Negative electrode for anode-free secondary battery, method for manufacturing same, and anode-free secondary battery comprising same

Abstract

The present invention relates to: a negative electrode for an anode-free secondary battery capable of improving the electrochemical characteristics and lifespan characteristics of an anode-free secondary battery by inducing uniform electrodeposition of a lithium metal layer while suppressing side reactions with an electrolyte; a method for manufacturing same; and an anode-free secondary battery.

Description

Negative electrode for anode-free secondary battery, method for manufacturing same, and anode-free secondary battery including same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0091774, filed July 11, 2024, and Korean Patent Application No. 10-2025-0085053, filed June 26, 2025, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to an anode for an anode-free secondary battery, a method for manufacturing the same, and an anode-free secondary battery, which can improve the electrochemical characteristics and lifespan characteristics of an anode-free secondary battery by inducing uniform deposition of a lithium metal layer while suppressing side reactions with an electrolyte.

[0004] Lithium metal batteries utilize lithium metal (Li-metal) as the anode active material. Compared to conventional graphite-based anodes, lithium metal batteries theoretically offer higher energy density and capacity. Therefore, research and development are ongoing to apply these lithium metal batteries to batteries requiring high energy densities.

[0005] Recently, interest in non-anode secondary batteries, also known as anode-free secondary batteries, has been increasing in order to further increase the energy density of the lithium metal batteries. Such anode-free secondary battery refers to a secondary battery that includes the anode current collector itself as the anode, without forming a separate lithium metal layer or anode active material layer on the anode current collector during the manufacturing process. Such an anode-free secondary battery can be defined as a battery that utilizes lithium metal as the anode active material by depositing lithium metal on the anode current collector during charging.

[0006] However, in these anode-free secondary batteries, side reactions can occur between the lithium metal deposited on the negative electrode and the electrolyte. However, because there is no spare lithium to replenish the lithium consumed by these side reactions or the formation of an electrode-electrolyte interfacial film, these batteries suffer from poor Coulombic efficiency and cycle life characteristics.

[0007] Moreover, in the case of the negative electrode for the anode-free secondary battery, since the metal current collector including copper, etc., is directly exposed to the electrolyte, side reactions with the electrolyte and consumption of the electrolyte may occur, and many problems have also occurred due to uneven lithium growth, such as corrosion of the current collector and growth of lithium dendrites.

[0008] Accordingly, there has been a continuous demand for technological development that can improve the efficiency and lifespan characteristics of anode-free secondary batteries by suppressing side reactions with the electrolyte and inducing uniform lithium deposition.

[0009] Accordingly, the present invention provides an anode for an anode-free secondary battery and a method for manufacturing the same, which can improve the coulombic efficiency and lifespan characteristics of an anode-free secondary battery by inducing uniform deposition of a lithium metal layer while suppressing side reactions with an electrolyte.

[0010] The present invention also provides an anode-free secondary battery exhibiting improved electrochemical characteristics and lifespan characteristics, including the negative electrode.

[0011] According to one embodiment of the invention, there is provided an anode for an anode-free secondary battery, comprising: a conductive metal layer; and a polymer protective layer formed on the conductive metal layer, wherein the polymer protective layer has a surface contact angle of 50° or more and less than 90° with respect to an ether-based non-aqueous organic solvent.

[0012] In the cathode of this embodiment, the conductive metal layer may include copper (Cu).

[0013] In addition, in the above negative electrode, the polymer protective layer may have a surface contact angle of 50° or more and less than 90° for an electrolyte containing a lithium salt and an ether-based non-aqueous organic solvent, and having a molar concentration of 4M of the lithium salt.

[0014] In a more specific example, the polymer protective layer may include a polymer having a hydrocarbon group having a carbon number of 8 or more and a plurality of fluorine-substituted groups bonded thereto, and a more specific example of such a polymer may be a poly[fluoroalkyl(meth)acrylate] polymer having a long-chain alkyl group having a carbon number of 8 or more and a fluorine-substituted group of 5 or more.

[0015] A polymer protective layer including such a polymer exhibits incompatibility with an electrolyte included in an anode-free secondary battery, thereby reducing side reactions between the negative electrode and the electrolyte or resulting electrolyte consumption, and inducing uniform deposition of a lithium metal layer.

[0016] Additionally, in the cathode of the above embodiment, the polymer protective layer may have a thickness of 1 to 1000 nm.

[0017] Meanwhile, according to another embodiment of the invention, a method for manufacturing a negative electrode for an anode-free secondary battery is provided, comprising a step of polymerizing the monomer on a conductive metal layer by chemical vapor deposition (iCVD) in the presence of a radical initiator and a gaseous monomer, wherein the monomer comprises a monomer having a hydrocarbon group having 8 or more carbon atoms and having a plurality of fluorine substitutions bonded thereto.

[0018] In the manufacturing method of these other embodiments, the chemical vapor deposition step may be performed at a temperature of 100°C to 300°C, and tert-butyl peroxide may be used as the radical initiator.

[0019] In addition, the monomer may include a fluoroalkyl (meth)acrylate compound having a long-chain alkyl group having 8 or more carbon atoms and substituted with 5 or more fluorines. By radical polymerizing this monomer and chemical vapor deposition on the conductive metal layer, the above-described polymer protective layer and an embodiment of the negative electrode including the same can be manufactured.

[0020] Meanwhile, according to a further embodiment of the invention, an anode-free secondary battery is provided, which comprises: a cathode according to the above-described embodiment; a cathode facing the cathode; a separator interposed between the cathode and the anode; and an electrolyte comprising a lithium salt and a non-aqueous organic solvent, wherein a lithium metal layer is deposited on a polymer protective layer of the cathode when charged.

[0021] Such an anode-free secondary battery may further include a solid electrolyte interphase layer formed on the polymer protective layer and containing 80 mol% or more of an inorganic material including a metal fluoride. The solid electrolyte interphase layer may have a ratio of the content of total non-metallic elements excluding carbon elements (atomic%) / the content of total carbon elements (atomic%) of 0.5 or more.

[0022] Additionally, in the anode-free secondary battery, the cathode may include a lithium transition metal oxide including lithium and at least one transition metal selected from the group consisting of nickel, manganese, cobalt, and aluminum as a cathode active material.

[0023] And, such a secondary battery may include an electrolyte including an ether-based non-aqueous organic solvent, and in a more specific example, may include an electrolyte including a lithium salt at a concentration of 1 M or more.

[0024] An anode for an anode-free secondary battery of one embodiment includes a polymer protective layer formed on a conductive metal layer, wherein the polymer protective layer exhibits incompatibility with a non-aqueous organic solvent or an electrolyte containing the same, as defined by a surface contact angle of 50° or more.

[0025] It was confirmed that the formation of such a polymer protective layer can suppress side reactions between the negative electrode and the electrolyte, decomposition of non-aqueous organic solvents, and corrosion of the conductive metal layer due to such reactions. In addition, it was confirmed that the action of the polymer protective layer reduces the overvoltage applied for nucleus formation during initial lithium electrodeposition, and as a stable solid electrolyte interfacial film substantially composed of inorganic materials is formed, the growth of lithium dendrites is suppressed during charge and discharge of an anode-free secondary battery, thereby inducing stable and uniform electrodeposition of a lithium metal layer.

[0026] As a result, it was confirmed that an anode-free secondary battery including the above-mentioned negative electrode can exhibit excellent life characteristics along with excellent electrochemical characteristics such as improved Coulombic efficiency.

[0027] FIG. 1 is a schematic diagram showing an example of a method for manufacturing a negative electrode for an anode-free secondary battery according to another embodiment of the invention.

[0028] Figure 2 is a drawing showing the results of measuring the surface contact angle by dropping an ether-based non-aqueous organic solvent or an electrolyte including a lithium salt and an ether-based non-aqueous organic solvent onto the cathode surface of Comparative Examples 1 to 4 and Examples 1 and 2.

[0029] Figure 3 is a graph showing the results of measuring the coulombic efficiency per cycle for half cells including the cathodes of Comparative Example 1 and Example 2.

[0030] Figure 4 is a graph showing the results of measuring the change in coulombic efficiency and discharge capacity per cycle for a full cell type secondary battery including the negative electrodes of Comparative Example 1 and Example 2.

[0031] FIG. 5 shows the results of elemental analysis by XPS (X-ray Photoelectron Spectroscope) of the solid electrolyte interfacial film formed after the cycle test of FIG. 3 for half cells including the negative electrodes of Comparative Example 1 and Example 2.

[0032] FIG. 6 is a graph showing the results of analyzing the composition of carbon elements and other non-metallic elements in the solid electrolyte interface film formed after the cycle test of FIG. 4 for a full cell type secondary battery including the negative electrodes of Comparative Example 1 and Example 2, by XPS analysis.

[0033] FIG. 7 is a photograph of a lithium metal layer deposited on a negative electrode after the cycle test of FIG. 3 for a half-cell including the negative electrodes of Comparative Example 1 and Example 2, analyzed by an electron microscope.

[0034] Figure 8 is a graph showing the results of measuring the change in current density per hour while maintaining the voltage of the negative electrode at 0 V in a half-cell including the negative electrodes of Comparative Example 1 and Example 2.

[0035] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless specifically stated otherwise.

[0036] The terms "about," "substantially," and the like, as used throughout this specification, are used in a sense of or near the numerical value when manufacturing and material tolerances inherent in the meanings referred to are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that mention exact or absolute numbers to aid understanding of the present disclosure.

[0037] The terms “step of” or “step of” as used throughout this specification do not mean “step for”.

[0038] Throughout this specification, terms indicating the scale of a component, such as “diameter” or “thickness,” may be interpreted to mean “maximum diameter” or “maximum thickness” of the component.

[0039] Furthermore, when a part such as a layer, film, region, or plate is said to be “on” another part, this includes not only cases where it is “directly on” the other part, but also cases where there is another part in between. Additionally, a part such as a film, region, or plate that is “on” the other part may have a portion thereof overlap with a portion of the other part in the thickness direction.

[0040] In addition, throughout this specification, the term “anode-free secondary battery” may refer to a secondary battery in which a separate negative electrode active material layer, such as a separate lithium metal layer or lithium alloy layer, does not exist on the negative electrode, the polymer protective layer, or the negative electrode current collector in a state before charging or discharging, for example, in a state immediately after manufacturing. Accordingly, the “anode-free secondary battery” may be defined as one that does not include a separate negative electrode active material layer (e.g., a lithium metal layer, etc.) on the negative electrode, the polymer protective layer, or the negative electrode current collector in a state before charging or discharging. However, it goes without saying that addition of a separate insulating layer or functional layer other than the negative electrode active material layer is not limited. In addition, the term “anode-free secondary battery” above cannot be interpreted as limiting the presence of a lithium-containing positive electrode active material, or limiting the presence of a lithium metal layer or a lithium-containing compound deposited on the negative electrode as a result of charging or discharging.

[0041]

[0042] Hereinafter, based on the above definitions, embodiments of the invention will be described in detail with reference to the attached drawings. However, these are presented as examples and are not intended to limit the invention. The invention is defined solely by the scope of the claims set forth below.

[0043] As described above, the negative electrode for an anode-free secondary battery of one embodiment includes a conductive metal layer; and a polymer protective layer formed on the conductive metal layer, wherein the polymer protective layer may have a surface contact angle of 50° or more and less than 90° with respect to an ether-based non-aqueous organic solvent. In addition, the negative electrode of one embodiment may have a surface contact angle of 50° or more and less than 90° not only with respect to the ether-based non-aqueous organic solvent, but also with respect to an electrolyte containing a lithium salt and an ether-based non-aqueous organic solvent, wherein the molar concentration of the lithium salt is 1 M or more, or 1 M to 5 M, or 4 M.

[0044] At this time, the surface contact angle can be measured using, for example, an ether-based non-aqueous organic solvent such as 1,2-dimethoxyethane (DME), or an electrolyte in which a lithium salt, for example, lithium bis(fluorosulfonyl)imide (LiFSI), is dissolved in the ether-based non-aqueous organic solvent at a molar concentration of 4 M. Specifically, the ether-based non-aqueous organic solvent or the electrolyte is dropped onto the polymer protective layer of the negative electrode, and the surface contact angle can be measured using a contact angle measuring device or the like. An example of measuring the surface contact angle using this method and the measurement results are shown in FIG. 2.

[0045] In particular, in the cathode of the above embodiment, the polymer protective layer may exhibit a surface contact angle of 50° to 90°, or 60° to 85°, or 70° to 83° with respect to the ether-based non-aqueous organic solvent, and may exhibit a surface contact angle of 50° to 90°, or 65° to 87°, or 70° to 83° with respect to the electrolyte.

[0046] This surface contact angle can define that the polymer protective layer exhibits non-affinity and low wettability with respect to the non-aqueous organic solvent, and further, with respect to the electrolyte containing the same. As this electrolyte-incompatible polymer protective layer is formed on a conductive metal layer such as copper, side reactions between the conductive metal layer, which is a negative electrode for an anode-free secondary battery, specifically a metal current collector, and the electrolyte can be suppressed.

[0047] As a result of suppressing these side reactions, during operation of an anode-free secondary battery, decomposition and consumption of non-aqueous organic solvents contained in the electrolyte, and corrosion of a metal current collector including a conductive metal layer can be suppressed. In addition, since decomposition of a lithium salt occurs instead of decomposition of the organic solvent, a stable solid electrolyte interphase layer composed of an inorganic material such as LiF and substantially no organic material is formed on the polymer protective layer, and a lithium metal layer can be uniformly deposited on this solid electrolyte interphase layer.

[0048] It was confirmed that due to the action of the polymer protective layer described above, the overvoltage applied for nucleation during initial lithium electrodeposition can also be reduced. In addition, due to the formation of the polymer protective layer and a stable solid electrolyte interfacial film, the growth of lithium dendrites can be suppressed during battery charging on the negative electrode of one embodiment, while a uniform lithium metal layer can be electrodeposited. Therefore, it was confirmed that an anode-free secondary battery including the negative electrode of one embodiment can exhibit excellent electrochemical characteristics, such as improved Coulombic efficiency, as well as excellent cycle life characteristics.

[0049] Meanwhile, in order for the polymer protective layer to exhibit the surface contact angle described above, the polymer protective layer may include a polymer in which a long-chain hydrocarbon group having 8 or more carbon atoms and having a predetermined substituent, for example, a plurality of fluorines substituted thereon, is bonded as a substituent to the main chain or side chain. In a more specific example, the substituent of the polymer may be a long-chain fluorinated hydrocarbon group having 8 to 30 carbon atoms, or 10 to 20 carbon atoms, for example, a long-chain fluorinated alkyl group, and such a long-chain fluorinated hydrocarbon group may have 5 or more, or 5 to 30, or 8 to 20 fluorines in a single substituent.

[0050] Due to the presence of these numerous fluorine-containing long-chain substituents, the polymer protective layer including the polymer can exhibit a large surface contact angle, low wettability, and non-affinity with respect to the ether-based non-aqueous organic solvent and the electrolyte including the same.

[0051] In addition, in a more specific embodiment, the polymer protective layer may include a poly(meth)acrylate polymer having the above-described long-chain fluorinated hydrocarbon group or long-chain fluorinated alkyl group bonded to the main chain or side chain, for example, a poly[fluoroalkyl(meth)acrylate] polymer having a long-chain alkyl group having 8 or more carbon atoms and containing 5 or more fluorines bonded to each substituent.

[0052] By using such poly(meth)acrylate polymers, a uniform polymer protective layer can be easily formed through radical polymerization and chemical vapor deposition methods described below.

[0053] The polymer protective layer including the above-described polymer exhibits low wettability and non-affinity with respect to the electrolyte included in the anode-free secondary battery, thereby reducing side reactions between the negative electrode and the electrolyte or decomposition and consumption of the electrolyte due to such reactions, and inducing uniform deposition of the lithium metal layer.

[0054] In the negative electrode of the above-described embodiment, the polymer protective layer may have a thickness of 1 to 1000 nm, or 1 to 150 nm, or 3 to 120 nm, or 5 to 100 nm, or 10 to 50 nm. Since the polymer protective layer has such a thickness, the overall thickness of the anode-free secondary battery can be reduced to further increase the energy density, while reducing the nucleation overvoltage during initial lithium deposition and forming a stable inorganic solid electrolyte interfacial film, thereby further improving the Coulombic efficiency and life characteristics of the secondary battery.

[0055] Meanwhile, the negative electrode for an anode-free secondary battery according to the above-described embodiment may include a conductive metal layer as a substrate supporting the above-described polymer protective layer. In this case, the conductive metal layer may be formed using any conductive metal that has been previously known to be usable as a negative electrode current collector, as a metal that does not cause chemical changes in the anode-free secondary battery, has relatively low reactivity, and has high conductivity.

[0056] Specific examples thereof include metals such as stainless steel, aluminum, nickel, titanium, or copper, or metals surface-treated with carbon, nickel, titanium, silver, or the like on the surface of copper, aluminum, or stainless steel. However, considering the excellent conductivity and light weight of the cathode of one embodiment, and the ease of manufacturing the porous metal layer, the conductive metal layer may include copper.

[0057] Such a conductive metal layer may have a thickness of, for example, 3 to 500 μm, or 5 to 300 μm, or 10 to 200 μm.

[0058] Meanwhile, according to another embodiment of the invention, a method for manufacturing the negative electrode of the above-described embodiment is provided. The method for manufacturing the negative electrode includes, for example, a step of performing initiated chemical vapor deposition (iCVD) while polymerizing the monomer on a conductive metal layer in the presence of a radical initiator and a gaseous monomer, wherein the monomer may include a monomer having a hydrocarbon group having 8 or more carbon atoms and having a plurality of fluorine substitutions bonded thereto.

[0059] FIG. 1 schematically illustrates an example of a method for manufacturing a negative electrode for an anode-free secondary battery according to another embodiment of the invention.

[0060] As illustrated in Fig. 1, a monomer having a long-chain hydrocarbon group having multiple fluorines bonded as a substituent may be vaporized and injected into a reaction chamber, while a radical initiator may be injected together therewith. The radical initiator forms radicals at a high temperature of, for example, 100°C or higher, and these radicals may induce the initiation and polymerization of the monomer. In addition, a polymer formed by the polymerization may be adsorbed onto a conductive metal layer having a relatively low temperature, for example, a temperature of 20 to 40°C, and deposited on the conductive metal layer to form a polymer protective layer.

[0061] In this way, through polymerization and initiated chemical vapor deposition (iCVD) in the presence of an initiator, a polymer having a substituent such as a long-chain fluorinated hydrocarbon group can be slowly grown and deposited, thereby forming a uniform polymer protective layer. In addition, in this method, the uniform polymer protective layer can be formed while maintaining the temperature of the conductive metal layer low at around room temperature without using a separate liquid medium such as a solvent. As a result, an anode of one embodiment including the above-described polymer protective layer can be manufactured without damaging the conductive metal layer serving as a metal current collector.

[0062] Meanwhile, the polymerization and chemical vapor deposition steps described above can be performed at a temperature of, for example, 100°C to 300°C. As a result, the polymerization of the monomer and the deposition of the polymer in the presence of the radical initiator can be efficiently performed while suppressing damage to the conductive metal layer. In order to raise the temperature within the reaction chamber to the polymerization and deposition temperature of 100°C or higher while maintaining the temperature of the conductive metal layer low at around room temperature, a plurality of filaments can be provided within the reaction chamber, and the temperature of these filaments can be heated to a temperature of 100°C to 300°C.

[0063] Additionally, tert-butyl peroxide can be used as the radical initiator without any particular limitation.

[0064] In addition, in the manufacturing method of the other embodiment, any radical polymerizable compound that enables the formation of a polymer included in the polymer protective layer described above may be used as the monomer. For example, the monomer may be an unsaturated compound to which a long-chain hydrocarbon group having 8 or more carbon atoms and substituted with a predetermined substituent, for example, a plurality of fluorines, is bonded. In a more specific example, the substituent of the monomer may be a long-chain fluorinated hydrocarbon group having 8 to 30 carbon atoms, or 10 to 20 carbon atoms, for example, a long-chain fluorinated alkyl group, and such a long-chain fluorinated hydrocarbon group may have 5 or more, or 5 to 30, or 8 to 20 fluorines in a single substituent.

[0065] In addition, in a more specific embodiment, the monomer may include a (meth)acrylate compound having a long-chain fluorinated hydrocarbon group or a long-chain fluorinated alkyl group bonded thereto, for example, a fluoroalkyl (meth)acrylate compound having a long-chain alkyl group having 8 or more carbon atoms and containing 5 or more fluorines in each substituent.

[0066] Meanwhile, according to a further embodiment of the invention, an anode-free secondary battery is provided comprising the negative electrode of the above-described embodiment. Such an anode-free secondary battery may comprise, for example, the negative electrode of the above-described embodiment; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte comprising a lithium salt and a non-aqueous organic solvent.

[0067] In such an anode-free secondary battery, the negative electrode does not include a separate negative electrode active material layer, such as a lithium metal layer, before charging or discharging. However, as the anode-free secondary battery is charged or discharged, lithium ions moved from the positive electrode may be deposited on the polymer protective layer of the negative electrode during charging, thereby forming a lithium metal layer or a lithium alloy layer, and such a lithium metal layer or the like may function as a negative electrode active material.

[0068] In the secondary battery of the above additional embodiment, a solid electrolyte interphase layer formed on the polymer protective layer may be further included. In a more specific example, the solid electrolyte interphase layer may include an inorganic material including a metal fluoride such as lithium fluoride (LiF) in an amount of 80 mol% or more, or 85 to 99 mol%, and an organic material in an amount so low that it may be substantially absent.

[0069] This is because the polymer protective film having the above-described electrolyte incompatibility can suppress side reactions of the conductive metal layer and the electrolyte and decomposition of the non-aqueous organic solvent. Accordingly, the solid electrolyte interfacial film can be formed by the reaction of lithium cations derived from the lithium salt and non-metallic anions other than carbon, such as fluorine, nitrogen, sulfur, or phosphorus derived from the lithium salt or the polymer protective film. As a result, the solid electrolyte interfacial film can substantially contain inorganic substances in a majority of the content and substantially contain no organic substances or contain only very low contents.

[0070] For reference, metal fluorides such as LiF can suppress the growth of lithium dendrites and ensure the uniform deposition of lithium metal layers due to their high affinity for lithium ions and high Young's modulus. Furthermore, the inorganic solid electrolyte interfacial layer exhibits excellent elastic modulus and mechanical properties, thereby contributing to the overall performance enhancement of secondary batteries.

[0071] In a more specific example, the solid electrolyte interfacial film may exhibit an element composition in which the ratio of the content (atomic %) of total non-metallic elements (e.g., fluorine, nitrogen, sulfur, or phosphorus elements) excluding carbon elements to the content (atomic %) of total carbon elements is 0.5 or more, 0.5 to 0.7, or 0.55 to 0.65. This may reflect that the carbon element content of the solid electrolyte interfacial film is very low because the polymer protective layer suppresses the decomposition of a non-aqueous organic solvent.

[0072] Meanwhile, in the anode-free secondary battery of the above additional embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector.

[0073] These positive electrodes can be manufactured by mixing an active material and a binder, and in some cases, a conductive material, a filler, etc. in a solvent to prepare a positive electrode slurry composition, and applying the composition to a positive electrode current collector.

[0074] The above-described positive electrode current collector may generally have a thickness of 3 to 500 μm. In addition, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may also form fine unevenness on its surface to increase the adhesive strength of the positive electrode active material, and various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric are possible.

[0075] And, in the case of the positive electrode active material, it may include a compound capable of reversible intercalation and deintercalation of lithium, specifically a lithium metal oxide including lithium and one or more metals such as iron, cobalt, manganese, nickel, or aluminum. In a more specific example, the positive electrode active material may include a lithium transition metal oxide including lithium and one or more transition metals selected from the group consisting of nickel, manganese, cobalt, and aluminum.

[0076] Specifically, the lithium metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn2-Z1 Co Z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2) etc.), lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5≤a≤+0.5, 0≤x≤0.5, 0≤b≤0.1), and any one or two or more compounds thereof may be included.

[0077] Among these, the positive electrode active material includes a lithium transition metal oxide including lithium and two or more metals selected from the group consisting of nickel, manganese, cobalt, and aluminum, and the lithium transition metal oxide may include nickel in an amount of 50 mol% or more, or 60 to 99 mol%, or 70 to 95 mol%, based on the total metal content excluding lithium. Such a lithium transition metal oxide may be represented by, for example, the following chemical formula 1:

[0078] [Chemical Formula 1]

[0079] Li x Ni a Co b M 1 c M 2 d O2

[0080] In the above chemical formula 1, the M 1 Mn and Al may be one or more selected from or a combination thereof, and M 2 may be at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and may be 0.90≤x≤1.1, or 0.95≤x≤1.08, or 1.0≤x≤1.08, and may be 0.50≤a<1.0, or 0.60≤a≤0.99, or 0.70≤a≤0.95. In addition, 0 <b≤0.3이고, 0<c≤0.3이고, 0≤d≤0.1일 수 있다.

[0081] By using a lithium transition metal oxide containing such a high nickel content as a positive electrode active material and combining it with an anode of one embodiment, the output and capacity characteristics, as well as the life characteristics, of an anode-free secondary battery can be further improved.

[0082] The above-described positive electrode active material may be included in an amount of 60 to 99 wt%, or 70 to 99 wt%, or 80 to 98 wt% based on the total weight of the positive electrode active material layer.

[0083] Meanwhile, the conductive material included in the positive electrode active material layer is a component for further improving the conductivity of the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. Among these, the conductive material can further lower the resistance of the anode-free secondary battery and improve the output characteristics, etc. by including a conductive nanomaterial such as carbon nanotubes or carbon nanofibers.

[0084] Typically, the conductive material may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0085] The binder optionally included in the above-described positive electrode active material layer is a component that assists in the bonding of the positive electrode active material and the conductive material, and in the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0086] Typically, the binder may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0087] Additionally, a filler may be optionally added to the positive electrode as a component that suppresses its expansion. Such filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes in the battery. Examples of fillers that can be used include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0088] The above-described positive electrode can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive agent in a dispersion medium (solvent) to make a slurry, applying the slurry on a metal current collector, and then drying and rolling. At this time, the dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.

[0089] Meanwhile, the anode-free secondary battery of the other embodiment may further include an electrolyte including a non-aqueous organic solvent and a lithium salt.

[0090] The lithium salt included in the above electrolyte is used as a medium for transferring ions within a secondary battery. Lithium salt is, for example, Li as a cation. + Including, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2- , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - It may include an anion selected from the group consisting of .

[0091] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBF2(C2O4), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2) and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2).

[0092] The concentration of the above lithium salt can be appropriately changed within a commonly usable range, and can be included in the electrolyte at a concentration of 0.4 M to 6 M, or a concentration of 0.5 M to 5 M.

[0093] In a more specific embodiment, the electrolyte may contain a lithium salt at a relatively low concentration of 0.4 M or more and less than 2 M, or 0.5 M to 1 M, but may also contain a lithium salt at a high concentration of 1 M or more, or 1 M to 6 M, or 2 M to 5 M. By using an electrolyte containing such a high concentration of lithium salt, the output characteristics of the secondary battery can be further improved.

[0094] Meanwhile, the type of non-aqueous organic solvent that can be included in the electrolyte is not particularly limited, and any organic solvent that has been previously known to be applicable to electrolytes of lithium ion batteries, etc., can be used. Examples of such organic solvents include at least one selected from the group consisting of carbonate solvents, ether solvents, nitrile solvents, phosphate solvents, and sulfone solvents. However, considering incompatibility with the polymer protective layer, etc., the non-aqueous organic solvent preferably includes an ether solvent.

[0095] More specifically, as the carbonate solvent, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate or methyl (2,2,2-trifluoroethyl) carbonate can be used, and as the phosphate solvent, trimethyl phosphate, triethyl phosphate or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide can be used.

[0096] In addition, as the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxy ethane, or tetrahydrofuran derivatives such as 2-methyl tetrahydrofuran can be used, and as the nitrile solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. In addition, as the sulfone solvent, dimethyl sulfone, ethylmethyl sulfone, or sulforane can be used.

[0097] Meanwhile, the anode-free secondary battery described above may further include a porous separator interposed between the positive electrode and the negative electrode.

[0098] These porous membranes can be made of olefin polymers such as polyethylene and polypropylene, glass fibers, etc. in the form of sheets, multi-membranes, microporous films, woven fabrics, and non-woven fabrics, but are not necessarily limited thereto. However, it may be preferable to use porous polyethylene or porous glass fiber non-woven fabric (glass filter) as the membrane, and it may be more preferable to use porous glass filter (glass fiber non-woven fabric) as the membrane. The membrane may be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the membrane may generally be in the range of 0.01 to 10 ㎛, and the thickness may generally be in the range of 5 to 300 ㎛, but is not limited thereto.

[0099] In addition, in another example of the anode-free secondary battery, the separator may be integrated with the electrolyte and interposed between the positive and negative electrodes in the form of an electrolyte layer or electrolyte film. In one example, the electrolyte layer or electrolyte film may be in the form of a gel electrolyte containing the lithium salt and a non-aqueous organic solvent described above within a polymer matrix, or in the form of a solid electrolyte. In addition, a well-known polymer-based solid electrolyte, etc. may be used as the polymer matrix.

[0100] The anode-free secondary battery of the above-described embodiment can be a semi-solid battery using a liquid electrolyte and a solid electrolyte in combination or an all-solid battery having a solid electrolyte layer, depending on whether the electrolyte layer is included and its shape, etc.

[0101] Meanwhile, the anode-free secondary battery of the above-described other embodiment can be manufactured according to a conventional method in the art. For example, the electrode assembly including the positive electrode, negative electrode, and separator can be manufactured by a method in which the electrode assembly is housed in a case and the electrolyte described above is injected and impregnated, or the electrode assembly including the positive electrode, negative electrode, and electrolyte layer can be manufactured by a method in which the electrode assembly is housed in a case.

[0102] These anode-free secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit cells in battery modules that serve as power sources for medium- to large-sized devices.

[0103]

[0104] Below, preferred embodiments of the invention, comparative examples to compare with them, and experimental examples for evaluating them are described. However, the following examples are merely preferred embodiments of the invention, and the present invention is not limited to the following examples.

[0105]

[0106] Comparative Example 1:

[0107] Copper foil having a thickness of 20 μm was used as the negative electrode for the anode-free secondary battery of Comparative Example 1.

[0108]

[0109] Comparative Example 2: Manufacturing of a negative electrode for an anode-free secondary battery

[0110] First, an iCVD reaction chamber equipped with multiple filaments as illustrated in Fig. 1 was used.

[0111] While the substrate temperature in the reaction chamber was maintained at 30°C, the copper foil having a thickness of 20 μm was placed in the reaction chamber. In addition, in order to induce sufficient vapor pressure, (dimethylaminomethyl) styrene [(DIMETHYLAMINOMETHYL)STYRENE] and the initiator tert-butyl peroxide (TBPO) were heated to 80°C and 30°C, respectively, and then vaporized and injected into the iCVD reaction chamber at flow rates of 0.38 sccm and 0.44 sccm, respectively. At this time, the pressure in the chamber was maintained as a vacuum state of 70 mTorr, and the radical polymerization reaction was performed while the filament in the reaction chamber was heated to 140°C. During the radical polymerization and deposition process, the deposition thickness of the polymer protective layer was monitored in real time through the view port. The process was terminated by lowering the filament temperature when a 15 nm polymer protective layer was deposited on the copper foil. Through this, a polymer protective layer of Comparative Example 2 having a thickness of 15 nm and a cathode including the same were manufactured, and it was confirmed that the polymer protective layer included a polymer of the following chemical formula 2.

[0112] [Chemical Formula 2]

[0113]

[0114]

[0115] Comparative Example 3: Manufacturing of a negative electrode for an anode-free secondary battery

[0116] A polymer protective layer and a cathode including the same of Comparative Example 3 were prepared in the same manner as Comparative Example 2, except that ethylene glycol dimethacrylate was used as a monomer instead of (dimethylaminomethyl) styrene. In this cathode, the polymer protective layer was confirmed to include a polymer of the following chemical formula 3 and to have a thickness of 15 nm:

[0117] [Chemical Formula 3]

[0118]

[0119]

[0120] Comparative Example 4: Manufacturing of a negative electrode for an anode-free secondary battery

[0121] A polymer protective layer and a cathode including the same of Comparative Example 4 were prepared in the same manner as Comparative Example 2, except that divinyl benzene was used as a monomer instead of (dimethylaminomethyl) styrene. In this cathode, the polymer protective layer was confirmed to include a polymer of the following chemical formula 4 and to have a thickness of 15 nm:

[0122] [Chemical Formula 4]

[0123]

[0124]

[0125] Example 1: Preparation of a negative electrode for an anode-free secondary battery

[0126] A polymer protective layer of Example 1 and a negative electrode including the same were prepared in the same manner as in Comparative Example 2, except that heptadecafluorodecyl acrylate was used as a monomer instead of (dimethylaminomethyl) styrene. In this negative electrode, the polymer protective layer was confirmed to include a polymer of the following chemical formula 5 and to have a thickness of 15 nm:

[0127] [Chemical Formula 5]

[0128]

[0129]

[0130] Example 2: Preparation of a negative electrode for an anode-free secondary battery

[0131] A polymer protective layer of Example 1 and a negative electrode including the same were prepared in the same manner as in Comparative Example 2, except that heptadecafluorodecyl methacrylate was used as a monomer instead of (dimethylaminomethyl) styrene. In this negative electrode, the polymer protective layer was confirmed to include a polymer of the following chemical formula 6 and to have a thickness of 15 nm:

[0132] [Chemical Formula 6]

[0133]

[0134]

[0135] Example 3: Preparation of a negative electrode for an anode-free secondary battery

[0136] Except for the following reaction conditions, a cathode was manufactured in the same manner as in Example 2. During radical polymerization and deposition in the reaction chamber, the deposition thickness of the polymer protective layer was monitored in real time through a view port. When a 5 nm thick polymer protective layer was deposited on the copper foil, the process was terminated by lowering the filament temperature. Through this, the polymer protective layer of Example 3 and the cathode including the same were manufactured. In this cathode, the polymer protective layer included the polymer of the same chemical formula 6 as in Example 2, and the only difference was that it had a thickness of 5 nm.

[0137]

[0138] Example 4: Preparation of a negative electrode for an anode-free secondary battery

[0139] Except for the following reaction conditions, a cathode was manufactured in the same manner as in Example 2. During radical polymerization and deposition in the reaction chamber, the deposition thickness of the polymer protective layer was monitored in real time through a view port. When a 100 nm thick polymer protective layer was deposited on the copper foil, the process was terminated by lowering the filament temperature. Through this, the polymer protective layer of Example 4 and the cathode including the same were manufactured. In this cathode, the polymer protective layer included the polymer of the same chemical formula 6 as in Example 2, and the only difference was that it had a thickness of 100 nm.

[0140]

[0141] Test Example 1: Measurement of surface contact angle of cathode and polymer protective layer

[0142] An ether-based non-aqueous organic solvent of 1,2-dimethoxyethane (DME) and an electrolyte in which a lithium salt of LiFSI (lithium bis(fluorosulfonyl)imide) was dissolved in the 1,2-dimethoxyethane (DME) at a concentration of 4 M were prepared.

[0143] One drop of 1,2-dimethoxyethane (DME) and electrolyte was dropped on the copper foil (Comparative Example 1) or the polymer protective layer (Comparative Examples 2 to 4, Examples 1 and 2) of Comparative Examples 1 to 4 and Examples 1 and 2, and the photograph after dropping is shown in Fig. 2. In addition, after dropping, the surface contact angle of each cathode and polymer protective layer for the solvent (DME) and electrolyte was measured using a contact angle meter, and the measurement results are shown in Fig. 2.

[0144] Referring to FIG. 2, the polymer protective layers of Examples 1 and 2 exhibit a surface contact angle of 50° or more and less than 90° with respect to the solvent (DME) and electrolyte, whereas the copper foil of Comparative Example 1 or the polymer protective layers of Comparative Examples 2 to 4 exhibit a very low surface contact angle, confirming electrolyte affinity and wettability.

[0145]

[0146] Test Example 2: Coulomb Efficiency Evaluation

[0147] The cathodes of the comparative examples or examples were used as the working electrodes of Li / Cu half-cells. Aurbach's Coulomb efficiency experiments were conducted on these half-cells.

[0148] More specifically, first, excess lithium was added at 0.5 mA / cm 2 , 5mAh / cm 2 After electrodeposition under the conditions of , all active lithium (active Li) was desorbed at the same current density. The Coulombic efficiency of initial excess electrodeposition and desorption was measured and calculated as the initial Coulombic efficiency.

[0149] After that, 0.5 mA / cm2 , 5mAh / cm 2 After re-electrodeposition of lithium under the condition of 0.5 mA / cm 2 , 1mAh / cm 2 The half-cell was operated for 9 cycles under the conditions. Afterwards, all remaining active lithium was removed to measure the Coulombic efficiency, which was calculated as the overall Coulombic efficiency. In addition, during the Coulombic efficiency measurement process, the overvoltage when the first lithium was deposited was additionally calculated as the nucleation overvoltage.

[0150] The results of these initial Coulombic efficiency, total Coulombic efficiency and nucleation overvoltage evaluations are shown in Table 1 below.

[0151] Nucleation Overvoltage (mV) Initial Coulombic Efficiency (%) Total Coulombic Efficiency (%) Comparative Example 155.4898.6999.27 Comparative Example 231.5095.1498.00 Comparative Example 341.0997.7498.89 Comparative Example 436.7297.8898.98 Example 126.0098.7399.34 Example 228.7498.9999.59 Example 327.6799.2299.51 Example 427.6798.9699.51

[0152] Referring to Table 1 above, Comparative Example 1 exhibits a large nucleation overvoltage of approximately 55.5 mV due to a naturally formed copper oxide film, and it was confirmed that the cathodes formed with polymer protective layers of Comparative Examples 2 to 4 also exhibited a higher nucleation overvoltage than the examples, although lower than Comparative Example 1.

[0153] In comparison, Examples 1 to 4, in which an electrolyte-incompatible polymer protective layer was formed, exhibited a reduced nucleation overvoltage, thereby confirming that lithium deposition was stably achieved.

[0154] In addition, it was confirmed that Comparative Example 1 had an initial Coulombic efficiency of 98.69% and an overall Coulombic efficiency of 99.27%, while Comparative Examples 2 to 4, which are solvent- and electrolyte-compatible, showed lower initial and overall Coulombic efficiencies than Comparative Example 1. In contrast, Examples 1 to 4, which are electrolyte-incompatible, were confirmed to show high initial and overall Coulombic efficiencies. In particular, it was confirmed that Example 2, in which the thickness of the polymer protective layer was about 15 nm, showed the highest overall Coulombic efficiency.

[0155]

[0156] Test Example 3: Cycle Characteristics Evaluation

[0157] The negative electrode of Comparative Example 1 or Example 2 was used as the working electrode of a Li / Cu half-cell. For these half-cells, the coulombic efficiency per cycle was evaluated using the following method, and the evaluation results are shown in Fig. 3.

[0158] Specifically, a in Fig. 3 is 0.5 mA / cm 2 , 1mAh / cm 2 The evaluation results of driving the half-cell under the general current density conditions are shown in Fig. 3b, which is 1 mA / cm. 2 , 1mAh / cm 2 This is the evaluation result of driving the above half-cell under the fast current density condition.

[0159] Referring to the above Figure 3, the half-cell using the cathode of Comparative Example 1 began to exhibit a rapid decrease in coulombic efficiency after approximately 100 cycles of operation, but when the cathode of Example 2 was used, it was confirmed that the cell was operated stably for approximately 350 cycles. This is expected to be because a stable interfacial film was formed on the cathode of Example 2 during cell operation.

[0160] Meanwhile, a full cell type battery was manufactured using the negative electrode of Comparative Example 1 or Example 2. This battery was manufactured using the negative electrode and NCM811 (LiNi 0.8 Co 0.1 Mn0.1 It included a cathode containing O2) as a cathode active material, a polyethylene separator, and 75 μl of an electrolyte containing lithium bis(fluorosulfonyl)imide (LiFSI) dissolved in 1,2-dimethoxyethane (DME) at a concentration of 4 M.

[0161] Using these secondary batteries, the batteries were driven at a formation cycle (0.1C / 0.1D) and then at 4.3V-2.8V, 0.2C / 0.5D, and through this, the coulombic efficiency and the change in discharge capacity per cycle were measured, and the measurement results are shown in Fig. 4. For reference, in Fig. 4, the number of cycles at which the discharge capacity of the first cycle becomes 50% is indicated by an arrow, which was confirmed to be 68 and 99 cycles in Comparative Example 1 and Example 2, respectively.

[0162] Referring to Fig. 4, it was confirmed that the battery including the negative electrode of Example 2 exhibited a smaller decrease in discharge capacity per cycle than that of Comparative Example 1, and exhibited superior life characteristics compared to Comparative Example 1. This is expected to be because, in Example 2, an electrolyte-incompatible polymer protective layer was formed, and an inorganic-based solid electrolyte interfacial film was formed by a lithium salt-derived component instead of a decomposition product of an organic solvent included in the electrolyte. It is expected that such an inorganic-based solid electrolyte interfacial film can contribute to maintaining excellent battery performance for a long time due to its low swelling rate.

[0163]

[0164] Test Example 4: Elemental Composition Analysis of Solid Electrolyte Interfacial Film

[0165] After evaluating the cycle characteristics of the above Test Example 3, for the half-cell including the negative electrode of Comparative Example 1 or Example 2, the solid electrolyte interface film formed on the negative electrode was subjected to elemental analysis using XPS (X-ray Photoelectron Spectroscope), thereby analyzing the elemental composition of the solid electrolyte interface film. The results of this analysis are as shown in Fig. 5.

[0166] Looking at the peaks related to F 1s in a and b of Fig. 5, the solid electrolyte interfacial film formed on the negative electrode of Comparative Example 1 contained SF, which is formed by less decomposition of lithium salt, and completely decomposed inorganic LiF at a ratio of 30 mol% and 70 mol%, respectively, whereas on the negative electrode of Example 2, it was confirmed that about 97.47 mol% of the solid electrolyte interfacial film existed as inorganic LiF, excluding some CF peaks derived from the polymer protective layer. LiF appears to be able to suppress lithium dendrite growth due to its high affinity for lithium ions and high Young's modulus.

[0167] Also, looking at the peaks related to O 1s in c and d of FIG. 5, when using the cathode of Comparative Example 1, -RO-COx-Li by decomposition of non-aqueous organic solvent was 93.4 mol%, and -NOx / SOx by decomposition of salt was 6.6 mol%, while on the cathode of Example 2, -NOx / SOx by decomposition of salt was 8.6 mol%, which was confirmed to be formed in greater amounts than in the Comparative Example.

[0168] Meanwhile, after evaluating the cycle characteristics of the above Test Example 3, for a full-cell type secondary battery including the negative electrode of Comparative Example 1 or Example 2, the solid electrolyte interface film formed on the negative electrode was subjected to elemental analysis using XPS (X-ray Photoelectron Spectroscope), and the results of analyzing the composition of carbon elements and other non-metallic elements in the solid electrolyte interface film are shown in Fig. 6.

[0169] Referring to Fig. 6, it was confirmed that the content of carbon element in the solid electrolyte interfacial film was lower when the cathode of Example 2 was used than in Comparative Example 1, and the content of other non-metallic elements such as fluorine, nitrogen, and sulfur excluding carbon element was relatively high. Specifically, in the cathode of Example 2, the element content (atomic%) ratio of (F+N+S) / C was approximately 0.57, whereas in the cathode of Comparative Example 1, the ratio was approximately 0.22, confirming that the content of carbon element was relatively high.

[0170] Through this, it was confirmed that when the negative electrode of the embodiment was used, a solid electrolyte interfacial film with a higher inorganic content was formed compared to the comparative example. Since the inorganic-based solid electrolyte interfacial film exhibits a relatively high elastic modulus and excellent mechanical properties, it is predicted that it can more effectively suppress the growth of lithium dendrites and contribute to improving the performance of secondary batteries.

[0171]

[0172] Test Example 4: Evaluation of lithium electrodeposition characteristics and electrolyte decomposition degree

[0173] After evaluating the cycle characteristics of the above Test Example 3, lithium electrodeposition was further performed on a half-cell including the negative electrode of Comparative Example 1 or Example 2, and the lithium metal layer deposited on the negative electrode was analyzed using an electron microscope, as shown in Fig. 7.

[0174] Figures 7a and b show high capacity (4 mAh / cm) after the above cycle characteristic evaluation. 2 ) is a cross-sectional image of a lithium electrodeposited electrode, 4 mAh / cm 2The theoretical thickness of the lithium metal layer is about 20 ㎛. However, when the negative electrode of Comparative Example 1 was used, the maximum thickness of the actually deposited lithium metal layer was about 25.4 ㎛, which was confirmed to be thicker than the theoretical thickness due to non-uniform lithium deposition. In contrast, when the negative electrode of Example 2 was used, lithium was confirmed to be deposited at about 20.34 ㎛, which is close to the theoretical thickness. This indicates that lithium is deposited uniformly during cell operation. In addition, referring to FIG. 7 c and d corresponding to the planar images of FIG. 7 a and b, it was confirmed that the lumps of lithium deposited in Example 2 were larger and the surface area was smaller than that of Comparative Example 1, and through this, it was confirmed that the lithium metal layer grew uniformly and horizontally. In addition, the low capacity (2 mAh / cm 2 ) when lithium was electrodeposited, it can be seen from Figure 7 e and f that lithium dendrite growth occurred more in Comparative Example 1 than in Example 2. This is believed to be because lithium was deposited at a higher density due to the high lithium affinity of the inorganic-based solid electrolyte interfacial film such as LiF and its excellent mechanical properties.

[0175] Meanwhile, the voltage of the half-cell was maintained at 0 V vs. Li, and the current density over time was measured, and the measurement results are shown in Fig. 8. From these experimental results, the degree of corrosion, in which lithium electrons move to the negative electrode and charge transfer occurs between the conductive metal layer of the negative electrode and the electrolyte, can be evaluated. Referring to Fig. 8, it can be confirmed that a lot of electrolyte decomposition occurred through the large change in current density during the first 15 hours in Comparative Example 1. In contrast, Example 2 showed a small change in current density and decomposition of the electrolyte, and a thinner solid electrolyte interfacial film was formed.

Claims

1. Conductive metal layer; and Including a polymer protective layer formed on the conductive metal layer, The above polymer protective layer is a negative electrode for an anode-free secondary battery having a surface contact angle of 50° or more and less than 90° with respect to an ether-based non-aqueous organic solvent.

2. In the first paragraph, the conductive metal layer is a negative electrode for an anode-free secondary battery containing copper (Cu).

3. In the first paragraph, the polymer protective layer comprises a lithium salt and an ether-based non-aqueous organic solvent, and has a surface contact angle of 50° or more and less than 90° for an electrolyte having a molar concentration of 4M of the lithium salt.

4. In the first paragraph, the polymer protective layer is a negative electrode for an anode-free secondary battery comprising a polymer having a plurality of fluorine-substituted hydrocarbon groups having 8 or more carbon atoms bonded thereto.

5. In the first paragraph, the polymer protective layer is a negative electrode for an anode-free secondary battery comprising a poly[fluoroalkyl(meth)acrylate] polymer having a long-chain alkyl group having 8 or more carbon atoms and 5 or more fluorine atoms substituted therein.

6. In the first paragraph, the polymer protective layer is a negative electrode for an anode-free secondary battery having a thickness of 1 to 1000 nm.

7. A step of initiating chemical vapor deposition (iCVD) by polymerizing the monomer on a conductive metal layer in the presence of a radical initiator and a gaseous monomer, A method for manufacturing a negative electrode for an anode-free secondary battery, wherein the monomer comprises a monomer having a hydrocarbon group having 8 or more carbon atoms and having multiple fluorine substitutions bonded thereto.

8. A method for manufacturing a negative electrode for an anode-free secondary battery, wherein the chemical vapor deposition step in paragraph 7 is performed at a temperature of 100°C to 300°C.

9. A method for producing a negative electrode for an anode-free secondary battery, wherein the radical initiator in claim 7 comprises tert-butyl peroxide.

10. A method for manufacturing a negative electrode for an anode-free secondary battery, wherein the monomer comprises a fluoroalkyl (meth)acrylate compound having a long-chain alkyl group having 8 or more carbon atoms and substituted with 5 or more fluorines.

11. The cathode of any one of paragraphs 1 to 6; An anode facing the cathode; a separator interposed between the cathode and the anode; and Containing an electrolyte comprising a lithium salt and a non-aqueous organic solvent, An anode-free secondary battery in which a lithium metal layer is deposited on the polymer protective layer of the negative electrode during charging.

12. An anode-free secondary battery further comprising a solid electrolyte interphase layer formed on the polymer protective layer and containing 80 mol% or more of an inorganic material including a metal fluoride, in accordance with claim 11.

13. An anode-free secondary battery in claim 12, wherein the ratio of the content (atomic%) of total non-metallic elements excluding carbon elements included in the solid electrolyte interfacial film / the content (atomic%) of total carbon elements is 0.5 or more.

14. An anode-free secondary battery comprising, as a cathode active material, a lithium transition metal oxide including lithium and at least one transition metal selected from the group consisting of nickel, manganese, cobalt, and aluminum, in the 11th paragraph.

15. An anode-free secondary battery according to claim 11, wherein the electrolyte comprises an ether-based non-aqueous organic solvent.

16. An anode-free secondary battery according to claim 11, wherein the electrolyte contains a lithium salt at a concentration of 1 M or more.

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