JPH06290772A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To achieve extending a life of a battery by relaxing changing volume of a lithium alloy at charge/discharge time, suppressing the alloy from pulverization and also holding electrical continuity of the alloy even when generated its pulverization, so as to prevent negative pole capacity from deteriorating. CONSTITUTION:In a compound of a negative pole 1 consisting of lithium alloy, organic polymer binder and carbon power of 1m<2>/g or more 100m<2>/g or less specific surface, a carbon powder amount is set to a 10 to 20vol.% range. By the negative pole 1 prepared by applying this negative pole compound to a metal collector, a battery is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery, and more particularly to a long-life, high energy density lithium secondary battery suitable for use as a power source for portable equipment and electric vehicles.

[0002]

2. Description of the Related Art A non-aqueous secondary battery using an alkali metal as a negative electrode has a higher energy density than a conventional aqueous secondary battery. A typical example thereof is a lithium secondary battery, which is expected to be used as a power source for portable devices such as laptop computers, video cameras, mobile phones, and electric vehicles.

However, when a simple substance of lithium metal is used as the negative electrode active material, dendrite-like deposition frequently occurs during charging, that is, in the process of depositing lithium on the surface of the negative electrode. The dendrite-like lithium easily drops off from the electrode substrate and reacts with the electrolytic solution, resulting in a decrease in battery capacity. Further, penetrating the separator may cause an internal short circuit and damage the battery. Therefore, a lithium alloy is used as a negative electrode active material instead of a simple substance of lithium metal. By alloying the precipitated lithium with the alloy base metal, the precipitated lithium can be taken into the alloy, and the dendrite precipitation and the inactivation reaction with the electrolytic solution can be suppressed. As such an alloy, Li-A
1, Li-Cd, Li-In, Li-Sn, Li-P
b, Li-Bi and the like.

However, when using the above lithium alloy as a negative electrode active material, the volume of the lithium alloy expands and contracts due to charge and discharge, and stress is generated inside the alloy, so that the lithium alloy collapses and becomes fine. Has become. For example, Li-obtained by a method of electrochemically absorbing lithium in a thin aluminum plate (Japanese Patent Laid-Open No. 1-115062)
With Al alloy, when charging and discharging are repeated, cracks occur on the electrode surface and the electrode active material falls off from the substrate, and good cycle characteristics cannot be expected.

As a method of suppressing alloy refinement, addition of other component metals in addition to the main base metal has been studied. For example, in a Li-Al alloy, Mg is 15 to 65% by weight (JP-A-60-86760), and Zn is 15 to 65%.
An alloy containing 65 wt% (Japanese Patent Laid-Open No. 60-89069),
An alloy containing at least one of Cd, Bi, In, and Sn in a Li-Pb alloy (Japanese Patent Publication No. 3-64988) has been proposed.

However, since the lithium alloy in which the base metal and other component metals are added is also miniaturized, it is possible to prevent the refined alloy from falling off the electrode base body and to provide electrical continuity between the alloys or between the alloy current collectors. It is necessary to keep. Therefore, for example, a method of binding Zn to Li-Al (JP-A-1-778).
No. 70), a method of providing a coating film made of a polymer compound having an alkali metal ion conductivity on the surface of a negative electrode (Japanese Patent Laid-Open Publication No. Sho 60 (1999) -58242).
No. 63-289759) or a method of packing a negative electrode with a porous conductive member that is hard to form an alloy with lithium (Japanese Patent Laid-Open No. 63-1508).
No. 67) is proposed. However, since all of these are methods of suppressing the drop of alloy from the electrode surface,
It is not possible to suppress the deterioration of the contact between the alloys or between the alloy current collectors due to the refinement of the alloy inside the electrode, and it is not possible to obtain good cycle characteristics.

[0007]

The electrode of the secondary battery needs to be stable against repeated charging and discharging.
As described above, it is an object to suppress the refinement of the lithium alloy and to maintain the electrical continuity between the alloys or between the alloy current collectors even when the refinement of the alloy occurs. The present invention aims at prolonging the life of a battery by solving these problems.

[0008]

Means for Solving the Problems When a lithium alloy is used as a negative electrode, the volume change of the alloy occurs due to the absorption and desorption of lithium during charge and discharge, and stress is generated inside the alloy. When the alloy collapses and the collapsed alloy falls off from the negative electrode substrate, the negative electrode capacity decreases. When a plate-shaped lithium alloy negative electrode is used, the surface is cracked and the alloy is significantly dropped. In the negative electrode in which lithium alloy powder is pressure-molded, the lithium alloys are directly pressure-bonded to each other to maintain the shape of the negative electrode. Since this decreases, the current collecting ability of the active material deteriorates and the internal resistance of the battery increases.

In order to prevent the negative electrode capacity from decreasing, it is necessary to prevent the alloy from becoming finer and to maintain the electrical continuity of the alloy even if the alloy becomes finer. Therefore, a negative electrode made of lithium alloy powder, an organic polymer binder, and carbon powder as a conductive agent was examined. It is considered that the presence of these substances between the alloy particles can alleviate the change in alloy volume and maintain the electrical continuity of the alloy even if the alloy is miniaturized. In particular, the amount of carbon powder in the negative electrode mixture is considered to have a great influence on the relaxation of changes in the alloy volume and the retention of electrical continuity of the alloy.
Various studies were conducted on the amount of carbon powder in the negative electrode mixture.

As a result, the sum of the respective volumes V _Li , V _b , and V _c obtained from the true densities of the lithium alloy powder, the organic polymer binder, and the carbon powder in the negative electrode mixture, that is, the voids of the negative electrode mixture were removed. It was found that when V _c with respect to the actual volume V _neg (= V _Li + V _b + V _c ) is in the range of 10 to 20 vol%, the negative electrode capacity is small and good cycle characteristics are exhibited. Further, when the void amount of the negative electrode obtained by pressure molding of the lithium alloy powder alone was examined, it was found to be in the range of 15 to 25 vol%, and the addition amount of the carbon powder was 10 vol.
It has been found that if the content is less than 1%, the amount of carbon powder filling the space between the alloys is insufficient, and the alloys are excessively pressure bonded to each other, so that the volume change cannot be alleviated. At the same time, it was found that the ratio of the insulating organic polymer occupied between the alloys was increased and the current collecting property was lowered.
On the other hand, when the amount of carbon powder was 20 vol% or more, it was found that, during repeated charging and discharging, an excessive electrolytic solution penetrated into the secondary pores of the carbon powder to swell the electrode, rather reducing the current collecting property. .

The effect of the specific surface area of the added carbon powder was also examined. It was found that by adding the carbon powder having a specific surface area of 1 m ² / g or more and 100 m ² / g or less, the negative electrode capacity was reduced less and good cycle characteristics were exhibited. It was found that the carbon powder having a specific surface area of less than 1 m ² / g has a large particle size and is not highly dispersed in the negative electrode mixture, and thus has a low function as a conductive agent. On the contrary, when a carbon powder having a particle size of more than 100 m ² / g is used, as described above, the excessive electrolytic solution penetrates into the secondary pores of the carbon powder, the electrode swells, and the current collecting property decreases. It was

Further, as a lithium alloy, Li-A
1, Li-Cd, Li-In, Li-Sn, Li-P
With the above negative electrode using b, Li-Bi, a long-life battery was obtained. Among them, a battery prepared by using a negative electrode in which the proportion of carbon powder in the negative electrode mixture using Li-Pb is 5 to 10 wt% and the proportion of carbon powder in the negative electrode mixture using Li-Al is 10 to 20 wt% is the most. It showed good cycle characteristics.

[0013]

[Function] The specific surface area of the carbon powder in the negative electrode mixture composed of lithium alloy, organic polymer binder and carbon powder is 1 m ² /
g or more and 100 m ² / g or less, and the addition amount is 1
By setting the content in the range of 0 to 20% by volume, it is possible to alleviate the volume change of the alloy and suppress the refinement of the alloy, maintain good electrical continuity even when the alloy is refined, and prevent the negative electrode capacity from decreasing. Therefore, a battery having a long life can be obtained.

[0014]

【Example】

Example 1 A Li-Pb alloy having a chemical formula of Li _3.5 Pb was ground in a mortar,
It was sieved to obtain a powder having a particle size of 45 μm or less. to this,
A acetylene black (AB) having a specific surface area of 61 m ² / g and a xylene solution of an ethylene-propylene-diene terpolymer (EPDM) having a concentration of 40 g / l were added in the composition shown in Table 1 to prepare a paste-like negative electrode mixture. I got an agent. The occupied volume of AB was determined from the true densities of Li-Pb alloy, EPDM, and AB of 4.59, 1.95, and 0.86 g / cm ³ , respectively.

[0015]

[Table 1]

These negative electrode mixtures were applied to expanded metal, vacuum-dried, and then pressure-molded at 1 ton / cm ² to give a diameter of 15 mm.
It was cut into a disk shape to obtain a negative electrode.

Further, LiMn ₂ O ₄ is 80 wt%, AB is 15 wt%, and tetrafluoroethylene (PTFE) is 5 wt%.
0.2 g of the positive electrode mixture mixed well in the proportion of wt% was
2ton / cm ² using a 5mm piston and cylinder mold
A disk-type positive electrode was obtained by pressure molding with. A propylene carbonate solution having a lithium hexafluorophosphate concentration of 1 mol / l was used as an electrolytic solution, and a propylene non-woven fabric was used as a separator, and various batteries with different carbon powder amounts of coin-shaped negative electrode mixture shown in FIG. 1 were prepared. . In the figure, 1 is a negative electrode, 2 is a positive electrode, 3 is a separator, 4 is a negative electrode side case, 5 is a positive electrode side case, and 6 is a gasket.

Using the above batteries, the final charge and discharge voltages were set to 3.6 V and 2.0 V, respectively, and repeated charge and discharge was performed at a current of 1 mA. FIG. 2 shows the change in battery capacity at that time, and it was found that the batteries of specification numbers 2 and 3 can be charged and discharged satisfactorily. It was found that the negative electrodes of these batteries can suppress the refinement of the alloy and can well maintain the electrical continuity of the alloy. On the other hand, it was found that the battery of specification number 1 had a large internal resistance and the negative electrode had a poor current collecting property. Further, when the batteries of specification numbers 4 and 5 were disassembled, it was found that the thickness of the negative electrode was increased by 1.3 to 1.5 times, and the current collecting property was lowered due to the swelling of the electrode.

Example 2 As in Example 1, a Li—Al alloy of the chemical formula LiAl was crushed in a mortar and sieved to obtain a powder having a particle size of 45 μm or less. AB with a specific surface area of 61 m ² / g and a concentration of 40
A g / l EPDM xylene solution having the composition shown in Table 2 was added to obtain a paste-like negative electrode mixture. The occupied volume of AB was determined from the true densities of Li-Al alloy, EPDM, and AB of 1.7, 1.95, and 0.86 g / cm ³ , respectively.

[0020]

[Table 2]

These negative electrode mixtures were applied to expanded metal, vacuum-dried, and then pressure-molded at 1 ton / cm ² , φ15 mm.
It was cut into a disk shape to obtain a negative electrode. In the same manner as in Example 1, various batteries having different amounts of carbon powder in the coin-type negative electrode mixture were prepared.

Using the above batteries, the final charge and discharge voltages were set to 3.6 V and 2.0 V, respectively, and repeated charge and discharge was performed at a current of 1 mA. FIG. 3 shows the change in battery capacity at that time, and it was found that the batteries of specification numbers 8 and 9 can be charged and discharged satisfactorily. It has been found that the negative electrodes of these batteries can suppress the refinement of the alloy and can well maintain the electrical continuity of the alloy. On the other hand, it was found that the batteries of specification numbers 6 and 7 had a large internal resistance and the negative electrode had poor current collecting ability. Furthermore, when the battery of specification number 10 was disassembled, the thickness of the negative electrode increased by 1.2 times,
It was found that the swelling of the electrode reduced the current collecting ability.

Example 3 A Li-Pb alloy having a chemical formula of Li _3.5 Pb was crushed in a mortar and then sieved to obtain a powder having a particle size of 45 μm or less. To this, a carbon powder having a composition shown in Table 3 having different specific surface areas and a xylene solution of an ethylene-propylene-diene triple copolymer (EPDM) having a concentration of 40 g / l were added to obtain a paste-like negative electrode mixture. .

[0024]

[Table 3]

These negative electrode mixtures were applied to expanded metal, vacuum dried, and pressure-molded at 1 ton / cm ² to give a diameter of 15 mm.
It was cut into a disk shape to obtain a negative electrode. And Example 1
In the same manner as above, various batteries having different specific surface areas of carbon powder in the coin-shaped negative electrode mixture were prepared.

Using the above batteries, the final charge and discharge voltages were set to 3.6 V and 2.0 V, respectively, and repeated charge and discharge was performed at a current of 1 mA. FIG. 4 shows changes in the battery capacity at that time, and it was found that the batteries of specification numbers 12, 13, and 14 can charge and discharge favorably. On the other hand, it was found that the battery of specification number 11 had a large internal resistance and the negative electrode had a poor current collecting property. Furthermore, when the battery of the specification number 15 was disassembled, it was found that the thickness of the negative electrode was increased by 1.6 times, and the current collecting property was lowered due to the swelling of the electrode.

Comparative Example A Li—Pb alloy having a chemical formula of Li _3.5 Pb was pulverized in a mortar and then sieved to obtain a powder having a particle size of 45 μm or less. φ
This powder was pressure-molded at 5 ton / cm ² using a 15 mm piston and cylinder mold to obtain a negative electrode. Then, in the same manner as in Example 1, a coin-type battery was created.

Using the above batteries, the charge / discharge end voltages were set to 3.6 V and 2.0 V, respectively, and charge / discharge was repeated at a current of 1 mA. FIG. 1 shows the change in the battery capacity at that time, and the battery capacity decreased after several cycles.

[0029]

EFFECTS OF THE INVENTION According to the present invention, the volume change of the lithium alloy during charging and discharging is alleviated to suppress the refinement of the alloy, and even if refinement occurs, the electrical continuity of the alloy is maintained and the negative electrode capacity is reduced. Can be suppressed. Therefore, the life of the battery can be extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of batteries manufactured in Examples 1 to 3 and Comparative Example.

FIG. 2 is a graph showing a change in capacity of batteries manufactured in Example 1 and Comparative Example.

FIG. 3 is a graph showing a change in capacity of the battery manufactured in Example 2.

FIG. 4 is a graph showing a change in capacity of the battery manufactured in Example 3.

[Explanation of symbols]

1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode side case, 5 ... Positive electrode side case, 6 ... Gasket.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Mamoru Mizumoto Inventor, Mamoru Mizumoto 7-1-1, Omika-cho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor, Tatsuo Horiba 7-chome, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (3)

[Claims] 1. A non-aqueous electrolytic solution containing an alkali metal ion,
In a secondary battery composed of a positive electrode reversibly occluding and releasing alkali metal ions and a negative electrode using an alkali metal alloy as an active material, the negative electrode is a negative electrode mixture composed of an alkali metal alloy powder, carbon powder and an organic polymer. It is composed of a metal current collector, and the specific surface area of the carbon powder is 1 m ² / g or more and 100 m ² / g or less, and the ratio of the carbon powder to the negative electrode mixture excluding the negative electrode voids is 10 to 20 vol%.
A non-aqueous secondary battery characterized in that 2. The alkali metal alloy in the negative electrode mixture is a lithium-lead alloy, and the proportion of carbon powder is 5 to 10 wt.
%, The non-aqueous secondary battery according to claim 1. 3. An alkali metal alloy in the negative electrode mixture is a lithium aluminum alloy, and the ratio of carbon powder is 1.
The non-aqueous secondary battery according to claim 1, which is 0 to 20 wt%.