A preparation method of an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation

Abstract

The present invention discloses a preparation method of an expanded graphite-based composite material based on molten salt intercalation and its controllable removal, belonging to the technical field of the preparation of modified expanded graphite. The preparation method of the expanded graphite-based composite material comprises the following steps: mixing a graphite substrate with an intercalating agent, and carrying out a molten salt intercalation reaction under a closed condition to obtain a graphite intercalation compound; under a semi-closed condition, performing a secondary temperature rise on the graphite intercalation compound to sublime and remove the intercalating agent to obtain the expanded graphite-based composite material based on molten salt intercalation and its controllable removal; the intercalating agent is a metal salt that can sublime under the condition of secondary temperature rise. The present invention uses a lower secondary treatment temperature to completely or partially remove the intercalating agent from the graphite intercalation compound, obtaining graphite with different expansion effects, and the residual rate of the intercalating agent is 0 to 100%, solving the technical problems of single product variety, production safety, and cost in the prior art for preparing expanded graphite by a strong oxidation method.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of modified expanded graphite, and more specifically relates to a method for preparing an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation. Background Art

[0002] Expanded graphite has a very wide range of applications. Its synthesis method generally uses graphite materials as the matrix, and under ice bath conditions, strong oxidants such as concentrated sulfuric acid, fuming nitric acid, and potassium permanganate are used for edge oxidation and internal intercalation. After separation and purification, graphite oxide is obtained, and then graphite oxide is heated at a high temperature above 900 °C or instantaneously heated by microwave to decompose sulfate ions into sulfur dioxide, and edge hydroxyl groups, epoxy groups, and carboxylic acids decompose into carbon dioxide, and the graphite layers are opened by the force generated by expansion. The expanded graphite obtained by the traditional strong oxidation method has an extremely high expansion degree and has been produced on a large scale. However, it also has several disadvantages: (1) It is not easy to control different expansion effects; (2) The volume will gradually collapse during storage, and it must be expanded immediately before use, otherwise key indicators such as porosity will fluctuate too much and cannot be calibrated; (3) High energy consumption; (4) High process safety risks. In order to make up for the defect of too few types of different expansion effects, researchers have developed expanded graphite with various different synthesis paths, such as the autoclave method using the supercritical effect of CO2, etc. The autoclave method increases the safety risk. Although it has certain value, it is currently difficult to mass-produce. In order to avoid excessive volume change, most of the commercially available expanded graphite currently appears in the form of expandable graphite (graphite oxide). Although the problem has been solved, it is extremely inconvenient. In order to reduce energy consumption and safety risks, researchers have introduced the weak acid electrolyte method, such as slowly oxidizing graphite with ammonium persulfate and dilute sulfuric acid. The expanded graphite prepared by the weak acid electrolyte method has a low expansion rate and low efficiency and cannot be widely promoted.

[0003] In view of the many problems existing in the above-mentioned preparation methods of expanded graphite, it is of great significance to research and obtain a preparation method of expanded graphite that can obtain various different expansion effects, has low cost, low energy consumption, and high stability. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation to solve the problems existing in the above-mentioned prior art, and to realize the preparation of expanded graphite that can obtain various different expansion effects, has low cost, low energy consumption, and high stability.

[0005] To achieve the above purpose, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention: provides a method for preparing an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation, including the following steps:

[0007] Mix the graphite substrate with the intercalating agent and carry out a molten salt intercalation reaction under airtight conditions to obtain a graphite intercalation compound;

[0008] Under semi-closed conditions, the graphite intercalation compound is heated for a second time to sublime and remove the intercalating agent to obtain the expanded graphite-based composite material based on molten salt intercalation and its controllable removal;

[0009] The intercalating agent is a metal salt that can sublime under the condition of the second heating.

[0010] Preferably, the graphite substrate includes one or more of natural graphite, artificial graphite, microcrystalline graphite, expanded graphite, and multi-layer graphene; the intercalating agent includes one or more of metal halides, metal sulfides, and metal oxides. The metal halides include one or more of aluminum chloride, molybdenum chloride, niobium chloride, titanium chloride, and gallium chloride. The metal sulfide includes mercury sulfide, and the metal oxide includes mercury oxide.

[0011] Preferably, the mass ratio of the graphite substrate to the intercalating agent is 1:0.1 - 14.

[0012] Preferably, the temperature of the molten salt intercalation reaction is 100 - 800 °C, the time is 0 - 24 h, and it is not 0.

[0013] Preferably, the temperature of the second heating is 100 - 800 °C, the heating rate is 10 °C / min, the time is 0 - 1 h, and it is not 0.

[0014] Preferably, the molten salt intercalation reaction further includes a step of controlling the stage number of the obtained graphite intercalation compound by using the chlorine partial pressure; the reagents providing the chlorine partial pressure include one or more of liquefied chlorine, N-chlorosuccinimide, phosphorus trichloride, phosphorus pentachloride, thionyl chloride, and sulfuryl chloride. By controlling the dosage of such reagents, different chlorine partial pressure values can be provided. On the premise of ensuring sufficient intercalating agent, the larger the dosage, the greater the pressure, and the more perfect the product stage number. Excessively high pressure is not conducive to safety protection. The chlorine partial pressure in the present invention is 5 - 8 MPa.

[0015] Furthermore, it is necessary to ensure that the reagent providing the chlorine partial pressure does not mix or contact with the reactants.

[0016] Furthermore, both the molten salt intercalation reaction and the second heating are carried out in a reaction kettle. Specifically: mix the graphite substrate with the intercalating agent, place it in a sealed reaction kettle to carry out the molten salt intercalation reaction to obtain a graphite intercalation compound; then adjust the reaction kettle to a semi-closed state and place it in a sealed recovery bottle for the second heating to obtain the expanded graphite-based composite material based on molten salt intercalation and its controllable removal.

[0017] After the secondary heating reaction of the present invention ends, the intercalating agent sublimes into the recovery bottle, and the product remains in the reaction kettle. The efficient recovery of the intercalating agent can be achieved by recovering the substances generated in the recovery bottle, thereby reducing the preparation cost.

[0018] In addition, during the secondary heating process, the intercalating agent is relatively active. Under semi-sealed conditions, sublimation occurs simultaneously with a small amount of oxidation. The presence of these oxides is beneficial to the room-temperature stability and performance of the graphite intercalation compound containing the intercalating agent.

[0019] Preferably, after the secondary heating, steps of impurity removal and drying of the product are further included.

[0020] Preferably, a step of modifying the expanded graphite composite material based on molten salt intercalation and its controllable deintercalation is further included.

[0021] Technical solution two of the present invention: Provide an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation prepared by the preparation method of the expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation. The residual rate of the intercalating agent in the expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation is 0-100%, and it is not 0.

[0022] Technical solution three of the present invention: Provide the application of the expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation in battery preparation.

[0023] The technical principle of the present invention is as follows:

[0024] The present invention provides a preparation method for an expanded graphite-based composite material with low cost, controllable expansion degree, safety and high efficiency, so as to solve the technical problems of the types, stability, production safety, and cost of the expanded graphite prepared by the prior art.

[0025] The present invention uses a low-boiling-point intercalating agent to prepare an intermediate product (graphite intercalation compound). Under the condition of instant high temperature, the low-boiling-point intercalating agent can generate an expansion thrust like an acid radical ion, and then expanded graphite is prepared. This method has the following advantages: (1) Different amounts of intercalating agent embedding can produce different expansion effects. By preparing pre-intercalated graphite with different intercalation orders, expanded graphite with different expansion effects can be controllably prepared; (2) The preparation temperature of the corresponding graphite intercalation compound of the low-boiling-point compound and the sublimation temperature of the post-treatment are relatively low, with less energy consumption and low cost; (3) The expanded graphite after a large amount of the intercalating agent is deintercalated still has a small amount of residual intercalating agent, which can make the structure of the expanded graphite relatively stable and maintain it for a longer time at room temperature; (4) The whole process does not involve strong acid reactants and ultra-high pressure process conditions, with a high safety factor; (5) Through effective process design, most of the deintercalated intercalating agent can be recovered, further reducing the cost.

[0026] The present invention prepares expanded graphite-based composites with different residual rates (different expansion effects) by using a specific type of intercalating agent, controlling the temperature and duration of secondary heating, and adjusting the residual rate of the intercalating agent. The expanded graphite-based composites can be used after impurity removal or directly used in the form of composites without impurity removal.

[0027] Compared with the existing process for preparing expanded graphite that requires a high expansion temperature (800 - 1000 °C), based on preparing graphite intercalation compounds of different orders using a specific type of intercalating agent, the present invention can achieve the preparation of expanded graphite with controllable expansion effects using a lower secondary heating temperature (100 - 800 °C). Compared with the prior art, the present invention reduces energy consumption and ensures lower preparation costs.

[0028] When preparing expanded graphite using the preparation method of the present invention, after a large amount of the intercalating agent has escaped, there is still a small amount of residual intercalating agent in the expanded graphite and oxides formed during the oxidation of the intercalating agent during sublimation, which can make the structure of the expanded graphite relatively stable, maintain it for a longer time at room temperature, and have higher product stability.

[0029] The present invention discloses the following technical effects:

[0030] 1. The present invention uses graphite intercalation compounds as intermediate products, and by using a lower secondary treatment temperature to completely or partially remove the intercalating agent from the graphite intercalation compounds, fully expanded and slightly expanded graphite is obtained, with the residual rate of the intercalating agent being 0 - 100%, solving the technical problems of product stability, production safety, and cost in the prior art of preparing expanded graphite by the strong oxidation method.

[0031] 2. The present invention can controllably prepare expanded graphite with different expansion effects, solving the problem that the existing preparation methods of expanded graphite cannot regulate the expansion effect to obtain expanded graphite with different expansion effects.

[0032] 3. The present invention has low energy consumption and low cost; the structure of the obtained product can be maintained for a longer time at room temperature; it has a high safety factor; the intercalating agent used can be recycled, which is environmentally friendly and sustainable; the synthesis method is simple to operate, has high production efficiency and high raw material utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flowchart of the preparation method of the present invention and a structural diagram of the device required for the preparation process, where 1 - quartz bottle, 2 - flange-type hydrothermal reaction kettle, 3 - steel recovery bottle, 4 - air leakage gap after adjusting airtightness, 5 - intercalating agent condensed on the wall of the recovery bottle after overflow;

[0034] Figure 2 It is the TG measurement results of the residual intercalating agent in Example 1, Example 3, Example 4, and Comparative Example 1;

[0035] Figure 3 Scanning electron microscope images of the products obtained in Comparative Examples 1-2 and Examples 1-4;

[0036] Figure 4 XRD patterns of the intermediate products obtained in Step S1 and the final products obtained in Step S3 in Comparative Examples 1-2 and Examples 1-4;

[0037] Figure 5 Performance diagrams of the batteries prepared from the final products obtained in Step S3 of Comparative Example 1 and Examples 2 and 4;

[0038] Figure 6 Crystallization of the intercalating agent on the wall of the flange-type hydrothermal reactor during the preparation process of Example 3. Detailed implementation manners

[0039] The present invention provides a preparation method of an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation (the specific process is as Figure 1 shown), including the following steps:

[0040] Mix a graphite substrate with an intercalating agent, and carry out a molten salt intercalation reaction under a closed condition to obtain a graphite intercalation compound;

[0041] Under a semi-closed condition, perform secondary heating on the graphite intercalation compound to sublime and remove the intercalating agent to obtain the expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation;

[0042] The intercalating agent is a metal salt that can sublime under the condition of secondary heating.

[0043] The intercalating agent in the preparation method of the present invention is mainly a metal compound that is easy to intercalate into the graphite layer and easy to sublime. By its one intercalation and one deintercalation, the expansion of graphite is realized. It can be understood that the core reaction of the present invention is the intercalation and deintercalation reaction of the intercalating agent in graphite.

[0044] In the present invention, the graphite intercalation compound is obtained by compounding an intercalating agent and a graphite substrate. The graphite substrate includes but is not limited to one or more of natural graphite, artificial graphite, microcrystalline graphite, expanded graphite, and multi-layer graphene; the intercalating agent includes but is not limited to one or more of metal halides, metal sulfides, and metal oxides. The metal halides include one or more of aluminum chloride, molybdenum chloride, niobium chloride, titanium chloride, and gallium chloride. The metal sulfide includes mercury sulfide, and the metal oxide includes mercury oxide.

[0045] In some embodiments, the graphite intercalation compound can be prepared by a direct mixing method, a molten salt method, and a two-chamber method.

[0046] In some embodiments, before mixing the graphite substrate with the intercalating agent, the graphite substrate is also dried; the drying temperature is 80 °C and the drying time is 4 h.

[0047] The present invention does not particularly limit the particle size of the graphite substrate, as long as it can ensure the preparation of the product.

[0048] The present invention does not particularly limit the mixing method of the graphite substrate and the intercalating agent, as long as uniform mixing can be ensured.

[0049] In the present invention, the mass ratio of the graphite substrate to the intercalating agent is preferably 1:0.1 - 14, more preferably 1:1 - 10, and even more preferably 1:4.

[0050] In the present invention, the temperature of the molten salt intercalation reaction is preferably 100 - 800 °C, more preferably 150 - 500 °C, and specifically can be: 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 400 °C, 500 °C; the time is preferably 0 - 24 h and not 0, more preferably 0.5 min - 23 h, and specifically can be: 0.5 min, 0.6 min, 0.8 min, 1 min, 2 min, 5 min, 8 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 15 h, 18 h, 19 h, 20 h, 22 h, 23 h or 24 h.

[0051] In the present invention, the temperature of the secondary heating is preferably 100 - 800 °C, more preferably 150 - 700 °C, and specifically can be: 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C or 800 °C; the heating rate is preferably 10 °C / min; the time is preferably 0 - 1 h and not 0, more preferably 0.25 - 50 min, and specifically can be: 0.25 min, 0.5 min, 0.6 min, 0.8 min, 1 min, 2 min, 5 min, 8 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min or 1 h.

[0052] In some embodiments, the molten salt intercalation reaction further includes a step of controlling the order of the obtained graphite intercalation compound by chlorine partial pressure. The chlorine partial pressure helps the intercalating agent to be embedded in the graphite. The reagents providing the chlorine partial pressure include one or more of liquefied chlorine, chlorosuccinimide, phosphorus trichloride, phosphorus pentachloride, thionyl chloride and sulfonyl chloride.

[0053] In the present invention, it is necessary to ensure that the reagent providing the chlorine partial pressure does not mix or contact with the reactants.

[0054] The dosage, temperature, pressure, and defect distribution of the intercalating agent all have certain effects on the order of the product. The influence of the chlorine partial pressure is an efficient control means that combines the influence of pressure and the doping and vacancy effects of chlorine atoms, and is a method for controlling the order of the product by reducing the reaction energy barrier.

[0055] In the present invention, the molten salt intercalation reaction and the secondary heating are both carried out in a reaction kettle. Specifically: the graphite substrate is mixed with the intercalating agent and placed in a sealed reaction kettle for the molten salt intercalation reaction to obtain a graphite intercalation compound; then the reaction kettle is adjusted to a semi-closed state and placed in a sealed recovery bottle for secondary heating to obtain the expanded graphite and expanded graphite-based composite materials based on molten salt intercalation and its controllable deintercalation.

[0056] In the present invention, the reaction kettle includes but is not limited to a general type hydrothermal reaction kettle, a stepped hydrothermal reaction kettle, a flanged hydrothermal reaction kettle, or a large-scale customized hydrothermal reaction kettle; the material of the recovery bottle includes but is not limited to steel, ceramic, or glass.

[0057] In some embodiments, if batch production is considered, the intercalating agent can also be embedded and deintercalated in an inert atmosphere; the inert atmosphere includes but is not limited to an argon atmosphere. In addition, an air injection and pressure control device needs to be designed separately for implementing the inert atmosphere.

[0058] After the secondary heating reaction of the present invention ends, the intercalating agent sublimes into the recovery bottle, and the product remains in the reaction kettle. The efficient recovery of the intercalating agent can be achieved by recovering the substances generated in the recovery bottle, reducing the preparation cost.

[0059] In some embodiments, a simple intercalating agent recovery device can be designed to recover the intercalating agent by using the specific heat capacity of the equipment and the furnace cooling sequence.

[0060] In other embodiments, if large-scale production is considered, a device for evacuating under high temperature can be designed to recover the intercalating agent.

[0061] In some embodiments, after the secondary heating, it further includes steps of impurity removal and drying of the product.

[0062] The graphite intercalation compound containing the intercalating agent itself has certain functionality, and the product with partial retention of the intercalating agent can be directly applied. In addition, the intercalating agent is relatively reactive and sublimes under semi-sealed conditions accompanied by a small amount of oxidation. The presence of these oxides is beneficial to the room temperature stability and performance of the graphite intercalation compound containing the intercalating agent and can also be retained. Therefore, whether to set the above steps of cleaning and impurity removal and drying can be determined according to application needs.

[0063] In addition, the expanded graphite obtained after the release reaction usually contains impurities, such as intercalants and their oxides. The above impurities are likely to affect the physical and chemical properties of the expanded graphite, and are not conducive to the subsequent oxidation, sulfidation, phosphation, selenization and other treatments to enrich the types of expanded graphite. The presence of impurities can easily reduce the efficiency and effect of oxidation, sulfidation, phosphation, and selenization. Therefore, some application scenarios require the expansion of graphite to be impurity-free.

[0064] The present invention does not impose any particular limitation on the method of removing impurities.

[0065] In some embodiments, the product can be cleaned with a cleaning agent to achieve the purpose of removing impurities; the cleaning agent includes but is not limited to one or more of deionized water, organic solvents and acid-base reagents; the organic solvents include but are not limited to one or more of ethanol, methanol and acetone; the acid-base reagents include but are not limited to hydrochloric acid. The above cleaning agents can remove impurities and have little effect on expanded graphite with a low degree of expansion. However, it is not good for expanded graphite with a high degree of expansion. Therefore, for expanded graphite with a high degree of expansion, try not to clean it, or use a very simple cleaning process.

[0066] In another embodiment, the expanded graphite can be immersed in a cleaning agent and left to stand for a period of time until the impurities are removed. Alternatively, the expanded graphite can be immersed in a cleaning agent and mechanical cleaning can be used to accelerate the removal of impurities; the mechanical cleaning method includes but is not limited to ultrasonic cleaning or magnetic stirring cleaning.

[0067] The present invention does not impose any special restrictions on the time of impurity removal, as long as the impurities are completely removed. The pH value and color of the washing liquid can be used as the judgment criteria, and the impurity removal is considered to be completed when the washing liquid is close to neutral and the washing liquid is almost transparent.

[0068] In some embodiments, the time for removing impurities is 0 to 24 hours, and is not 0.

[0069] In some embodiments, the expanded graphite obtained after the impurities are removed can be dried, and can be placed in a vacuum drying condition at 60-80° C. for 10-15 hours.

[0070] Since the graphite intercalation compounds have a certain structural stability, the expanded graphite prepared through the above steps inevitably still contains trace amounts of metal compound intercalants. In order to enrich the types of expanded graphite, the expanded graphite-based composite materials can also be modified by substitution reaction to obtain metal compound-modified expanded graphite that is difficult to prepare directly.

[0071] In some embodiments, the method further includes the step of modifying the expanded graphite-based composite material based on molten salt intercalation and its controllable release; the modification treatment includes but is not limited to oxidation treatment, sulfurization treatment, phosphating treatment or selenization treatment.

[0072] The present invention does not specifically limit the specific steps of oxidation treatment, sulfidation treatment, phosphidation treatment, and selenization treatment. The above treatments can be achieved by using common technical means in the art.

[0073] When the expanded graphite prepared by the present invention is subjected to oxidation treatment, the intercalating agent (metal compound) can be oxidized to metal oxide, that is, expanded graphite modified with metal oxide can be obtained. In some embodiments, the oxidation treatment includes, but is not limited to, air oxidation method, electromagnetic heating oxidation method, or microwave oxidation method.

[0074] When the expanded graphite prepared by the present invention is subjected to sulfidation treatment, the intercalating agent (metal compound) can be sulfided into metal sulfide, and thus expanded graphite modified with metal sulfide can be obtained. In some embodiments, the sulfur source for sulfidation treatment includes, but is not limited to, one or more of elemental sulfur, hydrogen sulfide, sulfur oxide, sodium sulfide, and thiourea; the sulfidation treatment includes, but is not limited to, elemental sulfur sulfidation method, carbon disulfide sulfidation method, or sulfur-containing organic compound sulfidation method.

[0075] When the expanded graphite prepared by the present invention is subjected to phosphidation treatment, the intercalating agent (metal compound) can be phosphidated into metal phosphide, that is, expanded graphite modified with metal phosphide can be obtained. In some embodiments, the phosphorus source for phosphidation treatment includes, but is not limited to, one or more of elemental phosphorus, phosphine, phosphoric acid, and sodium hypophosphite, and the phosphidation treatment includes, but is not limited to, elemental phosphorus phosphidation method or phosphorus-containing organic compound phosphidation method.

[0076] The present invention has extremely high production efficiency. The expanded graphite prepared by the present invention has the function of electrode material and can be extended to application fields such as aerospace phase change materials and military wave-absorbing materials. The conventional expanded graphite preparation process needs to first prepare graphite oxide in liquid phase, then wash and purify it, then expand it at high temperature to obtain expanded graphite, and then compound materials with specific functions into the expanded graphite through other composite methods. The present invention only needs a one-pot method and two temperature increases to achieve this step. The product of the present invention can also be washed or not washed according to application needs. Compared with multi-step methods, the one-pot method is more efficient.

[0077] The present invention has extremely high raw material utilization rate. The present invention can make the sublimated raw materials be reused repeatedly. It is found in experiments that after deducting the intercalation residue (related to the application scenario), the recovery rate can reach up to 90%. If industrial design is carried out, the recovery rate can be even higher.

[0078] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0079] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0080] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0081] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0082] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0083] It should be noted that the aspects not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0084] The original graphite PG used in the present invention was purchased from Shanghai Macklin Biochemical Co., Ltd. Other raw materials used are all commercially available products unless otherwise specified. The sources of the commercially available products do not affect the technical effects of the present invention.

[0085] The room temperature involved in the present invention is calculated as 25 ± 5 °C unless otherwise specified.

[0086] Example 1

[0087] This example provides a preparation method of an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation. The specific steps are as follows:

[0088] Step S1: 1 g of natural graphite with a particle size of 10 μm was dried at 120 °C for 4 h, then quickly added to 4 g of anhydrous molybdenum chloride, stirred and mixed at room temperature, vacuum dried at 120 °C for 1 h, and then transferred to a flanged hydrothermal reactor. 2 g of chlorosuccinimide (not mixed or contacted with the reactants) was additionally added to the gap of the flanged hydrothermal reactor. After sealing the flanged hydrothermal reactor, it was placed in a heating furnace and heated to 350 °C and kept warm for 24 h to obtain graphite intercalation compound, that is, the intermediate product, the 1st-order MoCl5-graphite intercalation compound.

[0089] Step S2: After the flanged hydrothermal reactor was completely cooled, the flange of the flanged hydrothermal reactor was loosened to facilitate gas overflow, then it was placed in a sealable steel recovery bottle and the recovery bottle was sealed. The whole was placed in a heating furnace and heated to 300 °C (heating rate was 10 °C / min) and kept warm for 1 h. During this process, the intercalants of the graphite intercalation compound obtained in Step S1 almost completely sublimated and escaped, triggering graphite expansion.

[0090] Step S3: After the container was completely cooled, the steel recovery bottle was opened, anhydrous MoCl5 was scraped off from the inside of the recovery bottle, collected, dried and sealed. The flanged hydrothermal reactor was opened, and the expanded graphite was scraped off from the inner liner and collected by sealing. The final product was an expanded graphite-based composite material with a very low residual intercalant content (content was 6%). Finally, 3.5 g of MoCl5 was recovered.

[0091] Example 2

[0092] This example provides a preparation method of an expanded graphite-based composite material based on molten salt intercalation and its controllable escape, and the specific steps are as follows:

[0093] Step S1: 1 g of natural graphite with a particle size of 10 μm was dried at 120 °C for 4 h, then quickly added to 1 g of anhydrous molybdenum chloride, stirred and mixed at room temperature, vacuum dried at 120 °C for 1 h, and then transferred to a flanged hydrothermal reactor. 1 g of chlorosuccinimide (not mixed or contacted with the reactants) was additionally added to the gap of the flanged hydrothermal reactor. After sealing the flanged hydrothermal reactor, it was placed in a heating furnace and heated to 350 °C and kept warm for 24 h to obtain graphite intercalation compound, that is, the intermediate product, the 3rd - 7th-order MoCl5-graphite intercalation compound.

[0094] Step S2: After the flanged hydrothermal reactor was completely cooled, the flange of the flanged hydrothermal reactor was loosened to facilitate gas overflow, then it was placed in a sealable steel recovery bottle and the recovery bottle was sealed. The whole was placed in a heating furnace and heated to 270 °C (heating rate was 10 °C / min) and kept warm for 5 min. During this process, part of the intercalants of the graphite intercalation compound obtained in Step S1 sublimated and escaped, triggering slight graphite expansion.

[0095] Step S3: Wait for the container to cool completely. Open the steel recovery bottle, scrape off the anhydrous MoCl5 from inside the recovery bottle, collect it, and seal it in a dry place. Open the flanged hydrothermal reactor, scrape off the expanded graphite from the inner liner, and collect it by sealing. The final product is an expanded graphite-based composite material with a very high residual intercalate content (50% content). Wash the obtained expanded graphite-based composite material with deionized water, alcohol, and acetone respectively, and then dry it at 80 °C for 12 h. Finally, 0.8 g of MoCl5 is recovered.

[0096] Example 3

[0097] This example provides a preparation method of an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation. The specific steps are as follows:

[0098] Step S1: Dry 1 g of natural graphite with a particle size of 10 μm at 120 °C for 4 h, then quickly add 9 g of anhydrous aluminum chloride, stir and mix at room temperature, vacuum dry at 120 °C for 1 h, and then transfer it to a flanged hydrothermal reactor. Additionally, add 2 g of chlorosuccinimide (not mixed or contacted with the reactants) to the gap of the flanged hydrothermal reactor. After sealing the flanged hydrothermal reactor, place it in a heating furnace and heat it to 200 °C and keep it warm for 12 h to obtain a graphite intercalation compound, that is, obtain an AlCl3-graphite intercalation compound of intermediate products of 1-2 orders.

[0099] Step S2: After the flanged hydrothermal reactor has cooled completely, loosen the flange of the flanged hydrothermal reactor to facilitate the overflow of gas, then place it in a sealable steel recovery bottle and seal the recovery bottle. Place the whole in a heating furnace and heat it to 200 °C (heating rate is 10 °C / min) and keep it warm for 1 h. During this process, almost all the intercalates of the graphite intercalation compound obtained in Step S1 are sublimated and deintercalated, triggering the expansion of graphite.

[0100] Step S3: Wait for the container to cool completely. Open the steel recovery bottle, scrape off the anhydrous AlCl3 from inside the recovery bottle, collect it, and seal it in a dry place. Open the flanged hydrothermal reactor, scrape off the expanded graphite from the inner liner, and collect it by sealing. The final product is an expanded graphite-based composite material with a very low residual intercalate content (3.1% content). Finally, 8 g of AlCl3 is recovered.

[0101] Example 4

[0102] This example provides a preparation method of an expanded graphite-based composite material based on molten salt intercalation and its controllable deintercalation. The specific steps are as follows:

[0103] Step S1: 1 g of natural graphite with a particle size of 10 μm was dried at 120 °C for 4 h and then quickly added to 4.5 g of anhydrous ferric chloride and 9 g of anhydrous aluminum chloride, followed by stirring and mixing at room temperature. After vacuum drying at 80 °C for 5 h, it was transferred to a flanged hydrothermal reactor. The flanged hydrothermal reactor was sealed and placed in a heating furnace, heated to 650 °C and held for 24 h to obtain graphite intercalation compounds, i.e., AlCl3-FeCl3-graphite intercalation compounds of intermediate products of stages 1 to 2.

[0104] Step S2: After the flanged hydrothermal reactor was completely cooled, the flange of the flanged hydrothermal reactor was loosened to facilitate gas overflow, and then it was placed in a sealable steel recovery bottle and the recovery bottle was sealed. The whole was placed in a heating furnace and heated to 200 °C (heating rate: 10 °C / min) and held for 1 h. During this process, almost all of the intercalating substance AlCl3 in the graphite intercalation compounds obtained in Step S1 was sublimated and removed, causing the graphite to expand, while FeCl3 was preserved.

[0105] Step S3: After the container was completely cooled, the steel recovery bottle was opened, anhydrous AlCl3 was scraped off from inside the recovery bottle, collected, dried and sealed. The flanged hydrothermal reactor was opened, and the expanded graphite was scraped off from the inner liner and collected in a sealed manner. The final product was a FeCl3-expanded graphite-based composite material. The obtained product was washed with deionized water, alcohol and acetone respectively and then dried at 80 °C for 12 h. Finally, 7 g of AlCl3 was recovered.

[0106] Example 5

[0107] The difference from Example 3 was that the reaction temperature in Step S1 was adjusted to 180 °C, and the others were the same as in Example 3. In Step S1, AlCl3-graphite intercalation compounds of intermediate products of stages 3 to 5 were obtained; in Step S3, the final product was an expanded graphite-based composite material with a residual intercalating substance content of 4.0%. Finally, 8 g of AlCl3 was recovered.

[0108] Example 6

[0109] The difference from Example 3 was that the reaction temperature in Step S2 was adjusted to 180 °C, and the others were the same as in Example 3. In Step S1, AlCl3-graphite intercalation compounds of intermediate products of stages 1 to 2 were obtained; in Step S3, the final product was an expanded graphite-based composite material with a residual intercalating substance content of 5.0%. Finally, 8 g of AlCl3 was recovered.

[0110] Example 7

[0111] The difference from Example 3 was that the reaction time in Step S1 was adjusted to 24 h, and the others were the same as in Example 3. In Step S1, AlCl3-graphite intercalation compounds of intermediate products of stages 1 to 2 were obtained; in Step S3, the final product was an expanded graphite-based composite material with a residual intercalating substance content of 3.0%. Finally, 8 g of AlCl3 was recovered.

[0112] Example 8

[0113] The difference from Example 3 is that the reaction time in Step S2 is adjusted to 0.5 h, and the others are the same as in Example 3. In Step S1, the intermediate product is the 1st to 2nd order AlCl₃-graphite intercalation compound; in Step S3, the final product is the expanded graphite-based composite material with the residual intercalate content of 3.5%. Finally, 8 g of AlCl₃ is recovered.

[0114] Example 9

[0115] The difference from Example 3 is that the addition of 2 g of chlorosuccinimide in Step S1 is omitted, and the others are the same as in Example 3. In Step S1, the intermediate product is the 3rd to 5th order AlCl₃-graphite intercalation compound; in Step S3, the final product is the expanded graphite-based composite material with the residual intercalate content of 3.1%. Finally, 8 g of AlCl₃ is recovered.

[0116] Comparative Example 1

[0117] Untreated raw graphite PG.

[0118] Figure 2 TG measurement results of the intercalating agent residues described in Example 1, Example 3, Example 4 and Comparative Example 1.

[0119] Comparative Example 2

[0120] Step S1: 15 ml of concentrated sulfuric acid and 8 ml of concentrated nitric acid are added to 8 ml of deionized water, and stirred in an ice bath; 2 g of graphite is added and stirred for 1 min; ice cubes are added, and 6 g of potassium permanganate is added (it can be added in portions according to the viscosity of the reactants), and a large amount of thick smoke is generated, and stirred for 90 min.

[0121] Step S2: Take 1 L of water in a 3 L large beaker and operate in a fume hood. Slowly add the concentrated sulfuric acid solution along a glass rod to the beaker; if the reactant has become a solid paste, add a large amount of deionized water; if the reactant is in a solution state, slowly transfer the reactant to a large amount of water, let it stand, pour out the upper solution, and centrifuge; wash with hydrogen peroxide to remove manganese oxide impurities, and the judgment criterion is that no bubbles emerge, and then wash until neutral (washed 3 times with water and 3 times with alcohol); after drying in a blast for about 3 h, transfer to a vacuum drying oven and vacuum dry at 80 °C for more than 24 h to obtain expandable graphite.

[0122] Step S3: Heat the large-bore tube furnace to 1000 °C. Take 50 mg of expandable graphite and quickly insert it into the constant temperature zone of the tube furnace under protection. Take it out after 20 s and cool to obtain the final product, conventional expanded graphite NEG.

[0123] The products obtained in Examples 1-4, Comparative Example 2 and the original graphite PG were characterized by scanning electron microscopy (SEM) and X-ray diffractometer (XRD), and the results are as Figure 3 and Figure 4 shown.

[0124] Figure 3 Figure Figure 4 shows the scanning electron micrographs of the products obtained in Comparative Examples 1-2 and Examples 1-4; Figure 4 Figure shows the XRD patterns of the intermediate products obtained in Step S1 and the final products obtained in Step S3 of Comparative Examples 1-2 and Examples 1-4.

[0125] From Figure 3 and Figure 4 it can be seen that Example 1 obtained low-intercalate-residual expanded graphite (MoCl5-based), and the product showed a significant worm-like expansion effect (close to the traditional expanded graphite preparation process). This material only retained a trace amount of MoCl5 and was suitable for general uses of expanded graphite. Example 2 obtained high-intercalate-residual expanded graphite (MoCl5-based), and the product only showed micro-expansion phenomena such as larger particle size and local edge opening. This material retained a large amount of MoCl5 and could be used as a battery electrode material. Example 3 obtained low-intercalate-residual expanded graphite (AlCl3-based), and the product showed a significant worm-like expansion effect (close to the traditional expanded graphite preparation process). This material only retained a trace amount of AlCl3 and was suitable for general uses of expanded graphite. Example 4 obtained FeCl3-expanded graphite composite, and the product showed a significant worm-like expansion effect (close to the traditional expanded graphite preparation process). This material retained a large amount of FeCl3 and a trace amount of AlCl3 and could be used as a battery electrode material.

[0126] Performance test:

[0127] The final products obtained in Comparative Example 1, Example 2 and Example 4 were used as electrode materials, and their electrochemical performance was evaluated with a button half-cell:

[0128] First, a battery was prepared, and the specific steps were as follows:

[0129] Using the final products obtained in Comparative Example 1, Example 2 and Example 4 as the positive electrode, lithium foil as the negative electrode, LB046 ether-based electrolyte, and adopting CR2032 battery components, the above components were assembled to obtain a half-cell.

[0130] Secondly, the electrochemical performance of the above-obtained lithium-ion half-cell was tested with a BlueTEC system, and the results are as Figure 5 shown.

[0131] Figure 5 Figure Figure 5 shows the performance diagrams of the batteries prepared from the final products obtained in Example 2, Example 4 and Comparative Example 1. At Figure 5Among them, the original graphite PG corresponds to Comparative Example 1.

[0132] As can be seen from Figure 5 it, the batteries assembled with the products of Example 2 and Example 4 have higher specific capacity and cycling stability, and still show significant performance improvement at a high rate of 3C. The cost of industrialization is the main bottleneck restricting the application of such materials. The preparation method of the present invention is expected to overcome the cost bottleneck and create favorable conditions for the application of such materials.

[0133] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other.

[0134] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A one-pot method for preparing an expanded graphite-based composite material with controllable expansion effect based on molten salt intercalation and controllable release thereof, characterized in that: The steps include: The graphite substrate is mixed with the intercalation agent, and a molten salt intercalation reaction is carried out under a closed condition to obtain a graphite intercalation compound; under a semi-closed condition, the graphite intercalation compound is heated for a second time to allow the intercalation agent to sublime and be released to obtain the expanded graphite-based composite material based on molten salt intercalation and controllable release thereof; The intercalant is a metal salt that can sublime under secondary heating conditions; The mass ratio of the graphite substrate to the intercalant is 1:0.1-14; The temperature of the molten salt intercalation reaction is 100-800°C, the time is 0-24h, and is not 0; The secondary heating temperature is 100-300°C, the heating rate is 10°C / min, the time is 0-1h, and is not 0; The molten salt intercalation reaction also includes a step of controlling the order of the obtained graphite intercalation compound by using chlorine partial pressure; the reagent providing the chlorine partial pressure includes one or more of liquefied chlorine, chlorosuccinimide, phosphorus trichloride, phosphorus pentachloride, thionyl chloride and sulfonyl chloride; the chlorine partial pressure is 5~8MPa.

2. The method for preparing an expanded graphite-based composite material with controllable expansion effect based on molten salt intercalation and controllable release thereof by one-pot method according to claim 1, characterized in that: The graphite substrate includes one or more of natural graphite, artificial graphite, microcrystalline graphite, expanded graphite and multilayer graphene; and / or the intercalant includes one or more of metal halides, metal sulfides and metal oxides.

3. The method for preparing an expanded graphite-based composite material with controllable expansion effect based on molten salt intercalation and controllable release thereof by one-pot method according to claim 1, characterized in that: After the second heating, the process also includes the steps of removing impurities and drying the product.

4. The method for preparing an expanded graphite-based composite material with controllable expansion effect based on molten salt intercalation and controllable release thereof by one-pot method according to claim 1, characterized in that: The method also includes a step of modifying the expanded graphite based on molten salt intercalation and controllable release thereof.

5. The method for preparing an expanded graphite-based composite material with controllable expansion effect based on molten salt intercalation and controllable release thereof by a one-pot method according to any one of claims 1 to 4 is characterized in that: The intercalation agent residual rate of the expanded graphite-based composite material with controllable expansion effect based on molten salt intercalation and controllable release is 0-100%, and is not 0.

6. Use of the expanded graphite-based composite material with controllable expansion effect based on molten salt intercalation and controllable release as claimed in claim 5 in battery preparation.

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