Method for preparing graphene aerogel by multistage intercalation-supercritical drying method

Abstract

The invention discloses a method for preparing graphene aerogel through a multistage intercalation-supercritical drying method, and belongs to the technical field of new energy material recovery and nano material preparation. The method comprises the following steps: treating the waste lithium battery to obtain graphite slag; the preparation method comprises the following steps: soaking graphite slag in a KNO3 solution and a FeCl3 solution, carrying out instantaneous expansion in an inert atmosphere to obtain pre-stripped graphite, carrying out oxidation to obtain a graphene oxide suspension, adding sodium lignin sulfonate, and carrying out a hydrothermal reaction to obtain reduced graphene; and placing the reduced graphene dispersion liquid in supercritical CO2 for drying treatment. According to the preparation method, the graphite negative electrode in the waste lithium battery is used as a raw material, and a multistage intercalation stripping process and a supercritical drying technology are combined, so that the stripping efficiency of graphene and the structural stability of aerogel are remarkably improved. The obtained product has high specific surface area, excellent conductivity and mechanical strength, and can be applied to the fields of supercapacitors, catalytic carriers and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling of waste batteries, and particularly relates to a method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method. Background Art

[0002] Due to its light weight, high conductivity and porous structure characteristics, graphene aerogel has broad application prospects in the fields of energy storage, environmental governance, etc. However, traditional preparation methods usually rely on high-purity graphite raw materials, which have problems such as high cost and complex processes, and traditional freeze-drying or atmospheric drying easily leads to the collapse of the aerogel structure. On the other hand, waste lithium batteries are rich in graphite anode materials, and direct abandonment or inefficient recycling easily causes waste of resources and environmental pollution. In the prior art, the process of extracting graphene from waste lithium batteries mostly uses single intercalation or strong acid oxidation methods, which have problems such as low exfoliation efficiency and many defects in the products, and it is difficult to maintain the complete porous structure of the aerogel during the subsequent drying process. Therefore, it is of great significance to develop a method for preparing graphene aerogel with waste lithium batteries as raw materials, which has both high-efficiency exfoliation and structure controllability. Summary of the Invention

[0003] Aiming at the problems of low exfoliation efficiency and many defects in the products in the process of extracting graphene from waste lithium batteries in the prior art, the purpose of the present invention is to propose a method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method based on the recycling of waste lithium batteries. This method significantly improves the graphite exfoliation efficiency through the synergistic effect of multi-stage intercalation and instantaneous high-temperature expansion. At the same time, by using sodium lignosulfonate and supercritical CO2 drying technology, the reduction of graphene and the construction of a three-dimensional network are realized, avoiding the structure collapse, and providing a new way for the high-value utilization of waste lithium batteries.

[0004] To achieve the above object, the present invention is realized through the following technical solutions:

[0005] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0006] Treat waste lithium batteries to obtain graphite slag;

[0007] Immerse the graphite slag in KNO3 solution and FeCl3 solution, and then instantaneously expand it in an inert atmosphere to obtain pre-exfoliated graphite;

[0008] Oxidize the pre-exfoliated graphite to obtain a graphene oxide suspension;

[0009] Add sodium lignosulfonate to the graphene oxide suspension and carry out a hydrothermal reaction to obtain reduced graphene;

[0010] The reduced graphene dispersion is placed in supercritical CO2 for drying treatment to obtain a three-dimensional porous graphene aerogel.

[0011] Further, the waste lithium batteries are processed to obtain graphite slag, including the following steps:

[0012] The waste lithium batteries are discharged, crushed, subjected to magnetic separation and pulverized and screened to obtain crushed materials with a particle size less than 0.8 mm;

[0013] The obtained crushed materials are calcined in a nitrogen / argon atmosphere to obtain battery powder;

[0014] The battery powder is leached in an acid solution to obtain graphite slag.

[0015] Further, the calcination temperature is 400 - 600 °C, the calcination time is 1 - 3 h, and the heating rate is 3 - 6 °C / min;

[0016] The leaching temperature is 80 - 90 °C, the leaching time is 3 - 4 h, and the solid-liquid ratio is 20 - 30 g / L.

[0017] Further, the soaking time is 30 - 60 min; the concentration of the KNO3 solution is 0.5 - 1.5 mol / L, the concentration of the FeCl3 solution is 0.2 - 0.8 mol / L, and the molar ratio of KNO3 to FeCl3 is 1:0.5 - 1:1.

[0018] Further, the temperature of the instantaneous expansion is 800 - 1000 °C, the heat preservation time of the instantaneous expansion is 5 - 10 min; the temperature is raised to 800 - 1000 °C at a heating rate of 10 - 20 °C / min.

[0019] Further, the specific process of oxidizing the pre-peeled graphite is as follows: After mixing the pre-peeled graphite with sulfuric acid, potassium permanganate is added, and after the oxidation reaction, it is diluted and ultrasonicated to obtain a graphene oxide suspension.

[0020] Further, the mass ratio of the pre-peeled graphite to sulfuric acid is 1:3 - 5, the mass of the sulfuric acid is at a concentration of 95 - 98%, and the mass ratio of potassium permanganate to graphite is 0.5 - 2:1;

[0021] The temperature of the oxidation reaction is 30 - 50 °C, the time is 2 - 4 h; the power of the ultrasonication is 300 - 500 W, and the time is 1 - 2 h.

[0022] Further, the mass ratio of graphene to sodium lignosulfonate is 1:0.1 - 0.3.

[0023] Further, the temperature of the hydrothermal reaction is 180 - 220 °C, the time is 6 - 12 h; after the hydrothermal reaction, it is washed with a 0.1 - 0.5 mol / L sodium hydroxide solution until the pH is neutral.

[0024] Further, the pressure for the drying treatment is 8 - 10 MPa, the temperature is 40 - 50 °C, and the treatment time is 4 - 8 h.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention uses waste lithium - ion battery graphite slag as raw material, and through the integrated innovation of multi - stage intercalation synergistic expansion, biomass - enhanced self - assembly and supercritical drying technology, realizes the efficient and low - cost preparation of high - performance graphene aerogel. Through the synergistic effect of double intercalating agents KNO3 and FeCl3 and instantaneous expansion, the controllable expansion of the graphite layer spacing is achieved, significantly improving the exfoliation efficiency; combined with oxidation and lignosulfonate - assisted hydrothermal self - assembly, an enhanced graphene framework with a three - dimensional porous network is constructed; finally, through supercritical CO2 drying, the microscopic pore structure is breakthrough retained. The obtained aerogel has both high conductivity (>100 S / m), ultra - low density (3 - 10 mg / cm 3 ) and excellent mechanical resilience (compression deformation recovery rate of 90% > 95%). The production cycle is shortened by 30% and the cost is reduced by 40% compared with the traditional process. At the same time, the full - volume high - value utilization of graphite resources from waste batteries is realized, showing significant technological advancement and environmental and economic benefits in the field of new energy material recycling and functional material preparation.

[0027] Further, the waste lithium - ion battery adopts an inert atmosphere calcination and gradient acid leaching process (80 - 90 °C, solid - liquid ratio of 20 - 30 g / L) to accurately remove the binder and metal impurities on the graphite surface, improving the raw material purity to over 90%. Brief Description of the Drawings

[0028] Figure 1 SEM image of the regenerated graphene aerogel in Example 1;

[0029] Figure 2 Raman image of the regenerated graphene aerogel in Example 1;

[0030] Figure 3 SEM image of the regenerated graphene aerogel in Comparative Example 1. Detailed Description of the Invention

[0031] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0032] A method for preparing graphene aerogel by a multi - stage intercalation - supercritical drying method of the present invention includes the following steps:

[0033] (1)Discharge, crush, magnetically separate and pulverize and screen the waste lithium batteries to obtain crushed materials with a particle size less than 0.8 mm. Place the obtained crushed materials in a tubular furnace and calcine them in a nitrogen / argon atmosphere. The calcination temperature is 400 - 600 °C, the calcination time is 1 - 3 h, and the heating rate is set at 3 - 6 °C / min to remove the organic binder and electrolyte and obtain battery powder materials;

[0034] (2)Place the calcined battery powder materials in a 30% nitric acid solution. The leaching temperature is 80 - 90 °C, the leaching time is 3 - 4 h, and the solid-liquid ratio is 20 - 30 g / L. After filtration and drying, obtain purified graphite slag;

[0035] (3)Immerse the separated graphite slag into a KNO3 solution and an FeCl3 solution in sequence. The soaking time for each stage is 30 - 60 min, and then instantaneously thermally expand it under an inert atmosphere to obtain pre-peeled graphite;

[0036] (4)Mix the pre-peeled graphite with concentrated sulfuric acid (mass concentration 95 - 98%) according to a certain mass ratio, add potassium permanganate, react at 30 - 50 °C for 2 - 4 h, dilute it with deionized water and then perform ultrasonic treatment (power 300 - 500 W) for 1 - 2 h to obtain a graphene oxide suspension;

[0037] (5)Add sodium lignosulfonate to the graphene oxide suspension, perform hydrothermal reaction at 180 - 220 °C for 6 - 12 h, and obtain reduced graphene after centrifugation;

[0038] (6)Place the reduced graphene dispersion in a supercritical CO2 device, and obtain a three-dimensional porous graphene aerogel by controlling the pressure, temperature and treatment time.

[0039] In step (3), the concentration of the KNO3 solution is 0.5 - 1.5 mol / L, the concentration of the FeCl3 solution is 0.2 - 0.8 mol / L, and the molar ratio of KNO3 to FeCl3 is 1:0.5 - 1:1.

[0040] In step (3), heat up to 800 - 1000 °C for instantaneous thermal expansion at a rate of 10 - 20 °C / min, and the thermal expansion holding time is 5 - 10 min.

[0041] In step (4), the mass ratio of the peeled graphite to the concentrated sulfuric acid is 1:3 - 5, and the mass ratio of potassium permanganate to the graphite is 0.5 - 2:1;

[0042] In step (5), the mass ratio of the graphene to the sodium lignosulfonate is 1:0.1 - 0.3.

[0043] In step (5), after the hydrothermal reaction, it is necessary to wash with a 0.1 - 0.5 mol / L sodium hydroxide solution until the pH is neutral.

[0044] In step (6), control the pressure at 8 - 10 MPa, the temperature at 40 - 50 °C, and process for 4 - 8 h.

[0045] The following are specific examples.

[0046] Example 1

[0047] A method for preparing graphene aerogel by a multi - stage intercalation - supercritical drying method, comprising the following steps:

[0048] (1) Place the waste lithium battery in a 1 mol / L NaCl solution and discharge it to 1.5 V. After taking it out and drying, put it into a machine for crushing, magnetic separation, and pulverizing and screening to obtain crushed materials with a particle size less than 0.8 mm. Place the obtained crushed materials in a tubular furnace and calcine them under a N2 atmosphere. The roasting temperature is 400 °C, the roasting time is 3 h, and the heating rate is set at 3 °C / min to remove the organic binder and electrolyte;

[0049] (2) Place the roasted battery powder in a nitric acid solution with a mass concentration of 30%. The leaching temperature is 80 °C, the leaching time is 3.5 h, and the solid - liquid ratio is 20 g / L. After filtration and drying, obtain purified graphite slag;

[0050] (3) Immerse the separated graphite slag successively in 0.5 mol / L KNO3 and 0.3 mol / L FeCl3 solutions. The molar ratio of KNO3 to FeCl3 is 1:0.5, and the soaking time for each stage is 30 min. Then, under an Ar2 atmosphere, heat it to 900 °C at a rate of 10 °C / min and hold for 5 min to obtain pre - exfoliated graphite;

[0051] (4) Mix the pre - exfoliated graphite with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:3, add potassium permanganate, and the mass ratio of potassium permanganate to graphite is 2:1. React at 30 °C for 2 h, dilute it with deionized water, and then perform ultrasonic treatment (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0052] (5) Add sodium lignosulfonate to the graphene oxide suspension. The mass ratio of graphene to sodium lignosulfonate is 1:0.1. Perform hydrothermal reaction at 180 °C for 12 h. After the reaction, wash with a 0.2 mol / L NaOH solution until the pH is neutral, and obtain reduced graphene after centrifugation;

[0053] (6) Place the reduced graphene dispersion in a supercritical CO2 device and process it at 8 MPa and 40 °C for 5 h to obtain three - dimensional porous graphene aerogel.

[0054] In Example 1, the exfoliation yield of graphene is 99-95%.

[0055] In Example 1, the porosity of the three-dimensional porous graphene aerogel is 95-97%, the conductivity is 135-150 S / m, the compression-rebound rate is 97-98%, and the density is 3-5 mg / cm 3 , and the specific surface area is 310-460 m 2 / g.

[0056] See Figure 1 , it can be seen that the graphene aerogel presents a three-dimensional porous network structure with intertwined sheets. This structure endows it with a large specific surface area, which is beneficial to the adsorption and diffusion of gases and liquids. At the same time, the material also has good flexibility and certain mechanical strength.

[0057] See Figure 2 , it can be seen that the D peak, G peak, and 2D peak appear in the figure. The intensity of the G peak is relatively high, indicating that the carbon atoms in the graphene aerogel have a good sp 2 hybrid structure and relatively high crystallinity. The I D / I G ratio is 0.146, which is relatively low, indicating a low degree of defect of the material. The I 2D / I G ratio is 0.465. Combining the characteristics of each peak, it can be inferred that the graphene aerogel has fewer layers, and it may be an aerogel structure composed of few-layer or single-layer graphene.

[0058] Based on the comprehensive Figure 1 and Figure 2 analysis, the graphene aerogel has the structural characteristics of high crystallinity, few defects, and possibly few layers, and at the same time has a three-dimensional porous macroscopic structure, which may have good application potential in the fields of adsorption, catalysis, and energy storage.

[0059] Example 2

[0060] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0061] (1) Place the waste lithium battery in a 1 mol / L NaCl solution and discharge it to 1.5 V. After taking it out and drying, put it into a machine for crushing, magnetic separation, and pulverization and screening to obtain crushed materials with a particle size less than 0.8 mm. Place the obtained crushed materials in a tubular furnace and calcine them in an N2 atmosphere. The calcination temperature is 500 °C, the calcination time is 3 h, and the heating rate is set at 5 °C / min to remove the organic binder and electrolyte;

[0062] (2) Place the calcined battery powder in a nitric acid solution with a mass concentration of 30%, the leaching temperature is 80 °C, the leaching time is 4 h, and the solid-liquid ratio is 20 g / L. After filtration and drying, purified graphite slag is obtained;

[0063] (3) Immerse the separated graphite slag successively in 0.8 mol / L KNO3 and 0.4 mol / L FeCl3 solutions. The molar ratio of KNO3 to FeCl3 is 1:0.6. The soaking time for each stage is 30 min. Subsequently, heat it to 800 °C at a rate of 10 °C / min under an Ar2 atmosphere and hold for 5 min to obtain pre-exfoliated graphite;

[0064] (4) Mix the pre-exfoliated graphite with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:3, add potassium permanganate, and the mass ratio of potassium permanganate to graphite is 1.5:1. React at 30 °C for 2 h, dilute with deionized water and then perform ultrasonic treatment (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0065] (5) Add sodium lignosulfonate to the graphene oxide suspension. The mass ratio of graphene to sodium lignosulfonate is 1:0.1. Perform hydrothermal reaction at 180 °C for 12 h. After the reaction, wash with 0.1 mol / L NaOH solution until the pH is neutral, and obtain reduced graphene by centrifugation;

[0066] (6) Place the reduced graphene dispersion in a supercritical CO2 device and treat it at 10 MPa and 40 °C for 5 h to obtain a three-dimensional porous graphene aerogel.

[0067] Example 3

[0068] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0069] (1) Place the used lithium battery in 1 mol / L NaCl solution and discharge it to 1.5 V. Take it out, dry it, put it into a machine for crushing, magnetic separation, and pulverization and screening to obtain crushed material with a particle size less than 0.8 mm. Place the obtained crushed material in a tubular furnace and calcine it under a N2 atmosphere. The calcination temperature is 600 °C, the calcination time is 2 h, and the heating rate is set at 5 °C / min to remove the organic binder and electrolyte;

[0070] (2) Place the calcined battery powder in a nitric acid solution with a mass concentration of 30%, the leaching temperature is 80 °C, the leaching time is 4 h, and the solid-liquid ratio is 30 g / L. After filtration and drying, purified graphite slag is obtained;

[0071] (3) Immerse the separated graphite slag into 1 mol / L KNO3 and 0.4 mol / L FeCl3 solutions in sequence. The molar ratio of KNO3 to FeCl3 is 1:0.8. The immersion time for each stage is 40 min. Subsequently, heat it up to 800 °C at a rate of 15 °C / min under Ar2 atmosphere and hold for 5 min to obtain pre-peeled graphite;

[0072] (4) Mix the pre-peeled graphite with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:3, then add potassium permanganate. The mass ratio of potassium permanganate to graphite is 1:1. React at 40 °C for 4 h. After dilution with deionized water, perform ultrasonic treatment (power 500 W) for 1.5 h to obtain a graphene oxide suspension;

[0073] (5) Add sodium lignosulfonate to the graphene oxide suspension. The mass ratio of graphene to sodium lignosulfonate is 1:0.1. Perform hydrothermal reaction at 200 °C for 10 h. After the reaction, wash it with 0.2 mol / L NaOH solution until the pH is neutral, and obtain reduced graphene by centrifugation;

[0074] (6) Place the reduced graphene dispersion in a supercritical CO2 device and treat it at 10 MPa and 40 °C for 5 h to obtain a three-dimensional porous graphene aerogel.

[0075] Example 4

[0076] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0077] (1) Place the waste lithium battery in 1 mol / L NaCl solution and discharge it to 1.5 V. Take it out, dry it, put it into a machine for crushing, magnetic separation, and pulverization and screening to obtain crushed materials with a particle size less than 0.8 mm. Place the obtained crushed materials in a tubular furnace and calcine them under N2 atmosphere. The calcination temperature is 550 °C, the calcination time is 1 h, and the heating rate is set at 5 °C / min to remove the organic binder and electrolyte;

[0078] (2) Place the calcined battery powder in a nitric acid solution with a mass concentration of 30%. The leaching temperature is 85 °C, the leaching time is 3.5 h, and the solid-liquid ratio is 25 g / L. After filtration and drying, obtain purified graphite slag;

[0079] (3) Immerse the separated graphite slag into 1.5 mol / L KNO3 and 0.5 mol / L FeCl3 solutions in sequence. The molar ratio of KNO3 to FeCl3 is 1:1. The immersion time for each stage is 60 min. Subsequently, heat it up to 800 °C at a rate of 15 °C / min under Ar2 atmosphere and hold for 5 min to obtain pre-peeled graphite;

[0080] (4) Mix the pre-exfoliated graphite with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:4, add potassium permanganate, with the mass ratio of potassium permanganate to graphite being 1:1, react at 40 °C for 4 h, dilute with deionized water and then perform ultrasonic treatment (power 500 W) for 1.5 h to obtain a graphene oxide suspension;

[0081] (5) Add sodium lignosulfonate to the graphene oxide suspension, with the mass ratio of graphene to sodium lignosulfonate being 1:0.1, perform hydrothermal reaction at 200 °C for 8 h, wash with 0.5 mol / L NaOH solution after the reaction until the pH is neutral, and obtain reduced graphene by centrifugation;

[0082] (6) Place the reduced graphene dispersion in a supercritical CO2 device, treat at 10 MPa and 40 °C for 5 h to obtain a three-dimensional porous graphene aerogel.

[0083] Example 5

[0084] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0085] (1) Place the waste lithium battery in 1 mol / L NaCl solution and discharge it to 1.5 V, take it out, dry it, put it into a machine for crushing, magnetic separation and pulverizing and screening to obtain crushed material with a particle size less than 0.8 mm, place the obtained crushed material in a tube furnace and calcine it under N2 atmosphere, the calcination temperature is 550 °C, the calcination time is 1 h, and the heating rate is set at 5 °C / min to remove the organic binder and electrolyte;

[0086] (2) Place the calcined battery powder in a nitric acid solution with a mass concentration of 30%, the leaching temperature is 85 °C, the leaching time is 3.5 h, the solid-liquid ratio is 25 g / L, and obtain purified graphite slag after filtration and drying;

[0087] (3) Immerse the separated graphite slag successively in 1.5 mol / L KNO3 and 0.5 mol / L FeCl3 solutions, the molar ratio of KNO3 to FeCl3 is 1:0.5, the soaking time for each stage is 60 min, and then heat up to 1000 °C at 20 °C / min under Ar2 atmosphere and keep it warm for 5 min to obtain pre-exfoliated graphite;

[0088] (4) Mix the pre-exfoliated graphite with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:4, add potassium permanganate, with the mass ratio of potassium permanganate to graphite being 1:1, react at 30 °C for 3 h, dilute with deionized water and then perform ultrasonic treatment (power 500 W) for 2 h to obtain a graphene oxide suspension;

[0089] (5) Sodium lignosulfonate was added to the graphene oxide suspension, and the mass ratio of graphene to sodium lignosulfonate was 1:0.1. Hydrothermal reaction was carried out at 220 °C for 6 h. After the reaction, it was washed with 0.5 mol / L NaOH solution until the pH was neutral, and reduced graphene was obtained by centrifugation;

[0090] (6) The reduced graphene dispersion was placed in a supercritical CO2 device and treated at 9 MPa and 50 °C for 6 h to obtain a three-dimensional porous graphene aerogel.

[0091] Example 5

[0092] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0093] (1) The used lithium battery was discharged to 1.5 V in 1 mol / L NaCl solution, taken out, dried, put into a machine for crushing, magnetic separation and pulverization screening to obtain crushed material with a particle size less than 0.8 mm. The obtained crushed material was placed in a tubular furnace and calcined in an N2 atmosphere. The roasting temperature was 550 °C, the roasting time was 1 h, and the heating rate was set at 5 °C / min to remove the organic binder and electrolyte;

[0094] (2) The roasted battery powder was placed in a nitric acid solution with a mass concentration of 30%, the leaching temperature was 90 °C, the leaching time was 3 h, and the solid-liquid ratio was 30 g / L. After filtration and drying, purified graphite slag was obtained;

[0095] (3) The separated graphite slag was successively immersed in 1.2 mol / L KNO3 and 0.6 mol / L FeCl3 solutions. The molar ratio of KNO3 to FeCl3 was 1:0.5. The soaking time for each stage was 50 min. Subsequently, it was heated to 1000 °C at a rate of 20 °C / min in an Ar2 atmosphere and held for 5 min to obtain pre-peeled graphite;

[0096] (4) After mixing the pre-peeled graphite with concentrated sulfuric acid (concentration 95-98%) at a mass ratio of 1:5, potassium permanganate was added. The mass ratio of potassium permanganate to graphite was 0.5:1. The reaction was carried out at 30 °C for 3 h. After dilution with deionized water, it was ultrasonically treated (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0097] (5) Sodium lignosulfonate was added to the graphene oxide suspension, and the mass ratio of graphene to sodium lignosulfonate was 1:0.1. Hydrothermal reaction was carried out at 220 °C for 6 h. After the reaction, it was washed with 0.5 mol / L NaOH solution until the pH was neutral, and reduced graphene was obtained by centrifugation;

[0098] (6) The reduced graphene dispersion was placed in a supercritical CO2 device and treated at 9 MPa and 40 °C for 6 h to obtain a three-dimensional porous graphene aerogel.

[0099] Example 6

[0100] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0101] (1) Place the waste lithium battery in a 1 mol / L NaCl solution and discharge it to 1.5 V. After taking it out and drying, put it into a machine for crushing, magnetic separation, and pulverizing and screening to obtain crushed materials with a particle size less than 0.8 mm. Place the obtained crushed materials in a tubular furnace and calcine them under a N2 atmosphere. The calcination temperature is 550 °C, the calcination time is 1 h, and the heating rate is set to 5 °C / min to remove the organic binder and electrolyte;

[0102] (2) Place the calcined battery powder in a nitric acid solution with a mass concentration of 30%. The leaching temperature is 90 °C, the leaching time is 3 h, and the solid-liquid ratio is 30 g / L. After filtration and drying, obtain purified graphite slag;

[0103] (3) Immerse the separated graphite slag successively in 1 mol / L KNO3 and 0.3 mol / L FeCl3 solutions. The molar ratio of KNO3 to FeCl3 is 1:0.5. The soaking time for each stage is 50 min. Then, heat it to 800 °C at a rate of 15 °C / min under an Ar2 atmosphere and hold it for 10 min to obtain pre-exfoliated graphite;

[0104] (4) Mix the pre-exfoliated graphite with concentrated sulfuric acid (concentration 95-98%) at a mass ratio of 1:5, add potassium permanganate, and the mass ratio of potassium permanganate to graphite is 1.5:1. React at 40 °C for 5 h, dilute it with deionized water, and then perform ultrasonic treatment (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0105] (5) Add sodium lignosulfonate to the graphene oxide suspension. The mass ratio of graphene to sodium lignosulfonate is 1:0.3. Perform hydrothermal reaction at 200 °C for 12 h. After the reaction, wash it with 0.25 mol / L NaOH solution until the pH is neutral, and centrifuge to obtain reduced graphene;

[0106] (6) Place the reduced graphene dispersion in a supercritical CO2 device and process it at 8 MPa and 50 °C for 8 h to obtain a three-dimensional porous graphene aerogel.

[0107] Example 7

[0108] A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, comprising the following steps:

[0109] (1) Place the waste lithium battery in 1 mol / L NaCl solution and discharge it to 1.5 V. After taking it out and drying, put it into a machine for crushing, magnetic separation, and pulverizing and screening to obtain crushed materials with a particle size less than 0.8 mm. Place the obtained crushed materials in a tubular furnace and calcine them under a N₂ atmosphere. The roasting temperature is 450 °C, the roasting time is 1.5 h, and the heating rate is set at 6 °C / min to remove the organic binder and electrolyte;

[0110] (2) Place the roasted battery powder in a 30% mass concentration nitric acid solution. The leaching temperature is 85 °C, the leaching time is 3 h, and the solid-liquid ratio is 20 g / L. After filtration and drying, obtain purified graphite slag;

[0111] (3) Immerse the separated graphite slag successively in 0.6 mol / L KNO₃ and 0.2 mol / L FeCl₃ solutions. The molar ratio of KNO₃ to FeCl₃ is 1:0.7, and the soaking time for each stage is 45 min. Subsequently, heat it to 850 °C at a rate of 15 °C / min under an Ar₂ atmosphere and hold for 8 min to obtain pre-peeled graphite;

[0112] (4) Mix the pre-peeled graphite with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:4, add potassium permanganate, and the mass ratio of potassium permanganate to graphite is 1:1. React at 50 °C for 2 h, dilute it with deionized water, and then perform ultrasonic treatment (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0113] (5) Add sodium lignosulfonate to the graphene oxide suspension. The mass ratio of graphene to sodium lignosulfonate is 1:0.2. Perform hydrothermal reaction at 190 °C for 8 h. After the reaction, wash it with 0.1 mol / L NaOH solution until the pH is neutral, and obtain reduced graphene after centrifugation;

[0114] (6) Place the reduced graphene dispersion in a supercritical CO₂ device and treat it at 8 MPa and 45 °C for 4 h to obtain a three-dimensional porous graphene aerogel.

[0115] Example 8

[0116] A method for preparing graphene aerogel by a multi-stage intercalation - supercritical drying method, comprising the following steps:

[0117] (1) Place the waste lithium battery in 1 mol / L NaCl solution and discharge it to 1.5 V. After taking it out and drying, put it into a machine for crushing, magnetic separation, and pulverizing and screening to obtain crushed materials with a particle size less than 0.8 mm. Place the obtained crushed materials in a tubular furnace and calcine them under a N₂ atmosphere. The roasting temperature is 550 °C, the roasting time is 2 h, and the heating rate is set at 4 °C / min to remove the organic binder and electrolyte;

[0118] (2) Place the calcined battery powder in a nitric acid solution with a mass concentration of 30%, the leaching temperature is 90 °C, the leaching time is 4 h, and the solid-liquid ratio is 30 g / L. After filtration and drying, purified graphite slag is obtained;

[0119] (3) Immerse the separated graphite slag successively in 1.3 mol / L KNO3 and 0.8 mol / L FeCl3 solutions. The molar ratio of KNO3 to FeCl3 is 1:0.9. The soaking time for each stage is 55 min. Then, under an Ar2 atmosphere, heat it to 950 °C at a rate of 20 °C / min and hold for 6 min to obtain pre-exfoliated graphite;

[0120] (4) Mix the pre-exfoliated graphite with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:5, add potassium permanganate, and the mass ratio of potassium permanganate to graphite is 2:1. React at 35 °C for 3 h. After dilution with deionized water, perform ultrasonic treatment (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0121] (5) Add sodium lignosulfonate to the graphene oxide suspension. The mass ratio of graphene to sodium lignosulfonate is 1:0.1. Perform hydrothermal reaction at 200 °C for 10 h. After the reaction, wash it with 0.2 mol / L NaOH solution until the pH is neutral, and obtain reduced graphene by centrifugation;

[0122] (6) Place the reduced graphene dispersion in a supercritical CO2 device and treat it at 10 MPa and 40 °C for 7 h to obtain a three-dimensional porous graphene aerogel.

[0123] Comparative Example 1

[0124] (1) Discharge the used lithium battery in 1 mol / L NaCl solution until 1.5 V, take it out, dry it, put it into a machine for crushing, magnetic separation, and pulverization and screening to obtain crushed material with a particle size less than 0.8 mm. Place the obtained crushed material in a tubular furnace and calcine it under a N2 atmosphere. The calcination temperature is 550 °C, the calcination time is 2 h, and the heating rate is set at 4 °C / min to remove the organic binder and electrolyte;

[0125] (2) Place the calcined battery powder in a nitric acid solution with a mass concentration of 30%, the leaching temperature is 90 °C, the leaching time is 4 h, and the solid-liquid ratio is 30 g / L. After filtration and drying, purified graphite slag is obtained;

[0126] (3) Mix the separated graphite slag with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:5, add potassium permanganate, and the mass ratio of potassium permanganate to graphite is 2:1. React at 35 °C for 3 h. After dilution with deionized water, perform ultrasonic treatment (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0127] (4) Sodium lignosulfonate was added to the graphene oxide suspension, and the mass ratio of graphene to sodium lignosulfonate was 1:0.1. Hydrothermal reaction was carried out at 200 °C for 10 h. After the reaction, it was washed with 0.2 mol / L NaOH solution until the pH was neutral, and reduced graphene was obtained by centrifugation;

[0128] (5) The reduced graphene was freeze-dried to obtain a graphene aerogel.

[0129] See Figure 3 , it can be seen that the graphene aerogel without using KNO3 and FeCl3 solutions for solution intercalation and supercritical CO2 drying shows irregular blocky and flaky structures, indicating that it fails to be effectively exfoliated. At the same time, the area is bright, indicating that the graphene aerogel obtained by this method has relatively poor conductivity.

[0130] Comparative Example 2

[0131] (1) The spent lithium battery was discharged to 1.5 V in 1 mol / L NaCl solution, taken out and dried, then put into a machine for crushing, magnetic separation and pulverizing and screening to obtain crushed materials with a particle size less than 0.8 mm. The obtained crushed materials were placed in a tubular furnace and calcined under N2 atmosphere, the roasting temperature was 550 °C, the roasting time was 2 h, and the heating rate was set at 4 °C / min to remove the organic binder and electrolyte;

[0132] (2) The roasted battery powder was placed in a nitric acid solution with a mass concentration of 30%, the leaching temperature was 90 °C, the leaching time was 4 h, and the solid-liquid ratio was 30 g / L. After filtration and drying, purified graphite slag was obtained;

[0133] (3) The separated graphite slag was mixed with concentrated sulfuric acid (concentration 95 - 98%) at a mass ratio of 1:2, then potassium permanganate was added, and the mass ratio of potassium permanganate to graphite was 3:1. The reaction was carried out at 35 °C for 3 h, and after dilution with deionized water, it was ultrasonically treated (power 500 W) for 1 h to obtain a graphene oxide suspension;

[0134] (4) Ethylenediamine was added to the graphene oxide suspension, and the mass ratio of graphene to ethylenediamine was 1:0.5. Hydrothermal reaction was carried out at 200 °C for 10 h. After the reaction, it was washed with 0.2 mol / L NaOH solution until the pH was neutral, and reduced graphene was obtained by centrifugation;

[0135] (5) The reduced graphene was freeze-dried to obtain a graphene aerogel.

[0136] Table 1 Key performance parameters of graphene aerogels prepared in each example and comparative example

[0137]

[0138] As can be seen from Table 1, the graphene aerogel in Comparative Example 1, which did not use KNO3 and FeCl3 solutions for solution intercalation and supercritical CO2 drying, exhibited irregular blocky and flaky structures and could not achieve effective exfoliation. In Comparative Example 2, although ethylenediamine was used to produce graphene aerogel, its overall performance was far inferior to that of sodium lignosulfonate, especially in terms of conductivity, which is very important for its subsequent application in electronic devices.

[0139] In this method of the present invention, waste lithium batteries are used as raw materials, and graphite slag is obtained through pretreatment steps such as discharging, crushing, and roasting purification. Then, three-dimensional porous graphene aerogel is prepared by nitrate / metal salt multi-stage intercalation, chemical oxidation exfoliation, hydrothermal reduction combined with supercritical CO2 drying technology. The innovation lies in using the graphite anode in waste lithium batteries as raw materials, combining multi-stage intercalation exfoliation process with supercritical drying technology, significantly improving the exfoliation efficiency of graphene and the structural stability of the aerogel. The obtained product has a high specific surface area, excellent conductivity, and mechanical strength, and can be applied to fields such as supercapacitors and catalytic carriers. The present invention realizes resource recycling, and the process is environmentally friendly and low-cost.

[0140] The above is only an illustration of the best embodiments of the present invention, but it should not be construed as a limitation of the claims. The present invention is not limited to the above embodiments, and its specific structure allows for changes. Any changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0141] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

Claims

1. A method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method, characterized in that, It includes the following steps: Process the waste lithium battery to obtain graphite slag; Soak the graphite slag in KNO3 solution and FeCl3 solution, and then instantaneously expand it under an inert atmosphere to obtain pre-exfoliated graphite; Oxidize the pre-exfoliated graphite to obtain a graphene oxide suspension; Add sodium lignosulfonate to the graphene oxide suspension and carry out a hydrothermal reaction to obtain reduced graphene; Place the reduced graphene dispersion in supercritical CO2 for drying treatment to obtain a three-dimensional porous graphene aerogel.

2. The method for preparing graphene aerogel by multi-stage intercalation-supercritical drying method according to claim 1, characterized in that, Processing the waste lithium battery to obtain graphite slag includes the following steps: Discharge, crush, magnetically separate and crush and screen the waste lithium battery to obtain crushed material with a particle size less than 0.8 mm; Calcine the obtained crushed material in a nitrogen / argon atmosphere to obtain battery powder; Leach the battery powder in an acid solution to obtain graphite slag.

3. The method for preparing graphene aerogel by multi-stage intercalation-supercritical drying method according to claim 2, wherein, The calcination temperature is 400 - 600 °C, the calcination time is 1 - 3 h, and the heating rate is 3 - 6 °C / min; The leaching temperature is 80 - 90 °C, the leaching time is 3 - 4 h, and the solid-liquid ratio is 20 - 30 g / L.

4. The method for preparing graphene aerogel by multi-stage intercalation-supercritical drying method according to claim 1, wherein, The soaking time is 30 - 60 min; the concentration of the KNO3 solution is 0.5 - 1.5 mol / L, the concentration of the FeCl3 solution is 0.2 - 0.8 mol / L, and the molar ratio of KNO3 to FeCl3 is 1:0.5 - 1:

1.

5. The method for preparing graphene aerogel by multi-stage intercalation-supercritical drying method according to claim 1, characterized in that, The temperature of the instantaneous expansion is 800 - 1000 °C, and the heat preservation time of the instantaneous expansion is 5 - 10 min; heat up to 800 - 1000 °C at a heating rate of 10 - 20 °C / min.

6. The method for preparing graphene aerogel by the multi-stage intercalation-supercritical drying method according to claim 1, characterized in that, The specific process of oxidizing the pre-exfoliated graphite is: after mixing the pre-exfoliated graphite with sulfuric acid, add potassium permanganate, carry out an oxidation reaction, dilute it, and then ultrasonicate to obtain a graphene oxide suspension.

7. The method for preparing graphene aerogel by multi-stage intercalation-supercritical drying method according to claim 6, characterized in that, The mass ratio of the pre-exfoliated graphite to sulfuric acid is 1:3 - 5, the mass concentration of sulfuric acid is 95 - 98%, and the mass ratio of potassium permanganate to graphite is 0.5 - 2:1; The temperature of the oxidation reaction is 30 - 50 °C, the time is 2 - 4 h; the power of ultrasonication is 300 - 500 W, and the time is 1 - 2 h.

8. The method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method according to claim 1, wherein, The mass ratio of graphene to sodium lignosulfonate is 1:0.1 - 0.

3.

9. The method for preparing graphene aerogel by multi-stage intercalation-supercritical drying method according to claim 1, wherein, The temperature of the hydrothermal reaction is 180 - 220 °C, the time is 6 - 12 h; after the hydrothermal reaction, wash it with 0.1 - 0.5 mol / L sodium hydroxide solution until the pH is neutral.

10. The method for preparing graphene aerogel by a multi-stage intercalation-supercritical drying method according to claim 1, wherein, The pressure of the drying treatment is 8 - 10 MPa, the temperature is 40 - 50 °C, and the treatment time is 4 - 8 h.

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