JP7436984B2 - Solid electrolyte composition, molded article using the same, and all-solid-state secondary battery - Google Patents

Description

The present invention relates to a solid electrolyte composition that exhibits excellent ionic conductivity even when press-molded not only at high pressure but also at low pressure, a molded article using the same, and an all-solid-state secondary battery.

In recent years, power storage devices, particularly lithium batteries, have been widely used in small electronic devices such as mobile phones and notebook computers, electric vehicles, and for power storage. Note that in this specification, the term lithium battery is used as a concept that also includes so-called lithium ion secondary batteries.

Lithium batteries currently on the market are mainly composed of positive and negative electrodes containing materials that can absorb and release lithium, and a non-aqueous electrolyte consisting of lithium salt and a non-aqueous solvent. The non-aqueous solvent is ethylene carbonate (EC). ), cyclic carbonates such as propylene carbonate (PC), and chain carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC). As lithium batteries use an electrolyte containing flammable organic solvents, measures must be taken to prevent leakage, and safety devices must be installed to prevent temperature rise during short circuits, as there is a risk of ignition in the event of a short circuit. A prevention structure is needed.
Under these circumstances, all-solid-state secondary batteries using inorganic solid electrolytes instead of organic electrolytes are attracting attention. Since the positive electrode, negative electrode, and electrolyte of all-solid-state batteries are all made of solid materials, it is possible to further improve safety and reliability, which is an issue with batteries that use organic electrolytes, and it is also possible to simplify safety devices. Since it is possible to achieve high energy density from this material, it is expected to be applied to electric vehicles, large storage batteries, etc.

Unlike conventional lithium-ion batteries that use electrolytes, in all-solid-state batteries, it is extremely important to form a good solid-solid interface from the viewpoint of achieving excellent ionic conductivity and long-term cycle characteristics. In order to form a good solid-solid interface, it is very important that the solid electrolyte has not only its own ionic conductivity but also high formability. As a solid electrolyte material used in all-solid-state batteries, many oxide solid electrolytes such as garnet-type cubic Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) have been reported and have been shown to have high ionic conductivity. However, if these oxide solid electrolytes are formed only by pressure molding without sintering at high temperatures, a good solid-solid interface cannot be formed, and the conductivity of the compact decreases significantly. It ends up. Furthermore, although it is possible to densify the molded body by heat treatment at a high temperature, when used as an electrode composite material layer, there is a concern that the electrode material and the oxide solid electrolyte may react during the heat treatment at a high temperature. On the other hand, sulfide-based solid electrolytes such as Li ₂ S-P ₂ S ₅ have high moldability, and can be formed with only pressurization at room temperature, with almost no interfaces between particles and fewer voids. It has been reported that a precisely dense molded body can be obtained. This property of sulfide-based solid electrolytes eliminates the need for high-temperature sintering to construct interfaces between solid electrolytes and between electrode materials and electrolytes, which simplifies the battery manufacturing process. It is expected that reactions at the electrolyte interface can also be reduced. Furthermore, in addition to simplifying the battery manufacturing process, it forms a good electrode-electrolyte interface and electrolyte-electrolyte interface in all-solid-state batteries, and maintains the interface well even during long cycles by using a dense molded body with few voids. can form continuous ion and electron paths over long periods of time. However, as mentioned above, by using a sulfide-based solid electrolyte, it is possible to densify a molded body simply by applying pressure at room temperature, but in order to make the molded body densified, it is necessary to mold it under extremely high pressure. . Non-Patent Document 1 reports the ionic conductivity of a molded body when the molding pressure is changed in a sulfide glass with Li ₂ S: P ₂ S ₅ = 75:25. For example, when the molding pressure is changed from 360 MPa to It has been reported that when the pressure is set to 180 MPa, the relative density decreases and the ionic conductivity decreases by about 20%.

A. Sakuda, A. Hayashi, and M. Tatsumisago, Sci. Rep., 3 (2013) 2261

The present invention provides a solid electrolyte composition that exhibits excellent ionic conductivity even when press-molded not only at high pressure but also at low pressure, a molded article using the same, and an all-solid-state secondary battery.

As a result of repeated research, the present inventors have developed a specific inorganic solid electrolyte that has conductivity for metal ions belonging to Group 1 of the periodic table in order to achieve excellent ion conductivity even when molded at low pressure. The present invention was completed based on the discovery that by containing a carboxylic acid ester compound, high ionic conductivity can be easily achieved even when molded at low pressure.

The present invention relates to a solid electrolyte composition, a molded article using the same, and an all-solid-state secondary battery.

That is, the present invention provides the following (1) to (3).

(1) A solid electrolyte composition containing an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table and a carboxylic acid ester compound represented by the following general formula (I).

（Ｒ^１～Ｒ^４はそれぞれ独立しており、少なくとも１つの水素原子がハロゲン原子で置換されていてもよい炭素数１～１２のアルキル基を表す。）

(R ¹ to R ⁴ are each independent and represent an alkyl group having 1 to 12 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom.)

(2) A molded article obtained by pressurizing a solid electrolyte composition, the molded article containing the solid electrolyte composition according to (1).

(3) An all-solid-state secondary battery comprising a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer, wherein at least one layer of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer is An all-solid-state secondary battery that is a layer containing the solid electrolyte composition according to (1).

According to the present invention, it is possible to provide a solid electrolyte composition that exhibits excellent ionic conductivity not only in high-pressure press molding but also in low-pressure press molding, a molded article using the same, and an all-solid-state secondary battery.

The present invention relates to a solid electrolyte composition, a molded article using the same, and an all-solid-state secondary battery.

[Solid electrolyte composition]
The solid electrolyte composition of the present invention is characterized by containing an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table, and a carboxylic acid ester compound represented by general formula (I). do.

[Periodic table]
The periodic table of the present invention refers to the periodic table of long-period elements based on the regulations of IUPAC (International Union of Pure and Applied Chemistry).

[Carboxylic acid ester compound]
The carboxylic acid ester compound used in the present invention is represented by the following general formula (I).

（Ｒ^１～Ｒ^４はそれぞれ独立しており、少なくとも１つの水素原子がハロゲン原子で置換されていてもよい炭素数１～１２のアルキル基を表す。）

(R ¹ to R ⁴ are each independent and represent an alkyl group having 1 to 12 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom.)

R ¹ to R ⁴ in the general formula (I) are each independent and represent an alkyl group having 1 to 12 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom. Note that R ¹ and R ² may be bonded to each other to form a ring structure.

R ¹ to R ⁴ in the general formula (I) include an alkyl group having 1 to 12 carbon atoms (an alkyl group in which no hydrogen atom is substituted), a halogenated alkyl group having 1 to 12 carbon atoms (at least one Preferred examples include alkyl groups in which a hydrogen atom is substituted with a halogen atom, and more preferred are alkyl groups having 1 to 6 carbon atoms and halogenated alkyl groups having 1 to 6 carbon atoms. All of R ¹ to R ⁴ are an alkyl group having 1 to 6 carbon atoms, or all of R ¹ to R ³ are an alkyl group having 1 to 6 carbon atoms, and More preferably, R ⁴ is a halogenated alkyl group having 1 to 6 carbon atoms. The halogenated alkyl group having 1 to 12 carbon atoms is preferably one in which carbon atoms other than the carbon atoms bonded to the oxygen atoms constituting the carboxylic acid ester structure are substituted with halogen atoms. The halogen atom is not particularly limited, but is preferably a fluorine atom.

Preferred examples of general formula (I) include the following compounds.

Among the above compounds, preferred are methyl pivalate (Structural formula 1), ethyl pivalate (Structural formula 2), butyl pivalate (Structural formula 3), hexyl pivalate (Structural formula 4), and octyl pivalate (Structural formula 5). ), trifluoroethyl pivalate (Structure 8), and methyl 1-methylcyclopropane-1-carboxylate (Structure 14). More preferably, methyl pivalate (Structural Formula 1), ethyl pivalate (Structural Formula 2), butyl pivalate (Structural Formula 3), hexyl pivalate (Structural Formula 4), and trifluoroethyl pivalate (Structural Formula 8) ).

The reason why the solid electrolyte composition of the present invention has excellent ionic conductivity even when press-molded at low pressure is not necessarily clear, but it is thought to be as follows.
The solid electrolyte composition of the present invention includes an inorganic solid electrolyte having conductivity of metal ions belonging to Group 1 of the periodic table and a specific carboxylic acid ester compound. Normally, if a large amount of carboxylic acid ester compound is added, it will dissolve excessively and react with the carboxylic acid ester compound when complexed with an inorganic solid electrolyte, especially a sulfide solid electrolyte, and the good ions inherent in the inorganic solid electrolyte will be dissolved. Conductivity cannot be obtained. On the other hand, the carboxylic acid ester compound used in the present invention has a structure in which all hydrogen atoms on the α carbon next to the carbonyl group are substituted with an alkyl group. This structure suppresses undesirable reactions with the inorganic solid electrolyte and allows the inorganic solid electrolyte to be appropriately dissolved. As a result, even in a molded article with many voids formed by low-pressure pressing, the voids are filled with the dissolved inorganic solid electrolyte, and it is thought that excellent ionic conductivity is exhibited. In addition, by using the solid electrolyte composition of the present invention, a molded product having excellent ionic conductivity can be obtained even when molded at low pressure (for example, molded at a pressure of 108 to 180 MPa), so it is possible to produce a molded product that has excellent ionic conductivity even when molded at low pressure (for example, molded at a pressure of 108 to 180 MPa). By using this method, it is possible to simplify the battery manufacturing process, and it is also possible to form a continuous ion path over a long period of time without using very strong restraint jigs, so it is expected to achieve excellent battery characteristics. be done.

In the solid electrolyte composition of the present invention, the content of each of the carboxylic acid ester compounds represented by the general formula (I) is 0.05% by volume or more and 20% by volume based on 100% by volume of the entire solid electrolyte composition. It is preferably less than % by volume. The content is more preferably 0.1% by volume or more, even more preferably 1% by volume or more, particularly preferably 2.5% by volume or more, based on 100% by volume of the entire solid electrolyte composition. Moreover, the upper limit is more preferably 18 volume% or less, further preferably 15 volume% or less, and particularly preferably 13.5 volume% or less.

[Inorganic solid electrolyte]
An inorganic solid electrolyte is an inorganic solid electrolyte, and a solid electrolyte is a solid electrolyte that can move ions within it. Since inorganic solid electrolytes are solid in a steady state, they are usually not dissociated or liberated into cations and anions. The inorganic solid electrolyte is not particularly limited as long as it has conductivity for metal ions belonging to Group 1 of the periodic table, and generally has almost no electronic conductivity.

In the present invention, the inorganic solid electrolyte has conductivity of metal ions belonging to Group 1 of the periodic table. Representative examples of the inorganic solid electrolyte include (A) a sulfide-based inorganic solid electrolyte and (B) an oxide-based inorganic solid electrolyte. In the present invention, a sulfide-based solid electrolyte is preferably used because it has high ionic conductivity and can form a dense compact with few grain boundaries simply by applying pressure at room temperature.

(A) Sulfide-based inorganic solid electrolyte The sulfide-based inorganic solid electrolyte contains a sulfur atom (S), has conductivity of metal ions belonging to Group 1 of the periodic table, and has electronic insulating properties. It is preferable to have the following. The sulfide-based inorganic solid electrolyte can be produced by reacting a sulfide containing a metal element belonging to Group 1 of the periodic table with at least one sulfide represented by the following general formula (II). Two or more types of sulfides represented by formula (II) may be used in combination.

（MはＰ、Ｓｉ、Ｇｅ、Ｂ、Ａｌ、Ｇａ、及びＳｂのいずれかを示し、ｘ及びｙは、Ｍの種類に応じて、化学量論比を与える数を示す。）

(M represents any one of P, Si, Ge, B, Al, Ga, and Sb, and x and y represent numbers that give the stoichiometric ratio depending on the type of M.)

The sulfide containing a metal element belonging to Group 1 of the periodic table is lithium sulfide, sodium sulfide, or potassium sulfide, with lithium sulfide and sodium sulfide being more preferred, and lithium sulfide being even more preferred.

The sulfide represented by general formula (II) is any one of P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ , Al ₂ S ₃ , Ga ₂ S ₃ and Sb ₂ S ₅ is preferred, and P ₂ S ₅ is particularly preferred.

The composition ratio of each element in the sulfide-based inorganic solid electrolyte produced as described above is as follows: a sulfide having a metal element belonging to Group 1 of the periodic table, a sulfide represented by the general formula (II), and It can be controlled by adjusting the amount of elemental sulfur.

The sulfide-based inorganic solid electrolyte used in the present invention may be amorphous glass, crystallized glass, or a crystalline material.

Preferred examples of the sulfide-based inorganic solid electrolyte include, but are not particularly limited to, the following combinations.
Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -Al ₂ S ₃ , Li ₂ S-GeS ₂ , Li ₂ S-Ga ₂ S ₃ , Li ₂ S-GeS ₂ -Ga ₂ S ₃ , Li ₂ S-GeS ₂ -P ₂ S ₅ , Li ₂ S-GeS ₂ -Sb ₂ S ₅ , Li ₂ S-GeS ₂ -Al ₂ S ₃ , Li ₂ S-SiS ₂ , Li ₂ S-Al _{2 S3 , Li2S} - _{SiS2 - Al2S3} , _Li2S - _{SiS2 -P2S5 , Li10GeP2S12 .}

Among the above combinations, LPS glass and LPS glass ceramics produced by combining Li ₂ SP ₂ S ₅ are preferred.

The mixing ratio of the sulfide having a metal element belonging to Group 1 of the periodic table and the sulfide represented by the general formula (II) is not particularly limited as long as it can be used as a solid electrolyte, but may be 50:50. The ratio is preferably 90:10 (molar ratio). If the molar ratio of the sulfide containing a metal element belonging to Group 1 of the periodic table is 50 or more and 90 or less, the ionic conductivity can be sufficiently improved. The mixing ratio (molar ratio) is more preferably from 60:40 to 80:40, even more preferably from 70:30 to 80:20.

The sulfide-based inorganic solid electrolyte contains LiI, LiBr, It may also contain at least one lithium salt selected from LiCl and LiF, such as lithium halide, lithium oxide, and lithium phosphate. However, the mixing ratio of the sulfide-based inorganic solid electrolyte and these lithium salts is preferably 60:40 to 95:5 (molar ratio), more preferably 80:20 to 95:5.

In addition, as sulfide-based inorganic solid electrolytes other than those mentioned above, algerodite-type solid electrolytes such as Li ₆ PS ₅ Cl and Li ₆ PS ₅ Br are also suitable.

The method for producing the sulfide-based inorganic solid electrolyte is preferably a solid phase method, a mechanical milling method, a solution method, a solution shaking method, a melt quenching method, etc., but is not particularly limited.

(B) Oxide inorganic solid electrolyte

The oxide-based inorganic solid electrolyte preferably contains an oxygen atom, has metal ion conductivity belonging to Group 1 of the periodic table, and has electronic insulation properties.

Examples of the oxide inorganic solid electrolyte include Li _3.5 Zn _0.25 GeO ₄ having a LISICON (Lithium super ionic conductor) type crystal structure, La _0.55 Li _0.35 TiO ₃ having a perovskite type crystal structure, LiTi ₂ P ₃ O ₁₂ with a NASICON (Natrium super ionic conductor) type crystal structure, Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) with a garnet type crystal structure, lithium phosphate (Li ₃ PO ₄ ), lithium phosphate LiPON in which a part of the oxygen in is replaced with nitrogen, Li ₃ BO ₃ -Li ₂ SO ₄ , Li ₂ O-B ₂ O ₃ -P ₂ O ₅ , Li ₂ O-SiO ₂ , and Li ₆ BaLa ₂ Ta ₂ Preferred examples include O ₁₂ and the like.

Although the volume average particle diameter of the inorganic solid electrolyte is not particularly limited, it is preferably 0.01 μm or more, more preferably 0.1 μm or more. The upper limit is preferably 100 μm or less, more preferably 50 μm or less.

[Method for preparing solid electrolyte composition]
The method for preparing the solid electrolyte composition of the present invention is not particularly limited. A preferred method is to add a carboxylic acid ester compound to a slurry containing an electrolyte.

The solid electrolyte composition of the present invention can be used in all-solid secondary batteries.

[All-solid-state secondary battery]
The all-solid-state secondary battery of the present invention comprises a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode, and the solid electrolyte composition of the present invention is contained in any of the solid electrolyte layer, the positive electrode, and the negative electrode. If so, the constituent members such as the positive electrode and the negative electrode can be used without any particular restrictions.

[Solid electrolyte layer]
The solid electrolyte layer contains at least a solid electrolyte, and may, for example, contain the solid electrolyte composition of the present invention, or if either the positive electrode or the negative electrode contains the solid electrolyte composition of the present invention, It may contain solid electrolyte compositions other than the solid electrolyte composition of the present invention. The method for forming the solid electrolyte layer is not particularly limited, and examples include a method of press-molding solid electrolyte powder and a carboxylic acid ester compound, or a method of mixing solid electrolyte powder and a carboxylic acid ester compound, and then forming the solid electrolyte layer. Preferred examples include a method in which a slurry is applied to an aluminum foil or stainless steel lath plate as a current collector, dried, and pressure-molded.

For example, as a positive electrode active material for a lithium secondary battery, a composite metal oxide containing lithium and one or more selected from the group consisting of cobalt, manganese, and nickel is used. These positive electrode active materials can be used alone or in combination of two or more.
Examples of such lithium composite metal oxides include LiCoO ₂ , LiCo _1-x M _x O ₂ (where M is Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and One or more elements selected from Cu, 0.001≦x≦0.05), LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01<x<1), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , a solid solution of Li ₂ MnO ₃ and LiMO ₂ (M is a transition metal such as Co, Ni, Mn, Fe, etc.), and LiNi _1/2 Mn _3/2 O ₄ One or more types are preferably mentioned, and two or more types are more preferable. Further, they may be used in combination, such as LiCoO ₂ and LiMn ₂ O ₄ , LiCoO ₂ and LiNiO ₂ , and LiMn ₂ O ₄ and LiNiO ₂ .

Furthermore, a lithium-containing olivine-type phosphate can also be used as the positive electrode active material. Particularly preferred is a lithium-containing olivine-type phosphate containing at least one selected from iron, cobalt, nickel, and manganese. Specific examples include LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ and the like.
A part of these lithium-containing olivine-type phosphates may be substituted with other elements, and a part of iron, cobalt, nickel, and manganese may be replaced with Co, Mn, Ni, Mg, Al, B, Ti, V, and Nb. , Cu, Zn, Mo, Ca, Sr, W, Zr, etc., or may be coated with a compound or carbon material containing these other elements. Among these, _LiFePO4 or _LiMnPO4 are preferred.
Moreover, the lithium-containing olivine-type phosphate can also be used, for example, in mixture with the above-mentioned positive electrode active material.

The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not undergo chemical changes. Examples include graphite such as natural graphite (scaly graphite, etc.), artificial graphite, and carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black. Further, graphite and carbon black may be mixed and used as appropriate. The amount of the conductive agent added to the positive electrode mixture is preferably 1 to 10% by mass, particularly preferably 2 to 5% by mass.

[Cathode active material layer]
The positive electrode active material layer contains at least the above-mentioned positive electrode active material and solid electrolyte, and optionally contains a conductive agent such as acetylene black or carbon black, and polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or styrene. It may also contain a binder such as a copolymer of acrylonitrile and butadiene (SBR), a copolymer of acrylonitrile and butadiene (NBR), carboxymethyl cellulose (CMC), or ethylene propylene diene terpolymer. The method for forming the positive electrode mixture layer is not particularly limited, and examples include a method of press-molding the positive electrode mixture powder, or a method of adding the positive electrode mixture powder to a solvent to form a slurry, and then collecting the positive electrode mixture. Preferred methods include applying the coating to an aluminum foil of an electric body, a stainless steel lath plate, etc., drying it, and molding it under pressure.

Negative electrode active materials for lithium secondary batteries include lithium metal, lithium alloys, and carbon materials capable of intercalating and deintercalating lithium (e.g., easily graphitizable carbon, and (002) plane spacing of 0.37 nm (nanometer)). ) or more non-graphitizable carbon, graphite with a (002) plane spacing of 0.34 nm or less], tin (single substance), tin compounds, silicon (single substance), silicon compounds, Li ₄ Ti ₅ O ₁₂ , etc. Lithium titanate compounds and the like can be used alone or in combination of two or more.
Among these, it is more preferable to use highly crystalline carbon materials such as artificial graphite and natural graphite in terms of lithium ion absorption and desorption ability, and the interplanar spacing (d ₀₀₂ ) of the lattice plane (002) is 0. It is particularly preferred to use a carbon material with a graphite-type crystal structure of 340 nm or less, in particular 0.335 to 0.337 nm.
Further, it is preferable that the highly crystalline carbon material (core material) is coated with a carbon material that is lower in crystallinity than the core material because the properties will be even better. The crystallinity of the coating carbon material can be confirmed by TEM.

Metal compounds capable of intercalating and deintercalating lithium as negative electrode active materials include Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, and Cu. Examples include compounds containing at least one metal element such as , Zn, Ag, Mg, Sr, and Ba. These metal compounds may be used in any form such as a simple substance, an alloy, an oxide, a nitride, a sulfide, a boride, an alloy with lithium, etc.; This is preferable because it can increase the capacity. Among these, those containing at least one element selected from Si, Ge, and Sn are preferable, and those containing at least one element selected from Si and Sn are particularly preferable because they can increase the capacity of the battery.

Other examples include metal oxides containing titanium atoms that can insert and release lithium as negative electrode active materials. These titanium-containing metal oxides have small expansion and contraction during charging and discharging and are flame retardant, so they are preferable in terms of improving battery safety. Among these, those containing Li ₄ Ti ₅ O ₁₂ are preferred because they improve battery characteristics.

[Negative electrode active material layer]
The negative electrode active material layer contains at least a negative electrode active material and a solid electrolyte, and may also contain the same conductive agent and binder as those used in producing the positive electrode.
The method for forming the negative electrode mixture layer is not particularly limited, and examples include a method of pressure molding the negative electrode mixture powder, a method of adding the negative electrode mixture powder to a solvent to form a slurry, and then collecting the negative electrode mixture. Preferred examples include a method in which it is applied to a copper foil or the like of an electric body, dried, and pressure-molded.

The surfaces of the positive electrode active material and the negative electrode active material may be coated with another metal oxide. Examples of the surface coating agent include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specifically, Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₂ O ₅ , LiTaO ₃ , LiNbO ₃ , LiAlO ₂ , Li ₂ ZrO ₃ , Li ₂ WO ₄ , Li ₂ TiO ₃ , Li ₂ B ₄ O ₇ , Examples include Li ₃ PO ₄ , Li ₂ MoO ₄ , Li ₃ BO ₃ , LiBO ₂ , Li ₂ CO ₃ , Li ₂ SiO ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , B ₂ O ₃ etc. .

There are no particular limitations on the structure of the lithium battery, and coin-type batteries, cylindrical batteries, prismatic batteries, laminate batteries, etc. having a single-layer or multi-layer separator can be applied.

[Example 1]
[Synthesis of sulfide-based inorganic solid electrolyte]
In a glove box under an argon atmosphere, lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ) were weighed so that the molar ratio of Li ₂ S:P ₂ S ₅ =75:25, A raw material composition was obtained by mixing in an agate mortar.
Next, zirconia balls (diameter 5 mm, 160 g) and 2 g of the obtained raw material composition were placed in an 80 mL zirconia pot, and the container was sealed under an argon atmosphere. This pot was set in a planetary ball mill, and mechanical milling was performed at a rotation speed of 510 rpm for 16 hours to obtain a yellow powder of sulfide-based inorganic solid electrolyte (LPS glass).

[Preparation of sulfide solid electrolyte composition]
A zirconia ball (diameter 4 mm, 20 g) was placed in an 80 mL zirconia pot, and the sulfide solid electrolyte (LPS glass) synthesized above and methyl pivalate (MTMA) as a carboxylic acid ester compound were added to LPS glass: MTMA = 96: It was added so that the volume ratio was 4. Thereafter, this pot was set in a planetary ball mill, and stirring was continued for 15 minutes at a rotation speed of 200 rpm to prepare the sulfide-based solid electrolyte composition of Example 1.

[Examples 2 to 3, Comparative Example 1, Reference Example 1]
The sulfide-based solid electrolyte composition of Example 1 was prepared in the same manner as the sulfide-based solid electrolyte composition of Example 1, except that the compounds shown in Table 1 below were used as the carboxylic acid ester compounds, and the blended amounts were changed to the amounts shown in Table 1. The sulfide-based solid electrolyte composition described in 1 was prepared.

[Measurement of physical properties of sulfide-based solid electrolyte composition]
100 mg of each of the above sulfide-based solid electrolyte compositions was weighed out, and these samples were pressed at room temperature (25° C.) for 10 minutes at varying pressing pressures to produce pellets. Note that the press pressure was as shown in Table 1.
<Ionic conductivity measurement>
The conductivity of the solid electrolyte layer was calculated by forming thin gold films on the upper and lower surfaces of the pellets by sputtering and measuring the impedance. The ionic conductivity was calculated from the thickness of the solid electrolyte layer and the resistance value on the real axis of the Cole-Cole plot. The results are shown in Table 1.
<Evaluation of relative density>
The relative density was calculated using the following formula using the pellet density of LPS glass calculated from the volume of the above pellet and the mass of LPS glass contained in the pellet and the density calculated from the density (true density) of LPS glass. .
Relative density (%) = (LPS glass pellet density/LPS glass density (true density)) x 100
The results are shown in Table 1.

In Table 1 above, Examples 1 to 3 of the sulfide-based solid electrolyte compositions of the present invention have higher ionic conductivity than Comparative Example 1 even when molded by a low-pressure press of 180 MPa. Even when compared with Reference Example 1 in which LPS glass was molded under a pressure of 360 MPa), it can be seen that it has the same ionic conductivity despite the low-pressure pressing.
From the above results, by using the sulfide-based solid electrolyte composition of the present invention, it is possible to obtain a molded body with excellent ionic conductivity even when molded at low pressure, so that the battery manufacturing process can be simplified. Furthermore, since a continuous ion path can be formed over a long period of time without using a very strong restraint jig, it is expected to have excellent battery characteristics.

Claims (4)

A solid electrolyte composition containing an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table and a carboxylic acid ester compound represented by the following general formula (I),
A solid electrolyte composition, characterized in that the carboxylic acid ester compound is contained in a proportion of 1% by volume or more and 20% by volume or less based on the solid electrolyte composition.

(R ¹ to R ⁴ are each independent and represent an alkyl group having 1 to 12 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom.) The solid electrolyte composition according to claim 1 , wherein the inorganic solid electrolyte is a sulfide-based solid electrolyte. A molded body obtained by pressurizing a solid electrolyte composition, the molded body comprising the solid electrolyte composition according to claim 1 or 2 . An all-solid-state secondary battery comprising a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer, wherein at least one layer of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer is Or an all-solid-state secondary battery which is a layer containing the solid electrolyte composition of 2 .