Negative electrode current collector and method for manufacturing the same

Abstract

The negative electrode current collector according to the present invention includes a copper thin film having peaks and valleys formed thereon, and metal particles disposed in at least some of the valleys, the metal particles having a higher standard reduction potential than lithium ions and 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 technology]

[0002] As technological development and demand for electric vehicles and energy storage systems (ESS) increase, the demand for batteries as an energy source is rapidly rising, and consequently, research is being conducted on batteries that can meet a variety of requirements. In particular, there is a lot of research being done on lithium-ion secondary batteries that have high energy density while also possessing excellent lifespan and cycle characteristics, for use as power sources for such devices.

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

[0004] On the other hand, lithium metal batteries use lithium metal as the negative electrode active material and utilize an electrochemical reaction in which, during discharge, the lithium metal in the negative electrode loses electrons and moves through the electrolyte to the positive electrode, and during charging, lithium ions move through the electrolyte to the negative electrode and are stored in the negative electrode active material. This has the advantage of theoretically having a significantly higher energy capacity compared to commercial lithium-ion batteries that use graphite or other materials as the negative electrode active material.

[0005] However, when charging and discharging a lithium metal battery using a copper thin film as a negative electrode current collector, lithium ion flux intensively gathers around defects (terraces, kinks and / or steps) contained in the copper thin film, which causes non-uniform lithium nucleation and dendrite growth. For example, when a copper thin film is used as a negative electrode current collector in a lithium metal battery, lithium dendrites randomly grow on the surface of the copper thin film during charge and discharge, which causes the problem that the separation membrane is penetrated by the lithium dendrites and a short circuit occurs between the positive electrode and the negative electrode.

[0006] Therefore, there is a demand for developing technology for suppressing random growth of lithium dendrites on a negative electrode current collector in a lithium metal battery. Summary of the Invention Problem to be Solved by the Invention

[0007] The present invention is intended to solve the above problem, and provides a negative electrode current collector capable of suppressing random growth of lithium dendrites on the negative electrode current collector, and a method for producing the same. Means for Solving the Problem

[0008] According to one embodiment of the present invention, there is provided a negative electrode current collector including: a copper thin film having protrusions (Peak) and recesses (Valley) formed therein; and metal particles disposed in at least a part of the recesses, the metal particles having a higher standard reduction potential than lithium ions and being capable of forming a solid solution with lithium (Li).

[0009] The metal particles may be silver (Ag).

[0010] The size of the metal particles may be 0.1 nm to 1000 nm.

[0011] The metal particles may be hydrophilic particles.

[0012] At least a portion of the recesses according to the present invention may contain hydrophilic groups.

[0013] At least a portion of the protrusions according to the present invention may contain hydrophobic groups. In that case, at least a portion of the protrusions may contain at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0014] The copper thin film according to the present invention may be an electrolytic copper foil or a rolled copper foil.

[0015] The negative electrode current collector according to the present invention has a thickness of 4 μm to 20 μm, or a centerline surface roughness (R a The particle size may be 0.1 μm to 0.5 μm.

[0016] According to another embodiment of the present invention, a method for manufacturing a negative electrode current collector is provided, comprising the steps of: manufacturing a copper thin film having protrusions and recesses formed thereon; and arranging metal particles in at least a portion of the recesses that have a higher standard reduction potential than lithium ions and can form a solid solution with lithium (Li).

[0017] The step of arranging metal particles capable of forming a solid solution with lithium (Li) in at least a portion of the recess may include the step of hydrophobic treatment of at least a portion of the protrusion and the step of coating the copper thin film with hydrophilic metal particles. In this case, the step of hydrophobic treatment of at least a portion of the protrusion may be the coating of the surface of the copper thin film with at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0018] In the method for manufacturing a negative electrode current collector of the present invention, the copper thin film may be manufactured by an electrolytic plating process.

[0019] According to yet another embodiment of the present invention, a lithium secondary battery is provided, comprising a negative electrode including the aforementioned negative electrode current collector, a positive electrode, and a separator membrane disposed between the negative electrode and the positive electrode. [Effects of the Invention]

[0020] The present invention is characterized by providing a negative electrode current collector in which metal particles with a higher standard reduction potential than lithium ions are arranged in recesses (Valleys) formed in a copper thin film. The metal particles act as seeds to cause a uniform lithium distribution on the negative electrode current collector during charging and discharging of the battery. Specifically, the metal particles cause lithium to be electrodeposited on the negative electrode current collector to be Li 0 By forming a solid solution with the lithium before forming the pure Li phase, the metal particles act as heterogeneous nucleation sites. As a result, the metal particles can lower the interface energy of the negative electrode current collector and regulate the nucleation that initiates lithium dendrite growth during battery charging and discharging to an appropriate level, thereby preventing dendritic development of lithium electrodeposited onto the negative electrode current collector and causing uniform lithium deposition. In addition, by suppressing the random growth of lithium dendrites on the surface of the copper thin film, it is possible to prevent the problem of the separation film being penetrated by the lithium dendrites and causing a short circuit between the positive and negative electrodes.

[0021] The method for manufacturing a negative electrode current collector according to the present invention does not involve artificial exposure etching (photolithography) or dry or chemical etching processes, thus simplifying the process and reducing manufacturing costs.

[0022] Furthermore, the method for manufacturing a negative electrode current collector according to the present invention is highly versatile because it can use both electrolytic copper foil and rolled copper foil as the copper thin film contained in the negative electrode current collector. [Brief explanation of the drawing]

[0023] The drawings attached to the specification illustrate preferred embodiments of the present invention and serve to further illustrate the technical concept of the present invention together with the content of the invention described above. Therefore, the present invention should not be construed as being limited only to the matters described in such drawings.

[0024] [Figure 1] This is a cross-sectional view of the negative electrode current collector according to the present invention. [Figure 2] This is a phase equilibrium diagram of lithium and copper. [Figure 3] This is a phase equilibrium diagram of lithium and silver. [Modes for carrying out the invention]

[0025] The advantages and features of the present invention, as well as methods for achieving them, will become apparent with reference to the embodiments described below in detail, along with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be realized in a variety of different forms. These embodiments are provided merely to complete the disclosure of the present invention and to allow a person ordinary in the art to which the invention belongs to to fully understand the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals indicate the same components.

[0026] Unless otherwise defined, all terms used herein (including technical and scientific terms) will be used in a sense that is commonly understood by those with ordinary skill in the art to which this invention pertains. Furthermore, terms defined in commonly used dictionaries will not be interpreted ideally or excessively unless otherwise clearly defined.

[0027] The terms used herein are for illustrative purposes only and do not limit the invention. In this specification, singular nouns include plural nouns unless otherwise specified in the statement. The terms “comprises” and / or “comprising” as used herein do not exclude the presence or addition of one or more other components in addition to those mentioned.

[0028] In this specification, when a part is said to contain a component, it means that, unless otherwise stated, it may contain other components rather than excluding them.

[0029] In this specification, the term "A and / or B" means A, B, or A and B.

[0030] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0031] <Negative electrode current collector> The negative electrode current collector according to the present invention includes a copper thin film having protrusions (peaks) and recesses (valleys) formed thereon, and metal particles arranged in at least a portion of the recesses, which have a higher standard reduction potential than lithium ions and can form a solid solution with lithium (Li).

[0032] The negative electrode current collector of the present invention will be described in more detail below with reference to Figure 1.

[0033] Figure 1 is a cross-sectional view of the negative electrode current collector 100 according to the present invention. The negative electrode current collector 100 of the present invention does not cause chemical changes in the battery and is conductive. As shown in Figure 1, the negative electrode current collector 100 includes a copper thin film 110 and metal particles 120.

[0034] The copper thin film 110 may be electrolytic copper foil or rolled copper foil. Specifically, the copper thin film 110 may be electrolytic copper foil manufactured by an electrolytic plating process. The copper thin film 110 includes protrusions (peaks) 112 and recesses (valleys) 114. Specifically, the copper thin film 110 may include defects, and the surface of the copper thin film 110 may have protrusions 112 and recesses 114 formed thereon.

[0035] The protrusion 112 refers to a region on the surface of the copper thin film 110 that protrudes relatively compared to the recess 114. At least a portion of the protrusion 112 may contain hydrophobic groups. Specifically, at least a portion of the protrusion 112 may contain an oil-based binder, and more specifically, at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). The protrusion 112 containing the hydrophobic substances listed above is hydrophobic.

[0036] The recessed area 114 refers to a valley region on the surface of the copper thin film 110 that is relatively recessed compared to the protruding portion 112. Since the copper thin film 110 of the present invention is an electrolytic copper foil and is hydrophilic, when a hydrophobic substance is coated on the protruding portion 112, the recessed area 114 becomes relatively hydrophilic.

[0037] On the other hand, the metal particles 120 may be arranged in at least a portion of the recess 114. Specifically, the metal particles 120 may be in physical contact with the copper located in the recess 114, or they may form an alloy with the copper located in the recess 114.

[0038] The metal particles 120 act as seeds to cause a uniform lithium distribution on the negative electrode current collector 100 during battery charging and discharging. Specifically, the metal particles 120 cause the lithium to be electrodeposited on the negative electrode current collector 100 to be Li 0By forming a solid solution with the lithium before forming the pure Li phase, it acts as a heterogeneous nucleation site.

[0039] The metal particles 120 may have a higher standard reduction potential than lithium ions in order to form a solid solution with the lithium electrodeposited on the negative electrode current collector 100. Specifically, the metal particles 120 may be silver (Ag).

[0040] Figure 2 shows the phase equilibrium diagram of lithium and copper (Cu), and Figure 3 shows the phase equilibrium diagram of lithium and silver (Ag). As shown in Figure 2, 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 a copper thin film without the metal particles 120 of the present invention is used as a negative electrode current collector, the random growth of dendrites due to lithium electrodeposited on the negative electrode current collector cannot be suppressed. In contrast, as shown in Figure 3, the silver particles used as metal particles 120 can form a solid solution with lithium even under relatively high lithium content conditions (e.g., 40-50 atomic%), thus hindering the dendritic development of lithium electrodeposited on the negative electrode current collector and suppressing the random growth of lithium dendrites, thereby causing uniform lithium deposition on the negative electrode current collector.

[0041] The size of the metal particles 120 may be between 0.1 nm and 1000 nm, more specifically between 0.1 nm and 500 nm, or more specifically between 0.5 nm and 100 nm. In this case, the size of the metal particles 120 can be measured by image analysis using a Hitachi FE-SEM instrument. When the size of the metal particles 120 satisfies the above numerical range, they can exist in a dispersed state in the solution before being placed on the copper thin film 110, and can be easily placed in the recesses 114 having a size of several μm without the need for other adhesive components when being placed on the copper thin film 110.

[0042] On the other hand, the thickness of the negative electrode current collector 100 may be 4 μm to 20 μm, specifically 5 μm to 15 μm, or more specifically 6 μm to 12 μm. When the thickness of the negative electrode current collector satisfies the above numerical range, it is possible to reduce the manufacturing cost of the battery produced from the negative electrode current collector and increase the energy density while ensuring the mechanical properties of the negative electrode current collector.

[0043] Surface roughness of the center line of the negative electrode current collector 100 (R a The surface roughness of the center line of the negative electrode current collector 100 (R a If the above numerical range is met, protrusions 112 and recesses 114 are formed on the surface of the copper thin film 110 manufactured by the electroplating method, so that metal particles 120 can be easily placed in the recesses 114.

[0044] <Manufacturing method for negative electrode current collector> Next, a method for manufacturing a negative electrode current collector according to the present invention will be described.

[0045] The method for manufacturing a negative electrode current collector according to the present invention includes the steps of manufacturing a copper thin film having protrusions and recesses formed thereon, and arranging metal particles capable of forming a solid solution with lithium (Li) in at least a portion 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 as described above.

[0046] The following describes in more detail each step of the method for manufacturing a negative electrode current collector according to the present invention.

[0047] (1) Step of manufacturing a copper thin film in which protrusions and recesses are formed. The method for manufacturing a negative electrode current collector according to the present invention begins with the step of manufacturing a copper thin film in which protrusions and recesses are formed.

[0048] Specifically, copper thin films can be manufactured by an electroplating process. The electroplating process is advantageous in terms of process flexibility and cost because the thickness of the plated foil can be easily adjusted by controlling the magnitude of the applied current, the current application time, and the temperature. Furthermore, using the electroplating process allows for the creation of thin copper thin films, thereby increasing the energy density of the battery.

[0049] For example, the method for manufacturing a copper thin film using electroplating is as follows: First, a reaction vessel is prepared, which is equipped with a negative electrode rotating drum and a positive electrode plate positioned opposite the negative electrode rotating drum. The reaction vessel is then filled with an electrolyte solution, which is a mixture of copper ions and water. Next, the negative electrode rotating drum is rotated while electricity is applied to the negative electrode rotating drum and the positive electrode plate, thereby electrodepositing copper onto the surface of the negative electrode rotating drum. Finally, the electrodeposited copper is continuously withdrawn from the reaction vessel, thereby ultimately manufacturing the copper thin film. The copper thin film manufactured as described above contains defects, so protrusions and recesses are formed on the surface of the copper thin film.

[0050] (2) Step of placing metal particles in at least a portion of the recess Next, metal particles that have a higher standard reduction potential than lithium ions and can form a solid solution with lithium (Li) are placed in at least a portion of the recess.

[0051] Specifically, the step of arranging metal particles capable of forming a solid solution with lithium (Li) in at least a portion of the recess may include the step of hydrophobic treatment of at least a portion of the protrusion and the step of coating the copper thin film with hydrophilic metal particles.

[0052] The step of hydrophobicizing at least a portion of the protrusions may be a step of placing a hydrophobic substance on the protrusions. For example, the hydrophobic substance can be placed on the protrusions by applying a liquid containing the hydrophobic substance to the surface of a copper thin film using a roller and then drying it. In this case, the liquid containing the hydrophobic substance does not penetrate into recesses having a size of several micrometers, so the hydrophobic substance is not placed in the recesses. The hydrophobic substance may include an oil-based binder, and specifically, it may include at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0053] The step of coating a copper thin film with hydrophilic metal particles may be a step of applying a solution containing metal particles to the surface of a copper thin film in which at least a portion of the protrusions have been hydrophobic treated, by spraying and / or dipping. In this case, the metal particles are arranged in at least a portion of the recesses, avoiding the hydrophobic protrusions.

[0054] Subsequently, by drying the copper thin film at 40°C to 50°C, the solvent in the colloidal solution coated / applied to the surface of the copper thin film can be removed.

[0055] The method for manufacturing a negative electrode current collector according to the present invention does not involve artificial exposure etching (photolithography) or dry or chemical etching processes, thus simplifying the process and reducing manufacturing costs.

[0056] <Lithium-ion secondary battery> The lithium secondary battery of the present invention may include a negative electrode, a positive electrode, a separator membrane, and an electrolyte. Here, the negative electrode includes the negative electrode current collector of the present invention as described above.

[0057] The negative electrode according to the present invention does not necessarily include a negative electrode active material layer disposed on the negative electrode current collector. In that case, the lithium secondary battery containing the negative electrode may be an anodeless battery. For example, in the lithium secondary battery of the present invention, lithium metal is formed on the surface of the negative electrode current collector during charging, and the lithium metal plays the role of the negative electrode active material.

[0058] The lithium secondary battery of the present invention prevents the dendritic development of lithium electrodeposited onto the negative electrode current collector and suppresses the random growth of lithium dendrites on the surface of the negative electrode current collector, thereby causing uniform lithium deposition on the negative electrode current collector and preventing the problem of short circuits between the positive and negative electrodes caused by lithium dendrites penetrating the separation film.

[0059] On the other hand, the positive electrode includes a positive electrode current collector. The positive electrode may also include a positive electrode active material layer formed on the positive electrode current collector.

[0060] The positive electrode current collector is not particularly limited, as long as it does not cause a chemical change in the battery and is conductive. For example, the current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surfaces have been treated with carbon, nickel, titanium, silver, etc.

[0061] The positive electrode current collector can have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesion strength of the positive electrode active material layer. For example, it can be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0062] The positive electrode active material layer may contain a positive electrode active material, and may further contain conductive materials, binders, etc., as needed.

[0063] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may comprise a lithium metal oxide containing lithium and one or more metals selected from cobalt, manganese, nickel, aluminum and the like. More specifically, the lithium metal oxide includes lithium-manganese based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt based oxides (e.g., LiCoO2, etc.), lithium-nickel based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese based oxides (e.g., LiNi 1-Y Mn Y O2 (wherein 0<Y<1), LiMn 2-Z Ni Z O4 (wherein 0<Z<2), etc.), lithium-nickel-cobalt based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (wherein 0<Y1<1), etc.), lithium-manganese-cobalt based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (wherein 0<Y2<1), LiMn 2-Z1 Co Z1 O4 (wherein 0<Z1<2), etc.), lithium-nickel-manganese-cobalt based oxides (e.g., Li(Ni p Co q Mn r )O2 (wherein 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each independently atomic fractions of elements, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), lithium iron phosphate (e.g., Li 1+a Fe1-x M x (PO 4-b )X b (Here, M is one or more selected from Al, Mg, and Ti, and X is one or more selected from F, S, and N, with -0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1), and one or more of these compounds may be included.

[0064] Among these, the lithium metal oxides that can improve the capacity characteristics and stability of the battery are LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxide (for example, Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2 etc.), lithium nickel manganese cobalt aluminum oxide (for example, Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 These include 02, lithium iron phosphorus oxide (e.g., LiFePO4), and one or more of these, or a mixture of two or more, may be used.

[0065] The positive electrode active material may be present in an amount of 60 to 99% by weight, preferably 70 to 99% by weight, and more preferably 80 to 98% by weight, relative to the total weight of the positive electrode active material layer.

[0066] The positive electrode conductive material is a component for further improving the conductivity of the positive electrode active material, and such conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with a highly developed crystalline structure; conductive fibers such as carbon fibers and metal fibers; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0067] Typically, the positive electrode conductive material may be present in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0068] The positive electrode binder is a component that assists in the bonding of active materials and conductive materials to the current collector.

[0069] Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0070] Typically, the positive electrode binder may be present in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0071] On the other hand, the separation membrane may be placed between the negative electrode and the positive electrode. The separation membrane can be any type that is normally used as a separation membrane in lithium secondary batteries, and it is particularly preferable that it has low resistance to the movement of ions in the electrolyte and excellent electrolyte moisture absorption capacity.

[0072] For example, the separation membrane may be a porous polymer film containing polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, the separation membrane may be a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers.

[0073] A 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, but is not particularly limited to, organic solvents and lithium salts commonly used in the art.

[0074] The aforementioned organic solvent can be used without particular limitations, as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; and carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0075] Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate, propylene carbonate, etc.) having high ionic conductivity and high dielectric constant to enhance the charge and discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is more preferred.

[0076] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

[0077] On the other hand, the non-aqueous electrolyte according to the present invention may further contain additives, although these are not essential, in order to further improve the physical properties of the secondary battery.

[0078] Examples of such additives include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, nitrile compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0079] The cyclic carbonate compound may be, for example, vinylene carbonate (VC), vinylethylene carbonate (VEC), or the like.

[0080] The halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0081] The nitrile compound may be, for example, succinonitrile, adiponitrile, hexanetricyanide, or 1,4-dicyano-2-butene.

[0082] The sultone compound may be, for example, 1,3-propanesultone or 1,3-propenesultone.

[0083] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0084] The phosphate compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalate) phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate.

[0085] The borate compound may be, for example, tetraphenylborate or lithium oxalyl difluoroborate (LiODFB).

[0086] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be triethanolamine, ethylenediamine, etc., and the silane-based compound may be tetravinylsilane, etc.

[0087] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2) and LiBF4).

[0088] On the other hand, the additives may be used individually or in a mixture of two or more types.

[0089] The total amount of the additive may be 1% to 20% by weight, preferably 1% to 15% by weight, relative to the total weight of the electrolyte. When the additive is included within the above range, a stable film can be formed on the electrode, suppressing ignition phenomena during overcharging, and preventing side reactions from occurring during the initial activation process of the secondary battery, as well as preventing the additive from remaining or precipitating.

[0090] The lithium secondary battery of the present invention can be manufactured by placing an electrode assembly, formed by placing a separation membrane between the positive and negative electrodes, into a battery case, then injecting an electrolyte and sealing it. Alternatively, it can be manufactured by stacking the electrode assemblies, then impregnating them with an electrolyte, and placing the resulting product into a battery case and sealing it.

[0091] The aforementioned battery case may be one that is commonly used in the field, and there are no restrictions on its external shape depending on the battery's application. For example, it may be cylindrical, rectangular, pouch-type, coin-type, etc., but is not limited to these.

[0092] A lithium secondary battery according to one embodiment of the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing multiple battery cells. Preferred examples of such medium- and large-sized devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems (ESS).

[0093] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative to aid in understanding the present invention and do not limit its scope. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the technical concept, and that such variations and modifications are included in the appended claims.

[0094] Examples and Comparative Examples Examples (1) Manufacturing of the negative electrode current collector A reaction vessel was prepared, which included a negative electrode rotating drum and a positive electrode plate positioned opposite the negative electrode rotating drum. The reaction vessel was then filled with an electrolyte solution, which was a mixture of copper sulfate and water. Next, with electricity applied to the negative electrode rotating drum and the positive electrode plate, the negative electrode rotating drum was rotated to electrodeposit copper onto the surface of the negative electrode rotating drum. Subsequently, an electrolytic copper foil with a thickness of 8 μm was obtained by continuously withdrawing the electrodeposited copper from the reaction vessel.

[0095] Next, the surface of the electrolytic copper foil was coated with silane, and then colloidal silver was sprayed onto the electrolytic copper foil to arrange silver particles on its surface. After that, the negative electrode current collector was manufactured by drying the solvent remaining on the electrolytic copper foil with hot air.

[0096] (2) Manufacturing of lithium secondary batteries As the negative electrode, the negative electrode current collector without another negative electrode active material layer was used.

[0097] A cathode slurry was prepared by adding LiCoO2, polyvinylidene fluoride (PVDF), carbon nanotubes (CNT), and carbon black in a weight ratio of 97.59:1.18:0.24:0.09 to N-methylpyrrolidone (NMP) solvent and stirring. The cathode slurry was then applied to one side of a 10 μm thick aluminum thin film at a concentration of 18.60 mg / cm². 2 The slurry was applied in a loading amount and then vacuum-dried. The dried cathode slurry was rolled (roll press), dried in a vacuum oven at 130°C for 6 hours, and then punched out to produce the cathode.

[0098] An electrode assembly was manufactured by stacking the negative electrode, positive electrode, and porous polyethylene separation membrane (thickness: 12 μm) produced as described above.

[0099] The electrolyte was prepared by dissolving LiPF6 in a solvent (mass ratio of EC:PC:EP:PP = 20:10:25:45) to a concentration of 1.2 M.

[0100] A lithium secondary battery (electrode-free battery) was manufactured by housing the electrode assembly in a battery case, pouring in the electrolyte, and then sealing it.

[0101] Comparative Example 1 The negative electrode current collector was manufactured in the same manner as in the example, except that the step of spraying colloidal silver onto the electrolytic copper foil was omitted.

[0102] A lithium secondary battery was manufactured in the same manner as in the example, except that a negative electrode current collector manufactured by the above method (i.e., a negative electrode current collector that does not contain silver particles) was used.

[0103] Comparative Example 2 The negative electrode current collector was manufactured in the same manner as in the example, except that the step of coating the surface of the electrolytic copper foil with silane was omitted.

[0104] A lithium secondary battery was manufactured in the same manner as in the example, except that a negative electrode current collector manufactured by the above method (i.e., a negative electrode current collector without a hydrophobic coating layer) was used.

[0105] Experimental Example 1 The lithium secondary batteries manufactured in each of the Examples and Comparative Examples 1 and 2 were charged and discharged at a temperature of 45°C, and the number of charge-discharge cycles until a short circuit between the positive and negative electrodes occurred was measured. Specifically, one cycle was defined as fully charging and then completely discharging the lithium secondary battery, and the total number of cycles until the separator membrane inside the lithium secondary battery opened and a short circuit between the positive and negative electrodes occurred was measured and is shown in Table 1 below.

[0106] [Table 1]

[0107] As shown in Table 1, in the example where silver particles are included in the recess of the negative electrode current collector, it can be confirmed that the total number of cycles until a short circuit occurs between the positive and negative electrodes is significantly higher compared to Comparative Example 1, which does not contain silver particles, and Comparative Example 2, which is coated with silver particles without hydrophobic coating. [Explanation of symbols]

[0108] 100 Negative electrode current collector 110 Copper thin film 112 Protrusion 114 recess 120 Metal particles

Claims

1. A copper thin film having protrusions and recesses formed therein, The recess contains metal particles that are arranged in at least a portion of the recess, have a higher standard reduction potential than lithium ions, and can form a solid solution with lithium (Li), A hydrophobic substance is placed on the aforementioned protruding portion. A negative electrode current collector in which the hydrophobic substance is not disposed in the recess and the metal particles.

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 0.1 nm to 1000 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 portion of the recess contains a hydrophilic group.

6. The negative electrode current collector according to claim 1, wherein the hydrophobic substance comprises at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

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

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

9. Centerline surface roughness (R ａ The negative electrode current collector according to claim 1, wherein the diameter is 0.1 μm to 0.5 μm.

10. A step of manufacturing a copper thin film in which protrusions and recesses are formed, The step includes arranging metal particles in at least a portion of the recess that have a higher standard reduction potential than lithium ions and can form a solid solution with lithium (Li), The step of placing metal particles capable of forming a solid solution with lithium (Li) in at least a portion of the recess is: The steps include placing a hydrophobic substance on the protruding portion, The step of placing a hydrophobic material on the protruding portion, followed by the step of coating the copper thin film with hydrophilic metal particles, A method for manufacturing a negative electrode current collector, wherein the hydrophobic substance is not disposed in the recess and the metal particles.

11. The method for producing a negative electrode current collector according to claim 10, wherein the hydrophobic substance comprises at least one of silane, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

12. The method for manufacturing a negative electrode current collector according to claim 10, wherein the copper thin film is manufactured by an electrolytic plating process.

13. A negative electrode including the negative electrode current collector described in claim 1, Positive electrode and, A lithium secondary battery comprising a separator membrane disposed between the negative electrode and the positive electrode.

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