JP2002025555A - Magnesium composite oxide for positive electrode active material of magnesium secondary battery, method for producing the same, and magnesium secondary battery using the same - Google Patents

Abstract

(57) [Summary] PROBLEM TO BE SOLVED: To reversibly store and release magnesium.
Provide material materials and provide methods for manufacturing the active material materials.
Offer. A new type of magnesium carrier
A rocking chair type magnesium secondary battery is provided. The active material has a composition formula of Mg._xM1_1-y
M2_yO_TwoOr Mg_xM1_{1- y}M2_yO_Two・ NH_TwoO (M1 is M
at least one selected from n and Fe;
Excluding transition metals and at least one selected from Al)
Magnesium complex acid having a layered crystal structure
A, which is a compound and a precursor_zM1_1-yM2_yO_TwoOr A_z
M1_1-yM2_yO_Two・ NH_TwoO (A is an alkali metal)
After that, they are synthesized by ion exchange in an aqueous solution of Mg salt.
You. A secondary battery is constructed using the active material as a positive electrode active material.
To achieve.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesium composite oxide for a positive electrode active material which can constitute a rocking chair type magnesium secondary battery using magnesium as a carrier, a method for producing the same, and the use of the same as a positive electrode active material. The present invention relates to a rocking chair type magnesium secondary battery configured.

[0002]

2. Description of the Related Art With the miniaturization of personal computers, video cameras, mobile phones, and the like, in the fields of information-related equipment and communication equipment, lithium secondary batteries have been put into practical use as a power source for these equipment, and have spread widely. I have. This lithium secondary battery generally includes a positive electrode using a LiCoO ₂ lithium transition metal composite oxide as a positive electrode active material, a negative electrode using metal lithium, a carbon material, or the like as a negative electrode active material, and a lithium salt as a supporting salt. And an electrolyte solution in which an organic solvent is dissolved.The battery reaction in which lithium desorbed from the positive electrode is occluded by the negative electrode during charging and lithium desorbed from the negative electrode is occluded by the positive electrode during discharging is repeated. It is a secondary battery. That is, it is a rocking chair type secondary battery using lithium as a carrier.

In this lithium secondary battery, the operating voltage is low because metallic lithium or a carbon material used as a negative electrode active material has a low reaction potential with lithium and uses a non-aqueous electrolytic solution as an electrolytic solution. It has the advantages of high energy density and high power,
Its applications are expanding rapidly.

However, lithium, which is a carrier of a lithium secondary battery, is extremely active, and there is a risk that, for example, it reacts with moisture in air and burns. This means
In the manufacturing process of the lithium secondary battery, sufficient consideration such as a dry environment without moisture is required, which leads to an increase in manufacturing cost. Therefore, a new type of rocking chair type secondary battery in which a substance serving as a carrier is changed has been desired.

The present inventor has sought a rocking chair type secondary battery using magnesium as a carrier instead of lithium. Until now, as for the battery using magnesium, for example, as shown in JP-A-5-225978, there is only a primary battery that can only be discharged. The reason for this is that no favorable positive electrode active material capable of reversibly inserting and extracting magnesium has been found.

[0006]

As a result of intensive studies and repeated experiments, the present inventors have found that some magnesium composite oxides can be used as a positive electrode active material capable of occluding and releasing magnesium. . The present invention is based on this finding, and has an object to provide a positive electrode active material that can constitute a rocking chair type secondary battery with a new idea using magnesium as a carrier. It is another object of the present invention to provide a method, and further to provide a magnesium secondary battery formed using the positive electrode active material.

[0007]

Means for Solving the Problems (1) The magnesium composite oxide for a positive electrode active material of a magnesium secondary battery according to the present invention comprises:
Composition formula _{Mg x M1 1-y M2 y} O 2 or _{Mg x M1 1-y M2 y} O 2 ·
nH ₂ O (M1 is at least one selected from Mn and Fe)
Species; M2 is at least one selected from transition metals other than M1 and Al; 0 <x ≦ 0.5; 0 ≦ y <0.4; n is 0.4 to 0.6); The structure is characterized by having a layered structure.

[0008] This magnesium composite oxide is, for example, Li used as a positive electrode active material for a lithium secondary battery.
It has a crystal structure similar to the layered rock salt structure, which is the crystal structure of CoO ₂ . The layered rock salt structure LiCoO ₂ has a hexagonal crystal structure, which is composed of a layer composed of lithium atoms (Li layer) -a layer composed of oxygen atoms (O layer) -a layer composed of cobalt atoms (Co layer). A layer composed of oxygen atoms (O
Layer) in the order of layers.
The magnesium composite oxide of the present invention comprises a layer composed of magnesium atoms (Mg layer) -O layer-a layer composed of M1 atoms (including M2 atoms when M2 is present, the same applies hereinafter) (M1 layer)
-O layer has a crystal structure in which each layer is repeatedly laminated in order, with the Co layer corresponding to the M1 layer and the Li layer
The crystal structure has been replaced with the g layer. In the case where hydration water is contained, when the three layers of the O layer, the M1 layer and the O layer are referred to as a composite layer, a double layer is formed between the composite layers and exists. The structure is such that the magnesium layer is located between the layers of Japanese water.

In the magnesium composite oxide of the present invention having such a crystal structure, magnesium atoms present in the Mg layer are desorbed as ions, and conversely, magnesium ions are occluded at sites of the Mg layer. A reversible reaction is easily realized. Therefore, the magnesium composite oxide of the present invention is a favorable cathode active material that can constitute a rocking chair type secondary battery using magnesium as a carrier. (2) The method for producing a magnesium composite oxide for a magnesium secondary battery positive electrode active material of the present invention is a production method for producing the magnesium composite oxide of the present invention,
Formula _{A z M1 1-y M2 y} O 2 or _{A z M1 1-y M2 y} O 2 · nH
₂ O (A is at least one selected from alkali metals;
0 <z ≦ 1), and an alkali metal composite oxide synthesizing step of synthesizing an alkali metal composite oxide having a layered crystal structure, and ion-exchanging the alkali metal composite oxide in an aqueous Mg salt solution. And a step of synthesizing the magnesium composite oxide of the present invention.

[0010] The magnesium composite oxide of the present invention comprises:
Although the manufacturing method is not particularly limited, the present invention
It can be manufactured by the manufacturing method described above. That is,
The production method of the present invention firstly comprises the hexagonal layer described above.
A having a rock-salt structure_zM1_{1- y}M2_yO_TwoOr A_zM1_1-y
M2_yO_Two・ NH_TwoAfter synthesizing O, this A_zM1_1-yM2_yO _Two
Or A_zM1_1-yM2_yO_Two・ NH_TwoO alkali metal layer
The alkali metals present in (A layer)
By replacing the layers, the Mg layer-O layer-M1 layer-O layer
The present invention having the above-described crystal structure in which each layer is repeatedly laminated
This is a method for producing a magnesium composite oxide. M
gIon exchange in salt solution is a very simple process
Therefore, the production method of the present invention is simple and inexpensive.
Manufacturing method. (3) The magnesium secondary battery of the present invention is
Using magnesium composite oxide as positive electrode active material
It is characterized by. The magnesium composite oxide of the present invention
By using it as a positive electrode active material, magnesium can be carried
A new type of rocking chair rechargeable battery
It will be realized.

[0011] Unlike a lithium secondary battery using extremely active lithium as a carrier, the magnesium secondary battery of the present invention uses magnesium as a carrier. The secondary battery is not required, and is excellent in manufacturing cost and safety during manufacturing.

Further, in the magnesium secondary battery of the present invention, metallic magnesium, a magnesium alloy or the like can be used as the negative electrode active material. Therefore, there is an advantage that the negative electrode and the battery case can be integrated with each other, which could not be realized with the lithium secondary battery, that is, the battery case can be manufactured using magnesium or the like which is a negative electrode active material, thereby achieving a considerable reduction in weight. Having.

Further, in the lithium secondary battery, a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent has to be used. However, in the magnesium secondary battery of the present invention, a magnesium salt as a supporting salt is used. An aqueous electrolyte dissolved in water can also be used. Therefore, in this case, since the secondary battery can be configured by the nonflammable components, the magnesium secondary battery of the present invention is a secondary battery having excellent safety.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The magnesium disulfide of the present invention is described below.
Magnesium composite oxide for secondary battery positive electrode active material
The production method of the present invention for producing
Each embodiment of the magnesium secondary battery of the present invention
The state will be described in detail. (1) Magnesium composite oxide (a) Composition The magnesium composite oxide of the present invention does not contain water of hydration.
If the composition is Mg _xM1_1-yM2_yO_Two(M1 is Mn, F
at least one selected from e; M2 is a transition excluding M1
Transfer metal, at least one selected from Al; 0 <x ≦
0.5; 0 ≦ y <0.4). In addition, the mug of the present invention
Nesium composite oxides contain water of hydration (interlayer water)
Well, in that case Mg_xM1_1-yM2_yO_Two・ NH_TwoO (n is
0.4-0.6).

Specifically, the composition formula Mg_xM1_1-yM2_yO_TwoIn
Do not replace the site of the central metal M1 with another element, and
Mg with metal M1 as Mn_xMnO_Two, Fe and Mg_xF
eO _Two, Mn and Fe both have a ratio of a: 1-a
Mg_xMn_aFe_1-aO_Two(0 <a <1). Ma
In addition, Mg in which a part of the site of the central metal M1 is substituted with M2_x
M1_1-yM2_yO_Two(Y> 0), where M2 is M1
With one selected from transition metals and Al other than
Or two or more substitutions
Good.

M1 serving as the central metal includes Mn and Fe
However, Mn has an advantage that it is stable in trivalence as compared with Fe and has a good crystallinity, that is, a magnesium complex acid having a stabilized layered structure can be obtained. Considering this advantage, M1 is
Desirably n. Further, Fe has the advantage of being inexpensive with a large amount of resources. Therefore, in consideration of this advantage, it is desirable that M1 be Fe.

M2 substituting a part of the site of the central metal M1
Has a function of stabilizing the crystal structure of the magnesium composite oxide, and is at least one selected from transition metals other than Al and M1. Specifically, Al, Co,
Ni or the like can be selected. Since Co and Ni have the advantage of stabilizing the layered structure, it is desirable to consider M2 as at least one of Co and Ni in consideration of this advantage. Further, since Al has the advantages of being trivalent and stable and having a large solid solution amount, it is desirable to set M2 to Al in consideration of this advantage.

The content ratio of Mg in the magnesium composite oxide, that is, the value of x in Mg _x M _{11 -y} M 2 _y O ₂ is 0 <
x ≦ 0.5. A composition that satisfies x = 0 and x> 0.5 cannot be theoretically considered. When functioning as a positive electrode active material in a secondary battery, the value of x changes depending on the state of charge. In order to achieve a better function as the positive electrode active material, it is more preferable that 0.2 ≦ x ≦ 0.5.

The substitution ratio of the central metal with M 2, that is, Mg _x
The value of y in M1 _1-y M2 y O ₂ is the y <0.4.
In the case of y ≧ 0.4, the central metal M1 is likely to have a random structure in which it is located between layers, and the periodicity of a layered structure of Mg layer-O layer-M1 layer-O layer described later is lost, and as a positive electrode active material. This is because the performance of the device is reduced. In order to obtain a positive electrode active material having better characteristics, it is desirable that y ≦ 0.2.

In the magnesium composite oxide of the present invention, in the manufacturing process, some impurities may inevitably enter the crystal. Thus, the composition formula _{Mg x M1 1-y M2 y} O 2 or _{Mg x M1 1-y M2 y} O 2 · nH 2 O which represents the magnesium complex acid of the invention, to include impurities such unavoidable It is not excluded. Similarly, the various composition formulas described in this specification do not exclude inclusion of unavoidable impurities.

(B) Crystal Structure The magnesium composite oxide of the present invention has a crystal structure of a layered structure. The layered structure referred to here is a layered structure belonging to a hexagonal system and means a so-called birnessite type crystal structure. The same atoms or the same kind of atoms form one layer, and this layer has a crystal structure in which the layers are regularly stacked. Each layer is made of Mg consisting of magnesium atoms.
A layer, an M1 layer composed of M1 atoms (including M2 if M2 is present) as a central metal, and an O layer composed of oxygen atoms. These layers are repeated in the order of Mg layer-O layer-M1 layer-O layer. It is laminated.

The lithium-cobalt composite oxide represented by the general composition formula LiCoO ₂ as a positive electrode active material of a lithium secondary battery has a hexagonal crystal structure called an ordered layered rock salt structure. As described above, the Li layer-O
The layers are repeatedly laminated in the order of layer-center metal layer (Co layer) -O layer. In other words, the crystal structure of the magnesium composite oxide of the present invention has a crystal structure in which the Li layer is replaced by the Mg layer in the layered rock salt structure. However, since lithium is monovalent and magnesium is divalent, M
The maximum number of magnesium atoms located in the g layer is の of the maximum number of lithium atoms located in the Li layer.

When the magnesium composite oxide of the present invention contains water of hydration, the water of hydration is divided into three layers of O layer-M1 layer-O layer as shown in FIG. Is called a composite layer, a double layer is formed between the composite layers, and the Mg layer is located between the layers of the water of hydration.

When the magnesium composite oxide of the present invention is used as a positive electrode active material, magnesium atoms move in the Mg layer due to charging, and are separated from the crystal end as ions outside the crystal. At the time of discharge, magnesium ions are inserted from the crystal end, move in the Mg layer, and are occluded at a predetermined site. In other words, the function is the same as the function of the lithium-cobalt composite oxide, which is the positive electrode active material of the lithium secondary battery, except that the carrier atoms are replaced by magnesium instead of lithium. By fulfilling such a function, the magnesium composite oxide of the present invention becomes a positive electrode active material that can constitute a completely new rocking chair type magnesium secondary battery.

(C) Presence or absence of water of hydration As described above, the magnesium composite oxide of the present invention comprises:
Be those represented by the composition formula _{Mg x M1 1-y M2 y} O 2 · nH 2 O containing water of hydration may also composition formula does not contain water of hydration Mg _x M1 _1-y M2 _y It may be represented by O ₂ . However, those containing no water of hydration have higher crystallinity and a stronger crystal structure. Therefore, taking into account the phenomenon of crystal structure collapse accompanying occlusion and desorption of magnesium, a magnesium secondary battery with less cycle deterioration due to charge and discharge can be constructed, and the composition formula Mg _x M1 containing no water of hydration can be obtained. and more preferably it is represented by _1-y M2 _y O _2.

As will be described later in detail in the section of the structure of the magnesium secondary battery, in the case of a magnesium secondary battery having a non-aqueous electrolyte as a constituent element, since water is not used as a solvent for the electrolyte, the charge and discharge are not performed. Is repeated, water of hydration is not taken into the magnesium composite oxide serving as the positive electrode active material. Therefore, in consideration of the above, in the case of a magnesium secondary battery using a non-aqueous electrolyte, in particular, the one represented by the composition formula Mg _x M _{11 -y} M 2 _y O ₂ containing no water of hydration may be used. desirable. (2) Production method of magnesium composite oxide The production method of the magnesium composite oxide of the present invention is not particularly limited. However, according to the manufacturing method of the present invention described below, it is possible to manufacture easily. The production method of the present invention comprises an alkali metal composite oxide synthesis step for synthesizing an alkali metal composite oxide to be a precursor, and magnesium for synthesizing a magnesium composite oxide as a final product from the alkali metal composite oxide. A composite oxide synthesis step.

(A) Step of synthesizing alkali metal composite oxide The step of synthesizing the alkali metal composite oxide is carried out according to the composition formula A_zM1_1-y
M2_yO_TwoOr A_zM1_{1- y}M2_yO_Two・ NH_TwoO (A is an arca
At least one metal selected from the group consisting of M and Mn;
At least one selected from the group consisting of: M2 is a transition other than M1
At least one selected from metal and Al; 0 <x ≦ 0.
5; 0 ≦ y <0.4; 0 <z ≦ 1; n is 0.4-0.
6) The alkali gold having a layered structure represented by 6)
This is a step of synthesizing a metal complex oxide. In this process,
Hexagonal layered rock as precursor of gnesium composite oxide
An alkali metal composite oxide having a salt structure is synthesized. This
Method for Synthesis of Alkali Metal Complex Oxide
Is not particularly limited, and is synthesized by various methods.
It is possible. Below, as an example, two synthesis
Of each alkali metal composite oxide by the method
Will be described.

(I) First Step of Synthesizing Alkali Metal Composite Oxide As the step of synthesizing the alkali metal composite oxide, the following steps can be employed. The process includes the M1 aqueous salt solution the salt and cations dissolved in water M1, and M2 aqueous salt solution the salt and cations dissolved in water M2 mixing as necessary, AOH the H ₂ O ₂ An aqueous solution of an alkali metal hydroxide H ₂ O ₂ dissolved in an aqueous solution is mixed to form a mixed solution, and the composition formula A _z M _{11 -y} M 2 _y O ₂ .nH ₂ O is added to the mixed solution.
This is a synthesis step including a precipitation step of depositing an alkali metal composite oxide having a layered structure represented by the following formula:

In the above-mentioned precipitation step, nitrates, sulfates, acetates and the like can be used as the salt having M1 as a M1 source as a cation. Specifically, when M1 is Mn, manganese nitrate, manganese sulfate, manganese acetate, etc.
When M1 is Fe, iron nitrate, iron sulfate, iron acetate and the like may be used. When M1 is Mn and Fe, a mixture of these may be used. When M1 is Mn and Fe, the Mn salt and the Fe salt may be mixed at a ratio corresponding to the composition ratio of Mn and Fe in the resulting alkali metal composite oxide.

When a part of the site of M1 is replaced with M2,
An M2 salt aqueous solution in which a salt having M2 as a cation is dissolved in water is mixed. In this case, similar to a salt having M1 as a cation as M1 source, a salt having M2 as a cation as cation may be a nitrate, a sulfate or an acetate.

A salt wherein M1 is a cation and M2
More preferably, any of the salts having a cation as a cation is a nitrate. This is because the use of nitrate is a strong acid which is desirable for the neutralization reaction and has the advantage that no ions remain in the product.

When replacing a part of the site of M1 with M2,
M1 mixing ratio of the aqueous salt solution and the M2 salt solution, the molar ratio of M1 and M2, according to the composition _{A z M1 1-y M2 y} O 2 · nH 2 O in the alkali metal composite oxide to be obtained , 1-y: y. M1 salt solution and M2
The concentration of the salt aqueous solution is desirably 0.2 to 5M.
This is because when less than 0.2M, the amount of precipitation is small,
If it exceeds 5M, the generation of oxygen increases, which may be dangerous.

As the alkali metal source, an alkali metal hydroxide AOH is used. And using aqueous H ₂ O ₂ solution as the solvent for dissolving the AOH is for oxidizing M1 ²⁺ soluble in M1 ³⁺ insoluble. The concentration of the aqueous H ₂ O ₂ solution is considered a safety reactions, in result of the alkali metal hydroxide aqueous solution of H ₂ O ₂ by dissolving AOH 1
It is desirable to set the concentration to be 10 wt% to 10 wt%.
The concentration of AOH dissolved in the aqueous solution of H ₂ O ₂ is desirably 0.2 to 5 M in order to perform a uniform reaction.

The alkali metal in the composite oxide synthesis step, considering that it can crystallinity obtain more material good alkali metal content, composition formula is an alkali metal and Li Li _z M1 _{1- y} M2 _y O ₂ or Li _z M1
It is desirable to synthesize a lithium composite oxide represented by _1-y M2 _y O ₂ .nH ₂ O. In this case, in this precipitation step, LiOH is used for the alkali metal hydroxide, and Li _z is used.
The _{M1 1-y M2 y O 2} · nH lithium composite oxide represented by ₂ O it is sufficient to deposit. Also, in consideration of the advantage that the alkali content is slightly reduced but inexpensive, a composition formula of Na _z M11 _-y M2 _{y in} which the alkali metal is Na is taken into consideration.
O ₂ or _{Na z M1 1-y M2 y} O it is desirable to ₂ · nH sodium complex oxide represented by ₂ O synthesized. In this case, NaOH is used as the alkali metal hydroxide, and Na _z M1
_What is necessary is just to deposit a lithium composite oxide represented by _1-y M2 _y O ₂ .nH ₂ O.

The M1 salt aqueous solution and M2 in this precipitation step
Salt solution and alkali metal hydroxide H _TwoO_TwoMixing with aqueous solution
The ratio is determined by the composition A of the alkali metal composite oxide to be obtained.
_zM1 _1-yM2_yO_Two・ NH_TwoChange according to O. However,
(M1 + M2): A is in a molar ratio of 1: 3 to 1:10.
It is desirable to mix as much as possible. Beyond 1: 3
If it is out of the above preferred range, MnO_TwoA subphase is formed
In some cases, and the preferred range exceeding 1:10
Is outside the range, a part of Mn is oxidized to tetravalent, and L
i_TwoMnO_ThreeIs a by-product. In addition,
Considering that the crystallinity is good and it is easy to obtain a single phase
Taking into account, the molar ratio of (M1 + M2): A is about 1: 5.
It is more desirable to mix them in such a manner. By the way, the above
When mixing at a mixing ratio in a preferred range, alkali
When the metal A is Li, approximately 0.4 ≦ z ≦ 0.7
The lithium composite oxide becomes Na as the alkali metal A.
When the sodium compound is approximately 0.2 ≦ z ≦ 0.4
A composite oxide precipitates.

[0036] In this precipitation step is carried out with M1 aqueous salt solution, and M2 salt solution to be mixed as needed, by uniformly mixing the alkali metal hydroxide aqueous H ₂ O _2. The method of mixing is not particularly limited. In order to ensure the uniformity of mixing, it is desirable to perform the mixing while stirring. The method of stirring is not particularly limited, and a known method of stirring a normal solution may be used. The reaction temperature for causing the precipitation reaction is desirably 10 to 30 ° C. because it involves an exothermic reaction. The reaction may be performed for 1 to 30 minutes, which is a relatively quick process.

[0037] If a portion of the M1 sites synthesizing alkali metal composite oxide was replaced with M2, mixed M1 aqueous salt solution, M2 salt solution, three aqueous solutions of alkali metal hydroxide aqueous solution of H ₂ O ₂ at a time In addition to M1 salts and M2
There may be a mode in which an aqueous solution in which a salt is dissolved is prepared in advance, and this aqueous solution is mixed with an aqueous solution of an alkali metal hydroxide H ₂ O ₂ . Therefore, the mixing of the solution in the precipitation step means that this embodiment is also included.

The alkali metal composite oxide deposited in the present precipitation step is obtained as a precipitate in the above mixed solution. Therefore, when attempting to produce a composition formula _{Mg x M1 1-y M2 y} O 2 · nH 2 O containing water of hydration as the final product was obtained as a precipitate _{A z M1 1-y M2 y} O ₂・ nH ₂ O
May be washed with water, filtered, dried if necessary, and then subjected to the next step of synthesizing a magnesium composite oxide.

The alkali metal composite oxide deposited in the above-mentioned deposition step is actually composed of the composition formula A _z M _{11 -y} M 2 _y O _2.
nH ₂ O (n is 0.4 to 0.6) is represented by, contain water of hydration. When synthesizing a alkali metal composite oxide represented by a composition formula _{A z M1 1-y M2 y} O 2 containing no water of hydration, alkali metal composite oxide synthesis step, after the deposition process, mixing after precipitation It is desirable to have a step including a hydrothermal step of aging at a temperature of 70 ° C. or higher in the solution. That is, after deposition, so-called aging may be performed, in which the temperature is maintained in a predetermined range.

The temperature to be maintained, that is, the aging temperature is set to 70 ° C. or higher because if the temperature is lower than 70 ° C., the aging reaction does not proceed. When the aging temperature exceeds 120 ° C., an alkali metal composite oxide represented by the composition formula A ₂ MnO ₃ is by-produced. Therefore, the ripening temperature is desirably 120 ° C. or lower in the sense of synthesizing an alkali metal composite oxide composed of a substantially single phase having a layered structure.

The aging time varies depending on the conditions such as the aging temperature and the like, but may be any time at which the aging reaction can be completely completed, and usually may be performed for 6 hours or more. Since aging after the completion of the reaction leads to prolongation of the entire alkali metal composite oxide synthesis step, it is desirable that the time be as short as possible.

For aging, specifically, for example, the mixed solution having undergone the above-described precipitation step may be placed in a predetermined container and maintained at a predetermined temperature for a predetermined time, and then cooled with water or gradually cooled in the container. By doing so, the temperature can be lowered to around room temperature and then taken out.
However, if the aging temperature is around 100 ° C. or more than 100 ° C., evaporation of the mixed solution itself becomes a problem. It is necessary to carry out under pressure by an autoclave container or the like. From the viewpoint of performing the aging step with a simpler apparatus, the aging temperature is 70
It is desirable that the temperature be in the range of not less than 90 ° C.

The alkali metal complex oxide obtained in this hydrothermal process, the composition formula of water of hydration has been removed A _z M1 _1-y M2
At the same time as those represented by _y O _2, crystallinity is enhanced it. Note that the value of z in the composition formula also changes. If an example of a specific change in the value of z is shown, the value of z in the composition formula of the alkali metal composite oxide containing water of hydration obtained in the above precipitation step is 0.3 ≦ z ≦ 0.7. In some cases, ripening temperature 80
In the case of an alkali metal composite oxide that has undergone the present hydrothermal step performed under the conditions of ° C. and an aging time of 12 hours, z ≧ 0.9 is approximately satisfied. Note that, depending on conditions, atoms of the alkali metal A may enter the M1 layer. In that case, the value of z may exceed 1, although slightly. In such cases,
The alkali metal A corresponding to an amount exceeding 1 is considered to be the inevitable impurity described above, and is interpreted as such.

In the present hydrothermal step, the alkali metal composite oxide containing no water of hydration is obtained as a precipitate. Therefore, it may be washed with water, filtered, dried if necessary, and then subjected to the next step of synthesizing the magnesium composite oxide.

As described above, unlike the synthesis method based on the reaction between the solid and liquid phases, the synthesis process of the alkali metal composite oxide, which includes the precipitation step and the hydrothermal step performed as necessary, is performed by a solution reaction. As a result, a sufficient mixing of the raw materials can be ensured, and the alkali metal composite oxide composite oxide having a layered structure having excellent composition uniformity and crystallinity can be easily synthesized. Further, when the above-mentioned hydrothermal step of removing water of hydration is adopted, the alkali metal composite oxide to be synthesized has higher crystallinity. Further, since the hydrothermal process is a process at a relatively low temperature different from firing or the like, it does not require as much energy as heating at a high temperature. Therefore, even when the hydrothermal process is adopted, the present alkali metal composite oxide synthesis process is a synthesis process with low fuel consumption and hence low production cost.

(Ii) Synthesis of second alkali metal composite oxide
Process The central element M1 is Mn and the composition formula is Mg._xMn_1-yM2_yO_TwoAlso
Is Mg_xMn_1-yM2_yO _Two・ NH_TwoMagnesium represented by O
In the case of producing a complex oxide, and the precursor and
The composition formula L containing at least Li in the alkali metal A
i_1-bA '_bM1_{1 -y}M2_yO_TwoOr Li_1-bA '_bM1_1-yM2
_yO_Two・ NH_TwoO (A 'is selected from alkali metals except Li)
At least one kind; alkali represented by 0 ≦ b <1)
When synthesizing a metal composite oxide, use an alkali metal composite
As the oxide synthesizing step, the following steps are employed.
Can be.

In this step, an aqueous solution of A′MnO ₄ and a Li compound are mixed to prepare a mixed aqueous solution, and the mixed aqueous solution is heated to form a composition Li _1-b A ′ _b M1
_And a hydrothermal step of producing an alkali metal composite oxide represented by _1-y M2 _y O ₂ .nH ₂ O. As in the first alkali metal composite oxide synthesis step, since the reaction of precipitation and aging from the aqueous solution is used, sufficient mixing of the raw materials is ensured, and the composition has excellent uniformity and crystallinity. An alkali metal composite oxide having a layered structure can be easily synthesized. In addition, the hydrothermal process is a relatively low-temperature process different from calcination or the like, and thus is a synthesis process with a similarly low production cost.

In the aqueous solution adjusting step, an aqueous solution of A'MnO ₄ serving as a source of manganese and an alkali metal and a Li compound serving as a source of lithium are obtained by mixing Li _{1 -b} A ' _b M11 _-y M2 _y
O ₂ or Li _1-b A ′ _b M11 _-y M2 _y O ₂ .nH ₂ O Li
This is a step of mixing in an amount corresponding to the composition ratio of / A ′. That is, the mixing ratio of both is Li and A′Mn in the Li compound.
The ratio may be such that A ′ in O ₄ is 1-b: b in a molar ratio.

Since the reaction between the Li compound and A′MnO ₄ is performed in an aqueous solution, the Li compound is preferably water-soluble, and is preferably mixed as an aqueous solution. Examples of the water-soluble lithium compound include LiCl, LiO
H, LiNO ₃ , lithium acetate, lithium butyrate, lithium oxalate, lithium citrate and the like can be used. The concentration of the A'MnO ₄ aqueous solution is 0.1 M to 0.3 M.
And when the Li compound is mixed as an aqueous solution, the concentration of the Li compound aqueous solution is preferably about 0.1 M to 5 M.

The hydrothermal step is a step in which the mixed aqueous solution is heated to a predetermined temperature to precipitate the alkali metal composite oxide from the aqueous solution to produce the mixed solution. Under saturated steam pressure, 12
It is desirable to carry out at 0 to 250 ° C. for a long time. If the heating temperature is lower than 120 ° C., the reaction between A′MnO ₄ and the Li compound does not proceed, and if it exceeds 250 ° C., the cost for the reaction and the like increases, which is not preferable. More preferably, 20
The temperature is preferably set to 0 ° C. or lower. In order to avoid evaporation of the aqueous solution, it is desirable to use a device such as an autoclave.

The produced alkali metal composite oxide is formed as a precipitate in the reaction vessel. This precipitate may be washed with water, filtered, dried if necessary, and then subjected to the next step. In this synthesis method that goes through such a process, a homogeneous composite oxide can be obtained only by mixing an aqueous solution material that is easy to handle and causing a gentle one-step reaction at around 200 ° C., which is a very simple and practical synthesis method. Is the way.

The alkali metal composite oxide synthesized after the completion of the hydrothermal step contains water of hydration and has a composition formula of Li _1-b A ′ _b M
_{1 1-y M2 y O 2} · nH 2 O (n is 0.4 to 0.6) has a one represented by. As described above, in order to further increase the crystallinity, it is more desirable to remove water of hydration.
The method of removing hydration water is not particularly limited. When synthesizing an alkali metal composite oxide represented by the composition formula Li _1-b A ′ _b M11 _-y M2 _y O ₂ that does not contain hydration water, for example, the alkali metal composite oxide synthesizing step is performed using the above-mentioned water. After the heating step, the composition formula Li _1-b A ′ _b M11 _-y M2 _y O ₂ generated in the hydrothermal step
A step including a heat dehydration step of heating an alkali metal composite oxide represented by nH ₂ O to remove water of hydration can be provided.

When performing the heating and dehydrating step,
It is preferably performed at a temperature of 250 ° C. If the heating temperature for the dehydration is less than 100 ° C., the dehydration becomes incomplete,
If the temperature is higher than 250 ° C., the crystal structure of the obtained double alkali metal oxide is disadvantageously changed from a layered structure to a spinel structure. Further, the dehydration step is preferably performed in an air atmosphere. If the dehydration step is performed under reduced pressure, the crystals may be reduced.

(B) Magnesium Composite Oxide Synthesis Step In the magnesium composite oxide synthesis step, the alkali metal composite oxide obtained in the alkali metal composite oxide synthesis step is ion-exchanged in an aqueous Mg salt solution to obtain a magnesium composite oxide. This is a step of synthesizing a composite oxide. In other words, this is a step in which the alkali metal in the alkali metal composite oxide as the precursor is ion-exchanged to magnesium to synthesize the magnesium composite oxide as the final product.

As the solute of the aqueous Mg salt solution used in this step, magnesium chloride, magnesium nitrate, magnesium sulfate or the like can be used. Among them,
In consideration of the fact that Mn in crystals may be eluted with an acidic salt, it is desirable to use magnesium chloride (MgCl ₂ ).

It is desirable that the concentration of the aqueous Mg salt solution is about 1 to 5M. Compared to those in this preferred range,
If it is less than 1M, the ion exchange becomes insufficient because the equilibrium between the alkali metal A and Mg is not biased toward the Mg side. In view of this, it is more desirable that the concentration be higher within the above-mentioned preferred range. However, if the concentration exceeds 5M, the crystal may be dissolved, although the reason is unknown.

The specific method of this step is not particularly limited. For example, the above-mentioned alkali metal composite oxide is charged and dispersed in a predetermined vessel containing the above-mentioned aqueous solution of Mg salt, and is then dispersed at a predetermined temperature. The ion exchange may be performed while stirring for a predetermined time.

The input amount of the alkali metal composite oxide is Mg
It is preferable that the molar ratio of A in the alkali metal composite oxide to Mg in the aqueous salt solution is Mg: A = 10: 1 to 100: 1. Compared with the preferable range, if the amount of the alkali metal composite oxide is too large, the reason is unknown, but the possibility of dissolution of the crystal occurs, and if the alkali metal composite oxide is too small, In addition, there is a possibility that a phase in which ion exchange does not completely proceed and A remains is present.

The reaction temperature for performing ion exchange is 20
It is desirably set to ５０50 ° C. When the reaction temperature is too high with respect to the temperature in this preferred range, the crystals are easily dissolved, and when the reaction temperature is too low, ion exchange becomes difficult. Further, the reaction time is desirably 6 hours or more. If the reaction time is too short, ion exchange will be insufficient. Further, making the reaction time too long only unnecessarily lengthens the time of the present step itself, and it is desirable to make the reaction time as short as possible in consideration of securing a quick step. Specifically, it is desirable to carry out for about 6 to 24 hours.

[0060] Magnesium composite oxide obtained through the present process, although the alkali metal complex oxide for the reaction represented by the composition formula _{A z M1 1-y M2 y} O 2 · nH 2 O containing water of hydration If the composition formula including water of hydration _{Mg x M1 1-y M2 y} O 2 · n
H ₂ represented as the result at O, _1-y M2 formula A _z M1 alkali metal complex oxide is reacted is free of water of hydration _y O ₂
In the case of those represented by the formula Mg containing no water of hydration
_x M11 _-y M2 _y O ₂ .

A set of alkali metal composite oxides as precursors
Formula A_zM1_1-yM2_yO_TwoOr A_zM1 _1-yM2_yO_Two・ NH_Two
The value of z in O and the magnesium complex acid as the final product
Formula Mg_xM1_1-yM2_yO_TwoOr Mg_xM1_1-yM2
_yO_Two・ NH_TwoThe relationship with the value of x in O
A and Mg are almost completely separated by ion exchange in the process
Because of the replacement, x か ら (１ ／) z.

Compositional formula Mg _x M _{11 -y} M 2 _y O ₂ or Mg _x M _{11 -y} M 2 _y O _{2 of} magnesium composite oxide as final product
When the value of x in nH ₂ O is a desired value, that is, when the content ratio of Mg in the magnesium composite oxide is desired, the composition formula of the alkali metal composite oxide as a precursor _{A z M1 1-y M2 y} O 2 or A _z M1 _1-y
The value of z in M2 _y O ₂ · nH ₂ O, that is, the alkali metal A
What is necessary is just to control the existence ratio. In order to control the value of z, an appropriate condition may be selected to perform the alkali metal composite oxide synthesis step.

The magnesium composite oxide obtained through this step has crystals having a layered structure as described above,
It becomes a magnesium composite oxide capable of reversibly inserting and extracting magnesium by electrochemical means. Also,
Since this step is a very simple step of stirring and holding in an aqueous solution at room temperature or a temperature close to room temperature, the method for producing the magnesium composite oxide of the present invention itself becomes simple. Since the magnesium composite oxide obtained through this step is present in the form of a powder in an aqueous solution, it may be subsequently washed with water, filtered, and dried to obtain a positive electrode active material for a magnesium secondary battery. . (3) Magnesium Secondary Battery The magnesium secondary battery of the present invention is a magnesium secondary battery using the magnesium composite oxide of the present invention as a positive electrode active material, and is a rocking chair type secondary battery using magnesium as a carrier. is there. The structure includes a positive electrode using the magnesium composite oxide as an active material, a negative electrode, an electrolytic solution, and essential components.

(A) Positive Electrode The positive electrode is prepared by mixing a powder of the magnesium composite oxide as a positive electrode active material with a conductive material and a binder to prepare a paste-like positive electrode mixture. The positive electrode mixture can be formed by coating the surface of the current collector.

The conductive material is for ensuring the electrical conductivity of the positive electrode, and may be one or a mixture of two or more of carbonaceous powders such as carbon black, acetylene black and graphite. it can. The binder plays a role of binding the active material particles and the conductive material particles, and is made of a fluorinated resin such as Teflon (registered trademark), polytetrafluoroethylene, polyvinylidene fluoride, fluororubber, or a heat-resistant resin such as polypropylene or polyethylene. A plastic resin can be used. The positive electrode mixture can also be adjusted by adding a solvent for the purpose of viscosity adjustment or the like, depending on the convenience of coating, and in that case, an organic solvent such as N-methyl-2-pyrrolidone is used. Can be. For the current collector, it is desirable to use a substance that is electrochemically stable against the positive electrode reaction,
For example, aluminum or the like can be used.

The positive electrode formed by coating the current collector made of metal foil has a sheet-like shape. The sheet-like positive electrode has various thicknesses according to the shape of the battery to be manufactured. It can be made into various sizes by means such as cutting. If necessary, the positive electrode mixture may be pressurized by means such as a press in order to increase the density.

(B) Negative Electrode The type of the active material constituting the negative electrode facing the positive electrode is not particularly limited. It suffices that magnesium can be reversibly inserted (precipitated) and desorbed, and its reaction potential is lower than the reaction potential of the magnesium composite oxide serving as the positive electrode active material. Examples of the substance having a sufficiently low reaction potential and sufficient reversible occlusion (precipitation) / desorption ability include magnesium metal and magnesium alloy. In the magnesium secondary battery of the present invention, these magnesium metal, magnesium alloy Is desirably used as a negative electrode active material. As a magnesium alloy, specifically, M
A g-Al alloy, a Mg-Zn alloy, a Mg-Mn alloy, or the like can be used.

When metal magnesium or a magnesium alloy is used as the negative electrode active material, for example, a material such as metal magnesium is formed into a foil or plate shape.
What is necessary is just to constitute a battery by setting it as a negative electrode and facing the said positive electrode.

(C) Electrolyte The electrolyte is a liquid containing magnesium as a carrier in an ionic state, and is obtained by dissolving a magnesium salt as a supporting salt in a solvent. In the magnesium secondary battery of the present invention, the battery can be constituted by any of a non-aqueous electrolyte using an organic solvent and an aqueous electrolyte using water as a solvent.

In the case of using a non-aqueous electrolyte, the
Mg (BF)_Four)_Two, Mg (PF₆)_Two,
Mg (ClO_Four)_Two, Mg (CF_ThreeSO_Three)_Two, Mg (As
F₆) _TwoEtc. can be used. In addition, organic solvents include
Protic organic solvents can be used. For example, a ring
Carbonate, chain carbonate, cyclic ester, ring
Or two or more ethers or chain ethers
A mixed solvent consisting of the above can be used. Annular carb
Examples of the nitrate include ethylene carbonate and propylene.
Carbonate, butylene carbonate, vinylene car
Carbonates, etc., are exemplified by dimethyl carbonate.
Leucarbonate, diethyl carbonate, methyl ethyl
Examples of cyclic esters include carbonates such as gamma
Butyrolactone, gamma valerolactone, etc.
Examples of ter include tetrahydrofuran, 2-methyl
Trahydrofuran and the like are examples of linear ethers
Methoxyethane, ethylene glycol dimethyl ether
And the like. Any of these things
One type can be used alone, or two or more types can be mixed
It can also be used. The supporting salt concentration in the non-aqueous electrolyte is
It is desirable to be 0.8-1.5M.

In the case of using an aqueous electrolyte, a mug serving as a supporting salt is used.
Nesium salts include Mg (OH)_Two, MgCl_Two, Mg (N
O_Three)_TwoEtc. can be used. There is metallic magnesium
Or negative electrode using magnesium alloy as negative electrode active material
The advantage that the deterioration (oxidation) of the negative electrode can be prevented.
Therefore, among the above supporting salts, Mg (OH) _Two
It is more desirable to use Support for aqueous electrolyte
Is salt concentration the reason why electrolyte conductivity can be increased?
Therefore, it is desirable to set the concentration at or near the saturation concentration.
New

An advantage of using a non-aqueous electrolytic solution is that the magnesium secondary battery can achieve a battery voltage exceeding the decomposition potential of water, which results in a high power density magnesium secondary battery. In consideration of taking advantage of this merit, it is desirable to use a non-aqueous electrolyte in the magnesium secondary battery of the present invention. Incidentally, in the case of a magnesium secondary battery using metallic lithium for the negative electrode, a battery using an aqueous electrolyte can be charged and discharged between about 1.1 V to about 1.6 V, whereas a non-aqueous battery can be used. In the case of using an electrolytic solution, charging and discharging can be performed between about 1.1 V to about 3.0 V.

An advantage of using an aqueous electrolyte is its safety. That is, since no organic solvent is used, there is little risk of fire or the like even when the temperature of the magnesium secondary battery rises due to, for example, overcharging. Therefore, in the case where a magnesium secondary battery with an emphasis on safety is configured, it is desirable to use a non-aqueous electrolyte in the magnesium secondary battery of the present invention.

(D) Other components, etc. In the magnesium secondary battery of the present invention, the positive electrode and the negative electrode are opposed to each other to form an electrode body, and this electrode body is inserted into a battery case together with an electrolytic solution. What is necessary is just to manufacture. When the positive electrode and the negative electrode face each other, a separator is interposed between the two. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and when using a non-aqueous electrolyte, a thin microporous film such as polyethylene or polypropylene, a nonwoven fabric,
When paper or the like is used as the aqueous electrolyte, nonwoven fabric, paper, or the like can be used.

The shape and size of the magnesium secondary battery of the present invention are not particularly limited, and may be various types such as a cylindrical type, a stacked type, a coin type and a card type. An appropriate battery case may be used depending on the shape of the battery to be manufactured and the like. The battery case may be provided with a positive electrode external terminal and a negative electrode external terminal, and a part of the battery case may be of a type that also serves as a positive electrode external terminal and a negative electrode external terminal. Regardless of which shape, type, etc. is adopted, the above-mentioned electrode body is housed in a battery case, and electrical connection is made between the positive electrode and the negative electrode to the positive electrode external terminal and the negative electrode external terminal, respectively, and the electrolytic solution is discharged. Inject, and then close the battery case to separate the battery system from the outside to complete the magnesium secondary battery.

In the magnesium secondary battery of the present invention, when metal magnesium or a magnesium alloy is used as the negative electrode active material, at least a part of the battery case is formed of metal magnesium or a magnesium alloy, and the part of the battery case also functions as the negative electrode. It can also be implemented in embodiments.
In a lithium secondary battery, metallic lithium and the like are extremely active in the air, particularly in the air containing moisture, and therefore, such a mode in which the battery case also serves as the negative electrode involves risks. On the other hand, in the magnesium secondary battery of the present invention, even when the battery case is made of metal magnesium or the like, the metal magnesium or the like is almost inactive in the air, so that it is safe. Therefore, the magnesium secondary battery of the present invention in which the battery case also functions as the negative electrode is a magnesium secondary battery in which the weight of the battery is reduced and the energy density and the power density are excellent. (4) The embodiments of the magnesium composite oxide for a magnesium secondary battery positive electrode active material, the method for producing the same, and the magnesium secondary battery using the same according to the present invention have been described above. The magnesium composite oxide for a magnesium secondary battery positive electrode active material of the present invention, a method for producing the same, and a magnesium secondary battery using the same are described in the above embodiments and various other examples based on the knowledge of those skilled in the art. The present invention can be implemented in various forms with modifications and improvements.

[0077]

EXAMPLE A magnesium composite oxide of the present invention was produced based on the above embodiment, and a magnesium secondary battery of the present invention was produced based on the above embodiment using the same as a positive electrode active material. The secondary battery was evaluated by performing a charge / discharge test. In addition, other types of magnesium composite oxides of the present invention were also manufactured and studied from various angles. The following describes the experiments performed. (1) Experiment 1 (a) Production and analysis of magnesium composite oxide
Observation In order to obtain a magnesium composite oxide having a layered structure represented by the composition formula Mg _x Mn _0.9 Al _0.1 O ₂ , a lithium composite oxide synthesis step including a precipitation step and a hydrothermal step according to the above embodiment, and a magnesium composite oxidation step And a product synthesis step.

In the precipitation step, Mn (N
O_Three)_Two27 mL of aqueous solution and 1 M Al (NO_Three)_Twowater
3 mL of a solution, and add a 1M concentration
150 mL of LiOH aqueous solution and 30 wt% of H_TwoO_TwoAqueous solution
LiOH / H mixed with 15mL _TwoO_TwoMix the aqueous solution at once
The mixture was reacted at 25 ° C for 10 minutes to precipitate a precipitate.
Let out. As a result of composition analysis, this precipitate has a composition formula Li
_0.5Mn_0.9Al_0.1O_Two・ 0.45H_TwoLichi represented by O
It was confirmed that the composite oxide was a composite oxide.

Next, the precipitate was placed in a container lined with Teflon together with the mixed aqueous solution after the reaction, and a hydrothermal step of aging at 80 ° C. for 15 hours was performed. After the hydrothermal process,
The precipitate was washed with water, filtered and dried. As a result of the composition analysis, the obtained powder had a composition formula Li from which water of hydration was removed.
It was a lithium composite oxide represented by Mn _0.9 Al _0.1 O ₂ .

FIG. 1 shows a scanning electron microscope (SEM) photograph of the lithium composite oxide, and FIG. 2 shows an XRD pattern obtained by X-ray diffraction analysis by a powder method using CuKα rays. By the way, FIG.
It is a SEM photograph of 0000 times.

As can be seen from the respective photographs in FIG. 1, the obtained lithium composite oxide was confirmed to be a powder composed of substantially hexagonal plate-like crystal particles, and the particles had a diagonal length of a hexagonal plane. Was about 70 nm on average, and the thickness was about 5 nm on average. Further, by analyzing the XRD pattern of FIG. 2, it was confirmed that the crystal structure of the present lithium composite oxide was a layered rock salt structure belonging to a hexagonal system.

The layered rock-salt-structured lithium composite oxide represented by the composition formula LiMn _0.9 Al _0.1 O ₂ was subjected to a magnesium composite oxide synthesis step. In this synthesis step, 2 g of the above lithium composite oxide was added and dispersed in 200 mL of a 5M aqueous solution of MgCl ₂ and dispersed at room temperature (25 ° C.).
Then, ion exchange is performed by stirring for 10 hours.
The magnesium composite oxide obtained by the present synthesis step is:
As a result of composition analysis, it was represented by the composition formula Mg _0.5 Mn _0.9 Al _0.1 O ₂ .

FIG. 3 shows an SEM photograph of this magnesium composite oxide, and FIG. 4 shows an XRD pattern obtained as a result of X-ray diffraction analysis by a powder method using CuKα radiation. By the way, Fig. 3 shows SE of 200,000 times.
It is an M photograph.

As can be seen from the respective photographs in FIG. 3, the obtained magnesium composite oxide was confirmed to be a powder composed of substantially hexagonal plate-like crystal particles, and the particles had a diagonal length of a hexagonal plane. Is about 70 nm on average, and the thickness is about 5 n on average
m was confirmed. As is clear from comparison with the photograph of FIG. 1 showing the above-described precursor lithium composite oxide, it can be considered that the basic skeleton in the crystal structure is maintained. By analyzing the XRD pattern of FIG. 4, it was confirmed that the crystal structure of the present magnesium composite oxide was a layered structure belonging to a hexagonal system. FIG.
It can be seen from the comparison with the XRD pattern of the lithium composite oxide shown in the above that the basic skeleton in the crystal structure is maintained.

The XRD pattern of FIG. 2 and the XRD of FIG.
In both patterns, a diffraction peak due to the (003) plane of each composite oxide crystal exists near 2θ = 18 ° (the diffraction angle is θ, the same applies hereinafter). As a result of the analysis, spacing d of (003) plane of the lithium composite oxide is a precursor ₍₀₀₃₎ is 4.70A, surface interval of (003) plane of the magnesium complex oxides d ₍₀₀₃₎ 4 .75Å
Met. Therefore, the lattice constant in the c-axis direction (the length of repeating the Li layer (Mg layer) -O layer-Mn layer-O layer three times) is 14.1% for the lithium composite oxide and magnesium for the lithium composite oxide. The composite oxide becomes 14.3%. This means that Li present in the Li layer of the lithium composite oxide is replaced by bulky (large atomic diameter) Mg atoms by ion exchange, thereby maintaining the basic skeleton while maintaining the basic skeleton.
This indicates that a magnesium composite oxide having a layered structure in which an O layer-Mn layer-O layer is repeated is synthesized.

(B) Preparation of Magnesium Secondary Battery A magnesium secondary battery using a magnesium composite oxide as a positive electrode active material was prepared. The positive electrode has a composition formula of Mg _0.5 Mn
_To 70 parts by weight of the magnesium composite oxide represented by _0.9 Al _0.1 O ₂ and having a layered structure, 25 parts by weight of Ketjen black as a conductive material and 5 parts by weight of Teflon as a binder were mixed to prepare a positive electrode mixture. Adjust the thickness of this positive electrode mixture to a thickness of 2
A sheet having a thickness of the positive electrode mixture of 50 μm was produced by pressure molding on the surface of a 2 μm aluminum foil current collector, and then a disk-shaped sheet was punched out of this sheet to a diameter of 15 mmφ.

For the negative electrode facing the positive electrode, metallic magnesium was used. Metal magnesium is 0.1m thick
m and a diameter of 15 mmφ were produced. A non-woven fabric having a thickness of 100 μm was used for the separator sandwiched between the positive electrode and the negative electrode. The magnesium secondary battery was completed by incorporating the positive electrode, the negative electrode, and the separator in a coin-type battery case (2016 type), impregnating the electrolyte, and then sealing the battery case. Note that a saturated aqueous solution of Mg (OH) ₂ , which is an aqueous electrolyte, was used as the electrolyte.

(C) Charge / Discharge Test and Evaluation of Magnesium Secondary Battery A charge / discharge test was performed on the magnesium secondary battery. In the charge / discharge test, the battery was charged at a constant current of a current density of 0.25 mA / cm ² up to a charge end voltage of 1.6 V.
Current density 0.25 mA / cm up to discharge end voltage 1.1 V
^The charge / discharge cycle of discharging at a constant current of ² was repeated.

As a result of the charge / discharge test, FIG. 5 shows charge / discharge curves of the magnesium secondary battery at the first and second cycles (a curve showing the relationship between the voltage between battery terminals and the capacity per positive electrode active material). ). As can be seen from this charge / discharge curve, in the first cycle, the charge capacity was about 45 mA.
h / g, and the discharge capacity was about 55 mAh / g. Although the reason for the difference in capacity has not been elucidated at present, it is considered that the difference is caused by some structural change of the magnesium composite oxide as the positive electrode active material. On the other hand, in the second cycle, both the charge capacity and the discharge capacity were about 4
5 mAh / g, and there is almost no capacity difference. Although not shown, the capacity after the third cycle is substantially the same as that of the second cycle.

Judging from these results, in the secondary battery using the magnesium composite oxide of the present invention as the positive electrode active material,
It is concluded that a secondary battery capable of reversibly charging and discharging a considerable capacity can be formed. The magnesium secondary battery manufactured in this experiment is a completely new type rocking chair type secondary battery using magnesium as a carrier. (2) Experiment 2 This experiment relates to a magnesium composite oxide having a layered structure containing water of hydration and synthesized by ion-exchange of a precursor of a layered rock salt structure alkali metal composite oxide containing water of hydration. The present magnesium composite oxide was produced by the following method comprising a sodium composite oxide synthesizing step in which the precipitation step according to the above embodiment was performed and the hydrothermal step was not performed, and a magnesium composite oxide synthesizing step.

In the precipitation step in the step of synthesizing the sodium composite oxide, a 30M aqueous solution of Mn (NO ₃ ) _{2 having} a concentration of 1M was used.
In L, 150 mL of 1 M NaOH aqueous solution and 30 w
NaOH / H ₂ mixed with 15 mL of t% H ₂ O ₂ aqueous solution
An O ₂ aqueous solution was mixed at once, and reacted at a temperature of 25 ° C. for 10 minutes to precipitate a precipitate. As a result of composition analysis, this precipitate was confirmed to be a sodium composite oxide represented by a composition formula of Na _0.3 MnO ₂ .0.5H ₂ O.

Next, the sodium composite oxide obtained in the above synthesis step was subjected to a magnesium composite oxide synthesis step. In this synthesis step, a 5M MgCl ₂ aqueous solution 20 was used.
2 g of the sodium composite oxide is added and dispersed in 0 mL, and the mixture is stirred at room temperature (25 ° C.) for 10 hours to perform ion exchange. As a result of the composition analysis, the magnesium composite oxide obtained by the present synthesis process has a composition formula M
g _0.15 MnO ₂ · 0.5H ₂ O

The sodium composite oxide as a precursor and the magnesium composite oxide as a final product were subjected to X-ray diffraction analysis by a powder method using CuKα radiation. FIG. 6 shows the respective XRD patterns obtained as a result. Incidentally, in the figure, the composition formula Na _0.3 Mn
X of sodium composite oxide represented by O ₂ · 0.5H ₂ O
The RD pattern is defined as “Na type” and the composition formula is Mg _0.15 MnO ₂
X of magnesium composite oxide represented by 0.5H ₂ O
The RD pattern is indicated as “Mg type”.
As a result of analyzing these XRD patterns, it can be confirmed that the crystal structure of each of the sodium composite oxide and the magnesium composite oxide is a layered structure, and that the basic skeleton in the crystal structure is maintained by ion exchange. .

However, the XRD of sodium composite oxide
In the pattern, a diffraction peak due to the (003) plane exists at 2θ ≒ 12 °, whereas in the XRD pattern of the magnesium composite oxide, a diffraction peak due to the (003) plane exists at 2θ ≒ 9 °. According to the analysis, spacing of (003) plane of sodium complex oxide d ₍₀₀₃₎ is about 7Å next, magnesium composite oxide (003) face of the lattice spacing d ₍₀₀₃₎ is about 10 Å. Therefore, the Na layer (Mg
Layer) -O layer-Mn layer-O layer
This indicates that the thickness is increased by ion exchange.

The reason will be described with reference to FIG. FIG. 7A schematically shows a crystal structure of a sodium composite oxide containing water of hydration, and FIG. 7B schematically shows a crystal structure of a magnesium composite oxide containing water of hydration. In each of the drawings, layers described as a truss structure above and below represent a composite layer including an O layer-Mn layer-O layer.

In the case of a sodium composite oxide containing water of hydration, as shown in FIG.
a is present in one layer. On the other hand, in the case of the magnesium composite oxide containing water of hydration, FIG.
As shown in Fig. 5, hydration water exists as a double layer between the composite layers, and a layer made of Mg is inserted between the layers of hydration water. This difference in crystal structure is due to the fact that Mg has a higher hydrophilicity than an alkali metal. Therefore, it is considered theoretically correct that the c-axis length in the crystal structure is extended by ion-exchanging Na of sodium composite oxide containing hydration water into Mg to synthesize magnesium composite oxide containing hydration water. Can be

FIG. 8 shows a transmission electron microscope (TEM) photograph of the synthesized magnesium composite oxide containing water of hydration. According to this photograph, it can be easily confirmed that the present magnesium composite oxide has a layered structure. The layer observed in black in the photograph is a composite layer composed of an O layer-Mn layer-O layer, and the layer observed in white is a double layer of hydration water and an Mg layer existing therebetween. The pitch of the composite layer (repetition length of the composite layer) is about 10 °, and this pitch is
Theoretically, the surface interval d _{(003) of the} (003) surface is obtained. In the case of the present magnesium composite oxide, the value of the interplanar spacing d ₍₀₀₃₎ obtained from the TEM photograph and the value of the interplanar spacing d ₍₀₀₃₎ obtained from the analysis result of the XRD pattern substantially coincide with each other. . (3) Experiment 3 A phenomenon confirmed by Experiment 2, in which the composite layer pitch of the magnesium composite oxide containing hydrated water synthesized by ion-exchanging the alkali metal composite oxide containing water of hydration elongates. Using the phenomenon, an experiment was conducted to investigate the ion exchange reaction time in the magnesium composite oxide synthesis step of the production method of the present invention. Hereinafter, this experiment will be described.

First, in order to obtain a magnesium composite oxide having a layered structure represented by the composition formula Mg _x MnO ₂ , a lithium composite oxide synthesizing step and a magnesium composite oxide synthesizing step in which the deposition step according to the above embodiment is performed are described. It was prepared by the following method comprising:

In the precipitation step, Mn (N
An aqueous solution of LiOH / H ₂ O _{2 obtained} by mixing 150 mL of a 1 M LiOH aqueous solution and 15 mL of a 30 wt% H ₂ O ₂ aqueous solution at once with 30 mL of an O ₃ ) ₂ aqueous solution is reacted at 25 ° C. for 10 minutes. To precipitate a precipitate. Next, this lithium composite oxide was subjected to a magnesium composite oxide synthesis step. In this synthesis step, a 5M Mg
In 200 mL of a Cl ₂ aqueous solution, 2 g of the lithium composite oxide is charged and dispersed, and ion exchange is performed by stirring at room temperature (25 ° C.) for a predetermined reaction time.
In addition, four kinds of magnesium composite oxides in which the above-mentioned predetermined reaction time was 1 hour, 6 hours, 24 hours (1 day) or 5 days were produced.

The lithium composite oxide and the four kinds of magnesium composite oxides were subjected to an X-ray diffraction analysis by a powder method using CuKα radiation. FIG. 9 shows the respective XRD patterns obtained as a result.

In the XRD pattern of the lithium composite oxide shown at the bottom in FIG. 9, (00
3) While there is a diffraction peak due to the plane, the XRD patterns of the respective magnesium composite oxides having different reaction times for ion exchange show that 2θ ≒ 9 ° and (00
3) There is a diffraction peak due to the plane. However, from the bottom 2
In the XRD pattern of the magnesium composite oxide subjected to the one-hour ion exchange described in the column, the diffraction peak is in a broad state, indicating that the ion exchange has not been completely completed. On the other hand, the XRD patterns of the magnesium composite oxides listed in the third, fourth, and top rows from the bottom after performing the ion exchange for 6 hours or more show considerably sharp diffraction peaks. It turns out that the thing has almost completed the ion exchange.

From the results of this experiment, the ion exchange reaction time in the magnesium composite oxide synthesis step of the present invention was as follows:
It can be confirmed that it is desirable that the time is 6 hours or more. Incidentally, it is considered that the magnesium composite oxide that has been subjected to ion exchange for more than 6 hours does not differ much in the XRD pattern from the magnesium composite oxide that has been subjected to ion exchange for 6 hours, and that there is almost no difference in crystal structure.

[0103]

The magnesium composite oxide for a positive electrode active material of a magnesium secondary battery according to the present invention has a layered structure as described above. Such a manesium composite oxide of the present invention is capable of reversibly occluding and releasing magnesium, and has a good positive electrode active material capable of forming a rocking chair type secondary battery using magnesium as a carrier. Become.

Further, in the production method of the present invention, which is a method for producing the above-mentioned magnesium composite oxide, the alkali metal composite oxide having a layered structure is synthesized as a precursor, and the precursor is ion-exchanged to obtain a composite oxide having a layered structure. It synthesizes things. Since such a process is very simple, the manufacturing method of the present invention is a simple and inexpensive manufacturing method. Further, the magnesium secondary battery of the present invention,
The present invention uses the magnesium composite oxide of the present invention as a positive electrode active material, and realizes a completely new type rocking chair type secondary battery using magnesium as a carrier.

[Brief description of the drawings]

FIG. 1 shows an SEM photograph of a lithium composite oxide synthesized as a precursor in Experiment 1.

FIG. 2 shows an XRD pattern obtained by an X-ray diffraction analysis performed on a lithium composite oxide synthesized as a precursor in Experiment 1.

FIG. 3 shows an SEM photograph of a magnesium composite oxide produced in Experiment 1.

FIG. 4 is a graph showing X obtained by X-ray diffraction analysis performed on a manufactured magnesium composite oxide in Experiment 1.
3 shows an RD pattern.

FIG. 5 shows charge / discharge curves of the first and second cycles of the produced magnesium secondary battery in Experiment 1.

FIG. 6 shows respective XRDs obtained by X-ray diffraction analysis performed on sodium composite oxide containing water of hydration synthesized as a precursor and magnesium composite oxide containing water of hydration produced in Experiment 2. Indicates a pattern.

FIG. 7 schematically shows a crystal structure of a sodium composite oxide containing water of hydration and a crystal structure of a magnesium composite oxide containing water of hydration.

FIG. 8 shows a TEM photograph of the produced magnesium composite oxide containing water of hydration in Experiment 2.

FIG. 9 shows each XRD pattern obtained by X-ray diffraction analysis performed on each magnesium composite oxide manufactured in Experiment 3 with different reaction times for ion exchange.

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[Submission date] December 6, 2000 (200.12.
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 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoshio Ukyo F-term (reference) at Toyota Central R & D Laboratories Co., Ltd. 1 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi, Japan 4G002 AA06 AB02 AD02 AE05 4G048 AA04 AA05 AB02 AC06 AD06 AE05 5H029 AJ01 AK03 AL11 AM00 AM02 AM07 CJ02 CJ08 CJ11 DJ16 DJ17 HJ02 HJ14 5H050 AA01 BA08 CA07 CB11 EA08 EA24 EA28 FA17 FA18 GA02 GA10 GA11 HA02 HA14

Claims (9)

[Claims] 1. A composition formula of Mg _x M11 _-y M2 _y O ₂ or Mg _x
M1 _1-y M2 _y at least one O ₂ · nH ₂ O (M1 is Mn, selected from Fe; M2 is a transition metal except the M1, Al
0 <x ≦ 0.5; 0 ≦ y
<0.4; n is 0.4 to 0.6), and a magnesium composite oxide for a magnesium secondary battery positive electrode active material having a layered crystal structure. 2. The method according to claim 1, wherein M1 is Mn, and the composition formula Mg_xMn
_1-yM2_yO_TwoOr Mg _xMn_1-yM2_yO_Two・ NH_TwoRepresented by O
The positive electrode active material for a magnesium secondary battery according to claim 1, wherein
For magnesium composite oxide. 3. The method according to claim 2, wherein M2 is Al, and the composition formula Mg_xM1
_1-yAl_yO_TwoOr Mg _xM1_1-yAl_yO_Two・ NH_TwoO (y
The magnesium secondary battery according to claim 1, which is represented by> 0).
Pond Magnesium composite oxide for positive electrode active material. 4. A composition not containing hydration water and having a composition formula of Mg _x M11 _-y M2.
magnesium secondary battery positive electrode active material for magnesium composite oxide according to claim 1, which is represented by _y O _2. 5. A composition formula of Mg _x M11 _-y M2 _y O ₂ or Mg _x
M1 _1-y M2 _y at least one O ₂ · nH ₂ O (M1 is Mn, selected from Fe; M2 is a transition metal except the M1, Al
0 <x ≦ 0.5; 0 ≦ y
<0.4; n is 0.4 to 0.6), and is a method for producing a magnesium composite oxide for a positive electrode active material of a magnesium secondary battery having a layered crystal structure, comprising a composition formula A _z M1 _1-y M2 y O ₂ or _{A z M1 1-y M2 y} O 2 · nH
₂ O (A is at least one selected from alkali metals;
0 <z ≦ 1), an alkali metal composite oxide synthesizing step of synthesizing an alkali metal composite oxide having a crystal structure having a layered structure, and ion-exchanging the alkali metal composite oxide in an aqueous solution of Mg salt. A method for producing a magnesium composite oxide for a positive electrode active material of a magnesium secondary battery, comprising: a magnesium composite oxide synthesizing step of synthesizing the magnesium composite oxide. 6. The step of synthesizing an alkali metal composite oxide comprises dissolving an M1 salt aqueous solution obtained by dissolving a salt having M1 as a cation in water, and optionally dissolving a salt having M2 as a cation in water. M2 and salt aqueous solution, a AOH and H ₂ O ₂ alkali metal dissolved in an aqueous solution hydroxide aqueous H ₂ O ₂ solution and the mixture to the mixed solution, the composition formula in the mixed solution a _z M1 _1-y M2 _y O ₂
Manufacturing method of the alkali metal complex oxide magnesium secondary battery positive electrode active material for magnesium composite oxide according to claim 5 consisting comprise precipitation step to precipitate the · nH represented by ₂ O. 7. A method for producing a composition formula _{Mg x M1 1-y M2 y} O 2 with the magnesium secondary battery positive electrode active material for magnesium composite oxide represented, the alkali metal complex oxide synthesis step after the precipitation step, deposited the composition formula _{A z M1 1-y M2 y} O 2
· The nH alkali metal composite oxide represented by ₂ O in the mixed solution after the precipitation was aged at 70 ° C. or higher, the alkali metal represented by the composition formula _{A z M1 1-y M2 y} O 2 7. A hydrothermal step for producing a composite oxide.
3. The method for producing a magnesium composite oxide for a magnesium secondary battery positive electrode active material according to 1.). 8. The composition formula Mg _x M11 _-y M2 _y O ₂ or Mg _x
M1 _1-y M2 _y at least one O ₂ · nH ₂ O (M1 is Mn, selected from Fe; M2 is a transition metal except the M1, Al
0 <x ≦ 0.5; 0 ≦ y
<0.4; n is 0.4 to 0.6), and a magnesium secondary battery using a magnesium composite oxide having a layered crystal structure as a positive electrode active material. 9. The magnesium secondary battery according to claim 8, comprising an aqueous electrolyte solution in which a magnesium salt serving as a supporting salt is dissolved in water.