JP5621732B2 - Metal secondary battery - Google Patents

Description

The present invention relates to a metal secondary battery having MgH ₂ as a negative electrode material and exhibiting high charge / discharge efficiency.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

For example, a conversion-type negative electrode active material that is a metal hydride (MHx) is known as a negative electrode active material used in a lithium battery. As a conversion-type negative electrode active material, for example, Patent Document 1 describes 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

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, in the metal secondary battery using the MgH _2, the charge and discharge efficiency is lowered.
This invention is made | formed in view of the said situation, and makes it a main objective to provide a metal secondary battery with high charging / discharging efficiency.

  As a result of intensive studies to solve the above problems, the present inventors have obtained knowledge that the charge / discharge efficiency of a metal secondary battery is greatly affected by the electrolytic solution. Thus, the present inventors who have obtained the above findings have found that the charge / discharge efficiency is greatly improved when a specific carbonate is used as the solvent of the electrolytic solution, and have completed the present invention.

That is, the present invention is a metal secondary battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer, wherein the negative electrode Provided is a metal secondary battery characterized in that the active material layer contains MgH ₂ and the electrolyte layer is composed of an electrolytic solution having a metal salt and a solvent containing a carbonate having 4 or more carbon atoms.

  According to the present invention, since the electrolytic solution contains a carbonate having 4 or more carbon atoms, the metal secondary battery can be stably operated, so that charge / discharge efficiency can be improved.

  In the present invention, the carbonate having 4 or more carbon atoms is preferably ethyl methyl carbonate (EMC).

  In the present invention, the solvent preferably further contains ethylene carbonate (EC) and dimethyl carbonate (DMC). It is because the solubility of a metal salt can be improved by containing EC. Moreover, it is because the metal secondary battery of this invention can be made into a thing with higher charging / discharging efficiency by having DMC.

In the present invention, the negative electrode active material layer preferably contains a metal catalyst that improves the reversibility of the conversion reaction. By adding the metal catalyst to MgH ₂ that is the negative electrode active material, for example, the reaction formula 2 can be promoted. Therefore, the charge / discharge efficiency of the metal secondary battery can be improved.

In the present invention, the average particle size of MgH ₂ is preferably 2 μm or less. This is because the reversibility of the conversion reaction can be further improved by reducing the particle size of MgH ₂ .

  The present invention has an effect that a metal secondary battery having high charge / discharge efficiency can be obtained by having the above-described electrolytic solution.

It is a schematic sectional drawing which shows an example of the metal secondary battery of this invention. It is a result of charge-and-discharge efficiency evaluation of the evaluation battery of Example 1. It is a result of charging / discharging efficiency evaluation of the evaluation battery of Example 2. It is a result of charge-and-discharge efficiency evaluation of the evaluation battery of a comparative example.

Hereinafter, the metal secondary battery of the present invention will be described in detail. The metal secondary battery of the present invention is a metal secondary battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. The negative electrode active material layer contains MgH ₂ , and the electrolyte layer is composed of an electrolytic solution having a metal salt and a solvent containing a carbonate having 4 or more carbon atoms. is there.

FIG. 1 is a schematic cross-sectional view showing an example of a metal secondary battery of the present invention. A metal secondary battery 10 in FIG. 1 includes a positive electrode active material layer 1, a negative electrode active material layer 2, an electrolyte layer 3 formed between the positive electrode active material layer 1 and the negative electrode active material layer 2, and a positive electrode active material layer. 1 has a positive electrode current collector 4 that collects current, a negative electrode current collector 5 that collects current of the negative electrode active material layer 2, and a battery case 6 that houses these members. In the present invention, the negative electrode active material layer 2 contains MgH ₂ , and the electrolyte layer 3 is composed of an electrolytic solution having a metal salt and a solvent containing a carbonate having 4 or more carbon atoms. And

  According to the present invention, since the electrolytic solution contains a carbonate having 4 or more carbon atoms, the metal secondary battery can be stably operated, and thus the charge / discharge efficiency can be improved.

Here, as described in Comparative Examples described later, when an electrolytic solution containing DMC and EC is used, the charge / discharge efficiency is significantly reduced. This is presumably because the electrolytic solution (mainly DMC) is decomposed by the nucleophilic reaction from MgH ₂ to the electrolytic solution.

On the other hand, the carbonate having 4 or more carbon atoms used in the solvent in the present invention has a chain structure (for example, EMC), a cyclic structure (for example, PC), etc., as shown by the following structural formula. Compared to the structure of DMC, the structure is bulky. Therefore, it is considered that the above-described chain structure, cyclic structure, or the like becomes a steric hindrance to the nucleophilic reaction of MgH _{2 in} a solvent, and it is possible to suppress decomposition of the electrolytic solution. The carbonate having 4 or more carbon atoms will be described later in detail.

  Hereinafter, each structure of the metal secondary battery of this invention is demonstrated.

1. Electrolyte Layer The electrolyte layer in the present invention will be described. The electrolyte layer in the present invention is composed of an electrolytic solution having a metal salt and a solvent. In this invention, the said electrolyte solution has the big characteristic in containing the solvent containing a C4 or more carbonate.

  Hereinafter, the electrolytic solution of the present invention will be described. The electrolytic solution contains a carbonate having 4 or more carbon atoms as a solvent. In addition, the upper limit of the carbon number of the carbonate having 4 or more carbon atoms used in the present invention is not particularly limited, but is usually about 20.

The carbonate having 4 or more carbon atoms may be a chain carbonate or a cyclic carbonate.
The chain carbonate may be a carbonate having a hydrocarbon group, and the hydrocarbon group may have a chain structure or a cyclic structure. Specific examples include ethyl methyl carbonate (EMC), diphenyl carbonate (DPC), di-n-butyl carbonate (DNBC), di-t-butyl carbonate (DTBC), diethyl carbonate (DEC), and the like.
On the other hand, specific examples of the cyclic carbonate include propylene carbonate (PC) and butylene carbonate (BC). These carbonates having 4 or more carbon atoms may be used singly or in combination of two or more, and are selected appropriately according to the viscosity of the solvent, the metal salt used, and the like. In the present invention, it is particularly preferable that EMC is contained.

Further, the content of the carbonate having 4 or more carbon atoms is not particularly limited as long as the decomposition of the electrolytic solution by MgH ₂ can be suppressed, and is 5% by volume or more with respect to the volume of the entire solvent. In particular, it is preferably 10% by volume or more, particularly preferably 30% by volume or more. If the above content is less than the above range, there is a possibility that it is difficult to suppress the decomposition of the electrolyte by the MgH _2.
The upper limit of the content of the carbonate having 4 or more carbon atoms may be 100% by volume, but is preferably about 50% by volume, for example. This is because if the content exceeds the above range, the solubility of the electrolytic salt may decrease, or the viscosity of the electrolytic solution may become too high, making it difficult to use it in the electrolyte layer.

  The electrolytic solution used in the present invention may have, for example, a high dielectric constant solvent in addition to the above-mentioned carbonate having 4 or more carbon atoms. By containing a high dielectric constant solvent, it becomes possible to improve the solubility of the metal salt described later, and therefore, it is possible to use a carbonate having a low solubility of the metal salt. The dielectric constant of the high dielectric constant solvent is preferably 30 or more, more preferably 60 or more, and particularly preferably 90 or more. Such a high dielectric constant solvent is not particularly limited as long as it can dissolve a metal salt. For example, ethylene carbonate (EC), γ-butyrolactone, sulfolactone, N-methyl-2-pyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone (DMI) and the like. In the present invention, it is particularly preferable that EC is contained. In addition, although it is a C4 or more carbonate, you may use PC and BC as a high dielectric constant solvent.

  The solvent in the present invention may further contain a film-forming solvent. Here, in a metal secondary battery, a coating (Solid Electrolyte Interphase (SEI)) is formed on the interface between the active material layer and the electrolyte layer, which is formed by decomposition of a part of the solvent during the battery reaction. ) Is known to form. Moreover, the said film can perform a battery reaction stably, so that the resistance is small, and can make charging / discharging efficiency high. Therefore, the electrolytic solution in the present invention preferably contains a film-forming solvent capable of forming a low-resistance film. Examples of such a film forming solvent include solvents such as DMC. In addition, although it is a C4 or more carbonate, you may use DEC as a solvent for film formation.

As the solvent in the present invention, a mixed solvent of carbonate / high dielectric constant solvent / film forming solvent having 4 or more carbon atoms is preferable, and a mixed solvent of EMC / EC / DMC is particularly preferable. . When the solvent is the mixed solvent described above, the charge / discharge efficiency of the metal secondary battery of the present invention can be further improved. Although the reason for this is not clear, it can be considered as follows.
In the present invention, when DMC is contained in the solvent, it is considered that a low-resistance film can be formed. However, when the solvent does not contain EMC as in the comparative example described later, the reaction of DMC and MgH ₂ further proceeds after the formation of the film, so that the electrolytic solution itself may be decomposed. On the other hand, when a carbonate having 4 or more carbon atoms such as EMC is contained as in Example 2 described later, it is possible to suppress decomposition of the electrolyte solution (mainly DMC) by MgH _2. Therefore, it is considered that the decomposition of the electrolytic solution after the above-described film formation can be suppressed.
Moreover, since the mixed solvent mentioned above can improve the solubility of a metal salt by having EC, it is thought that it can be set as a favorable electrolyte solution.

  The mixing ratio (volume ratio) of each solvent in the carbonate / high dielectric constant solvent / film forming solvent mixed solvent having 4 or more carbon atoms is not particularly limited, but is 100 volume parts of carbonate having 4 or more carbon atoms. On the other hand, the high dielectric constant solvent is preferably in the range of 5 to 60 parts by volume, in particular in the range of 10 to 50 parts by volume, particularly in the range of 20 to 40 parts by volume. Further, the solvent for forming a film is in the range of 5 to 60 parts by volume, particularly in the range of 10 to 50 parts by volume, particularly 20 parts by volume with respect to 100 parts by volume of the carbonate having 4 or more carbon atoms. It is preferable to be within a range of ˜40 parts by volume.

The electrolytic solution used for the electrolyte layer in the present invention has the above-described solvent and metal salt. The metal salt used in the electrolytic solution is appropriately selected according to the type of the metal secondary battery. For example, as the metal salt used in the lithium secondary battery, LiPF ₆ , LiBF ₄ , LiClO ₄ And inorganic lithium salts such as LiAsF ₆ ; and organic lithium salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ Can be mentioned. The concentration of the metal salt in the electrolytic solution is, for example, in the range of 0.5 mol / L to 3 mol / L.

  The thickness of the electrolyte layer varies greatly depending on 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. A separator may be disposed between the positive electrode active material layer and the negative electrode active material layer.

2. Next, the negative electrode active material layer in the present invention will be described. The negative electrode active material layer in the present invention contains at least MgH ₂ . Further, the negative electrode material used for the negative electrode active material layer is not particularly limited as long as it contains MgH ₂ , but more preferably contains a metal catalyst that improves the reversibility of the conversion reaction, and a conductive material. preferable.

MgH ₂ is usually used as an active material. In the present invention, MgH ₂ is preferably further refined. This is because the reversibility of the conversion reaction can be further improved by reducing the particle size of MgH ₂ . By particle size of MgH ₂ becomes smaller, why reversibility of the conversion reaction is improved, the particle size of MgH ₂ is decreased, the specific surface area is increased, believed Scheme 2 is to become liable . In addition, the particle size of MgH ₂ is reduced, Li diffusion paths are shortened, believed to improve reactivity. Moreover, since the particle size of MgH ₂ is reduced, there is an advantage that the overvoltage in the Li insertion reaction (the above reaction formula 1) is reduced.

The average particle size of MgH ₂ is not particularly limited, for example, preferably at 2μm or less, and more preferably in the range of 0.1 to 1 m. The average particle size of MgH ₂ is a SEM (scanning electron microscope) observation, measuring the particle size of MgH ₂ particles (n = 100), it can be calculated by obtaining the average. Further, when the average particle diameter of MgH _{2 and} the average particle diameter of the metal catalyst or conductive material described later are greatly different, the average particle diameter (d ₅₀ ) of the MgH ₂ particles is obtained by particle size distribution measurement. Also good.

The content of MgH ₂ in the negative electrode material is not particularly limited, for example, preferably 40 wt% or more, and more preferably in a range of 60% to 98% by weight.

  The negative electrode material preferably contains a metal catalyst that improves the reversibility of the conversion reaction. By adding the metal 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, and a metal catalyst performs one or both of these reactions. It is thought that it is promoting.

Next, an estimation mechanism by which the metal catalyst improves the reversibility of the conversion reaction will be described. When Li ⁺ is taken into MgH ₂ (the above reaction formula 1 occurs), Mg and LiH are generated. When this state is measured by X-ray diffraction (XRD), the Mg peak is observed and the LiH peak is not observed. Therefore, the crystalline Mg particles are formed in a floating island shape in the amorphous LiH. It is inferred that

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 the metal catalyst, and the dissociated and adsorbed hydrogen reacts with Mg, thereby generating MgH ₂ . That is, in this presumed mechanism, the metal catalyst promotes 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 hydrogen gas generated by the metal catalyst is dissociated and adsorbed, but the metal catalyst may adsorb hydrogen before the hydrogen desorbed from LiH becomes hydrogen gas. Conceivable. In addition, the metal catalyst may promote the LiH dissociation reaction itself.

MgH ₂ in the present invention normally functions as an active material, and for example, LiH and Mg are produced 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 . As described above, MgH ₂ has an extremely large Li storage capacity, but its reverse reaction (particularly, 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 using a metal catalyst.
Also, the metal catalyst may if in contact with MgH _2, it is preferable that carried on MgH _2. Further, as described above, the metal catalyst in the present invention preferably acts on at least one of a hydrogen desorption reaction from MH (M is, for example, Li) and a hydrogen addition reaction to Mg. This is because at least one of the hydrogen elimination reaction and the hydrogen addition reaction may be the rate-limiting of the reverse reaction of the conversion reaction (for example, the above reaction formula 2).

The metal catalyst in the present invention is not particularly limited as long as it can improve the reversibility of the conversion reaction. For example, it is a catalyst capable of dissociating LiH or a catalyst capable of dissociating and adsorbing H ₂ gas. Preferably there is. The “catalyst capable of dissociating and adsorbing H ₂ gas” means both a catalyst that dissociates and adsorbs H ₂ gas and a catalyst that adsorbs hydrogen before hydrogen desorbed from LiH becomes hydrogen gas. .

Moreover, it is preferable that the metal catalyst in this invention has a transition metal element. This is because 3d orbitals, 4d orbitals, 4f orbitals and the like in transition metal elements are considered to improve the reversibility of the conversion reaction. In addition, it is considered that these orbits may greatly contribute to LiH dissociation and H ₂ gas dissociative adsorption. The transition metal element is not particularly limited as long as it is classified as a transition metal element in the periodic table, but among them, Ti, V, Cr, Mn, Co, Ni, Zr, Nb, Pd It is preferably at least one selected from the group consisting of La, Ce and Pt. Moreover, as a kind of metal catalyst in this invention, a metal simple substance, an alloy, a metal oxide, etc. can be mentioned, for example. In particular, the metal catalyst in the present invention is preferably Ni simple substance or Ni alloy.

  The metal catalyst in the present invention is preferably further miniaturized. This is because the reversibility of the conversion reaction can be further improved by reducing the particle size of the metal catalyst. The average particle diameter of the metal catalyst is, for example, preferably 1 μm or less, and more preferably in the range of 10 nm to 500 nm. In addition, the average particle diameter of a metal catalyst can be determined by SEM observation and a particle size distribution measurement similarly to the above.

Ratio of the metal catalyst to MgH ₂ is not particularly limited, is preferably a fraction that can improve charge-discharge efficiency of the metal secondary battery as compared with the case of not using a metal catalyst. The ratio of the metal catalyst to MgH ₂ is preferably in the range of, for example, 0.1 at% to 10 at%, in particular, in the range of 0.5 at% to 6 at%, more preferably in the range of 1 at% to 5 at%, particularly It is preferable to be within the range of 2 at% to 4 at%. If the proportion of the metal catalyst is too small, the reversibility of the conversion reaction may not be sufficiently improved. If the proportion of the metal catalyst is too large, the proportion of MgH ₂ is relatively small, and the capacity is reduced. This is because it may become large. The ratio of the metal catalyst to MgH ₂ can be determined by SEM-EDX.

In particular, when the metal catalyst is Ni simple substance, the ratio of Ni simple substance to MgH ₂ is preferably such a ratio that the charge / discharge efficiency of the metal secondary battery can be improved as compared with the case where the metal catalyst is not used. Specifically, the ratio of the Ni simple substance is preferably 6 at% or less, more preferably in the range of 1 at% to 5 at%, and further preferably in the range of 2 at% to 4 at%. .

Further, the negative electrode material in the present invention may further contain a conductive material. This is because a negative electrode material having good electron conductivity can be obtained. Further, the conductive material is preferably in contact with MgH _2, and more preferably supported on MgH ₂ . This is because it is easy to secure an electron conduction path. The conductive material is not particularly limited, and examples thereof include carbon materials such as mesocarbon microbeads (MCMB), acetylene black, ketjen black, carbon black, coke, carbon fiber, and graphite.

  It is preferable that the conductive material in the present invention is further refined. This is because it can further contribute to the improvement of electron conductivity. The average particle diameter of the conductive material is preferably 2 μm or less, for example, and more preferably in the range of 0.1 μm to 1 μm. In addition, the average particle diameter of the conductive material can be determined by SEM observation and particle size distribution measurement in the same manner as described above.

The content of the conductive material in the negative electrode material of the present invention is not particularly limited, but is preferably in the range of 1% by weight to 60% by weight, for example, 2% by weight to 40% by weight. It is preferable to be within the range, particularly within the range of 5 to 20% by weight. If the proportion of the conductive material is too small, the electron conductivity may not be sufficiently improved, and if the proportion of the conductive material is too large, the proportion of MgH ₂ and the metal catalyst is relatively small. This is because there is a possibility that the decrease in capacity becomes large or the improvement in reversibility is reduced.

As a method of forming the negative electrode material described above is not particularly limited, but is preferably a method having a mechanical milling step of refining by mechanical milling of the raw material composition containing a MgH _2. 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). In addition, the metal catalyst and the conductive material can be uniformly dispersed on the surface of the MgH ₂ particles by miniaturization by mechanical milling. 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.

  Various conditions of mechanical milling are set so that a desired negative electrode material can be obtained. For example, when producing a negative electrode material by a planetary ball mill, a raw material composition and a ball for pulverization are added to a pot, and the treatment is performed at a predetermined rotation speed and time. The rotation speed of the base plate when performing the planetary ball mill is preferably in the range of, for example, 100 rpm to 1000 rpm, and more preferably in the range of 200 rpm to 600 rpm. Further, the treatment time when performing the planetary ball mill is preferably in the range of, for example, 1 hour to 100 hours, and more preferably in the range of 2 hours to 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 diameter.

In the above-described method for forming a negative electrode material, it is more preferable to perform a hydrogen storage / release process in which MgH ₂ -containing particles obtained by mechanical milling are refined by storing and releasing hydrogen in the gas phase after the mechanical milling process. . This is because hydrogen can be occluded and released to make the particles finer and improve the reversibility of the conversion reaction. As a result, the charge / discharge efficiency of the metal secondary battery of the present invention can be improved. In addition, the MgH ₂ -containing particles can be further miniaturized by performing miniaturization (chemical miniaturization) by occlusion and release of hydrogen after miniaturization by mechanical milling (mechanical miniaturization). In the hydrogen storage / release step, it is preferable that magnesium be stored in hydrogen (that is, a state in which a function as an active material can be exhibited).

The hydrogen absorption-desorption process, the MgH ₂ in MgH ₂ containing particles, by releasing occlude hydrogen through the gas phase, achieving finer particles. Moreover, it processes normally in order of hydrogen discharge | release and hydrogen occlusion. The method for releasing hydrogen is not particularly limited, and for example, a method for reducing the pressure can be mentioned. On the other hand, the method for occluding hydrogen is not particularly limited, and examples thereof include a method of pressurizing in a hydrogen gas atmosphere.

  The negative electrode active material layer in the present invention may further contain at least one of a conductive material and a binder as necessary, in addition to the negative electrode material described above. The content of the negative electrode material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 10 wt% to 80 wt%, for example, and more preferably in the range of 20 wt% to 60 wt%. preferable. Further, as described above, the negative electrode material itself may contain a conductive material, but the negative electrode active material 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. A specific example of the conductive material is as described above. Examples of the binder include a fluorine-containing binder such as polyvinylidene fluoride (PVDF). The thickness of the negative electrode active material layer is preferably in the range of 0.1 μm to 1000 μm, for example.

3. Next, the positive electrode active material layer in the present invention will be described. The positive electrode active material layer in the present invention is a layer containing at least a positive electrode active material, and may further contain at least one of a conductive material and a binder as necessary. The type of the positive electrode active material is preferably selected as appropriate according to the type of the metal secondary battery. For example, as a positive electrode active material used for a lithium secondary battery, a layered positive electrode active material such as LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiVO ₂ , LiCrO ₂ , LiMn ₂ Spinel type positive electrode active materials such as O ₄ , Li (Ni _0.25 Mn _0.75 ) ₂ O ₄ , LiCoMnO ₄ , Li ₂ NiMn ₃ O ₈ , and olivine type positive electrode active materials such as LiCoPO ₄ , LiMnPO ₄ , LiFePO ₄ Etc. Although content of the positive electrode active material in a positive electrode active material layer is not specifically limited, For example, it is preferable to exist in the range of 40 weight%-99 weight%.

  The positive electrode active material layer in the present invention may further contain at least one of a conductive material and a binder. The conductive material and the binder are the same as the contents described in the above “1. Negative electrode active material layer”, and thus description thereof is omitted here. The thickness of the positive electrode active material layer is preferably in the range of 0.1 μm to 1000 μm, for example.

4). Other Configurations The metal secondary battery of the present invention may further include a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Of these, aluminum is preferable. On the other hand, examples of the material for the negative electrode current collector include SUS, copper, nickel, and carbon. Of these, copper is preferable. Moreover, the battery case of a general metal secondary battery can be used for the battery case used for this invention. Examples of the battery case include a SUS battery case.

5. Metal secondary battery Examples of the metal secondary battery of the present invention include a lithium secondary battery, a sodium secondary battery, a potassium secondary battery, a magnesium secondary battery, and a calcium secondary battery. Secondary batteries, sodium secondary batteries, and potassium secondary batteries are preferable, and lithium secondary batteries are particularly preferable. Moreover, it is preferable that the metal secondary battery of this invention is used, for example as a vehicle-mounted battery. Examples of the shape of the metal secondary battery of the present invention include a coin type, a laminate type, a cylindrical type, and a square type. Moreover, the manufacturing method of the metal secondary battery of this invention will not be specifically limited if it is a method which can obtain the metal secondary battery mentioned above, It is the same as the manufacturing method of a general metal secondary battery. The method can be used.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Example 1]
(Preparation of negative electrode material)
First, MgH ₂ powder (average particle size 30 μm), Ni powder (average particle size 100 nm) and carbon powder (MCMB, average particle size 1 μm) were prepared as metal catalysts. This carbon powder was obtained by subjecting commercially available MCMB (average particle size 20 μm) to planetary ball milling (400 rpm × 5 hours).
Next, 3 at% of Ni powder was added to the MgH ₂ powder. Thereafter, the MgH ₂ powder and Ni powder and the carbon powder were mixed so as to have a weight ratio of (MgH ₂ powder + Ni powder): carbon powder = 90: 10 to obtain a raw material composition. Next, in an Ar atmosphere, the raw material composition and the pulverizing zirconia ball (φ = 10 mm) are used for a planetary ball mill so that the weight ratio of the raw material composition: the pulverizing zirconia ball is 1:40. Placed in a container and sealed. Thereafter, the container was attached to a planetary ball mill apparatus, and miniaturization was performed under conditions of a base plate rotation speed of 400 rpm and a processing time of 5 hours. In the obtained negative electrode material, the average particle diameter of the MgH ₂ powder was 0.5 μm, the average particle diameter of the Ni powder was 20 nm, and the average particle diameter of the carbon powder was 0.1 μm.

(Production of evaluation battery)
The negative electrode material described above, a conductive material (acetylene black 60 wt% + VGCF 40 wt%), and a binder (polyvinylidene fluoride, PVDF), negative electrode material: conductive material: binder = 45: 40: 15 weight The paste was obtained by mixing at a ratio and kneading. Next, the obtained paste was coated on a copper foil with a doctor blade, dried, and pressed to obtain a test electrode having a thickness of 10 μm.

Thereafter, a CR2032-type coin cell was used, the test electrode was used as a working electrode, Li metal was used as a counter electrode, and a porous separator of polyethylene / polypropylene / polyethylene was used as a separator. Further, as an electrolytic solution, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC: EMC = 1: 1, and LiPF ₆ as a supporting salt was added at a concentration of 1 mol / L. What was dissolved was used. The battery for evaluation was obtained using these.

[Example 2]
Example 1 except that the electrolyte used was a solution prepared by dissolving LiPF ₆ as a supporting salt at a concentration of 1 mol / L in a solvent mixed at a volume ratio of EC: DMC: EMC = 1: 1: 1. A battery for evaluation was obtained in the same manner.

[Comparative example]
The electrolytic solution was the same as that of Example 1 except that a solvent mixed at a volume ratio of EC: DMC = 1: 1 was prepared by dissolving LiPF ₆ as a supporting salt at a concentration of 1 mol / L. A battery for evaluation was obtained.

[Evaluation 1]

  The obtained evaluation battery was charged and discharged at a battery evaluation environmental temperature of 25 ° C. and a current rate of C / 50. The voltage range was 0.01V to 3.0V. The results of Example 1, Example 2, and Comparative Example are shown in Table 1, FIG. 2 (Example 1), FIG. 3 (Example 2), and FIG. 4 (Comparative Example).

As shown in Table 1 and FIGS. 2 to 4, in the comparative example, the normal battery reaction did not proceed as in Examples 1 and 2. Moreover, when the electrolyte solution in the battery for evaluation after completion | finish of charging / discharging was observed, discoloration of electrolyte solution was confirmed. This is probably because the electrolyte (mainly DMC) was decomposed by the nucleophilic reaction from MgH ₂ .
On the other hand, in Example 1, it was observed that the battery reaction proceeds and shows high charge / discharge efficiency. This seems to be because the decomposition reaction of the electrolytic solution can be suppressed by using EMC instead of DMC.
Moreover, in Example 2, charging / discharging efficiency improved notably. This is presumably because a good film was formed on the surface of MgH ₂ by the proper decomposition of DMC in the presence of EMC. In the comparative example, since EMC does not exist, it is considered that the decomposition reaction of DMC did not stop and the normal battery reaction did not proceed.

[Reference Example 1]
The MgH ₂ powder and carbon powder used in Example 1 were prepared. Next, the MgH ₂ powder and the carbon powder were mixed at a weight ratio of MgH ₂ powder: carbon powder = 90: 10 to obtain a raw material composition. A negative electrode material was obtained in the same manner as in Example 1 except that the obtained raw material composition was used.

[Reference Examples 2-1 to 2-21]
Example 1 was defined as Reference Example 2-1. In Reference Example 2-2 to Reference Example 2-21, a negative electrode material was obtained in the same manner as in Example 1 except that the metal catalyst was changed to the material described in Table 2.

[Evaluation 2]
A battery for evaluation was prepared using the negative electrode materials obtained in Reference Example 1 and Reference Examples 2-1 to 2-21, and charge / discharge efficiency was measured. The evaluation battery fabrication method and the charge / discharge efficiency measurement method are the same as described above. The results are shown in Table 2.

  As shown in Table 2, it was confirmed that the charge / discharge efficiency was dramatically improved by adding various metal catalysts. Each of Reference Examples 2-1 to 2-21 has a conductive material. When the same experiment was conducted without using a conductive material, high charge / discharge efficiencies as shown in Table 2 were not obtained. It was.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode active material layer 2 ... Negative electrode active material layer 3 ... Electrolyte layer 4 ... Positive electrode collector 5 ... Negative electrode collector 6 ... Battery case 10 ... Metal secondary battery

Claims (5)

A metal secondary battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer,
The negative electrode active material layer contains MgH ₂ particles ,
The electrolyte layer is composed of an electrolytic solution having a metal salt and a solvent containing a carbonate having 4 or more carbon atoms,
The carbonate having 4 or more carbon atoms is ethyl methyl carbonate (EMC), diphenyl carbonate (DPC), di-n-butyl carbonate (DNBC), di-t-butyl carbonate (DTBC), diethyl carbonate (DEC), propylene. A metal secondary battery comprising at least one of carbonate (PC) and butylene carbonate (BC).   The metal secondary battery according to claim 1, wherein the carbonate having 4 or more carbon atoms is ethyl methyl carbonate (EMC).   The metal secondary battery according to claim 2, wherein the solvent further contains ethylene carbonate (EC) and dimethyl carbonate (DMC).   The metal secondary battery according to any one of claims 1 to 3, wherein the negative electrode active material layer contains a metal catalyst that improves the reversibility of the conversion reaction. 5. The metal secondary battery according to claim 1, wherein an average particle diameter of the MgH ₂ particles is 2 μm or less.

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