Lithium secondary battery electrode comprising a perforated current collector, method for manufacturing the same, and lithium secondary battery comprising the same

Abstract

Disclosed are an electrode for a lithium secondary battery including a perforated current collector, which enables active materials to be combined through the holes of the perforated current collector, while improving the energy density of the battery by reducing weight even if a wet process and a conductive material and a binder, which are necessary components of a conventional electrode mixture, are excluded, and a manufacturing method thereof, and a lithium secondary battery including the electrode. The electrode for a lithium secondary battery includes a first electrode active material layer; a second electrode active material layer; and a perforated current collector interposed between the first electrode active material layer and the second electrode active material layer, and is characterized in that the first electrode active material layer and the second electrode active material layer are combined through the holes of the current collector.

Description

TECHNICAL FIELD

[0001] This application claims the priority benefit of Korean Patent Application No. 10-2020-0037717, filed March 27, 2020, and Korean Patent Application No. 10-2020-0104338, filed August 20, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to an electrode for a lithium secondary battery comprising a perforated current collector, a method of manufacturing the electrode, and a lithium secondary battery comprising the electrode, and more particularly to an electrode for a lithium secondary battery comprising a perforated current collector, which is capable of allowing active materials to be combined through the pores of the perforated current collector, while improving the energy density of the battery due to weight reduction even though a wet process and a conductive material and a binder, which are necessary components of an existing electrode mixture, are excluded. BACKGROUND

[0003] Recently, there is an increasing interest in energy storage technology. As its application fields are expanding to the energy of mobile phones, camcorders, notebook computers, and even electric vehicles, efforts for research and development of electrochemical devices are being actively made. Electrochemical devices are the most notable field in this regard, in which the development of secondary batteries such as lithium-sulfur batteries, which can be charged / discharged, is the focus of attention. Recently, in developing these batteries, research and development for new types of electrodes and battery designs have been made to improve the capacity density and specific energy.

[0004] Among these electrochemical devices such as lithium secondary batteries, lithium-sulfur (Li-S) batteries, in which sulfur (S) is used as a positive electrode, have a high energy density, and thus are attracting attention as a next-generation secondary battery that can replace lithium-ion batteries. However, such lithium secondary batteries such as lithium-sulfur batteries include a conductive material and a binder in the positive electrode, and also include an active material, a conductive material, and a metal current collector, in which the positive electrode mixture including the binder is coated onto the metal current collector, thus inevitably increasing the weight, and this weight increase results in a decrease in the energy density of the battery.

[0005] In the prior art, as a solution to these problems, efforts have been made to reduce the weight of the current collector in the positive electrode structure. In other words, in order to reduce the weight of the current collector, the application of a thinner current collector than the existing current collector to the positive electrode has been studied. However, it is pointed out that there is a limit to reducing the thickness to the extent that the weight can be significantly reduced. In addition, cases in which the weight of the positive electrode or the battery is reduced by manufacturing a perforated metal current collector or a mesh-type current collector have also been reported, but it was found that it is difficult to increase the energy density of the battery using only these. In addition, when an electrode is manufactured by slurry coating, i.e., a wet method, using a perforated current collector, there is a problem in that slurry flows to the lower portion through the holes, and there is also a problem in that there is a limit in controlling the open area ratio or the slurry viscosity. In addition, when the electrode process is performed by slurry coating, i.e., a wet method, there are problems caused by moisture remaining in the electrode and a cost problem caused by the mixing, coating, and drying processes.

[0006] On the other hand, in the case of manufacturing an electrode by a dry method, there is a limit to the change in the type and content of the binder, and in order to manufacture a double-sided electrode, there is a problem in that the process becomes complicated, for example, a lamination process and a coating process for imparting adhesion to the current collector must be accompanied. In addition, the conductive material and the binder, which are generally used to improve the conductivity of the electrode and impart adhesion, are also one of the main factors that reduce the energy density of the battery. In particular, since the binder also serves as a resistance element, it is desirable to minimize the use of the conductive material and the binder within a range that does not impair the physical properties.

[0007] In consideration of the above description in general, a scheme should be designed to exclude the wet method while using a perforated current collector that can reduce the weight of the current collector, and also to minimize the use of a conductive material and a binder that reduce the energy density of the battery. SUMMARY

[0008]

TECHNICAL PROBLEM

[0009] An object of the present application is to provide an electrode for a lithium secondary battery including a perforated current collector, a manufacturing method thereof, and a lithium secondary battery including the same, the electrode being capable of bonding between active materials through holes of the perforated current collector while improving the energy density of the battery due to weight reduction even though the wet method and a conductive material and a binder, which are necessary components of an existing electrode mixture, are excluded.

[0010]

TECHNICAL SOLUTION

[0011] To achieve the above object, the present application provides an electrode for a lithium secondary battery, comprising a first electrode active material layer, a second electrode active material layer, and a perforated current collector interposed between the first electrode active material layer and the second electrode active material layer, wherein the first electrode active material layer and the second electrode active material layer are combined through the holes of the current collector.

[0012] In addition, the present application provides a method of manufacturing an electrode for a lithium secondary battery, comprising the steps of: (a) filling a mold with an appropriate amount of electrode active material, then placing a perforated current collector thereon, and again filling the electrode active material thereon; (b) applying pressure to the composite of the electrode active material filled in the mold and the current collector; and (c) separating the pressure-applied composite from the mold.

[0013] In addition, the present application provides a lithium secondary battery comprising at least one of the electrodes for a lithium secondary battery.

[0014]

Advantages

[0015] The electrode for a lithium secondary battery comprising a perforated current collector, the method of manufacturing the same, and the lithium secondary battery comprising the same according to the present application, in which the active materials are combined with each other through the holes of the perforated current collector, the weight of the perforated current collector is reduced compared to the conventional current collector, and at the same time, by applying a dry method instead of a wet method, the mixing, coating, and drying processes performed during the wet method are omitted. Therefore, there are advantages in that, when the electrode is manufactured by the dry method, problems caused by the existing wet method, such as problems caused by moisture remaining in the electrode and cost problems caused by the mixing, coating, and drying processes, are eliminated.

[0016] In addition, the electrode for a lithium secondary battery comprising a perforated current collector, the method of manufacturing the same, and the lithium secondary battery comprising the same according to the present application, there are advantages in that, even when the perforated current collector is used and at the same time, the conductive material and the binder, which are essential components of the existing electrode mixture, are excluded, the energy density of the battery can be improved due to the weight reduction. In addition, there are advantages in that, since the electrode can be easily manufactured independently through a mold based on the electrode shape of the footprint (i.e., since it is manufactured in a single process, an electrode stamping process is not required), electrode waste caused by the existing roll to roll method of stamping the electrode can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic cross-sectional side view of an electrode for a lithium secondary battery comprising a perforated current collector according to one embodiment of the present application.

[0018] Figure 2is an image showing the state of an adhesion region formed between active materials in an electrode for a lithium secondary battery including a perforated current collector according to one embodiment of the present application.

[0019] Figure 3 is an image showing the state of manufacturing an electrode for a lithium secondary battery using a mold and a press according to the present application.

[0020] Figure 4 (a) is a real image of a mold, Figure 4 (b) is a real image of a perforated aluminum foil current collector, Figure 4 (c) is a real image of an electrode manufactured by a mold.

[0021] Figure 5 is a graph comparing the discharge capacity of lithium-sulfur batteries according to one embodiment and a comparative example of the present application. DETAILED DESCRIPTION

[0022] Hereinafter, the present application will be described in detail with reference to the accompanying drawings.

[0023] Figure 1 is a schematic cross-sectional side view of an electrode for a lithium secondary battery including a perforated current collector according to one embodiment of the present application. As shown in Figure 1 An electrode for a lithium secondary battery including a perforated current collector according to the present application includes a first electrode active material layer, a second electrode active material layer, and a perforated current collector interposed between the first electrode active material layer and the second electrode active material layer, in which the first electrode active material layer and the second electrode active material layer are combined through the holes of the current collector, as shown in

[0024] A lithium secondary battery includes active materials, a conductive material, and a binder as well as a metal current collector in an electrode, and thus, its weight is inevitably increased. Such an increase in weight results in a decrease in the energy density of the battery. Therefore, in the art, efforts to improve the energy density of a lithium secondary battery by reducing the thickness of a current collector, making the current collector in a perforated form, etc. have been continuously made, but no definite solution has been proposed. In addition, if a general wet method is applied during electrode manufacturing, problems caused by moisture remaining in the electrode and cost problems caused by mixing, coating, and drying processes occur, and the conductive material and the binder are also one of the main factors to decrease the energy density of the battery (in particular, the binder also serves as a resistance element), and thus, it is preferred to exclude the wet method, and to reduce the use of the conductive material and the binder to the minimum within a range in which physical properties are not deteriorated.

[0025] Accordingly, the applicant of the present invention has repeatedly conducted research from various angles to solve the above problems, and as a result, has completed a technology that even when using a perforated current collector capable of reducing the weight of the current collector, replaces a wet method with a dry method and also excludes or selectively uses an electrically conductive material and a binder that can reduce the energy density of a battery. The present invention can be said to be an original invention of the applicant that has not been found to date. Hereinafter, the present invention will be described in more detail.

[0026] First, a perforated current collector is used to reduce its own weight (in addition, to reduce the weight of the electrode and the battery), and is used for flexible bonding (or adhesion) between active materials. As shown in Figure 1 The perforated current collector can be a perforated metal foil (thin foil) or a perforated conductive film or sheet, as shown in

[0027] The size of the hole formed by perforation is not particularly limited, and likewise, in consideration of the degree of weight reduction of the current collector and the degree of bonding between the surface of the current collector and the electrode active material coated in the hole, it is desirable to form a hole of an appropriate size to meet the purpose. However, in order to maintain the bonding force between the active materials to a level or more, a hole having a size of 100 μm to 1 cm, preferably 100 μm to 1,000 μm, more preferably 100 μm to 500 μm can be formed. In addition, the thickness of the perforated current collector is also not particularly limited, and the thickness of a general current collector commonly used in the art can be applied with necessary modifications.

[0028] As described above, the perforated current collector can be a perforated metal foil, film or sheet, and examples of the metal include metals used as conventional metal current collectors, such as aluminum (Al), nickel (Ni), stainless steel (SUS; stainless steel), copper (Cu), iron (Fe), titanium (Ti), vanadium (V), and mixtures thereof, and among the above-mentioned exemplified metals, aluminum can be preferably used in consideration of low density and high electrochemical stability.

[0029] Next, the electrode active materials (the first electrode active material and the second electrode active material) coated on the surface of the current collector and the perforations can also be used without particular limitation, as long as they are commonly used in the art. However, when pressure is applied to sulfur (S), since sulfur itself has a characteristic of being compressed and shaped (granulated), in consideration of the characteristics of the present application using a mold (i.e., a means satisfying the pressure application condition), it is preferable that sulfur be substantially contained as an active material. In addition, since the present application does not use a binder or uses a small amount of a binder (i.e., exclusion or selective use), it is desirable to use sulfur, which is compressed and shaped when pressure is applied, as an active material, even in consideration of other characteristics of the present application in which adhesion between active materials must be made through the holes of the perforated current collector.

[0030] Accordingly, the electrode active material of the present application can preferably be a positive electrode active material, whereby the first electrode active material can preferably be a first positive electrode active material, and the second electrode active material can preferably be a second positive electrode active material.

[0031] On the other hand, it can be more desirable to introduce a sulfur-carbon composite material, which effectively improves the charge / discharge capacity and the lifespan of a lithium secondary battery, into the active material. The porous carbon material is a carbon-based material having porosity and electrical conductivity, and any porous carbon material can be used, as long as it is commonly used in the art.

[0032] For example, the porous carbon material can include 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 thermal-cracking 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); graphite, such as natural graphite, artificial graphite, and expanded graphite; carbon nanofilaments; carbon nanoribbons, carbon nanorods, and activated carbon. Preferably, the porous carbon material can include at least one selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0033] The sulfur can include at least one selected from the group consisting of inorganic sulfur, Li2S n(n > 1), a disulfide compound, an organic sulfur compound, and a carbon-sulfur polymer. The sulfur is located on at least one of the inner surface and the outer surface of the porous carbon material. At this time, the sulfur can exist in less than 100%, preferably 1% to 95%, more preferably 60% to 90%, of the entire inner surface and outer surface of the porous carbon material. When the sulfur exists on the inner surface and the outer surface of the porous carbon material in the above range, the greatest effect can be exhibited in terms of electron transfer area and wettability with the electrolyte. Specifically, since the sulfur is thinly and uniformly impregnated on the inner surface and the outer surface of the porous carbon material in the above range, the electron transfer contact area can be increased during the charging / discharging process. If the sulfur is located in 100% of the entire inner surface and outer surface of the porous carbon material, there can be a problem in that the wettability with the electrolyte is reduced since the carbon material is completely covered with the sulfur.

[0034] In the present application, the average diameter of the sulfur can be 1 nm to 1 μm, preferably 1 nm to 100 nm, whereby it can be coated on the inside and the surface of the porous carbon material with a thickness of 1 nm to 10 nm. The content of the porous carbon material can be 10% to 50% by weight, preferably 20% to 40% by weight, based on the total weight of the sulfur-carbon composite. Accordingly, the content of the sulfur can be 50% to 90% by weight, preferably 60% to 80% by weight, based on the total weight of the sulfur-carbon composite. That is, the weight ratio of the porous carbon material and the sulfur in the sulfur-carbon composite can be 60:40 to 80:20, preferably 65:35 to 75:25. However, this is only one example, and the range can not be particularly limited if the performance of the positive electrode or the battery can be improved.

[0035] On the other hand, the sulfur-carbon composite can preferably be in a form in which the sulfur is supported on the porous carbon material such as carbon nanotubes or graphene. In addition, the sulfur-carbon composite can also have a form in which the sulfur is supported on the carbon nanotubes and the graphene is additionally attached to the outer wall of the sulfur-supported carbon nanotubes. Here, the sulfur is preferably elemental sulfur in the form of particles. In the present application, the fact that the sulfur is supported on the carbon nanotubes can encompass a state in which the sulfur is attached or coated on the surface of the carbon nanotubes, a state in which the sulfur is attached, filled, or coated inside the carbon nanotubes, a state in which the sulfur penetrates and adheres between the carbon nanotubes, etc.

[0036] According to one embodiment of the present application, the manner in which sulfur is loaded on the carbon nanotube bundle can vary depending on the method of preparing the electrode active material (preferably, the positive electrode active material). As a non-limiting example, when sulfur is applied in the form of particles, the sulfur can be contained in a state in which it is attached to the outer wall surface of the carbon nanotube bundle. In addition, as a non-limiting example, when sulfur is dissolved in a solvent and applied in a liquid state, the sulfur can be contained in a state in which it is absorbed into the carbon nanotube bundle by capillary phenomenon, thereby filling the inside of the carbon nanotube bundle or forming a coating layer on the surface of the inner wall and the outer wall.

[0037] The electrode for lithium secondary batteries including a perforated current collector according to the present application mainly includes only the above-described perforated current collector, and an electrode active material coated on the surface and the holes of the perforated current collector, and is characterized in that a conductive material and a binder are excluded or selectively used (in other words, one or more of the conductive material and the binder can be contained in a small amount in order to further improve the conductivity or the binding force between the active materials). That is, in the present application, since the electrode active material forms a binding area (adhesion area) through the holes of the perforated current collector, and binding (adhesion) between the active materials is possible, high electrode adhesion can be ensured without adhesion between the current collector and the active material by not using a binder or even if a binder is used, by adding a small amount, (the adhesion force can be adjusted by adjusting the porosity (applied pressure) of the electrode and the open porosity of the perforated current collector). Figure 2 is an image showing a state in which an adhesion area is formed between active materials in the electrode for lithium secondary batteries including a perforated current collector according to one embodiment of the present application. As shown in Figure 2 As shown in

[0038] That is, by using a perforated current collector while excluding or selectively using a conductive material and a binder, which are necessary components of the existing electrode mixture, the present application significantly reduces the weight of the positive electrode, and thus can be of great significance in terms of significantly improving the energy density of the battery. In addition, since the electrode for lithium secondary batteries including a perforated current collector according to the present application is manufactured by a dry method rather than a wet method, it also has the advantage that moisture is not left in the electrode.

[0039] Next, a method of manufacturing an electrode for lithium secondary batteries including a perforated current collector will be described with reference to Figure 3 and Figure 4 . Figure 3 is an image showing a state in which an electrode for lithium secondary batteries is manufactured using a mold and a press according to the present application. Figure 4 (a) is a real image of a mold, Figure 4 (b) is a real image of a perforated aluminum foil current collector, Figure 4(c) is a physical image of an electrode manufactured by a mold. The method of manufacturing an electrode for a lithium secondary battery including a perforated current collector according to the present application includes the steps of: (a) filling a mold with an appropriate amount of an electrode active material, then placing a perforated current collector thereon, and again filling the electrode active material thereon; (b) applying pressure to a composite of the electrode active material filled in the mold and the current collector; and (c) separating the composite to which the pressure is applied from the mold.

[0040] The mold can be a general mold made of a material capable of accommodating an electrode active material in a recess portion and not deformed even when pressure is applied. In the present application, a recess portion (or an accommodation portion of the active material) suitable for the size of a target electrode can be formed. Step (a) is a procedure of filling a mold with an appropriate amount of an electrode active material (first filling), then placing a perforated current collector thereon, and again filling the electrode active material thereon (second filling). The appropriate amount at the time of the first filling can refer to an amount filling about half of the height of the recess portion in the mold, in consideration of the portion of the perforated current collector in the electrode.

[0041] However, in the case of placing the perforated current collector to be deviated to either direction based on the height direction of the electrode, the electrode active material can be filled to be less than or greater than half of the height of the recess portion in the mold. Accordingly, the second filling can be such that the additional electrode active material reaches or approaches the upper portion of the recess portion in the mold. However, when considering stable adhesion between the electrode active materials through the holes of the perforated current collector, it is preferable that the perforated current collector is located at the center of the electrode in the height direction. Accordingly, in this case, it is preferable that the amount of the electrode active material of the first filling and the amount of the electrode active material of the second filling are set to be equal (i.e., the electrode active material of the first filling and the electrode active material of the second filling are each filled in the same amount).

[0042] Step (b) is a procedure of applying a certain pressure to a composite of the electrode active material filled in the mold and the perforated current collector, and the time of applying the pressure can be several seconds to several tens of seconds, preferably 1 second to 10 seconds, more preferably 3 seconds to 7 seconds. In addition, since the porosity of the electrode depends on the pressure applied to the composite, the pressure can be different depending on the porosity of the electrode to be manufactured, and can be, for example, 5 MPa to 50 MPa. In addition, heating can also be performed during the application of pressure in step (b). In addition, the descriptions of the perforated current collector and the electrode active material are replaced by the contents previously mentioned in the section of the electrode for a lithium secondary battery.

[0043] As described above, since the method of manufacturing an electrode for a lithium secondary battery including a perforated current collector according to the present application uses a dry method without using a roll-to-roll process, and also excludes or selectively uses a conductive material and a binder, it is possible to manufacture an electrode while using a perforated current collector very simply and easily.

[0044] In this regard, conventionally, a positive electrode is manufactured through a wet / roll-to-roll process or a dry / roll-to-roll process. More specifically, electrode manufacturing through a wet / roll-to-roll process is completed through a process of mixing an active material, a conductive material, a binder, and a solvent to prepare a slurry, and roll-to-roll coating and drying the slurry on a current collector, and then calendering and punching according to a designed thickness. In addition, electrode manufacturing through a dry / roll-to-roll process is completed through a process of premixing (premixing or dry mixing) an active material, a conductive material, and a binder, and preparing a self-standing electrode in a manner similar to being extruded by a roll, then coating a thermoplastic resin on a current collector to impart adhesion, laminating the prepared self-standing electrode on both sides, and manufacturing and punching a double-sided electrode.

[0045] As described above, electrode manufacturing according to the prior art must go through a very cumbersome process, and in particular, in the case of using a perforated current collector as in the present application, when a wet method is applied, there are limitations in controlling the open porosity and the viscosity of the slurry since the slurry flows down through the holes; when a dry method is applied, there are many limitations that a binder must be used to maintain the structure of the electrode, etc.

[0046] However, in the method of manufacturing an electrode for a lithium secondary battery according to the present application, a dry method is applied instead of a wet method, thereby omitting the mixing, coating, and drying processes performed during the wet method. Therefore, problems caused by the existing wet method, such as problems due to moisture remaining in the electrode, and cost problems due to the mixing, coating, and drying processes, are eliminated. In addition, since it is possible to independently manufacture electrodes for pouch cells, etc. through a mold based on the electrode shape of the recess (i.e., since calendering is performed in a single process, an electrode punching process is not required), there is an advantage that electrode loss due to punching electrodes in the existing roll-to-roll method can also be reduced.

[0047] Finally, regarding the lithium secondary battery according to the present application, the lithium secondary battery includes at least one of the above-described electrode for a lithium secondary battery, and the lithium secondary battery can be a lithium-based secondary battery, such as a lithium-sulfur battery, a lithium metal battery, and a lithium-air battery, but the lithium-sulfur battery can be the most preferred. On the other hand, the electrode for a lithium secondary battery can be a positive electrode or a negative electrode, but it can preferably be a positive electrode in consideration of the binding force between active materials. On the other hand, the separator interposed between the electrodes and the electrolyte can be a conventional separator and electrolyte used in the art, and detailed descriptions thereof will be given below.

[0048] Separator

[0049] A separator is interposed between the positive electrode and the negative electrode to prevent short-circuiting therebetween and to provide a passage for lithium ion movement. As the separator, an olefin-based polymer such as polyethylene and polypropylene, glass fiber, or the like in the form of a sheet, a multi-film, a microporous film, a woven fabric, or a non-woven fabric can be used, but is not limited thereto. On the other hand, when a solid electrolyte such as a polymer (for example, an organic solid electrolyte, an inorganic solid electrolyte, or the like) is used as the electrolyte, the solid electrolyte can also function as the separator. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The separator can generally have a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm.

[0050] Electrolyte

[0051] The electrolyte or electrolytic solution is a non-aqueous electrolytic solution (non-aqueous organic solvent), and a carbonate, an ester, an ether, or a ketone can be used alone or in combination of two or more, but is not limited thereto. For example, a non-protic organic solvent such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, triester phosphate, dibutyl ether, N-methyl-2-pyrrolidone, 1,2-dimethoxyethane, tetrahydrofuran, tetrahydrofuran derivatives such as 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, methyl propionate, ethyl propionate, but is not limited thereto.

[0052] A lithium salt can also be added to the electrolytic solution (so-called non-aqueous electrolytic solution containing a lithium salt), and the lithium salt can be a well-known lithium salt that is easily dissolved in a non-aqueous electrolytic solution, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiPF3(CF2CF3)3, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, chloroborane lithium, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, or the like, but is not limited thereto.

[0053] For the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (condensed) glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. If necessary, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride can be further added to impart non-flammability, or carbon dioxide gas can be further added to improve high-temperature storage characteristics.

[0054] On the other hand, the lithium secondary battery of the present application can be manufactured according to conventional methods in the art. For example, the lithium secondary battery can be manufactured by placing a porous separator between a positive electrode and a negative electrode and adding a non-aqueous electrolyte solution. The lithium secondary battery according to the present application can be applied to a battery cell used as a power source for a small-sized device, and can be particularly and suitably used as a unit cell of a battery module, which is a power source for a medium- to large-sized device. In this regard, the present application also provides a battery module comprising two or more lithium secondary batteries electrically connected (in series or in parallel). Of course, the number of lithium secondary batteries included in the battery module can be variously adjusted in consideration of the use and capacity of the battery module.

[0055] Further, the present application provides a battery pack in which battery modules are electrically connected according to conventional techniques in the art. The battery module and the battery pack can be used as a power source for any one or more of medium- to large-sized devices among electric power tools; electric vehicle categories including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric trucks; electric commercial vehicles; or power storage systems, but are not limited thereto.

[0056] Embodiments

[0057] Hereinafter, preferred embodiments of the present application will be described in order to facilitate the understanding of the present application. However, it will be apparent to those skilled in the art that the following embodiments are merely examples of the present application, and various changes and modifications can be made within the scope and spirit of the present application, and such changes and modifications are within the scope of the appended claims.

[0058] [Example 1] Preparation of a positive electrode for a lithium secondary battery using a perforated current collector

[0059] First, after filling a sulfur-carbon nanotube composite material (cathode active material, Cnano Technology company, China) in which sulfur and carbon nanotubes are mixed at a weight ratio of 70:30 to about half of the recessed portion of a mold recessed in the shape of a cathode, a perforated aluminum foil current collector (Dexmet company, USA) was placed thereon, and a sulfur-carbon nanotube composite material having the same composition as the above-mentioned cathode active material was again filled to the full thereof. Subsequently, a press (Qmesys company, Korea) was used to apply a pressure of 10 MPa to the composite material of the cathode active material filled in the mold and the current collector for 5 seconds, and the composite material to which the pressure was applied was separated from the mold to prepare a cathode for a lithium secondary battery.

[0060] [Comparative Example 1] Preparation of a positive electrode for a lithium secondary battery using a conventional metal current collector

[0061] A sulfur-carbon nanotube composite material (cathode active material, Cnano Technology company, China) in which sulfur and carbon nanotubes are mixed at a weight ratio of 70:30, 87% by weight, carbon fibers (VGCF, manufactured by Showa Denko company) as a conductive material, 5% by weight, and lithium polyacrylate and polyvinyl alcohol as a binder, 7% by weight and 1% by weight, respectively, were mixed to prepare a cathode slurry composition. Subsequently, the above-prepared slurry composition was coated onto both surfaces of an aluminum current collector, and dried at 50°C for 12 hours to prepare a cathode for a lithium secondary battery.

[0062] [Comparative Example 2] Preparation of a positive electrode for a lithium secondary battery

[0063] The same procedure as in Example 1 was performed to prepare a cathode for a lithium secondary battery, except that, in addition to the cathode active material (sulfur-carbon nanotube composite material in which sulfur and carbon nanotubes are mixed at a weight ratio of 70:30, Cnano Technology company, China), a conductive material (carbon fibers (VGCF), manufactured by Showa Denko company) and a binder (lithium polyacrylate and polyvinyl alcohol) were each added to the upper and lower portions of a perforated aluminum foil current collector (Dexmet company, USA). At this time, the contents of the cathode active material, the conductive material, lithium polyacrylate, and polyvinyl alcohol contained in the upper portion of the perforated aluminum foil current collector were 87% by weight, 5% by weight, 7% by weight, and 1% by weight, respectively, and the contents of the cathode active material, the conductive material, lithium polyacrylate, and polyvinyl alcohol contained in the lower portion of the perforated aluminum foil current collector were also 87% by weight, 5% by weight, 7% by weight, and 1% by weight, respectively.

[0064] [Experimental Example 1] Weight measurement and evaluation of the positive electrode

[0065] The weight of each of the positive electrodes prepared in Example 1 and Comparative Example 1 was measured and confirmed with an electronic balance. As a result, it was confirmed that the weight of the positive electrode of Comparative Example 3, which was manufactured using a general metal current collector, a conductive material, and an adhesive, reached about 15 mg / cm 2 , which is a difference in weight due to whether the current collector is perforated. On the other hand, the weight of the positive electrode of Example 1, in which a perforated current collector is used without using a conductive material and an adhesive, was only about 10 mg / cm 2 . Based on the above results, it was confirmed that the weight of the positive electrode did not change little, which depends not only on the difference of whether the perforated current collector is used, but also on the difference of the presence / absence of the conductive material / adhesive.

[0066] [Example 2, Comparative Examples 3~4] Preparation of a lithium secondary battery

[0067] The positive electrodes prepared in Example 1 and Comparative Examples 1 and 2 were positioned to face the negative electrode (Li metal foil), and then a polyethylene separator was interposed therebetween, and then an electrolyte prepared by dissolving LiFSI in a dimethyl ether solvent at a concentration of 1M was injected, to manufacture a lithium sulfur battery in the form of a pouch cell having an energy of 30 Wh.

[0068] [Experimental Example 2] Evaluation of the energy density of the battery

[0069] The energy density of the lithium secondary batteries prepared in Example 2 and Comparative Example 3 was evaluated. As a result of the evaluation, not only the lightest weight, but also the battery of Example 2, in which a conductive material and an adhesive known as a factor to reduce the energy density were not used, showed a relatively excellent energy density value compared to the battery of Comparative Example 3. From this, it can be seen that the use of a perforated current collector and the non-addition of a conductive material / adhesive showed a significant synergistic effect.

[0070] [Experimental Example 3] Evaluation of the discharge capacity of the battery

[0071] For the lithium sulfur batteries prepared in Example 2 and Comparative Examples 3 and 4, the discharge capacity was evaluated at a charge current of 0.1C and a voltage of 1.9V to 2.5V, and the results are shown in Figure 5 . Figure 5 is a graph comparing the discharge capacity of lithium sulfur batteries according to one embodiment of the present application and comparative examples.

[0072] As a result of evaluating the discharge capacity of the lithium sulfur batteries as described above, as Figure 5As shown in the middle, it was confirmed that the lithium-sulfur battery of Example 2, in which the perforated current collector was used but the conductive material and the binder were not used, had superior battery performance compared to the lithium-sulfur battery of Comparative Example 3, in which the conventional metal current collector was used, and the lithium-sulfur battery of Comparative Example 4, in which the perforated current collector was used while the conductive material and the binder were included. From this, it can be seen that the use of the perforated current collector and the non-addition of the conductive material / binder showed a significant synergistic effect.

Claims

1. An electrode for a lithium secondary battery, the electrode comprising: First electrode active material layer; Second electrode active material layer; and A perforated current collector, wherein the perforated current collector is inserted between the first electrode active material layer and the second electrode active material layer. The first electrode active material layer and the second electrode active material layer are joined together through the holes of the current collector. The electrodes for the lithium secondary battery described herein do not contain conductive materials or adhesives. In the perforated current collector, the area occupied by the holes is 25% to 90% of the total area. The aperture size of the perforated current collector is greater than 100 μm and less than or equal to 1 cm. The perforated current collector mentioned above is a perforated aluminum foil current collector.

2. The electrode for a lithium secondary battery according to claim 1, wherein the first electrode active material layer and the second electrode active material layer comprise sulfur (S).

3. The electrode for a lithium secondary battery according to claim 1, wherein the first electrode active material layer and the second electrode active material layer comprise a sulfur-carbon composite material.

4. The electrode for a lithium secondary battery according to claim 1, wherein the electrode for a lithium secondary battery does not contain moisture.

5. The electrode for a lithium secondary battery according to claim 1, wherein the electrode for a lithium secondary battery is a positive electrode for a lithium secondary battery, the first electrode active material layer is a first positive electrode active material layer, and the second electrode active material layer is a second positive electrode active material layer.

6. A method for manufacturing an electrode for a lithium secondary battery according to claim 1, the method comprising the following steps: (a) Fill the mold with an appropriate amount of electrode active material, i.e., the first filling; then place the perforated current collector on it and fill it with electrode active material again, i.e., the second filling; (b) Applying pressure to the composite material of the electrode active material and the current collector filled in the mold; and (c) Separating the pressure-bearing composite material from the mold. The composite material in step (c) does not contain conductive materials or adhesives.

7. The method according to claim 6, wherein the first filled electrode active material and the second filled electrode active material in step (a) are each filled in equal amounts, such that the perforated current collector is located at the center of the electrode in the height direction.

8. The method of claim 6, wherein the pressure in step (b) is applied to the composite material for 1 to 10 seconds.

9. The method of claim 6, wherein the method of manufacturing an electrode for a lithium secondary battery does not include mixing, coating, drying, and electrode stamping.

10. The method of claim 6, wherein the electrode active material comprises a sulfur-carbon composite material.

11. The method of claim 6, wherein heating is also performed during the application of pressure in step (b).

12. A lithium secondary battery comprising at least one electrode for a lithium secondary battery according to claim 1.

13. The lithium secondary battery according to claim 12, wherein the lithium secondary battery is a lithium-sulfur battery.

Images