Anode for secondary battery and secondary battery including same

Abstract

An anode for a secondary battery according to the present invention comprises a porous polymer substrate and an anode active material supported in the porous polymer substrate. The porous polymer substrate has a grid structure including line portions and opening portions. Each of the opening portions of the porous polymer substrate is entirely or at least partially filled with the anode active material. The anode active material includes at least one of a lithium metal or a lithium alloy. The anode for a secondary battery comprises a porous polymer substrate having a grid structure, and thus has excellent mechanical strength and can suppress the formation of dendrites on the anode and volume expansion of the anode during charging / discharging.

Description

Negative electrode for secondary battery and secondary battery including same

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

[0002] This application claims priority to Korean Application No. 10-2023-0124313, filed September 18, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential and low self-discharge rate, are commercialized.

[0004] Lithium metal secondary batteries were the first commercialized lithium secondary batteries, and they use lithium metal as the anode. However, lithium metal secondary batteries suffered from volume expansion of the cell due to lithium dendrites forming on the surface of the lithium metal anode, a gradual decrease in capacity and energy density, short circuits caused by the continuous growth of dendrites, a decrease in cycle life, and cell stability issues (explosion and ignition). Therefore, production of lithium metal secondary batteries was discontinued after only a few years of commercialization. Therefore, carbon-based anodes, which are more stable and can stably store lithium in an ionic state within lattices or voids, were used instead of lithium metal, and the use of these carbon-based anodes led to the full-scale commercialization and popularization of lithium secondary batteries.

[0005] To date, lithium secondary batteries have primarily utilized carbon-based or non-carbon-based anode materials, with most anode material development focused on carbon-based (graphite, hard carbon, soft carbon, etc.) and non-carbon-based (silicon, tin, titanium oxide, etc.) materials. However, carbon-based materials have theoretical capacities below 400 mAh / g, while non-carbon-based materials, while exceeding 1,000 mAh / g, suffer from volume expansion and performance degradation during charge and discharge.

[0006] Meanwhile, with the recent activation of medium and large-sized lithium secondary batteries, high capacity and high energy density characteristics are required, but existing carbon-based or non-carbon-based negative electrode materials have limitations in meeting these performance requirements.

[0007] Accordingly, active research is underway to reuse lithium metal, such as in lithium-air batteries, and interest in lithium metal secondary batteries is growing again. Lithium is extremely lightweight and has the potential to achieve excellent energy densities, exceeding a theoretical capacity of 3,800 mAh / g.

[0008] However, applying lithium metal as an anode material for secondary batteries presents challenges. First, unlike graphite-based anode materials, lithium metal anodes undergo an electrochemical reaction in which lithium ions released from the anode are converted into neutral lithium through electrons transferred from the external conductor. This electrochemical reaction easily leads to the formation of highly irregular lithium clumps, often in the form of dendrites, on the surface of the lithium during charging. This uneven surface expands the overall volume, and during discharge, ions often dissociate directly from the lithium metal rather than being selectively separated from the lithium dendrites. Consequently, over a series of charge and discharge cycles, the surface of the lithium metal anode not only experiences extreme volume changes, but also develops an irregular and complex morphology within the formed dendrites. This complex surface pattern is not stable during cycling, constantly repeating the cycles of formation and disappearance, resulting in a highly irregular cycle life. In addition, the lithium dendrite formed during discharge may dissociate and fall off entirely into the electrolyte region, or the dendrite may continue to grow vertically, penetrate the separator, and contact the positive electrode surface on the opposite side directly or indirectly, causing a short circuit.

[0009] Furthermore, because lithium metal has low mechanical strength, manufacturing freestanding lithium metal anodes without a separate current collector often results in defective anodes during the manufacturing process. To address this shortcoming, attempts have been made to laminate lithium metal foil onto the current collector. However, this method significantly reduces the energy density of the battery due to the weight of the current collector.

[0010] The present invention solves the above-described problem and provides a negative electrode for a secondary battery having excellent mechanical strength.

[0011] In addition, the present invention provides a secondary battery having improved life characteristics and high energy density by applying the negative electrode to the secondary battery.

[0012] In order to solve the above problem, in one aspect of the present invention, a negative electrode for a secondary battery and a secondary battery of the following embodiments are provided.

[0013] The negative electrode for a secondary battery according to the first embodiment is

[0014] In a negative electrode for a secondary battery including a porous polymer substrate and a negative electrode active material,

[0015] The above porous polymer substrate has a lattice structure including a wire portion and an opening portion,

[0016] Each opening of the above porous polymer substrate is completely or at least partially filled with a negative electrode active material,

[0017] The above negative active material is characterized by including at least one of a lithium metal and a lithium alloy.

[0018] According to the second embodiment, in the first embodiment,

[0019] The above secondary battery negative electrode may be a freestanding type that does not have a separate current collector.

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

[0021] The above porous polymer substrate may have a line spacing of 80 µm to 400 µm.

[0022] According to the fourth embodiment, in any one of the first to third embodiments,

[0023] The above porous polymer substrate may have a line width of 10 µm to 40 µm.

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

[0025] The above grid structure may be a regular structure with a constant spacing between wires.

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

[0027] The thickness of the above porous polymer substrate may be 20 µm to 100 µm.

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

[0029] The porous polymer substrate may include polyester, polyolefin, polyethylene terephthalate or a mixture thereof.

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

[0031] The above negative electrode may be one in which the negative electrode active material is supported in at least 90 vol% of the opening of the porous polymer substrate relative to the total volume of the opening.

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

[0033] The cathode may have at least a portion of the wire portion exposed to the outside on one or both surfaces.

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

[0035] The above porous polymer substrate may be embedded in a negative electrode active material.

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

[0037] The wire portion may not be exposed on one side of the cathode, and the wire portion may be exposed entirely or partially on the other side.

[0038] According to the 12th embodiment, in the first to eighth embodiments, at least a portion of the porous polymer substrate may be included in the negative electrode active material.

[0039] According to the 13th embodiment, in the first to eighth embodiments,

[0040] More than 80 wt% of the above porous polymer substrate may be included in the negative electrode active material.

[0041] The secondary battery according to the 14th embodiment,

[0042] A secondary battery comprising a positive electrode; a negative electrode; and a separator positioned between the positive electrode and the negative electrode,

[0043] The above cathode is a cathode according to any one of the first to thirteenth embodiments,

[0044] The above positive electrode is characterized in that it contains sulfur as a positive electrode active material.

[0045] According to the 15th embodiment, in the 14th embodiment,

[0046] The above positive electrode may include a sulfur-carbon complex as a positive electrode active material.

[0047] According to the 16th embodiment, in the 14th embodiment or the 15th embodiment,

[0048] The above secondary battery may be a lithium-sulfur battery.

[0049] According to one aspect of the present invention, a negative electrode for a secondary battery is a free-standing type that does not include a separate current collector, and a secondary battery including the negative electrode for a secondary battery can have a high energy density.

[0050] According to one aspect of the present invention, a secondary battery anode comprises an anode active material contained within a porous polymer matrix, thereby exhibiting superior mechanical strength. Therefore, volume changes in the secondary battery anode can be suppressed, and dendrite growth and uneven lithium release from the anode during charge and discharge can be suppressed. Furthermore, during the anode manufacturing process, the porous polymer supports the anode active material, thereby improving the manufacturing processability.

[0051] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the matters described in these drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation.

[0052] Figure 1 is a schematic diagram of a porous polymer substrate according to one embodiment of the present invention.

[0053] Figure 2 is a schematic diagram of a cross-section of a negative electrode for a secondary battery according to one embodiment of the present invention.

[0054] Figure 3a is a schematic diagram illustrating a method for manufacturing a negative electrode for a secondary battery according to one embodiment of the present invention.

[0055] Figure 3b is a schematic diagram illustrating a method for manufacturing a negative electrode for a secondary battery according to one embodiment of the present invention.

[0056] Figure 3c is a schematic diagram illustrating a method for manufacturing a negative electrode for a secondary battery according to one embodiment of the present invention.

[0057] Figure 4 shows the cycle life of a lithium-sulfur battery according to one embodiment and a comparative example of the present invention.

[0058] Figure 5 shows the coulombic efficiency of a lithium-sulfur battery according to one embodiment and a comparative example of the present invention.

[0059] Figure 6 shows the increase rate in thickness of a negative electrode obtained from a lithium-sulfur battery according to one embodiment and a comparative example of the present invention.

[0060] Hereinafter, the present invention will be described in detail with reference to the drawings. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted in the sense and concept consistent with the technical spirit of the present invention.

[0061] Accordingly, the embodiments described in this specification and the configurations described in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that there may be various equivalents and modified examples that can replace them at the time of filing this application.

[0062] Additionally, throughout the specification, whenever a part is said to “include,” “comprise,” “have,” or “have” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0063] Throughout this specification, references to 'A and / or B' mean 'A or B or both.'

[0064] Unless otherwise specified throughout this specification, temperature refers to Celsius temperature, and the unit is ℃.

[0065]

[0066] According to one aspect of the present invention, a negative electrode for a secondary battery comprises:

[0067] A secondary battery negative electrode comprising a porous polymer substrate and a negative electrode active material,

[0068] The above porous polymer substrate has a lattice structure including a wire portion and an opening portion,

[0069] Each opening of the above porous polymer substrate is completely or at least partially filled with a negative electrode active material,

[0070] The above negative active material is characterized by including at least one of a lithium metal and a lithium alloy.

[0071]

[0072] Previously, lithium metal was used as an anode, but the problems included significant volume changes during charge / discharge processes, uneven lithium deposition, and severe dendrite formation. Furthermore, the weak mechanical strength of lithium metal during the anode manufacturing process led to poor processability.

[0073] However, the negative electrode for a secondary battery according to the present invention is one in which the negative electrode active material is filled in the openings of a porous polymer substrate having a lattice structure. Therefore, since the porous polymer substrate having a lattice structure supports the negative electrode active material, excellent processability can be secured even when lithium metal and / or lithium alloy having low mechanical rigidity is used as the negative electrode active material. In addition, since the porous polymer substrate suppresses volume change of the lithium metal and / or lithium alloy and enables lithium to be uniformly deposited, the life characteristics of the negative electrode can be improved.

[0074]

[0075] In one embodiment of the present invention, the negative electrode for a secondary battery may be a free-standing type that does not have a separate current collector, i.e., the negative electrode active material layer is not supported by a current collector and the negative electrode is composed only of the negative electrode active material layer. A secondary battery using a free-standing type negative electrode may have a high energy density.

[0076]

[0077] The porous polymer substrate according to the present invention has a lattice structure comprising a wire section and an opening. As used herein, the wire section refers to the lattice portion of the porous polymer substrate, which corresponds to the skeleton of the porous polymer substrate. The opening section refers to the empty space between the wire sections. The porous polymer substrate has a structure that extends from one side to the other with the opening interposed therebetween.

[0078] Fig. 1 is a schematic diagram of a porous polymer substrate (11) according to the present invention. Referring to Fig. 1, the porous polymer substrate (11) is a lattice structure including a polymeric wire portion (111) and an opening portion (112) which is an empty space between the wire portions.

[0079]

[0080] In one embodiment of the present invention, the line spacing of the wire portion of the porous polymer substrate can be 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 wire portion falls within the above range, the negative active material can be smoothly supported in the opening of the porous polymer substrate, and the porous polymer can secure sufficient mechanical strength.

[0081] The line spacing of the above wire sections may mean the shortest distance between adjacent wire sections arranged in parallel.

[0082]

[0083] In one embodiment of the present invention, the line width of the wire portion of the porous polymer substrate can be 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 wire portion falls within the above range, the mechanical strength of the porous polymer substrate can be sufficiently secured, the negative electrode active material contained within the porous polymer substrate can be sufficiently supported, and the volume change of the negative electrode active material occurring during the charge and discharge process can be suppressed.

[0084]

[0085] In one embodiment of the present invention, the lattice structure of the porous polymer substrate may be a regular structure. The regular structure does not mean that the line spacing between the wire portions is the same, but may mean that the line spacing between the wire portions has a certain range.

[0086] For example, the spacing between the wires may mean that the spacing between the wires is within 20%, within 15%, within 10%, within 5%, or within 3% of the average value of the spacing between all wires. Here, the spacing between the wires can be confirmed by taking an SEM image, and the spacing between 10 or 20 different wires can be confirmed and the average value thereof can be used as the average value of the spacing between all wires.

[0087] When the line spacing between the above-mentioned wire portions falls within the above-mentioned range, the porous polymer substrate can uniformly support the negative electrode active material being filled in various directions. As a result, the volume expansion of the negative electrode active material can be uniformly suppressed in various directions, and the formation of dendrites on the surface of the negative electrode active material can also be uniformly suppressed.

[0088]

[0089] In one embodiment of the present invention, the porous substrate has a weight per unit area of ​​0.2 mg / cm 2 2.5 mg / cm2 When the weight per unit area of ​​the porous substrate falls within the above range, the mechanical strength of the negative electrode can be secured while sufficiently securing the energy density of the secondary battery including the negative electrode.

[0090]

[0091] In one embodiment of the present invention, the thickness of the porous polymer substrate may be 20 μm to 100 μm. When the thickness of the porous polymer substrate falls within the above range, the negative electrode active material can be sufficiently filled into the openings of the porous polymer substrate, thereby ensuring sufficient negative electrode capacity and sufficient mechanical strength of the negative electrode.

[0092]

[0093] In one embodiment of the present invention, the porous polymer substrate may be one that does not physically and chemically react with lithium metal and / or a lithium alloy. For example, the porous polymer substrate may include polyester, polyolefin, polyethylene terephthalate, or a mixture thereof. Specifically, the polyolefin may include polyethylene, polypropylene, polybutene, polypentene, polymethylpentene, polybutene-1, polyolefin elastomer polyisobutylene, or a mixture thereof.

[0094]

[0095] In one embodiment of the present invention, with respect to the total volume of the openings of the porous polymer substrate, the negative electrode active material may be supported in 90 vol% or more, 95 vol% or more, or 98 vol% or more of the openings, and the openings may be filled with 100 vol% of the negative electrode active material. Since the porous polymer substrate in the present invention supports the negative electrode active material, the greater the amount of the negative electrode active material filled in the openings of the porous polymer substrate, the higher the energy density of the secondary battery including the negative electrode according to the present invention.

[0096]

[0097] The negative electrode for a secondary battery according to the present invention may be formed by laminating a porous polymer substrate and a negative electrode active material layer on at least one side of the porous polymer substrate, and pressing the laminate.

[0098] In addition, the negative electrode for a secondary battery formed by pressing the above laminate may have a porous polymer substrate embedded in a negative electrode active material.

[0099] For example, the negative electrode active material may be filled in the opening of the porous polymer substrate, and the outside of the porous polymer substrate may also be completely covered with the negative electrode active material. In addition, the negative electrode for a secondary battery formed by pressing the laminate may have at least a portion of the wire portion exposed to the outside on one surface or both surfaces of the porous polymer substrate. For example, the wire portion of the porous polymer substrate may not be exposed on one side, and the wire portion may be exposed entirely or partially on the opposite side. Preferably, the entire porous polymer substrate is not exposed to the outside, but is buried in the negative electrode active material. When the entire surface of the negative electrode is made of the negative electrode active material, lithium is smoothly desorbed from the negative electrode and inserted into the negative electrode in a secondary battery including the negative electrode according to the present invention.

[0100] That is, the negative electrode for the secondary battery may include a negative electrode active material and a porous polymer substrate at least partially contained within the negative electrode active material. In other words, at least a portion of the porous polymer substrate may be contained within the negative electrode active material.

[0101] In one embodiment of the present invention, 80 wt% or more, 85 wt% or more, 90 wt% or more, or 95 wt% or more of the porous polymer substrate may be included in the negative electrode active material. Preferably, the porous polymer substrate may be entirely included in the negative electrode active material.

[0102]

[0103] Figure 2 is a schematic cross-section of a negative electrode (10) for a secondary battery according to the present invention. Referring to Figure 2, the porous polymer substrate (11) is completely embedded within the negative electrode active material (12). That is, the porous polymer substrate (11) is completely covered with the negative electrode active material (12).

[0104]

[0105] In one embodiment of the present invention, 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).

[0106]

[0107] A method for manufacturing a negative electrode for a secondary battery according to one aspect of the present invention is as follows:

[0108] The method may include: preparing a porous polymer substrate; laminating a negative electrode active material layer on at least one side of the porous polymer substrate; and pressing the laminate. The negative electrode active material layer may include at least one of lithium metal and a lithium alloy, and preferably may be a lithium metal thin film.

[0109] The above pressing step may include rolling with a roll press.

[0110] The above lamination step may be performed by, for example, laminating and pressing a lithium metal thin film on one side of a porous polymer substrate, or by laminating and pressing a lithium metal thin film on both sides of a porous polymer substrate.

[0111]

[0112] FIGS. 3A to 3C are schematic diagrams illustrating a method for manufacturing a negative electrode for a secondary battery according to an embodiment of the present invention. Referring to FIGS. 3A to 3C, as illustrated in FIG. 3A, a negative electrode active material (12) is positioned above and below a porous polymer substrate (11), and as illustrated in FIG. 3B, the negative electrode active material (12) is pressed from both the upper and lower sides of the porous polymer substrate (11) to compress the porous polymer substrate (11) and the negative electrode active material (12), thereby manufacturing a negative electrode (10) for a secondary battery according to the present invention, as illustrated in FIG. 3C.

[0113] The above drawing 3c is intended to show that the porous polymer substrate is completely covered by the negative electrode active material, so that there is no portion of the porous polymer substrate protruding outside the negative electrode active material, and does not actually mean that the porous polymer substrate is projected into the negative electrode active material.

[0114]

[0115] A secondary battery according to one aspect of the present invention is a secondary battery including a positive electrode; a negative electrode; and a separator positioned between the positive electrode and the negative electrode, wherein the negative electrode may include the negative electrode for a secondary battery described above.

[0116]

[0117] In one embodiment of the present invention, the secondary battery may be a lithium-sulfur battery.

[0118]

[0119] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer applied to one or both surfaces of the positive electrode current collector.

[0120] The above-mentioned positive electrode current collector supports the positive electrode active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0121] The above positive electrode current collector can form fine irregularities on its surface to strengthen the bonding strength with the positive electrode active material, and can be used in various forms such as a film, sheet, foil, mesh, net, porous body, foam, and non-woven fabric.

[0122]

[0123] The above positive electrode active material layer includes a positive electrode active material and a binder polymer, and may optionally further include a conductive material and / or additive.

[0124] The above positive electrode active material may include sulfur (S). In the present specification, a compound including the sulfur is referred to as a "sulfur-based compound." The sulfur-based compound may include, for example, all sulfur-containing compounds that can be formed through a reduction reaction of inorganic sulfur (S8) or an oxidation reaction of lithium sulfide (Li2S), and more specifically, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, an integer of 2 ≤ x ≤ 8), disulfide compounds, and carbon-sulfur polymers ((C2S y ) n , y = 2.5 to 50, n≥2), lithium sulfide (Li2S), or two or more thereof.

[0125] The above positive electrode active material may preferably be a sulfur-carbon composite. The sulfur-carbon composite 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 exterior surface of the porous carbon material.

[0126] In one embodiment of the present invention, the porous carbon material is used to support a sulfur-based compound as a positive electrode active material, and to provide a framework in which the sulfur-based compound can be uniformly and stably fixed, while improving the conductivity of the positive electrode. Any porous carbon material can be used without particular limitation in its type.

[0127] The above porous carbon material can generally be manufactured by carbonizing precursors of various carbon materials. The porous carbon material includes pores that are not regular therein, and the average diameter of the pores ranges from 1 to 200 nm, and the porosity can range from 10 to 90 volume% of the total volume of the porous carbon material. If the average diameter of the pores is less than the above range, the pore size is only at the molecular level, making sulfur impregnation impossible. Conversely, if it exceeds the above range, the mechanical strength of the porous carbon material is weakened, making it undesirable for application to the electrode manufacturing process.

[0128] The above 'average pore diameter' can be measured according to a method known 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 may be measured according to a scanning electron microscope (SEM), a field emission electron microscope (laser diffraction method), a laser diffraction method, or the BET (Brunauer-Emmett-Teller) method. The measurement using the laser diffraction method may be performed using, for example, a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000). In addition, the measurement according to the BET method may be performed using, for example, an analyzer of the BELSORP series of BEL Japan Co., Ltd., but is not limited thereto.

[0129] The above 'porosity' refers to the ratio of the volume occupied by pores to the total volume of a structure, and uses % as its unit, and can be used interchangeably with terms such as porosity and porosity. In the present invention, the measurement of the porosity is not particularly limited, and according to one embodiment of the present invention, for example, it can be measured according to the BET method using nitrogen gas or the mercury penetration method (Hg porosimeter) and ASTM D2873.

[0130] The shape of the above porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular or bulk-shaped, and can be used without limitation as long as it is a shape commonly used in lithium-sulfur batteries.

[0131] The porous carbon material may be any material commonly used in the art that has a porous structure or a high specific surface area. For example, the porous carbon material may be at least one selected from the group consisting of graphite; graphene; carbon black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); and graphite and activated carbon such as natural graphite, artificial graphite, and expanded graphite, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

[0132] The method for manufacturing the above sulfur-carbon composite is not particularly limited in the present invention, and any method commonly used in the art may be used. For example, a method may be used in which the sulfur and porous carbon material are simply mixed and then heat-treated to form a composite.

[0133] In addition to the composition described above, the positive electrode active material may further include one or more selected from among transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur.

[0134] The above transition metal elements 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, etc., the above group IIIA elements include Al, Ga, In, Ti, etc., and the above group IVA elements may include Ge, Sn, Pb, etc.

[0135] The sulfur-carbon complex may be at least 50 wt% based on the total weight of the positive electrode. Specifically, the sulfur-carbon complex may be at least 80 wt%, at least 90 wt%, or at least 95 wt% based on the total weight of the positive electrode active material layer. Specifically, the sulfur-carbon complex may be included 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%, or 95 wt% to 97 wt%, or 96 wt% based on the total weight of the positive electrode active material layer.

[0136]

[0137] In one embodiment of the present invention, the binder polymer maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to further increase the bonding strength between them, and any binder polymer known in the art can be used.

[0138] For example, the binder polymer may be a fluororesin binder including polyvinylidene fluoride (PVdF), a polyvinylidene fluoride polymer including at least one vinylidene fluoride as a repeating unit, polytetrafluoroethylene (PTFE), or a mixture of two or more thereof; a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butidiene rubber, or styrene-isoprene rubber; an acrylic binder; a cellulose binder including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, or regenerated cellulose; a polyalcohol binder; a polyolefin binder including polyethylene or polypropylene; a polyimide binder; a polyester binder; and a silane-based binder; a mixture or copolymer of one or more selected from the group consisting of;

[0139] In one embodiment of the present invention, the content of the binder may be 1 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 deteriorate, causing the positive electrode active material and conductive material to fall off. If the content of the binder is more than the above range, the ratio of the positive electrode active material and conductive material in the positive electrode may relatively decrease, resulting in a decrease in battery capacity. Therefore, it is preferable to determine an appropriate content within the above-described range.

[0140]

[0141] In one embodiment of the present invention, the conductive material is a material that electrically connects the electrolyte and the positive electrode active material and serves as a path for electrons to move from the current collector to the positive electrode active material, and any conductive material that is physically distinct from the carbon contained in the sulfur-carbon complex and is a component of the electrode can be used without limitation.

[0142] 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, Summer 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 fluorocarbon, aluminum, or nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, or polypyrrole, which may be used alone or in combination.

[0143] In one embodiment of the present invention, the content of the conductive material may be 1 to 10 wt% based on the total weight of the positive electrode active material. If the content of the conductive material is less than the above range, electron transfer between the positive electrode active material and the current collector is not easy, resulting in a decrease in voltage and capacity. Conversely, if the content exceeds the above range, the proportion of the positive electrode active material may relatively decrease, thereby reducing the total energy (charge) of the battery. Therefore, it is preferable to determine an appropriate content within the above-mentioned range.

[0144]

[0145] In one embodiment of the present invention, the separator separates or insulates the positive and negative electrodes from each other and enables lithium ion transport between the positive and negative electrodes. The separator may be made of a porous non-conductive or insulating material, and may be used without special limitation as long as it is commonly used as a separator in a lithium secondary battery. The separator may be an independent member such as a film, or may be a coating layer added to the positive and / or negative electrodes.

[0146] It is preferable that the above separator have low resistance to ion movement of the electrolyte and excellent moisture absorption capacity for the electrolyte.

[0147] In one embodiment of the present invention, the separator may include a porous substrate, and any porous substrate typically used in secondary batteries may be used as the porous substrate, and a porous polymer film may be used alone or in a laminated manner. For example, a nonwoven fabric or a polyolefin porous film made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0148] 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 may be a polyolefin such as polyethylene, polypropylene, etc., a polyester such as polyethyleneterephthalate, polybutyleneterephthalate, polyamide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, It may include at least one material selected from the group consisting of poly(p-phenylene benzobisoxazole) and polyarylate.

[0149] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. The thickness range of the porous substrate is not limited to the above-mentioned range, but if the thickness is excessively thinner than the above-mentioned lower limit, the mechanical properties may deteriorate, and the separator may be easily damaged during battery use.

[0150] In one embodiment of the present invention, the average diameter and porosity of the pores present in the porous substrate are not particularly limited, but may be 0.001 to 50 ㎛ and 10 to 95 volume%, respectively.

[0151] 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 and including inorganic particles and a binder.

[0152] In one embodiment of the present invention, the inorganic particles and binder included in the porous coating layer may be used without particular limitation as long as they are commonly used in the porous coating layer of a separation membrane, and the manufacturing method thereof is also not particularly limited.

[0153]

[0154] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0155]

[0156] Example 1

[0157] <Manufacturing of the cathode>

[0158] A substrate having a thickness of 60 μm and formed with a lattice structure of polyethylene was prepared. At this time, the width of the polyethylene lines in the lattice structure of the polyethylene was 30 μm, the spacing between the polyethylene lines was 135 μm, and the weight per area of ​​the polyethylene lattice structure was 1.209 mg / cm. 2 It was used.

[0159] A 60 μm thick lithium metal film was laminated on one side of the above substrate. The laminate was rolled using a roll press to fill the lithium metal within the lattice structure of the polyethylene.

[0160]

[0161] <Manufacturing of secondary batteries>

[0162] As a cathode active material, inorganic sulfur (S8) and carbon nanotubes (CNT) were mixed to prepare a sulfur-carbon composite (weight ratio of sulfur:SWCNT = 75:25), and a cathode slurry composition was prepared by mixing 96.0 wt% of the prepared sulfur-carbon composite and 4.0 wt% of PAA (polyacrylate) as a binder polymer. The cathode slurry composition was applied to an aluminum current collector and then dried to prepare a cathode. The loading of the prepared cathode was 3.5 mAh / cm 2 It was.

[0163] An electrode assembly was prepared by positioning the positive and negative electrodes so that they face each other and interposing a polyethylene separator having a thickness of 16 ㎛ and a porosity of 68 vol% between them.

[0164] The prepared electrode assembly was stored in a pouch-type case, and a lithium-sulfur battery was manufactured by injecting an electrolyte solution containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt% lithium nitrate (LiNO3) dissolved in a solvent containing 1,3-dioxolane (DOL) and dimethyl ether (DME) in a volume ratio of 1:1.

[0165]

[0166] Example 2

[0167] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that a lithium metal film with a thickness of 30 μm was laminated on both sides of a polyethylene lattice structure and then pressed.

[0168]

[0169] Comparative Example 1

[0170] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that a lithium metal film with a thickness of 60 μm was used as the cathode.

[0171]

[0172] Comparative Example 2

[0173] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that a 30-μm-thick lithium metal film was laminated to each side of a 10-μm-thick copper current collector as the cathode.

[0174]

[0175] Comparative Example 3

[0176] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that a lithium metal film with a thickness of 30 μm was laminated to each side of a polyethylene nonwoven fabric with a thickness of 60 μm and a porosity of 80% as the cathode.

[0177]

[0178] Comparative Example 4

[0179] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that polyimide was used instead of polyethylene as the negative electrode material.

[0180]

[0181] Comparative Example 5

[0182] A polyethylene porous polymer substrate having a lattice structure with a thickness of 60 μm, a line width of 30 μm, and a line spacing of 72 μm was prepared. A 60 μm thick lithium metal thin film was laminated onto one side of the substrate. The laminate was rolled using a roll press. However, the lithium metal was not filled into the porous polymer substrate, and the substrate was destroyed. This is because the narrow line spacing of the substrate made it difficult to insert the lithium metal.

[0183]

[0184] Experimental Example 1: Tensile Strength Test

[0185] The results of measuring the tensile strength of the cathodes used in Example 1 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0186]

[0187] Tensile strength (MPa) Example 11.2 Comparative example 1313.8 Comparative example 236.6

[0188] The above tensile strength was measured using a UTM (universal testing machine) and a 20N load cell for each specimen, and the measurement conditions were a single strain rate of 0.01 / s (18 mm / min).

[0189] Referring to Table 1, the tensile strength of the negative electrode used in Example 1 was measured to be more than 30 times greater than that of the negative electrode of Comparative Example 1, which used only lithium metal as the negative electrode. Therefore, it was confirmed that the negative electrode according to the present invention has excellent mechanical strength and thus excellent manufacturing processability.

[0190] Meanwhile, the tensile strength of the negative electrode used in Example 1 was measured to be 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 at a level that could secure sufficient manufacturing processability. In addition, a copper current collector was used in Comparative Example 2, and the copper current collector had a density of 5.4 mg / cm. 2 The lithium-sulfur battery of Comparative Example 2 has a significant decrease in energy density because it is very heavy. On the other hand, the porous polymer substrate of the negative electrode used in Example 1 has a density of 1.209 mg / cm 2 Because it is very light, it can secure sufficient mechanical rigidity while also securing the energy density of a lithium-sulfur battery.

[0191]

[0192] Experimental Example 2: Cycle Life and Coulombic Efficiency Test

[0193] The lithium-sulfur batteries according to Examples 1 and 2 and Comparative Examples 1 to 4 were operated in CC mode with a cycle of 0.2C charging and 0.3C discharging at 25°C. At this time, the upper and lower limits of charging and discharging were set to 2.5 V and 1.8 V, respectively.

[0194] And, the results of measuring the cycle life and Coulomb efficiency are shown in Figs. 4 and 5.

[0195] Referring to FIGS. 4 and 5, it was confirmed that the lithium-sulfur batteries according to Examples 1 and 2 had the best cycle life and coulombic efficiency.

[0196] Compared to Comparative Example 1, which used a lithium metal thin film as a cathode, Examples 1 and 2, which introduced a porous polymer substrate, were confirmed to have improved cycle life while maintaining Coulombic efficiency.

[0197] Compared to Comparative Example 2, which used a copper current collector for the cathode, it was confirmed that both Examples 1 and 2 had excellent Coulombic efficiency and cycle life.

[0198] Compared to Comparative Example 3 using a polyethylene nonwoven fabric having an irregular structure, it was confirmed that Examples 1 and 2 had excellent cycle life and Coulomb efficiency.

[0199] Compared to Comparative Example 4, which used polyimide as a porous polymer substrate, it was confirmed that the lithium-sulfur battery and coulombic efficiency of Examples 1 and 2 were significantly superior. This is because the polyimide reacted with lithium metal, accelerating the deterioration of the negative electrode.

[0200]

[0201] Experimental Example 3: Cathode Thickness Increase Rate Test

[0202] Three lithium-sulfur batteries each according to Example 1 and Comparative Example 1 were prepared, and operated in CC mode for 75 cycles of 0.2C charging and 0.3C discharging at 25°C. At this time, the upper and lower limits of charging and discharging were 2.5 V and 1.8 V, respectively. Afterwards, 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. 6.

[0203] Referring to Fig. 6, it was confirmed that the increase rate of the thickness of the lithium metal thin film collected in Comparative Example 1 was significantly greater than that of the negative electrode collected in Example 1.

[0204]

[0205] As described above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. In a secondary battery negative electrode including a porous polymer substrate and a negative electrode active material, The above porous polymer substrate has a lattice structure including a wire portion and an opening portion, Each opening of the above porous polymer substrate is completely or at least partially filled with a negative electrode active material, A negative electrode for a secondary battery, characterized in that the negative active material comprises at least one of a lithium metal and a lithium alloy.

2. In paragraph 1, A secondary battery negative electrode characterized in that the above secondary battery negative electrode is of a freestanding type that does not have a separate current collector.

3. In paragraph 1, The above porous polymer substrate is a negative electrode for a secondary battery, characterized in that the line spacing of the wire portion is 80 ㎛ to 400 ㎛.

4. In paragraph 1, The above porous polymer substrate is a negative electrode for a secondary battery, characterized in that the wire portion has a wire width of 10 µm to 40 µm.

5. In paragraph 1, A negative electrode for a secondary battery, characterized in that the above grid structure is a regular structure in which the spacing between wire sections is constant.

6. A negative electrode for a secondary battery, characterized in that the thickness of the porous polymer substrate is 20㎛ to 100㎛.

7. In paragraph 1, A negative electrode for a secondary battery, characterized in that the porous polymer substrate comprises polyester, polyolefin, polyethylene terephthalate or a mixture thereof.

8. In paragraph 1, The negative electrode is a secondary battery negative electrode characterized in that the negative electrode active material is contained in 90 vol% or more of the total volume of the opening of the porous polymer substrate.

9. In paragraph 1, The above negative electrode is a negative electrode for a secondary battery, wherein at least a portion of the wire portion is exposed to the outside on one surface or both surfaces.

10. In paragraph 1, A negative electrode for a secondary battery, wherein the above porous polymer substrate is embedded in a negative electrode active material.

11. In paragraph 1, A secondary battery negative electrode, wherein the wire portion is not exposed on one side of the negative electrode, and the wire portion is exposed entirely or partially on the opposite side.

12. In paragraph 1, A negative electrode for a secondary battery, characterized in that at least a portion of the porous polymer substrate is included in the negative electrode active material.

13. In paragraph 1, A secondary battery negative electrode characterized in that 80 wt% or more of the porous polymer substrate is included in the negative electrode active material.

14. In a secondary battery including a positive electrode; a negative electrode; and a separator positioned between the positive electrode and the negative electrode, The above cathode is a cathode according to any one of claims 1 to 13, A secondary battery characterized in that the positive electrode contains sulfur as a positive electrode active material.

15. In paragraph 14, A secondary battery characterized in that the positive electrode includes a sulfur-carbon complex as a positive electrode active material.

16. In paragraph 14, A secondary battery characterized in that the secondary battery is a lithium-sulfur battery.

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