WO2017119493A1

WO2017119493A1 - Positive electrode active material for secondary battery, production method therefor, and secondary battery

Info

Publication number: WO2017119493A1
Application number: PCT/JP2017/000301
Authority: WO
Inventors: タイタスニャムワロマセセ; 鹿野　昌弘; 栄部　比夏里; 博妹尾; 光佐野
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2016-01-06
Filing date: 2017-01-06
Publication date: 2017-07-13
Also published as: JP6934665B2; JPWO2017119493A1

Abstract

Provided are a positive electrode active material for a secondary battery and a production method therefor, capable of constructing a secondary battery having high theoretical capacity, high theoretical electric potential, and high theoretical energy density at a low cost. Also provided is a secondary battery composed of said positive electrode active material for a secondary battery. The present invention comprises a magnesium compound represented by general formula (1) Mg_aX_bY_cO_d(here, in formula (1), X is at least one selected from the group consisting of Ni, Fe, Mn, Co, and Cu, and Y is Ge or Ti. Further, a represents 0.5-1.5, b represents 0.5-1.5, c represents 0.5-1.5, and d represents 3.8-4.1).

Description

Positive electrode active material for secondary battery, method for producing the same, and secondary battery

The present invention relates to a positive electrode active material for a secondary battery, a manufacturing method thereof, and a secondary battery.

An energy storage medium is indispensable for solving energy problems, and the development of a high-performance secondary battery is urgent. Currently, the secondary battery with the highest performance is a lithium ion secondary battery, but there are still problems in terms of capacity, cost, and safety in realizing electric vehicles and smart grids that can be considered for future use. For further development, it is necessary to develop an innovative secondary battery that transcends the current system, and one of the directions is a multivalent ion secondary battery that uses multivalent ions as carriers. For example, a secondary battery system using magnesium as a negative electrode has attracted attention because it has a high theoretical capacity density, is rich in resources, has a high melting point, and is safe.

Magnesium has a high theoretical weight and volume capacity, and exhibits a relatively base redox potential. Therefore, a secondary battery using magnesium as a negative electrode is expected to have 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 reserves of magnesium are abundant in the crust layer, and the problems of resource depletion and cost, which are disadvantages of lithium ion secondary batteries, can be cleared. Magnesium has a melting point of about 650 ° C., which is very high compared to Li (180 ° C.), Na (98 ° C.) and the like. The melting point is an indicator of metal stability, and secondary batteries using magnesium can be expected to improve safety. In the future, the safety of the negative electrode metal will be a very important factor when the metal negative electrode is put to practical use. Furthermore, lithium, sodium, and the like are difficult to handle because they react vigorously with moisture in the air, but magnesium is stable in the air and easy to handle. For these reasons, magnesium secondary batteries are regarded as candidates for post-lithium ion secondary batteries, and many studies have been conducted in recent years.

There are still some issues in the creation of the magnesium secondary battery system. In particular, in the positive electrode material, polyvalent ions have twice the Coulomb interaction with anions in the solid phase compared to lithium ions, and the ionic radius is smaller than lithium ions, so the distance from the anion. Becomes smaller and the interaction increases. As a result, multivalent ions are expected to be greatly affected by the electrostatic interaction in the positive electrode host compound, so the higher the valence ions, the more suitable the intercalation electrode based on the topochemical reaction is. Have difficulty.

On the other hand, in recent years, a large number of positive electrode materials for magnesium secondary batteries have been reported, and Mo ₆ T ₈ (T = S, Se), V ₂ O ₅ , TiS ₂ nanotubes / graphene- having a chevrel phase as a positive electrode. It has been reported that nanostructured materials such as likeMoS ₂ exhibit stable and reversible charge / discharge characteristics as magnesium secondary batteries (see, for example, Non-Patent Document 1).

However, in compounds containing soft bases such as sulfur ions, the reaction potential is lowered, and the chevrel phase has a large molecular weight and a low theoretical capacity, so that it can be used as a positive electrode as a device exceeding lithium ion secondary batteries. Has many challenges to become. From such a viewpoint, for example, development of a high true density polyanion compound which has high safety by a strong polyanionic acid skeleton and enables multiple electron transfer is demanded.

The present invention has been made in view of the above, and has a high theoretical capacity, a high potential, and a low cost, and can construct a secondary battery having a high theoretical energy density, and a positive electrode active material for a secondary battery and a method for producing the same. And it aims at providing the secondary battery comprised with the said positive electrode active material for secondary batteries.

As a result of intensive studies 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 subject matters described in the following sections.
Item 1. The following general formula (1)
Mg _a _Xb Y _c O _d (1)
(In the formula (1), X is at least one selected from the group consisting of Ni, Fe, Mn, Co, and Cu, Y is Ge or Ti, and 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.)
The positive electrode active material for secondary batteries containing the magnesium compound represented by these.
Item 2. A secondary battery comprising the positive electrode active material according to Item 1 as a constituent element.
Item 3. A method for producing a positive electrode active material for a secondary battery according to Item 1,
A manufacturing method provided with the heating process which heats the raw material mixture containing the raw material containing Mg, the raw material containing said X, and the raw material containing said Y.
Item 4. Item 4. The production method according to Item 3, wherein the heating temperature in the heating step is 500 to 1500 ° C.

According to the positive electrode active material for an ion secondary battery according to the present invention, a secondary battery having a high theoretical capacity, a high potential, a low cost, and a high theoretical energy density can be constructed.

The XRD pattern of the product obtained in Example 1 is shown. It shows an SEM image of MgMnGeO ₄ obtained in Example 1. The XRD pattern of the product obtained in Example 2 is shown. It shows an SEM image of MgCoGeO ₄ obtained in Example 2. The XRD pattern of the product obtained in Example 3 is shown. It shows an SEM image of MgNiGeO ₄ obtained in Example 3. It shows an SEM image of MgFeTiO ₄ obtained in Example 4. The charge / discharge characteristics when MgCoGeO ₄ obtained in Example 2 is used as the positive electrode material, and the relationship between each cycle and the discharge capacity are shown. The charge / discharge characteristics when MgFeTiO ₄ obtained in Example 4 is used as the positive electrode material, and the relationship between each cycle and the discharge capacity are shown. The result of the potential-time characteristic of all the Mg batteries when using MgMnGeO ₄ obtained in Example 1 as a positive electrode material is shown. The result of the potential-time characteristic of all the Mg batteries when using MgNiGeO ₄ obtained in Example 3 as a positive electrode material is shown. The result of the potential-time characteristic of all the Mg batteries when using MgFeTiO ₄ obtained in Example 4 as the positive electrode material is shown. The XRD pattern of the product obtained in Example 5 is shown. The XRD pattern of the product obtained in Example 6 is shown. The SEM image 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 baked in Examples 2, 3, 7-9 is shown. MgCo is a diagram illustrating a change in volume of _{_{_{1-x Ni x GeO 4 (}}} x = 0,0.25,0.5,0.75,1). The SEM image of the product obtained in Example 8 is shown. The SEM image of the product obtained in Example 9 is shown. The physical property changes of MgCo _1-x Ni _x GeO ₄ (x = 0, 0.25, 0.5, 0.75, ₁ ) are shown.

Hereinafter, embodiments of the present invention will be described in detail. In addition, when showing a range in this specification, all include the numerical value of both ends.

1. Positive electrode active material for secondary battery The positive electrode active material for a secondary battery of this embodiment is represented by the following general formula (1)
Mg _a _Xb Y _c O _d (1)
(In the formula (1), X is at least one selected from the group consisting of Ni, Fe, Mn, Co, and Cu, Y is Ge or Ti, and 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.

Such a magnesium compound is useful as a positive electrode active material for a magnesium ion secondary battery because it can insert and desorb magnesium ions.

In the general formula (1), when Y is Ge, X is preferably at least one selected from the group consisting of Ni, Mn and Co. In this case, the production of the magnesium compound is easy and low. A magnesium compound can be produced at low cost, and the capacity and potential of the secondary battery can be further improved.

In general formula (1), if Y is Ti, X is preferably Fe. In this case, a magnesium compound can be produced with high purity, and the capacity and potential of the secondary battery are further improved. Can be made.

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

The value b is more preferably 0.7 to 1.3, and more preferably 0.8 to 1.1, from the viewpoints of ease of insertion and desorption of magnesium ions, capacity, and high potential. It is particularly preferred. As a reminder, when X is two or more selected from the group consisting of Ni, Fe, Mn, Co and Cu, the value of b is the total amount of each of the two or more elements. Represents.

The value of c is more preferably 0.7 to 1.3, and more preferably 0.8 to 1.1, from the viewpoints of ease of insertion and desorption of magnesium ions, capacity, and high potential. It is particularly preferred.

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

Specific examples of the magnesium compound represented by the general formula (1) include MgNiGeO ₄ , MgMnGeO ₄ , MgCoGeO from the viewpoints of easy insertion and desorption of magnesium ions, low cost, capacity, and high potential. ₄ and MgFeTiO ₄ are preferable.

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). . For this reason, 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 as a material having a plurality of crystal structures unless the effects of the present invention are impaired. The crystal structure of the magnesium compound represented by the general formula (1) can be confirmed by X-ray diffraction measurement.

The magnesium compound represented by the general formula (1) can be in the form of a particulate powder, for example. In the case where the magnesium compound is in the form of particles, the average particle size is preferably 0.005 to 50 μm, preferably 0.01 to 0.5 μm from the viewpoints of easy insertion and desorption of magnesium ions, capacity, and high potential. 2 μm is more preferable. The average particle diameter of the magnesium compound represented by the general formula (1) is measured by observation with an electron microscope (SEM). The average particle diameter here refers to, for example, an arithmetic average value of equivalent circle diameters measured by direct observation with an electron microscope.

When a magnesium ion secondary battery is formed using the positive electrode active material for a secondary battery containing the magnesium compound represented by the general formula (1) as described above, the magnesium ion secondary battery can have a high capacity. . Moreover, in the positive electrode active material for a secondary battery containing the magnesium compound, a redox reaction in two steps of X ²⁺ / X ³⁺ and X ³⁺ / X ⁴⁺ occurs, which increases the capacity of the magnesium ion secondary battery. Cheap. Moreover, since the said magnesium compound can be manufactured with an inexpensive and easy process, according to the positive electrode active material for magnesium ion secondary batteries of this embodiment, a magnesium secondary battery can be provided at low cost. Therefore, the positive electrode active material for secondary batteries of this embodiment is suitable as a positive electrode material constituting a magnesium secondary battery with high energy density.

In addition, as long as the performance of the positive electrode active material for secondary batteries of the present embodiment is not hindered, other materials may be included in the positive electrode active material for secondary batteries. Moreover, the said positive electrode active material for secondary batteries can also contain an unavoidable impurity other than a magnesium compound. Examples of such inevitable impurities include a raw material mixture described later. For example, in the positive electrode active material for a secondary battery, about 10 mol% or less, preferably about 5 mol% or less, more preferably about 2 mol% or less. May be contained.

In the positive electrode active material for a secondary battery, the magnesium compound and a carbon material (for example, carbon black such as acetylene black) may form a composite. Thereby, since a carbon material suppresses the grain growth of a magnesium compound at the time of baking, it can become a fine particle-form positive electrode active material for secondary batteries excellent in the electrode characteristic. In this case, the content of the carbon material is preferably adjusted to 3 to 20% by mass, particularly 5 to 15% by mass in the positive electrode active material for an ion secondary battery.

2. Method for producing a positive active material for a secondary battery comprising a magnesium compound represented by the production method above general formula of the positive electrode active material for a secondary battery (1) is not particularly limited. For example, the magnesium compound is manufactured by a manufacturing method including a heating step of heating a raw material mixture including a raw material containing Mg, a raw material containing X, and a raw material containing Y. A positive electrode active material can be obtained. Hereinafter, this manufacturing method will be specifically described.

(1) Raw material mixture The raw material mixture in the said manufacturing method contains the raw material containing Mg, the raw material containing said X, and the raw material containing said Y. The raw material mixture may be three kinds of mixtures including one raw material containing Mg, one raw material containing X, and one raw material containing Y. Or the raw material containing Mg, the raw material containing X, and the raw material containing Y can all be one type or two or more types. Furthermore, the raw material mixture can use, as a part of the raw material, a compound containing Mg, two or more elements of X and Mn at the same time. 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 Mg element. Examples of the compound containing 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. Hydrate may be sufficient as the compound containing Mg element.

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

As a further embodiment of a compound containing a metal X, if X if it is Fe _FeC 2 _O 4, if X is Mn _MnC 2 _O 4, X is Ni, with Ni _(OH) 2, X is Co If there is CoC ₂ O ₄ and X is Cu, CuO is exemplified.

The raw material containing Y may be, for example, metal Y or a compound containing Y. As the compound containing Y (that is, germanium compound or titanium compound), for example, germanium oxide (GeO ₂ ), germanium tetrachloride (GeCl ₄ ), germanium tetrabromide (GeBr ₄ ), germanium tetraiodide (GeI ₄ ) , Germanium tetrafluoride (GeF ₄ ), germanium disulfide (GeS ₂ ), titanium oxide (TiO ₂ ), titanium tetrachloride (TiCl ₄ ), titanium tetrabromide (TiBr ₄ ), Ti tetraiodide (TiI ₄ ) , Titanium tetrafluoride (TiF ₄ ), titanium disulfide (TiS ₂ ), and the like.

It is preferable that the raw material mixture does not include Mg and other metal elements (particularly rare metal elements) other than the metals X and Y. As for other metal elements, those that are detached and volatilized by heat treatment in a non-oxidizing atmosphere are desirable.

In addition, as for the raw material containing Mg, the raw material containing X, and the raw material containing Y, any of commercially available products may be used, or they may be synthesized separately and used.

There is no particular limitation on the shape of the raw material mixture, and powder is preferable from the viewpoint of handleability. Further, from the viewpoint of reactivity, the particles are preferably fine, and a powder having an average particle size of 1 μm or less (particularly about 60 to 80 nm) is preferable. The average particle diameter of each raw material is measured by electron microscope observation (SEM).

The raw material mixture can be prepared by mixing a raw material containing Mg, a raw material containing X and a raw material containing Y in a predetermined blending ratio. The mixing method is not particularly limited, and for example, a method that can uniformly mix the raw materials can be employed. Specifically, mortar mixing, mechanical milling treatment, coprecipitation method, a method of mixing after each raw material is dispersed in a solvent, a method of mixing each raw material at once in a solvent, etc. may be adopted. it can. Among these, a magnesium compound can be obtained by a simpler method when mortar mixing is employed. A coprecipitation method can be employed to obtain a more uniformly mixed raw material mixture.

The mixing ratio of each raw material in each raw material mixture is not particularly limited. For example, it is preferable to blend each raw material so that a magnesium compound having a desired composition as a final product is obtained. 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 including a raw material containing Mg, a raw material containing X, and a raw material containing Y is heated.

The heating step can be performed, for example, in an inert gas atmosphere 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 structure. As a result, the crystallinity and electrode characteristics (particularly capacity and potential) of the obtained magnesium compound are likely to be improved.

The lower limit of the heating temperature in the heating step is preferably 700 ° C., particularly preferably 1150 ° C., if X is Fe. In addition, the upper limit of heating temperature can be suitably determined in the range which can operate easily in manufacture of a magnesium compound (for example, 1500 degreeC).

The heating time in the heating step is not particularly limited. For example, 10 minutes to 48 hours are preferable, and 30 minutes to 24 hours are more preferable.

After heating for a predetermined time, the desired magnesium compound is obtained by cooling. The cooling rate is not particularly limited. In addition, after cooling once, baking may be performed again at the heating temperature.

In addition, a magnesium compound can be manufactured by methods, such as a coprecipitation method, a sol gel method, a hydrothermal synthesis method, other than the said manufacturing method.

3. Secondary battery The secondary battery of the present embodiment includes the above-described positive electrode active material for a secondary battery as a constituent element. In particular, the positive electrode active material for a secondary battery is suitable as a component of a magnesium ion secondary battery.

The basic structure of the magnesium ion secondary battery shall be a known non-aqueous electrolyte magnesium ion secondary battery, except that the positive electrode active material for magnesium ion secondary battery is used as the positive electrode active material. Can do. For example, the positive electrode, the negative electrode, and the separator can be disposed 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 non-aqueous electrolyte into the battery container, the magnesium ion secondary battery can be manufactured by sealing the battery container. The magnesium ion secondary battery may be a magnesium secondary battery. In this specification, “magnesium ion secondary battery” means a secondary battery using magnesium ions as carrier ions, and “magnesium secondary battery” means a secondary that uses magnesium metal or a magnesium alloy as a negative electrode active material. Means battery.

The positive electrode can adopt a structure in which a positive electrode material containing a positive electrode active material for a magnesium ion secondary battery is supported on a positive electrode current collector. For example, the positive electrode active material for a magnesium ion secondary battery, a conductive additive, and, if necessary, a positive electrode mixture containing a binder can be produced by applying to a positive electrode current collector.

As the conductive aid, for example, carbon materials such as acetylene black, ketjen black, carbon nanotube, vapor grown carbon fiber, carbon nanofiber, graphite, and coke can be used. There is no restriction | limiting in particular in the shape of a conductive support agent, For example, a powder form etc. are employable.

Examples of the binder include fluorine resins such as polyvinylidene fluoride resin and polytetrafluoroethylene.

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

It should be noted that the amount of the positive electrode material applied to the positive electrode current collector is preferably determined as appropriate according to the use of the magnesium ion secondary battery.

Examples of the negative electrode active material constituting the negative electrode include magnesium metal; silicon; silicon-containing acrylate compound; magnesium alloy; M ¹ M ² ₂ O ₄ (M ¹ : Co, Ni, Mn, Sn, etc., M ² : Mn, Ternary or quaternary oxides represented by Fe, Zn, etc .; 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.) Oxides; graphite, hard carbon, soft carbon, graphene; the above-described carbon materials; organic compounds such as MgC ₈ H ₄ O ₄ , MgC ₈ H ₄ O ₄ .2H ₂ O, and the like. 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 Alloy containing magnesium, alloy containing magnesium and antimony as constituent elements, alloy containing magnesium and tin as constituent elements, alloy containing magnesium and indium as constituent elements; metal (scandium, titanium, vanadium, chromium, zirconium, niobium) , molybdenum, hafnium, MXene based alloy containing as constituent elements carbon and ^tantalum), _M 7 x BC ₃ alloy ^{(M 7: Sc, Ti,} V, Cr, Zr, Nb, Mo, Hf, T Quaternary layered carbide or nitride compound etc.) and the like; alloys containing magnesium and lead as a constituent element thereof.

The negative electrode can be composed of a negative electrode active material, and adopts a configuration in which a negative electrode material containing a negative electrode active material, a conductive additive, and a binder as necessary is supported on the negative electrode current collector. You can also. 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 additive, and a binder as necessary is applied to the negative electrode current collector. Can be manufactured.

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

In addition, when adopting a configuration in which the negative electrode material is supported on the negative electrode current collector, the types of the conductive auxiliary agent and the binder, and the negative electrode active material, the conductive auxiliary agent, and the binder content are those of the positive electrode described above. Can be applied. Examples of the material constituting the negative electrode current collector include aluminum, copper, nickel, and stainless steel. Examples of the shape of the negative electrode current collector include a porous body, a foil, a plate, and a mesh made of fibers. In addition, it is preferable to determine suitably the application quantity of the negative electrode material with respect to a negative electrode collector according to the use etc. of a magnesium ion secondary battery.

The separator is not limited as long as it is made of a material that can separate the positive electrode and the negative electrode in the battery and can hold the electrolytic solution to ensure the ionic conductivity between the positive electrode and the negative electrode. For example, polyolefin resin such as polyethylene, polypropylene, polyimide, polyvinyl alcohol, terminal aminated polyethylene oxide; fluorine resin such as polytetrafluoroethylene; acrylic resin; nylon; aromatic aramid; inorganic glass; Materials in the form of a membrane, nonwoven fabric, woven fabric, etc. can be used.

The non-aqueous electrolyte is preferably an electrolyte containing magnesium ions. Examples of such an electrolytic solution include a magnesium salt solution, an ionic liquid composed of an inorganic material containing magnesium, and the like. Examples of the electrolytic solution include a solution in which a magnesium salt is dissolved in a solvent and an ionic liquid composed of an inorganic material containing magnesium. However, the electrolytic solution is not limited to such examples. Examples of magnesium salts include magnesium halides such as magnesium chloride, magnesium bromide, magnesium iodide, and magnesium fluoride, magnesium perchlorate, magnesium tetrafluoroborate, magnesium hexafluorophosphate, magnesium hexafluoroarsenate, and the like. Magnesium inorganic salt compounds: magnesium such as bis (trifluoromethylsulfonyl) imido magnesium, magnesium benzoate, magnesium salicylate, magnesium phthalate, magnesium acetate, magnesium propionate, tris (pentafluoroethane) trifluorophosphate magnesium, Grignard reagent, etc. Examples include organic salt compounds, but are not limited to such examples.

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-methyltetrahydrofuran, diethyl ether, Such as diisopropyl ether, dibutyl ether, methoxymethane, N, N-dimethylformamide, glyme, N-propyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide, dimethoxyethane, dimethoxymethane, diethoxymethane, dietochiethane, propylene glycol dimethyl ether Ether compounds; acetonitrile and the like.

Further, a solid electrolyte can be used instead of the non-aqueous electrolyte. 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 _k Zr _m (PO ₄ ) _n (k, m = 1, 2, 4, 5, 7; n = 2, 4, 6, 8, 10 ), Magnesium ion conductors such as Mg (BH ₄ ) ₂ (NH ₃ ) _{2 and the} like are listed.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the embodiments.

Example 1
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), MnC ₂ O ₄ (high purity chemistry, 99.9% (3N)), GeO ₂ (rare metallic, 99.99%) (4N)) was used. MgO, MnC ₂ O ₄ and GeO ₂ were weighed so that the molar ratio of magnesium, manganese and germanium was 1: 1: 1, and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Thereafter, acetone is distilled off under reduced pressure, and then the recovered powder is pellet-molded at 40 MPa, and heated in a range of 800 ° C. to 1150 ° C. for 1 hour, 2 hours, 4 hours, or 6 hours under Ar flow. Baked. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

(Example 2)
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CoC ₂ O ₄ (high purity chemistry, 99.9% (2N)), GeO ₂ (rare metallic, 99.99%) (4N)) was used. MgO, magnesium _CoC 2 _{O 4} and GeO _2, the molar ratio of cobalt and germanium 1: 1: 1 and were weighed so as to obtain a raw material mixture is mixed for about 30 minutes in an agate mortar. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling acetone off under reduced pressure, the recovered powder was pellet-molded at 40 MPa and fired at a firing temperature of 1150 ° C. for 6 hours under an Ar stream. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

(Example 3)
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), Ni (OH) ₂ (high purity chemistry, 99.9% (3N)), GeO ₂ (rare metallic, 99.99) % (4N)). MgO, Ni (OH) ₂ and GeO ₂ were weighed so that the molar ratio of magnesium, nickel and germanium was 1: 1: 1, and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Thereafter, acetone is distilled off under reduced pressure, and then the recovered powder is pellet-molded at 40 MPa, and heated in a range of 800 ° C. to 1150 ° C. for 1 hour, 2 hours, 4 hours, or 6 hours under Ar flow. Baked. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

Example 4
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), FeC ₂ O ₄ · 2H ₂ O (Pure Chemical, 99.9% (3N)), TiO ₂ (A) (rare) Metallic, 99.99% (4N)) was used. MgO, FeC ₂ O ₄ and TiO ₂ were weighed so that the molar ratio of magnesium, iron and titanium was 1: 1: 1, and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Thereafter, acetone is distilled off under reduced pressure, and then the recovered powder is pellet-molded at 40 MPa, and heated in a range of 800 ° C. to 1150 ° C. for 1 hour, 2 hours, 4 hours, or 6 hours under Ar flow. Baked. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

(Example 5)
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), MnC ₂ O ₄ (high purity chemistry, 99.9% (3N)), Ni (OH) ₂ (high purity chemistry, 99.9% (3N)), GeO ₂ (rare metallic, 99.99% (4N)). Weigh MgO, MnC ₂ O ₄ , Ni (OH) ₂ and GeO _{2 so} that the molar ratio of magnesium, manganese, nickel and germanium is 2: 1: 1: 2, and mix for about 30 minutes in an agate mortar. A raw material mixture was obtained. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling acetone off under reduced pressure, the recovered powder was pellet-molded at 40 MPa and fired at 1150 ° C. for 6 hours under an Ar stream. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

(Example 6)
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CoC ₂ O ₄ (high purity chemistry, 99.9% (2N)), MnC ₂ O ₄ (high purity chemistry, 99 0.9% (3N)), GeO ₂ (rare metallic, 99.99% (4N)). MgO, CoC ₂ O ₄ , MnC ₂ O ₄ and GeO ₂ are weighed so that the molar ratio of magnesium, cobalt, manganese and germanium is 2: 1: 1: 2, and mixed in an agate mortar for about 30 minutes. A mixture was obtained. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling acetone off under reduced pressure, the recovered powder was pellet-molded at 40 MPa and fired at a firing temperature of 1150 ° C. for 6 hours under an Ar stream. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

(Example 7)
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CoC ₂ O ₄ (high purity chemistry, 99.9% (2N)), Ni (OH) ₂ (high purity chemistry, 99.9% (3N)), GeO ₂ (rare metallic, 99.99% (4N)). MgO, CoC ₂ O ₄ , Ni (OH) ₂ and GeO ₂ are weighed so that the molar ratio of magnesium, cobalt, nickel and germanium is 2: 1: 1: 2, and mixed in an agate mortar for about 30 minutes. A raw material mixture was obtained. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling acetone off under reduced pressure, the recovered powder was pellet-molded at 40 MPa and fired at a firing temperature of 1150 ° C. for 6 hours under an Ar stream. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

(Example 8)
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CoC ₂ O ₄ (high purity chemistry, 99.9% (2N)), Ni (OH) ₂ (high purity chemistry, 99.9% (3N)), was used GeO ₂ (Rare metallic, 99.99% (4N) a). Weigh MgO, CoC ₂ O ₄ , Ni (OH) ₂ and GeO _{2 so} that the molar ratio of magnesium, cobalt, nickel and germanium is 4: 1: 3: 4, and mix for about 30 minutes in an agate mortar. A raw material mixture was obtained. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling acetone off under reduced pressure, the recovered powder was pellet-molded at 40 MPa and fired at a firing temperature of 1150 ° C. for 6 hours under an Ar stream. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

Example 9
MgO (Wako Chemical, 0.05 μm, 99.9% (3N)), CoC ₂ O ₄ (high purity chemistry, 99.9% (2N)), Ni (OH) ₂ (high purity chemistry, 99.9% (3N)), was used GeO ₂ (Rare metallic, 99.99% (4N) a). MgO, CoC ₂ O ₄ , Ni (OH) ₂ and GeO ₂ are weighed so that the ratio of magnesium, cobalt, nickel and germanium is 4: 3: 1: 4 and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture Got. Thereafter, the raw material mixture was placed in a chrome steel container together with zirconia balls (15 mmΦ × 10), added with acetone, and pulverized and mixed at 400 rpm for 6 hours in a planetary ball mill (Fritsch; P-6). Then, after distilling acetone off under reduced pressure, the recovered powder was pellet-molded at 40 MPa and fired at a firing temperature of 1150 ° C. for 6 hours under an Ar stream. At this time, the temperature raising rate was set to 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter it 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 without contact with air.

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

[ICP-AES measurement]
ICP-AES measurement was performed using an inductively coupled plasma emission spectrometer (“iCAP6500” manufactured by Thermo Fisher Scientific).

[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 agglomerated so that the weight ratio is 85: 7.5: 7.5. The mixture was mixed in a mortar, and the resulting slurry was applied on an Al foil (thickness 20 μm) as a current collector, which was punched into a circle (diameter 8 mm) to obtain a positive electrode. The cell used was a CR2032-type coin cell. The Li box was used as the negative electrode, and the electrolyte used was an electrolyte obtained by dissolving LiPF ₆ at a concentration of 1M 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 started by charging using a voltage switch, setting the current to 10 mAg ⁻¹ , the upper limit voltage 4.8 V, and the lower limit voltage 1.5 V. Charge / discharge measurement was performed in a state where the cell was placed in a 55 ° C. constant temperature bath.

[Test Example 2: Investigation of magnesium ion desorption and insertion (Mg all battery)]
The cell used was a CR2032-type coin cell. The electrolyte solution was prepared by dissolving Mg (TFSI) ₂ in ethylene glycol dimethyl ether dimethoxyethylene glycol (trade name: monoglyme) so that its concentration was 0.5 M, using the Mg disk as the negative electrode. The constant current charge / discharge measurement was performed by using a voltage switch, setting the current to 5 mAg ⁻¹ , the upper limit voltage 3.6 V, and the lower limit voltage 0 V, and starting from charge. The measurement was performed at room temperature.

1 (a) and 1 (b) show XRD patterns of the product baked in Example 1 (baked at 1150 ° C. for 6 hours) ((b) is around 40 to 70 in (a). It is an enlarged view). The X-ray wavelength used is 1.5418 mm. As shown in FIG. 1B, it was found that satisfactory structural refinement was performed because a good fit was achieved even on the high angle side.

From FIG. 1, it was confirmed that the orthorhombic lattice index was assigned to all Bragg peaks of the sample fired at 1150 ° C. for 6 hours, and the presence of the impurity phase found in the starting materials and their products. You can see that it was not done. Further, from the results of XRD, MgMnGeO ₄ could be assigned to the orthorhombic system and the space group Pbnm (No. 62). The lattice constants refined by the Rietveld method are a = 4.9655 (5) Å, b = 10.5880 (12) Å, c = 6.1738 (7) Å, α = β = γ = 90 °, unit cell volume (V) is 323.95 (10) Å ^3, consistent with literature values. The MgMnGeO ₄ crystal density calculated by analysis was ρ = 4.41 gcm ⁻³ . The reliability factors were R _wp = 9.22%, R _p = 6.02%, and χ ² = 2.36.

FIG. 2 shows an SEM image of a product (MgMnGeO ₄ ) obtained by performing a heating process at 1150 ° C. for 6 hours in Example 1. In the figure, the scale bar indicates 0.5 μm. From this result, it can be seen that the MgMnGeO ₄ obtained in Example 1 has an average particle diameter of about 0.5 μm although the particles tend to aggregate.

FIG. 3 shows the XRD pattern of the product baked in Example 2. The X-ray wavelength used is 1.5418 mm.

From FIG. 3, it was confirmed that the orthorhombic lattice index was assigned to all the Bragg peaks of the sample fired at 1150 ° C. for 6 hours, and the presence of the impurity phase found in the starting materials and their products. You can see that it was not done. From the results of XRD, MgCoGeO ₄ could be assigned to the orthorhombic system, space group Fd-3m (No. 62). Ried lattice constant by the belt method a = b = c = 8.2831 ( 5) Å, α = β = γ = 90 °, the unit cell volume (V) is 568.29 ⁽³⁾ Å 3, the literature value Matches. The MgCoGeO ₄ crystal density calculated by analysis was ρ = 5.1386 gcm ⁻³ . Incidentally, the reliability _{_{factor, R wp = 4.04%, R}} p = 2.73%, was χ ² = 1.84.

Figure 4 shows an SEM image of MgCoGeO ₄ obtained in Example 2. In the figure, the scale bar indicates 1.66 μm. From this result, it can be seen that MgCoGeO ₄ obtained in Example 2 has an average particle diameter of around 0.5 μm.

FIG. 5 shows the XRD pattern of the product baked in Example 3. The X-ray wavelength used is 1.5418 mm.

From FIG. 5, it was confirmed that the orthorhombic lattice index could be assigned to all the Bragg peaks of the sample fired at 1150 ° C. for 6 hours, and the presence of the impurity phase found in the starting materials and their products. You can see that it was not done. From the results of XRD, MgNiGeO ₄ could be assigned to the orthorhombic system and the space group Pbnm (No. 62). REITs lattice constant a by the belt method = b = c = 8.2261 (3 ) Å, α = β = γ = 90 °, the unit cell volume (V) is 556.65 (2) Å ^3, the literature value Matches. The MgNiGeO ₄ crystal density calculated by analysis was ρ = 5.2402 gcm ⁻³ . The reliability factors were R _wp = 7.74%, R _p = 5.34%, and χ ² = 2.54.

FIG. 6 shows an SEM image of a product (MgNiGeO ₄ ) obtained by performing a heating process at 1150 ° C. for 6 hours in Example 3. In the figure, the scale bar indicates 1.66 μm. From this result, it can be seen that MgNiGeO ₄ obtained in Example 3 has an average particle diameter of around 0.5 μm.

FIG. 7 shows an SEM image of a product (MgFeTiO ₄ ) obtained by performing a heating process at 1150 ° C. for 6 hours in Example 4. In the figure, the scale bar indicates 2.04 μm. From this result, it can be seen that MgFeTiO ₄ obtained in Example 4 has an average particle diameter of around 0.5 μm.

FIG. 8 shows the results of Test Example 1 (charge / discharge characteristics and the relationship between each cycle and discharge capacity) when the positive electrode active material containing MgCoGeO ₄ obtained in Example 2 was used as the positive electrode material. Yes. From the results shown in FIG. 8, it can be seen that the drawable capacity (discharge capacity) is 160 mAhg ⁻¹ and the average operating potential is 3.9 V (approximately 3.2 V when converted to the Mg ²⁺ / Mg potential standard). It can also be seen that even when the charge / discharge cycle is repeated, there is almost no deterioration.

FIG. 9 shows the results of Test Example 1 (charge / discharge characteristics and the relationship between each cycle and the discharge capacity) when the positive electrode active material containing MgFeTiO ₄ obtained in Example 4 was used as the positive electrode material. Yes. From the results shown in FIG. 9, it can be seen that the capacity that can be extracted (discharge capacity) is 50 mAhg ⁻¹ , and the average operating potential is 2.6 V (approximately 2.0 V when converted to the Mg ²⁺ / Mg potential standard). It can also be seen that even when the charge / discharge cycle is repeated, there is almost no deterioration.

FIGS. 10 to 12 show, as positive electrode materials, positive electrode active materials for secondary batteries containing MgMnGeO ₄ obtained in Example 1, MgNiGeO ₄ obtained in Example 3, and MgFeTiO ₄ obtained in Example ₄ , respectively. The results of the potential-time characteristics (Test Example 2) of all Mg batteries when used are shown. From FIGS. 10 to 12, it was found that a potential response suggesting insertion and detachment of magnesium was observed in all cases.

Table 1 shows the results of elemental analysis by ICP of the products obtained in Examples 1 to 4.

Figure 13 shows the XRD pattern of the fired product in Example _{_{5 (MgMn 1-x Ni x}} GeO 4 (x = 0.5)). The X-ray wavelength used is 1.5418 mm. From FIG. 13, it was found that the product fired in Example 5 formed a mixed phase of MgMnGeO ₄ and MgNiGeO ₄ .

FIG. 14 shows the XRD pattern of the product (MgMn _1-x Co _x GeO ₄ (x = 0.5)) calcined in Example 6. The X-ray wavelength used is 1.5418 mm. From Figure 14, calcined product in Example 6 was found to form a mixed phase of MgMnGeO ₄ and MgCoGeO _4.

FIG. 15 shows an SEM image of the product (MgMn _1-x Co _x GeO ₄ (x = 0.5)) obtained in Example 6. In the figure, the scale bar indicates 5.55 μm.

FIG. 16 shows an SEM image of the product (MgCo _1-x Ni _x GeO ₄ (x = 0.5)) obtained in Example 7. In the figure, the scale bar indicates 16.6 μm.

FIG. 17 shows the XRD pattern of the product fired in Examples 2, 3, and 7-9, and FIG. 17 (b) is an enlarged view of part of (a). FIG. 17 shows that MgCo _1-x Ni _x GeO ₄ (x = 0.25, 0.75) forms a solid solution.

FIG. 18 is a diagram showing the volume change of MgCo _1-x Ni _x GeO ₄ (x = 0, 0.25, 0.5, 0.75, ₁ ). From FIG. 18, it is apparent that the product fired in Examples 7-9 forms a solid solution.

FIG. 19 shows an SEM image of the product obtained in Example 8. In the figure, the scale bar indicates 7.14 μm.

FIG. 20 shows an SEM image of the product obtained in Example 9. In the figure, the scale bar indicates 16.6 μm.

FIG. 21 shows changes in physical properties of MgCo _1-x Ni _x GeO ₄ (x = 0, 0.25, 0.50, 0.75, ₁ ). When the color of the obtained product was visually observed, it was found that the color was pink, brown, gray, light green, and green in the order of x = 0, 0.25, 0.50, 0.75, and 1.

Table 2 shows the Rietveld analysis results of the products (MgCo _1-x Ni _x GeO ₄ (x = 0, 0.25, 0.50, 0.75, 1)) obtained in Examples 2, 3, and 7-9. ing.

Claims

The following general formula (1)
Mg a Xb Y c O d (1)
(In the formula (1), X is at least one selected from the group consisting of Ni, Fe, Mn, Co, and Cu, Y is Ge or Ti, and 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.)
The positive electrode active material for secondary batteries containing the magnesium compound represented by these.
A secondary battery comprising the positive electrode active material according to claim 1 as a constituent element.
It is a manufacturing method of the positive electrode active material for secondary batteries of Claim 1, Comprising:
A manufacturing method provided with the heating process which heats the raw material mixture containing the raw material containing Mg, the raw material containing said X, and the raw material containing said Y.
The production method according to claim 3, wherein the heating temperature in the heating step is 500 to 1500 ° C.