Fe-Sn modified composite Li negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a Fe-Sn modified composite Li negative electrode material and a preparation method and application thereof, and belongs to the technical field of lithium metal batteries, the preparation method comprises the following steps: step A, adding triethylamine and fluoroethylene carbonate into ethylene glycol dimethyl ether, and stirring to obtain a composite solvent; b, FeF3 and SnF2 are added into the composite solvent obtained in the step A, heating and stirring are conducted, and Fe-Sn composite liquid is obtained; and step C, dropping the Fe-Sn composite liquid obtained in the step B on the surface of a lithium sheet, and standing to obtain the Fe-Sn modified composite negative electrode Li material, so as to solve the technical problems that lithium dendrites cause short-circuit potential safety hazards, the electrode structure is damaged by sudden change of lithium volume, the cycle life is shortened, lithium consumption and performance degradation are intensified by repeated damage of an unstable SEI film, and HF is generated by reaction to corrode a battery assembly.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to an Fe-Sn modified composite Li anode material, its preparation method, and its application. Background Technology

[0002] Lithium metal is considered an ideal anode material for next-generation high-energy-density batteries due to its extremely high theoretical specific capacity and the lowest electrochemical potential. However, lithium metal faces many challenges in practical applications, which severely restricts its commercialization process.

[0003] During battery charging and discharging, on the one hand, uneven deposition of lithium metal on the surface can easily occur, forming lithium dendrites. These lithium dendrites not only consume electrolyte but may also puncture the separator, causing a short circuit and posing a safety hazard. At the same time, lithium metal undergoes significant volume changes during deposition and stripping, which causes the electrode material to continuously pulverize and detach, damaging the integrity of the electrode structure and significantly reducing the battery's cycle life. On the other hand, the reaction between lithium metal and electrolyte is quite vigorous, forming an unstable solid electrolyte interphase (SEI) film. This SEI film is prone to rupture, and the newly exposed lithium metal after rupture will continue to react with the electrolyte, leading to repeated formation and destruction of the SEI film, further aggravating lithium consumption and battery performance degradation. Moreover, the reaction process may produce corrosive substances such as HF, which can damage various battery components and affect the overall performance of the battery.

[0004] To address the aforementioned issues, exploring methods for interface modification of lithium metal anodes is crucial for improving the performance of lithium metal batteries. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a Fe-Sn modified composite Li anode material, its preparation method and application, to solve the technical problems of short circuit safety hazards caused by lithium dendrites, drastic changes in lithium volume damaging the electrode structure and reducing cycle life, repeated damage to the unstable SEI film aggravating lithium consumption and performance degradation, and HF corrosion of battery components caused by the reaction.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for preparing Fe-Sn modified composite Li anode material, comprising the following steps: Step A: Measure triethylamine and fluoroethylene carbonate and add them to ethylene glycol dimethyl ether, stir, and obtain a composite solvent; Step B: Weigh FeF3 and SnF2 and add them to the composite solvent obtained in Step A. Heat and stir to obtain Fe-Sn composite solution. Step C: Drop the Fe-Sn composite liquid obtained in step B onto the surface of the lithium sheet and let it stand to obtain the Fe-Sn modified composite negative electrode Li material.

[0007] Further, the volume ratio of triethylamine, fluoroethylene carbonate (FEC), and ethylene glycol dimethyl ether in step A is 0.5-1:1:6.

[0008] Furthermore, the stirring speed in step A is 300 r / min, and the stirring time is 15 min.

[0009] Further, the mass ratio of FeF3 to SnF2 in step B is 0.05-0.113:0.104.

[0010] Furthermore, the heating temperature in step B is 45 ℃, the heating time is 120 min, and the stirring speed is 500 r / min.

[0011] The present invention also provides a Fe-Sn modified composite Li anode material, which is obtained by the above preparation method.

[0012] The Fe-Sn modified composite Li anode material prepared by the above method is applied to a lithium battery, wherein the lithium battery (button cell) is assembled sequentially from the following materials: anode shell, Fe-Sn modified composite Li anode material, separator, positive electrode sheet, gasket, spring sheet and positive electrode shell.

[0013] Furthermore, the Fe-Sn modified composite Li anode has a diameter of 12 mm.

[0014] Furthermore, the method for preparing the positive electrode sheet is as follows: S1. Weigh out NCM811, polyvinylidene fluoride and acetylene black and mix them to obtain a slurry; S2. Coat the obtained slurry onto aluminum foil, cut it into sheets, and obtain the positive electrode sheet.

[0015] Furthermore, the mass ratio of NCM811, polyvinylidene fluoride, and acetylene black in step S1 is 0.8:0.1:0.1, and the diameter of the positive electrode sheet in step S2 is 10 mm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The Fe-Sn modified composite Li anode material prepared in this application is produced by uniformly dispersing FeF3 and SnF2 powders in a mixed solvent containing dimethyl ethylene glycol (DME) and triethylamine, and then drop-coating them onto the surface of lithium metal. This allows the two fluorides to react in situ with lithium under electrochemical conditions, forming a composite interface layer with high ionic conductivity and excellent mechanical stability. The choice of DME solvent is crucial, as it not only provides good dispersibility for FeF3 and SnF2 but also avoids side reactions with lithium metal, ensuring the uniformity and controllability of the interface modification. Triethylamine, as a solvent component, can eliminate HF that may be generated during the reaction, preventing its corrosiveness from affecting battery performance.

[0017] The Fe-Sn modified composite Li anode material prepared in this application exhibits high Li affinity, excellent ionic conductivity, and high Young's modulus in its artificial interface layer, which can promote rapid ion adsorption and transport and induce Li... + Uniform deposition without dendrite formation is achieved. The LiF / Fe structure generated from the reaction of FeF3 with lithium forms the core functional unit of the interface layer. LiF provides an efficient channel for lithium-ion migration, while Fe nanoparticles, as a rigid reinforcing phase, enhance the overall mechanical stability of the interface layer and suppress local over-expansion through a framework effect. They also enhance SEI toughness and provide electron conduction pathways, reducing interface impedance, thereby promoting uniform lithium deposition and improving coulombic efficiency. To further optimize the interface structure, SnF2, with its faster reaction rate, is introduced simultaneously. The Sn nanoparticles generated from its reaction with lithium, with their excellent ductility, can precisely fill the micropores formed during the FeF3 reaction. The difference in reaction rates between the two forms a synergistic system of "rigid framework-flexible filling." This complementary structure effectively avoids interface wrinkles caused by uneven expansion during single fluoride reactions, ultimately ensuring the smoothness and integrity of the artificial interface layer.

[0018] The Fe-Sn modified composite Li anode material prepared in this application, in order to further ensure the integrity of the artificial interface layer and prevent its cracking from affecting the battery conversion efficiency, introduces fluoroethylene carbonate into the solvent to form a flexible SEI film on the surface of the artificial interface layer to repair microcracks; at the same time, the introduction of Fe can buffer the volume change during the lithium deposition / stripping process, significantly extending the battery life. Attached Figure Description

[0019] Figure 1 The coulombic efficiency and specific capacity of the composite negative electrode Li materials prepared in the examples and comparative examples are shown in the test graphs. Figure 2 (a) is Comparative Example 2. Figure 2 (b) is a SEM image of the composite negative electrode Li material prepared in Example 2; Figure 3Corrosion test image of the negative electrode battery surface of the composite negative electrode Li material prepared in Example 2; Figure 4 The impedance spectrum of the negative electrode sheet of the composite negative electrode Li material prepared in Example 2.

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0021] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0022] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0023] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0024] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0025] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0026] This invention discloses a Fe-Sn modified composite Li anode material. FeF3 and SnF2 powders are uniformly dispersed in a composite solvent and drop-coated onto a lithium metal surface. The two fluorides then react in situ with lithium under electrochemical conditions to form a composite interface layer. DME solvent provides good dispersibility for FeF3 and SnF2 without side reactions with lithium metal. Triethylamine eliminates HF that may be generated during the reaction to avoid affecting battery performance. Furthermore, fluoroethylene carbonate is introduced to form a flexible SEI film on the surface of the artificial interface layer to repair microcracks. The artificial interface layer prepared by this method exhibits high Li affinity, excellent ionic conductivity, and high Young's modulus, promoting rapid ion adsorption and transport, and inducing Li... + Uniform deposition without dendrite formation: In the LiF / Fe structure generated by the reaction of FeF3 and lithium, LiF provides an efficient channel for lithium ion migration, while Fe nanoparticles can improve the overall mechanical stability of the interface layer, suppress local over-expansion, enhance SEI toughness, provide an electronic conduction path, and reduce interface impedance. The Sn nanoparticles generated by the reaction of SnF2 and lithium can fill the tiny pores formed during the FeF3 reaction. The two form a synergistic system of "rigid framework-flexible filling", which avoids interface wrinkles caused by uneven expansion during single fluoride reaction, ensuring the flatness and integrity of the artificial interface layer. Moreover, the introduction of Fe can buffer the volume change during lithium deposition / stripping, significantly extending battery life.

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0029] The relevant test results in the following embodiments refer to Figures 1-4 Unless otherwise specified, all methods are conventional; the materials used in the following examples are all newly purchased materials unless otherwise specified.

[0030] Example 1: A method for preparing a Fe-Sn modified composite Li anode material includes the following steps: Step A: Measure 0.5 mL of triethylamine and 1 mL of fluoroethylene carbonate and add them sequentially to 6 mL of ethylene glycol dimethyl ether. Stir for 15 min at a speed of 300 r / min to obtain a composite solvent. Step B: Weigh 0.05 g FeF3 and 0.104 g SnF2 and add them to the composite solvent obtained in Step A. Heat the mixture for 120 min at a water bath temperature of 45 ℃ and stir at a speed of 500 r / min. After the mixture is finished, let it cool naturally to room temperature to obtain the Fe-Sn composite solution. Step C: Slowly drop the Fe-Sn composite solution obtained in step B onto the surface of a lithium sheet with a diameter of 12 mm, and let it stand at room temperature for 48 h to obtain the Fe-Sn modified composite negative electrode Li material.

[0031] This embodiment also provides an assembly method for a coin cell, wherein the coin cell includes the following materials: a negative electrode shell, a Fe-Sn modified composite Li negative electrode material, a PE-based separator, a positive electrode sheet, a gasket, a spring sheet, and a positive electrode shell, which are assembled into a coin cell in a glove box filled with an inert atmosphere.

[0032] The preparation method of the above-mentioned positive electrode is as follows: S1. Weigh 0.8 g NCM811, 0.1 g polyvinylidene fluoride and 0.1 g acetylene black and mix them evenly to obtain a slurry; S2. The slurry obtained in step S1 is evenly coated on aluminum foil, and then an electrode sheet with a diameter of 10 mm is cut to obtain the positive electrode sheet.

[0033] Example 2: A method for preparing a Fe-Sn modified composite Li anode material includes the following steps: Step A: Measure 0.8 mL of triethylamine and 1 mL of fluoroethylene carbonate and add them sequentially to 6 mL of ethylene glycol dimethyl ether. Stir for 15 min at a speed of 300 r / min to obtain a composite solvent. Step B: Weigh 0.08 g FeF3 and 0.104 g SnF2 and add them to the composite solvent obtained in Step A. Heat the mixture for 120 min at a water bath temperature of 45 ℃ and stir at a speed of 500 r / min. After the mixture is finished, let it cool naturally to room temperature to obtain the Fe-Sn composite solution. Step C: Slowly drop the Fe-Sn composite solution obtained in step B onto the surface of a lithium sheet with a diameter of 12 mm, and let it stand at room temperature for 48 h to obtain the Fe-Sn modified composite negative electrode Li material.

[0034] This embodiment also provides an assembly method for a coin cell, wherein the coin cell includes the following materials: a negative electrode shell, a Fe-Sn modified composite Li negative electrode material, a PE-based separator, a positive electrode sheet, a gasket, a spring sheet, and a positive electrode shell, which are assembled into a coin cell in a glove box filled with an inert atmosphere.

[0035] The preparation method of the above-mentioned positive electrode is as follows: S1. Weigh 0.8 g NCM811, 0.1 g polyvinylidene fluoride and 0.1 g acetylene black and mix them evenly to obtain a slurry; S2. The slurry obtained in step S1 is evenly coated on aluminum foil, and then an electrode sheet with a diameter of 10 mm is cut to obtain the positive electrode sheet.

[0036] Example 3: A method for preparing a Fe-Sn modified composite Li anode material includes the following steps: Step A: 1 mL of triethylamine and 1 mL of fluoroethylene carbonate were added sequentially to 6 mL of ethylene glycol dimethyl ether, and stirred for 15 min at a speed of 300 r / min to obtain a composite solvent. Step B: Weigh 0.113 g FeF3 and 0.104 g SnF2 and add them to the composite solvent obtained in Step A. Heat the mixture in a water bath at 45 °C for 120 min and stir at 500 r / min. After the mixture is finished, allow it to cool naturally to room temperature to obtain the Fe-Sn composite solution. Step C: Slowly drop the Fe-Sn composite solution obtained in step B onto the surface of a lithium sheet with a diameter of 12 mm, and let it stand at room temperature for 48 h to obtain the Fe-Sn modified composite negative electrode Li material.

[0037] This embodiment also provides an assembly method for a coin cell, wherein the coin cell includes the following materials: a negative electrode shell, a Fe-Sn modified composite Li negative electrode material, a PE-based separator, a positive electrode sheet, a gasket, a spring sheet, and a positive electrode shell, which are assembled into a coin cell in a glove box filled with an inert atmosphere.

[0038] The preparation method of the above-mentioned positive electrode is as follows: S1. Weigh 0.8 g NCM811, 0.1 g polyvinylidene fluoride and 0.1 g acetylene black and mix them evenly to obtain a slurry; S2. The slurry obtained in step S1 is evenly coated on aluminum foil, and then an electrode sheet with a diameter of 10 mm is cut to obtain the positive electrode sheet.

[0039] Comparative example: Comparative Example 1: A method for preparing a Fe-Sn modified composite Li anode material includes the following steps: Step A: Measure 0.8 mL of triethylamine and 1 mL of fluoroethylene carbonate and mix them. Stir the mixture at 300 r / min for 15 min to obtain a composite solvent. Step B: Weigh 0.08 g FeF3 and 0.104 g SnF2 and add them to the composite solvent obtained in Step A. Heat the mixture for 120 min at a water bath temperature of 45 ℃ and stir at a speed of 500 r / min. After the mixture is finished, let it cool naturally to room temperature to obtain the Fe-Sn composite solution. Step C: Slowly drop the Fe-Sn composite solution obtained in step B onto the surface of a lithium sheet with a diameter of 12 mm, and let it stand at room temperature for 48 h to obtain the Fe-Sn modified composite negative electrode Li material.

[0040] This comparative example also provides an assembly method for a coin cell, wherein the coin cell includes the following materials: a negative electrode shell, a Fe-Sn modified composite Li negative electrode material, a PE-based separator, a positive electrode sheet, a gasket, a spring sheet, and a positive electrode shell, which are assembled into a coin cell in a glove box filled with an inert atmosphere.

[0041] The preparation method of the above-mentioned positive electrode is as follows: S1. Weigh 0.8 g NCM811, 0.1 g polyvinylidene fluoride and 0.1 g acetylene black and mix them evenly to obtain a slurry; S2. The slurry obtained in step S1 is evenly coated on aluminum foil, and then an electrode sheet with a diameter of 10 mm is cut to obtain the positive electrode sheet.

[0042] Comparative Example 2: A method for preparing a Fe-Sn modified composite Li anode material includes the following steps: Step A: Measure 1 mL of fluoroethylene carbonate and 6 mL of ethylene glycol dimethyl ether and mix them. Stir at 300 r / min for 15 min to obtain a composite solvent. Step B: Weigh 0.08 g FeF3 and 0.104 g SnF2 and add them to the composite solvent obtained in Step A. Heat the mixture for 120 min at a water bath temperature of 45 ℃ and stir at a speed of 500 r / min. After the mixture is finished, let it cool naturally to room temperature to obtain the Fe-Sn composite solution. Step C: Slowly drop the Fe-Sn composite solution obtained in step B onto the surface of a lithium sheet with a diameter of 12 mm, and let it stand at room temperature for 48 h to obtain the Fe-Sn modified composite negative electrode Li material.

[0043] This comparative example also provides an assembly method for a coin cell, wherein the coin cell includes the following materials: a negative electrode shell, a Fe-Sn modified composite Li negative electrode material, a PE-based separator, a positive electrode sheet, a gasket, a spring sheet, and a positive electrode shell, which are assembled into a coin cell in a glove box filled with an inert atmosphere.

[0044] The preparation method of the above-mentioned positive electrode is as follows: S1. Weigh 0.8 g NCM811, 0.1 g polyvinylidene fluoride and 0.1 g acetylene black and mix them evenly to obtain a slurry; S2. The slurry obtained in step S1 is evenly coated on aluminum foil, and then an electrode sheet with a diameter of 10 mm is cut to obtain the positive electrode sheet.

[0045] Comparative Example 3: A method for preparing a Fe-Sn modified composite Li anode material includes the following steps: Step A: Measure 0.8 mL of triethylamine and 6 mL of ethylene glycol dimethyl ether and mix them. Stir at 300 r / min for 15 min to obtain a composite solvent. Step B: Weigh 0.08 g FeF3 and 0.104 g SnF2 and add them to the composite solvent obtained in Step A. Heat the mixture for 120 min at a water bath temperature of 45 ℃ and stir at a speed of 500 r / min. After the mixture is finished, let it cool naturally to room temperature to obtain the Fe-Sn composite solution. Step C: Slowly drop the Fe-Sn composite solution obtained in step B onto the surface of a lithium sheet with a diameter of 12 mm, and let it stand at room temperature for 48 h to obtain the Fe-Sn modified composite negative electrode Li material.

[0046] This comparative example also provides an assembly method for a coin cell, wherein the coin cell includes the following materials: a negative electrode shell, a Fe-Sn modified composite Li negative electrode material, a PE-based separator, a positive electrode sheet, a gasket, a spring sheet, and a positive electrode shell, which are assembled into a coin cell in a glove box filled with an inert atmosphere.

[0047] The preparation method of the above-mentioned positive electrode is as follows: S1. Weigh 0.8 g NCM811, 0.1 g polyvinylidene fluoride and 0.1 g acetylene black and mix them evenly to obtain a slurry; S2. The slurry obtained in step S1 is evenly coated on aluminum foil, and then an electrode sheet with a diameter of 10 mm is cut to obtain the positive electrode sheet.

[0048] The following performance tests were conducted on the composite Li anode materials prepared in the above embodiments and comparative examples: Figure 1The results show the coulombic efficiency and specific capacity of the composite negative electrode Li materials prepared in the examples and comparative examples. Among them, Example 2 showed the best overall performance in terms of specific capacity and coulombic efficiency after 500 cycles at a current density of 1C, with the specific capacity remaining stable at 167.8 mAh·g. -1 Between these two points, the Coulomb efficiency reaches 99.8%.

[0049] Figure 2 (a) is Comparative Example 1. Figure 2 (b) is a SEM image of the composite Li anode material prepared in Example 2, which clearly shows... Figure 2 (b) The uniform distribution of particles on the surface fully demonstrates that the DME solvent provides good particle dispersibility.

[0050] Figure 3 The images show the Tafel curves of the composite negative electrode Li materials prepared in the examples and comparative examples, with Example 2 showing the lowest corrosion current of 7.509 × 10⁻⁶. -6 Compared with Comparative Example 2, it can be concluded that the addition of triethylamine is very necessary to improve the corrosion of the negative electrode interface. Triethylamine can preferentially adsorb on the lithium surface to form a molecular protective film, directly reducing the contact and side reactions between the electrolyte and lithium. It helps to guide the formation of a denser and more stable SEI, prevents the formation of a loose and porous corrosion product layer, and thus improves the chemical stability of the interface.

[0051] Figure 4 The figures show the impedance test results of the composite negative electrode Li materials prepared in the examples and comparative examples. As can be seen from the figures, the impedance value of Example 2 is the lowest at 64 Ω. This is mainly due to the fact that Fe and Sn are "lithophile" metals, providing readily available, low-barrier nucleation sites for lithium deposition, which significantly reduces the charge transfer impedance. Furthermore, the generated LiF layer is very stable and has excellent ionic conductivity, which avoids the repeated formation of thick and uneven SEI layers, stabilizing the interface impedance at a low level.

[0052] In summary, this invention relates to the field of lithium metal battery technology, specifically to a Fe-Sn modified composite Li anode material, its preparation method, and its application. The Fe-Sn modified composite Li anode material is prepared by dispersing FeF3 and SnF2 in a composite solvent containing DME, triethylamine, and fluoroethylene carbonate, and then drop-coating it onto the surface of lithium metal. This allows the fluoride to react in situ with lithium to form a composite interface layer. DME ensures dispersibility and does not react with lithium, triethylamine eliminates HF, and fluoroethylene carbonate forms a CEI film to repair cracks. This interface layer exhibits high Li affinity, excellent ionic conductivity, and a high Young's modulus, and can induce Li... +Uniform deposition, with LiF providing ion channels, Fe enhancing mechanical stability, and Sn filling pores, forms a synergistic system that ensures the integrity of the interface layer. Fe can also buffer volume changes and extend battery life.

[0053] Obviously, the above comparative examples and embodiments are only a part of the comparative examples and embodiments of the present invention, and they, along with the comparative examples and embodiments referenced based on such examples, are all within the scope of protection of this invention.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0055] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

[0056] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for preparing a Fe-Sn modified composite Li anode material, characterized in that, Includes the following steps: Step A: Add triethylamine and fluoroethylene carbonate to ethylene glycol dimethyl ether and stir to obtain a composite solvent; Step B: Add FeF3 and SnF2 to the composite solvent obtained in step A, heat and stir to obtain Fe-Sn composite solution; Step C: Drop the Fe-Sn composite liquid obtained in step B onto the surface of the lithium sheet and let it stand to obtain the Fe-Sn modified composite negative electrode Li material.

2. The method for preparing the Fe-Sn modified composite Li anode material according to claim 1, characterized in that, In step A, the volume ratio of triethylamine, fluoroethylene carbonate, and ethylene glycol dimethyl ether is 0.5-1:1:

6.

3. The method for preparing the Fe-Sn modified composite Li anode material according to claim 1, characterized in that, In step A, the stirring speed is 300 r / min and the stirring time is 15 min.

4. The method for preparing the Fe-Sn modified composite Li anode material according to claim 1, characterized in that, In step B, the mass ratio of FeF3 to SnF2 is 0.05-0.113:0.

104.

5. The method for preparing the Fe-Sn modified composite Li anode material according to claim 1, characterized in that, In step B, the heating temperature is 45°C, the heating time is 120 min, and the stirring speed is 500 r / min.

6. A Fe-Sn modified composite Li anode material prepared by the preparation method of Fe-Sn modified composite Li anode material according to any one of claims 1-5.

7. The application of the Fe-Sn modified composite Li anode material as described in claim 6 in lithium batteries, characterized in that, The lithium battery is assembled from the following materials in sequence: negative electrode shell, Fe-Sn modified composite Li negative electrode material, separator, positive electrode sheet, gasket, spring sheet and positive electrode shell.

8. The application of the Fe-Sn modified composite Li anode material according to claim 7 in lithium batteries, characterized in that, The Fe-Sn modified composite Li anode material has a diameter of 12 mm.

9. The application of the Fe-Sn modified composite Li anode material according to claim 7 in lithium batteries, characterized in that, The method for preparing the positive electrode sheet is as follows: S1. Weigh out NCM811, polyvinylidene fluoride and acetylene black and mix them to obtain a slurry; S2. Coat the obtained slurry onto aluminum foil, cut it into sheets, and obtain the positive electrode sheet.

10. The application of the Fe-Sn modified composite Li anode material according to claim 9 in lithium batteries, characterized in that, In S1, the mass ratio of NCM811, polyvinylidene fluoride, and acetylene black is 0.8:0.1:0.

1. In S2, the diameter of the positive electrode is 10 mm.

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