WO2020004173A1

WO2020004173A1 - Electrochemical capacitor

Info

Publication number: WO2020004173A1
Application number: PCT/JP2019/024290
Authority: WO
Inventors: 武志部田; 裕一本田
Original assignee: 株式会社村田製作所
Priority date: 2018-06-28
Filing date: 2019-06-19
Publication date: 2020-01-02

Abstract

This electrochemical capacitor has a cathode and an anode disposed and spaced apart from each other in an electrolytic solution. The cathode and the anode contain, as an electrode active substance, a layered material including a plurality of layers. Each of the layers is represented by formula: M_n+1X_n (in the formula, M represents at least one group 3, 4, 5, 6, or 7 metal, X represents a carbon atom and/or a nitrogen atom, and n represents 1, 2, or 3), has a crystal lattice in which each X is positioned in the octahedral array of M, and includes, in at least one of the two opposite surfaces of each of the layers, the layered material having a terminal end T or at least one modification selected from the group consisting of a hydroxy group, a fluorine atom, an oxygen atom, and a hydrogen atom. The electrolytic solution contains gamma-butyrolactone as a solvent, and, as an electrolyte, lithium bis(trifluoromethanesulfonyl)imide and/or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

Description

Electrochemical capacitor

The present invention relates to an electrochemical capacitor, and more particularly, to an electrochemical capacitor in which a cathode and an anode are separated from each other in an electrolytic solution.

BACKGROUND ART An electrochemical capacitor is a capacitor that utilizes a capacity developed due to a physicochemical reaction between an electrode (electrode active material) and an ion (electrolyte ion) in an electrolytic solution, and is a device that stores electric energy (power storage). Device). In an electrochemical capacitor, a metal oxide or a layered material (or an intercalation compound) is used as an electrode active material, and a reaction involving transfer of electrons between an electrode and ions in an electrolytic solution (for example, an electrode active material) A capacitor that exhibits a capacitance (pseudo-capacitance) due to a change in the oxidation number of a metal element constituting the element is called a “pseudo capacitor” or a “redox capacitor”.

Conventionally, as such an electrochemical capacitor (particularly a pseudo capacitor), an electrochemical capacitor using MXene as an electrode active material has been known (see Patent Document 1 and Non-Patent Document 1). MXene is one kind of a so-called two-dimensional material, and as described later, is a layered material having a form of a plurality of layers, and each layer is composed of M _{n + 1} X _n (where M is at least one kind of a third third material). , 4, 5, 6, and 7 metals, X is a carbon and / or nitrogen atom, and n is 1, 2, or 3), and each X is within an octahedral array of M Is a material having a terminal (or modification) T such as a hydroxyl group, a fluorine atom, an oxygen atom and a hydrogen atom on the surface of each layer.

International Publication No. WO2018 / 066549

Generally, an aqueous electrolyte (an electrolyte in which an electrolyte is dissolved in an aqueous solvent) and a non-aqueous electrolyte (an electrolyte or an ionic liquid in which an electrolyte is dissolved in a nonaqueous solvent) can be used as an electrolyte for an electrochemical capacitor. (Electrolyte solution consisting of). In the case of aqueous electrolytes, the operating potential range of the electrochemical capacitor (referred to as the "potential window") is limited to a maximum of 1.2 V or less so as not to cause water electrolysis, and thus the energy density is limited. There are difficulties. Further, in the case of the aqueous electrolyte, there is also a drawback that the usable temperature range of the electrochemical capacitor is limited to a temperature at which water can be stably present as a liquid (a temperature at which freezing and vaporization do not occur). On the other hand, non-aqueous electrolytes have the advantage that such difficulties can be avoided. The energy density is generally calculated as ×× CV ² , where C is the specific capacity (more specifically, the capacity per unit volume of the electrode active material (F / cm ³ ) or the unit of the electrode active material). The capacity per mass (F / g), hereinafter, these are collectively referred to as “specific capacity”), V means the operating potential range (V), and the energy density is expressed in units of FV ^2. / Cm ³ or FV ² / g, but can generally be expressed in terms of units Wh / L or Wh / kg. However, if the measured value C _3p (F / cm ³ or F / g) obtained by measuring the specific capacity of one of the cathode and anode electrodes by three-electrode measurement is known, the electrode used for the other electrode is no longer used. The value of the specific capacity Cf (F / cm ³ or F / g) that can be measured by full cell measurement when one of them is also used to form an electrochemical capacitor can be conveniently calculated as being equal to 1 / 4C _3p. It is. A larger operating potential range contributes significantly to obtaining a higher energy density.

For example, in Non-Patent Document 1, in a three-electrode Swagelok cell, one of MXene, Ti ₃ C ₂ T _x (T _x means a surface functional group), is used for a working electrode, and excess activated carbon is used. The membrane was used as a counter electrode, an Ag wire was used as a reference electrode, and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMI-TFSI) was used as a non-aqueous electrolyte at 1M in acetonitrile (AN). It has been disclosed that the capacitor characteristics of an electrochemical capacitor were evaluated using a solution containing the same. However, such an electrochemical capacitor has a problem of a narrow operating potential range (approximately 1.6 V) which is assumed to be caused by electrolysis of acetonitrile, and therefore has a somewhat improved energy density as compared with the case of an aqueous electrolyte. Although it can be obtained, it is still not possible to obtain a large energy density.

Further, for example, in Patent Document 1, MXene is used as an electrode active material for one of two electrodes, and a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte that generates protons in the non-aqueous solvent is used. (See paragraphs 0029 to 0035 of Patent Document 1). More specifically, Patent Document 1 discloses that a three-electrode Swagelok cell uses Ti ₃ C ₂ T _s (T _s means a surface functional group), which is one of MXene, as a working electrode, Using an activated carbon membrane having a capacity as a counter electrode, an Ag wire as a reference electrode, and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMI-TFSI) and bis (trifluoromethane) as nonaqueous electrolytes It is disclosed that a mixture with sulfonyl) imide (HTFSI) was used to evaluate the capacitor properties of electrochemical capacitors. In such an electrochemical capacitor, a wider operating potential range (see paragraphs 0062 to 0063 of Patent Document 1, potential window 3.0 V) is realized, and an energy density larger than that of Non-Patent Document 1 can be obtained. Can be.

However, there is no known electrochemical capacitor that uses MXene for both the cathode and anode electrode active materials of the electrochemical capacitor and can achieve a large energy density. Conventionally, when MXene is used as an electrode active material in the cathode of an electrochemical capacitor, there is relatively abundant knowledge about an electrolytic solution that increases the specific capacity and the operating potential range, and thus the energy density. When MXene is used as the active material, there is almost no knowledge about an electrolytic solution that increases the specific capacity and the operating potential range, and thus the energy density.

Generally, an electrolytic solution that provides a large energy density when a certain material is used for a cathode electrode active material, and an electrolytic solution that provides a large energy density when a certain material is used for an anode electrode active material. It can be different from a liquid. When MXene is used as the electrode active material for both the cathode and the anode, it is impossible to predict an electrolyte capable of achieving a large energy density, and it is extremely difficult to find such an electrolyte.

The present invention relates to an electrochemical capacitor in which a cathode and an anode are spaced apart from each other in an electrolyte, using MXene as an electrode active material for both the cathode and the anode, and achieving a large energy density. It is an object to provide a stable electrochemical capacitor.

According to one aspect of the present invention, there is provided an electrochemical capacitor having a cathode and an anode spaced apart in an electrolyte,
The cathode and the anode are layered materials including a plurality of layers as an electrode active material, and each layer has the following formula:
M _{n + 1} X _n
Wherein M is at least one Group 3, 4, 5, 6, 7 metal;
X is a carbon atom, a nitrogen atom or a combination thereof;
n is 1, 2 or 3)
And each X has a crystal lattice located in an octahedral array of M, and at least one of two opposing surfaces of each layer has a group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom A layered material having at least one modification or termination T selected from the group consisting of:
An electrochemical capacitor, wherein the electrolytic solution contains gamma-butyrolactone as a solvent and at least one of lithium bis (trifluoromethanesulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide as an electrolyte. Is done.

According to another aspect of the present invention, there is provided an electrochemical capacitor having a cathode and an anode spaced apart in an electrolytic solution,
The cathode and the anode are layered materials including a plurality of layers as an electrode active material, and each layer has the following formula:
M _{n + 1} X _n
Wherein M is at least one Group 3, 4, 5, 6, 7 metal;
X is a carbon atom, a nitrogen atom or a combination thereof;
n is 1, 2 or 3)
And each X has a crystal lattice located in an octahedral array of M, and at least one of two opposing surfaces of each layer has a group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom A layered material having at least one modification or termination T selected from the group consisting of:
An electrochemical capacitor, wherein the electrolytic solution contains ethyl isopropyl sulfone as a solvent and at least one of sodium bis (trifluoromethanesulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide as an electrolyte. Provided.

According to the electrochemical capacitor of the present invention, the predetermined layered material (also referred to as “MXene” in the present specification) is used as the electrode active material for both the cathode and the anode, and gamma-butyrolactone is used as a solvent and an electrolyte is used. Or at least one of lithium bis (trifluoromethanesulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, or ethylisopropylsulfone as a solvent and sodium bis (trifluorofluoride) as an electrolyte A large energy density can be achieved by using an electrolyte containing at least one of (i) methanesulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide. The novel electrochemical capacitor is provided.

In one embodiment of the present invention, the formula M _{n + 1} X _n may be any selected from the group consisting of Ti ₃ C ₂ , Ti ₂ C and V ₂ C.

According to the present invention, in an electrochemical capacitor in which a cathode and an anode are arranged separately in an electrolytic solution, MXene is used as an electrode active material of both the cathode and the anode, and gamma-butyrolactone is used as a solvent, and as an electrolyte, An electrolytic solution containing at least one of lithium bis (trifluoromethanesulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, or ethylisopropylsulfone as a solvent and sodium bis (trifluoromethane) as an electrolyte By using an electrolyte containing at least one of sulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, a new energy density can be achieved. Electrochemical capacitors are provided.

1 is a schematic cross-sectional view illustrating an electrochemical capacitor according to one embodiment of the present invention. FIG. 1 is a schematic cross-sectional view showing MXene which is a layered material that can be used for an electrochemical capacitor according to one embodiment of the present invention.

実施 Embodiments of the electrochemical capacitor of the present invention will be described in detail below, but the present invention is not limited to such embodiments.

を Referring to FIG. 1, the electrochemical capacitor 20 of the present embodiment has a configuration in which the cathode 15 a and the anode 15 b are disposed separately in the electrolytic solution 13. The cathode 15a and the anode 15b are electrically connected to terminals A and B, respectively, and can function as electrodes. In the embodiment shown, the cathode 15a and the anode 15b are separated from each other in any suitable container (or cell) 11 in the electrolyte 13 by, for example, a separator 17 (although not essential to this embodiment). Can be arranged. As the separator 17, any suitable member can be used as long as it does not hinder the movement of the electrolyte ions in the electrolyte solution 13. For example, a porous film of a polyolefin such as polypropylene or polytetrafluoroethylene may be used. The material of the container 11 is not particularly limited, and may be, for example, a metal such as stainless steel, a resin such as polytetrafluoroethylene, or any other appropriate material. The container 11 may be closed or open, and the container 11 may or may not be empty. The cathode 15a and the anode 15b are arranged in the container 11 so as to be separated from each other in any appropriate form other than the illustrated form, such as being stacked and wound with the separator 17 interposed therebetween. May be.

Both the cathode 15a and the anode 15b contain a predetermined layered material including a plurality of layers as an electrode active material. The electrode active material refers to a material that exchanges electrons with electrolyte ions in the electrolyte 13.

The predetermined layered material that can be used in this embodiment is MXene, defined as follows:
A layered material comprising a plurality of layers, each layer having the following formula:
M _{n + 1} X _n
Wherein M is at least one Group 3, 4, 5, 6, 7 metal and is a so-called early transition metal such as Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and Mn may include at least one selected from the group consisting of:
X is a carbon atom, a nitrogen atom or a combination thereof;
n is 1, 2 or 3)
And each X has a crystal lattice located in an octahedral array of M, and at least one of two opposing surfaces of each layer has a group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom A layered material having at least one modification or termination T selected from the following (this is also referred to as “M _{n + 1} X _n T _s ”, where s is an arbitrary number, and conventionally, x is used instead of s) Sometimes).

Such MXene can be obtained by selectively etching A atoms from the MAX phase. The MAX phase has the following formula:
M _{n + 1} AX _n
Wherein M, X and n are as described above, and A is at least one group 12, 13, 14, 15, 16 element, usually a group A element, typically IIIA And at least one selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S and Cd, preferably Al)
And each X has a crystal lattice located in an octahedral array of M, and a layer composed of A atoms is located between layers represented by M _{n + 1} X _n. Have. In the MAX phase, roughly, one layer of X atoms is arranged between each of the n + 1 layers of M atoms (these layers are collectively referred to as “M _{n + 1} X _n layers”), and the (n + 1) th M layer is formed. As the next layer of the atomic layer, there is a repeating unit in which an A atomic layer (“A atomic layer”) is arranged. By selectively etching A atoms from the MAX phase, the A atomic layer is removed, and an etching solution (usually, an aqueous solution of fluorinated acid is used, which is used on the exposed surface of the M _{n + 1} X _n layer. (But not limited to) hydroxyl groups, fluorine atoms, oxygen atoms, hydrogen atoms, and the like present therein to modify and terminate such surfaces.

Typically, in the above formula, M can be titanium or vanadium and X can be a carbon or nitrogen atom. For example, MAX-phase _is Ti 3 AlC _2, MXene _is Ti ₃ C 2 _{T s.}

In the present invention, MXene may contain a relatively small amount of the remaining A atom, for example, 10% by mass or less based on the original A atom.

As schematically shown in FIG. 2, the MXene 10 thus obtained is such that the M _{n + 1} X _n layers 1 a, 1 b, 1 c are modified or terminated with surface modification or termination at

T

3 a, 5 a, 3 b, 5 b, 3 c, 5 c. Layered material having two or more

MXene layers

7a, 7b, 7c (this is also referred to as “M _{n + 1} X _n T _s ” and s is an arbitrary number). It is shown by way of example, but not limited thereto). The MXene 10 is a laminate (multi-layer structure) in which the plurality of MXene layers are separately separated from each other (single-layer structure), and the plurality of MXene layers are separated from each other and laminated. Or a mixture thereof. The MXene can be a collection of individual MXene layers (monolayer) and / or a stack of MXene layers (which may also be referred to as particles, powders or flakes). In the case of a laminate, two adjacent MXene layers (for example, 7a and 7b, 7b and 7c) do not necessarily need to be completely separated, and may be in partial contact.

Although not limiting the present embodiment, the thickness of each MXene layer (corresponding to the above MXene layers 7a, 7b, 7c) is, for example, 0.8 nm or more and 5 nm or less, particularly 0.8 nm or more and 3 nm or less. The maximum dimension in a plane (two-dimensional sheet plane) parallel to the layers (mainly, it may vary depending on the number of M atomic layers included in each layer) is, for example, 0.1 μm or more and 200 μm or less, particularly 1 μm or more and 40 μm or less. . When MXene is a laminate, the interlayer distance (or gap size, indicated by d in FIG. 1) of each laminate is, for example, 0.8 nm or more and 10 nm or less, particularly 0.8 nm or more and 5 nm or less, more particularly The thickness is about 1 nm, and the total number of layers may be 2 or more, for example, 50 to 100,000, particularly 1,000 to 20,000, and the thickness in the stacking direction is, for example, 0.1 μm or more. It is 200 μm or less, particularly 1 μm or more and 40 μm or less, and the maximum dimension in a plane (two-dimensional sheet surface) perpendicular to the laminating direction is, for example, 0.1 μm or more and 100 μm or less, particularly 1 μm or more and 20 μm or less. In addition, these dimensions are calculated | required as a number average dimension (for example, number average of at least 40 pieces) based on a scanning electron microscope (SEM) or a transmission electron microscope (TEM) photograph.

(4) The cathode 15a and the anode 15b may be substantially composed of only MXene, which is an electrode active material, or may be composed by adding a binder or the like thereto. MXene included in the cathode 15a and MXene included in the anode 15b may be the same. The binder can be typically a resin, and for example, at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, and the like can be used.

The cathode 15a and the anode 15b may be formed independently of each other in the form of a free-standing film or in the form of a film and / or a film on a current collector (not shown). The collector may be made of any suitable conductive material, and may be made of, for example, stainless steel, aluminum, an aluminum alloy, or the like.

The electrolyte 13 is
Gamma-butyrolactone (gBL) as a solvent;
Lithium bis (trifluoromethanesulfonyl) imide (Li-TFSI, also referred to as bis (trifluoromethane) sulfonimide lithium salt) and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMI-TFSI) as electrolytes , 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide).
Alternatively, the electrolyte 13 is
Ethyl isopropyl sulfone (EiPS) as a solvent;
Sodium bis (trifluoromethanesulfonyl) imide (Na-TFSI, also referred to as bis (trifluoromethane) sulfonimide sodium salt) and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMI-TFSI) as electrolytes ) Is included in combination.
The present inventor has found that the above specific combination of solvent and electrolyte can achieve high energy density while using MXene for both cathode and anode electrode active materials.

The molar concentration of the electrolyte (at least one of Li-TFSI and EMI-TFSI, or at least one of Na-TFSI and EMI-TFSI) in the electrolyte solution 13 (if both of the above “at least one” are present, each molar concentration) The total of the concentrations is not particularly limited, but may be, for example, 0.01 to 10 mol / L, particularly 0.2 to 2 mol / L (all based on the whole).

The electrolytic solution 13 may contain a solvent and an electrolyte and any appropriate additive in a relatively small amount.

(4) The terminals A and B of the electrochemical capacitor 20 can be connected to a load to perform discharge. Further, the terminals A and B of the electrochemical capacitor 20 can be connected to a power supply to perform charging. Although the present inventor is not bound by any theory, it is speculated that in the cathode, a large amount of cations are attracted from the electrolytic solution into the MXene layer, and the H atoms of the cations are oriented to the MXene to perform electron transfer, thereby producing capacity. In the anode, it can be inferred that capacity is developed by the exchange (ion exchange) of cations and anions.

According to the electrochemical capacitor of the present embodiment, an electrolyte using MXene as the electrode active material of both the cathode and the anode, and containing gBL as a solvent and at least one of Li-TFSI and EMI-TFSI as an electrolyte Alternatively, a large energy density can be achieved by using an electrolytic solution containing EiPS as a solvent and at least one of Na-TFSI and EMI-TFSI as an electrolyte. When the capacitor characteristics of the electrochemical capacitor of the present embodiment are evaluated at a voltage scanning speed of 5 mV / s, the energy density can be, for example, 10 Wh / L or more.

MXene has a larger gap between layers than an oxide-based material such as MnO ₂ . And, while the present invention is not bound by any theory, by the above specific combination of the solvent and the electrolyte in the present invention, in both the cathode and the anode, the solvent easily enters between the layers of MXene, and between the layers of MXene and the surface of the layers. It can be understood that a higher energy density is obtained because anions and cations have become more accessible to certain reaction fields.

電気 The electrochemical capacitor of the present embodiment can also exhibit a high power density. When the capacitor characteristics of the electrochemical capacitor of the present embodiment are evaluated at a voltage scanning speed of 5 mV / s, the power density can be, for example, 80 W / L or more, particularly 100 W / L or more.

Although not limiting the present embodiment, in order to obtain a higher power density, it is preferable to use MXene, which has a high electrical conductivity exceeding 1,000 S / cm, among MXene (1,000 S / cm). It should be noted that the conductivity exceeding cm is higher than activated carbon (conductivity of about 300 S / cm) or graphene (conductivity of 500 to 1,000 S / cm) that can be used for conventional electrochemical capacitors. As the MXene exhibiting a high conductivity of more than 1,000 S / cm, the MXene (X) wherein the above formula M _{n + 1} X _n is any one selected from the group consisting of Ti ₃ C ₂ , Ti ₂ C and V ₂ C More specifically, any one selected from the group consisting of Ti ₃ C ₂ T _s , Ti ₂ CT _s and V ₂ CT _s ), which exceeds 1,000 S / cm and 10,000 S / cm cm or less.

In addition, although not essential to the present embodiment, in the electrochemical capacitor, the mass m _c (g) of the cathode electrode active material and the mass m _a (g) of the anode electrode active material may be close to each other. it can. m _c (g): m _a (g) can be for example 1: 0.8 to 1.2, especially 1: 0.9 to 1.1, preferably 1: 1.

closer to each other and m _c and m _a it is, because it is easy to produce a electrochemical capacitor preferred. More specifically, in the case of mass production of electrochemical capacitors, each area of the cathode and anode was fixed, by varying the cathode and the thickness of the anode, generally be obtained m _c and m _a for the purpose although, in the case where m _c and m _a considerable different, cathode and one of the thickness of the anode is considerably greater (e.g., more than 80 [mu] m), and the example, the current collector with a predetermined thickness (for example, about 20 [mu] m) And / or when the electrochemical capacitor is operated, it may be difficult for the solvent to sufficiently penetrate between the layers of MXene (for example, 80 μm or more) which is considerably thick, and the specific capacity may be reduced. Problem can occur. If the m _c and m _a are close to each other, it can be avoided such a problem arises.

However, when MXene is used as the electrode active material, it is inherently not easy to bring them close to each other. In an electrochemical capacitor, theoretically, the charge Q _c (coulomb) stored in the cathode is equal to the charge Q _a (coulomb) stored in the anode.
_Qc = _Cc * _mc * _Vc
Q _a = C _a × m _a × V _a
_{_{_{Wherein, Q c, Q a, m}}} c, m a are as described above, _{C c} denotes a cathode electrode active material unit mass per volume (F / g), _{C a} is the anode electrode active material means a unit mass per volume (F / g), the _{V c} by means of the cathode voltage _(V), V _a denotes an anode voltage (V).
_Therefore, _C c satisfying _{_{_{Q c = Q a, m c}}} , V c, C a, m a, when selecting a _{V a} is not satisfied the preferred _{_(Q} c = Q _a, smaller one charge of This is because the electrode active material is stored in the cathode and the anode, respectively, and the excess mass of the electrode active material is wasted without being used as a capacitor.) close the m _c and _{m a} mutually, for _example, m _c: m a = 1: when 1, so as to satisfy the _{_{_{C c × V c = C a}}} × V a, C c, V c, C a , so that the matching of the _{V a.} However, when MXene is used for both the cathode and anode electrode active materials, C _c and C _a may be different from each other, and V _c and V _a may be different from each other, and these vary depending on the solvent and electrolyte used. , Can not be predicted.

In contrast, in the electrochemical capacitor of the present embodiment, the above specific combination of solvent and an electrolyte, and a m _c and m _a be brought closer to each other as described above, were confirmed by the present inventors. According to electrochemical capacitor according the present embodiment, it is possible to approximate the m _c and m _a to each other as in the conventional electrochemical capacitors, and the C _c × V _c and C _{_a} × V _a C _c since corresponding different equivalent not necessary not to adjust the designed different m _c and m _a to satisfy Q _{c =} Q _a in the case, the cathode and anode of the total mass (or volume), therefore the electrochemical capacitor The mass (or volume) can be made as small as possible, and the energy density as large as possible can be obtained.

In the electrochemical capacitor of the present embodiment, MXene is used for both the cathode and anode electrode active materials. In the case of using MXene, non-capacitance is hardly reduced even if the electrode thickness is increased to some extent, and a large capacity can be preferably secured as compared with the case of using MnO ₂ , so that the electrode thickness is further increased. For example, it is 3 μm or more, particularly 5 μm or more, and the upper limit is not particularly limited, but can be typically 50 μm or less.

In the electrochemical capacitor of the present embodiment, a sufficiently large specific capacity, particularly a capacity per unit volume of the electrode active material, can be achieved by the above specific combination of the solvent and the electrolyte. Electrode active material (MXene) per unit volume capacity, for example, 30F / cm ³ or more, particularly 50F / cm ³ or more, preferably 80F / cm ³ or higher, more preferably at 150F / cm ³ or more, the upper limit is not particularly limited Typically, it can be 1500 F / cm ³ or less.

In the electrochemical capacitor of the present embodiment, gBL and EiPS are understood as non-aqueous solvents, and the electrolyte 13 is composed of gBL and at least one of Li-TFSI and EMI-TFSI, or EiPS and Na-TFSI and EMI- It may be a non-aqueous electrolyte containing at least one combination of TFSI and not containing water. Such an electrochemical capacitor of the present embodiment can obtain a large operating potential range as compared with a case where an aqueous electrolyte is used and a case where a non-aqueous solvent containing acetonitrile is used as a solvent, and the use of an aqueous electrolyte. A wider usable temperature range (low to high temperature) can be obtained compared to the case. For example, the electrochemical capacitor of the present embodiment has an operating potential range (potential window) of 1.5 V or more, particularly 2.0 V or more, preferably 2.5 V or more, more preferably 3 V or more, and the upper limit is not particularly limited. Can be typically 4 V or less, and the usable temperature range can be −40 to 90 ° C., particularly −40 to 80 ° C.

Further, in the electrochemical capacitor of the present embodiment, the electrolytic solution 13 includes gBL and at least one combination of Li-TFSI and EMI-TFSI, or EiPS and at least one combination of Na-TFSI and EMI-TFSI, Unlike the electrochemical capacitor of Patent Document 1, it does not include an electrolyte that generates protons in a non-aqueous solvent. When the electrolytic solution contains an electrolyte (for example, HTFSI) that generates protons in a non-aqueous solvent, a member (so-called package, specifically, a container (cell)) that exhibits strong acidity and can come into contact with the electrolytic solution in an electrolytic capacitor. 11 and, if present, the separator 17 etc.) must be selected from materials which are not acid eroded by such electrolytes. On the other hand, the electrochemical capacitor according to the present embodiment does not need to use an acid-resistant material for the member, and is excellent in the degree of freedom of material selection.

(Example 1)
An electrochemical capacitor was assembled as follows, the energy density and the power density were measured, and the capacitor characteristics were evaluated.

・ Cathode and anode (MXene electrode)
First, in the same manner as in Example 1 of Patent Document 1, to obtain a flexible freestanding film consisting essentially Ti ₃ C ₂ T _s. Next, two punched freestanding film of the resulting _Ti 3 _C 2 _{T s} Thus the circle having a diameter of 5 mm, to obtain a two _{_{_{MXene (Ti 3 C 2 T s}}} ) electrodes (anode and cathode). The thickness of the obtained MXene electrode was 1.8 to 2.0 μm, and the specific gravity was 3.5 to 4.0 g / cm ³ . The mass of the MXene electrode used for the cathode was 0.213 mg, the mass of the MXene electrode used for the anode was 0.202 mg, and their mass ratio was approximately 1: 1.

Separator A separator membrane prepared by processing a commercially available separator (manufactured by GE Healthcare Life Sciences, Whatman (registered trademark), glass microfiber filter, grade GF / A) into a diameter of 6 mm was prepared.

・ Electrolyte solution A mixture of gBL (manufactured by Shigma Aldrich, product number B103608) as a solvent and EMI-TFSI (manufactured by Solvionic, product number Im0208a) as an electrolyte at a molar concentration of 1 mol / L (total basis) The mixture was prepared as an electrolyte.

・ Assembly of electrochemical capacitor Swagelok tube fittings (manufactured by Swagelok, Bored-Through Union Tee, product number SS-810-3BT, manufactured by SUS316) are used for the cell body, and ferrules ( Swagelok, PTFE Ferrule Set, product number T-810-SET, made of polytetrafluoroethylene) and extraction electrode (12 mm diameter, 40 mm length SUS316 round bar) used in combination, and the remaining opening is rubber The cell was sealed with a stopper to form a cell. In a glove box (both O ₂ concentration and H ₂ O concentration 0.1 ppm or less), the two MXene electrodes prepared as described above are opposed to each other as a cathode and an anode inside the cell body, and a separator film is interposed between them. Insert and fit the extraction electrode with the ferrule from each of the two openings facing each other in the cell body until it comes into contact with the MXene electrode, fill the cell body with the electrolytic solution, and replace the remaining openings with rubber. After sealing with a stopper, an electrochemical capacitor for evaluating a power storage device was assembled.

・ Evaluation of capacitor characteristics Connect the external electrodes to the electrochemical capacitor assembled above, and use the electrochemical measurement device VMP3 manufactured by Bio-Logic Science Instruments SAS and software EC-Lab V11.12 to vary the voltage scanning speed. After setting, the energy density and the power density were measured as the capacitor characteristics. Table 1 shows the results.

(Example 2)
The diameter of the MXene (Ti ₃ C ₂ T _s ) electrode (anode and cathode) was 3.86 mm, the mass of the MXene electrode used for the cathode was 0.055 mg, and the mass of the MXene electrode used for the anode was 0 0.056 mg (these mass ratios were almost 1: 1). As an electrolytic solution, gBL (manufactured by Shigma Aldrich, product number B103608) was added to Li-TFSI (Shigma Aldrich) as an electrolyte. Company number 544094) at a molar concentration of 1 mol / L (total basis) except that a mixture was used in the same manner as in Example 1, except that a mixture was used. Energy density and power density were measured. Table 2 shows the results.

(Example 3)
An electrochemical capacitor was assembled as follows, the energy density and the power density were measured, and the capacitor characteristics were evaluated.

・ Cathode and anode (MXene electrode)
First, in the same manner as in Example 1 of Patent Document 1, to obtain a flexible freestanding film consisting essentially Ti ₃ C ₂ T _s. Next, the resulting free standing films of Ti ₃ C ₂ T _s were punched out one by one into a circle having a diameter of 5 mm for the cathode and a circle having a diameter of 10 mm for the anode, and the stainless steel mesh ( It was pressed and adhered to Nilaco Co., Ltd., product number: 788500, SUS316, 500 mesh) at a pressure of 400 MPa to obtain a cathode and an anode as MXene (Ti ₃ C ₂ T _s ) electrodes. The MXene electrode used for the cathode has a thickness of 3 μm, a specific gravity of 2.9 g / cm ³ and a mass of 0.11 mg, and the MXene electrode used for the anode has a thickness of 5 μm, a specific gravity of 1.6 g / cm ³ and a mass of 0.1 g. 63 mg, and their mass ratio was approximately 5: 1.

Separator A separator membrane prepared by processing a commercially available separator (ADVANTEC (registered trademark) manufactured by Advantech Toyo Co., Ltd., model: GA-100, glass fiber filter paper) into a diameter of 16 mm was prepared.

Electrolyte A mixture of EiPS as a solvent and Na-TFSI as an electrolyte (manufactured by Tokyo Chemical Industry Co., Ltd., product number: S0989) at a molar concentration of 1 mol / L (total basis) is prepared as an electrolyte. did.

・ Assembly of electrochemical capacitor Using a button battery package (manufactured by MTI Corporation, product name: CR2032 Coin Cell Cases, manufactured by SS316) in the cell body, one O-ring gasket and one spacer (manufactured by MTI Corporation, product name: EQ) -CR2325-Spacer), under which two wave springs (MTI Corporation, product name: EQ-CR20WS-Spring) are used and sealed with a coin caulking machine (Hohsen Corp.) to form a cell. It was taken. In a dry room under a dry atmosphere (dew point: less than −60 ° C.), the two MXene electrodes prepared as described above are opposed to each other as a cathode and an anode inside the cell body, with a separator film interposed therebetween. The battery was placed, the electrolyte was filled in the cell body, the package was sealed with a coin caulking machine, and an electrochemical capacitor for evaluating a power storage device was assembled.

・ Evaluation of capacitor characteristics By connecting external electrodes to the electrochemical capacitor assembled above, using the electrochemical measurement device VMP manufactured by Bio-Logic Science Instruments SAS and software EC-Lab V11.20, the voltage scanning speed was varied. After setting, the energy density and the power density were measured as the capacitor characteristics. Table 3 shows the results.

(Example 4)
The MXene (Ti ₃ C ₂ T _s ) electrode used for the cathode had a diameter of 7 mm, a thickness of 5 μm, a specific gravity of 2.3 g / cm ³ and a mass of 0.36 mg, and the MXene (Ti ₃ C ₂ T _s) used for the anode ) The electrode had a diameter of 12 mm, a thickness of 4 μm, a specific gravity of 2.2 g / cm ³ and a mass of 0.1 mg (the mass ratio was approximately 3: 1), and was a solvent as an electrolyte. Example 3 was the same as Example 3 except that EiPS was mixed with an electrolyte EMI-TFSI (Kishida Chemical Co., Ltd., product number: ILD-28294) at a molar concentration of 1 mol / L (overall standard). Similarly, an electrochemical capacitor was assembled, and energy density and power density were measured as capacitor characteristics. Table 4 shows the results.

(Comparative Example 1)
The diameter of the MXene (Ti ₃ C ₂ T _s ) electrode (anode and cathode) was 3.86 mm, the mass of the MXene electrode used for the cathode was 0.082 mg, and the mass of the MXene electrode used for the anode was 0 0.087 mg (these mass ratios were approximately 1: 1), and ethylene carbonate (EC) (manufactured by Shigma Aldrich, product number 676802-1L) and diethyl carbonate (DEC) ( To a mixed solvent (volume ratio EC: DEC = 3: 7) of Shigma Aldrich, product number 517135) was added 1 mol / L (total basis) of Li-TFSI (electrode, product number 544094) as an electrolyte. An electrochemical capacitor was assembled in the same manner as in Example 1 except that a mixture obtained by mixing at a molar concentration was used. The density and power density were measured. Table 5 shows the results.

As can be understood from Tables 1 to 5, Examples 1 to 4 can obtain higher energy density and power density at the same voltage scanning speed as compared with Comparative Example 1, and particularly, the electrode active material. A larger value was obtained in the energy density per unit volume of the electrode active material (Wh / L) and the power density (W / L) than the energy density per unit mass (Wh / L) and the power density (W / L). . For example, when the voltage scanning speed is 5 mV / s, the energy density of 7 Wh / L and the power density of 64 W / L in Comparative Example 1 are 47 Wh / L and 65 Wh / L in Examples 1 to 4. , 15 Wh / L and 11 Wh / L and power densities of 251 W / L, 484 W / L, 97 W / L and 87 W / L. For example, when focusing on the maximum value of the energy density, the maximum of the energy density is 12 Wh / L in Comparative Example 1, whereas the maximum of the energy density is 49 Wh / L and 65 Wh / L in Examples 1 to 3. And 17 Wh / L.

活性 Among the electrode active materials used in conventional electrochemical capacitors, activated carbon can be operated at a low temperature to a high temperature and has a high degree of freedom in selecting materials for members constituting the capacitor. However, with activated carbon, it is difficult to obtain such a large energy density and power density. For example, when the capacitor characteristics of an electrochemical capacitor using activated carbon for both the cathode and anode electrode active materials are evaluated at a voltage scanning rate of 5 mV / s, the energy density can be at most less than 10 Wh / L, The density can be at most less than 100 W / L.

電気 The electrochemical capacitor of the present invention can be used in a wide variety of fields as a power storage device or the like, but is not limited thereto.

This application claims the benefit of U.S. Application No. 62 / 691,158, which was provisionally filed with the United States Patent and Trademark Office on June 28, 2018, the entire contents of which are hereby incorporated by reference. Incorporated.

1a, 1b, 1c M _{n + 1} X _n layer 3a, 5a, 3b, 5b, 3c, 5c Modification or termination T
7a, 7b, 7c MXene layer 10 MXene (layered material)
11 containers (cells)
13 Non-aqueous electrolyte 15a Cathode 15b Anode 17 Separator 20 Electrochemical capacitor A, B terminal

Claims

An electrochemical capacitor in which a cathode and an anode are spaced apart in an electrolyte,
The cathode and the anode are layered materials including a plurality of layers as an electrode active material, and each layer has the following formula:
M n + 1 X n
Wherein M is at least one Group 3, 4, 5, 6, 7 metal;
X is a carbon atom, a nitrogen atom or a combination thereof;
n is 1, 2 or 3)
And each X has a crystal lattice located in an octahedral array of M, and at least one of two opposing surfaces of each layer has a group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom A layered material having at least one modification or termination T selected from the group consisting of:
An electrochemical capacitor, wherein the electrolytic solution contains gamma-butyrolactone as a solvent and at least one of lithium bis (trifluoromethanesulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide as an electrolyte.
An electrochemical capacitor in which a cathode and an anode are spaced apart in an electrolyte,
The cathode and the anode are layered materials including a plurality of layers as an electrode active material, and each layer has the following formula:
M n + 1 X n
Wherein M is at least one Group 3, 4, 5, 6, 7 metal;
X is a carbon atom, a nitrogen atom or a combination thereof;
n is 1, 2 or 3)
And each X has a crystal lattice located in an octahedral array of M, and at least one of two opposing surfaces of each layer has a group consisting of a hydroxyl group, a fluorine atom, an oxygen atom, and a hydrogen atom A layered material having at least one modification or termination T selected from the group consisting of:
An electrochemical capacitor, wherein the electrolytic solution contains ethyl isopropyl sulfone as a solvent and at least one of sodium bis (trifluoromethanesulfonyl) imide and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide as an electrolyte.
3. The electrochemical capacitor according to claim 1, wherein the formula M n + 1 X n is any one selected from the group consisting of Ti 3 C 2 , Ti 2 C and V 2 C. 4.