A deep eutectic solvent, metal fluoride, lithium-ion battery cathode material and its preparation method

Abstract

This invention provides a deep eutectic solvent, a metal fluoride prepared from the deep eutectic solvent, and a lithium-ion battery cathode material prepared from the metal fluoride. The deep eutectic solvent comprises one or more metal nitrates and dimethyl sulfone. The preparation of metal fluorides using the deep eutectic solvent of this invention allows for the rapid and efficient synthesis of metal fluoride nanoparticles, avoiding the use of highly corrosive NF3 / HF gases and expensive ionic liquids. By controlling the ratio of different metal ions in the deep eutectic solvent, the morphology of the synthesized secondary metal fluoride particles can be controlled. The resulting three-dimensional porous brick-like morphology effectively increases the contact area between the electrode active material and the electrolyte, increases the active sites for electrochemical reactions, and improves the kinetic performance of the electrode reaction.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a deep eutectic solvent, a metal fluoride prepared from the deep eutectic solvent, and a lithium-ion battery cathode material prepared from the metal fluoride. The prepared lithium-ion battery cathode material is a hydrated iron trifluoride / C composite lithium-ion battery cathode material based on a conversion reaction and possessing high specific capacity and energy density. Background Technology

[0002] The application of rechargeable batteries in practical production and daily life is becoming increasingly widespread. The development of mobile devices and new energy vehicles has driven the development of energy storage technology. However, currently commercialized lithium-ion batteries are gradually failing to meet the requirements of high specific energy and large-scale energy storage. Furthermore, due to the insufficient abundance of metal minerals (such as cobalt) required for traditional cathode materials in the Earth's crust, their prices are constantly rising. Therefore, developing new cathode materials with high specific capacity and energy density at a low cost is of great significance.

[0003] Unlike cathode materials based on traditional intercalation reaction mechanisms, such as lithium cobalt oxide and lithium iron phosphate (which typically have capacities and energy densities below 275 mAh / g and 750 Wh / kg based on single-electron transfer), cathode materials based on conversion reactions can provide theoretical capacities close to or exceeding 1000 mAh / g and theoretical energy densities of 2000 Wh / kg through multi-electron transfer.

[0004] Metal fluoride cathodes have a compact structure and, as a type of cathode for transition reactions, leverage the strong electronegativity of fluorine to enhance the reaction potential of transition metal ions. Combined with the high theoretical specific capacity resulting from three-electron transfer, they can provide high energy densities (especially volumetric energy densities) comparable to those of O2 or S8 molecular cathodes. For example, iron trifluoride (FeF3), an element-rich and environmentally friendly cathode, can provide a high energy density of 1947 Wh / kg based on its theoretical specific capacity of 712 mAh / g and a thermodynamic potential of ~2.73 V generated by three-electron transfer, thus being considered a highly promising cathode candidate.

[0005] However, the low intrinsic electronic conductivity of iron fluoride cathodes easily leads to large charge-discharge polarization and low energy efficiency (<60%). Nanoparticle scaling and conductive framework modification strategies are commonly used to improve the electrochemical performance of fluorides. However, their synthesis often employs high-temperature, high-pressure solvothermal methods, or fluorination with corrosive gases such as HF and NF3, both of which pose significant risks. Another type of fluorination method utilizing fluorine-containing ionic liquids offers some improvement in safety, but these ionic liquids are relatively expensive. Summary of the Invention

[0006] In view of the limitations of the prior art, the present invention aims to provide a safe and inexpensive deep eutectic solvent, a metal fluoride prepared from the deep eutectic solvent, and a lithium-ion battery cathode material prepared from the metal fluoride.

[0007] In a first aspect, the present invention provides a deep eutectic solvent comprising one or more metal nitrates and dimethyl sulfone.

[0008] Preferably, the metal nitrate is selected from at least one of ferric nitrate nonahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and copper nitrate trihydrate.

[0009] Preferably, it includes ferric nitrate nonahydrate, dimethyl sulfone, and an auxiliary metal nitrate, wherein the auxiliary metal nitrate is selected from at least one of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and copper nitrate trihydrate.

[0010] Secondly, the present invention also provides a method for preparing metal fluorides, comprising: adding a fluorinating agent to a deep eutectic solvent as described above, reacting at a temperature of 50-70°C for 6-12 hours, washing, centrifuging, drying, and heat-treating the precipitate to obtain metal fluoride particles.

[0011] Preferably, the fluorinating agent is selected from at least one of ammonium bifluoride and ammonium fluoride.

[0012] Thirdly, the present invention also provides a metal fluoride, prepared by a method for preparing a metal fluoride as described above.

[0013] Preferably, the metal fluoride is a nanoparticle, an aggregated micron-sized particle, or a three-dimensional porous brick-shaped particle with a regular geometric shape.

[0014] According to the present invention, the deep eutectic solvent and the metal fluoride prepared from the deep eutectic solvent, wherein ferric nitrate nonahydrate and dimethyl sulfone are a Lewis acid-base pair, form a clear and homogeneous solution through Lewis acid-base interaction under heating conditions (50-70°C). The dimethyl sulfone itself is safe and non-toxic. The resulting deep eutectic solvent possesses properties similar to ionic liquids while also being safe and inexpensive. Furthermore, due to the presence of Fe metal ions... 3+ The interaction with Lewis bases lowers the bonding energy between metal ions and nitrate ions, facilitating contact bonding between metal ions and introduced fluoride ions, thereby reducing the difficulty of the fluorination reaction.

[0015] Fourthly, the present invention also provides the application of the metal fluoride described above in the preparation of cathode materials for lithium-ion batteries.

[0016] Fifthly, the present invention also provides a lithium-ion battery cathode material, comprising a metal fluoride / C composite material as the cathode active material, wherein the metal fluoride is prepared by a deep eutectic solvent as described above, and the metal fluoride / C composite material is a composite material in which conductive carbon black is loaded on metal fluoride particles.

[0017] Preferably, the metal fluoride is hydrated iron trifluoride, preferably FeF3·0.33H2O of hexagonal tungsten bronze phase; the conductive carbon black is selected from at least one of Ketjen black, Super-P, acetylene black, carbon nanotubes and graphene.

[0018] In a sixth aspect, the present invention also provides a method for preparing the lithium-ion battery cathode material as described above, comprising: mixing ferric nitrate nonahydrate and dimethyl sulfone to obtain a deep eutectic solvent, adding conductive carbon black and a fluorine source, reacting at a temperature of 50-70°C for 6-12 hours, washing, centrifuging, drying and heat-treating the precipitate to obtain a hydrated ferric trifluoride / C composite lithium-ion battery cathode material.

[0019] Preferably, the deep eutectic solvent further includes an auxiliary metal nitrate, wherein the auxiliary metal nitrate is selected from at least one of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and copper nitrate trihydrate, and the fluorine source is selected from at least one of ammonium fluoride and ammonium bifluoride.

[0020] Preferably, the hydrated iron trifluoride / C composite lithium-ion battery cathode material is a three-dimensional porous brick-shaped particle with a particle size of 50-300nm.

[0021] Preferably, in the hydrated iron trifluoride / C composite lithium-ion battery cathode material, the mass percentage content of the conductive carbon black is 10-25%.

[0022] Preferably, the molar ratio of ferric nitrate nonahydrate and auxiliary metal nitrate to dimethyl sulfone is 1:(1-3), and the molar ratio of ferric nitrate nonahydrate to auxiliary metal nitrate is (1-5):1.

[0023] According to this invention, for the first time, the morphology of metal fluorides is controlled by adjusting the proportion of metal ions in the deep eutectic solvent. This process is spontaneous, resulting in a uniform distribution of interparticle channels, which optimizes the contact area between the positive electrode active material and the electrolyte in lithium-ion cathode materials, expands the active sites for electrochemical reactions, and improves the kinetic performance of electrode reactions. Furthermore, the auxiliary metal ions used in this process (such as Co...) 2+ It does not participate in fluoride precipitation, can be recycled and reused, and avoids material waste.

[0024] The beneficial effects of this invention are:

[0025] (1) Metal fluorides can be prepared by deep eutectic solvent of the present invention, which can quickly and efficiently synthesize metal fluoride nanopowders, avoiding the use of highly corrosive NF3 / HF gas and expensive ionic liquids.

[0026] (2) By controlling the ratio of different metal ions in the deep eutectic solvent, the morphology of the synthesized secondary metal fluoride particles can be controlled. The resulting three-dimensional porous brick-like morphology can effectively increase the contact area between the electrode active material and the electrolyte, increase the active sites of the electrochemical reaction, and improve the kinetic performance of the electrode reaction.

[0027] (3) The hydrated iron trifluoride / C composite lithium-ion battery cathode material prepared by the deep eutectic solvent of the present invention can achieve high potential and high energy density charge and discharge behavior, and can be applied to large-size soft-pack batteries and ultra-low temperature batteries. Attached Figure Description

[0028] Figure 1 The XRD patterns are of the FeF3·0.33H2O / KB composite materials synthesized in Examples 1 and 2 of this invention.

[0029] Figure 2 This is a SEM image of the hydrated iron trifluoride cathode material synthesized in Example 1 of this invention;

[0030] Figure 3 This is a SEM image of the three-dimensional porous brick-shaped hydrated iron trifluoride cathode material synthesized in Example 2 of the present invention;

[0031] Figure 4 The image shows the XRD pattern of cobalt fluoride synthesized in Example 3 of this invention.

[0032] Figure 5 The cyclic voltammetry curves of lithium metal batteries using two different morphologies of FeF3·0.33H2O / KB as cathode materials in the LiTFSI / DOL-DME electrolyte system in Example 4 of this invention are shown.

[0033] Figure 6 This is a comparison chart of the specific capacity and coulombic efficiency of lithium metal batteries using FeF3·0.33H2O / KB and three-dimensional porous brick-shaped FeF3·0.33H2O / KB as positive electrode materials and LiTFSI / DOL-DME as electrolyte in Example 4 of the present invention at different current densities.

[0034] Figure 7 This demonstrates the long-cycle performance of the lithium metal battery using three-dimensional porous brick-shaped FeF3·0.33H2O / KB as the positive electrode material in the LiTFSI / DOL-DME electrolyte system in Example 4 of this invention.

[0035] Figure 8 The constant current charge-discharge curves of the lithium metal battery in Example 4 of this invention, which uses three-dimensional porous brick-shaped FeF3·0.33H2O / KB as the positive electrode material and LiTFSI / DOL-DME as the electrolyte, are shown.

[0036] Figure 9 The graph shows the relationship between energy density and power density of lithium metal batteries in Example 4 of this invention, which use FeF3·0.33H2O / KB with two different structural morphologies as positive electrode materials and LiTFSI / DOL-DME as electrolyte.

[0037] Figure 10 This invention demonstrates the long-cycle performance of a lithium metal battery assembled in Example 4 of this invention, using three-dimensional porous brick-shaped FeF3·0.33H2O / KB as the positive electrode material and LiTFSI / DOL-DME as the electrolyte, at low temperature (-20°C).

[0038] Figure 11 The discharge specific capacity and coulombic efficiency of the soft-pack battery using LiTFSI / DOL-DME as electrolyte in Example 5 of this invention are shown. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and the following embodiments. It should be understood that the drawings and the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0040] This invention discloses a metal fluoride prepared by deep eutectic solvent (DES) and a lithium-ion battery cathode material prepared from the metal fluoride.

[0041] <Deep Eutectic Solvent>

[0042] First, the deep eutectic solvent involved in this invention includes one or more metal nitrates and dimethyl sulfone, wherein the metal nitrates include, but are not limited to, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate trihydrate, etc.

[0043] In a preferred embodiment of the present invention, the deep eutectic solvent involved in the present invention includes ferric nitrate nonahydrate, dimethyl sulfone, and an auxiliary metal nitrate, wherein the auxiliary metal nitrate is a metal nitrate other than iron, such as cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate trihydrate, etc.

[0044] <Metal fluorides>

[0045] The present invention also provides a method for preparing metal fluorides using the above-mentioned deep eutectic solvent, comprising: adding a fluorinating agent to the above-mentioned deep eutectic solvent, reacting at a temperature of 50-70°C for 6-12 hours, washing, centrifuging, drying, and heat-treating the precipitate to obtain metal fluoride particles.

[0046] In the above-mentioned method for preparing metal fluorides, the fluorinating agent includes, but is not limited to, ammonium bifluoride, ammonium fluoride, or a mixture of the two.

[0047] The metal fluorides prepared by the above-described methods are nanoparticles, aggregated micron-sized particles, or three-dimensional porous brick-like particles with regular geometric shapes. In particular, the metal fluorides prepared using ferric nitrate nonahydrate, dimethyl sulfone, and an auxiliary metal nitrate as a deep eutectic solvent are three-dimensional porous brick-like particles with regular geometric shapes.

[0048] According to the present invention, the deep eutectic solvent and the metal fluoride prepared from the deep eutectic solvent, wherein ferric nitrate nonahydrate and dimethyl sulfone are a Lewis acid-base pair, can form a clear and homogeneous solution through Lewis acid-base interaction under heating conditions (50-70°C). The dimethyl sulfone itself is safe and non-toxic. The formed deep eutectic solvent possesses properties similar to ionic liquids while also being safe and inexpensive. Furthermore, due to the presence of Fe metal ions... 3+ The interaction with Lewis bases lowers the bonding energy between metal ions and nitrate ions, facilitating contact bonding between metal ions and introduced fluoride ions, thereby reducing the difficulty of the fluorination reaction.

[0049] <Metal fluoride / C composite material>

[0050] Metal fluoride / C composite materials, which serve as positive electrode active materials for lithium-ion batteries, can be prepared by combining the aforementioned metal fluorides with conductive carbon black. These metal fluoride / C composite materials can be composite materials in which conductive carbon black is supported on metal fluoride particles. The metal fluoride used for the positive electrode active material of lithium-ion batteries is typically hydrated iron trifluoride. In this invention, the metal fluoride used for the positive electrode active material of lithium-ion batteries is preferably FeF3·0.33H2O of the hexagonal tungsten bronze phase. The conductive carbon black includes, but is not limited to, Ketjen black, Super-P, acetylene black, carbon nanotubes, graphene, etc. In this invention, Ketjen black is selected as the conductive carbon black.

[0051] The hydrated iron trifluoride / C composite material of the present invention is prepared by the following method: ferric nitrate nonahydrate and dimethyl sulfone are mixed to obtain a deep eutectic solvent, conductive carbon black and fluorine source are added, and the mixture is reacted at 50-70°C for 6-12 hours. The precipitate is then washed, centrifuged, dried and heat-treated to obtain the hydrated iron trifluoride / C composite lithium-ion battery cathode material.

[0052] In the process of preparing hydrated iron trifluoride / C composite material of the present invention, the deep eutectic solvent also includes auxiliary metal nitrates, including but not limited to cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate trihydrate, etc., in addition to hydrated iron trifluoride. The fluorine source includes but is not limited to ammonium fluoride, ammonium hydrogen fluoride, or a mixture of the two.

[0053] The preparation of hydrated iron trifluoride / C composite material in this invention specifically includes the following steps:

[0054] Step (1): Mix one or more metal nitrates with dimethyl sulfone in a certain molar ratio and heat at, for example, 60°C until a clear and transparent solution is formed (for example, the amount of metal nitrate used is 1-5 millimoles).

[0055] Step (2): Add conductive carbon black of different mass percentages (e.g., 15-40 mg) as needed, and continue stirring under heating conditions for 1-5 hours;

[0056] Step (3): Add a certain amount of fluorine source required for fluorination (0.2-1g) and continue stirring for 6-12 hours;

[0057] Step (4): Centrifuge at 6000 rpm and wash with ethanol and acetone alternately, recover the supernatant, collect the precipitate, until the supernatant is colorless and transparent;

[0058] Step (5): Dry the cleaned powder in a vacuum oven at 80°C;

[0059] Step (6): Place the dried black powder in a quartz crucible and heat it to 150°C at a rate of 3°C per minute in an air atmosphere. Hold it at that temperature for 5 hours. Then continue to heat it to 250°C at a rate of 5°C per minute and hold it at that temperature for 5 hours. After that, cool it naturally to obtain the hydrated iron trifluoride / C composite material.

[0060] In the preparation of the hydrated ferric trifluoride / C composite material of the present invention, the mass percentage content of the conductive carbon black in the hydrated ferric trifluoride / C composite lithium-ion battery cathode material can be 10-25%. The molar ratio of the ferric nitrate nonahydrate and the auxiliary metal nitrate to the dimethyl sulfone can be 1:(1-3), for example 1:2, and the molar ratio of the ferric nitrate nonahydrate and the auxiliary metal nitrate can be (1-5):1.

[0061] The hydrated iron trifluoride / C composite material prepared by the above preparation method is a three-dimensional porous brick-shaped particle with a particle size of 50-300 nm.

[0062] <Lithium-ion battery cathode materials>

[0063] The battery is assembled using the above-mentioned hydrated iron trifluoride / C composite material as the positive electrode active material, lithium metal as the negative electrode, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium hexafluorophosphate (LiPF6) as the electrolyte solute, at least one of diethylene glycol dimethyl ether (DGM), triethylene glycol dimethyl ether (TEGDME), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), ethylene glycol dimethyl ether (DME), and 1,3-dioxolane (DOL) as the electrolyte solvent, and one of Celgard 2400 or glass fiber as the separator.

[0064] According to this invention, for the first time, the morphology of metal fluorides is controlled by adjusting the proportion of metal ions in the deep eutectic solvent, forming three-dimensional porous brick-like particles. This process is spontaneous, resulting in uniformly distributed pores between the particles. This optimizes the contact area between the positive electrode active material and the electrolyte in the lithium-ion cathode material, expands the active sites for electrochemical reactions, and improves the kinetic performance of the electrode reaction. Furthermore, the auxiliary metal ions used in this process (such as Co...) 2+ It does not participate in fluoride precipitation, can be recycled and reused, and avoids material waste.

[0065] The deep eutectic solvent of this invention enables the rapid and efficient synthesis of metal fluoride nanopowders, avoiding the use of highly corrosive NF3 / HF gases and expensive ionic liquids.

[0066] The morphology of secondary metal fluoride particles can be controlled by adjusting the ratio of different metal ions in the deep eutectic solvent. The resulting three-dimensional porous brick-like morphology can effectively increase the contact area between the electrode active material and the electrolyte, increase the active sites of the electrochemical reaction, and improve the kinetic performance of the electrode reaction.

[0067] The hydrated iron trifluoride / C composite lithium-ion battery cathode material prepared by the deep eutectic solvent of the present invention can achieve high potential and high energy density charge and discharge behavior, and can be applied to large-size pouch batteries and ultra-low temperature batteries.

[0068] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not necessarily limited to the specific values ​​in the examples below.

[0069] Example 1: Preparation of FeF3·0.33H2O / KB by deep eutectic solvent method:

[0070] Weigh 2.02 g of ferric nitrate nonahydrate and 0.94 g of dimethyl sulfone, mix them, and heat at 60 °C until a clear and transparent solution (i.e., a deep eutectic solvent) is formed. Add 40 mg of Ketjen Black (KB) and stir at 500 rpm for 3 hours. Add 0.5 g of ammonium bifluoride and continue stirring for 12 hours. Wash the precipitate alternately with acetone and ethanol, centrifuge at 6000 rpm, and wash and recover the supernatant multiple times until the supernatant becomes colorless. Place the precipitate in a vacuum oven and dry at 80 °C. Collect the dry powder and heat it in air at a rate of 3 °C per minute to 150 °C and hold for 5 hours. Then, continue heating at a rate of 5 °C per minute to 250 °C and hold for 5 hours. After natural cooling, collect the black powder FeF3·0.33H2O / KB composite active material, which is designated as FFH.

[0071] Its XRD diffraction pattern is attached. Figure 1 As shown, it exhibits characteristic diffraction peaks belonging to the hexagonal tungsten bronze phase of hydrated iron fluoride FeF3·0.33H2O. Figure 2 The SEM image shown shows that FFH exhibits a morphology of small particle aggregation. The primary particle size is less than 200 nanometers, and the secondary particles formed by aggregation vary in size, ranging from 1 to 2 micrometers.

[0072] Example 2: Preparation of three-dimensional porous brick-shaped FeF3·0.33H2O / KB:

[0073] Weigh 2.02 g of ferric nitrate nonahydrate, 1.45 g of cobalt nitrate hexahydrate, and 1.88 g of dimethyl sulfone. Mix the three and heat at 60 °C until a clear and transparent solution (i.e., a deep eutectic solvent) is formed. Add 40 mg of Ketjen Black (KB) and stir at 500 rpm for 3 hours. Add 1 g of ammonium bifluoride and continue stirring for 12 hours. Wash the precipitate alternately with acetone and ethanol, and centrifuge at 6000 rpm. Wash repeatedly to recover the supernatant containing Co until the supernatant becomes colorless. Place the precipitate in a vacuum oven and dry at 80 °C. Collect the dry powder and heat it in air at a rate of 3 °C per minute to 150 °C and hold for 5 hours. Then, continue heating at a rate of 5 °C per minute to 250 °C and hold for 5 hours. After natural cooling, collect the black powder FeF3·0.33H2O / KB composite active material, which is designated as FFH-C.

[0074] Its XRD diffraction pattern is attached. Figure 1 As shown, the main phase of FFH-C is the same as that of FFH, both being FeF3·0.33H2O with a hexagonal tungsten bronze structure, and also containing a very small amount of anhydrous rutile phase FeF3. SEM images are attached. Figure 3As shown, most of the fluoride particles in FFH-C spontaneously and orderly aggregate, exhibiting a porous square block-like morphology. The primary particle size is approximately between 50 and 100 nm. The secondary particles are surrounded or modified by surrounding spherical Ketjen black particles. The secondary particle size is 1-2 micrometers, and the Ketjen black particle size is less than 30 nm.

[0075] Example 3: Preparation of CoF2 by deep eutectic solvent method:

[0076] Weigh 1.45 g of cobalt nitrate hexahydrate and 0.94 g of dimethyl sulfone, mix them, and heat at 60 °C until a clear and transparent solution (i.e., a deep eutectic solvent) is formed. Add 0.5 g of ammonium bifluoride and continue stirring for 12 hours. Wash the precipitate alternately with acetone and ethanol, centrifuge at 6000 rpm, and wash repeatedly to recover the supernatant until the supernatant becomes colorless. Place the precipitate in a vacuum oven and dry at 80 °C. Collect the dried powder and perform heat treatment by placing the powder in air and heating it to 150 °C at a rate of 3 °C per minute, holding it at that temperature for 5 hours, and then continuing to raise the temperature to 250 °C at a rate of 5 °C per minute and holding it at that temperature for 5 hours. After natural cooling, collect the light pink powder CoF2.

[0077] Its XRD diffraction pattern is attached. Figure 4 As shown, this is the tetragonal phase of CoF2 (PDF#71-1969, space group P42 / mnm).

[0078] Example 4: Preparation, battery assembly, and testing of iron fluoride cathode material:

[0079] 1) Electrode preparation: FeF3·0.33H2O / KB(FFH) or FeF3·0.33H2O / KB(FFH-C) prepared according to Examples 1 and 2 were uniformly mixed with conductive agent Super-P and binder polyvinylidene fluoride (PVDF) at a mass ratio of 7:2:1 by grinding. An appropriate amount of N-methylpyrrolidone (NMP) was added dropwise to form a uniform slurry, which was then coated onto a clean aluminum foil current collector. After air drying, it was transferred to a vacuum oven at 80°C and dried for 12 hours. The dried aluminum foil loaded with iron fluoride was cut into circular pieces with a diameter of 8 mm, which served as the positive electrode material.

[0080] 2) Preparation of ether electrolyte: In an argon atmosphere glove box with both water and oxygen values ​​less than 0.1 ppm, weigh 574.2 mg of lithium bis(trifluoromethanesulfonylimide) (LiTFSI) and add it to a mixed solvent containing 1 mL of 1,3-dioxolane (DOL) and 1 mL of ethylene glycol dimethyl ether (DME) (the corresponding solute concentration is 1.0 mol / L). Stir continuously at room temperature for 24 hours to completely dissolve the white powder and obtain the ether electrolyte (LiTFSI / DOL-DME).

[0081] 3) Battery assembly and testing: CR2025 coin cells were assembled in an argon-atmosphere glove box with both water and oxygen levels less than 0.1 ppm for electrochemical performance testing. The positive electrode was any of the iron fluoride positive electrode sheets prepared above, the negative electrode was a lithium metal sheet, the electrolyte was an ether-based electrolyte, and the separator was Celgard 2400.

[0082] To investigate the effect of different structural morphologies on the conversion reaction potential of the iron fluoride cathode, cyclic voltammetry tests were conducted on batteries assembled with FFH and FFH-C as cathode materials and LiTFSI / DOL-DME as electrolyte. The scan rate was set at 0.2 mV / s, and the voltage range was 1.2–4.0 V. The results are shown in the appendix. Figure 5 As shown, the three-dimensional porous structure causes the oxidation peak of the FFH-C cathode material to shift towards lower voltage compared to FFH, resulting in a lower overpotential for the corresponding conversion reaction. This confirms that increasing the contact area between the electrode and the electrolyte, and increasing the active sites for electrochemical reactions, can greatly improve the kinetic performance of the electrode reaction.

[0083] To test the electrochemical performance of the two different morphologies of iron fluoride cathodes synthesized in Examples 1 and 2 in ether electrolyte systems, the assembled batteries were subjected to constant current charge-discharge tests on a Blue Electric CT2001A. The current density ranged from 100 to 2000 mA / g, and the charge-discharge voltage ranged from 1.2 to 4.0 V. The electrochemical performance of these batteries is shown in the attached figure. Figures 6-9 As shown, compared to the FeF3·0.33H2O / KB (FFH) cathode material obtained in Example 1, the three-dimensional porous brick-shaped FeF3·0.33H2O / KB (FFH-C) cathode exhibits better rate performance, indicating that the three-dimensional porous morphology provides better kinetic performance. Furthermore, when FFH-C undergoes constant current charge-discharge cycling, it still maintains a specific capacity of 284 mAh / g after 100 cycles at a current density of 100 mA / g. Moreover, the charge-discharge curves for the first 30 cycles show good battery stability, with no significant increase in the voltage difference between the charge-discharge plateaus. Both types of iron fluoride cathodes exhibit high energy and power densities, and the three-dimensional porous brick-shaped morphology further enhances the energy and power density performance of FFH-C, demonstrating the crucial role of morphology in the performance of cathode active materials.

[0084] To test the low-temperature cycling performance of the porous three-dimensional brick-shaped iron fluoride cathode obtained in Example 2 in an ether electrolyte system, the assembled button cell was placed on a CT2001A for constant current charge-discharge testing. The current density was 20 mA / g, and the charge-discharge voltage range was 1.2–4.0 V. The battery was first cycled 5 times at room temperature, and then immediately transferred to a low temperature (-20°C) for further constant current charge-discharge testing after being charged to 4 V. The long-term cycling performance of the battery is shown in the attached figure. Figure 10 As shown, the battery exhibits a high specific capacity of 236 mAh / g in the first cycle at low temperatures, and retains 80% of its capacity after 60 cycles. Even after 130 cycles, the battery still retains a high capacity retention of 60%.

[0085] Example 5: Assembly and testing of pouch cells using iron fluoride cathode material:

[0086] 1) Electrode preparation: The three-dimensional porous brick-shaped FeF3·0.33H2O / KB (FFH-C) prepared according to Example 2 was uniformly mixed with conductive agent Super-P and binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:0.5:1.5 by grinding. An appropriate amount of N-methylpyrrolidone (NMP) was added dropwise to form a uniform slurry, which was then coated onto a clean aluminum foil current collector. After natural air drying, it was transferred to a vacuum oven at 80°C and dried for 12 hours. The dried aluminum foil loaded with iron fluoride was cut into positive electrode sheets with dimensions of 75×55mm×mm.

[0087] 2) Battery Assembly and Testing: Pouch cells were assembled in an argon-atmosphere glove box with both water and oxygen levels less than 0.1 ppm for electrochemical performance testing. The positive electrode was a pre-prepared iron fluoride cathode, the negative electrode was a lithium metal sheet, the electrolyte was an ether-based electrolyte, and the separator was Celgard 2400. The assembled batteries were subjected to constant current charge-discharge testing on a Blue Electric CT2001A electrode at a current density of 20 mA / g and a charge-discharge voltage range of 1.2–4.0 V. The electrochemical performance of the pouch cells is shown in the attached figure. Figure 11 As shown, it can be stably cycled for nearly 15 cycles under conditions of lean electrolyte (electrolyte volume to active material mass ratio of 8 μL / mg) and has a capacitance close to 1 mAh / cm³. 2 The areal capacity indicates that this hydrated iron fluoride cathode has the potential for commercial application.

[0088] Finally, it is necessary to state that the above embodiments are only used to further illustrate the technical solution of the present invention in detail, and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A deep eutectic solvent, characterized in that, A deep eutectic solvent is obtained by mixing ferric nitrate nonahydrate and dimethyl sulfone.

2. A deep eutectic solvent, characterized in that, A deep eutectic solvent is obtained by mixing ferric nitrate nonahydrate, dimethyl sulfone, and an auxiliary metal nitrate, wherein the auxiliary metal nitrate is selected from at least one of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and copper nitrate trihydrate.

3. A method for preparing a metal fluoride, characterized in that, include: A fluorinating agent is added to the deep eutectic solvent as described in claim 1 or 2, and the mixture is reacted at 50-70°C for 6-12 hours. The precipitate is then washed, centrifuged, dried, and heat-treated to obtain metal fluoride particles.

4. The preparation method according to claim 3, characterized in that, The fluorinating agent is selected from at least one of ammonium bifluoride and ammonium fluoride.

5. A metal fluoride, characterized in that, Prepared by the method for preparing a metal fluoride as described in claim 3 or 4.

6. The metal fluoride according to claim 5, characterized in that, The metal fluoride is a nanoparticle, an aggregated micron-sized particle, or a three-dimensional porous brick-shaped particle with a regular geometric shape.

7. The application of the metal fluoride as described in claim 5 or 6 in the preparation of cathode materials for lithium-ion batteries.

8. A method for preparing a lithium-ion battery cathode material, characterized in that, The lithium-ion battery cathode material includes a metal fluoride / C composite material as the cathode active material, wherein the metal fluoride / C composite material is a composite material in which conductive carbon black is loaded on metal fluoride particles; the preparation method includes: mixing ferric nitrate nonahydrate and dimethyl sulfone to obtain a deep eutectic solvent, adding conductive carbon black and a fluorine source, reacting at a temperature of 50-70°C for 6-12 hours, washing, centrifuging, drying and heat-treating the precipitate to obtain a hydrated iron trifluoride / C composite lithium-ion battery cathode material.

9. The preparation method according to claim 8, characterized in that, The metal fluoride is hydrated iron trifluoride; the conductive carbon black is selected from at least one of Ketjen black, Super-P, acetylene black, carbon nanotubes, and graphene.

10. The preparation method according to claim 9, characterized in that, The metal fluoride is FeF3·0.33H2O in the hexagonal tungsten bronze phase.

11. The preparation method according to claim 8, characterized in that, The deep eutectic solvent also includes an auxiliary metal nitrate, which is selected from at least one of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and copper nitrate trihydrate, and the fluorine source is selected from at least one of ammonium fluoride and ammonium hydrogen fluoride.

12. The preparation method according to claim 8, characterized in that, The hydrated iron trifluoride / C composite lithium-ion battery cathode material is a three-dimensional porous brick-shaped particle with a particle size of 50-300nm.

13. The preparation method according to claim 8, characterized in that, In the hydrated iron trifluoride / C composite lithium-ion battery cathode material, the mass percentage content of the conductive carbon black is 10-25%.

14. The preparation method according to claim 11, characterized in that, The molar ratio of the nonahydrate ferric nitrate and the auxiliary metal nitrate to the dimethyl sulfone is 1:(1-3), and the molar ratio of the nonahydrate ferric nitrate and the auxiliary metal nitrate is (1-5):1.

Images