Lithium secondary battery electrode and manufacturing method therefor

Abstract

According to embodiments of the present disclosure, the electrode for a lithium secondary battery may comprise: an electrode current collector; a surface modification layer disposed on the electrode current collector; and a porous layer disposed on the surface modification layer. The lithium secondary battery may include an electrode for a lithium secondary battery and a counter electrode. Stability and electrochemical characteristics of the lithium secondary battery can be improved.

Description

Electrode for lithium secondary battery and method for manufacturing same

[0001] The present disclosure relates to an electrode for a lithium secondary battery, a lithium secondary battery including the same, and a method for manufacturing the electrode for a lithium secondary battery.

[0002]

[0003] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0004] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Lithium secondary batteries have high operating voltage and energy density per unit weight, and can be advantageous in terms of charging speed and weight reduction.

[0005] Graphite and silicon are commonly used as anode materials for lithium secondary batteries. However, graphite and silicon have high reaction potentials and low capacities, limiting their ability to increase the energy density and capacity of lithium secondary batteries. Lithium metal, however, possesses low potential and high capacity, potentially increasing the efficiency and energy density of lithium secondary batteries.

[0006] However, when using lithium metal, lithium can grow unevenly on the surface of the lithium metal during the charging process, forming lithium dendrites. This can lead to short circuits, overheating, and explosion of the electrode. Furthermore, the volume change of the electrode during the deposition and desorption of lithium from the lithium metal surface can increase, reducing the lifespan and stability of the lithium secondary battery.

[0007]

[0008] An object of the present disclosure is to provide an electrode for a lithium secondary battery having improved stability.

[0009] An object of the present disclosure is to provide a lithium secondary battery having improved stability.

[0010]

[0011] An electrode for a lithium secondary battery according to embodiments of the present disclosure includes an electrode current collector, a surface modification layer disposed on the electrode current collector, and a porous layer disposed on the surface modification layer.

[0012] In some embodiments, the surface modification layer may include a lithium-affinity material.

[0013] In some embodiments, lithium ions can be reduced to lithium metal on the lithium-affinity material at a voltage lower than the voltage at which the lithium-affinity material and lithium ions are alloyed.

[0014] In some embodiments, the surface modification layer may include boron nitride.

[0015] In some embodiments, the boron nitride may have an amorphous structure.

[0016] In some embodiments, the thickness of the surface modification layer may be thinner than the thickness of the porous layer.

[0017] In some embodiments, the porous layer may comprise a lithium-affinity material.

[0018] In some embodiments, the porous layer may comprise at least one metal selected from the group consisting of Cu, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi or Sb, an oxide thereof or an alloy of two or more thereof.

[0019] In some embodiments, the porous layer may include a matrix comprising the lithium-affinity material and pores formed on the surface and inside of the matrix.

[0020] In some embodiments, the porous layer may comprise a fiber or porous foam comprising the lithium-affinity material.

[0021] In some embodiments, the porous layer may include a framework comprising the lithium-affinity material and having a three-dimensional network structure.

[0022] In some embodiments, the porous layer may include metal-containing particles comprising the lithium-affinity material and pores formed between the metal-containing particles.

[0023] In some embodiments, the metal-containing particles may have a dendrite shape.

[0024] In some embodiments, the metal-containing particles comprise a core and a coating covering at least a portion of the core, wherein the coating may comprise the lithium-affinity material.

[0025] In some embodiments, the core may comprise at least one metal selected from the group consisting of Ni, Mn, Fe, Co, Cr, W, Ru, Cu, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi or Sb, an oxide thereof or an alloy of two or more thereof.

[0026] In some embodiments, at least some of the pores may be connected from the upper surface of the surface modification layer to the upper surface of the porous layer.

[0027] In some embodiments, the surface modification layer may have a nonporous structure.

[0028] A lithium secondary battery according to embodiments of the present disclosure may include an electrode for a lithium secondary battery, and a counter electrode facing the electrode for a lithium secondary battery.

[0029]

[0030] An electrode for a lithium secondary battery may include an electrode current collector, a surface modification layer formed on the electrode current collector and containing boron nitride, and a porous layer disposed on the surface modification layer. The top plating phenomenon in which lithium is deposited only on the upper portion of the porous layer can be suppressed, and bottom electrodeposition of lithium metal can be induced.

[0031] Lithium metal can be uniformly deposited within the porous layer, reducing volume changes in the electrode layer. This can suppress the growth of lithium dendrites caused by uneven lithium deposition. This can improve the stability and electrical properties of lithium secondary batteries.

[0032]

[0033] FIG. 1 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0034] FIG. 2 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0035] FIG. 3 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0036] FIG. 4 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0037] Figures 5 and 6 are schematic drawings showing metal-containing particles according to exemplary embodiments, respectively.

[0038] Figures 7a to 7d are images of electrodes for lithium secondary batteries of examples and comparative examples, respectively.

[0039] Figures 8a to 8d are SEM images of cross-sections of electrodes for lithium secondary batteries of examples and comparative examples, respectively.

[0040] Figure 9 is a graph showing the capacity retention rate of lithium secondary batteries of examples and comparative examples.

[0041]

[0042] According to embodiments of the present disclosure, an electrode for a lithium secondary battery and a lithium secondary battery including an electrode current collector, a surface modification layer, and a porous layer are provided.

[0043] Lithium secondary batteries according to embodiments of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, lithium secondary batteries according to embodiments of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, and other vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0044] The terms “upper”, “lower”, “top surface”, “bottom surface”, “bottom surface”, etc. used in this disclosure indicate the relative positions of each component and do not imply an absolute superior-subordinate relationship.

[0045] Unless otherwise specifically defined in this disclosure, when a part such as a layer, film, thin film, region, plate, etc. is said to be “on” or “over” another part, this may include not only cases where it is “directly on” the other part, but also cases where there is another part in between.

[0046] Hereinafter, the present disclosure will be described in detail with reference to the drawings. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0047] FIG. 1 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0048] Referring to FIG. 1, an electrode for a lithium secondary battery (hereinafter, abbreviated as “electrode”) may include an electrode current collector (100), a surface modification layer (110) disposed on the electrode current collector (100), and a porous layer (120) disposed on the surface modification layer (110).

[0049] The electrode current collector (100) may include gold, stainless steel, nickel, aluminum, iron, titanium, copper or an alloy thereof, for example, copper or a copper alloy.

[0050] The porous layer (120) may have a high affinity for lithium and may include, for example, a lithiophilic material. A lithiophilic material may refer to a material having a low reduction potential and reducing lithium ions on the surface to form lithium nuclei.

[0051] The voltage at which lithium metal is deposited on the lithium-affinity material may be lower than the voltage at which an alloying reaction occurs between the lithium-affinity material and lithium. Accordingly, lithium ions may be reduced to lithium metal rather than a lithium alloy on the porous layer (120), and lithium nuclei may be preferentially formed on the porous layer (120).

[0052] Lithium metal can be deposited and grown on the surface of the porous layer (120). For example, during charge and discharge, the electrodeposition and desorption reactions of lithium metal, rather than the oxidation and reduction reactions of the electrode active material, may be the main reversible reactions of the lithium secondary battery. In one embodiment, the lithium secondary battery may be provided as a lithium metal battery.

[0053] Therefore, lithium metal can grow within the porous layer (120) during charging and discharging of a lithium secondary battery. Lithium metal has a low reaction potential and high reversible capacity, so that the output characteristics and energy density of a lithium secondary battery can be improved.

[0054] In one embodiment, the porous layer (120) may include a lithiophilic metal as a lithium-affinity material. For example, the porous layer (120) may include a metal such as Cu, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi, or Sb, an oxide thereof, or an alloy of two or more thereof.

[0055] According to exemplary embodiments, the porous layer (120) may include a matrix including the lithium-affinity material and pores formed on the surface and inside of the matrix.

[0056] Current can be uniformly distributed within the porous layer (120) through the pores, thereby suppressing local current concentration. Accordingly, the uniform current density allows lithium metal to grow uniformly within the porous layer (120), and the growth of lithium dendrites can be suppressed.

[0057] For example, if the current density is unevenly distributed within the porous layer, the growth and deposition of lithium metal may be concentrated in certain areas due to localized current concentration. In this case, overvoltage may cause lithium dendrites or lithium ion crystals to grow in these areas. Lithium dendrites have low conductivity and easily lose electrical contact, which can reduce the capacity and energy density of lithium secondary batteries.

[0058] In one embodiment, at least some of the pores formed in the porous layer (120) may be connected from the upper surface of the surface modification layer (110) to the upper surface of the porous layer (120). Accordingly, lithium ions may smoothly move to the lower portion of the porous layer (120), for example, to the surface modification layer (110), so that top plating may be more suppressed.

[0059] In some embodiments, the porous layer (120) may include fibers comprising the lithium-affinity material.

[0060] For example, the fiber may have a nonwoven form formed by interweaving or entangling a plurality of wires. The plurality of wires may be formed of a lithium-compatible material.

[0061] FIG. 2 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0062] Referring to FIG. 2, the porous layer (120) may have a porous foam structure including the lithium-affinity material.

[0063] For example, the porous foam may mean a sponge-shaped porous structure formed of a lithium-affinity material and including a plurality of pores (122) therein.

[0064] In one embodiment, the porous foam may include open pores or closed pores. Open pores may refer to pores that are interconnected, while closed pores may refer to pores that are isolated from other pores.

[0065] FIG. 3 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0066] Referring to FIG. 3, the porous layer (120) may have a framework structure including the lithium-affinity material.

[0067] The above framework may have a three-dimensional network structure. For example, lithium-affinity wires (124) containing lithium-affinity materials may be connected to each other to form a three-dimensional network.

[0068] In one embodiment, the framework may have a mesh structure when viewed in a planar direction. For example, the lithium affinity wires (124) may extend to intersect each other and be connected to each other at the intersections.

[0069] FIG. 4 is a schematic cross-sectional view showing an electrode for a lithium secondary battery according to exemplary embodiments.

[0070] Referring to FIG. 4, the porous layer (120) may include metal-containing particles (126) including the lithium-affinity material.

[0071] For example, a porous layer may be formed when metal-containing particles (126) are randomly arranged and come into contact with each other. The metal-containing particles (126) may come into contact with each other to form a three-dimensional network.

[0072] A void (125) may be formed between the metal-containing particles (126). A space for electrodeposition of lithium metal may be provided by the void (125).

[0073] According to exemplary embodiments, the metal-containing particles (126) may each have a spherical shape, a donut shape, a rod shape, a bent rod shape, a cone shape, a needle shape, a flake shape, a dendrite shape, or a dendrimer shape.

[0074] FIG. 5 is a schematic drawing showing metal-containing particles according to exemplary embodiments.

[0075] Referring to FIG. 5, the metal-containing particles (126) may include a principal axis, and branches branching off from the principal axis or protrusions protruding from the principal axis. The principal axis (12) may refer to the center of the metal-containing particle (126) and may refer to a portion where a plurality of branches (14) or a plurality of protrusions are connected. For example, the principal axis (12) may be a branch having the most connection points among the branches of the metal-containing particle.

[0076] In one embodiment, the main shaft (12) may have a rod shape, a cone shape, a needle shape, or a bent rod shape. In one embodiment, the branch (14) may have a rod shape or a cone shape, and the protrusion may have a needle shape or a hemispherical shape.

[0077] In one embodiment, the protrusions or branches (14) may have a shorter length and smaller diameter than the main axis (12).

[0078] In one embodiment, the metal-containing particles (126) may have a dendritic shape. Accordingly, more voids may be formed between the metal-containing particles (126). For example, the adhesion of the metal-containing particles (126) may be reduced due to steric hindrance, thereby increasing the space for lithium metal deposition between the metal-containing particles (126).

[0079] Additionally, the surface area of ​​the metal-containing particles (126) may increase, and the electrodeposition sites of lithium metal within the porous layer (120) may increase. Additionally, as the movement of lithium ions to the lower portion of the porous layer (120) becomes smoother, lithium metal may grow from the lower portion of the porous layer (120).

[0080] According to exemplary embodiments, the metal-containing particles (126) may include pores. For example, a single through hole may be formed within the metal-containing particles (126), or a plurality of pores may be formed within and / or on the surface of the metal-containing particles (126). The pores may include open pores or closed pores.

[0081] As the metal-containing particles (126) include pores, the surface area of ​​the porous layer (120) can increase. In addition, the pores can provide additional space for lithium metal to grow.

[0082] FIG. 6 is a schematic drawing showing metal-containing particles according to exemplary embodiments.

[0083] Referring to FIG. 6, the metal-containing particle (126) may include a core (22) and a shell (24) covering at least a portion of the core (22). The core (22) may have the above-described spherical shape, donut shape, rod shape, bent rod shape, cone shape, needle shape, flake shape, dendrite shape, or dendrimer shape.

[0084] In one embodiment, the shell (26) may have a film shape that covers the entire surface of the core. In one embodiment, the shell may have an island shape that is locally formed on a portion of the surface of the core.

[0085] In some embodiments, the shell (24) may include the lithium-compatible metal, an oxide of the lithium-compatible metal, or an alloy of the lithium-compatible metal described above. Accordingly, lithium metal nuclei may be generated on the surface of the metal-containing particle (126), allowing the lithium metal to be deposited and grown.

[0086] For example, the shell (24) may include at least one metal selected from the group consisting of Cu, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi or Sb, an oxide thereof or an alloy of two or more thereof.

[0087] In one embodiment, when the shell (24) includes a lithium-affinity material, the core (22) may include a metal, a metal oxide, an alloy, a carbon-based compound, a polymer, and the like.

[0088] In one embodiment, the core (22) may be conductive. Accordingly, the current density on the surface of the metal-containing particle may be uniform, and the movement of lithium ions may be facilitated. Accordingly, lithium metal may be deposited more uniformly.

[0089] For example, the core (22) may include at least one metal selected from the group consisting of Ni, Mn, Fe, Co, Cr, W, Ru, Cu, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi or Sb, an oxide thereof or an alloy of two or more thereof.

[0090] In some embodiments, the length of the metal-containing particle (126) may be 1 μm to 10 μm. The length of the metal-containing particle (126) may refer to the length of the longest portion of the metal-containing particle (126), for example, the length of the main axis.

[0091] Within the above range, the capacity and energy density of the porous layer (120) can be further improved while suppressing uneven deposition of lithium metal.

[0092] In one embodiment, the length of the metal-containing particles (126) may be 2 μm to 9 μm, 2 μm to 8 μm, or 2 μm to 5 μm. Within this range, the stability and energy density of the lithium secondary battery may be further improved.

[0093] In some embodiments, the porous layer (120) may further include a binder (128).

[0094] For example, the binder (128) can bind metal-containing particles to each other. Accordingly, the structural stability of the electrode can be further improved, and the life characteristics of the lithium secondary battery can be further enhanced.

[0095] In one embodiment, the binder (128) is selected from the group consisting of styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, ethylene-propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, acrylate resin, polyvinyl alcohol, polyaniline (PANI), polythiophene (PT), polyacetylene, polypyrrole (PPy), poly(3,4-ethylene dioxythiophene) (PEDOT), polyvinylidene fluoride (PVdF), It may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl pyrrolidone (PVP), polytetrafluoroethylene (PTFE), polymethylmethacrylate, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), fluoroelastomer, etc. These may be used alone or in combination of two or more.

[0096] In one embodiment, the binder (128) may include polyvinylidene fluoride, polytetrafluoroethylene, fluoroelastomer, or the like, for example, polyvinylidene fluoride and / or polytetrafluoroethylene.

[0097] In one embodiment, the content of the binder (128) may be greater than 0 wt% and less than or equal to 50 wt%, or greater than 0 wt% and less than or equal to 10 wt% of the total weight of the porous layer (120).

[0098] In one embodiment, a mixture of metal-containing particles and / or a binder may be coated on a surface modification layer (110) to form a porous layer (120). The metal-containing particles may be randomly stacked on the surface modification layer (110) to form the porous layer (120).

[0099] In one embodiment, the mixture may further include a solvent. A solvent capable of uniformly mixing the metal-containing particles and the binder may be used. For example, the solvent may include water, acetone, formic acid, chloroform, isopropanol, N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, dimethyl sulfoxide (DMSO), or tetrahydrofuran (THF).

[0100] In one embodiment, the thickness of the porous layer (120) may be 0.5 μm to 100 μm, 1 μm to 90 μm, 2 μm to 80 μm, 3 μm to 60 μm, or 5 μm to 50 μm. Within the above range, lithium ion transport can be smoothly achieved while a sufficient amount of lithium metal can be stored. Accordingly, the capacity and energy density of the lithium secondary battery can be further improved.

[0101] The surface modification layer (110) may be formed on at least one surface of the electrode current collector (110), and may be formed on both surfaces (e.g., the upper surface and the lower surface). The surface modification layer (110) may be formed by applying or depositing a material for forming a surface modification layer on the electrode current collector (100).

[0102] For example, it can be grown by a deposition method for forming a surface modification layer on an electrode current collector (100). Deposition methods include chemical vapor deposition (CVD), atomic layer deposition (ALD), and plasma enhanced chemical vapor deposition (PECVD).

[0103] The surface modification layer (110) may include a lithium-compatible material. On the lithium-compatible material, the voltage at which lithium ions are alloyed with the lithium-compatible material is higher than the voltage at which lithium ions are reduced to lithium metal, so that electrodeposition of lithium metal may occur preferentially.

[0104] Since the surface modification layer (110) has a high affinity for lithium, lithium metal may be deposited from the surface modification layer (110) side. For example, since the voltage for generating lithium metal nuclei on the electrode current collector (100) is relatively high, it may have low reactivity toward lithium ions. Therefore, when charging and discharging the lithium secondary battery, lithium may be deposited first on the upper portion of the porous layer (120), causing the lithium metal to grow unevenly. In this case, the growth of lithium dendrites may be promoted, and the capacity and energy density of the lithium secondary battery may be reduced.

[0105] According to exemplary embodiments, as a surface modification layer (110) is formed on the surface of the electrode current collector (100), the resistance to lithium nucleation can be reduced and a high affinity for lithium can be achieved. Accordingly, top plating of lithium metal can be suppressed, so that lithium metal can be uniformly deposited within the porous layer (120), and the growth of lithium dendrites can be suppressed.

[0106] In some embodiments, the surface modification layer (110) may cover at least a portion of the surface of the electrode current collector (100), for example, may cover the entire surface of the electrode current collector (100). In one embodiment, the surface modification layer (110) may have a non-porous structure.

[0107] According to exemplary embodiments, the surface modification layer (110) may include the lithium-affinity metal described above, an oxide of the lithium-affinity metal, an alloy of the lithium-affinity metal, a carbon-based compound such as graphene, or boron nitride.

[0108] In some embodiments, the surface modification layer (110) may include boron nitride. Boron nitride is composed of nitrogen and boron with different electron densities, and thus is lithium-friendly while exhibiting high electron conductivity. Accordingly, lithium metal can be uniformly deposited from the bottom of the porous layer (120) by the surface modification layer (110). Accordingly, the growth of lithium dendrites and the resulting pressure can be suppressed, and the lifespan characteristics of the lithium secondary battery can be further improved.

[0109] In some embodiments, the boron nitride may have an amorphous structure. The irregularity of the atomic arrangement in the amorphous structure may further reduce resistance to lithium nucleation. Therefore, lithium metal may be more uniformly deposited on the surface modification layer (110). Furthermore, the low crystallinity of boron nitride allows for the formation of a surface modification layer (110) having a relatively thin thickness, and the mechanical strength of the surface modification layer (110) may be enhanced due to the amorphous boron nitride.

[0110] In some embodiments, the thickness of the surface modification layer (110) may be thinner than the thickness of the porous layer (120). As the thickness of the porous layer (120) becomes relatively larger, the content of lithium metal deposited may increase, and the volume change occurring during charge and discharge may be reduced.

[0111] In some embodiments, the thickness of the surface modification layer (110) may be 0.5 nm to 500 nm. Within this range, the energy density and output characteristics of the lithium secondary battery can be further improved while suppressing the growth of top electrodeposition and lithium dendrites.

[0112] A lithium secondary battery according to embodiments of the present disclosure may include an electrode for a lithium secondary battery according to the embodiments described above and a counter electrode facing the electrode for a lithium secondary battery.

[0113] In some embodiments, the electrode may be an anode. For example, the electrode for a lithium secondary battery may have a substantially anode-free structure.

[0114] In one embodiment, the positive electrode may be a lithium metal electrode. For example, the positive electrode may comprise lithium foil.

[0115] In one embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0116] For example, a positive electrode slurry can be prepared by mixing and stirring a positive electrode active material with a positive electrode binder, a conductive agent, and / or a dispersing agent in a solvent. The positive electrode slurry can be coated on at least one surface of a positive electrode current collector, followed by drying and rolling to prepare a positive electrode.

[0117] The positive electrode current collector may comprise stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also comprise aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0118] As an example of the positive electrode active material, it may include one or more compounds selected from lithium iron phosphate compounds, lithium cobalt oxides, lithium manganese oxides, lithium nickel oxides, or lithium composite oxides. For example, the positive electrode active material may include layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); LiV3O8, LiFe3O4, V2O 5　 It may include vanadium oxides such as Cu2VO7, lithium iron phosphate oxides such as LiFePO4, etc.

[0119] In some embodiments, the positive electrode active material may include a compound represented by the following chemical formula 1.

[0120] [Chemical Formula 1]

[0121] Li a Ni b M 1-b O2

[0122] In chemical formula 1, 0.95≤a≤1.08, b≥0.5, and M may be at least one element among Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0123] In one embodiment, the positive electrode active material includes nickel (Ni) and may further include at least one of cobalt (Co) and manganese (Mn). For example, a nickel-cobalt-manganese (NCM) lithium oxide may be used as the positive electrode active material.

[0124] For example, nickel (Ni) can be provided as a metal associated with the capacity of lithium secondary batteries. While a higher nickel content can improve the capacity and output of a lithium secondary battery, excessive nickel content can shorten its lifespan and compromise mechanical and electrical stability.

[0125] In one embodiment, the conductivity or resistance of a lithium secondary battery can be improved by cobalt (Co), and the mechanical and electrical stability of a lithium secondary battery can be improved by manganese (Mn).

[0126] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained within the lattice structure or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M may serve as the main active element of the positive electrode active material. Chemical Formula 1 is provided to express the bonding relationship of the main active element and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0127] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the positive electrode active material or the crystal structure. The auxiliary elements may be incorporated into the crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0128] The above positive electrode binder may be a material substantially identical to or similar to the materials described for the electrode for a lithium secondary battery. For example, a PVDF series binder may be used as the positive electrode binder.

[0129] The conductive material may be included to promote electron transport. For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0130] In some embodiments, a separator may be interposed between the electrode and the counter electrode for a lithium secondary battery. The separator may include a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. The separator may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, or the like.

[0131] According to exemplary embodiments, an electrode, a counter electrode, and a separator for a lithium secondary battery may be repeatedly arranged to form an electrode assembly. In some embodiments, the electrode assembly may be of a winding type, a stacking type, a z-folding type, or a stack-folding type.

[0132] An electrode assembly may be housed within a case to define a lithium secondary battery. The lithium secondary battery may be manufactured in a cylindrical, square, pouch, or coin shape using, for example, a can.

[0133] According to exemplary embodiments, an electrolyte may be housed within a case together with an electrode assembly. A non-aqueous electrolyte may be used as the electrolyte.

[0134] The non-aqueous electrolyte may include a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - is expressed as and the anion of the lithium salt (X - ) as F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - Examples include:

[0135] Examples of the organic solvent that can be used include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0136] In some embodiments, a solid electrolyte layer may be interposed between the electrode and the counter electrode for a lithium secondary battery. The solid electrolyte layer may include a sulfide-based electrolyte, an oxide-based electrolyte, or a polymer electrolyte. The polymer electrolyte may include an ion-conducting polymer or a gel polymer electrolyte.

[0137] In this case, the lithium secondary battery may not include a separator and an electrolyte. The solid electrolyte layer substantially functions as a separator and can prevent short circuits between the electrode and the counter electrode of the lithium secondary battery. In addition, the solid electrolyte layer allows lithium ions to move between the counter electrode and the electrode of the lithium secondary battery.

[0138] In one embodiment, the sulfide-based electrolyte may be represented by the following chemical formula 2.

[0139] [Chemical Formula 2]

[0140] Li e Y f P g S h Z i

[0141] In chemical formula 2, 0<e<12, 0≤f≤6, 0≤g≤6, 0<h≤12, 0≤i≤9, Y is at least one element selected from the group consisting of B, Al, Ga, In, Si, Ge, Sn, Pb, As, Sb, Bi, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, and W, and Z may be at least one element selected from the group consisting of F, Cl, Br, and I.

[0142] For example, the sulfide-based electrolyte may be an LPS-based solid electrolyte containing Li, P, and S, an LGPS-based solid electrolyte containing Li, P, Ge, and S, or an LSiPSCl-based solid electrolyte containing Li, Si, P, S, and Cl.

[0143] For example, as the sulfide-based electrolyte, Li2S-P2S5, Li 10 GeP2S 12 , Li 10 SnP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li 10 (Si 0.5 Ge 0.5 )P2S 12 , Li 10 (Ge 0.5 Sn 0.5 )P2S 12 , Li 10 (Si 0.5 Sn 0.5 )P2S 12 , Li 10 GeP2S 11.7 O 0.3 , Li 9.6 P3S 12 , Li9P3S9O3, Li 10.35 Ge 1.35 P 1.65 S 12 , Li 10.35 Si 1.35 P 1.65S 12 , Li 9.81 Sn 0.81 P 2.19 S 12 , Li 9.42 Si 1.02 P 2.1 S 9.96 O 2.04 , Li6PS5Cl, etc. can be used.

[0144] In one embodiment, the oxide-based electrolyte may include a metal oxide or an ion-conducting compound containing oxygen.

[0145] Examples of the above metal oxides include Al2O3, ZnO2, Ce2O3, TiO2, ZrO2, HfO2, MnO2, MgO, WO 2, Examples include V2O5.

[0146] Examples of the above ion conductive compounds include garnet compounds such as LLZO compounds; perovskite compounds such as LLTO compounds; Li 1+x Al x Ge 2-x (PO4)3(0 <x<2), Li 1+x Al x Ti 2-x (PO4)3(0 <x<2), Li 1+x Ti 2-x-y Al x Si y (PO4) 3-y (0≤x≤1, 0 <y≤1), LAGP계 화합물, LATP계 화합물, LiAl x Zr 2-x (PO4)3(0≤x≤1, 0≤y≤1), LiTi x Zr 2-x NASICON compounds such as (PO4)3(0≤x≤1, 0≤y≤1); LIPON compounds; Li6La2CaTa2O 12 ; Li6La2ANb2O 12 (A is Ca or Sr); Li2Nd3TeSbO 12 , Li3BO 2.5 N 0.5; Li9SiAlO8, etc. can be mentioned.

[0147] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0148]

[0149] (1) Manufacturing of metal-containing particles

[0150] An aluminum plate was placed in a first electrolyte containing dissociated copper chloride, and a spontaneous substitution reaction was performed at room temperature for a certain period of time. A copper powder in the shape of a dendrite was obtained on the surface of the aluminum plate.

[0151] The copper powder was immersed in a second electrolyte containing silver nitrate (AgNO3), silver hydrochloride (AgCl), silver sulfate (Ag2SO4), or silver fluoride (AgF). A silver-containing coating was formed on the copper powder by a spontaneous substitution reaction at room temperature for a certain period of time. Metal-containing particles were produced by forming a silver-containing coating on the copper powder.

[0152]

[0153] (2) Manufacturing of electrodes for lithium secondary batteries

[0154] Example 1

[0155] A surface modification layer was formed by depositing amorphous boron nitride on copper foil using CVD. An NMP solution (solids content: 60 wt%) containing 90 wt% metal-containing particles and 10 wt% PVdF was cast onto the surface modification layer using a doctor blade method. The cast solution was then dried to form a porous layer on the surface modification layer.

[0156] Comparative Example 1

[0157] An NMP solution (solid content: 60 wt%) containing 90 wt% of metal-containing particles and 10 wt% of PVdF was cast on copper foil in the same manner as in Example 1. The cast solution was dried to form a porous layer on the copper foil.

[0158] Comparative Example 2

[0159] A surface modification layer was formed by depositing amorphous boron nitride on copper foil using CVD. The copper foil on which boron nitride was deposited was used as an electrode without a porous layer formation process.

[0160] Comparative Example 3

[0161] Copper foil alone was used as an electrode current collector without forming a surface modification layer or porous layer.

[0162]

[0163] (3) Manufacturing of lithium secondary batteries

[0164] LiNi as positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, PVdF as a binder, and carbon black as a conductive material were mixed in a weight ratio of 95:2.5:2.5 to prepare a cathode slurry. The cathode slurry was applied to an aluminum foil, dried, and pressed to prepare a cathode.

[0165] A coin cell was manufactured using the above electrode and positive electrode for a lithium secondary battery.

[0166] Specifically, the electrode and positive electrode for the lithium secondary battery were each notched into a circular shape, and a circular polyethylene separator was interposed between the electrode and positive electrode for the lithium secondary battery to manufacture an electrode assembly.

[0167] The above electrode assembly was placed in a coin-shaped outer case, and an electrolyte was injected to manufacture a coin-shaped lithium secondary battery. The electrolyte used was ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (3:7 v / v) containing 1 M LiPF6 dissolved therein and 2 wt% fluoroethylene carbonate (FEC).

[0168]

[0169] Experimental example

[0170] (1) Evaluation of lithium deposition characteristics

[0171] The lithium secondary batteries manufactured in the examples and comparative examples were charged, and the electrodes for the lithium secondary batteries were disassembled in a charged state.

[0172] Figures 7a to 7d are sequential images of lithium secondary battery electrodes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0173] Figures 8a to 8d are SEM images of cross-sections of lithium secondary battery electrodes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

[0174] Referring to FIGS. 7a and 8a, in the electrode for a lithium secondary battery of Example 1, lithium metal is uniformly deposited, electrode expansion is suppressed, and the electrode has a uniform surface even when charged.

[0175] Referring to FIGS. 7b and 8b, the growth of lithium dendrites increased in the electrode for a lithium secondary battery of Comparative Example 1. Referring to FIGS. 7c and 8c, in the electrode for a lithium secondary battery of Comparative Example 2, lithium metal was directly formed on the current collector, resulting in volume expansion. Referring to FIGS. 7d ​​and 8d, in the electrode for a lithium secondary battery of Comparative Example 3, the growth of lithium dendrites increased, and the volume of the electrode expanded.

[0176]

[0177] (2) Life characteristics evaluation

[0178] For the lithium secondary batteries of the examples and comparative examples, charging (CC-CV 0.5C, 4.3 V cut-off) and discharging (CC 0.5C, 2.7 V cut-off) were repeated as one cycle. The initial discharge capacity in the first cycle was measured, and the discharge capacity in each cycle was calculated as a percentage of the initial discharge capacity to evaluate the capacity retention rate.

[0179] The measurement results are shown in Figure 9 below.

[0180] Referring to FIG. 9, the lithium secondary battery according to the embodiment maintained a capacity of 75% or more up to 90 cycles.

[0181] In Comparative Example 1, the capacity of the lithium secondary battery decreased to less than 8% after 100 cycles. The lithium secondary battery according to Comparative Example 2 did not operate after 80 cycles. The capacity of the lithium secondary battery according to Comparative Example 3 decreased rapidly from the initial cycles, and the capacity decreased to less than 10% after 40 cycles.

[0182]

[0183] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be further included without departing from the scope of the present disclosure.

Claims

1. Electrode current collector; A surface modification layer disposed on the electrode current collector; and An electrode for a lithium secondary battery, comprising a porous layer disposed on the surface modification layer.

2. An electrode for a lithium secondary battery according to claim 1, wherein the surface modification layer comprises a lithium-affinity material.

3. An electrode for a lithium secondary battery according to claim 2, wherein lithium ions are reduced to lithium metal on the lithium-affinity material at a voltage lower than the voltage at which the lithium-affinity material and lithium ions are alloyed.

4. An electrode for a lithium secondary battery according to any one of claims 2 or 3, wherein the surface modification layer comprises boron nitride.

5. An electrode for a lithium secondary battery according to claim 4, wherein the boron nitride has an amorphous structure.

6. An electrode for a lithium secondary battery according to any one of claims 1 to 5, wherein the thickness of the surface modification layer is smaller than the thickness of the porous layer.

7. An electrode for a lithium secondary battery according to any one of claims 1 to 6, wherein the porous layer comprises a lithium-affinity material.

8. An electrode for a lithium secondary battery according to claim 7, wherein the lithium-affinity material comprises at least one metal selected from the group consisting of Cu, Zn, Ti, Au, Pt, Mg, Sn, Ag, Al, In, Pb, Bi or Sb, an oxide thereof or an alloy of two or more thereof.

9. An electrode for a lithium secondary battery according to claim 7 or 8, wherein the porous layer comprises a matrix including the lithium-affinity material and pores formed on the surface and inside of the matrix.

10. An electrode for a lithium secondary battery according to claim 9, wherein the porous layer comprises a fiber or porous foam containing the lithium-affinity material.

11. An electrode for a lithium secondary battery according to claim 9 or 10, wherein the porous layer comprises a framework having a three-dimensional network structure and including the lithium-affinity material.

12. An electrode for a lithium secondary battery according to any one of claims 9 to 11, wherein the porous layer comprises metal-containing particles including the lithium-affinity material and pores formed between the metal-containing particles.

13. An electrode for a lithium secondary battery, wherein the metal-containing particles in claim 12 have a dendrite shape.

14. An electrode for a lithium secondary battery according to claim 12 or 13, wherein the metal-containing particles include a core and a coating covering at least a portion of the core, and the coating includes the lithium-affinity material.

15. An electrode for a lithium secondary battery according to claim 14, wherein the core comprises at least one metal selected from the group consisting of Ni, Mn, Fe, Co, Cr, W, Ru, Cu, Zn, Ti, Au, Ag, Pt, Mg, Sn, Al, In, Pb, Bi or Sb, an oxide thereof or an alloy of two or more thereof.

16. An electrode for a lithium secondary battery according to any one of claims 9 to 15, wherein at least some of the pores are connected from the upper surface of the surface modification layer to the upper surface of the porous layer.

17. An electrode for a lithium secondary battery according to any one of claims 1 to 16, wherein the surface modification layer has a non-porous structure.

18. An electrode for a lithium secondary battery according to any one of claims 1 to 17; and A lithium secondary battery comprising a counter electrode facing the above lithium secondary battery electrode.

Images