Electrode assembly and secondary battery containing the same

Abstract

The present invention provides an electrode assembly, comprising: a mono-cell group including one or more mono-cells; a single-sided electrode laminated on at least one of the upper and lower outermost sides of the mono-cell group; and a separator interposed between the mono-cell group and the single-sided electrode, the single-sided electrode comprising a current collector and an electrode layer only on one side of the current collector, the electrode layer having a porosity of 30% or less, and the single-sided electrode having a curl of 30 mm or less. The electrode assembly also includes a secondary battery and an energy storage device including the electrode assembly.

Description

Technical Field

[0001] The present invention relates to an electrode assembly and a secondary battery including the same, and more particularly, to an electrode assembly having a high energy density and excellent bending characteristics, and a secondary battery including the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0049212 filed on April 20, 2022, and all the contents disclosed in the specification and drawings of the application are incorporated herein.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy and clean energy has been increasing. As part of this, the field of power generation and power storage using electrochemistry is the most actively studied field. Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its application fields are gradually expanding. A lithium secondary battery, which is a representative example of such a secondary battery, can be used not only as an energy source for mobile devices but also recently as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. Its use fields are also expanding to applications such as a power auxiliary power source by grid connection.

[0004] In order to maximize the energy density of such a secondary battery, attempts have been made to apply a single-sided electrode to the outermost layer of a conventional full cell.

[0005] However, in the case of a single-sided electrode, a phenomenon in which the electrode bends more than a double-sided electrode, that is, curl occurs significantly. When a single-sided electrode with a large bend is applied, there is a problem that the occurrence of defects increases in the assembly process.

[0006] Therefore, there is an urgent need to develop an electrode assembly that can solve such problems.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention is for solving the above problems, and an object thereof is to provide an electrode assembly with improved curl characteristics by maximizing the energy density, and a secondary battery including the same.

Means for Solving the Problems

[0008] In order to solve the problems of the present invention, according to one aspect of the present invention, an electrode of the following embodiment is provided.

[0009] According to the first embodiment, there is provided an electrode assembly including a monocell group including one or more monocells, a single-sided electrode laminated on one or more of the upper and lower outermost sides of the monocell group, and a separation membrane interposed between the monocell group and the single-sided electrode. The single-sided electrode includes a current collector and an electrode layer provided only on one side surface of the current collector. The porosity of the electrode layer is 30% or less, and the curl of the single-sided electrode is 30 mm or less.

[0010] According to the second embodiment, in the first embodiment, the monocell group may include one monocell or two or more laminated monocells.

[0011] According to the third embodiment, in the first embodiment or the second embodiment, a half cell may further be interposed between the monocell group and the unit electrode.

[0012] According to the fourth embodiment, in any one of the first to third embodiments, the difference between the porosity of the electrode layer of the single-sided electrode and the porosity of the electrode layer of the other electrode facing the single-sided electrode may be 5% or less.

[0013] According to the fifth embodiment, in any of the first to fourth embodiments, the single-sided electrode comprises a current collector and an electrode layer located on the current collector and containing an active material and a binder, wherein the binder can be fibrousized to bind the active material.

[0014] According to the sixth embodiment, in the fifth embodiment, the electrode layer may include an active material, a conductive material, and a binder.

[0015] According to the seventh embodiment, in the fifth or sixth embodiment, the binder may include polytetrafluoroethylene (PTFE).

[0016] According to the eighth embodiment, in the sixth or seventh embodiment, the content of the active material may be 80 to 98 parts by weight, the content of the conductive material may be 0.5 to 10 parts by weight, and the content of the binder may be 0.5 to 5 parts by weight.

[0017] According to the ninth embodiment, in any of the fifth to eighth embodiments, the electrode current collector may further include a conductive primer layer on at least one surface.

[0018] According to the tenth embodiment, in any of the fifth to ninth embodiments, the electrode layer may be derived from a film for dry electrodes.

[0019] According to the 11th embodiment, in any of the first to tenth embodiments, the single-sided electrode may be manufactured by a manufacturing method that includes the steps of: manufacturing a mixture containing an active material and a binder; kneading the mixture at a temperature in the range of 70°C to 200°C and at a pressure of normal pressure or higher to manufacture a mixture mass; crushing the mixture mass to obtain a mixed powder for electrodes; feeding the mixed powder for electrodes between a plurality of rolls and calendering it to form an electrode film; and laminating the electrode film onto a current collector.

[0020] According to the 12th embodiment, in the 11th embodiment, the step of kneading to produce a mixture mass can be carried out in a kneader under a pressure of atmospheric pressure or higher.

[0021] According to the 13th embodiment, in the 11th or 12th embodiment, the rolling ratio of the electrode film in the laminating step may be 10% or less.

[0022] According to the 14th embodiment, a secondary battery is provided that includes an electrode assembly of any embodiment from the 1st to the 13th embodiment.

[0023] According to the 15th embodiment, an energy storage device is provided that includes a secondary battery according to the 14th embodiment as a unit battery. [Effects of the Invention]

[0024] According to one embodiment of the present invention, a single-sided electrode is applied to the outermost layer of the electrode assembly. In this case, by adjusting the porosity of the electrode film applied during the manufacturing of the single-sided electrode and controlling the rolling rate of the electrode film during lamination with the current collector, an electrode layer having a porosity of 30% or less is obtained, thereby providing an electrode assembly with maximum energy density and improved curl characteristics, and a secondary battery including the same.

[0025] The following drawings accompanying this specification illustrate preferred embodiments of the invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention; therefore, the invention should not be construed as being limited solely to what is shown in the drawings. [Brief explanation of the drawing]

[0026] [Figure 1] A schematic diagram of an electrode according to one embodiment of the present invention. [Figure 2] A schematic diagram for calculating the QBR value of the electrode layer. [Figure 3A]A schematic diagram of the manufacturing process for the electrode film used in an electrode assembly according to one embodiment of the present invention. [Figure 3B] A schematic diagram of the manufacturing process for the electrode film used in an electrode assembly according to one embodiment of the present invention. [Figure 4] A schematic diagram of the electrode lamination process for a double-sided electrode applied to an electrode assembly according to one embodiment of the present invention. [Figure 5] A schematic diagram of the electrode lamination process for a single-sided electrode applied to an electrode assembly according to one embodiment of the present invention. [Figure 6] A schematic diagram of an electrode assembly in which conventional double-sided electrodes are located in the outermost layer. [Figure 7] A schematic diagram of an electrode assembly in which a single-sided electrode is located in the outermost layer, according to one embodiment of the present invention. [Figure 8] A schematic diagram of an electrode assembly in which a single-sided electrode is located in the outermost layer, according to one embodiment of the present invention. [Figure 9] A photograph showing the curl measurement results of the single-sided electrode in Example 2. [Figure 10] A photograph showing the curl measurement results of the single-sided electrode in Comparative Example 1. [Modes for carrying out the invention]

[0027] The present invention will be described in more detail below to help you understand it better.

[0028] Terms and words used in this specification and in the claims are not to be interpreted in their ordinary and dictionary sense, but rather in a sense and concept appropriate to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself may appropriately define the concept of a term in order to best describe the invention.

[0029] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise clearly indicated by the context, singular expressions include plural expressions.

[0030] Furthermore, throughout the specification, when a part "includes" a certain component, this means, unless otherwise stated, that it may include other components rather than excluding them.

[0031] According to one aspect of the present invention, an electrode assembly is provided which includes a group of monocells containing one or more monocells, a single-sided electrode laminated on one or more of the upper and lower outermost surfaces of the group of monocells, and a separation membrane interposed between the group of monocells and the single-sided electrode, wherein the single-sided electrode comprises a current collector and an electrode layer on only one side surface of the current collector, the porosity of the electrode layer is 30% or less, and the curl of the single-sided electrode is 30 mm or less.

[0032] According to one embodiment of the present invention, the group of monocells may include one monocell or two or more stacked monocells.

[0033] In this context, the term "mono cell" refers to a unit assembly comprising a positive electrode, a negative electrode, and a separator membrane interposed between the positive and negative electrodes, where both the positive and negative electrodes are double-sided electrodes, i.e., electrodes comprising a current collector and electrode layers on both sides of the current collector.

[0034] According to one embodiment of the present invention, a half cell can be further interposed between the monocell group and the unit electrode. In this case, the half cell refers to a unit assembly that has only one type of electrode, either a positive electrode or a negative electrode, as an electrode, and the electrode of the half cell is a double-sided electrode having electrode layers on both sides of the current collector.

[0035] If the monocell group includes two or more stacked monocells, a separation membrane can be interposed between these adjacent monocells. If a halfcell is further interposed between the monocell group and the unit electrode, a separation membrane can be interposed between the monocell group and the halfcell, and between the halfcell and the unit electrode.

[0036] According to one embodiment of the present invention, the electrode assembly can be constructed by stacking in the order of "monocell group / separation membrane / single electrode", or by stacking in the order of "monocell group / separation membrane / half cell (double-sided electrode) / separation membrane / single electrode", or by stacking in the order of "single electrode / separation membrane / monocell group / separation membrane / single electrode", or by stacking in the order of "single electrode / separation membrane / monocell group / separation membrane / half cell (double-sided electrode) / separation membrane / single electrode", or by stacking in the order of "single electrode / separation membrane / half cell (double-sided electrode) / monocell group / separation membrane / half cell (double-sided electrode) / separation membrane / single electrode".

[0037] Figure 6 is a schematic diagram of an electrode assembly 300 in which a conventional double-sided electrode is placed on the outermost side. The electrode assembly 300 comprises a group of monocells, each having one or more monocells 330, each having a double-sided negative electrode 310 composed of a negative electrode layer 313 / negative electrode current collector 311 / negative electrode layer 312, a double-sided positive electrode 320 composed of a positive electrode layer 323 / positive electrode current collector 321 / positive electrode layer 322, and separation membranes 314 and 315 interposed between the double-sided negative electrode 310 and the double-sided positive electrode 320, with the double-sided negative electrode 310 placed on the outermost side of the monocell group.

[0038] In such conventional electrode assemblies 300, the outermost electrode layer of the outermost double-sided electrode, which does not face any other electrode layers, cannot be used in the actual battery, and thus the technical requirement to maximize the energy density of the secondary battery cannot be met.

[0039] To solve this problem, there was an attempt to apply single-sided electrodes to the outermost layer. However, with single-sided electrodes, bending occurs more significantly compared to double-sided electrodes, and applying single-sided electrodes with significant bending leads to an increase in defects during the assembly process.

[0040] In the present invention, as described above, by adjusting the porosity of the electrode film applied during the manufacture of the single-sided electrode, and by controlling the rolling rate of the electrode film during lamination with the current collector, it becomes possible to manufacture a single-sided electrode having an electrode layer with a porosity of 30% or less. An electrode assembly and secondary battery to which such a single-sided electrode is applied as the outermost layer can have its energy density maximized, thereby improving its curl characteristics.

[0041] Figures 7 and 8 show schematic diagrams of an electrode assembly in which a single-sided electrode is placed on the outermost side, according to one embodiment of the present invention.

[0042] The electrode assembly 400 shown in Figure 7 is configured by stacking the following components in the order of "single electrode / separation membrane / monocell group / separation membrane / half cell (double-sided electrode) / separation membrane / single electrode".

[0043] Specifically, the electrode assembly 400 shown in Figure 7 comprises a monocell group having one or more monocells 420 each, each having a double-sided negative electrode composed of a negative electrode layer 423 / negative current collector 421 / negative electrode layer 422, a double-sided positive electrode composed of a positive electrode layer 428 / positive current collector 426 / positive electrode layer 427, and separation films 424, 425 interposed between the double-sided negative electrode and the double-sided positive electrode; and a first single-sided positive electrode 410 composed of a positive electrode layer 416 / positive current collector 417 and a second single-sided positive electrode 430 composed of a positive electrode layer 431 / positive current collector 432, respectively, arranged on both sides of the outermost part of the monocell group, and further comprising a double-sided negative electrode (half-cell) 410' composed of a negative electrode layer 413 / negative current collector 411 / negative electrode layer 412 between the first single-sided positive electrode 410 and the monocell group. At this time, separation membranes 414 and 415 are interposed between the single-sided positive electrode, the double-sided negative electrode, and the monocell group.

[0044] The electrode assembly 500 shown in Figure 8 is configured by stacking monocell group / separation membrane / half-cell (double-sided electrode) / separation membrane / single electrode in that order.

[0045] Specifically, the electrode assembly 500 shown in Figure 8 comprises a monocell group having one or more monocells 420 each, each having a double-sided negative electrode composed of a negative electrode layer 423 / negative current collector 421 / negative electrode layer 422, a double-sided positive electrode composed of a positive electrode layer 428 / positive current collector 426 / positive electrode layer 427, and separation membranes 424, 425 interposed between the double-sided negative electrode and the double-sided positive electrode; and a single-sided positive electrode 410 disposed on one side of the outermost part of the monocell group, composed of a positive electrode layer 416 / positive current collector 417, and further comprising a double-sided negative electrode 410' composed of a negative electrode layer 413 / negative current collector 411 / negative electrode layer 412 between the single-sided positive electrode and the monocell group. In this case, separation membranes 414, 415 are interposed between the single-sided positive electrode, the double-sided negative electrode, and the monocell group.

[0046] According to one embodiment of the present invention, the single-sided electrode comprises a current collector and an electrode layer located on the current collector, which includes an active material and a binder, wherein the binder can be fibrousized to bind the active material.

[0047] The single-sided electrode is either a positive electrode or a negative electrode, and the active material may be a positive electrode active material or a negative electrode active material.

[0048] The positive electrode active material may include, but is not limited to, lithium transition metal oxides, lithium metallic iron phosphates, lithium nickel-manganese-cobalt oxides, and oxides in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with other transition metals, or two or more of these. Specifically, the positive electrode active material may include, for example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals, and a compound with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, and LiNi 1-x M xO2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3) - represented Ni-site type lithium nickel oxide, and chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn), and lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn), and lithium nickel - manganese - cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1), and an oxide in which a part of the lithium nickel - manganese - cobalt oxide is substituted with aluminum (lithium nickel - manganese - cobalt - aluminum oxide) Li a [Ni b Co c Mn d Al e 1-f M 1 f O2 (where the said M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≤ e ≤ 0.1, 0 ≤ f ≤ 0.1), disulfide compounds, and Fe2(MoO4)3 etc. are mentioned, but are not limited thereto. Specifically, the said lithium nickel - manganese - cobalt - aluminum oxide may be Li[Ni 0.87 Co 0.05 Mn 0.07 Al 0.01 O2 etc.

[0049] Also, as the said negative electrode active material, carbon such as graphitizable carbon and graphite - based carbon, and Li x Fe2O3 (0 ≤ x ≤ 1), Li​x WO2(0≦x≦1), Sn x Me 1-x Me' y O z Metal composite oxides such as (Me: Mn, Fe, Pb, Ge and Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogens; 0≦x≦1; 1≦y≦3; 1≦z≦8), lithium metal, lithium alloys, silicon alloys, tin alloys, silicon oxides such as SiO, SiO / C, SiO2, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetene, and Li-Co-Ni materials can be used.

[0050] According to one embodiment of the present invention, the single-sided electrode is a positive electrode, and the active material is more specifically a positive electrode active material, and more specifically, it may be a lithium transition metal oxide, lithium nickel-manganese-cobalt oxide, an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with Al or other transition metals, lithium iron phosphate, etc.

[0051] According to one embodiment of the present invention, the electrode layer further comprises a conductive material and may include an active material, a conductive material, and a binder.

[0052] The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. Examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, needle-shaped or branched conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers, and conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. More specifically, to ensure uniform mixing of the conductive material and improve conductivity, it may contain one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may contain activated carbon.

[0053] The binder may contain a fluorine-containing binder, a non-fluorine-containing binder, or two or more of these. The fluorine-containing binder may be a fluorine-containing polymer, and may contain polytetrafluoroethylene (PTFE) and PVdF-based copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), or two or more of these. Specifically, the fluorine-containing binder may contain polytetrafluoroethylene (PTFE). Furthermore, the fluorine-containing binder may contain polytetrafluoroethylene alone, or further contain polytetrafluoroethylene with one or more PVdF-based copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene). The non-fluorine-containing binder may contain polyolefins, polyethylene oxide (PEO), etc.

[0054] According to one embodiment of the present invention, the binder can be fibrousized to bind the active material, and if the electrode layer further contains a conductive material, the binder can be fibrousized to bind the active material and the conductive material.

[0055] The electrode may include a fibrous binder as a means of binding the active material or the active material to the conductive material. Such a fibrous binder exhibits less breakage than conventional non-fibrous binders and has excellent stretchability in the longitudinal direction, thereby improving the flexibility of the electrode layer and the electrode itself. The process of fibrousizing the binder will be specifically discussed in the electrode manufacturing method described later.

[0056] According to one embodiment of the present invention, the content of the active material may be 85 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, and the content of the binder may be 0.5 to 10 parts by weight.

[0057] Furthermore, the content of the active material may be 90 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, and the content of the binder may be 0.5 to 5 parts by weight.

[0058] When the content of the active material, conductive material, and binder meets these ranges, the binder can be sufficiently fiberized in the subsequent kneading process to form a mixture mass, and the electrode film can be easily manufactured by molding the mixed powder formed in the crushing process, ensuring the physical properties of the electrode film and ensuring the content of the active material, thereby preventing the problem of volume reduction and ensuring sufficient conductivity.

[0059] On the other hand, in some cases, a filler, which is a component that suppresses the expansion of the electrodes, can be further added to the electrode layer. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, orifine polymers such as polyethylene and polypropylene, and fibrous materials such as glass fibers and carbon fibers can be used.

[0060] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The current collector can also have minute irregularities formed on its surface to improve the adhesion of the positive electrode active material, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0061] Furthermore, the current collector may be coated entirely or partially with a conductive primer layer to reduce resistance on its surface and improve adhesion. Here, the conductive primer layer may include a conductive material and a binder for the primer layer. The conductive material is not limited to any material that is conductive, and may include, for example, carbon-based materials, metallic materials (metal powder or metal fibers), conductive whiskers, conductive metal oxides, conductive polymers, etc. Carbon-based materials include natural graphite, artificial graphite, graphene, carbon black, Denka Black, acetylene black, Ketjen Black, Super-P, Channel Black, Furnace Black, Lamp Black, Thermal Black, carbon nanotubes, graphite nanofibers, and carbon nanofibers. Metallic materials include copper, nickel, aluminum, and silver. Conductive whiskers include zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers. Conductive metal oxides include titanium oxide, and conductive polymers include polyphenylene derivatives. These can be used individually or as mixtures of two or more.

[0062] The binder for the primer layer is a solvent-soluble fluorine-based binder (including PVDF and PVDF copolymers) or acrylic-based binder, and may include water-based binders such as styrene-butadiene rubber (SBR).

[0063] The single-sided electrode comprises a current collector and an electrode layer on only one side of the current collector, and the porosity of the electrode layer is 30% or less. According to one embodiment of the present invention, the porosity of the electrode layer of the single-sided electrode may be 20 to 30%, or 22 to 30%, or 23 to 30%, or 25 to 30%, or 26 to 30%, or 26 to 29.4%, or 26 to 28.8%, or 26 to 27%, or 27 to 30%, or 27 to 29.4%, or 27 to 28.8%.

[0064] By ensuring that the porosity of the electrode layer of the single-sided electrode is 30% or less, electrolyte impregnation is improved, resulting in superior lifespan and output characteristics. Furthermore, since there is no need to increase the volume to achieve the same capacity, the energy density relative to the volume is improved.

[0065] The porosity of the electrode layer can be determined by measuring the external density of the composite film alone by subtracting the volume and weight of the current collector from the volume and weight of the electrode, and using the actual density calculated based on the actual density and composition of each component, according to the following relational formula. Porosity (%) = {1 - (Outer density / Actual density)} × 100

[0066] According to one embodiment of the present invention, the difference between the porosity of the electrode layer of the single-sided electrode and the porosity of the electrode layer of the other electrode facing the single-sided electrode may be 5% or less, or 1% to 5%, or 2% to 5%.

[0067] In this case, if the electrode assembly comprises a group of monocells, a single-sided electrode, and a separation membrane interposed between the group of monocells and the single-sided electrode, the other electrode opposite the single-sided electrode may mean the outermost electrode of the monocell group that corresponds to each other across the single-sided electrode and the separation membrane.

[0068] Furthermore, if the electrode assembly comprises a group of monocells, a single-sided electrode, a half-cell (double-sided electrode) interposed between the group of monocells and the single-sided electrode, and a separation membrane interposed between the group of monocells, the single-sided electrode, and the half-cell, then the other electrode opposite the single-sided electrode may refer to the electrode of the half-cell (double-sided electrode) that corresponds to each other across the single-sided electrode and the separation membrane.

[0069] When the difference between the porosity of the electrode layer of the single-sided electrode and the porosity of the electrode layer of the other electrode facing the single-sided electrode is controlled to 5% or less, the capacity and performance are more advantageous as long as the porosity of the single-sided electrode is no different from that of the other electrode facing it, i.e., the double-sided electrode. Generally speaking, in the case of a single-sided electrode with curl characteristics that take processability into consideration, the porosity can be controlled to be about 5% higher than that of a double-sided electrode. For this reason, in one embodiment of the present invention, the single-sided electrode located on the outermost side of the electrode assembly can have a porosity as similar as possible to that of a double-sided electrode, i.e., a porosity difference of 5% or less.

[0070] The curl of the single-sided electrode is 30 mm or less. According to one embodiment of the present invention, the curl of the single-sided electrode is 0 mm or more, 1 mm or more, 2 mm or more, 5 mm or more, 8 mm or more, 30 mm or less, 20 mm or less, 18 mm or less, or 8 mm or less, and specifically, it may be 0 to 30 mm, or 1 to 30 mm, or 2 to 20 mm, 5 to 18 mm, 5 to 8 mm, or 8 to 18 mm, 0 to 18 mm, or 0 to 8 mm, or 0 to 5 mm. When the curl of the single-sided electrode is 30 mm or less, even if such a single-sided electrode is placed on the outermost part of the electrode assembly, bending does not occur, and advantageous effects such as no defects occurring in the assembly process are achieved. On the other hand, if the curl of the single-sided electrode exceeds 30 mm, there is a high possibility that the plain portion of the single-sided electrode (the current collector region where the electrode layer is not formed) will get caught during the assembly process of the electrode assembly, or that a tear will occur at the interface between the plain portion and the textured portion (the current collector region where the electrode layer is formed), leading to fracture.

[0071] The curl of the single-sided electrode can be defined as the maximum height of the single-sided electrode after placing the single-sided electrode on the reference surface so that the electrode layer of the single-sided electrode faces the flat reference surface, and then measuring the height of the edges on both sides of the single-sided electrode raised from the reference surface in millimeters using a ruler.

[0072] In one embodiment of the present invention, the crystallinity of the binder in the electrode layer may be 10% or less.

[0073] In this invention, the degree of crystallinity (Xc) can be measured by differential scanning calorimetry (DSC), and is based on the temperature (peak temperature) at the point in time when the highest enthalpy is observed during crystallization. Specifically, the degree of crystallinity is expressed as a percentage by dividing the enthalpy of melt (β value) measured by DSC by the enthalpy of melt (β equilibrium heat of fusion) of a theoretical perfect crystal (100% crystallinity), and can be calculated by the following relational equation 1. Here, the enthalpy of melt of a theoretical perfect crystal can be found and used in a polymer handbook for well-known polymers, and for unknown substances or newly synthesized substances, it can be calculated by extrapolation, which involves extending the degree of crystallinity at two or more points. [Relationship 1] Xc(%)=(β m / β m 0 ) × 100

[0074] According to one embodiment of the present invention, the binder may contain a fluorine-containing binder, and the electrode layer may have a QBR (Quantified Binder Ratio) of 1.1 or less.

[0075] The aforementioned QBR is defined by the following formula. QBR=Bs / Bf

[0076] In the above formula, Bs represents the average value of the fluorine content in the surface region of the electrode layer from the outermost surface of the electrode layer to within 15% of the total thickness of the electrode layer, and Bf represents the average value of the fluorine content in the bottom region of the electrode layer from the interface of the electrode layer facing the current collector to within 15% of the total thickness of the electrode layer.

[0077] Figure 1 is a schematic diagram of an electrode according to one embodiment of the present invention. Referring to Figure 1, the electrode 10 comprises an electrode current collector 12 and an electrode layer 11 located on the electrode current collector 12 and containing an active material and a binder. In this case, the electrode layer may selectively further contain a conductive material.

[0078] The electrode layer 11 has a surface region 11s of the electrode layer from the outermost surface of the electrode layer to within 15% of the total thickness d of the electrode layer, and a bottom region 11f of the electrode layer from the interface of the electrode layer facing the current collector to within 15% of the total thickness d of the electrode layer.

[0079] In the above formula QBR, Bs represents the average value of the fluorine content in the surface region 11s of the electrode layer, and Bf represents the average value of the fluorine content in the bottom region 11f of the electrode layer.

[0080] In this case, QBR can be calculated using the following method.

[0081] First, an electrode to be examined for QBR is selected, and a cross-section of the selected electrode is fabricated using argon ion milling. Then, the constituent components within the electrode layer of the fabricated electrode cross-section are mapped using an energy dispersive X-ray spectroscopy (EDS) detector on a scanning electron microscope (SEM).

[0082] From the EDS mapping results, a line profile is extracted in the thickness direction of the electrode layer. From the extracted line profile results, the average value of the fluorine content in the surface region of the electrode layer (Bs) and the average value of the fluorine content in the bottom region of the electrode layer (Bf) are extracted, and the QBR value is calculated using the following formula. QBR=Bs / Bf

[0083] In this case, the surface region of the electrode layer is the region from the outermost surface in the thickness direction of the electrode layer to within 15% of the total thickness of the electrode layer, and the bottom region of the electrode layer is the region from the interface of the electrode layer facing the current collector to within 15% of the total thickness of the electrode layer.

[0084] Figure 2 is a schematic diagram for calculating the QBR value of the electrode layer. Referring to Figure 2, the X-axis represents the thickness of the electrode layer, i.e., the distance from the surface in the direction of the current collector, and the Y-axis represents the intensity of the fluorine component. Line A shows the intensity of the fluorine component of the fluorine-containing binder extracted by EDS mapping of the fluorine component in the electrode layer at the electrode cross-section, and line B is a trend line showing the trend of line A, and is shown smoothed using the LOWESS smoothing method, i.e., the Locally-Weighted Scatterplot Smoother method.

[0085] The QBR value is a numerical value that indicates the uniformity of the distribution of fluorine-containing binder in the electrode layer in the thickness direction, based on the ratio of the fluorine-containing binder content in the surface region to the fluorine-containing binder content in the bottom region of the electrode layer. In this case, the fluorine-containing binder content can be estimated based on the fluorine component contained in the fluorine-containing binder used.

[0086] The aforementioned QBR value is 1.1 or less, and according to one embodiment of the present invention, the aforementioned QBR value is 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and can also be between 0.95 and 1.05.

[0087] When the QBR value is within the range of 1.1 or less, the fluorine-containing binder migrates to the electrode surface, and the problem of the fluorine-containing binder content in the surface region being greater than the content in the bottom region of the electrode layer does not occur. As a result, the distribution of the binder in the electrode layer thickness direction becomes uniform, and the binder content in the part close to the current collector does not decrease. Therefore, the adhesion between the current collector and the electrode layer is improved, and the conductivity on the surface of the electrode layer and the charge / discharge rate thereafter can also be improved.

[0088] The fluorine-containing binder may specifically include polytetrafluoroethylene (PTFE) and PVdF-based copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), or two or more of these. Furthermore, the fluorine-containing binder may contain polytetrafluoroethylene alone, or in addition to polytetrafluoroethylene, it may further contain one or more PVdF-based copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene).

[0089] The electrode layer may be derived from a dry electrode film. Unlike conventional wet electrode manufacturing methods, which involve dissolving and / or dispersing an active material and a binder (which may further selectively contain conductive material) in a dispersion medium such as water or an organic solvent, and then applying the resulting slurry onto a current collector and drying it, the dry electrode film is manufactured using a dry manufacturing method that does not use a dispersion medium. The electrode film manufactured in this way is then laminated onto a current collector to finally produce an electrode. The specific manufacturing methods for the electrode film and the electrode will be described below.

[0090] According to one embodiment of the present invention, the single-sided electrode can be manufactured by a manufacturing method comprising the steps of: manufacturing a mixture containing an active material and a binder; kneading the mixture at a temperature in the range of 70°C to 200°C and at a pressure of normal pressure or higher to manufacture a mixture mass; crushing the mixture mass to obtain a mixed powder for electrodes; feeding the mixed powder for electrodes between a plurality of rolls and calendering it to form an electrode film; and laminating the electrode film onto a current collector.

[0091] The method for manufacturing a single-sided electrode applied to the electrode assembly according to the present invention will be described in more detail below. According to one embodiment of the present invention, in addition to the single-sided electrode applied to the electrode assembly according to the present invention, double-sided electrodes included in a monocell group or half-cell can also be manufactured by the following method.

[0092] First, a mixture containing the active material and binder is prepared. As described above, a conductive material may be selectively added to the mixture, and embodiments containing a conductive material are also described below, even if the conductive material is not explicitly mentioned.

[0093] In this case, the mixing for producing the mixture is carried out so that the active material and binder are uniformly distributed, and since they are mixed in powder form, the method is not limited to any method that enables simple mixing of these materials, and they can be mixed by various methods. However, since the electrodes of the present invention are manufactured by a dry manufacturing method that does not use a dispersion medium, the above mixing can be carried out by dry mixing, and can be done by putting the materials into a device such as a blender.

[0094] Furthermore, in order to ensure uniformity, the mixture can be manufactured by mixing in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, or more specifically, at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute.

[0095] According to one embodiment of the present invention, a supermixer or the like can be used in the mixing step for producing the mixture, and specifically, a method can be applied in which the mixture is mixed with a supermixer at 1,000 to 2,000 rpm for 5 to 10 minutes.

[0096] The binder can be microfibrillated by the step of manufacturing the mixed powder. This microfibrillation refers to a process of finely dividing a polymer, which can be done, for example, by using mechanical shear force. Specific examples of such binders are as described above.

[0097] Next, the mixture is kneaded at a temperature in the range of 70°C to 200°C and under a pressure of normal or higher pressure to produce a lump of mixture.

[0098] In well-known techniques, high-shear mixing, such as that performed by a jet mill, is used to fiberize the binder. However, this mixing can cause problems such as the micronization of the active material and the risk of the formed fibers being cut. Therefore, in the present invention, these problems are solved by using a low-shear compounding method instead of high-shear mixing.

[0099] The above-mentioned kneading is not limited to any particular method. In one specific embodiment of the present invention, the kneading can be carried out, for example, by a kneader.

[0100] Such kneading is a step in which the binder is fibrousized and bonds or connects the active material, or the active material and the conductive material, to form a mixture mass with 100% solid content.

[0101] Specifically, the above mixing can be controlled at a speed of 10 rpm to 100 rpm. For example, the above mixing can be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The above mixing can be carried out for 1 minute to 30 minutes. For example, it can be carried out for 3 minutes to 10 minutes at a speed of 20 rpm to 50 rpm within the above range. On the other hand, the above mixing can be controlled in a range of 10 / s to 500 / s in terms of shear rate. In a specific embodiment of the present invention, the above mixing can be carried out for 1 minute to 30 minutes, and the shear rate can be controlled in a range of 30 / s to 100 / s.

[0102] Furthermore, such mixing steps can be carried out under high temperature and pressure conditions above atmospheric pressure, and more specifically, under pressure conditions higher than atmospheric pressure.

[0103] More specifically, the above-mentioned kneading can be carried out at a temperature range of 70°C to 200°C, more precisely, 90°C to 180°C.

[0104] If the process is carried out at a temperature lower than the above temperature range, the binder will not fiberize properly during kneading and will not aggregate well, and film formation will not occur easily during calendering. If the process is carried out at an excessively high temperature, the binder will fiberize rapidly, and there is a risk that the already formed fibers will be cut by excessive shear force, which is undesirable.

[0105] Furthermore, the process can be carried out at or above atmospheric pressure, or under pressures of 1 atm to 60 atm, or 1 atm to 30 atm, or 1 atm to 10 atm, or 1 atm to 8 atm, or 1.1 atm to 7 atm, or 1.1 atm to 6 atm.

[0106] By satisfying the above pressure range, it is possible to prevent problems such as excessive shear force and pressure being applied, which could cause the formed fibers to break or the density of the mixture to be too high. In other words, according to the present invention, the intended effects can be achieved when a low-shear mixing process is performed under high temperature and pressure conditions above atmospheric pressure instead of high-shear mixing.

[0107] Next, the mixture mass is crushed to obtain a mixed powder for electrodes.

[0108] Specifically, the mixture mass produced by the aforementioned kneading can be immediately calendered. In this case, it is necessary to press the mixture mass to produce a thin film, which may result in the problem of not being able to obtain a uniform film. Therefore, according to the present invention, the prepared mixture mass undergoes the aforementioned grinding step. That is, if the electrode mixture powder obtained by grinding is excessively large or aggregated, bridges may be formed in the calendering process, potentially causing defects in the film's appearance such as pinholes or resulting in a film with non-uniform surface characteristics. Therefore, the electrode mixture powder is ground to obtain a uniform size before performing calendering.

[0109] In this case, the grinding step is not limited, but can be performed using a device such as a blender or grinder. Specifically, the grinding step can be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, or more precisely, at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0110] By satisfying the aforementioned grinding speed and time, sufficient grinding is achieved, enabling the formation of powder particles of a size suitable for film formation and preventing the problem of excessive differentiation in the mixture clumps. If necessary, a classification process can be carried out to filter out powder particles that exceed or fall below a certain size.

[0111] According to one embodiment of the present invention, a cutter mill, a fine mill, etc., can be used in the grinding step. In this case, the cutter mill can be used to coarsely grind the mixed mass produced by kneading to a level of several millimeters by operating at a rate of 400 to 500 rpm for several seconds. The fine mill can be used to uniformly grind the coarsely ground powder to a size below a certain level, and can be used at a rate of 3,000 to 8,000 rpm.

[0112] Next, the electrode mixture powder is fed between multiple rolls and calendered to form an electrode film.

[0113] Referring to Figures 3A and 3B, in the step 100 for forming the electrode film, a plurality of rolls 110 are arranged spaced apart, and the electrode mixed powder 120 obtained in the above step is fed between adjacent rolls 100 and rotated in a direction opposite to the rolls 100, thereby rolling the mixed powder 120, forming it into a sheet or film through a powder sheet step, and then finally obtaining an electrode film having the target thickness through multiple calendering processes.

[0114] According to one embodiment of the present invention, the spacing between multiple rolls in the process of forming an electrode film can be appropriately controlled considering the specifications and physical properties of the electrode film to be manufactured. For example, in Figure 3B, compared to Figure 3A, the spacing between the second and third rolls and the spacing between the fourth and fifth rolls can be controlled to be even larger.

[0115] Specifically, such calendering may involve processing the electrode mixture powder into a film, for example, to produce a film with an average thickness of 50 μm to 300 μm.

[0116] In this case, the calendering process can be performed, for example, by opposing rolls. According to one embodiment of the present invention, the calendering process can be repeated one or more times, for example, one to five times, three to four times, or four times.

[0117] In this case, the roll temperature can range from 50°C to 200°C.

[0118] The rotation speed ratio of the roll can be appropriately controlled depending on the size of the roll, the number of calendering cycles, and the thickness of the electrode film, and can be controlled in the range of, for example, 1 to 10 times, 1 to 8 times, 1 to 7 times, or 1.2 to 5 times.

[0119] Furthermore, the distance (gap) between the opposing pair of rolls can be variably adjusted according to the desired film thickness and density.

[0120] Specifically, narrowing the gap between the opposing pair of rolls increases the pressure, while widening the gap decreases the pressure. Since the gap between the opposing pair of rolls can vary depending on the film thickness, equipment tolerances, etc., it may be more appropriate to express it in terms of the force applied to a predetermined length or area.

[0121] According to one embodiment of the present invention, the force applied by the opposing pair of rolls may be 100 to 500 kgf, or 150 to 450 kgf, or 170 to 300 kgf, or 170 to 250 kgf, or 180 to 230 kgfg per 1 cm of roll width.

[0122] Once the process reaches this calendering step, a dry electrode film that acts as an electrode mixture can be manufactured. This type of dry electrode film is also conventionally known as a free-standing film.

[0123] The electrode film produced in this manner contains no solvent, has almost no fluidity, is easy to handle, and can be processed into desired shapes for use in the manufacture of various types of electrodes. Furthermore, when the electrode film of the present invention is used in the manufacture of electrodes, the drying process to remove the solvent can be omitted, which not only greatly improves the efficiency of electrode manufacturing but also solves problems that have plagued the manufacture of existing dry electrodes, such as the tearing of the active material and the breakage of the fibrous binder.

[0124] On the other hand, in one embodiment of the present invention, the porosity of the electrode film may be 20% to 35%, or 20% to 33%. In order to roll an electrode film having a porosity exceeding 35% to a porosity of 30% or less in the electrode layer of a single-sided or double-sided electrode obtained through a lamination step, high pressure is required. During the rolling process, curling occurs in the case of a single-sided electrode, and defects such as wrinkles and overlaps in the plain areas occur in the case of a double-sided electrode. However, in one embodiment of the present invention, if the porosity of the electrode film is within the range of 20% to 35%, such problems can be prevented. In one embodiment of the present invention, the porosity can be determined by measuring the external density of the electrode film and using the actual density calculated based on the actual density and composition of each constituent component, using the following formula. Porosity (%) = {1 - (Outer density / Actual density)} × 100

[0125] Next, the electrode film is laminated onto the metal current collector.

[0126] The lamination step may involve rolling and attaching the electrode film obtained in the above step to a current collector to a predetermined thickness. The lamination can also be performed using a laminating roll, in which case the laminating roll can be maintained at a temperature of 25 to 250°C.

[0127] According to one embodiment of the present invention, the compression ratio of the electrode film may be 30 to 50%, 35 to 50%, or 40 to 50%.

[0128] The compression ratio of the electrode film can be defined as the ratio of the thickness of the electrode film compressed at the moment of lamination, and can be expressed by the following equation 1. [Formula 1] Compression ratio (%) = T p / T1×100

[0129] In Equation 1, T p T1 refers to the thickness of the electrode film under pressure during the lamination step, while T1 refers to the thickness of the electrode film before the lamination step.

[0130] In the present invention, by adjusting the compression ratio in the lamination step to satisfy a specific range, it is possible to provide the electrode film with appropriate density and porosity, as well as excellent adhesion between the electrode film and the current collector.

[0131] When the compression ratio of the electrode film is within the range of 30 to 50%, the pressure applied to the electrode film is sufficient, improving the adhesion between the electrode film and the current collector. This prevents the problem of the electrode film peeling off from the current collector after the lamination process, and solves the problems of the electrode film's density increasing excessively, resulting in a porosity lower than the target porosity, or the current collector being damaged.

[0132] In one embodiment of the present invention, when electrode films are laminated to both sides of the current collector, the compression ratio (%) of formula 1 may mean the following formula 2. [Formula 2] 30 ≤ (T1 + 0.5T) c -0.5T gap ) / T1×100≦50

[0133] In Equation 2, T1 represents the thickness of the electrode film before the lamination step, and T c This refers to the thickness of the current collector, T gap This refers to the distance between the first and second rolling rolls.

[0134] Furthermore, the rolling ratio of the electrode film that has undergone the lamination step during the manufacturing of the double-sided electrode may be in the range of 20% or less, or 18% or less, or 15% or less, or 5% to 15%, or 6% to 15%, or 7% to 15%, or 9% to 13%.

[0135] The rolling ratio of the electrode film that has undergone the lamination step during the manufacture of a single-sided electrode according to one embodiment of the present invention may be in the range of 10% or less, or 3% to 10%, or 3.5% to 10%, or 3.7% to 7.1%, or 3.7% to 4.9%, or 4.9% to 7.1%.

[0136] Here, the rolling ratio can be defined as the ratio of the thickness of the electrode film after the lamination step to the thickness of the electrode film before the lamination step, and can be expressed by the following equation 3. [Formula 3] Rolling ratio (%) = (T1 - T2) / T1 × 100

[0137] In the above formula 3, T1 represents the thickness of the electrode film before the lamination step, and T2 represents the thickness of the electrode film after the lamination step.

[0138] When the rolling ratio satisfies the range described above, it is possible to achieve appropriate density and porosity of the electrode film, as well as adhesive strength between the electrode film and the current collector.

[0139] The percentage increase in the external density of the electrode film before and after lamination with the current collector can be shown by the following equation 4. [Formula 4] Increase rate of external density (%) = (D2 - D1) / D1 × 100

[0140] D1 is the apparent density (g / cm³) of the electrode film before the lamination step. 3 ) is shown, and D2 is the apparent density (g / cm³) of the electrode film after the lamination step. 3 ) indicates.

[0141] The increase rate of the appearance density before and after lamination with the current collector of the film for the electrode can be 5 to 30%, or 7 to 25%, or 10 to 20%.

[0142] D1 and D2 indicating the appearance density of the film for the electrode can be variously changed depending on the type of the active material. According to one embodiment of the present invention, when the active material is lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1), or an oxide in which a part of lithium nickel-manganese-cobalt oxide is substituted with aluminum (lithium nickel-manganese-cobalt-aluminum oxide) Li a [Ni b Co c Mn d Al e 1-f M 1 f O2 (where the M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1), etc., the D1 and D2 can be in the range of 2.75 g / cm 3 to 3.8 g / cm 3 .

[0143] On the other hand, when the increase rate of the appearance density of the film for the electrode satisfies the above range, the adhesive force between the film for the electrode and the current collector can be improved, and problems such as the porosity deviating from the target range or the active material or the current collector being damaged can be prevented.

[0144] ​The external density of the electrode film before and after lamination with the current collector can be calculated by measuring the weight and thickness of the electrode film before lamination, measuring the weight and thickness of the electrode after lamination, and then subtracting the weight and thickness of the current collector to obtain the weight and thickness of the film.

[0145] Furthermore, the active material load capacity of the electrode film is 3 mAh / cm². 2 From 15mAh / cm² 2 For more details, see 4mAh / cm². 2 From 10mAh / cm² 2 It is possible.

[0146] Here, the load amount of the active material is the value calculated using the following formula 5. [Formula 5] Loading capacity of active material (mAh / cm²) 2 ) = Active material capacity (mAh / g) × Weight content ratio of active material in dry electrode film (wt%) × Weight per unit area of ​​dry electrode film (g / cm²) 2 )

[0147] Furthermore, the interfacial resistance between the electrode film and the current collector is 5 Ω·cm. 2 For more details, see below: 2Ω·cm 2 The following is possible. Here, the interfacial resistance can be calculated by applying a current of 100 μA to the electrode using the MP (Multi Probe) resistance measurement method and measuring the resistance value between the dry electrode film and the current collector layer by measuring the potential difference between multiple probes. If the interfacial resistance range is satisfied, the battery performance of the secondary battery manufactured thereafter can be improved.

[0148] Figure 4 is a schematic diagram of the step of laminating electrode films to both sides of a current collector in a double-sided electrode applied to an electrode assembly according to one embodiment of the present invention. That is, in the lamination step (200), the electrode 240 is finally obtained by rolling and attaching the electrode film 230 obtained in the above step to the current collector 220 to a predetermined thickness using a pair of laminating rolls 210.

[0149] Figure 5 is a schematic diagram of the step of laminating an electrode film to one side of a current collector in a single-sided electrode applied to an electrode assembly according to one embodiment of the present invention. That is, in the lamination step (200), the electrode 240 is finally obtained by rolling and attaching the electrode film 230 obtained in the above step to the current collector 220 to a predetermined thickness using a pair of laminating rolls 210.

[0150] According to one aspect of the present invention, a secondary battery is provided that includes an electrode assembly according to the above-described embodiment of the present invention. A secondary battery is provided in which the electrode assembly is incorporated together with a lithium-containing non-aqueous electrolyte in a battery case (cylindrical case, rectangular case, pouch, etc.), and an energy storage device is provided that includes this as a unit battery.

[0151] Since the specific structure of the secondary battery and energy storage device is well known, a detailed explanation is omitted in this specification.

[0152] On the other hand, according to one embodiment of the present invention, a manufacturing apparatus for realizing the above-described method for manufacturing a unit electrode or double-sided electrode is provided, comprising: a blender for mixing a mixture raw material containing an active material, a binder, and (optionally further containing a conductive material); a kneader for kneading the mixture to produce a mixture mass; a pulverizer for crushing the mixture mass to form an electrode mixture powder; a calendar for forming the electrode mixture powder into a dry electrode film; and a laminating roll for arranging and laminating the dry electrode film on at least one surface of a current collector.

[0153] The blender is a mixer for mixing raw materials, and as described above, it can mix the raw materials for the mixture at a speed of 5,000 rpm to 20,000 rpm. A super mixer or the like can be used as the mixer.

[0154] The kneader is a device for fiberizing the binder and dispersing the raw materials of the mixture according to the present invention, and the mixture can be obtained as a mass by kneading with the kneader. In this case, the kneader for obtaining the results according to the present invention can be operated in a temperature range of 70°C to 200°C or 90°C to 180°C, and under atmospheric pressure or above, or under a pressure of 1 atm to 60 atm, or under a pressure of 1 atm to 30 atm, or under a pressure of 1 atm to 10 atm, or under a pressure of 1 atm to 8 atm, or under a pressure of 1.1 atm to 7 atm, or under a pressure of 1.1 atm to 6 atm.

[0155] The aforementioned crusher is a device that crushes such a mixture mass to form a mixed powder for electrodes, and this can also be a blender or grinder, and examples of grinders include cutter mills and fine mills.

[0156] The calender is a device for forming the electrode mixture powder into a film, and is, for example, a pair of opposing rollers, the thickness of the film can be adjusted by the distance between them.

[0157] The laminating roll serves to adhere and roll the dry electrode film, formed by the calender, onto at least one surface of the current collector.

[0158] The porosity of the dry electrode film according to the present invention can be determined by such a calender and laminating roll.

[0159] In other words, the dry electrode manufacturing apparatus according to the present invention is characterized by including a kneader and a grinder.

[0160] The specific structures of the aforementioned blender, kneader, calender, and laminating roll are conventionally known, and therefore, a detailed explanation is omitted in this specification.

[0161] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the examples described in detail below. Embodiments of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0162] Example 1 (1) Manufacturing of single-sided positive electrodes Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni) is used as the positive electrode active material. 0.87 Co 0.05 Mn 0.07 Al 0.01 960g of O2, 10g of carbon black as a conductive material, and 30g of polytetrafluoroethylene (PTFE) as a binder were placed in a blender and mixed at 10,000 rpm for 1 minute to prepare the mixture, which was then placed in a kneader.

[0163] The kneader temperature was stabilized at 150°C, and the mixture was placed in the kneader. The lid was then operated at a speed of 40 rpm for 5 minutes under a pressure of 1.1 atmospheres (atm) to obtain a mixture mass. The mixture mass was placed in a blender and crushed at 10,000 rpm for 30 seconds. It was then classified using a sieve with a pore size of 1 mm to obtain an electrode mixed powder. Subsequently, the manufactured electrode mixed powder was fed three times into a wrap calender (roll diameter: 160 mm, roll temperature: 100°C) to produce an electrode film. By adjusting the gap during calendering, it was possible to manufacture an electrode film with the desired density (porosity).

[0164] At this time, by adjusting the pressing force during the calendering process, it was possible to manufacture a dry electrode film with the desired porosity. The pressure applied by the pair of opposing rolls during the calendering process was 221 kgf per 1 cm of film width.

[0165] A single electrode film was placed on one side of a current collector (aluminum foil (15 μm thick) coated on both sides with a conductive primer layer of carbon black and PVDF binder mixed in a 1:2 weight ratio, with a thickness of 0.5 μm on each side), and laminated through a room-temperature compression roll (laminating roll) to produce a single-sided positive electrode.

[0166] At this time, the lamination conditions were that the diameter of the opposing pair of compression rolls was 200 mm, the peripheral speed ratio of the pair of compression rolls was 1:1, and the force applied by the compression rolls was 155 kgf per 1 cm of film width.

[0167] At this time, Table 1 shows the thickness, porosity, and loading of the electrode film before the lamination step, the rolling ratio in the lamination step, and the thickness, porosity, and loading of the electrode layer provided on one side of the current collector after the lamination step.

[0168] (2) Manufacturing of electrode assemblies 1) Manufacturing of double-sided negative electrodes A negative electrode mixture was prepared by mixing 97.6 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) as the negative electrode active material, 1.2 parts by weight of styrene-butadiene rubber (SBR) which functions as a binder, and 1.2 parts by weight of carboxymethylcellulose (CMC). A negative electrode mixture slurry was prepared by dispersing this negative electrode mixture in deionized water which functions as a solvent. A double-sided negative electrode was manufactured by coating both sides of a 20 μm thick copper foil with this slurry, drying, and pressing it.

[0169] 2) Manufacturing of double-sided positive electrodes Except for the manufacturing step of the single-sided positive electrode in which two electrode films were placed on both sides of the current collector and laminated, the double-sided positive electrode was manufactured using the same process as for the single-sided positive electrode. In this case, the load capacity of the double-sided electrode was 5.0 mAh / cm². 2 The porosity of the electrode layer was 26%.

[0170] 3) Manufacturing of electrode assemblies An electrode assembly was manufactured by stacking the aforementioned single-sided positive electrode, double-sided negative electrode, and double-sided positive electrode with a polyethylene membrane (thickness: 9 μm) as a separation membrane, in the order of single-sided positive electrode / separation membrane / double-sided negative electrode / separation membrane / double-sided positive electrode / separation membrane / double-sided negative electrode / separation membrane / double-sided positive electrode / separation membrane / separation membrane / double-sided negative electrode / separation membrane / double-sided positive electrode / separation membrane / double-sided negative electrode.

[0171] Example 2 Except for the fact that the thickness, porosity, and loading of the electrode film before the lamination step, the rolling rate in the lamination step, and the thickness, porosity, and loading of the electrode layer provided on one side of the current collector after the lamination step were set to the conditions shown in Table 1, a single-sided positive electrode and an electrode assembly were manufactured in the same manner as in Example 1.

[0172] At this time, by adjusting the pressing force during the calendering process, it was possible to manufacture a dry electrode film with the desired porosity. The pressure applied by the pair of opposing rolls during the calendering process was 170 kgf per 1 cm of film width.

[0173] At this time, the lamination conditions were that the diameter of the opposing pair of compression rolls was 200 mm, the peripheral speed ratio of the pair of compression rolls was 1:1, and the force applied by the compression rolls was 257 kgf per 1 cm of film width.

[0174] Example 3 Except for the fact that the thickness, porosity, and loading of the electrode film before the lamination step, the rolling rate in the lamination step, and the thickness, porosity, and loading of the electrode layer provided on one side of the current collector after the lamination step were set to the conditions shown in Table 1, a single-sided positive electrode and an electrode assembly were manufactured in the same manner as in Example 1.

[0175] At this time, by adjusting the pressing force during the calendering process, it was possible to manufacture a dry electrode film with the desired porosity. The pressure applied by the pair of opposing rolls during the calendering process was 264 kgf per 1 cm of film width.

[0176] At this time, the lamination conditions were as follows: the diameter of the opposing pair of compression rolls was 200 mm, the peripheral speed ratio of the pair of compression rolls was 1:1, and the force applied by the compression rolls was 190 kgf per 1 cm of film width.

[0177] Example 4 Except for the fact that the thickness, porosity, and loading of the electrode film before the lamination step, the rolling rate in the lamination step, and the thickness, porosity, and loading of the electrode layer provided on one side of the current collector after the lamination step were set to the conditions shown in Table 1, a single-sided positive electrode and an electrode assembly were manufactured in the same manner as in Example 1.

[0178] At this time, by adjusting the pressing force during the calendering process, it was possible to manufacture a dry electrode film with the desired porosity. The pressure applied by the pair of opposing rolls during the calendering process was 386 kgf per 1 cm of film width.

[0179] At this time, the lamination conditions were that the diameter of the opposing pair of compression rolls was 200 mm, the peripheral speed ratio of the pair of compression rolls was 1:1, and the force applied by the compression rolls was 85 kgf per 1 cm of film width.

[0180] Comparative Example 1 Except for the fact that the thickness, porosity, and loading of the electrode film before the lamination step, the rolling rate in the lamination step, and the thickness, porosity, and loading of the electrode layer provided on one side of the current collector after the lamination step were set to the conditions shown in Table 1, a single-sided positive electrode and an electrode assembly were manufactured in the same manner as in Example 1.

[0181] At this time, by adjusting the pressing force during calendering, it was possible to manufacture a dry electrode film with the desired porosity. The pressure applied by the pair of opposing rolls during calendering was 130 kgf per 1 cm of film width.

[0182] At this time, the lamination conditions were that the diameter of the opposing pair of compression rolls was 200 mm, the peripheral speed ratio of the pair of compression rolls was 1:1, and the force applied by the compression rolls was 575 kgf per 1 cm of film width.

[0183] Comparative Example 2 Except for the fact that the thickness, porosity, and loading of the electrode film before the lamination step, the rolling rate in the lamination step, and the thickness, porosity, and loading of the electrode layer provided on one side of the current collector after the lamination step were set to the conditions shown in Table 1, a single-sided positive electrode and an electrode assembly were manufactured in the same manner as in Example 1.

[0184] At this time, by adjusting the pressing force during calendering, it was possible to manufacture a dry electrode film with the desired porosity. The pressure applied by the pair of opposing rolls during calendering was 112 kgf per 1 cm of film width.

[0185] At this time, the lamination conditions were that the diameter of the opposing pair of compression rolls was 200 mm, the peripheral speed ratio of the pair of compression rolls was 1:1, and the force applied by the compression rolls was 210 kgf per 1 cm of film width.

[0186] Performance evaluation The single-sided electrodes (positive electrodes) constituting the electrode assemblies manufactured in Examples 1 to 4 and Comparative Examples 1 to 2 were evaluated as follows, and the results are shown in Table 1.

[0187] (1) Thickness The thickness was measured using a thickness measuring instrument (Mitutoyo, VL-50S-B).

[0188] (2) Load The load amount was calculated using the following relationship. Load capacity (mAh / cm²) 2 ) = [Active material capacity (mAh / g)] × [Weight content ratio of active material in electrode film (wt%)] × [Weight per unit area of ​​electrode film (g / cm²)] 2 )]

[0189] (3) Porosity (%) In this case, the porosity of the electrodes was determined by measuring the external density of the electrode layer alone by subtracting the volume and weight of the current collector from the volume and weight of the electrodes, and then using the actual density calculated based on the actual density and composition of each component, the actual porosity of each electrode was determined by the following relational equation. Porosity (%) = {1 - (Outer density / Actual density)} × 100

[0190] (4) Curl of single-sided electrode After placing the manufactured single-sided electrode on the reference surface so that its electrode layer faces the flat reference surface, the height of the edges on both sides of the single-sided electrode raised from the reference surface was measured in millimeters using a ruler, and the maximum height was defined as the curl of the single-sided electrode.

[0191] Figure 9 is a photograph showing the curl measurement results for a single-sided electrode in Example 2, and Figure 10 is a photograph showing the curl measurement results for a single-sided electrode in Comparative Example 1.

[0192] [Table 1]

[0193] Referring to Table 1, it is determined that the electrode assemblies of Examples 1 to 4 have an electrode layer with a porosity of 30% or less for the outermost single-sided electrode, a curl of 30 mm or less for the single-sided electrode, and a maximum energy density, thereby providing an electrode assembly with improved curl characteristics. On the other hand, in the case of the single-sided electrode applied to the electrode assembly of Comparative Example 1, the curl was severely entangled, making curl measurement impossible (NG), and in the case of the single-sided electrode applied to the electrode assembly of Comparative Example 2, the porosity of the electrode layer of the single-sided electrode showed a high value.

Claims

1. A group of monocells containing one or more monocells, A single-sided electrode is stacked on one or more of the upper and lower outermost parts of the monocell group, The group of monocells and the single-sided electrode are interposed in a separation membrane. The monocell comprises a double-sided positive electrode, a double-sided negative electrode, and a separation membrane between the double-sided positive electrode and the double-sided negative electrode. The single-sided electrode comprises a current collector and an electrode layer located only on one side of the current collector, which includes an active material and a binder, wherein the binder is fibrous and binds the active material, and the porosity of the electrode layer is 30% or less. The porosity of the electrode layer is determined from the external density and the actual density of the electrode layer by the formula: porosity (%) = {1 - (external density / actual density)} × 100. The curl of the aforementioned single-sided electrode is 30 mm or less. The curl of the single-sided electrode is the maximum of the measured heights of the edges on both sides of the single-sided electrode raised from the reference surface, with the electrode layer of the single-sided electrode facing a flat reference surface. An electrode assembly in which the electrode layer is derived from a film for dry electrodes.

2. The electrode assembly according to claim 1, wherein the monocell group includes one monocell or two or more stacked monocells.

3. The electrode assembly according to claim 1, wherein a half-cell is further interposed between the monocell group and the single-sided electrode, and the half-cell is a double-sided positive electrode or a double-sided negative electrode.

4. The electrode assembly according to claim 1 or 3, wherein the difference between the porosity of the electrode layer of the single-sided electrode and the porosity of the electrode layer of the other electrode facing the single-sided electrode is 5% or less.

5. The electrode assembly according to claim 1, wherein the electrode layer further comprises a conductive material.

6. The electrode assembly according to claim 1, wherein the binder comprises polytetrafluoroethylene (PTFE).

7. The electrode assembly according to claim 5, wherein the content of the active material is 80 to 98 parts by weight, the content of the conductive material is 0.5 to 10 parts by weight, and the content of the binder is 0.5 to 5 parts by weight.

8. The electrode assembly according to claim 1, wherein the current collector further comprises a conductive primer layer on at least one surface.

9. A secondary battery comprising the electrode assembly described in claim 1.

10. An energy storage device comprising the secondary battery described in claim 9 as a unit battery.

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