JP2020119640A - Collector - Google Patents

Abstract

To provide a collector which is low in resistance during normal use and high in PTC characteristics at high temperatures.SOLUTION: In the present disclosure, there is provided a collector for use in an all-solid-state lithium battery. The collector includes a collector layer and a PTC layer formed on one side of the collector layer. The PTC layer contains a polysilsesquioxane, a conductive material and a polymer.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a current collector used for an all-solid-state lithium battery.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones and communication devices in recent years, the development of batteries used as power sources thereof has been emphasized. Also in the automobile industry and the like, development of high-output and high-capacity batteries for electric vehicles or hybrid vehicles is under way. At present, among various types of batteries, lithium ion batteries are drawing attention because of their high energy density.

An all-solid-state lithium battery is a battery that has a solid electrolyte layer between a positive electrode layer and a negative electrode layer, and it is easier to simplify a safety device than a liquid battery that has an electrolytic solution containing a flammable organic solvent. Have advantages. For example, Patent Document 1 discloses an all-solid-state battery having a PTC film containing a conductive material, an insulating inorganic material, and a polymer between a current collector layer and an active material layer. The PTC is a "Positive Temperature Coefficient", and the PTC film is a film having a PTC characteristic in which the electronic resistance changes with a positive coefficient as the temperature rises.

On the other hand, Patent Document 2 discloses a non-aqueous battery containing a conductive material and polyvinylidene fluoride as a binder, although the technology is not related to an all-solid-state lithium battery. Similarly, although not related to an all-solid-state lithium battery, Patent Documents 3 and 4 disclose the use of silsesquioxane for the battery.

JP, 2008-014286, A JP2012-104422A JP, 2018-113194, A JP, 2013-191331, A

Patent Document 1 discloses an all-solid-state battery having a PTC film containing an insulating inorganic material. In an all-solid-state battery in which a constraining pressure is applied in the stacking direction, the PTC characteristics tend to deteriorate due to temperature rise, but the insulating inorganic substance contained in the PTC film has a function of suppressing the deterioration of the PTC characteristics. On the other hand, since the insulating inorganic substance contained in the PTC film literally has an insulating property, the resistance tends to be high during normal use.

The present disclosure has been made in view of the above circumstances, and its main purpose is to provide a current collector having low resistance during normal use and high PTC characteristics at high temperatures.

In order to achieve the above object, in the present disclosure, a current collector used for an all-solid-state lithium battery, wherein the current collector is formed on a current collecting layer and one surface side of the current collecting layer. And a PTC layer, and the PTC layer contains a polysilsesquioxane, a conductive material, and a polymer.

According to the present disclosure, since the PTC layer contains polysilsesquioxane, the current collector has low resistance during normal use and high PTC characteristics at high temperatures.

The present disclosure has an effect that it is possible to provide a current collector having low resistance during normal use and high PTC characteristics at high temperatures.

It is a schematic sectional drawing which shows an example of the electrical power collector in this indication. It is a graph which shows the result of electronic resistance measurement of an Example and a comparative example. It is a graph which shows the result of the PTC characteristic of an Example and a comparative example. It is a graph which compared the hardness of a PTC layer.

Hereinafter, the current collector in the present disclosure will be described in detail.
FIG. 1 is a schematic cross-sectional view showing an example of a current collector in the present disclosure. The current collector 10 shown in FIG. 1 has a current collecting layer 2 and a PTC layer 1 formed on one surface side of the current collecting layer 2, and the PTC layer 1 is a polysilsesquioxane 3 , Conductive material 4, and polymer 5.

According to the present disclosure, since the PTC layer contains polysilsesquioxane, the current collector has low resistance during normal use and high PTC characteristics at high temperatures.

Here, PTC layers are disclosed in Patent Documents 1 and 2 above. Patent Document 3 discloses that the active material layer of the negative electrode contains silsesquioxane. Further, Patent Document 4 discloses that the negative electrode contains a silicone resin (polyorganosilsesquioxane resin). However, none of the documents describes or suggests that the PTC layer contains polysilsesquioxane.

Hereinafter, each configuration of the current collector and the method for manufacturing the current collector in the present disclosure will be described in detail.

1. PTC Layer The PTC layer in the present disclosure is formed on one surface side of the current collecting layer, and contains polysilsesquioxane, a conductive material, and a polymer described later.

The thickness of the PTC layer is, for example, preferably 1 μm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less.

(1) Polysilsesquioxane Polysilsesquioxane in the present disclosure is a network-type polymer (polyhedral cluster) having a three-dimensional network structure represented by (RSiO _3/2 )n. R is a substituted or unsubstituted organic group having 1 to 20 carbon atoms, and examples thereof include a methyl group. Further, examples of R include alkoxysilane, chlorosilane, silanol and the like. That is, the polysilsesquioxane in the present disclosure includes polyorganosilsesquioxane. A cured product of polysilsesquioxane, which is cured by, for example, UV irradiation, can be used for the PTC layer in the present disclosure. Examples of the cured product of polysilsesquioxane include KMP-590, KMP591, and X-52-854, which are commercial products manufactured by Shin-Etsu Chemical Co., Ltd. Other examples include silserquioxane (POSS) manufactured by Sigma-Aldrich.

Polysilsesquioxane has the following advantages when compared with conventionally used insulating inorganic substances such as alumina. Since the resistance of polysilsesquioxane at room temperature is relatively low, the ratio of the resistance value at high temperature to the resistance value at room temperature is relatively large. Since polysilsesquioxane has a relatively small proportion of coarse particles and can enter between the conductive materials when the polymer resin is melted, the ionic conduction path can be cut well. Further, when the polymer resin is melted, aggregation is less likely to occur because the polysilsesquioxane has low fluidity. Due to these advantages, the PTC layer containing polysilsesquioxane can exhibit the above-mentioned effects.

Also, polysilsesquioxane is a relatively soft material. Therefore, the PTC layer containing polysilsesquioxane has a lower hardness than the PTC layer containing alumina or silica. Therefore, the PTC layer containing polysilsesquioxane can make good contact with the current collecting layer, the positive electrode mixture layer, or the negative electrode mixture layer, so that the resistance during normal use can be reduced.

The average particle size (D ₅₀ ) of the polysilsesquioxane is, for example, preferably 50 nm or more and 5 μm or less, and more preferably 100 nm or more and 2 μm or less.

The content of polysilsesquioxane in the PTC layer is, for example, preferably 50% by volume or more, and more preferably 60% by volume or more. This is because if the content of polysilsesquioxane is too low, it becomes insufficient to suppress the deformation and flow of the polymer melted when the temperature rises, and the electronic resistance may decrease. The content of polysilsesquioxane in the PTC layer may be such that stable electron conductivity can be secured during normal use, and is preferably 85% by volume or less, more preferably 80% by volume or less. .. When the content of polysilsesquioxane is too high, the content of the polymer is relatively decreased, and the volume-expanded polymer cannot increase the distance between the conductive materials, which causes an increase in electronic resistance. This is because there is a fear that it will be sufficient. Further, it is because the conductive path formed by the conductive material may be blocked by too much polysilsesquioxane, and the electronic conductivity of the PTC layer may be lowered.

(2) Conductive Material The conductive material is not particularly limited as long as it has a desired electronic conductivity, and examples thereof include a carbon material. Examples of the carbon material include carbon black such as furnace black, acetylene black, Ketjen black, and thermal black, carbon fibers such as carbon nanotubes and carbon nanofibers, activated carbon, carbon, graphite, graphene, and fullerenes. However, it is preferable to use the above carbon black. This is because the carbon black has the advantage of high electron conductivity with respect to the amount added. The shape of the conductive material is not particularly limited, but examples thereof include particles. The average primary particle diameter of the conductive material is, for example, preferably 10 nm or more and 200 nm or less, and more preferably 15 nm or more and 100 nm or less. Here, the average primary particle diameter of the conductive material is, for example, obtained by measuring 30 or more primary particle diameters based on image analysis using an electron microscope such as an SEM (scanning electron microscope), and calculating the arithmetic average of them. It is possible to adopt the value that is set.

The content of the conductive material in the PTC layer should be such that the electronic resistance can be increased when the temperature rises. For example, it is preferably 50% by volume or less, and more preferably 30% by volume or less. This is because if the content of the conductive material is too large, the distance between the conductive materials cannot be increased due to the volume expansion of the polymer, and the increase in electronic resistance becomes insufficient. Further, the content of the conductive material in the PTC layer may be such that stable electron conductivity can be secured during normal use, and is, for example, preferably 5% by volume or more, more preferably 10% by volume or more, and 20% by volume. % Or more is more preferable. This is because when the content of the conductive material is too small, the conductive paths formed are reduced and the electronic conductivity of the PTC layer is lowered.

(3) Polymer The polymer is not particularly limited as long as it can expand in volume when the temperature rises, and examples thereof include thermoplastic resins. Examples of the thermoplastic resin include polyvinylidene fluoride (PVDF), polypropylene, polyethylene, polyvinyl chloride, polystyrene, acrylonitrile butadiene styrene (ABS) resin, methacrylic resin, polyamide, polyester, polycarbonate, polyacetal and the like.
The melting point of the polymer may be higher than the temperature at which the battery is normally used, and is, for example, preferably 80° C. or higher and 300° C. or lower, and more preferably 100° C. or higher and 250° C. or lower. The melting point can be measured by, for example, differential thermal analysis (DTA).

The content of the polymer in the PTC layer may be such that the electronic resistance can be increased by volume expansion when the temperature rises, and is, for example, preferably 5% by volume or more, and more preferably 10% by volume or more. This is because when the content of the polymer is too low, the volume-expanded polymer cannot increase the distance between the conductive materials, resulting in an insufficient increase in electronic resistance. Further, the content of the polymer in the PTC layer may be such that stable electron conductivity can be secured during normal use, and is preferably 90% by volume or less, more preferably 80% by volume or less. This is because when the content of the polymer is too large, the conductive path formed by the conductive material is blocked by the polymer, and the electron conductivity of the PTC layer becomes low.

2. Current Collection Layer The current collection layer in the present disclosure is not particularly limited as long as it is a layer having electronic conductivity. Examples of the material of the current collecting layer include metal materials. Examples of the metal material include metal materials containing one or more elements such as Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge and In. ..

The thickness of the current collecting layer is, for example, 5 μm or more, and may be 10 μm or more. On the other hand, the thickness of the current collecting layer is, for example, 100 μm or less, and may be 50 μm or less.

3. Manufacturing Method of Current Collector The manufacturing method of the current collector is not particularly limited, but, for example, the above-mentioned conductive material, polysilsesquioxane, and polymer are mixed with an organic solvent such as N-methylpyrrolidone. Then, it may be formed into a paste, coated on the current collecting layer described above, and dried.

4. All-solid-state lithium battery The current collector in the present disclosure is used for an all-solid-state lithium battery. The all-solid-state lithium battery may be a primary battery or a secondary battery. The shape of the battery may be, for example, a coin type, a laminated type, a cylindrical type, a square type, or the like.

Note that the present disclosure is not limited to the above embodiment. The above-described embodiment is an exemplification, has substantially the same configuration as the technical idea described in the scope of claims of the present disclosure, and has any similar effects to the present invention. It is included in the technical scope of the disclosure.

[Example 1]
Furnace black (manufactured by Tokai Carbon Co., Ltd.) having an average primary particle diameter of 66 nm as a conductive material, a polyorganosilsesquioxane cured product having a mean particle diameter of 2 μm (KMP-manufactured by Shin-Etsu Silicone Co., Ltd.), which is a polymer of methyltrimethoxysilane. 590), and PVDF (KF polymer L#9130 manufactured by Kureha Co., Ltd.) was prepared as a polymer. Furnace black:polyorganosilsesquioxane:PVDF=10:60:30 The volume ratio of the mixture was mixed with N-methylpyrrolidone as a solvent to prepare a paste. After that, the paste is applied to an aluminum foil having a thickness of 15 μm so that the thickness after drying becomes 10 μm, and is dried in a stationary drying oven at 100° C. for 1 hour to form an aluminum foil having a PTC layer. did.

[Example 2]
As the polyorganosilsesquioxane cured product, the same procedure as in Example 1 was carried out except that X-52-854 manufactured by Shin-Etsu Silicone Co., Ltd., which was a polymer of methyltrimethoxysilane and had an average particle diameter of 0.7 μm, was used. An aluminum foil with a PTC layer was formed.

[Comparative Example 1]
An aluminum foil having a PTC layer was formed in the same manner as in Example 1 except that alumina having an average particle diameter of 2 μm (CBP-02 manufactured by Showa Denko KK) was used in place of the polyorganosilsesquioxane cured product. ..

[Comparative example 2]
An aluminum foil having a PTC layer was formed in the same manner as in Comparative Example 1 except that the alumina used in Comparative Example 1 was changed to alumina having an average particle size of 0.7 μm (DENKA AA-07). ..

[Evaluation]
(Electronic resistance measurement)
The aluminum foil provided with the PTC layer obtained in Examples 1 and 2 and Comparative Examples 1 and 2 is brought into contact with a copper foil, and a DC resistance type (manufactured by Hioki) crocodile terminal is attached to the copper foil and the aluminum foil. It was measured by that. A Kapton tape with a hole of 11.28 cm in diameter is attached to the copper foil, and a cylinder of 11.28 cm in diameter is installed in this hole, and a pressure of 100 N is applied by an autograph to make a 1 mA gap between the terminals. A constant current was applied, the voltage between the terminals was measured, and the electronic resistance value was calculated. In addition, it evaluated by the relative value on the basis of the result of the comparative example 1. The results are shown in Figure 2.

(PTC characteristics)
For the aluminum foil provided with the PTC layer obtained in Examples 1-2 and Comparative Examples 1-2, the value of electronic resistance during heating is divided by the value of electronic resistance before heating (at room temperature). evaluated. That is, the PTC characteristics were evaluated by calculating the rate of resistance increase from normal temperature to high temperature. The electronic resistance before heating was measured by the method described above. The electronic resistance during heating was measured as follows. The produced aluminum foil provided with the PTC layer was punched into a circular shape having a diameter of 11.28 cm, sandwiched between cylindrical terminals having the same diameter, and a binding pressure of 60 MPa was applied between the terminals. The terminals sandwiching the aluminum foil provided with the PTC layer were placed in a constant temperature bath, heated to 250° C., held for 1 hour, and the electronic resistance was measured with a direct current resistance system (manufactured by Hikiki). Results are shown in FIG.

As shown in FIG. 2, as compared with Comparative Examples 1 and 2 using alumina (insulating inorganic material), Examples 1 and 2 using polysilsesquioxane show remarkable electron resistance in normal use. It was confirmed to be low. It is speculated that this is because the alumina used in Comparative Examples 1 and 2 was hard, and it was difficult to make a contact between the PTC layer and the current collecting layer.

Further, as shown in FIG. 3, in Examples 1 and 2, it was confirmed that the electronic resistance before heating and during heating was larger than that before heating, and that excellent PTC characteristics were exhibited.

(Hardness characteristics)
With respect to the aluminum foil provided with the PTC layer obtained in Example 1 and Comparative Examples 1 and 2, the change in thickness with respect to pressure was confirmed and the hardness characteristics were evaluated as follows.
Twenty aluminum foils each having the produced PTC layer were punched and stacked to have a diameter of 11.28 cm. The stacked aluminum foil was placed on a pin (cross-sectional area = 0.25 cm ² ) and placed on an autograph. Unloading was performed by pressurizing in the compression direction with a pressure of 400 N, 800 N, 1200 N, 1600 N, and 2000 N using an autograph. Then, the change A of the thickness of the aluminum foil when a pressure of 2400 N was applied was confirmed. In addition, a thickness change B was also confirmed in the state of being placed on the pin without applying pressure. The hardness characteristics were obtained by the pressure (2400N)/(A-B), and the result of Comparative Example 1 was set to 1 and relatively evaluated. The results are shown in Fig. 4.

As shown in FIG. 4, it was confirmed that the PTC layers of Examples 1 and 2 containing polysilsesquioxane were softer than Comparative Example 1 containing alumina. Therefore, the PTC layer in the present disclosure containing polysilsesquioxane can make good contact with the current collecting layer, the positive electrode mixture layer, or the negative electrode mixture layer, and can reduce the resistance during normal use. It was suggested that it could be done.

1... PTC layer 2... Current collector layer 3... Polysilsesquioxane 4... Conductive material 5... Polymer 10... Current collector

Claims (1)

A current collector used for an all-solid-state lithium battery,
The current collector has a current collecting layer and a PTC layer formed on one surface side of the current collecting layer,
A current collector in which the PTC layer contains polysilsesquioxane, a conductive material, and a polymer.