Electrode for solid-state battery and solid-state battery
阅读说明：本技术 固体电池用电极和固体电池 (Electrode for solid-state battery and solid-state battery ) 是由 尾濑徳洋 铃木知哉 长谷川元 八十和夫 西村英晃 松下祐贵 于 2019-07-23 设计创作，主要内容包括：本发明涉及固体电池用电极和固体电池。该固体电池用电极特征在于,具备电极活性材料层、集电器和PTC电阻体层,PTC电阻体层配置在电极活性材料层与集电器之间且与电极活性材料层接触,PTC电阻体层含有导电材料、绝缘性无机物和聚合物,在将PTC电阻体层从靠近电极活性材料层的一侧起依次分为A层和B层使得在PTC电阻体层的任何部分的厚度方向上均为A层的厚度：B层的厚度＝1：2时,V<Sub>A</Sub><V<Sub>B</Sub>,其中V<Sub>A</Sub>是将A层中的导电材料、绝缘性无机物和聚合物的总体积设定为100体积％时A层中的绝缘性无机物的体积比例,V<Sub>B</Sub>是将B层中的导电材料、绝缘性无机物和聚合物的总体积设定为100体积％时B层中的绝缘性无机物的体积比例。(The present invention relates to an electrode for a solid-state battery and a solid-state battery. The electrode for a solid-state battery is characterized by comprising an electrode active material layer, a current collector, and a PTC resistor layer, wherein the PTC resistor layer is arranged between the electrode active material layer and the current collector and is in contact with the electrode active material layer, the PTC resistor layer contains a conductive material, an insulating inorganic substance, and a polymer, and the PTC resistor layer is divided into an A layer and a B layer in this order from the side close to the electrode active material layer so as to be provided on any one of the PTC resistor layersThe thickness direction of which part is the thickness of the A layer: thickness of B layer 1: at 2 time, V A <V B In which V is A V is the volume ratio of the insulating inorganic substance in the layer A when the total volume of the conductive material, the insulating inorganic substance and the polymer in the layer A is set to 100 vol% B The volume ratio of the insulating inorganic substance in the B layer is defined as the total volume of the conductive material, the insulating inorganic substance and the polymer in the B layer is 100 vol%.)
1. An electrode for a solid-state battery, characterized in that,
the electrode is provided with: an electrode active material layer, a current collector, and a PTC resistor layer disposed between the electrode active material layer and the current collector and in contact with the electrode active material layer,
the PTC resistor layer contains a conductive material, an insulating inorganic substance and a polymer,
dividing the PTC resistor layer into a layer a and a layer B in this order from the side close to the electrode active material layer such that the thickness of the layer a in the thickness direction of any portion of the PTC resistor layer is: thickness of B layer 1: at 2 time, V A<V BWherein
V AIs the volume ratio of the insulating inorganic substance in the layer A when the total volume of the conductive material, the insulating inorganic substance and the polymer in the layer A is set as 100 vol%,
V Bis the volume ratio of the insulating inorganic substance in the B layer, with the total volume of the conductive material, the insulating inorganic substance, and the polymer in the B layer being set to 100 vol%.
2. The electrode for solid-state batteries according to claim 1,
the volume ratio V is ADivided by the volume ratio V BAnd the value V obtained A/V B0.08 to 0.5.
3. The electrode for a solid-state battery according to claim 1 or 2, wherein,
the PTC resistor layer contains a carbon-containing conductive material as a conductive material and a fluorine-containing polymer as a polymer, and,
a value obtained by dividing the atomic percentage of carbon atoms contained in the A layer by the atomic percentage of fluorine atoms contained in the A layer is 2.4 to 3.9.
4. The electrode for solid-state batteries according to any one of claims 1 to 3, wherein,
the insulating inorganic substance is a metal oxide.
5. The electrode for solid-state batteries according to any one of claims 1 to 4,
the conductive material is carbon black.
6. A solid-state battery comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode,
at least one of the positive electrode and the negative electrode is the solid-state battery electrode according to any one of claims 1 to 5.
Technical Field
The present disclosure relates to an electrode for a solid-state battery and a solid-state battery provided with the same.
Background
When a battery used as a power source mounted in a vehicle, a power source for a personal computer, a portable terminal, or the like is internally short-circuited or overcharged, the temperature of the entire battery increases, and the battery itself and devices using the battery may be adversely affected.
As a measure for preventing such adverse effects, a technique has been attempted in which an electrode having a Positive Temperature Coefficient (PTC) resistor layer having electron conductivity at room Temperature and an electron resistance value increasing with an increase in Temperature is used.
Disclosure of Invention
Problems to be solved by the invention
However, the electrode including the PTC resistor layer containing an insulating inorganic substance as disclosed in
The present disclosure has been made in view of the above circumstances, and an object thereof is to provide an electrode for a solid-state battery including a PTC resistor layer having a low electronic resistance at room temperature while keeping the electronic resistance at a high temperature, and a solid-state battery including the electrode.
Means for solving the problems
The electrode for a solid-state battery of the present disclosure is characterized in that,
the disclosed device is provided with: an electrode active material layer, a current collector, and a PTC resistor layer disposed between the electrode active material layer and the current collector and in contact with the electrode active material layer,
the PTC resistor layer contains a conductive material, an insulating inorganic substance and a polymer,
the PTC resistor layer is divided into a layer a and a layer B in this order from the side close to the electrode active material layer so that the thickness direction of any portion of the PTC resistor layer is (the thickness of the layer a): (thickness of B layer) 1: at 2 time, V A<V BWherein
V AIs the volume ratio of the insulating inorganic substance in the layer A when the total volume of the conductive material, the insulating inorganic substance and the polymer in the layer A is set as 100 vol%,
V Bis the volume ratio of the insulating inorganic substance in the B layer, with the total volume of the conductive material, the insulating inorganic substance, and the polymer in the B layer being set to 100 vol%.
The volume ratio V is ADivided by the volume ratio V BThe value (V) thus obtained A/V B) Can be 0.08 to 0.5.
The PTC resistor layer contains a carbon-containing conductive material as a conductive material and a fluorine-containing polymer as a polymer, and a value obtained by dividing an atomic percentage of carbon atoms contained in the A layer by an atomic percentage of fluorine atoms contained in the A layer may be 2.4 to 3.9.
The insulating inorganic substance may be a metal oxide.
The conductive material may be carbon black.
The solid-state battery according to the present disclosure is a solid-state battery including a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the solid-state battery electrode.
Effects of the invention
Solids according to the present disclosureThe volume ratio V of the insulating inorganic substance in the layer A closer to the electrode active material layer in the PTC resistor layer is set to be higher than that in the PTC resistor layer AVolume ratio V of the insulating inorganic substance in the layer B closer to the current collector BThe contact between the PTC resistor layer and the electrode active material layer is excellent. As a result, when the electrode is used in a solid-state battery, it is possible to suppress an increase in the electronic resistance at the interface between the PTC resistor layer and the electrode active material layer under room temperature conditions without decreasing the electronic resistance at the interface between the PTC resistor layer and the electrode active material layer under high temperature conditions, and to suppress a decrease in the performance of the solid-state battery.
Drawings
Fig. 1 is a view showing an example of the layer structure of the electrode for a solid-state battery according to the present disclosure, and is a view schematically showing a cross section cut in the stacking direction.
Fig. 2 is a view showing an example of the layer structure of the solid-state battery of the present disclosure, and is a view schematically showing a cross section cut in the stacking direction.
Fig. 3 is a schematic diagram of an electronic resistance measurement circuit including an evaluation sample.
Fig. 4 is a graph showing a relationship between an electronic resistance of an evaluation sample of an electrode and a resistance of a solid-state battery including the electrode.
Description of the symbols
1 PTC resistor layer
1aA layer
1b B layer
2 electrode active material layer
3, 3' current collectors
10 solid-state battery electrode
20 electrolyte layer
30 other electrodes
40 micro tester (マイクロテスター)
50 evaluation sample
100 solid state battery
200 electronic resistance measuring circuit
Detailed Description
1. Electrode for solid battery
The electrode for a solid-state battery of the present disclosure is characterized in that,
the disclosed device is provided with: an electrode active material layer, a current collector, and a PTC resistor layer disposed between the electrode active material layer and the current collector and in contact with the electrode active material layer,
the PTC resistor layer contains a conductive material, an insulating inorganic substance and a polymer,
the PTC resistor layer is divided into a layer a and a layer B in this order from the side close to the electrode active material layer so that the thickness direction of any portion of the PTC resistor layer is (the thickness of the layer a): (thickness of B layer) 1: at 2 time, V A<V BWherein
V AIs the volume ratio of the insulating inorganic substance in the layer A when the total volume of the conductive material, the insulating inorganic substance and the polymer in the layer A is set as 100 vol%,
V Bis the volume ratio of the insulating inorganic substance in the B layer, with the total volume of the conductive material, the insulating inorganic substance, and the polymer in the B layer being set to 100 vol%.
It is known that in the case where a layer containing a conductive material and a polymer is provided between an electrode active material layer and a current collector, the layer exhibits a PTC resistor function in which the electronic resistance sharply increases when heated above the melting point of the polymer. The PTC resistor functions by peeling the conductive materials in contact with each other and blocking electron conduction due to the thermal expansion of the polymer. In the present disclosure, a layer exhibiting such a PTC resistor function is referred to as a PTC resistor layer.
In the solid-state battery including the PTC resistor layer, when the temperature of the solid-state battery increases due to overcharge or short-circuiting, electron conduction between the electrode active material layer and the current collector is inhibited, and thus the electrochemical reaction is stopped. Therefore, further temperature increase is suppressed, and adverse effects on the solid-state battery itself and the device using the solid-state battery can be prevented.
In addition, when a pressure is applied to the solid-state battery, the PTC resistor layer containing the conductive material and the polymer cannot maintain the structure due to deformation and flow of the polymer, and as a result, the PTC resistor may not function as a PTC resistor.
However, as a result of intensive studies, it has been found that in an electrode including a PTC resistor layer containing an insulating inorganic substance, the electronic resistance at the interface between the PTC resistor layer and the electrode active material layer is high in addition to the high electronic resistance inside the PTC resistor layer. This is presumably because the presence of a large amount of the insulating inorganic substance on the surface of the PTC resistor layer lowers the contact property at the interface between the PTC resistor layer and the electrode active material layer.
The solid-state battery electrode of the present disclosure passes through the volume ratio V of the insulating inorganic substance in the layer a closer to the electrode active material layer in the PTC resistor layer AVolume ratio V of the insulating inorganic substance in the layer B closer to the current collector BWhen the electrode is used in a solid-state battery, the performance degradation of the solid-state battery can be suppressed.
The electrode for a solid battery of the present disclosure is provided with an electrode active material layer, a current collector, and a PTC resistor layer.
Fig. 1 is a view showing an example of the layer structure of the electrode for a solid-state battery according to the present disclosure, and is a view schematically showing a cross section cut in the stacking direction. As shown in fig. 1, the solid-
As shown in fig. 1, the
The
These layers constituting the electrode for a solid-state battery will be described in detail below.
(1) PTC resistor layer
The PTC resistor layer contains a conductive material, an insulating inorganic substance, and a polymer, and is disposed between the electrode active material layer and the current collector, and is in contact with the electrode active material layer.
The conductive material contained in the PTC resistor layer is not particularly limited as long as it has conductivity. As the conductive material, for example: carbon-containing conductive materials such as carbon black, activated carbon, carbon fibers (carbon nanotubes, carbon nanofibers, and the like), and graphite, and among the carbon-containing conductive materials, carbon black is preferred. The conductive material may be in the form of particles or fibers.
The volume ratio of the conductive material in the PTC resistor layer is not particularly limited. When the total volume of the conductive material, the insulating inorganic material, and the polymer is set to 100 vol%, the volume ratio of the conductive material in the PTC resistor layer may be 7 vol% to 50 vol%, or 7 vol% to 10 vol%.
The insulating inorganic material contained in the PTC resistor layer has a function of suppressing deformation and flow of the PTC resistor layer due to high temperature and pressure in the electrode for a solid-state battery.
The insulating inorganic material is not particularly limited as long as it has an insulating property and a melting point higher than that of a polymer described later, and examples thereof include a metal oxide and a metal nitride. Examples of the metal oxide include: alumina, zirconia, silica, and the like, and examples of the metal nitride include silicon nitride and the like. Examples of the insulating inorganic substance include ceramic materials. Among these materials, the insulating inorganic substance is preferably a metal oxide.
The insulating inorganic material is usually in the form of particles. The insulating inorganic material may be primary particles or secondary particles.
Average particle diameter (D) of insulating inorganic substance 50) For example, the thickness may be 0.2 to 5 μm, or 0.4 to 2 μm. The particle distribution of the insulating inorganic substance is not particularly limited. The particle distribution of the insulating inorganic substance may show a normal distribution when represented by, for example, a frequency distribution.
The volume ratio of the insulating inorganic substance in the PTC resistor layer is not particularly limited. When the total volume of the conductive material, the insulating inorganic substance, and the polymer is set to 100 vol%, the volume ratio of the insulating inorganic substance in the PTC resistor layer may be 40 vol% to 85 vol%, or 50 vol% to 60 vol%. The "volume ratio of the insulating inorganic substance in the PTC resistor layer" referred to herein is a volume ratio V of the insulating inorganic substance contained in the layer a described later AAnd volume ratio V of insulating inorganic substance contained in layer B BAll of the values are correlated.
When the volume ratio of the insulating inorganic substance in the PTC resistor layer is too small, it may be difficult to sufficiently suppress deformation and flow of the PTC resistor layer due to heating and pressure. On the other hand, when the volume ratio of the insulating inorganic substance in the PTC resistor layer is too large, the volume ratio of the polymer is relatively decreased, and therefore, the effect of peeling the conductive materials from each other by the polymer cannot be sufficiently obtained, and there is a possibility that the increase in the electronic resistance becomes insufficient. In addition, when the volume ratio of the insulating inorganic substance in the PTC resistor layer is too large, the conductive path formed by the conductive material is blocked by the insulating inorganic substance, and there is a possibility that the electron conductivity of the PTC resistor layer in normal use is lowered. In the present disclosure, "electron conductivity of the PTC resistor layer" means a characteristic of conduction of electrons in the PTC resistor layer, and strictly speaking, is different from the conductivity of the PTC resistor layer (a characteristic of conduction of electricity in the PTC resistor layer).
In the present disclosure, the PTC resistor layer is divided into an a layer and a B layer in order from the side close to the electrode active material layer, so that the thickness direction of any portion of the PTC resistor layer is (the thickness of the a layer): (thickness of B layer) 1: 2. here, the thickness direction of the PTC resistor layer means a direction perpendicular to the direction in which the PTC resistor layer extends, in other words, a direction parallel to the lamination direction of a laminate including the electrode active material layer, the PTC resistor layer, and the current collector.
The layer a is a layer occupying one third of the thickness of the PTC resistor layer from the interface between the PTC resistor layer and the electrode active material layer. On the other hand, the layer B is a layer occupying two thirds of the thickness of the PTC resistor layer from the interface between the PTC resistor layer and the layer on the opposite side of the electrode active material layer (for example, the interface between the PTC resistor layer and the current collector layer) among the PTC resistor layers.
Volume ratio V of insulating inorganic substance in layer A AVolume ratio V of the insulating inorganic substance in the layer B is smaller than BIs one of the main features of the present disclosure. It should be noted that the volume ratio V AThe total volume of the conductive material, the insulating inorganic material, and the polymer in the layer a is set to 100 vol%. Volume ratio V BThe total volume of the conductive material, the insulating inorganic material, and the polymer in the B layer was set to 100 vol%.
As described above, in the conventional electrode including the PTC resistor layer containing an insulating inorganic substance, there is a problem that the electronic resistance at the interface between the PTC resistor layer and the electrode active material layer is large at room temperature (15 to 30 ℃). As described above, when an insulating inorganic substance is used to increase the electronic resistance under high temperature conditions, the electronic resistance at room temperature is also increased. However, merely reducing the content of the insulating inorganic substance lowers the electronic resistance under high temperature conditions, and thus the PTC resistor layer cannot sufficiently function.
Therefore, in order to reduce the electronic resistance at room temperature while maintaining high electronic resistance under high temperature conditions, the distribution of the insulating inorganic substance in the PTC resistor layer becomes important.In the present disclosure, the volume ratio V of the insulating inorganic substance in the layer A is adjusted AVolume ratio V of the insulating inorganic substance in the layer B is smaller than BThe amount of the insulating inorganic substance present at the interface between the PTC resistor layer and the electrode active material layer can be reduced. Therefore, more electronic contacts than ever can be provided at the interface between the PTC resistor layer and the electrode active material layer. Here, the term "electronic contact" means a contact point between the PTC resistor layer and the electrode active material layer, which is capable of conducting at least electrons.
Since the insulating inorganic material is generally harder than the conductive material and the polymer, when the layer a contains less insulating inorganic material than the layer B, the PTC resistor layer has improved flexibility, contact properties, and conformability to the electrode active material layer. As a result, at room temperature, the electronic resistance at the interface between the PTC resistor layer and the electrode active material layer can be suppressed, and the performance degradation of the solid-state battery including the electrode for a solid-state battery of the present disclosure can be suppressed. On the other hand, since it is not necessary to reduce the amount of insulating inorganic substances in the PTC resistor layer, the charge/discharge stop function of the solid-state battery can be exhibited at the time of occurrence of a failure, at the time of restraint, or the like without lowering the electronic resistance under high-temperature conditions.
In the present disclosure, the a layer and the B layer are defined such that in the thickness direction of any portion of the PTC resistor layer are (the thickness of the a layer): (thickness of B layer) 1: 2. in fact, since the layer a and the layer B are often formed integrally as a PTC resistor layer, it is often difficult to completely separate these layers. The above definition is merely set for convenience sake in comparing the volume ratio of the insulating inorganic substance on the side closer to the electrode active material layer in the PTC resistor layer with the volume ratio of the insulating inorganic substance on the side closer to the current collector.
The volume ratio V of the insulating inorganic substance in the layer A ADivided by the volume ratio V of the insulating inorganic substance in the B layer BThe value (V) thus obtained A/V B) Preferably 0.08 to 0.5, more preferably 0.1 to 0.45, and further preferably 0.15 to 0.4.
In (V) A/V B) At a value greater than 0.5, the volume ratio V AIf the size is too large, the PTC resistor layer may deteriorate flexibility, contact properties, and followability of the electrode active material layer. On the other hand, in (V) A/V B) At a value less than 0.08, the volume ratio V AIf the volume ratio of the insulating inorganic substance occupied by the PTC resistor layer is too small, the PTC resistor layer may occupy a small volume ratio, and as a result, a high electronic resistance under high temperature conditions may not be obtained.
Volume ratio V of insulating inorganic substance in layer B BPreferably 50% by volume or more, more preferably 55% by volume or more, and still more preferably 60% by volume or more. Volume ratio V BThe content may be less than 100% by volume or may be 90% by volume or less.
At volume ratio V BIf the volume ratio is too small, the volume ratio of the insulating inorganic substance occupied by the entire PTC resistor layer may be small, and as a result, high electronic resistance under high temperature conditions may not be obtained.
In this way, the volume ratio V of the insulating inorganic material in the B layer is preferably adjusted BWhile maintaining high degree, the volume ratio V of the insulating inorganic substance in the A layer is reduced AThereby, the volume ratio of the insulating inorganic substance in the PTC resistor layer is distributed. More specifically, by making the insulating inorganic substance in the a layer small, the conductive path at the interface between the PTC resistor layer and the electrode active material layer is large, while by making the insulating inorganic substance in the B layer large, the conductive path inside the PTC resistor layer is small, whereby the effect of suppressing the electronic resistance at room temperature and the effect of increasing the electronic resistance under high temperature conditions can be simultaneously achieved.
Volume ratio V AAnd volume ratio V BCalculated by the following method.
First, the electrode for the solid battery is subjected to cross-sectional processing by a cross-sectional polisher (CP). The cross section of the obtained PTC resistor layer was observed with a Field Emission Scanning electron microscope (FE-SEM).
Next, in the obtained SEM image, the PTC resistor layer was set as an a layer and a B layer in this order from the side close to the electrode active material layer so that the thickness direction of any portion of the PTC resistor layer was (the thickness of the a layer): (thickness of B layer) 1: 2. thus, the cross-sectional area of the a layer is 1/3 of the cross-sectional area of the entire PTC resistor layer, and the cross-sectional area of the B layer is 2/3 of the cross-sectional area of the entire PTC resistor layer. The layer a referred to here does not necessarily correspond to the second coating layer (layer on the side closer to the positive electrode active material layer) in the production method described later. The layer B does not necessarily correspond to the first coating layer (layer on the collector side) in the production method described later.
Then, the volume ratio V of the insulating inorganic substance in the a layer was calculated from the SEM image, assuming that the total volume of the conductive material, the insulating inorganic substance, and the polymer in the a layer was 100 vol% A(volume%). Similarly, the volume ratio V of the insulating inorganic substance in the B layer was calculated assuming that the total volume of the conductive material, the insulating inorganic substance and the polymer in the B layer was 100 vol% B(volume%).
Furthermore, by dividing the volume ratio V ADivided by the volume ratio V BTo obtain (V) A/V B) The value is obtained. In the electrode for a solid-state battery of the present disclosure, the volume ratio V ALess than volume ratio V BThus is (V) A/V B)＜1。
In this evaluation method, a solid-state battery provided with an electrode for a solid-state battery may be used instead of the electrode for a solid-state battery, or an evaluation sample described later may be used.
As a result of volume ratio V ABelow volume ratio V BExamples of the method (4) include a method of forming a PTC resistor layer by applying a second slurry to the surface of the first coating layer, as in the production method described below. In this case, it is preferable that the second slurry does not contain an insulating inorganic substance, or that the volume ratio (based on solid content) of the insulating inorganic substance contained in the second slurry is lower than the volume ratio of the insulating inorganic substance in the first coating layer.
In addition, the volume ratio V is also adjusted by adjusting the amount of the conductive material contained in the second paste, adjusting the coating thickness of the second paste, and the like ABelow volume ratio V BIs effective.
The polymer contained in the PTC resistor layer is not particularly limited as long as it has a property of expanding when heated above the melting point. Examples of the polymer include: and thermoplastic resins such as polypropylene, polyethylene, polyvinyl chloride, polyvinylidene fluoride (PVdF), polyvinyl fluoride, polystyrene, ABS resin, methacrylic resin, polyamide, polyester, polycarbonate, and polyacetal. These polymers may be used alone or in combination of two or more.
Among these, from the viewpoint of melting point, easy processability, and the like, fluoropolymers such as polyvinylidene fluoride and polyvinyl fluoride, and polyethylene are preferable, and polyvinylidene fluoride is particularly preferable.
The volume ratio of the polymer in the PTC resistor layer is not particularly limited. When the total volume of the conductive material, the insulating inorganic material, and the polymer is set to 100 vol%, the volume ratio of the polymer in the PTC resistor layer may be 8 vol% to 60 vol%, or 8 vol% to 45 vol%.
The thickness of the PTC resistor layer is not particularly limited, but is preferably from about 1 μm to about 30 μm.
The PTC resistor layer contains a carbon-containing conductive material as a conductive material and a fluorine-containing polymer as a polymer, and the value obtained by dividing the atomic percent (atomic%) of carbon atoms (C) contained in the A layer by the atomic percent (atomic%) of fluorine atoms (F) contained in the A layer (hereinafter sometimes referred to as C/F value) may be 2.4 to 3.9. The C/F value is preferably 2.5 to 3.8, more preferably 2.6 to 3.7.
When the C/F value in the layer a on the side closer to the electrode active material layer in the PTC resistor layer is within the above range, the thermal stability of the entire PTC resistor layer is improved, and the electron resistance value at high temperature is further increased. As a result, when the electrode for a solid-state battery of the present disclosure is used in a solid-state battery, the progress of the battery reaction can be suppressed when the battery temperature increases due to an internal short circuit or the like.
In the case where the C/F value is less than 2.4, the carbon content in the a layer is too small, and therefore there is a concern that: a sufficient amount of conductive path at the interface of the PTC resistor layer and the electrode active material layer cannot be ensured. On the other hand, if the C/F value is greater than 3.9, the carbon content in the a layer is too high, and therefore the thermal stability of the entire PTC resistor layer may be lowered.
The index of thermal stability referred to herein includes the electronic resistance under high temperature (e.g., 250 ℃ C.). The higher the electronic resistance under high temperature conditions, the more excellent the thermal stability of the solid-state battery electrode.
The calculation method of the C/F value in the present disclosure is as follows.
First, elemental analysis of the cross section of the A layer in the PTC resistor layer was performed by Flat QUAD-Energy dispersive X-ray Spectroscopy (FQ-EDX). The "cross section of the a layer in the PTC resistor layer" refers to the cross section of the a layer defined by the SEM image.
Then, from the results of the elemental analysis, the amount of C (atomic%) and the amount of F (atomic%) contained in the cross section of the a layer were calculated. The value obtained by dividing the amount of C (atomic%) by the amount of F (atomic%) was defined as the C/F value of the electrode for a solid-state battery.
In this evaluation method, a solid-state battery provided with an electrode for a solid-state battery may be used instead of the electrode for a solid-state battery, or an evaluation sample described later may be used.
The contact area of the PTC resistor layer with the electrode active material layer is not particularly limited. When the PTC resistor layer is in contact with the electrode active material layer, preferably 50% or more of the area of the electrode active material layer, more preferably 70% or more of the area of the electrode active material layer, and even more preferably 99% or more of the area of the electrode active material layer, the effect of suppressing an increase in the electronic resistance at the interface between the PTC resistor layer and the electrode active material layer is sufficiently exhibited.
Here, the contact area between the PTC resistor layer and the electrode active material layer is an area where the PTC resistor layer and the electrode active material layer apparently contact each other, regardless of the presence or absence of an electronic contact between these layers.
(2) Electrode active material layer
The electrode active material layer is not particularly limited as long as it contains at least an electrode active material, and may contain a binder, a conductive material, and a solid electrolyte as needed.
In the case where the electrode for a solid-state battery of the present disclosure is used as a positive electrode, the electrode active material is not particularly limited as long as it can be generally used as a positive electrode active material. As the positive electrode active material, for example, in the case where the ions to be transferred are lithium ions, there are listed: LiCoO 2、LiNiO 2Etc. having a layered structure, LiMn 2O 4And compounds having a spinel structure, LiFePO 4And the like having an olivine-type structure.
In the case where the electrode for a solid-state battery of the present disclosure is used as an anode, the electrode active material is not particularly limited as long as it can be generally used as an anode active material. As the negative electrode active material, for example, in the case where the transferred ions are lithium ions, there can be mentioned: carbon materials, lithium alloys and oxides, nitrides, and the like.
The binder is not particularly limited as long as it is chemically stable and electrically stable. Examples of the binder include: fluorine-containing binders such as polyvinylidene fluoride (PVDF) and Polytetrafluoroethylene (PTFE).
The conductive material is not particularly limited as long as it has conductivity. As the conductive material, for example: carbon materials such as carbon black, activated carbon, carbon fibers (carbon nanotubes, carbon nanofibers, etc.), and graphite.
The solid electrolyte material is not particularly limited as long as it has ion conductivity. Examples of the solid electrolyte material include: inorganic solid electrolyte materials such as sulfide solid electrolyte materials and oxide solid electrolyte materials. As the sulfide solid electrolyte material, for example: li 2S-SiS 2、LiI-Li 2S-SiS 2、LiI-Li 2S-P 2S 5、LiI-Li 2O-Li 2S-P 2S 5、LiI-Li 2S-P 2O 5、LiI-Li 3PO 4-P 2S 5、Li 2S-P 2S 5、Li 3PS 4、LiI-LiBr-Li 2S-P 2S 5、Li 2S-P 2S 5-GeS 2And the like.
(3) Current collector
The material of the current collector is not particularly limited as long as it has electron conductivity. As the material of the current collector, for example: al, Cu, Ni, SUS, Fe, etc. Among these, in the case of using the electrode for a solid battery of the present disclosure as a positive electrode, it is preferable to use Al as a material of a current collector. Among these, in the case of using the electrode for a solid battery of the present disclosure as an anode, Cu is preferably used as a material of a current collector.
(4) Properties of electrode for solid-state battery
When the solid-state battery is assumed to be used normally, the value of the electronic resistance of the electrode for a solid-state battery at room temperature (15 ℃ C. to 30 ℃ C.) is preferably small. In contrast, from the viewpoint of exhibiting a function of stopping the battery reaction at high temperatures, the value of the electronic resistance of the electrode for a solid-state battery under high-temperature conditions is preferably large.
The ratio of the electron resistance value of the electrode for a solid-state battery under high-temperature conditions to the electron resistance value of the electrode for a solid-state battery under room temperature is preferably 1.5 or more, more preferably 2 or more, and still more preferably 5 or more. If the ratio is too small, the battery characteristics that are excellent in normal use and the battery stopping function that is likely to occur when a malfunction occurs or when restraint occurs may not be compatible with each other. In addition, when the ratio is too small, the thermal stability of the electrode for a solid-state battery may be poor.
The ratio of the electron resistance value of the electrode for a solid-state battery under high-temperature conditions to the electron resistance value of the electrode for a solid-state battery under room temperature may be 20000 or less.
(5) Method for manufacturing electrode for solid battery
The method for producing the electrode for a solid-state battery is not particularly limited as long as the electrode for a solid-state battery can be obtained. Two embodiments of the method for producing an electrode for a solid-state battery will be described below, but the method for producing an electrode for a solid-state battery according to the present disclosure is not limited to these embodiments.
A. First embodiment
A first embodiment of a method for manufacturing an electrode for a solid-state battery includes: (a) a step of forming a first coating layer on a surface of a current collector; (b) a step of forming a PTC resistor layer by applying a second slurry onto the first coating layer surface; and (c) a step of laminating an electrode active material layer on the PTC resistor layer.
(a) Process for forming a first coating on a surface of a current collector
In the present process, a first coating layer is formed by coating a first slurry on the surface of the current collector and then drying.
The first paste contains a conductive material, an insulating inorganic substance, and a polymer. Details of these materials are as described above. The volume ratios and distributions of the conductive material, the insulating inorganic substance, and the polymer in the PTC resistor layer provided in the solid-state battery electrode can be adjusted as appropriate, by adjusting the content ratios of the conductive material, the insulating inorganic substance, and the polymer in the first paste and the second paste, which will be described later.
The content ratio of each material in the first slurry includes, for example: the volume ratio of the conductive material: polymer (b): insulating inorganic substance 10: 30: 60, etc.
The first paste may include a non-aqueous solvent in which a conductive material, an insulating inorganic substance, and a polymer are dissolved or dispersed. The kind of the nonaqueous solvent is not particularly limited, and N-methylpyrrolidone, acetone, methyl ethyl ketone, dimethylacetamide and the like can be mentioned, and N-methylpyrrolidone is preferable from the viewpoint of safety such as a high flash point and a small influence on the human body.
The content of the nonaqueous solvent in the first slurry is not particularly limited, and may be 80 to 93 vol%, or 82 to 90 vol%, when the total volume of the first slurry is 100 vol%.
The method of forming the first coating layer is not particularly limited, and generally, a first slurry obtained by dispersing a conductive material, an insulating inorganic material, and a polymer in a nonaqueous solvent is coated on a current collector and dried. In order to uniformly form the first coating layer, the solid content concentration of the first slurry including the conductive material, the insulating inorganic substance, and the polymer may be set to 13 to 40 mass%.
The thickness of the first coating layer is also not particularly limited, and is preferably about 1 μm to about 30 μm.
The drying conditions of the first slurry are not particularly limited, and may be temperature conditions to such an extent that the non-aqueous solvent can be distilled off.
(b) A step of forming a PTC resistor layer by applying a second slurry on the surface of the first coating layer
In the present process, the surface of the collector is coated with a coating layer
And a second paste, followed by drying, thereby forming a PTC resistor layer. Here, the PTC resistor layer is a layer composed of the solid component of the second slurry and the first coat layer.
The second paste contains a conductive material and a polymer. The second slurry may or may not further contain an insulating inorganic substance. In the case where the second paste does not contain an insulating inorganic substance, the contact property of the interface between the obtained PTC resistor layer and the electrode active material layer can be further improved as compared with the case where the second paste contains an insulating inorganic substance.
Examples of the content ratio of each material in the second slurry, in which the second slurry does not contain an insulating inorganic substance, include: the volume ratio of the conductive material: polymer 85: 15-20: 80, etc.
The content of the nonaqueous solvent in the second slurry is not particularly limited, and may be 75 to 95 vol%, or 85 to 90 vol%, when the total volume of the second slurry is 100 vol%.
A method of coating and drying the second slurry is not particularly limited, and generally, the second slurry obtained by dispersing the conductive material and the polymer in the nonaqueous solvent is coated on the current collector and dried. In order to uniformly apply the second paste, the solid content concentration of the second paste including at least the conductive material and the polymer may be set to 13 to 35% by mass.
The thickness of a layer corresponding to a portion obtained by applying and drying the second slurry (hereinafter, this layer may be referred to as a second coat layer) is also not particularly limited, but is preferably from about 1 μm to about 10 μm, and more preferably from 2 μm to 6 μm. The thickness of the second coating layer is determined by, for example, the difference between the thickness of the laminate before the second coating layer is formed and the thickness of the laminate after the second coating layer is formed.
In general, the PTC resistor layer is formed by integrating the first coating layer and the solid content of the second slurry after the second slurry is applied and dried.
The laminate of the current collector and the PTC resistor layer is preferably pressed before the electrode active material layer is laminated. As the pressing method, rolling, Cold Isostatic pressing (Cold Isostatic Press; CIP), Hot Isostatic pressing (Hot Isostatic Press; HIP), and the like can be used. When the pressing pressure is too high, cracks may occur in the PTC resistor layer. For example, in the case of roll pressing, it is preferable to set the pressing pressure to 5.6kN/cm to 14.2kN/cm in terms of line pressure.
(c) Step of laminating electrode active material layer on PTC resistor layer
By laminating an electrode active material layer on the PTC resistor layer, a laminate having the electrode active material layer, the PTC resistor layer, and the current collector was produced. Details of materials (electrode active material, binder, conductive material, and solid electrolyte) that can be used for the electrode active material layer are as described above.
The electrode active material layer can be formed by a method known in the art. For example, the electrode active material layer may be formed by sufficiently stirring a raw material mixture of the electrode active material layer, then coating the raw material mixture on the substrate or the PTC resistor layer, and appropriately drying.
Here, in the case of forming the electrode active material layer on the substrate, roll pressing under a high temperature condition (hot roll pressing) may be used. A more densified electrode active material layer can be obtained by hot roll pressing. In the case where the electrode active material layer is formed on the PTC resistor layer, there is a concern that the polymer in the PTC resistor layer may thermally expand when the heating temperature is too high at the time of hot rolling, and therefore the upper limit temperature at the time of hot rolling needs to be set in accordance with the polymer characteristics, the composition of the PTC resistor layer, and the like. Generally, it is preferred to perform hot rolling at less than the melting point of the polymer.
B. Second embodiment
A second embodiment of the method for manufacturing an electrode for a solid-state battery includes: (a) a step of forming a first coating layer on a surface of a current collector; (b') a step of forming a second coating layer on the surface of the electrode active material layer; and (c') a step of producing a laminate comprising the current collector, the PTC resistor layer, and the electrode active material layer.
Wherein (a) is the same as the first embodiment. Hereinafter, (b ') and (c') will be described.
(b') a step of forming a second coating layer on the surface of the electrode active material layer
In this process, a second coating layer is formed by applying a second slurry on the surface of the base material and then drying, and thereafter, a second coating layer is formed on the electrode active material layer by transferring the second coating layer from the base material to the electrode active material layer.
In the first embodiment, as described in the above (b), the second coating layer is formed on the first coating layer. In contrast, in the present step of the second embodiment, the second coating layer is formed on the electrode active material layer. As described above, in the two embodiments, the members to be formed with the second coating layer are different from each other.
By transferring the second coating layer from the substrate to the electrode active material layer, there is an advantage in that the solvent used for the second slurry does not exert an influence on the electrode active material layer.
As for the second slurry and the resulting second coating layer, the same as those of the first embodiment.
The base material for forming the second coating layer is also not particularly limited, and for example, Al, PET, Cu, SUS, or the like can be used.
(c') Process for producing a laminate comprising an electrode active material layer, a PTC resistor layer and a Current collector
In this step, the first coating layer on the surface of the current collector is laminated so as to be in contact with the second coating layer on the surface of the electrode active material layer, whereby the first coating layer and the second coating layer are integrated to form the PTC resistor layer. As a result, a laminate including the electrode active material layer, the PTC resistor layer, and the current collector can be produced.
(6) Measurement of electronic resistance of electrode for solid-state battery
One of evaluations of the electrode for a solid-state battery is measurement of electronic resistance. In the measurement of the electronic resistance, a solid-state battery including an electrode for a solid-state battery or an evaluation sample including an electrode for a solid-state battery is used.
Hereinafter, the sample for evaluation will be described. Fig. 3 is a schematic cross-sectional view of a sample for evaluation including the electrode for a solid-state battery according to the present disclosure. The solid-
As shown in fig. 3, the layer structure of the
An example of a method for producing the evaluation sample is as follows. First, a laminate of 2 PTC resistor layers and a current collector (hereinafter, sometimes referred to as laminate a) and a laminate of a positive electrode active material layer and a current collector (hereinafter, sometimes referred to as laminate B) were each prepared. Next, for 2 laminates B, the two laminates B were laminated such that the positive electrode active material layer of one laminate B was in contact with the current collector of the other laminate B. By peeling off one current collector positioned outside of the obtained laminate, a laminate having a structure as follows (hereinafter, sometimes referred to as laminate C) was produced: positive electrode active material layer/current collector/positive electrode active material layer. The laminate C corresponds to the central portion (positive electrode
Fig. 3 is a schematic diagram of an electronic resistance measurement circuit including an evaluation sample. As shown in fig. 3, a micro-tester 40 was connected to the
Instead of the
Fig. 4 is a graph showing the relationship between the electronic resistance of the evaluation sample including the PTC resistor layer and the resistance of the solid-state battery including the electrode including the PTC resistor layer. FIG. 4 is a graph in which the vertical axis represents the resistance (. omega. cm) of the solid-state battery 2) And the horizontal axis represents the electronic resistance (Ω · cm) of the sample for evaluation 2) The figure (a).
As is clear from fig. 4, when the electronic resistance of the evaluation sample increases, the resistance of the solid-state battery also increases. As described above, since the correlation between the electronic resistance of the evaluation sample and the resistance of the solid-state battery is high, the measurement result of the electronic resistance obtained using the evaluation sample can be said to be a test result reflecting the performance of the solid-state battery itself.
2. Solid-state battery
The solid-state battery according to the present disclosure is a solid-state battery including a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the solid-state battery electrode.
In the present disclosure, a solid battery refers to a battery including a solid electrolyte. Therefore, the solid-state battery of the present disclosure may be composed entirely of a solid component, or may contain both a solid component and a liquid component, as long as the solid-state battery contains a solid electrolyte.
Fig. 2 is a view showing an example of the layer structure of the solid-state battery of the present disclosure, and is a view schematically showing a cross section cut in the stacking direction. As shown in fig. 2, the solid-state battery 100 includes: an
Here, the solid-
The
The electrolyte layer 20 is not particularly limited as long as it is a layer having ion conductivity. The electrolyte layer 20 may be a layer containing only a solid electrolyte, or may be a layer containing both a solid electrolyte and a liquid electrolyte.
As the electrolyte layer containing only the solid electrolyte, for example: a polymer solid electrolyte layer, an oxide solid electrolyte layer, a sulfide solid electrolyte layer, and the like.
As the electrolyte layer containing both the solid electrolyte and the liquid electrolyte, for example: a porous solid electrolyte layer impregnated with an aqueous electrolyte solution or a nonaqueous electrolyte solution.
The shape of the solid-state battery of the present disclosure is not particularly limited. Examples of the shape of the solid-state battery include: coin type, flat plate type, cylinder type, and the like.
The solid-state battery of the present disclosure may be a single cell ( セル) as shown in fig. 2, or may be a battery assembly including 2 or more of the single cells. Examples of the battery assembly include: a stack in which 2 or more flat cells are stacked.
As described above, the electrode for a solid-state battery of the present disclosure exhibits an excellent effect of suppressing a decrease in performance of the solid-state battery under a condition where a pressure is applied. Therefore, the electrode for a solid-state battery according to the present disclosure exhibits excellent effects not only when the solid-state battery receives an unintended pressure, such as when a defect occurs due to an internal short circuit or overcharge, but also when an intentional pressure is applied, such as when a restraining member or the like is used for the solid-state battery. When a defect occurs in the solid-state battery, an unexpected local pressure is usually applied to the solid-state battery. In contrast, when the restraining member is used for the solid-state battery, a predetermined pressure is generally applied to the entire solid-state battery.
The constraining member may be a member capable of applying a constraining pressure to a laminate including 2 electrodes and an electrolyte layer located between the 2 electrodes in a direction substantially parallel to the lamination direction. A known solid-state battery restraint member can be used for the solid-state battery of the present disclosure. As a known binding member for a solid-state battery, for example, a binding member having: 2 sheets of 1 set of plate-like portions that sandwich the solid-state battery from the outside; 1 or 2 or more rod-shaped parts connecting the 2 plate-shaped parts; and an adjusting part which is connected with the rod-shaped part and can adjust the constraint pressure through a spiral structure and the like. In the case of this example, the confining pressure applied to the solid-state battery can be adjusted by appropriately controlling the adjusting portion.
The confining pressure is not particularly limited, but is preferably 0.1MPa or more, more preferably 1MPa or more, and still more preferably 5MPa or more. When the confining pressure is 0.1MPa or more, the layers constituting the solid-state battery are more favorably in contact with each other. On the other hand, the confining pressure is, for example, preferably 100MPa or less, more preferably 50MPa or less, and still more preferably 20MPa or less. When the confining pressure is 100MPa or less, a special confining member is not required.