Secondary battery

Abstract

A secondary battery is provided with a positive electrode, a negative electrode containing a magnesium-containing material, and an electrolyte solution 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 overvoltage represented by formula (1) is 0.22 V or less. E = E1-E2... (1) (E is an overvoltage (V) measured using a test secondary battery having a negative electrode as a test electrode and a nickel plate as a counter electrode, E1 is an 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, and E2 is a 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] The present technology relates to a secondary battery. Background Art

[0002] As various electronic devices such as mobile phones are becoming widespread, secondary batteries are being developed as power sources that are small and lightweight and have high energy density, and various studies have been conducted on the configuration of the secondary batteries.

[0003] Specifically, in the manufacturing process of a secondary battery using metal magnesium as a negative electrode active material, the surface of the metal magnesium is polished using polishing paper, thereby removing the oxide film formed on the surface of the metal magnesium, thereby activating the surface of the metal magnesium (for example, see Non-Patent Document 1).

[0004] Prior art literature

[0005] Non-patent literature

[0006] Non-patent literature 1: Batteries Supercaps, 3, 1239, 2020 Summary of the invention

[0007] Although various studies have been conducted on the configuration of secondary batteries, the battery characteristics of the secondary batteries are still insufficient and thus there is room for improvement.

[0008] A secondary battery capable of obtaining excellent battery characteristics is desired.

[0009] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode including a magnesium-containing material, and an electrolyte solution including anthracene and 9,10-dihydroanthracene. The ratio of the content of 9,10-dihydroanthracene in the electrolyte solution to the content of anthracene in the electrolyte solution is 0.03 or less. The overvoltage represented by formula (1) is 0.22 V or less.

[0010] E = E1 - E2 … (1)

[0011] (E is the overvoltage (V) measured using a test secondary battery having a negative electrode as a test electrode and a nickel plate as a counter electrode. E1 is at 0.1 mA / cm 2 The current density of the test secondary battery is used to discharge the test secondary battery until the voltage reaches -2.0V. The open circuit voltage (V) of E2 is 0.1mA / cm 2 The voltage (V) at which the test secondary battery is charged to a voltage of 2.5 V at a current density of 1.5 V.

[0012] The above-mentioned "magnesium-containing material" is a material containing magnesium as a constituent element. In addition, the details of the magnesium-containing material will be described below.

[0013] As described above, the "overvoltage" is measured by using a test secondary battery (so-called half-cell) having a test electrode (negative electrode) and a counter electrode (nickel plate) instead of a secondary battery having a positive electrode and a negative electrode. In addition, the details of the structure of the test secondary battery and the calculation procedure of the overvoltage will be described below.

[0014] When calculating the "ratio", a secondary battery having a positive electrode and a negative electrode may be used, or a test secondary battery having the test electrode and a counter electrode may be used. The details of the calculation procedure of the ratio will be described below.

[0015] A negative electrode of a secondary battery according to an embodiment of the present technology includes a magnesium-containing material, an electrolyte includes anthracene and 9,10-dihydroanthracene, a ratio of the content of 9,10-dihydroanthracene in the electrolyte to the content of anthracene in the electrolyte is 0.03 or less, and an overvoltage represented by formula (1) is 0.22 V or less, thereby achieving excellent battery characteristics.

[0016] In addition, the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0018] Figure 2 It is shown Figure 1 A cross-sectional view showing the structure of a battery element.

[0019] Figure 3 It is a cross-sectional view showing the structure of a test secondary battery. DETAILED DESCRIPTION

[0020] Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. In addition, the order of description is as follows.

[0021] 1. Secondary battery

[0022] 1-1. Composition

[0023] 1-2. Action

[0024] 1-3. Manufacturing method

[0025] 1-4. Function and effect

[0026] 2. Uses of secondary batteries

[0027] <1. Secondary batteries>

[0028] First, a secondary battery according to an embodiment of the present technology will be described.

[0029] The secondary battery described here is a secondary battery that utilizes the precipitation and dissolution of magnesium to perform charge and discharge reactions, and is a so-called magnesium secondary battery. In this secondary battery, magnesium precipitates and dissolves in the negative electrode, and magnesium is inserted and released in the positive electrode in an ionic state.

[0030] <1-1. Structure>

[0031] Figure 1 The three-dimensional structure of the secondary battery is shown, and Figure 2 Shows Figure 1 The cross-sectional structure of the battery element 20 shown in FIG. Figure 1 , the exterior film 10 and the battery element 20 are shown in a state where they are separated from each other, and a cross section of the battery element 20 along the XZ plane is shown by a dotted line.

[0032] like Figure 1 as well as Figure 2 As shown, the 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 , 42 .

[0033] As described above, the secondary battery described here uses the flexible or pliable exterior film 10 as an exterior member, and is therefore a so-called laminated film type secondary battery.

[0034] [Exterior film]

[0035] like Figure 1 As shown, the outer film 10 has a bag-like structure that is sealed with the battery element 20 stored therein. Thus, the outer film 10 stores a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte solution, which will be described later.

[0036] Here, the exterior film 10 is a sheet of film-shaped member, and is folded in the folding direction F. The exterior film 10 is provided with a recessed portion 10U (so-called deep-drawn portion) for accommodating the battery element 20 .

[0037] Specifically, the exterior film 10 is a three-layer laminated film in which a welding layer, a metal layer, and a surface protection layer are sequentially stacked from the inside, and when the exterior film 10 is folded, the outer peripheral edges of the welding layers facing each other are welded to each other. The welding 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.

[0038] 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.

[0039] [Battery components]

[0040] The battery element 20 is a power generation element housed inside the outer film 10. Figure 1 as well as Figure 2 As shown, the battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23 and an electrolyte (not shown).

[0041] Here, the battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are opposed to each other with the separator 23 interposed therebetween, and are wound around a winding axis P as the center. Figure 1 As shown, the winding axis P is a virtual axis extending in the Y-axis direction.

[0042] The three-dimensional shape of the battery element 20 is not particularly limited. Here, the battery element 20 has a flat three-dimensional shape, so the cross section of the battery element 20 intersecting the winding axis P (cross section along the XZ plane) is a flat shape defined by the major axis J1 and the minor axis J2.

[0043] 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 flat cylindrical shape, and therefore the cross-sectional shape of the battery element 20 is a flat, substantially elliptical shape.

[0044] (positive electrode)

[0045] like Figure 2 As shown, the positive electrode 21 includes a positive electrode collector 21A and a positive electrode active material layer 21B.

[0046] The positive electrode current collector 21A is a conductive support for supporting the positive electrode active material layer 21B, and has a pair of surfaces provided with the positive electrode active material layer 21B. The positive electrode current collector 21A includes a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

[0047] The positive electrode active material layer 21B is supported by the positive electrode current collector 21A and contains one or more positive electrode active materials that intercalate and deintercalate magnesium. However, the positive electrode active material layer 21B may also contain one or more other materials such as a positive electrode binder and a positive electrode conductor.

[0048] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode collector 21A. The method for forming the positive electrode active material layer 21B is not particularly limited, and specifically, any one or more of coating methods are used.

[0049] The type of positive electrode active material is not particularly limited as long as it is a material that intercalates and deintercalates magnesium. Specifically, the positive electrode active material is sulfur, graphite fluoride, metal oxides, and metal halides. The metal oxides and metal halides contain any one or two or more of metal elements such as scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc as constituent elements.

[0050] The positive electrode binder includes any one or two or more of resin materials such as fluorine-based resin, polyvinyl alcohol-based resin, and styrene-butadiene copolymer rubber. Specific examples of fluorine-based resins include polyvinylidene fluoride and polytetrafluoroethylene.

[0051] In addition, the positive electrode binder may also be a conductive polymer compound. Specific examples of the conductive polymer compound are polyaniline, polypyrrole, and polythiophene, etc., or a copolymer of two or more thereof. The conductive polymer compound may be unsubstituted or substituted with any one or more functional groups.

[0052] The positive electrode conductive agent includes any one or two or more of conductive materials such as carbon materials, metal materials, and conductive polymer compounds.

[0053] Specific examples of carbon materials include graphite (natural graphite and artificial graphite), carbon fiber, carbon black, and carbon nanotubes. Carbon fiber includes vapor grown carbon fiber (VGCF), etc. Carbon black includes acetylene black and Ketjen black, etc. Carbon nanotubes include single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), etc. The multi-walled carbon nanotubes include double-walled carbon nanotubes (DWCNT), etc. Specific examples of metal materials include nickel, etc.

[0054] (negative electrode)

[0055] The negative electrode 22 contains any one or two or more of magnesium-containing materials as negative electrode active materials. As described above, the magnesium-containing material is a material containing magnesium as a constituent element.

[0056] The magnesium-containing material may be a single substance of magnesium (so-called metallic magnesium), a magnesium alloy, a magnesium compound, or a mixture of two or more thereof. In addition, the purity of the metallic magnesium is not particularly limited, so the metallic magnesium may contain any amount of impurities.

[0057] The type of metal element (except magnesium) contained as a constituent element in the magnesium alloy is not particularly limited as long as it is any one or two or more of any metal elements. The magnesium compound contains any one or two or more of non-metallic elements such as carbon, oxygen, sulfur and halogen as constituent elements, and specific examples of the halogen are fluorine, chlorine, bromine and iodine.

[0058] Among them, the negative electrode active material preferably contains metal magnesium. This is because the charge and discharge reaction using the precipitation and dissolution of magnesium is easy to proceed fully and stably. Figure 2 2 shows the case where the negative electrode 22 includes metal magnesium. The metal magnesium may be a magnesium plate or a magnesium foil.

[0059] In addition, when the magnesium-containing material includes one or both of a magnesium alloy and 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.

[0060] 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 disposed. The negative electrode current collector includes a conductive material such as a metal material, and a specific example of the conductive material is nickel.

[0061] The negative electrode active material layer is supported by the negative electrode current collector and contains any one or two or more of the magnesium-containing materials. However, the negative electrode active material layer may also contain any one or two or more of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0062] The negative electrode active material layer may be provided on both sides of the negative electrode current collector or only on one side of the negative electrode current collector. The method for forming the negative electrode active material layer is not particularly limited, and specifically, any one or more of coating methods and the like are used.

[0063] The details about the negative electrode binder are the same as those about the positive electrode binder, and the details about the negative electrode conductor are the same as those about the positive electrode conductor.

[0064] (Diaphragm)

[0065] like Figure 2 As shown, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and prevents a short circuit between the positive electrode 21 and the negative electrode 22 while allowing magnesium to pass therethrough in an ionic state. The separator 23 is made of a polymer compound such as polyethylene.

[0066] (Electrolyte)

[0067] The electrolytic solution is a liquid electrolyte, and is impregnated in each of the positive electrode 21 and the separator 23. However, the electrolytic solution may also be impregnated in the negative electrode 22. The electrolytic solution contains a solvent, an electrolyte salt, and an additive.

[0068] The solvent includes any one or more of non-aqueous solvents (organic solvents), and the electrolyte solution including the non-aqueous solvent is a so-called non-aqueous electrolyte solution. The type of the non-aqueous solvent is not particularly limited, and the non-aqueous solvent preferably includes an ether compound. This is because the electrolyte salt is fully dissolved or dispersed.

[0069] The ether compound is a compound containing an ether bond (-O-). In addition, the ether compound may be chain-shaped or cyclic. In addition, the number of ether bonds contained in the ether compound may be only one or more than two.

[0070] Specific examples of the ether compound are dimethoxyethane, diglyme, tetraglyme, tetrahydrofuran, etc. Some of the series of specific examples described here are so-called glyme-based ethers.

[0071] The electrolyte salt includes any one or more of magnesium salts. Specific examples of magnesium salts are 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 magnesium bis(trifluoromethanesulfonyl)imide (Mg[N(CF3SO2)2]2).

[0072] The content (mol / kg) of the electrolyte salt (magnesium salt) in the electrolytic solution is not particularly limited and can be arbitrarily set. The content of the electrolyte salt described here is the content of the electrolyte salt relative to the solvent.

[0073] The additive includes anthracene and 9,10-dihydroanthracene. The additive includes anthracene because the electrochemical activity of the electrolyte solution is greatly improved even if the electrolyte solution includes an electrolyte salt (magnesium salt).

[0074] Specifically, even if the electrolyte solution contains a magnesium salt, if anthracene is not contained, sufficient electrochemical activity cannot be obtained in the electrolyte solution, and in some cases, no electrochemical activity can be obtained in the electrolyte solution at all.

[0075] In contrast, if the electrolyte contains a magnesium salt and anthracene, the structure of the magnesium complex formed from the magnesium salt changes appropriately, and the solubility of magnesium changes appropriately. As a result, the electrochemical properties of the electrolyte are improved, and thus excellent electrochemical activity is obtained in the electrolyte.

[0076] In addition, as described above, anthracene increases the electrochemical activity of the electrolyte, whereas 9,10-dihydroanthracene is formed by the reaction of anthracene on the surface of the negative electrode 22 (magnesium-containing material). That is, 9,10-dihydroanthracene is a reactant formed by the presence of the highly reactive magnesium-containing material, and more specifically, is a compound that is unintentionally formed in response to the deactivation of anthracene.

[0077] Here, as described above, anthracene functions to increase the electrochemical activity of the electrolyte solution, whereas 9,10-dihydroanthracene is a compound that is unintentionally formed in response to the deactivation of anthracene, and therefore does not function to increase the electrochemical activity of the electrolyte solution, as described above.

[0078] Therefore, as described later, in the manufacturing process of the secondary battery, after assembling the secondary battery, the secondary battery is subjected to a pre-charge and discharge treatment to suppress the reaction of forming 9,10-dihydroanthracene corresponding to the deactivation of anthracene, that is, the reaction of anthracene changing into 9,10-dihydroanthracene. As a result, the content of 9,10-dihydroanthracene in the electrolyte becomes sufficiently large relative to the content of anthracene in the electrolyte.

[0079] Specifically, the ratio of the content C2 (weight %) of 9,10-dihydroanthracene in the electrolyte to the content C1 (weight %) of anthracene in the electrolyte, i.e., the content ratio C, is 0.03 or less. This is because, since the content C1 is ensured, anthracene can easily and stably and continuously play a role in improving the electrochemical activity of the electrolyte. The content ratio C is calculated based on the calculation formula C=(C2 / C1)×100.

[0080] The lower limit of the content ratio C is not particularly limited. Therefore, the content ratio C may be 0 or may be greater than 0 as long as it is 0.03 or less.

[0081] In addition, the calculation steps of the content ratio C are as follows. First, the electrolyte is recovered by disassembling the secondary battery. Then, the electrolyte is analyzed by using a gas chromatography-mass spectrometer (GC-MS) to measure the contents C1 and C2. Finally, the content ratio C is calculated based on the above calculation formula.

[0082] When calculating the content ratio C, as described above, a secondary battery including the positive electrode 21 and the negative electrode 22 may be used, or a test secondary battery including the test electrode 51 and the counter electrode 52 described later may be used.

[0083] [Positive lead]

[0084] like Figure 1 as well as Figure 2 As shown, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode collector 21A of the positive electrode 21, and is led out to the outside of the outer film 10. The positive electrode lead 31 includes a conductive material such as a metal material, and a specific example of the conductive material is aluminum, etc. In addition, the shape of the positive electrode lead 31 is any one of a thin plate shape and a mesh shape.

[0085] [Negative lead]

[0086] like Figure 1 as well as Figure 2As shown, the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode 22, and is led out to the outside of the outer film 10. In addition, when the negative electrode 22 includes a negative electrode collector, the negative electrode lead 32 is connected to the negative electrode collector. Here, the lead-out direction of the negative electrode lead 32 is the same as the lead-out direction of the positive electrode lead 31. The negative electrode lead 32 includes a conductive material such as a metal material, and a specific example of the conductive material is copper. In addition, the details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[0087] [Sealing film]

[0088] The sealing film 41 is inserted between the outer film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0089] The sealing film 41 is a sealing member that prevents outside air and the like from intruding into the interior of the exterior film 10. The sealing film 41 contains a polymer compound such as polyolefin having adhesion to the positive electrode lead 31, and a specific example of the polymer compound is polypropylene and the like.

[0090] The sealing film 42 has the same configuration as the sealing film 41 except that it is a sealing member having adhesion to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin having adhesion to the negative electrode lead 32.

[0091] <1-2. Action>

[0092] This secondary battery operates in the battery element 20 as follows.

[0093] [Charge and discharge operation]

[0094] During discharge, the magnesium-containing material dissolves in the negative electrode 22, so magnesium is dissolved in the electrolyte and the magnesium is intercalated in the positive electrode 21. On the other hand, during charge, magnesium is deintercalated from the positive electrode 21 into the electrolyte and the magnesium is precipitated in the negative electrode 22.

[0095] [Overvoltage]

[0096] In particular, in the secondary battery, as described above, the content ratio C is 0.03 or less, so the electrochemical activity of the electrolyte solution is sufficiently improved. As a result, the overvoltage E of the secondary battery becomes sufficiently small.

[0097] Figure 3The cross-sectional structure of a test secondary battery used to measure the overvoltage E is shown. The test secondary battery is a so-called coin-type magnesium secondary battery. More specifically, the test secondary battery is a secondary battery (so-called half-cell) having a negative electrode 22 as a test electrode 51 and a nickel plate as a counter electrode 52 instead of a positive electrode 21.

[0098] Before describing the configuration of the test secondary battery, the range and calculation procedure of the overvoltage E will be described below.

[0099] like Figure 3 As shown, the test secondary battery includes 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 solution (not shown).

[0100] 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 each other via a separator 53, and the electrolyte is impregnated in each of the test electrode 51, the counter electrode 52, and the separator 53. The electrolyte is configured as described above. The outer cup 54 and the outer can 55 are fastened to each other via a gasket 56, so that the test electrode 51, the counter electrode 52, and the separator 53 are sealed by the outer cup 54 and the outer can 55.

[0101] The test electrode 51 has the same structure as 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. In addition, when the test electrode 51 includes a negative electrode collector and a negative electrode active material layer, the negative electrode active material layer is formed on a single surface of the negative electrode collector, and the negative electrode active material layer is arranged in a manner opposite to the counter electrode 52 via a separator 53.

[0102] The overvoltage E was measured using a test secondary battery. Specifically, the overvoltage E represented by the formula (1) was 0.22 V or less. This is because the battery capacity increased.

[0103] E = E1 - E2 … (1)

[0104] (E is an overvoltage (V) measured using a test secondary battery having the negative electrode 22 as the test electrode 51 and a nickel plate as the counter electrode 52. E1 is an overvoltage (V) measured at 0.1 mA / cm 2 The current density of the test secondary battery is used to discharge the test secondary battery until the voltage reaches -2.0V. The open circuit voltage (V) of E2 is 0.1mA / cm 2 The voltage (V) at which the test secondary battery is charged to a voltage of 2.5 V at a current density of 1.5 V.

[0105] The calculation procedure of the overvoltage E using the test secondary battery is as follows.

[0106] First, the test secondary battery is discharged to measure the voltage E1 of the test secondary battery. In this case, the voltage E1 of the test secondary battery is measured at 0.1 mA / cm 2 The test secondary battery was discharged at a current density of 200 MHz until the voltage reached -2.0 V. However, if the voltage did not reach -2.0 V during discharge, the discharge may be terminated when the battery capacity reached 1 mAh.

[0107] Next, the test secondary battery was charged to measure the voltage E2 of the test secondary battery. In this case, the voltage E2 of the test secondary battery was measured at 0.1 mA / cm 2 The test secondary battery was charged at a current density of 2.5 V until the voltage reached 2.5 V.

[0108] Finally, the overvoltage E is calculated based on the calculation formula shown in formula (1).

[0109] In addition, when a secondary battery (a secondary battery having a positive electrode 21 and a negative electrode 22) other than a test secondary battery (a secondary battery having a test electrode 51 and a counter electrode 52) is obtained to investigate the overvoltage E of the secondary battery, the test secondary battery is prepared using the secondary battery. In this case, after the negative electrode 22 is recovered by disassembling the secondary battery, the negative electrode 22 is used as the test electrode 51 to prepare the test secondary battery. The details of the preparation steps of the test secondary battery will be described below.

[0110] <1-3. Manufacturing method>

[0111] When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are prepared by the following steps, and after preparing an electrolyte, the secondary battery is assembled using the positive electrode 21, the negative electrode 22 and the electrolyte, and the assembled secondary battery is subjected to a preliminary charge and discharge process.

[0112] Hereinafter, a case where metallic magnesium is used as the magnesium-containing material will be described.

[0113] [Production of positive electrode]

[0114] First, a positive electrode mixture is prepared by mixing a positive electrode active material, a positive electrode binder and a positive electrode conductive agent. Next, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture into a solvent. The solvent can be an aqueous solvent or an organic solvent. Next, the positive electrode mixture slurry is applied to both sides of the positive electrode collector 21A to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B can also be compression-formed using a forming machine such as a roller press. In this case, the positive electrode active material layer 21B can be heated or compression-formed repeatedly. Thus, the positive electrode active material layer 21B is formed on both sides of the positive electrode collector 21A, thereby producing the positive electrode 21.

[0115] [Preparation of electrolyte]

[0116] After the electrolyte salt is put into the solvent, the additive (anthracene) is added to the solvent, whereby the electrolyte salt and the additive are dispersed or dissolved in the solvent, respectively, to prepare an electrolytic solution.

[0117] [Assembly of secondary battery]

[0118] First, the negative electrode 22 (metal magnesium) is prepared. As the metal magnesium, a magnesium plate is used.

[0119] Next, the positive electrode lead 31 is connected to the positive electrode collector 21A of the positive electrode 21 by a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode 22 by a joining method such as welding.

[0120] Next, after the positive electrode 21 and the negative electrode 22 are stacked on each other with the separator 23 interposed therebetween, a wound body (not shown) is formed by winding the positive electrode 21, the negative electrode 22 and the separator 23. Next, the wound body is pressed by a press machine or the like to be formed into a flat shape. The wound body after forming has the same structure as the battery element 20 except that the positive electrode 21, the negative electrode 22 and the separator 23 are not impregnated with an electrolyte.

[0121] Next, after the wound body is housed in the recessed portion 10U, the outer film 10 (welding layer / metal layer / surface protection layer) is folded so that the outer films 10 face each other. Next, the wound body is housed in the bag-shaped outer film 10 by bonding the outer peripheral edges of the two sides of the opposing welding layers to each other using an adhesive method such as a heat welding method.

[0122] Finally, after the electrolyte is injected into the bag-shaped outer film 10, the outer peripheral edge portions of the remaining one side of the mutually opposed welded layers are bonded to each other using a bonding method such as a heat welding method. In this case, the sealing film 41 is inserted between the outer film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32.

[0123] As a result, the wound body is impregnated with the electrolyte solution, and the battery element 20 as a wound electrode body is formed. Therefore, the battery element 20 is sealed inside the bag-shaped exterior film 10, and the secondary battery is assembled.

[0124] [Preliminary charge and discharge process of secondary battery]

[0125] The assembled secondary battery is used for preliminary charge and discharge treatment. Various conditions such as ambient temperature, charge and discharge times (number of cycles), and charge and discharge conditions can be set arbitrarily.

[0126] The reason for performing the pre-charge and discharge treatment is that, compared with the case where the grinding treatment is used 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 appropriately removed, and thus the surface state of the negative electrode 22 after the oxide film is removed is optimized. The reasons for this will be described in detail below.

[0127] Thereby, the state of the battery element 20 is electrochemically stabilized, and a secondary battery is completed.

[0128] <1-4. Functions and effects>

[0129] According to the secondary battery, the negative electrode 22 includes a magnesium-containing material, the electrolyte includes anthracene and 9,10-dihydroanthracene, the content ratio C is 0.03 or less, and the overvoltage E is 0.22 V or less. Therefore, excellent battery characteristics can be obtained for the reasons described below.

[0130] In a magnesium secondary battery that obtains battery capacity by precipitation 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, in order to improve the surface activity of the negative electrode 22, the oxide film needs to be removed.

[0131] As a method for removing the oxide film, a method of removing the oxide film by physically grinding the surface of the negative electrode 22 using grinding paper in the manufacturing process of the secondary battery can be considered. However, if the surface of the negative electrode 22 is physically ground, the oxide film is excessively removed, so that the surface of the negative electrode 22 with high reactivity is excessively exposed.

[0132] If the surface of the negative electrode 22 having high reactivity is excessively exposed, anthracene is likely to react on the surface of the negative electrode 22 , and thus 9,10-dihydroanthracene is likely to be formed from the anthracene.

[0133] In this case, the content ratio C becomes larger, more specifically, the content ratio C is greater than 0.03, so the electrochemical activity of the electrolyte decreases. As a result, the overvoltage E becomes larger, more specifically, the overvoltage E is greater than 0.22 V, so the battery capacity decreases. Therefore, it is difficult to obtain excellent battery characteristics.

[0134] In contrast, as a method for removing the oxide film, as described above, if the pre-charge and discharge treatment of the assembled secondary battery is performed in the manufacturing process of the secondary battery, the surface of the negative electrode 22 is electrochemically treated, so the oxide film is electrochemically removed. In this case, unlike the case of using the above-mentioned grinding treatment, the oxide film is appropriately removed, so the surface state of the negative electrode 22 having high reactivity is optimized.

[0135] If the surface state of the negative electrode 22 having high reactivity is optimized, anthracene is unlikely to react on the surface of the negative electrode 22 , and thus 9,10-dihydroanthracene is unlikely to be formed from the anthracene.

[0136] In this case, the content ratio C becomes smaller, more specifically, the content ratio C is less than 0.03, so the electrochemical activity of the electrolyte is improved. As a result, the overvoltage E becomes smaller, more specifically, the overvoltage E is less than 0.22V, so the battery capacity increases. Therefore, excellent battery characteristics can be obtained.

[0137] In this case, advantages can be obtained particularly from the viewpoints described below.

[0138] First, when a complex grinding process is used, the manufacturing process of the secondary battery is complicated. In contrast, when a pre-charge and discharge process is used, a simple process of charging and discharging the assembled secondary battery is sufficient. Therefore, by using the pre-charge and discharge process, a secondary battery with excellent battery characteristics can be easily realized.

[0139] Second, when the grinding process is used, the surface of the negative electrode 22 needs to be physically treated in advance in the manufacturing process of the secondary battery, so the manufacturing efficiency of the secondary battery is reduced. In contrast, when the pre-charge and discharge process is used, it is sufficient to perform an electrochemical treatment on the assembled secondary battery. Therefore, by using the pre-charge and discharge process, a secondary battery with excellent battery characteristics can be effectively realized.

[0140] Third, when the grinding process is used, the degree of the grinding process is prone to deviation. In contrast, when the pre-charge and discharge process is used, the degree of the pre-charge and discharge process is not prone to deviation. Therefore, by using the pre-charge and discharge process, a secondary battery with excellent battery characteristics can be stably achieved.

[0141] Fourth, when the grinding process is used, metal magnesium powder, which is a dangerous substance that is easy to catch fire, is generated. In contrast, when the pre-charge and discharge process is used, metal magnesium powder is not generated. Therefore, by using the pre-charge and discharge process, a secondary battery with excellent battery characteristics can be safely realized.

[0142] In particular, when the magnesium-containing material contains metallic magnesium, the charge and discharge reaction utilizing the precipitation and dissolution of magnesium is likely to proceed sufficiently and stably, and thus a higher effect can be obtained.

[0143] Furthermore, if the secondary battery is a magnesium secondary battery, sufficient battery capacity can be obtained by utilizing the precipitation and dissolution of magnesium, so that a higher effect can be obtained.

[0144] <2. Applications of secondary batteries>

[0145] The purpose (application example) of the secondary battery is not particularly limited. The secondary battery used as a power source can be a main power source or an auxiliary power source in electronic equipment and electric vehicles. The main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. The auxiliary power source can be a power source used instead of the main power source, or a power source switched from the main power source.

[0146] Specific examples of the use of secondary batteries are as follows: electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, stereo headphones, portable radios, and portable information terminals; storage devices such as backup power supplies and memory cards; power tools such as electric drills and electric saws; battery packs mounted on electronic devices, etc.; medical electronic devices such as pacemakers and hearing aids; electric vehicles such as electric vehicles (including hybrid vehicles); power storage systems such as household or industrial battery systems that store electricity in advance in case of emergencies. In these uses, one secondary battery or multiple secondary batteries can be used.

[0147] The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that uses a secondary battery as a driving power source, or a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, the power stored in the secondary battery as a power storage source can be used to use home electrical products, etc.

[0148] Example

[0149] Examples of the present technology will be described.

[0150] <Example 1 and Comparative Examples 1 to 3>

[0151] As described below, after the secondary battery was manufactured, the battery characteristics of the secondary battery were evaluated.

[0152] [Manufacturing of Secondary Batteries]

[0153] Here, through the steps described below, a Figure 3 The test secondary battery shown is a coin-type magnesium secondary battery.

[0154] First, a circular magnesium plate (diameter=16 mm) which is the negative electrode 22 (magnesium-containing material) is prepared as the test electrode 51 , and a circular nickel plate (diameter=17 mm) is prepared as the counter electrode 52 .

[0155] Next, an electrolyte salt (lithium chloride and magnesium bis(trifluoromethanesulfonyl)imide) and an additive (anthracene) were added to a solvent (diethylene glycol dimethyl ether as an ether compound), and the solvent was stirred to prepare an electrolytic solution.

[0156] In this case, the content of lithium chloride in the electrolyte was 0.4 mol / kg, the content of magnesium bis(trifluoromethanesulfonyl)imide in the electrolyte was 0.4 mol / kg, and the content of anthracene in the electrolyte was 0.01 mol / kg.

[0157] Next, after accommodating the counter electrode 52 inside the outer can 55, two diaphragms 53 are arranged on the counter electrode 52. In this case, after the first circular diaphragm 53 (glass filter paper GC-50 manufactured by Advantech, diameter = 19 mm) is arranged on the counter electrode 52, the second circular diaphragm 53 (glass filter paper GC-50 manufactured by Advantech, diameter = 16 mm) is arranged on the first diaphragm 53.

[0158] Next, the electrolyte solution was dripped from above the two separators 53 to impregnate the two separators 53. In this case, the amount of the electrolyte solution dripped was set to 200 μl (=200×10 -6 dm 3 ).

[0159] Next, after the test electrode 51 is disposed on the two separators 53 , the outer cup 54 is disposed on the test electrode 51 .

[0160] Next, the outer cup 54 and the outer can 55 are fastened to each other via the gasket 56 (polypropylene film). Thus, the test electrode 51 and the counter electrode 52 are sealed by the outer cup 54 and the outer can 55, and a test secondary battery is assembled.

[0161] Finally, after the assembled test secondary battery was left to stand (standing time = 48 hours), a preliminary charge and discharge treatment (charge and discharge times = 1) was performed on the test secondary battery. 2 The test secondary battery was discharged to a voltage of -2.0 V at a current density of 0.1 mA / cm 2 The test secondary battery was charged at a current density of 1.50 V until the voltage reached 2.5 V. Thus, the test secondary battery (Example 1) was completed.

[0162] In addition, for comparison, a series of test secondary batteries described below were produced.

[0163] First, a test secondary battery was produced by the same procedure except that the preliminary charge and discharge treatment was not performed (Comparative Example 1).

[0164] Second, a test secondary battery (Comparative Example 2) was produced by the same procedure except that a grinding process was performed instead of the pre-charge and discharge process. In this case, when preparing the test electrode 51, a grinding film (#600) was used to manually grind the surface of the test electrode 51 (magnesium plate) (grinding time = 5 minutes) until a metallic luster was obtained.

[0165] Third, a test secondary battery (Comparative Example 3) was produced by the same procedure except that a grinding process was further performed. The grinding process procedure was as described above.

[0166] After the test secondary battery was completed, the content ratio C and the overvoltage E (V) were investigated, and the results were shown in Table 1. The calculation procedures of the content ratio C and the overvoltage E were as described above.

[0167] [Evaluation of battery characteristics]

[0168] As battery characteristics, operating characteristics were evaluated, and the results shown in Table 1 were obtained.

[0169] (Action characteristics)

[0170] The test secondary battery is repeatedly charged and discharged in a normal temperature environment (temperature = 23°C), thereby measuring the battery capacity (mAh) until the test secondary battery short-circuits. Thus, the cumulative capacity (mAh), which is an indicator for evaluating the operating characteristics, is calculated. When calculating the cumulative capacity, the battery capacity obtained until the test secondary battery short-circuits is accumulated. In addition, the charge and discharge conditions are the same as those in the above-mentioned pre-charge and discharge treatment.

[0171] [Table 1]

[0172]

[0173] [Investigation]

[0174] As shown in Table 1, the cumulative capacity varies depending on the content ratio C and the overvoltage E.

[0175] Specifically, when neither the polishing process nor the preliminary charge and discharge process was performed and the content ratio C was 0.03 or less and the overvoltage E was greater than 0.22 V (Comparative Example 1), the test secondary battery could not be charged and discharged, and thus the cumulative capacity could not be obtained.

[0176] Furthermore, in the case where the polishing treatment was performed instead of the preliminary charge and discharge treatment, the content ratio C was greater than 0.03 and the overvoltage E was greater than 0.22 V (Comparative Example 2), the cumulative capacity decreased.

[0177] Furthermore, since both the polishing process and the preliminary charge and discharge process were performed, when the content ratio C was larger than 0.03 and the overvoltage E was larger than 0.22 V (Comparative Example 3), the cumulative capacity was significantly reduced.

[0178] On the other hand, when the preliminary charge and discharge process was performed instead of the polishing process and the content ratio C was 0.03 or less and the overvoltage E was 0.22 V or less (Example 1), the cumulative capacity increased significantly.

[0179] [Summarize]

[0180] According to the results shown in Table 1, a high cumulative capacity is obtained 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 0.22 V or less. Therefore, the operating characteristics are improved, and thus excellent battery characteristics are obtained in the secondary battery.

[0181] In the above, the present technology has been described by taking one embodiment and one example as examples, but the configuration of the present technology is not limited to the configuration described in one embodiment and one example, and thus various modifications are possible.

[0182] Specifically, the battery structure of the secondary battery is described as a laminated film type and a coin type, but 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.

[0183] In addition, the case where the element structure of the battery element is a winding type is described. However, the element structure of the battery element is not particularly limited, and may be a stacked type or a repeatedly folded type. In the stacked type, the positive electrode and the negative electrode are stacked on each other, and in the repeatedly folded type, the positive electrode and the negative electrode are folded into a zigzag shape.

[0184] The effects described in this specification are merely examples, and therefore the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects can also be obtained with respect to the present technology.

[0185] In addition, the present technology can also adopt the following configurations.

[0186] <1> A secondary battery comprising:

[0187] positive electrode;

[0188] a negative electrode comprising a magnesium-containing material; and

[0189] An electrolyte comprising anthracene and 9,10-dihydroanthracene,

[0190] The ratio of the content of the 9,10-dihydroanthracene in the electrolyte to the content of the anthracene in the electrolyte is 0.03 or less,

[0191] The overvoltage represented by the formula (1) is 0.22 V or less.

[0192] E = E1 - E2 … (1)

[0193] (E is the overvoltage (V) measured using a test secondary battery having a negative electrode as a test electrode and a nickel plate as a counter electrode. E1 is at 0.1 mA / cm 2 The current density of the test secondary battery is used to discharge the test secondary battery until the voltage reaches -2.0V. The open circuit voltage (V) of E2 is 0.1mA / cm 2 The voltage (V) at which the test secondary battery is charged to a voltage of 2.5 V at a current density of 1.5 V.

[0194] <2> The secondary battery according to <1>, wherein

[0195] The magnesium-containing material includes metallic magnesium.

[0196] <3> The secondary battery according to <1> or <2>, wherein

[0197] The secondary battery is a magnesium secondary battery.

Claims

1. A secondary battery comprising: positive electrode; a negative electrode comprising a magnesium-containing material; and An electrolyte comprising anthracene and 9,10-dihydroanthracene, The ratio of the content of the 9,10-dihydroanthracene in the electrolyte to the content of the anthracene in the electrolyte is 0.03 or less, The overvoltage represented by equation (1) is below 0.22V. E = E1 - E2 … (1) E is the overvoltage measured using a test secondary battery having a negative electrode as a test electrode and a nickel plate as a counter electrode, and E1 is an overvoltage at 0.1 mA / cm 2 The current density of the test secondary battery is used to discharge the open circuit voltage when the voltage reaches -2.0V. E2 is 0.1mA / cm 2 The voltage at which the test secondary battery is charged to a voltage of 2.5 V at a current density of . The unit of voltage is V.

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

3. The secondary battery according to claim 1 or 2, wherein: The secondary battery is a magnesium secondary battery.

Images