Negative electrode for secondary battery and method of manufacturing same

Abstract

The negative electrode for a secondary battery according to the present invention includes a carbon-based current collector, a porous polymer layer disposed on at least one surface of the carbon-based current collector, and a lithium-based material layer disposed on an upper surface of the porous polymer layer. The negative electrode for a secondary battery can have improved elongation, tensile strength, and elasticity, and a secondary battery including the negative electrode for a secondary battery can have improved cycle life.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a secondary battery and a method for manufacturing the same, and more particularly to a negative electrode for a secondary battery having excellent rigidity and lithium plating properties and a method for manufacturing the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0110407 filed on August 31, 2022, and Korean Patent Application No. 10-2022-0187919 filed on December 28, 2022, and the contents disclosed in the specifications and drawings of those applications are incorporated herein in their entirety. [Background technology]

[0003] Recently, interest in energy storage technology has been growing. As its application fields expand to include mobile phones, video cameras, laptops, and even the energy of electric vehicles, research and development efforts in electrochemical devices are becoming increasingly concrete. From this perspective, electrochemical devices are the field that has attracted the most attention, and efforts to develop rechargeable secondary batteries have become a particular focus of attention. Recently, in order to develop such batteries, research and development efforts have been actively conducted on novel electrode and battery designs to improve capacity density and specific energy.

[0004] Among the secondary batteries currently in use, lithium secondary batteries, developed in the early 1990s, have attracted attention due to their advantages of higher operating voltage and far higher energy density compared to conventional batteries that use aqueous electrolytes, such as Ni-MH, Ni-Cd, and sulfur-acid-lead batteries.

[0005] Among these secondary batteries, lithium-sulfur (LiS) batteries have been gaining attention as a next-generation secondary battery that will replace lithium-ion batteries due to their high energy density. Lithium-sulfur batteries use sulfur-based materials as the positive electrode active material. During discharge, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur within the lithium-sulfur battery. During this reaction, sulfur converts from a ring-shaped S8 to linear lithium polysulfides (Li2S2, Li2S4, Li2S6, Li2S8). These lithium-sulfur batteries exhibit a gradual discharge voltage until polysulfide (PS) is completely reduced to Li2-S.

[0006] Lithium metal can be used as the negative electrode of a lithium secondary battery. However, when using lithium metal as the negative electrode, due to the high reactivity of lithium, it is highly reactive with an electrolyte during charge and discharge. As charge and discharge are repeated, dendrites form on the surface of the negative electrode, causing an increase in the thickness of the electrode and reducing cycle performance and safety. In addition, due to the low rigidity of lithium metal, it is difficult to manufacture lithium metal as the negative electrode. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to provide a negative electrode for a secondary battery having improved elongation, rigidity, and safety, a method for manufacturing the same, and a secondary battery including the negative electrode. [Means for solving the problem]

[0008] In order to achieve the above object, according to one aspect of the present invention, there is provided a negative electrode for a secondary battery having the following configuration.

[0009] The negative electrode for a secondary battery according to the first aspect includes a carbon-based current collector, a porous polymer layer disposed on at least one surface of the carbon-based current collector, and a lithium-based material layer disposed on an upper surface of the porous polymer layer.

[0010] According to a second aspect, in the first aspect, the lithium-based material layer contains at least one of lithium metal and a lithium alloy.

[0011] According to a third aspect, in the first or second aspect, the lithium-based material layer is a lithium metal layer.

[0012] According to a fourth aspect, in any one of the first to third aspects, the porous polymer layer has one or more through holes formed therein, and the carbon-based current collector and the lithium-based material layer are bonded to each other via the through holes.

[0013] According to a fifth aspect, the fourth aspect is characterized in that the area occupied by the through-holes formed in the porous polymer layer is 15% to 60% of the total area of ​​the porous polymer layer.

[0014] According to a sixth aspect, in the third or fourth aspect, the through-holes formed in the porous polymer layer have a diameter of 0.5 cm to 3 cm.

[0015] According to a seventh aspect, in any one of the first to sixth aspects, the porous polymer layers are located on both sides of a carbon-based current collector.

[0016] According to an eighth aspect, in any one of the first to seventh aspects, the specific surface area of ​​the carbon-based current collector is 50 m 2 / g or more.

[0017] According to a ninth aspect, in any one of the first to eighth aspects, the areal density of the carbon-based current collector is 100 g / m2 The present invention is characterized by the following:

[0018] According to a tenth aspect, in any one of the first to ninth aspects, the carbon-based current collector layer is characterized by including graphite, graphene, carbon nanotubes (CNTs), graphite nanofibers (GNFs), carbon nanofibers (CNFs), activated carbon fibers (ACFs), or two or more of these.

[0019] According to an eleventh aspect, in any one of the first to tenth aspects, the porous polymer layer is characterized in that it contains polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or two or more selected from these.

[0020] According to another aspect of the present invention, there is provided a method for producing a negative electrode for a secondary battery having the following features.

[0021] A method for producing a negative electrode for a secondary battery according to a twelfth aspect includes the steps of: forming a laminate by stacking a carbon-based current collector, a porous polymer layer having one or more through-holes on at least one surface of the carbon-based current collector, and a lithium-based material layer on an upper surface of the porous polymer layer; and compressing the laminate using a rolling process.

[0022] According to a thirteenth aspect, in the twelfth aspect, the lithium-based material layer contains at least one of lithium metal and a lithium alloy.

[0023] According to a fourteenth aspect, in the twelfth or thirteenth aspect, the lithium-based material layer is a lithium metal layer.

[0024] According to a fifteenth aspect, in any one of the twelfth to fourteenth aspects, the step of pressing is carried out at a temperature range of 180° C. or less.

[0025] According to a 16th aspect, in any one of the 10th to 15th aspects, in the pressure-bonding step, the lithium-based material layer and the carbon-based current collector are bonded via through holes formed in the porous polymer layer.

[0026] According to still another aspect of the present invention, there is provided a secondary battery having the following configuration.

[0027] A secondary battery according to a seventeenth aspect is a secondary battery including a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the negative electrode according to any one of the first to eleventh aspects. [Effects of the Invention]

[0028] According to one embodiment of the present invention, the rigidity of a negative electrode for a secondary battery can be improved, particularly in the case of the present invention, a negative electrode for a secondary battery having improved stability, tensile strength, and elongation can be provided.

[0029] Furthermore, according to one embodiment of the present invention, it is possible to provide a negative electrode in which a lithium-based material is uniformly plated.

[0030] Furthermore, according to one embodiment of the present invention, the life of the negative electrode can be improved.

[0031] Furthermore, a secondary battery including the negative electrode for a secondary battery can have an improved cycle life.

[0032] In addition to these, the present invention can have various other effects, which will be explained in the sections for each embodiment, and explanations of effects that can be easily inferred by those skilled in the art will be omitted.

[0033] The drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the above-described content of the invention, serve to further understand the technical ideas of the present invention, and therefore the present invention should not be interpreted as being limited to the matters depicted in the drawings. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a schematic cross-sectional view of a negative electrode for a secondary battery according to one embodiment of the present invention; [Figure 2] 1 is a schematic cross-sectional view of a negative electrode for a secondary battery according to one embodiment of the present invention; [Figure 3] FIG. 10 is a graph showing the measurement results of tensile strength for an example of the present invention. [Figure 4] 1 is a diagram showing the measurement results of tensile strength for a comparative example of the present invention. [Figure 5] FIG. 10 is a diagram showing the evaluation results of cell performance for an example of the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be described in detail below with reference to the accompanying drawings. The terms and phrases used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, but rather as being construed in accordance with the meanings and concepts of the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0036] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalent and modified embodiments that can be substituted for them at the time of this application.

[0037] Furthermore, throughout this specification, when a part is said to "include," "comprise," "have," or "have" a certain element, this does not mean that other elements are excluded, and means that other elements may also be included, unless otherwise specified.

[0038] A negative electrode for a secondary battery according to one aspect of the present invention includes a carbon-based current collector, a porous polymer layer disposed on at least one surface of the carbon-based current collector, and a lithium-based material layer disposed on an upper surface of the porous polymer layer.

[0039] Conventionally, lithium metal alone or a current collector such as copper foil and lithium metal stacked together has been used as the negative electrode for secondary batteries. However, when lithium metal alone is used as the negative electrode, it has problems such as being prone to wrinkling and having low rigidity.

[0040] In the present invention, the use of a carbon-based current collector in the negative electrode improves the elasticity of the negative electrode, improving its tensile strength and processability. Furthermore, compared to conventional negative electrodes using lithium metal foil, the use of a carbon material with current-collecting properties improves the cell's discharge capacity and stabilizes its coulombic efficiency. Furthermore, compared to conventional copper foil current collectors, the carbon-based current collector is lighter, minimizing the reduction in cell energy density associated with the use of the current collector.

[0041] Furthermore, in the present invention, by using a porous polymer layer in the negative electrode, the elongation and elasticity of the negative electrode can be further improved, and by suppressing contact between the carbonaceous current collector and the bulk electrolyte, side reactions between the carbonaceous current collector and the electrolyte can be prevented, thereby improving the lifespan of the cell.

[0042] Furthermore, in the present invention, the use of a porous polymer layer in the negative electrode can improve the tensile strength and elongation. The improved tensile strength and elongation of the negative electrode can also improve the life of the negative electrode, the capacity of the secondary battery, and the stability.

[0043] In one embodiment of the present invention, the porous polymer layer may be located on at least one side of the carbon-based current collector, specifically on at least one surface of the carbon-based current collector, and the lithium-based material layer may be located on the upper side of the porous polymer layer, specifically on at least the upper surface of the porous polymer layer.

[0044] FIG. 1 is a schematic cross-sectional view of a negative electrode 10 for a secondary battery according to one embodiment of the present invention.

[0045] 1, porous polymer layers 200 are disposed on both sides of a carbon-based current collector 100. A lithium-based material layer 300 is disposed on the upper surface of each porous polymer layer 200.

[0046] In one embodiment of the present invention, when a porous polymer layer is located on at least one surface of a carbon-based current collector, the porous polymer layer may be located on the entire one surface of the carbon-based current collector, or may be located on only a part of the one surface.

[0047] In one embodiment of the present invention, the porous polymer layer may be in direct contact with the carbonaceous current collector and may be located on at least one side of the carbonaceous current collector, or other layers may be located partially or entirely between the porous polymer layer and the carbonaceous current collector. For example, lithium metal may be located between the carbonaceous current collector and the porous polymer layer.

[0048] The lithium-based material layer may be located above the porous polymer layer, specifically, on the upper surface of the porous polymer layer. More specifically, since a carbon-based current collector is located on the lower surface of the porous polymer layer, the lithium-based material layer may be located on the upper surface of the porous polymer layer.

[0049] For example, when a porous polymer layer is located on one side of a carbon-based current collector, the carbon-based current collector, the porous polymer layer, and the lithium-based material layer can be laminated in this order.Alternatively, when porous polymer layers are located on both sides of a carbon-based current collector, the first lithium-based material layer, the first porous polymer layer, the carbon-based current collector, the second porous polymer layer, and the second lithium-based material layer can be laminated in this order.

[0050] The lithium-based material layer may be located on the entire top surface of the porous polymer layer, or may be located on only a portion of the top surface.

[0051] In one embodiment of the present invention, the lithium-based material layer contains at least one of lithium metal and a lithium alloy, and the lithium-based material layer may be a lithium alloy layer or a lithium metal layer. The lithium alloy contains an element capable of alloying with lithium, such as 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.

[0052] In the negative electrode for a secondary battery according to an embodiment of the present invention, the porous polymer layer may have one or more through holes formed therein.

[0053] The negative electrode for a secondary battery according to the present invention may have a structure in which a carbon-based current collector, a porous polymer layer, and a lithium-based material layer are stacked in this order. However, the adhesive strength between the carbon-based current collector and the lithium-based material layer may be stronger than the adhesive strength between the porous polymer layer and the lithium-based material layer used in the present invention. Therefore, to further improve the adhesive strength of the laminate, one or more through-holes may be formed in the porous polymer layer, allowing the carbon-based current collector and the lithium-based material layer to directly contact each other through the through-holes.

[0054] As described above, the lithium-based material layer and the carbon-based current collector can be in direct contact with each other via the through-holes, but the through-holes described in this specification should be distinguished from pores formed in the porous polymer layer itself.

[0055] The porous polymer layer itself has pores, and at least one of the pores may penetrate from one side of the porous polymer layer to the other side of the porous polymer layer. However, the pores may not be formed along the shortest path from one side of the porous polymer layer to the other side, but may instead connect from one side of the porous polymer layer to the other side along a complex path. Therefore, it is difficult for the lithium-based material layer and the carbon-based current collector to directly contact each other through the pores formed in the porous polymer layer itself. In contrast, the through-holes in the present invention may be separately drilled in the porous polymer layer to allow direct contact between the lithium-based material layer and the carbon-based current collector layer.

[0056] 2 is a schematic cross-sectional view of an anode 10 for a secondary battery according to one embodiment of the present invention. Referring to FIG. 2, a laminate may be formed by placing a porous polymer layer 200 having through-holes 210 on at least one side of a carbon-based current collector 100, and placing a lithium-based material layer 300 on the upper surface of the porous polymer layer 200 having through-holes 210. In this case, the lithium-based material layer 300 and the carbon-based current collector 100 are in direct contact with each other and bonded via the through-holes 210 formed in the porous polymer layer 200, thereby more effectively maintaining adhesion between the layers of the laminate.

[0057] In an embodiment of the negative electrode for a secondary battery according to the present invention, the through-holes formed in the porous polymer layer may penetrate the porous polymer layer vertically. When the through-holes penetrate the porous polymer layer vertically, the lithium-based material layer can be in more efficient contact with the carbon-based current collector. However, the through-holes formed in the porous polymer layer are not necessarily limited to those that penetrate the porous polymer layer vertically, and any hole that allows efficient contact between the lithium-based material layer and the carbon-based current collector layer can be used.

[0058] In the negative electrode for a secondary battery according to one embodiment of the present invention, the diameter of the through-holes formed in the porous polymer layer may be larger than the diameter of the pores formed in the porous polymer layer. For example, the diameter of the through-holes may be 0.5 cm to 3.0 cm, or 1.0 cm to 2.0 cm. When the diameter of the through-holes is within the above range, the lithium-based material layer and the carbon-based current collector can be bonded to each other through the through-holes with sufficient adhesive strength.

[0059] The through-holes are preferably circular in shape. However, the present invention is not limited to circular shapes and may be formed in a variety of shapes such as squares and triangles. If the through-holes are not circular, the distance from the center to the farthest point of the through-hole may be 0.25 cm to 1.5 cm.

[0060] In the negative electrode for a secondary battery according to one embodiment of the present invention, the distance between the through holes formed in the porous polymer layer may be 0.5 cm to 1.5 cm. When the distance between the through holes falls within this range, the lithium-based material layer and the carbon-based current collector can be bonded with sufficient adhesive strength.

[0061] In an anode for a secondary battery according to one embodiment of the present invention, the area occupied by the through holes relative to the overall area of ​​the porous polymer layer may be 15% to 60% or 20% to 40%. When the area occupied by the through holes relative to the overall area of ​​the porous polymer layer falls within the above range, the tensile strength and elongation of the anode are improved while improving the adhesive strength between the layers of the anode laminate, and it is possible to maintain suitable elasticity and rigidity. The total area refers to the entire surface area of ​​the porous polymer layer when observed from above, and may refer to the area including the area occupied by the through holes in the porous polymer layer.

[0062] In the negative electrode for a secondary battery according to one embodiment of the present invention, the porosity of the porous polymer layer may be 40% to 70%. When the porosity falls within this range, ions can be smoothly conducted through the porous polymer layer, which is advantageous in ensuring sufficient ion conductivity.

[0063] In the negative electrode for a secondary battery according to one embodiment of the present invention, the specific surface area of ​​the carbon-based current collector is 30 m 2 / g or more, 50m 2 / g or more, 80m 2 / g or more, 100m 2 / g or more, and 2 When the specific surface area of ​​the carbon-based current collector is within the above range, a surface area sufficient to support the lithium negative electrode is ensured, which is advantageous in terms of lowering the current density per unit area and stabilizing lithium or lithium plating.

[0064] In the negative electrode for a secondary battery according to one embodiment of the present invention, the areal density of the carbon-based current collector is 100 g / m 2 Below 70g / m2 Below 50g / m 2 Below 30g / m 2 Below 15g / m 2 or less, or 8 g / m 2 It can be less than 0.1g / m 2 By keeping the surface density of the carbon-based current collector within the above range, it is possible to minimize the decrease in cell energy density due to the introduction of the current collector. The surface density is calculated by dividing the surface area (i.e., the external area) of the carbon-based current collector by its weight, assuming that the carbon-based current collector does not have pores.

[0065] In the negative electrode for a secondary battery according to one embodiment of the present invention, the thickness of the carbonaceous current collector may be 3 μm to 20 μm or 5 μm to 12 μm. When the thickness of the carbonaceous current collector falls within the above range, it is possible to provide the negative electrode for a secondary battery according to the present invention with suitable elongation, rigidity, and elasticity.

[0066] In the negative electrode for a secondary battery according to one embodiment of the present invention, the carbon-based current collector may include graphite, graphene, carbon nanotubes (CNT), graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF), or two or more selected from these. However, the carbon-based current collector is not limited to these materials, and any commonly used carbon-based material may be used as the carbon-based current collector in the present invention.

[0067] In an embodiment of the present invention, the carbonaceous current collector in the negative electrode for a secondary battery may have a porous structure formed by entanglement of carbonaceous materials. For example, the carbonaceous current collector may have a porous carbon nanotube composite structure formed by entanglement of carbon nanotubes. The carbonaceous current collector may also be a mat type that forms a free-standing (i.e., self-supporting) film. Therefore, the carbonaceous current collector can maintain its shape without a separate support.

[0068] In the negative electrode for a secondary battery according to an embodiment of the present invention, the carbon-based current collector may support a lithium-based material. Specifically, as the lithium metal moves during charging and discharging of the secondary battery, at least a portion of the lithium metal may be supported within the pores of the carbon-based current collector.

[0069] In the negative electrode for a secondary battery according to one embodiment of the present invention, the thickness of the porous polymer layer may be 6 μm to 20 μm, or 8 μm to 12 μm. When the thickness of the porous polymer layer falls within the above range, the elongation, tensile strength, and elasticity of the negative electrode for a secondary battery can be improved.

[0070] In an embodiment of the present invention, the porous polymer layer in a negative electrode for a secondary battery may include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or two or more selected from the group consisting of polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthalene, polyethylene terephthalate ...

[0071] In the negative electrode for a secondary battery according to one embodiment of the present invention, the thickness of the lithium-based material layer can be 10 μm to 80 μm, 10 μm to 60 μm, 20 μm to 60 μm, 20 μm to 40 μm, or 30 μm to 50 μm. When the thickness of the lithium-based material layer falls within the above range, it is possible to ensure sufficient negative electrode capacity.

[0072] A method for manufacturing a negative electrode for a secondary battery according to one aspect of the present invention includes the steps of: forming a laminate by stacking a carbon-based current collector, a porous polymer layer having a plurality of through-holes on at least one surface of the carbon-based current collector, and a lithium-based material layer on an upper surface of the porous polymer layer; and compressing the laminate using a rolling process.

[0073] In the method for manufacturing a negative electrode for a secondary battery according to one embodiment of the present invention, the compression bonding step may be performed at 180° C. or less, 150° C. or less, or 120° C. or less, or may be performed at room temperature in the range of 20° C. to 60° C. or 20° C. to 30° C. When the compression bonding step is performed within the above temperature range, it is possible to prevent the lithium-based material, such as lithium metal, from melting, to suppress the formation of an oxide layer on the lithium-based material that acts as a resistor, and to prevent the lithium from melting during the manufacturing process.

[0074] In the method for manufacturing a negative electrode for a secondary battery according to an embodiment of the present invention, the pressing step may be performed in a dry environment such as a dry room. For example, the pressing step may be performed in an environment where the dew point is maintained at −10° C. or lower, −30° C. or lower, or −45° C. or lower. When these conditions are met, contamination of the surface of the lithium-based material, such as the formation of a lithium hydroxide layer due to the lithium-based material reacting with moisture, can be suppressed.

[0075] In the pressing step of the method for manufacturing a negative electrode for a secondary battery according to an embodiment of the present invention, the lithium-based material layer and the carbon-based current collector may be bonded to each other through through-holes formed in the porous polymer layer. The lithium-based material layer is distorted by the pressing and drawn into the through-holes, thereby coming into contact with and bonding to the carbon-based current collector layer.

[0076] A secondary battery according to one aspect of the present invention includes a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is a negative electrode for the secondary battery according to the present invention.

[0077] According to one embodiment of the present invention, the secondary battery may be a lithium secondary battery, which includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium sulfur battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0078] According to one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector.

[0079] The positive electrode current collector can generally be fabricated to a thickness of approximately 3 μm to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like can be used. The positive electrode current collector can also be provided with minute irregularities on its surface to increase the adhesive strength of the positive electrode active material, and a wide variety of forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric, can be used as the positive electrode current collector.

[0080] The positive electrode active material layer may include a positive electrode active material, a conductive material, and a binder polymer.

[0081] The positive electrode active material may contain sulfur (S). In this specification, the sulfur-containing material is referred to as a "sulfur-based compound." The sulfur-based compound may include, for example, any sulfur-containing compound that can be formed using a reduction reaction of inorganic sulfur (S) or an oxidation reaction of lithium sulfide (LiS). More specifically, inorganic sulfur (S), lithium sulfide (LiS), lithium polysulfide (LiS), x , an integer 2≦x≦8), disulfide compounds, carbon-sulfur polymers ((C2S y ) n , y=2.5 to 50, n≧2), lithium sulfide (Li2S), or two or more of these.

[0082] The positive electrode active material may be a sulfur-carbon composite, which may include a porous carbon material and a sulfur-based compound supported on at least one of the interior of the pores of the porous carbon material and the outer surface of the porous carbon material.

[0083] The porous carbon material supports a sulfur-based compound as a positive electrode active material, provides a framework to which the sulfur-based compound can be uniformly and stably fixed, and improves the conductivity of the positive electrode. Any porous carbon material may be used without any particular limitation as long as it is a porous carbon material.

[0084] The porous carbon material can generally be prepared by carbonizing various carbon precursors. The porous carbon material contains pores with varying internal diameters, and the pores may have an average diameter of 1 nm to 200 nm, and the porosity may be in the range of 10% to 90% by volume of the total volume of the porous carbon material. If the average pore diameter is less than the above range, the pore diameter is merely at the molecular level, making sulfur impregnation impossible. Conversely, if the average pore diameter exceeds the above range, the mechanical strength of the porous carbon material is weakened, making it unsuitable for use in electrode manufacturing processes.

[0085] The "average pore diameter" can be measured by any known method in the art for measuring the pore diameter of a porous material, and the measurement method is not particularly limited. For example, the pore diameter can be measured by a scanning electron microscope (SEM), a field-emission scanning electron microscope, a laser diffraction method, or the Brunauer-Emmett-Teller (BET) method. Measurement using the laser diffraction method can be performed, for example, using a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000). Measurement using the BET method can be performed, for example, using a BELSORP series analyzer manufactured by BEL Japan, but is not limited thereto.

[0086] The term "porosity" refers to the ratio of the volume of pores to the total volume of any structure, and is expressed in units of %. It can be used interchangeably with terms such as void ratio, porosity, etc. In the present invention, the measurement of the porosity is not particularly limited, and according to one embodiment of the present invention, it can be measured, for example, by the BET method using nitrogen gas or by a mercury porosimeter in accordance with ASTM D2873.

[0087] The shape of the porous carbon material may be spherical, rod-like, needle-like, plate-like, tubular or bulk, and any shape commonly used in lithium-sulfur batteries may be used without limitation.

[0088] The porous carbon material may have a porous structure or a high specific surface area, and may be any material commonly used in the art. For example, the porous carbon material may be at least one selected from the group consisting of graphite, graphene, carbon black (e.g., denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black); carbon nanotubes (CNTs) (e.g., single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers (e.g., graphite nanofibers (GNFs)), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); graphite (e.g., natural graphite, artificial graphite, and expanded graphite), and activated carbon, but is not limited thereto. Preferably, the porous carbon material is carbon nanotubes.

[0089] The method for preparing the sulfur-carbon composite is not particularly limited in the present invention, and a method commonly used in the art may be used. For example, the sulfur and the porous carbon material may be simply mixed together and then heat-treated to prepare the composite.

[0090] In addition to the above-described composition, the positive electrode active material may further include at least one selected from a transition metal element, a Group IIIA element, a Group IVA element, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0091] The transition metal elements may include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg, the IIIA group elements may include Al, Ga, In, or Ti, and the IVA group elements may include Ge, Sn, or Pb.

[0092] The sulfur-carbon composite may be present in an amount of 50 wt % or more based on the total weight of the positive electrode. Specifically, the sulfur-carbon composite may be present in an amount of, for example, 80 wt % or more, 90 wt % or more, or 95 wt % or more based on the total weight of the positive electrode active material layer. Specifically, the sulfur-carbon composite may be present in an amount of 80 wt % to 100 wt %, more specifically, 85 wt % to 99 wt %, 90 wt % to 99 wt %, 95 wt % to 98 wt %, 95 wt % to 97 wt %, or 96 wt % based on the total weight of the positive electrode active material layer.

[0093] In one embodiment of the present invention, the binder polymer holds the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to each other to further enhance the binding strength therebetween. Any binder polymer known in the art may be used.

[0094] For example, the binder polymer may be any one or a mixture or copolymer of two or more selected from the group consisting of polyacrylic acid (PAA), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-based polymers containing at least one vinylidene fluoride repeating unit, fluororesin-based binders including polytetrafluoroethylene (PTFE) or a mixture of two or more thereof; rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isophrene rubber; acrylic binders; cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0095] In one embodiment of the present invention, the content of the binder may be 1 wt % to 10 wt % based on the total weight of the positive electrode active material layer. If the content of the binder is less than the above range, the physical properties of the positive electrode may be deteriorated, and the positive electrode active material and the conductive material may be separated from each other. If the content of the binder exceeds the above range, the ratio of the positive electrode active material to the conductive material in the positive electrode may be relatively reduced, and the battery capacity may be reduced. Therefore, it is preferable to determine an appropriate content within the above range.

[0096] In an embodiment of the present invention, the conductive material electrically connects the electrolyte and the positive electrode active material and serves as a path through which electrons move from a current collector to the positive electrode active material. The conductive material is a component of the electrode that is physically distinct from the carbon contained in the sulfur-carbon composite and may be any conductive material.

[0097] The conductive material may be, for example, carbon black such as Super-P, Denka Black, acetylene black, Ketjen Black, channel black, furnace black, lamp black, thermal black, or carbon black; carbon derivatives such as carbon nanotubes or fullerene; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, or polypyrrole, which may be used alone or in combination.

[0098] In one embodiment of the present invention, the content of the conductive material may be 1 wt % to 10 wt % based on the total weight of the positive electrode active material. If the content of the conductive material is below this range, electron transfer between the positive electrode active material and the current collector is difficult, resulting in a decrease in voltage and capacity. Conversely, if the content exceeds this range, the proportion of the positive electrode active material decreases relatively, which may result in a decrease in the total energy (charge amount) of the battery. Therefore, it is preferable to determine an appropriate content within the above range.

[0099] In one embodiment of the present invention, the separator separates or insulates the positive electrode and the negative electrode from each other and transports lithium ions between the positive electrode and the negative electrode. The separator may be made of a porous, non-conductive, or insulating material, and any material commonly used as a separator in lithium secondary batteries may be used without any particular limitation. The separator may be an independent member such as a film, or may be a coating layer attached to the positive electrode and / or the negative electrode.

[0100] The separator preferably has low resistance to the movement of ions of the electrolyte and has excellent moisture-absorbing ability for the electrolyte.

[0101] In one embodiment of the present invention, the separator may include a porous substrate. The porous substrate may be any porous substrate commonly used in secondary batteries. A porous polymer film may be used alone or in combination. For example, a nonwoven fabric or a polyolefin-based porous film made of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like may be used, but is not limited thereto.

[0102] The material of the porous substrate is not particularly limited in the present invention, and any porous substrate commonly used in electrochemical devices can be used. For example, the porous substrate can be made of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides, polyacetals, polycarbonates, polyimides, polyetheretherketones, polyethersulfones, polyphenylene oxides, polyphenylene sulfides, polyethylene naphthalenes, polytetrafluoroethylenes, polyvinylidene fluoride, polyvinyl chloride, etc. The material may include at least one material selected from the group consisting of poly(p-phenylene benzobisoxazole), polyacrylonitrile, cellulose, nylon, poly(p-phenylene benzobisoxazole), and polyarylate.

[0103] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited, but may be 1 μm to 100 μm, preferably 5 μm to 50 μm. Although the thickness of the porous substrate is not limited to the above range, if the thickness is much thinner than the above lower limit, there is a concern that the mechanical properties may be reduced, making the separator more susceptible to damage during use of the battery.

[0104] In one embodiment of the present invention, the average diameter and porosity of the pores present in the porous substrate are also not particularly limited, and may be 0.001 μm to 50 μm and 10 vol % to 95 vol %, respectively.

[0105] In one embodiment of the present invention, the separator may further include a porous coating layer formed on at least one surface of the porous substrate, the porous coating layer including inorganic particles and a binder. The inorganic particles and binder included in the porous coating layer may be any inorganic particles and binder commonly used in porous coating layers of separators, and the manufacturing method thereof is also not particularly limited.

[0106] In one embodiment of the present invention, the electrolyte solution includes a lithium salt as an electrolyte and an organic solvent for dissolving the lithium salt.

[0107] The lithium salt may be any of those commonly used in electrolytes for secondary batteries, such as LiNO3 and LiTFSI, and may be any of those anions, such as F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P- , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Any one selected from the group consisting of:

[0108] The organic solvent contained in the electrolytic solution may be any commonly used organic solvent without any particular limitation. Representative examples include at least one selected from the group consisting of propylene carbonate, ethylene carbonate, dimethyl ether (DME), 1,3-dioxolane (DOL), diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran.

[0109] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents with high dielectric constants, and are therefore suitable for use since they effectively dissociate lithium salts in the electrolyte. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte solution having high electrical conductivity can be prepared, making them even more suitable for use.

[0110] Optionally, the electrolyte stored in accordance with the present invention may further contain additives such as overcharge inhibitors that are typically included in electrolytes.

[0111] According to an embodiment of the present invention, a lithium secondary battery may be fabricated by forming an electrode assembly by disposing a separator between a positive electrode and a negative electrode, placing the electrode assembly in, for example, a pouch, a cylindrical battery case, or a prismatic battery case, and then injecting an electrolyte. Alternatively, the electrode assemblies may be stacked, impregnated with an electrolyte, and then placed in a battery case and sealed to form a lithium secondary battery.

[0112] The present invention will be described in detail below with reference to examples. However, the following examples are merely for the purpose of illustrating the present invention, and the scope of the present invention is not limited to these examples.

[0113] Example 1 A 50 μm thick lithium metal foil was used as the first lithium metal layer, a 10 μm thick polyethylene porous film was used as the first porous polymer layer, carbon nanotubes were used as the carbon-based current collector, a 10 μm thick polyethylene porous film was used as the second porous polymer layer, and a 50 μm thick lithium metal foil was used as the second lithium metal layer. These were laminated in this order and pressed together using a rolling (roll press) process at 25° C. to produce a negative electrode. At this time, the first porous polymer layer and the second porous polymer layer had one or more through holes, and the area occupied by the through holes formed in the first porous polymer layer and the second porous polymer layer was 50% of the total area of ​​the porous polymer layer, and the diameter of the through holes was 1.9 cm.

[0114] Comparative Example 1 A lithium metal foil with a thickness of 100 μm was prepared as the negative electrode.

[0115] Comparative Example 2 A 50 μm thick lithium metal foil was prepared as the first lithium metal layer, a 10 μm thick carbon nanotube film was prepared as the carbon-based current collector, and a 50 μm thick lithium metal foil was prepared as the second lithium metal layer. These were laminated in this order and pressed together using a rolling (roll press) process at 25°C to prepare a negative electrode.

[0116] Example 2 <Preparing the negative electrode> A negative electrode similar to that produced in Example 1 was prepared.

[0117] <Manufacturing lithium-sulfur batteries> A sulfur-carbon composite, in which sulfur is supported on carbon nanotubes, was prepared as a positive electrode active material. The weight ratio of carbon nanotubes to sulfur was 1:3. Polyacrylic acid (PAA) was added as a binder and carbon fiber as a conductive material to prepare a positive electrode slurry. The weight ratio of the positive electrode active material, conductive material, and binder was 88:5:7.

[0118] The prepared slurry was coated on an aluminum foil using a Matisse coating device, dried at a temperature of 50° C. for 24 hours, and then rolled to prepare a positive electrode.

[0119] As an electrolyte, a mixture of 0.75 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt% lithium nitrate (LiNO3) was prepared in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME = 1:1 (volume ratio)).

[0120] The prepared positive electrode and negative electrode were positioned facing each other, and a polyethylene separator having a thickness of 16 μm and a porosity of 46% was interposed between them. The resulting battery was then housed in a pouch-type battery case, and the electrolyte was then injected to prepare a lithium-sulfur battery.

[0121] Comparative Example 3 A lithium-sulfur battery was produced in the same manner as in Example 2, except that the negative electrode prepared in Comparative Example 1 was used as the negative electrode.

[0122] Experimental example 1: Tensile strength experiment Tensile strength was measured according to ASTM D-412 B.

[0123] Test specimens were prepared from the negative electrodes prepared in Example 1 and Comparative Examples 1 and 2 according to the standard ASTM D-412 B. Tests were then carried out on each test specimen using a Universal Testing Machine (UTM) and a 100 N load cell.

[0124] The maximum stress value was measured while applying a strain rate of 0.01 mm / s to each test piece to determine the tensile strength, which is shown in Table 1.

[0125] [Table 1]

[0126] FIG. 3 shows the measurement results of the tensile strength of the negative electrode in Example 1, and FIG. 4 shows the measurement results of the tensile strength of Comparative Examples 1 and 2.

[0127] Referring to Table 1, FIGS. 3 and 4, it can be seen that Example 1 has a significantly higher tensile strength than Comparative Example 1. It can be seen that the anode of Comparative Example 1 has low rigidity due to the presence of only lithium metal foil, and as a result, it elongates significantly as it is strained. Example 1 has a significantly longer elongation length at break than Comparative Example 2. This is due to the increased elongation rate caused by the inclusion of a porous polymer layer in Example 1.

[0128] Experimental Example 2: Capacity Retention Rate Experiment FIG. 5 is a graph showing the results of evaluating the cell performance of the lithium-sulfur batteries according to Example 2 and Comparative Example 3.

[0129] The lithium-sulfur batteries according to Example 2 and Comparative Example 3 were charged (0.3 C, CC mode) and discharged (0.5 C, CC mode) at 25° C., and the discharge capacity retention rate was calculated according to the following formula.

[0130] Discharge capacity retention rate (%) = [(discharge capacity after one cycle - discharge capacity after n cycles) / discharge capacity after one cycle] x 100

[0131] The lithium-sulfur battery of Example 2 maintained a capacity retention of 80% or more even after 250 cycles, whereas the lithium-sulfur battery of Comparative Example 3 was found to rapidly decrease in capacity retention before reaching 100 cycles.

[0132] As described above, the present invention has been described using limited embodiments and drawings, but the present invention is not limited to these, and it goes without saying that various modifications and variations can be made by a person having ordinary knowledge in the technical field to which the present invention belongs within the technical spirit of the present invention and the equivalent scope of the claims.

Claims

1. a carbon-based current collector; a porous polymer layer located on at least one surface of the carbon-based current collector; a lithium-based material layer located on an upper surface of the porous polymer layer; Including, The porous polymer layer has one or more through holes formed therein, and the carbon-based current collector and the lithium-based material layer are in contact with each other via the through holes.

2. The negative electrode for a secondary battery according to claim 1 , wherein the lithium-based material layer contains at least one of lithium metal and a lithium alloy.

3. 2. The negative electrode for a secondary battery according to claim 1, wherein the lithium-based material layer is a lithium metal layer.

4. 2. The negative electrode for a secondary battery according to claim 1, wherein the area occupied by the through holes formed in the porous polymer layer is 15% to 60% of the total area of ​​the porous polymer layer.

5. 2. The negative electrode for a secondary battery according to claim 1, wherein the through-holes formed in the porous polymer layer have a diameter of 0.5 cm to 3 cm.

6. The negative electrode for a secondary battery according to claim 1 , wherein the porous polymer layer is located on both sides of the carbon-based current collector.

7. The specific surface area of ​​the carbon-based current collector is 50 m ２ 2. The negative electrode for a secondary battery according to claim 1, wherein the negative electrode has a Mo / Si content of 0.1g or more.

8. The areal density of the carbon-based current collector is 100 g / m ２ 2. The negative electrode for a secondary battery according to claim 1, wherein:

9. 2. The negative electrode for a secondary battery according to claim 1, wherein the carbon-based current collector comprises graphite, graphene, carbon nanotubes (CNTs), graphite nanofibers (GNFs), carbon nanofibers (CNFs), activated carbon fibers (ACFs), or two or more thereof.

10. The porous polymer layer may be made of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, or polyimide.

2. The negative electrode for a secondary battery according to claim 1, comprising at least one selected from the group consisting of polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene, and the like.

11. forming a laminate by stacking a carbon-based current collector, a porous polymer layer having one or more through-holes on at least one surface of the carbon-based current collector, and a lithium-based material layer on the upper surface of the porous polymer layer; compressing the laminate using a rolling process; Including, the porous polymer layer has one or more through holes formed therein, and the carbon-based current collector and the lithium-based material layer are in contact with each other via the through holes.

12. The method for manufacturing a negative electrode for a secondary battery according to claim 11 , wherein the lithium-based material layer includes at least one of lithium metal and a lithium alloy.

13. The method for producing a negative electrode for a secondary battery according to claim 11 , wherein the lithium-based material layer is a lithium metal layer.

14. The method for manufacturing a negative electrode for a secondary battery according to claim 11 , wherein the pressure-bonding step is performed at a temperature range of 180° C. or less.

15. A secondary battery including a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte, The negative electrode of claim 1 , wherein the negative electrode is a negative electrode of claim 1 .

Images