KR102280793B1 - Density controlled organic compounds-based lithium secondary batteries and methods of forming the same - Google Patents

Abstract

A lithium secondary battery based on an organic compound, a positive electrode; electrolyte; and a cathode electrode. The positive electrode includes an organic compound including a carbon double bond and a functional group including at least one of nitrogen, oxygen, and sulfur, and the positive active material is in the range of 30 to 50% by weight based on the total weight of the positive electrode. ; 30 to 50% by weight of a conductive material based on the total weight of the positive electrode; and a binder, wherein the positive electrode has a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^{3 .}

Description

Density controlled organic compounds-based lithium secondary batteries and methods of forming the same

The technical idea of the present invention relates to an organic compound-based lithium secondary battery and a manufacturing method thereof, and more particularly, to a lithium secondary battery including an organic compound-based positive active material and a manufacturing method thereof.

Recently, as the demand for using lithium ion batteries in various applications such as small mobile devices and electric vehicles increases, the need to optimize the performance of lithium ion batteries according to various requirements for various applications is emerging. In particular, research on new positive electrode active material candidates that are inexpensive and eco-friendly while having a large capacity and high energy density is being actively conducted. Conventionally used transition metal oxide-based positive electrode active materials, such as lithium cobalt oxide or lithium nickel cobalt manganese oxide, have limitations in increasing the capacity. In addition, there is a problem of causing environmental pollution in the production and recycling process of these materials, so it is necessary to study alternative materials. In order to solve this problem, a secondary battery using an organic compound-based positive active material including a phenazine derivative has been proposed, but it is necessary to optimize the electrode manufacturing method to a level that can be employed as a positive electrode of a commercial secondary battery.

The technical problem to be achieved by the technical idea of the present invention is to provide a manufacturing method for forming an organic compound-based positive electrode having excellent electrochemical properties and high energy density.

Another technical problem to be achieved by the technical idea of the present invention is to provide a lithium secondary battery including an organic compound-based positive electrode having excellent electrochemical properties and high energy density.

An organic compound-based lithium secondary battery according to the technical idea of the present invention for achieving the above technical problem, a positive electrode; electrolyte; and a negative electrode, wherein the positive electrode includes an organic compound including a carbon double bond and a functional group including at least one of nitrogen, oxygen, and sulfur, based on the total weight of the positive electrode: 30 to 50 positive active material in the range of weight %; 30 to 50% by weight of a conductive material based on the total weight of the positive electrode; and a binder, wherein the positive electrode has a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^{3 .}

In exemplary embodiments, the organic compound is an organic compound-based lithium secondary battery, characterized in that it comprises at least one selected from the group consisting of a polymer having a redox activity, an organic sulfur compound, and a compound containing a carbonyl group.

In exemplary embodiments, the organic compound is dimethylphenazine, perylenetetracarboxylic anhydride, tetraethyl thiuram disulfide, TEMPO(2,2,6,6-tetramethylpiperidinyloxy), PEDOT(poly(3,4-) ethylenedioxythiophene)), DD-TCNQ (7,7,8,8-tetracyanoquinodimethane), and at least one selected from the group consisting of flavanthrone.

In exemplary embodiments, when charging the secondary battery using lithium metal as the negative electrode, the positive electrode exhibits a first plateau at 3.0 to 3.2 V, and a second at 3.6 to 3.8 V It can represent a plateau.

In exemplary embodiments, the binder may include bead-form PTFE, and the binder may be in a range of 10 to 30% based on the total weight of the positive electrode.

In example embodiments, the conductive material may include at least one of super P, carbon black, Ketjen black, and acetylene black.

In example embodiments, the weight of the positive active material included in the positive electrode may be greater than the weight of the conductive material included in the positive electrode.

In example embodiments, the positive active material may have an average particle size of 500 nanometers to 60 micrometers.

In example embodiments, the positive electrode may be a free standing type that does not include a positive current collector.

A method for manufacturing a lithium secondary battery based on an organic compound according to the technical idea of the present invention for achieving the above technical problem includes forming a positive electrode. The forming of the positive electrode may include: forming a first preliminary positive electrode by mixing 30 to 50% by weight of a positive electrode active material and 30 to 50% by weight of a conductive material in a solid phase; forming a second preliminary positive electrode by solid-phase mixing the first preliminary positive electrode and 10 to 30% by weight of a binder; and compressing the second preliminary positive electrode by a roll press, wherein the positive active material includes an organic compound including a carbon double bond and a functional group including at least one of nitrogen, oxygen, and sulfur .

In example embodiments, compressing the second preliminary positive electrode may be performed multiple times.

In example embodiments, compressing the second preliminary positive electrode may be performed multiple times so that the positive electrode has a density of 0.50 g/cm3 to 1.2 g/cm3.

In exemplary embodiments, the positive active material has a first particle size, the conductive material has a second particle size, and the binder has a third particle size larger than the first particle size and the second particle size. can have

In example embodiments, the first particle size may be 500 nanometers to 60 micrometers, the second particle size may be 10 to 100 nanometers, and the third particle size may be 1 to 5 millimeters.

In example embodiments, by the pressing, the positive electrode may be formed in a free standing type that does not include a positive current collector.

In exemplary embodiments, the forming of the positive electrode may be performed in an all solid-state state without addition of an organic solvent.

According to the present invention, chemical and thermal damage to the organic compound can be prevented by the method of manufacturing an organic compound-based positive electrode active material performed in an all-solid state, and a lithium secondary battery including such a positive electrode has excellent electrochemical properties can have In addition, since the positive electrode may be used as a free-standing type without a positive electrode current collector such as a conventional aluminum foil, a lithium secondary battery including the positive electrode may have a high energy density.

1 is a cross-sectional view schematically illustrating an organic compound-based lithium secondary battery according to exemplary embodiments.
2 is a schematic diagram illustrating an anode electrode according to exemplary embodiments.
3 is a flowchart illustrating a method of manufacturing an organic compound-based lithium secondary battery according to exemplary embodiments.
4 is a scanning electron microscope (SEM) image of an organic compound-based anode electrode according to example embodiments.
5 is a graph illustrating a voltage profile of an anode electrode according to example embodiments.
6 and 7 are graphs illustrating cycle characteristics of a positive electrode according to example embodiments.
8 is a graph illustrating internal resistance of a positive electrode according to example embodiments.
9 is a graph illustrating voltage profiles of positive electrodes having various densities according to example embodiments.
10 is a graph showing one-time charge capacity and one-time discharge capacity.
11 and 12 are graphs illustrating cycle characteristics according to density of anode electrodes according to exemplary embodiments.
13 is a graph illustrating internal resistance of a positive electrode according to example embodiments.
14 is a graph illustrating a voltage profile of an anode electrode according to example embodiments.
15 is a graph illustrating cycle characteristics of a positive electrode according to example embodiments.

In order to fully understand the configuration and effect of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and various modifications may be made. However, the description of the present embodiments is provided so that the disclosure of the present invention is complete, and to fully inform those of ordinary skill in the art to which the present invention belongs, the scope of the invention. In the accompanying drawings, the components are enlarged in size than the actual ones for convenience of explanation, and the proportions of each component may be exaggerated or reduced.

When an element is described as being “on” or “adjacent to” another element, it should be understood that another element may be directly on or connected to the other element, but another element may exist in between. something to do. On the other hand, when it is described that a certain element is "directly on" or "directly" of another element, it may be understood that another element does not exist in the middle. Other expressions describing the relationship between elements, for example, “between” and “directly between”, etc. may be interpreted similarly.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms may be used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component.

The singular expression includes the plural expression unless the context clearly dictates otherwise. Terms such as "comprises" or "having" are intended to designate that a feature, number, step, action, component, part, or combination thereof described in the specification exists, and includes one or more other features or numbers, It may be construed that steps, operations, components, parts, or combinations thereof may be added.

Unless otherwise defined, terms used in the embodiments of the present invention may be interpreted as meanings commonly known to those of ordinary skill in the art.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a cross-sectional view schematically showing an organic compound-based lithium secondary battery 1 according to exemplary embodiments.

Referring to FIG. 1 , an organic compound-based lithium secondary battery 1 includes a negative electrode 20 , a positive electrode 30 , a separator 50 , an electrolyte 60 , a case 72 , 74 ), and a sealing member 76 . The organic compound-based lithium secondary battery 1 may be a lithium secondary battery using lithium as a charge transfer medium. The positive electrode 30 may be attached to the positive electrode current collector 40 , and the separator 50 may be interposed between the positive electrode 30 and the negative electrode 20 . The negative electrode 20 , the positive electrode 30 , and the separator 50 may be accommodated in the cases 72 and 74 while being wetted in the electrolyte 60 . The lower case 72 and the upper case 74 may be fixed by the sealing member 76 so as not to be electrically connected to each other. The anode electrode 30 is electrically connected to the lower case 72, and the cathode electrode 20 is electrically connected to the upper case 74 so that the upper case 74 and the lower case 72 are each made of an organic compound based. It may act as electrical terminals of the lithium secondary battery 1 .

The negative electrode 20 may include lithium metal, graphite, a silicon-based material, a tin-based material, a mixture thereof, or the like. When the negative electrode 20 includes lithium metal, it may be configured as a single layer as shown in FIG. 1 . However, when the negative electrode 20 includes graphite, a silicon-based material, a tin-based material, a mixture thereof, or the like, the negative electrode 20 is, for example, a negative electrode current collector (not shown) made of copper foil or the like. ) may be attached to the

The positive electrode 30 may include organic compound-based positive active material particles. The positive electrode 30 may be of a free-standing type, and thus may not be attached to the positive electrode current collector. However, in other embodiments, the positive electrode 30 is attached to the positive electrode current collector of aluminum foil or nickel foil, or the positive electrode current collector is disposed under the positive electrode 30 to support the positive electrode 30 . may be The positive electrode 30 will be described in detail with reference to FIG. 2 below.

The separator 50 may have porosity, and may be composed of a single membrane or a multi-layered membrane of two or more layers. The separator 50 may include a polymer material, for example, may include at least one of polyethylene-based, polypropylene-based, polyvinylidene fluoride-based, polyolefin-based polymer, and the like.

The electrolyte solution 60 may include a non-aqueous solvent and an electrolyte salt. The non-aqueous solvent is not particularly limited as long as it is used as a non-aqueous solvent for a conventional non-aqueous electrolyte, for example, a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, or an aprotic solvent. It may contain a solvent. The non-aqueous solvent may be used alone or in a mixture of one or more, and when one or more of the non-aqueous solvents are mixed and used, the mixing ratio may be appropriately adjusted according to desired battery performance.

The electrolyte salt is not particularly limited as long as it is used as an electrolyte salt for a conventional non-aqueous electrolyte, and may be, for example, a salt having a structural formula of ^{A +} B ^-. Here, A ⁺ may be an ion including an alkali metal cation such as Li ⁺ , Na ⁺ , K ^{+ , or a combination thereof.} also. B ^- is PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , ASF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N(CF ₃ SO ₂ ) ₂ ^- , It may be an ion including an anion such as C(CF ₂ SO ₂ ) ₃ ^{− or a combination thereof.} For example, the electrolyte salt may be a lithium-based salt, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _{2x + 1} SO ₂ )(C _y F2 _{y + 1} SO ₂ ) where , x and y are natural numbers), LiCl, LiI, and LiB(C ₂ O ₄ ) ₂ It may include one or two or more selected from the group consisting of. These electrolyte salts may be used alone or in combination of two or more.

Although FIG. 1 exemplarily illustrates a coin-type battery as the lithium secondary battery 1 based on an organic compound, the technical spirit of the present invention is not limited thereto. Unlike the one shown in FIG. 1 , the organic compound-based lithium secondary battery 1 may be a cylindrical battery in which the positive electrode and the negative electrode are spirally wound inside a cylindrical case, or a rectangular-shaped case inside. It may be a prismatic battery in which the positive electrode and the negative electrode are accommodated in a wound state. Alternatively, it may be a polymer battery accommodated in a plastic pouch in a state in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked.

2 is a schematic diagram illustrating an anode electrode 30 according to exemplary embodiments.

Referring to FIG. 2 , the positive electrode 30 may include a positive active material 32 , a conductive material 34 , and a binder 36 .

In exemplary embodiments, the positive electrode 30 contains about 30 to 50% by weight of the positive active material 32 based on the total weight of the positive electrode, and about 30 to 50% by weight based on the total weight of the positive electrode 30 . The conductive material 34 and the binder 36 may include 10 to 30% by weight of the total weight of the positive electrode 30 .

In example embodiments, the positive active material may include an organic compound having a carbon double bond and a functional group including at least one of nitrogen, oxygen, and sulfur. For example, a carbon double bond or a functional group including at least one of nitrogen, oxygen, and sulfur included in the organic compound may act as an active region for a reversible oxidation reaction or reduction reaction with lithium ions.

In exemplary embodiments, the organic compound may include at least one selected from the group consisting of a polymer (or radical polymer) having redox activity, an organo sulfide compound, and a carbonyl compound. can For example, the radical polymer may have a discharge capacity of about 200 mAh/g or less, an average discharge potential of about 3.0 to 4.0 V (based on Li metal), and an energy density of ^{about 800 Wh/kg −1 or less.} For example, the organosulfur compound has a discharge capacity of approximately 100 to 800 mAh/g, an average discharge potential (based on Li metal) of approximately 1.5 to 3.0 V, and an energy density of ^{approximately 400 to 1500 Wh/kg −1} can For example, the carbonyl group-containing compound has a discharge capacity of about 100 to 300 mAh/g, an average discharge potential of about 1.5 to 3.0 V (based on Li metal), and an energy density of ^{about 1000 Wh/kg -1 or less.} can

In example embodiments, the cathode active material is dimethylphenazine (DMPZ), perylenetetracarboxylic dianhydride (PTCDA), tetraethyl thiuramdisulfide (TETD), TEMPO (2,2). , 6,6-tetramethylpiperidinyloxy), PEDOT (poly(3,4-ethylenedioxythiophene)), DD-TCNQ (7,7,8,8-tetracyanoquinodimethane), and may include at least one of flavanthrone.

For example, when the cathode active material includes dimethylphenazine or a derivative thereof, it may be represented by a compound of Formula 1 or Formula 2 below.

[Formula 1]

For example, the positive active material according to Formula 1 may be dimethyl phenazine (5,10-dihydro-5,10-dimethylphenazine).

[Formula 2]

For example, in the positive active material according to Formula 2, R and R' are each independently a C1-C5 alkyl group; C2~ C5 alkenyl group; C2~ C5 alkynyl group; C3~ C30 aliphatic cyclic group; C6~ C30 aromatic ring group; and a heterocyclic group including at least one heteroatom of oxygen (O), nitrogen (N) and sulfur (S); may be any one or more selected from the group consisting of.

In exemplary embodiments, the conductive material 34 may further provide conductivity to the positive electrode 30 , and may be a conductive material that does not cause chemical change in the organic compound-based lithium secondary battery 1 . The conductive material may include, for example, a carbon-based material such as Super P, carbon black, Ketjen black (eg, Ketjenblack 600JD®, Ketjenblack 700JD®), or acetylene black. The conductive material 34 may be contained less than the content of the positive electrode active material 32 based on the total weight of the positive electrode 30 . For example, the positive electrode active material 32 may be included in the positive electrode 30 in a first content and the conductive material 34 may be included in the positive electrode 30 in a second content smaller than the first content.

In exemplary embodiments, the binder 36 serves to attach the positive active material 32 particles to each other or to attach the positive active material 32 particles to the conductive material 34 . In addition, the binder 36 is mechanically attached to the positive electrode 30 to prevent the positive active material 32 particles from being separated or separated from the surface of the positive electrode 30 so that the positive electrode 30 can be maintained in a free-standing type. strength can be provided.

In exemplary embodiments, the binder 36 may be a polymer, such as polyimide, polyamideimide, polybenzimidazole, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylate. Voxylated polyvinylchloride, polyvinylfluoride, ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene, acrylated styrene- butadiene, an epoxy resin, or the like. In exemplary embodiments, the binder 36 may be a bead-type polytetrafluoroethylene (PTFE).

In exemplary embodiments, when charging the organic compound-based lithium secondary battery 1 using a lithium metal as the negative electrode 20 , the positive electrode 30 operates at about 3.0 V to about 3.2 V at the first plateau. and may exhibit a second plateau at about 3.6 V to about 3.8 V. For example, when the positive active material 32 includes dimethylphenazine (DMPZ), the first plateau is formed by an oxidation reaction in which one of the two nitrogen atoms shown in Formula 1 is ionized into a nitrogen cation. appears, and the second plateau may appear by an oxidation reaction in which the other one of the two nitrogen atoms is ionized into a nitrogen cation.

DMPZ → DMPZ ²⁺ + 2e ^- -(3)

In exemplary embodiments, the positive active material 32 may have an average particle size of about 500 nanometers to about 60 micrometers, but is not limited thereto. For example, when the average particle size of the positive electrode active material 32 is smaller than about 500 nanometers, the surface area of the positive electrode active material 32 is relatively increased, so that the positive electrode active material 32 is eluted in the electrolyte and the lithium secondary battery 1 ) may decrease, and when the average particle size of the positive active material 32 is greater than about 6 micrometers, it is difficult for lithium ions to be effectively transferred to the inside of the positive active material 32, so that the lithium secondary battery 1 High rate characteristics may be degraded.

In exemplary embodiments, the positive electrode 30 may have a thickness T1 of about 20 to 200 micrometers, and the positive electrode 30 may have a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^{3 .} can The density of the positive electrode 30 may be the density of the free-standing type positive electrode 30 itself that does not include a positive current collector, for example, the positive active material 32 relative to the volume of the positive electrode 30, It may indicate a ratio of the total weight of the conductive material 34 and the binder 36 .

In exemplary embodiments, the anode electrode 30 may exhibit excellent Coulombic efficiency while having a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^{3 , while exhibiting relatively high cycle characteristics.} In addition, the positive electrode 30 may have a relatively small electrode resistance as it has a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^{3 .}

For example, when the density of the positive electrode 30 is ^{less than 0.50 g/cm 3} (eg, about 0.42 g/cm ³ ), the initial discharge capacity may be relatively low (eg, about 3.0 V to A first plateau may appear insignificantly at about 3.2 V and a second plateau may not be observed at about 3.6 V to about 3.8 V, which may mean that the redox reaction in Chemical Formula 3 does not reversibly occur. ). When the density of the positive electrode 30 is 0.50 g/cm ³ to 1.2 g/cm ³ , the initial discharge capacity is excellent, and excellent coulombic efficiency of 70% or more and excellent cycle characteristics can be exhibited for 10 cycles. On the other hand, when the density of the positive electrode 30 ^{is greater than 1.2 g/cm 3} (eg, about 1.22 g/cm ³ ), the coulombic efficiency is reduced to 50% or less for 10 cycles, and the cycle characteristics may not be excellent. can

For example, in the impedance measurement results for the positive electrode, the positive electrode having a density of ^{0.50 g/cm 3} to 1.2 g/cm ^{3 is smaller than 0.50 g/cm 3} or larger than 1.2 g/cm ^{3 .} A smaller electrode resistance value may be exhibited. This is, for example, in ^{a positive electrode having a density smaller than 0.50 g/cm 3} , sufficient contact and electrical path between the positive active material and the conductive material is not provided, so that the resistance value of the entire positive electrode increases, and more than ^{1.2 g/cm 3} It can be understood that, in the anode electrode having a large density, the penetration and movement path of the electrolyte and lithium ions through the cathode electrode are not sufficiently provided, so that the resistance value of the entire cathode electrode increases. The electrochemical characteristics according to the density of the positive electrode 30 will be described again with reference to FIGS. 9 to 13 .

In exemplary embodiments, the positive electrode 30 may be manufactured according to a method for manufacturing an organic compound-based secondary battery including a two-step solid-state mixing method, which will be described with reference to FIG. 3 . This two-step solid-state mixing method can prevent chemical and thermal damage to the positive active material of the positive electrode 30 and allow the positive electrode 30 to be formed in a free-standing type, and thus the positive electrode 30 It is possible to significantly increase the energy density of the lithium secondary battery 1 based on the organic compound employed.

For example, compared to the positive electrode manufactured using the mixing method according to Comparative Example, the positive electrode manufactured using the two-step solid-phase mixing method has a further increased initial discharge capacity, a further increased coulombic efficiency, and better cycle characteristics. can represent In addition, compared to the positive electrode manufactured by using the mixing method according to the comparative example, the positive electrode manufactured using the two-step solid-phase mixing method may exhibit a smaller electrode resistance value as a result of impedance measurement. Therefore, it is understood that the active material and the conductive material can be more uniformly mixed by the two-step solid-phase mixing method, whereby the positive electrode 30 exhibits a further increased initial discharge capacity, a further increased coulombic efficiency, and better cycle characteristics. can be The electrochemical properties of the positive electrode using this two-step mixing method will be described again with reference to FIGS. 5 to 8 .

3 is a flowchart illustrating a method of manufacturing an organic compound-based lithium secondary battery according to exemplary embodiments.

Referring to FIG. 3 , a positive electrode active material, a conductive material, and a binder are prepared (step S10 ).

In example embodiments, the positive active material, the conductive material, and the binder may be provided in a solid state. Optionally, in order to remove moisture that may exist in the positive electrode active material, the conductive material, and the binder, the positive electrode active material, the conductive material, and the binder may be dried in a vacuum oven for several tens of minutes to several hours.

Thereafter, a positive electrode active material and a conductive material are mixed in a mixing container, and a first preliminary positive electrode electrode is formed by mixing the positive electrode active material and the conductive material in a solid phase (step S20 ).

In exemplary embodiments, the positive active material and the conductive material may be mixed without adding a liquid solvent or the like in the mixing container. In the entire process of solid-state mixing, the positive electrode active material and the conductive material are in a solid state, respectively, and as a mechanical shear force is applied to the positive electrode active material and the conductive material using a mixing rod such as a pestle, the positive electrode active material and the conductive material are uniformly can be mixed. For example, while the mixing rod collapses each of the positive active material and the conductive material in a solid state into small pieces, the positive active material and the conductive material fragments may be attached to each other by aggregation by mechanical shearing force by the mixing rod. A solid mass formed by mixing the positive electrode active material and the conductive material relatively uniformly may be referred to as a first preliminary positive electrode electrode. The first preliminary positive electrode may be formed in a lump shape having a relatively high viscosity in which the positive electrode active material and the conductive material particles are uniformly dispersed and substantially solid.

Thereafter, by mixing the binder in the mixing container, the first preliminary positive electrode and the binder are mixed in a solid phase to form a second preliminary positive electrode (step S30).

In exemplary embodiments, the binder may be mixed without adding a liquid solvent or the like in the mixing vessel. In the entire process of solid-state mixing, the first preliminary positive electrode and the binder are in a solid state, respectively, and as a mechanical shear force is applied to the first preliminary positive electrode and the binder by using a mixing rod, the first preliminary positive electrode and the binder are uniformly each other can be mixed. For example, the mixing rod may break the first preliminary positive electrode in a solid state into small pieces of positive electrode agglomerates while these positive electrode agglomerates are uniformly mixed with the binder so that they adhere to each other. A solid mass formed by mixing the positive electrode active material, the conductive material, and the binder relatively uniformly may be referred to as a second preliminary positive electrode electrode. The second preliminary positive electrode may be formed in a lump shape having a relatively high viscosity in which the positive electrode active material, the conductive material, and the binder particles are uniformly dispersed and substantially in a solid state.

For example, the positive active material and the conductive material may have a smaller particle size than the binder. The positive active material may have a first particle size of about 500 nanometers to 60 micrometers, the conductive material may have a second particle size of about 10 to 100 nanometers, and the binder may have a third particle size of about 1 to 5 millimeters. there is. The positive active material and the conductive material may be mixed and dispersed uniformly in the second preliminary positive electrode by first solid-mixing the positive active material and the conductive material and then solid-mixing the mixture with a binder having a larger particle size.

Thereafter, the second preliminary positive electrode is roll-pressed to form the positive electrode (step S40).

In exemplary embodiments, the roll pressing step may be performed once. In other embodiments, the roll pressing step may be performed two or more times. In some examples, the roll pressing step may be performed multiple times until the anode electrode has a target thickness, and one roll pressing step is followed by a waiting time of several minutes to several tens of minutes, followed by one roll pressing Steps may be performed.

In example embodiments, after roll pressing the second preliminary positive electrode, the positive electrode may have a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^{3 .}

Optionally, the step of drying the positive electrode before or after the roll pressing step may be further performed. After forming the positive electrode, the step of cutting the positive electrode may be additionally performed.

In general, a liquid-phase mixing method using an organic solvent may be used to form a conventional inorganic material-based electrode material. In particular, particles of an inorganic active material are mixed in an organic solvent such as N-methyl-2-pyrrolidone (NMP) and mixed to prepare a slurry for an electrode. Thereafter, the electrode material is prepared by applying the slurry for the electrode on the current collector and performing a baking process for volatilizing the organic solvent. However, the organic compound-based positive electrode active material is easily dissolved by an organic solvent such as NMP and chemical transformation occurs. Also, the organic compound-based positive electrode active material may be deformed by heat applied in the baking process for volatilizing the organic solvent, and in this case, the function as the positive electrode active material may not be performed or performance may be deteriorated. Therefore, it is required to develop a method capable of manufacturing a homogeneous electrode while minimizing chemical and thermal damage to the organic active material-based positive electrode active material.

In the manufacturing method according to the above-described exemplary embodiments, by sequentially performing the first solid-phase mixing step of the positive electrode active material and the conductive material, the following second solid-phase mixing step with the binder, and roll pressing, all solid state (all solid state) -state) can be used to form an anode electrode. In particular, since an organic solvent is not used in the step of mixing the active material, chemical and thermal damage to the positive active material by the organic solvent and by the organic solvent removal process can be prevented. In addition, by adopting the two-step solid-phase mixing method of the first solid-phase mixing and the second solid-phase mixing, the positive active material and the conductive material can be uniformly dispersed and mixed in the positive electrode even by the all-solid-state manufacturing method. In addition, by forming the positive electrode in a solid state by roll pressing, it may be easy to control the thickness and/or the density of the positive electrode.

Also, in general, when a slurry mixed with an organic solvent is applied to a current collector and formed, an increase in the weight of the secondary battery due to the current collector is inevitable. However, according to exemplary embodiments, the free-standing type positive electrode can be formed through the all-solid state manufacturing method and unnecessary current collectors can be omitted, so that the weight of the lithium secondary battery is reduced and the weight energy density is significantly improved. can

4 to 13 below, the electrochemical performance of the organic compound-based lithium secondary battery manufactured using the manufacturing method according to the exemplary embodiments described with reference to FIG. 3 will be described.

Experimental example

1) Preparation of positive electrode

DMPZ (5,10-dihydro-5,10-dimethylphenazine) and PTCDA were used as cathode active materials, respectively. As a conductive material and a binder, ketjen black® and PTFE (polytetrafluoroethylene) were used, respectively. The positive electrode active material, the conductive material, and the binder were mixed using a mortar in a mass ratio of 4:4:2, respectively. The positive electrode active material and the conductive material were first mixed in the mortar and mixed in the first solid phase, and then the binder was mixed and mixed in the second solid phase. Electrodes having various electrode densities were manufactured by using a roll press with respect to a uniformly mixed positive electrode. The positive electrodes were cut to a size of 1*1 cm ^{2 .} On the other hand, in the positive electrode according to the comparative example, the positive active material, the conductive material, and the binder were simultaneously mixed in the mortar and mixed in a solid state.

2) Preparation of lithium secondary battery

A coin cell of type 2032 was assembled using positive electrodes. A lithium foil was used as the negative electrode. Glass fiber filter paper (GF/F) was used as a separator, and 90 μL of 1.8 M LiTFSI/TEGDME solution was added into each coin cell as an electrolyte. The assembled coin cell was charged and discharged in the range of 2.5 - 4.0 V.

4 is a scanning electron microscope (SEM) image of an organic compound-based anode electrode according to example embodiments.

4A shows the positive electrode in a state in which it is cut in a free-standing type. It is possible to maintain the shape so that the positive electrode in which the positive electrode active material including DMPZ, the conductive material, and the binder are uniformly mixed can be used as a free standing type without a separate current collector. The positive electrode may have sufficient structural stability to be handled in the manufacturing process of a commercial lithium secondary battery.

4 (b) and (c) are images showing the surface of the positive electrode, and it can be confirmed that the positive active material particles and the conductive material particles of approximately spherical or oval shape are bonded to each other by a binder to have a relatively smooth surface morphology. there is. In addition, it can be seen that the positive active material particles have a relatively uniform distribution of particle sizes.

5 is a graph illustrating a voltage profile of an anode electrode according to example embodiments.

Referring to FIG. 5 , voltages and capacities in one charge and one discharge of Example 1 (EX1) and Comparative Example (CO1) are shown. Example 1 (EX1) is a positive electrode including DMPZ prepared by a two-step solid-phase mixing method, and Comparative Example (CO1) is a positive electrode manufactured by mixing positive electrode materials at the same time. In the charging step, it can be seen that both Example (EX1) and Comparative Example (CO1) exhibit a first plateau at about 3.0 V to about 3.2 V and a second plateau at about 3.6 V to about 3.8 V. For example, the first plateau appears by an oxidation reaction in which one nitrogen atom among two nitrogen atoms included in DMPZ is ionized into a nitrogen cation, and the other nitrogen atom among the two nitrogen atoms is ionized into a nitrogen cation. The second plateau may appear by the reaction.

DMPZ → DMPZ ²⁺ + 2e ^- -(3)

Example 1 (EX1) showed a discharge capacity of about 235 mAh/g, while Comparative Example (CO1) showed a discharge capacity of about 202 mAh/g. It can be seen that Example 1 (EX1) prepared by the two-step solid-phase mixing method exhibits superior initial discharge capacity compared to Comparative Example (CO1).

6 and 7 are graphs illustrating cycle characteristics of a positive electrode according to example embodiments. Specifically, FIG. 6 shows the discharge capacity (mAh/g) according to the number of cycles, and FIG. 7 shows the coulombic efficiency (%) according to the number of cycles. Coulombic efficiency (%) refers to the ratio of discharge capacity to charge capacity in each cycle.

6 and 7 , Example 1 (EX1) exhibits a discharge capacity of about 172 mAh/g and a coulombic efficiency of about 79% even after 10 cycles. That is, Example 1 (EX1) exhibits a capacity retention characteristic of about 73% after 10 cycles. On the other hand, Comparative Example (CO1) exhibits a discharge capacity of about 130 mAh/g and a coulombic efficiency of about 64% even after 10 cycles. That is, Comparative Example (CO1) exhibits a capacity retention characteristic of about 64% after 10 cycles. That is, it can be confirmed that Example 1 (EX1) prepared by the two-step solid-phase mixing method exhibits excellent cycle characteristics compared to Comparative Example (CO1).

On the other hand, in FIG. 6, in order to further confirm the electrode uniformity and reproducibility characteristics by the two-step solid-phase mixing method, three cut positive electrodes for each of Example 1 (EX1) and Comparative Example (CO1) were cycled. The discharge capacity was tested according to 6 shows the average value and standard deviation of three positive electrodes. It is confirmed that the standard deviation of the discharge capacity in Example 1 (EX1) is smaller than the standard deviation of the discharge capacity in Comparative Example (CO1). In particular, it is confirmed that the standard deviation of the discharge capacity is smaller as the number of cycles increases. As a result, it can be confirmed that Example 1 (EX1) prepared by the two-step solid-phase mixing method exhibits excellent electrode uniformity and reproducibility.

8 is a graph illustrating internal resistance of a positive electrode according to example embodiments. 8 shows Nyquist plots obtained from the impedance analysis method of Example 1 (EX1) and Comparative Example (CO1).

Referring to FIG. 8 , the impedance graph of Example 1 (EX1) has a semicircle with a smaller radius than the impedance graph of Comparative Example (CO1). In general, the smaller the radius of the semicircle in the Nyquist plot of the impedance analysis method, the smaller the resistance value. Accordingly, it can be seen that the positive electrode of Example 1 (EX1) has a smaller internal resistance value than the positive electrode of Comparative Example (CO1).

Example 1 (EX1) prepared by the two-step solid-phase mixing method can have a smaller electrode internal resistance than Comparative Example (CO1) as the positive electrode active material, the conductive material, and the binder are uniformly dispersed and mixed. can be understood

9 to 13 will be described with respect to the electrochemical performance of the density of the positive electrode according to exemplary embodiments. Experimental Examples 21 to 26 (EX21 to EX26), including DMPZ, were prepared to have densities of 0.42, 0.44, 0.45, 0.57, 0.96, and 1.22 g/cm ³ , respectively.

9 is a graph showing voltage profiles of positive electrodes having various densities according to exemplary embodiments, and FIG. 10 is a graph showing one-time charge capacity and one-time discharge capacity.

9 and 10 , ^{Example 21 (EX21) having a density of 0.42 g/cm 3} exhibits a relatively low charge capacity and discharge capacity (for example, a discharge capacity of about 110 mAh/g), It can be seen that the 1st plateau is slightly observed and the 2nd plateau is not observed.

On the other hand, it can be seen that Examples 22 to 26 (EX22 to EX26) exhibited both the first plateau and the second plateau, and exhibited high charge capacity and discharge capacity (discharge capacity of about 200 mAh/g or more). .

11 and 12 are graphs illustrating cycle characteristics according to density of anode electrodes according to exemplary embodiments. Specifically, FIG. 11 shows the discharge capacity (mAh/g) according to the number of cycles, and FIG. 12 shows the coulombic efficiency (%) according to the number of cycles. Coulombic efficiency (%) refers to the ratio of discharge capacity to charge capacity in each cycle.

11 and 12 , Examples 21 to 25 (EX21 to EX25) show a coulombic efficiency of about 70% or more after 10 cycles, whereas Example (EX26) shows about 47 after 10 cycles. It represents the coulombic efficiency in %. In addition, Examples 21 to 25 (EX21 to EX25) showed a discharge capacity of about 70% or more compared to the initial capacity after 10 cycles, whereas Example 26 (EX26) showed a discharge capacity of about 53% after 10 cycles indicates. According to this, ^{Example 26 (EX26) having a density of 1.22 g/cm 3} has a high initial discharge capacity, but it can be confirmed that the discharge capacity rapidly decreases as the number of cycles increases.

13 is a graph illustrating internal resistance of a positive electrode according to example embodiments. 13 shows Nyquist plots obtained from the impedance analysis method of Examples 21, 24, 25, and 26 (EX21, EX24, EX25, EX26).

Referring to FIG. 13 , the impedance graphs of Examples 24 and 25 ( EX24 and EX25 ) have a smaller radius than the impedance graphs of Examples 21 and 26 ( EX21 and EX26 ). In general, the smaller the radius of the semicircle in the Nyquist plot of the impedance analysis method, the smaller the resistance value. Accordingly, it can be seen that the positive electrodes of Examples 24 and 25 (EX24, EX25) have smaller internal resistance values than the positive electrodes of Examples 21 and 26 (EX21, EX26).

Analyzing the results in FIGS. 9 to 13 together, for example, in ^{a positive electrode having a density smaller than 0.50 g/cm 3} , sufficient contact and an electrical path between the positive electrode active material and the conductive material are not provided, so the resistance of the positive electrode as a whole As the value increases, in ^{the anode electrode with a density greater than 1.2 g/cm 3} , the penetration and migration path of the electrolyte and lithium ions through it into the anode electrode is not sufficiently provided, so it can be assumed that the resistance value of the whole anode electrode increases. can Moreover, when the density of the positive electrode is ^{less than 0.50 g/cm 3} (ie, Example 21 (EX21), about 0.42 g/cm ³ ), the initial discharge capacity may be relatively low, and the density of the positive electrode is 1.2 g/cm ^{If it is greater than 3} (eg, Example 26 (EX26), about 1.22 g/cm ³ ), the coulombic efficiency is reduced to 50% or less for 10 cycles, and the cycle characteristics may not be excellent. When the density of the positive electrode is 0.50 g/cm ³ to 1.2 g/cm ³ (eg, Examples 22 to 25 (EX22, EX23, EX24, EX25)), the initial discharge capacity is excellent, and 70 for 10 cycles % or more excellent coulombic efficiency and excellent cycle characteristics.

14 is a graph illustrating a voltage profile of an anode electrode according to example embodiments.

Referring to FIG. 14 , the voltage and capacity at one charge and one discharge of Example 3 (EX3) are shown. Example 3 (EX3) is a positive electrode comprising PTCDA prepared by a two-step solid-phase mixing method. In the charging phase, it can be seen that Example 3 (EX3) exhibits a single plateau at about 2.52 V to about 2.7 V. Such a plateau may be a plateau exhibited by a chemical reaction expressed in Equation (4) below.

PTCDA → PTCDA ⁺ + e ^- -(4)

Example 3 (EX3) showed a discharge capacity of about 230 mAh/g, which is similar to that of Example 1 (EX1) including the DMPZ described with reference to FIG. 5 .

15 is a graph illustrating cycle characteristics of a positive electrode according to example embodiments.

15 , Example 3 (EX3) exhibited an initial discharge capacity of about 230 mAh/g, a maximum discharge capacity of about 245 mAh/g in 5 cycles, and a high of about 220 mAh/g even after 40 cycles. Indicates the discharge capacity. That is, it can be seen that Example 3 (EX3) exhibits excellent capacity retention characteristics of about 90% compared to the maximum capacity even after 40 cycles.

Above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes by those skilled in the art within the technical spirit and scope of the present invention This is possible.

[Research] This research was conducted with the support of the National Research Foundation-Future Materials Discovery Project, funded by the government (Ministry of Science and ICT) (NRF-2017M3D1A1039561)

1: lithium secondary battery 20: negative electrode
30: positive electrode 32: positive active material
34: conductive material 36: binder
50: separator 60: electrolyte
72, 74: case 76: sealing member

Claims (16)

As a method for manufacturing a lithium secondary battery based on an organic compound comprising the step of forming a positive electrode,
The step of forming the anode electrode,
forming a first preliminary positive electrode by solid-phase mixing 30 to 50% by weight of a positive electrode active material and 30 to 50% by weight of a conductive material;
forming a second preliminary positive electrode by solid-phase mixing the first preliminary positive electrode and 10 to 30% by weight of a binder; and
Including; compressing the second preliminary positive electrode by a roll press;
The positive active material includes an organic compound including a carbon double bond and a functional group including at least one of nitrogen, oxygen, and sulfur,
The organic compound is dimethylphenazine (DMPZ), perylenetetracarboxylic dianhydride (PTCDA), tetraethyl thiuramdisulfide (TETD), TEMPO (2,2,6,6-tetramethylpiperidinyloxy) , PEDOT (poly (3,4-ethylenedioxythiophene)), DD-TCNQ (7,7,8,8-tetracyanoquinodimethane), and flavanthrone (flavanthrone) comprising at least one selected from the group consisting of,
Forming the positive electrode is a method of manufacturing an organic compound-based lithium secondary battery, characterized in that it is performed in an all solid-state without the addition of an organic solvent. According to claim 1,
The method of manufacturing an organic compound-based lithium secondary battery, characterized in that the step of pressing the second preliminary positive electrode is performed a plurality of times. According to claim 1,
The method of manufacturing an organic compound-based lithium secondary battery, characterized in that the step of pressing the second preliminary positive electrode so that the positive electrode has a density of 0.50 g/cm ³ to 1.2 g/cm ^{3 is performed a plurality of times.} According to claim 1,
The positive active material has a first particle size, the conductive material has a second particle size,
The binder is a method of manufacturing an organic compound-based lithium secondary battery, characterized in that it has a third particle size larger than the first particle size and the second particle size. 5. The method of claim 4,
The first particle size is 500 nanometers to 60 micrometers,
The second particle size is 10 to 100 nanometers,
The third particle size is a method of manufacturing an organic compound-based lithium secondary battery, characterized in that 1 to 5 millimeters. According to claim 1,
By the pressing, the positive electrode is a method of manufacturing an organic compound-based lithium secondary battery, characterized in that formed in a free standing (free standing) type that does not include a positive electrode current collector. According to claim 1,
The organic compound includes dimethylphenazine (DMPZ),
When charging the lithium secondary battery using lithium metal as a negative electrode, the positive electrode exhibits a first plateau at 3.0 to 3.2 V, and exhibits a second plateau at 3.6 to 3.8 V, characterized in that A method of manufacturing an organic compound-based lithium secondary battery. According to claim 1,
The organic compound comprises perylenetetracarboxylic anhydride (PTCDA),
When the lithium secondary battery is charged using lithium metal as a negative electrode, the positive electrode exhibits a plateau at 2.52 to 2.7 V. A method for manufacturing a lithium secondary battery based on an organic compound. According to claim 1,
The binder includes polytetrafluoroethylene (PTFE) in the form of beads,
The binder is a method of manufacturing an organic compound-based lithium secondary battery, characterized in that in the range of 10 to 30% based on the total weight of the positive electrode. According to claim 1,
The conductive material is a method of manufacturing an organic compound-based lithium secondary battery, characterized in that it comprises at least one of super P, carbon black, Ketjenblack®, and acetylene black. According to claim 1,
The cathode active material is a method of manufacturing an organic compound-based lithium secondary battery, characterized in that it has an average particle size of 500 nanometers to 60 micrometers. delete delete delete delete delete

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