Electrolytes for secondary batteries and secondary batteries

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

Technical Field

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

[0002] With the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as power sources that are compact, lightweight, and capable of providing high energy density. This secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution (electrolyte solution for a secondary battery), and various studies have been conducted on the configuration of the secondary battery.

[0003] Specifically, in a secondary battery in which a charge-discharge reaction proceeds utilizing precipitation and dissolution of magnesium, the electrolyte solution contains a compound having an unsaturated hydrocarbon skeleton such as anthracene (see, for example, Patent Document 1). Prior Art Documents Patent Documents

[0004] Patent Document 1 International Publication No. 2020 / 090946 Pamphlet Summary of the Invention

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

[0006] An electrolyte solution for a secondary battery and a secondary battery that can achieve excellent battery characteristics are desired.

[0007] An electrolyte for a secondary battery according to one embodiment of this technology comprises a magnesium salt and a cyclic unsaturated hydrocarbon compound. The cyclic unsaturated hydrocarbon compound comprises a monocyclic or bicyclic fused ring composed of multiple carbon atoms, the monocyclic or bicyclic fused ring contains two or more carbon-carbon double bonds, and the bicyclic fused ring does not contain a benzene ring. When the number of carbon atoms constituting the monocyclic ring is seven or less, the number of carbon-carbon double bonds is even. When the number of carbon atoms constituting the monocyclic ring is eight or more, the number of carbon-carbon double bonds is odd or even. The number of carbon-carbon double bonds in the bicyclic fused ring is odd or even.

[0008] A secondary battery according to one embodiment of this technology comprises a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte has the same configuration as the electrolyte for the secondary battery according to the above-described embodiment of this technology.

[0009] Here, a "monocyclic ring" is a single carbon ring composed of multiple carbon atoms. A "bicyclic fused ring," on the other hand, is a ring composed of multiple carbon atoms in which two carbon rings are fused together, and as mentioned above, does not contain a benzene ring. Further details on monocyclic and bicyclic fused rings will be discussed later.

[0010] In one embodiment of this technology, the electrolyte for a secondary battery and the secondary battery contain 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 contain a benzene ring, and the above-mentioned conditions regarding the number of carbon-carbon double bonds are satisfied, thus providing excellent battery characteristics.

[0011] Furthermore, the effects of this technology are not necessarily limited to those described herein, but may include any of the series of effects related to this technology described later. [Brief explanation of the drawing]

[0012] [Figure 1] Fig. 1 is a perspective view illustrating the configuration of a secondary battery according to an embodiment of the present technology. [Figure 2] Fig. 2 is a cross-sectional view illustrating the configuration of the battery element shown in Fig. 1. [Figure 3] Fig. 3 is a cross-sectional view illustrating the configuration of a test secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The order of description is as follows. 1. Electrolytic Solution for Secondary Batteries 1-1. Configuration 1-2. Manufacturing Method 1-3. Actions and Effects 2. Secondary Battery 2-1. Configuration 2-2. Operation 2-3. Manufacturing Method 2-4. Actions and Effects 3. Applications of Secondary Batteries

[0014] <1. Electrolytic Solution for Secondary Batteries> First, an electrolytic solution for a secondary battery (hereinafter simply referred to as "electrolytic solution") according to an embodiment of the present technology will be described.

[0015] The electrolytic solution described herein is used in a secondary battery that is an electrochemical device. However, the electrolytic solution may also be used in other electrochemical devices besides 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 any one or more types of magnesium salts.

[0018] Specific examples of magnesium salts include 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(hexamethyldisilazide) magnesium (Mg[N(Si(CH₃)₃)₂]₂), bis(trifluoromethanesulfonyl)imide magnesium (Mg[N(CF₃SO₂)₂]₂) and magnesium bis[tetra(hexafluoroisopropyl)] borate (Mg[B(OCH(CF₃)₂)₄]₂).

[0019] The content of the electrolyte salt in the electrolytic solution (mol / l (=mol / dm 3 ³)) is not particularly limited and can be set arbitrarily. However, the content of the electrolyte salt described herein refers to the content of the electrolyte salt relative to the solvent described below.

[0020] [Cyclic unsaturated hydrocarbon compound] The additive includes any one or two or more of cyclic unsaturated hydrocarbon compounds.

[0021] This cyclic unsaturated hydrocarbon compound includes one or both of monocyclic compounds and condensed ring compounds. The number of types of monocyclic compounds may be one, or two or more. Similarly, the number of types of condensed ring compounds may be one, or two or more.

[0022] (Monocyclic compound) The monocyclic compound includes a monocyclic ring formed by a plurality of carbon atoms. As described above, this monocyclic ring is a single carbocyclic ring formed by 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 to form one ring.

[0023] Therefore, heterocycles, in which multiple carbon atoms and non-carbon atoms are bonded to each other to form a single ring, are excluded from the monocycles described here. Specific examples of non-carbon atoms include boron, nitrogen, oxygen, phosphorus, and sulfur.

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

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

[0026] Therefore, a monoring can be a three-membered ring (number of carbon atoms in the monoring = 3), a four-membered ring (number of carbon atoms in the monoring = 4), a five-membered ring (number of carbon atoms in the monoring = 5), a six-membered ring (number of carbon atoms in the monoring = 6), a seven-membered ring (number of carbon atoms in the monoring = 7), or an eight-membered ring (number of carbon atoms in the monoring = 8). Of course, a monoring can also be a ring with nine or more carbon atoms.

[0027] Furthermore, the arrangement of the two or more carbon-carbon double bonds that constitute the monoring is not particularly limited.

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

[0029] However, the number of carbon-carbon double bonds that make up a monoring is set to a predetermined value depending on the number of carbon atoms that make up that monoring.

[0030] Specifically, when the number of carbon atoms constituting a monocyclic compound is seven or less, the number of carbon-carbon double bonds is even, not odd. In contrast, when the number of carbon atoms constituting a monocyclic compound is eight or more, the number of carbon-carbon double bonds may be odd or even. In other words, the number of carbon-carbon double bonds (odd or even) contained in a monocyclic compound differs depending on the number of carbon atoms constituting the monocyclic compound.

[0031] Specific examples of monocyclic compounds are as follows.

[0032] Specific examples of monocyclic compounds where the number of carbon atoms constituting the monocyclic ring is seven 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 the monocyclic ring = 6, number of carbon-carbon double bonds = 3) and cycloheptatriene (number of carbon atoms constituting the monocyclic ring = 7, number of carbon-carbon double bonds = 3), etc., are excluded from the specific examples of monocyclic compounds described here.

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

[0035] (Fused ring compounds) Condensed ring compounds contain a bicyclic fused ring composed of multiple carbon atoms. As described above, this bicyclic fused ring is a ring composed of multiple carbon atoms, in which two carbon rings are fused together. More specifically, it is a hydrocarbon ring in which these multiple carbon atoms are bonded to each other to form two rings.

[0036] Therefore, heterocycles in which multiple carbon atoms and non-carbon atoms are bonded to each other to form two rings are excluded from the bicyclic fused rings described here. Details regarding non-carbon atoms are as described above.

[0037] However, bicyclic fused rings do not contain a benzene ring. That is, in a bicyclic fused ring, as described above, two carbon rings are fused together, but neither of those two carbon 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 that ring. Consequently, if an unsaturated hydrocarbon group (a group containing a carbon-carbon double bond) is bonded to a carbon atom constituting the bicyclic fused ring, that 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; therefore, the number of carbon atoms constituting the bicyclic fused ring is not particularly limited.

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

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

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

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

[0044] Therefore, a bicyclic fused ring may be a fully conjugated system in which two or more carbon-carbon double bonds are alternately arranged via single carbon-carbon bonds, or it may be an incompletely conjugated system in which two or more carbon-carbon double bonds are not alternately arranged via single carbon-carbon bonds. If the bicyclic fused ring is an incompletely conjugated system, the arrangement of the two or more carbon-carbon double bonds can be arbitrarily determined.

[0045] The number of carbon-carbon double bonds constituting a bicyclic fused ring is not particularly limited and can be set arbitrarily. Specifically, the number of carbon-carbon double bonds may be odd or even. In other words, the number of carbon-carbon double bonds (odd or even) contained in a fused ring compound can be set arbitrarily, without depending on the number of carbon atoms constituting the bicyclic fused ring.

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

[0047] Therefore, tetraline, which is a fused ring of 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 of 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 of three six-membered rings, benzene (number of carbon atoms constituting the bicyclic fused ring = 14, number of carbon-carbon double bonds = 7), are excluded from the specific examples of fused ring compounds described here.

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

[0049] Furthermore, when investigating the presence or absence of cyclic unsaturated hydrocarbon compounds in the electrolyte and measuring the content of such compounds, the electrolyte is analyzed using one or more of the existing analytical methods. The type of analytical method is not particularly limited, but specifically, it may include inductively coupled plasma (ICP) emission spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-mass spectroscopy (GC-MS).

[0050] (reason) The electrolyte contains cyclic unsaturated hydrocarbon compounds because it facilitates the stable progression of oxidation-reduction reactions utilizing the precipitation and dissolution of magnesium. As a result, in secondary batteries using this electrolyte, the charge-discharge reaction proceeds more stably and continuously, and the battery capacity does not decrease easily even after repeated charging and discharging.

[0051] More specifically, when the electrolyte contains cyclic unsaturated hydrocarbon compounds, the activity of the magnesium during the magnesium precipitation and dissolution reaction is enhanced compared to when the electrolyte does not contain cyclic unsaturated hydrocarbon compounds. This facilitates the oxidation-reduction reaction utilizing the precipitation and dissolution of magnesium, thus facilitating the charge-discharge reaction in secondary batteries using electrolytes.

[0052] Note that if the electrolyte does not contain cyclic unsaturated hydrocarbon compounds, it means that the electrolyte does not contain additives, or that the electrolyte contains other compounds as additives instead of cyclic unsaturated hydrocarbon compounds. Specific examples of other compounds include anthracene, as mentioned above.

[0053] Furthermore, cyclic unsaturated hydrocarbon compounds undergo dianionization in the reduced state, becoming electrochemically stable active species in the electrolyte. Because these active species are resistant to decomposition in the electrolyte, their lifespan is extended even with repeated oxidation-reduction reactions.

[0054] As a result, in secondary batteries using electrolyte, even if a film forms on the surface of the negative electrode (magnesium-containing material described later) during charging and discharging, electrochemically stable active species continuously remove the film. In other words, electrochemically stable active species play a role in maintaining the activity of magnesium even when charging and discharging are repeated. Therefore, the charge-discharge reaction utilizing the deposition and dissolution of magnesium proceeds more easily even when charging and discharging are repeated.

[0055] These findings suggest that when the electrolyte contains cyclic unsaturated hydrocarbon compounds, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more stably and continuously in secondary batteries using that electrolyte, and the battery capacity is less likely to decrease even after repeated charging and discharging.

[0056] (Preferred configuration) In particular, cyclic unsaturated hydrocarbon compounds are preferably monocyclic, meaning they are preferable to fused ring compounds. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more easily, and the battery capacity does not decrease significantly even after repeated charging and discharging.

[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 is preferable to include annulene having a multiple of four carbon atoms. This is because cyclic unsaturated hydrocarbon compounds exhibit aromaticity in the reduced state. As a result, the active species derived from the cyclic unsaturated hydrocarbon compound are more electrochemically stabilized, thus extending the lifespan of the cyclic unsaturated hydrocarbon compound. However, as mentioned above, benzene and other compounds that do not have a multiple of four carbon atoms are excluded from the annulene described here.

[0058] Here, "a multiple of 4" refers to what is commonly known as 4n (where n is an integer greater than or equal to 1), and specific examples of multiples of 4 include 4, 8, 12, etc. Therefore, benzene, which has 4n+2 carbon atoms (where n is an integer greater than or equal to 1) (number of carbon atoms = 6), does not fall under the category of annulene, which has a multiple of 4 carbon atoms. Benzene, which has 4n+2 carbon atoms, exhibits aromaticity not only in the reduced state but also in the normal molecular state.

[0059] This annulene having a multiple of four carbon atoms is preferably one that contains cyclooctatetraene. This is because the active species derived from the cyclic unsaturated hydrocarbon compound are significantly stabilized electrochemically, thereby significantly extending the lifespan of the cyclic unsaturated hydrocarbon compound.

[0060] [solvent] Furthermore, the electrolyte may also contain one or more types of solvents. The type of solvent is not particularly limited, but specifically, it is a non-aqueous solvent (organic solvent). An electrolyte containing a non-aqueous solvent is a so-called non-aqueous electrolyte.

[0061] The type of non-aqueous solvent is not particularly limited, but it is preferable that the non-aqueous solvent contains an ether compound. This is because the electrolyte salt is more easily dispersed or dissolved by the ether compound, thereby stabilizing the state of the electrolyte.

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

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

[0064] <1-2. Manufacturing method> When preparing an electrolyte, an electrolyte salt and an additive (cyclic unsaturated hydrocarbon compound) are added to the solvent. This disperses or dissolves the electrolyte salt and the cyclic unsaturated hydrocarbon compound in the solvent, thus completing the electrolyte.

[0065] <1-3. Mechanism and Effects> According to this electrolyte, the electrolyte 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 proceeds more easily, 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 secondary batteries using electrolytes, the charge-discharge reaction proceeds more stably and continuously, and the battery capacity does not decrease easily even after repeated charging and discharging. Therefore, it is possible to realize a secondary battery with excellent battery characteristics.

[0067] In particular, if the cyclic unsaturated hydrocarbon compound contains a monocyclic compound, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more easily, and the battery capacity does not decrease significantly even after repeated charging and discharging, thus achieving a higher level of effectiveness.

[0068] In this case, if the monocyclic compound contains annulene with a multiple of four carbon atoms, the active species derived from the cyclic unsaturated hydrocarbon compound is electrochemically stabilized. Therefore, the lifespan of the active species is extended, resulting in an even greater effect.

[0069] In particular, if the annulene contains cyclooctatetraene, the active species derived from the cyclic unsaturated hydrocarbon compound are significantly stabilized electrochemically. Therefore, the lifespan of the active species is significantly extended, resulting in a remarkably high effect.

[0070] Furthermore, if the electrolyte also contains ether compounds, the electrolyte salt becomes more easily dispersed or dissolved by the ether compounds. Therefore, the state of the electrolyte is stabilized, and a higher effect can be obtained.

[0071] <2. Secondary battery> Next, we will describe a secondary battery that is one embodiment of this technology using an electrolyte.

[0072] The secondary battery described here is a secondary battery in which the charge-discharge reaction proceeds by utilizing the deposition and dissolution of magnesium, and the battery capacity is obtained by utilizing this charge-discharge reaction.

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

[0074] <2-1. Structure> Figure 1 shows a perspective view of the secondary battery, and Figure 2 shows a cross-sectional view of the battery element 20 shown in Figure 1. However, in Figure 1, the outer film 10 and the battery element 20 are shown separated from each other, and the cross-section of the battery element 20 along the XZ plane is shown with a dashed line.

[0075] As shown in Figures 1 and 2, this secondary battery comprises an outer film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42.

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

[0077] [Exterior film] As shown in Figure 1, the outer film 10 has a bag-like structure that is sealed with the battery element 20 housed inside. Thus, the outer film 10 houses the positive electrode 21, negative electrode 22, separator 23, and electrolyte, which will be described later.

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

[0079] Specifically, the outer 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. When the outer film 10 is folded, the outer edges of the opposing fusion layers are fused together. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metallic material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0080] However, the composition (number of layers) of the outer film 10 is not particularly limited; it may consist of one or two layers, or four or more layers.

[0081] [Battery element] The battery element 20 is a power generation element housed inside the outer film 10. As shown in Figures 1 and 2, this 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, facing each other via a separator 23. This winding axis P is a virtual axis extending in the Y-axis direction, as shown in Figure 1.

[0083] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 has a flattened three-dimensional shape, the shape of the cross-section of the battery element 20 intersecting the winding axis P (cross-section along the XZ plane) is a flattened shape defined by the major axis J1 and the minor axis J2.

[0084] The major axis J1 is a virtual axis extending in the X-axis direction and has a length greater than the length of the minor axis J2. The minor axis J2 is a virtual axis extending in the Z-axis direction intersecting the X-axis direction and has a length less than the length of the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flattened cylinder, 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 intercepts and releases magnesium in an ionic state, and this positive electrode active material contains one or more sulfur-containing materials. This is because magnesium is more easily intercepted and released in an ionic state in the positive electrode 21, which facilitates the charge-discharge reaction utilizing the precipitation and dissolution of the magnesium.

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

[0087] The types of metallic elements included as constituent elements in a sulfur alloy are not particularly limited, as long as they are one or more of any metallic elements. Sulfur compounds contain one or more nonmetallic elements such as carbon, oxygen, and halogens as constituent elements, with specific examples of halogens being fluorine, chlorine, bromine, and iodine.

[0088] In particular, the positive electrode active material preferably contains elemental sulfur. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more easily. Figure 2 shows the case where the positive electrode 21 contains elemental sulfur.

[0089] Although not specifically illustrated 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 such a conductive material is nickel.

[0091] The positive electrode active material layer is supported by a positive electrode current collector and contains one or more sulfur-containing materials that constitute the positive electrode active material. However, the positive electrode active material layer 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 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 one or more of the following methods, such as coating.

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

[0094] The positive electrode binder may also be a conductive polymer compound. Specific examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene, and copolymers of two or more of these may also be used. This 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 carbon materials, metal materials, and conductive polymer compounds.

[0096] Specific examples of carbon materials include graphite (natural graphite and artificial graphite), carbon fibers, carbon black, and carbon nanotubes. Carbon fibers include vapor-grown carbon fibers (VGCF), etc. Carbon black includes acetylene black and Ketjen black, etc. Carbon nanotubes include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and multi-walled carbon nanotubes include double-walled carbon nanotubes (DWCNTs), etc. Specific examples of metallic materials include nickel, etc.

[0097] (Negative electrode) The negative electrode 22 contains one or more types of magnesium-containing materials, which are the negative electrode active materials. This is because it facilitates the charge-discharge reaction that utilizes the precipitation and dissolution of magnesium.

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

[0099] The types of metallic elements (excluding magnesium) included as constituent elements in a magnesium alloy are not particularly limited, as long as they are any one or more of the available metallic elements. Magnesium compounds contain one or more nonmetallic elements such as carbon, oxygen, sulfur, and halogens as constituent elements, with specific examples of halogens including fluorine, chlorine, bromine, and iodine.

[0100] In particular, the negative electrode active material preferably contains elemental magnesium. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more easily. Figure 2 shows the case where the negative electrode 22 contains elemental magnesium.

[0101] The negative electrode 22 may have a configuration similar to that of the positive electrode 21. That is, although not specifically shown 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 such a conductive material is nickel.

[0103] The negative electrode active material layer is supported by a negative electrode current collector and contains one or more types of magnesium-containing materials that constitute the negative electrode active material. However, the negative electrode active material layer may further contain one or more types of 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 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 one or more of the following methods, such as coating.

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

[0106] (Separator) As shown in Figure 2, the separator 23 is an insulating porous membrane interposed between the positive electrode 21 and the negative electrode 22, allowing magnesium to pass through in an ionic state while preventing a short circuit between the positive electrode 21 and the negative electrode 22. This separator 23 contains a polymer compound such as polyethylene.

[0107] (electrolyte) The composition of the electrolyte is as described above. Specifically, the electrolyte contains a magnesium salt, which is the electrolyte salt, and a cyclic unsaturated hydrocarbon compound, which is an additive.

[0108] [Positive lead] As shown in Figures 1 and 2, 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 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. This positive electrode lead 31 contains a conductive material such as a metal material, a specific example of which is aluminum. The shape of the positive electrode lead 31 is either a thin plate shape or a mesh shape.

[0109] [Negative lead] The negative electrode lead 32 is a negative electrode wire connected to the negative electrode 22, as shown in Figures 1 and 2, and is led out to the outside of the outer 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 direction of lead generation for the negative electrode lead 32 is the same as the direction of lead generation for the positive electrode lead 31. This negative electrode lead 32 contains a conductive material such as a metal, a specific example of which is copper. Details regarding the shape of the negative electrode lead 32 are the same as those regarding the shape of the positive electrode lead 31.

[0110] [Sealing film] The sealing film 41 is inserted between the outer film 10 and the positive lead 31, and the sealing film 42 is inserted between the outer film 10 and the negative 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 other elements from entering the interior of the outer film 10. This sealing film 41 contains a polymer compound such as polyolefin that has good adhesion to the positive electrode lead 31, and a specific example of such a polymer compound is polypropylene.

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

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

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

[0115] <2-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and negative electrode 22 are prepared according to the example procedure described below, and then the secondary battery is assembled using the positive electrode 21, negative electrode 22, and electrolyte.

[0116] The following explanation will cover the 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. Since the electrolyte manufacturing procedure has already been explained, the explanation of that procedure will be omitted below.

[0117] [Preparing the positive electrode] First, a positive electrode mixture is prepared by mixing the positive electrode active material (sulfur powder, which is a sulfur-containing material), the positive electrode binder, and the positive electrode conductive agent. Next, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture to a solvent. This solvent may be an aqueous solvent or an organic solvent. Finally, a positive electrode active material layer is formed by applying the positive electrode mixture slurry to both sides of the positive electrode current collector. After this, the positive electrode active material layer may be compressed and 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, a positive electrode 21 is produced by forming a positive electrode active material layer on both sides of the positive electrode current collector.

[0118] [Preparing the negative electrode] For the negative electrode 22, a negative electrode active material (metallic magnesium, which is a magnesium-containing material) is prepared. Magnesium foil is used as this metallic magnesium.

[0119] [Assembly of rechargeable batteries] 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.

[0120] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via the separator 23, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to form a wound body (not shown). Subsequently, the wound body is pressed using a press or the like to form a flattened shape. The wound body after this molding has the same configuration as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with electrolyte.

[0121] Next, after housing the wound body inside the recessed portion 10U, the outer film 10 (fusion layer / metal layer / surface protection layer) is folded so that the outer films 10 face each other. Subsequently, using an adhesive method such as heat fusion, the outer edges of two sides of the opposing fusion layers are joined together, thereby housing the wound body inside the bag-shaped outer film 10.

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

[0123] As a result, the electrolyte is impregnated into the wound material, forming the battery element 20, which is a wound electrode body. Therefore, the battery element 20 is sealed inside the bag-shaped outer film 10, completing the secondary battery.

[0124] <2-4. Action and Effects> According to this secondary battery, the secondary battery is equipped with an electrolyte, and the electrolyte has the configuration described above. In this case, for the reasons described above, the charge-discharge reaction proceeds more stably and continuously, and the battery capacity does not decrease easily even when charge-discharge is repeated, thus providing 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 precipitation and dissolution of magnesium proceeds more easily, and the battery capacity does not decrease significantly even after repeated charging and discharging, thus 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 proceeds even more easily, and the battery capacity decreases even less, thus 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, thus achieving a higher level of efficiency.

[0127] <3. Applications of rechargeable batteries> The uses (examples of applications) of secondary batteries are not particularly limited. Secondary batteries used as power sources may be the primary power source or the auxiliary power source in electronic devices and electric vehicles, etc. A primary power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of the primary power source, or a power source that can be switched from the primary power source.

[0128] Specific examples of secondary battery applications are described below: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and electric saws; battery packs installed in electronic devices; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household or industrial battery systems that store power in preparation for emergencies. In these applications, one secondary battery may be used, or two or more secondary batteries may be used.

[0129] The battery pack may use individual cells or a battery pack. An electric vehicle is a vehicle that runs using a secondary battery as a power source, and may also be a hybrid vehicle equipped with other power sources in addition to the secondary battery. In a household power storage system, the electricity stored in the secondary battery, which is the power storage source, can be used to power household electrical appliances, etc. [Examples]

[0130] An example of this technology will be described below.

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

[0132] <Examples 1, 2 and Comparative Examples 1-4> First, the electrolyte was manufactured according to the procedure described below, and then its physical properties were evaluated.

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

[0134] As the electrolyte salt, a mixture of bis(trifluoromethanesulfonyl)imidomagnesium (MgTFSI2, manufactured by Toyama Pharmaceutical Co., Ltd.) and magnesium chloride (MgCl2, manufactured by Sigma-Aldrich) was used. In this case, the content of bis(trifluoromethanesulfonyl)imidomagnesium in the electrolyte was 0.2 mol / l (= 0.2 mol / dm³) relative to the solvent. 3 In addition, the magnesium chloride content in the electrolyte was set to 0.2 mol / L relative to the solvent.

[0135] Furthermore, magnesium chloride was used alone as the electrolyte salt. In this case, the magnesium chloride content in the electrolyte was set to 0.4 mol / l relative to the solvent.

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

[0137] For comparison, an electrolyte was prepared using the same procedure, except that no additives were used. Furthermore, for comparison, an electrolyte was prepared using the same procedure, except that a different compound (anthracene (ANT), manufactured by Tokyo Chemical Industry Co., Ltd.) was used as an additive instead of a cyclic unsaturated hydrocarbon compound.

[0138] After preparing the electrolyte, analysis of the electrolyte using ICP emission spectrometry confirmed that the electrolyte salt content and the additive content (cyclic unsaturated hydrocarbon compounds or other compounds) were as described above.

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

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

[0141] The "Redox Reactions" column in Table 1 shows the following trends.

[0142] The value "OK" indicates that the oxidation-reduction reaction proceeded, as activity was observed not only during magnesium deposition but also during magnesium dissolution. In other words, it indicates that the charge-discharge reaction proceeded in a secondary battery using an electrolyte.

[0143] On the other hand, "failure" indicates that the oxidation-reduction reaction did not proceed sufficiently because magnesium did not show activity during dissolution. In other words, it indicates that the charge-discharge reaction did not proceed in a secondary battery using an electrolyte.

[0144] [Table 1]

[0145] [Consideration] As shown in Table 1, the success or failure of the redox reaction varied depending on the composition of the electrolyte.

[0146] Specifically, when no additives were 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)imidomagnesium and magnesium chloride was used as the electrolyte salt (Comparative Example 1), the redox reaction proceeded. However, when only bis(trifluoromethanesulfonyl)imidomagnesium was used as the electrolyte salt (Comparative Example 2), the redox reaction did not proceed.

[0147] Similarly, when other compounds (anthracene) were used as additives (Comparative Examples 3 and 4), differences in the progress of the redox reaction occurred. Specifically, when a mixture of bis(trifluoromethanesulfonyl)imidomagnesium and magnesium chloride was used as the electrolyte salt (Comparative Example 3), the redox reaction proceeded. However, when only bis(trifluoromethanesulfonyl)imidomagnesium 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), differences in whether or not the redox reaction proceeded depended 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 or not the redox reaction proceeded. Specifically, when a mixture of bis(trifluoromethanesulfonyl)imidomagnesium and magnesium chloride was used as the electrolyte salt (Example 1), the redox reaction proceeded. Similarly, when only bis(trifluoromethanesulfonyl)imidomagnesium was used as the electrolyte salt (Example 2), the redox reaction also proceeded.

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

[0151] <Example 3 and Comparative Examples 5, 6> Next, after manufacturing a secondary battery using the procedure described below, the battery characteristics of that secondary battery were evaluated.

[0152] [Manufacturing of secondary batteries] Here, a test secondary battery was fabricated to perform a simplified evaluation of its battery characteristics. Figure 3 shows the cross-sectional configuration of the test secondary battery (a coin-type magnesium-sulfur secondary battery).

[0153] The following section will describe the configuration of the test secondary battery, followed by the manufacturing procedure for that test secondary battery.

[0154] (Configuration of a rechargeable battery for testing) As shown in Figure 3, this test rechargeable battery comprises a test electrode 51, a counter electrode 52, a separator 53, an outer cup 54, an outer can 55, a gasket 56, and an electrolyte (not shown).

[0155] The test electrode 51 is housed in an outer cup 54, and the counter electrode 52 is housed in an outer can 55. The test electrode 51 and the counter electrode 52 are stacked on top of each other via a separator 53, and the electrolyte is impregnated into the test electrode 51, the counter electrode 52, and the separator 53, respectively. The outer cup 54 and the outer can 55 are crimped together via a gasket 56, so the test electrode 51, the counter electrode 52, and the separator 53 are sealed by the outer cup 54 and the outer can 55.

[0156] (Manufacturing procedure for rechargeable batteries for testing) The manufacturing procedure for the rechargeable battery used for testing is as follows.

[0157] (Preparation of test electrode) First, a mixture was prepared by mixing 10 parts by mass of positive electrode active material (sulfur powder, a sulfur-containing material), 30 parts by mass of positive electrode binder (polytetrafluoroethylene, manufactured by AGC Inc.), and 60 parts by mass of positive electrode conductive agent (Ketjenbrak, ECP600JD, manufactured by Lion Corporation). Next, a mixture sheet (thickness = 100 μm) was formed by compression molding of the mixture using a roll press. Finally, the mixture sheet was punched out into a disc shape (diameter = 15 mm). This produced test electrode 51.

[0158] (Preparation for the opposite) A disc-shaped magnesium plate (thickness = 200 μm, diameter = 16 mm, purity = 99.9%, manufactured by Rikazai Co., Ltd.) was prepared as the counter electrode 52 (metallic magnesium, a magnesium-containing material).

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

[0160] (Assembly of a rechargeable battery for testing) First, the test electrode 51 was placed in the outer cup 54, and the counter electrode 52 was placed in the outer can 55. Next, the test electrode 51 in the outer cup 54 and the counter electrode 52 in the outer can 55 were stacked on top of each other via a separator 53 (glass fiber with a thickness of 200 μm, GC50 manufactured by Advantec Co., Ltd.) impregnated with 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 on top of each other via the separator 53, the outer cup 54 and the outer can 55 were crimped together via a gasket 56. As a result, the test electrode 51 and the counter electrode 52 were sealed in the outer cup 54 and the outer can 55, completing the test secondary battery.

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

[0162] To evaluate the cycle characteristics, the test secondary battery was first charged and discharged for two cycles in a room temperature environment (temperature = 25°C) to electrochemically stabilize its state.

[0163] Next, the discharge capacity (discharge capacity after 3 cycles) was measured by charging and discharging the test secondary battery for one cycle in the same environment. Subsequently, the discharge capacity (discharge capacity after 10 cycles) was measured by charging and discharging the test secondary battery for seven cycles in the same environment.

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

[0165] During discharge, a constant current discharge was performed at a current of 0.1 mA until the voltage reached 0.8 V. During charging, a constant current charge was performed at a current of 0.1 mA until the voltage reached 2.4 V.

[0166] [Table 2]

[0167] [Consideration] As shown in Table 2, the volume retention rate varied greatly depending on the electrolyte composition.

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

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

[0170] [summary] The results shown in Tables 1 and 2 indicate that a high capacity retention rate was obtained when the electrolyte contained magnesium salts and cyclic unsaturated hydrocarbon compounds. Therefore, the cycle characteristics were improved, resulting in excellent battery characteristics.

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

[0172] Specifically, the explanation focused on cases where the battery structure of the rechargeable battery is of the laminated film type and the coin type. However, the battery structure of the rechargeable battery is not particularly limited, and may also be cylindrical, rectangular, or button-type.

[0173] Furthermore, the case where the element structure of the battery element is of the wound type has been explained. However, the element structure of the battery element is not particularly limited, and may also be of the stacked type or the zigzag type. In the stacked type, the positive electrode and the negative electrode are stacked on top of each other, and in the zigzag type, the positive electrode and the negative electrode are folded in a zigzag pattern.

[0174] The effects described herein are illustrative only, and therefore the effects of this technology are not limited to those described herein. Accordingly, other effects may be obtained with respect to this technology.

[0175] Furthermore, this technology can also be configured as follows: <1> Positive electrode and, The negative electrode and, An electrolyte containing magnesium salts and cyclic unsaturated hydrocarbon compounds Equipped with, The cyclic unsaturated hydrocarbon compound comprises a monocyclic or bicyclic fused ring composed of multiple carbon atoms, The monocyclic or bicyclic fused ring contains two or more carbon-carbon double bonds. The aforementioned bicyclic fused ring does not contain a benzene ring. When the number of carbon atoms constituting the monoring is 7 or less, the number of carbon-carbon double bonds is even. When the number of carbon atoms constituting the monoring is eight or more, the number of carbon-carbon double bonds is odd or even. The number of carbon-carbon double bonds in the bicyclic fused ring is either odd or even. Secondary battery. <2> The cyclic unsaturated hydrocarbon compound includes the monoring, <1> The secondary battery described above. <3> The aforementioned monoring comprises an annulene having a multiple of 4 carbon atoms. <2> The secondary battery described above. <4> The aforementioned annulene contains cyclooctatetraene, <3> The secondary battery described above. <5> The positive electrode includes a sulfur-containing material, The aforementioned negative electrode includes a magnesium-containing material. <1> or <4> A rechargeable battery as described in one of the following. <6> The aforementioned sulfur-containing material contains elemental sulfur, The magnesium-containing material includes elemental magnesium. <5> The secondary battery described above. <7> The electrolyte further contains an ether compound. <1> or <6> A rechargeable battery as described in one of the following. <8> It is a magnesium-sulfur secondary battery. <1> or <7> A rechargeable battery as described in one of the following. <9> It contains magnesium salts and cyclic unsaturated hydrocarbon compounds, The cyclic unsaturated hydrocarbon compound comprises a monocyclic or bicyclic fused ring composed of multiple carbon atoms, The monocyclic or bicyclic fused ring contains two or more carbon-carbon double bonds. The aforementioned bicyclic fused ring does not contain a benzene ring. When the number of carbon atoms constituting the monoring is 7 or less, the number of carbon-carbon double bonds is even. When the number of carbon atoms constituting the monoring is eight or more, the number of carbon-carbon double bonds is odd or even. The number of carbon-carbon double bonds in the bicyclic fused ring is either odd or even. Electrolyte for secondary batteries.

Claims

1. Positive electrode and, The negative electrode and, An electrolyte containing magnesium salts and cyclic unsaturated hydrocarbon compounds Equipped with, The cyclic unsaturated hydrocarbon compound includes a monocyclic or bicyclic fused ring composed of multiple carbon atoms, The monocyclic or bicyclic fused ring contains two or more carbon-carbon double bonds. The aforementioned bicyclic fused ring does not contain a benzene ring. When the number of carbon atoms constituting the monoring is seven or less, the number of carbon-carbon double bonds is even. When the number of carbon atoms constituting the monoring is eight or more, the number of carbon-carbon double bonds is odd or even. The number of carbon-carbon double bonds in the bicyclic fused ring is either odd or even. The cyclic unsaturated hydrocarbon compound includes the monoring, The aforementioned monoring comprises an annulene having a multiple of 4 carbon atoms. Secondary battery.

2. The aforementioned annulene contains cyclooctatetraene, The secondary battery according to claim 1.

3. The positive electrode includes a sulfur-containing material, The aforementioned negative electrode includes a magnesium-containing material. A secondary battery according to claim 1 or claim 2.

4. The aforementioned sulfur-containing material contains elemental sulfur, The magnesium-containing material includes elemental magnesium, The secondary battery according to claim 3.

5. The electrolyte further contains an ether compound. A secondary battery according to claim 1 or claim 2.

6. It is a magnesium-sulfur secondary battery. A secondary battery according to claim 1 or claim 2.

7. It contains magnesium salts and cyclic unsaturated hydrocarbon compounds, The cyclic unsaturated hydrocarbon compound includes a monocyclic or bicyclic fused ring composed of multiple carbon atoms, The monocyclic or bicyclic fused ring contains two or more carbon-carbon double bonds. The aforementioned bicyclic fused ring does not contain a benzene ring. When the number of carbon atoms constituting the monoring is seven or less, the number of carbon-carbon double bonds is even. When the number of carbon atoms constituting the monoring is eight or more, the number of carbon-carbon double bonds is odd or even. The number of carbon-carbon double bonds in the bicyclic fused ring is either odd or even. The cyclic unsaturated hydrocarbon compound includes the monoring, The aforementioned monoring comprises an annulene having a multiple of 4 carbon atoms. Electrolyte for secondary batteries.

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