CN1585166A - Negative hydrogen storage material for high-temperature nickel hydrogen battery - Google Patents

Abstract

A hydrogen storing material used as cathode of Ni-H battery is of (Mm1-xDyx)Ni3.55CO0.75N0.4Al0.3, wherein 0<X is less than or equal to 0.065, Mm made from rare-earth mixture of La, Ce, Pr and Nd. The materials are molten and cast into ingots in a vacuumed induction furnace under argon gas protection, with higher electrochemical capacitance at high temperature and wide range of temperature suitably.

Description

Negative hydrogen storage material for high-temperature nickel-hydrogen battery

Technical Field

The invention belongs to the field of functional materials. In particular to a negative hydrogen storage material for preparing a nickel-hydrogen battery with high-temperature performance requirements.

Technical Field

In recent years, cordless rechargeable electric tools have been rapidly developed, which brings great convenience to people's work, and thus the demand for secondary rechargeable batteries has also increased greatly. The prior rechargeable battery used for electric tools is mainly a nickel-cadmium battery, but the nickel-cadmium battery has low capacity and serious environmental pollution, belongs to a rejected product, and is an optimal substitute because the nickel-hydrogen battery has the excellent characteristics of high capacity, long service life, no pollution and the like and has the voltage similar to that of the nickel-cadmium battery. Different from general electronic products, the electric tool requires large-current discharge in the use process, and in addition, the nickel-hydrogen battery is required to have a large-current charging function in order to shorten the charging time, and the energy consumed on the internal resistance of the battery is increased in the large-current charging and discharging processes, so that the temperature of the battery is increased (generally, the temperature is increased to about 40-55 ℃), in the nickel-hydrogen battery product in the prior art, the capacity of the battery is rapidly reduced along with the temperature increase, and the nickel-hydrogen battery mainly comprises a nickel hydroxide anode, a hydrogen storage alloy cathode, a diaphragm and a potassium hydroxide electrolyte. The performance of the whole battery is closely related to the performance of each component, and one main reason that the capacity of the battery decreases with the increase of the temperature is that the capacity of the negative electrode material decreases rapidly with the increase of the temperature, so that a negative electrode hydrogen storage material with good high-temperature performance is urgently needed, and particularly, people are making efforts to develop a rechargeable nickel-metal hydride battery for an electric vehicle, which needs the hydrogen storage material to have good large-current charging and discharging characteristics and high-temperature service performance and is more rigorous (the charging and discharging current is larger and the temperature rise is higher) than the requirement of the battery performance for an electric tool, so that research and development of the hydrogen storage material with good high-temperature electrochemical charging and discharging characteristics become urgent.

Disclosure of Invention

The invention aims to obtain a product with higher temperature (30-80 ℃) than the current market through component improvementThe negative hydrogen storage material with much higher electrochemical charge-discharge capacity of the sold product comprises the following components (atomic ratio): a. the₁B₅The hydrogen storage material is characterized in that in the hydrogen storage material of the negative electrode, A is La, Ce, Pr, Nd and Dy elements; b is Ni, Co, Mn, Al element; the material comprises the following components in percentage by weight: la 20.34-21.53%; ce 7.09-7.50%; pr 0.92-0.98%; nd2.47-2.61%; 0.50 to 2.50 percent of Dy; 10.43 to 10.46 percent of Co; 5.19 to 5.20 percent of Mn; 1.91 to 1.92 percent of All; the balance being Ni.

Compared with the prior cathode hydrogen storage material, the cathode hydrogen storage material has the characteristics of high-temperature electrochemical capacity, wide applicable temperature range and the like so as to meet the requirement of nickel-hydrogen battery products on high-temperature performance.

For the nickel-hydrogen battery at present, the used negative hydrogen storage material is mainly mixed rare earth MmNi₅The electrochemical capacity of the-type hydrogen storage alloy is about 300mAh/g generally, and in order to improve the capacity of the negative electrode hydrogen storage alloy, Zr-based AB is developed at present₂Type Laves phase alloy, Ti-Zr based AB type alloy and A₂Type B Mg₂Ni-Mg based alloys, but with a small proportion of AB removed for slow activation or poor cycle life₂Besides the type alloy, other alloys have not reached practical application.

AB₅The hydrogen storage alloy is an intermetallic compound composed of an element A (such as Mm, Ca, Zr) which is easy to generate stable hydride and other elements B (such as Ni, Al, Mn, Si, Zn, Cr, Fe, Cu, Co and the like), belonging to CaCu₅The hexagonal structure of the type, whose electrochemical charge and discharge capacity is mainly derived from the hydrogen ions from the electrolyte during the hydrogen absorption and desorption processes, undergoes electron transfer during the redox process on the hydrogen storage alloy electrode, and it is known that the electrochemical cell of the nickel-metal hydride battery is generally represented by the following charge and discharge reactions:

charging of electricity

At the negative electrode, when an electrode potential is applied to the negative electrode, water in the electrolyte is decomposed into hydrogen atoms, which are taken into the alloy, and hydroxide ions are left in the electrolyte:

(1)

at the positive electrode, the charging reaction is the oxidation of the same nickel hydroxide as in a nickel-cadmium battery:

(2)

discharge of electricity

At the negative electrode, hydrogen is released and combines with hydroxide ions to form water, which contributes an electron to form an electric current.

(3)

At the positive electrode, the nickel hydroxide is reduced to a reduced nickel protoxide.

(4)

The material initially forms α phase solid solution with low hydrogen content when absorbing hydrogen, α phase is transformed into β phase with high hydrogen content as the hydrogen absorbing amount increases, the hydrogen absorbing and releasing pressure of the mutual transformation process between α phase and β phase is usually a certain value as a gas-solid reaction, when the hydrogen absorbing amount is totally transformed into β phase, the equilibrium hydrogen pressure is increased, the process is usually represented by a pressure-concentration-isotherm (P-C-T curve) (see figure 1), because the cell usually works under one atmosphere, for the nickel-hydrogen cell application, hydrogen atoms enter the hydrogen storage alloy to contribute to the electrochemical capacity only when the hydrogen absorbing and releasing pressure is lower than one atmosphere, otherwise hydrogen molecules are transformed into gas to be separated out, figure l is an ideal P-C isotherm (Tl<T2<T3) of the hydrogen storage alloy, as can be seen in figure l, as the temperature increases, the P-C-T isotherm is increased, the hydrogen absorbing and releasing temperature is reduced along with the rising Hot-C isotherm of the hydrogen absorbing and releasing temperature is reduced, $1\mathrm{nP}=\frac{\mathrm{\&Delta;H}}{\mathrm{RT}}-\frac{\mathrm{\&Delta;S}}{R},$ and releases heat when absorbing hydrogen and absorbs heat when releasing hydrogen. According to the Van't Hoff equation, it can be known that hydrogen storage alloys having a good capacity at high temperatures absorb hydrogen at high temperaturesThe pressure must be relatively low and the stability of the hydride formation is increased.

The hydrogen storage alloy for the nickel-metal hydride battery at present mainly comprises Mm, Ni, Co, Mn and Al, and the typical component is MmNi_3.55Co_0.75Mn_0.4Al_0.3The Mm is the mixed rare earth with main components of La, Ce, Pr and Nd, and the electrochemical capacity of the alloy is reduced rapidly along with the increase of the temperature as can be seen from figure 2, and through our research, the addition of heavy rare earth element dysprosium (Dy, the weight percentage of Dy is more than 0 and less than 2.5 wt%) in the alloy can obviously improve the high-temperature performance of the alloy, thereby obtaining the hydrogen storage material which can meet the use requirement of the high-temperature nickel-hydrogen battery. Therefore, the negative hydrogen storage material for the high-temperature nickel-metal hydride battery comprises the following components (atomic ratio): (Mm)_1-xDy_x)₁Ni_3.55Co_0.75Mn_0.4Al_0.3(x is more than 0 and less than or equal to 0.065), wherein the composition of the mixed rare earth Mm is shown in Table 1.

FIG. 2 shows the electrochemical charge and discharge test results of different Dy contents at 30-80 deg.C, and it can be seen that the addition of Dy can significantly improve the high-temperature electrochemical charge and discharge capacity of the alloy, and the best results are that the electrochemical charge and discharge capacity at 50 deg.C is greater than 310mAh/g, the charge and discharge capacity at 70 deg.C is up to 260mAh/g, and the highest charge and discharge capacity at 80 deg.C is up to 223 mAh/g. Therefore, the negative hydrogen storage material has stronger advantages in high-temperature application.

Drawings

In the present description, the reference numerals are described as follows:

FIG. 1 is an ideal P-C isotherm for a hydrogen storage alloy (T1<T2<T3);

FIG. 2 shows the results of the high temperature capacity (30-80 ℃ C.) test of the hydrogen occluding alloy.

Detailed Description

According to alloy A in Table 2₁B₅The weight percentages of the elements areAnd (3) mixing materials, namely smelting the mixed alloy raw materials in an induction furnace which is vacuumized and is filled with argon for protection, casting ingots, and grinding the alloy into alloy powder with the particle size of less than 200 meshes at room temperature for later use after the as-cast hydrogen storage alloy is obtained. Then mixing negative electrode alloy powder less than 200 meshes and nickel powder according to the proportion of 1: 1, adding proper amount of polyvinyl alcohol solution as binder, cold-pressing to obtain round cake whose diameter is 15mm, and using it as negative electrode, and its positive electrode is identical to that of nickel-hydrogen cell [ Ni (OH)₂-NiOOH]An electrode, the capacity of the positive electrodebeing designed to be much higher than that of the negative electrode so that the negative electrode material is sufficiently saturated during charging, [ Hg/HgO/6M KOH]Is a reference electrode. In the process of testing the electrode performance, the negative hydrogen storage material is fully formed by adopting 60mA/g current at 30 ℃, and the forming system is as follows: charging with 60mA/g current for 400 min, stopping charging for 15 min, discharging with 60mA/g current until the negative electrode potential is-0.5V relative to the electrode potential of the reference electrode, and performing the next cycle of charging and discharging. The capacity of the negative electrode reaches a maximum value along with the formation, and relatively stabilizes, and the formation is finished. The maximum value is the hydrogen storage capacity of the material at 30 ℃, then the temperature of the system is raised, and the hydrogen storage capacity of the negative hydrogen storage material at different temperatures is tested by adopting the same charging and discharging system within the range of 30-80 ℃.

As can be seen from Table 3, the capacity of each of the alloys in the as-cast state at 30 ℃ is substantially equivalent, but as the temperature increases, the capacity of all the alloys gradually decreases, and the magnitude of the decrease varies depending on the composition of the alloy.

The alloy composition is increased from 0.5 wt% to 2.5 wt% in Dy (the atomic ratio x is about 0.065), the high-temperature electrochemical capacity of the alloy is increased and then reduced, and the high-temperature performance is best when the Dy content is 2.0 wt% (corresponding to the atomic ratio x is about 0.052). These alloys containing Dy element have improved capacity as compared with comparative examples having a Dy content of 0. The higher the temperature, the greater the magnitude of capacity increase, especially at higher temperatures, such as 80℃ the capacity can be increased from 159mAh/g (0.0% Dy) to 223mAh/g (2.0% Dy).

As described above, the misch metal nickel-based hydrogen storage alloy (ML)_1-xDy_x)₁(NiCoMnAl)₅Middle Dy elementThe content of elements affects the high-temperature charge and discharge performance of the alloy, and particularly, the charge and discharge capacity is improved to a certain extent at higher temperature.

In conclusion, the hydrogen storage alloy of the heavy rare earth metal Dy is added, so that the negative hydrogen storage material which has good high-temperature performance and is suitable for the high-temperature nickel-metal hydride battery can be obtained. The material has higher charge and discharge capacity obviously higher than that of the commercially available hydrogen storage alloy within the temperature range of 30-80 ℃, the electrochemical charge and discharge capacity at 50 ℃ is more than 310mAh/g, and the capacity at 70 ℃ reaches more than 260 mAh/g.

TABLE 1 contents of respective elements in misch metal

Element(s)	Weight percent (wt%)
		La	64.5-67.5
Ce	22.0-24.0
		Pr	2.5-3.5％
Nd	7.0-9.0

TABLE 2 comparison of the inventive examples with the prior art ingredients (wt%)

Composition (I)		La	Ce	Pr	Nd	Dy	Ni	Co	Mn	Al
											Book (I) Hair-like device Ming dynasty	Mm0.987Dy0.013Ni3.55Co0.75Mn0.4Al0.3	21.53	7.50	0.98	2.61	0.50	49.30	10.46	5.20	1.92
Mm0.974Dy0.026Ni3.55Co0.75Mn0.4Al0.3	21.23	7.40	0.97	2.57	1.00	49.27	10.45	5.20	1.91
										Mm0.961Dy0.039Ni3.55Co0.75Mn0.4Al0.3		20.93	7.30	0.95	2.54	1.50	49.23	10.44	5.19	1.91
Mm0.948Dy0.052Ni3.55Co0.75Mn0.4Al0.3	20.64	7.19	0.94	2.50	2.00	49.20	10.44	5.19	1.91
										Mm0.935Dy0.065Ni3.55Co0.75Mn0.4Al0.3		20.34	7.09	0.92	2.47	2.50	49.17	10.43	5.19	1.91
To pair Ratio of Example (b)	MmNi3.55Co0.75Mn0.4Al0.3	21.83	7.61	0.99	2.65	0.00	49.34	10.47	5.20												1.92

TABLE 3 discharge capacity (mAh/g) of hydrogen storage alloy at different temperatures

Claims (7)

1. The negative hydrogen storage material for nickel-metal hydride battery is characterized in that the expression is (Mm)_1-xDy_x)₁Ni_3.55Co_0.75Mn_0.4Al_0.3Wherein x is more than 0 and less than or equal to 0.065, and Mm is a rare earth mixture consisting of La, Ce, Pr and Nd.

2. The negative hydrogen storage material of claim 1, wherein x is 0.052.

3. The negative hydrogen storage material of claim 1, wherein the material has good high temperature capacity at higher temperatures.

4. The negative hydrogen storage material of claim 3, wherein the temperature is in the range of 30-80 ℃.

5. Negative hydrogen storage material according to claim 2, characterized in that the capacity of the material is increased to 223mAh/g at 80 ℃.

6. Use of a negative hydrogen storage material according to any of claims 1 to 5 for the manufacture of a nickel-metal hydride battery.

7. Use according to claim 6, the nickel-metal hydride battery having better high temperature performance.

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