KR20220067016A - Covalent organic nanosheet for high-performance sodium ion battery, and method for manufacturing same - Google Patents

Abstract

The present invention relates to a covalently bonded organic nanosheet prepared by covalently bonding (trimethylstannylthiophen-2-yl)benzo[c][1,2,5]thiadiazole and 2,4,6-tris(5-bromotiophene-2-yl)-1,3,5-triazine, a preparation method thereof, and a secondary battery comprising the same.

Description

Covalent organic nanosheet for high-performance sodium ion battery, and method for manufacturing same

The present invention relates to a covalently bonded organic nanosheet for a high-performance sodium-ion battery and a method for manufacturing the same.

Until recently, various porous materials with low density have been developed. For example, the porous material includes a porous organic polymer (POP), a hypercrosslinked polymer (HCP), a polymer of intrinsic microporosity (PIM), and a metal organic structure (metal). organic frameworks (MOFs) and covalent organic frameworks (COFs) are known. Among these porous materials, metal organic structures and covalent organic structures have a unique two-dimensional or three-dimensional structure and have very high crystallinity.

In particular, in the case of a covalent organic structure, it is rigid and is prepared with planar π-conjugated monomers. This covalent organic structure is similar to a graphite structure by self-assembly by π-π stacking. It has porous two-dimensional networks with meso-sized pores, and thus can have cylindrical channels.

Therefore, electrons can be delocalized through these two-dimensional networks, enabling electron movement between molecules through the π-π stacking, so that the covalent organic structure has intrinsic semiconductor properties and light harvesting. (light-harvesting) properties. Also, some guest molecules may be inserted into the meso-sized pore channels of the covalent organic construct. Accordingly, the porous material can be applied to common applications such as, for example, gas storage devices, separation devices, purification devices, heterogeneous catalysts, and the like, and further can be applied to a wide range of applications such as optoelectronic devices and photocatalysts.

In order to improve and optimize the properties as described above, the covalent organic structure must be stable under ambient conditions, and can be easily exfoliated to form a graphene-type sheet rather than a graphite-type sheet, thereby maximizing this. However, in the case of covalent organic structures, the sheets have a graphite shape stacked by π-π bonds, and most covalent organic structures have boronate anhydride, ester, borosilicate, imine ( Since it has been synthesized through a condensation reaction using functional groups such as imine) and hydrazone, most tend to be hydrolyzed at ambient humidity. It is known that it is very difficult to manufacture a structure in the form of a sheet.

On the other hand, as a similar prior literature thereto, Republic of Korea Patent Publication No. 10-2061964 is presented.

Republic of Korea Patent Publication No. 10-2061964 (2019.12.26)

An object of the present invention is to provide a covalently bonded organic nanosheet having large mesopores and a lower bandgap.

Another object of the present invention is to provide a secondary battery having excellent storage characteristics by being manufactured using the organic nanosheet.

However, the above purpose is illustrative, and the technical spirit of the present invention is not limited thereto.

One aspect of the present invention for achieving the above object relates to a covalently bonded organic nanosheet comprising a covalent bond-based repeating unit satisfying the following formula (1).

[Formula 1]

(In Formula 1,

X is a trivalent linking group represented by the following formula 1-1,

Y is a divalent linking group represented by the following formula 1-2,

n is an integer from 10 to 200,

* is a binding site.

[Formula 1-1]

[Formula 1-2]

)

)

In one aspect, the covalently bonded organic nanosheet may have mesopores having a size of 3.5 to 4.5 nm.

In one aspect, the covalently bonded organic nanosheet may have a band gap of 1.85 eV or less.

In addition, another aspect of the present invention relates to a method for preparing the above-described covalently bonded organic nanosheet, (trimethylstannylthiophen-2-yl)benzo[c][1,2,5]thiadiazole and 2,4,6-tris(5-bromothiophen-2-yl)-1,3,5-triazine to a covalent bond reaction; in a method for producing a covalently bonded organic nanosheet comprising the it's about

In another embodiment, the covalent bonding reaction may be performed through a reflux reaction or a solvothermal reaction.

In addition, another aspect of the present invention relates to a thin film and a secondary battery including the above-described covalently bonded organic nanosheet, and specifically, the secondary battery may be a sodium ion battery.

The present invention relates to a novel covalently bonded organic nanosheet having a graphene-type conjugated two-dimensional structure through a styrene cross-linking reaction between monomers, (trimethylstannylthiophen-2-yl)benzo[c][1,2,5 ]Covalent organic nanosheets prepared by covalent bonding of thiadiazole and 2,4,6-tris(5-bromothiophen-2-yl)-1,3,5-triazine are based on existing triazine It may have larger mesopores and a lower bandgap compared to covalently bonded organic nanosheets.

Accordingly, the covalently bonded organic nanosheet increases the conductivity of the charge carrier, so that when used in a secondary battery, it is possible to improve the storage capacity of the secondary battery.

1 is a reaction scheme of a covalently bonded organic nanosheet according to an embodiment of the present invention.
2 is a flowchart illustrating a method of manufacturing a covalently bonded organic nanosheet and a thin film according to an embodiment of the present invention.
3 is a transmittance mode FT-IR spectrum of a covalently bonded organic nanosheet and a monomer used in the reaction.
4 is a UV-vis absorbance spectrum of a covalently bonded organic nanosheet.
5 is a solid ¹³ C CP/MAS NMR spectrum of a covalently bonded organic nanosheet.
6 is a PXRD pattern of covalently bonded organic nanosheets.
7 is a nitrogen adsorption/desorption isotherm of a covalently bonded organic nanosheet.
8 is a BJH pore size distribution analysis result of covalently bonded organic nanosheets.
9 is a result of analysis of zeta potential and conductivity of covalently bonded organic nanosheets.
10 is a SEM image of D/A-CON-10.
11 is an SEM image of D/A-CON-16.
12 is a TEM image of D/A-CON-10.
13 is a TEM image of D/A-CON-16, and the red dotted line area in the inset image indicates the grid pattern of D/A-CON-16.
14 is a CV curve (scan speed of 0.1 mV/s) of D/A-CON-10.
15 is a CV curve (scan speed of 0.1 mV/s) of D/A-CON-16.
16 is a CV curve of D/A-CON-10 under various scan rates.
17 is a CV curve of D/A-CON-10 under various scan rates.
18 is a Cottrell plot of D/A-CON-10.
19 is a Cottrell plot of D/A-CON-16.
20 is a result of analyzing the charge/discharge profile of D/A-CON-10 at various current densities.
21 is a result of analyzing the charge/discharge profile of D/A-CON-16 at various current densities.
22A is an EIS plot of covalently bonded organic nanosheets and RGO, and FIG. 22B is data showing Warburg coefficients of covalently bonded organic nanosheets and RGO.
23 is a comparison of pseudocapacitive and diffusion-controlled charge storage processes of D/A-CON-10 at a scan rate of 0.8 mV/s.
FIG. 24 is a comparison of pseudocapacitive and diffusion-controlled charge storage processes of D/A-CON-16 at a scan rate of 0.8 mV/s.
FIG. 25 is a data comparison showing the contribution of pseudocapacitive and diffusion-controlled charge storage of D/A-CON-10 and D/A-CON-16 at various scan rates.
26 is data evaluating the discharge capacity of D/A-CON-10, CON-10 and RGO for 60 cycles.
27 is data evaluating the discharge capacity of D/A-CON-16, CON-16 and RGO for 60 cycles.
28 is data evaluating the discharge capacity of D/A-CON-10 and D/A-CON-16 for 150 cycles.

Hereinafter, a covalently bonded organic nanosheet for a high-performance sodium-ion battery and a method for manufacturing the same according to the present invention will be described in detail. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

One aspect of the present invention relates to a novel covalently bonded organic nanosheet having a graphene-type conjugated two-dimensional structure through a Stille cross-linking reaction between monomers, in detail including a covalent bond-based repeating unit satisfying the following Chemical Formula 1 It relates to covalently bonded organic nanosheets characterized in that.

[Formula 1]

(In Formula 1,

X is a trivalent linking group represented by the following formula 1-1,

Y is a divalent linking group represented by the following formula 1-2,

n is an integer from 10 to 200,

* is a binding site.

[Formula 1-1]

[Formula 1-2]

)

)

As such, (trimethylstannylthiophen-2-yl)benzo[c][1,2,5]thiadiazole and 2,4,6-tris(5-bromothiophen-2-yl)-1,3 Covalently bonded organic nanosheets prepared by covalent bonding of ,5-triazine may have larger mesopores and a lower bandgap than conventional triazine-based covalently bonded organic nanosheets.

More specifically, the covalently bonded organic nanosheet may have mesopores having a size of 3.5 to 4.5 nm, and more specifically, may have mesopores having a size of 3.8 to 4.3 nm, wherein the size is shown in FIG. As shown, it may mean the diameter of the mesopores. In addition, the covalently bonded organic nanosheet may have a band gap of 1.85 eV or less, specifically 1.80 eV or less, more specifically 1.75 eV or less, more specifically 1.50 to 1.70 eV or less. can

As such, in the covalent organic nanosheet, the conductivity of the charge carrier can be increased according to mesopores having a large diameter of 3.5 nm or more and a low band gap of 1.85 eV or less, and when used in a secondary battery, the storage capacity of the secondary battery It's good to be able to improve.

On the other hand, another aspect of the present invention is a method for preparing the covalently bonded organic nanosheet, (trimethylstannylthiophen-2-yl)benzo[c][1,2,5]thiadiazole and 2,4 , It relates to a method for producing a covalently bonded organic nanosheet, comprising: covalently reacting 6-tris(5-bromothiophen-2-yl)-1,3,5-triazine.

1 is a reaction scheme of a covalently bonded organic nanosheet according to an embodiment of the present invention. Referring to FIG. 1 , the covalently bonded organic nanosheet is a first monomer (M1) (trimethylstannylthiophen-2-yl)benzo [c] Sharing of [1,2,5]thiadiazole with 2,4,6-tris(5-bromothiophen-2-yl)-1,3,5-triazine as a second monomer (M2) It is prepared by a binding reaction, and in this case, mesitylene as a solvent and palladium (Pd ⁰ ) catalyst as a catalyst may be used, but this is only an example and the solvent and catalyst are not limited thereto.

The covalently bonded organic nanosheet prepared by the Stiletto cross-linking reaction between M1 and M2 may have a ring having a diameter of about 4.1 nm. That is, the covalently bonded organic nanosheet may include mesopores of about 4.1 nm.

Such covalently bonded organic nanosheets can be performed in two different ways as described below. That is, in order to establish an appropriate synthesis route, the covalently bonded organic nanosheets may be synthesized using two different synthesis conditions, and specifically, the covalent bonding reaction may be performed through a reflux reaction or a solvothermal reaction. At this time, the covalently bonded organic nanosheet prepared through the reflux reaction is referred to as “D/A-CON-10”, and the covalently bonded organic nanosheet prepared through the solvothermal reaction is referred to as “D/A-CON-16”. and, the D/A-CON-10 and D/A-CON-16 were synthesized through different synthetic routes, but are each prepared through the covalent bonding reaction of the same M1 and M2 monomers as shown in FIG. 1 .

As a more specific example, the refluxing reaction is performed by stirring, and may be performed at a temperature of 160 to 180° C., for example, may be performed at a temperature of 170° C. The reaction time may be carried out in the range of 1 to 100 hours, for example, it may be carried out for 72 hours.

Considering that the D/A-CON-10 prepared therefrom was synthesized in a reflux method by stirring, the catalyst was well mixed by stirring without the influence of convection, and thus the D/A-CON-10 was 2 It may be formed to be polymerized in a dimensional direction, and may represent a planar plate shape.

On the other hand, the solvothermal reaction is performed without stirring, and may be performed at a temperature of 160 to 180° C., for example, may be performed at a temperature of 170° C. The reaction time may be carried out in the range of 1 to 100 hours, for example, it may be carried out for 72 hours.

Considering that the D/A-CON-16 prepared therefrom was synthesized by solvothermal reaction without stirring, the Stiletto cross-linking reaction occurs rapidly in the one-dimensional direction, and thus the D/A-CON- 16 may be formed to be polymerized in a one-dimensional direction, and thus may exhibit a fibrous shape.

If necessary, in the step of forming the covalently bonded organic nanosheet, the forming material may be added to methanol to stop the Stiletto cross-linking reaction. Subsequently, any one selected from the group consisting of methanol, ethanol, methylene chloride, tetrahydrofuran (THF), methanol, ethanol, and acetone, etc. The covalently bonded organic nanosheet may be purified through sequential Soxhlet extraction using one or more mixed solvents.

By the step of forming the covalently bonded organic nanosheet, the covalently bonded organic nanosheet as a sheet-like polymer network is synthesized through a Stille cross-coupling reaction, and hydrolysis is prevented by forming a strong C-C bond and intermolecular interactions may be reduced. Due to this reduced intermolecular force, it is possible to form a dispersion solution by introducing the covalently bonded organic nanosheets in various dispersion solvents, and furthermore, drop casting on a substrate is possible.

Referring to FIG. 2 , the step of forming a covalent organic nanosheet by performing a Stiletto cross-linking reaction (S110); Forming a dispersion by inputting the covalently bonded organic nanosheets into a dispersion medium (S120); and drop-casting the dispersion on a substrate and drying to form a covalently bonded organic nanosheet thin film (S130).

In this case, step S110 is the same as the above-described method for manufacturing the covalently bonded organic nanosheet.

In the step 120 of forming the dispersion, the dispersion medium is, for example, chlorobenzene (CB) containing 4% by volume of 1-chloronaphthalene (1-CN), tetrahydrofuran ( It may be a mixed solvent such as tetrahydrofuran, THF), dimethylformamide (DMF), or dimethyl sulfoxide (DMSO).

Forming the covalently bonded organic nanosheet thin film (S130) may be performed by drop-casting the dispersion onto a substrate such as a silicon wafer and drying, thereby controlling the self-assembly of the covalently bonded organic nanosheet. can do.

In addition, another aspect of the present invention relates to a secondary battery including the above-described covalently bonded organic nanosheet, wherein the covalently bonded organic nanosheet can be utilized as an anode material of a secondary battery, specifically The secondary battery may be a sodium ion battery or the like.

As described above, when covalently bonded organic nanosheets having large mesopores of 3.5 nm or more and a low band gap of 1.85 eV or less are used as an anode material for a secondary battery, the conductivity of the charge carrier is increased to improve the storage capacity of the secondary battery. good to be able

Hereinafter, a covalently bonded organic nanosheet for a high-performance sodium-ion battery according to the present invention and a manufacturing method thereof will be described in more detail through examples. However, the following examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention. In addition, the unit of additives not specifically described in the specification may be weight %.

[Example 1] Synthesis of D/A-CON-10

2,4,6-tris(5-bromothiophen-2-yl)-1,3,5-triazine (M2, 0.05 g, 8.863 × 10 ^-5 mol), (trimethylstannylthiophen-2-yl )benzo[c][1,2,5]thiadiazole (M1, 0.083 g, 1.33 × 10 ^-4 mol), tetrakis(triphenylphosphine)palladium(0) stored in a glovebox filled with nitrogen gas (0) ( 0.0041 g) and mesitylene (3 ml) were refluxed with a condenser and refluxed under stirring at 170° C. for 72 hours.

After the reaction was completed, the solution was poured into methanol, and a pale orange precipitate was collected through a filter. This precipitate was sequentially purified by soxhlet extraction using methanol, ethanol, dichloromethane, tetrahydrofuran, methanol, ethanol and acetone for 4 hours per step, followed by drying in vacuo for 12 hours D/A -CON-10 was obtained.

[Example 2] Synthesis of D/A-CON-16

All monomers and solvents were prepared in the same manner as in Example 1 except that they were prepared in a glovebox under nitrogen condition, and the apparatus was flame sealed under vacuum at 77 K using liquid nitrogen after 3 freeze-pump-thaw cycles.

The reaction solution was subjected to solvothermal reaction without stirring in an oven at 170° C. for 72 hours. Thereafter, the purification process was performed in the same manner as in Example 1 to obtain D/A-CON-16.

[Comparative Example 1] CON-10

2,4,6-tris(5-bromothiophen-2-yl)-1,3,5-triazine (0.05 g, 8.863×10 ^-5 mol), 2,5-bis(trimethylstannyl)thi No-(3,2-b)thiophene (0.062 g, 1.331×10 ^-4 mol), tetrakis(triphenylphosphine)palladium(0) (0.0041 g) and mesitylene stored in a glovebox filled with nitrogen gas (3 mL) was refluxed with a condenser and refluxed under stirring at 170° C. for 72 hours.

After the reaction was completed, the solution was poured into methanol, and a red precipitate was collected through a filter. This precipitate was sequentially purified by Soxhlet extraction using methanol, ethanol, dichloromethane, tetrahydrofuran, methanol, ethanol and acetone for 4 hours per step, followed by drying in vacuo for 12 hours to CON-10 was obtained.

[Comparative Example 2] Synthesis of CON-16

All monomers and solvents were prepared in the same manner as in Comparative Example 1 except that they were prepared in a glovebox under nitrogen condition, and the device was sealed with a flame under vacuum at 77 K using liquid nitrogen after 3 freeze-pump-thaw cycles.

The reaction solution was subjected to solvothermal reaction without stirring in an oven at 170° C. for 72 hours. Thereafter, the purification process was performed in the same manner as in Comparative Example 1 to obtain CON-16.

[Characteristic Analysis]

Fourier transform infrared spectra were measured in the range of 650-4000 cm-1 with a Jasco FT/IR-4100 spectrometer. The UV-vis spectrum was measured in the 220-850 nm range using a tungsten iodine WI (Halogen) lamp and a deuterium lamp with a Shimadzu UV-2600 (Shimadzu, Japan) spectrometer. Powder X-ray diffraction analysis (XRD) was measured with Cu-Kα radiation (λ=1.5406 Å) with Ni-filter and Empyrean Series2 (PANanytical B.V., Netherland) with 5 mm fixed incident beam mask and 1.60 mm anti-scatter slit. . The measurement range angle was from 3° to 70°, and 0.0525° and 0.75s were performed for each process. Nitrogen adsorption-desorption isotherms were performed under nitrogen conditions at 77 K with Belsorp-miniII (Bel Japan Inc.). Scanning electron microscopy (SEM) was measured with a Quanta 250 FEG (FEI Company, Hillsboro, OR), the surface of the sample was coated with gold/palladium (Au/Pd) plasma for 60 seconds, and the sample image was imaged using a 15 kV electron beam. and measured. Transmission electron microscope (TEM) was measured with a voltage of 200 kV with a JEM-2100F (JEOL). The TEM sample was carried out by drop-casting method on a carbon film having a 200 mesh copper grid plate, and a solution dispersed in dimethylformamide (DMF) was used for the sample. The suspension was prepared by a Sonics VCX 130 ultrasonic processor (130 W power output, 20 kHz frequency) with a 3 mm homogenizer probe (Standard 630-0422, VibraCell™). The ultrasonic disperser was operated at 20% output for 30 minutes at a pulse interval of 2.5 seconds at 1 pulse per second. AFM samples were prepared by drop-casting DMF suspension on mica discs (V1 disc 10 mm, Probes). The suspension was prepared in the same way as for the TEM sample.

In addition, the sodium ion storage properties of CON were evaluated through electrochemical charge-discharge characterization using a battery tester. The active electrode was prepared as a slurry of active material (14 mg, 70 wt%), conductive carbon (SuperP, 4 mg, 20 wt%) and binder (polyacrylic acid, 2 mg, 10 wt%) in NMP solvent. Drop casting on a copper current collector to obtain a total mass of 1.2 mg/cm 2 by the doctor blading method, dried at 100° C. under a vacuum atmosphere for 16 hours, and then a standard CR2032 type coin cell using a 3501 type separator with argon (Ar) was prepared in a filled glovebox. Sodium metal on an aluminum plate was used as a counter electrode, and 1 M NaClO ₄ dissolved in propylene carbonate/fluoroethylene carbonate (98: 2, w/w) was adopted as an electrolyte. Constant current charge/discharge tests were performed at various constant current densities (100, 300, 500, 700, 900 and 1000 mAh/g).

Referring to FIG. 3 , the FT-IR spectrum of the covalently bonded organic nanosheets prepared in Examples 1 and 2 (hereinafter referred to as D/A-CON) is the C of the tris-triazine moiety at ˜1498 cm ⁻¹ =N elongation peak and CH out-of-plane vibration peak of thiophene unit at 802-788 cm ^-1 . In addition, characteristic peaks of thiadiazole residues were observed at -877 and -808 cm ^-1 .

However, all characteristic peaks of D/A-CON appeared much broader than the peaks of the corresponding characteristics, which indicates that these compounds (monomers and D/A-CON) have different molecular packing and self-assembled structures in the solid state. implying that it has

In order to compare the electronic structures of D/A-CON and the covalently bonded organic nanosheets prepared in Comparative Examples 1 and 2 (hereinafter referred to as CON), ultraviolet-visible light (UV-vis) absorption spectra were obtained. is shown in FIG. 4 .

The absorption initiation of D/A-CON was clearly red-shifted with respect to the absorption initiation of CON, a typical feature of D/A-type conjugated polymers with reduced bandgap.

However, when comparing the covalently bonded organic nanosheets prepared by the two routes from the same monomer, the synthetic route did not significantly affect the onset of the UV-vis spectrum, and the light absorption intensity showed that the solvothermal reaction was better than the other cases. It was found to be higher in the 500-700 nm (D/A-CON) and 400-600 nm (CON) ranges, respectively, when synthesized through the This suggests that synthetic pathways influence molecular self-assembly and molecular weight distribution.

Meanwhile, the band gaps of D/A-CON-10, D/A-CON-16, CON-10 and CON-16 were sequentially calculated as 1.65 eV, 1.60 eV, 1.91 eV, and 1.91 eV, respectively. Thus, these two types of spectroscopic analysis demonstrated that the donor and acceptor units were alternately conjugated throughout the sample framework.

As mentioned in the FT-IR study, ¹³ C NMR spectra of all covalently bonded organic nanosheets were measured to confirm the structural integrity of the covalently bonded organic nanosheets, and the results are shown in FIG. 5 . All covalently bonded organic nanosheets contain aromatic carbon regions, and no characterization peaks were detected except for the radial band of the aromatic carbon peaks in the aliphatic carbon chain region, which indicates that chemical degradation of conjugated and aromatic rings during polymerization is markedly significant. imply that there is

Referring to FIG. 5 , the carbon of the s-triazine motif is about 170 ppm and the carbon of the thiophene adjacent to the s-triazine ranges from 145 to 125 ppm. The characteristic carbon peak of thiophene appeared at about 115 ppm as indicated by the pale blue f letter and line for the series of n-CONs. In addition, the peak of most unshielded carbon in the benzothiadiazole unit (hereinafter referred to as the BT unit) peaks at about 151 ppm as indicated by the light green g letter and line for the series D/A-CON. appear. However, since the remaining peaks for the benzene motif may overlap those of thiophene, the intensities of the e and d regions for D/A-CON were improved compared to those for CON of Comparative Example.

Moreover, referring to energy dispersive X-ray spectroscopy (EDS) mapping, all elements were well dispersed throughout the framework. Therefore, it was confirmed that the material was well synthesized through the still-cross coupling reaction.

The powder crystals and structural sequence were investigated by powder X-ray diffraction (PXRD) analysis ( FIG. 6 ). The patterns of CON-10 and CON-16 showed a broad peak at 2θ 23°. These materials were shown to be amorphous with weak random π-π stacking, and the patterns of D/A-CON-10 and D/A-CON-16 also showed stronger peaks at the same position due to the π-π stacking. Although the luminosity of these peaks suggests a lack of long-range alignment, the higher peak intensities observed for D/A-CON were attributed to their BT units, which are known to favor the formation of more planar motifs than in their one-dimensional conjugates.

The unit structure of D/A-CON-10 was calculated at the B3LYP/6-31G density functional theory (DFT) level to confirm the flatness of this sample. Since the optimized unit structure is completely planar, the network structure of D/A-CON-10 can also be very planar. Therefore, all samples exhibited random turbostratic structures of reduced graphene oxide (RGO) due to random reassembly (exfoliation during synthesis) of nanosheets in the solid state.

40°에서 비대칭 넓은 피크에 의해 반영된 바와 같이, 다른 샘플보다 더 강력한 구조를 가졌다. 모든 공유결합 유기 나노시트가 저각 영역에서 XRD 피크를 갖지 않음을 주목할 필요가 있으며, 이들 공유결합 유기 나노시트가 결정학적 ab-면 및 c-축을 따라 무작위로 적층되어 있음을 알 수 있다.In particular, D/A-CON-10 showed 2θ in the PXRD pattern.

It had a more robust structure than the other samples, as reflected by the asymmetric broad peak at 40°. It is worth noting that not all covalently bonded organic nanosheets have XRD peaks in the low-angle region, and it can be seen that these covalently bonded organic nanosheets are randomly stacked along the crystallographic ab-plane and c-axis.

The nitrogen adsorption/desorption isotherms of all covalently bonded organic nanosheets can be classified as type II according to the IUPAC system (Fig. 7). Although all samples exhibited insignificant gas uptake at P/P ₀ < 1, this uptake increased gradually until P/P ₀ = about 0.8, and the sharp increase in absorption observed at 0.8 < P/P0 ≤ 1 was It is due to gas capillary condensation in the sample nanopores. However, at P/P ₀ < 0.1, CON-10 and CON-16 showed greater initial gas uptake than D/A-CON.

Brunauer-Emmett-Teller (BET) surface areas of 300, 202, 160 and 89 m 2 /g were obtained for CON-16, CON-10, D/A-CON-16 and D/A-CON-10. In addition, the samples prepared by solvothermal had a larger BET surface area than samples of the same composition prepared using the reflux method, and transmission electron microscopy (TEM) observations showed that the samples synthesized by solvothermal reaction corresponded to a lower density. It should be noted that it indicates that Diffusion of Pd(0) catalyst in polymerization reaction relies on the natural convective flow of solvent during solvothermal process as the solution is usually not mechanically stirred and the reflux system is stirred to obtain a homogeneous mixture. Therefore, covalently bonded organic nanosheets prepared by solvothermal generally have a more branched structure with lower packing density, whereas covalently bonded organic nanosheets prepared through the reflux method have a plate-like structure.

This trend also leads to morphological and pore structure differences between samples prepared using different methods. Here, the pore structure difference was analyzed in consideration of the pore size distribution calculated using the Barrett-Joyner-Halenda (BJH) method (FIG. 8). As can be seen from the XRD results, D/A-CON consisted of randomly stacked nanosheets, and no order was found along the crystallographic ab-plane and c-axis. This irregular layer stack in D/A-CON resulted in a very broad pore size distribution commonly found in the broad pore size distribution of RGO. All the covalently bonded organic nanosheets had irregular pores, but the covalently bonded organic nanosheets prepared with the solvent showed a larger number of large pores than those of the same composition obtained through the reflux reaction.

Charge polarizability was investigated by zeta potential analysis (FIG. 9). As expected, the surface charge of D/A-CON was more negative than that of n-CON due to the presence of strongly electronegative thiadiazole residues in the former case. As revealed by UV-vis spectroscopy, the lower bandgap of the sample resulted in greater conductivity. Synthetic pathways have also been found to influence material surface charge and conductivity.

The effect of synthetic pathways on molecular interactions was examined by scanning electron microscopy (SEM) and transmission electron microscopy (SEM) and transmission electron microscopy (SEM) and transmission electron microscopy (SEM) and transmission electron microscopy (SEM) and transmission electron microscopy (SEM) and transmission electron microscopy (SEM) of self-assembled CON morphology after drop-casting of N-methyl-2-pyrrolidone (NMP) solution on a silicon wafer and copper grid, respectively. It was investigated by microscopic (TEM) observation ( FIG. 10 ).

The shapes of CON-10 and CON-16 were the same as those reported in the previous patent (registration number 10-2061964), and D/A-CON-10 (FIG. 10) was randomly stacked in a typical shape of graphene and its derivatives. D/A-CON-16 (FIG. 11) showed a net-like morphology that was well consistent with the PXRD and nitrogen adsorption/desorption results.

Particle aggregation of D/A-CON complicated the identification of the sheet-like primary morphology by SEM. Therefore, this information was successfully confirmed by TEM measurements. Although D/A-CON-10 had an irregular shape, random stacking of multiple sheets was observed. Compared to the sheets of D/A-CON-10, the sheets of D/A-CON-16 were more porous, and the latter sheets of D/A-CON appeared to be stacked while maintaining the 2D structure. However, comparison of the contrast and brightness of the D/A-CON and n-CON stacked forms indicated that the previous n-CON samples had less stacked sheets. Therefore, as suggested by the PXRD and BET results, the D/A-CON samples were expected to delaminate more than their n-CON counterparts due to increased inter-sheet repulsion due to the delocalization of larger negative charges.

In particular, TEM analysis showed that the basal spacing of D/A CON was in the range of 0.34 to 0.38 nm, and showed a morphology quite similar to that of RGO as shown in FIGS. 12 and 13 . This result was rationalized by analyzing the brightness profile of the fringe region in the magnified TEM image. Together with the underlying spatial information, it was confirmed from the brightness profile that the number of stacked 2D sheets of D/A-CON was approximately less than 10 layers and thinner than that of RGO. Therefore, it was expected that the area of D/A-CON accessible to sodium ions was wider than that of the 2D carbon sheet, resulting in increased capacity.

The sodidation/desodiumization performance of D/A-CON was tested by applying 15 continuous cyclic voltammetry (CV) cycles at a scan rate of 0.1 mV/s for a potential window of 0.01 to 2.5 V (Fig. 14). and 15). In the first cycle, D/A-CON-10 exhibited large irreversible cathodic peaks at 0.22 and 0.91 V ( FIG. 14 ). The peak at 0.91 V is due to the interaction between sodium ions and S-containing functional groups, whereas the peak at 0.22 V is accompanied by electrolyte decomposition and solid-electrolyte interphase (SEI) at different active sites. due to the formation However, after the subsequent cycle, the reduction peak of D/A-CON-10 almost disappeared, and the CV profiles overlap each other after 5 scans, suggesting a reversible saturation/desodiumation process. The wide cathodic peak of 0.7 V that appears in the continuous cycling of D/A-CON-10 may be due to a capacitive process that may be attributed to a weak interaction not observed in the CON of Comparative Example. Unlike the case of D/A-CON-10, an irreversible cathodic peak at 0.91 V was not observed during the first CV scan of D/A-CON-16 (Fig. 15), but a strong cathodic corresponding to electrolyte decomposition. The peak and SEI layer formation were observed at 0.32 V. From the third scan, the CV profiles overlap each other, indicating a more reversible hydrogenation/dehydrogenation process than that of D/A-CON-10. In addition, a broad cathodic peak of 1.1 V appeared during the continuous scan of D/A-CON-16, indicating that there is an interaction between the containing CON framework and sodium ions, unlike the CON of the comparative example. The CV profile of D/A-CON showed strong redox peaks at 1.9/1.2 V for D/A-CON-16 and 1.9/0.8 V (vs Na/Na ⁺ ) for D/A-CON-10. . This high voltage hysteresis in the CV profile could be attributed to the highly crosslinked porous structure of the covalently bonded organic nanosheet framework.

If sodium ions are stored by covalent interactions with heteroatoms or double bonds in D/A-CON, the CV peak should be very sharp. However, in the CV profiles of D/A-CON after the first cycle, all CV peaks have very broad features, indicating that the interaction between sodium ions and D/A-CON is significantly weaker than that found in the literature. support that This suggests that the CV profile of D/A-CON suggests that the interaction between sodium and D/A-CON is based on a non-covalent bond.

The detailed charge storage mechanism was investigated by CV cycling of coin cells containing each synthesized CON at various scan rates (0.10 to 0.80 mV/s). CV profiles (Figs. 16 and 17) were recorded after 10 consecutive scans with a sweep rate of 0.1 mV/s to eliminate the effect of capacity fading in the early stages of cycling. And power law relationships were used to determine the charge storage mechanism (eg, the contribution of diffusion control to the Faraday and capacitive processes of the anode). The power law relationship is expressed as i = aν ^b , where I is the current, ν is the scan rate, and a and b are variables related to the charge storage operation. In particular, b is related to the charge storage mechanism of the anode, and the log(i) vs. log(i) vs. It can be derived from the slope of the log(v) plot ( FIGS. 18 and 19 ). In general, b = 0.5 indicates a diffusion-controlled Faraday mechanism, and b = 1 means that charge storage is controlled by a capacitive process. In the case of D/A-CON-10 (Fig. 18), b values of 0.71 and 0.63 were obtained at 0.6 (peak B in Fig. 16) and 2V (peak A in Fig. 16), respectively. For D/A-CON-16 (Fig. 19), b values of 0.79 and 0.66 were obtained at 0.6 (peak B in Fig. 17) and 2V (peak A in Fig. 17), respectively. D/A-CON has a much larger b-value than a conventional battery-type electrode having a b-value of 0.5. This high contribution of the capacitive process can be attributed to the weak interaction between sodium ions and the polarizable surface of D/A-CON. These results indicate that the sodium storage mechanism in D/A-CON is mainly dominated by the surface reaction, suggesting that the sodium storage reaction is related to the non-covalent interaction between sodium ions and the highly polarizable D/A-CON surface. do. In addition, given that the cathode and anode currents for all CV profiles are proportional to the square root of the scan rate, it can be seen that the charge storage mechanism of the D/A-CON sample is mainly governed by the mass transfer process.

Sodium-ion batteries at current densities of 100, 300, 500, 700, 900 and 1000 mA h/g, as bandgap, conductivity, morphology and porosity control by incorporation of CON monomers ultimately abnormally improved sodium storage performance. Charge-discharge measurements were performed on the covalently bonded organic nanosheets synthesized as anodes of Here each current density was applied for 5 consecutive cycles. Also, after several cycles at 1000 mAh/g, the current density returned to 100 mAh/g within a specific potential window (vs. Na ⁺ /Na) as shown in FIGS. 20 and 21 . In all samples, the first discharge cycle showed a well-developed plateau at 0.5 (±0.25) V with respect to the formation of the SEI layer. The first discharge capacities of D/A-CON-10 (FIG. 20) and D/A-CON-16 (FIG. 21) due to the SEI layer formation were 860 and 880 mAh/g, respectively, and the discharge capacity of CON-10 1,030 mAh/g). This means that the SEI layer formation is lower and the reversibility of D/A-CON is much higher because D/A-CON has a lower external surface area than CON of Comparative Example. As mentioned above, since the D/A-CON sample has a smaller bandgap than the CON sample of Comparative Example, the irreversible charge/discharge reaction was significantly suppressed compared to that occurring in the case of CON-10. The first cycle discharge capacity of CON-16 (850 mAh/g) is comparable to that of the low-bandgap D/A-CON, but the discharge capacity of the latter sample exceeds that of n-CON in each successive cycle. did. The low-gap D/A-CON sample suppressed the irreversible discharge/charge process more effectively. However, at a scan rate of 1000 mAh/g, all CON samples showed similar discharge capacities. That is, even D/A-CON at such a high scan rate could not be effectively polarized through the backbone for a large amount of stored sodium ions.

CON electrical conductivity and mass diffusivity were determined using electrochemical impedance spectroscopy (EIS) and compared to RGO (Fig. 22). In the EIS plot, the radius of the semicircle in the high frequency region is usually the charge carrier conductivity index, whereas the Warburg coefficient value in the low frequency range indicates the ion mobility. At high frequency, D/A-CON showed smaller semicircular radius than CON of comparative example, and RGO showed higher charge carrier conductivity. Also, the conductivity of D/A-CON-16 was higher than that of the other samples, but comparable to that of CON-16.

Therefore, according to X-ray diffraction, SEM, and TEM investigation of molecular packing structures, the loosely packed morphology of the superflow structured CON sample ensures better charge carrier conductivity and π-π through the backbone through p-orbital superposition. ^* imply that charge carrier transport is more favorable through intermolecular charge carrier hopping through transitions. In addition, the formation of the SEI layer was verified by comparison of the coulombic efficiency in the first charge/discharge cycle because the main factor of the large discharge capacity in the first cycle is due to the formation of the SEI. Therefore, in the first cycle, the coulombic efficiencies of D/A-CON-16 and D/A-CON-10 (68.5% and 58.0%, respectively) were significantly higher than that of CON-16 and CON-10 (39.2% and 33.4%, respectively). . These results support that the increased electrical conductivity due to the bandgap reduction prevents the formation of the SEI layer. This improved electrical conductivity of D/A-CON compared to the CON of the comparative example is clearly supported by the DFT calculation. Here, the D/A-CON has a much more planar structure than the CON of the comparative example. Contrary to the trend of charge carrier conductivity, RGO exhibited the lowest Warburg coefficient, and the CON sample of the comparative example exhibited a lower Warburg coefficient than the D/A-CON sample. That is, D/A-CON-10 and D/A-CON-16 showed poor ion transport properties (FIG. 22 (b)). This behavior is mainly due to the strong affinity of heteroatoms for sodium ions because (i) the concentration of heteroatoms in the RGO framework is much lower than in any CON sample and (ii) sodium ions can be easily ionized. Therefore, the sodium ion flux resistance of the entire RGO framework was lower than that of the CON sample of Comparative Example, and the Warburg coefficients of CON-10 and CON-16 were larger than those of RGO. According to this rationale, the lower Warburg modulus of CON-16 compared to CON-10 resulted in a larger surface area (300 vs. 200 m/g, loosely packed form of CON-16 as reported in the literature) in the previous case. . The inclusion of BT units in the similar structures of CON-10 and CON-16 to give D/A-CON-10 and D/A-CON-16 allows for the number of more electrostatically favorable heteroatoms such as S and N. increased. The density of heteroatoms in D/A-CON is much larger than that of n-CON, and D/A-CON has a greater polarizability for sodium ion storage than n-CON, so the energy density of D/A-CON is is improved

As a result, compared to the CON of the comparative example, D/A-CON has a more advantageous structure for sodium ion storage. Although this strong polarizability reduced ion mobility through their backbone, they had a higher capacity. 16-19, it has been found that the sodium storage mechanism of D/A-CON can be adequately explained by a quasi-capacitive process and diffusion-controlled Faraday mechanism. Therefore, by further analyzing the CV profile, the detailed contribution ratio of these two mechanisms can be clearly identified as shown in FIGS. 23 to 25 . As the scan rate increased from 0.1 to 0.8 mV/s, the pseudocapacitive contribution of D/A-CON-10 changed from 56.1 to 78.3%. Interestingly, D/A-CON-16 showed a significantly greater contribution of pseudo-dose than D/A-CON-10, varying from 61.5 to 81.2% at each scan rate. Because D/A-CON-16 has a more accessible surface area than D/A-CON-10 demonstrated in Fig. 7, the high contribution of the pseudo-dose to D/A-CON-16 is due to the non-specific surface interactions between sodium ions. can be attributed to Therefore, these results suggest that the mechanism of sodium storage in D/A-CON was mainly dominated by surface reactions, and the sodium storage reaction is related to non-covalent interactions between sodium ions and the highly polarized surface of D/A-CON. .

In order to better understand the effect of BT unit inclusion, the cycling performance and rate function of D/A-CON and CON samples of comparative examples were measured for discharge capacity according to constant current density change every 5 steps, and after the initial 30 cycles (first cycle) In the second cycle, the reversible discharge capacity of D/A-CON-10 at a constant current density of 100 mAh/g was 450 mAh/g, and that of CON-10 was 340 mAh/g. In addition, the average discharge capacity of D/A-CON-10 at 300, 500, 700, 900 and 1000 mAh/g, respectively, was 434, 373, 350, 273 and 133 mAh/g, respectively, whereas that of CON-10 was 236 , 173, 146, 101 and 97 mAh/g ( FIG. 26 ).

In addition, in the second cycle after the initial 30 cycles (first cycle), the reversible discharge capacity of D/A-CON-16 at a constant current density of 100 mAh/g was 534 mAh/g, and the reversible discharge capacity of CON-16 was 320 mAh /g. In addition, the average discharge capacity of D/A-CON-16 at 300, 500, 700, 900 and 1000 mAh/g, respectively, is 485, 402, 392, 353 and 245 mAh/g, respectively, whereas in the case of CON-16 253, 191, 164, 147 and 123 mAh/g (FIG. 27).

After returning to 100 mAh/g again, that is, in the third cycle, the average discharge capacity of D/A-CON-16 at a constant current density of 100 mAh/g was 453 mAh/g, which was 85% of the value of the second cycle, D/A-CON-10 recovered to 95% of the second cycle value at 430 mAh/g.

The discharge capacity of D/A-CON-10 after the 30th cycle showed a larger change than that of D/A-CON-16. Therefore, the average value was restored to a maximum of 85% of the value of the second period. Moreover, D/A-CON showed higher discharge capacity and rate performance than CON of comparative example synthesized through the same route and RGO. In addition, the value of D/A-CON-16 was consistently higher than that of D/A-CON-10. In particular, the discharge capacities of D/A-CON-10 and D/A-CON-16 were approximately 2 times and 1.8 times higher than those of CON-10 and CON-16, respectively. Low-bandgap covalent organic nanosheets containing BT units exhibited higher charge carrier conductivities than other CON and RGO, and the high discharge capacity increase with every cycle was mainly a result of strong electron-defects (in this case, BT ) revealed that it is a band gap through the introduction of units. Comparing the discharge capacities of D/A-CON-10 and D/A-CON-16 confirmed that it is important to increase the surface area between sodium ions and BT units for improving electrode performance. The long-term cycling performance of D/A-CON-10 and D/A-CON-16 was also investigated while maintaining the current density at 100 mA/g up to 150 cycles after 30 cycles ( FIG. 28 ). The results showed that D/A-CON-16 showed excellent reversible and stable charge/discharge properties, indicating faster charge transport and easy mass flux properties for long-term cycling.

The above-mentioned contents are summarized in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 D/A-CON-10 D/A-CON-16 CON-10 CON-16 Mesopore diameter (nm) 4.1 4.1 2.8 2.8 Bandgap (eV) 1.65 1.60 1.91 1.91 BET surface area (m2/g) 89 160 202 300 1 Cycle Coulomb Efficiency (%) 58.0 68.5 33.4 39.2 2 cycles
Discharge capacity (mAh/g) Constant current density 100 mAh/g 450 534 340 320 Constant current density 300 mAh/g 434 485 236 253 Constant current density 500 mAh/g 373 402 173 191 Constant current density 700 mAh/g 350 392 146 164 Constant current density 900 mAh/g 273 353 101 147 Constant current density 1000 mAh/g 133 245 97 123

Although the present invention has been described with reference to specific matters and limited examples as described above, these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and the present invention belongs to Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (8)

A covalently bonded organic nanosheet comprising a covalent bond-based repeating unit satisfying the following formula (1).
[Formula 1]

(In Formula 1,
X is a trivalent linking group represented by the following formula 1-1,
Y is a divalent linking group represented by the following formula 1-2,
n is an integer from 10 to 200,
* is a binding site.
[Formula 1-1]

[Formula 1-2]

)
The method of claim 1,
The covalently bonded organic nanosheet will have a mesopore size of 3.5 to 4.5 nm, the covalently bonded organic nanosheet.
The method of claim 1,
The covalently bonded organic nanosheet will have a band gap of 1.85 eV or less, the covalently bonded organic nanosheet.
A method for preparing the covalently bonded organic nanosheet of any one of claims 1 to 3,
(trimethylstannylthiophen-2-yl)benzo[c][1,2,5]thiadiazole and 2,4,6-tris(5-bromothiophen-2-yl)-1,3,5- Covalently reacting the triazine;
5. The method of claim 4,
The covalent bonding reaction will be carried out through a reflux reaction or a solvothermal reaction, a method for producing a covalently bonded organic nanosheet.
A thin film comprising the covalently bonded organic nanosheet of any one of claims 1 to 3.
A secondary battery comprising the covalently bonded organic nanosheet of any one of claims 1 to 3.
8. The method of claim 7,
The secondary battery is a sodium ion battery, a secondary battery.

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