CN100470893C - A kind of negative electrode active material of high-power nickel-metal hydride storage battery and its preparation method and nickel-hydrogen storage battery - Google Patents

Abstract

A high-power nickel-hydrogen storage battery negative electrode active material and its preparation method and nickel-hydrogen storage battery. The negative electrode active material is to deposit a layer of alloy film on the surface of hydrogen storage alloy powder. The alloy film contains metal nickel, palladium, The composition of one or more of platinum, gold, rhodium and the composition of one or two of the easily soluble metal elements aluminum, zinc, etc. in alkaline aqueous solution makes the surface of the hydrogen storage alloy form a rich A porous structure containing one or more of the metals nickel, palladium, platinum, gold, and rhodium. The preparation method of the negative electrode active material is to deposit a layer of alloy film on the surface of the hydrogen storage alloy powder, and place the hydrogen storage alloy powder after depositing the alloy film in high-temperature alkali for treatment, so that the surface of the hydrogen storage alloy is formed rich in metal nickel, palladium, Porous structure of one or more of platinum, gold and rhodium. The surface of the negative electrode of the nickel-metal hydride storage battery is coated with the above-mentioned negative electrode active material. The invention can effectively improve the anti-oxidation performance of the negative electrode of the nickel-metal hydride storage battery.

Description

A kind of negative electrode active material of high-power nickel-metal hydride storage battery and its preparation method and nickel-hydrogen storage battery

technical field

The invention relates to a negative active material for a nickel-hydrogen battery, in particular to a negative active material for a high-power nickel-hydrogen battery, a preparation method thereof, and a nickel-hydrogen battery.

Background technique

The negative electrode active material of alkaline secondary nickel-hydrogen battery generally adopts AB ₅ (LaNi ₅ ) hydrogen storage alloy. During the charging and discharging process of the battery, due to the local severe polarization or overcharging of the positive electrode of the battery, the positive electrode reaches the oxygen evolution potential, resulting in oxygen. The generated oxygen passes through the diaphragm and reaches the negative electrode, a part of the oxygen recombines at the negative electrode to form water, and there is always a part of the oxygen that cannot be recombined and oxidizes the hydrogen storage alloy. After the surface of the alloy powder is oxidized, the electrical contact and electrochemical activity of the powder decrease, which is the main reason for the capacity fading of the battery during cycling.

Ni-MH high-power batteries such as H-SC are mainly used in electric tools and toys. The charging and discharging current of this battery is required to be higher than that of conventional batteries, resulting in higher charging and discharging temperatures of the battery, and the higher the temperature, the hydrogen storage alloy The faster the oxidation rate, the more electrochemically inert oxide or hydroxide film is formed on the surface of the alloy powder. The inert film increases the contact resistance between the alloy powders, and at the same time makes the electrochemical reaction process of hydrogen atoms on the alloy surface In addition, due to the small specific surface of conventional hydrogen storage alloys, generally 0.01-0.1m ² /g, when the battery is discharged at a high current, the real current density of the negative electrode is very high and the polarization is serious. This leads to the reduction of the high-current discharge platform (discharge power) of the battery, and eventually leads to the premature failure of the battery.

In order to slow down the oxidation of the negative electrode, one of the traditional methods is to use high-temperature alkali treatment to dissolve the Mn and Al elements on the alloy surface into the solution, so that the Ni element is relatively enriched on the surface, thereby improving the oxidation resistance of the alloy powder, but the improvement of this method The effect is very limited. In addition, electroless plating is used for hydrogen storage alloys, and the reducing agent is sodium hypophosphite or sodium borohydride. However, taking electroless nickel plating as an example, the NI-P or NI-B alloy formed on the surface of alloy powder by electroless plating will reduce Alloy surface conductivity and electrochemical activity. In addition, the alloy film mentioned in the present invention and the porous structure that can significantly increase the specific surface area of the alloy powder cannot be formed by using the electroless plating method.

Contents of the invention

The purpose of the present invention is to solve the above problems, and to provide a battery that can effectively improve the oxidation resistance of the negative electrode of the battery and significantly increase the specific surface of the negative electrode of the battery, and make the battery prepared by it still maintain a good charge at the initial stage and after several cycles. Contact and electrochemical activity, to improve the large current discharge power and cycle life of the negative electrode active material of the battery; the purpose of the present invention is also to provide the preparation method of the negative electrode active material and the nickel-metal hydride storage battery containing the negative electrode active material.

In order to achieve the above object, the present invention provides a negative electrode active material, which is to deposit a layer of alloy film on the surface of hydrogen storage alloy powder, and the alloy film contains metal nickel, palladium, platinum, gold and rhodium that are not easily oxidized by oxygen. One or more compositions and one or more compositions of metal elements aluminum, zinc, etc. that are easily soluble in alkaline aqueous solution, and finally make the surface of the hydrogen storage alloy rich in metal nickel, A porous structure of one or more of palladium, platinum, gold, and rhodium.

The preferred alloy film is a nickel-aluminum or nickel-zinc alloy film, wherein the atomic ratio of aluminum or zinc is 1 to 50%, preferably the atomic ratio of aluminum or zinc is 10 to 40%, and the thickness of the alloy film is 0.01 ~1.0 μm, preferably 0.1-0.3 μm.

The present invention also provides a method for preparing the negative electrode active material. The method is to deposit a layer of alloy film on the surface of the hydrogen storage alloy powder. One or more compositions and one or two compositions of metal elements such as aluminum and zinc that are easily soluble in alkaline aqueous solution, and the hydrogen storage alloy powder after depositing the alloy film is placed in a high-temperature alkali treatment in an alkaline aqueous solution, so that the aluminum, zinc and other elements in the alloy film undergo pitting corrosion and dissolve into the alkaline aqueous solution, so that the surface of the hydrogen storage alloy is rich in one or more of the metals nickel, palladium, platinum, gold, and rhodium. More than one porous structure.

The deposition of the metal composition on the surface of the hydrogen storage alloy powder is to place the hydrogen storage alloy powder to be treated in a magnetron sputtering coating machine using a planar magnetron sputtering target. Alloys of one or more compositions of metal nickel, palladium, platinum, gold, rhodium, and compositions of one or two of metal elements easily soluble in alkaline aqueous solutions, such as aluminum and zinc, and alloys The powder falls freely by its own weight and passes through the sputtering target, or the alloy powder is thrown on a plane parallel to the target by ultrasonic waves, mechanical vibrations, etc., and the sputtering deposition process is completed at the same time. The hydrogen storage alloy powder is processed by multiple sputtering.

The hydrogen storage alloy powder deposited with the alloy thin film is placed in an alkaline aqueous solution, and after being stirred, it is washed with deionized water until the pH value is neutral, and then vacuum-dried.

The present invention also provides a nickel-metal hydride storage battery containing the negative active material. The nickel-hydrogen storage battery includes a positive pole, a diaphragm, a negative pole and an electrolyte, which are sealed in a battery casing, and it is characterized in that the surface of the negative pole is coated with the The negative electrode active material is a layer of alloy film deposited on the surface of the hydrogen storage alloy powder, and the alloy film contains one or more of metal nickel, palladium, platinum, gold, and rhodium that are not easily oxidized by oxygen The composition and the composition of one or more of the metal elements aluminum and zinc that are easily soluble in alkaline aqueous solution, and make the surface of the hydrogen storage alloy form a medium rich in metal nickel, palladium, platinum, gold and rhodium One or more porous structures.

The contribution of the invention is that it effectively solves the problem of surface oxidation of the negative electrode hydrogen storage alloy powder and significantly improves the specific surface of the electrode. Because a layer of alloy film is deposited on the surface of the hydrogen storage alloy, and the surface is treated with alkali to form a porous composition rich in one or more of the metals nickel, palladium, platinum, gold, and rhodium that are not easily oxidized by oxygen. structure, so that the film has good oxidation resistance, while forming a high specific surface area. The hydrogen storage alloy powder can still maintain good electrical contact and electrochemical activity at the initial stage of the battery and after several cycles, thereby ensuring the smooth progress of the negative electrode charge and discharge reaction on the surface of the alloy powder. The high-current discharge performance of the battery and the cycle performance of the battery are improved.

Description of drawings

Fig. 1 is a comparison curve of the median voltage of the battery prepared by using the negative electrode active material of the present invention and the comparative example 10C discharge cycle.

Fig. 2 is a comparison curve of the discharge cycle capacity of the battery prepared by using the negative electrode active material of the present invention and the comparative example 10C.

Detailed ways

The following examples are further explanations and illustrations of the present invention, and do not constitute any limitation to the present invention.

Example 1:

Put the hydrogen storage alloy master powder MmNi _3.55 Co _0.75 Mn _0.4 Al _0.3 (Mm means mixed rare earth composed of one or more of La, Ce, Pr, Nd) to be processed in a special magnetron sputtering coating machine, The hydrogen storage alloy master powder can be produced by a known method. The coating machine adopts planar magnetron sputtering target, and the target material is nickel, palladium, platinum, gold, rhodium and other metals that are not easy to be completely oxidized by oxygen, and is easy to dissolve in alkaline aqueous solution with aluminum and zinc. An alloy formed by a combination of one or two metals. In this example, nickel-aluminum alloy is preferred, wherein the preferred proportion of aluminum is 30% (atomic ratio), the target is set vertically and horizontally, the target height is about 3m, and the single processing capacity of the coating machine is 200kG. The powder to be treated falls freely from the top of the coating machine by its own weight and passes through the sputtering target, and the sputtering deposition process is completed at the same time. The powder is treated by multiple sputtering. After one sputtering is completed, the powder falls into the bottom of the coating machine, and the powder is lifted to the top of the coating machine by a conveying device, and the next sputtering starts. The time required from the completion of one sputtering to the next sputtering process is about 5 minutes. Because the surface of the powder facing the target surface is random during the free fall process, through multiple sputtering, a relatively uniform coating layer can be formed on all surfaces of the alloy powder.

Step 1. Set the vacuum degree to 8.5×10 ^-3 Pa. When the set vacuum degree is reached, argon gas is introduced to the vacuum degree of 3×10 ^-1 Pa, and the sputtering current is set to 8mA/cm ² . When the power is turned on, argon ions hit the nickel-aluminum alloy target at high speed, and the atoms of the target are ejected and deposited on the surface of the alloy powder. The deposition rate is 0.5 μm/min, and the hydrogen storage alloy powder is sputtered 6 times. Take the sputtered alloy powder and etch it with an argon ion gun, and then use AES to analyze the surface composition (using the American PHI company model PHI5800 Auger electron spectrometer), when the characteristic peak of La appears in the AES spectrum, the depth of etching About 0.2 μm. Therefore, it can be preliminarily determined that the thickness of the film formed on the surface of the alloy is about 0.2 μm.

Step 2. Place the plated hydrogen storage alloy powder in 30% KOH aqueous solution at 80°C, stir it for about 1 hour, wash it with deionized water until the pH is neutral, and dry it in vacuum. In this way, the present invention is produced. The negative electrode active material A. Using helium as the carrier gas and nitrogen as the adsorption gas, the BET specific surface of the alloy powder after sputtering was measured to be 0.5m ² /g (by using the SSA3500 specific surface analyzer of Beijing Biod Corporation).

Same as the above steps, only the nickel-aluminum alloy targets with different aluminum contents (10%, 20%, 40%) were used in step 1 to prepare negative active materials A1, A2, A3 respectively. The comparison of its BET specific surface and related data with A is shown in Table 1: (the contents are all atomic ratios)

Table 1

Compare Items/Treatment Categories A A1 A2 A3 Alloy target aluminum content (%) 30 10 20 40 Powder specific surface after treatment (m²/g) 0.5 0.2 0.3 0.5 Nickel content (%) after alkali treatment of the coating (relative to the coating amount before alkali treatment) 70 90 80 60

In the present invention, the content of aluminum or zinc in the nickel-aluminum/nickel-zinc alloy target material is no more than 50%, otherwise, under the same sputtering coating thickness, the best nickel-rich effect cannot be obtained on the surface of the hydrogen storage alloy ( nickel-rich amount), so the content of aluminum or zinc in the nickel-aluminum/nickel-zinc alloy target in the present invention ranges from 1 to 50%.

It can be seen from the data in Table 1 that with the increase of aluminum content, the specific surface of the powder after treatment also gradually increases. When the aluminum content is about 30%, the specific surface reaches the maximum value, and the specific surface does not increase significantly when the aluminum content is increased. However, the nickel enrichment effect (nickel content) is reduced.

Therefore, in the present invention, when the aluminum content in the alloy target is 30%, the best nickel-enriching effect (nickel content) is ensured at the same time on the premise of obtaining the largest specific surface area after treatment.

Step 3, get 100 parts of negative active material A, 0.5 part of conductive carbon black, 2 parts of nickel powder, 10 parts of adhesive HPMC (3% concentration), 2 parts of PTFE (60% concentration), 20 parts of deionized water, Stir well to prepare negative electrode slurry. The negative electrode slurry is evenly covered on both sides of the perforated nickel-plated steel strip by means of slurry drawing, and rolled to a thickness of 0.34~0.35mm by a roller mill, and cut into 35mm*320mm specifications to make a negative electrode sheet of SC3000mAh battery, and corresponding The positive electrode is matched with a Ni-MH SC3000mAh capacity battery, which is recorded as Class A;

Embodiment 2: The difference from Step 1 of Embodiment 1 is that the hydrogen storage alloy powder is sputtered twice in a vacuum sputter coating machine. The thickness of the film on the surface of the alloy is measured to be about 0.05 μm, and then the second step is carried out. After the treatment, the specific surface is about 0.15m ² /g, and the battery is made through the third step, which is recorded as B type;

Example 3:

The difference from Step 1 of Example 1 is that the hydrogen storage alloy powder is sputtered 15 times in a vacuum sputter coater. The thickness of the film on the surface of the alloy is measured to be about 0.5 μm, and then the second step is carried out. After the treatment, the specific surface is about 0.8m ² /g, and the battery is made through the third step, which is recorded as C type;

Example 4:

The difference from Step 1 of Example 1 is that the target material is a nickel-zinc alloy with a zinc content of 30% (atomic ratio), and the hydrogen storage alloy powder is subjected to 6 sputtering treatments in a vacuum sputtering coating machine. The thickness of the film on the surface of the alloy is measured to be about 0.2 μm, and then the second treatment is performed, and the specific surface after treatment is about 0.5 m ² /g. The battery made through step 3 is recorded as class D;

Comparative example 1:

Place the alloy master powder to be treated at an appropriate amount of 80°C, stir fully with 30% KOH aqueous solution for 1 hour, add 3% (relative to the weight of the alloy powder) sodium hypophosphite reducing agent and stir fully for 20 minutes, after the reaction is complete, use a deionized Wash it with water until pH = 7, and dry it in vacuum for later use. At the same time, its BET adsorption specific surface was tested to be 0.03m ² /g. The battery made through step 3 is recorded as Class E.

Comparative example 2:

Put 1 part of alloy master powder to be treated into 1 part of plating solution, and stir well. The composition of the plating solution is: nickel sulfate (NiSO ₄ ·7H ₂ O) 30g/L, sodium hypophosphite (NaH ₂ PO ₂ ·H ₂ O) 20g/L, ammonium citrate ((NH ₄ ) ₃ C ₆ H ₅ O ₇ ) 50g/L, the bath temperature is controlled at 90°C, the pH value is controlled at 8-10, and the treatment time is 15min. Wash the treated alloy powder with deionized water until pH = 7, and dry it in vacuum for later use. Meanwhile, its BET adsorption specific surface was tested to be 0.04m ² /g. The battery is made through step 3, which is recorded as Class F.

Batteries A to F were subjected to relevant comparative tests.

Test Methods:

Charge the battery at 1C for 65 minutes, put it aside for 5 minutes, discharge at 10C (30A) to 0.8V/cell, and record the discharge capacity and median voltage of the battery. Cycle test 200 times.

The test results are shown in Table 2: 10C (30A) discharge median voltage and capacity comparison and Figure 1 and Figure 2.

Table 2

battery type A B C D. E. f Initial median voltage (V) 1.131 1.118 1.115 1.125 1.070 1.074 After 200 times the median voltage (V) 1.110 1.078 1.080 1.100 1.000 0.999 Median voltage drop (mV) twenty one 40 35 25 70 75 Initial discharge capacity (mAh) 3020 3012 3005 3009 2940 2933 Discharge capacity after 200 times (mAh) 2849 2632 2741 2816 2332 2322 Capacity retention (%) 94.3 87.4 91.2 93.6 79.3 79.2

Remarks: A-F batteries have been fully activated before testing.

As shown in Table 2, the battery class A (Example 1) 10C (30A) discharge initial median voltage can reach 1.131V by using the negative active material of the present invention, indicating that the negative active material of the battery in Example 1 has excellent initial performance . After 200 cycles, the median voltage can still maintain 1.110V, the median voltage drop is only 21mV, and the discharge capacity can maintain more than 94% of the initial value, indicating that the negative active material of the battery in Example 1 can still maintain a relatively high level after 200 cycles. Good electrical contact and high electrochemical activity.

And class B battery (embodiment 2) 10C (30A) discharge initial median voltage is 1.118V, and the median voltage drop after 200 cycles reaches 40mV, and capacity retention is only 87.4%. It is estimated that because sputtering time is too short, in The film formed on the surface of the hydrogen storage alloy powder is partially incomplete.

Class C battery (embodiment 3) 10C (30A) discharge initial median voltage can reach 1.115V, and the median voltage drop after 200 cycles reaches 35mV, and capacity keeps 91.2%. Preliminary analysis is because the sputtering time is longer, storage The thin film formed on the surface of the hydrogen alloy is relatively thick. Although it can maintain good electrical contact, it affects the diffusion of hydrogen atoms from the surface of the alloy powder to the interior of the alloy powder and the diffusion and desorption speed of hydrogen atoms in the alloy powder phase to the alloy surface. That is, the electrochemical activity of the alloy powder is reduced.

Class D battery (embodiment 4) 10C (30A) discharge initial median voltage can reach 1.125V, and the median voltage drop after 200 cycles is 25mV, and capacity keeps 93.6%, illustrates that the nickel-zinc alloy thin film of plating can obtain and Similar results were obtained for nickel-aluminum alloy films.

Class E battery (comparative example 1) 10C (30A) discharge initial median voltage is 1.070V, and the median voltage drop after 200 cycles reaches 70mV, and the capacity is kept as 79.3%; F class battery (comparative example 2) 10C (30A) The initial median voltage of discharge was 1.074V, the median voltage drop after 200 cycles reached 75mV, and the capacity retention was 79.2%. Because the surface of the hydrogen storage alloy powder treated by the method of Comparative Example 1 and Comparative Example 2 cannot form the structure mentioned in the present invention, good electrical contact and electrochemical activity cannot be obtained initially and after several cycles.

To sum up, the present invention can significantly improve the high-current discharge capacity of the battery and significantly increase the cycle life of the battery.

Claims (7)

1, a kind of high power nickel-hydrogen accumulator negative electrode active substance, it is characterized in that, at hydrogen-storage alloy powder surface deposition one deck alloy firm, this alloy firm comprises and is difficult for by the metallic nickel of oxygen complete oxidation, palladium, platinum, gold, the composition of one or more in the rhodium and the metallic element aluminium that in alkaline aqueous solution, dissolves easily, the composition of one or more in the zinc, place the high-temperature alkaline aqueous solution to handle the hydrogen-bearing alloy powder behind the deposit alloy film, make the aluminium in the alloy firm, the zinc element dissolving enters in the alkaline aqueous solution, thereby forming, the surface that makes hydrogen-storage alloy is rich in metallic nickel, palladium, platinum, gold, the loose structure of one or more in the rhodium, the thickness of described alloy firm are 0.01～1 μ m.

2, high power nickel-hydrogen accumulator negative electrode active substance as claimed in claim 1 is characterized in that, preferred alloy firm is nickel-aluminum alloy films, and wherein the atomic ratio ratio of aluminium is 1～50%.

3, high power nickel-hydrogen accumulator negative electrode active substance as claimed in claim 1 is characterized in that, the thickness of described alloy firm is 0.1～0.3 μ m.

4, a kind of preparation method of negative electrode active material according to claim 1, it is characterized in that, at hydrogen-storage alloy powder surface deposition one deck alloy firm, this alloy firm is by being difficult for by the metallic nickel of oxygen complete oxidation, palladium, platinum, gold, the composition of one or more in the rhodium and the metallic element aluminium that in alkali, dissolves easily, the composition of one or both in the zinc is formed, place the high-temperature alkaline aqueous solution to handle the hydrogen-storage alloy powder behind the deposit alloy film, make the aluminium in the alloy film, the zinc element dissolving enters in the alkaline aqueous solution, make the surface formation of hydrogen-storage alloy be rich in metallic nickel, palladium, platinum, gold, the loose structure of one or more in the rhodium, the thickness of described alloy firm are 0.01～1 μ m.

5, preparation method as claimed in claim 4, it is characterized in that, the deposition of described metal composites on the hydrogen-storage alloy powder surface is pending hydrogen-storage alloy powder to be placed in the magnetron sputtering coater that adopts plane magnetic controlled sputtering target, target is by being difficult for by the metallic nickel of oxygen complete oxidation, palladium, platinum, gold, the composition of one or more in the rhodium and the metallic element aluminium that in alkali, dissolves easily, the alloy that the composition of one or both in the zinc is formed, alloy powder freely falls by deadweight or passes through ultrasonic wave, mechanical vibration method is thrown moving, and, finish sputter deposition process simultaneously by sputtering target.

6, preparation method as claimed in claim 5 is characterized in that, hydrogen-storage alloy powder adopts repeatedly sputter process.

7, a kind of nickel-hydrogen accumulator that contains the described negative electrode active material of claim 1, comprise positive pole, barrier film, negative pole and electrolyte, they are sealed in the battery case, it is characterized in that, described negative terminal surface is coated with described negative electrode active material, this negative electrode active material is at hydrogen-storage alloy powder surface deposition one deck alloy firm, this alloy firm comprises and is difficult for by the metallic nickel of oxygen complete oxidation, palladium, platinum, gold, the composition of one or more in the rhodium and the metallic element aluminium that in alkaline aqueous solution, dissolves easily, the composition of one or more in the zinc, place the high-temperature alkaline aqueous solution to handle the hydrogen-bearing alloy powder behind the deposit alloy film, make the aluminium in the alloy firm, the zinc element dissolving enters in the alkaline aqueous solution, thereby forming, the surface that makes hydrogen-storage alloy is rich in metallic nickel, palladium, platinum, gold, the loose structure of one or more in the rhodium, the thickness of described alloy firm are 0.01～1 μ m.

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