Composition for forming electrode protective film for lithium secondary battery and method for forming electrode protective film for lithium secondary battery using same

Abstract

The present invention relates to a composition for forming a protective film that is capable of protecting the surface of an electrode for a lithium secondary battery so as to prevent the growth of dendrites and improve the lifespan of the battery.

Description

Composition for forming an electrode protective film for a lithium secondary battery and method for forming an electrode protective film for a lithium secondary battery using the same

[0001] This invention claims the benefit of Korean Patent Application No. 10-2024-0122497 filed with the Korean Intellectual Property Office on September 9, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a composition for forming an electrode protective film for a lithium secondary battery, a method for forming an electrode protective film for a lithium secondary battery using the same, and an electrode for a lithium secondary battery comprising a protective film formed from the composition for forming a protective film. More specifically, the present invention relates to a composition for forming a protective film that protects the surface of an electrode for a lithium secondary battery, prevents the growth of dendrites, and improves the lifespan of the battery.

[0003]

[0004] Conventional lithium-ion batteries' anodes are most commonly made of graphite materials with a layered structure. However, graphite has limited lithium ion storage capacity, so attempts are ongoing to apply lithium metal, which has a very large theoretical capacity, as the anode. Metal batteries using metal materials, including lithium, as the anode material exhibit high capacity, high energy density, high output, and lightweight characteristics, and are therefore attracting attention as next-generation battery systems. In particular, lithium metal is the lightest metal in existence and has a low reduction potential, making it an anode material that exhibits higher capacity and energy density than existing commercial graphite anodes. This allows it to be combined with various cathode materials to create metal batteries.

[0005] However, lithium metal is highly reactive and reacts rapidly with almost all substances except inert gases, forming a passive film on the surface. Furthermore, unlike conventional electrode materials, lithium metal is a bulk material without a layered or coordination structure. Therefore, during charging and discharging, lithium ions are unevenly eluted and adsorbed, forming tree-like dendrites on the metal surface. These dendrites react with the electrolyte to deplete it, and if physically separated from the metal surface, they become dead lithium, which is known to drastically reduce the capacity and lifespan of the battery. Furthermore, if the growth of these dendrites pierces the separator and causes a short circuit to occur, there is a risk of fire or explosion.

[0006]

[0007] The technical problem to be achieved by the present invention is to provide a composition for forming an electrode protective film capable of improving the lifespan of a lithium metal negative electrode in a lithium secondary battery and a method for forming an electrode protective film for a lithium secondary battery using the composition.

[0008] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

[0009]

[0010] One embodiment of the present invention provides a composition for forming an electrode protective film for a lithium secondary battery, which composition comprises polyethyleneimine modified with epoxy alkane.

[0011] Another embodiment of the present invention provides a method for forming a protective film on an electrode for a lithium secondary battery, comprising: a step of surface-treating the electrode with a silane coupling agent containing an epoxy group; a step of coating a protective film-forming composition according to an embodiment of the present invention on the surface-treated electrode; and a step of heat-treating the electrode coated with the protective film-forming composition.

[0012] Another embodiment of the present invention provides an electrode for a lithium secondary battery, comprising: a metal substrate; and a protective film formed on the metal substrate, the protective film being formed from a composition for forming a protective film according to an embodiment of the present invention.

[0013]

[0014] When a protective film is formed on a metal electrode using a composition for forming a protective film according to an embodiment of the present invention, dendrite growth is prevented, thereby improving the lifespan of a lithium secondary battery including the same.

[0015] The effects of the present invention are not limited to the effects described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification and the attached drawings.

[0016]

[0017] Figure 1 is a schematic diagram showing the process of surface-treating a lithium metal surface with 3-glycidyloxypropyltrimethoxysilane (GPS), a silane coupling agent, in Example 1.

[0018] Figure 2 is a schematic diagram showing the process of introducing polyethyleneimine (PEI) modified with epoxy hexane (EH) onto a surface-treated lithium metal surface.

[0019] Figure 3 is a drawing showing the FT-IR analysis results of Experimental Example 1.

[0020] Figure 4 is a diagram showing the results of an evaluation of the atmospheric exposure stability of a lithium metal chip depending on whether a protective film is formed.

[0021] Figure 5 is a diagram showing the life of a Li / Li symmetric cell with a bare lithium metal cathode without any treatment.

[0022] FIG. 6 is a diagram showing the life of a Li / Li symmetric cell using a lithium metal chip forming a protective film as a cathode in Examples 1, 2-1, and 2-2.

[0023] Figure 7 is a diagram showing the life of a Li / Li symmetric cell using a lithium metal chip forming a protective film as a cathode in Examples 1, 3-1, and 3-2.

[0024] FIG. 8 is a diagram showing the life of a Li / Li symmetric cell using a lithium metal chip forming a protective film as a cathode in Examples 1, 4-1, and 4-3.

[0025]

[0026] Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0027] Throughout this specification, when it is said that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0028] Throughout this specification, the unit “parts by weight” may mean the weight ratio between each component.

[0029] Throughout this specification, “A and / or B” means “A and B, or A or B.”

[0030] Throughout this specification, "C n " means n carbon atoms.

[0031] One embodiment of the present invention provides a composition for forming an electrode protective film for a lithium secondary battery, which composition comprises polyethyleneimine modified with epoxy alkane.

[0032] An electrode for a lithium secondary battery to which a composition for forming a protective film according to one embodiment of the present invention is applied may be a metal electrode.

[0033] According to one embodiment of the present invention, the electrode for a lithium secondary battery may include at least one of lithium metal, sodium metal, magnesium metal, and aluminum metal. Preferably, the electrode for a lithium secondary battery may be a lithium metal electrode.

[0034] An electrode for a lithium secondary battery to which a composition for forming a protective film according to one embodiment of the present invention is applied may preferably be used as a negative electrode of a lithium secondary battery, and may also be applied to an electrode used as a positive electrode of a lithium secondary battery.

[0035] The composition for forming a protective film according to one embodiment of the present invention may further include an organic solvent.

[0036] According to one embodiment of the present invention, the organic solvent may be anhydrous tetrahydrofuran (THF), toluene, hexane, benzene, dichloromethane, anhydrous diethyl ether, or a mixture thereof.

[0037] According to one embodiment of the present invention, the polyethyleneimine modified with the epoxy alkane may be included in an amount of 0.1 part by weight or more and less than 5 parts by weight based on 100 parts by weight of the composition for forming a protective film. More specifically, the polyethyleneimine modified with the epoxy alkane may be included in an amount of 0.1 part by weight or more and less than 5 parts by weight, 0.1 part by weight or more and 4.5 parts by weight or less, 0.1 part by weight or more and 4 parts by weight or less, 0.1 part by weight or more and 3.5 parts by weight or less, 1 part by weight or more and less than 5 parts by weight, 1 part by weight or more and 4.5 parts by weight or less, 1 part by weight or more and 4 parts by weight or less, 1 part by weight or more and 3.5 parts by weight or less, 2 parts by weight or more and less than 5 parts by weight, 2 parts by weight or more and 4.5 parts by weight or less, 2 parts by weight or more and 4 parts by weight or less, or 2 parts by weight or more and 3.5 parts by weight or less, based on 100 parts by weight of the composition for forming a protective film. By satisfying the above-described range of the content of polyethyleneimine modified with epoxy alkane, the lifespan of a lithium secondary battery using a metal electrode formed with a protective film using the composition for forming a protective film of the present invention can be further improved.

[0038] Hereinafter, the composition for forming a protective film according to the present invention will be described in more detail.

[0039] Polyethyleneimine modified with epoxy alkane

[0040] According to one embodiment of the present invention, a composition for forming a protective film includes a polyethyleneimine modified with an epoxy alkane, thereby improving the lifespan of a lithium secondary battery using a metal electrode including a protective film formed using the composition. Specifically, by including a polyethyleneimine modified with an epoxy alkane, dendrite formation can be prevented. In addition, since the polyethyleneimine is modified with an epoxy alkane to introduce hydrophobic groups into the polymer, a protective film including the composition can be prevented from swelling in an environment where it is exposed to an electrolyte.

[0041] According to one embodiment of the present invention, the polyethyleneimine modified with the epoxy alkane may be formed by a reaction between an epoxy group of the epoxy alkane and an amine group of the polyethyleneimine.

[0042] In the present invention, epoxy alkane means a compound in which an epoxy group is bonded to an alkane chain.

[0043] According to one embodiment of the present invention, the epoxy alkane is C3 to C 20 It may include an epoxy alkane. More preferably, the epoxy alkane is C3 to C 10 May contain epoxy alkanes.

[0044] According to one embodiment of the present invention, the position of the epoxy group included in the epoxy alkane is not particularly limited.

[0045] According to one embodiment of the present invention, the epoxy alkane may have an epoxy group positioned at the end of the alkane chain.

[0046] According to one embodiment of the present invention, the alkane chain included in the epoxy alkane may be linear or branched.

[0047] According to one embodiment of the present invention, the epoxy alkane in which the epoxy group is located at the end of the alkane chain can be expressed by the following chemical formula 1.

[0048]

[0049] In chemical formula 1, R1 is C1 to C 18 is a straight or branched alkyl.

[0050] More preferably, in the above chemical formula 1, R1 is C1 to C8 straight or branched alkyl.

[0051] According to one embodiment of the present invention, examples of the epoxy alkane include 1,2-epoxypropane, 1,2-epoxybutane, 2,3-epoxybutane, 1,2-epoxypentane, 2,3-epoxypentane, 3,4-epoxypentane, 1,2-epoxy-3-methylbutane, 2,3-epoxy-2-methylbutane, 1,2-epoxyhexane, 2,3-epoxyhexane, 3,4-epoxyhexane, 2,3-epoxy-2-methylpentane, 1,2-epoxy-2,3-dimethylbutane, 1,2-epoxyheptane, 2,3-epoxyheptane, 3,4-epoxyheptane, 1,2-epoxy-5-methylhexane, 1,2-epoxyoctane, Examples thereof include, but are not limited to, 2,3-epoxyoctane, 3,4-epoxyoctane, 1,2-epoxy-2,4,4-trimethylpentane, 1,2-epoxynonane, 2,3-epoxynonane, 3,4-epoxynonane, 1,2-epoxydecane, 2,3-epoxydecane, and 3,4-epoxydecane.

[0052] According to one embodiment of the present invention, the polyethyleneimine modified with the epoxy alkane can be obtained by reacting polyethyleneimine and an epoxy alkane in a solvent. Specifically, an alkyl group can be introduced into polyethylenimine through a reaction between the amine group of the polyethyleneimine and the epoxy group of the epoxy alkane.

[0053] According to one embodiment of the present invention, the reaction of modifying the polyethyleneimine into an epoxy alkane can be performed at room temperature, and can be performed for 6 to 120 hours or 12 to 72 hours.

[0054] According to one embodiment of the present invention, the solvent used in the reaction of modifying the polyethyleneimine into an epoxy alkane may be a polar solvent. For example, methanol may be used as the solvent for the reaction.

[0055] According to one embodiment of the present invention, the weight average molecular weight of the polyethyleneimine may be 1,000 to 100,000.

[0056] According to one embodiment of the present invention, the polyethyleneimine is preferably branched. Branched polyethyleneimine contains more primary amines than linear polyethyleneimine, thereby allowing for a better reaction with epoxy groups. Therefore, branched polyethyleneimine can be easily modified with epoxy alkanes. In addition, since branched polyethyleneimine modified with epoxy alkanes contains more primary amines, it can better react with epoxy groups contained in a silane coupling agent treated on the surface to be formed with a protective film, thereby improving the durability of the formed protective film.

[0057] According to one embodiment of the present invention, the modification rate of the polyethyleneimine modified with the epoxy alkane may preferably be 10% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, or 50% or more. In the present invention, the modification rate of the polyethyleneimine can be calculated by [the number of moles of the epoxy alkane reacted with the polyethyleneimine] / [the number of moles of the total amine groups included in the polyethyleneimine before modification]*100. When the modification rate of the polyethyleneimine modified with the epoxy alkane satisfies the above-described range, the lifespan of a lithium secondary battery forming a protective film including the same can be further improved.

[0058] According to one embodiment of the present invention, the ratio of the number of moles of carbon atoms included in the polyethyleneimine modified with the epoxy alkane to the number of moles of carbon atoms included in the polyethyleneimine before modification may be 1.55 or more and 5 or less. Since the ratio of the number of moles of carbon atoms included in the polyethyleneimine modified with the epoxy alkane to the number of moles of carbon atoms included in the polyethyleneimine before modification satisfies the above-described range, the content of alkyl groups introduced into the polyethyleneimine is appropriate, so that the lifespan of a lithium secondary battery using the same can be further improved.

[0059] Method for forming an electrode protective film for a lithium secondary battery

[0060] Another embodiment of the present invention provides a method for forming a protective film on an electrode for a lithium secondary battery, comprising: a step of surface-treating the electrode with a silane coupling agent containing an epoxy group; a step of coating a protective film-forming composition according to an embodiment of the present invention on the surface-treated electrode; and a step of heat-treating the electrode coated with the protective film-forming composition.

[0061] According to one embodiment of the present invention, the silane coupling agent including the epoxy group may be a silane compound including an epoxy group and two to four C1 to C3 alkoxy groups.

[0062] According to one embodiment of the present invention, the epoxy group included in the silane coupling agent can form a covalent bond through a ring-opening reaction with the amine group of polyethyleneimine modified with an epoxy alkane included in the composition for forming a protective film according to one embodiment of the present invention. By forming a covalent bond between the silane coupling agent and polyethyleneimine, the durability of the protective film can be excellent.

[0063] Specifically, the silane coupling agent containing the epoxy group may be trimethoxysilane, dimethoxysilane, tridimethoxyethoxysilane, triethoxysilane, tetraethoxysilane, or a mixture thereof containing the epoxy group.

[0064] Examples of silane compounds containing an epoxy group and two to four C1 to C3 alkoxy groups include, but are not limited to, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyldimethoxymethylsilane, 3-glycidyloxypropyldiethoxymethylsilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

[0065] According to one embodiment of the present invention, the step of surface-treating the electrode with a silane coupling agent containing an epoxy group can be performed by applying a solution containing the silane coupling agent on the electrode surface, drying it to coat the silane coupling agent, and then reacting the coating layer at 50 to 200°C.

[0066] According to one embodiment of the present invention, in the step of surface-treating the electrode with a silane coupling agent containing an epoxy group, the silane coupling agent may be used in an amount of 1500 μg / cm² or more and 5000 μg / cm² or less per electrode surface area. By satisfying the above-described range in the amount of the silane coupling agent used, the polyethyleneimine modified with an epoxy alkane included in the composition for forming a protective film according to one embodiment of the present invention can be well introduced to the electrode surface through the silane coupling agent, and the protective film effect can be excellent.

[0067] According to one embodiment of the present invention, the step of coating the protective film forming composition according to one embodiment of the present invention on the surface-treated electrode can be performed by applying the above-described protective film forming composition on the surface-treated electrode and drying it.

[0068] According to one embodiment of the present invention, the step of heat-treating the electrode coated with the composition for forming a protective film may be performed in a vacuum oven at a temperature of 50 to 200°C, 100 to 200°C, or 100 to 150°C. By heat-treating the electrode coated with the composition for forming a protective film, a ring-opening reaction between the amine of polyethyleneimine and the epoxy group contained in the silane coupling agent may occur.

[0069] According to one embodiment of the present invention, in the step of coating the protective film-forming composition on the surface-treated electrode, the protective film-forming composition may be used in an amount such that the content of the polyethyleneimine modified with the epoxy alkane is 3 μg / cm² or more and 50 μg / cm² or less per electrode surface area. When the amount of the protective film-forming composition used satisfies the above-described range, the effect of the protective film can be excellent.

[0070] Another embodiment of the present invention provides an electrode for a lithium secondary battery, comprising: a metal substrate; and a protective film formed on the metal substrate, the protective film being formed from a composition for forming a protective film according to an embodiment of the present invention.

[0071] According to one embodiment of the present invention, the metal substrate may include a negative electrode active material.

[0072] According to one embodiment of the present invention, the metal substrate may include at least one of lithium metal, sodium metal, magnesium metal, and aluminum metal.

[0073] According to one embodiment of the present invention, the polyethyleneimine modified with the epoxy alkane may be included in an amount of 3 μg / cm² or more and 50 μg / cm² or less per surface area of ​​the metal substrate.

[0074]

[0075] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0076]

[0077] Manufacturing Example 1. Polyethyleneimine modified with epoxy hexane (PEI-EH#60)

[0078] Branched polyethyleneimine (PEI) having a weight-average molecular weight of approximately 25,000 g / mol as measured by the Light Scattering (LS) method and a number-average molecular weight of approximately 10,000 as measured by the gel chromatography (GPC) method was purchased from Sigma-Aldrich and used.

[0079] PEI and EH were dissolved in methanol at a concentration of 20 wt% so that the molar ratio of the -CH2-CH2-NH- repeating unit of polyethyleneimine and 1,2-epoxyhexane (hereinafter abbreviated as EH) was 1:1. Then, the solution was reacted at room temperature for 72 hours. The following chemical formula 2 represents a reaction in which the amine contained in PEI is modified through a ring-opening reaction with the epoxy group of EH.

[0080]

[0081] The unreacted EH was removed by dropping the reaction solution into hexane one drop at a time and stirring at room temperature for 30 minutes to precipitate. Specifically, after removing the supernatant containing the dissolved EH, the solvent remaining in the remaining polymer precipitate was first removed through a rotary evaporator, and then stored in a vacuum oven at 120°C for 48 h to remove the solvent, thereby producing PEI modified with dried EH.

[0082] Regarding the PEI modified with the EH manufactured above 1 The modification rate was measured through H NMR spectroscopy. The measured modification rate of polyethyleneimine was 60%. Here, the modification rate refers to the ratio of the number of moles of EH modified PEI when the number of moles of amine groups in PEI before modification is 100.

[0083] Specifically, at room temperature, CDCl₃ (Cambridge Isotope Laboratories) was used as a solvent, and tetramethylsilane (TMS) was used as a reference substance on an AscendTM 400 spectrometer (300 MHz). 1 H NMR spectra were recorded.

[0084] Manufacturing Example 2. Polyethyleneimine modified with epoxy hexane (PEI-EH#26)

[0085] PEI modified with EH was prepared in the same manner as in Manufacturing Example 1, except that PEI and EH were dissolved in methanol at a concentration of 20 wt% so that the molar ratio of the -CH2-CH2-NH- repeating unit of PEI and EH was 2:1, and the solution was reacted at room temperature for 16 hours. 1 The degree of modification was 26%, as measured by H NMR spectroscopy.

[0086] Manufacturing Example 3. Polyethyleneimine modified with epoxy hexane (PEI-EH#12)

[0087] PEI modified with EH was prepared in the same manner as in Manufacturing Example 1, except that PEI and EH were dissolved in methanol at a concentration of 20 wt% so that the molar ratio of the -CH2-CH2-NH- repeating unit of PEI and EH was 4:1, and the solution was reacted at room temperature for 6 hours. 1 The degree of modification was 12%, as measured by H NMR spectroscopy.

[0088] Example 1. Formation of a lithium metal electrode protective film

[0089] In a glove box filled with high-purity Ar gas, 95 μl of an anhydrous tetrahydrofuran (THF) solution containing 5 vol% of 3-glycidyloxypropyltrimethoxysilane (abbreviated as GPS), a silane coupling agent containing an epoxy group, was applied to the surface of a lithium metal chip (thickness: 250 μm, diameter: 16 mm, MTI Co.) in an air-dried state. Then, the chip was dried at atmospheric pressure to remove THF, and then transferred to a high-temperature vacuum oven installed in the glove box and reacted at 120°C for 1 hour to treat the surface of the lithium metal chip. Thereafter, the lithium metal chip was washed with THF solvent for 30 minutes, dried at atmospheric pressure once, and then dried again in a vacuum chamber to remove unreacted GPS.

[0090] Figure 1 is a schematic diagram showing the process of surface-treating a lithium metal surface with a silane coupling agent, 3-glycidyloxypropyltrimethoxysilane (GPS), in Example 1. As shown in Figure 1, the silane coupling agent is covalently bonded to the lithium metal surface through a dehydration condensation reaction between the hydroxyl group (-OH) present on the lithium metal surface and a small amount of moisture and GPS, and the epoxy group is exposed on the surface.

[0091] An anhydrous THF solution containing 3 wt% of PEI-EH#60 of Manufacturing Example 1 was prepared as a composition for forming a protective film.

[0092] 95 ㎕ of the composition for forming a protective film was applied onto the surface-treated lithium metal chip, and the chip was dried at atmospheric pressure to remove THF. Thereafter, the chip was transferred to a high-temperature vacuum oven installed in a glove box and reacted at 120°C for 1 hour. Fig. 2 is a schematic diagram showing the process of introducing polyethyleneimine (PEI) modified with epoxy hexane (EH) to the surface-treated lithium metal surface. As shown in Fig. 2, the epoxy group contained in the silane coupling agent can undergo a ring-opening reaction with the amine group contained in PEI, and therefore, the PEI modified with EH can be bonded to the surface of the lithium metal chip through the silane coupling agent. After the reaction was completed, the lithium metal needle was washed with a THF solvent for 30 minutes to remove unreacted PEI-EH, dried at atmospheric pressure for the first time, and then dried again in a vacuum chamber.

[0093] Example 2-1.

[0094] A protective film was formed on a lithium metal chip in the same manner as in Example 1, except that the polymer (PEI-EH#26) of Manufacturing Example 2 was used instead of Manufacturing Example 1.

[0095] Example 2-2.

[0096] A protective film was formed on a lithium metal chip in the same manner as in Example 1, except that the polymer (PEI-EH#12) of Manufacturing Example 3 was used instead of Manufacturing Example 1.

[0097] Example 3-1.

[0098] A protective film was formed on a lithium metal chip in the same manner as in Example 1, except that an anhydrous THF solution containing 1 wt% of PEI-EH#60 of Manufacturing Example 1 was prepared as a composition for forming a protective film.

[0099] Example 3-2.

[0100] A protective film was formed on a lithium metal chip in the same manner as in Example 1, except that an anhydrous THF solution containing 5 wt% of PEI-EH#60 of Manufacturing Example 1 was prepared as a composition for forming a protective film.

[0101] Example 4-1.

[0102] A protective film was formed on a lithium metal chip in the same manner as in Example 1, except that 60 μl, rather than 95 μl, of the silane coupling agent solution containing the above epoxy group was applied, and 60 μl, rather than 95 μl, of the composition for forming a protective film was applied.

[0103] Example 4-2.

[0104] A protective film was formed on a lithium metal chip in the same manner as in Example 1, except that 60 μL, instead of 95 μL, of the silane coupling agent solution containing the above epoxy group was applied.

[0105] Example 4-3.

[0106] A protective film was formed on a lithium metal chip in the same manner as in Example 1, except that 60 μl of the composition for forming a protective film was applied instead of 95 μl.

[0107] The conditions for the protective film formation process of each example are summarized in Table 1 below.

[0108]

[0109] PEI Modification Rate PEI Modified PEI Content GPS Solution Chart Amount of Protective Film Forming Composition Applying Amount of Protective Film Forming Composition Example 1 60 % 3 wt% 95 ㎕ 95 ㎕ Example 2 - 126 % 3 wt% 95 ㎕ 95 ㎕ Example 2 - 212 % 3 wt% 95 ㎕ 95 ㎕ Example 3 - 160 % 1 wt% 95 ㎕ 95 ㎕ Example 3 - 260 % ​​5 wt% 95 ㎕ 95 ㎕ Example 4 - 160 % 3 wt% 60 ㎕ 60 ㎕ Example 4 - 260 % ​​3 wt% 60 ㎕ 95 ㎕ Example 4 - 360 % 3 wt% 95 ㎕ 60 ㎕

[0110]

[0111] As a result of calculation based on the amount of GPS solution applied and the concentration of the GPS solution, when 60 ㎕ of the solution was applied, approximately 1250 ㎕ of GPS was applied per electrode surface area, and when 95 ㎕ was applied, approximately 2000 ㎕ of GPS was applied per electrode surface area.

[0112] Meanwhile, the content of PEI modified with EH included in the protective film formed under the conditions of Example 1 was about 14.88 μg / cm² per electrode surface area, and the content of PEI modified with EH included in the protective film formed under the conditions of Example 4-3 was about 3.133 μg / cm² per electrode surface area.

[0113] Experimental Example 1. FT-IR Analysis

[0114] FT-IR analysis was performed to confirm that a PEI-EH polymer protective film was introduced onto the lithium metal surface. FT-IR analysis was performed on a lithium metal chip without any treatment (Bare Li), a lithium metal chip surface-treated with a silane coupling agent as described in Example 1 (Li-GPS), and a lithium metal chip on which a protective film was formed in Example 1 (Li-PEI-EH#60).

[0115] Figure 3 is a diagram showing the results of FT-IR analysis. As shown in Figure 3, in the FT-IR spectrum for Li-GPS, a peak corresponding to the epoxy functional group is observed due to the epoxy group included in the silane coupling agent, but in the lithium metal chip forming the protective film, the peak corresponding to the epoxy functional group disappears and at the same time, the NH stretching peak originating from PEI amine is observed at 3300 cm -1 It was confirmed that it was observed in the vicinity. This indicates that a ring-opening reaction occurred between the epoxy group included in the silane coupling agent and the amine group of PEI, and that PEI-EH was well introduced.

[0116]

[0117] Experimental Example 2. Atmospheric Exposure Stability Evaluation

[0118] The atmospheric exposure stability of lithium metal chips was evaluated by exposing lithium metal chips without any treatment (Bare Li), lithium metal chips surface-treated with a silane coupling agent as described in Example 1 (Li-GPS), and lithium metal chips with a protective film formed in Example 1 (Li-PEI-EH#60) to an environment with a relative humidity of 65% and room temperature, and observing whether oxidation occurred.

[0119] FIG. 4 is a diagram showing the results of an evaluation of the atmospheric exposure stability of a lithium metal chip depending on whether a protective film was formed. As shown in FIG. 4, when an untreated lithium metal chip was exposed to a general atmospheric environment with a relative humidity of about 65%, oxidation began after 30 seconds and the entire surface was oxidized to blackness in just 20 minutes. In the case of a lithium metal chip surface-treated with a silane coupling agent and a lithium metal chip on which a protective film was formed in Example 1, oxidation began after 10 minutes and the entire surface was oxidized after 30 minutes. This indicates that the PEI-EH polymer layer according to the present invention acts as a protective film against exposure to the external environment.

[0120] Experimental Example 3. Life Evaluation in a Li / Li Symmetric Cell

[0121] A Li / Li symmetric cell was prepared using a lithium metal chip without any treatment or a lithium metal chip with a protective film formed in the example as a negative electrode, a lithium metal chip without any treatment as a positive electrode, and an electrolyte containing 1.2 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC=3:7 (vol / vol)), and adding 2 wt% of vinylene carbonate and 10 wt% of fluoroethylene carbonate (FEC). All cell components were assembled in an argon-filled glove box (O2<0.1 ppm, H2O<0.1 ppm).

[0122] To evaluate the life of the symmetric cell, the cell was charged at a temperature of 30°C and a current of 1.0 mA / cm 2 The cell was operated by repeatedly depositing Li for 1 hour at a current density and removing it for 1 hour, which is one cycle, and the point at which a short circuit occurs in the cell due to dendrites formed on the electrode surface was identified.

[0123] Figure 5 is a diagram illustrating the lifespan of a Li / Li symmetric cell with a bare lithium metal cathode without any treatment. As shown in Figure 5, the voltage curve changes irregularly and the lifespan ends after approximately 130 hours of operation.

[0124] FIG. 6 is a diagram showing the life of a Li / Li symmetric cell using a lithium metal chip forming a protective film as a cathode in Examples 1, 2-1, and 2-2.

[0125] As shown in Fig. 6, it was confirmed that the lifespan of a cell applying an electrode formed with a protective film including polyethyleneimine modified with an epoxy alkane was improved compared to the case where a bare lithium metal anode was applied. In particular, it was confirmed that the lifespan of a symmetrical cell was significantly improved to approximately 260 hours and 300 hours, respectively, when the epoxy modification ratio was 26% and 60%, compared to the case where the epoxy modification ratio was 12% and the case where bare lithium metal without a protective film was applied.

[0126] Figure 7 is a diagram showing the life of a Li / Li symmetric cell using a lithium metal chip forming a protective film as a cathode in Examples 1, 3-1, and 3-2.

[0127] As shown in Fig. 7, when the content of polyethyleneimine modified with epoxy alkane in the composition for forming a protective film was 3 wt%, the lifespan of the symmetrical cell was further improved compared to when it was 1 wt%. When the content of polyethyleneimine modified with epoxy alkane in the composition for forming a protective film was increased to 5 wt%, the lifespan of the symmetrical cell was shown to decrease again, confirming that the content of polyethyleneimine modified with epoxy alkane in the composition for forming a protective film had an optimal effect around 3 wt%.

[0128] FIG. 8 is a diagram showing the life of a Li / Li symmetric cell using a lithium metal chip forming a protective film as a cathode in Examples 1, 4-1, and 4-3.

[0129] Referring to the results of the symmetrical cell life test for Examples 1 and 4-1 to 4-3 in which the amount of silane coupling agent solution applied and the amount of the composition for forming a protective film were controlled, it was confirmed that a sufficient amount of the silane coupling agent must be applied to the lithium metal surface in order for the protective film according to the present invention to be well formed. In addition, by calculating the content of PEI modified with epoxy alkane included in the composition for forming a protective film in Examples 4-3 and 1, it was confirmed that when the PEI modified with epoxy alkane was coated in a content of 3 μg / cm² to 50 μg / cm² per electrode surface area, the lifespan improvement effect of the symmetrical cell was excellent.

[0130] Although the present invention has been described above through limited embodiments, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. A composition for forming an electrode protective film for a lithium secondary battery, A composition for forming a protective film comprising polyethyleneimine modified with an epoxy alkane.

2. In claim 1, A composition for forming a protective film, wherein the polyethyleneimine modified with the above epoxy alkane is formed by a reaction between the epoxy group of the epoxy alkane and the amine group of the polyethyleneimine.

3. In claim 1, The above epoxy alkane is C3 to C 20 A composition for forming a protective film comprising an epoxy alkane.

4. In claim 1, A composition for forming a protective film wherein the polyethyleneimine is branched.

5. In claim 1, A composition for forming a protective film, wherein the ratio of the number of moles of carbon atoms contained in the polyethyleneimine modified with the epoxy alkane to the number of moles of carbon atoms contained in the polyethyleneimine before modification is 1.55 or more and 5 or less.

6. In claim 1, A composition for forming a protective film, wherein the modification ratio of the polyethyleneimine modified with the above epoxy alkane is 10% or more.

7. In claim 1, A composition for forming a protective film further comprising an organic solvent.

8. In claim 1, A composition for forming a protective film, wherein the polyethyleneimine modified with the above epoxy alkane is contained in an amount of 0.1 parts by weight or more and less than 5 parts by weight based on 100 parts by weight of the composition for forming a protective film.

9. In claim 1, The above lithium secondary battery electrode is a composition for forming a protective film, which comprises at least one of lithium metal, sodium metal, magnesium metal, and aluminum metal.

10. A method for forming an electrode protective film for a lithium secondary battery, A step of surface treating the above electrode with a silane coupling agent containing an epoxy group; A step of coating a composition for forming a protective film according to any one of claims 1 to 8 on the surface-treated electrode; and A method for forming a protective film, comprising the step of heat-treating an electrode coated with the composition for forming a protective film.

11. In claim 10, A method for forming a protective film, wherein the silane coupling agent containing the above epoxy group is a silane compound containing an epoxy group and two to four C1 to C3 alkoxy groups.

12. In claim 10, A method for forming a protective film, wherein in the step of surface-treating the electrode with a silane coupling agent containing an epoxy group, the silane coupling agent is used in an amount of 1500 μg / cm² or more and 5000 μg / cm² or less per electrode surface area.

13. In claim 10, A method for forming a protective film, wherein in the step of coating the protective film forming composition on the surface-treated electrode, the protective film forming composition is used in an amount such that the content of polyethyleneimine modified with the epoxy alkane is 3 μg / cm² or more and 50 μg / cm² or less per electrode surface area.

14. In claim 10, A method for forming a protective film, wherein the electrode comprises at least one of lithium metal, sodium metal, magnesium metal, and aluminum metal.

15. A lithium secondary battery electrode comprising a metal substrate; and a protective film formed on the metal substrate, the protective film forming composition being formed from any one of claims 1 to 8.

16. In claim 15, An electrode for a lithium secondary battery, wherein the metal substrate comprises at least one of lithium metal, sodium metal, magnesium metal, and aluminum metal.

17. In claim 15, An electrode for a lithium secondary battery, wherein the polyethyleneimine modified with the above epoxy alkane is included in an amount of 3 μg / cm² or more and 50 μg / cm² or less per surface area of ​​the metal substrate.

18. In claim 15, An electrode for a lithium secondary battery, wherein the metal substrate includes a negative electrode active material.

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