JP2012114027A - Negative electrode material for metal secondary battery, negative electrode for metal secondary battery, and metal secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for a metal secondary battery enhancing the charge-discharge efficiency of a metal secondary battery, a negative electrode for a metal secondary battery, and a metal secondary battery offering high charge-discharge efficiency.SOLUTION: A negative electrode material for a metal secondary battery contains MgHand NbOin contact with the MgH, a negative electrode comprises the negative electrode material, and a metal secondary battery comprises the negative electrode.

Description

  The present invention relates to a negative electrode material for a metal secondary battery, more specifically, a negative electrode material including a predetermined metal hydride and a predetermined catalyst, a negative electrode for a metal secondary battery including the negative electrode material, and the negative electrode It is related with the metal secondary battery provided with.

  In recent years, from the viewpoint of protecting the global environment, a high-output and high-capacity power source is required to be applied to an electric vehicle or a hybrid vehicle as a low-pollution vehicle. Further, in fields other than automobiles and the like, power supplies capable of improving the performance of mobile tools are required due to the global spread of mobile tools such as information-related devices and communication devices. One promising high-performance power source is a lithium battery that has a high energy density and can be operated at a high voltage.

One type of lithium battery uses a metal hydride (MH _X ) as a conversion-type negative electrode active material. As a specific example of such a conversion-type negative electrode active material, for example, Patent Document 1 discloses MgH ₂ . The electrochemical behavior when MgH ₂ is used as the active material is as follows.
During charging: MgH ₂ + 2Li ⁺ + 2e ⁻ → Mg + 2LiH (Reaction Formula 1)
During discharge: Mg + 2LiH → MgH ₂ + 2Li ⁺ + 2e ⁻ (Reaction Formula 2)

US Patent Application Publication No. 2008/0286652

Here, MgH ₂ has a problem that the reversibility of the conversion reaction is low. Specifically, the reaction formula 2 is less likely to occur than the reaction formula 1. Therefore, the metal secondary battery using MgH ₂ has a problem that the charge / discharge efficiency is lowered.

In view of the above problems, the present applicant has been researching a metal secondary battery using MgH ₂ , has completed a metal secondary battery capable of solving the above problems, and has filed a patent application (Japanese Patent Application No. 2010-227476). . In the application, as a main metal catalyst (Ni, etc.) can contribute to the improvement reversibility of the conversion reaction of MgH _2.

Here, when a Ni catalyst is used as a catalyst for the conversion reaction of MgH ₂ , there is a possibility that the catalyst size does not function sufficiently as a catalyst when the catalyst size is on the order of μm. There was a fear that it was not possible. In order to solve the problem, for example, it is conceivable to make the Ni catalyst finer to the nm order. However, in the case of the nm order catalyst, there is a possibility that the catalyst is aggregated when the catalyst is added or when the electrode is applied.

  This invention is made | formed in view of the said problem, The negative electrode material for metal secondary batteries which can improve the charge / discharge efficiency of a metal secondary battery, the negative electrode for metal secondary batteries, and charge / discharge efficiency It is an object of the present invention to provide an improved metal secondary battery.

In order to solve the above problems, the present invention has the following configuration. That is,
A first aspect of the present invention include _Nb 2 _{O 5} in contact with the MgH _2, and the MgH _2, a negative electrode material for metal secondary battery.

In the first aspect of the present invention, Nb ₂ O ₅ may be in the form of particles, and the average particle diameter X may be 1 μm ≦ X <1000 μm. In the present invention, even if the average particle diameter of Nb ₂ O ₅ is relatively large, on the order of μm, it is possible to improve the charge / discharge efficiency.

  In the present application, the “average particle diameter” means the measured tangential diameter (Ferret diameter) of particles (n = 100) included in image data obtained by SEM (scanning electron microscope) observation. It is calculated by calculating the average.

  A second aspect of the present invention is a negative electrode for a metal secondary battery comprising the negative electrode material for a metal secondary battery according to the first aspect of the present invention.

  A third aspect of the present invention is a metal secondary battery including a positive electrode, an electrolyte, and a negative electrode according to the second aspect of the present invention.

  According to the present invention, a negative electrode material for a metal secondary battery capable of improving the charge / discharge efficiency of a metal secondary battery, a negative electrode for a metal secondary battery, and a metal secondary battery with improved charge / discharge efficiency Can be provided.

It is a figure showing roughly metal rechargeable battery 10 of the present invention concerning one embodiment. It is a figure which shows the charging / discharging curve of the metal secondary battery which concerns on an Example and a comparative example.

1. Anode material for metal secondary battery according to the negative electrode material the invention for metal secondary battery (hereinafter, simply referred to as "negative electrode material according to the present invention".) Is, MgH _2, and, in contact with the MgH ₂ Nb ₂ O ₅ is contained. MgH ₂ functions as a negative electrode active material, and Nb ₂ O ₅ functions as a catalyst that improves the reversibility of the conversion reaction of MgH ₂ .

1.1. About the mechanism of the conversion reaction Nb ₂ O ₅ causes a conversion reaction at a potential nobler than that of MgH ₂ which is an active material. For example, in the Li insertion process, Nb ₂ O ₅ conversion reaction occurs first. As a result, Nb ₂ O ₅ is pulverized and expresses a function as a catalyst in the subsequent charge / discharge process. That is, Nb ₂ O ₅ is finely pulverized in the initial reaction stage even if the particle diameter before the conversion reaction is as large as μm, and then functions appropriately as a catalyst.

When Nb ₂ O ₅ functions as a catalyst, for example, the reaction formula 2 can be promoted. Therefore, the charge / discharge efficiency of the metal secondary battery can be improved. For example, in order to promote the above reaction formula 2, a hydrogen elimination reaction from LiH (a LiH dissociation reaction) and a hydrogen addition reaction to Mg are important, but Nb ₂ O ₅ functions as a catalyst. Thus, it is considered that one or both of the reactions are promoted. The mechanism by which Nb ₂ O ₅ improves the reversibility of the conversion reaction is estimated as follows. That is, when Li ⁺ is taken into MgH ₂ and the above reaction formula 1 occurs, Mg and LiH are generated. When this state is measured by X-ray diffraction, the Mg peak is observed and the LiH peak is not observed, so that the crystalline Mg particles are formed in a floating island shape in the amorphous LiH. Inferred. On the other hand, it has been confirmed that a trace amount of hydrogen gas is generated in the electrochemical reaction of MgH ₂ and Li ⁺ . From this, it is considered that the generated hydrogen gas is dissociated and adsorbed by Nb ₂ O ₅ , and the dissociated and adsorbed hydrogen reacts with Mg to generate MgH ₂ . That is, in this presumed mechanism, Nb ₂ O ₅ functions as a catalyst to promote the hydrogen addition reaction to Mg. Moreover, this presumed mechanism can be considered to be similar to the reaction when the hydrogen storage alloy stores hydrogen.

In the above description, the generated hydrogen gas is assumed to be dissociated adsorbed by _{Nb 2 O 5, Nb 2 O} 5 , before the hydrogen desorbed from LiH is hydrogen gas, and the adsorption of hydrogen There is also a possibility. In addition, Nb ₂ O ₅ may promote the LiH dissociation reaction itself.

1.2. MgH ₂
In the negative electrode material according to the present invention, MgH ₂ normally functions as an active material, and generates LiH and Mg, for example, by reacting with Li ions. Further, Mg (zero-valent) generated by the reaction with Li ions further causes an alloying reaction with Li ions and occludes Li until it becomes Li ₃ Mg ₇ . Thus, MgH ₂ has a very large Li storage capacity, but its reverse reaction (the above reaction formula 2) hardly occurs, and thus there is a problem that the charge / discharge efficiency is lowered. In the present invention, this problem is solved by making Nb ₂ O ₅ function as a catalyst.

In the negative electrode material according to the present invention, it is preferable that MgH ₂ is refined. By reducing the particle size of MgH _2, it is possible to further improve the reversibility of the conversion reaction. The average particle diameter of MgH ₂ is preferably 2 μm or less, for example, and more preferably in the range of 0.1 μm to 1 μm. When miniaturizing MgH ₂ , for example, a known method such as a ball mill may be used.

In the negative electrode material according to the present invention, the content of MgH ₂ is not particularly limited, but it is preferably 40% by mass or more, preferably 60% by mass or more and 98% by mass with respect to 100% by mass of the entire negative electrode material. % Or less is more preferable.

1.3. Nb ₂ O ₅
In the negative electrode material according to the present invention, Nb ₂ O ₅ functions as a catalyst that improves the reversibility of the conversion reaction. Further, _Nb 2 _{O 5} has only to contact with the MgH _2, for example, may be one other is supported on one of MgH ₂ and _Nb 2 _{O 5.}

In the negative electrode material according to the present invention, Nb ₂ O ₅ may have an average particle size on the order of μm. Specifically, it may be 1 μm or more and less than 1000 μm. As described above, when the anode material according to the present invention is applied to a metal secondary battery, in the early stages of the cell reaction, Nb ₂ O ₅ undergoes a conversion reaction, to be micronized, is Nb ₂ O ₅ used Even relatively large particles can function properly as a catalyst. By making the Nb ₂ O ₅ particles in the order of μm, it is possible to simplify the process without agglomeration during addition or electrode coating, and with a form that is excellent in safety. can do.

Keep negative electrode material according to the present invention, the content of Nb ₂ O _5, if the amount enough to improve the charge-discharge efficiency as compared to metal secondary battery and the case of not contain Nb ₂ O _5, particularly limited Is not to be done. Specifically, the ratio of Nb ₂ O ₅ to MgH ₂ is preferably 0.1 at% or more and 10 at% or less, and more preferably 0.5 at% or more and 6 at% or less. If the amount of Nb ₂ O ₅ is too small, the reversibility of the conversion reaction may not be sufficiently improved. On the other hand, if the amount of Nb ₂ O ₅ is too large, the amount of MgH ₂ will be relatively small. When a secondary battery is used, the capacity may be greatly reduced. The ratio of _Nb 2 _{O 5} with respect to MgH ₂ can be confirmed by SEM-EDX.

1.4. Other Materials The negative electrode material according to the present invention may include a conductive material for improving conductivity in addition to the MgH ₂ and Nb ₂ O ₅ . A conductive path from the viewpoint of easily forming, conductive material is preferably in contact with the MgH _2, or, preferably carried on the MgH _2. As the conductive material, those conventionally used as negative electrode materials can be used without particular limitation. For example, mesocarbon microbeads (MCMB), acetylene black, ketjen black, carbon black, Carbon materials such as coke, carbon fiber, and graphite can be suitably used.

  In the negative electrode material according to the present invention, it is preferable to use a finer conductive material. Thereby, electroconductivity can further be improved. The average particle diameter of the conductive material is, for example, preferably 2 μm or less, and more preferably 0.1 μm or more and 1 μm or less. When the conductive material is miniaturized, for example, a known technique such as a ball mill may be used.

In the negative electrode material according to the present invention, the content of the conductive material is not particularly limited as long as it does not impair battery performance in the case of a metal secondary battery. For example, when the whole negative electrode material according to the present invention is 100% by mass, it is preferably 1% by mass or more and 50% by mass or less, and more preferably 2% by mass or more and 40% by mass or less. If the amount of the conductive material is too small, the conductivity may not be sufficiently improved. If the amount of the conductive material is too large, the amount of MgH ₂ is relatively reduced, resulting in a capacity when a metal secondary battery is obtained. There is a risk of a significant drop.

The negative electrode material according to the present invention can be produced by making the MgH ₂ and Nb ₂ O ₅ contact each other, arbitrarily making the conductive material at a predetermined ratio, and mixing the raw material composition. . In the case where MgH ₂ and Nb ₂ O ₅ are brought into contact with each other, in addition to a form in which these are simply mixed, a form in which one of MgH ₂ and Nb ₂ O ₅ is supported on the other may be employed. The mixing method is not particularly limited, and may be performed using a known mixing means. For example, it is preferable to mix by a mixing method capable of imparting mechanical energy such as mechanical milling. This is because the particle size of each material contained in the raw material composition can be easily reduced, and the reversibility of the conversion reaction can be further improved. In particular, it is considered that the reversibility of the conversion reaction is improved by reducing the particle diameter of MgH ₂ . The reason is considered to be that when the particle size of MgH ₂ is reduced, the specific surface area is increased, and for example, the reaction formula 2 is likely to occur. Moreover, it is thought that, for example, the Li diffusion path is shortened and the reactivity is improved by reducing the particle diameter of MgH ₂ . In addition, since the particle diameter of MgH ₂ is reduced, for example, there is an advantage that an overvoltage in a Li insertion reaction (the above reaction formula 1) is reduced. The mechanical milling is a method of pulverizing a sample while applying mechanical energy. Moreover, the particle | grains of each material contained in a raw material composition contact vigorously by refine | miniaturizing by mechanical milling. Thereby, each material contained in a raw material composition is remarkably refined rather than mere refinement | miniaturization (for example, refinement | miniaturization using a mortar). Moreover, by refining with mechanical milling, the Nb ₂ O ₅ and the conductive material, can be uniformly dispersed on the surface of the MgH ₂ particles. Examples of the mechanical milling in the present invention include a ball mill, a vibration mill, a turbo mill, and a disk mill. Among these, a ball mill is preferable, and a planetary ball mill is particularly preferable.

  Moreover, what is necessary is just to set the various conditions of mechanical milling so that a desired negative electrode material can be obtained. For example, when producing a negative electrode material by a planetary ball mill, each raw material and grinding balls are added to the pot, and processing is performed at a predetermined number of revolutions and time. The number of rotations of the base plate at the time of processing with the planetary ball mill is, for example, preferably in the range of 100 rpm to 1000 rpm, and more preferably in the range of 200 rpm to 600 rpm. Moreover, it is preferable that processing time is in the range of 1 hour-100 hours, for example, especially in the range of 2 hours-10 hours. In the present invention, it is preferable to perform mechanical milling so that each material included in the raw material composition has a predetermined average particle size.

As described above, the negative electrode material according to the present invention contains Nb ₂ O ₅ in addition to MgH ₂ and functions appropriately as a catalyst. Therefore, when the negative electrode is configured using this to form a metal secondary battery, The charge / discharge efficiency of the metal secondary battery can be improved. Here, the above-described reaction formulas 1 and 2 are intended for lithium secondary batteries, but the behavior of MgH _{2 in} the conversion reaction is considered to be the same for metals other than lithium. Therefore, the negative electrode material according to the present invention can also be used for negative electrodes of metal secondary batteries other than lithium secondary batteries. Specific examples of the metal secondary battery include a lithium secondary battery, a sodium secondary battery, a potassium secondary battery, a magnesium secondary battery, and a calcium secondary battery. Among these, a lithium secondary battery, a sodium secondary battery, and a potassium secondary battery are preferable, and a lithium secondary battery is particularly preferable.

2. Negative electrode for metal secondary battery The negative electrode material for metal secondary battery according to the present invention (hereinafter simply referred to as “the present invention”) by combining the negative electrode material and other optional materials according to the present invention described above with known negative electrode current collectors and the like. May be referred to as “a negative electrode according to the present invention”). The negative electrode of the embodiment, except that it contains the MgH ₂ and Nb ₂ O ₅ as a negative electrode material may be in the same form as the negative electrode for a known metal secondary battery. For example, a mode in which a negative electrode layer is formed by pressure molding the negative electrode material and arbitrarily disposed on the surface of the negative electrode current collector, a mode in which the negative electrode material is pressure molded with the negative electrode current collector, or the negative electrode The material can be dispersed in a solvent to prepare a coating liquid for forming a negative electrode, and the coating liquid can be produced by various methods such as a form in which the coating liquid is applied to the surface of the negative electrode current collector and dried. From the viewpoint of strengthening the negative electrode layer, a binder may be included together with the negative electrode material when the negative electrode layer is formed.

2.1. Negative electrode layer In the negative electrode according to the present invention, the negative electrode layer includes at least the negative electrode material according to the present invention, and optionally further includes a binder and a conductive material. In the negative electrode layer, the content of the negative electrode material according to the present invention is not particularly limited. For example, the entire negative electrode layer is 100% by mass, preferably 20% by mass or more, and 40% by mass or more 80 It is more preferable that the amount is not more than mass%. As described above, the negative electrode material itself according to the present invention may contain a conductive material, but the negative electrode layer may further contain a conductive material. The conductive material contained in the negative electrode material and the newly added conductive material may be the same material or different materials. Specific examples of the conductive material are as described above. Moreover, when a binder is included in the negative electrode layer, specific examples of the binder include fluorine-containing resins such as polyvinylidene fluoride (PVDF). Although the thickness of a negative electrode layer is not specifically limited, For example, it is preferable that they are 0.1 micrometer or more and 1000 micrometers or less.

2.2. Negative Electrode Current Collector The negative electrode according to the present invention is optionally provided with a negative electrode current collector. A known negative electrode current collector can be used, and is not particularly limited. For example, stainless steel, copper, nickel, or carbon can be used. Of these, copper is preferred. The shape of the negative electrode current collector is not particularly limited, and examples thereof include a plate shape, a foil shape, and a mesh shape.

  Thus, since the negative electrode according to the present invention includes the negative electrode material according to the present invention, it is possible to improve the charge / discharge efficiency of the metal secondary battery when applied to the metal secondary battery. It is.

3. Metal Secondary Battery The metal secondary battery according to the present invention includes a positive electrode, an electrolyte, and the negative electrode according to the present invention. FIG. 1 schematically shows a metal secondary battery 10 according to an embodiment. As shown in FIG. 1, the metal secondary battery 10 includes a power generation unit that includes a negative electrode 1, a positive electrode 2, and an electrolyte layer 3 provided between the negative electrode 1 and the positive electrode 2. In FIG. 1, other configurations such as wiring are omitted.

3.1. Negative electrode 1
As the negative electrode 1 of the metal secondary battery 10, the negative electrode according to the present invention may be used. Since details are as described above, description thereof is omitted.

3.2. Positive electrode 2
The positive electrode 2 of the metal secondary battery 10 includes a positive electrode layer containing a positive electrode active material and the like, and optionally includes a positive electrode current collector for collecting the positive electrode 2. The positive electrode layer is a layer including at least a positive electrode active material, and may further include at least one of a conductive material and a binder as necessary. The type of the positive electrode active material may be appropriately selected according to the type of the metal secondary battery 10. For example, when the metal secondary battery 10 is a lithium secondary battery, examples of the positive electrode active material include LiCoO ₂ and LiNiO. ₂ , layered positive electrode active materials such as LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiVO ₂ , LiCrO ₂ , LiMn ₂ O ₄ , Li (Ni _0.25 Mn _0.75 ) ₂ O ₄ , LiCoMnO ₄ , spinel-type positive electrode active materials such as Li ₂ NiMn ₃ O ₈ , and olivine-type positive electrode active materials such as LiCoPO ₄ , LiMnPO ₄ , and LiFePO ₄ . Although content of the positive electrode active material in a positive electrode layer is not specifically limited, For example, it is preferable to exist in the range of 40 mass%-99 mass%.

  The positive electrode layer in the present invention may further contain at least one of a conductive material and a binder. As the conductive material and the binder, those exemplified as those used for the negative electrode layer can be appropriately selected and used. The thickness of the positive electrode layer is preferably 0.1 μm or more and 1000 μm or less, for example.

  The positive electrode 2 is optionally provided with a positive electrode current collector. A well-known thing can be used as a positive electrode electrical power collector, It does not specifically limit. For example, stainless steel, aluminum, nickel, iron, titanium, carbon and the like can be mentioned. Of these, aluminum is preferable. The shape of the positive electrode current collector is not particularly limited, and examples thereof include a plate shape, a foil shape, and a mesh shape.

  The positive electrode 2 can be manufactured by the same method as the negative electrode 1. For example, a positive electrode layer is formed by pressure molding the positive electrode active material and the like, and a mode in which the positive electrode current collector and the positive electrode current collector are pressure molded with a positive electrode current collector, Alternatively, the positive electrode active material or the like can be dispersed in a solvent to prepare a positive electrode forming coating liquid, and the coating liquid can be manufactured by various methods such as a form in which the coating liquid is applied to the surface of the positive electrode current collector and dried. .

3.3. Electrolyte layer 3
The electrolyte layer 3 is a layer disposed between the positive electrode layer and the negative electrode layer, and includes at least an electrolyte. Metal ion conduction is performed between the positive electrode active material and the negative electrode active material through the electrolyte contained in the electrolyte layer. The form of the electrolyte layer is not particularly limited, and examples thereof include a liquid electrolyte layer, a gel electrolyte layer, and a solid electrolyte layer.

The liquid electrolyte layer is usually a layer using a non-aqueous electrolyte. The non-aqueous electrolyte usually contains a metal salt and a non-aqueous solvent. The type of metal salt is preferably selected as appropriate according to the type of metal secondary battery. For example, as a metal salt used for a lithium secondary battery, inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ ; and LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ And organic lithium salts such as F ₅ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ . Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), butylene carbonate (BC), γ-butyrolactone, sulfolane, Acetonitrile, 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and mixtures thereof can be exemplified. The concentration of the metal salt in the nonaqueous electrolytic solution is, for example, in the range of 0.5 mol / L to 3 mol / L. In the present invention, a low volatile liquid such as an ionic liquid may be used as the nonaqueous electrolytic solution. A separator may be disposed between the positive electrode layer and the negative electrode layer.

  The thickness of the electrolyte layer varies greatly depending on the type of electrolyte and the configuration of the battery. For example, the thickness of the electrolyte layer is preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 0.1 μm to 300 μm.

  The metal secondary battery 10 can have the same form as the conventional one except that the metal secondary battery 10 includes the negative electrode 1 including the negative electrode material according to the present invention. For example, the negative electrode 1 and the positive electrode 2 are manufactured separately, and the metal secondary battery 10 is manufactured by accommodating the negative electrode layer and the positive electrode layer in the battery case so that the electrolyte layer is interposed between the negative electrode layer and the positive electrode layer. it can. Or the form which laminates | stacks and press-molds material so that the negative electrode 1, the electrolyte layer 3, and the positive electrode 2 may be comprised in this order, and accommodates in a battery case may be sufficient. Or the form formed by winding a laminated body after laminating | stacking a material may be sufficient. The material and shape of the battery case are not particularly limited, and may be appropriately selected depending on the application.

  The metal secondary battery according to the present invention may be a lithium secondary battery, a sodium secondary battery, a potassium secondary battery, a magnesium secondary battery, a calcium secondary battery, or the like. Among these, a lithium secondary battery, a sodium secondary battery, and a potassium secondary battery are preferable, and a lithium secondary battery is particularly preferable. Moreover, the metal secondary battery which concerns on this invention can be used as a vehicle-mounted battery, for example. The shape of the metal secondary battery is not particularly limited, and examples thereof include a coin type, a laminate type, a cylindrical type, and a square type.

  Thus, since the metal secondary battery which concerns on this invention is equipped with the negative electrode containing the negative electrode material which concerns on this invention, charging / discharging efficiency improves from the conventional battery.

  Hereinafter, based on an Example, the metal secondary battery provided with the negative electrode containing the negative electrode material which concerns on this invention is explained in full detail.

<Example>
(Preparation of negative electrode material)
Commercially available MgH ₂ powder (manufactured by Alfa Aesar), Nb ₂ O ₅ powder (manufactured by Alba Rich) and MCMB carbon powder (manufactured by Osaka Gas Chemical Co., Ltd.) were mixed. In this case, _Nb 2 _{O 5} powder was added 1 at.% With respect to MgH _2, the mass ratio of carbon and MgH ₂ and _Nb 2 _{O 5} is set to be 90/10 wt%. The mixture was processed by a ball mill (mixture: ball = 1 mass%: 40 mass%, 400 rpm, 5 hours, Ar atmosphere) to produce a refined negative electrode material.

(Preparation of negative electrode)
The negative electrode material / conductive material / PVdF was kneaded at a mass ratio of 45:40:15 to prepare a negative electrode paste, and the paste was coated on a copper foil using a doctor blade, dried, and pressed. As a result, a negative electrode having a thickness of 10 μm was produced.

(Preparation of electrolyte)
The electrolyte is a mixture of EC (ethylene carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate) in a volume ratio of 3: 3: 4, and a concentration of lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt. It was made to melt | dissolve at 1 mol / L and the electrolyte solution was produced.

(Production of metal secondary battery)
The following lithium secondary battery was produced.
Battery type: CR2022 type coin cell Working electrode: Test electrode counter electrode: Metal Li
Separator: PP porous separator (PE / PP / PE)
Electrolyte: EC / DMC / EMC = 3: 3: 4, 1M-LiPF ₆

<Comparative example>
(Comparative Example 1)
A negative electrode and a metal secondary battery were produced in the same manner as in Example except that the negative electrode material was produced as follows.

Commercially available MgH ₂ powder and MCMB carbon powder were mixed at a mass ratio of 90:10 and ball milled (mixture: ball = 1% by mass: 40% by mass, 400 rpm, 5 hours, Ar atmosphere) and refined. A negative electrode material was produced.

(Comparative Example 2)
A negative electrode and a metal secondary battery were produced in the same manner as in Example except that the negative electrode material was produced as follows.

Commercially available MgH ₂ powder, Ni powder nano-sized as a catalyst (manufactured by Nippon Nanotech Co., Ltd.) and MCMB carbon powder were mixed. At this time, Ni powder was added to a 1 at.% With respect to MgH _2, the mass ratio of MgH ₂ and Ni powder and carbon is set to be 90/10 wt%. The mixture was processed by a ball mill (mixture: ball = 1 mass%: 40 mass%, 400 rpm, 5 hours, Ar atmosphere) to produce a refined negative electrode material.

<Evaluation of metal secondary battery>
Battery evaluation was performed at an environmental temperature of 25 ° C. and a current rate of C / 50, and charge / discharge (upper and lower limit voltage: 3.0 V to 0.01 V) was performed to evaluate the ratio between the discharge capacity and the charge capacity (charge / discharge efficiency).

FIGS. 2A and 2B show charge / discharge curves of lithium secondary batteries according to Examples and Comparative Examples 1 and 2, respectively. As is clear from FIGS. 2A and 2B, the example in which Nb ₂ O ₅ is added to the negative electrode material has dramatically improved reversibility and improved charge / discharge efficiency compared to the comparative example. I understand that Moreover, as can be seen from FIG. 2B, the charge / discharge curve according to the example to which Nb ₂ O ₅ was added passes slightly above (noble) the comparative example. This means that Li is inserted into Nb ₂ O ₅ prior to MgH ₂ . It is considered that Nb ₂ O ₅ is pulverized in this process.

Conversion reaction of MgH _{2 is,} MgH 2 + 2Li + 2e ^- proceed in the form of → 2LiH + Mg, then, Li is inserted to zero valence of Mg and Li is _Li 3 Mg ₇ by alloying reaction. In the absence of a catalyst, both the alloying reaction and the conversion reaction are inferior in reversibility, but by adding Nb ₂ O ₅ to function as a catalyst, Nb ₂ O ₅ is converted to a conversion reaction at a higher potential than the active material MgH _2. (MgH ₂ : 0.5V, Nb ₂ O ₅ : 1.1V), the conversion reaction of Nb ₂ O ₅ occurs first in the Li insertion process. As a result, Nb ₂ O ₅ is pulverized and expresses a function as a catalyst in the subsequent charge / discharge process. That is, since Nb ₂ O ₅ has a large particle size and is not coated with a conductive material, it is only pulverized at the initial reaction stage and does not function as an active material but functions as a catalyst. As a result, it was found that the reversibility of the alloying reaction was greatly improved and the reversibility of the conversion reaction was dramatically improved.

  The metal secondary battery according to the present invention can be suitably used as a power source for portable devices, electric vehicles, hybrid vehicles, and the like.

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Positive electrode 3 Electrolyte layer 10 Metal secondary battery

Claims (4)

MgH _2, and comprises _Nb 2 _{O 5} in contact with the MgH _2, a negative electrode material for metal secondary battery. _{2. The} negative electrode material for a metal secondary battery according to claim 1, wherein the Nb ₂ O ₅ is in the form of particles, and the average particle diameter X is 1 μm ≦ X <1000 μm.   A negative electrode for a metal secondary battery, comprising the negative electrode material for a metal secondary battery according to claim 1.   A metal secondary battery comprising a positive electrode, an electrolyte, and the negative electrode according to claim 3.