Electrodes for secondary batteries, methods for manufacturing the same, and secondary batteries containing the same

Abstract

To provide an electrode for a secondary battery having improved stability and charge / discharge characteristics, a method for manufacturing the same, and a secondary battery containing the same. [Solution] An electrode for a secondary battery, a method for manufacturing the same, and a secondary battery containing the same are provided. The electrode for the secondary battery includes a current collector, an active material layer disposed on the current collector and containing an active material, and a protective coating formed on at least a portion of the surface of the active material layer and containing an aryl ring-containing metal compound.

Description

Technical Field

[0001] The disclosure of the present application relates to an electrode for a secondary battery, a method for manufacturing the same, and a secondary battery including the same. More specifically, the disclosure relates to an electrode for a secondary battery including an active material layer, a method for manufacturing the same, and a secondary battery including the same.

Background Art

[0002] A secondary battery is a battery that can be repeatedly charged and discharged, and has been widely applied as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook computers with the development of the information communication and display industries. Recently, a battery pack including a secondary battery has also been developed and applied as a power source for environmentally friendly vehicles such as electric vehicles.

[0003] For example, lithium secondary batteries have high operating voltages and energy densities per unit weight, and are actively being researched and developed for their advantages in charging speed and weight reduction.

[0004] A secondary battery can include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolytic solution that impregnates the electrode assembly. The secondary battery can further include an exterior material, for example, in a pouch form, that houses the electrode assembly and the electrolytic solution.

[0005] When the charging and discharging of a secondary battery are repeated, side reactions may occur between the electrolytic solution components and the positive electrode or the negative electrode. For example, the electrode surface may be damaged and gas may be generated by an oxidation / reduction reaction between an additive contained in the electrolytic solution and an active material contained in the positive electrode or the negative electrode.

[0006] Therefore, research on a method for reducing side reactions with the electrolytic solution without inhibiting the charge / discharge characteristics within the electrode is necessary. ]

Summary of the Invention

Problems to be Solved by the Invention

[0007] One object of the present disclosure is to provide an electrode for a secondary battery having improved stability and charge-discharge characteristics.

[0008] One object of the present disclosure is to provide a method for manufacturing an electrode for a secondary battery having improved stability and charge-discharge characteristics.

[0009] One object of the present disclosure is to provide a secondary battery having improved stability and charge-discharge characteristics.

Means for Solving the Problems

[0010] The electrode for a secondary battery includes a current collector, an active material layer disposed on the current collector and containing an active material, and a protective coating covering at least a part of the surface of the active material or at least a part of the surface of the active material layer and containing an aryl ring-containing metal compound.

[0011] In some embodiments, the protective coating can contain a compound represented by the following Structural Formula 1.

Chemical formula

[0012] In some embodiments, in structural formula 1, M is an alkali metal or alkaline earth metal, and n may be 1 or 2.

[0013] In some embodiments, the active material layer further comprises a binder, and the protective coating can at least partially cover the surfaces of the active material and binder exposed on the outer surface of the active material layer.

[0014] In some embodiments, the protective coating may be present on the surface of the active material and also within the active material layer.

[0015] In some embodiments, the protective coating may include a first protective coating that covers the outer surface of the active material layer and a second protective coating that covers the surface of the active material.

[0016] In some embodiments, the first protective coating and the second protective coating can be merged with each other at the outer periphery of the active material layer.

[0017] In some embodiments, the protective coating can come into contact with the surface of the current collector.

[0018] In some embodiments, a solution obtained by eluting the components of the protective coating from the electrodes for the secondary battery is used. 1 In the 1H-NMR spectrum, multiplet peaks may be observed in the range of 7.2–7.4 ppm, and doublet peaks may be observed in the range of 7.6–7.7 ppm.

[0019] The secondary battery includes a positive electrode and a negative electrode opposite to the positive electrode. At least one of the positive electrode and the negative electrode includes the aforementioned secondary battery electrode.

[0020] In a method for manufacturing electrodes for secondary batteries, a current collector is prepared. An active material layer is formed on the current collector, which includes an active material and a protective coating containing an aryl ring-containing metal compound. The protective coating can be formed on the outer surface of the active material layer or on the surface of the active material.

[0021] In some embodiments, in forming the protective coating on the outer surface of the active material layer, the active material layer, which is coated on the current collector, can be supported in a coating solution containing the aryl ring-containing metal compound.

[0022] In some embodiments, in forming the protective coating on the surface of the active material, the active material may be mixed into a coating solution containing the aryl ring-containing metal compound before being coated onto the current collector.

[0023] In some embodiments, the active material can be mixed with the coating solution while vacuum drying.

[0024] In some embodiments, the concentration of the aryl ring-containing metal compound in the coating solution may be 0.1% by weight or more and less than 10% by weight. [Effects of the Invention]

[0025] The electrodes for secondary batteries according to embodiments of this disclosure include a protective coating formed on the active material layer and / or active material particles. The protective coating can block oxidation / reduction reactions due to electron transfer between the active material layer and the electrolyte.

[0026] The protective coating comprises an aryl ring-containing metal salt compound. The aryl ring-containing metal salt compound can selectively block electron transfer while maintaining or improving lithium ion conductivity. This makes it possible to improve the charge / discharge characteristics and rate characteristics of the secondary battery while reducing instability such as gas generation due to side reactions of the electrolyte.

[0027] The secondary batteries described above, according to the exemplary embodiments, are widely applicable in green technology fields, including electric vehicles, battery charging stations, and solar and wind power generation utilizing batteries. For example, by using secondary batteries in environmentally friendly electric vehicles and hybrid vehicles, air pollution and greenhouse gas emissions can be reduced, and climate change can be prevented. [Brief explanation of the drawing]

[0028] [Figure 1] Figure 1 is a schematic cross-sectional view showing an electrode for a secondary battery according to an exemplary embodiment. [Figure 2] Figure 2 is a schematic partially enlarged cross-sectional view showing an electrode for a secondary battery according to an exemplary embodiment. [Figure 3] Figure 3 is a schematic partially enlarged cross-sectional view showing an electrode for a secondary battery according to an exemplary embodiment. [Figure 4] Figure 4 is a schematic partially enlarged cross-sectional view showing an electrode for a secondary battery according to an exemplary embodiment. [Figure 5] Figure 5 is a schematic plan view showing a secondary battery according to an exemplary embodiment. [Figure 6] Figure 6 is a schematic cross-sectional view showing a secondary battery according to an exemplary embodiment. [Figure 7] Figure 7 shows the 1H NMR analysis graphs measured from the negative electrode components of Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0029] Embodiments of this disclosure provide an electrode for a secondary battery, including an active material layer and a protective coating. Furthermore, embodiments of a lithium secondary battery, including the said electrode, are also provided.

[0030] The embodiments of this disclosure will be described in more detail. However, since the drawings and embodiments attached to this specification are intended to help further understand the technical concept of this disclosure, this disclosure shall not be construed as being limited only to what is described in the drawings and embodiments.

[0031] Figure 1 is a schematic cross-sectional view showing an electrode for a secondary battery according to an exemplary embodiment.

[0032] Referring to Figure 1, the electrode for the secondary battery may include a current collector 50 and an active material layer 60 formed on the current collector 50. The electrode for the secondary battery may be a positive electrode or a negative electrode.

[0033] The active material layer 60 can be formed on at least one of the upper and lower surfaces of the current collector 50. As shown in Figure 1, the active material layer 60 can be formed on the upper and lower surfaces of the current collector 50, respectively.

[0034] The current collector 50 may include copper, stainless steel, nickel, aluminum, titanium, or alloys thereof. The current collector 50 may also be surface-treated with carbon, nickel, titanium, silver, etc. The thickness of the current collector 50 may be 5 μm to 50 μm.

[0035] When the electrode for the secondary battery is provided as a positive electrode, the current collector 50 may include aluminum or an aluminum alloy. When the electrode for the secondary battery is provided as a negative electrode, the current collector 50 may include copper or a copper alloy.

[0036] The active material layer 60 may contain a positive electrode active material or a negative electrode active material.

[0037] The positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0038] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystalline structure represented by the following chemical formula 1.

[0039] [Chemical formula 1] Li x Ni a M b O 2+z

[0040] In chemical formula 1, 0.9 ≤ x ≤ 1.2, 0.5 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.5, and -0.5 ≤ z ≤ 0.1 may also be true. As previously stated, M may include Co, Mn, and / or Al.

[0041] The chemical structure represented by chemical formula 1 shows the bonding relationships contained within the layered or crystalline structure of the positive electrode active material and does not exclude the presence of other additional elements. For example, M may include Co and / or Mn, and Co and Mn may be provided together with Ni as the main active elements of the positive electrode active material. Chemical formula 1 is provided to represent the bonding relationships of the aforementioned main active elements and should be understood as a formula that encompasses the introduction and substitution of additional elements.

[0042] In one embodiment, in addition to the main active element, auxiliary elements may be included to enhance the chemical stability of the positive electrode active material or the layered / crystalline structure. These auxiliary elements can be incorporated together into the layered / crystalline structure to form bonds, and in this case too, they should be understood to be within the range of the chemical structure represented by chemical formula 1.

[0043] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may also act as an auxiliary active element, such as Al, in conjunction with Co or Mn, contributing to the capacity / power activity of the positive electrode active material.

[0044] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystalline structure represented by the following chemical formula 1-1.

[0045] [Chemical formula 1-1] Li x Ni a M1 b1 M2 b2 O 2+z

[0046] In chemical formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the aforementioned auxiliary elements. In chemical formula 1-1, 0.9 ≤ x ≤ 1.2, 0.5 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.5, and -0.5 ≤ z ≤ 0.1 may also be true.

[0047] The positive electrode active material may further contain coating elements or doping elements. For example, elements substantially identical or similar to the aforementioned auxiliary elements may be used as coating elements or doping elements. For example, the aforementioned elements may be used individually or in combination of two or more as coating elements or doping elements.

[0048] The coating element or doping element may be present on the surface of the lithium-nickel metal oxide particles, or it may penetrate from the surface of the lithium-nickel metal oxide particles and be included in the bonding structure represented by chemical formula 1 or chemical formula 1-1.

[0049] The positive electrode active material may include nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content can be used.

[0050] Ni can function as a transition metal that contributes to the output and capacity of lithium secondary batteries. Therefore, by employing a composition with a high content (High-Ni) as the positive electrode active material, as described above, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0051] However, increasing the Ni content can relatively decrease the long-term storage stability and lifespan stability of the positive electrode or secondary battery, and may also increase side reactions with the electrolyte. In contrast, according to an exemplary embodiment, electrical conductivity can be maintained by including Co, while lifespan stability and capacity maintenance characteristics can be improved by Mn.

[0052] In some embodiments, the Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total number of moles of nickel, cobalt, and manganese) may be 0.6 or higher, 0.7 or higher, 0.8 or higher, 0.85 or higher, 0.87 or higher, or 0.90 or higher. In some embodiments, the Ni content may be 0.85 to 0.99, 0.85 to 0.97, 0.85 to 0.95, 0.87 to 0.95, or 0.90 to 0.95. Within the range of Ni content, the capacity characteristics of the positive electrode and the lithium secondary battery can be improved.

[0053] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0054] In some embodiments, the positive electrode active material may include, for example, an LLO (Li-rich layered oxide) / OLO (Over Lithiated Oxide) system active material having a chemical or crystalline structure represented by chemical formula 2, a Mn-rich system active material, a Co-less system active material, and the like. These can be used individually or in combination of two or more.

[0055] [Chemical Formula 2] p[Li2MnO3]·(1 - p)[Li q JO2]

[0056] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J can contain at least one element of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0057] As the negative electrode active material, any material known in the art that can occlude and deselect lithium ions can be used without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, lithium metal, lithium alloys, silicon-containing substances, or tin-containing substances can be used.

[0058] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber (MPCF), and the like.

[0059] Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0060] The lithium metal can include pure lithium metal or lithium metal with a protective layer formed for dendrite growth inhibition or the like. In one embodiment, a lithium metal-containing layer vapor-deposited or coated on the negative electrode current collector can be used as the negative electrode active material layer. In one embodiment, a lithium thin film layer can also be used as the negative electrode active material layer.

[0061] Examples of the elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, and the like.

[0062] The silicon-containing substance can provide increased capacity characteristics. The silicon-containing substance can include Si, SiOx (0 < x < 2), metal-doped SiOx (0 < x < 2), silicon-carbon composites, etc. The metal can include lithium and / or magnesium, and the metal-doped SiOx (0 < x < 2) can include metal silicate.

[0063] For example, the positive electrode active material or the negative electrode active material can be mixed in a solvent to produce an electrode binder or an electrode slurry (positive electrode slurry or negative electrode slurry). After coating the electrode slurry on the current collector 50 and drying and rolling, an electrode for a lithium secondary battery can be manufactured.

[0064] The coating process can include gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc. The electrode slurry can further include a binder and a conductive material.

[0065] Non-limiting examples of the solvent used in the production of the positive electrode slurry include organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. The solvent used in the production of the negative electrode slurry can include water, alcohol-based solvents, etc.

[0066] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), polyacrylic acid-based binders, polyethylenedioxythiophene (poly(3,4-ethylenedioxythiophene), PEDOT)-based binders, and the like.

[0067] In some embodiments, a PVDF-based binder can be used as the positive electrode binder. In some embodiments, a styrene-butadiene rubber (SBR)-based binder, a carboxymethylcellulose (CMC)-based binder, a polyacrylic acid-based binder, a polyethylenedioxythiophene (poly(3,4-ethylenedioxythiophene, PEDOT)-based binder, etc., can be used as the negative electrode binder.

[0068] The conductive material may be added to improve conductivity and / or lithium ion or electron mobility. For example, non-limiting examples of the conductive material include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, and perovskite materials such as LaSrCoO3 and LaSrMnO3.

[0069] According to embodiments of the present disclosure, the electrode for the secondary battery includes a protective coating 70. The protective coating 70 can be formed on at least a portion of the surface of the active material layer 60.

[0070] The protective coating 70 is formed on at least one of the surfaces of the active material layer 60 facing the current collector 50 and on both sides thereof, and may be at least partially exposed on the surface of the active material layer 60. The facing surface may be a surface of the active material layer 60 that faces the coating surface on the current collector 50 in the thickness direction. The side surface may be a surface that connects the facing surface and the coating surface.

[0071] The protective coating 70 may include a material having low electronic conductivity and high ionic conductivity (e.g., high lithium conductivity). By protecting the outer surface of the active material layer 60 at least partially with the protective coating 70, electron transfer between the active material layer 60 (or the electrode active material within the active material layer 60) and the electrolyte can be suppressed or blocked.

[0072] Therefore, the lithium conductivity can be improved or maintained while suppressing the oxidation / reduction reaction on the outer surface of the active material layer 60. This promotes the lithium charge-discharge reaction and allows the capacity characteristics of the secondary battery to be maintained even after repeated charging and discharging.

[0073] The protective coating 70 may contain a substance that is substantially insoluble in the electrolyte and has high thermal and chemical stability (oxidation / reduction stability). It may also contain a substance that has improved mechanical strength and impact resistance.

[0074] According to embodiments of the present disclosure, the protective coating 70 may include an aryl ring-containing metal compound, and may include, for example, salts of an aryl ring-containing anion and a metal cation.

[0075] According to an exemplary embodiment, the protective coating 70 may contain a compound represented by the following structural formula 1.

[0076] [ka]

[0077] In structural formula 1, R is hydrogen, deuterium, -F, -Cl, -Br, -I, hydroxyl group, cyano group, nitro group, or substituted or unsubstituted C1-C 60 Alkyl alkyl groups, substituted or unsubstituted C2-C 60 Alkenyl group, substituted or unsubstituted C2-C 60 Alkynyl group, substituted or unsubstituted C1-C 60 Alkoxy group, substituted or unsubstituted C3-C 60 Carbon ring group, substituted or unsubstituted C1-C 60 Heterocyclic groups, substituted or unsubstituted C6-C 60 Aryloxy group, substituted or unsubstituted C6-C 60 Arylthio group, substituted or unsubstituted C7-C 60 Arylalkyl groups, or substituted or unsubstituted C2-C 60 A heteroarylalkyl group may also be used.

[0078] In one embodiment, R is hydrogen or substituted or unsubstituted C1-C 60 It may be an alkyl group. In one embodiment, R may be hydrogen or a substituted or unsubstituted C1-C5 alkyl group.

[0079] M represents a metallic element, and a represents the number of R elements, which may be an integer from 1 to 5. n may be an integer from 1 to 4. If a is an integer from 2 to 5, the multiple R elements may be the same or different from one another.

[0080] In this specification, "substituted or unsubstituted" means, unless otherwise defined, that a molecule is substituted or unsubstituted with one or more substituents selected from the group consisting of deuterium atoms, halogen atoms, cyano groups, nitro groups, amino groups, silyl groups, boron groups, phosphine oxide groups, phosphine sulfide groups, alkyl groups, alkenyl groups, aryl groups, and heterocyclic groups. Furthermore, the substituents exemplified above may each be substituted or unsubstituted. For example, a biphenyl group may be interpreted as an aryl group, or as a phenyl group substituted with a phenyl group. Heterocyclic groups include aliphatic heterocyclics and aromatic heterocyclics (heteroaryl groups).

[0081] In one embodiment, the protective coating 70 may contain a benzoate metal salt. In one embodiment, the protective coating 70 may contain a benzoate alkali metal salt (n=1) such as lithium benzoate, sodium benzoate, or potassium benzoate; or a benzoate alkaline earth metal salt (n=2) such as calcium benzoate or magnesium benzoate.

[0082] In one embodiment, the protective coating 70 may contain a benzoate-based alkali metal salt.

[0083] In one embodiment, M in structural formula 1 may be an alkali metal other than lithium. The protective coating 70 may contain benzoate salts of alkali metals other than lithium. For example, the protective coating 70 may contain sodium benzoate and / or potassium benzoate.

[0084] By using alkali metals with a relatively larger ionic radius than lithium, the passivation effect on the surface of the active material layer 60 of a lithium secondary battery can be further improved. For example, the generation of lithium impurities on the surface of the active material layer 60 can be suppressed, thereby suppressing the elution of lithium.

[0085] In one embodiment, when the protective coating 70 contains a benzoate-based alkaline earth metal salt, multiple benzoate groups are distributed on the surface of the active material layer 60, thereby increasing the electrode passivation effect.

[0086] As described above, the protective coating 70 contains an ionic bonded material, allowing for the formation of a stable solid thin film on the surface of the active material layer 60. This enables high-speed charging and discharging while reducing side reactions with the electrolyte, compared to using a thick polymer protective film. Furthermore, the inclusion of an organic group having an aryl ring reduces solubility in the electrolyte, providing stable electrode passivation.

[0087] Furthermore, it is possible to manufacture secondary batteries with the protective coating 70 still formed before charging and discharging progresses, while suppressing the formation of the SEI (Solid Electrolyte Interface) film that is generated during charging and discharging. This effectively suppresses side reactions of the electrolyte caused by repeated charging and discharging, high temperatures, and overvoltage, while preventing the consumption of the electrolyte.

[0088] In some embodiments, the components of the protective coating 70 for the secondary battery electrodes are as follows: 1 In the 1H-NMR spectrum, a peak may be observed in the range of 7.2–7.4 ppm (e.g., quadruplet or higher multiplet) and a peak in the range of 7.6–7.7 ppm (dualt). For example, in the solution obtained by eluting the components of the protective coating 70 from the electrode for the secondary battery... 1 The aforementioned peak can be observed in the 1H-NMR spectrum.

[0089] The protective coating 70 can also be formed on the current collector 50. In some embodiments, the protective coating 70 can be continuously extended along the surface of the current collector 50, the side surface of the active material layer 60, and the opposing surface of the active material layer 60.

[0090] Figures 2 to 4 are schematic partially enlarged cross-sectional views showing electrodes for a secondary battery according to exemplary embodiments. For example, Figures 2 to 4 are schematic partially enlarged cross-sectional views of region A shown in Figure 1.

[0091] In Figures 2 to 4, the active material contained in the active material layer 60 is represented as active material particles.

[0092] Referring to Figure 2, the protective coating 70 can be formed on the outer surface of the active material layer 60. The protective coating 70 may also be a separate coating layer formed directly on the outer surface of the active material layer 60.

[0093] Active material particles 65 may be distributed within the active material layer 60 together with a binder 62. Conductive material 64 may be distributed between the active material particles 65 together with the binder 62. The protective coating 70 can come into contact with the active material particles 65, binder 62, and conductive material 64 exposed on the outer surface of the active material layer 60, and can at least partially cover the outer surface.

[0094] As described above, an electrode for a secondary battery can be formed by coating the current collector 50 with an electrode slurry containing active material particles 65, a binder 62, and a conductive material 64, and then drying and rolling it.

[0095] The aforementioned coating material for forming the protective coating 70 can be dissolved in a solvent to produce a coating solution. After supporting the produced electrode in the coating solution, the protective coating 70 can be formed by drying it at a predetermined temperature. According to an exemplary embodiment, the active material layer 60 can be coated onto the current collector 50 and then supported in the coating solution.

[0096] The solvent may include water, alcohol-based solvents such as ethanol, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and the like.

[0097] The concentration or content of the coating substance in the coating solution may be 0.1% by weight or more and less than 10% by weight, 0.1% by weight to 5% by weight, 0.5% by weight to 5% by weight, or 1% by weight to 5% by weight. The drying temperature may be 40°C to 100°C, 50°C to 80°C, or 50°C to 70°C.

[0098] According to the aforementioned concentration and drying conditions, oxidation / reduction due to side reactions of the electrolyte can be prevented without impeding the fast charging characteristics, initial efficiency, and rate characteristics of the secondary battery.

[0099] Referring to Figure 3, the protective coating 70 can be formed on the surface of each of the active material particles 65. This allows the protective coating 70 formed on the active material particles 65 arranged on the outer surface of the active material layer 60 to be exposed to the outer surface.

[0100] Within the active material layer 60, a binder 62 and / or conductive material 64 may be distributed between the protective coating 70 formed on adjacent active material particles 65.

[0101] According to an exemplary embodiment, a coating solution can be prepared by mixing the aforementioned coating material with a solvent used in the electrode slurry. This allows the active material particles 65 to be mixed into the coating solution before they are coated onto the current collector 50.

[0102] The concentration or content of the coating substance in the coating solution may be 0.1% by weight or more and less than 10% by weight, 0.1% by weight to 5% by weight, 0.5% by weight to 5% by weight, or 1% by weight to 5% by weight.

[0103] The coating solution can be mixed with active material particles 65 to form a coating slurry, which can then be stirred using a mixer. The solid content in the coating slurry may be 30% to 90% by weight, 40% to 85% by weight, 40% to 80% by weight, or 50% to 70% by weight.

[0104] According to the aforementioned coating conditions, oxidation / reduction due to side reactions of the electrolyte can be prevented without hindering the initial efficiency and rate characteristics of the secondary battery.

[0105] By performing vacuum drying while stirring for a predetermined time, the solvent can be removed and a protective coating 70 can be formed on the surface of the active material particles 65.

[0106] An electrode slurry can be manufactured as described above using active material particles 65 on which a protective coating 70 is formed. After coating the electrode slurry onto a current collector 50, it can be dried and rolled to manufacture an electrode for a secondary battery containing an active material layer 60.

[0107] Referring to Figure 4, the protective coating 70 can be formed on the outer surface of the active material layer 60 and on the surface of the active material particles 65.

[0108] The protective coating 70 may include a first protective coating 70a formed on the outer surface of the active material layer 60 and a second protective coating 70b formed on the surface of the active material particles 65. In some embodiments, the first protective coating 70a and the second protective coating 70b may be substantially merged with each other on the outer surface of the active material layer 60.

[0109] According to an exemplary embodiment, as described in Figure 3, a second protective coating 70b can be formed on the active material particles 65 before the formation of the active material layer 60. The active material particles 65 on which the second protective coating 70b is formed can be dispersed in a solvent together with a binder 62 and a conductive material 64 to produce an electrode slurry, and the electrode slurry can be coated onto the current collector 50, after which it can be dried and rolled to form the active material layer 60.

[0110] Subsequently, as explained in Figure 2, the electrode for the secondary battery containing the active material layer 60 can be supported in the coating solution and dried to form the first protective coating 70a.

[0111] Figures 5 and 6 are schematic plan and cross-sectional views and cross-sectional views, respectively, of a secondary battery according to an exemplary embodiment. For example, Figure 6 is a cross-sectional view taken in the thickness direction along line I-I' in Figure 5. The protective coating 70 is not shown in Figures 5 and 6.

[0112] Figures 5 and 6 provide illustrative secondary battery structures for illustrative purposes and do not limit the structures of secondary batteries of this disclosure.

[0113] Referring to Figures 5 and 6, a lithium secondary battery may include an electrode assembly 150 comprising a positive electrode 100 and a negative electrode 130. The electrode assembly 150 may further include a separator membrane 140. The electrode assembly 150 can be formed by stacking multiple positive electrodes 100 and multiple negative electrodes 130 with the separator membrane 140 in between. The electrode assembly 150 may be housed and impregnated with an electrolyte in a case 160.

[0114] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on at least one surface of the positive electrode current collector 105. The positive electrode active material layer 110 may include positive electrode active material particles as active material particles 65.

[0115] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on at least one surface of the negative electrode current collector 125. The negative electrode active material layer 120 may include negative electrode active material particles as active material particles 65.

[0116] At least one of the positive electrode 100 and the negative electrode 130 may include an electrode for a secondary battery with a protective coating 70, as described in Figures 1 to 4. In some embodiments, the aforementioned electrode for a secondary battery is applied as the negative electrode 130, which can improve lithium mobility within the negative electrode active material layer and block oxidation / reduction side reactions due to electron transfer with the electrolyte.

[0117] In some embodiments, the aforementioned secondary battery electrodes can be applied to the positive electrode 100 and the negative electrode 130, respectively.

[0118] A separation membrane 140 can be interposed between the positive electrode 100 and the negative electrode 130. The separation membrane 140 may include a porous polymer film or a porous nonwoven fabric.

[0119] The porous polymer film may include polyolefin polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers.

[0120] The porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, and the like. The separation membrane 140 may also include ceramic materials. For example, inorganic particles can be coated onto the polymer film or dispersed within the polymer film to improve heat resistance.

[0121] According to an exemplary embodiment, an electrode cell is defined by a positive electrode 100, a negative electrode 130, and a separator membrane 140, and multiple electrode cells can be stacked to form, for example, an electrode assembly 150. The electrode assembly 150 may be of the winding type, stacking type, z-folding type, or stack-folding type.

[0122] A lithium secondary battery can be defined by housing the electrode assembly 150 together with the electrolyte in a case 160. According to an exemplary embodiment, a non-aqueous electrolyte can be used as the electrolyte.

[0123] The non-aqueous electrolyte contains a lithium salt, which is the electrolyte, and an organic solvent. The lithium salt is, for example, Li + X - The anion (X) of the lithium salt is represented as follows. - ) as F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , (CF3CF2SO2)2N - These are some examples.

[0124] Examples of organic solvents that can be used include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These can be used individually or in combination of two or more.

[0125] As shown in Figure 5, electrode tabs (positive electrode tab and negative electrode tab) protrude from the positive electrode current collector 105 and negative electrode current collector 125 belonging to each electrode cell and can extend to one end of the case 160. The electrode tabs are fused together with the aforementioned end of the case 160 and can be connected to electrode leads (positive electrode lead 107 and negative electrode lead 127) that extend to or are exposed outside the case 160.

[0126] Figure 5 shows that the positive lead 107 and the negative lead 127 protrude from the top edge of the case 160 in the planar direction, but the position of the electrode leads is not limited to this. For example, the electrode leads may protrude from at least one of the sides of the case 160, or from the bottom edge of the case 160. Alternatively, the positive lead 107 and the negative lead 127 may be formed to protrude from different sides of the case 160, respectively.

[0127] The aforementioned lithium secondary battery can be manufactured, for example, in the form of a cylindrical, rectangular, pouch, or coin-shaped container using a can.

[0128] The following examples, including embodiments and comparative examples, are presented to aid in understanding this disclosure. These embodiments are merely illustrative and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the embodiments are possible within the scope of this disclosure and the technical concept, and that such variations and modifications naturally fall within the scope of the appended claims.

[0129] Example 1 LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode mixture was prepared by mixing positive electrode active material particles containing O2, Denka Black as a conductive material, and PVDF as a binder in a mass ratio of 97:2:1. The prepared positive electrode mixture was coated onto an aluminum current collector, and then dried and pressed to produce the positive electrode.

[0130] A negative electrode slurry was prepared containing 93% by weight of natural graphite particles as the negative electrode active material, 5% by weight of KS6, a flake-type conductive material, 1% by weight of styrene-butadiene rubber (SBR) as a binder, and 1% by weight of carboxymethylcellulose (CMC) as a thickener. The negative electrode was manufactured by coating the negative electrode slurry onto a copper substrate, drying it, and pressing it.

[0131] The positive and negative electrodes were supported in an ethanol solution containing sodium benzoate at a concentration of 1% by weight for about 10 seconds, then removed and dried in a convection oven at 60 degrees Celsius to form a protective coating on the surface of the active material layer.

[0132] The positive and negative electrodes manufactured as described above were notched to a predetermined size and stacked. A separator (polyethylene, 15 μm thick) was interposed between the positive and negative electrodes to form an electrode cell, and then the tab portions of the positive and negative electrodes were welded. The welded assembly of positive electrode / separator / negative electrode was placed in a pouch, and three sides were sealed, excluding the electrolyte injection surface. At this time, the portion with the electrode tabs was included in the sealed area. The electrolyte was injected through the electrolyte injection surface, and after sealing the electrolyte injection surface, it was impregnated for 12 hours or more. After that, chemical conversion charging and discharging was performed (charging conditions: CC-CV, 0.25C, 4.2V, 0.05C, CUT-OFF; discharging conditions: CC, 0.25C, 2.5V, CUT-OFF).

[0133] During the preparation of the electrolyte, a 1M LiPF6 solution was prepared using a mixed solvent of EC / EMC (30 / 70; volume ratio), and 1% by weight of vinylene carbonate (VC), 0.5% by weight of 1,3-propensultone (PRS), and 0.5% by weight of lithium bis(oxalato)borate (LiBOB) were added.

[0134] Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that instead of forming a protective coating after manufacturing the active material layer, a protective coating was formed on the positive electrode active material particles and negative electrode active material particles before manufacturing the positive and negative electrodes. Specifically, positive electrode active material particles and negative electrode active material particles were mixed in a planetary mixer with an NMP solution having a 1% by weight sodium benzoate concentration and an aqueous solution having a 1% by weight sodium benzoate concentration, respectively. After adjusting the solid content of the solution in the mixer to 50% by weight, stirring / mixing was performed while vacuum drying using a vacuum line.

[0135] Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that the sodium benzoate concentration in the coating solution was increased to 10% by weight.

[0136] Example 4 A secondary battery was manufactured in the same manner as in Example 1, except that the sodium benzoate concentration in the coating solution was reduced to 0.09% by weight.

[0137] Example 5 A secondary battery was manufactured in the same manner as in Example 1, except that magnesium benzoate was used as the coating material.

[0138] Example 6 A secondary battery was manufactured in the same manner as in Example 1, except that lithium benzoate was used as the coating material.

[0139] Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1, except that the formation of a protective coating was omitted.

[0140] Comparative Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that bis(oxalato)borate (LiBOB) was used as the coating substance in the coating solution.

[0141] Comparative Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that NaCl was used as the coating substance in the coating solution.

[0142] Evaluation example (1) Protective coating 1 H NMR analysis After performing chemical conversion charge-discharge in Example 1 and Comparative Example 1, the negative electrode was removed from the secondary battery, supported on DMC (dimethyl carbonate) for 3 days, and then dried. The active material layer was scraped from the dried negative electrode and mixed with D2O in a 1:2 weight ratio to prepare a sample solution. The sample solution was stirred for 1 day to elute the protective coating components, and then filtered through a syringe filter to obtain the measurement solution. Figure 7 shows the measurements of the negative electrode components for Example 1 and Comparative Example 1. 1 This is a graph of the 1H NMR analysis. Referring to Figure 7, Example 1 1 In the 1H-NMR spectrum, a multiplet peak was observed in the 7.2–7.4 ppm range, and a doublet peak was observed in the 7.6–7.7 ppm range.

[0143] (2) Evaluation of fast charging characteristics The secondary batteries manufactured in the examples and comparative examples were subjected to 200 cycles at room temperature within a DOD of 72% (SOC 8%-80%), consisting of step charging at C rates of 1.25C / 1.0C / 0.75C / 0.5C (CC / CV charging 4.2V 0.05C cut) and discharge at 1 / 3C (CC discharge 2.5V cut). A 10-minute rest time was provided between each cycle. After 200 cycles, the retention rate of the charge capacity relative to the discharge capacity of the initial cycle was measured.

[0144] (3) DC-IR evaluation The secondary battery was charged at 25°C (0.3C CC / CV charge, 4.2V, 0.05C cut), then rested for 10 minutes, and subsequently discharged (0.3C CC discharge, SOC 50% cut). Next, it was rested at SOC 50% for 1 hour, discharged at 1C for 10 seconds, and then rested again for 10 seconds. The discharge resistance (DC-IR) at SOC 50% was calculated by dividing the difference between the voltage after resting at SOC 50% for 1 hour and the voltage after the 1C discharge for 10 seconds by the 1C current value. The evaluation results are shown in Table 1 below.

[0145] [Table 1]

[0146] Referring to Table 1, it can be seen that in the examples in which a protective coating containing an aryl ring-containing metal compound was formed, a high fast charge capacity retention rate and low discharge resistance were ensured.

[0147] In Example 3, where the concentration of the coating substance in the coating solution was increased, the discharge resistance increased slightly with increasing coating thickness. In Example 4, where the concentration of the coating substance in the coating solution was decreased, the fast charging stability was reduced compared to Example 1.

[0148] In comparative examples where the protective coating was omitted, or where an organic or inorganic substance without aryl groups was used as a coating, the fast charging capacity retention rate was significantly lower compared to the examples.

[0149] In Example 6, which used lithium benzoate as the coating material, the fast charging stability decreased and the discharge resistance increased compared to Example 1, which used sodium benzoate.

Claims

1. Current collector and, Displaced on the current collector, an active material layer containing an active material, An electrode for a secondary battery, comprising a protective coating containing an aryl ring-containing metal compound, covering at least a portion of the surface of the active material or at least a portion of the surface of the active material layer.

2. The protective coating comprises a compound represented by the following structural formula 1, wherein the electrode for a secondary battery is as described in claim 1. 【Chemistry 1】 In Structural Formula 1, R is hydrogen, deuterium, -F, -Cl, -Br, -I, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C １ -C ６０ alkyl group, a substituted or unsubstituted C ２ -C ６０ alkenyl group, a substituted or unsubstituted C ２ -C ６０ alkynyl group, a substituted or unsubstituted C １ -C ６０ alkoxy group, a substituted or unsubstituted C ３ -C ６０ carbocyclic group, a substituted or unsubstituted C １ -C ６０ heterocyclic group, a substituted or unsubstituted C ６ -C ６０ aryloxy group, a substituted or unsubstituted C ６ -C ６０ arylthio group, a substituted or unsubstituted C ７ -C ６０ arylalkyl group, or a substituted or unsubstituted C ２ -C ６０ heteroarylalkyl group, and (M represents a metallic element, a is an integer from 1 to 5, and n is an integer from 1 to 4.)

3. The electrode for a secondary battery according to claim 2, wherein in structural formula 1, M is an alkali metal or alkaline earth metal, and n is 1 or 2.

4. The electrode for a secondary battery according to claim 1, wherein the active material layer further comprises a binder, and the protective coating at least partially covers the surfaces of the active material and binder exposed on the outer surface of the active material layer.

5. The electrode for a secondary battery according to claim 1, wherein the protective coating is present on the surface of the active material and also inside the active material layer.

6. The electrode for a secondary battery according to claim 5, wherein the protective coating comprises a first protective coating covering the outer surface of the active material layer and a second protective coating covering the surface of the active material.

7. The electrode for a secondary battery according to claim 6, wherein the first protective coating and the second protective coating are joined together at the outer periphery of the active material layer.

8. The electrode for a secondary battery according to claim 1, wherein the protective coating is in contact with the surface of the current collector.

9. A solution obtained by eluting the components of the protective coating from the electrodes for the secondary battery. １ The electrode for a secondary battery according to claim 1, wherein a multiplet peak is observed in the range of 7.2 to 7.4 ppm and a doublet peak is observed in the range of 7.6 to 7.7 ppm in the 1H-NMR spectrum.

10. It includes a positive electrode and a negative electrode opposite to the positive electrode, A secondary battery in which at least one of the positive electrode and the negative electrode includes an electrode for a secondary battery as described in claim 1.

11. Steps to prepare the current collector, The step of forming an active material layer on the current collector, which includes an active material and a protective coating containing an aryl ring-containing metal compound, The step of forming the active material layer is a step of forming the protective coating on the outer surface of the active material layer, or A method for manufacturing an electrode for a secondary battery, comprising the step of forming the protective coating on the surface of the active material.

12. The method for manufacturing an electrode for a secondary battery according to claim 11, wherein the step of forming the protective coating on the outer surface of the active material layer includes supporting the active material layer, which is coated on the current collector, in a coating solution containing the aryl ring-containing metal compound.

13. The method for manufacturing an electrode for a secondary battery according to claim 11, wherein the step of forming the protective coating on the surface of the active material includes mixing the active material with a coating solution containing the aryl ring-containing metal compound before coating the current collector.

14. The method for manufacturing an electrode for a secondary battery according to claim 13, wherein the mixing of the active material into the coating solution is performed together with vacuum drying.

15. The method for manufacturing an electrode for a secondary battery according to claim 12 or 13, wherein the concentration of the aryl ring-containing metal compound in the coating solution is 0.1% by weight or more and less than 10% by weight.

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