JP6529005B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery. More specifically, the present invention relates to a secondary battery that can be suitably used for storage of electric power, a power source of a hybrid vehicle or an electric vehicle, and a positive electrode active material and a positive electrode used therefor.

In recent years, miniaturization and higher capacity of secondary batteries have been desired. Thus, for example, general formula (X):
Mg _x MO ₂ (X)
Non-aqueous electrolyte batteries etc. which contain the magnesium compound represented by these as a positive electrode active material are proposed (for example, refer patent document 1).

JP 2001-76720 A

  However, new secondary batteries capable of securing high capacity are desired.

  The present invention has been made in view of the prior art, and an object of the present invention is to provide a new secondary battery capable of securing a high capacity, and a positive electrode active material and a positive electrode used therefor.

  The present invention comprises a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, a positive electrode containing a positive electrode active material, and an electrolytic solution interposed between the positive electrode and the negative electrode, and at the end of the discharge, the positive electrode The present invention provides a secondary battery characterized in that the active material contains a transition metal complex oxide having a rock salt structure. In the secondary battery according to the present embodiment, since the positive electrode active material contains the transition metal composite oxide having a rock salt structure at the end of the discharge, a high capacity can be secured.

  Further, the present invention is a positive electrode active material for use in a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, which comprises a transition metal composite oxide having a rock salt structure. The present invention provides a positive electrode active material characterized by According to the positive electrode active material according to the present embodiment, since the transition metal composite oxide having the rock salt structure is contained, in the secondary battery including the negative electrode containing metal magnesium or a magnesium alloy, high capacity is ensured. Can.

  Furthermore, the present invention is a positive electrode for use in a secondary battery comprising a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, wherein the positive electrode includes the above-described positive electrode active material. I will provide a. Since the positive electrode according to the present embodiment contains the positive electrode active material, it is possible to obtain the same effect as that of the positive electrode.

  According to the secondary battery, the positive electrode active material, and the positive electrode of the present invention, an excellent effect of ensuring a high capacity is exhibited.

It is a schematic explanatory drawing which shows the structure of the secondary battery which concerns on one Embodiment of this invention. It is a schematic explanatory drawing which shows the change of the crystal structure of the transition metal complex oxide contained in the positive electrode active material in the charging / discharging process of the secondary battery which concerns on one Embodiment of this invention. It is a schematic explanatory drawing which shows the change of the structure | tissue structure of the positive electrode active material before and behind the discharge reaction of the secondary battery concerning one Embodiment of this invention. In Example 1, it is a X-ray-diffraction figure which shows the result of having investigated the X-ray diffraction of magnesium cobalt complex oxide. It is a schematic explanatory drawing of the electrochemical cell used in Examples 1-6. (A) is a cyclic voltammogram when a process of inserting and removing a magnesium cation is performed using an electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide in Example 1 (B 2.) is a cyclic voltammogram when the lithium cation is inserted and removed using an electrochemical cell having a working electrode containing an electrode material containing the obtained magnesium-cobalt composite oxide. (A) In Example 2, using an electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide, the process of inserting and removing a magnesium cation while maintaining a predetermined potential The chronoamperometry-cyclic voltammogram (upper stage) and the figure (lower stage) showing the change in electric quantity thereof in Example 2 (B) is an electrochemical having a working electrode including an electrode material containing a magnesium-cobalt composite oxide. It is a figure (lower stage) which shows the chronoamperometry cyclic voltammogram (upper stage) at the time of performing insertion and detachment | desorption process of lithium cation, maintaining a predetermined | prescribed electric potential using a cell (lower stage). In Example 2, it is a figure which shows the result of having investigated the charge / discharge characteristic of the electrochemical cell which has a working electrode containing the electrode material containing magnesium cobalt complex oxide. In Example 2, it is a X-ray-diffraction figure which shows the result of having investigated the X-ray diffraction of magnesium cobalt complex oxide at the time of completion | finish of discharge, and full charge. In Example 2, it is a X-ray-diffraction figure which shows the result of having investigated the X-ray diffraction of the magnesium cobalt complex oxide at the time of completion | finish of discharge of a large capacity, and full charge. In Example 3, it is a X-ray-diffraction diagram which shows the result of having investigated the X-ray diffraction of obtained magnesium manganese complex oxide product A. FIG. In Example 3, using an electrochemical cell having a working electrode containing an electrode material containing a magnesium-manganese composite oxide and performing a process of inserting and removing a magnesium cation in the range of 1.5 to 4.5 V Cyclic voltammograms. In Example 4, it is a X-ray-diffraction diagram which shows the result of having investigated the X-ray diffraction of the obtained magnesium iron complex oxide. In Example 4, using an electrochemical cell having a working electrode containing an electrode material containing magnesium iron complex oxide, cyclic when magnesium cation is inserted and removed in the range of 2 to 3.8 V It is a voltammogram. In Example 5, it is a X-ray-diffraction diagram which shows the result of having investigated the X-ray diffraction of obtained product A. In Example 5, using an electrochemical cell having a working electrode containing an electrode material containing CoCo ₂ O ₄ (Co ₃ O ₄ ), the relationship between potential and current when discharging is performed while maintaining at 2 V is investigated. It is a figure which shows the result. In Example 5, a diagram illustrating a Q-t curve when using an electrochemical cell having a working electrode comprising an electrode material containing CoCo ₂ O _4, was subjected to discharge while maintaining the 2V. In Example 5, it is a X-ray-diffraction diagram which shows the result of having investigated the X-ray diffraction of the electrode material of the working electrode of an electrochemical cell. In Example 6, using an electrochemical cell having an electrolytic solution containing a glyme compound as an electrolytic solution and having a working electrode containing an electrode material containing magnesium cobalt composite oxide (Mg ₂ Co ₂ O ₄ ), It is a cyclic voltammogram at the time of performing the insertion and elimination process of magnesium cation. In Example 6, an electrochemical cell having an electrolytic solution containing a glyme compound as an electrolytic solution and having a working electrode containing an electrode material containing magnesium cobalt composite oxide (Mg ₂ Co ₂ O ₄ ) was 2 V at 2 V It is a figure which shows the Qt curve when hold | maintaining.

[Configuration of secondary battery]
A secondary battery according to an embodiment of the present invention includes a negative electrode containing metal magnesium, metal lithium or a magnesium lithium alloy, a positive electrode containing a positive electrode active material, and an electrolytic solution interposed between the positive electrode and the negative electrode. The device is characterized in that, at the end of the discharge, the positive electrode active material contains a transition metal complex oxide having a rock salt structure.

  In the present specification, “transition metal complex oxide” includes both transition metal complex oxides having a rock salt structure and transition metal complex oxides having a spinel structure. In the present specification, “transition metal complex oxide having rock salt structure” is described as “rock salt type transition metal complex oxide”, and “transition metal complex oxide having spinel structure” is “spinel type transition metal”. It may be described as "complex oxide".

  In the secondary battery according to the present embodiment, since the positive electrode active material containing the rock salt type transition metal complex oxide is used at the end of discharge, the magnesium cation which is a trivalent cation, or the magnesium cation and lithium are used. Both cations and can be used as charge carriers. Therefore, according to the secondary battery concerning this embodiment, high capacity is securable. The secondary battery according to the present embodiment uses a negative electrode containing metal magnesium, metal lithium or a magnesium alloy, and a positive electrode containing a positive electrode active material containing the rock salt type transition metal composite oxide at the end of discharge. Therefore, a high operating voltage can be secured. In addition, since the secondary battery according to the present embodiment uses the negative electrode containing metal magnesium, metal lithium or a magnesium alloy, a high energy density can be secured, and the handling property is excellent.

  First, the configuration of a secondary battery according to the present embodiment will be described with reference to the attached drawings. The configuration of the secondary battery according to the present embodiment is shown in FIG. The secondary battery 1 shown in FIG. 1 includes a battery body 2 and a heat retaining portion 3 for holding the battery body 2 at an operation temperature of a medium temperature range (50 to 300 ° C.). The secondary battery 1 can be used by being connected to various devices (21 in the figure).

  The battery body 2 is separated in a sealable battery container (not shown) so that the negative electrode 11, the positive electrode 12, the electrolytic solution 13 interposed between the negative electrode 11 and the positive electrode 12, the negative electrode 11 and the positive electrode 12 do not contact each other. And a separator 14 for the purpose. The electrolytic solution 13 is interposed between the negative electrode 11 and the positive electrode 12. Thereby, the negative electrode 11 and the positive electrode 12 are electrically connected. The negative electrode 11, the positive electrode 12 and the separator 14 are disposed such that the surface of the positive electrode material layer 12 b of the positive electrode 12 and the surface of the negative electrode material layer 11 b of the negative electrode 11 face each other with the separator 14 interposed therebetween. Thus, the negative electrode 11 and the positive electrode 12 are disposed so as not to be in direct contact with each other.

  The negative electrode 11 is an electrode containing metallic magnesium, metallic lithium or a magnesium-lithium alloy. In the secondary battery 1 shown in FIG. 1, the negative electrode 11 is an electrode including a current collector 11 a and a negative electrode material layer 11 b. The negative electrode 11 can be manufactured, for example, by applying a negative electrode material to the current collector 11a to form the negative electrode material layer 11b. The material of the current collector 11 a is preferably selected according to the type of the negative electrode material, the type of the electrolytic solution 13, and the like because it varies depending on the type of the negative electrode material, the type of the electrolytic solution 13, and the like. As a material which constitutes current collection object 11a, although aluminum, platinum, a carbon material, molybdenum, tungsten, etc. are mentioned, for example, the present invention is not limited only to this illustration. Examples of the shape of the current collector 11a include a plate, a ribbon, a foil, and a wire, but the present invention is not limited to such examples. The negative electrode material contains metal magnesium, metal lithium or a magnesium lithium alloy as a negative electrode active material. The negative electrode material may further contain a conductive aid and a binder, if necessary. Examples of the conductive aid include carbon powder such as acetylene black and ketjen black; oxygen deficient titanium oxide, metal fine powder and the like, but the present invention is not limited to such examples. Absent. The content of the conductive auxiliary in the positive electrode material is preferably determined according to the type of the conductive auxiliary, because it varies depending on the type of the conductive auxiliary and the like. The binder may be any one that can be used at a temperature in the medium temperature range (50 to 300 ° C.). Examples of the binder include thermoplastic fluorine resins such as polyvinylidene fluoride; glass, polyimide and the like, but the present invention is not limited to such examples. The content of the binder in the negative electrode material is preferably determined in accordance with the type of the binder because it varies depending on the type of the binder and the like. In the present invention, the negative electrode may not be a current collector, and may be an electrode made of metal magnesium, metal lithium or a magnesium lithium alloy.

  The positive electrode 12 is an electrode containing a positive electrode active material containing a transition metal composite oxide having a rock salt structure. In the secondary battery 1 shown in FIG. 1, the positive electrode 12 includes a current collector 12a and a positive electrode material layer 12b including a positive electrode active material containing a transition metal composite oxide having a rock salt structure at the end of discharge. And an electrode. As described above, since the positive electrode 12 includes the positive electrode active material containing the rock salt type transition metal composite oxide when the discharge is completed, a high capacity can be secured. The positive electrode material may further contain a conductive aid and a binder, as required. The conductive aid and the binder in the positive electrode material are the same as the conductive aid and the binder in the negative electrode material. For example, the positive electrode 12 is formed by applying a positive electrode material to the current collector 12a to form the positive electrode material layer 12b; the positive electrode material is directly applied to the current collector by a pulse laser deposition method, a sputtering method, a liquid phase synthesis method or the like. Can be deposited to form the positive electrode material layer 12b.

  The positive electrode active material is a positive electrode active material for use in a secondary battery provided with a negative electrode containing metallic magnesium or a magnesium alloy, and is characterized by containing a rock salt type transition metal complex oxide. According to such a positive electrode active material, since the rock salt type transition metal composite oxide is contained, high capacity can be secured in a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or a magnesium alloy. .

The rock salt type transition metal complex oxide has a rock salt structure at the end of discharge, and becomes a compound having a spinel structure at full charge. As the rock salt type transition metal complex oxide, for example, formula (I):
Li _a Mg _{1 + b} M ¹ ₂ O ₄ (I)
[Wherein, M ¹ represents a manganese atom, a cobalt atom or an iron atom, a represents the number of 0 to 2, b represents the number of 0 to 1, and a and b represent the formula (II):
a + 2b = 2 (II)
(In the formula, a and b are as defined above)
To satisfy
A compound represented by the formula (III):
Li _c Mg _d CoCo ₂ O ₄ (III)
[Wherein, c represents a number of 0 to 2, d represents a number of 0 to 1, and c and d represent a group of formula (IV):
c + 2d = 2 (IV)
(Wherein c and d are the same as above)
To satisfy
Although the compound etc. which are represented by are mentioned, this invention is not limited only to this illustration. The compound represented by the formula (I) and the transition metal complex compound represented by the formula (III) undergo a structural phase transition with the detachment and insertion of a cation, have a rock salt structure at the end of the discharge, and are fully charged It has common properties in that it sometimes becomes a compound having a spinel structure.

Examples of the compound represented by formula (I), for _{example, Mg 2 Mn 2 O 4,} Mg 2 Co 2 O 4, Mg 2 Fe 2 O 4, MgCoCo 2 O 4, Li 2 MgMn 2 O 4, Li 2 MgCo 2 O ₄ , Li ₂ MgFe ₂ O ₄ , Formula (Ia):
Li _a Mg _{1 + b} Mn ₂ O ₄ (Ia)
(Wherein, a and b are as defined above)
A compound represented by the formula (Ib):
Li _a Mg _{1 + b} Co ₂ O ₄ (Ib)
(Wherein, a and b are as defined above)
A compound represented by the formula (Ic):
Li _a Mg _{1 + b} Fe ₂ O ₄ (Ic)
(Wherein, a and b are as defined above)
Although the compound etc. which are represented by are mentioned, this invention is not limited only to this illustration.

Examples of the compound represented by the formula (III) include MgCoCo ₂ O ₄ , Li ₂ CoCo ₂ O ₄ , a formula (IIIa):
Li _c Mg _d CoCo ₂ O ₄ (IIIa)
(Wherein, c and d are as defined above)
Although the compound etc. which are represented by are mentioned, this invention is not limited only to this illustration.

Specifically, when the negative electrode is a negative electrode containing metallic magnesium, the positive electrode active material is, for example, Mg ₂ Mn ₂ O ₄ , Mg ₂ Co ₂ O ₄ , Mg ₂ Fe ₂ O ₄ at the end of discharge. Or a compound represented by Formula (I) such as MgCoCo ₂ O ₄ or a compound represented by Formula (III) such as MgCoCo ₂ O ₄ . In this case, the positive electrode active material is the compound shown in the right column of Table 1 when fully charged.

When the negative electrode is a metal lithium negative electrode, the positive electrode active material is, for example, a compound of formula (I) such as Li ₂ MgMn ₂ O ₄ , Li ₂ MgCo ₂ O ₄ , Li ₂ MgFe ₂ O ₄ at the end of discharge. Or a compound represented by Formula (III) such as Li ₂ CoCo ₂ O ₄ . In this case, the positive electrode active material is a compound shown in the right column of Table 2 when fully charged.

Furthermore, the negative electrode, if the magnesium lithium alloy negative electrode, at the time of the end of discharge, the positive electrode active material, for _{example, Li a Mg 1 + b Mn} 2 O 4 [Formula _{(Ia)], Li a Mg 1 + b Co} 2 A compound represented by the formula (I) such as O ₄ [formula (Ib)], Li _a Mg _{1 + b} Fe ₂ O ₄ [formula (Ic)], etc. or Li _c Mg _d CoCo ₂ O ₄ [formula (IIIa)] Etc. are contained in the compound represented by formula (III). In this case, the positive electrode active material becomes a compound shown in the right column of Table 3 when fully charged. In the table, a and b, c and d are the same as above.

In formula (I), M ¹ is a manganese atom, a cobalt atom or an iron atom. Manganese atoms, cobalt atoms and iron atoms are transition metal ions of the same cycle, and during deintercalation of cations, transition from divalent to trivalent or trivalent to divalent, trivalent to tetravalent or tetravalent to trivalent The secondary battery according to the present embodiment exhibits the same electrochemical behavior because it is possible to cause a transition to a valence. Among these, manganese atoms and cobalt atoms are preferred from the viewpoint of securing a higher capacity. In addition, a manganese atom is more preferable because the transition from trivalent to tetravalent or tetravalent to trivalent is easy, inexpensive and easily available. Moreover, a is a number of 0-2. b is a number from 0 to 1; However, a and b are numbers which satisfy Formula (II).

The transition metal complex oxide represented by the formula (I) is, for example,
(A) adding a solution containing an ionic species to a buffer to obtain a coprecipitate;
(B) The coprecipitate obtained in step (A) is subjected to a heat treatment to give a compound of formula (V):
MgM ¹ ₂ O ₄ (V)
(Wherein, M ¹ is the same as above)
And a process including the step of inserting at least a magnesium cation in the structure of the compound represented by the formula (V) obtained in the step (B), and the like.

  In step (A), a coprecipitate is obtained by adding a solution containing ionic species to a buffer and, if necessary, stirring the obtained mixture. In the step (A), it is preferable to add a solution containing an ionic species to the buffer solution because coprecipitation is easy to form.

The “solution containing ion species” may be a solution containing magnesium cation and manganese cation, cobalt cation or iron cation as a cation. Examples of the “solution containing an ion species” include a solution in which a compound giving an ion species is dissolved in a solvent such as water or ethylene glycol. The above-mentioned "compound giving ion species" includes a compound giving a magnesium cation, a compound giving a manganese cation, a compound giving a cobalt cation and a compound giving an iron cation. As a compound which gives a magnesium cation, although magnesium nitrate, magnesium sulfate, magnesium chloride etc. are mentioned, for example, this invention is not limited only to this illustration. As a compound which gives a manganese cation, although manganese nitrate, manganese sulfate, manganese chloride etc. are mentioned, for example, this invention is not limited only to this illustration. As a compound which gives a cobalt cation, although cobalt nitrate, cobalt sulfate, cobalt chloride etc. are mentioned, for example, the present invention is not limited only to this illustration. Compounds giving cobalt cation; compounds giving iron cation such as iron nitrate, iron sulfate, iron chloride and the like can be mentioned, but the present invention is not limited to such examples. Specifically, the “solution containing an ionic species” is, for example, an aqueous solution of magnesium nitrate [Mg (NO ₃ )] and the formula (VIa):
M ¹ (NO ₃ ) (VIa)
(Wherein, M ¹ is the same as above)
A mixture of a transition metal salt with an aqueous solution represented by the formula: Mg (SO ₄ ) and the formula (VIb):
M ¹ (SO ₄ ) (VIb)
(Wherein, M ¹ is the same as above)
A mixed aqueous solution containing the transition metal salt represented by the formula: MgCl ₂ and the formula (VIc):
M ¹ Cl ₂ (VIc)
(Wherein, M ¹ is the same as above)
Although the mixed aqueous solution etc. with which the transition metal salt represented by these was mix | blended etc. are mentioned, this invention is not limited only to this illustration.

  The content of the “compound giving ion species” in the “solution containing ion species” varies depending on the type of the compound and the like, and is preferably appropriately determined according to the type of the compound and the like. In addition, from the viewpoint of obtaining the compound represented by the formula (V) in high yield, the molar amount of manganese cation, cobalt cation or iron cation (M cation) with respect to magnesium cation (Mg cation) in the “solution containing ionic species”. The ratio (Mg cation / M cation) is preferably 1/1 to 1/2, more preferably 1 / 1.5 to 1/2.

  As the buffer, properties suitable for forming a coprecipitate when the “solution containing the ionic species” is added to the buffer, for example, the “solution containing the ionic species” in the buffer What is necessary is just to have the property to keep the pH of the mixed solution obtained when added in the alkaline region (preferably pH 10 to 13). Examples of the buffer include sodium carbonate buffer, acetate buffer, phosphate buffer, citrate buffer, borate buffer, tartaric acid buffer and the like, but the present invention is limited to only such examples. It is not something to be done. The pH of the buffer solution is preferably 10 or more, more preferably 11 or more from the viewpoint of precipitation, and preferably 13 or less, more preferably 12 or less from the viewpoint of securing a sufficient yield.

  In the step (A), the temperature of the buffer may be a temperature suitable for the formation of coprecipitate, and usually, the impurities (eg, sodium carbonate etc.) contained in the coprecipitate are dissolved It is preferably 25 ° C. or more, more preferably 70 ° C. or more from the viewpoint of removal, and preferably 99 ° C. or less, more preferably 90 ° C. or less from the viewpoint of suppressing boiling of the buffer solution.

  In the step (A), the amount of the solution containing the ion species per 100 parts by mass of the buffer solution varies depending on the type of the buffer solution, the type of the solution containing the ion species, etc. It is preferable to determine appropriately according to the type of solution and the like. The amount of the solution containing the ion species per 100 parts by mass of the buffer solution is usually preferably 1 to 5 parts by mass, from the viewpoint of securing the amount of anion required to keep the pH of the solution constant during coprecipitation. Preferably, it is 3 to 4 parts by mass.

  Next, in step (B), the coprecipitate obtained in step (A) is dried if necessary, and the coprecipitate is heat-treated to obtain a compound represented by formula (V) . The heat treatment for the coprecipitate is performed, for example, by raising the temperature of the coprecipitate to 350 to 650 ° C. at 1 to 10 ° C./min, maintaining the temperature at 350 to 650 ° C. for 2 to 24 hours, and cooling. be able to.

  Thereafter, in step (C), at least a magnesium cation is inserted into the structure of the compound represented by formula (V) obtained in step (B). The magnesium cation is, for example, an electrode having the compound represented by the formula (V) supported on a current collector as a positive electrode, an electrode made of metallic magnesium, metallic lithium or a magnesium lithium alloy as a negative electrode, and interposed between the positive electrode and the negative electrode. Can be inserted into the structure of the compound represented by the formula (V) by discharge using an electrolytic solution containing a solution containing magnesium cation. The discharge can be performed by, for example, a constant current test, a constant potential scan, or the like.

  In formula (III), c is a number of 0-2. d is a number from 0 to 1; However, c and d are numbers which satisfy Formula (IV).

  The transition metal complex compound represented by the formula (III) can be produced, for example, by a method including the step of calcining under the conditions in which the concentration ratio of cations and the amount of oxygen are defined.

  The electrolytic solution 13 is an electrolytic solution containing a solution containing at least one selected from the group consisting of a magnesium cation and a lithium cation as a cation. The electrolytic solution 13 may be an electrolytic solution which is liquid at the temperature of the above-mentioned medium temperature range. Since the electrolytic solution 13 varies depending on the type of the negative electrode 11, the type of the positive electrode 12, and the like, it is preferable to appropriately select the electrolytic solution 13 according to the type of the negative electrode 11, the type of the positive electrode 12, and the like. As the electrolytic solution 13, for example, an ionic liquid comprising at least one cation selected from the group consisting of magnesium cation and lithium cation and an anion; at least one kind selected from the group consisting of magnesium cation and lithium cation Although the solution etc. which contain a cation and glycol ether compounds, such as a glyme compound, etc. are mentioned, this invention is not limited only to this illustration.

  The cation is at least one cation selected from the group consisting of a magnesium cation and a lithium cation.

  Examples of the anion include those represented by the formula (VII):

(Wherein, R ¹ and R ² each independently represent a halogen atom or an alkyl group having 1 to 8 carbon atoms having a halogen atom)
A sulfonylamide anion represented by the formula (VIII):

(Wherein, R ³ represents a halogen atom or an alkyl group having 1 to 8 carbon atoms having the halogen atom)
A sulfonate anion represented by the formula (IX):
(AlX ¹ ₃ ) _q X ¹ (IX)
(Wherein, X ² represents a halogen atom and q represents a number of 1 to 2)
And the like. However, the present invention is not limited to such examples.

In Formula (VII), R ¹ and R ² each independently represent a halogen atom or an alkyl group having 1 to 8 carbon atoms having the halogen atom. As a halogen atom, although a fluorine atom, a chlorine atom, a bromine atom, an iodine atom etc. are mentioned, for example, this invention is not limited only to this illustration. Among the halogen atoms, a fluorine atom is preferable from the viewpoint of securing a higher mass energy density. The carbon number in the alkyl group having 1 to 8 carbon atoms having a halogen atom ensures hydrophobicity and sufficient thermal stability suitable for suppressing the penetration of the solvent into the void of the atomic arrangement structure of the cluster compound From the viewpoint, it is 1 or more, and from the viewpoint of securing the viscosity of the electrolytic solution suitable for obtaining high electromotive force, it is 8 or less, preferably 2 or less. As a C1-C8 alkyl group which has a halogen atom, a perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluoroheptyl group, perfluorohexyl group is mentioned, for example Group, a perfluoroalkyl group having 1 to 8 carbon atoms such as perfluorooctyl group; perchloromethyl group, perchloroethyl group, perchloropropyl group, perchlorobutyl group, perchloropentyl group, perchloroheptyl group, perchloroheptyl group Perchloroalkyl group having 1 to 8 carbon atoms, such as chlorohexyl group and perchlorooctyl group; perbromomethyl group, perbromoethyl group, perbromopropyl group, perbromobutyl group, perbromopentyl group, perbromoheptyl group , Perbromohexyl group, perbromooctyl group Perfluoroalkyl groups having 1 to 8 carbon atoms, such as periomethyl group, periodoethyl group, periodopyl group, periodobutyl group, periodobutyl group, perioptopentyl group, periodoheptyl group, periodihexyl group, periodine Although a C1-C8 periodalkyl group etc., such as an octyl group, etc. are mentioned, this invention is not limited only to this illustration. Among the C1-C8 alkyl groups having these halogen atoms, a C1-C8 perfluoroalkyl group is preferable from the viewpoint of securing the viscosity of the electrolytic solution suitable for obtaining a high electromotive force, A C1-C4 perfluoroalkyl group is more preferable, and a perfluoromethyl group is more preferable. As the sulfonylamide anion represented by the formula (VII), for example, bis (halogenosulfonyl) amide anions such as bis (fluorosulfonyl) amide anions; bis (halogenoalkylsulfonyl) amides such as bis (trifluoromethylsulfonyl) amide anions Although an anion etc. are mentioned, this invention is not limited only to this illustration.

In formula (VIII), R ³ is an alkyl group having 1 to 8 carbon atoms having a halogen atom. The carbon number of the alkyl group in the formula (VIII) is 1 to 8, preferably 1 to 6, and more preferably 1 to 4 to ensure the viscosity of the electrolyte suitable for obtaining a high electromotive force. The C1-C8 alkyl group which has a halogen atom in Formula (VIII) is the same as the C1-C8 alkyl group which has a halogen atom in Formula (VII). Examples of the sulfonate anion represented by the formula (VIII) include, for example, halogenoalkylsulfonate anions such as trifluoromethylsulfonate anion and pentafluoroethylsulfonate anion, and the like, but the present invention is limited to only such examples. It is not something to be done.

In formula (IX), X ¹ represents a halogen atom. As said halogen atom, although a fluorine atom, a chlorine atom, a bromine atom, an iodine atom etc. are mentioned, for example, this invention is not limited only to this illustration. Among the halogen atoms, fluorine atoms and chlorine atoms are preferable, and chlorine atoms are more preferable, from the viewpoint of achieving weight reduction and securing corrosion resistance. In formula (IX), q is a number of 1 to 2. The halogenoalkyl aluminate anion represented by the formula (IX), for example, tetrachloro aluminate anions (AlCl ₄ ^-), hepta-chloro-di aluminate anions (Al ₂ Cl ₇ ^-) but the like, the present invention is, It is not limited to only this example.

Examples of the non-coordinating halide anion include, for example, hexafluorophosphate anion (PF ₆ ⁻ ), tetrafluoroborate anion (BF ₄ ⁻ ) and the like, but the present invention is limited to only such an example. is not.

As the metal halide complex anion, for example, hexafluoroarsenate anion (AsF ₆ ⁻ ), hexafluoroniobate anion (NbF ₆ ⁻ ), hexafluorotantalate anion (TaF ₆ ⁻ ), heptafluorotungstate anion (WF) ₇ ⁻ ), hexafluorouranate anion (UF ₆ ⁻ ), tetrafluorooxovanadium anion (VOF ₄ ⁻ ), pentafluorooxomolybdenum anion (MoOF ₅ ⁻ ), and the like, but the present invention is not limited thereto. It is not limited.

As specific examples of the ionic liquid containing the magnesium cation, magnesium bis (trifluoromethylsulfonyl) amide [Mg (TFSA) ₂ ]; magnesium bis (trifluoromethylsulfonyl) amide [Mg (TFSA) ₂ ] and cesium bis ( Mixed solution with trifluoromethylsulfonyl) amide [CsTFSA]; mixed solution of magnesium bis (trifluoromethylsulfonyl) amide [Mg (TFSA) ₂ ] and DEMETFSA; magnesium bis (trifluoromethylsulfonyl) amide [Mg (TFSA) ) _2] and mixtures of PP13TFSA; magnesium bis (trifluoromethylsulfonyl) amide [Mg (TFSA) _2] and is a mixture and the like with P13TFSA, the present invention is limited only to those exemplified Not to.

As a specific example of the ionic liquid containing the magnesium cation and the lithium cation, lithium bis (trifluoromethylsulfonyl) amide (LiTFSA), lithium bis (trifluoromethylsulfonyl) amide (LiTFSA) and cesium bis (trifluoromethylsulfonyl) ) A mixture with an amide [CsTFSA]; a mixture of magnesium bis (trifluoromethylsulfonyl) amide [Mg (TFSA) ₂ ] and lithium bis (trifluoromethylsulfonyl) amide [LiTFSA] and DEMETFSA; magnesium bis (trifluoro) methylsulfonyl) amide [Mg (TFSA) _2] and lithium bis (trifluoromethylsulfonyl) mixture of amide [LiTFSA] and PP13TFSA; magnesium bis (G Fluoro methylsulfonyl) amide [Mg (TFSA) _2] and lithium bis (trifluoromethylsulfonyl) but a mixed solution of the amide [LiTFSA] and P13TFSA and the like, and the present invention is to be limited only to those exemplified Absent.

  The glyme compound is a symmetrical glycol ether in which the hydroxyl groups at both ends of the alkyl glycol are substituted with the same substituent. Here, examples of the substituent include alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, propyl and butyl, but the present invention is not limited to such examples. . Examples of the glycol ether compound include monoglyme (ethylene glycol dimethyl ether), ethyl monoglyme (ethylene glycol diethyl ether), butyl monoglyme (ethylene glycol dibutyl ether), methyl diglyme (diethylene glycol dimethyl ether), ethyl diglyme [diethylene glycol diethyl Ether], butyl diglyme [diethylene glycol dibutyl ether], methyl triglyme [triethylene glycol dimethyl ether], ethyl triglyme [tri ethylene glycol diethyl ether], butyl triglyme [triethylene glycol diethyl ether], methyl tetraglyme [tetra ethylene oxide Glycol dimethyl ether], ethyl tetraglyme Ethylene glycol diethyl ether], but glyme compound, such as butyl tetraglyme [tetraethylene glycol dibutyl ether], and the like, the present invention is not limited only to those exemplified.

  Examples of the separator 14 include porous films, porous glass, and porous bodies such as glass mesh, but the present invention is not limited to such examples. Although the separator 14 is provided between the negative electrode 11 and the positive electrode 12 in the secondary battery 1 according to the present embodiment, the separator 14 may not be provided if the negative electrode 11 and the positive electrode 12 do not contact each other directly.

  The heat retaining portion 3 is provided to cover the side of the battery body 2. A heater 3a for heating the battery body 2 and a heat insulating member 3b for maintaining the temperature of the battery body 2 at the operating temperature are provided. The heater 3a is provided inside the heat insulating member 3b. Thereby, the loss of the heat energy of the heater 3a can be suppressed, and the temperature of the battery body 2 can be maintained at a predetermined operating temperature with a low energy consumption.

  Examples of the shape of the secondary battery 1 include, for example, a cylindrical shape, a rectangular solid shape, a cylindrical shape, and a disk shape, but the present invention is not limited to such examples.

  The secondary battery according to the present embodiment can be favorably used at the operating temperature of the above-mentioned intermediate temperature range. The operating temperature is usually preferably 50 ° C. or more, more preferably 80 ° C. or more, and preferably 200 ° C. or less.

Below, the mechanism of insertion and detachment | desorption of the cation in the charging / discharging process of the secondary battery of this embodiment is demonstrated. The change of the crystal structure of the transition metal complex oxide contained in the positive electrode active material in the charging / discharging process of the secondary battery which concerns on one Embodiment of this invention is shown in FIG. In FIG. 2, in a magnesium secondary battery having a negative electrode containing metallic magnesium, a positive electrode active material containing Mg ₂ Co ₂ O ₄ which is a rock salt type transition metal complex oxide at the end of discharge is used as a positive electrode active material. The case will be described as an example. In FIG. 2, (A) shows the crystal structure of the transition metal complex oxide contained in the positive electrode active material during full charge (before discharge), (B) shows the tetrahedral region A in (A), and (C) shows discharge. A region corresponding to the tetrahedron region A at the end, (D) shows the crystal structure of the transition metal complex oxide at the end of the discharge. Further, in FIG. 2, “FCC O frame” indicates a frame composed of oxygen atoms in a face-centered cubic lattice structure, and “Co / Mg” indicates the positions of cobalt atoms or magnesium atoms. Moreover, the change of the structure | tissue structure of the positive electrode active material before and behind the discharge reaction of the secondary battery which concerns on one Embodiment of this invention is shown in FIG.

In the secondary battery according to the present embodiment, the positive electrode active material at the end of the discharge contains the rock salt type transition metal composite oxide. The rock salt type transition metal complex oxide has a rock salt structure having 16c + 16d octahedral sites, as shown in FIG. 2 (D). In addition, the positive electrode active material of the secondary battery when fully charged is made of MgCo ₂ O ₄ which is a spinel type transition metal composite oxide. MgCo ₂ O ₄ has a spinel structure having 16 d octahedral sites and 8 a tetrahedral sites as shown in FIG. 2 (A). In the discharge process in the middle temperature range (50 to 300 ° C.), as shown in FIG. 2 (B), magnesium atoms are inserted into the 16 c site. Next, the cobalt atom or magnesium atom at the 8a site moves to the 16c site. As a result, the atoms in the crystal structure are homogenized, and as shown in FIG. 2C, Mg ₂ Co ₂ O ₄ which is a rock salt type transition metal complex oxide is produced. On the other hand, in the charge process in the middle temperature range (50 to 300 ° C.), the magnesium atom behaves in reverse to the magnesium atom in the discharge process. Thus, in the discharge process in the medium temperature range (50 to 300 ° C.), the transition metal composite oxide undergoes a structural phase transition from a spinel structure to a rock salt structure, and charging in the medium temperature range (50 to 300 ° C.) The process causes a structural phase transition from rock salt structure to spinel structure. Thus, in the secondary battery according to the present embodiment, the rock salt type transition metal complex oxide causes a structural phase transition from the spinel structure to the rock salt structure with the progress of discharge, and the rock salt structure with the progress of charge. Causes a structural phase transition from spinel to spinel structure. The rock salt structure and the spinel structure have the same position of the lattice points of the unit cell in the crystal structure. Therefore, the transition metal complex oxide has excellent structural stability because it maintains the position of the lattice point of the unit cell in the crystal structure of the transition metal complex oxide during structural phase transition.

  As shown in FIG. 3, the positive electrode active material of the fully charged secondary battery is made of a spinel type transition metal composite oxide (101 in FIG. 3). In addition, the positive electrode active material of the secondary battery after discharge (that is, after insertion of a magnesium atom) is a spinel type transition metal complex oxide (101 in FIG. 3) and a rock salt type transition metal complex oxide ( In FIG. 3, 102) is mixed. In the secondary battery according to the present embodiment, the amount of the rock salt type transition metal complex oxide in the positive electrode active material increases with the progress of the discharge and decreases with the progress of the charge.

  As described above, according to the secondary battery, the positive electrode, and the positive electrode active material according to the present embodiment, a high capacity can be secured. Therefore, the secondary battery according to the present embodiment, the positive electrode and the positive electrode active material are secondary batteries for transportation equipment such as aircraft, hybrid vehicles, and electric vehicles; secondary batteries for mobile equipment; secondary batteries for storage of electric power It is expected to be used for batteries and the like.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In the following, “Mg (TFSA) ₂ ” is magnesium bis (trifluoromethylsulfonyl) amide, “CsTFSA” is cesium bis (trifluoromethylsulfonyl) amide, “LiTFSA” is lithium bis (trifluoromethylsulfonyl) amide "DEMETFSA" denotes N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) amide.

Example 1
(1) Preparation of MgCo ₂ O ₄ 0.35 M sodium carbonate buffer solution (pH 11) 0.2 L maintained at 70 ° C. in 100 mL of a mixed solution of 50 mL of 0.16 M magnesium nitrate aqueous solution and 50 mL of 0.32 M cobalt nitrate aqueous solution The solution was dropped over 0.5 hours. After dropwise addition, the resulting mixture was stirred at 500 rpm for 1 hour to obtain a coprecipitate.

  The resulting coprecipitate was dried and then placed in an electric furnace. The coprecipitate was fired by raising the temperature in the furnace to 350 ° C. at 5.5 ° C./min and holding it at 350 ° C. for 24 hours. Thereafter, the obtained product was cooled by furnace cooling to obtain a magnesium-cobalt composite oxide. The obtained magnesium cobalt composite oxide was analyzed by X-ray diffraction.

The result of examining the X-ray diffraction of the magnesium-cobalt composite oxide in Example 1 is shown in FIG. In the figure, (a) shows an X-ray diffraction pattern of the magnesium-cobalt composite oxide obtained in Example 1 (1), and (b) shows an X-ray diffraction pattern of MgCo ₂ O ₄ .

The results shown in FIG. 4 indicate that the magnesium-cobalt composite oxide obtained in Example 1 (1) is MgCo ₂ O ₄ .

(2) Preparation of electrode material Magnesium cobalt complex oxide obtained in Example 1 (1), carbon black and polyvinylidene fluoride, magnesium cobalt complex oxide / carbon black / polyvinylidene fluoride (mass ratio) 8 It mixed so that it might become / 1/1, and obtained the electrode material A.

(3) Construction of Electrochemical Cell Next, a three-electrode electrochemical cell 50 shown in FIG. 5 was constructed in a glove box maintained in an argon gas atmosphere. The constructed electrochemical cell 50 holds the inside of the working electrode 51, the counter electrode 52 made of a magnesium ribbon, the reference electrode 53, the electrolyte solution 54, the container 55, and the container 55 at a predetermined operating temperature. The heat insulating unit 56 is constituted. The working electrode 51 includes a current collector 51a made of an aluminum foil and an electrode material layer 51b provided on the current collector 51a. In the working electrode 51, the electrode material layer 51b was produced by applying the electrode material A on the surface of the current collector 51a so that the electrode material A was 10 to 20 μg / mm ² . The reference electrode 53 is integrally formed with a reference electrode body 53a made of lithium foil, a reference electrolyte solution 53b, a glass tube 53c separating the reference electrode body 53a from the electrolyte solution 54, and the glass tube 53c. A porous glass portion 53d is provided to secure the electrical connection between the inside and the outside of the glass tube portion 53c. The reference electrode main body 53 a is electrically connected to the working electrode 51 and the counter electrode 52, but is configured not to be in direct contact with the electrolyte solution 54. The container 55 includes a container body 55a and a lid 55b. The heat retaining portion 56 includes a heater 56a and an aluminum block 56b. The working electrode 51, the counter electrode 52 and the reference electrode 53 of the electrochemical cell 50 are connected to the potentiostat 61 via the electrode leads 61a, 61b and 61c, respectively. The reference electrolyte 53b is DEMETFSA containing 0.5 M LiTFSA. The electrolytic solution 54 is a mixed solution of Mg (TFSA) ₂ and CsTFSA [Mg (TFSA) ₂ / CsTFSA (atomic ratio): 1/9].

(4) Verification of Insertion and Desorption Process of Magnesium Cation The electrochemical cell 50 obtained in Example 1 (3) and the electrochemical measuring apparatus (Biologic (BioLogic), trade name: SP-300) Using the above, while maintaining the temperature (the temperature of the electrolytic solution) in the container 55 of the electrochemical cell 50 at 150 ° C., discharge (insertion of magnesium cation) and charge (desorption of magnesium cation) are repeated in this order, cyclic The voltammetry was performed. The scan rate in cyclic voltammetry is 1 mV / s.

  In Example 1, using a electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide, a cyclic voltammogram when magnesium cation is inserted and removed is shown in FIG. 6 (A). Show.

  From the results shown in FIG. 6 (A), in the magnesium-cobalt composite oxide contained in the electrode material A of the working electrode 51, insertion of magnesium cation [arrow (a) in FIG. 6 (A)] and detachment [ In FIG. 6 (A), it can be seen that the arrow (b)!

(5) Construction of Electrochemical Cell In Example 1 (3), instead of using the magnesium-made ribbon counter electrode, the lithium-made ribbon-made counter electrode 52 was used, and Mg (TFSA) ₂ was used as the electrolyte 54. Instead of using a mixed solution of Mg and CsTFSA (Mg (TFSA) ₂ / CsTFSA (atomic ratio): 1/9), a mixed solution of LiTFSA and CsTFSA (LiTFSA / CsTFSA (atomic ratio): 1/9) is used The same operation as in Example 1 (3) was performed except that the electrochemical cell 50 was obtained.

(6) Verification of Insertion and Desorption Process of Lithium Cation In Example 1 (4), the electrochemical cell obtained in Example 1 (5) was used instead of using the electrochemical cell 50 obtained in Example 1 (3). The same operation as in Example 1 (4) was performed except that an electrochemical cell was used, and cyclic voltammetry was performed.

  In Example 1, a cyclic voltammogram when lithium cation is inserted and removed using an electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide is shown in FIG. 6 (B). Show.

  From the results shown in FIG. 6 (B), in the magnesium-cobalt composite oxide contained in the electrode material A of the working electrode 51, insertion of lithium cation [arrow (a) in FIG. 6 (B)] and detachment [ In FIG. 6 (B), it can be seen that the arrow (b)!

(Example 2)
(1) Verification of Insertion and Desorption Process of Magnesium Cation The electrochemical cell 50 obtained in Example 1 (3) and the electrochemical measurement apparatus (Biologic (BioLogic), trade name: SP-300) While maintaining the temperature (the temperature of the electrolytic solution) in the container 55 of the electrochemical cell 50 at 150.degree. Maintain for 3 hours with Li ⁺ / Li ⁽ 1.0 V vs. Mg ²⁺ / Mg), rest for 5 hours, 4.0 V vs. Perform cyclic voltammetry (scanning rate: 1mV / s) and chronoamperometry under conditions of maintenance for 10 hours and rest for 24 hours with Li ⁺ / Li ⁽ 3.5 V vs. Mg ²⁺ / Mg) The

  FIG. 7 (A) shows that in Example 2, using an electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide, the process of inserting and removing a magnesium cation while maintaining a predetermined potential. The chronoamperometry cyclic voltammogram (upper stage) and its electric charge change (lower stage) in the case of performing are shown. In FIG. 7 (A), (a) shows a discharge process, (b) shows a 5-hour rest, (c) shows a charge process, and (d) shows a 24-hour rest.

  From the results shown in FIG. 7A, in the magnesium-cobalt composite oxide contained in the electrode material A of the working electrode 51, insertion and desorption of magnesium cations occur, and a capacity of about 200 mAh / g can be obtained I understand that.

(2) Verification of Insertion and Desorption Process of Lithium Cation The electrochemical cell 50 obtained in Example 1 (5) and the electrochemical measuring apparatus (Biologic (BioLogic), trade name: SP-300) While maintaining the temperature (the temperature of the electrolytic solution) in the container 55 of the electrochemical cell 50 at 150.degree. C., 2.0 V vs. 2 hours maintenance with Li ⁺ / Li ⁽ 1.5 V vs. Mg ²⁺ / Mg), 2 hours rest, 4.0 V vs. Perform cyclic voltammetry (scanning rate: 1mV / s) and chronoamperometry under conditions of maintenance for 2 hours and rest for 5 hours with Li ⁺ / Li ⁽ 3.5 V vs. Mg ²⁺ / Mg) The

  FIG. 7 (B) shows the process of inserting and removing lithium cations in Example 2 using an electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide while maintaining a predetermined potential. The chronoamperometry cyclic voltammogram (upper stage) and its electric charge change (lower stage) in the case of performing are shown. In FIG. 7 (B), (a) shows a discharge process, (b) shows a 2 hour rest, (c) shows a charge process, and (d) shows a 5 hour rest.

  From the results shown in FIG. 7B, in the magnesium-cobalt composite oxide contained in the electrode material A of the working electrode 51, insertion and detachment of lithium cations occur, and a capacity of about 200 mAh / g can be obtained I understand that. In addition, when FIG. 7 (A) and FIG. 7 (B) are contrasted, it turns out that charge behavior differs. The difference in charge behavior is considered to be due to the difference between the monovalent lithium cation and the divalent magnesium cation. In addition, from these results, when lithium cation is used as a charge carrier, two lithium cations are inserted in the spinel structure to reduce two cobalt cations in the magnesium-cobalt composite oxide, and 8b of the spinel structure It is believed that sites etc. may be used to accommodate extra lithium cations.

(3) Charge / Discharge Test A charge / discharge test was carried out using the electrochemical cell 50 obtained in Example 1 (3) and an electrochemical measurement apparatus (Biologic (BioLogic), trade name: SP-300). I did. In the charge / discharge test, a mixed solution of Mg (TFSA) ₂ and CsTFSA [Mg (TFSA) ₂ / CsTFSA (atomic ratio): 1/9] is used as the electrolyte 54 in the container 55 of the electrochemical cell 50. The temperature (the temperature of the electrolyte) was maintained at 150 ° C., and discharge (insertion of magnesium cation) and charge (desorption of magnesium cation) were repeated in this order at a rate of 1/10 C.

  The results of examining the charge / discharge characteristics of an electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide in Example 2 are shown in FIG. In the figure, (a) is the charge curve for the first charge, (b) is the charge curve for the second charge, and (c) is the charge curve for the third charge. (D) is the charge curve for the fourth charge, (e) is the discharge curve for the first discharge, (f) is the discharge curve for the second discharge, (( g) shows a discharge curve when the third discharge is performed, and (h) shows a discharge curve when the fourth discharge is performed.

  From the results shown in FIG. 8, the working potential is 1 to 2.5 V vs. It can be seen that Mg 2+ / Mg, and the extractable capacity can exceed 170 mAh / g. Further, it is understood from the results shown in FIG. 8 that the charge and discharge reaction can be reversibly performed by using the secondary battery having the positive electrode containing the positive electrode active material containing the magnesium-cobalt composite oxide.

(4) Structural analysis of magnesium-cobalt composite oxide after discharge charge-discharge reaction is carried out using the electrochemical cell obtained in Example 1 (3), and magnesium cobalt at the end of discharge of 120 mAh / g and at full charge The complex oxide was analyzed by X-ray diffraction.

The results of examining the X-ray diffraction of the magnesium-cobalt composite oxide at the end of the discharge and at the time of the full charge in Example 2 are shown in FIG. In the figure, (a) is an X-ray diffraction pattern of the magnesium-cobalt composite oxide obtained in Example 1 (1), (b) is an X-ray diffraction pattern of the magnesium-cobalt composite oxide at the end of discharge of 120 mAh / g. , (C) is the X-ray diffraction pattern of magnesium cobalt complex oxide at full charge, (d) is the X-ray diffraction pattern of CoO, (e) is the X-ray diffraction pattern of MgO, (f) is MgCo ₂ O ₄ X-ray diffraction pattern of

  The results shown in FIG. 9 suggest that the magnesium-cobalt composite oxide exhibits two phases, a spinel phase and a rock salt phase, after magnesium cation insertion at a discharge of 120 mAh / g. Further, when Rietveld analysis was performed, the degree of disorder of the spinel structure of the magnesium-cobalt composite oxide obtained in Example 1 (1) is about 0.43, while at the end of the discharge of 120 mAh / g The degree of disorder of the compound having a spinel structure among the magnesium-cobalt composite oxides of the above was about 0.37. The position occupancy rates of magnesium cation and cobalt cation in the magnesium-cobalt composite oxide having a rock salt structure are 0.49 and 0.51, respectively. From these results, in the magnesium-cobalt composite oxide, the magnesium cation is inserted at the 16c position in the spinel structure during the discharge process, and then the original cation present at the 8a position of the spinel structure is extruded at the 16c position, A structural phase transition from spinel structure to rock salt structure is considered to occur. On the other hand, it is considered that structural phase transition from rock salt structure to spinel structure occurs in the charging process.

  Moreover, charge / discharge reaction was carried out using the electrochemical cell obtained in Example 1 (3), and the magnesium cobalt composite oxide at the end of discharge of 170 mAh / g and at the time of full charge was analyzed by X-ray diffraction method. Furthermore, charge / discharge reaction was carried out using the electrochemical cell obtained in Example 1 (5), and the magnesium cobalt composite oxide at the end of discharge of 210 mAh / g and at the time of full charge was analyzed by X-ray diffraction.

In Example 2, the result of examining the X-ray diffraction of the magnesium cobalt composite oxide at the end of discharge of a large capacity and at the time of full charge is shown in FIG. In the figure, (a) is an X-ray diffraction pattern of the magnesium-cobalt composite oxide obtained in Example 1 (1), (b) is a mixed solution of Mg (TFSA) ₂ and CsTFSA as the electrolyte solution 54. In this case, the X-ray diffraction pattern of the electrode material of the working electrode 51 at the end of discharge of 170 mAh / g, (c) is 210 mAh / g when using a mixed solution of LiTFSA and CsTFSA as the electrolyte 54 The X-ray diffraction pattern of the electrode material of the working electrode 51 at the end of the discharge, (d) shows the working electrode 51 at full charge when the mixed solution of Mg (TFSA) ₂ and CsTFSA is used as the electrolyte 54 The X-ray diffraction pattern of the electrode material, (e) shows the X-ray diffraction pattern of the electrode material of the working electrode 51 when fully charged, in the case of using a mixture of LiTFSA and CsTFSA ((e) f) shows the X-ray diffraction pattern of MgCo ₂ O ₄ , (g) shows the X-ray diffraction pattern of CoO, (h) shows the X-ray diffraction pattern of MgO, and (i) shows the X-ray diffraction pattern of aluminum.

The results shown in FIG. 10 suggest that only a rock salt phase can be seen after a high capacity discharge of 170-210 mAh / g. From these results, in the case of a secondary battery having a negative electrode containing metallic magnesium, the electrode material of the working electrode 51 contains Mg ₂ Co ₂ O ₄ having a rock salt structure at the end of discharge, and a rock salt structure It is suggested that, when fully charged, Mg ₂ Co ₂ O ₄ having the following formula becomes MgCo ₂ O ₄ having a spinel structure. In addition, in the case of a secondary battery provided with a negative electrode containing metallic lithium, the electrode material of the working electrode 51 contains Li ₂ MgCo ₂ O ₄ having a rock salt structure at the end of discharge, and Li having a rock salt structure ₂ MgCo ₂ O ₄ is in the fully-charged, it is suggested that the MgCo ₂ O ₄ having a spinel structure.

Furthermore, from these results, MgCo ₂ O ₄ can insert both magnesium cation and lithium cation in the discharge process, so Li _a Mg _{1 + b} Co ₂ generated from MgCO ₂ O ₄ by the progress of discharge It is understood that O ₄ can be used as a positive electrode active material also in a secondary battery provided with a negative electrode containing a magnesium lithium alloy.

Therefore, from these results, Mg ₂ Co ₂ O ₄ having a rock salt structure, Li ₂ MgCo, as a positive electrode active material of a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, at the end of discharge It is suggested that high capacity can be secured by using a positive electrode active material containing ₂ O ₄ or Li _a Mg _{1 + b} Co ₂ O ₄ .

(Example 3)
(1) Preparation of MgMn ₂ O ₄ Mg ₂ Mn ₂ O ₄ is obtained by substituting cobalt atoms with manganese atoms in Mg ₂ Co ₂ O ₄ and contains metallic magnesium, metallic lithium or a magnesium-lithium alloy The secondary battery provided with the negative electrode is considered to exhibit the same behavior as Mg ₂ Co ₂ O ₄ . Therefore, first, to prepare a MgMn ₂ O ₄ which is a precursor of Mg ₂ Mn ₂ O _4.

  In Example 1 (1), the same operation as Example 1 (1) is carried out except that an aqueous solution of manganese nitrate is used instead of the aqueous solution of cobalt nitrate, and the firing temperature of the coprecipitate is 650 ° C. , A magnesium-manganese composite oxide was obtained. The obtained magnesium-manganese composite oxide was analyzed by X-ray diffraction.

The result of examining the X-ray diffraction of the obtained magnesium-manganese composite oxide in Example 3 is shown in FIG. In the figure, (a) shows an X-ray diffraction pattern of the magnesium-manganese composite oxide obtained in Example 3 (1), and (b) shows an X-ray diffraction pattern according to ICSD data of MgMn ₂ O ₄ .

From the results shown in FIG. 11, the magnesium-manganese composite oxide obtained in Example 3 (1) exhibits a peak similar to the X-ray diffraction pattern by the ICSD data of MgMn ₂ O ₄ shown in (b) From this, it can be seen that it is MgMn ₂ O ₄ .

(2) Preparation of electrode material The magnesium manganese composite oxide obtained in Example 3 (1), carbon black and polyvinylidene fluoride, magnesium manganese composite oxide / carbon black / polyimide (mass ratio) was 8/1 The mixture was mixed to obtain an electrode material B.

(3) Construction of Electrochemical Cell In the same manner as in Example 1 (3) except that electrode material B was used instead of electrode material A in Example 1 (3), an electrochemical cell 50 was obtained. Obtained.

(4) Verification of Insertion and Desorption Process of Magnesium Cation The electrochemical cell 50 obtained in Example 3 (2) and the electrochemical measuring apparatus (Biologic (BioLogic), trade name: SP-300) Using the above, discharge (insertion of magnesium cation) and charge (desorption of magnesium cation) are repeated in this order while maintaining the temperature (the temperature of the electrolytic solution) in the container 55 of the electrochemical cell 50 at 150.degree. Cyclic voltammetry (scan rate: 1 mV / s) in the range of 5 to 4.5 V was performed. The electrolytic solution 54 is a mixed solution of Mg (TFSA) ₂ and CsTFSA [Mg (TFSA) ₂ / CsTFSA (atomic ratio): 1/9].

  In Example 3, using an electrochemical cell having a working electrode containing an electrode material containing a magnesium-manganese composite oxide and performing a process of inserting and removing a magnesium cation in the range of 1.5 to 4.5 V The cyclic voltammogram of is shown in FIG.

From the results shown in FIG. 12, in the magnesium-cobalt composite oxide contained in the electrode material B of the working electrode 51, insertion of magnesium cation (arrows (a) and (b) in FIG. 12) and detachment (FIG. 12) Inside, it can be seen that arrows (c) and (d)] are happening. Since Mg ₂ Mn ₂ O ₄ is obtained by substituting cobalt atoms with manganese atoms in Mg ₂ Co ₂ O ₄ , in a secondary battery comprising a negative electrode containing metallic magnesium, metallic lithium or magnesium lithium alloy, It is considered to exhibit the same behavior as Mg ₂ Co ₂ O ₄ . Therefore, based on these results, Mg ₂ Mn ₂ O ₄ and Li ₂ MgMn ₂ O having a rock salt structure at the end of discharge are used as a positive electrode active material of a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or magnesium lithium alloy. by using the positive electrode active material containing ₄ or _{Li a Mg 1 + b Mn 2} O 4, the same mechanism as in the case of using a positive electrode active material containing Mg ₂ Co ₂ O ₄ having a rock salt structure at the end of discharge Suggests that a high capacity can be secured.

  From the results shown in FIG. 12, when the positive electrode active material containing a magnesium-manganese composite oxide is used, insertion of magnesium cation is observed twice between the end of discharge and the time of full charge. It can be seen that two desorptions of magnesium cation are observed from the time of full charge to the time of discharge end. From these results, it is suggested that the magnesium-manganese composite oxide having a rock salt structure can perform insertion and desorption of more cations.

(Example 4)
(1) Preparation of MgFe ₂ O ₄ Mg ₂ Fe ₂ O ₄ is obtained by substituting cobalt atoms with iron atoms in Mg ₂ Co ₂ O ₄ , and contains magnesium metal, lithium metal or magnesium lithium alloy The secondary battery provided with the negative electrode is considered to exhibit the same behavior as Mg ₂ Fe ₂ O ₄ . Therefore, first, to prepare a MgFe ₂ O ₄ which is a precursor of Mg ₂ Fe ₂ O _4.

  In Example 1 (1), the same operation as in Example 1 (1) was performed except that an aqueous iron nitrate solution was used instead of the aqueous cobalt nitrate solution, to obtain a magnesium-iron composite oxide.

The result of examining the X-ray diffraction of the obtained magnesium iron complex oxide in Example 4 is shown in FIG. In the figure, (a) shows an X-ray diffraction pattern of the magnesium-iron composite oxide obtained in Example 4 (1), and (b) shows an X-ray diffraction pattern according to ICSD data of MgFe ₂ O ₄ .

From the results shown in FIG. 13, the magnesium iron complex oxide obtained in Example 4 (1) exhibits the same peak as the X-ray diffraction pattern by the ICSD data of MgFe ₂ O ₄ shown in (b) From this, it can be understood that it is MgFe ₂ O ₄ .

(2) Preparation of Electrode Material Magnesium iron complex oxide obtained in Example 4 (1), carbon black and polyvinylidene fluoride, magnesium manganese complex oxide / carbon black / polyvinylidene fluoride (mass ratio) 8 It mixed so that it might become / 1/1, and obtained the electrode material C.

(3) Construction of Electrochemical Cell In the same manner as in Example 1 (3) except that electrode material C was used instead of electrode material A in Example 1 (3), an electrochemical cell 50 was obtained. Obtained.

(4) Verification of Insertion and Desorption Process of Magnesium Cation The electrochemical cell 50 obtained in Example 4 (2) and the electrochemical measuring apparatus (Biologic (BioLogic), trade name: SP-300) 2), while maintaining the temperature (the temperature of the electrolytic solution) in the container 55 of the electrochemical cell 50 at 150 ° C., repeating discharge (insertion of magnesium cation) and charge (desorption of magnesium cation) in this order, Cyclic voltammetry (scan rate: 0.1 mV / s) in the range of 3.8 V was performed. The electrolytic solution 54 is a mixed solution of Mg (TFSA) ₂ and CsTFSA [Mg (TFSA) ₂ / CsTFSA (atomic ratio): 1/9].

  In Example 4, using an electrochemical cell having a working electrode containing an electrode material containing magnesium iron complex oxide, cyclic when magnesium cation is inserted and removed in the range of 2 to 3.8 V The voltammogram is shown in FIG.

  From the results shown in FIG. 14, in the magnesium-cobalt composite oxide contained in the electrode material B of the working electrode 51, insertion of magnesium cation [arrow (a) in FIG. 14] and desorption [arrow in FIG. b) it can be seen that

(5) Structural analysis of magnesium iron complex oxide after discharge Further, as the electrolyte solution 54, a mixed solution of Mg (TFSA) ₂ and CsTFSA [Mg (TFSA) ₂ / CsTFSA (atomic ratio): 1/9] The magnesium iron complex oxide at the end of discharge of 200 mAh / g and at full charge was analyzed by X-ray diffraction.

As a result, the electrode material of the working electrode 51 contains Mg ₂ Fe ₂ O ₄ in the case of a secondary battery provided with a negative electrode containing Mg metal magnesium having a rock salt structure at the end of discharge of 200 mAh / g. And Mg ₂ Fe ₂ O ₄ having a rock salt structure was shown to be MgFe ₂ O ₄ having a spinel structure when fully charged. Since Mg ₂ Fe ₂ O ₄ is obtained by substituting cobalt atoms with iron atoms in Mg ₂ Co ₂ O ₄ , in a secondary battery provided with a negative electrode containing metal magnesium, metal lithium or magnesium lithium alloy, It is considered to exhibit the same behavior as Mg ₂ Co ₂ O ₄ . Therefore, from these results, Mg ₂ Fe ₂ O ₄ and Li ₂ MgFe ₂ O having a rock salt structure at the end of discharge are used as a positive electrode active material of a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or magnesium lithium alloy by using the positive electrode active material containing ₄ or _{Li a Mg 1 + b Fe 2} O 4, a positive electrode active material containing Mg ₂ Co ₂ O ₄ or Mg ₂ Mn ₂ O ₄ having a rock salt structure at the end of discharge It is suggested that a high capacity can be secured by the same mechanism as that used.

From the above results, as a positive electrode active material of a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, a transition metal complex oxide having a rock salt structure at the end of the discharge:
Li _a Mg _{1 + b} M ¹ ₂ O ₄ (I)
[Wherein, M ¹ represents a manganese atom, a cobalt atom or an iron atom, a represents the number of 0 to 2, b represents the number of 0 to 1, and a and b represent the formula (II):
a + 2b = 2 (II)
(In the formula, a and b are as defined above)
To satisfy
It is suggested that high capacity can be secured by using a positive electrode active material containing a compound represented by

(Example 5)
(1) Preparation of CoCo ₂ O ₄ MgCoCo ₂ O ₄ is one in which one of two magnesium atoms is substituted by a cobalt atom in Mg ₂ Co ₂ O ₄ , and metal magnesium, metal lithium or magnesium lithium alloy in secondary battery comprising a negative electrode containing, believed to show similar behavior as Mg ₂ Co ₂ O _4. Therefore, first, to prepare a CoCo ₂ O ₄ which is a precursor of MgCoCo ₂ O _4.

  Example 1 (except that 100 mL of 0.24 M cobalt nitrate aqueous solution was used instead of 100 mL of a mixed solution of 50 mL of 0.16 M magnesium nitrate aqueous solution and 50 mL of 0.32 M cobalt nitrate aqueous solution in Example 1 (1) The same operation as in 1) was performed to obtain a product A.

In Example 5, the result of examining the X-ray diffraction of the obtained product A is shown in FIG. In the figure, (a) shows the X-ray diffraction pattern of product A obtained in Example 5 (1), and (b) shows the X-ray diffraction pattern by ICSD data of Co ₃ O ₄ (CoCo ₂ O ₄ ).

From the results shown in FIG. 15, the product A obtained in Example 5 (1) exhibits the same peak as the X-ray diffraction pattern according to the ICSD data of CoCo ₂ O ₄ shown in (b). it can be seen that a CoCo ₂ O _4.

(2) Preparation of electrode material CoCo ₂ O ₄ obtained in Example 5 (1), carbon black and polyvinylidene fluoride, CoCo ₂ O ₄ / carbon black / polyvinylidene fluoride (mass ratio) 8/1 It mixed so that it might become / 1 and obtained the electrode material D.

(3) Construction of Electrochemical Cell In the same manner as in Example 1 (3) except that electrode material D was used instead of electrode material A in Example 1 (3), an electrochemical cell 50 was obtained. Obtained.

(4) Verification of Insertion of Magnesium Cation Using the electrochemical cell 50 obtained in Example 5 (2) and the electrochemical measuring apparatus (Biologic (BioLogic), trade name: SP-300), electrochemistry The temperature (the temperature of the electrolyte solution) in the container 55 of the cell 50 was maintained at 150 ° C., and was maintained at 2 V to perform discharge (insertion of magnesium cation). The electrolytic solution 54 is a mixed solution of Mg (TFSA) ₂ and CsTFSA [Mg (TFSA) ₂ / CsTFSA (atomic ratio): 1/9].

In Example 5, using an electrochemical cell having a working electrode containing an electrode material containing CoCo ₂ O ₄ , the relationship between potential and current when discharging was performed while maintaining at 2 V is shown in FIG. Show. Further, in Example 5, using an electrochemical cell having a working electrode containing an electrode material containing CoCo ₂ O ₄ , a Qt curve is shown in FIG. 17 when discharging is performed while maintaining at ₂ V.

From the results shown in FIGS. 16 and 17, it can be seen that magnesium cation is inserted into CoCO ₂ O ₄ and a capacity of 190 mAh / g can be obtained.

  Next, the electrode material of the working electrode at the end of discharge of 190 mAh / g at 2 V was analyzed by X-ray diffraction.

  The result of examining the X-ray diffraction of the electrode material of the working electrode of the electrochemical cell in Example 5 is shown in FIG.

The results shown in FIG. 18 suggest that a rock salt phase can be seen after a discharge of 190 mAh / g. Since MgCoCo ₂ O ₄ produced by the insertion of a magnesium cation in CoCo ₂ O ₄ is a Mg ₂ Co ₂ O ₄ substituted with one cobalt atom of two magnesium atoms, metal magnesium In a secondary battery including a negative electrode containing metal lithium or magnesium lithium alloy, it is considered that the same behavior as Mg ₂ Co ₂ O ₄ is exhibited. Therefore, from these results, MgCoCo ₂ O ₄ , Li ₂ CoCo ₂ O ₄ or MgCoCo ₂ O ₄ having a rock salt structure at the end of discharge is used as a positive electrode active material of a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or magnesium lithium alloy. By using a positive electrode active material containing Li _c Mg _d CoCo ₂ O ₄ , a positive electrode containing Mg ₂ Co ₂ O ₄ , Mg ₂ Mn ₂ O ₄ or Mg ₂ Fe ₂ O ₄ having a rock salt structure at the end of discharge The same mechanism as in the case of using the active material suggests that a high capacity can be secured.

(Example 6)
In Example 1 (2), it can be stably used at an operating temperature in the intermediate temperature range as in the case of a mixed solution of Mg (TFSA) ₂ and CsTFSA, a mixed solution of LiTFSA ₂ and CsTFSA, etc. as the electrolytic solution 54 An electrochemical cell 50 was obtained in the same manner as in Example 1 (2) except that a 0.5 M Mg (TFSA) ₂ triglyme solution was used. The temperature (the temperature of the electrolyte) in the container 55 of the electrochemical cell 50 is set to 100 using the obtained electrochemical cell 50 and the electrochemical measuring apparatus (Biologic (BioLogic), trade name: SP-300). Discharge (insertion of magnesium cation) and charge (desorption of magnesium cation) were repeated in this order, cyclic voltammetry was performed while maintaining the temperature at ° C. The scan rate in cyclic voltammetry is 1 mV / s.

In Example 6, using an electrochemical cell having an electrolytic solution containing a glyme compound as an electrolytic solution and having a working electrode containing an electrode material containing magnesium cobalt composite oxide (Mg ₂ Co ₂ O ₄ ), The cyclic voltammogram when the process of insertion and removal of magnesium cation is performed is shown in FIG. In Example 6, an electrochemical cell having a working electrode containing an electrode material containing a magnesium-cobalt composite oxide (Mg ₂ Co ₂ O ₄ ) and having an electrolytic solution containing a glyme compound as the electrolytic solution The Qt curve when held at 2 V is shown in FIG.

  From the results shown in FIGS. 19 and 20, the magnesium-cobalt composite oxide contained in the electrode material A of the working electrode 51 is magnesium, even when an electrolytic solution containing a magnesium cation and a glyme compound is used as the electrolytic solution. It can be seen that cation insertion and removal occur, and a capacity of 105 mAh / g is obtained. From these results, a secondary battery comprising a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, and a positive electrode comprising a positive electrode active material containing a transition metal composite oxide having a rock salt structure at the end of discharge Instead of using an ionic liquid consisting of at least one cation selected from the group consisting of magnesium cation and lithium cation as an electrolyte, at least one kind selected from the group consisting of magnesium cation and lithium cation It is understood that high capacity can be secured also when using a solution containing a cation and a glycol ether compound such as a glyme compound.

  Therefore, from these results, a secondary comprising a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, and a positive electrode comprising a positive electrode active material containing a transition metal composite oxide having a rock salt structure at the end of discharge In the battery, it is suggested that an electrolyte stable at an intermediate temperature range can be used, which contains at least one selected from the group consisting of a magnesium cation and a lithium cation as the cation.

As described above, the rock salt type transition metal complex oxide, for example, the compound represented by the formula (I), the compound represented by the formula (III), more specifically, for example, Mg ₂ Mn ₂ O ₄ , Mg ₂ Co ₂ O ₄ , Mg ₂ Fe ₂ O ₄ , MgCoCo ₂ O _{4 and the} like have a rock salt structure at the end of the discharge, and become a compound having a spinel structure when fully charged. Accordingly, such a rock salt type transition metal complex oxide undergoes a structural phase transition with the detachment and insertion of a cation, and has a rock salt structure at the end of the discharge and a spinel structure at the time of full charge. In a secondary battery including a negative electrode containing metal lithium or magnesium lithium alloy, a high capacity can be secured by using as a positive electrode active material containing a rock salt type transition metal composite oxide. Therefore, the secondary battery, the positive electrode, and the positive electrode active material according to one embodiment of the present invention are secondary batteries for transportation equipment such as aircraft, hybrid vehicles, and electric vehicles; secondary batteries for mobile equipment; It is expected to be used for secondary batteries and the like.

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Battery main body 3 Heat retention part 3a Heater 3b Heat insulation member 11 Negative electrode 11b Negative electrode material layer 11a Current collector 12 Positive electrode 12a Current collector 12b Positive electrode material layer 13 Electrolyte 14 Separator 50 Electrochemical cell 51 Working electrode 51a Current collection Body 51b Electrode material layer 52 Counter electrode 53 Reference electrode 53a Reference electrode body 53b Reference electrolyte 53c Glass tube 53d Porous glass portion 54 Electrolyte 55 Container 55a Container body 55b Cover 56 Heat retaining portion 56a Heater 56b Aluminum block 61a, 61b , 61c electrode lead 61 potentiostat

Claims (6)

A negative electrode containing magnesium metal, lithium metal or a magnesium lithium alloy, a positive electrode containing a positive electrode active material, and an electrolytic solution interposed between the positive electrode and the negative electrode,
The positive electrode active material contains a transition metal composite oxide having a rock salt structure at the end of discharge and a spinel structure at full charge,
At the end of the discharge, the transition metal complex oxide has the formula (I):
Li _a Mg _{1 + b} M ¹ ₂ O ₄ (I)
[Wherein, M ¹ represents a cobalt atom, a represents a number of 0 to 2, b represents a number of 0 to 1, and a and b represent a formula (II):
a + 2b = 2 (II)
(In the formula, a and b are as defined above)
To satisfy
A transition metal complex oxide represented by or a formula (III):
Li _c Mg _d CoCo ₂ O ₄ (III)
[Wherein, c represents a number of 0 to 2, d represents a number of 0 to 1, and c and d represent a group of formula (IV):
c + 2d = 2 (IV)
(Wherein c and d are the same as above)
To satisfy
It is a transition metal complex oxide represented by and the secondary battery characterized by the above-mentioned. The transition metal complex oxide having the rock salt structure causes a structural phase transition from a spinel structure to a rock salt structure as the discharge progresses, and causes a structural phase transition from a rock salt structure to a spinel structure as the charging progresses. Item 2. The secondary battery according to item 1 . The secondary battery according to claim 1, wherein the electrolytic solution contains a solution containing at least one selected from the group consisting of a magnesium cation and a lithium cation as a cation. It is a positive electrode active material for use in a secondary battery provided with a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, which has a rock salt structure at the end of discharge and a spinel structure at full charge. Contains the
At the end of the discharge, the transition metal complex oxide has the formula (I):
Li _a Mg _{1 + b} M ¹ ₂ O ₄ (I)
[Wherein, M ¹ represents a cobalt atom, a represents a number of 0 to 2, b represents a number of 0 to 1, and a and b represent a formula (II):
a + 2b = 2 (II)
(In the formula, a and b are as defined above)
To satisfy
A transition metal complex oxide represented by or a formula (III):
Li _c Mg _d CoCo ₂ O ₄ (III)
[Wherein, c represents a number of 0 to 2, d represents a number of 0 to 1, and c and d represent a group of formula (IV):
c + 2d = 2 (IV)
(Wherein c and d are the same as above)
To satisfy
It is a transition metal complex oxide represented by and the positive electrode active material characterized by the above-mentioned. The transition metal complex oxide having a rock salt structure causes a structural phase transition from a spinel structure to a rock salt structure as the discharge progresses, and a compound causes a structural phase transition from a rock salt structure to a spinel structure as the charging progresses. The positive electrode active material according to claim 4, which is A positive electrode for use in a secondary battery comprising a negative electrode containing metallic magnesium, metallic lithium or a magnesium lithium alloy, comprising:
The said positive electrode contains the positive electrode active material of Claim 4 or 5 , The positive electrode characterized by the above-mentioned.