JPH03190060A - Polyaniline battery - Google Patents

Abstract

PURPOSE:To ensure high utilization in a positive electrode even in high rate charge-discharge and to prevent decrease in charge-discharge capacity by forming the positive electrode out of a compressed molding of a mixture of polyaniline powder and titanium powder. CONSTITUTION:A positive electrode 7 is formed out of a compressed molding of a mixture of polyaniline powder and titanium powder, and a negative electrode 6 is made of lithium or a lithium alloy. As the positive electrode 7 is formed out of a compressed molding of a mixture of polyaniline powder and titanium powder, even if the surface of polyaniline particle gets undoped and high resistive, high electron-conductivity is ensured in the positive electrode 7 by the conductivity of the titanium powder, an insulated region which is not utilized for power generating reaction is rarely produced and decrease in charge-discharge capacity is restrained. Internal resistance is kept almost constant by electron conductivity even if discharge depth is varied. The preferable content of titanium powder in the positive electrode 7 is 5-20wt.% of the weight of the whole positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polyaniline battery using polyaniline as a positive electrode active material and lithium or a lithium alloy as a negative electrode active material.

[Conventional technology]

In general, polyaniline batteries use polyaniline as a positive electrode active material because polyaniline has the property of developing conductivity through ion doping, and utilizes changes in electrode potential caused by changes in the amount of ion doping in the conductor region. This allows it to function as a secondary battery.

In conventional polyaniline batteries, the positive electrode is
A polyaniline layer is formed on the surface of a net-like metal current collector by electrolytic oxidation polymerization, and then cut out to the required size, or a polyaniline powder obtained by electrolytic oxidation polymerization is compression molded. A molded body of the required size is used.

[Problem to be solved by the invention]

However, the conventional polyaniline batteries mentioned above have poor load characteristics, and although there is no problem when charging and discharging under light loads, when charging and discharging under heavy loads, the active material utilization rate decreases significantly and the charge/discharge capacity decreases. Furthermore, there was a drawback that the internal resistance changed depending on the depth of discharge, that is, the degree of discharge during one discharge.

In view of the above-mentioned circumstances, this invention improves the load characteristics so that even when charging and discharging under heavy loads, the decrease in charge and discharge capacity is small, and the internal resistance is almost constant regardless of the depth of discharge.
Therefore, it is an object of the present invention to provide a polyaniline battery that is highly practical and has fewer restrictions on usage.

[Means to solve the problem]

In order to achieve the above object, the inventors first investigated the causes of the above-mentioned difficulties in load characteristics in conventional polyaniline batteries, and found that when conventional batteries were charged and discharged under heavy loads, the positive electrode was activated. The surface of polyaniline, which is a material, becomes de-greyed and becomes a high-resistance material, resulting in the formation of many microscopic insulating parts inside the positive electrode, creating areas that are not used for battery reactions, and resulting in a decrease in the positive electrode utilization rate. It was found that this resulted in a decrease in discharge capacity.

As a result of further studies based on the above findings, the inventors found that by incorporating a specific conductive additive into the molded positive electrode using polyaniline powder, the above-mentioned insulating area could be improved even under heavy load charging and discharging. We have discovered that sufficient conductivity is ensured inside the positive electrode even if a He came up with an invention.

That is, the present invention includes a positive electrode made of a compression molded mixture of polyaniline powder and titanium powder, a negative electrode made of lithium or a lithium alloy, a separator interposed between these two electrodes, and a nonaqueous organic electrolyte. This relates to polyaniline batteries.

Further, in the present invention, a preferred embodiment is such that the titanium powder in the positive electrode accounts for 5 to 20% by weight of the entire positive electrode.

[Structure and operation of the invention]

As described above, in the polyaniline battery of the present invention, the positive electrode is formed of a compression molded mixture of polyaniline powder and titanium powder, so that the surface portion of the polyaniline particles is removed by charging and discharging under heavy loads. Even if the titanium powder becomes doped and has a high resistance, the conductive action of the titanium powder ensures high electronic conductivity inside the positive electrode. The internal resistance becomes extremely small, and even if the depth of discharge changes due to the above-mentioned electron conductivity, the internal resistance takes a substantially constant value.

Therefore, this polyaniline battery has almost no restrictions in terms of use due to light or heavy loads, and also exhibits stable internal resistance, so it has much higher practicality than conventional batteries.

The above titanium powder has excellent withstand voltage characteristics, has a large specific gravity and good dispersibility, and has no adverse effect on the mechanical strength of the molded positive electrode.
On the other hand, it has extremely advantageous properties as a conductive additive, giving good results to the energy density of the battery.

As for the particle size of such titanium powder, it is preferable that the average particle size is 20 μm or less (50 μm pass), and the amount used is 5 to 20% by weight of the entire positive electrode, that is, the total amount of the polyaniline powder. The range occupied by the active material is preferable; if it is too small, sufficient electronic conductivity cannot be ensured, and if it is too large, the amount of active material per unit volume of the positive electrode becomes too small, leading to deterioration of battery characteristics.

On the other hand, polyaniline powder, which is the positive electrode active material, is the same as that used in conventional positive electrodes made of compression molded bodies, and is a polymer synthesized by known polymerization methods such as chemical oxidation polymerization method and electrolytic oxidation polymerization method. Powders, especially those with an average particle size of 0.
Powder of about 1 to 2 μm is preferably used.

In order to form a positive electrode, the mixture of the polyaniline powder and titanium powder may be filled into a press mold according to a conventional method and compressed under pressure to form a compression molded body of a desired size.

The polyaniline battery of this invention belongs to lithium-based secondary batteries, and uses lithium or a lithium alloy as the negative electrode. Note that the lithium alloy herein includes not only metallurgical alloys but also those obtained by crimping and electrifying lithium foil and other metal foils such as aluminum.

As the non-aqueous organic electrolyte, LiBF, LiC' Oa
, L i Bφ4 (φ is a phenyl group), LiPF6
A lithium ion conductive electrolytic solution prepared by dissolving a lithium salt such as , LiAsFb, etc. in a non-aqueous organic solvent such as propion carbonate, T-butyrolactone, dimethoxyethane or dioxolane is suitable.

FIG. 1 shows an example of the structure of a polyaniline battery of the present invention applied to a button type battery.

In this figure, ■ is a battery case, in which a negative terminal plate 2 and a positive terminal plate 3, both plate-shaped, face each other, and their peripheral edges are covered with an annular gasket 4 made of an elastic insulating material such as synthetic rubber or synthetic resin. A flat airtight container is constructed by fitting and crimping with the two interposed.

Inside this case l, there is a negative electrode 6 made of lithium or lithium alloy bonded to the negative electrode terminal plate 2 via a current collector 5 such as stainless steel net, and the above-mentioned compression molded body bonded to the positive electrode terminal plate 3. A positive electrode 7 and a separator 8 made of a porous insulating material such as a polypropylene nonwoven fabric interposed between both electrodes 6 and 7 are loaded in a state of being immersed in a non-aqueous organic electrolyte.

Note that the present invention is applicable not only to the illustrated button-type battery but also to polyaniline/lithium-based secondary batteries of various forms and structures.

〔Effect of the invention〕

According to this invention, by using a compression molded mixture of polyaniline powder and titanium powder as the positive electrode, a high positive electrode utilization rate is ensured even under heavy load charging and discharging, and there is very little decrease in charge/discharge capacity. It has excellent load characteristics, exhibits a nearly constant internal resistance regardless of the depth of discharge, and therefore has fewer restrictions in terms of use (a highly practical polyaniline battery can be provided).

In addition, since the positive electrode made of the above-mentioned compression molded body uses titanium powder as a conductive additive, its mechanical strength is good and there is no problem such as cracking when assembling the battery. For example, when carbon powder is used as a conductive additive, the mechanical strength of the positive electrode is insufficient.
Although there is a risk of damage to battery characteristics due to cracks during assembly, the present invention has the advantage of not having such concerns at all.

Furthermore, in the present invention, by setting the amount of the titanium powder used to account for 5 to 20% by weight of the entire positive electrode, the effects of the positive electrode utilization rate, internal resistance, mechanical strength, etc. can be improved by controlling other battery characteristics. It can be fully utilized without causing any decrease in performance.

〔Example〕

Hereinafter, the present invention will be explained in more detail by describing examples.

Example 14.0 g of aniline and 31.4 g of a 42% by weight HBF aqueous solution were dissolved in 190 g of water to prepare a solution A.

Separately, 0.12.6 g of (NH4)zCr t and 78.4 g of a 42 wt% HB F aqueous solution were added to 2 g of water.
00 g to obtain liquid B. This liquid B was added dropwise to the above liquid A over 2 hours while stirring while cooling the system to 2°C. After the dropping was completed, the mixed liquid was further heated at 2°C for 3 hours. Stirred.

Next, the black-rimmed precipitate formed in the liquid was filtered out using a glass filter, thoroughly washed with water and acetone, and the resulting powder was vacuum-dried at 80°C for 3 hours, and further at 100°C. The mixture was vacuum dried for 5 hours to obtain polyaniline powder. When this polyaniline powder was observed under an electron microscope, the particles were found to be granular particles with an average particle size of 0.5 μm.

This polyaniline powder 50μm and average particle size 20μm (5μm)
The mixture was thoroughly mixed with 5 cm of titanium powder (0 μm bath), and this mixture was compression molded by a conventional method to produce a pellet-shaped molded body with a diameter of 15 m and a thickness of 0.37 m. Next, the above molded body was used as a positive electrode, and a thickness of 0.15 m was used as a negative electrode.
A Li-A1 alloy with a diameter of 15 mm made by crimping a lithium foil of 2-
A non-aqueous organic electrolyte prepared by dissolving 1 mol of LiBF4 dried in a mixed solvent with dimethoxyethane in a volume ratio of 1:1 was used to create a 20 m diameter, total A button-shaped polyaniline battery with a thickness of 1.6 nm was produced.

Comparative Example A button-shaped polyaniline battery was produced in the same manner as in the example except that a compression molded body of polyaniline powder alone was used as the positive electrode.

For the batteries of the above examples and comparative examples, as a charge/discharge test, 50μ
Constant current charging was carried out at A, constant current discharging was carried out at various current values until the current reached 2.0 ■, and the discharge capacity at each discharge current value was measured. The results were as shown in Table 1 below.

In the conventional battery (comparative example) made of the compression-molded body shown in Table 1, the discharge capacity decreased significantly as the charge/discharge load increased, whereas in the battery of the present invention (example), the discharge capacity decreased significantly as the load increased. It can be seen that the decrease in discharge capacity is very small and a high positive electrode utilization rate is maintained.

Next, the batteries of the above Examples and Comparative Examples were charged at a constant current of 5oOμA until the positive electrode became 3.4V with respect to the negative electrode, and then discharged at a constant current of 0.1mA. When the internal resistance (AC resistance of IKH2) was measured, the results shown in Table 2 below were obtained.

Table 2 From the results in the upper table, it can be seen that the battery with the conventional configuration (comparative example) has a large change in internal resistance depending on the depth of discharge, whereas the battery of the present invention (example) has a large change in internal resistance depending on the depth of discharge. It can be seen that the internal resistance value is almost constant regardless of the depth of discharge.

Next, we used the cracking strength measuring device shown in Figure 2 to measure how quickly cracks occur when a load is applied to the positive electrodes from the compression molded bodies used in the batteries of the above Examples and Comparative Examples. Upon investigation, the results shown in Table 3 below were obtained.

In addition, in Figure 2, 11 is a weight, 12 is a weight plate, and 13
14 is a dial gauge (load meter), 14 is a load rod, 15 is a positive electrode made of a compression molded product, and 16 is a sample support stand, and the sizes of the tip of the load rod 14, the positive electrode 15, and the support stand 16 are as shown in the figure. be.

Despite Table 3, its mechanical strength is not impaired in any way;
It is clear that the product maintains good mechanical strength comparable to that of a compression molded product made of polyaniline powder alone.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an example of the structure of a polyaniline battery according to the present invention, and FIG. 2 is an explanatory view showing a cracking strength measuring device for a positive electrode made of a compression molded body.

Claims (2)

[Claims] (1) A positive electrode made of a compression molded mixture of polyaniline powder and titanium powder, a negative electrode made of lithium or a lithium alloy, and a separator interposed between these two electrodes;
A polyaniline battery comprising a non-aqueous organic electrolyte. (2) Titanium powder in the positive electrode is 5 to 20% by weight of the entire positive electrode
The polyaniline battery according to claim 1, wherein the polyaniline battery comprises: