Anode material and current collector for Mg secondary batteries, and Mg secondary batteries using the same

Abstract

To provide a negative electrode material and a current collector material for a Mg secondary battery.SOLUTION: A cladding material consists of a Mg layer composed of Mg or a Mg-based alloy, and an Al layer composed of Al or an Al-based alloy, and consists of Mg-Ajmol%Xj (j=1, 2, ..., and n; n is a natural number of 1 or more), Xj targets an element solid-dissolved at 0.05 mol% or more with respect to Mg, Xj is composed of any one kind of element out of Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth), and Zn, a value of Aj is 0.02 mol% or more and 1 mol% or less, the Al-based alloy consists of Al-Bkmol%Yk (k=1, 2,..., and m; m is a natural number of 1 or more), Yk is composed of any one kind of element out of Si, Fe, Cu, Mn, Mg, Zn, Ti, Ag, Ga, and Li, a value of Bk is 0.02 mol% or more and 1 mol% or less, the Mg layer is a negative electrode material, and the Al layer is an Al current collector.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode material and current collector for a magnesium secondary battery, and a magnesium secondary battery using the same, which utilize a cladding material consisting of a magnesium layer made of magnesium or a magnesium alloy having excellent electrochemical properties, and an aluminum layer made of aluminum or an aluminum alloy. [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 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. For this reason, Patent Document 2 investigates the relationship between residual dislocation density and voltage-current cycle characteristics and discloses an Mg-based alloy anode material with a low residual dislocation density in the Mg matrix 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] On the other hand, rechargeable batteries, including secondary batteries, require terminals to draw current from the positive and negative electrodes to the outside, and these terminals utilize current collectors. These current collectors are required to have excellent electronic conductivity, to exist stably within the battery, to be able to shrink in volume within the battery, and to adhere closely to the positive and negative electrode materials.

[0007] Therefore, Patent Documents 4 and 5 disclose a negative electrode material in which Mg is coated by a plating method onto a current collector made of Cu, Al, stainless steel, Ni, or a carbon-based material. The thickness of the Mg is preferably 1 μm to 20 μm, and the plating method is not limited as long as it is a plating method that can form a plating layer with a homogeneous thin film structure. Patent Document 6 also discloses a current collector made of carbon, carbon paper, carbon cloth, or a mesh or foil of a precious metal, on which a paste material is deposited or, if necessary, heat-treated. Patent Documents 7 and 8 disclose a secondary battery in which one of Cu, Ni, stainless steel, or Fe is used as the current collector, and the Mg negative electrode material is joined to these current collectors by crimping, as one example.

[0008] However, from the perspective of weight reduction of secondary batteries, it is desirable to use a lightweight material as the current collector. In addition, it is essential that the process be simplified and the material be increased in size.

[0009] On the other hand, Patent Document 9 discloses a manufacturing method for creating a bulk body by overlapping workpieces and subjecting them to severe plastic deformation such as rolling. Targeting metal materials typified by stainless steel and Al alloys, good interfacial bonding and refinement of the matrix grain size (grain refinement) are achieved by increasing the strain introduced into the workpiece. However, the application and use sites of these rolled materials are structural members that require strength and ductility, and it is important to ensure the thickness of the created material. Therefore, it is characterized by overlapping the workpieces multiple times and rolling them.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Non-Patent Documents

[0011]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] The problem to be solved by the present invention is to provide a negative electrode material and a current collector for a Mg secondary battery that can reduce the weight of the secondary battery by using a lightweight material as the current collector and can also meet the demand for increasing the size of the battery materials from the viewpoints of simplifying the manufacturing process and ensuring the battery capacity.

Means for Solving the Problems

[0013] [1] The negative electrode material and the current collector for a Mg secondary battery of the present invention are a clad material composed of a Mg layer made of Mg or a Mg-based alloy and an Al layer made of Al or an Al-based alloy. The Mg-based alloy is Mg-A j mol% X j (j = 1, 2,..., n; n is a natural number of 1 or more), and X j is an element that solid-solves 0.05 mol% or more with respect to Mg, and X j is composed of any one of the elements Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth), Zn, and the value of A j is 0.02 mol% or more and 1 mol% or less. The Al-based alloy is Al-B k mol% Y k (k = 1, 2,..., m; m is a natural number of 1 or more), and Y k is composed of any one of the elements Si, Fe, Cu, Mn, Mg, Zn, Ti, Ag, Ga, Li, and the value of B k is 0.02 mol% or more and 1 mol% or less. The Mg layer made of the Mg or the Mg-based alloy is the negative electrode material, and the Al layer made of the Al or the Al-based alloy is the Al current collector. Regarding elements with a composition ratio of less than 0.02 mol%, they are regarded as inevitable impurities.

[0014] [2] In the Mg secondary battery negative electrode material and current collector material [1] of the present invention, preferably the thickness of the Mg layer is less than 100 μm and the thickness of the Al layer is less than 100 μm. [3] In the Mg secondary battery negative electrode material and current collector material [1] or [2] of the present invention, preferably the average crystal grain size of the Mg matrix of the Mg layer is 50 μm or less, and the average crystal grain size of the Al matrix of the Al layer is 50 μm or less. [4] In the Mg secondary battery negative electrode material and current collector material [1] to [3] of the present invention, preferably, a gap of less than 50% exists at the Al-Mg boundary in the cross section observed by an optical microscope or scanning electron microscope.

[0015] [5] In the Mg secondary battery negative electrode material and current collector material [1] to [4] of the present invention, it is preferable that the cycle characteristics are 20 or more cycles in cycle measurement using a two-electrode cell. [6] In the Mg secondary battery negative electrode material and current collector material [1] to [5] of the present invention, it is preferable that the Mg metal exhibits characteristics of an overvoltage of 30 mV or less in an electrochemical deposition and dissolution test. [7] In the Mg secondary battery negative electrode material and current collector material [1] to [6] of the present invention, preferably, in the electrochemical deposition and dissolution test of Mg metal, when the electrode potential is ±0.5V, ±10mAcm -2 The current density should be shown above.

[0016] [8] The present invention relates to a method for manufacturing a negative electrode material and current collector for a Mg secondary battery, comprising stacking an Mg layer made of Mg or an Mg-based alloy and an Al layer made of Al or an Al-based alloy, and applying a drawing process at a temperature of 300°C or higher to obtain a true strain of 0.05 or more and less than 5.

[0017] [9] In the method for manufacturing a negative electrode material and current collector material for a Mg secondary battery of the present invention [8], preferably the method for applying plastic strain is one of the following processing methods: extrusion, forging, rolling, drawing, and double-roll casting.

[0018]

[10] The Mg secondary battery of the present invention is composed of an Mg secondary battery negative electrode material and current collector as described in any of [1] to [7], an electrolyte and a positive electrode. [Brief explanation of the drawing]

[0019] [Figure 1] The image shows a cross-sectional view of the negative electrode material and current collector material for a magnesium secondary battery, as shown in Example 1, and was acquired using a scanning electron microscope. [Figure 2] The image shown is an example of cross-sectional microstructure observation of a negative electrode material and current collector material for a Mg secondary battery, as shown in Example 1, with the image acquired by electron beam backscatter diffraction being presented as an IQ image. [Figure 3] The electrochemical deposition and dissolution test example of the negative electrode material and current collector material for a Mg secondary battery shown in Example 1 displays the cycle voltage and current results. [Figure 4] The image shows an example of microstructural observation of a Mg alloy anode material, as shown in Example 2, and was acquired using a scanning electron microscope. [Figure 5] In Example 2, we show an example of cross-sectional microstructure observation of a negative electrode material and current collector material for a Mg secondary battery, with images obtained by electron beam backscatter diffraction shown as IQ images. [Figure 6] Example 2 shows an electrochemical deposition and dissolution test example of a negative electrode material and current collector material for a Mg secondary battery, with the cycle voltage and current results displayed. [Figure 7] This is a schematic diagram showing the general configuration of a magnesium secondary battery using the negative electrode material and current collector material for magnesium secondary batteries of the present invention. [Modes for carrying out the invention]

[0020] The negative electrode material and current collector material for a magnesium secondary battery of the present invention are constructed using a clad material consisting of a magnesium layer made of magnesium or a magnesium-based alloy and an aluminum layer made of aluminum or an aluminum-based alloy. The magnesium layer in this embodiment includes a pure magnesium layer and a magnesium alloy layer, and is used as a negative electrode material for a magnesium secondary battery. The Mg-based alloy used in the Mg layer of cladding material is Mg-A j mol%X j (j=1, 2, ..., n; n is a natural number greater than or equal to 1) j This refers to elements that are solid-soluble in Mg at a concentration of 0.05 mol% or more, and X j = One of the following elements: Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth elements), or Zn. Rare earth elements refer to elements of the same group, such as Y (yttrium), Gd (gadolinium), Ce (cerium), and Sc (scandium). Here, if n is 1, it represents a binary alloy, and if it is 2, it represents a ternary alloy. A j The value of is less than or equal to the maximum solid solution value for Mg, preferably 0.02 mol% or more and 1 mol% or less, more preferably 0.02 mol% or more and 0.5 mol% or less, and even more preferably 0.02 mol% or more and 0.3 mol% or less. j If the amount is less than 0.02 mol%, the added solute element does not affect the mechanical or electrochemical properties and exists as an impurity element. Furthermore, when pure Mg is used as a Mg-based alloy material, it consists of unavoidable components such as iron, nickel, silicon, and copper, with the remainder being Mg, and it is generally desirable that the purity of Mg be 99% or higher.

[0021] The Al layer of the cladding material is used as a current collector. The Al layer in this embodiment includes a pure Al layer and an Al alloy layer. That is, the Al layer may be pure Al or an Al alloy. The Al layer contains, for example, 99% by mass or more Al. The Al layer may contain trace amounts of impurities that are inevitably mixed in during manufacturing. The Al layer may also contain additive elements. Additive elements may be, for example, silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), zinc (Zn), titanium (Ti), etc., and may also be Ag (silver), Ga (gallium), or Li (lithium). That is, the Al-based alloy is Al-B k mol%Y k (k=1, 2, ..., m; m is a natural number greater than or equal to 1) kIt is preferable that the alloy be composed of one of the following elements: Si, Fe, Cu, Mn, Mg, Zn, Ti, Ag, Ga, or Li. Here, if m is 1, it represents a binary alloy, and if it is 2, it represents a ternary alloy. B k The value is between 0.02 mol% and 1 mol%, and elements with a composition ratio of less than 0.02 mol% are considered unavoidable impurities. Of course, considering the processability of the current collector and bonding properties with the Mg-based alloy anode material, an Al-based alloy with elements that form a solid solution in Al is also acceptable. Al alloys that can be used as the Al layer include, for example, alloy numbers "1085", "1070", "1050", "1N30", "1100", "3003", "3004", "8021", and "8079" as specified in "JIS H 4160: Aluminum and aluminum alloy foil". The Al layer may have a thickness of, for example, 5 μm to 50 μm. The Al layer may have a thickness of, for example, 10 μm to 20 μm.

[0022] The internal microstructure, thickness of the clad material, and bonding between Al and Mg are controlled by drawing processes, including rolling, for the Mg layer, which is composed of Mg or a Mg-based alloy, and the Al layer, which is composed of Al or an Al-based alloy. Although rolling is used as an example here, any method that allows control of the internal structure during solidification and simultaneous adjustment of thickness is acceptable, such as the twin-roll casting method. The layers may consist of two layers of Mg and Al, three layers of Mg, Al and Mg, four layers of Mg and Al and Mg and Al, or more. However, the order must be Mg and Al. Furthermore, in the case of a clad material consisting of three or more layers, the Mg layer may be composed of different Mg or Mg-based alloys, as long as it satisfies the requirement of being composed of Mg or a Mg-based alloy. For example, a combination of pure Mg and an Mg-Mn alloy, or an Mg-Mn alloy and an Mg-Al alloy is acceptable. Furthermore, the Mg-based alloys and Al-based alloys used in the Mg and Al layers of the cladding material may be commercial Mg-based alloys such as AZ31 alloy or commercial Al-based alloys such as 3000 series alloys. Known commercial Mg-based alloys include Mg-Al-Zn alloys (AZ91, AZ31, etc.), Mg-Al-Mn alloys (AM50, AM60, etc.), Mg-Zn-Zr alloys (ZK61, ZK60, etc.), and Mg-rare earth element alloys (EZ33, ZE41, WE43, EV31, etc.). Note that among commercial Mg-based alloys, alloys like AZ91, which are difficult to process into foils with a thickness of several hundred μm, are not suitable for negative electrode materials for Mg secondary batteries and are therefore excluded. For negative electrode materials for Mg secondary batteries, commercial Mg-based alloys that can be processed into foils are desired for weight reduction.

[0023] The thickness of the Mg layer and Al layer created by these methods is preferably 0.5 mm or less. More preferably, it is 0.3 mm or less, and even more preferably 0.15 mm or less. When used as a negative electrode material, the larger the surface area in contact with the electrolyte, the better the electrochemical efficiency. If the thickness exceeds 0.5 mm, it will cause a decrease in efficiency. In addition, the weight of the secondary battery will increase, reducing the benefits of weight reduction.

[0024] Next, the characteristics of the internal microstructure of the clad material are described. The average crystal grain size of each matrix phase of the Al and Mg layers is preferably 5 μm or larger, more preferably 10 μm or larger, and even more preferably 20 μm or larger. In metallurgy and electrical engineering, grain refinement, which introduces a large number of grain boundaries, is desirable to obtain excellent electrochemical properties, and the finer the crystal grain size, the better. However, in the case of foil material with a thin sample thickness, there are only a few to a few dozen crystal grains in the cross-sectional (=thickness) direction, and in order to ensure cycle characteristics of 10 or more cycles, it is necessary to be concerned about local dissolution of the crystal grain boundaries. Here, cycle characteristics refer to the potential-current correlation obtained by cycle measurement, and generally, the quality is evaluated using the number of cycles as a measure. In cyclic voltammetry (a method of measuring the current response by scanning the voltage at a constant speed and within a certain range), the evaluation is based on how many cycles the current value at a certain potential was maintained above a reference current value, and in constant current deposition dissolution, it is evaluated from the perspective of how many cycles a low overpotential was maintained.

[0025] Furthermore, the standard deviation of the crystal grain size is preferably the same as or less than the average crystal grain size (100% or less), more preferably 75% or less, and even more preferably 50% or less. When coarse and fine crystal grains are mixed, uniform charge-discharge cycles are unlikely to occur across the entire negative electrode surface, and heterogeneous microstructure areas consisting of coarse or fine crystal grain sizes tend to become short-circuit sites for precipitation and dissolution, making it impossible to obtain the desired cycle characteristics and electrochemical properties. It is desirable to measure the crystal grain size using the section method (also called the cutting method; see JIS H0501, G0551) based on JIS standards. However, when the crystal grain size is fine or the crystal grain boundaries are unclear, it is difficult to use the section method, so it is also acceptable to measure using bright-field images or electron beam backscatter diffraction images obtained by a transmission electron microscope.

[0026] Furthermore, regarding the cross-sectional appearance of the cladding material, it is desirable that there are no gaps at the boundary between the Al layer and the Mg layer. Cross-sectional observation is performed using an optical microscope or a scanning electron microscope, and the percentage of gaps is preferably less than 50%, more preferably less than 40%, and even more preferably less than 30%. If gaps of 50% or more occur, there will be a loss in the charge-discharge characteristics, and the effect and function as a current collector will be insufficient. In addition, electrolyte may enter the gaps, becoming reaction sites for dissolution and deposition, which may cause premature short circuits.

[0027] To obtain the above-mentioned clad material, a drawing method that can continuously introduce strain into the workpiece is desirable. Of course, as described above, it is not limited to rolling, but any method that can control the internal structure during solidification and simultaneously adjust the thickness is acceptable, such as the twin-roll casting method. The temperature during drawing is preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher. Furthermore, the strain applied, converted to true strain, is preferably 0.05 or more and less than 5, more preferably 0.075 or more and less than 4, and even more preferably 0.1 or more and less than 3. If the processing temperature is below 300°C, grain size refinement can be expected, but residual strain from processing remains in the Mg matrix. These tend to become short-circuit sites during charging and discharging, which is undesirable from the viewpoint of improving electrochemical properties. Applying a true strain of 5 or more to the workpiece is similarly undesirable. On the other hand, when a true strain of less than 0.05 is applied, it becomes difficult for Al and Mg to bond well, resulting in the creation of a clad material with many gaps.

[0028] The electrochemical properties of Mg alloys are described below. In cycle measurements using a bipolar cell, the alloy preferably exhibits cycle characteristics of 5 or more cycles, more preferably 10 or more cycles, and even more preferably 15 or more cycles. If the cycle characteristics are less than 5 cycles, it cannot be used as a negative electrode due to the problem of side reactions with the electrolyte. Here, cycle measurement refers to the relationship between potential and current obtained when a constant current / voltage or current / voltage is applied for a certain period of time using a potentiometer galvanostat, while repeatedly reversing the sign at a constant speed and within a certain range.

[0029] Furthermore, the overvoltage obtainable in the electrochemical deposition dissolution test is preferably 50mV or less, more preferably 30mV or less, and even more preferably 20mV or less. If the overvoltage is 50mV or higher, the battery voltage loss is large, making it unsuitable as a negative electrode. In the electrochemical deposition dissolution test, when the electrode potential is ±0.5V, the current value is preferably ±10mAcm. -2 The above is a comfortable ±20mAcm -2 More preferably ±25 mAcm -2 The above values ​​are shown. The current value is ±10mAcm. -2 If the value is less than the negative electrode, the electrical reaction will be rate-limited by the negative electrode, and therefore it cannot be used as a negative electrode. Here, the electrochemical deposition and dissolution test is the subject of evaluation in cycle measurement. Therefore, the cycle measurement described herein refers to the cycle measurement of electrochemical deposition and dissolution, and the cycle characteristics described herein refer to the cycle characteristics of electrochemical deposition and dissolution. [Examples]

[0030] A pure Mg foil material (99.96 mass%) with a thickness of 50 μm and a commercially available pure Al foil material (99 mass%) with a thickness of 50 μm were used. A rolling mill capable of heating the rolling rolls to 300°C was used for the rolling process. The Mg foil and Al foil materials were stacked, and the clad material was created by rolling at a rolling roll temperature of 300°C for two or more passes. The rolling process was carried out in air, with a reduction ratio of 10% per pass. The created clad material was cut using a precision cross-sectional cutting machine, and examples of microstructural observations obtained using a scanning electron microscope and electron backscatter diffraction are shown in Figures 1 and 2. From Figure 1, a difference in contrast can be seen at the boundary between Mg and Al. There are no gaps at the boundary, indicating that Mg and Al are well bonded at this observation magnification level. From Figure 2, it can be seen that the average grain sizes of Mg and Al are 15 μm and 10 μm, respectively. Furthermore, the uniform contrast within each crystal grain suggests the absence of residual strain within the grains.

[0031] To evaluate the electrochemical properties of Example 1, 0.5 mAcm -2 A constant current-voltage test was performed at the specified current density. In this test, an electrolyte solution was used, which consisted of tetrakis(hexafluoroisopropoxy)magnesium borate mixed with diethylene glycol dimethyl ether. Furthermore, the electrochemical properties were evaluated using a two-electrode cell, with a Mg alloy used as the working electrode and a porous carbon material with 0.2 mL of the above electrolyte solution dropped onto it, using a glass fiber filter as a separator, as the counter electrode. Figure 3 shows a constant current-voltage measurement profile as an example of the elution reaction. In the constant current-voltage measurement profile, with 0V vs. Mg as the reference, Mg deposition occurs in the region where a negative voltage is applied, and Mg dissolution occurs in the region where a positive voltage is applied. Furthermore, in both deposition and dissolution reactions, deviations from 0V vs. Mg correspond to overpotential. The Coulomb efficiency can be calculated by taking the ratio of the current required for Mg deposition to the current required for Mg dissolution in one deposition-dissolution cycle. The cycle characteristics shown at constant voltage indicate that a good dissolution and deposition reaction is occurring. On the other hand, a sharp voltage drop is observed at 45 cycles, suggesting a short circuit. Note that all electrochemical tests were performed in a glove box under an argon atmosphere. [Examples]

[0032] A clad material was created using pure Mg foil material with a thickness of 50 μm and pure Al foil material with a thickness of 50 μm, and the clad material was created using the same procedure as in Example 1, except that the Mg foil material, Al foil material, and Mg foil material were stacked in that order. Figure 4 shows an example of cross-sectional microstructure observation obtained by scanning electron microscopy. From the difference in contrast, it can be confirmed that the Al foil material is sandwiched between the Mg foil material and there is no gap at the boundary between Mg and Al. Furthermore, from the electron beam backscatter diffraction pattern shown in Figure 5, the average crystal grain sizes of Mg and Al are 25 μm and 10 μm, respectively, and the microstructure is extremely similar to that of Example 1, except that the Al foil material is sandwiched between the Mg foil material.

[0033] The electrochemical properties of Example 2 are shown in Figure 6. The electrochemical properties were evaluated under the same conditions as in Example 1, except that an electrolyte solution containing tetrakis(hexafluoroisopropoxy)magnesium aluminate combined with diethylene glycol dimethyl ether was used. It can be seen that it exhibits good charge-discharge characteristics and has a cycle life of 15 or more cycles.

[0034] Figure 7 is a schematic diagram showing the general configuration of a magnesium secondary battery in which the negative electrode material and current collector material for magnesium secondary batteries of the present invention are used. 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.

[0035] 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.

[0036] The negative electrode 12 uses the negative electrode material and current collector material for Mg secondary batteries of the present invention. The electrolyte 13 is held by a separator (not shown) and creates ionic conductivity between the positive electrode 11 and the negative electrode 12. The electrolyte 13 contains Mg ions. During discharge, Mg ions undergo a reduction reaction at the positive electrode 11 (for example, the reaction shown in equation (1) below) and an oxidation reaction at the negative electrode 12 (for example, the reaction shown in equation (2) below). During charging, Mg ions undergo an oxidation reaction at the positive electrode 11 (for example, the reaction shown in equation (3) below) and a reduction reaction at the negative electrode 12 (for example, the reaction shown in equation (4) below). These oxidation-reduction reactions enable the charging and discharging of the Mg secondary battery.

[0037] [C1] 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)

[0038] These positive electrode 11, negative electrode 12, and electrolyte 13 are sealed in a container 14. The material of the container 14 is not particularly limited as long as it does not leak the electrolyte and is corrosion-resistant, but it is preferable to use one that is formed by pressing a metal plate such as iron and has a nickel or the like plating layer formed on the entire inner and outer surface for corrosion resistance.

[0039] It should be noted that the embodiments of the present invention described above merely illustrate an example of a magnesium secondary battery and should not be interpreted restrictively, and include technical matters that are obvious in the art of magnesium secondary batteries. [Industrial applicability]

[0040] Because the anode material and current collector for Mg secondary batteries of the present invention exhibit excellent electrochemical properties, they can be used not only in Mg primary batteries but also in Mg secondary batteries. The negative electrode material and current collector material for Mg secondary batteries of the present invention can be used in Mg secondary batteries. [Explanation of Symbols]

[0041] 1...Mg secondary battery 11...Positive electrode 12...Negative electrode 13...Electrolyte 14...Container

Claims

1. A clad material comprising an Mg layer composed of Mg or an Mg-based alloy, and an Al layer composed of Al or an Al-based alloy, The aforementioned Mg-based alloy consists of Mg-Amol%X, where X is composed of at least one element selected from the group consisting of Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth elements), and Zn, and the value of A is 0.02 mol% or more and 1 mol% or less. The Al-based alloy consists of Al-Bmol%Y, where Y is composed of at least one element selected from the group consisting of Si, Fe, Cu, Mn, Mg, Zn, Ti, Ag, Ga, and Li, and the value of B is 0.02 mol% or more and 1 mol% or less. The Mg layer, which is composed of Mg or an Mg-based alloy, is the negative electrode material. The Al layer, which is composed of Al or an Al-based alloy, is an Al current collector. A negative electrode material and current collector material for Mg secondary batteries, characterized by the above.

2. A negative electrode material and current collector material for a magnesium secondary battery according to claim 1, A negative electrode material and current collector for a magnesium secondary battery, characterized in that the thickness of the Mg layer is less than 100 μm and the thickness of the Al layer is less than 100 μm.

3. A negative electrode material and current collector material for a magnesium secondary battery according to claim 1, The average crystal grain size of the Mg matrix in the Mg layer is 50 μm or less. A negative electrode material and current collector for a Mg secondary battery, characterized in that the average crystal grain size of the Al matrix phase in the Al layer is 50 μm or less.

4. A negative electrode material and current collector material for a magnesium secondary battery according to claim 1, A negative electrode material and current collector for a magnesium secondary battery, characterized in that a gap of less than 50% exists at the Al-Mg boundary in a cross-section observed by an optical microscope or scanning electron microscope.

5. A negative electrode material and current collector material for a magnesium secondary battery according to claim 1, A negative electrode material and current collector material for a magnesium secondary battery, characterized by exhibiting cycle characteristics of 20 or more cycles in cycle measurement using a two-electrode cell.

6. A negative electrode material and current collector material for a magnesium secondary battery according to claim 1, A negative electrode material and current collector for a magnesium secondary battery, characterized by exhibiting characteristics of overvoltage of 30 mV or less in an electrochemical deposition and dissolution test of magnesium metal.

7. A negative electrode material and current collector material for a magnesium secondary battery according to claim 1, In an electrochemical deposition and dissolution test of Mg metal, when the electrode potential is ±0.5V, the reaction rate is ±10 mA cm. －２ A negative electrode material and current collector material for Mg secondary batteries, characterized by exhibiting the above current density.

8. A method for manufacturing a negative electrode material and a current collector for a magnesium secondary battery as described in any one of claims 1 to 7, A method for manufacturing a negative electrode material and current collector material for a magnesium secondary battery, characterized by stacking a magnesium layer composed of magnesium or a magnesium alloy and an aluminum layer composed of aluminum or an aluminum alloy, and applying a drawing process at a temperature of 300°C or higher to impart plastic strain, wherein the true strain is 0.05 or more and less than 5.

9. A method for manufacturing a negative electrode material and a current collector for a Mg secondary battery according to claim 8, A method for manufacturing a negative electrode material and current collector material for a Mg secondary battery, characterized in that the method for applying plastic strain is one of the following processing methods: extrusion, forging, rolling, drawing, or twin-roll casting.

10. A magnesium secondary battery comprising a negative electrode material and a current collector material for a magnesium secondary battery according to any one of claims 1 to 7, an electrolyte, and a positive electrode.

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