Negative electrode for lithium secondary battery comprising current collector coated with primer and method for manufacturing the same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, the negative electrode comprising a negative electrode collector, a primer layer coated on the outer surface of the negative electrode collector, and a lithium-philic material (LPM) coated on at least a portion of the primer layer.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 2020-0050770, filed on Apr. 27, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a negative electrode for a lithium secondary battery comprising a current collector coated with a primer and a method for manufacturing the same, and more specifically, to a negative electrode for a lithium secondary battery and a method for manufacturing the same, wherein the negative electrode is configured to guide a lithium-philic material to the surface of the negative electrode current collector to expand the portion where lithium plating occurs on the surface of the negative electrode current collector, thereby preventing the formation of lithium dendrites in a specific portion of the negative electrode. Background Art

[0003] Reusable lithium secondary batteries with high energy density have attracted much attention as a new energy source with environmentally friendly characteristics because lithium secondary batteries not only significantly reduce the use of fossil fuels but also do not produce byproducts caused by the use of energy.

[0004] Lithium secondary batteries have attracted attention as power sources with high energy density suitable for wearable devices or portable devices and as high-output power sources for electric vehicles. Therefore, research on lithium secondary batteries with high operating voltage and energy density has been more actively conducted.

[0005] The operating voltage and energy density of lithium secondary batteries can be changed according to the type of electrode active material, the type of electrolyte solution and the loading amount of the electrode mixture layer. Lithium cobalt composite oxide or lithium-containing manganese composite oxide is used as the positive electrode active material, and lithium metal, carbon-based material or silicon is used as the negative electrode active material. Lithium metal has the advantage of high energy density, but the problem is that when lithium metal reacts with moisture in the air, by-products such as LiOH, Li2O and Li2CO3 are produced.

[0006] Byproducts produced by the reaction of lithium metal with the electrolyte solution can significantly degrade the performance of the battery and may cause an internal short circuit.

[0007] In addition, when lithium metal is used as a negative electrode, lithium dendrites may form on the surface of the lithium metal during charging and discharging of the battery. In the case where lithium dendrites grow and penetrate the separator, the life of the lithium secondary battery may be reduced and fatal problems related to safety may occur. For example, a micro short circuit may occur.

[0008] Patent Document 1 discloses a lithium polymer secondary battery configured to form a cross-linked polymer protective film using a diacrylic monomer on the surface of lithium metal to improve the safety of the lithium metal negative electrode, thereby improving the interface characteristics between the lithium metal electrode and the polymer electrolyte.

[0009] However, the protective film is easily peeled off from the electrode surface due to the driving of the battery, so it is difficult to fully obtain the lithium dendrite growth prevention effect.

[0010] Patent document 2 discloses an electrode for a lithium secondary battery, which includes an electrode active material layer containing lithium metal between a current collector and a protective layer, the protective layer containing a thermally conductive material, wherein during charging and discharging, heat is evenly distributed on the electrode surface, thereby causing lithium dendrites to grow evenly.

[0011] Patent Document 2 does not solve the problem of lithium dendrites growing on the surface of the negative electrode facing the positive electrode, thereby causing micro short circuits. As mentioned above, although lithium metal negative electrodes have the advantages of high energy density and high voltage, they have not been applied to related fields due to the growth of lithium dendrites.

[0012] (Prior art literature)

[0013] (Patent Document 1) Korean Registered Patent Gazette No. 0425585 (2004.03.22)

[0014] (Patent Document 2) Korean Patent Application Publication No. 2019-0013630 (February 11, 2019) Summary of the invention

[0015] [Technical issues]

[0016] The present invention is made in view of the above problems, and an object of the present invention is to provide a negative electrode for a lithium secondary battery and a method for manufacturing the same, wherein the negative electrode includes a current collector coated with a primer to prevent short circuit caused by lithium dendrites grown on a specific portion of the negative electrode surface contacting the positive electrode.

[0017] [Technical solution]

[0018] To achieve the above object, the negative electrode for a lithium secondary battery of the present invention includes a negative electrode collector, a primer layer coated on the outer surface of the negative electrode collector, and a lithium-philic material (LPM) coated on at least a portion of the primer layer.

[0019] The negative electrode current collector may include a first surface not facing the separator and a second surface facing the separator, and the primer layer may be applied to the first surface and / or the second surface of the negative electrode current collector.

[0020] Lithium plating (Li plating) can occur on lithiophilic materials.

[0021] The primer layer may comprise carbon.

[0022] The lithiophilic material may be coated only on the first surface.

[0023] The lithium-philic material may be at least one of metals including Au, Ag, Pt, Zn, Si, and Mg, and metal oxides including CuO, ZnO, CoO, and MnO.

[0024] In addition, the present invention provides a method for manufacturing the negative electrode. Specifically, the method comprises: 1) preparing a negative electrode current collector, 2) coating at least one surface of the negative electrode current collector with a primer to form a primer layer, and 3) coating the primer layer of step 2) with a lithium-philic material.

[0025] The coating solution of the lithiophilic material may include a metal salt and a reducing agent.

[0026] The lithiophilic material coating step may be performed by dipping, spin coating, dip coating, spray coating, doctor blade coating, solution casting, drop coating, physical vapor deposition (PVD), or chemical vapor deposition (CVD).

[0027] The content of the metal salt in the coating solution of the lithium-philic material may be 0.1 wt % or more and less than 50 wt %.

[0028] In addition, the present invention provides an electrode assembly including the negative electrode.

[0029] In a specific example, the negative electrode included in the electrode assembly may be configured by applying a first primer layer to a first surface of the negative electrode collector, applying a second primer layer to a second surface of the negative electrode collector, and each of the first primer layer and the second primer layer is coated with a lithium-philic material.

[0030] In another specific example, the negative electrode included in the electrode assembly may be configured to apply a first primer layer to a first surface of the negative electrode current collector, apply a second primer layer to a second surface of the negative electrode current collector, the first primer layer is coated with a lithium-philic material, the second primer layer is not coated with a lithium-philic material, and the second primer layer is arranged to face the positive electrode, and the separator is located between the second primer layer and the positive electrode.

[0031] In addition, the present invention provides a lithium secondary battery having an electrode assembly housed in a battery case together with an electrolyte solution or a solid electrolyte. In addition, the present invention provides a battery module or a battery pack including the lithium secondary battery as a unit cell.

[0032] [Beneficial Effects]

[0033] It is obvious from the above description that in the negative electrode for lithium secondary battery comprising a current collector coated with a primer and a method for manufacturing the same of the present invention, the entire surface of the negative electrode current collector is coated with a lithium-philic material in a dispersed state, whereby lithium plating can occur on the entire surface of the negative electrode current collector. Therefore, the lithium nucleation potential is reduced and a plurality of lithium nuclei can be formed.

[0034] In addition, due to the wide distribution of the lithium-philic material, the rate at which additional plating occurs on the widely dispersed plurality of lithium nuclei can be increased compared to the rate at which the lithium nuclei grow in the vertical direction on a specific region of the negative electrode current collector surface. Therefore, local lithium plating can be prevented from occurring on the negative electrode current collector surface, thereby preventing the growth of lithium dendrites.

[0035] In addition, assuming that the surface of a conventional negative electrode current collector not coated with a primer is a smooth 2D surface, since the primer contains a conductive agent and a binder, the primer formed by coating on the negative electrode current collector of the present invention has a 3D surface. Since the 3D negative electrode current collector of the present invention has a larger specific surface area than the 2D negative electrode current collector, the contact area with the electrolyte solution increases. As described above, since the size of the interface between the electrolyte solution and the negative electrode current collector increases, electrons can move over a larger area, thereby improving the rate characteristics.

[0036] Therefore, it is possible to prevent lithium dendrites from growing toward the positive electrode, thereby preventing a short circuit, thereby improving the life characteristics and safety of the lithium secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a SEM photograph of the negative electrode manufactured according to Example 1.

[0038] Figure 2 is a SEM photograph of the negative electrode manufactured according to Example 2.

[0039] Figure 3 is a SEM photograph of the negative electrode manufactured according to Example 3.

[0040] Figure 4 This is a photograph of the surface of the negative electrode manufactured according to Comparative Example 1.

[0041] Figure 5 This is a SEM photograph of the negative electrode manufactured according to Comparative Example 1.

[0042] Figure 6 This is a SEM photograph of the negative electrode manufactured according to Comparative Example 2.

[0043] Figure 7 This is a SEM photograph of the negative electrode manufactured according to Comparative Example 3. DETAILED DESCRIPTION

[0044] Now, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that the present invention can be easily implemented by those skilled in the art to which the present invention belongs. However, when describing in detail the operating principle of the preferred embodiments of the present invention, when the known functions and structures incorporated herein may confuse the subject matter of the present invention, the detailed description thereof will be omitted.

[0045] In addition, the same reference numerals will be used throughout the drawings to refer to components that perform similar functions or operations. In the case where a component is described as being connected to another component in the specification, not only can a component be directly connected to another component, but a component can also be indirectly connected to another component through other components. In addition, the inclusion of a certain element does not mean the exclusion of other elements, but means that these elements may be further included, unless otherwise specified.

[0046] In addition, the description embodying elements by limitation or addition is applicable to all inventions unless specifically limited, and does not limit a specific invention.

[0047] Furthermore, in the specification and claims of the present application, the singular form is intended to include the plural form unless otherwise stated.

[0048] Moreover, in the invention specification and claims of the present application, "or" includes "and", unless otherwise specified. Therefore, "including A or B" refers to three cases, namely, the case including A, the case including B, and the case including A and B.

[0049] Additionally, all numerical ranges include the lowest value, the highest value and all intermediate values ​​unless the context clearly dictates otherwise.

[0050] The negative electrode for a lithium secondary battery including a current collector coated with a primer of the present invention may include a negative electrode current collector, a primer layer applied to an outer surface of the negative electrode current collector, and a lithium-philic material (LPM) coated on at least a portion of the primer layer.

[0051] Generally, when lithium metal is used for the negative electrode, the negative electrode has the advantages of high energy density and high output. Lithium metal is lithium in a metallic state, and refers to pure lithium that is not alloyed with a metal other than lithium. However, lithium metal may form lithium nuclei on the surface of the negative electrode, and the lithium nuclei may grow into lithium dendrites. There is a high risk that lithium dendrites penetrate the diaphragm, thereby causing an internal short circuit.

[0052] Therefore, the present invention provides a negative electrode for a lithium secondary battery, which is configured to form a primer layer on the outer surface of a negative electrode collector, and to coat a lithium-philic material on at least a portion of the primer layer, thereby lithium plating occurs on the entire surface of the negative electrode collector formed with the primer layer.

[0053] Hereinafter, the negative electrode current collector refers not only to the negative electrode current collector itself but also includes a configuration in which a primer layer is applied to the outer surface of the negative electrode current collector and a configuration in which a lithium-philic material is coated on the primer layer applied to the negative electrode current collector.

[0054] Specifically, the lithium-philic material is a material with high reactivity with lithium, and lithium plating (Li plating) occurs on the lithium-philic material. Therefore, in the present invention, the entire surface of the negative electrode current collector on which the primer layer is formed is coated with a dispersed lithium-philic material, thereby preventing the local growth of lithium dendrites.

[0055] The negative electrode current collector includes a first surface that does not face the separator and a second surface that faces the separator, wherein the primer layer is applied to the first surface and the second surface of the negative electrode current collector.

[0056] The undercoat layer coating method is not particularly limited, and the same method as the lithium-philic material coating method to be described below may be used.

[0057] Therefore, the undercoat layer may be formed on the side surface in the thickness direction of the negative electrode current collector.

[0058] The negative electrode current collector of the present invention has low lithium affinity; however, since the undercoat layer is formed on the surface thereof, the lithium affinity of the negative electrode current collector is improved.

[0059] The primer layer includes a conductive agent and a binder, and the improvement of chemical lithium affinity caused by the components constituting the primer layer is not significant. However, the primer layer exhibits a higher lithium affinity than copper (which is generally used as a material for the negative electrode current collector). Moreover, when the primer layer is introduced to the negative electrode current collector, the specific surface area of ​​the negative electrode current collector increases. Therefore, the size of the physical lithium plating site increases, thereby preventing the local formation of lithium dendrites.

[0060] In addition, the lithium-philic material is coated on the undercoat layer, and the lithium-philic material further improves the lithium-philic property. That is, in the present invention, the undercoat layer and the lithium-philic material are applied to the negative electrode current collector. Therefore, even if the lithium-philic material is agglomerated and the undercoat layer is partially exposed between the agglomerated lithium-philic materials, the effect of preventing the local formation of lithium dendrites can be further improved compared to the negative electrode current collector without the undercoat layer.

[0061] In addition, adhesion at the interface between the negative electrode current collector and the separator may be increased.

[0062] The undercoat layer is not particularly limited as long as the undercoat layer is made of a material that exhibits conductivity and lithium affinity while not degrading the performance of the lithium secondary battery. For example, the undercoat layer may include carbon, a conductive polymer, or a mixture thereof. Specifically, the undercoat layer may include carbon.

[0063] The type of negative electrode current collector is not particularly limited, as long as the negative electrode current collector exhibits high conductivity and the negative electrode current collector does not cause any chemical changes in the lithium secondary battery. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium or sintered carbon, may be made of copper or stainless steel whose surface is treated with carbon, nickel, titanium or silver, or may be made of aluminum-cadmium alloy. In addition, the negative electrode current collector may be configured in any of various forms, such as a film, a sheet, a foil, a net, a porous body, a foam body and a non-woven fabric body, each of which has a micro-concave-convex pattern formed on its surface, or each of which has no micro-concave-convex pattern formed on its surface.

[0064] Although the thickness of the negative electrode current collector is not particularly limited, the thickness of the negative electrode current collector is preferably 5 μm to 30 μm, more preferably 10 μm to 20 μm. If the thickness of the negative electrode current collector is greater than 30 μm, the unit volume capacity of the electrode may be reduced. If the thickness of the negative electrode current collector is less than 5 μm, folding may occur when manufacturing the electrode.

[0065] In the present invention, an electrode active material layer may be optionally included. That is, the negative electrode of the present invention may be configured to form a lithium-philic material coated on an undercoat layer without including a negative electrode active material layer, or may include a negative electrode current collector having an undercoat layer coated with a lithium-philic material and an electrode active material layer.

[0066] The negative electrode active material may include at least one selected from the group consisting of a carbon material, a lithium alloy, a lithium metal composite oxide, a lithium-containing titanium composite oxide (LTO), and a combination thereof. At this time, the lithium alloy includes an element capable of alloying with lithium, and Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or an alloy thereof may be mentioned as an element capable of alloying with lithium.

[0067] The thickness of the negative electrode active material layer may be 0 μm to 40 μm, specifically 5 μm to 40 μm, and more specifically 10 μm to 20 μm.

[0068] In the present invention, the method for forming the negative electrode active material layer on the negative electrode current collector is not particularly limited, and methods known in the art can be used. For example, the negative electrode active material layer can be formed by depositing or coating lithium metal or lithium alloy on the current collector by a dry method or a wet method, or by laminating a prefabricated lithium metal sheet or foil on the current collector.

[0069] The lithiophilic material is located on the undercoat layer in a state of being dispersed on the undercoat layer. Alternatively, the lithiophilic material may be aggregated so as to be arranged in an island shape so that the undercoat layer is partially exposed.

[0070] In a specific example, the lithium-philic material can be distributed in the range of 5% to 100% of the total area of ​​the negative electrode current collector, specifically in the range of 10% to 90%, more specifically in the range of 30% to 80%. In addition, more specifically, the lithium-philic material can be distributed in the range of 50% to 70% of the total area of ​​the negative electrode current collector.

[0071] In the case where the area of ​​the lithium-philic material is less than 5% of the total area of ​​the negative electrode current collector, the distribution area of ​​the lithium-philic material is small, and thus it is difficult to obtain the effect provided by the lithium-philic material, which is undesirable. In the case where the area of ​​the lithium-philic material is greater than 100% of the total area of ​​the negative electrode current collector, this means that excess lithium-philic material is introduced, and the energy density is reduced, which is undesirable.

[0072] When lithium plating occurs on the lithium-philic material, when manufacturing the electrode assembly, the performance of the secondary battery can be improved when the lithium-philic material is not coated on the surface of the negative electrode current collector facing the positive electrode. Therefore, the lithium-philic material can be coated only on the first surface of the negative electrode current collector on which the primer layer is formed, and the first surface can be arranged as a surface that does not face the separator and the positive electrode, thereby manufacturing the electrode assembly.

[0073] The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery. Specifically, the method for manufacturing a negative electrode for a lithium secondary battery may include the steps of preparing a negative electrode current collector, coating the negative electrode current collector with a primer to form a primer layer, and coating the primer layer with a lithium-philic material.

[0074] The lithium-philic material coating solution may include a metal salt and a reducing agent. The metal salt may be a nitrate and a chloride. For example, the metal salt may be at least one selected from the group consisting of HAuCl4, H2PtCl6, AgNO3, AuCl, AuCl3, K(AuCl4), AuBr3, PtCl2, PtCl4, AgCl, AgCN and CuCl2.

[0075] The reducing agent may be at least one selected from the group consisting of hydrazine, glucose, ammonia, phosphorous acid, hydrogen peroxide, succinimide, formic acid, and sulfide.

[0076] The content of the metal salt in the lithium-philic material coating solution may be 0.1 wt % to less than 50 wt %, specifically 5 wt % to 30 wt %.

[0077] In the case where the content of the metal salt is less than 0.1 wt %, the growth rate of the lithium-philic material is low, so the processability is deteriorated, and since the amount of the lithium-philic material is small, it is difficult to fully obtain the lithium-philic property improvement effect. On the other hand, in the case where the content of the metal salt is more than 50 wt %, it is difficult to control the growth of particles forming the lithium-philic material layer, whereby the lithium-philic material layer may be unevenly formed, and thus lithium may grow unevenly, which is not desirable.

[0078] The coating method of the lithium-philic material is not particularly limited. For example, dipping, spin coating, dip coating, spray coating, doctor blade coating, solution casting, drop coating, physical vapor deposition (PVD) or chemical vapor deposition (CVD) may be used.

[0079] The present invention provides an electrode assembly including the negative electrode for a lithium secondary battery. The electrode assembly may include a negative electrode configured to apply a first primer layer to a first surface of a negative electrode current collector and a second primer layer to a second surface of the negative electrode current collector, wherein a separator is disposed between the negative electrode and the positive electrode.

[0080] For example, the positive electrode is manufactured by applying a positive electrode mixture containing a positive electrode active material to a positive electrode current collector and drying the positive electrode mixture. The positive electrode mixture may further optionally include a binder, a conductive agent, and a filler as required.

[0081] There is no particular limitation on the positive electrode current collector, as long as the positive electrode current collector exhibits high conductivity and the positive electrode current collector does not cause any chemical changes in the battery to which the positive electrode current collector is applied. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium or sintered carbon. Alternatively, the positive electrode current collector may be made of aluminum or stainless steel whose surface is treated with carbon, nickel, titanium or silver. In addition, the positive electrode current collector may be formed with a micro-concave-convex pattern on its surface to increase the adhesion of the positive electrode active material. The positive electrode current collector may be configured in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam body and a non-woven fabric body.

[0082] The positive electrode active material is a material that can initiate an electrochemical reaction. The positive electrode active material can be a lithium transition metal oxide containing two or more transition metals. For example, the positive electrode active material can be, but is not limited to: a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2) substituted with one or more transition metals; a lithium manganese oxide substituted with one or more transition metals; a LiNi 1-y M y Lithium nickel-based oxide represented by O2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, including at least one thereof, and 0.01≤y≤0.7); chemical formula Li 1+ z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e(wherein -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤0.8, 0≤d≤0.2, 0≤e≤0.2, b+c+d<1, M=Al, Mg, Cr, Ti, Si or Y, and A=F, P or Cl) represented by lithium nickel cobalt manganese composite oxide, such as Li 1+z Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2 or Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O2; or chemical formula Li 1+x M 1-y M' y PO 4-z X z (wherein M = transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, -0.5≤x≤0.5, 0≤y≤0.5, and 0≤z≤0.1).

[0083] The conductive agent is usually added so that the conductive agent accounts for 1% to 30% by weight of the total weight of the mixture containing the positive electrode active material. The conductive agent is not particularly limited as long as the conductive agent exhibits high conductivity without causing any chemical changes in the battery to which the conductive agent is applied. For example, as the conductive agent, it is possible to use: carbon; graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as fluorocarbon powders, aluminum powders or nickel powders; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0084] Binder is a component that helps the combination between active material and conductive agent and the combination with current collector. Based on the total weight of the mixture containing positive active material, the addition amount of binder is usually 1 wt % to 30 wt %. As an example of binder, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, fluororubber and various copolymers can be used.

[0085] The filler is an optional component for suppressing electrode expansion. The filler is not particularly limited as long as the filler is made of a fibrous material and does not cause chemical changes in the battery to which the filler is applied. As examples of the filler, olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber can be used.

[0086] The electrode assembly of the present invention includes a separator interposed between a positive electrode and a negative electrode.

[0087] As the separator, an insulating film showing high ion permeability and mechanical strength can be used. For example, the separator can be a porous substrate made of any one selected from the group consisting of polyethylene, polypropylene, polybutene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide and polyethylene naphthalate, or a mixture of two or more thereof.

[0088] In a specific example, the electrode assembly of the present invention may include a negative electrode for a lithium secondary battery, which is configured such that a first primer layer and a second primer layer are each coated with a lithium-philic material.

[0089] That is, in the case of manufacturing an electrode assembly having a structure in which a positive electrode, a separator, a negative electrode, a separator and a positive electrode are stacked in sequence, a negative electrode having a lithium-philic material formed on its two opposite surfaces can be used to prevent the local formation of lithium dendrites on the two opposite surfaces of the negative electrode facing the positive electrode.

[0090] In another specific example, the electrode assembly of the present invention may include a negative electrode for a lithium secondary battery, which is configured such that a first undercoat layer is coated with a lithium-philic material and a second undercoat layer is not coated with a lithium-philic material, wherein the second undercoat layer may be arranged to face the positive electrode, wherein the separator is located between the second undercoat layer and the positive electrode. Therefore, the growth of lithium dendrites toward the positive electrode can be prevented.

[0091] Hereinafter, the present invention will be described with reference to the following examples. These examples are provided only for easier understanding of the present invention and should not be construed as limiting the scope of the present invention.

[0092] Negative electrode manufacturing

[0093] <Example 1>

[0094] 95 wt % of a carbon conductive agent and 5 wt % of a binder were dispersed in N-methylpyrrolidone (NMP) to prepare an undercoating slurry, a copper current collector was coated with the undercoating slurry, and the undercoating slurry was dried to form an undercoat layer having a thickness of 3 μm.

[0095] AgCN, KCN and H3PO2 were mixed with each other in a ratio of 1:1:2 (weight %) to prepare a metal salt mixture, and pure water and ethanol were mixed with each other in a weight ratio of 1:1 to prepare a solvent. 80 weight % of the solvent and 20 weight % of the metal salt mixture were mixed with each other to prepare a lithium-philic material coating solution. When ethanol was used as a solvent, the wettability to the current collector was improved compared to the case of using only pure water.

[0096] The lithiophilic material coating solution was dropped onto the undercoat layer and spin-coated at 3,000 rpm for 1 minute to form a coating layer.

[0097] The copper current collector formed with the primer layer and the lithiophilic material coating layer was vacuum dried at 100° C. for 12 hours to manufacture a negative electrode.

[0098] The SEM image of the negative electrode manufactured according to Example 1 is shown in Figure 1 middle.

[0099] <Example 2>

[0100] The negative electrode was manufactured using the same method as in Example 1, except that in Example 1, 30 wt % of a mixture of AgCN, KCN, and H 3 PO 2 in a ratio of 1:1:2 (wt %) was used as the lithium-philic material coating solution.

[0101] The SEM image of the negative electrode manufactured according to Example 2 is shown in Figure 2 middle.

[0102] <Example 3>

[0103] The negative electrode was manufactured using the same method as in Example 1, except that in Example 1, 20 wt % of a mixture of HAuCl4 and KCN in a ratio of 1:1 (wt %) was used instead of a mixture of AgCN, KCN and H3PO2 in a ratio of 1:1:2 (wt %) as the lithium-philic material coating solution.

[0104] The SEM image of the negative electrode manufactured according to Example 3 is shown in Figure 3 middle.

[0105] <Comparative Example 1>

[0106] A copper current collector is prepared to be used as a negative electrode, on the surface of which an undercoat layer and a lithium-philic material coating are not formed and which is not heat-treated.

[0107] A photograph of the surface of the negative electrode manufactured according to Comparative Example 1 is shown in Figure 4 and the SEM photo of the negative electrode is shown in Figure 5 middle.

[0108] <Comparative Example 2>

[0109] The negative electrode was manufactured using the same method as in Example 1, except that in Example 1, a primer layer was formed on the copper current collector, but no lithium-philic material coating layer was formed on the copper current collector.

[0110] The SEM photograph of the negative electrode manufactured according to Comparative Example 2 is shown in Figure 6 middle.

[0111] <Comparative Example 3>

[0112] The negative electrode was manufactured using the same method as in Example 1, except that in Example 1, no primer layer was formed on the copper current collector, but a lithium-philic material coating was formed on the copper current collector, and 50 wt % of a mixture of AgCN, KCN and H3PO2 in a ratio of 1:1:2 (wt %) was used.

[0113] The SEM photograph of the negative electrode manufactured according to Comparative Example 3 is shown in Figure 7 middle.

[0114] Reference can be made to compare the coating extent of the lithium-philic material coating solution based on its concentration. Figure 1 and Figure 2 , the lower concentration Figure 1 It shows that a small amount of lithium-philic material is coated on the bottom layer, while a higher concentration Figure 2 It shows that a large amount of lithiophilic material is more extensively coated to the undercoat layer.

[0115] Short circuit test

[0116] Coin cells were manufactured using the negative electrodes manufactured according to Examples 1 to 3 and Comparative Examples 1 to 3.

[0117] In order to prepare the positive electrode forming slurry, NCM811 as a positive electrode active material, carbon as a conductive agent, and polyvinylidene fluoride as a binder were mixed with each other at a weight ratio of 95:2:3.

[0118] The positive electrode forming slurry was applied to an aluminum current collector using a doctor blade so as to have a thickness of 20 μm, and then vacuum dried at 120° C. for 4 hours.

[0119] The aluminum current collector having the vacuum-dried positive electrode forming slurry was rolled using a roll press to produce a 3 mAh / cm 2 The positive electrode.

[0120] To prepare a liquid electrolyte, ethylene carbonate and ethyl methyl carbonate were mixed with each other so that the volume ratio was 3:7 (vol %), and 1M LiPF6 as a lithium salt, 0.5 volume % of vinylene carbonate, and 1 volume % of fluoroethylene carbonate were added to the mixture.

[0121] A coin cell was manufactured using the liquid electrolyte, the positive electrode and the negative electrode. The coin cell was charged and discharged under the following conditions, while measuring the number of charge and discharge times when a short circuit occurred. The results are shown in Table 1 below.

[0122] Charging conditions: constant current (CC) / constant voltage (CV), 4.25V, 0.5C, 0.1C current cutoff

[0123] Discharge conditions: constant current (CC) condition 3V, 0.5C

[0124] The number of charge and discharge times when a short circuit occurs refers to a time point at which the voltage does not increase but remains constant or decreases even if the voltage does not reach the cutoff voltage when evaluating the life under charge and discharge conditions.

[0125] [Table 1]

[0126] Cycle (charge and discharge times) Example 1 25 Example 2 21 Example 3 22 Comparative Example 1 3 Comparative Example 2 11 Comparative Example 3 9

[0127] Referring to Table 1 above, it can be seen that when Comparative Example 1 and Comparative Example 2 are compared with each other, the undercoat layer reduces the current density of the negative electrode, thereby delaying the short circuit.

[0128] When comparing Comparative Example 2 having only the primer layer and the embodiment having both the primer layer and the lithiophilic material coating layer, the occurrence time of the short circuit is extended to more than twice due to the addition of the lithiophilic material coating layer.

[0129] The reason for this is that uniform lithium plating occurs due to a plurality of Ag or Au particles, which are lithium-philic materials formed on the undercoat layer. Therefore, when the negative electrode of the present invention is used, the life of the battery cell can be increased and the safety of the battery cell can be improved.

[0130] On the other hand, it can be seen that, in the case where Ag is unevenly coated in an excessively large shape as in Comparative Example 3, lithium plating occurs intensively on the unevenly coated Ag particles, thereby accelerating the occurrence of a short circuit.

[0131] Those skilled in the art to which the present invention pertains will appreciate that various applications and modifications are possible within the scope of the present invention based on the above description.

[0132] Industrial Applicability

[0133] It is obvious from the above description that in the negative electrode for lithium secondary battery comprising a current collector coated with a primer and a method for manufacturing the same of the present invention, the entire surface of the negative electrode current collector is coated with a lithium-philic material in a dispersed state, whereby lithium plating can occur on the entire surface of the negative electrode current collector. Therefore, the lithium nucleation potential is reduced and a plurality of lithium nuclei can be formed.

[0134] In addition, since the lithium-philic material is widely distributed, the rate at which additional plating occurs on the widely dispersed plurality of lithium nuclei can be increased compared to the rate at which the lithium nuclei grow in the vertical direction on a specific region of the negative electrode current collector surface. Therefore, local lithium plating can be prevented from occurring on the negative electrode current collector surface, thereby preventing the growth of lithium dendrites.

[0135] In addition, assuming that the surface of a conventional negative electrode current collector not coated with a primer is a smooth 2D surface, since the primer contains a conductive agent and a binder, the primer formed on the negative electrode current collector of the present invention has a 3D surface. Since the 3D negative electrode current collector of the present invention has a larger specific surface area than the 2D negative electrode current collector, the contact area with the electrolyte solution is increased. As described above, since the size of the interface between the electrolyte solution and the negative electrode current collector is increased, electrons can move over a larger area, thereby improving the rate characteristics.

[0136] Therefore, it is possible to prevent lithium dendrites from growing toward the positive electrode, thereby preventing a short circuit, thereby improving the life characteristics and safety of the lithium secondary battery.

Claims

1. A negative electrode for a lithium secondary battery, the negative electrode comprising: Anode current collector; a primer layer applied to the outer surface of the negative electrode current collector; as well as coating a lithium-philic material (LPM) formed on at least a portion of the undercoat layer, wherein the bottom coating has a 3D surface and is made of a material exhibiting electrical conductivity and lithium affinity; Wherein, the primer layer comprises a conductive agent and a binder, and increases the specific surface area of ​​the negative electrode current collector; wherein the lithium-philic material is formed by coating the undercoat layer with a lithium-philic material coating solution comprising a metal salt and a reducing agent, and Wherein, the lithium-philic material is at least one of Au, Ag, Pt and Mg.

2. The negative electrode according to claim 1, wherein The negative electrode current collector includes a first surface not facing the separator and a second surface facing the separator, and The primer layer is applied to the first surface and / or the second surface of the negative electrode collector.

3. The negative electrode according to claim 1, wherein Lithium plating occurs on the lithiophilic material.

4. The negative electrode according to claim 1, wherein The primer layer includes carbon.

5. The negative electrode according to claim 2, wherein Only the first surface is coated with the lithiophilic material.

6. The negative electrode according to claim 1, wherein The metal salt is at least one selected from the group consisting of HAuCl4, H2PtCl6, AgNO3, AuCl, AuCl3, K(AuCl4), AuBr3, PtCl2, PtCl4, AgCl and AgCN; and The reducing agent is at least one selected from the group consisting of hydrazine, glucose, ammonia, phosphorous acid, hydrogen peroxide, formic acid and sulfide.

7. A method for manufacturing the negative electrode according to any one of claims 1 to 6, the method comprising: 1) preparing the negative electrode current collector; 2) coating at least one surface of the negative electrode current collector with a primer to form a primer layer; as well as 3) coating the undercoat layer of step 2) with the lithium-philic material coating solution.

8. The method of claim 7, wherein: The step of coating the lithium-philic material is performed by dipping, spin coating, dip coating, spray coating, doctor blade coating, solution casting or drop coating.

9. The method of claim 7, wherein: The content of the metal salt in the lithium-philic material coating solution is greater than 0.1 wt % and less than 50 wt %.

10. An electrode assembly comprising the negative electrode according to claim 1, wherein A first primer layer is applied to a first surface of the negative electrode current collector, A second primer layer is applied to the second surface of the negative electrode current collector, and The first primer layer and the second primer layer are each coated with a lithiophilic material.

11. An electrode assembly comprising the negative electrode according to claim 1, wherein A first primer layer is applied to a first surface of the negative electrode current collector, A second primer layer is applied to the second surface of the negative electrode current collector, The first undercoat layer is coated with a lithium-philic material, The second undercoat layer is not coated with a lithiophilic material, and The second undercoat layer is arranged to face the positive electrode, and the separator is located between the second undercoat layer and the positive electrode.

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