JPH11345610A - Negative electrode for battery and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery with Mg as a negative electrode, having a high energy density and high cycle characteristic. SOLUTION: A negative electrode is used which has fine particles of magnesium or magnesium alloy with average particle size not more than 70 μm. In this case, magnesium amount in the magnesium alloy is preferably not less than 70 wt.%. In manufacturing, fine particles of magnesium or magnesium alloy are produced by a gas atomizing method, a ball mill method or a planetary ball mill method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for a battery using magnesium or a magnesium alloy as the negative electrode and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable devices and cordless devices, batteries as power sources thereof are required to have higher energy density. Li-ion batteries and nickel-metal hydride batteries have attracted attention in response to this demand. For higher energy density, metal Li
A battery system using as a negative electrode is considered to be promising.

As described above, L having a large weight energy density
By using i for the negative electrode, a battery with a high energy density can be obtained, but Li resources are present in dilution in seawater or rock salt water, and there is no prospect of cost reduction.

On the other hand, in a battery system using Mg for the negative electrode, two electrons move by the reaction of 1 mol of Mg on the negative electrode,
A battery with a high volume energy density that is theoretically higher than that of metal Li can be expected. Furthermore, it is abundant and inexpensive in terms of resources,
Since it is not harmful to the environment, it is a very promising negative electrode material. This is disclosed in JP-A-62-211861, JP-A-1-95469, or JP-A-4-2817.
No. 2, proposed.

[0005]

However, in this battery system, an electrochemically inactive substance is apt to be formed on the surface of the negative electrode, and it is difficult for a current to flow (polarization is large). Therefore, there is a problem that output characteristics, capacity, voltage and cycle characteristics are deteriorated. As a countermeasure, a method of pulverizing the alloy finely to increase the specific surface area and secure the current density can be considered. However, it is difficult to pulverize Mg having high ductility by a usual jet mill method or wet mechanical pulverization method, and when these pulverizations are performed, there is a problem that an oxide film is formed on the surface during the operation. For this reason, conventionally, only 10% to 2% of Mg, which is theoretically expected to have a high energy density,
The utilization rate of the negative electrode was only about 0%.

[0006]

Means for Solving the Problems To solve the above problems, the negative electrode for a battery according to the present invention is characterized by having magnesium particles or magnesium alloy particles having an average particle diameter of 70 μm or less.

At this time, In, Ga, Sn, Pb, C
It is effective to contain at least one of d, Mn, Co, and Zn.

[0008] It is effective to add Ni to the surface of magnesium particles or magnesium alloy particles.

At this time, it is desirable that the amount of magnesium in the magnesium alloy is 70% by weight or more.

As a method for producing the above materials, it is effective to produce magnesium particles or magnesium alloy particles by a gas atomization method, a ball mill method, or a planetary ball mill method.

A mixture of Ni in an amount of 10% by weight or less;
It is useful to add Ni by mechanofusion or plating.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies, it has been found that Mg or Mg alloy is produced by a gas atomizing method using an inert gas, or a mechanical alloying method such as a ball mill method or a planetary ball mill method in an inert gas. In addition, the polarization of the battery could be reduced, the utilization rate of the negative electrode was greatly increased, and a battery having excellent cycle characteristics could be realized.

When Mg is used for the negative electrode, a battery having a volume energy density that is theoretically higher than that of Li can be obtained. However, in practice, an electrochemically inactive coating such as an oxide coating or an organic coating is formed on the Mg surface. Therefore, in a battery using this, the polarization increases, the battery voltage decreases, the current density cannot be obtained, and a large energy density cannot be obtained.

In order to solve the above problems, it is considered effective to increase the specific surface area. But,
In a conventional jet mill or wet mechanical pulverization method, the ductility of Mg is large, so that it cannot be pulverized well. Even if pulverization is possible, an insulating film is formed on the Mg surface and polarization is increased. As a method for forming fine particles, a method in which fine particles are obtained in advance, such as a gas atomizing method using an inert gas, a ball mill method in an inert gas, or a planetary ball mill method (MA method) is effective. The average particle size is desirably 70 μm or less from the viewpoint of the negative electrode utilization factor and the output characteristics.

In addition, Mg, In, Ga, Sn, Pb, C
It was found that by using a magnesium alloy containing at least one of d, Mn, Co, and Zn, an oxide film or the like formed on the surface became a semiconductor, and the battery voltage, negative electrode utilization factor, and cycle characteristics could be significantly improved. At this time, 70% by weight or more of Mg is necessary for increasing the energy density. Furthermore, the presence of Ni on the surface of magnesium or a magnesium alloy further improved the electrochemical characteristics and cycle characteristics. As this means, a method of adding a small amount of Ni to the alloy composition, a method of applying a mechanical surface treatment such as a mechanofusion method, and a plating method are effective.

Hereinafter, embodiments of the present invention will be described in detail.

[0017]

EXAMPLES (Example 1) After Mg was melted in a high-frequency vacuum melting furnace, the molten metal was rapidly solidified by a gas atomizing method using Ar gas. The Mg fine particles obtained in this way are:
It was almost spherical and had an average particle size of 70 μm.

Next, an electrolyte obtained by dissolving 0.5 mol of magnesium perchlorate and 1 mol of water using dimethylacetamide (DMAA) as a solvent was added to the Mg powder to form a mixture, and a negative electrode paste was prepared. did. An air battery having the structure shown in FIG. 1 was manufactured using the negative electrode paste. FIG.
1 is an oxygen electrode (air electrode), 2 is a water-repellent film made of PTFE (polytetrafluoroethylene) which has gas diffusivity but does not allow liquid to pass through, 3 is an air intake hole, 4 is an oxygen electrode support and air 5 is a separator impregnated with an electrolytic solution, 6 is a gasket, and 7 is a negative electrode paste. Thus, a Mg negative electrode air battery (primary battery) having the same structure as the conventional zinc-air battery was manufactured. However, all of these assembling steps were performed in an Ar gas atmosphere.

Next, a discharge test was conducted at a discharge current of 1 mA / g and 1.2 V.
A discharge test was performed under cut conditions. As a battery of Comparative Example 1, an air battery having the same manufacturing method and structure was manufactured by using alloy fine particles obtained by grinding a cast Mg block by mechanical grinding and wet grinding to an average particle diameter of 70 μm as a conventional negative electrode. Further, as Comparative Example 2, a sample produced by a gas atomization method in the same manner as in this example was classified, and Mg having an average particle diameter of 75 μm was classified.
Particles were obtained. Using this, the same manufacturing method as the present embodiment,
An air battery having the structure was manufactured.

Table 1 shows a comparison between the average discharge voltage and the negative electrode utilization rate (actual capacity / theoretical capacity). As can be seen from Table 1, the air battery of this example had a higher average discharge voltage and a higher negative electrode utilization than the conventional mechanically pulverized Mg (Comparative Example 1). This is considered to be because strong oxidized film, hydroxylated film or organic film is formed on the surface by mechanically pulverized Mg, and polarization is increased.

When the particle size of Mg was large (Comparative Example 2), the reduction of the average discharge voltage was not so large, but the utilization rate of the negative electrode was greatly reduced. This is considered to be because the reduction in the specific surface area affected the rate characteristics. From this, it was found that an average particle size of 70 μm or less was effective.

[0022]

[Table 1]

(Example 2) Mg (100 mesh or less) 1
8 g and 2 g of Co (100 mesh or less) are inserted into a 1 L stainless steel ball mill pot, and a diameter of 19 g is placed thereon.
50 mm stainless steel balls and 60 stainless steel balls having a diameter of 12 mm were inserted. After the inside of the pot was replaced with argon, a ball mill (mechanical alloying) was performed at a rotation speed of 100 rpm for 10 days. MgCo recovered
The alloy fine particles had an average particle size of 21 μm. Using this alloy powder, an air battery having the same method and structure as in Example 1 was manufactured.

Next, a discharge test was conducted at a discharge current of 1 mA / g and 1.2 V.
As a result of performing a discharge test under cut conditions, the discharge average voltage was higher than in Example 1, and the negative electrode utilization rate was higher. This is considered to be because the conductivity of the oxide film formed on the surface of the negative electrode Mg alloy was improved and the polarization was suppressed.

(Embodiment 3) In the same manner as in Embodiment 2, Mg
(100 mesh or less) 16g and In (100 mesh or less)
4 g was inserted into a 1 L stainless steel ball mill pot and ball milled for 10 days. The recovered MgIn alloy fine particles had an average particle size of 35 μm. To 100 parts by weight of this Mg alloy powder, 3 parts by weight of PTFE powder as a binder was added, a small amount of DMAA was added to form a paste, applied to a punched metal core made of Mo, pressed, and then pressed in vacuum. At 180 ° C. for 30 minutes to melt the PTFE, thereby producing a negative electrode. An organic electrolyte in which 1 mol of magnesium perchlorate is dissolved in trimethyl sulfoxide (TMSO) is used as the electrolyte, and FeS _2, which is sufficiently larger than the capacity of the negative electrode, is used for the positive electrode. did.

Next, a charge / discharge test was performed at a charge current of 5 mA / g for 120 minutes.
% Charge and discharge were performed under the conditions of 5 mA / g and 1.2 V cut. As Comparative Example 3, a negative electrode-regulated nonaqueous electrolyte battery was produced in the same manner, using the same weight of MgIn alloy plate as the negative electrode. Table 1 shows the average discharge voltage, the negative electrode utilization rate, and the capacity retention rate (50 cycle capacity / initial capacity). Table 1 shows that the battery of the present example has a higher average discharge voltage than the MgIn alloy plate negative electrode,
It was found that the negative electrode utilization rate was high and the capacity retention rate was also high.

Example 4 Mg (100 mesh or less) 1
Example 2 using 4 g and 6 g of In (100 mesh or less)
Alloying was performed under the same manufacturing conditions as in Example 1. Thereafter, a negative electrode regulated liquid-rich battery was manufactured in the same manner as in Example 3. Also, for comparison, a battery (Comparative Example 4) having a negative electrode obtained by alloying 14 g of Mg with 7 g of In added (33% by weight) was also prepared.

As can be seen from Table 1, the negative electrode utilization of the battery of this example was slightly lower than that of Example 3, but the capacity retention was improved. In Comparative Example 4, the negative electrode utilization rate was significantly reduced. This is because the decrease in the amount of Mg in the alloy led to a decrease in the capacity, and it is considered that the amount of Mg is required to be 70% by weight or more.

(Examples 5 to 9) In Example 3, Ga, Sn, Cd, Mn, and Zn were added in place of In in an amount of 15% by weight based on the amount of Mg. Thereafter, ball milling was performed under the same conditions to produce various Mg alloys. A battery rich in a negative electrode regulating liquid was prepared in the same manner as in Example 3 using the Mg alloy fine particles prepared in this manner as a negative electrode. Table 1 shows various battery characteristics. In each case, higher voltage, higher negative electrode utilization ratio, and higher capacity retention ratio were obtained than the alloy plate negative electrodes of Comparative Examples 5 to 9.

Example 10 Mg (100 mesh or less)
8 g and 2 g of Pb (100 mesh or less) are placed in a 500 cc stainless steel planetary ball mill pot, and 20 stainless steel balls having a diameter of 20 mm and a diameter of 10 m are placed therein.
40 stainless steel balls were inserted. After the inside of the pot was replaced with argon, a planetary ball mill was performed at a rotation speed of 2000 rpm for 2 days. The recovered MgPb alloy fine particles had an average particle size of 35 μm. This MgPb alloy powder 10
After adding 3 parts by weight of PTFE powder as a binder to 0 parts by weight, adding a small amount of dimethyl sulfoxide (DMSO) to form a paste, applying it to a punched metal core made of Mo, pressing it, The PTFE was melted by heating at 180 ° C. for 30 minutes in a vacuum to produce a negative electrode. The electrolyte is D
The organic electrolyte containing dissolved magnesium perchlorate of 0.6mol to MSO, sufficiently larger capacity than the negative electrode capacity to the positive electrode Mo ₆
With S _8, to produce a liquid-rich negative cell regulation.

Next, in the same manner as in Example 3, the charging current was 5 mA / g, and
A charge / discharge test was performed under the conditions of 20 mA charge / discharge and 5 mA / g, 1.2 V cut. As Comparative Example 10, the battery characteristics when an MgPb alloy plate material was used for the negative electrode are shown in Table 1. Table 1
From this, it was found that the battery using the negative electrode of this example was superior in all respects to the plate material.

(Embodiment 11) In the same manner as in Embodiment 3, M
MgIn alloy powder having an average particle diameter of 35 μm was prepared from g16g and In4g by a ball mill.

Next, 15 g of the alloy particles were added with a particle size of 30 n.
1.3 g of Ni fine particles of m m were subjected to mechanofusion treatment in argon (using AM-15F manufactured by Hosokawa Micron, gap 1 mm, 1200 rpm, 15 minutes), and MgIn
Ni fine powder was uniformly adhered to the surface of the alloy particles.

Thereafter, 3 parts by weight of PTFE powder as a binder were added to 100 parts by weight of the composite particles, and a small amount of dimethylformamide (DMF) was added to form a paste. After coating and pressing, PTFE was melted by heating at 180 ° C. for 30 minutes in a vacuum to prepare a negative electrode. An organic electrolyte obtained by dissolving 1.5 mol of magnesium perchlorate in a mixed solvent of DMF and DMSO at a volume ratio of 1: 1 was used for the electrolyte, and V ₂ O ₅ having a capacity sufficiently larger than the capacity of the negative electrode was used for the positive electrode. A negative electrode regulated liquid-rich battery was produced.

Next, in the same manner as in Example 3, a charge / discharge test was performed at a charge current of 5 mA / g at 120% charge, and discharge was performed at 5 mA / g and 1.2 V cut. From Table 1, it was found that the battery using the negative electrode of this example was superior to Example 3 in which Ni was not treated in terms of cycle characteristics.

(Embodiment 12) In the same manner as in Embodiment 3, M
MgInNi having an average particle size of 20 μm from g16g, In2g, and Ni2g (100 mesh) by a ball mill.
An alloy powder was produced.

As a result of composition analysis of the alloy particles by EPMA (electron beam microanalysis), it was found that the composition distribution was almost uniform in the charging ratio.

Thereafter, 5 parts by weight of PE (polyethylene) powder was added as a binder to 100 parts by weight of the composite particles.
A small amount of DMF was added to form a paste, which was applied to a punched metal core made of Ti, pressed, and then pressed in a vacuum.
The PE was melted by heating at 30 ° C. for 30 minutes to produce a negative electrode. The electrolyte used was an organic electrolyte in which 1 mol of magnesium perchlorate was dissolved in a mixed solvent of DMAA and DMSO at a volume ratio of 2: 1. The cathode used was V ₈ O ₁₃ having a capacity sufficiently larger than the anode capacity. A regulated liquid-rich battery was fabricated.

Next, in the same manner as in Example 3, a charge / discharge test was performed at a charge current of 5 mA / g at 120% charge, and discharge was performed at 5 mA / g and 1.2 V cut conditions. From Table 1, it was found that the battery of the present example was superior to Example 3 in which Ni was not treated in terms of cycle characteristics. However, if the Ni content exceeds 10% by weight,
Although the cycle deterioration was suppressed, there was a disadvantage that the energy density was suddenly increased.

Example 13 In the same manner as in Example 1, Mg was melted in a high-frequency vacuum melting furnace, and the molten metal was rapidly solidified by Ar gas atomization to produce fine particles having an average particle diameter of 30 μm.

Next, 200 ml of a saturated aqueous solution of nickel nitrate was used.
10 g of the Mg fine particles was added to the cc, and the mixture was thoroughly stirred and mixed at room temperature for 2 minutes, then collected with a filter paper, washed with water and vacuum-dried to obtain a negative electrode active material. EPMA confirmed the presence of Ni on the alloy surface. This is considered to be due to displacement plating of Mg and Ni. It is considered that the plating amount is about 5% by weight.

To 100 parts by weight of the Mg composite particles, 5 parts by weight of PE powder were added as a binder, and a small amount of DMAA was added.
Was added to form a paste, and applied to a punched metal core made of Cu. After pressing, the mixture was heated in a vacuum at 130 ° C. for 30 minutes to melt PE, thereby producing a negative electrode. The electrolyte is DMAA
Then, an organic electrolyte in which 0.8 mol of magnesium bromide was dissolved was used, and V ₈ O ₁₃ having a capacity sufficiently larger than the capacity of the negative electrode was used for the positive electrode to prepare a liquid-rich battery regulated by the negative electrode.

Next, in the same manner as in Example 3, a charge / discharge test was performed at a charge current of 5 mA / g at 120% charge, and discharge was performed at 5 mA / g and 1.2 V cut conditions. The battery using the negative electrode of this example is Ni
It was found that the cycle characteristics were superior to the untreated one.

In Examples 11 to 13, the amount of Ni added is preferably 10% by weight or less from the viewpoint of energy density.

[0045]

As is clear from the above examples, the negative electrode for a battery and the method for producing the same according to the present invention can significantly increase the specific surface area by using Mg or Mg alloy fine particles (with an average particle diameter of 70 μm or less) and increase the polarization. And the rate characteristics and the utilization rate of the negative electrode are improved.

Further, In, Ga, Sn, Pb, Cd, M
A semiconductor film is formed on the surface by alloying with n, Co, and Zn, and the cycle characteristics are improved as the current collecting property is improved.

By providing the Ni layer on the surface of the alloy fine particles, the electrochemical characteristics are further improved, and the energy density and the life are further increased. However, the amount of Mg must be 70% by weight or more from the viewpoint of capacity.

As a method for producing fine particles, a gas atomizing method or a mechanical alloying method such as a ball mill method or a planetary ball mill method is effective because a pulverizing step is not required. In particular, the mechanical alloying method is a very effective means for alloying dissimilar metals having greatly different melting points or alloying metals having low boiling points.

Further, as a means for Ni treatment on the surface of magnesium or a magnesium alloy, the alloy composition may be made of Ni.
, A mechanical surface treatment such as a mechanofusion method, or a plating method.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an air battery according to Embodiment 1 of the present invention.

[Explanation of symbols]

 Reference Signs List 1 oxygen electrode (air electrode) 2 PTFE water-repellent film 3 air intake hole 4 diffusion paper 5 separator 6 gasket 7 negative electrode paste 8 negative electrode container 9 positive electrode container

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 10/40 H01M 10/40 Z 12/06 12/06 D

Claims (6)

[Claims] 1. A negative electrode for a battery comprising fine particles of magnesium or fine particles of a magnesium alloy having an average particle size of 70 μm or less. 2. In, Ga, Sn, Pb, Cd, Mn,
The negative electrode for a battery according to claim 1, wherein the negative electrode contains at least one of Co and Zn. 3. The negative electrode for a battery according to claim 1, wherein Ni is added to the surfaces of the fine particles of magnesium or the fine particles of a magnesium alloy. 4. The negative electrode for a battery according to claim 1, wherein the amount of magnesium in the magnesium alloy is 70% by weight or more. 5. The method for producing a negative electrode for a battery according to claim 1, wherein magnesium fine particles or magnesium alloy fine particles are produced by a gas atomization method, a ball mill method, or a planetary ball mill method. 6. The method for producing a negative electrode for a battery according to claim 3, wherein Ni is added by mixing Ni in an amount of 10% by weight or less, mechanofusion method, or plating method.