JP2000012016A - Negative electrode for battery and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conductivity of alloy surfaces, greatly increase the utilization factor of a negative electrode, and provide a battery superior in cycle characteristics, by using as a negative-electrode active material, an Mg alloy which contains at least one kind of In, Ga, Ti, Cd, Mn, Co, and Sn. SOLUTION: When an Mg alloy containing Mg and at least one kind of In, Ga, Ti, Cd, Mn, Co, and Sn, is manufactured as a negative-electrode active material, it is preferable that the amount of Mg in the Mg alloy be 70 atom% or more in order to heighten the energy density. As an alloying method, a high-frequency melting method, or a mechanical alloying method such as a ball mill method and a planetary ball mill method in an inert gas, or a thermal diffusion method in which Mg is impregnated in a liquid metal and then thermally diffused, is effective. By adding Ni or Cu of 10 wt.% or less to surfaces of the Mg alloy, stability of electrochemical characteristics is increased. As a means therefor, there is a mechanical surface treatment method, a plating method, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a negative electrode using an Mg alloy as a negative electrode active material for a battery 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. To further increase the energy density, a battery system using metal Li for the negative electrode is considered to be effective.

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 seawater or rock salt water in dilution, and there is no prospect that mass production will reduce the cost.

On the other hand, in a battery system using Mg as the negative electrode, two electrons move by the reaction of 1 mole of the negative electrode Mg, so that a battery having a higher volume energy density than metal Li can be expected theoretically. Furthermore, since it is abundant and inexpensive in terms of resources and is not harmful in terms of the environment, it is a highly promising negative electrode material. For example, JP-A-62-121861, JP-A-1-95469 or JP-A-4-28172.
No. gazette.

[0005]

However, in this battery system, an insulator is easily formed on the surface of the negative electrode, and current hardly flows (large overvoltage). For this reason, there is a disadvantage that the 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, the conventional jet mill method or wet mechanical pulverization method has a problem in that an oxide film or a hydroxide film, which is a strong insulator, is formed on the surface during the operation, and the output characteristics are rather deteriorated. For this reason, in the past, the anode utilization rate was only about 10% to 20% of the theoretical capacity of Mg, which is expected to have a high energy density.

As a result of our intensive studies, we have found that Mg can be converted into In, Mg by mechanical alloying such as a high-frequency melting furnace method, a ball mill method in an inert gas, or a planetary ball mill method.
By producing an Mg alloy containing at least one of Ga, Tl, Cd, Mn, and Co, the conductivity of the alloy surface is improved, the overvoltage is reduced, the utilization rate of the negative electrode is greatly increased, and the cycle characteristics are also excellent. Battery realized.

[0007]

In order to solve the above problems, a negative electrode for a battery according to the present invention comprises In, Ga, Tl, C
M containing at least one of d, Mn, Co, and Sn
The g alloy is a negative electrode active material.

At this time, it is effective that the Mg content in the Mg alloy is 70 atomic% or more. It is effective that Ni or Cu is attached to the surface of the Mg alloy.

At this time, the amount of Ni or Cu attached is 1
It is effective that the content is 0% by weight or less.

[0010] The above-mentioned materials are produced by a high-frequency melting method,
Ball mill method, planetary ball mill method or heat diffusion method
It is characterized by producing a g alloy.

Further, Ni or Cu is adhered to the surface of the Mg alloy by a mechanofusion method or a plating method.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the negative electrode active material is made of Mg
A negative electrode comprising a Mg alloy containing at least one of n, Ga, Tl, Cd, Mn, Co, and Sn.

At this time, the Mg content in the Mg alloy is 70 atomic%.
It is desirable for the above to be higher for higher energy density. Further, Ni or Cu is added to the surface of the Mg alloy by 10%.
By adding the amount of not more than% by weight, the stability of the electrochemical characteristics is increased, and the cycle characteristics can be further improved. As this means, there are a mechanical surface treatment method such as a mechanofusion method and a hybridization method, and an electrochemical method such as a plating method.

The alloying method may be a high frequency melting method, a mechanical milling (MA) method such as a ball mill method in an inert gas, a planetary ball mill method, or a thermal diffusion method in which Mg is immersed in a liquid metal and then thermally diffused. The law is valid.

By using Mg for the negative electrode, a battery having a volume energy density higher than that of Li in theory can be obtained. But,
Actually, since an oxide film or a hydroxide film is formed on the Mg surface, the polarization (overvoltage) increases, the battery voltage decreases, the current density cannot be obtained, and a high energy density cannot be obtained. Therefore, increasing the specific surface area is considered to be an effective means. However, the conventional jet mill or wet mechanical pulverization method has a drawback that an insulating film is formed on the Mg surface and the overvoltage is increased. Therefore, Mg, In, Ga, T
When an Mg alloy containing at least one of l, Cd, Mn, Co, and Sn is used as a negative electrode active material, an oxide film or a hydroxide film formed on the surface becomes a semiconductor, and the overvoltage is reduced. It was also found that the cycle characteristics could be greatly improved. At this time, the Mg content was 70 atomic%.
The above is necessary for higher energy density. Further, by attaching Ni or Cu to the surface of the Mg alloy, the electrochemical characteristics were stabilized, and the cycle characteristics were further improved.

As an alloying method, since arc heating, electron beam melting, resistance heating, etc., heat non-uniformly, segregation tends to increase in low-boiling metals such as Mg.

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

[0018]

Example 1 After melting 80 atomic% of Mg and 20 atomic% of Co in a high-frequency vacuum melting furnace, this molten metal was poured into a water-cooled mold and rapidly solidified. After preparing the MgCo alloy (bulk) in this way, it was coarsely pulverized by a Joe Crusher mill in an argon gas atmosphere, and finely pulverized by an argon gas jet mill to an average particle size of 38 μm.

Next, dimethylacetamide (DMAA) and 0.6 mol of Mg were added to 100 parts by weight of the MgCo alloy powder.
A small amount of an electrolyte solution of (ClO ₄ ) ₂ was added, and 3 parts by weight of polytetrafluoroethylene (PTFE) powder was added as a binder to prepare a negative electrode paste. This negative electrode paste is
After being applied to a perforated metal core material made of o and pressed, it was heated in a vacuum at 180 ° C. for 30 minutes to melt PTFE, thereby producing a negative electrode. The electrolyte solution includes DMAA and 0.5 mol of Mg.
A non-aqueous electrolyte composed of (ClO ₄ ) ₂ and electrolytic manganese dioxide (MnO ₂ ) having a capacity sufficiently larger than the capacity of the negative electrode were used for the positive electrode, and a negative electrode-regulated liquid-rich battery was produced using a bipolar test cell.

Next, a charge / discharge test was conducted at a charge current of 2 mA / g for 120 minutes.
% Charge and discharge were performed under the conditions of 2 mA / g and 1.1 V cut. As Comparative Example 1, a bulk containing only Mg was produced by a casting method in the same manner as in Example 1, and Mg having an average particle size of 40 μm was obtained by mechanical pulverization.
Fine particles were prepared, a negative electrode was prepared in the same manner as in the example,
A battery was configured.

For comparison of the manufacturing method, the charging ratio of Mg and Co was set to be the same as that of the present embodiment, and an alloy prepared by an arc melting furnace, electron beam melting and resistance heating was used. Pulverization, production of a negative electrode, battery configuration, and characteristic evaluation were performed by the method (Comparative Examples 2 to 4).

Table 1 shows a comparison between the average discharge voltage, the negative electrode utilization rate (actual capacity / theoretical capacity), and the capacity retention rate (50 cycle capacity / initial capacity).

As can be seen from Table 1, the battery according to the present embodiment uses the conventional Mg (Comparative Example 1) and other manufacturing methods (Comparative Examples 2 to 4).
, The average discharge voltage was higher and the utilization rate of the negative electrode was greatly improved. This is considered to be because a strong oxide film or a hydroxide film is formed on the surface of the Mg negative electrode, and the overvoltage increases. On the other hand, it was found that in the arc melting method, the electron beam melting method and the resistance heating method, only Mg was initially melted and Co segregated. It is considered that the properties of Mg alone appeared strongly.

[0024]

[Table 1]

Example 2 A total of 20 g of Mg (100 mesh or less) and Mn (100 mesh or less) in a ratio of 70 atom% and 30 atom% was put into a 1 L stainless steel ball mill pot. went. The recovered MgMn alloy fine particles had an average particle size of 30 μm. Using this MgMn alloy powder, a nonaqueous electrolyte negative electrode regulating liquid-rich battery was produced in the same manner and in the same manner as in Example 1.

Next, a charge / discharge test was conducted at a charge current of 2 mA / g for 120 minutes.
% Charge and discharge were performed under the conditions of 2 mA / g and 1.1 V cut. Table 1 shows the average discharge voltage, the negative electrode utilization rate, and the capacity retention rate. For comparison, instead of Mn, Fe, Al, Si,
A battery in which Cr, Cu, and Ti were added at 30 at% each was produced, and a battery was constructed in the same manner as in this example, and the characteristics were evaluated (Comparative Examples 5 to 10).

From Table 1, it can be seen that the battery of this embodiment has an average discharge voltage,
It was found that the negative electrode utilization rate was high and the capacity retention rate was also high. On the other hand, the average discharge voltage and the negative electrode utilization rate were low in the Mg alloy having another composition such as Fe, and the effect of improving the characteristics by alloying was not recognized. Further, when the amount of Mn added exceeds 30 atomic%, the amount of Mg is reduced, so that the discharge capacity itself is significantly reduced. This tendency is due to Co other than Mn,
In, Ga, Tl, Cd and Sn were also observed.

Example 3 Mg plate (2 cm × 4 cm × 0.2 mm)
5 mm) was immersed in a Ga bath at 80 ° C. in an argon atmosphere for 8 hours.
Heat treatment was performed at 00 ° C. for 10 hours. As a result of composition analysis of the cross section by EPMA (electron beam micro analysis), it was found that Ga was diffused almost uniformly to the inside of the Mg plate. G
The amount of a was about 8 at%. A Ni lead was attached to this MgGa alloy plate by spot welding to form a negative electrode. With the same battery configuration as in Example 1, a non-aqueous electrolyte negative electrode regulation liquid-rich battery was produced.

Next, a charge / discharge test was performed at a charge current of 2 mA / g for 120 minutes.
% Charge and discharge were performed under the conditions of 2 mA / g and 1.1 V cut. For comparison, a battery using an Mg plate as the negative electrode was manufactured under the same manufacturing conditions (Comparative Example 11).

Table 1 shows the average discharge voltage, the negative electrode utilization rate and the capacity retention rate. Although the negative electrode utilization rate was lower than that of the pulverized products such as Example 1 and Example 2, compared to Comparative Example 11,
Significant improvement in properties was observed.

Example 4 In Example 3, In was used instead of Ga. 200 ° C in an argon atmosphere
After immersion in an In bath for 8 hours, the Mg plate was taken out and heat-treated at 500 ° C. for 10 hours in argon. Section E
As a result of composition analysis by PMA, it was found that In was diffused almost uniformly to the inside of the Mg plate. The amount of In was about 6 at%. A negative electrode regulated liquid rich battery was manufactured under the same configuration and conditions as in Example 3.

Table 1 shows the characteristics of various batteries. The results are higher voltage, higher negative electrode utilization rate, and higher capacity retention rate than the Mg plate negative electrode.

Example 5 Mg (100 mesh or less) and Cd (100 mesh or less) were put into a 500 cc stainless steel ball mill pot at a ratio of 90 at% and 10 at% in a total amount of 10 g. Twenty 20 stainless steel balls having a diameter of 20 mm and 40 stainless steel balls having a diameter of 10 mm were inserted. After the inside of the pot was purged with argon, a planetary ball mill was performed at a rotation speed of 2000 rpm for 3 days.
The recovered MgCd alloy fine particles had an average particle size of 25 μm. Using this MgCd alloy powder, a non-aqueous electrolyte negative electrode regulating liquid-rich battery was produced in the same manner and in the same manner as in Example 1.

Next, in the same manner as in the first embodiment, 1
A charge / discharge test was performed under conditions of 20% charge and discharge at 2 mA / g and 1.1 V cut.

Table 1 shows various battery characteristics, and it was found that the battery of this example was excellent in all aspects of the discharge voltage, the negative electrode utilization rate, and the capacity retention rate.

(Examples 6 and 7) An MgTl alloy (Tl5 at%) was prepared by the same high-frequency melting method as in Example 1,
An MgTI alloy powder having an average particle size of 32 μm was produced by mechanical pulverization.

Next, 15 g of the alloy particles were added with a particle size of 30 n.
1.3 g (8% by weight) of Ni fine particles having a m of 1.5 m were mechanofusion treated with argon (AM-15 manufactured by Hosokawa Micron).
F use, gap 1mm, 1200rpm, 15 minutes)
Then, fine Ni powder was uniformly attached to the surfaces of the MgTl alloy particles.

Using the MgTl alloy powder (Example 5) and the Ni-adhered composite particles (Example 6), a nonaqueous electrolyte negative electrode regulating liquid-rich battery was produced in the same manner and in the same manner as in Example 1.

Next, in the same manner as in Example 1, a charge / discharge test was performed at a charge current of 2 mA / g at 120%, and discharge was performed at 2 mA / g and 1.1 V cut. From Table 1, it was found that the cycle characteristics (capacity maintenance rate) of the battery were improved by attaching Ni to the alloy surface.

(Examples 8 and 9) Mg (75 at%) and Sn (25 at%) were melted in a high-frequency vacuum melting furnace, and then MgSn alloy foil was produced by a roll quenching method. Next, this alloy foil (5 mm x 5 cm x 0.2 mm)
A lead wire is attached to the cathode, this is used as a cathode, an aqueous solution of copper sulfate is used as a plating bath, and a Cu plate is used as an anode.
u was electrolytically plated (4% by weight). After washing with water and drying, a nonaqueous electrolyte negative electrode regulating liquid-rich battery (Example 9) having the same structure as in Example 1 was produced using this alloy foil as the negative electrode. A battery using the alloy foil before plating as a negative electrode was similarly manufactured (Example 8).

Next, in the same manner as in Example 1, a charge / discharge test was performed at a charge current of 2 mA / g at 120%, and discharge was performed at 2 mA / g and 1.1 V cut. MgSn alloy foil batteries have discharge voltage,
It was found that the negative electrode utilization rate and the capacity retention rate were all superior to the Mg plate battery (Comparative Example 11). It was found that the discharge voltage and the utilization rate of the negative electrode slightly decreased in the case of Cu plating, but the capacity retention rate was greatly improved.

[0042]

As is apparent from the above examples, the battery of the present invention and the method for producing the same are characterized in that In, Ga, T
By using a Mg alloy containing at least one of l, Cd, Mn, Co, and Sn, a semiconductor is formed on the surface and the resistance component is reduced. Therefore, the overvoltage is significantly reduced, and the rate characteristics and the anode utilization rate are improved. And the high energy density of Mg. In addition, N
By providing an i layer and a Cu layer, the electrochemical characteristics are stabilized,
The cycle characteristics are improved and the life is extended. However, the amount of Mg must be 70 atomic% or more from the viewpoint of capacity.

As a method for producing the alloy, a mechanical alloying method such as a high-frequency melting method, a ball mill method, and a planetary ball mill method or a heat diffusion method is effective. 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 treating Ni or Cu on the surface of the Mg alloy, there is a mechanical surface treatment such as a mechanofusion method or an electrochemical treatment such as a plating method for the alloy composition.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 10/40 H01M 10/40 Z (72) Inventor Shuji Ito 1006 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial In-house F term (reference) 4K018 BA07 BC16 BC20 BC22 KA38 5H003 AA01 AA02 AA04 BA00 BA01 BA07 BB00 BB02 BC01 BC05 BD04 5H014 AA02 BB01 BB08 BB12 EE05 HH01 5H029 AJ03 AJ05 AK02 AL11 AM01 AM02 C07 C02

Claims (6)

[Claims] 1. The method according to claim 1, wherein Mg is In, Ga, Tl, Cd, Mn,
A negative electrode for a battery, wherein a Mg alloy containing at least one of Co and Sn is a negative electrode active material. 2. The negative electrode for a battery according to claim 1, wherein the amount of Mg in the Mg alloy is 70 atomic% or more. 3. The battery negative electrode according to claim 1, wherein Ni or Cu is attached to the surface of the Mg alloy. 4. An adhesion amount of Ni or Cu is 10% by weight.
The negative electrode for a battery according to claim 3, wherein: 5. The method for producing a negative electrode for a battery according to claim 1, wherein the Mg alloy is produced by a high frequency melting method, a ball mill method, a planetary ball mill method or a thermal diffusion method. 6. The method for producing a negative electrode for a battery according to claim 3, wherein Ni or Cu is adhered to the surface of the Mg alloy by a mechanofusion method or a plating method.