KR19980060826A - Nickel hydrogen secondary battery using pretreatment method of hydrogen storage alloy and pretreated hydrogen storage alloy as negative electrode - Google Patents

Abstract

The present invention provides a method for pretreatment of a hydrogen storage alloy by electrolysis using an alkaline solution under a reducing atmosphere, and a nickel-hydrogen secondary battery employing the hydrogen storage alloy pretreated by this method as a negative electrode. According to the pretreatment method of the present invention, the nickel hydride secondary battery employing the pre-treated hydrogen storage alloy as a negative electrode by generating hydrogen on the surface of the alloy and precipitating impurities which cause self-discharge beforehand has a large initial activation rate. Is increased.

Description

Nickel hydrogen secondary battery adopting pretreatment method of hydrogen storage alloy and pretreated hydrogen storage alloy as negative electrode

The present invention relates to a nickel-hydrogen secondary battery, and more particularly, to a nickel-hydrogen secondary battery in which the activation rate is greatly improved by employing a pretreatment method of a hydrogen storage alloy and a hydrogen storage alloy pretreated by the method as a negative electrode. will be.

Hydrogen can be used as a clean energy source, and when burned, it becomes water without generating carbon dioxide gas such as fossil fuel. By applying these characteristics electrochemically, hydrogen that has released (discharged) electrical energy is oxidized to water, and when it is given (charged) to electrical energy again, it can be returned to hydrogen. In this case, if oxygen is used as the anode, undesirable occurrence of hydrogen and oxygen mixing in the container occurs unless a special cell structure is used. Therefore, nickel is used as the anode and hydrogen storage alloy is used as the cathode to prevent this. This battery is a nickel-metal hydride battery.

In particular, nickel-hydrogen secondary batteries using a hydrogen storage alloy as a negative electrode active material are nickel zinc batteries or nickel due to the fact that the hydrogen storage alloy has no change in shape, high utilization rate, and specific gravity higher than cadmium or zinc. It can be said that it is important compared with the cadmium battery.

The nickel-hydrogen secondary battery includes an electrolyte formed of an alkaline aqueous solution and a separator having high hydrophilicity and stable in an alkaline electrolyte, in addition to a cathode formed of a nickel anode and a hydrogen storage alloy powder.

In such a nickel-hydrogen secondary battery, the cell reaction at the positive electrode and the negative electrode can be represented by the following formula:

Positive _{electrode: Ni (OH) 2 + OH} - → NiOOH + H 2 O + e -

Negative _{electrode: M + H 2 O + e} - → MH + OH -

Battery: Ni (OH) ₂ + M → NiOOH + MH

(In the formula, M means hydrogen storage alloy).

Hydrogen storage alloys are materials that can reversibly absorb and release hydrogen. The hydrogen storage alloy occludes the hydrogen produced at the cathode during charging and releases the hydrogen at the discharge. Refers to alloys that can occur.

Typical hydrogen storage alloys identified to date are A-type heat-generating metals and B-endothermic metals, which are largely based on AB type (eg TiFe), AB _{2 type} (eg ZrMn ₂ , ZrV ₂ and ZrNi ₂ ), AB ₅ systems (e.g. CaNi ₅ , LaNi ₅ and MmNi ₅ , where Mm refers to a collection of rare earth elements such as La or Ce called misch metals) and A ₂ B systems (e.g. Mg ₂ Ni and Mg ₂ Cu) Classified as

The requirements for such hydrogen storage alloys for batteries are

① should have good hydrogen storage capacity,

② The equilibrium pressure of hydrogen occlusion release should be about 0.1 to 5 atm,

③ corrosion resistance should be high.

In the active material as a hydrogen storage alloy constituting the negative electrode of a nickel-metal hydride battery, especially metal components such as cobalt, manganese, vanadium, etc. are decomposed well in an alkaline solution and present as impurities, and thus, when used for a long time in a strong alkali solution used as an electrolyte solution of a battery As the composition of the negative electrode is changed, durability decreases and battery performance decreases.

Therefore, in order to use the hydrogen storage alloy as a material of the electrode, it is necessary to remove the oxide film formed on the surface of the alloy in advance to change the surface composition of the alloy.

For this reason, conventionally, the hydrogen storage alloy as the negative electrode active material was put in an aqueous alkali solution, and then subjected to a pretreatment process of stirring with a glass rod at 80 ° C. for several hours or using mechanical stirring with a propeller. When the pretreatment is performed in this manner, the oxide film formed on the surface of the hydrogen storage alloy is removed, and specific metal components are eluted from the surface of the alloy to change the surface composition of the alloy. When the negative electrode of the nickel hydride battery is manufactured using the pre-treated hydrogen storage alloy, the performance of the nickel hydride battery may be improved.

In the case of the AB ₅ -based hydrogen storage alloy, the electrode prepared from the hydrogen storage alloy is sufficiently activated after only an initial 2-3 cycles through a pretreatment step of etching in an alkaline solution to exhibit a capacity. However, in the case of the AB ₂ -based hydrogen storage alloy containing Zr or Ti as a main component, activation is not performed smoothly only by the alkali pretreatment as described above, and thus charging and discharging of about 10 cycles to about 20 cycles is required.

Accordingly, a technical problem to be achieved in the present invention is a method of pretreating a hydrogen storage alloy to increase the initial activation rate of a nickel-metal hydride battery employing, as an anode, an AB ₂ -based hydrogen storage alloy based on Zr or Ti as an active material. And a nickel-hydrogen secondary battery employing the pretreated hydrogen storage alloy as a negative electrode as described above.

In order to achieve the above object, in the present invention, a method of pretreatment of a hydrogen storage alloy and an anode of the hydrogen storage alloy, comprising the step of treating the hydrogen storage alloy with an alkaline solution in a reducing atmosphere using an electrolysis method. By employing the same, a nickel-hydrogen secondary battery with improved activation rate is provided.

Preferably, the reducing atmosphere is maintained by nitrogen purging and the temperature at the treatment is maintained at 60-120 ° C.

As the alkaline solution, an electrolyte solution commonly used in nickel-hydrogen batteries such as KOH may be used, and the concentration of the alkaline solution is preferably the same as or higher than that of the electrolyte solution.

That is, in the present invention, the hydrogen storage alloy is treated by electrolysis using a high temperature alkaline solution in a reducing atmosphere to generate hydrogen on the surface of the alloy, thereby pre-treating the impurities that cause self-discharge in advance. The initial activation rate of the nickel-hydrogen secondary battery finally obtained by producing a negative electrode using the hydrogen storage alloy thus obtained is greatly increased.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.

Example

Hydrogen storage alloy (ZrNi _1.1 V _0.3 Mn _0.4 Cr _0.1 Co _0.1 ) was prepared using a high frequency induction furnace, and then pulverized to select a powder having a particle size of about 75 μm. The 500 g of the powder thus selected was placed in an electrode made of nickel mesh and then installed in a surface treatment apparatus. A 31 wt% potassium hydroxide aqueous solution was sufficiently added thereto as an electrolyte, and a nickel hydroxide electrode was installed as a counter electrode, and nitrogen gas was slowly injected into the lower portion of the nickel network electrode for stirring. Subsequently, the nickel network electrode was charged for 20 hours at a current of 40 mA / g based on the amount of alloy while maintaining the temperature of the aqueous potassium hydroxide solution at 80 ° C. Using the pretreated alloy, Cachant Black, PVA (polyvinyl alcohol) and water, the paste was prepared as a paste according to a conventional electrode manufacturing method, and then the paste was filled into a nickel foam having a porosity of 95% or more, dried and rolled. A hydrogen storage alloy negative electrode was prepared. A half cell was formed using a nickel hydroxide anode having a double capacity with respect to this anode as a counter electrode and 31% aqueous potassium hydroxide solution as the electrolyte. For this half cell, charge 150% at 0.1C for 15 hours at a negative electrode capacity, repeat the cycle of discharging until the battery voltage reaches 0.9V at 0.1C, and measure the degree of activation. 1 is shown.

Comparative example

For comparison, except that the pretreatment process was performed using conventional potassium hydroxide solution as in the prior art, half cells were made in the same manner as in Example, and the activation levels thereof were measured. The results are shown in Table 1 below.

Cycle count 1 time 3rd time 10th 20 times Example 260 mAh / g 320 mAh / g 325 mAh / g 325 mAh / g Comparative example 50 mAh / g 100 mAh / g 250 mAh / g 320 mAh / g

As apparent from the results of the above examples and comparative examples, the battery employing the hydrogen storage alloy pretreated according to the present invention has a significantly increased activation rate compared to the battery employing the hydrogen storage alloy pretreated by the conventional method. It became.

As described above, according to the method of the present invention, the hydrogen storage alloy is pretreated by electrolysis using a high temperature alkaline solution in a reducing atmosphere to generate hydrogen on the surface of the alloy, thereby preliminarily depositing impurities causing self discharge. Therefore, the nickel hydride secondary battery employing the pretreated hydrogen storage alloy as a negative electrode greatly increases the initial activation rate.

Claims (5)

A method for pretreatment of a hydrogen storage alloy, wherein the hydrogen storage alloy is treated with an alkaline solution in a reducing atmosphere using an electrolysis method. The method of claim 1, wherein the reducing atmosphere is maintained by nitrogen purging. The method of claim 1, wherein the temperature during the treatment is maintained in the range of 60-120 ℃. The method of pretreatment of a hydrogen storage alloy according to claim 1, wherein said alkali is potassium hydroxide. A nickel hydrogen secondary battery, wherein a hydrogen storage alloy pretreated according to the method of any one of claims 1 to 4 is employed as a negative electrode.