KR20250147113A - Method for preparing polymer electrolyte - Google Patents

Abstract

The present invention relates to a method for producing a polymer electrolyte, comprising the steps of: preparing a precursor solution by adding a lithium salt and a cross-linking polymer monomer to a solvent; and dropping the precursor solution onto a substrate and performing a heat treatment to polymerize in situ.

Description

Method for preparing polymer electrolyte

The present invention relates to a method for producing a polymer electrolyte through in-situ cationic polymerization.

Lithium-ion batteries were first commercialized in the 1990s and have since expanded their applications to encompass a wide range of applications, from portable devices to electric vehicles. While lithium-ion batteries offer the advantages of being lightweight and compact yet offering significant energy density and efficiency, they also pose risks, such as explosions caused by electrolyte leakage.

The electrolyte is one of the most crucial components of lithium-ion batteries, playing a crucial role in lithium ion transport, battery life, and cell performance. Liquid electrolytes are widely used due to their excellent electrochemical performance, particularly with regard to room-temperature (RT) ionic conductivity. Liquid organic solvents can offer high dielectric constants, fluidity, and electrode compatibility, but can also suffer from issues such as reduced thermal stability, reduced flame retardancy, and electrolyte leakage.

Safety concerns regarding these liquid electrolytes have led to increased development of polymer electrolytes, which exhibit superior thermal stability compared to liquid electrolytes and superior mechanical strength to mitigate the risk of lithium dendrites. Furthermore, polymer electrolytes can provide high energy density for high-capacity lithium-ion batteries.

However, the practical application of polymer electrolytes in lithium-ion batteries is limited due to their low ionic conductivity at room temperature and significant interfacial resistance between the electrolyte and electrode. To overcome these limitations, polymer electrolytes have been extensively studied for decades.

In general, all-solid-state polymer electrolytes (ASPEs) can form close contact with electrodes at high temperatures and pressures, achieving ionic conductivity values similar to those of liquid electrolytes. However, the demanding electrolyte plate manufacturing process limits their production scale and application. In contrast, many previous studies have demonstrated that gel polymer electrolytes (GPEs) can exhibit relatively high room-temperature ionic conductivity and satisfactory electrode interface compatibility, despite their more affordable production process.

The manufacturing of GPE can be divided into physical and chemical methods. In general, the physical method involves dissolving the polymer matrix in a solvent and mixing it with additives. After evaporating the solvent, the resulting dried polymer film is immersed in a liquid electrolyte solution to form a gel polymer electrolyte. However, after elevated temperatures and long-term aging, the polymer matrix dissolves or deforms in the liquid electrolyte, resulting in solution leakage and deterioration of battery performance. Furthermore, the low thermal stability of the prepared GPE limits its practical application. In the chemical method, an initiator and lithium salt are first dissolved in a monomer or liquid electrolyte to form a precursor electrolyte solution. Polymerization is then initiated by thermal, radical, or electrochemical methods to obtain a cross-linked GPE. The chemical method provides an assay process for preparing the electrolyte and battery assembly, also known as "in-situ" polymerization. The resulting GPE exhibits high thermal and mechanical stability, good contact with the electrode, and satisfactory electrochemical performance.

Meanwhile, linear polymers with an ethylene oxide structure have been extensively studied in terms of polymer matrix due to their high number of lithium ion donors and chain flexibility. Poly(ethylene oxide) (PEO), the most well-known polymer matrix, exhibits promising physicochemical properties, particularly with regard to high lithium salt solubility and dielectric constant. However, the high crystallinity of PEO restricts ion mobility, resulting in poor room-temperature ionic conductivity and limitations in meeting electrolyte requirements.

Therefore, research on polymer electrolytes with improved ionic conductivity and stability is needed.

The background technology of this application, Korean Patent Publication No. 10-2055265, relates to a polymer electrolyte membrane for a lithium ion battery, a method for manufacturing the same, and a lithium ion battery.

The present invention is intended to solve the problems of the above-mentioned prior art and provides a method for manufacturing a polymer electrolyte.

In addition, a polymer electrolyte manufactured by the above manufacturing method is provided.

In addition, a lithium ion battery including the polymer electrolyte is provided.

However, the technical tasks to be achieved by the embodiments of the present invention are not limited to the technical tasks described above, and other technical tasks may exist.

As a technical means for achieving the above-mentioned technical task, the first aspect of the present invention provides a method for producing a polymer electrolyte, comprising the steps of: preparing a precursor solution by adding a lithium salt and a cross-linked polymer monomer to a solvent; and dropping the precursor solution onto a substrate and performing a heat treatment to polymerize in-situ.

According to one embodiment of the present invention, the lithium salt may be, but is not limited to, bis(fluorosulfonyl)imide lithium salt (LiFSI).

According to one embodiment of the present invention, the LiFSI may act as a polymerization initiator in the in-situ polymerization step, but is not limited thereto.

According to one embodiment of the present invention, the crosslinked polymer monomer may be, but is not limited to, trimethylolpropane triglycidyl ether.

According to one embodiment of the present invention, the lithium salt in the precursor solution may be added at a molar concentration of 0.1 M to 3 M, but is not limited thereto.

According to one embodiment of the present invention, the heat treatment may be performed at a temperature range of 40°C to 80°C, but is not limited thereto.

According to one embodiment of the present invention, the solvent may include, but is not limited to, a cyclic carbonate and/or a linear carbonate.

According to one embodiment of the present invention, the cyclic carbonate may include, but is not limited to, one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and combinations thereof.

According to one embodiment of the present invention, the linear carbonate may include, but is not limited to, one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and combinations thereof.

Additionally, the second aspect of the present invention provides a polymer electrolyte manufactured according to the first aspect of the present invention.

In addition, the third aspect of the present invention provides a lithium ion battery including a polymer electrolyte according to the second aspect of the present invention.

The above-described problem-solving methods are merely exemplary and should not be construed as limiting the present invention. In addition to the exemplary embodiments described above, additional embodiments may be included in the drawings and detailed description of the invention.

The method for manufacturing a polymer electrolyte according to the present invention uses LiFSI, which was used as a lithium salt in a conventional lithium ion battery, as a polymerization initiator, and trimethylolpropane triglycidyl ether, which was used as a crosslinking agent, as a polymer monomer, and manufactures the polymer electrolyte through in-situ polymerization under mild conditions, thereby enabling the manufacture of a polymer electrolyte in a simpler and simpler manner compared to the conventional method in which an initiator and a crosslinking agent for polymerization were added separately.

In addition, the polymer electrolyte manufactured through the manufacturing method according to the present invention has relatively high ionic conductivity and lithium ion transfer number at room temperature, and can exhibit excellent electrode compatibility.

In addition, a battery including a polymer electrolyte manufactured by the method according to the present invention can have excellent cycling performance at room temperature, have an appropriate discharge capacity, and exhibit high Coulombic efficiency.

However, the effects that can be obtained from this center are not limited to the effects described above, and other effects may exist.

Figure 1 is a schematic diagram of the in-situ cationic ring-opening polymerization process and final chemical structure of a polymer electrolyte according to one embodiment of the present invention.
Figure 2 is a schematic diagram of a process for manufacturing a polymer electrolyte and assembling a cell including the same according to one embodiment of the present invention.
Figure 3a is a macroscopic comparative image of the electrolyte state before and after in situ polymerization of a polymer electrolyte according to an experimental example of the present invention, and Figure 3b is an FT IR result of a polymer electrolyte according to Examples 1 to 3 of the present invention compared to pure trimethylolpropane triglycidyl ether (TMPTE).
Figure 4a is a TGA result of a polymer electrolyte (GNPE) and pure trimethylolpropane triglycidyl ether (TMPTE) according to one embodiment of the present invention, Figure 4b is a DSC result, and Figure 4c is an XRD result.
Figure 5 is a temperature plot of the ionic conductivity (σ) value of GNPE according to an experimental example of the present invention.
Figures 6a to 6c show the chronocurrent profile and AC impedance before and after polarization at a voltage of 10 mV of GNPE according to an experimental example of the present invention.
Figure 7a shows the LSV profile results of GNPE from 0 V to 6 V at a sweep rate of 1 mV/s, and Figure 7b shows the cyclic voltammogram results of LiFePO ₄ /GNPE-1/Li foil half-cell performed at a scan rate of 0.1 mV/s.
Figure 8a is the voltage profile of the LFP/GNPE-1/graphite battery at selected cycles below 0.2C, Figure 8b is the rate performance of the LFP/GNPE-1/graphite battery, and Figure 8c is the coulombic efficiency and discharge capacity of the LFP/GNPE-1/graphite battery at 0.2C after 100 cycles at RT.
Figures 9a and 9b are SEM images of the cross-section of GNPE-1 before and after 100 cycles on the LFP cathode, respectively.
Figure 10 shows the results of high-resolution XPS characterization (S 2p, C 1s, F 1s, Li 1s, N 1s, and O 1s) of the GNPE-1 component of the graphite anode after a cycling test according to an experimental example of the present invention.

Below, with reference to the attached drawings, embodiments of the present invention are described in detail to facilitate easy implementation by those skilled in the art. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, irrelevant parts have been omitted for clarity, and similar reference numerals have been used throughout the specification to indicate similar elements.

Throughout this specification, when a part is said to be "connected" to another part, this includes not only cases where it is "directly connected" but also cases where it is "electrically connected" with another element in between.

Throughout this specification, when it is said that a member is located “on,” “above,” “upper,” “lower,” “lower” or “lower” another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

The terms "about," "substantially," and the like, as used herein, are used to mean at or near the numerical value when manufacturing and material tolerances inherent to the meanings referred to are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that contain precise or absolute numerical values to aid understanding of the present disclosure. Furthermore, throughout the present disclosure, the terms "step of ~" or "step of ~" do not mean "step for ~."

Throughout this specification, the term "combination thereof" included in the expressions in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expressions in the Makushi format, and means including one or more selected from the group consisting of said components.

Throughout this specification, references to “A and/or B” mean “A, B, or A and B.”

Hereinafter, the method for manufacturing the polymer electrolyte of the present invention will be described in detail with reference to implementation examples, examples, and drawings. However, the present invention is not limited to these implementation examples, examples, and drawings.

As a technical means for achieving the above-mentioned technical task, the first aspect of the present invention provides a method for producing a polymer electrolyte, comprising the steps of: preparing a precursor solution by adding a lithium salt and a cross-linked polymer monomer to a solvent; and dropping the precursor solution onto a substrate and performing a heat treatment to polymerize in-situ.

The method for manufacturing a polymer electrolyte according to the present invention uses LiFSI, which is used as a lithium salt in conventional lithium ion batteries, as a polymerization initiator, and trimethylolpropane triglycidyl ether, which is used as a crosslinking agent, as a polymer monomer, thereby manufacturing the polymer electrolyte through in-situ polymerization under mild conditions, thereby making it possible to manufacture the polymer electrolyte in an easier manner compared to the conventional method in which an initiator and a crosslinking agent for polymerization are added separately.

In addition, the polymer electrolyte manufactured through the manufacturing method according to the present invention has relatively high ionic conductivity and lithium ion transfer number at room temperature, and can exhibit excellent electrode compatibility.

In addition, a battery including a polymer electrolyte manufactured by the method according to the present invention can have excellent cycling performance at room temperature, have an appropriate discharge capacity, and exhibit high Coulombic efficiency.

First, a precursor solution is prepared by adding a lithium salt and a cross-linked polymer monomer to a solvent.

According to one embodiment of the present invention, the lithium salt may be, but is not limited to, bis(fluorosulfonyl)imide lithium salt (LiFSI).

In the case of the above LiFSI lithium salt, it has excellent ionic conductivity, viscosity, and thermal stability, and can be used as a polymerization initiator in the in situ polymerization step described below to catalyze the reaction.

According to one embodiment of the present invention, the crosslinked polymer monomer may be, but is not limited to, trimethylolpropane triglycidyl ether.

The above trimethylolpropane triglycidyl ether has a tri-epoxy functional group and can be used as a polymer monomer while also acting as a crosslinking agent in the reaction.

According to one embodiment of the present invention, the lithium salt in the precursor solution may be added at a molar concentration of 0.1 M to 3 M, but is not limited thereto.

If the lithium salt is added at a molar concentration exceeding 3 M, the bonds between FSI and epoxy may become too numerous, thereby restricting polymer chain movement, which may result in a decrease in ionic conductivity. Furthermore, if the lithium salt is added at a molar concentration less than 0.1 M, the reaction rate may be slowed, and the reaction may not be completely induced, which may deteriorate the performance of the polymer electrolyte. Therefore, it may be preferable to add the lithium salt at a molar concentration of 0.1 M to 3 M.

According to one embodiment of the present invention, the solvent may include, but is not limited to, a cyclic carbonate and/or a linear carbonate.

According to one embodiment of the present invention, the cyclic carbonate may include, but is not limited to, one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and combinations thereof.

According to one embodiment of the present invention, the linear carbonate may include, but is not limited to, one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and combinations thereof.

Next, the precursor solution is dropped onto the substrate and heat-treated to polymerize in-situ.

According to one embodiment of the present invention, the LiFSI may act as a polymerization initiator in the in-situ polymerization step, but is not limited thereto.

Figure 1 is a schematic diagram of the in-situ cationic ring-opening polymerization process and final chemical structure of a polymer electrolyte according to one embodiment of the present invention.

Referring to Fig. 1, the lithium ions and sulfonimide anions formed after LiFSI dissociates in a solvent can react with trace amounts of impurities such as water or alcohol to generate a superacid initiator H ⁺ FSIOH ^- (R1 in Fig. 1). The Brønsted superacid H ⁺ FSIOH ^- can rapidly protonate the cyclic epoxy monomer to form a secondary oxonium species (R2 in Fig. 1). Subsequently, cationic ring-opening polymerization can occur under the S _N 2 attack of the nucleophilic cyclic ether monomer on the secondary oxonium species (R3 in Fig. 1). Finally, a network polymer can be formed after continuous and repeated attacks of the cyclic epoxy on the heterocyclic intermediate.

According to one embodiment of the present invention, the heat treatment may be performed at a temperature range of 40°C to 80°C, but is not limited thereto.

Since the manufacturing method according to the present invention performs the reaction under relatively mild temperature conditions, it is possible to manufacture a polymer electrolyte more stably and energy-efficiently than conventional methods.

Additionally, the second aspect of the present invention provides a polymer electrolyte manufactured according to the first aspect of the present invention.

Regarding the polymer electrolyte according to the second aspect of the present application, detailed descriptions of parts overlapping with the first aspect of the present application have been omitted, but even if the descriptions have been omitted, the contents described in the first aspect of the present application can be equally applied to the second aspect of the present application.

In addition, the third aspect of the present invention provides a lithium ion battery including a polymer electrolyte according to the second aspect of the present invention.

Regarding the lithium ion battery according to the third aspect of the present application, detailed descriptions of parts overlapping with the first aspect and/or the second aspect of the present application are omitted, but even if the descriptions are omitted, the contents described in the first aspect and/or the second aspect of the present application can be equally applied to the third aspect of the present application.

The present invention will be described in more detail through the following examples; however, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[Example 1] GNPE-1

Figure 2 is a schematic diagram of a process for manufacturing a polymer electrolyte and assembling a cell including the same according to one embodiment of the present invention.

LFP cathode manufacturing

LiFePO ₄ , carbon black, and PVDF were mixed in a mass ratio of 80:10:10, and NMP (N-methyl-2-pyrrolidone) was added as a solvent. The mixture was sufficiently ground in a ball mill to prepare a slurry. The obtained slurry was used to coat aluminum foil, and then dried at 120°C to remove the NMP solvent. The active material was loaded onto the foil in an amount of 12 mg/cm ² . The obtained negative electrode foil was punched into circular pieces with a diameter of 16 mm, and then dried at 100°C for 12 h before cell assembly.

Graphite anode manufacturing

It was manufactured using the same process as the LFP cathode, but using a slurry of graphite, carbon black, and PVDF in a mass ratio of 85:5:10.

Gel network polymer electrolyte (GNPE) manufacturing and cell assembly

First, a precursor solution was prepared by dissolving LiFSI at a concentration of 1.0 M in a mixture of trimethylolpropane triglycidyl ether (TMPTE) and ethylene carbonate (EC)/diethyl carbonate (DEC) (50:50/v:v).

Next, the precursor solution was added dropwise to the LFP cathode and polymerized in situ at 60°C for 12 hours.

Afterwards, the LiFePO ₄ /GNPE/graphite cell was assembled into a GNPEs-LFP plate and aged at room temperature for 24 h.

All preparations, including in situ polymerization and cell assembly, were performed in an argon glove box (H ₂ O and O ₂ < 1 ppm).

[Example 2] GNPE-1.5

It was manufactured in the same manner as Example 1, but LiFSI was dissolved in the precursor solution at a concentration of 1.5 M.

[Example 3] GNPE-2

It was manufactured in the same manner as Example 1, but LiFSI was dissolved in the precursor solution at a concentration of 2.0 M.

[Experimental Example 1] Analysis of polymerization characteristics of polymer electrolytes

Figure 3a is a macroscopic comparative image of the electrolyte state before and after in situ polymerization of a polymer electrolyte according to an experimental example of the present invention, and Figure 3b is an FT IR result of a polymer electrolyte according to Examples 1 to 3 of the present invention compared to pure trimethylolpropane triglycidyl ether (TMPTE).

Referring to Fig. 3a, a macroscopic comparison of the polymer electrolyte states before and after in situ polymerization confirmed that all materials, including LiFSI, TMPTE, and EC/DEC, were sufficiently dissolved in each other to obtain a transparent, clear, and viscous precursor solution. Furthermore, viscosity increased with increasing LiFSI molar ratio. After in situ polymerization, an elastic gel polymer electrolyte was formed in the obtained electrolyte without excessive fluid liquid, which is advantageous for future coin cell assembly.

Meanwhile, in situ polymerization was monitored by FT-IR. Referring to Figure 3b, pure TMPTE exhibited three peaks at 2876, 1093, and 902 cm ^-1 , corresponding to CH, C-O-C stretching, and epoxide bending vibrations, respectively. As the reaction progressed, the intensity of the characteristic peak for epoxide bending decreased rapidly, and the addition of EC/DEC solvent caused the C=O stretching peak to appear at 1804 to 1742 cm ^-1 .

This confirmed the occurrence of cationic ring-opening polymerization of TMPTE using LiFSI during the in situ polymerization process.

[Experimental Example 2] Analysis of thermal properties of polymer electrolytes

TGA and DSC analyses were performed to investigate the thermal properties of the gel network polymer electrolyte (GNPE) according to Examples 1 to 3.

Figure 4a is a TGA result of a polymer electrolyte (GNPE) and pure trimethylolpropane triglycidyl ether (TMPTE) according to one embodiment of the present invention, Figure 4b is a DSC result, and Figure 4c is an XRD result.

Referring to Fig. 4a, it was confirmed that a single weight loss occurred at 184°C for pure TMPTE. On the other hand, due to the addition of lithium salt and EC/DEC solvent, the example (GNPE) of the present disclosure showed a weight loss of approximately 5% at 150°C. The second weight loss of GNPE was observed above 170°C for GNPE-1 and GNPE-1.5, and above 160°C for GNPE-2.

Referring to Fig. 4b, to confirm the glass transition temperature of GNPEs, DSC measurements were performed in the temperature range of -60 to 150°C, and the Tg values of GNPE-1, GNPE-1.5, and GNPE-2 were observed at -23, -25, and -23°C, respectively. The DSC results demonstrated that these GNPEs could provide sufficient chain flexibility at room temperature (RT) or sub-zero temperatures. In addition, there was no exothermic peak in the investigated temperature range for these GNPEs, suggesting that the obtained electrolytes exhibited an amorphous phase. Combining the TGA and DSC data revealed that the prepared GNPEs were thermally stable at approximately -25 to 150°C, which was close to the values of conventional PEO and PMMA-based polymer electrolytes. On the other hand, lithium ion transport within the polymer matrix could also occur over a wide temperature range.

Referring to Fig. 4c, XRD analysis was performed to further investigate the crystallization of TMPTE and GNPE. As a result, no characteristic diffraction peaks with an intense shape indicating the crystalline phase of TMPTE and GNPE were observed. A broad diffraction peak was found at 18° to 20°, which indicated the amorphous phase of TMPTE and GNPE, which was consistent with the DSC results. On the other hand, GNPE-2 showed a theta degree similar to the other polymers, but it appeared to have a lower theta degree than the other samples, and a small peak at 69°, which was because GNPE-2 was prepared with a high concentration of lithium salt that affected the polymer arrangement.

[Experimental Example 3] Electrochemical Performance of GNPE

To calculate the ionic conductivity (σ) of GNPE, EIS values of electrolyte samples were collected using an asymmetric dummy cell with stainless steel as a blocking electrode. The Nyquist plot was fitted with a common equivalent electric circuit model in Z-view. σ was calculated using the equation σ = L/Rb A, where L is the thickness, and Rb and A are the bulk resistance and contact area of the polymer electrolyte, respectively.

Figure 5 is a temperature plot of the ionic conductivity (σ) value of GNPE according to an experimental example of the present invention.

Referring to Fig. 5, the σ value monotonically increased with increasing measurement temperature. The σ value was found to be 10 ^-4 to 10 ^-5 S/cm. It is well known that the mobility of polymer segments can be enhanced at high temperatures due to increased chain flexibility. As a result, lithium ions could be easily transported in the polymer electrolyte at high temperatures. In addition, the electrolytes of GNPE-1, GNPE-1.5, and GNPE-2 showed σ values of 2.63 × 10 ^-4 S/cm, 1.17 × 10 ^-4 S/cm, and 6.21 × 10 ^-5 S/cm, respectively, at room temperature (RT). These σ values decreased with increasing LiFSI concentration at low temperatures. GNPE-2 exhibited slightly higher ionic conductivity than GNPE-1.5 at 50 to 80°C. However, GNPE-1 still maintained the highest σ value at all measurement temperatures. These results are because too much bonding between FSI and epoxy may restrict polymer chain movement and also reduce the free volume of the polymer matrix, which may affect the ion transport of the polymer electrolyte.

The highest value for GNPE-1 is consistent with the XRD results showing that GNPE-1 has the largest FWHM and smallest particle size, indicating sufficient free volume in the polymer matrix. The tLi ⁺ of GNPE was calculated from the Bruce-Vincent equation using AC impedance spectroscopy coupled with DC polarization at RT. The electrolyte was sandwiched between lithium chips using a CR2032 coin cell.

Figures 6a to 6c show the chronocurrent profile and AC impedance before and after polarization at a voltage of 10 mV of GNPE according to an experimental example of the present invention.

Referring to Figures 6a to 6c, the resulting AC impedance values of GNPE-1, GNPE-1.5, and GNPE-2 were 0.58, 0.46, and 0.42, respectively. GNPE-1 still exhibited the best lithium transport behavior due to the appropriate LiFSI concentration.

Meanwhile, linear sweep voltammetry (LSV) was performed to further confirm the maximum irreversible oxidation voltage and electrochemical stability of GNPE. These parameters are related to the energy density and capacity of lithium-ion batteries. The fabricated GNPE was assembled into a structure of stainless steel (SS)/GNPEs/Li foil, where SS served as the working electrode and Li foil served as the counter electrode and reference electrode, respectively.

Figure 7a shows the LSV profile results of GNPE from 0 V to 6 V at a sweep rate of 1 mV/s, and Figure 7b shows the cyclic voltammogram results of LiFePO ₄ /GNPE-1/Li foil half-cell performed at a scan rate of 0.1 mV/s.

Referring to Fig. 7a, GNPE-1 exhibited positive polarity stability up to 4.15 V, GNPE-1.5 exhibited a lower stable voltage of less than 4 V, and GNPE-2 decomposed at a very low voltage (approximately 1.5 V). This confirmed that GNPE-1 can meet the voltage requirements of LFP-based lithium-ion batteries (2.5–4.2 V).

Also, referring to Fig. 7b, cyclic voltammetry (CV) was performed to confirm the plating and stripping of lithium ions, and the voltammogram exhibited anodic and cathodic peaks at approximately 4.0 and 2.8 V vs. Li/Li+, respectively, corresponding to lithium ion delithiation (oxidation) and lithiation (reduction). Remarkably, these peaks were maintained at similar voltages from the 3rd to the 10th cycle, indicating excellent reversibility of the redox reaction at the GNPE/electrode interface.

[Experimental Example 4] Cycle Performance Analysis of GNPE

Rate and long-term cycling performance are the most important parameters for rechargeable lithium-ion batteries. To evaluate the cell performance of the electrolyte, GNPE-1 was charged and discharged at room temperature from 2.5 V to 4.2 V, achieving the best ionic conductivity and electrochemical window.

Figure 8a is the voltage profile of the LFP/GNPE-1/graphite battery at selected cycles below 0.2C, Figure 8b is the rate performance of the LFP/GNPE-1/graphite battery, and Figure 8c is the coulombic efficiency and discharge capacity of the LFP/GNPE-1/graphite battery at 0.2C after 100 cycles at RT.

Referring to Fig. 8a, GNPE-1 exhibited a maximum discharge capacity of 127.03 mAh/g at 0.2 C, and the capacity decreased as the cycle increased, dropping to 78.28 mAh/g (61.62% of the initial capacity) after 100 cycles.

Referring to Fig. 8b, when the current density rate was 0.1 C again, the discharge capacity returned to 126.54 mAh/g, suggesting the excellent reversibility and stability of GNPE-1 in a secondary lithium-ion battery.

Referring to Fig. 8c, the cell using GNPE-1 exhibited a coulombic efficiency of over 97% and a capacity of 98 mAh/g at 0.2C after 100 cycles, retaining 85% of its initial capacity. The cycling performance further confirmed that GNPE-1 has satisfactory stability over long cycles when applied to lithium-ion batteries. The promising initial capacity of the cell using GNPE-1 may be due to the excellent wettability of the polymer electrolyte on the LiFePO ₄ electrode, which can form a stable interface on the electrode.

Meanwhile, the interface between GNPE-1 and LiFePO ₄ electrodes before and after cycling tests was compared by FE-SEM.

Figures 9a and 9b are SEM images of the cross-section of GNPE-1 before and after 100 cycles on the LFP cathode, respectively.

Referring to Figure 9a, it can be confirmed that the prepared GNPE (top) is in close contact with the LFP cathode (bottom), as the precursor electrolyte solution penetrates the LFP cathode well. Due to the aging process, a close contact interface with the electrode was formed after in situ polymerization. This connection between the electrode and electrolyte was also observed during cycle testing.

Referring to Fig. 9b, a cross-sectional SEM image of GNPE-1 after 100 cycles of cell testing was observed, confirming that the GNPE-1 layer still exhibited excellent compatibility with the LPF cathode and maintained mechanical integrity even after the cycle test. These results not only demonstrate that the in situ-manufactured GNPE-1 possesses excellent mechanical stability, but also indicate that the formed cross-linked network can suppress the growth of lithium dendrites and ensure a long lifespan of lithium-ion batteries.

Additionally, XPS was performed to investigate the chemical surface composition of the graphite anode after cycling tests. LiF was formed after the electrochemical reduction of LiFSI via S-F bond cleavage. These results may explain the high content of LiF in the SEI when imide-based lithium salts are applied to the electrolyte.

Figure 10 shows the results of high-resolution XPS characterization (S 2p, C 1s, F 1s, Li 1s, N 1s, and O 1s) of the GNPE-1 component of the graphite anode after a cycling test according to an experimental example of the present invention.

Referring to Fig. 10, the LiF peaks of F 1s (684.5 eV) and Li 1s (55.2 eV) indicate that an SEI layer was formed on the graphite anode after the cell test. The main peak at 687.29 eV in the F 1s spectrum is attributed to SO ₂ F of LiFSI, which can also be found in the 168.99 eV peak in the S 2p spectrum. Moreover, the S=O species located at 539.29 eV in the O 1s spectrum overlapped with the CO species. Switching to the C 1s scan, the peaks from 284.83 to 289.78 eV were mainly assigned to the solvent EC/DEC and CH ₂ -CH ₂ -O chains after the epoxy ring-opening polymerization. The corresponding peak of CH ₂ -CH ₂ -O chains was also investigated in the O 1s spectrum at 531.59 eV, in accordance with previous reports. Finally, the N 1s spectrum showed two peaks at 400.93 and 399.44 eV corresponding to SN and NH ₂ of the FSI ^- anion.

The above description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims (11)

A step of preparing a precursor solution by adding a lithium salt and a cross-linked polymer monomer to a solvent; and
A step of dropping the precursor solution onto a substrate and performing heat treatment to polymerize in-situ;
including,
Method for producing polymer electrolyte.
In the first paragraph,
The above lithium salt is bis(fluorosulfonyl)imide lithium salt (LiFSI).
Method for producing polymer electrolyte.
In the second paragraph,
In the above in-situ polymerization step, the LiFSI acts as a polymerization initiator.
Method for producing polymer electrolyte.
In the first paragraph,
The above cross-linked polymer monomer is trimethylolpropane triglycidyl ether.
Method for producing polymer electrolyte.
In the first paragraph,
In the above precursor solution, the lithium salt is added at a molar concentration of 0.1 M to 3 M.
Method for producing polymer electrolyte.
In the first paragraph,
The above heat treatment is performed under a temperature range of 40°C to 80°C.
Method for producing polymer electrolyte.
In the first paragraph,
A method for producing a polymer electrolyte, wherein the solvent comprises a cyclic carbonate and/or a linear carbonate.
In paragraph 7,
A method for producing a polymer electrolyte, wherein the cyclic carbonate comprises one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and combinations thereof.
In paragraph 7,
A method for producing a polymer electrolyte, wherein the linear carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and combinations thereof.
A polymer electrolyte manufactured according to any one of claims 1 to 9.
A lithium ion battery comprising a polymer electrolyte according to claim 10.