Trimagnesium disulfide-containing compound and secondary battery

Abstract

Provided is a secondary battery with which excellent battery characteristics can be obtained. The secondary battery comprises a positive electrode which includes a sulfur-containing material, a negative electrode which includes a magnesium-containing material, and an electrolyte, wherein the sulfur-containing material in a discharged state includes trimagnesium disulfide (Mg3S2).

Description

Trimagnesium disulfide-containing compound and secondary battery

[0001] The present technology relates to a trimagnesium disulfide-containing compound and a secondary battery.

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as power sources that are small, lightweight, and have high energy density. In particular, secondary batteries using sulfur as the positive electrode active material have attracted attention.

[0003] Specifically, a secondary battery with a sulfur-containing positive electrode and a magnesium-containing negative electrode has been proposed, and the reversibility of the charge-discharge reaction has been evaluated using X-ray photoelectron spectroscopy (see, for example, Non-Patent Document 1). In addition, in a magnesium secondary battery in which the battery reaction proceeds reversibly, magnesium sulfide, which is a discharge product, has a zincblende-type crystal structure (see, for example, Non-Patent Document 2).

[0004] Angew. Chem. Int. Ed. 2017, 56, 13526 -13530, Reversible S0 / MgSx Redox Chemistry in a MgTFSI2 / MgCl2 / DME Electrolyte for Rechargeable Mg / S Batteries, Tao Gao, Singyuk Hou, Fei Wang, Zhaohui Ma, Xiaogang Li, Kang Xu, and Chunsheng Wang

[0005] Chem. Mater. 2018, 30, 6318・6324,Zinc Blended Magnesium Sulfide in Rechargeable Magnesium-Sulfur Batteries,Yuri Nakayama, Ryuhei Matsumoto, Kiyoshi Kumagae, Daisuke Mori, Yoshifumi Mizuno, Shizuka Hosoi, Kazuhiro Kamiguchi, Naoki Koshitani, Yuta Inaba, Yoshihiro Kudo,Hideki Kawasaki, Elizabeth C. Miller, Johanna Nelson Weker, and Michael F. Toney

[0006] Although various studies have been conducted on the composition of secondary batteries, the battery characteristics of the secondary batteries are still insufficient and there is room for improvement. In this case, it is also important to develop new materials containing sulfur as a constituent element in order to improve the battery characteristics.

[0007] There is a demand for a trimagnesium disulfide-containing compound and a secondary battery that can provide excellent battery characteristics.

[0008] In one embodiment of the present technology, the trimagnesium disulfide-containing compound is trimagnesium disulfide (Mg 3　 S 2　 ) is included.

[0009] A secondary battery according to an embodiment of the present technology includes a positive electrode containing a sulfur-containing material, a negative electrode containing a magnesium-containing material, and an electrolyte solution, and the sulfur-containing material is trimagnesium disulfide (Mg 3　 S 2　 ) is included.

[0010] According to another embodiment of the present technology, there is provided a secondary battery including a positive electrode containing a sulfur-containing material, a negative electrode containing a magnesium-containing material, and an electrolyte solution. The sulfur-containing material contains sulfur and magnesium as constituent elements in a discharged state. Analysis of the positive electrode in a discharged state using magnesium-25 nuclear magnetic resonance spectroscopy detects a first peak within a chemical shift range of −70 ppm to 0 ppm.

[0011] Here, the term "sulfur-containing material" is a general term for materials containing sulfur as a constituent element, and the term "magnesium-containing material" is a general term for materials containing magnesium as a constituent element. Details of the sulfur-containing material and the magnesium-containing material will be described later.

[0012] The "discharged state" is not particularly limited as long as it is a state in which the secondary battery is discharged. Details of the discharged state will be described later.

[0013] According to one embodiment of the present technology, the trimagnesium disulfide-containing compound contains trimagnesium disulfide, and therefore excellent electrochemical properties can be obtained in electrochemical devices such as secondary batteries to which the trimagnesium disulfide-containing compound is applied.

[0014] According to a secondary battery of one embodiment of the present technology, the positive electrode contains a sulfur-containing material, the negative electrode contains a magnesium-containing material, and the sulfur-containing material contains trimagnesium disulfide in a discharged state, thereby achieving excellent battery characteristics.

[0015] According to another embodiment of the secondary battery of the present technology, the positive electrode contains a sulfur-containing material, the negative electrode contains a magnesium-containing material, and the sulfur-containing material contains sulfur and magnesium as constituent elements in a discharged state. A first peak is detected in the analysis results of the positive electrode using magnesium-25 nuclear magnetic resonance spectroscopy in a discharged state, and therefore excellent battery characteristics can be obtained.

[0016] 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.

[0017] FIG. 1 is a perspective view showing the configuration of a secondary battery according to an embodiment of the present technology. FIG. 2 is a cross-sectional view showing the configuration of the battery element shown in FIG. 1. FIG. 3 is a cross-sectional view showing another configuration of the battery element shown in FIG. 1. FIG. 4 is a diagram for explaining the analysis results of a positive electrode of a secondary battery in a discharged state using magnesium-25 nuclear magnetic resonance spectroscopy. FIG. 5 is a diagram for explaining the analysis results of a positive electrode of a secondary battery in a discharged state using sulfur-33 nuclear magnetic resonance spectroscopy. FIG. 6 is a cross-sectional view showing the configuration of a test secondary battery.

[0018] 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. Trimagnesium disulfide-containing compound 1-1. Configuration 1-2. Manufacturing method 1-3. Action and effect 2. Secondary battery 2-1. Configuration 2-2. Physical properties 2-3. Operation 2-4. Manufacturing method 2-5. Action and effect 3. Modification 4. Use of secondary battery

[0019] <1. Trimagnesium disulfide-containing compound> First, a trimagnesium disulfide-containing compound according to one embodiment of the present technology will be described.

[0020] <1-1. Composition> This trimagnesium disulfide-containing compound contains sulfur as a constituent element and is a novel substance that absorbs and releases magnesium. Specifically, the trimagnesium disulfide-containing compound is a compound that contains magnesium as a constituent element together with sulfur, and more specifically, trimagnesium disulfide (Mg 3　 S 2　 )

[0021] The use of the trimagnesium disulfide-containing compound is not particularly limited as long as it is in any device. In particular, the use of the trimagnesium disulfide-containing compound is preferably in an electrochemical device that utilizes a charge / discharge reaction. This is because, in an electrochemical device to which the trimagnesium disulfide-containing compound is applied, excellent electrochemical properties can be obtained by utilizing the properties of the trimagnesium disulfide-containing compound.

[0022] The type of electrochemical device is not particularly limited, but specific examples include batteries and capacitors, etc. The battery may be a primary battery or a secondary battery.

[0023] <1-2. Production Method> The method for producing the trimagnesium disulfide-containing compound is not particularly limited.

[0024] This trimagnesium disulfide-containing compound may be formed using an existing synthesis method. Furthermore, when applied to an electrochemical device, the trimagnesium disulfide-containing compound may be formed during the operation of the electrochemical device. For example, in an electrochemical device such as a battery, the trimagnesium disulfide-containing compound may be formed by utilizing an electrochemical reaction that proceeds during the operation of the electrochemical device.

[0025] A specific procedure for producing the trimagnesium disulfide-containing compound will be described later, taking as an example the case where the compound is formed during operation of a secondary battery, which is an electrochemical device.

[0026] <1-3. Actions and Effects> Because this trimagnesium disulfide-containing compound contains trimagnesium disulfide, it has excellent magnesium absorption and desorption capabilities. Therefore, in electrochemical devices to which the trimagnesium disulfide-containing compound is applied, the electrochemical reaction using the trimagnesium disulfide-containing compound tends to proceed stably, and excellent electrochemical properties can be obtained.

[0027] In particular, when a trimagnesium disulfide-containing compound is applied to a secondary battery, the charge-discharge reaction utilizing the absorption and release of magnesium tends to proceed stably, thereby achieving a high battery capacity and realizing a secondary battery with excellent battery characteristics.

[0028] 2. Secondary Battery First, a secondary battery according to an embodiment of the present technology will be described, which is an example of an electrochemical device to which the above-described trimagnesium disulfide-containing compound is applied.

[0029] The secondary battery described here utilizes the absorption and release of magnesium by the trimagnesium disulfide-containing compound, as well as the precipitation and dissolution of that magnesium, which allows charge and discharge reactions to proceed in the secondary battery, thereby achieving battery capacity.

[0030] 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. Details of the sulfur-containing material and the magnesium-containing material will be described later.

[0031] <2-1. Configuration> Fig. 1 shows a perspective configuration of a secondary battery. Fig. 2 and Fig. 3 each show 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.

[0032] As shown in FIGS. 1 to 3, 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 .

[0033] The secondary battery described here is a so-called laminate film type secondary battery, since it uses an exterior film 10 that is a flexible or pliable exterior member.

[0034] 1, the exterior film 10 has a bag-like structure that is sealed when the battery element 20 is 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.

[0035] 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 for accommodating the battery element 20, and the recessed portion 10U is a so-called deep-drawn portion.

[0036] 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.

[0037] 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.

[0038] [Battery Element] As shown in FIGS. 1 to 3, the battery element 20 is a power generating element housed in an exterior film 10, and includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0039] Here, battery element 20 is a so-called wound electrode body. Therefore, positive electrode 21 and negative electrode 22 are wound around winding axis P while facing each other with separator 23 interposed therebetween. This winding axis P is a virtual axis extending in the Y-axis direction, as shown in FIG. 1 .

[0040] 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 of battery element 20 intersecting winding axis P is a flat shape defined by major axis J1 and minor axis J2. The cross section described here is a cross section along the XZ plane.

[0041] 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.

[0042] 2, the positive electrode 21 contains a positive electrode active material that occludes and releases magnesium, and the positive electrode active material contains one or more types of sulfur-containing materials. This is because magnesium is easily occluded and released in the positive electrode 21, and therefore, a charge-discharge reaction utilizing the deposition and dissolution of the magnesium is easily promoted.

[0043] As described above, the sulfur-containing material is a general term for materials containing sulfur as a constituent element. Therefore, the sulfur-containing material may be elemental sulfur (S), a sulfur alloy, a sulfur compound, or a mixture of two or more of these.

[0044] The purity of the elemental sulfur is not particularly limited, and the elemental sulfur may contain any amount of impurities.

[0045] The type of metallic element contained as a constituent element in the sulfur alloy is not particularly limited, as long as it is any one or more of any metallic elements. The sulfur compound contains any one or more of non-metallic elements such as carbon, oxygen, and halogens as constituent elements, and specific examples of the halogens include fluorine, chlorine, bromine, and iodine. However, trimagnesium disulfide-containing compounds are excluded from the sulfur compounds described here.

[0046] Among these, the sulfur-containing material preferably contains elemental sulfur, because this allows the charge-discharge reaction utilizing the precipitation and dissolution of magnesium to proceed sufficiently.

[0047] Hereinafter, the state of a secondary battery before discharge is referred to as the “undischarged state,” and the state of a secondary battery after discharge is referred to as the “discharged state.” In a magnesium-sulfur secondary battery, the state immediately after completion (the initial state before charging or discharging) is the fully charged state, and this fully charged state is included in the “undischarged state.”

[0048] Here, the sulfur-containing material in an undischarged state contains one or more of elemental sulfur, sulfur alloys, and sulfur compounds, as described above. Among these, the sulfur-containing material preferably contains elemental sulfur, as described above.

[0049] In contrast, the sulfur-containing material contains a trimagnesium disulfide-containing compound in a discharged state. As described above, this trimagnesium disulfide-containing compound contains trimagnesium disulfide.

[0050] That is, the composition of the sulfur-containing material is different before and after discharge. Specifically, the sulfur-containing material does not contain the trimagnesium disulfide-containing compound in the undischarged state, but contains the trimagnesium disulfide-containing compound in the discharged state.

[0051] The reason why the sulfur-containing material contains the trimagnesium disulfide-containing compound in a discharged state is that, as will be described later, the trimagnesium disulfide-containing compound is a substance (a so-called discharge product) formed when the secondary battery is discharged.

[0052] The term "discharged state" refers to a state in which the secondary battery has already been discharged. Therefore, as described above, the state of the secondary battery in the discharged state is not particularly limited as long as the secondary battery is in a discharged state. In other words, the battery voltage of the secondary battery in the discharged state is not particularly limited as long as the secondary battery is discharged, and can be set arbitrarily. This is because, even if the secondary battery is slightly discharged, a trimagnesium disulfide-containing compound is formed during the discharge of the secondary battery.

[0053] More specifically, the discharged state is a state in which the secondary battery is discharged until the battery voltage reaches 0.4 V when elemental magnesium is used as the negative electrode active material (magnesium-containing material) described below. That is, the discharged state is a state in which the magnesium-containing material is dissolved in the negative electrode 22, and therefore magnesium is occluded in the positive electrode 21. Note that conditions such as the ambient temperature and discharge current during discharge are not particularly limited and can be set arbitrarily.

[0054] When discharging a secondary battery until the battery voltage reaches 0.4 V to put the secondary battery into a discharged state, a test secondary battery (coin-type magnesium-sulfur secondary battery) is fabricated using elemental magnesium (magnesium plate) as the negative electrode 22 (magnesium-containing material), as will be described later in Example 1. Thereafter, the test secondary battery is discharged at a current of 0.2 mA in a room temperature environment (temperature = 25°C) until the battery voltage reaches 0.4 V.

[0055] Here, the state in which the secondary battery is discharged until the battery voltage reaches 0.4 V is considered to be the discharged state because the trimagnesium disulfide-containing compound is sufficiently formed by discharging the secondary battery until the battery voltage reaches 0.4 V. Therefore, as will be described later, the trimagnesium disulfide-containing compound can be detected by analyzing the positive electrode 21 recovered from the discharged secondary battery.

[0056] In contrast, the undischarged state refers to a state in which the secondary battery has not yet been discharged. More specifically, when elemental magnesium is used as the negative electrode active material (magnesium-containing material) described below, the battery voltage is 1.0 V or higher, and therefore the magnesium-containing material has not yet been dissolved in the negative electrode 22. That is, the undischarged state refers to a state in which the magnesium-containing material has not yet been dissolved but precipitated in the negative electrode 22, and therefore magnesium has not yet been occluded in the positive electrode 21.

[0057] The sulfur-containing material contains the trimagnesium disulfide-containing compound in the discharged state because, compared to when the sulfur-containing material does not contain the trimagnesium disulfide-containing compound in the discharged state, the electrochemical state of the positive electrode 21 is improved during charging and discharging of the secondary battery, thereby obtaining a high battery capacity.

[0058] Specifically, when the sulfur-containing material does not contain a trimagnesium disulfide-containing compound in a discharged state, increasing the areal density of the sulfur-containing material in the positive electrode 21 significantly increases the electrical resistance of the positive electrode 21. This makes it difficult for the charge-discharge reaction utilizing the precipitation and dissolution of magnesium to proceed, so that even if the areal density of the sulfur-containing material is increased, the energy density of the positive electrode 21 decreases. Therefore, even if the precipitation and dissolution of magnesium is utilized, a high battery capacity cannot be obtained. In this case, particularly depending on the areal density of the sulfur-containing material, the charge-discharge reaction fundamentally does not proceed, and therefore, the battery capacity cannot be obtained in the first place.

[0059] In addition, when the sulfur-containing material does not contain a trimagnesium disulfide-containing compound in a discharged state, reducing the areal density of the sulfur-containing material in the positive electrode 21 reduces, rather than increases, the electrical resistance of the positive electrode 21. However, naturally, the energy density of the positive electrode 21 decreases due to the reduction in the areal density of the sulfur-containing material, and thus a high battery capacity cannot be obtained.

[0060] In contrast, when the sulfur-containing material contains a trimagnesium disulfide-containing compound in a discharged state, the properties of the trimagnesium disulfide-containing compound are utilized to increase the amount of magnesium absorbed by the sulfur-containing material. Furthermore, even if the areal density of the sulfur-containing material in the positive electrode 21 is increased, the properties of the trimagnesium disulfide-containing compound are utilized to suppress an increase in the electrical resistance of the positive electrode 21. This increases the energy density of the positive electrode 21 and facilitates stable charge-discharge reactions utilizing the precipitation and dissolution of magnesium. Therefore, as described above, the electrochemical state of the positive electrode 21 is improved during charge and discharge of the secondary battery, allowing for high battery capacity to be achieved by utilizing the precipitation and dissolution of magnesium.

[0061] Here, the trimagnesium disulfide-containing compound is a discharge product that is specifically formed by discharging a secondary battery having a predetermined configuration. Therefore, even if a secondary battery that does not have the predetermined configuration is discharged, the trimagnesium disulfide-containing compound is not formed. Details of the predetermined configuration of the secondary battery described here will be described later.

[0062] It is preferable that the sulfur-containing material further contains magnesium sulfide (MgS) in a discharged state. That is, it is preferable that the sulfur-containing material contains magnesium sulfide together with trimesengine disulfide in a discharged state. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium tends to proceed more stably, thereby obtaining a higher battery capacity.

[0063] The crystal structure of magnesium sulfide is not particularly limited, but it is particularly preferred that the magnesium sulfide has a zinc blende-type crystal structure. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more stably, thereby achieving a higher battery capacity. The procedure for confirming the crystal structure of magnesium sulfide will be described later.

[0064] 3, the positive electrode 21 may include a positive electrode current collector 21A and a positive electrode active material layer 21B. This is because the current collecting ability of the positive electrode 21 is improved, and a high battery capacity can be stably obtained. However, the positive electrode current collector 21A may be omitted.

[0065] The positive electrode current collector 21A is a conductive member that supports the positive electrode active material layer 21B, and has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains one or more conductive materials such as metal materials, and specific examples of the conductive materials include nickel and stainless steel.

[0066] The positive electrode active material layer 21B is supported by a positive electrode current collector and contains one or more sulfur-containing materials as positive electrode active materials, but may also contain one or more other materials such as a positive electrode binder and a positive electrode conductive agent.

[0067] The positive electrode active material layer 21B may be provided on both sides of the positive electrode current collector 21A, or may be provided on only one side of the positive electrode current collector 21A. Note that Fig. 3 shows the case where the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. The method for forming the positive electrode active material layer 21B is not particularly limited, and specifically, it may be any one or more of coating methods.

[0068] 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.

[0069] 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.

[0070] The positive electrode conductive agent contains one or more conductive materials such as a carbon material, a metal material, and a conductive polymer compound.

[0071] Carbon materials include graphite, carbon fiber, carbon black, and carbon nanotubes. Specific examples of graphite include natural graphite and artificial graphite. Specific examples of carbon fiber include vapor-grown carbon fiber (VGCF). Specific examples of carbon black include acetylene black and ketjen black. Specific examples of carbon nanotubes include single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), and a specific example of the multi-walled carbon nanotube is double-walled carbon nanotubes (DWCNT). Specific examples of metal materials include nickel.

[0072] Here, the surface density (mg / cm) of the sulfur-containing material in the positive electrode active material layer 21B 2　) is not particularly limited, but is preferably sufficiently large, because this makes it easier for a trimagnesium disulfide-containing compound to be formed in a discharged state.

[0073] This surface density is the unit area (cm 2　 ) and, more specifically, the weight (mg) of the sulfur-containing material per area of ​​the positive electrode active material layer 21B facing the negative electrode 22.

[0074] A sufficiently high areal density of the sulfur-containing material described herein is one of the predetermined configurations of the secondary battery necessary for forming the above-mentioned discharge product, the trimagnesium disulfide-containing compound.

[0075] Specifically, the surface density of the sulfur-containing material is 1 mg / cm 2　 ~10 mg / cm 2　 is preferable because the trimagnesium disulfide-containing compound can be sufficiently easily formed.

[0076] In addition, the surface density of the sulfur-containing material is 1 mg / cm 2　 ~10 mg / cm 2　 When the capacity of the positive electrode 21 is increased, more specifically, when the capacity of the positive electrode 21 is increased to 1 mAh / cm 2　 That's all.

[0077] The procedure for calculating the surface density of the sulfur-containing material is as follows: In the following, a case where the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A will be described.

[0078] First, the secondary battery is disassembled to recover the positive electrode 21. In this case, it is not particularly limited whether the secondary battery is discharged or not. Next, the positive electrode 21 is washed with a washing solvent to remove the electrolyte adhering to the positive electrode 21. The type of washing solvent is not particularly limited, but specifically, it is any one or more of non-aqueous solvents such as ethyl-n-propyl sulfone, dimethoxyethane, and dimethyl carbonate.

[0079] Next, the dimensions of one of the two positive electrode active material layers 21B are measured to determine the area (cm 2　 For example, when the shape of the positive electrode active material layer 21B is rectangular, the length (cm) and width (cm) of the positive electrode active material layer 21B are measured, and the area (= length × width) is calculated based on the length and width.

[0080] Next, the positive electrode active material layer 21B whose area has been calculated is analyzed using an analytical method such as inductively coupled plasma (ICP) emission spectroscopy, thereby measuring the weight (mg) of sulfur atoms contained in the positive electrode active material layer 21B.

[0081] Finally, the areal density (mg / cm 2　 ) = weight of sulfur atoms (mg) / area of ​​positive electrode active material layer 21B (cm 2　 ) is used to calculate the areal density of the sulfur-containing material.

[0082] (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.

[0083] As described above, the magnesium-containing material is a general term for materials containing magnesium as a constituent element. Therefore, the magnesium-containing material may be magnesium as a single element, a magnesium alloy, a magnesium compound, or a mixture of two or more of these. Note that the purity of the magnesium as a single element is not particularly limited, and the magnesium as a single element may contain any amount of impurities.

[0084] 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, as constituent elements, any one or more of non-metallic elements such as carbon, oxygen, sulfur, and halogens, and specific examples of the halogens include fluorine, chlorine, bromine, and iodine.

[0085] Among these, it is preferable that the magnesium-containing material contains elemental magnesium, because this allows the charge-discharge reaction that utilizes the precipitation and dissolution of magnesium to proceed sufficiently.

[0086] 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.

[0087] The negative electrode current collector is a conductive member 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 one or more conductive materials such as metal materials, and specific examples of the conductive materials include nickel and stainless steel.

[0088] 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.

[0089] 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 coating methods or the like.

[0090] The details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and the details regarding the negative electrode conductive agent are the same as those regarding the positive electrode conductive agent.

[0091] 2 and 3, 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 while preventing short-circuiting between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0092] (Electrolyte) The electrolyte is a liquid electrolyte and contains a solvent and an electrolyte salt.

[0093] The solvent contains one or more types of non-aqueous solvents (organic solvents), and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The type of non-aqueous solvent is not particularly limited, but it is preferable that the non-aqueous solvent be capable of promoting the formation of a trimagnesium disulfide-containing compound during discharge of the secondary battery.

[0094] The ability of the non-aqueous solvent described herein to promote the formation of the trimagnesium disulfide-containing compound is one of the predetermined configurations of the secondary battery that are necessary for forming the above-mentioned trimagnesium disulfide-containing compound.

[0095] Specifically, the nonaqueous solvent contains one or both of a dialkyl sulfone and an ether compound. This is because the trimagnesium disulfide-containing compound is more likely to be formed during discharge of the secondary battery. The dialkyl sulfone may be of one type or two or more types. Similarly, the ether compound may be of one type or two or more types.

[0096] Dialkyl sulfone is a compound represented by formula (1). The types of R1 and R2 may be the same or different.

[0097] R1-S(=O) 2　 -R2 (1) (wherein R1 and R2 are each an alkyl group.)

[0098] The type of alkyl group is not particularly limited. Therefore, the alkyl group may be linear or branched. The number of carbon atoms in the alkyl group is not particularly limited, but is preferably 4 or less. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, an s-butyl group, and a t-butyl group.

[0099] Specific examples of dialkyl sulfones include dimethyl sulfone, methyl ethyl sulfone, methyl-n-propyl sulfone, methyl-i-propyl sulfone, methyl-n-butyl sulfone, methyl-i-butyl sulfone, methyl-s-butyl sulfone, methyl-t-butyl sulfone, ethyl methyl sulfone, diethyl sulfone, ethyl-n-propyl sulfone, ethyl-i-propyl sulfone, ethyl-n-butyl sulfone, ethyl-i-butyl sulfone, ethyl-s-butyl sulfone, ethyl-t-butyl sulfone, di-n-propyl sulfone, di-i-propyl sulfone, n-propyl-n-butyl sulfone, n-butyl ethyl sulfone, i-butyl ethyl sulfone, s-butyl ethyl sulfone, and di-n-butyl sulfone.

[0100] Among these, dialkyl sulfones such as ethyl-n-propyl sulfone and ethyl-i-propyl sulfone are preferred, because the trimagnesium disulfide-containing compound is sufficiently formed when the secondary battery is discharged.

[0101] An ether compound is a general term for compounds 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.

[0102] Specific examples of the ether compound include dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and tetrahydrofuran.

[0103] The electrolyte salt contains one or more types of magnesium salts, because the charge-discharge reaction utilizing the deposition and dissolution of magnesium proceeds sufficiently.

[0104] The type of magnesium salt is not particularly limited, but it is preferable that the magnesium salt be capable of promoting the formation of a trimagnesium disulfide-containing compound during discharge of the secondary battery. The ability of the magnesium salt described herein to promote the formation of a trimagnesium disulfide-containing compound is one of the predetermined configurations of the secondary battery that are necessary for forming the above-mentioned trimagnesium disulfide-containing compound.

[0105] Specific examples of magnesium salts include magnesium chloride (MgCl 2　 ) and bis(trifluoromethanesulfonyl)imide magnesium (Mg[N(CF 3　 SO 2　 ) 2　 ] 2　 ) etc. This is because a sufficient amount of trimagnesium disulfide-containing compound is formed during discharge of the secondary battery.

[0106] The electrolyte salt may further contain one or more of other magnesium salts. Specific examples of other magnesium salts include 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　 ) and magnesium bis[tetra(hexafluoroisopropyl)]borate (Mg[B(OCH(CF) 3　 ) 2　 ) 4　 ] 2　 ) etc.

[0107] 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.

[0108] [Positive Electrode Lead] As shown in FIGS. 1 to 3 , 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. When the positive electrode 21 includes a positive electrode current collector 21A, the positive electrode lead 31 is connected to the positive electrode current collector 21A. The positive electrode lead 31 includes a conductive material such as a metal material, and specific examples of the conductive material are one or more types of metal materials such as nickel and stainless steel. 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 to 3 , 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. The lead-out direction of the negative electrode lead 32 is not particularly limited, but specifically, it is the same direction as the lead-out direction of the positive electrode lead 31. The negative electrode lead 32 contains a conductive material such as a metal material, and specific examples of the conductive material are one or more types of metal materials such as copper. Details regarding the shape of the negative electrode lead 32 are the same as the details regarding 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. Physical Properties> The positive electrode 21 has predetermined physical properties.

[0114] [Physical property conditions] Figure 4 shows the magnesium-25 nuclear magnetic resonance spectroscopy ( 25 In order to explain the analysis results of the positive electrode 21 using Mg-NMR, the analysis results of the positive electrode 21 ( 25 4 shows an example of the results of Mg-NMR analysis. In Fig. 4, the horizontal axis indicates chemical shift (ppm) and the vertical axis indicates intensity (arbitrary unit).

[0115] As described above, the positive electrode 21 contains a sulfur-containing material, which is a positive electrode active material, in an undischarged state, and the sulfur-containing material contains a trimagnesium disulfide-containing compound, which is a discharge product, in a discharged state. As described above, this trimagnesium disulfide-containing compound contains trimagnesium disulfide. Therefore, in a discharged state, 25 When the positive electrode 21 is analyzed using Mg-NMR to examine its physical properties, it is found that the positive electrode 21 has predetermined physical properties.

[0116] In addition, when the positive electrode 21 includes the positive electrode current collector 21A and the positive electrode active material layer 21B, in a discharged state, 25 The positive electrode active material layer 21B is analyzed using Mg-NMR.

[0117] 25 ​When analyzing the positive electrode 21 using Mg-NMR, an 800 MHz solid-state nuclear magnetic resonance spectrometer (measurement magnetic field strength = 18.79 T) manufactured by JEOL Ltd. equipped with a Magic Angle Spinning (MAS) probe (diameter = 3.2) mm is used as the nuclear magnetic resonance spectrometer.

[0118] The analytical conditions were: resonance frequency = 49.00 MHz, observation range = 294 kHz, MAS rotation speed = 15 kHz, chemical shift standard = MgCl 2　 Aqueous solution (0 ppm), measurement pulse sequence = single pulse method, measurement pulse width = 1.3 μsec (30° pulse), repetition time = 1 sec, number of accumulations = approximately 80,000 times.

[0119] Specifically, the sulfur-containing material contains sulfur and magnesium as constituent elements in a discharged state because magnesium dissolved in the negative electrode 22 is absorbed in the positive electrode 21, as described above.

[0120] In this case, 25 As a result of analyzing the positive electrode 21 using Mg-NMR, an NMR spectrum 4A is obtained, as shown in Fig. 4. In this NMR spectrum 4A, since the positive electrode 21 contains a trimagnesium disulfide-containing compound, as described above, a peak P1 (first peak) is detected in the chemical shift range of -70 ppm to 0 ppm. In Fig. 4, the chemical shift range of -70 ppm to 0 ppm is shaded.

[0121] This peak P1 is a peak detected due to the presence of a trimagnesium disulfide-containing compound, and can be used to confirm the presence or absence of the trimagnesium disulfide-containing compound.

[0122] As described above, the trimagnesium disulfide-containing compound is a discharge product formed by discharging a secondary battery having a predetermined configuration. Therefore, after discharging a secondary battery having a predetermined configuration, 25When the positive electrode 21 is analyzed using Mg-NMR, an NMR spectrum 4A having a peak P1 is obtained as shown in FIG.

[0123] In contrast, when a secondary battery not having the predetermined configuration is discharged, NMR spectrum 4B is obtained instead of NMR spectrum 4A, as shown in Fig. 4. In this case, no trimagnesium disulfide-containing compound is formed, and therefore peak P1 is not detected.

[0124] As a result, when a trimagnesium disulfide-containing compound, which is a discharge product, is formed in a discharge state, an NMR spectrum 4A is obtained, and peak P1 is detected. However, when a trimagnesium disulfide-containing compound, which is a discharge product, is not formed in a discharge state, an NMR spectrum 4B is obtained, and peak P1 is not detected. Therefore, based on whether or not peak P1 is detected, it is possible to confirm whether or not the sulfur-containing material in positive electrode 21 contains a trimagnesium disulfide-containing compound.

[0125] In Fig. 4, in order to easily distinguish between NMR spectra 4A and 4B, NMR spectrum 4A is shown by a solid line and NMR spectrum 4B is shown by a dashed line. Also, in order to easily distinguish between NMR spectra 4A and 4B, the positions of NMR spectrum 4A and NMR spectrum 4B are shifted vertically so that they do not overlap.

[0126] In the NMR spectrum 4A, the surface density of the sulfur-containing material in the positive electrode 21 is 3 mg / cm 3 In the NMR spectrum 4B, the surface density of the sulfur-containing material in the positive electrode 21 is 0.6 mg / cm 3 is.

[0127] Here, the number of peaks P1 is not particularly limited, and therefore the number of peaks P1 may be one or two or more.

[0128] Furthermore, the shape of the peaks P1 is not particularly limited. Therefore, the shape of the peaks P1 may be sharp or broad. When there are two or more peaks P1, the shapes of some of the peaks P1 may be sharp and the shapes of the remaining peaks P1 may be broad.

[0129] When the number of peaks P1 is two or more, the peaks P1 may overlap with each other, resulting in broadening, depending on the resolution during analysis.

[0130] (Peak P2) As described above, the sulfur-containing material preferably further contains magnesium sulfide in a discharged state. As a result, as shown in FIG. 4, in the NMR spectrum 4A, since the positive electrode 21 contains magnesium sulfide, it is preferable that peak P2 (second peak) be detected within a chemical shift range of 60 ppm to 80 ppm. In FIG. 4, the chemical shift range of 60 ppm to 80 ppm is shaded.

[0131] This peak P2 is a peak detected due to the presence of magnesium sulfide, and can be used to confirm whether or not magnesium sulfide is present.

[0132] Unlike the discharge product, trimagnesium disulfide-containing compound, magnesium sulfide is formed by discharging a secondary battery in which the positive electrode 21 contains a sulfur-containing material, regardless of whether the secondary battery has a predetermined configuration. Therefore, after discharging a secondary battery in which the positive electrode 21 contains a sulfur-containing material, 25 When the positive electrode 21 is analyzed using Mg-NMR, an NMR spectrum 4A having a peak P2 in addition to a peak P1 is obtained, as shown in FIG.

[0133] As shown in FIG. 4, since the positive electrode 21 contains magnesium sulfide, a peak P2 is also detected in the NMR spectrum 4B.

[0134] That is, when the positive electrode 21 contains a sulfur-containing material, NMR spectrum 4A or NMR spectrum 4B is obtained in a discharged state. As a result, peak P2 is detected in both NMR spectrum 4A and NMR spectrum 4B. Therefore, based on whether or not peak P2 is detected, it is possible to confirm whether or not the sulfur-containing material in the positive electrode 21 contains magnesium sulfide.

[0135] 4, in the NMR spectrum 4A, the peak P1 has an intensity I1, and the peak P2 has an intensity I2. The intensity I1 is the maximum intensity of the peak P1, and the intensity I2 is the maximum intensity of the peak P2.

[0136] Here, the peak intensity ratio, which is the ratio of intensity I1 to intensity I2, is not particularly limited. In particular, the peak intensity ratio is preferably 0.05 or more. This is because the relationship between intensity I1 and intensity I2 is optimized, thereby enabling a high battery capacity to be stably obtained. This peak intensity ratio is calculated based on the formula: Peak intensity ratio = I1 / I2.

[0137] To determine the intensities I1 and I2, a baseline BL is drawn using a calculation function installed in the nuclear magnetic resonance spectrometer, as shown in Figure 4. After that, the intensity I1 is determined by measuring the maximum intensity of peak P1 based on the baseline BL. Furthermore, the intensity I2 is determined by measuring the maximum intensity of peak P2 based on the baseline BL.

[0138] [Identification of Trimagnesium Disulfide-Containing Compounds] As described above, 25 When the positive electrode 21 is analyzed using Mg-NMR, a peak P1 is detected in the NMR spectrum 4A, confirming that the sulfur-containing material contains a trimagnesium disulfide-containing compound in a discharged state. 25 The trimagnesium disulfide-containing compound is identified based on the detection of peak P1 in the Mg-NMR analysis results, and it is therefore confirmed that the trimagnesium disulfide-containing compound, which is a discharge product, is formed during discharge of the secondary battery.

[0139] The reason why the trimagnesium disulfide-containing compound is identified based on the detection of this peak P1 is as follows.

[0140] Here, we use first-principles calculations to predict a stable structure consisting of magnesium (Mg) and sulfur (S). This results in the predicted positions (chemical shift ranges) of NMR parameters for the structure of trimagnesium disulfide, and 25 The position (chemical shift range) of peak P1 detected in NMR spectrum 4A, which is the Mg-NMR analysis result, coincides with each other. Therefore, based on the detection of peak P1, it is determined that the trimagnesium disulfide-containing compound has been identified.

[0141] 25 Peak P1 detected in NMR spectrum 4A, which is the result of Mg-NMR analysis, is a characteristic peak detected due to the trimagnesium disulfide-containing compound. Thus, detection of peak P1 in the chemical shift range of −70 ppm to 0 ppm in NMR spectrum 4A indicates that the trimagnesium disulfide-containing compound is present in the sulfur-containing material in a discharged state.

[0142] [Other physical property conditions] Figure 5 shows the results of sulfur-33 nuclear magnetic resonance spectroscopy ( 33 In order to explain the analysis results of the positive electrode 21 using S-NMR, the analysis results of the positive electrode 21 ( 33 5-NMR analysis results) and corresponds to FIG. 33 Even when using the S-NMR analysis results, 25 As in the case of using the Mg-NMR analysis results, it is possible to confirm that the sulfur-containing material contains a trimagnesium disulfide-containing compound in a discharged state.

[0143] The main component of natural sulfur is sulfur-32. 33 In the analysis of the positive electrode 21 using S-NMR, a sulfur-containing material is used which uses sulfur 33 as a starting material, and a trimagnesium disulfide-containing compound obtained from the sulfur-containing material in a discharged state is analyzed.

[0144] ​​33 When analyzing the positive electrode 21 using S-NMR, an 800 MHz solid-state nuclear magnetic resonance spectrometer (measurement magnetic field strength = 18.79 T) manufactured by JEOL Ltd. equipped with a Magic Angle Spinning (MAS) probe (diameter = 3.2) mm is used as the nuclear magnetic resonance spectrometer.

[0145] The analysis conditions were as follows: resonance frequency = 61.42 MHz, observation range = 123 kHz, MAS rotation speed = 15 kHz, chemical shift standard = calcium sulfide (-29 ppm), measurement pulse sequence = single pulse method, measurement pulse width = 1 μsec (30° pulse), repetition time = 0.5 sec, and number of accumulations = approximately 160,000.

[0146] (Peak P3) Specifically, 33 As a result of analyzing the positive electrode 21 using S-NMR, an NMR spectrum 5A is obtained, as shown in FIG. 5. In this NMR spectrum 5A, because the positive electrode 21 contains a trimagnesium disulfide-containing compound, peak P3 is detected within the chemical shift range of -220 ppm to -190 ppm. Note that in FIG. 5, the chemical shift range of -220 ppm to -190 ppm is shaded. This peak P3, like peak P1, is a peak detected due to the presence of the trimagnesium disulfide-containing compound.

[0147] In contrast, when the positive electrode 21 does not contain the trimagnesium disulfide-containing compound, the NMR spectrum 5B is obtained instead of the NMR spectrum 5A, as shown in Fig. 5. In this case, the trimagnesium disulfide-containing compound is not formed, and therefore the peak P3 is not detected. Therefore, based on whether or not the peak P3 is detected, it is possible to confirm whether or not the sulfur-containing material in the positive electrode 21 contains the trimagnesium disulfide-containing compound.

[0148] In FIG. 5, similarly to FIG. 4, NMR spectrum 5A is shown by a solid line and NMR spectrum 5B is shown by a broken line, and the positions of NMR spectrum 5A and NMR spectrum 5B are shifted vertically from each other.

[0149] (Peak P4) Furthermore, when the sulfur-containing material further contains magnesium sulfide in a discharged state, peak P4 is detected in the chemical shift range of −280 ppm to −250 ppm in NMR spectrum 5A as shown in FIG. 5. In FIG. 5, the chemical shift range of −280 ppm to −250 ppm is shaded. This peak P4 is a peak detected due to the presence of magnesium sulfide.

[0150] 5, since the positive electrode 21 contains magnesium sulfide, a peak P4 is also detected in the NMR spectrum 5B. Therefore, whether or not the sulfur-containing material in the positive electrode 21 contains magnesium sulfide can be confirmed based on whether or not the peak P4 is detected.

[0151] (Identification of Trimagnesium Disulfide-Containing Compound) As described above, 33 As a result of analyzing the positive electrode 21 using S-NMR, a peak P3 was detected in the NMR spectrum 5A, confirming that the sulfur-containing material contains a trimagnesium disulfide-containing compound in a discharged state. 33 The trimagnesium disulfide-containing compound is identified based on the detection of peak P3 in the S-NMR analysis results.

[0152] In this case, as described above, a stable structure consisting of magnesium and sulfur is predicted using first-principles calculations, and then the positions of the NMR parameters predicted for the structure of trimagnesium disulfide and 33 The position of peak P3 detected in NMR spectrum 5A, which is the S-NMR analysis result, coincides with each other. Therefore, the trimagnesium disulfide-containing compound is identified based on the detection of peak P3.

[0153] Based on these findings, a sulfur-containing material using sulfur 33 as a starting material is used to analyze a trimagnesium disulfide-containing compound obtained from the sulfur-containing material in a discharged state. As a result, the peak of trimagnesium disulfide predicted based on first-principles calculations is as follows: 25 Peak P1 and33 Since the peaks P3 detected in the S-NMR analysis results match, the compound is identified as a trimagnesium disulfide-containing compound.

[0154] [Procedure for Confirming the Crystal Structure of Magnesium Sulfide] When the sulfur-containing material contains magnesium sulfide in a discharged state, the procedure for confirming the crystal structure of the magnesium sulfide is as follows. Here, the procedure is described for the case where the positive electrode 21 includes the positive electrode current collector 21A and the positive electrode active material layer 21B.

[0155] First, after discharging the secondary battery, the secondary battery is disassembled to recover the positive electrode 21. Next, the positive electrode 21 is vacuum-dried without being washed, thereby volatilizing and removing the electrolyte adhering to the positive electrode 21. In this way, a sample (positive electrode 21) for analysis is obtained.

[0156] Next, a sample (diameter = 3.2 mm) was placed in the sample tube, and then solid magnesium 25 nuclear magnetic resonance spectroscopy (solid 25 The sample (positive electrode active material layer 21B) was analyzed using Mg-NMR, and the analysis results of the sample (solid 25 Mg-NMR analysis results) are obtained.

[0157] In this case, an 800 MHz solid-state nuclear magnetic resonance spectrometer (measurement magnetic field strength = 18.79 T) manufactured by JEOL Ltd. was used as the nuclear magnetic resonance spectrometer, and the sample tube was set in a Magic Angle Spinning (MAS) probe (diameter = 3.2 mm) attached to the 800 MHz solid-state nuclear magnetic resonance spectrometer.

[0158] The analytical conditions were: resonance frequency = 49.00 MHz, observation range = 294 kHz, MAS rotation speed = 15 kHz, chemical shift standard = MgCl 2　 Aqueous solution (0 ppm), measurement pulse sequence = single pulse method, measurement pulse width = 1.3 μsec (30° pulse), repetition time = 1 sec, number of accumulations = approximately 80,000 times.

[0159] Finally, solid 25 The crystal structure of magnesium sulfide is determined based on the results of Mg-NMR analysis.

[0160] Specifically, if a peak is detected within a chemical shift range of 60 ppm to 80 ppm, the magnesium sulfide has a zinc blende-type crystal structure. On the other hand, if no peak is detected within a chemical shift range of 60 ppm to 80 ppm, the magnesium sulfide does not have a zinc blende-type crystal structure. Therefore, based on whether or not the peaks described here are detected, it is possible to confirm whether or not the magnesium sulfide has a zinc blende-type crystal structure.

[0161] If a peak is detected within the chemical shift range of -10 ppm to 10 ppm, the magnesium sulfide has a rock-salt crystal structure. On the other hand, if no peak is detected within the chemical shift range of -10 ppm to 10 ppm, the magnesium sulfide does not have a rock-salt crystal structure. Therefore, based on whether or not the peaks described here are detected, it is possible to confirm whether or not the magnesium sulfide has a rock-salt crystal structure.

[0162] <2-3. Operation> The secondary battery operates in the battery element 20 as follows.

[0163] During discharge, the magnesium-containing material dissolves in the negative electrode 22, and magnesium is eluted into the electrolyte. As a result, magnesium is absorbed in the positive electrode 21.

[0164] Therefore, after the secondary battery is discharged, a trimagnesium disulfide-containing compound is formed in the positive electrode 21, and therefore the sulfur-containing material contains magnesium disulfide in a discharged state.

[0165] On the other hand, during charging, magnesium is released from the positive electrode 21 into the electrolyte, causing magnesium to precipitate on the negative electrode 22.

[0166] Therefore, after the secondary battery is charged, the trimagnesium disulfide-containing compound disappears from the positive electrode 21, and the sulfur-containing material does not contain magnesium disulfide in an undischarged state.

[0167] By repeatedly charging and discharging the secondary battery, the above-mentioned reactions during discharge and charge are alternately repeated, resulting in repeated formation and disappearance of the trimagnesium disulfide-containing compound. As a result, the trimagnesium disulfide-containing compound is a reversible discharge product that is repeatedly formed and disappeared in response to the charge and discharge of the secondary battery.

[0168] <2-4. Manufacturing Method> When manufacturing a secondary battery, the following example procedure is used.

[0169] 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, and a case where the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B will be described.

[0170] [Fabrication 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 surfaces of the positive electrode current collector 21A to form the positive electrode active material layer 21B. Then, the positive electrode active material layer 21B may be compression-molded using a compression device such as a roll press. In this case, the positive electrode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, the positive electrode active material layer 21B is formed on both surfaces of the positive electrode current collector 21A, thereby fabricating the positive electrode 21.

[0171] When producing this positive electrode 21, as described above, it is preferable to make the surface density of the sulfur-containing material sufficiently large in order to promote the formation of the trimagnesium disulfide-containing compound, which is a discharge product, during discharge of the completed secondary battery.

[0172] [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.

[0173] [Preparation of Electrolyte Solution] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dissolved or dispersed in the solvent, thereby preparing an electrolyte solution.

[0174] When preparing this electrolyte solution, as described above, it is preferable to use a specific type of solvent and a specific type of electrolyte salt in order to promote the formation of the trimagnesium disulfide-containing compound, which is a discharge product, when the completed secondary battery is discharged.

[0175] Specifically, it is preferable to use a non-aqueous solvent such as a dialkyl sulfone or an ether compound as the solvent, and it is preferable to use a magnesium salt such as magnesium chloride or bis(trifluoromethanesulfonyl)imide magnesium as the electrolyte salt.

[0176] [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. In this case, the positive electrode lead 31 is connected to the positive electrode current collector 21A.

[0177] 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 compression device such as a press to form the wound body into 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.

[0178] Next, after the roll is accommodated in 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 opposing fusion layers are joined together using an adhesive method such as heat fusion, thereby accommodating the roll in the bag-shaped exterior film 10.

[0179] Finally, after injecting the 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.

[0180] 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 in the bag-shaped exterior film 10, completing the secondary battery.

[0181] <2-5. Actions and Effects> According to this secondary battery, the positive electrode 21 contains a sulfur-containing material, the negative electrode 22 contains a magnesium-containing material, and the sulfur-containing material contains trimesgense disulfide, which is a trimagnesium disulfide-containing compound, in a discharged state.

[0182] In this case, as described above, the properties of trimagnesium disulfide are utilized to increase the amount of magnesium absorbed in the sulfur-containing material. Moreover, even if the areal density of the sulfur-containing material in the positive electrode 21 is increased, the properties of trimagnesium disulfide are utilized to suppress an increase in the electrical resistance of the positive electrode 21. This increases the energy density of the positive electrode 21 and facilitates stable charge-discharge reactions utilizing the precipitation and dissolution of magnesium. Therefore, a high battery capacity can be obtained by utilizing the precipitation and dissolution of magnesium, resulting in excellent battery characteristics.

[0183] In particular, if the sulfur-containing material further contains magnesium sulfide in a discharged state, the charge-discharge reaction utilizing the deposition and dissolution of magnesium proceeds sufficiently stably, and therefore a greater effect can be obtained.

[0184] In this case, if the magnesium sulfide has a zinc blende crystal structure, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more stably, and therefore an even greater effect can be obtained.

[0185] Furthermore, if the sulfur-containing material contains elemental sulfur, the charge-discharge reaction utilizing the deposition and dissolution of magnesium will proceed sufficiently, and a higher effect can be obtained.

[0186] The positive electrode 21 includes a positive electrode active material layer 21B, and the surface density of the sulfur-containing material in the positive electrode active material layer 21B is 1 mg / cm 2　 ~10 mg / cm 2　 In this case, trimagnesium disulfide is more likely to be formed sufficiently, and a greater effect can be obtained.

[0187] Furthermore, if the solvent in the electrolytic solution contains one or both of a dialkyl sulfone and an ether compound, and the electrolyte salt contains a magnesium salt, trimagnesium disulfide is more likely to be formed when the secondary battery is discharged, thereby achieving a greater effect.

[0188] Furthermore, if the magnesium-containing material contains elemental magnesium, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium will proceed sufficiently, and a higher effect can be obtained.

[0189] 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.

[0190] In addition, the positive electrode 21 contains a sulfur-containing material, the negative electrode 22 contains a magnesium-containing material, and the sulfur-containing material contains sulfur and magnesium as constituent elements in a discharged state. 25 Peak P1 is detected in the analysis results of the positive electrode 21 using Mg-NMR. As a result, for the reasons described above, the energy density of the positive electrode 21 increases, and the charge-discharge reaction utilizing the precipitation and dissolution of magnesium tends to proceed stably. Therefore, a high battery capacity can be obtained by utilizing the precipitation and dissolution of magnesium, and excellent battery characteristics can be obtained.

[0191] especially, 25If peak P2 is further detected in the analysis results of the positive electrode 21 using Mg-NMR, for the reasons described above, the charge / discharge reaction utilizing the precipitation and dissolution of magnesium proceeds sufficiently stably, and a higher effect can be obtained.

[0192] Furthermore, if the peak intensity ratio is 0.05 or more, the relationship between the intensity I1 and the intensity I2 is optimized, and therefore a high battery capacity can be stably obtained, resulting in a greater effect.

[0193] 3. Modifications Next, modifications of the secondary battery will be described. Note that the series of modifications described below may be combined with each other as appropriate.

[0194] [Modification 1] The trimagnesium disulfide-containing compound is a reversible discharge product, and is therefore formed when the secondary battery is discharged and disappears when the secondary battery is charged.

[0195] However, the trimagnesium disulfide-containing compound may not disappear during charging of the secondary battery, and some or all of the trimagnesium disulfide-containing compound may remain. In this case, the amount of the trimagnesium disulfide-containing compound may increase as the secondary battery is repeatedly charged and discharged. Even in this case, the properties of the trimagnesium disulfide-containing compound can be utilized to obtain the same effect.

[0196] [Variation 2] The trimagnesium disulfide-containing compound is a discharge product, and therefore is formed by utilizing the discharge reaction of a secondary battery. However, the trimagnesium disulfide-containing compound may not be a discharge product, and may be formed using an existing synthesis method.

[0197] In this case, in the undischarged state, the sulfur-containing material may contain a trimagnesium disulfide-containing compound. As described above, this trimagnesium disulfide-containing compound contains trimagnesium disulfide. In this case, too, the properties of the trimagnesium disulfide-containing compound can be utilized to obtain the same effect.

[0198] 2 and 3, an electrolyte solution that is a liquid electrolyte is used. However, although not specifically shown here, an electrolyte layer that is a gel electrolyte may be used instead of the electrolyte solution.

[0199] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are wound facing each other with the separator 23 and the electrolyte layer interposed therebetween. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0200] Specifically, the electrolyte layer contains one or more polymer compounds together with an electrolytic solution, and the electrolytic solution is held by the polymer compounds, which prevents leakage of the electrolytic solution. The composition of the electrolytic solution is as described above.

[0201] Specific examples of polymer compounds include polyacrylonitrile, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate. Among these, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, and polyethylene oxide are preferred because they improve the electrochemical stability of the polymer compound.

[0202] When forming the electrolyte layer, a precursor solution containing an electrolytic solution, a polymer compound, and a solvent is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 21 and the negative electrode 22 .

[0203] Even when this electrolyte layer is used, the same effect can be obtained because magnesium can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, leakage of the electrolyte solution is prevented as described above, and therefore a greater effect can be obtained.

[0204] 4. 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 used as a main power source or an auxiliary power source in applications such as electronic devices and electric vehicles. A main 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 main power source or a power source that can be switched from the main power source.

[0205] 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.

[0206] 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. The home power storage system can use the power stored in the secondary battery, which is a power storage source, to power home electrical appliances, etc.

[0207] An embodiment of the present technology will be described.

[0208] <Examples 1 and 2 and Comparative Examples 1 to 3> As described below, a secondary battery including a test electrode 51 described later was fabricated, and then the physical properties of the test electrode 51 were evaluated, and the battery characteristics of the secondary battery were evaluated.

[0209] [Fabrication of Secondary Battery] Here, a test secondary battery was fabricated to simply evaluate the physical properties and battery characteristics. Fig. 6 shows the cross-sectional structure of the test secondary battery, which was a coin-type magnesium-sulfur secondary battery.

[0210] Below, the configuration of the test secondary battery will be explained, and then the procedure for fabricating the test secondary battery will be explained.

[0211] (Configuration of Test Secondary Battery) As shown in FIG. 6, 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).

[0212] The test electrode 51 is housed in a vessel-shaped exterior cup 54, and the counter electrode 52 is housed in a vessel-shaped 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 is housed in the exterior can 55, and the exterior cup 54 and the exterior can 55 are crimped together with a gasket 56. As a result, the test electrode 51, the counter electrode 52, and the separator 53 are sealed inside the exterior cup 54 and the exterior can 55.

[0213] (Procedure for Producing Test Secondary Batteries) The procedure for producing test secondary batteries is as follows.

[0214] (Preparation of Test Electrode) First, 10 parts by mass of a positive electrode active material (sulfur-containing material, elemental sulfur (S, purity = 99% or more) manufactured by Sigma-Aldrich), 30 parts by mass of a positive electrode binder (polytetrafluoroethylene manufactured by AGC Inc.), and 60 parts by mass of a positive electrode conductive agent (Ketjenblack ECP600JD manufactured by Lion Corporation) were mixed together to prepare a positive electrode mixture.

[0215] Subsequently, the positive electrode mixture was molded into a layer using a molding machine to form a positive electrode active material layer. In this case, the surface density of the sulfur-containing material was 3.0 mg / cm. 2　 It was decided.

[0216] Subsequently, the positive electrode active material layer was punched out into a disk shape (diameter = 15 mm), thereby obtaining a disk-shaped positive electrode active material layer.

[0217] Finally, a positive electrode active material layer was placed on one surface of a positive electrode current collector (nickel foil), and then the positive electrode active material layer was pressure-bonded to the positive electrode current collector using a molding machine, thereby producing test electrode 51.

[0218] For comparison, the surface density of the sulfur-containing material is 0.6 mg / cm 2　 A test electrode 51 was fabricated in the same manner except for the above change.

[0219] (Preparation of Counter Electrode) A disk-shaped magnesium plate was prepared as the counter electrode 52 (elementary magnesium (Mg) as a magnesium-containing material). In this case, a magnesium plate (thickness = 0.2 mm, diameter = 16 mm, purity = 99.9%) manufactured by Rikazai Corporation was used.

[0220] (Preparation of Electrolyte Solution) Inside a glove box (argon gas atmosphere, dew point = -90°C to -80°C), a solvent (a non-aqueous solvent, such as a dialkyl sulfone or ether compound) was stirred using a stirrer while an electrolyte salt (magnesium salt) was added to the solvent. In this case, the mixing ratio (molar ratio) of the solvent to the electrolyte salt was solvent:electrolyte salt = 80:10.

[0221] The dialkyl sulfone used was ethyl-n-propyl sulfone (EnPS) manufactured by Toyama Pharmaceutical Co., Ltd., which is a dehydration grade for batteries. The ether compound used was dimethoxyethane (DME). The magnesium salt used was anhydrous magnesium chloride (MgCl) manufactured by Sigma-Aldrich. 2　 ) and magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)) manufactured by Toyama Pharmaceutical Co., Ltd. 2　 ) was used.

[0222] Thus, an electrolyte solution was prepared. The specific composition of the electrolyte solution is shown in Table 1.

[0223] When ethyl-n-propyl sulfone was used as the solvent and magnesium chloride was used as the electrolyte salt, the content of the electrolyte salt in the electrolyte solution was 1 mol / l (=1 mol / dm 3　 )

[0224] When dimethoxyethane was used as the solvent and a mixture of magnesium chloride and bis(trifluoromethanesulfonyl)imide magnesium was used as the electrolyte salt, the content of the electrolyte salt (magnesium chloride) in the electrolyte solution was 2 mol / L (=2 mol / dm 3　 ), and the content of the electrolyte salt (bis(trifluoromethanesulfonyl)imide magnesium) in the electrolyte solution was 1 mol / L (=1 mol / dm 3　 )

[0225] For comparison, an electrolyte solution was prepared in the same manner except that a cyclic carbonate (propylene carbonate (PC)) was used as the non-aqueous solvent instead of dialkyl sulfone. In this case, the electrolyte salt was not sufficiently dissolved, so the content of the electrolyte salt in the electrolyte solution was 1 mol / L (=1 mol / dm 3　 ) or less.

[0226] For comparison, water (H 2　 An electrolyte solution was prepared in the same manner except that 1 mol / L (=1 mol / dm) was used. In this case, the electrolyte salt was not sufficiently dissolved, so the content of the electrolyte salt in the electrolyte solution was 1 mol / L (=1 mol / dm) relative to the solvent. 3　 ) or less.

[0227] (Assembly of test secondary battery) First, a spacer (stainless steel plate, thickness = 0.5 μm) was spot-welded to the inner bottom surface of the exterior cup 54. In this case, the welding position of the spacer relative to the exterior cup 54 was adjusted so that when the test electrode 51 was housed in the exterior cup 54 in a later process, the spacer would be interposed between the exterior cup 54 and the test electrode 51. Note that the spacer is not shown in FIG. 6.

[0228] Next, the test electrode 51 was placed in an exterior cup 54, and the counter electrode 52 was placed in an 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 with a separator 53 (glass filter GC50 manufactured by Advantec Co., Ltd.) impregnated with an electrolyte interposed therebetween. In this case, the test electrode 51 was positioned so that the positive electrode active material layer formed on one side of the positive electrode current collector faced the counter electrode 52 with the separator 53 interposed therebetween. Finally, with the test electrode 51 and the counter electrode 52 stacked together with the separator 53 interposed therebetween, the exterior cup 54 and the exterior can 55 were crimped together with a gasket 56. As a result, the test electrode 51 and the counter electrode 52 were sealed inside the exterior cup 54 and the exterior can 55, completing a test secondary battery.

[0229] [Evaluation of Physical Properties] When the physical properties of the test electrode 51 were evaluated, the results shown in Table 1 were obtained.

[0230] When evaluating the physical properties of the test electrode 51, the test secondary battery was first discharged at a current of 0.2 mA until the battery voltage reached 0.4 V. Then, the test secondary battery was disassembled to recover the test electrode 51. 25 The test electrode 51 was analyzed using Mg-NMR, and the analysis results of the test electrode 51 ( 25 In this case, the positive electrode active material layer containing the sulfur-containing material was analyzed.

[0231] lastly, 25 Based on the Mg-NMR analysis results, the presence or absence of detection of each of the peaks P1 and P2 was examined, and the peak intensity ratio was calculated. Details of the analysis procedure and calculation procedure are as described above.

[0232] [Evaluation of Battery Characteristics] When the capacity characteristics were evaluated as the battery characteristics, the results shown in Table 1 were obtained.

[0233] When evaluating the capacity characteristics, in order to electrochemically stabilize the state of the test secondary battery, the test secondary battery was subjected to two cycles of charge and discharge in a room temperature environment (temperature = 25° C.) After this, the test secondary battery was charged and discharged in the same environment to measure the battery capacity (mAh), which is an index for evaluating the capacity characteristics.

[0234] During discharge, the battery was discharged at a constant current of 0.2 mA until the battery voltage reached 0.4 V, and during charging, the battery was charged at a constant current of 0.2 mA until the battery voltage reached 2.4 V.

[0235]

[0236] [Discussion] As shown in Table 1, the battery capacity varied greatly depending on the configuration of the test secondary battery.

[0237] in particular, 25 When peak P1 was not detected in the Mg-NMR analysis results, that is, when the sulfur-containing material did not contain the trimagnesium disulfide-containing compound, which is a discharge product in a discharged state (Comparative Examples 1 to 3), a high battery capacity was not obtained.

[0238] In particular, when the solvent contained neither dialkyl sulfone nor ether compound (Comparative Examples 2 and 3), the charge / discharge reaction did not proceed at all.

[0239] In contrast, 25 When peak P1 was detected in the Mg-NMR analysis results, that is, when the sulfur-containing material contained a trimagnesium disulfide-containing compound, which is a discharge product in a discharged state (Examples 1 and 2), a high battery capacity was obtained.

[0240] especially, 25 When peak P1 was detected in the Mg-NMR analysis results, a series of trends were obtained, as explained below.

[0241] First, 25When peak P2 was further detected in the Mg-NMR analysis results, it was determined that the sulfur-containing material contained magnesium sulfide together with trimagnesium disulfide in the discharged state, resulting in a high battery capacity. 25 When the test electrode 51 was analyzed using Mg-NMR, it was confirmed that the magnesium sulfide had a zinc blende-type crystal structure.

[0242] Second, when the sulfur-containing material contained elemental sulfur, trimagnesium disulfide was formed, resulting in a high battery capacity.

[0243] Third, the surface density of the sulfur-containing material in the test electrode 51 is 1 mg / cm 2　 ~10 mg / cm 2　 In this case, trimagnesium disulfide was formed, resulting in a high battery capacity.

[0244] In contrast, the surface density of the sulfur-containing material in the test electrode 51 is 1 mg / cm 2　 If the concentration is less than this, trimagnesium disulfide is not formed, and therefore a high battery capacity cannot be obtained.

[0245] Fourth, when the solvent contained a dialkyl sulfone or ether compound and the electrolyte salt contained a magnesium salt, trimagnesium disulfide was formed, resulting in a high battery capacity.

[0246] In contrast, even if the electrolyte salt contained a magnesium salt, if the solvent did not contain a dialkyl sulfone or an ether compound, the charge / discharge reaction did not proceed fundamentally, as described above.

[0247] Fifth, when the magnesium-containing material in the counter electrode 52 contained elemental magnesium, trimagnesium disulfide was formed, resulting in a high battery capacity.

[0248] Sixth, when the peak intensity ratio was 0.05 or more, a high battery capacity was obtained.

[0249] [Summary] From the results shown in Table 1, when the positive electrode 21 contains a sulfur-containing material, the negative electrode 22 contains a magnesium-containing material, and the sulfur-containing material contains trimagnesium disulfide in the discharged state, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeded stably, resulting in a high battery capacity. Therefore, the capacity characteristics were improved, and excellent battery characteristics were obtained.

[0250] Furthermore, from the results shown in Table 1, it can be seen that the positive electrode 21 contains a sulfur-containing material, the negative electrode 22 contains a magnesium-containing material, and 25 When peak P1 was detected in the analysis results of test electrode 51 using Mg-NMR, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeded stably, resulting in a high battery capacity. Therefore, the capacity characteristics were improved, and excellent battery characteristics were obtained.

[0251] Furthermore, when the trimagnesium disulfide-containing compound, trimagnesium disulfide, was applied to a secondary battery, the secondary battery exhibited high battery capacity. Thus, electrochemical devices with excellent electrochemical properties were realized using the trimagnesium disulfide-containing compound.

[0252] 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.

[0253] Specifically, the battery structure of the secondary battery has been described as being a laminate film type and a coin type. However, the battery structure of the secondary battery is not particularly limited, and may be a cylindrical type, a square type, a button type, or the like.

[0254] 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.

[0255] The effects described in this specification are merely examples, and 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.

[0256] The present technology can also be configured as follows: <1> A battery including a positive electrode containing a sulfur-containing material, a negative electrode containing a magnesium-containing material, and an electrolyte, wherein the sulfur-containing material is trimagnesium disulfide (Mg 3　 S 2　 <2> The secondary battery according to <1>, wherein the sulfur-containing material further contains magnesium sulfide (MgS) in a discharged state. <3> The secondary battery according to <2>, wherein the magnesium sulfide has a zinc blende crystal structure. <4> The secondary battery according to any one of <1> to <3>, wherein the sulfur-containing material contains elemental sulfur (S). <5> The positive electrode includes a positive electrode active material layer, wherein the positive electrode active material layer contains the sulfur-containing material, and wherein an areal density of the sulfur-containing material in the positive electrode active material layer is 1 mg / cm 2　 10mg / cm or more 2　The secondary battery according to any one of <1> to <4>, wherein: <6> The secondary battery according to any one of <1> to <5>, wherein the electrolytic solution contains a solvent and an electrolyte salt, the solvent contains at least one of a dialkyl sulfone and an ether compound, and the electrolyte salt contains a magnesium salt. <7> The secondary battery according to any one of <1> to <6>, wherein the magnesium-containing material contains elemental magnesium (Mg). <8> The secondary battery according to any one of <1> to <7>, wherein the secondary battery is a magnesium-sulfur secondary battery. <9> A secondary battery comprising: a positive electrode containing a sulfur-containing material; a negative electrode containing a magnesium-containing material; and an electrolytic solution, wherein the sulfur-containing material contains sulfur and magnesium as constituent elements in a discharged state, and wherein analysis of the positive electrode using magnesium-25 nuclear magnetic resonance spectroscopy in a discharged state detects a first peak in a chemical shift range of -70 ppm to 0 ppm. <10> The secondary battery according to <9>, wherein a second peak is further detected in a chemical shift range of 60 ppm to 80 ppm in a result of analysis of the positive electrode in a discharged state using magnesium-25 nuclear magnetic resonance spectroscopy. <11> The secondary battery according to <10>, wherein a ratio of the peak intensity of the first peak to the peak intensity of the second peak is 0.05 or more. <12> The secondary battery according to <10>, wherein the ratio of the peak intensity of the first peak to the peak intensity of the second peak is 0.05 or more. 3　 S 2　 ) Trimagnesium disulfide-containing compounds.

[0257] 21... Positive electrode, 21A... Positive electrode current collector, 21B... Positive electrode active material layer, 22... Negative electrode

Claims

1. A positive electrode containing a sulfur-containing material, A negative electrode containing a magnesium-containing material, Electrolyte and Equipped with, The sulfur-containing material, in the discharge state, trimagnesium disulfide (Mg 3 S 2 ) including, Secondary battery.

2. The sulfur-containing material further contains magnesium sulfide (MgS) in the discharge state. The secondary battery according to claim 1.

3. The magnesium sulfide has a zincblende-type crystal structure. The secondary battery according to claim 2.

4. The sulfur-containing material contains elemental sulfur (S), A secondary battery according to any one of claims 1 to 3.

5. The positive electrode includes a positive electrode active material layer, The positive electrode active material layer includes the sulfur-containing material, The surface density of the sulfur-containing material in the positive electrode active material layer is 1 mg / cm². 2 10mg / cm or more 2 The following is: A secondary battery according to any one of claims 1 to 3.

6. The electrolyte comprises a solvent and an electrolyte salt. The solvent comprises at least one of a dialkyl sulfone and an ether compound. The aforementioned electrolyte salt contains a magnesium salt. A secondary battery according to any one of claims 1 to 3.

7. The magnesium-containing material includes elemental magnesium (Mg), A secondary battery according to any one of claims 1 to 3.

8. It is a magnesium-sulfur secondary battery. A secondary battery according to any one of claims 1 to 3.

9. A positive electrode containing a sulfur-containing material, A negative electrode containing a magnesium-containing material, Electrolyte and Equipped with, The sulfur-containing material contains sulfur and magnesium as constituent elements in the discharge state. In the analysis of the positive electrode using magnesium-25 nuclear magnetic resonance spectroscopy in the discharge state, a first peak is detected within the range where the chemical shift is between -70 ppm and 0 ppm. Secondary battery.

10. In the analysis results of the positive electrode using magnesium-25 nuclear magnetic resonance spectroscopy in the discharge state, a second peak is detected within the range of a chemical shift of 60 ppm to 80 ppm. The secondary battery according to claim 9.

11. The ratio of the peak intensity of the first peak to the peak intensity of the second peak is 0.05 or greater. The secondary battery according to claim 10.

12. Trimagnesium disulfide (Mg 3 S 2 ) including, A compound containing trimagnesium disulfide.