Negative electrode for Mg battery and Mg secondary battery using the same

Abstract

To provide a negative electrode material for a magnesium battery that exhibits low initial overvoltage and uniform dissolution and deposition of magnesium ions at the negative electrode. [Solution] An Mg negative electrode material having elongated grooves on its surface with a spacing of 0.1 μm or more and 5000 μm or less, a width of 0.1 μm or more and 25 μm or less, and a depth of 0.05 μm or more and 25 μm or less, with an area ratio of 0.1% or more, resulting in a low initial overvoltage during constant current voltage testing and melting behavior occurring along the laser-processed marks. For example, laser processing is used to form the elongated grooves.

Description

[Technical Field]

[0001] This invention relates to a negative electrode for a magnesium battery using a magnesium or magnesium alloy that has been surface-treated and has excellent electrochemical properties, and to a magnesium secondary battery using the same. [Background technology]

[0002] Mobile electronic devices such as smartphones and laptops require a power source (battery). Due to their high electromotive force and high energy density, the vast majority of these use lithium-ion batteries. However, in recent years, magnesium (Mg) batteries have been attracting attention. The main reason for this is the number of cations; lithium ions are monovalent, while magnesium ions are divalent, theoretically giving them twice the energy capacity of lithium batteries. In addition, magnesium is abundant in the Earth's reserves, has the second highest density among practical metallic elements after lithium, and bulk Mg is extremely stable and easy to handle, among other advantages.

[0003] Typically, rechargeable batteries, including secondary batteries, consist of a negative electrode material, a positive electrode active material, and an electrolyte. The inventors focused on the negative electrode material and made the following proposal. Patent Document 1 discloses a negative electrode material characterized by the segregation of added elements at the grain boundaries, achieved by utilizing plastic processing methods including rolling. The amount of added elements is kept within the solid solution range of each element, and the added element is one of the elements that are solid-solution in Mg, such as Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth elements), and Zn.

[0004] Furthermore, the inventors have proposed in Non-Patent Document 1 that refining the crystal grain size of the Mg matrix phase has the potential to improve electrochemical properties. Normally, the internal microstructure of metal materials created by processes such as rolling and extrusion changes significantly depending on plastic processing conditions, including temperature and deformation. In particular, in bulk materials in which crystal grain refinement has been achieved, strain introduced during processing often remains in the matrix phase. For this reason, Patent Document 2 and Non-Patent Document 2 investigate the relationship between residual dislocation density and voltage-current cycle characteristics and disclose an Mg-based alloy anode material with a low residual dislocation density in the Mg matrix phase and excellent electrochemical properties.

[0005] In addition to Mg-based alloy anode materials with controlled internal structure of the Mg matrix based on metallurgy, the inventors have also disclosed in Patent Document 3 an Mg-based anode material made of an Mg-based composite material containing one or more of the following: carbon, carbide, nitride, and oxide, in order to further improve electrochemical properties.

[0006] However, magnesium (Mg) secondary batteries using Mg-based alloy negative electrode materials have two problems. Firstly, because Mg is an active metal, it very easily forms an oxide (MgO) on its surface. Although the thickness of this oxide is only a few nanometers to tens of nanometers, it acts as a barrier to the transfer of Mg ions and is considered problematic because it causes a large overvoltage. Therefore, the oxide on the Mg surface is usually removed using a file or abrasive paper in a glove box under an argon atmosphere, and then immediately used as a negative electrode material for magnesium secondary batteries. However, these mechanical surface treatment methods introduce strain into the metal, and as mentioned above, there are concerns about premature short circuits caused by residual strain. Naturally, there is also a demand for a simple surface treatment method that can reduce the overvoltage.

[0007] The second problem is the heterogeneity of the dissolution and precipitation behavior. Dissolution and precipitation reactions occur at the positive and negative electrodes due to the transfer of Mg ions, but the dissolution and precipitation behavior at the negative electrode does not occur homogeneously on the Mg surface, but rather heterogeneously and in a concentrated manner, which has been pointed out as a cause of short circuits. The mechanism is being diligently investigated, but at present the clear principle and mechanism are not understood. On the other hand, in order to extend the lifespan of Mg secondary batteries (increase the number of charge-discharge cycles), it is required that dissolution and precipitation occur homogeneously.

[0008] On the other hand, Patent Document 4 discloses a magnesium alloy anode material containing calcium, which exhibits excellent electrochemical properties. This material is characterized by lining the inside of the anode with porous magnesium alloy particles or by creating fine grooves. However, the examples only disclose cases related to the dispersion of porous particles, and there is no description of the groove effect on electrochemical properties such as charge vs. discharge characteristics. Furthermore, since the magnesium metal anode contains calcium, it is thought that the disclosed properties are not due to the form of the anode, but rather to the alloy composition.

[0009] Furthermore, Patent Document 5 discloses a Mg-air battery with excellent electrochemical properties achieved by shaping the Mg-based alloy sheet material into a corrugated form. However, since the subject of the invention is a primary battery and the Mg-based alloy has unavoidable impurities dissolved in it, its effect on secondary batteries is unknown. In particular, the corrugated form is intended to increase the surface area in contact with the electrolyte, but as mentioned above, the mechanism of dissolution and precipitation reactions in secondary batteries is unknown. Therefore, it is unclear whether these forms can be influencing factors. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] WO2021 / 166655 publication [Patent Document 2] Japanese Patent Publication No. 2023-26887 [Patent Document 3] Japanese Patent Publication No. 2022-178801 [Patent Document 4] Japanese Patent Publication No. 2016-54078 [Patent Document 5] Japanese Patent Publication No. 2015-82497 [Non-patent literature]

[0011] [Non-Patent Document 1] Bandai, Somekawa, Chemical Communications 56 (2020) 12122 [Non-Patent Document 2] Bandai, Somekawa, Batteries & Supercaps 2022, 5, e202200153 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention aims to provide a negative electrode for a magnesium battery in which the dissolution and precipitation of magnesium ions occur homogeneously at the negative electrode. Furthermore, the present invention aims to provide a magnesium secondary battery with low initial overvoltage and an increased number of charge / discharge cycles compared to conventional products. [Means for solving the problem]

[0013] [1] The negative electrode for a Mg battery of the present invention has at least one elongated groove on its surface, and the surface area occupied by the elongated groove is 0.1% or more and 50% or less of the surface area of ​​the surface of the Mg battery that the negative electrode faces the positive electrode of the Mg battery. Here, the term "negative electrode for Mg batteries" encompasses both negative electrodes using pure magnesium and negative electrodes using Mg-based alloys. However, in metallurgy, the term "Mg-based alloy" is used, referring to the main element of the alloy, to distinguish it from pure magnesium (e.g., 3N or 2N purity).

[0014] [2] In the negative electrode for the Mg battery of the present invention [1], preferably the elongated grooves are unidirectional, grid-like, helical, or concentric. [3] In the negative electrode [1] or [2] for the Mg battery of the present invention, preferably, the interval between the elongated grooves is 0.1 μm or more and 5000 μm or less. [4] In any one of the negative electrodes [1] to [3] for the Mg battery of the present invention, preferably, the width of the elongated groove is 0.1 μm or more and 25 μm or less. [5] In any one of the negative electrodes [1] to [4] for the Mg battery of the present invention, preferably, the depth of the elongated groove is 0.05 μm or more and 25 μm or less.

[0015] [6] In any one of the negative electrodes [1] to [5] for the Mg battery of the present invention, preferably, in the electrochemical dissolution test, the potential 3 minutes after the start of the test is 0.34 V or less in absolute value, and the electrochemical dissolution test evaluates the electrochemical characteristics in a two-electrode cell. A Mg alloy is used for the positive electrode, the negative electrode for the Mg battery with the elongated groove introduced is used for the negative electrode, and magnesium tetrakis (hexafluoroisopropoxy) aluminate salt is blended with diethylene glycol dimethyl ether for the electrolyte to adjust the magnesium ion concentration to 0.3 mol / dm 3 and the prepared one is used. A glass fiber filter with 0.2 mL of the above electrolyte dropped thereon is used for the separator, and the current density is 1 mA / cm 2 is preferable. [7] In the negative electrode [6] for the Mg battery of the present invention, preferably, in the electrochemical dissolution test, the potential 6 minutes after the start of the test is 0.33 V or less in absolute value. [8] In the negative electrode [6] for the Mg battery of the present invention, preferably, in the electrochemical dissolution test, the dissolution of Mg ions occurs on or around the elongated groove.

[0016] [9] In any one of the negative electrodes [1] to [8] for the Mg battery of the present invention, preferably, the negative electrode for the Mg battery is composed of magnesium and inevitable impurities, and as the inevitably contained impurity elements, Al, Zn, Mn, Fe, Si, Cu, Ni, Ca, Li, Y are contained in a total amount of 0 mass% or more and 0.3 mass% or less, and C, N, B are contained in a total amount of 0 mass% or more and 0.2 mass% or less.

[10] In any one of the negative electrodes for Mg batteries [1] to [5] of the present invention, preferably the negative electrode for Mg batteries is made of an Mg-based alloy and unavoidable impurities. The aforementioned Mg-based alloy may be any of the following as specified in JIS H4201 (Magnesium Alloy Sheets and Strips) or JIS H4205 (Magnesium Alloy Forgings): AZ31, AZ61, AZ80, AZX611, AZX612, AZX811, AZX911, AZX912, AM60, AM610, AM620, AZ21, ZK30, ZK60, ZM21, LZ21, WE54, WE43, WZ73, or WZ75.

[0017]

[11] The Mg secondary battery of the present invention is composed of any one of the Mg battery negative electrodes from [1] to

[10] , an electrolyte, and a positive electrode. The electrolyte can be a liquid electrolyte, a solid electrolyte, or a gel electrolyte. A liquid electrolyte is an electrically conductive solution obtained by dissolving an ionic substance (electrolyte) in water or the like.

[0018] According to the negative electrode for Mg batteries of the present invention, a negative electrode for Mg batteries can be obtained in which the dissolution and deposition of Mg ions at the negative electrode occur homogeneously. Therefore, the Mg secondary battery using the negative electrode for Mg batteries of the present invention has a low initial overvoltage and an increased number of charge / discharge cycles compared to conventional products, resulting in a long-life Mg secondary battery. [Brief explanation of the drawing]

[0019] [Figure 1A] The image shows a surface observation example of a negative electrode material for a magnesium battery, as shown in Example 1, after laser processing, and was acquired using a laser microscope. [Figure 1B] This is a schematic diagram relating to an elongated groove for obtaining the effects of the present invention. [Figure 2] The image shows a surface observation example of a magnesium battery anode material after laser processing, as shown in Example 1, and was acquired using a scanning electron microscope. [Figure 3] Example 1 shows an electrochemical dissolution test of a negative electrode material for a magnesium battery, illustrating the relationship between potential and time. [Figure 4]The image shows a surface observation example of the Mg battery anode material after the first electrochemical dissolution test, as shown in Example 1, and was acquired using a scanning electron microscope. [Figure 5] The image shows a surface observation example of the Mg battery anode material after the second electrochemical dissolution test, as shown in Example 1, and was acquired using a scanning electron microscope. [Figure 6] The image shows a surface observation example of the negative electrode material for a Mg battery after the first electrochemical dissolution test, as shown in Example 2, and was acquired using a scanning electron microscope. [Figure 7] The image shows the two-dimensional surface profile of the Mg battery anode material obtained by laser microscopy using a laser microscope, as shown in Example 8. [Figure 8] The image shows the surface appearance after laser processing of the Mg battery anode material shown in Example 9, as obtained by laser microscopy. [Figure 9] This is a schematic diagram showing the general configuration of a magnesium secondary battery using the magnesium battery negative electrode material of the present invention. [Modes for carrying out the invention]

[0020] For each elongated groove processed into the negative electrode material for Mg batteries to obtain the effects of the present invention, the spacing, width, and depth of the elongated grooves are influencing factors (variables of form). The definition of an elongated groove is a linear depression or recessed area provided on the surface of the negative electrode material for Mg batteries facing the positive electrode of the Mg secondary battery. Figure 1B is a schematic diagram relating to the elongated grooves for obtaining the effects of the present invention.

[0021] Firstly, the spacing between the elongated grooves is preferably 0.1 μm or more and 5000 μm or less, more preferably 0.5 μm or more and 2500 μm or less, and even more preferably 1 μm or more and 1000 μm or less. If the spacing between the elongated grooves is less than 0.1 μm, it is the same as the width of the elongated grooves, and the entire surface of the Mg negative electrode material is covered by elongated grooves (= there are no untreated areas). On the other hand, if the spacing between the elongated grooves exceeds 5000 μm, it is difficult to process the elongated grooves to that value, which is undesirable from the viewpoint of operability and workability. In addition, the proportion of untreated surface on the Mg surface is large, that is, the laser-processed area ratio is small, making it difficult to obtain the effects of the present invention.

[0022] Next, regarding the width of the elongated groove, it is preferably 0.1 μm or more and 25 μm or less, more preferably 0.5 μm or more and 20 μm or less, and even more preferably 1 μm or more and 15 μm or less. If the width of the elongated groove is less than 0.1 μm, it is difficult to process the elongated groove using the method shown below, which is undesirable from the standpoint of operability and industrial use. Also, if the width of the elongated groove exceeds 25 μm, since the thickness of the foil material used for the negative electrode material of Mg batteries is 25 μm to 50 μm, the width of the laser processing becomes larger than the foil thickness. As the volume of the Mg negative electrode material decreases, it becomes impossible to continuously supply Mg ions through dissolution behavior, which leads to a decrease in charge-discharge cycle characteristics during electrochemical testing.

[0023] Furthermore, the depth of the elongated grooves is preferably 0.05 μm or more and 25 μm or less, more preferably 0.5 μm or more and 10 μm or less, and even more preferably 1 μm or more and 5 μm or less. If the depth of the elongated grooves is less than 0.05 μm, it is similar to the depth of polishing scratches introduced to the metal surface by general-purpose automatic polishing equipment or manual polishing, making it difficult to obtain the effects of the present invention. Also, since the thickness of the foil material used for the negative electrode material of Mg batteries is 25 μm to 40 μm, if the depth of the elongated grooves exceeds 25 μm, it corresponds to more than half of the foil thickness, raising concerns about a decrease in the strength of the negative electrode material itself.

[0024] In this invention, elongated grooves are introduced perpendicularly from two directions, vertical and horizontal, but processing in only one direction is also acceptable. Furthermore, the elongated grooves do not need to be parallel to each other and may be random. Of course, they may be zigzag, letter-shaped, or curved. However, the proportion of the surface occupied by the elongated grooves on the negative electrode is preferably 0.1% or more, more preferably 0.5% or more, and even more preferably 1% or more. If the area ratio is less than 0.1%, it is the minimum value that exists due to unavoidable forces such as during operation, and it is difficult to obtain the effects of this invention. The area ratio of the elongated grooves can be measured by methods such as the point calculation method (see Kento Sakuma and Taiji Nishizawa, "Quantitative Metallography," Bulletin of the Japan Institute of Metals 10 (1971), p. 279) or by using binary valency images.

[0025] This method involves introducing elongated grooves into the negative electrode material for Mg batteries. While a laser processing machine is used as an example here, any method that allows control over the width, depth, and spacing of the elongated grooves without using mechanical polishing techniques is acceptable, such as integrated ion beam (FIB) or electron beam methods. However, methods that introduce elongated grooves by applying strain, such as automatic polishing, manual polishing, or blasting, introduce residual stress into the Mg metal. This leads to concentrated dissolution behavior near these areas, causing problems such as premature short circuits.

[0026] Furthermore, the negative electrode material for the Mg battery, which has elongated grooves, may be pure Mg composed of Mg and other impurity elements, or it may be an Mg-based alloy containing Mg and elements that solid-solve in Mg. The impurity elements that are inevitably included are, for example, those specified in JIS H4201 (Magnesium alloy sheets and strips) or JIS H4205 (Magnesium alloy forgings), such as Al, Zn, Mn, Fe, Si, Cu, Ni, Ca, Li, and Y in a total of 0% to 0.3% by mass, and C, N, and B in a total of 0% to 0.2% by mass.

[0027] Typical examples of Mg-based alloys include AZ31, AZ61, AZ80, AZX611, AZX612, AZX811, AZX911, AZX912, AM60, AM610, AM620, AZ21, ZK30, ZK60, ZM21, LZ21, WE54, WE43, WZ73, and WZ75, as specified in JIS H4201 (Magnesium Alloy Sheets and Strips) or JIS H4205 (Magnesium Alloy Forgings), but the chemical composition of Mg-based alloys is not limited to these.

[0028] The electrochemical properties of the Mg battery anode material with the elongated grooves described above will now be explained. In a constant current voltage test using a two-electrode cell, when the Mg battery anode material with the elongated grooves is used as the anode, the potential 3 minutes after the start of the constant current dissolution test preferably shows an absolute value of 0.50V or less, more preferably an absolute value of 0.40V or less, and even more preferably an absolute value of 0.34V or less. Furthermore, the potential 6 minutes after the start of the test preferably shows an absolute value of 0.45V or less, more preferably an absolute value of 0.40V or less, and even more preferably an absolute value of 0.33V or less.

[0029] In the aforementioned constant current voltage test, a two-electrode cell was used, with a magnesium alloy for the positive electrode and a magnesium battery negative electrode material with elongated grooves for the negative electrode. A glass fiber filter was used as a separator, and a mixture of tetrakis(hexafluoroisopropoxy)aluminate magnesium salt and diethylene glycol dimethyl ether was used to achieve a magnesium ion concentration of 0.3 mol / dm³. 3 The solution prepared as described above is used as the electrolyte. The current density is 1 mA / cm². 2 That is the case. This method for measuring electrochemical properties is disclosed in the inventor's previously published paper (T. Mandai et al., Mater. Adv. 2021, 2,6283). [Examples]

[0030] Figure 1A shows an example of surface observation after laser processing of a negative electrode material for a Mg battery, representing Example 1, and displays an image acquired with an optical microscope. In Example 1, elongated grooves are processed at equal intervals of 100 μm. Pure Mg material (99.96 mass%) with a thickness of 200 μm was used. Laser processing was performed using a Keyence laser processing machine, with the scribing width (= elongated grooves referred to in this invention) set to 100 μm, output at 20%, scan speed at 200 mm / s, and switch wavelength at 100 kHz. Figure 2 shows an example of surface observation of a negative electrode material for a Mg battery, as shown in Example 1, after laser processing, and displays an image acquired with a laser microscope. From Figure 2, it can be confirmed that the width of the elongated groove is approximately 10 μm.

[0031] To evaluate the electrochemical properties of Example 1, 1 mA / cm 2 A constant current-voltage test was performed using the current density and a measurement time of 1 hour. In this test, an electrolyte solution was used, which was a mixture of tetrakis(hexafluoroisopropoxy)magnesium aluminate with diethylene glycol dimethyl ether. Furthermore, the electrochemical properties were evaluated using a two-electrode cell, with a Mg alloy as the positive electrode and a Mg battery negative electrode material with elongated grooves introduced as the negative electrode. A glass fiber filter to which 0.2 mL of the above electrolyte solution was dropped was used as the separator. As an example of the dissolution reaction, Figure 3 shows the voltage change against time obtained by the constant current test. In this voltage vs. time curve, 0V vs. Mg is used as the reference, and the deviation from 0V vs. Mg corresponds to the overvoltage. All electrochemical tests were performed in a glove box under an argon atmosphere. After measurement, the negative electrode was promptly removed, and the negative electrode surface was observed using a scanning electron microscope. After observing the negative electrode surface, a constant current-voltage test was performed under the same conditions as above, and a voltage-vs.time curve was obtained (second time). After observing the negative electrode surface again, a constant current-voltage test was performed under the same conditions as above, and a voltage-vs.time curve was obtained (third time).

[0032] Figures 4 and 5 show images of the surface of the Mg metal negative electrode after the first and second constant current voltage tests, obtained by scanning electron microscopy. From Figure 4, it can be seen that dissolution behavior occurs in various places, but the elongated grooves become the preferred sites for dissolution. Furthermore, on the negative electrode surface after the second constant current voltage test, it can be seen that the dissolution reaction is further promoted along the elongated grooves (Figure 5). Table 1 shows the electromotive force at 3 minutes and 6 minutes after the start of the first constant current voltage measurement test. A decrease in electromotive force can be seen compared to the comparative example. The potential at 3 minutes after the start of the first, second, and third constant current voltage measurement tests is listed in Table 2.

[0033] [Table 1] [Table 2]

[0034] In Example 2, laser processing was performed under all the same conditions as in Example 1, except that the spacing between the elongated grooves was changed from 100 μm to 200 μm. A constant current test was also conducted under the same conditions as in Example 1. Figure 6 shows the surface appearance after the first dissolution test, and Figure 3 shows the constant current voltage measurement vs. time curve. Similar to Figures 4 and 5, it can be seen that the dissolution behavior preferentially occurs along the elongated grooves. The potentials after 3 minutes and 6 minutes in each constant current voltage measurement test are summarized in Tables 1 and 2.

[0035] In Example 3, laser processing was performed under all the same conditions as in Example 1, except that the spacing between the elongated grooves was changed from 100 μm to 10 μm. A constant current test was also performed under the same conditions as in Example 1. Tables 1 and 2 show the potentials at 3 minutes and 6 minutes after the start of the constant current voltage test.

[0036] In Example 4, laser processing was performed under all the same conditions as in Example 1, except that the spacing between the elongated grooves was changed from 100 μm to 50 μm. A constant current test was also performed under the same conditions as in Example 1. Tables 1 and 2 show the potentials at 3 minutes and 6 minutes after the start of the constant current voltage test.

[0037] In Example 5, laser processing was performed under all the same conditions as in Example 1, except that the spacing between the elongated grooves was changed from 100 μm to 500 μm. A constant current test was also performed under the same conditions as in Example 1. Tables 1 and 2 show the potentials at 3 minutes and 6 minutes after the start of the constant current voltage test.

[0038] In Examples 6-8, the spacing between the elongated grooves was set to 100 μm, and the output and scan speed during laser processing in Example 1 were adjusted to change the width of the elongated grooves to 15 μm-25 μm and the depth of the elongated grooves to 0.2 μm-2.5 μm. Figure 7 shows the two-dimensional surface profile of the Mg battery anode material from Example 8, obtained using a laser microscope after laser processing. The processed area shows irregularities, and it can be seen that the width and depth of the elongated grooves are 15 μm and 0.2 μm, respectively. A constant current test was also performed under the same conditions as in Example 1. Table 3 shows the potentials at 3 minutes and 6 minutes after the start of the constant current voltage test in Examples 6 to 8.

[0039] In Example 9, laser processing was performed under all the same conditions as in Example 1, except that the spacing between the elongated grooves was set to 100 μm and the shape during laser processing was changed to a circular shape. Figure 8 shows the surface appearance of the Mg battery anode material in Example 9, obtained using a laser microscope, after laser processing. The white areas are the processed areas, and circular processing with a diameter of 8 μm can be confirmed. A constant current test was also performed under the same conditions as in Example 1. Table 3 shows the potentials at 3 minutes and 6 minutes after the start of the constant current voltage test in Example 9. [Table 3] Comparative Example

[0040] A pure Mg material (99.96 mass%) with a thickness of 200 μm was used. To remove oxides present on the Mg surface, the Mg surface was mechanically polished with abrasive paper in a glove box under an argon atmosphere before the electrochemical test. This oxide film removal method is a commonly used technique in the field of Mg secondary batteries. Immediately after surface polishing, a constant potential test was performed. Table 1 shows the potentials 3 minutes and 6 minutes after the start of the constant current voltage test.

[0041] Figure 9 is a schematic diagram showing the general configuration of a magnesium secondary battery using the magnesium battery negative electrode material of the present invention. As shown in Figure 7, the magnesium secondary battery 1 comprises a positive electrode 11, a negative electrode 12, an electrolyte 13, and a container 14. The surface area occupied by the elongated grooves in the negative electrode 12 should be determined such that the ratio of the surface area of ​​the negative electrode 12 to the surface area of ​​the surface facing the positive electrode 11 is between 0.1% and 50%.

[0042] In the positive electrode 11, a positive electrode active material (not shown) is held by a positive electrode current collector (not shown). The positive electrode current collector has the function of donating electrons to the positive electrode active material during discharge. Nickel, iron, stainless steel, titanium, aluminum, etc. are preferred materials for the positive electrode current collector because they have relatively good corrosion resistance and are inexpensive. The material used for the positive electrode active material is not particularly limited as long as it can insert and remove Mg ions, but MgFeSiO4, MgMn2O4, or V2O5 are preferred. A specific configuration of the positive electrode 11 is, for example, a configuration in which V2O5 is coated on stainless steel.

[0043] The negative electrode 12 uses the negative electrode material for Mg batteries of the present invention. The electrolyte 13 is held by a separator (not shown) and generates ionic conductivity between the positive electrode 11 and the negative electrode 12. The electrolyte 13 contains Mg ions. During discharge, the Mg ions undergo a reduction reaction at the positive electrode 11 (e.g., the reaction of formula (1) described later) and an oxidation reaction at the negative electrode 12 (e.g., the reaction of formula (2) described later). During charging, the Mg ions undergo an oxidation reaction at the positive electrode 11 (e.g., the reaction of formula (3) described later) and a reduction reaction at the negative electrode 12 (e.g., the reaction of formula (4) described later). These oxidation-reduction reactions enable the charging and discharging of the Mg secondary battery.

[0044] [Chemical Formula 1] V2O5 + Mg 2+ + 2e - → MgV2O5… Formula (1) Mg → Mg 2+ + 2e - … Formula (2) MgV2O5 → V2O5 + Mg 2+ + 2e - … Formula (3) Mg 2+ + 2e - → Mg … Formula (4)

[0045] These positive electrode 11, negative electrode 12, and electrolyte 13 are enclosed in a container 14. The material of the container 14 and the like is not particularly limited as long as there is no leakage of the electrolyte and it has corrosion resistance. However, those formed by pressing a metal plate such as iron and having a plating layer of nickel or the like for corrosion resistance formed on the entire surface of the inner and outer surfaces are preferably used.

[0046] Note that the above-described embodiment of the present invention is merely an example of an Mg secondary battery and should not be construed restrictively, and also includes technical matters obvious in the technical field of Mg secondary batteries.

Industrial Applicability

[0047] The negative electrode for Mg batteries of the present invention provides a negative electrode for Mg batteries in which the dissolution and deposition of Mg ions occur uniformly. Therefore, a Mg secondary battery using the negative electrode of the present invention has a low initial overvoltage and an increased number of charge-discharge cycles compared to conventional products, resulting in a long-life Mg secondary battery. Furthermore, the negative electrode for Mg batteries of the present invention can be used not only in Mg secondary batteries, but also in Mg primary batteries, Mg-air primary batteries, and Mg-air secondary batteries. [Explanation of Symbols]

[0048] 1...Mg secondary battery 11...Positive electrode 12...Negative electrode 13...Electrolyte 14...Container

Claims

1. At least one elongated groove is provided on the surface of the negative electrode for the Mg battery. A negative electrode for a magnesium battery in which the surface area occupied by the elongated groove is 0.1% or more and 50% or less of the surface area of ​​the surface facing the positive electrode of the magnesium battery.

2. The negative electrode for a Mg battery according to claim 1, wherein the elongated grooves are unidirectional, grid-like, helical, or concentric.

3. The negative electrode for a Mg battery according to claim 1 or 2, wherein the spacing between the elongated grooves is 0.1 μm or more and 5000 μm or less.

4. The negative electrode for a Mg battery according to any one of claims 1 to 3, wherein the width of the elongated groove is 0.1 μm or more and 25 μm or less.

5. The negative electrode for a Mg battery according to any one of claims 1 to 4, wherein the depth of the elongated groove is 0.05 μm or more and 25 μm or less.

6. In the electrochemical dissolution test, the potential after 3 minutes from the start of the test is 0.34 V or less in absolute value, The aforementioned electrochemical dissolution test evaluates electrochemical properties using a two-electrode cell, A magnesium alloy is used for the positive electrode. The negative electrode used is the Mg battery negative electrode with elongated grooves introduced into it. The electrolyte is composed of tetrakis(hexafluoroisopropoxy)magnesium aluminate mixed with diethylene glycol dimethyl ether, resulting in a magnesium ion concentration of 0.3 mol / dm³. ３ Use the preparation made as follows: A glass fiber filter to which 0.2 mL of the electrolyte solution has been dropped is used as the separator. Current density is 1 mA / cm² ２ That is, A negative electrode for a magnesium battery according to any one of claims 1 to 5.

7. In the electrochemical dissolution test described above, the potential after 6 minutes from the start of the test is 0.33 V or less in absolute value. The negative electrode for a magnesium battery according to claim 6.

8. In the electrochemical dissolution test described above, the dissolution of Mg ions occurs on or around the elongated groove. The negative electrode for a magnesium battery according to claim 6.

9. The negative electrode for the aforementioned Mg battery consists of magnesium and unavoidable impurities. A negative electrode for a magnesium battery according to any one of claims 1 to 8, wherein the negative electrode contains, as inevitably present impurity elements, Al, Zn, Mn, Fe, Si, Cu, Ni, Ca, Li, and Y in a total amount of 0% to 0.3% by mass, and C, N, and B in a total amount of 0% to 0.2% by mass.

10. The negative electrode for the Mg battery consists of an Mg-based alloy and unavoidable impurities. The Mg-based alloy is one of AZ31, AZ61, AZ80, AZX611, AZX612, AZX811, AZX911, AZX912, AM60, AM610, AM620, AZ21, ZK30, ZK60, ZM21, LZ21, WE54, WE43, WZ73, WZ75 as specified in JIS H4201 or JIS H4205, wherein the negative electrode for an Mg battery according to any one of claims 1 to 8.

11. A magnesium secondary battery comprising a negative electrode for a magnesium battery according to any one of claims 1 to 10, an electrolyte, and a positive electrode.

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