JP2011023358A - Nickel-metal hydride battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a drop of a discharge voltage and reduction of a battery output by suppressing an increase of polarization of a battery caused by a separator during high rate discharge. <P>SOLUTION: This nickel-metal hydride battery includes a hydrophilic nonwoven fabric separator made of polyolefin, and the separator is contained in a battery case in a pressed state by a positive electrode plate and a negative electrode plate. In this separator in the pressed state by the positive electrode and the negative electrode, the accumulated porous volume of pores each of which has a pore size of not larger than 40 μm is 10-30% of the whole porous volume. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nickel metal hydride battery.

  Nickel / metal hydride batteries with a positive electrode mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy have high energy density and excellent high-rate discharge performance. Commercially available as a power source. In a general nickel-metal hydride battery configuration, a non-woven separator is disposed between the positive electrode and the negative electrode. As a material for the separator, a polyolefin resin excellent in alkali resistance and subjected to a hydrophilic treatment is preferable. When such a hydrophilic polyolefin nonwoven fabric is used as a separator, the positive electrode and the negative electrode are electrically insulated to prevent an internal short circuit, and the electrolyte is held in the pores between the fibers of the nonwoven fabric, and the charge / discharge reaction Can be advanced. As the pore diameter of the pores between the fibers becomes smaller, the holding power of the electrolytic solution becomes higher, and it is possible to prevent the separator from draining. However, particularly when the battery is discharged at a high rate, the separator interposed between the positive electrode and the negative electrode increases the polarization of the battery, and the discharge voltage is lowered, and the output of the battery may be lowered.

  As described above, the conventional technique has a problem that the polarization of the battery is increased by the separator. In the future, in order to improve the output of the nickel-metal hydride battery, the polarization caused by the nonwoven fabric separator must be suppressed. Therefore, an object of the present invention is to reduce the polarization of a battery due to a separator.

  In order to solve the above-mentioned problems, the present invention provides a nickel-metal hydride battery comprising a polyolefin nonwoven fabric separator subjected to a hydrophilic treatment by at least one of an acrylic acid graft polymerization treatment or a fluorine gas treatment. In addition, the nickel-metal hydride battery is characterized in that the cumulative pore volume of pores having a pore diameter of 40 μm or less in the separator is 10 to 30 percent with respect to the total pore volume.

  According to the present invention, the polarization of the battery due to the separator can be reduced.

It is a figure which shows the pore size distribution in the separator measured by the mercury intrusion method. It is a figure which shows transition of the discharge capacity of a nickel metal hydride battery.

  The nickel-metal hydride battery of the present invention is a nickel-metal hydride battery comprising a polyolefin nonwoven fabric separator subjected to hydrophilic treatment by at least one of acrylic acid graft polymerization treatment or fluorine gas treatment, In the separator, the accumulated pore volume of pores having a pore diameter of 40 μm or less is 10 to 30% with respect to the total pore volume, and by using such a separator, the cycle life The output at the time of high rate discharge of the alkaline storage battery can be improved without degrading the performance.

  There are various reasons for this, but it can be generally explained as follows. That is, in the charge / discharge reaction, ion transfer between the positive electrode and the negative electrode is indispensable. In a general alkaline storage battery, this is performed through an electrolytic solution retained in the pores of the nonwoven fabric separator. If there are many pores in the nonwoven fabric, the path of the electrolyte solution between the positive electrode and the negative electrode becomes longer, ion migration becomes difficult, and polarization is considered to increase. In addition, when the electrolyte path becomes longer, the electrical resistance between the positive electrode and the negative electrode increases, which is considered to be a factor for increasing the polarization.

  In the non-woven fabric in the nickel-metal hydride battery, if the cumulative void volume with a pore diameter of 40 μm or less is set to 30% or less with respect to the total void volume, ion migration can be sufficiently performed even during high rate discharge, An increase in polarization can be suppressed. In addition, when the cumulative pore volume with a pore diameter of 40 μm or less is set to be 10% or more with respect to the total pore volume, the pores retain sufficient electrolyte even after repeated charge / discharge cycles. It is considered that an increase in internal resistance due to withering can be suppressed. In addition, the hole diameter said by this invention is a hole diameter computed by the mercury intrusion method.

  As the material of the separator, it is preferable to use polyolefin fibers having a fiber diameter in the range of 10 to 30 μm because it is suitable for the production of the nonwoven fabric having the above-mentioned pore diameter distribution. Moreover, as a structure of a nonwoven fabric, when a nonwoven fabric with a fabric weight of 45-75 g / m2 thickness 130-200 micrometers is sufficient, since sufficient air permeability is obtained and an internal short circuit can be prevented, it is suitable. Also, when polyolefin resin is used as the material for the nickel-metal hydride battery separator, it is necessary to perform a hydrophilic treatment, and as a means for this, it is possible to perform acrylic acid graft polymerization treatment or fluorine gas treatment. And it is preferable because it is economical.

  The invention is illustrated by examples. The positive electrode was produced by the following method. That is, to the nickel hydroxide powder obtained by coprecipitation of nickel, cobalt and zinc, a metal cobalt powder and an aqueous methylcellulose solution were added and kneaded to obtain a paste. The paste was filled into a foamed nickel porous body, pressed, dried, and cut into a predetermined size to obtain a positive electrode plate. The negative electrode was produced by the following method. That is, misch metal (hereinafter referred to as Mm. The main components are La: about 45 wt%, Ce: about 5 wt%, Pr: about 10 wt%, Nd: about 40 wt%), Ni, Co, Mn and An Al metal material was melted in a high-frequency induction furnace so as to have a desired composition, and was cast into a mold and solidified. The composition of the obtained alloy is MmNi3.6Co0.8Al0.4Mn0.2. The oxide layer on the surface of the alloy lump was removed by polishing. Thereafter, the alloy lump was pulverized and sieved to obtain a hydrogen storage alloy powder having an average particle size of several tens of μm. This hydrogen storage alloy powder, metal nickel powder and polyvinyl alcohol aqueous solution were kneaded to obtain a paste. The paste was applied to a nickel-plated perforated steel sheet, dried and pressed, and cut into a predetermined size to obtain a negative electrode plate.

  (Example battery 1) As the separator, a non-woven fabric made of polyolefin fibers having an average fiber diameter of about 20 μm was subjected to a hydrophilic treatment by acrylic acid graft polymerization. Here, the acrylic acid graft polymerization was performed by immersing the nonwoven fabric in an aqueous solution of acrylic acid (vinyl monomer) and a polymerization initiator and irradiating ultraviolet rays in a nitrogen atmosphere. The obtained separator has a thickness of about 0.18 mm and a basis weight of about 65 g / m 2. Three positive electrode plates and four negative electrode plates wrapped with a separator were alternately laminated to form an element. This element was inserted into a nickel-plated iron battery case (height 67 mm, width 17 mm, thickness 5.6 mm), and a 6 mol / l aqueous solution of KOH was poured into a sealed battery. Next, chemical conversion consisting of several times of charge and discharge was performed.

  (Example battery 2) The separator used was a nonwoven fabric made of polyolefin fibers having an average fiber diameter of about 10 μm and subjected to a hydrophilic treatment by acrylic acid graft polymerization. The thickness and basis weight of the obtained separator are almost the same as those of Example Battery 1. Except for the separator, a battery was constructed in the same manner as in Example Battery 1, and chemical charge / discharge was performed.

  (Example battery 3) As the separator, the same nonwoven fabric as in Example battery 1 was subjected to a hydrophilization treatment with fluorine gas. Here, the treatment of the fluorine gas was performed by leaving the nonwoven fabric in a mixture of fluorine gas and oxygen gas. Except for the separator, a battery was constructed in the same manner as in Example Battery 1, and chemical charge / discharge was performed.

  (Comparative Example Battery 1) The separator used was a nonwoven fabric made of polyolefin fibers having an average fiber diameter of about 50 μm and subjected to a hydrophilic treatment by acrylic acid graft polymerization. Except for the separator, a battery was constructed in the same manner as in Example Battery 1, and chemical charge / discharge was performed.

  (Comparative battery 2) The separator used was a nonwoven fabric made of polyolefin fibers having an average fiber diameter of about 5 μm and subjected to a hydrophilic treatment by acrylic acid graft polymerization. Except for the separator, a battery was constructed in the same manner as in Example Battery 1, and chemical charge / discharge was performed.

  (Comparative Example Battery 3) As the separator, a non-woven fabric similar to that of the present invention battery 1 was immersed in an aqueous solution of a nonionic surfactant and subjected to a hydrophilic treatment. Except for the separator, a battery was constructed in the same manner as in Example Battery 1, and chemical charge / discharge was performed.

  The pore size distribution of the separator was measured as follows. First, in order to reproduce the pore size distribution of the separator in the battery, the separator was sandwiched between two resin plates and pressed. In the complete battery, the degree of compression is set to the same level as the compression received by the separator from the electrode plate. And about the separator of the state which applied the pressure in this way, the hole diameter distribution was measured with the mercury intrusion type hole diameter distribution measuring apparatus (Shimadzu pore sizer 9310).

  The results are shown in FIG. In Example Battery 1, the cumulative pore volume with a pore diameter of 40 μm or less is about 12% of the total pore volume. In Example Battery 2, the cumulative pore volume with a pore diameter of 40 μm or less is about 26 with respect to the total pore volume. %Met. Moreover, although not shown in the figure, Example Battery 1, Example Battery 3 and Comparative Example Battery 3 all showed the same pore size distribution because they used the same base fabric separator.

  The discharge output characteristics of the battery were measured as follows. That is, for the battery after chemical conversion is completed, the first cycle is charged at 1 CmA (1000 mA) for 66 minutes, paused for 30 minutes, discharged to 1.0 V at 0.2 CmA (200 mA), and low rate discharge The discharge intermediate voltage was determined. In the second cycle, similarly to the first cycle, after charging and resting, discharging is performed at 3 CmA (3000 mA) until the voltage reaches 1.0 V, and a discharge intermediate voltage at high rate discharge is obtained. It was. In addition, the atmospheric temperature at the time of a charge / discharge test is 25 degreeC. The discharge intermediate voltage at the time of 0.2 CmA discharge and at the time of 3 CmA discharge is shown in Table 1 below.

  In Comparative Example Battery 2, the discharge intermediate voltage at the time of high rate discharge was low, but this was influenced by the fact that the separator of Comparative Example Battery 2 had many pores having a small hole diameter and decreased ion movement in the separator. it seems to do.

  The cycle life of the battery was measured as follows. First, the battery subjected to the high-rate discharge test was discharged to 1.0 V at 0.2 CmA. And charging / discharging cycle was performed on the conditions that it charged for 66 minutes at 1 CmA, and discharged to 1.0V at 1 CmA. The discharge capacity was confirmed under the condition that every 100 cycles, the battery was charged at 1 CmA for 66 minutes and discharged to 0.2 V at 0.2 CmA.

  FIG. 2 shows the transition of the discharge capacity. The life of the comparative example battery 1 was shorter than that of the example batteries 1 to 3, but this is because the separator of the comparative example battery 1 has many pores with large pore diameters, and the electrolyte in the separator tends to decrease. It is thought that this has influenced. In addition, the battery of Comparative Example 3 has a remarkably short life. This is considered to be because the effect of hydrophilization by the surfactant did not last for a long time, and it was found that acrylic grafting treatment or fluorine treatment excellent in durability was suitable for hydrophilizing the polyolefin nonwoven fabric.

  In the above embodiment, the nonwoven fabric made of fibers having a specific diameter is shown as an example, but the pore diameter distribution of the separator is shown in claim 1 of this application, regardless of the fiber having any fiber diameter. If it falls within the range, the same effect can be obtained. Further, in the above-described examples, the pore size distribution of the separator in the battery after chemical conversion is shown as an example. However, the pore size distribution of the separator in the battery after the charge / discharge cycle has progressed is shown in the claims. If it is within the range, the same effect can be obtained. The battery may be in a charged state or a discharged state.

  The method for producing the nonwoven fabric may be any method such as wet, dry, and melt blow. In the above-described embodiments, specific examples of the hydrophilization treatment method have been described. However, the acrylic acid graft polymerization conditions and the fluorine gas treatment conditions can be appropriately changed.

Claims (1)

  A nickel-metal hydride battery comprising a polyolefin nonwoven fabric separator having hydrophilicity and housed in a battery case in a state where the separator is pressed by a positive electrode plate and a negative electrode plate, the positive electrode plate and the negative electrode plate A nickel-metal hydride battery characterized in that the accumulated pore volume of pores having a pore diameter of 40 μm or less in the pressed separator is 10 to 30 percent of the total pore volume.