Method for manufacturing battery

Abstract

To improve the quality of a relatively large battery.SOLUTION: The method includes a first liquid-injecting step S03 of injecting a first electrolytic solution into the case, and a second liquid-injecting step S03 of injecting a second electrolytic solution into the case after the first liquid-injecting step S04. The wound electrode body is formed in a flat shape by winding a positive electrode sheet, a separator, and a negative electrode sheet around a winding axis in a state where the positive electrode sheet, the separator, and the negative electrode sheet overlap each other. The length of the wound body in the winding axis direction is equal to or greater than 20cm. An additive is added to the first electrolyte solution and the second electrolyte solution. A concentration of the additive in the first electrolyte solution is higher than a concentration of the additive in the second electrolyte solution.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Japanese Patent Laid-Open Publication No. 2000-195549 discloses a method for manufacturing a battery, which is characterized by dispensing two or more types of electrolyte solutions having the same solvent composition but different electrolyte concentrations in order of lowest electrolyte concentration. According to Japanese Patent Laid-Open Publication No. 2000-195549, the use of such a method increases the impregnation speed of the electrolyte solution and shortens the time required for the electrolyte solution injection step, thereby improving battery productivity.

[0003] Japanese Patent Application Laid-Open Publication No. 2015-028875 discloses a method for manufacturing a nonaqueous electrolyte secondary battery, including a first filling step, a first charge / discharge step, a second filling step, and a third charge / discharge step. In the first filling step, a nonaqueous electrolyte containing a predetermined additive but not containing a difluorophosphate is filled into a battery case. In the first charge / discharge step, the battery is charged / discharged for the first time after the first filling step. In the second filling step, a nonaqueous electrolyte containing a difluorophosphate but not containing a predetermined additive is filled into the battery case after the first filling step. In the second charge / discharge step, the battery is charged / discharged for the second time after the second filling step. This manufacturing method is said to suppress the reaction of the predetermined additive with a film derived from difluorophosphate. As a result, it is said that a high-performance nonaqueous electrolyte secondary battery can be obtained by suppressing an increase in battery resistance and more appropriately utilizing the functions of the difluorophosphate and the additive.

[0004] Japanese Patent Application Laid-Open Publication No. 2017-098114 discloses a method for manufacturing a sealed battery, which involves preparing a first electrolytic solution and a second electrolytic solution in which a tracer gas is dissolved, injecting the first electrolytic solution into a battery case under reduced pressure, and then injecting the second electrolytic solution into the battery case under atmospheric pressure. According to this manufacturing method, the injection of the first electrolytic solution under reduced pressure can shorten the injection process. Furthermore, because a separate process for injecting a tracer gas is not required, the method also shortens the manufacturing time of a sealed battery that enables high-precision leak testing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-195549 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-028875 [Patent Document 3] Japanese Patent Application Publication No. 2017-098114 Summary of the Invention [Problem to be solved by the invention]

[0006] Meanwhile, the inventors of the present invention would like to improve the quality of relatively large batteries. [Means for solving the problem]

[0007] The battery manufacturing method disclosed herein involves injecting an electrolyte into a case housing a wound electrode assembly formed into a flat shape by winding a positive electrode sheet, a separator, and a negative electrode sheet in a stacked state around a winding axis. This battery manufacturing method includes a first liquid injection step of injecting a first electrolyte into the case housing the wound electrode assembly, and a second liquid injection step of injecting a second electrolyte into the case after the first liquid injection step. The length of the wound electrode assembly in the winding axis direction is 20 cm or more. An additive is added to the first and second electrolyte solutions. The concentration of the additive in the first electrolyte solution is higher than the concentration of the additive in the second electrolyte solution. This manufacturing method can improve the quality of relatively large batteries. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view schematically showing a battery. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 3 is a schematic diagram of a wound electrode body. [Figure 4] FIG. 4 is a flowchart showing an example of a method for manufacturing a battery. [Figure 5] FIG. 5 is a schematic diagram of the liquid injection device. [Figure 6] FIG. 6 is a graph showing the results of resistance measurement in Test Example 1, Test Example 2, and Comparative Example 1. [Figure 7] FIG. 7 is a graph showing the results of boron concentration measurements in Test Example 1, Test Example 2, and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the technology disclosed herein will be described below with reference to the drawings. The embodiment described herein is, of course, not intended to limit the present invention. The drawings are schematic and do not necessarily reflect the actual product. Furthermore, identical reference numerals are used for components and parts that perform the same function, and redundant explanations will be omitted where appropriate. The reference numerals X, Y, and Z in the drawings represent the thickness direction, width direction, and height direction, respectively. The Y direction is perpendicular to the X direction. The Z direction is perpendicular to the X and Y directions. However, these directions are merely provided for convenience of explanation and do not limit the installation form of the battery 10.

[0010] FIG. 1 is a perspective view schematically showing a battery 10. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. In FIG. 2, a wound electrode assembly 20 is shown in a partially broken cross-sectional view. In this specification, a lithium-ion secondary battery will be used as an example of the battery 10. However, the type of battery 10 is not limited to a lithium-ion secondary battery, and may be a sodium-ion secondary battery, a magnesium-ion secondary battery, or the like. As shown in FIG. 2, the battery 10 includes a case 11, a wound electrode assembly 20, and an electrolyte 30.

[0011] The case 11 includes a case body 12 and a sealing plate 14. As shown in FIG. 1, the case body 12 is formed in a substantially rectangular parallelepiped shape. The shape of the case body 12 is not limited to a substantially rectangular parallelepiped shape and may be, for example, a cylindrical shape. The case body 12 has a bottom surface 12a, a pair of narrow sides 12b, and a pair of wide sides 12c. The bottom surface 12a extends in the X direction and the Y direction. The pair of narrow sides 12b face each other in the Y direction. The pair of narrow sides 12b extend upward from both ends of the bottom surface 12a in the Y direction. The pair of wide sides 12c face each other in the X direction. The pair of wide sides 12c extend upward from both ends of the bottom surface 12a in the X direction. The pair of narrow sides 12b and the pair of wide sides 12c form side surfaces of the case body 12. The top of the case body 12 is open. The case body 12 is made of, for example, aluminum or an aluminum alloy containing aluminum as the main component, from the viewpoint of ensuring light weight and required rigidity.

[0012] The sealing plate 14 is attached to the opening of the case body 12. The sealing plate 14 closes the opening of the case body 12. The sealing plate 14 is joined to the case body 12, for example, by welding. By joining the sealing plate 14 to the case body 12, the interior of the case 11 is sealed. The sealing plate 14 forms the top surface of the case 11. The sealing plate 14 may be made of the same material as the case body 12. From the viewpoint of achieving weight reduction and ensuring the required rigidity, the sealing plate 14 may be made of, for example, aluminum or an aluminum alloy mainly containing aluminum. The sealing plate 14 has a gas release valve 15, a positive electrode terminal 16, a negative electrode terminal 17, and a liquid injection port 18.

[0013] Gas release valve 15 is provided in the center of sealing plate 14 in the Y direction. Gas release valve 15 breaks when the pressure inside case 11 rises above a predetermined value. This allows gas inside case 11 to be released to the outside of case 11 when the pressure inside case 11 reaches or exceeds the predetermined value.

[0014] The positive electrode terminal 16 and the negative electrode terminal 17 are provided as a pair at both ends of the sealing plate 14 in the Y direction. As shown in FIG. 2 , the positive electrode terminal 16 includes an external terminal 16a and an internal terminal 16b. The external terminal 16a is attached to the outside of the sealing plate 14 via a gasket 19a. The internal terminal 16b is attached to the inside of the sealing plate 14 via an insulator 19b. The internal terminal 16b extends in the vertical direction. The internal terminal 16b is electrically connected to the wound electrode body 20 inside the case 11.

[0015] The negative electrode terminal 17 includes an external terminal 17a and an internal terminal 17b. The external terminal 17a is attached to the outside of the sealing plate 14 via a gasket 19a. The internal terminal 17b is attached to the inside of the sealing plate 14 via an insulator 19b. The internal terminal 17b extends in the vertical direction. The internal terminal 17b is electrically connected to the wound electrode body 20 inside the case 11.

[0016] The liquid filling port 18 is an opening for pouring the electrolyte solution 30 into the case 11 after the sealing plate 14 is assembled to the case body 12. The liquid filling port 18 is formed as a through-hole that penetrates the sealing plate 14 in the Z direction. The liquid filling port 18 is disposed between the gas release valve 15 and the positive electrode terminal 16 in the Y direction. The arrangement of the liquid filling port 18 is not limited to the arrangement shown in FIG. 1 . For example, the liquid filling port 18 may be disposed between the gas release valve 15 and the negative electrode terminal 17 in the Y direction.

[0017] FIG. 3 is a schematic diagram of a wound electrode body 20. The wound electrode body 20 includes a positive electrode sheet 21, a negative electrode sheet 22, and sheet-like separators 24 and 25. The wound electrode body 20 is configured by winding the positive electrode sheet 21, the separators 24 and 25, and the negative electrode sheet 22 in a stacked state in the longitudinal direction around a winding axis WL to form a flat shape. As shown in FIG. 2, the wound electrode body 20 is housed inside a case 11. In the form shown in FIG. 2, the wound electrode body 20 is arranged inside the case 11 so that the winding axis WL is approximately parallel to the Y direction.

[0018] As shown in FIG. 3 , the positive electrode sheet 21 includes a foil-shaped positive electrode collector 21a and a positive electrode active material layer 21b formed on both sides of the positive electrode collector 21a along the longitudinal direction. The positive electrode active material layer 21b includes various materials, such as a positive electrode active material, a binder, and a conductive material. Materials used in conventional lithium-ion secondary batteries can be used without particular restrictions for the positive electrode collector 21a and the positive electrode active material layer 21b that constitute the positive electrode sheet 21. Furthermore, one side edge of the wound electrode assembly 20 in the Y direction of the battery 10 is free of the positive electrode active material layer 21b, providing an unformed portion 21a1 where the positive electrode collector 21a is exposed. Multiple positive electrode tabs 21t are intermittently provided in the unformed portion 21a1 at predetermined positions along the longitudinal direction of the positive electrode sheet 21. Each of the multiple positive electrode tabs 21t protrudes in the Y direction of the positive electrode sheet 21. 3, the positive electrode tabs 21t are arranged so that the positions of the positive electrode tabs 21t are aligned in the wound state. As shown in FIG. 2, the positive electrode tabs 21t are electrically connected to the internal terminal 16b of the positive electrode terminal 16.

[0019] As shown in FIG. 3 , the negative electrode sheet 22 includes a foil-shaped negative electrode current collector 22a and a negative electrode active material layer 22b formed on one or both sides of the negative electrode current collector 22a along the longitudinal direction. The negative electrode active material layer 22b contains various materials, such as a negative electrode active material and a binder. Materials used in conventional lithium-ion secondary batteries can be used without particular restrictions for the negative electrode current collector 22a and the negative electrode active material layer 22b that constitute the negative electrode sheet 22. The other side edge of the wound electrode assembly 20 in the Y direction of the battery 10 does not have the negative electrode active material layer 22b formed thereon, forming an unformed portion 22a1 where the negative electrode current collector 22a is exposed. Multiple negative electrode tabs 22t are intermittently provided in the unformed portion 22a1 along the longitudinal direction of the negative electrode sheet 22 at predetermined positions. Each of the multiple negative electrode tabs 22t protrudes in the Y direction of the negative electrode sheet 22. 3, the negative electrode tabs 22t are arranged so that the positions of the negative electrode tabs 22t are aligned in the wound state. As shown in FIG. 2, the negative electrode tabs 22t are electrically connected to the internal terminal 17b of the negative electrode terminal 17.

[0020] The separators 24, 25 are interposed between the positive electrode sheet 21 and the negative electrode sheet 22 to prevent direct contact between the positive electrode sheet 21 and the negative electrode sheet 22. Although not shown, the separators 24, 25 have a plurality of fine pores formed therein. These fine pores are configured to allow charge carriers to move between the positive electrode sheet 21 and the negative electrode sheet 22. Note that charge carriers are free particles that carry electric charge. In the case of a lithium-ion secondary battery, the charge carriers are lithium ions. The separators 24, 25 are made of a resin sheet or the like having the required heat resistance. Separators 24, 25 can be made of any material that can be used in conventional, general lithium-ion secondary batteries, without any particular restrictions.

[0021] The electrolyte solution 30 is accommodated in the case 11 together with the wound electrode assembly 20. The electrolyte solution 30 is a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte salt of a predetermined concentration. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and γ-butyrolactone (γBL). Examples of the non-aqueous solvent include chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). As the solvent, only one of the above non-aqueous solvents may be used, or a mixed solvent containing two or more of them may be used. When a mixed solvent is used, a mixture of a cyclic carbonate and a chain carbonate is preferable. This allows the electrolyte solution 30 to achieve both high levels of electrical conductivity and electrochemical stability. A suitable example of such a mixed solvent is a mixed solvent of EC, DMC, and EMC. The ratio of EC, DMC, and EMC may be EC:DMC:EMC=1-2:1-2:1-2. The ratio of EC, DMC, and EMC may be EC:DMC:EMC=1:1:1.

[0022] Examples of electrolyte salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(trifluoromethanesulfonyl)imide (Li(CFSO)N), lithium bis(fluorosulfonyl)imide (Li(FSO)N), and lithium trifluoromethanesulfonate (LiCFSO). The electrolyte solution 30 may contain only one of the above electrolyte salts, or two or more of them. The concentration of the electrolyte salt in the electrolyte solution 30 may be, for example, about 0.7 mol / L to 1.5 mol / L.

[0023] An additive is added to the electrolyte solution 30 contained in the case 11. The additive is, for example, a film-forming agent. The film-forming agent is a compound that decomposes at a lower voltage than other components (typically, the solvent) of the electrolyte solution 30 and forms an SEI film on the surface of the negative electrode sheet 22. The formed film contributes to reducing the resistance of the wound electrode body 20 and improving battery performance. Examples of the film-forming agent include lithium bis(oxalato)borate (LiBOB:LiB(C2O4)2), lithium difluorooxalatoborate (LiBF2(C2O4)2), lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2), lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), ethylene sulfite (ES), and propane sultone (PS). The electrolyte solution 30 may contain only one of the above additives, or two or more of them.

[0024] The additive may be lithium bis(oxalato)borate, lithium difluorophosphate, etc. When lithium bis(oxalato)borate is added to the electrolyte solution 30, the concentration of the lithium bis(oxalato)borate may be 0.1 wt% to 3 wt%. When lithium difluorophosphate is added to the electrolyte solution 30, the concentration of the lithium difluorophosphate may be 0.1 wt% to 5 wt%.

[0025] After the wound electrode body 20 is accommodated in the case 11, the electrolyte 30 is poured through the liquid pouring port 18. Specifically, in the form shown in Fig. 2, the wound electrode body 20 is accommodated in the case main body 12, the sealing plate 14 is attached to the opening at the top of the case main body 12, the case main body 12 is sealed, and then the electrolyte 30 is poured through the liquid pouring port 18 provided in the sealing plate 14.

[0026] The present inventors have confirmed that desired performance may not be achieved in relatively large batteries having a relatively large wound electrode assembly, such as one with a length in the winding axis direction of 20 cm or more. Therefore, the present inventors conducted disassembly and other investigations of such relatively large batteries to investigate the cause. As a result, it was confirmed that in such relatively large batteries, a large difference occurs in the resistance value of the wound electrode assembly between both ends and the center in the winding axis direction of the wound electrode assembly.

[0027] The present inventors conducted extensive research into the cause of this difference in resistance value and came to the following conclusion. When the electrolyte solution injected through the inlet impregnates the wound electrode body, it penetrates from both ends of the wound electrode body in the winding axis direction toward the center. Therefore, the center of the wound electrode body in the winding axis direction tends to be more difficult to impregnate with the electrolyte than the both ends in the winding axis direction. In particular, in relatively large batteries having a relatively large wound electrode body with a length in the winding axis direction of 20 cm or more, the distance from both ends in the winding axis direction to the center is long. Therefore, in relatively large batteries, differences in the impregnation state of the electrolyte are likely to occur between both ends and the center in the winding axis direction of the wound electrode body, and so-called impregnation unevenness is likely to occur.

[0028] The electrolyte solution contains, for example, a coating-forming additive. The coating-forming additive decomposes during charging and discharging of the battery, forming a coating on the surface of the negative electrode sheet. It is desirable that the coating be uniformly formed on the surface of the negative electrode sheet. However, if uneven impregnation of the electrolyte occurs in the winding axis direction, the amount of additive varies depending on the position in the winding axis direction. Furthermore, when the electrolyte solution impregnates the wound electrode body from both ends in the winding axis direction toward the center, the additive is likely to be adsorbed by the wound electrode body, resulting in a relatively high additive concentration at both ends in the winding axis direction and a relatively low additive concentration in the center. For these reasons, the coating is not uniformly formed on the surface of the negative electrode sheet, and the quality of the coating varies depending on the position in the winding axis direction of the wound electrode body. If the quality of the coating is uneven, the resistance of the negative electrode sheet may vary locally, affecting the performance of the battery.

[0029] Based on the above, the inventors of the present application speculated that in relatively large batteries, differences in the concentration of additives occur between the both ends and the center in the winding axis direction of the wound electrode body, resulting in large differences in resistance value. Therefore, the inventors of the present application investigated a manufacturing method that would reduce the differences in the concentration of additives between the both ends and the center in the winding axis direction, even for relatively large wound electrode bodies with a length in the winding axis direction of 20 cm or more.

[0030] 4 is a flowchart showing an example of a method for manufacturing the battery 10. The method for manufacturing the battery 10 includes a preparation step S01, an assembly step S02, a first liquid injection step S03, and a second liquid injection step S04.

[0031] In the preparation step S01, the case body 12, the sealing plate 14, and the wound electrode body 20 are each prepared. Note that the method for preparing these components prepared in the preparation step S01 is not particularly limited. The case body 12 is prepared, for example, by bending and shaping a rectangular flat plate. The sealing plate 14 is prepared, for example, by machining a rectangular flat plate, such as by drilling holes, and attaching a positive electrode terminal 16 and a negative electrode terminal 17 to the holes. The wound electrode body 20 is prepared using various conventionally known methods for manufacturing wound electrode bodies. In the preparation step S01, the length of the wound electrode body 20 prepared in the direction of the winding axis WL is 20 cm or more. That is, in the preparation step S01, a relatively large wound electrode body is prepared, in which the width of the wound electrode body 20 is 20 cm or more.

[0032] In the assembly step S02, the wound electrode body 20 is inserted into the case body 12 through an opening in the case body 12. Furthermore, in the assembly step S02, with the wound electrode body 20 inserted inside the case body 12, the sealing plate 14 is attached to the opening in the case body 12, and the case body 12 and the sealing plate 14 are joined together. The method for joining the case body 12 and the sealing plate 14 is not particularly limited. For example, laser welding or the like may be used to join the case body 12 and the sealing plate 14.

[0033] 5 is a schematic diagram of the liquid injection device 50. The liquid injection device 50 is a device for injecting the electrolyte into the case 11 in the first liquid injection step S03 and the second liquid injection step S04. The liquid injection device 50 includes a storage chamber 51, a first tank 54, a second tank 55, a liquid injection flow path 56, a first liquid injection valve 57, a second liquid injection valve 58, and a liquid injection nozzle 59.

[0034] The storage chamber 51 is configured to be able to store the battery 10. The storage chamber 51 includes a chamber body 52 and a lid 53. The chamber body 52 is formed in a rectangular parallelepiped shape and is open at the top. The lid 53 is configured to be able to open and close the opening of the chamber body 52. ​​Note that the configuration of the storage chamber 51 is not particularly limited as long as it is configured to be able to store the battery 10.

[0035] The first tank 54 stores the first electrolytic solution 31, and the second tank 55 stores the second electrolytic solution 32. The first electrolytic solution 31 and the second electrolytic solution 32 contain the same type and composition of non-aqueous solvent. The first electrolytic solution 31 and the second electrolytic solution 32 contain the same type of electrolyte salt. The first electrolytic solution 31 and the second electrolytic solution 32 contain the same type of additive. The concentration of the additive in the first electrolytic solution 31 is higher than the concentration of the additive in the second electrolytic solution 32. The concentration of the additive in the first electrolytic solution 31 may be approximately 1.5 to 5 times the concentration of the additive in the second electrolytic solution 32.

[0036] The liquid injection flow path 56 connects the first tank 54 and the liquid injection nozzle 59, and also connects the second tank 55 and the liquid injection nozzle 59. The liquid injection flow path 56 is provided to penetrate the lid 53 of the storage chamber 51. The liquid injection nozzle 59 is provided at the tip of the liquid injection flow path 56. The liquid injection nozzle 59 is a member that serves as a discharge port for the first electrolytic solution 31 and the second electrolytic solution 32. The first liquid injection valve 57 is provided between the first tank 54 and the liquid injection nozzle 59. When the first liquid injection valve 57 is opened, the first electrolytic solution 31 is injected from the first tank 54 through the liquid injection flow path 56 into the inside of the case 11. The second liquid injection valve 58 is provided between the second tank 55 and the liquid injection nozzle 59. When the second liquid injection valve 58 is opened, the second electrolytic solution 32 is injected from the second tank 55 through the liquid injection flow path 56 into the inside of the case 11.

[0037] In the first liquid injection step S03, the first electrolytic solution 31 is injected into the case 11. The first liquid injection valve 57 is opened, thereby injecting the first electrolytic solution 31 into the inside of the case 11. In the first liquid injection step S03, a predetermined amount of the first electrolytic solution 31 is injected.

[0038] The second liquid injection step S04 is performed a predetermined time after the first liquid injection step S03 is completed. For example, the second liquid injection step S04 may be started 30 to 120 seconds after the first liquid injection step S03 is completed. In the second liquid injection step S04, the second electrolytic solution 32 is injected into the case 11. The second liquid injection valve 58 is opened to inject the second electrolytic solution 32 into the case 11. As a result, the first electrolytic solution 31 and the second electrolytic solution 32 are mixed inside the case 11 to form the above-described electrolytic solution 30. In the second liquid injection step S04, a predetermined amount of the second electrolytic solution 32 is injected so that the concentration of the additive in the electrolytic solution 30 in the case 11 becomes a predetermined concentration.

[0039] Test examples in which the manufacturing method disclosed herein was carried out will be described below, although it is not intended that the present invention be limited to the following test examples.

[0040] The battery was prepared by housing a wound electrode body having a width of 30 cm and a height of 8 cm in an aluminum case formed in a substantially rectangular parallelepiped shape.

[0041] The following first electrolytic solution was prepared for Test Example 1. The solvent for the first electrolytic solution was a mixed solvent of EC, DMC, and EMC. The ratio of EC, DMC, and EMC was EC:DMC:EMC=1:1:1. Lithium hexafluorophosphate was used as the electrolyte salt for the first electrolytic solution. The concentration of lithium hexafluorophosphate in the first electrolytic solution was 1.0 mol / L. Lithium bis(oxalato)borate was added to the first electrolytic solution as an additive. The concentration of lithium bis(oxalato)borate in the first electrolytic solution was 1.5 wt%.

[0042] The following second electrolytic solution was prepared for Test Example 1. The solvent for the second electrolytic solution was a mixed solvent of EC, DMC, and EMC. The ratio of EC, DMC, and EMC was EC:DMC:EMC=1:1:1. Lithium hexafluorophosphate was used as the electrolyte salt for the second electrolytic solution. The concentration of lithium hexafluorophosphate in the second electrolytic solution was 1.0 mol / L. Lithium bis(oxalato)borate was added to the second electrolytic solution as an additive. The concentration of lithium bis(oxalato)borate in the second electrolytic solution was 0.5 wt%.

[0043] In Test Example 1, 150 mL of the first electrolyte solution was injected into the case as the first injection step. 60 seconds after the injection of the first electrolyte solution was completed, 150 mL of the second electrolyte solution was injected into the case as the second injection step. After the injection of the second electrolyte solution, the battery was left for two hours, allowing the first and second electrolyte solutions to be impregnated into the wound electrode body. Two hours after the injection of the second electrolyte solution, the battery was charged and discharged, and then the battery was disassembled and the wound electrode body was removed from the case. The removed wound electrode body was then thoroughly dried. A portion of the negative electrode sheet was cut from the dried wound electrode body along the winding axis. Resistance values ​​were measured at several locations on the cut negative electrode sheet. Furthermore, to evaluate unevenness in the formation of the coating on the negative electrode sheet, the boron concentration was measured at several locations on the cut negative electrode sheet. The boron concentration was measured using ICP analysis.

[0044] In Test Example 2, lithium bis(oxalato)borate was added as an additive to the first electrolytic solution. The concentration of lithium bis(oxalato)borate in the first electrolytic solution was 2.0 wt%. In Test Example 2, lithium bis(oxalato)borate was added as an additive to the second electrolytic solution. The concentration of lithium bis(oxalato)borate in the second electrolytic solution was 0.5 wt%. In Test Example 2, other conditions and procedures were the same as in Test Example 1.

[0045] In Comparative Example 1, only one type of electrolyte solution was prepared. The type and composition of the solvent of the electrolyte solution in Comparative Example 1 were the same as in Test Example 1. The type and concentration of the electrolyte salt of the electrolyte solution in Comparative Example 1 were the same as in Test Example 1. Lithium bis(oxalato)borate was added to the electrolyte solution as an additive. In Comparative Example 1, the concentration of lithium bis(oxalato)borate was 1.0 wt%. In Comparative Example 1, 300 mL of the electrolyte solution was poured into the case. As in Test Example 1, the battery was left for two hours after pouring the electrolyte solution, and the wound electrode body was impregnated with the electrolyte solution. As in Test Example 1, charging and discharging were performed two hours after pouring the electrolyte solution, and then the battery was disassembled and the wound electrode body was removed from the case. Thereafter, the resistance value and boron concentration were measured at several locations of the cut negative electrode sheet using the same procedure as in Test Example 1.

[0046] Table 1 shows the concentrations of lithium bis(oxalato)borate in the electrolyte solutions in Test Example 1, Test Example 2, and Comparative Example 1.

[0047] [Table 1]

[0048] FIG. 6 is a graph showing the results of resistance measurements in Test Example 1, Test Example 2, and Comparative Example 1. In FIG. 6, (a) is a graph showing the results of Test Example 1, (b) is a graph showing the results of Test Example 2, and (c) is a graph showing the results of Comparative Example 1. In graphs (a) to (c) of FIG. 6, the horizontal axis indicates the position in the winding axis direction of the wound electrode body, and the vertical axis indicates the resistance value. On the horizontal axis of graphs (a) to (c) of FIG. 6, 0 mm indicates one end of the negative electrode sheet in the winding axis direction, and 300 mm indicates the other end of the negative electrode sheet in the winding axis direction. As can be seen from FIG. 6, the variation in resistance value depending on the position in the winding axis direction was smaller in Test Example 1 and Test Example 2 than in Comparative Example 1.

[0049] FIG. 7 is a graph showing the results of boron concentration measurements in Test Example 1, Test Example 2, and Comparative Example 1. In FIG. 7, (a) is a graph showing the results of Test Example 1, (b) is a graph showing the results of Test Example 2, and (c) is a graph showing the results of Comparative Example 1. In graphs (a) to (c) of FIG. 7, the horizontal axis indicates the position in the winding axis direction of the wound electrode body, and the vertical axis indicates the resistance value. On the horizontal axis of graphs (a) to (c) of FIG. 7, 0 mm indicates one end of the negative electrode sheet in the winding axis direction, and 300 mm indicates the other end of the negative electrode sheet in the winding axis direction. As can be seen from FIG. 7, the variation in boron concentration depending on the position in the winding axis direction was smaller in Test Example 1 and Test Example 2 than in Comparative Example 1. Therefore, it is presumed that the unevenness in coating formation depending on the position in the winding axis direction is smaller in Test Example 1 and Test Example 2 than in Comparative Example 1.

[0050] In Test Example 3, a first electrolytic solution and a second electrolytic solution containing lithium difluorophosphate as an additive were prepared. The concentration of lithium difluorophosphate in the first electrolytic solution was 3.0 wt%. The concentration of lithium difluorophosphate in the second electrolytic solution was 1.0 wt%. Other conditions were the same as those in Test Example 1. For Test Example 3, the resistance value and phosphorus concentration of the negative electrode sheet were measured using the same procedure as in Test Example 1 above. For comparison with Test Example 3, an electrolytic solution containing lithium difluorophosphate at a concentration of 2.0 wt% was prepared as Comparative Example 2. Other conditions for Comparative Example 2 were the same as those for Comparative Example 1. For Comparative Example 2, the resistance value and phosphorus concentration of the negative electrode sheet were measured using the same procedure as in Comparative Example 1 above. As a result, in Test Example 3, the variation in resistance depending on the position in the winding axis direction was smaller than in Comparative Example 2, and the variation in phosphorus concentration depending on the position in the winding axis direction was also smaller. Therefore, the electrolyte solution containing lithium difluorophosphate as an additive also showed the same tendency as the electrolyte solution containing lithium bis(oxalato)borate as an additive.

[0051] As described above, the manufacturing method of battery 10 disclosed herein includes a first liquid injection step S03 of injecting a first electrolytic solution 31 into case 11 containing wound electrode body 20, and a second liquid injection step S04 of injecting a second electrolytic solution 32 into case 11 after completion of first liquid injection step S03. The concentration of the additive in first electrolytic solution 31 is higher than the concentration of the additive in second electrolytic solution 32. This makes it possible to improve the quality even of a relatively large battery 10 configured by housing a relatively large wound electrode body 20, such as one having a length of 20 cm or more in the winding axis WL direction, in case 11. The reason for this is believed to be as follows.

[0052] In the first liquid injection step S03, a first electrolyte solution 31 with a high concentration of additive is injected, so that a certain amount of additive reaches the central portion of the wound electrode body 20 in the winding axis WL direction, which is difficult to impregnate with the electrolyte. Then, in the second liquid injection step S04, a second electrolyte solution 32 with a low concentration of additive is injected, so that the wound electrode body 20 is impregnated with the electrolyte solution 30 so that the additive concentration is uniform in the winding axis WL direction. This makes it possible to suppress variations in the additive concentration in the winding axis WL direction, even for relatively large batteries 10. This reduces unevenness in the formation of the coating in the winding axis WL direction, and reduces variations in the resistance value in the winding axis WL direction. This makes it possible to improve the quality of relatively large batteries 10.

[0053] The additives added to the first electrolytic solution 31 and the second electrolytic solution 32 may be film-forming agents such as lithium bis(oxalato)borate and lithium difluorophosphate. Adding such film-forming agents to the electrolytic solution 30 can suppress a decrease in battery capacity due to decomposition of the solvent, and can also form a suitable film uniformly on the surface of the negative electrode sheet 22. This can improve the quality of the battery 10.

[0054] When a coating is formed on the surface of the negative electrode sheet 22 during charging and discharging of the battery 10, some of the electrolyte salt, such as lithium hexafluorophosphate, contained in the electrolyte solution 30 may also be decomposed to form a coating. Therefore, even if the concentrations of the electrolyte salt in the first electrolyte solution 31 and the second electrolyte solution 32 are different, the same effect as when the concentrations of the additives are different can be obtained. That is, by making the concentration of the electrolyte salt in the first electrolyte solution 31 higher than that in the second electrolyte solution 32, unevenness in the formation of the coating in the winding axis WL direction can be reduced, and the variation in the resistance value in the winding axis WL direction can be reduced. When the concentration of the electrolyte salt in the first electrolyte solution 31 is higher than that in the second electrolyte solution 32, the first electrolyte solution 31 and the second electrolyte solution 32 do not need to contain an additive. The second liquid injection step S04 of injecting the second electrolytic solution 32 may be started 30 to 120 seconds after the completion of the first liquid injection step S03 of injecting the first electrolytic solution 31. The concentration of the electrolyte salt in the first electrolytic solution 31 may be 1.5 to 3 times the concentration of the electrolyte salt in the second electrolytic solution 32.

[0055] The manufacturing method of battery 10 disclosed herein may include steps other than those described above. For example, the manufacturing method of battery 10 may include a depressurizing step of depressurizing the inside of case 11 between assembly step S02 and first liquid filling step S03. Furthermore, the manufacturing method of battery 10 may include an opening step of opening the inside of case 11 to the atmosphere after second liquid filling step S04. By performing such a depressurizing step and an opening step, the time required for impregnation with electrolyte solution 30 can be shortened.

[0056] The technology disclosed herein has been described in various ways. Unless otherwise specified, the embodiments and the like described herein do not limit the present invention. Furthermore, the technology disclosed herein can be modified in various ways, and as long as no particular problems arise, each component and each process described herein can be omitted or combined as appropriate. Furthermore, this specification includes the disclosures described in the following sections.

[0057] Section 1: A method for manufacturing a battery, comprising: injecting an electrolyte into a case that houses a wound electrode body formed into a flat shape by winding a positive electrode sheet, a separator, and a negative electrode sheet in a superposed state around a winding axis; a first liquid injection step of injecting a first electrolytic solution into the case that houses the wound electrode body; a second liquid injection step of injecting a second electrolytic solution into the case after the first liquid injection step, The length of the wound electrode body in the winding axis direction is 20 cm or more, an additive is added to the first electrolytic solution and the second electrolytic solution; A method for manufacturing a battery, wherein the concentration of the additive in the first electrolytic solution is higher than the concentration of the additive in the second electrolytic solution.

[0058] Section 2: Item 2. The method for producing a battery according to Item 1, wherein the additive is a film-forming agent that forms a film on the wound electrode body.

[0059] Section 3: Item 3. The method for producing a battery according to Item 2, wherein the film-forming agent is lithium bis(oxalato)borate.

[0060] Section 4: Item 3. The method for producing a battery according to Item 2, wherein the film-forming agent is lithium difluorophosphate.

[0061] Section 5: Item 5. The method for producing a battery according to any one of items 1 to 4, wherein the concentration of the additive in the first electrolytic solution is 1.5 to 5 times the concentration of the additive in the second electrolytic solution.

[0062] Item 6: A method for manufacturing a battery, comprising: injecting an electrolyte into a case that houses a wound electrode body formed into a flat shape by winding a positive electrode sheet, a separator, and a negative electrode sheet in a superposed state around a winding axis; a first liquid injection step of injecting a first electrolytic solution into the case that houses the wound electrode body; a second liquid injection step of injecting a second electrolytic solution into the case after the first liquid injection step, The length of the wound electrode body in the winding axis direction is 20 cm or more, A method for manufacturing a battery, wherein the concentration of the electrolyte salt in the first electrolytic solution is higher than the concentration of the electrolyte salt in the second electrolytic solution.

[0063] Section 7: Item 7. The method for producing a battery according to item 6, wherein the concentration of the electrolyte salt in the first electrolytic solution is 1.5 to 3 times the concentration of the electrolyte salt in the second electrolytic solution.

[0064] Section 8: 8. The method for manufacturing a battery according to any one of items 1 to 7, wherein the second liquid injection step is carried out 30 to 120 seconds after the first liquid injection step is completed. [Explanation of symbols]

[0065] 10 batteries 11 cases 18 Filling port 20 Wound electrode body 21 Positive electrode sheet 22 Negative electrode sheet 24 Separator 25 Separator 30 Electrolyte 31 First electrolyte 32 Second electrolyte 50 Injection device

Claims

1. A method for manufacturing a battery, comprising: injecting an electrolyte into a case that houses a wound electrode body formed into a flat shape by winding a positive electrode sheet, a separator, and a negative electrode sheet in a superposed state around a winding axis; a first liquid injection step of injecting a first electrolytic solution into the case that houses the wound electrode body; a second liquid injection step of injecting a second electrolytic solution into the case after the first liquid injection step, The length of the wound electrode body in the winding axis direction is 20 cm or more, an additive is added to the first electrolytic solution and the second electrolytic solution; A method for manufacturing a battery, wherein a concentration of the additive in the first electrolytic solution is higher than a concentration of the additive in the second electrolytic solution.

2. The method for manufacturing a battery according to claim 1 , wherein the additive is a film-forming agent that forms a film on the wound electrode body.

3. The method for manufacturing a battery according to claim 2 , wherein the film-forming agent is lithium bis(oxalato)borate.

4. The method for manufacturing a battery according to claim 2 , wherein the film-forming agent is lithium difluorophosphate.

5. 2. The method for producing a battery according to claim 1, wherein the concentration of the additive in the first electrolytic solution is 1.5 to 5 times the concentration of the additive in the second electrolytic solution.

6. A method for manufacturing a battery, comprising: injecting an electrolyte into a case that houses a wound electrode body formed into a flat shape by winding a positive electrode sheet, a separator, and a negative electrode sheet in a superposed state around a winding axis; a first liquid injection step of injecting a first electrolytic solution into the case that houses the wound electrode body; a second liquid injection step of injecting a second electrolytic solution into the case after the first liquid injection step, The length of the wound electrode body in the winding axis direction is 20 cm or more, A method for manufacturing a battery, wherein a concentration of an electrolyte salt in the first electrolytic solution is higher than a concentration of an electrolyte salt in the second electrolytic solution.

7. 7. The method for manufacturing a battery according to claim 6, wherein the concentration of the electrolyte salt in the first electrolytic solution is 1.5 to 3 times the concentration of the electrolyte salt in the second electrolytic solution.

8. 8. The method for manufacturing a battery according to claim 1, wherein the second liquid injection step is performed 30 to 120 seconds after the first liquid injection step is completed.

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