Lithium-ion battery manufacturing method

Abstract

A method for manufacturing a lithium ion battery, comprising the steps of: forming an adhesive PGLYD polymer by urethane bonding the PGLYD polymer; forming a positive electrode containing lithium, iron, phosphorus, and amorphous carbon; forming a negative electrode containing graphite and amorphous carbon; and placing the positive electrode, the negative electrode, and a predetermined electrolyte in a predetermined container and sealing it, wherein at least one of the positive electrode and the negative electrode contains the adhesive PGLYD polymer as a binder.

Description

[Technical Field]

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

[0002] Lithium-ion batteries are known to have high energy density, are capable of rapid charging and discharging, and are expected to have a long life. It is also known that lithium-ion batteries can be constructed from a variety of materials, such as ternary lithium-ion batteries that use nickel, manganese, and cobalt as positive electrode materials, and lithium iron phosphate-ion batteries that use lithium iron phosphate (LFP: LiFePO4) as the positive electrode material (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-212045 Summary of the Invention [Problem to be solved by the invention]

[0004] In lithium-ion batteries, PVDF (Polyvinylidene Difluoride) and other materials are used as electrode binders from the viewpoints of mechanical properties, chemical stability, and adhesive ability. However, PVDF has poor ionic and electronic conductivity, and the addition of substances with higher ionic and electronic conductivity has been considered. Thus, there has been a demand for binders that have high ionic and electronic conductivity while maintaining mechanical properties, chemical stability, and adhesive ability.

[0005] The present invention has been made in view of these points, and has an object to increase the ionic conductivity and electronic conductivity of a binder used in a lithium ion battery. [Means for solving the problem]

[0006] In a first aspect of the present invention, there is provided a method for manufacturing a lithium ion battery, comprising the steps of: forming an adhesive PGLYD polymer by urethane bonding a polyglycidol (PGLYD) polymer; forming a positive electrode comprising a positive electrode active material and amorphous carbon or carbon fiber; forming a negative electrode comprising a negative electrode active material and amorphous carbon or carbon fiber; and placing the positive electrode, the negative electrode, and a predetermined electrolyte in a predetermined container and sealing it, wherein at least one of the positive electrode and the negative electrode contains the adhesive PGLYD polymer as a binder.

[0007] In the step of forming the positive electrode, the positive electrode may be formed by applying a positive electrode slurry using a positive electrode material having a positive electrode active material, amorphous carbon or carbon fiber, and the PGLYD polymer to which adhesive properties have been imparted, to a substrate and drying the slurry, and the positive electrode material may contain 1 wt % or more and 50 wt % or less of the PGLYD polymer.

[0008] In the step of forming the negative electrode, the negative electrode may be formed by applying a negative electrode slurry using a negative electrode material containing a negative electrode active material, amorphous carbon or carbon fiber, and the PGLYD polymer to which adhesive properties have been imparted, to a substrate and drying the slurry, and the negative electrode material may contain 1 wt % or more and 50 wt % or less of the PGLYD polymer.

[0009] In a second aspect of the present invention, there is provided a lithium ion battery comprising: a positive electrode containing a positive electrode material and amorphous carbon or carbon fiber; a negative electrode containing a negative electrode active material and amorphous carbon or carbon fiber; and an electrolyte, wherein at least one of the positive electrode and the negative electrode has a PGLYD polymer that has been given adhesiveness by a urethane bond. [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain an effect of increasing the ionic conductivity and electronic conductivity of a binder used in a lithium ion battery. [Brief explanation of the drawings]

[0011] [Figure 1] 1 shows an example of a schematic configuration of a lithium iron phosphate battery 10 according to this embodiment. [Figure 2] The basic synthetic route for PGLYD polymers is shown. [Figure 3] 1 shows a synthetic route for a PGLYD polymer having adhesive properties according to an embodiment of the present invention. [Figure 4] The molecular structure of the adhesive PGLYD polymer is shown. [Figure 5] An example of a manufacturing flow of the lithium iron phosphate battery 10 according to this embodiment will be described. [Figure 6] 1 shows an example of the configuration of a lithium iron phosphate battery 10 according to this embodiment. [Figure 7] An example of an assembly flow for the lithium iron phosphate battery 10 according to this embodiment will be described below. [Figure 8] 1 shows an example of charge / discharge characteristics of the lithium iron phosphate ion battery 10 according to this embodiment. [Figure 9] 1 shows an example of the charge / discharge cycle characteristics of the lithium iron phosphate battery 10 according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] <General configuration of the lithium iron phosphate battery 10> In this example, a lithium iron phosphate ion battery will be described as an example of a lithium ion battery. FIG. 1 shows an example of the schematic configuration of a lithium iron phosphate ion battery 10 according to this embodiment. The lithium iron phosphate ion battery 10 is a rechargeable secondary battery. The lithium iron phosphate ion battery 10 includes a positive electrode 20, a negative electrode 30, a separator 40, an electrolyte 50, and a storage container 60.

[0013] The positive electrode 20 contains lithium, iron, phosphorus, and amorphous carbon. The active material of the positive electrode 20 is lithium iron phosphate. The positive electrode 20 is an electrode formed, for example, from lithium iron phosphate, amorphous carbon, and a binder as positive electrode materials. Here, the amorphous carbon is a conductive additive such as ketjen black or acetylene black. The amorphous carbon may also be carbon fiber. The conductive additive is a material used to reduce the resistance of the electrode when forming an electrode for a lithium ion battery. The binder will be described later.

[0014] The negative electrode 30 includes graphite and amorphous carbon. The active material of the negative electrode 30 is graphite. The negative electrode 30 is an electrode formed from negative electrode materials such as amorphous carbon, a thickener such as CMC (Carboxymethyl Cellulose), and a binder. The amorphous carbon may be carbon fiber. The binder will be described later.

[0015] The separator 40 separates the positive electrode 20 and the negative electrode 30 while allowing lithium ions to move between the positive electrode 20 and the negative electrode 30. The separator 40 is, for example, a film having a thickness of about several tens of micrometers and having a plurality of through-holes of 1 μm or less. The separator 40 is made of, for example, polyethylene, polypropylene, or the like.

[0016] The electrolyte 50 ionizes lithium into positive and negative ions, allowing the ions to move. The electrolyte 50 is a solvent, solution, gel-like substance, or the like. The electrolyte 50 is, for example, an organic electrolytic solution in which approximately 1 mol of lithium salt (LiPF6, LiBF4, LiClO4, etc.) is dissolved in an organic solvent. Examples of organic solvent materials include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0017] The storage container 60 accommodates the positive electrode 20, the negative electrode 30, the separator 40, and the electrolyte 50. The storage container 60 is preferably a container that seals the positive electrode 20, the negative electrode 30, the separator 40, and the electrolyte 50. The storage container 60 has a positive terminal 61 electrically connected to the positive electrode 20 and a negative terminal 62 electrically connected to the negative electrode 30.

[0018] The lithium iron phosphate battery 10 is charged when a power source is connected to the positive terminal 61 and the negative terminal 62. When the lithium iron phosphate battery 10 is charged, electrons move from the positive electrode 20 to the negative electrode 30, and lithium ions pass from the positive electrode 20 through the electrolyte 50 and are stored in the negative electrode 30, generating a potential difference between the positive electrode 20 and the negative electrode 30.

[0019] On the other hand, lithium iron phosphate ion battery 10 discharges when a discharge circuit such as a load is connected to positive terminal 61 and negative terminal 62. When lithium iron phosphate ion battery 10 is discharged, electrons flow from negative electrode 30 to positive electrode 20 through the discharge circuit, and lithium ions stored in negative electrode 30 move to positive electrode 20 through electrolyte 50, where they combine with electrons in positive electrode 20 and are reduced to lithium oxide.

[0020] The lithium iron phosphate ion battery 10 according to this embodiment uses a PGLYD polymer with high ionic and electronic conductivity as a binder for at least one of the positive electrode 20 and the negative electrode 30. However, typical PGLYD polymers have poor mechanical properties and adhesive properties, making them difficult to use as a binder for the lithium iron phosphate ion battery 10.

[0021] Therefore, the inventors have imparted mechanical properties and adhesive properties to PGLYD polymer by urethane bonding, and have found that the PGLYD polymer to which adhesive properties have been imparted in this way functions as a binder with high ionic and electronic conductivity while retaining mechanical properties, chemical stability, and adhesive ability.

[0022] <PGLYDポリマー> Figure 2 shows the basic synthesis route for PGLYD polymer. Glycidol is placed in a flask and a nitrogen atmosphere is created. The starting material, tetraethylene glycol, the catalyst tin octoate, and DMF (dimethylformamide) are added to the flask and stirred until homogeneous, then the temperature is raised to 90°C to polymerize. The resulting polymerization solution is poured into acetone, and the precipitate is washed with acetone and dried under reduced pressure to obtain the polymer (hbPG). PGLYD polymer synthesized by this basic synthesis route has poor adhesive properties and cannot be used as a binder.

[0023] <PGLYD polymer with adhesive properties> Figure 3 shows the synthesis route for the adhesive PGLYD polymer according to this embodiment. A flask is charged with a predetermined amount of DMF, hexamethylene diisocyanate, and pentanediol, and the catalyst stannous octoate is added. The mixture is stirred at 80°C for 24 hours. Glycidol (GL) is added dropwise to the flask, and the mixture is polymerized at 130°C for 24 hours. The resulting solution is poured into acetone to obtain a polymer powder. The resulting polymer is dissolved in DMF, and mesyl chloride and triethylamine are added. The mixture is stirred at room temperature for 24 hours.

[0024] 1-Methylimidazole is added to the resulting solution after stirring, and the mixture is heated at 90°C for 24 hours. After the temperature is lowered to room temperature, LiTFSI (lithium bis(trifluoromethane)sulfonimide) is added. The resulting reaction solution is poured into acetone, decanted, and dried at 100°C to yield a PGLYD polymer with adhesive properties provided by urethane bonds. Figure 4 shows the molecular structure of the adhesive PGLYD polymer.

[0025] The inventors have found that using a PGLYD polymer with an appropriate amount of adhesiveness as a binder can increase the ionic and electronic conductivity of the electrode compared to binders such as PVDF. This allows materials with lower ionic or electronic conductivity to be used as the electrolyte 50. In other words, using a PGLYD polymer with adhesiveness as a binder increases the options for the electrolyte 50, thereby improving the design freedom of the lithium iron phosphate battery 10. A method for manufacturing such a lithium iron phosphate battery 10 is now described.

[0026] <Manufacturing flow for lithium iron phosphate batteries 10> 5 shows an example of a manufacturing flow of the lithium iron phosphate ion battery 10 according to this embodiment. In this embodiment, the manufacturing flow of a coin-type battery with a diameter of about 13 mm will be described as an example of the lithium iron phosphate ion battery 10.

[0027] First, a PGLYD polymer having adhesive properties is formed (S80). As described above, the PGLYD polymer having adhesive properties can be formed by bonding the PGLYD polymer with urethane bonds.

[0028] Next, the positive electrode 20 and the negative electrode 30 are formed. For example, the positive electrode 20 and the negative electrode 30 are formed separately. The positive electrode 20 and the negative electrode 30 may be formed in parallel in time, or may be formed at different times. For example, the negative electrode 30 may be formed after the positive electrode 20, or alternatively, the positive electrode 20 may be formed after the negative electrode 30. FIG. 5 shows an example in which the positive electrode 20 and the negative electrode 30 are formed in parallel in time.

[0029] First, the formation of the cathode 20 containing lithium, iron, phosphorus, and amorphous carbon will be described. The film composition of the cathode 20 is, for example, a weight ratio of lithium iron phosphate, amorphous carbon, and adhesive PGLYD polymer of 84:4:12. The amorphous carbon of the cathode material may be other conductive materials. For example, the amorphous carbon of the cathode material is carbon fiber.

[0030] More specifically, first, the LFP cathode material of lithium, iron, and phosphorus is vacuum-dried (S81). For example, the LFP cathode material is placed in a vacuum chamber, and after creating a vacuum with a vacuum pump, the LFP cathode material is dried at a temperature of approximately 200°C for about 5 hours.

[0031] Next, the adhesive PGLYD polymer is dissolved in a solvent such as N-methyl pyrrolidone (NMP) and a predetermined amount is measured. The dried LFP cathode material and amorphous carbon are added to the measured solution and stirred to form a cathode slurry (S82). NMP is then added to the cathode slurry and stirred until the cathode slurry has a predetermined concentration. The predetermined concentration is, for example, a solids content of 55% by weight.

[0032] Next, a cathode slurry using a cathode material containing lithium iron phosphate, amorphous carbon, and an adhesive PGLYD polymer is applied to a substrate and dried to form a cathode 20 (S83). The substrate is, for example, aluminum foil with a graphite coating on its surface. For example, the graphite has a thickness of about 1 μm, and the aluminum foil has a thickness of about 12 μm. It is desirable to apply a predetermined amount of the cathode slurry to the substrate so that a predetermined dry film thickness is formed. For example, the predetermined dry film thickness is about 80 μm. It is also desirable to apply the cathode slurry using a slot die coater or the like.

[0033] The applied positive electrode slurry is dried in air at a temperature of about 110°C for about 15 minutes, for example, to form a coating of the positive electrode material with a dry thickness. The coating of the positive electrode material is then pressed to form a predetermined thickness. The predetermined thickness is, for example, about 70 μm. The coating of the positive electrode material with such a predetermined thickness is cut into a predetermined shape to form the positive electrode 20.

[0034] Next, the formation of the negative electrode 30 containing graphite and amorphous carbon will be described. The film composition of the negative electrode 30 is, for example, a 94:2:2:2 weight ratio of graphite, amorphous carbon, CMC, and SBR. The amorphous carbon may be ketjen black, acetylene black, or the like. The amorphous carbon of the negative electrode material may be another conductive material. For example, the amorphous carbon of the negative electrode material is carbon fiber.

[0035] More specifically, first, a negative electrode slurry is formed (S84). For example, a predetermined amount of graphite powder and amorphous carbon is added to an aqueous CMC solution and stirred, and then a predetermined amount of SBR solution is added and stirred to form a negative electrode slurry. The aqueous CMC solution contains, for example, 2 wt% CMC. Distilled water is then added to the negative electrode slurry and stirred until the negative electrode slurry has a predetermined concentration. For example, the predetermined concentration is 40 wt% solids.

[0036] Next, a negative electrode 30 is formed by applying a negative electrode slurry made of a negative electrode material containing graphite, amorphous carbon, and an adhesive PGLYD polymer to a substrate and drying it (S85). The substrate is, for example, a copper foil with a carbon nanotube coating on its surface. The carbon nanotube film thickness is, for example, about 1 μm, and the copper foil thickness is, for example, about 6 μm. It is desirable to apply a predetermined amount of the negative electrode slurry to the substrate so that a predetermined dry film thickness is formed. For example, the predetermined dry film thickness is, for example, about 80 μm. It is also desirable to apply the negative electrode slurry using a slot die coater or the like.

[0037] The applied negative electrode slurry is dried in air at a temperature of about 80°C for about 10 minutes, for example, to form a coating of negative electrode material with a dry film thickness. The coating of negative electrode material is then pressed to form a predetermined thickness. The predetermined thickness is, for example, about 60 μm. The coating of negative electrode material with such a predetermined thickness is cut into a predetermined shape to form the negative electrode 30.

[0038] After the positive electrode 20 and the negative electrode 30 are formed, the positive electrode 20, the negative electrode 30, and a predetermined electrolyte 50 are placed in a predetermined container and sealed, thereby assembling the lithium iron phosphate ion battery 10 (S86). In this manner, the lithium iron phosphate ion battery 10 can be formed.

[0039] <Configuration example of lithium iron phosphate battery 10> Fig. 6 shows an example of the configuration of the lithium iron phosphate ion battery 10 according to this embodiment. Fig. 7 shows an example of the assembly flow of the lithium iron phosphate ion battery 10 according to this embodiment. In other words, Figs. 6 and 7 are diagrams illustrating details of the operation of S86 for assembling the lithium iron phosphate ion battery 10 described in Fig. 5.

[0040] The lithium iron phosphate ion battery 10 further includes a case 11, a gasket 12, a spacer 13, a washer 14, and a cap 15. The case 11 and the cap 15 are fitted together to form a container 60. Before assembling the lithium iron phosphate ion battery 10, the positive electrode 20 and the negative electrode 30 are preferably dried using a vacuum chamber or the like. In this case, for example, the positive electrode 20 is dried at approximately 110°C for approximately 8 hours, and the negative electrode 30 is dried at approximately 90°C for approximately 8 hours. The separator 40 is also cut into a predetermined shape.

[0041] First, the gasket 12 is attached to the case 11 (S91). Next, the positive electrode 20 is placed in the case 11 (S92). Next, the separator 40 is placed on the positive electrode 20 inside the case 11 (S93). The separator 40 is, for example, a microporous membrane made of polyolefin. Next, a predetermined amount of electrolyte is dropped onto the separator 40 inside the case 11 using a pipette or the like (S94). As an example, the electrolyte is an organic electrolyte solution in which approximately 1 mole of lithium salt (LiPF6) is dissolved in EC, DMC, and EMC in a weight ratio of 1:1:1. It is desirable that the electrolyte be dropped to such an extent that the positive electrode 20, the negative electrode 30, and the separator 40 are sufficiently immersed in the electrolyte solution.

[0042] Next, negative electrode 30 is placed on separator 40 containing the electrolyte (S95). Next, spacer 13 is placed on negative electrode 30 inside case 11 (S96). Next, washer 14 is placed on spacer 13 inside case 11 (S97). Next, cap 15 is placed on gasket 12 attached to case 11 (S98). Next, pressure is applied from above cap 15, and case 11 and cap 15 are fitted together via gasket 12 (S99).

[0043] This completes the assembly of the lithium iron phosphate ion battery 10. Note that the assembly steps S91 to S99 are preferably performed in an argon atmosphere or a dry atmosphere with a water dew point of -50°C or lower. The characteristics of the lithium iron phosphate ion battery 10 thus fabricated will now be described.

[0044] <Example of characteristics of lithium iron phosphate battery 10> FIG. 8 shows an example of the charge / discharge characteristics of the lithium iron phosphate ion battery 10 according to this embodiment. This figure shows the charge / discharge characteristics of the lithium iron phosphate ion battery 10 fabricated according to the manufacturing and assembly flows described in FIGS. 5 to 7. The horizontal axis of FIG. 8 represents the capacity, and the vertical axis represents the cell voltage and current. As can be seen from FIG. 8, the charge voltage curve, discharge voltage curve, and charge current curve show characteristics comparable to those of a conventional lithium iron phosphate ion battery that uses PVDF as a binder.

[0045] Fig. 9 shows an example of the charge / discharge cycle characteristics of the lithium iron phosphate ion battery 10 according to this embodiment. The charge / discharge cycle characteristics are plotted by repeating the charge / discharge cycle as shown in Fig. 8 and plotting the discharge current capacity and charge current capacity after each cycle. Fig. 9 shows that there is no sudden deterioration in the cycle characteristics, and that the lithium iron phosphate ion battery 10 fully functions as a rechargeable battery.

[0046] The lithium iron phosphate ion battery 10 according to the present embodiment has been described above as an example in which the positive electrode 20 contains a PGLYD polymer that has been imparted with adhesiveness as a binder, but the present invention is not limited to this. The lithium iron phosphate ion battery 10 may contain a PGLYD polymer that has been imparted with adhesiveness as a binder in the negative electrode 30, or may contain the PGLYD polymer that has been imparted with adhesiveness as a binder in both the positive electrode 20 and the negative electrode 30.

[0047] Furthermore, although the lithium iron phosphate ion battery 10 according to this embodiment has been described as having 12 wt % of PGLYD polymer in the positive electrode 20, the present invention is not limited to this. The amount of the adhesive PGLYD polymer contained in at least one of the positive electrode 20 and the negative electrode 30 is preferably 1 wt % or more and 50 wt % or less, based on the weight of the material. The amount of the adhesive PGLYD polymer may be 5 wt % or more and 15 wt % or less, or may be 7 wt % or more and 12 wt % or less, based on the weight of the electrode material.

[0048] Although the lithium iron phosphate battery 10 according to the present embodiment has been described above as an example of a coin-type battery, the present invention is not limited to this. The lithium iron phosphate battery 10 may have any other structure as long as it has a PGLYD polymer with adhesive properties as a binder in at least one of the positive and negative electrodes.

[0049] The lithium iron phosphate ion battery 10 according to the present embodiment described above is an example of a lithium ion battery, and the technology of using an adhesive PGLYD polymer as a binder is not limited to the lithium iron phosphate ion battery 10. The adhesive PGLYD polymer can be applied to lithium ion batteries that can be constructed using various materials, such as ternary lithium ion batteries that use nickel, manganese, and cobalt as the positive electrode materials.

[0050] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0051] 10 Lithium iron phosphate battery 11 cases 12 Gasket 13 Spacer 14 Washer 15 Cap 20 positive electrode 30 negative electrode 40 Separator 50 electrolytes 60 Containment Container 61 positive terminal 62 negative terminal

Claims

1. A method of producing a polymer comprising the steps of: adding glycidol to hexamethylene diisocyanate and pentanediol to form a polyglycidol (PGLYD) polymer; a step of dissolving the formed PGLYD polymer in DMF (dimethylformamide), adding mesyl chloride and triethylamine to the solution, and then adding 1-methylimidazole and LiTFSI (lithium bis(trifluoromethane)sulfonimide) to form a urethane bond by reacting the PGLYD polymer with hexamethylene diisocyanate and pentanediol, thereby forming an adhesive PGLYD polymer; forming a positive electrode comprising a positive electrode active material and amorphous carbon or carbon fiber; forming a negative electrode comprising a negative electrode active material and amorphous carbon or carbon fiber; a step of sealing the positive electrode, the negative electrode, and a predetermined electrolyte in a predetermined container; and At least one of the positive electrode and the negative electrode comprises the PGLYD polymer having adhesive properties as a binder.

2. In the step of forming the positive electrode, a positive electrode slurry using a positive electrode material including a positive electrode active material, amorphous carbon or carbon fiber, and the PGLYD polymer to which adhesiveness has been imparted is applied to a substrate and dried to form the positive electrode; the cathode material comprises 1 wt. % or more and 50 wt. % or less of the PGLYD polymer; The method for manufacturing the lithium ion battery according to claim 1 .

3. In the step of forming the negative electrode, a negative electrode slurry using a negative electrode material including a negative electrode active material, amorphous carbon or carbon fiber, and the PGLYD polymer to which adhesiveness has been imparted is applied to a substrate and dried to form the negative electrode; the anode material comprises 1 wt. % or more and 50 wt. % or less of the PGLYD polymer; The method for producing the lithium ion battery according to claim 1 or 2.

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