KR102168273B1 - Stretchable Batteries with Gradient Multilayer Conductors - Google Patents

Abstract

The present invention relates to a conductive composite comprising a conductive material and a stretchable polymer, and is made of a multilayer to have a gradient.
The conductive composite is easy to mass-produce due to a simple manufacturing process, is not limited in stretchability and orientation, and it is possible to adjust stretchability and conductivity for various uses. In addition, since the multilayered structure can control the composite internal architecture at several scales, it can induce metallic conductivity in both the side and cross-section at a strain rate of up to 300%. .

Description

Stacked density gradient stretchable electrodes and high-elastic high-efficiency batteries based thereon {Stretchable Batteries with Gradient Multilayer Conductors}

The present invention relates to a stacked density gradient stretchable electrode and a high-elastic, high-efficiency battery based thereon.

The rapid development of stretchable electronics has led to an increasing demand for wearable healthcare devices, electronic skin, artificial muscles and neuroprosthetic implants. It accelerated as it did. The basic condition for broadening the spectrum of such devices is to develop a conductive composite that maintains stable electrical conductivity in a large mechanical strain.

There are two of the most used strategies for designing conductive composites.

The first strategy is to deposit a conductive material on the surface of an elastomeric substrate to achieve stable conductivity during deformation. The surface of this conductive composite has a buckled, wrinkled, waved, crumpled, or island structure, and accommodates mechanical stress while maintaining a percolation network. Although the above method can realize stable conductivity at high elasticity, since the volume of the conductive layer is small and the manufacturing process is complicated, the applicability of the structure is low.

The second strategy is to prepare a polymer nanocomposite that obtains conductivity through conductive fillers dispersed in elastomeric polymers. The method has the advantage that it is possible to manufacture a composite including various nanoparticles (NPs), nanowires, and nanotubes, and the manufacturing cost is low due to a simple process.

However, the polymer nanocomposite has a trade-off relation between stretchability and conductivity, making it difficult to maintain stable conductivity during stretching. For example, a composite having a high content of elastomer (elastomer) generally exhibits high strain behavior, but has low electrical conductivity. On the other hand, high loading of a conductive component has high electrical conductivity, but a mechanical failure occurs, showing low elasticity.

Therefore, the problem of how to fabricate a composite having high conductivity and elasticity still exists.

The inventors of the present invention fabricated a conductive composite through vacuum-assisted filtration (VAF) and a layer-by-layer assembly (LbL) method using the self-assembly property of a stretchable polymer and a conductive filler. Since the LbL lamination method can produce highly ordered structures, high conductivity is possible through sequential assembly, and fine nanoscale control of the thickness is possible. The structure is controlled through material engineering techniques according to the present invention, and multi-scale conductive composites including nano-, micro- and macro-scale structures can be fabricated.

An object of the present invention is to provide a conductive composite of a new concept in which two types of polymer composites are stacked in order to maintain high elasticity and stable electrical conductivity.

The present invention provides a conductive layer including a first stretchable polymer and a first conductive material; And

Including an elastic layer comprising a second elastic polymer and a second conductive material,

The content of the first conductive material in the conductive layer is 80 to 95% by weight,

The content of the second conductive material in the stretchable layer is 40 to 90% by weight,

The first conductive material has a higher content than the second conductive material, the conductive layer and the stretchable layer are alternately stacked, both of the outermost layers are conductive layers, and a total number of layers is 3 or more.

In addition, the present invention includes the steps of (S1) forming a conductive layer using a first mixture including a first stretchable polymer and a first conductive material;

(S2) forming a stretchable layer on the conductive layer by using a second mixture including a second stretchable polymer and a second conductive material; And

(S3) comprising the step of forming a conductive layer on the stretchable layer by using a first mixture containing a first stretchable polymer and a first conductive material,

It provides a method of manufacturing the above-described conductive composite in which the above steps (S2) and (S3) are performed at least once to prepare a conductive composite having a total number of layers of three or more.

In addition, the present invention is the conductive composite described above; And

It provides an electrode for an electrochemical device including an electrode active material layer positioned on the conductive composite.

In addition, the present invention is a positive electrode;

cathode; And

Including an electrolyte positioned between the positive electrode and the negative electrode,

At least one of the anode and the cathode provides an electrochemical device which is the electrode for an electrochemical device described above.

In the present invention, it is possible to provide a conductive composite including a conductive material and a stretchable polymer, and is manufactured in a multi-layered manner. The conductive composite is easy to mass-produce due to a simple manufacturing process, is not limited in stretchability (stretchability) and orientation, and stretchability and conductivity can be adjusted to suit various uses. In addition, since the multilayered structure can control the composite internal architecture at several scales, it is possible to achieve metallic conductivity in both the horizontal (side) and vertical (cross-sectional) directions at high strain rates. You can induce.

The conductive composite according to the present invention can be applied to a lithium-ion battery that maintains stable chemical performance at a very high strain rate to constitute a flexible energy storage device.

In addition, the conductive composite can be applied to various material designs for future energy conversion and storage devices as well as biomimetic electronics.

1 is a schematic diagram of a conductive composite (GAP multilayer conductors), showing a layered assembly of a single-layer AuPU film having various concentrations of gold nanoparticles (AuNP). The photographs in FIG. 1 show the conductive composite in relaxed and strained conditions.
2 shows the measurement results of the physical properties of the single-layer AuPU film.
3 shows the result of TGA (Thermogravimetric Analysis) measurement of the conductive composite.
Figure 4 shows the structure-controlled (Architecture-controlled) conductive composite.
Specifically, FIG. 4 is a schematic diagram showing a) high-gradient and b) low-gradient conductive composites in which the number of layers of the intermediate layer increases, and a cross section showing elemental mapping images of carbon and gold (Au). -sectional) SEM image. The scale bar for all images is 20 μm.
5 and 6 show the mechanical properties of the conductive composite.
5a represents the stress-strain curves of the conductive composite, and 5b and c represent the Young's modulus and rupture point of the high-gradient and low-gradient conductive composites.
In addition, the results of finite element analysis of the von Mises stress distribution in the horizontal (6a) and vertical (6b) directions of the 5L and 9L low-gradient conductive composites at 50% strain are shown.
7 and 8 show the electrical properties of the conductive composite, and SAXS analysis results for the AuNP percolation network in the Pu matrix under strain.
7a is a graph showing the normalized resistance at the top surface of the outermost layer of 3L and 9L high-gradient and low-gradient conductive composites under various strain conditions.
7b is a graph showing the vertical conductivity of the low-gradient conductive composite with increasing number of layers.
7c is a graph showing the change in vertical conductivity of 5L and 9L low-gradient conductive composites under deformation.
8a is a schematic diagram showing an in-situ SAXS measurement experiment setup.
8b shows the SAXS pattern at selected uniaxial strains of 0%, 50% and 100% for pure Pu and 50 wt% AuPu films, and the behavior of AuNPs (yellow spheres) in the matrix and under the strain determined by SAXS analysis. It represents changes in the electrical pathway (red line).
8c shows the calculated Herman's orientation factor, f, for pure Pu and 50 wt% AuPU films.
9 shows the electrochemical performance of a flexible aqueous lithium ion battery including a conductive composite.
9a is a three-electrode system using Pt electrode and Ag/AgCl electrode as counter electrode and reference electrode, respectively, and 1M Li ₂ SO ₄ as electrolyte, GAP anode (PI/CNT) and GAP cathode (LMO) at various current densities. /CNT).
9b and 9c show the galvanostatic charge-discharge curves of the GAP negative electrode and the GAP positive electrode, respectively.
9d represents the cycling performance of a full cell with a current density of 0.5 A/g at 0.0 to 2.2 V in 1M Li ₂ SO ₄ for 1,000 cycles.
9e is a schematic diagram of a flexible water-based rechargeable lithium-ion battery manufactured using a GAP positive electrode and a negative electrode having a coplanar layout.
9f shows the cycle performance of the stretchable full cell at a current density of 0.5 A/g at various strains of 0-30% over 100 cycles.
9g represents capacity retention as a function of cycle at a current density of 0.5 A/g.
9h is a photograph of an LED bulb operated using stretchable aqueous lithium-ion cells at 0% and 30% strain.

The present invention provides a conductive layer including a first stretchable polymer and a first conductive material; And

It provides a conductive composite comprising an elastic layer including a second elastic polymer and a second conductive material.

Since the conductive composite according to the present invention includes a conductive layer and a stretchable layer in which the content of the stretchable polymer and the conductive material is controlled, both stretchability and conductivity are excellent, and a composite having excellent electrical conductivity can be manufactured even in the process of stretching and contracting.

In the present invention, the conductive composite may be expressed as a GAP (gradient assembled polyurethane) multilayer conductor or GAP.

Each layer included in the conductive composite in the present invention can be expressed as a single-layer AuPU film. The single-layer AuPU film includes a negatively charged conductive material and a positively charged stretchable polymer capable of controlling both nano- and meso-scale structures. And, it is possible to design a conductive composite having a gradient using the films (FIG. 1). Specifically, micro- and macro-scale structures can be controlled by laminating each single-layer AuPU film containing a conductive material in various ratios.

According to an embodiment of the present invention to be described later, the conductive composite may have mechanical stretchability against a strain of 300% or more in a high-gradient structure, and in a low-gradient structure, by increasing the number of intermediate layers, Through-plane conductivity can be improved.

Hereinafter, the conductive composite according to the present invention will be described in more detail.

In the present invention, the conductive layer may impart conductivity within the conductive composite.

In one embodiment, the conductive layer includes a first stretchable polymer and a first conductive material, and the content of the first conductive material in the conductive layer may be 80 to 95% by weight, 85 to 92% by weight, or 90% by weight. have. In addition, the content of the first stretchable polymer may be 5 to 20% by weight, 8 to 15% by weight, or 10% by weight. In the above range, a composite having excellent conductivity can be prepared, and outside the above content range, there is a concern that it is difficult to apply it to an electrochemical device.

In addition, in the present invention, the stretchable layer may impart stretchability within the conductive composite.

In one embodiment, the stretchable layer includes a second stretchable polymer and a second conductive material, and the content of the second conductive material in the stretchable layer is 40 to 90% by weight, 40 to 60% by weight, or 80 to 90% by weight. I can. In addition, the content of the second stretchable polymer may be 10 to 60% by weight, 40 to 60% by weight, or 10 to 20% by weight. The content of the second conductive material may be lower than that of the first conductive material. In the above range, a composite having excellent conductivity and elasticity can be prepared, and outside the above content range, there is a concern that it may be difficult to apply to an electrochemical device. In particular, in the present invention, since the stretchable layer includes a conductive material, a composite having conductivity in a vertical direction as well as a horizontal direction can be manufactured.

For example, the content of the second conductive material can be adjusted to 40 to 60% by weight, 45 to 55% by weight, or 48 to 52% by weight, and when the content range is used, a high-gradient conductive composite can be formed. . In this case, the content of the first conductive material may be 85 to 95% by weight.

In addition, for example, the content of the second conductive material may be adjusted to 80 to 90% by weight, 82 to 88% by weight, or 85% by weight, and when the content range is used, a low-gradient conductive composite can be formed. In this case, the content of the first conductive material may be 90 to 95% by weight, and the first conductive material may have a higher content than the second conductive material.

In one embodiment, the stretchable polymer is not particularly limited as long as it has stretchability. For example, as a first stretchable polymer and a second stretchable polymer, polyurethane (polyurethane, PU), polystyrene, polybutadiene, and polybutylene, respectively. One or more selected from the group consisting of polyethylene and polyisoprene may be used. In an embodiment of the present invention, polyurethane (PU) was used as the first stretchable polymer and the second stretchable polymer.

In one embodiment, the first conductive material and the second conductive material may each be at least one selected from the group consisting of gold nanoparticles, silver nanoparticles, copper particles, carbon nanotubes, and graphene. In an embodiment of the present invention, gold nanoparticles (AuNPs) are used as the first conductive material and the second conductive material. The gold nanoparticles are suitable as the conductive material of the present invention, since they can exhibit a greater degree of freedom in the modified polymer matrix.

Each of the first conductive material and the second conductive material may have an average diameter (average particle diameter in the case of nanoparticles) of 1 to 100 nm, 10 to 50 nm, or 15 to 30 nm. It is excellent in dispersibility in the stretchable polymer within the above range, and high electrical conductivity can be imparted. The conductive material may be used commercially or synthesized in a laboratory.

The conductive composite according to the present invention includes the aforementioned conductive layer and stretchable layer, and the conductive layer and stretchable layer may be alternately stacked. When three or more layers of the conductive layer and the stretchable layer are stacked, both layers of the outermost layer may be conductive layers. By placing the conductive layer on the outermost side, the structural stability of the conductive composite may be improved, and it may be stable against external impact.

In addition, the total number of layers of the conductive composite according to the present invention may be 3 or more, 3 to 15 layers, or 3 to 9 layers. In the present invention, the conductive composite may be expressed as 3L (consisting of 3 layers), 5L (consisting of 5 layers), etc. according to the total number of layers. In addition, since both outermost layers of the conductive composite are composed of conductive layers, layers other than the outermost layer may be referred to as interlayers.

In one embodiment, when the conductive composite is composed of 3L, it may have a structure of a conductive layer/stretchable layer/conductive layer, and if composed of 5L, it may have a structure of a conductive layer/stretchable layer/conductive layer/stretchable layer/conductive layer. have. In particular, in the present invention, physical properties such as Young's modulus can be further improved by increasing the number of intermediate layers.

In one embodiment, when the conductive composite includes two or more stretchable layers, each of the stretchable layers may have the same composition or different compositions. In addition, when two or more conductive layers are included, each of the conductive layers may have the same composition or different compositions.

In addition, in one embodiment, the thickness of the conductive composite may be 10 to 100 μm. It is easy to apply to an electrochemical device in the above thickness range. Meanwhile, the thickness of the outermost layer of the conductive composite may be 2 to 10 μm. When the total number of layers of the conductive composite increases, the total number of layers may be increased by dividing the number of intermediate layers without increasing the total thickness of the conductive composite.

In addition, the present invention relates to a method of manufacturing the above-described conductive composite.

The method of manufacturing a conductive composite according to the present invention includes the steps of (S1) forming a conductive layer using a first mixture including a first stretchable polymer and a first conductive material;

(S2) forming a stretchable layer on the conductive layer by using a second mixture including a second stretchable polymer and a second conductive material; And

(S3) forming a conductive layer on the stretchable layer using a first mixture including a first stretchable polymer and a first conductive material.

In the steps (S1) to (S3), the stretchable polymer and the conductive material may be used without limitation, without limitation.

In one embodiment, a conductive layer may be formed through step (S1), an elastic layer may be formed through step (S2), and a conductive layer may be formed through step (S3). That is, the conductive layer and the stretchable layer may be alternately stacked, and steps (S2) and (S3) may be performed at least once to prepare a conductive composite having a total number of layers of 3 or more. When three or more layers of the conductive layer and the stretchable layer are stacked, both layers of the outermost layer may be conductive layers.

In addition, the total number of layers of the conductive composite manufactured by the present invention may be 3 or more, 3 to 15 layers, or 3 to 9 layers.

In the present invention, a conductive layer or a stretchable layer is prepared through vacuum-assisted filtration (VAF), and a conductive composite may be prepared by stacking the layers through a multilayer thin film lamination method (LbL). Through the vacuum filtration, a certain level of nanoscale structure can be controlled, and a larger strain can be provided. In one embodiment, vacuum filtration may be performed using filter paper having a pore size of 0.1 to 5 μm. In addition, it is possible to implement a highly ordered structure through LbL lamination, enable high conductivity through sequential assembly, and control fine thickness.

In addition, the present invention is the conductive composite described above; And

It relates to an electrode for an electrochemical device including an electrode active material layer positioned on the conductive composite.

The conductive composite according to the present invention may use the conductive composite described above, and specifically, a conductive layer including a first stretchable polymer and a first conductive material; And a stretchable layer comprising a second stretchable polymer and a second conductive material, wherein the content of the first conductive material in the conductive layer is 80 to 95% by weight, and the content of the second conductive material in the stretchable layer is 40 to 90% by weight, the first conductive material has a higher content than the second conductive material, the conductive layer and the elastic layer are alternately stacked, both of the outermost layers are conductive layers, and the total number of layers is 3 or more. It can be a complex.

The conductive composite may serve as a current collector in the electrode. Since the electrode for an electrochemical device according to the present invention includes a conductive composite, the electrode for an electrochemical device according to the present invention may have flexibility in stretching and contraction, and excellent strength. In addition, since the conductive material is present in both the conductive layer and the stretchable layer, it may have conductivity not only in a horizontal direction but also in a vertical direction, and electrical conductivity may be maintained before and after stretching and contracting. Accordingly, the battery to which the electrode is applied can exhibit flexibility, safety, and electrochemical performance.

Further, in one embodiment, the electrode active material layer is located on the conductive composite. Such an electrode active material layer may directly form an electrode active material layer on the conductive composite, and may be transferred onto the conductive composite after forming an electrode active material layer on a separate conductive film.

The electrode active material layer may include an electrode active material having an average particle diameter of 100 to 500 nm. In this case, when the electrode is a negative electrode, it may include at least one negative active material selected from the group consisting of graphite, silicon (Si), germanium (Ge), TiO ₂ and L ₄ Ti ₅ O ₁₂ , and the like, and the electrode In the case of the positive electrode, at least one positive electrode active material selected from the group consisting of LiCoO ₂ , LiMnO ₂ , LiFePO ₄ , and the like may be included.

The electrode active material layer may have a thickness of 0.1 to 10 μm.

In addition, the present invention is a positive electrode;

cathode; And

Including an electrolyte positioned between the positive electrode and the negative electrode,

At least one of the anode and the cathode provides an electrochemical device which is the electrode for an electrochemical device described above.

In the present invention, by applying the above-described electrode to any one of the positive electrode and the negative electrode, it is possible to implement a thin thickness, exhibit excellent flexibility, and provide an electrochemical device that is safe and has excellent lifespan characteristics. have.

In one embodiment, the electrochemical device may be an aqueous secondary metal ion battery, a lithium secondary battery, a sodium secondary battery, or a super capacitor.

In addition, the electrochemical device is a so-called "stretchable energy storage system", and is suitable for application to wearable devices, flexible devices, and the like.

In the electrochemical device, an electrolyte used in the art may be used. The electrolyte may separate the positive electrode and the negative electrode, provide a passage for moving metal ions, and maintain their shape during stretching and contracting.

In one embodiment, poly dimethlysiloxane (PDMS) or the like may be used as a packaging material for the electrochemical device.

Hereinafter, preferred embodiments are presented to aid in understanding the present invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present invention and the scope of the technical idea, but it is natural that such changes and modifications belong to the appended claims.

Example

Manufacturing example 1. Synthesis of gold nanoparticles

Gold (III) chloride trihydrate (HAuCl ₄ * 3H ₂ O, Sigma-Aldrich) 360.0 mg was added to 500 ml of deionized water to prepare a gold precursor solution. The gold precursor solution was heated with vigorous stirring at 95° C. for 20 minutes, and then 100 ml (34 mM) of a citric acid solution was added. Then, it was heated for 20 minutes and cooled at room temperature.

The average diameter of the gold nanoparticles prepared in Preparation Example 1 was 21.5±5.3 nm.

In the present invention, negatively charged gold nanoparticles (AuNP) stabilized by citrate may be prepared, and the gold nanoparticles may be used as a conductive material for stretchable conductors. Since nanowires and nanotubes also have a high aspect ratio, they can be used as conductive composites, but the nanoparticles (NP) prepared in Preparation Example 1 have a greater degree of freedom in a polymer matrix with deformation. It is preferable because it can represent.

Manufacturing example 2. Single-layer AuPU Film manufacturing

A positively charged water-dispersible PU suspension was used as an elastic polymer (elastomeric component) to prepare a conductive composite.

1.0 vol% polyurethane aqueous solution (Mw: about 92,000, Hepce Chem, Korea) 0.50, 1.0 or 4.0 mL of the gold nanoparticles (AuNP) dispersion prepared in Preparation Example 1 250 mL (gold nanoparticle concentration: 0.1 g/L to 1 g/L) was added slowly while stirring to prepare a mixture (AuPU mixture) having a gold nanoparticle content of 90, 85, or 50 wt%, respectively, and stirred for an additional 5 minutes.

Each mixture was vacuum filtered using filter paper having a pore size of 0.8 μm and a diameter of 47 mm. After the prepared film was completely dried at room temperature for 1 day, the film was peeled from the filter paper.

The prepared single-layer AuPU film may be represented by AuPU, and may be represented by ~% by weight (wt%) AuPU film according to the content of gold nanoparticles.

On the other hand, 1.0 vol% polyurethane aqueous solution was vacuum filtered (vacuum filtration conditions are the same as for single-layer AuPU film production) to prepare a neat PU film.

Experimental example 1. single-layer AuPU Measurement of film properties

The physical properties of the single-layer AuPU film prepared in Preparation Example 2 were measured.

The measurement results are shown in FIG. 2.

In the case of a neat PU film, it showed a stretchability of 615%. In the case of a PU matrix, that is, a single-layer AuPU film, when the content of gold nanoparticles (AuNP) in the film is increased from 50% to 85% and 90% by weight, the elasticity of the AuPU film is from 380% to 140%, respectively. It decreased sharply to 2%. In contrast, the 90% by weight AuPU film showed a resistivity of less than 1 Ω, which was similar to a metal conductor. In addition, no change in resistance was observed in the film in 100 bending cycles.

Therefore, in order to overcome the limitations related to the conductivity and stretchability of each single-layer AuPU film, in the present invention, a multilayer is formed by laminating a single-layer AuPU film manufactured using the VAF and LbL lamination method. Eggplant designed a new structural conductive composite.

Manufacturing example 3. Conductive composite (GAP multilayer conductor) fabrication

A 90% by weight AuPU film was used as a conductive layer on both the upper and lower outermost layer surfaces, and a 50% by weight AuPU film or an 85% by weight AuPU film was used as an elastic layer therebetween. This new design features high-gradient (i.e. 95% by weight AuPU film and 50% by weight AuPU film) and low-gradient (i.e. 95% by weight AuPU film and 85% by weight AuPU film) with gold nanoparticles distributed throughout the conductor. A multi-layered structure can be provided. The multilayer structure consists of three layers, and can be expressed as a three-layer GAP multilayer conductor (3L).

(1) 3L high- gradient Fabrication of conductive composite

The layered multilayer structure was prepared by alternating physical trapping of single-layer AuPU films under vacuum.

First, a conductive layer was prepared by vacuum filtering an AuPU mixture having a content of gold nanoparticles of 90% by weight, and then vacuum filtering an AuPU mixture having a content of gold nanoparticles of 50% by weight to prepare a stretchable layer.

Finally, the AuPU mixture containing 90% by weight of gold nanoparticles was vacuum filtered to prepare a conductive layer, thereby preparing a 3L high-gradient (ie, 95/50/95% by weight) conductive composite.

(2) 3L low- gradient Fabrication of conductive composite

First, a conductive layer was prepared by vacuum filtering an AuPU mixture having a content of gold nanoparticles of 90% by weight, and then vacuum filtering an AuPU mixture having a content of gold nanoparticles of 85% by weight to prepare a stretchable layer.

Finally, the AuPU mixture having a content of 90% by weight of gold nanoparticles was vacuum filtered to prepare a conductive layer, thereby preparing a 3L low-gradient (ie, 95/85/95% by weight) conductive composite.

(3) 3L or more conductive composite fabrication

In order to prepare a stacked structure more than 3L, the mixture used as the conductive layer and the mixture used as the stretchable layer were alternately subjected to additional vacuum filtration to prepare 5L, 7L, and 9L conductive composites.

That is, the interlayers of the conductive composite have a structure uniformly divided into a plurality of layers by adding an additional conductive layer between the 3L stretchable layers.

Experimental example 2. Numerical simulation of conductive composite (GAP multilayer conductor)

In order to demonstrate the mechanical and electrical properties of single-layer AuPU films and conductive composites, finite element simulations were performed using ABAQUS/Standard 6.14 software (Dassault System).

In order to confirm the stress distribution of the layer, linear elastic analysis was performed under uniaxial tension. In addition, in order to confirm the change in the vertical conductivity of the conductive composite, electrical conduction analysis was performed. Steady state analysis was performed in both analyses. The contact layer between the conductive layer and the stretchable layer was considered assuming a 1 to 1 contact ratio. The experimentally measured elastic properties of each layer of the conductive composite, the dimensions of the conductive composite, and the electrical properties according to the deformation were performed in all simulations.

(One) TGA analysis

TGA analysis was performed on 3L to 9L high-gradient or low-gradient conductive composites.

As shown in FIG. 3, as a result of Thermogravimetric Analysis (TGA), the specific content of gold nanoparticles of the high-gradient and low-gradient conductive composites was approximately the same as 75% by weight and 88% by weight. These results suggest that the number of layers and gradient distribution of the conductive composite can be precisely controlled without changing the composition ratio of the conductive material and the stretchable polymer.

(2) structural analysis of conductive composite

The structure of the conductive composite (GAP multilayer conductor) prepared in Preparation Example 3 was confirmed using a cross-sectional scanning electron microscopy (SEM) (FIG. 4). The multilayer structure was clearly observed through the relative contrast between gold nanoparticles and stretchable polymer (PU) in each layer.

The corresponding energy dispersive X-ray spectroscopy (EDS) image showed a gradient distribution of gold and carbon, which indicates that both gold nanoparticles and polyurethane are distributed in the entire conductive composite, and the concentration gradient It suggests that it represents (Figs. 4A and 4B).

(3) elasticity of the conductive composite and Young's modulus analysis

The high-gradient conductive composite exhibited stretchability of 300% or more, but the stretchability of the low-gradient conductive composite exhibited a strain of less than 100% (FIG. 5A). The rupture point of the high-gradient and low-gradient conductive composites gradually decreased. As the number of intermediate layers increased, the Young's modulus increased (FIGS. 5b and 5c). The Young's modulus of the high-gradient conductive composite was lower than that of the low-gradient conductive composite, and when the ratio of gold nanoparticles to polyurethane in the low-gradient conductive composite was high, a hard and hard conductive composite was formed, indicating low elasticity.

Meanwhile, in the present invention, changes in the morphology and internal structure of the conductive composite under deformation were confirmed using SEM. The top surface image shows 3D interconnected microporous networks of Au NP-anchored PU chains. Voids and cracks increase with deformation, resulting in an increase in porosity, but a good structural recovery of the conductive composite due to the rigid polyurethane was observed. However, in the cross-sectional SEM image of the 9L high-gradient conductive composite, some stress failure of the conductive composite due to nano- and micro-cracks under deformation was confirmed. This result demonstrates that it has excellent structural recovery as well as an electrically conductive surface by preventing the conductive layer from rupturing in the upper and lower outermost layers without severe cracking. In addition, due to the high affinity and compatibility of the same and uniform components in each layer, there was no delamination of the layer from the lower layer.

(4) Measurement of stress distribution

In order to check the rupture point of the conductive composite through crack propagation starting from the intermediate layer, horizontal in 5L and 9L low-gradient conductive composites using the ABAQUS software package. And the stress distribution in the vertical direction was mechanically simulated.

The horizontal stress σx of the 9L conductive composite according to the stretching direction was higher than that of the 5L conductive composite (Fig. 6a), whereas the vertical stress σz of the 9L conductive composite was -40.5 kPa ( That is, compression) was significantly reduced (Fig. 6b). This decreased as the number of intermediate layers of the GAP conductor increased, and this was consistent with the results shown in FIG. 5. Also, the stress was more concentrated in the middle layer than in the outermost layer. As a result, the concentrated stress of the intermediate layer started to rupture of the conductive composite rather than starting from the outermost conductive layer, which was consistent with the previous cross-sectional SEM image. Accordingly, it was confirmed that the multilayered structure is advantageous in dispersing the stress concentration during stretching.

On the other hand, it is important to consider the electrical connection of the intermediate layer in the deformation. However, the high-gradient conductive composite has a limitation since only the upper surface has conventional conductivity like a conventional structurally designed conductor. In contrast, the low-gradient conductive composite is completely conductive from the top to the bottom surface, which has much lower tensile strength than the high-gradient conductive composite, but the 3L low-gradient conductive composite has a low vertical (cross) of ~50 Ω. Has directional resistance.

(5) Analysis of change in vertical conductivity

The vertical conductivity of the low-gradient conductive composite was theoretically calculated to prove the existence of a conductive path through the stretchable layer as a function of the number of intermediate layers (Fig. 7).

It was confirmed that the vertical conductivity was increased by increasing the number of intermediate layers, so that through-plane electrical conduction from the top surface to the bottom surface is easy.

In addition, the change in vertical conductivity in the 5L and 9L low-gradient conductive composites was investigated in consideration of the strain-dependent conductivity of each layer (Fig. 7c). In contrast to the results of the horizontal conductivity of the outermost layer of the conductor, the conductivity in the vertical direction increased as the number of intermediate layers increased, and it was confirmed that increasing the number of intermediate layers was advantageous for electrical conductivity.

(6) Electrical conductivity measurement

Electrical conductivity is closely related to the connectivity between conductive materials. In order to maintain stable electrical conductivity in the conductive composite, the behavior of the conductive material during deformation is important.

In this regard, in-situ x-ray small-angle X-ray scattering (SAXS) is a way to better understand the behavior of conductive materials in an elastic matrix (Figs. 8a-c). SAXS analysis of the samples was performed at a constant stretching rate of 80 μm/s in the strain range of 0-100%. 8B shows the 2D SAXS pattern of pure PU and 50% by weight AuPU films at 0%, 50% and 100% uniaxial strains. In the initial non-deformed state, the 2D patterns of pure PU and AuPU films showed isotropic scattering geometry, indicating random dispersion of hard segments of polyurethane and gold nanoparticles.

However, the two samples start to show different scattering patterns upon stretching. The pattern of the pure PU film changes from circular to elliptical shapes upon deformation, indicating that the hard segments of the PU are aligned along the stretching direction (FIG. 8B). In contrast, AuPU films exhibited a butterfly-like pattern upon stretching due to the affine relative displacements of gold nanoparticles in the polymer matrix upon deformation. The AuNP of the film has a higher electron density than the PU matrix, indicating that the SAXS pattern of the film is derived from AuNP. As the deformation increases, the gold nanoparticles gradually form clusters of raft-like structures that are perpendicular to the strain axis due to Poisson contraction. Aligned banded AuNP clusters are formed. This phenomenon can induce alignment and increased interconnection of gold nanoparticles under uniaxial strain, and can effectively maintain electrical conductivity during deformation.

(7) Herman's Measurement of orientation factor(f)

In addition, in order to quantitatively confirm the degree of self-assembly of the AuPU into a conductive band according to the stretching direction in the AuPU film, Herman's orientation factor (f) was calculated.

When the transformation is applied, the alignment quality of the PU increases along the stretching direction due to the orientation of the segment domains (FIG. 8C). In contrast, the orientation factor of the gold nanoparticles begins to collapse at a strain rate of 80% of the percolation network in the stretching direction, which coincides with the point of a sharp increase in resistance shown in FIG. 7A.

Manufacturing example 4. Battery production

(1) active substance synthesis

100 mg of CNT (10-15 nm in diameter and ~ 200 μm in length) and 250 mg of KMnO4 (Aldrich) were mixed together in an agate mortar.

The mixed powder was poured into 100 mL of water and stirred for 10 minutes. 0.5 mL of H ₂ SO ₄ (95%, Samchun) was added to the mixture with stirring for 30 minutes. The mixture was heated in an oil bath at 80° C. while stirring for 1 hour. The precipitate was collected by filtration and washed repeatedly with deionized water and ethanol. Then, the product was dried in an oven at 60° C. for 12 hours to obtain MnO ₂ /CNT.

In order to prepare LMO/CNT, 0.25 g of MnO ₂ /CNT prepared above and 0.26 g of LiOH H ₂ O (Sigma Aldrich) were mixed with 60 mL of deionized water. 80 mL of the mixture was transferred to an autoclave and heated at 160° C. for 12 hours. After hydrothermal treatment, the produced precipitate was filtered and washed with distilled water. After cooling the autoclave to room temperature, the product was dried in an oven at 60° C. for 12 hours. Finally, the product was heated in an air atmosphere at 200° C. for 3 hours in a furnace. Through this, LMO/CNT was prepared.

PI/CNT anode materials were synthesized and modified using a previously reported protocol. Additionally, 2.3 mmol of 1,4,5,8-naphthalenetetracarboxylic dianhydride (1,4,5,8-naphthalenetetracarboxylic dianhydride) and 0.50 g of CNT were mixed with 40 g of 4-chlorophenol, Stir at 55 °C until thoroughly mixed.

0.15 mL of ethylenediamine was added to the mixture, followed by heating and refluxing at 200° C. for 6 hours. The mixture was cooled to room temperature, and the solid product was rinsed with ethanol and then vacuum filtered. The obtained product was dried at 300° C. for 8 hours under N ₂ atmosphere to remove residual solvent.

(2) battery production

The electrode is a mixture consisting of an active material (LMO/CNT or PI/CNT), a conductive material (super P), and a binder (weight ratio: 8:1:1) on a hot plate at 60°C. spray coating). The electrodes were cut into rectangular shapes (30 mm x 10 mm).

Electrochemical properties of the half-cell and full-cell were measured using a VSP (Bio-Logic Science Instruments, France) having 1 M LiSO4 aqueous electrolyte. A Pt electrode and an Ag/AgCl electrode were used as a counter electrode and a reference electrode, respectively. The loading density of the active material was 0.5 mg/cm. Full cells were performed at room temperature between 0.0 V and 2.2 V, and were measured using a two-electrode system. In addition, in order to remove oxygen, a full cell was tested in a beaker cell containing 1M Li2SO4 with continuous bubbling nitrogen. PDMS was used as the packaging material (35 mm x 40 mm x 1 mm) and the spacer of the stretchable full cell. The 500 μm thin spacer provided enough space to fill the aqueous electrolyte.

The stretchable cathode and anode were attached parallel to the bottom layer using an uncured PDMS solution. Then, the upper layer, the spacer, and the lower layer were assembled using O2 plasma (CUTE, Femto Science, Korea) treatment. Finally, the prepared aqueous electrolyte was carefully injected using a syringe.

Experimental example 3. Measurement of electrochemical performance of a battery containing a conductive composite

Mechanical properties of the fabricated electrode were measured using a tensile strength tester (DA-01, Petrol LAB, Korea). The test piece was cut into a dog-bone shape, and the tensile strength measurement speed was 10 mm/min.

Electrical conductivity was measured using a four-point probe machine (FPP-RS8, Dasol Eng, Korea). The change in resistance during strain and release was measured using a multi-meter. The crystal structure of LMO/CNT was characterized by a Rigaku D/MAX X-ray diffractometer (X-ray diffractomete, XRD) at 2500 V. The morphology of the electrode and the active material was measured using a field-emission scanning electron microscopy (FE-SEM, Hitachi S-4800). Transmission electron microscopy (TEM) images were taken in bright-field mode using JEM 2100 (JEOL, Japan). The FT-IR spectrum of PI/CNT was measured using a Varian 670 IR spectrometer. The mass content of LMO and PI was calculated using thermogravimetric analysis (TGA, TA instruments, Q50, USA). In situ SAXS measurements were performed on a 6D UNIST-PAL beam line at Pohang Accelerator Laboratory in Korea. The energy of the X-ray was 11.6 keV (wavelength, λ=1.0668 A).

The electrochemical performance of the GAP electrode was measured by cyclic voltammetry (CV) using a 3-electrode system with 1 M Li ₂ SO ₄ electrolyte.

In FIG. 9A, the CV curves of the GAP anode and GAP cathode with increasing scan rates show typical redox peaks of PI and LMO. The conductive composite clearly exhibits electrochemical stability within the operating voltage range, showing that the conductive composite can be used as a current collector of a battery system.

5B shows the GAP cathode voltage profile between 0.0 and 1.2 V at various current densities. Specific capacities of 132 and 102 mA/h were seen at 1 and 5 A/g, respectively. The speed performance of the GAP anode at various current rates ranging from 2 to 15 A/g in a voltage window of 0.0 to -1.0 V was shown (Fig. 5c). The GAP anode is capable of delivering 95 mA/h even at a high current density of 15 A/g.

In addition, the electrochemical performance of a full cell composed of a GAP anode and a GAP cathode having an aqueous electrolyte solution was evaluated in a voltage range of 0.0 V to 2.2 V without modification. The discharge capacities of the full cell were 100 mA/h at a current density of 0.5 A/g; The discharge times were about 2 minutes. In addition, the long-term cycle performance of the full cell showed a very stable cycle retention rate of 96% at a current density of 0.5 A/g even after 1000 cycles (Fig. 5d).

More specifically, in order to demonstrate the electrochemical performance during deformation, a flexible water-based rechargeable lithium-ion battery was designed to be practically applied to a deformable electronic device (FIG. 5E).

The stretchable water-based rechargeable lithium-ion battery was cycled at 0% and 30% strain at a current density of 0.5%/g (FIG. 5F); At 30% strain, the stretchable water-based lithium-ion battery exhibited excellent capacity retention of 72% over 10 cycles compared to the non-modified condition. After releasing the deformation, the specific capacity of the stretchable aqueous secondary lithium-ion battery completely recovered its initial value.

In order to confirm the electrochemical stability of the stretchable battery, cycling performance was measured at a current density of 0.5A/g while performing 20 stretching cycles at a strain rate of 30% per 20 cycles (FIG. 5G). ). 5H shows that, while stretching at 30% strain, stretchable cells connected in series can turn on orange light-emitting diodes (LEDs).

As a new function appearing in the conductive composite, it controls the spatial distribution of the charge transport pathways, as exemplified by changes in the primary charge transport pathways of the low-gradient and high-gradient conductive composites. It becomes possible.

In addition, since the conductive composite according to the present invention can be applied as a flexible aqueous secondary lithium-ion battery, it is possible to provide a stable output at a high rate capability under a high strain rate.

The conductive composite according to the present invention not only produces flexible and wearable electronic devices, but also provides a conductive combination of charge transport and mechanical properties typified by damage-resistant batteries. It can also be extended for other devices as needed.

Claims (15)

A conductive layer including a first stretchable polymer and a first conductive material; And
Including an elastic layer comprising a second elastic polymer and a second conductive material,
The content of the first conductive material in the conductive layer is 80 to 95% by weight,
The content of the second conductive material in the stretchable layer is 40 to 90% by weight,
The first conductive material has a higher content than the second conductive material, the conductive layer and the stretchable layer are alternately stacked, both of the outermost layers are conductive layers, and the total number of layers is 3 or more,
The first conductive material and the second conductive material are each a conductive composite having an average diameter of 1 to 100 nm.
The method of claim 1,
The content of the first conductive material in the conductive layer is 85 to 95% by weight,
The conductive composite in which the content of the second conductive material in the stretchable layer is 40 to 60% by weight.
The method of claim 1,
The content of the first conductive material in the conductive layer is 90 to 95% by weight,
The content of the second conductive material in the stretchable layer is 80 to 90% by weight,
The conductive composite in which the first conductive material has a higher content than the second conductive material.
The method of claim 1,
The first stretchable polymer and the second stretchable polymer are polyurethane, polystyrene, polybutadiene, and polybutylene, respectively. Polyethylene (polyethylene) and polyisoprene (polyisoprene) at least one conductive composite selected from the group consisting of.
The method of claim 1,
The first conductive material and the second conductive material are at least one selected from the group consisting of gold nanoparticles, silver nanoparticles, copper particles, carbon nanotubes, and graphene, respectively.
delete The method of claim 1,
The total number of layers of the conductive layer and the stretchable layer included in the conductive composite is 3 to 15.
The method of claim 1,
The conductive composite has a thickness of 10 to 100 μm.
(S1) forming a conductive layer using a first mixture containing a first stretchable polymer and a first conductive material;
(S2) forming a stretchable layer on the conductive layer by using a second mixture including a second stretchable polymer and a second conductive material; And
(S3) comprising the step of forming a conductive layer on the stretchable layer by using a first mixture containing a first stretchable polymer and a first conductive material,
The method of manufacturing a conductive composite according to claim 1, wherein the steps (S2) and (S3) are performed at least once to produce a conductive composite having a total number of layers of three or more.
The method of claim 9,
A method of manufacturing a conductive composite in which the total number of layers of the conductive layer and the stretchable layer included in the conductive composite is 3 to 15.
The method of claim 9,
The conductive layer and the stretchable layer is a method of manufacturing a conductive composite to be prepared in the form of a film by vacuum filtration of the first mixture and the second mixture, respectively.
Conductive composite; And
Including an electrode active material layer positioned on the conductive composite,
The conductive composite may include a conductive layer including a first stretchable polymer and a first conductive material; And
Including an elastic layer comprising a second elastic polymer and a second conductive material,
The content of the first conductive material in the conductive layer is 80 to 95% by weight,
The content of the second conductive material in the stretchable layer is 40 to 90% by weight,
The first conductive material has a higher content than the second conductive material, the conductive layer and the stretchable layer are alternately stacked, both of the outermost layers are conductive layers, and the total number of layers is 3 or more,
The first conductive material and the second conductive material are each electrode for an electrochemical device having an average diameter of 1 to 100 nm.
The method of claim 12,
The electrode active material layer has a thickness of 0.1 to 10 µm.
anode;
cathode; And
Including an electrolyte positioned between the positive electrode and the negative electrode,
At least one of the positive and negative electrodes is an electrochemical device for an electrochemical device according to claim 12.
The method of claim 14,
An electrochemical device is an aqueous secondary metal ion battery, a lithium secondary battery, a sodium secondary battery, or an electrochemical device that is a super capacitor.

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