Negative electrode current collector and manufacturing method thereof

Abstract

The negative electrode current collector according to the present invention comprises: a copper thin film in which peaks and recesses are formed; and metal particles which are provided in at least a portion of the recess, have a higher standard reduction potential than lithium ions, and are capable of forming a solid solution with lithium (Li).

Description

Technical Field

[0001] The present invention relates to a negative electrode current collector and a method for manufacturing the same. Background Art

[0002] As the technological development and demand for electric vehicles and energy storage systems (ESS) increase, the demand for batteries as an energy source has increased significantly. Therefore, research has been conducted on batteries that can meet various demands. In particular, as a power source for such devices, research on lithium secondary batteries with excellent life and cycle characteristics and high energy density has been actively carried out.

[0003] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The negative electrode may have a structure in which a negative electrode active material layer is stacked on one or both surfaces of a negative electrode current collector, and a copper thin film is mainly used as the negative electrode current collector.

[0004] A lithium metal battery is a battery that utilizes the following electrochemical reaction, in which by using lithium metal as a negative electrode active material, during battery discharge, the lithium metal at the negative electrode loses electrons and moves to the positive electrode through the electrolyte, and during battery charging, lithium ions move to the negative electrode through the electrolyte and are stored in the negative electrode active material. The advantage of a lithium metal battery is that, compared with commercial lithium ion batteries using graphite or the like as a negative electrode active material, it has a very high energy capacity in theory.

[0005] However, in the case of charging and discharging a lithium metal battery using a copper thin film as a negative electrode current collector, the lithium ion flow concentrates around defects (platforms, kinks, and / or steps) contained in the copper thin film. Therefore, lithium nucleation and dendrite growth proceed unevenly. For example, in the case of using a copper thin film as a negative electrode current collector in a lithium metal battery, during charging and discharging, lithium dendrites randomly grow on the surface of the copper thin film, and since the lithium dendrites penetrate the separator, there is a problem of short circuit between the positive electrode and the negative electrode.

[0006] Therefore, there is a need to develop a technology for suppressing the random growth of lithium dendrites on a negative electrode current collector in a lithium metal battery. Summary of the Invention

[0007] Technical Problem

[0008] One aspect of the present invention provides a negative electrode current collector and a method for manufacturing the same that can suppress the random growth of lithium dendrites on the negative electrode current collector.

[0009] Technical Solution

[0010] According to an embodiment of the present invention, a negative electrode current collector is provided, including a copper thin film formed with peaks and recesses; and metal particles disposed in at least a part of the recesses, having a standard reduction potential higher than that of lithium ions and capable of forming a solid solution with lithium (Li).

[0011] The metal particles may be silver (Ag).

[0012] The size of the metal particles may be in the range of 0.1 nm to 1,000 nm.

[0013] The metal particles may be hydrophilic particles.

[0014] At least a part of the recesses according to the present invention may include hydrophilic groups.

[0015] At least a part of the peaks according to the present invention may include hydrophobic groups. In this case, at least a part of the peaks may include at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0016] The copper thin film according to the present invention may be an electrolytic copper foil or a rolled copper foil.

[0017] The thickness of the negative electrode current collector according to the present invention may be 4 μm to 20 μm, or the center line surface roughness Ra may be 0.1 μm to 0.5 μm.

[0018] According to another embodiment of the present invention, a method for manufacturing a negative electrode current collector is provided, including the steps of: manufacturing a copper thin film formed with peaks and recesses, and disposing metal particles capable of forming a solid solution with lithium (Li) in at least a part of the recesses.

[0019] Disposing metal particles capable of forming a solid solution with lithium (Li) in at least a part of the recesses may include the steps of: performing a hydrophobic treatment on at least a part of the peaks, and coating the copper thin film with hydrophilic metal particles. In this case, performing a hydrophobic treatment on at least a part of the peaks may include coating the surface of the copper thin film with at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0020] In the method for manufacturing a negative electrode current collector of the present invention, the copper thin film may be manufactured through an electroplating process.

[0021] According to another embodiment of the present invention, a lithium secondary battery is provided, including a negative electrode containing the above negative electrode current collector, a positive electrode, and a separator disposed between the negative electrode and the positive electrode.

[0022] Advantageous Effects

[0023] The present invention is characterized in that a negative electrode current collector is provided, in which metal particles having a standard reduction potential higher than that of lithium ions are provided in recesses formed in a copper thin film. The metal particles can act as seeds for inducing uniform distribution of lithium on the negative electrode current collector during charging and discharging of the battery. Specifically, before lithium electrodeposited on the negative electrode current collector forms a Li 0 phase (pure Li phase), the metal particles act as heterogeneous nucleation sites by forming a solid solution with lithium. As a result, the metal particles can reduce the interfacial energy of the negative electrode current collector and can prevent dendritic growth of lithium electrodeposited on the negative electrode current collector and induce uniform lithium deposition by controlling crystal nucleation, which is the starting point of lithium dendrite growth during battery charging and discharging, to an appropriate level. In addition, by suppressing random growth of lithium dendrites on the surface of the copper thin film, problems such as short circuits occurring between the positive and negative electrodes due to lithium dendrites penetrating the separator can be prevented.

[0024] Since the method for manufacturing a negative electrode current collector according to the present invention does not perform artificial lithography or dry or chemical etching processes, the method can simplify the process procedure and can reduce the manufacturing cost.

[0025] In addition, since both electrolytic copper foil and rolled copper foil can be used as the copper thin film included in the negative electrode current collector, the method for manufacturing a negative electrode current collector according to the present invention has high practicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings attached to the present specification illustrate preferred embodiments of the present invention by way of examples, and together with the detailed description of the present invention given below, are used to further understand the technical concept of the present invention. Therefore, the present invention should not be construed only by the matters in these drawings.

[0027] Figure 1 is a cross-sectional view of a negative electrode current collector according to the present invention.

[0028] Figure 2 is a phase equilibrium diagram of lithium and copper.

[0029] Figure 3 is a phase equilibrium diagram of lithium and silver. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Advantages, features, and implementation methods of the present invention will become clear through the following embodiments described with reference to the drawings. However, the present invention can be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Instead, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In addition, the present invention is defined only by the scope of the claims. Throughout the text, the same reference numerals refer to the same elements.

[0031] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be intended to have the meanings understood by those skilled in the art. In addition, unless specifically defined clearly, terms defined in general dictionaries should not be interpreted in an unusual or inflated manner.

[0032] The terms used herein are for the purpose of describing particular example embodiments only and are not intended to limit the invention. In this specification, unless stated to the contrary, the singular forms of terms may include the plural forms. It will be further understood that when used in this specification, the terms "comprising" and / or "including" specify the presence of the stated components, but do not preclude the presence or addition of one or more other components.

[0033] In this specification, when describing a part as "comprising" a certain component, unless otherwise specifically stated to the contrary, this means that other components may be further included rather than excluding other components.

[0034] In this specification, the description of "A and / or B" means A, or B, or A and B.

[0035] In this specification, unless otherwise clearly stated, the expression "%" represents weight %.

[0036] <Negative current collector>

[0037] The negative current collector according to the present invention includes a copper thin film formed with peak portions and recessed portions, and metal particles disposed in at least a part of the recessed portions, having a standard reduction potential higher than that of lithium ions and capable of forming a solid solution with lithium (Li).

[0038] Hereinafter, reference will be made to Figure 1 describe the negative current collector of the present invention in more detail.

[0039] Figure 1 is a cross-sectional view of the negative current collector 100 according to the present invention. The negative current collector 100 of the present invention has conductivity and does not cause chemical changes in the battery. As Figure 1 shown, the negative current collector 100 includes a copper thin film 110 and metal particles 120.

[0040] The copper thin film 110 may be an electrolytic copper foil or a rolled copper foil. Specifically, the copper thin film 110 may be an electrolytic copper foil manufactured by an electrolytic plating process. The copper thin film 110 includes peak portions 112 and recessed portions 114. Specifically, the copper thin film 110 includes defects, and the peak portions 112 and the recessed portions 114 may be formed on the surface of the copper thin film 110.

[0041] The peak portion 112 refers to a region protruding relative to the recessed portion 114 on the surface of the copper thin film 110. At least a part of the peak portion 112 may contain a hydrophobic group. Specifically, at least a part of the peak portion 112 may contain an oil-based binder, and more specifically may contain at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). The peak portion 112 containing the hydrophobic materials listed above may have hydrophobicity.

[0042] The recessed portion 114 refers to a recessed area recessed relative to the peak portion 112 on the surface of the copper thin film 110. Since the copper thin film 110, which is an electrolytic copper foil in the present invention, has hydrophilicity, the recessed portion 114 may relatively have hydrophilicity when the peak portion 112 is coated with a hydrophobic material.

[0043] The metal particles 120 may be disposed in at least a part of the recessed portion 114. Specifically, the metal particles 120 may be in physical contact with the copper located in the recessed portion 114, or may form an alloy with the copper located in the recessed portion 114.

[0044] The metal particles 120 may act as seeds for inducing uniform distribution of lithium on the negative electrode current collector 100 during battery charge and discharge. Specifically, before lithium electrodeposited on the negative electrode current collector 100 forms a Li 0 phase (pure Li phase), the metal particles 120 act as heterogeneous nucleation sites by forming a solid solution with lithium.

[0045] The standard reduction potential of the metal particles 120 may be higher than that of lithium ions so as to form a solid solution with lithium electrodeposited on the negative electrode current collector 100. Specifically, the metal particles 120 may be silver (Ag).

[0046] Figure 2 is a phase equilibrium diagram of lithium and copper (Cu), Figure 3 is a phase equilibrium diagram of lithium and silver (Ag). As Figure 2 shown, the copper contained in the copper thin film 110 forms a solid solution with lithium only under relatively very low lithium content conditions. Therefore, when using a copper thin film that does not contain the metal particles 120 of the present invention as the negative electrode current collector, it may not be possible to suppress the random growth of dendrites caused by lithium electrodeposited on the negative electrode current collector. In contrast, as Figure 3 shown, since silver particles used as the metal particles 120 can form a solid solution with lithium even under relatively high lithium content conditions (for example, 40 to 50 atomic %), it can suppress the random growth of lithium dendrites by interfering with the dendritic development of lithium electrodeposited on the negative electrode current collector, and can induce uniform lithium deposition on the negative electrode current collector.

[0047] The size of the metal particles 120 may be in the range of 0.1 nm to 1,000 nm, particularly 0.1 nm to 500 nm, and more particularly 0.5 nm to 100 nm. In this case, the size of the metal particles 120 can be measured by an image analysis method using a field emission-scanning electron microscope (FE-SEM) of Hitachi High-Technologies Corporation. When the size of the metal particles 120 satisfies the above numerical range, the metal particles can exist in a dispersed state in a solution before being disposed on the copper thin film 110, and can be easily disposed in the recesses 114 having a size of several μm without an additional binder component when disposed on the copper thin film 110.

[0048] The thickness of the negative electrode current collector 100 may be in the range of 4 μm to 20 μm, particularly 5 μm to 15 μm, and more particularly 6 μm to 12 μm. When the thickness of the negative electrode current collector satisfies the above numerical range, the mechanical properties of the negative electrode current collector can be ensured, while the manufacturing cost of the battery manufactured from the negative electrode current collector can be reduced, and the energy density can be improved.

[0049] The center line surface roughness Ra of the negative electrode current collector 100 may be in the range of 0.1 μm to 0.5 μm, particularly 0.2 μm to 0.5 μm, and more particularly 0.3 μm to 0.5 μm. When the center line surface roughness Ra of the negative electrode current collector 100 satisfies the above numerical range, since the peak portions 112 and the recesses 114 are formed on the surface of the copper thin film 110 manufactured by an electrolytic plating method, the metal particles 120 can be easily disposed in the recesses 114.

[0050] <Method for manufacturing a negative electrode current collector>

[0051] Next, a method for manufacturing a negative electrode current collector according to the present invention will be described.

[0052] The method for manufacturing a negative electrode current collector according to the present invention includes the following steps: manufacturing a copper thin film formed with peak portions and recesses, and disposing metal particles capable of forming a solid solution with lithium (Li) in at least a part of the recesses. In this case, the negative electrode current collector manufactured by the above method may be the negative electrode current collector of the present invention described above.

[0053] Hereinafter, each step of the method for manufacturing a negative electrode current collector according to the present invention will be described in more detail.

[0054] (1) Step of manufacturing a copper thin film formed with peak portions and recesses

[0055] The method of manufacturing a negative electrode current collector according to the present invention starts with the step of manufacturing a copper thin film formed with peak portions and recessed portions.

[0056] Specifically, the copper thin film can be manufactured through an electrolytic plating process. Since it is easy to control the thickness of the plated foil by adjusting the magnitude of the applied current, the current application time, the temperature, etc., the electrolytic plating process has advantages in terms of process flexibility and cost. In addition, since a copper thin film with a thin thickness can be achieved if the electrolytic plating process is used, the energy density of the battery can be improved.

[0057] For example, the method of manufacturing a copper thin film through an electrolytic plating method is as follows. First, a reaction tank equipped with a cathode rotating drum and an anode plate arranged to face the cathode rotating drum is prepared, and the reaction tank is filled with an electrolyte in which copper ions and water are mixed. Next, copper is electrodeposited on the surface of the cathode rotating drum by rotating the cathode rotating drum while applying electricity to the cathode rotating drum and the anode plate. Finally, the copper thin film can be finally manufactured by continuously taking out the electrodeposited copper from the reaction tank. Since the copper thin film manufactured as described above contains defects, peak portions and recessed portions can be formed on the surface of the copper thin film.

[0058] (2) Step of disposing metal particles in at least a part of the recessed portions

[0059] Next, metal particles having a standard reduction potential higher than that of lithium ions and capable of forming a solid solution with lithium (Li) are disposed in at least a part of the recessed portions.

[0060] Specifically, disposing metal particles capable of forming a solid solution with lithium (Li) in at least a part of the recessed portions may include the following steps: subjecting at least a part of the peak portions to a hydrophobic treatment, and coating the copper thin film with hydrophilic metal particles.

[0061] Subjecting at least a part of the peak portions to a hydrophobic treatment may be the step of disposing a hydrophobic material on the peak portions. For example, the hydrophobic material can be disposed on the peak portions by applying a liquid containing the hydrophobic material to the surface of the copper thin film using a roller and then drying it. In this case, since the liquid containing the hydrophobic material does not penetrate into the recessed portions having a size of several μm, the hydrophobic material is not disposed in the recessed portions. The hydrophobic material may contain an oil-based binder, and specifically may contain at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0062] Coating the copper thin film with hydrophilic metal particles may be a step of applying a solution containing metal particles onto the surface of the copper thin film where at least a part of the peak portions have been subjected to hydrophobic treatment, by means of a spraying method and / or an impregnation method. In this case, the metal particles may be disposed in at least a part of the recess while avoiding the peak portions having hydrophobicity.

[0063] Thereafter, the solvent in the colloidal solution coated / applied on the surface of the copper thin film may be removed by drying the copper thin film at 40°C to 50°C.

[0064] Since the method for manufacturing the negative electrode current collector according to the present invention does not perform artificial photolithography or dry or chemical etching processes, the method can simplify the process procedure and can reduce the manufacturing cost.

[0065] <Lithium secondary battery>

[0066] The lithium secondary battery of the present invention may include a negative electrode, a positive electrode, a separator, and an electrolyte. In this case, the negative electrode includes the negative electrode current collector of the present invention described above.

[0067] The negative electrode according to the present invention may not include a negative electrode active material layer provided on the negative electrode current collector. In this case, the lithium secondary battery including the negative electrode may be a non-aqueous negative electrode battery. For example, when the lithium secondary battery of the present invention is charged, lithium metal is formed on the surface of the negative electrode current collector, and the lithium metal may serve as a negative electrode active material.

[0068] The lithium secondary battery of the present invention can induce uniform lithium deposition on the negative electrode current collector by preventing dendritic growth of lithium electrodeposited on the negative electrode current collector and suppressing random growth of lithium dendrites on the surface of the negative electrode current collector, and can prevent a problem of short circuit occurring between the positive electrode and the negative electrode due to lithium dendrites penetrating the separator.

[0069] The positive electrode includes a positive electrode current collector. In addition, the positive electrode may include a positive electrode active material layer formed on the positive electrode current collector.

[0070] There is no particular limitation on the positive electrode current collector 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 one of carbon, nickel, titanium, or silver may be used as the current collector.

[0071] The thickness of the positive current collector may be from 3 μm to 500 μm and may have minute surface irregularities to increase the adhesion to the positive active material layer. For example, the positive current collector may be used in various different shapes such as a film, sheet, foil, net, porous body, foam body, non-woven fabric body, etc.

[0072] The positive active material layer may contain a positive active material and may also contain a conductive agent and a binder as required.

[0073] The positive active material is a compound capable of reversibly inserting and extracting lithium, where the positive active material may specifically include a lithium metal oxide containing lithium and at least one metal such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide may include lithium manganese-based oxides (e.g., LiMnO 2 , LiMn 2 O 4 etc.), lithium cobalt-based oxides (e.g., LiCoO 2 etc.), lithium nickel-based oxides (e.g., LiNiO 2 etc.), lithium nickel manganese-based oxides (e.g., LiNi 1-Y Mn Y O 2 (where 0 < Y < 1), LiMn 2-Z Ni z O 4 (where 0 < Z < 2) etc.), lithium nickel cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O 2 (where 0 < Y1 < 1) etc.), lithium manganese cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O 2 (where 0 < Y2 < 1), LiMn 2-Z1 Co z1 O 4 (where 0 < Z1 < 2) etc.), lithium nickel manganese cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O 2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O 4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2) etc.), lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mnr2 M S2 ) 2 (wherein M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg) and molybdenum (Mo), and p2, q2, r2 and s2 are the atomic fractions of each independent element, wherein 0 <p2<1,0<q2<1,0<r2<1,0<S2<1,并且p2+q2+r2+S2=1)等)、或锂铁磷酸盐(例如,Li 1+ a Fe 1-x M x (PO 4-b )X b (wherein M is at least one selected from Al, Mg and Ti, X is at least one selected from fluorine (F), sulfur (S) and nitrogen (N), -0.5≤a≤0.5, 0≤x≤0.5, and 0≤b≤0.1), and may include any one thereof or a mixture of two or more thereof.

[0074] Among these materials, the lithium metal oxide may be LiCoO in terms of improving the capacity characteristics and stability of the battery. 2 、LiMnO 2 、LiNiO 2 , lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ) 2 、Li(Ni 0.6 Mn 0.2 Co 0.2 ) 2 、Li(Ni 0.5 Mn 0.3 Co 0.2 ) 2 、Li(Ni 0.7 Mn 0.15 Co 0.15 ) 2 、Li(Ni 0.8 Mn 0.1 Co 0.1 ) 2 etc.), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.8 Co 0.15 Al 0.05 O 2 etc.), lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ) 2) or lithium iron phosphate (e.g., LiFePO 4 ), and any one of them or a mixture of two or more thereof can be used.

[0075] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 60% by weight to 99% by weight, preferably 70% by weight to 99% by weight, more preferably 80% by weight to 98% by weight.

[0076] The positive electrode conductive agent is a component that further improves the conductivity of the positive electrode active material. There is no particular limitation on the conductive agent as long as it has conductivity and does not cause chemical changes in the battery. For example, conductive materials can be used, such as: carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal cracking carbon black; graphite powder, such as natural graphite, artificial graphite or graphite with well-developed crystal structure; conductive fiber, such as carbon fiber or metal fiber; fluorocarbon powder; conductive powder, such as aluminum powder and nickel powder; conductive whisker, such as zinc oxide whisker and potassium titanate whisker; conductive metal oxide, such as titanium oxide; or polyphenylene derivative.

[0077] Based on the total weight of the positive electrode active material layer, the content of the positive electrode conductive agent can generally be 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight.

[0078] The positive electrode binder is a component that helps the binding between the active material and the conductive agent and the binding with the current collector.

[0079] Examples of the binder can be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, or various copolymers.

[0080] Based on the total weight of the positive electrode active material layer, the content of the positive electrode binder can generally be 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight.

[0081] The separator can be disposed between the negative electrode and the positive electrode. Any separator can be used without particular limitation as long as it is commonly used in lithium secondary batteries. In particular, a separator having high moisture retention ability for the electrolyte and low resistance to electrolyte ion transfer is preferred.

[0082] For example, as the separator, a porous polymer film containing a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used. In addition, a usual porous nonwoven fabric such as a nonwoven fabric formed of high melting point glass fiber or polyethylene terephthalate fiber can be used as the separator.

[0083] The lithium secondary battery according to one embodiment of the present invention may include an electrolyte. In this case, the electrolyte may be a non-aqueous electrolyte. The non-aqueous electrolyte may include an organic solvent and a lithium salt commonly used in the art, but is not particularly limited.

[0084] Any organic solvent can be used without particular limitation as long as it can be used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; an aromatic hydrocarbon-based solvent such as benzene and fluorobenzene; or a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC) can be used.

[0085] Among these solvents, a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, which can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is preferably used.

[0086] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in the lithium secondary battery. Specifically, as the lithium salt, LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ), 2 , LiN(C 2 F5 SO 2 ) 2 、LiN(CF 3 SO 2 ) 2 、LiCl, LiI or LiB(C 2 O 4 ) 2 . Preferably, the electrolyte contains the lithium salt at a concentration of about 0.6 mol% to about 2 mol%.

[0087] Although not essential, the non-aqueous electrolyte according to the present invention may further contain an additive to further improve the physical properties of the secondary battery.

[0088] Examples of the additive may be at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate / salt compounds, nitrile compounds, sultone compounds, sulfate / salt compounds, phosphate / salt compounds, borate / salt compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0089] The cyclic carbonate / salt compound may be, for example, vinylene carbonate (VC) or ethylene vinylene carbonate (VEC).

[0090] For example, the halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC).

[0091] For example, the nitrile compound may be succinonitrile, adiponitrile, hexane tricarbonitrile, or 1,4-dicyano-2-butene.

[0092] For example, the sultone compound may be 1,3-propane sultone or 1,3-propene sultone.

[0093] For example, the sulfate / salt compound may be ethylene sulfite (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), etc.

[0094] For example, the phosphate / salt compound may be at least one compound selected from the group consisting of lithium difluoro (bisoxalato) phosphate, lithium difluorophosphate, tetramethyl trimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite.

[0095] For example, the borate / salt compound may be tetraphenyl borate / salt or lithium difluorooxalate borate (LiODFB).

[0096] For example, the benzene-based compound may be fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetraethenylsilane.

[0097] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and the lithium salt-based compound may be selected from the group consisting of LiPO 2 F 2 , LiODFB, LiBOB (lithium bis(oxalato)borate (LiB(C 2 O 4 )) 2 ), and LiBF 4 , and at least one compound selected from the group consisting thereof.

[0098] The additive may be used alone or as a mixture of two or more thereof.

[0099] Based on the total weight of the electrolyte, the total amount of the additive may be in the range of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%. When the additive within the above range is included, a film can be stably formed on the electrode, the ignition phenomenon during overcharging can be suppressed, and at the same time, side reactions during the initial activation process of the secondary battery or the residue or precipitation of the additive can be prevented.

[0100] The lithium secondary battery of the present invention can be manufactured by the following method: placing an electrode assembly formed by disposing the separator between the positive electrode and the negative electrode into a battery case, injecting the electrolyte, and then sealing the battery case. In addition, the lithium secondary battery can be manufactured by the following method: stacking the electrode assemblies, impregnating them with the electrolyte, placing the obtained product into a battery case, and sealing the battery case.

[0101] A battery case commonly used in the art can be selected as the battery case, and the shape of the battery case is not limited according to the use of the battery. For example, a cylindrical, square, pouch-type, or coin-type battery case can be used, but the present invention is not limited thereto.

[0102] The lithium secondary battery according to the present invention can be used not only as a battery cell for a power source of a small device, but also as a unit cell in a medium- and large-sized battery module including a plurality of battery cells. Preferred examples of medium- and large-sized devices may be electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems (ESS).

[0103] Invention Mode

[0104] Hereinafter, the present invention will be described in detail according to specific embodiments. However, the following embodiments are provided only to illustrate the present invention, and the scope of the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and changes can be made within the scope and technical spirit of the present invention, and such modifications and changes fall within the scope of the claims included herein.

[0105] Examples and Comparative Examples

[0106] Example

[0107] (1) Manufacture of negative electrode current collector

[0108] Prepare a reaction tank equipped with a cathode drum and an anode plate arranged to face the cathode drum, and fill the reaction tank with an electrolyte in which copper sulfate and water are mixed. Next, copper is electrodeposited on the surface of the cathode drum by rotating the cathode drum while applying electricity to the cathode drum and the anode plate. Then, an electrolytic copper foil with a thickness of 8 μm is obtained by continuously removing the electrodeposited copper from the reaction tank.

[0109] Next, after coating the surface of the electrolytic copper foil with silane, colloidal silver is sprayed on the electrolytic copper foil, so that silver particles are provided on the surface of the electrolytic copper foil. Thereafter, the solvent remaining on the electrolytic copper foil is dried with hot air, thereby manufacturing a negative electrode current collector.

[0110] (2) Manufacture of lithium secondary battery

[0111] Use the above negative electrode current collector on which no separate negative electrode active material layer is provided as the negative electrode.

[0112] LiCoO 2 , polyvinylidene fluoride (PVdF), carbon nanotubes (CNT), and carbon black are added to an N-methylpyrrolidone (NMP) solvent in a weight ratio of 97.59:1.18:0.24:0.09 and stirred to manufacture a positive electrode paste. The positive electrode paste is applied to one surface of a 10-μm-thick aluminum film at a loading amount of 18.60 mg / cm 2 , and then vacuum dried. The dried positive electrode paste is roll-pressed, dried in a vacuum oven at 130 °C for 6 hours, and then stamped to manufacture a positive electrode.

[0113] An electrode assembly is manufactured by assembling the negative electrode, positive electrode, and porous polyethylene separator (thickness: 12 μm) manufactured as described above using a stacking method.

[0114] By dissolving LiPF 6 in a solvent (EC:PC:EP:PP = 20:10:25:45 mass ratio) to make LiPF6 An electrolyte was produced with a concentration of 1.2 M.

[0115] A lithium secondary battery (a non-negative electrode battery) was produced by housing the electrode assembly in a battery case, injecting the electrolyte, and then sealing the battery case.

[0116] Comparative Example 1

[0117] The negative electrode current collector was produced in the same manner as in the Example, but the process of spraying colloidal silver on the electrolytic copper foil was not performed.

[0118] A lithium secondary battery was produced in the same manner as in the Example, but during the production of the lithium secondary battery, the negative electrode current collector produced by the above method (i.e., the negative electrode current collector not containing silver particles) was used.

[0119] Comparative Example 2

[0120] The negative electrode current collector was produced in the same manner as in the Example, but the process of coating the surface of the electrolytic copper foil with silane was not performed.

[0121] A lithium secondary battery was produced in the same manner as in the Example, but during the production of the lithium secondary battery, the negative electrode current collector produced by the above method (i.e., the negative electrode current collector not containing a hydrophobic coating) was used.

[0122] Experimental Example 1

[0123] When charging and discharging the lithium secondary batteries produced in the Example and Comparative Examples 1 and 2, respectively, at a temperature of 45°C, the number of charge-discharge cycles until a short circuit occurred between the positive electrode and the negative electrode was measured. Specifically, when defining a complete charge and then a complete discharge of the lithium secondary battery as 1 cycle, the total number of cycles until the separator in the lithium secondary battery was pierced, resulting in a short circuit between the positive electrode and the negative electrode, was measured and is shown in Table 1 below.

[0124]

[0125] As shown in Table 1, for the Example in which silver particles were included in the recesses of the negative electrode current collector, it was confirmed that the total number of cycles until a short circuit occurred between the positive electrode and the negative electrode was significantly higher than the total number of cycles in Comparative Example 1 in which silver particles were not included and Comparative Example 2 in which silver ions were coated without a hydrophobic coating.

[0126] <Symbol Explanation>

[0127] 100: Negative electrode current collector

[0128] 110: Copper thin film

[0129] 112: Peak portion

[0130] 114: Recess

[0131] 120: Metal particle

Claims

1. A negative electrode current collector, comprising: A copper thin film formed with peaks and recesses; and Metal particles disposed in at least a part of the recesses, having a standard reduction potential higher than that of lithium ions and capable of forming a solid solution with lithium (Li).

2. The negative electrode current collector according to claim 1, wherein the metal particles are silver (Ag).

3. The negative electrode current collector according to claim 1, wherein the size of the metal particles is in the range of 0.1 nm to 1,000 nm.

4. The negative electrode current collector according to claim 1, wherein the metal particles are hydrophilic particles.

5. The negative electrode current collector according to claim 1, wherein at least a part of the recesses contains hydrophilic groups.

6. The negative electrode current collector according to claim 1, wherein at least a part of the peaks contains hydrophobic groups.

7. The negative electrode current collector according to claim 1, wherein at least a part of the peaks contains at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

8. The negative electrode current collector according to claim 1, wherein the copper thin film is an electrolytic copper foil or a rolled copper foil.

9. The negative electrode current collector according to claim 1, wherein the thickness of the negative electrode current collector is in the range of 4 μm to 20 μm.

10. The negative electrode current collector according to claim 1, wherein the centerline surface roughness Ra of the negative electrode current collector is in the range of 0.1 μm to 0.5 μm.

11. A method for manufacturing a negative electrode current collector, the method comprising the following steps: Manufacturing a copper thin film formed with peaks and recesses; and Disposing metal particles having a standard reduction potential higher than that of lithium ions and capable of forming a solid solution with lithium (Li) in at least a part of the recesses.

12. The method according to claim 11, wherein disposing the metal particles capable of forming a solid solution with lithium (Li) in at least a part of the recesses comprises the following steps: Performing a hydrophobic treatment on at least a part of the peaks, and Coating the copper thin film with hydrophilic metal particles.

13. The method according to claim 12, wherein performing a hydrophobic treatment on at least a part of the peaks includes coating the surface of the copper thin film with at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

14. The method according to claim 11, wherein the copper thin film is manufactured by an electrolytic plating process.

15. A lithium secondary battery, comprising: A negative electrode comprising the negative electrode current collector according to claim 1; A positive electrode; and A separator disposed between the negative electrode and the positive electrode.

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