KR102587960B1 - Methods of preparing sulfide-based solid electrolytes, sulfide-based solid electrolytes prepared therefrom, and solid state rechargable batteries containing the same - Google Patents

Abstract

A first step of obtaining a precursor by mixing at least Li ₂ S, P ₂ S ₅ and LiI as starting materials in a first solvent and a second step of reacting the precursor in a second solvent to obtain a sulfide-based solid electrolyte, , the first solvent contains a cyclic ether compound substituted or unsubstituted by an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms, and the second solvent is a sulfide-based solid containing an alkoxy group-substituted hydrocarbon. A method for producing an electrolyte is disclosed.

Description

Method for producing sulfide solid electrolyte, sulfide-based solid electrolyte produced thereby, and solid secondary battery containing the same {Methods of preparing sulfide-based solid electrolytes, sulfide-based solid electrolytes prepared therefrom, and solid state rechargable batteries containing the same}

The present invention relates to a method for producing a sulfide solid electrolyte using an organic solvent, a sulfide-based solid electrolyte produced thereby, and a solid secondary battery containing the same.

Lithium-ion secondary batteries (lithium-ion rechargeable batteries) have high energy density and are used for electric automobiles and portable information terminals. In order to improve the performance of these solid secondary batteries, research is being conducted on solid electrolytes with high ion conductivity and safety.

Lithium-ion secondary batteries using an electrolyte solution have had problems with performance degradation and stability, such as loss of capacity and deterioration of cycle characteristics, as intermediates of active materials generated during the charging and discharging process are dissolved in the electrolyte solution. On the other hand, lithium ion secondary batteries using a solid electrolyte (hereinafter referred to as solid secondary batteries) have higher safety compared to lithium ion secondary batteries using an electrolyte, and can be made lighter and more compact, and depending on their composition, the battery It is also possible to lengthen lifespan.

As a solid electrolyte for such solid secondary batteries, sulfide-based solid electrolytes with excellent ionic conductivity are attracting attention. Such sulfide-based solid electrolytes are generally manufactured by a solid-phase synthesis method using a mechanical milling method or the like (Patent Document 1). Additionally, a solution method for producing a sulfide-based solid electrolyte by mixing starting materials, such as Li ₂ S and P ₂ S ₅ in an organic solvent, has been proposed (Patent Document 2).

However, the solid-phase synthesis method using mechanical milling has the problem of not only the energy input during synthesis being very large, but also the synthesis time being long. Therefore, it is difficult to increase the scale of the process and also difficult to reduce the synthesis cost. On the other hand, the solution method requires less energy input during synthesis and has a shorter reaction time, making it possible to lower the synthesis cost while increasing the process scale. Therefore, there is a demand for a solution method that can produce a sulfide-based solid electrolyte with better properties. It continues.

[Patent Document 1] Japanese Patent Publication No. 2017-117753

[Patent Document 2] Japanese Patent Publication No. 2015-232965

In general, the ionic conductivity of sulfide-based solid electrolytes is relatively high, but it is easily dependent on temperature. If the temperature dependence of ionic conductivity is high, ionic conductivity may decrease in low temperature areas. In order to lower the temperature dependence of ionic conductivity, it is required to use a sulfide-based solid electrolyte with low activation energy.

Therefore, the purpose of the present invention is to provide a sulfide-based solid electrolyte with low activation energy and excellent ionic conductivity, a method for producing a sulfide-based solid electrolyte that can efficiently produce the same, a sulfide-based solid electrolyte resulting from the same, and a solid secondary battery using the same. do.

According to one aspect of the present invention, a first process of obtaining a precursor by mixing at least Li ₂ S, P ₂ S ₅ and LiI as starting materials in a first solvent; And a second step of reacting the precursor in a second solvent to obtain a sulfide-based solid electrolyte.

The first solvent includes a cyclic ether compound substituted or unsubstituted by an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms,

A method for producing a sulfide-based solid electrolyte is provided wherein the second solvent includes an alkoxy group-substituted hydrocarbon.

According to another aspect of the present invention, a sulfide-based solid electrolyte prepared by the method for producing the sulfide-based solid electrolyte is provided.

According to another aspect of the present invention, a solid secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte layer located between the positive electrode and the negative electrode, wherein the solid electrolyte layer is A solid secondary battery containing a sulfide solid electrolyte manufactured by the above-described manufacturing method is provided.

According to the present invention, a sulfide-based solid electrolyte with low activation energy and excellent ionic conductivity can be efficiently produced.

1 is a cross-sectional view schematically showing the layer structure of a solid secondary battery.
Figure 2 is a graph showing the powder X-ray diffraction spectra of the sulfide-based solid electrolytes of Examples 1 to 3 and Comparative Example 1.
Figure 3 is a graph showing the powder X-ray diffraction spectra of the sulfide-based solid electrolytes of Example 4, Comparative Example 2, and Comparative Example 3.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawings, components having substantially the same functional configuration are given the same reference numerals and redundant description is omitted.

[Method for producing sulfide-based solid electrolyte]

A method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention will be described.

A method for producing a sulfide-based solid electrolyte according to an embodiment includes a first step of obtaining a precursor by mixing at least Li ₂ S, P ₂ S ₅ and LiI in a first solvent, and reacting the precursor in a second solvent to produce a sulfide-based solid. A second process for obtaining an electrolyte may be included.

In this case, the first solvent may contain a cyclic ether compound substituted or unsubstituted by an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms, and the second solvent may contain a hydrocarbon substituted with an alkoxy group. there is.

It is unclear by what reaction path the sulfide-based solid electrolyte was formed in the above process, but the following reaction path is assumed. First, in the first step, Li ₂ S and P ₂ S ₅ react in the first solvent to produce a solvate such as Li ₃ PS ₄ (for example, Li ₃ PS _4· 3THF solvate), and in the second step, It may be thought that this solvate and the halogen component react to form crystals of a sulfide-based solid electrolyte, but this route is not certain.

(1st process)

In the first process, starting materials for the sulfide-based solid electrolyte are mixed and processed in a first solvent to obtain a precursor.

Starting materials for the sulfide-based solid electrolyte may include at least Li ₂ S, P ₂ S ₅ and LiI. Additionally, the starting raw material may further include LiBr and/or LiCl. By performing synthesis using these starting materials, a sulfide-based solid electrolyte with low activation energy and high ionic conductivity can be obtained.

The ratio of Li ₂ S, P ₂ S ₅ and LiI is not particularly limited and can be changed depending on the composition of the sulfide-based solid electrolyte to be manufactured. For example, in relation to this process, Li ₂ S and P ₂ S ₅ react to produce compounds such as Li ₃ PS ₄ , Li ₄ P ₂ S ₆ , Li ₄ P ₂ S ₇ , and Li ₇ P ₃ S ₁₁ . can do. Therefore, the ratio of Li ₂ S and P ₂ S ₅ can be appropriately changed to obtain the desired compound. For example, among the above compounds, the ratio of Li ₂ S and P ₂ S ₅ can be set to produce Li ₃ PS ₄ . At this time, since the molar ratio of the components containing the starting raw materials is the same as the molar ratio of the sulfide-containing components obtained therefrom, when preparing the sulfide solid electrolyte with the desired composition ratio, the mixing ratio of the starting raw materials is adjusted to adjust the molar ratio of the components containing the starting raw materials. Just make it the same as the composition ratio of sulfide.

Meanwhile _, the ratio _{of Li} . As a result, it becomes possible to obtain almost the same properties as the solid electrolyte material that can be obtained by the solid-phase method using the solution method.

In particular, a sulfide-based solid electrolyte of the formula (1) below can be obtained.

(1-x)LiI·xLiBr·2Li₃P.S.₄ (One)

Meanwhile, GeS ₂ , P ₂ S ₃ , P ₂ O ₅ , SiO ₂ , B ₂ S ₃ , Al ₂ S ₃ , B ₂ O ₃ or one or more types thereof may be further added as starting materials in the first organic solvent. You can. As a result, the ionic conductivity of the sulfide-based solid electrolyte can be further improved. When the starting raw material contains such compounds, the sulfide-based solid electrolyte may be, for example, Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , Li ₂ SP ₂ S ₅ -SiS ₂ , or Li ₂ SP ₂ S ₅ -GeS ₂ and the like may be included as components.

Additionally, as described above, the first solvent may include a cyclic ether compound substituted or unsubstituted by an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms. By employing this first solvent, the reaction between Li ₂ S and P ₂ S ₅ can proceed very smoothly while preventing decomposition of the raw materials.

The cyclic ether skeleton constituting this cyclic ether compound is not particularly limited, but may be a cyclic ether with 4 to 10 carbon atoms, and specifically, for example, may be a cyclic ether with 4 to 6 carbon atoms. The skeleton of this cyclic ether may specifically include an oxetane skeleton, a tetrahydrofuran skeleton, or a tetrahydropyran skeleton.

Additionally, the substituent that can be substituted on the cyclic ether skeleton may be an alkyl group with 1 to 3 carbon atoms, or an alkoxy group with 1 to 3 carbon atoms, as described above. The substituent may specifically include a methyl group, ethyl group, n-propyl group, iso-propyl group, methoxy group, ethoxy group, n-propoxy group, or iso-propoxy group.

Cyclic ether compounds may include, for example, tetrahydrofuran, oxetane, tetrahydropyran, etc.

In addition, the concentration of the starting material (substrate concentration) in the mixture containing the first solvent and the starting material may be 1 to 10 mass%, and specifically, for example, may be 2 to 8 mass%.

In addition, the reaction time (mixing time) of the raw material and the first solvent in this first process is not particularly limited, but may be 0.5 to 48 hours, specifically, for example, 1 hour to 24 hours. As a result, the reaction of the raw materials can sufficiently proceed in this first process.

Additionally, the mixing temperature of the raw material and the first solvent in this first process is not particularly limited, but may be 30°C to 80°C, and specifically, for example, may be 35°C to 60°C. As a result, the reaction of the raw materials can sufficiently proceed in this process.

Additionally, the atmosphere of this first process may be an inert gas atmosphere such as argon or nitrogen.

Additionally, in relation to this first process, stirring may be performed to ensure a uniform reaction when mixing the raw materials.

According to the embodiment described above, a reaction solution containing a precursor of a sulfide-based solid electrolyte can be obtained. Meanwhile, the first solvent in the obtained reaction solution can be removed by an appropriate method. For example, the first solvent can be removed by methods such as reduced pressure removal using a rotary evaporator, vacuum drying, etc., or filtration.

(2nd process)

In the second process, a sulfide-based solid electrolyte can be obtained by reacting the precursor obtained in the first process in a second solvent.

At this time, the second solvent may include a hydrocarbon substituted with an alkoxy group. The precursor generated in the first process may further react in the second solvent to produce a sulfide-based solid electrolyte.

The hydrocarbon skeleton constituting the hydrocarbon substituted with an alkoxy group is a chain hydrocarbon having 1 to 10 carbon atoms, specifically, for example, 2 to 8 carbon atoms, or a cyclic hydrocarbon having 3 to 10 carbon atoms, specifically, for example, 3 to 8 carbon atoms. May contain hydrocarbons.

Chain hydrocarbons can be straight-chain or branched alkanes, such as methane, ethane, propane, 2-methyl propane, 2, 2-dimethyl propane, butane, 2-methyl butane, 2, 2-dimethyl butane, 2, 3-dimethyl butane, pentane, 2-methyl pentane, 2, 2-dimethyl pentane, 2, 3-dimethyl pentane, 2, 4-dimethyl pentane, 3-ethyl pentane, hexane, heptane, octane, nonane, or decane. It may include etc.

Cyclic hydrocarbons may include, for example, cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, or compounds substituted with alkyl groups such as methyl or ethyl groups. You can. Additionally, the number of substitutions for a compound substituted with an alkyl group is not particularly limited, but may be substituted with 1 or 2 alkyl groups.

The alkoxy group constituting the hydrocarbon substituted with an alkoxy group may include, for example, a straight-chain or branched alkoxy group having 1 or more carbon atoms. Such alkoxy groups may include, for example, methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group, sec-butoxy group, iso-butoxy group, or tert-butoxy group. . The alkoxy group may be, more specifically, a methoxy group, an ethoxy group, or an iso-propoxy group. In addition, among hydrocarbons substituted with alkoxy groups, the number of alkoxy groups may be 1 to 8, specifically, for example, 1 to 6.

Specific examples of hydrocarbons substituted with alkoxy groups include dimethyl ether, methyl ethyl ether, diethyl ether, methyl n-propyl ether, ethyl n-propyl ether, di-n-propyl ether, methyl iso-propyl ether, ethyl iso-propyl ether. , di-iso-propyl ether, n-propyl iso-propyl ether, methyl n-butyl ether, ethyl n-butyl ether, n-propyl n-butyl ether, iso-propyl n-butyl ether, methyl sec-butyl ether, ethyl sec-butyl ether, n-propyl sec-butyl ether, iso-propyl sec-butyl ether, methyl iso-butyl ether, ethyl iso-butyl ether, n-propyl iso-butyl ether, iso-propyl iso-butyl ether, Methyl tert-butyl ether, ethyl tert-butyl ether, n-propyl tert-butyl ether, iso-propyl tert-butyl ether, di-n-butyl ether, di-sec-butyl ether, di-iso-butyl ether, sec -butyl n-butyl ether, iso-butyl n-butyl ether, tert-butyl n-butyl ether, iso-butyl sec-butyl ether, tert-butyl sec-butyl ether, or tert-butyl iso-butyl ether,

Dimethoxy ethane, diethoxy ethane, methoxy ethoxy ethane, 1,3-dimethoxy propane, 1,3-diethoxy propane, 1-methoxy 3-ethoxy propane, 1,2-dimethoxy propane, 1, 2-diethoxy propane, 1-methoxy 2-ethoxy propane, or 1-ethoxy 2-methoxy propane,

Cyclopropyl methyl ether, cyclopropyl ethyl ether, cyclobutyl methyl ether, cyclobutyl ethyl ether, cyclobutyl n-propyl ether, cyclobutyl iso-propyl ether, cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl n-propyl ether , Cyclopentyl iso-propyl ether, Cyclopentyl n-butyl ether, Cyclopentyl iso-butyl ether, Cyclopentyl sec-butyl ether, Cyclopentyl tert-butyl ether, Cyclohexyl methyl ether, Cyclohexyl ethyl ether, Cyclohexyl n- It may include propyl ether, cyclohexyl iso-propyl ether, cyclohexyl n-butyl ether, cyclohexyl iso-butyl ether, cyclohexyl sec-butyl ether, or cyclohexyl tert-butyl ether.

As a more specific example, the second solvent may include dimethoxy ethane, diethoxy ethane, diethyl ether, di-iso-propyl ether, cyclopentylmethyl ether, or one or more types thereof.

Additionally, the concentration of the precursor (substrate concentration) in the mixture containing the second solvent and the precursor may be 1 to 10 mass%, and specifically, for example, may be 2 to 8 mass%.

The second process can be performed, for example, by reacting a mixed solution of a precursor and a second solvent for a predetermined time and then removing the second solvent from the reaction solution. The reaction time (mixing time) of the precursor and the second solvent in this second process is not particularly limited, but may be 0.5 to 48 hours, and specifically, for example, 1 to 24 hours. As a result, the reaction of the raw materials can sufficiently proceed in the second process.

Additionally, the mixing temperature of the precursor and the second solvent in this second process is not particularly limited, but may be 80°C to 200°C, and specifically, for example, may be 100°C to 180°C. As a result, the reaction of the precursor can sufficiently proceed in this process.

Additionally, the atmosphere when mixing the precursor and the second solvent may be an inert gas atmosphere, for example, an argon atmosphere or a nitrogen atmosphere to suppress oxidation of the solid electrolyte material.

Additionally, when mixing the precursors in the second process, stirring may be performed to ensure a uniform reaction.

Additionally, the mixed solution of the precursor and the second solvent may be heated in the second process. As a result, the reaction of the precursor can be further promoted and the crystal structure of the sulfide-based solid electrolyte obtained as a result of the reaction can be controlled.

At this time, the heating temperature is not particularly limited, but may be 100°C to 200°C, and specifically, for example, may be 100°C to 180°C. Meanwhile, the heating time is not particularly limited, but may be 30 minutes to 300 minutes, specifically, for example, 60 minutes to 300 minutes.

Additionally, heating of the mixture in the second step can be performed under a reduced pressure atmosphere. This makes it possible to remove the second solvent along with heating the precursor. The pressure at the time of decompression may be 0.01 MPa to 2 MPa, specifically, for example, 0.1 MPa to 1 MPa.

Optionally, the heating in the second process can be performed after separating the majority of the second solvent from the mixture. As a result, it is possible to prevent boiling of the second solvent and at the same time, control of the pressure within the reaction system can be made easier. Separation of the second solvent can be performed, for example, by filtration or the like.

A sulfide-based solid electrolyte can be obtained by performing the first and second processes described above. In addition, the obtained sulfide-based solid electrolyte can be additionally washed and dried.

According to the method for producing a sulfide-based solid electrolyte according to the present embodiment, a sulfide-based solid electrolyte to which a halogen component is added can be efficiently produced by a solution method. The sulfide-based solid electrolyte obtained by the production method related to the present embodiment has excellent ionic conductivity and relatively low activation energy.

In addition, by the above-described production method, for example, a powder of a sulfide-based solid electrolyte with a particle diameter of 1 μm or less can be obtained. As a result, the grinding process or classification process required in the solid phase synthesis method can be omitted. Therefore, the method for producing a sulfide-based solid electrolyte according to this embodiment is advantageous over the case of employing a solid-phase synthesis method, not only from the viewpoint of the energy required for synthesis of the sulfide-based solid electrolyte, but also from the viewpoint of simplicity of post-synthesis processing.

[Characteristics of sulfide-based solid electrolyte]

The sulfide-based solid electrolyte prepared according to the method for producing a sulfide-based solid electrolyte related to the present embodiment has a characteristic crystal form. Specifically, the sulfide-based solid electrolyte manufactured according to the manufacturing method related to this embodiment has 2θ of 19.9 ± 0.5° and 23.5 ± 1 in the X-ray diffraction spectrum measured using Cu-Kα line. It has peaks at positions of 0.5° and 29.3±0.5°, respectively. At this time, when the intensity of the peak at the 19.9 ± 0.5° position is IA and the intensity of the peak at the 17.0 ± 0.5° position is IB, IB/IA may be less than 0.50. From the positions of these peaks and the relative ratio of peak intensities, it can be seen that the sulfide-based solid electrolyte related to this embodiment has a characteristic crystal form.

In addition, the sulfide-based solid electrolyte that can be obtained according to the method for producing a sulfide-based solid electrolyte according to the present embodiment has, for example, 1.0 × 10 ^-5 S/cm or more, or 5.0 × 10 ^-4 S/cm at 25°C. It has an ionic conductivity of more than cm. For example, the sulfide-based solid electrolyte may have an ionic conductivity of 1.0×10 ^-5 S/cm to 1.0×10 ^-2 S/cm at 25°C.

Furthermore, the activation energy of the sulfide-based solid electrolyte obtained according to the method for producing the sulfide-based solid electrolyte according to the present embodiment may be 40 kJ/mol or less, and specifically, for example, 35 kJ/mol or less. More specifically, the activation energy of the sulfide-based solid electrolyte may be 30 kJ/mol to 40 kJ/mol. This activation energy reduces the temperature dependence of ionic conductivity, thereby preventing a decrease in ionic conductivity, especially in low-temperature regions.

Meanwhile, measurement of ionic conductivity and calculation of activation energy of a sulfide-based solid electrolyte can be performed by the following methods. Pellets are produced by pressing the pulverized sulfide-based solid electrolyte using an agate mortar (pressure 400 MPa/cm ² ). Ion conductivity can be obtained by attaching In foil (50㎛ thickness) to both sides of this pellet and measuring the alternating current impedance of the pellet. Additionally, activation energy can be calculated using the Arrhenius equation based on the measured ionic conductivity.

σ = (σ ₀ /T)exp(-Ea/kT)

σ is the ionic conductivity, σ ₀ is the pre-exponential factor, T is the temperature, Ea is the activation energy for ionic conduction, and k is the Boltzmann constant.

[Solid secondary battery]

Hereinafter, a solid secondary battery according to an exemplary embodiment of the present invention will be described in detail. 1 is a cross-sectional view schematically showing the layer structure of a solid secondary battery according to an embodiment. As shown in FIG. 1, the solid secondary battery 1 according to one embodiment includes an anode layer 10, a cathode layer 20, and a solid electrolyte layer ( 30). In addition, in the solid secondary battery 1, for at least one of the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, for example, the positive electrode layer 10 and the solid electrolyte layer 30 ) The sulfide-based solid electrolyte described above can be used.

(anode layer)

The positive electrode layer 10 may include a positive electrode current collector 11 and a positive electrode active material layer 12.

The positive electrode current collector 11 is made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), It may include plates or foils made of zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. Optionally, the positive electrode current collector 11 may be omitted. Additionally, the positive electrode current collector 11 may be connected to wiring through a terminal not shown.

The positive electrode active material layer 12 may include a positive electrode active material and a solid electrolyte. Additionally, the solid electrolyte included in the positive electrode active material layer 12 may be the same as or different from the solid electrolyte included in the solid electrolyte layer 30. Details of the solid electrolyte are described in detail in the section on the solid electrolyte layer 30.

The positive electrode active material may be a positive electrode active material capable of reversibly inserting and releasing lithium ions. The positive electrode active material is, for example, lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide ( It can be formed using lithium salts such as NCM), lithium manganese oxide (LMO), lithium iron phosphate (LFP), nickel sulfide, copper sulfide, sulfur, iron oxide, or vanadium oxide. . These positive electrode active materials can be used individually or in combination of two or more types.

Among the positive electrode active materials exemplified above, the positive electrode active material may be, in particular, a lithium salt of a transition metal oxide having a layered rock salt type structure. In this specification, “layered” means a thin sheet shape, and “rock salt-type structure” is a sodium chloride-type structure, which is a type of crystal structure, and the face-centered cubic lattice formed by each of the cations and anions is a unit lattice. This means that only 1/2 of the corners are misaligned. The lithium salt of the transition metal oxide having such a layered rock salt structure is, for example, LiNi _x Co _y Al _z O ₂ (NCA), or LiNi _x Co _y Mn _z O ₂ (NCM) (0 < x < 1, It may include a lithium salt of a ternary transition metal oxide such as 0<y<1, 0<z<1, on the other hand, x+y+z=1). When the positive electrode active material includes a lithium salt of a ternary transition metal oxide having a layered rock salt-type structure as described above, the energy density and thermal stability of the solid secondary battery 1 can be improved.

The positive electrode active material may be covered by a coating layer. The coating layer of this embodiment may be a known coating layer for the positive electrode active material of a solid secondary battery. The coating layer may include, for example, Li ₂ O-ZrO ₂ .

On the other hand, when the positive electrode active material is formed of a lithium salt of a ternary transition metal oxide containing nickel, such as NCA or NCM, metal elution from the positive electrode active material in a charged state is prevented by increasing the capacity density of the solid secondary battery 1. It can be reduced. As a result, the solid secondary battery 1 according to the present embodiment can improve long-term reliability and cycle characteristics in a charged state.

Here, the shape of the positive electrode active material may include, for example, a particle shape such as a spherical shape or an oval shape. Additionally, the particle diameter of the positive electrode active material is not particularly limited and may be within a range applicable to the positive electrode active material of a conventional solid secondary battery. Additionally, the content of the positive electrode active material in the positive electrode active material layer 12 is not particularly limited, and may be within a range applicable to the positive electrode layer of a conventional solid secondary battery.

In addition to the positive electrode active material and solid electrolyte described above, the positive electrode active material layer 12 may contain, for example, conducting agents, binders, fillers, dispersing agents, and ion conducting agents. It may further contain additives such as agents).

Conductive agents that can be mixed into the positive electrode active material layer 12 may include, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, etc. In addition, binders that can be mixed in the positive electrode active material layer 12 may include, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. You can. In addition, fillers, dispersants, ion conductive agents, etc. that can be mixed in the positive electrode layer 10 can be known materials that are generally used in electrodes of solid secondary batteries.

(Cathode layer)

The negative electrode layer 20 may include a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 is made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), It may include plates or foils made of zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. Optionally, the negative electrode current collector 21 may be omitted. Additionally, the negative electrode current collector 21 may be connected to wiring through a terminal not shown.

The negative electrode active material layer 22 may include metallic lithium or a lithium-containing alloy. That is, the negative electrode active material layer 22 may be composed of only metallic lithium or may be a lithium-containing alloy of metallic lithium and other metallic active materials (indium (In), aluminum (Al), tin (Sn), silicon (Si), etc.). . For example, when the negative electrode active material layer 22 is composed only of metallic lithium, that is, when it is a metallic lithium layer, the energy density of the solid secondary battery 1 can thereby be improved.

(Solid electrolyte layer)

The solid electrolyte layer 30 is disposed between the anode layer 10 and the cathode layer 20 and may include a solid electrolyte.

The solid electrolyte may include a sulfide-based solid electrolyte prepared according to the manufacturing method related to this embodiment.

Additionally, the solid electrolyte may further include a known sulfide-based solid electrolyte. Sulfide-based solid electrolyte materials include, for example, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX (X is a halogen element, for example I, Cl), Li ₂ SP ₂ S ₅ -Li ₂ O , Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B2S3-LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (m, n are integers, Z is either Ge, Zn or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _p MO _q (p, q are integers, M is one of P, Si, Ge, B, Al, Ga, or In), etc.

Additionally, the solid electrolyte layer 30 may further include a binder. The binder included in the solid electrolyte layer 30 may include, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. . The binder in the solid electrolyte layer 30 may be the same as or different from the binder in the positive electrode active material layer 12.

[Method for manufacturing solid secondary battery]

Next, a method for manufacturing the solid secondary battery 1 according to one embodiment will be described. The solid secondary battery 1 related to the present embodiment produces a sulfide-based solid electrolyte by the method described above, and then uses the sulfide-based solid electrolyte to form, for example, a positive electrode layer 10 and a negative electrode layer 20. ), it can be manufactured by manufacturing the solid electrolyte layer 30 or its constituent materials separately and then stacking each of the above layers.

(Manufacture of sulfide-based solid electrolyte)

In relation to the manufacturing method of the solid secondary battery related to this embodiment, the sulfide-based solid electrolyte is manufactured by the above-described manufacturing method of the sulfide-based solid electrolyte. Therefore, the manufacturing method of the solid secondary battery related to this embodiment may include the above-described first process and second process.

(Production of solid electrolyte layer)

The solid electrolyte layer 30 can be manufactured using the sulfide-based solid electrolyte manufactured according to this embodiment.

The sulfide-based solid electrolyte prepared according to this embodiment can be manufactured into the solid electrolyte layer 30 using, for example, aerosol deposition, cold spray, sputter, etc. there is. Alternatively, the solid electrolyte layer 30 can be manufactured by pressing sulfide-based solid electrolyte powder. Alternatively, the solid electrolyte layer 30 can be manufactured by mixing a sulfide-based solid electrolyte, a solvent, and a binder, applying, drying, and pressing.

(Production of anode layer)

The anode layer 10 can be manufactured by, for example, the following method. The positive electrode active material, the sulfide-based solid electrolyte prepared by the above-described method, and various additives are mixed and added to a solvent such as water or an organic solvent to form a slurry or paste. The positive electrode layer 10 can then be obtained by applying the formed slurry or paste to the current collector, drying it, and then rolling it. Alternatively, the positive electrode layer 10 can be manufactured by pressurizing and rolling a mixture of a sulfide-based solid electrolyte, a positive electrode active material, and various additives.

(Production of cathode layer)

The cathode layer 20 can be manufactured in the same way as the anode layer 10. Specifically, the materials constituting the negative electrode active material layer 22, such as a negative electrode active material, are mixed and added to a solvent such as water or an organic solvent to form a slurry or paste. The negative electrode layer 20 can then be obtained by applying the formed slurry or paste to a current collector, drying it, and then rolling it. Alternatively, the negative electrode layer 20 can be obtained by applying a negative electrode active material to the negative electrode current collector 31 by sputtering to form the negative electrode active material layer 22.

(Manufacture of solid secondary battery)

The solid secondary battery 1 according to the present embodiment can be manufactured by laminating the solid electrolyte layer 30, the positive electrode layer 10, and the negative electrode layer 20 produced by the above-described method. Specifically, the solid electrolyte layer 30, the anode layer 10, and the cathode layer 20 are stacked and pressed so that the solid electrolyte layer 30 is disposed between the anode layer 10 and the cathode layer 20. The solid secondary battery 1 related to this embodiment can be manufactured.

As described above, the sulfide-based solid electrolyte can be produced by a solution method by dividing the production step of the sulfide-based solid electrolyte into two stages and using a specific solvent in each step. The sulfide-based solid electrolyte thus obtained has a characteristic crystal structure, has a relatively low activation energy, and has a relatively high ionic conductivity.

[Example]

Hereinafter, the manufacturing method of the sulfide-based solid electrolyte related to the embodiment will be described in detail with reference to Examples and Comparative Examples. In addition, the examples shown below are provided for illustrative purposes only, and the present invention is not limited to the examples below.

(Example 1)

Li ₇ P ₂ using LiI (99.9% purity, Aldreich), Li ₂ S (99.9% purity, Mitsuwa Chemicals), and P ₂ S ₅ (99% purity, Aldrich) in a glove box under Ar atmosphere. 1.5 g of powder was prepared to have the composition of S ₈ I.

The powder prepared above was mixed with 40 ml of tetrahydrofuran (THF) as the first organic solvent in a beaker with a volume of 50 ml in an Ar atmosphere, and stirred at 40°C overnight to allow reaction. After completion of the reaction, the first organic solvent was removed at about 40°C using a rotary evaporator to obtain a precursor (first process).

Next, this precursor was stirred in 100 ml of DEE (diethyl ether) as a second organic solvent for 2 hours in an Ar atmosphere and at a temperature of 150°C. After stirring, the remaining precursor powder was vacuum dried at 150°C for 1 hour to completely remove the remaining second solvent. The powder remaining after vacuum drying was cooled to room temperature and then recovered to obtain the sulfide-based solid electrolyte of this example (second process).

The obtained sulfide-based solid electrolyte was evaluated by measuring ionic conductivity, calculating activation energy, and performing a powder X-ray diffraction test.

Specifically, the powder of the sulfide-based solid electrolyte prepared in this example was placed in a mold with a diameter of 10 mm and pressed at a pressure of 350 mPa to form a pellet. A thin film of indium (In) was coated on both sides of this pellet to create a sample for measuring ionic conductivity. For this sample, the ionic conductivity was measured at 25°C using AUTOLAB PGSTAT30 (Metrohm Autolab). Furthermore, the ionic conductivity was measured in a temperature range from 17°C to 140°C, and the activation energy was calculated according to the Arrhenius equation.

The ionic conductivity obtained from the above measurements was 6.9×10 ^-4 S/cm at 25°C, and the activation energy was 35.0 kJ/mol.

The powder X-ray diffraction spectrum was measured for the powder of the sulfide-based solid electrolyte of Example 1 using a powder .

As shown in Figure 2, clear peaks were observed at 2θ=19.9° and 2θ=23.5°. Meanwhile, the peak at 2θ = 29.3° cannot be clearly confirmed in FIG. 2 because its signal intensity is weak, but as a result of separate analysis, it was confirmed that it exists in the same powder X-ray diffraction spectrum. When the diffraction intensity of the peak at 2θ = 19.9° was set to IA and the diffraction intensity of the peak at 2θ = 17.0 ± 0.5° was set to IB, the value of IB/IA was less than 0.5°. Meanwhile, in the graph of FIG. 2, the peak indicated by a triangle is considered to be a peak resulting from the LiBr phase, and the peak indicated by a circle is considered to be a peak resulting from a phase having high ionic conductivity.

These material evaluation results suggested that a specific crystalline phase existed in the sulfide-based solid electrolyte of Example 1.

(Example 2)

Using the same method as Example 1, sulfide-based solid electrolyte powder was prepared to have a composition of LI ₇ P ₂ S ₈ I _0.67 Br _0.33 .

Regarding the sulfide-based solid electrolyte powder of Example 2, the material was evaluated by measuring ion conductivity, calculating activation energy, and measuring powder X-ray diffraction spectrum, as in Example 1, and the powder X-ray diffraction spectrum was is shown in Figure 2.

As a result of ionic conductivity measurement, the ionic conductivity of the sulfide-based solid electrolyte of Example 2 was 1.1Х10 ^-3 S/cm at 25°C, and the activation energy was 33.2 kJ/mol. Additionally, as shown in Figure 2, clear peaks were observed for 2θ = 19.9°, 23.5°, and 29.3° in the powder X-ray diffraction spectrum for the sulfide-based solid electrolyte of Example 2. On the other hand, when the diffraction intensity of the peak at 2θ = 19.9° was set to IA and the diffraction intensity of the peak at 2θ = 17.0 ± 0.5° was set to IB, the value of IB/IA was less than 0.50.

These material evaluation results suggested that a specific crystalline phase existed in the sulfide-based solid electrolyte of Example 2.

[Example 3]

Using the same method as Example 1, sulfide-based solid electrolyte powder was prepared to have a composition of LI ₇ P ₂ S ₈ I _0.5 Br _0.5 .

Regarding the sulfide-based solid electrolyte powder of Example 3, the material was evaluated by measuring ionic conductivity, calculating activation energy, and measuring powder X-ray diffraction spectrum as in Example 1, and the powder X-ray diffraction spectrum was is shown in Figure 2.

As a result of ionic conductivity measurement, the ionic conductivity of the sulfide-based solid electrolyte of Example 3 was 2.1Х10 ^-3 S/cm at 25°C, and the activation energy was 33.6 kJ/mol. Additionally, as shown in Figure 2, clear peaks were observed for 2θ = 19.9°, 23.5°, and 29.3° in the powder X-ray diffraction spectrum for the sulfide-based solid electrolyte of Example 3. On the other hand, when the diffraction intensity of the peak at 2θ = 19.9° was set to IA and the diffraction intensity of the peak at 2θ = 17.0 ± 0.5° was set to IB, the value of IB/IA was less than 0.50.

These material evaluation results suggested that a specific crystalline phase existed in the sulfide-based solid electrolyte of Example 3.

[Example 4]

In the second process for producing sulfide-based solid electrolyte powder, the same method as Example 1 was used, except that dimethoxyethane was used as the second organic solvent, so that the composition was LI ₇ P ₂ S ₈ I _0.5 Br _0.5 . Sulfide-based solid electrolyte powder was prepared.

Regarding the sulfide-based solid electrolyte powder of Example 4, the material was evaluated by measuring ionic conductivity, calculating activation energy, and measuring powder X-ray diffraction spectrum, as in Example 1, and the powder X-ray diffraction spectrum was is shown in Figure 3.

As a result of ionic conductivity measurement, the ionic conductivity of the sulfide-based solid electrolyte of Example 4 was 2.6Х10 ^-4 S/cm at 25°C, and the activation energy was 35.0 kJ/mol. Additionally, as shown in Figure 3, clear peaks were observed for 2θ = 19.9°, 23.5°, and 29.3° in the powder X-ray diffraction spectrum for the sulfide-based solid electrolyte of Example 4. On the other hand, when the diffraction intensity of the peak at 2θ = 19.9° was set to IA and the diffraction intensity of the peak at 2θ = 17.0 ± 0.5° was set to IB, the value of IB/IA was less than 0.50.

These material evaluation results suggested that a specific crystalline phase existed in the sulfide-based solid electrolyte of Example 4.

[Comparative Example 1]

Using the same method as Example 1, LI ₇ P ₂ S ₈ Br A sulfide-based solid electrolyte powder was prepared to have the composition.

For the sulfide-based solid electrolyte powder of Comparative Example 1, the material was evaluated by measuring ion conductivity, calculating activation energy, and measuring powder X-ray diffraction spectrum as in Example 1, and the powder X-ray diffraction spectrum was is shown in Figure 3.

As a result of ionic conductivity measurement, the ionic conductivity of the sulfide-based solid electrolyte of Comparative Example 1 was 3.7Х10 ^-4 S/cm at 25°C, and the activation energy was 35.7 kJ/mol. In addition, clear peaks were observed at 2θ = 19.9° and 29.3° in the powder On the other hand, when the diffraction intensity of the peak at 2θ = 19.9° was set to IA and the diffraction intensity of the peak at 2θ = 17.0 ± 0.5° was set to IB, the value of IB/IA was less than 0.50.

From these material evaluation results, it was suggested that the specific crystalline phase suggested in the sulfide-based solid electrolytes of Examples 1 to 4 did not exist in the sulfide-based solid electrolyte of Comparative Example 1.

[Comparative Example 2]

A sulfide-based solid electrolyte powder was prepared to have the same composition as Comparative Example 1 using the same method as Comparative Example 1, except that N-dimethylformamide was used as the second organic solvent in the second process for producing sulfide-based solid electrolyte powder. was manufactured.

Regarding the sulfide-based solid electrolyte powder of Comparative Example 2, the material was evaluated by measuring ion conductivity, calculating activation energy, and measuring powder X-ray diffraction spectrum, as in Comparative Example 1, and the powder X-ray diffraction spectrum was is shown in Figure 3.

As a result of ionic conductivity measurement, the ionic conductivity of the sulfide-based solid electrolyte of Comparative Example 2 was 5.6Х10 ^-8 S/cm at 25°C. In addition, as shown in FIG. 3, no clear peaks were observed for 2θ = 19.9° and 23.5° in the powder X-ray diffraction spectrum for the sulfide-based solid electrolyte of Comparative Example 2.

From these material evaluation results, it was suggested that the specific crystalline phase suggested in the sulfide-based solid electrolytes of Examples 1 to 4 did not exist in the sulfide-based solid electrolyte of Comparative Example 2.

Although preferred embodiments of the present invention have been described in detail with reference to the attached drawings, the present invention is not limited thereto. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can derive various changes or modifications within the scope of the technical idea described in the claims, and about these. However, it is naturally understood that it falls within the technical scope of the present invention.

It may be apparent to those skilled in the art that various modifications and variations may be made to the structure of the disclosed embodiments without departing from the scope or spirit of the present disclosure. In light of the foregoing, the present disclosure is intended to cover modifications and variations of the present disclosure that fall within the scope of the following claims and their equivalents.

1: solid secondary battery 10: anode layer
11: positive electrode current collector 12: positive electrode active material layer
20: cathode layer 21: cathode current collector
22: negative electrode active material layer 30: solid electrolyte layer

Claims (20)

A first step of obtaining a precursor by mixing at least Li ₂ S, P ₂ S ₅ and LiI as starting materials in a first solvent; and
A second process of reacting the precursor in a second solvent to obtain a sulfide-based solid electrolyte,
The first solvent includes a cyclic ether compound substituted or unsubstituted by an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms,
The second solvent contains an alkoxy group-substituted hydrocarbon,
During the second process, the temperature at which the precursor is reacted in the second solvent is 100°C to 200°C, and the reaction time is 30 minutes to 300 minutes. The method of claim 1, wherein the first solvent includes a compound having an oxetane skeleton, a tetrahydrofuran skeleton, or a tetrahydropyran skeleton. The method of claim 1, wherein the first solvent is tetrahydrofuran. The method of claim 1, wherein GeS ₂ , P ₂ S ₃ , P ₂ O ₅ , SiO ₂ , B ₂ S ₃ , Al ₂ S ₃ , B ₂ O ₃ or one of these is added to the first organic solvent in the first process. A method for producing a sulfide-based solid electrolyte by adding more than one species. The method of claim 1, wherein the concentration of the starting material in the mixture containing the first solvent and the starting material is 1 to 10% by mass. The method of claim 1, wherein the temperature of the mixture of the starting material and the first solvent during the first process is 30°C to 80°C. The method of claim 1, wherein the hydrocarbon skeleton of the alkoxy group-substituted hydrocarbon includes a chain hydrocarbon having 1 to 10 carbon atoms, or a cyclic hydrocarbon having 3 to 10 carbon atoms. The method of claim 1, wherein the second solvent is dimethyl ether, methyl ethyl ether, diethyl ether, methyl n-propyl ether, ethyl n-propyl ether, di-n-propyl ether, methyl iso-propyl ether, ethyl iso- Propyl ether, di-iso-propyl ether, n-propyl iso-propyl ether, methyl n-butyl ether, ethyl n-butyl ether, n-propyl n-butyl ether, iso-propyl n-butyl ether, methyl sec-butyl Ether, ethyl sec-butyl ether, n-propyl sec-butyl ether, iso-propyl sec-butyl ether, methyl iso-butyl ether, ethyl iso-butyl ether, n-propyl iso-butyl ether, iso-propyl iso-butyl Ether, methyl tert-butyl ether, ethyl tert-butyl ether, n-propyl tert-butyl ether, iso-propyl tert-butyl ether, di-n-butyl ether, di-sec-butyl ether, di-iso-butyl ether , sec-butyl n-butyl ether, iso-butyl n-butyl ether, tert-butyl n-butyl ether, iso-butyl sec-butyl ether, tert-butyl sec-butyl ether, tert-butyl iso-butyl ether,
Dimethoxy ethane, diethoxy ethane, methoxy ethoxy ethane, 1,3-dimethoxy propane, 1,3-diethoxy propane, 1-methoxy 3-ethoxy propane, 1,2-dimethoxy propane, 1, 2-diethoxy propane, 1-methoxy 2-ethoxy propane, 1-ethoxy 2-methoxy propane,
Cyclopropyl methyl ether, cyclopropyl ethyl ether, cyclobutyl methyl ether, cyclobutyl ethyl ether, cyclobutyl n-propyl ether, cyclobutyl iso-propyl ether, cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl n-propyl ether , Cyclopentyl iso-propyl ether, Cyclopentyl n-butyl ether, Cyclopentyl iso-butyl ether, Cyclopentyl sec-butyl ether, Cyclopentyl tert-butyl ether, Cyclohexyl methyl ether, Cyclohexyl ethyl ether, Cyclohexyl n- A method for producing a sulfide-based solid electrolyte comprising propyl ether, cyclohexyl iso-propyl ether, cyclohexyl n-butyl ether, cyclohexyl iso-butyl ether, cyclohexyl sec-butyl ether, or cyclohexyl tert-butyl ether. The preparation of a sulfide-based solid electrolyte according to claim 1, wherein the second solvent includes dimethoxyethane, diethoxyethane, diethyl ether, di-iso-propyl ether, cyclopentylmethyl ether, or one or more mixtures thereof. method. The method of claim 1, wherein in the first process, the precursor is a solvate solvated with a first solvent. The method for producing a sulfide-based solid electrolyte according to claim 10, wherein the solvate reacts in the second step. The method of claim 1, wherein the heating of the precursor is performed under a reduced pressure atmosphere. The method of claim 1, wherein the first process and the second process are performed under an inert gas atmosphere. The method for producing a sulfide-based solid electrolyte according to claim 1, wherein the sulfide-based solid electrolyte obtained after the second process is further washed or dried. The method of claim 1, wherein the sulfide-based solid electrolyte can be expressed by the following formula (1):
(1-x)LiI·xLiBr·2Li ₃ PS ₄ (1)
In the above formula (1), x is 0<x<1.0. The method of claim 1, wherein the sulfide-based solid electrolyte has peaks at positions where 2θ is 19.9±0.5°, 23.5±0.5°, and 29.3±0.5°, respectively, in X-ray diffraction spectrum measurement using Cu-Kα line. ,
When the intensity of the peak at the position where 2θ is 19.9 ± 0.5° is IA, and the intensity of the peak at the position where 2θ is 17.0 ± 0.5° is IB, IB/IA is less than 0.50. A method for producing a sulfide-based solid electrolyte. The method of claim 1, wherein the sulfide-based solid electrolyte has an ionic conductivity of 1.0Х10 ^-5 S/cm to 1.0Х10 ^-2 S/cm at 25°C. The method of claim 1, wherein the sulfide-based solid electrolyte has an activation energy of 30 kJ/mol to 40 kJ/mol. A sulfide-based solid electrolyte produced by the method for producing a sulfide-based solid electrolyte according to any one of claims 1 to 18. A solid secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte layer located between the positive electrode and the negative electrode,
A solid secondary battery wherein the solid electrolyte layer includes a sulfide solid electrolyte prepared according to any one of claims 1 to 18.