Manufacturing method for secondary battery

Abstract

In the present invention, a manufacturing method for improving the performance of a secondary battery is achieved. The manufacturing method comprises: a negative electrode formation step of forming a negative electrode that includes a negative electrode active material and a first electrolyte; a positive electrode formation step of forming a positive electrode that includes a positive electrode active material and a second electrolyte; a cell formation step of forming a cell in which a separator is located between the negative electrode and the positive electrode; and a pre-charging step of pre-charging the cell. The composition ratio of components of the first electrolyte and the composition ratio of components of the second electrolyte are different from each other.

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a secondary battery. [Background technology]

[0002] Patent Document 1 discloses an electricity storage device including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a first nonaqueous electrolyte in contact with the positive electrode active material, a second nonaqueous electrolyte in contact with the negative electrode active material, and a solid electrolyte membrane. In the electricity storage device, the first nonaqueous electrolyte and the second nonaqueous electrolyte are separated by the solid electrolyte membrane. Furthermore, the composition of the first nonaqueous electrolyte and the composition of the second nonaqueous electrolyte are different from each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-21677 Summary of the Invention

[0004] A method for manufacturing a secondary battery according to one embodiment of the present disclosure 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 cell forming step of forming a cell in which a separator permeable to the first electrolytic solution and the second electrolytic solution is positioned between the negative electrode and the positive electrode; and a pre-charging step of pre-charging the cell, wherein a composition ratio of components contained in the first electrolytic solution and a composition ratio of components contained in the second electrolytic solution are different from each other.

[0005] Furthermore, a method for manufacturing a secondary battery according to one embodiment of the present disclosure includes a cell formation step of forming a cell in which a separator, through which a first electrolytic solution and a second electrolytic solution can permeate, is positioned between a negative electrode and a positive electrode; a first electrolytic solution injection step of injecting the first electrolytic solution into the negative electrode; a second electrolytic solution injection step of injecting the second electrolytic solution into the positive electrode; and a pre-charging step of pre-charging the cell, wherein the composition ratio of components contained in the first electrolytic solution and the composition ratio of components contained in the second electrolytic solution are different from each other. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a perspective view showing the appearance of a secondary battery according to the present disclosure. [Figure 2] FIG. 1 is a perspective view showing the appearance of a cell according to the present disclosure. [Figure 3] FIG. 2 is an exploded model diagram showing a cross section taken along line III-III in FIG. [Figure 4] FIG. 4 is an exploded model diagram showing a cross section taken along line IV-IV in FIG. [Figure 5] FIG. 3 is a cross-sectional view showing a specific structure of an electrode body. [Figure 6] 3 is a flowchart showing a method for manufacturing a secondary battery according to the first embodiment of the present disclosure. [Figure 7] 5A to 5C are schematic diagrams illustrating a method for manufacturing a secondary battery according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Embodiment 1] (Structure of secondary battery) FIG. 1 is a perspective view showing the appearance of a 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 may be mounted in an electricity storage device for use in a home, a base station, an automobile, a robot such as a drone, or a medical device. The secondary battery 1 may include a cell 10, connection terminals 21 and 22, and a second housing 50. The configuration of the cell 10 will be described later.

[0008] The second container 50 may contain the cells 10. The second container 50 may be formed of, for example, an aluminum pouch film or a laminate film having a metal foil layer such as stainless steel or nickel. The aluminum pouch film may be a film on which aluminum is vapor-deposited, or a film laminated with aluminum foil. The film material may be, for example, polypropylene, polyethylene, nylon, or polyethylene terephthalate. The thickness of the second container 50 may be 50 μm or more and 300 μm or less, for example, 200 μm.

[0009] When the second housing 50 is an aluminum pouch film, the second housing 50 may have a configuration in which two aluminum pouch films are located on both sides in the stacking direction (Z-axis direction) of the cells 10. Furthermore, when the second housing 50 is an aluminum pouch film, the second housing 50 may have a configuration in which one aluminum pouch film is folded in half, with the cells 10 located inside.

[0010] The connection terminals 21 and 22 may be terminals that are connected to external terminals in order to extract power from or supply power to the secondary battery 1. The connection terminals 21 and 22 may protrude from the inside to the outside of the second housing 50. The connection terminals 21 and 22 may be made of, for example, copper, aluminum, or nickel. The connection terminals 21 and 22 may have a thickness of 50 μm or more and 500 μm or less, for example, 200 μm. The connection terminals 21 and 22 may also be subjected to a surface treatment to improve adhesion to an adhesive member (not shown). The adhesive member bonds the connection terminals 21 and 22 to the second housing 50 located above and below the connection terminals 21 and 22 to determine the positions of the connection terminals 21 and 22 relative to the second housing 50.

[0011] Fig. 2 is a perspective view showing the appearance of the cell 10. As shown in Fig. 2, the cell 10 may include an electrode assembly 14 and a first container 15. The electrode assembly 14 may have a sheet-like shape. The sheet-like electrode assembly 14 may include a negative electrode 11 and a positive electrode 12.

[0012] The first housing 15 may house the electrode assembly 14. When a plurality of first housings 15 housing the electrode assembly 14 are stacked, the plurality of first housings 15 may be adhered to each other by an adhesive layer (not shown). The material of the first housing 15 may be, for example, a film-like PET (polyethylene terephthalate) or nylon. More specifically, for example, two first housings 15 may be configured to be located on both sides in the stacking direction (Z-axis direction) of the cells 10. The thickness of the base material of the first housing 15 may be, for example, 10 μm or more and 40 μm or less, for example, 25 μm. The material of the adhesive layer may be, for example, polypropylene or polyethylene.

[0013] The first housing 15 may be transparent, for example. Figure 2 is a diagram showing how the electrode assembly 14 can be seen through the first housing 15 by using a transparent first housing 15 for the cell 10.

[0014] The negative electrode 11 may have an exposed portion 11e exposed from the first housing 15. The positive electrode 12 may have an exposed portion 12e exposed from the first housing 15. The connection terminals 21 and 22 may be electrically connected to the exposed portions 11e and 12e, respectively, by, for example, ultrasonic welding, laser welding, or resistance welding. The negative electrode 11 and the positive electrode 12 will be described in detail later.

[0015] The secondary battery 1 may have a configuration in which the cell 10, in which the negative electrode 11 and the positive electrode 12 are housed in a first housing 15, is further housed in a second housing 50. With this configuration, the electrode assembly 14 is housed doubly, thereby improving the safety of the secondary battery 1. The second housing 50 may also be housed in an additional housing. However, the secondary battery 1 only needs to include the negative electrode 11 and the positive electrode 12, and only needs to be housed in at least one housing.

[0016] In the first embodiment, the secondary battery 1 has a configuration in which a plurality of cells 10 are stacked, for example, ten layers of cells 10 are stacked. However, the secondary battery 1 according to the present disclosure may have a plurality of layers of cells 10 other than ten, or may have only one layer. When the secondary battery 1 has a plurality of layers of cells 10, the cells 10 may be stacked. When the secondary battery 1 shown in FIG. 1 is viewed from above, the portion excluding the connection terminals 21 and 22 may be substantially rectangular or may have a different shape. When the cell 10 shown in FIG. 2 is viewed from above, the portion excluding the exposed portions 11e and 12e may be substantially rectangular or may have a different shape.

[0017] Fig. 3 is a model diagram showing an exploded cross section taken along line III-III in Fig. 1. Fig. 4 is a model diagram showing an exploded cross section taken along line IV-IV in Fig. 1. For simplicity, the second container 50 is omitted from Figs. 3 and 4. Figs. 3 and 4 mainly show the positional relationship of each component. Therefore, the thickness relationships of each component are not necessarily as shown in Figs. 3 and 4.

[0018] 3 and 4, the negative electrode 11 may have an electrode conductor 11a and a negative electrode active material layer 11b, and the positive electrode 12 may have an electrode conductor 12a and a positive electrode active material layer 12b.

[0019] 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, for example, 10 μm. 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, for example, 10 μm.

[0020] 5 is a cross-sectional view showing a specific structure of the electrode body 14. The cross-sectional view shown in FIG. 5 is taken immediately after the production of the electrode body 14. As shown in FIG. 5, the negative electrode active material layer 11b is a mixture of a negative electrode active material 11c, a conductive additive 11d, and a first electrolytic solution 11f. negative electrode The positive electrode active material layer 12b may be a layer of a material. The positive electrode active material layer 12b may be a mixture of a positive electrode active material 12c, a conductive additive 12d, and a second electrolytic solution 12f. positive electrode The negative electrode active material 11c may be, for example, graphite, silicon, or lithium titanate. The positive electrode active material 12c may be, for example, lithium cobalt oxide, lithium nickel oxide, lithium iron phosphate, or lithium manganese oxide. The conductive additives 11d and 12d may be, for example, carbon black or acetylene black. However, the negative electrode active material 11c, the positive electrode active material 12c, and the conductive additives 11d and 12d are not limited to these. Furthermore, the conductive additives 11d and 12d may be omitted in the following description.

[0021] The first and second electrolytic solutions may be prepared by dissolving a Li salt and an additive in a solvent. Specific components and composition ratios of the first and second electrolytic solutions will be described later.

[0022] The negative electrode material may have a clay-like property, obtained by mixing a first electrolyte solution into a mixture of a negative electrode active material 11c and a conductive additive 11d. The positive electrode material may have a clay-like property, obtained by mixing a second electrolyte solution into a mixture of a positive electrode active material 12c and a conductive additive 12d. The negative electrode 11 may be an electrode in which the negative electrode material is coated on an electrode conductor 11a. The positive electrode 12 may be an electrode in which the positive electrode material is coated on an electrode conductor 12a.

[0023] The electrode assembly 14 may further include a separator 13. The negative electrode 11, the positive electrode 12, and the separator 13 may be positioned 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 cell 10 may have a structure in which the negative electrode 11 and the positive electrode 12 are stacked with the separator 13 interposed therebetween. The separator 13 may function as an insulating member that insulates the negative electrode 11 and the positive electrode 12. The separator 13 may be, for example, a sheet-like nonwoven fabric or a porous material. This allows the first electrolytic solution and the second electrolytic solution to permeate the separator 13.

[0024] Immediately after the electrode assembly 14 is manufactured, only the first electrolytic solution is present on the negative electrode 11 side relative to the separator 13, and only the second electrolytic solution is present on the positive electrode 12 side. However, the first electrolytic solution can permeate the separator 13 from the negative electrode 11 side and migrate to the positive electrode 12 side. Similarly, the second electrolytic solution can permeate the separator 13 from the positive electrode 12 side and migrate to the negative electrode 11 side. Therefore, after the electrode assembly 14 is manufactured, a mixed electrolytic solution of the first electrolytic solution and the second electrolytic solution is present on both the negative electrode 11 side and the positive electrode 12 side relative to the separator 13. After a sufficient amount of time has passed since the manufacture of the electrode assembly 14, there will be no difference in the composition ratio of the electrolytic solution components on the negative electrode 11 side and the positive electrode 12 side relative to the separator 13. In the following description, the mixed electrolytic solution of the first electrolytic solution and the second electrolytic solution will be referred to as a mixed electrolytic solution.

[0025] When a porous material is used as separator 13, specifically, a porous film made of a thermoplastic resin having a melting point of about 80°C to 140°C may be used. Examples of the thermoplastic resin that may be used include polyolefin polymers such as polypropylene and polyethylene, and polyethylene terephthalate. Separator 13 may also be a porous film made of a thermoplastic resin coated with a porous ceramic layer.

[0026] When using a negative electrode material and a positive electrode material having clay-like properties, a binder is not required between the negative electrode 11 and the positive electrode 12 and the separator. Furthermore, an electrolyte is mixed into the negative electrode material and the positive electrode material before forming the negative electrode 11 and the positive electrode 12. This improves the performance of the negative electrode 11 and the positive electrode 12. By mixing the electrolyte into the negative electrode material and the positive electrode material, the number of steps required for forming the negative electrode 11 and the positive electrode 12 can be reduced compared to when using negative electrode material and positive electrode material that do not contain an electrolyte. Furthermore, the step of injecting the electrolyte can be eliminated from the secondary battery manufacturing process. Furthermore, compared to when using negative electrode material and positive electrode material that do not contain an electrolyte, the negative electrode material and positive electrode material can be applied thicker to the electrode conductor. Therefore, when realizing a secondary battery with a predetermined storage capacity, fewer electrode conductors and separators can be used than when using negative electrode material and positive electrode material that do not have clay-like properties. This reduces component costs and increases energy density.

[0027] The negative electrode material and the positive electrode material do not need to have clay-like properties. In this case, the negative electrode active material 11c and the positive electrode active material 12c do not need to contain an electrolyte solution. For example, the negative electrode material may be a negative electrode slurry containing a mixture of the negative electrode active material 11c and the conductive additive 11d, a binder, and a solvent. The negative electrode slurry may be applied to the electrode conductor 11a and dried to form the negative electrode active material layer 11b. The solvent for the negative electrode slurry may be, for example, water. The positive electrode material may be a positive electrode slurry containing a mixture of the positive electrode active material 12c and the conductive additive 12d, a binder, and a solvent. The positive electrode slurry 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), polyethylene oxide (PEO), or the like. The solvent for the positive electrode slurry may be an organic solvent such as N-methyl-2-pyrrolidone (NMP), etc. In this case, the cell 10 is filled with an electrolyte solution, and the electrolyte solution may be held by being impregnated into the separator 13.

[0028] (Secondary battery manufacturing method) 6 is a flowchart showing a method for manufacturing the secondary battery 1 according to the first embodiment. The method for manufacturing the secondary battery 1 is as follows. First, a negative electrode 11 containing a negative electrode active material 11c and a 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 a positive electrode active material 12c and a 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.

[0029] Furthermore, a cell 10 is formed in which a separator 13 is positioned between the formed negative electrode 11 and positive electrode 12 (S3, cell formation step). Specifically, the negative electrode 11 may be stacked on one side of the separator 13 so that the negative electrode active material layer 11b side is in contact with the separator 13. Furthermore, the positive electrode 12 may be stacked on the other side of the separator 13 so that the positive electrode active material layer 12b side is in contact with the separator 13. Thereafter, the cell 10 is pre-charged (S4 pre-charging step). A secondary battery 1 can be manufactured by stacking multiple cells 10 after pre-charging. Alternatively, pre-charging may be performed on cells 10 that have already been stacked.

[0030] In the pre-charging step, the mixed electrolyte on the negative electrode 11 side relative to the separator 13 is decomposed, whereby an SEI (Solid Electrolyte Interface) coating is formed on the surface of the negative electrode active material 11c. In addition, in the pre-charging step, the mixed electrolyte on the positive electrode 12 side relative to the separator 13 is decomposed, whereby a CEI (Cathode Electrolyte Interface) coating is formed on the surface of the positive electrode active material 12c. The SEI coating and the CEI coating are formed by Li + In other words, the SEI coating and the CEI coating are films that exhibit conductivity due to the movement of ions and do not exhibit conductivity due to the movement of electrons. + It has the function of inserting and removing.

[0031] Also, when the mixed electrolyte decomposes, Li+ The SEI coating and CEI coating have the function of reducing further decomposition of the mixed electrolyte solution after the SEI coating and CEI coating are formed. Therefore, the SEI coating and CEI coating are necessary coatings for reducing decomposition of the mixed electrolyte solution. However, if the SEI coating and CEI coating are too thick, the electrical resistance increases, which adversely affects the performance of the secondary battery 1. Specific examples of the performance of the secondary battery 1 include the capacity retention rate and area specific impedance after a certain number of charge / discharge cycles.

[0032] To improve the performance of the secondary battery 1, it is sufficient to form a good SEI coating on the negative electrode active material 11c and a good CEI coating on the positive electrode active material 12c. Specifically, a good SEI coating or CEI coating can be said to have a thickness of 100 nm or less, 50 nm or less, or even 30 nm or less, with little thickness variation. A good SEI coating or CEI coating may also be stable, have no electronic conductivity, and have high Li-ion conductivity.

[0033] (electrolyte) As described above, the first and second electrolytic solutions are prepared by dissolving a Li salt and an additive in a solvent. The composition ratio of the components contained in the first electrolytic solution in the negative electrode formation step is different from the composition ratio of the components contained in the second electrolytic solution in the positive electrode formation step.

[0034] As described above, after a sufficiently long time has passed since the manufacture of the cell 10, there will be no difference in the composition ratio of the components of the mixed electrolyte solution between the negative electrode 11 side and the positive electrode 12 side relative to the separator 13. However, before a sufficiently long time has passed since the manufacture of the cell 10, there will be a difference in the composition ratio of the components of the mixed electrolyte solution between the negative electrode 11 side and the positive electrode 12 side. The pre-charging step is performed before a sufficient time has passed since the manufacture of the cell 10. Therefore, in the pre-charging step, pre-charging is performed in a state where there is a difference in the composition ratio of the components of the mixed electrolyte solution between the negative electrode 11 side and the positive electrode 12 side.

[0035] In the electrolyte solution, the components that contribute to forming a good SEI coating on the surface of the negative electrode active material 11c are different from the components that contribute to forming a good CEI coating on the surface of the positive electrode active material 12c. In secondary batteries with a solid electrolyte membrane, ionic species contained in the electrolyte solution permeate the solid electrolyte membrane, but organic solvent molecules do not. Therefore, as disclosed in Patent Document 1 and elsewhere, secondary batteries have traditionally had different composition ratios of electrolyte solution components on the negative electrode side and the positive electrode side. In contrast, secondary batteries with porous separators have traditionally used a single electrolyte solution on both the negative electrode side and the positive electrode side because the electrolyte solution is permeable. As a result, in conventional secondary batteries with porous separators, 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 poor, resulting in reduced performance of the secondary battery.

[0036] The inventors of the present disclosure conducted extensive research and discovered the following: Specifically, an SEI coating and a CEI coating formed when there is a difference in the composition ratio of components contained in the mixed electrolyte solution between the negative electrode 11 and the positive electrode 12 affect the performance of the secondary battery 1 even after the difference in the composition ratio of components contained in the mixed electrolyte solution between the negative electrode 11 and the positive electrode 12 disappears. Based on this discovery, the inventors of the present disclosure completed a method for manufacturing a secondary battery 1 according to the present disclosure, in which a good SEI coating and a CEI coating are formed by differentiating the composition ratio of components contained in a first electrolytic solution from the composition ratio of components contained in a second electrolytic solution. This manufacturing method can improve the performance of a secondary battery 1 that uses a separator, such as a porous material with low electrical resistivity, rather than a separator formed of a solid material with high electrical resistivity.

[0037] Furthermore, some components of the electrolytic solution may not have a positive or negative effect on the performance of the secondary battery 1 when the SEI coating and the CEI coating are formed, but may have a positive effect on the performance of the secondary battery 1 after the SEI coating and the CEI coating are formed. The performance of the secondary battery 1 can also be improved by making the composition ratio of such components different between the first electrolytic solution and the second electrolytic solution.

[0038] (solvent) The first electrolytic solution contains a first solvent that forms a good SEI coating on the surface of the negative electrode active material 11c during the pre-charging step. The volume percent concentration of the first solvent contained in the first electrolytic solution may be higher than the volume percent concentration of the first solvent contained in the second electrolytic solution. In other words, the second electrolytic solution may contain the first solvent at a volume percent concentration lower than the volume percent concentration of the first solvent contained in the first electrolytic solution. Alternatively, the second electrolytic solution may not contain the first solvent.

[0039] The first solvent may be ethylene carbonate. The higher the volume percent concentration of ethylene carbonate contained in the mixed electrolyte solution on the negative electrode 11 during the pre-charging step, the better the SEI coating formed on the surface of the negative electrode active material 11c. Therefore, by making the volume percent concentration of ethylene carbonate contained in the first electrolyte solution higher than the volume percent concentration of ethylene carbonate contained in the second electrolyte solution, a good SEI coating can be formed on the surface of the negative electrode active material 11c.

[0040] The second electrolytic solution may also contain a second solvent as a solvent, the presence of which on the negative electrode 11 during the pre-charging step would cause problems. Examples of the second solvent include propylene carbonate and γ-butyrolactone. The volume percent concentration of the second solvent contained in the second electrolytic solution may be higher than the volume percent concentration of the second solvent contained in the first electrolytic solution. In other words, the first electrolytic solution may contain the second solvent at a volume percent concentration lower than the volume percent concentration of the second solvent contained in the second electrolytic solution. Alternatively, the first electrolytic solution may not contain the second solvent.

[0041] Propylene carbonate has the disadvantage of not forming a good SEI coating on the surface of the negative electrode active material 11c during the pre-charging step. Also, γ-butyrolactone has the disadvantage of forming a coating with high electrical resistivity on the surface of the negative electrode active material 11c during the pre-charging step. However, after the SEI coating is formed, the above disadvantages caused by the presence of propylene carbonate and γ-butyrolactone on the negative electrode 11 side are smaller than before the SEI coating is formed. On the other hand, propylene carbonate and γ-butyrolactone have a lower freezing point than ethylene carbonate, which has a positive effect on the performance of the secondary battery 1 in low-temperature environments.

[0042] By making the volume percent concentration of the second solvent contained in the second electrolytic solution higher than the volume percent concentration of the second solvent contained in the first electrolytic solution, the second solvent migrates from the positive electrode 12 side to the negative electrode 11 side over time after the pre-charging step. As a result, the concentration of the second solvent on the negative electrode 11 side increases after the formation of the SEI coating, improving the performance of the secondary battery 1 in low-temperature environments.

[0043] The second solvent may contain a nitrile-sulfone solvent other than propylene carbonate or γ-butyrolactone. These solvents have high oxidation resistance and low reduction resistance. Therefore, it is preferable that the amount of these solvents be greater near the surface of the positive electrode active material 12c than near the surface of the negative electrode active material 11c during the pre-charging step.

[0044] (additives) The first electrolytic solution and the second electrolytic solution may contain an additive, and the composition of the additive contained in the first electrolytic solution may be different from the composition of the additive contained in the second electrolytic solution.

[0045] The additives contained in the first and second electrolytic solutions include a first additive that forms a good SEI coating on the surface of the negative electrode active material 11c during the pre-charging step. The mass % concentration of the first additive contained in the first electrolytic solution may be higher than the mass % concentration of the first additive contained in the second electrolytic solution. In other words, the second electrolytic solution may contain the first additive at a mass % concentration lower than the mass % concentration of the first additive contained in the first electrolytic solution. Alternatively, the second electrolytic solution may not contain the first additive.

[0046] The first additive may include, for example, one or more of vinylene carbonate, fluoroethylene carbonate, succinic anhydride, maleic anhydride, 1,3 propane sultone, ethylene sulfate, ethylene sulfite, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate. Vinylene carbonate, fluoroethylene carbonate, maleic anhydride, 1,3 propane sultone, ethylene sulfate, ethylene sulfite, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate are reduced at a potential lower than that of the solvent in the first electrolytic solution. Using such an additive as the first additive allows for the formation of a good SEI coating on the surface of the negative electrode active material 11c.

[0047] The first electrolytic solution may contain, as a first additive, a larger amount of, for example, methyl benzoate, succinic anhydride, succinimide, dialkylpyrocarbonate, etc. than the second electrolytic solution. These additives are not reduced themselves, but react with an intermediate or product obtained by reduction of the solvent, and can form a good SEI coating on the surface of the negative electrode active material 11c.

[0048] The additives contained in the first and second electrolytic solutions include a second additive that forms a good CEI coating 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 electrolytic solution may be higher than the mass % concentration of the second additive contained in the first electrolytic solution. In other words, the first electrolytic solution may contain the second additive at a mass % concentration lower than the mass % concentration of the second additive contained in the second electrolytic solution. Alternatively, the first electrolytic solution may not contain the second additive.

[0049] The second additive may include, for example, one or more of vinylene carbonate; fluoroethylene carbonate; ethylene sulfate; adiponitrile; biphenyl; and lithium difluorophosphate (LiPO2F2). For example, vinylene carbonate and biphenyl undergo oxidative polymerization on the surface of the positive electrode active material 12c to form a CEI coating. Fluoroethylene carbonate and lithium difluorophosphate (LiPO2F2) undergo oxidative decomposition to form stable CEI coatings, such as LiF or Li3PO4. Dinitrile compounds, such as adiponitrile, form CEI coatings with functional groups that coordinate to the surface of the positive electrode active material 12c and block active sites on the surface of the positive electrode active material 12c. Ethylene sulfate adsorbs to the surface of the positive electrode active material 12c to form a CEI coating that deactivates the active sites of the positive electrode active material 12c, thereby reducing CO2 generation and preventing an increase in interfacial resistance. By using such an additive as the second additive, a good CEI coating can be formed on the surface of the positive electrode active material 12c.

[0050] Fluoroethylene carbonate and ethylene sulfate can function as either the first additive or the second additive depending on the materials of the negative electrode active material 11c and the positive electrode active material 12c, and for this reason, fluoroethylene carbonate and ethylene sulfate are listed as both the first additive and the second additive.

[0051] (Li salt) The first and second electrolytic solutions may contain a Li salt, and the composition of the Li salt contained in the first electrolytic solution may be different from the composition of the Li salt contained in the second electrolytic solution.

[0052] The first electrolytic solution may contain a first Li salt that generates hydrofluoric acid (HF) upon hydrolysis. The molar concentration of the first Li salt contained in the first electrolytic solution may be higher than the molar concentration of the first Li salt contained in the second electrolytic solution. In other words, the second electrolytic solution may contain the first Li salt at a molar concentration lower than the molar concentration of the first Li salt contained in the first electrolytic solution. Alternatively, the second electrolytic solution may not contain the first Li salt. The first Li salt may include one or more of LiPF6 and LiBF4.

[0053] HF generated by hydrolysis of the first Li salt contributes to the formation of a good SEI coating on the surface of the negative electrode active material 11c during the pre-charging step. On the other hand, HF promotes the elution of transition metals from the positive electrode active material 12c, thereby degrading the performance of the secondary battery 1. By including a large amount of the first Li salt in the first electrolytic solution, a good SEI coating can be formed on the surface of the negative electrode active material 11c.

[0054] Furthermore, when the electrode conductor 12a is made of aluminum, HF forms a passivation film of fluoride (AlF) on the electrode conductor 12a during the pre-charging step, thereby reducing corrosion of the electrode conductor 12a. Therefore, when the electrode conductor 12a is made of aluminum, the second electrolytic solution may contain a small amount of the first Li salt. Specifically, the second electrolytic solution may contain the first Li salt in a range of 1 mol / L or less.

[0055] The first electrolytic solution may further contain one or more of LiFSI and LiTFSI. The molar concentration of LiFSI or LiTFSI contained in the first electrolytic solution may be higher than the molar concentration of LiFSI or LiTFSI contained in the second electrolytic solution. In other words, the second electrolytic solution may contain LiFSI and LiTFSI at a molar concentration lower than the molar concentrations of LiFSI and LiTFSI contained in the first electrolytic solution. Alternatively, the second electrolytic solution may not contain LiFSI or LiTFSI.

[0056] LiFSI and LiTFSI form a coating derived from FSI on the surface of the negative electrode active material 11c. The coating derived from FSI improves the cycle characteristics of the secondary battery 1 and also increases the Coulombic efficiency in the initial charge / discharge cycle (see, for example, Journal of Power Sources 375 (2018) 43-52). Therefore, by increasing the molar concentration of LiFSI or LiTFSI contained in the first electrolyte solution, deterioration of the performance of the secondary battery 1 can be reduced.

[0057] Furthermore, LiFSI and LiTFSI corrode aluminum. However, as described above, when the electrode conductor 12a is aluminum and the second electrolyte solution contains a small amount of the first Li salt, a passivation film is formed on the electrode conductor 12a. This passivation film is formed on the electrode conductor 12a made of LiFSI and LiTFSI. Corrosion of Therefore, in this case, LiFSI or LiTFSI contained in the first electrolytic solution may be present in large amounts on the negative electrode 11 side during the pre-charging step and may migrate to the positive electrode 12 side over time.

[0058] (Example) The performance of the secondary battery 1 manufactured by the manufacturing method according to this embodiment and the performance of the secondary battery manufactured by the manufacturing method of the comparative example will be described below.

[0059] Table 1 shows the composition ratios of five components contained in the first and second electrolytic solutions for the manufacturing method according to this embodiment and the manufacturing method according to the comparative example. In Table 1, LiPF6 (first Li salt) is a Li salt. EC (ethylene carbonate, first solvent), PC (propylene carbonate, second solvent), and GBL (γ-butyrolactone, second solvent) are solvents. VC (vinylene carbonate, first additive) is an additive.

[0060] [Table 1] In the comparative examples, the composition ratios of the components contained in the first electrolytic solution and the second electrolytic solution were the same. In Example 1, the mass % concentration of VC, the first additive, in the first electrolytic solution was higher than the mass % concentration in the second electrolytic solution. In Example 2, the volume % concentration of EC, the first solvent, in the first electrolytic solution was higher than the volume % concentration in the second electrolytic solution, and the volume % concentration of GBL, the second solvent, in the second electrolytic solution was higher than the volume % concentration in the first electrolytic solution. In Example 3, the molar concentration of LiPF6, the first Li salt, in the first electrolytic solution was higher than the molar concentration in the second electrolytic solution.

[0061] Table 2 shows the performance of two samples of the secondary batteries of the Examples and Comparative Examples shown in Table 1 after 100 charge / discharge cycles at a charge / discharge rate of 0.3 C in a 45°C environment. In Table 2, Capacity retention indicates the capacity retention rate. ASI indicates area specific impedance. N1 and N2 indicate the secondary battery samples of the Examples and Comparative Examples.

[0062] [Table 2] Regarding the capacity retention rate, secondary batteries with a larger value have higher performance than secondary batteries with a smaller value. Regarding the area specific impedance, secondary batteries with a smaller value have higher performance than secondary batteries with a larger value. As shown in Table 2, all of the samples according to the examples exhibit higher performance than the sample with higher performance in the comparative example. Therefore, it can be said that the manufacturing methods according to the examples were able to manufacture secondary batteries with higher performance than the manufacturing methods according to the comparative examples.

[0063] In the manufacturing method according to this embodiment, the molar concentration of LiPF as the first Li salt is not limited to the value in this example. For example, the molar concentration of LiPF in the first electrolytic solution may be 0.3 mol / L or more and 3.0 mol / L or less, and the molar concentration of LiPF in the second electrolytic solution may be 0 mol / L or more and 2.0 mol / L or less.

[0064] In the manufacturing method according to the present embodiment, the volume percent concentration of ethylene carbonate as the first solvent is not limited to the value in this example. For example, the volume percent concentration of ethylene carbonate in the first electrolytic solution may be 20% to 80% by volume, and in the second electrolytic solution may be 0% to 50% by volume.

[0065] In the manufacturing method according to the present embodiment, the volume percent concentration of propylene carbonate as the second solvent is not limited to the value in this example. For example, the volume percent concentration of propylene carbonate in the first electrolytic solution may be 0% to 50% by volume, and in the second electrolytic solution may be 20% to 80% by volume.

[0066] In the manufacturing method according to this embodiment, the volume percent concentration of γ-butyrolactone as the second solvent is not limited to the value in this example. For example, the volume percent concentration of γ-butyrolactone in the first electrolytic solution may be 0% to 50% by volume, and in the second electrolytic solution may be 20% to 80% by volume.

[0067] In the manufacturing method according to the present embodiment, the mass % concentration of vinylene carbonate as the first additive is not limited to the value in this example. For example, the mass % concentration of vinylene carbonate in the first electrolytic solution may be 2 mass % or more and 10 mass % or less, and in the second electrolytic solution may be 0 mass % or more and 5 mass % or less.

[0068] As described above, the method for manufacturing a secondary battery according to the present disclosure can improve the performance of the secondary battery. This reduces the consumption of the secondary battery and the amount of secondary battery waste. This effect also contributes to achieving, for example, Goal 12 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Responsible Consumption and Production."

[0069] [Embodiment 2] Fig. 7 is a schematic diagram showing a method for manufacturing a secondary battery 1 according to embodiment 2. In Fig. 7, reference numeral 701 is a schematic diagram showing a negative electrode formation step, reference numeral 702 is a schematic diagram showing a positive electrode formation step, and reference numeral 703 is a schematic diagram showing a cell formation step.

[0070] As indicated by reference numeral 701, in the negative electrode formation step according to the second embodiment, the electrode conductor 11a and the negative electrode active material 11c previously applied to the electrode conductor 11a are impregnated with a first electrolytic solution 11f in a vacuum to form the negative electrode 11. Also, as indicated by reference numeral 702, in the positive electrode formation step according to the second embodiment, the electrode conductor 12a and the positive electrode active material 12c previously applied to the electrode conductor 12a are impregnated with a second electrolytic solution 12f in a vacuum to form the positive electrode 12.

[0071] In the cell formation step according to the second embodiment, 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 the reference numeral 703, a cell 10 is formed in which a separator 13 is positioned between the negative electrode 11 and the positive electrode 12. After the cell 10 is formed, pre-charging is performed as described in the manufacturing method according to the first embodiment.

[0072] In the manufacturing method according to the second embodiment, 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, and therefore the manufacturing method according to the second embodiment also achieves the same effects as the manufacturing method according to the first embodiment.

[0073] [Embodiment 3] In both the manufacturing methods according to the first and second embodiments, the negative electrode 11 contains the first electrolytic solution and the positive electrode 12 contains the second electrolytic solution at the time when the cell 10 is formed. However, after forming a cell in which the negative electrode does not contain the first electrolytic solution and the positive electrode does not contain the second electrolytic solution, the first electrolytic solution may be injected into the negative electrode and the second electrolytic solution may be injected into the positive electrode.

[0074] The manufacturing method according to the third embodiment will be described below. First, a negative electrode containing a negative electrode active material 11c and not containing a first electrolytic solution is formed. Then, a positive electrode containing a positive electrode active material 12c and not containing a second electrolytic solution is formed. A cell is formed between the negative electrode and the positive electrode, with a separator permeable to the first and second electrolytic solutions positioned therebetween (cell formation step).

[0075] A first electrolytic solution is injected into the negative electrode of the formed cell (first electrolytic solution injection step), and a second electrolytic solution is further injected into the positive electrode (second electrolytic solution injection step). The first electrolytic solution injection step and the second electrolytic solution injection step may be performed in this order, in the reverse order, or simultaneously. The cell after the first electrolytic solution injection step and the second electrolytic solution injection step are performed is pre-charged (pre-charging step).

[0076] The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0077] 1 Secondary battery 10 cells 11 Negative electrode 11c negative electrode active material 12 Positive electrode 12c positive electrode active material 13 Separator

Claims

1. a negative electrode forming step of forming a negative electrode including a negative electrode active material and a first electrolytic solution; a positive electrode forming step of forming a positive electrode including a positive electrode active material and a second electrolytic solution; a cell forming step of forming a cell in which a separator permeable to the first electrolytic solution and the second electrolytic solution is located between the negative electrode and the positive electrode; a pre-charging step of pre-charging the cell, A method for manufacturing a secondary battery, wherein a composition ratio of components contained in the first electrolytic solution and a composition ratio of components contained in the second electrolytic solution are different from each other.

2. a cell forming step of forming a cell in which a separator permeable to the first electrolytic solution and the second electrolytic solution is located between a negative electrode including a negative electrode active material and a positive electrode including a positive electrode active material; a first electrolyte solution injection step of injecting the first electrolyte solution into the negative electrode; a second electrolyte solution injection step of injecting the second electrolyte solution into the positive electrode; a pre-charging step of pre-charging the cell, A method for manufacturing a secondary battery, wherein a composition ratio of components contained in the first electrolytic solution and a composition ratio of components contained in the second electrolytic solution are different from each other.

3. the first electrolytic solution contains, as a solvent, a first solvent that forms a good SEI coating on the negative electrode active material in the pre-charging step; 3 . The method for producing a secondary battery according to claim 1 , wherein a volume percent concentration of the first solvent contained in the first electrolytic solution is higher than a volume percent 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 first electrolytic solution and the second electrolytic solution contain an additive; The method for producing a secondary battery according to claim 1 , wherein the additive contained in the first electrolytic solution and the additive contained in the second electrolytic solution have different compositions.

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

7. 7. The method of claim 6, wherein the first additive comprises one or more of vinylene carbonate; fluoroethylene carbonate; maleic anhydride; 1,3 propane sultone; ethylene sulfate; ethylene sulfite; lithium bis(oxalato)borate; and lithium difluoro(oxalato)borate.

8. the additive contains a second additive that forms a good CEI coating on the positive electrode active material in the pre-charging step; 6. The method for producing a secondary battery according to claim 5, wherein a mass % concentration of the second additive contained in the second electrolytic solution is higher than a mass % concentration of the second additive contained in the first electrolytic solution.

9. The method of claim 8 , wherein the second additive comprises at least one of vinylene carbonate; fluoroethylene carbonate; ethylene sulfate; adiponitrile; biphenyl; and lithium difluorophosphate.

10. the first electrolyte solution contains a first Li salt that generates HF upon hydrolysis; a molar concentration of the first Li salt contained in the first electrolytic solution is higher than a molar concentration of the first Li salt contained in the second electrolytic solution; The first Li salt is LiPF ６ and LiBF ４ The method for producing a secondary battery according to claim 1 , further comprising one or more of the following steps:

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