WO2020045853A1 - Aqueous electrolyte and pseudocapacitor comprising same - Google Patents

Abstract

The present invention relates to an aqueous electrolyte for a pseudocapacitor and a pesudocapacitor comprising same and, more specifically, to an aqueous electrolyte for a pseudocapacitor and a pseudocapacitor comprising the aqueous electrolyte, the aqueous electrolyte comprising: an aqueous solvent; a lithium salt, of which the concentration is not less than a predetermined concentration; and a zwitterionic compound.

Description

Aqueous Electrolyte and Pseudo Capacitors Comprising the Same

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0101953 dated August 29, 2018 and Korean Patent Application No. 10-2019-0097202 dated August 9, 2019. All content disclosed in the literature is included as part of this specification.

The present invention relates to an aqueous electrolyte for a pseudo capacitor comprising a lithium salt and an amphoteric ionic compound of a certain concentration or more, and a pseudo capacitor including the aqueous electrolyte, in order to improve the low temperature stability of the electrolyte.

The next generation energy storage systems that have been recently developed are all based on electrochemical principles, such as lithium (Li) secondary batteries and electrochemical capacitors. Secondary batteries are excellent in terms of the amount of energy (energy density) that can be accumulated per unit weight or volume, but there is still much room for improvement in terms of the period of use, charging time, and the amount of energy (output density) that can be used per unit time. .

However, although the electrochemical capacitor is smaller than the secondary battery in terms of energy density, the electrochemical capacitor is very superior to the secondary battery in terms of use time, charging time, and output density. Therefore, in the case of electrochemical capacitors, research and development are being actively conducted to improve energy density.

In particular, supercapacitors are energy storage power source devices that have inherent performance characteristics in areas that conventional electrolytic capacitors and new secondary batteries do not have. These supercapacitors are electrical double layer capacitors (EDLC) using the principle of electrical double layer and pseudocapacitors using the principle of electrochemical faradaic reaction according to the electrochemical storage mechanism. Are distinguished.

The electric double layer capacitor uses ions of the electrolyte solution to be physically adsorbed and desorbed while forming an electric double layer on the electrode surface. The electric double layer capacitor exhibits excellent power density due to the development of pores on the carbon surface used as the electrode. However, since charges are accumulated only on the surface of the electrical double layer, there is a disadvantage in that the energy density is lower because the storage capacity is lower than that of the metal oxide-based or electrically conductive polymer-based supercapacitor using the Faraday reaction.

Metal oxide-based supercapacitors using pseudo capacitors are capacitors using metal oxides having several valences that can be oxidized and reduced. The reason why it is called a pseudo capacitor is that the characteristics of the capacitor are generally due to the formation of the electric double layer like the electric double layer capacitor, and the characteristics of the capacitor are shown in some metal oxides instead of the characteristics of the battery even though the characteristics of the capacitor are hard to come out by the electrochemical reaction. to be. The supercapacitor of the metal oxide electrode using such a pseudo capacitor has a higher specific capacitance than the electric double layer capacitor because the supercapacitor exhibits an accumulation mechanism in which protons move by oxidation and reduction of the metal oxide. In addition, the electrode active material of the metal oxide-based supercapacitor is required to have a high specific surface area, and the electrode active material has a high specific surface area because the ions and electrons required for oxidation and reduction during charge and discharge must move at a high speed in the electrolyte and the electrode. Conductivity is required.

In general, electrolytes used in capacitors are classified into aqueous electrolytes, non-aqueous electrolytes, and solid electrolytes. Non-aqueous electrolytes generally have a higher viscosity than aqueous electrolytes and have conductivity as low as 1/10 to 1/100 times. Therefore, when the aqueous electrolyte is used, the internal resistance of the electrolyte is reduced and the output characteristics of the capacitor are improved. However, since the freezing point of the electrolyte (melting point) of the electrolyte is relatively higher than that of the non-aqueous electrolyte, the electrolyte may freeze when exposed to a low temperature environment, there is a problem that the utilization range is significantly reduced.

[Preceding technical literature]

[Patent Documents]

Republic of Korea Patent Publication No. 2014-0081276 (2014.07.01), "Lithium ion capacitor"

In order to solve the above-mentioned problems, the inventors of the present invention, after conducting various studies to improve the low temperature stability of the pseudo capacitor, add a lithium salt and an amphoteric ionic compound of a certain concentration to the aqueous electrolyte of the capacitor, The present invention was completed by confirming that stable operation of the capacitor is possible without the electrolyte being frozen.

Accordingly, an object of the present invention is to provide an aqueous electrolyte for pseudo capacitors with improved low temperature stability.

In addition, an object of the present invention is to provide a pseudo capacitor having excellent cryogenic stability and excellent charge and discharge efficiency, energy density and power density including the aqueous electrolyte.

In order to achieve the above object, the present invention,

An aqueous electrolyte for a pseudo capacitor comprising an aqueous solvent, a lithium salt, and an amphoteric ionic compound is provided.

One embodiment of the present invention is that the aqueous solvent is at least one selected from the group consisting of ultra pure water (DI water), 2-butoxy ethanol and isopropyl alcohol (iso-propyl alcohol).

One embodiment of the present invention is that the zwitterionic compound is a quaternary ammonium alkyl carboxylate compound represented by the following formula (1).

[Formula 1]

(Wherein R ₁ to R ₃ are each independently the same or different linear or branched alkyl groups)

One embodiment of the present invention is that the zwitterionic compound is betaine (betaine) represented by the following formula (2).

[Formula 2]

In one embodiment of the present invention, the lithium salt and the zwitterionic compound are each included in a concentration of 1 to 10 mol (m).

In one embodiment of the present invention, the lithium salt and the zwitterionic compound are each included in a concentration of 3 to 10 mol (m).

In one embodiment of the present invention, the lithium salt and the zwitterionic compound are included in a ratio of 9: 1 to 1: 9.

One embodiment of the present invention is that the lithium salt and the zwitterionic compound is contained in a ratio of 2: 1 to 1: 2.

One embodiment of the present invention is that the lithium salt is contained in 6 mol (m) concentration, the zwitterionic compound is contained in a concentration of 3 to 10 mol (m).

One embodiment of the invention is made by any one of the lithium salt is _{Li (OH), Li 2 O} , LiCO 3, LiNO 3, Li 2 SO 4, LiNO 3 , and CH ₃ COOLi.

One embodiment of the present invention is that the melting point of the electrolyte is -30 ℃ or less.

In addition, the present invention,

anode; cathode; And

Provided is a pseudo capacitor comprising the electrolyte described above.

According to the present invention, by including a lithium salt and an amphoteric ionic compound of a certain concentration or more in the aqueous electrolyte, it is possible to improve the freezing problem of the electrolyte in the cryogenic environment, the specific capacitance, charge and discharge efficiency, energy density of the pseudo capacitor comprising the same And the output density can be greatly improved.

FIG. 1 shows a Ragone Plot in which an electrolyte according to Example 2 of the present invention is measured by three electrodes with respect to LiMn ₂ O ₄ (anode).

FIG. 2 shows discharge capacities of three electrodes measured on LiMn ₂ O ₄ (anode) of the electrolyte according to Example 2 of the present invention.

FIG. 3 shows specific capacitance, energy density, and cyclic voltage current curve (CV curve) measured by three electrodes of an electrolyte according to Example 2 of LiMn ₂ O ₄ (anode).

4 is a two-electrode measured lifetime for a full-cell capacitor (on glassy carbon electrode) composed of an electrolyte, LiMn ₂ O ₄ (anode) and LiTi ₂ (PO ₄ ) ₃ (cathode) according to Example 2 of the present invention. It is characteristic.

FIG. 5 shows a Ragone Plot obtained by measuring an electrode according to Comparative Example 1 of the present invention with respect to LiMn ₂ O ₄ (anode).

FIG. 6 shows discharge capacities of three electrodes measured for LiMn ₂ O ₄ (anode) of an electrolyte according to Comparative Example 1 of the present invention.

FIG. 7 shows specific capacitance, energy density, and cyclic voltage current curve (CV curve) measured by three electrodes of an electrolyte according to Comparative Example 1 of the present invention with respect to LiMn ₂ O ₄ (anode).

FIG. 8 illustrates a Ragone Plot obtained by measuring an electrode according to Comparative Example 2 of the present invention with respect to LiMn ₂ O ₄ (anode).

9 shows discharge capacities of three electrolytes of LiMn ₂ O ₄ (anode) of an electrolyte according to Comparative Example 2 of the present invention.

FIG. 10 shows specific capacitance, energy density, and cyclic voltage current curve (CV curve) of three electrodes measured with respect to LiMn ₂ O ₄ (anode) of an electrolyte according to Comparative Example 2 of the present invention.

Figure 11 shows the image of the cryogenic freezing experiment results of the electrolyte according to Comparative Example 2 of the present invention.

FIG. 12 shows a cyclic voltage current curve (CV curve) obtained by measuring three electrodes with respect to LiMn ₂ O ₄ (anode) according to Examples 1 to 4 of the present invention under 10 mV / sec.

FIG. 13 shows a cyclic voltammogram (CV curve) of three electrodes measured for LiMn ₂ O ₄ (anode) of an electrolyte according to Comparative Examples 3 to 5 of the present invention under 10 mV / sec.

14 is a cyclic voltage current curve (CV curve) of three electrolytes measured at 1 mV / sec with respect to LiMn ₂ O ₄ (anode) of an electrolyte according to Examples 1 to 4 and Comparative Examples 3 to 5 of the present invention. It is shown.

FIG. 15 shows a cyclic voltage current curve (CV curve) of three electrolytes of LiMn ₂ O ₄ (anode) according to Comparative Examples 3 to 5 of the present invention under 1 mV / sec.

Hereinafter, with reference to the accompanying drawings to be easily carried out by those skilled in the art will be described in detail. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the scope of the present invention.

The terms or words used in this specification and claims are not to be construed as being limited to the common or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meanings and concepts corresponding to the technical idea of the present invention based on the principle that the present invention.

The present invention provides an aqueous electrolyte containing an aqueous solvent, a lithium salt, and an amphoteric ionic compound as an aqueous electrolyte for a pseudo capacitor.

Hereinafter, the present invention will be described in detail.

The aqueous electrolyte according to the present invention includes an aqueous solvent as an electrolyte, and further includes a lithium salt and an amphoteric ionic compound to prevent freezing of the electrolyte in a cryogenic environment, thereby providing stable driving of the pseudo capacitor including the electrolyte. Make it possible. Therefore, the capacitor including the electrolyte including the aqueous solvent, the lithium salt and the zwitterionic compound can improve the low temperature stability and exhibit excellent charge and discharge efficiency, energy density and output density.

The aqueous solvent is not particularly limited, but at least one of ultrapure water (DI water), 2-butoxy ethanol, and isopropyl alcohol may be used.

As the lithium salt. If you are not particularly limited to a lithium salt which can be applied to pseudo-capacitors can be used without _{limitation, Li (OH), Li 2} O, LiCO 3, LiNO 3, Li 2 SO 4, LiNO 3 , and CH _It may be any one of ₃ COOLi, preferably LiNO ₃ .

The zwitterionic compound is a compound that is electrically positive and negative at the same time and is neutral in the compound, and is commonly referred to as 'zwitterion'.

The amphoteric ionic compound according to the present invention may be a quaternary ammonium alkyl carboxylate compound represented by the following formula (1).

[Formula 1]

(Wherein R ₁ to R ₃ are each independently the same or different linear or branched alkyl groups)

The compound represented by Chemical Formula 1 may be a compound that is generally neutral by forming a quaternary ammonium on one side and cationicity on the other side, and simultaneously having anionicity of the carboxylate.

The zwitterionic compound according to the present invention may be preferably betaine (betaine) represented by the following formula (2) wherein R ¹ to R ³ are all methyl (-CH ₃ ).

[Formula 2]

In the case of betaine, the portion containing quaternary ammonium shows cationicity, and the portion containing carboxylate group shows anionicity at the same time, corresponding to 'zwitterion' showing neutrality on the basis of all betaine molecules.

In order to improve the cryogenic stability of the aqueous electrolyte according to the present invention, the lithium salt and the zwitterionic compound may be included in a concentration of 1 to 10 mol (m), preferably 3 to 10 mol (m) based on the aqueous electrolyte It may be included in a concentration, more preferably may be included in a concentration of 3 to 6 mol (m). In addition, one embodiment of the present invention is that the lithium salt is contained in a concentration of 6 mol (m) based on the aqueous electrolyte, the zwitterionic compound is included in a concentration of 3 mol (m) based on the aqueous electrolyte. When the concentration of the lithium salt and the zwitterionic compound is less than the above range, low temperature stability may not be sufficiently secured, and if the concentration exceeds the range, the lithium salt and the zwitterionic compound may not be sufficiently dissolved in the electrolyte. It is preferable that the concentration of the lithium salt and the zwitterionic compound satisfy the above range.

In the case of betaine, which is an amphoteric ionic compound according to an embodiment of the present invention, one side of the charged beta is surrounded by a cluster of water molecules due to the structural characteristics of the betaine having a structure of zwitter ions, and thus surrounded by betaine The water molecule clusters are reduced in bonding strength with each other, so that the structure of the so-called 'water cluster in salt' has the effect of preventing the freezing of the aqueous electrolyte even in cryogenic environments. Herein, the structure of 'water in salt' refers to the principle that the excess salt is added to the electrolyte, thereby preventing the freezing of the water by interfering with the bonds between the water molecules, thereby reducing the activity of the water and inhibiting the decomposition of the water. It is possible to exhibit the effect of increasing the driving voltage range of the capacitor.

If the amount of the lithium salt is fixed, if the concentration of the zwitterionic compound is less than 1 mol (m) concentration, it may not surround the water molecule cluster sufficiently, the low temperature stability may decrease, and the concentration of 10 mol (m) If exceeded, it may not be sufficiently dissolved in the aqueous electrolyte, and in addition, the ionic conductivity of the aqueous electrolyte may decrease, so it is appropriately adjusted within the above range.

The lithium salt and the zwitterionic compound may be included in a molar (m) concentration ratio of 9: 1 to 1: 9, preferably in a molar ratio (m) of 2: 1 to 1: 2, More preferably, it may be included in a molar (m) concentration ratio of 2: 1 to 3: 5. According to one embodiment of the present invention, the lithium salt and the zwitterionic compound are included in a molar ratio of 2: 1.

If the ratio of the molal (m) concentration of the lithium salt and the zwitterionic compound exceeds the above range, there is a problem that the electrochemical performance of the capacitor is greatly reduced, and the molal (m) concentration of the lithium salt and the zwitterionic compound If the ratio is less than the above range, there is a problem that the electrolyte can be frozen in the cryogenic environment, it is preferable that the ratio of the molar (m) concentration of the lithium salt and the zwitterionic compound satisfy the above range.

Since the aqueous electrolyte according to the present invention may prevent freezing of the aqueous electrolyte in a cryogenic environment, including the lithium salt and the zwitterionic compound of the same concentration and ratio, the melting point of the electrolyte may be -30 ℃ or less, Pseudo-capacitors also have the advantage of being able to drive stably in cryogenic environments below -30 ℃.

The pseudo capacitor according to the present invention may be composed of a first current collector, a first electrode, an electrolyte, a separator, a second electrode, a second current collector and a case, and include a first current collector, an electrolyte, a separator, a second current collector, and Since the case may use existing known techniques, detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the scope and contents of the present invention are not limited or interpreted by the following examples. In addition, if it is based on the disclosure of the present invention including the following examples, it will be apparent that those skilled in the art can easily carry out the present invention, the results of which are not specifically presented experimental results, these modifications and modifications are attached to the patent It goes without saying that it belongs to the claims.

Example 1 Preparation of Aqueous Electrolyte

Deionized water (DI Water) in a the LiNO ₃ (Junsei社) lithium salt relative to 50ml 6 molal (m) the concentration, the ampholytic ion compound is a beta _{(betaine, (CH 3) 3} N + CH 2 CO 2 -, Sigma -Aldrich Co., Ltd. was dissolved at a concentration of 3 mol (m), and stirred for 30 minutes to prepare an aqueous electrolyte for a pseudo capacitor.

Example 2 Preparation of Aqueous Electrolyte

Based on 50 ml of DI water, lithium salt LiNO ₃ (Junsei) and the zwitterionic compound betaine (CH ₃ ) ₃ N ⁺ CH ₂ CO ₂ ^- and Sigma-Aldrich) were each used. An aqueous electrolyte for pseudocapacitors was prepared by dissolving at a molar (m) concentration and stirring for 30 minutes.

Example 3 Preparation of Aqueous Electrolyte

Deionized water (DI Water) in a the LiNO ₃ (Junsei社) lithium salt relative to 50ml 6 molal (m) the concentration, the ampholytic ion compound is a beta _{(betaine, (CH 3) 3} N + CH 2 CO 2 -, Sigma -Aldrich Co., Ltd. was dissolved at a concentration of 10 mol (m) and stirred for 30 minutes to prepare an aqueous electrolyte for a pseudo capacitor.

Example 4 Preparation of Aqueous Electrolyte

Deionized water (DI Water) in a the LiNO ₃ (Junsei社) lithium salt relative to the 50ml 3 molal (m) the concentration, the ampholytic ion compound is a beta _{(betaine, (CH 3) 3} N + CH 2 CO 2 -, Sigma -Aldrich Co., Ltd. was dissolved at a concentration of 6 molal (m) and stirred for 30 minutes to prepare an aqueous electrolyte for a pseudo capacitor.

Comparative Example 1 Preparation of an Aqueous Electrolyte

Aqueous electrolyte for pseudocapacitors was prepared in the same manner as in Example 2, except that LiNO ₃ , a lithium salt, was set at a concentration of 2 mol (m) based on 50 ml of ultra pure water (DI Water).

Comparative Example 2 Preparation of an Aqueous Electrolyte

An aqueous electrolyte for pseudocapacitors was prepared, which did not contain an amphoteric ionic compound and contained only lithium salt LiNO ₃ having a concentration of 2 mol (m) based on 50 ml of ultra pure water (DI Water).

Comparative Example 3 Preparation of Aqueous Electrolyte

A zwitterion compound, beta _{(betaine, (CH 3) 3} N + CH 2 CO 2 -, Sigma-Aldrich社) and is in the same manner as in Example 1 except for using a substitute choline bicarbonate (Choline bicarbonate) An aqueous electrolyte for the pseudo capacitor was prepared.

Comparative Example 4 Preparation of an Aqueous Electrolyte

And it is in the same manner as in Example 1 except for using instead of to L- alanine (L-Alanine) ^- a zwitterion compound, beta (, Sigma-Aldrich社betaine, (CH 3) 3 N + CH 2 CO 2) To prepare an aqueous electrolyte for the pseudo capacitor.

Comparative Example 5 Preparation of Aqueous Electrolyte

The following L-histidine (L-Histidine) was dissolved in 1 molal (m) concentration instead of the zwitterionic compound betaine (CH ₃ ) ₃ N ⁺ CH ₂ CO ₂ ^- and Sigma-Aldrich Co., Ltd. Was prepared in the same manner as in Example 1 to prepare an aqueous electrolyte for a pseudo capacitor.

Table 1 summarizes the additives and the contents of the aqueous electrolyte for the pseudo capacitor.

	Aqueous Electrolyte Additive
	Ultrapure Water (DI Water, ml)	Lithium salt (LiNO 3 ) (molar (m) concentration)	Amphoteric ionic compounds	Molal (m) concentration
Example 1	50	6	Betaine 1	3
Example 2	50	6	Betaine 1	6
Example 3	50	6	Betaine 1	10
Example 4	50	3	Betaine 1	6
Comparative Example 1	50	2	Betaine 1	6
Comparative Example 2	50	2	-	-
Comparative Example 3	50	6	Choline Bicarbonate	3
Comparative Example 4	50	6	L-alanine	3
Comparative Example 5	50	6	L-histidine	One

(1: Betaine ^{_{(CH 3) 3 N + CH}} 2 CO 2 -)

Experimental Example 1 Evaluation of Electrochemical Characteristics of Pseudo Capacitors

After fabricating a three-electrode pseudo capacitor for the aqueous electrolytes of Examples 1 to 4 and Comparative Examples 1 to 5, cyclic voltammetry (VSP / VMP3, Bio-Logics, Inc.) was used as follows. Physical properties were measured by the method, and are shown in FIGS. 1 to 3, 5 to 10, 12 to 15, and Table 2. Measuring method is using the working electrode (LiMn ₂ O ₄ ) comprising a working electrode, a platinum plate counter electrode (Counter Electrode), Ag / AgCl reference electrode (Reference Electrode) using the Examples 1 to 4 and Comparative Example 1 It was measured according to different scanning rates in the aqueous electrolyte of 5 to 5.

(1) 3-electrode measurement

Cyclic voltammetry was used to measure the voltage under positive conditions of -0.2 to 1.1V, 10 mV / sec and 1 mV / sec for the positive electrode.

(2) 2 electrode measurement

LiMn ₂ O ₄ was used as the working electrode and LiTi ₂ (PO ₄ ) ₃ was used as the counter and reference electrode.

By cyclic voltammetry, the voltage was measured at 0.3 to 2.1 V and 10 mV / sec.

Measurements were made under charge / discharge conditions (constant current 1.398 mA, voltage 0.3-2.1 V) using the constant-current discharge method.

As for the aqueous electrolytes of Examples 1 to 4 and Comparative Examples 3 to 5, the results of the three-electrode measurement measured under the conditions of 10 mV / sec and 1 mV / sec are shown in Table 2 below.

	Discharge Capacity (F / g) 10mV / s	Discharge Energy (Wh / kg) 10mV / s	Discharge Capacity (F / g) 1mV / s	Discharge Energy (Wh / kg) 1mV / s
Example 1	314.82	108.80	340.60	121.85
Example 2	271.09	86.28	329.29	115.27
Example 3	270.21	83.09	319.86	110.98
Example 4	294.41	91.12	305.56	103.56
Comparative Example 3	337.43	99.78	475.02	84.74
Comparative Example 4	369.44	96.55	363.82	55.46
Comparative Example 5	300.95	80.11	198.81	23.55

The electrolytes according to Examples 1 to 4 were found to have excellent overall discharge capacity and energy density. In addition, when the electrolyte according to Example 2 was used, the lithium salt concentration (2 mol (m) concentration) is low, the comparative example of a high ratio (1: 3) of the mol mol (m) concentration of the lithium salt and the zwitterionic compound. It can be seen that it has an overall superior output density, discharge capacity, specific capacitance and energy density compared to 1. In addition, in Comparative Example 2, the electrolyte according to Example 2 in terms of output density, discharge capacity, specific capacitance and energy density. Although similar results were shown, but as described below, the freezing experiment at -30 ℃ as a result of the freezing of the aqueous electrolyte in the cryogenic environment (-30 ℃), the cryogenic driving characteristics were poor. Thus, it was found that the aqueous electrolytes of Comparative Examples 1 and 2 were not suitable as the aqueous electrolyte of the pseudo capacitor.

From this, it can be seen that when the ratio of the molal (m) concentration of the lithium salt and the zwitterionic compound is outside the ratio of the molal (m) concentration of 2: 1 to 1: 2, it is not suitable as an aqueous electrolyte of a pseudo capacitor. there was.

Meanwhile, Choline bicarbonate (Comparative Example 3), L-Alanine (L-Alanine, Comparative Example 4) and L-Histidine (Choline bicarbonate) having a similar structure to the compounds represented by Formulas 1 and 2 according to the present invention but having different structures It was found that the aqueous electrolytes of Comparative Examples 3 to 5 using L-Histidine, Comparative Example 5) were also not suitable as the aqueous electrolyte of the pseudo capacitor.

Specifically, in the case of Comparative Example 3, the discharge capacity appears to be high due to the redox peak generated due to the side reaction, but the energy density is relatively very low, so the electrochemical characteristics are poor, and lithium salt and choline bicarbonate are Precipitation occurred and it was found that it was not suitable as an aqueous electrolyte of a pseudo capacitor. In addition, Comparative Example 4 also showed a high discharge capacity, but relatively low energy density, the electrochemical properties were poor, it was found that it is not suitable as an aqueous electrolyte of a pseudo capacitor. In addition, in the case of Comparative Example 5, both the discharge capacity and the energy density is lower than the embodiment according to the present invention, in particular, L- histidine is low solubility in an aqueous solvent, so that it does not dissolve more than 1 molal (m) concentration, It was found that it is not suitable as an aqueous electrolyte of a capacitor.

Experimental Example 2 Evaluation of Cryogenic Driving Characteristics of Pseudocapacitors

Using a glassy carbon electrode, a cathode including LiMn ₂ O ₄ , a cathode including LiTi ₂ (PO ₄ ) ₃ and the aqueous electrolyte of Examples 2 and Comparative Examples 1 to 2 A pseudo capacitor was fabricated and the driving characteristics of the capacitor were evaluated in a cryogenic (-30 ° C.) environment.

Referring to FIG. 4, in the case of the pseudocapacitor including the aqueous electrolyte according to Example 2, it was confirmed that long-term life stability was maintained even in a cryogenic environment, whereas in Comparative Example 1, the aqueous electrolyte was not frozen in the cryogenic environment. Including the lithium salt (LiNO ₃ ) of the ratio relative to betaine it was found that the constant current measurement results are not very good as shown in Figures 5 and 6.

In Comparative Example 2, only the lithium salt (LiNO ₃ ) was included in the aqueous electrolyte, and only lithium salt (LiNO ₃ ) was used. It was confirmed that this was frozen. (Figure 11)

Experimental Example 3 Measurement and Evaluation of Ion Conductivity of an Aqueous Electrolyte

Ion conductivity of the aqueous electrolyte prepared in Examples 1 to 4 and Comparative Examples 1 to 5 was measured by an ion conductivity meter (Mettler Toledo, Inc.), and the results are shown in Table 3 below.

	Ion Conductivity (mS / cm)
Example 1	79.69
Example 2	43.09
Example 3	32.30
Example 4	17.89
Comparative Example 1	23.51
Comparative Example 2	108.4
Comparative Example 3	106.8
Comparative Example 4	85.14
Comparative Example 5	115.8

Referring to Table 3, in the case of the aqueous electrolyte prepared in Examples 1 to 4, although it contains a high content of lithium salt and amphoteric ionic compound, it can be seen that it shows excellent ionic conductivity.

Through the above Examples and Experimental Examples, by providing a pseudo capacitor using the aqueous electrolyte of the present invention, a pseudo capacitor having a greatly improved output density, discharge capacity, specific capacitance, ion conductivity, energy density and long-life life stability even in cryogenic environments It could be confirmed that it can be produced.

Claims (12)

1. An aqueous electrolyte for pseudo capacitors comprising an aqueous solvent, a lithium salt, and an amphoteric ionic compound.
2. The method of claim 1,

   The aqueous solvent is an aqueous electrolyte for pseudo capacitors, characterized in that at least one selected from the group consisting of ultra pure water (DI water), 2-butoxy ethanol (2-butoxy ethanol) and isopropyl alcohol (iso-propyl alcohol).
3. The method of claim 1,

   The amphoteric ionic compound is a quaternary ammonium alkyl carboxylate compound represented by the following formula (1).

   [Formula 1]

   

   (Wherein R ₁ to R ₃ are each independently the same or different linear or branched alkyl groups)
4. The method of claim 1,

   The zwitterionic compound is an aqueous electrolyte for a pseudo capacitor of betain (betaine) represented by the following formula (2).

   [Formula 2]

   
5. The method of claim 1,

   The lithium salt and the zwitterionic compound are each an aqueous electrolyte for a pseudo capacitor, characterized in that contained in a concentration of 1 to 10 mol (m).
6. The method of claim 1,

   The lithium salt and the zwitterionic compound are each an aqueous electrolyte for a pseudo capacitor, characterized in that it comprises a concentration of 3 to 10 mol (m).
7. The method of claim 6,

   The lithium salt and the zwitterionic compound is an aqueous electrolyte for a pseudo capacitor, characterized in that contained in a molar (m) concentration ratio of 9: 1 to 1: 9.
8. The method of claim 6,

   The lithium salt and the zwitterionic compound are aqueous electrolytes for pseudo capacitors, characterized in that contained in a molar (m) concentration ratio of 2: 1 to 1: 2.
9. The method of claim 1,

   The lithium salt is contained in a concentration of 6 mol (m), the amphoteric ionic compound is an aqueous electrolyte for a pseudo capacitor, characterized in that it is contained in a concentration of 3 to 10 mol (m).
10. The method of claim 1,

    The lithium salt is an aqueous electrolyte for a pseudo capacitor, characterized in that made of any one of Li (OH), Li ₂ O, LiCO ₃ , LiNO ₃ , Li ₂ SO ₄ , LiNO ₃ and CH ₃ COOLi.
11. The method of claim 1,

    The electrolyte is an aqueous electrolyte for a pseudo capacitor that has a melting point of -30 ° C or less.
12. anode; cathode; And

    A pseudo capacitor comprising the electrolyte according to claim 1.

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