Secondary batteries

Abstract

This secondary battery comprises a positive electrode, a negative electrode including a magnesium-containing material, and an electrolytic solution including anthracene and 9,10-dihydroanthracene. The ratio of the 9,10-dihydroanthracene content in the electrolytic solution to the anthracene content in the electrolytic solution is 0.03 or less. The overvoltage expressed by equation (1) is 0.22 V or less.　(1) E = E1 – E2 (E is an overvoltage (V) measured using a test secondary battery provided with a negative electrode as a test electrode and a nickel plate as a counter electrode. E1 is the open circuit voltage (V) when the test secondary battery is discharged at a current density of 0.1 mA / cm2 until the voltage reaches –2.0 V. E2 is the voltage (V) when the test secondary battery is charged at a current density of 0.1 mA / cm2 until the voltage reaches 2.5 V.

Description

[Technical Field]

[0001] This technology relates to secondary batteries. [Background technology]

[0002] With the widespread use of various electronic devices such as mobile phones, development of secondary batteries is progressing as a power source that is small, lightweight, and can achieve high energy density. Various studies are being conducted on the configuration of these secondary batteries.

[0003] Specifically, in the manufacturing process of secondary batteries using metallic magnesium as the negative electrode active material, the surface of the metallic magnesium is polished using abrasive paper. This removes the oxide film formed on the surface of the metallic magnesium, thereby activating the surface of the metallic magnesium (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Batteries Supercaps ,3 ,1239,2020 [Overview of the Initiative]

[0005] Although various studies have been conducted on the configuration of secondary batteries, their battery characteristics are still not satisfactory, and there is room for improvement.

[0006] There is a need for a secondary battery that can achieve excellent battery characteristics.

[0007] A secondary battery according to one embodiment of this technology comprises a positive electrode, a negative electrode containing a magnesium-containing material, and an electrolyte containing anthracene and 9,10-dihydroanthracene. The ratio of the content of 9,10-dihydroanthracene in the electrolyte to the content of anthracene in the electrolyte is 0.03 or less. The overpotential expressed by formula (1) is 0.22V or less.

[0008] E = E1 - E2 ... (1) (E is the overvoltage (V) measured using a test secondary battery equipped with a negative electrode as the test electrode and a nickel plate as the counter electrode. E1 is 0.1 mA / cm 2 This is the open-circuit voltage (V) when the test secondary battery is discharged until the voltage reaches -2.0V at a current density of 0.1mA / cm². 2 This is the voltage (V) obtained when the test secondary battery was charged to 2.5V at the given current density.

[0009] The "magnesium-containing materials" mentioned above are materials that contain magnesium as a constituent element. Further details regarding magnesium-containing materials will be provided later.

[0010] As mentioned above, "overvoltage" is measured using a test secondary battery (a so-called half-cell) equipped with a test electrode (negative electrode) and a counter electrode (nickel plate), instead of a secondary battery equipped with a positive and negative electrode. Details regarding the configuration of the test secondary battery and the procedure for calculating overvoltage will be described later.

[0011] When calculating the "ratio," a secondary battery equipped with a positive electrode and a negative electrode may be used, or a test secondary battery equipped with the test electrode and counter electrode described above may be used. Details of the procedure for calculating the ratio will be described later.

[0012] In one embodiment of this technology, the secondary battery has a negative electrode containing a magnesium-containing material, and the electrolyte contains anthracene and 9,10-dihydroanthracene. The ratio of the 9,10-dihydroanthracene content in the electrolyte to the anthracene content is 0.03 or less, and the overvoltage shown in formula (1) is 0.22V or less, thus providing excellent battery characteristics.

[0013] Furthermore, the effects of this technology are not necessarily limited to those described herein, but may include any of the series of effects related to this technology described later.

Brief Description of Drawings

[0014] [Figure 1] It is a perspective view showing the configuration of a secondary battery in one embodiment of the present technology. [Figure 2] It is a cross-sectional view showing the configuration of the battery element shown in FIG. 1. [Figure 3] It is a cross-sectional view showing the configuration of a test secondary battery.

Modes for Carrying Out the Invention

[0015] Hereinafter, with respect to one embodiment of the present technology, it will be described in detail while referring to the drawings. The order of description is as follows. 1. Secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Action and effect 2. Applications of secondary batteries

[0016] <1. Secondary battery> First, a secondary battery according to one embodiment of the present technology will be described.

[0017] The secondary battery described here is a secondary battery in which a charge / discharge reaction proceeds by utilizing the precipitation and dissolution of magnesium, that is, a so-called magnesium secondary battery. In this secondary battery, magnesium is precipitated and dissolved at the negative electrode, and magnesium is occluded and released in an ionic state at the positive electrode.

[0018] <1-1. Configuration> FIG. 1 shows the perspective configuration of the secondary battery, and FIG. 2 shows the cross-sectional configuration of the battery element 20 shown in FIG. 1. However, in FIG. 1, a state where the exterior film 10 and the battery element 20 are separated from each other is shown, and a cross-section of the battery element 20 along the XZ plane is shown by a broken line.

[0019] As shown in Figures 1 and 2, this secondary battery comprises an outer film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42.

[0020] The secondary battery described here, as mentioned above, uses a flexible or pliable outer film 10 as an outer component, and is therefore a so-called laminate film type secondary battery.

[0021] [Exterior film] As shown in Figure 1, the outer film 10 has a bag-like structure that is sealed with the battery element 20 housed inside. Thus, the outer film 10 houses the positive electrode 21, negative electrode 22, separator 23, and electrolyte, which will be described later.

[0022] Here, the outer film 10 is a single film-like component that is folded in the folding direction F. The outer film 10 is provided with a recessed portion 10U (a so-called deep-drawn portion) for housing the battery element 20.

[0023] Specifically, the outer film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside out. When the outer film 10 is folded, the outer edges of the opposing fusion layers are fused together. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metallic material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0024] However, the composition (number of layers) of the outer film 10 is not particularly limited; it may consist of one or two layers, or four or more layers.

[0025] [Battery element] The battery element 20 is a power generation element housed inside the outer film 10. As shown in Figures 1 and 2, this battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0026] Here, the battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are wound around a winding axis P, facing each other via a separator 23. This winding axis P is a virtual axis extending in the Y-axis direction, as shown in Figure 1.

[0027] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 has a flattened three-dimensional shape, the shape of the cross-section of the battery element 20 intersecting the winding axis P (cross-section along the XZ plane) is a flattened shape defined by the major axis J1 and the minor axis J2.

[0028] The major axis J1 is a virtual axis extending in the X-axis direction and has a length greater than the length of the minor axis J2. The minor axis J2 is a virtual axis extending in the Z-axis direction intersecting the X-axis direction and has a length less than the length of the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flattened cylinder, the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape.

[0029] (positive electrode) As shown in Figure 2, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0030] The positive electrode current collector 21A is a conductive support 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. This positive electrode current collector 21A contains a conductive material such as a metal material, a specific example of which is aluminum.

[0031] The positive electrode active material layer 21B is supported by the positive electrode current collector 21A and contains one or more types of positive electrode active materials that intercalate and deintercalate magnesium. However, the positive electrode active material layer 21B may further contain one or more types of other materials such as positive electrode binders and positive electrode conductive agents.

[0032] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, it is one or more of the following methods, such as coating.

[0033] The type of positive electrode active material is not particularly limited, as long as it is a material that intercalates and deintercalates magnesium. Specifically, positive electrode active materials include sulfur, graphite fluoride, metal oxides, and metal halides. Each of the metal oxides and metal halides contains one or more of the following metallic elements as constituent elements: scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc.

[0034] The positive electrode binder contains one or more resin materials, such as fluororesins, polyvinyl alcohol-based resins, and styrene-butadiene copolymer rubber. Specific examples of fluororesins include polyvinylidene fluoride and polytetrafluoroethylene.

[0035] The positive electrode binder may also be a conductive polymer compound. Specific examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene, and copolymers of two or more of these may also be used. This conductive polymer compound may be unsubstituted or substituted with any one or more functional groups.

[0036] The positive electrode conductive agent contains one or more conductive materials, such as carbon materials, metallic materials, and conductive polymer compounds.

[0037] Specific examples of carbon materials include graphite (natural graphite and artificial graphite), carbon fibers, carbon black, and carbon nanotubes. Carbon fibers include vapor-grown carbon fibers (VGCF), etc. Carbon black includes acetylene black and Ketjen black, etc. Carbon nanotubes include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and multi-walled carbon nanotubes include double-walled carbon nanotubes (DWCNTs), etc. Specific examples of metallic materials include nickel, etc.

[0038] (Negative electrode) The negative electrode 22 contains one or more of the magnesium-containing materials that are negative electrode active materials, and as described above, these magnesium-containing materials are materials that contain magnesium as a constituent element.

[0039] This magnesium-containing material may be elemental magnesium (so-called metallic magnesium), a magnesium alloy, a magnesium compound, or a mixture of two or more of these. The purity of the metallic magnesium is not particularly limited, and it may contain any amount of impurities.

[0040] The types of metallic elements (excluding magnesium) included as constituent elements in a magnesium alloy are not particularly limited, as long as they are any one or more of the available metallic elements. Magnesium compounds contain one or more nonmetallic elements such as carbon, oxygen, sulfur, and halogens as constituent elements, with specific examples of halogens including fluorine, chlorine, bromine, and iodine.

[0041] In particular, the negative electrode active material preferably contains metallic magnesium. This is because the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds sufficiently and stably. Figure 2 shows the case where the negative electrode 22 contains metallic magnesium. This metallic magnesium may be a magnesium plate or a magnesium foil.

[0042] Furthermore, if the magnesium-containing material includes either or both a magnesium alloy and / or a magnesium compound, the negative electrode 22 may have a configuration similar to that of the positive electrode 21. That is, although not specifically shown here, the negative electrode 22 may include a negative electrode current collector and a negative electrode active material layer.

[0043] The negative electrode current collector is a conductive support that supports the negative electrode active material layer and has a pair of surfaces on which the negative electrode active material layer is provided. This negative electrode current collector contains a conductive material such as a metal material, and a specific example of such a conductive material is nickel.

[0044] The negative electrode active material layer is supported by a negative electrode current collector and contains one or more magnesium-containing materials. However, the negative electrode active material layer may further contain one or more other materials such as a negative electrode binder and a negative electrode conductive agent.

[0045] The negative electrode active material layer may be provided on both sides of the negative electrode current collector, or on only one side of the negative electrode current collector. The method for forming the negative electrode active material layer is not particularly limited, but specifically, it may be one or more of the following methods, such as coating.

[0046] Details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and details regarding the negative electrode conductivity are the same as those regarding the positive electrode conductive agent.

[0047] (Separator) As shown in Figure 2, the separator 23 is an insulating porous membrane interposed between the positive electrode 21 and the negative electrode 22, allowing magnesium to pass through in an ionic state while preventing a short circuit between the positive electrode 21 and the negative electrode 22. This separator 23 contains a polymer compound such as polyethylene.

[0048] (electrolyte) The electrolyte is a liquid electrolyte and is impregnated into the positive electrode 21 and the separator 23, respectively. However, the electrolyte may also be impregnated into the negative electrode 22. This electrolyte contains a solvent, an electrolyte salt, and additives.

[0049] The solvent contains one or more non-aqueous solvents (organic solvents), and the electrolyte containing these non-aqueous solvents 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 contains an ether compound, because the electrolyte salt is sufficiently dissolved or dispersed.

[0050] This ether compound is a compound containing an ether bond (-O-). The ether compound may be linear or cyclic. Furthermore, the ether compound may contain one ether bond or two or more.

[0051] Specific examples of ether compounds include dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and tetrahydrofuran. Some of the specific examples described here are so-called glyme ethers.

[0052] Electrolyte salts contain one or more types of magnesium salts. Specific examples of magnesium salts include magnesium chloride (MgCl2), magnesium perchlorate (Mg(ClO4)2), magnesium nitrate (Mg(NO3)2), magnesium sulfate (MgSO4), magnesium acetate (Mg(CH3COO)2), magnesium trifluoroacetate (Mg(CF3COO)2), magnesium tetrafluoroborate (Mg(BF4)2), magnesium tetraphenylborate (Mg(B(C6H5)4)2), magnesium hexafluorophosphate (Mg(PF6)2), magnesium hexafluoroarsenate (Mg(AsF6)2), and bis(trifluoromethanesulfonyl)imidomagnesium (Mg[N(CF3SO2)2]2).

[0053] The content (mol / kg) of electrolyte salt (magnesium salt) in the electrolyte solution is not particularly limited and can be set arbitrarily. The electrolyte salt content described here is the content of the electrolyte salt relative to the solvent.

[0054] The additives include anthracene and 9,10-dihydroanthracene. The reason the additives include anthracene is that it significantly improves the electrochemical activity of the electrolyte, even if the electrolyte contains an electrolyte salt (magnesium salt).

[0055] More specifically, even if the electrolyte contains magnesium salts, if it does not contain anthracene, sufficient electrochemical activity cannot be obtained in that electrolyte, and in some cases, no electrochemical activity can be obtained at all.

[0056] In contrast, when the electrolyte contains anthracene along with a magnesium salt, the structure of the magnesium complex formed from the magnesium salt changes appropriately, and the solubility of magnesium also changes appropriately. As a result, the electrochemical properties of the electrolyte are improved, and excellent electrochemical activity can be obtained in the electrolyte.

[0057] Furthermore, while anthracene improves the electrochemical activity of the electrolyte as described above, 9,10-dihydroanthracene is formed as a result of the reaction of anthracene on the surface of the negative electrode 22 (magnesium-containing material). In other words, 9,10-dihydroanthracene is a reactant formed due to the presence of a highly reactive magnesium-containing material, and more specifically, it is a compound that is unintentionally formed in response to the deactivation of anthracene.

[0058] Here, as mentioned above, anthracene plays the role of improving the electrochemical activity of the electrolyte. In contrast, 9,10-dihydroanthracene, as mentioned above, is a compound that is unintentionally formed in response to the deactivation of anthracene, and therefore does not play the role of improving the electrochemical activity of the electrolyte.

[0059] Therefore, as will be described later, in the secondary battery manufacturing process, after assembling the secondary battery, a pre-charge / discharge treatment is performed on the secondary battery to suppress the reaction in which 9,10-dihydroanthracene is formed in response to the deactivation of anthracene, that is, the reaction in which anthracene is converted to 9,10-dihydroanthracene. As a result, the content of 9,10-dihydroanthracene in the electrolyte is sufficiently large compared to the content of anthracene in the electrolyte.

[0060] Specifically, the content ratio C, which is the ratio of the content of 9,10-dihydroanthracene C2 (weight%) in the electrolyte to the content of anthracene C1 (weight%) in the electrolyte, is 0.03 or less. This is because the content C1 is ensured, making it easier for anthracene to stably and continuously exert its function of improving the electrochemical activity of the electrolyte. This content ratio C is calculated based on the formula C = (C2 / C1) × 100.

[0061] The lower limit of the content ratio C is not particularly limited. Therefore, the content ratio C may be 0 or greater than 0, as long as it is 0.03 or less.

[0062] The procedure for calculating the content ratio C is as follows: First, the electrolyte is recovered by disassembling the secondary battery. Next, the content of C1 and C2 is measured by analyzing the electrolyte using a gas chromatograph-mass spectrometer (GC-MS). Finally, the content ratio C is calculated based on the calculation formula described above.

[0063] When calculating the content ratio C, a secondary battery equipped with a positive electrode 21 and a negative electrode 22 may be used as described above, or a test secondary battery equipped with a test electrode 51 and a counter electrode 52, as described later, may be used.

[0064] [Positive lead] As shown in Figures 1 and 2, the positive electrode lead 31 is a positive electrode wire connected to the positive electrode current collector 21A of the positive electrode 21 and is led out to the outside of the outer film 10. This positive electrode lead 31 contains a conductive material such as a metal material, a specific example of which is aluminum. The shape of the positive electrode lead 31 is either a thin plate shape or a mesh shape.

[0065] [Negative lead] The negative electrode lead 32 is a negative electrode wire connected to the negative electrode 22, as shown in Figures 1 and 2, and is led out to the outside of the outer film 10. If the negative electrode 22 includes a negative electrode current collector, the negative electrode lead 32 is connected to the negative electrode current collector. Here, the direction of lead generation for the negative electrode lead 32 is the same as the direction of lead generation for the positive electrode lead 31. This negative electrode lead 32 contains a conductive material such as a metal, a specific example of which is copper. Details regarding the shape of the negative electrode lead 32 are the same as those regarding the shape of the positive electrode lead 31.

[0066] [Sealing film] The sealing film 41 is inserted between the outer film 10 and the positive lead 31, and the sealing film 42 is inserted between the outer film 10 and the negative lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0067] The sealing film 41 is a sealing member that prevents outside air and other elements from entering the interior of the outer film 10. This sealing film 41 contains a polymer compound such as polyolefin that has good adhesion to the positive electrode lead 31, and a specific example of such a polymer compound is polypropylene.

[0068] The structure of the sealing film 42 is the same as that of the sealing film 41, except that it is a sealing member that adheres to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as a polyolefin that adheres to the negative electrode lead 32.

[0069] <1-2. Operation> This secondary battery operates as follows in the battery element 20.

[0070] [Operation during charging and discharging] During discharge, the magnesium-containing material dissolves at the negative electrode 22, causing magnesium to dissolve into the electrolyte, and this magnesium is absorbed at the positive electrode 21. Conversely, during charging, magnesium is released from the positive electrode 21 into the electrolyte, and this magnesium is deposited at the negative electrode 22.

[0071] [Overvoltage] In particular, in secondary batteries, as mentioned above, the content ratio C is 0.03 or less, which significantly improves the electrochemical activity of the electrolyte. As a result, the overvoltage E of the secondary battery is sufficiently low.

[0072] Figure 3 shows the cross-sectional configuration of a test secondary battery used to measure the overvoltage E, which is a so-called coin-type magnesium secondary battery. More specifically, the test secondary battery is a secondary battery (so-called half-cell) that has a negative electrode 22 as the test electrode 51 and a nickel plate instead of a positive electrode 21 as the counter electrode 52.

[0073] The following sections will describe the configuration of the test secondary battery, followed by a description of the range and calculation procedure for the overvoltage E.

[0074] As shown in Figure 3, this test secondary battery comprises a test electrode 51, a counter electrode 52, a separator 53, an outer cup 54, an outer can 55, a gasket 56, and an electrolyte (not shown).

[0075] The test electrode 51 is housed in an outer cup 54, and the counter electrode 52 is housed in an outer can 55. The test electrode 51 and the counter electrode 52 are stacked on top of each other via a separator 53, and the electrolyte is impregnated into the test electrode 51, the counter electrode 52, and the separator 53, respectively. The composition of the electrolyte is as described above. The outer cup 54 and the outer can 55 are crimped together via a gasket 56, so the test electrode 51, the counter electrode 52, and the separator 53 are sealed by the outer cup 54 and the outer can 55.

[0076] The configuration of the test electrode 51 is the same as that of the negative electrode 22. The counter electrode 52 is a nickel plate. The thickness of the nickel plate is not particularly limited and can be set arbitrarily. If the test electrode 51 includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is formed on one side of the negative electrode current collector and is positioned to face the counter electrode 52 via a separator 53.

[0077] The overvoltage E is measured using a test secondary battery. Specifically, the overvoltage E expressed by equation (1) is 0.22V or less, because the battery capacity increases.

[0078] E = E1 - E2 ... (1) (E is the overvoltage (V) measured using a test secondary battery equipped with a negative electrode 22 as the test electrode 51 and a nickel plate as the counter electrode 52. E1 is 0.1 mA / cm 2 This is the open-circuit voltage (V) when the test secondary battery is discharged until the voltage reaches -2.0V at a current density of 0.1mA / cm². 2This is the voltage (V) obtained when the test secondary battery was charged to 2.5V at the given current density.

[0079] The procedure for calculating the overvoltage E using a test secondary battery is as follows.

[0080] First, the voltage E1 of the test rechargeable battery is measured by discharging it. In this case, it is 0.1 mA / cm². 2 Discharge the test secondary battery at the specified current density until the voltage reaches -2.0V. However, if the voltage does not reach -2.0V during discharge, the discharge may be terminated when the battery capacity reaches 1mAh.

[0081] Next, the voltage E2 of the test rechargeable battery is measured by charging it. In this case, it is 0.1 mA / cm². 2 Charge the test rechargeable battery at the specified current density until the voltage reaches 2.5V.

[0082] Finally, the overvoltage E is calculated based on the formula shown in equation (1).

[0083] Furthermore, when investigating the overvoltage E of a secondary battery other than the test secondary battery (a secondary battery equipped with a test electrode 51 and a counter electrode 52), a test secondary battery will be fabricated using that secondary battery. In this case, the negative electrode 22 will be recovered by disassembling the secondary battery, and then the negative electrode 22 will be used as the test electrode 51 to fabricate the test secondary battery. Details of the procedure for fabricating the test secondary battery will be described later.

[0084] <1-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and negative electrode 22 are prepared according to the example procedure described below, and the electrolyte is prepared. Then, the secondary battery is assembled using the positive electrode 21, negative electrode 22, and electrolyte, and the assembled secondary battery is subjected to a pre-charge / discharge treatment.

[0085] The following section will explain the case where metallic magnesium is used as the magnesium-containing material.

[0086] [Fabrication of the positive electrode] First, a positive electrode mixture is prepared by mixing the positive electrode active material, positive electrode binder, and positive electrode conductive agent with each other. Next, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture to a solvent. This solvent may be an aqueous solvent or an organic solvent. Subsequently, a positive electrode active material layer 21B is formed by applying the positive electrode mixture slurry to both sides of the positive electrode current collector 21A. Finally, the positive electrode active material layer 21B may be compression-molded using a molding machine 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, a positive electrode 21 is produced by forming a positive electrode active material layer 21B on both sides of the positive electrode current collector 21A.

[0087] [Preparation of electrolyte solution] After adding the electrolyte salt to the solvent, an additive (anthracene) is added to the solvent. This disperses or dissolves the electrolyte salt and the additive in the solvent, thus preparing the electrolyte solution.

[0088] [Assembly of rechargeable batteries] First, prepare the negative electrode 22 (metallic magnesium). A magnesium plate is used as this metallic magnesium.

[0089] Next, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode 22 using a joining method such as welding.

[0090] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via the separator 23, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to form a wound body (not shown). Subsequently, the wound body is pressed using a press or the like to form a flattened shape. The wound body after this molding has the same configuration as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with electrolyte.

[0091] Next, after housing the wound body inside the recessed portion 10U, the outer film 10 (fusion layer / metal layer / surface protection layer) is folded so that the outer films 10 face each other. Subsequently, using an adhesive method such as heat fusion, the outer edges of two sides of the opposing fusion layers are joined together, thereby housing the wound body inside the bag-shaped outer film 10.

[0092] Finally, after injecting the electrolyte into the bag-shaped outer film 10, the outer edges of the remaining sides of the opposing fused layers are joined together using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the outer film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32.

[0093] As a result, the electrolyte is impregnated into the wound material, forming the battery element 20, which is a wound electrode body. Therefore, the battery element 20 is sealed inside the bag-shaped outer film 10, and the secondary battery is assembled.

[0094] [Pre-charging and discharging of secondary batteries] Pre-charge and discharge processing is performed using the assembled secondary battery. Various conditions such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions can be set arbitrarily.

[0095] The reason for performing the pre-charge / discharge treatment is that, compared to using polishing to activate the surface of the negative electrode 22 (magnesium-containing material), the oxide film formed on the surface of the negative electrode 22 is properly removed, thereby optimizing the surface condition of the negative electrode 22 after the removal of the oxide film. Further details of the reasons explained here will be described later.

[0096] This electrochemically stabilizes the state of the battery element 20, thus completing the secondary battery.

[0097] <1-4. Mechanism and Effects> In this secondary battery, the negative electrode 22 contains a magnesium-containing material, the electrolyte contains anthracene and 9,10-dihydroanthracene, the content ratio C is 0.03 or less, and the overvoltage E is 0.22V or less. Therefore, for the reasons explained below, excellent battery characteristics can be obtained.

[0098] In magnesium secondary batteries, which obtain battery capacity by utilizing the deposition and dissolution of magnesium, an oxide film is formed on the surface of the highly reactive negative electrode 22 (magnesium-containing material), which reduces the surface activity of the negative electrode 22. Therefore, it is necessary to remove the oxide film in order to improve the surface activity of the negative electrode 22.

[0099] One method for removing the oxide film is to physically polish the surface of the negative electrode 22 using abrasive paper during the manufacturing process of the secondary battery. However, when the surface of the negative electrode 22 is physically polished, the oxide film is removed excessively, resulting in excessive exposure of the highly reactive surface of the negative electrode 22.

[0100] When the surface of the highly reactive negative electrode 22 is excessively exposed, anthracene becomes more readily reactive on the surface of the negative electrode 22, making it easier for 9,10-dihydroanthracene derived from that anthracene to be formed.

[0101] In this case, the content ratio C increases, more specifically, C becomes greater than 0.03, which reduces the electrochemical activity of the electrolyte. As a result, the overvoltage E increases, more specifically, E becomes greater than 0.22V, which reduces the battery capacity. Therefore, it becomes difficult to obtain excellent battery characteristics.

[0102] In contrast, as a method for removing the oxide film, as described above, if a pre-charge / discharge treatment is performed on the assembled secondary battery during the secondary battery manufacturing process, the surface of the negative electrode 22 is electrochemically treated, and the oxide film is electrochemically removed. In this case, unlike when the polishing treatment described above is used, the oxide film is properly removed, and the surface condition of the highly reactive negative electrode 22 is optimized.

[0103] When the surface state of the highly reactive negative electrode 22 is optimized, anthracene becomes less reactive on the surface of the negative electrode 22, making it less likely for 9,10-dihydroanthracene derived from that anthracene to form.

[0104] In this case, the content ratio C decreases, more specifically, to 0.03 or less, which improves the electrochemical activity of the electrolyte. As a result, the overvoltage E decreases, more specifically, to 0.22V or less, which increases the battery capacity. Therefore, excellent battery characteristics can be obtained.

[0105] In this case, advantages can be obtained, particularly from the perspectives described below.

[0106] Firstly, using a complex polishing process complicates the manufacturing process of secondary batteries. In contrast, using a pre-charge / discharge process only requires a simple process of charging and discharging the assembled secondary battery. Therefore, by using a pre-charge / discharge process, secondary batteries with superior battery characteristics can be easily realized.

[0107] Secondly, when polishing is used, the surface of the negative electrode 22 must be physically treated in advance during the manufacturing process of the secondary battery, which reduces the manufacturing efficiency of the secondary battery. In contrast, when pre-charge / discharge treatment is used, only electrochemical treatment of the assembled secondary battery is required. Therefore, by using pre-charge / discharge treatment, it is possible to efficiently realize a secondary battery with excellent battery characteristics.

[0108] Thirdly, when polishing is used, the degree of polishing tends to vary. In contrast, when pre-charge / discharge treatment is used, the degree of pre-charge / discharge treatment tends to vary less. Therefore, by using pre-charge / discharge treatment, it is possible to stably realize secondary batteries with excellent battery characteristics.

[0109] Fourth, when using polishing, metallic magnesium powder, a highly flammable and hazardous material, is generated. In contrast, when using pre-charge / discharge processing, metallic magnesium powder is not generated. Therefore, by using pre-charge / discharge processing, it is possible to safely realize secondary batteries with excellent battery characteristics.

[0110] In particular, if the magnesium-containing material contains metallic magnesium, the charge-discharge reaction utilizing the precipitation and dissolution of magnesium proceeds more readily and stably, thus yielding a higher effect.

[0111] Furthermore, if the secondary battery is a magnesium secondary battery, sufficient battery capacity can be obtained by utilizing the deposition and dissolution of magnesium, thus achieving a higher level of efficiency.

[0112] <2. Applications of rechargeable batteries> The uses (examples of applications) of secondary batteries are not particularly limited. Secondary batteries used as power sources may be the primary power source or the auxiliary power source in electronic devices and electric vehicles, etc. A primary power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of the primary power source, or a power source that can be switched from the primary power source.

[0113] Specific examples of secondary battery applications are described below: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and electric saws; battery packs installed in electronic devices; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household or industrial battery systems that store power in preparation for emergencies. In these applications, one secondary battery may be used, or multiple secondary batteries may be used.

[0114] The battery pack may use individual cells or a battery pack. An electric vehicle is a vehicle that runs using a secondary battery as a power source, and may also be a hybrid vehicle equipped with other power sources in addition to the secondary battery. In a household power storage system, the electricity stored in the secondary battery, which is the power storage source, can be used to power household electrical appliances, etc. [Examples]

[0115] An example of this technology will be described below.

[0116] <Example 1 and Comparative Examples 1-3> As explained below, after manufacturing the rechargeable batteries, their battery characteristics were evaluated.

[0117] [Manufacturing of secondary batteries] Here, a test secondary battery (a coin-type magnesium secondary battery) shown in Figure 3 was fabricated using the procedure described below.

[0118] First, a circular magnesium plate (diameter = 16 mm), which was the negative electrode 22 (magnesium-containing material), was prepared as the test electrode 51, and a circular nickel plate (diameter = 17 mm) was prepared as the counter electrode 52.

[0119] Next, electrolyte salts (lithium chloride and bis(trifluoromethanesulfonyl)imidomagnesium) and an additive (anthracene) were added to the solvent (diethylene glycol dimethyl ether, an ether compound), and the solvent was then stirred. This prepared the electrolyte.

[0120] In this case, the lithium chloride content in the electrolyte was set to 0.4 mol / kg, the bis(trifluoromethanesulfonyl)imido magnesium content in the electrolyte was set to 0.4 mol / kg, and the anthracene content in the electrolyte was set to 0.01 mol / kg.

[0121] Next, the counter electrode 52 was placed inside the outer container 55, and then two separators 53 were placed on top of the counter electrode 52. In this case, the first circular separator 53 (glass filter paper GC-50 manufactured by Advantec Co., Ltd., diameter = 19 mm) was placed on top of the counter electrode 52, and then the second circular separator 53 (glass filter paper GC-50 manufactured by Advantec Co., Ltd., diameter = 16 mm) was placed on top of the first separator 53.

[0122] Next, the electrolyte was dropped onto the two separators 53, thereby impregnating them with the electrolyte. In this case, the amount of electrolyte dropped was 200 μl (= 200 × 10 -6 dm 3 )

[0123] Next, the test electrode 51 was placed on top of the two separators 53, and then the outer cup 54 was placed on top of the test electrode 51.

[0124] Next, the outer cup 54 and outer can 55 were crimped together via a gasket 56 (polypropylene film). This sealed the test electrode 51 and counter electrode 52 within the outer cup 54 and outer can 55, thus assembling the test secondary battery.

[0125] Finally, after leaving the assembled test secondary battery to stand (standing time = 48 hours), pre-charge and discharge treatment (number of charge and discharge cycles = 1) of the test secondary battery was performed. In this case, the test secondary battery was discharged at a current density of 0.1 mA / cm 2 until the voltage reached -2.0 V, and then the test secondary battery was charged at a current density of 0.1 mA / cm 2 until the voltage reached 2.5 V. Thereby, the test secondary battery was completed (Example 1).

[0126] For comparison, a series of test secondary batteries described below were fabricated.

[0127] First, a test secondary battery was fabricated by the same procedure except that pre-charge and discharge treatment was not performed (Comparative Example 1).

[0128] Second, a test secondary battery was fabricated by the same procedure except that polishing treatment was performed instead of pre-charge and discharge treatment (Comparative Example 2). In this case, when preparing the test electrode 51, the surface of the test electrode 51 (magnesium plate) was artificially polished (polishing time = 5 minutes) using a lapping film sheet (#600) until a metallic luster was obtained.

[0129] Third, a test secondary battery was fabricated by the same procedure except that further polishing treatment was performed (Comparative Example 3). The procedure for the polishing treatment is as described above.

[0130] After completion of the test secondary battery, the content ratio C and the overvoltage E (V) were examined, and the results shown in Table 1 were obtained. The calculation procedures for the content ratio C and the overvoltage E are as described above.

[0131] [Evaluation of Battery Characteristics] When evaluating the operating characteristics as battery characteristics, the results shown in Table 1 were obtained.

[0132] (Operating Characteristics) The battery capacity (mAh) of a test secondary battery was measured by repeatedly charging and discharging it in a room temperature environment (temperature = 23°C) until a short circuit occurred. The cumulative capacity (mAh), an index for evaluating operating characteristics, was then calculated. This cumulative capacity was calculated by accumulating the battery capacity obtained until the test secondary battery short-circuited. The charging and discharging conditions were the same as those used during the pre-charging and discharging process described above.

[0133] [Table 1]

[0134] [Consideration] As shown in Table 1, the cumulative capacity varied depending on the content ratio C and the overvoltage E.

[0135] Specifically, because neither polishing nor pre-charge / discharge treatment was performed, the content ratio C was 0.03 or less, but when the overvoltage E was greater than 0.22V (Comparative Example 1), it was not possible to charge or discharge the test secondary battery, and therefore the cumulative capacity could not be obtained.

[0136] Furthermore, because polishing was performed instead of pre-charge / discharge treatment, the cumulative capacity decreased when the content ratio C was greater than 0.03 and the overvoltage E was greater than 0.22V (Comparative Example 2).

[0137] Furthermore, because both polishing and pre-charge / discharge treatments were performed, the cumulative capacity decreased significantly when the content ratio C was greater than 0.03 and the overvoltage E was greater than 0.22V (Comparative Example 3).

[0138] In contrast, when a pre-charge / discharge treatment was performed instead of polishing, the cumulative capacity increased significantly when the content ratio C was 0.03 or less and the overvoltage E was 0.22V or less (Example 1).

[0139] [summary] As shown in Table 1, when the negative electrode 22 contains a magnesium-containing material, the electrolyte contains anthracene and 9,10-dihydroanthracene, the content ratio C is 0.03 or less, and the overvoltage E is 0.22V or less, a high integrated capacity was obtained. Therefore, the operating characteristics were improved, resulting in excellent battery characteristics for the secondary battery.

[0140] Although the present technology has been described above with reference to one embodiment and one example, the configuration of the present technology is not limited to the configuration described in the one embodiment and one example, and can be modified in various ways.

[0141] Specifically, the explanation focused on cases where the battery structure of the rechargeable battery is laminate film type and coin type. However, the battery structure of the rechargeable battery is not particularly limited, and cylindrical, rectangular, and button-type batteries are also acceptable.

[0142] Furthermore, the case where the element structure of the battery element is of the wound type has been explained. However, the element structure of the battery element is not particularly limited, and may also be of the stacked type or the zigzag type. In the stacked type, the positive electrode and the negative electrode are stacked on top of each other, and in the zigzag type, the positive electrode and the negative electrode are folded in a zigzag pattern.

[0143] The effects described herein are illustrative only, and therefore the effects of this technology are not limited to those described herein. Accordingly, other effects may be obtained with respect to this technology.

[0144] Furthermore, this technology can also be configured as follows: <1> Positive electrode and, A negative electrode containing a magnesium-containing material, An electrolyte containing anthracene and 9,10-dihydroanthracene Equipped with, The ratio of the content of 9,10-dihydroanthracene in the electrolyte to the content of anthracene in the electrolyte is 0.03 or less. The overvoltage expressed by equation (1) is 0.22V or less. Secondary battery. E = E1 - E2 ... (1) (E is the overvoltage (V) measured using a test secondary battery equipped with a negative electrode as the test electrode and a nickel plate as the counter electrode. E1 is 0.1 mA / cm 2 This is the open-circuit voltage (V) when the test secondary battery is discharged until the voltage reaches -2.0V at a current density of 0.1mA / cm². 2 This is the voltage (V) obtained when the test secondary battery was charged to 2.5V at the given current density. <2> The magnesium-containing material includes metallic magnesium. <1> The secondary battery described above. <3> It is a magnesium secondary battery. <1> or <2> The secondary battery described above.

Claims

1. Positive electrode and, A negative electrode containing a magnesium-containing material, An electrolyte containing at least anthracene and Equipped with, The electrolyte contains 9,10-dihydroanthracene in such a ratio that the ratio of the content of 9,10-dihydroanthracene in the electrolyte to the content of anthracene in the electrolyte is 0 or more and 0.03 or less. The overvoltage expressed by equation (1) is 0.22V or less. Secondary battery. E=E1-E2...(1) (E is the overvoltage (V) measured using a test secondary battery equipped with a negative electrode as the test electrode and a nickel plate as the counter electrode. E1 is 0.1 mA / cm) 2 This is the open-circuit voltage (V) when the test secondary battery is discharged until the voltage reaches -2.0V at the given current density. E2 is 0.1 mA / cm². 2 This is the voltage (V) when the test secondary battery was charged to 2.5V at the given current density.

2. The magnesium-containing material includes metallic magnesium. The secondary battery according to claim 1.

3. It is a magnesium secondary battery. A secondary battery according to claim 1 or claim 2.

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