JP7060866B2 - A method for manufacturing a positive electrode active material for a secondary battery, a secondary battery, and a positive electrode active material for a secondary battery. - Google Patents

Description

The present invention relates to a magnesium compound, a positive electrode active material for a secondary battery, a secondary battery, and a method for producing a magnesium compound.

In recent years, research on multivalent ion secondary batteries using multivalent ions as carriers has been actively conducted. For example, a calcium secondary battery with Ca ²⁺ as a carrier, a berylium secondary battery with Be ²⁺ as a carrier, a manganese secondary battery with Mn ²⁺ as a carrier, a nickel secondary battery with Ni ²⁺ as a carrier, and a Zn ²⁺ carrier. Examples thereof include a zinc secondary battery, an yttrium secondary battery having Y ³⁺ as a carrier, an aluminum secondary battery having Al ³⁺ as a carrier, and a magnesium secondary battery having Mg ²⁺ as a carrier. Recently, research on magnesium secondary batteries has attracted attention.

Since magnesium has a high theoretical weight and volume capacity and exhibits a relatively low redox potential, it is expected that a secondary battery using magnesium as a negative electrode has a high energy density. In particular, the theoretical capacity per volume is higher than that of lithium, which is advantageous in that a large capacity can be packed in a limited space (volume) such as a secondary battery for an electric vehicle. Furthermore, the magnesium reserves are abundant in the crustal layer, and the problems of resource depletion and cost, which are the drawbacks of lithium-ion secondary batteries, can be solved.

Further, magnesium has a melting point of about 650 ° C., which is much higher than that of Li (180 ° C.), Na (98 ° C.) and the like. The melting point is an index of metal stability, and from this point of view, the secondary battery using magnesium is expected to improve the safety. Looking ahead to the practical application of metal negative electrodes in the future, the safety of negative electrode metals will be a very important factor. Further, lithium, sodium and the like are difficult to handle because they react violently with moisture in the air, but magnesium is stable in the air and easy to handle. For these reasons, magnesium ion secondary batteries are regarded as candidates for post-lithium ion secondary batteries, and numerous studies have been conducted so far. For example, in Non-Patent Document 1, a secondary battery using Mo ₆ S ₈ (including expensive Mo) having a chevrel phase as a positive electrode exhibits stable and reversible charge / discharge characteristics as a magnesium ion secondary battery. Is disclosed.

Prototype systems for rechargeable magnesium batteries, Nature 407, 724-727 (2000)

However, there are many problems to be overcome in order to realize the above-mentioned multivalent ion secondary battery, and the development of the positive electrode material is particularly important. Compared to lithium ions, polyvalent ions dramatically increase the Coulomb interaction with anions in the solid phase, so the diffusion of polyvalent ions in the positive electrode host compound is slower, which greatly limits the reaction. It can be a factor. Even in a compound containing a soft base such as sulfur ion as disclosed in Non-Patent Document 1, the reaction potential tends to decrease (about 1.1 V), and the chevrel phase has a large molecular weight and a low theoretical capacity (the theoretical capacity is low). There was also a problem of about 116 mAhg ^-1 ). From this point of view, in order to solve the problem of diffusion in the solid phase in the positive electrode and to draw out the potential of the secondary battery, the development of a high-capacity positive electrode material consisting of resource-rich elements similar to the negative electrode. Was sought after.

The present invention has been made in view of the above, and is a novel magnesium compound capable of constructing a magnesium secondary battery having a high theoretical capacity, a high potential, and a high theoretical energy density, and a positive electrode containing the magnesium compound. It is an object of the present invention to provide a method for producing an active material and a magnesium compound.

As a result of diligent research to achieve the above object, the present inventor has found that the above object can be achieved by a magnesium compound having a specific composition, and has completed the present invention.

That is, the present invention includes, for example, the subjects described in the following sections.
Item 1. The following general formula (1)
Mg _a X _b Mn _{c Od} (1)
(Here, in the formula (1), X is at least one selected from the group consisting of Fe and Cu. In addition, a is 0.5 to 1.5, b is 0.5 to 1.5, and c. Indicates 0.5 to 1.5, and d indicates 3.8 to 4.1.)
A magnesium compound represented by.
Item 2. The following general formula (2)
Mg _a Y _b Mn _{c Od} (2)
(Here, in the formula (2), Y is at least one selected from the group consisting of Fe, Cu, Mn, Co and Ni. In addition, a is 0.5 to 1.5 and b is 0.5. ~ 1.5, c indicates 0.5 to 1.5, d indicates 3.8 to 4.1.)
A positive electrode active material for a secondary battery containing a magnesium compound represented by.
Item 3. A secondary battery containing the positive electrode active material according to item 2 above as a component.
Item 4. The method for producing a magnesium compound according to Item 1 above.
A production method comprising a heating step of heating a raw material mixture containing a raw material containing Mg, the raw material containing X, and the raw material containing Mn.
Item 5. Item 4. The production method according to Item 4, wherein the heating temperature in the heating step is 500 to 1500 ° C.

The magnesium compound according to the present invention is suitable as a positive electrode active material for constituting a magnesium secondary battery having a high energy density, can have a high capacity of a magnesium ion secondary battery, and has magnesium ions at low cost. It is a material that can provide a secondary battery.

Further, since the positive electrode active material for a magnesium ion secondary battery according to the present invention contains the above magnesium compound, it is suitable for use in a magnesium secondary battery.

The XRD pattern of the product obtained in Example 1 is shown. The XRD patterns of the product obtained in Example 1 (upper row) and each raw material used in Example 1 (lower row) are shown. The XRD pattern of MgFeMnO ₄ obtained in Example 1 and the XRD pattern of iron-based manganate compounds (Li ₂ FeMnO ₄ , LiFeMnO ₄ , K ₂ FeMnO ₄ ) containing different cations are shown. The SEM image of MgFeMnO ₄ obtained in Example 1 is shown. The result of the open circuit potential measurement of MgFeMnO ₄ obtained in Example 1 is shown. The charge / discharge characteristics when MgFeMnO ₄ obtained in Example 1 is used as a positive electrode material, and the relationship between each cycle and the discharge capacity are shown. The results of the potential-time characteristics of all Mg batteries when MgFeMnO ₄ obtained in Example 1 is used as a positive electrode material are shown. The results of investigating the relationship between each cycle of all Mg batteries and the discharge capacity when MgFeMnO ₄ obtained in Example 1 is used as a positive electrode material are shown. The XRD pattern of the product obtained in Example 2 is shown. The SEM image of MgCuMnO ₄ obtained in Example 2 is shown. The result of the open circuit potential measurement of MgCuMnO ₄ obtained in Example 2 is shown. The charge / discharge characteristics when MgCuMnO ₄ obtained in Example 2 is used as a positive electrode material, and the relationship between each cycle and the discharge capacity are shown. The results of the potential-time characteristics of all Mg batteries when MgCuMnO ₄ obtained in Example 2 is used as a positive electrode material are shown. The XRD pattern of the product obtained in Example 3 is shown. The SEM image of the product obtained in Example 4 is shown. The XRD patterns of the products obtained in Examples 4 to 5 are shown. The results of the potential-time characteristics of all Mg batteries when MgComnO ₄ obtained in Example 4 is used as a positive electrode material are shown. The SEM image of the product obtained in Example 5 is shown. The XRD pattern of the product obtained in Examples 6 and 7 is shown. The SEM image of the product obtained in Example 6 is shown. A high resolution SEM image of the product obtained in Example 6 is shown. The SEM image of the product obtained in Example 7 is shown. It is a graph plotting the change of the lattice constant of MgFe _1-x Cu _x MnO ₄ (x = 0,0.5,1). The SEM-EDX of the product obtained in Example 6 is shown. The SEM image of the product obtained in Example 7 is shown. The XRD pattern of the product obtained in Example 8 is shown. The SEM image of the product obtained in Example 8 is shown. The XRD pattern of each compound is shown.

Hereinafter, embodiments of the present invention will be described in detail. In addition, when the range is shown in this specification, the numerical values at both ends are included in each case.

1. 1. Magnesium compound The magnesium compound of this embodiment has the following general formula (1).
Mg _a X _b Mn _{c Od} (1)
(Here, in the formula (1), X is at least one selected from the group consisting of Fe and Cu. A is 0.5 to 1.5, b is 0.5 to 1.5, and c is 0. .5 to 1.5, d indicates 3.8 to 4.1.)
Since such a magnesium compound can insert and desorb magnesium ions, it is useful as a positive electrode active material for a magnesium ion secondary battery.

In the general formula (1), X is any one selected from the group consisting of Fe and Cu. A magnesium compound can be produced at low cost by using at least one selected from the group consisting of Fe and Cu.

The value of a is more preferably 0.8 to 1.3, more preferably 0.9 to 1.1, from the viewpoint of ease of insertion and desorption of magnesium ions, capacity, and high potential. Is particularly preferred.

The value of b is more preferably 0.5 to 1.1, more preferably 0.8 to 1.1, from the viewpoint of ease of insertion and desorption of magnesium ions, capacity, and high potential. Is particularly preferred. As a reminder, when X contains two types of Fe and Cu at the same time, the value of b represents the total amount of each element of these two types.

The value of c is more preferably 0.5 to 1.1, more preferably 0.8 to 1.1, from the viewpoint of ease of insertion and desorption of magnesium ions, capacity, and high potential. Is particularly preferred.

The value of d is more preferably 3.8 to 4.0, more preferably 3.9 to 4.0, from the viewpoint of ease of insertion and desorption of magnesium ions, capacitance, and high potential. Is particularly preferred.

Specifically, as the magnesium compound represented by the general formula (1), MgFeMnO ₄ and MgCuMnO ₄ are preferable from the viewpoints of ease of insertion and desorption of magnesium ions, low cost, capacity, and high potential. ..

The valence of X in the general formula (1) is preferably divalent, and the valence of Mn is preferably tetravalent. That is, the magnesium compound in the general formula (1) is preferably MgX 2 ⁺ Mn ^{4 +} O ₄ . In this case, insertion and desorption of magnesium ions are likely to occur, and when used as a positive electrode active material for a magnesium ion secondary battery, the magnesium ion secondary battery is likely to have a high capacity and a high potential.

The crystal structure of the magnesium compound is not particularly limited. For example, since X in the general formula (1) contains at least one selected from the group consisting of Fe and Co, the magnesium compound can have a cubic system (Fd-3m space group) and thus form a spinel-type structure. It's easy to do. A magnesium compound having such a spinel-type structure can have a higher capacity in a magnesium ion secondary battery when used as a positive electrode active material for a magnesium ion secondary battery.

In the magnesium compound, the abundance of the crystal structure as the main phase is not particularly limited, and is preferably 80 mol% or more, more preferably 90 mol% or more, based on the entire magnesium compound represented by the general formula (1). .. Therefore, the magnesium compound represented by the general formula (1) can be formed as a material having a single-phase crystal structure. However, the magnesium compound represented by the general formula (1) may be formed of a material having a plurality of crystal structures as long as the effects of the present invention are not impaired. The crystal structure of the magnesium compound represented by the general formula (1) can be confirmed by X-ray diffraction measurement.

In the X-ray diffraction measurement of the magnesium compound represented by the general formula (1), the diffraction angles represented by 2θ are 17.1 to 19.1 °, 29.2 to 31.0 °, 34.4 to 36. 4 °, 36.7 to 38.4 °, 42.1 to 44.5 °, 52.6 to 54.2 °, 56.2 to 58.2 °, 61.6 to 63.7 °, 73. It preferably has peaks at 1-75.4 ° and 78.3-79.6 °. In this case, the crystal structure of the magnesium compound represented by the general formula (1) can be a spinel type structure, and when used as a positive electrode active material for a magnesium ion secondary battery, the capacity of the magnesium ion secondary battery. Is easy to improve.

The magnesium compound represented by the general formula (1) having the above-mentioned crystal structure and composition can be in the form of, for example, a particulate powder. When the magnesium compound is in the form of particles, the average particle size thereof is preferably 0.005 to 50 μm, preferably 0.01 to 0., From the viewpoint of ease of insertion and desorption of magnesium ions, volume, and high potential. 2 μm is more preferable. The average particle size of the magnesium compound represented by the general formula (1) is measured by observation with an electron microscope (SEM). The average particle size referred to here means, for example, an arithmetic mean value of a circle-equivalent diameter measured by direct observation with an electron microscope.

2. 2. Positive electrode active material for secondary batteries (positive electrode active material)
The positive electrode active material for a secondary battery of this embodiment has the following general formula (2).
Mg _a Y _b Mn _{c Od} (2)
(Here, in the formula (2), Y is at least one selected from the group consisting of Fe, Cu, Mn, Co and Ni. A is 0.5 to 1.5 and b is 0.5 to 1. .5, c indicates 0.5 to 1.5, and d indicates 3.8 to 4.1). That is, in the positive electrode active material of the present embodiment, in addition to the magnesium compound described above (Y in the formula (2) is at least one selected from the group consisting of Fe and Cu), Y is Mn, Co and / or Ni. Including some cases. Here, when Y is Mn, one Mn and the other Mn have different valences.

The value of a is more preferably 0.8 to 1.3, more preferably 0.9 to 1.1, from the viewpoint of ease of insertion and desorption of magnesium ions, capacity, and high potential. Is particularly preferred.

The value of b is more preferably 0.5 to 1.1, more preferably 0.8 to 1.1, from the viewpoint of ease of insertion and desorption of magnesium ions, capacity, and high potential. Is particularly preferred. As a reminder, when Y contains two or more kinds selected from the group consisting of Fe, Cu, Mn, Co and Ni at the same time, the value of b represents the total amount of each of these elements.

The value of c is more preferably 0.5 to 1.1, more preferably 0.8 to 1.1, from the viewpoint of ease of insertion and desorption of magnesium ions, capacity, and high potential. Is particularly preferred.

The value of d is more preferably 3.8 to 4.0, more preferably 3.9 to 4.0, from the viewpoint of ease of insertion and desorption of magnesium ions, capacitance, and high potential. Is particularly preferred.

When, for example, a magnesium ion secondary battery is formed by using the positive electrode active material represented by the general formula (2) as described above, the magnesium ion secondary battery can have a high capacity. Moreover, in the positive electrode active material represented by the above general formula (2), a redox reaction occurs in two stages of Y ²⁺ / Y ³⁺ and Y ³⁺ / Y ⁴⁺ , so that the capacity of the magnesium ion secondary battery is high. Prone. Further, since the magnesium compound can be produced by an inexpensive and easy process, the magnesium secondary battery can be provided at low cost according to the positive electrode active material of the present embodiment. Therefore, the positive electrode active material of the present embodiment is suitable as a positive electrode material constituting a magnesium secondary battery having a high energy density (for example, a magnesium ion secondary battery).

In the general formula (2), if Y is any one selected from the group consisting of Fe and Cu, the magnesium compound can be produced at low cost. Further, in the general formula (2), if Y is at least one selected from the group consisting of Co and Ni, it is easy to improve the potential of the secondary battery.

In addition, other materials may be contained in the positive electrode active material as long as the performance of the positive electrode active material of this embodiment is not impaired. Further, the positive electrode active material may contain unavoidable impurities in addition to the magnesium compound. Examples of such unavoidable impurities include a raw material mixture described later, and for example, about 10 mol% or less, preferably about 5 mol% or less, more preferably 2 mol% in the positive electrode active material for a magnesium ion secondary battery. It can be contained to the following extent.

In the positive electrode active material, the magnesium compound and a carbon material (for example, carbon black such as acetylene black) may form a complex. As a result, since the carbon material suppresses the grain growth of the magnesium compound during firing, it can be a fine particle-like positive electrode active material having excellent electrode characteristics. In this case, the content of the carbon material is preferably adjusted to be 3 to 40% by mass, particularly 5 to 15% by mass in the positive electrode active material.

3. 3. Method for Producing Magnesium Compound The method for producing the magnesium compound represented by the general formula (1) and the positive electrode active material represented by the general formula (2) is not particularly limited. For example, a magnesium compound represented by the general formula (1) is produced by a production method comprising a heating step of heating a raw material mixture containing a raw material containing Mg, a raw material containing X, and a raw material containing Mn. Can be manufactured. Alternatively, the positive electrode activity represented by the general formula (2) can be obtained by a production method comprising a heating step of heating a raw material mixture containing a raw material containing Mg, a raw material containing Y, and a raw material containing Mn. The substance can be manufactured. Hereinafter, a method for producing a magnesium compound will be specifically described. Since Y includes X, the magnesium compound represented by the general formula (1) is a raw material mixture containing a raw material containing Mg, a raw material containing Y, and a raw material containing Mn. Can also be produced by a production method comprising a heating step of heating.

(1) Raw Material Mixture The raw material mixture in the above-mentioned production method includes a raw material containing Mg, a raw material containing Y, and a raw material containing Mn. The raw material mixture may be a three-kind mixture containing one each of the Mg-containing raw material, the Y-containing raw material, and the Mn-containing raw material. The raw material containing Mg, the raw material containing Y and the raw material containing Mn can all be one kind or two or more kinds. Further, as the raw material mixture, a compound containing Mg, two or more elements of the above Y and Mn at the same time can be used as a part of the raw material. In this case, the raw material mixture is a mixture of less than three types.

The raw material containing Mg may be, for example, metallic Mg or a compound containing an Mg element. Examples of the compound containing the Mg element include magnesium oxide (MgO), magnesium hydroxide (Mg (OH) ₂ ), magnesium chloride (MgCl ₂ ), magnesium carbonate (MgCO ₃ ), and magnesium nitrate (Mg (NO ₃ ) ₂ ). ), Magnesium oxalate (MgC ₂ O ₄ ), magnesium acetate (Mg (CH ₃ COO) ₂ ) and the like are exemplified. The compound containing the Mg element may be a hydrate.

The raw material containing Y may be a simple substance of a metal or a compound containing a metal Y. Examples of the compound containing the metal Y include oxides, hydroxides, chlorides, carbonates, nitrates, and oxalates of the metal Y. The compound containing the metal Y may be a hydrate.

As a further specific example of the compound containing the metal Y, if Y is Fe, FeC _{2 O 4, if Y is Mn, MnC 2 O 4 , if} Y is Ni, Ni (OH) ₂ , and Y is Co. If there is CoC ₂ O ₄ , and if Y is Cu, CuO is exemplified.

The raw material containing Mn may be, for example, metallic Mn or a compound containing Mn element. Examples of the compound containing the Mn element include manganese oxide (MnO ₂ ), manganese hydroxide (Mn (OH) ₂ ), manganese chloride (MnCl ₂ ), manganese carbonate (MgCO ₃ ), and manganese acetate (Mn (CH ₃ COO). ) ₂ ) etc. are exemplified. The compound containing the Mn element may be a hydrate.

Regarding the raw material containing Mn, when the above Y is also Mn, the valence of one Mn and the valence of the other Mn are set to be different. For example, the raw material containing Y (= Mn) may be MnC ₂ O ₄ containing divalent Mn, and the raw material containing Mn may be manganese oxide (Mn O ₂ ) containing tetravalent Mn. can.

It is preferable that the raw material mixture does not contain Mg and other metal elements (particularly rare metal elements) other than the above metals Y and Mn. Further, it is desirable that other metal elements are separated and volatilized by heat treatment in a non-oxidizing atmosphere.

As the raw material containing Mg, the raw material containing Y, and the raw material containing Mn, a commercially available product may be used, or a separately synthesized raw material may be used.

The shape of the raw material mixture is not particularly limited, and is preferably in the form of powder from the viewpoint of handleability. From the viewpoint of reactivity, the particles are preferably fine, and are preferably in the form of powder having an average particle diameter of 1 μm or less (particularly about 60 to 80 nm). The average particle size of each raw material is measured by electron microscopy (SEM).

The raw material mixture can be prepared by mixing the raw material containing Mg, the raw material containing Y, and the raw material containing Mn in a predetermined blending ratio. The mixing method is not particularly limited, and for example, a method capable of uniformly mixing each raw material can be adopted. Specifically, mortar mixing, mechanical milling treatment, coprecipitation method, a method of dispersing each raw material in a solvent and then mixing, a method of dispersing each raw material in a solvent at once and mixing, etc. can be adopted. can. Among these, the magnesium compound can be obtained by a simpler method by adopting the mortar mixing. When obtaining a more uniform mixed raw material mixture, the coprecipitation method can be adopted.

The mixing ratio of each raw material in each raw material mixture is not particularly limited. For example, it is preferable to mix each raw material so as to obtain a magnesium compound having a desired composition as a final product. Specifically, it is preferable to adjust the blending ratio of each raw material so that the ratio of each element contained in each raw material is the same as the ratio of each element in the target magnesium compound.

(2) Heating Step In the heating step, a raw material mixture containing a raw material containing Mg, the raw material containing Y, and a raw material containing Mn is heated.

The heating step can be performed, for example, in an atmosphere of an inert gas such as argon or nitrogen. Alternatively, the heating step may be performed under reduced pressure such as vacuum.

The heating temperature (that is, the firing temperature) in the heating step is preferably 500 to 1500 ° C. In this case, the operation of the heating step can be performed more easily, and the obtained magnesium compound can easily form a spinel-type structure. As a result, the crystallinity and electrode characteristics (particularly, capacitance and potential) of the obtained magnesium compound are likely to be improved.

If Y is Fe, the lower limit of the heating temperature in the heating step is preferably 700 ° C, particularly preferably 800 ° C. The upper limit of the heating temperature can be appropriately determined within a range in which the operation in the production of the magnesium compound can be easily performed (for example, 1500 ° C.).

If Y is Cu, Mn (Mn ²⁺ ), Co or Ni, the lower limit of the heating temperature in the heating step is preferably 500 ° C, more preferably 800 ° C, and more preferably 1150 ° C. Especially preferable. The upper limit of the firing temperature can be appropriately determined within a range in which the operation in the production of the magnesium compound can be easily performed (for example, 1500 ° C.).

The heating time in the heating step is not particularly limited, and is preferably 10 minutes to 48 hours, more preferably 30 minutes to 24 hours, for example. When the above Y is Cu, Mn (Mn ²⁺ ), Co or Ni, the heating time is preferably 1 hour or more, more preferably 12 hours or more, still more preferably 24 hours or less.

A desired magnesium compound can be obtained by heating for a predetermined time and then cooling. Further, after cooling once, the heating treatment may be performed again at the heating temperature to perform firing.

The magnesium compound can be produced by, for example, a coprecipitation method, a sol-gel method, a hydrothermal synthesis method, a Pecchini method, or the like, in addition to the above-mentioned production method.

4. Secondary battery The secondary battery of the present embodiment has the positive electrode active material for the secondary battery as a component. In particular, the positive electrode active material for a secondary battery is suitable as a component of a magnesium ion secondary battery.

The magnesium ion secondary battery can be configured with reference to a known non-aqueous electrolyte magnesium ion secondary battery, except that the positive electrode active material for the secondary battery is used as the positive electrode active material. .. For example, the positive electrode, the negative electrode, and the separator can be arranged in the battery container so that the positive electrode and the negative electrode are separated from each other by the separator. Then, after filling the battery container with the non-aqueous electrolytic solution, the magnesium ion secondary battery can be manufactured by sealing the battery container or the like. The magnesium ion secondary battery may be a magnesium secondary battery. In the present specification, the "magnesium ion secondary battery" means a secondary battery using magnesium ion as a carrier ion, and the "magnesium secondary battery" is a secondary battery using a magnesium metal or a magnesium alloy as a negative electrode active material. Means a battery.

As the positive electrode, a structure in which a positive electrode material containing a positive electrode active material for a secondary battery is supported on a positive electrode current collector can be adopted. For example, it can be produced by applying a positive electrode mixture containing the positive electrode active material for a secondary battery, a conductive auxiliary agent, and a binder, if necessary, to a positive electrode current collector.

As the conductive auxiliary material, for example, carbon materials such as acetylene black, ketjen black, carbon nanotubes, vapor phase carbon fibers, carbon nanofibers, graphite, and cokes can be used. The shape of the conductive auxiliary agent is not particularly limited, and for example, a powder or the like can be adopted.

Examples of the binder include polyvinylidene fluoride resin, fluororesin such as polytetrafluoroethylene, and the like.

The content of various components in the positive electrode material is not particularly limited and can be appropriately determined. For example, the positive electrode active material for a secondary battery is 50 to 95% by volume (particularly 70 to 90% by volume), and the conductive auxiliary agent. Is preferably contained in an amount of 2.5 to 25% by volume (particularly 5 to 15% by volume), and the binder is preferably contained in an amount of 2.5 to 25% by volume (particularly 5 to 15% by volume).

Examples of the material constituting the positive electrode current collector include aluminum, titanium, platinum, molybdenum, stainless steel, and copper. Examples of the shape of the positive electrode current collector include a porous body, a foil, a plate, and a mesh made of fibers.

The amount of the positive electrode material applied to the positive electrode current collector is preferably determined as appropriate according to the application of the magnesium ion secondary battery and the like.

Examples of the negative electrode active material constituting the negative electrode of the magnesium ion secondary battery include magnesium metal; silicon; silicon-containing Krathrate compound; magnesium alloy; M ¹ M ² ₂ O ₄ (M ¹ : Co, Ni, Mn, Sn, etc.). , M ² : Mn, Fe, Zn, etc.) ternary or quaternary oxide; M ³ ₃ O ₄ (M ³ : Fe, Co, Ni, Mn, etc.), M ⁴ ₂ O ₃ (M ⁴ ) : Fe, Co, Ni, Mn, etc.), MnV ₂ O ₆ , M ⁵ O ₂ (M ⁵ : Sn, Ti, etc.), M ⁶ O (M ⁶ : Fe, Co, Ni, Mn, Sn, Cu, etc.) Metal oxides represented by, etc .; graphite, hard carbon, soft carbon, graphene; the above-mentioned carbon materials; organic compounds such as MgC ₈ H ₄ O ₄ , _{MgC 8} H ₄ O 4.2 H ₂ O, etc. Can be mentioned. Examples of magnesium alloys include alloys containing magnesium and aluminum as constituent elements, alloys containing magnesium and zinc as constituent elements, alloys containing magnesium and manganese as constituent elements, alloys containing magnesium and bismuth as constituent elements, magnesium and nickel. Alloys containing magnesium and antimon as constituent elements, alloys containing magnesium and tin as constituent elements, alloys containing magnesium and indium as constituent elements; metals (scandium, titanium, vanadium, chromium, zirconium, niobium) , Molybdenum, Hafnium, Tantal, etc.) and ^MXene alloys containing carbon as constituent elements _, M7 _x BC3 alloys (M7: Sc, Ti, ^V , Cr, Zr, Nb, Mo, Hf, Ta, etc.), etc. Quaternary layered carbonized or nitrided compounds; alloys containing magnesium and lead as constituent elements can be mentioned.

The negative electrode may be composed of a negative electrode active material, and a negative electrode material containing a negative electrode active material, a conductive auxiliary agent, and, if necessary, a binder is supported on the negative electrode current collector. You can also do it. When adopting a configuration in which the negative electrode material is supported on the negative electrode current collector, a negative electrode mixture containing a negative electrode active material, a conductive auxiliary agent, and, if necessary, a binder is applied to the negative electrode current collector. Can be manufactured.

When the negative electrode is composed of a negative electrode active material, the above negative electrode active material can be obtained by molding into a shape (plate shape or the like) suitable for the electrode.

Further, when the structure in which the negative electrode material is supported on the negative electrode current collector is adopted, the types of the conductive auxiliary agent and the binder, and the contents of the negative electrode active material, the conductive auxiliary agent and the binder are those of the above-mentioned positive electrode. Can be applied. Examples of the material constituting the negative electrode current collector include aluminum, copper, nickel, stainless steel and the like. Examples of the shape of the negative electrode current collector include a porous body, a foil, a plate, a mesh made of fibers, and the like. The amount of the negative electrode material applied to the negative electrode current collector is preferably determined as appropriate according to the application of the magnesium ion secondary battery and the like.

The separator is not limited as long as it is made of a material that can isolate the positive electrode and the negative electrode in the battery and can secure the ionic conductivity between the positive electrode and the negative electrode by holding the electrolytic solution. For example, it is made of a polyolefin resin such as polyethylene, polypropylene, polyimide, polyvinyl alcohol, and terminal amination polyethylene oxide; a fluororesin such as polytetrafluoroethylene; an acrylic resin; a nylon; an aromatic aramid; an inorganic glass; and a porous material such as ceramics. Materials in the form of a quality film, non-woven fabric, woven cloth and the like can be used.

The non-aqueous electrolytic solution is preferably an electrolytic solution containing magnesium ions. Examples of such an electrolytic solution include a solution of a magnesium salt, an ionic liquid composed of an inorganic material containing magnesium, and the like.

Further, when the secondary battery is a magnesium ion secondary battery, the electrolytic solution can contain a magnesium cation. Examples of such an electrolytic solution include, but are not limited to, a solution in which a magnesium salt is dissolved in a solvent, an ionic liquid composed of an inorganic material containing magnesium, and the like. Examples of the magnesium salt include magnesium halides such as magnesium chloride, magnesium bromide, and magnesium iodide, magnesium perchlorate, magnesium tetrafluoroborate, magnesium hexafluorophosphate, magnesium hexafluorophosphate, and other magnesium inorganic salts. Compounds; Magnesium organic salt compounds such as bis (trifluoromethylsulfonyl) imidemagnesium, tris (pentafluoroethane) trifluorophosphofate magnesium, magnesium benzoate, magnesium salicylate, magnesium phthalate, magnesium acetate, magnesium propionate, glignal reagent, etc. However, the present invention is not limited to this example.

Examples of the solvent include carbonate compounds such as propylene carbonate, ethylene carbonate, dimethol carbonate, ethylmethyl carbonate and diethyl carbonate; lactone compounds such as γ-butyrolactone and γ-valerolactone; tetrahydrofuran, 2-methyltetrachloride, diethyl ether, etc. Diisopropyl ether, dibutyl ether, methoxymethane, N, N-dimethylformamide, glyme, N-propyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide, dimethoxyethane, dimethoxymethane, dietoquimethane, dietkietan, propylene glycol dimethyl ether, etc. Ether compounds; acetonitrile and the like can be mentioned.

Further, a solid electrolyte can be used instead of the non-aqueous electrolyte solution. Examples of the solid electrolyte include (Mg _0.1 Hf _0.9 ) _{4 / 3.8} Nb (PO ₄ ) ₃ , (Mg _0.1 Hf _0.9 ) _{4 / 3.8} (Nb _1-y W). _y ) (PO ₄ ) ₃ (0 ≦ y ≦ 3), Mg _a Zr _b (PO ₄ ) _c (a, b = 1, 2, 4, 5, 7; c = 2, 4, 6, 8, 10 ), Mg (BH ₄ ) ₂ (NH ₃ ) ₂ , etc. Magnesium ion conductors and the like are listed.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the embodiments of these Examples.

(Example 1)
As raw material powder, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), FeC ₂ O _{4.2H 2} O (Junsei Chemical, 99.9% (3N)), MnO ₂ (rare metallic, 99). .99% (4N)) was used. MgO, FeC _{2 O 4.2H 2 O and MnO 2 were weighed so} that the molar ratio of magnesium, iron and manganese was 1: 1: 1 and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined at a firing temperature of 800 ° C. for 1 hour, 2 hours, 4 hours or 6 hours under an Ar stream. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

(Example 2)
As raw material powder, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CuO (High Purity Chemistry, 99.99% (4N)), MnO ₂ (Rare Metallic, 99.99% (4N)) ) Was used. MgO, CuO and MnO ₂ were weighed so that the molar ratio of magnesium, copper and manganese was 1: 1: 1 and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined at a firing temperature of 800 ° C. for 1 hour, 2 hours, 4 hours or 6 hours under an Ar stream. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

(Example 3)
As raw material powders, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), MnC ₂ O ₄ (high purity chemistry, 99.9% (3N)) and MnO ₂ (rare metallic, 99.99%). (4N)) was used. MgO, MnC ₂ O ₄ and MnO ₂ were weighed so that the molar ratio of magnesium, Mn ²⁺ and Mn ⁴⁺ was 1: 1: 1 and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined under an Ar stream at a firing temperature of 800 to 1150 ° C. for 3 hours or 8 hours. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

(Example 4)
As raw material powders, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CoC ₂ O ₄ (high purity chemistry, 99% (2N)) and MnO ₂ (rare metallic, 99.99% (4N)). )) Was used. MgO, CoC ₂ O ₄ and MnO ₂ were weighed so that the molar ratio of magnesium, cobalt and manganese was 1: 1: 1 and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined under an Ar stream at a firing temperature of 800 to 1150 ° C. for 3 hours or 8 hours. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

(Example 5)
As raw material powders, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), Ni (OH) ₂ (high purity chemistry, 99.9% (3N)) and MnO ₂ (rare metallic, 99.99). % (4N)) was used. MgO, Ni (OH) ₂ and MnO ₂ were weighed so that the molar ratio of magnesium, nickel and manganese was 1: 1: 1 and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined under an Ar stream at a firing temperature of 800 to 1150 ° C. for 3 hours or 8 hours. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

(Example 6)
As raw material powder, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CuO (High Purity Chemistry, 99.99% (4N)), FeC ₂ O _{4.2H 2} O (Junsei Chemical, 99) 9.9% (3N)) and MnO ₂ (rare metallic, 99.99% (4N)) were used. MgO, CuO, FeC 2O _{4.2H 2O} and MnO ₂ are weighed so that the molar ratio of magnesium, copper, iron and manganese is ₂ : 1: 1: 2, and mixed in a mortar for about 30 minutes. Obtained a raw material mixture. Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined under an Ar stream at a firing temperature of 800 ° C. for 1 hour. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

(Example 7)
As raw material powder, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), Ni (OH) 2 (high purity chemistry, 99.9% (3N)), FeC ₂ O _{4.2H 2} O ( Junsei Chemical, 99.9% (3N)) and MnO ₂ (rare metallic, 99.99% (4N)) were used. Weigh MgO, Ni (OH) ₂ , FeC 2O _{4.2H 2O} and MnO ₂ so that the molar ratio of magnesium, nickel, iron and manganese is ₂ : 1: 1: 2, and in a mortar and pestle. Mixing for 30 minutes gave a raw material mixture. Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined under an Ar stream at a firing temperature of 800 ° C. for 1 hour. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

(Example 8)
As raw material powder, MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CuO (High Purity Chemistry, 99.99% (4N)), Ni (OH) ₂ (High Purity Chemistry, 99.9) % (3N)), MnO ₂ (rare metallic, 99.99% (4N)) was used. Weigh MgO, CuO, Ni (OH) ₂ and MnO ₂ so that the molar ratio of magnesium, copper, nickel and manganese is 2: 1: 1: 2, and mix them in a mortar for about 30 minutes to mix the raw materials. Got Then, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces), acetone was added, and the mixture was pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling off acetone under reduced pressure, the recovered powder was pellet-molded at 40 MPa and calcined under an Ar stream at a firing temperature of 800 ° C. for 1 hour. At this time, the temperature rising rate was set to 400 ° C./h. The cooling rate was 100 ° C./h up to 300 ° C., and thereafter, the mixture was allowed to cool to room temperature by natural cooling. The product obtained after firing was brought into a glove box kept in an Ar atmosphere and stored in an environment where there was no contact with air.

<Evaluation method>
[Powder X-ray diffraction (XRD) measurement]
The sample synthesized by using an X-ray diffractometer (RINT-UltimaIII / G manufactured by Rigaku Co., Ltd.) was measured. CuKα rays were used as the X-ray source, and the applied voltage was 40 kV and the current value was 40 mA. The measurement was performed at a scanning speed of 0.02 ° / sec in an angle range of 10 ° to 80 °.

[ICP-AES measurement]
The ICP-AES measurement was performed using an inductively coupled plasma emission spectrophotometer (“iCAP6500” manufactured by Thermo Fisher Scientific Co., Ltd.”.

[Test Example 1: Examination of cation desorption and insertion (Li half cell)]
In order to perform charge / discharge measurement, the product obtained in the example, acetylene black (AB), and polyvinylidene fluoride (PVDF) are mixed in an agate mortar so that the weight ratio is 80:10:10. The obtained slurry was applied onto an Al foil (thickness 20 μm) which was a current collector, and this was punched into a circle (diameter 8 mm) to form a positive electrode. A CR2032 type coin cell was used as the cell. A Li box was used as the negative electrode, and the electrolytic solution used was an electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 M as a supporting electrolyte in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 2. .. The constant current charge / discharge measurement was performed by using a voltage switch, setting the current to 10 mAg ^-1 , the upper limit voltage of 4.8 V, and the lower limit voltage of 1.5 V, and starting from charging. Charge / discharge measurement was performed with the cell placed in a constant temperature bath at 55 ° C.

[Test Example 2: Examination of Magnesium Ion Desorption and Insertion (Mg All Battery)]
A CR2032 type coin cell was used as the cell. The electrolytic solution was prepared by dissolving Mg (TFSI) ₂ in ethylene glycol dimethyl ether dimethoxyethylene glycol (trade name: monoglycyme) so that the concentration thereof was 0.5 M, using the Mg plate as the negative electrode. The constant current charge / discharge measurement was performed by using a voltage switcher, setting the current to 5 mAg ^-1 , the upper limit voltage to 3.6 V, and the lower limit voltage to 0 V, and starting from charging. The measurement was performed at room temperature.

FIG. 1 shows the XRD pattern of the product fired at various firing times in Example 1. The firing temperature is 800 ° C. The X-ray wavelength used is 1.5418 Å.

From FIG. 1, when the firing temperature is 650 ° C. or higher, at least 2θ values are 29.2 to 31.0 °, 34.4 to 36.4 °, 42.1 to 44.5 °, and 56.2 to 58. It can be seen that multiple major peaks are seen at .2 ° or 61.6-63.7 °. Since these peaks correspond to the single-phase MgFeMnO ₄ , it can be seen that the single-phase MgFeMnO ₄ is obtained as a product. Further, since the peak having a 2θ value of 34.4 to 36.4 ° becomes stronger as the firing time is longer, it can be seen that the firing time is preferably 6 hours or more.

FIG. 2 shows a comparison between the product (upper) obtained by performing the heating step at 800 ° C. for 1 hour in Example 1 and the XRD pattern of each raw material (lower). From the obtained X-ray diffraction pattern of MgFeMnO ₄ , it was found that a single phase of MgFeMnO ₄ can be synthesized because no peak derived from the starting material and its related impurity phase is observed.

In FIG. 3, the XRD pattern of MgFeMnO ₄ (sintering time is 1 hour) obtained in Example 1 and iron-based manganate compounds (Li ₂ FeMnO ₄ , LiFeMnO ₄ , K ₂ FeMnO) containing different cations are shown. The XRD pattern of ₄ ) is shown.

From FIG. 3, the crystals of MgFeMnO ₄ obtained in Example 1 have diffraction angles of 17.1 to 19.1 ° and 29.2 to 31 represented by 2θ in the X-ray diffraction pattern by powder X-ray diffraction. .0 °, 34.4 to 36.4 °, 36.7 to 38.4 °, 42.1 to 44.5 °, 52.6 to 54.2 °, 56.2 to 58.2 °, 61 It can be seen that the peaks are at 6.6 to 63.7 °, 73.1 to 75.4 ° and 78.3 to 79.6 °. The peak position of MgFeMnO ₄ is similar to that of LiFeMnO ₄ as compared with the iron-based manganate compound containing a different cation. It can be seen that the lattice constant of MgFeMnO ₄ is almost close to the lattice constant of LiFeMnO ₄ .

Further, since the peak position and intensity of MgFeMnO ₄ are similar to those of Hausmannite type MnFe ₂ O ₄ , it was found that MgFeMnO ₄ has a spinel structure.

As a result of the structural analysis of the above-mentioned MgFeMnO ₄ obtained in Example 1 by the Rietveld method, the obtained crystal of MgFeMnO ₄ has a cubic crystal structure (Fd-3m space group) and the lattice constant is a = b. It was found that the crystal had = c = 8.4043 (6) Å, α = β = γ = 90 °, and the unit lattice volume (V) was 593.6 (0) Å ³ . The reliability factors were R _wp = 4.65%, R _p = 3.61%, and χ ² = 1.04. When the elemental composition in the crystal was examined by ICP analysis, it was confirmed that it was Mg _0.9 FemnO ₄ .

FIG. 4 shows an SEM image of MgFeMnO ₄ (sintering time is 1 hour) obtained in Example 1. In the figure, the scale bar indicates 100 nm. In MgFeMnO ₄ obtained in Example 1, the particles tend to be aggregated, but it can be seen that the average particle diameter is around 100 nm.

FIG. 5 shows the result (result of open circuit potential measurement) of Test Example 1 of MgFeMnO ₄ (sintering time is 1 hour) obtained in Example 1. It was found that the open circuit potential of the MgFeMnO ₄ sample was about 3.2 V. This is 2.5 Vvs. When converted to the magnesium potential standard. Since it is Mg ²⁺ , the material obtained in Example 1 can be used as a high-potential positive electrode material.

FIG. 6 shows the results of Test Example 1 when MgFeMnO ₄ (sintering time is 1 hour) obtained in Example 1 was used as the positive electrode material (charge / discharge characteristics and relationship between each cycle and discharge capacity). Is shown. In FIG. 6, the intersection of the discharge curve when the first discharge is performed and the charge curve when the second charge is performed, the charge curve when the second charge is performed, and the second discharge are performed. The intersection with the discharge curve at that time overlaps. From this result, it can be seen that by using the obtained positive electrode material, the charge / discharge reaction can be reversibly performed in the charge / discharge after the second cycle. It can also be seen from the results shown in the figure that the operating potential is 3.2 V. Further, the withdrawable capacity (discharge capacity) is 105 mAhg ^-1 , and it can be seen that there is almost no deterioration even after repeating the charge / discharge cycle.

FIG. 7 shows the results of Test Example 2 (results of the potential-time characteristics of all Mg batteries) when MgFeMnO ₄ (sintering time is 1 hour) obtained in Example 1 was used as the positive electrode material. .. Initially it does not work very well, but over time there is a potential response suggestive of magnesium insertion and desorption.

FIG. 8 shows the results of Test Example 2 when MgFeMnO ₄ (sintering time is 1 hour) obtained in Example 1 was used as the positive electrode material (the relationship between each cycle of all Mg batteries and the discharge capacity was investigated. The result) is shown. It can be seen that the withdrawable capacity increases with the higher-order cycle, and the discharge capacity is 100 mAhg ^-1 at the 50th cycle.

FIG. 9 shows the XRD pattern of the products (sintering time is 3 hours) obtained at various firing temperatures in Example 2. The firing time is 1 hour. The X-ray wavelength used is 1.5418 Å.

When the firing temperature is 800 ° C. or higher, at least 2θ values are 17.75 to 19.36 °, 29.8 to 31.21 °, 32.16 to 33.13 °, 34.95 to 36.82 °, 37.15 to 37.91 °, 38.39 to 39.46 °, 43.05 to 44.29 °, 48.04 to 49.58 °, 53.55 to 54.84 °, 56.94 to 58 .92 °, 61.0 to 62.18 °, 62.77 to 63.90 °, 65.72 to 66.90 °, 67.70 to 68.89 °, 74.08 to 76.61 ° or 78 It can be seen that multiple major peaks can be seen at .96 to 80.94 °. Since these peaks correspond to the single-phase MgCuMnO ₄ , it can be seen that in Example 2, the single-phase MgCuMnO ₄ is obtained as a product.

FIG. 10 shows an SEM image of MgCuMnO ₄ (sintering time is 3 hours) obtained in Example 2. It can be seen that the MgCuMnO ₄ obtained in Example 2 is in the form of particles. Further, it can be seen that the MgCuMnO ₄ obtained in Example 2 also tends to have agglomerated particles, but has an average particle diameter of about 1 to 10 μm.

FIG. 11 shows the result (result of open circuit potential measurement) of Test Example 1 of MgCuMnO ₄ (sintering time is 3 hours) obtained in Example 2. It was found that the open circuit potential of the MgCuMnO ₄ sample was about 3.25 V. This is 2.55 Vvs. Since it is Mg ²⁺ , the material obtained in Example 2 can be used as a high-potential positive electrode material.

FIG. 12 shows the results of Test Example 1 when MgCuMnO ₄ (sintering time is 3 hours) obtained in Example 2 was used as the positive electrode material (charge / discharge characteristics and relationship between each cycle and discharge capacity). Is shown. In FIG. 12, the intersection of the discharge curve when the first discharge is performed and the charge curve when the second charge is performed, the charge curve when the second charge is performed, and the second discharge are performed. The intersection with the discharge curve at that time overlaps. From this result, it can be seen that by using the obtained positive electrode material, the charge / discharge reaction can be reversibly performed in the charge / discharge after the second cycle. It can also be seen from the results shown in the figure that the average operating potential is about 3.0 V. Further, the capacity (discharge capacity) that can be drawn out in the higher-order cycle is 110 mAhg ^-1 , and it can be seen that there is almost no deterioration even after repeating the charge / discharge cycle.

FIG. 13 shows the results of Test Example 2 (relationship between each cycle of all Mg batteries and the discharge capacity) when MgCuMnO ₄ (sintering time is 3 hours) obtained in Example 2 was used as the positive electrode material. The result) is shown. It was found that when MgCuMnO ₄ was used as the positive electrode material, a potential response suggesting the insertion and desorption of magnesium was observed.

FIG. 14 shows the XRD patterns of the products obtained at various firing temperatures and firing times in Example 3. The X-ray wavelength used is 1.5418 Å.

When the firing temperature is 800 ° C. or higher, at least the 2θ value is 17.21 to 19.14 °, 28.52 to 28.92 °, 30.57 to 31.84 °, 32.22 to 34.10 °, 35.12 to 37.63 °, 38.01 to 39.99 °, 42.67 to 46.75 °, 49.53 to 52.69 °, 53.88 to 55.27 °, 56.13 to 57 Multiple to .68 °, 58.49 to 59.72 °, 60.08 to 63.73 °, 64.23 to 66.69 °, 67.65 to 71.45 ° or 74.03 to 80.68 ° It can be seen that the main peak of is seen. Since these peaks correspond to the single-phase MgMn 2 ⁺ Mn 4 ⁺ O ₄ , it can be seen that in Example 3, the single-phase Mg Mn 2 ⁺ Mn ^{4 +} O ₄ is obtained as a product.

FIG. 15 shows an SEM image of MgComnO ₄ (sintering time is 3 hours) obtained in Example 4. It can be seen that the MgComnO ₄ obtained in Example 4 is in the form of particles. Further, as shown in FIG. 15, it can be seen that the average particle size is about 1 to 6 μm.

FIG. 16 shows the XRD patterns of the various products obtained in Examples 4 to 5 (sintering time is 3 hours). The X-ray wavelength used is 1.5418 Å. It can be seen that in Example 4, a single-phase MgCoMnO ₄ (MgCo 2 ⁺ Mn 4 ⁺ O ₄ ) was obtained as a product, and in Example 5, a single-phase MgNiMnO ₄ (MgNi 2 ⁺ Mn ^{4 +} O ₄ ) was obtained as a product.

FIG. 17 shows the results of Test Example 2 when MgComnO ₄ (sintering time is 3 hours) obtained in Example 4 was used as the positive electrode material (the relationship between each cycle of all Mg batteries and the discharge capacity was investigated. The result) is shown. It was found that when MgCoMnO ₄ (MgCo 2 ⁺ Mn ^{4 +} O ₄ ) was used as the positive electrode material, a potential response suggesting the insertion and desorption of magnesium was observed.

FIG. 18 shows an SEM image of MgNiMnO ₄ (sintering time is 3 hours) obtained in Example 5. It can be seen that the MgNiMnO ₄ obtained in Example 5 is in the form of particles. Further, as shown in FIG. 18, it can be seen that the average particle size is about 1 to 3 μm.

Table 1 shows the lattice constant parameters of the products obtained in each example (that is, the magnesium compound represented by the general formula (2); MgYMnO ₄ (Y = Fe, Cu, Co, Mn, Ni)). show.

From Table 1, it can be seen that MgFeMnO ₄ and MgComnO ₄ have a cubic crystal system (Fd-3m space group), and the crystal structure forms a spinel type structure.

Table 2 shows the ICPs of the products obtained in Examples 1, 2, 5 and 4 (that is, the magnesium compound represented by the general formula (2); MgYMnO ₄ (Y = Fe, Cu, Ni, Co)). The results of elemental analysis according to the above are shown. From Table 1, it was found that the compound was formed in a composition ratio commensurate with the amount of the raw material used.

FIG. 19 is an XRD pattern of the products obtained in Example 6 (MgCu _0.5 Fe _0.5 MnO ₄ ) and Example 7 (MgNi _0.5 Fe _0.5 MnO ₄ ). It can be seen that the solid solutions of MgCu _0.5 Fe _0.5 MnO ₄ and MgNi _0.5 Fe _0.5 MnO ₄ have been synthesized.

FIG. 20 shows an SEM image of the product obtained in Example 6.

FIG. 21 shows a high resolution SEM image of the product obtained in Example 6.

From FIGS. 20 and 21, it can be seen that the product (MgCu _0.5 Fe _0.5 MnO ₄ ) obtained in Example 6 is in the form of particles.

FIG. 22 shows an SEM image of the product obtained in Example 7. From FIG. 22, it can be seen that the product (MgNi _0.5 Fe _0.5 MnO ₄ ) obtained in Example 7 is in the form of particles.

Table 3 is a table showing changes in the lattice constant of MgFe _1-x Cu _x MnO ₄ (x = 0, 0.5, 1).

From Table 3, it can be seen that the lattice constant of MgFe _1-x Cu _x MnO ₄ is reduced by introducing Cu. This result indicates that lattice shrinkage occurs because the ionic radius of Cu ²⁺ is smaller than that of Fe ²⁺ .

FIG. 23 is a graph plotting changes in the lattice constant of MgFe _1-x Cu _x MnO ₄ (x = 0, 0.5, 1). The product (MgCu _0.5 Fe _0.5 MnO ₄ ) obtained in Example 6 shows that a solid solution can be formed.

FIG. 24 shows the SEM-EDX results of the product (MgCu _0.5 Fe _0.5 MnO ₄ ) obtained in Example 6. This result shows that in MgCu _0.5 Fe _0.5 MnO ₄ obtained in Example 6, Cu and Fe are equal amounts.

FIG. 25 shows an SEM image of the product obtained in Example 7. From FIG. 25, it can be seen that the product (MgNi _0.5 Fe _0.5 MnO ₄ ) obtained in Example 7 is in the form of particles.

FIG. 26 is an XRD pattern of the product (MgCu _0.5 Ni _0.5 MnO ₄ ) obtained in Example 8. It can be seen that a solid solution of MgCu _0.5 Ni _0.5 MnO ₄ has been synthesized.

FIG. 27 shows an SEM image of the product obtained in Example 8. From FIG. 27, it can be seen that the product obtained in Example 8 is in the form of particles.

FIG. 28 is an XRD pattern of MgNi ²⁺ MnO ₄ , MgCu ²⁺ MnO ₄ , MgCo ²⁺ MnO ₄ , MgFe ²⁺ MnO ₄ , and MgMn ²⁺ MnO ₄ . The XRD peak shifts to the high angle side in the order of Fe ²⁺ , Co ²⁺ , Cu ²⁺ , Ni ²⁺ , Cu ²⁺ , Co ²⁺ , Fe ²⁺ , and the lattice contraction occurs. Understand.

Claims (4)

The following general formula (2)
Mg _a Cu _b Mn _{c Od} (2)
(Here, in the formula (2) , a is 0.5 to 1.5, b is 0.5 to 1.5, c is 0.5 to 1.5, and d is 3.8 to 4.1. show.)
A positive electrode active material for a secondary battery containing a magnesium compound represented by. A secondary battery comprising the positive electrode active material according to claim 1 as a component. The method for producing a positive electrode active material for a secondary battery according to claim 1.
A manufacturing method comprising a heating step of heating a raw material mixture containing a raw material containing Mg, a raw material containing Cu , and a raw material containing Mn. The manufacturing method according to claim 3 , wherein the heating temperature in the heating step is 500 to 1500 ° C.

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