KR20210033305A - Aqueous electrolyte and pseudocapacitor comprising the same - Google Patents

Abstract

The present invention relates to an aqueous electrolyte comprising a zinc salt in a molar concentration of 0.005 to 0.05, and to a lithium ion capacitor or a sodium ion capacitor including the same. By including the zinc salt, the voltage range of a negative electrode can be extended, thereby suppressing a water decomposition reaction.

Description

Aqueous electrolyte and water capacitor containing the same {AQUEOUS ELECTROLYTE AND PSEUDOCAPACITOR COMPRISING THE SAME}

The present invention relates to an aqueous electrolyte and a water capacitor including the same.

Due to the growing interest in the environment and energy, research on energy storage systems such as lithium secondary batteries and capacitors has been actively conducted. In particular, supercapacitors and lithium secondary batteries that can be applied to fields requiring high capacity and high output characteristics have recently attracted much attention.

A capacitor is a device that stores electricity by using an electrochemical mechanism generated by adsorption or desorption of ions in an electrolyte on the surface of an electrode, and uses a capacitance generated by applying a voltage between two electrodes in the electrolyte. These capacitors can be charged and discharged with a large current, exhibit high output, and have the advantage of being able to maintain the initial performance even after tens of thousands of times of charging and discharging. Super capacitors have higher capacitance than general capacitors, and are also called ultracapacitors.

These supercapacitors are an electric double layer capacitor (EDLC) using the principle of an electrical double layer according to an electrochemical storage mechanism, and a pseudocapacitor using the principle of an electrochemical Faraday reaction. It is distinguished.

The electric double layer capacitor uses physical adsorption and desorption of ions of an electrolyte solution while forming an electric double layer on the electrode surface, and shows excellent power density because pores are developed on the carbon surface used as an electrode. However, since charges are accumulated only in the electric double layer on the surface, there is a disadvantage in that the capacitance and energy density are lower than that of a water capacitor using a Faraday reaction.

The water capacitor is a capacitor that uses a material having several valences that can be oxidized or reduced as an electrode material. The reason why it is called a water capacitor is that the characteristic of a capacitor is generally formed by the formation of an electric double layer like an electric double layer capacitor, and it is difficult to obtain a capacitor characteristic by an electrochemical reaction.Some electrodes such as chemically modified carbon materials, metal oxides, and conductive polymers This is because the properties of the capacitor come out of the material instead of the properties of the battery. Specifically, an electrode material using a water capacitor exhibits an accumulation mechanism in which protons move through oxidation and reduction reactions, and thus has a higher capacitance than an electric double layer capacitor.

In general, various types of electrolytes such as aqueous electrolytes, non-aqueous electrolytes, and solid electrolytes are used for capacitors. The non-aqueous electrolyte generally has a higher viscosity than an aqueous electrolyte and has a conductivity of about 1/100 to 1/10 times lower than that of an aqueous electrolyte. In the case of using an aqueous electrolyte, as it exhibits high ionic conductivity, the internal resistance of the electrolyte is reduced, the output characteristics of the capacitor are improved, and stability is ensured. However, since aqueous electrolytes contain water, the operating voltage range is limited, and the freezing point (or freezing point) of the electrolyte is relatively higher than that of non-aqueous electrolytes, so when exposed to a low temperature environment, freezing of the electrolyte is difficult. There is a problem that can occur, and the scope of its use is considerably reduced.

In addition, in the aqueous electrolyte, a water decomposition reaction occurs in a certain voltage range, and in particular, there is a problem that the hydrogen generation reaction at the cathode occurs more violently than the oxygen generation at the anode. In order to solve this problem, the water-in-salt (WIS) method was applied as a method to widen the voltage range, but there was a limit in expressing high output due to a large decrease in ionic conductivity due to an excessive amount of salt.

Accordingly, there is a need for development of an aqueous electrolyte capable of expressing high output while solving the above problems.

Republic of Korea Patent Publication No. 10-2017-0094424

Accordingly, the present inventors conducted various studies to solve the above problem. As a result, when the aqueous electrolyte contains a zinc salt having a molal concentration of 0.005 to 0.05, water decomposition by expanding the voltage range of the negative electrode without affecting the ionic conductivity. The present invention was completed by confirming that the reaction can be suppressed and high output characteristics can be expressed.

Accordingly, an object of the present invention is to provide an aqueous electrolyte for a water capacitor that suppresses a water decomposition reaction.

In addition, an object of the present invention is to provide a water capacitor containing the aqueous electrolyte.

To achieve the above object,

The present invention is a eutectic solvent containing an amide compound and a lithium salt;

Methanesulfonate compounds;

Zinc salt; And

Including; an aqueous solvent,

The zinc salt provides an aqueous electrolyte for a water capacitor contained in a molal concentration of 0.005 to 0.05.

In addition, the present invention is a positive electrode; cathode; And a water capacitor comprising the aqueous electrolyte of the present invention,

The positive electrode active material of the positive electrode and the negative electrode active material of the negative electrode provide a water capacitor including a lithium compound or a sodium compound.

The aqueous electrolyte for a water capacitor of the present invention can expand the voltage range of the negative electrode as it contains a zinc salt, thereby suppressing the water decomposition reaction, and the zinc salt does not affect ionic conductivity. Can provide.

1 is a graph measuring a linear scanning potential method (Linear Sweep Voltammetry, LSV) of _{a positive electrode (LiMn 2} O ₄ ) and a negative electrode (LiTi ₂ (PO ₄ ) ₃ ) using the aqueous electrolyte of Example 1 and Comparative Example 1 to be.
2 is a graph measuring a linear scanning potential method (Linear Sweep Voltammetry, LSV) of _{a negative electrode (LiTi 2} (PO ₄ ) ₃ ) using the aqueous electrolytes of Examples 1, 2 and Comparative Example 2.
3 is a graph measuring a linear scanning potential method (Linear Sweep Voltammetry, LSV) of _{a negative electrode (LiTi 2} (PO ₄ ) ₃ ) using the aqueous electrolytes of Examples 1 and 3. FIG.
4 is a graph measuring cyclic voltammetry (CV) of _{a negative electrode (LiTi 2} (PO ₄ ) ₃ ) using the aqueous electrolyte of Example 1. FIG.
5 is a graph measuring cyclic voltammetry (CV) of _{a negative electrode (LiTi 2} (PO ₄ ) ₃ ) using the aqueous electrolyte of Comparative Example 1. FIG.
6 is a graph measuring the life characteristics of a coin cell using the aqueous electrolyte of Example 1. FIG.

Hereinafter, the present invention will be described in more detail.

The next-generation energy storage system being developed recently uses an electrochemical principle, and a super capacitor and a lithium secondary battery are typical. In particular, super capacitors exhibit high output in a short time, have long-term reliability, enable fast charging and discharging cycles, and use eco-friendly raw materials, so they are expected to be used as high-output power in various fields.

A non-aqueous organic electrolyte is mainly used for such a super capacitor. However, the non-aqueous organic electrolyte _{contains a salt such as expensive LiPF 6,} and the manufacturing process of the battery must be performed in a dry space without moisture, and the ionic conductivity of the non-aqueous organic electrolyte is relatively low, so high power is required. The use of furnace is limited. In addition, the non-aqueous organic electrolyte has a risk of ignition or explosion due to ignition or side reactions due to the use of an organic solvent, and this has been pointed out as a disadvantage in terms of safety. In particular, power and safety are required in the case of a power source for an electric vehicle. However, in the case of using a non-aqueous electrolyte containing an organic solvent, it is difficult to satisfy stability and reliability, and thus it has not been used.

Recently, in order to solve the above-described problem, research on a method of using an aqueous electrolyte in a super capacitor has been actively conducted. Aqueous electrolytes are obtained by dissolving a salt in an aqueous solvent such as water or alcohol, and not only ensure stability, but also have high ionic conductivity, and thus have excellent energy density and output characteristics. In addition, the aqueous electrolyte has an advantage in that the manufacturing process and manufacturing cost are inexpensive, and also in terms of environment.

However, in the case of an aqueous electrolyte, as the basic solvent includes an aqueous solvent, the operating voltage range is narrow, so that a water decomposition reaction occurs in a certain voltage range, and in particular, a hydrogen generation reaction occurs very violently at the cathode.

Accordingly, in the present invention, it is intended to provide an aqueous electrolyte for a water capacitor capable of suppressing the water decomposition reaction by expanding the operating voltage range and exhibiting high output characteristics.

That is, the present invention is a eutectic solvent containing an amide compound and a lithium salt; Methanesulfonate compounds; Zinc salt; And an aqueous solvent; and an aqueous electrolyte for a water capacitor, wherein the zinc salt is contained in a molar concentration (m) of 0.005 to 0.05.

The zinc salt is dissociated in the aqueous electrolyte and exists in the form of zinc ions, and the zinc ions expand the voltage range of the negative electrode to suppress the water decomposition reaction, thereby suppressing the generation of hydrogen at the negative electrode.

The hydrogen generation potential is as follows.

^{_{2H 2 O + 2e - → H}} 2 + 2OH -, E 0 (V) = -0.83V

In addition, the reduction potential of the zinc ion is as follows.

^{Zn 2+ + 2e - → Zn,} E 0 (V) = -0.76V

That is, since the reduction potential of zinc ions precedes that of hydrogen, generation of hydrogen at the cathode can be suppressed to suppress a water decomposition reaction.

Since the zinc ions play a role of suppressing hydrogen generation and do not affect ionic conductivity, the water capacitor including the aqueous electrolyte of the present invention can exhibit high output characteristics.

The zinc salt is contained in an aqueous electrolyte at a molar concentration of 0.005 to 0.05 (m), and preferably may be contained at a molar concentration of 0.01 to 0.03.

If the zinc salt is contained in a molar concentration of less than 0.005, the effect of inhibiting the generation of hydrogen at the negative electrode is insignificant, and thus water decomposition reaction cannot be inhibited.If the zinc salt is contained in a molar concentration exceeding 0.05, a lithium compound or a sodium compound is included as an electrode active material. It is reduced at the surface of the electrode and the electrode surface is doped with zinc, resulting in a problem that the electrochemical activity of the electrode is deteriorated.

The zinc salt is not particularly limited in its kind, but preferably zinc sulfate (ZnSO ₄ ), zinc chlorate (Zn(ClO ₃ ) ₂ ), zinc nitrate (Zn(NO ₃ ) ₂ ), zinc acetate (Zn( OAc) ₂ ), trifluoromethanesulfonate zinc (Zn(CF ₃ SO ₃ ) ₂ ), bis(trifluoromethanesulfonyl) imide zinc (Zn(TFSI) ₂ ) and zinc hydroxide (Zn(OH) ₂ ) Contains at least one selected from the group consisting of, and may preferably contain zinc nitrate in terms of cost and solubility.

The zinc salt may be included in an amount of 0.05 to 0.3 parts by weight, preferably 0.1 to 0.2 parts by weight, based on 100 parts by weight of the combined eutectic solvent and the methanesulfonate compound. If the zinc salt is contained in an amount of less than 0.05 parts by weight, the effect of extending the voltage range by zinc appears insignificant, and if it exceeds 0.3 parts by weight, zinc is doped on the electrode surface to reduce the electrochemical activity of the electrode.

In addition, in the aqueous electrolyte of the present invention, the eutectic solvent including the amide compound and the lithium salt, and the methanesulfonate compound serve not only to extend the operating voltage range, but also to improve low-temperature stability.

The deep eutectic solvent (DES) generally refers to a material whose melting temperature (or freezing temperature) is lowered by mixing two or more materials, and refers to a mixed salt that is liquid at room temperature. At this time, room temperature means an upper limit of 100°C, and in some cases, 60°C. By using the eutectic solvent, the low-temperature stability of the aqueous electrolyte can be improved, and the activity of water can be suppressed.

In the present invention, the eutectic solvent includes a lithium salt as a hydrogen bond accepter (HBA) material and an amide compound as a hydrogen bond donor (HBD) material.

One of the components of the eutectic solvent, the hydrogen bonding donor material, is a carbonyl group (-C=O) or a thioketone group (-C=S) and an amine group (-NH ₂ ), which are two different polar functional groups in the molecule. It includes an amide group-containing compound. The amide compound acts as a complexing agent to weaken the bond between the cation and the anion of the ionizable lithium salt by having different polar functional groups, such as acidic and basic functional groups, in the molecule, thereby forming a eutectic solvent. The melting temperature of will decrease. In addition to the above-described functional groups, a compound capable of forming a eutectic solvent by including two different polar functional groups in a molecule capable of weakening the bond between a cation and an anion of an ionizable lithium salt also falls within the scope of the present invention.

The amide compound may have a linear structure containing an amide group, a cyclic structure, or a mixture thereof, and non-limiting examples thereof include an alkyl amide having 1 to 10 carbon atoms, an alkenylamide compound, or an arylamide compound. In addition, all of the primary, secondary and tertiary amide compounds can be used.

For example, the amide compound is acetamide, urea, methyl urea, thiourea, methyl carbamate, ethyl carbamate, caprolactam ( caprolactam) and valerolactam. Preferably, the amide compound may be at least one selected from the group consisting of urea, thiourea, and acetamide, and more preferably, the amide compound may be urea.

The amide compound may be contained in a molar concentration of 1 to 12, preferably 3 to 9 molar concentration. If the concentration of the amide compound is less than 1 molar concentration, a freezing problem may occur at -30°C, and if the concentration of the amide compound exceeds 12 molar concentration, ionic conductivity may decrease and output characteristics may be deteriorated.

Another hydrogen bond acceptor, which is one of the components of the eutectic solvent, includes a lithium salt. The lithium salt is an ionizable lithium salt and can be expressed ^{as Li +} X ^-. The lithium salt is a lithium cation (Li ⁺⁾ is a carbonyl group and coordinated with, and wherein the lithium salt anion (X ^-) present in the amide compound of weakening in combination respective components by forming the amine group and the hydrogen bonding present in the amide compound Is planned. As a result, the melting point of the amide compound and the lithium salt that existed in the solid state is lowered to form a liquid eutectic solvent at room temperature.

The lithium salt is not particularly limited, but any lithium salt applicable to a capital capacitor may be used without limitation. For example, the lithium salt is lithium hydroxide (LiOH), lithium oxide (Li ₂ O), lithium carbonate (LiCO ₃ ), lithium chloride (LiCl), lithium nitrate (LiNO ₃ ), lithium sulfate (Li ₂ SO ₄ ), lithium perchlorate (LiClO ₄ ), and lithium acetate (LiCH ₃ COO). However, it is most preferable to include lithium nitrate having excellent solubility and ionic conductivity in order to secure high output characteristics of a water-based capacitor containing an aqueous electrolyte.

The lithium salt may be contained in a molar concentration of 1 to 10, preferably 3 to 6 molar concentration. When the concentration of the lithium salt is less than 1 molar concentration, it may be difficult to secure an ionic conductivity suitable for driving an electrochemical device including the aqueous electrolyte of the present invention, that is, a water capacitor. On the contrary, when the concentration exceeds 10 molal, the lithium salt is not completely dissolved, and the performance of the battery may be degraded by the precipitated lithium salt without dissolving. Therefore, it is appropriately adjusted within the above range.

The melting temperature of the eutectic solvent may vary depending on an amide compound, a lithium salt, etc., and is not particularly limited, but it is preferably present in a liquid state at room temperature (25°C).

The eutectic solvent may be prepared according to a conventional method known in the art. For example, the above-described amide compound and lithium salt are mixed at room temperature and then reacted at an appropriate temperature of 70° C. or lower, and then purified. have.

In the eutectic solvent, the molar ratio of the amide compound and the lithium salt may be 1:10 to 10:1, preferably 3:6 to 6:3. When the ratio between the above-described compositions is less than the above range, it is not possible to sufficiently secure the floating property effect at -30°C. Conversely, when the ratio between the above-described compositions exceeds the above range, ionic conductivity decreases, resulting in a problem in output characteristics.

As the aqueous electrolyte of the present invention contains a eutectic solvent containing the composition and structure as described above, water molecules contained in the aqueous solvent are trapped in a network formed by bonding between the constituents of the eutectic solvent, and the activity of water decreases sharply. Cryogenic stability can be improved by significantly lowering the freezing point of the aqueous electrolyte. In addition, the aqueous electrolyte according to the present invention exhibits a wider electrochemical window compared to the non-aqueous electrolyte including a conventional organic solvent due to the high thermal and chemical stability peculiar to the eutectic solvent. The operating voltage range can be extended. In fact, the upper limit of the electrochemical wound of the conventional non-aqueous electrolyte containing an ionic liquid and an organic solvent is about 4 to 4.5 V, whereas the upper limit of the electrochemical wound of the eutectic solvent of the present invention is in the range of 4.5 to 5.5 V, It can show an extended electrochemical window than conventional non-aqueous electrolytes.

In addition, since the eutectic solvent contained in the aqueous electrolyte of the present invention is in a very stable form, side reactions in the electrochemical device can be suppressed. In fact, since the co-fusion mixture possesses a wide temperature range as a liquid, high solvation ability, and non-coordinating binding properties, it is known that it has physicochemical properties as an environmentally friendly solvent that can replace the existing toxic organic solvent. , Compared to the conventional ionic liquid, it is easy to synthesize and has a high ion concentration, so it can be predicted to have a wider range of applications.

In the aqueous electrolyte according to the present invention, the eutectic solvent may be included in an amount of 40 to 80% by weight, preferably 50 to 60% by weight, based on 100% by weight of the total amount of the aqueous electrolyte. If the content of the eutectic solvent is less than 40% by weight, the output characteristics are degraded due to the decrease in ionic conductivity. On the contrary, if the content of the eutectic solvent is more than 80% by weight, freezing problems may occur at -30°C. It is desirable to do it.

The methanesulfonate compound of the present invention is a compound containing a sulfonate functional group, and due to the difference in electronegativity between the oxygen element and the sulfur element contained in the molecule, the oxygen element and the sulfur element have a partial charge, and have a charge due to structural characteristics. One side surrounds a water molecule cluster, and the water molecule clusters surrounded by betaine decrease the bonding strength between each other, and thus have a so-called'water-in-salt (WIS)' structure, even in a cryogenic environment. The effect of preventing freezing of the aqueous electrolyte is exhibited. Here, the structure of'water-in-salt (WIS)' refers to the principle that water does not freeze by interfering with the bonding between water molecules by adding an excessive amount of salt to the electrolyte. As the decomposition of water is suppressed, the effect of increasing the operating voltage range of the capacitor can also be exhibited.

The methanesulfonate compound is one or more selected from the group consisting of methanesulfonate, potassium methanesulfonate, methyl methanesulfonate, and ethyl methanesulfonate. Can include. Preferably it may be sodium methanesulfonate.

The methanesulfonate compound may be included in a 1 to 10 molar concentration, preferably 3 to 6 molar concentration. If the concentration of the methanesulfonate compound is less than 1 molar concentration, it may not sufficiently surround the water molecule cluster, resulting in a problem of lowering the low-temperature stability. Conversely, if the concentration of the methanesulfonate compound exceeds 10 molar concentration, the ionic conductivity of the aqueous electrolyte may decrease. Therefore, it is desirable to determine an appropriate content within the above-described range.

In the aqueous electrolyte according to the present invention, the methanesulfonate compound may be included in an amount of 5 to 30% by weight, preferably 10 to 20% by weight, based on 100% by weight of the total amount of the aqueous electrolyte. If the content of the methanesulfonate is less than 10% by weight, the antifreeze property and high long-term stability effect at -30°C cannot be secured. On the contrary, if it exceeds 30% by weight, a low output problem due to low ionic conductivity may occur. Therefore, it is desirable to determine an appropriate content within the above-described range.

The aqueous electrolyte according to the present invention includes an aqueous solvent as a medium through which ions involved in the electrochemical reaction of the device, that is, lithium ions, can move. The aqueous solvent is a solvent containing water and is not particularly limited. Accordingly, the main solvent used in the aqueous electrolyte of the present invention is water. At this time, water may be used alone as a solvent, but a solvent miscible with water may be used in combination.

The water-miscible solvent may be a polar solvent, and may include, for example, one or more selected from the group consisting of C1 to C5 alcohols and C1 to C10 glycol ethers.

For example, the C1 to C5 alcohol is methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1 ,4-butanediol, glycerol, and 1,2,4-butanetriol may be one or more selected from the group consisting of, but is not limited thereto.

The glycol ethers of C1 to C10 are ethylene glycol monomethyl ether (MG), diethylene glycol monomethyl ether (MDG), triethylene glycol monomethyl ether (MTG), polyethylene glycol monomethyl ether (MPG), ethylene glycol monoethyl Ether (EG), diethylene glycol monoethyl ether (EDG), ethylene glycol monobutyl ether (BG), diethylene glycol monobutyl ether (BDG), triethylene glycol monobutyl ether (BTG), propylene glycol monomethyl ether ( MFG) and dipropylene glycol monomethyl ether (MFDG) may be one or more selected from the group consisting of, but is not limited thereto.

In the aqueous electrolyte according to the present invention, the aqueous solvent is included in the balance so that the total weight of the aqueous electrolyte is 100% by weight.

In addition, the aqueous electrolyte of the present invention may further contain a manganese salt.

The manganese salt is dissociated in the aqueous electrolyte and exists in the form of manganese ions, and as the manganese salt is included, the voltage range of the negative electrode can be further extended, thereby suppressing a water decomposition reaction.

The reduction potential of the manganese ion is as follows.

^{Mn 2+ + 2e - → Mn,} E 0 (V) = -1.18V

That is, since the reduction potential of manganese ions precedes the reduction potential of hydrogen, the use of manganese ions together with zinc ions can further suppress the water decomposition reaction.

If manganese salt is used alone without zinc salt, side reactions may occur in the electrode and extreme heat may be generated. Therefore, it is most preferable to use the manganese salt together with a zinc salt.

The zinc salt and manganese salt are included in a molar ratio of 4:1 to 1:1, and preferably may be included in a molar ratio of 1:1 to 2:1.

When the manganese contained in less than the above range may be minimal voltage range expansion effect of the manganese oxide, if included in excess of the above range or use manganese alone the manganese ions in the positive electrode as manganese oxide (MnO ₂₎ It is not desirable because it can cause extreme heat.

The manganese salt is not particularly limited in its kind, but may preferably include one or more selected from the group consisting of manganese acetate, manganese nitrate, manganese sulfate, manganese chloride and manganese carbonate, preferably manganese nitrate It may include.

The manganese salt may be included in an amount of 0.05 to 0.1% by weight, preferably 0.075 to 0.095% by weight, based on 100% by weight of the total aqueous electrolyte. If the manganese salt is contained in an amount of less than 0.05% by weight, the effect of expanding the voltage range due to the manganese salt may be insignificant, and if it is contained in an amount exceeding 0.1% by weight, manganese ions are oxidized to manganese oxide (MnO ₂ ) at the anode, resulting in extreme heat. I can.

In addition to the above-described composition, the aqueous electrolyte of the present invention may additionally include additives commonly used for the purpose of improving its function in the relevant technical field, if necessary. For example, a conventionally known overcharge prevention agent, a property improvement aid for improving capacity retention characteristics and cycle characteristics after high temperature storage, and the like may be mentioned.

The aqueous electrolyte according to the present invention includes an aqueous solvent, and includes a zinc salt having a molal concentration of 0.005 to 0.05, thereby extending the voltage range of the negative electrode and suppressing the water decomposition reaction, thereby suppressing hydrogen generated in the negative electrode. , The zinc salt in the molar concentration range does not affect ionic conductivity, and thus high output characteristics can be expressed.

In addition, since the eutectic solvent including the amide compound and the lithium salt, and the methanesulfonate compound exhibit a freezing point of -30°C or less, freezing of the electrolyte in a cryogenic environment can be prevented. It enables stable operation.

Therefore, the aqueous electrolyte of the present invention can suppress the water decomposition reaction by expanding the voltage range of the negative electrode, and can have excellent effects of low temperature stability.

In addition, the present invention relates to an electrochemical device comprising the aqueous electrolyte of the present invention.

More specifically, the electrochemical device may be an electrochemical energy storage device, and may be a capacitor, preferably a water capacitor.

The water capacitor is a positive electrode; cathode; And an aqueous electrolyte, wherein the aqueous electrolyte is the aqueous electrolyte of the present invention, and the positive electrode active material of the positive electrode and the negative electrode active material of the negative electrode include at least one selected from the group consisting of a lithium compound or a sodium compound.

That is, the water capacitor of the present invention may be a lithium ion water capacitor or a sodium ion water capacitor.

In general, when a zinc metal or a zinc compound is included as an active material of a positive electrode or an active material of a negative electrode, an excess amount of zinc ions should be included in the electrolyte. However, in the present invention, although the active material of the positive electrode and the negative electrode include a lithium compound, sodium, or sodium compound, the zinc salt is included in the aqueous electrolyte at a low concentration of 0.005 to 0.05 molar concentration, so that the zinc ions affect the ionic conductivity. A water capacitor capable of expressing high output characteristics without affecting can be provided, and a problem in which zinc is doped to the electrode due to a high concentration can be prevented.

The lithium compound is a lithium-manganese-based oxide, lithium-nickel-manganese-based oxide, lithium-manganese-cobalt-based oxide, lithium-nickel-manganese-cobalt-based oxide, lithium-nickel-cobalt-based oxide, lithium-titanium phosphate, It may include one or more selected from the group consisting of lithium-iron oxide and lithium-tungsten oxide, but is not limited thereto.

For example, the positive electrode active material is a group consisting of lithium-manganese-based oxide, lithium-nickel-manganese-based oxide, lithium-manganese-cobalt-based oxide, lithium-nickel-manganese-cobalt-based oxide, and lithium-nickel-cobalt-based oxide It may include one or more selected from, but is not limited thereto.

For example, the negative active material may include at least one selected from the group consisting of lithium-titanium phosphate, lithium-iron oxide, and lithium-tungsten oxide, but is not limited thereto.

The sodium compound is selected from the group consisting of sodium-nickel-based oxide, sodium-cobalt-based oxide, sodium-nickel-manganese-based oxide, sodium-nickel-cobalt-manganese-based oxide, and sodium-nickel-cobalt-aluminum-based oxide. It may include more than one species, but is not limited thereto.

When the sodium compound is applied as a positive electrode active material and a negative electrode active material, the types of the positive electrode active material and the negative electrode active material should be different from each other.

The positive electrode may include a positive electrode current collector and a positive electrode active material applied to one or both surfaces of the positive electrode current collector, and the positive electrode active material is as described above.

The positive electrode current collector supports a positive electrode active material, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, nickel, titanium, palladium, calcined carbon, aluminum or stainless steel surface treated with carbon, nickel, silver, or the like may be used.

The positive electrode current collector may form fine irregularities on its surface to enhance the bonding strength with the positive electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and nonwoven fabrics may be used.

The positive active material may include a positive active material and optionally a conductive material and a binder.

The conductive material is a material that acts as a path through which electrons move from the current collector to the positive electrode active material by electrically connecting the electrolyte and the positive electrode active material, and does not cause chemical changes in the capacitor, and is limited as long as it has porosity and conductivity. Can be used without.

For example, a carbon-based material having a porosity may be used as the conductive material, and examples of such a carbon-based material include carbon black, graphite, graphene, activated carbon, carbon fiber, and the like, and metallic fibers such as metal mesh; Metallic powders such as copper, silver, nickel, and aluminum; Or an organic conductive material such as a polyphenylene derivative. The conductive materials may be used alone or in combination.

Products currently marketed as conductive materials include acetylene black (Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC (Armak Company). Company), Vulcan XC-72 (made by Cabot Company) and Super P (made by MMM). For example, acetylene black, carbon black, graphite, etc. are mentioned.

In addition, the positive electrode may further include a binder, and the binder further enhances binding strength between components constituting the positive electrode and between them and a current collector, and any binder known in the art may be used.

For example, the binder may include a fluororesin binder including polyvinylidenefluoride (PVdF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; Poly alcohol-based binder; Polyolefin-based binders including polyethylene and polypropylene; Polyimide binders; Polyester binder; And a silane-based binder; one, two or more mixtures or copolymers selected from the group consisting of may be used.

The positive electrode can be manufactured by a conventional method known in the art. For example, after preparing a slurry by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a positive electrode active material, it is applied (coated) to a current collector of a metal material, compressed, and dried to prepare a positive electrode. have.

The negative electrode may include a negative electrode current collector and a negative active material disposed on the negative electrode current collector.

The negative electrode current collector is for supporting the negative electrode active material, as described for the positive electrode.

In addition, the negative active material is as described above.

The negative electrode may further include the negative electrode active material and optionally a conductive material and a binder. At this time, the conductive material and the binder are as described in the positive electrode active material.

The method of forming the cathode is not particularly limited, and a layer or film forming method commonly used in the art may be used. For example, a method such as compression, coating, or evaporation may be used. In addition, a case in which a metal lithium thin film is formed on a metal plate by initial charging after assembling a battery without a lithium thin film in the current collector is also included in the negative electrode of the present invention.

The electrolyte contains lithium ions, and is used to cause an electrochemical oxidation or reduction reaction in the positive electrode and the negative electrode through this, as described above.

The injection of the electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before assembling the electrochemical device or at the final stage of assembling the electrochemical device.

A separator may be additionally included between the above-described anode and cathode. The separator is for physically separating both electrodes in a water capacitor, and if it is used as a separator in a water capacitor, it can be used without particular limitation. In particular, it is preferable that the separator has low resistance against ion migration of the electrolyte and has excellent electrolyte-moisturizing ability. Do.

The separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used in an electrochemical device, and for example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto. .

Examples of the polyolefin-based porous membrane include polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, alone or as a mixture of them. There is one membrane.

As the nonwoven fabric, in addition to the polyolefin nonwoven fabric, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide and polyethylene naphthalate, etc. Alternatively, a nonwoven fabric formed from a polymer mixed with them may be mentioned. The structure of the nonwoven fabric may be a sponbond nonwoven fabric composed of long fibers or a melt blown nonwoven fabric.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 µm and 10 to 95%, respectively.

The shape of the electrochemical device according to the present invention is not particularly limited, and may be in various shapes such as a cylindrical shape, a stacked type, and a coin type, but is preferably a coin type.

Hereinafter, a preferred embodiment is presented to aid in the understanding of the present invention, but it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the scope of the technical idea, but the following examples are only illustrative of the present invention, It is natural that such modifications and modifications fall within the scope of the appended claims.

<Manufacture of aqueous electrolyte for water capacitor>

Example 1.

_{Lithium nitrate (LiNO 3} , manufactured by Junsei) 6 Molar concentration (m), urea (CO(NH ₂ ) ₂ , manufactured by Daejeong) 2 Molar concentration, sodium methanesulfonate in 30 mL of ultrapure water (DI water) CH ₃ SO ₃ Na, Sigma Aldrich) 3 molal concentration and zinc nitrate (Zn(NO ₃ ) ₂ , Sigma Aldrich) 0.01 molal concentration was added, and sufficiently stirred. An aqueous electrolyte for a water capacitor was prepared.

Example 2.

An aqueous electrolyte for a water capacitor was prepared in the same manner as in Example 1, except that zinc nitrate was added at a molar concentration of 0.03.

Example 3.

_{Lithium nitrate (LiNO 3} , manufactured by Junsei) 6 Molar concentration (m), urea (CO(NH ₂ ) ₂ , manufactured by Daejeong) 2 Molar concentration, sodium methanesulfonate in 30 mL of ultrapure water (DI water) CH ₃ SO ₃ Na, manufactured by Sigma Aldrich) 3 Molar concentration, zinc nitrate (Zn(NO ₃ ) ₂ , manufactured by Sigma Aldrich) 0.01 molar concentration and manganese nitrate (Mn(NO ₃₎ ) ₂ , manufactured by Sigma Aldrich) 0.01 molal concentration was added and stirred sufficiently to prepare an aqueous electrolyte for a water capacitor.

Comparative Example 1.

_{Lithium nitrate (LiNO 3} , manufactured by Junsei) 6 Molar concentration (m), urea (CO(NH ₂ ) ₂ , manufactured by Daejeong) 2 Molar concentration, sodium methanesulfonate in 30 mL of ultrapure water (DI water) CH ₃ SO ₃ Na, manufactured by Sigma Aldrich) 3 A molar concentration was added and stirred sufficiently to prepare an aqueous electrolyte for a water capacitor.

Comparative Example 2.

_{Lithium nitrate (LiNO 3} , manufactured by Junsei) 6 Molar concentration (m), urea (CO(NH ₂ ) ₂ , manufactured by Daejeong) 2 Molar concentration, sodium methanesulfonate in 30 mL of ultrapure water (DI water) CH ₃ SO ₃ Na, manufactured by Sigma Aldrich) 3 molar concentration and manganese nitrate (Mn(NO ₃ ) ₂ , manufactured by Sigma Aldrich) 0.01 molar concentration was added, and sufficiently stirred. An aqueous electrolyte for a water capacitor was prepared.

Experimental Example 1. Evaluation of electrochemical properties of water capacitors

Experimental Example 1-1. Linear Sweep Voltammetry (LSV) measurement (3-electrode measurement)

For the aqueous electrolytes of Examples 1 to 3 and Comparative Examples 1 to 2, a three-electrode type water capacitor was fabricated, and then a linear scanning potential method (Linear Sweep Voltammetry, LSV) was measured.

_{At this time, a negative electrode was prepared by coating LiMn 2} O ₄ as a positive electrode active material on a nickel foil and coating a working electrode (WE) or LiTi ₂ (PO ₄ ) ₃ as a negative electrode active material, respectively, and platinum The plate was used as a counter electrode (CE) and a saturated calomel electrode (SCE) as a reference electrode (RE), respectively. In addition, in the case of the positive electrode voltage (based on SHE) 0 to 1.75V, 1 mV/sec, in the case of the negative electrode voltage -1.25 to 0V, 1 mV/sec, the entire voltage range -1.25 to 1.75V (based on SHE) linear scanning under conditions The potential method (Linear Sweep Voltammetry, LSV) was measured, and the results are shown in FIGS. 1 to 3.

In the case of the positive electrode, the results of Example 1 and Comparative Example 1 were measured very similarly, from which it was confirmed that the positive electrode was not affected by zinc ions.

For the cathode,

From the results of Example 1 and Comparative Example 1, it was confirmed that the voltage range of the cathode was increased by about 0.5V (FIG. 1). Therefore, it can be seen that the zinc ions contained in the aqueous electrolyte extend the voltage range of the negative electrode to suppress water decomposition.

From the results of Example 1, Example 2, and Comparative Example 2, it was confirmed that the voltage range of the negative electrode was expanded as the concentration of zinc ions increased. In addition, in Comparative Example 2 including manganese ions, no expansion of the voltage range of the zinc ions was observed, and extreme heat was generated due to the occurrence of a side reaction in the counter electrode (FIG. 2).

From the results of Examples 1 and 3, it was confirmed that the voltage range of the negative electrode was further expanded when zinc ions and manganese ions were used together in an aqueous electrolyte (FIG. 3).

Experimental Example 1-2. Cathode (LiTi ₂ (PO ₄ ) ₃ ) Of Cyclic Voltammetry (CV) measurement (3-electrode measurement)

After fabricating a three-electrode water capacitor for the aqueous electrolytes of Example 1 and Comparative Example 1, cyclic voltammetry (CV) was measured in a beaker cell.

At this time, a negative electrode was prepared _{by coating LiTi 2} (PO ₄ ) ₃ as a negative electrode active material on a nickel foil, and a platinum plate was used as a counter electrode (CE) and a SCE (saturated calomel electrode) as a reference electrode. It was used as (reference electrode, RE), respectively. In addition, cyclic voltammetry (CV) was measured under the conditions of voltage (based on SHE) -0.8 to 0V and 10 mV/sec.

In the result of FIG. 4, which measured the circulating voltage current in the aqueous electrolyte of Example 1, the negative electrode surface was doped with zinc, and as the cycle progressed, the redox peak decreased. This is a result observed by measuring the negative electrode in a Vickers cell, and it can be seen that the absolute concentration of zinc ions increases regardless of the molar concentration of the zinc salt, so that the redox peak is lowered due to zinc doping on the surface of the negative electrode.

In the result of FIG. 5, which measured the circulating voltage current in the aqueous electrolyte of Comparative Example 1, the redox peak was constant even when the cycle proceeded.

From the above results, it can be seen that in the case of the Vickers cell, since a large amount of the electrolyte is contained in the cell, the absolute amount of zinc ions increases and the electrochemical performance decreases. Therefore, it can be seen that the aqueous electrolyte is not suitable for use in a Vickers cell.

Experimental Example 1-3. Measurement of life characteristics of water capacitors

After fabricating a two-electrode type water capacitor for the aqueous electrolyte of Example 1, the lifespan characteristics were evaluated. _{At this time, a positive electrode was prepared by coating LiMn 2} O ₄ as a positive electrode active material on a nickel foil, and a negative electrode was prepared by coating LiTi ₂ (PO ₄ ) ₃ as a negative electrode active material. In addition, by using a constant-current discharge method, it was measured under charging/discharging conditions (constant current 150mA (=-5A/g), voltage 0.4-2.1V), and the results are shown in FIG. 6.

As a result, it can be seen that the aqueous electrolyte of Example 1 including zinc ions exhibits excellent capacitance retention efficiency. When the concentration of zinc ions is high, zinc ions doped the entire surface of the negative electrode, resulting in a rapid decrease in capacity, resulting in poor lifespan characteristics. Accordingly, since zinc ions did not dope the surface of the cathode, the lifespan characteristics were very excellent.

That is, in the case of a coin cell, since the amount of the aqueous electrolyte is controlled, the degree of redox peak may vary greatly depending on the concentration of zinc salt. It can be seen that the life characteristics are excellent.

Therefore, when the aqueous electrolyte of the present invention is included, zinc ions do not affect ionic conductivity, and the capacity of the water capacitor including the same is stably maintained, thereby ensuring improved stability and lifespan characteristics, and the above It is preferable that the water capacitor is a coin cell.

Claims (16)

A eutectic solvent containing an amide compound and a lithium salt;
Methanesulfonate compounds;
Zinc salt; And
Including; an aqueous solvent,
The zinc salt is an aqueous electrolyte for a water capacitor contained in a molal concentration of 0.005 to 0.05. The method of claim 1,
The amide compound comprises at least one selected from the group consisting of acetamide, urea, methyl urea, thiourea, methyl carbamate, ethyl carbamate, caprolactam, and valerlactam. The method of claim 1,
The lithium salt is a water system for a water capacitor, characterized in that it contains at least one selected from the group consisting of lithium hydroxide, lithium oxide, lithium carbonate, lithium chloride, lithium nitrate, lithium sulfate, lithium perchlorate, and lithium acetate Electrolyte. The method of claim 1,
The methanesulfonate compound is an aqueous electrolyte for a water capacitor, characterized in that it comprises at least one selected from the group consisting of sodium methanesulfonate, potassium methanesulfonate, methyl methanesulfonate and ethyl methanesulfonate. The method of claim 1,
The zinc salt comprises at least one selected from the group consisting of zinc sulfate, zinc chlorate, zinc nitrate, zinc acetate, zinc trifluromethanesulfonate, bis(trifluoromethanesulfonyl)imide zinc, and zinc hydroxide. An aqueous electrolyte for a water capacitor, characterized in that. The method of claim 1,
The amide compound is 1 to 12 molar concentration, the lithium salt is 1 to 10 molar concentration, and the methanesulfonate compound is a water-based electrolyte for a water capacitor, characterized in that contained in a 1 to 10 molar concentration. The method of claim 1,
The eutectic solvent comprises the amide compound and the lithium salt in a molar ratio of 1:10 to 10:1. The method of claim 1,
An aqueous electrolyte for a water capacitor, characterized in that containing 40 to 80% by weight of the eutectic solvent and 5 to 30% by weight of the methanesulfonate compound based on 100% by weight of the total of the aqueous electrolyte. The method of claim 1,
The zinc salt is an aqueous electrolyte for a water capacitor, characterized in that contained in an amount of 0.05 to 0.3 parts by weight based on 100 parts by weight of the sum of the eutectic solvent and the methanesulfonate compound. The method of claim 1,
The aqueous electrolyte is an aqueous electrolyte for a water capacitor, characterized in that it further comprises a manganese salt. The method of claim 10,
The zinc salt and manganese salt are water-based electrolyte for a water capacitor, characterized in that contained in a molar ratio of 4:1 to 1:1. The method of claim 10,
The manganese salt is an aqueous electrolyte for a water capacitor, characterized in that it contains at least one selected from the group consisting of manganese acetate, manganese nitrate, manganese sulfate, manganese chloride and manganese carbonate. anode; cathode; And a water capacitor comprising the aqueous electrolyte of any one of claims 1 to 12,
The positive electrode active material of the positive electrode and the negative electrode active material of the negative electrode may include a lithium compound or a sodium compound. The method of claim 13,
The lithium compound is a lithium-manganese-based oxide, lithium-nickel-manganese-based oxide, lithium-manganese-cobalt-based oxide, lithium-nickel-manganese-cobalt-based oxide, lithium-nickel-cobalt-based oxide, lithium-titanium phosphate, A water capacitor comprising at least one selected from the group consisting of lithium-iron oxide and lithium-tungsten oxide. The method of claim 13,
The sodium compound is selected from the group consisting of sodium-nickel-based oxide, sodium-cobalt-based oxide, sodium-nickel-manganese-based oxide, sodium-nickel-cobalt-manganese-based oxide, and sodium-nickel-cobalt-aluminum-based oxide. A water capacitor comprising more than one species. The method of claim 13,
A water capacitor, characterized in that the shape of the water capacitor is a coin type.

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