Preparation method and application of fluorinated reduced graphene oxide film

Abstract

The invention discloses a preparation method and application of a fluorinated reduced graphene oxide film, and relates to the field of all-solid-state lithium batteries, fluorine is introduced in the preparation process to form a stable carbon fluoride group (CFx), and the stable carbon fluoride group (CFx) is introduced between a negative electrode and an electrolyte sheet of an all-solid-state lithium ion battery as an interlayer, so that the performance of the film is improved. The problems of interface reaction, performance degradation, lithium dendrite generation and the like caused by direct contact between the electrolyte and the lithium metal negative electrode in the all-solid-state lithium ion battery are solved; and the effects of optimizing the electron and ion conductivity of the negative electrode, keeping the electrochemical stability of the battery, inhibiting the generation of lithium dendrites, improving the safety of the battery and preventing electrolyte decomposition and side reaction are achieved.

Description

Technical Field

[0001] The present invention relates to the field of all-solid-state lithium batteries, and in particular to a preparation method and application of a fluorinated reduced graphene oxide film. Background Art

[0002] Lithium metal batteries have become a research hotspot for the next generation of energy storage technology due to their high energy density and long cycle life. Compared with traditional lithium-ion batteries, lithium metal batteries use lithium metal as the negative electrode and have a higher specific capacity (about 3860 mAh / g), so the energy density is greatly improved. However, the practical application of lithium metal batteries still faces many challenges, mainly including the growth of lithium dendrites and their impact on battery performance and safety.

[0003] During the charge and discharge process of lithium metal batteries, lithium metal often shows non-uniform growth when deposited on the surface of the negative electrode, leading to the formation of lithium dendrites. The growth of lithium dendrites not only seriously affects the cycle stability of lithium batteries, but may also cause safety problems such as internal short circuits and thermal runaway of the battery. Therefore, how to effectively inhibit the growth of lithium dendrites is one of the main challenges facing current lithium metal battery technology. In order to improve the safety and stability of lithium metal negative electrodes, researchers have tried a variety of modification strategies, such as adding electrolyte additives, designing solid electrolytes, and using protective films. However, most of these methods have certain limitations, such as the lack of significant improvement in battery cycle performance and difficulty in maintaining stability under high-rate charge and discharge conditions.

[0004] As a two-dimensional material, graphene has excellent conductivity, mechanical strength and chemical stability. It has been widely studied and applied in the negative electrode, conductive additives and electrolytes of lithium batteries. In terms of negative electrode modification, graphene and its derivatives (such as reduced graphene oxide, rGO) are considered to be ideal candidate materials for inhibiting the growth of lithium dendrites due to their high surface area, good electronic conductivity and high chemical stability. Nevertheless, the pure rGO material lacks stable chemical functional groups on the surface, making it difficult to effectively form a strong interface protection layer with the surface of the lithium metal negative electrode, resulting in the lithium metal negative electrode still prone to dendrite growth. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing a fluorinated reduced graphene oxide film and its application.

[0006] The objective of the present invention is achieved through the following technical solutions: <First aspect> The present invention provides a method for preparing a fluorinated reduced graphene oxide film, comprising the following steps: S1, preparing a graphene oxide film from a slurry containing graphene oxide by a filtration deposition method, and drying the film; S2, placing the graphene oxide film in a fluorine-containing gas environment for fluorination treatment, and then washing and drying to obtain a fluorinated graphene oxide film; S3: placing the fluorinated graphene oxide film in an inert atmosphere for reduction treatment, and then cooling it to room temperature to obtain a fluorinated reduced graphene oxide film.

[0007] As an embodiment, the method for preparing a slurry containing graphene oxide is to react graphite powder with a particle size of 1 to 50 μm, a strong oxidant and a reaction medium to obtain a reaction solution containing graphene oxide, and dilute the reaction solution with deionized water to stop the reaction, wash the prepared graphene oxide, and use deionized water to configure it into a slurry with a concentration of 1-5 g / mL.

[0008] As an embodiment, the mass of deionized water used to dilute the reaction solution containing graphene oxide is 10 to 20 times that of the reaction medium.

[0009] As an embodiment, the strong oxidant includes one or more of potassium permanganate, potassium chlorate, hydrogen peroxide, and ozone.

[0010] As an embodiment, the mass ratio of the graphite powder to the strong oxidant is 1: (3~9).

[0011] As an embodiment, the reaction medium includes one or more of concentrated sulfuric acid and concentrated nitric acid.

[0012] As an embodiment, the usage ratio of the graphite powder and the reaction medium is 1g: 40~100mL.

[0013] As an embodiment, the reaction temperature when preparing graphene oxide from the graphite powder is 25-100° C., and the reaction time is 0.5-10 h.

[0014] In some embodiments, the graphite powder has a particle size of 30 μm, the strong oxidant is potassium permanganate, the reaction medium is concentrated sulfuric acid, the ratio of the three is 1 g: 5 g: 50 mL, the reaction temperature of graphene oxide is 60° C., and the reaction time is 2 h.

[0015] As an embodiment, the graphite powder is prepared from natural graphite or artificial graphite.

[0016] As an embodiment, the graphite powder is prepared by ball milling.

[0017] As an embodiment, in step S2, the fluorine-containing gas is one or more of hydrogen fluoride, carbon tetrafluoride, nitrogen trifluoride, and sulfur hexafluoride.

[0018] As an embodiment, during the fluorination treatment, the reaction chamber is a closed reaction chamber filled with fluorine-containing gas at a pressure of 0.1-1.0 MPa at room temperature.

[0019] As an embodiment, during the fluorination treatment, the pressure of the fluorine-containing gas in the reaction chamber is 0.2-0.5 MPa at room temperature.

[0020] As an embodiment, during the fluorination treatment, the pressure of the fluorine-containing gas in the reaction chamber is 0.2-0.3 MPa at room temperature.

[0021] As an embodiment, the fluorination treatment parameters are maintained at 200~1000°C for 1~6h.

[0022] As an embodiment, the fluorination treatment parameters are maintained at 200-700° C. for 1-6 hours.

[0023] In some embodiments, the fluorination treatment parameters are 200° C. for 5 hours.

[0024] As an embodiment, in step S3, the inert atmosphere includes one or more of argon, nitrogen, and helium.

[0025] As an embodiment, in step S3, the reduction treatment is to keep the fluorinated graphene oxide film at 200-800° C. for 1-12 h in an argon environment and then cool it to room temperature.

[0026] As an embodiment, in step S3, the parameters of the reduction treatment are: keeping warm at 300-700°C for 2-4h.

[0027] As an embodiment, in step S3, the parameters of the reduction treatment are: keeping warm at 500° C. for 2 to 3 hours.

[0028] In some embodiments, in step S3, the reduction treatment parameters are: keeping warm at 500° C. for 2 hours.

[0029] <Second Aspect> The present invention discloses an application of a fluorinated reduced oxide graphene film in an all-solid-state battery.

[0030] As an embodiment, the fluorinated reduced graphene oxide film is placed between the electrolyte sheet and the negative electrode in an all-solid-state battery.

[0031] As an embodiment, the electrolyte sheet is formed by pressing a sulfide solid electrolyte.

[0032] In some embodiments, the sulfide solid electrolyte is selected from Li 5.5 PS 4.5 Cl1.5 .

[0033] As an embodiment, the negative electrode is lithium metal.

[0034] As an embodiment, the positive electrode material in the battery is formed by mixing and pressing a nickel cobalt manganese oxide lithium positive electrode material, a sulfide solid electrolyte and a conductive material.

[0035] In some embodiments, the cathode material is NCM811 and a sulfide solid electrolyte (Li 5.5 PS 4.5 Cl 1.5 ) and conductive carbon fiber (VGCF) are mixed and pressed in a mass ratio of 70:29:1.

[0036] Compared with the prior art, the present invention has the following beneficial effects: 1) The fluorinated reduced graphene oxide film prepared by the present invention introduces fluorine element through the fluorination process, and forms a stable fluorinated carbon group (CFx) through the synergistic effect of the reduction treatment, so that the film has a lower surface energy and friction coefficient and a stronger electrical conductivity. It is introduced as a separator between the negative electrode and the electrolyte sheet of the all-solid-state lithium-ion battery, isolating the direct contact between the electrolyte and the lithium metal negative electrode, and forming a uniform and stable protective layer on the surface of the negative electrode. It can also transfer electrons and ions through conductivity, optimize the electronic and ionic conductivity of the negative electrode, maintain the electrochemical stability of the battery, and reduce the performance degradation caused by interface reactions.

[0037] 2) From the perspective of interface optimization, on the one hand, the film can effectively guide the uniform deposition of lithium ions during the charge and discharge process, reduce the uneven deposition phenomenon inside the battery, optimize the deposition morphology of lithium, and prevent lithium metal from being deposited too quickly and excessively locally on the negative electrode surface, thereby effectively inhibiting the formation of lithium dendrites, reducing the risk of battery short circuit and improving battery safety; on the other hand, by synergistically optimizing the fluorinated carbon groups through fluorination and reduction treatment, the film acts as a chemically stable protective layer, which improves the interface between the lithium metal negative electrode and the electrolyte, isolates the direct contact between the electrolyte and the negative electrode, and thus prevents the demarcation of the electrolyte and the occurrence of side reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 This is a SEM image of the fluorinated reduced graphene oxide prepared in Example 5 of the present invention; Figure 2 The voltage-specific capacity performance test results of the all-solid-state batteries prepared in some embodiments and comparative examples of the present invention are shown. DETAILED DESCRIPTION

[0039] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0040] For ease of understanding, the abbreviations of graphene derivatives mentioned below are first explained: Go: graphene oxide; GO-F: fluorinated graphene oxide; rGo-F: fluorinated reduced graphene oxide; rGo: reduced graphene oxide.

[0041] This specific embodiment provides a method for preparing a fluorinated reduced graphene oxide film, comprising the following steps: S1. Prepare graphene oxide film, the specific steps are: S11. Graphite powder with a particle size of 1 to 50 μm, a strong oxidant and a reaction medium are reacted to obtain a reaction solution containing graphene oxide, and the reaction solution is diluted with deionized water (the mass of which is 10 to 20 times that of the reaction medium) to stop the reaction.

[0042] Furthermore, the strong oxidant includes one or more of potassium permanganate, potassium chlorate, hydrogen peroxide, and ozone.

[0043] Furthermore, the reaction medium includes one or more of concentrated sulfuric acid and concentrated nitric acid.

[0044] Furthermore, the preparation method of graphene oxide may be: (1) Hummers method: graphite powder and potassium permanganate are mixed, and then the mixture is added to concentrated sulfuric acid for reaction to obtain graphene oxide; (2) Staudenmaier method, in which graphene oxide is obtained by reacting with potassium chlorate as a strong oxidant in a system of concentrated nitric acid and concentrated sulfuric acid; (3) After reacting graphite powder and concentrated sulfuric acid at low temperature, sulfuric acid solution is added, ozone is introduced, and hydrogen peroxide solution is added to react to obtain graphene oxide (see Chinese invention patent "A method for preparing graphene oxide" with announcement number CN106395808B).

[0045] S12. The pH of the diluted solution containing graphene oxide is adjusted to neutral (pH=7) by adding 1 M sodium hydroxide solution.

[0046] S13, washing the graphene oxide, and using deionized water to prepare a mixed solution with a concentration of 1-5 g / mL of the washed graphene oxide, and performing ultrasonic dispersion to obtain a graphene oxide slurry.

[0047] S14, filtering the graphene oxide slurry, and depositing the graphene oxide into a film.

[0048] S2, fluorinating the graphene oxide film and then washing it to obtain a fluorinated graphene oxide film, the specific steps being: The graphene oxide film is placed in a closed 0.2-0.5 MPa hydrogen fluoride gas environment for fluorination treatment.

[0049] Furthermore, during the fluorination process, the mass ratio of graphene oxide to hydrogen fluoride gas in the reaction chamber is 1: (2~5) g.

[0050] Furthermore, the temperature during the fluorination treatment is 100-250 °C, and the time is 1-6 h.

[0051] Furthermore, after the fluorination treatment, the film is cooled to room temperature, and is cleaned with deionized water, ethanol, acetone or other solvents.

[0052] S3. Performing reduction treatment on the fluorinated graphene oxide film to obtain a fluorinated reduced graphene oxide film. The specific steps are: placing the fluorinated graphene oxide film in an inert atmosphere, keeping it at 300-700 °C for 1-4 hours, and cooling it to room temperature to obtain a fluorinated reduced graphene oxide film (hereinafter referred to as rGO-F film).

[0053] In this specific embodiment, the source of graphite powder includes natural graphite powder or artificial graphite powder. The graphite powder is placed in a 100 mL zirconia ball mill under argon protection and ball milled at 500 rpm (ball to material ratio 1:20, using zirconia ball milling beads), and sieved to obtain graphite powder with D50=30 μm.

[0054] The method for preparing rGO-F film using natural graphite powder is specifically introduced below through several embodiments.

[0055] Example 1 In this embodiment, a method for preparing rGO-F film using natural graphite powder is specifically introduced.

[0056] In S1, the preparation parameters of graphene oxide (GO) film are: Graphite powder comes from natural graphite powder; Graphene oxide was prepared by the Hummers method, that is, 5 g of graphite powder and 25 g of potassium permanganate were mixed and added to 250 mL of concentrated sulfuric acid, stirred and reacted at 60 °C for 2 h, and then 2500 mL of deionized water was added to the reaction system for dilution to reduce the concentration of the reaction system until the reaction stopped, thereby obtaining a reaction solution containing graphene oxide; Using sodium hydroxide to adjust the pH of the reaction solution to neutral; The graphene oxide was washed with deionized water; The washed graphene oxide and deionized water were prepared into a slurry with a concentration of 2 g / mL, and ultrasonicated for 3 h to make it evenly dispersed to obtain a graphene oxide slurry; The graphene oxide slurry is filtered and dried using filter paper to obtain a graphene oxide film.

[0057] In S2, the preparation parameters of fluorinated graphene oxide (GO-F) film are: 1 g of graphene oxide film was placed in a reaction furnace with 0.3 MPa of hydrogen fluoride gas in the reaction chamber (the pressure here refers to the pressure at room temperature, and the pressure increases when the temperature is increased). The temperature was increased at a rate of 1°C / min, and after being maintained at 200°C for 5 h, it was naturally cooled to room temperature, and the film was washed with deionized water and dried to obtain a fluorinated graphene oxide film.

[0058] In S3, the preparation parameters of the fluorinated reduced graphene oxide (rGO-F) film are as follows: the fluorinated graphene oxide film is calcined in a muffle furnace in a glove box in an argon environment (flow rate of 10 L / min), the temperature is increased at a heating rate of 1°C / min, and after being kept at 500°C for 2 h, it is naturally cooled to room temperature to obtain an rGO-F film with a thickness of 103 nm.

[0059] Example 2 In this embodiment, a method for preparing rGO-F film using natural graphite powder is specifically introduced.

[0060] The steps are basically the same as those in Example 1, except that: In step S3, the reduction treatment temperature is 500 °C and maintained for 3 h.

[0061] Other parameters are the same as those in Example 1.

[0062] The thickness of the obtained rGO-F film is 109 nm.

[0063] Example 3 In this embodiment, a method for preparing rGO-F film using natural graphite powder is specifically introduced.

[0064] The steps are basically the same as those in Example 1, except that: In step S3, the reduction treatment temperature is 300 °C and maintained for 4 h.

[0065] Other parameters are the same as those in Example 1.

[0066] The thickness of the obtained rGO-F film is 123 nm.

[0067] Example 4 In this embodiment, a method for preparing rGO-F film using natural graphite powder is specifically introduced.

[0068] The steps are basically the same as those in Example 1, except that: In step S3, the reduction treatment temperature is 700 °C and maintained for 2 h.

[0069] Other parameters are the same as those in Example 1.

[0070] The thickness of the obtained rGO-F film is 113 nm.

[0071] Comparative Example 1 In this embodiment, a method for preparing a GO-F film using natural graphite powder is specifically introduced.

[0072] The steps are basically the same as those in Example 1, except that: Step S1 and step S2 are performed to obtain a fluorinated graphene oxide film without performing step S3.

[0073] Other parameters are the same as those in Example 1.

[0074] The thickness of the obtained GO-F film is 78 nm.

[0075] Comparative Example 2 In this embodiment, a method for preparing a GO film using natural graphite powder is specifically introduced.

[0076] The steps are basically the same as those in Example 1, except that: Step S1 is performed to obtain a graphene oxide film, and steps S2 and S3 are not performed.

[0077] Other parameters are the same as those in Example 1.

[0078] The thickness of the obtained GO film is 98 nm.

[0079] Comparative Example 3 In this embodiment, a method for preparing rGO film using natural graphite powder is specifically introduced.

[0080] The steps are basically the same as those in Example 1, except that: Step S1 is performed to obtain a graphene oxide film, and step S3 is directly performed without performing step S2.

[0081] Other parameters are the same as those in Example 1.

[0082] The thickness of the obtained rGO film is 80 nm.

[0083] The following is a detailed introduction to the method of preparing rGO-F film using artificial synthetic graphite powder through several embodiments.

[0084] Example 5 In this embodiment, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0085] The steps are basically the same as those in Example 1, except that: In S1, the graphite powder is artificially synthesized graphite powder, which is ball-milled at a speed of 500 rpm and sieved to obtain graphite powder with D50 = 30 μm; Other parameters are the same as those in Example 1.

[0086] The thickness of the obtained rGO-F film is 100 nm and the morphology is as follows Figure 1 shown.

[0087] Example 6 In this embodiment, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0088] The steps are basically the same as those in Example 5, except that: In step S2, the parameters of the fluorination treatment are: 1 g of graphene oxide film was placed in a reactor with 0.2 MPa of hydrogen fluoride gas in the reaction chamber. The temperature was increased at a rate of 1 °C / min and maintained at 200 °C for 5 h. The film was naturally cooled to room temperature and washed with deionized water and dried to obtain a fluorinated graphene oxide film.

[0089] Other parameters are the same as those in Example 5.

[0090] The thickness of the obtained rGO-F film is 105 nm.

[0091] Example 7 In this embodiment, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0092] The steps are basically the same as those in Example 5, except that: In step S2, the parameters of the fluorination treatment are: 1 g of graphene oxide film was placed in a reactor with 0.5 MPa of hydrogen fluoride gas in the reaction chamber. After being kept at 200 °C for 5 h, it was naturally cooled to room temperature, and the film was washed with deionized water and dried to obtain a fluorinated graphene oxide film.

[0093] Other parameters are the same as those in Example 5.

[0094] The thickness of the obtained rGO-F film is 114 nm.

[0095] Example 8 In this embodiment, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0096] The steps are basically the same as those in Example 5, except that: In step S2, the temperature of the fluorination treatment is 100 °C and maintained for 6 h.

[0097] The other parameters are the same as those in Example 5.

[0098] The thickness of the obtained rGO-F film is 89 nm.

[0099] Example 9 In this embodiment, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0100] The steps are basically the same as those in Example 5, except that: In step S2, the temperature of the fluorination treatment is 250 °C and maintained for 1 h.

[0101] Other parameters are the same as those in Example 5.

[0102] The thickness of the obtained rGO-F film is 92 nm.

[0103] Example 10 In this embodiment, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0104] The steps are basically the same as those in Example 5, except that: In step S2, the parameters of the reduction treatment are: placing the fluorinated graphene oxide film in argon gas, keeping it at 300 °C for 4 h, and then cooling it to room temperature.

[0105] Other parameters are the same as those in Example 5.

[0106] The thickness of the obtained rGO-F film is 78 nm.

[0107] Embodiment 11 In this embodiment, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0108] The steps are basically the same as those in Example 5, except that: In step S2, the parameters of the reduction treatment are: placing the fluorinated graphene oxide film in argon gas, keeping it at 700 °C for 1 h, and then cooling it to room temperature.

[0109] Other parameters are the same as those in Example 5.

[0110] The thickness of the obtained rGO-F film is 65 nm.

[0111] Comparative Example 4 In this embodiment, a method for preparing a GO-F film using artificial synthetic graphite powder is specifically introduced.

[0112] The steps are basically the same as those in Example 5, except that: Steps S1 and S2 are performed to obtain a fluorinated graphene oxide film without performing step S3.

[0113] The parameters are the same as those in Example 5.

[0114] The thickness of the obtained fluorinated graphene oxide GO-F film is 89 nm.

[0115] Comparative Example 5 In this embodiment, a method for preparing rGO film using artificial graphite powder is specifically introduced.

[0116] The steps are basically the same as those in Example 5, except that: Step S1 is performed to obtain a graphene oxide film, and step S3 is directly performed without performing step S2.

[0117] Other parameters are the same as those in Example 5.

[0118] The thickness of the obtained rGO film is 90 nm.

[0119] Comparative Example 6 In this comparative example, a method for preparing a graphene oxide film using artificially synthesized graphite powder is specifically introduced.

[0120] The steps are basically the same as those in Example 5, except that: Step S1 is performed to obtain a graphene oxide film without performing steps S2 and S3.

[0121] The parameters are the same as those in Example 5.

[0122] The thickness of the obtained graphene oxide film is 153 nm.

[0123] Comparative Example 7 In this comparative example, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0124] The steps are basically the same as those in Example 1, except that: In S1, the graphene oxide slurry is obtained without filtering to prepare the graphene film, but is directly subjected to S2 fluorination treatment, and then filtered to obtain the fluorinated graphene oxide film.

[0125] Other parameters are the same as those in Example 1.

[0126] The thickness of the obtained rGO-F film is 90 nm.

[0127] Comparative Example 8 In this comparative example, a method for preparing rGO-F film using artificial synthetic graphite powder is specifically introduced.

[0128] The steps are basically the same as those in Example 5, except that: The graphene oxide film obtained in step S1 is first fully reduced by S3, and then fluorinated by S2 to obtain a reduced graphene fluorinated film.

[0129] Other parameters are the same as those in Example 5.

[0130] The thickness of the obtained rGO-F film is 87 nm.

[0131] This specific embodiment also provides an assembly method of an all-solid-state battery, wherein: Cathode material: NCM811 and sulfide solid electrolyte (Li 5.5 PS 4.5 Cl 1.5 ) and conductive carbon fiber (VGCF) were placed in a mortar at a mass ratio of 70:29:1 and hand-ground for 1 hour to completely mix them to obtain NCM811 composite positive electrode material; Negative electrode: Li metal is used as the negative electrode; Electrolyte sheet: Sulfide solid electrolyte (Li 5.5 PS 4.5 Cl 1.5 ); A graphene derivative film (the GO, rGO, GO-F or rGO-F film prepared in the above embodiments) is placed between the negative electrode and the electrolyte sheet to assemble an all-solid-state battery.

[0132] The following is a detailed introduction to the assembly method of the all-solid-state battery through an example, and in order to ensure the consistency and effectiveness of the test data, the dosage of each substance and the pressing process are as follows: The mass of the electrolyte sheet was 100 mg, and the electrolyte sheet was pressed at a pressure of 160 MPa in a 10 mm stainless steel tablet press mold; Then, 10 mg of cathode material was added to one side of the electrolyte sheet, pressed again at a pressure of 360 MPa, and then demolded; In the battery test mold, a film with a diameter of 10 mm (obtained after cutting) is first added to the other side of the electrolyte sheet, and then a lithium sheet with a diameter of 9 mm and a thickness of 100 μm is added; Finally, the Al sheet current collector is placed on the positive electrode side, and the Cu current collector is placed on the negative electrode side to complete the packaging; The battery mold was taken out, placed in a battery fixture, and pressed at a pressure of 50 MPa to obtain a sandwich-type all-solid-state battery.

[0133] The graphene derivative films obtained in the above-mentioned Examples 1 to 11 and Comparative Examples 1 to 8 were placed between the negative electrode and the electrolyte layer, respectively, and the all-solid-state batteries corresponding to the examples and comparative examples were assembled.

[0134] Comparative Example 9 In this comparative example, no protective layer is added between the negative electrode and the electrolyte layer, and the negative electrode is directly brought into contact with the electrolyte layer to assemble an all-solid-state battery.

[0135] Performance testing: The graphene derivative films corresponding to the embodiments and comparative examples were tested for surface energy, friction coefficient and ionic conductivity: 1) Surface energy testing is mainly carried out by measuring the contact angle of the liquid on the surface of the all-solid electrolyte to calculate the surface energy. The surface of the all-solid electrolyte membrane sample is cleaned and flattened. Use a microsyringe to drop diiodomethane liquid with known surface tension on the sample surface. Use a contact angle meter to record the contact angle of the droplet. The data obtained is combined with the surface energy calculation model (Owens-Wendt) to calculate the surface energy; 2) The friction coefficient test mainly calculates the friction coefficient by measuring the friction force when two surfaces slide relative to each other. Fix the all-solid electrolyte membrane on the test platform, and use another solid electrolyte membrane as the counter-membrane material. Start the equipment and make the counter-membrane material slide on the surface of the electrolyte membrane. By using a friction and wear tester, set the sliding speed, load and sliding distance, and record the friction force during the sliding process. Calculate the friction coefficient (μ = F / N) based on the friction force (F) and normal load (N); 3) Ionic conductivity is mainly tested by electrochemical impedance spectroscopy (EIS). The impedance is measured by applying alternating current and the ionic conductivity is calculated. The ionic conductivity calculation formula is δ=l / R*S (δ is ionic conductivity, l is electrolyte membrane thickness, R is impedance, and S is the effective area of ​​the electrolyte).

[0136] The test results are shown in Table 1; The all-solid-state batteries corresponding to each film and the all-solid-state battery prepared in Comparative Example 9 were subjected to a capacitance discharge test. The first cycle discharge specific capacity and coulombic efficiency were tested at room temperature and a rate of 0.1C. The test results are shown in Table 1. The voltage-specific capacity performance test results of some embodiments and comparative examples are shown in Table 1. Figure 2 shown.

[0137]

[0138] As can be seen from Table 1, both artificial graphite and natural graphite after oxidation, fluorination and reduction treatment show three significant characteristics: higher surface energy, lower friction coefficient than the matrix material, and significantly improved ionic conductivity. The increased active surface energy improves the interfacial reaction efficiency, the reduced friction coefficient improves the mechanical stability, and the enhanced ion transport capacity greatly improves the charge transfer kinetics, which together explain why fluorinated reduced graphene oxide exhibits excellent electrochemical performance in all-solid-state batteries.

[0139] It can be seen from Table 1 that only when the reduced graphene oxide is fully fluorinated can it truly play the role of a protective film between the negative electrode and the electrolyte. Simple fluorination or reduction cannot achieve the purpose of inhibiting the occurrence of side reactions or the growth of lithium dendrites.

[0140] from Figure 1 It can be seen that the reduced graphene oxide obtained in Example 2 is evenly distributed in the form of flakes.

[0141] from Figure 2 It can be seen that in the all-solid-state battery, the system with fluorinated reduced graphene oxide as the protective layer between the negative electrode and the electrolyte has a smaller polarization voltage and better electrochemical performance.

[0142] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a fluorinated reduced graphene oxide film, characterized in that: The following steps are involved: S1, preparing a graphene oxide film from a slurry containing graphene oxide by a filtration deposition method, and drying the film; S2, placing the graphene oxide film in a fluorine-containing gas environment for fluorination treatment, and then washing and drying to obtain a fluorinated graphene oxide film; S3: placing the fluorinated graphene oxide film in an inert atmosphere for reduction treatment at 300-700° C. for 2-4 hours, and then cooling it to room temperature to obtain a fluorinated reduced graphene oxide film.

2. The method for preparing a fluorinated reduced graphene oxide film according to claim 1, characterized in that: The method for preparing a slurry containing graphene oxide comprises reacting graphite powder with a particle size of 1 to 50 μm, a strong oxidant and a reaction medium to obtain a reaction solution containing graphene oxide, diluting the reaction solution with deionized water to stop the reaction, washing the prepared graphene oxide, and configuring it into a slurry with deionized water.

3. The method for preparing a fluorinated reduced graphene oxide film according to claim 2, characterized in that: It also includes one or more of the following technical features: A. The strong oxidant includes one or more of potassium permanganate, potassium chlorate, hydrogen peroxide, and ozone; B. The reaction medium includes one or more of concentrated sulfuric acid and concentrated nitric acid; C. The graphite powder is prepared from natural graphite or artificial graphite.

4. The method for preparing a fluorinated reduced graphene oxide film according to claim 2, characterized in that: It also includes one or more of the following technical features: A. The mass ratio of the graphite powder to the strong oxidant is 1: (3-9); B. The amount ratio of the graphite powder to the reaction medium is 1g: 40-100mL; C. The reaction temperature for preparing graphene oxide from the graphite powder is 25-100°C, and the reaction time is 0.5-10h.

5. The method for preparing a fluorinated reduced graphene oxide film according to claim 1, characterized in that: In step S2, the fluorine-containing gas is one or more of hydrogen fluoride, carbon tetrafluoride, nitrogen trifluoride, and sulfur hexafluoride.

6. The method for preparing a fluorinated reduced graphene oxide film according to claim 5, characterized in that: It also includes one or more of the following technical features: A. During the fluorination treatment, the reaction chamber is a closed reaction chamber containing fluorine-containing gas with a pressure of 0.1-1 MPa at room temperature; B. The fluorination treatment parameters are: maintaining at 200~1000°C for 1~6h.

7. The method for preparing a fluorinated reduced graphene oxide film according to claim 1, characterized in that: In step S3, the inert atmosphere includes one or more of argon, nitrogen, and helium.

8. Use of a fluorinated reduced graphene oxide film prepared by the method according to any one of claims 1 to 7 in an all-solid-state battery, characterized in that: The fluorinated reduced graphene oxide film is placed between the electrolyte sheet and the negative electrode in the all-solid-state battery.

9. The use of the fluorinated reduced graphene oxide film in an all-solid-state battery according to claim 8, characterized in that: It also includes one or more of the following technical features: A. The electrolyte sheet is formed by pressing a sulfide solid electrolyte; B. The negative electrode is lithium metal.

10. The use of the fluorinated reduced graphene oxide film in an all-solid-state battery according to claim 8, characterized in that: The positive electrode material in the battery is formed by mixing and pressing a nickel-cobalt-manganese-oxide lithium positive electrode material, a sulfide solid electrolyte and a conductive material.

Images