KR20230118028A - Lithium sulfide, solid electrolyte for secondary battery including the same and method of preparing the same - Google Patents

Abstract

Lithium sulfide may be obtained from a reactant produced by reacting a sulfur (S) raw material including at least one of thiourea, carbon disulfide, and isothiocyanate-based compounds with a lithium base. Accordingly, high-purity lithium sulfide can be produced at low cost, and stability and productivity of the process can be improved. In addition, a solid electrolyte for a secondary battery containing the above-described lithium sulfide and a lithium secondary battery are provided.

Description

Lithium sulfide, a solid electrolyte for a secondary battery containing the same and a method for manufacturing the same

The present invention relates to a method for producing lithium sulfide, lithium sulfide, and a solid electrolyte for a secondary battery containing lithium sulfide. More specifically, it relates to a method for producing lithium sulfide using a sulfur source and lithium salt, a lithium sulfide prepared therefrom, and a solid electrolyte for a secondary battery including the same.

Lithium sulfide (Li ₂ S) is not produced as a natural mineral product and is not obtained from nature, and it is necessary to obtain lithium sulfide through synthesis. Methods for producing lithium sulfide include a dry process using a gas and a wet process using a solvent.

As an example of the dry method, there is a method of directly reacting a gaseous sulfur source such as hydrogen sulfide or sulfur vapor with metallic lithium or lithium hydroxide (LiOH). However, in the case of the dry method, equipment and processes for managing gaseous sulfur sources may be additionally generated, which may decrease productivity and increase costs. In addition, it is not suitable for mass production of lithium sulfide because it is difficult to handle large quantities of raw materials in order to prevent leakage of gaseous sulfur sources and maintain stability.

As an example of the wet method, lithium sulfate (Li ₂ SO ₄ ) is heated and reduced to carbon such as organic matter, carbon black, graphite, etc. under an inert gas atmosphere or vacuum, and lithium hydrogen sulfide ethanol (2LiSH C ₂ H ₅ OH) is converted to hydrogen There is a method of heating and decomposing in an air stream. However, in the case of the wet method, a pressure vessel is required to suppress volatilization of the solvent and hydrogen sulfide, and piping and a high-pressure reactor may be required for handling and transporting hydrogen sulfide. Accordingly, facilities and equipment for manufacturing may become large, and costs may increase.

For example, lithium sulfide can be used as a solid electrolyte material for secondary batteries. A secondary battery is a battery capable of repeating charging and discharging and is widely used as a power source for portable electronic devices such as power tools, cameras, camcorders, mobile phones, and notebook computers. In addition, secondary batteries are being applied as power sources for large vehicles such as electric vehicles and hybrid vehicles.

Although a non-aqueous electrolyte is used as an electrolyte used in a secondary battery, stability problems such as volatilization and leakage of the electrolyte, or short circuit and ignition due to the electrolyte may occur. Therefore, recently, a solid electrolyte has been used as an electrolyte for a secondary battery, and lithium sulfide has been applied as a sulfide-based solid electrolyte.

Accordingly, it is required to develop a manufacturing method capable of reducing manufacturing facility construction and operation costs, suppressing gas leaks such as hydrogen sulfide, and producing high-purity lithium sulfide.

For example, Japanese Patent Laid-Open No. 09-278423 discloses a method for producing lithium sulfide using lithium hydroxide and a gaseous sulfur source. For example, Japanese Patent Publication No. 2010-163356 discloses a method for producing lithium sulfide using lithium hydroxide, a hydrocarbon-based organic solvent, and hydrogen sulfide gas.

Japanese Patent Publication No. 09-278423 Japanese Patent Publication No. 2010-163356

One object of the present invention is to provide a method for producing lithium sulfide with improved stability and low cost.

One object of the present invention is to provide high purity lithium sulfide.

One object of the present invention is to provide a solid electrolyte for a secondary battery and a secondary battery containing high purity lithium sulfide.

According to exemplary embodiments, a sulfur (S) raw material including at least one of thiourea, carbon disulfide, and isothiocyanate-based compounds may be reacted with a lithium base. Lithium sulfide may be obtained from a reactant of the sulfur (S) raw material and the lithium base.

In some embodiments, the sulfur (S) raw material and the lithium base may react in an aqueous solution.

In some embodiments, lithium sulfide may be obtained from the reactant by drying an aqueous solution containing the reactant.

In some embodiments, the reactant may include LiSH.

In some embodiments, the lithium sulfide may be dissolved in an organic solvent, the organic solvent in which the lithium sulfide is dissolved may be filtered, and the filtered organic solvent may be distilled off.

In one embodiment, the solubility of the lithium base in the organic solvent may be lower than the solubility of the lithium sulfide in the organic solvent.

In one embodiment, the organic solvent may include alcohol having 1 to 6 carbon atoms.

In one embodiment, the lithium base may include at least one of LiH, LiOH, Li ₂ CO ₃ , and a lithium alkoxide having 1 to 10 carbon atoms. For example, lithium alkoxide can be represented by LiOR ² (R ² is an alkyl group having 1 to 10 carbon atoms).

In some embodiments, the isothiocyanate-based compound may be represented by Formula 1 below.

[Formula 1]

In Formula 1, R ¹ is an alkyl group having 1 to 12 carbon atoms, a haloalkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 2 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, and a carbon atom having 3 to 12 carbon atoms. It may be a cycloalkenyl group of 12, a cycloalkynyl group of 3 to 12 carbon atoms, an aryl group of 6 to 12 carbon atoms, a haloaryl group of 6 to 12 carbon atoms, or an arylalkyl group of 7 to 12 carbon atoms.

In some embodiments, the isothiocyanate-based compound may include at least one of compounds represented by Formulas 2 to 11 below.

[Formula 2]

[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

[Formula 9]

[Formula 10]

[Formula 11]

In some embodiments, the sulfur (S) raw material includes carbon disulfide, and the content of the lithium base may be 3.5 moles to 5.5 moles based on 1 mole of the sulfur (S) raw material.

In one embodiment, the sulfur (S) raw material includes carbon disulfide, and the reaction between the sulfur (S) raw material and the lithium base may be performed at 20 ° C to 45 ° C.

In some embodiments, the sulfur (S) raw material includes a thiourea or isothiocyanate-based compound, and the content of the lithium base may be 1.5 to 2.5 moles based on 1 mole of the sulfur (S) raw material. .

In one embodiment, the sulfur (S) raw material includes a thiourea or isothiocyanate-based compound, and the reaction of the sulfur (S) raw material and the lithium base may be performed at 20 ° C to 100 ° C.

In some embodiments, while the sulfur (S) raw material and the lithium base are reacted in the reactor, a gas generated by the reaction of the sulfur (S) raw material and the lithium base may be discharged to the outside of the reactor.

In one embodiment, the reactor may include a gas outlet through which the gas is discharged to the outside of the reactor.

In one embodiment, when gas is not discharged to the outside of the reactor, the reaction of the sulfur (S) raw material and the lithium base may be terminated.

Lithium sulfide according to exemplary embodiments may be manufactured by the above-described method.

A solid electrolyte for a secondary battery according to exemplary embodiments may include lithium sulfide prepared by the above-described method.

A secondary battery according to example embodiments may include a positive electrode, a negative electrode facing the positive electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode and containing the aforementioned lithium sulfide.

According to embodiments of the present invention, lithium sulfide may be produced by reacting a lithium source and a sulfur (S) source. The sulfur (S) raw material may include at least one of thiourea, carbon disulfide, and isothiocyanate-based compounds. Therefore, toxic gases such as hydrogen sulfide are not used during the manufacturing process, and therefore, facilities or equipment for storing, transporting, and introducing gases are not required. Therefore, high-purity lithium sulfide can be mass-produced at low cost, and environmental and safety risks can be suppressed.

A lithium base may be used as a lithium source. Lithium base may be easy to handle due to low ignitability and low hygroscopicity. In one embodiment, lithium sulfide may be selectively extracted and purified using an organic solvent. Thus, the purity of lithium sulfide can be improved.

1 is a process flow chart illustrating a method for manufacturing lithium sulfide according to exemplary embodiments.

According to embodiments of the present invention, lithium sulfide may be produced using a lithium source and a sulfur source. In addition, a solid electrolyte for a secondary battery and a secondary battery including lithium sulfide prepared by the above-described method may be provided.

Hereinafter, embodiments of the present invention will be described in detail.

When there are isomers of a compound represented by a chemical formula used in this specification, the compound represented by the chemical formula means a representative chemical formula including the isomer.

As used herein, the term “X compound” may refer to a compound X or a derivative of a compound X.

<Method for producing lithium sulfide>

1 is a process flow chart illustrating a method for manufacturing lithium sulfide according to exemplary embodiments.

A method for producing lithium sulfide according to exemplary embodiments may include steps, processes, or actions described as S10, S20, and/or S30 below. For example, some of the following processes S10, S20, and S30 may be sequentially performed, or all of them may be sequentially performed, and may be changed according to process conditions.

Referring to FIG. 1, a lithium raw material and a sulfur (S) raw material may be reacted (eg, step S10).

The sulfur (S) raw material may include thiourea (CH ₄ N ₂ S), carbon disulfide (CS ₂ ), and/or isothiocyanate-based compounds.

As hydrogen sulfide is not used as a source of elemental sulfur, costs for construction and operation of manufacturing facilities are reduced, and environmental and safety hazards can be suppressed. For example, when a gaseous sulfur source such as hydrogen sulfide is used as a source of elemental sulfur, production costs may increase because containers and pipes for storage, transport, and reaction are required. In addition, safety problems may occur due to leakage and volatilization of the gaseous sulfur source, and the purity and yield of lithium sulfide may be reduced.

A lithium base may be used as the lithium source. For example, the lithium raw material may be a lithium-containing alkali material having basicity in an aqueous solution state.

Lithium base has low pyrophoric and hygroscopicity, so handling can be easy. Accordingly, processability and economic feasibility may be improved, and mass production of lithium sulfide may be possible.

In addition, since the lithium base has high reactivity with the sulfur raw materials, the purity and productivity of lithium sulfide can be improved.

In example embodiments, the lithium base may include at least one of LiH, LiOH, Li ₂ CO ₃ , and a lithium alkoxide having 1 to 10 carbon atoms. For example, lithium alkoxide can be represented by LiOR ² . R ² may be an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an alkynyl group having 2 to 10 carbon atoms.

Preferably, LiOH or Li ₂ CO ₃ may be used as the lithium base. In this case, mass production may be possible at low cost while maintaining high purity and yield of lithium sulfide.

In some embodiments, the isothiocyanate-based compound may be represented by Formula 1 below.

[Formula 1]

In Formula 1, R ¹ is an alkyl group having 1 to 12 carbon atoms, a haloalkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 2 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, and a carbon atom having 3 to 12 carbon atoms. It may be a cycloalkenyl group of 12, a cycloalkynyl group of 3 to 12 carbon atoms, an aryl group of 6 to 12 carbon atoms, a haloaryl group of 6 to 12 carbon atoms, or an arylalkyl group of 7 to 12 carbon atoms.

In the aforementioned alkyl group, haloalkyl group, alkenyl group, alkynyl group, cycloalkyl group, cycloalkenyl group, cycloalkynyl group, aryl group, haloaryl group and arylalkyl group, at least one hydrogen atom may be substituted with a substituent. For example, the substituent is a hydroxy group, a halogen atom, an amino group, a nitro group, a sulfinyl group, a sulfonyl group, a sulfanyl group, a carboxyl group, a phosphine sulfide group, a phosphine oxide group, a silyl group, an oxy group, a carbonyl group, an ester group, etc. can be heard

Among the above substituents, multivalent substituents such as an amino group, a phosphine sulfide group, a phosphine oxide group, a sulfinyl group, a sulfonyl group, a sulfanyl group, a silyl group, an oxy group, a carbonyl group, and an ester group have different binding sites having carbon atoms It may be further substituted with an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

When the isothiocyanate-based compound is a compound represented by Formula 1, reactivity with a lithium base may be further improved. Thus, productivity and purity of lithium sulfide can be further improved.

Preferably, R ¹ in Formula 1 is an alkyl group having 1 to 6 carbon atoms, a haloalkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an arylalkyl group having 6 to 10 carbon atoms. can In this case, the carbon number and steric effect of the isothiocyanate-based compound are appropriately controlled, so that the reactivity with the lithium base can be further improved. In addition, the purity of lithium sulfide may be improved by increasing the solubility in an organic solvent to be described later.

More preferably, the isothiocyanate-based compound may include at least one of the compounds represented by Formulas 2 to 11 below.

[Formula 2]

[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

[Formula 9]

[Formula 10]

[Formula 11]

According to exemplary embodiments, the reaction between the lithium base and the sulfur raw material may be performed in an aqueous solution. For example, a lithium base and a sulfur raw material may be mixed in a solvent containing water and reacted.

In some embodiments, water alone may be used as the solvent of the aqueous solution. In this case, the lithium base and the sulfur source may be uniformly mixed in the aqueous solution, and the reactivity between the lithium base and the sulfur source may be further improved.

In some embodiments, when the sulfur source is carbon disulfide, a mixed solution of water and an ether-based solvent may be used as a solvent of the aqueous solution. Ether-based solvents have high solubility in carbon disulfide, so their reactivity in aqueous solutions can be further improved.

For example, the ether-based solvent may include ethyl methyl ether, diethyl ether, isopropyl ether, glycol dimethyl ether, glycol diethyl ether, tetrahydrofuran, and the like.

In one embodiment, lithium sulfide may be obtained through the reaction of carbon disulfide and a lithium base (eg, LiOH) as illustrated in Scheme 1 below.

<Scheme 1>

In some embodiments, when the source of sulfur (S) is carbon disulfide, the reaction between the lithium base and the source sulfur may proceed at a temperature below the boiling point of carbon disulfide. For example, the reaction temperature of the lithium base and the sulfur raw material may be 20 °C to 45 °C. Reactivity can be further improved while preventing decomposition of the sulfur raw material within the above range.

In some embodiments, when the sulfur (S) raw material is carbon disulfide, the amount of the lithium base may be 3.5 to 5.5 moles based on 1 mole of the sulfur (S) raw material.

Within the above range, the efficiency of the process and the yield of lithium sulfide may be improved, and the economics of the process may be improved. For example, when the content of the lithium base is less than 3.5 mol with respect to 1 mol of carbon disulfide, the reaction rate of carbon disulfide may decrease. For example, when the content of the lithium base is greater than 5.5 mol with respect to 1 mol of carbon disulfide, the remaining amount of unreacted lithium base may increase.

In one embodiment, lithium sulfide may be obtained through the reaction of an isothiocyanate-based compound and a lithium base (eg, LiOH) as illustrated in Scheme 2 below.

<Scheme 2>

In one embodiment, lithium sulfide can be obtained through the reaction of thiourea and a lithium base (eg, LiOH) as illustrated in Scheme 3 below.

<Scheme 3>

In some embodiments, when the sulfur (S) raw material is a thiourea and/or isothiocyanate-based compound, the reaction temperature of the lithium base and the sulfur raw material may be 20 ° C to 100 ° C, for example, 20°C to 90°C, or 20°C to 60°C.

For example, a thiourea or isothiocyanate-based compound may generate gases such as carbon dioxide, ammonia, or amine through a hydrolysis reaction with a lithium base. As the reaction temperature is adjusted within the above range, the amount of gas generated can be controlled and the reaction efficiency and stability can be further improved.

In some embodiments, when the sulfur (S) raw material is a thiourea and/or isothiocyanate-based compound, the amount of the lithium base may be 1.5 to 2.5 moles based on 1 mole of the sulfur (S) raw material. there is.

Within the above range, the efficiency of the process and the yield of lithium sulfide may be improved, and the economics of the process may be improved. For example, when the content of the lithium base is less than 1.5 moles based on 1 mole of the thiourea or isothiocyanate-based compound, the amount of unreacted sulfur raw material may increase and the yield of lithium sulfide may decrease. For example, when the content of the lithium base is greater than 2.5 moles with respect to 1 mole of the thiourea or isothiocyanate-based compound, the lithium base may remain in the reactant and the purity of lithium sulfide may decrease.

In some embodiments, the reaction of the lithium base and the sulfur raw material may proceed in a reactor.

In one embodiment, the reaction may proceed in an open system state. For example, gas generated by the reaction may be discharged/removed to the outside of the reactor while the lithium base and the sulfur raw material are reacted. Thus, reaction stability and efficiency can be further improved. For example, gas such as carbon dioxide, ammonia, and amine may reduce the reaction rate of the lithium base and the sulfur raw material, and side reactions may occur or the reactor may expand, resulting in deterioration in stability.

In one embodiment, the reactor may include a gas outlet through which gas generated by the reaction of the lithium base and the sulfur raw material is discharged to the outside of the reactor.

In one embodiment, the reaction termination point may be selected/adjusted by observing whether or not the gas is discharged to the outside of the reactor. For example, the reaction of the sulfur raw material and the lithium base may be terminated when no gas is discharged to the outside of the reactor.

For example, a gas outlet of the reactor may be connected to a container containing a solvent such as toluene through a tube or the like. Gas generation can be confirmed by observing whether bubbles are generated in the container.

In one embodiment, gas generation can be confirmed while additional heating. For example, while heating the reactor at a temperature of 20 ° C to 60 ° C, it is possible to check whether bubbles are generated. In one embodiment, gas generation can be confirmed while slowly raising the temperature of the reactor to a temperature higher than the reaction temperature of the raw material sulfur and lithium base. In this case, it is possible to more accurately confirm whether or not the reaction is complete.

Lithium sulfide (Li ₂ S) may be obtained from a reaction product of a lithium base and a sulfur source (eg, step S20).

For example, it may be converted into lithium sulfide by additionally reacting a reactant of a lithium base and a sulfur source. For example, an oxidation reaction, a reduction reaction, a dehydration reaction, a polymerization reaction, and the like may be performed depending on the type of the reactant.

In one embodiment, the reactant of the lithium base and the sulfur raw material may include LiSH. For example, LiSH formed by the reaction of the lithium base and the sulfur source may be converted into lithium sulfide. LiSH can be easily converted into lithium sulfide by a dehydration process in an aqueous solution. Therefore, as LiSH is formed as an intermediate product of the process, lithium sulfide can be synthesized in high yield while evaporating the aqueous solution without an additional conversion process.

In one embodiment, lithium sulfide may be formed while evaporating an aqueous solution in which the reactant is dissolved through a drying process. For example, the drying process may be performed by vacuum drying or heat drying. As the aqueous solution evaporates, LiSH may dehydrate and condense to form lithium sulfide.

In one embodiment, the temperature of the drying process may be 25 °C to 100 °C, for example, 50 °C to 100 °C, 50 °C to 90 °C, or 60 °C to 85 °C. Within the above range, the conversion rate of the reactant into lithium sulfide may be increased while the aqueous solution is completely evaporated. In addition, a decrease in yield due to side reactions, reverse reactions, and decomposition of lithium sulfide can be prevented.

According to exemplary embodiments, lithium sulfide may be extracted using an organic solvent (eg, step S30).

In some embodiments, the lithium sulfide may be dissolved in an organic solvent.

For example, after converting a reactant of a lithium base and a sulfur source into lithium sulfide, the aqueous solution may be evaporated to obtain a solid mixture containing lithium sulfide. The solid mixture may be mixed with the organic solvent.

In one example, the solid mixture may further include an unreacted material. For example, the unreacted material may include an unreacted lithium base and a sulfur source, or may include a reactant of a lithium base and a sulfur source that are not converted into lithium sulfide.

In some embodiments, a solvent having a higher solubility in lithium sulfide than a lithium base may be used as the organic solvent. Accordingly, selective dissolution of lithium sulfide may be possible, and the purity and yield of lithium sulfide may be further improved.

In one embodiment, the solubility of the organic solvent in lithium sulfide may be greater than the solubility in reactants such as raw material sulfur and LiSH.

In one embodiment, the organic solvent may include an alcohol-based solvent having 1 to 6 carbon atoms. For example, the organic solvent is methanol, ethanol, n-propanol, isopropanol, n-butanol, t-butanol, isobutanol, n-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, n-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, and the like.

The above-described alcohol-based solvent has low solubility in lithium bases such as LiOH and Li ₂ CO ₃ and sulfur raw materials such as thiourea, carbon disulfide, and isothiocyanate, and high solubility in lithium sulfide. In addition, the above-described alcohol-based solvent has no chemical reactivity with lithium sulfide and a lithium base, so that lithium sulfide can be selectively extracted without side reactions, and has a relatively low boiling point, so it can be easily removed after extraction.

In one embodiment, ethanol may be used as the organic solvent. Since ethanol has high solubility, low reactivity and boiling point for lithium sulfide, the reaction efficiency of the process and the yield and purity of lithium sulfide can be further improved.

In some embodiments, the solid compound remaining in the organic solvent may be removed by filtering the organic solvent in which the lithium sulfide is dissolved. In one embodiment, the filtration process may be performed repeatedly until a solid compound, for example, a white powder, is not observed in the organic solvent.

In some embodiments, the filtered organic solvent may be distilled off. Thus, high-purity lithium sulfide can be obtained.

In one embodiment, the distillation removal process may be performed by a heat drying process or a vacuum drying process. For example, the distillation removal process may be performed as a vacuum drying process. In this case, decomposition of lithium sulfide and decrease in purity due to heat treatment can be prevented.

Lithium sulfide may be obtained by distilling off the filtered organic solvent and recovering the remaining solid compound.

<Solid electrolyte for secondary battery and secondary battery>

A solid electrolyte for a secondary battery according to embodiments of the present invention may include the above-described lithium sulfide. Lithium sulfide has high ionic conductivity and stability, so the electrochemical properties of the solid electrolyte can be further improved.

In some embodiments, the solid electrolyte for the secondary battery may further include an electrolyte other than the above-described lithium sulfide. For example, the solid electrolyte for a secondary battery may further include a sulfide-based electrolyte, an oxide-based electrolyte, or a polymer electrolyte.

In some embodiments, the sulfide-based electrolyte is an LPS-based solid electrolyte including Li, P, and S, an LGPS-based solid electrolyte including Li, P, Ge, and S, or Li, Si, P, S and It may be an LSiPSCl-based solid electrolyte containing Cl.

For example, as the sulfide-based electrolyte, Li ₂ SP ₂ S ₅ , Li ₁₀ GeP ₂ S ₁₂ , Li ₁₀ SnP ₂ S ₁₂ , Li _9.54 Si _1.74 P _1.44 S _11.7 Cl _0.3 , Li ₁₀ (Si _0.5 Ge _0.5 )P ₂ S ₁₂ , Li ₁₀ (Ge _0.5 Sn _0.5 )P ₂ S ₁₂ , Li ₁₀ (Si _0.5 Sn _0.5 )P ₂ S ₁₂ , Li ₁₀ GeP ₂ S _11.7 O _0.3 , Li _9.6 P ₃ S ₁₂ , Li ₉ P ₃ S ₉ O ₃ , LI _10.35 GE _1.35 p _1.65 s _{12 ,} LI _10.35 SI _1.35 p _1.65 s ₁₂ , Li _9.81 s _0.81 p _2.19 S ₁₂ , LI _{9.42 SI 1.02} p _2.1 s _9.96 o _2.04 can be used

In some embodiments, the oxide-based electrolyte may include an ion-conducting compound containing oxygen. For example, as examples of the oxide-based solid electrolyte, LLTO-based compounds, Li ₆ La ₂ CaTa ₂ O ₁₂ , Li ₆ La ₂ CaNb ₂ O ₁₂ , Li ₂ Nd ₃ TeSbO ₁₂ , Li ₃ BO _2.5 N _0.5 , Li ₉ SiAlO ₈ , LAGP-based compound, LATP-based compound, Li _1+x Ti _2-x Al _x Si _y (PO ₄ ) _3-y (0≤x≤1, 0≤y≤1), LiAl _x Zr _{2- x} (PO ₄ ) ₃ (0≤x≤1, 0≤y≤1), LiTi _x Zr _2-x (PO ₄ ) ₃ (here, 0≤x≤1, 0≤y≤1), LISICON series compounds, LIPON-based compounds, perovskite-based compounds, Nasicon-based compounds, and LLZO-based compounds, and the like.

In one embodiment, the solid electrolyte for the secondary battery is a metal oxide such as Al ₂ O ₃ , ZnO ₂ , Ce ₂ O ₃ , TiO ₂ , ZrO ₂ , HfO 2 , MnO _{2 ,} MgO, WO _{2 ,} V ₂ O ₅ may further include.

In some embodiments, the content of lithium sulfide in the solid electrolyte for a secondary battery may be 10% by weight or more, for example, 20% by weight or more, 30% by weight or more, 50% by weight or more, or 70% by weight or more.

In some embodiments, the content of lithium sulfide in the solid electrolyte for a secondary battery may be 100% by weight or less, 90% by weight or less, or 80% by weight or less.

In some embodiments, the solid electrolyte for the secondary battery may be composed of the above-described lithium sulfide.

A secondary battery according to embodiments of the present invention may include a positive electrode, a negative electrode facing the positive electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

In one embodiment, the secondary battery may be a lithium secondary battery, and may be, for example, an all-solid battery that does not contain an electrolyte solution. An all-solid-state battery can have high stability because it does not use a liquid electrolyte as an electrolyte.

In addition, the lithium secondary battery may be manufactured in a cylindrical, prismatic, coin or pouch type. In addition, the lithium secondary battery may be classified into a bulk type and a thin film type according to the size.

In some embodiments, the cathode may include a cathode current collector and a cathode active material layer formed on the cathode current collector.

The cathode current collector may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and may include, for example, aluminum or an aluminum alloy.

The cathode active material layer may include a cathode active material. The cathode active material may include a compound capable of reversibly intercalating and deintercalating lithium.

In one embodiment, as the cathode active material, lithium-containing transition metal oxides, that is, lithium cobalt-based oxide, lithium manganese-based oxide, lithium copper oxide, lithium nickel-based oxide, lithium manganese composite oxide, and lithium-nickel-manganese-cobalt system oxide etc. are mentioned.

For example, the cathode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c ) O ₂ (0<a<1, 0<b<1, 0<c< 1, a+b+c=1), LiNi _1-y Co _y O ₂ (O<y<1), LiCo _1-y Mn _y O ₂ (O<y<1), LiNi _1-y Mn _y O ₂ (O≤y<1), Li(Ni _a Co _b Mn _c )O ₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn _{2 -z} Ni _z O ₄ (0<z<2), LiMn _2-z Co _z O ₄ (0<z<2), LiCoPO ₄ and LiFePO ₄ It may include at least one selected from the group consisting of.

In one embodiment, the positive electrode active material layer may include a binder, a conductive material, and/or the above-described solid electrolyte.

For example, as the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl Pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like may be used.

The conductive material may impart conductivity to the anode. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder such as copper, nickel, aluminum, and silver, and metal fiber.

In some embodiments, the negative electrode may include a negative electrode current collector and a negative active material layer formed on the negative electrode current collector.

The anode current collector may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and may include, for example, copper or a copper alloy.

The anode active material layer may include an anode active material. The negative electrode active material may include a material capable of reversibly intercalating and deintercalating lithium ions.

In one embodiment, a carbon-based material, lithium metal, an alloy of lithium metal, a silicon-based compound, or a transition metal oxide may be used as the negative electrode active material.

The carbon-based material may include crystalline carbon or amorphous carbon. Examples of the crystalline carbon include graphite such as amorphous, platy, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and the like.

The lithium metal alloy is at least selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. An alloy of one metal and lithium may be used.

Examples of the silicon-based compound include Si or SiO _x (0<x<2). In addition, the silicon-based compound may include silicon carbide, a material in which silicon is coated on the surface of graphite particles, or a material in which silicon and carbon are simultaneously coated on the surface of graphite particles.

Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

In one embodiment, the negative active material layer may further include a binder, a conductive material, and/or the above-described solid electrolyte.

For example, the negative electrode active material layer may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including ethylene oxide, Binders such as polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon can include more.

For example, the negative electrode active material layer may further include a conductive material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder such as copper, nickel, aluminum, silver, or metal fiber. there is.

The solid electrolyte layer prevents contact and short circuit between the positive electrode and the negative electrode, and can mediate the movement of lithium ions between the positive electrode and the negative electrode. Therefore, lithium ion conductivity can be secured even if the positive electrode and the negative electrode are not impregnated with the liquid electrolyte.

In one embodiment, a separator may not be disposed between the positive electrode and the negative electrode. Therefore, an increase in the irreversible capacity of the lithium secondary battery can be prevented, and electrochemical characteristics can be further improved.

In some embodiments, the solid electrolyte layer may include the above-described solid electrolyte. Lithium sulfide has high reaction stability and lithium ion conductivity, so the lifespan and output characteristics of a lithium secondary battery can be further improved.

For example, as the solid electrolyte layer directly contacts the positive electrode and the negative electrode, the solid electrolyte may be oxidized or reduced or an internal crystal structure may be destroyed by a reaction with the electrodes. In addition, the ion conductivity of the lithium secondary battery may decrease due to the increase in contact resistance.

According to exemplary embodiments, as the solid electrolyte includes lithium sulfide prepared by the above-described method, it may have high reaction stability and low contact resistance for an electrode. Thus, a lithium secondary battery having high capacity and improved stability can be provided.

In one embodiment, the solid electrolyte layer may further include other electrolytes in addition to the above-described solid electrolyte for a lithium secondary battery. For example, the solid electrolyte layer may further include a sulfide-based electrolyte, an oxide-based electrolyte, or a polymer electrolyte.

Hereinafter, experimental examples including specific examples are presented to aid understanding of the present invention, but these are only illustrative of the present invention and do not limit the scope of the appended claims, and within the scope and spirit of the present invention It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible, and it is natural that these changes and modifications fall within the scope of the appended claims.

Example

Example 1

<Scheme 4>

As illustrated in Scheme 4 above, lithium sulfide was obtained from carbon disulfide and lithium base.

Specifically, a magnetic bar and 100 g of water were placed in a two-necked 250 mL round bottom flask, CS ₂ (0.1 mol, 7.6 g) and LiOH ^. H ₂ O (0.4 mol, 16.4 g) was added and dissolved by stirring at 25 °C for 1 hour. A thermometer was installed at one inlet of the flask, and the other inlet was blocked with a rubber stopper, and an injection needle was inserted into the rubber stopper to volatilize and remove gas generated during the reaction. Thereafter, the mixture was stirred at 25° C. for 24 hours.

After removing the rubber stopper from the flask, a vacuum pump was connected. Thereafter, water was distilled off to obtain solid LiSH and Li ₂ CO ₃ . The temperature of the flask was raised to 80° C. and a vacuum pump was additionally connected to remove H ₂ O by heating and distillation to obtain a solid mixture of white powder in which Li ₂ S and Li ₂ CO ₃ were mixed.

50 g of ethanol was added to the obtained Li ₂ S mixture and stirred for 1 hour to selectively dissolve Li ₂ S. Thereafter, solids not dissolved in ethanol were removed using a glass filter, and the obtained ethanol solution was vacuum-dried to obtain 10.6 g of Li ₂ S (63% yield).

Example 2

LiOH ^. 10.1 g of Li ₂ S (60% yield) was obtained in the same manner as in Example 1, except that Li ₂ CO ₃ (0.2 mol, 14.8 g) was used instead of H ₂ O (0.4 mol, 16.4 g). .

Example 3

<Scheme 5>

As illustrated in Scheme 5 above, lithium sulfide was obtained from isothiocyanate and lithium base.

A magnetic bar and 100 g of water were added to a two-necked 250 mL round bottom flask, methylisothiocyanate (0.1 mol, 7.3 g) and LiOH ^. H ₂ O (0.2 mol, 8.2 g) was added and dissolved by stirring at 25 °C for 1 hour. A thermometer was installed at one inlet of the flask, and the other inlet was blocked with a rubber stopper, and an injection needle was inserted into the rubber stopper to volatilize and remove methylamine gas generated during the reaction. An injection needle was connected to the tube and one end of the tube was connected to a beaker filled with toluene. Thereafter, the mixture was stirred at 25° C. for 24 hours and additionally heated at 50° C. to confirm whether or not gas was generated.

After confirming that no gas was generated, the rubber stopper was removed from the flask and a vacuum pump was connected. Thereafter, water was distilled off to obtain solid LiSH and Li ₂ CO ₃ . The temperature of the flask was raised to 80° C. and a vacuum pump was additionally connected to remove H ₂ O by heating and distillation to obtain a solid mixture of white powder in which Li ₂ S and Li ₂ CO ₃ were mixed.

50 g of ethanol was added to the obtained Li ₂ S mixture and stirred for 1 hour to selectively dissolve Li ₂ S. Thereafter, solids not dissolved in ethanol were removed using a glass filter, and the obtained ethanol solution was vacuum-dried to obtain 5.3 g of Li ₂ S (63% yield).

Example 4

LiOH ^. Li ₂ S 5.1g (55% yield) was obtained in the same manner as in Example 3, except that Li ₂ CO ₃ (0.1 mol, 7.4 g) was used instead of H ₂ O (0.2 mol, 8.2 g). .

Example 5

<Scheme 6>

Lithium sulfide was obtained from thiourea and lithium base as illustrated in Scheme 6 above.

A magnetic bar and 100 g of water were added to a two-necked 250 mL round bottom flask, thiourea (0.1 mol, 7.6 g) and LiOH ^. H ₂ O (0.2 mol, 8.2 g) was added and dissolved by stirring at 25 °C for 1 hour. A thermometer was installed at one inlet of the flask, and the other inlet was blocked with a rubber stopper, and an injection needle was inserted into the rubber stopper to volatilize and remove carbon dioxide and ammonia generated during the reaction. An injection needle was connected to the tube and one end of the tube was connected to a beaker filled with toluene. Thereafter, the mixture was stirred at 25° C. for 24 hours and additionally heated at 50° C. to confirm whether or not gas was generated.

After confirming that no gas was generated, the rubber stopper was removed from the flask and a vacuum pump was connected. Thereafter, water was distilled off to obtain solid LiSH. The temperature of the flask was raised to 80° C. and a vacuum pump was additionally connected to distill H ₂ O by heating to obtain a solid mixture of white powder in which Li ₂ S, LiOH and thiourea were mixed.

50 g of ethanol was added to the obtained Li ₂ S mixture and stirred for 1 hour to selectively dissolve Li ₂ S. Thereafter, solids not dissolved in ethanol were removed using a glass filter, and the obtained ethanol solution was vacuum-dried to obtain 4.8 g of Li ₂ S (52% yield).

Example 6

LiOH ^. Li ₂ S 5.1g (55% yield) was obtained in the same manner as in Example 5, except that Li ₂ CO ₃ (0.1 mol, 7.4 g) was used instead of H ₂ O (0.2 mol, 8.2 g). .

Referring to the embodiments, toxic gases such as hydrogen sulfide are not used during the manufacturing process, and hydrogen sulfide is not generated during the reaction. Therefore, additional facilities or devices for transporting, removing, and handling hydrogen sulfide are not required, so costs can be reduced and the risk of safety accidents can be reduced.

In addition, by using a wet method using an aqueous solution and an organic solvent, lithium sulfide can be synthesized even at low temperature and pressure. In addition, as the lithium source and the sulfur source are reacted in a solution state, handling is easy and the reactivity and yield of the manufacturing process can be improved.

In addition, by-products generated in the process can be easily removed, and lithium sulfide can be selectively separated, so that the purity of lithium sulfide can be higher. Therefore, high-purity lithium sulfide can be mass-produced at low cost.

Claims (20)

reacting a sulfur (S) source containing at least one of thiourea, carbon disulfide, and isothiocyanate-based compounds with a lithium base; and
A method for producing lithium sulfide comprising the step of converting the reactant of the sulfur (S) raw material and the lithium base into lithium sulfide. The method of claim 1, wherein the sulfur (S) raw material and the lithium base react in an aqueous solution. The method of claim 2, wherein the converting the reactant into lithium sulfide comprises drying an aqueous solution containing the reactant. The method of claim 1, wherein the reactant includes LiSH. The method of claim 1, further comprising dissolving the lithium sulfide in an organic solvent, filtering the organic solvent in which the lithium sulfide is dissolved, and distilling off the filtered organic solvent. The method of claim 5, wherein the solubility of the lithium base in the organic solvent is lower than that of the lithium sulfide in the organic solvent. The method of claim 5, wherein the organic solvent includes an alcohol-based solvent having 1 to 6 carbon atoms. The method of claim 1, wherein the lithium base includes at least one of LiH, LiOH, Li ₂ CO ₃ and a lithium alkoxide having 1 to 10 carbon atoms. The method according to claim 1, wherein the isothiocyanate-based compound is represented by Formula 1 below:
[Formula 1]

(In Formula 1, R ¹ is an alkyl group having 1 to 12 carbon atoms, a haloalkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 2 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or a carbon atom 3 cycloalkenyl group of 12 to 12, cycloalkynyl group of 3 to 12 carbon atoms, aryl group of 6 to 12 carbon atoms, or arylalkyl group of 7 to 12 carbon atoms). The method of claim 1, wherein the isothiocyanate-based compound includes at least one of compounds represented by Formulas 2 to 11 below:
[Formula 2]

[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

[Formula 9]

[Formula 10]

[Formula 11]
. The method of claim 1, wherein the sulfur (S) raw material includes carbon disulfide, and the content of the lithium base is 3.5 to 5.5 mol based on 1 mole of the sulfur (S) raw material. The method of claim 11, wherein the reaction of the sulfur (S) raw material and the lithium base is performed at 20 ° C to 45 ° C. The method according to claim 1, wherein the sulfur (S) raw material includes a thiourea or isothiocyanate-based compound, the content of the lithium base is 1.5 to 2.5 moles of lithium sulfide based on 1 mole of the sulfur (S) raw material manufacturing method. The method according to claim 13, wherein the reaction of the sulfur (S) raw material and the lithium base is performed at 20 ° C to 100 ° C, the method for producing lithium sulfide. The production of lithium sulfide according to claim 1, wherein the sulfur (S) raw material and the lithium base are reacted in a reactor while a gas generated by the reaction of the sulfur (S) raw material and the lithium base is discharged to the outside of the reactor. method. The method of claim 15, wherein the reactor includes a gas outlet through which the gas is discharged to the outside of the reactor. The method of claim 15, wherein the reaction between the sulfur (S) raw material and the lithium base is terminated when gas is not discharged to the outside of the reactor. Lithium sulfide prepared by the method according to claim 1. A solid electrolyte for a secondary battery comprising the lithium sulfide according to claim 18. anode;
a cathode facing the anode; and
A secondary battery comprising a solid electrolyte layer disposed between the positive electrode and the negative electrode and containing the lithium sulfide according to claim 18 .