CN107082439B - A kind of preparation method of nanoscale lithium aluminate - Google Patents

Abstract

The invention relates to a preparation method of nanoscale lithium aluminate. Wherein, the AAO template is vacuum-impregnated in a saturated solution of lithium nitrate or lithium acetate, then frozen, vacuum freeze-dried, and calcined to form nano-scale lithium aluminate with a porous structure. The nano-scale lithium aluminate inherits the porous morphology of the AAO template, has a larger specific surface area, and can be better compounded with the positive electrode material of the lithium ion battery and fully exert the function of the lithium aluminate. Moreover, the process is simple, the process is easy to control, and the cost is low, which provides a new method for the preparation of nanoporous materials.

Description

A kind of preparation method of nanoscale lithium aluminate

technical field

The invention relates to a preparation method of nanoscale lithium aluminate.

Background technique

Lithium aluminate was early industrially used as an electrolyte support material for molten carbonate fuel cells and as a tritium breeding material in fusion-fission reactors in the nuclear field. In 2003, Kim et al. synthesized lithium aluminate nanotubes by hydrothermal template method, and characterized the mobility of lithium ions in lithium aluminate by nuclear magnetic resonance NMR, and found that lithium ions have migration ability in lithium aluminate. The application of lithium aluminate in lithium-ion batteries is mainly as an effective additive to improve the conductivity of polymer electrolytes. Adding micron or nanoscale lithium aluminate particles to polymer electrolytes can improve the conductivity of polymers. and electrolyte/electrode interfacial compatibility. The application of lithium aluminate in lithium ion batteries shows that the introduction of lithium aluminate can effectively improve the lithium ion conductivity and comprehensive electrochemical performance of the matrix material.

In the past, the preparation of lithium aluminate mainly focused on simply mixing aluminum source and lithium source and calcining it by solid-phase method. This preparation method produces lithium aluminate particles with large particles, serious agglomeration, and small specific surface area. Its functions cannot be fully exerted during use.

Contents of the invention

(1) Technical problems to be solved

The purpose of the present invention is to provide a method for preparing lithium aluminate that can be better compounded with the positive electrode material of lithium ion batteries and fully exert the function of lithium aluminate.

(2) Technical solution

In order to achieve the above object, the main technical solutions adopted in the present invention include:

The invention provides a preparation method of nano-scale lithium aluminate, comprising the following steps: S1, vacuum impregnating the AAO template in a saturated solution of lithium nitrate or lithium acetate to form AAO with a saturated solution of lithium nitrate or lithium acetate Template; S2, freezing the AAO template with a saturated solution of lithium nitrate or lithium acetate; S3, vacuum freeze-drying the frozen product; S4, calcining the vacuum freeze-dried product to form a porous structure Nanoscale lithium aluminate.

According to the present invention, in step S1, the AAO template is immersed in a saturated solution of lithium nitrate or lithium acetate for vacuum impregnation, the vacuum degree is less than 0.1Pa, and the vacuum impregnation time is 1.5-2.5h; in step S2, the freezing time is 18- 22h; in step S3, the temperature is lower than -50°C, the vacuum degree is lower than 5Pa, and the time is 35-40h; in step S4, the calcination temperature is 550-650°C, and the calcination time is 4.5-5.5h.

According to the present invention, the AAO template used in step S1 is prepared by the following steps: a, using an aluminum plate as an anode, a nickel plate as a cathode, and a mixture of phosphoric acid and ethanol as an electrolyte for anodic oxidation, and the aluminum plate forms a primary oxidation product; b 1. Soak the primary oxidation product in chromic acid solution to remove the holes produced by anodic oxidation; c. Use the primary oxidation product soaked in chromic acid solution as the anode, the nickel plate as the cathode, and the mixed solution of phosphoric acid and ethanol as the electrolyte, Carry out anodic oxidation, the primary oxidation product after chromic acid solution immersion forms secondary oxidation product; d, the secondary oxidation product is put into saturated mercuric chloride solution and soaks, removes the aluminum plate that is positioned at central position in secondary oxidation product, obtains AAO template blanks on both sides; e. Rinse one or two AAO template blanks with ethanol and deionized water respectively, and dry to form one or two AAO templates.

According to the present invention, in step c, after the anodic oxidation for a preset time is completed, the voltage is stepped down until the current drops to 0, and step c ends.

According to the present invention, in step a, the distance between the anode and the cathode is 5-8cm, anodic oxidation is carried out at a constant voltage of 160-200V, and the oxidation time is 25-35min; in step b, the mass fraction of the chromic acid solution is 5 -7wt.%, the temperature is 55-65°C, and the soaking time is 2.5-3.5h; in step c, the distance between the anode and the cathode is equal to the distance between the anode and the cathode in step a, and the constant voltage value is equal to that in step a, The oxidation time is 2.5-3.5 hours, and the voltage is reduced stepwise by 20V each time; in step d, the soaking time is 3.5-4.5 hours; in step e, the drying temperature is 75-85°C.

According to the present invention, before step a, the mixed solution of phosphoric acid and ethanol is stirred with a magnetic stirrer, and the rotating speed of the rotor of the magnetic stirrer is 160-200r/min.

According to the present invention, the aluminum plate used in step a is treated as follows: soak the aluminum plate in acetone to remove surface grease; soak the aluminum plate in sodium hydroxide solution to remove surface oxides; carry out ethanol ultrasonic cleaning on the aluminum plate to remove Make it smooth.

According to the present invention, in step a, the purity of the aluminum plate is 99.99%, the thickness is 0.2-0.4mm, the width is 2-3cm, and the side surface area is 6-10cm ² , the purity of the nickel plate is 99.95%, and the width is 2-3cm , the length is 6-10cm, and the thickness is 0.4-0.6mm.

According to the present invention, in the electrolyte, the concentration of the phosphoric acid is 0.1-0.3 mol/L; the volume ratio of the ethanol to the electrolyte is 1:4-1:2.

According to the present invention, the depth at which the anode is inserted into the electrolyte in step c is the same as the depth at which the anode is inserted into the electrolyte in step a; the depth at which the cathode is inserted into the electrolyte in step c is the same as the depth at which the cathode is inserted into the electrolyte in step a.

(3) Beneficial effects

The beneficial effects of the present invention are:

The present invention synthesizes nano-scale lithium aluminate based on AAO template by vacuum impregnation combined with freezing, vacuum freeze-drying and calcination, and prepares nano-scale lithium aluminate with a porous structure, which inherits the porous morphology of AAO template and has a large specific The surface area can be better combined with the positive electrode material of lithium-ion batteries and fully exert the function of lithium aluminate. Moreover, the process is simple, the process is easy to control, and the cost is low, which provides a new method for the preparation of nanoporous materials.

Description of drawings

Fig. 1 is the schematic flow chart of the preparation method of the nanoscale lithium aluminate of the embodiment 1 provided as follows;

FIG. 2 is an XRD pattern of the porous nanoscale lithium aluminate prepared in Example 1 provided below.

FIG. 3 is an SEM image of the porous nanoscale lithium aluminate prepared in Example 1 provided below.

FIG. 4 is an XRD pattern of the porous nanoscale lithium aluminate prepared in Example 2 provided below.

FIG. 5 is an SEM image of the porous nanoscale lithium aluminate prepared in Example 2 provided below.

FIG. 6 is an XRD pattern of the porous nanoscale lithium aluminate prepared in Example 3 provided below.

FIG. 7 is an SEM image of the porous nanoscale lithium aluminate prepared in Example 3 provided below.

FIG. 8 is an XRD pattern of the porous nanoscale lithium aluminate prepared in Example 4 provided below.

FIG. 9 is an SEM image of the porous nanoscale lithium aluminate prepared in Example 4 provided below.

Detailed ways

In order to better explain the present invention and facilitate understanding, the present invention will be described in detail below through specific embodiments in conjunction with the accompanying drawings.

Embodiment one

Referring to Fig. 1, a kind of preparation method of nanoscale lithium aluminate is provided in the present embodiment, comprises the following steps:

S1. Vacuum impregnation of the AAO template in a saturated solution of lithium nitrate to form an AAO template with a saturated solution of lithium nitrate;

S2, freezing the AAO template with a saturated solution of lithium nitrate, so that the saturated solution of lithium nitrate is sealed in the pores of the AAO template in a solid state;

S3, vacuum freeze-dry the product after freezing (i.e., the AAO template that is sealed with a solid lithium nitrate solution), fully sublimate and remove the moisture of the lithium nitrate solution in the holes of the AAO template, and leave lithium nitrate attached to the AAO template the surface of the hole;

S4. Calcining the vacuum freeze-dried product (that is, the AAO template with lithium nitrate attached to the pores) to form nano-scale lithium aluminate with a porous structure.

Therefore, the nano-scale lithium aluminate inherits the porous morphology of the AAO template, has a larger specific surface area, and can be better compounded with the positive electrode material of the lithium ion battery and fully exert the function of the lithium aluminate. Moreover, the process is simple, the process is easy to control, and the cost is low, which provides a new method for the preparation of nanoporous materials.

Specifically, in this embodiment, the following steps are specifically performed to prepare an AAO template:

Step 1, according to the volume of the electrolytic cell and the size of the anode and cathode, it is determined to prepare 500mL of electrolyte. A mixture of phosphoric acid and ethanol is used as the electrolyte. In the electrolyte, the concentration of phosphoric acid is 0.3mol/L. The specific volume value is determined according to the density of phosphoric acid. The volume ratio of ethanol to electrolyte is 1:2, that is, 250mL is selected. Ethanol, and then add an appropriate amount of deionized water to make up 500mL of electrolyte.

Step 2, put 500mL electrolyte in a beaker (the beaker is used as an electrolytic cell), then place the beaker in a temperature-controlled circulating oil tank, set the temperature to -5°C, and stir the electrolyte with the oil under the stirring action of a magnetic stirrer. The temperature of the bath was kept constant, ie, the temperature of the electrolyte was -5°C. Wherein, the rotating speed of the rotor of the magnetic stirrer is 160-200r/min.

Step 3, soak the aluminum plate in acetone to remove surface grease; then soak the aluminum plate in a sodium hydroxide solution with a concentration of 1mol/L to remove surface oxides; then perform ethanol ultrasonic cleaning on the aluminum plate to make its surface bright and clean. Finally, the purity of the aluminum plate is 99.99%, the thickness is 0.2-0.4mm, the width is 2-3cm, and the side surface area is 8cm ² .

Step 4, put the above-mentioned aluminum plate as anode and nickel plate (purity is 99.95%, width is 2-3cm, length is 6-10cm, thickness is 0.4-0.6mm) as cathode into the beaker of above-mentioned step 2, The distance between the anode and the cathode is 6cm, anodic oxidation is carried out at a constant voltage of 200V, a chemical reaction 2Al-6e ^- +3H ₂ O→Al ₂ O ₃ (S)+6H ⁺ occurs, and the oxidation time is 30min. The aluminum plate forms a primary oxidation product. Among the primary oxidation products, the central position is an unoxidized aluminum plate, and the surfaces on both sides are aluminum oxide formed by oxidation. At this time, the aluminum oxide is porous, but the porous structure is irregular. .

Step 5, soak the primary oxidation product in chromic acid solution at 60°C for 3 hours, a chemical reaction Al ₂ O ₃ (S) + 6H ⁺ → 2Al ³⁺ + 3H ₂ O occurs, and the irregular anodic oxidation on the surface is removed. In the generated holes, the mass fraction of the chromic acid solution is 6wt.%.

Step 6, put the primary oxidation product soaked in chromic acid solution as the anode and the nickel plate as the cathode into the beaker of step 2, the distance between the anode and the cathode is 6cm, the depth of the anode inserted into the electrolyte is the same as that of the anode inserted into the electrolyte in step 4 The depth is the same, and the depth of the cathode inserted into the electrolyte is the same as the depth of the cathode inserted into the electrolyte in step 4. Anodic oxidation was carried out at a constant voltage of 200V, and the secondary oxidation time was 3h. After 3 hours, stepwise reduce the voltage until the current drops to 0, stop power supply, and the primary oxidation product after soaking in the chromic acid solution forms a secondary oxidation product, the secondary oxidation product includes the aluminum plate at the central position and the The two layers on the side surface are aluminum oxide films with regular regular hexagonal porous structure. Wherein, the specific method of stepwise lowering the voltage is to lower the voltage by 20V each time, and then lower the voltage by 20V again after the current is stabilized after the 20V is lowered.

Step 7, soak the secondary oxidation product in a saturated mercuric chloride solution for 4 hours, remove the central aluminum plate in the secondary oxidation product, and obtain aluminum oxide films on both sides, thus obtaining two AAO template blanks .

In step 8, wash an AAO template blank with ethanol and deionized water respectively, and dry it in an oven at 80° C. to form an AAO template with regular and ordered pores. Of course, when multiple nanoscale lithium aluminates need to be prepared, the two AAO template blanks are rinsed and dried together to form two AAO templates.

So far, the AAO template is prepared, and the AAO template is used to further prepare nano-scale lithium aluminate. The specific steps are as follows:

Prepare a saturated solution of lithium nitrate, and the lithium nitrate solution is analytically pure.

In the vacuum impregnation step (ie, step S1), the AAO template is vacuum impregnated in a saturated lithium nitrate solution, the vacuum degree is less than 0.1 Pa, and the vacuum impregnation time is 2 hours. Because the diameter of the pores of the AAO template is very small, about 300-400nm, if it is directly immersed in the lithium nitrate solution, it is difficult for the lithium nitrate solution to enter the pores due to the effect of surface tension, and the lithium nitrate cannot fully contact the AAO template. Vacuum impregnation, under the action of negative pressure, can make the saturated solution of lithium nitrate enter the pores of the AAO template, make the lithium nitrate and AAO template fully contact, and form the AAO template with the saturated solution of lithium nitrate. In the next stage of calcination, it can be more completely transformed into nano-scale lithium aluminate.

In the freezing step (ie, step S2), the product of the vacuum impregnation step is frozen in a freezer for 20 hours. First of all, the solution can only be freeze-dried using a freeze dryer when it is fully frozen and in a solid state. Therefore, this freezing step prepares for the subsequent vacuum freeze-drying, so that the saturated solution of lithium nitrate is sealed into the pores of the AAO template in a solid state. Secondly, freezing can seal the saturated solution of lithium nitrate into the pores of the AAO template, and then through subsequent freeze-drying, the water in the lithium nitrate solution in the pores can be fully sublimated and removed, leaving lithium nitrate attached to the surface of the pores. If ordinary drying is used, during the drying process, the liquid in the pores will flow out, and lithium nitrate will be brought out at the same time, resulting in the loss of lithium nitrate in the pores. In the vacuum freeze-drying step (ie, step S3), vacuum freeze-dry the product after the freezing step in a vacuum freeze-drying oven at a temperature lower than -50° C. and a vacuum degree of less than 5 Pa for 36 hours. The vacuum freeze-drying step can make lithium nitrate more widely contact with the surface and pores of the AAO template.

Calcination step (i.e. step S4), calcining the product after the vacuum freeze-drying step in a tube furnace, the calcination temperature is 600°C, the calcination time is 5h, and the chemical reaction 2Al ₂ O ₃ +4LiNO ₃ → 4LiAlO ₂ +4NO ₂ (g) + O ₂ (g).

So far, nano-scale lithium aluminate inheriting the porous structure of AAO template is formed.

Referring to Fig. 2 and Fig. 3, it can be seen that the product obtained by the method of this embodiment is nano-scale lithium aluminate with a porous structure, and its appearance is a submicron sphere formed by agglomeration of spherical primary particles. The pore structure composed of these submicron spheres well inherits the pore structure of the AAO template and has a large specific surface area.

Of course, this embodiment is not limited to the self-made AAO template using the above method, and directly purchased AAO templates can also be used, but the cost of self-made AAO templates is lower.

Example 2

In this embodiment, a preparation method of nano-scale lithium aluminate is provided, comprising the following steps:

S1. Vacuum impregnation of the AAO template in a saturated solution of lithium nitrate to form an AAO template with a saturated solution of lithium nitrate;

S2, freezing the AAO template with a saturated solution of lithium nitrate, so that the saturated solution of lithium nitrate is sealed in the pores of the AAO template in a solid state;

S3, vacuum freeze-dry the product after freezing (i.e., the AAO template that is sealed with a solid lithium nitrate solution), fully sublimate and remove the moisture of the lithium nitrate solution in the holes of the AAO template, and leave lithium nitrate attached to the AAO template the surface of the hole;

S4. Calcining the vacuum freeze-dried product (that is, the AAO template with lithium nitrate attached to the pores) to form nano-scale lithium aluminate with a porous structure.

Specifically, in this embodiment, the following steps are specifically performed to prepare the AAO template:

Step 1, according to the volume of the electrolytic cell and the size of the anode and cathode, it is determined to prepare 500mL of electrolyte. A mixture of phosphoric acid and ethanol is used as the electrolyte. In the electrolyte, the concentration of phosphoric acid is 0.2mol/L. The specific volume value is determined according to the density of phosphoric acid. The volume ratio of ethanol to electrolyte is 1:4, that is, 125mL is selected. Ethanol, and then add an appropriate amount of deionized water to make up 500mL of electrolyte.

Step 2, put 500mL electrolyte in a beaker (the beaker is used as an electrolytic cell), then place the beaker in a temperature-controlled circulating oil tank, set the temperature at 5°C, and stir the electrolyte with the oil bath under the stirring action of a magnetic stirrer. The temperature is kept consistent, that is, the temperature of the electrolyte is 5°C. Wherein, the rotating speed of the rotor of the magnetic stirrer is 160-200r/min.

Step 3, soak the aluminum plate in acetone to remove surface grease; then soak the aluminum plate in a sodium hydroxide solution with a concentration of 1mol/L to remove surface oxides; then perform ethanol ultrasonic cleaning on the aluminum plate to make its surface bright and clean. Finally, the aluminum plate has a purity of 99.99%, a thickness of 0.2-0.4 mm, a width of 2-3 cm, and a side surface area of 6 cm ² .

Step 4, put the above-mentioned aluminum plate as anode and nickel plate (purity is 99.95%, width is 2-3cm, length is 6-10cm, thickness is 0.4-0.6mm) as cathode into the beaker of above-mentioned step 2, The distance between the anode and the cathode is 8cm, anodic oxidation is carried out at a constant voltage of 160V, a chemical reaction 2Al-6e ^- +3H ₂ O→Al ₂ O ₃ (S)+6H ⁺ occurs, the oxidation time is 30min, and the aluminum plate forms a primary oxidation product . Among the primary oxidation products, the central position is an unoxidized aluminum plate, and the surfaces on both sides are aluminum oxide formed by oxidation. At this time, the aluminum oxide is porous, but the porous structure is irregular. .

Step 5, soak the primary oxidation product in chromic acid solution at 60°C for 3 hours, a chemical reaction Al ₂ O ₃ (S) + 6H ⁺ → 2Al ³⁺ + 3H ₂ O occurs, and the irregular anodic oxidation on the surface is removed. In the generated holes, the mass fraction of the chromic acid solution is 6wt.%.

Step 6, put the primary oxidation product soaked in chromic acid solution as the anode and the nickel plate as the cathode into the beaker of step 2, the distance between the anode and the cathode is 6cm, the depth of the anode inserted into the electrolyte is the same as that of the anode inserted into the electrolyte in step 4 The depth is the same, and the depth of the cathode inserted into the electrolyte is the same as the depth of the cathode inserted into the electrolyte in step 4. Anodic oxidation was carried out at a constant voltage of 200V, and the secondary oxidation time was 3h. After 3 hours, stepwise reduce the voltage until the current drops to 0, stop power supply, and the primary oxidation product after soaking in the chromic acid solution forms a secondary oxidation product, the secondary oxidation product includes the aluminum plate at the central position and the The two layers on the side surface are aluminum oxide films with regular regular hexagonal porous structure. Wherein, the specific method of stepwise lowering the voltage is to lower the voltage by 20V each time, and then lower the voltage by 20V again after the current is stabilized after the 20V is lowered.

Step 7, soak the secondary oxidation product in a saturated mercuric chloride solution for 4 hours, remove the central aluminum plate in the secondary oxidation product, and obtain aluminum oxide films on both sides, thus obtaining two AAO template blanks .

In step 8, wash an AAO template blank with ethanol and deionized water respectively, and dry it in an oven at 80° C. to form an AAO template with regular and ordered pores. Of course, when multiple nanoscale lithium aluminates need to be prepared, the two AAO template blanks are rinsed and dried together to form two AAO templates.

So far, the AAO template is prepared, and the AAO template is used to further prepare nano-scale lithium aluminate. The specific steps are as follows:

Prepare a saturated solution of lithium nitrate, and the lithium nitrate solution is analytically pure.

In the vacuum impregnation step (ie, step S1), the AAO template is vacuum impregnated in a saturated lithium nitrate solution, the vacuum degree is less than 0.1Pa, and the vacuum impregnation time is 2h to form an AAO template with a saturated lithium nitrate solution.

In the freezing step (ie, step S2), the product of the vacuum impregnation step is frozen in a freezer for 20 hours, so that the saturated solution of lithium nitrate is sealed in the pores of the AAO template in a solid state.

Vacuum freeze-drying step (i.e. step S3), vacuum freeze-drying the product after the freezing step in a vacuum freeze-drying oven, the temperature is lower than -50°C, the vacuum degree is less than 5Pa, and the time is 36h. The water in the lithium nitrate solution was fully sublimated and removed, leaving lithium nitrate attached to the surface of the pores of the AAO template.

Calcination step (i.e. step S4), calcining the product after the vacuum freeze-drying step in a tube furnace, the calcination temperature is 600°C, the calcination time is 5h, and the chemical reaction that occurs is 2Al ₂ O ₃ +4LiNO ₃ →4LiAlO ₂ +4NO ₂ (g)+O ₂ (g).

So far, nano-scale lithium aluminate inheriting the porous structure of AAO template is formed.

Referring to Fig. 4 and Fig. 5, it can be seen that the product obtained by the method of this implementation is nano-scale lithium aluminate with a porous structure, and its appearance is a submicron sphere formed by agglomeration of spherical primary particles. The pore structure composed of these submicron spheres well inherits the pore structure of the AAO template and has a large specific surface area.

Embodiment Three

Specifically, a preparation method of nano-scale lithium aluminate is provided in this embodiment, comprising the following steps:

S1. Vacuum impregnation of the AAO template in a saturated solution of lithium acetate to form an AAO template with a saturated solution of lithium acetate;

S2, freezing the AAO template with a saturated solution of lithium acetate, so that the saturated solution of lithium acetate is sealed in the pores of the AAO template in a solid state;

S3, vacuum freeze-dry the product after freezing (i.e., the AAO template that is sealed with a solid lithium acetate solution), fully sublimate and remove the moisture of the lithium acetate solution in the holes of the AAO template, and leave lithium acetate attached to the AAO template the surface of the hole;

S4. Calcining the vacuum freeze-dried product (that is, the AAO template with lithium acetate attached to the pores) to form nano-scale lithium aluminate with a porous structure.

Specifically, in this embodiment, the following steps are specifically performed to prepare the AAO template:

Step 1, according to the volume of the electrolytic cell and the size of the anode and cathode, it is determined to prepare 500mL of electrolyte. A mixture of phosphoric acid and ethanol is used as the electrolyte. In the electrolyte, the concentration of phosphoric acid is 0.1mol/L, and the specific volume value is determined according to the density of phosphoric acid; the volume ratio of ethanol to electrolyte is 83:250, that is, 166mL is selected. Ethanol, and then add an appropriate amount of deionized water to make up 500mL of electrolyte.

Step 2, put 500mL electrolyte in a beaker (the beaker is used as an electrolytic cell), then place the beaker in a temperature-controlled circulating oil tank, set the temperature to 0°C, and stir the electrolyte with the oil bath under the stirring action of a magnetic stirrer. The temperature is kept consistent, that is, the temperature of the electrolyte is 0°C. Wherein, the rotating speed of the rotor of the magnetic stirrer is 160-200r/min.

Step 3, soak the aluminum plate in acetone to remove surface grease; then soak the aluminum plate in a sodium hydroxide solution with a concentration of 1mol/L to remove surface oxides; then perform ethanol ultrasonic cleaning on the aluminum plate to make its surface bright and clean. Finally, the aluminum plate has a purity of 99.99%, a thickness of 0.2-0.4 mm, a width of 2-3 cm, and a side surface area of 10 cm ² .

Step 4, put the above-mentioned aluminum plate as anode and nickel plate (purity is 99.95%, width is 2-3cm, length is 6-10cm, thickness is 0.4-0.6mm) as cathode into the beaker of above-mentioned step 2, The distance between the anode and the cathode is 7cm, anodic oxidation is carried out at a constant voltage of 180V, a chemical reaction 2Al-6e ^- +3H ₂ O→Al ₂ O ₃ (S)+6H ⁺ occurs, the oxidation time is 30min, and the aluminum plate forms a primary oxidation product . Among the primary oxidation products, the central position is an unoxidized aluminum plate, and the surfaces on both sides are aluminum oxide formed by oxidation. At this time, the aluminum oxide is porous, but the porous structure is irregular. .

Step 5, soak the primary oxidation product in chromic acid solution at 60°C for 3 hours, a chemical reaction Al ₂ O ₃ (S) + 6H ⁺ → 2Al ³⁺ + 3H ₂ O occurs, and the irregular anodic oxidation on the surface is removed. In the generated holes, the mass fraction of the chromic acid solution is 6wt.%.

Step 6, put the primary oxidation product soaked in chromic acid solution as the anode and the nickel plate as the cathode into the beaker of step 2, the distance between the anode and the cathode is 6cm, the depth of the anode inserted into the electrolyte is the same as that of the anode inserted into the electrolyte in step 4 The depth is the same, and the depth of the cathode inserted into the electrolyte is the same as the depth of the cathode inserted into the electrolyte in step 4. Anodic oxidation was carried out at a constant voltage of 200V, and the secondary oxidation time was 3h. After 3 hours, stepwise reduce the voltage until the current drops to 0, stop power supply, and the primary oxidation product after soaking in the chromic acid solution forms a secondary oxidation product, the secondary oxidation product includes the aluminum plate at the central position and the The two layers on the side surface are aluminum oxide films with regular regular hexagonal porous structure. Wherein, the specific method of stepwise lowering the voltage is to lower the voltage by 20V each time, and then lower the voltage by 20V again after the current is stabilized after the 20V is lowered.

Step 7, soak the secondary oxidation product in a saturated mercuric chloride solution for 4 hours, remove the central aluminum plate in the secondary oxidation product, and obtain aluminum oxide films on both sides, thus obtaining two AAO template blanks .

In step 8, wash an AAO template blank with ethanol and deionized water respectively, and dry it in an oven at 80° C. to form an AAO template with regular and ordered pores. Of course, when multiple nanoscale lithium aluminates need to be prepared, the two AAO template blanks are rinsed and dried together to form two AAO templates.

So far, the AAO template is prepared, and the AAO template is used to further prepare nano-scale lithium aluminate. The specific steps are as follows:

Prepare a saturated solution of lithium acetate, and the lithium acetate solution is analytically pure.

In the vacuum impregnation step (ie, step S1), the AAO template is vacuum impregnated in a saturated lithium acetate solution, the vacuum degree is less than 0.1Pa, and the vacuum impregnation time is 2h to form an AAO template with a saturated lithium acetate solution.

In the freezing step (ie, step S2), the product of the vacuum impregnation step is frozen in a freezer for 20 hours, so that the saturated solution of lithium acetate is sealed in the pores of the AAO template in a solid state.

Vacuum freeze-drying step (i.e. step S3), vacuum freeze-drying the product after the freezing step in a vacuum freeze-drying oven, the temperature is lower than -50°C, the vacuum degree is less than 5Pa, and the time is 36h. The water in the lithium acetate solution was fully sublimated and removed, leaving lithium acetate attached to the surface of the pores of the AAO template.

Calcination step (i.e. step S4), calcining the product after the vacuum freeze-drying step in a tube furnace, the calcination temperature is 600°C, the calcination time is 5h, and the chemical reaction that occurs is Al ₂ O ₃ +2LiCH ₃ COO→2LiAlO ₂ +4CO(g)+3H ₂ O(g).

So far, nano-scale lithium aluminate inheriting the porous structure of AAO template is formed.

Referring to Fig. 6 and Fig. 7, it can be seen that the product obtained by the method of this implementation is nano-scale lithium aluminate with a porous structure, and its appearance is a submicron sphere formed by agglomeration of spherical primary particles. The pore structure composed of these submicron spheres well inherits the pore structure of the AAO template and has a large specific surface area.

Embodiment four

Specifically, a preparation method of nano-scale lithium aluminate is provided in this embodiment, comprising the following steps:

S1. Vacuum impregnation of the AAO template in a saturated solution of lithium acetate to form an AAO template with a saturated solution of lithium acetate;

S2, freezing the AAO template with a saturated solution of lithium acetate, so that the saturated solution of lithium acetate is sealed in the pores of the AAO template in a solid state;

S3, vacuum freeze-dry the product after freezing (i.e., the AAO template that is sealed with a solid lithium acetate solution), fully sublimate and remove the moisture of the lithium acetate solution in the holes of the AAO template, and leave lithium acetate attached to the AAO template the surface of the hole;

S4. Calcining the vacuum freeze-dried product (that is, the AAO template with lithium acetate attached to the pores) to form nano-scale lithium aluminate with a porous structure.

Specifically, in this embodiment, the following steps are specifically performed to prepare an AAO template:

Step 1, according to the volume of the electrolytic cell and the size of the anode and cathode, it is determined to prepare 500mL of electrolyte. A mixture of phosphoric acid and ethanol is used as the electrolyte. In the electrolyte, the concentration of phosphoric acid is 0.2mol/L. The specific volume value is determined according to the density of phosphoric acid. The volume ratio of ethanol to electrolyte is 2:5, that is, 200mL is selected. Ethanol, and then add an appropriate amount of deionized water to make up 500mL of electrolyte.

Step 2, put 500mL electrolyte in a beaker (the beaker is used as an electrolytic cell), then place the beaker in a temperature-controlled circulating oil tank, set the temperature to -5°C, and stir the electrolyte with the oil under the stirring action of a magnetic stirrer. The temperature of the bath was kept constant, ie, the temperature of the electrolyte was -5°C. Wherein, the rotating speed of the rotor of the magnetic stirrer is 160-200r/min.

Step 3, soak the aluminum plate in acetone to remove surface grease; then soak the aluminum plate in a sodium hydroxide solution with a concentration of 1mol/L to remove surface oxides; then perform ethanol ultrasonic cleaning on the aluminum plate to make its surface bright and clean. Finally, the aluminum plate has a purity of 99.99%, a thickness of 0.2-0.4 mm, a width of 2-3 cm, and a side surface area of 7 cm ² .

Step 4, put the above-mentioned aluminum plate as anode and nickel plate (purity is 99.95%, width is 2-3cm, length is 6-10cm, thickness is 0.4-0.6mm) as cathode into the beaker of above-mentioned step 2, The distance between the anode and the cathode is 5cm, anodic oxidation is carried out at a constant voltage of 180V, a chemical reaction 2Al-6e ^- +3H ₂ O→Al ₂ O ₃ (S)+6H ⁺ occurs, the oxidation time is 30min, and the aluminum plate forms a primary oxidation product . Among the primary oxidation products, the central position is an unoxidized aluminum plate, and the surfaces on both sides are aluminum oxide formed by oxidation. At this time, the aluminum oxide is porous, but the porous structure is irregular. .

Step 5, soak the primary oxidation product in chromic acid solution at 60°C for 3 hours, a chemical reaction Al ₂ O ₃ (S) + 6H ⁺ → 2Al ³⁺ + 3H ₂ O occurs, and the irregular anodic oxidation on the surface is removed. In the generated holes, the mass fraction of the chromic acid solution is 6wt.%.

Step 6, put the primary oxidation product soaked in chromic acid solution as the anode and the nickel plate as the cathode into the beaker of step 2, the distance between the anode and the cathode is 6cm, the depth of the anode inserted into the electrolyte is the same as that of the anode inserted into the electrolyte in step a The depth is the same, and the depth of the cathode inserted into the electrolyte is the same as the depth of the cathode inserted into the electrolyte in step a. Anodic oxidation was carried out at a constant voltage of 200V, and the secondary oxidation time was 3h. After 3 hours, stepwise reduce the voltage until the current drops to 0, stop the power supply, and the primary oxidation product after soaking in the chromic acid solution forms a secondary oxidation product, which includes the aluminum plate at the central position and the two sides of the aluminum plate. The two layers on the side surface are aluminum oxide films with regular regular hexagonal porous structure. Wherein, the specific method of stepwise lowering the voltage is to lower the voltage by 20V each time, and then lower the voltage by 20V again after the current is stabilized after the 20V is lowered.

Step 7, soak the secondary oxidation product in a saturated mercuric chloride solution for 4 hours, remove the central aluminum plate in the secondary oxidation product, and obtain aluminum oxide films on both sides, thus obtaining two AAO template blanks .

In step 8, wash an AAO template blank with ethanol and deionized water respectively, and dry it in an oven at 80° C. to form an AAO template with regular and ordered pores. Of course, when multiple nanoscale lithium aluminates need to be prepared, the two AAO template blanks are rinsed and dried together to form two AAO templates.

So far, the AAO template is prepared, and the AAO template is used to further prepare nano-scale lithium aluminate. The specific steps are as follows:

Prepare a saturated solution of lithium acetate, and the lithium acetate solution is analytically pure.

In the vacuum impregnation step (ie, step S1), the AAO template is vacuum impregnated in a saturated lithium acetate solution, the vacuum degree is less than 0.1Pa, and the vacuum impregnation time is 2h to form an AAO template with a saturated lithium acetate solution.

In the freezing step (ie, step S2), the product of the vacuum impregnation step is frozen in a freezer for 20 hours, so that the saturated solution of lithium acetate is sealed in the pores of the AAO template in a solid state.

Vacuum freeze-drying step (i.e. step S3), vacuum freeze-drying the product after the freezing step in a vacuum freeze-drying oven, the temperature is lower than -50°C, the vacuum degree is less than 5Pa, and the time is 36h. The water in the lithium nitrate solution was fully removed by sublimation, leaving lithium acetate attached to the surface of the pores of the AAO template.

Calcination step (i.e. step S4), calcining the product after the vacuum freeze-drying step in a tube furnace, the calcination temperature is 600°C, the calcination time is 5h, and the chemical reaction that occurs is Al ₂ O ₃ +2LiCH ₃ COO→2LiAlO ₂ +4CO(g)+3H ₂ O(g).

So far, nano-scale lithium aluminate inheriting the porous structure of AAO template is formed.

Referring to Fig. 8 and Fig. 9, it can be seen that the product obtained by the method of this implementation is nano-scale lithium aluminate with a porous structure, and its appearance is a submicron sphere formed by agglomeration of spherical primary particles. The pore structure composed of these submicron spheres well inherits the pore structure of the AAO template and has a large specific surface area.

Combining the above-mentioned Embodiment 1 to Embodiment 4, the preparation method of nano-scale lithium aluminate provided by the present invention can be standardized into the following scheme:

The preparation method of nanoscale lithium aluminate of the present invention comprises the steps:

S1. Vacuum impregnation of the AAO template in a saturated solution of lithium acetate to form an AAO template with a saturated solution of lithium acetate;

S2, freezing the AAO template with a saturated solution of lithium acetate;

S3, vacuum freeze-drying the product after freezing;

S4. Calcining the vacuum freeze-dried product to form nanoscale lithium aluminate with a porous structure.

Preferably, in step S1, the AAO template is immersed in a saturated solution of lithium acetate for vacuum impregnation, the vacuum degree is less than 0.1Pa, and the vacuum impregnation time is 1.5-2.5h.

Preferably, in step S2, the freezing time is 18-22 hours.

Preferably, in step S3, the temperature is lower than -50°C, the vacuum degree is lower than 5Pa, and the time is 35-40h.

Preferably, in step S4, the calcination temperature is 550-650° C., and the calcination time is 4.5-5.5 h.

Preferably, the AAO template used in step S1 is prepared by the following steps:

a, with the aluminum plate as the anode, the nickel plate as the cathode, the mixed solution of phosphoric acid and ethanol as the electrolyte, anodic oxidation is carried out, and the aluminum plate forms a primary oxidation product; (see step 4 in embodiments one to four)

B, the primary oxidation product is soaked in the chromic acid solution, removes the hole that anodic oxidation produces; (see step 5 among the embodiment one to four)

C, carry out anodic oxidation with the primary oxidation product after chromic acid solution immersion as anode, nickel plate as the mixed solution of negative electrode, phosphoric acid and ethanol, and the primary oxidation product after chromic acid solution immersion forms secondary oxidation product; ( Refer to step 6 in Embodiments 1 to 4)

d. Soak the secondary oxidation product in a saturated mercuric chloride solution, remove the central aluminum plate in the secondary oxidation product, and obtain the AAO formwork blanks on both sides; (see step 7 in Examples 1 to 4)

e. Rinse one or two AAO template blanks with ethanol and deionized water respectively, and dry them to form one or two AAO templates. (referring to step 8 among the embodiment one to four)

Preferably, before step a, the electrolyte solution is placed in the electrolytic cell, and then the electrolytic cell is placed in a temperature-controlled circulating oil tank, the temperature is set at -5°C to 5°C, and the mixed solution of phosphoric acid and ethanol is mixed with a magnetic stirrer. (that is, the electrolyte solution) is stirred to keep the temperature of the electrolyte solution consistent with that of the oil bath, that is, the temperature of the electrolyte solution is -5°C. The rotating speed of the rotor of the magnetic stirrer is 160-200r/min. (referring to step 2 among the embodiment one to four)

Preferably, in step a, the distance between the anode and the cathode is 5-8 cm, anodic oxidation is performed at a constant voltage of 160-200V, and the oxidation time is 25-35 min.

Preferably, in step a, in the electrolyte, the phosphoric acid concentration is 0.1-0.3 mol/L, and the volume ratio of the ethanol to the electrolyte is 1:4-1:2. (referring to step 1 among the embodiment one to four)

Preferably, the aluminum plate adopted in step a is processed as follows:

Soak the aluminum plate in acetone to degrease the surface;

Soak the aluminum plate in sodium hydroxide solution to remove surface oxide;

Ultrasonic clean the aluminum plate with ethanol to make the surface smooth. (see step 3 in Examples 1 to 4)

Preferably, in step a, the aluminum plate has a purity of 99.99%, a thickness of 0.2-0.4mm, a width of 2-3cm, and an area of ^6-10cm2 , and a nickel plate of 99.95% purity, a width of 2-3cm, and a length of 6-10cm, thickness 0.4-0.6mm. (see step 3 in Examples 1 to 4)

Preferably, in step b, the mass fraction of the chromic acid solution is 5-7wt.%, the temperature is 55-65°C, and the soaking time is 2.5-3.5h.

Preferably, in step c, the distance between the anode and the cathode is equal to the distance between the anode and the cathode in step a, the constant voltage value is equal to that in step a, the oxidation time is 2.5-3.5h, and the stepwise voltage is reduced by 20V each time . And after finishing the anodizing for the preset time, the voltage is lowered stepwise until the current drops to 0, and step c is ended.

Preferably, the depth at which the anode is inserted into the electrolyte in step c is the same as the depth at which the anode is inserted into the electrolyte in step a; the depth at which the cathode is inserted into the electrolyte in step c is the same as the depth at which the cathode is inserted into the electrolyte in step a.

Preferably, in step d, the soaking time is 3.5-4.5h;

Preferably, in step e, the drying temperature is 75-85°C.

The above content is only a preferred embodiment of the present invention. For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and application scope. limits.

Claims (7)

1. a kind of preparation method of nanoscale lithium aluminate, which is characterized in that include the following steps：

S1, AAO templates are carried out to vacuum impregnation in the saturated solution of lithium nitrate or lithium acetate, vacuum degree is less than 0.1Pa, vacuum Dip time is 1.5-2.5h, forms the AAO templates of the saturated solution with lithium nitrate or lithium acetate；

S2, the AAO templates with lithium nitrate or the saturated solution of lithium acetate are freezed；

S3, vacuum freeze drying is carried out to the product after freezing；

S4, the product after vacuum freeze drying is calcined, forms the nanoscale lithium aluminate in porous structure；

Wherein, the AAO templates used in step S1 are made by following steps：

A, anodic oxidation is carried out as anode, nickel plate as the mixed liquor of cathode, phosphoric acid and ethyl alcohol as electrolyte using aluminium sheet, Aluminium sheet forms once oxidation product, wherein the distance of anode and cathode is 5-8cm, and anode is carried out under 160-200V constant voltages Oxidation, oxidization time 25-35min；

B, once oxidation product is immersed in chromic acid solution, removes hole caused by anodic oxidation, wherein chromic acid solution Mass fraction is 5-7wt.%, and temperature is 55-65 DEG C, soaking time 2.5-3.5h；

C, once oxidation product after being impregnated using chromic acid solution as anode, nickel plate as cathode, phosphoric acid and ethyl alcohol mixed liquor As electrolyte, anodic oxidation is carried out, the once oxidation product after chromic acid solution impregnates forms secondary oxidation product, wherein sun The distance of pole and cathode is equal at a distance from step a Anodics and cathode, and constant pressure value is equal with step a, and oxidization time is 2.5-3.5h, after the anodic oxidation for completing 2.5-3.5h, staged reduces voltage, and staged reduces every time when reducing voltage 20V, until after electric current is down to 0, end step c；

D, secondary oxidation product is put into the mercuric chloride solution of saturation and is impregnated, removed centrally located in secondary oxidation product Aluminium sheet, obtain the AAO template blanks of both sides, wherein soaking time 3.5-4.5h；

E, one or two AAO template blank is rinsed with ethyl alcohol and deionized water respectively, and be dried, drying temperature 75- 85 DEG C, form one or two AAO template.

2. the preparation method of nanoscale lithium aluminate according to claim 1, which is characterized in that

In step s 2, cooling time 18-22h；

In step s3, temperature is less than -50 DEG C, and vacuum degree is less than 5Pa, time 35-40h；

In step s 4, calcination temperature is 550-650 DEG C, calcination time 4.5-5.5h.

3. the preparation method of nanoscale lithium aluminate according to claim 1, which is characterized in that

Before step a, the mixed liquor of phosphoric acid and ethyl alcohol is stirred using magnetic stirring apparatus, the rotor of magnetic stirring apparatus Rotating speed is 160-200r/min.

4. the preparation method of nanoscale lithium aluminate according to claim 1, which is characterized in that

The aluminium sheet used in step a is by following processing：

Aluminium sheet is impregnated in acetone, to remove surface grease；

Aluminium sheet is immersed in sodium hydroxide solution, to remove oxide on surface；

EtOH Sonicate cleaning is carried out to aluminium sheet, so that its any surface finish.

5. the preparation method of nanoscale lithium aluminate according to claim 1, which is characterized in that

In step a, the purity of aluminium sheet is 99.99%, thickness 0.2-0.4mm, width 2-3cm, side surface area 6- 10cm², the purity of nickel plate is 99.95%, width 2-3cm, length 6-10cm, thickness 0.4-0.6mm.

6. the preparation method of nanoscale lithium aluminate according to claim 1, which is characterized in that

In the electrolyte, a concentration of 0.1-0.3mol/L of the phosphoric acid；

The volume ratio of the ethyl alcohol and the electrolyte is 1:4-1:2.

7. the preparation method of nanoscale lithium aluminate according to claim 1, which is characterized in that

It is identical that the depth and step a Anodics of step c Anodics insertion electrolyte are inserted into the depth of electrolyte；

Cathode is inserted into the depth of electrolyte in step c and the cathode insertion depth of electrolyte is identical in step a.