Negative electrode for lithium metal battery

Abstract

The present invention relates to a negative electrode for a lithium metal battery, and provides a negative electrode for a lithium metal battery, the negative electrode comprising a base material and a porous layer on the base material, the porous layer containing a metal powder, the porosity of the porous layer according to XRM analysis being 30% or more before electrodeposition of lithium metal or when the lithium metal is fully discharged.

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 also has a low reduction potential (-3.04V vs. SHE) and a high theoretical capacity (3860mAh / g), so lithium metal batteries using lithium metal itself as the negative electrode active material are being developed.

[0003] In lithium-ion secondary batteries using lithium metal as an electrode, thin lithium metal electrodes are required to maximize battery efficiency and energy density. However, existing lithium foils are manufactured using a physical rolling process, which has limitations in producing lithium foils with thicknesses below a certain level.

[0004] In recent years, research on electrodeless batteries has been actively underway. Electrodeless batteries use a negative electrode that does not contain a lithium metal negative electrode active material (layer) during battery manufacturing, and the battery is driven by the reduction of lithium ions during charging and the deposition of lithium on the surface of the negative electrode current collector to form a lithium metal coating.

[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, thus resulting in rapid degradation of battery life. Furthermore, negative electrodeless batteries suffer from uneven lithium deposition and dendrite growth during charging, and there are many issues to be addressed regarding battery performance and stability, such as severe volume changes in the electrodes during charging and discharging.

[0006] In addition, various methods are being explored to improve electrodeposition efficiency and suppress dendrite growth by increasing the uniformity of lithium electrode deposition. For example, coating the negative electrode current collector surface of the plate-like structure with a lithium-affinity metal such as silver (Ag), a carbon material such as carbon black, or a mixture of the lithium-affinity metal and carbon material, or using a three-dimensional structure.

[0007] However, the resulting coating has limitations such as high resistance or low charge / discharge efficiency, and is considered to have low economic viability and practical application potential. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] Therefore, the objective of a specific embodiment of the present invention is to provide a negative electrode for lithium metal batteries that can suppress the growth of lithium dendrites by inducing uniform deposition of lithium.

[0010] Furthermore, one specific embodiment of the present invention aims to provide a negative electrode that improves battery stability by suppressing volume changes of the electrode during charging and discharging.

[0011] Furthermore, one specific embodiment of the present invention aims to improve the electrochemical characteristics of lithium metal batteries by using the negative electrode as described above.

[0012] (II) Technical Solution

[0013] One aspect of the present invention provides a negative electrode for a lithium metal battery. According to one embodiment, the negative electrode may include a substrate and a porous layer on the substrate. The porous layer may contain metal powder. Based on lithium metal electrodeposition or full discharge, the porosity of the porous layer, as analyzed by X-ray microscopy (XRM), may be 30% or more.

[0014] Based on the condition before lithium metal electrodeposition or at full discharge, the porosity of the porous layer, as determined by XRM analysis, can be above 30% and below 95%.

[0015] Based on the condition before lithium metal electrodeposition or during full discharge, the closed-pore ratio of the porous layer can be below 0.05%.

[0016] The thickness of the porous layer can be from 0.5 μm to 100 μm.

[0017] The metal powder may contain at least one metal selected from 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.

[0018] The porous layer may further comprise at least one carbon material selected from graphitic carbon nitride, phosphorus-doped graphitic carbon nitride, and boron-doped graphitic carbon nitride.

[0019] The porous layer may further comprise at least one conductive polymer selected from poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), polyaniline (PANI), polypyrrole (PPy), polythiophene (PT), polyacetylene (PA), and polyp-phenylenevinylene (PPV).

[0020] The porous layer may further contain an adhesive.

[0021] The adhesive may be a fluorinated adhesive.

[0022] The adhesive may contain at least one selected from polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polytetrafluoroethylene, and fluororubber.

[0023] The metal powder can be particles with an aspect ratio greater than 1.

[0024] The major axis length of the metal powder can be from 1 μm to 100 μm.

[0025] The metal powder can be rod-shaped particles.

[0026] The metal powder can be a rod-shaped particle with one or more inflection points, where the direction of travel changes from one end to the other.

[0027] The bending angle β that changes along the direction of travel at the inflection point can be greater than 5° and less than 90°.

[0028] The metal powder may have two or more branches.

[0029] The metal powder may have a main branch and at least one side branch connected to the main branch.

[0030] The porous layer may include a first layer on the surface side of the substrate and a second layer on the outer surface side of the porous layer, wherein the particle size of the metal powder in the first layer may be smaller than the particle size of the metal powder in the second layer.

[0031] Lithium metal can be electrodeposited within the pores of the porous layer.

[0032] The substrate can be a current collector.

[0033] (III) Beneficial Effects

[0034] The lithium metal battery anode according to the present invention can store lithium metal in the pores of a porous layer formed on the surface of a substrate, and can increase the contact surface area between lithium metal and current collector, thereby improving electrochemical characteristics.

[0035] Furthermore, the lithium metal battery anode according to the present invention has a high specific surface area, which can reduce the local current density of the anode and thereby provide a uniform electron distribution within the anode.

[0036] Furthermore, the negative electrode for lithium metal batteries according to the present invention can prevent the formation and growth of lithium dendrites during charging and discharging, thereby improving battery stability.

[0037] Furthermore, the negative electrode for lithium metal batteries according to the present invention can provide sufficient space for lithium deposition during battery charging / discharging, thereby suppressing battery volume expansion. Attached Figure Description

[0038] Figure 1 A conceptual diagram showing the charging and discharging states of a battery without a negative electrode is provided, wherein (a) is a conceptual diagram showing the negative electrode cross-section in the discharging state, and (b) is a conceptual diagram showing the negative electrode cross-section in the charging state.

[0039] Figure 2 A schematic diagram illustrating an example of a rod-shaped metal powder according to the present invention.

[0040] Figure 3 A schematic diagram illustrating an example of a rod-shaped metal powder having more than one inflection point.

[0041] Figure 4 A schematic diagram illustrating an example of a metal powder having two or more branches.

[0042] Figure 5 This is a schematic diagram showing the cross-section of a metal powder with through holes.

[0043] Figure 6 This is a schematic diagram showing the negative electrode cross-section in the discharge and charging states of a negative electrode with a porous layer of metal powder formed on the surface of the negative electrode current collector. In (a), the negative electrode in the discharge state is shown, and in (b), the negative electrode in the charging state is shown.

[0044] Figure 7 To take photographs of the metal powder used in the negative electrode of Examples 1 to 4 respectively.

[0045] Figure 8 To take a photograph of the cross-section of the negative electrode in the charging state of Example 1 and a magnified photograph of a portion thereof.

[0046] Figure 9 A photograph showing the internal pore structure of the porous layer of the negative electrode in the discharge state of Example 1.

[0047] Figure 10 To take a photograph of the cross-section of the negative electrode in the charging state of Example 1 and a magnified photograph of a portion thereof.

[0048] Figure 11 To take photographs of the cross-section of the negative electrode in the charged state of Comparative Example 1 and Comparative Example 2, where (a) is the negative electrode of Comparative Example 1 and (b) is the negative electrode of Comparative Example 2.

[0049] Figure 12 The graph shows the specific capacity of the batteries using the negative electrodes of Example 1, Comparative Example 1, and Comparative Example 3 as a function of the number of cycles.

[0050] Figure 13 A graph showing the specific capacity of batteries using the negative electrodes of Examples 2 to 4 as a function of the number of cycles. Best practice

[0051] This invention relates to a negative electrode for lithium metal batteries, specifically, to a negative electrode comprising a porous layer formed of metal powder on the surface of a substrate.

[0052] In this specification, a lithium metal battery is a battery that uses lithium metal as the negative electrode active material. A battery in which lithium metal is not pre-contained in the negative electrode current collector is called a negative electrode-free battery. Figure 1 The diagram schematically shows the cross-section of the negative electrode of the electrodeless battery described above and the negative electrode during charging. Figure 1 (a) shows a cross-section of the negative electrode 10 of a battery without a negative electrode, and (b) shows a cross-section of the charged negative electrode 10'. Figure 1 As shown in (a), a plate-shaped body of conductive metal such as copper is used as the substrate, i.e., the negative electrode current collector 11, as follows: Figure 1 As shown in (b), during charging, lithium metal is electrodeposited on the negative electrode current collector 11 to form a lithium layer 13. In the negative electrode of this electrodeless battery, due to the uneven deposition of the lithium layer on the negative electrode current collector, electron density inhomogeneity occurs, which may lead to the formation of lithium dendrites.

[0053] This invention provides a negative electrode for lithium metal anode batteries, specifically, a negative electrode applicable to electrodeless batteries. According to a specific embodiment of the present invention, the negative electrode for lithium metal anode batteries may include a substrate and a porous layer on the substrate. Based on the conditions before lithium metal electrodeposition or at full discharge, the porosity of the porous layer, as determined by XRM analysis, may be 30% or higher. Hereinafter, the porous layer is also referred to as a porous storage layer or a porous coating.

[0054] The negative electrode of the present invention will now be described in more detail.

[0055] According to one embodiment of the present invention, the negative electrode includes a substrate and a porous layer with a high surface area on the substrate. The porous layer may be formed directly on the substrate, or other layers may be further included between the porous layer and the substrate.

[0056] The substrate can function as a current collector, specifically as a negative electrode current collector. Any material commonly used as a negative electrode current collector can be appropriately used as the substrate. For example, the use of the substrate is not particularly limited, 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 these metals, such as aluminum-cadmium alloys, or calcined carbon. Furthermore, substrates with surface treatments of copper or stainless steel surfaces using carbon, nickel, titanium, silver, etc., can be used as negative electrode current collectors. Additionally, polymers coated with conductive metals or conductive polymers can also be used as the substrate of this invention.

[0057] Furthermore, the substrate can be in various forms, such as film, sheet, foil, mesh, porous body, foam, nonwoven fabric, etc.

[0058] The thickness of the substrate is not particularly limited; for example, the thickness of the substrate can be from 1 μm to 100 μm. More specifically, the thickness of the substrate can be from 3 μm to 50 μm or from 4 μm to 30 μm, and even more specifically, it can be from 4 μm to 12 μm.

[0059] As described above, the negative electrode of the present invention comprises a porous layer on the surface of the substrate (e.g., one or both sides of the substrate). The porous layer can be formed using metal powder.

[0060] The metal powder can be particles with an aspect ratio greater than 1, where the aspect ratio is the ratio of horizontal length to vertical length or the ratio of major axis length to minor axis length, and the metal powder can have an aspect ratio greater than 1 but less than 100. For example, the metal powder can be 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 but less than 100, less than 90, less than 80, less than 70, less than 60, less than 50, less than 40, less than 30, less than 20, or less than 10.

[0061] As described above, because the aspect ratio of the metal powder exceeds 1 and it has a long particle shape along one direction, a porous layer with well-developed pores can be provided on the negative electrode current collector of the present invention. For example, by using the metal powder particles described above to form a porous coating, the metal powder can contact in various forms, thereby providing pores in the porous coating.

[0062] The metal powder is not particularly limited, but for example, the major axis length of the metal powder can be from 1 μm to 100 μm. For example, the metal powder can be rod-shaped particles. Figure 2 Examples of rod-shaped metal powders are shown in the figure.

[0063] like Figure 2 As shown in (a), the rod-shaped metal powder 20 has a straight shape, and the cross-sectional diameter and cross-sectional shape of the metal powder particles can be constant.

[0064] The diameter of the cross-section of the rod-shaped metal powder can vary. For example, as... Figure 2 As shown in (b), the diameter of the cross-section of the rod-shaped metal powder can decrease regularly or irregularly in one direction. As a specific example, the rod-shaped metal powder can have the following characteristics: Figure 2 The needle-like shape shown in (c). Furthermore, as... Figure 2 As shown in (d), the diameter of the cross-section of the rod-shaped metal powder can decrease regularly or irregularly in two directions, or, although not shown in the figure, the diameter of the cross-section can increase regularly or irregularly in two directions.

[0065] As another specific implementation, the rod-shaped metal powder may include more than one inflection point, at which the direction of travel from one end to the other changes. Figure 3 An example of the rod-shaped metal powder with an inflection point described above is shown in the figure.

[0066] For the rod-shaped metal powder, such as Figure 3 As shown in (a), the diameter or shape of the cross-section of the metal powder can be uniform and the direction of travel from one end to the other changes more than once, thus having more than one inflection point P, and as... Figure 3 As shown in (b), the diameter and / or shape of the cross-section of the metal powder may vary and have more than one inflection point.

[0067] Reference Figure 3 (a) provides a more detailed explanation of the aforementioned metal powders with inflection points. (Refer to...) Figure 3 The specific implementation schemes described in (a) can also be applied to Figure 3 (b) Metal powder.

[0068] like Figure 3 As shown in (a), when one end of the rod-shaped metal powder is designated as P0 and the other end as P nWhen n is a natural number greater than or equal to 2, the rod-shaped metal powder may include one or more inflection points P, at which point P flows from P0 towards P0. n The direction of travel changes. By giving the rod-shaped metal powder more than one inflection point, when forming a coating on the substrate, finer pores can be formed between the metal powder particles, and the number of pores formed within the coating can be increased.

[0069] In the rod-shaped metal powder, when the inflection points are sequentially set as P0, P1, P2, P3…P… n (Including both ends) the distance between any inflection point and its adjacent inflection point, for example, the distance between P0 and P1 (L1), the distance between P1 and P2 (L2), or P n-1 With P n The distance between (L) n They can be the same or different.

[0070] As described above, in the rod-shaped metal powder, the direction of travel from one end to the other can be changed with reference to an adjacent inflection point. In this case, the direction of travel can be changed by a predetermined angle. Specifically, the direction of travel can be changed by an acute angle of 90° or less. This angle is the angle formed by the two straight lines of each line segment (bending angle) between two adjacent line segments with reference to an inflection point.

[0071] For example, such as Figure 3 As shown in (a), a rod-shaped metal powder comprising a line segment traveling in the direction from P0 to P1 may include a line segment whose direction of travel changes at the inflection point P1 according to the bending angle and travels in the direction comprising a line segment from P1 to P2. In this case, the bending angle formed by line segments P0-P1 and P1-P2 may be β.

[0072] Although not shown in the figure, a change in the direction of travel in a curved form can also be considered as including more than one inflection point of the present invention. Therefore, in the present invention, the rod-shaped metal powder can be a straight rod or a curved rod.

[0073] The bending angle β included in the rod-shaped metal powder is not limited to this, but the bending angle β 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 more, or 30° or more, and can be 90° or less, 85° or less, or 75° or less.

[0074] As another specific implementation, in the rod-shaped metal powder, there is an imaginary surface comprising two line segments that share a common inflection point and are adjacent to each other, and the included angle between the two line segments. Another imaginary surface adjacent to the imaginary surface may be parallel to each other or not parallel to each other.

[0075] For example, such as Figure 3 As shown in (a), in the rod-shaped metal powder 20, the imaginary surface P0-P1-P2 (including line segments P0-P1 and P1-P2 that share a common inflection point P1 and are adjacent to each other, and the included angle α between the two line segments) and the imaginary surface P1-P2-P3 adjacent to the imaginary surface P0-P1-P2 may not be parallel to each other, although not shown, the two surfaces may be parallel to each other.

[0076] As another specific embodiment, the metal powder may have two or more branches. For example, the metal powder may be a branched metal powder having a main branch and at least one side branch connected to the main branch. For example, as... Figure 2 The rod-shaped metal powder shown in (a) to (d) or as Figure 3 The rod-shaped metal powder with an inflection point shown in (a) or (b) can be the main branch, and more than one side branch can be formed on the main branch. In this case, the side branch can also be the rod-shaped metal powder as described above.

[0077] More specifically, such as Figure 4 As shown in (a) to (b), the metal powder can be a dendritic metal powder having one main branch 22 and one or more side branches 24, and as Figure 4 As shown in (c), the metal powder can be a metal powder with a protrusion shape having a main branch and one or more side branches with a diameter smaller than the main branch.

[0078] like Figure 5 As shown in (a) and (b), the interior of the metal powder may have more than one through-hole 26. The through-hole may be formed in the main branch or in the side branch of the metal powder. At least one of the through-holes may be open and connected to the outside. The opening position of the through-hole is not particularly limited; for example, it may be at the end of the main branch and / or the side branch.

[0079] like Figure 5 As shown, the diameter of the through hole can vary and is not particularly limited.

[0080] The metal powder may be a metal powder containing a metal having properties that allow lithium metal to be electrodeposited on its surface. The metal contained in the metal powder is not particularly limited.

[0081] As one embodiment, the metal powder may comprise a metal, an oxide of the metal, or an alloy of the metal, wherein the metal may be a lithiophilic metal or a non-lithiophilic metal. The lithiophilic metal may be at least one of the lithiophilic metals selected from Si, Zn, Ti, Au, Ag, Pt, Mg, Sn, In, and Bi, and the non-lithiophilic metal may be at least one selected from Cu, Ge, Al, Pb, Sb, Ni, Mn, Fe, Co, Cr, W, and Ru. By forming a porous layer using metal powder comprising the metal, metal oxide, or metal alloy as described above, uniform electrodeposition of lithium can be induced within the porous layer, the formation and growth of lithium dendrites can be suppressed, and the lithium electrodeposition density can be increased, thereby contributing to extending the lifetime characteristics of the negative electrode.

[0082] The metal powder may further contain carbon materials or polymers. For example, the metal powder can be formed by mixing the aforementioned metal, metal oxide, or metal alloy with the carbon materials or polymers.

[0083] Examples of carbon materials that can be included in the metal powder include natural graphite, artificial graphite, hard carbon, soft carbon, carbon black, carbon nanotubes, Ketjen black, acetylene black, fullerene, carbon fiber, fluorocarbons, or carbonitrides. For example, the carbonitride can be at least one carbon material selected from graphitic carbon nitride, phosphorus-doped graphitic carbon nitride, and boron-doped graphitic carbon nitride.

[0084] Furthermore, the polymer can be a conductive polymer, specifically, it can be at least one conductive polymer selected from poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), polyaniline (PANI), polypyrrole (PPy), polythiophene (PT), polyacetylene (PA), and poly(p-phenylenevinylene) (PPV).

[0085] In addition, the metal powder may contain at least one selected from polyimide (PI), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyetherimide (PEI), but is not limited thereto.

[0086] The metal powder contained in the porous layer on the negative electrode current collector can be formed into a predetermined shape through a spontaneous substitution reaction. Specifically, the metal powder can be prepared by using a spontaneous substitution reaction process that utilizes the difference in the reducing power of the metal and a reaction activation process that utilizes hydrogen bubbles generated in an electrolyte containing chloride ions, etc. According to the method described above, metal powder with a high specific surface area can be prepared in a short time using a simple process.

[0087] The spontaneous substitution reaction has been well-proven in theory, and therefore the conditions for carrying out the spontaneous substitution reaction process can be easily selected, which will not be described in detail here. For example, the reaction rate of the spontaneous substitution reaction can be adjusted by regulating the concentration of metal ions contained in the electrolyte.

[0088] Specifically, a plurality of metal powders as described above can be used to provide a negative electrode including a coating, wherein the negative electrode includes a coating on the surface of a substrate that can serve as a negative electrode current collector. As described above, due to the high surface area of ​​the metal powders, the porous layer formed by the metal powders on the surface of the substrate can be a porous layer with well-developed pores, including a large number of pores.

[0089] During the charging process of a battery including the porous layer described 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 battery volume expansion. According to another embodiment, the negative electrode including the porous layer has well-developed pores, thereby allowing for uniform lithium metal deposition and suppressing the formation and growth of lithium dendrites during charging and discharging. Furthermore, the lithium electrodeposition density can be increased, thereby contributing to extended negative electrode lifespan characteristics.

[0090] In this invention, Figure 6 An example of a porous layer formed from the metal powder is schematically shown in (a). Figure 6 A cross-section of the negative electrode 10 is schematically shown in (a), the negative electrode 10 comprising, for example, using Figure 4 The porous layer 41 formed by dendritic metal powder shown in (a) is as follows: Figure 6 As shown in (a), a porous layer with well-developed pores can be formed by randomly arranging the metal powder particles. The pores within the porous layer can connect with each other to form a three-dimensional pore network.

[0091] By forming a porous layer with a three-dimensional pore network as described above on the surface of the substrate, lithium ions moving from the positive electrode during charging can move through the pores of the porous layer into the interior of the coating, thereby enabling lithium metal to be electrodeposited inside the pores.

[0092] Figure 6 (b) is a conceptual diagram showing a charged negative electrode 10' including a porous layer 43 in a charged state, wherein lithium metal 13 is deposited on the electrode through charging. Figure 6 The interior of the porous layer shown in (a).

[0093] As described above, the porous layer formed from metal powder contains numerous pores, thus providing storage space for lithium metal. This prevents uneven lithium electrodeposition during charging and increases the contact surface area between lithium and the negative electrode current collector, thereby improving electrochemical characteristics. Furthermore, since lithium is deposited within the porous layer, volume changes in the negative electrode due to lithium electrodeposition and desorption are prevented, thus maintaining the performance of the negative electrode and battery stability.

[0094] The porous layer according to the present invention can be a single layer or multiple layers of two or more. For example, as... Figure 6 As shown in (a), a single layer can be formed using metal powder. Furthermore, multiple layers can be formed using two or more metal powders with different particle shapes or 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 particle size of the metal powder contained in the first layer may be smaller than the particle size of the metal powder located in the second layer. In the porous layer, a first coating with a small pore size can be included using a first metal powder with a small particle size on the current collector side, and a second coating with a larger pore size can be included using a second metal powder with a larger particle size on the first coating.

[0095] Since the metal powder in the first layer located on the negative electrode current collector side has a smaller particle size, it forms smaller pores, thereby improving the uniformity of lithium electrodeposition in the porous layer, thus improving the electrodeposition efficiency and suppressing dendrite growth.

[0096] Although not limited to this, the thickness of the first layer in the porous layer may be greater than the thickness of the second layer.

[0097] For the particle size of the metal powder, the outer boundary determined by the main branch and side branch in a metal powder can be set as the particle boundary, and the particle size can be determined based on the volume.

[0098] The porous layer may simultaneously contain the metal powder and the binder. For example, the porous layer described above can be prepared by: forming a slurry with a metal powder having a high surface area, a binder, and a solvent on the surface of a substrate provided as a negative electrode current collector, and then casting the slurry onto the surface of the substrate and drying it.

[0099] The binder included in the preparation of the slurry is not particularly limited, and binders commonly used in electrode manufacturing can also be appropriately used in this invention. For example, the binder may contain a selection from styrene-butadiene rubber, acrylated styrene-butadiene rubber, nitrile rubber, polybutadiene rubber (BR), acrylic rubber, butyl rubber, ethylene-propylene copolymer, polyepoxychloropropane, 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 (PPy), polypyrrole (PPy), poly(3,4-ethylene dioxythiophene) (PEDOT), polyvinylidene fluoride (PVdF), and poly(vinylidene fluoride-co-hexafluoropropylene copolymer (Poly(vinylidene fluoride-co-hexafluoropropylene)). At least one of the following: fluoride-co-hexafluoropropylene, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), polymethyl methacrylate, and fluororubber.

[0100] In one embodiment, the adhesive may be a styrene-butadiene rubber (SBR) based adhesive, carboxymethyl cellulose (CMC), polyacrylic acid based adhesive, poly(3,4-ethylenedioxythiophene) (PEDOT) based adhesive, or a fluorinated adhesive. More specifically, the adhesive may be a fluorinated adhesive, for example, the fluorinated adhesive may be at least one selected from polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polytetrafluoroethylene, and fluororubber.

[0101] The binder is not particularly limited, but its content can be from 1% to 30% by weight relative to the solid weight of the slurry. When the binder content is less than 1% by weight, the adhesion of the porous layer may decrease; when the binder content exceeds 30% by weight, the resistance may increase, which may lead to a decrease in conductivity and potentially further reduce lithium deposition performance. More specifically, the binder content can be 1% or more, 1.2% or more, 1.5% or more, 2% or more, or 3% or more, and can be less than 30% by weight, less than 25% by weight, less than 20% by weight, less than 15% by weight, or less than 12% by weight.

[0102] Furthermore, the solvent is not particularly limited, and solvents commonly used in the manufacture of electrodes may also be appropriately used in this invention. For example, the solvent may include at least one selected from water, acetone, formic acid, chloroform, isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (MF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF).

[0103] The solvent is not particularly limited, but the solvent content in the slurry can be from 30% to 60% by weight.

[0104] The method of applying the slurry according to the invention to the surface of a substrate is not particularly limited, and methods such as rod coating, casting, spraying, or doctor blade coating can be used. Specifically, a wet coating method can be used. The thickness of the porous layer can be easily controlled by adjusting, for example, the viscosity of the slurry or the height of the doctor blade.

[0105] At this point, the thickness of the porous layer is not limited to this, but the thickness of the porous layer can be from 0.5 μm to 100 μm. Since the porous layer has the function of storing lithium metal, it can be formed to a minimum thickness capable of storing lithium metal. In this respect, the thickness of 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.

[0106] Furthermore, when the porous layer is too thick, lithium-ion transport may be hindered, potentially reducing or making it difficult to ensure the desired effect. On the other hand, excessive thickness of the porous layer may lead to a loss of energy density per unit volume and weight. In the aspects described above, the thickness of the porous layer of the present invention can be less than 100 μm, less than 90 μm, less than 80 μm, less than 70 μm, less than 60 μm, or less than 50 μm.

[0107] The porous layer obtained by this invention is not limited thereto, but based on the condition before lithium metal electrodeposition or at full discharge, the porosity of the porous layer analyzed by X-ray microscopy (XRM) can be 30% or more and 95% or less. Specifically, the porosity of the porous layer can be 50% or more, 70% or more, 80% or more, or 85% or more. Furthermore, with respect to the porous layer according to the invention, the high porosity described above can be achieved by connecting the pores to each other to form a porous layer.

[0108] Based on the conditions before lithium metal electrodeposition or during full discharge, the closed-pore ratio (representing the proportion of pores that are not connected to each other) of the porous layer can be less than 0.05%, less than 0.03%, less than 0.01%, or less than 0.0095%. That is, the negative electrode according to the present invention has a very developed porosity, and the pores are connected to each other to form a three-dimensional pore network, thereby improving the lithium ion insertion and extraction characteristics during charging and discharging.

[0109] Furthermore, based on the condition before lithium metal electrodeposition or at full discharge, the specific surface area of ​​the porous layer according to the present invention can be 300 m². 2 / m 3 The porous layer described above can have a high specific surface area.

[0110] Furthermore, in the porous layer according to the invention, the pores are formed by metal powder with a high surface area, thus allowing for the inclusion of pores of various sizes. For example, the porous layer according to the invention can contain pores ranging from nanoscale to medium-sized.

[0111] As described above, the porous layer formed on the negative electrode current collector can contain pores of various sizes, so lithium metal can be electrodeposited in the pores of the porous layer.

[0112] The negative electrode provided in this invention comprises a porous layer on the surface of a substrate (provided as a negative electrode current collector), and lithium batteries are deposited within the pores of the porous layer, thereby increasing the electrodeposition density and thus improving battery life.

[0113] Furthermore, since lithium is stably electrodeposited within the pores, the formation of lithium dendrites can be suppressed, and the contact area between lithium metal and the current collector can be increased. Moreover, the high specific surface area reduces the local current density of the negative electrode, thereby providing a uniform electron distribution within the lithium electrode. This prevents the formation and growth of lithium dendrites during charging / discharging, thus improving battery stability.

[0114] Furthermore, when using the current collector according to the present invention, sufficient space can be provided for lithium deposition during battery charging / discharging, thereby suppressing battery volume expansion. Detailed Implementation

[0115] The present invention will now be described in more detail through embodiments. However, these embodiments are merely examples of the present invention and are not intended to limit the scope of the invention.

[0116] Preparation of metal powders

[0117] Preparation Example 1

[0118] 1.0M sodium chloride and 0.2M hydrogen chloride were added as reaction promoters to the electrolyte at room temperature where copper sulfate (CuSO4) (concentration: 0.1M) was dissociated.

[0119] An aluminum plate (10cm×8cm) with a reducing power higher than that of copper sulfate is added to the electrolyte at room temperature, and the reaction is carried out for 20 minutes while hydrogen bubbles are generated in the electrolyte.

[0120] Copper powder is prepared by spontaneous substitution reaction of copper, taking advantage of the difference in reducing power between the aluminum plate and copper in the electrolyte.

[0121] The prepared copper powder was photographed and shown. Figure 7 In (a), the size of the metal powder was measured using field emission scanning electron microscopy (FESEM), and the results are shown in Table 1 below.

[0122] Preparation Example 2

[0123] Copper powder was prepared using the same method 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.

[0124] The copper powder prepared above was photographed and shown. Figure 7 In (b), the size of the metal powder was measured using FESEM, and the results are shown in Table 1 below.

[0125] Preparation Example 3

[0126] Copper powder was prepared using the same method 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.

[0127] The copper powder prepared above was photographed and shown. Figure 7 In (c), the size of the metal powder was measured using FESEM, and the results are shown in Table 1 below.

[0128] Preparation Example 4

[0129] Copper powder was prepared using the same method 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.

[0130] The copper powder prepared above was photographed and shown. Figure 7 In (d), the size of the metal powder was measured using FESEM, and the results are shown in Table 1 below.

[0131] [Table 1]

[0132]

[0133] Example 1

[0134] A slurry was prepared by adding 90% by weight of the dendritic copper metal powder obtained in Preparation Example 1 and 10% by weight of polyvinylidene fluoride (PVdF) binder to NMP solvent. The solids and solvent were added in a weight ratio of 60:40. The prepared slurry was cast onto one side of a copper current collector (4 μm thick) using a doctor blade method and dried to form a porous layer with a thickness of 48 μm, thereby fabricating the negative electrode.

[0135] The porosity and closed-pore ratio of the porous layer of the obtained negative electrode were measured by mercury intrusion porosimetry (MIP) and X-ray microscopy (XRM), and the results are shown in Table 2.

[0136] A cross-section of the aforementioned manufactured negative electrode was photographed, and the photograph is shown below. Figure 8 In (a). Furthermore, a portion of the photograph is enlarged and shown. Figure 8 In (b).

[0137] Furthermore, the pore distribution of the porous layer obtained above was captured in 3D and shown in [the image / image]. Figure 9Specifically, for the negative electrode with the porous layer formed thereon, a three-dimensional structure of the pores was obtained using a Zeiss Xraida 520 Versa X-ray microscope (an X-ray microscope is a device equipped with an X-ray source and a detector, and consists of a magnifying lens between the detectors). The obtained three-dimensional structure image was then rendered using GEODICT software to obtain a 3D image of the internal pore structure of the negative electrode mixture layer. This is shown in... Figure 9 middle.

[0138] Examples 2 to 4

[0139] The negative electrode was manufactured using the same method as in Example 1, except that the metal powders obtained in Preparation Examples 2 to 4 were used.

[0140] In addition, the porosity characteristics of the porous layers of the negative electrode obtained in each embodiment were analyzed, and the results are shown in Table 2.

[0141] [Table 2]

[0142]

[0143] As shown in Table 2, the negative electrodes manufactured in each embodiment have a porosity of over 85%, exhibiting highly developed porosity, with a closed-pore rate of less than 0.01%. The pores are open and interconnected, forming a three-dimensional pore network. Figure 8 (a) A cross-sectional view of the negative electrode with a porous layer in Example 1 and Figure 8 (b)( Figure 8 As shown in the enlarged view of (a), dendritic metal powder aggregates and forms a porous layer on the surface of the copper current collector. Visual observation also reveals well-developed pores between the metal powder particles in the porous layer. Furthermore, the image showing the internal pore structure of the porous layer... Figure 9 It can be confirmed that the porous layer obtained in Embodiment 1 has well-developed pores inside, and these pores are connected to each other to form a three-dimensional pore network structure.

[0144] Comparative Example 1

[0145] The copper current collector used to form the coating in Example 1 was used as the negative electrode current collector, and no separate coating was formed.

[0146] Comparative Example 2

[0147] The mixture will contain carbon powder (particle size 40 nm, specific surface area 62 m²). 2 / g, powder density is 0.16g / cm³ 3The slurry (trade name: Supe-P Li, Timcal Corporation) was cast onto the same copper current collector as in Example 1 to create a negative electrode with a carbon coating.

[0148] The same method as in Example 1 was used, except that carbon powder was used instead of the dendritic metal powder in Example 1 to prepare the slurry.

[0149] The porosity of the coating thus formed on the copper current collector was measured, and the porosity was less than 30%.

[0150] Comparative Example 3

[0151] Silver was coated onto the same copper current collector as in Example 1 using a sputtering coating method to create a negative electrode with a silver coating that is non-porous and has a thickness of 100 nm.

[0152] [Battery manufacturing and battery performance evaluation]

[0153] - Negative electrode of Example 1 and Comparative Examples 1 to 3 -

[0154] Each negative electrode manufactured using Example 1 and Comparative Examples 1 to 3 above contains NCM 622 (3mAh / cm³). 2 A coin-shaped full cell (N / P ratio = 2.3) is manufactured using a positive electrode as the positive electrode active material and a carbonate-based electrolyte.

[0155] First, the batteries using the negative electrodes manufactured in Example 1, Comparative Example 1 and Comparative Example 2 were charged, and the charged negative electrodes were disassembled to observe their cross-sections.

[0156] A cross-section of the negative electrode manufactured in Example 1, showing its charging state, is photographed and illustrated. Figure 10 In (a), a magnified photograph of a portion of it is shown. Figure 10 In (b).

[0157] from Figure 10 As shown in (a) and (b), lithium ions are deposited within the pores of the porous layer formed on the surface of the negative electrode current collector. As described above, through charging, lithium ions are electrodeposited within the porous coating of the negative electrode, and... Figure 8 Compared to (a), it can be seen that the thickness of the negative electrode has not changed, which confirms that the volume expansion of the negative electrode caused by charging and discharging is suppressed.

[0158] In addition, a cross-section of the negative electrode of the planar copper current collector manufactured in Comparative Example 1 was photographed and shown. Figure 11 In (a). From Figure 11As shown in (a), lithium metal is electrodeposited on the surface of the copper current collector 11, thereby forming a lithium metal layer 13. It is known that due to the formation of the lithium metal layer as described above, the volume of the negative electrode expands, which may lead to the problem of battery volume expansion caused by charging and discharging.

[0159] In addition, a cross-section of the negative electrode with a carbon coating on the planar copper current collector manufactured in Comparative Example 2 was photographed and shown. Figure 11 In (b). From Figure 11 As shown in (b), lithium metal is electrodeposited on the surface of the carbon coating 45 formed on the copper current collector 11, thereby forming a lithium layer. Due to the surface shape of the carbon coating, the problem of volume expansion caused by lithium electrodeposition is reduced compared to the negative electrode of Comparative Example 1. However, there is electrodeposited lithium on the surface of the carbon on the outermost surface of the negative electrode, so the problem of battery volume expansion caused by charging and discharging still exists.

[0160] Although the negative electrode of Comparative Example 3 is not shown separately, the negative electrode of Comparative Example 3 also has the same planar surface as Comparative Example 1. Due to the silver coating, it can provide the result of increasing the lithium electrodeposition density, but it is known that there is a problem of volume expansion of the negative electrode during charging and discharging.

[0161] Although the negative electrode of Comparative Example 3 is not shown separately, the negative electrode of Comparative Example 3 also has the same planar surface as Comparative Example 1. Due to the silver coating, it can provide the result of increasing the lithium electrodeposition density, but it is known that there is a problem of volume expansion of the negative electrode during charging and discharging.

[0162] In addition, for batteries using the negative electrodes of Example 1, Comparative Example 1, and Comparative Example 3, charge-discharge conditions of 0.2C and 0.3C were performed to evaluate their lifespan characteristics. The evaluation results are shown below. Figure 12 middle.

[0163] from Figure 12 It can be seen that in the battery including the negative electrode according to Example 1, the battery capacity hardly changes and remains constant until about 45 cycles. However, in the battery 2 including the negative electrode of Comparative Example 1, the capacity tends to gradually decrease from the point of never reaching 10 cycles. In the case of the battery 3 including the negative electrode of Comparative Example 3, the capacity decreases from about the 25th cycle.

[0164] -Negative electrodes of Examples 2 to 4-

[0165] The battery is manufactured using the same method as battery 1 using the negative electrode of Example 1, except that the negative electrodes manufactured in Examples 2 to 4 above are used.

[0166] For each battery manufactured above, charge and discharge conditions of 0.2C and 0.3C were applied to evaluate its lifespan characteristics, and the evaluation results are presented below. Figure 13 middle.

[0167] from Figure 13 It can be seen that in each battery including the negative electrode of Examples 2 to 4, the battery capacity hardly changes and remains constant until about 30 cycles are run, and the battery including the negative electrode of Example 4 shows excellent results in that the capacity does not change and remains constant until 45 cycles.

[0168] [Explanation of reference numerals in the attached figures]

[0169] 10: Negative electrode

[0170] 10': Charged negative terminal

[0171] 11: Negative electrode current collector

[0172] 13: Lithium metal

[0173] 20: Metal powder

[0174] 22: Main Branch

[0175] 24: Lateral branches

[0176] 26: Through hole

[0177] 30: Adhesive

[0178] 41: Porous layer

[0179] 43: Charged porous layer

[0180] P, P0, P1, P2, P3, Pn: Inflection Points

[0181] α: included angle

[0182] β: Bending angle

Claims

1. A negative electrode for a lithium metal battery, comprising a substrate and a porous layer on the substrate, in, The porous layer contains metal powder. Based on the condition before lithium metal electrodeposition or at full discharge, the porosity of the porous layer, as analyzed by X-ray microscopy (XRM), is greater than 30%.

2. The negative electrode for a lithium metal battery according to claim 1, wherein, Based on the condition before lithium metal electrodeposition or at full discharge, the porosity of the porous layer, as determined by XRM analysis, is greater than 30% and less than 95%.

3. The negative electrode for a lithium metal battery according to claim 1, wherein, Based on the condition before lithium metal electrodeposition or during full discharge, the closed-porosity of the porous layer is less than 0.05%.

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

5. The negative electrode for a lithium metal battery according to claim 1, wherein, The metal powder comprises at least one metal selected from 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 negative electrode for a lithium metal battery according to claim 1, wherein, The porous layer further comprises at least one carbon material selected from graphitic carbon nitride, phosphorus-doped graphitic carbon nitride, and boron-doped graphitic carbon nitride.

7. The negative electrode for a lithium metal battery according to claim 1, wherein, The porous layer further comprises at least one conductive polymer selected from poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), polyaniline (PANI), polypyrrole (PPy), polythiophene (PT), polyacetylene (PA), and poly(p-phenylenevinylene) (PPV).

8. The negative electrode for a lithium metal battery according to claim 1, wherein, The porous layer further comprises an adhesive.

9. The negative electrode for a lithium metal battery according to claim 8, wherein, The adhesive is a fluorinated adhesive.

10. The negative electrode for a lithium metal battery according to claim 8, wherein, The adhesive comprises at least one selected from 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 with an aspect ratio greater than 1.

12. The negative electrode for a lithium metal battery according to claim 1, wherein, The major axis length of the metal powder is from 1 μm 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 with one or more inflection points, at which 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 that changes along the direction of travel at the inflection point is greater than 5° and less than 90°.

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 negative electrode for a lithium metal battery according to claim 1, wherein, 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, wherein the particle size of the metal powder in the first layer is smaller than the particle size of 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 within 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.

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