Negative current collector for lithium-free battery, electrode assembly including the same, and lithium-free battery

Abstract

The negative electrode current collector for a lithium-free battery according to an embodiment of the present invention is a negative electrode current collector for a lithium-free battery, and the negative electrode current collector includes: a metal current collecting substrate; a conductive layer formed on at least one surface of the metal current collecting substrate and including a conductive material; and a metal layer formed on the conductive layer and having grain boundaries, wherein the metal layer includes a metal powder layer, a metal wire layer, or a mixed layer thereof.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10-2020-0055159, filed on May 8, 2020, and 10-2021-0016113, filed on February 4, 2021, the disclosures of which are incorporated herein by reference in their entirety.

[0003] The present disclosure relates to a negative electrode current collector for a lithium-free battery, an electrode assembly including the negative electrode current collector for a lithium-free battery, and a lithium-free battery. Background Art

[0004] Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy is increasing day by day, and the most active research field is the field of power generation and power storage using electrochemistry.

[0005] Currently, secondary batteries are representative examples of electrochemical devices that utilize such electrochemical energy, and their scope of use tends to gradually expand.

[0006] In recent years, with the increase in the development of technologies and demands for mobile devices such as laptop computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased rapidly. Among such secondary batteries, many studies have been conducted on environmentally friendly lithium secondary batteries that exhibit high charge / discharge characteristics and life characteristics, and they have been commercialized and widely used.

[0007] Generally, a lithium secondary battery has a structure in which a non-aqueous electrolyte is impregnated into an electrode assembly including a positive electrode, a negative electrode, and a porous separator. In addition, generally, a positive electrode is prepared by coating a positive electrode mixture including a positive electrode active material on an aluminum foil, and a negative electrode is prepared by coating a negative electrode mixture including a negative electrode active material on a copper foil.

[0008] Generally, the positive electrode active material is a lithium transition metal oxide, and a carbon-based material is used as the negative electrode active material.

[0009] However, recently, lithium metal batteries using lithium metal itself as the negative electrode active material have been commercialized. In addition, lithium-free batteries are being actively studied, in which only a current collector is used as the negative electrode when preparing the electrode, lithium is provided from the positive electrode by discharging, and the resulting lithium metal is used as the negative electrode active material. From the perspective of high energy density, lithium-free batteries are considered a battery concept capable of achieving the highest energy density.

[0010] However, in the negative electrode made only of a current collector, a lithium layer is formed by electrodeposition due to charging. At this time, a lithium layer with a low deposition density is formed on the current collector, and side reactions of the electrolyte are severe, resulting in rapid deterioration of life characteristics.

[0011] Therefore, it is necessary to develop a current collector for the negative electrode of a lithium-free battery that can solve the above problems. Summary of the Invention

[0012] Technical problem

[0013] The present disclosure aims to solve the above problems and other unsolved technical problems.

[0014] Specifically, an object of the present disclosure is to provide a current collector for the negative electrode, in which a lithium layer with a high deposition density can be formed by a simpler method.

[0015] Another object of the present disclosure is to prevent side reactions of the electrolyte of a lithium-free battery using the current collector for the negative electrode, thereby improving life characteristics.

[0016] Technical solution

[0017] To achieve the above object, according to an embodiment of the present disclosure, there is provided a current collector for the negative electrode of a lithium-free battery, the current collector for the negative electrode comprising: a metal current collecting substrate; a conductive layer formed on at least one surface of the metal current collecting substrate and containing a conductive material; and a metal layer formed on the conductive layer and having grain boundaries, wherein the metal layer includes a metal powder layer, a metal wire layer, or a mixed layer thereof.

[0018] The metal current collecting substrate may be at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy.

[0019] The metal current collecting substrate may be a metal containing copper.

[0020] The conductive layer may be a primer layer, a conductive polymer layer, or a conductive epoxy layer.

[0021] The primer layer may contain a conductive material and an adhesive material, and the conductive material may include at least one selected from the group consisting of natural graphite, artificial graphite, graphene, carbon black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon nanotubes, graphite nanofibers, carbon nanofibers, aluminum, nickel, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives.

[0022] The conductive polymer layer may include at least one conductive polymer selected from the group consisting of poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate and / or poly(4-styrenesulfonate) (PEDOT / PSS), polyaniline (PANI), polypyrrole (PPy), polythiophene (PT), polyacetylene (PA), and poly(p-phenylene vinylene) (PPV).

[0023] The conductive epoxy layer may include a conductive filler and an adhesive, and the conductive filler may include at least one selected from the group consisting of: metal powders of gold, platinum, silver, copper, or nickel, carbon or carbon fibers, graphite, and composite powders.

[0024] The metal layer may be in a morphology in which at least one material selected from copper, stainless steel, aluminum, nickel, titanium, calcined carbon, aluminum-cadmium alloy, Mg, Ca, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg has grain boundaries, and the diameter of the metal powder of the metal powder layer or the metal wire of the metal wire layer is from 0.01 μm to 30 μm.

[0025] The aspect ratio (wire length / wire diameter) of the metal wire may be 3 or more.

[0026] The mixed layer may include at least one metal powder selected from the group consisting of copper, stainless steel, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, and at least one metal wire selected from the group consisting of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg.

[0027] The mixed layer may include at least one metal powder selected from the group consisting of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg, and at least one metal wire selected from the group consisting of copper, stainless steel, nickel, titanium, calcined carbon, and aluminum-cadmium alloy.

[0028] The total thickness of the conductive layer and the metal layer may be in the range of 0.1 μm to 60 μm.

[0029] The thickness of the conductive layer may be in the range of 0.1 μm to 20 μm.

[0030] The thickness of the metal layer may be in the range of 0.1 μm to 40 μm.

[0031] According to another embodiment of the present disclosure, an electrode assembly is provided, the electrode assembly including: the above-mentioned negative electrode current collector; a positive electrode having a structure in which a positive electrode mixture including an active material is applied to at least one surface of a positive electrode current collector; and a separator interposed between the negative electrode current collector and the positive electrode.

[0032] According to another embodiment of the present disclosure, a lithium-free battery is provided, the lithium-free battery including a positive electrode, a negative electrode, a separator, and a lithium non-aqueous electrolyte, wherein the negative electrode includes the negative electrode current collector described in item 1 and a lithium layer formed on the negative electrode current collector. At this time, the lithium layer can be formed by charging the lithium-free battery. Detailed implementation manners

[0033] Hereinafter, the present disclosure will be described in more detail to facilitate the understanding of the present invention.

[0034] The terms and words used in this specification and claims should not be construed as limited to the common meanings or the meanings in the dictionary, but should be interpreted based on the principle that the inventor has appropriately defined the concepts of the terms so as to describe the present invention in the best way, using meanings and concepts consistent with the technical scope of the present invention.

[0035] The terms provided herein are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure. Unless otherwise clearly indicated in the context, the singular forms "a", "an", and "the" are also intended to include the plural forms.

[0036] In addition, throughout the specification, unless otherwise stated, when a part is referred to as "including" a certain component, this means that the part may also include other components, without excluding other components.

[0037] According to an embodiment of the present disclosure, a negative electrode current collector for a lithium-free battery is provided, the negative electrode current collector including: a metal current collecting substrate; a conductive layer formed on at least one surface of the metal current collecting substrate and including a conductive material; and a metal layer formed on the conductive layer and having grain boundaries, wherein the metal layer includes a metal powder layer, a metal wire layer, or a mixed layer thereof.

[0038] The metal current collecting substrate may be at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy. The copper may be copper surface-treated with a different metal, and the stainless steel may be stainless steel surface-treated with a different metal.

[0039] Specifically, due to conductivity, cost, safety, etc., the metal current collecting substrate may be a metal containing copper, and more specifically, may be formed of copper.

[0040] The thickness of this metal current collecting substrate has no significant difference from that of the negative electrode current collector used in a conventional lithium-free battery. Specifically, it may be formed to have a thickness of 3 μm to 200 μm, preferably 5 μm to 40 μm, and more preferably 8 μm to 20 μm.

[0041] Conventionally, such a metal current collector substrate is used as a negative electrode current collector in a lithium-free battery.

[0042] However, as described above, when only such a metal current collector substrate is used as the negative electrode current collector and lithium is electrodeposited by charging and discharging, a lithium layer with a low deposition density is formed, and side reactions of the electrolyte are severe, resulting in rapid deterioration of the life characteristics. This is because the specific surface area of the metal used as the metal current collector substrate is small and the affinity with lithium is low, so when lithium is electrodeposited, it is randomly electrodeposited.

[0043] To solve these problems, according to the present embodiment, as a thin layer on the metal current collector substrate, a metal layer having grain boundaries is formed, whereby the specific surface area is increased and the resistance is reduced. When lithium is electrodeposited by subsequent charging / discharging, a lithium layer with a high deposition density can be formed.

[0044] On the other hand, at the same time, when a conductive layer is formed between the metal layer and the metal current collector substrate, not only can higher electron conductivity be ensured to prevent a decrease in electron conductivity due to the formation of a metal layer having grain boundaries, but also the bonding force between the metal layer and the metal current collector substrate can be enhanced.

[0045] The conductive layer may be a primer layer, a conductive polymer layer, or a conductive epoxy layer. The primer layer may contain a conductive material and an adhesive material.

[0046] The conductive material is not particularly limited as long as it is a component that maintains conductivity by electrically connecting the metal current collector substrate and the metal layer. For example, the conductive material may contain at least one selected from the group consisting of natural graphite, artificial graphite, graphene, carbon black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon nanotubes, graphite nanofibers, carbon nanofibers, aluminum, nickel, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives.

[0047] The adhesive material is used to fix the conductive material to the current collector, form a coating film, and achieve the bonding between the metal current collector substrate and the metal layer. Examples of the adhesive material may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose (HPC), regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene, and fluororubber.

[0048] When the primer layer contains both a conductive material and an adhesive material at the same time, the weight ratio of the conductive material to the adhesive material may be 1:99 to 99:1, preferably 3:7 to 7:3.

[0049] When the weight ratio is lower than the above range, the content of the conductive material is too small, and due to the increase in internal resistance, the operating characteristics of the battery deteriorate. On the contrary, when the weight ratio exceeds the above range, the content of the adhesive material is too small, and thus sufficient bonding strength cannot be obtained.

[0050] The method of forming the primer layer can utilize the film-forming methods commonly used in the art. For example, the methods that can be used include: wet coating methods such as concave coating, slot die coating, spin coating, spraying, bar coating, dip coating; and dry coating methods such as thermal evaporation, electron beam evaporation, chemical vapor deposition (CVD), and sputtering.

[0051] The conductive polymer layer may contain polymers generally referred to as conductive polymers. Examples of the conductive polymers may include at least one conductive polymer selected from the group consisting of poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) and / or poly(4-styrenesulfonate) (PEDOT / PSS), polyaniline (PANI), polypyrrole (PPy), polythiophene (PT), polyacetylene (PA), and poly(p-phenylene vinylene) (PPV).

[0052] The conductive polymer layer can be formed by: generating a mixed solution obtained by melting the conductive polymer or dissolving it in a solvent, and using various wet coating methods as described in the coating method of the primer layer. At this time, when the conductive polymer is mixed with the solvent, the solvent can be a polar organic solvent, examples of which include chloroform, dichloromethane, m-cresol, tetrahydrofuran (THF), dimethylformamide (DMF), etc.

[0053] On the other hand, since the polymer itself in the conductive polymer layer exhibits bonding strength, a separate adhesive material or the like is not required.

[0054] However, for stronger bonding, an adhesive material disclosed in the conductive polymer layer can also be included. At this time, based on the total weight of the conductive polymer layer, the content of the adhesive material can be 0.1 wt% to 10 wt%.

[0055] In addition, the conductive epoxy layer may contain a conductive filler and an adhesive.

[0056] Specifically, the conductive epoxy layer is used as an adhesive by mixing a conductive filler and an adhesive.

[0057] The conductive filler can be at least one selected from the group consisting of: metal powders of gold, platinum, silver, copper, or nickel, carbon or carbon fibers, graphite, and composite powders.

[0058] The binder is a component that binds the conductive filler, but is not limited thereto. Examples thereof may be at least one selected from the group consisting of polymer materials such as acrylics, epoxies, polyurethanes, polysiloxanes, polyimides, phenols, polyesters, composite polymer resins, and low melting point glasses.

[0059] On the other hand, the conductive epoxy layer can be classified into a normal temperature drying type, a normal temperature curing type, a heat curing type, a high temperature calcination type, a UV curing type, etc. according to its manufacturing method. The normal temperature drying type can be formed by containing a conductive filler in an adhesive such as acrylic and a solvent and drying at normal temperature, and the normal temperature curing type can be formed by additionally containing a two-component highly reactive curing agent and curing the solvent containing the conductive filler and the adhesive.

[0060] In addition, the heat curing type can be formed by mainly using an epoxy adhesive and heating the solvent containing the conductive filler, the high temperature calcination type can be formed by performing heat treatment at a high temperature and curing, and the UV curing type can be formed by UV radiation curing.

[0061] At this time, the conductive filler and the binder may also be included in a weight ratio of 1:99 to 99:1, specifically a weight ratio of 7:3 to 3:7.

[0062] When the content of the conductive filler is very small and exceeds the above range, the conductivity decreases and the resistance increases, and when the content of the binder is very small, the binding force of the conductive filler cannot be obtained, which is not preferable.

[0063] On the other hand, the metal layer can play a role in increasing the deposition density of lithium by increasing the actual specific surface area. The metal layer may include a metal powder layer, a metal wire layer, or a mixed layer thereof, where the metal layer may be, for example, in a form in which at least one material selected from copper, stainless steel, aluminum, nickel, titanium, calcined carbon, aluminum-cadmium alloy, Mg, Ca, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg has grain boundaries. At this time, the diameter of the metal powder of the metal powder layer or the metal wire of the metal wire layer may be 0.01 μm to 30 μm.

[0064] When the diameter of the form is too small and exceeds the above range, it is difficult to manufacture, and when the diameter of the form is too large and exceeds the above range, the effect of increasing the specific surface area is not obvious, so it is not preferable.

[0065] In addition, the aspect ratio (wire length / wire diameter) of the metal wire may be 3 or more. More specifically, the aspect ratio may be 3 or more and 2000 or less.

[0066] On the other hand, the mixed layer may include at least one metal powder selected from the group consisting of copper, stainless steel, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, and at least one metal wire selected from the group consisting of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg. Alternatively, the mixed layer may include at least one metal powder selected from the group consisting of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg, and at least one metal wire selected from the group consisting of copper, stainless steel, nickel, titanium, calcined carbon, and aluminum-cadmium alloy.

[0067] At this time, the content when the metal powder and the metal wire are mixed is not limited, and it may be from 1:99 to 99:1 by weight, specifically, 8:2 to 2:8, and more specifically, 3:7 to 7:3.

[0068] That is to say, the mixed layer may be in a form in which metal powder and metal wire are mixed. As described above, the materials belonging to the above-mentioned group consisting of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg are metals that form alloys with Li, and by the effects of increasing the specific surface area and partial alloying of the metal, a lithium layer with a higher deposition density can be formed.

[0069] The metal powder layer, the metal wire layer, or the mixed layer is not limited in terms of the manufacturing method, but they can be prepared, for example, by coating a dispersion in which the metal powder or the metal wire is dispersed on the conductive layer and drying.

[0070] In addition, specifically, for the firm bonding of the metal, in addition to including metal powder and / or metal wire, the metal layer may further include an adhesive material as described for the primer layer.

[0071] When the metal layer having grain boundaries is included in this way, the specific surface area of the negative electrode current collector increases, and the sites where lithium ions generated by charging and discharging can be electrodeposited increase, so that a lithium layer with improved deposition density can be obtained.

[0072] The thickness of the metal layer may be 0.1 μm to 40 μm, specifically 1 μm to 30 μm, and more specifically 1 μm to 20 μm.

[0073] When the metal layer is formed too thick and outside the above range, the volume increases and the energy density decreases. When the metal layer is formed too thin, the effect of improving the deposition density of the lithium layer desired in the present disclosure cannot be obtained, so it is not preferred.

[0074] Similarly, the conductive layer may have a thickness of 0.1 μm to 20 μm, specifically 1 μm to 10 μm, and more specifically 1 μm to 5 μm.

[0075] When the conductive layer is formed too thick and outside the above range, the total thickness of the negative electrode current collector increases, which is not preferable. When the conductive layer is formed too thin, the effect of restoring conductivity cannot be exerted, which is not preferable.

[0076] In the negative electrode current collector for a non-lithium battery according to the present embodiment, the total thickness of the conductive layer and the metal layer may be in the range of 0.1 μm to 60 μm. In particular, the total thickness may be in the range of 0.2 μm to 60 μm, or the total thickness may be in the range of 2 μm to 20 μm.

[0077] When the thickness is too thin and outside the above range, it is difficult to obtain the effect of improving the deposition density of the lithium layer as expected in the present disclosure. When the thickness is too thick, the total thickness of the negative electrode current collector increases, so the energy density decreases, which is not preferable.

[0078] According to another embodiment of the present disclosure, there is provided an electrode assembly including: the above-mentioned negative electrode current collector; a positive electrode having a structure in which a positive electrode mixture containing an active material is applied to at least one surface of a positive electrode current collector; and a separator interposed between the negative electrode current collector and the positive electrode.

[0079] According to the present embodiment, since the negative electrode current collector is used as the negative electrode when initially manufacturing the electrode assembly of the non-lithium battery, the negative electrode in the electrode assembly can be formed by the negative electrode current collector.

[0080] Thereafter, the negative electrode current collector receives lithium from the positive electrode in response to the charging of the subsequently prepared non-lithium battery and forms a lithium layer on the current collector, and the lithium layer serves as an active material.

[0081] On the other hand, the positive electrode has a structure in which a positive electrode mixture containing an active material is applied to at least one surface of a positive electrode current collector.

[0082] The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector may be 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the binding force of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

[0083] The positive electrode active material as the active material may be, for example: a layered compound such as lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium manganese oxide such as the chemical formula Li 1+x Mn 2-x O4 (where x is from 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide such as LiV3O8, LiFe3O4, V2O5 and Cu2V2O7; Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); lithium manganese composite oxide represented by the chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of Li in the chemical formula is replaced by alkaline earth metal ions; disulfide; Fe2(MoO4)3, etc., but not limited thereto.

[0084] The positive electrode mixture may further contain a conductive material and a binder on the basis of the above positive electrode active material.

[0085] Based on the total weight of the positive electrode mixture layer, the addition amount of the conductive material is generally 0.1% by weight to 30% by weight, specifically 1% by weight to 10% by weight, and more specifically 1% by weight to 5% by weight. The conductive material is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, graphite such as natural graphite and artificial graphite can be used; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal cracking carbon black; conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorocarbon powder, aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives.

[0086] The binder is a component that helps to bond the active material, conductive material, etc. and bond with the current collector, and based on the total weight of the positive electrode mixture layer, it can generally be added in an amount of 0.1% by weight to 30% by weight, specifically 1% by weight to 10% by weight, and more specifically 1% by weight to 5% by weight. Examples of the binder may include polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber, fluororubber, various copolymers, etc.

[0087] The separator is an insulating film having high ion permeability and mechanical strength. The pore size of the separator is generally 0.01 μm to 10 μm, and the thickness is generally 5 μm to 300 μm. As such a separator, for example, an olefin polymer such as polypropylene that is chemically resistant and hydrophobic is used; a sheet or non - woven fabric made of glass fiber or polyethylene. When a solid electrolyte (such as a polymer) is used as the electrolyte, the solid electrolyte can also be used as the separator.

[0088] According to another embodiment of the present disclosure, a lithium - free battery is provided, which includes a positive electrode, a negative electrode, a separator, and a lithium non - aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector according to the above - mentioned embodiment, and a lithium layer formed on the negative electrode current collector.

[0089] At this time, as described above, the lithium layer can be formed on the negative electrode current collector by subsequently charging the lithium - free battery.

[0090] More specifically, the lithium - free battery is prepared by loading an electrode assembly including a negative electrode current collector, a positive electrode, and a separator together with a lithium non - aqueous electrolyte into a battery case, sealing the battery case, and then activating it.

[0091] At this time, lithium ions present in the non - aqueous electrolyte that are ionized from the positive electrode during the activation process undergo an electrochemical reaction with the negative electrode current collector according to the present disclosure, and a lithium layer is deposited on the surface of the negative electrode current collector, and the lithium layer serves as the negative electrode active material.

[0092] The lithium non - aqueous electrolyte generally includes a lithium salt and a non - aqueous solvent. As the non - aqueous solvent, non - aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc. are used, but are not limited thereto.

[0093] Examples of the non-aqueous electrolyte may include aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate esters, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate.

[0094] Examples of the solid organic electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polylysine alginate, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups, etc.

[0095] Examples of the inorganic solid electrolyte include nitrides, halides, and sulfates of lithium (Li), such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2.

[0096] The lithium salt is a material soluble in the non-aqueous electrolyte. The lithium salt may include, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, imide salts, etc.

[0097] In addition, in order to improve charge / discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte may further contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, diethylene glycol dimethyl ether, hexamethylphosphoramide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, in order to impart non-flammability, the electrolyte may further contain halogen-containing solvents such as carbon tetrachloride and trifluoroethylene. In addition, in order to improve high-temperature retention characteristics, the electrolyte may further contain carbon dioxide gas. In addition, fluoroethylene carbonate (FEC), propylene sultone (PRS), etc. may also be included.

[0098] The battery case is not limited as long as it has a structure capable of accommodating the electrode assembly, and it can be a pouch-type battery known in the prior art or a prismatic or cylindrical battery case made of a metal can.

[0099] Hereinafter, preferred embodiments of the present disclosure, comparative examples for comparison therewith, and test examples for evaluating them will be described. However, it will be obvious to those skilled in the art that these embodiments are merely examples of the present disclosure and various changes and modifications can be made within the scope and technical gist of the present disclosure, and such changes and modifications of course fall within the scope of the appended claims.

[0100] <Example 1>

[0101] Lithium transition metal oxide (LiNi 0.33 Co 0.33 Mn 0.33 O2) was used as the positive electrode active material, PVdF was used as the binder, and Super-P was used as the conductive material. The positive electrode active material: binder: conductive material was added to NMP at a weight ratio of 96:2:2 to prepare an active material slurry, and then it was coated on aluminum foil at 4 mAh / cm per side 2 It was dried in a dryer at 130 °C in an air atmosphere and then calendered to prepare a positive electrode.

[0102] A graphene dispersion of graphene 1 wt% / PVDF 2.5 wt% / H-NBR 2.5 wt% / NMP 94 wt% was coated on a 15-μm copper foil and then dried to prepare a 3-μm-thick primer layer. A metal layer slurry (solid content = 50%) in which copper metal powder (average diameter (D50): 3 μm) and binder (PVDF) were mixed at a weight ratio of 9:1 in an NMP solvent was coated thereon and dried to form a metal layer with grain boundaries having a thickness of 7 μm, thereby obtaining a negative electrode.

[0103] A 20-μm-thick SRS separator was assembled on the positive electrode and the negative electrode using a stacking method. The assembled battery was placed in an aluminum pouch-type battery case, and a solution of 3.5 M LiFSI dissolved in a volume ratio of 3:7 of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) was injected, and then the battery case was sealed to prepare a single cell.

[0104] <Example 2>

[0105] A single cell was prepared in the same manner as in Example 1, except that in Example 1, a metal layer slurry prepared by mixing Zn powder (particle size (D50): 3 μm) and binder (PVDF) was coated and dried to form a metal layer with grain boundaries having a thickness of 7 μm.

[0106] <Example 3>

[0107] The single cell was prepared in the same manner as in Example 1, except that in Example 1, a mixture of copper metal powder (average diameter (D50): 3 μm) and silicon powder (average diameter (D50): 3 μm) with a weight ratio of 5:5 was mixed with a binder (PVDF) to prepare a metal layer slurry, which was then coated and dried to form a metal layer with grain boundaries having a thickness of 7 μm.

[0108] <Example 4>

[0109] The single cell was prepared in the same manner as in Example 1, except that in Example 1, a mixture of copper metal wire (average diameter (D50): 500 nm, aspect ratio: 10) and silicon powder (average diameter (D50): 3 μm) with a weight ratio of 5:5 was mixed with a binder (PVDF) to prepare a metal layer slurry, which was then coated and dried to form a metal layer with grain boundaries having a thickness of 7 μm.

[0110] <Example 5>

[0111] The single cell was prepared in the same manner as in Example 1, except that in Example 1, a slurry of 95 wt% silver / 5 wt% acrylic binder was coated on a 15-μm copper foil and dried to form a conductive epoxy layer, and a metal layer slurry in which copper metal powder (average diameter (D50): 3 μm) and binder (PVDF) were mixed at a weight ratio of 9:1 in an NMP solvent (solid content = 50%) was coated thereon and dried to form a metal layer with grain boundaries having a thickness of 7 μm, thereby obtaining a negative electrode.

[0112] <Comparative Example 1>

[0113] The single cell was prepared in the same manner as in Example 1, except that in Example 1, a 15-μm thick copper foil was used as the negative electrode as it was, without a primer layer and a metal layer on the negative electrode.

[0114] <Comparative Example 2>

[0115] The single cell was prepared in the same manner as in Example 1, except that in Example 1, only a 3-μm thick primer layer was coated on a 15-μm thick copper foil, and the resulting negative electrode was used as it was, without a metal layer on the negative electrode.

[0116] <Comparative Example 3>

[0117] The single cell was prepared in the same manner as in Example 1, except that in Example 1, Ag with a thickness of 20 nm was vacuum deposited on a 15-μm copper foil to prepare a conductive layer instead of the primer layer, and a metal layer was applied on the conductive layer.

[0118] <Experimental Example 1>

[0119] The cells prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were charged under the following conditions, and then the cells were disassembled to calculate the thickness and deposition density of the lithium electrodeposition layer formed on the negative electrode. The results are shown in Table 2 below.

[0120] Charging: 0.2C, CC / CV, 4.25V, 1 / 20C cut-off

[0121] For the measurement of the electrodeposition layer thickness, the average value of the thickness was obtained by selecting two arbitrary points, and the deposition density of the electrodeposition layer was digitalized by calculating the deposition mass and deposition volume.

[0122] [Table 1]

[0123] Lithium layer thickness (μm) Lithium layer deposition density (g / cc) Example 1 45 0.23 Example 2 37 0.28 Example 3 40 0.26 Example 4 35 0.30 Example 5 44 0.23 Comparative Example 1 95 0.11 Comparative Example 2 90 0.12 Comparative Example 3 48 0.22

[0124] (The theoretical density of lithium metal: 0.54 g / cm 3 )

[0125] Referring to Table 1, it can be seen that in the case of including the metal layers of Examples 1 to 5 according to the present disclosure, the thickness of the lithium layer is thin and the density is increased, thereby forming a denser layer, while in the case without a metal layer (Comparative Examples 1 and 2), the deposition density is very low.

[0126] Furthermore, when comparing Examples 1 to 3 with Example 4, it can be seen that the form of mixing metal powder and metal wire has the most excellent lithium layer deposition density.

[0127] <Experimental Example 2>

[0128] The cells of Examples 1 to 5 and Comparative Examples 1 to 3 were charged and discharged at 0.2C, and the primary discharge capacity was measured. They were further charged and discharged under the following conditions, and then the 150th discharge capacity retention rate relative to the primary discharge capacity was calculated. The results are shown in Table 2.

[0129] Charging: 0.2C, CC / CV, 4.25V, 1 / 20C cut-off

[0130] Discharging: 0.5C, CC, 3.0V, cut-off

[0131] [Table 2]

[0132] Initial capacity (mAh) Capacity retention rate after 150 cycles (%) Example 1 58.9 85 Example 2 59.3 91 Example 3 58.8 89 Example 4 59.5 95 Example 5 59.1 80 Comparative Example 1 58.1 20 Comparative Example 2 58.2 30 Comparative Example 3 58.9 65

[0133] Referring to Table 2, it can be confirmed that Examples 1 to 5 have excellent life characteristics while the lithium layer density increases. From these results, it can be confirmed that the metal layer increases the deposition density while reducing the negative electrode resistance, and it is considered that this improves the life accordingly.

[0134] In addition, when Example 5 is compared with Comparative Example 3, it can be seen that forming a conductive epoxy layer containing metal particles in the form of metal particles is much more favorable for life characteristics than an Ag metal with a thin electrodeposited thickness as a conductive layer.

[0135] This is considered to be because when a thin Ag metal film is formed, it is difficult for the Ag metal film to maintain its shape and is consumed during the charge / discharge process of lithium, which results in limitations in playing the role of the conductive layer.

[0136] Those skilled in the art will understand that various applications and modifications can be made without departing from the gist and scope of the present invention based on the above description.

[0137] [Industrial Applicability]

[0138] As described above, the negative electrode current collector according to the embodiment of the present disclosure has a form including a conductive layer and a metal layer having grain boundaries on at least one surface of the metal current collecting substrate, and when used as the negative electrode of a lithium-free battery, lithium electrodeposition caused by charging and discharging proceeds uniformly, thereby effectively increasing the deposition density of the lithium layer thus formed.

[0139] In addition, this enables minimizing the side reaction of the electrolyte of the lithium-free battery including the negative electrode current collector, thereby improving the life characteristics.

Claims

1. A lithium-free battery, the lithium-free battery comprising a positive electrode, a negative electrode, a separator, and a lithium non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode current collector and a lithium layer formed on the negative electrode current collector, and the negative electrode current collector comprises: a metal current collecting substrate; a conductive layer which is formed immediately on at least one surface of the metal current collecting substrate and contains a conductive material; and a metal layer which is formed on the conductive layer and has grain boundaries, Among them, the metal layer comprises a metal powder layer, a metal wire layer or a mixed layer thereof, wherein, the thickness of the conductive layer is in the range of 0.1 μm to 20 μm, the thickness of the metal layer is in the range of 0.1 μm to 40 μm, and wherein the lithium layer is deposited on the surface of the negative electrode current collector by charging the lithium-free battery.

2. The lithium-free battery according to claim 1, wherein: the metal current collecting substrate is at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy.

3. The lithium-free battery according to claim 1, wherein: the metal current collecting substrate is a metal containing copper.

4. The lithium-free battery according to claim 1, wherein: the conductive layer is a primer layer, a conductive polymer layer or a conductive epoxy layer, wherein the primer layer contains a conductive material and an adhesive material, and the conductive material contains at least one selected from the group consisting of natural graphite, artificial graphite, graphene, channel black, furnace black, lamp black, thermal cracking furnace black, carbon nanotubes, carbon nanofibers, aluminum, nickel, and zinc oxide; the conductive polymer layer contains at least one conductive polymer selected from the group consisting of poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) (PEDOT / PSS), polyaniline (PANI), polypyrrole (PPy), polythiophene (PT), polyacetylene (PA), and poly(p-phenylenevinylene) (PPV); the conductive epoxy layer contains a conductive filler and an adhesive, and the conductive filler contains at least one selected from the group consisting of metal powders of gold, platinum, silver, copper or nickel, and carbon.

5. The lithium-free battery according to claim 1, wherein: the conductive layer is a primer layer, the primer layer contains a conductive material and an adhesive material, and the conductive material contains at least one selected from the group consisting of carbon black and graphite nanofibers.

6. The lithium-free battery according to claim 1, wherein: the metal layer is in a morphology in which at least one material selected from copper, stainless steel, aluminum, nickel, titanium, calcined carbon, aluminum-cadmium alloy, Mg, Ca, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg has grain boundaries, and the diameter of the metal powder of the metal powder layer or the metal wire of the metal wire layer is 0.01 μm to 30 μm.

7. The lithium-free battery according to claim 6, wherein: the aspect ratio (wire length / wire diameter) of the metal wire is 3 or more.

8. The lithium-free battery according to claim 6, wherein: The mixed layer contains at least one metal powder selected from the group consisting of copper, stainless steel, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, and at least one metal wire selected from the group consisting of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg.

9. The lithium-free battery according to claim 6, wherein: The mixed layer contains at least one metal powder selected from the group consisting of Mg, Ca, Al, Si, Ge, Sn, Pb, As, Sb, Bi, Ag, Zn, Cd, P, and Hg, and at least one metal wire selected from the group consisting of copper, stainless steel, nickel, titanium, calcined carbon, and aluminum-cadmium alloy.

10. The lithium-free battery according to claim 4, wherein: The conductive filler contains carbon fiber.

11. The lithium-free battery according to claim 4, wherein: The conductive filler contains graphite.