WO2018217044A1 - Electrochemical device comprising carbon quantum dot ionic compound electrolyte - Google Patents

Abstract

The present invention relates to an electrochemical device comprising a carbon quantum dot ionic compound electrolyte and, more specifically, to an electrochemical device comprising a first electrode, a second electrode spaced from the first electrode, and an electrolyte filled between the first electrode and the second electrode, wherein the electrolyte comprises a carbon quantum dot ionic compound in the form of salts of metal cations and anions of graphene quantum dots having an average diameter within the range of 0.1-8 nanometers (nm) and having a surface charge of at most -20. The present invention provides an electrochemical device which not only allows an improvement in the reliability and performance of the device by improving selective ionic conduction with particular cations and inhibiting a side reaction caused by an electrolyte in the device, but also has drastically increased reliability, efficiency, and durability by applying, as the electrolyte, a carbon quantum dot ionic compound which can be applied as any of a liquid phase, a gel, and a solid phase and thus has high applicability.

Description

Electrochemical device containing carbon quantum dot ionic compound electrolyte

The present invention relates to an electrochemical device including a carbon quantum dot ion compound electrolyte, and more particularly, a first electrode; A second electrode spaced apart from the first electrode; In an electrochemical device including an electrolyte filled between the first electrode and the second electrode, the electrolyte has a graphene quantum dot anion and a metal having an average diameter of 2 to 12 nanometers (nm) and a surface charge of -20 or less An electrochemical device comprising a carbon quantum dot ionic compound in the form of a salt of a cation.

As the use of renewable energy increases rapidly, the necessity of improving the efficiency and reliability of electrochemical devices such as secondary batteries, electrochromic devices and dye-sensitized solar cells is increasing.

Electrolytes, on the other hand, form an ohmic contact between the electrode and the solution through the flow and exchange of ions in the solution, which is an essential component for the operation of the electrochemical device. The electrolyte does not directly participate in the oxidation / reduction reaction but supports the electrochemical reaction. Electrolytes may be classified into liquid electrolytes, ceramic electrolytes, inorganic solid electrolytes, and polymer electrolytes. Recently, there is a great interest in polymer electrolytes having processability, mechanical strength, and operating temperature suitable for electrochromic devices. However, the conventional electrochromic device has a problem in terms of stability because the counter electrode layer and the electrochromic layer are in contact with the electrolyte and thus the reversibility of insertion and desorption of ions (H ⁺ , Li ^+, etc.) is broken. Currently used liquid electrolytes have stability problems such as ignition, evaporation and leakage. On the other hand, solid electrolytes are still more stable than liquid electrolytes, but exhibit low ionic conductivity and have problems such as increased interfacial contact resistance and deterioration of devices.

Complex phenomena occur in electrolytes containing conductive salts. For example, when the concentration of salt increases, the conductivity increases, resulting in a decrease in the diffusion coefficient of the ions, resulting in lower ionic conductivity. In addition, it is difficult to secure the stability of the device due to side reactions with the electrode or other materials. In particular, the deterioration of electrochemical device reliability due to the low diffusion coefficient and transport rate of the metal cation is a problem, for example, in the case of lithium secondary batteries, there is a competition between lithium ions and ionic liquids. When the diffusion coefficient of lithium ions is lower than that of the cation constituting the ionic liquid, it is difficult for lithium ions to approach the surface of the electrode and lithium ions cannot be inserted into the electrode. Therefore, the electrochemical reaction does not occur. In addition, LiPF ₆ is mainly applied to lithium ion batteries that are currently used commercially, because LiPF ₆ has excellent overall physical properties such as ion mobility, ion pair dissociation, solubility, and SEI formation. However, LiPF6 has a problem of poor thermal stability and side reactions even in a small amount of water.In particular, when the temperature rises, the following side reactions accelerate the continuous decomposition of the electrolyte and induce the gas to inflate the battery and lead to explosion. There are side effects.

On the other hand, electrochromic device (ECD) refers to a device for changing the light transmission characteristics by changing the color of the electrochromic material by the electro-redox reaction in response to the application of an electric field, using the electrochromic device The most successful applications include a rearview mirror for cars that automatically adjusts the glare of the light at the rear at night, and a smart window, a window that can be automatically adjusted according to the light intensity. The smart window is changed to a darker color tone to reduce the amount of light when there is a large amount of insolation, and the energy saving efficiency is excellent by changing to a lighter color tone on a cloudy day. In addition, the development to be applied to the display, such as an electronic board (e-book), etc. is continuously made. An electrochromic device is similar to a battery component, and refers to a device in which an electrochromic layer (anode) / electrolyte (Li +, H +) / relative electrode layer (cathode) is thinned. Briefly explaining the principle of the electrochromic, it is colored when the cation and electrons such as Li + or H + are injected into the electrochromic layer (WxOy, MoxOy, etc.) as a reducing coloring material, and becomes transparent when released. On the contrary, the positive electrode layer (VxOy, NixOy, etc.), which is an oxide coloring material, is colored when the cations and electrons such as Li + and H + are released, and becomes transparent when injected.

The electrochromic layer constituting the electrochromic device is divided into a reducing coloring material and an oxidizing coloring material. The reducing coloring material is a material that is colored when obtaining electrons. On the contrary, the oxidative coloring material is a material that is colored when the electrons are lost, and examples thereof include nickel oxide and cobalt oxide. In addition, representative electrochromic materials include inorganic metal oxides such as V2O5, Ir (OH) x, NiOxHy, TiO2, and MoO3, PEDOT (poly-3,4-ethylenedioxythiophene), polypyrrole, polyaniline, polyazulene, polythiophene, poly There are conductive polymers such as pyridine, polyindole, polycarbazole, polyazine and polyquinone, and organic discoloring materials such as viologen, anthraquinone and phenocyazine. In order to improve the safety and color change efficiency of the electrochromic device, a method of directly attaching a color change material to a first electrode has been developed. In this case, an ion storage medium must be formed on the counter electrode and an electrolyte must be included between the two electrodes to complete the electric circuit of the electrochromic device. Therefore, in order to realize a high efficiency, high stability electrochromic device, it is necessary to improve the electrochemical properties of the electrolyte, the color change material, and the ion storage medium, and to improve the structure of the color change device. Tungsten oxide, which has been studied extensively as an electrochromic material, causes irreversible chemical reaction with lithium ions embedded in an electrochromic device, and lithium ions are trapped in each layer of the electrochromic device, thereby decomposing each layer of the electrochromic device. In addition, the characteristics of the electrochromic device are degraded due to the thin flake layer, and it is deformed into a material which can no longer be electrochromic or can cause the device to leak electrolyzed in a short time. NJ Dudney, J. Power Sources, 89 (2000) 17; G. Leftheriotis, S. Papaefthimiou, P. Yianoulis, Solar Energy Materials and Solar Cells, 83 (2004) 115).

Several attempts have been proposed to solve these problems. Recently, solvent-free hybrid electrolytes based on nanoscale organic / silica hybrid materials (NOHM) have been constructed with lithium salts [Nugent, J.L. et al, Adv. Mater., 2010, 22, 3677; Lu, Y. et al, J. Mater. Chem., 2012, 22, 4066]. The electrolyte has a uniformly dispersed nanoparticle core, to which the polyethylene glycol (PEG) chain is covalently bonded. This electrolyte is self-suspended to provide a homogeneous fluid, wherein the PEG oligomers simultaneously act as a suspension medium for the nanoparticle core and as an ion-conducting network for lithium ion transport. WO2010 / 083041 also discloses a NOHM based hybrid electrolyte comprising a polymer corona doped with a lithium salt, a polymer corona attached to an inorganic nanoparticle core. chaefer, J.L. et al. (J. Mater. Chem., 2011, 21, 10094) also covalently binds to dense brushes of oligo-PEG chains doped with lithium salts, in particular lithium bis (trifluoromethanesulfonimide). The disclosed Si02 nanoparticle hybrid electrolyte is disclosed. This electrolyte is made from polyethylene glycol dimethyl ether (PEGDME) and provides good ion conductivity. However, the negative ions of lithium salts move freely through the electrolyte, and two-thirds of the current is carried by the negative ions, resulting in high concentrations of polarization, thus causing internal resistance and voltage losses. In addition, Korean Patent Publication No. 10-2015-0004124 discloses a nanoparticulate organic hybrid material comprising inorganic nanoparticles covalently grafted with one or more anions of an organic sodium salt or an organic lithium salt through a linker group, Particulate hybrid materials are formula (I)

Nanoparticulate organic hybrid materials, which are characterized by having: Wherein Np represents an inorganic nanoparticle; L is a linker group selected from a C1-C6 alkylene group and a phenyl-C1-C4-alkylene group;

Is an anion of an organic sodium salt or an organic lithium salt; X + is sodium or lithium cation. In addition, Korean Patent Publication No. 10-2011-0003505 includes a material having an amide group, and a solvent having the following structure:

(Wherein X is an aryl group optionally having a substituent on a carbon atom, a nitrogen atom, an oxygen atom or an aryl ring, provided that R2 does not exist when X is a nitrogen atom and R1 and R2 when X is an oxygen atom) None is present, and when X is an aryl group, none of R1, R2 and R5 are present, R1 is a hydrogen atom or a carbon-based group, R2 is a hydrogen atom or a carbon-based group, R3 is a hydrogen atom or a carbon-based group; R4 and R5 are individually selected from hydrogen atoms or carbon-based groups, or R4 and R5 together form a carbon-based group to give a ring structure to the solvent; And a mixture of ionizable materials forming a solution with the solvent, an electrolyte characterized by solvating a polymer in the mixture.

However, the electrolyte for the conventional electrochromic device including the above-mentioned document has a problem that the discoloration material, the electrolyte, and the electrode are highly likely to deform if the voltage is increased to improve the transport rate as well as the transport rate is low because the amount of charge is not large. In some cases, solvent evaporation and solvent decomposition may occur. In addition, there is a problem that the organic-based electrolyte is weak durability.

In addition, the commercialized lithium ion battery is difficult to be used as a large-scale power storage device due to the scarcity of lithium resources and the resulting cost increase. In addition, dendrites formation of lithium metal in batteries has a problem of stability causing internal overheating and combustion. In order to solve this problem, studies are being conducted to use metal cations such as sodium (Na ⁺ ), potassium (K ⁺ ), and magnesium (Mg ^{2 +} ). However, due to the difficulty of electrode materials suitable for such metal cations, low ion conductivity and low energy density, it has not been commercialized yet. Therefore, there is no risk of explosion and ignition, and a new type of electrolyte for high performance electrochemical devices is required. In addition, the physical properties required for the electrolyte is required to be flame retardant, nonvolatile, non-toxic, etc. for safety during use and after disposal. For these materials, several classes of electrolytes have been studied as replacements for conventional liquid electrolytes with inorganic or organic properties. Typical materials used in the manufacture of polymers, polymer composites, hybrids, gels, ionic liquids, ceramics or solid electrolytes are derived from inorganic matrices such as β-alumina and nanoparticle oxides such as Nasicon and silicon dioxide. It may be a simple lithium halide with improved grain boundaries defects or sulfide glass in a SiS 2 + Li 2 S + Lil system. However, due to the low ion conductivity (10 ⁻⁴ S / cm) and low energy density of gels and solid electrolytes, they are not commercially available. For example, in the case of magnesium (Mg) secondary batteries, dendritic growths are not formed on the electrode surface during the charging / discharging process, and thus they are spotlighted as high energy density and high output next generation ion batteries. Incompatible with In addition, they are all brittle materials, causing stresses and possibly cracking in the electrolyte due to unavoidable volume changes in operation.

In order to obtain an electrolyte that is compliant with the change in volume, it is preferable to use an organic polymer mattress. Typical examples include polyethylene oxide, polypropylene oxide or polyethyleneimine and copolymers thereof. These materials are used in combination with suitable lithium salts such as lithium bis (trifluoromethane sulfonyl imide [Li (CF3S02) 2N] and lithium tetrafluoroborate (LiBF4), referred to below as LiTFSI. The main disadvantage of the electrolyte is its ambipolar conductivity: When current is applied, both the anion and the cation are mobile such that about one third of the current through the electrolyte is carried by the cation and two thirds by the anion. This aspect is defined as t + = σ cation / σ cation + σ anion = D cation / D cation + D anion, where σ and D are the transport number t +, where conductivity and diffusion of each charge species is In most battery electrode systems, only positive ions react at the electrode, so electroneutrality accumulates salt around the anode, and salt near the cathode Since both overcondensed and depleted electrolytes have very low conductivity, the polarization of the cell increases significantly with decreasing power capacity. For example, US 5,569,560 discloses the use of an anionic complexing agent comprising a polyamine with a strong electron-removing unit CF3S02 attached to slow the anion, whereby lithium cations are used on a larger scale in electrochemical cells. However, the effect on the transport rate t + is negligible.In recent years, solvent-free hybrid electrolytes based on nanoscale organic / silica hybrid materials (NOHM) have been developed with lithium salts. Nugent, JL et al, Adv. Mater., 2010, 22, 3677; Lu, Y. et al, J. Mater. Chem., 2012, 22, 4066. mouth It has a purple core, and covalently bonded polyethylene glycol (PEG) chain to the particle. This electrolyte is self-suspended to provide a homogeneous fluid, wherein the PEG oligomers simultaneously act as a suspension medium for the nanoparticle core and as an ion-conducting network for lithium ion transport. WO2010 / 083041 also discloses a NOHM based hybrid electrolyte comprising a polymer corona doped with a lithium salt, a polymer corona attached to an inorganic nanoparticle core. Chaefer, J. L. et al. (J. Mater. Chem., 2011, 21, 10094) also covalently binds to dense brushes of oligo-PEG chains doped with lithium salts, in particular lithium bis (trifluoromethanesulfonimide). The disclosed Si02 nanoparticle hybrid electrolyte is disclosed. This electrolyte is made from polyethylene glycol dimethyl ether (PEGDME) and provides good ion conductivity. However, the negative ions of lithium salts move freely through the electrolyte, and two-thirds of the current is carried by the negative ions, resulting in high concentrations of polarization, thus causing internal resistance and voltage losses.

Accordingly, the technical problem to be achieved by the present invention is to form an electrochemical device and to cause side reactions with the electrode material constituting the electrode in which the reversible electrochemical redox reaction occurs, thereby causing decomposition of the material or deformation of the ionic salt. As a result, it is possible to prevent electrochemical device stability and performance deterioration, to improve electrochemical durability, and to provide an electrochemical device capable of increasing the efficiency and performance of the electrochemical device.

In order to achieve the above technical problem, the present invention and the first electrode; A second electrode spaced apart from the first electrode; In an electrochemical device in which an electrolyte is filled between the first electrode and the second electrode, and a reversible electrochemical redox reaction occurs at at least one electrode of the first electrode and the second electrode, the electrolyte has an average diameter of 2 The present invention provides an electrochemical device comprising a carbon quantum dot ionic compound in the form of a salt of a carbon quantum dot anion and a metal cation having a surface potential of -20 mV or less in a range of 12 nanometers (nm).

In addition, the present invention is an electrochemical device, characterized in that the metal is at least one selected from the group consisting of Li, Na, K, Mg and Zn.

In addition, the present invention provides an electrochemical device, characterized in that the electrochemical device is one selected from the group consisting of a secondary battery, a solar cell, an electrochromic device and an electroluminescent device.

In addition, the present invention provides an electrochemical device, characterized in that the secondary battery is a lithium ion battery or a lithium polymer battery.

In the present invention, the dissociation energy of the anion and the cation is very small, and thus the ion conductivity is improved, and the movement speed of the anion is relatively slow compared to the metal cation. Since the polarization is large and the anion's thermochemical / electrochemical stability is high, no side reactions occur during device driving, thereby improving selective ion conductivity with specific cations and suppressing side reactions by electrolytes in the device, thereby improving reliability and performance of the device. In addition to the liquid, gel, and solid phase, it is applicable to all of the liquid phase, it is possible to provide an electrochemical device that can significantly increase the reliability, efficiency and durability of the device by applying a carbon quantum dot ionic compound having high application as an electrolyte.

1 is a schematic diagram of an electrochromic device as an example of an electrochemical device according to the present invention

Figure 2 (a) is a schematic diagram for understanding the electron micrograph and structure of the carbon quantum dot ionic compound applied to the electrochemical device of the present invention, (b) is a graph showing the absorption and emission region of the carbon quantum dot ionic compound

[Correction under Article 91 of the Rule 17.07.2018]
FIG. 3 shows various ferricyanide concentrations under a three-electrode system consisting of a working electrode, a platinum (Pt) counter electrode, and a reference electrode (Ag / AgCl) including a discoloring material in an aqueous solution containing a carbon quantum dot ionic compound according to one embodiment of the present invention. Cyclic Voltammetry (CV) Measurement Results

4 (a) shows the results of performing cyclic voltammetry (CV) at a scan rate of 0.02 V / s under the three-electrode system of the present invention in which Prussian blue is coated on a working electrode. And (b) measuring the current change while varying the scan rate.

FIG. 5 is an electrochemical impedance spectroscopy of the electrochemical devices of Example 1 and Comparative Example 1 measured by changing metal cations in carbon quantum dot ionic compounds under three-electrode system conditions.

6 is -0.16 for an electrochromic device at 700 nm while generating a color change reaction by applying a pulse voltage of 1.2 V (colored state) to -2.2 V (colored state) with a pulse width of 10 seconds in an embodiment of the present invention. Transmittance and current change rate due to voltage switching between V (discolored state) and +0.4 V (colored state)

Figure 7 (a) is the result of testing the durability of each electrolyte in the electrochromic device as an example of the electrochemical device prepared in Examples and Comparative Examples according to the present invention and (b) is the durability of the carbon quantum anion-potassium cation electrolyte Test result

8 is a result of measuring the change in transmittance according to the voltage switching of the electrochromic device in one embodiment according to the present invention, the insertion degree is a color / color photo according to the electrochromic device transmittance

9 is a light emission intensity measurement results according to the carbon quantum dot ion compound concentration under the two-electrode system conditions for the electroluminescent device in one embodiment according to the present invention

10 is a lithium secondary battery charge / discharge test results applied carbon quantum dot ion compound in one embodiment according to the present invention

Figure 11 (a) to (c) is the concentration of the carbon quantum anion-lithium cation ion compound electrolyte prepared according to the present invention (0.125, 0.25, 0.5 and 0.5M, respectively) and (d) is 1.1M LiPF6 for contrast Cyclic voltammetry measurement results using electrolyte

12 (a) shows the results of cycling test under the condition of the current density of 160mA / g in the embodiment of the present invention and (b) the change of the current density of each concentration

FIG. 13 (a) is a voltage-capacitance measurement result measured at an electrode of a lithium ion battery to which a carbon quantum dot ion compound electrolyte and a LiPF6 electrolyte of the present invention are applied in Example 5 of the present invention, and (b) is a voltage Differential results

14 is a result of measuring I0 and Iss (top) and R0 and Rss measurement (bottom) to calculate the charge transfer index of lithium ions as cations in a lithium ion battery, which is a kind of electrochemical device of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the present specification, the term 'electrochemical device' refers to a first electrode, a second electrode spaced apart from the first electrode, and to form an electrically opposite electrode, and an electrolyte is filled between the first electrode and the second electrode. The device refers to a device in which reversible electrochemical redox reaction occurs in at least one of the first electrode and the second electrode, and the term 'carbon quantum point' has an average diameter in the range of 2 to 12 nm and anion on the surface and / or the edge. Quantum dots in the form of graphite oxide having at least one or more oxygen functional groups and having a surface potential of-(minus) of 20 mV or less, or carbon quantum dot derivatives formed through polymerization with a polymerizable inducer and the quantum dots in the form of graphite oxide, Carbon quantum dot anion 'means a carbon quantum dot of the oxygen functionalized form anion.

Electrochemical device of the present invention, the first electrode; A second electrode spaced apart from the first electrode to form an electrically opposite electrode; An electrolyte filled between the first electrode and the second electrode, wherein the reversible electrochemical redox reaction occurs at at least one of the first electrode and the second electrode, the electrolyte has an average diameter of 0.1 And a carbon quantum dot ionic compound in the form of a salt of a carbon quantum dot anion and a metal cation having a range of from 8 nanometers (nm) and a surface charge of-(minus) of 20 mV or less.

The electrochemical device of the present invention includes a first electrode and a second electrode spaced apart from the first electrode to form an electrically opposite electrode. In the present invention, the first electrode may be a working electorde or an anode, and the second electrode forming an electrically opposite electrode may be a counter electorde or a cathode. At least one electrode of the first electrode or the second electrode is accompanied by a reversible electrochemical redox reaction.

Carbon quantum anion in the present invention has a polyanionic (A ^n- ) form, the inside is an aromatic structure, and has oxygen functional groups on the surface and edge. The carbon quantum dot anion is combined with a metal cation to produce a salt type ionic compound. Figure 2 (a) is a schematic diagram for understanding the electron micrograph and structure of the carbon quantum dot ionic compound applied to the electrochemical device of the present invention, (b) is a graph of the absorption and emission region of the carbon quantum dot ionic compound. Carbon quantum dot ionic compounds as shown in Figure 2 can be expected the following characteristics. 1) Due to the surface negative charges, ionic bonds with various metal cations such as alkali metals, alkaline earth metals and transition metals are possible, and 2) large size and large surface charges, which have a large polarity and lattice energy. 3) Delocalization of the electron cloud is large due to resonance of the internal structure. In addition, 4) it is a macromolecular anion, so there is almost no mass transport in the solution, and 5) there is no side reaction at the electrode interface due to electrochemical / thermal stability, thereby improving device driving reliability. . The carbon quantum dot ionic compound of the present invention is not only easy to disperse in aqueous solutions and non-aqueous solvents, but also relatively free of mixing with organic solvents having low viscosity, low volatility, and high permittivity. This enables the implementation of a liquid electrolyte with high ionic conductivity.

In the present invention, the metal cation in the carbon quantum dot ionic compound may be an alkali metal, an alkaline earth metal or a transition metal, for example, Li, Na, K, Mg or Zn. The carbon quantum dot ionic compound can be used in liquid, gel, solid form, it is possible to adjust the appropriate content according to the form.

The carbon quantum dot ion compound electrolyte applied to the electrochemical device of the present invention has at least one oxygen functional group having an average diameter in the range of 2 to 12 nm, more preferably in the range of 5 to 8 nm, and which may be an anion on the surface and / or the edge. It is preferable that it is an ionic compound of a carbon quantum point anion and a metal cation having a surface potential of -20 mV or less. If the average diameter of the carbon quantum point is less than 2nm, the carbon quantum point anion is moved to the anode by the potential formed on the electrode of the electrochemical device. This decreases the t ₊ (ion transport number), resulting in a decrease in the efficiency of the electrochromic device, and also reduces the lattice energy of the carbon quantum dots, resulting in a decrease in ion conductivity. On the other hand, if the average diameter of carbon quantum dots is 12 nm or more, the π-π interaction between the carbon quantum dots increases, which may cause agglomeration between carbon quantum dots in the electrochromic device, which may cause crystallization and degrade the reliability of the device to be.

The carbon quantum dot ionic compound electrolyte applied to the electrochemical device of the present invention may be dissolved in an aqueous solvent (methanol, ethanol), a non-aqueous solvent (acetonitrile, dimethyl carbonate, ethylene carbonate), and an aqueous solution, and used in a liquid phase. It can be used in the form of a gel by dispersing in an appropriate dispersion medium / matrix according to. The present applicant has filed a patent application regarding the properties of the carbon quantum dot ionic compound electrolyte and its manufacturing method through Korean Patent Application No. 10-2017-0064227 with respect to the carbon quantum dot ionic compound electrolyte described above. Details of the present invention may be referred to the applicant's patent application, which will not be described in detail herein.

1 is a schematic diagram of an electrochromic device which is one example of electrochemical devices according to the present invention. As can be seen in Figure 1, the electrochemical device of the present invention comprises a first electrode (working electrode); A second electrode (relative electrode) spaced apart from the first electrode; It includes an electrolyte filled between the first electrode and the second electrode, and further includes a reference electrode due to the characteristics of the device. In an embodiment of the present invention, an electrochromic device is used as an example of an electrochemical device, but the electrochemical device of the present invention is not limited to an electrochromic device, and is a work electrode such as an electrochemical light emitting device, a secondary battery, or a solar cell. This applies to all electrochemical devices with reversible electrochemical redox reactions at the (material) or anode (cathode).

Due to the low diffusion coefficient and transport rate of the conventional electrolyte metal cation, the reliability and performance of the electrochemical device is degraded. For example, when the diffusion coefficient of the metal cation in the electrochromic device or the like is lower than that of the cation constituting the ionic liquid, the cation cannot be inserted into the color change material. Therefore, the color change material is difficult to maintain an electrically neutral state, the color change efficiency is degraded or the decomposition of the material occurs, the electrochromic device reliability and performance is reduced. The electric field is formed by the voltage applied in the electrochromic device, which causes the electrolyte anions to move along the direction of the electric field. At this time, the negative ions cause chemical reactions with the discoloring material and the electrode, thereby reducing the reliability and performance of the electrochromic device. In the case of a two-electrode electrochromic device having a sandwich form, a material capable of performing an oxidation / reduction reaction should be included. Otherwise, charge imbalance occurs on both electrode interfaces, thereby degrading the reliability and performance of the electrochromic device. In the electrochemical device according to the present invention, among the electrochromic devices, by applying a carbon quantum dot ion compound as an electrolyte, the above-described side reactions can be suppressed to increase the reliability and durability of the electrochemical device, as well as the electrode and electrolyte (quality). By controlling the inter-charge imbalance, the efficiency of the electrochromic device can be improved by increasing the conversion efficiency between electric energy and chemical energy.

The present invention will be described in more detail with reference to the following examples. However, the following examples are intended to assist in understanding the present invention, and the scope of the present invention is not limited thereto.

Example 1 (Manufacture of an electrochromic device including a carbon quantum dot electrolyte)

A color change material is formed by using a conductive transparent substrate in an aqueous solution containing 0.05 M HCl, 0.05 MK ₃ Fe (CN) ₆ , and 0.05 M FeCl ₃ 6H ₂ O. At this time, the thickness of the discolored material is controlled by controlling the current and time by using a time-potential potentiation method (chronopotentiometry). In the present invention, a color change material was formed on the working electrode for 40 uA and 140 s. Subsequently, the conductive transparent substrate was immersed in 5 mM ZnCl ₂ , 0.1 M KCl, and oxygen-saturated aqueous solution, and then ZnO buffer layer was formed for 1000 s while applying −1 V at room temperature. Subsequently, the transparent electrode in which the ZnO buffer layer was continuously formed was immersed in 0.5 mM ZnCl ₂ , 0.1 M KCl, and saturated oxygen solution, and then ZnO NWs layer (nanowire layer) was applied at 80 ° C. and 1000 s while applying -1 V. Formed. This was used as a counter electrode. The working electrode and the counter electrode were attached in the form of a sandwich using a thermal tape. At this time, the distance between the two electrodes is 60um. Subsequently, a carbon quantum dot ionic compound having a concentration of 0.5 M was charged with Li, Na and K, respectively, through the fine pores formed in the counter electrode. At this time, the pH of the aqueous electrolyte solution was adjusted to 4.

Comparative Example 1 (Manufacture of Electrochromic Device Including Potassium Chloride Electrolyte)

An electrochromic device was manufactured in the same manner as in Example 1, except that 0.5 M potassium chloride (KCl) was used as the electrolyte.

The electrochemical properties of each of the electrochromic devices prepared in Example 1 and Comparative Example 1 were compared. FIG. 3 (a) shows a first electrode (working electrode), a platinum (Pt) second electrode (relative electrode) and a reference electrode containing a color change material in an aqueous solution containing a carbon quantum dot ionic compound in Example 1 of the present invention. The structure of the three-electrode electrochemical cell composed of Ag / AgCl) and 3 (b) are the results of cyclic voltammetry measurements according to the concentration of Ferricyanide. 4 (a) shows cyclic voltammetry (CV) at a scanning speed of 0.02 V / s under the three-electrode system condition of the present invention in which Prussian blue is coated on a working electrode. And (b) the change of current while measuring the scan speed. The characteristics of the electrochromic device were analyzed by applying voltage at -0.14 / 0.4 V and 10 s / 10 s (50% duty cycle) by using a chronoamperometry method. As can be seen in Figure 4 (b), the electrochemical device of the present invention can be seen that the oxidation / reduction current value of the color change material corresponding thereto even if the scan speed is increased (oxidation current is a color reaction (color reaction, PB) and the reduction current shows a colorless reaction (PW). In addition, Table 1 below shows the diffusion rate value according to the metal cation of the carbon quantum dot ionic compound under the three-electrode system conditions.

In addition, Figure 5 is an electrochemical impedance spectroscopy graph measured in the three-electrode system, Table 2 summarizes the measured impedance measurement by the color reaction and color reaction using the cyclic current voltage method in the three-electrode system .

[Correction under Article 91 of the Rule 17.07.2018]
In addition, the durability of the electrochromic devices prepared in Example 1 and Comparative Example 1 was tested. Figure 7 (a) is the result of testing the durability of each electrolyte of the electrochromic device as an example of the electrochemical device prepared in Examples and Comparative Examples according to the present invention and (b) is a durability test of carbon quantum anion-potassium cation electrolyte The result is. As can be seen in Figure 7, in the case of the electrochromic device using a conventional KCl electrolyte, while the color change efficiency is reduced to less than the initial half level within 50 cycles (C-dot) -K + to the embodiment of the present invention For the electrochromic device used, it can be seen that the discoloration efficiency remains constant even after 1000 cycles. This means that the electrochromic device durability using the (C-dot) -K + electrolyte is excellent. Specifically, (1) means that the (C-dot) -K + ionic compound serves as an electrolyte, (2) the electrochemical durability of the (C-dot) -K + electrolyte is excellent, and (3) It means less electrochemical side reactions. The coloration efficiency (CE) is based on the change in absorbance from the amount of charge required for a chromogenic or discolored state (ΔOD (λ) = log T _b / T _c , T _b and T _c mean transmission values at 700 nm). Is determined by The discoloration efficiency values of 0.5 M KCl and (C-dot) ⁺ -K ^- electrolyte were measured as 81.6 cm ² C ^-1 and 103.0 cm ² C ^-1 , respectively. Therefore, compared with KCl electrolyte, electrochromic devices containing carbon quantum dot ionic compounds are relatively suppressed from side reactions, indicating that the electrochromic stability is increased and the discoloration efficiency is excellent due to the conversion efficiency between electrical energy and chemical energy.

In order to apply the actual electrochromic device system, sandwich type electrochromic device characteristics were evaluated. In the device test, the change in device transmittance at 700 nm was monitored according to the applied voltage change. The device generates a discoloration reaction by applying a pulse voltage of 1.2 V (colored state) to -2.2 V (colored state) with a pulse width of 10 seconds, and it can be observed that the repetitive and reversible changes (FIG. 6). . Theoretically, the sandwich type electrochromic device has a relatively high voltage charge injection due to the voltage drop phenomenon compared to the electrochromic device of the three-electrode system.

In addition, Figure 8 is a result of measuring the change in transmittance according to the voltage switching of the electrochromic device in Example 1 and Comparative Example 1 according to the present invention, the insertion degree is a color / color photo according to the electrochromic device transmittance. As can be seen in Figure 8, it can be seen that the electrochromic device according to the present invention is significantly superior to the case of using a conventional electrolyte in the color and bleaching reaction rate and efficiency.

Example 3 (electrochemical light emitting device)

(1) A thin film of TiO ₂ particles is formed on the surface of the cathode.

(2) In order to increase the conductivity and permeability of the TiO ₂ thin film, heat treatment is performed at 120 degrees for 10 minutes.

(3) The cathode in which the TiO ₂ thin film was formed was immersed in a solution in which the emitter was melted for 55 degrees 6 hours.

(4) After 6 hours, the surface of the cathode was washed with ethanol.

(5) The negative electrode and the positive electrode are attached using a thermal tape.

(6) The solution containing the light-emitting body and the electrolyte is injected through the hole formed in the anode.

(7) Seal the hole.

9 is a light emission intensity measurement result according to the carbon quantum dot ion compound concentration under the two-electrode system conditions for the electroluminescent device in one embodiment according to the present invention. As can be seen in Figure 9, as the carbon quantum point anion-metal cation ion compound concentration increases, the ionic conductivity is improved to reduce the resistance in the device and eventually increase the luminescence intensity.

Example 4 (lithium secondary battery)

FIG. 10 shows the results of measuring the specific capacitance measured after charging and discharging the carbon quantum anion-lithium metal cation ion compound electrolyte of the present invention instead of the LiPF ₆ electrolyte of the conventional secondary battery in a lithium secondary battery. The negative electrode of the battery was constructed using Li ₄ Ti ₅ O ₁₂ (active material), 10 wt% PVDF (binder), NMP (Solvent), and the positive electrode was graphite. In addition, the concentration of the carbon quantum point anion-lithium metal cation ion compound electrolyte was 0.5M. As can be seen in Figure 10, it was found that a stable charge / discharge cycle is observed in the secondary battery as an example of the electrochemical device of the present invention.

Example 5 (lithium secondary battery electrolyte evaluation)

Various experiments were performed on the lithium ion battery of Example 4 to check the characteristics of the electrolyte. First, the cyclic voltammetry was performed with varying concentrations of the electrolyte of the present invention. The results are summarized in FIG. 11 (a) to (c) are cyclic voltammetry measurements according to the concentrations (0.125, 0.25 and 0.5M, respectively) of the carbon quantum point anion-lithium cation ion compound electrolyte prepared according to the present invention, and (d) Is a cyclic voltammetry measurement using 1.1M LiPF6 electrolyte for contrast. As can be seen in Figure 11, the higher the electrolyte concentration (the higher the content) showed the same tendency as the charge-discharge data, it can be seen that the difference in electrochemical performance. The 0.25M sample showed unstable anodic region from 2.5 V or higher, while the 0.5M sample showed a slight anodic / cathodic peak, although slightly shifted from 1.6 V, which is the theoretical Li ion intercalation / deintercalation region of LTO. I could see that. Table 4 below shows the results of measuring polarization according to each concentration.

In addition, cycling was performed at various current densities of 80 to 400 mA / g in order to determine the rate characteristic of the electrolyte at each concentration, and the results are shown in FIG. 12. Figure 12 (a) is the result of the 0.5M concentration electrolyte, (b) is the result of measuring the cycle for each concentration. As can be seen in Figure 12, it can be seen that the rate characteristic of the relatively high concentration of 0.5M sample is the best, and when the average capacity for each current density is calculated, the capacity of 0.5 sample is the best at all current density Showed capacity. Table 5 summarizes the results.

	0.125	0.25	0.5
80 mA / g	193.47	194.28	194.33
160 mA / g	166.45	161.96	171.67
240mA / g	148.38	151.61	162
320 mA / g	121.36	134.46	149.33
400 mA / g	78.91	104.28	134.33

As can be seen from Table 5, especially when the current density of 320, 400 mA / g is the largest difference in the performance of each sample appears to be due to the concentration of the electrolyte, that is, the difference in the content of Li ion.

In addition, after the half cell system was constructed in the lithium ion battery of Example 4, the specific capacity change of the anode (Li) metal / electrolyte / graphite (cathode) battery system was observed while changing the voltage. In addition, for comparison, a lithium ion battery employing LiPF 6 as an electrolyte was prepared and the same observation was performed. FIG. 13 (a) is a voltage-capacitance measurement result measured at an electrode of a lithium ion battery to which a carbon quantum dot ionic compound electrolyte and a LiPF6 electrolyte of the present invention are applied, and (b) is a result of differentiating voltage. As shown in FIG. 13, when LiPF6 was used as an electrolyte, a reaction estimated to form SEI at 0.75 V was observed, but when using as a carbon-dots electrolyte, a reaction at 0.75 V was not observed, but at 0.5 V. The reaction was observed. This is estimated by graphite and Li reaction.

In addition, the ion mobility of lithium ions which are cations when the electrolyte of the present invention was used was measured. Formula 1 below is a formula for obtaining the ion mobility index of the cation. The formula has a number from 0 to 1, and the closer to 1, the higher the contribution of charge transfer by cation.

[Calculation 1]

Where t _C = Cation transference number, I _C = Current carried by cations, I _A = Current carried by anions

Equation 1 can be expressed as shown in Equation 2 below to measure the ion mobility index of Li ions.

[Calculation 2]

In equation 2, t _Li = Lithium transference number, V = Applied potential, R _O = Initial resistance of the passivation layer, R _SS = Resistance of the passivation layer, I _O = Initial current , I _SS = Steady state current.

Preparation Li metal / electrolyte cell of the symmetrical / Li metal, and an initial impedance measurement: We (frequency range 100 kHz-0.1Hz) R _O measurement, progress I _SS, I _O measure the DC polarization experiment at 0.05 mV, the back impedance It was measured to determine the R _SS . 14 and Table 6 summarize the results, and the result of using LiPF6 as the electrolyte in the same manner was measured as a comparative example.

As can be seen in Figure 14 and Table 6, the carbon quantum point anion-lithium cation ion compound electrolyte of the present invention was found to be 1.5 to 2 times higher charge transfer index by the cation than LiPF6. In general, when t _Li is small, the overall resistance of the cell due to concentration polarization of anions in the electrolyte is increased. The cation yield is influenced by the temperature, the concentration of salt in the electrolyte and the radius of the ions, and the high t _Li seen in the electrolyte of the present invention in the above experiments is due to the large anion radius of the carbon dot.

One embodiment of the present invention described above should not be construed as limiting the technical spirit of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can change and change the technical idea of the present invention in various forms. Therefore, such improvements and modifications will fall within the protection scope of the present invention, as will be apparent to those skilled in the art.

Claims (5)

1. A first electrode; A second electrode spaced apart from the first electrode; In the electrochemical device comprising an electrolyte filled between the first electrode and the second electrode, the reversible electrochemical redox reaction occurs at at least one electrode of the first electrode and the second electrode,

   The electrolyte is an electrochemical device comprising a carbon quantum dot ionic compound in the form of a salt of a carbon quantum dot anion and a metal cation having an average diameter of 0.1 to 8 nanometers (nm) and a surface charge of -20 mV or less.
2. The method of claim 1,

   The metal is an electrochemical device, characterized in that the alkali metal, alkaline earth metal or transition metal.
3. The method of claim 2,

   The metal is an electrochemical device, characterized in that at least one selected from the group consisting of Li, Na, K, Mg and Zn.
4. The method of claim 1,

   The electrochemical device is an electrochemical device, characterized in that the secondary battery, solar cell, electrochromic device or electroluminescent device.
5. The method of claim 4, wherein

   The secondary battery is an electrochemical device, characterized in that the lithium ion battery or lithium polymer battery.

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