Positive electrode comprising positive electrode electrolyte interface layer, secondary battery comprising same, method for forming positive electrode electrolyte interface layer, and gel polymer electrolyte composition for forming same

Abstract

A gel polymer electrolyte composition according to an embodiment of the present disclosure includes a monomer, a lithium salt, an additive, and a solvent, wherein the additive includes phosphorus and an aromatic ring, at least one of the aromatic rings is an aromatic ring substituted with a functional group containing fluorine, a ratio of a phosphorus element and a fluorine element in the additive is 1:3 to 1:15, and the additive and the monomer may be included in a weight ratio of 1:5 to 1:20.

Description

Anode comprising a positive electrode electrolyte interface layer, secondary battery comprising the same, method for forming a positive electrode electrolyte interface layer, and gel polymer electrolyte composition for forming the same

[0001] The present disclosure relates to an anode comprising an anode electrolyte interface layer, a secondary battery comprising the same, a method for forming an anode electrolyte interface layer, and a gel polymer electrolyte composition for forming the same.

[0002] Gel polymer electrolytes possess properties intermediate between liquid and all-solid electrolytes, enabling the simultaneous realization of the diffusivity of liquids and the cohesiveness of solids. Curable gel polymer electrolytes can be manufactured through the chemical crosslinking of polymerizable monomers initiated by thermal or light (UV) energy. This allows for high ionic conductivity comparable to that of liquid electrolytes (approximately 10 -4 ~10 -3 It can possess flexible properties (S / cm) and, in addition, good mechanical stability, leakage prevention, low volatility, and electrochemical stability characteristic of all-solid electrolytes; thus, it has high applicability as it can simultaneously overcome the fundamental limitations of both liquid and solid electrolytes.

[0003] However, curable gel polymer electrolytes may contain unreacted residual monomers after curing, and these unreacted monomers can interfere with lithium ion conduction and cause adverse reactions with the electrodes, which are known to affect the degradation of battery performance. Therefore, to ensure a stable battery life, it is important to minimize unreacted monomers and suppress cell performance degradation caused by them, and research is needed to address this.

[0004] The present disclosure is intended to provide a positive electrode comprising a positive electrolyte interface layer, a secondary battery comprising the same, a method for forming a positive electrolyte interface layer, and a gel polymer electrolyte composition for forming the same.

[0005] A gel polymer electrolyte composition according to one embodiment of the present disclosure comprises a monomer, a lithium salt, an additive, and a solvent, wherein the additive comprises phosphorus and an aromatic ring, and at least one of the aromatic ring is an aromatic ring substituted with a functional group including fluorine, and the ratio of the phosphorus element and the fluorine element in the additive is 1:3 to 1:15, and the additive and the monomer may be included in a weight ratio of 1:5 to 1:20.

[0006] The above monomer may have (meth)acrylic or (meth)acrylate-based crosslinking groups.

[0007] The above monomer may have 2 to 4 crosslinking groups.

[0008] The above monomer may be one or more selected from the group consisting of trimethylolpropane ethoxylate triacrylate, trimethylolpropane triacrylate, and polyethylene glycol.

[0009] The above additive may be a fluorinated phosphine-based additive.

[0010] The above additive may be one or more selected from the group consisting of tris(4-fluorophenyl)phosphine, tris(pentafluorophenyl)phosphine, tris(3-fluorophenyl)phosphine, and tris(3,5-difluorophenyl)phosphine.

[0011] A secondary battery according to another embodiment of the present disclosure comprises a positive electrode, a negative electrode, and a gel polymer electrolyte, wherein the positive electrode comprises a positive current collector, a positive composite layer formed on the positive current collector, and a positive electrolyte interface layer (CEI layer) formed on the positive composite layer, and the CEI layer may be formed from the gel polymer electrolyte composition described above.

[0012] The above additive may be present in the above CEI layer.

[0013] When XPS elemental analysis is performed on the outermost surface of the above CEI layer, based on the total elements of F, C, and O, the atomic concentration ratio of F may be 18.5% or more, the atomic concentration ratio of C may be less than 59.5%, and the atomic concentration ratio of O may be less than 22%.

[0014] The gel polymer electrolyte may be a cured gel polymer electrolyte composition.

[0015] When analyzing the above gel polymer electrolyte via FT-IR, at 1805 cm⁻¹ -1 (C=O vibration) and 1070 cm -1 When normalized based on the characteristic peak of ethylene carbonate (EC) appearing in (CO stretching), 1580 to 1600 cm⁻¹ -1 A peak may exist within the range.

[0016] The gel polymer electrolyte described above includes an additive, wherein the additive comprises phosphorus and an aromatic ring, and at least one of the aromatic ring is an aromatic ring substituted with a functional group containing fluorine, and the ratio of phosphorus element to fluorine element among the additive may be 1:3 to 1:15.

[0017] The above gel polymer electrolyte may include tris(4-fluorophenyl)phosphine (TFPP).

[0018] A method for forming an anode electrolyte interface layer according to another embodiment of the present disclosure may form an anode electrolyte interface layer (CEI layer) on the anode by impregnating the anode, on which an anode composite layer is formed on an anode current collector, with the gel polymer electrolyte composition described above and then curing it, applying a certain voltage to the anode, and performing charge and discharge multiple times. The voltage may be less than the voltage at which the monomer decomposes and greater than or equal to the voltage at which the additive decomposes.

[0019] The above voltage may be less than the voltage at which the oxidative decomposition reaction of the monomer occurs.

[0020] The voltage at which the monomer or additive decomposes may be the voltage in the section where the current density increases in the LSV (Linear sweep voltammetry) graph measured for the liquid electrolyte containing the monomer or additive.

[0021] The voltage at which the oxidative decomposition reaction of the above monomer occurs may be the voltage at the position where a peak occurs in the dQ / dV plot measured for the liquid electrolyte containing the monomer.

[0022] A gel polymer electrolyte composition according to one embodiment of the present disclosure can form a stable electrode interface when used in a cell such as a lithium secondary battery.

[0023] An anode according to one embodiment of the present disclosure may have a lower interfacial resistance.

[0024] A lithium secondary battery including a positive electrode according to one embodiment of the present disclosure can have improved capacity performance (initial capacity and capacity retention rate).

[0025] A method for forming an anode electrolyte interface layer according to one embodiment of the present disclosure can form a stable electrode interface on the anode.

[0026] The anode comprising an anode electrolyte interface layer of the present disclosure, a secondary battery comprising the same, a method for forming an anode electrolyte interface layer, and a gel polymer electrolyte composition for forming the same can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other applications utilizing batteries, such as solar power generation and wind power generation. Furthermore, the anode comprising an anode electrolyte interface layer of the present disclosure, a secondary battery comprising the same, a method for forming an anode electrolyte interface layer, and a gel polymer electrolyte composition for forming the same can be used in eco-friendly electric vehicles, hybrid vehicles, etc., to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0027] FIG. 1 shows graphs of the cycle performance for an initial capacity and 100 cycles and the rate capability characteristics for 21 cycles for Comparative Examples 1 to 4 of the present disclosure, FIG. 1 (a) shows the cycle performance for an initial capacity and 100 cycles, and FIG. 1 (b) shows the rate capability characteristics for 21 cycles.

[0028] FIG. 2 shows a graph analyzing the change in the magnitude of interfacial resistance through EIS (electrochemical impedance spectroscopy) analysis for Comparative Examples 5 and 6 of the present disclosure before aging (a), after aging for 10 hours (b), and after initial charging (c), respectively.

[0029] Figure 3 (a) is an LSV analysis graph for ETPTA, TFPP, and liquid electrolyte, respectively, and Figure 3 (b) is a graph showing a more magnified section of the rapid increase in current density for ETPTA and TFPP.

[0030] FIG. 3 (c) is a graph showing the result of a dQ / dV plot peak analysis to measure the voltage at which oxidative decomposition occurs during the initial charge-discharge process for the monomer (ETPTA), and FIG. 3 (d) shows an example of an initial-activation protocol prepared in consideration of the results of FIG. 3 (a) to (c).

[0031] FIG. 4 shows graphs of dQ / dV plot peak analysis performed on Comparative Examples 6 and 9, divided into cases where the Voltage Hold Method is not applied and cases where it is applied. FIG. 4 (a) is the result graph for Comparative Example 6 when the Voltage Hold Method is not applied, FIG. 4 (b) is the result graph for Comparative Example 9 when the Voltage Hold Method is not applied. FIG. 4 (c) is the result graph for Comparative Example 9 when the Voltage Hold Method is applied, and FIG. 4 (d) is the result graph for Comparative Example 6 when the Voltage Hold Method is applied.

[0032] FIG. 5 is a graph showing the results of a cycle performance evaluation for Comparative Examples 6 to 9 of the present disclosure. FIG. 5 (a) is a graph showing the change in discharge capacity when the Voltage Hold Method is not applied to Comparative Examples 7 and 8, and when the Voltage Hold Method is applied to Comparative Example 8 at 3.6V and 3.7V. FIG. 5 (b) is a graph showing the change in discharge capacity when the Voltage Hold Method is not applied to Comparative Examples 6 and 9, and when the Voltage Hold Method is applied to Comparative Example 9 at 3.6V and 3.7V. FIG. 5 (c) is a graph showing the Coulombic Efficiency according to the number of cycles for each case of FIG. 5 (b). FIG. 5 (d) is a graph showing a comparison of the voltage at 50% State of Charge (SOC) according to the number of cycles for each case of FIG. 5 (b).

[0033] Figure 6 (a) is a graph showing the results of EIS analysis for Comparative Example 9 when the Voltage Hold Method was not performed and when the Voltage Hold Method was performed at 3.7V, and (b) is a graph showing the respective electrode interface resistance values ​​(Rcei) obtained from the EIS analysis results.

[0034] Figure 7 is a graph showing the results of the cycle performance evaluation in a cured semi-solid electrolyte system.

[0035] Figure 8 is a graph showing the results of the analysis of the magnitude of the interfacial resistance measured through EIS analysis in a cured semi-solid electrolyte system.

[0036] Figure 9 is a graph showing the results of battery performance evaluation according to the content ratio of monomers and additives.

[0037] Figure 10 is a graph showing the results of battery performance evaluation according to the maintenance voltage.

[0038] Figure 11 is a graph showing the results of evaluating battery performance and interfacial resistance with and without TPFPP additive, Figure 11 (a) is a graph showing the results of measuring capacity retention rate after 100 charge-discharge cycles, and Figure 11 (b) is a graph showing the results of measuring interfacial resistance.

[0039] The present disclosure is subject to various modifications and may have various embodiments, and the present disclosure is to be described in detail with respect to specific embodiments. However, this is not intended to limit the present disclosure to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present disclosure.

[0040] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as “comprising” or “having” are intended to specify the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0041] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which this disclosure pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0042] Hereinafter, an embodiment of the present disclosure will be described in more detail.

[0043] Gel polymer electrolyte composition

[0044] A gel polymer electrolyte composition according to one embodiment of the present disclosure is in a liquid state, and after injecting the gel polymer electrolyte composition into an electrode assembly (e.g., a pouch containing an electrode assembly), a gel polymer electrolyte can be formed through energy transfer such as thermal curing or light irradiation. The gel polymer electrolyte composition may include a precursor that can be polymerized, and, for example, may include a monomer or an oligomer as the precursor.

[0045] A gel polymer electrolyte composition according to one embodiment of the present disclosure may comprise a monomer, a lithium salt, an additive, and a solvent. The additive comprises phosphorus and an aromatic ring, wherein at least one of the aromatic ring is an aromatic ring substituted with a functional group containing fluorine, and the ratio of phosphorus elements to fluorine elements in the additive may be 1:3 to 1:15. Additionally, the additive and the monomer may be included in a weight ratio of 1:5 to 1:20.

[0046] The additive included in the gel polymer electrolyte composition of the present disclosure may include phosphorus and aromatic rings, specifically may have a structure in which a plurality of aromatic rings are bonded to a single phosphorus, and more specifically may have a structure in which a plurality of aromatic rings substituted with one to five fluorine elements are bonded to a single phosphorus. Additionally, the additive included in the gel polymer electrolyte composition may have a structure in which three aromatic rings are bonded to a single phosphorus, and each aromatic ring bonded to the phosphorus may be independently substituted with one to five fluorine elements, and more specifically, each aromatic ring bonded to the phosphorus may be substituted with one to five fluorine elements in the same structure.

[0047] The additive included in the gel polymer electrolyte composition of the present disclosure may have a ratio of phosphorus element and fluorine element of 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, or 1:15 depending on the number of fluorine elements substituted in each aromatic ring.

[0048] The additive included in the gel polymer electrolyte composition may be a fluorinated phosphine-based compound. Examples of the additives include, but are not limited to, tris(4-fluorophenyl)phosphine (TFPP), tris(3-fluorophenyl)phosphine, tris(3,5-difluorophenyl)phosphine, and tris(pentafluorophenyl)phosphine (TPFPP). The additive included in the gel polymer electrolyte composition may be one or more selected from the group consisting of tris(4-fluorophenyl)phosphine, tris(3-fluorophenyl)phosphine, tris(3,5-difluorophenyl)phosphine, and tris(pentafluorophenyl)phosphine, and more specifically, one or more selected from the group consisting of tris(4-fluorophenyl)phosphine and tris(pentafluorophenyl)phosphine.

[0049] The monomer included in the gel polymer electrolyte composition of the present disclosure may be capable of forming a gel polymer electrolyte and may be, for example, a monomer having 2 to 5, 2 to 4, 2 to 3, or 3 crosslinking groups. The crosslinking groups may be thermosetting or photocurable crosslinking groups and may be, for example, (meth)acrylic or (meth)acrylate-based crosslinking groups.

[0050] For example, the monomer may further include ether groups, for example, 2 to 5, 2 to 4, 2 to 3, or 3 ether groups.

[0051] For example, the monomer may include 2 to 4 crosslinking groups and may include 2 to 4 ether groups. The crosslinking groups may be (meth)acrylic or (meth)acrylate-based crosslinking groups.

[0052] For example, the monomer may include three crosslinking groups and three ether groups. The crosslinking groups may be (meth)acrylic or (meth)acrylate-based crosslinking groups.

[0053] For example, the monomers include trimethylolpropane ethoxylate triacrylate (ETPTA), trimethylolpropane ethoxylate triacrylate (TMPTA), polyethylene glycol, etc. Specifically, one or more selected from the group consisting of ETPTA, TMPTA, and PEO may be used, and more specifically, ETPTA may be used.

[0054] The additives and monomers included in the gel polymer electrolyte composition of the present disclosure may be included in a weight ratio of 1:5 to 1:20, specifically in a weight ratio of 1:5 to 1:15, and more specifically in a weight ratio of 1:5 to 1:10. If the weight ratio of the additives and monomers deviates from the range of 1:5 to 1:20, an incomplete electrode interface may be formed in a lithium secondary battery containing the gel polymer electrolyte composition, which may increase electrode interface resistance, decrease the initial capacity of the lithium secondary battery, or decrease the capacity retention rate.

[0055] Although not limited thereto, the additives and monomers included in the gel polymer electrolyte composition of the present disclosure may be selected by comparing the energy levels of their respective HOMOs (Highest Occupied Molecular Orbitals). Specifically, when forming a cathode-electrolyte interphase layer (CEI layer) at the anode, the HOMO energy level of the additive may be higher than the HOMO energy level of the monomer. Accordingly, it is expected that oxidation stability at the anode can be increased, and oxidation stability at the anode is expected to improve as the difference between the HOMO energy levels of the additive and the monomer increases. For example, since the HOMO energy level of TFPP as an additive has a higher value compared to the HOMO energy level of ETPTA as a monomer, ETPTA and TFPP can be used as suitable monomers and additives, respectively.

[0056] The gel polymer electrolyte composition of the present disclosure may include an electrolyte.

[0057] The electrolyte comprises a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - It is expressed as, and the anion (X) of the above lithium salt - As F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N- , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples of the back can be given.

[0058] The above organic solvent may include an organic compound that has sufficient solubility for the lithium salt and additive and does not have reactivity in the battery. For example, the above organic solvent may include at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.As the above organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, and tetraethylene glycol Dimethyl ether (tetraethylene glycol dimethyl ether, TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite may be used. These may be used alone or in combination of two or more.

[0059] The electrolyte may further include other additives. The other additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sulfone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds.

[0060] The above-mentioned cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0061] The above fluorine-substituted carbonate-based compounds may include fluoroethylene carbonate (FEC), etc.

[0062] The above sulfone-based compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0063] The above-mentioned cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0064] The above-mentioned cyclic sulfite compounds may include ethylene sulfite, butylene sulfite, etc.

[0065] The above phosphate-based compounds may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0066] The above borate-based compounds may include lithium bis(oxalate) borate, etc.

[0067] In some embodiments, the gel polymer electrolyte composition may be cured to produce a gel polymer electrolyte. For example, the gel polymer electrolyte composition may be injected into a battery case containing an electrode assembly, and then a thermal curing reaction may be induced in a situ manner to form a gel polymer electrolyte.

[0068] A secondary battery according to another embodiment may include an electrode assembly comprising a positive electrode and a negative electrode. The electrode assembly may be accommodated in a case together with a gel polymer electrolyte according to the exemplary embodiments described above. For example, the electrode assembly may further include a solid electrolyte interposed between the positive electrode and the negative electrode. Optionally, a separator may further include between the positive electrode and the negative electrode.

[0069] anode

[0070] A cathode according to another embodiment of the present disclosure comprises a cathode current collector, a cathode composite layer formed on the cathode current collector, and a cathode electrolyte interphase layer (CEI layer) formed on the cathode composite layer, wherein the CEI layer may be formed from the gel polymer electrolyte composition described above. The CEI layer may be rich in LiF, and accordingly, the oxidative decomposition of electrolyte components such as residual unreacted monomers can be suppressed to prevent deterioration of the cathode.

[0071] The additive may be present in the CEI layer formed on the anode according to another embodiment of the present disclosure. The additive or a decomposition product of the additive may be present in the CEI layer.

[0072] The anode may include an anode current collector and an anode composite layer disposed on at least one surface of the anode current collector.

[0073] The positive current collector may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive current collector may also include aluminum surface-treated with carbon, nickel, titanium, or silver, or stainless steel surface-treated with carbon, nickel, titanium, or silver. Additionally, the positive current collector may be a polymer substrate coated with a conductive metal such as nickel, aluminum, titanium, or silver.

[0074] The above positive current collector may be in various forms, such as foil, foam, net, porous material, or nonwoven material, as non-limiting examples. In addition, the above positive current collector may have a thickness of 10 to 50 μm, although it is not limited thereto.

[0075] The positive electrode composite layer may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0076] According to exemplary embodiments, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0077] In some embodiments, the positive active material or the lithium-nickel metal oxide may comprise a layered structure or a crystalline structure represented by the following chemical formula 1.

[0078] [Chemical Formula 1]

[0079] Li x Ni a M b O 2+z

[0080] In Chemical Formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1 may be used. As described above, M may include Co, Mn, and / or Al.

[0081] The chemical structure represented by Chemical Formula 1 represents the bonding relationships contained within the layered or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn may be provided as the main active element of the positive electrode active material together with Ni. Chemical Formula 1 is provided to express the bonding relationships of the main active elements and should be understood as encompassing the introduction and substitution of additional elements.

[0082] In one embodiment, auxiliary elements may be further included to enhance the chemical stability of the anode active material or the layered structure / crystal structure by adding to the main active element. The auxiliary elements may be incorporated together within the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the range of the chemical structure represented by Chemical Formula 1.

[0083] The above auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The above auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the cathode active material together with Co or Mn, such as Al.

[0084] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0085] [Chemical Formula 1-1]

[0086] Li x Ni a M1 b1 M2 b2 O 2+z

[0087] In Chemical Formula 1-1, M1 may include Co, Mn and / or Al. M2 may include the auxiliary element described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0088] The above-described positive active material may further include a coating element or a doping element. For example, elements substantially identical or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, any of the elements described above may be used alone or in combination of two or more as coating elements or doping elements.

[0089] The coating element or doping element may be present on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal oxide particles and be included within the bonding structure represented by Formula 1 or Formula 1-1.

[0090] The above-mentioned positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0091] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by adopting a high-Ni composition in the cathode active material as described above, a high-capacity cathode and a high-capacity lithium secondary battery can be provided.

[0092] However, as the Ni content increases, the long-term storage stability and lifespan stability of the anode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, lifespan stability and capacity retention characteristics can be improved through Mn while maintaining electrical conductivity by including Co.

[0093] The content of Ni in the above NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0094] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0095] In some embodiments, the positive electrode active material may include, for example, a Mn-rich active material having a chemical structure or crystal structure represented by Formula 2, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) active material, or a Co-less active material.

[0096] [Chemical Formula 2]

[0097] p[Li2MnO3]·(1-p)[Li q JO2]

[0098] Of chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0099] For example, an anode slurry can be prepared by mixing the anode active material in a solvent. An anode composite layer can be prepared by coating the anode slurry onto an anode current collector, followed by drying and rolling.

[0100] The above coating process may be carried out using methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, but is not limited thereto.

[0101] The above anode composite layer may further include a binder and optionally further include a conductive material, a thickener, etc.

[0102] The solvents used to prepare the anode slurry above are not limited to, but include, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0103] The above binder may include polyvinylidenefluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as the anode binder.

[0104] The above conductive material may be added to enhance the conductivity of the anode composite layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, ketjenblack, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, etc., and / or metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0105] If necessary, the anode composite may further include a thickener and / or a dispersant, etc. In one embodiment, the anode composite may include a thickener such as carboxymethyl cellulose (CMC).

[0106] Anode electrolyte interface layer and method for forming the same

[0107] A positive electrolyte interface layer (CEI) according to another embodiment of the present disclosure can be formed by impregnating an electrode assembly with the gel polymer electrolyte composition described above, curing it, applying a certain voltage for a certain period of time, and performing charge and discharge multiple times. Here, the voltage may be less than the voltage at which the monomer decomposes and greater than or equal to the voltage at which the additive decomposes.

[0108] The above electrode assembly may include an anode having an anode composite layer formed on an anode current collector.

[0109] In the present disclosure, the step of applying a constant voltage for a certain period of time may be referred to as an initial-activation process, and the step of performing charge and discharge multiple times may be referred to as a formation process.

[0110] The gel polymer electrolyte composition can be cured for a time of about 30 minutes to 300 minutes at a temperature range of about 50 to 100°C, for example, but is not limited thereto.

[0111] An initial activation process, in which a constant voltage is applied for a certain period of time, is performed prior to a formation process in which multiple charge-discharge cycles are subsequently carried out. A voltage hold method may be utilized, and the voltage within a certain range applied through the voltage hold method can be referred to as the holding voltage. By selecting the holding voltage within the above range, the decomposition reaction of residual unreacted monomers is suppressed during the subsequent formation process, while the additives are predominantly decomposed, thereby enabling the formation of a stable CEI layer on the anode interface.

[0112] The time during which the initial-activation process is carried out may be approximately 5 to 50 hours, specifically approximately 7 to 30 hours, and more specifically approximately 8 to 20 hours.

[0113] The voltage at which the monomer decomposes and the voltage at which the additive decomposes can be measured through linear sweep voltammetry (LSV) analysis, and may be the voltage in the region where an increase in current density occurs in the LSV graph measured for a liquid electrolyte (a solution containing a lithium salt and a solvent) containing the monomer or additive. Specifically, for LSV analysis, a Li|Stainless Steel (SS) cell containing a liquid electrolyte without monomers or additives, a Li|SS cell containing a liquid electrolyte with the monomers added, and a Li|SS cell containing a liquid electrolyte with the additives added can be prepared, and each cell can be analyzed using linear sweep voltammetry. By continuously applying voltage, the monomers, additives, and liquid electrolytes can each decompose independently through reduction reactions above a specific voltage. In a cell containing only liquid electrolyte, it is possible to determine whether the liquid electrolyte components decompose within the analyzed voltage range. In a cell containing a liquid electrolyte to which a monomer or additive is added, it is possible to determine at which voltage range the monomer or additive decomposes within the analyzed voltage range. Specifically, for a liquid electrolyte containing a monomer or additive, the decomposition reaction of the monomer or additive can be considered to begin in the range where the current density increases, and the corresponding voltage range can be determined as the voltage at which the monomer decomposes or the voltage at which the additive decomposes. Although not limited thereto, LSV analysis can be measured, for example, at a scan rate of about 1 mV / s in a voltage analysis range of about 3.0 to 6.0 V at room temperature (about 25°C). Any known liquid electrolyte can be used as the liquid electrolyte containing the monomer or additive, and for example, the liquid electrolyte component included in the gel polymer electrolyte composition of the present disclosure can be used.

[0114] In addition, the holding voltage may be lower than the voltage at which the oxidative decomposition reaction of the monomer occurs. If the voltage at which the oxidative decomposition reaction of the monomer occurs is lower than the monomer decomposition voltage measured through LSV analysis, the oxidative decomposition of residual unreacted monomer can be suppressed during the voltage holding method by selecting the holding voltage within a range lower than the voltage at which the oxidative decomposition reaction of the monomer occurs. Here, the voltage at which the oxidative decomposition reaction of the monomer occurs can be measured through differential capacity plot (dQ / dV plot) analysis and may be the voltage at the location where a peak occurs in the dQ / dV plot measured for a liquid electrolyte (a solution containing a lithium salt and a solvent) containing the monomer. Specifically, the dQ / dV plot can be constructed by differentiating the voltage curve of the constant current charge / discharge results. Here, the oxidative decomposition reaction of the monomer at which a peak occurs can be considered to exist, and the voltage at the location where the peak occurs can be interpreted as the reaction voltage. A dQ / dV plot for the monomer can be obtained by, for example, by performing a single charge-discharge cycle at 0.1C / 0.1C in a voltage analysis range of about 3.0 to 4.3V at room temperature (about 25°C) for an NCM712|lithium metal (Li metal) half cell containing a liquid electrolyte to which the monomer is added, and then obtaining a voltage curve and differentiating the obtained voltage curve to obtain a dQ / dV plot. In a single charge-discharge cycle, charging can be performed under constant voltage and constant current conditions, and discharging can be performed under constant current conditions. Here, the single charge-discharge cycle may be performed under charge-discharge conditions that are carried out in a subsequent formation process. Any known liquid electrolyte can be used as the liquid electrolyte containing the monomer, and for example, the liquid electrolyte component included in the gel polymer electrolyte composition of the present disclosure can be used.

[0115] By means of a holding voltage, the potential of the positive electrode of a lithium secondary battery can be fixed at a certain level, and the additive can be selectively decomposed in the CEI layer at the positive electrode interface to form a stable CEI layer.

[0116] The above holding voltage can be appropriately selected by considering the potential change of the cathode and anode according to the State of Charge (SOC), and by performing the Voltage Hold Method at the selected holding voltage, a more stable and thin CEI layer can be formed on the anode.

[0117] For example, the State of Charge (SOC) at which only the additive among the monomer, additive, and liquid electrolyte has a potential capable of decomposition is determined relative to the anode, and after determining the potential of the cathode at that SOC, the value corresponding to the difference between the potentials of the anode and the cathode can be selected as the holding voltage. The holding voltage value selected based on a complete cell may be smaller than the holding voltage value selected based on a half-cell.

[0118] Although not bound by any specific theory, by implementing a voltage maintenance method, the additive can be selectively decomposed to preferentially form a LiF-rich CEI layer, thereby suppressing further decomposition of the electrolyte and monomer.

[0119] According to one embodiment, the CEI layer may have a high F content and low C and O content. For example, when XPS elemental analysis is performed on the outermost surface of the CEI layer, the atomic concentration ratio of F based on the total F, C, and O elements may be 18.5% or more, 19% or more, 20% or more, 21% or more, or 23% or more, the atomic concentration ratio of C may be less than 59.5%, 59.4% or less, 59% or less, less than 59%, 57% or less, less than 57%, 55% or less, or less than 55%, and the atomic concentration ratio of O may be 22% or less or less than 22%. Although not limited to this, for example, when XPS elemental analysis is performed on the outermost surface of the CEI layer, the atomic concentration ratio of F based on the total F, C, and O elements may be 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, 29% or less, 28% or less, 27% or less, 26% or less, 25% or less, or 24% or less, the atomic concentration ratio of C may be 40% or more, 45% or more, 50% or more, 51% or more, 52% or more, 53% or more, or 54% or more, and the atomic concentration ratio of O may be 15% or more, 17% or more, 20% or more, or 21% or more.

[0120] Any known cathode can be used as the cathode in the above cell.

[0121] The cathode may include a cathode current collector and a cathode composite layer disposed on at least one surface of the cathode current collector.

[0122] The negative current collector may include stainless steel, copper, nickel, titanium, or an alloy thereof. The negative current collector may include copper surface-treated with carbon, nickel, titanium, or silver, or stainless steel surface-treated with carbon, nickel, titanium, or silver. Additionally, the negative current collector may be a polymer substrate coated with a conductive metal such as nickel, aluminum, titanium, or silver.

[0123] The above-mentioned cathode current collector may be in various forms, such as foil, foam, net, porous material, or nonwoven material, as non-limiting examples. In addition, the above-mentioned cathode current collector may have a thickness of 10 to 50 μm, although it is not limited thereto.

[0124] The cathode composite layer may include a cathode active material. As the cathode active material, a material capable of adsorbing and desorbing lithium ions may be used. For example, the cathode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber; a silicon (Si)-containing material or a tin (Sn)-containing material.

[0125] Examples of the above-mentioned amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0126] Examples of the above-mentioned crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0127] The above silicon-containing material can provide increased capacity characteristics. The above silicon-containing material is Si, SiOx(0 <x<2), 금속 도핑된 SiOx(0<x<2), 실리콘-탄소 복합체 등을 포함할 수 있다. 상기 금속은 리튬 및 / 또는 마그네슘을 포함할 수 있으며, 금속 도핑된 SiOx(0<x<2)는 금속 실리케이트를 포함할 수 있다.

[0128] For example, a cathode slurry can be prepared by mixing the cathode active material in a solvent. The cathode composite layer may further include a binder and optionally further include a conductive material, a thickener, etc.

[0129] A cathode composite layer can be manufactured by coating / depositing the above cathode slurry onto a cathode current collector, followed by drying and rolling. The coating process may be carried out using methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, but is not limited thereto.

[0130] In some embodiments, the cathode may be a lithium metal cathode or a non-cathode. When the cathode is a lithium metal cathode or a non-cathode, lithium metal particles may be used as an active material for an electrode for a lithium secondary battery. For example, the electrodeposition and desorption reactions of lithium metal, rather than the oxidation and reduction reactions of the electrode active material during charging and discharging, may be the main reversible reactions of the lithium secondary battery. The lithium metal cathode may include a lithium metal-containing layer. The lithium metal-containing layer may include lithium metal or a lithium metal alloy. The lithium metal-containing layer may be a pure lithium metal or lithium metal alloy layer, or the lithium metal or lithium metal alloy may be contained within a porous storage layer. The lithium metal cathode may further include a protective layer for inhibiting dendrite growth, etc., on the lithium metal-containing layer, or may further include a coating layer between the current collector and the lithium metal-containing layer to allow the lithium metal to be uniformly electrodeposited.

[0131] Non-limiting examples of solvents for the above-mentioned cathode mixture include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc.

[0132] The above binder may include polyvinylidenefluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (Poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, as a cathode binder, a styrene-butadiene rubber (SBR)-based binder, carboxymethyl cellulose (CMC), a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene), PEDOT-based binder, etc. may be used.

[0133] The above binder may be included in an amount of about 1.5 to about 5 weight percent based on the total weight of the cathode composite layer.

[0134] The above conductive material may be added to enhance the conductivity of the cathode composite layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, ketjenblack, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, etc., and metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0135] In one embodiment, the conductive agent may be included in an amount of about 0.05 to about 0.2 weight percent based on the total weight of the cathode composite layer.

[0136] If necessary, the cathode composite layer may further include a thickener and / or a dispersant, etc. In one embodiment, the cathode composite layer may include a thickener such as carboxymethyl cellulose (CMC).

[0137] According to exemplary embodiments, an electrode assembly may be formed by repeating a positive electrode, a negative electrode, and a gel polymer electrolyte. The electrode assembly may further include a separator. In some embodiments, the electrode assembly may be winding, stacking, z-folding, or stack-folding.

[0138] The above gel polymer electrolyte can be formed by curing the gel polymer electrolyte composition described above.

[0139] The gel polymer electrolyte described above may include a polymer comprising units derived from the monomer described above, the additive described above, the lithium salt described above, and the solvent described above.

[0140] The gel polymer electrolyte composition may be cured, for example, at a temperature range of about 50 to 100°C for a time of about 30 minutes to 300 minutes, but is not limited thereto. During the curing process, the additive may not decompose or undergo structural and / or chemical modification. For example, when the additive is TFPP, FT-IR analysis of the electrolyte after curing yields 1805 cm⁻¹ -1 (C=O vibration) and 1070 cm -1 When normalized based on the characteristic peak of EC appearing in (CO stretching), 1580 to 1600 cm⁻¹ -1 A peak may be observed in the range, and the peak may indicate that the aromatic ring of TFPP maintains its original molecular structure even after curing.

[0141] secondary battery

[0142] A secondary battery according to another embodiment of the present disclosure comprises a positive electrode, a negative electrode, and a gel polymer electrolyte, wherein the positive electrode comprises a positive current collector, a positive composite layer formed on the positive current collector, and a positive electrolyte interface layer (CEI layer) formed on the positive composite layer, and the CEI layer may be formed from the gel polymer electrolyte composition described above. The gel polymer electrolyte may be a cured gel polymer electrolyte composition described above.

[0143] The gel polymer electrolyte described above includes an additive, wherein the additive comprises phosphorus and an aromatic ring, and at least one of the aromatic ring is an aromatic ring substituted with a functional group containing fluorine, and the ratio of phosphorus element to fluorine element among the additive may be 1:3 to 1:15.

[0144] The additive included in the gel polymer electrolyte composition may be a fluorinated phosphine-based compound. Examples of the additives include, but are not limited to, tris(4-fluorophenyl)phosphine (TFPP), tris(3-fluorophenyl)phosphine, tris(3,5-difluorophenyl)phosphine, and tris(pentafluorophenyl)phosphine (TPFPP). The additive included in the gel polymer electrolyte composition may be one or more selected from the group consisting of tris(4-fluorophenyl)phosphine, tris(3-fluorophenyl)phosphine, tris(3,5-difluorophenyl)phosphine, and tris(pentafluorophenyl)phosphine, and more specifically, one or more selected from the group consisting of tris(4-fluorophenyl)phosphine and tris(pentafluorophenyl)phosphine.

[0145] LiF may be abundant in the above CEI layer, and accordingly, further decomposition of the electrolyte and monomer can be suppressed.

[0146] According to one embodiment, the CEI layer may have a high F content and low C and O content. For example, when XPS elemental analysis is performed on the outermost surface of the CEI layer, the atomic concentration ratio of F based on the total F, C, and O elements may be 18.5% or more, 19% or more, 20% or more, 21% or more, or 23% or more, the atomic concentration ratio of C may be less than 59.5%, less than 59%, less than 57%, or less than 55%, and the atomic concentration ratio of O may be less than 22%.

[0147] When analyzing the above gel polymer electrolyte via FT-IR, at 1805 cm⁻¹ -1 (C=O vibration) and 1070 cm -1 When normalized based on the characteristic peak of ethylene carbonate (EC) appearing in (CO stretching), 1580 to 1600 cm⁻¹ -1 A peak may exist in the range of 1580 to 1600 cm⁻¹. -1 The peak appearing in the range may indicate that, even after curing of the gel polymer electrolyte, the aromatic ring of the additive, which is an aromatic ring comprising phosphorus and an aromatic ring, wherein at least one of the aromatic rings is substituted with a functional group containing fluorine, maintains its original molecular structure.

[0148] In the above lithium secondary battery, for example, electrode tabs (positive tabs and negative tabs) may protrude from a positive current collector and a negative current collector, respectively, and extend to one side of a battery case. For example, the battery case may be a pouch-type case, a prismatic case, a cylindrical case, a coin-type case, etc.

[0149] The electrode tabs may, for example, be extended or exposed to the outside from one side of the battery case and connected to electrode leads (positive lead and negative lead). If the battery case is a pouch-type case, the electrode tab extending to the outside from one side of the battery case may be fused together with the battery case.

[0150] Examples

[0151] In the following, embodiments of the present disclosure are further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present disclosure and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the present disclosure, and that such variations and modifications fall within the scope of the appended claims.

[0152] Example 1

[0153] A slurry of cathode active material (NCM712), conductive material (SuperP), and binder (PVDF) mixed in a weight ratio of 90:5:5 is applied to an Al foil approximately 20 μm thick at a rate of 1.5 mAh / cm² 2 (7.7 mg / cm 2 A positive electrode prepared by coating with a loading of ) was used. A lithium metal (Li metal) negative electrode with a thickness of 300 μm was used as the reference electrode.

[0154] A gel polymer electrolyte composition was prepared using ETPTA as a monomer, TFPP as an additive, AIBN as a thermal polymerization initiator, and a liquid electrolyte (a solution of EC and DEC mixed in a 1:1 volume ratio with LiPF6 added as a lithium salt to make the concentration 1M, and FEC added to make the concentration 10% by weight relative to the total weight of the liquid electrolyte). The gel polymer electrolyte composition contained about 5% by weight of ETPTA, about 1% by weight of TFPP, and about 0.05% by weight of AIBN, with the remainder being the liquid electrolyte.

[0155] A coin cell was prepared using the above anode, cathode, and gel polymer electrolyte composition, and cured at a temperature of about 70°C for 40 minutes to produce a coin cell containing a gel polymer electrolyte (GPE).

[0156] Example 2

[0157] It was prepared in the same manner as Example 1, but contained about 0.25 wt% of TFPP.

[0158] Example 3

[0159] It was prepared in the same manner as Example 1, but contained about 0.5% by weight of TFPP.

[0160] Example 4

[0161] It was prepared in the same manner as Example 1, but contained about 0.5% by weight of TPFPP instead of TFPP as an additive.

[0162] Comparative Example 1

[0163] It was prepared in the same manner as Example 1, but a gel polymer electrolyte composition that did not contain TFPP was used, and no separate curing was performed.

[0164] Comparative Examples 2 to 4

[0165] A gel polymer electrolyte was formed by preparing the same as Comparative Example 1, but curing the gel polymer electrolyte composition at a temperature of about 70°C for 20 minutes, 40 minutes, and 60 minutes, respectively.

[0166] Comparative Example 5

[0167] It was prepared in the same manner as Example 1, but instead of the gel polymer electrolyte, only a liquid electrolyte (LE) containing the same lithium salt and solvent was used, and no separate curing was performed.

[0168] Comparative Example 6

[0169] It was prepared in the same manner as Comparative Example 5, but additionally used as a monomer, and the gel polymer electrolyte composition contained 5% by weight of ETPTA.

[0170] Comparative Example 7

[0171] It was prepared in the same manner as Comparative Example 6, but the gel polymer electrolyte composition contained 2.5% by weight of ETPTA.

[0172] Comparative Example 8

[0173] It was prepared in the same manner as Comparative Example 7, but with the additional use of TFPP as an additive, and the gel polymer electrolyte composition contained 1% by weight of TFPP.

[0174] Comparative Example 9

[0175] It was prepared in the same manner as Comparative Example 6, but with the additional use of TFPP as an additive, and the gel polymer electrolyte composition contained 1% by weight of TFPP.

[0176] Comparative Example 10

[0177] The gel polymer electrolyte composition was prepared in the same manner as in Example 1, but was left at room temperature (25℃) for about 10 hours to cure.

[0178] Comparative Example 11

[0179] A gel polymer electrolyte composition was prepared in the same manner as in Example 1, but without the additive (TFPP).

[0180] Comparative Example 12

[0181] It was prepared in the same manner as Example 1, but contained about 2% by weight of TFPP.

[0182] Comparative Example 13

[0183] A coin cell was manufactured in the same manner as Comparative Example 5, but with lithium metal (Li) and stainless steel as electrodes.

[0184] Comparative Example 14

[0185] A coin cell was manufactured in the same manner as Comparative Example 6, but with lithium metal (Li) and stainless steel as electrodes.

[0186] Comparative Example 15

[0187] It was prepared in the same manner as Comparative Example 13, but with additional addition of TFPP to the liquid electrolyte, and the TFPP in the liquid electrolyte was contained at 5% by weight.

[0188] (1) Evaluation of initial capacity, cycle performance, and rate capability characteristics

[0189] For Comparative Examples 1 to 4, the initial capacity, cycle performance for 100 cycles, and rate capability characteristics for 21 cycles were evaluated, and the results are shown in FIG. 1.

[0190] To evaluate the initial capacity and cycle performance for 100 cycles, a total of 100 charge-discharge cycles were performed, with one cycle defined as charging and discharging at 1C at approximately 25°C and 3.0–4.3V. Here, charging was performed using the CC / CV method and discharging was performed using the CC method, and the results are shown in Figure 1 (a).

[0191] To evaluate the rate capability for 21 cycles, three pre-cycles were performed, each consisting of charging and discharging at 0.1C at approximately 25°C and 3.0–4.3V as one cycle, and a total of 21 charge-discharge cycles were performed, each consisting of charging and discharging at approximately 25°C and 3.0–4.3V as one cycle. During the 21 charge-discharge cycles, charging was performed at 0.2C, and discharging was performed at 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 5C. In the pre-cycle and subsequent charge-discharge cycles, charging was performed in the CC / CV manner, and discharging was performed in the CC manner. The results are shown in Figure 1 (b).

[0192] Referring to Figures 1 (a) and (b), it was confirmed that the cycle performance and rate capability characteristics deteriorated rapidly as the curing time of the gel polymer electrolyte became shorter. This is believed to be because the amount of residual unreacted monomer decreases as the curing time of the gel polymer electrolyte becomes longer.

[0193] (2) Analysis of changes in interfacial resistance due to unreacted monomers

[0194] For the coin cells of Comparative Examples 5 and 6, the change in the magnitude of the interfacial resistance was analyzed through EIS (electrochemical impedance spectroscopy) analysis before aging (a), after aging for 10 hours (b), and after the first charge (c), respectively, and the results are shown in Figure 2 and Table 1.

[0195] The above aging was carried out in a constant temperature chamber at about 25°C for about 10 hours.

[0196] The above initial charge was performed once at 0.1C at approximately 25°C and 3.0–4.3V. The charging was carried out using the CC / CV method.

[0197] Interface Resistance Ri(Ω) Before Aging (a) Δ(Difference) After Aging for 10 Hours (b) Δ(Difference) After Initial Charging (c) Comparative Example 5 1 12.22 -5.30 10 6.92 -8 3.69 23.23 Comparative Example 6 1 21.45 +4.23 1 25.68 +24.16 14 6.84

[0198] It was confirmed that there was no significant change in the magnitude of the interfacial resistance before (a) and after (b) aging, but after the initial charging (c), the coin cell of Comparative Example 5, which does not contain monomer, formed a stable electrode interface and the magnitude of the interfacial resistance decreased significantly, whereas the coin cell of Comparative Example 6, which contains monomer, formed an unstable electrode interface and the magnitude of the interfacial resistance increased significantly. From this, it was found that it is important to form a stable electrode interface in the initial stage of the formation process to suppress the performance degradation of the cell caused by unreacted monomer.

[0199] (3) Measurement of decomposition voltage of monomer (ETPTA) and additive (TFPP)

[0200] Using the coin cells of Comparative Examples 13 to 15, the voltage at which the monomer (ETPTA) and the additive (TFPP) each decompose was measured through Linear Sweep Voltammetry (LSV) analysis, and the results are shown in Figures 3 (a) and (b). Figure 3 (a) shows the LSV analysis results in which the current density was measured in a voltage range of 3 to 6 V for each of the monomer (ETPTA 5 wt% and liquid electrolyte), the additive (TFPP 5 wt% and liquid electrolyte), and the liquid electrolyte, and Figure 3 (b) shows an enlarged view of the section where the current density rapidly increases for the monomer and the additive.

[0201] Looking at Figure 3 (b), the increase in current density for TFPP began to appear between approximately 3.7 and 3.8 V, while the increase in current density for ETPTA began to appear between approximately 3.8 and 3.9 V. Therefore, it can be confirmed that the TFPP additive decomposes at a voltage lower than the voltage at which the ETPTA monomer decomposes, and it was confirmed that the TFPP additive has lower oxidation stability than the ETPTA monomer and can decompose preferentially.

[0202] (4) Measurement of the oxidative decomposition voltage of the monomer (ETPTA)

[0203] Using the coin cell of Comparative Example 6, the voltage at which the monomer (ETPTA) undergoes oxidative decomposition during the initial charge-discharge process was measured through dQ / dV plot peak analysis. As shown in Fig. 3(d), the coin cell of Comparative Example 6 was aged at approximately 25°C for about 10 hours, then a voltage of approximately 3.8V was applied and maintained for about 18 hours, followed by a pre-cycle at 0.1C. The pre-cycle was performed for a total of 3 cycles, with one cycle consisting of charging and discharging at 0.1C at approximately 25°C and 3.0–4.3V. Charging was performed using the CC / CV method, and discharging was performed using the CC method.

[0204] After obtaining a voltage curve for each cycle during the 3-cycle pre-cycle, the obtained voltage curve was differentiated to obtain a dQ / dV plot, and the results are shown in Fig. 3 (c). From this, it was confirmed that the monomer (ETPTA) undergoes oxidative decomposition at approximately 3.8 V.

[0205] Based on the voltages measured in (3) and (4) above, a voltage range for the initial activation of a secondary battery can be derived. Specifically, the voltage for initial activation may be lower than the voltage at which the monomer decomposes and higher than the voltage at which the additive decomposes. In a secondary battery using a monomer (ETPTA) and an additive (TFPP), initial activation can be performed at a voltage of approximately 3.7V or 3.8V, which is lower than the voltage at which ETPTA decomposes (between approximately 3.8 and 3.9V) and the voltage at which it oxidatively decomposes (approx. 3.83V), and higher than the voltage at which TFPP decomposes (around approximately 3.7V). At this time, initial activation can be performed using a Voltage Hold Method that maintains the voltage at approximately 3.8V for a certain period of time. An initial activation protocol including such initial activation is shown in FIG. 3(d). A CEI layer can be formed during the initial activation process, and since the additive is selectively decomposed instead of the residual unreacted monomer at the electrode interface, problems such as electrode performance degradation caused by the residual unreacted monomer can be prevented.

[0206] (5) Photoelectron spectroscopy analysis of the CEI layer

[0207] The constituent elements of Example 1 and Comparative Example 7 at the outermost surface of the CEI layer (sputtering time = 0 sec) were analyzed using X-ray photoelectron spectroscopy (XPS). It was confirmed that the CEI layer of Comparative Example 7 was composed of an atomic concentration ratio of 59.6% C, 22.1% O, and 18.3% F, and the CEI layer of Example 1 was composed of an atomic concentration ratio of 54.5% C, 21.9% O, and 23.6% F.

[0208] (6) Analysis of dQ / dV plot peaks based on whether Voltage Hold Method was performed and the presence or absence of additives

[0209] For each of Comparative Example 6 (without additive) and Comparative Example 9 (with additive), a dQ / dV plot peak analysis was performed by dividing the cases into when the Voltage Hold Method was not performed and when it was performed, and the results are shown in Figure 4.

[0210] Figure 4 (a) is a graph of the result when the Voltage Hold Method is not performed for Comparative Example 6, and (b) is a graph of the result when the Voltage Hold Method is not performed for Comparative Example 9.

[0211] Figure 4 (c) is a graph showing the result of applying the Voltage Hold Method to Comparative Example 9, and (d) is a graph showing the result of applying the Voltage Hold Method to Comparative Example 6. Here, the voltage was maintained at approximately 3.7V, and the overall initial-activation protocol was as shown in Figure 3(d).

[0212] In the case where the Voltage Hold Method is not performed without additives (Fig. 4(a)), an oxidative decomposition peak associated with the monomer was observed near 3.8V during charging.

[0213] When the additive is included but the Voltage Hold Method is not performed (Fig. 4(b)), a peak related to the monomer decomposition reaction was observed near 3.8V, but the size of the oxidative decomposition peak related to the monomer was significantly reduced.

[0214] When the Voltage Hold Method was performed with the addition of an additive (Fig. 4(c)), it was confirmed that no decomposition peaks related to the monomer were observed. Compared to Fig. 4(b), it was confirmed that by performing the Voltage Hold Method, the additive was selectively decomposed to form a stable CEI layer, thereby suppressing further decomposition of residual unreacted monomers.

[0215] When the Voltage Hold Method was performed without additives (Fig. 4(d)), oxidative decomposition reaction peaks associated with monomers were observed, and compared to the case in Fig. 4(c), it can be seen that the additives participate in the formation of the CEI layer and can form a stable electrode interface.

[0216] From these results, it can be confirmed that the degradation of residual unreacted monomers can be suppressed by the introduction of additives, and furthermore, the degradation of residual unreacted monomers can be further suppressed through initial activation using a voltage-maintaining method.

[0217] (7) Cycle performance evaluation based on whether the Voltage Hold Method is implemented

[0218] Cycle performance evaluations were performed for Comparative Examples 6 and 7 (without additives) and Comparative Examples 8 and 9 (with additives), respectively, and the results are shown in FIG. 5.

[0219] Figure 5 (a) is a graph showing the change in discharge capacity after performing a total of 100 cycles of charge and discharge under 0.5C / 0.5C conditions for Comparative Examples 7 and 8 without performing the Voltage Hold Method, and for Comparative Example 8 with the Voltage Hold Method performed for 18 hours at 3.6V and 3.7V. It was confirmed that when the additive is included (Comparative Example 8), the initial capacity and capacity retention rate increase even without performing the Voltage Hold Method compared to Comparative Example 7 without the additive. Furthermore, it was confirmed that when the Voltage Hold Method is performed with the additive, the initial capacity and capacity retention rate increase even more. Specifically, Comparative Example 8, in which the Voltage Hold Method was performed at 3.7V, showed an excellent capacity retention rate of 92.14%, whereas Comparative Example 7, in which the Voltage Hold Method was not performed without the additive, showed a capacity retention rate of only 87.31%.

[0220] Figure 5 (b) is a graph showing the change in discharge capacity after performing a total of 100 charge-discharge cycles under 0.5C / 0.5C conditions for Comparative Examples 6 and 9 without performing the Voltage Hold Method, and for Comparative Example 9 with the Voltage Hold Method performed at 3.6V and 3.7V for 18 hours. It was confirmed that Comparative Example 9 had the highest capacity retention rate when the Voltage Hold Method was performed at 3.7V. It is determined that when the Voltage Hold Method was performed at 3.6V for Comparative Example 9, the additive was not sufficiently decomposed, resulting in a lower capacity retention rate compared to when the Voltage Hold Method was performed at 3.7V, as a stable CEI layer could not be formed.

[0221] Figure 5 (c) shows the Coulombic Efficiency according to the cycle for each case of Figure 5 (b), and it can be interpreted that the closer it is to 100%, the more stable and excellent the cycle performance. It was confirmed that when the Voltage Hold Method is performed at 3.7V with the additive included, a high Coulombic Efficiency close to 100% is achieved, and a stable Coulombic Efficiency is maintained as the cycle progresses.

[0222] Figure 5(d) shows the voltage at 50% State of Charge (SOC) according to the cycle for each case of Figure 5(b), and it can be interpreted that the lower the voltage, the lower the internal resistance of the cell and the less overpotential occurs. It was found that the cell containing the additive and subjected to the Voltage Hold Method at 3.7V maintained the lowest voltage value as the cycle progressed, and accordingly, the internal resistance of the cell was the lowest and the occurrence of overpotential was minimal.

[0223] (8) Interfacial resistance analysis

[0224] After performing 100 cycles of charging and discharging in (7) above, the change in the magnitude of the interfacial resistance was analyzed through EIS (electrochemical impedance spectroscopy) analysis for Comparative Example 9, in the case where the Voltage Hold Method was not performed and in the case where the Voltage Hold Method was performed at 3.7V, and the results are shown in Figure 6 and Table 2.

[0225] FIG. 6 (a) is a graph showing the EIS analysis results for Comparative Example 9 when the Voltage Hold Method was not performed and when the Voltage Hold Method was performed at 3.7V, and (b) is the respective electrode interface resistance value (R) obtained therefrom. cei This is a graph representing ).

[0226] No Hold3.7V HoldR b (Ω)5.364.85R cei (Ω)25.0618.98R ct (Ω)55.2456.51

[0227] In each case, the electrolyte resistance (R b , Bulk Resistance) and Charge Transfer Resistance (R ct Although there was no significant difference in Charge Transfer Resistance, electrode interface resistance (R cei There was a significant difference in ). Specifically, for Comparative Example 9, when the Voltage Hold Method was not performed, the electrode interface resistance (R cei ) was approximately 25.06Ω, and when the Voltage Hold Method was performed at 3.7V, the electrode interface resistance (R cei It was confirmed that the resistance was significantly reduced to approximately 18.98Ω. From this, it was found that a stable CEI layer is formed while performing the Voltage Hold Method, leading to a reduction in interface resistance as the cycle progresses.

[0228] (9) Evaluation of cycle performance in a hardened semi-solid electrolyte system

[0229] This evaluation was conducted to verify whether a stable CEI layer is formed in a cured semi-solid electrolyte system following the addition of additives and the implementation of the Voltage Hold Method.

[0230] Coin cells of Comparative Examples 1 and 10 were used, respectively. The coin cell of Comparative Example 1 did not contain TFPP additives, did not perform the Voltage Hold Method, and was subjected to 60 cycles of charge and discharge. The coin cell of Comparative Example 10 contained TFPP additives, and was subjected to 60 cycles of charge and discharge after performing the Voltage Hold Method at 3.7V for 18 hours. Here, one cycle was defined as charging and discharging at 0.5C / 0.5C at approximately 25°C and 3.0–4.3V, and the results are shown in Fig. 7. Charging was performed using the CC / CV method, and discharging was performed using the CC method.

[0231] Referring to Fig. 7, it was confirmed that the coin cell of Comparative Example 10 had a slightly increased initial capacity compared to the coin cell of Comparative Example 1, and that the capacity retention rate after 60 cycles was higher at 93.18%.

[0232] (10) Analysis of interfacial resistance in cured semi-solid electrolyte systems

[0233] After performing 60 cycles of charging and discharging in (9) above, the magnitude of the interfacial resistance was analyzed for each coin cell through EIS (electrochemical impedance spectroscopy), and the results are shown in Figure 8 and Table 3.

[0234] No Hold3.7V HoldR b (Ω)6.064.71R cei (Ω)74.3229.94

[0235] In each case, the electrolyte resistance (R b Although there was no significant difference in Bulk Resistance, the electrode interface resistance (R cei There was a significant difference in ). Specifically, when the Voltage Hold Method was not performed, the electrode interface resistance (R cei) was approximately 74.32Ω, and when the Voltage Hold Method was performed at 3.7V with the addition of additives, the electrode interface resistance (R cei It was confirmed that the resistance was significantly reduced to approximately 29.94Ω. From this, it was found that while performing the Voltage Hold Method, a stable CEI layer is formed by the additive, leading to a reduction in interfacial resistance as the cycle progresses.

[0236] (11) Evaluation of battery performance based on the ratio of monomer and additive content

[0237] Using the coin cells of Examples 1 to 3 and Comparative Examples 11 and 12, each was charged and discharged at a current density of 0.1C at approximately 25°C and 3.0–4.3V for a total of 3 cycles (pre-cycle). Subsequently, 100 cycles of charging and discharging were performed at 1C / 1C, and the results are shown in FIG. 9. The capacity retention rate after 100 cycles is shown in Table 4. For the pre-cycle, the current density was 0.15 mA / cm² at 25°C, 3.0–4.3V, and C / 10 CV. 2 Each cycle was performed to achieve the following. For 100 charge-discharge cycles, the current density was 1.5 mA / cm² at 25℃, 3.0–4.3V, and 1C CV. 2 Each cycle was performed to achieve the following. For Examples 1 to 3 and Comparative Example 11, the Voltage Hold Method was performed at 3.8V for 18 hours prior to the precycle.

[0238] Dose Retention Rate (%) Example 188.30 Example 286.16 Example 391.87 Comparative Example 1184.63 Comparative Example 1282.75

[0239] Comparative Example 11 is a case without additives, Examples 1 to 3 contain additives and monomers in weight ratios of 1:5, 1:20, and 1:10, respectively, and Comparative Example 12 contains additives and monomers in a weight ratio of 1:2.5. The Voltage Hold Method was not performed on Comparative Example 11, while the Voltage Hold Method was performed at 3.8V on Examples 1 to 3 and Comparative Example 12. A capacity retention rate of 85% or higher was observed in Examples 1 to 3, whereas a capacity retention rate of less than 85% was observed in Comparative Examples 11 and 12.

[0240] (12) Evaluation of battery performance based on maintenance voltage

[0241] Using the coin cells of Example 1 and Comparative Example 11, each was pre-cycled under the same conditions as in (10) above, and then 100 cycles of charge-discharge were performed at 1C / 1C, and the results are shown in FIG. 10. Here, the coin cell of Comparative Example 11 did not perform the Voltage Hold Method, and four batteries corresponding to Example 1 were prepared and each was set to correspond to the case where the Voltage Hold Method was not performed, the case where the Voltage Hold Method was performed at 3.7V for 18 hours, the case where the Voltage Hold Method was performed at 3.8V for 18 hours, and the case where the Voltage Hold Method was performed at 3.9V for 18 hours, and the capacity retention rate was measured after 100 cycles of charge-discharge, and the results are shown in Table 5.

[0242] Voltage Holding Method Capacity Holding Rate (%) Example 1 No Hold 79.6 03.7V Hold 82.6 43.8V Hold 88.3 03.9V Hold - Comparative Example 11 No Hold 80.91

[0243] The coin cell of Comparative Example 11 had a capacity retention rate of approximately 80.91%. When the Voltage Hold Method was not applied to the battery corresponding to Example 1, it showed a lower capacity retention rate (79.60%) than Comparative Example 11. At holding voltages of 3.7V and 3.8V, a higher capacity retention rate than Comparative Example 11 was observed (82.64% and 88.30%, respectively). At a holding voltage of 3.9V, it appears that the monomer decomposed along with the additive, causing rapid degradation of battery performance, and consequently, it was not possible to complete all 100 cycles.

[0244] (13) Evaluation of battery performance and interfacial resistance with and without TPFPP additive

[0245] Coin cells of Example 4 (containing TPFPP as an additive) and Comparative Example 11 (without an additive) were each pre-cycled under the same conditions as in (10), and then 100 cycles of charge-discharge were performed at 1C / 1C, and the results are shown in FIG. 11 and Table 6. Here, the coin cell of Comparative Example 11 did not undergo the Voltage Hold Method, while Example 4 underwent the Voltage Hold Method at 3.8V for 18 hours, and the capacity retention rate and interface resistance were measured after 100 cycles of charge-discharge and are shown in FIG. 11 (a) and (b), respectively. Interface resistance was measured using EIS analysis.

[0246] Comparative Example 11 Example 4R b (Ω)4.983.10R cei (Ω)40.9026.77

[0247] Referring to Fig. 11 (a), the initial capacity of Example 4 was higher and the capacity retention rate was better compared to Comparative Example 11.

[0248] Referring to Fig. 11 (b) and Table 6, in each case, the electrolyte resistance (R b Although there was no significant difference in Bulk Resistance, the electrode interface resistance (R ceiThere was a significant difference in ). Specifically, in Comparative Example 11, in which the Voltage Hold Method was not performed, the electrode interface resistance (R cei In Example 4, where the Voltage Hold Method was performed at 3.8V and the ) was approximately 40.90Ω, the electrode interface resistance (R cei It was confirmed that ) was significantly reduced to about 26.77Ω.

[0249] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention as described in the claims.

[0250] For example, the present disclosure may be implemented by deleting some components from the above-described embodiments, and each embodiment may be implemented in combination with one another.

[0251] Aspect 1) A gel polymer electrolyte composition comprises a monomer, a lithium salt, an additive, and a solvent, wherein the additive comprises phosphorus and an aromatic ring, and at least one of the aromatic ring is an aromatic ring substituted with a functional group containing fluorine, and the ratio of phosphorus element to fluorine element in the additive is 1:3 to 1:15, and the additive and the monomer may be included in a weight ratio of 1:5 to 1:20.

[0252] Side 2) In Side 1, the monomer may have (meth)acrylic or (meth)acrylate-based crosslinking groups.

[0253] Aspect 3) In aspect 1 or 2, the monomer may have 2 to 4 crosslinking groups.

[0254] Aspect 4) In any one of aspects 1 to 3, the monomer may be one or more selected from the group consisting of trimethylolpropane ethoxylate triacrylate, trimethylolpropane triacrylate, and polyethylene glycol.

[0255] Aspect 5) In any one of aspects 1 to 4, the additive may be a fluorinated phosphine-based additive.

[0256] Aspect 6) In any one of aspects 1 to 5, the additive may be one or more selected from the group consisting of tris(4-fluorophenyl)phosphine, tris(pentafluorophenyl)phosphine, tris(3-fluorophenyl)phosphine, and tris(3,5-difluorophenyl)phosphine.

[0257] Side 7) A secondary battery comprises a positive electrode, a negative electrode, and a gel polymer electrolyte, wherein the positive electrode comprises a positive current collector, a positive composite layer formed on the positive current collector, and a positive electrolyte interface layer (CEI layer) formed on the positive composite layer, and the CEI layer may be formed from a gel polymer electrolyte composition of any one of Sides 1 to 6.

[0258] Side 8) In Side 7, the additive may be present in the CEI layer.

[0259] Side 9) In side 7 or 8, when XPS elemental analysis is performed on the outermost surface of the CEI layer, the atomic concentration ratio of F may be 18.5% or more, the atomic concentration ratio of C may be less than 59.5%, and the atomic concentration ratio of O may be less than 22% based on the total elements of F, C, and O.

[0260] Side 10) In any one of sides 7 to 9, the gel polymer electrolyte may be a cured gel polymer electrolyte composition.

[0261] Side 11) In Side 10, when FT-IR analysis was performed on the gel polymer electrolyte, 1805 cm-1 (C=O vibration) and 1070 cm -1 When normalized based on the characteristic peak of ethylene carbonate (EC) appearing in (CO stretching), 1580 to 1600 cm⁻¹ -1 A peak may exist within the range.

[0262] Aspect 12) In aspect 10 or 11, the gel polymer electrolyte comprises an additive, wherein the additive comprises phosphorus and an aromatic ring, and at least one of the aromatic ring is an aromatic ring substituted with a functional group containing fluorine, and the ratio of phosphorus element to fluorine element among the additive may be 1:3 to 1:15.

[0263] Side 13) In any one of sides 10 to 12, the gel polymer electrolyte may include tris(4-fluorophenyl)phosphine (TFPP).

[0264] Side 14) A method for forming an anode electrolyte interface layer is to impregnate a positive electrode, on which a positive electrode composite layer is formed on a positive electrode current collector, with a gel polymer electrolyte composition of any one of Sides 1 to 6 and then cure it; apply a certain voltage to the positive electrode; and perform charge and discharge multiple times to form a CEI layer on the positive electrode composite layer, wherein the voltage may be less than the voltage at which the monomer decomposes and greater than or equal to the voltage at which the additive decomposes.

[0265] Side 15) In Side 14, the voltage may be less than the voltage at which the oxidative decomposition reaction of the monomer occurs.

[0266] Side 16) In Side 14 or 15, the voltage at which the monomer or additive decomposes may be the voltage in the section where the current density rises in the LSV (Linear sweep voltammetry) graph measured for the liquid electrolyte containing the monomer or additive.

[0267] Side 17) In Side 15 or 16, the voltage at which the oxidative decomposition reaction of the monomer occurs may be the voltage at the position where a peak occurs in the dQ / dV plot measured for the liquid electrolyte containing the monomer.

[0268] As described above, the features of the present invention may be applied to a positive electrode comprising a positive electrolyte interface layer in whole or in part, a secondary battery comprising the same, a method for forming a positive electrolyte interface layer, and a gel polymer electrolyte composition for forming the same.

Claims

1. Contains a monomer, a lithium salt, an additive, and a solvent, The above additive includes phosphorus and an aromatic ring, and At least one of the above aromatic rings is an aromatic ring substituted with a fluorine-containing functional group, and The ratio of phosphorus elements and fluorine elements among the above additives is 1:3 to 1:15, and A gel polymer electrolyte composition comprising the above additive and the above monomer in a weight ratio of 1:5 to 1:

20.

2. In Paragraph 1, The above monomer is a gel polymer electrolyte composition having (meth)acrylic or (meth)acrylate-based crosslinking groups.

3. In Paragraph 1, The above monomer is a gel polymer electrolyte composition having 2 to 4 crosslinking groups.

4. In Paragraph 1, A gel polymer electrolyte composition in which the monomer is one or more selected from the group consisting of trimethylolpropane ethoxylate triacrylate, trimethylolpropane triacrylate, and polyethylene glycol.

5. In Paragraph 1, The above additive is a gel polymer electrolyte composition that is a fluorinated phosphine-based additive.

6. In Paragraph 1, A gel polymer electrolyte composition in which the above additive is one or more selected from the group consisting of tris(4-fluorophenyl)phosphine, tris(pentafluorophenyl)phosphine, tris(3-fluorophenyl)phosphine, and tris(3,5-difluorophenyl)phosphine.

7. Comprising an anode, a cathode, and a gel polymer electrolyte, The above anode comprises an anode current collector, an anode composite layer formed on the anode current collector, and an anode electrolyte interface layer (CEI layer) formed on the anode composite layer. A secondary battery in which the above CEI layer is formed from a gel polymer electrolyte composition of any one of claims 1 to 6.

8. In Paragraph 7, A secondary battery in which the above additive is present in the above CEI layer.

9. In Paragraph 7, A secondary battery in which, based on the total elements of F, C, and O, the atomic concentration ratio of F is 18.5% or more, the atomic concentration ratio of C is less than 59.5%, and the atomic concentration ratio of O is less than 22% when XPS elemental analysis is performed on the outermost surface of the above CEI layer.

10. In Paragraph 7, The above gel polymer electrolyte is a secondary battery in which the above gel polymer electrolyte composition is cured.

11. In Paragraph 10, When analyzing the above gel polymer electrolyte via FT-IR, at 1805 cm⁻¹ -1 (C=O vibration) and 1070 cm -1 When normalized based on the characteristic peak of ethylene carbonate (EC) appearing in (CO stretching), 1580 to 1600 cm⁻¹ -1 A secondary battery with a peak in the range.

12. In Paragraph 10, The above gel polymer electrolyte includes additives, and The above additive includes phosphorus and an aromatic ring, and A secondary battery, wherein at least one of the aromatic rings is an aromatic ring substituted with a fluorine-containing functional group, and the ratio of phosphorus element to fluorine element among the additives is 1:3 to 1:

15.

13. In Paragraph 10, The above gel polymer electrolyte comprises tris(4-fluorophenyl)phosphine (TFPP), a secondary battery.

14. A gel polymer electrolyte composition of any one of claims 1 to 6 is impregnated into an anode having an anode composite layer formed on an anode current collector, and then cured; A constant voltage is applied to the above anode; A multiple charge and discharge cycle is performed to form an anode electrolyte interface layer (CEI layer) on the anode composite layer, and A method for forming an anode electrolyte interface layer, wherein the above voltage is less than the voltage at which the monomer decomposes and greater than the voltage at which the additive decomposes.

15. In Paragraph 14, A method for forming an anode electrolyte interface layer, wherein the above voltage is less than the voltage at which the oxidative decomposition reaction of the monomer occurs.

16. In Paragraph 14, A method for forming an anode electrolyte interface layer, wherein the voltage at which the monomer or additive decomposes is the voltage in the region where the current density increases in the LSV (Linear sweep voltammetry) graph measured for a liquid electrolyte containing the monomer or additive.

17. In Paragraph 15, A method for forming an anode electrolyte interface layer, wherein the voltage at which the oxidative decomposition reaction of the monomer occurs is the voltage at the position where a peak occurs in a dQ / dV plot measured for a liquid electrolyte containing the monomer.

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