Lithium metal battery anode

Abstract

The present invention relates to a negative electrode for a lithium metal battery, and provides a negative electrode comprising a substrate and a porous layer on the substrate, the porous layer comprising a plurality of metal powders and a plurality of pores, the metal powders having a core portion and a shell portion coated on at least a portion of the surface of the core portion.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a lithium metal battery. [Background technology]

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

[0003] In the case of a lithium secondary battery using lithium metal as an electrode, a thin lithium metal electrode is required to maximize the efficiency and energy density of the battery. However, conventional lithium foils have been manufactured by a physical rolling method, but this rolling method has limitations in manufacturing lithium foils having a thickness below a certain level.

[0004] Recently, research into anode-less batteries has been actively progressing. Anode-less batteries use an anode that does not contain a lithium metal anode active material (layer) during battery manufacturing, and the battery operates by electrodepositing lithium onto the surface of the anode current collector as lithium ions are reduced during charging, 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 severe side reactions with the electrolyte, resulting in rapid deterioration of the battery life. Furthermore, the negative electrode of a negative electrode-less battery has many problems to be solved in terms of battery performance and stability, such as uneven lithium electrodeposition and dendrite growth during charging, and severe volume changes of the electrode during charging and discharging.

[0006] Meanwhile, various methods have been attempted to increase the uniformity of lithium electrodeposition, improve electrodeposition efficiency, and suppress dendrite growth, such as coating the surface of the above-mentioned plate-shaped negative electrode current collector with a lithiophilic metal having an affinity for lithium, such as silver (Ag), a carbon material, such as carbon black, or a mixture of the above-mentioned lithiophilic metal, such as silver, and a carbon material, or using a three-dimensional structure.

[0007] However, the coating layer formed by this method has limitations such as high resistance or low charge / discharge efficiency, and is therefore considered to be economically and practically unfeasible. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, one embodiment of 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, one embodiment of the present invention provides a negative electrode that suppresses volume changes of the electrode during charge and discharge, 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 above-described negative electrode. [Means for solving the problem]

[0011] The present invention provides, in one embodiment, a negative electrode for a lithium metal battery, the negative electrode including a substrate and a porous layer on the substrate, the porous layer including a plurality of metal powder particles and a plurality of pores, the metal powder particles having a core portion and a shell portion formed on at least a portion of the surface of the core portion.

[0012] The shell portion may include at least one lithium affinity metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi.

[0013] The shell portion may be 1 nm to 1 μm.

[0014] The metal powder may have an aspect ratio of more than 1 and 100 or less.

[0015] The metal powder may have a major axis length of 1 to 100 μm.

[0016] The metal powder may be rod-shaped particles having one or more inflection points where the direction of travel changes from one end to the other end.

[0017] The metal powder may have a bending angle β at which the direction of travel is changed at the inflection point of 5° or more and 90° or less.

[0018] The metal powder may include at least one through-hole therein, and at least one end of the through-hole may be open to the outside.

[0019] The metal powder may have two or more branches.

[0020] The metal powder may have a main branch and at least one side branch connected to the main branch.

[0021] The metal powder may include a core portion of a first metal and a shell portion of a second metal, and the first metal may have a higher reducing power than the second metal.

[0022] The first metal may include at least one metal selected from the group consisting of Cu, Si, Ge, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru, an oxide of the metal, or an alloy of the metal.

[0023] The second metal may include at least one metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi, an oxide of the metal, or an alloy of the metal.

[0024] The porous layer may have a porosity of 30% or more and 95% or less as determined by XRM analysis.

[0025] The porous layer may have a closed porosity of 0.05% or less.

[0026] The porous layer may have a thickness of 0.5 to 100 μm.

[0027] The porous layer may further include a binder.

[0028] The binder can be a fluorine-containing binder.

[0029] The binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polytetrafluoroethylene, and fluorine rubber.

[0030] In any one of the above embodiments, the porous layer includes a first layer on the substrate surface side and a second layer on the outer surface side of the porous layer, and the metal powder in the first layer may have a smaller particle size than the metal powder in the second layer.

[0031] In any one of the above embodiments, the negative electrode may be formed by electrodepositing lithium metal into the pores of the porous layer.

[0032] The substrate can be a current collector. [Effects of the Invention]

[0033] The negative electrode for a lithium metal battery according to the present invention can store lithium metal in the pores of the porous layer formed on the surface of the substrate, and can improve the contact surface area between the lithium metal and the current collector, thereby improving electrochemical properties.

[0034] In addition, the negative electrode for a lithium metal battery according to the present invention has a high specific surface area, which can reduce the local current density of the negative electrode, thereby providing a uniform electron distribution within the lithium electrode.

[0035] In addition, the negative electrode for a lithium metal battery according to the present invention can improve battery stability by preventing the formation and growth of lithium dendrites during charge and discharge.

[0036] Furthermore, the negative electrode for a lithium metal battery according to the present invention can provide a sufficient space for deposition of lithium during charging and discharging of the battery, thereby suppressing volume expansion of the battery. [Brief explanation of the drawings]

[0037] [Figure 1] 1A and 1B are diagrams conceptually showing cross sections of a negative electrode-less battery in a charged and discharged state, where FIG. 1A shows a cross section of a negative electrode in a discharged state, and FIG. 1B shows a cross section of a negative electrode in a charged state. [Figure 2] 1 is a diagram schematically illustrating an example of a rod-shaped metal powder according to the present invention. [Figure 3] 1 is a diagram schematically illustrating an example of a rod-shaped metal powder having one or more inflection points. [Figure 4] 1 is a diagram schematically illustrating an example of a metal powder having two or more branches. [Figure 5] 1 is a diagram showing an example of a cross section of a metal powder having through holes; [Figure 6] 1A and 1B are diagrams illustrating cross sections of a negative electrode in a discharged and charged state, in which a porous layer made of metal powder is formed on the surface of a negative electrode current collector, where (a) shows the negative electrode in a discharged state and (b) shows the negative electrode in a charged state. [Figure 7]1 shows photographs of metal powders used in the negative electrodes of Examples 1 to 4. [Figure 8] 1 shows a photograph of a cross section of a negative electrode in a charged state in Example 1 and a partially enlarged photograph of the cross section. [Figure 9] 3 is a photograph showing an image of the internal pore structure of the porous layer of the negative electrode in a discharged state in Example 1. [Figure 10] 1 shows a photograph of a cross section of a negative electrode in a charged state in Example 1 and a partially enlarged photograph of the cross section. [Figure 11] 1 shows photographs of cross sections of negative electrodes in a charged state in 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. FIG. [Figure 12] 1 is a graph showing the change in specific capacity depending on the number of cycles of batteries using the negative electrodes of Example 1, Comparative Example 1, and Comparative Example 3. [Figure 13] 1 is a graph showing the change in specific capacity depending on the number of cycles of batteries using the negative electrodes of Examples 2 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention relates to a negative electrode for a lithium metal battery, and specifically provides a negative electrode comprising a porous layer made of metal powder on the surface of a substrate.

[0039] In this specification, a lithium metal battery is a battery that uses lithium metal as the negative electrode active material, and among them, a battery that does not preemptively include lithium metal in the negative electrode current collector is called a non-negative electrode battery.

[0040] The negative electrode of such a negative electrode-less battery and a cross section of the negative electrode during charging are shown schematically in FIG. 1. FIG. 1(a) shows a cross section of a negative electrode 10 of the negative electrode-less battery, and FIG. 1(b) shows a cross section of a charged negative electrode 10'. As shown in FIG. 1(a), a plate of a conductive metal such as copper is used as a substrate, i.e., a negative electrode current collector 11. During charging, lithium metal is electrodeposited on the negative electrode current collector 11, forming a lithium layer 13 as shown in FIG. 1(b). In such a negative electrode of a negative electrode-less battery, non-uniform deposition of the lithium layer on the negative electrode current collector causes non-uniform electron density, which can lead to the formation of lithium dendrites.

[0041] The present invention provides a negative electrode for a lithium metal battery, specifically, a negative electrode applicable to a negative electrode-less battery. The negative electrode includes a substrate and a porous layer on the substrate. The porous layer includes a plurality of metal powder particles and a plurality of pores. The metal powder particles may have a core portion and a shell portion formed on at least a portion of the surface of the core portion. Hereinafter, the porous layer may also be referred to as a porous storage layer or a porous coating layer.

[0042] The negative electrode of the present invention will be described in more detail below.

[0043] An embodiment of the present invention provides a negative electrode comprising a substrate and a porous layer having a high surface area on the substrate. The porous layer may be formed directly on the substrate, or another layer may be further included between the porous layer and the substrate.

[0044] The substrate functions as a current collector, specifically, a negative electrode current collector. Any material that can be used as a negative electrode current collector can be used as the substrate. For example, the substrate can be any material that is conductive and does not undergo chemical changes during battery operation. Examples include metals such as copper, stainless steel, aluminum, nickel, and titanium, alloys containing at least one of the above metals, such as aluminum-cadmium alloys, and calcined carbon. Substrates in which metal surfaces, such as copper or stainless steel, are surface-treated with carbon, nickel, titanium, silver, or the like can be used as negative electrode current collectors. Furthermore, polymers coated with conductive metals or conductive polymers can also be used as the substrate of the present invention.

[0045] Furthermore, the substrate may be in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam body, or a nonwoven fabric body.

[0046] The thickness of the substrate is not particularly limited and can be, for example, 1 to 100 μm. More specifically, the thickness of the substrate can be 3 to 50 μm or 4 to 30 μm, and even more specifically, 4 to 12 μm.

[0047] As described above, the negative electrode of the present invention includes a porous layer on the surface of the substrate, for example, on one or both sides of the substrate. The porous layer can be formed using a metal powder, and the metal powder can have a core-shell structure including a core portion and the core portion.

[0048] The core portion provides and maintains the shape of the metal powder of the present invention, and a shell portion capable of inducing electrodeposition of lithium may be formed on the surface of the core portion.

[0049] Any material can be used for the core portion as long as it can maintain the shape of the metal powder as described above and can form a shell portion on the surface. For example, the core portion can be made of metal.

[0050] The metal forming the core portion may include, for example, at least one metal selected from the group consisting of Cu, Si, Ge, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru, an alloy of the above metal, or an oxide of any one of the above metals.

[0051] In one embodiment, the core portion may include a lithium affinity metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi, an alloy of the lithium affinity metal, or an oxide of any one of the above metals. By including the lithium affinity metal in the core portion, the core portion can contribute to the electrodeposition of lithium even when the shell portion is partially formed on the core portion.

[0052] The metal powder of the present invention includes a shell portion on the surface of the core portion. The shell portion may include a component capable of electrodepositing lithium during the charging process of the battery, such as a metal.

[0053] The metal component contained in the shell portion is not particularly limited as long as it can electrodeposit lithium, but the shell portion can contain a lithium affinity metal. When the metal powder contains a lithium affinity metal, lithium can be uniformly electrodeposited not only on the substrate provided as the negative electrode current collector but also within the porous layer formed by the metal powder, thereby increasing the electrodeposition density of lithium. This can suppress the formation and growth of lithium dendrites in the negative electrode, thereby extending the life characteristics.

[0054] The lithium affinity metal contained in the shell portion may include, but is not limited to, at least one metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi, or an oxide or alloy of these metals. In this case, the lithium affinity metal constituting the shell portion may be different from the metal constituting the core portion.

[0055] The shell portion may be formed of the lithium affinity metal as described above, or may contain a metal other than the lithium affinity metal, or may be an alloy of the lithium affinity metal and the other metal.

[0056] The shell portion may have a thickness of, but is not particularly limited to, 1 nm to 1 μm, for example, 1 nm or more, 2 nm or more, 3 nm or more, 5 nm or more, 7 nm or more, 10 nm or more, 15 nm or more, or 20 nm or more, and may be 1 μm or less, 0.9 μm or less, 0.8 μm or less, 0.7 μm or less, or 0.5 μm or less.

[0057] The core-shell structured metal powder of the present invention has a thin shell formed on the surface of a core, and the shell can be formed over the entire core or on a part of the core, and the thickness can be uniform or non-uniform, and is not particularly limited.

[0058] In the metal powder of the present invention, the core portion provides the shape of the metal powder and maintains that shape, and the shell portion is provided on the core portion. The overall shape of the metal powder can be determined by the shape of the core portion, although the thickness of the shell portion can be changed.

[0059] The shape of the metal powder is not particularly limited, but may be particles having an aspect ratio of more than 1 and not more than 100. For example, the metal powder may be particles having an aspect ratio of more than 1, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, or 7 or more, and not more than 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 not more than 10. By having a particle shape with an aspect ratio of more than 1 and a long length in one direction, a porous layer with developed pores can be provided on the negative electrode current collector of the present invention.

[0060] The metal powder is not particularly limited, but may have a major axis length of 1 to 100 μm, for example. The metal powder may be, for example, rod-shaped particles. Some examples of rod-shaped particles are exemplarily shown in FIG. 2.

[0061] As shown in Figure 2(a), the rod-shaped metal powder 20 has a linear outer shape and includes a core portion 32 and a shell portion 34 outside the core portion, and the cross-sectional diameter and cross-sectional shape of the rod-shaped metal powder can be constant.

[0062] The rod-shaped metal powder may have a varying cross-sectional diameter. For example, as shown in FIG. 2(b), a rod-shaped metal powder 20 including a core portion 32 and a shell portion 34 may have a cross-sectional diameter that decreases or increases regularly or irregularly in one direction. A specific example of this is a metal powder 20 having a needle shape as shown in FIG. 2(c). As shown in FIG. 2(d), the rod-shaped metal powder 20 may have a cross-sectional diameter that decreases regularly or irregularly in both directions, or, although not shown in the drawing, may have a cross-sectional diameter that increases regularly or irregularly in both directions.

[0063] In another embodiment, the rod-shaped metal powder may have one or more inflection points where the direction of travel from one end to the other end changes. The rod-shaped metal powder having the inflection points will be described with reference to FIG. 3.

[0064] As shown in Fig. 3(a), the rod-shaped metal powder 20 includes a core portion 32 and a shell portion 34, and while the cross-sectional diameter and shape of the metal powder are uniform, the direction of travel from one end to the other may change one or more times, resulting in one or more inflection points P. Also, as shown in Fig. 3(b), the core-shell structured metal powder may have one or more inflection points as the cross-sectional diameter and / or shape change.

[0065] As shown in FIG. 3(a), one end of the rod-shaped metal powder is designated as P0, and the other end is designated as P n (n is a natural number of 2 or more), the rod-shaped metal powder is n The rod-shaped metal powder may include one or more inflection points P where the direction of travel changes from ≈0 to ≈1. When the rod-shaped metal powder has one or more inflection points, more pores can be formed between the metal powder particles when a coating layer is formed on a substrate, and the number of pores in the coating layer can be increased, resulting in the formation of finer pores.

[0066] In the rod-shaped metal powder, the inflection points are arranged in the order P0, P1, P2, P3...P n When the distance between any one inflection point and the adjacent inflection point is L1 between P0 and P1, L2 between P1 and P2, or P n-1 and P n Distance L between n may be the same or different.

[0067] As described above, the rod-shaped metal powder particles may change their traveling direction from one end to the other end based on an adjacent inflection point, and at this time, the traveling direction may be changed by a predetermined angle. Specifically, between two adjacent line segments based on an inflection point, the traveling direction may be changed by an acute angle of 90° or less than 90°, which is the angle formed by two straight lines including each line segment (bending angle).

[0068] For example, as shown in Figure 3(a), a rod-shaped metal powder including a line segment moving in the direction from P0 to P1 may have a line segment moving in the direction including the line segment from P1 to P2, with the direction of movement being changed by the bending angle at the inflection point of P1. In this case, the bending angle formed by the line segment P0-P1 and the line segment P1-P2 can be expressed as β.

[0069] On the other hand, although not shown in the drawings, even when the direction of travel changes in a curved shape, this 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.

[0070] The bending angle β of the rod-shaped metal powder may be, but is not limited to, 5° or more and 90° or less, more specifically, 5° or more, 10° or more, 15° or more, 20° or more, 25° or more, or 30° or more, and may be 90° or less, 85° or less, 80° or less, or 75° or less.

[0071] In another embodiment, the rod-shaped metal powder has one imaginary surface including two adjacent line segments that share an inflection point and an angle between the two line segments, and another imaginary surface adjacent to the one imaginary surface, which may or may not be parallel to each other.

[0072] For example, as shown in (a) of Figure 3, in the rod-shaped metal powder 20, the adjacent line segments P0-P1 and P1-P2 that share the inflection point P1, the imaginary plane P0-P1-P2 that includes the angle α between the two line segments, and the imaginary plane P1-P2-P3 that is adjacent to the imaginary 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.

[0073] In another embodiment, the metal powder may have two or more branches. For example, the metal powder may be a branch-like metal powder having one main branch and at least one side branch connected to the main branch. For example, the rod-shaped metal powder as shown in Figure 2 (a) to (d) or the rod-shaped metal powder having an inflection point as shown in Figure 3 (a) or (b) may be a main branch 22, and one or more side branches 24 may be formed on the main branch. In this case, the side branch may also be a rod-shaped metal powder as described above.

[0074] More specifically, the rod-shaped metal powder may be a dendritic metal powder having one main branch 22 and one or more side branches 24, as shown in FIGS. 4(a) to 4(b).

[0075] As shown in Figures 5(a) and 5(b), the metal powder may include one or more through holes 26 therein. The one or more through holes may be formed in the main branch or the side branch of the metal powder. At least one of the through holes may be open and connected to the outside. The position where the through hole is open is not particularly limited, and may be, for example, at the end of the main branch and / or the side branch.

[0076] As shown in FIG. 5, the diameter of the through-holes may vary and is not particularly limited.

[0077] The metal powder can be manufactured by forming a core portion in a predetermined shape through a spontaneous substitution reaction and then forming a shell portion on the core portion, thereby manufacturing a metal powder having a core-shell structure.

[0078] The core part can be manufactured in a predetermined shape through a spontaneous substitution reaction of metals. Specifically, the core part can be manufactured using a spontaneous substitution reaction that utilizes the difference in reducing power between different metals and a reaction activation process using hydrogen bubbles generated in an electrolyte containing chloride ions. This method allows the core part to be manufactured with a high specific surface area in a short time through a simple process.

[0079] Specifically, the metal powder may include a core portion of a first metal and a shell portion of a second metal, and the first metal may be a metal having a higher reducing power than the second metal.

[0080] For example, when a metal (hereinafter referred to as a sacrificial metal) having a higher reducing power than the first metal is immersed in a first electrolyte solution containing ions of the first metal, the ions of the first metal having a lower reducing power receive electrons from the sacrificial metal and undergo a spontaneous substitution reaction to be produced as powder of the first metal, thereby obtaining metal particles that can be used as the core portion.

[0081] The sacrificial metal can be selected in consideration of the type of the first metal and the reducing power of the first metal, and the sacrificial metal is not particularly limited.

[0082] Furthermore, the spontaneous substitution reaction is theoretically well established, and the conditions for carrying out the spontaneous substitution reaction process can be easily selected, so a detailed description will not be given here. For example, the reaction rate of the spontaneous substitution reaction can be controlled by adjusting the concentration of the first metal ion contained in the first electrolyte solution.

[0083] The first metal may be at least one metal selected from the group consisting of, but not limited to, Cu, Si, Ge, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru, or may be an oxide of the above metal, or may be an alloy of the above metal.

[0084] The second metal may be at least one metal selected from the group consisting of, but not limited to, Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi, or may be an oxide of the above metal, or may be an alloy of the above metal.

[0085] The electrolyte may contain an accelerator containing chloride ions and sulfide ions, and therefore, the electrolyte may be used by dissociating metal ions from metal sulfides and metal chlorides containing the first metal.

[0086] The shell portion can also be formed on the core portion produced above by a spontaneous substitution reaction.

[0087] Specifically, by supporting core particles of a first metal in a second electrolyte solution containing ions of a second metal that has a lower reducing power than the first metal of the core particles produced above and causing a spontaneous substitution reaction, the surface of the core particles of the first metal can be coated with the second metal to form a shell portion, thereby obtaining a metal powder with a core-shell structure.

[0088] The second electrolyte solution is an electrolyte solution containing ions of the second metal forming the shell portion, and may be an inorganic acid salt of the metal. The inorganic acid salt may be at least one electrolyte solution selected from the group consisting of, but not limited to, nitrates, hydrochlorides, sulfates, and hydrofluorides.

[0089] The spontaneous substitution reaction step of forming the shell portion may include chloride ions as an accelerator of the spontaneous substitution reaction.

[0090] In this case, the second metal can be selected in consideration of the first metal and the reducing power of the first metal, and the second metal can be appropriately selected from metals that can be used for the shell portion in consideration of its relationship with the first metal. The spontaneous substitution reaction can be controlled in reaction rate and shell thickness by adjusting the concentration of the second metal ion contained in the second electrolyte.

[0091] In the present invention, various core-shell structured metal powders can be obtained by spontaneous substitution reactions utilizing the difference in reducing power due to the natural potential difference of the metals. The obtained metal powders can be used to provide a porous coating layer on the surface of a substrate.

[0092] Specifically, a negative electrode including a coating layer on a substrate, which may be a negative electrode current collector, may be provided using a plurality of such metal powders. The porous layer formed on the substrate by the metal powder may be a porous layer with a large number of pores due to the high surface area of ​​the metal powder.

[0093] During charging of a battery including the porous layer, the anode can provide sufficient space for lithium deposition, and the anode according to one embodiment of the present invention can suppress volume expansion of the battery. According to another embodiment, the anode including the porous layer has developed pores, allowing lithium metal to be uniformly deposited, and suppressing the formation and growth of lithium dendrites during charging and discharging.

[0094] An example of a porous layer formed using the metal powder in the present invention is shown schematically in Figure 6(a). Figure 6(a) shows a schematic cross-section of an anode 10 including a porous layer 41 formed using the dendritic metal powder 20 shown in Figure 4(a). As shown in Figure 6(a), the metal powder particles may be randomly arranged to form a porous layer with developed pores. The pores in the porous layer may be interconnected to form a three-dimensional pore network.

[0095] By forming a porous layer having such a three-dimensional pore network on the surface of the substrate, lithium ions that migrate from the positive electrode during charging can migrate into the coating layer through the pores of the porous layer, allowing lithium metal to be electrodeposited inside the pores.

[0096] FIG. 6(b) is a conceptual diagram of a charged negative electrode 10′ including a porous layer 43 in a charged state in which lithium metal 13 has been electrodeposited inside the pores of the porous layer of FIG. 6(a) upon charging.

[0097] The porous layer formed from the metal powder contains a large number of pores, providing storage space for lithium metal, preventing uneven lithium electrodeposition during charging and increasing the contact surface area between the lithium and the negative electrode current collector, thereby improving electrochemical properties. Furthermore, because lithium is electrodeposited within the porous layer, volume changes in the negative electrode due to lithium electrodeposition and desorption can be prevented, thereby maintaining negative electrode performance and battery stability.

[0098] The porous layer according to the present invention may be a single layer or may be two or more layers. For example, as shown in FIG. 6(a), a single layer can be formed using a metal powder. Alternatively, multiple layers can be formed using two or more metal powders with different particle shapes or sizes. For example, a first coating layer with small pores can be formed on the current collector side using a first metal powder with a small particle size, and a second coating layer with larger pores can be formed on the first coating layer using a second metal powder with a larger particle size than the first metal powder.

[0099] In this case, the particle size of the metal powder can be determined on a volume basis by setting the outer periphery of one metal powder, which is determined by the main branch and the side branch, as the boundary of the particle.

[0100] The porous layer may include a binder along with the metal powder. For example, the porous layer may be prepared by mixing a metal powder having a high surface area on the surface of a substrate serving as a negative electrode current collector with a binder in a solvent to form a paste, which is then cast on the surface of the substrate and dried.

[0101] The binder contained in the paste preparation is not particularly limited, and binders commonly used in the manufacture of electrodes can be suitably used in the present invention. For example, the binder may be styrene-butadiene rubber, acrylated 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), vinylidene fluoride-hexafluoropropylene copolymer (Poly(vinylidene The adhesive may include at least one selected from the group consisting of polyethylene, ethylene-propylene-co-hexafluoropropylene, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), polymethylmethacrylate, and fluororubber.

[0102] In one embodiment, the binder may be a styrene-butadiene rubber (SBR)-based binder, carboxymethyl cellulose (CMC), polyacrylic acid-based binder, polyethylenedioxythiophene (poly(3,4-ethylenedioxythiophene) (PEDOT))-based binder, or a fluorine-containing binder. More specifically, the binder may be a fluorine-containing binder, and for example, the fluorine-containing binder may be at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polytetrafluoroethylene, and fluorine-containing rubber.

[0103] The binder is not particularly limited, but may be included in a content of 1 to 30 wt% based on the solid weight of the paste. If the binder content is less than 1 wt%, the adhesive strength of the porous layer may be reduced, and if it exceeds 30 wt%, the resistance may be increased, resulting in a decrease in electrical conductivity and further degrading lithium deposition performance. More specifically, the binder content may be 1 wt% or more, 1.2 wt% or more, 1.5 wt% or more, 2 wt% or more, or 3 wt% or more, and 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, or 12 wt% or less.

[0104] Meanwhile, the solvent is not particularly limited, and solvents commonly used in electrode manufacturing can be suitably used in the present invention, for example, at least one selected from the group consisting of water, acetone, formic acid, chloroform, isopropanol, N-methylpyrrolidone (NMP), MF (Dimethylformamide), DMAc (Dimethylacetamide), DMSO (Dimethyl sulfoxide), and THF (Tetrahydrofuran).

[0105] The solvent is not particularly limited, but may be contained in the paste in an amount of 30 to 60% by weight.

[0106] The method for applying the paste according to the present invention to the surface of a substrate is not particularly limited, and coating methods such as bar coating, casting, spraying, doctor blading, etc., specifically, wet coating methods, can be used. 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.

[0107] In this case, the thickness of the porous layer may be, but is not limited to, 0.5 to 100 μm. Since the porous layer serves to store lithium metal, it may be formed to a thickness that allows the minimum amount of lithium metal to be stored. In this regard, the porous layer may 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.

[0108] On the other hand, if the porous layer is too thick, lithium ions may not be transported smoothly, and the effects obtained by including the porous layer may be halved or may be difficult to achieve. In another aspect, if the porous layer is too thick, it may result in a loss of energy density per volume and weight. In this aspect, the porous layer of the present invention may be 100 μm or less, or may be 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, or 50 μm or less.

[0109] The porous layer obtained according to the present invention may have a porosity of 30% to 95%, specifically 50% or more, 70% or more, 80% or more, or 85% or more, as determined by X-ray microscope (XRM) analysis before lithium metal electrodeposition or after full discharge, but is not limited thereto. Furthermore, the porous layer according to the present invention achieves such high porosity by forming a porous layer in which pores are interconnected. The porous layer may have a closed porosity, which indicates the ratio of pores that are not interconnected, of 0.05% or less, 0.03% or less, 0.01% or less, or 0.0095% or less before lithium metal electrodeposition or after full discharge. That is, the anode according to the present invention has highly developed porosity and pores that are interconnected to form a three-dimensional pore network, thereby improving lithium ion insertion and desorption characteristics during charge and discharge.

[0110] Furthermore, the porous layer of the present invention has a specific surface area of ​​300 m2 when fully discharged. 2 / m 3 With this or more, it is possible to have a high specific surface area.

[0111] Meanwhile, the porous layer according to the present invention can include pores of various sizes, for example, nano-sized pores to meso-sized pores, because the pores are formed by the metal powder having a high surface area.

[0112] As described above, the porous layer formed on the negative electrode current collector can include pores of various sizes, so that lithium metal can be electrodeposited into the pores.

[0113] For example, the porous layer may have a multi-layer structure, including a first layer located on a surface of the substrate serving as a negative electrode current collector and a second layer located on an outer surface of the porous layer, and the metal powder included in the first layer may have a smaller particle size than the metal powder included in the second layer.

[0114] The metal powder in the porous layer located on the negative electrode current collector side has a smaller particle size, which can form smaller pores and increase the uniformity of lithium electrodeposition in the porous layer, improving electrodeposition efficiency and suppressing dendrite growth.

[0115] Although not limited thereto, the thickness of the first layer may be greater than the thickness of the second layer in the porous layer.

[0116] The negative electrode provided by the present invention includes a porous layer on the surface of a substrate serving as a negative electrode current collector, and lithium is electrodeposited into the pores of the porous layer, thereby improving the electrodeposition density and improving the battery life.

[0117] In addition, the stable electrodeposition of lithium within the pores can suppress the formation of lithium dendrites and increase the contact area between the lithium metal and the current collector. The high specific surface area can reduce the local current density of the anode and provide uniform electron distribution within the lithium electrode, thereby preventing the formation and growth of lithium dendrites during charge and discharge, thereby improving battery stability.

[0118] Furthermore, when the current collector according to the present invention is used, a sufficient space can be provided for deposition of lithium during charging and discharging of the battery, and volume expansion of the battery can be suppressed. [Example]

[0119] 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 the present invention.

[0120] [Metal powder manufacturing] Manufacturing Example 1 1.0M sodium chloride and 0.2M hydrogen chloride were added as reaction accelerators to a room-temperature electrolyte containing dissociated copper sulfate (CuSO4) (concentration: 0.1M). An aluminum plate (10cm x 8cm), which has a stronger reducing power than the copper sulfate, was placed in the room-temperature electrolyte, and the reaction was allowed to proceed for 20 minutes while hydrogen bubbles were generated in the electrolyte, producing copper powder in the electrolyte.

[0121] The copper powder was collected and then placed in an electrolyte containing AgNO3 (Ag 30 wt%) and maintained at room temperature for 20 minutes to induce a spontaneous substitution reaction, forming a silver (Ag) coating layer on the surface of the copper powder. This produced a core-shell structured metal powder consisting of a copper core and a silver shell.

[0122] The core-shell structured metal powder thus produced was photographed using an SEM, and the photograph is shown in Figure 7(a). The size of the metal powder was also measured using a field emission scanning electron microscope (FESEM), and the results are shown in Table 1 below.

[0123] Manufacturing Example 2 A core-shell structured metal powder was prepared in the same manner as in Example 1, except that the reaction for producing copper powder in the electrolyte was carried out for 30 minutes instead of 20 minutes.

[0124] The core-shell structured metal powder produced above was photographed using an SEM, and the photograph is shown in Figure 7(b). The size of the metal powder was also measured using an FESEM, and the results are shown in Table 1 below.

[0125] Manufacturing Example 3 Copper powder was prepared in the same manner as in Example 1, except that the reaction for producing copper powder in the electrolyte was carried out for 40 minutes instead of 20 minutes.

[0126] The core-shell structured metal powder produced above was photographed using an SEM, and the photograph is shown in Figure 7(c). The size of the metal powder was also measured using an FESEM, and the results are shown in Table 1 below.

[0127] Manufacturing Example 4 Copper powder was prepared in the same manner as in Example 1, except that the reaction for producing copper powder in the electrolyte was carried out for 60 minutes instead of 20 minutes.

[0128] The core-shell structured metal powder produced above was photographed using an SEM, and the photograph is shown in Figure 7(b). The size of the metal powder was also measured using an FESEM, and the results are shown in Table 1 below.

[0129] [Table 1]

[0130] As can be seen from (a) to (d) of Figure 7, it was found that the metal powders obtained in the above Production Examples 1 to 4 had a shell portion formed by coating silver on a core portion of copper powder having a dendritic shape.

[0131] [Manufacturing of negative electrodes] Example 1 A paste was prepared by adding 90 wt% of the core-shell dendritic metal powder obtained in Preparation Example 1 and 10 wt% of a PVDF binder to an NMP solvent. The paste had a solid content of 60 wt%.

[0132] The prepared paste was cast onto one side of a copper current collector (thickness: 4 μm) by a doctor blade method, dried, and then a porous layer having a thickness of 48 μm was formed to prepare a negative electrode.

[0133] The porosity and closed pore ratio of the porous layer of the obtained negative electrode were measured by MIP (Mercury Intrusion Porosimetry) analysis and XRM (X-ray microscope) analysis. The results are shown in Table 2.

[0134] Furthermore, a cross section of the negative electrode produced above was photographed, and the photograph is shown in Figure 8(a), and a part of it is enlarged and shown in Figure 8(b).

[0135] Furthermore, the pore distribution of the obtained porous layer was photographed in 3D, and is shown in Figure 9. Specifically, the 3D structure of the pores was obtained using a Zeiss X-ray microscope (Xraida 520 Versa), which is equipped with an X-ray source, a detector, and a lens between the detectors that can magnify the source, for the negative electrode on which the porous layer was formed. The obtained image of the 3D structure was then 3D rendered using software GEODICT to obtain a 3D image of the internal pore structure of the negative electrode mixture layer.

[0136] Examples 2 to 4 Negative electrodes were manufactured in the same manner as in Example 1, except that the metal powders obtained in Preparation Examples 2 to 4 were used.

[0137] In addition, the pore characteristics of the porous layer of the negative electrode obtained in each example were analyzed, and the results are shown in Table 2.

[0138] [Table 2]

[0139] As can be seen from Table 2 above, the negative electrodes prepared in the examples have highly developed porosity with a porosity of 85% or more, and a closed pore ratio of less than 0.01%, indicating that the pores are open and interconnected to form a three-dimensional pore network. As can be seen from Figure 8(a), a cross-sectional photograph of the negative electrode having a porous layer in Example 1, and Figure 8(b), a magnified view of a portion thereof, it is clear that the dendrite-shaped metal powder particles aggregate to form a porous layer on the surface of the copper current collector, and that the porous layer has developed pores between the metal powder particles. Furthermore, Figure 9, which shows an image of the internal pore structure of the porous layer, confirms that the porous layer prepared in Example 1 has developed pores internally, and that the pores are interconnected to form a three-dimensional pore network structure.

[0140] Comparative Example 1 The copper current collector used for forming the coating layer in Example 1 was used as a negative electrode current collector without forming a separate coating layer.

[0141] Comparative Example 2 Carbon powder (particle size 40 nm, specific surface area 62 m) was placed on the same copper current collector as in Example 1. 2 / g, powder density 0.16g / cm 3 A paste containing ethylenediamine diamine (trade name: Supe-P Li, manufactured by Timcal Co.) was cast onto a cathode to form a carbon coating layer.

[0142] In Example 1, carbon powder (powder density 0.16 g / cm) was used instead of the dendritic metal powder. 3 The same method as in Example 1 was carried out, except that a paste was prepared using the same material as in Example 1. As a result, a carbon coating layer with a composite density of 1.4 g / cc was formed on the copper current collector.

[0143] The porosity was measured using the true density of the carbon powder, and the porosity was found to be less than 30% based on the true density of amorphous carbon (2.0 g / cc).

[0144] Comparative Example 3 The same copper current collector as in Example 1 was coated with silver by sputter coating to prepare a negative electrode having a 100 nm silver coating layer.

[0145] [Battery manufacturing and evaluation of battery characteristics] -Negative electrodes of Example 1 and Comparative Examples 1 to 3- Each of the negative electrodes prepared in Example 1 and Comparative Examples 1 to 3 was charged with NCM 622 (3 mAh / cm 2 A coin-type full-cell battery was fabricated using a positive electrode containing 1,2-dichloroethane as a positive active material and a carbonate-based electrolyte (N / P ratio=2.3).

[0146] First, the batteries using the negative electrodes produced in Example 1 and Comparative Examples 1 and 2 were charged, and the negative electrodes in the charged state were disassembled to observe their cross sections.

[0147] A photograph of a cross section of the negative electrode prepared in Example 1 in a charged state is shown in FIG. 10(a), and a partially enlarged photograph of the cross section is shown in FIG. 10(b).

[0148] As can be seen from Figure 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 charging, lithium ions were electrodeposited within the porous coating layer of the negative electrode, and the thickness of the negative electrode did not change compared to Figure 8(a). This confirmed that the volume expansion of the negative electrode due to charging and discharging was suppressed.

[0149] Meanwhile, a cross-section of the negative electrode using the flat 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), lithium metal was electrodeposited on 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 problem of volume expansion of the battery during charge and discharge.

[0150] In addition, a cross-section of the anode having a carbon coating layer on a flat copper current collector prepared in Comparative Example 2 was photographed and is shown in Figure 11(b). As can be seen from Figure 11(b), a lithium layer was formed by electrodeposition of lithium metal on the surface of carbon coating layer 45 formed on copper current collector 11. Due to the surface shape of the carbon coating layer, the problem of volume expansion due to lithium electrodeposition was reduced compared to the anode of Comparative Example 1. However, the presence of lithium electrodeposited on the surface of the carbon located on the outermost surface of the anode still caused the problem of volume expansion of the battery during charge and discharge.

[0151] Although the anode of Comparative Example 3 is not shown separately, the anode of Comparative Example 3 also has the same flat surface as Comparative Example 1 and has a silver coating layer, which can result in improved lithium electrodeposition density. However, it was found that there was a problem with volume expansion of the anode during charge and discharge.

[0152] Meanwhile, the life characteristics were evaluated for the batteries using the negative electrodes of Example 1 and Comparative Examples 1 and 3 by charging and discharging them under the conditions of charging at 0.2 C and discharging at 0.3 C. The evaluation results are shown in FIG.

[0153] As can be seen from FIG. 12 , the battery including the negative electrode of Example 1 showed almost no change in battery capacity and remained constant until approximately 45 cycles of operation, whereas Battery 2 including the negative electrode of Comparative Example 1 showed a tendency for the capacity to gradually decrease before reaching 10 cycles, and Battery 3 including the negative electrode of Comparative Example 3 showed a decrease in capacity from approximately 25 cycles.

[0154] -Negative electrodes of Examples 2 to 4- Batteries were fabricated in the same manner as Battery 1 using the negative electrode of Example 1, except that the negative electrodes fabricated in Examples 2 to 4 were used.

[0155] Each of the batteries manufactured above was charged and discharged at a charge rate of 0.2 C and a discharge rate of 0.3 C to evaluate the life characteristics. The evaluation results are shown in FIG.

[0156] As can be seen from FIG. 13, the battery capacity of each of the batteries including the negative electrodes of Examples 2 to 4 remained constant with almost no change until approximately 30 cycles of operation, and the battery including the negative electrode of Example 4 maintained its capacity constant with no change until 45 cycles, demonstrating excellent results. [Explanation of symbols]

[0157] 10:Negative electrode 10': Charged negative electrode 11: Negative electrode current collector 13: Lithium metal 20: Metal powder 22: Main branch 24: Lateral branch 26:Through hole 32: Core section 34: Shell part 30: Binder 41: Porous layer 43: Charged porous layer P, P0, P1, P2, P3, Pn: Inflection point α: included angle

Claims

1. a substrate and a porous layer on the substrate, the porous layer includes a plurality of metal powders; The metal powder has a core portion and a shell portion formed on at least a part of the surface of the core portion.

2. 2. The negative electrode for a lithium metal battery according to claim 1, wherein the shell portion contains at least one lithium affinity metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi.

3. 2. The negative electrode for a lithium metal battery according to claim 1, wherein the shell portion has a thickness of 1 nm to 1 μm.

4. 2. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder has an aspect ratio of more than 1 and 100 or less.

5. 5. The negative electrode for a lithium metal battery according to claim 4, wherein the metal powder has a major axis length of 1 to 100 μm.

6. 2. 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 end.

7. 7. The negative electrode for a lithium metal battery according to claim 6, wherein the metal powder has a bending angle β at which the direction of movement is changed at an inflection point of 5° or more and 90° or less.

8. 2. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder contains at least one through-hole therein, and at least one end of the through-hole is open to the outside.

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

10. 2. 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.

11. 2. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder comprises a core portion of a first metal and a shell portion of a second metal, and the first metal has a higher reducing power than the second metal.

12. 12. The negative electrode for a lithium metal battery according to claim 11, wherein the first metal comprises at least one metal selected from the group consisting of Cu, Si, Ge, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru, an oxide of the metal, or an alloy of the metal.

13. 12. The negative electrode for a lithium metal battery according to claim 11, wherein the second metal comprises at least one metal selected from the group consisting of Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi, an oxide of the metal, or an alloy of the metal.

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

15. 10. The negative electrode for a lithium metal battery according to claim 1, wherein the porous layer further comprises a fluorine-containing binder.

16. 16. The negative electrode of claim 15, wherein the binder is a fluorine-containing binder.

17. 17. The negative electrode for a lithium metal battery according to claim 16, wherein the binder comprises at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polytetrafluoroethylene, and fluororubber.

18. the porous layer includes a first layer on the substrate surface side and a second layer on the outer surface side of the porous layer; 2. The negative electrode for a lithium metal battery according to claim 1, wherein the metal powder of the first layer has a smaller particle size than the metal powder of the second layer.

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

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

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