JP6819369B2 - Method of forming a solid electrolyte layer - Google Patents

Description

The present invention relates to a method for forming a solid electrolyte layer.

A technique using an aerosol deposition method for forming a solid electrolyte layer on a substrate is known. For example, Patent Document 1 relates to a method for producing a lithium solid-state battery, in which a solid electrolyte layer composed of a sulfide solid electrolyte material and containing no binder is provided on the positive electrode active material and the negative electrode active material layer, respectively. It is described that it is formed by the position method.

Patent Document 2 describes that an active material layer is formed on a current collector layer by an aerosol deposition method. Further, it is described that if the negative electrode particles coated with the conductive substance on the surface of the negative electrode active material particles are sprayed on the negative electrode current collector layer at high speed by the conveying gas, there is a problem of damaging the current collector layer. ing.

Japanese Unexamined Patent Publication No. 2016-100069 Japanese Unexamined Patent Publication No. 2008-305608

Lithium lanthanum zirconate (LLZ) is known as a solid electrolyte material having high lithium ion conductivity.

However, in the prior art, it is known that an LLZ-containing solid electrolyte layer containing LLZ as a solid electrolyte is formed on a substrate such as a laminate whose outermost surface is an active material layer by an aerosol deposition method. Not.

According to the studies by the present inventors, it has been found that when a solid electrolyte layer containing LLZ is formed on the substrate by the aerosol deposition method, there is a problem that the substrate is scraped. On the other hand, if the aerosol deposition method is carried out under mild conditions such that the substrate is not scraped, the LLZ-containing solid electrolyte layer cannot be formed.

The present invention has been made in view of the above. Therefore, an object of the present invention is to provide a method for forming an LLZ-containing solid electrolyte layer having high lithium ion conductivity on a substrate by an aerosol deposition method while suppressing scraping of the substrate.

The present invention
A method of forming a solid electrolyte layer by injecting solid electrolyte particles onto a substrate by an aerosol deposition method.
Crystalline oxidation in which the solid electrolyte particles have a composition of Li _7-x La ₃ Zr _2-x M _x O ₁₂ (M is Nb or Ta, and x is a number of 0 or more and 0.75 or less). The ratio LC ₁ / LC _∞ between the lattice constant LC ₁ of the crystalline oxide and the lattice constant LC _∞ when the crystalline oxide is fired at 1,200 ° C. for 30 hours is 1 .0001 or more and 1.0007 or less,
Regarding the method.

According to the present invention, there is provided a method for forming an LLZ-containing solid electrolyte layer having high lithium ion conductivity on a substrate by an aerosol deposition method while suppressing scraping of the substrate.

FIG. 1 is a schematic diagram for explaining an outline of the aerosol deposition method. FIG. 2 is a graph showing the relationship between the lattice constant of the crystalline oxide obtained in Example 1 and the calcination time at 1,200 ° C. FIG. 3 shows the relationship between the layer thickness and lithium ion conductivity of the solid electrolyte layer obtained in Example 1 and LC ₁ / LC _∞ of the crystalline oxide used as the solid electrolyte particles of the aerosol deposition method. It is a graph. FIG. 4 shows the lithium ion conductivity of the solid electrolyte layer obtained in Example 2 and the x value in Li _7-x La ₃ Zr _2-x Nb _x O ₁₂ used as the solid electrolyte particles of the aerosol deposition method. It is a graph which shows the relationship of.

The method of the present invention for forming a solid electrolyte layer is
A method of forming a solid electrolyte layer by injecting solid electrolyte particles onto a substrate by an aerosol deposition method.
Crystalline oxidation in which the solid electrolyte particles have a composition of Li _7-x La ₃ Zr _2-x M _x O ₁₂ (M is Nb or Ta, and x is a number of 0 or more and 0.75 or less). The ratio LC ₁ / LC _∞ between the lattice constant LC ₁ of the crystalline oxide and the lattice constant LC _∞ when the crystalline oxide is fired at 1,200 ° C. for 30 hours is 1 It is .0001 or more and 1.0007 or less.

Hereinafter, the present invention will be described with reference to preferred embodiments as examples.

<Solid electrolyte particles>
The solid electrolyte particles used in this embodiment have a composition of Li _7-x La ₃ Zr _2-x M _x O ₁₂ (M is Nb or Ta, and x is a number of 0 or more and 0.75 or less). It is composed of a crystalline oxide having. The ratio LC ₁ / LC _∞ between the lattice constant LC ₁ of this crystalline oxide and the lattice constant LC _∞ when the crystalline oxide is fired at 1,200 ° C. for 30 hours is 1.0001 or more and 1.0007. It is as follows.

The crystalline oxide may have x = 0, that is, the composition of Li ₇ La ₃ Zr ₂ O ₁₂ , but contains Nb or Ta in the range where x in the above formula is 0 or more and 0.75 or less. Then, the lithium ion conductivity is improved, which is preferable. The value of x may be, for example, 0.125 or more, 0.15 or more, or 0.20 or more, for example, 0.50 or less, 0.40 or less, 0.35 or less, or 0.30 or less. It may be there.

For the crystalline oxide having the above composition, the raw materials are mixed with a predetermined composition, wet-pulverized, and then calcinated at 950 ° C. for 10 hours, and if necessary, further wet-pulverized, and then 1 , Can be produced by performing the main firing at 200 ° C. Here, the crystal structure gradually becomes firm as the processing time of the main firing increases. Along with this, the lattice constant of the crystalline oxide gradually decreases and reaches a steady value after about 20 to 30 hours, and even if the main firing time is further extended, the crystal structure does not change further. It will be stable.

The steady-state value of the lattice constant depends on the value of x in the above composition formula. For example, when x = 0, the steady-state value of the lattice constant is 12.983 Å. When M is Nb and X = 0.25, that is, the constant value of the lattice constant of the crystalline oxide having the composition of Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ is 12.945 Å. Is.

In the present embodiment, when a crystalline oxide whose lattice constant LC ₁ does not reach the above-mentioned constant value is used as the solid electrolyte particles and the particles are injected by the aerosol deposition method, the solid is solid on the substrate without damaging the substrate. It is possible to form an electrolyte layer.

In the present embodiment, the lattice constant LC _∞ when the crystalline oxide is calcined at 1,200 ° C. for another 30 hours is regarded as a constant value of the lattice constant, and the lattice constant LC of the crystalline oxide is regarded as a reference value. Evaluate ₁ .

From the results of Examples described later, it was confirmed that the lattice constant LC ₁ of the crystalline oxide had already reached a steady value when the firing time at 1,200 ° C. was 20 to 30 hours. It is considered that there is no further decrease in the lattice constant LC ₁ even if the firing at 1,200 ° C. is continued for more than 30 hours.

For crystalline oxides whose firing time is unknown, it is unclear how long the crystalline oxide should be calcined at 1,200 ° C. to reach a steady value. However, from the results of the examples, it can be considered that the lattice constant LC _∞ after firing the crystalline oxide at 1,200 ° C. for another 30 hours is equal to the steady value of the lattice constant. Therefore, the lattice constant LC _∞ when the crystalline oxide is fired at 1,200 ° C. for another 30 hours is regarded as a steady value of the lattice constant, and the lattice constant LC ₁ of the crystalline oxide is evaluated based on this value. You can do it.

From the viewpoint of enabling the formation of a solid electrolyte layer while suppressing damage to the substrate, the lattice constant LC ₁ of the crystalline oxide and the lattice when the crystalline oxide is fired at 1,200 ° C. for 30 hours. the ratio _LC 1 / LC _∞ with constant LC _∞ is required to be at 1.0001 or more, for example, 1.00015 or more, may be at 1.0002 or higher, or 1.0003 or more.

However, if the crystal structure is excessively incomplete, that is, if the ratio of LC ₁ to LC _∞ is excessively large, the lithium ion conductivity of the formed solid electrolyte layer is impaired. Therefore, from the viewpoint of increasing the lithium ion conductivity of the solid electrolyte layer, the lattice constant LC ₁ of the crystalline oxide and the lattice constant LC _∞ when the crystalline oxide is fired at 1,200 ° C. for 30 hours The ratio of LC ₁ / LC _∞ needs to be 1.0007 or less, and may be, for example, 1.00065 or less, 1.0006 or less, 1.00055 or less, or 1.0005 or less.

The particle size of the solid electrolyte particles is not particularly limited as long as it is applicable to the aerosol deposition method. The particle size of the solid electrolyte particles may be, for example, 0.1 μm or more, 0.5 μm or more, 1 μm or more, 3 μm or more, or 5 μm or more, and for example, 100 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm. It may be:

The substrate on which the solid electrolyte layer is formed by the method of the present invention is arbitrary. For example, it may be an active material layer or a laminate having an active material layer on the outermost surface. The active material layer may be, for example, a positive electrode active material layer or a negative electrode active material layer.

<Aerosol deposition method>
In the present embodiment, the solid electrolyte particles composed of the above crystalline oxides are injected by the aerosol deposition method to form the solid electrolyte layer.

FIG. 1 shows a schematic diagram for explaining an aerosol deposition method preferably used in the method of the present embodiment.

The apparatus shown in FIG. 1 includes a chamber 21, a vacuum pump 24, and an aerosol generator 27. A pedestal 22 is installed in the chamber 21, and a base 23 is arranged on the pedestal 22. The vacuum pump 24 can control the inside of the chamber 21 to an arbitrary depressurized state. The raw material particles 26 are arranged inside the aerosol generator 27, and the raw material particles 26 are aerosolized by the transport gas supplied from the gas cylinder 25. The aerosolized raw material particles are ejected from the nozzle 28 installed in the chamber 21 toward the base 23, and are broken and deformed on the surface of the base 23 and deposited to form a film made of the raw material particles. ..

In the present embodiment, an arbitrary substrate is used as the substrate 23, and solid electrolyte particles composed of the crystalline oxide described above are used as the raw material particles 26 to form a solid electrolyte layer on the surface of the substrate. Form.

The pressure in the chamber when forming the solid electrolyte layer by the aerosol deposition method may be appropriately set according to the desired density of the layer and the density of the layer. The lower the pressure at the time of forming the solid electrolyte layer, the higher the density of the layer tends to be, but if this pressure is excessively high, the denseness of the layer may be impaired. Considering these points, the pressure in the chamber when forming the solid electrolyte layer may be, for example, 100 Pa or more, or 120 Pa or more, and may be, for example, 400 Pa or less, or 350 Pa or less.

The carrier gas may be, for example, an inert gas such as helium, argon or nitrogen, or dry air may be used. The flow rate of the transport gas may be, for example, 3 L / min or more, 5 L / min or more, 8 L / min or more, or 10 L / min or more, for example, 30 L / min or less, 25 L / min or less, 20 L / min or less, Alternatively, it may be 15 L / min or less. The ejection pressure of the transport gas may be, for example, 5 kPa or more, 10 kPa or more, or 20 kPa or more, and may be, for example, 100 kPa or less, 80 kPa or less, or 60 kPa or less.

When the solid electrolyte layer is formed by the aerosol deposition method, the positional relationship between the substrate 23, which is a substrate, and the nozzle 28 is relatively moved for the purpose of forming a uniform layer in a desired region. You can. The relative moving speed at this time is arbitrary. For example, it may be 10 mm / min or more, 20 mm / min or more, 30 mm / min or more, or 40 mm / min or more, and may be, for example, 120 mm / min or less, 100 mm / min or less, 90 mm / min or less, or 80 mm / min or less.

The formation of the solid electrolyte layer by the aerosol deposition method may be carried out in the form of a one-way scanning of the layer forming region only once, or may be performed multiple times to obtain the required layer thickness. The number of scans is arbitrary.

<Example 1>
1. 1. Synthesis of solid electrolyte particles LiOH (H ₂ O), La (OH) ₃ , ZrO ₂ , and Nb ₂ O ₅ are _{mixed in} a proportion of Li _6.75 La ₃ Zr _1.75 Nb _0.25 O _12. Mixed. Ethanol was added as a solvent to the obtained mixture, and wet ball mill pulverization was performed by repeating a cycle of operation for 3 minutes and rest for 3 minutes at a rotation speed of 700 rpm 40 times.

Then, it was held at 90 ° C. for 1 hour to remove ethanol, and then calcined in air at 950 ° C. for 10 hours to obtain a calcined product.

Ethanol was added as a solvent to the obtained calcined product, and wet ball mill pulverization was performed by a method of repeating a cycle of operation for 3 minutes and rest for 3 minutes at a rotation speed of 700 rpm 40 times.

Then, after holding at 90 ° C. for 1 hour to remove ethanol, the main firing was carried out in air at 1,200 ° C. with a change in the firing time in the range of 1 hour to 30 hours. Solid electrolyte crystals composed of

The particle size of the solid electrolyte particles was adjusted to 1,000 nm as the median diameter.

2. 2. Measurement of Lattice Constant of Crystalline Oxide The lattice constant LC ₁ of the crystalline oxide constituting each of the solid electrolyte particles obtained above was measured by X-ray diffraction analysis. The results are shown in Table 1 and FIG.

From the results of Table 1 and FIG. 2, it is understood that the lattice constant LC ₁ of the crystalline oxide has already reached the steady value LC _∞ when the firing time is 20 to 30 hours. Firing lattice constant of the time of 30 hours the crystalline oxide, the then assumed to be equal to the constant value LC _∞ lattice constant for crystalline oxide, steady-state value LC _∞ lattice constant LC ₁ for each crystalline oxide The ratio to Table 1 is shown.

3. 3. Formation of a solid electrolyte layer by the aerosol deposition method A solid electrolyte layer was formed on the SUS304 substrate by the aerosol deposition method using each of the solid electrolyte particles obtained above as a raw material particle. The conditions of the aerosol deposition method are as follows.
Chamber pressure: 0.1 kPa
Transport gas type: Argon Transport gas flow rate: 4 L / min Transport gas ejection pressure: 40 kPa
Substrate movement speed: 60 mm / min Number of scans: 5 times

The relationship between the layer thickness and lithium ion conductivity of the obtained solid electrolyte layer and the L ₁ / L _∞ ratio of the crystalline oxide used is shown in Table 1 and FIG. The layer thickness values in Tables 1 and 3 are values obtained by subtracting the amount of scraping of the substrate from the thickness of the formed solid electrolyte layer.

From the results of Table 1 and FIG. 3, the obtained solid electrolyte layer suppresses the scraping of the base material as the LC ₁ / LC _∞ value of the crystalline oxide used is larger, that is, the degree of firing is lower. The layer thickness could be increased, but the ionic conductivity was low. On the other hand, the smaller the LC ₁ / LC _∞ value, that is, the higher the degree of firing, the higher the lithium ion conductivity, but the greater the scraping of the substrate and the thinner the layer thickness. From these results, it is understood that the solid electrolyte particles used for forming the solid electrolyte layer by the aerosol deposition method are preferably those in which the ratio LC ₁ / LC _∞ is 1.0001 or more and 1.0007 or less. To.

<Example 2>
LiOH (H ₂ O), La (OH) ₃ , ZrO ₂ , and Nb ₂ O ₅ were mixed at the ratio with the value of x in Li _7-x La ₃ Zr _2-x Nb _x O ₁₂ as a variable. Solid electrolyte particles composed of crystalline oxides having an LC ₁ / LC _∞ value of 1.0000 to 1.012 were obtained in the same manner as in Example 1 except that the firing time at 1,200 ° C. was appropriately changed. It was. The particle size of each solid electrolyte particle was adjusted to 1,000 nm as a median diameter.

Using each of the above solid electrolyte particles, a solid electrolyte layer was formed on the SUS304 substrate by the aerosol deposition method in the same manner as in Example 1, and the lithium ion conductivity thereof was examined. The results are shown in Table 2 and FIG.

From the results of Table 2 and FIG. 4, the x value in the composition Li _7-x La ₃ Zr _2-x Nb _x O ₁₂ of the crystalline oxide used as the solid electrolyte particles of the aerosol deposition method is 0 or more and 0.75. It was found that a solid electrolyte layer exhibiting a high lithium ion conductivity can be obtained in the following cases, particularly preferably 0.125 or more and 0.5 or less.

21 Chamber 22 Pedestal 23 Base 24 Vacuum Pump 25 Gas Cylinder 26 Raw Material Particles 27 Aerosol Generator 28 Nozzles

Claims (1)

A method of forming a solid electrolyte layer by injecting solid electrolyte particles onto a substrate by an aerosol deposition method.
Crystalline oxidation in which the solid electrolyte particles have a composition of Li _7-x La ₃ Zr _2-x M _x O ₁₂ (M is Nb or Ta, and x is a number of 0 or more and 0.75 or less). The ratio LC ₁ / LC _∞ between the lattice constant LC ₁ of the crystalline oxide and the lattice constant LC _∞ when the crystalline oxide is fired at 1,200 ° C. for 30 hours is 1. 0001 or more and 1.0007 or less,
The method.

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