Negative electrode for lithium metal batteries

Abstract

The present invention relates to a negative electrode for a lithium metal battery, comprising a substrate and a porous layer on the substrate, wherein the porous layer contains metal powder, and the porous layer has a porosity of 30% or more as determined by reference XRM analysis before lithium metal electrodeposition or during complete discharge.

Description

[Technical Field]

[0001] This invention relates to a negative electrode for lithium metal batteries. [Background technology]

[0002] Lithium is not only the lightest metal, but it also has a low reduction potential (-3.04V vs. SHE) and a large theoretical capacity (3860mAh / g), which is why lithium metal batteries that use lithium metal itself as the negative electrode active material are being developed.

[0003] In the case of lithium secondary batteries that use the above-mentioned lithium metal as electrodes, thin lithium metal electrodes are necessary to maximize the battery's efficiency and energy density. However, conventional lithium foil is manufactured by a physical rolling method, and this rolling method has limitations in producing lithium foil with a thickness below a certain level.

[0004] Recently, research on electrodeless batteries has also been progressing actively. Electrodeless batteries use a negative electrode that does not contain lithium metal negative electrode active material (layer) during battery manufacturing. During charging, lithium ions are reduced, and lithium is electrodeposited onto the surface of the negative electrode current collector, forming a lithium metal plating film.

[0005] However, the lithium layer formed on the negative electrode current collector has a low electrodeposition density and undergoes vigorous side reactions with the electrolyte, resulting in a rapid deterioration of the battery's lifespan. Furthermore, the negative electrode of a non-negative electrode battery has problems such as uneven lithium electrodeposition and dendrite growth during charging, and significant volume changes in the electrode during charging and discharging, among other issues that need to be resolved in terms of battery performance and stability.

[0006] On the other hand, various methods have been attempted to improve the uniformity of lithium electrodeposition, thereby increasing electrodeposition efficiency and suppressing dendrite growth. These methods include coating the surface of the plate-shaped negative electrode current collector with a lithiophilic metal (such as silver (Ag)), a carbon material such as carbon black, or a mixture of a lithiophilic metal like silver and a carbon material, or by utilizing a three-dimensional structure.

[0007] However, the resulting coating layer has limitations, such as high resistance or low charge / discharge efficiency, and is therefore considered to have low economic viability and practical application potential. [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, as one embodiment, the present invention provides a negative electrode for a lithium metal battery that can induce uniform deposition of lithium and suppress the growth of lithium dendrites.

[0009] Furthermore, as one embodiment, the present invention provides a negative electrode in which the volume change of the electrode during charging and discharging is suppressed, thereby improving the stability of the battery.

[0010] Furthermore, in one embodiment, the present invention improves the electrochemical properties of a lithium metal battery by using the negative electrode described above. [Means for solving the problem]

[0011] The present invention provides, in principle, a negative electrode for a lithium metal battery, and in one embodiment, the negative electrode comprises a substrate and a porous layer on the substrate, the porous layer comprises metal powder, and the porous layer can have a porosity of 30% or more as determined by reference XRM analysis before lithium metal electrodeposition or at complete discharge.

[0012] The above porous layer may have a porosity of 30% to 95% based on standard XRM analysis before lithium metal electrodeposition or during complete discharge.

[0013] The above porous layer may have a standard closed porosity of 0.05% or less before lithium metal electrodeposition or during complete discharge.

[0014] The porous layer described above can have a thickness of 0.5 to 100 μm.

[0015] The above metal powder may include at least one metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, Bi, Cu, Ge, Al, Pb, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru, an oxide of the above metal, or an alloy of the above metal.

[0016] The above porous layer is made of graphitic carbon nitride, phosphorus-doped graphitic carbon nitride (phospho ru The material may further include at least one carbon material selected from the group consisting of s-doped graphitic carbon nitride and boron-doped graphitic carbon nitride.

[0017] The porous layer described above may further contain at least one conductive polymer selected from the group consisting of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)), PANI (poly aniline), PPy (poly pyrrole), PT (polythiophene), PA (polyacetylene), and PPV (polyp-phenylene vinyl).

[0018] The porous layer described above may further contain a binder.

[0019] The above binder may be a fluorine-containing binder.

[0020] The above binder can include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE ) and and fluororubber.

[0021] The above metal powder can be particles having an aspect ratio greater than 1.

[0022] The above metal powder can have a major axis length of 1 to 100 μm.

[0023] The above metal powder can be rod-shaped particles.

[0024] The above metal powder can be rod-shaped particles having one or more inflection points where the traveling direction changes from one end to the other end.

[0025] The bending angle β at which the traveling direction changes at the above inflection point can be 5° or more and 90° or less.

[0026] The above metal powder can have two or more branches.

[0027] The above metal powder can have a main branch and at least one side branch connected to the main branch.

[0028] The above porous layer includes a first layer on the substrate surface side and a second layer on the outer surface side of the porous layer. The metal powder of the above first layer can have a smaller particle size than the metal powder of the second layer.

[0029] Lithium metal can be electrodeposited in the pores of the above porous layer.

[0030] The above substrate can be a current collector.

Advantages of the Invention

[0031] The negative electrode for lithium metal batteries according to the present invention can store lithium metal in the pores of a porous layer formed on the surface of the substrate, thereby improving the contact surface area between the lithium metal and the current collector and improving the electrochemical properties.

[0032] Furthermore, because the negative electrode for lithium metal batteries according to the present invention has a high specific surface area, it is possible to reduce the local current density of the negative electrode, thereby providing uniform electron distribution within the electrode.

[0033] Furthermore, the negative electrode for lithium metal batteries according to the present invention can improve battery stability by preventing the formation and growth of lithium dendrites during charging and discharging.

[0034] Furthermore, the negative electrode for lithium metal batteries according to the present invention can provide sufficient space for lithium deposition during battery charging and discharging, thereby suppressing volume expansion of the battery. [Brief explanation of the drawing]

[0035] [Figure 1] These diagrams conceptually show cross-sections of the charging and discharging states of a non-negative electrode battery. (a) shows a cross-section of the negative electrode in the discharged state, and (b) shows a conceptual cross-section of the negative electrode in the charging state. [Figure 2] This is a schematic diagram showing an example of a rod-shaped metal powder according to the present invention. [Figure 3] This diagram schematically shows an example of a rod-shaped metal powder having one or more inflection points. [Figure 4] This diagram schematically shows an example of a metal powder having two or more branches. [Figure 5] This is a diagram illustrating a cross-section of a metal powder having through holes. [Figure 6] This diagram illustrates the cross-sections of a negative electrode in the discharge and charge states, where a porous layer of metal powder is formed on the surface of the negative electrode current collector. (a) shows the negative electrode in the discharge state, and (b) shows the negative electrode in the charge state. [Figure 7] These are photographs of the metal powders used as negative electrodes in Examples 1 to 4. [Figure 8] This is a photograph of the cross-section of the negative electrode in Example 1, and a magnified photograph of a part thereof. [Figure 9] This is a photograph illustrating the internal pore structure of the porous layer of the negative electrode in the discharge state of Example 1. [Figure 10] These are photographs of the cross-section of the negative electrode in the charged state in Example 1, and a magnified view of a part of it. [Figure 11] These are photographs of the cross-sections of the negative electrodes in the charged state of Comparative Examples 1 and 2, where (a) is the negative electrode of Comparative Example 1 and (b) is the negative electrode of Comparative Example 2. [Figure 12] This graph shows the change in specific capacity with respect to the number of cycles of batteries using the negative electrodes of Example 1, Comparative Example 1, and Comparative Example 3. [Figure 13] This graph shows the change in specific capacity with respect to the number of cycles of batteries using the negative electrodes of Examples 2 to 4. [Modes for carrying out the invention]

[0036] The present invention relates to a negative electrode for lithium metal batteries, and more specifically, provides a negative electrode that includes a porous layer of metal powder on the surface of a substrate.

[0037] In this specification, a lithium metal battery is a battery that uses lithium metal as the negative electrode active material, and among these, a battery that does not preemptively contain lithium metal in the negative electrode current collector is called a negative electrode-free battery. Figure 1 schematically shows the cross-sections of the negative electrode and the negative electrode during charging of such a negative electrode-free battery. Figure 1(a) shows a cross-section of the negative electrode 10 of the negative electrode-free battery, and (b) shows a cross-section of the charged negative electrode 10'. As shown in Figure 1(a), a plate-like body of a conductive metal such as copper is used as the base material, i.e., the negative electrode current collector 11, and during the charging process, lithium metal is electrodeposited onto the negative electrode current collector 11 to form a lithium layer 13 as shown in Figure 1(b). In such a negative electrode-free battery, the non-uniform deposition of the lithium layer on the negative electrode current collector causes non-uniformity of electron density, which allows lithium dendrites to be formed.

[0038] The present invention provides a negative electrode for lithium metal batteries, and more specifically, a negative electrode applicable to non-negative batteries. A negative electrode for lithium metal batteries according to one embodiment of the present invention includes a substrate and a porous layer on the substrate, wherein the porous layer can have a porosity of 30% or more as determined by XRM analysis, based on the state before lithium metal electrodeposition or at the time of complete discharge. Hereinafter, the porous layer will also be referred to as a porous storage layer or a porous coating layer.

[0039] The negative electrode of the present invention will be described in more detail below.

[0040] A negative electrode according to one embodiment of the present invention comprises a substrate and a high i ratio It includes a porous layer with a large surface area. The porous layer may be formed directly on the substrate, and other layers may be further included between the porous layer and the substrate.

[0041] The aforementioned substrate can function as a current collector, specifically a negative electrode current collector, and any substrate that can normally be used as a negative electrode current collector can be suitable as the above substrate. For example, the above substrate can be used without particular limitations as long as it does not induce chemical changes during battery operation and is conductive. Examples include metals such as copper, stainless steel, aluminum, nickel, and titanium, or alloys containing at least one of the above metals, such as aluminum-cadmium alloy, or calcined carbon. A substrate with a metal surface such as copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., can be used as a negative electrode current collector. Furthermore, a polymer coated with a conductive metal or a conductive polymer can also be used as the substrate of the present invention.

[0042] Furthermore, the above-mentioned substrate can take various forms, such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0043] The thickness of the above substrate is not particularly limited and can be, for example, 1 to 100 μm. More specifically, the substrate can be 3 to 50 μm or 4 to 30 μm, and more specifically, 4 to 12 μm.

[0044] As described above, the negative electrode of the present invention includes a porous layer on the surface of the substrate, for example, one or both sides of the substrate. The porous layer can be formed using metal powder.

[0045] The above metal powder can consist of particles with an aspect ratio greater than 1, which is the ratio of the horizontal length to the vertical length or the ratio of the major axis length to the minor axis length, and can have an aspect ratio greater than 1 and less than or equal to 100. For example, the above metal powder can consist of particles with an aspect ratio greater than 1, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, or 7 or more, and less than or equal to 100, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, 30 or less, 20 or less, or 10 or less.

[0046] By having a particle shape with an aspect ratio greater than 1 and a length that is long in one direction, it is possible to provide a porous layer with developed pores on the negative electrode current collector of the present invention. For example, by forming a porous coating layer using the above-described metal powder particles, the metal powder can come into contact in various forms and provide pores to the porous coating layer.

[0047] The above metal powder is not particularly limited, but for example, its major axis length can be 1 to 100 μm. The above metal powder can be, for example, rod-shaped particles. Some examples of rod-shaped metal powder are shown illustratively in Figure 2.

[0048] As shown in Figure 2(a), the rod-shaped metal powder 20 has a linear outer shape, and the cross-sectional diameter and cross-sectional shape of the metal powder particles can be constant.

[0049] The above rod-shaped metal powder can have a change in cross-sectional diameter. For example, as shown in Figure 2(b), the diameter of the cross-section of the above rod-shaped metal powder can decrease regularly or irregularly in one direction, and as a specific example, Figure 2( d The above rod-shaped metal powder can have a needle-like shape as shown in Figure 2. c As shown in the drawing, the diameter of the cross-section can decrease regularly or irregularly in both directions, or, although not shown in the drawing, the diameter of the cross-section can increase regularly or irregularly in both directions.

[0050] In another embodiment, the rod-shaped metal powder may contain one or more inflection points where the direction of travel from one end to the other changes. An example of a rod-shaped metal powder having such inflection points is shown illustratively in Figure 3.

[0051] As shown in Figure 3(a), the rod-shaped metal powder may have a uniform diameter and shape in its cross-section, but its direction of travel from one end to the other changes one or more times, resulting in one or more inflection points P. Alternatively, as shown in Figure 3(b), it may have one or more inflection points while its cross-sectional diameter and / or shape changes.

[0052] The metal powder having the above-mentioned inflection point will be explained in more detail with reference to Figure 3(a). Each embodiment described with reference to Figure 3(a) can also be applied to the metal powder in Figure 3(b).

[0053] As shown in Figure 3(a), one end of the rod-shaped metal powder is designated as P0, and the other end as P n When n is a natural number greater than or equal to 2, the above rod-shaped metal powder is from P0 to P n It can include one or more inflection points P where the direction of propagation changes as it moves toward the target. When the above rod-shaped metal powder has one or more inflection points and forms a coating layer on the substrate, between the metal powder tiny Pores can be formed, and the number of pores formed within the coating layer can be increased. kill .

[0054] In the above rod-shaped metal powder, including both ends, the inflection points are numbered P0, P1, P2, P3...P n In this case, the distance between any one inflection point and adjacent inflection points, for example, the distance L1 between P0 and P1 and the distance L2 between P1 and P2, or P n-1 and P n Distance L n They may be the same, or they may be different.

[0055] As described above, the direction of travel of the rod-shaped metal powder can be changed from one end to the other with respect to one adjacent inflection point, and in this case, the direction of travel can be changed by a predetermined angle. Specifically, between two adjacent line segments with respect to one inflection point, the direction of travel can be changed by an acute angle of 90° or less than 90°, which is the angle (bending angle) formed by the two lines containing each line segment.

[0056] For example, as shown in Figure 3(a), a rod-shaped metal powder containing a line segment traveling from P0 to P1 may have its direction of travel changed by the bending angle at the inflection point of P1, and may include a line segment traveling in the direction containing the line segment from P1 to P2. In this case, the bending angle between the line segments P0-P1 and P1-P2 can be β.

[0057] Although not shown in the drawings, even when the direction of travel changes in a curved form, it can be considered to include one or more inflection points of the present invention. Therefore, in the present invention, the rod-shaped metal powder may be a straight rod or a curved rod.

[0058] The bending angle β contained in the above-mentioned rod-shaped metal powder is not limited to this, but can be 5° or more and 90° or less, more specifically it can be 5° or more, 10° or more, 15° or more, 20° or more, 25° or more, or 30° or more, and can be 90° or less, 85° or less, 80° or less, or 75° or less.

[0059] In another embodiment, the rod-shaped metal powder may or may not have a virtual plane that includes two adjacent line segments sharing one inflection point and the angle between the two line segments, and another virtual plane adjacent to the first virtual plane.

[0060] For example, as shown in Figure 3(a), in a rod-shaped metal powder 20, the line segments P0-P1 and P1-P2, which are adjacent to each other while sharing an inflection point P1, and the virtual plane P0-P1-P2 containing the angle α between the two line segments, and the virtual plane P1-P2-P3 adjacent to the virtual plane P0-P1-P2, do not have to be parallel to each other, and although not shown, the two planes may be parallel to each other.

[0061] In other embodiments, the metal powder may have two or more branches. For example, it may be a branch-shaped metal powder with one main branch and at least one lateral branch connected to the main branch. For example, the main branch may be a rod-shaped metal powder as shown in Figures 2(a) to 2(d) or a rod-shaped metal powder having an inflection point as shown in Figure 3(a) or 3(b), with one or more lateral branches formed on the main branch. In this case, the lateral branches may also be rod-shaped metal powders as described above.

[0062] More specifically, as shown in Figures 4(a) and 4(b), the metal powder can be dendritic in shape, having one or more lateral branches 24 on a single main branch 22, or, as shown in Figure 4(c), it can be a protruding metal powder in which one or more lateral branches smaller in diameter than the main branch are formed on a single main branch.

[0063] The metal powder may have one or more through holes 26 inside, as shown in Figures 5(a) and 5(b). These one or more through holes may be formed in the main branch of the metal powder, or in the side branches. At least one of the through holes may be open and connected to the outside. The location where the through hole is opened is not particularly limited and may be, for example, at the end of the main branch and / or side branches.

[0064] As shown in Figure 5, the diameter of the through hole can vary and is not particularly limited.

[0065] The above-mentioned metal powder may be a metal powder containing a metal that has the property of allowing lithium metal to be electrodeposited onto its surface. The metal contained in the above-mentioned metal powder is not particularly limited.

[0066] In one embodiment, the metal powder may include a metal, an oxide of the metal, or an alloy of the metal, and the metal may be a lithium-affinity metal or a non-lithium-affinity metal. The lithium-affinity metal may be at least one of the lithium-affinity metals such as Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi, and the non-lithium-affinity metal may be at least one selected from the group consisting of Cu, Ge, Al, Pb, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru. By forming a porous layer with a metal powder containing such a metal, metal oxide, or metal alloy, uniform electrodeposition of lithium can be induced within the porous layer, the formation and growth of lithium dendrites can be suppressed, and furthermore, the electrodeposition density of lithium can be increased, contributing to extending the lifespan of the negative electrode.

[0067] The above metal powder may further contain carbon materials or polymers. For example, the above metal powder may be a mixture of the above-mentioned metal, metal oxide, or metal alloy; and the above carbon material or polymer, formed into a metal powder.

[0068] Examples of carbon materials that can be included in the above metal powder include natural graphite, artificial graphite, hard carbon, soft carbon, carbon black, carbon nanotubes, Ketjenblack, acetylene black, fullerene, carbon fiber, fluorinated carbon, or carbon nitrides. Examples of the above carbon nitrides include graphitic carbon nitride and phosphorus-doped graphitic carbon nitride. ruIt can be at least one carbon material selected from the group consisting of s-doped graphitic carbon nitride and boron-doped graphitic carbon nitride.

[0069] Furthermore, the above polymer can be a conductive polymer, and specifically, it can be at least one conductive polymer selected from the group consisting of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)), PANI (poly aniline), PPy (Poly pyrrole), PT (Polythiophene), PA (Polyacetylene), and PPV (Polyp-phenylene Vinylene).

[0070] Furthermore, the above-mentioned metal powder may include, but is not limited to, at least one selected from the group consisting of polyimide (PI), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyetherimide (PEI).

[0071] The metal powder contained in the porous layer on the negative electrode current collector can be manufactured in a predetermined shape through a spontaneous substitution reaction. Specifically, the metal powder can be manufactured using a spontaneous substitution reaction step that utilizes the difference in reducing power of the metals and a reaction activation step that uses hydrogen bubbles generated in an electrolyte containing chloride ions, etc. This method allows for the manufacture of metal powder with a high specific surface area in a short time through a simple process.

[0072] The above spontaneous substitution reaction is theoretically well-established, and the conditions for carrying out the spontaneous substitution reaction can be easily selected; therefore, it will not be explained in detail here. For example, the reaction rate of the above spontaneous substitution reaction can be adjusted by adjusting the concentration of metal ions contained in the electrolyte.

[0073] Specifically, by using multiple metal powders as described above, a negative electrode can be provided that includes a coating layer on the surface of a substrate which may be a negative electrode current collector. The porous layer formed on the surface of the substrate as described above using the metal powder has high properties. ratio Depending on the surface area, it can be a porous layer with well-developed pores containing a large number of air pockets.

[0074] During the charging process of a battery containing the porous layer provided above, the negative electrode can provide sufficient space for lithium deposition, and the negative electrode according to one embodiment of the present invention can suppress the volume expansion of the battery. Furthermore, according to other embodiments, the negative electrode containing the porous layer can develop pores that allow for uniform deposition of lithium metal, and can suppress the formation and growth of lithium dendrites during charging and discharging. It can also contribute to increasing the lithium electrodeposition density and extending the lifespan of the negative electrode.

[0075] In the present invention, an example of a porous layer formed by the above-mentioned metal powder is schematically shown in Figure 6(a). Figure 6(a) schematically shows a cross-section of a negative electrode 10 including a porous layer 41 formed using the dendrite-shaped metal powder shown in Figure 4(a). As shown in Figure 6(a), a porous layer can be formed in which pores have developed by randomly arranging the metal powders. The pores within the porous layer can be connected to each other to form a three-dimensional pore network.

[0076] By forming a porous layer with such a three-dimensional pore network on the substrate surface, lithium ions that have moved from the positive electrode during the charging process can move into the coating layer through the pores of the porous layer, and lithium metal can be electrodeposited inside the pores.

[0077] Figure 6(b) is a conceptual diagram showing a charged negative electrode 10' which includes a charged porous layer 43 in which lithium metal 13 is electrodeposited inside the pores of the porous layer in Figure 6(a) by charging.

[0078] The porous layer formed from the metal powder in this manner contains a large number of pores, providing a storage space for lithium metal. This prevents uneven electrodeposition of lithium during the charging process, improves the contact surface area between lithium and the negative electrode current collector, and enhances electrochemical properties. Furthermore, since lithium is electrodeposited within the porous layer, volume changes in the negative electrode due to lithium electrodeposition and desorption can be prevented, maintaining the performance of the negative electrode and the stability of the battery.

[0079] The porous layer according to the present invention may be a single layer or a multilayer of two or more layers. For example, as shown in Figure 6(a), a single layer can be formed using metal powder. Alternatively, a multilayer can be formed using two or more metal powders with different particle shapes and particle sizes. For example, the porous layer may include a first layer located on the surface side of the substrate provided as a negative electrode current collector and a second layer located on the outer surface side of the porous layer, wherein the metal powder contained in the first layer may have a smaller particle size than the metal powder located in the second layer. The porous layer may include a first coating layer having a small pore size using a first metal powder with a small particle size on the current collector side, and a second coating layer having a larger pore size using a second metal powder with a larger particle size than the first metal powder on the first coating layer.

[0080] The first layer of metal powder located on the negative electrode current collector side has a smaller particle size, which allows for the formation of smaller pores, thereby increasing the uniformity of lithium electrodeposition within the porous layer, improving electrodeposition efficiency, and suppressing dendrite growth.

[0081] While not limited to this, the thickness of the first layer in the above porous layer may be even greater than the thickness of the second layer.

[0082] The particle size of the above-mentioned metal powder can be determined by setting the outer boundary, which is determined by the main and side branches of a single metal powder, as the particle boundary, and using volume as the basis for determining the particle size.

[0083] The porous layer described above may include a binder together with the metal powder. For example, such a porous layer may be applied to the surface of a substrate provided as a negative electrode current collector. i ratio It can be manufactured by pasteuring metal powder with a surface area together with a binder and a solvent, casting this paste onto the surface of a substrate, and drying it.

[0084] The binder included in the manufacture of the paste described above is not particularly limited, and any binder commonly used in the manufacture of electrodes can be appropriately used in this invention. For example, the above binders include styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylonitrile-butadiene rubber, polybutadiene rubber (BR), acrylic rubber, butyl rubber, ethylene-propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol resin, acrylate resin, polyaniline (PANI), polythiophene (PT), polyacetylene, polypyrrole (PPy), PEDOT (poly(3,4-ethylene dioxythiophene)), polyvinylidene fluoride (PVdF), and vinylidene fluoride-hexafluoropropylene copolymer (Poly(vinylidene Fluoride-co-hexafluoropropylene, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE) )、 It may include at least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), polymethyl methacrylate, and fluororubber.

[0085] In one embodiment, the binder may be a styrene-butadiene rubber (SBR) binder, a carboxymethylcellulose (CMC) binder, a polyacrylic acid (polyacrylic acid) binder, a polyethylene dioxythiophene (poly(3,4-ethylenedioxythiophene), PEDOT) binder, or a fluorine-containing binder. More specifically, the above binder may be a fluorine-containing binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) ) and It can be at least one selected from the group consisting of fluororubber.

[0086] The above binder is not particularly limited, but can be included in an amount of 1 to 30% by weight relative to the solid content weight of the paste. If the binder content is less than 1% by weight, the adhesive strength of the porous layer may decrease, and if it exceeds 30% by weight, it may increase resistance and lead to a decrease in electrical conductivity, and further may reduce lithium deposition performance. More specifically, it can be 1% or more by weight, 1.2% or more by weight, 1.5% or more by weight, 2% or more by weight, or 3% or more by weight, and 30% or less by weight, 25% or less by weight, 20% or less by weight, 15% or less by weight, or 12% or less by weight.

[0087] On the other hand, the above solvent is not particularly limited, and solvents commonly used in electrode manufacturing can also be used in accordance with the present invention, for example, water, acetone, formic acid, chloroform, isopropanol, N-methylpyrrolidone (NMP), D It may include at least one selected from the group consisting of MF (Dimethylformamide), DMAc (dimethylacetamide), DMSO (dimethyl sulfoxide), and THF (Tetrahydrofuran).

[0088] The solvent is not particularly limited, but it can be included in the paste in a content of 30 to 60% by weight.

[0089] The method for applying the paste according to the present invention to the substrate surface is not particularly limited, and methods such as bar coating, casting, spraying, doctor bladeding, and specifically wet coating methods can be applied. The thickness of the porous layer can be easily controlled, for example, by adjusting the viscosity of the paste or the height of the doctor blade.

[0090] In this case, the thickness of the porous layer is not limited to this, but can be between 0.5 and 100 μm. Since the porous layer has the role of storing lithium metal, it can be formed with a thickness that allows for the minimum amount of lithium metal to be stored. In this respect, the porous layer can be 0.5 μm or more, 1 μm or more, 1.5 μm or more, 2 μm or more, 3 μm or more, or 5 μm or more.

[0091] On the other hand, if the porous layer is excessively thick, lithium ion transfer may not be smooth, potentially halving or making it difficult to secure the effects obtained by including the porous layer. Also, in other respects, if the porous layer is excessively thick, it may result in losses of energy density per unit volume and weight. In light of these respects, the porous layer of the present invention can be 100 μm or less, or 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, or 50 μm or less.

[0092] The porous layer obtained by the present invention, although not limited thereto, can have a porosity of 30% to 95% based on XRM (X-ray Microscope) analysis before lithium metal electrodeposition or during complete discharge. Specifically, the porous layer can have a porosity of 50% or more, 70% or more, 80% or more, or 85% or more. Furthermore, the porous layer according to the present invention can achieve such high porosity by having pores interconnected to form a porous layer.

[0093] The porous layer described above may have a closed porosity, which indicates the ratio of pores that are not interconnected, of 0.05% or less, or 0.03% or less, or 0.01% or less, or 0.0095% or less, based on the state before lithium metal electrodeposition or during complete discharge. In other words, the negative electrode according to the present invention has a highly developed porosity, and the pores are interconnected to form a three-dimensional pore network, thereby improving the insertion and extraction characteristics of lithium ions during charging and discharging.

[0094] Furthermore, the porous layer according to the present invention has a reference specific surface area of ​​300 m² before lithium metal electrodeposition or at complete discharge. 2 / m 3 This allows for a high specific surface area.

[0095] On the other hand, the porous layer according to the present invention is high i ratio Since pores are formed by metal powders with surface area, the porous layer can contain pores of various sizes. For example, the porous layer according to the present invention can contain pores ranging from nano-sized to meso-sized.

[0096] As described above, the porous layer formed on the negative electrode current collector can contain pores of various sizes, and therefore, lithium metal can be electrodeposited into the pores of the porous layer.

[0097] The negative electrode provided in this invention includes a porous layer on the surface of a substrate provided as a negative electrode current collector, and lithium is electrodeposited into the pores of the porous layer, thereby improving the electrodeposition density and thus improving battery life.

[0098] Furthermore, the stable electrodeposition of lithium within the pores suppresses the formation of lithium dendrites, improving the contact area between the lithium metal and the current collector. The high specific surface area reduces the local current density of the negative electrode, resulting in a more uniform electron distribution within the lithium electrode. This prevents the formation and growth of lithium dendrites during charging and discharging, thereby improving battery stability.

[0099] Furthermore, according to the present invention Negative electrode for lithium metal batteries When using this method, sufficient space can be provided for lithium deposition during battery charging and discharging, thereby suppressing the volume expansion of the battery. [Examples]

[0100] The present invention will be described in more detail below with reference to examples. However, the following examples are merely examples of the present invention and are not intended to limit it.

[0101] [Manufacturing of metal powders] Manufacturing Example 1 Sodium chloride (1.0 M) and hydrogen chloride (0.2 M) were added as reaction accelerators to an electrolyte solution at room temperature in which copper sulfate (CuSO4) (concentration: 0.1 M) had dissociated.

[0102] An aluminum plate (10cm x 8cm), which has a higher reducing power than the copper sulfate mentioned above, was placed in the electrolyte solution at room temperature, and the reaction was carried out for 20 minutes while generating hydrogen bubbles in the electrolyte solution.

[0103] Copper powder was produced by a spontaneous substitution reaction of copper due to the difference in reducing power between the above-mentioned aluminum plate and the copper in the electrolyte.

[0104] The manufactured copper powder was photographed and is shown in Figure 7(a). The size of the metal powder was measured using FESEM (Field Emission Scanning Electron Microscopy), and the results are shown in Table 1 below.

[0105] Manufacturing Example 2 manufacturing The copper powder was produced in the same manner as in Example 1, except that the reaction to generate copper powder in the electrolyte was carried out for 30 minutes instead of 20 minutes in Example 1.

[0106] The copper powder produced as described above was photographed and is shown in Figure 7(b). The size of the metal powder was measured using FESEM, and the results are shown in Table 1 below.

[0107] Manufacturing Example 3 manufacturing The copper powder was produced in the same manner as in Example 1, except that the reaction to generate copper powder in the electrolyte was carried out for 40 minutes instead of 20 minutes in Example 1.

[0108] The copper powder produced as described above was photographed and is shown in Figure 7(c). The size of the metal powder was measured using FESEM, and the results are shown in Table 1 below.

[0109] Manufacturing Example 4 manufacturing The copper powder was produced in the same manner as in Example 1, except that the reaction to generate copper powder in the electrolyte was carried out for 60 minutes instead of 30 minutes in Example 1.

[0110] The copper powder produced as described above was photographed and is shown in Figure 7(d). The size of the metal powder was measured using FESEM, and the results are shown in Table 1 below.

[0111] [Table 1]

[0112] Example 1 A paste was prepared by adding 90% by weight of the dendrite-type copper metal powder and 10% by weight of the PVDF binder obtained in the above production example 1 to NMP solvent. At this time, the weight ratio of the solid content to the solvent was 60:40. The prepared paste was cast onto one surface of a copper current collector (thickness 4 μm) using the doctor blade method and dried, and then a porous layer with a thickness of 48 μm was formed to produce a negative electrode.

[0113] The porosity and closed pore ratio of the porous layer of the anode obtained above were measured using MIP (Mercury Intrusion Porosimetry) analysis and XRM analysis (X-ray microscope), and the results are shown in Table 2.

[0114] A photograph of the cross-section of the manufactured negative electrode is shown in Figure 8(a). A magnified portion of it is also shown in Figure 8(b).

[0115] Furthermore, the pore distribution of the porous layer obtained above was captured in 3D, and this is shown in Figure 9. Specifically, the three-dimensional structure of the pores was obtained using a Zeiss Xraida 520 Versa X-ray microscope, which consisted of an X-ray source and detector on the negative electrode where the porous layer was formed, and a lens that could magnify the source between the detectors. The image of the obtained three-dimensional structure was then rendered in 3D using the GEODICT software. porous layer A 3D image of the internal pore structure was obtained, which is shown in Figure 9.

[0116] Examples 2-4 The negative electrode was manufactured in the same manner as in Example 1, except that the metal powders obtained in Manufacturing Examples 2 to 4 were used.

[0117] Furthermore, the porosity characteristics of the porous layer were analyzed for the negative electrodes obtained in each example, and the results are shown in Table 2.

[0118] [Table 2]

[0119] As can be seen from Table 2 above, the negative electrodes manufactured in each of the examples had a porosity of 85% or more and a highly developed pore ratio, with a closed pore ratio of less than 0.01% and the pores being open and interconnected to form a three-dimensional pore network. As can be seen from Fig. 8(a) showing a cross-section of the negative electrode having the porous layer of Example 1 and Fig. 8(b) showing an enlarged part thereof, dendritic metal powders aggregated to form a porous layer on the surface of the copper current collector, and visually, it was also found that pores were developed between the metal powders in the porous layer. Furthermore, from Fig. 9 showing an internal pore structure image of the porous layer, it was confirmed that the porous layer obtained in Example 1 above had pores developed inside, and the pores were interconnected to form a three-dimensional pore network structure.

[0120] Comparative Example 1 The copper current collector used for forming the coating layer in Example 1 above was used as a negative electrode current collector without forming a separate coating layer.

[0121] Comparative Example 2 A negative electrode having a carbon coating layer formed by casting a paste containing carbon powder (particle size 40 nm, specific surface area 62 m 2 / g, powder density 0.16 g / cm 3 , trade name: Supe r -P Li, Timcal) on the same copper current collector as in Example 1 was manufactured.

[0122] It was carried out in the same manner as in Example 1 except that a paste was manufactured using carbon powder instead of the dendritic metal powder in Example 1.

[0123] As a result negative electrode The porosity of the coating layer formed on the current collector was measured, and the porosity was less than 30%.

[0124] Comparative Example 3 The same as in Example 1 negative electrodeA negative electrode was manufactured by coating a current collector with silver using a sputter coating method, thereby forming a 100 nm thick silver coating layer that does not have pores.

[0125] [Battery manufacturing and evaluation of battery characteristics] -Negative electrodes of Example 1 and Comparative Examples 1-3- The negative electrodes produced in Example 1 and Comparative Examples 1-3 above were subjected to NCM 622 (3mAh / cm²). 2 A coin-type full-cell battery was manufactured using a positive electrode containing ) as the positive electrode active material and a carbonate-based electrolyte (N / P ratio = 2.3).

[0126] First, batteries using the negative electrodes manufactured in Example 1, Comparative Examples 1 and 2 were charged, and the negative electrodes in the charged state were disassembled and their cross-sections were observed.

[0127] A cross-sectional view of the charged state of the negative electrode manufactured in Example 1 above is shown in Figure 10(a), and a magnified photograph of a part of it is shown in Figure 10(b).

[0128] As can be seen from Figures 10(a) and (b), lithium was electrodeposited within the pores of the porous layer formed on the surface of the negative electrode current collector. Even with this type of charging, lithium ions were electrodeposited within the porous coating layer of the negative electrode, and it was found that there was no change in the thickness of the negative electrode compared to Figure 8(a), thus confirming that the volume expansion of the negative electrode due to charging and discharging was suppressed.

[0129] On the other hand, a cross-section of the negative electrode using the planar copper current collector manufactured in Comparative Example 1 was photographed and is shown in Figure 11(a). As can be seen from Figure 11(a), it was found that lithium metal was electrodeposited onto the surface of the copper current collector 11, forming a lithium metal layer 13. It was found that the formation of such a lithium metal layer causes the volume of the negative electrode to expand, which may cause the volume expansion problem of the battery due to charging and discharging.

[0130] Furthermore, a cross-section of the negative electrode having a carbon coating layer on a planar copper current collector manufactured in Comparative Example 2 was photographed and is shown in Figure 11(b). As can be seen from Figure 11(b), it was found that lithium metal was electrodeposited onto the surface of the carbon coating layer 45 formed on the copper current collector 11, forming a lithium layer. Due to the surface shape of the carbon coating layer, the problem of volume expansion due to lithium electrodeposition was reduced compared to the negative electrode of Comparative Example 1. However, the presence of lithium electrodeposited on the surface of the carbon located on the outermost surface of the negative electrode meant that the problem of battery volume expansion due to charging and discharging still existed.

[0131] Although not shown separately, the negative electrode of Comparative Example 3 also has the same planar surface as that of Comparative Example 1, and can provide results in improved lithium electrodeposition density with a silver coating layer. However, it was found that there is a problem of volume expansion of the negative electrode during the charge-discharge process.

[0132] On the other hand, the life characteristics of batteries using the negative electrodes of Example 1, Comparative Examples 1 and 3 were evaluated by charging and discharging under conditions of 0.2C and 0.3C. The evaluation results are shown in Figure 12.

[0133] As can be seen from Figure 12, the battery with a negative electrode according to Example 1 maintained a constant capacity with almost no change until approximately 45 cycles of operation. However, battery 2 with a negative electrode according to Comparative Example 1 showed a tendency for the capacity to gradually decrease from before 10 cycles, and battery 3 with a negative electrode according to Comparative Example 3 showed a decrease in capacity from approximately 25 cycles.

[0134] -Negative electrodes of Examples 2-4- Except for using the negative electrodes manufactured in Examples 2 to 4 above, the battery was manufactured in the same manner as battery 1 using the negative electrode of Example 1.

[0135] The lifespan characteristics of each of the manufactured batteries were evaluated by charging and discharging them under conditions of 0.2C and 0.3C, and the evaluation results are shown in Figure 13.

[0136] As can be seen from Figure 13, each of the batteries including the negative electrode in Examples 2 to 4 maintained a constant capacity with almost no change until approximately 30 cycles of operation, and the battery including the negative electrode in Example 4 showed excellent results, maintaining a constant capacity without change until 45 cycles. [Explanation of Symbols]

[0137] 10: Negative electrode 10': Charged negative electrode 11: Negative electrode current collector 13: Lithium metal layer 20: Metal powder 22: Main branch 24: Lateral branch 26: Through hole 30: Binder 41: Porous layer 43: Charged porous layer P, P0, P1, P2, P3, Pn: Inflection point α: included angle β: bending angle

Claims

1. The material includes a substrate and a porous layer on the substrate, The porous layer contains metal powder, The porous layer has a porosity of 30% or more as determined by standard XRM analysis before lithium metal electrodeposition or during complete discharge, and is a negative electrode for a lithium metal battery.

2. The anode for a lithium metal battery according to claim 1, wherein the porous layer has a porosity of 30% or more and 95% or less as determined by reference XRM analysis before lithium metal electrodeposition or during complete discharge.

3. The anode for a lithium metal battery according to claim 1, wherein the porous layer has a standard closed porosity of 0.05% or less before lithium metal electrodeposition or during complete discharge.

4. The porous layer has a thickness of 0.5 to 100 μm, the negative electrode for a lithium metal battery according to claim 1.

5. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder comprises at least one metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, Bi, Cu, Ge, Al, Pb, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru, an oxide of the metal, or an alloy of the metal.

6. The anode for a lithium metal battery according to claim 1, wherein the porous layer further comprises at least one carbon material selected from the group consisting of graphitic carbon nitride, phosphorous-doped graphitic carbon nitride, and boron-doped graphitic carbon nitride.

7. The anode for a lithium metal battery according to claim 1, wherein the porous layer further comprises at least one conductive polymer selected from the group consisting of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)), PANI (polyaniline), PPy (polypyrrole), PT (polythiophene), PA (polyacetylene), and PPV (polyp-phenylene vinylene).

8. The anode for a lithium metal battery according to claim 1, wherein the porous layer further comprises a binder.

9. The negative electrode for a lithium metal battery according to claim 8, wherein the binder is a fluorine-containing binder.

10. The negative electrode for a lithium metal battery according to claim 8, wherein the binder comprises at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polytetrafluoroethylene, and fluororubber.

11. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder is a particle having an aspect ratio greater than 1.

12. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder has a major axis length of 1 to 100 μm.

13. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder is in the form of rod-shaped particles.

14. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder is a rod-shaped particle having one or more inflection points where the direction of travel changes from one end to the other.

15. The negative electrode for a lithium metal battery according to claim 14, wherein the bending angle β at which the direction of travel changes at the inflection point is 5° or more and 90° or less.

16. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder has two or more branches.

17. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder has a main branch and at least one side branch connected to the main branch.

18. The porous layer includes a first layer on the surface side of the substrate and a second layer on the outer surface side of the porous layer. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder in the first layer has a smaller particle size than the metal powder in the second layer.

19. The negative electrode for a lithium metal battery according to claim 1, wherein lithium metal is electrodeposited in the pores of the porous layer.

20. The negative electrode for a lithium metal battery according to claim 1, wherein the substrate is a current collector.

Images