Electrochemical device

Abstract

This electrochemical device comprises: a positive electrode; a negative electrode having a negative electrode active material layer that contains magnesium, and a coating layer that is formed from a polymeric material having magnesium ion conductivity and covers the negative electrode active material layer; and an electrolyte solution containing at least one among polycyclic aromatic hydrocarbon compounds and annulene compounds.

Description

Electrochemical Devices

[0001] The present invention relates to an electrochemical device.

[0002] Patent Document 1 describes a magnesium ion battery (electrochemical device) using a positive electrode containing sulfur and a negative electrode containing magnesium. The electrolyte of the magnesium ion battery in Patent Document 1 contains a two-dimensional fused ring compound such as anthracene.

[0003] Non-Patent Document 1 describes a magnesium ion battery using, as a negative electrode, magnesium metal coated with either a mixed material of a sulfonated tetrafluoroethylene-based copolymer and polyvinylidene fluoride (PVDF), a mixed material of a sulfonated polyether ether ketone and PVDF, or a mixed material of polyacrylonitrile and magnesium trifluoromethanesulfonate.

[0004] International Publication No. 2020 / 090946

[0005] ACS Appl. Mater. Interfaces 2023, 15, 33013-33027

[0006] There is a demand for improved cycle characteristics in magnesium ion batteries (electrochemical devices) that use a negative electrode containing magnesium. Patent Document 1 does not describe a technology for coating the negative electrode. Non-Patent Document 1 uses an expensive and special coating material, which may be difficult to use in magnesium ion batteries as is.

[0007] An object of the present invention is to provide an electrochemical device that can improve cycle characteristics.

[0008] An electrochemical device according to one embodiment includes a positive electrode, a negative electrode having a magnesium-containing negative electrode active material layer, and a coating layer formed of a polymer material having magnesium ion conductivity and covering the negative electrode active material layer, and an electrolyte solution containing at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound.

[0009] According to the electrochemical device of the present invention, the cycle characteristics can be improved.

[0010] FIG. 1 is a conceptual diagram of a magnesium electrode-based secondary battery according to an embodiment. FIG. 2 is an exploded perspective view schematically illustrating the configuration of a secondary battery according to an embodiment. FIG. 3 is a cross-sectional view illustrating the configuration of an electrode body according to an embodiment. FIG. 4 is an explanatory diagram illustrating the configuration of a secondary battery (coin cell) according to an example. FIG. 5 is a flowchart illustrating a method for manufacturing a negative electrode according to Example 1. FIG. 6 is a graph illustrating the cycle characteristics of secondary batteries according to Example 1 and a comparative example. FIG. 7 is a flowchart illustrating a method for manufacturing a negative electrode according to Example 2. FIG. 8 is a graph illustrating the cycle characteristics of secondary batteries according to Example 2 and a comparative example.

[0011] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to these embodiments.

[0012] 1 is a conceptual diagram of a magnesium electrode-based secondary battery according to an embodiment. Note that Fig. 1 is a conceptual diagram for explaining the operation of the secondary battery 1, and specific configuration examples of the positive electrode 210, the negative electrode 220, etc. will be described later with reference to Fig. 2 and subsequent figures.

[0013] The secondary battery 1 according to the embodiment is a magnesium secondary battery in which a sulfur-containing material is used as the positive electrode 210 and a magnesium-containing material is used as the negative electrode 220. The negative electrode 220 has a negative electrode active material layer 222 containing magnesium, and a coating layer 223 formed of a polymer material having magnesium ion conductivity and covering the negative electrode active material layer 222.

[0014] As shown in FIG. 1, during charging, magnesium ions (Mg ２＋ ) moves from the positive electrode 210 through the electrolyte layer 240 to the negative electrode 220, converting electrical energy into chemical energy and storing the electricity. During discharge, magnesium ions return from the negative electrode 220 through the electrolyte layer 240 to the positive electrode 210, generating electrical energy.

[0015] 2 is an exploded perspective view showing a schematic configuration of a secondary battery according to an embodiment. The secondary battery 1 shown in FIG. 2 is a laminated secondary battery. As shown in FIG. 2, the secondary battery 1 includes a battery element 20, an exterior member 30, and an adhesive 32.

[0016] The battery element 20 is provided inside the exterior member 30. As shown in FIG. 2 , the battery element 20 includes an electrode body 200, a positive electrode lead 21, and a negative electrode lead 22. The positive electrode lead 21 is a terminal drawn from a positive electrode 210 (described later) to the outside of the exterior member 30. That is, the positive electrode lead 21 is a terminal that serves as a positive electrode of the secondary battery 1. In FIG. 2 , the positive electrode lead 21 is provided on an end surface of the electrode body 200. The negative electrode lead 22 is a terminal drawn from the inside of a negative electrode 220 (described later) to the outside of the exterior member 30. That is, the negative electrode lead 22 is a terminal that serves as a negative electrode of the secondary battery 1. In FIG. 2 , the negative electrode lead 22 is provided on an end surface of the electrode body 200. Details of the electrode body 200 will be described later.

[0017] The exterior member 30 is a case in which the battery element 20 is housed. The exterior member 30 includes two exterior sheets 30a and 30b. The exterior sheets 30a and 30b each include an insulating layer, a metal layer, and an outermost layer. In the example of FIG. 2 , the exterior sheet 30a has a recess 31. As a result, the battery element 20 is housed in the exterior member 30 by housing the battery element 20 in the recess 31 and bonding the peripheral edges of the exterior sheets 30a and 30b.

[0018] The exterior sheets 30a, 30b are constructed by laminating an insulating layer, a metal layer, and an outermost layer in this order from the inside, i.e., the side where the battery element 20 is provided, and then bonding them together by lamination or other processing. The insulating layers of the exterior sheets 30a, 30b are made of resins such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, and polyolefin resins containing ethylene or propylene as monomers. This allows the exterior sheets 30a, 30b to reduce the moisture permeability of the secondary battery 1 and improve its airtightness. The metal layers of the exterior sheets 30a, 30b are metal plate or foil materials such as aluminum, stainless steel, nickel, and iron. The outermost layer may be made of any material, but is preferably made of the same resin as the insulating layer or a material with high resistance to tearing and punctures, such as nylon.

[0019] The adhesive 32 is a member for making the exterior member 30 airtight. The adhesive 32 is provided between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22. The material of the adhesive 32 preferably has adhesion to the positive electrode lead 21 and the negative electrode lead 22. For example, when the positive electrode lead 21 and the negative electrode lead 22 are made of a metal material, the adhesive 32 is made of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene. This allows the adhesive 32 to seal the gap between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22, thereby making the interior of the exterior member 30 airtight.

[0020] Fig. 3 is a cross-sectional view showing the configuration of an electrode assembly according to an embodiment. More specifically, Fig. 3 is a cross-sectional view showing a portion of one layer of a positive electrode 210 and one layer of a negative electrode 220 of an electrode assembly 200. As shown in Fig. 3, the electrode assembly 200 includes a positive electrode 210, a negative electrode 220, and a separator 230. In the secondary battery 1, the electrode assembly 200 has a structure in which the positive electrode 210 and the negative electrode 220 are stacked with the separator 230 interposed therebetween. The positive electrode 210 and the negative electrode 220 included in the electrode assembly 200 are layered members for the charge / discharge reaction of the secondary battery 1 according to the embodiment.

[0021] The positive electrode 210 includes a positive electrode current collector 211 and a positive electrode active material layer 212. In the positive electrode 210, the positive electrode current collector 211 is laminated between the positive electrode active material layers 212.

[0022] The positive electrode current collector 211 is a conductive support that supports the positive electrode active material layer and contains a conductive material such as nickel. In the example of Fig. 2, the positive electrode current collector 211 has a rectangular sheet shape with protrusions on the positive electrode lead 21 side. The protrusions of the positive electrode current collector 211 are connected to the positive electrode lead 21.

[0023] The positive electrode active material layer 212 is a layer containing a positive electrode active material. The positive electrode active material contains a sulfur-containing material. This makes it easier for magnesium to be absorbed and released in an ionic state in the positive electrode 210, and therefore makes it easier for a charge-discharge reaction to proceed using the deposition and dissolution of magnesium.

[0024] The sulfur-containing material contains sulfur as a constituent element. That is, the sulfur-containing material may be elemental sulfur, a sulfur alloy, a sulfur compound, or a mixture of two or more of these. Note that the purity of elemental sulfur is not particularly limited, and the elemental sulfur may contain any amount of impurities.

[0025] The type of metallic element contained as a constituent element in a sulfur alloy is not particularly limited. For example, a sulfur compound contains at least one of non-metallic elements such as carbon, oxygen, and halogens as a constituent element. Specific examples of halogens include fluorine, chlorine, bromine, and iodine.

[0026] More preferably, the positive electrode active material contains elemental sulfur, which allows the secondary battery 1 to easily undergo a charge-discharge reaction utilizing the deposition and dissolution of magnesium.

[0027] The positive electrode active material layer 212 is not limited to the above-mentioned materials, and may further contain, for example, a positive electrode binder, a positive electrode conductive additive, and a dispersant.

[0028] The positive electrode binder contains fluorine. The positive electrode binder may be any material, and may include, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene-butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Examples of polymer compounds include polyvinylidene fluoride (PVDF) and polyimide.

[0029] The positive electrode conductive additive may be any material, including, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive additive is not limited to these materials, and may be a metal material, a conductive polymer, or the like, as long as it is a conductive material.

[0030] The negative electrode 220 includes a negative electrode current collector 221, a negative electrode active material layer 222, and a coating layer 223. In the negative electrode 220, the negative electrode current collector 221 is stacked between the negative electrode active material layers 222. The coating layer 223 is provided to cover the surface of the negative electrode active material layer 222 opposite to the negative electrode current collector 221.

[0031] The negative electrode current collector 221 is a conductor, and for example, nickel foil, magnesium foil, etc. In the example of Fig. 2, the shape of the negative electrode current collector 221 is a rectangular sheet having protrusions on the side of the negative electrode lead 22. The protrusions of the negative electrode current collector 221 are connected to the negative electrode lead 22.

[0032] The negative electrode active material layer 222 is a layer containing a negative electrode active material. The negative electrode active material layer 222 is not limited to being composed only of a negative electrode active material, and may contain, for example, a conductive additive and a binder. The negative electrode active material layer 222 may also be a magnesium foil integrated with the above-mentioned negative electrode current collector 221.

[0033] The negative electrode active material is a magnesium-containing material. The magnesium-containing material is a general term for materials containing magnesium as a constituent element. That is, the magnesium-containing material may be magnesium alone (pure magnesium metal), a magnesium alloy, a magnesium compound, or a mixture of two or more of these. The purity of magnesium alone is not particularly limited, and therefore magnesium alone may contain any amount of impurities.

[0034] The types of metallic elements (except magnesium) contained as constituent elements in magnesium alloys are not particularly limited. Magnesium compounds may contain non-metallic elements such as carbon, oxygen, sulfur, and halogens as constituent elements. Specific examples of halogens include fluorine, chlorine, bromine, and iodine.

[0035] More preferably, the negative electrode active material contains magnesium as a simple substance, which allows the secondary battery 1 to easily undergo a charge-discharge reaction that utilizes the deposition and dissolution of magnesium.

[0036] 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 additive are the same as those regarding the positive electrode conductive additive.

[0037] The coating layer 223 is formed of a polymeric material having magnesium ion conductivity. The coating layer 223 may contain a fluororesin. Fluororesin is a general term for materials containing polymers containing fluorine as a constituent element. For example, the coating layer 223 may be polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), ethylene tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVF), ethylene chlorotrifluoroethylene copolymer (ECTFE), or a mixture of two or more of these. The coating layer 223 may also contain at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound. The polycyclic aromatic hydrocarbon compound and the annulene-based compound are the same as the materials contained in the electrolyte solution described below.

[0038] The separator 230 is a film that insulates the positive electrode 210 from the negative electrode 220. The separator 230 is provided between the positive electrode 210 and the negative electrode 220 so that the positive electrode 210 and the negative electrode 220 do not come into direct contact with each other. The shape of the separator 230 is a rectangular sheet when viewed in a plan view in the thickness direction.

[0039] The separator 230 is preferably made of a material that is electrically stable, chemically stable with respect to the positive electrode active material, the negative electrode active material, and the electrolyte, and is insulating. The separator 230 can be made of, for example, a polymer nonwoven fabric, a porous film, or a layer of glass or ceramic fibers. The separator 230 is more preferably made of a porous polyolefin film. This improves battery safety by preventing short circuits and providing a shutdown effect.

[0040] The electrolyte solution is impregnated into the separator 230. In the example of Fig. 2, the electrolyte solution is filled into the space inside the exterior member 30. The electrolyte solution contains a solvent, a magnesium salt as an electrolyte salt, and a polycyclic aromatic hydrocarbon compound or an annulene-based compound as an additive.

[0041] A specific example of the magnesium salt, which is an electrolyte salt, is magnesium chloride (MgCl ２ ), magnesium perchlorate (Mg(ClO ４ ) ２ ), magnesium nitrate (Mg(NO ３ ) ２ ), magnesium sulfate (MgSO ４ ), magnesium acetate (Mg(CH ３ COO) ２ ), magnesium trifluoroacetate (Mg(CF ３ COO) ２ ), magnesium tetrafluoroborate (Mg(BF ４ ) ２ ), magnesium tetraphenylborate (Mg(B(C ６ H ５ ) ４ ) ２ ), magnesium hexafluorophosphate (Mg(PF ６ ) ２ ), magnesium hexafluoroarsenate (Mg(AsF６ ) ２ ), bis(hexamethyldisilazide)magnesium (Mg[N(Si(CH ３ ) ３ ) ２ ] ２ ), bis(trifluoromethanesulfonyl)imide magnesium (Mg[N(CF ３ SO ２ ) ２ ] ２ and magnesium bis[tetra(hexafluoroisopropyl)]borate (Mg[B(OCH(CF ３ ) ２ ) ４ ] ２ ) etc.

[0042] The content of electrolyte salt in the electrolyte solution (mol / L (= mol / dm ３ However, the content of the electrolyte salt described here is the content of the electrolyte salt relative to the solvent described below.

[0043] The electrolyte solution contains at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound as an additive.

[0044] The electrolyte solution contains anthracene, which is a polycyclic aromatic hydrocarbon compound, as shown in formula (1). As shown in formula (1), anthracene is a fused ring compound having a ring structure in which three benzene rings are fused together.

[0045]

[0046] As the fused ring compound contained in the electrolyte solution of this embodiment, a fused ring compound having an anthracene skeleton as shown in the following formula (2) may be used.

[0047]

[0048] In formula (1), R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ , R ８ , R ９ and R １０are each independently a hydrogen atom, a hydrocarbon group, a halogen atom, an oxygen-containing functional group, a nitrogen-containing functional group, or a sulfur-containing functional group.

[0049] In formula (2), R １ From R １０ The hydrocarbon groups may each independently be an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an araliphatic hydrocarbon group. The aliphatic hydrocarbon group, the aromatic hydrocarbon group, and the araliphatic hydrocarbon group do not necessarily have a linear structure, but may have a branched structure. The aliphatic hydrocarbon group may be a saturated hydrocarbon or an unsaturated hydrocarbon. The number of carbon atoms in each of such hydrocarbon groups may be approximately 1 to 50 (e.g., 1 to 40, 1 to 30, 1 to 20, or 1 to 10).

[0050] In formula (2), R １ From R １０ The oxygen-containing functional group is a functional group containing at least an oxygen atom, such as a hydroxy group, a carboxy group, an epoxy group, and / or an aldehyde group. The oxygen-containing functional group may also correspond to an ether bond site or an ester bond site. The nitrogen-containing functional group is a functional group containing at least a nitrogen atom, such as an amino group, a nitro group, and / or a nitroso group. The sulfur-containing group is a functional group containing at least a sulfur atom, such as a thiol group, a sulfide group, a disulfide group, a sulfonyl group, a sulfo group, a thiocarbonyl group, and / or a thiourea group. The oxygen-containing functional group, nitrogen-containing functional group, and sulfur-containing group used herein may each have the same concept as the other, and may also fall within the category of a hydrocarbon group (an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an araliphatic hydrocarbon group).

[0051] Furthermore, each ring in the anthracene skeleton is not limited to a homocyclic ring but may be a heterocyclic ring. In the heterocyclic ring, the heteroatom may be, for example, a nitrogen atom, an oxygen atom, and / or a sulfur atom.

[0052] Although this is merely an example of one preferred embodiment, when the fused ring compound is anthracene, the anthracene skeleton is composed of a homocyclic ring, and R １ From R １０ are all hydrogen atoms. Therefore, such a fused ring compound is preferably used as an electrolyte additive in an electrochemical device with a magnesium electrode, particularly in an electrochemical device with a magnesium-sulfur electrode.

[0053] In addition, as an example of another preferred embodiment, the anthracene skeleton is composed of a homocyclic ring, and R ９ or R １０ may be a halogeno group (i.e., a halogen) or an aryl group, with all other R being hydrogen atoms. The halogen may be a fluorine atom (F), a chlorine atom (Cl), a bromine atom (Br), or an iodine atom (I). The aryl group is not particularly limited, but may be a phenyl group, a naphthyl group, an anthranyl group, a phenanthryl group, a biphenyl group, or the like. In other words, a fused ring compound may be formed in which a functional group (a functional group other than hydrogen) is introduced into the 9th or 10th position of anthracene. Such fused ring compounds may also be suitably used as electrolyte additives in magnesium electrode-based electrochemical devices, particularly in magnesium-sulfur electrode-based electrochemical devices.

[0054] The fused ring compound having an anthracene skeleton is charged together with the magnesium salt into an electrolyte solution containing a linear ether, but the amount may be small, and in particular may be extremely small. Although it may depend on the type of linear ether and / or magnesium salt in the electrolyte solution, the content of the fused ring compound having an anthracene skeleton in the electrolyte solution is 0.1 mol / dm ３ or less, and even 0.05 mol / dm ３ or less, and in some embodiments, 0.01 mol / dm ３ That is, the concentration of the fused ring compound having an anthracene skeleton may be greater than 0 (excluding 0) and less than 0.1 mol / dm ３The following concentration, for example, is greater than 0 (excluding 0) and 0.05 mol / dm ３ Concentration below 0.01 mol / dm or greater than 0 (excluding 0) ３ The following concentrations may be used:

[0055] The polycyclic aromatic hydrocarbon compound in the electrolyte solution is not limited to anthracene represented by formula (1), and may contain other fused ring compounds. Examples of the fused ring compound include at least one selected from the group consisting of pentalene, indene, naphthalene, azulene, heptalene, biphenylene, as-indacene, s-indacene, acenaphthylene, fluorene, phenalene, phenanthrene, fluoranthene, acephenanthrylene, aceanthrylene, triphenylene, pyrene, chrysene, tetracene, pleiadene, picene, perylene, pentaphene, pentacene, tetraphenylene, and hexaphene, and derivatives thereof.

[0056] The electrolyte is not limited to polycyclic aromatic hydrocarbon compounds and may contain an annulene-based compound as an additive. Annulene-based compounds are cyclic unsaturated hydrocarbon compounds having a number of carbon atoms that is a multiple of four. This allows the cyclic unsaturated hydrocarbon compound to exhibit aromaticity in a reduced state, and the active species derived from the cyclic unsaturated hydrocarbon compound are electrochemically stabilized, thereby extending the life of the cyclic unsaturated hydrocarbon compound. However, benzene and other compounds that do not have a number of carbon atoms that is a multiple of four are excluded from the annulene described here.

[0057] Here, "multiples of four" means so-called 4n (n is an integer of 1 or more), and specific examples of multiples of four are 4, 8, 12, etc. Therefore, benzene (number of carbon atoms = 6) having so-called 4n + 2 (n is an integer of 1 or more) carbon atoms does not fall under annulene having a number of carbon atoms that is a multiple of four. Benzene having 4n + 2 carbon atoms, for example, exhibits aromaticity not only in the reduced state but also in the normal molecular state.

[0058] The annulene having a carbon atom number that is a multiple of four preferably contains cyclooctatetraene (COT), which significantly stabilizes the active species derived from the cyclic unsaturated hydrocarbon compound electrochemically, thereby significantly extending the life of the cyclic unsaturated hydrocarbon compound.

[0059] In addition, when checking for the presence or absence of polycyclic aromatic hydrocarbon compounds or annulene-based compounds in the electrolyte solution and measuring the content of polycyclic aromatic hydrocarbon compounds or annulene-based compounds in the electrolyte solution, the electrolyte solution is analyzed using one or more of the existing analytical methods, which are not particularly limited, but specifically include nuclear magnetic resonance spectroscopy (NMR) and gas chromatography-mass spectrometry (GC-MS).

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

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

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

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

[0064] As described above, in this embodiment, the electrolyte solution contains at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound, which facilitates stable oxidation-reduction reactions utilizing the precipitation and dissolution of magnesium. Specifically, when the electrolyte solution contains at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound, the activity of magnesium is improved during the magnesium precipitation and dissolution reaction compared to when the electrolyte solution does not contain a polycyclic aromatic hydrocarbon compound or an annulene-based compound. As a result, in the secondary battery 1 of this embodiment, the oxidation-reduction reactions utilizing the precipitation and dissolution of magnesium are facilitated, which facilitates the charge-discharge reaction.

[0065] However, when focusing on the behavior of secondary battery 1 using an electrolyte solution containing a polycyclic aromatic hydrocarbon compound or an annulene-based compound, fine magnesium particles may be precipitated on the surface of negative electrode 220. If the fine magnesium particles are detached, the detached magnesium particles will no longer have an electrical conduction path from negative electrode 220 and will therefore be unable to contribute to the charge / discharge function, which may ultimately lead to a deterioration in cycle characteristics.

[0066] In this embodiment, a coating layer 223 is provided to cover the negative electrode active material layer 222. The coating layer 223 is formed of a polymer material having magnesium ion conductivity, such as PVDF. This allows magnesium ions to migrate from the negative electrode 220 through the coating layer 223 to the positive electrode 210, or from the positive electrode 210 through the coating layer 223 to the negative electrode 220, during charging and discharging of the secondary battery 1. Furthermore, even if magnesium fine particles precipitate on the negative electrode 220 during charging and discharging of the secondary battery 1, the coating layer 223 can suppress detachment of the magnesium particles. This facilitates stable and continuous progress of the charge and discharge reaction in the secondary battery 1 of this embodiment, and also suppresses detachment of the magnesium fine particles, making it less likely for the battery capacity to decrease even with repeated charging and discharging. Therefore, the secondary battery 1 of this embodiment has improved cycle characteristics compared to a secondary battery 1 without the coating layer 223.

[0067] (Example 1) Fig. 4 is an explanatory diagram for explaining the configuration of a secondary battery (coin cell) according to an example. Fig. 5 is a flowchart showing a method for manufacturing a negative electrode according to Example 1. Fig. 6 is a graph showing the cycle characteristics of secondary batteries according to Example 1 and a comparative example. Note that the present invention is not limited to the following examples.

[0068] FIG. 4 is a schematic exploded view of a secondary battery 50 according to Example 1. As shown in FIG. 4, the secondary battery 50 according to Example 1 includes a negative electrode 51, a positive electrode 52, a separator 53, an anode cup 54, a cathode cup 55, and an electrolyte (not shown). The positive electrode 52 and the negative electrode 51 are stacked with the separator 53 interposed therebetween. The stacked positive electrode 52, the negative electrode 51, and the separator 53 are sealed inside the anode cup 54 and the cathode cup 55. The electrolyte is impregnated into the positive electrode 52, the negative electrode 51, and the separator 53, respectively.

[0069] First, a method for treating the negative electrode 220 according to Example 1 will be described. As shown in FIG. 5 , a coating solution for forming the coating layer 223 is prepared. Specifically, N,N-dimethylacetamide (DMAc) manufactured by Nacalai Tesque, Inc. is prepared as the solvent (Step ST1), and Solef 5130 manufactured by Solvay is prepared as the PVDF (Step ST2). The mixture is heated and stirred at 80°C for 1 hour to dissolve the PVDF in the DMAc (Step ST3). This prepares a coating solution with a PVDF concentration of 1.25 wt % (Step ST4).

[0070] In the secondary battery 50 (coin cell) according to Example 1, a magnesium (Mg) disk (diameter 16 mm) was used as the negative electrode 51. An Mg plate (purity 99.9%, thickness 200 μm) manufactured by Rikazai Corporation was used as the negative electrode 51, and the surface was polished (step ST5).

[0071] Next, a thin film of the PVDF solution was formed on the surface of the magnesium metal by spin coating (step ST6). Specifically, the magnesium metal with its surface polished was fixed to a glass plate and rotated at 1000 rpm, and 150 μL of the coating solution was dropped onto it to form a thin film. After 30 seconds, the plate was placed on a hot plate at 80° C. and heated for 3 minutes (step ST7).

[0072] As described above, the negative electrode 51 can be formed in which a coating layer made of PVDF is formed on the surface of the magnesium metal (negative electrode active material layer).

[0073] The positive electrode 52 of the secondary battery 50 (coin cell) according to Example 1 used sulfur crystal (S) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. as the positive electrode active material, highly conductive carbon black (Ketjen Black) manufactured by Lion Specialty Chemicals Corporation as the conductive additive, and polytetrafluoroethylene (PTFE) manufactured by AGC Inc. as the binder. The sulfur content in the positive electrode active material was 10 wt %. The positive electrode current collector of the positive electrode 52 was nickel (Ni) with a diameter of 15 mm.

[0074] The electrolyte of the secondary battery 50 (coin cell) according to Example 1 was 0.3 mol / L Mg[B(hfip) ４ ] ２ To the HCl / DME, 0.01 mol / L of anthracene and 0.05 mol / L of cyclooctatetraene were added. ４ ] ２ is magnesium bishexafluoroisopropoxyborate manufactured by KRI Co., Ltd. DME is dimethoxyethane manufactured by Toyama Pharmaceutical Co., Ltd. Anthracene and cyclooctatetraene were reagents manufactured by Tokyo Chemical Industry Co., Ltd.

[0075] The separator 53 was made of glass fiber (GC-50) manufactured by Advantec.

[0076] The negative electrode 51 and the positive electrode 52 are stacked with the separator 53 interposed therebetween and are placed inside the anode cup 54 and the cathode cup 55, which are then crimped. In this way, the anode cup 54 and the cathode cup 55 are sealed to form an exterior body, thereby producing a coin cell.

[0077] The secondary battery according to the comparative example differs from that of Example 1 in that it does not have a coating layer made of PVDF. The other configurations of the negative electrode, positive electrode, and electrolyte are the same as those of Example 1.

[0078] In the evaluation of the cycle characteristics shown in FIG. 6, the charge-discharge test was carried out under the following conditions: Discharge conditions: CC discharge 0.05 mA / 0.7 V cutoff Charge conditions: CC charge 0.05 mA / 2.5 V cutoff Temperature: 25 degrees Celsius

[0079] 6, the secondary battery 1 according to Example 1 has a larger discharge capacity than the comparative example. Moreover, Example 1 can suppress the decrease in discharge capacity even after multiple cycles of charge / discharge testing, and has improved cycle characteristics compared to the comparative example.

[0080] Example 2 Fig. 7 is a flowchart showing a method for manufacturing a negative electrode according to Example 2. Fig. 8 is a graph showing the cycle characteristics of secondary batteries according to Example 2 and a comparative example.

[0081] The secondary battery 1 according to Example 2 differs from Example 1 in that the coating layer 223 contains anthracene in addition to PVDF.

[0082] A method for treating the negative electrode 220 according to Example 2 will be described. As shown in Fig. 7, in steps ST11 to ST14, a coating solution with a PVDF concentration of 1.25 wt% is prepared, similarly to steps ST1 to ST4 shown in Fig. 5.

[0083] N,N-dimethylacetamide (DMAc) manufactured by Nacalai Tesque, Inc. is prepared as a solvent (step ST15), and anthracene manufactured by Tokyo Chemical Industry Co., Ltd. is prepared (step ST16). Anthracene is dissolved in DMAc by external ultrasonic irradiation (step ST17). This prepares a coating solution with an anthracene concentration of 0.5 wt % (step ST18).

[0084] The PVDF solution obtained in step ST14 and the anthracene solution obtained in step ST18 are mixed and stirred in a volume ratio of 1:1 to prepare a coating solution containing PVDF and anthracene (step ST19).

[0085] A coating layer made of PVDF and anthracene is formed on the surface of magnesium metal (negative electrode active material layer) using a coating solution containing PVDF and anthracene (steps ST20 to ST22). Note that steps ST20 to ST22 are similar to steps ST5 to ST7 in FIG. 5, and therefore repeated explanations will be omitted.

[0086] 8, the secondary battery 1 according to Example 2 can obtain a larger discharge capacity than the comparative example in a charge-discharge test of at least two cycles or less. Moreover, it was shown that Example 2 has a discharge capacity equivalent to that of the comparative example even after multiple cycles of the charge-discharge test.

[0087] In the embodiment, the configuration of a secondary battery 1 is shown as an electrochemical device, but this is merely an example and is not intended to be limiting. The present disclosure can also be applied to other electrochemical devices, such as capacitors and fuel cells. Furthermore, the configuration of a laminate film-type battery is shown as the secondary battery 1, but is not limited to this. The secondary battery 1 of the present disclosure may be, for example, a cylindrical, coin, or button battery.

[0088] The above-described embodiments are provided to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the present invention, and equivalents thereof are also included in the present invention.

[0089] The present disclosure may also have the following configurations.

[0090] (1) An electrochemical device comprising: a positive electrode; a negative electrode having a negative electrode active material layer containing magnesium; and a coating layer formed of a polymer material having magnesium ion conductivity and covering the negative electrode active material layer; and an electrolyte solution containing at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound. (2) The electrochemical device according to (1), in which the positive electrode has a positive electrode active material layer containing a sulfur-containing material. (3) The electrochemical device according to (1) or (2), in which the coating layer contains polyvinylidene fluoride. (4) The electrochemical device according to any one of (1) to (3), in which the electrolyte solution contains anthracene as the polycyclic aromatic hydrocarbon compound. (5) The electrochemical device according to any one of (1) to (3), in which the electrolyte solution contains cyclooctatetraene as the annulene-based compound. (6) The electrochemical device according to any one of (1) to (5), in which the coating layer contains at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound.

[0091] REFERENCE SIGNS LIST 1, 50 Secondary battery 20 Battery element 21 Positive electrode lead 22 Negative electrode lead 30 Exterior member 30a, 30b Exterior sheet 31 Depression 32 Adhesive 200 Electrode body 210, 52 Positive electrode 211 Positive electrode current collector 212 Positive electrode active material layer 220, 51 Negative electrode 221 Negative electrode current collector 222 Negative electrode active material layer 223 Coating layer 230 Separator 240 Electrolyte layer

Claims

1. An electrochemical device comprising: a positive electrode; a negative electrode having a negative electrode active material layer containing magnesium; and a coating layer formed of a polymer material having magnesium ion conductivity and covering the negative electrode active material layer; and an electrolyte solution containing at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound.

2. The electrochemical device according to claim 1, wherein the positive electrode has a positive electrode active material layer containing a sulfur-containing material.

3. The electrochemical device according to claim 1 or 2, wherein the coating layer contains polyvinylidene fluoride.

4. The electrochemical device according to any one of claims 1 to 3, wherein the electrolyte solution contains anthracene as the polycyclic aromatic hydrocarbon compound.

5. The electrochemical device according to any one of claims 1 to 3, wherein the electrolyte solution contains cyclooctatetraene as the annulene-based compound.

6. The electrochemical device according to any one of claims 1 to 5, wherein the coating layer contains at least one of a polycyclic aromatic hydrocarbon compound and an annulene-based compound.

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