JP2012174535A - Electrode active material, and metal secondary battery comprising negative electrode containing the electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode active material offering cycle characteristics superior to conventional negative electrode active materials when used in a metal secondary battery, and a metal secondary battery comprising a negative electrode containing the electrode active material.SOLUTION: The electrode active material contains a half-Heusler compound of the composition represented by the general formula (1): αβγ, where α represents an element selected from the group consisting of Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, and Au, β represents an element selected from the group consisting of Ti, V, Cr, Mn, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, and Ta, and γ represents an element selected from the group consisting of Al, Si, Ga, Ge, As, In, Sn, Sb, Tl, Pd, and Bi.

Description

  When used in a metal secondary battery, the present invention contains an electrode active material capable of improving cycle characteristics over a metal secondary battery using a conventional negative electrode active material, and the electrode active material in the negative electrode. The present invention relates to a metal secondary battery.

  The secondary battery converts the decrease in chemical energy associated with the chemical reaction into electrical energy, and can discharge the battery. The battery can be stored (charged). Among secondary batteries, a metal secondary battery represented by a lithium secondary battery has a high energy density, and is therefore widely applied as a power source for notebook personal computers, cellular phones, and the like.

In the lithium secondary battery, when graphite (expressed as C) is used as the negative electrode active material, the reaction of the following formula (I) proceeds in the negative electrode during discharge.
Li _x C → C + xLi ⁺ + xe ⁻ (I)
(In the above formula (I), 0 <x <1.)
The electrons generated by the reaction of the above formula (I) reach the positive electrode after working with an external load via an external circuit. Then, lithium ions (Li ⁺ ) generated by the reaction of the above formula (I) move from the negative electrode side to the positive electrode side by electroosmosis in the electrolyte sandwiched between the negative electrode and the positive electrode.

When lithium cobaltate (Li _1-x CoO ₂ ) is used as the positive electrode active material, the reaction of the following formula (II) proceeds at the positive electrode during discharge.
Li _1-x CoO ₂ + xLi ⁺ + xe ⁻ → LiCoO ₂ (II)
(In the above formula (II), 0 <x <1.)
At the time of charging, reverse reactions of the above formulas (I) and (II) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (Li _x C) containing lithium by graphite intercalation is Since lithium cobaltate (Li _1-x CoO ₂ ) is regenerated, re-discharge is possible.

Currently, carbon materials such as graphite are generally used as negative electrode materials for lithium ion secondary batteries. However, since the graphite-based carbon material has a theoretical limit on the discharge capacity, it is not suitable for increasing the battery capacity. In addition, although non-graphitic carbon materials have a large discharge capacity, they have a large irreversible capacity and have a drawback of causing a large loss at the stage of battery design.
On the other hand, a negative electrode material that has a large capacity and can be used as a substitute for a carbon material has been proposed. For example, an example in which a metal oxide containing Sn or the like, or a metal nitride containing Co or Mn or the like is applied to a negative electrode material is known. Patent Document 1 discloses a negative electrode material for a non-aqueous secondary battery manufactured by a rapid solidification method, which includes at least one element of Fe, Ni, and Co and Sn and is composed of one or more compound phases. Is described.

JP 2006-236835 A

As can be seen from the paragraphs [0058] and [Table 1] of the document, the negative electrode material described in Patent Document 1 has very low initial charge / discharge efficiency. This is because when an alloy containing Sn is used in a lithium secondary battery, the crystal structure changes greatly due to a chemical reaction such as insertion / extraction of Li, resulting in a problem in the reversibility of the reaction. It is done.
The present invention has been accomplished in view of the above circumstances, and when used in a metal secondary battery, an electrode active that can improve cycle characteristics over a metal secondary battery using a conventional negative electrode active material. It aims at providing the metal secondary battery which contains a substance and the said electrode active material in a negative electrode.

The electrode active material of the present invention is characterized by containing a half-Heusler compound having a composition represented by the following general formula (1).
αβγ General formula (1)
(In the general formula (1), α is an element selected from the group consisting of Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, and Au, and β is Ti, V, Cr, Mn, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, and Ta are elements selected from the group consisting of Al, Si, Ga , Ge, As, In, Sn, Sb, Tl, Pd, and Bi.

  The metal secondary battery of the present invention is a metal secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode, wherein the negative electrode contains the electrode active material. It is characterized by that.

  According to the present invention, the insertion site of lithium ions can be secured by having a half-Heusler structure, and as a result, when the electrode active material according to the present invention is used in a metal secondary battery, the cycle characteristics of the battery are improved. be able to.

It is a cross-sectional schematic diagram which shows an example of the metal secondary battery of this invention. 2 is a discharge curve of lithium secondary batteries of Example 2 and Comparative Example 1. It is the figure which showed the crystal structure of the half-Heusler compound.

1. Electrode active material The electrode active material of this invention contains the half-Heusler compound which has a composition represented by following General formula (1), It is characterized by the above-mentioned.
αβγ General formula (1)
(In the general formula (1), α is an element selected from the group consisting of Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, and Au, and β is Ti, V, Cr, Mn, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, and Ta are elements selected from the group consisting of Al, Si, Ga , Ge, As, In, Sn, Sb, Tl, Pd, and Bi.

FIG. 3 is a diagram showing the crystal structure of the half-Heusler compound. As can be seen from FIG. 3, the crystal structure of the half-Heusler compound is a C1 _b structure consisting α atom 11, beta atoms 12 and γ atoms 13. The unit cell of the C1 _b structure is a structure obtained by removing one α atom 11 from four face-centered cubic lattices.
Since the electrode active material of the present invention has a half-Heusler structure as shown in FIG. 3, it is possible to ensure a lithium ion insertion site mainly in the void 14 indicated by a broken-line circle in FIG. When the electrode active material according to the present invention is used in a metal secondary battery, the cycle characteristics of the battery can be improved.

  Α in the general formula (1) is not particularly limited as long as it is a Group 8 to Group 12 element, but Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt Or it is preferable that it is Au. Of these, α is more preferably Ni, Fe, Co, or Cu.

  Β in the general formula (1) is not particularly limited as long as it is a Group 3 to Group 7 element, but Ti, V, Cr, Mn, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er , Tm, Yb, Lu, Hf or Ta are preferred. Of these, β is more preferably Ti, V, Cr, Mn, Zr or Hf.

  Γ in the general formula (1) is not particularly limited as long as it is a Group 13 to Group 15 element, but it is preferably a semiconductor element or a nonmagnetic metal element, and Al, Si, Ga, Ge, As, In, Sn, Sb, Tl, Pd or Bi are preferable. Of these, γ is more preferably Al, Ga, Ge, Sn, or Sb.

Specific examples of the half-Heusler compound having the composition represented by the general formula (1) include NiTiSn, NiZrSn, NiHfSn, CoTiSb, CoZrSn, and FeMoSb.
Among these half-Heusler compounds, the electrode active material of the present invention particularly preferably contains NiTiSn from the viewpoint of having a high energy density.

  The NiTiSn alloy can be manufactured by a known method. That is, nickel (Ni), titanium (Ti), and tin (Sn) are prepared in equimolar amounts, and a uniformly mixed mixture is fired to obtain a NiTiSn alloy.

2. Metal secondary battery The metal secondary battery of the present invention is a metal secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode. It contains a substance.

FIG. 1 is a schematic cross-sectional view showing an example of the metal secondary battery of the present invention. The battery according to the present invention is not necessarily limited to this example.
In the metal secondary battery 100, the negative electrode active material layer 2, the electrolyte 3, and the positive electrode active material layer 4 are sequentially stored in the negative electrode can 1 from the bottom of the can, and the positive electrode can 5 is fitted as a battery lid. ing. The negative electrode can 1, the negative electrode active material layer 2 and the electrolyte 3, and the positive electrode can 5 are insulated from each other by a gasket 6. As shown in FIG. 1, the spacer 7 and the spring 8 may be further laminated and brought into close contact with each other by applying pressure to the negative electrode active material layer 2, the electrolyte 3, and the positive electrode active material layer 4. In the example shown in FIG. 1, the negative electrode can 1 and the negative electrode active material layer 2 constitute a negative electrode, and the positive electrode can 5, the spring 8, the spacer 7, and the positive electrode active material layer 4 form a positive electrode. The negative electrode can 1 serves as a negative electrode current collector and a battery case, and the positive electrode can 5 serves as a positive electrode current collector and a battery case. Furthermore, the spacer 7 and the spring 8 also serve as a positive electrode current collector.
In the metal secondary battery 100 illustrated in FIG. 1, the negative electrode active material layer 2 includes the electrode active material described above. Hereinafter, a positive electrode, a negative electrode, an electrolyte, a separator and a battery case that are preferably used, which constitute the metal secondary battery according to the present invention, will be described in detail.

(Positive electrode)
The positive electrode of the metal secondary battery according to the present invention preferably has a positive electrode active material layer containing a positive electrode active material, and is usually connected to the positive electrode current collector and the positive electrode current collector. The positive electrode lead is provided.

(Positive electrode active material layer)
When the present invention is a lithium secondary battery, specific examples of the positive electrode active material used in the present invention include LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ . _{4, LiNiO 2, LiMn 2 O} 4, LiCoMnO 4, Li 2 NiMn 3 O 8, Li 3 Fe 2 (PO 4) 3 and _Li 3 _V 2 _{(PO 4)} may be mentioned ₃ or the like. Among these, in the present invention, LiCoO ₂ is preferably used as the positive electrode active material.

  The thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the metal secondary battery, but is preferably in the range of 10 to 250 μm, preferably in the range of 20 to 200 μm. It is particularly preferred that it is most preferably in the range of 30 to 150 μm.

  The average particle diameter of the positive electrode active material is, for example, preferably in the range of 1 to 50 μm, more preferably in the range of 1 to 20 μm, and particularly preferably in the range of 3 to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because. The average particle diameter of the positive electrode active material can be determined by measuring and averaging the particle diameter of the active material carrier observed with, for example, a scanning electron microscope (SEM).

The positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
The conductive material contained in the positive electrode active material layer used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved. For example, carbon such as acetylene black and ketjen black Black etc. can be mentioned. Moreover, although the content rate of the electroconductive material in a positive electrode active material layer changes with kinds of electroconductive material, it is in the range of 1 mass%-10 mass% normally.

  Examples of the binder included in the positive electrode active material layer used in the present invention include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the content ratio of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content rate of a binder is in the range of 1-10 mass% normally.

(Positive electrode current collector)
The positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer. Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Among these, aluminum and SUS are preferable. Moreover, as a shape of a positive electrode electrical power collector, foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.

  The method for producing the positive electrode used in the present invention is not particularly limited as long as it is a method capable of obtaining the positive electrode. In addition, after forming a positive electrode active material layer, in order to improve an electrode density, you may press a positive electrode active material layer.

(Negative electrode)
The negative electrode in the metal secondary battery according to the present invention contains the above-described half-Heusler compound as a negative electrode active material. The negative electrode preferably includes a negative electrode active material layer containing the half-Heusler compound, and generally includes a negative electrode current collector and a negative electrode lead connected to the negative electrode current collector.

(Negative electrode active material layer)
The negative electrode active material layer in the metal secondary battery according to the present invention contains the above-described half-Heusler compound. The half-Heusler compound may be used alone as a catalyst, or may be used as a mixture with another catalyst.
The other catalyst used for the negative electrode active material layer is not particularly limited as long as it can occlude / release metal ions. In the case where the present invention is a lithium secondary battery, examples of other catalysts in the negative electrode active material layer used in the present invention include metal lithium, alloys containing lithium elements, metal oxides containing lithium elements, Examples thereof include metal sulfides containing lithium element, metal nitrides containing lithium element, and carbon materials such as graphite. The negative electrode active material may be in the form of a powder or a thin film.
Examples of the alloy containing lithium element include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy. Moreover, as a metal oxide containing a lithium element, lithium titanium oxide etc. can be mentioned, for example. Examples of the metal nitride containing a lithium element include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. Further, lithium coated with a solid electrolyte can also be used for the negative electrode layer.

The negative electrode active material layer may contain only the negative electrode active material, or may contain at least one of a conductive material and a binder in addition to the negative electrode active material. For example, when the negative electrode active material has a foil shape, a negative electrode active material layer containing only the negative electrode active material can be obtained. On the other hand, when the negative electrode active material is in a powder form, a negative electrode layer having a negative electrode active material and a binder can be obtained. Note that the conductive material and the binder are the same as the contents described in the above-mentioned “positive electrode active material layer”, and thus the description thereof is omitted here.
Although it does not specifically limit as a film thickness of a negative electrode active material layer, For example, it is preferable to exist in the range of 10-100 micrometers, especially in the range of 10-50 micrometers.

  The electrode active material layer of at least one of the positive electrode and the negative electrode can also be configured to contain at least an electrode active material and an electrode electrolyte. In this case, as the electrode electrolyte, a solid electrolyte such as a solid oxide electrolyte or a solid sulfide electrolyte, a polymer electrolyte described later, a gel electrolyte, or the like can be used.

(Negative electrode current collector)
As the material and shape of the negative electrode current collector, the same materials and shapes as those of the positive electrode current collector described above can be employed.

(Electrolytes)
The electrolyte in the metal secondary battery according to the present invention is held between the positive electrode active material layer and the negative electrode active material layer and has a function of exchanging metal ions between the positive electrode active material layer and the negative electrode active material layer.
As the electrolyte, an aqueous electrolyte and a non-aqueous electrolyte can be used.

As the non-aqueous electrolyte, a non-aqueous electrolyte solution and a non-aqueous gel electrolyte can be used.
The type of non-aqueous electrolyte is preferably selected as appropriate according to the type of conductive metal ion. For example, a non-aqueous electrolyte solution for a lithium secondary battery usually contains a lithium salt and a non-aqueous solvent. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ ; LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ (Li-TFSI), LiN (SO ₂ C ₂ F ₅ ) Organic lithium salts such as ₂ and LiC (SO ₂ CF ₃ ) ₃ can be mentioned. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl carbonate, butylene carbonate, γ-butyrolactone, and sulfolane. , Acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO) and A mixture thereof can be exemplified. The concentration of the lithium salt in the nonaqueous electrolytic solution is, for example, in the range of 0.5 to 3 mol / L.
In the present invention, examples of the non-aqueous electrolyte or non-aqueous solvent include N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP13TFSI), N-methyl-N-propylpyrrolidinium. Bis (trifluoromethanesulfonyl) imide (P13TFSI), N-butyl-N-methylpyrrolidinium Bis (trifluoromethanesulfonyl) imide (P14TFSI), N, N-diethyl-N-methyl-N- (2-methoxyethyl) Low volatile liquids such as ionic liquids such as ammonium bis (trifluoromethanesulfonyl) imide (DEMETFSI), N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide (TMPATFSI) Using Good.

Further, the non-aqueous gel electrolyte used in the present invention is usually a gel obtained by adding a polymer to a non-aqueous electrolyte solution. For example, the non-aqueous gel electrolyte is obtained by adding a polymer such as polyethylene oxide (PEO), polyacrylonitrile (PAN), or polymethyl methacrylate (PMMA) to the above-described non-aqueous electrolyte and gelling. Can do. As the non-aqueous gel electrolyte of the lithium secondary battery, for example, a LiTFSI (LiN (CF ₃ SO ₂ ) ₂ ) -PEO-based non-aqueous gel electrolyte can be used.

It is preferable that the type of the aqueous electrolyte is appropriately selected according to the type of the conductive metal ion. For example, as an aqueous electrolyte solution for a lithium secondary battery, a solution containing lithium salt in water is usually used. Examples of the lithium salt include lithium salts such as LiOH, LiCl, LiNO ₃ , and CH ₃ CO ₂ Li.

  A solid electrolyte can be further mixed and used in the aqueous electrolyte and the non-aqueous electrolyte. As the solid electrolyte, for example, a Li—La—Ti—O based solid electrolyte can be used.

(Separator)
A separator can be used for the metal secondary battery of the present invention. The separator is provided between the positive electrode current collector and the negative electrode current collector described above, and usually has a function of preventing contact between the positive electrode active material layer and the negative electrode active material layer and holding the solid electrolyte. . Examples of the material for the separator include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among these, polyethylene and polypropylene are preferable. The separator may have a single layer structure or a multilayer structure. Examples of the separator having a multilayer structure include a separator having a two-layer structure of PE / PP and a separator having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric. Moreover, the film thickness of the said separator is not specifically limited, It is the same as that of the separator used for a general metal secondary battery.
These materials that can be used for the separator can also be used as a support material for the electrolytic solution by impregnating the above-described electrolytic solution.

(Battery case)
The metal secondary battery according to the present invention usually has a battery case that houses a positive electrode, an electrolytic solution, a negative electrode, and the like. Specific examples of the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminate type.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited only to these Examples.

1. Preparation of electrode active material [Example 1]
First, 0.59 g of nickel (Ni), 0.48 g of titanium (Ti), and 1.19 g of tin (Sn) were uniformly mixed with a mortar. Next, the mixture was baked for 12 hours under an inert atmosphere to obtain the electrode active material of Example 1.

2. Structural analysis of electrode active material The chemical structure of the electrode active material of Example 1 was examined by powder X-ray diffraction (XRD). For the measurement, a powder X-ray diffractometer (Rint 2200, Rigaku) was used. Measurement conditions, using a Cu K _alpha line, the acceleration voltage was set to 40 kV, applied current was 40 mA.

  As a result of structural analysis by XRD, diffraction peaks could be confirmed near 2θ = 26 °, 30 °, 43 °, 53 °, 62 °, 69 °, 71 °, 79 °, and 85 ° in the XRD pattern. Therefore, it became clear that the main component of the electrode active material of Example 1 is a NiTiSn alloy having a half-Heusler structure. However, from the results of XRD structural analysis, it was found that about 40% of unreacted raw materials (Sn, Ni, and Ti) remained as impurities in the electrode active material of Example 1.

3. Production of Lithium Secondary Battery In order to measure the potential of the electrode active material based on lithium, lithium secondary batteries of Example 2 and Comparative Example 1 below were produced. Each of the following secondary batteries uses lithium metal as a negative electrode active material and each electrode active material as a positive electrode active material.

[Example 2]
First, the electrode active material of Example 1 was prepared as the positive electrode active material, PTFE as the binder, and acetylene black (product name HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material. Positive electrode active material: Binder: Conductive material = 70% by mass: 5% by mass: Mixed so as to be 25% by mass to prepare a positive electrode mixture.

Next, a positive electrode can and a negative electrode can were prepared. Lithium metal was bonded to the bottom of the negative electrode can to produce a negative electrode. The positive electrode mixture was applied to the inside of the positive electrode can to produce a positive electrode.
LiPF ₆ was dissolved in an ethylene carbonate-diethylene carbonate mixed solvent (EC-DEC) so as to have a concentration of 1 M to obtain an electrolytic solution. The electrolyte solution is sandwiched between the positive electrode and the negative electrode so as to be a negative electrode can-lithium metal-electrolyte solution-positive electrode mixture layer-positive electrode can, and is appropriately sealed with a gasket. A secondary battery was produced.
All the above steps were performed in a glove box under a nitrogen atmosphere.

[Comparative Example 1]
Example 2 except that a positive electrode mixture was prepared using lithium titanate (Li ₄ Ti ₅ O ₁₂ ; manufactured by Ishihara Sangyo Co., Ltd.) instead of the electrode active material of Example 1 above as the positive electrode active material. In the same manner, a lithium secondary battery of Comparative Example 1 was produced.

4). Evaluation of Charging / Discharging Characteristics of Lithium Secondary Battery For the lithium secondary batteries of Example 2 and Comparative Example 1, discharging was performed under the conditions of a current of 0.02 mA and a charging / discharging range of 0.5 to 3.0 V by the constant current charging / discharging method. Went.
FIG. 2 is a discharge curve of the lithium secondary battery of Example 2 and Comparative Example 1. In FIG. 2, the thick line graph represents the data of Example 2, and the thin line graph represents the data of Comparative Example 1.
As can be seen from FIG. 2, the graph of Example 2 has a voltage parallel portion (so-called plateau) at 0.8V. On the other hand, the graph of Comparative Example 1 has a plateau at 1.5V. That is, the graph of Comparative Example 1 has a plateau at a potential higher by 0.7 V than the graph of Example 2. From the viewpoint that the negative electrode material of the lithium secondary battery preferably has a lower potential with respect to lithium, the NiTiSn alloy used in Example 2 is more negative electrode material than Li ₄ Ti ₅ O ₁₂ used in Comparative Example 1. As you can see it is excellent.

As described in the description of the structural analysis, the electrode active material of Example 1 contains Sn as a raw material as an impurity. Since the capacity of 0.5 V or less is considered to contribute to Sn, by using a NiTiSn alloy from which the alloy is purified and impurities are removed, a lithium secondary battery using Li ₄ Ti ₅ O ₁₂ is used. This suggests that a lithium secondary battery having a large capacity can be obtained.

In FIG. 2, the plateau near 0.8 V in the graph of Example 2 has a half-Heusler structure in which the NiTiSn alloy used for the positive electrode of the lithium secondary battery of Example 2 has a site for inserting and desorbing lithium ions. It shows having. In general, Sn is known as an electrode material, but a reaction in which lithium ions are inserted and desorbed in Sn is not known, and a discharge curve of a battery using Sn as an electrode material has such a plateau. There is nothing. FIG. 2 shows that the lithium insertion potential of the NiTiSn alloy is 1.0 V and the lithium desorption potential is 0.5 V. From FIG. The capacity within the range of 6 to 0.9 V is considered to contribute to the NiTiSn alloy.
As described above, from the result of the XRD structure analysis, unreacted raw materials remain as impurities in the electrode active material of Example 1. In order to estimate how much this impurity contributes to the discharge reaction, the inventor of the present application examined the change in discharge capacity represented by the plateau near 0.8 V in the graph of Example 2, and the lithium ion of Example 2 was examined. The cycle characteristics of the secondary battery were evaluated.

About the lithium secondary battery of Example 2, it discharged by the conditions of current 0.02mA and charging / discharging range 0.5-3.0V by the constant current charging / discharging method, and the cycling characteristics of the lithium secondary battery of Example 2 Evaluated. Specifically, for the lithium secondary battery of Example 2, the discharge capacities of the first cycle, the second cycle, the fifth cycle, the tenth cycle, and the 50th cycle were measured.
Table 1 below shows the discharge capacity C _n (mAh) of the first cycle, the second cycle, the fifth cycle, the tenth cycle, and the 50th cycle represented by the plateau near 0.8 V of the lithium secondary battery of Example 2. / G) and the maintenance rate (%) of the discharge capacity. Here, the discharge capacity maintenance rate is a product of 100 and the ratio of the discharge capacity C _n of each cycle to the discharge capacity C ₁ of the first cycle, represented by a plateau near 0.8V.

As can be seen from Table 1, the discharge capacity of the first cycle represented by the plateau near 0.8 V is maintained at 90% or more after 50 cycles. This result shows that the lithium secondary battery of Example 2 has extremely high cycle characteristics as compared with a battery using a conventional electrode material containing Sn. It can also be seen that the impurities in the electrode active material of Example 1 hardly affect the cycle characteristics of the lithium secondary battery of Example 2.
In each cycle, the discharge capacity C _n is 40 mAh / g or less, which suggests that the discharge capacity can be drastically improved by further refining the NiTiSn alloy of Example 1. .

DESCRIPTION OF SYMBOLS 1 Negative electrode can 2 Negative electrode active material layer 3 Electrolyte 4 Positive electrode active material layer 5 Positive electrode can 6 Gasket 7 Spacer 8 Spring 11 α atom 12 β atom 13 γ atom 14 Air gap 100 Metal secondary battery

Claims (2)

An electrode active material comprising a half-Heusler compound having a composition represented by the following general formula (1).
αβγ General formula (1)
(In the general formula (1), α is an element selected from the group consisting of Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, and Au, and β is Ti, V, Cr, Mn, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, and Ta are elements selected from the group consisting of Al, Si, Ga , Ge, As, In, Sn, Sb, Tl, Pd, and Bi. A metal secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode,
The said secondary electrode contains the electrode active material of the said Claim 1, The metal secondary battery characterized by the above-mentioned.

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