JP2023049024A - Solid electrolyte and solid electrolyte cell - Google Patents

Abstract

To provide a solid electrolyte having high ionic conductivity and a solid electrolyte cell.SOLUTION: There is provided a solid electrolyte cell 10 comprising a cathode 1, an anode 2 and a solid electrolyte layer 3, wherein when the specific surface area is S (m2/g), the average particle diameter is D (μm) and the real density is ρ (g/cm3), the solid electrolyte layer 3 is composed of a compound satisfying the following expression (1): S>6/(ρD) (1). Further, the cathode 1 has a cathode current collector 1A and a cathode active material layer 1B containing a cathode active material. The anode 2 has an anode current collector 2A and an anode active material layer 2B containing an anode active material.SELECTED DRAWING: Figure 1

Description

The present invention relates to solid electrolytes and solid electrolyte batteries.

2. Description of the Related Art In recent years, the development of electronics technology has been remarkable, and efforts have been made to reduce the size, weight, thickness, and functions of portable electronic devices. Along with this, there is a strong demand for batteries that serve as power sources for electronic devices to be smaller, lighter, thinner, and more reliable. For this reason, solid electrolyte batteries using a solid electrolyte as the electrolyte have attracted attention. Known solid electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, complex hydride-based solid electrolytes, and the like.

Patent Document 1 describes a powder represented by the general formula: ABO ₃ , containing at least one of La and Sr at the A site and containing Co at the B site as a main component, and comprising a perovskite oxide as a main component, The average particle diameter (Dr) based on the scattering method is 0.1 μm or more and 1 μm or less, and the average particle diameter (Dr) with respect to the ideal particle diameter (Di), which is the equivalent sphere diameter calculated from the specific surface area based on the BET method. A perovskite-type oxide powder having a ratio (Dr/Di) of 2.5 or more and 5 or less is disclosed.

JP 2018-37158 A

However, in conventional solid electrolyte batteries, the ionic conductivity of the solid electrolyte used in the solid electrolyte layer is insufficient. For this reason, conventional solid electrolyte batteries have not been able to obtain sufficient discharge capacity. The present invention has been made in view of the above problems, and an object of the present invention is to provide a solid electrolyte having high ionic conductivity. Another object of the present invention is to provide a solid electrolyte layer containing the above-described solid electrolyte, and a solid electrolyte battery including the same and having a large discharge capacity.

In order to solve the above problems, the inventors have made extensive studies. As a result, when the specific surface area of the solid electrolyte is S (m ² /g), the average particle diameter is D (μm), and the true density is ρ (g/cm ³ ), a solid electrolyte satisfying the following formula (1) was obtained. The inventors have found that it is good to use it, and have conceived of the present invention.
S>6/(ρD) (1)
That is, the present invention relates to the following inventions.

[1] A compound that satisfies the following formula (1), where S (m ² /g) is the specific surface area of the solid electrolyte, D (μm) is the average particle size, and ρ (g/cm ³ ) is the true density of the solid electrolyte. Solid electrolyte containing.
S>6/(ρD) (1)

[2] A solid electrolyte battery comprising a solid electrolyte layer, a positive electrode and a negative electrode, wherein at least one selected from the solid electrolyte layer, the positive electrode and the negative electrode contains the solid electrolyte according to [1].

According to the present invention, a solid electrolyte with high ionic conductivity can be provided. Further, in the solid electrolyte battery of the present invention, at least one selected from the solid electrolyte layer, the positive electrode, and the negative electrode contains the solid electrolyte of the present invention having high ionic conductivity. Therefore, the solid electrolyte battery of the present invention has a small internal resistance and a large discharge capacity.

It is a cross-sectional schematic diagram of the solid electrolyte battery concerning this embodiment.

The solid electrolyte, solid electrolyte layer and solid electrolyte battery containing the solid electrolyte of the present invention are described below in detail.
[Solid electrolyte]
^The solid electrolyte of the present embodiment has ^the following formula (1 ) is a solid electrolyte containing a compound that satisfies
S>6/(ρD) (1)

The methods for measuring the specific surface area S, average particle diameter D and true density ρ of the solid electrolyte are as follows. The specific surface area S is determined by the BET (Brunauer, Emmet and Teller) method. Argon gas or nitrogen gas is used as the gas to be measured.

The average particle diameter D is obtained with a particle size distribution analyzer. The solid electrolyte is dispersed in a solvent in which the solid electrolyte is not dissolved, such as toluene, and measured with a particle size distribution analyzer. A solid electrolyte often has primary particles aggregated to form secondary particles, and the average particle size D obtained here is the average particle size of the secondary particles obtained by aggregating the primary particles of the solid electrolyte. . The true density ρ is obtained by the pycnometer method. A solvent in which the solid electrolyte does not dissolve, such as toluene, is used as the solvent for measurement.

The solid electrolyte of the present embodiment may be in the state of powder (particles) made of the above compound, or may be in the state of a sintered body obtained by sintering the powder made of the above compound. Further, the solid electrolyte of the present embodiment includes a molded body obtained by compressing powder, a molded body obtained by molding a mixture of powder and a binder, and a powder, a binder, and a solvent after applying a paint containing the powder, a binder, and a solvent. may be in the form of a coating film formed by removing the

The solid electrolyte of the present embodiment has the following formula (1) when the specific surface area of the solid electrolyte is S (m ² /g), the average particle size is D (μm), and the true density is ρ (g/cm ³ ). is a solid electrolyte containing a compound that satisfies
S>6/(ρD) (1)

(Method for producing solid electrolyte)
When the solid electrolyte of the present embodiment is in a powder state, it can be produced, for example, by mixing raw materials containing predetermined elements in a predetermined molar ratio and reacting them. When the solid electrolyte of the present embodiment is powder, it can be produced by, for example, a mechanochemical method. A planetary ball mill, for example, is used to cause the mechanochemical reaction. A planetary ball mill device puts media (balls to promote grinding or mechanochemical reaction) and materials into a closed container, rotates and revolves, and applies kinetic energy to the material to cause grinding or mechanochemical reaction. It is a device. Typically, planetary ball milling equipment does not come with cooling or heating devices. However, kinetic energy may be converted to thermal energy, heating the enclosure (and thus the material within the enclosure). Therefore, some planetary ball mills are equipped with a cooling device so that the material is not heated. There is also a planetary ball mill apparatus that has a heating mechanism that heats the closed container (and thus the material in the closed container) so that the mechanochemical reaction can be promoted.

In a planetary ball mill, the place where the material reacts is inside the closed container, so basically there is no place for the material to escape. there is). Further, when the materials are reacted using a planetary ball mill equipped with a cooling device, the materials during the reaction are less likely to reach a high temperature, so phase separation is less likely to occur. On the other hand, for example, when materials are reacted by a firing process, phase separation occurs when the temperature returns to room temperature after the chemical reaction at high temperature, and the target compound may not be obtained.

A planetary ball mill uses, for example, a closed container made of zirconia. A raw material containing a predetermined raw material in a predetermined ratio and a ball made of zirconia are put into this sealed container. If the raw material is likely to be hydrolyzed by moisture, the raw material is handled in a glove box with a dew point of −99° C. and an oxygen concentration of 1 ppm, in which argon gas is circulated, for example. The raw material may be powder or liquid. For example, titanium chloride ( _TiCl4 ) and tin chloride ( _SnCl4 ) are liquid at room temperature. After putting the raw materials into the airtight container, the lid made of zirconia is screwed to seal it. After that, it is operated for a predetermined time at a predetermined rotation speed and revolution speed. By this method, a mechanochemical reaction occurs and a powdery solid electrolyte made of a compound having a predetermined composition is obtained.

The powdery solid electrolyte thus obtained may be compressed into a compact using, for example, a hot press method, or may be sintered using a hot isostatic sintering technique (HIP). It may be in a solid state. Alternatively, the powdery solid electrolyte, the binder and the solvent are mixed to prepare a paint, which is applied to a film or the like, the solvent is removed, and if necessary, the state of the coating film is obtained by pressing. may be

Moreover, when the solid electrolyte of the present embodiment is in the state of a sintered body, it can be produced, for example, by the method shown below. First, predetermined raw materials are mixed in a predetermined ratio. Next, the mixed raw materials are formed into a predetermined shape and sintered in vacuum or in an inert gas atmosphere. The halide raw material contained in the raw material tends to evaporate when the temperature is raised. Therefore, a halogen gas may coexist in the atmosphere during sintering to compensate for the halogen. Alternatively, sintering may be performed by a hot press method using a highly airtight mold. In this case, since the mold is highly sealed, evaporation of the halide raw material due to sintering can be suppressed. By sintering in this manner, a solid electrolyte in the form of a sintered body made of a compound having a predetermined composition is obtained.

The solid electrolyte of the present embodiment is composed of a compound composed of an alkali metal, the above specific metal element, and an element of Group 17 of the periodic table. Therefore, the solid electrolyte of this embodiment has high ionic conductivity.

Moreover, since the compound in the solid electrolyte of the present embodiment is a compound represented by Formula (1), it has high ionic conductivity. Although the details are unknown, the reason is considered as follows. In the compound represented by the formula (1), the ionic conductivity of the particulate solid electrolyte is divided into ionic conduction inside the particles (so-called bulk ionic conduction) and ionic conduction between particles. Bulk ionic conduction is derived from the crystal structure and composition. On the other hand, ionic conduction between solid electrolyte particles is considered to be affected by the bonding state of the interface between solid electrolyte particles, that is, the interface state (contact area, contact strength). When the surfaces of the solid electrolyte particles are smooth and have no irregularities, the contact area between the solid electrolyte particles and between the solid electrolyte particles and the active material particles is like point contact, resulting in a small contact area and a low ionic conductivity. On the other hand, when the surface of the solid electrolyte particles has irregularities, the contact area between the solid electrolyte particles increases and the ionic conductivity increases. The unevenness of the particles can be expressed by Equation (1). Assuming that the particles are spherical, their specific surface area S' is S'=6/(ρD). On the other hand, the specific surface area S of the solid electrolyte of the present application is S>6/(ρD). That is, the specific surface area of the solid electrolyte of the present application is larger than the specific surface area when the solid electrolyte is assumed to be a true sphere. In such a solid electrolyte, the primary particles of the solid electrolyte are strongly bonded to each other, and it is considered that the contact area between the solid electrolyte particles is large. As a result, the ionic conductivity of the solid electrolyte as a whole is increased. In addition, when the ionic conductivity of the solid electrolyte increases, the internal resistance of the battery using this decreases, resulting in an increase in discharge capacity.

[Solid electrolyte battery]
FIG. 1 is a schematic cross-sectional view of a solid electrolyte battery according to this embodiment. A solid electrolyte battery 10 shown in FIG. 1 includes a positive electrode 1 , a negative electrode 2 and a solid electrolyte layer 3 . Solid electrolyte layer 3 is sandwiched between positive electrode 1 and negative electrode 2 . The solid electrolyte layer 3 contains the solid electrolyte described above. An external terminal (not shown) is connected to the positive electrode 1 and the negative electrode 2, and is electrically connected to the outside.

The solid electrolyte battery 10 is charged or discharged by transferring ions between the positive electrode 1 and the negative electrode 2 through the solid electrolyte layer 3 . The solid electrolyte battery 10 may be a laminated body in which the positive electrode 1, the negative electrode 2 and the solid electrolyte layer 3 are laminated, or may be a wound body obtained by winding the laminated body. Solid electrolyte batteries are used in, for example, laminate batteries, prismatic batteries, cylindrical batteries, coin batteries, button batteries, and the like.

"Positive electrode and negative electrode"
As shown in FIG. 1, the positive electrode 1 has, for example, a positive electrode current collector 1A and a positive electrode active material layer 1B containing a positive electrode active material. The negative electrode 2 has, for example, a negative electrode current collector 2A and a negative electrode active material layer 2B containing a negative electrode active material.

(positive electrode)
As shown in FIG. 1, the positive electrode 1 includes a positive electrode mixture layer 1B provided on a plate-like (foil-like) positive electrode current collector 1A.
(Positive electrode current collector)
The positive electrode current collector 1A may be made of an electronically conductive material that resists oxidation during charging and does not easily corrode. For example, metals such as aluminum, stainless steel, nickel, and titanium, or conductive resins can be used. The positive electrode current collector 1A may be in the form of powder, foil, punched, or expanded.
(Positive electrode mixture layer)
The positive electrode mixture layer 1B contains a positive electrode active material and, if necessary, a solid electrolyte, a binder and a conductive aid.

(Positive electrode active material)
The positive electrode active material is not particularly limited as long as it can reversibly progress lithium ion absorption/release, insertion/deintercalation (intercalation/deintercalation), and known lithium ion secondary batteries. can be used. Examples of positive electrode active materials include lithium-containing metal oxides and lithium-containing metal phosphates.
Examples of lithium-containing metal oxides include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and general formula: LiNi _x Co _{y Mnz} O ₂ ( x + y + z = 1), lithium vanadium compounds (LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ ), olivine-type LiMPO ₄ (where M is selected from Co, Ni, Mn, Fe at least one of which is used), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the like.

A positive electrode active material that does not contain lithium can also be used. Such positive electrode active materials include lithium-free metal oxides ( _MnO2 , _{V2O5 ,} etc.), lithium-free metal sulfides ( _MoS2, etc.), lithium-free fluorides ( _FeF3 , VF3 _, etc.). ) and the like. When using these positive electrode active materials that do not contain lithium, the negative electrode may be doped with lithium ions in advance, or a negative electrode containing lithium ions may be used.

(binder)
The positive electrode mixture layer 1B is provided with a preferably contains a binder. Properties required for the binder include oxidation resistance and good adhesion.

Binders used in the positive electrode mixture layer 1B include polyvinylidene fluoride (PVDF) or its copolymer, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole ( PBI), polyethersulfone (PES), polyacrylic acid (PA) and its copolymer, metal ion cross-linked polyacrylic acid (PA) and its copolymer, maleic anhydride-grafted polypropylene (PP) , maleic anhydride-grafted polyethylene (PE), or mixtures thereof. Among these, it is particularly preferable to use PVDF as the binder.

The content of the solid electrolyte in the positive electrode mixture layer 1B is not particularly limited, but is preferably 1% by volume to 50% by volume based on the total mass of the positive electrode active material, the solid electrolyte, the conductive aid, and the binder. It is preferably 5% to 30% by volume, and more preferably 5% by volume to 30% by volume.

The content of the binder in the positive electrode mixture layer 1B is not particularly limited, but is preferably 1% by mass to 15% by mass based on the total mass of the positive electrode active material, the solid electrolyte, the conductive aid and the binder. , 3% by mass to 5% by mass. If the amount of binder is too small, there is a tendency that the positive electrode 1 with sufficient adhesive strength cannot be formed. Conversely, if the amount of binder is too large, it tends to be difficult to obtain a sufficient volume or mass energy density because general binders are electrochemically inactive and do not contribute to discharge capacity.

(Conductivity aid)
The conductive aid is not particularly limited as long as it improves the electron conductivity of the positive electrode mixture layer 1B, and known conductive aids can be used. Examples include carbon materials such as carbon black, graphite, carbon nanotubes, and graphene, metals such as aluminum, copper, nickel, stainless steel, iron, and amorphous metals, conductive oxides such as ITO, and mixtures thereof.
The conductive aid may be in the form of powder or fiber.

The content of the conductive aid in the positive electrode mixture layer 1B is not particularly limited. , preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 5% by mass.

(negative electrode)
As shown in FIG. 1, the negative electrode 2 has a negative electrode mixture layer 2B provided on a negative electrode current collector 2A.
(Negative electrode current collector)
The negative electrode current collector 2A may be conductive, and for example, metals such as copper, aluminum, nickel, stainless steel, and iron, or conductive resin foils can be used. The negative electrode current collector 2A may be in the form of powder, foil, punched, or expanded.
(Negative electrode mixture layer)
The negative electrode mixture layer 2B contains a negative electrode active material and, if necessary, a solid electrolyte, a binder, and a conductive aid.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can reversibly progress the absorption and release of lithium ions and the insertion and extraction of lithium ions, and negative electrode active materials used in known lithium ion secondary batteries are used. can do. Examples of negative electrode active materials include carbon materials such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fibers (MCF), cokes, vitreous carbon, and baked organic compounds, Si, SiO _x , Sn, and aluminum. metals that can be combined with lithium, alloys thereof, composite materials of these metals and carbon materials, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), oxides such as SnO ₂ , metallic lithium, and the like.

(binder)
The negative electrode mixture layer 2B is provided with a preferably contains a binder. Properties required for the binder include reduction resistance and good adhesiveness. Binders used in the negative electrode mixture layer 2B include polyvinylidene fluoride (PVDF) or its copolymer, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole ( PBI), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PA) and copolymers, metal ion crosslinked polyacrylic acid (PA) and copolymers, maleic anhydride grafted polypropylene (PP), maleic anhydride-grafted polyethylene (PE), or mixtures thereof. Among these, as the binder, it is preferable to use one or more selected from SBR, CMC and PVDF.

The content of the solid electrolyte in the negative electrode mixture layer 2B is not particularly limited, but is preferably 1% by volume to 50% by volume based on the total mass of the negative electrode active material, the solid electrolyte, the conductive aid, and the binder. It is preferably 5% to 30% by volume, and more preferably 5% by volume to 30% by volume.

The content of the binder in the negative electrode mixture layer 2B is not particularly limited, but is preferably 1% by mass to 15% by mass based on the total mass of the negative electrode active material, conductive aid and binder. It is more preferably 5% by mass to 10% by mass. If the binder amount is too small, there is a tendency that the negative electrode 2 having sufficient adhesive strength cannot be formed. Conversely, if the binder amount is too large, the binder is generally electrochemically inactive and does not contribute to the discharge capacity, making it difficult to obtain a sufficient volume or mass energy density.

(Conductivity aid)
As the conductive aid that may be contained in the negative electrode mixture layer 2B, the same conductive aid that may be contained in the positive electrode mixture layer 1B, such as a carbon material, can be used.

The content of the conductive aid in the negative electrode mixture layer 2B is not particularly limited. , 1% by mass to 12% by mass.

(Exterior body)
In the solid electrolyte battery 10 of the present embodiment, a battery element composed of the positive electrode 1, the solid electrolyte layer 3, and the negative electrode 2 is housed and sealed in an exterior body. The exterior body is not particularly limited as long as it can prevent moisture or the like from entering from the outside to the inside. For example, as the exterior body, a metal laminate film formed by coating both sides of a metal foil with a polymer film can be used in the form of a bag. Such an exterior body is hermetically sealed by heat-sealing the opening. As the metal foil forming the metal laminate film, for example, an aluminum foil, a stainless steel foil, or the like can be used. As the polymer film arranged outside the exterior body, it is preferable to use a polymer having a high melting point, such as polyethylene terephthalate (PET) or polyamide. It is preferable to use, for example, polyethylene (PE), polypropylene (PP), or the like as the polymer film arranged inside the exterior body.

(external terminal)
A positive electrode terminal is electrically connected to the positive electrode 1 of the battery element, and a negative electrode terminal is electrically connected to the negative electrode 2 . In this embodiment, the positive electrode terminal is electrically connected to the positive electrode current collector 1A, and the negative electrode terminal is electrically connected to the negative electrode current collector 2A. A connection portion between the positive electrode current collector or the negative electrode current collector and the external terminals (the positive electrode terminal and the negative electrode terminal) is arranged inside the exterior body.
As the external terminal, for example, one made of a conductive material such as aluminum or nickel can be used.

Maleic anhydride-grafted PE (hereinafter sometimes referred to as “acid-modified PE”) or maleic anhydride-grafted PP (hereinafter referred to as “acid-modified PP ) is preferably arranged. By heat-sealing the portion where the film made of acid-modified PE or acid-modified PP is arranged, the solid electrolyte battery has good adhesion between the exterior body and the external terminals.

[Manufacturing method of solid electrolyte battery]
Next, a method for manufacturing the solid electrolyte battery according to this embodiment will be described. First, the solid electrolyte described above, which will be the solid electrolyte layer 3 provided in the solid electrolyte battery 10 of the present embodiment, is prepared. In this embodiment, a powdery solid electrolyte is used as the material of the solid electrolyte layer 3 . The solid electrolyte layer 3 can be produced using a powder forming method. Further, for example, the positive electrode 1 is manufactured by applying a paste containing a positive electrode active material onto the positive electrode current collector 1A and drying it to form the positive electrode mixture layer 1B. Further, for example, the negative electrode 2 is manufactured by applying a paste containing a negative electrode active material onto the negative electrode current collector 2A and drying it to form the negative electrode mixture layer 2B.

Next, for example, a guide having a hole is placed on the positive electrode 1, and the guide is filled with a solid electrolyte. Thereafter, the surface of the solid electrolyte is smoothed, and the negative electrode 2 is placed on the solid electrolyte. As a result, the solid electrolyte is sandwiched between the positive electrode 1 and the negative electrode 2 . After that, pressure is applied to the positive electrode 1 and the negative electrode 2 to pressure-mold the solid electrolyte. A laminated body in which the positive electrode 1, the solid electrolyte layer 3, and the negative electrode 2 are laminated in this order is obtained by pressure molding. Next, external terminals are welded to the positive electrode current collector of the positive electrode 1 and the negative electrode current collector of the negative electrode 2 forming the laminate by a known method, respectively, and the positive electrode current collector or the negative electrode current collector and the external terminal are welded. and electrically connected. After that, the laminate connected to the external terminals is housed in an exterior body, and the opening of the exterior body is heat-sealed to seal. Solid electrolyte battery 10 of the present embodiment is obtained through the above steps.

In the method for manufacturing the solid electrolyte battery 10 described above, the case where the solid electrolyte in the powder state is used has been described as an example, but the solid electrolyte in the state of a sintered body may be used as the solid electrolyte. In this case, a solid electrolyte battery 10 having a solid electrolyte layer 3 is obtained by sandwiching a solid electrolyte in the state of a sintered body between the positive electrode 1 and the negative electrode 2 and subjecting them to pressure molding.

The solid electrolyte layer 3 of the present embodiment contains the solid electrolyte of the present embodiment having high ionic conductivity. Therefore, the solid electrolyte battery 10 of the present embodiment having the solid electrolyte layer 3 of the present embodiment has a small internal resistance and a large discharge capacity.

In addition, the solid electrolyte battery of the present embodiment may be one in which a solid electrolyte is filled in the pores of a battery body composed of a positive electrode, a separator, and a negative electrode. Such a solid electrolyte battery can be manufactured, for example, by the method shown below. First, a solid electrolyte paint containing a powdery solid electrolyte and a solvent is prepared. Also, a battery body comprising a positive electrode, a separator, and a negative electrode is produced. After the battery body is impregnated with the solid electrolyte paint, the solvent is removed. As a result, a solid electrolyte battery is obtained in which the pores of the battery body are filled with the solid electrolyte.

The embodiments of the present invention have been described in detail above with reference to the drawings. Each configuration and combination thereof in each embodiment is an example, and addition, omission, replacement, and other modifications of the configuration are possible without departing from the scope of the present invention.

(Examples 1 to 13 and Comparative Examples 1 to 3)
A planetary ball mill and a zirconia container with an inner volume of 45 ml used therein were prepared. A zirconia ball with a diameter of 5 mmφ was put into this zirconia container. Next, raw material powders containing raw materials having the molar ratios and amounts shown in Table 1 were put into a zirconia container and set in a planetary ball mill. This planetary ball mill was mixed for 24 hours at an autorotation speed of 500 rpm, a revolution speed of 500 rpm, and the rotation direction of the revolution was reversed to cause a mechanochemical reaction.

In Examples 1 to 13 and Comparative Examples 1 to 3, as shown in Table 1, the total input amount of raw materials was changed. The smaller the total input amount of raw materials, the greater the kinetic energy of the zirconia balls applied per unit weight of raw materials. As the kinetic energy applied to the raw material increases, the average particle size of the primary particles of the product decreases. In addition, the primary particles fuse with each other, and the specific surface area becomes smaller than the specific surface area when the solid electrolyte particles are assumed to be true spheres. Conversely, the greater the total input amount of raw materials, the less the kinetic energy of the zirconia balls applied per unit weight of raw materials. The less kinetic energy imparted to the raw material, the larger the average particle size of the product. In addition, the primary particles become difficult to fuse, and their specific surface area becomes larger than the specific surface area when the solid electrolyte particles are assumed to be true spheres.

Zirconia was used as the sealed container and balls for the planetary ball mill. Therefore, there is a possibility that zirconium originating from the sealed container and the ball is mixed in the manufactured compound as contamination. Table 1 describes the charging composition of the raw materials used in the synthesis of each example.

Under the conditions shown in Table 1, solid electrolytes of Examples 1 to 12 and Comparative Examples 1 to 3 in powder form were produced. Example 13 is a solid electrolyte taken out again from a solid electrolyte battery produced using the solid electrolyte produced in Example 1, which will be described later. The composition, ionic conductivity, specific surface area, density and average particle size of the produced solid electrolyte were measured.

The specific surface area of each solid electrolyte was measured by the BET method. Nitrogen gas was used as the gas for measuring the specific surface area, toluene was used as the solvent for measuring the particle size distribution with a particle size distribution analyzer, and toluene was used as the solvent for measuring the density by the pycnometer method.

The composition of each solid electrolyte was determined by a method of analyzing each element using an ICP (Inductively Coupled Plasma Emission Spectrometry) device (manufactured by Shimadzu Corporation). The solid electrolyte containing SO ₄ ^2- was analyzed using an ion chromatography device (manufactured by Thermo Fisher Scientific Co., Ltd.).

(Measurement of ionic conductivity)
The solid electrolytes of Examples 1 to 13 and Comparative Examples 1 to 3 were filled in a pressure molding die, respectively, and pressure molded at a pressure of 373 MPa to obtain pellets of test specimens. More specifically, a PEEK (polyetheretherketone) die with a diameter of 10 mm and upper and lower punches with a diameter of 9.99 mm were prepared. The material of the upper and lower punches is die steel (SKD11 material). A lower punch was inserted into the PEEK die, and 110 mg of the solid electrolyte powders of Examples 1 to 13 and Comparative Examples 1 to 3 were charged from above. An upper punch was inserted above the solid electrolyte powder. This was set in a press and molded at a pressure of 373 MPa. Hereafter, a set in which upper and lower punches are inserted into a die is called a set. The set was removed from the press.

Two stainless discs and two bakelite discs each having a diameter of 50 mm and a thickness of 5 mm were prepared. The stainless steel disc and bakelite disc have four screw holes. The stainless steel disc and bakelite disc were placed on the top and bottom of the set, and screws were passed through four screw holes and tightened. Specifically, a stainless disc/bakelite disc/set/bakelite disc/stainless disc was laminated in this order and crimped with a screw. The solid electrolyte is now under pressure. The pressurization pressure is about 85 MPa. There are screw holes for inserting screws on the sides of the upper and lower punches. Screws were inserted into the upper and lower punches to make terminals for ion conductivity measurement.

After that, the ionic conductivity of each specimen housed in a set of jigs for measuring ionic conductivity was measured. Ionic conductivity was measured by electrochemical impedance measurements using a potentiostat equipped with a frequency response analyzer. The measurement was performed under conditions of a frequency range of 7 MHz to 0.1 Hz, an amplitude of 10 mV, and a temperature of 25.degree. The results are shown in Table 2.

[Production of solid electrolyte battery]
Solid electrolyte batteries each having a solid electrolyte layer composed of the solid electrolytes of Examples 1 to 13 and Comparative Examples 1 to 3 were produced by the method described below. The solid electrolyte battery was fabricated in a glove box in an argon atmosphere with a dew point of −70° C. or lower. In addition, a charge/discharge test was performed by the method shown below to measure the discharge capacity. First, lithium cobalt oxide (LiCoO ₂ ): Solid electrolytes of Examples 1 to 13 and Comparative Examples 1 to 3: carbon black = 81:16:3 parts by weight, and They were mixed to form a positive electrode mixture. Next, graphite: each solid electrolyte of Examples 1 to 13 and Comparative Examples 1 to 3: carbon black = 67:30:3 parts by weight, mixed in an agate mortar, negative electrode A mixture was used.

A lower punch was inserted into the die, and 110 mg of solid electrolytes of Examples 1 to 13 and Comparative Examples 1 to 3 were charged from above the die. An upper punch was inserted above the solid electrolyte. This set was placed on a press and molded at a pressure of 50 MPa. The set was removed from the press and the upper punch removed. 20 mg of the positive electrode mixture was placed on the solid electrolyte in the die, an upper punch was inserted thereon, and the set was placed in a press machine and molded at a pressure of 50 MPa. The set was then removed, turned upside down and the lower punch removed. 10 mg of the negative electrode mixture was put on the solid electrolyte (pellet), a lower punch was inserted thereon, the set was left still in a press, and molded at a pressure of 290 MPa. Thus, a battery element composed of a positive electrode, a solid electrolyte, and a negative electrode was produced in the dice. This was set on the jig for ion conductivity measurement. Screws were inserted into the screw holes on the sides of the upper and lower punches as charge/discharge terminals. Hereinafter, this will be called a battery body.

An aluminum laminate material was prepared as an outer package for enclosing the battery body. This is a laminate material consisting of PET(12)/Al(40)/PP(50). PET is polyethylene terephthalate and PP is polypropylene. The values in parentheses indicate the thickness of each layer (unit: μm). This aluminum laminate material was cut into A4 size and folded back at the middle of the long side so that the PP was on the inside.

A nickel foil (4 mm wide, 40 mm long, and 100 μm thick) was prepared as a positive electrode terminal and a negative electrode terminal. Each of these external terminals (positive terminal and negative terminal) was wound with acid-modified PP and thermally bonded to the exterior body. This is to improve the sealing performance between the external terminals and the exterior body.

A positive electrode terminal and a negative electrode terminal were placed so as to be sandwiched between the aluminum laminate material and heat-sealed at the middle of each of the two opposing sides of the folded aluminum laminate material. After that, the battery body was inserted into the outer package, and the positive electrode and the positive electrode terminal were electrically connected by connecting the screw on the side surface of the upper punch and the positive electrode terminal in the outer package with a lead wire. Moreover, the negative electrode and the negative electrode terminal were electrically connected by connecting the screw on the side surface of the lower punch and the negative electrode terminal in the outer package with a lead wire. After that, the opening of the outer package was heat-sealed to obtain a solid electrolyte battery.

A charge/discharge test was performed in a constant temperature bath at 25°C. The notation of the charge/discharge current is hereinafter referred to as the C (see) rate notation. nC (mA) is the current that can charge and discharge the nominal capacity (mAh) at 1/n (h). For example, for a battery with a nominal capacity of 70 mAh, the current at 0.05 C is 3.5 mA (calculation formula 70×0.05=3.5). Similarly, a current of 0.2C is 14mA and a current of 2C is 140mA. Charging was carried out at 0.2C to 4.2V with constant current and constant voltage (referred to as CCCV). Charging was terminated until the current became 1/20C. Discharge was performed at 0.2C to 3.0V. The results are shown in Table 2.

As shown in Table 2, the solid electrolytes of Examples 1 to 13 all had sufficiently high ionic conductivity compared to Comparative Examples 1 to 3. Further, all of the solid electrolyte batteries having solid electrolyte layers made of the solid electrolytes of Examples 1 to 13 had sufficiently large discharge capacities compared to those of Comparative Examples 1 to 3.

DESCRIPTION OF SYMBOLS 1... Positive electrode, 1A... Positive electrode collector, 1B... Positive electrode mixture layer, 2... Negative electrode, 2A... Negative electrode collector, 2B... Negative mixture layer, 3... Solid electrolyte layer, 10... Solid electrolyte battery.

Claims (3)

A solid electrolyte containing a compound that satisfies the following formula (1) when the solid electrolyte has a specific surface area S (m ² /g), an average particle size D (μm), and a true density ρ (g/cm ³ ).
S>6/(ρD) (1) The solid electrolyte according to claim 1, comprising a compound represented by the following formula (2).
A _a E _b G _c X _d (2)
(In formula (1), A is at least one element selected from the group consisting of Li, Cs and Ca. E is selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanides. at least _{one element G is O, OH, BO2, BO3, BO4, B3O6, B4O7 , CO3 , NO3 , AlO2 , SiO3 , SiO4 , Si2 O7} , _{Si3O9 , Si4O11 , Si6O18} , _PO3 , _{PO4 , P2O7} , _{P3O10 , SO3} , _{SO4 , SO5} , _{S2O3 , S2 O4} , _{S2O5 , S2O6 , S2O7} , _{S2O8 ,} BF4 _{, PF6} , _BOB , (COO) ₂ , N, _{AlCl4 , CF3SO3} , _CH3COO , _CF3COO , OOC-( _CH2 ) ₂ -COO, OOC-CH2-COO, OOC-CH(OH)-CH(OH)-COO, _OOC -CH(OH)-CH2 _- COO, _{C6H 5SO3} , OOC-CH=CH-COO, OOC-CH=CH-COO, C ₍ OH)( _CH2COOH ) _2COO , _AsO4 , _BiO4 , _CrO4 , _MnO4 , _PtF6 , _PtCl6 , PtBr ₆ , PtI ₆ , SbO ₄ , SeO ₄ , TeO ₄ , HCOO, CH ₃ COO, CN, SCN, X is at least one group selected from the group consisting of F, Cl, Br, I is at least one element selected from 0.5≦a<6, 0<b<2, 0≦c≦6, 0≦d≦6.1 BOB is bisoxalate borate; OOC-(CH ₂ ) ₂ -COO is succinate, OOC-CH ₂ -COO is malonate, OOC-CH(OH)-CH(OH)-COO is tartrate, OOC-CH(OH)-CH ₂ -COO is malate, C ₆ H ₅ SO ₃ is benzenesulfonate, OOC-CH=CH-COO is fumarate, OOC-CH=CH-COO is maleate, and C(OH)( _CH2COOH ) _2COO is the citrate.) A solid electrolyte battery comprising a solid electrolyte layer, a positive electrode, and a negative electrode, wherein at least one selected from the solid electrolyte layer, the positive electrode, and the negative electrode contains the solid electrolyte according to claim 1 or 2.

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