Preparation method of lithium ion battery negative electrode material

Abstract

The invention provides a preparation method of a lithium ion battery negative electrode material, which comprises the following steps: respectively dispersing nano silicon monoxide in an organic solution, then adding a carbon source for compounding, and sequentially carrying out ultrasonic dispersion, high-speed stirring and high-temperature carbonization to obtain a SiO / C composite material; naturally cooling the SiO / C composite material, crushing, and carrying out acid treatment by using a hydrofluoric acid solution; and impregnating the SiO / C composite material subjected to acid treatment in a carbon source, drying, and carrying out high-temperature carbonization to obtain the lithium ion battery negative electrode material. According to the preparation method disclosed by the invention, the volume expansion of silicon is remarkably reduced, the cycle life of the lithium ion battery is effectively prolonged, the mechanical strength of the porous nano silicon is improved, the compaction density of the porous nano silicon / carbon is improved, the specific surface area of the composite material is reduced, and the first coulombic efficiency of the lithium ion battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material preparation technology, and in particular relates to a method for preparing a lithium-ion battery anode material. Background Technology

[0002] Lithium-ion batteries, with their superior performance characteristics such as high operating voltage, small size, long cycle life, high specific energy, and no memory effect, are now widely used as power sources for small electronic devices such as mobile phones, computers, and cameras. They are also involved in various technological fields including aviation, marine, and artificial satellites, making them an ideal energy source for the 21st century. Currently, the most widely used anode material is graphite, but its theoretical specific capacity is only 372 mAh / g, which is far from sufficient for the future development of new energy fields.

[0003] With in-depth research, silicon is considered a promising anode material for next-generation lithium-ion batteries, with a theoretical specific capacity as high as 4200 mAh / g. However, in practical applications, silicon anodes experience significant volume expansion during Li-ion insertion and extraction, with expansion reaching up to 300%. This leads to particle breakage, material pulverization during charge and discharge, and electrode structure damage, resulting in a significant decrease in cycle performance. Although SiO has better cycle performance than silicon, it generates Li2O and Li4SiO4 during the first charge, causing low coulombic efficiency. To address this issue, CN108987668A discloses a silicon-carbon composite anode material, its preparation method, and a lithium-ion battery. This patent aims to solve the problems of particle pulverization and decreased cycle performance caused by the volume expansion of silicon particles during charge and discharge. Its core technical solution is to construct a composite structure of porous silicon-based particles and a carbon layer, including: a porous structure: providing internal space for the volume expansion of silicon, effectively buffering stress and preventing particle breakage; and a carbon coating layer: acting as a conductive network to improve the conductivity of the material, and acting as an "elastic binding layer" to constrain the silicon particles together, preventing them from easily dispersing even during expansion, thus maintaining the integrity of the electrode structure. This patent, through micro-nano structure design, "turns the harm into benefit" of silicon expansion (utilizing pores to accommodate expansion), which is one of the most mainstream technical routes in the industry. US 2021 / 0151554 A1 discloses a pre-lithiated silicon-based negative electrode active material for lithium-ion batteries and its preparation method. This patent uses pre-lithiation—before battery assembly and the first charge, to pre-add a portion of the lithium source to the negative electrode material, that is, to treat silicon-based materials (which can be nano-silicon or SiO) with stable lithium metal powder or lithides in a specific atmosphere, so that a portion of the lithium reacts with the silicon in advance, compensating for the irreversible lithium consumed in the subsequent formation of the SEI film and the generation of Li2O in the battery. Pre-lithiation technology can significantly improve the initial coulombic efficiency and overall energy density of batteries. However, the existing technologies mentioned above all suffer from problems such as complex operation and unsatisfactory cycle performance. Therefore, the market urgently needs to design novel anode materials for the future development of lithium-ion batteries. Summary of the Invention

[0004] In view of this, the present invention aims to overcome the defects in the prior art and proposes a method for preparing a negative electrode material for lithium-ion batteries.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a lithium-ion battery anode material, comprising the following steps: S1: After dispersing nano-silica in an organic solution, a carbon source is added for composite formation. The SiO / C composite material is obtained by ultrasonic dispersion, high-speed stirring and high-temperature carbonization in sequence. S2: The SiO / C composite material was naturally cooled and then crushed, and then acid-treated with hydrofluoric acid solution. S3: The acid-treated SiO / C composite material is impregnated with a carbon source, dried, and then carbonized again at high temperature to obtain the lithium-ion battery anode material.

[0006] Preferably, the ultrasonic dispersion and high-speed stirring in step S1 are performed alternately for a duration of 2 to 2.5 hours.

[0007] Preferably, the heating rate of the high-temperature carbonization in steps S1 and S3 is 4.8~5.2℃ / min, the constant temperature is 780~820℃, and the holding time is 1~1.2h.

[0008] Preferably, the median particle size D50 of the nano-silica is 40 nm to 1000 nm.

[0009] Preferably, the carbon source in steps S1 and S3 is one or more of asphalt, phenolic resin, and biomass materials.

[0010] Preferably, the mass ratio of carbon source to nano-silica in step S1 is (0.95~1.05):(0.95~1.05).

[0011] Preferably, the high-temperature carbonization in steps S1 and S3 is carried out under vacuum conditions, with a vacuum degree of 1×10⁻⁶. - 1 Pa-1×10 -5 Pa.

[0012] Preferably, an inert gas is introduced during the high-temperature carbonization process in steps S1 and S3, and the inert gas is one or a mixture of several of argon, helium, and nitrogen.

[0013] Preferably, the acid treatment method in step S2 is as follows: using a 1.2wt%~2.4wt% HF solution to treat for 60min~65min at a temperature of 60℃-80℃.

[0014] Preferably, the carbon content in the lithium-ion battery anode material accounts for 75%-85% of the total mass.

[0015] Secondly, the present invention also provides a lithium-ion battery anode material prepared by the above preparation method.

[0016] Thirdly, the present invention also provides the application of the above-mentioned lithium-ion battery anode material in the preparation of lithium-ion batteries.

[0017] Compared with the prior art, the present invention has the following advantages: (1) In the prior art, silicon suboxide is used as the negative electrode material of lithium-ion batteries. During the first lithium intercalation process, Li2O and Li4SiO4 are generated, resulting in a relatively low initial coulombic efficiency of the battery, which affects the electrochemical performance of the battery. In contrast, the present invention converts the carbon source into carbon through high-temperature carbonization and coats it on the surface of silicon suboxide. This improves the conductivity of SiO, delays the volume expansion of the particles, and enhances the cycle stability of the lithium-ion battery. At the same time, the coated carbon layer reduces the reactivity of nano-SiO with hydrofluoric acid, making it easier to control the reaction rate. (2) For silicon-based anode materials, the smaller the particle size, the smaller the expansion effect. The method of the present invention suppresses the severe volume effect in silicon-based anode materials and provides the best reaction conditions. The SiO2 component in the SiO / C composite material is removed by hydrofluoric acid treatment to obtain a porous nano-silicon / carbon composite material. The Si particles with a size of 2-3 nanometers in SiO are retained, which significantly reduces the volume expansion of silicon. Then, through further impregnation, the pores of the porous nano-silicon are filled with carbon, which significantly reduces the volume expansion of silicon, effectively prolongs the cycle life of lithium-ion batteries, improves the mechanical strength of porous nano-silicon, increases the compaction density of porous nano-silicon / carbon, reduces the specific surface area of ​​the composite material, and improves the first coulombic efficiency of lithium-ion batteries. (3) The operation process of this invention is simple and the required conditions are easy to achieve. After the novel negative electrode material prepared is assembled into a button cell and its performance is tested, it is found that the specific capacity of the battery after 100 cycles reaches 823 mAh / g-910 mAh / g, which has excellent cycle performance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the lithium-ion battery anode material prepared according to the present invention; Figure 2 The pore size distribution before and after carbon filling in Example 1; Figure 3 The discharge specific capacity curve of the negative electrode material prepared in Example 1 is shown. Figure 4 The discharge specific capacity curve of the negative electrode material prepared in Example 2 is shown. Figure 5 This is a discharge specific capacity curve of the negative electrode material prepared in Example 3; Figure 6 The discharge specific capacity curves of the negative electrode materials prepared in Comparative Examples 4 and 5 and Comparative Examples 1 and 2 are shown. Figure 7 The discharge specific capacity curves of the negative electrode materials prepared in Comparative Examples 6 and 7 and Comparative Examples 1 and 3 are shown. Figure 8 Here is a SEM image of the negative electrode material obtained in Comparative Example 4; Figure 9 Here is a SEM image of the negative electrode material obtained in Comparative Example 5; Figure 10 Here is a SEM image of the negative electrode material obtained in Comparative Example 6; Figure 11 This is a SEM image of the negative electrode material obtained in Comparative Example 7. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0020] In this document, 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 application pertains.

[0021] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0022] In this article, the terms "multiple" or "more than" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0023] In this document, the terms "preferred" and "more preferred" are used only to describe implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0024] In this document, terms such as "further" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0025] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0026] In this document, the term "about" means a specified value of + / - 10%, preferably + / - 5%, and more preferably + / - 1%.

[0027] In this article, the terms “include,” “including,” “have,” “contain,” etc., are all open-ended terms, meaning that they include but are not limited to.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention.

[0029] The present invention will be described in detail below with reference to the embodiments.

[0030] Example 1

[0031] S1: Asphalt was mixed with tetrahydrofuran solvent to obtain an impregnation solution. Silica with a median particle size D50 of 50 nm was then added for composite formation, wherein the mass ratio of asphalt to silica was 1:1. The SiO / C composite material was obtained by ultrasonic dispersion, high-speed stirring, and high-temperature carbonization. Ultrasonic dispersion and high-speed stirring were alternated for 2 hours, with a heating rate of 5℃ / min, a constant temperature of 800℃, and a holding time of 1 hour.

[0032] S2: After the SiO / C composite material has cooled naturally, it is crushed and classified, and then treated with 1.2wt%HF at 80℃ for 65 min. S3: The acid-treated SiO / C composite material is immersed in the impregnation solution, dried, and then subjected to a vacuum of 1×10⁻⁶. -1 High-temperature carbonization under Pa conditions yields lithium-ion battery anode materials.

[0033] In step S1, after the asphalt is calcined and carbonized at high temperature, a dense protective layer is formed and adheres to the SiO surface, thereby inhibiting the volume expansion of SiO. In step S2, the SiO2 component in the SiO / C composite material is removed using hydrofluoric acid treatment, resulting in a porous nano-silicon / carbon composite material that retains silicon grains with a size of less than 3 nm in the SiO medium. In step S3, the pores left by the removal of SiO2 component from SiO by hydrofluoric acid are filled with carbon, improving the mechanical strength of the porous silicon, thereby increasing the compaction density of the silicon-carbon composite material and further improving its energy density. The pore size distribution before and after filling is as follows: Figure 2 As shown in Figure 2, by filling with carbon, the conductivity of silicon is enhanced, the specific surface area of ​​porous silicon is reduced, and the first coulombic efficiency of silicon-carbon materials is improved.

[0034] The carbon content in the negative electrode material prepared in this embodiment reached 78% through testing. The prepared negative electrode material was then assembled into a button cell for electrochemical performance testing, and the results are as follows: Figure 2 As shown, the final specific capacity remained at 910 mAh / g after 100 cycles.

[0035] Example 2

[0036] S1: Phenolic resin was mixed with tetrahydrofuran solvent to obtain an impregnation solution. Silica with a median particle size D50 of 40 nm was then added for composite formation. The mass ratio of bitumen to silica was 0.95:1.05. SiO / C composite materials were obtained through ultrasonic dispersion, high-speed stirring, and high-temperature carbonization. Ultrasonic dispersion and high-speed stirring were alternated for 2 hours, with a heating rate of 4.8℃ / min, a constant temperature of 820℃, and a holding time of 1.2 hours.

[0037] S2: After the SiO / C composite material has cooled naturally, it is crushed and classified, and then treated with 1.2wt%HF at 60℃ for 60 min. S3: The acid-treated SiO / C composite material is immersed in the impregnation solution, dried, and then subjected to a vacuum of 1×10⁻⁶. -5 High-temperature carbonization under Pa conditions yields lithium-ion battery anode materials.

[0038] The carbon content in the negative electrode material prepared in this embodiment reached 80% through testing. The prepared negative electrode material was then assembled into a button cell for electrochemical performance testing, and the results are as follows: Figure 4 As shown, this novel anode material exhibits high discharge specific capacity, initial coulombic efficiency, and good cycle stability, which is attributed to the filling of porous silicon pores. The final specific capacity remains at 851 mAh / g after 100 cycles.

[0039] Example 3

[0040] S1: Phenolic resin was mixed with tetrahydrofuran solvent to obtain an impregnation solution. Silica with a median particle size D50 of 1000 nm was then added for composite formation. The mass ratio of bitumen to silica was 1.05:0.95. SiO / C composite materials were obtained through ultrasonic dispersion, high-speed stirring, and high-temperature carbonization. Ultrasonic dispersion and high-speed stirring were alternated for 2.2 h, with a heating rate of 5.2 °C / min, a constant temperature of 780 °C, and a holding time of 1 h.

[0041] S2: After the SiO / C composite material has cooled naturally, it is crushed and classified, and then treated with 2.4wt%HF at 60℃ for 60 min. S3: The acid-treated SiO / C composite material is immersed in the impregnation solution, dried, and then subjected to a vacuum of 1×10⁻⁶. -5 High-temperature carbonization under Pa conditions yields lithium-ion battery anode materials.

[0042] The carbon content in the negative electrode material prepared in this embodiment reached 85% through testing. The prepared negative electrode material was then assembled into a button cell for electrochemical performance testing, and the results are as follows: Figure 5As shown, this novel anode material exhibits high discharge specific capacity, initial coulombic efficiency, and good cycle stability, which is attributed to the filling of porous silicon pores. The final specific capacity remains at 823 mAh / g after 100 cycles.

[0043] Comparative Example 1 Electrochemical performance tests were conducted on button cells constructed using nano-silicon suboxide with a median particle size (D50) of 50 nm as the negative electrode material. The results are as follows: Figure 6 , Figure 7 As shown, the anode material exhibits a high specific capacity of 2048 mAh / g during the first discharge. However, after 100 cycles, the exposed SiO particles expand dramatically, causing its final discharge specific capacity to remain at 28 mAh / g.

[0044] Comparative Example 2 Carbon materials were obtained by high-temperature carbonization of asphalt at a heating rate of 5℃ / min and a constant temperature of 800℃. After natural cooling, the materials were pulverized and graded to obtain the negative electrode material. Electrochemical performance tests were conducted on button cells using the carbon derived from asphalt conversion as the negative electrode material. The results are as follows: Figure 6 As shown, the specific capacity of this anode material remains at 389 mAh / g after 100 cycles.

[0045] Comparative Example 3 Phenolic resin was carbonized at high temperature to obtain carbon material, with a heating rate of 5℃ / min and a constant temperature of 800℃. After natural cooling, the material was pulverized and graded to obtain the negative electrode material. The carbon converted from phenolic resin was used as the negative electrode material to construct a button cell for electrochemical performance testing. The results are as follows: Figure 7 As shown, the specific capacity of this anode material remains at 256 mAh / g after 100 cycles.

[0046] Comparative Example 4 Asphalt was mixed with tetrahydrofuran solvent to obtain an impregnation solution, and silica suboxide with a median particle size D50 of 50 nm was added for composite formation, wherein the mass ratio of asphalt to silica suboxide was 1:1. SiO / C composite materials were obtained by ultrasonic dispersion, high-speed stirring, and high-temperature carbonization. Ultrasonic dispersion and high-speed stirring were alternated for 2 h, the heating rate was 5 °C / min, and the isothermal temperature was 800 °C.

[0047] Through the above steps, after the asphalt is calcined and carbonized at high temperature, a dense protective layer is formed and adheres to the SiO surface, thereby inhibiting the volume expansion of SiO. To demonstrate that a well-coated anode material is obtained through the above method, it is subjected to electron microscopy scanning, and the results are as follows: Figure 7 As shown, a smooth and dense carbon layer does indeed exist on the surface of SiO, which has an uneven morphology and sharp edges. The SiO particle size distribution is between 50 nm and 500 nm.

[0048] Testing revealed that the carbon content in the prepared anode material reached 40%. The prepared anode material was then assembled into a button cell for electrochemical performance testing, and the results were as follows: Figure 6 As shown, the anode material exhibits good stability in the first 50 cycles. However, in the latter 50 cycles, the repeated charging and discharging of the battery causes the SiO volume to expand dramatically, breaking the constraint of the surface carbon layer on the SiO. This results in a significant decrease in specific capacity, which eventually settles at 520 mAh / g.

[0049] Comparative Example 5 S1: Asphalt was mixed with tetrahydrofuran solvent to obtain an impregnation solution. Silica with a median particle size D50 of 50 nm was then added for composite formation, wherein the mass ratio of asphalt to silica was 1:1. The SiO / C composite material was obtained by ultrasonic dispersion, high-speed stirring, and high-temperature carbonization. Ultrasonic dispersion and high-speed stirring were alternated for 2 hours, with a heating rate of 5℃ / min and a constant temperature of 800℃.

[0050] S2: After the SiO / C composite material is naturally cooled, it is crushed and classified, and then treated with 1.2wt% HF at 80℃ for 65 min to prepare the negative electrode material.

[0051] Through the above steps, hydrofluoric acid removes the SiO2 component from SiO, retaining silicon grains smaller than 3 nm. The resulting anode material was subjected to electron microscopy, and the results are as follows: Figure 6 As shown, the degree of etching of SiO2 in the bulk material by the HF solution can be observed.

[0052] Testing revealed that the carbon content in the novel anode material reached 60%. Electrochemical performance tests were conducted on the anode material assembled into button cells, and the results were as follows: Figure 6 As shown, the final specific capacity of this anode material remains at 610 mAh / g after 100 cycles.

[0053] Comparative Example 6 Phenolic resin was used as the carbon source, tetrahydrofuran as the solvent, and composited with silicon suboxide. The mass ratio of phenolic resin to silicon suboxide was 1:1. The SiO / C composite material was obtained by ultrasonic dispersion, high-speed stirring, and high-temperature carbonization. Ultrasonic dispersion and high-speed stirring were alternated for 2 hours, with a heating rate of 5 °C / min and a constant temperature of 800 °C. After the SiO / C composite material cooled naturally, it was pulverized and graded to obtain a well-coated anode material.

[0054] Through the above steps, the phenolic resin undergoes high-temperature calcination and carbonization, forming a carbon layer that adheres to the SiO surface, thereby inhibiting the volume expansion of SiO. To demonstrate that the carbon-coated anode material is obtained through the above method, it is subjected to electron microscopy scanning, and the results are as follows: Figure 10 As shown, a carbon layer does indeed exist on the surface of SiO. The SiO particle size distribution is between 50 nm and 500 nm.

[0055] The carbon content in the negative electrode material prepared in this embodiment reached 30% through testing. The prepared negative electrode material was then assembled into a button cell for electrochemical performance testing, and the results are as follows: Figure 7 As shown, this anode material exhibits stable cycling performance, which is attributed to the numerous pores in the carbon layer converted from phenolic resin, which strongly constrains the volume expansion of SiO. The final specific capacity remains at 550 mAh / g after 100 cycles.

[0056] Comparative Example 7 S1: Phenolic resin was mixed with tetrahydrofuran solvent to obtain an impregnation solution. Silica with a median particle size D50 of 50 nm was then added for composite formation. The mass ratio of bitumen to silica was 1:1. SiO / C composite materials were obtained through ultrasonic dispersion, high-speed stirring, and high-temperature carbonization. Ultrasonic dispersion and high-speed stirring were alternated for 2 hours, with a heating rate of 5℃ / min and a constant temperature of 800℃.

[0057] S2: After the SiO / C composite material has cooled naturally, it is crushed and classified, and then treated with 1.2wt% HF at 80℃ for 65 min.

[0058] Through the above steps, hydrofluoric acid removes the SiO2 component from SiO, retaining silicon nanocrystals of approximately 3 nm. To demonstrate that a porous nano-silicon anode material is obtained through the above method, it is subjected to electron microscopy scanning, and the results are as follows. Figure 11 As shown, the etching effect of HF solution on SiO2 in the material matrix can be seen. The particle surface is relatively smooth, which is attributed to the presence of pores in the carbon layer converted from phenolic resin, which facilitates HF to cross the carbon layer and etch the internal SiO particles.

[0059] Testing revealed that the carbon content in the prepared anode material reached 70%. The prepared anode material was then assembled into a button cell for electrochemical performance testing, and the results were as follows: Figure 7 As shown, this novel anode material exhibits good cycle stability and high discharge specific capacity, which is attributed to the removal of SiO2 components and the retention of 3 nm silicon grains. The final specific capacity after 100 cycles remains at 740 mAh / g.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium-ion battery anode material, characterized in that: Includes the following steps: S1: After dispersing nano-silica in an organic solution, a carbon source is added for composite formation. The SiO / C composite material is obtained by ultrasonic dispersion, high-speed stirring and high-temperature carbonization in sequence. S2: The SiO / C composite material was naturally cooled and then crushed, and then acid-treated with hydrofluoric acid solution. S3: The acid-treated SiO / C composite material is impregnated with a carbon source, dried, and then carbonized again at high temperature to obtain the lithium-ion battery anode material.

2. The method for preparing the lithium-ion battery anode material according to claim 1, characterized in that: In step S1, ultrasonic dispersion and high-speed stirring are performed alternately for a duration of 2 to 2.2 hours.

3. The method for preparing the lithium-ion battery anode material according to claim 1, characterized in that: The median particle size D50 of the nano-silica is 40 nm-1000 nm.

4. The method for preparing the lithium-ion battery anode material according to claim 1, characterized in that: The carbon source in steps S1 and S3 is one or more of asphalt, phenolic resin, and biomass materials.

5. The method for preparing the lithium-ion battery anode material according to claim 1, characterized in that: The mass ratio of carbon source to nano-silica in step S1 is (0.95~1.05):(0.95~1.05).

6. The method for preparing the lithium-ion battery anode material according to claim 1, characterized in that: The heating rate for high-temperature carbonization in steps S1 and S3 is 4.8~5.2℃ / min, the isothermal temperature is 780-820℃, and the holding time is 1~1.2h; the high-temperature carbonization in steps S1 and S3 is carried out under vacuum conditions with a vacuum degree of 1×10⁻⁶. -1 Pa-1×10 - 5 Pa.

7. The method for preparing the lithium-ion battery anode material according to claim 1, characterized in that: The acid treatment method in step S2 is as follows: use a 1.2wt%-2.4wt% HF solution to treat for 60min-65min at a temperature of 60℃-80℃.

8. The method for preparing the lithium-ion battery anode material according to claim 1, characterized in that: The carbon content in the lithium-ion battery anode material accounts for 75%-85% of the total mass.

9. The lithium-ion battery anode material is prepared by the preparation method according to any one of claims 1-8.

10. The application of the lithium-ion battery anode material according to claim 9 in the preparation of lithium-ion batteries.

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