Electrolyte solution for secondary batteries, and secondary battery

Abstract

A secondary battery according to the present invention is provided with: a positive electrode; a negative electrode; and an electrolyte solution that contains a magnesium salt and a cyclic unsaturated hydrocarbon compound. The cyclic unsaturated hydrocarbon compound contains a monocyclic or bicyclic fused ring that is composed of a plurality of carbon atoms, the monocyclic or bicyclic fused ring comprises two or more carbon-carbon double bonds, and the bicyclic fused ring does not comprise a benzene ring. In cases where the number of the plurality of carbon atoms that constitute the monocyclic ring is 7 or less, the number of the carbon-carbon double bonds is even. In cases where the number of the plurality of carbon atoms that constitute the monocyclic ring is 8 or more, the number of the carbon-carbon double bonds is odd or even. The number of the carbon-carbon double bonds in the bicyclic fused ring is odd or even.

Description

Electrolyte for secondary battery and secondary battery

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

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as small, lightweight power sources that can provide high energy density. These secondary batteries include a positive electrode, a negative electrode, and an electrolyte (secondary battery electrolyte), and various studies have been conducted on the configuration of these secondary batteries.

[0003] Specifically, in a secondary battery in which charge / discharge reactions proceed using the deposition and dissolution of magnesium, the electrolyte contains a compound having an unsaturated hydrocarbon skeleton such as anthracene (see, for example, Patent Document 1).

[0004] International Publication No. 2020 / 090946

[0005] The battery characteristics of secondary batteries are still insufficient, and there is room for improvement.

[0006] There is a demand for an electrolyte solution for a secondary battery and a secondary battery that can provide excellent battery characteristics.

[0007] According to one embodiment of the present technology, an electrolyte solution for a secondary battery includes a magnesium salt and a cyclic unsaturated hydrocarbon compound. The cyclic unsaturated hydrocarbon compound includes a monocyclic or bicyclic fused ring composed of multiple carbon atoms, the monocyclic or bicyclic fused ring including two or more carbon-carbon double bonds, and the bicyclic fused 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 fused ring is an odd number or an even number.

[0008] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte solution, and the electrolyte solution has a configuration similar to that of the electrolyte solution for a secondary battery according to the embodiment of the present technology described above.

[0009] Here, a "monocyclic ring" refers to a single carbocyclic ring composed of multiple carbon atoms. A "bicyclic fused ring" refers to a ring composed of multiple carbon atoms and in which two carbocyclic rings are fused together, and as described above, does not contain a benzene ring. Details of monocyclic and bicyclic fused rings will be described later.

[0010] In an embodiment of the present technology, the secondary battery electrolyte and secondary battery include an electrolyte containing a magnesium salt and a cyclic unsaturated hydrocarbon compound, the cyclic unsaturated hydrocarbon compound containing a monocyclic or bicyclic fused ring, the monocyclic or bicyclic fused ring containing two or more carbon-carbon double bonds, the bicyclic fused ring not containing a benzene ring, and the number of carbon-carbon double bonds satisfies the above-mentioned condition, thereby achieving excellent battery characteristics.

[0011] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below.

[0012] Fig. 1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. Fig. 2 is a cross-sectional view illustrating a configuration of a battery element illustrated in Fig. 1. Fig. 3 is a cross-sectional view illustrating a configuration of a test secondary battery.

[0013] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order: 1. Electrolyte for secondary battery 1-1. Configuration 1-2. Manufacturing method 1-3. Action and effect 2. Secondary battery 2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Use of secondary battery

[0014] 1. Electrolyte for Secondary Battery First, an electrolyte for a secondary battery (hereinafter simply referred to as "electrolyte") according to an embodiment of the present technology will be described.

[0015] The electrolyte solution described here is used in a secondary battery, which is an electrochemical device. However, the electrolyte solution may also be used in electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices include primary batteries and capacitors.

[0016] <1-1. Configuration> The electrolytic solution is a liquid electrolyte and contains an electrolyte salt and an additive.

[0017] [Electrolyte Salt] The electrolyte salt contains one or more types of magnesium salts.

[0018] Specific examples of magnesium salts include magnesium chloride (MgCl ２　 ), magnesium perchlorate (Mg(ClO ４　 ) ２　 ), magnesium nitrate (Mg(NO ３　 ) ２　 ), magnesium sulfate (MgSO ４　 ), magnesium acetate (Mg(CH ３　 COO) ２　 ), magnesium trifluoroacetate (Mg(CF ３　 COO) ２　 ), magnesium tetrafluoroborate (Mg(BF ４　 ) ２　 ), magnesium tetraphenylborate (Mg(B(C ６　 H ５　 ) ４　 ) ２　 ), magnesium hexafluorophosphate (Mg(PF ６　 ) ２　 ), magnesium hexafluoroarsenate (Mg(AsF ６　 ) ２　 ), bis(hexamethyldisilazide)magnesium (Mg[N(Si(CH ３　 ) ３　 ) ２　 ] ２　 ), bis(trifluoromethanesulfonyl)imide magnesium (Mg[N(CF ３　 SO ２　 ) ２　 ] ２　 and magnesium bis[tetra(hexafluoroisopropyl)]borate (Mg[B(OCH(CF ３　 ) ２　 ) ４　 ] ２　 ) etc.

[0019] The content of electrolyte salt in the electrolyte solution (mol / l (= mol / dm ３　 However, the content of the electrolyte salt described here is the content of the electrolyte salt relative to the solvent described below.

[0020] [Cyclic Unsaturated Hydrocarbon Compound] The additive contains one or more cyclic unsaturated hydrocarbon compounds.

[0021] The cyclic unsaturated hydrocarbon compound includes one or both of a monocyclic compound and a fused ring compound. The monocyclic compound may be of one type or two or more types. Similarly, the fused ring compound may be of one type or two or more types.

[0022] (Monocyclic Compound) A monocyclic compound includes a monocyclic ring composed of multiple carbon atoms. As described above, this monocyclic ring is a single carbon ring composed of multiple carbon atoms, and more specifically, a hydrocarbon ring in which the multiple carbon atoms are bonded to each other to form a single ring.

[0023] Therefore, heterocycles in which atoms other than carbon atoms are bonded together to form a ring together with a plurality of carbon atoms are excluded from the monocycles described herein. Specific examples of atoms other than carbon atoms include boron, nitrogen, oxygen, phosphorus, and sulfur atoms.

[0024] This monocyclic ring contains two or more carbon-carbon double bonds (>C=C<). These two or more carbon-carbon bonds constitute the monocyclic ring and are therefore part of the monocyclic ring. Therefore, when an unsaturated hydrocarbon group (a group containing a carbon-carbon double bond) is bonded to a carbon atom constituting the monocyclic ring, the carbon-carbon double bond is not part of the monocyclic ring and is therefore excluded from the carbon-carbon double bonds described here.

[0025] The type of monocycle is not particularly limited as long as it is a hydrocarbon ring containing two or more carbon-carbon double bonds, and therefore the number of carbon atoms constituting the monocycle is not particularly limited.

[0026] For this reason, the monocycle may be a three-membered ring (the number of carbon atoms constituting the monocycle = 3), a four-membered ring (the number of carbon atoms constituting the monocycle = 4), a five-membered ring (the number of carbon atoms constituting the monocycle = 5), a six-membered ring (the number of carbon atoms constituting the monocycle = 6), a seven-membered ring (the number of carbon atoms constituting the monocycle = 7), or an eight-membered ring (the number of carbon atoms constituting the monocycle = 8). Of course, the monocycle may also be a ring having 9 or more carbon atoms.

[0027] The arrangement of the two or more carbon-carbon double bonds constituting the monocyclic ring is not particularly limited.

[0028] Therefore, the monocycle may be a completely conjugated system in which two or more carbon-carbon double bonds are arranged alternately via carbon-carbon single bonds (≡C-C≡), or a non-completely conjugated system in which two or more carbon-carbon double bonds are not arranged alternately via carbon-carbon single bonds. When the monocycle is a non-completely conjugated system, the arrangement of the two or more carbon-carbon double bonds can be set arbitrarily.

[0029] However, the number of carbon-carbon double bonds constituting the monocycle is set to a predetermined value according to the number of carbon atoms constituting the monocycle.

[0030] Specifically, 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, not an odd number. On the other hand, when the number of carbon atoms constituting the monocyclic ring is 8 or more, the number of carbon-carbon double bonds may be either an odd number or an even number. In other words, the number of carbon-carbon double bonds contained in the monocyclic compound (odd number or even number) varies depending on the number of carbon atoms constituting the monocyclic ring.

[0031] Specific examples of the monocyclic compound are as described below.

[0032] Specific examples of monocyclic compounds in which the number of carbon atoms constituting the monocyclic ring is 7 or less include cyclotetradiene (number of carbon atoms constituting the monocyclic ring=4, number of carbon-carbon double bonds=2) and cyclopentadiene (number of carbon atoms constituting the monocyclic ring=5, number of carbon-carbon double bonds=2).

[0033] Therefore, benzene (number of carbon atoms constituting a single ring = 6, number of carbon-carbon double bonds = 3) and cycloheptatriene (number of carbon atoms constituting a single ring = 7, number of carbon-carbon double bonds = 3) are excluded from the specific examples of monocyclic compounds described here.

[0034] Specific examples of monocyclic compounds in which the number of carbon atoms constituting the monocyclic ring is 8 or more include cyclooctatetraene (number of carbon atoms constituting the monocyclic ring=8, number of carbon-carbon double bonds=4), cyclooctatriene (number of carbon atoms constituting the monocyclic ring=8, number of carbon-carbon double bonds=3), cyclotetradecaheptaene (number of carbon atoms constituting the monocyclic ring=14, number of carbon-carbon double bonds=7), and cyclooctadecanonaene (number of carbon atoms constituting the monocyclic ring=18, number of carbon-carbon double bonds=9).

[0035] (Fused Ring Compound) The fused ring compound contains a bicyclic fused ring composed of multiple carbon atoms. As described above, this bicyclic fused ring is a ring composed of multiple carbon atoms and formed by condensing two carbon rings together, more specifically, a hydrocarbon ring in which the multiple carbon atoms are bonded to form two rings.

[0036] Therefore, heterocycles in which atoms other than carbon atoms are bonded together to form two rings together with a plurality of carbon atoms are excluded from the bicyclic fused rings described herein, with the details regarding atoms other than carbon atoms being as described above.

[0037] However, the bicyclic fused ring does not contain a benzene ring, i.e., in a bicyclic fused ring, as described above, two carbocyclic rings are fused to each other, but neither of the two carbocyclic rings is a benzene ring.

[0038] This bicyclic fused ring contains two or more carbon-carbon double bonds. These two or more carbon-carbon bonds constitute the bicyclic fused ring and are therefore 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 here.

[0039] The type of 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 fused to each other, and therefore the number of carbon atoms constituting the bicyclic fused ring is not particularly limited.

[0040] For this reason, the bicyclic fused ring may be a fused ring between two three-membered rings (the number of carbon atoms constituting the bicyclic fused ring = 4), a fused ring between a three-membered ring and a four-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 5), a fused ring between two four-membered rings (the number of carbon atoms constituting the bicyclic fused ring = 6), a fused ring between a four-membered ring and a five-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 7), a fused ring between two five-membered rings (the number of carbon atoms constituting the bicyclic fused ring = 8), or a fused ring between a five-membered ring and a six-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 9).

[0041] The bicyclic fused ring may be a fused ring between two six-membered rings (the number of carbon atoms constituting the bicyclic fused ring = 10), a fused ring between a six-membered ring and a seven-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 11), a fused ring between two seven-membered rings (the number of carbon atoms constituting the bicyclic fused ring = 12), a fused ring between a seven-membered ring and an eight-membered ring (the number of carbon atoms constituting the bicyclic fused ring = 13), or a fused ring between two eight-membered rings (the number of carbon atoms constituting the bicyclic fused ring = 14).

[0042] Of course, the bicyclic fused ring may be a fused ring other than the series of fused rings described above.

[0043] Furthermore, the arrangement of the two or more carbon-carbon double bonds constituting the bicyclic fused ring is not particularly limited.

[0044] Therefore, the bicyclic fused ring may be a completely conjugated system in which two or more carbon-carbon double bonds are arranged alternately via carbon-carbon single bonds, or may be a non-completely conjugated system in which two or more carbon-carbon double bonds are not arranged alternately via carbon-carbon single bonds. When the bicyclic fused ring is a non-completely conjugated system, the arrangement of the two or more carbon-carbon double bonds can be set arbitrarily.

[0045] The number of carbon-carbon double bonds constituting the bicyclic fused ring is not particularly limited and can be set arbitrarily. Specifically, the number of carbon-carbon double bonds may be an odd number or an even number. That is, the number of carbon-carbon double bonds contained in the fused ring compound (odd number or even number) can be set arbitrarily, regardless of the number of carbon atoms constituting the bicyclic fused ring.

[0046] Specific examples of fused ring compounds include pentalene, which is a compound formed by the fusion of two five-membered rings (the number of carbon atoms constituting the bicyclic fused ring is 8, and the number of carbon-carbon double bonds is 4), azulene, which is a compound formed by the fusion of a five-membered ring and an eight-membered ring (the number of carbon atoms constituting the bicyclic fused ring is 11, and the number of carbon-carbon double bonds is 5), and heptalene, which is a compound formed by the fusion of two seven-membered rings (the number of carbon atoms constituting the bicyclic fused ring is 12, and the number of carbon-carbon double bonds is 6).

[0047] Therefore, specific examples of fused ring compounds described here do not include tetralin, which is a fused ring formed by two six-membered rings, cyclohexane and benzene (number of carbon atoms constituting the bicyclic fused ring = 10, number of carbon-carbon double bonds = 3), naphthalene, which is a fused ring formed by two six-membered rings, benzene (number of carbon atoms constituting the bicyclic fused ring = 10, number of carbon-carbon double bonds = 5), and anthracene, which is a fused ring formed by three six-membered rings, benzene (number of carbon atoms constituting the bicyclic fused ring = 14, number of carbon-carbon double bonds = 7).

[0048] (Content) The content of the cyclic unsaturated hydrocarbon compound in the electrolyte solution is not particularly limited and can be set arbitrarily. As described above, the cyclic unsaturated hydrocarbon compound may contain only a monocyclic compound, may contain only a fused ring compound, or may contain both the monocyclic compound and the fused ring compound.

[0049] In addition, when checking for the presence or absence of cyclic unsaturated hydrocarbon compounds in the electrolyte solution and measuring the content of cyclic unsaturated hydrocarbon compounds in the electrolyte solution, the electrolyte solution is analyzed using one or more of existing analytical methods, which are not particularly limited, but specifically include inductively coupled plasma (ICP) optical emission spectroscopy, nuclear magnetic resonance spectroscopy (NMR), and gas chromatography mass spectrometry (GC-MS).

[0050] (Reason) The electrolyte contains a cyclic unsaturated hydrocarbon compound because it facilitates stable oxidation-reduction reactions that utilize the deposition and dissolution of magnesium. As a result, in secondary batteries using the electrolyte, charge-discharge reactions tend to proceed stably and continuously, and the battery capacity is less likely to decrease even after repeated charge-discharge.

[0051] Specifically, when the electrolyte solution contains a cyclic unsaturated hydrocarbon compound, the activity of magnesium is improved during the magnesium precipitation and dissolution reaction compared to when the electrolyte solution does not contain a cyclic unsaturated hydrocarbon compound, which facilitates the oxidation-reduction reaction utilizing the magnesium precipitation and dissolution, thereby facilitating the charge-discharge reaction in a secondary battery using the electrolyte solution.

[0052] The electrolyte solution does not contain a cyclic unsaturated hydrocarbon compound when it does not contain an additive, or when it contains another compound as an additive instead of the cyclic unsaturated hydrocarbon compound, such as anthracene.

[0053] Furthermore, the cyclic unsaturated hydrocarbon compound becomes a dianion in a reduced state, and thus becomes an electrochemically stable active species in the electrolyte. Because this active species is not easily decomposed in the electrolyte, the lifetime of the active species is extended even when redox reactions are repeated.

[0054] As a result, in a secondary battery using an electrolyte, even if a 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 film. That is, the electrochemically stable active species maintains the activity of magnesium even after repeated charge and discharge. Therefore, the charge and discharge reaction utilizing the deposition and dissolution of magnesium is more likely to proceed even after repeated charge and discharge.

[0055] For these reasons, when an electrolyte solution contains a cyclic unsaturated hydrocarbon compound, in a secondary battery using that electrolyte solution, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium tends to proceed stably and continuously, and the battery capacity is less likely to decrease even with repeated charge and discharge.

[0056] (Preferred Configuration) Among these, the cyclic unsaturated hydrocarbon compound preferably contains a single ring, i.e., it is preferable to contain a single ring compound rather than a fused ring compound, because this facilitates sufficient progress of the charge / discharge reaction utilizing the precipitation and dissolution of magnesium, and also makes it difficult for the battery capacity to decrease even after repeated charge / discharge.

[0057] This monocycle is preferably a fully conjugated system in which two or more carbon-carbon double bonds are alternately arranged via carbon-carbon single bonds, and more specifically, it preferably contains an annulene having a number of carbon atoms that is a multiple of four. This is because the cyclic unsaturated hydrocarbon compound exhibits aromaticity under reduced conditions. This makes the active species derived from the cyclic unsaturated hydrocarbon compound more electrochemically stable, thereby extending the life of the cyclic unsaturated hydrocarbon compound. However, as mentioned above, benzene and other compounds that do not have a number of carbon atoms that is a multiple of four are excluded from the annulene described here.

[0058] Here, "multiples of four" means so-called 4n (n is an integer of 1 or more), and specific examples of multiples of four are 4, 8, 12, etc. Therefore, benzene (number of carbon atoms = 6) having so-called 4n + 2 (n is an integer of 1 or more) carbon atoms does not fall under annulene having a number of carbon atoms that is a multiple of four. Benzene having 4n + 2 carbon atoms, for example, exhibits aromaticity not only in the reduced state but also in the normal molecular state.

[0059] It is particularly preferable that the annulene having a carbon atom number that is a multiple of four contains cyclooctatetraene, because the active species derived from the cyclic unsaturated hydrocarbon compound are electrochemically remarkably stabilized, thereby significantly extending the life of the cyclic unsaturated hydrocarbon compound.

[0060] [Solvent] The electrolytic solution may further contain one or more of the solvents. The type of the solvent is not particularly limited, but specifically, it is a non-aqueous solvent (organic solvent). The electrolytic solution containing the non-aqueous solvent is a so-called non-aqueous electrolytic solution.

[0061] The type of non-aqueous solvent is not particularly limited, but it is preferable that the non-aqueous solvent contains an ether compound, because the ether compound makes it easier for the electrolyte salt to be dispersed or dissolved, thereby stabilizing the state of the electrolyte solution.

[0062] The ether compound is a compound containing an ether bond (—O—). The ether compound may be linear or cyclic. The number of ether bonds may be one or two or more.

[0063] Specific examples of the ether compound include dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and tetrahydrofuran.

[0064] <1-2. Manufacturing Method> When manufacturing an electrolytic solution, an electrolyte salt and an additive (a cyclic unsaturated hydrocarbon compound) are added to a solvent, whereby the electrolyte salt and the cyclic unsaturated hydrocarbon compound are dispersed or dissolved in the solvent, thereby completing the electrolytic solution.

[0065] <1-3. Actions and Effects> 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.

[0066] In this case, as described above, the oxidation-reduction reaction utilizing the precipitation and dissolution of magnesium is facilitated, and the active species derived from the cyclic unsaturated hydrocarbon compound maintain the activity of magnesium during the precipitation and dissolution reaction. As a result, in a secondary battery using the electrolyte, the charge and discharge reaction is facilitated to proceed stably and continuously, and the battery capacity is less likely to decrease even with repeated charge and discharge. Therefore, a secondary battery with excellent battery characteristics can be realized.

[0067] In particular, if the cyclic unsaturated hydrocarbon compound contains a single ring, that is, if the cyclic unsaturated hydrocarbon compound contains a monocyclic compound, the charge / discharge reaction utilizing the precipitation and dissolution of magnesium is more likely to proceed sufficiently, and the battery capacity is less likely to decrease even after repeated charge / discharge, thereby achieving a greater effect.

[0068] In this case, if the single ring contains annulene having a carbon atom number that is a multiple of 4, the active species derived from the cyclic unsaturated hydrocarbon compound will be electrochemically more stabilized, thereby extending the life of the active species and achieving even greater effects.

[0069] In particular, when annulene contains cyclooctatetraene, the active species derived from the cyclic unsaturated hydrocarbon compound are electrochemically remarkably stabilized, thereby significantly extending the life of the active species and achieving a remarkably high effect.

[0070] Furthermore, if the electrolyte solution further contains an ether compound, the electrolyte salt is more easily dispersed or dissolved by the ether compound, which stabilizes the state of the electrolyte solution and provides a greater effect.

[0071] 2. Secondary Battery Next, a secondary battery using an electrolytic solution according to an embodiment of the present technology will be described.

[0072] The secondary battery described here utilizes the deposition and dissolution of magnesium to cause charge and discharge reactions to proceed, and therefore is a secondary battery that utilizes the charge and discharge reactions to obtain battery capacity.

[0073] More specifically, the secondary battery described below is a so-called magnesium-sulfur secondary battery, since the positive electrode contains a sulfur-containing material and the negative electrode contains a magnesium-containing material. In this secondary battery, magnesium is precipitated and dissolved at the negative electrode, and magnesium is absorbed and released in an ionic state at the positive electrode. Details of the sulfur-containing material and the magnesium-containing material will be described later.

[0074] <2-1. Configuration> Fig. 1 shows a perspective configuration of a secondary battery, and Fig. 2 shows a cross-sectional configuration of the battery element 20 shown in Fig. 1. However, Fig. 1 shows a state in which the exterior 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.

[0075] As shown in FIGS. 1 and 2, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and .

[0076] The secondary battery described here is a laminate film type secondary battery that uses a flexible (or pliable) exterior film 10 as an exterior member.

[0077] 1, the exterior film 10 has a bag-like structure that is sealed with the battery element 20 housed therein. As a result, the exterior film 10 houses a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte solution, which will be described later.

[0078] Here, the exterior film 10 is a single film-like member that is folded in a folding direction F. The exterior film 10 is provided with a recessed portion 10U (a so-called deep drawn portion) for accommodating the battery element 20.

[0079] Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside out, and when the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0080] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0081] [Battery Element] The battery element 20 is a power generating element housed inside the exterior film 10. As shown in Figures 1 and 2, the battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0082] Here, the battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are wound around a winding axis P while facing each other with a separator 23 interposed therebetween. As shown in FIG. 1 , the winding axis P is a virtual axis extending in the Y-axis direction.

[0083] There are no particular limitations on the three-dimensional shape of battery element 20. Here, battery element 20 has a flat three-dimensional shape, and therefore the shape of a cross section (cross section along the XZ plane) of battery element 20 intersecting winding axis P is a flat shape defined by major axis J1 and minor axis J2.

[0084] 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 intersecting the X-axis direction and has a length less than that of the major axis J1. Here, the three-dimensional shape of the battery element 20 is a flattened cylinder, and therefore the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape.

[0085] (Positive Electrode) The positive electrode 21 contains a positive electrode active material that absorbs and releases magnesium in an ionic state, and the positive electrode active material contains one or more sulfur-containing materials. This is because magnesium is more likely to be absorbed and released in an ionic state in the positive electrode 21, and therefore a charge-discharge reaction utilizing the deposition and dissolution of the magnesium is more likely to proceed.

[0086] The sulfur-containing material is a material containing sulfur as a constituent element. That is, the sulfur-containing material may be elemental sulfur, a sulfur alloy, a sulfur compound, or a mixture of two or more of these. Note that the purity of elemental sulfur is not particularly limited, and therefore the elemental sulfur may contain any amount of impurities.

[0087] The type of metallic element contained as a constituent element in a sulfur alloy is not particularly limited as long as it is any one or more of any metallic elements. A sulfur compound contains, as a constituent element, any one or more of non-metallic elements such as carbon, oxygen, and halogens, and specific examples of the halogens include fluorine, chlorine, bromine, and iodine.

[0088] In particular, the positive electrode active material preferably contains elemental sulfur, because this facilitates sufficient progress of the charge-discharge reaction utilizing the deposition and dissolution of magnesium. Figure 2 shows a case in which the positive electrode 21 contains elemental sulfur.

[0089] Although not specifically shown here, the positive electrode 21 may include a positive electrode current collector and a positive electrode active material layer.

[0090] The positive electrode current collector is a conductive support that supports the positive electrode active material layer and has a pair of surfaces on which the positive electrode active material layer is provided. This positive electrode current collector contains a conductive material such as a metal material, and a specific example of the conductive material is nickel.

[0091] The positive electrode active material layer is supported by the positive electrode current collector and contains one or more sulfur-containing materials as positive electrode active materials, but may further contain one or more other materials such as a positive electrode binder and a positive electrode conductive agent.

[0092] The positive electrode active material layer may be provided on both sides of the positive electrode current collector, or may be provided on only one side of the positive electrode current collector. The method for forming the positive electrode active material layer is not particularly limited, but specifically, it may be any one or more of coating methods.

[0093] The positive electrode binder contains one or more resin materials such as a fluorine-based resin, a polyvinyl alcohol-based resin, and a styrene-butadiene copolymer rubber. Specific examples of the fluorine-based resin include polyvinylidene fluoride and polytetrafluoroethylene.

[0094] The positive electrode binder may be a conductive polymer compound. Specific examples of the conductive polymer compound include polyaniline, polypyrrole, and polythiophene, and may also be copolymers of two or more of these. The conductive polymer compound may be unsubstituted or substituted with any one or more functional groups.

[0095] The positive electrode conductive agent contains one or more conductive materials such as a carbon material, a metal material, and a conductive polymer compound.

[0096] Specific examples of carbon materials include graphite (natural graphite and artificial graphite), carbon fiber, carbon black, and carbon nanotubes. Carbon fibers include vapor-grown carbon fiber (VGCF). Carbon black includes acetylene black and ketjen black. Carbon nanotubes include single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), and multi-walled carbon nanotubes include double-walled carbon nanotubes (DWCNT). Specific examples of metal materials include nickel.

[0097] (Negative Electrode) The negative electrode 22 contains one or more types of magnesium-containing materials, which are negative electrode active materials, because this facilitates the progress of charge / discharge reactions that utilize the deposition and dissolution of magnesium.

[0098] The magnesium-containing material is a material containing magnesium as a constituent element. That is, the magnesium-containing material may be magnesium alone, a magnesium alloy, a magnesium compound, or a mixture of two or more of these. Note that the purity of the metallic magnesium is not particularly limited, and the metallic magnesium may contain any amount of impurities.

[0099] The types of metallic elements (except magnesium) contained as constituent elements in magnesium alloys are not particularly limited as long as they are any one or more of any metallic elements. Magnesium compounds contain one or more of non-metallic elements such as carbon, oxygen, sulfur, and halogens as constituent elements, and specific examples of halogens include fluorine, chlorine, bromine, and iodine.

[0100] In particular, the negative electrode active material preferably contains magnesium as a simple substance, because this facilitates sufficient progress of the charge-discharge reaction that utilizes the deposition and dissolution of magnesium. Figure 2 shows a case in which the negative electrode 22 contains magnesium as a simple substance.

[0101] The negative electrode 22 may have a configuration similar to that of the positive electrode 21. That is, although not specifically illustrated here, the negative electrode 22 may include a negative electrode current collector and a negative electrode active material layer.

[0102] The negative electrode current collector is a conductive support that supports the negative electrode active material layer and has a pair of surfaces on which the negative electrode active material layer is provided. This negative electrode current collector contains a conductive material such as a metal material, and a specific example of the conductive material is nickel.

[0103] The negative electrode active material layer is supported by the negative electrode current collector and contains one or more magnesium-containing materials as negative electrode active materials, but may further contain one or more other materials such as a negative electrode binder and a negative electrode conductive agent.

[0104] The negative electrode active material layer may be provided on both sides of the negative electrode current collector, or may be provided on only one side of the negative electrode current collector. The method for forming the negative electrode active material layer is not particularly limited, but specifically, it may be any one or more of coating methods.

[0105] The details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and the details regarding the negative electrode conductivity are the same as those regarding the positive electrode conductivity agent.

[0106] 2, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows magnesium to pass through in an ionic state while preventing a short circuit between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0107] (Electrolyte) 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.

[0108] [Positive Electrode Lead] As shown in FIGS. 1 and 2 , the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode 21 and is led out of the exterior film 10. If 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 includes a conductive material such as a metal material, and a specific example of the conductive material is aluminum. The positive electrode lead 31 has a shape such as a thin plate or a mesh.

[0109] [Negative Electrode Lead] As shown in FIGS. 1 and 2 , the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode 22 and is led out of the exterior film 10. If 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 lead-out direction of the negative electrode lead 32 is the same as the lead-out direction of the positive electrode lead 31. The negative electrode lead 32 includes a conductive material such as a metal material, and a specific example of the conductive material is copper. 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.

[0110] [Sealing Film] The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0111] The sealing film 41 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. This sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and a specific example of the polymer compound is polypropylene.

[0112] The configuration of the sealing film 42 is the same as the configuration of the sealing film 41, except that the sealing film 42 is a sealing member that has adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32.

[0113] <2-2. Operation> The secondary battery operates in the battery element 20 as follows.

[0114] During discharge, the magnesium-containing material dissolves in the negative electrode 22, causing magnesium to elute into the electrolyte, and the magnesium is absorbed in an ionic state in the positive electrode 21. On the other hand, during charge, magnesium is released in an ionic state from the positive electrode 21 into the electrolyte, and the magnesium is precipitated at the negative electrode 22.

[0115] <2-3. Manufacturing Method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are prepared according to the procedure described below as an example, and then the positive electrode 21, the negative electrode 22, and the electrolyte are used to assemble the secondary battery.

[0116] In the following, a case where elemental sulfur (sulfur powder) is used as the sulfur-containing material and elemental magnesium (metallic magnesium) is used as the magnesium-containing material will be described. Note that, since the procedure for producing the electrolyte solution has already been described, the description of the procedure for producing the electrolyte solution will be omitted below.

[0117] [Preparation of Positive Electrode] First, a positive electrode active material (sulfur powder, which is a sulfur-containing material), a positive electrode binder, and a positive electrode conductive agent are mixed together to form a positive electrode mixture. Next, the positive electrode mixture is introduced into a solvent to prepare a paste-like positive electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Finally, the positive electrode mixture slurry is applied to both sides of a positive electrode current collector to form a positive electrode active material layer. Then, the positive electrode active material layer may be compression-molded using a roll press or the like. In this case, the positive electrode active material layer may be heated, or the compression molding may be repeated multiple times. As a result, positive electrode active material layers are formed on both sides of the positive electrode current collector, thereby producing the positive electrode 21.

[0118] [Preparation of Negative Electrode] A negative electrode active material (metallic magnesium, which is a magnesium-containing material) is prepared as the negative electrode 22. Magnesium foil is used as this metallic magnesium.

[0119] [Assembly of Secondary Battery] First, the positive electrode lead 31 is connected to the positive electrode 21 by a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode 22 by a joining method such as welding.

[0120] Next, the positive electrode 21 and the negative electrode 22 are stacked one on top of the other with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to form a wound body (not shown). Next, the wound body is pressed using a press or the like to form a flat shape. The wound body after this formation has a configuration similar to that of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte solution.

[0121] Next, after the roll is housed inside the recess 10U, the exterior film 10 (fusion layer / metal layer / surface protection layer) is folded to face each other. Next, the outer peripheral edges of two sides of the facing fusion layers are joined together using an adhesive method such as heat fusion, thereby housing the roll inside the bag-shaped exterior film 10.

[0122] Finally, after injecting an electrolyte solution into the bag-shaped exterior film 10, the outer peripheral edges of the remaining sides of the opposing fusion layers are joined together using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32.

[0123] As a result, the wound body is impregnated with the electrolyte, forming the wound electrode body, which is the battery element 20. The battery element 20 is then sealed inside the bag-shaped exterior film 10, completing the secondary battery.

[0124] <2-4. Actions and Effects> According to this secondary battery, the secondary battery includes an electrolyte solution having the above-described configuration. In this case, for the reasons described above, the charge / discharge reaction tends to proceed stably and continuously, and the battery capacity is less likely to decrease even with repeated charge / discharge, thereby achieving excellent battery characteristics.

[0125] In particular, if the positive electrode 21 contains a sulfur-containing material and the negative electrode 22 contains a magnesium-containing material, the charge-discharge reaction utilizing the deposition and dissolution of magnesium is facilitated to proceed sufficiently, and the battery capacity is not likely to decrease even after repeated charge-discharge, thereby achieving a higher effect. In this case, if the sulfur-containing material contains elemental sulfur and the magnesium-containing material contains elemental magnesium, the charge-discharge reaction is facilitated to proceed more easily and the battery capacity is not likely to decrease, thereby achieving an even higher effect.

[0126] Furthermore, if the secondary battery is a magnesium-sulfur secondary battery, sufficient battery capacity can be obtained by utilizing the deposition and dissolution of magnesium, and therefore a greater effect can be obtained.

[0127] 3. Uses of Secondary Batteries There are no particular limitations on the uses (application examples) of secondary batteries. Secondary batteries used as power sources may be the main power source or auxiliary power source in electronic devices, electric vehicles, and the like. The main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. The auxiliary power source may be a power source used in place of the main power source or a power source that can be switched from the main power source.

[0128] Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals; Storage devices such as backup power supplies and memory cards; Power tools such as power drills and power saws; Battery packs installed in electronic devices; Medical electronic devices such as pacemakers and hearing aids; Electric vehicles such as electric cars (including hybrid cars); Power storage systems such as home or industrial battery systems that store power in preparation for emergencies, etc. In these uses, only one secondary battery may be used, or two or more secondary batteries may be used.

[0129] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that runs on a secondary battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, power stored in a secondary battery, which is a power storage source, can be used to power home electrical appliances, etc.

[0130] An embodiment of the present technology will be described.

[0131] As will be described below, after the electrolyte solution and secondary battery were produced, the physical properties of the electrolyte solution and the battery characteristics of the secondary battery were evaluated.

[0132] Examples 1 and 2 and Comparative Examples 1 to 4 First, electrolytic solutions were produced according to the procedures described below, and then the physical properties of the electrolytic solutions were evaluated.

[0133] [Preparation of Electrolyte Solution] An electrolyte salt (magnesium salt) and an additive (a cyclic unsaturated hydrocarbon compound, cyclooctatetraene (COT), manufactured by Tokyo Chemical Industry Co., Ltd.) were added to a solvent (an ether compound, diethylene glycol dimethyl ether (DGDE), manufactured by Toyama Pharmaceutical Co., Ltd.), and the solvent was stirred to prepare an electrolyte solution.

[0134] The electrolyte salt is magnesium bis(trifluoromethanesulfonyl)imide (MgTFSI ２　 , manufactured by Toyama Pharmaceutical Co., Ltd.) and magnesium chloride (MgCl ２　 In this case, the content of bis(trifluoromethanesulfonyl)imide magnesium in the electrolyte was 0.2 mol / L (=0.2 mol / dm ３　 ) and the content of magnesium chloride in the electrolyte was 0.2 mol / L relative to the solvent.

[0135] Magnesium chloride was used alone as the electrolyte salt, and the content of magnesium chloride in the electrolyte solution was 0.4 mol / L relative to the solvent.

[0136] The content of cyclooctatetraene in the electrolyte was 0.05 mol / L relative to the solvent.

[0137] For comparison, an electrolyte solution was prepared in the same manner except that no additive was used. Also, for comparison, an electrolyte solution was prepared in the same manner except that another compound (anthracene (ANT), manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the additive instead of the cyclic unsaturated hydrocarbon compound.

[0138] After preparing the electrolyte solution, the electrolyte solution was analyzed using ICP atomic emission spectroscopy, and 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.

[0139] [Evaluation of Physical Properties] When the oxidation-reduction characteristics were evaluated as physical properties, the results shown in Table 1 were obtained.

[0140] To evaluate the redox characteristics, first, the working electrode (platinum), reference electrode (magnesium), and counter electrode (magnesium) were immersed in the electrolyte. Next, the correlation between potential and current (cyclic voltammogram) was measured using cyclic voltammetry in a room temperature environment (temperature = 25°C). In this case, the sweep rate was 25 mV / sec, the potential range was -2 V to 2 V, and the number of cycles was 10. Finally, based on the cyclic voltammogram, the progress of the redox reaction, which is an index for evaluating the redox characteristics, was determined.

[0141] The "oxidation-reduction reaction" column in Table 1 shows the following trends.

[0142] The "OK" indicates that the redox reaction proceeded because the electrolyte showed activity not only during magnesium deposition but also during magnesium dissolution. In other words, it indicates that the charge-discharge reaction proceeded in the secondary battery using the electrolyte.

[0143] On the other hand, "Fail" indicates that the oxidation-reduction reaction did not proceed sufficiently because the electrolyte did not show activity when dissolving magnesium. In other words, this indicates that the charge-discharge reaction did not proceed in the secondary battery using the electrolyte.

[0144]

[0145] [Discussion] As shown in Table 1, whether or not the oxidation-reduction reaction proceeded varied depending on the composition of the electrolyte solution.

[0146] Specifically, when no additive was used (Comparative Examples 1 and 2), there was a difference in whether or not the redox reaction proceeded. That is, when a mixture of bis(trifluoromethanesulfonyl)imide magnesium and magnesium chloride was used as the electrolyte salt (Comparative Example 1), the redox reaction proceeded. However, when only bis(trifluoromethanesulfonyl)imide magnesium was used as the electrolyte salt (Comparative Example 2), the redox reaction did not proceed.

[0147] Similarly, when another compound (anthracene) was used as an additive (Comparative Examples 3 and 4), the progress of the redox reaction also differed. That is, when a mixture of bis(trifluoromethanesulfonyl)imide magnesium and magnesium chloride was used as the electrolyte salt (Comparative Example 3), the redox reaction proceeded. However, when only bis(trifluoromethanesulfonyl)imide magnesium was used as the electrolyte salt (Comparative Example 4), the redox reaction did not proceed.

[0148] Therefore, when no additive was used (Comparative Examples 1 and 2) and when another compound (anthracene) was used as an additive (Comparative Examples 3 and 4), the progress of the redox reaction varied depending on the type of electrolyte salt.

[0149] In contrast, when a cyclic unsaturated hydrocarbon compound (cyclooctatetraene) was used as an additive (Examples 1 and 2), there was no difference in whether the redox reaction proceeded. That is, when a mixture of bis(trifluoromethanesulfonyl)imide magnesium and magnesium chloride was used as the electrolyte salt (Example 1), the redox reaction proceeded. Similarly, when only bis(trifluoromethanesulfonyl)imide magnesium was used as the electrolyte salt (Example 2), the redox reaction proceeded.

[0150] Therefore, when a cyclic unsaturated hydrocarbon compound was used as an additive (Examples 1 and 2), the oxidation-reduction reaction proceeded stably, regardless of the type of electrolyte salt.

[0151] Example 3 and Comparative Examples 5 and 6 Next, secondary batteries were manufactured according to the procedures described below, and then the battery characteristics of the secondary batteries were evaluated.

[0152] [Fabrication of Secondary Battery] A test secondary battery was fabricated to perform a simple evaluation of battery characteristics. Fig. 3 shows the cross-sectional structure of the test secondary battery (coin-type magnesium-sulfur secondary battery).

[0153] Below, the configuration of the test secondary battery will be explained, and then the manufacturing procedure of the test secondary battery will be explained.

[0154] (Configuration of Test Secondary Battery) As shown in FIG. 3, this test secondary battery includes a test electrode 51, a counter electrode 52, a separator 53, an exterior cup 54, an exterior can 55, a gasket 56, and an electrolyte (not shown).

[0155] The test electrode 51 is housed in an exterior cup 54, and the counter electrode 52 is housed in an exterior can 55. The test electrode 51 and the counter electrode 52 are stacked together with a separator 53 interposed therebetween, and the test electrode 51, the counter electrode 52, and the separator 53 are each impregnated with an electrolyte. The exterior cup 54 and the exterior can 55 are crimped together with a gasket 56, so that the test electrode 51, the counter electrode 52, and the separator 53 are sealed by the exterior cup 54 and the exterior can 55.

[0156] (Procedure for Manufacturing Test Secondary Battery) The procedure for manufacturing the test secondary battery is as follows.

[0157] (Preparation of Test Electrode) First, 10 parts by mass of a positive electrode active material (sulfur powder, a sulfur-containing material), 30 parts by mass of a positive electrode binder (polytetrafluoroethylene, manufactured by AGC Corporation), and 60 parts by mass of a positive electrode conductive agent (Ketjen Black, manufactured by Lion Corporation, ECP600JD) were mixed together to prepare a mixture. 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 disk shape (diameter = 15 mm). This produced a test electrode 51.

[0158] (Preparation of Counter Electrode) A disk-shaped magnesium plate (thickness = 200 μm, diameter = 16 mm, purity = 99.9%, manufactured by Rikazai Corporation) was prepared as the counter electrode 52 (metallic magnesium, which is a magnesium-containing material).

[0159] (Preparation of Electrolyte Solutions) The electrolyte solutions of Example 1 and Comparative Examples 1 and 3 described above were prepared.

[0160] (Assembly of Test Secondary Battery) First, the test electrode 51 was placed in the exterior cup 54, and the counter electrode 52 was placed in the exterior can 55. Next, the test electrode 51 placed in the exterior cup 54 and the counter electrode 52 placed in the exterior can 55 were stacked together via a separator 53 (glass fiber having a thickness of 200 μm, GC50 manufactured by Advantec Co., Ltd.) impregnated with an electrolyte. In this case, the test electrode 51 was positioned so that the positive electrode active material layer faced the counter electrode 52 via the separator 53. Finally, with the test electrode 51 and the counter electrode 52 stacked together via the separator 53, the exterior cup 54 and the exterior can 55 were crimped together via the gasket 56. As a result, the test electrode 51 and the counter electrode 52 were sealed in the exterior cup 54 and the exterior can 55, completing a test secondary battery.

[0161] [Evaluation of Battery Characteristics] When the cycle characteristics were evaluated as the battery characteristics, the results shown in Table 2 were obtained.

[0162] When evaluating the cycle characteristics, first, the test secondary battery was subjected to two cycles of charge and discharge in a room temperature environment (temperature = 25°C) in order to electrochemically stabilize the state of the test secondary battery.

[0163] Subsequently, the test secondary battery was subjected to one cycle of charge and discharge in the same environment to measure the discharge capacity (discharge capacity at the third cycle). Subsequently, the test secondary battery was subjected to seven cycles of charge and discharge in the same environment to measure the discharge capacity (discharge capacity at the tenth cycle).

[0164] Finally, the capacity retention rate, which is an index for evaluating cycle characteristics, was calculated based on the formula: capacity retention rate (%)=(discharge capacity at 10th cycle / discharge capacity at 3rd cycle)×100.

[0165] During discharge, the battery was discharged at a constant current of 0.1 mA until the voltage reached 0.8 V, and during charging, the battery was charged at a constant current of 0.1 mA until the voltage reached 2.4 V.

[0166]

[0167] [Discussion] As shown in Table 2, the capacity retention rate varied greatly depending on the composition of the electrolyte solution.

[0168] Specifically, when the electrolyte solution contained a cyclic unsaturated hydrocarbon compound (cyclooctatetraene) as an additive (Example 3), the capacity retention rate increased compared to when the electrolyte solution did not contain any additive (Comparative Example 5) and when the electrolyte solution contained another compound (anthracene) as an additive (Comparative Example 6).

[0169] In particular, when the electrolyte solution contained a cyclic unsaturated hydrocarbon compound as an additive, a sufficient capacity retention rate was obtained when the solvent contained an ether compound (diethylene glycol dimethyl ether).

[0170] [Summary] From the results shown in Tables 1 and 2, it can be seen that when the electrolyte solution contained a magnesium salt and a cyclic unsaturated hydrocarbon compound, a high capacity retention rate was obtained. Therefore, the cycle characteristics were improved, and excellent battery characteristics were obtained.

[0171] The present technology has been described above with reference to an embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

[0172] Specifically, the battery structure of the secondary battery has been described as being of a laminate film type and a coin type. However, the battery structure of the secondary battery is not particularly limited, and may be of a cylindrical type, a square type, a button type, or the like.

[0173] The battery element has been described as having a wound structure. However, the structure of the battery element is not particularly limited, and may be a stacked structure or a zigzag structure. In the stacked structure, the positive and negative electrodes are stacked on top of each other, and in the zigzag structure, the positive and negative electrodes are folded in a zigzag pattern.

[0174] The effects described in this specification are merely examples, and therefore the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

[0175] The present technology may also be configured as follows. <1> A secondary battery comprising: a positive electrode; a negative electrode; and an electrolyte solution containing a magnesium salt and a cyclic unsaturated hydrocarbon compound, wherein the cyclic unsaturated hydrocarbon compound includes a monocyclic ring or a bicyclic fused ring composed of a plurality of carbon atoms, wherein the monocyclic ring or the bicyclic fused ring includes two or more carbon-carbon double bonds, and wherein the bicyclic fused ring does not include a benzene ring, wherein 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, and 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, and wherein the number of carbon-carbon double bonds in the bicyclic fused ring is an odd number or an even number. <2> The secondary battery according to <1>, wherein the cyclic unsaturated hydrocarbon compound includes the monocyclic ring. <3> The secondary battery according to <2>, wherein the monocyclic ring includes an annulene having a number of carbon atoms that is a multiple of four. <4> The secondary battery according to <3>, wherein the annulene contains cyclooctatetraene. <5> The secondary battery according to any one of <1> to <4>, wherein the positive electrode contains a sulfur-containing material, and the negative electrode contains a magnesium-containing material. <6> The secondary battery according to <5>, wherein the sulfur-containing material contains elemental sulfur, and the magnesium-containing material contains elemental magnesium. <7> The secondary battery according to any one of <1> to <6>, wherein the electrolyte further contains an ether compound. <8> The secondary battery according to any one of <1> to <7>, wherein the secondary battery is a magnesium-sulfur secondary battery.<9> An electrolyte solution for a secondary battery, comprising: a magnesium salt; and a cyclic unsaturated hydrocarbon compound; wherein the cyclic unsaturated hydrocarbon compound comprises a monocycle or a bicyclic fused ring constituted by a plurality of carbon atoms; wherein the monocycle or the bicyclic fused ring comprises two or more carbon-carbon double bonds; and wherein the bicyclic fused ring does not comprise a benzene ring; wherein when the number of carbon atoms constituting the monocycle is 7 or less, the number of carbon-carbon double bonds is an even number; when the number of carbon atoms constituting the monocycle is 8 or more, the number of carbon-carbon double bonds is an odd number or an even number; and wherein the number of carbon-carbon double bonds in the bicyclic fused ring is an odd number or an even number.

Claims

1. A positive electrode and a negative electrode; an electrolyte containing a magnesium salt and a cyclic unsaturated hydrocarbon compound; Equipped with The cyclic unsaturated hydrocarbon compound contains a monocyclic or bicyclic fused ring composed of a plurality of carbon atoms, the monocyclic ring or the bicyclic fused ring contains two or more carbon-carbon double bonds; the bicyclic fused ring does not contain a benzene ring, when the number of carbon atoms constituting the monocycle is 7 or less, the number of carbon-carbon double bonds is an even number, when the number of the carbon atoms constituting the monocycle 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 fused ring is an odd number or an even number; Secondary battery.

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

3. The single ring includes an annulene having a carbon atom number that is a multiple of 4. The secondary battery according to claim 2 .

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

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

6. the sulfur-containing material includes elemental sulfur; The magnesium-containing material includes magnesium as an elemental element. The secondary battery according to claim 5 .

7. The electrolyte solution further contains an ether compound. The secondary battery according to any one of claims 1 to 4.

8. Magnesium sulfur secondary battery, The secondary battery according to any one of claims 1 to 4.

9. containing a magnesium salt and a cyclic unsaturated hydrocarbon compound, The cyclic unsaturated hydrocarbon compound contains a monocyclic or bicyclic fused ring composed of a plurality of carbon atoms, the monocyclic ring or the bicyclic fused ring contains two or more carbon-carbon double bonds; the bicyclic fused ring does not contain a benzene ring, when the number of the carbon atoms constituting the monocycle is 7 or less, the number of carbon-carbon double bonds is an even number, when the number of the carbon atoms constituting the monocycle 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 fused ring is an odd number or an even number; Electrolyte for secondary batteries.