Electrode for secondary battery and secondary battery comprising same

Abstract

The present invention relates to an electrode for a secondary battery having excellent oxidation resistance, stability, and durability by including a protective layer having a thin and uniform thickness, and to a secondary battery comprising same. The electrode comprises: a substrate layer; and a protective layer provided on the substrate layer, wherein the protective layer satisfies Equation 1 below. [Equation 1] 0 < IQR / Median ≤ 0.5 In Equation 1, IQR denotes the interquartile range for thickness data of at least 100 arbitrary points of the protective layer, and Median denotes the median of the thickness data.

Description

Electrode for a secondary battery and a secondary battery including the same

[0001] The present invention relates to an electrode for a secondary battery and a secondary battery including the same.

[0002]

[0003] In the electric vehicle market, lithium metal batteries are being commercialized by using lithium metal instead of graphite as a next-generation electrode material to improve energy density and maximize capacity. Representative lithium metal batteries include lithium-sulfur batteries and all-solid-state batteries that use lithium metal as the electrode material. In particular, all-solid-state batteries have the advantage of excellent stability and the ability to operate over a wide temperature range. However, all-solid-state batteries have a problem in which lithium dendrites grow from the interface between the electrode and the solid electrolyte, causing a short circuit.

[0004] Specifically, the causes of the formation and growth of lithium dendrites include the non-uniformity of the surface due to the oxidation of lithium during the manufacturing process and the increase in interfacial resistance between the lithium metal and the solid electrolyte during charging and discharging.

[0005] Accordingly, there is a need to develop a modification technology for electrode materials that prevents the formation or growth of lithium dendrites and satisfies the durability required by the electrode material.

[0006]

[0007] The present invention provides an electrode for a secondary battery having excellent oxidation resistance, stability, and durability by including a protective layer having a thin and uniform thickness, and a secondary battery including the same.

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

[0009]

[0010] One embodiment of the present invention provides an electrode for a secondary battery comprising: a substrate layer; and a protective layer provided on the substrate layer; wherein the protective layer satisfies the following mathematical formula 1:

[0011] [Mathematical Formula 1]

[0012] 0 < IQR / Median ≤ 0.5

[0013] In the above mathematical formula 1, IQR represents the InterQuartile Range for thickness data at any 100 points or more of the protective layer, and Median represents the median of the thickness data.

[0014] According to one embodiment of the present invention, the thickness data may include thickness data at 100 or more points of the protective layer.

[0015] According to one embodiment of the present invention, the thickness data may include measured thickness data of the protective layer at intervals of 0.1 μm or more and 0.5 μm or less along the surface direction of the protective layer with respect to a cross-sectional image of the protective layer.

[0016] According to one embodiment of the present invention, the thickness of the protective layer may be 1 nm or more and 1,000 nm or less.

[0017] According to one embodiment of the present invention, the protective layer may comprise a compound derived from a monomer comprising at least one of a silicon-containing monomer, an unsaturated group-containing carboxylic acid monomer, a cyanide group-containing monomer, an unsaturated group-containing aromatic monomer, a hydroxyl group-containing (meth)acrylate monomer, a halogen element-containing (meth)acrylate monomer, an epoxy group-containing (meth)acrylate monomer, and an amino group-containing (meth)acrylate monomer.

[0018] According to one embodiment of the present invention, the protective layer further comprises an additive, and the additive may comprise at least one of an initiator, a crosslinking agent, and an inorganic material.

[0019] According to one embodiment of the present invention, the protective layer comprises two or more protective layers, and the protective layer may include a first protective layer provided on the substrate; and a second protective layer provided on the first protective layer.

[0020] According to one embodiment of the present invention, the substrate layer may comprise lithium metal, lithium alloy, silicon, or a silicon compound.

[0021] According to one embodiment of the present invention, the electrode for the secondary battery may have a color change (delta E) of 5 or less before and after leaving it for 15 minutes under conditions of room temperature and 40% relative humidity.

[0022] According to one embodiment of the present invention, the electrode for the secondary battery has 1 mA / cm 2 Charging and 1 mA / cm 2 When charged and discharged under discharge conditions, the time to reach an overvoltage of 0.2 V may be 270 hours or more.

[0023] According to one embodiment of the present invention, the electrode for the secondary battery may have a lifespan of 75% or more after 100 cycles of operation when charged and discharged under 1 C conditions.

[0024] One embodiment of the present invention provides a secondary battery comprising the electrode for the secondary battery.

[0025]

[0026] An electrode for a secondary battery according to one embodiment of the present invention may have excellent oxidation resistance, stability, and durability.

[0027] A secondary battery according to one embodiment of the present invention may have excellent oxidation resistance, stability, and durability by including the electrode for the secondary battery.

[0028] The effects of the present invention are not limited to those described above, and unmentioned effects will be clearly understood by those skilled in the art from the present specification and the accompanying drawings.

[0029]

[0030] FIG. 1 is a cross-sectional image of an electrode for a secondary battery manufactured in Example 1-1 of the present invention.

[0031] FIG. 2 is a cross-sectional image of an electrode for a secondary battery manufactured in Examples 3 to 5 of the present invention.

[0032] Figure 3 is a box plot graph created using thickness data of the protective layer included in the electrode for a secondary battery manufactured in Example 1-1 of the present invention.

[0033] Figure 4 is a box plot graph created using thickness data of the protective layer included in the electrode for a secondary battery manufactured in Example 6 of the present invention.

[0034] Figure 5 is a photograph showing the oxidation behavior in air of a secondary battery electrode prepared in Example 1-1 of the present invention and a conventional lithium metal foil.

[0035] FIG. 6 is a voltage graph showing the operation of a symmetric cell manufactured by introducing the electrode for a secondary battery of Example 1-1 of the present invention and a symmetric cell manufactured by introducing the lithium metal of Comparative Example 1.

[0036] Figure 7 is an image of a deionized water droplet dropped onto the electrode for a secondary battery prepared in Example 2-1 of the present invention and the electrode for a secondary battery prepared in Example 7.

[0037]

[0038] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0039] Throughout this specification, when a component is described as being located "on" another component, this includes not only cases where a component is in contact with another component, but also cases where another component exists between the two components.

[0040] Throughout this specification, terms including ordinal numbers, such as "first" and "second," are used for the purpose of distinguishing one component from another and are not limited by said ordinal numbers. For example, within the scope of the invention, the first component may also be named the second component, and similarly, the second component may be named the first component.

[0041] Throughout this specification, "(meth)acrylate" is used to refer collectively to acrylates and methacrylates.

[0042] Throughout the entire specification, "electrode" may be a "negative electrode".

[0043]

[0044] The present specification will be described in more detail below.

[0045] One embodiment of the present invention provides an electrode for a secondary battery comprising: a substrate layer; and a protective layer provided on the substrate layer, wherein the protective layer satisfies the following mathematical formula 1.

[0046] [Mathematical Formula 1]

[0047] 0 < IQR / Median ≤0.5

[0048] In the above mathematical formula 1, IQR represents the InterQuartile Range for thickness data at any 100 points or more of the protective layer, and Median represents the median of the thickness data.

[0049] An electrode for a secondary battery according to one embodiment of the present invention may have excellent oxidation resistance, stability, and durability. Specifically, the protective layer satisfies the thickness properties according to Equation 1, thereby ensuring that the overall thickness of the protective layer is very uniform. That is, by having a uniform thickness of the protective layer, the performance degradation of the electrode for a secondary battery can be prevented and its durability improved. If the thickness properties according to Equation 1 are not satisfied, a problem may occur in which the lifespan of the negative electrode material is reduced because localized areas where the protective layer is thin due to thickness variation act as nucleation sites for lithium dendrites.

[0050]

[0051] According to one embodiment of the present invention, the thickness property of the protective layer calculated through the following mathematical formula 2 may be greater than 0 and less than or equal to 0.5.

[0052] [Mathematical Formula 2]

[0053] Thickness property = IQR / Median

[0054] In the above mathematical formula 2, IQR represents the InterQuartile Range for thickness data at any 100 points or more of the protective layer, and Median represents the median of the thickness data.

[0055] Specifically, the thickness properties of the protective layer calculated through the above mathematical formula 2 may be greater than 0 and less than or equal to 0.4, greater than 0 and less than or equal to 0.3, greater than or equal to 0.1 and less than or equal to 0.5, greater than or equal to 0.1 and less than or equal to 0.4, greater than or equal to 0.1 and less than or equal to 0.3, greater than or equal to 0.2 and less than or equal to 0.5, or greater than or equal to 0.3 and less than or equal to 0.4.

[0056] As described above, the protective layer, having thickness properties calculated through the above mathematical formula 2 that satisfy the above range, can be provided with a uniform thickness on one side of the substrate layer. That is, since the thickness of the protective layer is uniform, it is possible to prevent performance degradation of the electrode for a secondary battery, improve durability, and suppress the formation of an unstable solid electrolyte interface (SEI) layer.

[0057] According to one embodiment of the present invention, the thickness data may include thickness data at 100 or more points of the protective layer. Specifically, the thickness data may include thickness data of the protective layer at 100 points or more and 300 points or less, 100 points or more and 270 points or less, 100 points or more and 250 points or less, 100 points or more and 200 points or less, 120 points or more and 300 points or less, 120 points or more and 270 points or less, 120 points or more and 250 points or less, 120 points or more and 200 points or less, 150 points or more and 300 points or less, 150 points or more and 270 points or less, 150 points or more and 250 points or less, 150 points or more and 200 points or less, 200 points or more and 300 points or less, 200 points or more and 270 points or less, or 200 points or more and 250 points or less. If the number of points for obtaining thickness data of the protective layer is within the aforementioned range, the reliability of the thickness data of the protective layer can be improved. That is, the protective layer on one surface of the substrate layer can have a uniform thickness throughout.

[0058] According to one embodiment of the present invention, the thickness data may include measured thickness data of the protective layer at intervals of 0.1 μm or more and 0.5 μm or less along the surface direction of the protective layer with respect to the cross-sectional image of the protective layer. Specifically, the cross-sectional image may be a cross-sectional image of a divided area formed by dividing the entire surface area of ​​the protective layer into 10 or more and 30 or fewer areas. Specifically, the area of ​​the protective layer for obtaining the cross-sectional image may be 10 or more and 25 or fewer areas, 10 or more and 20 or fewer areas, 15 or more and 30 or fewer areas, 15 or more and 25 or fewer areas, 15 or more and 20 or fewer areas, 20 or more and 30 or fewer areas, or 20 or more and 25 or fewer areas.

[0059] At this time, the cross-sectional image may be an image of a cross-section passing through the center of the partitioned area. The cross-sectional image can be obtained using devices and methods used in the industry. For example, after treating the surface of the protective layer with a Focused Ion Beam (FIB), an SEM image of the protective layer can be obtained as a cross-sectional image.

[0060] In addition, the interval for measuring the thickness of the protective layer may be 0.1 μm or more and 0.4 μm, 0.1 μm or more and 0.3 μm, 0.2 μm or more and 0.5 μm, 0.2 μm or more and 0.4 μm, 0.2 μm or more and 0.3 μm, 0.3 μm or more and 0.5 μm, or 0.3 μm or more and 0.4 μm. By measuring the thickness data of the protective layer along the surface direction of the protective layer within the aforementioned interval range with respect to the cross-sectional image of the protective layer, more precise thickness data for the protective layer can be obtained. That is, the reliability of the data regarding the thickness properties of the protective layer calculated by Equation 2 can be improved, and through this, it can be confirmed that the protective layer can be formed with a uniform thickness. At this time, the surface direction of the protective layer may be a direction perpendicular to the thickness direction of the protective layer.

[0061] According to one embodiment of the present invention, the thickness of the protective layer may be 1 nm or more and 1,000 nm or less. Specifically, the thickness of the protective layer may be 1 nm or more and 800 nm or less, 1 nm or more and 600 nm or less, 1 nm or more and 400 nm or less, 5 nm or more and 1,000 nm or less, 5 nm or more and 800 nm or less, 5 nm or more and 600 nm or less, 5 nm or more and 400 nm or less, 10 nm or more and 1,000 nm or less, 10 nm or more and 800 nm or less, 10 nm or more and 600 nm or less, 10 nm or more and 400 nm or less, 20 nm or more and 1,000 nm or less, 20 nm or more and 800 nm or less, 20 nm or more and 600 nm or less, 20 nm or more and 400 nm or less, 40 nm or more and 1,000 nm or less, 40 nm or more and 800 nm or less, 40 nm or more and 600 nm or less, or 40 nm or more and 400 nm or less. If the thickness of the protective layer is within the aforementioned range, it is possible to prevent the destruction of the protective layer during the shrinkage and expansion process and to prevent an increase in the electrical resistance of the protective layer.

[0062] According to one embodiment of the present invention, the protective layer may comprise a compound derived from a monomer comprising at least one of a silicon-containing monomer, an unsaturated group-containing carboxylic acid monomer, a cyanide group-containing monomer, an unsaturated group-containing aromatic monomer, a hydroxyl group-containing (meth)acrylate monomer, a halogen element-containing (meth)acrylate monomer, an epoxy group-containing (meth)acrylate monomer, and an amino group-containing (meth)acrylate monomer.

[0063] Specifically, the silicon-containing monomer may include at least one of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane (V3D3), and hexavinyl disiloxane (HVDS). However, the types of silicon-containing monomers are not limited thereto, and silicon-containing monomers used in the industry may also be used.

[0064] Specifically, the above unsaturated group-containing carboxylic acid monomer may include acrylic acid (AA). However, the type of the above unsaturated group-containing carboxylic acid monomer is not limited to this, and unsaturated group-containing carboxylic acid monomers used in the industry may also be used.

[0065] Specifically, the cyanobacteria-containing monomer may include acrylonitrile (AN). However, the types of cyanobacteria-containing monomers are not limited to this, and cyanobacteria-containing monomers used in the industry may also be used.

[0066] Specifically, the above unsaturated group-containing aromatic monomer may include at least one of divinylbenzene (DVB) and 4-vinylpyridine (4-VP). However, the type of the above unsaturated group-containing aromatic monomer is not limited thereto, and an unsaturated group-containing aromatic monomer used in the art may also be used.

[0067] Specifically, the hydroxyl group-containing (meth)acrylate monomer may include at least one of 2-hydroxyethyl methacrylate (2-HEMA) and ethylene glycol dimethacrylate (EGDMA). However, the types of the hydroxyl group-containing (meth)acrylate monomer are not limited thereto, and hydroxyl group-containing (meth)acrylate monomers used in the industry may also be used.

[0068] Specifically, the above halogen element-containing (meth)acrylate monomer may include at least one of 1H,1H,2H,2H-perfluorodecyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate, and 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate. However, the types of the above-mentioned halogen element-containing (meth)acrylate-based monomers are not limited to these, and halogen element-containing (meth)acrylate-based monomers used in the industry may also be used.

[0069] Specifically, the above epoxy group-containing (meth)acrylate monomer may include glycidyl methacrylate (GMA). However, the types of the above epoxy group-containing (meth)acrylate monomer are not limited to this, and epoxy group-containing (meth)acrylate monomers used in the industry may also be used.

[0070] Specifically, the amino group-containing (meth)acrylate monomer may include 2-dimethylaminoethyl methacrylate. However, the type of amino group-containing (meth)acrylate monomer is not limited to this, and amino group-containing (meth)acrylate monomers used in the industry may also be used.

[0071] By selecting the monomer used to form the above protective layer as described above, a protective layer with excellent oxidation resistance, dendrite resistance, and durability can be easily realized.

[0072] According to one embodiment of the present invention, a compound derived from the monomer may include a polymer of the monomer. In this case, the polymer may include a copolymer. The copolymer may be polymerized by selecting two or more of the monomers, and there are no particular restrictions on the selection and combination thereof. The copolymer may include a combination of monomers having roles such as hydrophilicity, water repellency, and improved bonding strength. The proportion of each monomer constituting the copolymer may be 1% or more and 99% or less based on 100% of the total weight of the monomers.

[0073] According to one embodiment of the present invention, the protective layer further comprises an additive, and the additive may comprise at least one of an initiator, a crosslinking agent, and an inorganic material. Specifically, the additive may comprise at least an initiator.

[0074] According to one embodiment of the present invention, the volume ratio of the monomer and the additive for forming the protective layer may be 1:0.1 to 1:10. Specifically, the volume ratio of the monomer to the additive is 1:0.1 to 1:8, 1:0.1 to 1:5, 1:0.1 to 1:3, 1:0.1 to 1:2, 1:0.1 to 1:1, 1:0.2 to 1:10, 1:0.2 to 1:8, 1:0.2 to 1:5, 1:0.2 to 1:3, 1:0.2 to 1:2, 1:0.2 to 1:1, 1:0.5 to 1:10, 1:0.5 to 1:8, 1:0.5 to 1:5, 1:0.5 to 1:3, 1:0.5 to 1:2, 1:0.5 to 1:1, 1:1 to 1:10, 1:1 to 1:8, 1:1 to The ratio may be 1:5, 1:1 to 1:3, or 1:1 to 1:2. By adjusting the volume ratio of the monomer and additive used to form the protective layer to within the aforementioned range, a protective layer can be easily formed on the substrate layer.

[0075] According to one embodiment of the present invention, the initiator may include at least one of a thermal initiator and a photoinitiator. Specifically, the thermal initiator may include at least one of a peroxide-based compound, a persulfate-based compound, and an azo-based compound, and more specifically, may include tert-butyl peroxide (TBPO). Specifically, the photoinitiator may include benzophenone. By using the aforementioned types of initiators, a protective layer can be stably formed on the substrate layer.

[0076] According to one embodiment of the present invention, the crosslinking agent may include at least one of butanediol diacrylate, pentaerythritol, glycidyl methacrylate, trimethylolpropane trimethyl acrylate, and dicyclopentenyloxyethyl methacrylate. As described above, by including a crosslinking agent in the protective layer, oxidation resistance and durability can be improved.

[0077] According to one embodiment of the present invention, the inorganic material may include a metal oxide. Specifically, the inorganic material is Al2O x , SiO x and TiO x It may include at least one of (x is an integer between 1 and 10). As described above, by including an inorganic material in the protective layer, oxidation resistance and durability can be improved.

[0078] According to one embodiment of the present invention, the protective layer may be composed of a single layer or multiple layers. If the protective layer is multiple layers, each layer may be formed of a polymer layer having a different function. Additionally, if the protective layer is multiple layers, each layer may have a different thickness. Additionally, if the protective layer is multiple layers, each layer may have a different type of monomer used.

[0079] According to one embodiment of the present invention, the protective layer comprises two or more protective layers, and the protective layer may include a first protective layer provided on the substrate; and a second protective layer provided on the first protective layer. As described above, by including the first protective layer, oxidation can be prevented and the formation of lithium dendrites can be suppressed, and by including the second protective layer, the wettability of the electrolyte can be improved and the electrode slurry can be prepared easily.

[0080] According to one embodiment of the present invention, the first protective layer may be a protective layer comprising a compound derived from a monomer comprising at least one of a silicon-containing monomer, an unsaturated group-containing carboxylic acid monomer, a cyanide group-containing monomer, an unsaturated group-containing aromatic monomer, a hydroxyl group-containing (meth)acrylate monomer, a halogen element-containing (meth)acrylate monomer, an epoxy group-containing (meth)acrylate monomer, and an amino group-containing (meth)acrylate monomer. The specific types of the above silicon-containing monomer, unsaturated group-containing carboxylic acid monomer, cyanide group-containing monomer, unsaturated group-containing aromatic monomer, hydroxyl group-containing (meth)acrylate monomer, halogen element-containing (meth)acrylate monomer, epoxy group-containing (meth)acrylate monomer, and amino group-containing (meth)acrylate monomer may include those described above in the protective layer. By selecting the monomer used to form the first protective layer as described above, a protective layer with excellent oxidation resistance, dendrite resistance, and durability can be easily realized.

[0081] According to one embodiment of the present invention, the second protective layer may be a protective layer comprising a compound derived from a monomer comprising at least one of a hydroxyl group-containing (meth)acrylate-based monomer and an amino group-containing (meth)acrylate-based monomer. The specific types of the hydroxyl group-containing (meth)acrylate-based monomer and the amino group-containing (meth)acrylate-based monomer may include those described above in the protective layer. By selecting the monomer used to form the second protective layer as described above, a protective layer with excellent hydrophilicity and improved wettability can be easily realized.

[0082] According to one embodiment of the present invention, the substrate layer may comprise lithium metal, lithium alloy, silicon, or a silicon compound. By selecting the material of the substrate layer as described above, energy density can be improved.

[0083] According to one embodiment of the present invention, the thickness of the substrate layer may be 100 μm or more and 1,000 μm or less. Specifically, the thickness of the substrate layer may be 100 μm or more and 800 μm or less, 100 μm or more and 700 μm or less, 100 μm or more and 600 μm or less, 100 μm or more and 500 μm or less, 200 μm or more and 1,000 μm or less, 200 μm or more and 800 μm or less, 200 μm or more and 700 μm or less, 200 μm or more and 600 μm or less, 200 μm or more and 500 μm or less, 250 μm or more and 1,000 μm or less, 250 μm or more and 800 μm or less, 250 μm or more and 700 μm or less, 250 μm or more and 600 μm or less, or 250 μm or more and 500 μm or less. When the thickness of the above-mentioned substrate layer is within the aforementioned range, the electrode for the secondary battery may have excellent durability and electrochemical properties.

[0084] According to one embodiment of the present invention, the electrode for a secondary battery may have a color change (delta E) of 4 or less before and after being left for 30 minutes under conditions of 25°C and 60°RH. Specifically, the electrode for a secondary battery may have a color change (delta E) of 0 or more and 4 or less, or greater than 0 and 4 or less, before and after being left for 30 minutes under conditions of 25°C and 60°RH. The electrode for a secondary battery that satisfies the aforementioned range of color change may have excellent oxidation resistance.

[0085] According to one embodiment of the present invention, the electrode for a secondary battery may have a discoloration degree (△E) of 7 or less after being left for 1 hour at 25°C and 60% relative humidity. Specifically, the electrode for a secondary battery may have a discoloration degree (△E) of 0 or more and 7 or less, 0 or more and 5 or less, 0 or more and 4 or less, 0 or more and 3.5 or less, 0 or more and 3 or less, 0 or more and 2.7 or less, 0.5 or more and 7 or less, 0.5 or more and 5 or less, 0.5 or more and 4 or less, 0.5 or more and 3.5 or less, 0.5 or more and 3 or less, 0.5 or more and 2.7 or less, 1 or more and 7 or less, 1 or more and 5 or less, 1 or more and 4 or less, 1 or more and 3.5 or less, 1 or more and 3 or less, or 1 or more and 2.7 or less. The electrode for the secondary battery described above, which satisfies the aforementioned range of discoloration, may have excellent oxidation resistance.

[0086] According to one embodiment of the present invention, the electrode for a secondary battery may have a discoloration degree (△E) of 5 or less after being left for 15 minutes at room temperature (25 ℃) and 40% relative humidity. Specifically, the electrode for a secondary battery may have a discoloration degree (△E) of 0 or more and 5 or less, 0 or more and 4 or less, 0 or more and 3.5 or less, 0 or more and 3 or less, 0 or more and 2.7 or less, 0.5 or more and 5 or less, 0.5 or more and 4 or less, 0.5 or more and 3.5 or less, 0.5 or more and 3 or less, 0.5 or more and 2.7 or less, 1 or more and 5 or less, 1 or more and 4 or less, 1 or more and 3.5 or less, 1 or more and 3 or less, or 1 or more and 2.7 or less. The electrode for a secondary battery that satisfies the aforementioned range of discoloration degree may have excellent oxidation resistance.

[0087] Color change (delta E) and color change (△E) have the same meaning and can be calculated using the following mathematical formula 3, and can be calculated using CIE76, but are not limited thereto.

[0088] [Mathematical Formula 3]

[0089] △E = {(△L) 2 +(△a) 2 +(△b) 2} 1 / 2

[0090] In the above mathematical formula 3, △E can represent the geometric distance between two points in the CIELAB L, a and b color space.

[0091] According to one embodiment of the present invention, the electrode for the secondary battery has 1 mA / cm 2 Charging and 1 mA / cm 2 When charged and discharged under discharge conditions, the time to reach an overvoltage of 0.2 V may be 270 hours or more. Specifically, the time for the electrode for the secondary battery to reach an overvoltage of 0.2 V may be 270 hours or more and 1,000 hours or less, 270 hours or more and 900 hours or less, 270 hours or more and 800 hours or less, 300 hours or more and 1,000 hours or less, 300 hours or more and 900 hours or less, 300 hours or more and 800 hours or less, 380 hours or more and 1,000 hours or less, 380 hours or more and 900 hours or less, 380 hours or more and 800 hours or less, 450 hours or more and 1,000 hours or less, 450 hours or more and 900 hours or less, 450 hours or more and 800 hours or less, 500 hours or more and 1,000 hours or less, 500 hours or more and 900 hours or less, or 500 hours or more and 800 hours or less. The electrode for the secondary battery, which satisfies the aforementioned range for the time to reach an overvoltage of 0.2 V, can achieve excellent dendrite resistance.

[0092] At this time, the time to reach an overvoltage of 0.2 V of the electrode for the secondary battery can be measured by the following lithium symmetric cell evaluation method.

[0093] To fabricate a lithium symmetric cell, the positive and negative electrodes each use lithium metal (purity 99.9% or higher), and the electrolyte may contain a carbonate-based compound containing 1 M LiPF6 salt.

[0094] Specifically, the electrolyte may be prepared by mixing 1 M LiPF6 with ethylene carbonate and diethylene carbonate in a volume ratio of 3:7 (ethylene carbonate:diethylene carbonate) and then adding 10 wt% of fluoroethylene carbonate.

[0095] Subsequently manufactured lithium symmetric cells at 1 mA / cm² 2 Charging and 1 mA / cm 2 Under discharge conditions, the time to reach an overvoltage of 0.2 V can be measured by repeating the charge / discharge cycle with a charge / discharge tester (Won-A Tech, WBCS3000).

[0096] According to one embodiment of the present invention, the electrode for a secondary battery may have a lifespan of 75% or more after 100 cycles of operation when charged and discharged under 1 C conditions. Specifically, the lifespan of the electrode for a secondary battery may be 75% or more and 100% or less, 75% or more and 98% or less, 75% or more and 95% or less, 80% or more and 100% or less, 80% or more and 98% or less, 80% or more and 95% or less, 85% or more and 100% or less, 85% or more and 98% or less, or 85% or more and 95% or less after 100 cycles of operation. The electrode for a secondary battery whose remaining lifespan after 100 cycles satisfies the aforementioned range may have excellent durability.

[0097] At this time, the remaining lifespan of the electrode for the secondary battery can be measured using the following coin cell test method.

[0098] An electrolyte containing 1 M LiPF6 and 5% fluoroethylene carbonate added to a mixture containing ethylene carbonate and diethylene carbonate in a 3:7 volume ratio may be used. 1 wt% Super P is used as a conductive material, 2.5 wt% styrene-butadiene rubber (SBR) and 1.5 wt% carboxymethyl cellulose (CMC) are used as binders, and 5.399 mg / cm² is used as the cathode material. 2 After manufacturing a cell with a composite density of 1.46 g / cc, 0.5 T Space, and 2032 coin cell electrode size using lithium metal with a loading level and an average thickness of 700 μm as a separator and polyethylene with an average thickness of 900 μm, a charge / discharge test can be performed using a charge / discharge tester (Won-A Tech, WBCS3000) under 1 C conditions. For the anode material, silicon anode material and graphite anode material can be mixed and used in a weight ratio of 5:95.

[0099]

[0100] One embodiment of the present invention provides a method for manufacturing an electrode for a secondary battery, comprising the steps of: positioning a substrate inside a reactor; preparing a monomer; and supplying the monomer into the reactor to manufacture a protective layer on the substrate.

[0101] Specifically, the method for manufacturing an electrode for a secondary battery according to the present embodiment may be the method for manufacturing an electrode for a secondary battery according to the aforementioned embodiment. That is, the substrate, monomer, additive, and protective layer in the method for manufacturing an electrode for a secondary battery according to the present embodiment may each be identical to the substrate layer, monomer, additive, and protective layer of the electrode for a secondary battery according to the aforementioned embodiment.

[0102] According to one embodiment of the present invention, the substrate may include lithium metal, a lithium alloy, or silicon. By selecting the type of substrate as described above, energy density can be improved.

[0103] According to one embodiment of the present invention, the step of placing the substrate inside a reactor can be performed under a pressure of 1 Torr or less and a temperature of 10°C or more and 300°C or less. That is, the substrate can be placed inside the reactor, and the conditions inside the reactor can be controlled to a pressure of 1 Torr or less and a temperature of 10°C or more and 300°C or less.

[0104] Specifically, the pressure inside the reactor into which the above-mentioned material is introduced may be 1 mTorr or more and 1 Torr or less, 1 mTorr or more and 500 mTorr or less, 1 mTorr or more and 100 mTorr or less, 1 mTorr or more and 60 mTorr or less, 10 mTorr or more and 1 Torr or less, 10 mTorr or more and 500 mTorr or less, 10 mTorr or more and 100 mTorr or less, 10 mTorr or more and 60 mTorr or less, 40 mTorr or more and 1 Torr or less, 40 mTorr or more and 500 mTorr or less, or 40 mTorr or more and 100 mTorr or less. By adjusting the pressure inside the reactor to the aforementioned range, a protective layer can be stably formed thereafter.

[0105] In addition, the temperature inside the reactor into which the substrate is introduced may be 10°C or higher and 200°C or lower, 10°C or higher and 100°C or lower, 10°C or higher and 80°C or lower, 10°C or higher and 50°C or lower, 25°C or higher and 200°C or lower, 25°C or higher and 100°C or lower, 25°C or higher and 80°C or lower, or 25°C or higher and 50°C or lower. By controlling the temperature inside the reactor to the aforementioned range, a protective layer can be stably formed thereafter.

[0106] According to one embodiment of the present invention, the step of preparing the monomer may control the temperature of the monomer to a temperature of 10°C or higher and 300°C or lower. Specifically, the temperature of the monomer before being introduced into the reactor may be 10°C or higher and 300°C or lower, 10°C or higher and 200°C or lower, 10°C or higher and 120°C or lower, 25°C or higher and 300°C or lower, 25°C or higher and 200°C or lower, 25°C or higher and 120°C or lower, 50°C or higher and 100°C or lower, or 50°C or higher and 120°C or lower. By controlling the temperature of the monomer before being introduced into the reactor to the aforementioned range, the protective layer can be effectively formed on one surface of the substrate layer.

[0107] According to one embodiment of the present invention, the method for manufacturing an electrode for a secondary battery may further include the step of preparing an additive. The additive may include at least the aforementioned initiator. Specifically, the temperature of the additive before being introduced into the reactor may be 10°C or higher and 200°C or lower, 10°C or higher and 100°C or lower, 10°C or higher and 80°C or lower, 10°C or higher and 50°C or lower, 25°C or higher and 200°C or lower, 25°C or higher and 100°C or lower, 25°C or higher and 80°C or lower, 25°C or higher and 50°C or lower, 10°C or higher and 35°C or lower, 15°C or higher and 35°C or lower, 20°C or higher and 35°C or lower, or 25°C or higher and 35°C or lower. By controlling the temperature of the additive before it is introduced into the reactor to the aforementioned range, the protective layer can be effectively formed on one side of the substrate layer.

[0108] According to one embodiment of the present invention, the pressure ratio of monomer and additive supplied into the reactor may be 1:0.1 to 1:10. Specifically, the pressure ratio of the monomer and the additive may be 1:0.1 to 1:8, 1:0.1 to 1:5, 1:0.1 to 1:3, 1:0.1 to 1:2, 1:0.1 to 1:1, 1:0.5 to 1:10, 1:0.5 to 1:8, 1:0.5 to 1:5, 1:0.5 to 1:3, 1:0.5 to 1:2, 1:0.5 to 1:1, 1:1 to 1:10, 1:1 to 1:8, 1:1 to 1:5, 1:1 to 1:3, 1:1 to 1:2, 1:2 to 1:10, 1:2 to 1:8, 1:2 to 1:5, or 1:2 to 1:3. By adjusting the pressure ratio of the monomer and additive to within the aforementioned range, a protective layer can be easily formed on the substrate.

[0109] According to one embodiment of the present invention, the step of supplying a monomer onto the substrate to manufacture a protective layer may utilize a vapor deposition method. Specifically, the vapor deposition method may be a dry vapor deposition method, and more specifically, may include a chemical vapor deposition method.

[0110] According to one embodiment of the present invention, the step of manufacturing the protective layer may be performed at a pressure of 1 mTorr or more and 500 Torr or less, at a temperature of 10 ℃ or more and 500 ℃ or less, for a time of 1 minute or more and 600 minutes or less.

[0111] Specifically, the step of manufacturing the protective layer comprises 1 mTorr or more and 500 Torr or less, 1 mTorr or more and 100 Torr or less, 1 mTorr or more and 10 Torr or less, 1 mTorr or more and 1 Torr or less, 10 mTorr or more and 500 Torr or less, 10 mTorr or more and 100 Torr or less, 10 mTorr or more and 10 Torr or less, 10 mTorr or more and 1 Torr or less, 50 mTorr or more and 500 Torr or less, 50 mTorr or more and 100 Torr or less, 50 mTorr or more and 10 Torr or less, 50 mTorr or more and 1 Torr or less, 100 mTorr or more and 500 Torr or less, 100 mTorr or more and 100 Torr or less, 100 mTorr or more and 1 Torr or less, 100 mTorr or more and 1 Torr or less, 150 mTorr or more It can be performed at a pressure of 500 mTorr or less, 150 mTorr or more and 100 Torr or less, 150 mTorr or more and 10 Torr or 150 mTorr or more and 1 Torr or less. By controlling the pressure inside the reactor during the manufacture of the protective layer to the aforementioned range, the reaction rate of the monomer is controlled and the additive is easily activated, thereby allowing the protective layer to be stably formed on the substrate.

[0112] Specifically, the step of manufacturing the protective layer may be performed at a temperature of 10 ℃ or higher and 500 ℃ or lower, 10 ℃ or higher and 350 ℃ or lower, 10 ℃ or higher and 270 ℃ or lower, 25 ℃ or higher and 500 ℃ or lower, 25 ℃ or higher and 350 ℃ or lower, 25 ℃ or higher and 270 ℃ or lower, 50 ℃ or higher and 500 ℃ or lower, 50 ℃ or higher and 350 ℃ or lower, 50 ℃ or higher and 270 ℃ or lower, 100 ℃ or higher and 500 ℃ or lower, 100 ℃ or higher and 350 ℃ or lower, 100 ℃ or higher and 270 ℃ or lower, 150 ℃ or higher and 500 ℃ or lower, 150 ℃ or higher and 350 ℃ or lower, or 150 ℃ or higher and 270 ℃ or lower. By controlling the temperature inside the reactor during the manufacture of the protective layer to the aforementioned range, the protective layer can be stably formed.

[0113] Specifically, the step of manufacturing the protective layer may be performed for a time of 1 minute or more and 600 minutes or less, 1 minute or more and 300 minutes or less, 1 minute or more and 150 minutes or less, 1 minute or more and 120 minutes or less, 1 minute or more and 60 minutes or less, 2 minutes or more and 300 minutes or less, 3 minutes or more and 150 minutes or less, 3 minutes or more and 120 minutes or less, 3 minutes or more and 60 minutes or less, 5 minutes or more and 600 minutes or less, 5 minutes or more and 300 minutes or less, 5 minutes or more and 150 minutes or less, 5 minutes or more and 120 minutes or less, or 5 minutes or more and 60 minutes or less. By adjusting the time for manufacturing the protective layer to the aforementioned range, the protective layer can be manufactured stably. In addition, by adjusting the reaction time, the thickness of the manufactured protective layer can be controlled.

[0114]

[0115] One embodiment of the present invention provides a secondary battery comprising the electrode for the secondary battery.

[0116] A secondary battery according to one embodiment of the present invention may have excellent oxidation resistance, stability, and durability by including the electrode for the secondary battery.

[0117] According to one embodiment of the present invention, a secondary battery comprising the electrode for the secondary battery can be manufactured according to conventional methods known in the art, and there are no particular limitations thereto.

[0118]

[0119] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0120]

[0121] Comparative Example 1: Uncoated lithium

[0122] A lithium metal foil with a thickness of 250 μm (manufacturer: Honjo Metal) was prepared.

[0123]

[0124] Comparative Example 2: Uncoated silicone

[0125] A silicon wafer with a thickness of 500 μm (manufacturer: AETS) was prepared.

[0126]

[0127] Manufacturing of electrodes for secondary batteries equipped with a protective layer

[0128] To manufacture an electrode for a secondary battery, a polymer deposition apparatus (Dipsmartec) equipped with a monomer canister and an initiator canister was used.

[0129]

[0130] Example 1-1

[0131] 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4; Merck, 97%) was prepared as a monomer. Tert-butyl peroxide (TBPO; Merck, 95%) was prepared as an initiator. The input materials underwent degassing first to remove internal dissolved oxygen, etc.

[0132] Subsequently, 100 mL of monomer was added to the monomer canister, and 100 mL of initiator was added to the initiator canister. Next, the temperature of the monomer canister was adjusted to 65 ℃, and the temperature of the initiator canister was adjusted to 35 ℃. A lithium metal foil with a thickness of 250 μm (manufacturer: Honjo Metal) was placed in the coating effective area within the polymer deposition equipment, and the temperature was maintained at 30 ℃ to reach 50 mTorr or less. A needle valve was used to adjust the pressure ratio of the monomer and initiator to 1:2.

[0133] Subsequently, to activate the initiator, the monomer and initiator were supplied to control the filament temperature inside the reactor to approximately 250 °C and maintain the internal pressure of the reactor at 150 mTorr. The reaction time was maintained for 30 minutes to produce an electrode for a secondary battery with a protective layer formed. At this time, the thickness of the protective layer was prepared to be approximately 85 nm.

[0134]

[0135] Examples 1-2 to 1-5

[0136] In the above Example 1-1, an electrode for a secondary battery equipped with a protective layer was manufactured in the same manner as in Example 1-1, except that the process conditions were adjusted as follows.

[0137] Monomer Canister Temperature Protection Layer Formation Time Example 1 - 165 ℃ 30 Example 1 - 285 ℃ 15 Example 1 - 390 ℃ 12 Example 1 - 495 ℃ 10 Example 1 - 5100 ℃ 8 min

[0138]

[0139] Example 2-1

[0140] 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4; Merck, 97%) was prepared as a monomer and tert-butyl peroxide (TBPO; Merck, 95%) was prepared as an initiator. The input materials were degassed first to remove internal dissolved oxygen, etc.

[0141] Subsequently, 100 mL of monomer was added to the monomer canister, and 100 mL of initiator was added to the initiator canister. Next, the temperature of the monomer canister was adjusted to 63°C and the temperature of the initiator canister to 35°C. A silicon wafer (manufacturer: AETS) was placed in the coating effective area of ​​the polymer deposition equipment, and the temperature was maintained at 30°C and lowered to 50 mTorr or less. A needle valve was used to adjust the pressure ratio of the monomer and initiator to 1:2.

[0142]

[0143] Subsequently, to activate the initiator, the monomer and initiator were supplied to control the filament temperature inside the reactor to approximately 200 ℃ and maintain the internal pressure of the reactor at 150 mTorr. The reaction time was maintained for 30 minutes to manufacture an electrode for a secondary battery with a protective layer formed. At this time, the thickness of the protective layer was manufactured to be approximately 50 nm.

[0144]

[0145] Examples 2-2 to 2-5

[0146] In the above Example 2-1, an electrode for a secondary battery equipped with a protective layer was manufactured in the same manner as in Example 2-1, except that the process conditions were adjusted as follows.

[0147] Monomer Canister Temperature Protection Layer Formation Time Example 2 - 163 ℃ 30 Lost Example 2 - 287 ℃ 15 Lost Example 2 - 392 ℃ 12 Lost Example 2 - 497 ℃ 10 Lost Example 2 - 5103 ℃ 8 min

[0148] Example 3

[0149] 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate (PFDMA; Merck, 97%) was prepared as a monomer and tert-butyl peroxide (TBPO; Merck, 95%) was prepared as an initiator. The materials underwent degassing first to remove internal dissolved oxygen, etc.

[0150] Subsequently, 100 mL of monomer was added to the monomer canister, and 100 mL of initiator was added to the initiator canister. Next, the temperature of the monomer canister was adjusted to 70 ℃ and the temperature of the initiator canister to 35 ℃. A lithium metal foil (manufacturer: Honjo Metal) with a thickness of 250 μm was placed in the coating effective area within the polymer deposition equipment, and the temperature was maintained at 30 ℃ to reach 50 mTorr or less. A needle valve was used to adjust the pressure ratio of the monomer and initiator being added to 1:2.

[0151] Subsequently, the monomer and initiator were supplied to activate the initiator by adjusting the filament temperature inside the reactor to approximately 200 ℃ and maintaining the internal pressure of the reactor at approximately 150 mTorr. The reaction time was maintained for 30 minutes to manufacture an electrode for a secondary battery with a protective layer formed thereon. At this time, the thickness of the protective layer was manufactured to be approximately 90 nm.

[0152]

[0153] Example 4

[0154] 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4; Merck, 97%) was prepared as a monomer and tert-butyl peroxide (Merck, 95%) was prepared as an initiator. The input materials were degassed first to remove internal dissolved oxygen, etc.

[0155] Subsequently, 100 mL of monomer was added to the monomer canister, and 100 mL of initiator was added to the initiator canister. Next, the temperature of the monomer canister was adjusted to 60 ℃ and the temperature of the initiator canister to 35 ℃. A lithium metal foil with a thickness of 250 μm (manufacturer: Honjo Metal) was placed in the coating effective area within the polymer deposition equipment, and the temperature was maintained at 30 ℃ to reach 50 mTorr or less. A needle valve was used to adjust the pressure ratio of the monomer and initiator being added to 1:2.

[0156] Subsequently, the monomer and initiator were supplied to activate the initiator by adjusting the filament temperature inside the reactor to approximately 250 ℃ and maintaining the internal pressure of the reactor at approximately 150 mTorr. The reaction time was maintained for about 30 minutes to manufacture an electrode for a secondary battery with a protective layer formed thereon. At this time, the thickness of the protective layer was manufactured to be approximately 45 nm.

[0157]

[0158] Example 5

[0159] 2,4,6,8-tetramethyl-3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate (PFDMA; Merck, 97%) and divinylbenzene (DVB; 80%, Merck) were prepared as monomers, and tert-butyl peroxide (TBPO; Merck, 95%) was prepared as an initiator. The input materials underwent degassing first to remove internal dissolved oxygen, etc.

[0160] Subsequently, 100 mL of PFDMA was added to the first monomer canister, 100 mL of DVB was added to the second monomer canister, and 100 mL of initiator was added to the initiator canister.

[0161] Next, the temperature of the first monomer canister into which PFDMA was introduced was adjusted to approximately 75 ℃, the temperature of the second monomer canister into which DVB was introduced was adjusted to approximately 30 ℃, and the temperature of the initiator canister was adjusted to approximately 35 ℃. A lithium metal foil with a thickness of 250 μm (manufacturer: Honjo Metal) was placed in the coating effective area within the polymer deposition equipment, and the temperature was maintained at 30 ℃ to reach 50 mTorr or less. Using a needle valve, the pressure ratio of the introduced monomers and initiator was adjusted to PFDMA:DVB:TBPO = 1:0.1:2.

[0162] Subsequently, the monomers and the initiator were supplied to activate the initiator by adjusting the filament temperature inside the reactor to approximately 250 ℃ and maintaining the internal pressure of the reactor at approximately 150 mTorr. The reaction time was maintained for about 120 minutes to produce an electrode for a secondary battery with a protective layer formed thereon. At this time, the thickness of the protective layer was produced to be approximately 370 nm.

[0163]

[0164] Example 6

[0165] 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane (V3D3) (Merck, 97%) was prepared as a monomer and tert-butyl peroxide (Merck, 90%) was prepared as an initiator. The input materials were degassed first to remove internal dissolved oxygen, etc.

[0166] Subsequently, 100 mL of monomer was added to the monomer canister, and 100 mL of initiator was added to the initiator canister.

[0167] Next, the temperature of the monomer canister and the initiator canister were adjusted to 35°C. A silicon wafer (manufacturer: AETS) with a thickness of 500 μm was placed in the coating effective area of ​​the polymer deposition equipment, and the temperature was maintained at 30°C to reach 50 mTorr or less. A needle valve was used to adjust the pressure ratio of the monomer and initiator to 1:2.

[0168] Subsequently, the monomer and initiator were supplied to activate the initiator by adjusting the filament temperature inside the reactor to approximately 200 ℃ and maintaining the internal pressure of the reactor at 400 mTorr. The reaction time was maintained for about 30 minutes to manufacture an electrode for a secondary battery with a protective layer formed thereon. At this time, the thickness of the protective layer was manufactured to be approximately 100 nm.

[0169]

[0170] Example 7

[0171] Acrylic acid (AA; Merck, 95%) was prepared as a monomer and tert-butyl peroxide (TBPO; Merck, 95%) as an initiator. The input materials were degassed first to remove internal dissolved oxygen, etc.

[0172] Subsequently, 100 mL of monomer was added to the monomer canister, and 100 mL of initiator was added to the initiator canister. Then, the temperature of the monomer canister and the initiator canister were adjusted to 35 ℃, and a secondary battery electrode prepared from silicon 2-1 was placed in the coating effective area of ​​the polymer deposition equipment. The temperature was maintained at 30 ℃ and reached below 50 mTorr. A needle valve was used to adjust the pressure ratio of the monomer and initiator to 1:2.

[0173] Subsequently, to activate the initiator, the monomer and initiator were supplied to control the filament temperature inside the reactor to approximately 200 ℃ and maintain the internal pressure of the reactor at 150 mTorr. The reaction time was maintained for 20 minutes to produce an electrode for a secondary battery with a protective layer formed. At this time, the thickness of the protective layer was prepared to be approximately 50 nm.

[0174]

[0175] Experimental Example

[0176] 1. Cross-sectional image analysis and thickness analysis of the protective layer

[0177] A cross-sectional image of the protective layer was obtained using an FIB analysis device (FEI Company (Helios 600i)), and thickness data of the protective layer was obtained through the obtained cross-sectional image.

[0178] FIG. 1 is a cross-sectional image of an electrode for a secondary battery manufactured in Example 1-1 of the present invention. Specifically, FIG. 1 is an SEM image taken with an FIB analysis device for 20 regions of the electrode for a secondary battery manufactured in Example 1-1.

[0179] FIG. 2 is a cross-sectional image of a secondary battery electrode prepared in Examples 3 to 5 of the present invention. Specifically, FIG. 2 (a) is an SEM image taken with an FIB analysis device of the secondary battery electrode prepared in Example 3, (b) is an electrode prepared in Example 4, and (c) is an SEM image of the secondary battery electrode prepared in Example 5. As shown in FIG. 2, it can be seen that the surface of the substrate layer and the surface of the protective layer of the secondary battery electrode are both uniform.

[0180] In addition, referring to FIG. 2(a) above, the thickness of the protective layer of the electrode for a secondary battery prepared in Example 3 was measured to be 90.73 nm. Referring to FIG. 2(b), the thickness of the protective layer of the electrode for a secondary battery prepared in Example 4 was measured to be 46.22 nm. Referring to FIG. 2(c), the thickness of the protective layer of the electrode for a secondary battery prepared in Example 5 was measured to be 368.1 nm.

[0181]

[0182] Table 3 below shows the values ​​obtained by measuring the thickness of the protective layer at 10 points at 0.3 μm intervals for each of the 20 cross-sectional images of Figure 1 above, and extracting thickness data at a total of 200 points.

[0183] Point No Thickness Point No Thickness Point No Thickness Point No.Thickness197.15198.710198.815197.7297.15299.410299.115298.1398.05399.010397.715399.0499.55499.410499.915499.2599.25599.410598.315599.3698.65697.110698.215699.3799.95798.310798.115797.5899.75897.210897.215899.1999.65999.810997.515997.41097.26098.611 098.116097.81197.96199.011199.616197.61298.66298.711298.016299.71397.26398.911399.416399.41498.26497.611499.916498.01598.76599.011597.216599.31699.66698.211699.416698.31799.56799.611799.216797.91899.06897.411899.216898.61999.26998.811997.216997 .92099.47099.312097.917099.82197.87198.112198.517197.52298.87297.512297.217299.02397.77397.912398.117397.62497.27497.812498.517498.12599.97598.012599.717598.82699.87698.412697.617699.42797.67798.312797.217799.22899.07898.312897.217898.22998.879 98.712999.617997.83098.88097.113099.018097.43198.38199.313198.818199.73297.68298.513297.518299.43398.18399.613399.218398.93499.28498.213497.918497.23597.88597.813598.518599.33697.98698.513698.418699.13799.58799.113797.318798.83897.28899.613899.818899.43998.38998.513998.918998.64097.29097.614099.019099.14199.59199.214198.119199.04299.79297.614298.919298.54399.29399.014398.219397.34498.59498.014498.11949 7.44597.79599.014598.019599.54698.89699.014699.619697.74798.69798.514798.619799.64899.69899.214897.619898.64997.59997.414998.519998.35097.910099.915099.820098.2.

[0184] FIG. 4 is a box plot graph created using thickness data of a protective layer included in an electrode for a secondary battery manufactured in Example 6 of the present invention. Specifically, FIG. 4 is a box plot graph for Table 4.

[0185] Based on Figure 4 and Table 4 above, the value obtained by dividing the IQR (the third quartile minus the first quartile) by the median (IQR / Median) was calculated to be 0.014.

[0186]

[0187] Table 5 below shows the IQR / Median values ​​measured by extracting thickness data at any 200 points of the protective layer prepared in Examples 1-1 to 1-5 above.

[0188] Uniformity of protective layer thickness (IQR / Median) Example 1-10.045 Example 1-20.12 Example 1-30.22 Example 1-40.31 Example 1-50.43

[0189]

[0190] Table 6 below shows the IQR / Median values ​​measured by extracting thickness data at any 200 points of the protective layer prepared in Examples 2-1 to 2-5 above.

[0191] Uniformity of protective layer thickness (IQR / Median) Example 2-10.014 Example 2-20.14 Example 2-30.21 Example 2-40.33 Example 2-50.47

[0192]

[0193] 2. Oxidation resistance test

[0194] The electrode prepared in Example 1-1 above and a lithium metal foil with a thickness of 250 μm (Manufacturer: Honjo Metal) were left in the atmosphere at room temperature (25℃, 40% relative humidity) to observe the appearance.

[0195]

[0196] Figure 5 is a photograph showing the oxidation behavior in air of a secondary battery electrode prepared in Example 1-1 of the present invention and a conventional lithium metal foil.

[0197] Specifically, FIG. 5 is a photograph of the electrode and lithium metal foil prepared in Example 1-1 of the present invention after being left for 15 minutes. As shown in FIG. 5, it can be seen that blackening discoloration occurs within 15 minutes of exposure to the air in the case of the uncoated lithium metal foil, whereas in the case of the lithium metal foil with a protective layer formed thereis, discoloration is minimal even after 15 minutes of exposure. In other words, it can be confirmed that the oxidation resistance of the electrode including the protective layer has increased.

[0198]

[0199] Table 7 below shows the measured values ​​of the degree of discoloration in air of the electrodes prepared in Examples 1-1 to 1-5 and the lithium metal of Comparative Example 1.

[0200] Degree of discoloration (△E) after leaving for 15 minutes at room temperature (25 ℃) and 40% relative humidity Example 1-11.7 Example 1-21.9 Example 1-32.4 Example 1-43.2 Example 1-54.7 Comparative Example 1>10

[0201]

[0202] The degree of discoloration (△E) was calculated using CIE76 and measured under conditions of SCE color difference coordinates, D50, and 10 degrees. As shown in Table 7 above, it was confirmed that in Comparative Example 1, where no protective layer was formed, the degree of discoloration (△E) exceeded 10. On the other hand, in Examples 1-1 to 1-5, where the IQR / Median of the protective layer thickness was 0.5 or less, it was confirmed that the degree of discoloration (△E) was 5 or less, thereby suppressing discoloration.

[0203]

[0204] 3. Dendritic resistance test

[0205] After manufacturing a symmetric cell by introducing the electrode prepared in Example 1-1 above and a symmetric cell by introducing the lithium metal of Comparative Example 1, 1 mA / cm² 2 , 1 mAh / cm 2 The system was operated for 500 hours under these conditions, and the point at which overvoltage occurs due to lithium metal dendrites was analyzed.

[0206]

[0207] FIG. 6 is a voltage graph showing the operation of a symmetric cell manufactured by introducing the electrode for a secondary battery of Example 1-1 of the present invention and a symmetric cell manufactured by introducing the lithium metal of Comparative Example 1.

[0208] Specifically, as shown in FIG. 6(a), it was confirmed that in the symmetric cell manufactured by introducing the lithium metal of Comparative Example 1, dendrites formed and overvoltage occurred after 200 hours of operation. On the other hand, in the symmetric cell manufactured by introducing the electrode prepared in Example 1-1, dendrite formation was suppressed until 450 hours of operation, and no overvoltage occurred. In addition, as shown in FIG. 6(b), it was confirmed that the symmetric cell manufactured by introducing the electrode prepared in Example 1-1 had a narrower range of voltage variation compared to the symmetric cell manufactured by introducing the lithium metal of Comparative Example 1. In other words, it was confirmed that the formation of a protective layer on the lithium metal delayed the point at which overvoltage occurred, thereby increasing dendrite resistance.

[0209]

[0210] After manufacturing a symmetric cell by introducing the electrodes prepared in Examples 1-1 to 1-5 above and a symmetric cell as follows by introducing the lithium metal of Comparative Example 1, 1 mA / cm² 2 Charging, 1 mA / cm 2 The point at which the overvoltage of 0.2 V was reached due to lithium metal dendrites was analyzed while repeatedly charging and discharging with a charge / discharge tester (Won-A Tech, WBCS3000) under discharge conditions.

[0211] A symmetric cell was prepared by using lithium metal (purity 99.9% or higher) as the positive and negative electrodes, respectively, and by using 1 M LiPF6 as the electrolyte mixed with ethylene carbonate and diethylene carbonate in a volume ratio of 3:7 (ethylene carbonate:diethylene carbonate) followed by the addition of 10 wt% of fluoroethylene carbonate.

[0212]

[0213] Table 8 below shows the time at which an overvoltage of 0.2 V is reached by driving a symmetric cell manufactured by introducing the electrodes prepared in Examples 1-1 to 1-5 and a symmetric cell manufactured by introducing the lithium metal of Comparative Example 1.

[0214] Time at which overvoltage of 0.2 V is reached during symmetrical cell test Example 1 - 1800 hours Example 1 - 2750 hours Example 1 - 3520 hours Example 1 - 4380 hours Example 1 - 5270 hours Comparison Example 1 - 250 hours

[0215]

[0216] As shown in Table 8 above, in Comparative Example 1, where no protective layer was formed, it was confirmed that the time to reach an overvoltage of 0.2V was 250 hours. On the other hand, in Examples 1-1 to 1-5, where the IQR / Median of the protective layer thickness was 0.5 or less, it was confirmed that the time to reach an overvoltage of 0.2V was 270 hours or more, indicating that the time to reach the overvoltage was delayed and the dendrite resistance was increased.

[0217] 4. Residual life test

[0218] After manufacturing a symmetric cell by introducing the electrodes prepared in Examples 2-1 to 2-5 and a coin cell by introducing the silicon of Comparative Example 2 as follows, the remaining lifespan was analyzed by driving 100 cycles under 1 C conditions.

[0219] For the coin cell, the electrolyte was prepared by adding 5% fluoroethylene carbonate to a mixture containing 1 M LiPF6 and ethylene carbonate and diethylene carbonate in a 3:7 volume ratio. 1 wt% Super P was used as the conductive material, 2.5 wt% styrene-butadiene rubber (SBR) and 1.5 wt% carboxymethyl cellulose (CMC) were used as binders, and a cross-sectional value of 5.399 mg / cm² was used as the cathode material. 2A cell was manufactured using lithium metal with a loading level and an average thickness of 700 μm, and polyethylene with an average thickness of 900 μm as a separator, with a composite density of 1.46 g / cc, 0.5 T Space, and a 2032 coin cell electrode size. For the anode material, silicon anode material and graphite anode material were mixed in a weight ratio of 5:95.

[0220] Afterwards, a charge / discharge test was conducted using a charge / discharge tester (Won-A Tech, WBCS3000) under 1 C conditions.

[0221]

[0222] Table 9 below shows the measured values ​​of the remaining lifespan after driving 100 cycles of a symmetric cell manufactured by introducing the electrodes prepared in Examples 2-1 to 2-5 and a symmetric cell manufactured by introducing the silicon of Comparative Example 2.

[0223] Remaining life (%) after 100 cycles of operation Example 2-192% Example 2-291% Example 2-388% Example 2-480% Example 2-576% Comparative Example 273%

[0224]

[0225] As shown in Table 9 above, it was confirmed that in Comparative Example 2, in which no protective layer was formed, the remaining lifespan after 100 cycles was 73% or less. On the other hand, in Examples 2-1 to 2-5, in which the IQR / Median of the protective layer thickness was 0.5 or less, the remaining lifespan after 100 cycles was 76% or more, confirming that the durability was superior.

[0226] Referring to the experimental data described above, it can be seen that the electrode for a secondary battery according to one embodiment of the present invention achieves improved oxidation resistance, dendrite resistance, and durability by implementing a protective layer having a thin thickness with excellent uniformity.

[0227]

[0228] 5. Wetness test of multilayer protective layer

[0229] The contact angle of the secondary battery electrode prepared in Example 2-1 and the secondary battery electrode prepared in Example 7 was measured by dropping a 5 µl drop of deionized water onto them using a contact angle measuring device (FemtoBioMed, Smart_drop_one) in an environment of 25 ℃ and 60% relative humidity.

[0230]

[0231] FIG. 7 is an image of a deionized water droplet dropped onto a secondary battery electrode prepared in Example 2-1 of the present invention and a secondary battery electrode prepared in Example 7. Specifically, FIG. 7 (a) is an image of a deionized water droplet dropped onto a secondary battery electrode prepared in Example 2-1, and (b) is an image of a deionized water droplet dropped onto a secondary battery electrode prepared in Example 7.

[0232] The contact angle measured using the image of Fig. 7 above and a contact angle measuring instrument was 98.6 degrees for the secondary battery electrode prepared in Example 2-1 and 21.7 degrees for the secondary battery electrode prepared in Example 7.

[0233] Therefore, it was confirmed that wettability was improved in the case of the electrode with a multilayer protective layer.

Claims

1. Substrate layer; and A protective layer provided on the above substrate layer; comprising, The above protective layer is an electrode for a secondary battery satisfying the following mathematical formula 1: [Mathematical Formula 1] 0 < IQR / Median ≤ 0.5 In the above mathematical formula 1, IQR represents the interquartile range for thickness data at any 100 or more points of the protective layer, and Median refers to the median of the thickness data above.

2. In Paragraph 1, An electrode for a secondary battery in which the above thickness data includes thickness data at 100 or more points of the protective layer.

3. In Paragraph 1, An electrode for a secondary battery, wherein the thickness data comprises measured thickness data of the protective layer at intervals of 0.1 μm or more and 0.5 μm or less along the surface direction of the protective layer with respect to a cross-sectional image of the protective layer.

4. In Paragraph 1, An electrode for a secondary battery having a protective layer thickness of 1 nm or more and 1,000 nm or less.

5. In Paragraph 1, The above protective layer comprises a compound derived from a monomer including at least one of a silicon-containing monomer, an unsaturated group-containing carboxylic acid monomer, a cyanide group-containing monomer, an unsaturated group-containing aromatic monomer, a hydroxyl group-containing (meth)acrylate monomer, a halogen element-containing (meth)acrylate monomer, an epoxy group-containing (meth)acrylate monomer, and an amino group-containing (meth)acrylate monomer.

6. In Paragraph 1, The above protective layer further includes additives, and The above additive comprises at least one of an initiator, a crosslinking agent, and an inorganic material, for an electrode for a secondary battery.

7. In Paragraph 1, The above protective layer includes two or more protective layers, and The above protective layer is a first protective layer provided on the above substrate; and An electrode for a secondary battery comprising a second protective layer provided on the first protective layer.

8. In Paragraph 1, The above substrate layer comprises lithium metal, lithium alloy, silicon, or a silicon compound, forming an electrode for a secondary battery.

9. In Paragraph 1, The electrode for the secondary battery above is, An electrode for a secondary battery having a color change (delta E) of 5 or less before and after being left for 15 minutes at room temperature and 40% relative humidity.

10. In Paragraph 1, The electrode for the secondary battery above is, 1 mA / cm 2 Charging and 1 mA / cm 2 When charged and discharged under discharge conditions, An electrode for a secondary battery having a time of 270 hours or more to reach an overvoltage of 0.2 V.

11. In Paragraph 1, The electrode for the secondary battery above is, When charged and discharged under 1 C conditions, An electrode for a secondary battery having a lifespan of 75% or more after 100 cycles of operation.

12. A secondary battery comprising an electrode for a secondary battery according to paragraph 1.

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