Preparation method of negative electrode material and battery

Abstract

The application provides a preparation method of a negative electrode material, comprising the following steps: (1) providing a precursor solution, wherein the precursor solution comprises tin tetrachloride and ammonium fluoride; (2) providing a pretreated substrate material; (3) soaking the substrate material into the precursor solution; (4) taking out the substrate material, and growing a fluorine-doped tin dioxide sample on the surface of the pretreated substrate material; and (5) placing the sample obtained in the step (4) in a CVD furnace to perform surface in-situ graphene growth, and obtaining a fluorine-doped tin dioxide / graphene material grown on the surface of the substrate material. In the application, the tin dioxide is doped with fluorine when the tin dioxide is synthesized, so that the tin dioxide has conductivity, then the in-situ graphene growth is performed on the surface of the fluorine-doped tin dioxide, so that the conductivity of the tin dioxide is further improved, and the expansion of the tin dioxide is inhibited, which provides an important reference for the research and application of the tin dioxide negative electrode.

Description

Technical Field

[0001] This invention relates to the field of graphene materials, and in particular to a negative electrode material and a battery containing such a negative electrode material. Background Technology

[0002] With the rapid development of energy storage technology, especially the rapid development of lithium-ion power batteries under the "dual-carbon policy," the high capacity and fast-charging performance of lithium-ion batteries have attracted much attention. Compared with the relatively mature development of high-capacity cathode materials such as high-nickel ternary materials, the research and development of high-capacity anode materials for lithium-ion batteries has been slower. The theoretical lithium intercalation capacity of traditional graphite anodes is 372 mAh / g, while emerging anode materials such as silicon-based, tin-based, and transition metal oxides have higher lithium intercalation capacities. Among them, tin dioxide has a theoretical lithium intercalation capacity as high as 782 mAh / g, making it one of the more ideal next-generation high-capacity anode materials. However, tin dioxide as an anode material has two drawbacks: poor conductivity and volume expansion (-300%), which are also the two major pain points faced by tin-based materials in the application of anode materials. Summary of the Invention

[0003] To address the aforementioned problems, a method for preparing an anode material is provided. Tin dioxide is used as the active material, and its conductivity is improved and its volume expansion is suppressed through fluorine doping and in-situ graphene growth modification on the tin dioxide surface. Generally, the reaction equation between tin-based oxides as anode materials and lithium is:

[0004] SnO2+4Li + →Sn+2Li2O

[0005] Sn+xLi + +xe - →Li x Sn (0≤x≤4.4)

[0006] The first step in the reaction of tin dioxide with lithium is to remove the Sn from the tin dioxide. 4+The lithium reduction process generates metallic tin and lithium oxide. The first stage of the reaction is an irreversible reduction-substitution reaction. The second stage involves the alloying of the generated metallic tin with lithium. This second stage is the main source of reversible capacity, but the alloying process of metallic tin and lithium causes significant volume changes, affecting the battery's cycle performance. In the synthesis of tin dioxide, fluorine doping enhances its conductivity, improving its intrinsic conductivity. Then, graphene is grown in situ on the surface of the fluorine-doped tin dioxide using chemical vapor deposition. The in-situ grown graphene not only further improves the conductivity of tin dioxide but also helps to suppress its volume expansion. Furthermore, during the in-situ graphene growth process, the carbon atoms in the high-temperature atmosphere reduce the tin atoms on the tin dioxide surface, allowing lithium ions to directly alloy with the reduced tin, further suppressing volume expansion to some extent. The preparation method of this negative electrode material is as follows:

[0007] (1) A precursor solution is provided, wherein the precursor solution comprises tin tetrachloride and ammonium fluoride. Preferably, the mass fraction of tin tetrachloride is 10-30%, and the mass fraction of ammonium fluoride is 0.01-0.05%. The addition of ammonium fluoride within this mass fraction range can achieve fluorine doping of tin oxide, so that the non-conductive tin oxide forms conductive fluorine-doped tin oxide, thereby improving the conductivity of the negative electrode material. In addition, fluorine doping is beneficial to provide a fluorine source during the formation of the SEI film, reducing the loss of fluorine source in the electrolyte components and reducing the decomposition of fluorine-containing components in the electrolyte, thus ensuring the efficiency of the electrolyte. Typically, but not limitingly, the mass fraction of tin tetrachloride is 10%, 15%, 20%, 25%, or 30%, and the mass fraction of ammonium fluoride is 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%.

[0008] (2) Provide a pretreated substrate material, wherein the substrate material is a growth substrate for fluorine-doped tin dioxide for in-situ growth of graphene on the surface.

[0009] Preferably, the substrate material is carbon fiber cloth. The pretreatment involves immersing the carbon fiber cloth in a 0.5-2M nitric acid solution for 10-24 hours. After immersion, the cloth is removed and washed with deionized water until the pH value is neutral. To ensure thorough immersion, the cloth can be immersed in a heated plate at 50-80°C. Pretreatment of the carbon fiber cloth with nitric acid gives it a more ideal load-bearing capacity. Furthermore, using carbon fiber cloth as the substrate material eliminates the need for coating, unlike traditional anode materials, allowing it to be used directly as a thin-film anode.

[0010] Preferably, the substrate material is a flat substrate similar to FTO glass or metal foil, and is preferably any one of FTO glass or metal foil. The pretreatment refers to vertically placing the substrate material into an ethanol dispersion of polystyrene microspheres and evaporating it to dryness at 60-90°C. The mass fraction of the ethanol dispersion of polystyrene microspheres is 0.02-1%, which ensures that the polystyrene microspheres are fully dispersed in the solution and avoids agglomeration and deposition. In addition, the polystyrene microspheres are monodisperse polystyrene microspheres. The purpose of evaporating the substrate material into the ethanol dispersion of polystyrene microspheres is to ensure that the polystyrene microspheres in the dispersion are neatly loaded and arranged on the substrate surface, thereby forming a honeycomb structure, providing an ideal expansion buffer space for subsequent tin dioxide.

[0011] Of course, the choice of substrate material is not limited to the above preferred methods.

[0012] (3) Immerse the pretreated substrate material in the precursor solution for a preferred time of 0.5-2h, so that the pretreated substrate material contains fluoride ions and tin ions.

[0013] (4) Growth of fluorine-doped tin dioxide samples on the surface of the pretreated substrate material. The substrate material is subjected to high-temperature treatment and / or microwave irradiation treatment. The high-temperature treatment temperature is 600-700℃, and the microwave irradiation treatment is microwave irradiation at a power of 800-1000W for 5-10 minutes. In this way, trace amounts of fluorine-doped tin dioxide can be grown on the substrate material. The introduction of fluorine ions enables the non-conductive tin dioxide active material particles to become conductive.

[0014] (5) The sample obtained in step (4) is placed in a CVD furnace for in-situ surface graphene growth to obtain fluorine-doped tin dioxide / graphene material grown on the surface of the substrate material. The growth temperature of the graphene is 900-1150℃, and the carbon source for growth is one or more of ethylene, methane, acetylene, propylene, and butane, preferably ethylene. By growing velvety graphene in situ on the surface of fluorine-doped tin dioxide, the volume expansion of tin dioxide active material particles during lithium ion insertion / extraction is suppressed to a certain extent, further improving the conductivity of tin dioxide active material. At the same time, during the in-situ growth of graphene, carbon atoms in the high-temperature atmosphere have a reducing effect on tin atoms on the surface of tin dioxide, and lithium ions can be directly alloyed with the reduced tin on the surface, which suppresses the volume expansion to a certain extent.

[0015] On the other hand, a battery is provided that includes the negative electrode material prepared by the above-described preparation method.

[0016] The beneficial effects of this invention are as follows:

[0017] 1. Improve the intrinsic conductivity of tin dioxide by doping with trace amounts of fluorine, so that the non-conductive tin dioxide active material particles become conductive;

[0018] 2. Graphene is grown in situ on the surface of tin dioxide by CVD, which further improves the conductivity of the active material of tin dioxide. At the same time, during the in-situ growth of graphene, carbon atoms in the high-temperature atmosphere have a reducing effect on tin atoms on the surface of tin dioxide. Lithium ions can be directly alloyed with the reduced tin on the surface, which suppresses volume expansion to a certain extent.

[0019] 3. This application provides important reference and guidance for the research and application of tin dioxide anodes. Implementation

[0020] The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and does not limit the description of the features and characteristics of the invention, in order to suggest the best mode for carrying out the invention and to enable those skilled in the art to practice the invention. However, it should be understood that various modifications and variations can be made without departing from the scope of the invention as defined by the appended claims. The detailed description should be considered illustrative only and not restrictive, and any such modifications and variations shall fall within the scope of the invention described herein. Furthermore, the background art is intended to illustrate the current state of research and development and significance of the technology, and is not intended to limit the invention or the scope of application of this application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0023] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0024] Example 1: This example provides a method for preparing a carbon fiber cloth film / fluorine-doped tin dioxide / graphene anode material. The specific steps are as follows:

[0025] 1) Preparation of precursor solution: Prepare an ethylene glycol solution containing 0.2% by mass of PVP-K30. Stir until PVP-K30 is completely dissolved, and then slowly add 20% by mass of tin tetrachloride, 0.3% by mass of hydrochloric acid and 0.03% by mass of ammonium fluoride under stirring. Continue stirring for 8 hours to obtain the precursor solution.

[0026] 2) Carbon fiber cloth pretreatment: Cut 5cm*5cm carbon fiber cloth and put it into 1M nitric acid solution. Soak it in a 70℃ heated plate for 10 hours. After soaking, take it out and wash it several times with deionized water until the pH of the cleaning solution is neutral.

[0027] 3) Immerse the pretreated carbon fiber cloth obtained in step 2) in the precursor solution prepared in step 1) and let it stand for 1 hour.

[0028] 4) The sample obtained in step 3) is transferred to a microwave oven and irradiated with microwave at 900W power for 8 minutes. The carbon fiber cloth is then removed and washed repeatedly with deionized water until the pH value of the cleaning solution is neutral. The cloth is then removed and transferred to a 70℃ forced-air drying oven to dry the moisture, thus obtaining a fluorine-doped tin dioxide sample grown in situ on the surface of the carbon fiber cloth.

[0029] 5) Place the thin film sample obtained in step 4) in a cold-wall CVD furnace for in-situ surface graphene growth, introduce ethylene / argon mixed gas, grow at 950℃ for 2 hours, and remove the sample after the furnace has cooled to room temperature to obtain a carbon fiber cloth film / fluorine-doped tin dioxide / graphene sample.

[0030] The obtained carbon fiber cloth film / fluorine-doped tin dioxide / graphene sample was directly cut into 12mm discs and used directly as the negative electrode for coin cell assembly and performance testing. The results showed that the resistivity of this negative electrode material was 0.941 Ω·cm, exhibiting excellent conductivity. At the initial charge / discharge of 0.1C / 0.1C, the discharge specific capacity was 652 mAh / g, and under 0.5C / 1C cycling conditions, the capacity retention reached 80% after 517 cycles. The nano-sized fluorine-doped tin dioxide and the in-situ grown graphene not only improved conductivity but also significantly suppressed the volume expansion problem of the negative electrode substrate, achieving relatively ideal cycle performance.

[0031] Example 2 differs from Example 1 in that, in step 5), argon gas is introduced for atmosphere protection instead of ethylene. All other steps are the same as in Example 1. The purpose is to investigate the effect of in-situ graphene growth on the performance of this anode material. Results show that the resistivity of this anode material is 2.732 Ω·cm; the discharge specific capacity is 663 mAh / g at the first charge / discharge at 0.1C / 0.1C; and the capacity retention reaches 80% after 427 cycles under 0.5C / 1C cycling conditions. This can be attributed to the fact that while the lack of in-situ graphene modification increases the electrode resistivity, it also weakens the suppression of volume expansion of the anode material, leading to decreased cycle performance.

[0032] Example 3 differs from Example 1 in that hydrogen gas is used instead of ethylene gas in step 5), and a hydrogen / argon mixed gas is used for treatment. The remaining steps are the same as in Example 1. The purpose is to investigate the effects of tin dioxide surface reduction and oxygen etching on the performance of this anode material. Results show that the conductivity of this anode material is 2.906 Ω·cm; the discharge specific capacity is 697 mAh / g during the first charge / discharge at 0.1C / 0.1C; and the capacity retention reaches 80% after 474 cycles under 0.5C / 1C cycling conditions. This can be attributed to the partial reduction of the tin dioxide surface by H2 at high temperatures, leading to a certain imbalance in fluorine doping, thus slightly increasing the electrode resistivity. According to the anode reaction mechanism: SnO2 + 4Li + →Sn + 2Li₂O, Sn + xLi + +xe - →Li x For Sn (0≤x≤4.4), it can be seen that lithium ions can be directly alloyed with surface-reduced tin, which suppresses volume expansion to a certain extent, thus slightly improving cycle performance.

[0033] Example 4 differs from Example 1 in that ammonium fluoride is not added during the preparation of the precursor solution in step 1), i.e., tin dioxide is not fluorinated. Other steps are the same as in Example 1. The purpose is to investigate the effect of fluorine doping on the performance of the anode material. Results show that the conductivity of this anode material is 2.33 Ω·cm; the discharge specific capacity is 644 mAh / g during the first charge / discharge at 0.1C / 0.1C; and the capacity retention reaches 80% after 375 cycles under 0.5C / 1C cycling conditions. This can be attributed to the lack of fluorine doping, which reduces the conductivity of the tin dioxide particles and hinders electron transfer between particles. Furthermore, the absence of fluorine doping leads to the loss of some fluorine-containing components in the electrolyte during SEI film formation, resulting in decreased electrolyte efficiency and thus reduced cycle performance.

[0034] Example 5: This example provides a method for preparing a copper foil / inverse protein structure fluorine-doped tin dioxide / graphene anode material. The specific steps are as follows:

[0035] 1) Preparation of precursor solution: Prepare an aqueous solution containing 0.01%-0.05% by mass of ammonium fluoride and 20% by mass of tin tetrachloride.

[0036] 2) Copper foil pretreatment: The copper foil was ultrasonically cleaned with acetone, ethanol and deionized water respectively to remove the dust and organic impurities on the surface of the copper foil. The copper foil was then placed vertically into a transparent glass bottle containing an ethanol dispersion of 0.8% by mass of polystyrene microspheres, with the copper foil close to the bottle wall and the growth side exposed in the dispersion. The transparent glass bottle was then transferred to an oven at 75°C and allowed to stand and evaporate to dryness. The purpose of this method is to utilize the surface tension of the liquid surface during the evaporation of the ethanol solution and the slow descent of the liquid level to neatly load and arrange the polystyrene microspheres in the polystyrene microsphere dispersion on the surface of the copper foil.

[0037] 3) Immerse the copper foil with neatly arranged polystyrene microspheres obtained in step 2) in the precursor solution prepared in step 1) and let it stand for 1 hour. The copper foil is placed vertically, and the polystyrene microspheres on its surface absorb fluoride ions and tin ions by immersion.

[0038] 4) After soaking, the sample is taken out and transferred to a muffle furnace for heat treatment at 600-700℃ in air atmosphere. Fluorine-doped tin dioxide samples with copper foil / inverse opal structure are obtained by in-situ growth.

[0039] 5) Transfer the sample obtained in step 4) to a CVD furnace and grow a graphene layer in situ on the surface of a fluorine-doped tin dioxide framework at 1000℃. The carbon source gas is ethylene gas, and the auxiliary gas is a mixture of 10% hydrogen and 90% nitrogen gas to obtain a copper foil / inverse opal structure fluorine-doped tin dioxide / graphene anode material.

[0040] The prepared copper foil / inverse opal structure fluorine-doped tin dioxide / graphene anode material, due to its unique layered honeycomb structure, provides an ideal expansion buffer space for the tin dioxide active material. The obtained sample was directly cut into sheets and used as an anode for coin cell assembly and performance testing. The results showed that the conductivity of this anode material was 1.14 Ω·cm; the discharge specific capacity was 621 mAh / g at the first charge / discharge at 0.1C / 0.1C; and the capacity retention reached 80% after 1291 cycles under 0.5C / 1C cycling conditions. This embodiment showed a significant improvement in cycle performance compared to Example 1, while other properties remained largely unchanged. This can be attributed to the long-range ordered arrangement of polystyrene microspheres in the anode prepared in this embodiment, which, after sintering, yields a layered, long-range ordered inverse opal structure, providing excellent suppression of volume expansion and thus achieving better cycle performance.

[0041] Comparative Example 1 differs from Example 1 in that ammonium fluoride is not added during the preparation of the precursor solution in step 1), i.e., tin dioxide is not fluorinated; and argon gas is introduced for atmosphere protection instead of ethylene in step 5). The remaining steps are the same as in Example 1. The purpose is to investigate the effects of fluorine doping and in-situ graphene growth on the performance of the anode material using carbon fiber cloth as a substrate. The results show that the resistivity of this anode material is 6.07 Ω·cm; the discharge specific capacity is 488 mAh / g during the first charge / discharge at 0.1C / 0.1C; and the capacity retention reaches 80% after 174 cycles under 0.5C / 1C cycling conditions. This can be attributed to the lack of fluorine doping and in-situ graphene surface modification, resulting in poor conductivity of the anode sheet, difficulty in electron transfer between the main material particles and the copper foil current collector, higher internal resistance, and deteriorated cycling performance.

[0042] Comparative Example 2 differs from Example 5 in that ammonium fluoride is not added during the preparation of the precursor solution in step 1), i.e., tin dioxide is not fluorinated; and in step 5), a mixture of 10% hydrogen and 90% nitrogen is introduced for protection instead of ethylene. The remaining steps are the same as in Example 5. The purpose is to investigate the effects of fluorine doping and in-situ graphene growth on the performance of the anode material using copper foil as a substrate. The results show that the resistivity of this anode material is 2.13 Ω·cm; the discharge specific capacity is 573 mAh / g during the first charge / discharge at 0.1C / 0.1C, with an initial efficiency of 58.5%; and under 0.5C / 1C cycling conditions, the capacity retention reaches 80% after 618 cycles.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a negative electrode material, characterized in that, The steps include: (1) providing a precursor solution, wherein the precursor solution comprises tin tetrachloride and ammonium fluoride; (2) Provide pretreated substrate material; (3) Immerse the substrate material in the precursor solution; (4) Take out the substrate material and perform high temperature treatment and / or microwave irradiation treatment. The high temperature treatment temperature is 600-700℃, and the microwave irradiation treatment is microwave irradiation at 800-1000W power for 5-10 minutes, so as to grow fluorine-doped tin dioxide sample on the surface of the pretreated substrate material; (5) Place the sample obtained in step (4) in a CVD furnace to grow graphene in situ on the surface, and obtain fluorine-doped tin dioxide / graphene material grown on the surface of the substrate material.

2. A method for preparing the negative electrode material according to claim 1, characterized in that, The tin tetrachloride has a mass fraction of 10-30%, and the ammonium fluoride has a mass fraction of 0.01-0.05%.

3. A method for preparing the negative electrode material according to claim 1, characterized in that, The soaking time in step (3) is 0.5-2 hours.

4. A method for preparing the negative electrode material according to claim 1, characterized in that, When the sample obtained in step (4) is placed in an inert gas atmosphere in a CVD furnace for in-situ surface graphene growth, the carbon source for growth is one or more of ethylene, methane, acetylene, propylene, and butane gases, and the carbon source gas partially reduces the fluorine-doped tin dioxide.

5. A method for preparing the negative electrode material according to claim 4, characterized in that, The carbon source for growth is ethylene.

6. A method for preparing the negative electrode material according to claim 1, characterized in that, The substrate material is carbon fiber cloth. Before immersing the carbon fiber cloth in the precursor solution, the carbon fiber cloth is immersed in a 0.5-2M nitric acid solution for 10-24 hours. After immersion, the carbon fiber cloth is taken out and washed with deionized water until the pH value is neutral.

7. A method for preparing the negative electrode material according to claim 1, characterized in that, The substrate material is either FTO glass or metal foil. The substrate material is characterized in that, before immersing it in the precursor solution, it is placed vertically in an ethanol dispersion of polystyrene microspheres and evaporated to dryness at 60-90°C.

8. A method for preparing the negative electrode material according to claim 7, characterized in that, The mass fraction of the ethanol dispersion of the polystyrene microspheres is 0.02-1%.

9. A battery, characterized in that, The negative electrode material includes the preparation method described in any one of claims 1-8.