KR102859662B1 - A solid electrolyte for secondary batteries, a method of manufacturing the same, and a lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a solid electrolyte for a secondary battery, a method for producing the same, and a lithium secondary battery comprising the same. According to the present invention, a solid electrolyte for a secondary battery having improved output characteristics and enhanced electrochemical stability through the interaction between succinonitrile, a vinyl monomer, and a lithium salt, a method for producing the same, and a lithium secondary battery comprising the same can be provided.

Description

A solid electrolyte for secondary batteries, a method of manufacturing the same, and a lithium secondary battery including the same

The present invention relates to a solid electrolyte for a secondary battery, a method for producing the same, and a lithium secondary battery comprising the same, and more particularly, to a solid electrolyte for a secondary battery comprising succinonitrile and a vinyl monomer, which improves the output characteristics of a secondary battery and enhances the electrochemical stability through interaction between succinonitrile, a vinyl monomer, and a lithium salt, a method for producing the same, and a lithium secondary battery comprising the same.

Various approaches are being explored to improve the energy density of lithium-ion batteries, one of which is the use of lithium metal as the anode. However, lithium-ion batteries using lithium metal anodes are vulnerable to lithium dendrite formation during charge and discharge. In particular, the flammable liquid electrolyte used in conventional lithium-ion batteries, based on its high ionic conductivity, directly compromises the stability of the lithium metal anode.

To improve this, research is actively being conducted on the development of solid-state batteries using non-solvent solid electrolytes with high ionic conductivity and electrochemical stability.

In general, in all-solid-state batteries, linear or cross-linked polymers of homopolymers or copolymers with ethylene oxide as a unit are mainly used as ion-conducting polymers. However, these polymers have low ion conductivity due to their structure that is easy to crystallize in the low-temperature range, which limits the performance of all-solid-state batteries.

Therefore, there is a need for the development of a polymer electrolyte that has excellent ionic conductivity at low temperatures and high electrochemical properties with minimal solvent.

KR 10-2177718 B1 KR 10-2038621 B1

The purpose of the present invention is to provide a solid electrolyte for a secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

In addition, another object of the present invention is to provide a solid electrolyte for a secondary battery having excellent electrochemical stability by improving the mobility of lithium ions while minimizing the amount of residual internal solvent, a method for producing the same, and a lithium secondary battery including the same.

According to one aspect of the present invention, the solid electrolyte for a secondary battery of the present invention includes a solid phase represented by the following chemical formula 1.

[Chemical Formula 1]

[Chemical Formula 2]

In the above chemical formula 1, Linker ₁ , Linker ₂ and Linker ₃ are each an independent single bond or chemical formula 2, m is a natural number from 1 to 50, and n is a natural number from 1 to 50.

In one embodiment, based on 100 parts by weight of the solid electrolyte, the solid electrolyte comprises 40 to 70 parts by weight of succinonitrile, 30 to 50 parts by weight of lithium salt, 10 to 30 parts by weight of vinyl monomer, 10 to 30 parts by weight of acrylic crosslinking agent, and 1 to 5 parts by weight of initiator.

In one embodiment, the solid electrolyte may be prepared by mixing the succinonitrile and the lithium salt and heat-treating them to prepare a first mixture, and then adding the vinyl monomer, the acrylic crosslinking agent, and the initiator to the first mixture at room temperature to prepare a second mixture, and the first mixture may include an amorphous phase formed by irreversibly inducing a phase transition due to the interaction between the succinonitrile and the lithium salt.

In one embodiment, the heat treatment may be performed at a temperature of 40° C. to 80° C. for 1 to 3 hours so that the primary mixture is in a liquid phase, the liquid primary mixture is cooled to room temperature to undergo a phase transition into an amorphous phase, the vinyl monomer, the acrylic crosslinking agent, and the initiator are added to the primary mixture including the amorphous phase to produce a secondary mixture, and the secondary mixture is UV-cured to form an amorphous phase solid electrolyte.

In one embodiment, the primary mixture may be formed by mixing the succinonitrile:lithium salt in a weight ratio of 3 to 2:2 to 2.5.

In one embodiment, the vinyl monomer may be included in the primary mixture at 10 wt% to 20 wt%.

In one embodiment, the succinonitrile is in an amorphous phase at -30°C to 60°C, and the primary mixture may be in an amorphous phase at 25°C to 60°C.

In one embodiment, the amorphous phase is provided by mixing a gauche isomer and a trans isomer, and the trans isomer may be included in an amount of 18 mol% to 25 mol%.

In one embodiment, the lithium salt may include at least one selected from lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO ₄ ), lithium nitrate (LiNO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bis(oxalato)borate (LiBOB), and lithium bis(fluorosulfonyl)amide (LiFSI).

In one embodiment, the vinyl monomer may include at least one selected from vinylethylenecarbonate (VEC), butylacrylate (BUA), 2-hydroxyethylmethacrylate (HMA), and trimethylolpropaneethoxylatetriacrylate (TRA).

In one embodiment, the solid electrolyte may include an ionic conductivity of 1.0 to 3.0 mS/cm at room temperature, a lithium cation transport rate of 0.7 to 1.0, and a positive electrode LSV (Linear sweep voltammetry) value of 5.0 to 5.3 V.

According to another aspect of the present invention, a method for manufacturing a solid electrolyte for a secondary battery of the present invention comprises a first mixture forming step of mixing succinonitrile and a lithium salt and performing heat treatment and cooling; a second mixture forming step of adding a vinyl monomer, an acrylic crosslinking agent, and an initiator to the first mixture; and a UV curing step of UV curing the second mixture to form a solid phase.

In one embodiment, the first mixture forming step may include a process of heat treating at a temperature of 40°C to 80°C for 1 to 3 hours and then cooling to room temperature.

In one embodiment, the primary mixture may be formed by mixing the succinonitrile:lithium salt in a weight ratio of 3 to 2:2 to 2.5.

In one embodiment, the vinyl monomer may be included in the primary mixture at 10 wt% to 20 wt%.

In one embodiment, the primary mixture may include an amorphous phase formed by irreversibly inducing a phase transition through interaction between the succinonitrile and the lithium salt.

In one embodiment, the succinonitrile is in an amorphous phase at -30°C to 60°C, and the primary mixture may be in an amorphous phase at 25°C to 60°C.

In one embodiment, the amorphous phase is provided by mixing a gauche isomer and a trans isomer, and the trans isomer may be included in an amount of 18 mol% to 25 mol%.

In one embodiment, the solid phase may be represented by the following chemical formula 1.

[Chemical Formula 1]

[Chemical Formula 2]

In the above chemical formula 1, Linker ₁ , Linker ₂ and Linker ₃ are each an independent single bond or chemical formula 2, m is a natural number from 1 to 50, and n is a natural number from 1 to 50.

In one embodiment, the lithium salt may include at least one selected from lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO ₄ ), lithium nitrate (LiNO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bis(oxalato)borate (LiBOB), and lithium bis(fluorosulfonyl)amide (LiFSI).

In one embodiment, the vinyl monomer may include at least one selected from vinylethylenecarbonate (VEC), butylacrylate (BUA), 2-hydroxyethylmethacrylate (HMA), and trimethylolpropaneethoxylatetriacrylate (TRA).

In one embodiment, the solid electrolyte may include an ionic conductivity of 1.0 to 3.0 mS/cm at room temperature, a lithium cation transport rate of 0.7 to 1.0, and a positive electrode LSV (Linear sweep voltammetry) value of 5.0 to 5.3 V.

According to another aspect of the present invention, a secondary battery including a solid electrolyte for a secondary battery of the present invention may include a positive electrode; a negative electrode opposing the positive electrode; and a solid electrolyte provided between the positive electrode and the negative electrode.

In one embodiment, the solid electrolyte may include an ionic conductivity of 1.0 to 3.0 mS/cm at room temperature, a lithium cation transport rate of 0.7 to 1.0, and a positive electrode LSV (Linear sweep voltammetry) value of 5.0 to 5.3 V.

According to the present invention as described above, a solid electrolyte for a secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same can be provided.

In addition, according to the present invention, a solid electrolyte for a secondary battery having excellent electrochemical stability, a method for producing the same, and a lithium secondary battery including the same can be provided by improving the mobility of lithium ions while minimizing the amount of residual internal solvent.

In addition, according to the present invention, a solid electrolyte for a secondary battery, which exhibits excellent ion conductivity characteristics even at low temperatures through smooth dissociation of lithium salt and increased mobility of lithium cations, and is electrochemically stable at high pressure in the operating environment of a battery, a method for producing the same, and a lithium secondary battery including the same can be provided.

FIG. 1 is a photograph of a solid electrolyte manufactured according to one embodiment of the present invention.
Figure 2 is a DFT-D simulation analysis result model according to one embodiment of the present invention.
Figure 3 is a graph showing the results of DFT-D simulation analysis according to one embodiment of the present invention.
Figure 4 is a graph of FT-IR measurement results according to one embodiment of the present invention.
Figure 5 is a graph of XRD analysis results according to one embodiment of the present invention.
Figure 6 is a graph of DSC analysis results according to one embodiment of the present invention.
Figure 7 is a graph showing the results of ion conductivity measurement according to one embodiment of the present invention.
Figure 8 is a graph showing the results of electrochemical stability (LSV) measurement according to one embodiment of the present invention.
Fig. 9 is a graph showing the measurement results of lithium transference number (LTN) according to one embodiment of the present invention.
Figure 10 is a graph evaluating lithium stripping/plating according to one embodiment of the present invention.
Fig. 11 is an SEM analysis photograph according to one embodiment of the present invention.
Figure 12 is an XPS analysis graph according to one embodiment of the present invention.
Figure 13 is a performance analysis graph of a lithium ion battery manufactured by combining LFP as a cathode material according to one embodiment of the present invention.
Figure 14 is a performance analysis graph of a lithium ion battery manufactured by combining NCM811 as a cathode material according to one embodiment of the present invention.

Specific details of other embodiments are included in the detailed description and drawings.

The advantages and features of the present invention, and the methods for achieving them, will become clear with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and unless otherwise specified in the following description, all numbers, values, and/or expressions expressing components, reaction conditions, and contents of components in the present invention are to be understood as being modified in all cases by the term "about" because such numbers are approximations that reflect various uncertainties of measurement that occur in obtaining such values, among other things. In addition, when a numerical range is disclosed herein, such range is continuous and includes every value from the minimum value to the maximum value inclusive, unless otherwise indicated. Furthermore, when such a range refers to an integer, every integer from the minimum value to the maximum value inclusive, unless otherwise indicated, is included.

Additionally, when a range is described for a variable in the present invention, it will be understood that the variable includes all values within the described range including the described endpoints of the range. For example, the range "5 to 10" will be understood to include the values 5, 6, 7, 8, 9, and 10, as well as any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and also any value between integers that fall within the described range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. For example, a range of "10% to 30%" would be understood to include values such as 10%, 11%, 12%, 13%, etc., and all integers up to and including 30%, as well as any subranges such as 10% to 15%, 12% to 18%, 20% to 30%, and any value between reasonable integers within the stated range, such as 10.5%, 15.5%, 25.5%, etc.

The present invention relates to a solid electrolyte for a secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

Typically, the development of lithium metal batteries using lithium metal as the anode is necessary to improve the energy density of lithium-ion batteries. Conventionally used flammable liquid electrolytes are highly reactive with lithium metal, forming an unstable solid electrolyte intermediate (SEI). Furthermore, they significantly reduce safety due to the risk of leakage and fire. Furthermore, the formation of a stable solid electrolyte intermediate (SEI) plays a crucial role in suppressing lithium dendrites, a major cause of cell short-circuiting.

A solid electrolyte for a secondary battery according to one embodiment of the present invention may include a solid phase represented by the following chemical formula 1.

[Chemical Formula 1]

[Chemical Formula 2]

In the above chemical formula 1, Linker ₁ , Linker ₂ and Linker ₃ are each an independent single bond or chemical formula 2, m is a natural number from 1 to 50, and n is a natural number from 1 to 50.

Based on 100 parts by weight of the above solid electrolyte, it contains 40 to 70 parts by weight of succinonitrile (SN), 30 to 50 parts by weight of lithium salt, 10 to 30 parts by weight of vinyl monomer, 10 to 30 parts by weight of acrylic crosslinking agent, and 1 to 5 parts by weight of initiator.

The above succinonitrile (SN) is known to undergo a crystal-plastic phase transition at about 58°C, and is thermodynamically stable by forming a uniform magnetic field by including a cyanide group with a large dipole moment, thereby inhibiting lithium dendrite growth.

The above succinonitrile can maintain an amorphous phase as a complex through interaction with the lithium salt. In addition, it can generally be used to increase the stability of the electrode interface and ion conductivity output.

If the amount of the succinonitrile is less than 40 parts by weight, it is not sufficient to suppress lithium dendrite growth, and if it exceeds 70 parts by weight, it may cause problems by reducing the mobility of lithium ions. Specifically, the amount of the succinonitrile may be 40 parts by weight to 65 parts by weight, or 50 parts by weight to 65 parts by weight, or 55 parts by weight to 65 parts by weight.

The above lithium salt can improve the ionic conductivity of lithium ions by being included within the above-mentioned range.

The lithium salt may include at least one selected from lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO ₄ ), lithium nitrate (LiNO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bis(oxalato)borate (LiBOB), and lithium bis(fluorosulfonyl)amide (LiFSI).

The above vinyl monomer may include at least one selected from vinylethylene carbonate (VEC), butylacrylate (BUA), 2-hydroxyethylmethacrylate (HMA), and trimethylolpropaneethoxylatetriacrylate (TRA).

If the vinyl monomer is less than 10 parts by weight, the mobility of lithium cations within the solid electrolyte may be reduced, which may be problematic, and if it exceeds 30 parts by weight, the flexible performance of the solid electrolyte may be reduced, which may be problematic. Specifically, the vinyl monomer may be 10 to 25 parts by weight, or 15 to 25 parts by weight.

The above vinyl ethylene carbonate (VEC) is a pentagonal cyclic carbonate containing a polymerizable vinyl group, which is easy to form a crosslinker, and the dangling cyclic carbonate after polymerization is less affected by the segmental movement of the polymer body, so that it conducts lithium cations through interactions between C=O groups and C-O groups, allowing lithium cations to move easily even at low temperatures.

The above acrylic crosslinking agent is trimethylolpropaneethoxylatetriacrylate (TRA), polyethyleneglycoldiacrylate (PEGDA), polyethyleneglycoldimethacrylate (PEGDMA), polypropyleneglycoldiacrylate (PPGDA), diethyleneglycoldiacrylate (DEGDA), glycidylmethacrylate (GMA), diethyleneglycoldimethacrylate (DEGDMA), dipropyleneglycoldiacrylate (DPGDA), triethyleneglycoldimethacrylate (TEGDMA), tripropyleneglycoldiacrylate (Tripropyleneglycoldiacrylate, Diacrylate series compounds such as tetraethylene glycol diacrylate (TPGDA), tetraethylene glycol diacrylate (TTEGDA), and butanediol diacrylate (1,4-Butanedioldiacrylate) can be used.

If the amount of the acrylic crosslinking agent is less than 10 parts by weight, the crosslinking within the solid electrolyte may become loose, causing problems with the bonding strength. If the amount is more than 30 parts by weight, the crosslinking may become strong, causing problems with the physical properties of the solid electrolyte. Specifically, the amount of the acrylic crosslinking agent may be 10 to 25 parts by weight, or 15 to 25 parts by weight.

The above initiator may include at least one selected from 1-hydroxycyclohexyl phenyl ketone, benzoyl peroxide, m-toluoyl peroxide, isobutyryl peroxide, diisopropylperoxydicarbonate, dimethoxyisopropylperoxydicarbonate, and diethoxyperoxydicarbonate.

If the initiator is less than 1 part by weight, UV curing may not occur properly, which may cause problems. If it is more than 5 parts by weight, unreacted initiator may remain after UV curing, which may cause problems. Specifically, the initiator may be present in an amount of 1 to 4 parts by weight, or 1 to 3 parts by weight.

The above solid electrolyte can be prepared by mixing the succinonitrile and the lithium salt and heat-treating them to prepare a first mixture, and then adding the vinyl monomer, the acrylic crosslinking agent, and the initiator to the first mixture at room temperature to prepare a second mixture.

The above primary mixture may include an amorphous phase formed by irreversibly inducing a phase transformation through the interaction between the succinonitrile and the lithium salt.

The above heat treatment is performed at a temperature between 40°C and 80°C for 1 to 3 hours so that the primary mixture can be provided in a liquid phase, and the liquid primary mixture can be cooled to room temperature to undergo a phase transformation into an amorphous phase.

A secondary mixture may be prepared by adding the vinyl monomer, the acrylic crosslinking agent, and the initiator to the primary mixture including the amorphous phase, and the secondary mixture may be UV-cured to form an amorphous phase solid electrolyte.

The above primary mixture can be formed by mixing the above succinonitrile: the above lithium salt = 3~2: 2~2.5 in a weight ratio.

For the above primary mixture, the vinyl monomer may be included in an amount of 10 wt% to 20 wt%.

If the vinyl monomer is less than 10 wt% with respect to the primary mixture, the mobility of lithium cations in the solid electrolyte may be reduced, which may be a problem, and if it is more than 20 wt%, the flexible performance of the solid electrolyte may be reduced, which may be a problem.

The above succinonitrile is in an amorphous phase at -30°C to 60°C, and the first mixture can be in an amorphous phase at 25°C to 60°C.

The amorphous phase is prepared by mixing a gauche isomer and a trans isomer, and the trans isomer may be included in an amount of 18 mol% to 25 mol%.

The above solid electrolyte may include an ionic conductivity of 1.0 to 3.0 mS/cm at room temperature, a lithium cation transport rate of 0.7 to 1.0, and a positive electrode LSV (Linear sweep voltammetry) value of 5.0 to 5.3 V.

When the ionic conductivity is less than 1.0 mS/cm, it may not affect the crystal behavior due to the aggregation of the succinonitrile, which may cause a problem in that the bonding energy between the succinonitrile and the vinyl monomer becomes weak. When it exceeds 3.0 mS/cm, the bonding energy between the succinonitrile and the vinyl monomer becomes excessively strong, which increases the cohesion of the succinonitrile, and a plastic solid phase may be formed. Specifically, the ionic conductivity is preferably 1.5 to 3.0 mS/cm or 2.0 to 2.8 mS/cm.

When the lithium cation transport rate is less than 0.7, the bond energy between the succinonitrile and the vinyl monomer is weakly formed, so that the formation of an amorphous solid electrolyte is not smooth, and the ionic conductivity is low, which may cause a problem of a decrease in the cation transport rate. When it exceeds 1.0, the bond energy between the succinonitrile and the vinyl monomer is strong, so that a crystalline phase is formed, and thus the mobility of lithium ions may be decreased. Specifically, the lithium cation transport rate is preferably 0.7 to 0.9 or 0.7 to 0.8.

The above LSV (Linear sweep voltammetry) is a method of checking whether oxidation or reduction occurs at a specific potential by sweeping the potential of the working electrode in the positive (+) or negative (-) direction at a constant rate from the initial potential to the final potential, and then including the value obtained by measuring the current value according to the applied voltage over time.

If the above positive LSV (Linear sweep voltammetry) value exceeds 5.3 V, instability may increase, increasing the internal pressure of the battery, which may increase the risk of leakage, external deformation, explosion, and fire. Specifically, the positive LSV (Linear sweep voltammetry) value is preferably 5.1 to 5.3 V or 5.2 V.

A method for manufacturing a solid electrolyte for a secondary battery according to one embodiment of the present invention comprises a first mixture forming step of mixing succinonitrile and a lithium salt and performing heat treatment and cooling; a second mixture forming step of adding a vinyl monomer, an acrylic crosslinking agent, and an initiator to the first mixture; and a UV curing step of UV curing the second mixture to form a solid electrolyte in a solid state.

The wavelength of the UV lamp in the above UV curing step may include 300 to 400 nm. Specifically, the wavelength of the UV lamp is preferably 365 nm.

A lithium secondary battery including a method for manufacturing a solid electrolyte for a secondary battery according to one embodiment of the present invention comprises: a positive electrode; a negative electrode opposing the positive electrode; and a solid electrolyte provided between the positive electrode and the negative electrode.

The method for manufacturing a solid electrolyte for a secondary battery according to one embodiment of the present invention and the respective components and numerical ranges of the solid electrolyte used in a lithium secondary battery including the same are the same as the components and numerical ranges of the solid electrolyte described above according to one embodiment of the present invention, so detailed descriptions thereof are omitted.

Hereinafter, examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the scope of the present invention is not limited by the following examples.

(Experimental Example 1) DFT-D (Dispersion-corrected density functional theory) simulation analysis

The values of the calculated binding energy by analyzing the binding energy between succinonitrile (SN) and vinyl monomer are shown in Table 1 below. The equipment used for the above binding energy simulation analysis was GGA-PBE, DNP3.5 together with the Dmol3 module of Material Studio (BIOVIA).

FIG. 2 is a model showing the results of a DFT-D simulation analysis of the interaction between succinonitrile (SN) and a vinyl monomer according to one embodiment of the present invention, and FIG. 3 is a graph showing the results of a DFT-D simulation analysis of the binding energy due to the interaction between succinonitrile (SN) and a vinyl monomer according to one embodiment of the present invention.

Types of vinyl monomers SN _gauche (eV) SN _trans (eV) VEC -0.438 -0.488 BUA -0.191 -0.252 HMA -0.169 -0.232 TRA -0.075 -0.158

Looking at the above Table 1, Figures 2 and 3, the present invention was able to find out through the DFT-D experiment that the interaction between succinonitrile (SN) and vinyl monomer actually occurred rather than the interaction between succinonitrile (SN). In order to determine what effect this result had on the crystal behavior due to the aggregation of succinonitrile (SN), various experiments were conducted by controlling the vinyl monomer.

(Example 1) Lithium secondary battery manufactured by the method for manufacturing a solid electrolyte for a secondary battery of the present invention

Succinonitrile (SN, 99%), vinylethylene carbonate (VEC, 99%), trimethylolpropane ethoxylate triacrylate (TRA, average M _n = 428), 1-hydroxycyclohexylphenyl ketone (PI184, 99%), and lithium bistrifluoro methanesulfonylimide (LiTFSI, 99.95%) were purchased from Sigma-Aldrich, and all chemicals were used as received without further purification.

All manufacturing processes were carried out in a glove box filled with argon (Ar) gas ( _H2O < 0.1 ppm).

A primary mixture was obtained by uniformly mixing 600 mg of succinonitrile (SN) and 400 mg of lithium bistrifluoro methanesulfonimide (LiTFSI), heating the mixture at 60°C for 2 hours, and then cooling it to room temperature. Here, lithium bistrifluoro methanesulfonimide (LiTFSI) was dried under vacuum at 150°C for 6 hours before use.

To 1000 mg of the above primary mixture, 200 mg of vinylethylene carbonate (VEC), used as a vinyl monomer, was added, and 200 mg of trimethylolpropane oxylate triacrylate (TRA) and 20 mg of 1-hydroxycyclohexylphenyl ketone (PI184) were added, and then mixed uniformly to obtain a secondary mixture, a solid electrolyte.

After that, the solid electrolyte was directly applied (in-situ) to the electrode (SS, Li) and UV cured at a wavelength of 365 nm for 10 minutes.

Fig. 1 is a photograph of a solid electrolyte manufactured according to Example 1. Referring to Fig. 1, it was determined that the solid electrolyte manufactured by the method for manufacturing a solid electrolyte for a secondary battery of the present invention was well polymerized without unreacted monomers.

(Comparison Example 1)

In the above Example 1, butylacrylate (BUA) was used as a vinyl monomer instead of vinylethylene carbonate (VEC), and the remaining processes were carried out in the same manner. Here, the butylacrylate (BUA) was purchased from Samjeon Pure Chemical Industry Co., Ltd. located in Gyeonggi-do and used as received without further purification.

(Comparison Example 2)

In the above Example 1, 2-hydroxyethyl methacrylate (HMA) was used as a vinyl monomer instead of vinyl ethylene carbonate (VEC), and the remaining processes were carried out in the same manner. Here, the 2-hydroxyethyl methacrylate (HMA) was purchased from Samjeon Pure Chemical Industry Co., Ltd. located in Gyeonggi-do and used as received without further purification.

(Comparison Example 3)

In the above Example 1, trimethylolpropane ethoxylate triacrylate (TRA) was used as a vinyl monomer instead of vinylethylene carbonate (VEC), and the remaining processes were carried out in the same manner. Here, the trimethylolpropane ethoxylate triacrylate (TRA) was purchased from Sigma-Aldrich and used as received without further purification.

(Experimental Example 2) FT-IR Analysis

In order to determine whether the polymerization of the electrolyte synthesized in Example 1 was complete, an analysis was performed by recording 32 scans at a resolution of 4 cm ^-1 using a Cary 630 (Agilent) FT-IR spectrometer. Figure 4 is a graph showing the results of FT-IR measurement according to one embodiment of the present invention.

Referring to Figure 4, it was confirmed that complete polymerization had occurred as peaks around 1650 cm ^-1 and 1636 cm ^-1 corresponding to the double bonds of the vinyl monomers disappeared.

(Experimental Example 3) XRD Analysis

In order to confirm what difference the binding energies confirmed through the DFT-D experiment conducted in Experimental Example 1 actually cause in the crystal characteristics due to aggregation between succinonitrile (SN) of the solid electrolytes manufactured by Example 1 and Comparative Examples 1 to 3, an XRD analysis experiment was conducted. XRD measurements were performed using Cu-Kα radiation (λ=0.154 nm) in X-Pert PRO at a condition of 0.2°/min. Fig. 5 is a graph of the XRD analysis results according to one embodiment of the present invention.

Referring to the above Figure 5, it was confirmed that the peaks of (0 1 1) and (0 0 2), which are unique peaks of succinonitrile (SN), disappeared in the order of the strength of the binding energy according to the experimental results of Table 1 (VEC>BUA>HMA>TRA), and accordingly, it was found that the strength of the interaction with succinonitrile (SN) increased in the order of the strength of the binding energy.

(Experimental Example 4) DSC Analysis

In order to confirm whether the binding energies confirmed to be different through the DFT-D experiment conducted in Experimental Example 1 actually cause any difference in the thermal behavior of the solid electrolytes manufactured by Example 1 and Comparative Examples 1 to 3 due to the crystal characteristics caused by the aggregation between succinonitrile (SN), a DSC analysis experiment was conducted. The DSC analysis experiment was conducted using an aluminum pan at a temperature between -60°C and -70°C under a nitrogen flow, with two cycles of analysis at a rate of 10°C/min. Figure 6 is a graph of the DSC analysis results according to one embodiment of the present invention.

Referring to the above Figure 6, the changes in the unique peaks [T _pc , T _m ] of succinonitrile (SN) were observed in the order of the strength of the binding energy (VEC > BUA > HMA > TRA) according to the experimental results of Table 1, and the descending order of T _m was found to be the same as the order of the strength of the binding energy, and when VEC was used as the vinyl monomer, both the peaks of T _pc and T _m disappeared due to the strongest binding energy, indicating a completely amorphous phase at room temperature.

(Experimental Example 5) Ionic conductivity measurement

The ionic conductivity of the solid electrolytes manufactured by the above Example 1 and Comparative Examples 1 to 3 was calculated using the following mathematical equation 1 using the electrochemical impedance measurement method (EIS). An alternating current with an amplitude of 10 mV in the frequency range of 1 Hz was used, and a symmetrical cell (SS/SPE/SS) type cell was used using stainless steel (SS) during the measurement, and the impedance of a CR2032 coin cell was measured using an Ivium n-Stat electrochmical analyzer, and the resistance of the bulk electrolyte was obtained from the intersection of the semicircle or straight line of the impedance trace with the real side, and the ionic conductivity of the solid electrolyte membrane was calculated from the area and thickness of the sample.

Figure 7 is a graph (NyquistPlot) showing the results of ionic conductivity measurements according to one embodiment of the present invention. The ionic conductivities of the solid electrolytes manufactured according to Example 1 and Comparative Examples 1 to 3 were calculated using the following mathematical formula 1 and are shown in Table 2 below.

σ: ionic conductivity (S/cm)

R: Intersection of the impedance trace and the real axis

A: Area of the solid polymer electrolyte membrane

t: Thickness of the solid polymer electrolyte membrane

Mixing ratio (weight %) Ionic conductivity (mS/cm at 25℃) SN LiTFSI vinyl monomer TRA Example 1 42.9 28.6 14.3 14.2 2.6 Comparative Example 1 42.9 28.6 14.3 14.2 0.45 Comparison Example 2 42.9 28.6 14.3 14.2 0.19 Comparative Example 3 42.9 28.6 14.3 14.2 0.09

Referring to the above Figure 7 and Table 2, the descending order of T _m (VEC>BUA>HMA>TRA) of the results of Experimental Example 4 was found to be consistent with the order of high ionic conductivity at room temperature (VEC>BUA>HMA>TRA), and accordingly, it was found to be consistent with the order of high binding energy according to Experimental Example 1. Therefore, it was confirmed that the order of binding energy affects the crystal behavior due to aggregation of succinonitrile (SN) and also affects ionic conductivity.

(Experimental Example 6) Measurement of electrochemical stability (LSV)

Electrochemical stability of the solid electrolytes manufactured by the above Example 1 and Comparative Examples 1 to 3 was measured by manufacturing a coin cell using SUS as a measuring electrode and lithium metal as a counter electrode, and inserting the manufactured electrolyte membrane between these electrodes. Electrochemical measurements were performed using linear sweep voltammetry (LSV) up to 6 V at a scan rate of 10 mV/s.

Figure 8 is a graph showing the results of electrochemical stability measurements according to one embodiment of the present invention. The LSV results of the solid electrolytes manufactured according to Example 1 and Comparative Examples 1 to 3 are shown in Table 3 below.

Mixing ratio (weight %) Electrochemical stability (V) SN LiTFSI vinyl monomer TRA Example 1 42.9 28.6 14.3 14.2 5.2 Comparative Example 1 42.9 28.6 14.3 14.2 5.1 Comparison Example 2 42.9 28.6 14.3 14.2 5.1 Comparative Example 3 42.9 28.6 14.3 14.2 5.1

Referring to the above Figure 8 and Table 3, the results of measuring the electrochemical stability showed that the value of Example 1 using vinyl ethylene carbonate (VEC) as a vinyl monomer was the highest, but relatively similar values were shown, and it was confirmed that this was due to the excellent oxidation stability of succinonitrile (SN) itself.

(Experimental Example 7) Lithium transference number (LTN) measurement

The mobility of lithium cations was measured for the solid electrolytes manufactured according to Example 1 and Comparative Examples 1 to 3. Measurements were performed using an Ivium n-Stat electrochemical analyzer, and a voltage of 10 mV was applied. During the measurement, the solid electrolyte was placed between lithium metal disks to use a symmetrical cell (Li/solid electrolyte/Li) type cell.

Figure 9 is a graph showing the measurement results of lithium transference number (LTN) according to one embodiment of the present invention. The LTN of the solid electrolytes manufactured according to Example 1 and Comparative Examples 1 to 3 was calculated using the following mathematical formula 2 and is shown in Table 4 below.

I ₀ : Initial current

I _ss : Current after polarization

R ₀ : Resistance before polarization

R _ss : Resistance after polarization

Mixing ratio (weight %) LTN SN LiTFSI vinyl monomer TRA Example 1 42.9 28.6 14.3 14.2 0.79 Comparative Example 1 42.9 28.6 14.3 14.2 0.54 Comparison Example 2 42.9 28.6 14.3 14.2 0.43 Comparative Example 3 42.9 28.6 14.3 14.2 0.30

Referring to the above Figure 9, the results of the lithium transference number (LTN) measurement showed that the LTN result value increased in the order of high ionic conductivity (VEC>BUA>HMA>TRA), that is, in the order of low crystallinity, as shown in the results of Experimental Example 5. This confirmed that the larger the amorphous phase (the smaller the crystalline phase), the more smoothly lithium ions moved.

(Experimental Example 8) Lithium stripping/plating characteristics

The stripping/plating of lithium was evaluated using VEC_X-link_3SN2Li (Example 1) and TRA_X-link_3SN2Li (Comparative Example 3), which were prepared using monomers showing the strongest and weakest binding energies for the solid electrolytes prepared in Example 1 and Comparative Example 3. Measurements were made using a Li/SPE/Li symmetric cell under conditions of 0.2 mA/cm2 with an Ivium n-Stat electrochemical analyzer. Fig. 10 is a graph showing the evaluation of the stripping/plating of lithium according to one embodiment of the present invention.

Referring to the above Figure 10, the result of the solid electrolyte manufactured by the above Example 1 showed that when the binding energy with succinonitrile (SN) was the strongest and the crystal formation behavior of succinonitrile (SN) was best suppressed when an interaction was formed, it showed relatively excellent cycle (600 h) characteristics, and it was confirmed that smooth ion conduction was achieved. On the other hand, the result of the solid electrolyte manufactured by the comparative example 3 showed a large fluctuation in the voltage value around 100 h, which indicated that the cell was unstable due to the formation of dendrites.

(Experimental Example 9) SEM Analysis

In the cell cycle analyzed in Experimental Example 8 above, when 100 h had elapsed, the cell was disassembled and the surface of the lithium electrode was observed by measuring it using SEM (VEGA3 SBH). Fig. 11 is an SEM analysis photograph according to one embodiment of the present invention.

Referring to the above FIG. 11, the SEM measurement result of the solid electrolyte manufactured by the above Example 1 showed that no dendrites were formed at 100 h and a smooth and dense surface was observed, whereas the SEM measurement result of the solid electrolyte manufactured by the above Comparative Example 3 showed that a considerable number of dendrites were formed at 100 h. Through this, it was confirmed that vinylethylene carbonate (VEC), a vinyl monomer of Example 1 with relatively strong binding energy, has the effect of suppressing side reactions by inhibiting direct contact of succinonitrile (SN) with the lithium electrode.

(Experimental Example 10) XPS Analysis

In the cell cycle analyzed in Experimental Example 8 above, when 100 h had elapsed, the cell was disassembled and the solid electrolyte intermediate phase (SEI) formed was analyzed through XPS analysis of the lithium electrode. Fig. 12 is an XPS analysis graph according to one embodiment of the present invention.

Referring to the above Figure 12, elements such as LiF, Li ₃ N, and Li ₂ CO ₃ with excellent ionic conductivity and stability were confirmed.

(Experimental Example 11) Lithium-ion Battery Performance Analysis

In order to analyze the performance of a lithium ion battery using the solid electrolyte manufactured by Example 1 (VEC_X-link_3SN2Li) showing the best ion conductivity characteristics, the possibility of operating a lithium metal battery was evaluated by combining various cathodes (LFP, NCM811). Here, LFP (MTI Corporation) and NCM811 (POSCO Chemical) were used as the positive electrode active materials. Fig. 13 is a performance analysis graph of a lithium ion battery manufactured by combining LFP as a positive electrode material according to an embodiment of the present invention, and Fig. 14 is a performance analysis graph of a lithium ion battery manufactured by combining NCM811 as a positive electrode material according to an embodiment of the present invention.

Referring to the above Figures 13 and 14, the solid electrolyte manufactured in Example 1 was used, and LFP and NCM811 were applied as positive electrode materials, respectively, to evaluate the possibility of operation as a lithium ion battery. As a result, it was confirmed that the energy density was constant as the cell cycle was repeated, and the ionic conductivity was excellent at a constant voltage, so that it could be applied to a lithium metal battery.

Accordingly, the method for manufacturing a solid electrolyte for a secondary battery of the present invention and the secondary battery including the same can provide a solid electrolyte for a secondary battery having excellent ionic conductivity even at low temperatures, a high cation transport rate, and excellent electrochemical stability, a method for manufacturing the same, and a lithium secondary battery including the same.

Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering its technical spirit or essential characteristics. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (24)

A solid electrolyte for a secondary battery comprising a solid phase represented by the following chemical formula 1:
[Chemical Formula 1]

[Chemical Formula 2]

In the above chemical formula 1, Linker ₁ , Linker ₂ and Linker ₃ are each an independent single bond or chemical formula 2, m is a natural number from 1 to 50, and n is a natural number from 1 to 50. In the first paragraph,
A solid electrolyte for a secondary battery, which is manufactured by including 40 to 70 parts by weight of succinonitrile (SN), 30 to 50 parts by weight of a lithium salt, 10 to 30 parts by weight of a vinyl monomer, 10 to 30 parts by weight of an acrylic crosslinking agent, and 1 to 5 parts by weight of an initiator, based on 100 parts by weight of the above solid electrolyte. In the second paragraph,
The above solid electrolyte is,
After mixing and heat-treating the above succinonitrile and the lithium salt to prepare a first mixture, the first mixture is prepared into a second mixture by adding the vinyl monomer, the acrylic crosslinking agent, and the initiator at room temperature.
The above primary mixture is a solid electrolyte for a secondary battery including an amorphous phase by irreversibly inducing a phase transformation through the interaction of the succinonitrile (SN) and the lithium salt. In the third paragraph,
The above heat treatment is performed at a temperature between 40°C and 80°C for 1 to 3 hours, so that the primary mixture is in a liquid phase,
The above liquid primary mixture is cooled to room temperature and undergoes a phase transformation into an amorphous phase.
A secondary mixture is prepared by adding the vinyl monomer, the acrylic crosslinking agent, and the initiator to the primary mixture containing the amorphous phase,
A solid electrolyte for a secondary battery, comprising a secondary mixture formed into an amorphous solid electrolyte by UV curing. In the third paragraph,
The above primary mixture is,
A solid electrolyte for a secondary battery formed by mixing the above succinonitrile: lithium salt = 3~2: 2~2.5 in a weight ratio. In the third paragraph,
A solid electrolyte for a secondary battery, wherein the vinyl monomer is included in the primary mixture in an amount of 10 wt% to 20 wt%. In the third paragraph,
The above succinonitrile is in an amorphous phase at -30°C to 60°C,
A solid electrolyte for a secondary battery, wherein the above primary mixture is in an amorphous phase at 25°C to 60°C. In the third paragraph,
The above amorphous phase is prepared by mixing gauche isomers and trans isomers,
A solid electrolyte for a secondary battery, wherein the trans isomer is contained in an amount of 18 mol% to 25 mol%. In the second paragraph,
The above lithium salt is,
A solid electrolyte for a secondary battery comprising at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO ₄ ), lithium nitrate (LiNO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bis(oxalato)borate (LiBOB), and lithium bis(fluorosulfonyl)amide (LiFSI). In the second paragraph,
The above vinyl monomer,
A solid electrolyte for a secondary battery comprising at least one selected from vinylethylene carbonate (VEC), butylacrylate (BUA), 2-hydroxyethylmethacrylate (HMA), and trimethylolpropaneethoxylatetriacrylate (TRA). In the first paragraph,
The above solid electrolyte is,
A solid electrolyte for a secondary battery having an ionic conductivity of 1.0 to 3.0 mS/cm at room temperature, a lithium cation transport rate of 0.7 to 1.0, and a positive electrode LSV (linear sweep voltammetry) value of 5.0 to 5.3 V. A first mixture formation step of mixing succinonitrile and lithium salt and performing heat treatment and cooling;
A second mixture forming step of adding a vinyl monomer, an acrylic crosslinking agent, and an initiator to the first mixture; and
A method for manufacturing a solid electrolyte for a secondary battery according to any one of claims 1 to 11, comprising a UV curing step of forming a solid phase by UV curing the secondary mixture. In paragraph 12,
The above first mixture formation step is,
A method for manufacturing a solid electrolyte for a secondary battery, comprising a process of heat-treating at a temperature of 40°C to 80°C for 1 to 3 hours and then cooling to room temperature. In paragraph 12,
The above primary mixture is,
A method for manufacturing a solid electrolyte for a secondary battery, wherein the above succinonitrile: lithium salt is mixed in a weight ratio of 3 to 2: 2 to 2.5. In Article 12,
A method for producing a solid electrolyte for a secondary battery, wherein the vinyl monomer is included in the primary mixture in an amount of 10 wt% to 20 wt%. In paragraph 12,
The above primary mixture is,
A method for manufacturing a solid electrolyte for a secondary battery, comprising an amorphous phase formed by irreversibly inducing a phase transition through the interaction of the above succinonitrile and the above lithium salt. In Article 12,
The above succinonitrile is in an amorphous phase at -30°C to 60°C,
A method for manufacturing a solid electrolyte for a secondary battery, wherein the above primary mixture is in an amorphous phase at 25°C to 60°C. In Article 16,
The above amorphous phase is prepared by mixing gauche isomers and trans isomers,
A method for producing a solid electrolyte for a secondary battery, wherein the trans isomer is included in an amount of 18 mol% to 25 mol%. In Article 12,
A method for manufacturing a solid electrolyte for a secondary battery, wherein the solid phase is represented by the following chemical formula 1:
[Chemical Formula 1]

[Chemical Formula 2]

In the above chemical formula 1, Linker ₁ , Linker ₂ and Linker ₃ are each an independent single bond or chemical formula 2, m is a natural number from 1 to 50, and n is a natural number from 1 to 50. In Article 12,
The above lithium salt is,
A method for manufacturing a solid electrolyte for a secondary battery, comprising at least one selected from among lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO ₄ ), lithium nitrate (LiNO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium bis(oxalato)borate (LiBOB), and lithium bis(fluorosulfonyl)amide (LiFSI). In Article 12,
The above vinyl monomer,
A solid electrolyte for a secondary battery comprising at least one selected from vinylethylene carbonate (VEC), butylacrylate (BUA), 2-hydroxyethylmethacrylate (HMA), and trimethylolpropaneethoxylatetriacrylate (TRA). In paragraph 12,
The above solid electrolyte is,
A method for manufacturing a solid electrolyte for a secondary battery, comprising: an ionic conductivity of 1.0 to 3.0 mS/cm at room temperature, a lithium cation transport rate of 0.7 to 1.0, and a positive electrode LSV (Linear sweep voltammetry) value of 5.0 to 5.3 V. anode;
a cathode opposing the anode; and
A solid electrolyte is provided between the positive electrode and the negative electrode,
The above solid electrolyte is a secondary battery comprising a solid electrolyte for a secondary battery according to any one of claims 1 to 10. In Article 23,
The above solid electrolyte is,
A secondary battery having an ionic conductivity of 1.0 to 3.0 mS/cm at room temperature, a lithium cation transport rate of 0.7 to 1.0, and a positive electrode LSV (linear sweep voltammetry) value of 5.0 to 5.3 V.