KR100237137B1 - Electrode material alloy for secondary cell composed of ni/mh - Google Patents

Abstract

The present invention is a secondary electrode composed of nickel and hydrogen storage alloys for the purpose of developing a Ti-Zr-V-Cr-Mn-Ni-based hydrogen storage alloy, which is an electrode material for Ni / MH (Metal Hydride MH) secondary batteries. It relates to an electrode material alloy for batteries.

The present invention has a basic configuration consisting of nickel and hydrogen storage alloy and the hydrogen storage alloy is composed of Ti, Zr, Mn, Cr, V, Ni while the composition of the hydrogen storage alloy is (Ti _0.5 -xZr _{0.5 +} x) ( Mn _a Cr _b V _c Ni _d ) -0.1? X? 0.1, 0.1? A? 0.3, 0.4? B? 0.6, -0.15? V? 0.35, and 0.8? D? 1.1.

Compared to the conventional commercially available AB5 hydrogen storage alloy, the present invention exhibits similar characteristics to that of the AB5 hydrogen storage alloy, which has a large discharge capacity and excellent current density dependency. In addition, the present invention can replace the existing commercially available AB5-based hydrogen storage alloy by improving the reduction of the discharge capacity.

Description

Electrode material alloy for secondary battery composed of nickel and hydrogen storage alloy

The present invention relates to the development of a Ti-Zr-V-Cr-Mn-Ni-based hydrogen storage alloy, which is an electrode material for Ni / MH (hereinafter referred to as MH) secondary battery. To date, the performance of Ni / MH cells is known to depend on the metal hydride (MH) constituting the negative electrode.

Ti-Zr-Mn-Ni-based hydrogen storage alloys developed by H. Miyamura and T. Sakai have a discharge capacity of about 300mAh / g, which is larger than that of AB5-based hydrogen low-alloy alloys. The discharge capacity is much smaller. In the case of this alloy system, there is a behavior in which the characteristics of the alloy deteriorate within 200 cycles.

The Ti-Zr-Mn-V-Ni-Fe-based hydrogen storage alloy developed by G. Xupeing et al. Has excellent lifespan but has a discharge capacity of 280-291mAh / g at a current density of 0.2C. It can be seen that the discharge capacity is much lower than. In addition, the current density dependency has very poor characteristics compared to the conventional commercially available AB5 hydrogen storage alloy and the alloy developed in the present invention.

The Ti-Zr-Mn-V-Ni-based hydrogen storage alloy developed by K. Morii et al. Has an equilibrium hydrogen pressure of around 10 atm at room temperature and has excellent hysteresis and sloping characteristics. However, the alloys they developed have a higher Zr content than Ti compared with the alloys developed in the present invention, and their studies are used as heat storage or hydrogen storage alloys for storage of hydrogen rather than as a hydrogen storage alloy for Ni / MH secondary batteries. It is to.

In order to achieve high capacity and high performance of Ni / MH batteries, high performance and high capacity of MH cathodes are essential. In order to use a hydrogen storage alloy as an electrode material for a secondary battery, it has to have excellent hydrogenation characteristics and low manufacturing price, such as moderate flat pressure, large hydrogen storage capacity, and long cycle life. do.

On the other hand, Ti-Mn-Ni-based hydrogen storage alloys have a larger hydrogen storage capacity than conventional hydrogen storage alloys and have a relatively low alloy production price, which makes them very promising as hydrogen storage alloys for electrodes. have. However, when the Ti-Mn-Ni-based hydrogen storage alloy is charged / discharged in the electrolyte, the alloy degenerates within tens of cycles, so that hydrogen absorption / emission in the electrolyte no longer occurs. Not suitable for use The cause of such Ti-based hydrogen storage alloy deterioration is due to the increase in contact act resistance and charge transfer resistance due to the thick TiO ₂ film formed on the electrode surface of the Ti-based hydrogen storage alloy. It is known because

Therefore, in order to use the Ti-Mn-Ni-based hydrogen storage alloy as an electrode material, the Ti-Mn-Ni-based hydrogen storage alloy should have a long life without deterioration during charge / discharge in the electrolyte.

1 is a result of measuring the PCT curve at 30 ℃ of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5- x CrxNi _0.8 alloy (x = 0, 0.2, 0.5).

2 shows the change of discharge capacity according to the charge / discharge cycles in the electrolyte of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5- x CrxNi _0.8 alloy (x = 0, 0.2, 0.3, 0.4, 0.5).

3 shows the change of charge / discharge potential according to charge / discharge cycles of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy and Ti _0.8 Zr _0.2 V _0.5 Cr _0.5 Ni _0.8 alloy.

4 is an analysis result of the electrochemical impedance according to the charge / discharge cycle of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy and Ti _0.8 Zr _0.2 V _0.5 Cr _0.5 Ni _0.8 alloy.

5 is a result of analyzing the depth profile of the AES (auger electron spectroscopy) observed after the Ti _0.8 Zr _0.2 V _0.5 Mn _0.5- x CrxNi _0.8 alloy (x = 0, 0.5) electrode.

6 is a SEM photograph of the surface of the Ti _0.5 Zr _0.5 V _0.5 Mn _0.5- x CrxNi _0.8 alloy (x = 0, 0.2, 0.5) alloy electrode after fully activated.

Fig. 6 (a) also shows Ti _0.5 Zr _0.5 V _0.5 Mn _0.5 Ni _0.8 alloy after 43 cycles.

6 (b) is a Ti _0.5 Zr _0.5 V _0.5 Mn _0.3 Cr _0.2 Ni _0.8 alloy after 50 cycles.

6 (c) is a Ti _0.5 Zr _0.5 V _0.5 Cr _0.5 Ni _0.8 alloy after 87 cycles.

7 is the result of the PCT curve measured at 30 ° C. of Ti _0.5 Zr _0.5 V _0.5 Mn _0.5- xCr _0.2+ xNi _0.8 alloy (x = 0, 0.3,).

8 shows the change of discharge capacity according to the charge / discharge cycle in the electrolyte of Ti _0.5 Zr _0.5 Mn _0.5- xCr _0.2+ xNi _0.8 alloy (x = 0, 0.15, 0.3).

FIG. 8 shows SEM and EDS analysis results for Ti _0.5 Zr _0.5 Mn _0.5- xCr _0.2+ xNi _0.8 alloy (x = 0, 0.15, 0.3) alloy.

FIG. 9 shows SEM analysis results after dissolution of Ti _0.5 Zr _0.5 Mn _0.5- xCr _0.2+ xNi _0.8 alloy.

FIG. 10 is a PCT curve measured at 30 ° C. for Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy.

FIG. 11 is a diagram illustrating the AES depth profile of the surface after the charge / discharge cycle of Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy.

12 shows the change of discharge capacity according to the charge / discharge cycle in the electrolyte of Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy.

FIG. 13 shows the change of discharge capacity according to the discharge current density of Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy.

In the present invention, to develop a hydrogen storage alloy having a long service life and a high capacity by adjusting the fraction of each element or by substituting a new alloy element for Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy which rapidly degenerates in the electrolyte. It was. The alloy used in the invention was prepared by arc melting under argon atmosphere, and the alloy was mechanically ground in air. In order to investigate the thermodynamic properties of the alloy, the PCT curve was measured using an automatic pressure-composition-temperature (PCT) measuring device. The structural analysis of the alloy was carried out simultaneously with XRD analysis, SEM and EDS analysis. The pulverized alloy was separated from the powder of 400 mesh or less and cold pressed with Ni powder to prepare an electrode. The prepared electrode was subjected to a half cell experiment, and the charge / discharge current density was 100 mA / g and charged for 6 hours.

1 is a result of measuring the PCT curve of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5-x Cr _x Ni _0.8 alloy (x = 0, 0.2 0.5). As the amount of Cr substituted instead of Mn increases, the overall hydrogen storage capacity and the flat pressure range decrease rapidly. This is because the SEM analysis resulted in the formation of the V-Cr rich phase, which hardly absorbs hydrogen, which is the second phase deposited inside the alloy.

FIG. 2 shows the degradation behavior of the Ti _0.8 Zr _0.2 V _0.5 Mn _0.5-x Cr _x Ni _0.8 alloy (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) according to the charge / discharge in the electrolyte. As the Cr content is increased, the discharge capacity is also reduced as in the PCT curve, while the life of the alloy electrode is improved. Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy has a discharge capacity of about 400mAh / g, but it can be seen that it rapidly degenerates within 10 cycles. 3 shows the charge / discharge curves according to the cycles of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy and Ti _0.8 Zr _0.2 V _0.5 Cr _0.5 Ni _0.8 alloy.

In the case of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy, the charging potential increases and the discharging potential decreases as the cycle progresses.Ti _0.8 Zr _0.2 V _0.5 Cr _0.5 Ni _In the case of the _0.8 alloy, it can be seen that there is no significant change in dislocation due to charge / discharge. 4 is an analysis result of impedance according to charge / discharge cycles of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy and Ti _0.8 Zr _0.2 V _0.5 Cr _0.5 Ni _0.8 alloy. In the case of Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 alloy, the reaction resistance increased greatly as the charge / discharge cycle proceeded, whereas in the case of Ti _0.8 Zr _0.2 V _0.5 C r _0.5 Ni _0.8 alloy, the charge / discharge cycle proceeded. Accordingly, it can be seen that the reaction resistance does not change significantly. Also, as the cycle progressed, it was found that a large amount of Mn in the electrolyte was eluted or precipitated on the surface of the electrode. Degraded Ti _0.8 Zr _0.2 V _0.5 Mn _0.5 Ni _0.8 It can be seen that the surface of the electrode is stacked with thick oxide films of thick TiO ₂ , ZrO ₂ , and MnO ₂ (FIG. 5). In addition, since V is easily dissolved in the electrolyte, it does not appear on the surface, and the amount of Ni on the surface is very small. Such surface conditions can be expected to have a very small catalytic activity or electronic conductivity for the charge transfer reaction. On the other hand, when a part of Mn is replaced with Cr, as shown in FIG. 4, it can be seen that the reaction resistance to the charge transfer reaction does not increase significantly even after 60 cycles.

FIG. 6 shows the SEM photographs observed after the Ti _0.8 Zr _0.2 V _0.5 Mn _0.5-x Cr _x Ni _0.8 alloy (x = 0, 0.2, 0.5) electrode was sufficiently activated. It can be seen that as the amount of Cr gradually increases, the pulverization rate of the electrode decreases. In addition, as shown in FIG. 5, in the case of the Ti _0.8 Zr _0.2 V _0.5 Cr _0.5 Ni _0.8 alloy, the concentration of oxygen on the surface is very low and the concentration of Ni is high. In other words, it can be seen that the formation of an oxide layer on the surface is much more suppressed in the case of an alloy having Cr than in the case of an alloy having much Mn. However, this alloy has a disadvantage in that the discharge capacity is too small to be used as an electrode material for Ni / MH batteries. From the above research results, it is considered very difficult to develop a hydrogen storage alloy for secondary batteries having a sufficient lifetime and a large discharge capacity in an alloy system having a high Ti concentration.

Therefore, in order to develop a hydrogen storage alloy for electrodes having a high capacity and an appropriate lifetime, Ti _0.5 Zr _0.5 Mn _0.5-x Cr which removed V, which easily forms a solid solution with Cr, from the alloying element and increased the amount of Zr instead of Ti _{A 0.2 + x} Ni _0.8 alloy (x = 0, 0.3) was developed and its characteristics investigated. 7 shows the PCT curve of Ti _0.5 Zr _0.5 Mn _0.5-x Cr _{0.2 + x} Ni _0.8 alloy (x = 0, 0.3) alloy. Similar to the results of the previous alloy, it can be seen that as the amount of Cr increases, the plateau region decreases.

8 shows the change of discharge capacity according to the charge / discharge cycle in the electrolyte of Ti _0.5 Zr _0.5 Mn _0.5-x Cr _{0.2 + x} Ni _0.8 alloy (x = 0, 0.15, 0.3) alloy. It can be seen that as the content of Cr substituted for Mn increases, the activation characteristics of the electrode decreases, and the discharge capacity decreases, but the lifetime improves. 9 is a SEM analysis result immediately after the alloy is manufactured for this alloy system. It can be seen that this alloy consists of a matrix of C14 phase and a small amount of TiNi phase. A small amount of V was added to the alloy system to increase the stoichiometric ratio while maintaining the flat pressure to remove the second phase and increase the discharge capacity.

The composition of this alloy was Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy, and the structure was found from XRD analysis. FIG. 10 shows that the PCT curve of Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy has a wide flat pressure range and an appropriate equilibrium hydrogen pressure. 11 illustrates the change of discharge capacity according to the charge / discharge cycles in the electrolyte of Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy. It can be seen that it has an excellent discharge capacity and excellent cycle characteristics compared to the existing Ti-based hydrogen storage alloy. FIG. 12 is a view illustrating the surface after the Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 charge / discharge cycle with an AES depth profile. It can be seen that the surface of the alloy has a relatively low concentration of oxygen and a relatively high concentration of Ni. 3 is a diagram illustrating the change in discharge capacity according to the discharge current density of Ti _0.5 Zr _0.5 Mn _0.2 Cr _0.5 V _0.2 Ni _0.9 alloy. It can be seen that the discharge efficiency at high current density of 700mA / g or more is about 85% or more, which is superior to the existing AB2 hydrogen storage alloy.

Example 1

Preparation of the alloy developed in the present invention was prepared through the following method.

The pure metal fragments were quantified in Ti _0.5 , Zr _0.5 , Mn _0.2 , Cr _0.5 , V _0.2 , and Ni _0.8 , and then arc-dissolved under argon gas atmosphere. At this time, the weight of the prepared alloy was about 5g.

The alloy produced was ground in air. The powder thus prepared was separated into a powder having a predetermined size or less using a fine state. The powder of the alloy was mixed with Ni powder in a weight ratio of 1: 3, and then cold-pressed to prepare an electrode. The prepared electrode was subjected to a half cell test, and the charge / discharge current density was 100 m / A / g and was charged for 6 hours.

Example 2

In the same manner as in Example 1, an alloy was prepared in a composition of Ti _0.8 , Zn _0.2 , V _0.5 , Cr _0.5 , and Ni _0.8 .

Example 3

An alloy was prepared in the same manner as in Example 1 and having a composition of Ti _0.8 , Zn _0.2 , V _0.5 , Mn _0.5 , and Ni _0.8 .

The above embodiments are only for carrying out the present invention, and the technical scope of the present invention is not limited to these examples.

Experimental Example

In the present invention, in order to determine the optimum conditions of the metal composition, such as Ti, Zr, Mn, V, Cr, Ni, the discharge capacity according to the composition ratio and the life of the battery is shown as shown in Table 1.

The present invention relates to the development of an electrode material alloy for Ni / MH secondary batteries. The alloy developed in this study has a much higher discharge capacity and a higher current density dependence than the conventional commercially available AB5 hydrogen storage alloy. Unlike storage alloys, it shows similar characteristics to AB5-based hydrogen storage alloys with excellent current density dependence. In addition, the present invention is thought to be able to replace the conventional commercially available AB5 hydrogen storage alloy by greatly improving the reduction of discharge capacity due to metal degradation in the electrolyte pointed out as a problem of Ti-based hydrogen storage alloy. It can accelerate the development of Ni / MH secondary battery, which has much higher discharge capacity than the existing developed battery, and can promote the development of electric vehicle, which is the actual performance of high capacity and high performance secondary battery.

Claims (3)

Electrode material alloy for secondary batteries, characterized in that consisting of nickel and hydrogen storage alloy. The electrode material alloy of claim 1, wherein the hydrogen storage alloy is composed of Ti, Zr, Mn, Cr, V, and Ni. The composition of the hydrogen storage alloy according to claim 2, wherein the composition of the electrode material alloy for secondary battery (Ti _0.5-x Zr _{0.5 + x} ) (Mn _a Cr _b V _c Ni _d ) -0.1 ≤ x ≤0.1, 0.1 ≤ a ≤ 0.3, 0.4 ≤ b ≤ 0.6, -0.15 ≤ v ≤ 0.35, 0.8 ≤ d ≤ 1.1.

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