Preparation method of iron fluoride cathode and its application in sulfide all-solid-state batteries

Abstract

This invention discloses a method for preparing an iron fluoride cathode, comprising preparing an intermediate product FeF3·0.33H2O using an Fe source and an F source, and then sintering the intermediate product FeF3·0.33H2O to obtain anhydrous FeF3 material FeF3-HT. The features and beneficial effects of this invention are: an anhydrous FeF3 material FeF3-HT, particularly suitable for sulfide all-solid-state batteries, is prepared using the intermediate product FeF3·0.33H2O, thereby obtaining a sulfide all-solid-state battery with ultra-high cycle performance and high capacity.

Description

Technical Field

[0001] This invention relates to the field of manufacturing sulfide all-solid-state lithium metal batteries, specifically to a method for preparing an iron fluoride cathode and its application in sulfide all-solid-state batteries. 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 intercalated reactive cathode materials are approaching their theoretical energy density limits, and further improvements may jeopardize battery safety. Furthermore, commercial cathodes based on cobalt or nickel are expensive and toxic, leading to severe pollution and resource depletion. Therefore, developing low-cost, high-energy-density cathodes 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. However, using FeF3 as a cathode results in volume changes due to phase transitions, causing microscopic contact failure between the active material and the conductive agent.

[0004] Iron fluoride materials are produced by varying amounts of water of crystallization, resulting in different elemental distributions, crystal structures, water of crystallization contents, morphologies, and lithium-ion transport channels, thus exhibiting different electrochemical properties. Studies have found that the water of crystallization in ferric fluoride affects the microstructure and morphology, thereby influencing the charge-discharge reaction mechanism of the cathode. Furthermore, the water of crystallization released during the conversion reaction of ferric fluoride containing water of crystallization may also have side effects, impacting battery performance.

[0005] Sulfide solid electrolytes generally have high room temperature ionic conductivity (>10). -4 Scm -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 -2S / 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.

[0006] While sulfide solid electrolytes, due to their softer texture, can achieve close contact with ferric fluoride materials, they can only partially overcome the volume changes of ferric fluoride during the conversion process. Furthermore, the presence and concentration of water of crystallization in the ferric fluoride material affect its volume changes during conversion, potentially leading to microscopic contact failure between the active material and the conductive agent, resulting in energy decay in the sulfide solid-state battery. In addition, the water of crystallization in ferric fluoride can also affect the decomposition of sulfide solid-state electrolytes. Summary of the Invention

[0007] This invention addresses the problems in the prior art by disclosing a method for preparing an iron fluoride cathode, thereby preparing a cathode material particularly suitable for sulfide all-solid-state batteries, resulting in a sulfide all-solid-state battery with ultra-high cycle performance and high capacity.

[0008] This invention is achieved through the following technical solution:

[0009] This invention provides a method for preparing iron fluoride cathodes, including preparing an intermediate product FeF3·0.33H2O using Fe and F sources, and then sintering the intermediate product FeF3·0.33H2O to obtain anhydrous FeF3 material FeF3-HT.

[0010] In the above design of the present invention, water molecules are fixed within a large hexagonal cavity in the intermediate product FeF3·0.33H2O. 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 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. Observation of the morphology of anhydrous FeF3-HT obtained by sintering FeF3·0.33H2O precursor shows that its morphology is still hexagonal prism.

[0011] As a further embodiment, the preparation method of the anhydrous FeF3 material FeF3-HT includes:

[0012] S1: Fe(NO3)3·9H2O was added to anhydrous ethanol and stirred to obtain a reddish-brown solution;

[0013] S2: Add HF solution dropwise to S1 until a colorless and transparent solution is obtained;

[0014] S3: The colorless and transparent solution from S2 is added to the reactor and reacted at 115℃-125℃ to form a light green precipitate. The precipitate is filtered, washed, and dried at 75℃-90℃ to obtain a light green intermediate product FeF3·0.33H2O. The product is then sintered at 390℃-410℃ to obtain a dark brown anhydrous FeF3 material, FeF3-HT.

[0015] In the above preparation method, the mixed solution of Fe(NO3)3·9H2O and HF solution is reacted at 115℃-125℃ before precipitation. Due to the low resistance of the colorless and transparent solution and the promoting effect of the high temperature of 115℃-125℃, the structure of the product is made into a hexagonal close-packed structure, which helps to reduce the content of crystal water bound to FeF3, thus obtaining the light green intermediate product FeF3·0.33H2O. Since FeF3·0.33H2O has a low crystal water content and is dried again before sintering, the crystal water in the FeF3·0.33H2O material can be removed stepwise, which helps to reduce the volume change of the ferric fluoride material during the conversion process, so that the anhydrous FeF3 material has the structural characteristics of the intermediate product FeF3·0.33H2O material.

[0016] 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 in S1 is (50mL-70mL):(1.116g-2.116g):(5g-7g), wherein the mass percentage of HF in the HF solution is 40%.

[0017] As a further embodiment, in step S3, 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.

[0018] As a further embodiment, the preparation method of the iron fluoride cathode further includes step S4: grinding the anhydrous FeF3 material FeF3-HT, the sulfide solid electrolyte, and the conductive agent to obtain the iron fluoride cathode. By grinding the anhydrous FeF3 material FeF3-HT, the conductive agent, and the relatively soft sulfide electrolyte to obtain a composite cathode, the sulfide electrolyte can be in close contact with the FeF3 material. Furthermore, since the obtained anhydrous FeF3 material FeF3-HT is obtained by sintering the intermediate product FeF3·0.33H2O, the volume change caused by the phase transition of the anhydrous FeF3 material FeF3-HT during sintering is small. This allows the sulfide electrolyte to overcome the volume change caused by the phase transition of the FeF3 material, thereby improving the capacity and cycle performance of the sulfide solid-state battery.

[0019] As a further embodiment, the anhydrous FeF3 material FeF3-HT exhibits characteristic diffraction peaks at 23.7°, 33.3°, 48.5°, and 54.3° in its X-ray powder diffraction pattern expressed as a diffraction angle of 2θ.

[0020] As a further embodiment, the intermediate product FeF3·0.33H2O material exhibits characteristic diffraction peaks at 13.8°, 23.6°, and 27.8° in the X-ray powder diffraction pattern expressed as a diffraction angle of 2θ.

[0021] As a further option, the intermediate product FeF3·0.33H2O has a hexagonal prism morphology.

[0022] As a further refinement, the intermediate product FeF3·0.33H2O has a particle size of 4-5 μm.

[0023] As a further embodiment, the anhydrous FeF3 material FeF3-HT has a hexagonal prism morphology.

[0024] As a further improvement, the anhydrous FeF3 material FeF3-HT has a particle size of 3-5 μm.

[0025] The present invention also provides an iron fluoride cathode obtained by the above-described method for preparing iron fluoride cathode.

[0026] As a further embodiment, the iron fluoride cathode also includes a conductive agent and a sulfide solid electrolyte.

[0027] As a further embodiment, the conductive agent includes SuperP(SP); the sulfide solid electrolyte is Li6PS5Cl.

[0028] As a further improvement, the mass ratio of the anhydrous FeF3 material FeF3-HT, Li6PS5Cl and SuperP(SP) is 35:50:15.

[0029] This invention also provides the application of the iron fluoride cathode prepared by the above-described iron fluoride cathode preparation method in sulfide solid-state batteries.

[0030] The features and beneficial effects of this invention are as follows: an anhydrous FeF3 material, FeF3-HT, which is particularly suitable as a cathode material for sulfide all-solid-state batteries, was prepared by using the intermediate product FeF3·0.33H2O, thereby obtaining a sulfide all-solid-state battery with ultra-high cycle performance and high capacity. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments 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.

[0032] Figure 1 XRD patterns of ferric fluoride materials with different water of crystallization contents.

[0033] 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 2 e 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.

[0034] 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℃.

[0035] 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;

[0036] Figure 4c 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.

[0037] Figure 5 For different composite cathodes at 0.1 mVs -1 Cyclic voltammetry curves at scan rate, where, Figure 5 a is a FeF3·3H2O composite cathode at 0.1 mVs -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 mVs -1 Cyclic voltammetry curves at scan rate; Figure 5 d represents the FeF3-HT composite cathode at 0.1 mVs -1 Cyclic voltammetry curves at scan rate.

[0038] Figure 6 Different composite cathodes at 0.1C (1C = 500 mAg) -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=500mAg) -1 Charge-discharge curves at current density; Figure 6 b is a FeF3·0.33H2O composite cathode at 0.1C (1C=500mAg) -1 Charge-discharge curves at current density; Figure 6 c represents the FeF3-RT composite cathode at 0.1C (1C = 500 mAg). -1 Charge-discharge curves at current density; Figure 6 d represents the FeF3-HT composite cathode at 0.1C (1C = 500 mAg). -1 Charge-discharge curves at current density; Figure 6 e represents the cycle performance of four composite cathodes at 0.1C.

[0039] Figure 7The 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.

[0040] 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.

[0041] Figure 9 Four composite cathodes at 0.3C (1C = 500 mAg) -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=500mAg) -1 Charge-discharge curves under ( ); Figure 9 b is a FeF3·0.33H2O composite cathode at 0.3C (1C=500mAg) -1 Charge-discharge curves under ( ); Figure 9 c represents the FeF3-RT composite cathode at 0.3C (1C = 500 mAg). -1 Charge-discharge curves under ( ); Figure 9 d represents the FeF3-HT composite cathode at 0.3C (1C = 500 mAg). -1 Charge-discharge curves under ( ); Figure 9 e represents the long-cycle performance of four composite cathodes at 0.3C.

[0042] Figure 10 Four composite cathodes at 1C (1C = 500 mAg) -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=500mAg) -1 Charge-discharge curves under ( ); Figure 10b is a FeF3·0.33H2O composite cathode at 1C (1C=500mAg) -1 Charge-discharge curves under ( ); Figure 10 c represents the FeF3-RT composite cathode at 1C (1C = 500 mAg). -1 Charge-discharge curves under ( ); Figure 10 d represents the FeF3-HT composite cathode at 1C (1C = 500 mAg). -1 Charge-discharge curves under ( ); Figure 10 e represents the long-cycle performance of four composite cathodes at 1C.

[0043] Figure 11 Four composite cathodes were tested at different scan rates (0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mVs). -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 11 g 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.

[0044] 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. Detailed Implementation

[0045] 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; the experimental methods, unless otherwise specified, are conventional methods.

[0046] Example 1:

[0047] 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:

[0048] (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;

[0049] (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).

[0050] (3) Prepare another colorless and transparent solution (denoted as solution B) by following the same two steps above;

[0051] (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).

[0052] (5) After stirring solution B at room temperature for 0.5 h, add the colorless and transparent mixed solution to 100 mL of 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, place it in a vacuum drying oven and dry at 80 °C for 12 h to obtain light green FeF3·0.33H2O. Then, sinter it at 400 °C for 3 h under an argon atmosphere to obtain dark brown anhydrous iron fluoride (denoted as FeF3-HT).

[0053] Example 2:

[0054] 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 SuperP(SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0055] (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.

[0056] (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.

[0057] (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. After tightening the screws, apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0058] (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 0.1C rate. All embodiments followed the standard of 1C = 0.5A / g.

[0059] Example 3:

[0060] 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 SuperP(SP) were used as conductive agents, and Li-In alloy was used as negative electrodes.

[0061] (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.

[0062] (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.

[0063] (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. After tightening the screws, apply vacuum silicone grease to the outside of the battery casing to seal it and isolate it from the air.

[0064] (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.

[0065] Example 4:

[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 SuperP(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. After tightening the screws, 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 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 120 times at a rate of 0.3C.

[0071] Example 5:

[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 SuperP(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. After tightening the screws, 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-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.

[0077] Example 6:

[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 SuperP(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. After tightening the screws, 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 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 mVs). -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.

[0083] Example 7:

[0084] 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.

[0085] Analysis of verification results:

[0086] 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 phase transition during the use of FeF3 as a cathode material causes volume changes, 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. Through experiments and verification, this invention reveals that the anhydrous FeF3 material FeF3-HT (FeF3-HT), obtained from the intermediate FeF3·0.33H2O, exhibits minimal volume changes due to the phase transition. This allows the sulfide electrolyte to overcome the volume changes caused by the phase transition in the anhydrous FeF3-HT. Moreover, the anhydrous FeF3-HT retains the structural characteristics of the intermediate FeF3·0.33H2O, with a hexagonal prism morphology, which is beneficial for Li-ion transport. + Provides a fast transmission channel.

[0087] 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 (PDFfile No. 32–0464); all characteristic peaks of FeF3·0.33H2O prepared by the solvothermal method were consistent with the FeF3·0.33H2O standard card (PDFfile 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 (PDFfile 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.

[0088] 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.

[0089] 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.

[0090] 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 possesses a ReO3 structure (twisted) and, due to its lack of water of crystallization, holds significant research value as a cathode for conversion reactions. However, when using FeF3 as a cathode, a phase transition occurs, leading to volume changes and causing microscopic contact failure between the active material and the conductive agent. A composite cathode is obtained by grinding a softer sulfide electrolyte and iron fluoride, allowing the sulfide electrolyte to maintain close contact with the anhydrous FeF3 material (FeF3-HT). This binds the anhydrous FeF3-HT material to the sulfide electrolyte, overcoming the volume changes caused by the phase transition and thus improving the battery's electrochemical performance.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Figure 5Four 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 in ferric fluoride materials, the water of crystallization released during the conversion reaction of hydrated ferric fluoride can have side effects on battery performance, thus its cycle performance is lower than that of ahydrous ferric fluoride. Furthermore, FeF3-HT, prepared from the intermediate FeF3·0.33H2O, retains the structural advantages of the original FeF3·0.33H2O, featuring a unique hexagonal cavity filled with Li. + Provides a fast transmission channel.

[0095] 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... +It provides a fast transmission channel. However, the phase transition of iron fluoride materials causes volume changes, resulting in the failure of microscopic contact between the active material and the conductive agent. We grind the softer sulfide electrolyte and iron fluoride to obtain a composite positive electrode, which allows the sulfide electrolyte to make close contact with the FeF3-HT material. This allows the sulfide electrolyte to bind the FeF3-HT material, overcoming the volume changes caused by the phase transition of the FeF3-HT composite material. This allows the FeF3-HT material to maintain its original structural advantages while further improving the battery's capacity and cycle performance.

[0096] 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。

[0097] 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.

[0098] Figure 9The 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.

[0099] 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.

[0100] 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 mVs. -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.

[0101] 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).

[0102] In summary, the particle size of the four materials—FeF3-HT, FeF3-RT, FeF3·0.33H2O, and FeF3·3H2O—follows the following order: FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O. The electrochemical performance of the four materials, from highest to lowest, follows the trend: FeF3-HT > FeF3-RT > FeF3·0.33H2O > FeF3·3H2O. Anhydrous FeF3-HT, prepared from the intermediate FeF3·0.33H2O, retains the structural advantages of FeF3·0.33H2O, featuring a unique hexagonal cavity filled with Li. +This study provides a rapid transport channel for the composite cathode prepared by co-grinding FeF3-HT material and a sulfide solid electrolyte. This allows the relatively soft sulfide electrolyte to maintain close contact with the FeF3-HT material. Due to the small volume phase transition in FeF3-HT, the sulfide solid electrolyte can overcome the volume changes caused by the phase transition in the FeF3-HT composite material. This allows the FeF3-HT material to retain its original structural advantages while further improving the battery's capacity and cycle performance. The iron fluoride cathode synthesized in this work has achieved great success in sulfide all-solid-state lithium batteries, providing insights for the synthesis of other metal fluorides and further research in the field of all-solid-state batteries.

[0103] 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 an iron fluoride cathode, characterized in that, The process includes preparing the intermediate product FeF3·0.33H2O using Fe source and F source, and then sintering the intermediate product FeF3·0.33H2O to obtain the anhydrous FeF3 material FeF3-HT; Specifically, it includes: S1: Fe(NO3)3·9H2O was added to anhydrous ethanol and stirred to obtain a reddish-brown solution; S2: Add HF solution dropwise to S1 until a colorless and transparent solution is obtained; S3: The colorless and transparent solution in S2 is added to the reaction vessel and reacted at 115℃-125℃ to form a light green precipitate. The precipitate is filtered, washed, and dried at 75℃-90℃ to obtain a light green intermediate product FeF3·0.33H2O. The product is sintered at 390℃-410℃ to obtain a dark brown anhydrous FeF3 material FeF3-HT. S4: The anhydrous FeF3 material FeF3-HT, sulfide solid electrolyte and conductive agent are ground to obtain iron fluoride positive electrode; The intermediate product FeF3·0.33H2O has a hexagonal prism morphology, and the anhydrous FeF3 material FeF3-HT also has a hexagonal prism morphology.

2. The method for preparing the iron fluoride cathode according to claim 1, characterized in that, 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).

3. The method for preparing the iron fluoride cathode according to claim 1, characterized in that, In step S3, 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.

4. The method for preparing the iron fluoride cathode according to claim 1, characterized in that, The anhydrous FeF3 material FeF3-HT exhibits characteristic diffraction peaks at 23.7°, 33.3°, 48.5°, and 54.3° in the X-ray powder diffraction pattern expressed at a diffraction angle of 2θ; the intermediate product FeF3·0.33H2O exhibits characteristic diffraction peaks at 13.8°, 23.6°, and 27.8° in the X-ray powder diffraction pattern expressed at a diffraction angle of 2θ.

5. The method for preparing the iron fluoride cathode according to claim 1, characterized in that, The particle size of the FeF3·0.33H2O is 4-5 μm.

6. The method for preparing the iron fluoride cathode according to claim 1, characterized in that, The anhydrous FeF3 material FeF3-HT has a particle size of 3-5 μm.

7. The iron fluoride cathode obtained by the preparation method of any one of claims 1-6.

8. The iron fluoride positive electrode according to claim 7, characterized in that, The iron fluoride cathode also includes a conductive agent and a sulfide solid electrolyte.

9. The iron fluoride positive electrode according to claim 8, characterized in that, The conductive agent includes Super P; the sulfide solid electrolyte is Li6PS5Cl.

10. The iron fluoride positive electrode according to claim 9, characterized in that, The mass ratio of the anhydrous FeF3 material FeF3-HT, Li6PS5Cl and Super P is 35:50:

15.

11. The application of the iron fluoride cathode prepared by the method of any one of claims 1-6 in a sulfide solid-state battery.

Images