WO2022154382A1 - Electrolyte containing allylphenyl sulfone for lithium secondary battery and lithium secondary battery including same - Google Patents

Abstract

In order to improve the interfacial stability of lithium metal oxide in a Ni-rich layer, the present invention is characterized by an electrolyte for a secondary battery and a secondary battery including same, wherein the electrolyte contains allyl phenyl sulfone (APS), which is a functional electrolyte additive modified with allyl and sulfone functional groups. The sulfone functional group introduced into the cathode-electrolyte interphase (CEI) can effectively suppress electrolyte decomposition during cycling and the allyl functional group allows for desired chemical reactivity promotive of an additional crosslinking reaction between CEIs, whereby the CEI can be established more robustly. In addition, the allyl functional group selectively scavenges fluorine species (F-) within the cell to reduce the concentration of F-, thereby enhancing the overall electrochemical performance of the cell.

Description

Electrolyte for lithium secondary battery containing allylphenyl sulfone and lithium secondary battery containing same

The present invention relates to an electrolyte solution for a lithium secondary battery containing allylphenyl sulfone and a lithium secondary battery containing the same, and more specifically, to an allylphenyl sulfone (APS) additive, a solvent, and a lithium salt comprising the same The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same.

The demand for energy storage/conversion devices is growing exponentially as electric vehicles (EVs) become one of the alternative environmentally friendly means of transportation in the near future.

Among many types of energy storage/conversion devices, lithium-ion batteries (LIBs) have been widely investigated as the main power source for EVs because of their stable electrochemical performance, such as long-term cycling retention and moderate rate capacity.

One of the technical challenges facing the EV industry entails the need to increase the driving mileage after a single charge.

Moreover, the increase in the energy density of LIBs has become the most important task in the battery industry to meet the specifications required for current EVs.

In this regard, many kinds of advanced electrode materials have been intensively developed in the past few years.

Among many electrode materials, layered oxides have been recognized as advanced cathode materials for LIBs. Although many kinds of layered lithium metal oxide exist, the most popular cathode material is nickel-rich layered nickel metal oxide (LiNi _x Co _y Mn _z O ₂ , x ≥ 0.6, Ni-rich because of its large capacity during electrochemical charging/discharging). abbreviated as NCM).

In Ni-rich NCM cathode materials, the specific capacity is dominated by the electrochemical reaction of Ni and Co.

Considering that the electrochemical redox property of Ni species is lower than that of Co species in the general blocking charging protocol, the specific capacity can be increased by increasing the Ni content in the layered structure of the NCM cathode material.

In this regard, increasing the Ni content of NCM anode materials can be a promising strategy for improving the energy density of cells, so various Ni-rich NCM cathode materials composed of 70% Ni, 80% Ni, and 90% Ni have been developed in the battery industry. has been developed intensively in

Nevertheless, there is an important bottleneck in the use of Ni-rich NCM cathode materials. Ni-rich NCM cathode materials show relatively low cycle performance compared to other anode materials.

In terms of surface stability, Ni-rich NCM cathode materials continuously undergo unwanted side reactions such as electrolyte decomposition and transition metal component decomposition during electrochemical charging/discharging.

This phenomenon is due to the relatively unstable nature of the Ni ⁴⁺ species (filled products).

The electrolyte (with many single pair electrons in the molecular structure of the solvent) can easily decompose in the cell in that Ni ⁴⁺ species are extremely unstable and therefore tend to decrease, increasing the cell's surface resistance at high states of charge.

In addition, when the electrolyte is decomposed through an electrochemical reaction, fluorine (F ⁻ ) species are generated in the cell, and these F ⁻ species decompose the transition metal component of the NCM cathode material through chemical erosion. In addition, the Ni-rich NCM cathode material has poor mechanical properties, so micro-cracks are continuously formed according to the electrochemical cycle. It results in a sharp decrease in the cycle performance of the ashes.

Therefore, it is necessary to alleviate the unstable interface characteristics of Ni-rich NCM cathode materials.

[Prior art literature]

(Patent Document 1) Republic of Korea Patent No. 10-0867535

Although nickel-rich lithium metal oxide is attracting attention as an advanced cathode material for lithium-ion batteries, its poor cycling performance at high temperatures is a major problem in its application.

The present invention relates to an electrolyte solution for a lithium secondary battery containing allylphenyl sulfone and a lithium secondary battery containing the same, and more specifically, to an allylphenyl sulfone (APS) additive, a solvent, and a lithium salt comprising the same The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same.

In order to solve the above technical problem, the present invention proposes the use of allyl phenyl sulfone (APS), which is a functional electrolyte additive functionalized by allyl and sulfone chemical moieties (Fig. 1).

Sulfone (-SO ₂ -)) functional group is a chemical component that effectively increases the surface stability of the NCM cathode material because it can act as an ion conductor and an electronic insulator on the surface of the NCM cathode material.

Therefore, once the -SO ₂ - functional group is embedded on the surface of the NCM cathode material, it is expected to effectively inhibit the electrolyte decomposition during electrochemical charging/discharging.

On the other hand, the Allyl (-C-C=C-) functional group group allows all radicals (formed by electrochemical reactions) to participate in additional cross-linking reactions during cathode-electrolyte interphase (CEI) layer formation. It is recognized as an effective modifier of the anode-electrolyte mesophase (CEI) layer because it makes the CEI layer more rigid when taken into account.

Therefore, the incorporation of sulfone and allyl functional groups into the molecular structure of the additive can improve the electrochemical performance of Ni-rich NCM cathode materials because unwanted surface reactions in the cell can be controlled. In the present invention, the electrochemical suitability of the APS additive for the above additive design is determined, and the basic chemistry can be explained through systematic analysis.

Among the additives, the allyl functional group removes F ^- through a reaction with a nucleophilic F ^- species.

The additive is characterized in that it contains 0.1% by weight or more and less than 0.5% by weight based on the weight of the electrolyte.

The solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), vinyl It is characterized in that it comprises at least one selected from the group consisting of ene carbonate (VC), vinyl ethylene carbonate (VEC), propylene carbonate (PC), and butylene carbonate (BC), but is not limited thereto.

The solvent preferably contains ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a ratio of 1:2.

The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiCl and LiI It may be at least one selected from the group consisting of, but is not limited thereto.

The lithium salt concentration is characterized in that it has a concentration of 0.01 to 2M.

According to another embodiment of the present invention, the positive electrode; cathode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the electrolyte layer is characterized in that the lithium secondary battery includes the above-described electrolyte.

A cathode-electrolyte interphase (CEI) layer is formed between the cathode and the electrolyte, and the cathode-electrolyte interphase (CEI) layer includes a sulfone functional group and an allyl functional group. characterized in that

The anode-electrolyte intermediate phase (CEI) layer includes a sulfone functional group that functions as an ion conductor and an electronic insulator on the anode surface.

Since the present invention features an electrolyte for a lithium secondary battery containing Allyl Phenyl Sulfone (APS), a functional electrolyte additive modified by allyl and sulfone functional groups, Ni-rich layer can improve the interface stability of lithium metal oxide.

The sulfone functional group introduced into the positive-electrolyte intermediate phase (CEI) can effectively inhibit the electrolyte degradation during cycling, and the allyl functional group makes the CEI more robust because its desirable chemical reactivity promotes additional cross-linking reactions between the CEIs. can make it

In addition, the allyl functional group selectively removes fluorine (F ⁻ ) species in the cell, thereby reducing the F ⁻ concentration and improving the overall electrochemical performance of the cell.

The results of ex-situ nuclear magnetic resonance spectroscopy confirmed that the addition of APS effectively reduced F-species through a chemical scavenging reaction.

Regarding the cycling performance of the half-cell, the cells cycled with the APS additive showed significantly improved cycling retention at high temperatures (78.9%), while the cells cycled with standard electrolytes struggled due to persistent preservation fading (64.3%). suffered

1 is a schematic diagram of an NCM811 cathode material using APS.

2 is (a) color change after 24 hours reaction with TBAF, (b) ¹ H NMR spectrum of APS, (c) ¹ H NMR spectrum of TBAF, and (d) ¹ H NMR spectrum of APS reacted with TBAF It is a drawing showing

3 shows (a) APS mechanism for HF scavenging reaction, (b) ionic conductivity of standard electrolyte (black) and APS control electrolyte: 0.1 APS (red), 0.25 APS (blue), 0.5 APS (green) (c) ) is a diagram showing the LSV results for the standard electrolyte (black) and the APS control electrolyte (orange).

4 shows (a) potential profile of the cell in the second cycle, (b) specific capacity at 45° C., (c) average coulombic efficiency, (d) APS (black: NCM811, red: 0.1 APS, blue: A diagram showing the Rate Capability of a cell cycled at 0.25 APS and green: 0.5 APS).

Figure 5 shows (a) cycle NCM811 anode using standard electrolyte, (b) cycling NCM811 anode, SEM analysis of cycle NCM811 anode using 0.25 APS control electrolyte, (c) cell formation and (d) NCM811 electrode after 50 cycles. Figures showing EIS analysis (black: NCM811 and blue: 0.25 APS).

6 is a diagram showing a) the XPS spectra of a cycled NCM811 electrode (top) and 0.25 APS (bottom): C1, F1s, P2p and S2p and (b) quantitative analysis of transition metals formed at the cathode.

7 shows (a) the potential profile of the cell in the formation cycle, (b) the specific capacity at 25°C, (c) the potential profile with respect to the C-rate change, and (d) the potential capacity of the cell cycled using APS. (black: NCM811, 0.1 APS, blue: 0.25 APS and green: 0.5 APS).

Figure 8 is a diagram showing (a) the voltage profile of the cell in the initial cycle, (b) retention at 45°C (black: NCM811, blue: 0.25APS).

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for helping the understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

Experiment

The chemical reactivity between the APS additive and F ⁻ was investigated as follows: 0.01 mol APS (Aldrich) and 0.01 mol tetrabutylammonium fluoride (TBAF, Aldrich) were placed in a plastic bottle and stirred for 24 hours. The resulting solution was collected and analyzed by nuclear magnetic resonance spectroscopy (Agilent 400-MR, Agilent) using CDCl ₃ (Aldrich) as an NMR solvent.

To measure the ionic conductivity, each electrolyte was prepared as follows: APS additive (0.1, 0.25, 0.5 wt%) was added to a glove box filled with argon as standard electrolyte (ethylene carbonate:ethyl methyl carbonate=1:2 + 1 M LiPF). ₆ , anabolic electrolytes) (each electrolyte is abbreviated as 0.1, 0.25, and 0.5 APS-controlled electrolytes).

Each electrolyte (15 mL) was placed in a conductivity meter (CM-41X, TOA-DKK) for ionic conductivity measurements at room temperature.

For linear sweep voltage measurement (LSV), a three-electrode cell assembled from free carbon (working electrode), platinum wire (counter electrode), and Ag/Ag ⁺ (reference electrode) was prepared, and its potential was 3.75 V (vs. Li/Li ⁺ ) to 5.0V (vs. Li/Li ⁺ ) were scanned at a rate of 1 mVs ⁻¹ .

To evaluate the cycle performance of the cell, NCM811 (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ) anodes were prepared as follows: 1.8 g NCM811 (ecopro), 0.1 g poly(vinylidene fluoride), 0.1 g carbon conductive agent (Super) P) was dispersed in 1.7 mL N-methylpyrrolidone (Aldrich) and mixed for 1 hour. The NCM811 slurry was coated on an aluminum current collector and then dried at 120° C. for 3 hours and dried in a vacuum oven at 120° C. for 12 hours. The load density of the NCM811 anode is 8.62 ± 0.3 mg cm ^-2 .

A 2032 coin cell was prepared using an NCM811 positive electrode, a lithium metal negative electrode, and a poly(propylene)/poly(ethylene)/poly(propylene) separator, each using the prepared electrolyte. For cycle performance evaluation, the cells were run from 3.0 V (vs Li/Li ⁺ ) to 4.3 V (vs, Li/Li ⁺ ) at room temperature or 45° C. at a current of 0.1 C for 2 cycles (formation phase), 0.5 for 100 cycles. It was cycled with a current of C.

For Rate Capability evaluation, the cells were charged/discharged to the same potential range, but the charge/discharge current densities were varied at 0.1C, 0.2C, 0.3C, 0.5C, 1.0C and 2.0C.

After cycling was complete, the cells were disassembled in an Ar-filled glove box, and the recovered NCM811 positive electrode was washed with dimethyl carbonate for 5 seconds. The recovered material was analyzed by field emission scanning electron microscopy (JSM-7800F, JEOL) to determine the surface morphology of the cycled NCM811 anode. Electrochemical impedance spectroscopy (EIS) analysis was performed on an electrochemical workstation (Wonatech, ZiveMP1) at 10 mV amplitudes from 1 M to 10 mHz. The chemical composition of the cycled NCM811 anode was quantified by X-ray photoelectron spectroscopy (XPS, Thermo-Scientific), and the transition metal component formed on the cathode surface was quantified by inductively coupled plasma mass spectroscopy (ICP-MS, FluoTime300/MicroTime100, Thermo).

Results and discussion

The F ^- scavenging performance of the APS additive was determined by ex-situ NMR analysis (Fig. 2). The F ^- equivalent, TBAF, served as the F ^- source in the chemical reaction between TBAF and the APS additive and reacted to determine whether the APS additive effectively traps the F ^- species. The solution consisting of APS additive and TBAF was colorless when placed in a plastic bottle, but eventually turned yellow and black. This color change indicates that the APS additive chemically reacted with TBAF. Ex-situ NMR analysis of the black solution indicates that the chemical state of the solution is clearly altered.

All ¹ H peaks in the APS additive were clearly observed in the ¹ H NMR spectrum (5.79 ppm (multiple value), 5.35 ppm (doublet), 5.17 ppm (doublet), 3.82 ppm (doublet)), but after the chemical reaction was completed, has disappeared. This phenomenon showed that the Allylic position of the APS additive participated in a chemical reaction with the F ⁻ species in solution, indicating that the F ⁻ species could be removed through chemical interaction with the APS additive. The allyl functional group can readily react with a nucleophile via an S _N2 reaction. Nucleophilic F ^- species can attack the C ₁ or C ₃ site of any carbon position during nucleophilic addition and removal reactions. Through this phenomenon, the F ⁻ concentration in the cell is expected to decrease.

The physical, chemical and electrochemical behaviors of APS control electrolytes were investigated (Fig. 3). The existing standard electrolyte showed an ionic conductivity of 9.20 mS cm ^-1 , which is a reliable value as reported elsewhere.

The ionic conductivity of the APS control electrolyte decreased with increasing APS (8.94, 8.77, and 8.61 mS cm ⁻¹ for 0.1, 0.25 and 0.5 APS control electrolyte, respectively).

Nevertheless, this ionic conductivity can still be applied to conventional LIBs. As shown in the LSV results, the standard electrolyte continued to decompose when the potential exceeded 4.3 V (versus Li/Li ⁺ ), meaning that oxidative decomposition occurred in the cell. In contrast, electrolyte degradation was well suppressed in the APS control electrolyte, except that a slightly increased oxidation current was momentarily observed at about 4.17 V (versus Li/Li ⁺ ). This intrinsic oxidation current observed at 4.17 V (Li/Li ⁺ ) was speculated to be a result of the electrochemical oxidation of the APS additive in the cell, suggesting that APS can generate a CEI layer on the electrode surface through an electrochemical oxidation reaction. do.

The room temperature cycling performance of the cell was measured as in FIG. 7 . During the initial cycle, the overall shape of the potential profile of the cell was approximately the same, but the initial specific discharge capacity of the cell circulating with the APS control electrolyte decreased slightly (209.7 and 208.3 for standard electrolytes and 0.1, 0.25, and 0.5 APS control electrolytes, respectively). , 208.3, 207.8 mAhg ⁻¹ ). This finding may be due to differences in the ionic conductivity of the electrolytes: given that this initial electrochemical action is primarily affected by the ionic conductivity of the electrolyte, cells cycled with APS-controlled electrolytes have higher discharge costs than cells cycled with standard electrolytes. quantity is slightly lower. With respect to standard electrolyte cyclic storage, all cells showed similar specific capacity retention after 100 cycles, equivalent to 166.2, 168.1, 165.9, and 164.9 mAhg ^-1 for standard electrolyte and 0.1, 0.25, and 0.5 APS control electrolyte, respectively.

The cycling performance of the cells during high temperature cycling was significantly different (Fig. 4). In terms of the initial potential profile, all cells showed similar potential curves, indicating that the difference in ionic conductivity between electrolytes moderated with increasing evaluation temperature. With respect to cycling preservation, cells cycled with standard electrolytes showed a continuous fading of cycling preservation, with only 64.3% preservation observed after 100 cycles. Given that electrolyte degradation is significantly accelerated at high temperatures, cells cycling with standard electrolytes suffered from reduced cyclic retention.

In contrast, cells cycled with the APS control electrolyte had improved cyclic storage. Cells cycled with 0.1 and 0.25 APS control electrolyte showed retention values of 77.6% and 78.9%, respectively. However, the 0.5 APS control electrolyte showed a relatively low retention rate of 69.5%.

In terms of average coulombic efficiency, the efficiencies of cells cycled with the standard electrolyte and 0.5 APS control electrolyte were 98.5% and 98.4%, respectively, lower than those of the 0.1 and 0.25 APS control electrolytes (99.4% and 99.3%, respectively).

These results showed that the use of APS additive effectively improved the electrochemical performance of the NCM811 cathode material, whereas the use of 0.5wt% APS additive seemed too excessive to satisfy the balancing of physical and chemical properties and electrochemical properties during cycling.

In terms of rate capacity, all cells showed similar discharge specific capacity at current charging conditions up to 0.5C, but cells cycled with 0.25 APS control electrolyte also exhibited similar discharge specific capacity at high current charging (>1.0C) compared to cycling with standard electrolyte. An improved discharge specific capacity was exhibited. A possible explanation for this feature is that if the APS additive is decomposed in the cell, an APS-based CEI layer can be formed on the surface of the NCM811 anode. This CEI layer contains a group of sulfone functional groups that can accelerate ion transport in the intermediate phase between the NCM811 anode and the electrolyte through an ion hopping mechanism. Overall, the 0.25 APS control electrolyte improved cycling retention with rate capacity.

After evaluating the cycling performance, the recovered NCM811 positive electrode was analyzed by SEM ( FIGS. 5A-5B ). The SEM image showed that the surface morphology of the recovered NCM811 positive electrode cycled with the standard electrolyte was significantly changed compared to the initial state. Decomposition products from electrolytic decomposition significantly covered the surface of the NCM811 anode, which means that an unwanted reaction has occurred seriously. In contrast, the NCM811 anode cycled with 0.25 APS control electrolyte was relatively clean, and the boundaries between primary particles could be well observed.

This difference in surface morphology affects the internal resistance of the cell (Figs. 5c-5d). After the initial cycle, the R _CEI and R _CT of the cell were almost similar, but the internal resistance of the cell cycled with 0.25 APS control electrolyte was similar to that of the cell cycled with standard electrolyte (R _CEI ) as a new CEI layer was formed on the anode surface. : 10.4Ω and R _CT : 30.9Ω) and slightly increased (R _CEI : 12.6Ω and R _CT : 32.5Ω).

However, as the number of cycles increased, cells cycled with 0.25 APS control electrolyte had internal resistance (R _CEI :27.7 Ω and R _CT :80.3 Ω) compared to standard electrolytes (R _CEI :22.7 Ω, R _CT :67.2 Ω). This increased significantly.

These results were supported in XPS analysis (Fig. 6a). In the C 1s spectrum, resolved additives related to CO (286.2 eV), RCOR (287.1 eV), C=O (289.3 eV) and CF (290.7 eV) were found in the cycled NCM811 anode: however, the overall peak intensities were standard It was lower in cells cycled with 0.25 APS control electrolyte than in cells cycled with electrolyte. These features indicate that electrolyte degradation occurred severely in cells cycled with standard electrolytes. Similar spectroscopic behaviors were observed in the F 1s and P 2p spectra. The strength of decomposed additives such as Li _x PO _y F _z (688.3 eV in F1s, 134.1 eV in P2p), Li _x PF _y (687.7 eV in F1s, 136.5 V in P2p) and LiF (685.1 eV in F1s) is 0.25 significantly higher in cells cycled with standard electrolyte than in cells cycled with APS control electrolyte. These results indicate that electrolyte degradation was clearly suppressed when the APS additive was used as a functional additive.

In addition, intrinsic S peaks, such as S-C (164.1 eV), S-O (165.7 eV), and S=O (168.5 eV) of the S 2p spectrum, were observed in cells cycled with 0.25 APS control electrolyte even after 100 cycles, indicating that the NCM811 anode surface It is shown that the electrochemical oxidation of the APS additive forms a functional group-based CEI layer, and this functional group-based CEI layer effectively inhibits electrolyte degradation during the electrochemical process, thereby improving the cycling preservation.

The study results on the reduction of electrolyte decomposition were also supported by ICP-MS analysis of the cycled negative electrode (Fig. 6b). When electrolytic decomposition occurs, F ⁻ species should be formed in the cell, which species readily corrode the transition metal component of the anode material. When the transition metal component is dissolved into the electrolyte, it migrates to the surface of the anode and is easily reduced.

Therefore, quantification of the cathode can be a reasonable approach to estimate the degree of electrolyte degradation in the cell. As a result of the analysis, standard electrolytes (Ni, Co, Mn, respectively) 0.25 APS control electrolyte (Ni, Co, Mn respectively) than cells with 45,108, 5,694 and 6,267 ppb). 17,784, 1,951 and 2,745 ppb) had a lower amount of dissolved transition metal components in the anode cycle. Therefore, it can be concluded that electrolyte degradation is well suppressed in cells composed of APS as electrolyte additive.

Based on the above results, the full-cell cycle performance of the APS additive was evaluated ( FIG. 8 ).

Half-cell results showed that cells cycled with standard electrolyte had poor cycling retention, with only 74.5% of specific capacity remaining at the end of cycling.

In contrast, cells cycled with 0.25 APS control electrolyte showed a retention rate of 78.2% after 100 cycles, demonstrating that the improved surface stability of the NCM811 positive electrode mainly dominates the cycling performance of the full-cell. These results indicate that the use of APS additives is an effective means to increase the electrochemical performance of the NCM811 anode. This is because it effectively stabilizes the interface performance of the anode.

conclusion

To improve the interface stability of the NCM811 anode, we propose the use of APS, a functional electrolyte additive modified by allyl and sulfone functional groups. Ex-situ NMR analysis showed that the allyl functional group in the molecular structure of the APS additive participates in a chemical reaction with the F ⁻ species, resulting in a decrease in the F ⁻ concentration in the cell. The LSV results showed that the electrochemical oxidation of APS can produce a CEI layer on the surface of the NCM811 anode at about 4.17 V (versus Li/Li ⁺ ). The use of the APS additive did not significantly affect the room temperature cycling performance of the cell, but apparently did change the high temperature cycling performance. Cells cycled with standard electrolyte showed a sustained fading (64.3%) of periodic conservation, whereas cells cycled with 0.25 APS control electrolyte showed significantly improved periodic conservation with an increase in average coulombic efficiency and rate capacity. The SEM analysis results for the cycled NCM811 positive electrode showed that the surface morphology of the recovered NCM811 positive electrode cycled with 0.25 APS control electrolyte was not damaged compared to the initial state, and this result is strongly supported by EIS, XPS and ICP-MS analysis. indicated that there is Based on these results, the APS additive effectively improved the interface stability of the NCM811 anode by significantly inhibiting unwanted reactions such as electrolyte decomposition and decomposition of transition metal components through the formation of reliable CEI on the surface of the NCM811 anode. conclusion can be drawn.

Claims (12)

1. An electrolyte for a lithium secondary battery comprising an allyl phenyl sulfone (APS) additive, a solvent, and a lithium salt.
2. According to claim 1,

   The allyl phenyl sulfone (Allyl phenyl sulfone, APS) additive is an electrolyte for a lithium secondary battery, characterized in that it comprises a sulfone (Sulfone) functional group and an allyl (Allyl) functional group.
3. According to claim 1,

   An electrolyte for a lithium secondary battery, characterized in that the allyl functional group among the additives removes F ^- through a reaction with the nucleophilic F ^- species.
4. According to claim 1,

   The additive is an electrolyte for a lithium secondary battery, characterized in that it contains 0.1% by weight or more and less than 0.5% by weight based on the weight of the electrolyte.
5. The method of claim 1,

   The solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), vinyl An electrolyte for a lithium secondary battery, comprising at least one selected from the group consisting of ene carbonate (VC), vinyl ethylene carbonate (VEC), propylene carbonate (PC), and butylene carbonate (BC).
6. 6. The method of claim 5,

   The solvent is an electrolyte for a lithium secondary battery, characterized in that EC (ethylene carbonate):EMC (ethyl methyl carbonate) is included in a ratio of 1:2 (v/v%).
7. According to claim 1,

   The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiCl and LiI Electrolyte for a lithium secondary battery, characterized in that at least one selected from the group consisting of.
8. According to claim 1,

   The lithium salt concentration is an electrolyte for a lithium secondary battery, characterized in that having a concentration of 0.01 to 2M.
9. anode; cathode; and an electrolyte layer disposed between the positive electrode and the negative electrode,

   The electrolyte layer is a lithium secondary battery comprising the electrolyte according to any one of claims 1 to 8.
10. 10. The method of claim 9,

    A cathode-electrolyte interphase (CEI) layer is formed between the cathode and the electrolyte, and the cathode-electrolyte interphase (CEI) layer includes a sulfone functional group and an allyl functional group. Lithium secondary battery, characterized in that.
11. 11. The method of claim 10,

    A lithium secondary battery, characterized in that the positive electrode-electrolyte intermediate phase (CEI) layer included in the sulfone functional group serves as an ion conductor and an electronic insulator on the surface of the positive electrode.
12. 11. The method of claim 10,

    The positive electrode-electrolyte intermediate phase (CEI) layer included in the allyl (Allyl) functional group is a lithium secondary battery, characterized in that the removal of F ^- through a reaction with a nucleophilic F ^- species.

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