Positive electrode, method for producing same, and lithium secondary battery including same

Abstract

The present invention relates to a dry positive electrode comprising a positive electrode active material comprising an overlithiated manganese-rich oxide, and a method for producing same. The positive electrode comprises: a current collector; and a film-shaped positive electrode mixture layer disposed on the current collector and including a positive electrode active material, a fiberized binder, and a conductive material, wherein the positive electrode active material includes a predetermined overlithiated manganese-rich oxide, and the porosity of the positive electrode mixture layer may be 22% or more and less than 28%.

Description

Positive electrode, method for manufacturing the same, and lithium secondary battery comprising the same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0119244, filed September 3, 2024, and Korean Patent Application No. 10-2025-0123068, filed September 1, 2025, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a positive electrode, a method for manufacturing the same, and a lithium secondary battery including the same, and more particularly, to a method for manufacturing the positive electrode, a positive electrode having improved porosity and energy density, a method for manufacturing the same, and a lithium secondary battery including the same.

[0004] With the rapid development of the electronics, communications, and computer industries, the application of energy storage technology is expanding to include camcorders, mobile phones, laptops, PCs, and even electric vehicles. Consequently, the development of lightweight, long-lasting, and highly reliable high-performance secondary batteries is underway.

[0005] Among electrochemical devices, interest is growing in the development of rechargeable secondary batteries, and in particular, lithium secondary batteries developed in the early 1990s are attracting attention due to their high operating voltage and superior energy density.

[0006] Lithium secondary batteries are generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that serves as a medium for transferring lithium ions, and then sealing the electrode assembly.

[0007] Recently, as demand for high-energy-density secondary batteries, such as those for electric vehicle batteries, has increased, development of high-voltage and high-capacity secondary batteries that operate at high voltages is actively underway.

[0008] In particular, interest in and research on lithium manganese-rich oxides as next-generation cathode active materials for the manufacture of high-capacity secondary batteries has recently increased. However, these lithium manganese-rich oxides not only generate significant gas during activation and charge / discharge processes, but also have high internal porosity, making it difficult to achieve high energy density and cycle life characteristics due to the secondary particles easily breaking during rolling. Therefore, ongoing efforts are being made to improve the energy density and cycle life characteristics of cathodes containing lithium manganese-rich oxides, while reducing the amount of gas generated.

[0009] Accordingly, one embodiment of the invention provides a cathode including lithium manganese rich oxide as a cathode active material, and exhibiting reduced gas generation along with excellent capacity and life characteristics, and a method for manufacturing the same.

[0010] According to one embodiment of the invention, the invention comprises the steps of forming a positive electrode powder by mixing a positive electrode active material, a fiberizable binder, and a conductive material in a solid phase; and the step of forming a positive electrode mixture layer by calendering the positive electrode powder into a film form.

[0011] The above positive electrode active material includes a layered crystal structure, a molar ratio of lithium to the molar number of all metals excluding lithium exceeds 1, and a method for manufacturing a positive electrode including a lithium manganese-rich oxide containing manganese in a content of 50 mol% or more among all metals excluding lithium is provided.

[0012] In the manufacturing method of this embodiment, the lithium manganese rich oxide may be represented by the following chemical formula 1:

[0013] [Chemical Formula 1]

[0014] Li a [Mn b Ni c M d ] 2-a O2

[0015] In the above chemical formula 1, a is greater than 1, b is 0.5 or more and less than 1, c and d are each 0 or more and 0.5 or less, but 0 <c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

[0016] In addition, in the manufacturing method of the above embodiment, the porosity of the positive electrode mixture layer may be 22% or more and less than 28%, or 22% or more and less than 25%.

[0017] In the above manufacturing method, the fiberizable binder may include a plurality of fluorine-substituted polyolefin resins, for example, polytetrafluoroethylene (PTFE).

[0018] In addition, the conductive material may include at least one selected from the group consisting of carbon-based materials, metal powders, metal fibers, conductive fibers, conductive whiskers, metal oxides, and conductive polymers.

[0019] In the manufacturing method of the above embodiment, the step of forming the positive electrode powder may include a first step of mixing a positive electrode active material, a fiberizable binder, and a conductive material to form a mixture; a second step of kneading the mixture to form a mixture mass; and a third step of grinding the mixture mass to form the positive electrode powder.

[0020] In a specific embodiment, based on the total weight of the positive electrode powder, the content of the positive electrode active material may be 95 wt% or more and 98.9 wt% or less, the binder may be 1 wt% or more and 3 wt% or less, and the conductive material may be 0.1 wt% or more and 2 wt% or less.

[0021] In addition, the manufacturing method may further include a step of forming a positive electrode by laminating the positive electrode mixture layer on a current collector, and the adhesion of the positive electrode mixture layer to the current collector may be 100 gf / 20 mm or more, or 100 gf / 20 mm to 200 gf / 20 mm.

[0022] Meanwhile, according to another embodiment of the invention, a positive electrode is provided, comprising: a current collector; and a film-shaped positive electrode mixture layer disposed on the current collector and including a positive electrode active material, a fiberized binder, and a conductive material; wherein the positive electrode active material has a layered crystal structure, a molar ratio of lithium to the molar number of total metals excluding lithium exceeds 1, and includes a lithium manganese-rich oxide containing manganese in a content of 50 mol% or more among total metals excluding lithium, and wherein the porosity of the positive electrode mixture layer is 22% or more and less than 28%, or 22% or more and less than 25%.

[0023] In the positive electrode of these other embodiments, the lithium manganese rich oxide may be represented by the following chemical formula 1:

[0024] [Chemical Formula 1]

[0025] Li a [Mn b Ni c M d ] 2-a O2

[0026] In the above chemical formula 1, a is greater than 1, or 1.1 <a<1.3이고, b는 0.5 이상 1 미만, 혹은 0.5≤b≤0.9이고, c 및 d는 각각 0 이상 0.5 이하이되, 0.1≤c≤0.5이고, 0≤d≤0.1일 수 있고, 0<c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

[0027] In a specific embodiment, the lithium manganese rich oxide may include a rock salt structure compound and a layered structure compound in a mixed state, and may be represented by, for example, the following chemical formula 2:

[0028] [Chemical Formula 2]

[0029] X*Li2MnO3·(1-X)*Li[NiwMnyMz]O2

[0030] In the above chemical formula 2,

[0031] M is at least one selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.2≤X≤0.5, 0≤w≤0.5, 0.4≤y<1, 0≤z≤0.2, but 0 <w+z≤0.5임.

[0032] In the positive electrode of the other embodiment, the fiberized binder may include a plurality of fluorine-substituted polyolefin resins, for example, polytetrafluoroethylene (PTFE). In addition, the conductive material may include a carbon-based material such as carbon blank.

[0033] Meanwhile, according to an additional embodiment of the invention, a lithium secondary battery is provided, including the positive electrode, the negative electrode, and a separator or electrolyte layer interposed between the positive electrode and the negative electrode of the other embodiment described above.

[0034] Such lithium secondary batteries may further include an electrolyte including a lithium salt and a non-aqueous organic solvent.

[0035] According to embodiments of the invention, a cathode comprises a high-capacity lithium manganese-rich oxide as a cathode active material, and this cathode active material is incorporated into a dry-manufactured cathode mixture layer. As a result, it was confirmed that the porosity of the cathode mixture layer is low and the amount of gas generated from the lithium manganese-rich oxide can be reduced.

[0036] Accordingly, the above positive electrode exhibits excellent life characteristics and energy density, along with reduced gas generation, and thus can be preferably used in next-generation lithium secondary batteries.

[0037] Figure 1 is a graph evaluating the amount of gas generated at high temperature (45°C) for lithium secondary batteries of examples and comparative examples.

[0038] Figure 2 is a graph evaluating the amount of gas generated after high-temperature (65°C) storage for lithium secondary batteries of examples and comparative examples.

[0039] Hereinafter, with reference to the attached drawings, implementation examples of the invention will be described in detail so that a person having ordinary knowledge in the technical field to which the invention pertains can easily carry out the invention.

[0040] In the following specification, “lithium manganese rich oxide” or “manganese rich positive electrode active material” may refer to a lithium metal oxide having a layered crystal structure, a molar ratio of lithium to the number of moles of total metals excluding lithium exceeding 1, and containing manganese in an amount of 50 mol% or more among the total metals excluding lithium.

[0041] In addition, the term “film-like” positive electrode mixture layer hereinafter is used to define a positive electrode mixture layer manufactured by a dry process, unlike a positive electrode mixture layer manufactured by a wet process. For example, the “film-like” positive electrode mixture layer may refer to a positive electrode active material, a binder (e.g., a fiberizable binder), and a conductive material formed by mixing in a dry state and calendering under pressure, unlike a positive electrode mixture layer formed by applying and drying a slurry in which a positive electrode active material, a binder, and a conductive material are dispersed in an organic solvent to a current collector or the like, and forming the positive electrode mixture layer. Such a “film-like” positive electrode mixture layer may have a form and characteristics that are distinct from the positive electrode mixture layer formed by the wet process, for example, in terms of residual solvent, the form of the fiberized binder, or the porosity immediately after manufacturing.

[0042] Furthermore, when we say that a layer, membrane, region, plate, or other part is "above" or "on" another part, this includes not only cases where it is "directly above" the other part, but also cases where there are other parts in between. When we say that a part is "directly above" another part, we mean that there are no other parts in between. Furthermore, saying that a part is "above" or "on" a reference part means that it is located above or below the reference part, and does not necessarily mean that it is located "above" or "on" in the direction opposite to gravity.

[0043] Also, when a part is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0044]

[0045] Hereinafter, a method for manufacturing a positive electrode, a positive electrode, and a lithium secondary battery according to embodiments of the invention will be described.

[0046] A method for manufacturing an anode according to an embodiment includes a step of forming a powder for an anode by mixing a fiberizable binder and a conductive material in a solid phase; and a step of forming a positive electrode mixture layer by calendering the positive electrode powder into a film form.

[0047] The above positive electrode active material may include a layered crystal structure, a molar ratio of lithium to the molar number of all metals excluding lithium exceeding 1, and a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more among all metals excluding lithium.

[0048] The above lithium manganese-rich oxide is known as a next-generation cathode active material with higher capacity characteristics because it can develop capacity by utilizing not only the redox reaction of transition metal cations but also the redox reaction of oxygen anions. However, this lithium manganese-rich oxide requires improvement in its relatively high porosity and low density, as well as the large amount of gas generated during activation and charge / discharge processes.

[0049] As confirmed in the examples below, when the lithium manganese-rich oxide is used as a cathode active material and a cathode including the same is manufactured by a dry process to include a cathode composite layer on a film, it was confirmed that it is possible to manufacture a cathode having a low porosity, reduced gas generation, and high density while exhibiting electrical and chemical properties such as high capacity characteristics unique to the manganese-rich cathode active material.

[0050] In the above manufacturing method, the step of forming a positive electrode powder by mixing a positive electrode active material, a binder, and a conductive material in a solid phase is a step of dry manufacturing the positive electrode active material, a binder, and a conductive material without a solvent.

[0051] In one embodiment, the lithium manganese rich oxide, which is a main component of the positive electrode active material, may be represented by the following chemical formula 1:

[0052] [Chemical Formula 1]

[0053] Li a [Mn b Ni c M d ] 2-a O2

[0054] In the above chemical formula 1, a is greater than 1, b is 0.5 or more and less than 1, c and d are each 0 or more and 0.5 or less, but 0 <c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

[0055] The above lithium manganese-rich oxide may have a molar ratio of lithium to the total number of moles of metals excluding lithium of greater than 1, or 1.1 to 1.5, or 1.3 to 1.5. In one example, the molar ratio of lithium may be calculated from the equation “a / (2-a)” in the above chemical formula 1. In addition, in the above chemical formula 1, a is a molar ratio of Li in the lithium manganese-rich oxide, and a in the above chemical formula 1 may satisfy 1.1≤a≤1.5, 1.1≤a≤1.4, 1.1≤a≤1.3, or 1.14≤a≤1.3.

[0056] As the molar ratio of lithium to the above-described a and the remaining metals satisfies the above-described ranges, the chemical and crystallographic stability of the lithium manganese-rich oxide can be maintained while achieving a higher capacity and excellent rate characteristics. In addition, if the molar ratio of lithium to the remaining metals is excessively high, the electrical conductivity may decrease and the rock salt phase (Li2MnO3) may increase, which may accelerate the degradation rate, and if it is too low, the effect of improving the energy density may be minimal.

[0057] The above b is the molar ratio of Mn in the lithium manganese rich oxide, and can satisfy 0.5≤b<1, 0.5≤b≤0.9, or 0.55≤b≤0.8 in the above chemical formula 1. As a result, the excellent capacity characteristics unique to the lithium manganese rich oxide can be exhibited.

[0058] The above c is the molar ratio of Ni in the lithium manganese rich oxide, and can satisfy 0≤c≤0.5, 0≤c<0.5, 0.1≤c≤0.5, 0.1≤c≤0.45, or 0.3≤c≤0.4 in the above chemical formula 1.

[0059] The above d is a molar ratio of element M added to the lithium manganese rich oxide or added in the form of doping, etc., and may be 0≤d≤0.5, 0≤d<0.5, 0≤d≤0.2, or 0≤d≤0.1 in the above chemical formula 1. If the content of the additional element M is too high, not only may it have a negative effect on the capacity of the active material, but there is also a concern that the life characteristics may be deteriorated due to the increased oxygen-redox reaction, which may aggravate gas generation and deterioration of the positive electrode active material.

[0060] A more suitable example of the above M may be at least one selected from the group consisting of Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr, and in a more specific embodiment, at least one selected from the group consisting of Co, Zn, Ti, Al, Mg and B may be added to the lithium manganese rich oxide in the form of doping or the like.

[0061] In addition, in a specific embodiment, the lithium manganese-rich oxide may contain additional elements M or the like only on the surface in the form of doping elements, and may contain nickel: manganese in a molar ratio of 25:75 to 50:50, or 25:75 to 45:55, or 30:70 to 40:60. In the above-described range, if the molar ratio of manganese is excessively small, the proportion of the rock salt phase may not be sufficient, resulting in insufficient capacity or deterioration of crystallographic and chemical stability. Conversely, if the molar ratio of manganese is excessively large, the stability of the lithium manganese-rich oxide may be deteriorated.

[0062] Meanwhile, in one example of the above chemical formula 1, b+c+d may satisfy 1, but in another example, it may have a value greater than or equal to 0.9 and less than 1. The fact that b+c+d is less than 1 may indicate that the above chemical formula 1 further includes an additional metal element in addition to manganese, nickel, and the additional element M. However, it is of course understood that such additional metal elements may be added within the limit of maintaining the crystal structure characteristic of the lithium manganese-rich oxide.

[0063] In a specific embodiment of the positive active material of one embodiment, the lithium manganese rich oxide may be a compound represented by the following chemical formula 1a:

[0064] [Chemical Formula 1a]

[0065] Li a [Mn b Ni c M d ] 2-a O2

[0066] In the above chemical formula 1, 1.1 <a<1.3이고, 0.5≤b≤0.9, 0.1≤c≤0.5이고, 0≤d≤0.1이고, 이고, M은 Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

[0067] Meanwhile, in the case of lithium manganese-rich oxides containing an excess of lithium, compounds having a rock salt structure, for example, Li2MnO3, and compounds having a layered structure, for example, Li[Ni w Mn y M z ]O2 can be included in a mixed state. Accordingly, the lithium manganese rich oxide can be represented by the following chemical formula 2:

[0068] [Chemical Formula 2]

[0069] X*Li2MnO3·(1-X)* Li[Ni w Mn y M z ]O2

[0070] In the above chemical formula 2,

[0071] M is at least one selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.2≤X≤0.5, 0≤w≤0.5, 0.4≤y<1, 0≤z≤0.2, but 0 <w+z≤0.5임.

[0072] The above X represents the ratio of the rock salt phase (Li2MnO3 phase) in the lithium manganese rich oxide, and the above w, y, and z represent the molar ratios of Ni, Mn, and additional element M in the layered structure compound, respectively.

[0073] Meanwhile, if necessary, a coating layer may be further included on the surface of the lithium manganese-rich oxide. In this case, the coating layer suppresses contact between the lithium manganese-rich oxide and the electrolyte, thereby reducing electrolyte side reactions and improving life characteristics.

[0074] The coating layer may include a coating element M1, and the coating element M1 may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, for example. The coating element M1 may include two or more types, and may include, for example, Al and Co.

[0075] The above coating element may exist in the form of an oxide, i.e., M1Oz (1≤z≤4), within the coating layer.

[0076] The above coating layer can be formed through methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, formation through atomic layer deposition is preferable because it can form a large coating layer area.

[0077] The formation area of ​​the above coating layer may be 10% to 100%, 30% to 100%, or 50% to 100% based on the total surface area of ​​the positive electrode active material particles including the lithium manganese rich oxide. When the formation area of ​​the coating layer satisfies the above range, the effect of improving the life characteristics is excellent.

[0078] Meanwhile, in the manufacture of positive electrodes, a conventional wet process was applied, in which a slurry having fluidity was prepared by mixing positive electrode active materials, binders, conductive agents, and solvents for viscosity and dispersion. Subsequently, a coating process was performed to apply the slurry onto a current collector, followed by a drying process to remove the solvent contained in the slurry. Furthermore, the electrode was rolled to a predetermined thickness and dried to form the positive electrode.

[0079] However, in the case of the lithium manganese-rich oxide described above, the sphericity of the active material was low and the porosity within the particles was high, which caused the secondary particles to easily break during rolling. This made it difficult to sufficiently roll the electrode and achieve high energy density. Furthermore, the wet manufacturing method could not coat the slurry on the current collector above a certain level.

[0080]

[0081] In contrast, in the method of one embodiment, a powder for a cathode is manufactured by a dry process without using a solvent, so that even if a lithium manganese-rich oxide is used as a cathode active material, a cathode with a reduced porosity and improved energy density can be provided.

[0082] Any resin or polymer that can be fiberized under the application of shear force can be used as the binder used in this dry process. Examples of such fiberizable binders include a plurality of fluorine-substituted polyolefin resins, such as polytetrafluoroethylene (PTFE). In addition, the binder may further include additional polymers such as polyethylene oxide (PEO), polyvinylidenefluoride (PVdF), or polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) in addition to the fiberizable resin.

[0083] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery. For example, the conductive material may include at least one selected from the group consisting of carbonaceous materials such as graphite or carbon black, metal powders, metal fibers, conductive fibers, conductive whiskers, metal oxides, and conductive polymers. Specifically, the conductive material may 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, and thermal black; carbonaceous materials such as carbon fibers, single-walled carbon nanotubes, and multi-walled carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive fibers; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. More suitably, a carbonaceous material such as carbon black may be used as the conductive material.

[0084] The method for manufacturing the anode using a dry process can follow a standard method. Examples of such standard dry manufacturing processes are disclosed in U.S. Patent Publication No. 8,815,443, U.S. Patent Publication No. 1,015,3096, and others.

[0085] In one embodiment, the step of forming a powder for the positive electrode includes a first step of mixing a positive electrode active material, a fiberizable binder, and a conductive material to form a mixture, a second step of kneading the mixture to form a mixture mass, and a third step of grinding the mixture mass to form a powder for the positive electrode.

[0086] The first step involves dry mixing the aforementioned positive electrode active material, a fiberizable binder, and a conductive agent. The positive electrode active material, the binder, and the conductive agent are provided in powder form and can be mixed in a device such as a blender or supermixer without a solvent.

[0087] The above mixing may be performed at 5000 rpm to 20000 rpm, or 10000 rpm to 15000 rpm for 30 seconds to 20 minutes to ensure uniformity.

[0088] In one embodiment, based on the total weight of the positive electrode powder, the content of the positive electrode active material may be 95 wt% or more and 98.9 wt% or less, the content of the binder may be 1 wt% or more and 3 wt% or less, and the content of the conductive material may be 0.1 wt% or more and 2 wt% or less.

[0089] If the binder content is too high outside the above range, the binder may be excessively fiberized in the subsequent mixing process, which may adversely affect the process. If it is too low, sufficient fiberization may not occur, and the mixture may not be coagulated enough to form a lump, which may cause a problem of deterioration in the properties of the positive electrode mixture layer on the film. In addition, if the conductive material content is too high outside the above range, the content of the active material may be relatively reduced, which may cause a problem of reduced capacity, or the properties of the positive electrode mixture layer may be deteriorated. If it is too low, there is a problem of not being able to secure sufficient conductivity.

[0090] The second step is a kneading step to fiberize the binder within the mixture formed in the first step. This step can be performed in a kneading machine, such as a kneader. Through kneading, the binder within the mixture fiberizes, binding or connecting the positive electrode active material and conductive materials, and forming a mixture mass.

[0091] Specifically, the mixing step can be performed at a speed of 10 rpm to 100 rpm for 1 to 30 minutes. At this time, the shear rate can be performed in the range of 10 / s to 500 / s.

[0092] Additionally, this mixing step can be performed under conditions of high temperature and pressure higher than atmospheric pressure (1 atm), and more specifically, the mixing can be performed at a temperature of 70°C to 200°C, specifically, 90°C to 180°C, or 90°C to 150°C.

[0093] If the process is performed at a low temperature outside the above range, the fiberization and lump formation by the kneading of the binder during kneading are not performed well, so film formation is not easily performed during calendaring, and if the process is performed at an excessively high temperature, the fiberization of the binder occurs rapidly and the fibers already formed may be cut by excessive shear force, which is not preferable.

[0094] Additionally, it can be performed at a pressure higher than atmospheric pressure, specifically, at a pressure of 1 atm to 60 atm, or at a pressure of 1 atm to 30 atm, or at a pressure of 1 atm to 10 atm, or at a pressure of 1 atm to 3 atm, or at a pressure of 1.1 atm to 3 atm.

[0095] If the process is performed at a pressure that is too high beyond the above range, it is not desirable because excessive shear force and pressure may be applied, causing the formed fibers to break or the density of the mixture mass to become too high.

[0096] The third step is to grind the mixture lump formed in the second step again to form a powder for the positive electrode.

[0097] Specifically, the mixture lump manufactured through kneading in the second step may be directly calendered, but in this case, the mixture lump may need to be pressed under strong pressure and high temperature to be manufactured into a thin film, and thus, problems may arise in which the density of the film becomes too high or a uniform film cannot be obtained. Therefore, according to one embodiment of the method, the manufactured mixture lump undergoes the pulverization step.

[0098] At this time, the grinding is not limited, but may be performed with a blender, or a grinder such as a cutter mill or a fine impact mill, and the grinding may be performed specifically at a speed of 500 rpm to 20,000 rpm for 30 seconds to 10 minutes, and more specifically at a speed of 1,000 rpm to 10,000 rpm for 30 seconds to 1 minute.

[0099] If the process is performed outside the above range at too low a rpm or too short, sufficient grinding may not be achieved, which may result in powder particles of an unsuitable size for filming. If the process is performed at too high a rpm or too long, a large amount of fine particles may be generated in the mixture lump, which is not desirable.

[0100]

[0101] After the positive electrode powder is formed through the first to third steps described above, a step of forming a positive electrode mixture layer by calendering the positive electrode powder into a film is performed.

[0102] Specifically, the positive electrode composite layer can be manufactured by powder sheeting and calendaring the positive electrode powder and rolling it into a film form.

[0103] Powder sheeting and calendaring can be performed by a roll rotating at a constant speed, wherein the roll temperature can be from 50°C to 200°C and the roll rotation speed can be from 10 rpm to 50 rpm.

[0104] By proceeding to the calendaring stage, a positive electrode composite layer that functions as an electrode composite can be manufactured. This positive electrode composite layer is also referred to as a free-standing film.

[0105] The cathode composite layer manufactured as described above contains no solvent and thus exhibits minimal fluidity, making it easy to handle and process. Furthermore, since the cathode composite layer adheres to the current collector as a free-standing film, the sliding phenomenon that occurs when the electrode edge is pulled out during the conventional process of applying and drying cathode slurry onto the current collector can be minimized.

[0106] In addition, since the above-mentioned positive electrode mixture layer omits the drying process for solvent removal, the time and number of processes required for electrode manufacturing can be reduced compared to the conventional wet process, and the electrode manufacturing processability can be significantly improved. Furthermore, if the positive electrode mixture layer manufactured by the dry process falls short of the designed target value, it can be reused, thereby further improving the electrode manufacturing productivity.

[0107] As described above, the porosity of the positive electrode mixture layer manufactured by a dry method according to one embodiment of the invention can satisfy a range of 22% to 28%, and possibly 22% to 25%. This range is lower than the porosity of the positive electrode mixture layer manufactured by a conventional wet method. When manufacturing the positive electrode mixture layer by a conventional wet method, there was a limit to reducing the porosity because the solvent evaporates during the slurry drying process, widening the gap within the electrode. In contrast, the positive electrode mixture layer manufactured by a dry method does not contain a solvent, and thus the porosity can be further reduced compared to the positive electrode mixture layer manufactured by a wet method. That is, the method for manufacturing a positive electrode according to one embodiment of the invention can provide a positive electrode mixture layer having high energy density and output characteristics and excellent mechanical properties by satisfying the above porosity.

[0108] Meanwhile, in this specification, the porosity is calculated by the following equation 1.

[0109] [Formula 1]

[0110] Porosity (%) = {1-(density of the positive electrode mixture layer on the film / density of the positive electrode powder solid content)} x 100

[0111] After the above calendaring, a lamination step is performed to form a positive electrode by laminating a positive electrode mixture layer on a current collector. In the lamination step, the positive electrode mixture layer is positioned on at least one surface of the current collector and then laminated using a lamination roll.

[0112] Lamination can be performed by a lamination roll, wherein the lamination roll can be maintained at a temperature of room temperature (25°C) to 200°C.

[0113] Once lamination is complete, a positive electrode according to another embodiment of the invention can be formed. In addition, a lithium secondary battery comprising a positive electrode manufactured by the above-described method can be provided.

[0114] The positive electrode comprises a current collector; and a film-shaped positive electrode mixture layer disposed on the current collector and including a positive electrode active material, a fiberized binder, and a conductive material; wherein the positive electrode active material comprises a layered crystal structure, a molar ratio of lithium to the molar number of all metals excluding lithium exceeds 1, and a lithium manganese-rich oxide containing manganese in a content of 50 mol% or more among all metals excluding lithium; and the porosity of the positive electrode mixture layer may be 22% or more and less than 28%.

[0115] At this time, the positive electrode mixture layer and the positive electrode active material are as described above with respect to the manufacturing method of one embodiment, and the positive electrode mixture layer contains a binder that is fiberized during the dry process.

[0116] In addition, the current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and does not react within the voltage range of the battery. For example, the current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0117] The positive electrode composite layer formed by the above-described dry process can be attached to the current collector with an adhesive strength of 100 gf / 20 mm or more, or 100 gf / 20 mm to 200 gf / 20 mm. This can be achieved depending on the results of the above-described dry process.

[0118] Such adhesion may be measured, for example, by using an Ultimate tensile strength (UTS) measuring device and performing a peel test on an electrode sample in which the positive electrode composite layer on the film is attached to a current collector.

[0119] Meanwhile, a lithium secondary battery including such a positive electrode may include the positive electrode, the negative electrode, and a separator or electrolyte layer interposed between the positive electrode and the negative electrode. The lithium secondary battery may optionally further include an electrolyte including a lithium salt and a non-aqueous organic solvent. In this case, since the positive electrode is the same as described above, a detailed description is omitted, and only the remaining components are specifically described below.

[0120] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode composite layer positioned on the negative electrode current collector.

[0121] The 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, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0122] The above negative electrode composite layer optionally includes a binder and a conductive material together with a negative electrode active material.

[0123] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 <β< 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode mixture layer.

[0124] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode mixture layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0125] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode mixture layer. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0126] The negative electrode mixture layer may be manufactured by applying and drying a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry on a separate support, and then laminating the resulting film on a negative electrode current collector by peeling it off from the support. In another example, the negative electrode mixture layer may also be manufactured in the form of a film through a dry process similar to the positive electrode mixture layer described above.

[0127] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0128] Meanwhile, the lithium secondary battery may include the separator, but may also include an electrolyte layer separately from the separator, or may include a laminate in which an electrolyte layer is laminated on the separator. In a specific example, the electrolyte layer may be a gel electrolyte layer including a gel electrolyte, or a solid electrolyte layer.

[0129] In a more specific example, the electrolyte layer including the gel electrolyte may include a matrix including, for example, a polyurethane-based or polyacrylic-based cross-linked polymer, a lithium salt, and a non-aqueous organic solvent, and may have a form in which the lithium salt and the non-aqueous organic solvent are dispersed or encapsulated within the matrix. However, since the types of cross-linked polymers, lithium salts, and organic solvents that may be included in the gel electrolyte are apparent to those skilled in the art, further description thereof will be omitted.

[0130] In addition, in another specific example, the solid electrolyte layer may include any solid electrolyte, for example, at least one selected from the group consisting of a polymer-based solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, and a halogenated solid electrolyte. However, since the composition of the solid electrolyte layer may be based on a general solid electrolyte layer known in the past, further description is omitted.

[0131] Meanwhile, the lithium secondary battery described above may further include an electrolyte including a lithium salt and a non-aqueous organic solvent.

[0132] The above non-aqueous organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc., can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0133] The above lithium salt can be used without any special restrictions as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt may be at least one selected from the group consisting of F-, Cl-, Br-, I-, NO3-, N(CN)2-, BF4-, CF3CF2SO3-, (CF3SO2)2N-, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN-, and (CF3CF2SO2)2N-, and the lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2.LiCl, LiI, or LiB(C2O4)2 can be used. It is recommended that the concentration of the lithium salt be within the range of 0.1 to 4.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0134] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0135] The lithium secondary battery described above exhibits excellent discharge capacity, output characteristics, and stable life characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0136] In addition, there is no particular limitation on the external shape of the lithium secondary battery, but it can be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0137] In addition, the lithium secondary battery described above can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0138] Examples of the above medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0139]

[0140] In order to help understand the invention below, preferred embodiments are presented; however, the following embodiments are only illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the invention, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0141]

[0142] [Cathode manufacturing and property evaluation]

[0143] (1) Manufacturing of anode

[0144] Preparation of the positive electrode of Examples 1 and 2

[0145] A mixture was prepared by placing a positive electrode active material, a binder, and a conductive agent in a weight ratio of 71:14:15 in a super mixer as shown in Table 1 below and mixing at 10,000 rpm for 1 minute. The mixture was then placed in a Banbury Kneader and kneaded at 90°C and 50 rpm for 5 minutes to prepare a mixture lump.

[0146] Afterwards, the mixture lump was put into a cutter mill and a positive electrode powder was obtained at 10,000 rpm for 1 minute.

[0147] Then, the above-mentioned positive electrode powder was put into a calendar (roll temperature: 100°C, roll rotation speed: 30 rpm) and calendered and rolled to produce a film. Compared to the film of Example 1, the film of Example 2 was further rolled. The manufactured films of Examples 1 and 2 were provided on both sides of a 12 μm thick aluminum foil in the loading amounts shown in Table 1 below and laminated to produce positive electrodes of Examples 1 and 2, respectively.

[0148]

[0149] Manufacturing of the anode of Comparative Example 1

[0150] A positive electrode active material slurry having a weight ratio of active material: conductive material: binder of 96:1:3 was prepared using a positive electrode active material, a binder, and a conductive material with the compositions shown in Table 1 below, and N-methylpyrrolidone (NMP) as a solvent. Then, the positive electrode active material slurry was coated on both sides of a 12 μm thick aluminum foil in an amount equivalent to the loading amount shown in Table 1 below, and rolled and dried to prepare a positive electrode of Comparative Example 1.

[0151]

[0152] Distinctive positive electrode active material binder charge loading amount (mAh / cm) 2 )Example 1Li 1.15 [Ni 0.36 Mn 0.64 ] 0.85 O2PTFECarbon Black 4.002Example 2Li 1.15 [Ni 0.36 Mn0.64 ] 0.85 O2PTFECarbon Black 3.913Comparative Example 1Li 1.15 [Ni 0.36 Mn 0.64 ] 0.85 O2PVDF carbon nanotube 3.959

[0153] (2) Evaluation of the physical properties of the anode

[0154] Table 2 below shows the physical properties of the positive electrodes of Example 1, Example 2, and Comparative Example 1 manufactured above.

[0155] Classification Porosity (%) Anode thickness (㎛) Anode adhesion (gf / 20mm) Brittle slope (gf / mm) Toughness (kgf·mm) Example 127.5132.4149.02.1948.28 Example 224.6125.5121.71.6548.86 Comparative example 127.5132.458.92.3974.53

[0156] Referring to Table 2 above, the porosity of the anode of Example 1 is 27.5%, the same as the porosity of the anode of Comparative Example 1, and the porosity of the anode of Example 2 is 24.6%, which is lower than the anode of Comparative Example 1.

[0157] It can be confirmed that the positive electrodes of Examples 1 and 2 have adhesive strengths that are more than twice as strong as those of Comparative Example 1. This is a characteristic of the dry manufacturing method of the positive electrode, and it is thought that the adhesive strength is improved during the process of laminating the free-standing film to the current collector.

[0158] In addition, it can be confirmed that the anodes of Examples 1 and 2 have lower inclination and toughness than the anode of Comparative Example 1. Accordingly, the anodes of Examples 1 and 2 have lower porosity and a lower probability of short circuits or cracks occurring in the electrode than the anode of Comparative Example 1, and can be expected to be easy to handle.

[0159]

[0160] [Evaluation of the physical properties of lithium secondary batteries]

[0161] (1) Manufacturing of batteries of Example 1, Example 2, and Comparative Example 1

[0162] (1-1) Manufacturing of cathode

[0163] The cathode was manufactured by depositing lithium metal on copper foil to a thickness of 8 μm.

[0164]

[0165] (1-2) Preparation of electrolyte

[0166] A liquid electrolyte was prepared by dissolving 1.2 M lithium salt (LiPF6) in a mixed solvent of ethylene carbonate, ethylene methyl carbonate, and diethylene carbonate.

[0167]

[0168] (1-3) Battery assembly

[0169] A C-type Bicell composed of a cathode-anode-cathode was manufactured using the anode, cathode, and separator of Example 1, Example 2, or Comparative Example 1 manufactured above. At this time, SV9 fabric with a thickness of 9 mm was used as the separator.

[0170] As a result, using the positive electrode of Example 1, a battery cell of Example 1 having a capacity of 88.398 mAh was manufactured. Using the positive electrode of Example 2, a battery cell of Example 2 having a capacity of 86.392 mAh was manufactured. Using the positive electrode of Comparative Example 1, a battery cell of Comparative Example 1 having a capacity of 87.460 mAh was manufactured.

[0171]

[0172] (2) Evaluation of physical properties of lithium secondary batteries

[0173] (2-1) Evaluation of the increase rate of resistance at high temperature (45℃)

[0174] For the electrodes of Examples 1, 2, and Comparative Example 1 assembled in the above (1-3), the electrodes were charged and discharged under the conditions of 0.33C / 4.35V constant current-constant voltage 4.35V / 0.33C at 25℃ to adjust the state of charge by lowering the capacity by 10% of SOC (state of charge) to 100~0%, and then the voltage drop that appears when a discharge pulse is given for 30 seconds at a constant current of 2.5C was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A) to obtain the initial resistance value.

[0175] Afterwards, the battery was charged under the condition of constant current-constant voltage 4.35V / 0.33C at 0.33C / 4.35V in the voltage driving range of 2.5V to 4.35V to adjust the battery's state of charge to 100% SOC, and charging and discharging were repeated at 45℃ with the end voltage of charge set to 4.35 V and the end voltage of discharge set to 2.5 V.

[0176] The initial resistance value, the resistance value at 100 cycles, the resistance value at 200 cycles, and the resistance value at 300 cycles measured during the above process are shown in Table 3 below.

[0177]

[0178] RPT Initial 100 cycles 200 cycles 300 cycles Example 10.76 1.05 1.20 1.40 Example 20.78 1.06 1.19 1.38 Comparative example 10.83 1.12 1.28 1.48

[0179] Referring to Table 3 above, it can be confirmed that the batteries of Examples 1 and 2 have lower resistance values ​​from the initial resistance until 300 cycles compared to the battery of Comparative Example 1, and have superior resistance characteristics.

[0180] (2-2) Evaluation of high temperature (45℃) gas generation

[0181] The batteries of Examples 1, 2, and Comparative Example 1 assembled in the above (1-3) were subjected to 0.33C charge / discharge at 45°C in a voltage operating range of 2.5 V to 4.35 V with an SOC of 0-100%. The gases generated during the charge / discharge process were captured and measured using gas chromatography (GC). Table 4 below shows the amount of gas generated, and Fig. 1 illustrates the specific types and amounts of gases.

[0182] Distinctive gas generation amount (㎕) 50 cycles Example 1598 Example 2672 Comparative example 1678 100 cycles Example 1679 Example 2821 Comparative example 1826

[0183] Referring to FIG. 1 and Table 4, it can be confirmed that the batteries of Examples 1 and 2 have a maximum 17.2% reduction in gas generation compared to the battery of Comparative Example 1. This is thought to be due to the fact that the batteries of Examples 1 and 2 have lower resistance values ​​than the battery of Comparative Example 1.

[0184]

[0185] (2-3) Evaluation of capacity retention after high temperature (60℃) storage

[0186] The batteries of Example 1, Example 2, and Comparative Example 1 were charged at 25°C under constant current / constant voltage (CC / CV) conditions of 0.33C / 4.25V and constant current / constant voltage (CC / CV) conditions of 4.25V / 0.05C, respectively, and discharged at a constant current of 0.33C / 3.0V. At this time, the discharge capacity measured using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A) after cell assembly and before high-temperature storage was defined as the initial discharge capacity.

[0187] Next, each secondary battery was set to a 100% SOC charge state and stored at 60°C, and the discharge capacity was measured at 4-week intervals.

[0188] As above, the discharge capacity was measured, and the initial discharge capacity (mAh / g) according to the voltage of each battery of Example 1, Example 2, and Comparative Example 1 is shown in Table 5 below, and the discharge capacity (mAh / g) after 4 weeks is shown in Table 6 below.

[0189] Initial discharge capacity (mAh / g) 3.5 V or more 3.5 V or less Example 158.78 34.31 Exemplary Example 257.04 33.72 Comparative Example 158.22 31.57

[0190] Discharge capacity (mAh / g) after 4 weeks 3.5V or more 3.5V or less Example 144.7431.71 Exemplary Example 241.1531.11 Comparative Example 141.8631.02

[0191] Referring to Tables 5 and 6 above, it can be seen that, for the initial discharge capacity at 3.5 V or higher, the batteries of Example 1, Example 2, and Comparative Example 1 showed similar values, but the discharge capacity after 4 weeks was greatly improved in Example 1.

[0192] In addition, it can be confirmed that, for the initial discharge capacity below 3.5 V, Examples 1 and 2 are better than the battery of Comparative Example 1.

[0193]

[0194] In addition, by measuring the discharge capacity as above, the energy retention rate, total capacity retention rate, and 3.5 V or higher capacity retention rate for the battery of Example 1 and the battery of Comparative Example 1 for 8 weeks are shown in Table 7 below.

[0195] Meanwhile, the total capacity retention rate was calculated according to Equation 2 below.

[0196] [Formula 2]

[0197] Total capacity retention rate (%) = {(discharge capacity at RPT) / (initial discharge capacity)} x 100

[0198]

[0199] Energy retention rate (%) Total capacity retention rate (%) Capacity retention rate above 3.5 V Example 172.1073.4163.35 Comparative example 167.7369.8255.87

[0200] Referring to Table 7 above, it can be confirmed that the battery of Example 1 has superior energy retention rate, total capacity retention rate, and capacity retention rate (%) above 3.5 V after high temperature storage compared to the battery of Comparative Example 1 having the same porosity. This is thought to be because the degradation level of the dry electrode is lower than that of the wet electrode, thereby improving the nominal voltage drop and resistance, while at the same time having superior capacity retention rate.

[0201]

[0202] (2-4) Evaluation of resistance increase rate after 4 weeks of storage at high temperature (60℃)

[0203] The batteries of Examples 1, 2, and Comparative Example 1 assembled in the above (1-3) were each subjected to a formation process at 45°C at a rate of 0.1C for 20 hours, then charged at 25°C at a rate of 0.33C to 4.35V under 4.35V conditions, and discharged at a rate of 0.33C to 2.5V under CC conditions. Two cycles of initial charge and discharge were performed, with the charge and discharge as one cycle. The initial voltage was measured using a PNE-0506 charger and discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A), and the resistance value was calculated therefrom.

[0204] Next, the initially charged and discharged lithium secondary battery was charged at a rate of 0.33C to 4.25V under CC-CV conditions to adjust the battery's state of charge to 100% SOC, stored at 60℃ for 4 weeks, and then discharged again at 2.5C for 10 seconds at 50% SOC to measure the voltage after high-temperature storage. The voltage was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A).

[0205] The resistance value was calculated as above, and the resistance increase rate (%) was calculated according to Equation 3 below and shown in Table 8 below.

[0206] [Formula 3]

[0207] Resistance increase rate (%) = [{R(current point)-R(initial)} / R(initial)]x 100

[0208] In the above equation 3, R is the resistance value measured at SOC 50, discharge direction pulse, 10s.

[0209] RPT Initial 4-week Example 10.750.95 Example 20.811.09 Comparative Example 10.821.1

[0210] Referring to Table 8 above, it can be confirmed that the batteries of Examples 1 and 2 have a superior resistance increase rate after 4 weeks of storage at a high temperature (60°C) compared to the battery of Comparative Example 1.

[0211] (2-5) Evaluation of high temperature (65℃) gas generation

[0212] The batteries of Examples 1, 2, and Comparative Example 1 assembled in the above (1-3) were subjected to 0.33C charge / discharge at 65°C in a voltage operating range of 2.5 V to 4.35 V with an SOC of 0-100%. The gases generated during the charge / discharge process were captured and measured using gas chromatography (GC). Table 9 below shows the amount of gas generated, and Fig. 2 illustrates the specific types and amounts of gases.

[0213] Distinctive gas volume (㎕) 4 weeks Example 1196 Example 2192 Comparative example 13188 weeks Example 1277 Example 2239 Comparative example 1432

[0214] Referring to FIG. 2 and Table 9, it can be confirmed that the batteries of Examples 1 and 2 have a gas generation amount reduced by at least 35% and at most 44.7% compared to the battery of Comparative Example 1.

[0215] This is thought to be influenced by the fact that the resistance increase rate of the batteries of Examples 1 and 2 is lower than that of the battery of Comparative Example 1.

[0216]

[0217] Although the preferred embodiments of the invention have been described in detail above, the scope of the invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the invention defined in the claims also fall within the scope of the invention.

Claims

1. A step of forming a powder for an anode by mixing an anode active material, a fiberizable binder, and a conductive material in a solid phase; and The method includes the step of forming an anode composite layer by calendering the above anode powder into a film form; A method for manufacturing a cathode comprising an over-lithium manganese-rich oxide, wherein the cathode active material comprises a layered crystal structure, the molar ratio of lithium to the total number of moles of metals excluding lithium exceeds 1, and the manganese content among the total metals excluding lithium is 50 mol% or more.

2. In claim 1, the method for manufacturing an anode represented by the following chemical formula 1, wherein the lithium-over-manganese-rich oxide is: [Chemical Formula 1] Li a [Mr b Ni c M d ] 2-a O2 In the above chemical formula 1, a is greater than 1, b is 0.5 or more and less than 1, c and d are each 0 or more and 0.5 or less, but 0 <c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

3. In paragraph 1, A method for manufacturing an anode in which the porosity of the anode composite layer is 22% or more and less than 28%.

4. In paragraph 1, A method for manufacturing an anode comprising a plurality of fluorine-substituted polyolefin resins, wherein the above-mentioned fiberizable binder.

5. In paragraph 1, A method for manufacturing an anode comprising one or more types selected from the group consisting of carbon-based materials, metal powders, metal fibers, conductive fibers, conductive whiskers, metal oxides, and conductive polymers.

6. In paragraph 1, The step of forming the above-mentioned anode powder is, A first step of forming a mixture by mixing a positive active material, a fiberizable binder, and a conductive material; A second step of kneading the above mixture to form a mass of the mixture; and A method for manufacturing an anode comprising a third step of grinding the above mixture lumps to form the above anode powder.

7. In paragraph 1, A method for manufacturing a cathode, wherein, based on the total weight of the powder for the cathode, the content of the cathode active material is 95% by weight or more and 98.9% by weight or less, the binder is 1% by weight or more and 3% by weight or less, and the conductive material is 0.1% by weight or more and 2% by weight or less.

8. In Paragraph 1, A method for manufacturing an anode, further comprising the step of forming an anode by laminating the above anode composite layer onto a current collector.

9. In Paragraph 7, A method for manufacturing an anode in which the adhesion strength of the anode composite layer to the above current collector is 100gf / 20mm or more.

10. The whole house; and A positive composite layer on a film disposed on the above-mentioned current collector and comprising a positive active material, a fibrous binder, and a conductive material; comprising, The above-mentioned positive electrode active material comprises a layered crystal structure, a molar ratio of lithium to the total number of moles of metals excluding lithium exceeding 1, and a lithium-rich manganese oxide containing manganese in an amount of 50 mol% or more among the total metals excluding lithium, and An anode having a porosity of 22% or more and less than 28% of the above anode composite layer.

11. In claim 10, the lithium-over-manganese-rich oxide is an anode represented by the following chemical formula 1: [Chemical Formula 1] Li a [Mr b Ni c M d ] 2-a O2 In the above chemical formula 1, a is greater than 1, b is 0.5 or more and less than 1, c and d are each 0 or more and 0.5 or less, but 0 <c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

12. In claim 10, the above-mentioned lithium manganese-rich oxide is an anode represented by the following chemical formula 1a: [Chemical Formula 1a] Li a [Mr b Ni c M d ] 2-a O2 In the above chemical formula 1, 1.1 <a<1.3이고, 0.5≤b≤0.9, 0.1≤c≤0.5이고, 0≤d≤0.1이고, 이고, M은 Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

13. In claim 10, the above-mentioned lithium manganese-rich oxide comprises a mixed state of rock salt structural compounds and layered structural compounds.

14. In claim 10, the lithium-over-manganese-rich oxide is an anode represented by the following chemical formula 2: [Chemical Formula 2] X*Li2MnO3·(1-X)*Li[NiwMnyMz]O2 In the above chemical formula 2, M is at least one selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.2≤X≤0.5, 0≤w≤0.5, 0.4≤y<1, 0≤z≤0.2, but 0 <w+z≤0.5임.

15. In Paragraph 10, The above-mentioned fiberized binder is an anode comprising a plurality of fluorine-substituted polyolefin resins.

16. In Paragraph 10, The above conductive material is an anode containing a carbon-based material.

17. A lithium secondary battery comprising a positive electrode, a negative electrode according to claim 10, and a separator or electrolyte layer interposed between the positive electrode and the negative electrode.

18. A lithium secondary battery comprising, in addition to the electrolyte comprising a lithium salt and a non-aqueous organic solvent, the lithium secondary battery according to claim 17.

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