Method for manufacturing solid electrolyte layer, all-solid-state battery, and method for manufacturing same

Abstract

Provided is a method which is for manufacturing a solid electrolyte layer and with which grain boundaries are less likely to form due to crystal growth during firing, and ion conduction is less likely to be inhibited.　The method for manufacturing a solid electrolyte layer constituting an all-solid-state battery comprises: a step for irradiating, with laser light, a powder material that contains a carbon material and a solid electrolyte material including NASICON crystals, and melting and solidifying the powder material to form a solid electrolyte precursor; and a step for heat-treating the solid electrolyte precursor.

Description

Method for manufacturing solid electrolyte layer, all-solid-state battery and method for manufacturing the same

[0001] The present invention relates to a method for manufacturing a solid electrolyte layer, a method for manufacturing an all-solid-state battery including the method for manufacturing a solid electrolyte layer, and an all-solid-state battery.

[0002] In recent years, with the widespread use of mobile devices and electric vehicles, the development of electricity storage devices such as lithium-ion secondary batteries and sodium-ion secondary batteries has progressed rapidly. Although organic electrolyte solutions used in electricity storage devices exhibit high ionic conductivity, they are liquid and flammable, raising concerns about the risk of electrolyte leakage and fire when used in electricity storage devices. Therefore, development of all-solid-state batteries using solid electrolytes instead of organic electrolyte solutions and having solid cathodes and anodes has been progressing (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 5-205741

[0004] The solid electrolyte layer constituting an all-solid-state battery is usually produced by forming a raw material powder into a paste or green sheet and then firing the paste or green sheet. However, in the solid electrolyte layer produced by firing the raw material powder, grain boundaries are formed due to crystal growth, and these grain boundaries may inhibit ionic conduction in the solid electrolyte layer. In particular, when NASICON (sodium superionic conductor) crystals are used as the raw material for the solid electrolyte layer, there is a problem that ionic conduction is easily inhibited by grain boundary formation.

[0005] An object of the present invention is to provide a method for manufacturing a solid electrolyte layer in which grain boundaries due to crystal growth during firing are unlikely to occur and ion conduction is unlikely to be inhibited, a method for manufacturing an all-solid-state battery including the method for manufacturing a solid electrolyte layer, and an all-solid-state battery.

[0006] A method for manufacturing a solid electrolyte layer according to a first aspect of the present invention is a method for manufacturing a solid electrolyte layer constituting an all-solid-state battery, and is characterized by comprising the steps of: irradiating a powder material containing a solid electrolyte material including NASICON crystals and a carbon material with laser light to melt and solidify the powder material to form a solid electrolyte precursor; and heat-treating the solid electrolyte precursor.

[0007] In the method for producing a solid electrolyte layer according to Aspect 2, in Aspect 1, it is preferable that the temperature of the heat treatment is 800° C. or higher and 1100° C. or lower.

[0008] In the method for manufacturing a solid electrolyte layer according to Aspect 3, in Aspect 1 or Aspect 2, the wavelength of the laser light may be in a wavelength range of 450 nm to 1600 nm, and the NASICON crystal may be a material that does not absorb light in the wavelength range of the laser light.

[0009] In the method for producing a solid electrolyte layer according to Aspect 4, in any one of Aspects 1 to 3, the laser light is a semiconductor laser, a YAG laser, a Yb fiber laser, or a YVO ４ It may also be a laser.

[0010] In the method for producing a solid electrolyte layer according to Aspect 5, in any one of Aspects 1 to 4, the NASICON crystals are Na ３ Zr ２ Si ２ P.O. １２ , Na ３．２ Zr １．３ Si ２．２ P ０．８ O １０．５ , Na ３ Zr １．６ Ti ０．４ Si ２ P.O. １２ , Na ３ Hf ２ Si ２ P.O. １２ , Na ３．４ Zr ０．９ Hf １．４ Al ０．６ Si １．２ P １．８ O １２ , Na ３ Zr １．７ Nb ０．２４ Si ２ P.O. １２ , Na ３．６ Ti ０．２ Y ０．８ Si ２．８ O ９ , Na ３ Zr １．８８ Y ０．１２Si ２ P.O. １２ , Na ３．１２ Zr １．８８ Y ０．１２ Si ２ P.O. １２ , Na ３．０５ Zr ２ Si ２．０６ P ０．９５ O １２ , Na ３．４ Zr ２ Si ２．４ P ０．６ O １２ , Na ３．４ Zr １．９ Mg ０．１ Si ２．４ P ０．６ O １２ , Na ３．４ Zr １．９ Zn ０．１ Si ２．４ P ０．６ O １２ , Na ３．４ Zr １．９ Mg ０．１ Si ２．２ P ０．８ O １２ , Na ３．４ Zr １．９ Zn ０．１ Si ２．２ P ０．８ O １２ , Na ３．６ Zr ０．１３ Yb １．６７ Si ０．１１ P ２．９ O １２ , or Na ５ YSi ４ O １２ It is preferable that:

[0011] In the method for producing a solid electrolyte layer according to Aspect 6, in any one of Aspects 1 to 5, it is preferable that the carbon material is at least one selected from the group consisting of acetylene black, carbon black, carbon nanotubes, graphene, graphite, and hard carbon.

[0012] In the method for producing a solid electrolyte layer according to Aspect 7, in any one of Aspects 1 to 6, it is preferable that the content of the carbon material contained in the powder material is 0.2 parts by mass or more and 6 parts by mass or less per 100 parts by mass of the solid electrolyte material.

[0013] In the method for manufacturing a solid electrolyte layer according to Aspect 8, in any one of Aspects 1 to 7, the powder material may be melted and solidified by powder bed fusion when irradiating the laser light.

[0014] A ninth aspect of the method for producing a solid electrolyte layer is the method for producing a solid electrolyte layer according to any one of the first to eighth aspects, wherein the solid electrolyte layer is made of ZrO ２ It may contain crystals.

[0015] A method for producing an all-solid-state battery according to Aspect 10 of the present invention is characterized by including a step of obtaining a solid electrolyte layer by the method for producing a solid electrolyte layer according to any one of Aspects 1 to 9.

[0016] The all-solid-state battery according to aspect 11 of the present invention comprises ZrO ２ The present invention is characterized by comprising a solid electrolyte layer containing NASICON crystals.

[0017] According to the present invention, it is possible to provide a method for manufacturing a solid electrolyte layer in which grain boundaries due to crystal growth during firing are unlikely to occur and ion conduction is unlikely to be inhibited, a method for manufacturing an all-solid-state battery including the method for manufacturing a solid electrolyte layer, and an all-solid-state battery.

[0018] FIG. 1 is a schematic cross-sectional view showing an all-solid-state battery manufactured by a manufacturing method for an all-solid-state battery according to one embodiment of the present invention. FIG. 2 is a diagram illustrating a laser light irradiation method in Example 1. FIGS. 3(a) to 3(d) are diagrams illustrating a laser light irradiation method in Example 1. FIG. 4 is a scanning electron microscope photograph showing a cross section of a pellet after laser light irradiation in Example 1. FIG. 5 is a diagram showing the relationship between the laser light output and the thickness of the dense layer. FIG. 6 is a diagram showing the relationship between the acetylene black content and the thickness of the dense layer. FIG. 7 is a diagram showing an X-ray diffraction pattern of a pellet after laser light irradiation in Example 1. FIG. 8 is a diagram showing an X-ray diffraction pattern of a layer after heat treatment in Example 1. FIG. 9 is a scanning electron microscope photograph showing a cross section of a crystalline layer after heat treatment at 1000°C for 10 hours in Example 1. FIG. 10 is a diagram showing a Nyquist plot of a sample produced in Example 2. FIG. 11 is a photograph showing a green compact after laser light irradiation in Example 3. Figure 12 is a scanning electron micrograph showing a cross section of the thin flake obtained in Example 3. Figure 13 is a scanning electron micrograph showing a cross section of an untreated NZSP crystal.

[0019] Preferred embodiments will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.

[0020] [Method for Producing a Solid Electrolyte Layer] The method for producing a solid electrolyte layer of the present invention is a method for producing a solid electrolyte layer that constitutes an all-solid-state battery.

[0021] The method for producing a solid electrolyte layer of the present invention includes a step of irradiating a powder material containing a solid electrolyte material including NASICON crystals and a carbon material with laser light to melt and solidify the powder material to form a solid electrolyte precursor (laser light irradiation step), and a step of heat-treating the solid electrolyte precursor (heat treatment step).

[0022] The method for producing a solid electrolyte layer of the present invention has the above-mentioned configuration, and therefore can provide a solid electrolyte layer in which grain boundaries due to crystal growth during firing are unlikely to occur and ion conduction is unlikely to be inhibited. This can be explained as follows.

[0023] Conventionally, solid electrolyte layers constituting all-solid-state batteries have been manufactured by forming raw material powders into pastes or green sheets, followed by firing. However, in solid electrolyte layers manufactured by firing raw material powders, grain boundaries are formed due to crystal growth, and these grain boundaries can sometimes inhibit ionic conduction in the solid electrolyte layer. In particular, when NASICON crystals are used as the raw material for the solid electrolyte layer, there is a problem in that ionic conduction is easily inhibited by the formation of grain boundaries.

[0024] In contrast, in the method for producing a solid electrolyte layer of the present invention, a powder material containing a solid electrolyte material containing NASICON crystals and a carbon material is irradiated with laser light, so even when NASICON crystals that do not absorb light at the wavelength (oscillation wavelength) of the laser light are used, the carbon material is heated by irradiating the powder material with laser light, thereby melting the NASICON crystals, thereby amorphizing the NASICON crystals and forming a dense amorphous material layer.

[0025] In this way, the method for manufacturing a solid electrolyte layer of the present invention allows a dense amorphous material layer to be formed in advance, and when this amorphous material layer is sintered, the amorphous material can be crystallized at a relatively low temperature to form NASICON crystals, resulting in a dense solid electrolyte layer. Furthermore, sintering the amorphous material layer at a low temperature makes it less likely that grain boundaries will form due to crystal growth, as occurs when raw powder of NASICON crystals is sintered at a high temperature, and therefore a solid electrolyte layer in which ion conduction is less likely to be inhibited can be obtained.

[0026] Hereinafter, each step of the method for producing a solid electrolyte layer of the present invention will be described in detail.

[0027] (Laser Light Irradiation Step) In the laser light irradiation step, first, a powder material containing a solid electrolyte material including NASICON crystals and a carbon material is prepared.

[0028] The solid electrolyte material is a material having sodium ion conductivity and includes NASICON crystals.

[0029] NASICON crystals have the general formula Na ｓ A1 ｔ A2 ｕ O ｖ (A1 is at least one selected from Al, Y, Yb, Nd, Nb, Ti, Hf, and Zr; A2 is at least one selected from Si and P; s = 1.4 to 5.2, t = 1 to 2.9, u = 2.8 to 4.1, v = 9 to 14). Here, A1 is preferably at least one selected from Y, Nb, Ti, and Zr. By doing so, the NASICON crystal can be made into a crystal with superior ionic conductivity.

[0030] The preferred ranges of the coefficients in the above general formula are as follows:

[0031] Preferably, s is 1.4 to 5.2, more preferably 2.5 to 4.0, and even more preferably 2.8 to 3.6. If s is too small, the amount of sodium ions will decrease, which will tend to reduce the ionic conductivity of the NASICON crystal. On the other hand, if s is too large, the excess sodium will form compounds such as sodium phosphate and sodium silicate that do not contribute to ionic conduction, which will tend to reduce the ionic conductivity of the NASICON crystal.

[0032] t is preferably 1 to 2.9, more preferably 1 to 2.5, and even more preferably 1.3 to 2. If t is too small, the three-dimensional network structure in the NASICON crystal is reduced, which tends to reduce the ionic conductivity of the NASICON crystal. On the other hand, if t is too large, compounds that do not contribute to ionic conduction, such as zirconia and alumina, are formed, which tends to reduce the ionic conductivity of the NASICON crystal.

[0033] u is preferably 2.8 to 4.1, more preferably 2.8 to 4, even more preferably 2.9 to 3.2, and particularly preferably 2.95 to 3.1. If u is too small, the three-dimensional network structure in the NASICON crystal is reduced, and the ionic conductivity of the NASICON crystal is likely to decrease. On the other hand, if u is too large, crystals that do not contribute to ionic conduction are formed, and the ionic conductivity of the NASICON crystal is likely to decrease.

[0034] v is preferably 9 to 14, more preferably 9.5 to 12, and even more preferably 11 to 12. If v is too small, A1 (e.g., aluminum component) will have a low valence, which will tend to reduce electrical insulation. On the other hand, if v is too large, a peroxidized state will occur, and sodium ions will be bound by the lone electron pairs of oxygen atoms, which will tend to reduce the ionic conductivity of the NASICON crystal.

[0035] The NASICON crystal is preferably a monoclinic crystal, a hexagonal crystal, or a trigonal crystal, and more preferably a monoclinic crystal or a trigonal crystal, which can further improve the ionic conductivity of the NASICON crystal.

[0036] Specific examples of NASICON crystals include Na ３ Zr ２ Si ２ P.O. １２ , Na ３．２ Zr １．３ Si ２．２ P ０．８ O １０．５ , Na ３ Zr １．６ Ti ０．４ Si ２ P.O. １２ , Na ３ Hf ２ Si ２ P.O. １２ , Na ３．４ Zr ０．９ Hf １．４ Al ０．６ Si １．２ P １．８ O １２ , Na ３ Zr １．７ Nb０．２４ Yes ２ PO １２ 、No ３．６ Today ０．２ Y ０．８ Yes ２．８ O ９ 、No ３ Zr １．８８ Y ０．１２ Yes ２ PO １２ 、No ３．１２ Zr １．８８ Y ０．１２ Yes ２ PO １２ 、No ３．０５ Zr ２ Yes ２．０６ P ０．９５ O １２ 、No ３．４ Zr ２ Yes ２．４ P ０．６ O １２ 、No ３．４ Zr １．９ Zn ０．１ Yes ２．４ P ０．６ O １２ 、No ３．４ Zr １．９ Mg ０．１ Yes ２．４ P ０．６ O １２ 、No ３．４ Zr １．９ Mg ０．１ Yes ２．２ P ０．８ O １２ 、No ２．８ Zr ２ Yes ２．４ P ０．６ O １２ 、No ３．６ Zr ０．１３ Yb １．６７ Yes ０．１１ P ２．９ O １２ 、No ５ YSi ４ O １２ 、No ３．１ Zr １．９５ Mg ０．０５ Yes ２ PO １２ 、No ３．１ Zr １．９ Yes０．１ Yes ２ PO １２ 、No ３．１ Zr １．９ N$ ０．１ Yes ２ PO １２ 、No ３．１ Zr １．９ Y ０．１ Yes ２ PO １２ 、No ３．２５６ Zr １．８７２ Mg ０．１２８ Yes ２ PO １２ 、No ３．２ Zr １．９ Ca ０．１ Yes ２ PO １２ 、No ３．２ Zr １．９ Mg ０．１ Yes ２ PO １２ 、No ３．２ Zr ２ Yes ２．２ P ０．８ O １２ 、No ３．３８ Zr １．８０ Al ０．２６ Yes ２．０６ P ０．８８ O １２ 、No ３．４３ Zr １．８３ Zn ０．２２ Yes １．９３ P １．０２ O １２ 、No ３．４ Sc ０．４ Zr １．６ Yes ２ PO １２ 、No ３．４ Zr １．８ Mg ０．２ Yes ２ PO １２ 、No ３．４ Zr １．９ Zn ０．１ Yes ２．２ P ０．８ O １２ 、No ３．５７ Zr １．７２ Yes ０．２１ Yes ２．０８ P ０．９２ O １２, Na ３ Zr １．９８ Nb ０．０８ Si ２ P.O. １２ , Na ３ Zr １．９ Ce ０．１ Si ２ P.O. １２ , Na ３ Zr １．９ Gd ０．１ Si ２ P.O. １２ , Na ３ Zr １．９ Ti ０．１ Si ２ P.O. １２ , Na ３ Zr １．９ Yb ０．１ Si ２ P.O. １２ These may be used alone or in combination. Among them, NASICON crystals are ３ Zr ２ Si ２ P.O. １２ , Na ３．４ Zr ２ Si ２．４ P ０．６ O １２、 or Na ３．０５ Zr ２ Si ２．０６ P ０．９５ O １２ Preferably, Na ３ Zr ２ Si ２ P.O. １２ In this case, the ionic conductivity of the NASICON crystal can be further improved.

[0037] The content of NASICON crystals in the solid electrolyte material is preferably 70% by mass or more, more preferably 90% by mass or more, and is preferably 99.9% by mass or less, more preferably 99.5% by mass or less. When the content of NASICON crystals is within the above range, a solid electrolyte layer with even higher ion conductivity can be obtained.

[0038] The solid electrolyte material may contain other additives, such as sodium ion conductive glass powder. The content of the other additives in the solid electrolyte material may be, for example, 0.1 mass % or more and 5 mass % or less.

[0039] Examples of the carbon material that can be used include acetylene black, carbon black, carbon nanotubes, graphene, graphite, and hard carbon. These may be used alone or in combination. Among these, acetylene black is preferred as the carbon material.

[0040] The content of the carbon material is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of the solid electrolyte material, and is preferably 6 parts by mass or less, more preferably 5.5 parts by mass or less, and even more preferably 5 parts by mass or less. When the content of the carbon material is within the above range, a more dense solid electrolyte layer can be obtained. Furthermore, when the content of the carbon material is equal to or less than the above upper limit, a solid electrolyte layer with even higher ion conductivity can be obtained.

[0041] Next, the powder material is irradiated with laser light to melt and solidify the powder material, thereby amorphizing the NASICON crystals and forming a solid electrolyte precursor having a dense amorphous material layer.

[0042] The wavelength of the laser light is preferably in a wavelength range that is not absorbed by the NASICON crystal but is absorbed by the carbon material. In other words, in the wavelength range of the laser light, the NASICON crystal is preferably a material that does not absorb light, and the carbon material is preferably a material that absorbs light.

[0043] The wavelength range of such laser light can be, for example, 450 nm to 1600 nm. The wavelength of the laser light is preferably in the near-infrared region to the infrared region, more preferably 750 nm to 1600 nm, more preferably 900 nm to 1400 nm, even more preferably 950 nm to 1200 nm, and particularly preferably 1000 nm to 1100 nm.

[0044] Therefore, it is preferable that the laser light be capable of irradiating light of the above wavelengths, and for example, a semiconductor laser, a YAG laser, a Yb fiber laser, or a YVO ４ A laser can be used.

[0045] The output of the laser beam is not particularly limited, but is preferably 100 mW or more, more preferably 1 W or more, and is preferably 40 W or less, more preferably 15 W or less. The scanning speed of the laser beam is not particularly limited, but is preferably 20 mm / s or more, more preferably 50 mm / s or more, and is preferably 1000 mm / s or less, more preferably 500 mm / s or less.

[0046] When irradiating a powder material with laser light, for example, pellets of the powder material can be prepared and the prepared pellets can be irradiated with laser light. Alternatively, a paste prepared by adding a solvent such as N-methylpyrrolidone or a binder such as polypropylene carbonate (PPC) or polyvinyl butyral resin to the powder material as needed can be thinly applied to a substrate to form a paste layer, and the formed paste layer can be irradiated with laser light. Alternatively, a powder compact can be prepared by press-molding the powder material, and the powder compact can be irradiated with laser light by powder bed fusion. When the powder material is melted and solidified by powder bed fusion, a thinner solid electrolyte layer can be prepared.

[0047] (Heat Treatment Step) In the heat treatment step, the solid electrolyte precursor is heat-treated. In the laser light irradiation step, the powder material is melted and solidified, thereby amorphizing the NASICON crystals. The amorphized NASICON crystals can then be recrystallized by heat treatment in the heat treatment step. This allows a dense solid electrolyte layer to be obtained.

[0048] The heat treatment temperature in the heat treatment step is not particularly limited, but is preferably 800°C or higher, more preferably 850°C or higher, and even more preferably 900°C or higher, and is preferably 1100°C or lower, more preferably 1050°C or lower, and even more preferably 1030°C or lower. When the heat treatment temperature is equal to or higher than the above lower limit, a denser solid electrolyte layer can be obtained. On the other hand, when the heat treatment temperature is equal to or lower than the above upper limit, grain boundaries due to crystal growth, which occur when NASICON crystal raw material powder is sintered at high temperatures, can be more unlikely to occur, and a solid electrolyte layer in which ion conduction is less likely to be inhibited can be obtained.

[0049] The heat treatment time in the heat treatment step is not particularly limited, but is preferably 0.5 hours or more, more preferably 1 hour or more, even more preferably 3 hours or more, and preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less. When the heat treatment time is equal to or greater than the above-mentioned lower limit, a denser solid electrolyte layer can be obtained. On the other hand, when the heat treatment time is equal to or less than the above-mentioned upper limit, grain boundaries due to crystal growth, which occur when NASICON crystal raw material powder is sintered at high temperatures, can be more unlikely to occur, and thus a solid electrolyte layer in which ion conduction is less likely to be inhibited can be obtained.

[0050] The heat treatment in the heat treatment step may be carried out, for example, in an air atmosphere or a nitrogen atmosphere.

[0051] According to the method for producing a solid electrolyte layer of the present invention, a thin solid electrolyte layer can be obtained. The thickness of the solid electrolyte layer is preferably 300 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. The lower limit of the thickness of the solid electrolyte layer is not particularly limited, but can be, for example, 1 μm.

[0052] The solid electrolyte layer is made of ZrO ２ It may contain crystals. ２The crystal is preferably a cubic crystal, a tetragonal crystal, or a monoclinic crystal, and more preferably a cubic crystal or a tetragonal crystal, which can further increase the mechanical strength of the solid electrolyte layer and more effectively prevent cracks due to strain caused by expansion and contraction of the electrodes during charging and discharging of the all-solid-state battery.

[0053] In addition, ZrO ２ The crystal structure of the crystal can be confirmed by the X-ray diffraction pattern. ２ The crystal structure of the crystal can be identified using, for example, the Powder Diffraction File (PDF) published by the International Centre for Diffraction Data (ICDD). ２ The ICDD PDF card for the crystal is 01-089-9069, and it is tetragonal ZrO ２ The ICDD PDF card for the crystal is 01-072-7115, and it is monoclinic ZrO ２ The ICDD PDF card for the crystal is 01-070-2491.

[0054] [Method for Manufacturing an All-Solid-State Battery] FIG. 1 is a schematic cross-sectional view showing an all-solid-state battery manufactured by a method for manufacturing an all-solid-state battery according to one embodiment of the present invention.

[0055] 1 , the all-solid-state battery 1 includes a solid electrolyte layer 2, a positive electrode layer 3, a negative electrode layer 4, a first current collector layer 5, and a second current collector layer 6. The all-solid-state battery 1 is an all-solid-state sodium ion secondary battery. An example of a manufacturing method for the all-solid-state battery 1 will be described below.

[0056] In the method for manufacturing the all-solid-state battery 1, first, the solid electrolyte layer 2 is manufactured according to the above-described method for manufacturing a solid electrolyte layer of the present invention.

[0057] Next, the positive electrode layer 3 is formed on the first main surface 2 a of the solid electrolyte layer 2. The positive electrode layer 3 can be produced using a slurry containing a positive electrode active material precursor powder and, as necessary, a solid electrolyte powder and a conductive additive. A binder, a plasticizer, a solvent, and the like are added to the slurry as necessary. The positive electrode layer 3 can be produced, for example, by applying the above-mentioned slurry to the first main surface 2 a of the solid electrolyte layer 2, drying the slurry, and then firing the resulting mixture.

[0058] Next, the anode layer 4 is formed on the second main surface 2b of the solid electrolyte layer 2. The anode layer 4 can be prepared using a slurry containing an anode active material precursor powder and, as necessary, a solid electrolyte powder and a conductive additive. A binder, a plasticizer, a solvent, and the like are added to the slurry as necessary. The anode layer 4 can be prepared, for example, by applying the slurry to the second main surface 2b of the solid electrolyte layer 2, drying the slurry, and then firing the resulting mixture. The order in which the cathode layer 3 and the anode layer 4 are formed is not particularly limited. Therefore, the anode layer 4 may be formed first, and then the cathode layer 3 may be formed. Alternatively, the cathode layer 3 and the anode layer 4 may be formed by firing them simultaneously.

[0059] Next, if necessary, a first current collector layer 5 and a second current collector layer 6 are formed. The method for forming the first current collector layer 5 and the second current collector layer 6 is not particularly limited, and examples thereof include physical vapor deposition methods such as vapor deposition or sputtering, and chemical vapor deposition methods such as thermal CVD, MOCVD, and plasma CVD. The first current collector layer 5 and the second current collector layer 6 may be formed after the positive electrode layer 3 and the negative electrode layer 4 are formed on the solid electrolyte layer 2, respectively. Alternatively, the first current collector layer 5 may be formed on the positive electrode layer 3 in advance, and the second current collector layer 6 may be formed on the negative electrode layer 4 in advance, and then these may be combined to obtain the all-solid-state battery 1.

[0060] The method for producing the all-solid-state battery 1 includes a step of producing the solid electrolyte layer 2 according to the method for producing a solid electrolyte layer of the present invention described above. This makes it possible to further increase the ionic conductivity of the solid electrolyte layer 2, thereby improving the battery characteristics of the all-solid-state battery 1, such as the high-rate charge / discharge characteristics and cycle characteristics.

[0061] The positive electrode active material contained in the positive electrode layer 3 is not particularly limited, but may be a material having the general formula Na ｘ M ｙ P ２ O ｚ (1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, M is at least one element selected from the group consisting of Fe, Ni, Co, Mn, and Cr) is preferred. ｘ MP ２ O ７ (1≦x≦2, M is at least one element selected from the group consisting of Fe, Ni, Co, Mn, and Cr) is more preferable. ２ FeP ２ O ７ , Na ２ CoP ２ O ７ , Na ２ NiP ２ O ７ etc. can be used.

[0062] The positive electrode layer 3 may also contain a solid electrolyte and a conductive additive. The proportions of the materials in the positive electrode layer 3 may be, for example, in mass %, 30% to 95% positive electrode active material, 5% to 70% solid electrolyte, and 0% to 20% conductive additive.

[0063] The solid electrolyte may be, for example, the NASICON crystal described above. The conductive additive may be, for example, conductive carbon. Examples of conductive carbon include acetylene black, carbon black, ketjen black, and vapor-grown carbon fiber (VGCF). The conductive additive is preferably a carbon-based conductive additive made of the above-described material. The thickness of the positive electrode layer 3 may be, for example, 3 μm or more and 300 μm or less.

[0064] The negative electrode active material contained in the negative electrode layer 4 is not particularly limited, and may be, for example, a carbon electrode material such as hard carbon or soft carbon. The carbon electrode material is preferably hard carbon. However, the negative electrode active material may also contain metallic sodium or an alloy-based negative electrode active material capable of absorbing sodium, such as tin, bismuth, lead, or phosphorus.

[0065] The anode layer 4 may further contain a solid electrolyte and a conductive additive. The proportions of the materials in the anode layer 4 may be, for example, in mass %, 60% to 95% anode active material, 5% to 35% solid electrolyte, and 0% to 5% conductive additive. The solid electrolyte and conductive additive may be, for example, those described in the section on the cathode layer 3. The thickness of the anode layer 4 may be, for example, 0.3 μm or more and 300 μm or less.

[0066] The materials for the first current collector layer 5 and the second current collector layer 6 are not particularly limited, but may be metal materials such as aluminum, titanium, silver, copper, stainless steel, or alloys thereof. The above metal materials may be used alone or in combination. These alloys are alloys containing at least one of the above metals. The thicknesses of the first current collector layer 5 and the second current collector layer 6 are not particularly limited, but may be, for example, 0.01 μm or more and 1000 μm or less.

[0067] In the all-solid-state battery 1, the solid electrolyte layer 2 is made of ZrO ２ It may contain ZrO crystals and NASICON crystals. ２ As the crystal, those described in the section on the manufacturing method of the solid electrolyte layer can be used. ２ When the solid electrolyte layer 2 contains ZnO crystals and NASICON crystals, the ionic conductivity and mechanical strength of the solid electrolyte layer 2 can be further increased, and cracks due to strain caused by expansion and contraction of the electrodes during charging and discharging of the all-solid-state battery 1 can be more effectively prevented.

[0068] In the solid electrolyte layer 2, ZrO ２The content of the NASICON crystals in the solid electrolyte layer 2 can be, for example, 1% by mass or more and 10% by mass or less. The content of the NASICON crystals in the solid electrolyte layer 2 can be, for example, 90% by mass or more and 99% by mass or less.

[0069] In addition, in the solid electrolyte layer 2, ZrO ２ The average particle size of the crystals is preferably 1000 nm or less, more preferably 500 nm or less, even more preferably 200 nm or less, particularly preferably 100 nm or less, and is preferably 1 nm or more, more preferably 2 nm or more, even more preferably 5 nm or more, particularly preferably 10 nm or more. In this case, the mechanical strength of the solid electrolyte layer 2 can be further increased, and cracks due to strain caused by expansion and contraction of the electrodes during charging and discharging of the all-solid-state battery 1 can be more effectively prevented. ２ The average grain size of the crystals can be determined, for example, by measurement through observation with a SEM (scanning electron microscope) or by calculation using the Scherrer equation from the half-width of the diffraction peak of XRD (X-ray diffraction).

[0070] The present invention will be described in more detail below with reference to examples. However, the following examples are merely illustrative and are not intended to limit the scope of the present invention.

[0071] (Synthesis Example 1) In Synthesis Example 1, Na was used as a solid electrolyte material containing NASICON crystals. ３ Zr ２ Si ２ P.O. １２ (NZSP) was prepared by the sol-gel method.

[0072] Specifically, 15.707 g of tetraethyl orthosilicate (TEOS) as raw materials, 34.734 g of ethanol, and 27.141 g of distilled water were mixed (molar ratio 1:10:20), and 20 g of citric acid was further added to the mixed solution, which was stirred for 1 hour on a hot stirrer at 60°C to obtain Solution 1. ３ (10% excess) 10.573 g and ZrO(NO ３ ) ２ 2H ２ 20.150 g of NH O was mixed to obtain Solution 2.４ H ２ P.O. ４ 4.336 g of Solution 3 was prepared.

[0073] Next, solutions 2 and 3 were added to solution 1 and mixed at 80°C for 3 hours to obtain a gel. The obtained gel was dried in the air. The dried gel was then pulverized. The powder obtained by pulverization was then pre-fired at 550°C for 5 hours and at 850°C for 12 hours. The pre-fired powder was press-molded at 40 MPa to obtain pellets with a diameter of 13 mm. The obtained pellets were then heat-treated at 1200°C for 10 hours in the air to obtain NZSP as a solid electrolyte material containing NASICON crystals.

[0074] Example 1 The NZSP obtained in Synthesis Example 1 was pulverized and then mixed with acetylene black as a laser light absorber to obtain a powder material. Acetylene black was mixed in proportions of 1 part by mass, 2 parts by mass, 3 parts by mass, 4 parts by mass, and 5 parts by mass per 100 parts by mass of the solid electrolyte material, and the mixture was press-molded at 40 MPa to obtain pellets with a diameter of 13 mm and a thickness of 1 mm.

[0075] Next, as shown in FIG. 2, the pellet 10 was placed on a fixed stage 11, and a laser beam was irradiated onto the pellet 10 from a laser beam irradiation source 12, causing the pellet 10 to melt and solidify.

[0076] The laser light irradiation source 12 used was a pulse wave (wavelength λ = 1064 nm) Yb fiber laser marker FL-MK-30W-kit (manufactured by Kokyo Co., Ltd.). The laser light was controlled in any direction using a reflecting mirror, and the laser light (beam diameter: 0.04 mm) was pinpoint irradiated onto the pellet 10. The laser pattern was formed to have a rectangular shape of 30 mm x 20 mm, as shown in Figures 3(a) to (d). The laser light was scanned in parallel with an interval of 0.04 mm. The scanning speed of the laser light was 100 mm / s to 200 mm / s. The output power of the laser light was 6 W to 15 W.

[0077] FIG. 4 is a scanning electron microscope photograph showing the cross section of a pellet after irradiating with laser light in Example 1. The pellet observed was prepared with an acetylene black content of 5 parts by mass. The laser light was irradiated at a scanning speed of 200 mm / s and an output of 12 W. The scanning electron microscope photograph was taken at a magnification of 1000 times using a scanning electron microscope (manufactured by Keyence Corporation, product number "VE-8800"). It can be seen from FIG. 4 that the pellet melts and solidifies upon irradiation with laser light, forming a dense layer (dense layer).

[0078] It was also confirmed that a dense layer was formed when the laser beam output was changed to 6 W, 9 W, and 15 W. As shown in Figure 5, the dense layer became thicker as the laser beam output increased (the vertical axis in Figure 5 represents the dense layer thickness). This is thought to be because the pellets were densified further to the inside as the laser beam output increased.

[0079] It was also confirmed that a dense layer was formed when the acetylene black content was changed to 1 part by mass, 2 parts by mass, 3 parts by mass, and 4 parts by mass. As shown in Figure 6, it can be seen that the thickness of the dense layer decreases as the acetylene black content increases (the vertical axis in Figure 6 represents the thickness of the dense layer). When the acetylene black content is too high, the amount of acetylene black present on the surface also increases, which is thought to be partly preventing the laser light from reaching the interior.

[0080] FIG. 7 shows the X-ray diffraction pattern of the pellets after laser irradiation in Example 1. The pellets were prepared with an acetylene black content of 5 parts by mass. The laser scanning speed was 200 mm / s, and the laser output was 6 W, 9 W, 12 W, and 15 W. For comparison, the X-ray diffraction pattern of untreated NASICON crystals (NZSP crystals) before laser irradiation is also shown. For X-ray diffraction measurement, CuKα radiation (wavelength 1.541 Å) was used as the X-ray source. An "Ultima IV" X-ray diffractometer manufactured by Rigaku Corporation was used.

[0081] As shown in FIG. 7, the peaks derived from NZSP crystals disappeared upon irradiation with laser light, and the peaks derived from ZrO ２ The appearance of peaks derived from the NZSP crystals indicates that they have become amorphous. These results confirm that a dense amorphous material layer is formed by irradiating the pellet with laser light. ２ The peaks derived from tetragonal ZrO ２ This is a peak derived from crystals.

[0082] Next, the fabricated amorphous material layer was heat-treated in an air atmosphere for 10 hours at heat treatment temperatures of 900° C., 1000° C., 1100° C., and 1200° C. The amorphous material layer was fabricated with a laser beam output of 12 W.

[0083] Fig. 8 is a diagram showing the X-ray diffraction pattern of the layer after heat treatment in Example 1. The X-ray diffraction pattern was measured in the same manner as in Fig. 7. The peaks indicated by triangles in Fig. 8 are those of tetragonal ZrO ２ This is a peak derived from crystals.

[0084] As shown in Figure 8, a peak derived from the NZSP crystal appears due to heat treatment at 1000°C or higher, which indicates that the NZSP crystal is recrystallized. Also, as shown in Figure 8, the NZSP crystal and tetragonal ZrO ２ It can be seen that a solid electrolyte (solid electrolyte layer) containing both crystalline and amorphous phases is formed.

[0085] Fig. 9 is a scanning electron microscope photograph showing a cross section of a crystal layer after heat treatment at 1000°C for 10 hours in Example 1. Fig. 13 is a scanning electron microscope photograph showing a cross section of an untreated NZSP crystal. The untreated NZSP crystal is an untreated NZSP crystal before irradiation with laser light. The scanning electron microscope photographs of Figs. 9 and 13 were observed under the same conditions as Fig. 4.

[0086] As shown in Fig. 9, a dense crystal layer with few grain boundaries was obtained in the crystal layer after heat treatment at 1000°C for 10 hours, whereas as shown in Fig. 13, in the untreated NZSP crystal, many grain boundaries due to crystal growth were present.

[0087] Example 2: Measurements were performed using an AC impedance method on samples of the crystal layer obtained by the heat treatment. In Example 2, the content of acetylene black in the powder material was 5 parts by mass, and the laser light irradiation conditions were a laser light scanning speed of 100 mm / s and a laser light output of 30 W. The heat treatment conditions were only 1000°C and 10 hours. Other conditions were the same as in Example 1, and a dense crystal layer sample was produced.

[0088] First, the sample to be measured was subjected to gold sputtering using a sputtering device (ULVAC, QUICK CORTER VPS-020) at a current value of 5 mA for 10 minutes to prepare gold electrodes on the sample surface. Two semicircular gold electrodes with a diameter of 6.8 mm were prepared on the sample surface, with a distance of 1 mm between the electrodes. Next, AC impedance measurements were performed on the sample after electrode preparation using a Bio-Logic SP-300 high-performance electrochemical measurement system under the following conditions: a sweep frequency of 7 MHz-100 mHz, 300 sweep points, an applied voltage of 100 mV, and one average. The obtained impedance pattern was analyzed using Zview software and fitted to an equivalent circuit. Resistivity (Ωcm) was calculated from the obtained resistance, electrode distance, and electrode diameter.

[0089] Fig. 10 is a diagram showing the Nyquist plot of the sample prepared in Example 2. For comparison, Fig. 10 also shows an untreated NZSP sample (an untreated NZSP crystal sample before laser light irradiation).

[0090] As shown in FIG. 10, the sample (dense crystal layer) prepared in Example 2 clearly exhibits reduced grain boundary resistance and enhanced ionic conductivity compared to the untreated NZSP sample.

[0091] (Example 3) A powder material (acetylene black content: 1 part by mass) prepared in the same manner as in Example 1 was press-molded (uniaxial pressing conditions: 5 MPa, 30 seconds) to prepare a disk-shaped green compact having a diameter of 13 mm and a thickness of 1 mm.

[0092] The prepared powder compact was irradiated with a laser beam by powder bed fusion bonding under the following laser beam irradiation conditions: wavelength of laser beam 1064 nm, spot size (spacing) 50 μm, laser beam output 30 W, laser beam scanning speed 100 mm / s, and laser beam irradiation area 5 mm × 5 mm.

[0093] Figure 11 is a photograph showing the powder compact after laser light irradiation in Example 3. The gray part shown in Figure 11 is the laser light irradiated part. Only this laser light irradiated part was extracted to obtain a thin piece, which was then washed and its cross section was observed using a scanning electron microscope. From the resulting scanning electron microscope photograph shown in Figure 12, it was confirmed that the thickness of the extracted thin piece was 300 μm and that a dense layer had been formed by laser light irradiation.

[0094] REFERENCE SIGNS LIST 1... all-solid-state battery 2... solid electrolyte layer 2a, 2b... first and second principal surfaces 3... positive electrode layer 4... negative electrode layer 5... first current collector layer 6... second current collector layer 10... pellet 11... fixing stage 12... laser light irradiation source

Claims

1. A method for manufacturing a solid electrolyte layer constituting an all-solid-state battery, the method comprising: irradiating a powder material containing a solid electrolyte material containing NASICON crystals and a carbon material with laser light to melt and solidify the powder material to form a solid electrolyte precursor; and heat-treating the solid electrolyte precursor.

2. The method for manufacturing a solid electrolyte layer according to claim 1, wherein the temperature of the heat treatment is 800°C or higher and 1100°C or lower.

3. The method for manufacturing a solid electrolyte layer according to claim 1 or 2, wherein the wavelength of the laser light is in the wavelength range of 450 nm to 1600 nm, and the NASICON crystal is a material that does not absorb light in the wavelength range of the laser light.

4. The laser light is a semiconductor laser, a YAG laser, a Yb fiber laser, or a YVO ４ laser, and the method for manufacturing a solid electrolyte layer according to claim 3.

5. The NASICON crystal is Na ３ Zr ２ Si ２ PO １２ 、Na ３．２ Zr １．３ Si ２．２ P ０．８ O １０．５ 、Na ３ Zr １．６ Ti ０．４ Si ２ PO １２ 、Na ３ Hf ２ Si ２ PO １２ 、Na ３．４ Zr ０．９ Hf １．４ Al ０．６ Si １．２ P １．８ O １２ 、Na ３ Zr １．７ Nb ０．２４ Si ２ PO １２ 、Na ３．６ Ti ０．２ Y ０．８ Si ２．８ O ９ 、Na ３ Zr １．８８ Y ０．１２ Si ２ PO １２ 、Na ３．１２ Zr １．８８ Y ０．１２ Si ２ PO １２ 、Na ３．０５ Zr ２ Si ２．０６ P ０．９５ O １２ 、Na ３．４ Zr ２ Si ２．４ P ０．６ O １２ 、Na ３．４ Zr １．９ Mg ０．１ Si ２．４ P ０．６ O １２ 、Na ３．４ Zr １．９ Zn ０．１ Si ２．４ P ０．６ O １２ , Na ３．４ Zr １．９ Mg ０．１ Si ２．２ P ０．８ O １２ , Na ３．４ Zr １．９ Zn ０．１ Si ２．２ P ０．８ O １２ , Na ３．６ Zr ０．１３ Yb １．６７ Si ０．１１ P ２．９ O １２ , or Na ５ YSi ４ O １２ The method for manufacturing a solid electrolyte layer according to claim 3, wherein it is 6. The method for manufacturing a solid electrolyte layer according to claim 1 or 2, wherein the carbon material is at least one selected from the group consisting of acetylene black, carbon black, carbon nanotubes, graphene, graphite, and hard carbon.

7. The method for manufacturing a solid electrolyte layer according to claim 1 or 2, wherein the content of the carbon material contained in the powder material is 0.2 parts by mass or more and 6 parts by mass or less with respect to 100 parts by mass of the solid electrolyte material.

8. The method for manufacturing a solid electrolyte layer according to claim 1 or 2, wherein when irradiating the laser light, the powder material is melted and solidified by a powder bed fusion method.

9. The solid electrolyte layer contains ZrO ２ crystals, and the method for manufacturing the solid electrolyte layer according to claim 1 or 2.

10. A method for manufacturing an all-solid-state battery, the method comprising obtaining a solid electrolyte layer by the method for manufacturing a solid electrolyte layer according to claim 1 or 2.

11. ZrO ２ An all-solid-state battery comprising a solid electrolyte layer containing ZrO crystal and NASICON crystal.

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