Lithium-ion secondary battery manufacturing method and battery pack

Abstract

To provide a method for manufacturing a lithium ion secondary battery that allows the ratio between the resistance of a negative electrode and the resistance of an electrolyte to be adjusted to a value where it is difficult for lithium ions to precipitate regardless of the tolerance of the negative electrode.SOLUTION: When a step of forming a negative electrode current collector of a battery cell is completed (S10), a step of measuring a resistance value of the negative electrode current collector is executed (S12). Next, a step of forming a negative electrode composite material layer on a surface of the negative electrode current collector is performed (S14). Then, a step of measuring the resistance of a negative electrode on which the negative electrode composite layer is formed is executed (S16). Next, a step of calculating the resistance value of the negative electrode composite material layer is performed by subtracting the resistance value of the negative electrode current collector from the resistance value of the negative electrode (S18). The amount of additive added to the electrolyte solution is determined according to the deviation of the resistance value of the negative electrode composite material layer from a reference value (S20).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a lithium ion secondary battery and a battery pack. [Background technology]

[0002] For example, a lithium ion secondary battery is described in Patent Document 1. In this secondary battery, the negative electrode active material has a predetermined distribution in order to suppress lithium deposition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-33824 Summary of the Invention [Problem to be solved by the invention]

[0004] When mass-producing secondary batteries, tolerances arise in physical quantities such as the distribution of the negative electrode active material, which can lead to deviations from the appropriate physical quantities for suppressing lithium precipitation. [Means for solving the problem]

[0005] The means for solving the above problems and their effects will be described below. 1. A method for manufacturing a lithium ion secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, the electrolyte containing a solvent, the method comprising: a measurement step of measuring a value of a negative electrode resistance variable which is a variable indicating the electrical resistance of the negative electrode; and an adjustment step of adjusting the amount of an additive to be added to the solvent in accordance with the difference between a reference value of the negative electrode resistance variable and the value of the negative electrode resistance variable measured in the measurement step.

[0006] The ease of lithium ion deposition varies depending on the ratio of the negative electrode resistance variable to the resistance of the electrolyte. Furthermore, the resistance of the electrolyte changes depending on the amount of additive added to the solvent. Therefore, in the above method, the amount of additive added is adjusted depending on the value of the negative electrode resistance variable. This allows the ratio of the negative electrode resistance variable to the resistance of the electrolyte to be adjusted to a value that makes lithium ion deposition difficult, even if there is variation in the value of the negative electrode resistance variable due to tolerance.

[0007] 2. A method for producing a lithium ion secondary battery according to item 1 above, wherein the negative electrode is formed by forming a negative electrode active material layer on a negative electrode current collector, and the negative electrode resistance variable is a variable indicating the resistance of the negative electrode active material layer, the method comprising a forming step of forming the negative electrode active material layer on the negative electrode current collector, the measuring step including a current collector resistance value measuring step, a negative electrode resistance value measuring step, and a resistance variable value calculating step, the current collector resistance value measuring step being a step of measuring the resistance value of the negative electrode current collector prior to the forming step, the negative electrode resistance value measuring step being a step of measuring the resistance value of the negative electrode after the forming step, and the resistance variable value calculating step being a step of calculating the value of the negative electrode resistance variable by subtracting the resistance value of the negative electrode current collector from the resistance value of the negative electrode.

[0008] When the resistance of the negative electrode active material layer is high, current tends to flow through the electrolyte contained in the negative electrode active material layer. In this case, the reaction concentrates near the boundary between the negative electrode current collector and the negative electrode active material layer. On the other hand, when the resistance of the negative electrode active material layer is low, current tends to flow through the negative electrode active material layer. In this case, the reaction concentrates on the surface of the negative electrode active material layer. When the reaction concentration becomes significant, lithium tends to precipitate.

[0009] Therefore, in the above method, the amount of additive added is adjusted according to the resistance of the negative electrode active material layer, thereby adjusting the ratio of the resistance of the negative electrode active material layer to the resistance of the electrolyte to a value that makes it difficult for lithium to deposit.

[0010] 3. The method for producing a lithium ion secondary battery according to 1 or 2 above, wherein the electrolytic solution contains a supporting electrolyte in addition to the solvent, and the additive is added to a solution containing the solvent and the supporting electrolyte.

[0011] According to the above method, by adjusting the amount of additive added that is separate from the supporting electrolyte, there is no need to adjust the amounts of the solvent and supporting electrolyte in order to compensate for the effect of the tolerances of the negative electrode.

[0012] 4. A method for producing a lithium ion secondary battery according to any one of the above 1 to 3, wherein the additive has a function of lowering the electrical resistance of the electrolyte by increasing the amount added, and the adjustment step includes a step of reducing the amount of the additive added when the value of the negative electrode resistance variable measured in the measurement step is greater than the reference value, compared to when the value of the negative electrode resistance variable is the reference value.

[0013] In the above configuration, when the value of the negative electrode resistance variable is larger than the reference value, the amount of the electrolyte is reduced to increase the electrical resistance of the electrolyte, thereby making it possible to bring the electrical resistance of the electrolyte closer to a value commensurate with the value of the negative electrode resistance variable.

[0014] 5. A method for producing a lithium ion secondary battery according to any one of 1 to 3 above, wherein the additive has a function of increasing the electrical resistance of the electrolyte by increasing the amount added, and the adjustment step includes a step of increasing the amount of the additive added when the value of the negative electrode resistance variable measured in the measurement step is greater than the reference value, compared to when the value of the negative electrode resistance variable is the reference value.

[0015] In the above configuration, when the value of the negative electrode resistance variable is larger than the reference value, the amount of the electrolyte is increased to increase the electrical resistance of the electrolyte, thereby making it possible to bring the electrical resistance of the electrolyte closer to a value commensurate with the value of the negative electrode resistance variable.

[0016] 6. An assembled battery comprising a plurality of battery cells, wherein the battery cells are lithium ion secondary batteries and comprise a negative electrode, a positive electrode, and an electrolyte, the electrolyte containing a solvent, and the amount of additive added to the solvent differs between a first battery cell and a second battery cell among the plurality of battery cells.

[0017] To prevent lithium precipitation in a battery cell, it is desirable to maintain an appropriate ratio between the resistance of the negative electrode and the resistance of the electrolyte. However, the magnitude of the resistance of the negative electrode in each battery cell constituting a battery pack may vary due to tolerance. Here, the magnitude of the resistance of the electrolyte can be adjusted by the amount of additive added. Therefore, in the above configuration, the amount of additive added to the solvent is set for each battery cell. This allows the ratio of the resistance of the negative electrode to the resistance of the electrolyte in each battery cell to be maintained at an appropriate ratio, even if tolerance occurs in the resistance of the negative electrode.

[0018] If the additive has the function of lowering the electrical resistance of the electrolyte by increasing the amount added, the amount of additive added to a battery cell with a high electrical resistance may be smaller than the amount of additive added to a battery cell with a low electrical resistance. If the additive has the function of raising the electrical resistance of the electrolyte by increasing the amount added, the amount of additive added to a battery cell with a high electrical resistance may be larger than the amount of additive added to a battery cell with a low electrical resistance.

[0019] The electrolytic solution may contain a supporting electrolyte in addition to a solvent, and the additive may be a substance added to a solution containing the solvent and the supporting electrolyte. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view of a battery pack. [Figure 2] FIG. 2 is a perspective view showing a battery cell that constitutes the battery pack of FIG. [Figure 3] FIG. 3 is a perspective view showing the electrode assembly in an expanded state. [Figure 4] 4(a) to 4(d) are diagrams showing equivalent circuits of the negative electrode sheet. [Figure 5] FIG. 5 is a flow chart showing part of the manufacturing process of the battery cell. [Figure 6] 6(a) and 6(b) are diagrams showing examples of adjusting the amount of additive added. [Figure 7] 7(a) and 7(b) are diagrams illustrating distributions of additive amounts in battery cells that make up a battery pack. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment will be described below with reference to the drawings. [Battery pack and battery cell configuration] 1 shows a battery pack 1. The battery pack 1 is a series connection of multiple battery cells 10(1), 10(2), .... In the following, the battery cells 10(1), 10(2), ... will be collectively referred to as battery cells 10.

[0022] As shown in FIG. 2, the battery cell 10 is, for example, a lithium-ion secondary battery. The battery cell 10 includes a case 12 and a lid 14. The case 12 houses the electrode assembly 20. The case 12 has a flat, bottomed, rectangular (rectangular) shape with an opening on the upper side. The lid 14 closes the opening of the case 12. The case 12 and the lid 14 are made of a metal such as aluminum or an aluminum alloy.

[0023] The lid 14 is provided with two external terminals 16A, 16B. The external terminals 16A, 16B are used for charging and discharging power. The positive electrode side uncoated portion 32A, which is the end of the electrode body 20 on the positive electrode side, is electrically connected to the positive electrode external terminal 16A via the positive electrode side current collecting member 18A. The negative electrode side uncoated portion 42A, which is the end of the electrode body 20 on the negative electrode side, is electrically connected to the negative electrode external terminal 16B via the negative electrode side current collecting member 18B. The positive electrode side current collecting member 18A and the negative electrode side current collecting member 18B penetrate the lid 14 and are connected to the external terminals 16A, 16B. An insulating gasket is disposed between the lid 14 and the positive electrode side current collecting member 18A and the negative electrode side current collecting member 18B. The gasket electrically insulates the positive and negative current collecting members 18A, 18B from the lid 14, and seals the gap between the positive and negative current collecting members 18A, 18B and the lid 14. A nonaqueous electrolyte is injected into the case 12 through an injection port 15. The shape of the external terminals 16A, 16B is not limited to that shown in FIG. 2 and may be any shape.

[0024] [Electrode body] As shown in FIG. 3 , the electrode assembly 20 is a flat wound body formed by winding a laminate in which a long positive electrode sheet 30 and a negative electrode sheet 40 are stacked with a separator 50 interposed therebetween. The positive electrode sheet 30, the negative electrode sheet 40, and the separator 50 are stacked so that their respective longitudinal directions coincide with the longitudinal direction D1. In the laminate before winding, the positive electrode sheet 30, the separator 50, the negative electrode sheet 40, and the separator 50 are stacked in this order in the thickness direction. The electrode assembly 20 has a structure in which the positive electrode sheet 30 and the negative electrode sheet 40, stacked with the separator 50 sandwiched between them, are wound around a winding axis L1 extending in the width direction D2 of the strip shape.

[0025] The positive electrode sheet 30 includes a positive electrode current collector 32 and a positive electrode composite layer 34. The positive electrode current collector 32 is an electrode base material. The positive electrode current collector 32 is a foil-like member formed in a long strip. The positive electrode composite layer 34 is provided on each of two opposing surfaces of the positive electrode current collector 32. The positive electrode current collector 32 includes a positive electrode-side uncoated portion 32A at one end in the width direction D2 where the positive electrode composite layer 34 is not formed and the positive electrode current collector 32 is exposed.

[0026] The positive electrode current collector 32 is a metal foil made of aluminum or an alloy containing aluminum as a main component. The positive electrode current collector 32 functions as a current collector for the positive electrode. The positive electrode mixture layer 34 is a hardened liquid positive electrode mixture paste. The positive electrode mixture paste includes a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. The positive electrode mixture layer 34 is formed by drying the positive electrode mixture paste and evaporating the positive electrode solvent. Therefore, the positive electrode mixture layer 34 includes a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0027] The positive electrode active material is a lithium-containing composite metal oxide that can absorb and release lithium ions, which are charge carriers in the battery cell 10. The lithium-containing composite oxide is an oxide that contains lithium and a metal element other than lithium.

[0028] The positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent. Examples of the positive electrode conductive material include carbon black such as acetylene black and ketjen black, carbon fibers such as carbon nanotubes and carbon nanofibers, and graphite. The positive electrode binder is an example of a resin component contained in the positive electrode mixture paste. Examples of the positive electrode binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and styrene butadiene rubber (SBR).

[0029] The positive electrode sheet 30 may include an insulating layer at the boundary between the positive electrode uncoated portion 32A and the positive electrode composite layer 34. The insulating layer contains an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0030] [Negative electrode sheet] The negative electrode sheet 40 includes a negative electrode current collector 42 and a negative electrode composite layer 44. The negative electrode current collector 42 is an electrode base material. The negative electrode current collector 42 is a foil-like material formed into a long strip. The negative electrode composite layer 44 is provided on each of two opposing surfaces of the negative electrode current collector 42. The negative electrode current collector 42 includes a negative electrode-side uncoated portion 42A at one end in the width direction D2, opposite the positive electrode-side uncoated portion 32A, where the negative electrode composite layer 44 is not formed and the negative electrode current collector 42 is exposed.

[0031] A metal foil made of copper or an alloy containing copper as a main component is used for the negative electrode current collector 42. The negative electrode current collector 42 functions as a current collector for the negative electrode. The negative electrode mixture layer 44 is a hardened product of a liquid negative electrode mixture paste. The negative electrode mixture paste includes a negative electrode active material, a negative electrode solvent, a negative electrode thickener, and a negative electrode binder. The negative electrode mixture layer 44 is formed by drying the negative electrode mixture paste and evaporating the negative electrode solvent. Therefore, the negative electrode mixture layer 44 includes the negative electrode active material, and further includes a negative electrode thickener and a negative electrode binder as additives. The negative electrode mixture layer 44 may further include an additive such as a conductive material.

[0032] The negative electrode active material is a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and carbon nanotubes. One example of the negative electrode solvent is water. One example of the negative electrode dispersant is carboxymethyl cellulose (CMC). One example of the negative electrode binder is the same as the positive electrode binder. One example of the negative electrode binder is SBR.

[0033] [Separator] The separator 50 prevents contact between the positive electrode sheet 30 and the negative electrode sheet 40, and also holds the non-aqueous electrolyte between the positive electrode sheet 30 and the negative electrode sheet 40. When the electrode assembly 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the ends of the separator 50 toward the center.

[0034] The separator 50 may be a nonwoven fabric made of polypropylene or the like. The separator 50 may be made of, for example, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or an ion-conductive polymer electrolyte membrane.

[0035] [Nonaqueous electrolyte] The nonaqueous electrolyte is a composition in which a supporting electrolyte is contained in a nonaqueous solvent. For example, ethylene carbonate may be used as the nonaqueous solvent. However, the nonaqueous solvent is not limited to ethylene carbonate, and one or more materials selected from the group consisting of propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. may be used. Furthermore, one or more lithium compounds (lithium salts) may be used as the supporting electrolyte. Examples of lithium compounds include LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, and LiI.

[0036] Lithium bis(oxalato)borate (LiBOB) is added as a lithium salt to a solution consisting of a nonaqueous solvent and a supporting electrolyte. For example, LiBOB is added to the solution so that the LiBOB concentration in the solution is 0.001 to 0.1 mol / L. LiBOB is an additive intended to suppress the growth of an SEI (Solid Electrolyte Interface) coating. That is, LiBOB suppresses the growth of the SEI coating by forming a stable coating on the surface of the negative electrode active material particles.

[0037] The additive is not limited to LiBOB. For example, it may be a propionate-based compound. For example, it may be VC (vinylene carbonate). For example, it may be PS (propane sultone). For example, it may be BP (biphenyl). For example, it may be a methylene bissulfonate derivative. The purpose of the additive is not limited to suppressing the growth of the SEI film. It is not essential to use only one type of additive. The amount of additive added may be less than the amount of supporting electrolyte in the non-aqueous solvent.

[0038] [Lithium Deposition] FIG. 4( a ) shows an equivalent circuit of the negative electrode sheet 40 . FIG. 4(a) shows a negative electrode active material 44a constituting a negative electrode composite layer 44 formed on a negative electrode current collector 42 in a negative electrode sheet 40. Also shown is a composite resistance Re, which is the resistance of the negative electrode composite layer 44. The composite resistance Re quantifies the resistance to the flow of current within the negative electrode composite layer 44. Also shown in FIG. 4(a) is an electrolyte resistance Rion, which is the resistance of the non-aqueous electrolyte 60. The electrolyte resistance Rion quantifies the resistance that occurs in the movement of ions within the non-aqueous electrolyte 60.

[0039] Fig. 4(b) shows the current distribution during charging of the battery cell 10. As shown in Fig. 4(b), the current flows through both the path that passes through the composite resistance Re and the path that passes through the electrolyte resistance Rion.

[0040] 4(c) shows a case where the composite resistance Re is larger than that shown in FIG. 4(b). When the composite resistance Re is large, the amount of current flowing through the electrolyte resistance Rion increases. Therefore, the reaction tends to concentrate near the boundary between the negative electrode current collector 42 and the negative electrode composite layer 44.

[0041] 4(d) shows a case where the value of the electrolyte resistance Rion is larger than that shown in FIG. 4(b). When the value of the electrolyte resistance Rion is large, the amount of current flowing through the composite resistance Re increases. Therefore, the reaction tends to concentrate near the surface of the negative electrode composite layer 44.

[0042] When the reaction is concentrated locally, lithium is likely to be deposited in the vicinity. Therefore, lithium precipitation is suppressed by adjusting the ratio between the composite resistance Re and the electrolyte resistance Rion. Specifically, conditions are sought that prevent lithium precipitation at the maximum charging current expected during use of the battery cell 10. These conditions include the concentration of the supporting electrolyte and the concentration of the additive added to the solvent of the nonaqueous electrolyte 60. These conditions also include the thickness of the negative electrode composite layer 44, etc.

[0043] In this way, after identifying the optimal conditions for suppressing lithium precipitation, the battery cells 10 are manufactured according to those conditions. However, in the mass production process of the battery cells 10, variations occur in the thickness of the negative electrode composite layer 44, etc., which can cause deviations from the optimal conditions. Therefore, the amount of additive in the solution containing the solvent and supporting electrolyte of the nonaqueous electrolyte solution 60 is adjusted for each individual battery cell 10 during the manufacturing process.

[0044] "Battery cell manufacturing process" FIG. 5 shows part of the manufacturing process for the battery cell 10. 5, first, the negative electrode current collector 42 is formed (S10). Next, the current collector resistance value Rg of the negative electrode current collector 42 is measured (S12). This is performed by applying electrodes to both of the pair of surfaces of the sheet-like negative electrode current collector 42. The current collector resistance value Rg is the resistance value in the thickness direction of the negative electrode current collector 42. In other words, it is the resistance value of the negative electrode current collector 42 in the direction in which the negative electrode current collector 42 and the positive electrode current collector 32 face each other.

[0045] Next, negative electrode composite layers 44 are formed on both sides of the negative electrode current collector 42 for which the collector resistance value Rg has been measured (S14). Then, a negative electrode resistance value Rn, which is the resistance value of the negative electrode sheet 40, which is the negative electrode current collector 42 on which the negative electrode composite layers 44 have been formed, is measured (S16). This is performed by applying an electrode to each of the two negative electrode composite layers 44 on the side opposite to the side facing the negative electrode composite layer 44. In other words, this is performed by sandwiching the negative electrode composite layers 44 formed on both sides of the negative electrode current collector 42 between the electrodes. As a result, the negative electrode resistance value Rn is the total resistance value of the negative electrode current collector 42 and the pair of negative electrode composite layers 44. In other words, the negative electrode resistance value Rn is the resistance value in the thickness direction of the negative electrode sheet 40.

[0046] Then, the value of composite resistance Re, which is the resistance value of negative electrode composite layer 44, is calculated by subtracting current collector resistance Rg from negative electrode resistance Rn (S18). The value of composite resistance Re is twice the resistance value of one negative electrode composite layer 44 in the thickness direction.

[0047] Next, the amount of additive to be added is determined based on the value of the composite resistance Re (S20). Here, the value of the composite resistance Re is measured in advance when the optimal conditions for suppressing lithium precipitation have been found. Hereinafter, the value of the composite resistance Re measured in this manner will be referred to as the reference value. Note that not only the process of finding the optimal conditions but also the process of setting the reference value may be performed prior to the mass production process of the battery cells 10.

[0048] The difference between the composite resistance Re calculated in step S18 and the reference value indicates the individual difference between the battery cells 10. In step S20, the amount of additive is adjusted according to the individual difference information of the battery cells 10 indicated by the composite resistance Re. Methods for adjusting the amount of additive are described below for the following two cases.

[0049] Case 1: The composite resistance Re calculated in step S18 is smaller than the reference value. In this case, if the state shown in FIG. 4(b) is realized by the reference value, and the amount of additive added is set according to the reference value, the battery cell 10 will realize the state shown in FIG. 4(d). To prevent this from happening, the amount of additive is adjusted.

[0050] In the case of an additive of a type that decreases the conductivity of the nonaqueous electrolyte solution when added in an increased amount, the amount of the additive is reduced relative to the amount corresponding to the reference value. An additive of a type that increases the conductivity of the nonaqueous electrolyte solution when added in an increased amount is, for example, an additive whose conductivity is lower than the conductivity of a solution in which a supporting electrolyte is added to a solvent. Also, for example, an additive whose conductivity is lower than the conductivity of the solvent.

[0051] FIG. 6 illustrates this case. FIG. 6(a) shows the relationship between the density of the active material in negative electrode composite layer 44 and the value of composite resistance Re. In FIG. 6(a), the reference value of composite resistance Re is set to 100. When the density is higher than the reference value, the value of composite resistance Re becomes smaller. FIG. 6(a) illustrates an example of a value Re1 of composite resistance Re that is 20% lower than the reference value Re0. When a negative electrode sheet 40 having such a value is used, the electrolyte resistance Rion can be reduced by a predetermined amount by reducing the amount of additive, as shown in FIG. 6(b).

[0052] On the other hand, in the case of an additive of a type that increases the conductivity of the non-aqueous electrolyte solution when added, the amount of the additive is increased relative to the amount corresponding to the reference value. An additive of a type that increases the conductivity of the non-aqueous electrolyte solution when added is, for example, an additive that has a higher conductivity than the conductivity of a solution in which a supporting electrolyte is added to a solvent. Also, for example, an additive that has a higher conductivity than the conductivity of the solvent.

[0053] Case 2: The composite resistance Re calculated in step S18 is greater than the reference value. In this case, if the state shown in FIG. 4(b) is realized by the reference value, and the amount of additive added is set according to the reference value, the battery cell 10 will realize the state shown in FIG. 4(c). To prevent this from happening, the amount of additive is adjusted.

[0054] Here, in the case of an additive of a type that decreases the conductivity of the non-aqueous electrolyte when increased, the amount of the additive is increased relative to the amount corresponding to the reference value, whereas in the case of an additive of a type that increases the conductivity of the non-aqueous electrolyte when increased, the amount of the additive is decreased relative to the amount corresponding to the reference value.

[0055] Returning to FIG. 5, the amount of additive in the nonaqueous electrolyte to be injected into the battery cell 10 provided with the negative electrode sheet 40 is adjusted so as to achieve the determined amount of additive (S22). Fig. 7 shows the relationship between the composite resistance Re of battery cell 10(1) and battery cell 10(2) in an assembled battery 1 including a plurality of battery cells 10 manufactured using the steps shown in Fig. 5 and the amount of additive added. In Fig. 7, battery cell 10(1) is referred to as "cell 1" and battery cell 10(2) is referred to as "cell 2." Fig. 7 also shows a case where the composite resistance Re of battery cell (1) is greater than the composite resistance Re of battery cell (2).

[0056] 7(a) shows a case where an additive of a type that increases the conductivity of the nonaqueous electrolyte solution by increasing the amount is used, in which the amount of additive added to battery cell (1) is less than the amount of additive added to battery cell 10(2).

[0057] 7(b) shows a case where an additive of a type that reduces the conductivity of the nonaqueous electrolyte solution when added is used, in which the amount of additive added to battery cell (1) is greater than the amount of additive added to battery cell 10(2).

[0058] Here, the operation and effects of this embodiment will be described. In the manufacturing process of the battery cell 10, when the negative electrode current collector 42 is formed, the current collector resistance value Rg is measured. Furthermore, when the negative electrode composite layer 44 is formed on the negative electrode current collector 42, the negative electrode resistance value Rn is measured. Then, the current collector resistance value Rg is subtracted from the negative electrode resistance value Rn to calculate the composite resistance value Re. The amount of additive added to the solution containing the solvent and supporting electrolyte of the nonaqueous electrolyte is individually adjusted depending on the composite resistance value Re.

[0059] This allows the amount of additive to be optimized according to the individual differences between the negative electrode sheets 40 that make up each battery cell 10. This makes it possible to suppress lithium deposition. <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problem" column is as follows. Below, the correspondence is shown for each number of the means for solving the problem described in the "Means for Solving the Problem" column. [1, 3, 4, 5] The negative electrode corresponds to the negative electrode sheet 40. The positive electrode corresponds to the positive electrode sheet 30. The negative electrode active material layer corresponds to the negative electrode composite layer 44. The measurement process corresponds to steps S12, S16, and S18. The adjustment process corresponds to steps S20 and S22. The value of the negative electrode resistance variable corresponds to the value of the composite resistance Re. [2] The formation process corresponds to step S14. The current collector resistance value measurement process corresponds to step S12. The negative electrode resistance value measurement process corresponds to step S16. The resistance variable value calculation process corresponds to step S18. [6] Corresponds to Figures 7(a) and 7(b).

[0060] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0061] "About the adjustment process" The adjusting step is not limited to adjusting the amount of one type of additive added to a solution consisting of a solvent and a supporting electrolyte. For example, it may be a step of adding multiple types of additives and adjusting the amounts of two or more of the additives. Even when multiple types of additives are added, it is also possible to adjust the amount of only one type of additive in the adjusting step.

[0062] The adjusting step is not limited to a step of adjusting the amount of additive added to a solution containing a solvent and a supporting electrolyte. For example, it may be a step of adjusting the amount of supporting electrolyte. The adjustment of the amount of additive to be added in the adjustment step is not limited to either the additive to the solution consisting of a solvent and a supporting electrolyte or the supporting electrolyte. For example, the adjustment may be made to both the additive to the solution consisting of a solvent and a supporting electrolyte and the supporting electrolyte.

[0063] "others" The electrode assembly 20 may not be a wound body, but may be a laminate in which the positive electrode sheet 30 and the negative electrode sheet 40 are laminated with the separator 50 interposed therebetween and housed in the case 12.

[0064] The battery cell 10, which is a lithium-ion secondary battery, may be installed in automatic transport vehicles, special-purpose cargo handling vehicles, electric vehicles, hybrid vehicles, computers, and other electronic devices, or may be part of other systems. For example, it may be installed in a mobile object such as a ship or aircraft, or it may be a power supply system that supplies power from a power plant via a substation to a building or home where a secondary battery is installed.

[0065] <Notes> As used herein, the phrase "at least one" or similar expressions means "one or more" of the desired options. As an example, the phrase "at least one" used herein means "only one option" or "both of two options" when the number of options is two. As another example, the phrase "at least one" or similar expressions used herein means "only one option" or "any combination of two or more options" when the number of options is three or more. [Explanation of symbols]

[0066] 1. Battery pack 10...Battery cell 12…Case 14...lid body 15...Inlet 16A,16B…External terminal 18A...Positive electrode current collecting member 18B...Negative electrode side current collecting member 20...Electrode body 30...Positive electrode sheet 32...Positive electrode current collector 32A: Uncoated area on the positive electrode side 34...Positive electrode mixture layer 40...Negative electrode sheet 42...Negative electrode current collector 42A: Uncoated area on negative electrode side 44...Negative electrode composite layer 44a...Negative electrode active material 50...Separator 60...Nonaqueous electrolyte

Claims

1. A method for manufacturing a lithium ion secondary battery including a negative electrode, a positive electrode, and an electrolyte solution, The electrolyte solution contains a solvent, the negative electrode is a negative electrode current collector having a negative electrode active material layer formed thereon, a measuring step of measuring a value of a negative electrode resistance variable which is a variable indicating the electrical resistance of the negative electrode; an adjusting step of adjusting the amount of additive to be added to the solvent according to the difference between a reference value of the negative electrode resistance variable and the value of the negative electrode resistance variable measured in the measuring step; the value of the negative electrode resistance variable is a value obtained by subtracting the electrical resistance value of the negative electrode current collector from the electrical resistance value of the negative electrode, The adjustment step is a step of reducing the amount of the additive when the additive has a function of lowering the electrical resistance of the electrolyte solution and the measured value of the negative electrode resistance variable is larger than the reference value, or a step of increasing the amount of the additive when the additive has a function of increasing the electrical resistance of the electrolyte solution and the measured value of the negative electrode resistance variable is larger than the reference value.

2. The negative electrode resistance variable is a variable indicating the resistance of the negative electrode active material layer, a forming step of forming the negative electrode active material layer on the negative electrode current collector, the measuring step includes a current collector resistance value measuring step, a negative electrode resistance value measuring step, and a resistance variable value calculating step, the current collector resistance value measuring step is a step of measuring a resistance value of the negative electrode current collector prior to the forming step, the negative electrode resistance value measuring step is a step of measuring a resistance value of the negative electrode after the forming step, 2. The method for manufacturing a lithium ion secondary battery according to claim 1, wherein the resistance variable value calculation step calculates the value of the negative electrode resistance variable by subtracting the resistance value of the negative electrode current collector from the resistance value of the negative electrode.

3. The electrolytic solution contains a supporting electrolyte in addition to the solvent, The method for producing a lithium ion secondary battery according to claim 1 , wherein the additive is added to a solution containing the solvent and the supporting electrolyte.

4. A battery pack including a plurality of battery cells, the battery cell is a lithium ion secondary battery and includes a negative electrode, a positive electrode, and an electrolyte; The electrolyte solution contains a solvent, the negative electrode is a negative electrode current collector having a negative electrode active material layer formed thereon, a value of a negative electrode resistance variable of a first battery cell among the plurality of battery cells is greater than a value of a negative electrode resistance variable of a second battery cell among the plurality of battery cells; the value of the negative electrode resistance variable is a value obtained by subtracting the electrical resistance value of the negative electrode current collector from the electrical resistance value of the negative electrode, An assembled battery in which an additive added to the solvent has a function of lowering the electrical resistance of the electrolyte, and the amount of the additive added to the solvent of the first battery cell is less than the amount of the additive added to the solvent of the second battery cell, or in which the additive has a function of increasing the electrical resistance of the electrolyte, and the amount of the additive added to the solvent of the first battery cell is greater than the amount of the additive added to the solvent of the second battery cell.

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