WO2021096113A1

WO2021096113A1 - Organic compound-based lithium secondary battery, and method for producing same

Info

Publication number: WO2021096113A1
Application number: PCT/KR2020/014818
Authority: WO
Inventors: 송재용; 신호선; 박선화; 박지혜
Original assignee: 한국표준과학연구원
Priority date: 2019-11-11
Filing date: 2020-10-28
Publication date: 2021-05-20

Abstract

This organic compound-based lithium secondary battery includes: a positive electrode, an electrolytic solution, and a negative electrode. The positive electrode includes: 30-50 wt% of a positive electrode active material with respect to the total weight of the positive electrode; 5-20 wt% of carbon nanotubes with respect to the total weight of the positive electrode; a conductive material; and a binder. The positive electrode active material includes an organic compound comprising: a carbon double bond; and a functional group containing at least one among nitrogen, oxygen, and sulfur.

Description

Organic compound-based lithium secondary battery and manufacturing method thereof

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

Recently, as the demand for using lithium ion batteries in various applications such as small mobile devices and electric vehicles has increased, there is a need to optimize the performance of lithium ion batteries according to various requirements for various applications. In particular, research on a new cathode active material candidate material that has a large capacity and a large energy density and is inexpensive and eco-friendly 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 their capacity. In addition, there is a problem that causes environmental pollution during the production and recycling of these materials, so research on alternative materials is required. To solve this problem, a secondary battery using a positive electrode active material based on an organic compound containing a phenazine derivative has been proposed, but it is necessary to improve the electrochemical performance such as cycle characteristics to a level that can be adopted as a positive electrode of a commercial secondary battery. have.

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 anode electrode having excellent electrochemical properties, excellent cycle characteristics, 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, excellent cycle characteristics, 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 includes: 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, and 30 to 50 based on the total weight of the positive electrode. A positive electrode active material in the range of% by weight; Carbon nanotubes in the range of 5 to 20% by weight based on the total weight of the positive electrode; Conductive material; And a binder.

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 flavanthrone.

In exemplary embodiments, the organic compound includes dimethylphenazine, and when charging the lithium secondary battery by using a lithium metal as the negative electrode, the positive electrode is a first plateau ( plateau), and a second plateau at 3.6 to 3.8 V.

In example embodiments, the carbon nanotubes may include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and bundle-type carbon nanotubes (nanotube rope).

In exemplary embodiments, the carbon nanotubes may have a purity of 90% to 99.99%.

In example embodiments, the anode electrode may further include less than 1% by weight of metal atoms attached to both ends of the carbon nanotube in the length direction.

In exemplary embodiments, the metal atom is copper (Cu), nickel (Ni), cobalt (Co), silver (Ag), titanium (Ti), aluminum (Al), tungsten (W), and molybdenum (Mo ) May include at least one of.

In exemplary embodiments, the binder may include polytetrafluoroethylene (PTFE) in the form of beads, and the binder may range from 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 conductive material may range from 30 to 50% based on the total weight of the positive electrode.

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

A method of 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. In the forming of the positive electrode, 30 to 50% by weight of a positive electrode active material, 5 to 20% by weight of carbon nanotubes, 30 to 50% by weight of a conductive material, and 10 to 30% by weight of a binder are mixed in a solid state to prepare a preliminary step. Forming an anode electrode; And compressing the preliminary positive electrode by a roll press, wherein the positive electrode 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, the carbon nanotubes have a purity of 90% to 99.99%, and less than 1% by weight of metal atoms attached to the surface of the carbon nanotubes may be further included.

In example embodiments, the step of compressing the preliminary anode electrode so that the anode electrode has a density of ^{0.50 g/cm 3} to 1.2 g/cm ^{3 may be performed a plurality of times.}

In example embodiments, the positive electrode 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. I can have it.

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 step, the positive electrode may be formed in a free standing type that does not include a positive electrode current collector.

In example embodiments, the step of forming the anode electrode may be performed in an all solid-state without adding an organic solvent.

According to the present invention, carbon nanotubes in the range of 5 to 20% by weight may serve to provide an electrical path between the positive electrode active material and the conductive material even if the organic compound-based positive electrode active material is eluted into the electrolyte as the number of cycles increases. . Accordingly, as the number of cycles increases, the positive electrode active material is eluted from the positive electrode to prevent an increase in the overall resistance of the positive electrode, and a lithium secondary battery including such a positive electrode may have excellent cycle characteristics. 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.

An organic compound-based lithium secondary battery according to the technical idea of the present invention for achieving the above technical problem includes: 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, and 30 to 50 based on the total weight of the positive electrode. A positive electrode active material in the range of% by weight; 30 to 50% by weight of a conductive material based on the total weight of the positive electrode; And a binder, and the positive electrode has a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^3.

In exemplary embodiments, the organic compound includes at least one selected from the group consisting of a polymer having redox activity, an organic sulfur compound, and a carbonyl group-containing compound.

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 flavantron (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 plateau at 3.6 to 3.8 V. It can represent a plateau.

In example embodiments, the binder includes PTFE in the form of a bead, and the binder may range from 10 to 30% based on the total weight of the positive electrode.

In example embodiments, the weight of the positive electrode 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 electrode current collector.

A method of 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 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 anode electrode by solid-phase mixing the first preliminary anode electrode and 10 to 30% by weight of a binder; And compressing the second preliminary positive electrode by a roll press; wherein the positive electrode 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, the step of compressing the second preliminary anode electrode may be performed a plurality of times.

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

According to the present invention, chemical and thermal damage to the organic compound can be prevented by the method of manufacturing a positive electrode active material based on an organic compound performed in a 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.

An organic compound-based lithium secondary battery according to the technical idea of the present invention for achieving the above technical problem includes: 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, and 30 to 50 based on the total weight of the positive electrode. A positive electrode active material in the range of% by weight; A conductive material in the range of 30 to 50% by weight based on the total weight of the positive electrode; And a binder in the range of 10 to 30% by weight based on the total weight of the positive electrode, the conductive material does not decompose at 1.5V to 4.0V, and the conductive material has a BET specific surface area of ^{500 to 2000 m 2 /g.} Have.

In example embodiments, the conductive material may have a pore volume of ^{about 1.0 to 5.0 cm 3 /g.}

In exemplary embodiments, the organic compound is dimethylphenazine (DMPZ), perylenetetracarboxylic anhydride (PTCDA), tetraethyl thiuram disulfide (TETD), 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 flavantrons.

In exemplary embodiments, the organic compound may include dimethylphenazine, and when charging the lithium secondary battery using lithium metal as the negative electrode, the positive electrode is the first plate at 3.0 to 3.2 V. It represents a plateau and can represent a second plateau at 3.6 to 3.8 V.

In example embodiments, the conductive material may be Ketjenblack®.

In example embodiments, the positive electrode active material may have an average particle size of 500 nanometers to 60 micrometers, and the conductive material may have an average particle size of 10 to 100 nanometers.

A method of 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 preliminary positive electrode by solid-phase mixing 30 to 50% by weight of a positive electrode active material, 30 to 50% by weight of a conductive material, and 10 to 30% by weight of a binder; Comprising the preliminary positive electrode by a roll press; Including, the positive electrode active material includes an organic compound containing a carbon double bond and a functional group containing at least one of nitrogen, oxygen, and sulfur, the conductive The material includes Ketjen Black, and the conductive material has a BET specific surface area of ^{500 to 2000 m 2 /g.}

In example embodiments, the step of compressing the preliminary anode electrode may be performed a plurality of times.

According to the present invention, the conductive material may have a BET specific surface area of ^{500 to 2000 m 2 /g.} Such a conductive material not only serves to provide an electrical connection between the positive electrode active materials, but also has a large specific surface area, and thus acts like a capacitor electrode to exhibit capacity due to capacitance. A lithium secondary battery including such a positive electrode may have excellent electrochemical properties. In addition, since the positive electrode is formed in a solid state without the addition of an organic solvent, chemical and thermal damage to the positive electrode active material by the organic solvent can be prevented. 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.

The lithium secondary battery based on the organic compound according to the present invention may have excellent cycle characteristics and excellent electrochemical characteristics. 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 exemplary embodiments.

5 and 6 are graphs showing voltage profiles of an anode electrode according to exemplary embodiments.

7 and 8 are graphs showing charging and discharging profiles according to an increase in the number of cycles for Comparative Examples and Examples.

9 are graphs showing discharge capacity (mAh/g) and Coulomb efficiency (%) according to an increase in the number of cycles for Comparative Examples and Examples.

10 are graphs showing internal resistance of an anode electrode according to exemplary embodiments.

11 is a schematic diagram illustrating an anode electrode according to other exemplary embodiments.

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

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

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

15 and 16 are graphs showing cycle characteristics of an anode electrode according to exemplary embodiments.

17 are graphs showing internal resistance of an anode electrode according to exemplary embodiments.

18 are graphs showing voltage profiles of anode electrodes having various densities according to exemplary embodiments.

19 are graphs showing one-time charge capacity and one-time discharge capacity.

20 and 21 are graphs showing cycle characteristics according to a density of an anode electrode according to exemplary embodiments.

22 are graphs showing internal resistance of an anode electrode according to exemplary embodiments.

23 is a graph showing a voltage profile of an anode electrode according to example embodiments.

24 is a graph showing cycle characteristics of an anode electrode according to exemplary embodiments.

25 is a schematic diagram illustrating an anode electrode according to other exemplary embodiments.

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

27 is a graph showing a voltage profile of an anode electrode according to example embodiments.

28 and 29 are graphs showing cycle characteristics of an anode electrode according to exemplary embodiments.

30 and 31 are graphs showing voltage profiles and cycle characteristics of an anode electrode according to exemplary embodiments.

FIG. 32 is a graph showing a discharge capacity based on a mass of a positive electrode active material and a discharge capacity based on a mass of a positive electrode according to the amount of the positive electrode active material.

33 are graphs showing internal resistance of an anode electrode according to example embodiments.

34 is a graph showing a voltage profile of an anode electrode according to Example 4 (EX4) and Comparative Example (CO1).

35 is a graph showing discharge capacity (mAh/g) and Coulomb efficiency (%) according to an increase in the number of cycles of the positive electrode according to Example 4 (EX4) and Comparative Example (CO1).

36 are graphs showing internal resistance of a positive electrode according to Example 4 (EX4) and Comparative Example (CO1).

37 is a graph showing the adsorption amount for BET specific surface area measurement of Ketjen Black (EX21) and Super P (CO21).

In order to fully understand the configuration and effects 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, but may be implemented in various forms and various changes may be added. However, the description of the embodiments is provided to complete the disclosure of the present invention, and to fully inform the scope of the invention to those of ordinary skill in the art to which the present invention pertains. In the accompanying drawings, the size of the constituent elements is enlarged from the actual size for convenience of description, and the ratio of each constituent element may be exaggerated or reduced.

When a component is described as being "on" or "adjacent" to another component, it should be understood that it may be directly in contact with or connected to another component, but another component may exist in the middle. something to do. On the other hand, when a component is described as being "directly above" or "directly" of another component, it may be understood that another component does not exist in the middle. Other expressions describing the relationship between components, such as "between" and "directly," can be interpreted as well.

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

Singular expressions include plural expressions, unless the context clearly indicates otherwise. Terms such as "comprises" or "have" are used to designate the presence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification, and one or more other features or numbers, It may be interpreted that steps, actions, components, parts, or combinations thereof may be added.

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

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

1 is a cross-sectional view schematically illustrating 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 solution 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 cathode electrode 20, the anode electrode 30, and the separator 50 may be accommodated in the

cases

72 and 74 while being soaked in the electrolyte solution 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 organic compound-based. It can act as electrical terminals of the rechargeable lithium battery 1.

The negative electrode 20 may include lithium metal, graphite, a silicon-based material, a tin-based material, a mixture thereof, and 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, or a mixture thereof, the negative electrode 20 is a negative electrode current collector (not shown) composed of, for example, copper foil. ) Can also be attached.

The positive electrode 30 may include positive electrode active material particles based on an organic compound. The positive electrode 30 may be 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 anode 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 layer or a multilayer of two or more layers. The separator 50 may include a polymer material, and may include at least one of a polyethylene-based, polypropylene-based, polyvinylidene fluoride-based, and polyolefin-based polymer.

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, and for example, a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent or aprotic It may contain a solvent. The non-aqueous solvent may be used alone or in combination of one or more, and the mixing ratio in the case of using one or more mixtures may be appropriately adjusted according to the desired battery performance.

The electrolyte salt is not particularly limited as long as it is used as a conventional electrolyte salt for a 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 more selected from the group consisting of. These electrolyte salts may be used alone or in combination of two or more.

1 illustrates a coin-type battery as an organic compound-based lithium secondary battery 1 as an example, but the technical idea of the present invention is not limited thereto. Unlike that shown in FIG. 1, the organic compound-based lithium secondary battery 1 may be a cylindrical battery in which a positive electrode and a negative electrode are spirally wound inside a cylindrical case, or a rectangular case. It may be a prismatic battery accommodated in a state in which the positive electrode and the negative electrode are wound. Alternatively, it may be a polymer battery accommodated in a vinyl 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 electrode active material 32, a conductive material 34, a binder 36, and a carbon nanotube 38.

In exemplary embodiments, the positive electrode 30 includes about 30 to 50% by weight of the positive electrode active material 32 based on the total weight of the positive electrode 30, and about 30 to 50% by weight based on the total weight of the positive electrode 30. Containing a conductive material 34, a binder 36 of 10 to 30% by weight of the total weight of the positive electrode 30, and about 5 to about 20% by weight of carbon nanotubes based on the total weight of the positive electrode 30 can do.

In example embodiments, the positive electrode 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 included in the organic compound or a functional group including at least one of nitrogen, oxygen, and sulfur may serve as an active region for a reversible oxidation 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. I can. For example, the radical polymer may have a discharge capacity of approximately 200 mAh/g or less, an average discharge potential of approximately 3.0 to 4.0 V (based on Li metal), and an energy density of ^{approximately 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 of approximately 1.5 to 3.0 V (based on Li metal), and an energy density of ^{approximately 400 to 1500 Wh/kg -1.} I can. For example, the carbonyl group-containing compound may have a discharge capacity of approximately 100 to 300 mAh/g, an average discharge potential of approximately 1.5 to 3.0 V (based on Li metal), and an energy density of ^{approximately 1000 Wh/kg -1 or less.} have.

In exemplary embodiments, the positive electrode 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 flavantron (flavanthrone).

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

[Formula 2]

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

In example 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 changes 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®), and acetylene black. The conductive material 34 may be contained less than the amount of the positive electrode active material 32 based on the total weight of the positive electrode 30. For example, the positive active material 32 may be included in the positive electrode 30 in a first amount, and the conductive material 34 may be included in the positive electrode 30 in a second amount less than the first amount.

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

In exemplary embodiments, the binder 36 may be a polymer, for example, polyimide, polyamideimide, polybenzimidazole, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, polyvinylchloride, carboxylate. Polyvinyl chloride, polyvinylfluoride, ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene, acrylated styrene- It may be a butadiene, an epoxy resin, and the like. In exemplary embodiments, the binder 36 may be a bead type of polytetrafluoroethylene (PTFE).

In exemplary embodiments, the carbon nanotubes 38 are attached to the surface of the particles of the positive electrode active material 32 and the conductive material 34 so that the positive electrode active material 32 particles or the conductive material 34 particles are attached to the positive electrode 30 ) May serve as a support for preventing separation from the positive electrode active material 32, or may serve to provide an electrical path between the positive electrode active material 32 and the conductive material 34 even if particles of the positive electrode active material 32 are eluted into the electrolyte.

For example, the carbon nanotube 38 may have a nano-sized rod shape or a fiber shape extending in the longitudinal direction. The length or weight of the carbon nanotube 38 may be variously selected. The carbon nanotube 38 includes at least one of a single wall carbon nanotube, a multi-wall carbon nanotube, a carbon nanotube rope, and a carbon fiber. It can be, but is not limited thereto. For example, the carbon nanotubes 38 may include a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.

In example embodiments, a trace amount of metal atoms, for example, less than 1% by weight of metal atoms may be attached to the carbon nanotubes 38. For example, the metal atom may include copper (Cu), nickel (Ni), cobalt (Co), silver (Ag), titanium (Ti), aluminum (Al), tungsten (W), molybdenum (Mo), and the like. However, it is not limited thereto. The type of the trace amount of metal atoms attached to the carbon nanotubes 38 may vary depending on the method of manufacturing the carbon nanotubes 38, and the content of the trace amounts of metal atoms also includes the method and purity of the carbon nanotubes 38 ( purity). For example, when tungsten carbide is used as a catalyst in the process of synthesizing the carbon nanotubes 38, a trace amount of tungsten atoms may be attached to the surface of the carbon nanotubes 38. For example, the carbon nanotube 38 may have a purity of about 90 to 99.99%, and as the purity of the carbon nanotube 38 increases, the amount of metal atoms added may be reduced.

In example embodiments, the carbon nanotubes 38 may be included in an amount of about 5 to 20% by weight based on the total weight of the positive electrode 30. When the content of the carbon nanotubes 38 is less than about 5% by weight, the effect of preventing an increase in electrode resistance due to the elution of the positive electrode active material may be insignificant, and the content of the carbon nanotubes 38 is about 20% by weight. When a larger amount is included, since the ratio of the active material (ie, the positive electrode active material) for redox of lithium ions in the positive electrode 30 is reduced, the discharge capacity may be reduced. As the carbon nanotubes 38 are contained in an amount of about 5 to 20% by weight, the anode electrode 30 has a relatively high discharge capacity, while preventing an increase in electrode resistance due to the elution of the organic compound to an electrolyte solution, thereby providing an excellent cycle. Can show characteristics.

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

^{^{DMPZ → DMPZ 2+ + 2e - -}} (3)

In other embodiments, when the positive electrode active material 32 includes perylenetetracarboxylic anhydride (PTCDA), the positive electrode 30 may exhibit a single plateau at about 2.52 V to about 2.7 V.

In example embodiments, the positive active material 32 may have an average particle size of about 500 nanometers (nm) to about 60 micrometers (µm), but is not limited thereto. For example, when the average particle size of the positive electrode active material 32 is smaller than about 500 nm, 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 solution, and thus the lithium secondary battery 1 The cycle characteristics of may be deteriorated, and when the average particle size of the positive electrode active material 32 is larger than about 60 μm, it is difficult to effectively transfer lithium ions to the inside of the positive electrode active material 32. high rate) characteristics may be deteriorated.

In exemplary embodiments, the anode electrode 30 may have a thickness T1 of about 20 to 200 micrometers, and the anode electrode 30 may have a density ^{of 0.50 g/cm 3} to 1.2 g/cm ^3. I can. The density of the positive electrode 30 may be the density of the free-standing type positive electrode 30 itself, which does not include a positive electrode current collector. For example, the positive electrode active material 32 relative to the volume of the positive electrode 30, It may refer to the ratio of the total weight of the conductive material 34, the binder 36, and the carbon nanotubes 38.

In example embodiments, as the anode electrode 30 contains 5 to 20% by weight of the carbon nanotubes 38, even if the number of cycles increases, the voltage range of the first plateau and the second plateau in the initial cycle A first plateau and a second plateau may appear in a similar voltage range. For example, in the case of the comparative example in which the carbon nanotubes 38 are not included, the voltage profile may be deformed and the plateau may not be observed as the number of cycles increases, but in the case of the embodiment including the carbon nanotubes 38 Even if the number of cycles increases, the voltage profile is not modified and the first and second plateaus can be observed in a voltage range similar to that in the initial cycle. A detailed description of the carbon nanotube 38 and its electrochemical properties will be described with reference to FIGS. 5A to 8.

In example embodiments, the positive electrode 30 may be manufactured according to a method of manufacturing an organic compound-based secondary battery including a solid-phase mixing method described with reference to FIG. 3. This solid-phase mixing method can prevent chemical and thermal damage to the positive electrode active material of the positive electrode 30 and allow the positive electrode 30 to be formed in a free standing type. The energy density of the compound-based lithium secondary battery 1 can be remarkably increased.

3, a positive electrode active material, a conductive material, a binder, and a carbon nanotube are prepared (step S10).

In example embodiments, the positive electrode active material, the conductive material, the binder, and the carbon nanotube may be provided in a solid state. For example, the positive electrode active material has a first particle size of about 500 nanometers to about 60 micrometers, the conductive material has a second particle size of about 10 to 100 nanometers, and the binder has a third particle size of about 1 to 5 millimeters. It can have a particle size. The carbon nanotube may be at least one of a single wall carbon nanotube, a multi-wall carbon nanotube, a carbon nanotube rope, and a carbon fiber. The carbon nanotube 38 may have a purity of about 90 to 99.99%, and a trace amount of metal atoms, for example, less than 1% by weight of metal atoms may be attached to the surface of the carbon nanotube 38 to be provided.

Optionally, in order to remove moisture that may exist in the positive electrode active material, the conductive material, the binder, and the carbon nanotubes, at least one of the positive electrode active material, the conductive material, the binder, and the carbon nanotubes is put in a vacuum oven for several tens of minutes to several hours. Can be dried.

Thereafter, a positive electrode active material, a conductive material, a binder, and a carbon nanotube are mixed in a mixing container, and a positive electrode active material, a conductive material, a binder, and a carbon nanotube are solidly mixed to form a preliminary positive electrode (step S20).

In exemplary embodiments, the positive electrode active material, the conductive material, the binder, and the carbon nanotubes may be mixed without adding a liquid solvent or the like in the mixing container. In the entire process of mixing the solid phase, the positive electrode active material, the conductive material, the binder, and the carbon nanotube are each in a solid state, and a mixing rod such as a mortar is used for the positive electrode active material, the conductive material, the binder, and the carbon nanotube By applying a mechanical shear force, the positive electrode active material, the conductive material, the binder, and the carbon nanotubes may be uniformly mixed with each other.

For example, while the mixing rod collapses each of the positive electrode active material, the conductive material, and the binder in a solid lump state into small pieces, the positive electrode active material, the conductive material, and the binder pieces may be aggregated and attached to each other by mechanical shearing force by the mixing rod. In the mixing process, the carbon nanotubes may be uniformly mixed with the positive electrode active material, the conductive material, and the binder, and in particular, may be formed by being attached to the surfaces of the positive electrode active material and the conductive material particles. The carbon nanotubes may be included in a length relatively longer than the positive electrode active material particle size, and thus, one carbon nanotube may be disposed in a manner attached to the surfaces of the plurality of positive electrode active material particles and the plurality of conductive material particles.

A solid mass formed by relatively uniformly mixing a positive electrode active material, a conductive material, a binder, and a carbon nanotube may be referred to as a preliminary positive electrode. The preliminary anode electrode may be formed in a lump shape having a relatively high viscosity that is substantially solid.

Thereafter, the preliminary anode electrode is roll pressed to form an anode electrode (step S30).

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, followed by a waiting time of several minutes to tens of minutes after one roll pressing step, and then one roll pressing Steps can be performed.

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

In general, a liquid mixing method using an organic solvent may be used to form an electrode material based on a conventional inorganic material. Particularly, particles of an inorganic active material are mixed in an organic solvent such as NMP (N-methyl-2-pyrrolidone) and mixed to prepare a slurry for an electrode. Thereafter, an electrode material is prepared by applying the electrode slurry 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 and chemically transformed by an organic solvent such as NMP. In addition, the organic compound-based positive electrode active material may be deformed due to 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 degraded. Therefore, there is a need to develop a method for manufacturing a homogeneous electrode while minimizing chemical and thermal damage to an organic active material-based positive electrode active material.

In the manufacturing method according to the above-described exemplary embodiments, a positive electrode may be formed by mixing a positive electrode active material, a conductive material, a binder, and a carbon nanotube in an all solid-state state. In particular, since the organic solvent is not used in the mixing step of the active material, chemical and thermal damage to the positive electrode active material by the organic solvent and the organic solvent removal process can be prevented. In addition, the positive electrode active material and the conductive material are uniformly dispersed in the positive electrode, and a sufficient electrical connection path between the positive electrode active material and the conductive material may be provided through the carbon nanotubes. Therefore, the anode electrode formed by this manufacturing method can exhibit excellent electrical properties.

In addition, 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 by the current collector is inevitable. However, according to exemplary embodiments, since a free-standing type positive electrode can be formed and unnecessary current collectors can be omitted through the manufacturing method in an all-solid state, the weight of the lithium secondary battery is reduced and the weight energy density is remarkably improved. I can.

In FIGS. 4 to 10 below, electrochemical performance of an organic compound-based lithium secondary battery including the positive electrode 30 according to exemplary embodiments described with reference to FIG. 3 will be described.

Experimental example

1) Preparation of anode electrode

DMPZ (5,10-dihydro-5,10-dimethylphenazine), ketjen black®, and PTFE (polytetrafluoroethylene) were used as a positive electrode active material, a conductive material, and a binder, respectively. As carbon nanotubes, low-purity multi-walled carbon nanotubes, high-purity multi-walled carbon nanotubes, and high-purity single-walled carbon nanotubes were included in each positive electrode sample. The positive electrode active material, the conductive material, the binder, and the carbon nanotube were mixed using a mortar at a mass ratio of 4:3.5:1.5:0.5, respectively. A positive electrode active material, a conductive material, a binder, and a carbon nanotube were mixed in the mortar and mixed in a solid state. The uniformly mixed positive electrode was pressed using a roll press, and then the positive electrodes were cut to a size of ^{1*1 cm 2.} Meanwhile, the positive electrode according to the comparative example did not contain a carbon nanotube, and a positive electrode active material, a conductive material, and a binder were mixed in a mass ratio of 4:3.5:1.5, respectively.

2) Manufacture of lithium secondary battery

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

4A shows the anode electrode cut in a free standing type. Even without a separate current collector, the positive electrode active material, the conductive material, the binder, and the positive electrode in which the carbon nanotubes are uniformly mixed can be maintained in shape so that the positive electrode can be used as a free standing type. The positive electrode may have sufficient structural stability to the extent that it can be handled in the manufacturing process of a commercial lithium secondary battery.

4B and 4C are images showing the surface of the positive electrode, and it can be seen that the positive electrode active material particles and conductive material particles of approximately spherical or elliptical shape are bonded to each other by a binder to have a relatively smooth surface morphology. have. In addition, it can be seen that the positive electrode active material particles have a relatively uniform particle size, and a relatively long carbon nanotube is attached to and disposed on the surfaces of the plurality of positive electrode active material particles and the plurality of conductive material particles.

5 and 6 are graphs showing voltage profiles of an anode electrode according to exemplary embodiments. FIG. 5 shows the voltage and capacity in one charge and one discharge in Comparative Example (CO1), and FIG. 6 shows the voltage in one charge and one discharge in Examples 1 to 3 (EX1, EX2, EX3). And doses are shown. Comparative Example (CO1) is an anode electrode without carbon nanotubes, Example 1 (EX1) is an anode electrode including low-purity multi-walled carbon nanotubes, and Example 2 (EX2) is a high-purity multi-walled carbon nanotube. An anode electrode including a tube, and Example 3 (EX3) is an anode electrode including a high-purity single-walled carbon nanotube. Here, low purity refers to a purity of about 90%, and high purity refers to a purity of about 98%.

5 and 6, in the charging step, Examples 1 to 3 (EX1, EX2, EX3) and Comparative Example (CO1) all show a first plateau at about 3.0 V to about 3.2 V, and about 3.6 V. It can be seen that the second plateau is represented at about 3.8 V. For example, the first plateau appears by an oxidation reaction in which one nitrogen atom of two nitrogen atoms contained in DMPZ is ionized to a nitrogen cation, and the other nitrogen atom of the two nitrogen atoms is ionized to a nitrogen cation. The second plateau may appear by reaction.

^{^{DMPZ → DMPZ 2+ + 2e - -}} (3)

Example 1 (EX1) showed a discharge capacity of about 160 mAh/g, whereas Comparative Example (CO1) showed a discharge capacity of about 185 mAh/g. This may be understood as a decrease in capacity due to a decrease in the content of the positive electrode active material included in the positive electrode of the same mass, as the carbon nanotubes were not included in the comparative example (CO1). In addition, it can be seen that the carbon nanotubes do not function as active regions for oxidation and reduction reactions for storage of lithium ions.

It can be seen that Examples 2 and 3 (EX2, EX3) exhibit a discharge capacity of about 145 mAh/g. Since Example 2 (EX2) including multi-walled carbon nanotubes and Example 3 (EX3) including single-walled carbon nanotubes exhibit similar voltage profiles and discharge capacity, significant differences according to the type of carbon nanotubes It can be confirmed that does not exist.

7 and 8 are graphs showing charging and discharging profiles according to an increase in the number of cycles for Comparative Examples and Examples. 7 shows the charging and discharging profiles in the first, fifth, and tenth cycles of Comparative Example (CO1), and FIG. 8 is the first, fifth, and fifth cycles of Example 1 (EX1). The charging and discharging profiles in the 10th cycle are shown.

7 and 8, in Comparative Example CO1, a significant decrease in discharge capacity was observed in the fifth and tenth cycles compared to the discharge capacity in the first cycle. On the other hand, it is observed that Example 1 (EX1) slightly decreased in the 5th and 10th cycles compared to the discharge capacity in the first cycle, but exhibited a relatively high discharge capacity.

In addition, in Comparative Example (CO1), the first plateau at about 3.0 to about 3.2 V was observed in the first cycle, whereas the first plateau was not clearly observed in the fifth cycle and the tenth cycle. On the other hand, in Example 1 (EX1), the first plateau at about 3.0 V to about 3.2 V can be clearly observed in all of the first, fifth, and tenth cycles. That is, it can be seen that the anode electrode according to exemplary embodiments including the carbon nanotubes exhibits significantly improved cycle characteristics compared to the anode electrode without the carbon nanotubes.

The reason that the positive electrode of the comparative example that does not contain carbon nanotubes does not show a plateau as the cycle progresses because the positive electrode active material is eluted into the electrolyte and the positive electrode active material is separated from the positive electrode, or the positive electrode active material eluted into the electrolyte. This may be because the electrical path between the positive electrode active material and the conductive material is cut off, thereby increasing the resistance of the entire positive electrode.

On the other hand, the positive electrode of the embodiment including the carbon nanotubes exhibits a similar plateau even if the cycle proceeds, as the carbon nanotubes are attached to the surfaces of the positive electrode active material and the conductive material, so that the positive electrode active material particles or conductive material particles are removed from the positive electrode. It can be understood because it serves as a support to prevent separation. In addition, since the carbon nanotubes provide an electrical path between the positive electrode active material and the conductive material, even if a part of the positive electrode active material is eluted into the electrolyte and separated from the positive electrode as charging and discharging of the positive electrode is performed, the remaining positive active material and carbon It can be understood that this is because the electrical path between the nanotubes is secured and thus the resistance of the entire anode electrode does not increase.

In addition, although not shown in Figs. 7 and 8, Examples 2 and 3 (EX2, EX3) also showed similar cycle characteristics to Example 1 (EX1), and accordingly, electricity of the anode electrode according to the type of carbon nanotubes. It can be seen that there is no significant difference in chemical performance.

Referring to FIG. 9, the comparative example CO1 shows a relatively high initial discharge capacity, while a significant decrease in discharge capacity is observed after 10 cycles. On the other hand, Example 1 (EX1) shows a lower initial discharge capacity than Comparative Example (CO1), but shows a discharge capacity of approximately 120mAh/g even after 10 cycles, so it can be seen that it shows a capacity retention rate of approximately 75%. .

In addition, Comparative Example (CO1) exhibits a Coulomb efficiency of about 70% after 10 cycles, whereas Example 1 (EX1) shows a remarkably high Coulomb efficiency of about 90% after 10 cycles. As described above, it can be assumed that the carbon nanotubes added to the exemplary embodiments serve to provide an electrical path between the positive electrode active material and the conductive material even if the positive electrode active material is eluted into the electrolyte.

10 are graphs showing internal resistance of an anode electrode according to exemplary embodiments. In FIG. 10, Nyquist plots obtained from the impedance analysis method of Comparative Example (CO1), Example 1 (EX1), and Example 2 (EX2) are shown.

Referring to FIG. 10, the impedance graph of Example 1 (EX1) has a semicircle of a smaller radius than the impedance graph of Comparative Example (CO1). In general, in the Nyquist plot of the impedance analysis method, the smaller the radius of the semicircle, the smaller the resistance value. Accordingly, it can be seen that the anode electrode of Example 1 (EX1) has a smaller internal resistance value than that of the anode electrode of Comparative Example (CO1).

In particular, it was found that Example 1 (EX1) including low-purity multi-walled carbon nanotubes has a remarkably low resistance value. This appears to be smaller than the resistance value of Example 2 (EX2) including high-purity multi-walled carbon nanotubes. It can be assumed that this is a difference due to a trace amount of metal atoms attached to the carbon nanotubes. For example, a trace amount of metal atoms originating from a metal catalyst may be attached to the surface of the low-purity carbon nanotube (for example, at both ends of the carbon nanotube in the longitudinal direction). In particular, the content of metal atoms attached to the low-purity carbon nanotubes may be greater than the content of metal atoms attached to the high-purity carbon nanotubes. Therefore, it is believed that Example 1 (EX1) including low-purity carbon nanotubes can have a smaller electrode internal resistance compared to Comparative Examples (CO1) and Example 2 (EX2) due to trace metal atoms present therein. Can be understood.

11 is a schematic diagram illustrating an anode electrode 30A according to other exemplary embodiments.

Referring to FIG. 11, the positive electrode 30A may include a positive electrode active material 32, a conductive material 34, and a binder 36.

In exemplary embodiments, the positive electrode 30A includes 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 30A. A conductive material 34 and a binder 36 of 10 to 30% by weight of the total weight of the positive electrode 30A may be included.

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. I can. For example, the radical polymer may have a discharge capacity of approximately 200 mAh/g or less, an average discharge potential of approximately 3.0 to 4.0 V (based on Li metal), and an energy density of ^{approximately 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 of approximately 1.5 to 3.0 V (based on Li metal), and an energy density of ^{approximately 400 to 1500 Wh/kg -1.} I can. For example, the carbonyl group-containing compound has a discharge capacity of approximately 100 to 300 mAh/g, an average discharge potential of approximately 1.5 to 3.0 V (based on Li metal), and an energy density of ^{approximately 1000 Wh/kg -1 or less.} I can.

[Formula 1]

[Formula 2]

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

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

^{^{DMPZ → DMPZ 2+ + 2e - -}} (3)

In example 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 solution, and the lithium secondary battery 1 ) Cycle characteristics may be deteriorated, and when the average particle size of the positive electrode active material 32 is larger than about 6 micrometers, it is difficult to effectively transfer lithium ions to the inside of the positive electrode active material 32. High rate characteristics may be degraded.

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

In example embodiments, as the anode electrode 30A ^{has a density of 0.50 g/cm 3} to 1.2 g/cm ³ , while exhibiting excellent Coulomb efficiency, it may exhibit relatively high cycle characteristics. In addition, the anode electrode 30A 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 anode electrode 30A 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 The first plateau slightly appears at about 3.2 V and the second plateau may not be observed at about 3.6 V to about 3.8 V, which may mean that the redox reaction in Formula 3 does not reversibly occur. ). When the density of the anode electrode 30A is 0.50 g/cm ³ to 1.2 g/cm ³ , the initial discharge capacity is excellent, and excellent coulomb efficiency of 70% or more for 10 cycles and excellent cycle characteristics may be exhibited. On the other hand, when the density of the anode electrode 30 ^{is greater than 1.2 g/cm 3} (for example, about 1.22 g/cm ³ ), the Coulomb efficiency decreases to 50% or less for 10 cycles, and the cycle characteristics are not excellent. I can.

For example, in the impedance measurement results for the anode electrode, the anode electrode having a density of ^{0.50 g/cm 3} to 1.2 g/cm ³ ^{was less than 0.50 g/cm 3} or greater than 1.2 g/cm ^3. It can represent a smaller electrode resistance value. This is, for example, in ^{the positive electrode having a density smaller than 0.50 g/cm 3} , sufficient contact and electrical path between the positive electrode active material and the conductive material are not provided, so that the resistance value of the entire positive electrode increases, and is less than ^{1.2 g/cm 3.} In the positive electrode having a high density, it can be understood that the electrolyte and lithium ions through the same are not sufficiently provided to penetrate and move into the positive electrode, thereby increasing the resistance value of the entire positive electrode. The electrochemical characteristics according to the density of the anode electrode 30A will be described again with reference to FIGS. 18 to 22.

In example embodiments, the positive electrode 30A may be manufactured according to a method of manufacturing an organic compound-based secondary battery including a two-step solid-phase mixing method described with reference to FIG. 12. This two-step solid-phase mixing method can prevent chemical and thermal damage to the positive electrode active material of the positive electrode 30A, and allow the positive electrode 30A to be formed in a free standing type, thereby forming the positive electrode 30A. The energy density of the organic compound-based lithium secondary battery 1 to be employed can be remarkably increased.

For example, compared to the anode electrode manufactured by using the mixing method according to the comparative example, the anode electrode manufactured by using the two-stage solid-phase mixing method has a further increased initial discharge capacity, an increased coulomb efficiency, and better cycle characteristics. Can represent. In addition, compared to the positive electrode prepared using the mixing method according to the comparative example, the positive electrode prepared 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 evenly mixed by the two-step solid-phase mixing method, whereby the anode electrode 30A exhibits a further increased initial discharge capacity, increased coulomb efficiency, and more excellent cycle characteristics. Can be. The electrochemical properties of the anode electrode using this two-step mixing method will be described again with reference to FIGS. 14 to 17.

Referring to FIG. 12, a positive electrode active material, a conductive material, and a binder are prepared (step S10).

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

Thereafter, the positive electrode active material and the conductive material are mixed in the mixing container, and the positive electrode active material and the conductive material are solidly mixed to form a first preliminary positive electrode (step S20).

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

Thereafter, a binder is mixed in the mixing container, and the first preliminary anode electrode and the binder are solidly mixed to form a second preliminary anode electrode (step S30).

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

For example, the positive electrode active material and the conductive material may have a smaller particle size than that of the binder. The positive electrode active material has a first particle size of about 500 nanometers to 60 micrometers, the conductive material has 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. have. The positive electrode active material and the conductive material may be uniformly mixed and dispersed in the second preliminary positive electrode by mixing the positive electrode active material and the conductive material in a solid state and then mixing the mixture in a solid state with a binder having a larger particle size.

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

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

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

In FIGS. 13 to 24 below, electrochemical performance of an organic compound-based lithium secondary battery including the positive electrode 30A manufactured using the manufacturing method according to exemplary embodiments described with reference to FIG. 10 is described. Do it.

Experimental example

1) Preparation of anode electrode

DMPZ (5,10-dihydro-5,10-dimethylphenazine) and PTCDA were used as positive electrode 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 each mixed in a 4:4:2 mass ratio using a mortar. In the mortar, the positive electrode active material and the conductive material were first mixed and mixed in a first solid phase, and then a binder was mixed and mixed in a second solid phase. Electrodes having various electrode densities were manufactured using a roll press for the uniformly mixed positive electrode. The anode electrodes were cut to a size of 1*1 cm ^2. Meanwhile, in the positive electrode according to the comparative example, a positive electrode active material, a conductive material, and a binder were simultaneously mixed in a mortar and mixed in a solid phase.

2) Manufacture of lithium secondary battery

13A shows the anode electrode cut in a free standing type. Even without a separate current collector, the shape can be maintained so that a positive electrode in which a positive electrode active material including DMPZ, a conductive material, and a binder are uniformly mixed can be used as a free standing type. The positive electrode may have sufficient structural stability to the extent that it can be handled in the manufacturing process of a commercial lithium secondary battery.

13B and 13C are images showing the surface of the positive electrode, and it can be seen that the positive electrode active material particles and conductive material particles of approximately spherical or elliptical shape are bonded to each other by a binder to have a relatively smooth surface morphology. have. In addition, it can be seen that the positive electrode active material particles have a relatively uniform particle size.

Referring to FIG. 14, voltage and capacity in one charge and one discharge of Example 1 (EX1) and Comparative Example (CO1) are shown. Example 1 (EX1) is an anode electrode including DMPZ manufactured by a two-step solid-phase mixing method, and Comparative Example (CO1) is an anode electrode manufactured by simultaneously mixing anode electrode materials. In the charging step, it can be seen that both Example (EX1) and Comparative Example (CO1) exhibited 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 of two nitrogen atoms contained in DMPZ is ionized to a nitrogen cation, and the other nitrogen atom of the two nitrogen atoms is ionized to a nitrogen cation. The second plateau may appear by reaction.

^{^{DMPZ → DMPZ 2+ + 2e - -}} (3)

Example 1 (EX1) showed a discharge capacity of about 235 mAh/g, whereas 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).

15 and 16 are graphs showing cycle characteristics of an anode electrode according to exemplary embodiments. Specifically, FIG. 15 shows the discharge capacity (mAh/g) according to the number of cycles, and FIG. 16 shows the Coulomb efficiency (%) according to the number of cycles. Coulomb efficiency (%) refers to the ratio of the discharge capacity to the charge capacity in each cycle.

15 and 16, Example 1 (EX1) exhibits a discharge capacity of about 172mAh/g and a Coulomb 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 130mAh/g and a Coulomb 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 seen that Example 1 (EX1) prepared by the two-step solid-phase mixing method exhibits excellent cycle characteristics compared to Comparative Example (CO1).

Meanwhile, in FIG. 15, in order to further confirm electrode uniformity and reproducibility characteristics by the two-step solid-phase mixing method, cycles for three cut anode electrodes for each of Example 1 (EX1) and Comparative Example (CO1). The discharge capacity according to was tested. In FIG. 15, the average value and standard deviation of the three anode electrodes are shown. 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), and in particular, the standard deviation of the discharge capacity is smaller as the number of cycles increases. Thereby, it can be seen that Example 1 (EX1) prepared by the two-step solid-phase mixing method exhibits excellent electrode uniformity and reproducibility.

17 are graphs showing internal resistance of an anode electrode according to exemplary embodiments. In FIG. 17, Nyquist plots obtained from the impedance analysis method of Example 1 (EX1) and Comparative Example (CO1) are shown.

Referring to FIG. 14, the impedance graph of Example 1 (EX1) has a semicircle of a smaller radius than the impedance graph of Comparative Example (CO1). In general, in the Nyquist plot of the impedance analysis method, the smaller the radius of the semicircle, the smaller the resistance value. Accordingly, it can be seen that the anode electrode of Example 1 (EX1) has a smaller internal resistance value than that of the anode electrode of Comparative Example (CO1).

Example 1 (EX1) prepared by the two-step solid-phase mixing method was uniformly dispersed and mixed with the positive electrode active material, the conductive material, and the binder, so that the electrode internal resistance may be smaller than that of the comparative example (CO1). Can be understood.

18 to 22 will be described with respect to the electrochemical performance of the density of the anode electrode according to exemplary embodiments. Experimental Examples 21 to 26 (EX21 to EX26) included DMPZ, and were prepared to have a density of 0.42, 0.44, 0.45, 0.57, 0.96, and 1.22 g/cm ^{3, respectively.}

18 are graphs showing voltage profiles of anode electrodes having various densities according to exemplary embodiments, and FIG. 19 is graphs showing one-time charge capacity and one-time discharge capacity.

18 and 19, ^{Example 21 (EX21) having a density of 0.42 g/cm 3} shows a relatively low charging capacity and a discharge capacity (for example, a discharge capacity of about 110 mAh/g), It can be seen that the 1 plateau is insignificantly observed and the second 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 charging capacity and discharge capacity (discharge capacity of approximately 200 mAh/g or more). .

20 and 21 are graphs showing cycle characteristics according to a density of an anode electrode according to exemplary embodiments. Specifically, FIG. 20 shows the discharge capacity (mAh/g) according to the number of cycles, and FIG. 21 shows the Coulomb efficiency (%) according to the number of cycles. Coulomb efficiency (%) refers to the ratio of the discharge capacity to the charge capacity in each cycle.

20 and 21, Examples 21 to 25 (EX21 to EX25) exhibited about 70% or more Coulomb efficiency after 10 cycles, whereas Example (EX26) was about 47 after 10 cycles. Represents the coulombic efficiency in %. In addition, Examples 21 to 25 (EX21 to EX25) exhibited 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. Show. According to this, it can be seen that Example 26 (EX26) having a density of 1.22 g/cm ³ has a high initial discharge capacity, but the discharge capacity rapidly decreases as the number of cycles increases.

22 are graphs showing internal resistance of an anode electrode according to exemplary embodiments. In Fig. 22, Nyquist plots obtained from the impedance analysis method of Examples 21, 24, 25, and 26 (EX21, EX24, EX25, EX26) are shown.

Referring to FIG. 22, the impedance graphs of Examples 24 and 25 (EX24 and EX25) have a semicircle of a smaller radius than the impedance graphs of Examples 21 and 26 (EX21 and EX26). In general, in the Nyquist plot of the impedance analysis method, the smaller the radius of the semicircle, the smaller the resistance value. Accordingly, it can be seen that the anode electrodes of Examples 24 and 25 (EX24 and EX25) have a smaller internal resistance value than that of the anode electrodes of Examples 21 and 26 (EX21 and EX26).

Analyzing the results in FIGS. 18 to 22 together, for example, in ^{a positive electrode having a density smaller than 0.50 g/cm 3} , sufficient contact and electrical path between the positive electrode active material and the conductive material were not provided, so the resistance of the entire positive electrode. The value increases, and in ^{the anode electrode with a density greater than 1.2 g/cm 3} , it is assumed that the resistance value of the entire anode electrode increases because the electrolyte solution and lithium ions through it do not sufficiently provide penetration and movement paths into the anode electrode. I can. Moreover, when the density of the anode 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 anode electrode is 1.2 g/cm ^{If it is greater than 3} (for example, Example 26 (EX26), about 1.22 g/cm ³ ), the Coulomb 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 (for example, Examples 22 to 25 (EX22, EX23, EX24, EX25)), the initial discharge capacity was excellent, and 70 for 10 cycles. It can show excellent coulomb efficiency of% or more and excellent cycle characteristics.

Referring to FIG. 23, voltage and capacity in one charge and one discharge of Example 3 (EX3) are shown. Example 3 (EX3) is a positive electrode containing PTCDA manufactured by a two-step solid-phase mixing method. In the charging step, it can be seen that Example 3 (EX3) exhibits a single plateau at about 2.52 V to about 2.7 V. This plateau may be a plateau expressed 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 can be seen to be a high value similar to the discharge capacity of Example 1 (EX1) including DMPZ described with reference to FIG. 14.

Referring to FIG. 24, Example 3 (EX3) shows 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.

25 is a schematic diagram illustrating an anode electrode 30B according to other exemplary embodiments.

Referring to FIG. 25, the positive electrode 30B may include a positive electrode active material 32, a conductive material 34, and a binder 36.

In exemplary embodiments, the positive electrode 30B includes 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 30B. A conductive material 34 and a binder 36 of 10 to 30% by weight of the total weight of the positive electrode 30 may be included.

In example embodiments, the positive electrode active material 32 may be similar to the positive electrode active material 32 described with reference to FIG. 11, and a detailed description thereof will be omitted.

In example 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 changes in the organic compound-based lithium secondary battery 1. The conductive material 34 may include a stable material that does not decompose at about 1.5 V to 4.0 V. The conductive material may include, for example, a carbon-based material such as Super P, carbon black, Ketjen black (eg, Ketjenblack 600JD®, Ketjenblack 700JD®), and acetylene black. The conductive material 34 may have an average particle size of about 10 to 100 nanometers.

In example embodiments, the conductive material 34 may have a BET specific surface area of ^{500 to 2000 m 2 /g.} In addition, the conductive material 34 may have a pore volume of ^{about 1.0 to 5.0 cm 3 /g.} The conductive material 34 may have a relatively large surface area, and accordingly, a relatively large surface of the conductive material 34 functions as an electrode of the capacitor in the charging and discharging step of the anode electrode 30, and the capacity due to capacitance Can contribute to For example, the conductive material 34 may include Ketjen Black, but is not limited thereto.

In exemplary embodiments, the binder 36 serves to attach the particles of the positive active material 32 to each other or to attach the particles of the positive active material 32 to the conductive material 34. Since the detailed description of the binder 36 has been described with reference to FIG. 11, it will be omitted here.

In exemplary embodiments, when charging the lithium secondary battery 1 based on an organic compound using lithium metal as the negative electrode 20, the positive electrode 30B is the first plateau at about 3.0 V to about 3.2 V. (plateau) and a second plateau at about 3.6 V to about 3.8 V. For example, when the positive electrode active material 32 contains 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 to a nitrogen cation. Appears, and the second plateau may appear by an oxidation reaction in which the other nitrogen atom of the two nitrogen atoms is ionized into a nitrogen cation.

^{^{DMPZ → DMPZ 2+ + 2e - -}} (3)

In other embodiments, when the positive electrode active material 32 includes perylenetetracarboxylic anhydride (PTCDA), the positive electrode 30B may exhibit a single plateau at about 2.52 V to about 2.7 V.

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

In example embodiments, charging capacity and discharging capacity may be obtained by the conductive material 34 as well as the positive electrode active material 32 included in the positive electrode 30B. In particular, when the conductive material 34 contains Ketjen Black, and the total of the positive electrode active material 32 and the conductive material 34 is 60 to 90% by weight based on the total weight of the positive electrode 30, the positive electrode 30 ) May exhibit excellent initial discharge capacity, excellent coulomb efficiency, and excellent cycle characteristics.

For example, the content of the cathode active material 32 is 30 to 50% by weight, the content of the conductive material 34 is 30 to 50% by weight, and the sum of the content of the cathode active material 32 and the content of the conductive material 34 is In the case of 80% by weight, the anode electrode 30B exhibits excellent initial discharge capacity, excellent Coulomb efficiency, and excellent cycle characteristics.

First, the content of the positive active material 32 may be 30 to 50% by weight, and may be included in the positive electrode 30B. When the content of the positive electrode active material 32 is less than 30%, the discharge capacity may decrease as the content of the active material for reversible oxidation and reduction reactions during charging and discharging decreases. When the content of the positive electrode active material 32 is greater than 50% by weight, the content of the conductive material 34 decreases, a sufficient electrical path to the positive electrode active material 32 may not be provided, and the internal resistance of the positive electrode 30 Can increase.

The content of the conductive material 34 may be 30 to 50% by weight, and may be included in the positive electrode 30B. When the content of the conductive material 34 is less than 30%, a sufficient electrical path to the positive electrode active material 32 may not be provided, and the internal resistance of the positive electrode 30B may increase. When the content of the conductive material 34 is greater than 50%, the content of the cathode active material 32 included in the anode electrode 30B may be reduced, and accordingly, the content of the active material for reversible oxidation and reduction reactions during charging and discharging As this decreases, the discharge capacity may decrease.

Additionally, even if the content of the positive electrode active material 32 (ie, x wt%) decreases and the content of the conductive material 34 (ie, 80-x wt%) increases, the initial discharge capacity of the positive electrode 30B is approximately 70 To 90 mAh/g. Here, it will be understood that the fact that the initial discharge capacity is maintained within an approximately certain range even when the content of the positive electrode active material 32 is decreased, means that the conductive material 34 together with the positive electrode active material 32 contribute to a certain portion of the discharge capacity. I can. Features contributing to the electrochemical capacity of the conductive material 34 will be described again later with reference to FIGS. 30 to 32.

In example embodiments, the positive electrode 30B may be manufactured according to a method of manufacturing an organic compound-based secondary battery including a solid-phase mixing method described with reference to FIG. 26. This solid-phase mixing method can prevent chemical and thermal damage to the positive electrode active material of the positive electrode 30B and allow the positive electrode 30B to be formed in a free standing type, and accordingly, an organic method employing the positive electrode 30B. The energy density of the compound-based lithium secondary battery 1 can be remarkably increased.

Referring to FIG. 26, a positive active material, a conductive material, and a binder are prepared (step S10).

In example embodiments, the positive electrode active material, the conductive material, and the binder may be provided in a solid state. For example, the positive electrode active material has a first particle size of about 500 nanometers to 60 micrometers, the conductive material has a second particle size of about 10 to 100 nanometers, and the binder is about 1 to 5 millimeters of third particles It can have a size. Optionally, in order to remove moisture that may be present 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 put in a vacuum oven and dried for several tens of minutes to several hours.

Thereafter, the positive electrode active material, the conductive material, and the binder are mixed in the mixing container, and the positive electrode active material, the conductive material, and the binder are solidly mixed to form a preliminary positive electrode (step S20).

In example embodiments, in the mixing container, the positive electrode active material, the conductive material, and the binder may be mixed without adding a liquid solvent or the like. In the whole process of solid-phase mixing, the positive electrode active material, the conductive material, and the binder are each in a solid state, and the positive electrode active material is applied to the positive electrode active material, the conductive material, and the binder by applying a mechanical shear force to the positive electrode active material, the conductive material, and the binder using a mixing rod such as a mortar. , The conductive material, and the binder may be uniformly mixed with each other.

For example, the mixing rod collapses each of the positive electrode active material, the conductive material, and the binder in a solid lump state into small pieces, while the positive electrode active material, the conductive material, and the binder pieces are aggregated and attached to each other by the mechanical shear force by the mixing rod. have. A solid mass formed by relatively uniformly mixing a positive electrode active material, a conductive material, and a binder may be referred to as a preliminary positive electrode. The preliminary anode electrode may be formed in a lump shape having a relatively high viscosity that is substantially solid.

In particular, the conductive material may have a BET specific surface area of ^{about 500 to 2000 m 2} /g and a pore volume of ^{about 1.0 to 5.0 cm 3 /g.} The conductive material may have a relatively high surface area compared to the general conductive material material, and thus the positive electrode active material, the conductive material, and the binder may be more evenly dispersed and mixed.

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

In the manufacturing method according to the above-described exemplary embodiments, a positive electrode may be formed by mixing a positive electrode active material, a conductive material, and a binder in an all solid-state. In particular, since the organic solvent is not used in the mixing step of the active material, chemical and thermal damage to the positive electrode active material by the organic solvent and the organic solvent removal process can be prevented. In addition, by forming the solid anode electrode by roll pressing, it may be easy to control the thickness and/or the density of the anode electrode.

27 to 37 below, electrochemical performance of an organic compound-based lithium secondary battery including the positive electrode 30B according to exemplary embodiments described with reference to FIG. 25 will be described.

Experimental example

1) Preparation of anode electrode

DMPZ (5,10-dihydro-5,10-dimethylphenazine), Ketjenblack®, and PTFE (polytetrafluoroethylene) were used as the positive electrode active material, conductive material, and binder of Examples 1 to 7 (EX1 to EX7), respectively. . The positive electrode active material, the conductive material, and the binder were mixed using a mortar at the mass ratio shown in Table 1 below. A positive electrode active material, a conductive material, and a binder were mixed in the mortar and mixed in a solid state. Electrodes having various electrode densities were manufactured using a roll press for the uniformly mixed positive electrode. The anode electrodes were cut to a size of 1*1 cm ^2. On the other hand, the positive electrode according to the comparative example was prepared using Super P as a conductive material and a mass ratio of the positive active material, the conductive material, and the binder of 4:4:2.

	양극 활물질(중량%)Positive electrode active material (% by weight)	도전재(중량%)Conductive material (% by weight)	바인더(중량%)Binder (% by weight)
실시예 1(EX1)Example 1 (EX1)	7070	1010	2020
실시예 2(EX2)Example 2 (EX2)	5050	3030	2020
실시예 3(EX3)Example 3 (EX3)	4545	3535	2020
실시예 4(EX4)Example 4 (EX4)	4040	4040	2020
실시예 5(EX5)Example 5 (EX5)	3535	4545	2020
실시예 6(EX6)Example 6 (EX6)	3030	5050	2020
실시예 7(EX7)Example 7 (EX7)	1010	7070	2020

2) Manufacture of lithium secondary battery

27 is a graph showing a voltage profile of an anode electrode according to example embodiments. In Fig. 27, the voltage and capacity in one charge and one discharge of Examples 1 to 7 (EX1 to EX7) are shown. FIG. 27 is a graph showing the charge capacity and discharge capacity obtained in the charge/discharge test calculated based on the total mass of the positive electrode, where the total mass of the positive electrode means the sum of the weights of the positive electrode active material, the conductive material, and the binder. do.

Referring to FIG. 27, in Example 1 (EX1), the first plateau clearly appears in the discharging stage, but the second plateau does not appear, and exhibits a considerably steep voltage-capacitance profile from 4.0 V to 3.3 V. Example 1 (EX1) includes 70% by weight of a positive electrode active material and 10% by weight of a conductive material. Therefore, it is assumed that this is because the content of the conductive material included in Example 1 (EX1) is too small to increase the internal resistance of the positive electrode, and it is difficult to develop the second plateau due to a relatively large overpotential of the positive electrode. Can be. By the absence of the second plateau, Example 1 (EX1) shows a rather low initial discharge capacity (about 65 mAh/g).

In Example 2 (EX2) to Example 6 (EX6), it can be seen that the first plateau and the second plateau appear in both the charging step and the discharging step. Example 2 (EX2) contains 50% by weight of a positive electrode active material and 30% by weight of a conductive material, Example 3 (EX3) contains 45% by weight of a positive electrode active material and 35% by weight of a conductive material, Example 4 (EX4) Contains 40% by weight of a positive active material and 40% by weight of a conductive material, Example 5 (EX5) contains 35% by weight of a positive electrode active material and 45% by weight of a conductive material, and Example 6 (EX6) contains 30% by weight of a positive electrode active material And 50% by weight of a conductive material. All of Examples 2 to 6 (EX2 to EX6) exhibit a relatively large initial discharge capacity corresponding to approximately 70 to 85 mAh/g.

In Example 7 (EX7), the first plateau and the second plateau do not clearly appear in the discharging step. It represents the voltage-capacity profile of a sloped curve with a relatively weak shoulder section rather than a plateau from 4.0 V to 2.5 V. Example 7 (EX7) includes 10% by weight of a positive electrode active material and 70% by weight of a conductive material. Example 7 (EX7) shows a relatively low initial discharge capacity of approximately 40 mAh/g.

According to exemplary embodiments, Examples 2 to 6 (EX2 to EX6) contain about 30 to 50% by weight of a positive electrode active material and about 30 to 50% by weight of a conductive material, and have a stable voltage capacity in a charge/discharge test. While showing the profile, it can be seen that it shows a relatively high initial discharge capacity.

28 and 29 are graphs showing cycle characteristics of an anode electrode according to exemplary embodiments. Specifically, FIG. 28 shows the discharge capacity (mAh/g) according to the number of cycles, and FIG. 29 shows the Coulomb efficiency (%) according to the number of cycles. Coulomb efficiency (%) refers to the ratio of the discharge capacity to the charge capacity in each cycle. 28 and 29 are graphs showing the discharging capacity obtained in the cycle test based on the total mass of the positive electrode, wherein the total mass of the positive electrode means the sum of the weights of the positive electrode active material, the conductive material, and the binder.

28 and 29, Examples 2 to 6 (EX2 to EX6) exhibit relatively excellent discharge capacity and Coulomb efficiency. In particular, Examples 1 to 3 (EX1 to EX3) exhibit excellent Coulomb efficiency of about 85% or more even after 15 cycles. On the other hand, Example 7 (EX7) shows a low initial capacity of about 40 mAh/g, and shows a low discharge capacity of about 25 mAh/g even after 15 cycles.

In conclusion, referring to FIGS. 27 to 29 together, Example 1 (EX1) exhibits an unstable voltage profile such as that the second plateau in the high voltage region is not developed, and thus shows a relatively low initial discharge capacity. Example 7 (EX7) shows a voltage profile of a steep slope curve having shoulder regions instead of the first and second plateaus, and thus shows a lower initial discharge capacity than that of Example 1 (EX1). On the other hand, Examples 2 to 6 (EX1 to EX6) exhibit excellent initial discharge capacity and excellent cycle characteristics. In addition, in Examples 2 to 6 (EX2 to EX6), the first plateau and the second plateau are stably observed in the charging and discharging stages. Therefore, according to exemplary embodiments, the positive electrode including about 30 to 50% by weight of a positive electrode active material and about 30 to 50% by weight of a conductive material (that is, Examples 2 to 6 (EX1 to EX6)) is excellent. It can be seen that it has electrochemical performance and cycle characteristics.

30 and 31 are graphs showing voltage profiles and cycle characteristics of an anode electrode according to exemplary embodiments. In FIG. 30, voltage and capacity in one charge and one discharge of Examples 1 to 7 (EX1 to EX7) are calculated based on the mass of the positive electrode active material. In addition, in FIG. 31, the discharge capacity according to the number of cycles of Examples 1 to 7 (EX1 to EX7) is calculated based on the mass of the positive electrode active material (for reference, in FIGS. 27 to 29, the discharge capacity is the entire positive electrode. It was calculated and displayed based on the mass of, and the total mass of the positive electrode means the total weight of the positive electrode active material, the conductive material, and the binder).

Referring to FIGS. 30 and 31, Examples 1 to 7 (EX1 to EX7) are shown to exhibit a smaller discharge capacity as the content of the positive electrode active material increases. For example, referring to FIG. 30 together with FIG. 27, Example 1 (EX1) has an initial discharge capacity of about 65 mAh/g based on the mass of the positive electrode (see FIG. 27), while about 90 based on the mass of the positive electrode active material. It has an initial discharge capacity of mAh/g (see Fig. 30). That is, since Example 1 (EX1) contains about 70% of the positive electrode active material with respect to the total mass of the positive electrode, such a difference in discharge capacity occurs.

For example, Example 4 (EX4) has an initial discharge capacity of about 75 mAh/g based on the mass of the positive electrode electrode (see Fig. 27), while having an initial discharge capacity of about 185 mAh/g based on the mass of the positive electrode active material ( See Fig. 30). On the other hand, Example 6 (EX6) has an initial discharge capacity of about 78 mAh/g (see Fig. 30) and an initial discharge capacity of about 255 mAh/g based on the mass of the positive electrode active material (see Fig. 30).

For example, in Examples 2 to 6 (EX2 to EX6), showing approximately similar discharge capacity corresponding to approximately 70 to 85 mAh/g based on the positive electrode, there are other factors contributing to the discharge capacity in addition to the positive electrode active material. It can mean doing. For example, when the content of the positive electrode active material increases from 30% by weight to 50% by weight, the discharge capacity does not increase in proportion to the content of the positive electrode active material. I can guess.

Referring to FIG. 32, the discharge capacity based on the mass of the positive electrode active material decreases as the positive electrode active material content increases. On the other hand, the discharge capacity based on the mass of the anode electrode rapidly increased in Example 2 (EX2) having 30% by weight and had a maximum value in Example 4 (EX4) having 40% by weight, and then began to decrease. In addition, in Examples 2 to 6 (EX2 to EX6), it may have a relatively excellent discharge capacity of 70 mAh/g.

On the other hand, Example 7 (EX7) has a slightly low content of the positive electrode active material of 10% by weight, it can be seen that a remarkably high discharge capacity of 380 mAh/g based on the mass of the positive electrode active material. This can be presumed to be because a part of the conductive material included in Example 7 (EX7) can act as an electrode of a capacitor through a large specific surface area, and thus contribute to charging and discharging capacity due to capacitance.

33 are graphs showing internal resistance of an anode electrode according to example embodiments. In FIG. 33, Nyquist plots obtained from the impedance analysis method of Example 2 (EX2), Example 4 (EX4), and Example 6 (EX6) are shown.

Referring to FIG. 33, the impedance graph of Example 4 (EX4) has a semicircle of a smaller radius compared to the impedance graphs of Example 2 (EX2) and Example 6 (EX6). In general, in the Nyquist plot of the impedance analysis method, the smaller the radius of the semicircle, the smaller the resistance value. Accordingly, it can be seen that the anode electrode of Example 4 (EX4) has a smaller internal resistance value than that of the anode electrodes of Example 2 (EX2) and Example 6 (EX6).

This resistance analysis result is also consistent with the result of the discharge capacity based on the mass of the positive electrode shown in FIG. 32. For example, Example 4 (EX4) has the smallest internal resistance and the highest discharge capacity based on the mass of the positive electrode. Therefore, it can be confirmed that the positive electrode of Example 4 (EX4) including 40% by weight of the positive electrode active material, 40% by weight of the conductive material, and the binder has the smallest internal resistance, and thus shows the best electrochemical properties. have.

Hereinafter, electrochemical characteristics according to the type of conductive material will be described with reference to FIGS. 34 to 36.

34 is a graph showing a voltage profile of an anode electrode according to Example 4 (EX4) and Comparative Example (CO1). 35 is a graph showing discharge capacity (mAh/g) and Coulomb efficiency (%) according to an increase in the number of cycles of the positive electrode according to Example 4 (EX4) and Comparative Example (CO1). 36 are graphs showing internal resistance of a positive electrode according to Example 4 (EX4) and Comparative Example (CO1).

34 to 36, Comparative Example (CO1) including Super P as a conductive material exhibits a discharge capacity of about 140 mAh/g, whereas Example 4 (EX4) including Ketjen Black as a conductive material It can be seen that the discharge capacity is about 185 mAh/g. Meanwhile, it can be seen that Example 4 (EX4) shows a discharge capacity of approximately 65% after 10 cycles, and Comparative Example (CO1) shows a discharge capacity of approximately 55% after 10 cycles. However, in the case of the internal resistance measured in the Nyquist plot, it can be seen that Example 4 (EX4) and Comparative Example (CO1) show approximately similar values.

According to exemplary embodiments, since Ketjen Black is used as the conductive material, the discharge capacity may be significantly increased. In particular, since the anode electrode of Ketjen Black and Super P has substantially the same internal resistance, this increase in capacity can be assumed to be a contribution of the discharge capacity due to Ketjen Black. That is, in example embodiments, it can be assumed that Ketjen Black contained in an amount of 30 to 50% by weight acts as an electrode of a capacitor.

37 is a graph showing the adsorption amount of nitrogen gas for measuring the BET specific surface area of Ketjen Black (EX21) and Super P (CO21).

Referring to FIG. 37, Super P (CO1) exhibits a low adsorption amount over the entire range of relative pressure, while Ketjen Black (EX21) exhibits a high adsorption amount over the entire range of relative pressure, as well as adsorption due to increase in relative pressure It can be seen that the amount increase (or the slope in the graph of FIG. 16) is remarkably high.

In order to measure the BET specific surface area, the amount of nitrogen gas physically adsorbed on the surface of the porous material can be measured according to a change in the _{relative pressure (P/P 0 ).} In FIG. 37, the relative pressure (P/P ₀ ) is plotted on the x-axis and the amount of adsorbed nitrogen gas is plotted on the y-axis. From the slope of the gas adsorption amount with respect to such relative pressure (P/P ₀ ), the BET specific surface area and pore volume can be calculated using the following Langmuir theory (multilayer model).

	BET 비표면적(m²/g)BET specific surface area (m ² /g)	포어 볼륨(cm³/g)Pore volume (cm ³ /g)
케첸 블랙 (EX21)Ketjen Black (EX21)	1309.67661309.6766	2.3515182.351518
슈퍼 P (CO21)Super P (CO21)	50.206850.2068	0.1388890.138889

According to Table 2, Super P (CO21) exhibits ^{a BET specific surface area of about 50 m 2} /g, whereas Ketjen Black (EX21) exhibits a BET specific surface area ^{of about 1310 m 2 /g.} In addition, Super P (CO21) exhibited ^{a pore volume of about 0.139 cm 2} /g, while Ketjen Black (EX21) exhibited a pore volume ^{of about 2.35 cm 2 /g.} That is, it can be seen that Ketjen Black (EX21) has a significantly larger surface area and significantly higher pore volume than Super P (CO21). That is, it can be assumed that the surface of Ketjen Black EX21 acts as an electrode of the capacitor due to the relatively large surface area of Ketjen Black EX21, contributing to the charging and discharging capacity in the charging and discharging steps of the anode electrode. .

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 of ordinary skill in the art within the spirit and scope of the present invention This is possible.

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

Claims

As an organic compound-based secondary battery,

Anode electrode;

Electrolyte; And

Including a cathode electrode,

The anode electrode,

A positive electrode active material comprising an organic compound containing a carbon double bond and a functional group containing at least one of nitrogen, oxygen, and sulfur, and in the range of 30 to 50% by weight based on the total weight of the positive electrode;

Carbon nanotubes in the range of 5 to 20% by weight based on the total weight of the positive electrode;

Conductive material; And

An organic compound-based secondary battery comprising a binder.
The organic compound-based lithium secondary battery according to claim 1, wherein the organic compound comprises at least one selected from the group consisting of a polymer having redox activity, an organic sulfur compound, and a carbonyl group-containing compound.
The method of claim 2, wherein 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 flavantron (flavanthrone), characterized in that it comprises at least one selected from the group consisting of an organic compound-based lithium secondary battery.
The method of claim 1, wherein the organic compound comprises dimethylphenazine,

When charging the lithium 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 plateau at 3.6 to 3.8 V. Lithium secondary battery based on organic compounds.
The organic compound-based lithium secondary battery of claim 1, wherein the carbon nanotubes comprise at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and bundle-type carbon nanotubes.
The organic compound-based lithium secondary battery of claim 1, wherein the carbon nanotubes have a purity of 90% to 99.99%.
The organic compound-based lithium secondary battery of claim 1, wherein the positive electrode further comprises less than 1% by weight of metal atoms attached to both ends of the carbon nanotube in the length direction.
The method of claim 7, wherein the metal atoms are copper (Cu), nickel (Ni), cobalt (Co), silver (Ag), titanium (Ti), aluminum (Al), tungsten (W), and molybdenum (Mo). An organic compound-based lithium secondary battery comprising at least one of.
The method of claim 1, wherein the binder comprises polytetrafluoroethylene (PTFE) in the form of beads,

The binder is an organic compound-based lithium secondary battery, characterized in that the range of 10 to 30% based on the total weight of the positive electrode.
The organic compound-based lithium secondary battery of claim 1, wherein the conductive material comprises at least one of super P, carbon black, Ketjenblack®, and acetylene black.
The organic compound-based lithium secondary battery according to claim 1, wherein the conductive material is in the range of 30 to 50% based on the total weight of the positive electrode.
The organic compound-based lithium secondary battery according to claim 1, wherein the positive electrode has a density of 0.50 g/cm 3 to 1.2 g/cm 3.
As a method of manufacturing a secondary battery based on an organic compound comprising the step of forming a positive electrode,

Forming the anode electrode,

Forming a preliminary positive electrode by solid-mixing 30 to 50% by weight of a positive electrode active material, 5 to 20% by weight of carbon nanotubes, 30 to 50% by weight of a conductive material, and 10 to 30% by weight of a binder; And

Comprising the preliminary anode electrode by a roll press; Including,

The positive electrode 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 method of claim 13, wherein the carbon nanotubes have a purity of 90% to 99.99%,

A method of manufacturing a lithium secondary battery based on an organic compound, characterized in that less than 1% by weight of metal atoms attached to the surface of the carbon nanotubes are further included.
The method of claim 13, wherein the step of compressing the 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. Manufacturing method.
The method of claim 13, wherein the positive electrode active material has a first particle size, the conductive material has a second particle size,

The method of manufacturing a lithium secondary battery based on an organic compound, wherein the binder has a third particle size larger than the first particle size and the second particle size.
The method of claim 16, wherein the first particle size is 500 nanometers to 60 micrometers,

The second particle size is 10 to 100 nanometers,

The method of manufacturing a lithium secondary battery based on an organic compound, characterized in that the third particle size is 1 to 5 millimeters.
14. The method of claim 13, wherein by the pressing step, the positive electrode is formed in a free standing type that does not include a positive electrode current collector.
14. The method of claim 13, wherein the forming of the positive electrode is performed in an all solid-state without adding an organic solvent.
As an organic compound-based lithium secondary battery,

Anode electrode;

Electrolyte; And

Including a cathode electrode,

The anode electrode,

A positive electrode active material comprising an organic compound containing a carbon double bond and a functional group containing at least one of nitrogen, oxygen, and sulfur, and 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

Contains a binder,

The positive electrode is an organic compound-based lithium secondary battery, characterized in that it has a density of 0.50 g / cm 3 to 1.2 g / cm 3.
As a method for manufacturing a lithium secondary battery based on an organic compound comprising the step of forming a positive electrode,

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 anode electrode by solid-phase mixing the first preliminary anode electrode and 10 to 30% by weight of a binder; And

Comprising; compressing the second preliminary anode electrode by a roll press; Including,

The positive electrode active material includes an organic compound including a carbon double bond and a functional group including at least one of nitrogen, oxygen, and sulfur.
As an organic compound-based lithium secondary battery,

Anode electrode;

Electrolyte; And

Including a cathode electrode,

The anode electrode,

A positive electrode active material comprising an organic compound containing a carbon double bond and a functional group containing at least one of nitrogen, oxygen, and sulfur, and in the range of 30 to 50% by weight based on the total weight of the positive electrode;

A conductive material in the range of 30 to 50% by weight based on the total weight of the positive electrode; And

It includes a binder in the range of 10 to 30% by weight based on the total weight of the positive electrode,

The conductive material does not decompose at 1.5 V to 4.0 V, and the conductive material has a BET specific surface area of 500 to 2000 m 2 /g.
As a method for manufacturing a lithium secondary battery based on an organic compound comprising the step of forming a positive electrode,

Forming the anode electrode,

Forming a preliminary positive electrode by solid-phase mixing 30 to 50% by weight of a positive electrode active material, 30 to 50% by weight of a conductive material, and 10 to 30% by weight of a binder;

Comprising the preliminary anode electrode by a roll press; Including,

The positive electrode 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 conductive material includes Ketjen Black, and the conductive material has a BET specific surface area of 500 to 2000 m 2 /g.