A negative electrode for an all-solid-state battery including a coating layer and an ion transfer layer, and a lithium secondary battery including the same.

Abstract

To provide a negative electrode for all-solid-state batteries capable of preventing degradation in performance of a lithium secondary battery, particularly an all-solid-state battery having high energy density, due to lithium dendrites and extending the lifespan of the lithium secondary battery, thereby improving yield, and a lithium secondary battery including the same.SOLUTION: The present invention relates to a negative electrode for an all-solid-state battery, and a lithium secondary battery including the negative electrode for an all-solid-state battery. The negative electrode for an all-solid-state battery includes: a negative electrode current collector made of an electrically conductive metal material; a coating layer added to one surface or both surfaces of the negative electrode current collector, the coating layer including a lithiophilic material; and an ion transport layer located on the coating layer, the ion transport layer including amorphous carbon configured to allow lithium ions to move therethrough.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention claims the benefit of priority based on Korean Patent Application No. 2020-0146810 filed on November 05, 2020, and Korean Patent Application No. 2021-0034266 filed on March 16, 2021, and all the contents disclosed in the corresponding Korean patent application documents are incorporated herein by reference.

[0002] The present invention relates to a negative electrode for an all-solid-state battery including a coating layer and an ion conduction layer, and a lithium secondary battery including the same. Specifically, the present invention relates to a technique for preventing local lithium plating from occurring in the negative electrode and preventing a short circuit from occurring between the positive electrode and the negative electrode by specifying the electrodeposition position of lithium.

Background Art

[0003] Lithium secondary batteries that are reusable and have a high energy density not only can significantly reduce the use of fossil fuels but also do not generate by-products due to energy use, so they are attracting attention as a new environmentally friendly energy source.

[0004] The lithium secondary battery is attracting attention not only as an energy source for wearable devices or portable devices but also for devices having high output and high energy density such as electric vehicles. As a result, research on lithium secondary batteries with high operating voltage and high energy density has become more active.

[0005] In a lithium secondary battery, charging and discharging are performed through the process of lithium ions moving between the positive electrode and the negative electrode. However, some of the lithium ions that have moved to the negative electrode adhere to the surface of the negative electrode to form lithium nuclei, and the lithium nuclei can become lithium dendrites, which are dendritic crystals while growing.

[0006] When lithium dendrites formed and grown on the surface of the negative electrode come into contact with the positive electrode, it can cause a short circuit in the lithium secondary battery. This can also be a problem in shortening the lifespan of the lithium secondary battery and ensuring stable performance.

[0007] Conventional lithium secondary batteries have the disadvantage of low energy density due to using graphite as the negative electrode material to address such problems.

[0008] In order to increase the energy density, it has been proposed to use lithium as the negative electrode active material in a highly stable all-solid-state battery. As methods of using lithium as the negative electrode active material, there are methods of using lithium or a lithium alloy as the negative electrode active material, or methods of using lithium deposited at the interface between the negative electrode current collector and the solid electrolyte during charging without forming a negative electrode active material layer on the negative electrode current collector as the active material.

[0009] When using lithium as the negative electrode active material, lithium is deposited on the negative electrode side during charging, and when not forming a negative electrode active material layer, lithium is deposited on the negative electrode current collector. The lithium deposited on the negative electrode side in this way can grow into lithium dendrites through the gaps in the solid electrolyte when the all-solid-state battery repeats charge and discharge. The lithium dendrites can cause a short circuit or a decrease in the battery capacity.

[0010] Patent Document 1 discloses an electrode including a composite layer composed of a first lithium affinity layer, a second lithium affinity layer, and a perovskite layer in order to prevent the generation of lithium dendrites.

[0011] Patent Document 1 discloses that by applying a structure in which lithium affinity layers are sequentially arranged on the surface of the electrode, lithium ions can uniformly adhere to the surface of the electrode, so that the generation of lithium dendrites can be prevented.

[0012] Patent Document 1 presents an improvement in the lifespan characteristics of lithium secondary batteries containing a liquid electrolyte, and recognizes a method to prevent the formation of lithium dendrites by lowering the potential at which lithium nuclei are generated, but it does not present a technique for identifying the location where lithium adheres.

[0013] In lithium-ion secondary batteries, there is a strong need for technologies that not only prevent lithium ions from being locally plated onto a portion of the negative electrode surface, but also prevent lithium dendrites from growing on the positive electrode side, even if lithium nuclei are formed. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Chinese Patent No. 110571413 Specification [Overview of the project] [Problems that the invention aims to solve]

[0015] The present invention aims to solve the above-mentioned problems and to provide a negative electrode for a lithium-ion battery and a lithium-ion battery containing the same, which can prevent the performance of a lithium-ion battery from degrading due to lithium dendrites and improve yield by extending the life of the lithium-ion battery, particularly in a lithium-ion battery having a high energy density. [Means for solving the problem]

[0016] To achieve these objectives, the present invention provides a negative electrode for an all-solid-state battery, comprising: a negative electrode current collector made of an electrically conductive metal material; a coating layer attached to one or both sides of the negative electrode current collector and containing a lithium-affinity material; and an ion transfer layer located on the coating layer and containing amorphous carbon on which lithium ions can move.

[0017] The ion transport layer may further contain a binder.

[0018] A negative electrode mixture layer does not necessarily need to be formed on the negative electrode current collector.

[0019] The lithium-affinity material may be one or more of the following: metals containing Au, Ag, Pt, Zn, Si, and Mg, and metal oxides containing CuO, ZnO, CoO, and MnO.

[0020] The lithium-affinity material constituting the coating layer may be in the form of nanoparticles, or it may be in the form of metal nanoparticles or metal oxide nanoparticles attached to the negative electrode current collector.

[0021] Furthermore, the present invention provides a method for manufacturing a negative electrode for an all-solid-state battery, which specifically includes (a) a step of preparing a negative electrode current collector, (b) a step of forming a coating layer containing a lithium-affinity material on at least one of the outer surfaces of the negative electrode current collector, and (c) a step of forming an ion transfer layer on the coating layer, and each of the above steps may be performed sequentially.

[0022] Furthermore, the present invention provides a lithium secondary battery comprising the negative electrode, solid electrolyte layer, and positive electrode for an all-solid-state battery.

[0023] In the lithium secondary battery according to the present invention, the negative electrode for the all-solid-state battery has the lithium-affinity material dispersed in a coating layer, and lithium plating (Li plating) can occur on the lithium-affinity material.

[0024] In the lithium secondary battery according to the present invention, lithium electrodeposition can be performed on one surface of the ion transfer layer facing the negative electrode current collector of the all-solid-state battery.

[0025] In the lithium secondary battery according to the present invention, the negative electrode for the all-solid-state battery may include a monocell in which a coating layer and an ion transfer layer are formed only on the first of the two surfaces of the negative electrode current collector, and a positive electrode is placed on the first surface.

[0026] In the monocell, a coating layer may be formed on the negative electrode current collector, and the ion transfer layer may be formed on the coating layer.

[0027] In the lithium secondary battery according to the present invention, the negative electrode for the all-solid-state battery is a lithium secondary battery including a bicell in which a coating layer and an ion transfer layer are formed on the first and second surfaces of the negative electrode current collector, and a first positive electrode and a second positive electrode are arranged on the first and second surfaces, respectively.

[0028] In the aforementioned bicell, a coating layer may be formed on the negative electrode current collector, and the ion transfer layer may be formed on the coating layer.

[0029] Furthermore, the present invention can also be provided in forms that combine various means for solving the aforementioned problems. [Effects of the Invention]

[0030] As described above, in the present invention, since the lithium-affinity material is widely dispersed on the negative electrode current collector for all-solid-state batteries, the lithium that has moved to the negative electrode can be widely distributed. Therefore, it is possible to prevent an increase in lithium nucleation energy due to localized adhesion of lithium to the surface of the negative electrode current collector.

[0031] Furthermore, since an ion transfer layer containing amorphous carbon is formed on the coating layer containing the lithium-affinity material, lithium ions can move toward the negative electrode current collector, and since lithium is deposited on one surface of the ion transfer layer toward the negative electrode current collector, even if lithium dendrites are formed, their growth toward the positive electrode through the ion transfer layer can be delayed.

[0032] This structure, consisting of a coating layer containing a lithium-affinity material and an ion transfer layer, can induce uniform electrodeposition of lithium on the surface of the negative electrode current collector.

[0033] Therefore, in all-solid-state batteries including such a negative electrode, the lifespan can be improved and safety can be ensured. [Brief explanation of the drawing]

[0034] [Figure 1] This is a schematic diagram illustrating the process for manufacturing the negative electrode according to the present invention. [Figure 2] This is an SEM image of the negative electrode manufactured in Example 2. [Figure 3] This is an SEM image of the cross-section of the negative electrode manufactured in Example 2. [Figure 4] This is an SEM image of the negative electrode manufactured in Comparative Example 1. [Figure 5] This is an SEM image of the negative electrode manufactured in Comparative Example 2. [Figure 6] This is an SEM image of the negative electrode manufactured in Comparative Example 3. [Figure 7] This is an SEM image of the cross-section of the negative electrode manufactured in Comparative Example 6. [Figure 8] This is an SEM image of the negative electrode manufactured in Comparative Example 7. [Figure 9] This is an SEM image of the negative electrode manufactured in Comparative Example 8. [Modes for carrying out the invention]

[0035] Hereinafter, with reference to the attached drawings, embodiments that allow a person with ordinary skill in the art to carry out the present invention will be described in detail. However, in describing the operating principle of a preferred embodiment of the present invention in detail, if it is determined that a specific description of a related known function or configuration may unnecessarily obscure the gist of the present invention, such a detailed description will be omitted.

[0036] Furthermore, the same reference numerals shall be used for parts that have similar functions and operations throughout the entire drawing. Throughout the specification, when one part is said to be connected to another part, this includes not only direct connections but also indirect connections through other elements in between. Also, the inclusion of one component does not exclude other components unless otherwise stated, but rather means that other components may be included.

[0037] Furthermore, explanations that specify or add components are applicable to all inventions unless otherwise specified, and are not limited to explanations of a particular invention.

[0038] Furthermore, throughout the description of this invention and the claims, the singular notation includes plural nouns unless otherwise specified.

[0039] Furthermore, throughout the description and claims of this invention, "or" includes "and" unless otherwise specified. Therefore, "including A or B" means including A, including B, or all three of the aforementioned cases including A and B.

[0040] Furthermore, all numerical ranges include the values ​​at both ends and all intermediate values ​​between them, unless otherwise explicitly stated.

[0041] The negative electrode for an all-solid-state battery according to the present invention may include a negative electrode current collector made of an electrically conductive metal material, a coating layer containing a lithium-affinity material attached to one or both sides of the negative electrode current collector, and an ion transfer layer located on the coating layer and containing amorphous carbon on which lithium ions can move.

[0042] The negative electrode for an all-solid-state battery according to the present invention is a configuration that does not include a separate negative electrode mixture layer on the negative electrode current collector. Therefore, in this specification, the expression that a coating layer is formed on the surface of the negative electrode is used in the same sense as that a coating layer is formed on the surface of the negative electrode current collector.

[0043] The type of negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the lithium secondary battery and is conductive. For example, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. Furthermore, various forms can be used, such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics, with or without fine irregularities on the surface.

[0044] For example, when using a sulfide-based solid electrolyte, copper sulfate may form if a copper negative electrode current collector is used. To prevent this, a nickel or stainless steel negative electrode current collector can be used.

[0045] The thickness of the negative electrode current collector is not particularly limited, but may be 5 μm to 30 μm, and more specifically, 10 μm to 20 μm. If the thickness of the negative electrode current collector exceeds 30 μm, there is a problem that the capacitance per unit volume of the electrode decreases, and if the thickness of the negative electrode current collector is less than 5 μm, a folding phenomenon may occur during the manufacture of the electrode.

[0046] The lithium-affinity material constituting the coating layer is a material that is highly reactive with lithium. A battery cell is manufactured by bonding a positive electrode to a negative electrode on which the coating layer and ion transfer layer are formed. When the battery cell is charged and discharged, lithium plating and electrodeposition occur on the lithium-affinity material constituting the coating layer with the lithium ions that have moved to the negative electrode.

[0047] The lithium-affinity material contained in the coating layer may be one or more of the following: metals including Au, Ag, Pt, Zn, Si, and Mg, and metal oxides including CuO, ZnO, CoO, and MnO.

[0048] In this invention, the lithium-affinity material is evenly dispersed on the surface of the negative electrode current collector, but the lithium-affinity material may aggregate and exist in island-like structures, partially exposing the negative electrode current collector.

[0049] In one specific example, the lithium-affinity material can be distributed in a range of 5% to 100% of the total area of ​​the negative electrode current collector, more specifically in a range of 10% to 90%, and even more specifically in a range of 30% to 80%. Furthermore, in even more detail, the lithium-affinity material can be distributed in a range of 50% to 70% of the total area of ​​the negative electrode current collector.

[0050] If the area of ​​the lithium-affinity material is less than 5% of the total area of ​​the negative electrode current collector, it is undesirable because the distribution area of ​​the lithium-affinity material is small, making it difficult to obtain the desired effect.

[0051] Thus, in the negative electrode for an all-solid-state battery according to the present invention, the lithium-affinity material is not locally electrodeposited on only a portion of the surface of the negative electrode current collector, but is dispersed over a wide area, thereby lowering the lithium nucleation potential. In other words, the formation of lithium nuclei in specific areas on the surface of the negative electrode current collector can be minimized. Therefore, lithium can be uniformly electrodeposited and grown on the surface of the negative electrode current collector, and the formation of lithium dendrites can be suppressed.

[0052] Furthermore, although the present invention has an ion transfer layer formed on the coating layer, the ion transfer layer does not hinder the movement of lithium ions from the positive electrode to the negative electrode, or from the negative electrode back to the positive electrode, and can transmit lithium ions moving to the negative electrode in the direction of the negative electrode current collector.

[0053] In connection with this, Figure 1 schematically shows the process for manufacturing the negative electrode according to the present invention.

[0054] Referring to Figure 1, a coating layer containing lithium-affinity material (LPM) is formed on the negative electrode current collector, and an ion transfer layer containing amorphous carbon is formed on the coating layer. Subsequently, a battery is manufactured by stacking the negative electrode thus produced with a solid electrolyte layer and a positive electrode. When charging and discharging are performed, lithium ions that have moved to the negative electrode through the ion transfer layer adhere to and are plated onto the lithium-affinity material. However, even if lithium grows, it becomes impossible for it to penetrate the ion transfer layer.

[0055] In other words, when lithium plated on the coating layer grows, its growth is inhibited by the ion transfer layer, thus preventing the conventional problem of lithium dendrites, in which lithium nuclei have grown, extending towards the positive electrode and coming into contact with it.

[0056] In the negative electrode for an all-solid-state battery according to the present invention, the ion transfer layer may be made of carbon black such as acetylene black, Kechen black, channel black, polytetrafluoroethylene black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives. More specifically, the ion transfer layer may contain amorphous carbon such as carbon black.

[0057] The amorphous carbon has a small hexagonal network of carbon atoms, resulting in a disordered structure with poorly developed layer growth. The individual microcrystallites formed by the hexagonal network are either intertwined with each other or mixed with the amorphous phase. As a result, lithium ions can be inserted not only between the planes of the graphite layer, but also into the defects in the carbon layer and into the voids and tip surfaces created by the incomplete layer structure.

[0058] The ion transfer layer of the present invention contains amorphous carbon, which smoothly transfers lithium ions to the negative electrode current collector side. Electrodeposition of lithium occurs on the outer surface of the ion transfer layer facing the negative electrode current collector, but not on the outer surface facing the opposite direction. Therefore, lithium dendrites do not form on the outer surface of the ion transfer layer facing the positive electrode, which can improve the lifespan characteristics of the lithium secondary battery.

[0059] On the other hand, when an ion transfer layer is formed using crystalline graphite, such as natural graphite or artificial graphite, which is generally used as a negative electrode active material, lithium is inserted into the crystalline graphite, and then the lithium is electrodeposited onto the outer surface of the ion transfer layer facing the positive electrode. As the lithium is electrodeposited in this way, it grows into lithium dendrites, and when these dendrites pass through the solid electrolyte layer, they induce a short circuit.

[0060] As a result, when an ion transfer layer containing amorphous carbon is included, as in the present invention, safety can be ensured compared to when crystalline graphite is used as the ion transfer layer.

[0061] In one specific example, the ion transport layer may further contain a binder to ensure the bonding force between the carbon agents that are the main components constituting the ion transport layer.

[0062] Furthermore, the ion transfer layer may include a binder to improve the bonding force of the ion transfer layer to the coating layer and / or the negative electrode current collector.

[0063] In other words, the binder can be used to ensure the bonding force between the constituent materials of the ion transfer layer, or to ensure the bonding force between the ion transfer layer and the coating layer and / or the negative electrode current collector.

[0064] The binder may include, for example, one or more selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butylene rubber, fluororubber, and copolymers thereof.

[0065] Furthermore, the present invention provides a method for manufacturing a negative electrode for an all-solid-state battery, which specifically includes (a) a step of preparing a negative electrode current collector, (b) a step of forming a coating layer containing a lithium-affinity material on at least one of the outer surfaces of the negative electrode current collector, and (c) a step of forming an ion transfer layer on the coating layer, and each of the above steps may be performed sequentially.

[0066] The lithium-affinity material constituting the coating layer may be in the form of nanoparticles, or it may be in the form of metal nanoparticles or metal oxide nanoparticles attached to the negative electrode current collector.

[0067] The method for forming a coating layer on the negative electrode current collector and the method for forming an ion transfer layer can be independently carried out by one or more of the group including immersion, spin coating, dip coating, spray coating, doctor blade, solution casting, drop coating, PVD (Physical Vapor Deposition), and CVD (Chemical Vapor Deposition).

[0068] The method for forming the coating layer and the ion transfer layer on the negative electrode current collector can be carried out by a dry coating method.

[0069] The present invention includes a lithium secondary battery in which an electrode assembly including the negative electrode for the all - solid - state battery, a solid electrolyte layer, and a positive electrode is housed in a battery case.

[0070] The positive electrode is manufactured, for example, by applying a positive electrode mixture containing a positive electrode active material on a positive electrode current collector and then drying it. The positive electrode mixture may optionally further contain a binder, a conductive material, a filler, and the like.

[0071] The positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface - treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Also, the positive electrode current collector can increase the adhesive force of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non - woven fabric body, etc. are possible.

[0072] The positive electrode active material is a substance capable of undergoing an electrochemical reaction and can contain at least one of the positive electrode active materials represented by the following chemical formulas 1 to 3.

[0073] Li

[0074] , 1-z , y , , a , ، 1-x ، z ، ، a ، 2-y ، ، x ، ، Co 1-x M x O2(1)<000033-2>Li a Mn 2-y M[[ID=--29]] y O4(2) Li a Fe 1-z M z PO4(3) In the above formula, 0.8≦a≦1. ; 0≦x≦0.8; 0≦y≦0.6, 0≦z≦0.5, [[ID=--42]]M is one or more selected from the group consisting of Ti, Cd, Cu, Cr, Mo, Mg, Al, Ni, Nb, V, and Zr.

[0074] Note: There seems to be a minor formatting issue in the original text where some tags might be misaligned or have incorrect hyphens. The translation is done as accurately as possible based on the provided text.In other words, the positive electrode active material may include one or more substances selected from the group consisting of a layered lithium metal oxide represented by chemical formula 1, a spinel-structured lithium manganese oxide represented by chemical formula 2, and an olivine-structured lithium-containing phosphorus oxide represented by chemical formula 3.

[0075] The layered lithium metal oxide is not limited in type, but examples include one or more selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium nickel-manganese-cobalt oxide, and substances in which other elements are substituted or doped.

[0076] The aforementioned lithium nickel-manganese-cobalt oxide is Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (Here, -0.5≦z≦0.5, 0.1≦b≦0.8, 0.1≦c≦0.8, 0≦d≦0.2, 0≦e≦0.2, and b+c+d<1. M=Al, Mg, Cr, Ti, Si or Y, and A=F, P or Cl.) This can be expressed as follows.

[0077] The aforementioned lithium manganese oxide with a spinel structure is not limited in type, but examples include one or more selected from the group consisting of lithium manganese oxide, lithium nickel manganese oxide, and substances in which other elements are substituted or doped.

[0078] Furthermore, the lithium-containing phosphate salts with the olivine structure are not limited in type, but examples include lithium iron phosphate and those in which other elements are substituted or doped therewith.

[0079] The aforementioned other elements may be one or more elements selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, and doped substances.

[0080] The binder is a component that promotes bonding between the active material and the conductive material, and bonding to the current collector, and is usually added in an amount of 1% to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include one or more selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), styrene-butylene rubber, fluororubber, and copolymers thereof.

[0081] The conductive material is usually added in an amount of 1% to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Such a conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, the conductive material may include graphite such as natural graphite or artificial graphite; carbon black such as ethylene black, acetylene black, Kechen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, graphene, and carbon nanotubes.

[0082] The filler is used selectively as a component to suppress electrode expansion, does not induce chemical changes in the battery, and is not particularly limited as long as it is a fibrous material. For example, the filler can be a polyolefin polymer such as polyethylene or polypropylene; or a fibrous material such as glass fiber or carbon fiber.

[0083] The solid electrolyte may be a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a polymer-based solid electrolyte.

[0084] The sulfide-based solid electrolyte contains sulfur atoms (S) and may have ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, as well as electronic insulation properties. Preferably, the sulfide-based solid electrolyte contains at least Li, S, and P as elements and has lithium ion conductivity, but may contain other elements besides Li, S, and P depending on the purpose or circumstances.

[0085] Specific sulfide-based inorganic solid electrolytes include, for example, Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, L i2S-LiBr-P2S5, Li2SLi2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, Li2S-P2 S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS 2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, and Li 10 GeP2S 12 These can be used in various ways.

[0086] Amorphization methods can be used to synthesize sulfide-based inorganic solid electrolyte materials. Examples of such amorphous methods include mechanical milling, solution methods, or melt-quenching methods. This is because processing can be carried out at room temperature (25°C), simplifying the manufacturing process.

[0087] The oxide-based solid electrolyte is preferably a compound that contains oxygen atoms (O), has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is an electronically insulating compound.

[0088] As the oxide-based solid electrolyte, for example, Li xa La ya TiO3 [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li xb La yb Zr zb M bb mb O nb (M bb () is at least one element from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, where xb satisfies 5 ≤ ​​xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ ​​nb ≤ 20. xc B yc M cc zc O nc (M cc (xc is at least one element from C, S, Al, Si, Ga, Ge, In, and Sn, and xc satisfies 0 ≤ xc ≤ 5, yc satisfies 0 ≤ yc ≤ 1, zc satisfies 0 ≤ zc ≤ 1, and nc satisfies 0 ≤ nc ≤ 6.) Li xd (Al,Ga) yd (Ti,Ge) zd Si ad P md O nd (However, 1≦xd≦3, 0≦yd≦1, 0≦zd≦2, 0≦ad≦1, 1≦md≦7, 3≦nd≦13), Li (3-2xe) M ee xe D ee O(xe represents a number between 0 and 0.1, and M ee This indicates a divalent metal atom. ee This indicates a halogen atom or a combination of two or more halogen atoms. ), Li xf Si yf O zf (1≦xf≦5, 0 <yf≦3、1≦zf≦10)、Li xgS yg O zg (1 ≤ xg ≤ 3, 0 <yg≦2、1≦zg≦10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 Li3PO (4-3 / 2w) N w (where w < 1), Li has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 La, which has a perovskite crystal structure, is GeO4. 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li 1+xh+yh (Al,Ga) xh (Ti,Ge) 2-xh Si yh P 3-yh O 12 (where 0≦xh≦1, 0≦yh≦1), Li7La3Zr2O has a garnet-type crystal structure. 12 Examples include (LLZ). Alternatively, phosphorus compounds containing Li, P, and O can also be used as the oxide-based solid electrolyte, such as lithium phosphate (Li3PO4), LiPON and LiPOD obtained by substituting some of the oxygen in lithium phosphate with nitrogen. 1 (D 1 Examples include at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au. Alternatively, LiA may be used as the oxide-based solid electrolyte. 1 ON(A 1 Other materials (at least one selected from Si, B, Ge, Al, C, and Ga, etc.) can also be used.

[0089] The aforementioned polymer solid electrolyte may be a solid polymer electrolyte formed by adding a polymer resin to a lithium salt that has been independently solvated, or a polymer gel electrolyte in which an organic electrolyte containing an organic solvent and a lithium salt is incorporated into a polymer resin.

[0090] For example, the solid polymer electrolyte is an ion-conducting material and is not particularly limited as long as it is a polymer material that is commonly used as a solid electrolyte material for all-solid-state batteries. The solid polymer electrolyte may include, for example, polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene oxide, polyethylene derivatives, alkylene oxide derivatives, phosphate ester polymers, polyetiation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, or polymers containing ionic dissociation groups. Alternatively, the solid polymer electrolyte may be a polymer resin, which may include branched copolymers, comb-like polymers, and crosslinked polymer resins obtained by copolymerizing an amorphous polymer such as polymethyl methacrylate (PMMA), polycarbonate, polysiloxane, and / or phosphazene with a PEO (polyethylene oxide) main chain as a copolymer.

[0091] The polymer gel electrolyte comprises an organic electrolyte containing a lithium salt and a polymer resin, wherein the organic electrolyte contains 60 to 400 parts by weight based on the weight of the polymer resin. The polymer applied to the gel electrolyte is not limited to specific components, but may include, for example, polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), etc.

[0092] In the negative electrode for the all-solid-state battery, lithium plating occurs on the lithium-affinity material dispersed in the coating layer, and the ion transfer layer can block the passage of lithium aggregated by the lithium plating. Therefore, the growth of plated lithium can only occur between the ion transfer layer and the coating layer.

[0093] In one specific example, the electrode assembly may be a mono-cell containing one positive electrode and one negative electrode. The negative electrode comprises a coating layer containing the lithium-affinity material and an ion transfer layer containing amorphous carbon. Considering the objective of preventing lithium dendrites from growing towards the positive electrode, in the negative electrode for the all-solid-state battery, the coating layer and the ion transfer layer may be formed only on the first of the two rectangular outer surfaces of the negative electrode current collector, and the positive electrode may be placed on the first surface.

[0094] As described above, a negative electrode in which a coating layer and an ion transfer layer are formed only on the first surface of the negative electrode is also applicable to a C-type bi-cell in which negative electrodes are placed on each of the two sides of the positive electrode, and the first surface of the negative electrode can be positioned facing the positive electrode.

[0095] In another specific example, the electrode assembly may be a type A bicell in which positive electrodes are placed on each of the two sides of the negative electrode. The negative electrode comprises a coating layer containing the lithium-affinity material and an ion transfer layer containing amorphous carbon, and in consideration of the purpose of preventing lithium dendrites from growing on the positive electrode side, the negative electrode for the all-solid-state battery may have a coating layer and an ion transfer layer formed on each of the first and second rectangular outer surfaces of the negative electrode current collector, and a first positive electrode and a second positive electrode may be placed on each of the first and second surfaces. [Examples]

[0096] The following description will be based on examples of the present invention, provided for a more easily understandable context, and without limiting the scope of the invention.

[0097] <Example 1> To manufacture positive electrodes for all-solid-state batteries, LiNi is used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 A positive electrode slurry was prepared by dispersing O2, argyrodite (Li6PS5Cl) as a solid electrolyte, furnace black as a conductive material, and polytetrafluoroethylene as a binder in a weight ratio of 77.5:19.5:1.5:1.5 in anisole and stirring. The positive electrode slurry was then applied to an aluminum current collector with a thickness of 14 μm using a doctor blade, and the positive electrode was manufactured by vacuum drying at 100°C for 12 hours.

[0098] To produce the solid electrolyte layer, a solid electrolyte layer slurry was prepared by dispersing argyrodite (Li6PS5Cl) as the solid electrolyte and polytetrafluoroethylene as the binder in a weight ratio of 95:5 in anisole and stirring. This slurry was then coated onto a polyethylene terephthalate release film, and the solid electrolyte layer was produced by vacuum drying at 100°C for 12 hours.

[0099] To manufacture a negative electrode for an all-solid-state battery, including a coating layer and an ion transfer layer, a coating layer consisting of Ag was formed by sputtering Ag onto a 10 μm thick nickel current collector at a size of 30 nm. Subsequently, an ion transfer layer was formed by coating the Ag layer with a slurry of acetylene black and polyvinylidene fluoride mixed in a weight ratio of 97:3, and then drying to manufacture a negative electrode with a multilayer structure.

[0100] A lithium secondary battery was manufactured by sequentially stacking the positive electrode, solid electrolyte layer, and negative electrode.

[0101] <Example 2> A lithium secondary battery was manufactured using the same method as in Example 1, except that furnace black was used instead of acetylene black to manufacture the ion transfer layer.

[0102] <Comparative Example 1> A lithium secondary battery was manufactured using the same method as in Example 1, except that a nickel current collector was used alone as the negative electrode, without including a coating layer or an ion transfer layer.

[0103] <Comparative Example 2> A lithium secondary battery was manufactured using the same method as in Example 1, except that, as the negative electrode, Ag was sputtered onto a nickel current collector at a size of 30 nm to form only a coating layer.

[0104] <Comparative Example 3> A lithium secondary battery was manufactured using the same method as in Example 1, except that, as the negative electrode, a slurry of furnace black and polyvinylidene fluoride mixed in a 97:3 weight ratio was coated onto a nickel current collector to form only an ion transfer layer.

[0105] <Comparative Example 4> A lithium secondary battery was manufactured using the same method as in Example 1, except that, as the negative electrode, a slurry of synthetic graphite and polyvinylidene fluoride mixed in a weight ratio of 97:3 was coated onto a nickel current collector to form only an ion transfer layer.

[0106] <Comparative Example 5> A lithium secondary battery was manufactured using the same method as in Example 1, except that natural graphite was used to manufacture the ion transport layer.

[0107] <Comparative Example 6> A lithium secondary battery was manufactured using the same method as in Example 1, except that artificial graphite was used to manufacture the ion transport layer.

[0108] <Comparative Example 7> A battery was manufactured using the same method as in Example 1, except that a mixture of furnace black and Ag in a weight ratio of 3:1 was prepared as the negative electrode, and a mixed layer consisting of the mixture and polyvinylidene fluoride in a weight ratio of 97:3 was formed on a nickel current collector.

[0109] <Comparative Example 8> A battery was manufactured using the same method as in Example 2, except that an ion transfer layer manufactured in Example 2 was formed on a nickel current collector as the negative electrode, and a coating layer was formed on the ion transfer layer.

[0110] <Experimental Example 1> The batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 8 were charged at 0.05C in constant current-constant voltage mode to 4.25V at 60°C, and discharged at 0.05C to 3.0V to measure their initial charge / discharge capacity and efficiency. The measured charge capacity, discharge capacity, charge / discharge efficiency, and short-circuit rate are shown in Table 1 below.

[0111] [Table 1]

[0112] Referring to Table 1 above, the charge and discharge efficiencies of all lithium secondary batteries manufactured in each example and comparative example were measured at similar levels, with the exception of Comparative Example 1.

[0113] In Comparative Example 1, where only the negative electrode current collector was used as the negative electrode, the nucleation potential was high, making it difficult to suppress the growth of lithium dendrites. As a result, the charge-discharge efficiency was low, and the short-circuit rate was also the highest.

[0114] In Comparative Example 2, where only a coating layer is formed on the negative electrode current collector, and in Comparative Example 3, where only an ion transfer layer is formed on the negative electrode current collector, it can be confirmed that the short-circuit occurrence rate is significantly reduced compared to Comparative Example 1.

[0115] Comparative Examples 4, 5, and 6, which use crystalline carbon, exhibit a very high rate of short-circuit occurrence.

[0116] As in Examples 1 and 2, when a coating layer and an ion transfer layer are sequentially formed on the current collector, the nucleation potential can be reduced, and lithium dendrites cannot grow through the ion transfer layer, thus preventing short circuits.

[0117] In Comparative Example 7, where the ion transfer layer and the coating layer were mixed, the short-circuit occurrence rate was low. However, referring to Experimental Example 2 below, it can be confirmed that there are problems with the number of charge-discharge cycles.

[0118] In Comparative Example 8, where an ion transfer layer is formed on the current collector and a coating layer is formed on the ion transfer layer, the short-circuit rate is still measured to be high, which is considered to be due to lithium being deposited on the surface of the ion transfer layer and / or on the coating layer.

[0119] Thus, when a negative electrode using amorphous carbon in the ion transfer layer is included, it is possible to manufacture lithium secondary batteries with improved safety.

[0120] <Experimental Example 2> To evaluate the life characteristics of each battery manufactured in Example 1, Example 2, and Comparative Examples 1 to 8, charging and discharging were performed under conditions of 0.1C charging / 0.1C discharging in a voltage range of 4.2V to 3.7V.

[0121] Charging and discharging were performed until a short circuit occurred, and Table 2 below shows the number of cycles and capacity retention rate up to just before the short circuit occurred.

[0122] [Table 2]

[0123] Referring to Table 2 above, in Examples 1 and 2, no short circuits occurred until 400 charge-discharge cycles were performed.

[0124] Compared to Comparative Example 1, Comparative Example 2, which has a coating layer, and Comparative Example 3, which has an ion transfer layer, show an increase in the number of charge / discharge cycles and an improvement in lifespan characteristics. However, compared to Examples 1 and 2, they still show a low capacity retention rate.

[0125] Comparative Examples 4, 5, and 6, which use crystalline carbon, exhibit a very low number of charge-discharge cycles.

[0126] In Comparative Example 7, which uses a mixed layer in which the ion transfer layer and the coating layer are mixed, the capacity retention rate was improved compared to Comparative Examples 2 and 3. In Comparative Example 8, which has the current collector, ion transfer layer, and coating layer formed in that order, the short-circuit occurrence was delayed compared to Comparative Example 3. However, it can be seen that the batteries of Examples 1 and 2 have improved lifespan characteristics by more than twice as much as the battery of Comparative Example 7 and by more than eight times as much as the battery of Comparative Example 8.

[0127] Comparative Examples 5 and 6, which differ only in that crystalline graphite is used in the ion transfer layer, not only show a significantly lower number of charge-discharge cycles but also exhibit a capacity retention rate of 70% to 80%, while Examples 1 and 2, which use amorphous carbon in the ion transfer layer, show a capacity retention rate of over 80% even after 400 charge-discharge cycles.

[0128] Therefore, it can be confirmed that the cycle characteristics are improved when amorphous carbon is included in the ion transport layer.

[0129] SEM images of the negative electrodes manufactured in Example 2, Comparative Examples 1 to 3, and Comparative Examples 6 to 8 are shown in Figures 2 to 9. Figure 2 is an SEM image of the negative electrode manufactured in Example 2, and Figure 3 is an SEM image of the cross-section of the negative electrode manufactured in Example 2. Figures 4, 5, and 6 are SEM images of the negative electrodes manufactured in Comparative Examples 1, 2, and 3, respectively, and Figure 7 is an SEM image of the cross-section of the negative electrode manufactured in Comparative Example 6. Figures 8 and 9 are SEM images of the negative electrodes manufactured in Comparative Examples 7 and 8, respectively.

[0130] Referring to Figures 2 to 9, the negative electrodes in Figure 2 (Example 2) and Figure 6 (Comparative Example 3) have an ion transfer layer formed on their surface. Since many pores are formed inside the ion transfer layer, it can be seen that lithium ions are in a form that allows them to move towards the negative electrode. In the case of Example 2, the distribution range of lithium ions in the coating layer is wide, which lowers the nucleation potential. Therefore, lithium nuclei are less likely to be formed by lithium ions that pass through the ion transfer layer, and even if lithium nuclei are formed, they cannot grow to the extent that they penetrate the ion transfer layer. Thus, it can be interpreted that a short-circuit rate of 0% was observed.

[0131] However, in the case of Comparative Example 3 (Figure 6), which does not include a coating layer, the nucleation potential is high and localized lithium nucleus growth occurs, resulting in a lower lifetime characteristic than that of Comparative Example 2 (Figure 5).

[0132] In Figure 4 (Comparative Example 1), the negative electrode is the surface of a nickel current collector, while in Figures 5 (Comparative Example 2) and 9 (Comparative Example 8), a coating layer is formed on the surface of the negative electrode. As can be seen from the experimental results, in the case of Comparative Example 8, the short-circuit occurrence rate is higher and the lifespan characteristics are worse than in Comparative Example 2.

[0133] In Figure 8 (Comparative Example 7), the negative electrode has a mixed layer formed on its surface, resulting in a short-circuit rate of 0%. However, the negative electrode in Figure 8 (Comparative Example 7) exhibits inferior lifespan characteristics compared to Examples 1 and 2, in which an ion transfer layer was formed on the coating layer.

[0134] Figure 3 is an SEM image of the cross-section of the negative electrode manufactured in Example 2, and Figure 7 is an SEM image of the cross-section of the negative electrode manufactured in Comparative Example 6.

[0135] Referring to Figure 3, it can be confirmed that in Example 2, lithium was electrodeposited on one side of the negative electrode current collector (Ni foil) in the ion transfer layer containing furnace black.

[0136] Referring to Figure 7, it can be confirmed that in Comparative Example 6, lithium was electrodeposited on one side of the ion transfer layer containing artificial graphite, opposite to the side facing the negative electrode current collector (Ni foil).

[0137] In other words, when crystalline graphite, such as artificial graphite, is included in the ion transport layer, lithium electrodeposition occurs on the outer surface of the ion transport layer facing the positive electrode. Consequently, lithium dendrites grow and can penetrate the solid electrolyte layer and come into contact with the positive electrode, resulting in a short circuit occurring after a short number of charge-discharge cycles.

[0138] On the other hand, when an ion transfer layer containing amorphous carbon such as furnace black is included, lithium electrodeposition is performed only on the outer surface of the ion transfer layer in the direction of the negative electrode current collector, thereby ensuring high cycle characteristics and capacity retention, and as a result, a lithium secondary battery with improved performance can be provided.

[0139] Anyone with ordinary skill in the field to which this invention belongs will be able to make various applications and modifications within the scope of this invention based on the above-described content. [Industrial applicability]

[0140] The present invention relates to a negative electrode for an all-solid-state battery including a coating layer and an ion transfer layer, and a lithium secondary battery including the same. Specifically, it relates to a technology that can prevent localized lithium plating on the negative electrode and prevent short circuits between the positive and negative electrodes by specifying the lithium electrodeposition position, and is therefore industrially applicable.

Claims

1. A negative electrode for an all-solid-state battery, A negative electrode current collector made of an electrically conductive metal material; A coating layer containing a lithium-affinity material is added to one or both sides of the negative electrode current collector; An ion transfer layer located on the coating layer and containing amorphous carbon on which lithium ions can move; Includes, The lithium-affinity material is Ag, A negative electrode for an all-solid-state battery, wherein the negative electrode current collector is partially exposed on the surface to which the coating layer is applied.

2. The negative electrode for an all-solid-state battery according to claim 1, wherein the ion transfer layer further comprises a binder.

3. The negative electrode for an all-solid-state battery according to claim 1 or 2, wherein a negative electrode mixture layer is not formed on the negative electrode current collector.

4. The negative electrode for an all-solid-state battery according to any one of claims 1 to 3, wherein the coating layer is distributed in a range of 10% to 90% based on the total area of ​​the negative electrode current collector.

5. A lithium secondary battery comprising a negative electrode, a solid electrolyte layer, and a positive electrode for an all-solid-state battery according to any one of claims 1 to 4.

6. The negative electrode for the all-solid-state battery has the lithium-affinity material dispersed in the coating layer. The lithium secondary battery according to claim 5, wherein lithium plating occurs on the lithium-affinity material.

7. The lithium secondary battery according to claim 5 or 6, wherein lithium electrodeposition is performed on one surface of the ion transfer layer facing the negative electrode current collector.

8. In the negative electrode for the all-solid-state battery, the coating layer and the ion transfer layer are formed only on the first surface of the negative electrode current collector, of which two surfaces are the first surface. A lithium secondary battery according to any one of claims 5 to 7, comprising a monocell in which a positive electrode is disposed on the first surface.

9. The lithium secondary battery according to claim 8, wherein the coating layer is formed on the negative electrode current collector and the ion transfer layer is formed on the coating layer.

10. The negative electrode for the all-solid-state battery has the coating layer and the ion transfer layer formed on the first and second surfaces of the negative electrode current collector, respectively. A lithium secondary battery according to any one of claims 5 to 7, comprising a bicell in which a first positive electrode and a second positive electrode are arranged on the first surface and the second surface, respectively.

11. The lithium secondary battery according to claim 10, wherein the coating layer is formed on the negative electrode current collector and the ion transfer layer is formed on the coating layer.

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