Negative electrode for secondary battery and secondary battery comprising same

Abstract

The negative electrode for a secondary battery according to the present invention comprises a porous polymer substrate and a negative electrode active material supported in the porous polymer substrate. The porous polymer substrate has a lattice structure including line portions and opening portions. All or at least a portion of each opening of the porous polymer substrate is filled with the negative electrode active material. The negative electrode active material includes at least one of a lithium metal or a lithium alloy. The negative electrode for a secondary battery comprises a porous polymer substrate having a lattice structure, and thus has excellent mechanical strength and can suppress dendritic crystal formation on the negative electrode and volume expansion of the negative electrode during charging and discharging.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode for a secondary battery and a secondary battery including the negative electrode.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0124313 filed on September 18, 2023, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0003] With the technological development and increased demand for mobile devices, the demand for secondary batteries as energy sources has dramatically increased, and among secondary batteries, lithium secondary batteries having high energy density and operating potential and low self-discharge rate have been commercialized.

[0004] Lithium metal secondary battery is the first commercialized lithium secondary battery, and lithium metal is used as negative electrode. However, due to the lithium dendrites on the surface of the lithium metal negative electrode, the lithium metal secondary battery will have problems, such as battery volume expansion, capacity and energy density gradually decline, short circuit caused by the continuous growth of dendrites, cycle life reduction and battery stability problems (explosion and fire), and its production was stopped only a few years after commercialization. Carbon-based negative electrodes are used instead of lithium metal. Because carbon-based negative electrodes are more stable and can stably store lithium in ionic form in lattices or gaps, the use of carbon-based negative electrodes puts lithium secondary batteries into practical and widespread use.

[0005] So far, lithium secondary batteries mainly contain carbon-based or non-carbon-based negative electrode materials, and in most cases, the development of negative electrode materials has focused on carbon-based materials (graphite, hard carbon, soft carbon, etc.) and non-carbon-based materials (silicon, tin, titanium oxide, etc.). However, the theoretical capacity of carbon-based materials does not exceed 400mAh / g, and non-carbon-based materials are materials with a theoretical capacity of more than 1000mAh / g, but they have problems with volume expansion and performance degradation during charge and discharge.

[0006] On the other hand, with the widespread use of medium and large lithium secondary batteries, high capacity and high energy density characteristics are required, but the existing carbon-based or non-carbon-based negative electrode materials are not sufficient to meet the performance requirements.

[0007] Under these circumstances, the use of lithium metal, such as lithium-air batteries, has recently been studied, and under this trend, lithium metal secondary batteries have once again attracted attention. Because lithium is very light and has a theoretical capacity of more than 3800 mAh / g, it has the potential to achieve high energy density.

[0008] However, there are challenges in using lithium metal as a negative electrode material for secondary batteries. First, unlike graphite-based negative electrode materials, in the case of lithium metal negative electrodes, the lithium in the form of ions released from the positive electrode becomes neutral lithium through an electrochemical reaction with electrons from an external conductor, thereby forming very irregular lithium deposits in the shape of dendrites on the lithium surface during charging. The uneven surface causes the overall volume to expand, and during discharge, ions selectively do not detach from the lithium dendrites but dissociate directly from the lithium metal more often. Therefore, the lithium metal negative electrode surface undergoes very severe volume changes during a series of charge and discharge cycles, and the dendrites exhibit irregular and complex morphologies. This complex form of the surface is unstable during cycling, resulting in very irregular cycle life through repeated deposition and dissolution. In addition, the lithium dendrites formed during discharge may dissociate and dissolve into the electrolyte, or the dendrites may continue to grow in the vertical direction and pass through the separator to directly or indirectly contact the positive electrode surface on the opposite side, causing a short circuit.

[0009] Furthermore, because lithium metal has low mechanical strength, defects often occur during the manufacturing process in the production of free-standing lithium metal anodes without a current collector. To address this issue, attempts have been made to laminate lithium metal foil onto the current collector, but in this case, the energy density of the battery is significantly reduced due to the weight of the current collector. Summary of the Invention

[0010] Technical issues

[0011] In order to solve the above-mentioned problems, the present disclosure is directed to providing a negative electrode for a secondary battery having high mechanical strength.

[0012] The present disclosure further provides a secondary battery including the negative electrode, which has improved lifespan characteristics and high energy density.

[0013] Technical Solution

[0014] In order to solve the above-mentioned problems, one aspect of the present disclosure provides a negative electrode for a secondary battery and a secondary battery according to the following embodiments.

[0015] A negative electrode for a secondary battery according to a first embodiment includes:

[0016] Porous polymer substrate and negative electrode active material,

[0017] wherein the porous polymer substrate has a lattice structure comprising line portions and opening portions,

[0018] wherein all or at least a portion of each opening of the porous polymer substrate is filled with the negative electrode active material, and

[0019] The negative electrode active material comprises at least one of lithium metal and lithium alloy.

[0020] According to the second embodiment, in the first embodiment,

[0021] The negative electrode for a secondary battery may be a self-standing type without a current collector.

[0022] According to a third embodiment, in the first or second embodiment,

[0023] A line pitch of the line portion of the porous polymer substrate may be between 80 μm and 400 μm.

[0024] According to a fourth embodiment, in any one of the first to third embodiments,

[0025] The line width of the line portion of the porous polymer substrate may be between 10 μm and 40 μm.

[0026] According to a fifth embodiment, in any one of the first to fourth embodiments,

[0027] The lattice structure may have a fixed structure having a constant interval between the line portions.

[0028] According to a sixth embodiment, in any one of the first to fifth embodiments,

[0029] The thickness of the porous polymer substrate may be in the range of 20 μm to 100 μm.

[0030] According to a seventh embodiment, in any one of the first to sixth embodiments,

[0031] The porous polymer substrate may comprise polyester, polyolefin, polyethylene terephthalate, or mixtures thereof.

[0032] According to an eighth embodiment, in any one of the first to seventh embodiments,

[0033] The negative electrode may include the negative electrode active material loaded into 90 volume % or more of the openings based on the total volume of the openings of the porous polymer substrate.

[0034] According to a ninth embodiment, in any one of the first to eighth embodiments,

[0035] At least a portion of the line portion may be exposed to the outside on one surface or both surfaces of the negative electrode.

[0036] According to a tenth embodiment, in any one of the first to eighth embodiments,

[0037] The porous polymer substrate may be embedded in the negative electrode active material.

[0038] According to an eleventh embodiment, in any one of the first to eighth embodiments,

[0039] The line portion may not be exposed on one surface of the negative electrode, and may be completely or partially exposed on the opposite surface.

[0040] According to a twelfth embodiment, in any one of the first to eighth embodiments, at least a portion of the porous polymer substrate may be included in the negative electrode active material.

[0041] According to a thirteenth embodiment, in any one of the first to eighth embodiments,

[0042] 80 wt % or more of the porous polymer substrate may be contained in the negative electrode active material.

[0043] A secondary battery according to a fourteenth embodiment includes:

[0044] a positive electrode; a negative electrode; and a separator interposed between the positive electrode and the negative electrode,

[0045] wherein the negative electrode is defined in any one of the first to thirteenth embodiments, and

[0046] The positive electrode contains sulfur as a positive electrode active material.

[0047] According to the fifteenth embodiment, in the fourteenth embodiment,

[0048] The positive electrode may include a sulfur-carbon composite as the positive electrode active material.

[0049] According to a sixteenth embodiment, in the fourteenth or fifteenth embodiment,

[0050] The secondary battery may be a lithium-sulfur battery.

[0051] Beneficial effects

[0052] A negative electrode for a secondary battery according to one aspect of the present disclosure is a free-standing electrode having no current collector, and a secondary battery including the negative electrode for a secondary battery can have high energy density.

[0053] The secondary battery negative electrode according to one aspect of the present disclosure includes a negative electrode active material loaded into a porous polymer substrate, thereby generating high mechanical strength. Therefore, the volume change of the secondary battery negative electrode can be suppressed, and dendrite growth and uneven lithium dissolution at the negative electrode can be suppressed during charge and discharge. In addition, because the porous polymer can support the negative electrode active material during the negative electrode manufacturing process, the manufacturing process efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the foregoing disclosure, are used to provide a better understanding of the technical aspects of the present disclosure, and therefore the present disclosure is not to be construed as being limited to the accompanying drawings. In the accompanying drawings, for clarity of description, the shape, size, scale or proportion of elements may be exaggerated for emphasis.

[0055] Figure 1 is a diagram of a porous polymeric substrate according to an embodiment of the present disclosure.

[0056] Figure 2 is a cross-sectional view of a negative electrode for a secondary battery according to an embodiment of the present disclosure.

[0057] Figure 3a is a diagram illustrating a method of manufacturing a negative electrode for a secondary battery according to an embodiment of the present disclosure.

[0058] Figure 3b is a diagram illustrating a method of manufacturing a negative electrode for a secondary battery according to an embodiment of the present disclosure.

[0059] Figure 3c is a diagram illustrating a method of manufacturing a negative electrode for a secondary battery according to an embodiment of the present disclosure.

[0060] Figure 4 The cycle life of lithium-sulfur batteries according to examples and comparative examples of the present disclosure is shown.

[0061] Figure 5 The coulombic efficiencies of lithium-sulfur batteries according to examples and comparative examples of the present disclosure are shown.

[0062] Figure 6 The increase in thickness of the negative electrode of the lithium-sulfur batteries according to the examples and comparative examples of the present disclosure is shown. DETAILED DESCRIPTION

[0063] Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings. It should be understood that the terms used in the specification and the appended claims should not be interpreted as limited to the general meaning and dictionary meaning, but should be interpreted based on the meaning and concept corresponding to the technical aspects of the present disclosure based on the principle of allowing the inventor to appropriately define the terms for the best interpretation.

[0064] Therefore, the embodiments described herein and the illustrations in the accompanying drawings are provided to describe the present disclosure by way of example, but are not intended to be limiting, and it should be understood that other equivalents and modifications may exist at the time the application is filed.

[0065] It will also be understood that when used in the specification, “comprising,” “including,” or “having” specifies the presence of stated elements, and does not preclude the presence or addition of one or more other elements, unless explicitly stated otherwise.

[0066] In the specification, "A and / or B" as used herein means A or B or both.

[0067] Unless otherwise indicated, temperatures as used herein are in degrees Celsius and are expressed in °C.

[0068] A negative electrode for a secondary battery according to one aspect of the present disclosure includes:

[0069] Porous polymer substrate and negative electrode active material,

[0070] wherein the porous polymer substrate has a lattice structure comprising line portions and opening portions,

[0071] wherein all or at least a portion of each opening of the porous polymer substrate is filled with the negative electrode active material, and

[0072] The negative electrode active material comprises at least one of lithium metal and lithium alloy.

[0073] When lithium metal is used as the negative electrode, the negative electrode suffers from severe volume changes and uneven lithium deposition during charge and discharge, causing dendrite formation. In addition, the low mechanical strength of lithium metal leads to low process efficiency during the manufacture of the negative electrode.

[0074] However, the negative electrode for a secondary battery according to the present disclosure includes a negative electrode active material filled in the openings of a porous polymer substrate having a lattice structure. Therefore, since the porous polymer substrate of the lattice structure supports the negative electrode active material, high process efficiency can be achieved even when lithium metal and / or lithium alloys having low mechanical strength are used as the negative electrode active material. In addition, because the porous polymer substrate suppresses the volume change of lithium metal and / or lithium alloys and promotes uniform lithium deposition, the life characteristics of the negative electrode can be improved.

[0075] In an embodiment of the present disclosure, the negative electrode for a secondary battery may be a self-supporting electrode without a current collector, i.e., the negative electrode active material layer is not supported by a current collector, and the negative electrode only comprises the negative electrode active material layer. A secondary battery comprising such a self-supporting negative electrode may have a high energy density.

[0076] The porous polymer substrate according to the present disclosure has a lattice structure comprising linear portions and openings. In this specification, the linear portions refer to the lattice structure of the porous polymer substrate and correspond to the skeleton of the porous polymer substrate. Furthermore, the openings refer to the spaces between the linear portions. The porous polymer substrate has a structure that penetrates from one side to the other, with openings located therebetween.

[0077] Figure 1 is a diagram showing a porous polymer substrate 11 according to the present disclosure. Figure 1 The porous polymer substrate 11 has a lattice structure including polymer lines 111 and openings 112 or spaces between the lines.

[0078] In an embodiment of the present disclosure, the line spacing of the line portion of the porous polymer substrate may be in the range of 80 μm to 400 μm, 100 μm to 400 μm, 120 μm to 350 μm, or 120 μm to 300 μm. When the line spacing of the line portion is within the above range, the negative electrode active material can be smoothly loaded into the opening portion of the porous polymer substrate, and the porous polymer can have sufficient mechanical strength.

[0079] The line pitch of the line portions may refer to a shortest distance between adjacent line portions arranged in parallel.

[0080] In an embodiment of the present disclosure, the line width of the line portion of the porous polymer substrate may be in the range of 10 μm to 40 μm, 10 μm to 30 μm, 15 μm to 40 μm, 15 μm to 35 μm, 20 μm to 35 μm, or 20 μm to 30 μm. When the line width of the line portion is within the above range, sufficient mechanical strength of the porous polymer substrate can be achieved, the negative electrode active material loaded into the porous polymer substrate can be fully supported, and the volume change of the negative electrode active material occurring during charge and discharge can be suppressed.

[0081] In an embodiment of the present disclosure, the lattice structure of the porous polymer substrate may be a regular structure. A regular structure does not mean that the line spacings of the line portions are equal, but may mean that the line spacings of the line portions are within a specific range.

[0082] For example, the line spacing may be less than 20%, less than 15%, less than 10%, less than 5%, or less than 3% of the average line spacing of the entire line portion. Here, the line spacing may be determined using a scanning electron microscope (SEM) image, and the average of 10 or 20 different line spacings may be the average line spacing of the entire line portion.

[0083] When the line spacing is within the above range, the porous polymer substrate can uniformly support the negative electrode active material from different directions. As a result, the volume expansion of the negative electrode active material can be uniformly suppressed from different directions, and the formation of dendrites on the surface of the negative electrode active material can be uniformly suppressed.

[0084] In one embodiment of the present disclosure, the weight per unit area of the porous substrate may be 0.2 mg / cm 2 Up to 2.5 mg / cm 2When the weight per unit area of the porous substrate is within the above range, mechanical strength of the negative electrode and sufficient energy density of a secondary battery including the negative electrode may be achieved.

[0085] In an embodiment of the present disclosure, the thickness of the porous polymer substrate may be in the range of 20 μm to 100 μm. When the thickness of the porous polymer substrate is within the above range, the negative electrode active material can be sufficiently filled in the openings of the porous polymer substrate, and sufficient capacity and mechanical strength of the negative electrode can be achieved.

[0086] In embodiments of the present disclosure, the porous polymer substrate may not physically or chemically react with lithium metal and / or lithium alloys. For example, the porous polymer substrate may comprise polyester, polyolefin, polyethylene terephthalate, or a mixture thereof. Specifically, the polyolefin may comprise polyethylene, polypropylene, polybutylene, polypentene, polymethylpentene, polybutene-1, a polyolefin elastomer, polyisobutylene, or a mixture thereof.

[0087] In one embodiment of the present disclosure, the negative electrode active material may be loaded into 90% by volume or more, 95% by volume or more, or 98% by volume or more of the opening relative to the total volume of the opening of the porous polymer substrate, and the opening may be filled with 100% by volume of the negative electrode active material. In the present disclosure, because the porous polymer substrate supports the negative electrode active material, the more the amount of the negative electrode active material filled in the opening of the porous polymer substrate increases, the more the energy density of the secondary battery including the negative electrode according to the present disclosure can be increased.

[0088] The negative electrode for a secondary battery according to the present disclosure may be formed by stacking negative electrode active material layers on at least one surface of a porous polymer substrate and applying pressure to the stack.

[0089] Furthermore, the negative electrode for a secondary battery formed by applying pressure to a stack may include a porous polymer substrate buried in a negative electrode active material.

[0090] For example, the negative electrode active material can be filled in the opening portion of the porous polymer substrate, and the outside of the porous polymer substrate can be completely covered by the negative electrode active material. In addition, in the negative electrode for a secondary battery formed by applying pressure to the stack, at least a portion of the line portion on one or both surfaces of the porous polymer substrate may be exposed to the outside. For example, on one surface, the line portion of the porous polymer substrate is not exposed, and on the opposite surface, the line portion may be completely or partially exposed. Preferably, the entire porous polymer substrate is not exposed to the outside and can be buried in the negative electrode active material. When the entire surface of the negative electrode contains the negative electrode active material, the lithium insertion and extraction at the negative electrode in the secondary battery containing the negative electrode according to the present disclosure can be enhanced.

[0091] That is, the negative electrode for a secondary battery may include a negative electrode active material and a porous polymer substrate at least partially contained in the negative electrode active material. In other words, at least a portion of the porous polymer substrate may be contained in the negative electrode active material.

[0092] In one embodiment of the present disclosure, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more of the porous polymer substrate may be contained in the negative electrode active material. Preferably, the porous polymer substrate may be completely contained in the negative electrode active material.

[0093] Figure 2 : is a cross-sectional view of a negative electrode 10 for a secondary battery according to the present disclosure. Figure 2 , the porous polymer substrate 11 is completely buried in the negative electrode active material 12. That is, the porous polymer substrate 11 is completely covered by the negative electrode active material 12.

[0094] In an embodiment of the present disclosure, the lithium alloy may be an alloy of lithium (Li) and a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al) and tin (Sn).

[0095] A method of manufacturing a negative electrode for a secondary battery according to one aspect of the present disclosure may include the following steps:

[0096] The method comprises preparing the porous polymer substrate, stacking the negative electrode active material layer on at least one surface of the porous polymer substrate, and applying pressure to the stack. The negative electrode active material layer may include at least one of lithium metal and lithium alloy, and preferably lithium metal foil.

[0097] The step of applying pressure may include calendaring using a roller press.

[0098] The stacking step may include, for example, stacking a lithium metal foil on one surface of the porous polymer substrate and applying pressure, or stacking a lithium metal foil on both surfaces of the porous polymer substrate and applying pressure.

[0099] Figures 3a to 3c A method for manufacturing a negative electrode for a secondary battery according to an embodiment of the present disclosure is shown. Figures 3a to 3c ,like Figure 3a As shown, the negative electrode active material 12 is placed above and below the porous polymer substrate 11, as shown in FIG. Figure 3b As shown, the negative electrode active material 12 is pressed from the upper and lower surfaces of the porous polymer substrate 11 to compress the porous polymer substrate 11 and the negative electrode active material 12, producing a Figure 3cA negative electrode 10 for a secondary battery according to the present disclosure is shown.

[0100] Figure 3c The porous polymer substrate is shown to be completely covered by the negative electrode active material, and no part of the porous polymer substrate is exposed to the outside of the negative electrode active material, and is not intended to mean that the porous polymer substrate can be seen in the negative electrode active material.

[0101] A secondary battery according to one aspect of the present disclosure may include a positive electrode; a negative electrode; and a separator interposed between the positive electrode and the negative electrode, wherein the negative electrode may include the negative electrode for a secondary battery as described above.

[0102] In an embodiment of the present disclosure, the secondary battery may be a lithium-sulfur battery.

[0103] In one embodiment of the present disclosure, the positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector.

[0104] The positive electrode current collector may include, but is not limited to, those that support the positive electrode active material and have high conductivity without causing chemical changes to the corresponding battery. For example, the positive electrode current collector may include copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon, copper or stainless steel treated with carbon, nickel or silver on the surface, or aluminum-cadmium alloy.

[0105] The positive electrode current collector may have a finely concavoconvex surface to increase bonding with the positive electrode active material, and may be used in various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and non-woven fabrics.

[0106] The positive electrode active material layer may include a positive electrode active material and a binder polymer, and optionally, may further include a conductive material and / or an additive.

[0107] The positive electrode active material may contain sulfur (S). In this specification, the material containing sulfur is referred to as a "sulfur compound". The sulfur compound may include, for example, any sulfur-containing compound that can be formed by a reduction reaction of inorganic sulfur (S8) or an oxidation reaction of lithium sulfide (Li2S), and more specifically, may include inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2S), and the like. x , an integer of 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 thereof.

[0108] The positive electrode active material may preferably be a sulfur-carbon composite. The sulfur-carbon composite may include a porous carbon material and the sulfur-based compound supported on at least one of the interior of pores of the porous carbon material or the outer surface of the porous carbon material.

[0109] In an embodiment of the present disclosure, the porous carbon material may be used to provide a framework for supporting the sulfide compound and uniformly and stably fixing the sulfide compound, and may include, but is not limited to, any porous carbon material.

[0110] The porous carbon material can generally be produced by carbonizing precursors of various carbon materials. The porous carbon material contains irregular pores in the interior, and the average pore diameter can be in the range of 1 nm to 200 nm, and the porosity can be in the range of 10% to 90% by volume of the total volume of the porous carbon material. When the average pore diameter is less than the above range, the pore size is only at the molecular level, making it impossible to load sulfur. Conversely, when the average pore diameter is greater than the above range, the mechanical strength of the porous carbon material is low and it is not suitable for use in the electrode manufacturing process.

[0111] The "average pore size" can be measured by a known method for measuring the pore size of any porous material in the corresponding technical field, and the measurement method is not limited to a specific method. For example, the pore size can be measured by a scanning electron microscope (SEM), a field emission electron microscope, a laser diffraction method, or a Brunauer-Emmett-Teller (BET) method. Measurement using the laser diffraction method can be performed, for example, using a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000). In addition, measurement by the BET method can be performed using an analyzer, such as the BELSORP series of BEL Japan Co., Ltd., but is not limited thereto.

[0112] "Porosity" refers to the ratio of the volume occupied by pores in a structure to the total volume, and its unit is %, and this term can be used interchangeably with void ratio or void ratio. In the present disclosure, the measurement of porosity is not limited to a specific method, and according to an embodiment of the present disclosure, the porosity can be measured, for example, by the BET method using nitrogen or a Hg porosimeter and ASTM D2873.

[0113] The porous carbon material may have any shape commonly used in lithium-sulfur batteries, such as spherical, rod-like, needle-like, plate-like, tubular, or bulky shapes, but is not limited thereto.

[0114] The porous carbon material may include, but is not limited to, those having a porous structure or a high specific surface area commonly used in the art. For example, the porous carbon material may include at least one selected from the group consisting of: graphite; graphene; carbon black, including Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; carbon nanotubes (CNTs), including single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers, including graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); graphite, including natural graphite, artificial graphite, expandable graphite, and activated carbon, but not limited thereto. Preferably, the porous carbon material may include carbon nanotubes.

[0115] The method of manufacturing the sulfur-carbon composite is not limited to the specific method in the present disclosure, and may include any method commonly used in the art. For example, sulfur and porous carbon materials may be simply mixed and heat-treated to form a composite.

[0116] In addition to the above composition, the positive electrode active material may further include at least one selected from transition metal elements, Group IIIA elements, Group IVA elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0117] The transition metal element 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 Group IIIA element may include Al, Ga, In, Ti, and the Group IVA element may include Ge, Sn, Pb.

[0118] The sulfur-carbon composite may comprise 50% by weight or greater based on the total weight of the positive electrode. Specifically, the sulfur-carbon composite may comprise 80% by weight or greater, 90% by weight or greater, or 95% by weight or greater, based on the total weight of the positive electrode active material layer. Specifically, the sulfur-carbon composite may comprise 80% by weight to 100% by weight, more specifically 85% by weight to 99% by weight, 90% by weight to 99% by weight, 95% by weight to 98% by weight, 95% by weight to 97% by weight, or 96% by weight, based on the total weight of the positive electrode active material layer.

[0119] In an embodiment of the present disclosure, the binder polymer may be used to hold the positive active material on the positive current collector and hold positive active material particles together to enhance bonding therebetween, and may include any known binder polymer in the corresponding technical field.

[0120] For example, the binder polymer may include one selected from the group consisting of: a fluororesin-based binder, including polyvinylidene fluoride (PVDF), a polyvinylidene fluoride-based polymer containing at least one vinylidene fluoride as a repeating unit, polytetrafluoroethylene (PTFE), or a mixture of two or more thereof; a rubber-based binder, including styrene-butadiene rubber (SBR), nitrile rubber, and styrene isoprene rubber; an acrylic-based binder; a cellulose-based binder, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; a polyol-based binder; a polyolefin-based binder, including polyethylene and polypropylene; a polyimide-based binder; a polyester-based binder; and a silane-based binder, or a mixture of two or more thereof or a copolymer of two or more thereof.

[0121] In an embodiment of the present disclosure, the amount of the binder may be 1% to 10% by weight of the total weight of the positive electrode active material layer. When the amount of the binder is less than the above range, the positive electrode may have poor physical properties, and the positive electrode active material and the conductive material may fall off. When the amount of the binder is greater than the above range, the battery capacity may decrease due to a small ratio of the positive electrode active material and the conductive material in the positive electrode. Therefore, it is preferable to determine the optimal amount within the above range.

[0122] In one embodiment of the present disclosure, the conductive material is a material that electrically connects the electrolyte to the positive electrode active material and serves as a movement path for electrons from the current collector to the positive electrode active material, and may include but is not limited to any conductive material that is an electrode component that is physically different from the carbon contained in the sulfur-carbon composite.

[0123] The conductive material includes, for example, carbon black, such as Super-P, Danka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon black; carbon derivatives, such as carbon nanotubes or fullerenes; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as fluorocarbons, aluminum and nickel powders; or conductive polymers, such as polyaniline, polythiophene, polyacetylene and polypyrrole, which can be used alone or in combination.

[0124] In an embodiment of the present disclosure, the amount of the conductive material may be 1% to 10% by weight of the total weight of the positive electrode active material. When the amount of the conductive material is less than the above range, the voltage and capacity may decrease due to slow electron transfer between the positive electrode active material and the current collector. On the contrary, when the amount of the conductive material is greater than the above range, the total energy (charge) of the battery may decrease due to the low ratio of the positive electrode active material, so it is preferred to determine the optimal amount within the above range.

[0125] In an embodiment of the present disclosure, the separator may be used to separate or insulate the positive electrode from the negative electrode and to transport lithium ions between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material and may include, but is not limited to, any separator commonly used in lithium secondary batteries. The separator may be an independent element such as a membrane, or a coating added to the positive electrode and / or the negative electrode.

[0126] The separator may preferably have low resistance to electrolyte ion migration and high wettability by the electrolyte.

[0127] In an embodiment of the present disclosure, the separator may include a porous substrate, and the porous substrate may include any porous substrate commonly used in secondary batteries, and the porous polymer film may be used alone or in a stack, and for example, the porous substrate may include a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber or a polyolefin-based porous film, but is not limited thereto.

[0128] The porous substrate is not limited to the specific materials in the present disclosure and may include any porous substrate commonly used in electrochemical devices. For example, the porous substrate may include at least one selected from the group consisting of polyolefins such as polyethylene or polypropylene, polyesters such as polyethylene terephthalate or polybutylene terephthalate, polyamides, polyacetals, polycarbonates, polyimides, polyetheretherketones, polyethersulfones, polyphenylene oxides, polyphenylene sulfides, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, poly(p-phenylene)benzobisoxazole, and polyarylates.

[0129] In the embodiment of the present disclosure, the porous substrate is not limited to a specific thickness, but the thickness of the porous substrate may be in the range of 1 μm to 100 μm, and preferably in the range of 5 μm to 50 μm. The thickness range of the porous substrate is not limited to the above range, but when the thickness is too less than the above lower limit, the separator may be easily damaged during use of the battery due to poor mechanical properties.

[0130] In the embodiment of the present disclosure, the porous substrate is not limited to a specific average pore diameter and porosity, but the average pore diameter may be in the range of 0.001 μm to 50 μm, and the porosity may be in the range of 10 vol % to 95 vol %.

[0131] In an embodiment of the present disclosure, the separator may further include a porous coating layer on at least one surface of the porous substrate, the porous coating layer including inorganic particles and a binder.

[0132] In one embodiment of the present disclosure, the inorganic particles and the binder contained in the porous coating layer may include those commonly used in the porous coating layer of a separator, and they are not limited to a specific manufacturing method.

[0133] Hereinafter, the present disclosure will be described in more detail through examples, but the following examples are provided to describe the present disclosure by way of illustration, and the scope of the present disclosure is not limited thereto.

[0134] Example 1

[0135] <Manufacturing of negative electrode>

[0136] A substrate having a thickness of 60 μm and a polyethylene lattice structure was prepared. In this case, the polyethylene line width in the polyethylene lattice structure was 30 μm, the polyethylene line spacing was 135 μm, and the unit area weight of the polyethylene lattice structure was 1.209 mg / cm 2 .

[0137] A 60 μm thick lithium metal foil was stacked on one surface of the substrate and the stack was rolled using a roller press to fill the polyethylene lattice structure with lithium metal.

[0138] <Manufacturing of Secondary Batteries>

[0139] Inorganic sulfur (S8) and carbon nanotubes (CNTs) as positive electrode active materials were mixed to prepare a sulfur-carbon composite (sulfur:SWCNT weight ratio = 75:25), and 96.0 wt% of the prepared sulfur-carbon composite and 4.0 wt% of polyacrylate (PAA) as a binder polymer were mixed to prepare a positive electrode slurry composition. The positive electrode slurry composition was coated on an aluminum current collector and dried to manufacture a positive electrode. The loading capacity of the manufactured positive electrode was 3.5 mAh / cm 2 .

[0140] The positive electrode and the negative electrode were placed with a polyethylene separator having a thickness of 16 μm and a porosity of 68 volume % interposed therebetween to prepare an electrode assembly.

[0141] The electrode assembly thus prepared was placed in a pouch-type case and injected with an electrolyte to fabricate a lithium-sulfur battery, in which 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt % lithium nitrate (LiNO3) were dissolved in a solvent containing 1,3-dioxolane (DOL) and dimethyl ether (DME) in a volume ratio of 1:1.

[0142] Example 2

[0143] A lithium-sulfur battery was fabricated by the same method as in Example 1, except that 30 μm-thick lithium metal foils were stacked on both surfaces of the polyethylene lattice structure and pressed.

[0144] Comparative Example 1

[0145] A lithium-sulfur battery was manufactured by the same method as in Example 1, except that a 60 μm thick lithium metal foil was used as the negative electrode.

[0146] Comparative Example 2

[0147] A lithium-sulfur battery was manufactured by the same method as in Example 1, except that a 30 μm-thick lithium metal foil was laminated on each of both surfaces of a 10 μm-thick copper current collector and used as a negative electrode.

[0148] Comparative Example 3

[0149] A lithium-sulfur battery was manufactured by the same method as in Example 1, except that a 30 μm thick lithium metal foil was laminated on each of both surfaces of a polyethylene nonwoven fabric having a thickness of 60 μm and a porosity of 80% and used as a negative electrode.

[0150] Comparative Example 4

[0151] A lithium-sulfur battery was manufactured by the same method as in Example 1, except that polyimide was used as the substrate of the negative electrode instead of polyethylene.

[0152] Comparative Example 5

[0153] A 60-μm-thick polyethylene porous polymer substrate with a lattice structure of 30-μm line width and 72-μm line spacing was prepared. A 60-μm-thick lithium metal foil was stacked on one surface of the substrate. This stack was rolled using a roller press. However, the lithium metal did not fill the porous polymer substrate, and the substrate was damaged. This is because the narrow line spacing of the substrate makes it difficult to embed the lithium metal.

[0154] Experimental Example 1: Tensile Strength Test

[0155] The measurement results of the tensile strength of the negative electrodes used in Example 1 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0156]

[0157] The tensile strength was measured for each sample using a universal testing machine (UTM) and a 20 N load cell, and the measurement condition was a single strain rate of 0.01 / s (18 mm / min).

[0158] Referring to Table 1, the measured tensile strength of the negative electrode used in Example 1 is at least 30 times greater than the measured tensile strength of the negative electrode of Comparative Example 1 using only lithium metal as the negative electrode. Therefore, it was confirmed that the negative electrode according to the present disclosure has high mechanical strength and high manufacturing process efficiency.

[0159] On the other hand, the measured tensile strength of the negative electrode used in Example 1 was lower than that of the negative electrode used in Comparative Example 2. However, the tensile strength of the negative electrode used in Example 1 was high enough to achieve sufficient manufacturing process efficiency. In addition, a copper current collector was used in Comparative Example 2, and since the copper current collector weighed 5.4 mg / cm 2 , the energy density of the lithium-sulfur battery of Comparative Example 2 is significantly reduced. On the contrary, because the porous polymer substrate of the negative electrode used in Example 1 is as light as 1.209 mg / cm 2 , so it achieves sufficient mechanical strength and high energy density of lithium-sulfur batteries.

[0160] Experimental Example 2: Cycle Life and Coulombic Efficiency Test

[0161] The lithium-sulfur batteries according to Examples 1 and 2 and Comparative Examples 1 to 4 were cycled in CC mode at 0.2 C charge and 0.3 C discharge at 25° C. In this case, the upper and lower limits of charge and discharge were set to 2.5 V and 1.8 V, respectively.

[0162] in addition, Figure 4 and Figure 5 The results of measuring cycle life and coulombic efficiency are shown in FIG.

[0163] refer to Figure 4 and 5 , confirming that the lithium-sulfur batteries according to Examples 1 and 2 have the longest cycle life and the highest coulombic efficiency.

[0164] It was confirmed that Examples 1 and 2 including the porous polymer substrate improved the cycle life while maintaining the coulombic efficiency, compared to Comparative Example 1 using a lithium metal foil as the negative electrode.

[0165] It was confirmed that Examples 1 and 2 were superior in coulombic efficiency and cycle life compared to Comparative Example 2 using a copper current collector as the negative electrode.

[0166] It was confirmed that Examples 1 and 2 were superior in cycle life and coulombic efficiency compared to Comparative Example 3 using a polyethylene nonwoven fabric having a non-fixed structure.

[0167] The lithium-sulfur batteries of Examples 1 and 2 were found to be significantly superior in cycle life and coulombic efficiency compared to Comparative Example 4, which used polyimide as the porous polymer substrate. This is because the reaction between polyimide and lithium metal causes the negative electrode to deteriorate more rapidly.

[0168] Experimental Example 3: Negative electrode thickness increase test

[0169] Three lithium-sulfur batteries according to each of Example 1 and Comparative Example 1 were prepared and cycled for 75 cycles at 0.2C charge and 0.3C discharge in CC mode at 25°C. In this case, the upper and lower limits of charge and discharge were 2.5V and 1.8V. Subsequently, each battery was disassembled, and the thickness of the negative electrode was measured using a thickness gauge (Mitutoyo, VL-50S-B), and the measurement results are shown in FIG. Figure 6 middle.

[0170] refer to Figure 6 It was confirmed that the lithium metal foil of Comparative Example 1 had a greater negative electrode thickness increase rate than the negative electrode of Example 1.

[0171] Although the present disclosure has been described above with respect to a limited number of embodiments and drawings, the disclosure is not limited thereto, and it will be apparent to those skilled in the art that various modifications and changes may be made thereto within the technical aspects of the disclosure and the scope of the appended claims and their equivalents.

Claims

1. A negative electrode for a secondary battery, comprising: Porous polymer substrate and negative electrode active material, wherein the porous polymer substrate has a lattice structure comprising line portions and opening portions, wherein all or at least a portion of each opening of the porous polymer substrate is filled with the negative electrode active material, and The negative electrode active material comprises at least one of lithium metal and lithium alloy.

2. The negative electrode for a secondary battery according to claim 1, The negative electrode for a secondary battery is a self-standing type having no current collector.

3. The negative electrode for a secondary battery according to claim 1, The line spacing of the line portion of the porous polymer substrate is between 80 μm and 400 μm.

4. The negative electrode for a secondary battery according to claim 1, The line width of the line portion of the porous polymer substrate is between 10 μm and 40 μm.

5. The negative electrode for a secondary battery according to claim 1, The lattice structure has a fixed structure with a constant spacing between the line portions.

6. The secondary battery negative electrode according to claim 1, The thickness of the porous polymer substrate is in the range of 20 μm to 100 μm.

7. The negative electrode for a secondary battery according to claim 1, The porous polymer substrate comprises polyester, polyolefin, polyethylene terephthalate or a mixture thereof.

8. The negative electrode for a secondary battery according to claim 1, The negative electrode includes the negative electrode active material loaded into 90 volume % or more of the openings based on the total volume of the openings of the porous polymer substrate.

9. The negative electrode for a secondary battery according to claim 1, At least a portion of the line portion is exposed to the outside on one surface or both surfaces of the negative electrode.

10. The negative electrode for a secondary battery according to claim 1, The porous polymer substrate is embedded in the negative electrode active material.

11. The secondary battery negative electrode according to claim 1, The line portion is not exposed on one surface of the negative electrode, and the line portion is completely or partially exposed on the opposite surface of the negative electrode.

12. The negative electrode for a secondary battery according to claim 1, At least a portion of the porous polymer substrate is contained in the negative electrode active material.

13. The secondary battery negative electrode according to claim 1, wherein 80 wt % or more of the porous polymer substrate is contained in the negative electrode active material.

14. A secondary battery comprising: a positive electrode; a negative electrode; and a separator interposed between the positive electrode and the negative electrode, wherein the negative electrode is defined in any one of claims 1 to 13, and The positive electrode contains sulfur as a positive electrode active material.

15. The secondary battery according to claim 14, The positive electrode comprises a sulfur-carbon composite as the positive electrode active material.

16. The secondary battery according to claim 14, The secondary battery is a lithium-sulfur battery.

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