JP6278440B2 - Lithium battery electrode manufacturing method and lithium battery manufacturing apparatus using the same - Google Patents

Description

  The present invention relates to a method of manufacturing an electrode for a lithium secondary battery and a lithium secondary battery using the same, and relates to a shaft seal structure optimal for a rotary pump for transferring an electrode mixture slurry mixed with electrode materials. Is.

  As an example of a lithium secondary battery, a lithium ion secondary battery is a secondary battery having a large charge / discharge capacity. It is indispensable for people's lives by being used in transportation equipment such as power supplies, automobiles, and bicycles with electric motors.

Lithium ion secondary battery is an electrode mixture slurry prepared by mixing an active material, a binder, a conductive additive, and a dispersion medium with a stirrer such as a ball mill or a roll mill. It is applied by.
Then, it is manufactured by punching to a predetermined size, forming a terminal connected to an external circuit, winding or laminating, and enclosing it in a metal can and a film exterior together with an electrolytic solution.

Although the electrode mixture slurry is transferred by various pumps, the rotary pump has a feature that the discharge amount can be easily adjusted by changing the rotation speed.
In the case of a rotary pump such as a gear pump, a mechanism for preventing leakage of electrode mixture slurry flowing inside the pump casing along the rotation axis to the outside of the pump casing is required. In addition, leakage of the electrode mixture slurry may result in dirt on the manufacturing site and production stoppage. Moreover, even if there is a slight leak, the flow rate in the piping may change and affect the quality of the product.
When a soft rubber O-ring is used as a sealing member for the rotary shaft of the pump used for transferring the slurry, a secondary seal O-ring is used to prevent the slurry from entering the O-ring loading space. A mechanical seal for slurry fluid provided with an O-ring for preventing slurry intrusion can be given (see, for example, Patent Document 1). Conventionally, it has been important to use a material that does not easily wear for a sealing member of a dynamic part such as a rotating shaft in a pump for electrode mixture slurry for a battery.

JP 2007-138965 A

  However, when the secondary seal O-ring is provided on one of the rotating shaft and the seal case, the structure of the seal portion becomes complicated, and there is a problem that maintenance work increases for long-term operation. Therefore, the present invention provides a seal having a simple structure and high durability for the dynamic part of a pump for transferring an electrode mixture slurry for producing a battery electrode.

  An object of the present invention is solved by a lithium secondary battery manufacturing apparatus including a shaft sealing device having a housing for loading an O-ring and a sleeve for mounting the O-ring, wherein the O-ring is made of silicone rubber. be able to.

  When the electrode mixture slurry is sandwiched in the gap between the O-ring and the sleeve in the shaft seal device, when the O-ring made of silicone rubber is worn by the electrode active material, the active material particles adhere to the surface and the O-ring is crushed. This eliminates the cost and prevents leakage of the electrode mixture slurry.

FIG. 1 is a cross-sectional view illustrating a shaft seal device according to an embodiment of the present invention. FIG. 2 is a view for explaining the relationship of the main members of the shaft seal device according to the embodiment of the present invention. FIG. 3 is a diagram for explaining piping for the electrode mixture slurry transfer process according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of the gear pump. FIG. 5 is a diagram for explaining a biaxial gear pump. FIG. 6 is a cross-sectional view illustrating the shaft seal device. FIG. 7 is a diagram illustrating a state where the surface of the O-ring is covered with the positive electrode active material. FIG. 8 is a diagram for explaining an embodiment of the present invention. FIG. 9 is a diagram illustrating a state of the O-ring on the sleeve surface side.

The present invention uses an O-ring made of silicone rubber as a sealing member for a dynamic part such as a rotating shaft of a pump for an electrode mixture slurry containing an electrode active material and a binder.
Surprisingly, the leakage resistance of the electrode mixture slurry from the rotating shaft of the pump can be improved by using an O-ring made of silicone rubber, which is considered inappropriate because it is easily worn on the dynamic part. It has been found that it becomes possible.
The reason why leakage of the electrode mixture slurry is prevented is not certain, but when an O-ring made of silicone rubber is used for the sealing member of the rotating shaft, the O-ring gradually wears, but a certain time has passed. From the stage, it was confirmed that the progress of wear of the silicone rubber O-ring was suppressed, and the electrode slurry would not leak even if the O-ring alone was worn down to a state where the sealing performance would be lowered. Confirmed the event.

  On the other hand, when ethylene propylene rubber having higher wear resistance than silicone rubber was used, it was clearly confirmed that leakage started at an earlier stage than silicone rubber. Considering these points, at least one or more of the electrode active material and the binder constituting the electrode mixture slurry for the battery remain in the portion where the silicone rubber O-ring is worn, and the residue is O It is possible to consider the possibility that the electrode mixture slurry is sealed together with the ring to suppress the wear of the O-ring beyond a certain level.

FIG. 1 is a schematic view showing a shaft seal portion of a rotary shaft of a rotary pump, for explaining one embodiment of the present invention, and is a cross-sectional view of the central portion of the rotary shaft.
In the method for producing a secondary battery of the present invention, a shaft sealing device 100 for rotating a shaft of a slurry pump for applying an electrode mixture includes a rotating shaft 101 that transmits a rotating motion from an electric motor (not shown). A sleeve 102 is provided to cover the outer periphery.
On the surface of the sleeve 102, the O-ring 103 attached to the sleeve is used as a boundary to prevent the electrode mixture slurry from moving.
The sleeve 102 has a tubular member made of an electrically insulating member in close contact with the rotating shaft 101. The sleeve 102 is preferably made of an insulating ceramic material having a chemically stable electrical resistivity of 10 ⁶ Ω · m or more, such as alumina or zirconia.

By using a chemically stable high electrical insulating member for the sleeve 102 in this way, the granular material generated by the wear of the sleeve may cause an abnormal chemical reaction in the manufactured battery, and the produced lithium secondary It is possible to prevent the formation of an undesired energization circuit inside the battery.
The sleeve 102 preferably has a Vickers hardness of 1200 Hv or more.
By having a high hardness, it is possible to reduce damage caused by a material having a high hardness such as lithium manganese composite oxide used in the production of an electrode mixture slurry for batteries, and it is possible to extend the service life. is there.

Examples of the silicone rubber O-ring 103 usable in the present invention include JIS type C vinyl methyl silicone rubber and fluorosilicone rubber.
Further, as shown in FIG. 2 as an example of the size of each part, the O-ring outer diameter d3 and the housing groove diameter d6 are designed so that the expansion rate S of the O-ring 103 is in the range of 3% to 7%. Thus, good sealing properties can be obtained.

However, Formula 1 Elongation rate S = (d3-d6) / d3 × 100
Formula 2 O-ring thickness reduction ratio R = 0.56 + 0.59 × S + 0.046 × S ²
Formula 3 Effective sectional area of O-ring d2 * = d2 * − (R / 100) × d2
Formula 4 Crushing rate C = (d2 * -t) / d2 * × 100
Formula 5 Maximum housing occupancy F = π × (d2 * / 2) ² / (t × b)
d2: O-ring thickness, d2 *: O-ring effective cross-sectional area d3: O-ring outer diameter, d5: Sleeve outer diameter, d6: Housing groove diameter t: Housing depth

Further, the expansion rate S is substituted into the above formulas 2 and 3, and the thickness reduction rate R of the O-ring and the effective sectional area d2 * of the O-ring are calculated. Here, the outer diameter d5 of the sleeve is designed so as to be calculated using Equation 4 so that the crushing allowance C of the O-ring is 0% to 6%.
In addition, the maximum housing occupancy F is designed to be 85% or less using Equation 5.

In the production of the lithium secondary battery of the present invention, an active material, a binder, a conductive auxiliary agent, and a dispersion medium, which are lithium secondary battery materials, are mixed with a stirrer such as a ball mill, a roll mill, a high-speed impeller mill, a jet mill, or a kneader. Disperse well.
Examples of the positive electrode active material include layered oxide materials such as LiCoO2, LiNiO2, LiNi1-xCoO2, LiNix (CoAl) 1-xO2, Li2MO3-LiMO2, LiNi1 / 3Co1 / 3Mn1 / 3O2, LiMn2O4, LiMn1.5Ni0. Spinel materials such as 5O4 and LiMn2-xMxO4, olivine materials such as LiMPO4, fluorinated olivine materials such as Li2MPO4F and Li2MSiO4F, vanadium oxide materials such as V2O5, or some of these elements substituted with other elements The thing etc. can be mentioned, These 1 type (s) or 2 or more types can be mixed and used.
Negative electrode active materials include carbon materials such as graphite, amorphous carbon, diamond-like carbon, fullerene, carbon nanotube, and carbon nanohorn, lithium metal materials, alloy materials such as silicon and tin, and oxide materials such as Nb2O5 and TiO2. A material or a composite of these can be used.

  As binder, fluororesin such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene copolymer (SBR), polyacrylate, polyimide, polyethylene, polypropylene, ethylene propylene terpolymer (EPDM) At least one of them can be used.

Further, at least one of acetylene black, carbon black, graphite, vapor grown carbon fiber (VGCF), carbon nanotube, and mesocarbon microbead (MCMB) can be used as the conductive assistant.
As the dispersion medium, at least one of N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone (MEK), cyclohexane, water and the like can be used.

FIG. 3 is a diagram illustrating an example of a coating process.
The dispersed electrode mixture slurry is supplied from the storage tank 154 to the coating die 158 through the filter 164 and the three-way valve 157 using the rotary pump 155. In addition, a pressure gauge 156 is attached to each pipe.
The coating die 158 and the backup roll 162 have a gap of 0.02 mm to 0.5 mm, and the electrode mixture slurry extruded from the lip tip of the coating die is applied to the web 163 wound around the backup roll and dried. By doing so, the positive electrode and negative electrode which are electrodes for batteries are formed.
The rotary pump 155 can be a screw pump, a gear pump, a vane pump, or a spiral pump.
The prepared positive electrode and negative electrode are laminated or wound via a separator made of polypropylene, polyethylene, or the like, and a positive electrode terminal is electrically connected to the positive electrode, and a negative electrode terminal is electrically connected to the negative electrode. A lithium ion secondary battery can be obtained by housing a part other than the negative electrode terminal together with the electrolyte in the battery container.

FIG. 4 is a diagram for explaining a gear pump given as a representative example of the rotary pump, and is a cross-sectional view perpendicular to the rotation axis.
A drive shaft 115 that transmits rotational motion from the electric motor, a follow-up shaft 116 that transmits rotational motion from the drive shaft via a gear 120, a bearing 118, a housing 119, a gear rotor 120, a pump cover 121, and a housing 122 are included. .

FIG. 5 is a cross-sectional view of the biaxial gear pump. When the gear rotor 120 is rotated by the power of the electric motor, the electrode mixture slurry is drawn from the suction port 124 and discharged from the discharge port 125. By continuously performing the suction and discharge operations, the electrode mixture slurry having a constant volume flow rate can be sent to the coating die.
As the shaft seal device continuously rotates, the shaft 101 and the sleeve 102 rotate together as shown in FIG. 1 and rub against the O-ring and the electrode mixture slurry.
The surface of the O-ring is worn due to friction with the sleeve 102, but an electrode mixture containing an electrode active material and a binder remains between the O-ring and the sleeve 102, thereby suppressing the progress of friction. At this time, it can be inferred that the slurry of the electrode mixture that has entered the vicinity of the O-ring stays and does not immediately leak even if the O-ring wears. Furthermore, when silicone rubber is used for the O-ring, the silicone rubber not only has excellent heat resistance, but also has excellent rebound resilience, so that the electrode mixture that has entered between the O-ring and the sleeve 102 is leaked. It can be inferred that it was held without any further.
Moreover, since the O-ring surface is covered with an electrode active material or the like, the progress of wear with the sleeve 102 is suppressed.
As a result, it is possible to prevent the electrode mixture slurry in the liquid feeding space 123 from leaking through the shaft seal device.

FIG. 6 is a cross-sectional view illustrating the shaft seal device.
In the lithium ion secondary battery manufacturing apparatus of the present invention, the electrode mixture slurry 111 remains in the gap between the O-ring 103 and the sleeve 102 in the shaft seal device 100 in the shaft seal device 100.
As a result, as shown in FIG. 7, it can be inferred that the electrode mixture slurry does not leak even when the O-ring wears and the crushing margin of the O-ring is eliminated.
In addition, the O-ring made of silicone rubber covers the surface of the O-ring by attaching a part of the positive electrode active material particles to the uneven surface of the surface caused by friction with the electrode active material.
In particular, it was confirmed that when a lithium oxide-based hard material is used as the active material, the active material easily adheres to the surface of the O-ring, and the effects of the present invention appear more remarkably.

Example 1
As shown in FIG. 8, an electrode mixture obtained by mixing an active material, a binder, and a conductive additive in the electrode manufacturing process is not supplied from a storage tank 154 to a coating die 158 using a gear pump as a rotary pump 155. The three-way valve 157 was switched, and the electrode mixture supplied by the rotary pump 155 was returned to the storage tank 154 again.

In this example, 90.6 parts by mass of lithium manganese composite oxide, 0.03 parts by mass of vapor grown carbon fiber (VGCF), 0.03 parts by mass of PVDF, and 0.34 parts by mass of NMP were weighed. The electrode mixture was stirred with a ball mill to prepare an electrode mixture for a lithium ion secondary battery. It was stored in the storage tank and supplied as described above.
The sleeve 102 is made of 99.0% pure alumina and has an outer diameter of 37.05 ± 0.01 mm. The material of the O-ring 103 was VGFS-6035 silicone manufactured by US Seal Manufacturing, the thickness was 6.10 ± 0.13 mm, and the outer diameter was 51.06 ± 0.64 mm. The groove diameter of the housing 100 was 48.49 ± 0.01 mm, and the groove width was 6.16 ± 0.06 mm.
From these dimensions, when calculated using the above-mentioned formula 1, formula 2, formula 3, formula 4, and formula 5 as described above, the expansion ratio S falls within the range of 3.8% to 6.2%. When C is in the range of 0.0% to 5.7%, the maximum housing occupancy F is 82.8%.
The pump was operated at a rotational speed of 100 RPM equipped with a shaft seal device of this design, and the time until leakage was measured. As a result, the time until leakage was 960 hours.
Further, as shown in a cross-sectional view in FIG. 9, the sleeve 102 surface side of the O-ring 103 is coated with a positive electrode active material 109.

Comparative Example 1
A similar experiment was performed using the electrode mixture used in Example 1. The material of the sleeve 102 was alumina having a purity of 99.0%, and its outer diameter was 37.05 ± 0.01 mm. As the O-ring 103, an EPDM O-ring was used.
The thickness is 6.10 ± 0.13 mm, the outer diameter is 51.06 ± 0.64 mm, the groove diameter of the housing 100 is 48.49 ± 0.01 mm, and the groove width is 6.16 ± 0.06 mm. Things were used.
From these dimensions, when calculated using Equation 1, Equation 2, Equation 3, Equation 4, and Equation 5 as described above, the expansion ratio S is in the range of 3.8% to 6.2%, and the crushing margin C is The maximum housing occupancy F is 82.8% in the range of 0.0% to 5.7%.
The gear amplifier with the shaft seal device of this design is operated at a rotational speed of 100 RPM and the time until leakage is measured. As a result, the time until leakage was 336Hr.

Comparative Example 2
The sleeve 102 is made of alumina having a purity of 99.0%, and its outer diameter is 39.00 ± 0.01 mm. The material of the O-ring 103 is JIS type 4 C, the thickness is 6.99 ± 0.13 mm, and the outer diameter is 52.84 ± 0.64 mm. The groove diameter of the housing 100 is 51.00 ± 0.05 mm, and the groove width is 7.70 ± 0.06 mm.
From these dimensions, when calculated using Equation 1, Equation 2, Equation 3, Equation 4, and Equation 5 as described above, the expansion ratio S is in the range of 2.2% to 4.7%, and the crushing margin C is In the range of 9.2% to 14.5%, the maximum housing occupancy F is 84.0%.
The gear pump equipped with the shaft seal device of this design was operated at a rotational speed of 100 RPM and the time until leakage was measured. As a result, the time until leakage is 48 hours.

  The present invention comprises a shaft seal device having a housing for loading an O-ring and a sleeve for mounting the O-ring, and the O-ring is a manufacturing apparatus for a lithium ion secondary battery made of silicone rubber. A slurry of an active material that is stable for a long time can be used in the production of the slurry.

  DESCRIPTION OF SYMBOLS 100 ... Shaft seal device, 101 ... Rotary shaft, 102 ... Sleeve, 103 ... O-ring, 109 ... Positive electrode active material, 154 ... Storage tank, 155 ... Rotary pump, 164 ... Filter, 157 ... Three-way valve, 158 ... Coating die, 156 ... Pressure gauge, 162 ... Backup roll, 163 ... Web, 115 ... Drive shaft, 120 ..Gear, 116 ... following shaft, 118 ... bearing, 110 ... housing, 120 ... gear rotor, 121 ... pump cover, 122 ... housing, 123 ... liquid feeding Space, 124 ... Suction port, 125 ... Discharge port

Claims (5)

A method for producing an electrode for a lithium battery obtained by applying an electrode mixture slurry containing an electrode active material and a binder,
The pump for conveying the electrode mixture slurry is:
A method for producing an electrode for a lithium battery, comprising: a shaft sealing device having a housing for loading an O-ring and a sleeve for mounting the O-ring, wherein the O-ring is made of silicone rubber.   2. The manufacturing method of an electrode for a lithium battery according to claim 1, wherein the O-ring has an expansion rate of 3% to 7%, a crushing amount of 0% to 6%, and a maximum value of the housing occupancy rate of 85%. Method. 3. The method for manufacturing an electrode for a lithium battery according to claim 1, wherein the sleeve is an insulating ceramic having an electrical resistivity of 10 ⁶ Ω · m or more. 4.   The method for producing an electrode for a lithium battery according to claim 1, wherein the sleeve has a Vickers hardness of 1200 Hv or more. An electrode mixture slurry conveying apparatus including an electrode active material and a binder,
The pump for conveying the electrode mixture slurry is:
A device for transporting electrode mixture slurry, comprising: a shaft sealing device having a housing for loading an O-ring and a sleeve for mounting the O-ring, wherein the O-ring is made of silicone rubber.

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