JPH01267950A - Separator for battery - Google Patents

Abstract

PURPOSE:To provide a battery with less self-discharge and excellent charging/ discharging cyclic lifetime even though it is stored in high temp. atmosphere for a long period of time by fixing a terminal of polyolefin resin to the surface of polyolefin type resin fibers, and affixing a hydrophile organic substance having anti-electrolyte property. CONSTITUTION:Particles 3 of polyolefin resin are fixed to the surface of polyolefin resin fibers 2, and a hydrophile organic substance having anti- electrolyte property is dispersed on or covers the surfaces of these fibers 2 or particles 3. Accordingly the separator material is not dissolved or does not produce impurity ions even in an alkaline electrolyte with high temp. and high concentration, which prevents promotion of the self-discharging caused by separator material. Because particles 3 of polyolefin resin are fixed to the surfaces of the fibers 2, the electrolyte is retained in voids between the particles 3 and fibers 2 to enhance the liquid retaining property of the separator, which should enhance the charging/discharging cyclic lifetime.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a battery separator using a resinous non-woven fabric or woven fabric as the main constituent material, which improves battery storage characteristics, particularly self-discharge characteristics under high temperature atmosphere. and cycle life.

BACKGROUND OF THE INVENTION Generally speaking, battery separators have two important characteristics from the viewpoint of improving battery safety and charging/discharging characteristics: preventing short circuits between the positive and negative electrodes and retaining electrolyte. Furthermore, recently, batteries used as power supplies for portable devices are required to have improved storage characteristics, particularly self-discharge characteristics in high-temperature atmospheres, and improved charge/discharge cycle life. Generally, a factor that promotes self-discharge of a battery is that impurities within the battery often participate in the redox reaction of the positive and negative electrodes.

In particular, when stored in a high-temperature atmosphere for a long period of time, there is a problem that the separator, which is a constituent material of the battery, decomposes and promotes self-discharge.

For example, as conventional battery separators, especially for sealed batteries such as N1-Ctl electrolyte that uses alkaline electrolyte, non-woven fabrics and woven fabrics made of polyamide fibers are used in consideration of electrolyte retention and alkali resistance. It has been the most commonly used. However, polyamide fibers decompose when stored at high temperatures in highly concentrated alkaline electrolytes for long periods of time, or due to oxygen gas generated during overcharging.

There is a problem in that the generated impurity (No. 3) participates in the redox reaction of the positive and negative electrodes and promotes self-discharge.

Therefore, polyolefin resins such as polypropylene have attracted attention as separator materials that are stable in high-concentration alkaline electrolytes even when left in a high-temperature atmosphere for a long period of time.

However, polyolefin resins have a disadvantage that they have poor affinity for electrolyte solutions and poor electrolyte retention properties, which are important for separators, and the following proposals have been made regarding hydrophilic treatment.

(1) Attach a surfactant to the surface of the resin.

(2) Graft polymerization of a hydrophilic group (acrylic acid, etc.).

(3) The resin is irradiated with plasma to chemically adsorb 10HO groups and the like.

Problems to be Solved by the Invention However, in the above method, when the battery is stored at high temperature,
When the separator is in a high-temperature, highly concentrated alkaline electrolyte and comes into contact with oxygen gas generated at the positive electrode during overcharging, it can cause (1) the generation of impurity ions due to decomposition of the surfactant, (2) the generation of acrylic acid ions, etc. (3) Elimination of the -CHO group occurs, and these impurity ions participate in the redox reaction of the positive and negative electrodes to promote the self-discharge reaction of the active material. Further, due to the expansion of the positive and negative electrode plates due to repeated charging and discharging cycles, the separator is compressed, and the electrolyte in the separator is absorbed into the positive and negative plates. As a result, the internal resistance of the battery increases due to repeated charging and discharging cycles, resulting in capacity deterioration.

The present invention solves the above problems, and aims to provide a separator that can realize a battery with less self-discharge and excellent cycle life characteristics.

Means for Solving the Problems In order to achieve this object, the present invention immobilizes polyolefin resin particles on the surface of polyolefin resin fibers, and a hydrophilic organic substance having electrolyte resistance is attached to the fibers and particles. It is a structure in which the material is dispersed over or coated on the surface of the surface.

Function: With this configuration, the separator material does not decompose or generate impurity ions even in a high-temperature, high-concentration alkaline electrolyte, so that promotion of self-discharge caused by the separator material can be prevented.

In addition, because the polyolefin resin particles are immobilized on the surface of the fibers, the electrolyte is retained in the gaps between the particles and the fibers, improving the liquid retention properties of the separator, resulting in a shorter charge/discharge cycle life. It will improve.

Example The present invention will be explained below with reference to Examples.

An aggregate of polypropylene fibers having an average diameter of about 15 μm and an average size of 4Qj 1 ml is loosened and dispersed to form a nonwoven fabric. The obtained nonwoven fabric is passed between heated rolls at 150'C to heat-fuse each fiber to each other, and finally the thickness is 0.
．． 21+1. A polypropylene nonwoven fabric having a porosity of about 60% is obtained.

This nonwoven fabric was immersed in a solution containing carboxymethyl cellulose in which polypropylene powder with a particle size of 2 μm was dispersed, and in a solution containing polyvinyl alcohol in which the same polypropylene powder as above was dispersed, and dried at 160°C to form polypropylene fibers. Two types of hydrophilic separators having polypropylene particles immobilized on their surfaces are obtained. As a comparative example, the same nonwoven fabric was immersed in a solution containing only carboxymethyl cellulose and a solution containing only polyalkyl nonylphenyl ether as a surfactant and dried to obtain two types of separators having only hydrophilic properties for polypropylene fibers. Separate each separator in order a, b, c, d
shall be. FIG. 1 shows a schematic diagram of the obtained nonwoven fabric a. FIG. 2 shows a schematic diagram of nonwoven fabric C as a comparative example. In FIG. 1, 1 is carboxymethyl cellulose, 2 is polypropylene fiber, 3 is polypropylene particles, and 4 is a portion where the polypropylene particles are immobilized on the base material. Furthermore, the shaded area 6 in the same figure is the area where carboxymethyl cellulose coats the surfaces of the polypropylene fibers and immobilized particles 3. The nonwoven fabric b of this example is also the same as that shown in FIG.

A hydrogen storage alloy negative electrode that electrochemically absorbs and releases hydrogen as an active material and a nickel oxide positive electrode are spirally wound through the respective separators obtained above to form an electrolytic solution with a specific gravity of 1. The electrolyte solution saturated with lithium hydroxide was poured into the potassium hydroxide aqueous solution in step 3, and the capacity was 10oomAh.
We constructed various sealed nickel and hydrogen storage batteries that were sized for five people. As another comparative example, a similar sealed nickel-hydrogen storage battery was constructed using a conventional polyamide nonwoven fabric. After these batteries were fully charged, they were stored at 46°C for a predetermined period of time and then discharged to examine their remaining capacity. Third
The figure shows the relationship between storage period and remaining capacity ratio. The remaining capacity ratio is the ratio of remaining capacity to standard capacity. The relationship between the self-discharge ratio and the remaining capacity is expressed by the following equation.

Remaining capacity ratio (%) = 100 (%) - Self-discharge ratio (%)
) In addition, a battery prepared in a similar manner was charged for 4.6 hours with Hamam in an atmosphere of 20°C, and then the battery was charged at 0.
1.50mm. The charge/discharge cycle life characteristics were investigated under conditions of discharging up to Ov. FIG. 4 shows the relationship between the number of charge/discharge cycles and discharge capacity. Table 1 also shows the types of separators and the discharge capacity after 500 cycles.

(Left below) As is clear from Fig. 3, the sealed nickel-metal hydride storage batteries using separators according to the present invention and comparative example C, indicated by symbols a and b, have little self-discharge, with a temperature of 30% at 46°C.
It can be seen that it retains more than 60% of its capacity even after being stored for several days. Further, as shown in FIG. 4, in cases a and b of the present invention, which use a separator in which polypropylene powder is immobilized on fibers and imparted with hydrophilic properties, the discharge capacity does not decrease even after 500 cycles. However, Comparative Example C, which exhibits good self-discharge characteristics, suffers from a decrease in capacity due to charging and discharging cycles.

Carboxymethyl and polyvinyl alcohol, which impart hydrophilicity to polyolefin resins, have high electrolyte resistance, so they are difficult to decompose within the battery even if stored in a high-temperature atmosphere for a long period of time. Therefore, impurity ions are not generated by decomposition and the self-decomposition reaction of the active material is not promoted.
Self-discharge caused by decomposition of the separator material is suppressed. Moreover, FIG. 6 shows a state in which the electrolytic solution is held in the gap between the fiber 2 of the present invention a and the polypropylene particles 3 in a battery into which the electrolytic solution is injected. As described above, since the liquid retention property of the separator is improved, even if the separator is compressed due to expansion of the positive and negative electrode plates due to repeated charging and discharging, the state in which the electrolytic solution is retained in the separator is maintained. Therefore, capacity deterioration due to an increase in internal resistance of the battery can be prevented.

Note that although this example describes only nonwoven fabrics, similar effects can be observed for woven fabrics as well.

A similar effect can also be obtained by using a separator made of a nonwoven or woven fabric made of fibers to which particles of polyolefin resin are fixed on the surface of polyolefin fibers and carboxymethyl cellulose or polyvinyl alcohol is attached.

Effects of the Invention As described above, according to the present invention, a polyolefin resin terminal is fixed on the surface of a polyolefin resin fiber, and a hydrophilic organic substance having electrolyte resistance is attached, so that it can be used in a high temperature atmosphere. There is little self-discharge even after long-term storage,
The effect is that it is possible to provide a battery with excellent charge/discharge cycle life.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a nonwoven fabric in an embodiment of the present invention, and FIG.
The figure is a schematic diagram of a conventional nonwoven fabric, Figure 3 is a diagram of self-discharge characteristics of sealed nickel-metal hydride storage batteries using various separators, Figure 4 is a diagram showing life characteristics, and Figure 6 is a diagram of the implementation of the present invention. It is a figure which shows the state in which the electrolyte solution was held between the fiber and particle in an example. 1... Carboxymethyl cellulose, 2...
... Polypropylene fiber, 3 ... Polypropylene particle, 4 ... Fixed part of fiber and particle, 5.
... Carboxymethyl cellulose coating the particles, 6 ... Space portion, 7 ...
・Electrolyte solution. Name of agent: Patent attorney Toshio Nakao and 1 other person/-
--Ganosiho (thousand dimethyl death) L/I17-nu No. 1
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Claims (2)

[Claims] (1) A battery separator made of a nonwoven or woven fabric of fibers whose main constituent material is polyolefin resin, in which particles of the polyolefin resin are immobilized on the surface of the fibers, and which has electrolyte resistance. A battery separator in which a hydrophilic organic substance having a hydrophilic organic substance is dispersed on or coats the surfaces of the fibers and particles. (2) The battery separator according to claim 1, wherein the hydrophilic organic substance is a cellulose adhesive or polyvinyl alcohol.