Preparation method and application of rGO-FeF3 composite material

Abstract

The application discloses a preparation method of rGO-FeF3 composite material, which comprises the following steps: preparing an intermediate product rGO-FeF3.0.33H2O by using a Fe source, a F source and GO sheets; and sintering the intermediate product rGO-FeF3.0.33H2O to obtain an anhydrous rGO-FeF3 composite material. The rGO-FeF3 composite material obtained by sintering the intermediate product rGO-FeF3.0.33H2O is used as a positive electrode, and a full solid-state lithium battery is constructed by matching the rGO-FeF3 composite material with a sulfide electrolyte (Li6PS5Cl), so that the safety, reversible capacity and long cycle life of the sulfide full solid-state battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of cathode material manufacturing, specifically to the preparation method and application of rGO-FeF3 composite materials. Background Technology

[0002] Rechargeable lithium-ion batteries, as promising energy storage devices, have been widely used in grid energy storage and the electric vehicle industry. However, commercial lithium-ion batteries based on intercalation reactive cathode materials are approaching their theoretical energy density limits, and further improvements may jeopardize battery safety. Furthermore, commercial cathode materials based on cobalt or nickel are expensive and toxic, leading to severe pollution and resource depletion. Therefore, developing low-cost and high-energy-density cathode materials for next-generation rechargeable lithium-ion batteries is urgent and important.

[0003] Conversion-type cathodes (such as elemental sulfur, sulfides, oxides, and transition metal halides) are considered the most promising next-generation cathode materials to replace current commercial cathodes due to their ultra-high theoretical specific capacity. Among transition metal fluorides, low-cost FeF3 has a high theoretical specific capacity of 712 mAh / g (through a three-electron conversion reaction), a high average potential of approximately 2.74 V, and provides a theoretical energy density of 1947 Wh / Kg. Iron fluoride materials are produced by adjusting the amount of crystal water, resulting in different elemental distributions, crystal structures, crystal water contents, morphologies, and lithium-ion transport channels, thus exhibiting different electrochemical performances. Studies have found that the crystal water in water-containing iron fluoride affects the microstructure and morphology, thereby influencing the charge-discharge reaction mechanism of the cathode. Furthermore, the crystal water released during the conversion reaction of water-containing iron fluoride may also have side effects affecting battery performance.

[0004] Sulfide solid electrolytes generally have high room temperature ionic conductivity (>10). -4 S cm -1 Some sulfide electrolytes can achieve ionic conductivity comparable to that of organic electrolytes (such as Li). 10 GeP2S 12 Li7P3S 11 and Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 The ionic conductivity is 1.2 × 10⁻⁶. -2 S / cm, 1.7×10 -2 S / cm and 2.5×10 -2 S / cm, all reaching 10 -2(S / cm level). In addition, sulfide solid electrolytes also have advantages such as high thermal stability and non-flammability. Therefore, sulfide all-solid-state lithium batteries have become the most promising next-generation energy storage devices due to their high energy density and high safety.

[0005] Since the presence and content of water of crystallization in iron fluoride (FeF3) materials affect their volume change during conversion, its application in sulfide solid-state batteries presents a challenge. Because the sulfide solid electrolyte is relatively soft while the iron fluoride is relatively hard, the sulfide solid electrolyte may be unable to overcome the volume change of FeF3, potentially leading to electrode structure collapse and poor cycle stability. Furthermore, the water of crystallization in iron fluoride can also affect the decomposition of the sulfide solid electrolyte. Summary of the Invention

[0006] This invention addresses the problems in the prior art by disclosing a method for preparing rGO-FeF3 composite materials. By exploring the volume changes of FeF3 containing different amounts of water of crystallization during the conversion process and their impact on performance, we selected and developed a better synthetic route for introducing rGO into FeF3. This allows the softer rGO to successfully overcome the volume changes of FeF3, enabling FeF3 to grow well on rGO. Furthermore, rGO can successfully limit the aggregation and growth of FeF3 particles, thereby significantly improving the electronic conductivity of FeF3. This allows the rGO-FeF3 composite material to maintain excellent conductive electronic pathways during cycling.

[0007] This invention is achieved through the following technical solution:

[0008] This invention provides a method for preparing rGO-FeF3 composite material, which includes preparing an intermediate product rGO-FeF3·0.33H2O using Fe source, F source and GO sheet, and then sintering the intermediate product rGO-FeF3·0.33H2O to obtain anhydrous rGO-FeF3 composite material.

[0009] In the above design of the present invention, water molecules are fixed within a large hexagonal cavity in the FeF3·0.33H2O structure. The water molecules in the FeF3·0.33H2O structure act as a structural stabilizer, stabilizing the large hexagonal cavity and preventing the crystal structure from expanding and contracting during the expansion and contraction process (Li). +The insertion and extraction processes cause collapse, and the FeF3·0.33H2O particles are individually dispersed, which is conducive to the rapid transport of lithium ions. During sintering, the weight loss of FeF3·0.33H2O is small, and the morphological characteristics do not change significantly. Morphological observation of the anhydrous FeF3 material obtained by sintering the FeF3·0.33H2O precursor shows that its morphology is still hexagonal prism. When rGO is introduced into anhydrous FeF3 material with a FeF3·0.33H2O structure, the low water content in the FeF3·0.33H2O structure results in a small volume change during the conversion process. This allows rGO to overcome the volume change during the FeF3·0.33H2O conversion. Furthermore, the presence of rGO can serve as a template for FeF3 particle growth, enabling the converted FeF3 to grow well on rGO. The presence of rGO also effectively prevents the aggregation of FeF3 particles. In addition, the sulfide solid electrolyte can cooperate with the soft rGO to adapt to the volume change caused by the FeF3 phase transition, ensuring close contact between FeF3, rGO, and the sulfide solid electrolyte. This allows for the formation of an excellent ion / electron conductivity network inside the battery, which is beneficial for improving the electrochemical performance of sulfide solid batteries.

[0010] As a further embodiment, the preparation method of the anhydrous rGO-FeF3 composite material includes:

[0011] S1: A mixed solution is prepared by adding HF solution and GO tablets to anhydrous ethanol;

[0012] S2: Add Fe(NO3)3·9H2O to S1 and stir to obtain a colorless and transparent solution;

[0013] S3: The colorless and transparent solution from S2 is added to the reactor and reacted at 115℃-125℃ to form a precipitate. The precipitate is filtered, washed, and dried at 75℃-85℃ to obtain the intermediate product rGO-FeF3·0.33H2O. The product is then sintered at 390℃-410℃ to obtain anhydrous rGO-FeF3 composite material.

[0014] In the above preparation method, the mixed solution obtained by S2 is reacted at 115℃-125℃. Due to the low resistance of the colorless and transparent solution, the intermediate product is promoted to have a hexagonal close-packed structure under the high temperature of 115℃-125℃, which is beneficial to reduce the crystal water content of the anhydrous FeF3 composite material, thereby obtaining the intermediate product rGO-FeF3·0.33H2O. Because FeF3·0.33H2O has a low water of crystallization content and undergoes a second drying process before sintering, the water of crystallization in the FeF3·0.33H2O material can be removed in a stepwise manner. This helps to reduce the volume change of the iron fluoride material during the conversion process, so that the anhydrous FeF3 composite material has the structural characteristics of the intermediate product FeF3·0.33H2O material. Meanwhile, the GO flakes in the solution are reduced to surface-depressed rGO at high temperature. The obtained FeF3·0.33H2O may be located in the depressions on the surface of rGO, which is more conducive to overcoming the volume change caused by the release of water of crystallization of FeF3·0.33H2O and can provide a template for the growth of FeF3 particles.

[0015] As a further embodiment, the ratio of the volume of anhydrous ethanol, the mass of Fe(NO3)3·9H2O, and the mass of 40wt.% HF solution is (50mL-70mL):(1.116g-2.116g):(5g-7g), wherein the HF in the HF solution accounts for 40% of the total mass.

[0016] As a further step, the mixed solution prepared in S1 is subsequently subjected to ultrasonication for 1.5-2.5 hours, the reaction time in the reactor is 9-11 hours, the drying time is 10-14 hours, and the drying environment is under vacuum; the sintering time is 2-4 hours, and the sintering must be carried out in an inert atmosphere of argon.

[0017] As a further embodiment, the rGO-FeF3 composite material is composed of FeF3 with a hexagonal prism morphology uniformly attached to the rGO surface.

[0018] As a further option, the diameter of the hexagonal prism-shaped FeF3 is 1-4 μm.

[0019] As a further option, the rGO-FeF3 composite material has a mesoporous structure.

[0020] As a further embodiment, the rGO-FeF3 composite material exhibits characteristic diffraction peaks at 23.7°, 33.3°, 48.5°, and 54.3° in the X-ray powder diffraction pattern expressed as a diffraction angle of 2θ.

[0021] As a further improvement, the Raman spectrum of the rGO-FeF3 composite material shows a value of 1358 cm⁻¹. -1and 1590cm -1 Characteristic diffraction peaks.

[0022] As a further embodiment, the mass ratio of rGO in the rGO-FeF3 composite material ranges from (1-10) wt.%.

[0023] As a further embodiment, the mass ratio of rGO in the rGO-FeF3 composite material ranges from (5 ± 0.3) wt.%.

[0024] As a further embodiment, in the rGO-FeF3 composite material, GO is graphene oxide; as an even further embodiment, rGO is reduced graphene oxide after graphene oxide has been reduced.

[0025] The present invention also provides the application of the composite material obtained by the preparation method of the rGO-FeF3 composite material and the sulfide solid electrolyte in the positive electrode or battery.

[0026] As a further option, the sulfide electrolyte is Li6PS5Cl.

[0027] The features and beneficial effects of this invention are as follows: using the rGO-FeF3 composite material obtained by sintering the intermediate product rGO-FeF3·0.33H2O as the positive electrode and combining it with a sulfide electrolyte (Li6PS5Cl) to construct an all-solid-state lithium battery can improve the electrochemical performance of the sulfide all-solid-state battery, such as safety, reversible capacity and long cycle life. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the invention or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 XRD patterns of ferric fluoride materials with different water of crystallization contents.

[0030] Figure 2 The diagrams show the crystal structures of three iron fluoride materials with different water of crystallization contents. Figure 2 a has a FeF3·3H2O crystal structure; Figure 2 b has a FeF3·0.33H2O crystal structure; Figure 2 c represents the structure of FeF3; Figure 2 d is the projection of FeF3·3H2O along the

[001] crystal orientation; Figure 2e is the projection of FeF3·0.33H2O along the

[001] crystal orientation; Figure 2 f is the projection of FeF3 along the

[010] crystal direction.

[0031] Figure 3 Thermogravimetric curves of two iron fluoride materials with different water of crystallization contents in the temperature range from room temperature to 800℃ are shown. Figure 3 a is the thermogravimetric curve of FeF3·3H2O in the temperature range from room temperature to 800℃; Figure 3 b is the thermogravimetric curve of FeF3·0.33H2O in the temperature range from room temperature to 800℃.

[0032] Figure 4 SEM images of ferric fluoride materials with different water of crystallization contents at 10 μm and 5 μm scales are shown. Figure 4 a is a SEM image of FeF3·3H2O on a 10μm scale; Figure 4 b is the SEM image of FeF3·3H2O on a 5μm scale;

[0033] Figure 4 c is the SEM image of FeF3·0.33H2O on a 10μm scale; Figure 4 d is the SEM image of FeF3·0.33H2O on a 5 μm scale; Figure 4 e is a SEM image of FeF3-RT on a 10 μm scale; Figure 4 f is the SEM image of FeF3-RT on a 5μm scale; Figure 4 g is a SEM image of FeF3-HT on a 10 μm scale; Figure 4 h is the SEM image of FeF3-HT on a 5 μm scale.

[0034] Figure 5 For different composite cathodes at 0.1 mV s -1 Cyclic voltammetry curves at scan rate, where, Figure 5 a is a FeF3·3H2O composite cathode at 0.1mV s -1 Cyclic voltammetry curves at scan rate; Figure 5 b is a FeF3·0.33H2O composite cathode at 0.1 mVs -1 Cyclic voltammetry curves at scan rate; Figure 5 c represents the FeF3-RT composite cathode at 0.1 mV s -1 Cyclic voltammetry curves at scan rate; Figure 5 d represents the FeF3-HT composite cathode at 0.1 mV s -1 Cyclic voltammetry curves at scan rate.

[0035] Figure 6 Different composite cathodes at 0.1C (1C = 500mA g)-1 The charge-discharge curves and cycle performance graphs at current density are shown, among which... Figure 6 a is a FeF3·3H2O composite cathode at 0.1C (1C=500mA g) -1 Charge-discharge curves at current density; Figure 6 b is a FeF3·0.33H2O composite cathode at 0.1C (1C=500mA g) -1 Charge-discharge curves at current density; Figure 6 c represents the FeF3-RT composite cathode at 0.1C (1C = 500 mA g). -1 Charge-discharge curves at current density; Figure 6 d represents the FeF3-HT composite cathode at 0.1C (1C = 500 mA g). -1 Charge-discharge curves at current density; Figure 6 e represents the cycle performance of four composite cathodes at 0.1C.

[0036] Figure 7 The Nyquist plots are shown for four composite cathodes before charge / discharge and after 40 cycles. Figure 7 a is the Nyquist plot of the four composite cathodes before charging and discharging. Figure 7 b is the Nyquist plot of the four composite cathodes after 40 cycles.

[0037] Figure 8 The chart shows the charge-discharge curves (all selected from cycles 1, 6, 11, 16, 21, and 26) of four composite cathodes at specific rates, and the rate performance graphs of the four composite cathodes. Figure 8 a represents the charge-discharge curve of FeF3·3H2O at a specific rate; Figure 8 b is the charge-discharge curve of FeF3·0.33H2O at a specific rate; Figure 8 c represents the charge-discharge curve of FeF3-RT at a specific rate; Figure 8 d represents the charge-discharge curve of FeF3-HT at a specific rate; Figure 8 e represents the rate performance of the four-composite cathode.

[0038] Figure 9 Four composite cathodes were used at 0.3C (1C = 500mA g) -1 The charge-discharge curves (cycles 1, 3, 10, 60, and 120) and long-cycle performance graphs of four composite cathodes at 0.3C are shown. Figure 9 a is a FeF3·3H2O composite cathode at 0.3C (1C=500mA g) -1 Charge-discharge curves under ( ); Figure 9 b is a FeF3·0.33H2O composite cathode at 0.3C (1C=500mA g)-1 Charge-discharge curves under ( ); Figure 9 c represents the FeF3-RT composite cathode at 0.3C (1C = 500mA g). -1 Charge-discharge curves under ( ); Figure 9 d represents the FeF3-HT composite cathode at 0.3C (1C = 500 mA g). -1 Charge-discharge curves under ( ); Figure 9 e is a graph showing the long-cycle performance of four composite cathodes at 0.3C.

[0039] Figure 10 Four composite cathodes at 1C (1C = 500 mA g) -1 The charge-discharge curves (all selected from cycles 1, 100, 200, and 400) and the long-cycle performance graphs of the four composite cathodes at 1C are shown. Figure 10 a is a FeF3·3H2O composite cathode at 1C (1C=500mA g) -1 Charge-discharge curves under ( ); Figure 10 b is a FeF3·0.33H2O composite cathode at 1C (1C=500mA g) -1 Charge-discharge curves under ( ); Figure 10 c represents the FeF3-RT composite cathode at 1C (1C = 500 mA g). -1 Charge-discharge curves under ( ); Figure 10 d represents the FeF3-HT composite cathode at 1C (1C = 500 mA g). -1 Charge-discharge curves under ( ); Figure 10 e represents the long-cycle performance of four composite cathodes at 1C.

[0040] Figure 11 Four composite cathodes were tested at different scan rates (0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mV / s). -1 Cyclic voltammetry curves and bar charts showing the percentage capacity contribution at different scan rates are shown below. Figure 11 a represents the cyclic voltammetry curves of the FeF3·3H2O composite cathode at different scan rates; Figure 11 b represents the cyclic voltammetry curves of the FeF3·0.33H2O composite cathode at different scan rates; Figure 11 c represents the cyclic voltammetry curves of the FeF3-RT composite cathode at different scan rates; Figure 11 d represents the cyclic voltammetry curves of the FeF3-HT composite cathode at different scan rates; Figure 11 e is a bar chart showing the percentage capacity contribution of the FeF3·3H2O composite cathode at different scan rates; Figure 11 f is a bar chart showing the percentage capacity contribution of the FeF3·0.33H2O composite cathode at different scan rates; Figure 11g is a bar chart showing the percentage capacity contribution of the FeF3-RT composite cathode at different scan rates; Figure 11 h is a bar chart showing the percentage capacity contribution of the FeF3-HT composite cathode at different scan rates.

[0041] Figure 12 This is a comparison chart of the number of cycles and capacity of the iron fluoride cathode in this work and other literature reports.

[0042] Figure 13 The XRD pattern of the FeF3·0.33H2O and rGO-FeF3·0.33H2O composite materials provided in the embodiments of the present invention.

[0043] Figure 14 The XRD pattern of the FeF3 and rGO-FeF3 composite material provided in the embodiments of the present invention.

[0044] Figure 15 DC polarization curves of FeF3 and four rGO-FeF3 composite materials provided in the embodiments of the present invention.

[0045] Figure 16 The electronic conductivity (logarithmic) of FeF3 and four rGO-FeF3 composite materials provided in the embodiments of the present invention is shown in the figure.

[0046] Figure 17 The cycling performance of the pure FeF3 and rGO-FeF3 composite cathode provided in this embodiment of the invention is shown in the figure at 0.1C.

[0047] Figure 18 The cycling performance of the pure FeF3 and rGO-FeF3 composite cathode provided in this embodiment of the invention is shown in the figure at 0.4C.

[0048] Figure 19 The rate performance diagram of pure FeF3 and rGO-FeF3 composite cathode provided in the embodiments of the present invention.

[0049] Figure 20 Raman spectra of FeF3 and 5wt.%rGO-FeF3 provided for embodiments of the present invention.

[0050] Figure 21 Nitrogen adsorption-desorption curves of FeF3 and 5wt.%rGO-FeF3 provided for embodiments of the present invention.

[0051] Figure 22 SEM images and corresponding EDS elemental distribution maps of FeF3 and 5wt.%rGO-FeF3 composite materials provided in embodiments of the present invention; wherein Figure 22 a and Figure 22 b is the SEM image of FeF3. Figure 22 c- Figure 22 f is the corresponding EDS elemental distribution diagram of FeF3; Figure 22 g and Figure 22 h is a SEM image of the 5wt.%rGO-FeF3 composite material. Figure 22 i- Figure 22 l is the EDS elemental distribution diagram of the 5wt.%rGO-FeF3 composite material.

[0052] Figure 23 The charge-discharge curve of the 5wt.%rGO-FeF3 composite cathode provided in the embodiment of the present invention at 0.1C.

[0053] Figure 24 Charge-discharge curves of the 5wt.%rGO-FeF3 composite cathode at different rates provided in embodiments of the present invention.

[0054] Figure 25 The charge-discharge curve of the 5wt.%rGO-FeF3 composite cathode provided in the embodiment of the present invention at 1C.

[0055] Figure 26 The cycling performance of the pure FeF3 and 5wt.%rGO-FeF3 composite cathode provided in the embodiments of the present invention at 1C is shown in the figure. Detailed Implementation

[0056] To make the objectives, technical solutions, and process advantages of this invention clearer, the invention will be described in detail below with reference to embodiments and accompanying drawings. Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods, unless otherwise specified, are conventional methods.

[0057] We conducted the following experiments to introduce rGO into anhydrous iron fluoride and explore the effect of rGO on the electrochemical performance of the anhydrous iron fluoride material. First, we investigated the effect of iron fluoride with different water of crystallization contents as a negative electrode material on sulfide solid-state batteries (as shown in Examples 1-7). We found that the presence and content of water of crystallization in the iron fluoride material both affect the volume change of the iron fluoride material during the conversion process. However, the anhydrous FeF3-HT material converted from FeF3·0.33H2O with a lower water of crystallization content not only possesses the structural characteristics of FeF3·0.33H2O, but also experiences less weight loss and structural changes during the conversion process. The negative electrode prepared using the anhydrous FeF3-HT material exhibits the best electrochemical performance in sulfide solid-state batteries. Building upon this foundation, we introduced rGO during the preparation of anhydrous FeF3-HT material using FeF3·0.33H2O to further explore the effect of rGO on the anhydrous FeF3-HT material (as shown in Examples 8-13). By introducing rGO, we prepared an rGO-FeF3 composite cathode and found that FeF3 can grow well on rGO. Furthermore, using the rGO-FeF3 composite material as the cathode in conjunction with a sulfide electrolyte (Li6PS5Cl) in an all-solid-state lithium battery can improve the electrochemical performance of the sulfide all-solid-state battery, including safety, reversible capacity, and long cycle life.

[0058] Example 1:

[0059] In this embodiment, Fe(NO3)3·9H2O was used as the Fe source, HF solution as the F source, and anhydrous ethanol as the solvent. FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT materials were prepared using room temperature liquid-phase method, solvothermal method, and high-temperature sintering method, respectively. The specific steps are as follows:

[0060] (1) Add 1.616 g Fe(NO3)3·9H2O to 60 mL of anhydrous ethanol solution and stir magnetically for 1 h to obtain a reddish-brown solution;

[0061] (2) After the mixer is finished, use a dropper to add 5 mL of 40 wt.% HF solution dropwise to the above solution. You can see that the original reddish-brown solution gradually turns into a light red solution and then into a colorless and transparent solution (referred to as solution A).

[0062] (3) Prepare another colorless and transparent solution (denoted as solution B) by following the same two steps above;

[0063] (4) Solution A was kept at room temperature and stirred for 12 hours to obtain a pink precipitate. After filtration and washing, it was placed in a vacuum oven and dried at 80°C for 12 hours to obtain pink FeF3·3H2O. Then, it was sintered at 400°C for 3 hours under an argon atmosphere to obtain yellowish-brown anhydrous iron fluoride (denoted as FeF3-RT).

[0064] (5) After stirring solution B at room temperature for 0.5 h, add the colorless and transparent mixed solution to a 100 mL reaction vessel and place it in a forced-air drying oven. React at 120 °C for 10 h. After the reaction vessel cools down, a light green precipitate is obtained. After filtration and washing, it is placed in a vacuum drying oven and dried at 80 °C for 12 h to obtain light green FeF3·0.33H2O. Then, it is sintered at 400 °C for 3 h under an argon atmosphere to obtain dark brown anhydrous iron fluoride (denoted as FeF3-HT).

[0065] Example 2:

[0066] The materials synthesized in Example 1, such as FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT, were used as positive electrodes, sulfide electrolytes Li6PS5Cl and Super P(SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0067] (1) One of the following materials, FeF3·3H2O, FeF3·0.33H2O, FeF3-RT and FeF3-HT, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0068] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and sulfide electrolyte become a whole.

[0069] (3) Place an indium foil with a thickness of 40 μm and a diameter of 9.5 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t, tighten the screws, and then apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0070] (4) The assembled all-solid-state lithium batteries using four different cathodes were tested on a Blue Electric device. A charge-discharge cycle program was set to allow the batteries to undergo 40 charge-discharge cycles at a rate of 0.1C. All embodiments followed the standard of 1C = 0.5A / g.

[0071] Example 3:

[0072] The materials synthesized in Example 1, such as FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT, were used as positive electrodes, sulfide electrolytes Li6PS5Cl and Super P(SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0073] (1) One of the following materials, FeF3·3H2O, FeF3·0.33H2O, FeF3-RT and FeF3-HT, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0074] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and sulfide electrolyte become a whole.

[0075] (3) Place an indium foil with a thickness of 40 μm and a diameter of 9.5 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t, tighten the screws, and then apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0076] (4) The assembled all-solid-state lithium battery using four types of positive electrodes was tested on the Blue Electric device. The charge and discharge cycle program was set so that the battery was charged and discharged 5 times in sequence at 0.1C, 0.2C, 0.5C, 1C and 0.1C rates to complete the rate performance test.

[0077] Example 4:

[0078] The materials synthesized in Example 1, such as FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT, were used as positive electrodes, sulfide electrolytes Li6PS5Cl and Super P(SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0079] (1) One of the following materials, FeF3·3H2O, FeF3·0.33H2O, FeF3-RT and FeF3-HT, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0080] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and sulfide electrolyte become a whole.

[0081] (3) Place an indium foil with a thickness of 40 μm and a diameter of 9.5 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t, tighten the screws, and then apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0082] (4) The assembled all-solid-state lithium battery using four types of positive electrodes was tested on the Blue Electric device. The charge and discharge cycle program was set so that the battery was charged and discharged 120 times at a rate of 0.3C.

[0083] Example 5:

[0084] The materials synthesized in Example 1, such as FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT, were used as positive electrodes, sulfide electrolytes Li6PS5Cl and Super P(SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0085] (1) One of the following materials, FeF3·3H2O, FeF3·0.33H2O, FeF3-RT and FeF3-HT, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0086] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and sulfide electrolyte become a whole.

[0087] (3) Place an indium foil with a thickness of 40 μm and a diameter of 9.5 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t, tighten the screws, and then apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0088] (4) The assembled all-solid-state lithium battery using four types of positive electrodes was tested on the Blue Electric device. The charge-discharge cycle program was set so that the battery was charged and discharged twice at a rate of 0.1C and then charged and discharged 395 times at a rate of 1C.

[0089] Example 6:

[0090] The materials synthesized in Example 1, such as FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT, were used as positive electrodes, sulfide electrolytes Li6PS5Cl and Super P(SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0091] (1) One of the following materials, FeF3·3H2O, FeF3·0.33H2O, FeF3-RT and FeF3-HT, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0092] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and sulfide electrolyte become a whole.

[0093] (3) Place an indium foil with a thickness of 40 μm and a diameter of 9.5 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t, tighten the screws, and then apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0094] (4) The assembled all-solid-state lithium battery using four different cathodes was tested on an electrochemical workstation, with different scan rates (0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mV s). -1 The four batteries were subjected to CV tests, and the percentage of capacity contributed by the surface control process was calculated according to the formula.

[0095] Example 7:

[0096] The FeF3·3H2O and FeF3·0.33H2O materials synthesized in Example 1 were placed in an alumina crucible and heated from room temperature to 800°C at a heating rate of 10°C / min under a nitrogen protective atmosphere to obtain thermogravimetric curves.

[0097] Examples 8-13 of this invention use composite materials of 1wt.% rGO-FeF3, 3wt.% rGO-FeF3, 5wt.% rGO-FeF3, and 10wt.% rGO-FeF3 as examples for comparison and analysis with FeF3. The above-mentioned mass percentages are the mass percentages of GO sheets in the anhydrous FeF3 rGO-FeF3 composite material.

[0098] Example 8:

[0099] In this embodiment, Fe(NO3)3·9H2O was selected as the Fe source, HF solution as the F source, GO sheets as the carbon material, and anhydrous ethanol as the solvent. x%rGO-FeF3 composite materials (x = 1wt, 3wt, 5wt, and 10wt) were synthesized using a solvothermal method. The specific steps are as follows:

[0100] (1) The freeze-dried GO tablets were added to a mixed solution consisting of 60 mL of anhydrous ethanol and 5 mL of 40 wt.% HF solution. After sonication for 2 hours, 1.616 g of Fe(NO3)3·9H2O was added and the mixture was stirred magnetically for 30 minutes.

[0101] (2) Add the above colorless and transparent mixed solution to 100 mL of stainless steel reaction vessel, tighten it, and place it in a forced-air drying oven at 120 °C for 10 hours;

[0102] (3) After the reaction is complete and cooled to room temperature, the obtained material is filtered and washed and then placed in a vacuum oven to dry at 80°C for 12 hours to obtain the intermediate product FeF3·0.33H2O composite material.

[0103] (4) The dried FeF3·0.33H2O composite material was placed in an alumina crucible and placed in a muffle furnace. It was sintered at 400°C for 3 hours in a high-purity argon atmosphere to obtain the final rGO-FeF3 composite material.

[0104] (5) Pure FeF3 material was obtained by following the same preparation process as described above without adding GO sheets.

[0105] Example 9:

[0106] The x%rGO-FeF3 composite material (x = 1wt, 3wt, 5wt and 10wt) synthesized in Example 8 and the control group FeF3 material were used as positive electrodes, sulfide electrolyte Li6PS5Cl and Super P (SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0107] (1) One of the rGO-FeF3 composite material and FeF3 material, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0108] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and solid electrolyte become a whole.

[0109] (3) Place an indium foil with a thickness of 50 μm and a diameter of 10 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t. After tightening the screws, apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0110] (4) The assembled all-solid-state lithium batteries using five different cathodes were tested on a Blue Electric device, and a charge-discharge cycle program was set to allow the batteries to undergo 50 charge-discharge cycles at a rate of 0.1C. All embodiments followed the standard of 1C = 0.5A / g.

[0111] Example 10:

[0112] The x%rGO-FeF3 composite material (x = 1wt, 3wt, 5wt and 10wt) synthesized in Example 8 and the control group FeF3 material were used as positive electrodes, sulfide electrolyte Li6PS5Cl and Super P (SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0113] (1) One of the rGO-FeF3 composite material and FeF3 material, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0114] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and solid electrolyte become a whole.

[0115] (3) Place an indium foil with a thickness of 50 μm and a diameter of 10 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t. After tightening the screws, apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0116] (4) The assembled all-solid-state lithium battery using five types of positive electrodes was tested on the Blue Electric device. The charge-discharge cycle program was set so that the battery was charged and discharged 5 times at a rate of 0.1C and then charged and discharged 115 times at a rate of 0.4C.

[0117] Example 11:

[0118] The x%rGO-FeF3 composite material (x = 1wt, 3wt, 5wt and 10wt) synthesized in Example 8 and the control group FeF3 material were used as positive electrodes, sulfide electrolyte Li6PS5Cl and Super P (SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0119] (1) One of the rGO-FeF3 composite material and FeF3 material, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0120] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and solid electrolyte become a whole.

[0121] (3) Place an indium foil with a thickness of 50 μm and a diameter of 10 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t. After tightening the screws, apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0122] (4) The assembled all-solid-state lithium battery using five different positive electrodes was tested on the Blue Electric device. The charge-discharge cycle program was set so that the battery was charged and discharged 5 times in sequence at 0.1C, 0.2C, 0.5C, 1C and 0.1C rates to complete the rate performance test.

[0123] Example 12:

[0124] The x%rGO-FeF3 composite material (x = 1wt, 3wt, 5wt and 10wt) synthesized in Example 8 and the control group FeF3 material were used as positive electrodes, sulfide electrolyte Li6PS5Cl and Super P (SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0125] (1) One of the rGO-FeF3 composite material and FeF3 material, sulfide electrolyte Li6PS5Cl, and conductive agent SP are weighed in a certain ratio (35:50:15) and ground in a mortar for 1 hour to obtain a composite positive electrode.

[0126] (2) Weigh 3mg of composite cathode material and place it in a battery mold with an inner diameter of 10mm and flatten it with tweezers. Then weigh 80mg of solid electrolyte Li6PS5Cl and place it in the battery mold and flatten it with tweezers. Then press it with a press for 7t to make the composite cathode and solid electrolyte become a whole.

[0127] (3) Place an indium foil with a thickness of 50 μm and a diameter of 10 mm on the other side of the electrolyte, and then place a lithium foil with a thickness of 30 μm and a diameter of 8 mm on top of the indium foil. Use a press to press the three layers of materials (negative electrode, electrolyte, and positive electrode) to 2 t. After tightening the screws, apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0128] (4) The assembled all-solid-state lithium battery using five types of positive electrodes was tested on the Blue Electric device. The charge-discharge cycle program was set so that the battery was charged and discharged twice at a rate of 0.1C and then charged and discharged 295 times at a rate of 1C.

[0129] Example 13:

[0130] The x% rGO-FeF3 (x = 1wt, 3wt, 5wt and 10wt) composite materials synthesized in Example 8 and the control FeF3 material were used as research samples to investigate the changes in their electronic conductivity, so as to prove that the introduction of different proportions of rGO can effectively improve electronic conductivity.

[0131] (1) Take out one of the rGO-FeF3 composite material and FeF3 material, weigh 80mg and put it into a battery mold with an inner diameter of 10mm.

[0132] (2) Place the battery mold in the center of the press and press it for 7t to form the powder material into a dense sheet. After tightening the screws, apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0133] (3) Place the assembled mold on the electrochemical workstation, test the DC polarization, apply an absolute voltage of 0.5V, and test for 10 hours. Each material is tested three times.

[0134] (4) After the mold is removed after the test, the thickness of the dense sheet is tested, and finally the electronic conductivity of each material is calculated.

[0135] Verification Result Analysis:

[0136] Due to its high theoretical specific capacity and energy density, and low cost, FeF3 is the most promising next-generation cathode material to replace current commercial cathodes. However, the use of FeF3 as a cathode material involves volume changes due to phase transitions, leading to microscopic contact failure between the active material and the conductive agent. Furthermore, iron fluoride materials, resulting from the regulation of varying water of crystallization content, exhibit different elemental distributions, crystal structures, water of crystallization contents, morphologies, and lithium-ion transport channels, thus displaying varying electrochemical performance. In this invention, through experiments and verification, we found that the anhydrous FeF3 material FeF3-HT (FeF3-HT), obtained from the intermediate FeF3·0.33H2O, exhibits minimal volume changes due to phase transitions and retains the structural characteristics of the intermediate FeF3·0.33H2O, with a hexagonal prism morphology, which is beneficial for lithium... + Providing a fast transport channel, we further discovered that introducing rGO into the anhydrous FeF3 material obtained by sintering the intermediate product FeF3·0.33H2O can serve as a template for FeF3 particle growth, effectively preventing the aggregation of FeF3 particles. Furthermore, the soft texture of rGO and the sulfide solid electrolyte can adapt to the volume changes caused by the phase transition of FeF3, ensuring close contact between FeF3, rGO, and the sulfide solid electrolyte. This allows for the formation of an excellent ion / electron conductivity network inside the battery, which is beneficial for improving the electrochemical performance of sulfide solid batteries.

[0137] like Figure 1As shown, in the X-ray powder diffraction patterns (expressed as diffraction angle 2θ) of different iron fluoride composite cathode materials, we found that all characteristic peaks of FeF3·3H2O prepared by the room temperature liquid phase method were consistent with the FeF3·3H2O standard card (PDF file No. 32–0464); all characteristic peaks of FeF3·0.33H2O prepared by the solvothermal method were consistent with the FeF3·0.33H2O standard card (PDF file No. 76–1262). No impurity phases were found in the XRD patterns of either water-soluble material. Since anhydrous iron fluoride easily adsorbs moisture in humid air and forms other iron fluoride materials containing water of crystallization, both materials were tested with a transparent thin film covering them, where the peak of the thin film was at 21.3°. After sintering at 400℃, FeF3-RT and FeF3-HT tend to be more amorphous than the more crystalline FeF3·3H2O and FeF3·0.33H2O, as evidenced by increased full width at half maximum (FWHM) and weaker peak intensity of their characteristic diffraction peaks. The characteristic peaks of anhydrous FeF3-RT and FeF3-HT are consistent with the FeF3 standard card (PDF file No. 85–0481). The XRD pattern of FeF3-RT shows no other impurities, while the XRD pattern of FeF3-HT shows an impurity peak at 26.7° belonging to FeF2. This may be related to the reduction of FeF3 to FeF2 in the FeF3·0.33H2O precursor, which contains lower water of crystallization, during the later stages of sintering.

[0138] like Figure 2 The diagram shows schematic representations of the three crystal structures of FeF3·3H2O, FeF3·0.33H2O, and anhydrous FeF3, along with their projections in different crystal orientations. Figure 2 As shown in Figure a, in the FeF3·3H2O (tetragonal structure with space group P4 / n) crystal structure, each iron atom is surrounded by six ligands, forming an almost octahedral shape. The projection of FeF3·3H2O along the

[001] direction shows that two oxygen atoms are covalently bonded to the central Fe atom. Together with two fluorine atoms, they statistically occupy four positions in the square surrounding the iron atom. The other two fluorine atoms at the apex of the twisted octahedron are shared by adjacent octahedra and form a chain along the

[001] direction. It can be clearly observed that many vacant channels appear around the octahedral chain. Figure 2 d) These vacant channels can hold more lithium ions and provide larger channels, thus facilitating faster lithium ion conduction.

[0139] like Figure 2 b and Figure 2As shown in Figure e, in the structure of FeF3·0.33H2O (space group Cmcm), each iron atom is surrounded by six ligands in an octahedral form. These six octahedrons are connected by sharing vertices to form a special hexagonal cavity, which is Li. + Providing a fast transport channel, the conduction in lithium-ion materials is one-dimensional along the

[001] direction. In the structure of FeF3·0.33H2O, water molecules are fixed in a huge hexagonal cavity ( Figure 2 e). It is generally believed that the presence of water of crystallization reduces the content of electrochemically active components and induces electrolyte degradation, thus impairing the electrochemical performance of cathode materials. However, in the structure of FeF3·0.33H2O, water molecules can act as structural stabilizers, stabilizing the large hexagonal cavity and preventing the crystal structure from deteriorating during expansion and contraction (Li). + The intercalation and deintercalation processes lead to collapse. In contrast, the excess water of crystallization in FeF3·3H2O may cause structural instability, which is one of the reasons why FeF3·0.33H2O has superior electrochemical performance compared to FeF3·3H2O in single-electron-based intercalation reactions.

[0140] like Figure 2 c and Figure 2 As shown in f, in the structure of anhydrous FeF3 (R3c space group), FeF atoms are centered on Fe atoms. 6 / 2 All vertices of an octahedron are shared with other identical octahedrons, and they are connected to form a three-dimensional spatial structure (see...). Figure 2 f). FeF3 has a ReO3 structure (twisted) and, due to the absence of water of crystallization, it is of significant research value as a positive electrode for conversion reactions. However, when FeF3 is used as the positive electrode, a volume change occurs due to a phase transition. The relatively soft texture of sulfide solid electrolytes cannot overcome the volume change of FeF3, causing microscopic contact failure between the active material and the conductive agent, thus reducing the electrochemical performance of sulfide solid batteries.

[0141] To further investigate the decrystallization of the two hydrated water compounds during sintering, we observed the mass changes of FeF3·3H2O and FeF3·0.33H2O in the temperature range from room temperature to 800℃ under a nitrogen atmosphere and a heating rate of 10℃ / min. Figure 3 ).like Figure 3As shown in Figure a, the weight loss of FeF3·3H2O during the entire testing process can be mainly divided into three parts: first, a slight decrease in mass occurring between room temperature and 105℃, attributed to the disappearance of adsorbed water in the sample material itself; second, a significant weight loss of 32.4% occurring at 161.5℃, corresponding to the phase transition of FeF3·3H2O into anhydrous FeF3 by losing three molecules of water of crystallization; and third, a weight loss occurring between 225℃ and 800℃, which may correspond to the partial reduction of FeF3 to FeF2. Figure 3 As shown in b, FeF3·0.33H2O also exhibits three distinct stages: the significant weight loss at 142.8℃ is attributed to the elimination of adsorbed water and ethanol from the sample surface (mass loss of 4.98%); the most significant weight loss occurs at 263.8℃, corresponding to the loss of water of crystallization in FeF3·0.33H2O (weight loss ratio of 5.05%); and the weight loss in the temperature range of 320℃ to 800℃ may be due to the partial reduction of FeF3 to FeF2. Our comparison reveals that the weight loss of FeF3·0.33H2O is significantly smaller than that of FeF3·3H2O. We believe that the large weight loss of FeF3·3H2O is the reason for the significant structural changes in FeF3·3H2O, while the smaller weight loss of FeF3·0.33H2O results in less structural changes after weight loss.

[0142] Figure 4 The morphologies of four iron fluoride materials were shown by SEM characterization. For example... Figure 4As shown in a and b, FeF3·3H2O particles are composed of numerous small tetragonal particles, forming irregular spheres with a diameter ranging from 8 to 10 μm. FeF3·0.33H2O particles are hexagonal prisms with a particle size of approximately 4 to 5 μm. Compared to FeF3·3H2O, FeF3·0.33H2O particles are individually dispersed, thus facilitating rapid lithium-ion transport. The morphology of anhydrous FeF3-RT obtained by sintering the FeF3·3H2O precursor changes significantly compared to the precursor. Firstly, the particle morphology changes from irregular spheres to more dense, regular spheres; secondly, the particle size decreases to approximately 5 μm; and finally, its surface becomes rougher due to sintering. Observation of the morphology of anhydrous FeF3-HT obtained by sintering the FeF3·0.33H2O precursor reveals that its morphology is still hexagonal prisms, but the particle size is slightly reduced, mainly distributed between 3 and 5 μm. SEM results show that the particle size distribution follows this order: FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O. Smaller particle sizes can reduce the diffusion path of lithium ions, thereby accelerating lithium ion transport within the composite cathode and improving the electrochemical performance of the battery. It is evident that FeF3-HT, prepared using FeF3·0.33H2O as an intermediate product, retains the structural advantages of FeF3·0.33H2O, maintaining its hexagonal prism morphology.

[0143] We further prepared different composite cathodes by grinding the above four materials together with sulfide solid electrolyte and conductive agent, and then compared the electrochemical performance of different composite cathodes in sulfide all-solid-state batteries.

[0144] Figure 5 Four composite cathodes were tested using cyclic voltammetry (CV) in the voltage range of 0.6–2.4 V (vs. Li-In) to analyze their reaction mechanisms during charge and discharge. Overall, the CV curves of the four composite cathodes showed significant differences, indicating variations in their charge-discharge reaction mechanisms. The high overlap of the first five CV curves for FeF3-HT and FeF3-RT cathodes suggests high reversibility. Furthermore, the polarization voltage between the redox peaks based on the intercalation reaction was lowest for FeF3-HT, followed by FeF3-RT. The polarization voltages of the two anhydrous iron fluoride cathodes were lower than those of the FeF3·0.33H2O and FeF3·3H2O cathodes containing crystal water. Therefore, the sulfide all-solid-state battery prepared with FeF3-HT exhibits the highest reversibility and superior cycle performance. We believe that FeF3-HT, prepared from the intermediate FeF3·0.33H2O, retains the structural advantages of the original FeF3·0.33H2O, forming a unique hexagonal cavity, the cavity being Li... + Provides a fast transmission channel.

[0145] We further investigated the cycle performance and corresponding coulombic efficiency of four composite cathodes at low discharge rates, such as... Figure 6 The charge-discharge curves and cycle performance of four composite cathodes—FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT—at 0.1C are shown. The first-cycle discharge specific capacities of FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT are 346.4 mAh / g, 565 mAh / g, 732.8 mAh / g, and 616.4 mAh / g, respectively, with corresponding coulombic efficiencies of 43.9%, 102%, 56.8%, 92.8%, and 93.2%. After 40 cycles, reversible capacities of 278 mAh / g, 487.4 mAh / g, 577.3 mAh / g, and 629.3 mAh / g were maintained. It can be observed that, in terms of cycling performance, FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O. We further verified the above viewpoint because FeF3-HT possesses the structural advantages of the original FeF3·0.33H2O, forming a unique hexagonal cavity, with the cavity being Li... + Provides a fast transmission channel.

[0146] Figure 7 The EIS test results for four cathodes—FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT—are presented before cycling and after 40 cycles at 0.1C. As shown in the figure, the impedance values ​​before and after cycling exhibit the following pattern: FeF3-HT <FeF3-RT<FeF3·0.33H2O<FeF3·3H2O。

[0147] We further compared the rate performance of sulfide solid electrolyte batteries prepared with different composite cathodes, and the results are as follows: Figure 8 As shown, the specific discharge capacities of the FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT composite cathodes at the 5th cycle (0.1C) were 388.6 mAh / g, 462 mAh / g, 461.8 mAh / g, and 549 mAh / g, respectively. After passing through 0.2C to 1C and back to 0.1C, the specific discharge capacities at the 30th cycle were 412.5 mAh / g, 503 mAh / g, 549.5 mAh / g, and 647 mAh / g, respectively, with corresponding capacity retention rates of 106.2%, 108.9%, 119%, and 117.9%. Considering the specific discharge capacity and capacity retention rate at each rate, FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O.

[0148] Figure 9 The charge-discharge curves and cycle performance of four composite cathodes—FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT—at 0.3C were presented. The first-cycle discharge specific capacities of the FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT cathodes were 605 mAh / g, 441 mAh / g, 599.8 mAh / g, and 530.4 mAh / g, respectively, with corresponding coulombic efficiencies of 46.3%, 91.1%, 61.1%, and 86.45%. After 120 cycles, the reversible capacities of the FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT composite cathodes were 302.1 mAh / g, 408.6 mAh / g, 439.8 mAh / g, and 519.9 mAh / g, respectively, with corresponding capacity retention rates of 92.55%, 102.4%, 108.4%, and 103.6% (relative to the second discharge cycle specific capacity). It is evident that at a 0.3C discharge rate, in terms of battery cycle performance and capacity, FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O.

[0149] Figure 10 The charge-discharge curves and cycle performance of four composite cathodes—FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT—at 1C were displayed. All batteries underwent two activation cycles at 0.1C before the long-term 1C cycle test. Figure 10 a- Figure 10As shown in Figure d, the discharge specific capacities of the FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT cathodes in the first cycle (1C) were 292.7 mAh / g, 358.4 mAh / g, 415.5 mAh / g, and 477.9 mAh / g, respectively, with corresponding coulombic efficiencies of 67.3%, 75.3%, 76.8%, and 73.4%. Except for the FeF3·3H2O cathode, which showed no significant capacity increase after 400 cycles, the other three cathodes all showed significant capacity increases in the first 100 cycles, with the FeF3-HT composite cathode showing the largest increase (even reaching 456.5 mAh / g in the 90th cycle). After 400 cycles, the specific discharge capacities of the positive electrodes FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT were 177 mAh / g, 297.2 mAh / g, 327.4 mAh / g, and 340.7 mAh / g, respectively, with corresponding capacity retention rates of 60.5%, 82.9%, 78.8%, and 71.3%. Based on the specific capacity after 400 cycles, at a 1C discharge rate, the cycle performance of the batteries is: FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O.

[0150] Figure 11 The positive electrodes FeF3·3H2O, FeF3·0.33H2O, FeF3-RT, and FeF3-HT were demonstrated at 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mV s. -1 The CV curves at different scan rates clearly show that as the scan rate increases, the peak current intensity of all oxidation / reduction peaks continuously increases, while the positions of the oxidation (reduction) peaks gradually shift to higher (lower) potentials. This is consistent with the phenomenon that the polarization voltage increases with increasing current density in charge-discharge tests. If this process is determined by surface-controlled behavior, the current is linearly related to the scan rate (ν). However, if the process is determined by diffusion-controlled behavior, the current is linearly related to the square root of the scan rate (ν). 1 / 2 The relationship is linear. Diffusion control (k2ν) 1 / 2 The surface-controlled (k1ν) process and the surface-controlled (k1ν) process can be calculated separately using the following formula: i / (ν) 1 / 2 )=k1ν 1 / 2+k2. Based on the above formula, a series of k1 values ​​were obtained by linearly fitting the square root of different current ratios and the square root of the scan rate. Then, the percentage of capacity contributed by surface diffusion control was calculated. The calculations show that the percentage of capacity contributed by the surface control process can be ranked as follows: FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O. The FeF3-HT cathode shows the highest percentage of capacity contributed by the surface control process, explaining its superior discharge specific capacity and rate performance compared to other cathodes at high current densities. This ranking is also completely consistent with the electrochemical performance test results, indicating that this explanation effectively elucidates the underlying reasons.

[0151] Figure 12 A comparative graph showing the number of cycles and capacity of the iron fluoride cathode in this work and other literature reports is presented. From Figure 12 It is evident that liquid lithium batteries (blue dots) based on different iron fluoride cathodes generally exhibit poor cycle counts and reversible capacities. The vast majority have reversible capacities less than 400 mAh / g and cycle counts below 100, primarily due to the low electronic conductivity of iron fluoride and the dissolution of the transition metal Fe. Furthermore, recent literature reports that solid-state batteries based on oxide and polymer solid electrolytes paired with FeF3 cathodes demonstrate strong cycling performance (250 cycles and above), but these batteries were all tested at low current densities. This work investigated the electrochemical performance of four iron fluoride cathode materials based on a sulfide-based all-solid-state lithium battery system. The anhydrous FeF3-HT cathode exhibited the best performance, maintaining a reversible capacity of 519.9 mAh / g (340.7 mAh / g) after 120 (300) cycles, even at 0.3C (1C). Figure 12 It can be seen that the application of anhydrous FeF3-HT composite cathode in sulfide all-solid-state batteries makes the sulfide all-solid-state batteries significantly superior to liquid lithium batteries and other solid-state lithium batteries in terms of both cycle performance and capacity (red area).

[0152] Through the above experiments, we found that the electrochemical performance of the sulfide solid-state batteries prepared from the four materials follows the trend from high to low: FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O. Anhydrous FeF3-HT, prepared from the intermediate FeF3·0.33H2O, exhibits higher cycle performance and capacity than anhydrous iron fluoride (FeF3-RT) obtained from other intermediates (FeF3·3H2O). We believe that the FeF3-HT material retains the structural advantages of FeF3·0.33H2O, and the structural changes of FeF3·0.33H2O after weight loss are relatively small. Therefore, anhydrous FeF3-HT is a special hexagonal cavity, and the cavity is composed of Li... +We further selected anhydrous iron fluoride sintered from the intermediate product FeF3·0.33H2O and introduced rGO to obtain rGO-FeF3 composite material. We then compared the effects of different mass percentages of GO sheets on sulfide solid-state batteries.

[0153] like Figure 13 As shown, we analyzed the X-ray powder diffraction patterns (expressed as diffraction angle 2θ) of the intermediate product rGO-FeF3·0.33H2O composite material corresponding to the synthesized x% rGO-FeF3 (x = 1wt, 3wt, 5wt and 10wt) composite materials, as well as the control FeF3·0.33H2O composite material. We found that the characteristic peaks of all intermediate product rGO-FeF3·0.33H2O composite materials were consistent with those of FeF3·0.33H2O (PDF file No. 76–1262) and there were no other impurity peaks. This indicates that the introduction of rGO did not change the structure of FeF3·0.33H2O.

[0154] like Figure 14 As shown, in the X-ray powder diffraction patterns (expressed as diffraction angle 2θ) of the synthesized x%rGO-FeF3 composites (x = 1wt, 3wt, 5wt, and 10wt) and the control FeF3 material, the x%rGO-FeF3 composites (x = 1wt, 3wt, 5wt, and 10wt) exhibit characteristic diffraction peaks at 21.5°, 24.5°, and 26.7°. Figure 14 As can be seen from the results, after sintering, the main peaks of the obtained rGO-FeF3 composite material are consistent with those of FeF3 (PDF file No. 85-0481), indicating that anhydrous iron fluoride material has been successfully prepared. At the same time, there is a heterogeneous peak at 26.7° belonging to the FeF2 phase, which may be related to the reduction of some FeF3 to FeF2 at high temperature.

[0155] like Figure 15 As shown, the DC polarization curves of pure FeF3 and rGO-FeF3 composites at room temperature are displayed. The rGO-FeF3 composite with the addition of rGO is better than that of pure FeF3.

[0156] We investigated the effect of reduced graphene oxide (rGO) addition on the electronic conductivity of the rGO-FeF3 composite material, and the results are as follows: Figure 16 As shown, the electronic conductivity of FeF3 and four different proportions of rGO-FeF3 composites increases with the increase of reduced graphene oxide (rGO) content, indicating that the introduction of rGO significantly improves the electronic conductivity of FeF3.

[0157] We further investigated the effect of reduced graphene oxide addition on the cycle performance of x% rGO-FeF3 (x = 1wt, 3wt, 5wt, and 10wt) composite cathodes at a discharge rate of 0.1C on sulfide all-solid-state batteries. The results are as follows: Figure 17 As shown, the initial discharge specific capacities of FeF3, 1wt.%rGO-FeF3, 3wt.%rGO-FeF3, 5wt.%rGO-FeF3, and 10wt.%rGO-FeF3 were 546.1 mAh / g, 559.1 mAh / g, 672.1 mAh / g, 622.9 mAh / g, and 552.5 mAh / g, respectively, with corresponding coulombic efficiencies of 80.0%, 96.1%, 89.2%, 92.8%, and 83.11%. After 50 cycles, they retained reversible capacities of 472.4 mAh / g, 649.4 mAh / g, 619.9 mAh / g, 742.7 mAh / g, and 621.5 mAh / g, respectively, corresponding to capacity retention rates of 86.5%, 116.1%, 92.2%, 119.2%, and 112.4%. It can be seen that the discharge capacity and cycle performance of FeF3 cathode are greatly improved after the introduction of rGO, and x%rGO-FeF3 (x=5wt) achieved the best performance. We believe that this may be because too much rGO is added, which will affect the density of the composite cathode and reduce the capacity of the composite cathode.

[0158] We further investigated the effect of reduced graphene oxide addition on the cycle performance of x% rGO-FeF3 (x = 1wt, 3wt, 5wt, and 10wt) composite cathodes at a discharge rate of 0.4C on sulfide all-solid-state batteries, such as... Figure 18As shown, the first-cycle (0.1C) discharge specific capacities of FeF3, 1wt.%rGO-FeF3, 3wt.%rGO-FeF3, 5wt.%rGO-FeF3, and 10wt.%rGO-FeF3 cathodes were 523 mAh / g, 588.4 mAh / g, 586 mAh / g, 692 mAh / g, and 573.5 mAh / g, respectively, with corresponding coulombic efficiencies of 78.8%, 101.2%, 88.74%, 93.57%, and 87.78%. After 5 cycles of 0.1C activation and 120 cycles, the discharge specific capacities of the FeF3, 1wt.%rGO-FeF3, 3wt.%rGO-FeF3, 5wt.%rGO-FeF3, and 10wt.%rGO-FeF3 cathodes were 427.1 mAh / g, 535.2 mAh / g, 522 mAh / g, 568.8 mAh / g, and 502.8 mAh / g, respectively. It can be seen that the introduction of rGO significantly improved the discharge capacity and cycle performance of the FeF3 cathode, with x%rGO-FeF3 (x=5wt) achieving the best performance. We believe this may be because adding too much rGO reduces the relative content of the active material, thus affecting the battery's cycle performance and capacity.

[0159] We further compared the effect of reduced graphene oxide addition on the discharge specific capacity of x% rGO-FeF3 (x = 1wt, 3wt, 5wt, and 10wt) composites at different discharge rates, such as... Figure 19As shown, the pure FeF3 cathode exhibited discharge specific capacities of 432 mAh / g, 395 mAh / g, 353 mAh / g, and 316 mAh / g at 0.1, 0.2, 0.5, and 1C, respectively. In contrast, the four rGO-FeF3 composite cathodes showed higher rate performance. The 1wt.% rGO-FeF3 composite cathode exhibited reversible specific capacities of 612 mAh / g, 543 mAh / g, 472 mAh / g, and 405 mAh / g at 0.1C, 0.2C, 0.5C, and 1C, respectively; the 3wt.% rGO-FeF3 composite cathode exhibited reversible discharge specific capacities of 593 mAh / g, 550 mAh / g, 481 mAh / g, and 408 mAh / g at 0.1C, 0.2C, 0.5C, and 1C, respectively; and the 10wt.% rGO-FeF3 composite cathode exhibited reversible discharge specific capacities of 493 mAh / g, 458 mAh / g, 400 mAh / g, and 352 mAh / g at 0.1C, 0.2C, 0.5C, and 1C, respectively. It is evident that the rGO-FeF3 composite cathode, when incorporating rGO, exhibits improved reversible discharge specific capacity at different discharge rates compared to the pure FeF3 cathode. Among these, the 5 wt.% rGO-FeF3 composite cathode demonstrates the best rate performance, exhibiting reversible discharge specific capacities of 698 mAh / g, 655 mAh / g, 585 mAh / g, and 509 mAh / g at 0.1C, 0.2C, 0.5C, and 1C, respectively. Furthermore, the discharge specific capacities of FeF3, 1wt.%rGO-FeF3, 3wt.%rGO-FeF3, 5wt.%rGO-FeF3, and 10wt.%rGO-FeF3 cathodes in the first cycle (0.1C) were 563.5 mAh / g, 607.4 mAh / g, 689.3 mAh / g, 709.7 mAh / g, and 623 mAh / g, respectively. After cycling from 0.2C to 1C and back to 0.1C, the discharge specific capacities in the 30th cycle were... The specific capacities were 463.9 mAh / g, 649 mAh / g, 628.5 mAh / g, 777.5 mAh / g, and 537.3 mAh / g, with corresponding capacity retention rates of 82.3%, 106.8%, 91.2%, 109.6%, and 86.2%. Clearly, when the discharge temperature returned to 0.1C, the discharge specific capacity of the 5 wt.% rGO-FeF3 cathode was higher than the initial specific capacity at 0.1C, and the capacity retention rate was the highest. Therefore, we further selected a reduced graphene oxide addition amount of 5 ± 0.3% in the rGO-FeF3 composite material.

[0160] We further compared the Raman spectra of 5 wt.% rGO-FeF3 and FeF3, as follows: Figure 20 As shown, pure FeF3 in the range of 300-2000 cm⁻¹ -1There were no peaks within the range, while 5 wt.% rGO-FeF3 showed a peak at 1358 cm⁻¹. -1 (D peak) and 1590cm -1 There are two distinct peaks at (G peak). Among them, the G peak corresponds to the sp of the two-dimensional hexagonal lattice. 2 The D peak is related to the stretching vibrations of carbon atoms, while the D peak is attributed to defects and disorder in the hexagonal graphite layers. The ratio of the intensities of the D peak to the G peak (I) D / I G It can be used to estimate the defect situation of carbon materials. The ratio of the D peak to the G peak of 5% wt. rGO-FeF3 is 0.956, which is similar to the ratio of the D peak to the G peak of rGO prepared from GO in the literature, indicating that rGO was successfully obtained by solvothermal method.

[0161] Figure 21 Nitrogen adsorption-desorption curves for FeF3 and 5% wt. rGO-FeF3 are shown. Both isotherms can be identified as Type IV isotherms with an H3-type hysteresis loop, indicating that both FeF3 and 5% wt. rGO-FeF3 are mesoporous structures. The calculated BET surface areas of FeF3 and 5% rGO-FeF3 are 5.57 and 6.83 m², respectively. 2 g -1 We believe that the 5% wt.rGO-FeF3 composite material has a higher specific surface area, which allows for more sufficient contact between the active material and the sulfide solid electrolyte, thereby improving electrochemical performance.

[0162] We further compared the SEM structural characterization images and EDS elemental distributions of 5 wt.% rGO-FeF3 and FeF3, as shown in the figure. Figure 22 As shown, FeF3 with an average length of 4-12 μm exhibits a regular hexagonal prismatic morphology. In contrast, the 5 wt.% rGO-FeF3 composite material with a size distribution of 1-4 μm and a hexagonal prismatic morphology is uniformly attached to the rGO surface. Figure 22 g and Figure 22 h). Clearly, the presence of rGO serves as a template for FeF3 particle growth, effectively preventing FeF3 particle aggregation; therefore, the particle size distribution of 5 wt.% rGO-FeF3 is significantly smaller than that of pure FeF3. Furthermore, the soft rGO nanosheets can adapt to the volume changes caused by the FeF3 phase transition, ensuring close contact between FeF3 and rGO. The elemental distribution of FeF3 and the 5 wt.% rGO-FeF3 composite was characterized by EDS. According to the elemental distribution diagram of FeF3, Fe and F are uniformly distributed throughout the sample. The presence of C may be due to the carbonization of residual ethanol solvent (…). Figure 22 c- Figure 22 f). For example Figure 22 i- Figure 22As shown in Figure 1, Fe and F are uniformly distributed throughout the 5 wt.% rGO-FeF3 sample, indicating that FeF3 particles are uniformly attached to rGO.

[0163] We tested the capacity retention of the battery using a 5 wt.% rGO-FeF3 composite cathode at a discharge rate of 0.1C, and the results are as follows: Figure 23 As shown, its initial discharge specific capacity is 622.9 mAh / g, with an initial efficiency of 92.8%. The discharge capacity subsequently increases with the number of cycles, reaching 742.7 mAh / g after 50 cycles, with a capacity retention rate as high as 119.2%. We believe that the combination of rGO, FeF3, and the sulfide electrolyte, along with the soft texture of rGO and the sulfide electrolyte, forms a tightly contacted structure, thus establishing an excellent electronic conductivity pathway. This also overcomes the interference of FeF3 in Li intercalation during battery charging and discharging. + The volume change during the process maintains the electronic conduction pathway, thereby improving the high reversible capacity of sulfide solid-state batteries.

[0164] Figure 24 The charge-discharge curves of the 5wt.%rGO-FeF3 composite cathode at different rates are shown. The 5wt.%rGO-FeF3 composite cathode exhibits the best rate performance, with reversible discharge specific capacities of 698mAh / g, 655mAh / g, 585mAh / g, and 509mAh / g at 0.1, 0.2, 0.5, and 1C, respectively.

[0165] Figure 25 The charge-discharge curves of the 5wt.% rGO-FeF3 composite cathode at 1C were shown. After the first two activation cycles, its first discharge specific capacity at 1C was 520.5mAh / g, with an initial efficiency of 79.2%. After 300 cycles, the discharge specific capacity was 409.2mAh / g, with a capacity retention rate as high as 78.6%.

[0166] We compared the cycling performance of pure FeF3 and 5 wt.% rGO-FeF3 composite cathodes at 1C, and the results are as follows: Figure 26 The initial discharge specific capacities of FeF3 and 5wt.% rGO-FeF3 were 332.9 mAh / g and 520.5 mAh / g, respectively, with coulombic efficiencies of 70.4% and 79.2%. After 300 cycles at 1C, the reversible capacities of the FeF3 cathode and the 5wt.% rGO-FeF3 composite cathode were 302.8 mAh / g and 409.2 mAh / g, respectively. These represent the best cycle performance exhibited by iron fluoride cathodes at such high current densities to date, with the 5wt.% rGO-FeF3 composite cathode significantly outperforming the FeF3 cathode. This demonstrates that the introduction of rGO can improve the cycle performance and capacity of sulfide solid-state batteries.

[0167] In summary, anhydrous iron fluoride prepared from the intermediate product FeF3·0.33H2O exhibits better capacity and rate performance than anhydrous iron fluoride prepared from other types of iron fluoride with varying water content. This is because the weight loss of FeF3·0.33H2O during sintering is relatively small, and the morphological changes are not significant. Morphological observation of the anhydrous FeF3 material obtained by sintering the FeF3·0.33H2O precursor reveals that its morphology remains hexagonal prisms. However, sulfide solid electrolytes are relatively soft and cannot overcome the volume changes during preparation, resulting in poorer safety, reversible capacity, and cycle life of the fabricated sulfide solid-state batteries. Building upon this, we introduced rGO and discovered that due to the low water of crystallization content in the FeF3·0.33H2O structure, rGO can overcome the volume change during the FeF3·0.33H2O conversion process. Since the reduction of GO sheets at high temperatures generates surface-depression rGO, the presence of rGO can serve as a template for FeF3 particle growth, effectively preventing FeF3 particle aggregation. Furthermore, the soft texture of rGO, combined with the sulfide solid electrolyte, can adapt to the volume change caused by the FeF3 phase transition, ensuring close contact between FeF3, rGO, and the sulfide solid electrolyte. This allows for the formation of an excellent ionic / electron conductivity network within the battery, which is beneficial for improving the electrochemical performance of sulfide solid-state batteries.

[0168] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing rGO-FeF3 composite material, characterized in that, The process involves preparing an intermediate product rGO-FeF3·0.33H2O using Fe source, F source and GO sheet, and then sintering the intermediate product rGO-FeF3·0.33H2O to obtain an anhydrous rGO-FeF3 composite material; the rGO-FeF3 composite material is characterized by FeF3 with a hexagonal prism morphology uniformly attached to the surface of rGO. The preparation method of the anhydrous rGO-FeF3 composite material includes: S1: A mixed solution is prepared by adding HF solution and GO tablets to anhydrous ethanol; S2: Add Fe(NO3)3·9H2O to S1 and stir to obtain a colorless and transparent solution; S3: The colorless and transparent solution in S2 is added to the reaction vessel and subjected to a solvothermal reaction at 115℃-125℃ to form a precipitate. The precipitate is filtered, washed, and dried at 75℃-85℃ to obtain the intermediate product rGO-FeF3·0.33H2O. The product is then sintered at 390℃-410℃ to obtain anhydrous rGO-FeF3 composite material. The ratio of the volume of anhydrous ethanol, the mass of Fe(NO3)3·9H2O, and the mass of 40wt.% HF solution is (50mL-70mL):(1.116g-2.116g):(5g-7g).

2. The method of claim 1, wherein the rGO-FeF3 composite is prepared by the steps of: The mixed solution obtained by S1 is then subjected to ultrasonication for 1.5-2.5 hours, the reaction time in the reactor is 9-11 hours, and the drying time is 10-14 hours in a vacuum environment; the sintering time is 2-4 hours, and the sintering must be carried out in an inert atmosphere of argon. 3.The method of claim 1, wherein the rGO-FeF 3 composite is prepared by the steps of, The diameter of the hexagonal prism-shaped FeF3 is 1-4µm; the rGO-FeF3 composite material has a mesoporous structure.

4. The method of claim 1, wherein the rGO-FeF3 composite is prepared by the steps of: The rGO-FeF3 composite material exhibits characteristic diffraction peaks at 23.7°, 33.3°, 48.5°, and 54.3° in its X-ray powder diffraction pattern expressed at a diffraction angle of 2θ; the Raman spectrum of the rGO-FeF3 composite material shows a peak at 1358 cm⁻¹. -1 and 1590 cm -1 Characteristic diffraction peaks. 5.The method of claim 1, wherein the rGO-FeF 3 composite is prepared by the steps of, The mass ratio of rGO in the rGO-FeF3 composite material ranges from (1-10) wt.%. 6.The method of claim 1, wherein the rGO-FeF 3 composite is prepared by the steps of, The mass ratio of rGO in the rGO-FeF3 composite material ranges from (5 ± 0.3) wt.%. 7.The method of claim 1, wherein the rGO-FeF 3 composite is prepared by the steps of, The rGO-FeF3 composite material, where GO is graphene oxide; and rGO is reduced graphene oxide after graphene oxide has been reduced.

8. The application of the composite material obtained by the preparation method of the rGO-FeF3 composite material according to any one of claims 1-7 and the sulfide solid electrolyte in the positive electrode or battery.

9. The application according to claim 8, wherein the sulfide solid electrolyte is Li6PS5Cl.

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