CN105720277A - A kind of three-dimensional porous perovskite catalyst LaxSr1-xCoyFe1-yO3 and its preparation method - Google Patents

Abstract

The invention discloses a three-dimensional porous perovskite type catalyst La_xSr_1?xCo_yFe_1?yO₃The catalyst is used as a cathode catalyst of a lithium-air battery, and the specific surface area of the catalyst is 20-30 m²(ii) a three-dimensional porous channel within the housing, the porous channel providing a transport channel for ions and gases and a storage space for reaction products; the method comprises the following steps: weighing four nitrates according to a certain proportion, dissolving the four nitrates in a mixed solution of methanol and glycol, and uniformly stirring and mixing to obtain a nitrate solution; soaking the PS microsphere template in a nitrate solution; will be soaked withAnd taking out the PS microsphere template of the nitrate solution, drying, and then calcining to burn off the template to obtain the required catalyst. The catalyst can meet the requirements of cathode materials of lithium-air batteries, has the advantages of simple preparation process, convenient operation, low cost, no pollution and the like, and can realize large-scale production.

Description

A kind of three-dimensional porous perovskite catalyst LaxSr1-xCoyFe1-yO3 and its preparation method

technical field

The invention belongs to the field of battery catalyst preparation, and more specifically relates to a three-dimensional porous perovskite catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ and a preparation method thereof.

Background technique

A lithium-air battery is a battery that uses lithium as the anode and oxygen in the air as the cathode reactant. It has a theoretical energy density very close to the combustion value of gasoline and is considered to be the most promising power battery for future electric vehicles. The non-aqueous lithium-air battery has a higher energy density and has become a research hotspot. It is mainly composed of a porous air electrode, a polymer diaphragm (loaded with organic electrolyte), and a lithium metal anode. After lithium releases electrons, it becomes lithium cation (Li ⁺ ), Li ⁺ passes through the lithium ion electrolyte material, and combines with oxygen and electrons flowing from the external circuit at the air cathode to form lithium oxide (Li ₂ O) or lithium peroxide (Li ₂ O ₂ ), and stay in the cathode, because the products Li ₂ O and Li ₂ O ₂ are both insulated and non-conductive, as the discharge reaction proceeds, they will gradually block the porous electrode and the reaction will be terminated, and the charging reaction will also be due to the pore obstructed by obstruction. Therefore, the actual energy density of lithium-air batteries is far lower than the theoretical value, and there are disadvantages such as high overpotential and poor cycle performance.

Using high-performance bifunctional catalysts to accelerate the decomposition of products is an effective way to solve the above problems, among which the perovskite oxide La _x Sr _1-x Co _y Fe _1-y O ₃ (LSCF) has good catalytic activity, It can be used as a cathode catalyst for lithium-air batteries. The traditional preparation methods of perovskite oxide La _x Sr _1-x Co _y Fe _1-y O ₃ are solid phase reaction method, co-precipitation method, sol-gel method, etc., and the powder prepared by traditional method Most of them are granular, with a specific surface area below 10m ² /g. Using the above-mentioned perovskite oxide with a low specific surface area and a granular structure as a cathode catalyst for lithium-air batteries is not conducive to the transmission of Li ⁺ and oxygen. Lithium air The overpotential of the battery is still too high, and the cycle performance is poor. Therefore, perovskite-type oxides prepared by traditional methods do not meet the needs of lithium-air batteries for cathode materials.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a three-dimensional porous perovskite catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ and its preparation method, wherein the precursor solution is used to soak the poly Styrene microsphere template, and then remove the template to prepare LSCF, the catalyst powder with a specific surface area of 20-30m ² /g and a three-dimensional porous and orderly structure can be prepared. This catalyst can meet the needs of lithium-air battery cathode materials, greatly The overpotential of the battery is reduced, the cycle performance thereof is improved, and the preparation process is simple, the operation is convenient, and the like.

In order to achieve the above purpose, according to one aspect of the present invention, a three-dimensional porous perovskite catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ is proposed, and the three-dimensional porous perovskite catalyst is used as a lithium-air battery The cathode catalyst has a specific surface area of 20-30m ² /g, and has a three-dimensional porous channel inside, which provides transport channels for ions and gases, and provides storage space for reaction products

As a further preference, the diameter of the porous channel is 200nm-300nm.

According to another aspect of the present invention, there is provided a method for preparing a three-dimensional porous perovskite catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ , the method comprising the steps of:

1) La(NO ₃ ) ₂ ·6H ₂ O, Sr(NO ₃ ) ₂ , Co(NO ₃ ) ₂ ·6H ₂ O, Fe(NO ₃ ) ₃ ·9H ₂ O four nitrates according to the molar ratio x : 1-x: y: 1-y ratio weighed, then dissolved in a certain amount of methanol and ethylene glycol mixed solution, stirred at room temperature, until all the nitrates were dissolved and mixed uniformly to obtain a nitrate solution;

2) soaking the PS microsphere template in the above-mentioned nitrate solution;

3) Take out the PS microsphere template soaked in nitrate solution and dry it, then calcinate it at 500°C-700°C for 5h to burn off the PS microsphere template, and obtain the perovskite catalyst La _x with a three-dimensional porous structure inside Sr _1-x Co _y Fe _1-y O ₃ .

As a further preference, in step 1), the volume ratio of methanol to ethanol is 1:1, and the total concentration of the nitrate solution is 1 to 2 mol·L ⁻¹ ; in step 2), the PS microsphere template is in the nitrate solution The best soaking time is 1h ~ 2h.

As a further preference, in step 3), the drying temperature of the PS microsphere template is 50°C-60°C, the drying time is 4h-5h, and the heating rate of the calcination is 1°C/min.

As further preferred, in step 2), the PS microsphere template is prepared in the following manner:

A) a certain amount of sodium dodecylbenzenesulfonate and potassium persulfate are dissolved in the mixed solution of water and ethanol, then above-mentioned mixed solution is placed in the there-necked flask of 250ml;

b) Add <5ml of styrene to the above solution, feed _N2 atmosphere, and stir at constant temperature;

c) After the stirring is completed, the temperature is lowered, and then the mixed solution is transferred to a centrifuge tube for centrifugal washing;

d) drying the above-mentioned washed substance to obtain a PS microsphere template.

As a further preference, the volume ratio of water and ethanol in step a) is 2:5, and the total volume is 70ml.

As a further preference, the stirring temperature in step b) is 60°C-70°C, and the stirring time is 6h-7h.

As a further preference, the centrifugal washing liquid in step c) is absolute ethanol, and the number of washings is 3 to 5 times, wherein, the first centrifugal speed is 2000r/min, the centrifugal time is 16h to 20h, and the centrifugal speed of the subsequent washing is 4000r/min, centrifugation time is 1h.

As a further preference, in step d), drying is carried out in a vacuum freeze-drying oven, and the drying time is 4h-6h.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

1. In the present invention, polystyrene microspheres (PS microspheres) are soaked in LSCF nitrate precursor, dried and then calcined at a suitable temperature to remove the template to prepare LSCF, which can be prepared with a specific surface area of 20-30m ² /g , The catalyst powder with a three-dimensional porous and orderly structure can meet the needs of lithium-air battery cathode materials, greatly reduce the overpotential during the charging and discharging process of lithium-air batteries, greatly improve its capacity and cycle performance, and has a preparation process It has the advantages of simplicity, convenient operation, low cost, and no pollution, and can realize large-scale production.

2. The three-dimensional porous LSCF catalyst of the present invention can be used as a cathode catalyst for a non-aqueous lithium-air battery, which can provide sufficient active sites for battery reactions, realize the maximum utilization of catalyst active sites, and the interaction of electrons, ions, electrolytes, and oxygen in the reaction. Rapid diffusion; in addition, the perovskite oxide LSCF has good electrical conductivity and ion conductivity, and the oxygen defect structure of the perovskite material itself can promote the adsorption and desorption of oxygen during the reaction process, providing rapid transport for oxygen ions channel, which can reduce the overpotential of the lithium-air battery during charging and discharging, and improve the capacity and cycle stability of the battery. Compared with the current lithium-air battery, the overpotential is reduced by about 5-8%, and the capacity is increased to 1.5-2 times , The number of cycles can reach about 200 times.

Description of drawings

Fig. 1 is the SEM picture of the three-dimensional porous LSCF catalyst prepared in Example 1 of the present invention;

Fig. 2 is the SEM picture of the ordered polystyrene microsphere template prepared in Example 1 of the present invention;

Fig. 3 is the XRD pattern of the three-dimensional porous LSCF catalyst prepared in Example 1 of the present invention;

Fig. 4 is the charging and discharging capacity diagram of the lithium-air battery prepared in Example 2 of the present invention;

Figure 5(a) and (b) are the cycle performance graphs of the lithium-air battery prepared in Example 2 of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

As shown in Figure 1, a three-dimensional porous perovskite catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ (LSCF) provided by the present invention is not prepared by traditional solid-state reaction method and sol-gel method. The powder is granular, but has a three-dimensional porous and ordered structure, so it has a large specific surface area, specifically 20-30m ² /g, and has a porous channel inside, and the diameter of the channel is specifically 200nm-300nm. As a lithium-air battery The porous channels provide transport channels for ions and gases and favorable storage spaces for reaction products when used as cathode catalysts. When the three-dimensional porous perovskite catalyst is used as a lithium-air battery catalyst, the three _- dimensional porous channel can provide a transport channel for Li ⁺ and oxygen during the reaction process, and provide a storage space for the insulating product _Li2O2 , combined with the LSCF structure itself Oxygen deficiency can effectively promote the formation of reaction products during discharge and the decomposition of products during charging, thereby reducing the overpotential of the battery and improving the cycle performance of the battery.

The preparation method of the three-dimensional porous perovskite catalyst of the present invention is described and illustrated in detail below, and the preparation method specifically includes the following steps:

1) La(NO ₃ ) ₂ ·6H ₂ O, Sr(NO ₃ ) ₂ , Co(NO ₃ ) ₂ ·6H ₂ O, Fe(NO ₃ ) ₃ ·9H ₂ O four nitrates according to the molar ratio x :1-x:y:1-y ratio weighed, then dissolved in a certain amount of methanol and ethylene glycol mixed solution, stirred at a constant temperature of 20 ~ 30 ℃, until all nitrates are dissolved and mixed evenly, to obtain nitric acid saline solution. As a preferred embodiment, the volume ratio of methanol to ethanol is 1:1, and the total concentration of the nitrate solution is 1˜2 mol·L ⁻¹ .

2) Soak the PS microsphere (polystyrene microsphere) template in the above nitrate solution, wherein the PS microsphere template is prepared by the microsolution method and then self-assembled by centrifugation. The particle size of the microsphere is about 400nm. During the sintering process, the microspheres will be burned to form micropores, and the volume of the micropores will shrink to become an ordered channel of 200-300nm. Specifically include the following steps:

a) Dissolve a certain amount of sodium dodecylbenzenesulfonate (SDS) and potassium persulfate (KPS) in a mixed solution of water and ethanol, and then place the above mixed solution in a 250ml three-necked flask. Wherein, the dosages of SDS and KPS are both 0.0002mol. Since the dispersibility of water and ethanol will affect the pore size distribution of microspheres, in order to obtain microspheres with uniform pore size distribution, the volume ratio of water and ethanol is preferably 2:5, and the total volume is 70ml, that is, 20ml distilled water and 50ml ethanol;

b) Add <5ml of styrene to the above solution, pass through _N2 atmosphere, and stir at constant temperature, wherein the stirring temperature is 60°C-70°C, and the stirring time is 6h-7h;

c) After the stirring is completed, the temperature is lowered to 20-30° C., and then the mixed liquid after the above reaction is transferred to a centrifuge tube for centrifugal washing (centrifugal self-assembly). As a preferred embodiment, the centrifugal washing liquid is absolute ethanol, the number of washings is 3 to 5 times, the first centrifugal speed is 2000r/min, the centrifugal time is 16h～20h, the centrifugal speed of subsequent washing is 4000r/min, the centrifugal time for 1h;

d) Dry the above-mentioned washed material to obtain an orderly arranged PS microsphere template, as shown in Figure 2, wherein the drying process is carried out in a vacuum freeze-drying box, and the drying time is 4h to 6h ;

3) After soaking for 1h to 2h, take out the PS microsphere template soaked in the nitrate solution and dry it, and then calcinate it at 500°C to 700°C for 5h to burn off the PS microsphere template, and the perovskite forms during the calcination process. The obtained XRD pattern is shown in Figure 3. As a preferred embodiment, since PS microspheres are easy to decompose when the temperature is higher than 80°C, the drying temperature of the PS microsphere template is selected to be 50°C-60°C, and the dry microsphere template can be obtained after drying for 4h-5h. The calcining can be carried out in a muffle furnace, and the heating rate of the calcining is 1° C./min.

The following are specific embodiments of the present invention.

Example 1

Prepare PS microsphere template:

Dissolve 0.065g of sodium dodecylbenzenesulfonate and 0.0489g of potassium persulfate in a mixed solution of 20ml of distilled water and 50ml of ethanol, and place them in a 250ml three-neck flask after dissolving; add about 3ml of styrene to the solution, Stir at a constant temperature of 70°C for 6.5 hours in a N ₂ atmosphere; after the stirring is completed, cool down, transfer the mixed solution into a centrifuge tube for centrifugation washing, the centrifugation rate is 2000r/min, the time is 16h, the washing liquid is ethanol, and the number of washings is 3 times ; Finally, dry in a vacuum freeze-drying oven for 5 hours to obtain polystyrene microsphere templates arranged in an orderly manner.

Preparation of perovskite catalyst La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ :

_{Weigh 0.006mol , _ _ _ _ _ _ _ _} 0.004mol, 0.002mol, 0.008mol, dissolved in a mixed solution of 10ml of methanol and 10ml of ethylene glycol, stirred evenly, soaked the PS microsphere template prepared in this example, took it out after about 1.5h and put it in an oven for 60 ℃ constant temperature drying for 5 hours, and then put into a muffle furnace for calcination at 650 ℃ for 5 hours, the heating rate is 1 ℃/min, remove the PS spherical template, and obtain a three-dimensional porous structure perovskite catalyst La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ , as shown in Figure 1. Among them, the perovskite oxide La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ forms a phase during the calcination process, as shown in FIG. 3 .

Example 2

The LSCF material in Example 1 is used as the cathode catalyst of the non-aqueous lithium-air battery, that is, the LSCF is mixed with the carbon material SuperP and the binder to make a slurry, and the cathode electrode sheet is made on the carbon paper by screen printing , and then assemble the electrode sheet into a battery for testing. In the test, when preparing the cathode slurry, the ratio of the powder to the binder PVDF (polyvinylidenefluoride) was 90:10, and the mass ratio of the catalyst LSCF to the carbon powder SuperP in the powder was 35:55. Specifically include the following steps:

PVDF is first dissolved in NMP (N-methyl-2-pyrrolidone, N-methyl-2-pyrrolidone) solvent, and then the catalyst LSCF and carbon powder SuperP powder are weighed according to the stated ratio, and the powder and binder PVDF are placed on the agate Grind in a mortar, add an appropriate amount of NMP dropwise, and grind for about 2.5 hours to obtain a uniform slurry; use screen printing to evenly coat the slurry on carbon paper, and then place it in an oven at 80-100°C Dry at a constant temperature for 12 hours to obtain negative electrode sheets. The active material coated on each electrode sheet is about 2 mg; then place the electrode sheet and the materials required for battery preparation in an argon glove box to make a button battery; take out the battery Sealing, standing still, and then carrying out the charge-discharge capacity test in a pure oxygen environment, the results are shown in Figure 4. According to Figure 4, the addition of the 3D-LSCF catalyst can make the charge-discharge capacity of the lithium-air battery from 3217mAhg ^-1 to 1787mAhg ^-1 was increased to 6693mAhg ^-1 and 4704mAhg ^-1 respectively, about twice as much as SP; the battery prepared according to the same process was tested for cycle performance, the results are shown in Figure 5(a) and (b), according to Figure 5 It can be seen that 3D-LSCF can increase the number of cycles from 58 to 198, which greatly improves the cycle performance of lithium-air batteries.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. A three-dimensional porous perovskite catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ , characterized in that, the three-dimensional porous perovskite catalyst is used as a cathode catalyst for a lithium-air battery, and its specific surface area is 20-30m ² /g, and has a three-dimensional porous channel inside, which provides transmission channels for ions and gases, and provides storage space for reaction products. 2. The three-dimensional porous perovskite catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ according to claim 1, characterized in that the diameter of the porous channel is 200nm-300nm. 3. a kind of preparation method of three-dimensional porous perovskite type catalyst La _x Sr _1-x Co _y Fe _1-y O ₃ as claimed in claim 1 or 2, it is characterized in that, the method comprises the steps: 1) La(NO ₃ ) ₂ ·6H ₂ O, Sr(NO ₃ ) ₂ , Co(NO ₃ ) ₂ ·6H ₂ O, Fe(NO ₃ ) ₃ ·9H ₂ O four nitrates according to the molar ratio x : 1-x: y: 1-y ratio weighed, then dissolved in a certain amount of methanol and ethylene glycol mixed solution, stirred at room temperature, until all the nitrates were dissolved and mixed uniformly to obtain a nitrate solution; 2) soaking the PS microsphere template in the above-mentioned nitrate solution; 3) Take out the PS microsphere template soaked in nitrate solution and dry it, then calcinate it at 500°C-700°C for 5h to burn off the PS microsphere template, and obtain the perovskite catalyst La _x with a three-dimensional porous structure inside Sr _1-x Co _y Fe _1-y O ₃ . 4. The preparation method according to claim 3, characterized in that, in step 1), the volume ratio of methanol to ethanol is 1:1, and the total concentration of the nitrate solution is 1 to 2mol L ^-1 ; step 2) In , the soaking time of PS microsphere template in nitrate solution is 1h～2h. 5. The preparation method according to claim 3, characterized in that, in step 3), the drying temperature of the PS microsphere template is 50°C to 60°C, the drying time is 4h to 5h, and the heating rate of the calcination is 1 °C/min. 6. preparation method according to claim 3, is characterized in that, step 2) in, described PS microsphere template is prepared in the following manner: A) a certain amount of sodium dodecylbenzenesulfonate and potassium persulfate are dissolved in the mixed solution of water and ethanol, then above-mentioned mixed solution is placed in the there-necked flask of 250ml; b) Add <5ml of styrene to the above solution, feed _N2 atmosphere, and stir at constant temperature; c) After the stirring is completed, the temperature is lowered, and then the mixed solution is transferred to a centrifuge tube for centrifugal washing; d) drying the above-mentioned washed substance to obtain a PS microsphere template. 7. The preparation method according to claim 6, wherein the volume ratio of water and ethanol in step a) is 2:5, and the total volume is 70ml. 8. The preparation method according to claim 6, characterized in that, in step b), the stirring temperature is 60°C-70°C, and the stirring time is 6h-7h. 9. The preparation method according to claim 6, characterized in that, in step c), the centrifugal washing liquid is dehydrated alcohol, and the number of washings is 3 to 5 times, wherein, the first centrifugal speed is 2000r/min, and the centrifugal time is 2000r/min. The centrifugation speed is 4000r/min for subsequent washing, and the centrifugation time is 1h. 10. The preparation method according to claim 6, characterized in that, in step d), drying is carried out in a vacuum freeze-drying oven, and the drying time is 4h-6h.