Electrolyte for secondary battery, and secondary battery

Abstract

The secondary battery includes: a first electrode; a positive electrode; a negative electrode; and an electrolyte solution containing a magnesium salt and a cyclic unsaturated hydrocarbon compound. The cyclic unsaturated hydrocarbon compound contains a monocyclic or bicyclic fused ring comprising a plurality of carbon atoms, the monocyclic or bicyclic fused ring containing two or more carbon-carbon double bonds, and the bicyclic fused ring excluding a benzene ring. The number of carbon-carbon double bonds is an even number when the number of the plurality of carbon atoms constituting the single ring is 7 or less. The number of carbon-carbon double bonds is an odd number or an even number when the number of the plurality of carbon atoms constituting the single ring is 8 or more. The number of carbon-carbon double bonds in the bicyclic condensed ring is an odd number or an even number.

Description

Technical Field

[0001] The present technology relates to an electrolyte for a secondary battery and a secondary battery. Background Art

[0002] A variety of electronic devices such as mobile phones are becoming popular. Therefore, as a small, lightweight, and high-energy-density power source, the development of secondary batteries is underway. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte (electrolyte for a secondary battery). Regarding the configuration of the secondary battery, various studies have been conducted.

[0003] Specifically, in a secondary battery that uses the precipitation and dissolution of magnesium for charge and discharge reactions, the electrolyte contains a compound having an unsaturated hydrocarbon skeleton such as anthracene (for example, refer to Patent Document 1).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Pamphlet of International Publication No. 2020 / 090946 Summary of the Invention

[0007] The battery characteristics of the secondary battery are not yet sufficient, and thus there is room for improvement.

[0008] There is a desire to obtain an electrolyte for a secondary battery and a secondary battery having excellent battery characteristics.

[0009] The electrolyte for a secondary battery according to one embodiment of the present technology contains a magnesium salt and a cyclic unsaturated hydrocarbon compound. The cyclic unsaturated hydrocarbon compound includes a monocyclic or bicyclic condensed ring composed of a plurality of carbon atoms. The monocyclic or bicyclic condensed ring contains two or more carbon-carbon double bonds, and the bicyclic condensed ring does not include a benzene ring. When the number of carbon atoms constituting the monocyclic ring is 7 or less, the number of carbon-carbon double bonds is an even number. When the number of carbon atoms constituting the monocyclic ring is 8 or more, the number of carbon-carbon double bonds is an odd number or an even number. The number of carbon-carbon double bonds in the bicyclic condensed ring is an odd number or an even number.

[0010] A secondary battery according to one embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte, and the electrolyte has the same configuration as that of the electrolyte for a secondary battery according to one embodiment of the present technology described above.

[0011] Herein, a "monocyclic ring" is a single carbon ring composed of a plurality of carbon atoms. In addition, a "bicyclic condensed ring" is a ring composed of a plurality of carbon atoms and in which two carbon rings are condensed with each other, and as described above, does not include a benzene ring. The details of the monocyclic ring and the bicyclic condensed ring will be described later.

[0012] In a secondary battery electrolyte and a secondary battery according to an embodiment of the present technology, the secondary battery electrolyte contains a magnesium salt and a cyclic unsaturated hydrocarbon compound. The cyclic unsaturated hydrocarbon compound contains a monocyclic or bicyclic fused ring. The monocyclic or bicyclic fused ring contains two or more carbon-carbon double bonds. The bicyclic fused ring does not include a benzene ring. The number of carbon-carbon double bonds satisfies the above conditions, so excellent battery characteristics can be obtained.

[0013] In addition, the effects of the present technology are not necessarily limited to the effects described herein, and may be any of a series of effects associated with the present technology described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a perspective view showing the configuration of a secondary battery according to an embodiment of the present technology.

[0015] Figure 2 is a cross-sectional view showing Figure 1 the configuration of the battery element shown.

[0016] Figure 3 is a cross-sectional view showing the configuration of a test secondary battery. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. In addition, the order of description is as follows.

[0018] 1. Secondary battery electrolyte

[0019] 1-1. Configuration

[0020] 1-2. Manufacturing method

[0021] 1-3. Action and effect

[0022] 2. Secondary battery

[0023] 2-1. Structure

[0024] 2-2. Operation

[0025] 2-3. Manufacturing method

[0026] 2-4. Action and effect

[0027] 3. Use of the secondary battery

[0028] <1. Secondary battery electrolyte>

[0029] First, a secondary battery electrolyte (hereinafter, simply referred to as "electrolyte") according to an embodiment of the present technology will be described.

[0030] The electrolyte described herein is used for a secondary battery as an electrochemical device. However, the electrolyte can also be used for other electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices are primary batteries and capacitors, etc.

[0031] <1-1. Constitution>

[0032] The electrolyte is a liquid electrolyte and contains an electrolyte salt and an additive.

[0033] [Electrolyte salt]

[0034] The electrolyte salt contains any one or two or more of magnesium salts.

[0035] Specific examples of the magnesium salt are magnesium chloride (MgCl2), magnesium perchlorate (Mg(ClO4)2), magnesium nitrate (Mg(NO3)2), magnesium sulfate (MgSO4), magnesium acetate (Mg(CH3COO)2), magnesium trifluoroacetate (Mg(CF3COO)2), magnesium tetrafluoroborate (Mg(BF4)2), magnesium tetraphenylborate (Mg(B(C6H5)4)2), magnesium hexafluorophosphate (Mg(PF6)2), magnesium hexafluoroarsenate (Mg(AsF6)2), bis(hexamethyldisilazane)magnesium (Mg[N(Si(CH3)3)2]2), bis(trifluoromethanesulfonyl)imide magnesium (Mg[N(CF3SO2)2]2), and magnesium bis[tetrakis(hexafluoroisopropyl)]borate (Mg[B(OCH(CF3)2)4]2), etc.

[0036] The content (mol / l (=mol / dm 3 )) of the electrolyte salt in the electrolyte is not particularly limited and can therefore be set arbitrarily. However, the content of the electrolyte salt described herein is the content of the electrolyte salt relative to the solvent described later.

[0037] [Cyclic unsaturated hydrocarbon compound]

[0038] The additive contains any one or two or more of cyclic unsaturated hydrocarbon compounds.

[0039] The cyclic unsaturated hydrocarbon compound contains one or both of a monocyclic compound and a polycyclic compound. The type of the monocyclic compound can be only one kind or two or more kinds. Similarly, the type of the polycyclic compound can be only one kind or two or more kinds.

[0040] (Monocyclic compound)

[0041] The monocyclic compound contains a monocyclic ring composed of a plurality of carbon atoms. As described above, the monocyclic ring is a single carbon ring composed of a plurality of carbon atoms, and more specifically, it is a hydrocarbon ring in which the plurality of carbon atoms are bonded to each other in a manner of forming a ring.

[0042] Therefore, heterocycles in which atoms other than carbon atoms are bonded to each other in such a way as to form a ring together with multiple carbon atoms are excluded from the monocycles described herein. Specific examples of atoms other than carbon atoms are boron atoms, nitrogen atoms, oxygen atoms, phosphorus atoms, sulfur atoms, and the like.

[0043] The monocycle contains two or more carbon-carbon double bonds (>C=C<). Since these two or more carbon-carbon bonds form a monocyclic ring, they are part of the monocyclic ring. Therefore, when an unsaturated hydrocarbon group (a group including a carbon-carbon double bond) is bonded to a carbon atom constituting the monocyclic ring, this carbon-carbon double bond is not part of the monocyclic ring, and thus is excluded from the carbon-carbon double bonds described herein.

[0044] The type of the monocyclic ring is not particularly limited as long as it is a hydrocarbon ring containing two or more carbon-carbon double bonds. Therefore, the number of multiple carbon atoms constituting the monocyclic ring is not particularly limited.

[0045] Therefore, the monocyclic ring can be a three-membered ring (the number of multiple carbon atoms constituting the monocyclic ring = 3), a four-membered ring (the number of multiple carbon atoms constituting the monocyclic ring = 4), a five-membered ring (the number of multiple carbon atoms constituting the monocyclic ring = 5), a six-membered ring (the number of multiple carbon atoms constituting the monocyclic ring = 6), a seven-membered ring (the number of multiple carbon atoms constituting the monocyclic ring = 7), or an eight-membered ring (the number of multiple carbon atoms constituting the monocyclic ring = 8). Of course, the monocyclic ring can also be a ring with 9 or more carbon atoms.

[0046] In addition, the arrangement of two or more carbon-carbon double bonds constituting the monocyclic ring is not particularly limited.

[0047] Therefore, the monocyclic ring can be a completely conjugated system in which two or more carbon-carbon double bonds are alternately arranged via carbon-carbon single bonds (≡C-C≡), or a non-completely conjugated system in which two or more carbon-carbon double bonds are not alternately arranged via carbon-carbon single bonds. In the case where the monocyclic ring is a non-completely conjugated system, the arrangement of two or more carbon-carbon double bonds can be arbitrarily set.

[0048] However, the number of carbon-carbon double bonds constituting the monocyclic ring is set to a specified value according to the number of multiple carbon atoms constituting the monocyclic ring.

[0049] Specifically, when the number of multiple carbon atoms constituting the monocyclic ring is 7 or less, the number of carbon-carbon double bonds is not an odd number but an even number. In contrast, when the number of multiple carbon atoms constituting the monocyclic ring is 8 or more, the number of carbon-carbon double bonds can be an odd number or an even number. That is, the number of carbon-carbon double bonds (odd number or even number) contained in the monocyclic compound varies according to the number of multiple carbon atoms constituting the monocyclic ring.

[0050] Specific examples of the monocyclic compound are as follows.

[0051] Specific examples of monocyclic compounds when the number of multiple carbon atoms forming the monocyclic ring is 7 or less are cyclotetradiene (the number of multiple carbon atoms forming the monocyclic ring = 4, the number of carbon-carbon double bonds = 2), cyclopentadiene (the number of multiple carbon atoms forming the monocyclic ring = 5, the number of carbon-carbon double bonds = 2), and the like.

[0052] Therefore, benzene (the number of multiple carbon atoms forming the monocyclic ring = 6, the number of carbon-carbon double bonds = 3), cycloheptatriene (the number of multiple carbon atoms forming the monocyclic ring = 7, the number of carbon-carbon double bonds = 3), and the like are excluded from the specific examples of monocyclic compounds described herein.

[0053] Specific examples of monocyclic compounds when the number of multiple carbon atoms forming the monocyclic ring is 8 or more are cyclooctatetraene (the number of multiple carbon atoms forming the monocyclic ring = 8, the number of carbon-carbon double bonds = 4), cyclooctatriene (the number of multiple carbon atoms forming the monocyclic ring = 8, the number of carbon-carbon double bonds = 3), cyclotetradecaheptaene (the number of multiple carbon atoms forming the monocyclic ring = 14, the number of carbon-carbon double bonds = 7), cyclooctadecaennea (the number of multiple carbon atoms forming the monocyclic ring = 18, the number of carbon-carbon double bonds = 9), and the like.

[0054] (Fused-ring compound)

[0055] The fused-ring compound includes a bicyclic fused-ring composed of multiple carbon atoms. As described above, the bicyclic fused-ring is a ring composed of multiple carbon atoms and in which two carbon rings are condensed with each other. More specifically, it is a hydrocarbon ring in which the multiple carbon atoms are bonded to each other in a manner that forms two rings.

[0056] Therefore, heterocycles in which atoms other than carbon atoms are bonded to each other in a manner that forms two rings together with multiple carbon atoms are excluded from the bicyclic fused-rings described herein. In addition, the details regarding atoms other than carbon atoms are as described above.

[0057] However, the bicyclic fused-ring does not include a benzene ring. That is, in the bicyclic fused-ring, as described above, two carbon rings are condensed with each other, but neither of the two carbon rings is a benzene ring.

[0058] The bicyclic fused-ring contains two or more carbon-carbon double bonds. Since the two or more carbon-carbon bonds form the bicyclic fused-ring, they are a part of the bicyclic fused-ring. Therefore, when an unsaturated hydrocarbon group (a group containing a carbon-carbon double bond) is bonded to a carbon atom constituting the bicyclic fused-ring, the carbon-carbon double bond is excluded from the carbon-carbon double bonds described herein.

[0059] The type of the bicyclic fused-ring is not particularly limited as long as it is a hydrocarbon ring containing two or more carbon-carbon double bonds and in which two rings are condensed with each other. Therefore, the number of multiple carbon atoms constituting the bicyclic fused-ring is not particularly limited.

[0060] Therefore, the bicyclic fused ring can be a fused ring of three-membered rings with each other (the number of carbon atoms constituting the bicyclic fused ring = 4), or a fused ring of a three-membered ring and a four-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 5), or a fused ring of four-membered rings with each other (the number of carbon atoms constituting the bicyclic fused ring = 6), or a fused ring of a four-membered ring and a five-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 7), or a fused ring of five-membered rings with each other (the number of carbon atoms constituting the bicyclic fused ring = 8), or a fused ring of a five-membered ring and a six-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 9).

[0061] In addition, the bicyclic fused ring can be a fused ring of six-membered rings with each other (the number of carbon atoms constituting the bicyclic fused ring = 10), or a fused ring of a six-membered ring and a seven-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 11), or a fused ring of seven-membered rings with each other (the number of carbon atoms constituting the bicyclic fused ring = 12), or a fused ring of a seven-membered ring and an eight-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 13), or a fused ring of eight-membered rings with each other (the number of carbon atoms constituting the bicyclic fused ring = 14).

[0062] Of course, the bicyclic fused ring can also be a fused ring other than the above series of fused rings.

[0063] In addition, the configuration of two or more carbon-carbon double bonds constituting the bicyclic fused ring is not particularly limited.

[0064] Therefore, the bicyclic fused ring can be a completely conjugated system in which two or more carbon-carbon double bonds are alternately arranged via carbon-carbon single bonds, or a non-completely conjugated system in which two or more carbon-carbon double bonds are not alternately arranged via carbon-carbon single bonds. In the case where the bicyclic fused ring is a non-completely conjugated system, the configuration of two or more carbon-carbon double bonds can be set arbitrarily.

[0065] The number of carbon-carbon double bonds constituting the bicyclic fused ring is not particularly limited, and thus can be set arbitrarily. Specifically, the number of carbon-carbon double bonds can be an odd number or an even number. That is, the number of carbon-carbon double bonds (odd number or even number) contained in the fused ring compound does not depend on the number of carbon atoms constituting the bicyclic fused ring and can be set arbitrarily.

[0066] Specific examples of condensed ring compounds are pentalene, which is a fused ring of five-membered rings with each other (the number of carbon atoms constituting the bicyclic condensed ring = 8, the number of carbon-carbon double bonds = 4), azulene, which is a fused ring of a five-membered ring and an eight-membered ring (the number of carbon atoms constituting the bicyclic condensed ring = 11, the number of carbon-carbon double bonds = 5), and heptalene, which is a fused ring of seven-membered rings with each other (the number of carbon atoms constituting the bicyclic condensed ring = 12, the number of carbon-carbon double bonds = 6), etc.

[0067] Therefore, tetralin, which is a fused ring of cyclohexane and benzene, both of which are six-membered rings (the number of carbon atoms constituting the bicyclic condensed ring = 10, the number of carbon-carbon double bonds = 3), naphthalene, which is a fused ring of benzene with each other, both of which are six-membered rings (the number of carbon atoms constituting the bicyclic condensed ring = 10, the number of carbon-carbon double bonds = 5), and anthracene, which is a fused ring of benzene with each other, both of which are six-membered rings (the number of carbon atoms constituting the bicyclic condensed ring = 14, the number of carbon-carbon double bonds = 7), etc. are excluded from the specific examples of the condensed ring compounds described herein.

[0068] (Content)

[0069] The content of the cyclic unsaturated hydrocarbon compound in the electrolyte is not particularly limited, and thus can be arbitrarily set. As described above, the cyclic unsaturated hydrocarbon compound may contain only monocyclic compounds, may contain only condensed ring compounds, or may contain both the monocyclic compounds and the condensed ring compounds.

[0070] In addition, when investigating the presence or absence of the cyclic unsaturated hydrocarbon compound in the electrolyte and measuring the content of the cyclic unsaturated hydrocarbon compound in the electrolyte, any one or two or more of the existing analytical methods are used to analyze the electrolyte. The type of the analytical method is not particularly limited. Specifically, it is high-frequency inductively coupled plasma (ICP) emission spectrometry, nuclear magnetic resonance spectrometry (NMR), gas chromatography-mass spectrometry (GC-MS), etc.

[0071] (Reason)

[0072] The electrolyte contains the cyclic unsaturated hydrocarbon compound because the redox reaction of magnesium deposition and dissolution can be easily and stably carried out. Thereby, in the secondary battery using the electrolyte, the charge-discharge reaction can be easily and stably and continuously carried out, and even if the charge-discharge is repeated, the battery capacity is hardly reduced.

[0073] Specifically, when the electrolyte contains a cyclic unsaturated hydrocarbon compound, the activity of magnesium is increased during the precipitation-dissolution reaction of magnesium as compared with the case where the electrolyte does not contain a cyclic unsaturated hydrocarbon compound. As a result, the redox reaction utilizing the precipitation-dissolution of magnesium easily proceeds, and thus, in a secondary battery using the electrolyte, the charge-discharge reaction easily proceeds.

[0074] In addition, the case where the electrolyte does not contain a cyclic unsaturated hydrocarbon compound is the case where the electrolyte does not contain an additive, and the case where the electrolyte contains other compounds as additives instead of the cyclic unsaturated hydrocarbon compound. Specific examples of the other compounds are anthracene and the like described above.

[0075] Moreover, since the cyclic unsaturated hydrocarbon compound is dianionized in the reduced state, it becomes an electrochemically stable active species in the electrolyte. This active species is difficult to decompose in the electrolyte, and even if the redox reaction is repeated, the lifetime of this active species is prolonged.

[0076] As a result, in a secondary battery using the electrolyte, even if a coating film is formed on the surface of the negative electrode (a magnesium-containing material described later) during charge and discharge, the electrochemically stable active species continuously removes the coating film. That is, even if charge and discharge are repeated, the electrochemically stable active species functions to maintain the activity of magnesium. Therefore, even if charge and discharge are repeated, the charge-discharge reaction utilizing the precipitation-dissolution of magnesium more easily proceeds.

[0077] Therefore, if the electrolyte contains a cyclic unsaturated hydrocarbon compound, in a secondary battery using the electrolyte, the charge-discharge reaction utilizing the precipitation-dissolution of magnesium easily proceeds stably and continuously, and even if charge and discharge are repeated, the battery capacity is hardly reduced.

[0078] (Preferred configuration)

[0079] Among them, the cyclic unsaturated hydrocarbon compound preferably contains a single ring, and compared with a polycyclic compound, a single-ring compound is preferably contained. This is because the charge-discharge reaction utilizing the precipitation-dissolution of magnesium easily proceeds sufficiently, and even if charge and discharge are repeated, the battery capacity is hardly reduced sufficiently.

[0080] The single ring is particularly preferably a completely conjugated system in which two or more carbon-carbon double bonds are alternately arranged via carbon-carbon single bonds. More specifically, a annulene having a multiple of 4 carbon atoms is preferably included. This is because the cyclic unsaturated hydrocarbon compound shows aromaticity in the reduced state. As a result, the active species derived from the cyclic unsaturated hydrocarbon compound is stabilized electrochemically, and thus the lifetime of this cyclic unsaturated hydrocarbon compound is further prolonged. However, as described above, benzene and the like that do not have a multiple of 4 carbon atoms are excluded from the annulenes described herein.

[0081] Here, "a multiple of 4" means 4n (where n is an integer of 1 or more), and specific examples of such a multiple of 4 are 4, 8, 12, etc. Therefore, benzene having 4n + 2 carbon atoms (the number of carbon atoms = 6) etc. does not correspond to annulenes having a multiple of 4 carbon atoms. Benzene having 4n + 2 carbon atoms etc. is not limited to the reduced state and exhibits aromaticity even in the normal molecular state.

[0082] The annulenes having such a multiple of 4 carbon atoms preferably particularly include cyclooctatetraene. This is because the active species from the cyclic unsaturated hydrocarbon compound are significantly stabilized electrochemically, and thus the lifetime of the cyclic unsaturated hydrocarbon compound is significantly prolonged.

[0083] [Solvent]

[0084] In addition, the electrolytic solution may further contain any one or two or more of solvents. The type of the solvent is not particularly limited, and specifically, it is a non-aqueous solvent (organic solvent). The electrolytic solution containing a non-aqueous solvent is a so-called non-aqueous electrolytic solution.

[0085] The type of the non-aqueous solvent is not particularly limited, and among them, the non-aqueous solvent preferably includes ether compounds. This is because the electrolyte salt is easily dispersed or dissolved by the ether compound, so the state of the electrolytic solution is stabilized.

[0086] The ether compound is a compound containing an ether bond (-O-). In addition, the ether compound may be linear or cyclic. Furthermore, the number of ether bonds may be only one or two or more.

[0087] Specific examples of the ether compound are dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and tetrahydrofuran, etc.

[0088] <1-2. Manufacturing method>

[0089] In the case of manufacturing an electrolytic solution, an electrolyte salt and an additive (cyclic unsaturated hydrocarbon compound) are added to a solvent. Thereby, the electrolyte salt and the cyclic unsaturated hydrocarbon compound are dispersed or dissolved in the solvent, and thus the electrolytic solution is completed.

[0090] <1-3. Function and effect>

[0091] According to this electrolytic solution, the electrolytic solution contains an electrolyte salt and an additive, the electrolyte salt contains a magnesium salt, and the additive contains a cyclic unsaturated hydrocarbon compound.

[0092] In this case, as described above, the redox reaction utilizing the precipitation and dissolution of magnesium easily proceeds, and the active species derived from the cyclic unsaturated hydrocarbon compound maintain the activity of magnesium during the precipitation and dissolution reaction. Thus, in a secondary battery using the electrolyte solution, the charge-discharge reaction easily proceeds stably and continuously, and even if the charge-discharge is repeated, the battery capacity is hardly reduced. Therefore, a secondary battery having excellent battery characteristics can be achieved.

[0093] In particular, if the cyclic unsaturated hydrocarbon compound contains a single ring, that is, the cyclic unsaturated hydrocarbon compound contains a monocyclic compound, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium easily proceeds sufficiently, and even if the charge-discharge is repeated, the battery capacity is hardly reduced sufficiently. Therefore, a higher effect can be obtained.

[0094] In this case, if the single ring includes annulene having a multiple of 4 carbon atoms, the active species derived from the cyclic unsaturated hydrocarbon compound are more electrochemically stabilized. Therefore, the lifetime of the active species is prolonged, and thus a higher effect can be obtained.

[0095] Among them, if the annulene includes cyclooctatetraene, the active species derived from the cyclic unsaturated hydrocarbon compound are significantly electrochemically stabilized. Therefore, the lifetime of the active species is significantly prolonged, and thus a higher effect can be obtained more significantly.

[0096] In addition, if the electrolyte solution further contains an ether compound, the electrolyte salt is easily dispersed or dissolved by the ether compound. Therefore, since the state of the electrolyte solution is stabilized, a higher effect can be obtained.

[0097] <2. Secondary battery>

[0098] Next, a secondary battery according to an embodiment of the present technology using the electrolyte solution will be described.

[0099] The secondary battery described herein is a secondary battery that obtains battery capacity by utilizing the charge-discharge reaction that utilizes the precipitation and dissolution of magnesium.

[0100] More specifically, the secondary battery described below is a so-called magnesium-sulfur secondary battery because the positive electrode contains a sulfur-containing material and the negative electrode contains a magnesium-containing material. In this secondary battery, magnesium precipitates and dissolves in the negative electrode, and magnesium is inserted and extracted in an ionic state in the positive electrode. In addition, details of the sulfur-containing material and the magnesium-containing material will be described later.

[0101] <2-1. Structure>

[0102] Figure 1 The three-dimensional structure of the secondary battery is shown, and Figure 2 is shown Figure 1The cross-sectional structure of the battery element 20 shown. However, in Figure 1 it shows a state where the outer packaging film 10 and the battery element 20 are separated from each other, and the cross-section of the battery element 20 along the XZ plane is shown by a dashed line.

[0103] As Figure 1 and Figure 2 shown, this secondary battery includes an outer packaging film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42.

[0104] The secondary battery described herein is a laminated film type secondary battery that uses a flexible outer packaging film 10 as an outer packaging component.

[0105] [Outer packaging film]

[0106] As Figure 1 shown, the outer packaging film 10 has a bag-like structure that is sealed with the battery element 20 housed inside. Thus, the outer packaging film 10 houses the positive electrode 21, negative electrode 22, separator 23, and electrolyte described later.

[0107] Here, the outer packaging film 10 is a sheet-like member that is folded in the folding direction F. A recessed portion 10U (so-called deep draw portion) for housing the battery element 20 is provided in the outer packaging film 10.

[0108] Specifically, the outer packaging film 10 is a three-layer laminated film having a welding layer, a metal layer, and a surface protective layer laminated in order from the inside. In the state where the outer packaging film 10 is folded, the outer peripheral edge portions of the welding layers facing each other are welded to each other. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

[0109] However, the constitution (number of layers) of the outer packaging film 10 is not particularly limited, and thus it may be one layer or two layers, or four layers or more.

[0110] [Battery element]

[0111] The battery element 20 is a power generation element housed inside the outer packaging film 10. As Figure 1 and Figure 2 shown, this battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0112] Here, the battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 face each other with the separator 23 interposed therebetween, and are wound around a winding axis P. As Figure 1 shown, this winding axis P is an imaginary axis extending in the Y-axis direction.

[0113] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 has a flat three-dimensional shape, the shape of the cross-section of the battery element 20 that intersects the winding axis P (the cross-section along the XZ plane) is a flat shape defined by the major axis J1 and the minor axis J2.

[0114] The major axis J1 is an imaginary axis extending in the X-axis direction and has a length greater than that of the minor axis J2. The minor axis J2 is an imaginary axis extending in the Z-axis direction that intersects the X-axis direction and has a length smaller than that of the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the shape of the cross-section of the battery element 20 is a flat approximate elliptical shape.

[0115] (Positive electrode)

[0116] The positive electrode 21 contains a positive electrode active material in which magnesium is intercalated and deintercalated in an ionic state, and the positive electrode active material contains any one or two or more of sulfur-containing materials. This is because in the positive electrode 21, magnesium is easily intercalated and deintercalated in an ionic state, so the charge-discharge reaction utilizing the precipitation and dissolution of this magnesium is easily carried out.

[0117] The sulfur-containing material is a material containing sulfur as a constituent element. That is, the sulfur-containing material can be a monomer of sulfur, an alloy of sulfur, a compound of sulfur, or a mixture of two or more of them. In addition, the purity of the sulfur monomer is not particularly limited, so the sulfur monomer can also contain any amount of impurities.

[0118] The type of metal element contained as a constituent element in the alloy of sulfur is not particularly limited as long as it is any one or two or more of any metal elements. The sulfur compound contains any one or two or more of non-metal elements such as carbon, oxygen, and halogen as constituent elements, and specific examples of the halogen are fluorine, chlorine, bromine, and iodine, etc.

[0119] Among them, the positive electrode active material preferably contains a monomer of sulfur. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium is easily carried out sufficiently. In Figure 2 , the case where the positive electrode 21 contains a monomer of sulfur is shown.

[0120] In addition, although not specifically illustrated here, the positive electrode 21 may also include a positive electrode current collector and a positive electrode active material layer.

[0121] The positive electrode current collector is a conductive support for supporting the positive electrode active material layer and has a pair of surfaces on which the positive electrode active material layer is provided. The positive electrode current collector contains a conductive material such as a metal material, and specific examples of the conductive material are nickel, etc.

[0122] The positive electrode active material layer is supported by the positive electrode current collector and contains any one or two or more of sulfur-containing materials as the positive electrode active material. However, the positive electrode active material layer may also contain any one or two or more of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0123] The positive electrode active material layer may be provided on both sides of the positive electrode current collector or may be provided only on one side of the positive electrode current collector. The method for forming the positive electrode active material layer is not particularly limited. Specifically, it is any one or two or more of coating methods and the like.

[0124] The positive electrode binder contains any one or two or more of resin materials such as fluorine-based resins, polyvinyl alcohol-based resins, and styrene-butadiene copolymer rubbers. Specific examples of the fluorine-based resin are polyvinylidene fluoride and polytetrafluoroethylene.

[0125] In addition, the positive electrode binder may also be a conductive polymer compound. Specific examples of the conductive polymer compound are polyaniline, polypyrrole, and polythiophene, and may also be copolymers of two or more of them. The conductive polymer compound may be unsubstituted or may be substituted with any one or two or more functional groups.

[0126] The positive electrode conductive agent contains any one or two or more of conductive materials such as carbon materials, metal materials, and conductive polymer compounds.

[0127] Specific examples of the carbon material are graphite (natural graphite and artificial graphite), carbon fiber, carbon black, and carbon nanotubes. The carbon fiber is vapor-grown carbon fiber (VGCF) and the like. The carbon black is acetylene black and Ketjen black and the like. The carbon nanotubes are single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), and the multi-walled carbon nanotubes are double-walled carbon nanotubes (DWCNT) and the like. Specific examples of the metal material are nickel and the like.

[0128] (Negative electrode)

[0129] The negative electrode 22 contains any one or two or more of magnesium-containing materials as the negative electrode active material. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium is easy to carry out.

[0130] The magnesium-containing material is a material containing magnesium as a constituent element. That is, the magnesium-containing material may be a monomer of magnesium, an alloy of magnesium, a compound of magnesium, or a mixture of two or more of them. In addition, the purity of metallic magnesium is not particularly limited, so the metallic magnesium may also contain any amount of impurities.

[0131] The type of metal element (other than magnesium) contained as a constituent element in the magnesium alloy is not particularly limited as long as it is any one or two or more of any metal elements. The magnesium compound contains any one or two or more of non-metal elements such as carbon, oxygen, sulfur, and halogen as constituent elements, and specific examples of the halogen are fluorine, chlorine, bromine, iodine, etc.

[0132] Among them, the negative electrode active material preferably contains magnesium monomers. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium can be easily and fully carried out. In Figure 2 it shows the case where the negative electrode 22 contains magnesium monomers.

[0133] In addition, the negative electrode 22 may also have a structure similar to that of the positive electrode 21. That is, although not specifically illustrated here, the negative electrode 22 may also include a negative electrode current collector and a negative electrode active material layer.

[0134] The negative electrode current collector is a conductive support for supporting the negative electrode active material layer and has a pair of surfaces for disposing the negative electrode active material layer. The negative electrode current collector includes a conductive material such as a metal material, and specific examples of the conductive material are nickel, etc.

[0135] The negative electrode active material layer is supported by the negative electrode current collector and contains any one or two or more of magnesium-containing materials as the negative electrode active material. However, the negative electrode active material layer may also contain any one or two or more of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0136] The negative electrode active material layer may be disposed on both surfaces of the negative electrode current collector or only on one surface of the negative electrode current collector. The formation method of the negative electrode active material layer is not particularly limited, and specifically, it is any one or two or more of coating methods, etc.

[0137] The details about the negative electrode binder are the same as those about the positive electrode binder, and the details about the negative electrode conductive agent are the same as those about the positive electrode conductive agent.

[0138] (Separator)

[0139] As Figure 2 shown, the separator 23 is an insulating porous membrane between the positive electrode 21 and the negative electrode 22, preventing the short circuit between the positive electrode 21 and the negative electrode 22 and allowing magnesium to pass through in an ionic state. The separator 23 contains a polymer compound such as polyethylene.

[0140] (Electrolyte)

[0141] The composition of the electrolyte is as described above. That is, the electrolyte contains a magnesium salt as an electrolyte salt and a cyclic unsaturated hydrocarbon compound as an additive.

[0142] [Positive electrode lead]

[0143] As Figure 1 and Figure 2 shown, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode 21 and is led out to the outside of the outer packaging film 10. Further, when the positive electrode 21 includes a positive electrode current collector, the positive electrode lead 31 is connected to the positive electrode current collector. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum or the like. Further, the shape of the positive electrode lead 31 is any one of a thin plate shape, a mesh shape, and the like.

[0144] [Negative electrode lead]

[0145] As Figure 1 and Figure 2 shown, the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode 22 and is led out to the outside of the outer packaging film 10. Further, when the negative electrode 22 includes a negative electrode current collector, the negative electrode lead 32 is connected to the negative electrode current collector. Here, the leading-out direction of the negative electrode lead 32 is the same direction as the leading-out direction of the positive electrode lead 31. The negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper or the like. Further, the details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[0146] [Sealing film]

[0147] The sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0148] The sealing film 41 is a sealing member that prevents external gases and the like from entering the inside of the outer packaging film 10. The sealing film 41 contains a polymer compound such as polyolefin having adhesiveness to the positive electrode lead 31, and a specific example of the polymer compound is polypropylene or the like.

[0149] The configuration of the sealing film 42 is the same as that of the sealing film 41 except that it is a sealing member having adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin having adhesiveness to the negative electrode lead 32.

[0150] <2-2. Operation>

[0151] This secondary battery operates in the battery element 20 in the following manner.

[0152] During discharging, the magnesium-containing material dissolves in the negative electrode 22, so magnesium is eluted into the electrolytic solution, and this magnesium is embedded in the positive electrode 21 in an ionic state. On the other hand, during charging, magnesium is deintercalated from the positive electrode 21 into the electrolytic solution in an ionic state, and this magnesium precipitates in the negative electrode 22.

[0153] <2-3. Manufacturing Method>

[0154] In the case of manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are prepared through the steps of an example described below, and then the secondary battery is assembled using the positive electrode 21, the negative electrode 22, and the electrolyte.

[0155] Hereinafter, the case of using sulfur monomer (sulfur powder) as the sulfur-containing material and magnesium monomer (metallic magnesium) as the magnesium-containing material will be described. In addition, regarding the manufacturing steps of the electrolyte, they have been described, so the description of the manufacturing steps of the electrolyte will be omitted hereinafter.

[0156] [Preparation of Positive Electrode]

[0157] First, a positive electrode mixture is made by mixing a positive electrode active material (sulfur powder as the sulfur-containing material), a positive electrode binder, and a positive electrode conductive agent. Then, a paste-like positive electrode mixture slurry is prepared by putting the positive electrode mixture into a solvent. This solvent can be an aqueous solvent or an organic solvent. Finally, a positive electrode active material layer is formed by coating the positive electrode mixture slurry on both sides of the positive electrode current collector. Thereafter, the positive electrode active material layer can also be compression-molded using a roll press or the like. In this case, the positive electrode active material layer can be heated, or compression molding can be repeated multiple times. Thus, a positive electrode active material layer is formed on both sides of the positive electrode current collector, thereby manufacturing the positive electrode 21.

[0158] [Preparation of Negative Electrode]

[0159] As the negative electrode 22, a negative electrode active material (metallic magnesium as the magnesium-containing material) is prepared. As this metallic magnesium, magnesium foil is used.

[0160] [Assembly of Secondary Battery]

[0161] First, the positive electrode lead 31 is connected to the positive electrode 21 using a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode 22 using a joining method such as welding.

[0162] Next, after laminating the positive electrode 21 and the negative electrode 22 with the separator 23 interposed therebetween, a wound body (not shown) is formed by winding the positive electrode 21, the negative electrode 22, and the separator 23. Then, the wound body is formed into a flat shape by pressing the wound body using a press or the like. The formed wound body has the same configuration as that of the battery element 20 except that the electrolyte is not impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23.

[0163] Next, after winding bodies are housed inside the recessed portion 10U, the outer packaging film 10 (welding layer / metal layer / surface protective layer) is folded so that the outer packaging films 10 face each other. Next, using an adhesive method such as a hot melt bonding method, by joining the outer peripheral edge portions of both sides in the welding layers facing each other to each other, the winding bodies are housed inside the bag-shaped outer packaging film 10.

[0164] Finally, after electrolytic solution is injected inside the bag-shaped outer packaging film 10, using an adhesive method such as a hot melt bonding method, the outer peripheral edge portions of the remaining one side in the welding layers facing each other are joined to each other. In this case, a sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32.

[0165] Thereby, the electrolytic solution is impregnated in the winding bodies, thereby forming the battery element 20 as a wound electrode body. Therefore, the battery element 20 is sealed inside the bag-shaped outer packaging film 10, thereby completing the secondary battery.

[0166] <2-4. Function and effect>

[0167] According to this secondary battery, the secondary battery includes an electrolytic solution having the above-described configuration. In this case, for the above reasons, the charge and discharge reactions are likely to proceed stably and continuously, and even if the charge and discharge are repeated, the battery capacity is hardly reduced. Therefore, excellent battery characteristics can be obtained.

[0168] In particular, if the positive electrode 21 contains a sulfur-containing material and the negative electrode 22 contains a magnesium-containing material, the charge and discharge reaction utilizing the precipitation and dissolution of magnesium is likely to proceed sufficiently, and even if the charge and discharge are repeated, the battery capacity is hardly reduced sufficiently. Therefore, higher effects can be obtained. In this case, if the sulfur-containing material contains sulfur monomers and the magnesium-containing material contains magnesium monomers, the charge and discharge reaction is more likely to proceed and the battery capacity is more difficult to reduce. Therefore, higher effects can be obtained.

[0169] In addition, if the secondary battery is a magnesium-sulfur secondary battery, a sufficient battery capacity is obtained by utilizing the precipitation and dissolution of magnesium. Therefore, higher effects can be obtained.

[0170] <3. Use of the secondary battery>

[0171] The use (application example) of the secondary battery is not particularly limited. In the secondary battery used as a power source, in electronic devices and electric vehicles, etc., it can be a main power source or an auxiliary power source. The main power source is a power source that is preferentially used regardless of the presence or absence of other power sources. The auxiliary power source can be a power source used instead of the main power source or a power source switched from the main power source.

[0172] Specific examples of the uses of secondary batteries are as follows: electronic devices such as cameras, digital still cameras, mobile phones, laptop computers, stereo headphones, portable radios, and portable information terminals; storage devices such as backup power supplies and memory cards; power tools such as electric drills and saws; battery packs mounted on electronic devices, etc.; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles), etc.; power storage systems such as household or industrial battery systems that store electricity in advance for emergencies, etc. In these uses, one secondary battery may be used alone, or two or more secondary batteries may be used.

[0173] The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that travels using a secondary battery as a driving power source, and may also be a hybrid vehicle that has other driving sources in addition to the secondary battery. In a household power storage system, the power stored in the secondary battery as a power storage source can be used to operate household electrical products, etc.

[0174] Examples

[0175] Examples of the present technology will be described.

[0176] As described below, after manufacturing the electrolyte and the secondary battery, the physical properties of the electrolyte and the battery characteristics of the secondary battery were evaluated.

[0177] <Examples 1, 2 and Comparative Examples 1 - 4>

[0178] First, after manufacturing the electrolyte through the steps described below, the physical properties of the electrolyte were evaluated.

[0179] [Manufacture of electrolyte]

[0180] After adding an electrolyte salt (magnesium salt) and an additive (cyclooctatetraene (COT) as a cyclic unsaturated hydrocarbon compound, manufactured by Tokyo Chemical Industry Co., Ltd.) to a solvent (diethylene glycol dimethyl ether (DGDE) as an ether compound, manufactured by Toyama Chemical Co., Ltd.), the solvent was stirred. Thus, an electrolyte was prepared.

[0181] As the electrolyte salt, a mixture of magnesium bis(trifluoromethanesulfonyl)imide (MgTFSI2, manufactured by Toyama Chemical Co., Ltd.) and magnesium chloride (MgCl2, manufactured by Sigma - Aldrich) was used. In this case, the content of magnesium bis(trifluoromethanesulfonyl)imide in the electrolyte was 0.2 mol / l (= 0.2 mol / dm 3 ) relative to the solvent, and the content of magnesium chloride in the electrolyte was 0.2 mol / l relative to the solvent.

[0182] In addition, magnesium chloride is used alone as the electrolyte salt. In this case, the content of magnesium chloride in the electrolyte solution is 0.4 mol / l relative to the solvent.

[0183] The content of cyclooctatetraene in the electrolyte solution is 0.05 mol / l relative to the solvent.

[0184] In addition, for comparison, an electrolyte solution was prepared by the same procedure except that no additive was used. Further, for comparison, an electrolyte solution was prepared by the same procedure except that another compound (anthracene (ANT), manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of the cyclic unsaturated hydrocarbon compound as the additive.

[0185] After preparing the electrolyte solution, the electrolyte solution was analyzed by ICP emission spectrometry, and as a result, it was confirmed that the content of the electrolyte salt and the content of the additive (cyclic unsaturated hydrocarbon compound or other compound) were as described above.

[0186] [Evaluation of Physical Properties]

[0187] As physical properties, the redox characteristics were evaluated, and the results shown in Table 1 were obtained.

[0188] In the case of evaluating the redox characteristics, first, the working electrode (platinum), the reference electrode (magnesium), and the counter electrode (magnesium) were immersed in the electrolyte solution. Then, in a normal temperature environment (temperature = 25°C), the correlation between potential and current (cyclic voltammogram) was measured using cyclic voltammetry. In this case, the scan rate = 25 mV / sec, the potential range = -2 V to 2 V, and the number of cycles = 10 cycles. Finally, based on the cyclic voltammogram, it was determined whether the redox reaction, which is an index for evaluating the redox characteristics, could proceed.

[0189] In the "Redox Reaction" column shown in Table 1, the following tendencies are shown.

[0190] "Possible" shows activity not only during magnesium deposition but also during magnesium dissolution, and thus indicates that a redox reaction has occurred. That is, it indicates that a charge-discharge reaction has occurred in the secondary battery using the electrolyte solution.

[0191] On the other hand, "Impossible" does not show activity during magnesium dissolution, and thus indicates that the redox reaction has not occurred sufficiently. That is, it indicates that a charge-discharge reaction has not occurred in the secondary battery using the electrolyte solution.

[0192]

Table 1

[0193]

[0194] [Discussion]

[0195] As shown in Table 1, whether the redox reaction can occur varies depending on the composition of the electrolyte solution.

[0196] Specifically, in the case where no additive was used (Comparative Examples 1 and 2), a difference was observed in whether the redox reaction could occur. That is, in the case where a mixture of magnesium bis(trifluoromethanesulfonyl)imide and magnesium chloride was used as the electrolyte salt (Comparative Example 1), the redox reaction occurred. However, in the case where only magnesium bis(trifluoromethanesulfonyl)imide was used as the electrolyte salt (Comparative Example 2), the redox reaction did not occur.

[0197] In addition, in the case where other compounds (anthracene) were used as additives (Comparative Examples 3 and 4), a difference was also observed in whether the redox reaction could occur. That is, in the case where a mixture of magnesium bis(trifluoromethanesulfonyl)imide and magnesium chloride was used as the electrolyte salt (Comparative Example 3), the redox reaction occurred. However, in the case where only magnesium bis(trifluoromethanesulfonyl)imide was used as the electrolyte salt (Comparative Example 4), the redox reaction did not occur.

[0198] Therefore, in the case where no additive was used (Comparative Examples 1 and 2) and in the case where other compounds (anthracene) were used as additives (Comparative Examples 3 and 4), depending on the type of electrolyte salt, a difference was observed in whether the redox reaction could occur.

[0199] In contrast, in the case where a cyclic unsaturated hydrocarbon compound (cyclooctatetraene) was used as an additive (Examples 1 and 2), no difference was observed in whether the redox reaction could occur. That is, in the case where a mixture of magnesium bis(trifluoromethanesulfonyl)imide and magnesium chloride was used as the electrolyte salt (Example 1), the redox reaction occurred. In addition, in the case where only magnesium bis(trifluoromethanesulfonyl)imide was used as the electrolyte salt (Example 2), the redox reaction also occurred.

[0200] Therefore, in the case where a cyclic unsaturated hydrocarbon compound was used as an additive (Examples 1 and 2), the redox reaction occurred stably regardless of the type of electrolyte salt.

[0201] <Examples 3 and Comparative Examples 5 and 6>

[0202] Next, after manufacturing a secondary battery through the steps described below, the battery characteristics of the secondary battery were evaluated.

[0203] [Manufacture of Secondary Battery]

[0204] Here, for the evaluation of the battery characteristics, in order to perform a simple evaluation, a test secondary battery was fabricated. Figure 3 The cross-sectional structure of the test secondary battery (coin-type magnesium-sulfur secondary battery) is shown.

[0205] Prior to the description of the structure of the test secondary battery, the manufacturing steps of the test secondary battery will be described below.

[0206] (Structure of the test secondary battery)

[0207] As Figure 3 shown, the test secondary battery includes a test electrode 51, a counter electrode 52, a separator 53, an outer packaging cup 54, an outer packaging can 55, a gasket 56, and an electrolytic solution (not shown).

[0208] The test electrode 51 is housed in the outer packaging cup 54, and the counter electrode 52 is housed in the outer packaging can 55. The test electrode 51 and the counter electrode 52 are stacked on top of each other with the separator 53 in between, and the electrolytic solution is impregnated in each of the test electrode 51, the counter electrode 52, and the separator 53. The outer packaging cup 54 and the outer packaging can 55 are fastened to each other with the gasket 56 in between, so that the test electrode 51, the counter electrode 52, and the separator 53 are enclosed by the outer packaging cup 54 and the outer packaging can 55.

[0209] (Manufacturing steps of the test secondary battery)

[0210] The manufacturing steps of the test secondary battery are as follows.

[0211] (Fabrication of the test electrode)

[0212] First, a mixture was prepared by mixing 10 parts by mass of a positive electrode active material (sulfur powder as a sulfur-containing material), 30 parts by mass of a positive electrode binder (polytetrafluoroethylene, manufactured by AGC Inc.), and 60 parts by mass of a positive electrode conductive agent (Ketjenblack, ECP600JD manufactured by Lion Corp.). Next, the mixture was compression-molded using a roll press to form a mixture sheet (thickness = 100 μm). Finally, the mixture sheet was punched into a disc shape (diameter = 15 mm). Thus, the test electrode 51 was fabricated.

[0213] (Preparation of the counter electrode)

[0214] As the counter electrode 52 (metallic magnesium as a magnesium-containing material), a disc-shaped magnesium plate (thickness = 200 μm, diameter = 16 mm, purity = 99.9%, manufactured by Rikazai Corp.) was prepared.

[0215] (Preparation of the electrolytic solution)

[0216] The electrolytic solutions of Example 1 and Comparative Examples 1 and 3 described above were prepared.

[0217] (Assembly of the test secondary battery)

[0218] First, the test electrode 51 is housed in the outer packaging cup 54, and the counter electrode 52 is housed in the outer packaging can 55. Next, the test electrode 51 housed in the outer packaging cup 54 and the counter electrode 52 housed in the outer packaging can 55 are stacked on top of each other with a separator 53 (glass fiber with a thickness of 200 μm, GC50 manufactured by Advantech Co., Ltd.) impregnated with an electrolytic solution in between. In this case, the test electrode 51 is arranged such that the positive electrode active material layer faces the counter electrode 52 with the separator 53 in between. Finally, with the test electrode 51 and the counter electrode 52 stacked on top of each other with the separator 53 in between, the outer packaging cup 54 and the outer packaging can 55 are fastened to each other with a gasket 56 in between. Thus, the test electrode 51 and the counter electrode 52 are sealed in the outer packaging cup 54 and the outer packaging can 55, thereby completing the test secondary battery.

[0219] [Evaluation of battery characteristics]

[0220] The cycle characteristics were evaluated as battery characteristics, and the results shown in Table 2 were obtained.

[0221] When evaluating the cycle characteristics, first, in order to electrochemically stabilize the state of the test secondary battery, the test secondary battery was charged and discharged for 2 cycles in a normal temperature environment (temperature = 25°C).

[0222] Next, by charging and discharging the test secondary battery for 1 cycle in the same environment, the discharge capacity (discharge capacity of the 3rd cycle) was measured. Then, by charging and discharging the test secondary battery for 7 cycles in the same environment, the discharge capacity (discharge capacity of the 10th cycle) was measured.

[0223] Finally, based on the calculation formula of capacity retention rate (%) = (discharge capacity of the 10th cycle / discharge capacity of the 3rd cycle) × 100, the capacity retention rate, which is an index for evaluating the cycle characteristics, was calculated.

[0224] In addition, during discharge, constant current discharge was performed at a current of 0.1 mA until the voltage reached 0.8 V, and during charging, constant current charging was performed at a current of 0.1 mA until the voltage reached 2.4 V.

[0225]

Table 2

[0226]

[0227] [Discussion]

[0228] As shown in Table 2, the capacity retention rate varies significantly depending on the composition of the electrolytic solution.

[0229] Specifically, when the electrolytic solution contains a cyclic unsaturated hydrocarbon compound (cyclooctatetraene) as an additive (Example 3), the capacity retention rate increases compared with the case where the electrolytic solution does not contain an additive (Comparative Example 5) and the case where the electrolytic solution contains another compound (anthracene) as an additive (Comparative Example 6).

[0230] In particular, when the electrolytic solution contains a cyclic unsaturated hydrocarbon compound as an additive, if the solvent contains an ether compound (diethylene glycol dimethyl ether), a sufficient capacity retention rate is obtained.

[0231] [Summary]

[0232] From the results shown in Table 1 and Table 2, it can be seen that if the electrolytic solution contains a magnesium salt and a cyclic unsaturated hydrocarbon compound, a high capacity retention rate is obtained. Therefore, excellent battery characteristics are obtained due to the improved cycle characteristics.

[0233] As described above, the present technology has been described by taking one embodiment and examples as an example, but the configuration of the present technology is not limited to the configuration described in one embodiment and examples, and thus various modifications can be made.

[0234] Specifically, the case where the battery structure of the secondary battery is a laminated film type and a coin type has been described. However, the battery structure of the secondary battery is not particularly limited, and it may also be a cylindrical type, a square type, a button type, etc.

[0235] In addition, the case where the element structure of the battery element is a wound type has been described. However, the element structure of the battery element is not particularly limited, and it may also be a stacked type, a repeatedly folded type, etc. In the stacked type, the positive electrode and the negative electrode are stacked on each other, and in the repeatedly folded type, the positive electrode and the negative electrode are folded into a zigzag shape.

[0236] The effects described in this specification are merely illustrative, and thus the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects can also be obtained with respect to the present technology.

[0237] In addition, the present technology can also adopt the following configuration.

[0238] <1> A secondary battery, comprising:

[0239] A positive electrode;

[0240] A negative electrode; and

[0241] An electrolytic solution containing a magnesium salt and a cyclic unsaturated hydrocarbon compound,

[0242] The cyclic unsaturated hydrocarbon compound contains a monocyclic or bicyclic fused ring composed of multiple carbon atoms,

[0243] The monocyclic or bicyclic fused ring contains more than two carbon-carbon double bonds,

[0244] The bicyclic fused ring does not include a benzene ring,

[0245] When the number of the plurality of carbon atoms constituting the monocyclic ring is 7 or less, the number of the carbon-carbon double bonds is an even number,

[0246] When the number of the plurality of carbon atoms constituting the monocyclic ring is 8 or more, the number of the carbon-carbon double bonds is an odd number or an even number,

[0247] The number of the carbon-carbon double bonds in the bicyclic fused ring is an odd number or an even number.

[0248] <2> The secondary battery according to <1>, wherein,

[0249] The cyclic unsaturated hydrocarbon compound contains the monocyclic ring.

[0250] <3> The secondary battery according to <2>, wherein,

[0251] The monocyclic ring includes annulene having a multiple of 4 carbon atoms.

[0252] <4> The secondary battery according to <3>, wherein,

[0253] The annulene includes cyclooctatetraene.

[0254] <5> The secondary battery according to any one of <1> to <4>, wherein,

[0255] The positive electrode contains a sulfur-containing material,

[0256] The negative electrode contains a magnesium-containing material.

[0257] <6> The secondary battery according to <5>, wherein,

[0258] The sulfur-containing material includes sulfur monomer,

[0259] The magnesium-containing material includes magnesium monomer.

[0260] <7> The secondary battery according to any one of <1> to <6>, wherein,

[0261] The electrolytic solution further contains an ether compound.

[0262] <8> The secondary battery according to any one of <1> to <7>, wherein,

[0263] The secondary battery is a magnesium-sulfur secondary battery.

[0264] <9> An electrolytic solution for a secondary battery,

[0265] comprising a magnesium salt and a cyclic unsaturated hydrocarbon compound,

[0266] The cyclic unsaturated hydrocarbon compound comprises a monocyclic or bicyclic fused ring composed of a plurality of carbon atoms,

[0267] The monocyclic or bicyclic fused ring comprises two or more carbon-carbon double bonds,

[0268] The bicyclic fused ring does not include a benzene ring,

[0269] When the number of the plurality of carbon atoms constituting the monocyclic ring is 7 or less, the number of the carbon-carbon double bonds is an even number,

[0270] When the number of the plurality of carbon atoms constituting the monocyclic ring is 8 or more, the number of the carbon-carbon double bonds is an odd number or an even number,

[0271] The number of the carbon-carbon double bonds in the bicyclic fused ring is an odd number or an even number.

Claims

1. A secondary battery, comprising: a positive electrode; a negative electrode; and an electrolytic solution containing a magnesium salt and a cyclic unsaturated hydrocarbon compound, wherein the cyclic unsaturated hydrocarbon compound includes a monocyclic or bicyclic condensed ring composed of a plurality of carbon atoms, the monocyclic or bicyclic condensed ring includes two or more carbon-carbon double bonds, the bicyclic condensed ring does not include a benzene ring, when the number of the plurality of carbon atoms constituting the monocyclic ring is 7 or less, the number of carbon-carbon double bonds is an even number, when the number of the plurality of carbon atoms constituting the monocyclic ring is 8 or more, the number of carbon-carbon double bonds is an odd number or an even number, the number of carbon-carbon double bonds in the bicyclic condensed ring is an odd number or an even number.

2. The secondary battery according to claim 1, wherein the cyclic unsaturated hydrocarbon compound includes the monocyclic ring.

3. The secondary battery according to claim 2, wherein the monocyclic ring includes an annulene having a multiple of 4 carbon atoms.

4. The secondary battery according to claim 3, wherein the annulene includes cyclooctatetraene.

5. The secondary battery according to any one of claims 1 to 4, wherein the positive electrode contains a sulfur-containing material, the negative electrode contains a magnesium-containing material.

6. The secondary battery according to claim 5, wherein the sulfur-containing material includes sulfur monomers, the magnesium-containing material includes magnesium monomers.

7. The secondary battery according to any one of claims 1 to 6, wherein the electrolytic solution further contains an ether compound.

8. The secondary battery according to any one of claims 1 to 7, wherein the secondary battery is a magnesium-sulfur secondary battery.

9. An electrolytic solution for a secondary battery, containing a magnesium salt and a cyclic unsaturated hydrocarbon compound, wherein the cyclic unsaturated hydrocarbon compound includes a monocyclic or bicyclic condensed ring composed of a plurality of carbon atoms, the monocyclic or bicyclic condensed ring includes two or more carbon-carbon double bonds, the bicyclic condensed ring does not include a benzene ring, when the number of the plurality of carbon atoms constituting the monocyclic ring is 7 or less, the number of carbon-carbon double bonds is an even number, when the number of the plurality of carbon atoms constituting the monocyclic ring is 8 or more, the number of carbon-carbon double bonds is an odd number or an even number, the number of carbon-carbon double bonds in the bicyclic condensed ring is an odd number or an even number.

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