it difficult for the interfacial resistance to increase. By using such an additive as the second additive, a good CEI film can be formed on the surface of the positive electrode active material 12c.

[0064] Depending on the materials of the negative electrode active material 11c and the positive electrode active material 12c, fluoroethylene carbonate and ethylene sulfite can function as either the first additive or the second additive. Therefore, fluoroethylene carbonate and ethylene sulfite are listed in both the first additive and the second additive.

[0065] (Li salt)

[0066] The first electrolyte and the second electrolyte can contain a Li salt. The composition of the Li salt contained in the first electrolyte and the composition of the Li salt contained in the second electrolyte can be different from each other.

[0067] The first electrolyte can contain a first Li salt that generates hydrofluoric acid (HF) through hydrolysis. The molar concentration of the first Li salt contained in the first electrolyte can be higher than the molar concentration of the first Li salt contained in the second electrolyte. In other words, the second electrolyte can contain the first Li salt at a molar concentration lower than the molar concentration of the first Li salt contained in the first electrolyte. Additionally, the second electrolyte may not contain the first Li salt. The first Li salt can contain one or more of LiPF6 and LiBF4.

[0068] HF generated by hydrolysis of the first Li salt helps to form a good SEI film on the surface of the negative electrode active material 11c during the pre-charging step. On the other hand, HF deteriorates the performance of the secondary battery 1 by promoting the dissolution of transition metals from the positive electrode active material 12c. By making the first electrolyte contain more of the first Li salt, a good SEI film can be formed on the surface of the negative electrode active material 11c.

[0069] In addition, when the electrode conductor 12a is aluminum, HF forms a passivation film of fluoride (AlF3) on the electrode conductor 12a during the pre-charging step, so as to achieve the effect of reducing the corrosion of the electrode conductor 12a. Therefore, when the electrode conductor 12a is aluminum, the second electrolyte may contain a small amount of the first Li salt. Specifically, the second electrolyte may contain the first Li salt in a range of 1 mol / L or less.

[0070] In addition, the first electrolyte may contain one or more of LiFSI and LiTFSI. The molar concentration of LiFSI or LiTFSI contained in the first electrolyte may be higher than the molar concentration of LiFSI or LiTFSI contained in the second electrolyte. In other words, the second electrolyte may contain LiFSI and LiTFSI at a molar concentration lower than the molar concentration of LiFSI and LiTFSI contained in the first electrolyte. In addition, the second electrolyte may not contain LiFSI and LiTFSI.

[0071] LiFSI and LiTFSI form a film derived from FSI on the surface of the negative electrode active material 11c. The film derived from FSI improves the cycle characteristics of the secondary battery 1, so as to further improve the Coulomb efficiency in the first charge and discharge (for example, refer to Journal of Power Sources 375 (2018) 43-52). Therefore, by increasing the molar concentration of LiFSI or LiTFSI contained in the first electrolyte, the deterioration of the performance of the secondary battery 1 can be reduced.

[0072] In addition, LiFSI and LiTFSI corrode aluminum. However, as described above, when the electrode conductor 12a is aluminum and the second electrolyte contains a small amount of the first Li salt, a passivation film is formed on the electrode conductor 12a. This passivation film also reduces the corrosion of the electrode conductor 12a caused by LiFSI and LiTFSI. Therefore, in this case, LiFSI or LiTFSI contained in the first electrolyte exists more on the negative electrode 11 side during the pre-charging step and can move to the positive electrode 12 side over time.

[0073] (Example)

[0074] The performance of the secondary battery 1 manufactured by the manufacturing method of the present embodiment and the secondary battery manufactured by the manufacturing method of the comparative example will be described below.

[0075] Table 1 is a table showing the composition ratios of five components contained in the first electrolyte and the second electrolyte for the manufacturing method of the present embodiment and the manufacturing method of the comparative example. In Table 1, LiPF6 (the first Li salt) is the Li salt. In addition, EC (ethylene carbonate, the first solvent), PC (propylene carbonate, the second solvent), and GBL (γ-butyrolactone, the second solvent) are solvents. In addition, VC (vinylene carbonate, the first additive) is an additive.

[0076] Table 1

[0077]

[0078] In the comparative example, the composition ratios of the components contained in the first electrolyte and the second electrolyte were set to be the same as each other. In Example 1, the mass% concentration of VC as the first additive in the first electrolyte was set to be higher than that in the second electrolyte. In Example 2, the volume% concentration of EC as the first solvent in the first electrolyte was set to be higher than that in the second electrolyte, and the volume% concentration of GBL as the second solvent in the second electrolyte was set to be higher than that in the first electrolyte. In Example 3, the molar concentration of LiPF6 as the first Li salt in the first electrolyte was set to be higher than that in the second electrolyte.

[0079] Table 2 is a table showing the performance of two samples of the secondary batteries of the examples and comparative examples shown in Table 1 after repeating charge and discharge 100 times at a charge and discharge rate of 0.3C in an environment of 45°C. In Table 2, Capacity retention refers to the capacity retention rate. ASI refers to the area specific impedance. N1 and N2 represent the samples of the secondary batteries of the examples and comparative examples.

[0080] Table 2

[0081]

[0082] Regarding the capacity retention rate, the performance of the secondary battery with a larger value is higher than that of the secondary battery with a smaller value. Regarding the area specific impedance, the performance of the secondary battery with a smaller value is higher than that of the secondary battery with a larger value. As shown in Table 2, the samples of the examples all showed higher performance than the samples with higher performance in the comparative example. Therefore, it can be said that according to the manufacturing methods of the respective examples, secondary batteries with performance higher than that of the manufacturing method of the comparative example can be manufactured.

[0083] In the manufacturing method of the present embodiment, the molar concentration of LiPF6 as the first Li salt is not limited to the value of this example. The molar concentration of LiPF6 can be, for example, 0.3 mol / L or more and 3.0 mol / L or less in the first electrolyte, and 0 mol / L or more and 2.0 mol / L or less in the second electrolyte.

[0084] In addition, in the manufacturing method of the present embodiment, the volume% concentration of ethylene carbonate as the first solvent is not limited to the value of this example. The volume% concentration of ethylene carbonate can be, for example, 20% by volume or more and 80% by volume or less in the first electrolyte, and 0% by volume or more and 50% by volume or less in the second electrolyte.

[0085] In addition, in the manufacturing method of the present embodiment, the volume% concentration of propylene carbonate as the second solvent is not limited to the value of this example. The volume% concentration of propylene carbonate can be, for example, 0% by volume or more and 50% by volume or less in the first electrolyte, and 20% by volume or more and 80% by volume or less in the second electrolyte.

[0086] In addition, in the manufacturing method of the present embodiment, the volume% concentration of γ-butyrolactone as the second solvent is not limited to the value of this example. The volume% concentration of γ-butyrolactone can be, for example, 0% by volume or more and 50% by volume or less in the first electrolyte, and 20% by volume or more and 80% by volume or less in the second electrolyte.

[0087] In addition, in the manufacturing method of the present embodiment, the mass% concentration of vinylene carbonate as the first additive is not limited to the value of this example. The mass% concentration of vinylene carbonate can be, for example, 2% by mass or more and 10% by mass or less in the first electrolyte, and 0% by mass or more and 5% by mass or less in the second electrolyte.

[0088] As described above, according to the manufacturing method of the secondary battery of the present invention, the performance of the secondary battery can be improved. Therefore, the consumption of the secondary battery can be reduced, and the amount of waste of the secondary battery can be reduced. Such an effect contributes, for example, to achieving Goal 12, "Responsible production and consumption," of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0089] [Embodiment 2]

[0090] Figure 7 is a schematic diagram showing the manufacturing method of the secondary battery 1 of Embodiment 2. In Figure 7 it, reference numeral 701 is a schematic diagram showing the negative electrode formation step. Reference numeral 702 is a schematic diagram showing the positive electrode formation step. Reference numeral 703 is a schematic diagram showing the battery cell formation step.

[0091] As shown by reference numeral 701, in the negative electrode forming step of Embodiment 2, the negative electrode 11 is formed by immersing the electrode conductor 11a and the negative electrode active material 11c previously coated on the electrode conductor 11a in the first electrolytic solution 11f in a vacuum. Further, as shown by reference numeral 702, in the positive electrode forming step of Embodiment 2, the positive electrode 12 is formed by immersing the electrode conductor 12a and the positive electrode active material 12c previously coated on the electrode conductor 12a in the second electrolytic solution 12f in a vacuum.

[0092] In the battery cell forming step of Embodiment 2, excess first electrolytic solution is removed from the surface of the negative electrode 11 formed as described above, and excess second electrolytic solution is removed from the surface of the positive electrode 12. In this state, as shown by reference numeral 703, the battery cell 10 is formed with the spacer 13 positioned between the negative electrode 11 and the positive electrode 12. After the battery cell 10 is formed, pre-charging is performed as described in the manufacturing method of Embodiment 1.

[0093] Even in the manufacturing method of Embodiment 2, the composition ratio of the components contained in the first electrolytic solution can be made different from the composition ratio of the components contained in the second electrolytic solution. Therefore, the manufacturing method of Embodiment 2 also exhibits the same effects as the manufacturing method of Embodiment 1.

[0094] [Embodiment 3]

[0095] In the manufacturing methods of Embodiments 1 and 2, at the moment when the battery cell 10 is formed, the negative electrode 11 contains the first electrolytic solution, and the positive electrode 12 contains the second electrolytic solution. However, it is possible to form a battery cell in which the negative electrode does not contain the first electrolytic solution and the positive electrode does not contain the second electrolytic solution, and then inject the first electrolytic solution into the negative electrode and the second electrolytic solution into the positive electrode.

[0096] Hereinafter, the manufacturing method of Embodiment 3 will be described. First, a negative electrode containing the negative electrode active material 11c and not containing the first electrolytic solution is formed. Further, a positive electrode containing the positive electrode active material 12c and not containing the second electrolytic solution is formed. A battery cell (battery cell forming step) is formed in which a spacer through which the first electrolytic solution and the second electrolytic solution can permeate is positioned between these negative electrode and positive electrode.

[0097] The first electrolytic solution is injected into the negative electrode of the formed battery cell (first electrolytic solution injection step), and further the second electrolytic solution is injected into the positive electrode (second electrolytic solution injection step). The first electrolytic solution injection step and the second electrolytic solution injection step can be executed in this order, in the reverse order, or simultaneously. Pre-charging (pre-charging step) is performed on the battery cell after the first electrolytic solution injection step and the second electrolytic solution injection step are executed.

[0098] As described above, the invention of the present invention has been described with reference to the respective drawings and embodiments. However, the invention of the present invention is not limited to the above-described embodiments. That is, the invention of the present invention can be variously modified within the scope shown in the present invention, and embodiments obtained by appropriately combining technical means separately disclosed in different embodiments are also included in the technical scope of the invention of the present invention. That is, those skilled in the art can easily make various deformations or corrections based on the present invention. In addition, it should be noted that these deformations or corrections are included in the scope of the present invention.

[0099] Description of Reference Numerals

[0100] 1: Secondary battery.

[0101] 10: Battery cell.

[0102] 11: Negative electrode.

[0103] 11c: Negative electrode active material.

[0104] 12: Positive electrode.

[0105] 12c: Positive electrode active material.

[0106] 13: Separator.

Claims

1. A method for manufacturing a secondary battery, wherein, the method for manufacturing the secondary battery includes: a negative electrode forming step of forming a negative electrode containing a negative electrode active material and a first electrolytic solution; a positive electrode forming step of forming a positive electrode containing a positive electrode active material and a second electrolytic solution; a battery cell forming step of forming a battery cell in which a separator through which the first electrolytic solution and the second electrolytic solution can penetrate is located between the negative electrode and the positive electrode; and a pre-charging step of pre-charging the battery cell, the composition ratios of the components contained in the first electrolytic solution are different from the composition ratios of the components contained in the second electrolytic solution.

2. A method for manufacturing a secondary battery, wherein, the method for manufacturing the secondary battery includes: a battery cell forming step of forming a battery cell in which a separator through which a first electrolytic solution and a second electrolytic solution can penetrate is located between a negative electrode containing a negative electrode active material and a positive electrode containing a positive electrode active material; a first electrolytic solution injecting step of injecting the first electrolytic solution into the negative electrode; a second electrolytic solution injecting step of injecting the second electrolytic solution into the positive electrode; and a pre-charging step of pre-charging the battery cell, the composition ratios of the components contained in the first electrolytic solution are different from the composition ratios of the components contained in the second electrolytic solution.

3. The method for manufacturing a secondary battery according to claim 1 or 2, wherein, the first electrolytic solution contains a first solvent as a solvent, and the first solvent forms a good SEI film on the negative electrode active material during the pre-charging step, the volume% concentration of the first solvent contained in the first electrolytic solution is higher than the volume% concentration of the first solvent contained in the second electrolytic solution.

4. The method for manufacturing a secondary battery according to claim 3, wherein, the first solvent is ethylene carbonate.

5. The method for manufacturing a secondary battery according to any one of claims 1 to 4, wherein, the first electrolytic solution and the second electrolytic solution contain additives, the composition of the additives contained in the first electrolytic solution is different from the composition of the additives contained in the second electrolytic solution.

6. The method for manufacturing a secondary battery according to claim 5, wherein, the additives contain a first additive, and the first additive is reduced at a lower potential than the solvent of the first electrolytic solution during the pre-charging step, the mass% concentration of the first additive contained in the first electrolytic solution is higher than the mass% concentration of the first additive contained in the second electrolytic solution.

7. The method for manufacturing a secondary battery according to claim 6, wherein, the first additive includes one or more of vinylene carbonate, fluoroethylene carbonate, maleic anhydride, 1,3-propane sultone, ethylene sulfite, ethylenesulfite, lithium bis(oxalate)borate, and lithium difluoro(oxalate)borate.

8. The method for manufacturing a secondary battery according to claim 5, wherein, the additives contain a second additive, and the second additive forms a good CEI film on the positive electrode active material during the pre-charging step, The mass % concentration of the second additive contained in the second electrolyte is higher than the mass % concentration of the second additive contained in the first electrolyte.

9. The method for manufacturing a secondary battery according to claim 8, wherein the second additive includes one or more of vinylene carbonate, fluoroethylene carbonate, ethyl sulfite, adiponitrile, biphenyl, and lithium difluorophosphate.

10. The method for manufacturing a secondary battery according to claim 1 or 2, wherein the first electrolyte contains a first Li salt that generates HF by hydrolysis, the molar concentration of the first Li salt contained in the first electrolyte is higher than the molar concentration of the first Li salt contained in the second electrolyte, the first Li salt includes one or more of LiPF6 and LiBF4.

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