KR100472928B1 - Electrolyte for Nickel-Metal Hydride Secondary Battery and Nickel-Metal Hydride Secondary Battery Having the Electrolyte - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte solution containing palladium and a nickel hydride secondary battery having the electrolyte, wherein palladium is added to an electrolyte of a nickel hydride secondary battery so that palladium is plated on the surface of the battery during charging. It is an object of the present invention to provide an electrolytic solution and a nickel hydride secondary battery having the electrolyte, which can further improve and further improve the electrode capacity, as well as simplify the manufacturing process of the nickel hydride secondary battery.

This invention makes the summary the nickel hydride secondary battery which uses the electrolyte solution for nickel hydride secondary batteries which added palladium, and the electrolyte solution for nickel hydride secondary batteries which added palladium as electrolyte solution.

Description

Electrolyte for nickel hydride secondary battery and nickel hydride secondary battery including the same {Electrolyte for Nickel-Metal Hydride Secondary Battery and Nickel-Metal Hydride Secondary Battery Having the Electrolyte}

The present invention relates to a nickel hydride secondary battery, and more particularly, to an electrolytic solution to which palladium is added and a nickel hydride secondary battery having the electrolyte.

Ni-MH secondary battery replaces the cadmium pole with hydrogen storage alloy in the conventional nickel cadmium battery, and hydrogen storage alloy (M) is used for the negative electrode and nickel hydroxide (Ni (OH) ₂ / NiOOH) for the positive electrode. Alkali-resistant nylon nonwovens, polypropylene nonwovens and polyamide nonwovens such as Ni-Cd batteries are used.

The hydrogen storage alloy used as the negative electrode of the nickel hydride secondary battery is a material having the property of reversibly absorbing and releasing hydrogen, and when charged, hydrogen ions generated by electrolysis of water are stored in the hydrogen storage alloy. In the reduction reaction, a reaction occurs in which the Ni (OH) ₂ is oxidized to NiOOH at the positive electrode.

At the time of discharging, on the contrary, the hydrogen atom of the hydrogen compound is oxidized to water at the cathode, and NiOOH is reduced to Ni (OH) ₂ at the anode.

The charge and discharge reactions occurring at both poles are as follows.

Anode: Ni (OH) ₂ + OH- → NiOOH + H ₂ O + e-

Cathode: M + H ₂ O + e- → MH + OH-

Total reaction: Ni (OH) ₂ + M → NiOOH + MH

In Schemes (2) and (3), M represents a hydrogen storage alloy.

The composition of the hydrogen storage alloy acts as the largest factor that can determine the performance of the battery, such as battery capacity, battery withstand pressure, rapid charge and discharge characteristics, life, low temperature characteristics, self-discharge characteristics.

The hydrogen storage alloys developed so far with respect to the hydrogen storage alloy for electrodes are classified as follows according to the crystal structure and composition.

AB system: TiFe,

AB ₂ system: ZrMn ₂ , ZrV ₂ , ZrNi ₂

AB _{5 type} : CaNi ₅ , LaNi ₅ , MmNi ₅ (Mm: metals containing rare earth such as La, Ce, etc.)

A ₂ B system: Mg ₂ Ni, Mg ₂ Cu

Among the hydrogen storage alloys, the material having the largest theoretical hydrogen absorption and emission capacity is Mg ₂ Ni material, and the electrochemical theoretical discharge capacity reaches 999 mAh / g.

On the other hand, the electrolyte of the nickel-hydrogen secondary battery is composed of a high concentration of KOH (potassium hydroxide) solution of 2 to 10 M, preferably 5 to 8 M, or those made by adding a small amount of LiOH and NaOH, etc., and these are known. The electrolytic solution is a highly corrosive alkaline solution with a pH of 14 or less.

Therefore, when the electrode (cathode) is manufactured from a hydrogen storage alloy, there is a problem that the activation of the electrode is reduced and the life of the electrode is reduced due to corrosion and passivation of the electrode surface.

In order to solve the above problems, methods for obtaining a catalytic effect of hydrogen occlusion by performing electrode pretreatment, such as containing palladium (Pd) and platinum in the electrode or coating the electrode, are known.

In addition, a method of improving the life of an electrode by containing a small amount of yttrium in the electrode when making a negative electrode active material is known.

As described above, palladium or the like contained in or coated on the electrode plays a catalytic role in hydrogen occlusion, thereby contributing to an increase in discharge capacity of the electrode, and also before forming a passivation film such as Mg (OH) ₂ on the electrode surface, Formation on the surface protects the electrode and contributes to extending the life of the electrode.

However, as described above, in the case of coating or plating palladium or the like on the electrode, as the charge and discharge of the battery proceeds, the palladium layer and the electrode active material plated on the electrode surface are crushed or destroyed during the hydrogenation reaction, thereby extending the electrode life and There is a problem that there is a limit to the improvement of electrode capacity.

The present inventors conducted research and experiments to solve the above-mentioned problems of the prior art, and based on the results, the present invention proposes the present invention. The present invention adds palladium to an electrolyte solution of a nickel hydride secondary battery, Palladium is plated on the surface of the electrode during the charging process to provide an electrolyte solution and a nickel hydride secondary battery having the electrolyte, which can not only improve electrode life and electrode capacity, but also simplify the manufacturing process of the nickel hydride secondary battery. The purpose is to do that.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention relates to an electrolyte for nickel hydride secondary batteries to which palladium is added.

Moreover, this invention relates to the nickel hydride secondary battery which uses the electrolyte solution for nickel hydride secondary batteries to which palladium was added as electrolyte solution.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention relates to an improved electrolytic solution for nickel hydride secondary batteries and a nickel hydride secondary battery having the improved electrolytic solution.

The electrolytic solution for nickel hydride secondary batteries of the present invention is formed by adding palladium to a conventional electrolytic solution for nickel hydride secondary batteries.

As described above, the palladium added to the electrolyte of the nickel hydride secondary battery is plated on the electrode surface during the charging process of the battery to play a catalytic role in hydrogen occlusion, thereby contributing to an increase in the discharge capacity of the electrode, and also to Mg (OH). By forming a palladium film on the electrode surface before the passivation film such as ₂ ) is formed, it contributes to prolonging the life of the electrode by protecting the electrode.

The palladium is preferably added in the form of palladium chloride (PdCl ₂ ).

When palladium is added to the conventional nickel-metal hydride secondary battery according to the present invention, the addition effect is shown, but if the addition amount is too small, the addition effect is insufficient, if too much is added, the plating layer is formed too thick on the electrode surface The hydrogen absorption and release reaction of the electrode cannot be expected, and the ion conductivity of the electrolyte is lowered, making it difficult to smoothly move the ions.

Therefore, it is preferable to set the addition amount of palladium to 0.0002-0.0008M, More preferably, it is 0.00045-0.0006M, Most preferably, it is set to 0.0005M.

According to the present invention, a conventional nickel hydride secondary battery electrolyte to which palladium is added is not particularly limited. Examples thereof include an electrolyte solution containing a 2-10 M KOH aqueous solution, preferably a 5-8 M KOH aqueous solution, and an electrolyte solution in which LiOH.H ₂ O or NaOH is added to the aqueous solution.

Preferred electrolyte solutions of the present invention are prepared by adding 0.00045 to 0.0006 M of PdCl ₂ to a conventional electrolyte solution containing 5 to 8 M KOH + 0.5 to 1.5 M LiOH.H ₂ O or 5 to 8 M KOH + 0.5 to 1.5 M NaOH. More preferred electrolyte solution is one formed by adding 0.0005M of PdCl ₂ to a conventional electrolyte solution containing 5-8 M KOH + 0.5-1.5 M LiOH.H ₂ O or 5-8 M KOH + 0.5-1.5 M NaOH, The most preferred electrolyte is one formed by adding 0.0005M of PdCl ₂ to a conventional electrolyte containing 6M KOH + 1M LiOH.H ₂ O or 6M KOH + 1M NaOH.

Moreover, this invention relates to the nickel hydride secondary battery which uses the electrolyte solution to which palladium was added as above as electrolyte solution.

The nickel hydride secondary battery to which the electrolyte solution of the present invention can be applied is not particularly limited, and any one can be used as long as it is commonly used.

As described above, the nickel hydride secondary battery uses a hydrogen storage alloy (M) for the negative electrode and nickel hydroxide (Ni (OH) ₂ / NiOOH) for the positive electrode, and an alkali-resistant nylon nonwoven fabric such as a Ni-Cd battery as the separator. , Polypropylene nonwovens, polyamide nonwovens, and the like are used.

The hydrogen storage alloy (M) used in the nickel-metal hydride secondary battery negative electrode is TiFe, ZrMn ₂ , ZrV ₂ , ZrNi ₂ , CaNi ₅ , LaNi ₅ , MmNi ₅ (Mm: called Mishu metal, rare earth such as La, Ce, etc. Metal containing), Mg ₂ Ni, Mg ₂ Cu and the like.

The hydrogen storage alloy (M) to which the electrolyte solution of the present invention can be more preferably applied is Mg ₂ Ni.

In the case of using the electrolytic solution of the present invention prepared as described above as an electrolytic solution of a nickel hydride secondary battery, the palladium added to the electrolytic solution of the nickel hydride secondary battery is plated on the electrode surface during the charging process, and thus the charge and discharge are performed. Even if the palladium layer on the surface is damaged, the damaged portion can be compensated for, thus improving the electrode life and the electrode capacity, and furthermore, the pretreatment process before charging and discharging the electrode can be omitted, thereby simplifying the manufacturing process of the nickel hydride secondary battery. .

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)

The raw powders of Mg and Ni were charged together with stainless balls into a high energy ball mill, and after 120 hours of ball milling to produce an alloy powder, powders of 10 nm or less were selected. The alloy powder was prepared into a pellet-shaped electrode according to a conventional electrode production method, and then filled with nickel foam and rolled to prepare a cathode made of a hydrogen storage alloy.

With respect to this negative electrode, the half cell (invention material 1) was comprised using the mercury oxide electrode (Hg / HgO) as a counter electrode.

The electrolyte solution used in the battery was prepared by adding 0.0005 g / L palladium chloride to 6 g / L potassium hydroxide.

In order to evaluate the characteristics of the electrode manufactured as described above, after charging at a current density of 50 mAh / g for 10 hours, the charging and discharging cycle of discharging was repeated until the battery voltage reached 0.6 V, and the result was chlorinated. It is shown in Table 1 and FIG. 1 together with the results of evaluating the characteristics of the electrode of the battery without the palladium (prior art 1).

Cycle count Inventive Example 1 (KOH-Pd)  Conventional Example 1 (KOH) 1 cycle 381 mAh / g 349 mAh / g 10 cycle 206 mAh / g 55 mAh / g 20 cycle 177 mAh / g 18 mAh / g 30 cycle 175 mAh / g 20 mAh / g 40 cycle 167 mAh / g 22 mAh / g 50 cycle 166 mAh / g 16 mAh / g 60 cycle 147 mAh / g 15 mAh / g 70 cycle 143 mAh / g 11 mAh / g 80 cycle 152 mAh / g 11 mAh / g 90 cycle 156 mAh / g 14 mAh / g 100cycle 153 mAh / g 16 mAh / g

As shown in Table 1 and Figure 1, when using the electrolytic solution to which palladium chloride is added according to the present invention (invention material 1), the initial discharge capacity of the electrode compared to the case of using a conventional electrolyte solution (conventional material 1) It can be seen that the electrode life and current density characteristics are greatly improved.

(Example 2)

A battery was prepared in the same manner as in Example 1, except that 0.0001M, 0.00045M, 0.0005M, 0.00055M, 0.0006M, and 0.001M of PdCl ₂ were added to the electrolyte solution of 6M KOH + 1M LiOH.H ₂ O. After the preparation, the electrode characteristics (discharge capacity and lifespan, etc.) were evaluated in the same manner as in Example 1, and the discharge capacity results of using the electrolyte solution containing 0.00045M, 0.0005M, 0.00055M, and 0.0006M of PdCl ₂ added 2 is shown.

2 also shows discharge capacity results for using an electrolyte solution without PdCl ₂ .

As shown in FIG. 2, when an electrolyte solution containing 0.00045M, 0.0005M, 0.00055M, or 0.0006M of PdCl ₂ was added to the electrolyte of 6M KOH + 1M LiOHH ₂ O, the initial discharge capacity was 320-460mAh / g. It was higher than without adding palladium chloride, and the electrode life was maintained at 20 to 50% or more of the maximum discharge capacity up to 100 cycles, which means that the discharge capacity was less than 10 cycles when the electrolyte solution without palladium chloride was used. Compared with all degenerating, the electrode life is greatly improved.

On the other hand, when the electrolyte solution containing 0.0001M of PdCl ₂ was added to the electrolyte solution of 6M KOH + 1M LiOH.H ₂ O, the charge and discharge characteristics of the electrolyte solution without the addition of palladium chloride were almost similar.

In addition, even when an electrolyte solution containing 0.001 M of PdCl ₂ was added to an electrolyte of 6M KOH + 1M LiOH · H ₂ O, the degree of improvement of electrode characteristics was not large. This is because the plating layer was formed too thick on the electrode surface to absorb hydrogen from the electrode. It is believed that the release reaction hardly occurs and the ion conductivity of the electrolyte is reduced, making it difficult to move ions smoothly.

As described above, the present invention not only improves the electrode life and the electrode capacity by adding palladium to the electrolyte of the nickel hydride secondary battery, but also can eliminate the pretreatment process before charging and discharging the electrode. The effect is to simplify the process.

1 is a graph showing the change in discharge capacity according to the number of cycles for the invention using the electrolyte according to the present invention and the conventional material using the conventional electrolyte

Figure 2 is a graph showing the change in discharge capacity according to the number of cycles for the case of using the palladium-added electrolyte according to the present invention and when the palladium is not added

Claims (18)

In the electrolytic solution for nickel hydride secondary battery consisting of a solution containing 2 to 10 M KOH, Electrolyte solution for nickel hydride secondary battery, characterized in that the palladium is added 0.00045 ~ 0.0006M to the solution The electrolyte solution for nickel hydride secondary batteries according to claim 1, wherein the solution is a solution containing 5 to 8 M KOH. The electrolyte solution for a nickel hydride secondary battery according to claim 1, wherein the solution is a solution containing 5 to 8 M KOH + 0.5 to 1.5 M LiOH.H ₂ O or 5 to 8 M KOH + 0.5 to 1.5 M NaOH. The electrolyte solution for nickel hydride secondary batteries according to claim 1, wherein the solution is a solution containing 6M KOH + 1M LiOH.H ₂ O or 6M KOH + 1M NaOH. delete The electrolyte solution for nickel hydride secondary batteries according to claim 1, wherein the amount of palladium added is 0.0005M. In a nickel hydride secondary battery comprising an electrolyte solution and an electrode consisting of a solution containing 2 ~ 10 M KOH, Ni-MH secondary battery, characterized in that the palladium is added 0.00045 ~ 0.0006M to the solution The nickel hydride secondary battery of claim 7, wherein the solution is a solution containing 5-8 M KOH. The nickel hydride secondary battery of claim 7, wherein the solution is a solution containing 5-8 M KOH + 0.5-1.5 M LiOH.H ₂ O or 6 M KOH + 0.5-1.5 M NaOH. The nickel hydride secondary battery of claim 7, wherein the solution is a solution containing 6M KOH + 1M LiOH.H ₂ O or 6M KOH + 1M NaOH. delete The nickel hydride secondary battery according to claim 7, wherein the amount of palladium added is 0.0005M. The method according to any one of claims 7 to 10, wherein the cathode is TiFe, ZrMn ₂ , ZrV ₂ , ZrNi ₂ , CaNi ₅ , LaNi ₅ , MmNi ₅ (Mm: metal containing rare earth such as La, Ce, etc.), Nickel-hydrogen secondary battery, characterized in that it is composed of one selected from the group consisting of Mg ₂ Ni and Mg ₂ Cu delete The method of claim 12, wherein the cathode is TiFe, ZrMn ₂ , ZrV ₂ , ZrNi ₂ , CaNi ₅ , LaNi ₅ , MmNi ₅ (metal including rare earths such as Mm: La, Ce), Mg ₂ Ni and Mg ₂ Cu Nickel-hydrogen secondary battery, characterized in that consisting of one selected from the group consisting of The nickel hydride secondary battery of claim 13, wherein the negative electrode is made of Mg ₂ Ni. delete 16. The nickel hydride secondary battery of claim 15, wherein the negative electrode is made of Mg ₂ Ni.