CN1155520C - Process for preparing superfine lithium aluminate used for membrane of fused carbonate fuel battery - Google Patents

Abstract

A preparation technology of γ-LiAlO ₂ superfine material for molten carbonate fuel cell diaphragm, characterized in that it follows the following steps: mixing Li ₂ CO ₃ , γ-AlOOH, KCl, and NaCl as raw materials and adding anhydrous ball milling medium Ball milling; react at a high temperature of 550-750°C for 0.5-1 hour; repeatedly wash the reacted material with deionized water; roast the above hydrate at a high temperature of 450-650°C for _0.5-2 hours; Add an anti-sintering agent to the fine material, and bake it at 850-950°C for 1-2 hours to produce γ-LiAlO ₂ superfine material. The process of the invention is simple and reliable, and the energy consumption is low, and is suitable for mass production of powder materials and preparation of large-capacity battery separators.

Description

Preparation method of lithium aluminate superfine material for molten carbonate fuel cell diaphragm

The invention relates to a molten carbonate fuel cell, and in particular provides a preparation technology of gamma- _LiAlO2 superfine material for the diaphragm of the molten carbonate fuel cell.

Molten carbonate fuel cells operate at high temperatures (650-700°C), and high-pressure reaction gases: hydrogen and oxygen are passed through both sides of the diaphragm inside the battery. The separator is one of the core components of the battery. The material that constitutes the separator is generally LiAlO ₂ powder, and LiAlO ₂ powder has three different crystal forms of α, β and γ. γ-LiAlO ₂ is made of α- and β-LiAlO ₂ It is obtained by long-term roasting at 900°C, so the crystal structure of γ-LiAlO ₂ is relatively stable. Generally _, γ-LiAlO ₂ powder is used to prepare separators, and the thickness of γ-LiAlO ₂ is matched. 1 μm) fine (grain size <1 μm) matching material to prepare the diaphragm has high gas barrier properties, good thermomechanical properties and high electrolyte storage capacity. Existing technologies for preparing lithium metaaluminate mainly contain the following: 1.Arendt RH (J.Electrochem.Soc.1980,127(8):1660-1667) and others use the chloride method to prepare β-LiAlO _2. Fine material (including α-LiAlO ₂ ), which uses LiOH·H ₂ O and Al ₂ O ₃ ·3H ₂ O as raw materials, plus 50wt% chloride (NaCl+KCl) and ball milling medium methanol, etc. After ball milling→drying→reaction (662～672℃)→cleaning→β-LiAlO ₂ regeneration (500～600℃). Since the X-ray diffraction peaks of β-LiAlO ₂ hydrate and β-LiAlO ₂ are almost the same, Arendt et al. failed to realize the process of β-LiAlO ₂ →β-LiAlO ₂ hydrate →β-LiAlO ₂ . Finally, the BET specific surface area of the β-LiAlO ₂ fine material is ≤80M ² /g, and the particle size is 0.34 μm. 2. Poeppelmeier KR (Inorganic Chemistry 1988, 27: 4523-4524) et al. used LiOH·H ₂ O and Al(OH) ₃ as raw materials to prepare α-LiAlO ₂ fine material by wet reaction (ie salt inhalation reaction mechanism). After the raw materials are uniformly mixed by ball milling, α-LiAlO ₂ is obtained by passing water air at 400°C for 100 hours, with a particle size of about 1 μm and a BET specific surface area of about 60M ² /g. 3. Mason David.M. (United States Patent.1976, 3,998,939) et al. used Li ₂ CO ₃ and α-LiAlO ₂ as raw materials, and mixed them uniformly by ball milling, and then prepared them in carbonate (Li-K-Na or K- Na) to prepare β-LiAlO ₂ . The first stage: 480-550°C, 4-15 hours; the second stage: 600-650°C, 20-100 hours. In the process of preparing β-LiAlO ₂ (containing α- and a small amount of γ-LiAlO ₂ ), the purity requirements of raw materials are relatively high, and the total impurity content should not exceed 0.1%. 4. Kadokura Hidekimi (United States Patent. 1987, 4,704,266) and others used LiOH·H ₂ O and alkyl aluminum oxide as raw materials to prepare γ-LiAlO ₂ . Under the action of water and ethanol, the alkyl aluminum oxide is hydrolyzed to produce Al(OH) ₃ . Al(OH) ₃ reacts with LiOH·H ₂ O to generate α-LiAlO ₂ . In the presence of water, α-LiAlO ₂ undergoes hydration to produce α-LiAlO ₂ hydrate. The hydrate is calcined at 650-1000°C for 3 hours, and finally becomes γ-LiAlO ₂ . Its BET specific surface area is ≤20M ² /g. In the preparation of molten carbonate fuel cell membranes, γ-LiAlO ₂ is generally used, and γ-LiAlO ₂ is obtained by calcination of α- or β-LiAlO ₂ at 900°C for a long time. None of the above three methods have been developed into a technology for preparing γ-LiAlO ₂ ultrafine materials, and some of them have high energy consumption, such as passing water and air at 400°C for 100 hours, or 600-650°C for 20-100 hours, The β-LiAlO ₂ powder produced by the third method has no particle size and specific surface area data, and LiOH·H ₂ O is used as raw material, its properties are unstable, and finally it becomes Li ₂ O (melting point > 1700°C), resulting in the preparation of fine materials Difficulties. The γ-LiAlO ₂ prepared by the fourth method above has no particle size data. It can also be seen from the above that it is difficult to prepare fine materials using LiOH·H ₂ O as a raw material. Therefore, the fourth method is called the preparation of γ-LiAlO ₂ fine materials at best. technology, not to mention the technology for preparing γ-LiAlO ₂ ultrafine materials.

The purpose of the present invention is to provide a preparation technology of gamma- _LiAlO2 for molten carbonate fuel cell diaphragm, the process is simple, reliable, low energy consumption, suitable for mass production of powder and preparation of large-capacity battery diaphragm.

The invention provides a kind of gamma- _LiAlO superfine material preparation technology for molten carbonate fuel cell membrane, it is characterized in that following steps are carried out:

(1) Ingredients

Mix Li ₂ CO ₃ , γ-AlOOH, KCl, and NaCl as raw materials and add anhydrous ball milling media for ball milling until the particle size of the reactant is less than 1 μm; the molar ratio of Li ₂ CO ₃ to γ-AlOOH is 1.02/2～1.05/2, The molar ratio of KCl to NaCl is 0.9/1～1.1/1; the weight of chloride accounts for 50～80% of the total material;

(2) High temperature reaction

Dry the above materials, crush them, and react at a high temperature of 550-750°C for 0.5-1 hour to generate α-LiAlO ₂ ;

(3) Cleaning and hydration of α- _LiAlO2

Wash the reacted material repeatedly with deionized water to remove K ⁺ , Na ⁺ , Cl ^- ions, and hydrate α-LiAlO ₂ to form white hydrate;

(4) Regeneration of α-LiAlO ₂

Calcining the above hydrate at a high temperature of 450-650°C for 0.5-2 hours;

(5) Generation of α-LiAlO ₂ ultrafine material

Add an anti-sintering agent to the α- _LiAlO2 fine material generated above, the anti-sintering agent is selected from the carbonaceous material of carbon black and acetylene black, and the addition is 2 to 5% by weight; ball milling in anhydrous ball milling medium for 5 to 20 hour, dry the material; finally bake at 850-950° C. for 1-2 hours to produce γ-LiAlO ₂ superfine material.

In addition, sodium citrate, potassium, sodium oxalate, potassium, sodium tartrate, potassium can be added in the cleaning step of the present invention as anion flocculants to remove chloride ions in the powder. The anhydrous ball milling medium used in the present invention is anhydrous organic reagents such as absolute ethanol, anhydrous methanol, and anhydrous acetone, and the added weight is equivalent to that of the materials.

The gamma- _LiAlO provided by the present invention The mechanism of each step of the preparation technology of ultrafine material is as follows:

(1) Ingredients

The key of this step is to select LiCO ₃ as the Li source material, and ball mill the reaction material to <1 μm. Due to the stable nature of _LiCO3 , appropriately increasing the reaction temperature can increase the fluidity of the molten salt and the uniformity of the reaction, increase the speed of the surface reaction and weaken the diffusion reaction, thereby making the particle size of the reaction product smaller. In addition, the ball milling process of the reactants can make the particle size of the reactants smaller, and the reaction to form α-LiAlO ₂ is mainly based on the rapid reaction on the surface, and the reaction can be completed in a short time, while avoiding high-temperature sintering.

(2) High temperature reaction

In this step, Li ₂ CO ₃ and chloride form a ternary eutectic, which exists in an ion state, γ-AlOOH is dispersed in the melt as particles, and Li ⁺ is sucked into the crystal surface of the layered compound γ-AlOOH react with Al ³⁺ in the crystal gap to generate LiAlO ₂ , that is, the salt (Li ⁺ ) inhalation reaction mechanism, because the particle size of the reactant is small (particle size <1 μm) and the surface atomic ratio is high, the reaction to generate α-LiAlO ₂ is based on The rapid surface reaction is the main one, and the reaction is completed within 1 hour, and the particle size of the reactant γ-AlOOH determines the particle size of the product.

(3) Cleansing and Hydration

The key of this step is the removal of chloride ions, which are the flocculant of α- _LiAlO2 powder and its high-temperature sintering agent, so the chloride ions should be thoroughly cleaned until no chloride ions can be detected with silver nitrate solution. During cleaning, as the concentration of chloride ions becomes lower, the powder is suspended in the aqueous solution, which increases the difficulty of cleaning. An anionic flocculant, such as sodium citrate (potassium) and sodium oxalate (potassium), is added to the powder suspension. And sodium tartrate (potassium), etc. During the cleaning process, α-LiAlO ₂ simultaneously produced hydration:

(1) The white hydrate was obtained by filtration, and the hydrate was found to be (LiAlO ₂ ) ₂ ·5H ₂ O (n=5) through X-ray and thermogravimetric analysis.

(4) Regeneration of α-LiAlO ₂

The essence of this step is to lose crystal water and generate α-LiAlO ₂ , the process:

Due to the quasi-reversible process, the particle size of α-LiAlO ₂ is further reduced to 0.33 μm, and the BET specific surface area is 130-140M ² /g.

(5) Generation of γ-LiAlO ₂ ultrafine material

In this step, due to the small particle size of the α- _LiAlO2 fine material, the high proportion of surface atoms, the surface atoms and lattice are very active, and the short-term high-temperature reaction can complete the crystal transformation. At the same time, when the crystal transformation reaction is carried out at 900 ° C, α-LiAlO ₂ is first converted into amorphous form, and after absorbing surface energy, the amorphous form is gradually converted into γ-LiAlO ₂ , and the surface energy is released at the same time. Due to the small particle size of the powder, α-LiAlO ₂ → Amorphous → γ-LiAlO ₂ process is accompanied by atomic rearrangement reaction, and the high-temperature treatment ends when the γ-LiAlO ₂ grains have not yet grown.

In a word, the difference between the present invention and the prior art is:

(1) The particle size of the reactant is small and the proportion of surface atoms is high. In the reaction of forming α-LiAlO ₂ , the rapid reaction on the surface is the main reaction, and the reaction can be completed within 1 hour at high temperature. After the reaction, the chloride ion (α-LiAlO ₂ flocculant and sintering agent), etc., after dehydration of α-LiAlO ₂ hydrate, the product α-LiAlO ₂ fine material has a particle size of 0.33 μm and a BET specific surface area of 130-140M ² /g.

(2) The α-LiAlO ₂ fine material has a small particle size and a high surface atomic ratio. When roasted at 900 ° C, a rapid crystal transformation reaction occurs, and the crystal transformation can be completed in a short time. The addition of an anti-sintering agent avoids high-temperature sintering. α-LiAlO ₂ is first transformed into an intermediate transition type-amorphous form, and then transformed into γ-LiAlO ₂ , which is accompanied by atomic rearrangement reactions. The addition of anti-sintering agents promotes this process, and the final product γ-LiAlO ₂ ultrafines are even smaller than their predecessor α- _LiAlO2 fines.

The above two points are the technical characteristics (or technical key) in the process of preparing α- _LiAlO2 fine material and γ- _LiAlO2 ultrafine material respectively, the former is the basis of the latter, and the latter is the inevitable result of the former; On the basis, technical measures have been further strengthened, such as adding anti-sintering agent and so on. The two points before and after constitute an inseparable and complete technology for the preparation of γ-LiAlO ₂ ultrafine materials, which has never been seen in previous literature.

The present invention uses Li ₂ CO ₃ and γ-AlOOH as raw materials to prepare γ-LiAlO ₂ superfine material by the chloride method, the particle size is less than 0.18 μm, and the BET specific surface area is greater than 40M ² /g. The process is novel, simple and reliable. The energy consumption is about 10% of the previous methods in the literature, which fully meets the needs of mass production of powder materials and preparation of large-capacity battery separators.

The present invention is described in detail below by way of examples.

Figure 1 is the X-ray diffraction pattern of γ-LiAlO ₂ ultrafine material obtained at 900°C for different times.

Figure 2 is the particle size distribution curve of γ-LiAlO ₂ superfine material.

Fig. 3 is a molten carbonate fuel cell (MCFC) (NiO-Ni) I-V characteristic curve, and the utilization ratios of fuel gas and oxidant are both 20%.

Example 1

Li ₂ CO ₃ (analytical pure): 510 grams (for complete reaction, Li ₂ CO ₃ excess 2%), γ-AlOOH: 810.8 grams, plus 60 wt% chloride (KCl+NaCl, Mol. _KCl /Mol. _NaCl ≌1.0), plus absolute ethanol. The preparation is carried out according to the following main steps: ball mill Li ₂ CO ₃ , γ-AlOOH, chloride and absolute ethanol for 30 hours, dry at 100°C for 10 hours, and then bake at 650°C for 1 hour, then use deionized Wash with water and anionic flocculant, filter and dry, bake at 550°C for 1 hour, add anti-sintering agent and absolute ethanol, ball mill for 10 hours, and bake at 900°C for 1 to 2 hours, X-ray analysis, the product The crystal form is γ-LiAlO ₂ , see attached drawing 1, without other impurities; the yield is 90% (a small part is lost during cleaning), its particle size is less than 0.18 μm, and the BET specific surface area is greater than 40M ² /g, see attached drawing 2.

Example 2

Li ₂ CO ₃ (analytical pure): 612 grams, γ-AlOOH: 973 grams, add chloride and dehydrated alcohol as above, prepare according to the above process steps, and obtain the reaction product as γ-LiAlO _Ultrafine material, the yield is 91%, the particle size is less than 0.17 μm, and the BET specific surface area is >43M ² /g.

Example 3

The particle size of the γ-LiAlO ₂ coarse material is 3.98 μm, and the particle size of the ultrafine material is less than 0.18 μm. The battery diaphragm is prepared with such a thickness matching material (the ultrafine material is 5 to 15 wt%), and the battery is assembled with such a diaphragm. With high performance, the IV curve of the battery is shown in Fig. 3. It can be seen from the figure that when the reaction pressure is as high as 0.9MPa/cm ² , the utilization rate of the reaction gas is 20%, and when the discharge is at 200 and 300mA/cm ² , the output voltage of the battery is above 0.85 and 0.75V respectively, indicating that the separator has a high Gas barrier performance, after 10 restarts, the performance of the battery basically does not drop, which also shows that the thermomechanical performance of the separator is good.

Claims (3)

1. A gamma-LiAlO _superfine material preparation method for molten carbonate fuel cell diaphragm is characterized in that it is carried out according to the following steps: (1) Ingredients Mix Li ₂ CO ₃ , γ-AlOOH, KCl, and NaCl as raw materials and add anhydrous ball milling media for ball milling until the particle size of the reactant is less than 1 μm; the molar ratio of Li ₂ CO ₃ to γ-AlOOH is 1.02/2～1.05/2, The molar ratio of KCl to NaCl is 0.9/1～1.1/1; the weight of chloride accounts for 50～80% of the total material; (2) High temperature reaction Dry the above materials, crush them, and react at a high temperature of 550-750°C for 0.5-1 hour to generate α-LiAlO ₂ ; (3) Cleaning and hydration of α- _LiAlO2 Wash the reacted material repeatedly with deionized water to remove K ⁺ , Na ⁺ , Cl ^- ions, and hydrate α-LiAlO ₂ to form white hydrate; (4) Regeneration of α-LiAlO ₂ Roast the above hydrate at a high temperature of 450-650°C for 0.5-2 hours: (5) Generation of α-LiAlO ₂ ultrafine material Add an anti-sintering agent to the α- _LiAlO2 fine material generated above, the anti-sintering agent is selected from the carbonaceous material of carbon black and acetylene black, and the addition is 2 to 5% by weight; ball milling in anhydrous ball milling medium for 5 to 20 hour, dry the material; finally bake at 850-950° C. for 1-2 hours to produce γ-LiAlO ₂ superfine material. 2. according to the preparation method of the described lithium metaaluminate superfine material of molten carbonate fuel cell diaphragm of claim 1, it is characterized in that: add sodium citrate, potassium in the cleaning step, sodium oxalate, potassium, sodium tartrate, Potassium acts as an anionic flocculant to remove chloride ions in the powder. 3. According to the preparation method of lithium metaaluminate superfine material for molten carbonate fuel cell diaphragm according to claim 1, it is characterized in that: the anhydrous ball milling medium is anhydrous organic reagent, and the added weight is equivalent to the material.