Dry manufacturing method of positive electrode for lithium secondary battery, the positive electrode manufactured thereby, and the lithium secondary battery comprising the positive electrode

Abstract

The present invention relates to a dry manufacturing method for a positive electrode for a lithium secondary battery, a positive electrode manufactured according to the same, and a lithium secondary battery including the positive electrode. It can provide a positive electrode including a positive electrode composite layer having an appropriate density and has the effect of achieving effective adhesion between the positive electrode composite layer and a current collector.

Description

Technology Field

[0001] The present invention relates to a dry manufacturing method for a positive electrode for a lithium secondary battery, a positive electrode manufactured according to the same, and a lithium secondary battery comprising the positive electrode. Background Technology

[0003] Recently, the demand for rechargeable batteries as an energy source has been increasing rapidly. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

[0004] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. Among these, the positive electrode may include a positive active material, a conductive material, and a binder.

[0005] In the conventional process for manufacturing anodes, an anode slurry is prepared by using a solvent to disperse or dissolve an anode active material, a conductive material, and a binder, and then the anode slurry is coated onto a current collector, dried, and then rolled under high pressure to manufacture the anode. Therefore, considering the viscosity and other factors suitable for the anode manufacturing process, there is a problem in that there is an upper limit on the content of the binder and conductive material that can be introduced into the solvent, and an upper limit on the solid content of the manufactured anode slurry.

[0006] In addition, when manufacturing an anode using an anode slurry containing a solvent, defects such as pinholes or cracks may occur as the solvent contained in the electrode mixture evaporates during the drying process. Furthermore, since the inner and outer surfaces of the slurry coating layer are not dried uniformly, a powder floating phenomenon caused by differences in solvent evaporation rates may occur; that is, powders from the area that dries first rise to form a gap with the area that dries relatively later, which may degrade the electrode quality. Accordingly, drying devices capable of controlling the solvent evaporation rate while ensuring uniform drying of the inner and outer surfaces of the active layer are being considered; however, such drying devices are expensive and require significant costs and time for operation, which presents disadvantages in terms of manufacturing processability.

[0007] To solve these problems, a method for manufacturing an electrode without using an anode slurry is proposed. Specifically, the above manufacturing method involves mixing an anode active material, a binder, and a conductive material without a liquid medium such as a solvent or a dispersion medium, and then passing the mixed powder through a calender roll to produce a composite film. Then, the composite film can be laminated onto a current collector to manufacture an anode having a structure in which an anode composite layer is formed on the current collector.

[0008] Meanwhile, in the above lamination process, a rolling process is performed simultaneously or separately to increase the density of the anode composite layer and to apply pressure for adhesion between the anode composite layer and the current collector. However, if the gap between the first and second rolls in the above rolling process is less than a predetermined range, the density of the anode composite layer increases more than necessary, resulting in a porosity lower than the target porosity, or there is a problem of damage to the active material or the current collector. Alternatively, if the gap between the first and second rolls exceeds a predetermined range, there is a problem of reduced adhesion between the anode composite layer and the current collector.

[0009] Therefore, when manufacturing a cathode using a solvent-free dry electrode manufacturing method, there is a need to develop a method for manufacturing a cathode for a lithium secondary battery that includes a cathode composite layer with appropriate density while also achieving effective adhesion between the cathode composite layer and the current collector. Prior art literature

[0011] Republic of Korea Published Patent No. 10-2020-0017821 The problem to be solved

[0012] Accordingly, the objective of the present invention is to provide a dry manufacturing method for a positive electrode for a lithium secondary battery that includes a positive electrode composite layer having appropriate density and porosity, while also enabling effective adhesion between the positive electrode composite layer and the current collector, a positive electrode manufactured according to this method, and a lithium secondary battery including the positive electrode. means of solving the problem

[0014] In order to solve the aforementioned problem,

[0015] In one embodiment, the present invention,

[0016] The method includes a lamination step of laminating a composite film comprising a positive active material, a conductive material, and a binder onto one or both sides of a current collector, and

[0017] A dry manufacturing method for a positive electrode for a lithium secondary battery is provided, characterized in that, in the above lamination step, the composite film satisfies the compression ratio (%) of Formula 1:

[0018] [Equation 1]

[0019] 30 ≤ T p / T1×100 ≤ 50

[0020] In Equation 1,

[0021] T p represents the pressure thickness during the lamination stage, and

[0022] T1 refers to the thickness of the composite film before the lamination step.

[0023] At this time, during the lamination step, the density increase rate (%) of the composite film can satisfy the following Equation 2:

[0024] [Equation 2]

[0025] 8 ≤ (D2-D1) / D1×100 ≤ 15

[0026] D1 represents the density of the composite film before the lamination step, and

[0027] D2 represents the density of the composite film after the lamination step.

[0028] In addition, in the above lamination step, the rolling rate of the composite film may be 20% or less.

[0029] In addition, prior to the lamination step, a primer layer forming step may be further included, in which a primer layer comprising a conductive material and a binder is formed on one or both sides of the current collector.

[0030] Furthermore, the dry manufacturing method for a positive electrode for a lithium secondary battery according to the present invention may further include the step of obtaining a composite powder by dry mixing a positive electrode active material, a conductive material, and a binder; and the step of manufacturing a composite film by calendering the composite powder.

[0031] In a specific example, the step of obtaining the composite powder may include a process of mixing an anode active material, a conductive material, and a binder to obtain a mixture; a process of applying shear stress to the mixture to fiberize the binder to form a lump-shaped composite bulk; and a process of crushing the composite bulk to obtain the composite powder.

[0032] In addition, the lamination step may be performed by a roll press, and the temperature of the roll press may be in the range of an average of 40°C to 200°C.

[0034] In addition, in one embodiment, the present invention,

[0035] Primer layer formed on the entire house, one side or both sides of the entire house; and

[0036] It comprises an anode composite layer located on the upper surface of a primer layer and including an anode active material, a conductive material, and a binder, and

[0037] The above anode composite layer has a structure in which the binder is fiberized, and 2 g / cm² 3 Up to 4 g / cm² 3 Provides a positive electrode for a lithium secondary battery having a density of

[0038] Meanwhile, the anode composite layer may comprise 85 to 98 parts by weight of an anode active material; 0.5 to 5 parts by weight of a conductive material; and 0.5 to 10 parts by weight of a binder. Additionally, the binder of the anode composite layer may include polytetrafluoroethylene (PTFE).

[0039] In addition, the primer layer may include a conductive material and a binder, wherein the conductive material and the binder may be in a weight ratio of 1:10 to 9:10.

[0040] In addition, the binder included in the primer layer may be one or more selected from the group consisting of acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, polyvinylidene fluoride, polyvinylidene fluoride copolymer, and acrylic resin.

[0042] Furthermore, in one embodiment, the present invention,

[0043] A lithium secondary battery comprising a positive electrode; a negative electrode; and a separator located between the positive electrode and the negative electrode is provided. Effects of the invention

[0045] According to the dry manufacturing method of a positive electrode for a lithium secondary battery of the present invention, the positive electrode manufactured according to the same, and the lithium secondary battery including the positive electrode, there is an effect of being able to achieve effective adhesion between the positive electrode composite layer and the current collector. Brief explanation of the drawing

[0047] FIG. 1 is a schematic diagram showing the lamination process conditions in a dry manufacturing method for a positive electrode for a lithium secondary battery according to one embodiment of the present invention. Specific details for implementing the invention

[0048] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are to be described in detail in the detailed description.

[0049] However, this is not intended to limit the invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0050] In the present invention, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0051] Furthermore, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "immediately above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "immediately below" the other part, but also cases where there is another part in between. Additionally, in the present application, being "placed on" may include cases where it is placed on the lower part as well as on the upper part.

[0053] The present invention will be described in more detail below.

[0055] Dry manufacturing method for a positive electrode for a lithium secondary battery

[0056] In one embodiment, the present invention,

[0057] The method includes a lamination step of laminating a composite film comprising a positive active material, a conductive material, and a binder onto one or both sides of a current collector, and

[0058] A dry manufacturing method for a positive electrode for a lithium secondary battery, characterized in that, in the above lamination step, the composite film satisfies the compression ratio (%) of Formula 1:

[0059] [Equation 1]

[0060] 30 ≤ T p / T1×100 ≤ 50

[0061] In Equation 1,

[0062] T p represents the pressure thickness of the composite film during the lamination stage, and

[0063] T1 refers to the thickness of the composite film before the lamination step.

[0065] The dry manufacturing method for a positive electrode for a lithium secondary battery according to the present invention can manufacture the positive electrode through a lamination process that integrates the composite film and the current collector while removing the wound composite film and the wound current collector. The lamination step involves simultaneously performing lamination and rolling of the composite film on one or both sides of the current collector, and can be performed using a roll press. However, it is not limited thereto, and the lamination step may include, if necessary, a process of obtaining a laminate by laminating a composite film comprising a positive electrode active material, a conductive material, and a binder on one or both sides of the current collector, and a process of rolling the laminate so that the compression ratio of the composite film laminated on the current collector satisfies Equation 1.

[0066] In a specific example, a dry manufacturing method for a positive electrode for a lithium secondary battery according to the present invention may be performed by preparing a composite film comprising a positive electrode active material, a conductive material, and a binder, and laminating the composite film so as to be integrated with a current collector such that the compression ratio of the composite film satisfies Equation 1. Meanwhile, the pressure thickness (T) of the composite film p) refers to the thickness of the composite film when the composite film is pressed with a roll press, which will be described later.

[0067] Here, the composite film may be manufactured by calendering a mixed powder obtained by dry mixing an anode active material, a conductive material, and a binder. Specifically, the composite film may be obtained by performing the steps of: dry mixing an anode active material, a conductive material, and a binder to obtain a composite powder; and calendering the composite powder to manufacture a composite film.

[0068] In one example, the step of obtaining the composite powder can be performed by mixing an anode active material, a conductive material, and a binder to obtain a mixture; applying shear stress to the mixture to fiberize the binder and form a composite bulk in the form of a lump; and crushing and classifying the composite bulk to obtain the composite powder. Meanwhile, the process of forming the composite bulk may involve kneading the mixture at a temperature range of 70°C to 200°C and a pressure below atmospheric pressure, and the process of obtaining the composite powder may involve crushing and classifying the composite bulk to have a particle size of 2 mm or less, or 1 mm or less. For example, the step of obtaining the above-mentioned composite powder may involve introducing each component into a blender and stirring at 5,000 rpm to 15,000 rpm for 30 seconds to 10 minutes, then introducing the mixture into a kneader at a temperature of 70°C to 200°C and mixing at a speed of 20 rpm to 100 rpm for 1 minute to 10 minutes to obtain a composite bulk. The above-mentioned composite bulk may be introduced into a blender and ground at 5,000 rpm to 15,000 rpm for 10 seconds to 5 minutes to obtain a composite powder. Then, the above-mentioned composite powder may be introduced into a calender at a temperature of 80°C to 150°C to manufacture a composite film.

[0069] In another example, prior to the lamination step, a primer layer forming step may be included in which a primer layer comprising a conductive material and a binder is formed on one or both sides of the current collector.

[0070] Specifically, the process of forming a primer layer comprising a conductive material and a binder on one or both sides of the current collector may involve preparing a slurry for forming a primer layer comprising a conductive material, a binder, and a solvent, and then applying and drying the slurry for forming a primer layer on one or both sides of the current collector to form the primer layer. The solvent may be water, methanol, ethanol, ethylene glycol, diethylene glycol, glycerol, methylpyrrolidone, or a mixture thereof. At this time, by further including a primer coating layer on the current collector, the adhesion between the current collector and the composite film can be improved in the lamination step described later.

[0071] In addition, the lamination step may laminate the composite film onto one or both sides of the current collector using a roll press. Furthermore, in the lamination step, the composite film and the current collector may be laminated such that the compression ratio of the composite film satisfies Equation 1. Specifically, the compression ratio of the composite film may be satisfied as 30% to 50%, 35% to 50%, or 40% to 50%. Here, the compression ratio is the ratio of the pressure thickness (T) of the composite film in the lamination step to the thickness (T1) of the composite film prior to the lamination step. p The ratio of ) (T p / T1) refers to. In the present invention, by adjusting the compression ratio to satisfy a specific range during the lamination step, it is possible to provide appropriate density and porosity of the composite film and excellent adhesion between the composite film and the current collector.

[0072] If the compression ratio of the composite film in Equation 1 is less than 30%, the pressure applied to the composite film is low, which reduces the adhesion between the composite film and the current collector, and a problem may occur in which the composite film peels off from the current collector after the lamination process. In addition, if the compression ratio of the composite film exceeds 50%, the density of the composite film increases more than necessary, resulting in a porosity lower than the target porosity or damage to the current collector.

[0073] In addition, in the above lamination step, when the compression ratio of the composite film integrated into the current collector satisfies Equation 1, the density increase rate (%) of the composite film can satisfy Equation 2 below:

[0074] [Equation 2]

[0075] 8 ≤ (D2-D1) / D1×100 ≤ 15

[0076] D1 is the density of the composite film (g / cm³) before the lamination step. 3 Representing ),

[0077] D2 is the density of the composite film (g / cm³) after the lamination step. 3 It represents ).

[0078] Specifically, in the lamination step, the density increase rate of the composite film can be satisfied as 8–15%, 9–15%, or 10–15%. The above D1 and D2 are 2 g / cm³. 3 Up to 4 g / cm² 3 The range may be. Meanwhile, if the density increase rate of the composite film is less than 8%, the adhesion between the composite film and the current collector may decrease as previously explained, and if it exceeds 15%, the porosity may decrease, and problems such as damage to the positive active material or the current collector may occur.

[0079] In one example, when a composite film is laminated on both sides of the current collector, the compression ratio (%) of Equation 1 above may mean Equation 3 below.

[0080] [Equation 3]

[0081] 30 ≤ (T1 + 0.5T c - 0.5T gap ) / T1×100 ≤ 50

[0082] In Equation 3, T1 represents the thickness of the composite film before the lamination step, and T c represents the thickness of the entire house, and T gap represents the gap between the first and second rolling rolls.

[0083] Meanwhile, the rolling rate of the composite film that has undergone the lamination step may be 20% or less, specifically, it may be in the range of 18% or less, 15% or less, 5% to 15%, 6% to 15%, 7% to 15%, or 9% to 13%. Here, the rolling rate represents the ratio of the thickness of the composite film after the lamination step to the thickness of the composite film before the lamination step ((T1-T2) / T1×100). The present invention can achieve an appropriate density of the composite film and adhesion between the composite film and the current collector by satisfying the above-described range of the rolling rate.

[0084] In addition, the lamination step can be performed under temperature conditions satisfying a specific range to optimize the density of the composite film and provide excellent adhesion between the composite film and the current collector.

[0085] Specifically, the lamination step may be performed by a roll press, and the temperature of the roll press may be controlled within an average range of 40°C to 200°C. Specifically, the temperature of the roll press may be controlled to a temperature condition of 40°C to 200°C; 80°C to 150°C; or 100°C to 150°C. If, during the lamination step, the temperature of the roll press is below 40°C, the composite film may not adhere easily to the current collector, and if the temperature of the roll press exceeds 200°C, the current collector or the composite film may be damaged due to the high temperature. Therefore, during the lamination step, the temperature of the roll press within the above range is preferred.

[0086] The dry manufacturing method for a positive electrode for a lithium secondary battery according to the present invention can be performed by preparing a composite film comprising a positive electrode active material, a conductive material, and a binder, and by laminating the composite film so as to be integrated with a current collector such that the compression ratio of the composite film satisfies Equation 1. Accordingly, the manufactured positive electrode can realize a positive electrode composite layer of appropriate density and has the effect of realizing effective adhesion between the positive electrode composite layer and the current collector.

[0088] cathode for lithium secondary batteries

[0089] In addition, in one embodiment, the present invention,

[0090] The whole house;

[0091] A primer layer formed on one or both sides of the entire house; and

[0092] It comprises an anode composite layer located on the upper surface of a primer layer and including an anode active material, a conductive material, and a binder, and

[0093] The above anode composite layer has a structure in which the binder is fiberized, and 2 g / cm² 3 Up to 4 g / cm² 3 Provides a positive electrode for a lithium secondary battery having a density of

[0095] The positive electrode for a lithium secondary battery according to the present invention comprises a positive electrode composite layer manufactured by laminating and rolling a composite film obtained by a dry process on a primer layer formed on one or both sides of a current collector, and the positive electrode composite layer has a composition containing a positive electrode active material, a conductive material, and a binder.

[0096] At this time, the binder included in the anode composite layer may have a fibrous structure. Specifically, when manufacturing the composite film in the dry manufacturing method of the anode described above, the binder forms a network that physically connects the mixtures during the mixing process.

[0097] In addition, the cathode for a lithium secondary battery according to the present invention can provide an appropriate density of the cathode composite layer by satisfying the compression ratio of Equation 1 during the rolling step. Specifically, the density of the cathode composite layer is 2 g / cm³. 3 Up to 4 g / cm² 3 It may be within the range. By having a density of the anode composite layer, it may be possible to realize high capacity and high energy density.

[0098] Any material capable of absorbing and releasing lithium ions by containing lithium can be used as the above-mentioned positive active material. For example, the above-mentioned positive active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-xM x Lithium manganese composite oxide represented as O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 ~ 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiNi x Mn 2-x It may include, but is not limited to, a lithium manganese composite oxide with a spinel structure represented by O4; LiMn2O4 in which a portion of the Li in the chemical formula is substituted with an alkaline earth metal ion; a disulfide compound; Fe2(MoO4)3, etc. Additionally, the anode may have an anode composite layer comprising lithium metal, a carbon material, a metal compound, and a mixture thereof. The metal compound may be a compound containing one or more metal elements selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, and Ba, or a mixture thereof.

[0099] In addition, the conductive material of the anode composite layer may include one or more selected from the group consisting of activated carbon, natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, Channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes. For example, the conductive material may include one or more selected from the group consisting of carbon black, Ketjen black, and carbon nanotubes.

[0100] In addition, the binder serves to bind the cathode active material and the conductive material together, and any binder having this function can be used without particular limitation. Specifically, the binder may include polytetrafluoroethylene (PTFE). In a specific example, the binder may include polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof, and more specifically, may include polytetrafluoroethylene (PTFE). In another example, the polytetrafluoroethylene may be included in an amount of 60% by weight or more based on the total binder weight of the cathode composite layer. At this time, it goes without saying that the binder may additionally include polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP), etc.

[0101] In addition, the anode composite layer may comprise 85 to 98 parts by weight of an anode active material; 0.5 to 10 parts by weight of a conductive material; and 0.5 to 10 parts by weight of a binder, based on a total of 100 parts by weight. In one example, the anode composite layer may comprise 88 to 97 parts by weight of an anode active material, 0.5 to 5 parts by weight of a conductive material, and 1 to 5 parts by weight of a binder, based on a total of 100 parts by weight. In another example, the anode composite layer may comprise 90 to 96 parts by weight of an anode active material, 1 to 5 parts by weight of a conductive material, and 2 to 5 parts by weight of a binder, based on a total of 100 parts by weight.

[0102] In addition, the average thickness of the anode composite layer is not particularly limited and may be 10㎛ to 300㎛, and specifically may be 50㎛ to 250㎛; 100㎛ to 240㎛; 120㎛ to 220㎛; 130㎛ to 200㎛; or 150㎛ to 180㎛.

[0103] Meanwhile, the positive electrode for a lithium secondary battery according to the present invention may use a current collector having high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., may be used, and in the case of aluminum or stainless steel, a surface-treated material such as carbon, nickel, titanium, silver, etc., may be used. In addition, the current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics are possible. Furthermore, the average thickness of the current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0104] In addition, the positive electrode for a lithium secondary battery according to the present invention includes a primer coating layer between the positive electrode composite layer and the current collector to provide excellent adhesion between the positive electrode composite layer and the current collector. The primer layer may be formed by preparing a slurry for forming a primer layer comprising a conductive material, a binder, and a solvent, and applying and drying the slurry for forming a primer layer on one or both sides of the current collector. At this time, the conductive material included in the primer layer is capable of realizing the surface roughness of the primer layer and providing conductivity, and is not particularly limited as long as it has conductivity without causing chemical changes in the battery. Examples of conductive materials may be used include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives. For example, the conductive material of the primer layer may be carbon black.

[0105] The binder above serves to bind and fix each conductive material particle to one another so that the conductive material can achieve surface roughness, and may include one or more selected from the group consisting of acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, polyvinylidene fluoride, polyvinylidene fluoride-based polymer, and acrylic resin. The acrylic resin above may use an acrylate-based polymer. For example, the acrylate-based polymer may include one or more selected from the group consisting of 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, acrylamide, 1,4-benzenedicarboxylic acid, and acrylonitrile.

[0106] The conductive material and the polymer binder may be included in a weight ratio of 1:10 to 9:10. More specifically, the conductive material and the polymer binder may be included in a weight ratio of 3:10 to 9:10; a weight ratio of 5:10 to 9:10; or a weight ratio of 7:10 to 9:10. When the above weight ratios are satisfied, conductivity of the primer coating layer can be achieved, and delamination of the primer layer can be prevented.

[0107] As described above, the positive electrode for a lithium secondary battery according to the present invention comprises a positive electrode composite layer manufactured by laminating and rolling a composite film obtained by a dry process onto a primer layer formed on one or both sides of a current collector. In particular, the positive electrode composite layer has an appropriate density, thereby enabling the realization of high capacity and high energy density.

[0109] lithium secondary battery

[0110] Furthermore, in one embodiment of the present invention,

[0111] The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode according to the present invention described above.

[0112] Here, the cathode may be manufactured by applying, drying, and pressing a cathode active material onto a cathode current collector, or by manufacturing it dry as in the method for manufacturing the anode described above, and, if necessary, may optionally include a conductive material, an organic binder polymer, an additive, etc., as in the anode.

[0113] In addition, the above-mentioned cathode active material may include, for example, a carbon material and a silicon material. The above-mentioned carbon material refers to a carbon material having carbon atoms as its main component. Such carbon materials may include graphite, which has a completely layered crystal structure like natural graphite; soft carbon, which has a low-crystallinity layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers); hard carbon, in which such structures are mixed with amorphous portions; artificial graphite; expanded graphite; carbon fiber; non-graphitized carbon; carbon black; acetylene black; ketjen black; carbon nanotubes; fullerene; activated carbon; graphene; carbon nanotubes; and, preferably, one or more selected from the group consisting of natural graphite, artificial graphite, and carbon nanotubes. More preferably, the above-mentioned carbon material may include natural graphite and / or artificial graphite, and together with the natural graphite and / or artificial graphite, one or more of carbon black and carbon nanotubes. In this case, the carbon material may comprise 0.1 to 10 parts by weight of carbon black and / or carbon nanotubes per 100 parts by weight of the total carbon material, and more specifically, may comprise 0.1 to 5 parts by weight or 0.1 to 2 parts by weight of carbon black and / or carbon nanotubes per 100 parts by weight of the total carbon material.

[0114] In addition, the above silicon material is a particle containing silicon (Si) as a main component as a metallic component, comprising silicon (Si) particles and silicon oxide (SiO₂). X It may include one or more of the particles (1≤X≤2). As one example, the silicon material may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or a mixture of these particles.

[0115] In addition, the silicon material may have a form in which crystalline particles and amorphous particles are mixed, and the ratio of the amorphous particles may be 50 to 100 parts by weight, specifically 50 to 90 parts by weight; 60 to 80 parts by weight; or 85 to 100 parts by weight, based on 100 parts by weight of the total silicon material. By controlling the ratio of amorphous particles contained in the silicon material to the above range, the present invention can improve thermal stability and flexibility without degrading the electrical properties of the electrode.

[0116] In addition, the silicon material may include a carbon material and a silicon material, and may be included in an amount of 1 to 20 parts by weight per 100 parts by weight of the cathode composite layer, and specifically, may be included in an amount of 5 to 20 parts by weight; 3 to 10 parts by weight; 8 to 15 parts by weight; 13 to 18 parts by weight; or 2 to 7 parts by weight per 100 parts by weight of the cathode composite layer.

[0117] The present invention can improve the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery by controlling the content of carbon material and silicon material included in the negative electrode active material to the ranges described above.

[0118] As one example, the negative electrode active material may comprise 95 ± 2 parts by weight of graphite and 5 ± 2 parts by weight of a mixture of silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles uniformly mixed, based on 100 parts by weight of the negative electrode composite layer. By controlling the content of carbon material and silicon material included in the negative electrode active material to the above range, the present invention can improve the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery.

[0119] In addition, the cathode composite layer may have an average thickness of 50㎛ to 200㎛, and specifically, may have an average thickness of 50㎛ to 180㎛, 100㎛ to 150㎛, 120㎛ to 200㎛, 140㎛ to 200㎛, or 140㎛ to 160㎛.

[0120] In addition, the above-mentioned negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, surface-treated carbon, nickel, titanium, silver, etc. may be used. Furthermore, similar to the positive electrode current collector, the above-mentioned negative electrode current collector may form fine irregularities on its surface to strengthen the bonding force with the negative electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible. In addition, the average thickness of the above-mentioned negative electrode current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0121] In addition, the separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The separator is not particularly limited as long as it is commonly used in the industry, but specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene; glass fiber; or polyethylene may be used, and in some cases, a composite separator in which inorganic particles / organic particles are coated by an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator. Furthermore, the pore diameter of the separator may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0122] Meanwhile, the above positive and negative electrodes may be wound into a jelly roll form and stored in a cylindrical battery, a prismatic battery, or a pouch-type battery, or stored in a pouch-type battery in a folding or stack-and-folding form, but are not limited thereto.

[0123] In addition, the lithium salt-containing electrolyte according to the present invention may consist of an electrolyte and a lithium salt, and the electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0124] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. may be used.

[0125] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociator, etc.

[0126] As the above-mentioned inorganic solid electrolyte, for example, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc., may be used.

[0127] The above lithium salt is a substance that dissolves well in a non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl 10LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylboronicate, imide, etc. may be used.

[0128] In addition, for the purpose of improving charge / discharge characteristics and flame retardancy, the electrolyte may be further enriched with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, 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. In some cases, to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further enriched, carbon dioxide gas may be further enriched to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), etc.

[0130] Meanwhile, in one embodiment, the present invention provides a battery module comprising the above-described secondary battery as a unit cell, and a battery pack comprising the battery module.

[0131] The above battery pack can be used as a power source for medium-to-large devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. Specific examples of such medium-to-large devices include power tools that are powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems. More specifically, hybrid electric vehicles (HEVs) can be cited, but are not limited thereto.

[0133] The present invention will be explained in more detail below through examples and experimental examples.

[0134] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0136] Examples 1–7, Comparative Examples 1–4. Preparation of cathodes for lithium secondary batteries

[0137] A positive electrode active material, activated carbon and carbon black, and a binder, polytetrafluoroethylene, were introduced into a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture. Then, the temperature of the kneader was stabilized to 150°C, the mixture was placed into the kneader, and the mixture was operated at a speed of 50 rpm for 5 minutes to prepare a composite bulk. Next, the composite bulk was introduced into a blender and ground at 10,000 rpm for 40 seconds to obtain a composite powder for electrodes. Subsequently, the prepared composite powder for electrodes was introduced into a wrap calender (roll diameter: 88 mm, roll temperature: 100°C, 20 rpm) to produce a composite film.

[0138] A slurry for forming a primer layer was applied to an aluminum foil and dried to form a primer layer on a current collector. The primer layer contained carbon black and an acrylic binder in a weight ratio of 5:6. Then, an anode was manufactured by performing a lamination process using a roll press maintained at 150°C so that two composite films could be laminated onto both sides of the aluminum foil (average thickness: 19 μm) on which the primer layer was formed. At this time, the composition of the composite film and the conditions for the rolling step are shown in Table 1 below. In the active materials in Table 1 below, LMO represents LiMnO2 and LFP represents LiFePO4 (see Fig. 1).

[0139] Composition of composite film (parts by weight) composite film Total thickness of the house (T c , ㎛) Gap thickness (T gap , ㎛) Compression ratio (%) active material Conductive agent (activated carbon: carbon black) Binder (PTFE) Thickness (T1, μm) Density (D1, g / cm³) 3 ) Example 1 LMO 94 1:2 3 192.4 2.67 19 250 40.0 Example 2 LMO 94 1:2 3 187.7 2.57 19 220 46.5 Example 3 LMO 94 1:2 3 155.0 2.84 19 210 38.4 Example 4 LFP 94 0.5:2 3.5 144.6 2.27 19 180 44.2 Example 5 LFP 94 0.5:2 3.5 151.9 2.30 19 200 40.3 Example 6 LFP 94 0.5:2 3.5 148.1 2.31 19 210 35.4 Example 7 LFP 94 0.5:2 3.5 151.0 2.21 19 220 33.4 Comparative Example 1 LMO 94 1:2 3 179.3 2.72 19 190 52.3 Comparative Example 2 LMO 94 1:2 3 195.8 2.47 19 300 28.2 Comparative Example 3 LFP 94 0.5:2 3.5 160.8 2.26 19 170 53.0 Comparative Example 4 LFP 94 0.5:2 3.5 149.7 2.43 19 230 29.5

[0140] Experimental Example.

[0141] To evaluate the performance of the cathode for a lithium secondary battery according to the present invention, the following experiment was performed.

[0143] 1) Measurement of density growth rate

[0144] Before laminating the composite film onto the current collector, the thickness, area, and mass of the composite film were measured to calculate the density (D1). Then, after laminating the composite film onto the current collector, the thickness of the composite film was calculated from the thickness of the anode measured, and the density (D2) of the composite film after the lamination process was calculated.

[0145] And, the density increase rate was calculated using the formula (D2- D1) / D1×100. Here, D1 represents the density of the composite film before the lamination step, and D2 represents the density of the composite film after the lamination step.

[0147] 2) Measurement of rolling rate

[0148] The thickness (T1, T2) of the composite film before and after the lamination process was measured, respectively, and the rolling rate of the composite film was calculated. Specifically, it was calculated using the formula (T2-T1) / T1×100. Here, T1 represents the thickness of the composite film before the lamination step, and T2 represents the thickness of the composite film after the lamination step.

[0150] 3) Measurement of flexural strength

[0151] After winding the anodes prepared in the examples and comparative examples onto a sus-bar with a diameter of 8 mm, the occurrence of cracks in the composite film and the adhesion between the composite film and the current collector were observed visually.

[0153] Composite film (before rolling) Total thickness of the house (T c , ㎛) Gap thickness of the rolling roll (T gap , ㎛) Compression ratio (%) Composite film (after rolling) Visual observation when bending the electrode Thickness (T1, μm) Density (D1, g / cm³) 3 ) Thickness (T1, μm) Density (D1, g / cm³) 3 ) Rolling rate (%) Density growth rate (%) Example 1 192.4 2.67 19 250 40.0 171.1 3.00 11.1 12.5 Good Example 2 187.7 2.57 19 220 46.5 164.2 2.94 12.5 14.3 Good Example 3 155.0 2.78 19 210 38.4 144.5 3.05 6.8 9.7 Good Example 4 144.6 2.27 19 180 44.2 129.5 2.53 10.4 11.7 Good Example 5 151.9 2.30 19 200 40.3 137.3 2.54 9.6 10.6 Good Example 6 148.1 2.31 19 210 35.4 136.9 2.50 7.6 8.2 Good Example 7 151.0 2.21 19 220 33.4 139.3 2.51 7.7 8.4 Good Comparative Example 1 179.3 2.72 19 190 52.3 150.5 3.24 16.1 19.1 Cracks occur Comparative Example 2 195.8 2.47 19 300 28.2 180.5 2.68 7.8 8.4 Interfacial peeling Comparative Example 3 160.8 2.26 19 170 53.0 137.0 2.65 14.8 17.4 Cracks occur Comparative Example 4 149.7 2.43 19 230 29.5 146.1 2.49 2.4 2.5 Interfacial peeling

[0154] Referring to Table 2 above, the compression ratio of the composite film in the anode of the embodiment according to the present invention was controlled to 30 to 50%. As a result, the density increase rate of the composite film was found to be in the range of 8 to 15%.

[0155] In particular, when the compression ratio and density increase rate of the composite film satisfied Equation 1 and Equation 2, respectively, no cracking of the composite film or delamination of the composite film from the current collector was observed during the measurement of the electrode's flexural strength. On the other hand, cracking was observed in the composite films of Comparative Examples 1 and 3. In addition, delamination from the current collector was observed in the composite films of Comparative Examples 2 and 3. Even though the composite films of the anodes prepared in the Comparative Examples had a density similar to that of the Examples, cracking occurred in the composite film or delamination occurred from the current collector due to differences in the compression ratio or density increase rate. Specifically, it was confirmed that cracking occurred in the composite film when the compression ratio and density increase rate were high, and that delamination occurred from the current collector when the compression ratio and density increase rate were low.

[0156] From these results, the dry manufacturing method for a positive electrode for a lithium secondary battery according to the present invention includes the step of laminating a composite film onto a current collector, wherein the composite film is laminated onto the current collector such that the compression ratio of the composite film satisfies Equation 1, thereby enabling the manufacturing of a positive electrode having a positive electrode composite layer of appropriate density and the effect of achieving effective adhesion between the positive electrode composite layer and the current collector.

[0158] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and technical scope of the invention as described in the claims set forth below.

[0159] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

Claim 1 A dry manufacturing method for a positive electrode for a lithium secondary battery, comprising: a primer layer forming step of forming a primer layer comprising a conductive material and a first binder on one or both sides of a current collector; and a lamination step of laminating a composite film comprising a positive electrode active material, a conductive material, and a second binder onto the primer layer of the current collector, wherein the primer layer comprises the conductive material and the first binder in a weight ratio of 1:10 to 9:10, and in the lamination step, the composite film satisfies the compression ratio (%) of Formula 1: [Formula 1] 30 ≤ T p / T1×100 ≤ 50 In equation 1, T p represents the thickness of the composite film when the composite film is pressed during the lamination step, and T1 represents the thickness of the composite film before the lamination step. Claim 2 In claim 1, the density increase rate (%) of the composite film in the lamination step satisfies the following Equation 2 in a dry manufacturing method for a positive electrode for a lithium secondary battery: [Equation 2] 8 ≤ (D2-D1) / D1×100 ≤ 15 D1 represents the density of the composite film before the lamination step, and D2 represents the density of the composite film after the lamination step. Claim 3 A dry manufacturing method for a positive electrode for a lithium secondary battery, wherein, in the lamination step, the rolling rate of the composite film is 20% or less. Claim 4 delete Claim 5 A dry manufacturing method for a positive electrode for a lithium secondary battery, comprising: a step of obtaining a composite powder by dry mixing a positive electrode active material, a conductive material, and a second binder in claim 1; and a step of manufacturing a composite film by calendering the composite powder. Claim 6 In claim 5, the step of obtaining the composite powder comprises: a process of mixing a positive electrode active material, a conductive material, and a second binder to obtain a mixture; a process of applying shear stress to the mixture to fiberize the second binder to form a lump-shaped composite bulk; and a process of crushing the composite bulk to obtain a composite powder, comprising a dry manufacturing method for a positive electrode for a lithium secondary battery. Claim 7 A dry manufacturing method for a positive electrode for a lithium secondary battery, wherein, in claim 1, the lamination step is performed by a roll press. Claim 8 A dry manufacturing method for a positive electrode for a lithium secondary battery according to claim 7, wherein the temperature of the roll press is in the range of an average of 40℃ to 200℃. Claim 9 A current collector; a primer layer formed on one or both sides of the current collector and comprising a conductive material and a first binder; and an anode composite layer located on the upper surface of the primer layer and comprising an anode active material, a conductive material, and a second binder, wherein the primer layer comprises the conductive material and the first binder in a weight ratio of 1:10 to 9:10, and the anode composite layer has a structure in which the second binder is fiberized, and 2 g / cm² 3 Up to 4 g / cm² 3 A positive electrode for a lithium secondary battery having a density of Claim 10 In claim 9, the anode composite layer comprises 85 to 98 parts by weight of an anode active material; 0.5 to 5 parts by weight of a conductive material; and 0.5 to 10 parts by weight of a second binder, for an anode for a lithium secondary battery. Claim 11 In claim 9, the second binder of the anode composite layer comprises polytetrafluoroethylene (PTFE), an anode for a lithium secondary battery. Claim 12 delete Claim 13 In claim 9, the first binder of the primer layer is one or more selected from the group consisting of acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, polyvinylidene fluoride, polyvinylidene fluoride copolymer, and acrylic resin, for a positive electrode for a lithium secondary battery. Claim 14 A lithium secondary battery comprising a positive electrode according to claim 9; a negative electrode; and a separator located between the positive electrode and the negative electrode.

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