KR20230032095A - Method for preparing a solid electrolyte membrane for all solid-state battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a solid electrolyte membrane for an all-solid-state battery, which can secure excellent ion conductivity by improving the dissociation degree of a solid electrolyte to lithium salt. The present invention includes the steps of: manufacturing a lithium salt dissociation solution by mixing lithium salt and a solvent; manufacturing a mixed solution by mixing the lithium salt dissociation solution and a siloxane-based polymer; and applying the mixed solution on a substrate.

Description

Manufacturing method of solid electrolyte membrane for all-solid battery {METHOD FOR PREPARING A SOLID ELECTROLYTE MEMBRANE FOR ALL SOLID-STATE BATTERY}

The present invention relates to a method for manufacturing a solid electrolyte membrane for an all-solid-state battery.

A secondary battery refers to a device that converts external electrical energy into chemical energy, stores it, and generates electricity when needed. The term “rechargeable battery” is also used to mean that it can be recharged multiple times. Commonly used secondary batteries include lead acid batteries, nickel cadmium batteries (NiCd), nickel hydrogen batteries (NiMH), and lithium secondary batteries. Secondary batteries provide both economic and environmental advantages compared to disposable primary batteries.

On the other hand, as wireless communication technology gradually develops, portable devices or automobile accessories, etc. are required to be lightweight, thin, and miniaturized, and demand for secondary batteries used as energy sources for these devices is increasing. In particular, as hybrid vehicles and electric vehicles are put into practical use in terms of preventing environmental pollution, studies to reduce manufacturing cost and weight and extend lifespan by using secondary batteries for next-generation vehicle batteries are emerging. Among various secondary batteries, lithium secondary batteries that are lightweight, exhibit high energy density and operating potential, and have a long cycle life have recently been in the limelight.

In general, a lithium secondary battery is manufactured by mounting an electrode assembly composed of a negative electrode, a positive electrode, and a separator in a cylindrical or prismatic metal can or a pouch-type case of an aluminum laminate sheet, and injecting an electrolyte into the electrode assembly.

However, in the case of a lithium secondary battery, since a cylindrical, prismatic, or pouch-shaped case having a certain space is required, there are limitations in developing various types of portable devices. Accordingly, there is a demand for a lithium secondary battery of a novel type in which the shape can be easily changed. In particular, as an electrolyte included in a lithium secondary battery, an electrolyte having no fear of leakage and excellent ionic conductivity is required.

Conventionally, as an electrolyte for a lithium secondary battery, a liquid electrolyte obtained by dissolving a lithium salt in a non-aqueous organic solvent has been mainly used. However, such a liquid electrolyte has a high possibility of deterioration of electrode materials and volatilization of organic solvents, as well as occurrence of combustion or explosion due to an increase in the ambient temperature and the temperature of the battery itself, and there is a risk of leakage, resulting in high safety. It is difficult to implement various types of lithium secondary batteries.

On the other hand, an all-solid-state battery using a solid electrolyte has the advantage of being able to manufacture an electrode assembly in a safe and simple form because it excludes an organic solvent.

The solid electrolyte must have excellent ion conductivity, and dissociation of lithium salt is required for ion transfer. Polymeric compounds used as solid electrolytes are being developed as alternatives that can significantly improve the safety of lithium secondary batteries, but are currently under research due to their low ionic conductivity and occurrence of polarization due to the concentration gradient of lithium salts. In order to improve this, a method of improving solubility through polymer modification has been used, but the degree of improvement is insignificant, so continuous research is required.

Republic of Korea Patent No. 10-1028970 Republic of Korea Patent Publication No. 10-2015-0101235

Accordingly, the present inventors have conducted various studies to solve the above problems. As a result, in the step of manufacturing a solid electrolyte membrane for an all-solid-state battery, when lithium salt is dissociated in a solvent, and then a siloxane-based polymer is mixed with the solution in which the lithium salt is dissociated , The present invention was completed by confirming that the degree of dissociation of the siloxane-based polymer to the lithium salt was improved to secure the ionic conductivity of the solid electrolyte membrane.

Accordingly, an object of the present invention is to provide a method for producing a solid electrolyte membrane for an all-solid-state battery having high ionic conductivity while dissociating a lithium salt.

In order to achieve the above purpose,

The present invention comprises (1) preparing a lithium salt dissociation solution by mixing a lithium salt and a solvent;

(2) preparing a mixed solution by mixing the lithium salt dissociation solution and the polysiloxane-based polymer; and

(3) applying the mixed solution on a substrate; provides a method for manufacturing a solid electrolyte membrane for an all-solid-state battery comprising the.

The method of manufacturing a solid electrolyte membrane for an all-solid-state battery of the present invention has an excellent dissociation degree of a lithium salt of a siloxane-based polymer, which is a solid electrolyte, and thus has an effect of high ionic conductivity.

1 is a flowchart of a method for manufacturing a solid electrolyte membrane for an all-solid-state battery according to an embodiment of the present invention.
2 is a photograph of a polysiloxane-based polymer in a liquid state at room temperature.
Figure 3 is a photograph of the mixed solution of Example 1 and Comparative Examples 1 to 3.

Hereinafter, the present invention will be described in more detail.

The terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of terms in order to best describe his/her invention. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as 'include' or 'have' are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Lithium secondary batteries have been applied to small fields such as mobile phones and laptop computers, but recently, their application fields are expanding to medium and large fields such as electric vehicles and energy storage devices. In this case, since the operating environment is harsh and more batteries must be used, unlike the small size, it is necessary to secure stability with excellent performance.

Most currently commercialized lithium secondary batteries use a liquid electrolyte in which lithium salt is dissolved in an organic solvent. The organic solvent contained in the liquid electrolyte is easily volatilized and has flammability, which poses a potential risk of ignition and explosion, and leakage. There is a concern that this may occur, and long-term reliability is insufficient.

Accordingly, development of an all-solid-state battery in which the liquid electrolyte of the lithium secondary battery is replaced with a solid electrolyte is being developed. Since all-solid-state batteries do not contain volatile organic solvents, there is no risk of explosion or fire, and they are in the spotlight as batteries that are excellent in economics and productivity and can manufacture high-output batteries.

Solid electrolytes used in all-solid-state batteries include polymer-based compounds, sulfide-based compounds, or oxide-based compounds. Among them, the polymer-based compound can improve the safety of the lithium secondary battery, but has a problem of low ionic conductivity due to a low degree of dissociation of the lithium salt.

On the other hand, siloxane-based polymers are particularly interesting in the field of ion conductive polymers because they exhibit attractive properties such as fast segmental dynamics and have a completely amorphous structure and low glass transition temperature. However, in spite of these advantages, the siloxane-based polymer has a low dissociation degree of lithium salt, so there is a limit to its use as a solid electrolyte for an all-solid-state battery.

Therefore, in the present invention, while using a siloxane-based polymer as a solid electrolyte, it is intended to provide a method for manufacturing a solid electrolyte membrane for an all-solid-state battery that can improve dissociation of lithium salt and thereby improve ionic conductivity.

The present invention relates to a method for manufacturing a solid electrolyte membrane for an all-solid-state battery,

(1) preparing a lithium salt dissociation solution by mixing a lithium salt and a solvent;

(2) preparing a mixed solution by mixing the lithium salt dissociation solution and the siloxane-based polymer; and

(3) applying the mixed solution on a substrate; includes.

Step (1) is a step of preparing a lithium salt dissociation solution by mixing a lithium salt and a solvent.

The lithium salt is an ionizable lithium salt and can be expressed as Li ⁺ X ^- . The anion of the lithium salt is not particularly limited, but F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- etc. may be exemplified, preferably (CF ₃ SO ₂ ) ₂ N ^- .

The solvent is not particularly limited as long as it is a non-polar or low-polarity solvent capable of dissociating the lithium salt and dissolving or swelling the siloxane-based polymer, but is preferably ethanol or dimethylformamide. (dimethylformamide), dimethyl sulfoxide, xylene, toluene, isopropyl alcohol, hexane, nitromethane, ethylene glycol, purple With perfluorotributylamine, perfluorodecalin, acetonitrile, propylene carbonate, diisopropylamine, triethylamine and petane It may include one or more selected from the group consisting of, and more preferably may include ethanol.

The concentration of the lithium salt in the lithium salt dissociation solution is not particularly limited, and a lithium salt sufficient to sufficiently dissociate the lithium salt may be included in the solvent. For example, the lithium salt may be included in an amount of 10 to 200 parts by weight, preferably 20 to 150 parts by weight, and more preferably 50 to 100 parts by weight, based on 100 parts by weight of the solvent.

In addition, the lithium salt is 10, 20, 30, 40, 50, 60, 70, 80 or more than 90, 20, 30, 40, 50, 60, 20, 30, 40, 50, 60, 70, 80, 90 or 100 parts by weight or less. Specifically, it may be included in 10 to 100 parts by weight, preferably 15 to 80 parts by weight, and most preferably 20 to 50 parts by weight.

Dissociation of the lithium salt and high ionic conductivity may be obtained by including the lithium salt in the above weight part range. However, if the lithium salt is included in an amount of less than 10 parts by weight, the content of the lithium salt in the solid electrolyte is insignificant, and thus the solid electrolyte cannot exhibit an ionic conductivity effect. In addition, if the lithium salt is included in an amount exceeding 100 parts by weight, the lithium salt is included in an excessively large amount, so that the effect of improving the degree of dissociation of the siloxane-based polymer to the lithium salt cannot be expected.

Step (2) is a step of preparing a mixed solution by mixing the lithium salt dissociation solution prepared in step (1) with a siloxane-based polymer.

The siloxane-based polymer is a polymer that is liquid at room temperature.

In addition, the siloxane-based polymer may be a polymer including a structural unit represented by Formula 1 below.

[Formula 1]

In Formula 1,

Wherein R ₁ and R ₂ are the same as or different from each other, and each independently represent a hydrocarbon group having 1 to 30 carbon atoms not containing hydrogen or a hetero atom;

Wherein R ₃ and R ₄ are the same as or different from each other, and each independently represents a hydrocarbon group having 1 to 30 carbon atoms with or without a hetero atom;

Said n is an integer from 10 to 100,000.

In the siloxane-based polymer, preferably R ₁ and R ₂ are the same as or different from each other, each independently represent hydrogen or an alkyl group having 1 to 5 carbon atoms, and R ₃ and R ₄ may be an alkyl group having 1 to 5 carbon atoms. .

Also, most preferably, R ₁ and R ₂ are the same as or different from each other, each independently represent hydrogen or a methyl group, and R ₃ and R ₄ may represent a methyl group.

In addition, the siloxane-based polymer may preferably be polymethylhydrosiloxane or polymethylsiloxane.

If R ₁ and R ₂ are substituents containing O, N or S, which are hetero atoms, the siloxane-based polymer has excellent dissociation rate for lithium salt, and thus the dissociation rate of lithium salt is excellent in the method for manufacturing a solid electrolyte membrane for an all-solid-state battery of the present invention. The effect of improvement cannot be ascertained. In the present invention, since it is intended to provide a method for preparing a solid electrolyte for an all-solid-state battery having excellent ionic conductivity by improving the dissociation degree of a siloxane-based polymer with poor lithium salt dissociation, the R ₁ and R ₂ do not contain a hetero atom It is preferable to use a hydrocarbon group having 1 to 30 carbon atoms.

The number average molecular weight (Mn) of the siloxane-based polymer may be 500 to 200,000, preferably 1000 to 150,000, and most preferably 5000 to 100,000.

When the number average molecular weight of the siloxane-based polymer is 500 to 200,000, the degree of dissociation to the lithium salt is low. In the present invention, it is intended to increase the degree of dissociation of the lithium salt by mixing the siloxane-based polymer having a low dissociation degree with respect to the lithium salt with the solvent in step (1).

If the number average molecular weight of the siloxane-based polymer is less than 500, R3 and R4 in Formula 1 may affect the degree of dissociation, so that the increase in the degree of dissociation of the siloxane-based polymer to lithium salt cannot be evaluated, and if it exceeds 200,000, the viscosity increases. It can become very high and cause a problem that a non-uniform solution is prepared.

The mixing weight ratio of the lithium salt dissociation solution and the siloxane-based polymer is not particularly limited, but is 0.3:1 to 1:1, preferably 0.5:1 to 0.9:1, more preferably 0.6:1 to 0.8:1. They can be mixed in weight ratio.

Unlike the steps (1) and (2) of the production method of the present invention, if a mixed solution is prepared by mixing a lithium salt and a siloxane-based polymer and then mixing a solvent with the mixture, the mixed solution is phase separated. Alternatively, gelation occurs, making it impossible to manufacture a solid electrolyte membrane for an all-solid-state battery. This is because the siloxane-based polymer and the solvent undergo physical or/and chemical bonding before dissociation of the lithium salt.

Therefore, after preparing the lithium salt dissociation solution in step (1), a solid electrolyte membrane for an all-solid-state battery should be prepared by mixing a siloxane-based polymer with the lithium salt dissociation solution in step (2). When the siloxane-based polymer is mixed with the lithium salt dissociation solution, the high viscosity of the siloxane-based polymer is lowered due to the solvent, and since lithium ions dissociated in the solvent at a uniformly low concentration combine with the siloxane-based polymer, problems such as phase separation or gelation are avoided. It is possible to provide a solid electrolyte membrane for an all-solid-state battery having excellent ion conductivity because the dissociation degree of lithium salt is improved.

Step (3) is a step of applying the mixed solution prepared in step (2) on a substrate, and is a step in which a solid electrolyte membrane for an all-solid-state battery is finally manufactured.

The type of the substrate is not particularly limited as long as it is used in the art, and in one embodiment of the present invention, a substrate including a nonwoven fabric was used on the top of the SUS.

The coating method may use a method commonly used in the art, for example, slot die (slot die), gravure coating, spin coating, spray coating, roll coating, curtain coating, extrusion, casting, screen printing, Alternatively, a known coating method such as inkjet printing may be used, but is not limited thereto.

After the application, a drying process may be additionally performed. The drying is not limited to a specific method as long as it can remove the solvent from the mixed solution and may be performed in various ways. For example, the drying may be applied by selecting an appropriate drying method such as natural drying, heat drying, blow drying, hot air drying, cold air drying, or vacuum drying. In the present invention, vacuum drying may be preferable, and the drying temperature is preferably controlled in the range of about 50 to 150 °C.

Through the above steps, a solid electrolyte membrane for an all-solid-state battery can be finally manufactured.

In the method for manufacturing a solid electrolyte membrane for an all-solid-state battery of the present invention, a lithium salt dissociation solution is prepared using a solvent capable of dissociating lithium salt, and then a siloxane-based polymer having poor dissociation degree to the lithium salt is mixed with the solution. Since the solvent is a solvent capable of dissociating the lithium salt and dissolving or swelling the siloxane-based polymer, the solid for an all-solid-state battery using the siloxane-based polymer having an improved dissociation degree to the lithium salt through the manufacturing method of the present invention. electrolytes can be prepared. In addition, it is possible to prepare a solid electrolyte for an all-solid-state battery in which sufficient ionic conductivity is secured according to the improved dissociation of the lithium salt.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are merely illustrative of the present invention, and various changes and modifications are possible within the scope and spirit of the present invention. It is obvious to those skilled in the art, It goes without saying that these variations and modifications fall within the scope of the appended claims.

<Production of Solid Electrolyte Membrane for All-Solid Battery>

Example 1.

1.5 g of LiTFSI was added to 1.5 g of ethanol and stirred for 12 hours to prepare a lithium salt dissociation solution.

5 g of polymethylhydrosiloxane (Mn 1700-3200, Sigma Aldrich) was added to the lithium salt dissociation solution and stirred for 12 hours to prepare a mixed solution. At this time, 30 parts by weight of LiTFSI was included with respect to 100 parts by weight of polymethylhydrosiloxane.

After placing the nonwoven fabric on the SUS substrate, the mixed solution was applied thereon, and dried in a vacuum oven at 100 ° C. for 24 hours to prepare a solid electrolyte membrane for an all-solid-state battery.

Example 2.

A solid electrolyte membrane for an all-solid-state battery was prepared in the same manner as in Example 1, except that 2.5 g of LiTFSI was used.

At this time, LiTFSI is included in 50 parts by weight based on 100 parts by weight of polymethylhydrosiloxane.

Example 3.

A solid electrolyte membrane for an all-solid-state battery was prepared in the same manner as in Example 1, except that polydimethylsiloxane (Mn 110,000, Sigma Aldrich) was used instead of polymethylhydrosiloxane.

Comparative Example 1.

1.5 g of LiTFSI was added to 5 g of polymethylhydrosiloxane (Mn 1700-3200, Sigma Aldrich) and stirred for 12 hours to prepare a mixed solution. At this time, 30 parts by weight of LiTFSI was included with respect to 100 parts by weight of polymethylhydrosiloxane.

After placing the nonwoven fabric on the SUS substrate, the mixed solution was applied thereon, and dried in a vacuum oven at 100 ° C. for 24 hours to prepare a solid electrolyte membrane for an all-solid-state battery.

Comparative Example 2.

A solid electrolyte membrane for an all-solid-state battery was prepared in the same manner as in Comparative Example 1 except that 2.5 g of LiTFSI was used.

At this time, LiTFSI is included in 50 parts by weight based on 100 parts by weight of polymethylhydrosiloxane.

Comparative Example 3.

1.5 g of LiTFSI was added to 5 g of polymethylhydrosiloxane (Mn 1700-3200, Sigma Aldrich) and stirred for 12 hours. At this time, 30 parts by weight of LiTFSI was included with respect to 100 parts by weight of polymethylhydrosiloxane.

1.5 g of ethanol was added to the solution and stirred for 12 hours to prepare a mixed solution.

After placing the nonwoven fabric on the SUS substrate, the mixed solution was applied thereon, and dried in a vacuum oven at 100 ° C. for 24 hours to prepare a solid electrolyte membrane for an all-solid-state battery.

Experimental Example 1. Measurement of Ion Conductivity of Solid Electrolyte Membrane for All-Solid Battery

The ionic conductivity of the solid electrolyte membrane for an all-solid-state battery prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured.

The thickness of the solid electrolyte membrane was 20 μm, and ionic conductivity was measured for an area of 2 cm ² at a temperature of 25° C.

The ionic conductivity was measured for electrochemical impedance at room temperature using an analyzer (VMP3, Bio logic science instrument) under conditions of an amplitude of 10 mV and a scan range of 500 kHz to 0.1 mHz, and the measurement conditions and results are shown in Table 1 below.

Ionic Conductivity (S/cm) Resistance (Ohm) Example 1 ^1.66X10-5 120 Example 2 ^1.91X10-5 105 Example 3 ^1.81X10-5 110 Comparative Example 1 not measurable not measurable Comparative Example 2 not measurable not measurable Comparative Example 3 not measurable not measurable

From the results of Table 1, the solid electrolyte membranes of Examples 1 to 3 prepared by the manufacturing method of the present invention exhibited excellent ionic conductivity. In addition, from the results of Examples 1 and 2, it was found that the ionic conductivity increased as the content of the lithium salt increased.

In Comparative Examples 1 and 2, a solid electrolyte membrane was prepared by mixing the lithium salt and a siloxane-based polymer without dissociating the lithium salt into a solvent, and when the lithium salt was mixed with the siloxane-based polymer in a liquid state, the lithium salt did not dissociate. showed results. Therefore, in Comparative Examples 1 and 2, measurement of ionic conductivity was not possible.

In Comparative Example 3, ethanol as a solvent was added after mixing the lithium salt and the siloxane-based polymer. The ethanol is a solvent capable of dissolving the lithium salt and the siloxane-based polymer, but phase separation or gelation occurs when the lithium salt and the siloxane-based polymer are first mixed and then the solvent is added. Therefore, in Comparative Example 3, measurement of ionic conductivity was not possible.

From this, the present invention provides a method for preparing a solid electrolyte membrane for an all-solid-state battery by preparing a lithium salt dissociation solution and then adding a siloxane-based polymer to the solution, so that the lithium salt dissociation rate of the siloxane-based polymer with low dissociation to lithium salt is provided. It can be improved, and it can be seen that excellent ionic conductivity can be secured accordingly.

Claims (7)

(1) preparing a lithium salt dissociation solution by mixing a lithium salt and a solvent;
(2) preparing a mixed solution by mixing the lithium salt dissociation solution and the siloxane-based polymer; and
(3) a method for manufacturing a solid electrolyte membrane for an all-solid-state battery comprising the step of applying the mixed solution on a substrate.
According to claim 1,
The solvent in step (1) is ethanol, dimethylformamide, dimethyl sulfoxide, xylene, toluene, isopropyl alcohol, hexane, nitromethane, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, A method for producing a solid electrolyte membrane for an all-solid-state battery comprising at least one selected from the group consisting of propylene carbonate, diisopropylamine, triethylamine and pentane.
According to claim 1,
The siloxane-based polymer is a solid electrolyte membrane manufacturing method for an all-solid-state battery that is liquid at room temperature.
According to claim 3,
The siloxane-based polymer is a solid electrolyte membrane manufacturing method for an all-solid-state battery represented by the following formula (1):
[Formula 1]

In Formula 1,
Wherein R ₁ and R ₂ are the same as or different from each other, and each independently represent a hydrocarbon group having 1 to 30 carbon atoms not containing hydrogen or a hetero atom;
Wherein R ₃ and R ₄ are the same as or different from each other, and each independently represents a hydrocarbon group having 1 to 30 carbon atoms with or without a hetero atom;
Said n is an integer from 10 to 100,000.
According to claim 4,
The siloxane-based polymer is a solid electrolyte membrane manufacturing method for an all-solid-state battery comprising polymethylhydrosiloxane or polymethylsiloxane.
According to claim 4,
The number average molecular weight of the siloxane-based polymer is a solid electrolyte membrane manufacturing method for an all-solid-state battery of 500 to 200,000.
According to claim 1,
The lithium salt is a solid electrolyte membrane manufacturing method for an all-solid-state battery containing 10 to 100 parts by weight based on 100 parts by weight of the siloxane-based polymer.

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