Anode for an all-solid-state secondary battery using a cathode current collector containing iron and an all-solid-state secondary battery comprising the same

Abstract

The present invention relates to a negative electrode for an all-solid-state secondary battery comprising a solid electrolyte layer, the negative electrode current collector comprising iron (Fe); and a negative electrode active material layer disposed on the negative electrode current collector.

Description

Technology Field

[0001] The present invention relates to an all-solid-state secondary battery, and more specifically, to a negative electrode for an all-solid-state secondary battery using Fe foil instead of Cu foil as a negative electrode current collector, and an all-solid-state secondary battery including the same. Background Technology

[0002] As lithium-ion batteries are applied in various fields, such as electric vehicles and energy storage systems, there is a growing demand for high energy capacity. However, safety concerns have arisen regarding the liquid electrolytes used in conventional lithium-ion batteries due to their high flammability. Consequently, all-solid-state batteries, which utilize solid electrolytes, are garnering significant interest from academia and industry as an alternative to address this issue.

[0003] In particular, since electric vehicle batteries undergo long-term cycling under high charge conditions, the stability of additional inert components, such as current collectors as well as electrode active materials, is crucial for maintaining battery performance and safety.

[0004] In conventional liquid battery manufacturing, electrode slurries are cast onto metal foils to allow electrons generated from the active material to move easily through external circuits; therefore, the metal foil used as the current collector must be able to withstand high and low voltages during battery operation. For this reason, Cu foil is commonly used as a negative electrode current collector in lithium-ion batteries due to its high electrochemical equilibrium potential and electron conductivity, and is also used as a negative electrode current collector in all-solid-state batteries.

[0005] However, sulfide-based solid electrolytes used in all-solid-state batteries exhibit low electrochemical stability, leading to reactivity with the current collector. Degradation of the current collector due to this reaction with the solid electrolyte hinders electron transfer between the cathode active material and the current collector, ultimately resulting in a decrease in the capacity and output of the lithium-ion battery. This suggests the importance of understanding the degradation mechanism of current collectors using Cu foil in all-solid-state batteries and indicates the need for the development of alternative current collectors to ensure long-term durability.

[0006] Therefore, it is necessary to understand the degradation mechanism of current collectors using Cu foil in all-solid-state batteries and to develop new current collectors with excellent long-term durability to address this issue.

[0007] Korean Published Patent No. 10-2020-0085398, which is the technical background of the present invention, relates to a negative electrode current collector for an all-solid-state secondary battery, a method for manufacturing the same, and an all-solid-state secondary battery including the same. The problem to be solved

[0008] The present invention aims to solve the problems of the aforementioned conventional technology by providing a negative electrode for an all-solid-state secondary battery with excellent long-term durability.

[0009] In addition, an all-solid-state secondary battery comprising the above-described negative electrode for an all-solid-state secondary battery is provided.

[0010] In addition, a method for manufacturing a negative electrode current collector for an all-solid-state secondary battery is provided.

[0011] In addition, an energy storage system including the above-mentioned all-solid-state secondary battery is provided.

[0012] In addition, a wearable device including the above-described all-solid-state secondary battery is provided.

[0013] However, the technical problems that the embodiments of the present invention aim to solve are not limited to the technical problems described above, and other technical problems may exist. means of solving the problem

[0014] As a technical means for achieving the above-mentioned technical problem, the first aspect of the present invention provides a negative electrode for an all-solid-state secondary battery comprising a solid electrolyte layer, a negative electrode current collector comprising iron (Fe), and a negative electrode active material layer disposed on the negative electrode current collector.

[0015] According to one embodiment of the present invention, an iron oxide layer may be formed on the surface of the iron, but is not limited thereto.

[0016] According to one embodiment of the present invention, the formation of sulfides on the iron surface when in contact with the solid electrolyte layer may be suppressed by the iron oxide layer, but is not limited thereto.

[0017] According to one embodiment of the present invention, the solid electrolyte layer may comprise a sulfide-based solid electrolyte, but is not limited thereto.

[0018] According to one embodiment of the present invention, the sulfide-based solid electrolyte is Li 7-x PS 6-x Cl x (0 <x<2), Li 7-x PS 6-x Br x (0 <x<2), Li 7-x PS 6-x I x (0 <x<2), Li2S-P2S5, Li2S-P2S5-LiX(여기서, X는 할로겐 원소임), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (Here, m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Lip MO q (Here, p, q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, In) and combinations thereof may include, but are not limited to, those selected from the group consisting of combinations thereof.

[0019] According to one embodiment of the present invention, the negative electrode active material layer may comprise a negative electrode active material selected from the group consisting of graphite, lithium metal, hard carbon, soft carbon, silicon, tin, germanium, lithium titanium oxide, titanium oxide, and combinations thereof, but is not limited thereto.

[0020] According to one embodiment of the present invention, the negative electrode active material layer may additionally include a solid electrolyte material of the same or different type as the solid electrolyte included in the solid electrolyte layer, but is not limited thereto.

[0021] According to one embodiment of the present invention, the negative electrode active material layer may additionally include a binder for combining the solid electrolyte material and the negative electrode active material, but is not limited thereto.

[0022] According to one embodiment of the present invention, the binder may comprise a binder selected from the group consisting of nitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), polyacrylic acid (PAA), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polyimide (PI), polyvinylidene fluoride (PVDF) and combinations thereof, but is not limited thereto.

[0023] In addition, a second aspect of the present invention provides an all-solid-state secondary battery comprising a negative electrode for an all-solid-state secondary battery according to the first aspect of the present invention; a positive electrode; and a solid electrolyte layer disposed between the negative electrode and the positive electrode.

[0024] According to one embodiment of the present invention, the positive electrode may comprise a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, but is not limited thereto.

[0025] According to one embodiment of the present invention, the anode current collector may comprise, but is not limited to, a material selected from the group consisting of aluminum (Al), stainless steel (STS), nickel (Ni), titanium (Ti), and combinations thereof.

[0026] According to one embodiment of the present invention, the positive electrode active material may comprise, but is not limited to, a material selected from the group consisting of lithium metal, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), nickel cobalt manganese oxide (NCM), nickel cobalt aluminum oxide (NCA), and combinations thereof.

[0027] According to one embodiment of the present invention, the all-solid-state secondary battery may have a form selected from the group consisting of prismatic batteries, cylindrical batteries, pouch batteries, and thin-film batteries, but is not limited thereto.

[0028] In addition, the third aspect of the present invention provides a method for manufacturing a negative electrode current collector for an all-solid-state secondary battery comprising a solid electrolyte layer, the method comprising the steps of: preparing an iron (Fe) foil; and forming an iron oxide layer on the surface of the iron foil, wherein the iron oxide layer serves as a protective layer that suppresses a sulfidation reaction with the solid electrolyte layer on the surface of the iron foil.

[0029] According to one embodiment of the present invention, the iron oxide layer may be formed on the surface of the iron foil through natural oxidation, but is not limited thereto.

[0030] In addition, the fourth aspect of the present invention provides an energy storage system comprising an all-solid-state secondary battery according to the second aspect of the present invention.

[0031] Additionally, the fifth aspect of the present invention provides a wearable device comprising an all-solid-state secondary battery according to the second aspect of the present invention.

[0032] The means for solving the problem described above are merely exemplary and should not be interpreted as intended to limit the present invention. In addition to the exemplary embodiments described above, additional embodiments may exist in the drawings and the detailed description of the invention. Effects of the invention

[0033] The negative electrode for an all-solid-state secondary battery according to the present invention provides superior electrochemical stability and long-term durability compared to conventional Cu current collectors by using an iron (Fe) current collector. Specifically, the iron oxide layer formed on the surface of the Fe current collector acts as a protective layer that suppresses chemical reactions with the sulfide-based solid electrolyte, thereby preventing degradation of the current collector and maintaining a stable electron transport path.

[0034] Furthermore, the all-solid-state secondary battery according to the present invention exhibits excellent lifespan characteristics due to improved interfacial stability between the Fe current collector and the sulfide-based solid electrolyte. Specifically, the Fe current collector is Fe / Fe 2+ Equilibrium potential is Cu / Cu +Despite the low contrast, the iron oxide layer on the surface remains stable, suppressing the sulfidation reaction with the solid electrolyte. On the other hand, the surface oxide of the Cu current collector is unstable, so copper sulfide is continuously formed upon contact with the solid electrolyte, and as its thickness increases, the performance of the battery deteriorates. Therefore, an all-solid-state secondary battery using an Fe current collector can maintain stable electrochemical characteristics even after long-term cycling.

[0035] Furthermore, the Fe current collector according to the present invention can be simply manufactured through natural oxidation, making the process easy and economical. All-solid-state secondary batteries using such Fe current collectors can be utilized as power storage devices requiring long-term reliability in various application fields, such as energy storage systems or wearable devices.

[0036] However, the effects obtainable from this invention are not limited to those described above, and other effects may exist. Brief explanation of the drawing

[0037] Figure 1 is a schematic diagram of the surface electrochemical behavior at the cathode using Cu (top) and Fe (bottom) current collectors. Figure 2 is the first voltage profile of an all-solid-state battery cell using Cu and Fe as current collectors. Figure 3 is a dQ / dV graph showing the first voltage profile of an all-solid-state battery cell using Cu and Fe as current collectors. Figure 4 shows optical and SEM images of a Cu foil in contact with LPSCl after 0, 5, 12, and 24 hours. Figure 5 shows optical and SEM images of Fe foil in contact with LPSCl after 0, 5, 12, and 24 hours. Figure 6 shows the CV results of Cu and Fe foil working electrodes in LPSCl-ASSB. Figure 7 shows the CV curves at various cut-off potentials in LPSCl-ASSB of a Cu foil current collector. Figure 8 shows the CV curves at various cut-off potentials in LPSCl-ASSB of an Fe foil current collector. Figure 9 is a schematic diagram of the XPS analysis results of Cu foil after 5 and 24 hours of LPSCl contact and the formation of sulfides on the surface of Cu foil. Figure 10 is a schematic diagram of the XPS analysis results of Fe foil after 5 hours and 24 hours of LPSCl contact and the formation of sulfides on the surface of Fe foil. Figure 11 shows the in-situ XRD patterns of a mixture of Cu and Fe LPSCl (5:5 weight ratio) at various temperatures. Figure 12 is a graph of the sulfide substitution energy of metal oxide clusters. Figure 13 shows the linear scanning thermocurrent measurement results of Cu and Fe foil working electrodes in LPSCl-ASSB. Figure 14 is a graph of the cell life and Coulomb efficiency of an all-solid-state battery (graphite:LPSCl:Li) using an Fe current collector. Figure 15 is a graph comparing the performance of all-solid-state batteries using graphite cathodes reported in the literature. Specific details for implementing the invention

[0038] Embodiments of the present invention are described below with reference to the attached drawings to enable those skilled in the art to easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification are denoted by similar reference numerals.

[0039] Throughout this specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "electrically connected" with other elements interposed between them.

[0040] Throughout the entire specification, when a component is described as being located "on," "on top," "on top," "under," "on bottom," or "on bottom" of another component, this includes not only cases where the component is in contact with the other component but also cases where another component exists between the two components.

[0041] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0042] As used herein, terms of degree such as “about,” “substantially,” etc., are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding the invention. Furthermore, throughout this specification, “a step of” or “a step of” does not mean “a step for”.

[0043] Throughout this specification, the term “combination thereof” included in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including one or more selected from the group consisting of said components.

[0044] Throughout the entire specification, the description "A and / or B" means "A, B, or A and B".

[0045] Hereinafter, the negative electrode for an all-solid-state secondary battery and an all-solid-state secondary battery including the same according to the present invention will be described in detail with reference to embodiments, examples, and drawings. However, the present invention is not limited to these embodiments, examples, and drawings.

[0047] As a technical means for achieving the above-mentioned technical problem, the first aspect of the present invention provides a negative electrode for an all-solid-state secondary battery comprising a solid electrolyte layer, a negative electrode current collector comprising iron (Fe), and a negative electrode active material layer disposed on the negative electrode current collector.

[0048] Here, the negative electrode current collector containing iron may be a current collector made of pure iron (Fe) metal, for example, in the form of an iron foil. The negative electrode active material layer comprises a negative electrode active material, which may be made of a material capable of inserting and extracting lithium ions through an electrochemical reaction.

[0049] The above-mentioned negative current collector serves to provide a conductive path for electrons generated in the negative active material layer to move to an external circuit. In particular, the iron current collector has an oxide layer formed on its surface, which can suppress chemical reactions with the solid electrolyte, thereby providing a negative electrode for an all-solid-state secondary battery with excellent long-term lifespan characteristics.

[0050] Through this configuration, the negative electrode for an all-solid-state secondary battery according to the present invention has improved interface stability with the solid electrolyte, thereby enabling the realization of an all-solid-state secondary battery with excellent long-term life characteristics.

[0051] According to one embodiment of the present invention, an iron oxide layer may be formed on the surface of the iron, but is not limited thereto.

[0052] In one embodiment of the present invention, an iron oxide layer may be formed on the surface of the iron current collector. The iron oxide layer may be formed due to natural oxidation of the surface of the iron current collector, and this can be formed without any additional processes.

[0053] The iron oxide layer may include iron oxide compounds such as, for example, FeO, Fe2O3, Fe3O4, etc. Such an iron oxide layer may be formed with a uniform thickness and may serve as a protective layer to protect the underlying iron substrate.

[0054] In particular, the iron oxide layer is electrochemically stable, so additional reactions can be suppressed even when in contact with a solid electrolyte. This can contribute to improving the long-term life characteristics of an all-solid-state secondary battery.

[0055] According to one embodiment of the present invention, the formation of sulfides on the iron surface when in contact with the solid electrolyte layer may be suppressed by the iron oxide layer, but is not limited thereto.

[0056] In one embodiment of the present invention, the iron oxide layer serves as a protective layer that suppresses the formation of sulfides that may occur at the interface between the solid electrolyte layer and the iron current collector. This protective layer prevents chemical reactions with the solid electrolyte on the surface of the iron current collector, thereby preventing the deterioration of the current collector.

[0057] Referring to Fig. 1, differences in surface electrochemical behavior between copper and iron current collectors can be observed. As illustrated at the top of Fig. 1, a conversion reaction occurs between the copper oxide present on the surface of the copper current collector and the sulfide-based solid electrolyte (LPSCl). Due to this reaction, CuS expands into the interior of the Cu foil and is formed; the formed CuS is then decomposed into Li2S and nano-sized copper metal through electrochemical reactions. As this process of converting the nano-sized copper back into CuS is repeated, the resistance of the current collector increases.

[0058] On the other hand, in the case of the iron current collector shown at the bottom of Fig. 1, the oxide on the surface is thick and dynamically stable, so no conversion reaction with LPSCl occurs. Therefore, the surface contact between the iron current collector and LPSCl is stably maintained, allowing for smooth electron transfer during battery cycling, thereby enabling stable operation of the solid electrolyte-based battery.

[0059] According to one embodiment of the present invention, the solid electrolyte layer may comprise a sulfide-based solid electrolyte, but is not limited thereto.

[0060] In one embodiment of the present invention, the solid electrolyte layer may include a sulfide-based solid electrolyte. Sulfide-based solid electrolytes have higher ionic conductivity compared to oxide-based solid electrolytes and are widely used as electrolyte materials for all-solid-state batteries.

[0061] The above-mentioned sulfide-based solid electrolyte possesses characteristics that enable the rapid movement of lithium ions, thereby improving the charge and discharge characteristics of the battery. Furthermore, the sulfide-based solid electrolyte exhibits excellent ionic conductivity even at room temperature, which is an advantage favorable for the practical application of the battery.

[0062] However, sulfide-based solid electrolytes have the disadvantage of relatively low chemical stability, which can lead to interfacial reactions with battery components. However, in the present invention, the iron oxide layer on the surface of the iron current collector can effectively suppress such interfacial reactions, thereby allowing the full utilization of the advantages of sulfide-based solid electrolytes.

[0063] According to one embodiment of the present invention, the sulfide-based solid electrolyte is Li 7-x PS 6-x Cl x (0 <x<2), Li 7-x PS 6-x Br x (0 <x<2), Li 7-x PS 6-x I x(0 <x<2), Li2S-P2S5, Li2S-P2S5-LiX(여기서, X는 할로겐 원소임), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (Here, m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Here, p, q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, In) and combinations thereof may include, but are not limited to, those selected from the group consisting of combinations thereof.

[0064] In one embodiment of the present invention, the sulfide-based solid electrolyte may include various types of lithium ion conductive materials. In particular, Li having an argyrodite structure 7-x PS 6-x X x (X = Cl, Br, I; 0 <x<2)계 물질, 티오포스페이트(thiophosphate)계 물질, 티오실리케이트(thiosilicate)계 물질 등이 사용될 수 있다.

[0065] Among these sulfide-based solid electrolytes, materials doped with halogen elements can exhibit particularly excellent ionic conductivity. For example, Li 7-x PS 6-x Cl x Azirodite-based materials such as [material] can achieve enhanced ionic conductivity by optimizing the movement pathway of lithium ions through doping with halogen elements.

[0066] Furthermore, Li2S-P2S5-based materials can simultaneously improve electrochemical stability and ionic conductivity through combinations with various additives. For example, in Li2S-P2S5-Li2O systems, chemical stability can be enhanced by introducing oxygen, while in Li2S-SiS2-based systems, ionic conductivity can be improved by adding halogen compounds.

[0067] These various sulfide-based solid electrolytes can be used selectively depending on their respective characteristics, and it is also possible to use a combination of two or more materials.

[0068] According to one embodiment of the present invention, the negative electrode active material layer may comprise a negative electrode active material selected from the group consisting of graphite, lithium metal, hard carbon, soft carbon, silicon, tin, germanium, lithium titanium oxide, titanium oxide, and combinations thereof, but is not limited thereto.

[0069] According to one embodiment of the present invention, the negative electrode active material layer may additionally include a solid electrolyte material of the same or different type as the solid electrolyte included in the solid electrolyte layer, but is not limited thereto.

[0070] In one embodiment of the present invention, the negative electrode active material layer may additionally include a solid electrolyte material of the same or different type as the solid electrolyte included in the solid electrolyte layer. This is intended to promote the smooth movement of lithium ions within the negative electrode active material layer and to secure ion conduction pathways between active material particles.

[0071] Using the same solid electrolyte material in the cathode active material layer as the solid electrolyte in the solid electrolyte layer has the advantage of minimizing interfacial resistance between the two layers. For example, if a sulfide-based solid electrolyte is used in the solid electrolyte layer, including the same sulfide-based solid electrolyte in the cathode active material layer allows for smooth ion conduction at the interface.

[0072] Meanwhile, if a different type of solid electrolyte material is used in the negative electrode active material layer compared to the solid electrolyte layer, an optimized ion conduction environment tailored to the characteristics of the negative electrode active material can be provided. This can improve the electrochemical characteristics of the battery.

[0073] According to one embodiment of the present invention, the negative electrode active material layer may additionally include a binder for combining the solid electrolyte material and the negative electrode active material, but is not limited thereto.

[0074] In one embodiment of the present invention, the negative electrode active material layer may further include a binder for combining a solid electrolyte material and a negative electrode active material. The binder serves to improve the mechanical strength of the electrode and ensure structural stability by binding the active material particles and the solid electrolyte particles together.

[0075] In particular, the use of binders in all-solid-state batteries plays an important role in improving the manufacturing processability of electrodes and maintaining the structural stability of electrodes. For example, the addition of binders during slurry preparation enables uniform dispersion of electrode materials and can improve adhesion when coating electrodes onto current collectors.

[0076] Furthermore, by maintaining the structural stability of the electrode even in the event of volume changes of the active material during the charging and discharging process, it can contribute to improving the lifespan characteristics of the battery. Such a binder must be able to provide sufficient binding strength without hindering the movement of ions and electrons within the electrode.

[0077] According to one embodiment of the present invention, the binder may comprise a binder selected from the group consisting of nitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), polyacrylic acid (PAA), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polyimide (PI), polyvinylidene fluoride (PVDF) and combinations thereof, but is not limited thereto.

[0079] In addition, a second aspect of the present invention provides an all-solid-state secondary battery comprising a negative electrode for an all-solid-state secondary battery according to the first aspect of the present invention; a positive electrode; and a solid electrolyte layer disposed between the negative electrode and the positive electrode.

[0080] Regarding the all-solid-state secondary battery according to the second aspect of the present invention, detailed descriptions of parts that overlap with the first aspect of the present invention have been omitted, but even if such descriptions are omitted, the contents described in the first aspect of the present invention can be applied equally to the second aspect of the present invention.

[0081] The all-solid-state secondary battery according to the present invention may be composed of a negative electrode including an iron current collector, a positive electrode, and a solid electrolyte layer disposed between them. In the all-solid-state secondary battery, the safety of the battery can be improved by using a solid electrolyte instead of a liquid electrolyte. The solid electrolyte layer not only provides a pathway for the movement of lithium ions but also performs the role of physically separating the positive electrode and the negative electrode.

[0082] In particular, by using a cathode containing an iron current collector according to the present invention, an all-solid-state secondary battery with improved interface stability with a solid electrolyte can be realized. The iron oxide layer on the surface of the iron current collector can suppress side reactions with the solid electrolyte, thereby improving the long-term life characteristics of the battery.

[0083] Through this configuration, it is possible to provide an all-solid-state secondary battery with excellent safety and lifespan characteristics, which can be applied in various fields such as electric vehicles and energy storage systems.

[0084] According to one embodiment of the present invention, the positive electrode may comprise a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, but is not limited thereto.

[0085] The positive current collector serves to provide a pathway for the movement of electrons generated in the positive active material layer. Such positive current collectors can be composed of metal materials that have excellent electrical conductivity and electrochemical stability.

[0086] The positive active material layer includes a positive active material capable of inserting and extracting lithium ions during the charging and discharging process. In addition to the active material, this positive active material layer may additionally include a conductive material, a binder, a solid electrolyte, etc., to improve the electrochemical properties and structural stability of the electrode.

[0087] The positive active material layer can be formed on the positive current collector by various methods such as coating or rolling, thereby ensuring excellent adhesion and electrical contact between the positive current collector and the positive active material layer.

[0088] According to one embodiment of the present invention, the anode current collector may comprise, but is not limited to, a material selected from the group consisting of aluminum (Al), stainless steel (STS), nickel (Ni), titanium (Ti), and combinations thereof.

[0089] According to one embodiment of the present invention, the positive electrode active material may comprise, but is not limited to, a material selected from the group consisting of lithium metal, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), nickel cobalt manganese oxide (NCM), nickel cobalt aluminum oxide (NCA), and combinations thereof.

[0090] According to one embodiment of the present invention, the all-solid-state secondary battery may have a form selected from the group consisting of prismatic batteries, cylindrical batteries, pouch batteries, and thin-film batteries, but is not limited thereto.

[0092] In addition, the third aspect of the present invention provides a method for manufacturing a negative electrode current collector for an all-solid-state secondary battery comprising a solid electrolyte layer, the method comprising the steps of: preparing an iron (Fe) foil; and forming an iron oxide layer on the surface of the iron foil, wherein the iron oxide layer serves as a protective layer that suppresses a sulfidation reaction with the solid electrolyte layer on the surface of the iron foil.

[0093] Regarding the method for manufacturing a negative current collector for an all-solid-state secondary battery according to the third aspect of the present invention, detailed descriptions of parts that overlap with the first and / or second aspects of the present invention have been omitted, but even if such descriptions have been omitted, the contents described in the first and / or second aspects of the present invention may be applied equally to the third aspect of the present invention.

[0094] First, in the step of preparing the iron foil, an iron foil with appropriate thickness and purity suitable for use as a negative electrode current collector for all-solid-state secondary batteries is selected. At this stage, it is desirable that the iron foil used has excellent electrical conductivity and adequate mechanical strength.

[0095] Next, a step is performed to form an iron oxide layer on the surface of the prepared iron foil. This iron oxide layer acts as a protective layer that prevents direct contact between the solid electrolyte and the iron foil. In particular, this iron oxide layer can effectively suppress the reaction with the sulfide-based solid electrolyte, thereby preventing the deterioration of the current collector.

[0096] The above iron oxide layer must be uniformly formed on the surface of the iron foil, which plays an important role in ensuring the long-term stability of the all-solid-state battery. This iron oxide protective layer is electrochemically stable, so its structure and characteristics can be maintained even during the operation of the battery.

[0097] According to one embodiment of the present invention, the iron oxide layer may be formed on the surface of the iron foil through natural oxidation, but is not limited thereto.

[0098] An iron oxide layer on the surface of iron foil can be formed through a natural oxidation process. This has the advantage of forming a protective layer without the need for separate additional processes or equipment. The formation of the iron oxide layer through natural oxidation occurs as the iron foil naturally reacts with oxygen in the atmosphere. This method has the advantages of being simple, economical, and environmentally friendly. Furthermore, the iron oxide layer formed through natural oxidation can possess stable and uniform characteristics.

[0099] The iron oxide layer formed in this way acts as a protective layer at the interface with the solid electrolyte, effectively suppressing the sulfidation reaction. In particular, the iron oxide layer formed through natural oxidation has excellent adhesion to the iron foil substrate, allowing it to stably perform the role of a protective layer for a long period.

[0101] In addition, the fourth aspect of the present invention provides an energy storage system comprising an all-solid-state secondary battery according to the second aspect of the present invention.

[0102] Regarding the energy storage system according to the fourth aspect of the present invention, detailed descriptions of parts that overlap with the first to third aspects of the present invention have been omitted, but even if such descriptions are omitted, the contents described in the first to third aspects of the present invention may be applied equally to the fourth aspect of the present invention.

[0103] An energy storage system is a system that stores electricity and supplies it when needed, and can be used for various purposes such as the efficient utilization of renewable energy, power peak management, and power quality improvement. Based on its excellent safety and long-term lifespan characteristics, the all-solid-state secondary battery of the present invention can be utilized as a core component of an energy storage system.

[0104] In particular, the all-solid-state secondary battery of the present invention is suitable for energy storage systems requiring long-term charging and discharging, based on excellent interfacial stability with the solid electrolyte resulting from the use of an iron current collector. Furthermore, since it offers superior safety by not using a liquid electrolyte, it can be applied to large-scale energy storage systems.

[0106] Additionally, the fifth aspect of the present invention provides a wearable device comprising an all-solid-state secondary battery according to the second aspect of the present invention.

[0107] Regarding the wearable device according to the fifth aspect of the present invention, detailed descriptions of parts that overlap with the first to fourth aspects of the present invention have been omitted, but even if such descriptions have been omitted, the contents described in the first to fourth aspects of the present invention may be applied equally to the fifth aspect of the present invention.

[0108] Wearable devices are electronic devices that can be worn on the body by a user and can be implemented in various forms, such as smartwatches, fitness bands, and smart glasses. Safety and miniaturization are very important for such wearable devices, and the all-solid-state secondary battery of the present invention can satisfy these requirements.

[0109] The all-solid-state secondary battery of the present invention does not use a liquid electrolyte, so there is no risk of electrolyte leakage and it has excellent safety, making it suitable for wearable devices. In addition, the excellent interfacial stability resulting from the use of an iron current collector can improve the long-term reliability of wearable devices.

[0110] The present invention is to be explained in more detail through the following examples, but the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0112] [Example 1] Preparation of Fe Current Collector-Based Cathode Composite

[0113] Graphite powder, solid electrolyte (LPSCl), and nitrile butadiene rubber (NBR) were uniformly mixed using a mortar and pestle. Isobutyl isobutyrate (TCI) was added to this to prepare a slurry electrode, which was then cast onto an Fe current collector and dried in a vacuum oven at 80°C.

[0114] [Example 2] Preparation of an all-solid-state battery based on an Fe current collector

[0115] A 10 mm thick solid electrolyte layer was fabricated using 100 mg of solid electrolyte (LPSCl). At this time, the compression pressure of the solid electrolyte layer was set to 120 MPa. An all-solid-state battery was fabricated by uniformly placing the cathode composite cast on the Fe foil prepared in Example 2 onto the solid electrolyte layer and using lithium metal as the counter electrode.

[0116] [Example 3] Manufacture of an all-solid-state battery based on an Fe current collector

[0117] A 10 mm thick solid electrolyte layer was fabricated using 100 mg of solid electrolyte (LPSCl). The compression pressure of the solid electrolyte layer was set to 120 MPa. An all-solid-state battery was fabricated by placing only an Fe current collector on the solid electrolyte layer as the negative electrode and placing lithium metal as the counter electrode on the opposite side.

[0118] [Example 4] Preparation of Contact Evaluation Composite

[0119] A contact evaluation composite was prepared by uniformly mixing equal amounts of Fe powder and LPSCl powder.

[0121] [Comparative Example 1] Preparation of Cu current collector-based cathode composite

[0122] Graphite powder, solid electrolyte (LPSCl), and nitrile butadiene rubber (NBR) were uniformly mixed using a mortar and pestle. Isobutyl isobutyrate (TCI) was added to this to prepare a slurry electrode, which was then cast onto a Cu current collector and dried in a vacuum oven at 80°C.

[0123] [Comparative Example 2] Manufacture of a Cu Current Collector-Based All-Solid State Battery

[0124] A 10 mm thick solid electrolyte layer was fabricated using 100 mg of solid electrolyte (LPSCl). At this time, the compression pressure of the solid electrolyte layer was set to 120 MPa. An all-solid-state battery was fabricated by uniformly placing the negative electrode composite, which was cast on the Cu foil prepared in Comparative Example 2, onto the solid electrolyte layer and using lithium metal as the counter electrode.

[0125] [Comparative Example 3] Manufacture of a Cu Current Collector-Based All-Solid State Battery

[0126] A 10 mm thick solid electrolyte layer was fabricated using 100 mg of solid electrolyte (LPSCl). The compression pressure of the solid electrolyte layer was set to 120 MPa. An all-solid-state battery was fabricated by placing only a Cu current collector on the solid electrolyte layer as the negative electrode and placing lithium metal as the counter electrode on the opposite side.

[0127] [Comparative Example 4] Preparation of Contact Evaluation Composite

[0128] A contact evaluation composite was prepared by uniformly mixing equal amounts of Cu powder and LPSCl powder.

[0130] [Experimental Example 1] Evaluation of Electrochemical Characteristics of an All-Solid State Battery

[0131] Charge-discharge analysis was performed on the all-solid-state batteries prepared in Example 2 and Comparative Example 2. Specifically, 0.001 V to 2.5 V vs. Li / Li + The experiment was conducted at room temperature with the first cycle at 0.1C and subsequent cycles at a C-rate of 0.33C.

[0132] Referring to Fig. 2, when a Cu current collector is used, 409.2 mAh g -1 Although the charging capacity was achieved, at discharge it is 2.0 V vs. Li / Li + Abnormal phenomena were observed with the occurrence of a voltage plateau in the vicinity, which appears to have been caused by the oxidation of the Cu current collector. On the other hand, when an Fe current collector was used, the voltage plateau seen in the sample using the Cu current collector did not appear, and lithium insertion and extraction occurred stably. At this time, the charge and discharge capacities were 486.0 mAh g⁻¹, respectively. -1 and 357.8 mAh g -1 Thus, it was confirmed that reversible lithium insertion and extraction became possible by replacing the current collector with Fe. Furthermore, the discharge capacity was at the same level as that of a commercial graphite anode.

[0133] Referring to the differential capacity curve shown in Figure 3, when an Fe current collector was used, the polarization was smaller than when a Cu current collector was used, and the reversibility of the graphite electrode was also improved. Based on this, it can be concluded that the discharge capacity of the graphite electrode is greater when an Fe current collector is used. In other words, it can be seen that the Fe current collector is more effective when using a graphite-LPSCl composite electrode.

[0134] [Experimental Example 2] Evaluation of Contact Properties of All-Solid State Batteries

[0135] Contactability with an LPSCl solid electrolyte was evaluated for the all-solid-state batteries prepared in Example 3 and Comparative Example 3. Specifically, after contacting Cu and Fe current collectors with the LPSCl electrolyte, changes in surface morphology were observed by controlling the contact time from 0 to 24 hours.

[0136] Referring to Figure 4, it was confirmed that a dark brown byproduct was deposited on the foil surface of the Cu current collector after contact with LPSCl for 5 hours. At this time, the dark area expanded as the contact time with LPSCl increased to 12 hours and 24 hours, indicating that chemical deterioration occurred in the Cu current collector upon exposure to LPSCl.

[0137] Field-Electro-SEM (FE-SEM) analysis confirmed that localized corrosion occurred on the initially flat surface of the Cu current collector upon contact with LPSCl. After 5 hours of contact, several corrosion spots with a diameter of 2 μm or less were observed. Since the current collector surface is covered with copper oxide, the formation of dark brown localized corrosion is attributed to the chemical degradation of surface oxides and the subsequent formation of copper sulfides. As the contact time increased, more large and deep corrosion spots were observed, confirming that the oxide layer of the Cu foil failed to prevent corrosion or maintain stability when in contact with LPSCl.

[0138] On the other hand, referring to Fig. 5, the Fe foil maintained its metallic surface and showed no change in color even after contact with LPSCl for 24 hours. SEM image analysis also showed that the initial flat surface of the Fe foil was well preserved, and no distinct corrosion spots due to Fe corrosion were observed even after contact for 5, 12, and 24 hours.

[0139] A particularly noteworthy point is, Fe / Fe 2+ The equilibrium potential is -0.440 V vs. NHE for Cu / Cu +Despite being lower than 0.52 V vs. NHE, the degradation reaction of the LPSCl electrolyte on the Fe foil was suppressed, unlike on the Cu foil. Through these results, it was confirmed that the Fe foil has superior stability at the interface with the solid electrolyte compared to the Cu foil.

[0140] [Experimental Example 3] Evaluation of Electrochemical Characteristics of All-Solid State Battery

[0141] The individual electrochemical behavior of the current collectors in the all-solid-state batteries prepared in Example 3 and Comparative Example 3 was investigated. Cyclic Voltammetry (CV) tests were performed to analyze the electrochemical reactions induced by potential control between the current collector and the solid electrolyte. The CV test was conducted at 10 mV s⁻¹. -1 2.5V ~ -0.1V vs. Li / Li at scan rate + It was carried out within the voltage range.

[0142] Referring to Fig. 6, for the Cu current collector, approximately 0.0 V vs. Li / Li during the first cycle. + Lithium plating and dissolution current peaks were observed, and a small current spike unrelated to the lithium plating and dissolution peaks was observed at 2.0 V, the end of the first oxidation curve. After 60 minutes of contact with LPSCl, a new reduction current peak appeared at 1.4 V on the second reduction curve, and the final oxidation current peak above 2.0 V appeared at a higher position than the initial cycle. This current behavior is amplified as the contact time increases, which can be confirmed in the CV curves at 120, 180, 240, and 300 minutes.

[0143] The additional current peaks appearing at high voltage become stronger in subsequent cycles than in the first, whereas the lithium plating and dissolution current peaks around 0.0 V become progressively smaller in subsequent cycles than in the first. This decrease in the lithium plating and dissolution current peaks indicates that using Cu foil as a current collector in all-solid-state batteries is not as effective as its application as a current collector in conventional liquid electrolyte-based lithium-ion batteries. Generally, copper sulfide is known to exhibit electrochemical conversion reactions to Li2S and Cu metal at 1.4 V and 2.0 V. The additional current peaks, excluding lithium metal plating and dissolution, coincide with the electrochemical conversion of copper sulfide. Therefore, it is determined that copper sulfide is generated by simple contact between Cu and LPSCl.

[0144] In contrast, the Fe current collector showed a stable CV curve even after prolonged contact with LPSCl. The Fe cell exhibited nearly constant lithium plating and dissolution current peaks near 0V in all cycles for various contact times. There were almost no sulfide switching current peaks observed in the all-solid-state cell using the Fe current collector, indicating that the Fe foil is electrochemically stable without other harmful reactions.

[0145] Referring to Figures 7 and 8, the systematic electrochemical sulfidation behavior between LPSCl and a metal foil was measured using a combination of CV steps with various potential ranges. After performing an initial CV cycle over the entire potential range from 2.5 to -0.1 V, five additional CV scans were performed from a high cut-off potential of 2.5 V to various low cut-off potentials of 2.2, 1.8, 1.4, and 1.0 V to accelerate the electrochemical oxidation reaction of the metal.

[0146] In the case of the Cu foil, a pair of current peaks at 0 V due to lithium plating and dissolution was observed in the first cycle curve, while the current for electrochemical sulfide conversion was not significantly observed. In the subsequent full CV scan, the peaks associated with the lithium plating and dissolution processes decreased, while increased peaks at 1.2 V and 2.0 V, characteristic of electrochemical sulfide conversion, were observed. In particular, these oxidation current peaks maintained stable intensity throughout the narrow-range cycling process. This suggests that copper sulfide formation was not significantly accelerated even under the oxidation conditions of the Cu metal.

[0147] Meanwhile, in the case of Fe foil, no significant current change attributed to the LPSCl interface was observed even after additional oxidation CV scans. Fe foil exhibited strong resistance to sulfide formation, and this characteristic led to excellent stability at the metal / LPSCl interface, along with a reduction in the pulverization effect caused by electrochemical conversion reactions. These electrochemical behaviors demonstrate the excellent stability of Fe foil in all-solid-state batteries.

[0148] [Experimental Example 4] Surface Analysis of All-Solid State Battery

[0149] X-ray photoelectron spectroscopy (XPS) analysis was performed to observe chemical changes resulting from the interaction between the LPSCl electrolyte and the surfaces of Cu and Fe foils.

[0150] Referring to Fig. 9, in the XPS spectrum measured without Ar etching after contacting the Cu foil with LPSCl for 5 hours, S, O, and Cu appeared at atomic ratios of 10.7%, 23.1%, and 29.5%, respectively. The peaks at 163.0 eV and 161.7 eV in the S 2p spectrum are S 2-This corresponds to, and this peak almost disappeared after 120 seconds of Ar etching. This suggests the presence of a thin sulfide byproduct on the surface of the Cu foil. O1s XPS shows peaks at 531.8 eV and 530.0 eV, indicating the presence of natural CuO.

[0151] Extending the contact time to 24 hours accelerated surface sulfidation between LPSCl and copper. Upon 24 hours of contact, the sulfur content on the top surface increased to 18.6%, while oxygen-related peaks decreased to 8.1%. Notably, depth profiling results for 120 seconds showed that the sulfur content was higher than the oxygen content below the interface. This indicates that more sulfidation reactions occurred in the Cu foil after 24 hours of LPSCl contact compared to the sample contacted for 5 hours. Sulfur was also detected after 180 seconds of etching, accompanied by a relative decrease in oxygen concentration. These ionic byproducts were also identified in the Cu spectrum, demonstrating an increase in CuS-related compounds on the surface due to long-term contact with LPSCl.

[0152] Referring to Fig. 10, Fe exhibited more stable surface behavior even after contact with LPSCl. The thick iron oxide layer remained stable and was not converted into sulfides, and no characteristic sulfide-related peaks were detected on the iron surface. Strong oxides were continuously detected before and during the Ar etching process. Particularly noteworthy is that the iron oxide structure remained stable even after prolonged contact with LPSCl, so no conversion into sulfides such as FeS occurred.

[0153] The surface of Fe was dominated by an oxide film, and no sulfide conversion was observed upon contact with LPSCl. The thickness of the oxide film also remained almost unchanged. These results demonstrate that the oxide on the Fe surface remains stable without converting into sulfide, even with prolonged LPSCl exposure time.

[0154] [Experimental Example 5] Evaluation of Contact Properties of the Complex

[0155] High-temperature X-ray diffraction (HT-XRD) analysis of the contact evaluation composites according to Example 4 and Comparative Example 4 was performed to study the thermodynamic behavior of intermediate compound formation through the reaction between LPSCl and Cu or Fe metal and to observe the formation of compounds according to temperature.

[0156] Referring to Fig. 11, in the HT-XRD pattern of the Cu and LPSCl mixture, the XRD patterns of LPSCl (JCPDF #34-0688) and Cu (JCPDF #003-1018) were initially observed at room temperature. When the temperature rose to about 150°, a new peak corresponding to the crystal pattern of Cu2S appeared near 26.7°, and at temperatures above 150°, the Cu2S peak became more distinct and the original crystallinity of Cu and LPSCl decreased. This indicates that side reactions between LPSCl and Cu occur even in a low temperature range such as 150°.

[0157] Copper sulfides form negative Gibbs free energy (CuS=-53.6, Cu2S=-86.2 kJ mol -1 It has ) and exhibits a spontaneous reaction, but the sulfide is an oxide (CuO=-129, Cu2O=-146 kJ mol -1 Compared to ), the Gibbs free energy is higher in the negative direction. The oxide layer on the Cu metal acts as a passivation layer, slowing down the diffusion of sulfide paper into the underlying copper, thereby kinetically hindering sulfide formation.

[0158] In contrast, the HT-XRD pattern of the Fe and LPSCl mixture was more stable, with the initial Fe metal (JCPDF#6-0696) and LPSCl (JCPDF#34-0688) phases consistently maintained. This original XRD pattern was observed even at 300°C, and as the temperature increased to 350°C, the XRD pattern of Fe weakened, but no iron sulfide byproducts were observed.

[0159] Referring to Figures 12 and 13, the DFT calculation results and LSV measurement results regarding sulfur substitution of surface oxide clusters can be confirmed. During the LSV experiment, the voltage was reduced from OCV (1.3 V) to 0.5 V, and a change in current due to byproduct formation was detected. As the temperature increased, a sharp increase in current was observed in the cell with the Cu current collector, which suggests that the increase in temperature accelerated both the decomposition and corrosion rates of LPSCl. On the other hand, the current in the cell with the Fe current collector was much lower, indicating that less decomposition of LPSCl occurred on the Fe foil.

[0160] DFT calculations showed that the formation of sulfides from iron oxides was not favored due to high energy barriers (0.001 eV along the z-axis and 0.002 eV in the plane). On the other hand, the energy difference for Cu-S bond formation was calculated to be -0.001 eV, indicating that copper sulfides can be easily formed when the argyrodite solid electrolyte comes into contact with the Cu current collector. These results demonstrate that Fe foil has lower reactivity to LPSCl than Cu foil, and that the robust surface iron oxide acts as a passivation agent that inhibits iron sulfide formation.

[0161] [Experimental Example 6] Evaluation of Long-Term Life Characteristics of All-Solid State Batteries

[0162] The long-term life characteristics of the all-solid-state batteries prepared in Example 2 and Comparative Example 2 were evaluated.

[0163] Referring to Fig. 14, the all-solid-state battery using Fe current collector demonstrated stable operation without short circuits up to 1,000 cycles. In particular, in the long-term life evaluation, the average Coulomb efficiency was confirmed to be 99.8%, indicating excellent reversibility.

[0164] Compared to other results reported in Figure 15, the lifespan characteristics of the all-solid-state battery using an iron current collector were found to be significantly superior. It exhibited superior lifespan characteristics compared to Ref. 18a (LPSCl solid electrolyte-based all-solid-state battery reported by S. Yang et al. in ACS Applied Energy Materials), Ref. 18b (sulfide-based all-solid-state battery reported by X. Xing et al. in ACS Energy Letters), Ref. 18c (composite electrode-based all-solid-state battery reported by B. Pang et al. in ACS Applied Materials & Interfaces), Ref. 18d (argyrodite electrolyte-based all-solid-state battery reported by T. Palaniselvam et al. in Journal of Physical Chemistry C), and Ref. 18e (Li3PS4 electrolyte-based all-solid-state battery reported by K. Kuratani et al. in ACS Applied Materials & Interfaces). This suggests that the replacement of the current collector has a significant impact on improving the durability of sulfide-based all-solid-state batteries.

[0165] In particular, it was confirmed that the iron current collector can significantly improve the lifespan characteristics of the all-solid-state battery (ASSB) by effectively mitigating cycle degradation caused by sulfidation of the metal surface resulting from contact with the solid electrolyte.

[0167] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical concept or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0168] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and the concept of equivalents thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A negative electrode for an all-solid-state secondary battery comprising a sulfide-based solid electrolyte layer, the negative electrode current collector comprising iron (Fe); and a negative electrode active material layer disposed on the negative electrode current collector; wherein an iron oxide layer is formed on the surface of the iron, and the iron oxide layer acts as a protective layer that suppresses the formation of sulfides on the surface of the iron when in contact with the sulfide-based solid electrolyte layer. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 In claim 1, the sulfide-based solid electrolyte layer is Li 7-x PS 6-x Cl x (0 <x<2), Li 7-x PS 6-x Br x (0 <x<2), Li 7-x PS 6-x I x (0 <x<2), Li2S-P2S5, Li2S-P2S5-LiX(여기서, X는 할로겐 원소임), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (Here, m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q A negative electrode for an all-solid-state secondary battery comprising a group consisting of (wherein p, q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, In) and combinations thereof. Claim 6 A negative electrode for an all-solid-state secondary battery according to claim 1, wherein the negative electrode active material layer comprises a negative electrode active material selected from the group consisting of graphite, lithium metal, hard carbon, soft carbon, silicon, tin, germanium, lithium titanium oxide, titanium oxide, and combinations thereof. Claim 7 A negative electrode for an all-solid-state secondary battery according to claim 6, wherein the negative electrode active material layer further comprises a solid electrolyte material of the same or different type as the solid electrolyte included in the sulfide-based solid electrolyte layer. Claim 8 A negative electrode for an all-solid-state secondary battery according to claim 7, wherein the negative electrode active material layer further comprises a binder for combining the solid electrolyte material and the negative electrode active material. Claim 9 A negative electrode for an all-solid-state secondary battery according to claim 8, wherein the binder comprises a binder selected from the group consisting of nitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), polyacrylic acid (PAA), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polyimide (PI), polyvinylidene fluoride (PVDF), and combinations thereof. Claim 10 A solid-state secondary battery comprising: a negative electrode for a solid-state secondary battery according to claim 1; a positive electrode; and a sulfide-based solid electrolyte layer disposed between the negative electrode and the positive electrode. Claim 11 In claim 10, the all-solid-state secondary battery comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. Claim 12 In claim 11, the all-solid-state secondary battery comprises a positive current collector selected from the group consisting of aluminum (Al), stainless steel (STS), nickel (Ni), titanium (Ti), and combinations thereof. Claim 13 A solid-state secondary battery according to claim 11, wherein the positive active material comprises a material selected from the group consisting of lithium metal, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), nickel cobalt manganese oxide (NCM), nickel cobalt aluminum oxide (NCA), and combinations thereof. Claim 14 In claim 10, the all-solid-state secondary battery is a solid-state secondary battery having a form selected from the group consisting of prismatic batteries, cylindrical batteries, pouch batteries, and thin-film batteries. Claim 15 A method for manufacturing a negative electrode current collector for an all-solid-state secondary battery comprising a sulfide-based solid electrolyte layer, comprising the steps of: preparing an iron (Fe) foil; and forming an iron oxide layer on the surface of the iron foil; wherein the iron oxide layer serves as a protective layer that suppresses a sulfidation reaction with the sulfide-based solid electrolyte layer on the surface of the iron foil. Claim 16 A method for manufacturing a negative current collector for an all-solid-state secondary battery, wherein, in claim 15, the iron oxide layer is formed on the surface of the iron foil through natural oxidation. Claim 17 An energy storage system comprising an all-solid-state secondary battery according to claim 10. Claim 18 A wearable device comprising an all-solid-state secondary battery according to claim 10.

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