JP2018129198A - Method for manufacturing separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a separator having a structure in which a fine particle layer is stacked on a base material, which enables both of the achievement of a low resistance in the state of being incorporated in a battery and the prevention of a short circuit.SOLUTION: A method for manufacturing a separator includes: a corona treatment step (2) of performing a corona treatment on the surface of a film-like separator base material 7; a coating step (3) of coating the surface of the separator base material 7 with a particle dispersion for forming a polyethylene particle layer thereon after the corona treatment; and a drying step (4) of drying the coating layer on the surface of the separator base material after the coating step. In the method, a value (P/(V×L×T))[W×min/(m×μm)] as a result of division of an amplifier output P[W] in the corona treatment step by a conveyance velocity V[m/min], an electrode length L[m], and a film thickness T[μm] of the separator base material is within a range of 7.5 or more and 16.7 or less; and of polyethylene particles in the particle dispersion used in the coating step, particles accounting for at least 90 wt.% or more thereof are 3 μm or more in particle diameter.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of manufacturing a separator that is laminated together with a positive electrode plate and a negative electrode plate in a battery and prevents direct contact between the positive electrode plate and the negative electrode plate. More specifically, the present invention relates to a separator manufacturing method in which a low resistance separator is obtained in a battery while having a particle deposition layer on the surface.

  Conventionally, in the manufacture of this type of separator, a resin fine particle layer is formed on the surface of the separator. Patent document 1 is also an example which discloses such a technique. In the technique of this document, corona treatment is performed on the surface of the base material on which the resin fine particle layer is formed prior to applying the resin fine particle slurry (coating material). Thereby, the surface of the base material is hydrophilized. It is for improving the applicability | paintability of a coating material by hydrophilization. In the corona treatment, the alteration of the base material by the treatment can be limited only to the surface ([0064] of Patent Document 1).

JP-A-2015-199027

  However, the conventional techniques described above have the following problems. That is, a separator having a fine particle layer tends to have a high resistance in a state where it is incorporated in a battery. This is because the movement distance of ions between the positive electrode plate and the negative electrode plate is longer in the battery due to the presence of the fine particle layer. This resistance problem can be alleviated by making the particle layer thinner. For this purpose, the coating material must be applied thinly on the substrate. However, by simply reducing the amount of coating material, the coating layer becomes uneven and a uniform layer thickness cannot be obtained. In order to eliminate this, it is necessary to further improve the wettability (hydrophilicity) of the base material. However, if the power of the corona treatment is increased for that purpose, there is a possibility that a hole is formed in the base material itself. This may allow direct contact between the positive and negative electrode plates in the battery. Thus, it was difficult to achieve both low resistance and short circuit prevention.

  The present invention has been made to solve the above-described problems of the prior art. That is, the problem is to provide a method for manufacturing a separator that has a structure in which a fine particle layer is laminated on a base material and that has both low resistance and prevention of short circuit when incorporated in a battery.

In the method for producing a separator according to one embodiment of the present invention, a corona treatment step for corona treatment on the surface of a film-like separator substrate, and a polyethylene particle layer on the surface of the separator substrate after the corona treatment are performed. A coating process for coating the particle dispersion and a drying process for drying the coating layer on the surface of the separator substrate after coating are performed. Here, the value (P / (V) obtained by dividing the amplifier output P [W] in the corona treatment step by the conveyance speed V [m / min], the electrode length L [m], and the film thickness T [μm] of the separator substrate. · L · T)) [W · min / (m ² · μm)] is in the range of 7.5 to 16.7, among the polyethylene particles contained in the particle dispersion used in the coating process At least 90% by weight or more is 3 μm or more in particle size.

  In the separator manufacturing method in the above aspect, through-holes are formed in the separator substrate by performing a corona treatment step. This through-hole becomes an ion movement path during the battery reaction. And by performing a coating process, a through-hole is covered with a polyethylene particle layer, and a micro short circuit is prevented. In addition, since the polyethylene particles themselves do not enter the through holes, the ion movement path is not impaired. Moreover, since the corona treatment is applied strongly, the polyethylene particle layer is not uneven.

  According to this configuration, there is provided a method of manufacturing a separator that has a structure in which a fine particle layer is laminated on a base material, and that has both low resistance and prevention of short-circuiting when incorporated in a battery.

It is a block diagram of the equipment which enforces the manufacturing method of the separator which concerns on embodiment. It is a graph which shows the Gurley value about each separator of Table 1. It is a graph which shows the membrane resistance about each separator of Table 1. It is a graph which shows the Gurley value about each separator of Table 2. It is a graph which shows the membrane resistance about each separator of Table 2. It is a graph which shows the Gurley value about each separator of Table 3. It is a graph which shows the membrane resistance about each separator of Table 3. It is a graph which shows the Gurley value about each separator of Table 4. It is a graph which shows the membrane resistance about each separator of Table 4. It is a graph which shows the presence or absence of the micro short circuit about each separator of Table 2-Table 4. FIG. It is a graph which shows the membrane resistance about each separator of Table 2-Table 4. It is a graph which shows the difference in film resistance by the presence or absence of a polyethylene particle layer. It is a graph which shows the Gurley value about each separator of Table 5. It is a graph which shows the membrane resistance about each separator of Table 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. First, the structure of the equipment which implements the manufacturing method of this form is shown in FIG. 1 includes a base material supply unit 1, a corona treatment unit 2, a coating unit 3, a drying unit 4, an inspection unit 5, and a collection unit 6. Thereby, the separator base material 7 is supplied from the base material supply part 1, and it collect | recovers to the collection | recovery part 6 through each said process part. The separator substrate 7 is a polyethylene porous film. The film thickness T of the separator substrate 7 in this embodiment, the conveyance speed V, and the winding tension D in the collection unit 6 are as follows.
Film thickness T: 12 to 20 μm (details will be described later)
Conveying speed V: 5 to 40 m / min (standard is 20 m / min)
Winding tension D: 30N

  In the corona treatment unit 2, the wettability of the surface of the separator substrate 7 is improved. In the coating unit 3, the coating material is applied to the surface of the separator substrate 7 that has passed through the corona treatment unit 2. In the drying unit 4, the coating layer formed in the coating unit 3 is dried. The inspection unit 5 inspects the presence or absence of a defective portion in the coating layer after drying and records the location when there is a defect. In the manufacturing equipment of FIG. 1, a characteristic part as the present invention is the contents of processing in the corona processing unit 2 and the coating unit 3. Hereinafter, the processing contents in these places will be described sequentially.

(Corona treatment)
The wettability improving process performed in the corona treatment unit 2 is a corona treatment in which the surface of the separator substrate 7 is exposed to corona discharge. In the corona treatment unit 2 of the present embodiment, the electrode length L of the discharge electrode, that is, the treatment width with respect to the transport direction is 1.35 m. In this embodiment, the concept of processing force F is considered for the corona treatment in the corona treatment unit 2. The processing force F is defined by the input energy value per area of the separator base material 7 to be processed. Accordingly, the processing force F is given by the following equation.
F = P / (V · L) [W · min / m ² ]
P: Amplifier output of corona treatment unit 2 [W]

For example, when the amplifier output P is 675 W and the conveyance speed V is 20 m / min, the processing force F is 25.0 [W · min / m ² ]. The processing force F is adjusted by adjusting the amplifier output P or the conveyance speed V.

In this embodiment, a concept of processing intensity S of corona processing is further considered. The processing strength S is a value obtained by dividing the processing force F described above by the film thickness T [μm] of the separator substrate 7. Accordingly, the processing intensity S is given by the following equation.
S = P / (V · L · T) [W · min / (m ² · μm)]

  In the present embodiment, the condition that the processing intensity S is in the range of 7.5 to 16.7 is mainly used. This condition is considerably stronger than the corona treatment condition that is normally used for the purpose of improving the wettability of the separator substrate 7. For this reason, by performing the corona treatment under the conditions of this embodiment, the separator base material 7 is locally melted in some places and a large number of through holes are formed. For this reason, the resistance to the movement of ions between the positive electrode plate and the negative electrode plate in the battery is low.

(Coating)
Next, the separator base material 7 subjected to the corona treatment is subjected to coating in the coating unit 3. The coating material applied here is a slurry obtained by kneading polyethylene particles with a solvent. The feature here is that polyethylene particles having a diameter of 3 μm or more are used. This particle size is considerably larger than that used for normal separator coating. The reason for using the large-diameter polyethylene particles in this way is to prevent the polyethylene particles from entering the through holes formed in the separator substrate 7 by the aforementioned corona treatment and closing the through holes. Because. If the through hole is blocked, the battery resistance is high when the separator is incorporated in the battery, which is not preferable. Note that 90% by weight or more of all polyethylene particles in the slurry may have a particle diameter of 3 μm or more. In addition, as a method for measuring the particle diameter, for example, a call counter method can be used.

Among the slurry to be coated, the components other than polyethylene particles may be the same as those usually used. As the kneading solvent, water, NMP (N-methyl-2-pyrrolidone) or the like can be used. Further, additives such as CMC (carboxymethylcellulose, thickener) and PVDF (polyvinylidene fluoride, binder) may be included. Here, the solid component ratio was 30% by weight, and the blending ratio of the solid content was as follows.
Polyethylene particles: 96.6 parts by weight Thickener: 0.4 parts by weight Binder: 3.0 parts by weight

  Although there is no special limitation about the format of the coating part 3, a gravure coating machine can be used, for example. By applying the coating material as described above at the coating portion 3, the above-described through-holes of the separator base material 7 are covered with the coating layer. For this reason, even if a through-hole is formed in the separator base material 7 by corona treatment, the through-hole does not cause a micro short circuit in the battery. In this embodiment, the thickness of the coating layer can be made relatively thin. This is because the corona treatment described above is applied more strongly and the coating is performed in a state where the wettability of the separator substrate 7 is very good.

  The configuration of the drying unit 4 is not particularly limited. For example, a four-zone configuration of 45 ° C. → 50 ° C. → 60 ° C. → 60 ° C. is suitable. In the separator exiting the drying unit 4, the kneading solvent is removed from the coating layer to form a deposited layer of polyethylene particles. That is, a separator having a structure in which a polyethylene particle layer is laminated on the separator substrate 7 is obtained.

Thus, the separator manufactured by the method of the present embodiment achieves both low resistance in the battery and prevention of short circuit. As described above, short circuit prevention is due to the fact that the above-mentioned through-holes of the separator base material 7 are covered with the polyethylene particle layer. The low resistance is due to the low resistance of ion migration in the battery reaction due to the following four factors.
1. The above-mentioned through-hole formed in the separator base material 7 has a larger diameter than the original pore in the porous film.
2. The large diameter polyethylene particles cannot enter the aforementioned through-holes of the separator substrate 7.
3. The polyethylene particle layer should be thin.
4). Because the polyethylene particle layer is made of large-diameter polyethylene particles, there must be a wide gap between the particles.

(Case 1)
Hereinafter, experimental examples (Examples and Comparative Examples) will be described. Case 1 is an evaluation of various characteristics without performing coating in order to see the influence of the treatment intensity S of the corona treatment. Table 1 shows the contents of each experimental example of Case 1. In Table 1, “T”, “F”, and “S” all have the same meaning as described above, including the unit. “E” is the layer thickness [μm] of the polyethylene particle layer, and “R” is the particle size [μm] of the polyethylene particles by the coal counter method. The “short circuit” column indicates the presence or absence of a micro short circuit by a spike leak test in a 3 Ah (ampere hour) class electrode laminate produced using the separator substrate 7 and the positive and negative electrode plates after corona treatment. The “untreated” sample was not treated with corona.

  As can be seen in the “Short-Circuit” column of Table 1, there were no micro-shorts in the three samples with a processing strength S of less than 7.5, but in all four samples with a processing strength S of 7.5 or more, A minute short circuit was observed. The graph of FIG. 2 shows the Gurley value (air density) [sec / 100 cc] measured for each separator in Table 1. From FIG. 2, it can be seen that the Gurley value tends to be lower in the four samples with the micro short circuit as compared with the three samples without the micro short circuit. From this, it is understood that in the four samples having the treatment strength S of 7.5 or more, the through holes are formed in the separator base material 7 by the corona treatment. However, it is not necessarily bad that the through holes are formed in the separator base material 7 by the corona treatment. From the results shown in Table 1 and FIG. 2, it can be seen that a treatment strength S of 7.5 or more is required in order to form through holes in the separator substrate 7 by corona treatment.

  FIG. 3 shows the results of measuring the membrane resistance [mΩ] for the three samples that did not have a micro short circuit. As shown in FIG. 3, the resistance values were 68 to 73 mΩ, which were slightly higher. This is understood because the through-holes are not formed in the separator base material 7 and the ion movement resistance in the thickness direction of the separator base material 7 is high. Note that the membrane resistance values in FIG. 3 are calculated from the result of measuring the impedance of each coin cell manufactured by changing the number of separators from 1 to 3. The four samples with micro shorts were not measured because they may not be measured correctly.

(Case 2)
Next, case 2 which is an experimental example when a polyethylene particle layer having a thickness of 8 μm is formed by coating will be described. Table 2 shows the contents of each experimental example of Case 2. In case 2, since coating was performed, the corona treatment was always performed. That is, there is no sample corresponding to “no processing” in case 1 in case 2.

  As seen in the “Short-Circuit” column of Table 2, only a sample with a treatment strength S of 22.5 showed a minute short-circuit in Case 2. That is, even if a through hole is formed in the separator substrate 7 with a corona treatment strength S of 7.5 or more, if the treatment strength S is less than 22.5, the through hole is covered with a polyethylene particle layer. Therefore, it is not a short circuit. As shown in the Gurley value graph of FIG. 4, the samples “2-3” to “2-5” in Case 2 are compared to the samples “1-3” to “1-5” in Case 1. The sensitivity is slightly higher. This is considered to be due to the fact that the through holes are covered with the polyethylene particle layer.

  In case 2 as well, the film resistance [mΩ] was measured for a sample without a micro short circuit. The result is shown in FIG. According to FIG. 5, the film resistance values of the samples “2-3” to “2-5” are about 61 to 66 mΩ. This is a value considerably lower than 78 to 79 mΩ which is the film resistance value of “2-1” and “2-2”. Even when compared with 68 to 72 mΩ which is the film resistance value of case 1, it is a low value. From this, it can be seen that in the samples of “2-3” to “2-5” of case 2, the separator resistance can be reduced while preventing a minute short circuit.

(Case 3)
In Case 3, the thickness T of the separator substrate 7 is changed from 20 μm to 16 μm. Table 3 shows the contents of each experimental example in Case 3. In the case 3, the processing force F is not changed from the case 2 (except “3-2”), but the processing strength S is increased compared to the case 2 because the film thickness T is reduced. . As a result, in Case 3, a micro short circuit was observed in two samples having a processing strength S of 18.8 or more. Therefore, according to Case 3, a value of 18.8 or more as the value of the processing intensity S is excluded from the preferable range.

  The Gurley value for each sample of Case 3 is shown in the graph of FIG. Further, the film resistance [mΩ] of each sample of case 3 without the micro short circuit is shown in the graph of FIG. From these, it can be seen that the samples “3-3” and “3-4” of the case 3 have no particular problem in the density and the film resistance value is sufficiently low.

(Case 4)
Case 4 is the film thickness T of the separator substrate 7 further lowered to 12 μm. Table 4 shows the contents of each experimental example of Case 4. In the case 4, the processing strength S is increased compared to the sample having the same processing power F in the case 3 as the film thickness T is further reduced. As a result, in Case 4, a short-circuit was observed in two samples having a processing strength S of 20.8 or more. On the other hand, for “4-4” having a treatment strength S of 16.7, no micro short circuit was observed. Therefore, according to Case 4, it can be seen that the processing intensity S is up to 16.7 within the preferable range.

  The Gurley value for each sample of Case 4 is shown in the graph of FIG. The graph of FIG. 9 shows the film resistance [mΩ] of each sample in Case 4 that did not have a micro short circuit. From these, it can be seen that the samples of “4-3” and “4-4” in the case 4 have no particular problem in the density and the film resistance value is sufficiently low.

  The presence or absence of a micro short circuit for cases 2 to 4 is shown in the graph of FIG. In the graph of FIG. 10, the horizontal axis represents the processing force F of the corona treatment, and the vertical axis represents the film thickness T of the separator substrate 7. Furthermore, a straight line corresponding to 16.7 is drawn as the processing intensity S in the graph. In FIG. 10, all samples on the straight line and on the upper left side (below 16.7) have no micro short circuit, and all samples on the lower right side (above 16.7) have a micro short circuit. . From this, it can be seen that the upper limit of the degree of corona treatment is 16.7 (including 16.7) as the treatment strength S. Note that FIG. 10 merely shows the upper limit of the degree of corona treatment from the presence or absence of a micro short circuit in the state after coating. As described above, the lower limit of the degree of corona treatment is determined by the through hole formation state before coating.

  Furthermore, the film resistance values for cases 2 to 4 are shown in the graph of FIG. In the graph of FIG. 11, the horizontal axis represents the treatment intensity S of the corona treatment, and the vertical axis represents the membrane resistance value. The plot points in the graph of FIG. 11 are a group in which the processing strength S is 5.0 or less and the membrane resistance is 70 [mΩ] or more, and a group in which the processing strength S is 7.5 or more and the membrane resistance is 66 [mΩ] or less. And 2 minutes. From the comparison of case 1 with FIG. 3, it can be said that the former group is a group having no effect of reducing the film resistance, and the latter group is a group having an effect of reducing the film resistance. This is considered to be due to the mechanism that when the treatment strength S of the corona treatment is 7.5 or more, a through-hole is formed in the separator base material 7 and the film resistance is lowered. Therefore, it can be seen that the lower limit of the degree of corona treatment is 7.5 (including 7.5) in terms of the treatment strength S.

  FIG. 12 is a graph showing the difference in film resistance depending on the presence or absence of a polyethylene particle layer. FIG. 12 shows the film resistance values for case 1 “no treatment” (no polyethylene particle layer) and case 4 “4-3” and “4-4” (both have a polyethylene particle layer). . As for these three samples, as can be seen from the “T” column and “E” column in Tables 1 and 4, the total of the film thickness T of the separator substrate 7 and the layer thickness E of the polyethylene particle layer is 20 μm. From FIG. 12, it is clear that “4-3” and “4-4” have lower resistance than “no processing”. The polyethylene particle layer naturally has tackiness (adhesiveness), which is the original purpose. From this, it can be said that in this embodiment, the film resistance is reduced while obtaining tackiness by appropriately forming the polyethylene particle layer.

(Case 5)
Next, Case 5 which is an experimental example on the influence of the size of polyethylene particles will be described. In case 5, only the particle diameter R of the polyethylene particles was changed based on “2-1” and “2-4” of case 2. That is, in the samples “5-1” and “5-2”, the particle size R was changed to 6 μm (5-1) and 1 μm (5-2) while using the condition “2-1” as a reference. Similarly, in the samples “5-3” and “5-4”, the particle diameter R was changed to 6 μm (5-3) and 1 μm (5-4) while using the condition “2-4” as a reference. Table 5 shows the contents of each experimental example of Case 5 (including “2-1” and “2-4”). In the “Short-circuit” column of Table 5, none of the samples has a micro-short circuit. However, the above three are samples in which the treatment intensity S of the corona treatment is insufficient as described above.

  FIG. 13 shows the Gurley value of each sample in Table 5. The samples “5-3” and “5-4” have slightly lower Gurley values than the samples “2-4”. FIG. 14 shows the film resistance value of each sample in Table 5. The “5-3” sample has a slightly lower membrane resistance than the “2-4” sample, but the “5-4” sample is clearly higher than the “2-4” sample, The film resistance value is comparable to the sample of “2-1”.

  From this, the effect of reducing the film resistance by the polyethylene particle layer is not obtained in the sample (5-4) having a particle size R that is too small (1 μm), but even if the particle size R exceeds 3 μm (6 μm, 5 -3) It turns out that it is obtained. This shows that the particle diameter of the polyethylene particles to be applied in the coating process needs to be 3 μm or more. The reason why the membrane resistance increases when the particle size R is too small is that polyethylene particles enter and close the through-holes of the separator substrate 7, thereby closing the ion movement path during the battery reaction. It is presumed that

  As described above in detail, according to the present embodiment, the separator substrate 7 is subjected to corona treatment with a predetermined treatment strength S so that a through hole is formed in the separator substrate 7. Then, a coating process is performed thereon so that the through hole is covered with the polyethylene particle layer without being blocked. As a result, a separator manufacturing method has been realized that can achieve tackiness by providing a polyethylene particle layer, and also achieve prevention of minute short-circuiting and reduction of film resistance.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the above-described various numerical values other than the processing strength S and the particle size R are examples, and may not be exactly the same. Further, the particle size R may be at least 90% by weight or more of the entire polyethylene particles.

2 Corona treatment part 3 Coating part 4 Drying part 7 Separator base material

Claims (1)

A corona treatment step for corona treatment on the surface of the film separator substrate;
A coating step of coating a particle dispersion for forming a polyethylene particle layer on the surface of the separator substrate after the corona treatment;
A drying process for drying the coating layer on the surface of the separator substrate after coating,
The value obtained by dividing the amplifier output P [W] in the corona treatment step by the conveying speed V [m / min], the electrode length L [m], and the film thickness T [μm] of the separator substrate (P / (V · L · T)) [W · min / (m ² · μm)] is in the range of 7.5 to 16.7,
A method for producing a separator, wherein at least 90% by weight or more of the polyethylene particles contained in the particle dispersion used in the coating step are 3 μm or more in particle size.

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