CN1272461C - Non crystal state hydrogen storge composite material and its producing method - Google Patents

Abstract

An amorphous hydrogen storage composite material and its manufacturing method, characterized in that: the general chemical formula of the composite material is: RE _1-x M _x Mg _12-y N _y +zNi, where 0≤x≤0.5, 0≤y≤3, RE is one or more of the rare earth metals Ce, La, Pr, Nd, Sm, cerium-rich mixed rare earth metal Mm, and lanthanum-rich mixed rare earth metal Ml, and M is capable of reacting with hydrogen to form metal hydrogenation One of the metal elements Ca, Ti, V, Zr, N is one of the transition elements Y, Ni, Co, Fe, Cr, 0.5≤z≤1.5, z is the weight of Ni and RE _1-x M The ratio of _x Mg _12-y N _y weight. Compared with the existing hydrogen storage electrode alloy, the outstanding advantage of the present invention is that it can electrochemically store hydrogen at room temperature. The electrode made of this material has an abnormally high discharge capacity, and is especially suitable for high specific energy nickel-hydrogen batteries. .

Description

A kind of amorphous hydrogen storage composite material and its manufacturing method

Technical field:

The invention relates to an alkaline secondary battery negative electrode active material mainly composed of magnesium, rare earth metal and nickel, in particular to an amorphous hydrogen storage composite material and a manufacturing method thereof.

Background technique:

Nickel-metal hydride (Ni/MH) battery is a high-capacity alkaline secondary battery with a hydrogen storage electrode alloy as the negative electrode active material, and has achieved large-scale industrialization so far. At present, the anode active materials of almost all commercial nickel-metal hydride batteries use rare earth AB ₅ type hydrogen storage electrode alloys, which are multi-element alloys developed on the basis of typical binary LaNi ₅ alloys. The theoretical electrochemical capacity of LaNi ₅ is 372mAh·g ^-1 , while the discharge capacity of commercially available practical AB ₅ multi-element hydrogen storage electrode alloy is only 280-320mAh·g ^-1 , which is about 75-85% of the theoretical discharge capacity of LaNi ₅ .

Due to the rapid development and popularization of electronic products such as computers, communication equipment, audio-visual equipment, and electric vehicles, higher requirements have been placed on the high capacity, miniaturization and light weight of secondary batteries. Several new and improved materials have been proposed, among which some titanium-based AB ₂ -type Laves phase electrode alloys have a discharge capacity of 380-420mAh·g ^-1 , and vanadium-based solid solution-type electrode alloys have a discharge capacity of 350-420mAh· ^{g- 1} , are significantly higher than the rare earth AB ₅ multi-element alloy.

Pure magnesium and magnesium-based hydrogen storage alloys have the highest hydrogen storage density per unit weight among all kinds of hydrogen storage alloys that have appeared so far. Pure magnesium reaches 7.6%; Mg ₂ Ni alloy is 3.6%; The weight hydrogen storage density of magnesium-based alloys (such as typical CeMg ₁₂ , La ₂ Mg ₁₇ ) is between pure magnesium and Mg ₂ Ni, which is 4.5-6.0%, which is much higher than the 1.4% gas density of rare earth AB ₅ alloys. Solid reaction hydrogen storage capacity. However, pure magnesium or magnesium alloys prepared by conventional methods and without any modification treatment cannot achieve gas-solid reaction reversible hydrogen storage or electrochemical reversible hydrogen storage at room temperature. For this reason, various improvement technologies have been researched and proposed, among which, the most effective method is to prepare the magnesium-based alloy into an amorphous structure. In this way, the electrochemical hydrogen storage at room temperature is realized, and literature [2, 3] provides an amorphous prepared by ball milling a mixture of Mg ₂ Ni and Ni, which also realizes electrochemical hydrogen storage at room temperature.

Invention content:

The object of the present invention is to provide a composite material capable of electrochemically storing a large amount of hydrogen at room temperature and a manufacturing method thereof, and the composite material is particularly suitable as a negative electrode active material of a high specific energy nickel-hydrogen battery. The hydrogen storage composite material of the present invention is an amorphous hydrogen storage composite material formed by ball milling a binary or multi-component 1:12 metal compound crystalline rare earth-magnesium-based hydrogen storage alloy and nickel powder. The high hydrogen storage capacity of the rare earth-magnesium-based alloy with the original crystalline structure is maintained, and the disadvantage that the original crystalline alloy cannot electrochemically absorb and desorb hydrogen at room temperature is overcome. Therefore, using this new hydrogen storage composite material instead of the rare earth AB ₅ type electrode alloy as the negative electrode active material of the nickel-metal hydride battery can greatly increase the rated capacity of the battery with the same volume, or greatly increase the volume of the battery with the same rated capacity. decrease.

An amorphous hydrogen storage composite material, characterized in that: the general chemical formula of the composite material is RE _1-x M _x Mg _12-y N _y +zNi, where 0≤x≤0.5, 0≤y≤3 , RE is one or more of rare earth metals Ce, La, Pr, Nd, Sm, cerium-rich mixed rare earth metal Mm, and lanthanum-rich mixed rare earth metal Ml, and M is a metal element Ca that can react with hydrogen to form a metal hydride , one of Ti, V, Zr, N is one of the transition elements Y, Ni, Co, Fe, Mn, Cr, 0.5≤z≤1.5, z is the weight of Ni and RE _1-x M _x Mg _{12 -y} N Ratio of _y weights.

A method for manufacturing an amorphous hydrogen storage composite material, characterized in that the following steps are used:

A) According to the ingredients in the chemical formula RE _1-x M _x Mg _12-y N _y and the weight percentage of the ingredients, put them in an argon-protected vacuum induction furnace to melt them into crystalline alloy ingots, and break the alloy ingots into particles smaller than 75μm alloy powder;

B) Put the above alloy powder and nickel powder 0.5 to 1.5 times the weight of the alloy powder together into a ball mill ball tank for ball milling, the ball to material ratio is 20:1, and continue ball milling for 30 to 50 hours to obtain an amorphous hydrogen storage composite material ; The particle size of the nickel powder is less than 75 μm.

The rare earth-magnesium-based hydrogen storage alloy and nickel powder that make up the composite hydrogen storage material of the present invention are materials that are easily amorphized. In particular, the mixing and ball milling of the two together has the effect of mutually promoting amorphization, and the composite material is amorphous. The higher the degree, that is, the higher the proportion of amorphous state in the composite material, the higher the electrochemical capacity of the composite material at room temperature. The ball milling process is a mechanical grinding process, which is very important for the transformation of crystalline rare earth-magnesium-based alloys into small amorphous states with high specific areas, and the participation of nickel powder in ball milling is essential. It changes the energy transmission and distribution in the grinding process system, so that the rare earth-magnesium-based alloy particles and nickel powder itself can obtain fine amorphous instead of nanocrystalline in a shorter time. The increase of nickel powder shortens the time of ball milling into amorphous, and the degree of amorphization of the composite material is higher; while the proportion of rare earth-magnesium-based alloy in the amorphous composite material increases, the electrochemical hydrogen storage capacity of the obtained amorphous composite material increases. Therefore, the highest electrochemical hydrogen storage capacity can be obtained by using the lowest amount of nickel powder while ensuring that all amorphous composite materials are obtained. When this tiny amorphous composite material is made into an electrode sample, the discharge capacity test is carried out at a constant current of 50mAh g ^-1 in a three-electrode system. At a temperature of 25° _C , the measured discharge capacity is as high as 1000-1200mAh g _-x M _x Mg _12-y N _y ) ^-1 , which is 2 to 3 times that of the currently available rare earth electrode alloys in the market. During the test, the auxiliary electrode is Ni(OH) ₂ /NiOOH, the reference electrode is Hg/HgO, alkali The liquid is 6MKOH, and the discharge cut-off potential is -0.55V (relative to the HgO/Hg electrode).

Example 1:

An amorphous hydrogen storage composite material whose general chemical formula is RE _1-x M _x Mg _12-y N _y +zNi, where RE is Ce, x=0, y=0, z is 0.75, namely Ni The powder weight is 75% of the weight of CeMg ₁₂ , and the weight ratio of Ce and Mg is calculated according to the chemical formula CeMg _12. In the raw material, Ce is metal cerium with a purity of 98%, and Mg is metal magnesium with a purity of 99%. Carry out smelting in a vacuum induction furnace to obtain crystalline CeMg ₁₂ alloy ingots, crush the alloy ingots into alloy powders less than 75 μm, and place them in the spherical tank of a ball mill, then add 75% of the weight of CeMg ₁₂ nickel powder to a ball-to-material ratio of 20 :1 ball mill together, the particle size of the nickel powder is less than 75 μm, the spindle speed of the ball mill is 225 rpm, and the fine amorphous composite material can be obtained after continuous ball milling for 50 hours. The resulting composite material was made into an electrode, and the discharge capacity test was carried out in an alkaline three-electrode system with a constant current of 50mAh g ^-1 , the test temperature was 25°C, the discharge cut-off potential was -0.55V, and the actual discharge capacity was 1050mAh· g(CeMg ₁₂ ) ^-1 .

Example 2:

Preferably, in the general chemical formula RE _1-x M _x Mg _12-y N _y +zNi, RE is Ce, x=0.2, M is Ca, N is Ni, y=1, and z is 1.5, which constitutes Ce _0.8 Ca _0.2 Mg ₁₁ Ni+1.5Ni alloy. Calculate the weight proportion of Ce, Ca, Mg, Ni by chemical formula Ce _0.8 Ca _0.2 Mg ₁₁ Ni, in the raw material, Ca is metallic calcium with a purity of 98%, Ni is electrolytic nickel with a purity of 99%, and the purity of other raw materials is the same as in Example 1. Smelting in a vacuum induction furnace protected by argon to obtain crystalline Ce _0.8 Ca _0.2 Mg ₁₁ Ni alloy ingots, then crushed into alloy powders less than 75 μm, and then ball milled with 150% nickel powder whose weight is the amount of alloy powder, The particle size of the nickel powder is less than 75 μm, and the ball milling process is the same as in Example 1. After 40 hours of continuous ball milling, the mixture is transformed into an amorphous composite material. The measured discharge capacity is 1010mAh·g(Ce _0.8 Ca _0.2 Mg ₁₁ Ni) ^-1 . The electrochemical test method and parameters are the same as in Example 1.

Example 3:

Preferably, in the general chemical formula RE _1-x M _x Mg _12-y N _y +zNi, RE is Ce, x=0.2, M is Ca, N is Y, y=1, z=1.0, constitute Ce _0.8 Ca _0.2 Mg ₁₁ Y+1.0Ni mixed material, calculate the weight ratio of Ce, Ca, Mg and Y according to the chemical formula Ce _0.8 Ca _0.2 Mg ₁₁ Y, Y in the raw material is metal yttrium with a purity of 99%, and the purity of other raw materials is the same as that in Example 2. Smelting Same as embodiment 1 with ball milling process, nickel powder weight and Ce _0.8 Ca _0.2 Mg ₁₁ Y weight ratio is 1.0, ball milling time is 40 hours, and the discharge capacity of the amorphous composite material made is 1150mAh g (Ce _0.8 Ca _0.2 Mg ₁₁ Ni) ^-1 . The electrochemical test method and parameters are the same as in Example 1.

Document [1]: Chinese invention patent CN 1044175C

Literature [2]: J.Alloys and Compounds, 1998 Vol.267, pp76-78

Literature [3]: J.Alloys and Compounds, 1998, Vol.270, pp142-144

Claims (3)

1. An amorphous hydrogen storage composite material, characterized in that: the general chemical formula of the composite material is RE _1-x M _x Mg _12-y N _y+ zNi, where 0≤x≤0.5; 0≤y ≤3; RE is one or more of the rare earth metals La, Ce, Pr, Nd, Sm, cerium-rich mixed rare earth metal Mm, and lanthanum-rich mixed rare earth metal Ml; M is a metal that can react with hydrogen to form a metal hydride One of the elements Ca, Ti, V, Zr; N is one of the transition elements Y, Ni, Co, Fe, Mn, Cr, 0.5≤z≤1.5, z is the weight of Ni and RE _1-x M _x Mg _12-y N _y weight ratio. 2. A method for implementing the amorphous hydrogen storage composite material according to claim 1, characterized in that the following steps are adopted: A) According to the ingredients in the chemical formula RE _1-x M _x Mg _12-y N _y and the weight percentage of the ingredients, put them in an argon-protected vacuum induction furnace to melt them into crystalline alloy ingots, and break the alloy ingots into particles smaller than 75μm alloy powder; B) Put the above alloy powder and nickel powder 0.5 to 1.5 times the weight of the alloy powder together in a spherical tank of a ball mill for ball milling, with a ball-to-material ratio of 20:1, and continue ball milling for 30 to 50 hours to obtain an amorphous hydrogen storage compound Material. 3. The manufacturing method according to claim 2, characterized in that: Ni in the chemical formula refers specifically to nickel powder, and the particle size of the nickel powder used in the manufacturing process is less than 75 μm.