JP2011124021A - Electrolyte for electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for electrochemical devices, having a wide potential window and low toxicity. <P>SOLUTION: According to the invention, an electrolyte for electrochemical devices has a dicyanoether compound-BF<SB>3</SB>complex indicated by the chemical formula (1) (where R<SB>1</SB>and R<SB>2</SB>each indicate a hydrocarbon chain which may include a branch). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrolyte for an electrochemical device having a wide potential window and low toxicity. The electrolytic solution for electrochemical devices of the present invention can be suitably used as an electrolytic solution for a secondary battery using a positive electrode active material having a high charging voltage or an electrolytic solution for a capacitor having a high withstand voltage.

A conventional lithium ion battery uses lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), a solid solution thereof, lithium manganate (LiMn ₂ O ₄ ) or the like as a positive electrode, and consists of carbon such as graphite as a negative electrode. A negative electrode material is used. An electrolytic solution in which a liquid organic compound such as ethylene carbonate or propylene carbonate is dissolved in a solvent and a lithium salt as a solute is used.

In order to further increase the energy density of such a lithium ion battery, a search for a new positive electrode active material is underway. For example, _Li 2 NiPO ₄ F in Patent Documents 1 and _2, LiNiPO _4, LiCoPO 4 and _Li 2 CoPO ₄ F has been proposed as a high positive electrode active material energy density. If these positive electrode active materials having a large energy density are used in a lithium ion battery, theoretically, a lithium ion battery having a large charge capacity should be obtained.

  However, since the charge reaction of such a positive electrode active material occurs at an extremely high potential, the conventional lithium ion battery electrolyte using an organic solvent such as cyclic carbonate or chain carbonate is used after the solvent is oxidized and decomposed. There was a problem that it was impossible. For this reason, there is a problem that the capacity that can be actually taken out is less than half of the theoretical capacity (Non-Patent Document 1).

  On the other hand, in the field of electrolytic solutions for capacitors, an electrolytic solution having a wide potential window has been demanded in order to improve the withstand voltage.

Under such circumstances, an electrolytic solution using a boron trifluoride (BF ₃ ) -ether complex as a solvent has been proposed as an electrolytic solution having a wide potential window that can withstand a higher potential than conventional electrolytic solutions ( Patent Documents 3 and 4). BF ₃ exhibits properties as a strong Lewis acid because a boron atom is bonded to three fluorine atoms having a high electronegativity. For this reason, the vacant orbit of BF ₃ is strongly coordinated to the oxygen lone pair present in the ether molecule to form a complex, and the electron density of oxygen decreases. As a result, the oxidation resistance of the ether molecules is improved, and the electrolytic solution has a wide potential window. For this reason, it can be used without being decomposed even at a high potential that cannot be used with a conventional electrolyte solution for a lithium ion battery using a cyclic carbonate or a chain carbonate.

  On the other hand, the present inventors have found that an electrolytic solution containing a dinitrile compound having a nitrile group bonded to both ends of a hydrocarbon chain has a wide potential window and is difficult to be decomposed even at a high positive potential. An electrolytic solution for a lithium ion battery has been developed (Patent Document 5).

Patent No. 3624205 Patent No. 3631202 JP 2008-94825 A JP 2008-273893 A JP 2009-158240 A

Journal of Power Sources 146 (2005) 565-569

However, the potential window of the electrolytic solution containing the boron trifluoride (BF ₃ ) -ether complex in the solvent is 6 V or less, which is not yet sufficiently wide, and further expansion of the potential window has been desired.
Moreover, the electrolytic solution containing the above dinitrile compound has high toxicity of the dinitrile compound, and it is necessary to give sufficient consideration to the working environment at the time of battery production and leakage of the electrolytic solution.
The present invention has been made in view of the above-described conventional situation, and an object to be solved is to provide an electrolytic solution for an electrochemical device having a wide potential window and low toxicity.

In the electrolyte solution containing the boron trifluoride (BF ₃ ) -ether complex as a solvent, the present inventors have a particularly wide potential window when a complex of a cyano ether compound having one nitrile group and BF ₃ is used. I paid attention to it. Since the nitrile group has an electron withdrawing property similar to BF ₃ , it is considered that the nitrile group has an effect of widening the potential window, like BF ₃ . If this idea is correct, the potential window could be expanded further by using a complex of BF ₃ and a cyanoether compound having two or more nitrile groups. The invention has been completed.

That is, the electrolytic solution for an electrochemical device of the present invention has a dicyano ether compound represented by the following chemical formula (1) (wherein R ₁ and R ₂ represent a hydrocarbon chain which may have a branch) as a solvent. wherein the -BF ₃ complexes are included.

In the lithium ion battery electrolyte of the present invention, a complex of BF ₃ and a dicyanoether compound in which a nitrile group is bonded to hydrocarbon chains (R ₁ and R ₂ in the following chemical formula (1)) on both sides of an ether bond is formed. include. In this complex (1), the vacancy of BF ₃ is strongly coordinated to the lone pair of oxygen present in the ether molecule, and the electron density of oxygen is reduced. Furthermore, electrons are attracted from oxygen present in the ether due to the electron-withdrawing properties of the nitrile groups present at the ends of the hydrocarbon chains (R ₁ and R ₂ in the above chemical formula (1)) on both sides across the ether bond. To do. For this reason, the oxidation resistance of the ether molecules is improved, and the electrolytic solution has a particularly wide potential window. The dicyano ether compound also has an advantage that it is less toxic than a dinitrile compound in which a nitrile group is bonded to both ends of an alkyl group.

  Examples of the dicyano ether compound include oxydipropionitrile, oxydiacetonitrile, oxydibutyronitrile, oxydipentionitrile and the like. These dicyano ether compounds are not particularly limited in carbon number, but are preferably 20 or less.

In the electrolytic solution for electrochemical devices of the present invention, it is preferable that at least one of cyclic carbonate, cyclic ester and chain carbonate is further contained in the solvent.
In this case, since at least one of a cyclic carbonate, a cyclic ester, and a chain carbonate is mixed in the dicyano ether compound-BF ₃ complex having a high viscosity, the viscosity is lowered and the specific conductivity is also increased.
In addition, in this case, even though at least one of a cyclic carbonate, a cyclic ester, and a chain carbonate having no particularly wide potential window is contained in the solvent, it has a wide potential window. Although the reason for this is not necessarily clear, it can be considered as follows. That is, among the organic solvents used in the electrolytic solution for electrochemical devices of the present invention, the cyanoether compound plays a role of expanding the potential window. In addition, chain carbonate is presumed to play a role of increasing specific conductivity in order to lower the viscosity. Cyclic carbonates and cyclic esters dissolve many lithium salts and form a protective film called SEI on the carbon negative electrode, thereby improving the reduction resistance and allowing the passage of Li ions. Can be granted. Therefore, it is considered that the effect can be exerted on the enlargement of the potential window on the negative side and the positive side.
From the above, it is preferable to use a chain carbonate and a cyclic carbonate and / or a cyclic ester in combination. More preferably, it is a combined use of a chain carbonate and a cyclic carbonate. Specifically, diethyl carbonate and ethylene carbonate are used in combination. The blending ratio of both is not particularly limited, but the same amount is preferable.

When the electrolytic solution for electrochemical devices of the present invention is used as an electrolytic solution for a lithium ion battery, a lithium salt is added to the electrolytic solution. Among the lithium salts, LiPF ₆ , LiBF ₄ , LiTFSI, and LiBETI are preferable because they are stable even at a high potential. Thus, the fourth aspect of the lithium ion battery electrolyte solution of the present _invention, LiPF _6, LiBF 4, LiTFSI, it was decided to include at least one of LiBETI. More preferred are LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate) and LiTFSI (lithium bis (trifluoromethanesulfonyl) imide).

  The concentration of the lithium salt is 0.01 mol / L or more, and is preferably lower than the saturated state. When the concentration of the lithium salt is less than 0.01 mol / L, since the number of dissociated Li ions is small, the Li ion conductivity becomes extremely small and Li ion conduction cannot be ensured. Therefore, there is a possibility that the overvoltage is increased and the potential of the original electrolyte is greatly shifted. On the other hand, when the concentration of the lithium salt is in a saturated state, the dissolved lithium salt may be precipitated due to a change in temperature, and the electrode or the like may be deformed.

Moreover, when using the electrolyte solution for electrochemical devices of the present invention as an electrolyte solution for sodium ion batteries, the sodium salts include NaPF ₆ , NaBF ₄ , (CF ₃ SO ₂ ) ₂ NNa, and (C ₂ F ₅ SO ₂ ) ₂ NNa can be used. These sodium salts may be used alone or in combination of two or more kinds. Particularly preferred is NaPF _6.

Further, the electrochemical device for dicyano ether compound -BF ₃ complexes contained in the electrolytic solution of the present invention, it is preferable that the concentration is less than 100% by volume or more 1 volume% to the solvent. When the concentration of the dicyano ether compound-BF ₃ complex is less than 1% by volume, the effect of expanding the potential window becomes small. More preferably, it is 5 volume% or more and less than 90 volume%. When the concentration of the dicyano ether compound-BF ₃ complex is 90% by volume or more, the solubility of the electrolyte is lowered and the viscosity is also increased, so that the conductivity is lowered, and the internal resistance of the battery is increased.

When the electrolyte for an electrochemical device of the present invention is used as an electrolyte for a lithium ion battery, a high potential redox positive electrode in which the potential for charging is present in a region exceeding 5.2 V (vs. Li / Li ⁺ ). An active material can be used. For this reason, it can be set as a battery with a large electromotive force and high energy density.

3 is a potential-current curve of Test Example 1. 6 is a potential-current curve of Test Example 2. 10 is a potential-current curve of Test Example 3. 6 is a potential-current curve of Test Example 4.

(Embodiment 1)
In Embodiment 1, the case where the electrolytic solution for an electrochemical device of the present invention is applied to an electrolytic solution for a lithium ion battery will be described.

In this lithium ion battery electrolyte, a lithium salt is dissolved in a solvent containing a dicyano ether compound-BF ₃ complex. Here, the dicyano ether compound has a nitrile group (that is, a total of two nitrile groups) at the ends of the hydrocarbon chains (R ₁ and R ₂ ) on both sides of the ether bond, as shown in Chemical Formula 2 below. Yes. Here, R ₁ and R ₂ may be a branched hydrocarbon chain. And the vacant orbit of BF ₃ is coordinated to the lone pair of oxygen present in the ether molecule to form a dicyano ether compound-BF ₃ complex. Furthermore, electrons are attracted from oxygen present in the ether by the electron withdrawing property of the nitrile group present at the ends of the hydrocarbon chains on both sides of the ether bond. For this reason, the oxidation resistance of the dicyano ether compound is improved, and the electrolytic solution has a particularly wide potential window. Moreover, the dicyano ether compound which has a nitrile group also has the advantage that toxicity is lower than the dinitrile compound which the nitrile group couple | bonded with the both terminal of the alkyl group.

To produce the complex (1) can be obtained widely and diethyl ether -BF ₃ complex marketed by substitution reaction with dicyano ether compound. More specifically, it can be easily obtained by mixing a diethyl ether-BF ₃ complex and a dicyano ether compound and distilling off the low-boiling component diethyl ether.

As the electrolyte containing lithium ions, lithium salts used in lithium ion batteries can be used. For example, LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiTFSI (lithium bis (trifluoromethanesulfonyl) imide), LiTFS (lithium trifluoromethanesulfonate) and LiBETI (lithium bis (penta Fluoroethanesulfonyl) imide) and the like. These lithium salts have a sufficient potential window that does not decompose even at high potentials. Among these, it is preferable that at least one of LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate) and LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) is contained. LiPF ₆ (lithium hexafluorophosphate) and LiBF ₄ (lithium tetrafluoroborate) form fluoride on aluminum often used as the electrode substrate of the positive electrode of lithium ion batteries, and prevent corrosion of aluminum. I can do it. Furthermore, they are also more effective in expanding the potential window than LiTFS (lithium trifluoromethanesulfonate) and LiBETI (lithium bis (pentafluoroethanesulfonyl) imide). LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) has a particularly high decomposition temperature, improved heat resistance, high solubility, and high specific conductivity.

In addition, it is also preferable to contain the cyclic carbonate, cyclic ester, and chain carbonate which are the solvents conventionally used for the lithium ion battery as a solvent. If this, in ether complexes of the BF ₃ high viscosity cyano ether compound, cyclic carbonate, because the at least one of cyclic ester and the chain carbonate are mixed, the viscosity is low, the ratio conductivity even growing.
Examples of the cyclic carbonate include ethylene carbonate and propylene carbonate. Moreover, (gamma) -butyllactone etc. are mentioned as cyclic ester. Further, examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like.

The above is the case where the electrolytic solution for electrochemical devices of the present invention is applied to the electrolytic solution of a lithium ion battery, but can also be applied to a sodium ion battery. When the electrolytic solution for the sodium ion battery, a sodium _salt, NaPF _6, NaBF _4, can be used (CF ₃ SO _{2) 2} NNa and _{(C 2 F 5 SO 2)} 2 NNa. These sodium salts may be used alone or in combination of two or more kinds. Particularly preferred is NaPF _6.

Hereinafter, Examples 1 and 2 in which the electrolyte for an electrochemical device of the present invention is embodied as an electrolyte for a lithium ion battery, and Test Examples 1 and 2 in which a dicyano ether compound that is not a BF ₃ complex is used as a solvent. Further details will be described.

(Test Example 1)
In Test Example 1, an electrolyte solution for a lithium ion battery having the following composition was prepared.
Solvent: oxy dipropionate nitrile _{(NCCH 2 CH 2 -O-CH} 2 CH 2 CN)
Electrolyte: LiPF ₆ 0.1 mol / L

(Test Example 2)
In Test Example 2, an electrolyte solution for a lithium ion battery having the following composition was prepared.
Solvent: Oxydipropionitrile: EC (ethylene carbonate): DEC
(Diethyl carbonate) = 50: 25: 25 (volume ratio)
Electrolyte: LiPF ₆ 0.5 mol / L

(Test Example 3)
In Test Example 3, an electrolyte solution for a lithium ion battery having the following composition was prepared.
Solvent: oxy dipropionate nitrile _{(NCCH 2 CH 2 -O-CH} 2 CH 2 CN)
Electrolyte: LiBF ₄ 0.1 mol / L

(Test Example 4)
In Test Example 4, an electrolyte solution for a lithium ion battery having the following composition was prepared.
Solvent: Oxydipropionitrile: EC (ethylene carbonate): DEC
(Diethyl carbonate) = 50: 25: 25 (volume ratio)
Electrolyte: LiBF ₄ 1 mol / L

-Evaluation-
(Measurement of potential-current curve)
About the electrolyte solution for lithium ion batteries of Test Examples 1 to 4 prepared as described above, a potential-current curve was measured. A potentiogalvanostat was used for measurement, glassy carbon was used for the working electrode, and a platinum wire was used for the counter electrode. Further, metallic lithium was used for the reference electrode. The potential sweep rate was 5 mV / sec. The results are shown in FIGS.

As a result, as shown in FIG. 1 and FIG. 3, the potential window of the electrolytes of Test Example 1 and Test Example 3 is 8 V or more with respect to (Li / Li ⁺ ) (the judgment criterion of the potential window is 50 μA / cm ² ). The same applies hereinafter), and it was found to have an extremely wide potential window.

  Moreover, also in Test Example 2 and Test Example 4 in which EC and DEC were added in 25% by volume to the solvent, as shown in FIG. 2 and FIG. 4, it was found that the potential window was 7 V or more and had a wide potential window. . Since the electrolyte solutions of Test Example 2 and Test Example 4 each contain 25% by volume of EC and DEC having a lower viscosity than oxydipropionitrile, the viscosity is lowered and the specific conductivity is also increased.

Although EC and DEC alone do not have such a wide potential window, the reason why the electrolyte of Test Example 2 containing these organic solvents has such a wide potential window becomes clear. It is not considered as follows.
That is, oxydipropionitrile, which is a dicyano ether compound among organic solvents, plays a role of expanding the potential window. In addition, DEC, which is a chain carbonate, is presumed to play a role in increasing specific conductivity in order to lower the viscosity. And EC which is cyclic carbonate is excellent in the solubility of lithium salt, and by forming a protective film called SEI on the carbon negative electrode, it is possible to pass Li ions while improving reduction resistance. Can be granted. It is considered that an SEI film is also formed on the positive electrode, so that it is possible to exert an effect on the enlargement of the negative and positive potential windows.

Example 1
In Example 1, an electrolytic solution for a lithium ion battery having the following composition is prepared.
Solvent: oxy dipropionate nitrile _{(NCCH 2 CH 2 -O-CH} 2 CH 2 CN)
BF ₃ complex Electrolyte: LiPF ₆ 0.1 mol / L
The BF ₃ complex of oxydipropionitrile (NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN) is a mixture of commercially available BF ₃ diethyl ether complex and oxydipropionitrile, and the diethyl ether is distilled off. Can be easily obtained.

(Example 2)
In Example 2, an electrolyte solution for a lithium ion battery having the following composition is prepared.
Solvent: BF ₃ complex of oxydipropionitrile: EC (ethylene carbonate)
G): DEC (diethyl carbonate) = 50: 25: 25 (volume ratio)
Electrolyte: LiPF ₆ 0.1 mol / L

(Example 3)
In Example 3, an electrolyte solution for a lithium ion battery having the following composition is prepared.
Solvent: oxy dipropionate nitrile _{(NCCH 2 CH 2 -O-CH} 2 CH 2 CN)
BF ₃ complex Electrolyte: LiBF ₄ 0.1 mol / L

Example 4
In Example 4, an electrolyte solution for a lithium ion battery having the following composition is prepared.
Solvent: BF ₃ complex of oxydipropionitrile: EC (ethylene carbonate)
G): DEC (diethyl carbonate) = 50: 25: 25 (volume ratio)
Electrolyte: LiBF ₄ 0.5 mol / L

When the potential-current curve of the electrolyte solution for lithium ion battery of Example 1 prepared as described above is measured, the potential window becomes wider than that of the electrolyte solution of Test Example 1. This is because the oxydipropionitrile contained in the electrolyte solution of Example 1 is complexed by BF ₃ coordination. For this reason, an ether-bonded oxygen lone pair is attracted to BF ₃ . Furthermore, electrons are further withdrawn from oxygen present in the ether due to the electron withdrawing property of the nitrile group of oxydipropionitrile. For this reason, the oxidation resistance of oxydipropionitrile is remarkably improved, and the electrolytic solution has a particularly wide potential window. Oxydipropionitrile also has an advantage that it is less toxic than a dinitrile compound in which a nitrile group is bonded to both ends of an alkyl group.
In Example 3 from that was only changing the LiPF ₆ is used as an electrolyte of the electrolytic solution of Example 1 LiBF _4, it is clear that the same effects as described above.

Further, in Example 2 in which EC and DEC are added to the solvent by 25% by volume, for the same reason, a wide potential window is provided. Furthermore, since it contains 25% by volume of EC and DEC, each having a lower viscosity than the BF ₃ complex of oxydipropionitrile, the viscosity is lowered and the specific conductivity is also increased.
In Example 4, since the only found a new LiPF ₆ is used as an electrolyte of the electrolytic solution of Example 2 LiBF _4, it is clear that the same effects as described above.

The present invention is applied to lithium ion batteries and sodium ion batteries.
These secondary batteries include an electrolytic solution, a positive electrode, a negative electrode, a separator, and a case.

(Positive electrode)
The positive electrode includes a positive electrode active material and a current collector.
(Positive electrode active material for lithium batteries)
The positive electrode active material for a lithium battery refers to “a material in which lithium is inserted / extracted in the crystal structure at a higher potential than that of the negative electrode, and oxidation / reduction is performed accordingly”.
Examples of the positive electrode active material for a lithium battery include (1) an oxide type, (2) a phosphate type having an olivine type crystal structure, and (3) an olivine fluoride type.

(1) Oxide-based 1-1 specific substances As oxide-based materials, Li _1-x CoO ₂ (x = 0 to 1: layered structure), Li _1-x NiO ₂ (x = 0 to ₁ : layered structure) ), Li _1-x Mn ₂ O ₄ (x = 0 to 1: spinel structure), Li _2−y MnO ₃ (y = 0 to 2) and their solid solutions (herein, solid solutions are those of the above oxide series) In the positive electrode active material, it refers to a material in which metal atoms are mixed in a free ratio. Moreover, what doped the metal atom of these with the other metal atom is also contained. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction. For example, one or more of Li, Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used.
1-2 Characteristics The general discharge potential of this positive electrode active material is less than 5 V (vs Li / Li ⁺ ). However, LiNi _0.5 Mn _1.5 O ₄ partially substituted with Ni in the LiMn ₂ O ₄ system has a discharge potential of 4.7 V, and takes into account overvoltage when performing rapid charging, and 5 V May require a charging voltage exceeding. Further, since LiCoMnO ₄ starts with a discharge voltage of about 5.2V, the charge voltage also exceeds 5V. In addition, oxide systems generally decompose at less than 300 ° C., and have a relatively large exothermic reaction as oxygen is generated. Therefore, a control circuit that does not cause overcharging is required.

(2) Phosphate-based 2-1 specific substance having olivine-type crystal structure As phosphate-based substances having olivine-type crystal structure, Li _1-x NiPO ₄ (x = 0 to ₁ ), Li _1-x CoPO ₄ (x = 0 to ₁ ), Li _1-x MnPO ₄ (x = 0 to ₁ ), Li _1-x FePO ₄ (x = 0 to 1) and their solid solutions (herein the solid solution is the above-mentioned phosphorus In the acid salt positive electrode active material, it refers to a material in which metal atoms are mixed in a free ratio. Moreover, what doped the metal atom of these with the other metal atom is also contained. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction. For example, one or more of Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used (see JP 2008-130525 A).
2-2 Characteristics The oxidation-reduction potential of this positive electrode active material is attracting attention because, unlike the above oxide system, if it is less than 300 ° C., the exothermic reaction is small, oxygen is not generated, and safety is high. Of the phosphate systems, the LiCoPO ₄ system has a discharge potential of about 4.8 V, and an electrolyte having a withstand voltage of 5 V or more is required for rapid charging. It is suggested that LiNiPO _{4 has} a discharge potential of 5.2 V (vs Li / Li ⁺ ).

(3) Olivine fluoride system 3-1 Specific substances Li _2-x NiPO ₄ F (x = 0 to 2), Li _2-x CoPO ₄ F (x = 0 to 2) are known, and other Li _{2 -x MnPO 4 F (x = 0~2} ), Li 2-x FePO 4 F (x = 0~2) are considered.
Further, these solid solutions (herein, the solid solution refers to a material in which metal atoms are mixed in a free ratio in the olivine fluoride-based positive electrode active material) can also be mentioned. Furthermore, the thing which doped the metal atom of these with another metal atom is also contained. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction. For example, one or more of Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used.
3-2 Characteristics Similar to the olivine system, the redox potential of this positive electrode active material is different from that of the above oxide system. The effect of battery ignition is considered to be small, and is attracting attention in terms of safety. Moreover, the electric capacity density (mAh / g) of a battery can be made higher than the said phosphate system (refer Unexamined-Japanese-Patent No. 2003-229126). However, for example, the Li ₂ CoPO ₄ F system has an average discharge potential of about 4.8 V, and an electrolytic solution having a withstand voltage of 5 V or more is required for rapid charging. Further, the discharge potential of the Li ₂ NiPO ₄ F system is about 5.2 V (vs Li / Li ⁺ ), and an electrolytic solution having a withstand voltage at 5 V or more is required.

(4) Others In addition, lithium-free FeF ₃ , a conjugated polymer using an organic conductive material, a chevrel phase compound, or the like can also be used. In addition, transition metal chalcogenides, vanadium oxides and lithium salts thereof, niobium oxides and lithium salts thereof, and a plurality of different positive electrode active materials may be used in combination.
The average particle diameter of the positive electrode active material particles is not particularly limited, but is preferably 10 nm to 30 μm.

(Positive electrode active material for sodium batteries)
The positive electrode active material for a sodium battery refers to “a substance that can be reversibly oxidized and reduced by charge and discharge as a positive electrode of a secondary battery”. Further, the positive electrode active material of the sodium ion battery is required to be a material capable of reversibly intercalating and deintercalating sodium ions.
Examples of such a positive electrode active material include NaFeO ₂ , NaNiO ₂ , NaCoO ₂ , NaMnO ₂ , NaFe _1-x M ¹ _x O ₂ , and NaNi _1-x M ¹ _{x described in} JP2009-129741A. O ₂ , NaCo _1-x M ¹ _x O ₂ , NaMn _1-x M ¹ _x O ₂ (where M ¹ is one or more elements selected from the group consisting of trivalent metals, and 0 ≦ x <0 .5)) and the like. Among these, a composite oxide mainly containing iron and sodium, and using a composite oxide having a hexagonal crystal structure as a positive electrode active material, a high discharge voltage can be obtained. A secondary battery having a high density can be obtained.

More preferably, the positive electrode active material is a composite oxide mainly containing iron and sodium, has a hexagonal crystal structure, and has an interplanar spacing of 2 in the X-ray diffraction analysis of the composite oxide. A composite oxide having a value obtained by dividing the intensity of a peak of 20 angstroms by the intensity of a peak of 5.36 angstroms in plane spacing is 2 or less. In heating a metal compound mixture containing a sodium compound and an iron compound in a temperature range of 400 ° C. or more and 900 ° C. or less, the atmosphere is heated as an inert atmosphere in a temperature range of less than 100 ° C. during the temperature increase. Is preferred.
Moreover, what doped the transition metal atom of these compounds with the other metal atom may be used. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction.

(Current collector for positive electrode)
The positive electrode current collector is a conductive substrate carrying a positive electrode active material.
The molding material for the current collector of the positive electrode is required to be stable during charging. In particular, when using a phosphate-based and olivine fluoride-based positive electrode active material having an olivine-type crystal structure with a high redox potential, it is preferable to use a material excellent in corrosion resistance.
For example, when LiPF ₆ or LiBF ₄ is used as the electrolyte, austenitic stainless steel, Ni, Al, Ti, or the like can be used, but it is preferable to select them appropriately in consideration of the operating potential of the positive electrode active material to be used.
Further, when LiTFSI is used as the electrolyte, it is preferable that LiPF ₆ coexists in order to form a corrosion-resistant film on the surface of the positive electrode current collector. LiBETI and LiTFS are the same as in LiTFSI.
In addition, a conductive metal material such as Al coated with conductive DLC (diamond-like carbon) by a well-known method can be used as a current collector. When the electrolyte is a lithium salt such as LiBF ₄ or LiPF ₆ that easily forms a fluoride film, a thick fluoride film is formed on the aluminum and the corrosion resistance is improved, but the electronic conductivity is lowered, and consequently The increase in output accompanying the increase in ohmic overvoltage is impeded. If the conductive metal material such as Al is coated with the conductive DLC, the fluoride film is generated only in a very small area of the defective portion of the conductive DLC. For this reason, even if the voltage is increased, the decrease in electron conductivity is negligible, and it is possible to prevent the decrease in output due to the increased voltage, which is a concern.
Here, the conductive diamond-like carbon is carbon having an amorphous structure in which both diamond bonds (SP ₃ hybrid orbital bonds between carbons) and graphite bonds (SP ₂ hybrid orbital bonds between carbons) are mixed. Among them, the one whose conductivity is 1000 Ωcm or less. However, in addition to the amorphous structure, those having a phase composed of a crystal structure partially composed of a graphite structure (that is, a hexagonal crystal structure composed of SP ₂ hybrid orbital bonds) and thereby exhibiting conductivity are also included. . Diamond-like carbon having properties intermediate between graphite and diamond adjusts the conductivity by adjusting the ratio of SP ₂ hybrid orbital bonds and SP ₃ hybrid orbital bonds of the carbon atoms constituting diamond-like carbon during film formation. be able to.
Of course, you may coat | cover the said corrosion-resistant electroconductive metal material with electroconductive DLC.
The shape and structure of the current collector can be arbitrarily designed according to the structure of the positive electrode active material and the battery.

(Pretreatment of positive electrode)
The positive electrode for a secondary battery is immersed in a pretreatment electrolytic solution in which a lithium salt is dissolved in an organic solvent containing 1% by volume or more of a nitrile compound before being incorporated into a lithium ion battery or a sodium ion battery. Steps are performed, and a positive voltage treatment step for applying a positive voltage to the electrodes is further performed. The electrode thus pretreated has a wide potential window even when used in an electrolyte solution containing no nitrile compound or in a lithium ion battery using an electrolyte solution with a small amount of nitrile compound added. It becomes difficult to disassemble (see Japanese Patent Application No. 2009-180007). The reason why the electrode has such a wide potential window is presumed to be that a corrosion-resistant film containing nitrogen as a component is formed on the electrode.

(Negative electrode)
The negative electrode includes a negative electrode active material and a current collector.
(Anode active material for lithium battery)
The negative electrode active material for a lithium battery refers to “a material in which lithium is inserted / extracted in the crystal structure at a potential lower than that of the positive electrode, and oxidation / reduction is performed accordingly”.
Examples of the negative electrode active material for a lithium battery include various carbon materials such as artificial graphite, natural graphite, and hard carbon, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), H ₂ Ti ₁₂ O ₂₅ , and H ₂ Ti ₆ O. ₁₃ , Fe ₂ O _{3 and the} like. Moreover, the composite material which mixed these suitably can also be mentioned. Further, there are Si fine particles and Si thin films, and fine particles and thin films in which these Si are Si-based alloys such as Si—Ni, Si—Cu, Si—Nb, Si—Zn, Si—Sn, and the like. Further, SiO oxide, Si-SiO ₂ composite, Si-SiO ₂ - can be given complex, etc., such as carbon.

(Anode active material for sodium batteries)
The negative electrode active material for a sodium battery is “a substance that allows sodium ions to enter and exit as a negative electrode of a secondary battery and reversibly repeat oxidation and reduction”, and in the present invention, Li ₄ Ti ₅ O _12. Is used.
(Current collector for negative electrode)
The current collector for the negative electrode can be formed of a general-purpose conductive metal material, Cu, Al, Ni, Ti, austenitic stainless steel, or the like.
However, it is necessary to select appropriately according to the combination of the operating potential of the negative electrode used and the electrolyte.

(Electroconductive member for positive electrode)
Some positive electrode active materials have low electrical conductivity. Therefore, it is preferable to provide a sufficient electron conduction path between the positive electrode active material and the current collector by interposing a conductive electron conduction member.
Here, the form of the electron conducting member is not particularly limited as long as an electron conducting path can be formed between the positive electrode active material and the current collector. For example, carbon black such as acetylene black, graphite powder, diamond-like carbon, glassy Conductive powder (conductive aid) such as carbon can be used. Diamond-like carbon and glassy carbon have a much wider potential window than carbon black and graphite, and are excellent in corrosion resistance when a high potential is applied, and therefore can be suitably used. Moreover, it is also preferable that metal fine particles are supported on these conductive assistants. Examples of the metal fine particles include Pt, Au, Ni and the like. These may be used alone or an alloy thereof.
As the electron conductive material, a conductive film (such as a DLC film) covering the positive electrode active material or a conductive thin film (such as a gold thin film) in which the positive electrode active material is embedded can be used.

(Electroconductive member for negative electrode)
The thing similar to the electron conductive member for positive electrodes can be used.

(Separator)
The separator is immersed in the electrolytic solution, separates the positive electrode and the negative electrode to prevent a short circuit therebetween, and allows passage of Li ions and Na ions.
Examples of such separators include porous films made of polyolefin resins such as polyethylene and polypropylene.

(Case)
The case is formed of a material having corrosion resistance against the electrolytic solution. The shape can be arbitrarily designed according to the intended use of the battery.
When using an electrolytic solution in which a lithium salt or a sodium salt is dissolved, a base material made of austenitic stainless steel, a case made of Ti, Ni and / or Al can be used. However, there are cases where it is necessary to select appropriately depending on the operating potential of the positive electrode and negative electrode active material to be used.
When the case also serves as a current collector or is electrically coupled to the current collector, the case is formed of the same or the same material as the current collector forming material of each electrode.

  The present invention is not limited to the description of the embodiment of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

Claims (5)

The solvent includes a dicyanoether compound-BF ₃ complex represented by the following chemical formula (1) (wherein R ₁ and R _{2 each} represents a hydrocarbon chain which may have a branch): Electrolytic solution for electrochemical devices.

  2. The electrolytic solution for an electrochemical device according to claim 1, wherein the dicyano ether compound is oxydipropionitrile.   The electrolyte solution for electrochemical devices according to claim 1, wherein the solvent further contains at least one of a cyclic carbonate, a cyclic ester, and a chain carbonate. The electrolytic solution for an electrochemical device according to any one of claims 1 to 3, wherein at least one of LiPF ₆ , LiBF ₄ , LiTFSI, and LiBETI is dissolved as an electrolyte. 4. The electrolyte according to claim 1, wherein at least one of NaPF ₆ , NaBF ₄ , (CF ₃ SO ₂ ) ₂ NNa and (C ₂ F ₅ SO ₂ ) ₂ NNa is dissolved as an electrolyte. The electrolyte solution for electrochemical devices according to Item.

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