JP4831804B2 - Electrode film drying equipment - Google Patents

Description

The present invention is related to the drying apparatus of the electrode film for drying the electrode film wound.

In recent years, nonaqueous electrolyte secondary batteries have attracted attention as storage batteries for power storage and as power sources for mobile objects. As a lithium secondary battery which is a kind of nonaqueous electrolyte secondary battery, for example, a rectangular one as shown in Patent Document 1 is exemplified.
FIG. 6 shows a lithium secondary battery described in Patent Document 1. The lithium secondary battery 1 includes a plurality of positive electrodes 2, 2..., Negative electrodes 3, 3..., Positive electrodes 2, 2. Are mainly composed of separators 4, 4...
The positive electrodes 2, 2..., The negative electrodes 3, 3..., The separators 4, 4, and the nonaqueous electrolyte are accommodated in a battery case 5 made of stainless steel or the like. A sealing body 6 is attached to the opening of the battery case 5.
In the battery case 5, a plurality of positive electrodes 2, 2,..., Separators 4, 4,.
The positive electrode tabs 12a, 12a,... Are formed at one ends of the positive electrodes 2, 2,..., And the positive electrode leads 12b that connect the positive electrode tabs 12a, 12a,. Is attached.
And the positive electrode terminal 7 which penetrates the sealing body 6 is attached to the upper part of the positive electrode lead 12b.
In addition, negative electrode tabs 13a, 13a,... Are formed at one end of the negative electrodes 3, 3,..., And negative electrodes that connect the negative electrode tabs 13a, 13a,. A lead 13b is attached.
And the negative electrode terminal 8 which penetrates the sealing body 6 is attached to the upper part of the negative electrode lead 13b.
In addition, a liquid injection port 9 is provided substantially at the center of the sealing body 6.

In the above-described lithium secondary battery, the nonaqueous electrolytic solution is a solution in which a lithium salt as an electrolyte is dissolved in a nonaqueous electrolytic solution solvent such as ethylene carbonate or propylene carbonate. Examples of the lithium salt, for _{example, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiClO 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiSbF 6, LiAlO 4, LiAlCl 4, LiN (C x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI and the like can be exemplified.

  The positive electrode or the negative electrode of such a lithium secondary battery is made of an electrode film in which a film made of an electrode forming material is formed on a current collector made of metal. For example, a method of applying an electrode-forming substance to the body and drying it with a vacuum processing apparatus described in Patent Document 2 can be used. In such a method for producing an electrode film, drying is a very important step. In other words, moisture is a substance that may deteriorate the battery performance. When moisture is mixed in the lithium secondary battery, active lithium reacts with moisture as shown in the following chemical reaction formula (1). Since active lithium hydroxide is formed, the battery capacity may be reduced. In addition, as shown in the chemical reaction formula (2) below, the lithium salt dissolved in the nonaqueous electrolytic solution reacts with water to form an acid that is a deterioration promoting substance, which may shorten the life. . For this reason, the water content is usually reduced to about 100 ppm by drying. With this amount of water, charging and discharging for about 500 cycles was possible.

Japanese Patent Laying-Open No. 2002-025542 (FIG. 1) Japanese Patent Laid-Open No. 8-027574

Incidentally, non-aqueous electrolyte secondary batteries such as lithium secondary batteries are required to further improve battery performance. For example, further improvement of charge / discharge cycles, that is, longer battery life is desired. Longer battery life is achieved by reducing the amount of water in the electrode, but in order to reduce the amount of water more than before, the drying time has to be lengthened and productivity has been reduced. . In particular, since the electrode film is usually wound, the portion wound inside is not exposed and is difficult to dry. Therefore, in order to reduce the moisture content of the portion wound inside, it was necessary to further increase the drying time or lower the degree of vacuum. Therefore, productivity has been reduced, and special high-performance vacuum devices have to be used.
The present invention has been made in view of the circumstances, it shall be the object of the invention to provide a drying apparatus in a short time the electrode film can be dried to a low moisture content the entire wound electrode film.

The electrode film drying apparatus of the present invention is an electrode film drying apparatus for drying a wound electrode film, and unwinds and feeds the wound electrode film, and is fed by the feeding means. It comprises heating means for heating the exposed electrode film surface, and a drying container for accommodating the electrode film together with the feeding means and the heating means .
According to such a drying apparatus, the electrode film wound by the feeding means is unwound, and the exposed electrode film surface is heated and dried by the heating means, so that the inner part of the winding is also easily dried. it can. As a result, the entire wound electrode film can be dried to a low moisture content in a short time.

In the electrode film drying apparatus of the present invention, the heating means is preferably a heating roll in contact with the electrode film surface. If the heating means is a heating roll, the electrode film is directly heated, so that it can be dried in a shorter time.
Moreover, it is preferable to provide the via roll which changes the moving direction of the drawn-out electrode film. If the via roll is provided, the exposed area on the surface of the electrode film can be increased, so that it can be dried in a shorter time.

Moreover, in the drying apparatus of the electrode film of this invention, you may comprise the said several heating roll from which the moving direction of the said electrode film changes between each other. The feeding means may include an attachment roll to which the wound electrode film is attached, and a winding roll to rewind the electrode film unwound and fed by the rotation of the attachment roll. .

According to the drying apparatus of the electrode film of the present invention, Ru can dried to a low moisture content of the entire wound electrode film in a short time.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
First, an electrode film drying apparatus will be described.
In FIG. 1, the drying apparatus 20 (henceforth the drying apparatus 20) of the electrode film of this embodiment is shown. The drying apparatus 20 includes a feeding unit 22 that feeds the wound electrode film 21, a heating roll 24 (heating unit) that contacts and heats the exposed electrode film surface 23 that is fed out by the feeding unit 22, and a feeding unit. 22 and the drying container 25 which accommodates the heating roll 24 are comprised roughly.
Further, the feeding means 22 includes an attachment roll 26 for attaching the wound electrode film 21 to be dried, and a winding roll 27 that is rotated by a driving means (not shown) and winds the electrode film again. is doing.

  Further, a dehumidifying means 30 is connected to the drying container 25 via a pipe 31 and a pump 32. In this way, if the dehumidifying means 30 is connected to the drying container 25 via the pipe 31 and the pump 32, the gas discharged from the drying container 25 by the pump 32 is passed through the dehumidifying means 30 to remove moisture in the gas. The gas can be removed and supplied again into the drying vessel 25. Therefore, the gas filled in the drying container 25 from the cylinder 33 before drying can be reused. Moreover, the inside of the drying container 25 can be made into a dry atmosphere.

Hereinafter, each component of the drying apparatus 20 mentioned above is demonstrated.
The feeding means 22 preferably determines the rotation speed of the winding roll 27 so that the electrode film has a desired moisture content. If the moving speed of the electrode film (also referred to as “winding speed”) determined by the rotation speed of the winding roll 27 is slow, the time for which the electrode film surface is in contact with the drying atmosphere becomes longer. However, if the time is excessively slow, the drying time becomes long, so that the effects of the present invention may not be sufficiently exhibited.
FIG. 2 shows a tendency of the battery capacity with respect to the rotation speed of the winding roll 27. As shown in the graph of FIG. 2, the battery capacity is high in the region where the rotation speed is low, but the battery capacity decreases as the rotation speed increases to some extent. In addition, in the example of FIG. 2, the electrode film exposure length is made constant.

The heating roll 24 is a roll incorporating a heater. The heating roll 24 also serves as a via roll. Here, the via roll is one in which the drawn-out electrode film comes into contact with the roll surface and changes the moving direction of the electrode film. If a via roll is provided and the electrode film is brought into contact with the via roll, the exposed area on the surface of the electrode film can be increased, so that it can be dried to a lower moisture content.
The temperature of the heating roll 24 is preferably set so that the temperature of the electrode film surface is heated to 110 to 130 ° C. If the temperature of the heating roll 24 is in the above-described range, the drying rate can be further increased and at the same time, energy consumption required for drying can be suppressed.

The temperature in the drying container 25 is preferably 0 to 300 ° C. If the temperature in the drying container 25 is 0 to 300 ° C., it can be dried in a shorter time and with a smaller amount of energy. On the other hand, if it is less than 0 degreeC, drying time may become long, and if it exceeds 300 degreeC, the amount of energy required for drying may increase.
The pressure in the drying container 25 is preferably lower than normal pressure. If the pressure in the drying container 25 is lower than normal pressure, the moisture is more likely to volatilize and the drying rate is further increased.
The inside of the drying container 25 is preferably an inert gas atmosphere. If the inside of the drying container 25 is an inert gas atmosphere, oxidation of the current collector constituting the electrode film can be prevented. As the inert gas, for example, nitrogen gas, argon gas, helium gas or the like is used.

  Further, the drying container 25 is provided with doors 35a and 35b for taking in and out the wound electrode film, and one of the doors 35b is in contact with a drying region 36 such as a dry room that accommodates an apparatus for the next process. It is preferable. As described above, if one of the doors of the drying container 25 is in contact with the drying region 36, the electrode film is taken out from the door 35b, so that moisture can be prevented from being taken into the dried electrode film again, and the moisture content can be reduced. The dried electrode film can be used for the next step.

  Furthermore, it is preferable that a moisture measuring means 37 such as an infrared meter or a dew point meter for measuring the moisture content of the electrode film surface 23 is provided in the drying container 25. If the moisture content is measured by moisture measuring means 37 such as an infrared meter or a dew point meter, and the moving speed of the electrode film is controlled based on the moisture content, the moisture content can be reliably and efficiently dried to the desired moisture content.

  In the electrode film drying method using the electrode film drying apparatus 20 described above, the wound electrode film 21 is fed by the feeding means 22 and the electrode film is wound again. In this way, the surface of the electrode film is sequentially exposed, and the heated roll 24 is brought into contact with the exposed electrode film surface 23 to heat and dry the electrode film.

  It is preferable that the moisture content of the electrode film is 20 ppm or less by such a drying device 20. If the moisture content of the electrode film is 20 ppm or less, the charge / discharge cycle can be improved to about 4000 cycles. 4000 cycles corresponds to a lifetime of about 10 years.

  In the drying apparatus 20 described above, the electrode film 21 wound by the feeding means 22 is once unwound, and the electrode film surface 23 exposed when unwound is brought into contact with the heating roll 24 and heated, dried, and again. Since it winds, it can dry to the inside of the wound electrode film 21 for a short time. That is, the entire wound electrode film 21 can be dried to a low moisture content in a short time.

Next, an electrode for a lithium secondary battery (hereinafter abbreviated as an electrode) and a lithium secondary battery in this embodiment will be described. The electrode in this embodiment is composed of the electrode film dried by the above-described drying apparatus, and the lithium secondary battery includes the electrode. Examples of the form of the lithium secondary battery include a square lithium secondary battery shown in FIG. Further, it may be a coin type or a cylindrical type.
In this lithium secondary battery, since the amount of water contained in the electrode is reduced, the formation of inactive lithium hydroxide due to the reaction between active lithium and moisture is suppressed, and the battery capacity is improved. . In addition, since the formation of acid due to the reaction between the lithium salt dissolved in the non-aqueous electrolyte and moisture is suppressed, the lifetime is long. In this lithium secondary battery, if at least one of the positive electrode and the negative electrode is the above electrode, the above effect is exhibited. However, if both the positive electrode and the negative electrode are the above electrode, the above effect is more effective. Demonstrated.

Note that the present invention is not limited to the above-described embodiments. For example, in the drying apparatus 20 described above, one heating roll 24 that also serves as a via roll is provided, but a plurality of heating rolls 24 may be provided. FIG. 3 shows a drying apparatus 40 having four via rolls (also heating rolls) 41, 41, 41, 41. If the number of via rolls heated in this way is increased, the surface of the electrode film can be further heated, and the exposed area of the surface of the electrode film in a dry atmosphere is increased, so that the amount of water removed can be reduced.
FIG. 4 shows the tendency of the battery capacity with respect to the electrode exposure length (electrode exposure area). As shown in this graph, as the electrode exposure length increases, the amount of water removed increases, and the battery capacity is improved. However, if the electrode exposure length is increased to some extent, the battery capacity does not increase even if the electrode film exposure length is increased. In addition, in the example of FIG. 4, the rotational speed of the winding roll is made constant.

In the drying apparatus 20 described above, the heating means is the heating roll 24 that also serves as a via roll. However, as shown in FIG. 5, the heating means is a hot air heater 42 and does not include the via roll. It may be. With such a drying device 43, damage to the electrode film surface can be prevented.
Moreover, a heating block can also be used instead of a heating roll.

Example 1
90% by weight of lithium manganate as a positive electrode active material, 5% by weight of graphite as a conductive agent, 5% by weight of polyvinylidene fluoride as a binder, and a solid content of 50% by weight in N-methylpyrrolidone as a solvent It mixed so that it might become a slurry. The slurry was dried at 80 ° C. to form a coating film while being continuously applied to an aluminum foil having a width of 200 mm as a current collector in a range of 140 mm in a width of 140 mm, and this was wound into a roll. Next, the coating film on the current collector was molded with a roller press so that the film density was 2.4 g / cm ³ , thereby producing a positive electrode. Next, the positive electrode was wound and dried at 110 ° C. for 72 hours while reducing the pressure to 100 Pa or less.
Further, 90% by weight of graphite as a negative electrode active material and 10% by weight of polyvinylidene fluoride as a binder were mixed in a solvent such as N-methylpyrrolidone so as to have a solid content of 50% by weight to form a slurry. . The slurry was dried at 80 ° C. to form a coating film while being continuously applied to an aluminum foil having a width of 200 mm as a current collector in a range of 140 mm in a width of 140 mm, and this was wound into a roll. Next, the coating film on the current collector was molded with a roller press so that the film density was 1.4 g / cm ³ , thereby preparing a negative electrode. Next, this negative electrode was fed out in a drying apparatus in a nitrogen atmosphere at normal pressure and 130 ° C., and dried by winding at a winding speed of 0.5 m / sec through a heating roll heated to 150 ° C. The drying time was 9 hours including the winding time.
Next, after cutting the middle part (100 m from the end in the length direction) of the wound negative electrode into a size of 50 × 50 mm, the moisture was measured with a Karl Fischer moisture meter (MKC-510N, manufactured by Kyoto Electronics Industry Co., Ltd.). .
Further, the positive electrode and the negative electrode were cut so as to have a circular shape with an area of 2 cm ² , and these were combined and a coin-type battery was produced by sandwiching a separator between both electrodes. And the charging / discharging test of this coin type battery was done. As the non-aqueous electrolyte for the coin-type battery, ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed so that the mixing ratio EC: DMC = 1: 2, and LiPF ₆ is added to the mixed solvent. What was melt | dissolved so that it might become a density | concentration of 1 mol / liter was used.
Table 1 shows the results of the drying conditions, water content, and charge / discharge test. In the charge / discharge test, the initial capacity was set to 100%, and the battery capacity retention rate after 500 cycles was determined.

(Examples 2 to 11)
A coin-type battery was produced in the same manner as in Example 1 except that the drying conditions of the negative electrode were as shown in Table 1. Table 1 shows the water content and the results of the charge / discharge test.

(Comparative Example 1)
When the negative electrode was made, the negative electrode was “dried by winding the negative electrode and winding it at a winding speed of 0.5 m / second while passing through a heated roll heated to 150 ° C.” A coin-type battery was fabricated in the same manner as in Example 1, except that the film was heated and dried at 130 ° C. for 72 hours while reducing the pressure to 100 Pa or less. Table 2 shows the water content and the results of the charge / discharge test.

(Comparative Examples 2 to 13)
A coin-type battery was fabricated in the same manner as in Example 1 except that the drying conditions of the negative electrode were as shown in Table 2 or Table 3. The water content and the results of the charge / discharge test are shown in Table 2 or Table 3.

  In addition, in Examples 1-4, it investigated about the influence of winding speed, Example 5-7 investigated about the influence of pressure, Example 1, 8, 9 investigated about the influence of dry gas, and in Examples 10-12, it heated. The influence of the number of rolls was investigated.

In Examples 1 to 8, since the negative electrode was fed and dried by winding it through a heated roll heated to 150 ° C., the drying time was not lengthened, and the amount of moisture could be reduced without extremely reducing the pressure. It was.
On the other hand, in Comparative Examples 1 to 8, although the moisture content was low, the drying time was long and the pressure had to be extremely low. Moreover, since the positive electrode was not dried in Comparative Example 9, the moisture content of the positive electrode was high, and in Comparative Example 10, the negative electrode was not dried, so the moisture content of the negative electrode was high. In Comparative Example 11, the amount of water was high because the negative electrode was not drawn out.

From the results of Examples 1 to 4, as shown in FIG. 7, if the winding speed is slow, the amount of water in the electrode decreases, and if the winding speed is 4 m / second or less, the water content can be 20 ppm or less. There was found.
Further, from the results of Examples 5 to 7 and Comparative Example 12, as shown in FIG. 8, it was found that the water content in the electrode decreases when the pressure is low, and the water content can be 20 ppm or less when the pressure is 80 kPa or less. .
From the results of Examples 1, 8, and 9, it was found that the battery capacity after 500 cycles would be 96% or more when an inert gas was used, as shown in FIG.
Further, from the results of Examples 10 to 12, as shown in FIG. 10, when the number of heating rolls increases, the amount of water decreases, and when the number of heating rolls is four or more, the drying time is 1 hour, the winding speed. It has been found that the water content can be reduced to 20 ppm or less even at 4 m / second or less.

  Moreover, it turned out that the moisture content in an electrode becomes low from the result of Comparative Examples 1-10 as shown in FIG. Furthermore, as shown in FIGS. 13 and 14, if the moisture content is 120 ppm or less for the positive electrode and the moisture content is 20 ppm or less for the negative electrode, the retention rate of the battery capacity after 500 cycles may be 80% or more. found.

It is a schematic diagram which shows one embodiment of the drying apparatus of the electrode film in this invention. It is a graph which shows the relationship between the rotational speed of a winding roll, and battery capacity. It is a schematic diagram which shows the other embodiment example of the drying apparatus of the electrode film in this invention. It is a graph which shows the relationship between an electrode film surface exposure length and battery capacity. It is a schematic diagram which shows the other embodiment example of the drying apparatus of the electrode film in this invention. It is a perspective view which shows a square-shaped lithium secondary battery. It is a graph which shows the relationship between a winding speed and the moisture content in an electrode. It is a graph which shows the relationship between a pressure and the moisture content in an electrode. It is a graph which shows the battery capacity maintenance rate with respect to the kind of gas. It is a graph which shows the relationship between a heating roll number and a moisture content. It is a graph which shows the relationship between the drying time of a positive electrode, and a moisture content. It is a graph which shows the relationship between the drying time of a negative electrode, and a moisture content. It is a graph which shows the relationship between the moisture content of a positive electrode, and a battery capacity maintenance factor. It is a graph which shows the relationship between the moisture content of a negative electrode, and a battery capacity maintenance factor.

Explanation of symbols

1 Lithium secondary battery (non-aqueous electrolyte secondary battery)
2 Positive electrode (electrode for non-aqueous electrolyte secondary battery)
3 Negative electrode (electrode for non-aqueous electrolyte secondary battery)
20, 40, 43 Electrode film drying device 21 Wound electrode film 22 Feeding means 23 Electrode film surface 24 Heating roll (heating means)
41 Via Roll

Claims (5)

An electrode film drying apparatus for drying a wound electrode film,
Unwinding means for unwinding and unwinding the wound electrode film, heating means for heating the exposed electrode film surface unwound by the unwinding means, and a drying container for housing the electrode film together with the unwinding means and the heating means When drying device electrode film characterized by comprising a.   The said heating means is a heating roll which contacts the electrode film surface, The drying apparatus of the electrode film of Claim 1 characterized by the above-mentioned. The electrode film drying apparatus according to claim 1, further comprising a via roll that changes a moving direction of the electrode film accommodated in the drying container . The apparatus for drying an electrode film according to claim 2, comprising a plurality of the heating rolls that change the moving direction of the electrode film between each other. The feeding means has a mounting roll to which the wound electrode film is attached, and a winding roll for rewinding the electrode film unwound and rotated by rotation of the mounting roll. The electrode film drying apparatus according to any one of claims 1 to 4.

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