Carbon-silicon nanofiber negative electrode material and preparation method thereof

Abstract

The application discloses a carbon-silicon nanofiber negative material and a preparation method thereof, and the carbon-silicon nanofiber negative material is prepared by the following steps: mixing lignin sulfonate powder and polyvinyl alcohol powder, dissolving and stirring to obtain a lignin sulfonate-polyvinyl alcohol solution; adding porous silicon powder into the lignin sulfonate-polyvinyl alcohol solution and uniformly dispersing to uniformly disperse the porous silicon powder in the lignin sulfonate-polyvinyl alcohol to form a unique structure; and after electrostatic spinning and carbonization, a high-porosity composite material is obtained. The carbon-silicon nanofiber negative material can effectively improve the first round coulomb efficiency of a battery and relieve the problem of volume expansion of the micron-level silicon material, and a lithium ion battery assembled from the carbon-silicon nanofiber negative material has better cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a carbon silicon nanofiber anode material and its preparation method. Background Technology

[0002] In the field of new energy, lithium-ion batteries have become a global research focus due to their high specific energy, long lifespan, and portability, and are widely used in various electronic devices, electric vehicles, and portable storage devices. As an emerging anode material for lithium-ion batteries, silicon has a theoretical specific capacity as high as 4000 mAh / g. However, it suffers from significant volume expansion during charging and discharging, is prone to pulverization and shedding, and has poor conductivity at the micron level. These problems severely limit its lifespan. Especially during the initial charge, lithium ions react with silicon oxide to form compounds, consuming a large amount of active lithium and resulting in low initial charging efficiency.

[0003] To improve the electrical conductivity and control the volume expansion of silicon-based materials, industry experts have adopted various strategies, such as nano-sizing, carbon coating, and composite with graphite. These technologies can improve the conductivity of the material to some extent while avoiding direct contact between the electrolyte and silicon, which is beneficial for stabilizing the solid electrolyte interphase (SEI) film. However, these improvements still face many challenges, including limited improvement in cycle performance and low initial charge efficiency, with a typical cycle life of only around 500 cycles. Therefore, developing a carbon-silicon anode material that can effectively reduce volume expansion, ensure battery cycle stability, and simultaneously possess high initial charge efficiency and excellent cycle performance remains an urgent technological challenge for the lithium-ion battery field. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, this invention proposes a carbon silicon nanofiber anode material and its preparation method, which can effectively improve the first-round coulombic efficiency of the battery and alleviate the problem of volume expansion of micron-sized silicon materials. The lithium-ion battery assembled from it has better cycle performance.

[0005] The present invention proposes a method for preparing a carbon-silicon nanofiber anode material, comprising the following steps:

[0006] S1. After mixing water-soluble lignin sulfonate powder and polyvinyl alcohol powder, add deionized water to dissolve completely to obtain lignin sulfonate-polyvinyl alcohol solution.

[0007] S2. Add porous silica powder to the lignin sulfonate-polyvinyl alcohol solution and disperse it evenly to obtain a precursor solution;

[0008] S3. The precursor solution is electrospinned to obtain lignin sulfonate-silicon nanofibers.

[0009] S4. The lignin sulfonate-silicon nanofibers are first pre-carbonized by heating, and then carbonized at high temperature under an inert atmosphere to obtain carbon silicon nanofiber anode material.

[0010] In this invention, the addition of lignin sulfonate increases the structural porosity of the porous silicon outer carbon layer material, improves the material's conductivity, and forms an excellent internal conductive network. The porous silicon is dispersed in the high-porosity carbon fiber structure formed by carbonization, effectively preventing silicon aggregation and expansion during battery charging and discharging. This structural design significantly improves the material's cycle performance, effectively increasing the battery's initial coulombic efficiency and alleviating the problem of volume expansion of micron-sized silicon materials. The lithium-ion battery assembled from it has better cycle performance.

[0011] In S1, the dissolution method may be, for example, heating and stirring. The preferred temperature for heating and stirring is 25 to 90°C, such as 25°C, 35°C, 45°C, 55°C, 65°C, 75°C, or 90°C.

[0012] In step S1, after complete dissolution, a cooling step may also be included, with the cooling time preferably being 24 to 36 hours, for example, 24 hours, 30 hours, or 36 hours.

[0013] Preferably, the mass ratio of the water-soluble lignin sulfonate powder to the polyvinyl alcohol powder is 0.8–1.2:1. In this invention, by controlling the ratio of lignin sulfonate to polyvinyl alcohol, the fibers obtained by electrospinning can be guaranteed to have excellent formability and uniformity, which is beneficial to further improving the structural stability and conductivity of the final carbon-silicon nanofiber anode material.

[0014] Preferably, the ratio of the total mass of the water-soluble lignin sulfonate powder and polyvinyl alcohol powder to the mass of the porous silica powder is 8:1 to 3, for example, 8:1, 8:2, or 8:3. In this invention, by controlling the content of porous silica powder in the precursor, the carbon-silicon nanofiber anode material can possess both high specific capacity and good volume expansion rate, thus exhibiting excellent comprehensive performance.

[0015] Preferably, in S1, the ratio of the water-soluble lignin sulfonate powder to deionized water is 2g:10-20mL.

[0016] Preferably, in S2, the dispersion step includes: stirring for 1 to 4 hours, followed by ultrasonic dispersion for 1 to 4 hours; for example, stirring for 1 hour, 2 hours, 3 hours, and 4 hours; and ultrasonic dispersion for 1 hour, 2 hours, 3 hours, and 4 hours.

[0017] Preferably, the specific surface area of ​​the porous silica powder is 50–320 m². 2 / g, with a pore size of 2-15nm. In this invention, by controlling the specific surface area and pore size of porous silicon micropowder, the specific capacity of the material can be further improved, the volume expansion can be buffered, and the material can have better electrochemical performance.

[0018] Preferably, the method for preparing the porous silicon micropowder includes: adding a silicon-aluminum alloy to an acid solution and stirring the reaction at room temperature to obtain the product; preferably, the concentration of the acid solution is 0.2 mol / L to 0.8 mol / L; preferably, the acid solution is one or a mixture of several of hydrochloric acid solution, sulfuric acid solution, and carbonic acid solution; preferably, the stirring reaction time is 6 to 18 hours. After the stirring reaction, conventional post-processing steps may be included, including: solid-liquid separation, washing, and drying; the drying method may be, for example, vacuum drying or freeze drying.

[0019] Preferably, the porous silica powder is porous silica powder coated with polydiallyldimethylammonium chloride.

[0020] Preferably, the method for preparing the polydiallyldimethylammonium chloride-coated porous silica powder includes:

[0021] A silicon-aluminum alloy is added to an acid solution and stirred at room temperature to obtain porous silicon micropowder. Preferably, the concentration of the acid solution is 0.2 mol / L to 0.8 mol / L. Preferably, the acid solution is one or a mixture of several of hydrochloric acid, sulfuric acid, and carbonic acid solutions. Preferably, the stirring reaction time is 6 to 18 hours. After the stirring reaction, conventional post-processing steps may be included, including solid-liquid separation, washing, and drying. The solid-liquid separation method may be centrifugation or filtration, and the drying method may be vacuum drying or freeze drying.

[0022] The porous silicon powder is dispersed in water to obtain an aqueous dispersion of porous silicon powder; preferably, the solid content of the aqueous dispersion of porous silicon powder is 1-3%.

[0023] Polydiallyldimethylammonium chloride is added to an aqueous dispersion of porous silica powder and stirred at room temperature to obtain porous silica powder coated with polydiallyldimethylammonium chloride. Preferably, the mass of the polydiallyldimethylammonium chloride is equivalent to 10% to 20% of the mass of the porous silica powder. Preferably, the stirring reaction time is 1 to 4 hours. After the stirring reaction, conventional post-processing steps may be included, including solid-liquid separation, washing, and drying. The solid-liquid separation method may be centrifugation or filtration, and the drying method may be vacuum drying or freeze drying.

[0024] In this invention, by coating porous silicon micropowder with polydiallyldimethylammonium chloride, it can be more tightly bound to sodium lignosulfonate through electrostatic interaction. After carbonization, a carbon layer can be formed on the surface of porous silicon, thereby improving the bonding stability between porous silicon and high-porosity carbon fibers, further improving the structural stability of the formed carbon silicon nanofiber anode material, and thus improving the cycle performance and conductivity of the material.

[0025] Preferably, in step S3, the electrospinning conditions include: a voltage of 20 kV, a flow rate of 0.6–1 mL / h, and a collection distance of 14–16 cm. In this invention, controlling appropriate electrospinning parameters facilitates the production of more uniform fibers, thereby further improving the structural stability of the final carbon-silicon nanofiber anode material.

[0026] Preferably, in S4, the pre-carbonization temperature is 200-300°C; for example, it can be 200°C, 250°C, or 300°C.

[0027] Preferably, in S4, the pre-carbonization time is 4 to 6 hours; for example, it can be 4 hours, 5 hours, or 6 hours.

[0028] Preferably, in S4, the high-temperature carbonization temperature is 700-900°C; for example, it can be 700°C, 750°C, 800°C, 850°C, or 900°C.

[0029] Preferably, in S4, the high-temperature carbonization time is 1 to 3 hours; for example, it can be 1 hour, 2 hours, or 3 hours.

[0030] In this invention, by controlling the temperature and time of pre-carbonization and high-temperature carbonization of the precursor fibers, the fibers can be carbonized more fully, thereby further improving the structural stability and conductivity of the silicon carbon nanofiber anode material.

[0031] In S4, after high-temperature carbonization, conventional post-processing steps may also be included, such as cooling and grinding.

[0032] In this invention, an inert atmosphere refers to a non-reactive atmosphere, namely an atmosphere formed by nitrogen or one or more inert gases such as argon and helium.

[0033] This invention also proposes a carbon-silicon nanofiber anode material, which is prepared by the aforementioned method.

[0034] This invention also proposes the application of the aforementioned carbon-silicon nanofiber anode material as a lithium-ion battery anode material.

[0035] The beneficial effects of this invention are as follows:

[0036] This invention discloses a carbon-silicon nanofiber anode material and its preparation method. The method involves grinding and dissolving lignin sulfonate powder and polyvinyl alcohol powder to obtain a lignin sulfonate-polyvinyl alcohol solution. Porous silica microparticles are then added to the lignin sulfonate-polyvinyl alcohol solution and dispersed uniformly, forming a unique structure within the lignin sulfonate-polyvinyl alcohol. After electrospinning and carbonization, a high-porosity composite material is obtained. The carbon-silicon nanofiber anode material of this invention can effectively improve the initial coulombic efficiency of batteries and alleviate the problem of volume expansion of micron-sized silicon materials. Lithium-ion batteries assembled from this material exhibit superior cycle performance. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the preparation process of the carbon-silicon nanofiber anode material proposed in this invention and a schematic diagram of the structure of the obtained carbon-silicon nanofiber anode material.

[0038] Figure 2 The image shows the XRD pattern of the silicon-carbon nanofiber anode material prepared in Example 1.

[0039] Figure 3 The image shows the Raman spectrum of the carbon-silicon nanofiber anode material prepared in Example 1.

[0040] Figure 4 The graph shows the cycling performance of the carbon-silicon nanofiber anode material prepared in Example 1.

[0041] Figure 5 The first charge-discharge curve of the carbon-silicon nanofiber anode material prepared in Example 1 is shown. Detailed Implementation

[0042] The technical solution of the present invention will now be described in detail through specific embodiments.

[0043] Example 1

[0044] A method for preparing a silicon-carbon nanofiber anode material includes the following steps:

[0045] S1. Mix 2g sodium lignosulfonate powder and 2g polyvinyl alcohol powder and grind them evenly. Then add 15mL of deionized water and heat and stir at 50℃ until completely dissolved. Then cool for 18h to obtain lignosulfonate-polyvinyl alcohol solution.

[0046] S2. 10g of silicon-aluminum alloy was added to 500mL of 0.5mol / L hydrochloric acid solution and stirred at room temperature for 9h. The mixture was then vacuum filtered, washed with deionized water, and vacuum dried to obtain porous silicon micropowder with a specific surface area of ​​132m². 2 / g, with a pore size of 2–15 nm;

[0047] Add 1.5g of the porous silica powder obtained above to the lignin sulfonate-polyvinyl alcohol solution obtained in S1, stir for 2 hours, and then ultrasonically disperse for 2 hours to obtain the precursor solution.

[0048] S3. Transfer the precursor solution obtained in S2 to a 20 mL syringe and perform electrospinning to obtain lignin sulfonate-silicon nanofibers. The electrospinning voltage is 20 kV, the flow rate is 0.8 mL / h, and the collection distance between the syringe needle and the collector is 15 cm.

[0049] S4. The lignin sulfonate-silicon nanofibers obtained in S3 are first kept at 260℃ for 5 hours, then carbonized at 800℃ under nitrogen atmosphere, cooled to room temperature, and then ground uniformly to obtain carbon silicon nanofiber anode material.

[0050] The carbon-silicon nanofiber anode material obtained in Example 1 was characterized. Figure 2 The image shows the XRD pattern of the silicon-carbon nanofiber anode material prepared in Example 1. Figure 3 The image shows the Raman spectrum of the silicon-carbon nanofiber anode material prepared in Example 1. Figure 2 , Figure 3 It can be seen that no other impurity phases were detected in the composite material. The Raman diagram shows the presence of amorphous carbon, which introduces surface vacancies and lattice defects into the material. Due to the presence of these defects, the electrochemical reaction surface area of ​​the material can be increased, providing more active sites for the reaction and promoting charge transport and mass diffusion. In addition, defects can also modulate the lattice structure and electronic structure of the material, changing its band structure and electron affinity, thereby further improving its electrochemical performance.

[0051] The electrochemical performance of the carbon-silicon nanofiber anode material obtained in Example 1 was tested. Figure 4 This is a cycling performance diagram of the silicon-carbon nanofiber anode material prepared in Example 1. Figure 5 This is the first charge-discharge curve of the carbon-silicon nanofiber anode material prepared in Example 1. From... Figure 4 , Figure 5 It can be seen that the prepared material has a high initial discharge specific capacity of 1384.6 mAh / g, and can still maintain a high capacity after 100 charge-discharge cycles at a current density of 0.2C, with a capacity retention rate of 98.5%.

[0052] Example 2

[0053] A method for preparing a silicon-carbon nanofiber anode material includes the following steps:

[0054] S1. Mix 2g sodium lignosulfonate powder and 2g polyvinyl alcohol powder and grind them evenly. Then add 15mL of deionized water and heat and stir at 50℃ until completely dissolved. Then cool for 18h to obtain lignosulfonate-polyvinyl alcohol solution.

[0055] S2. 10g of silicon-aluminum alloy was added to 500mL of 0.8mol / L hydrochloric acid solution and stirred at room temperature for 6h. The mixture was then vacuum filtered, washed with deionized water, and vacuum dried to obtain porous silicon micropowder with a specific surface area of ​​184m². 2 / g, with a pore size of 2–15 nm;

[0056] Add 1g of the porous silica powder obtained above to the lignin sulfonate-polyvinyl alcohol solution obtained in S1, stir for 2 hours, and then ultrasonically disperse for 2 hours to obtain the precursor solution.

[0057] S3. Transfer the precursor solution obtained in S2 to a 20 mL syringe and perform electrospinning to obtain lignin sulfonate-silicon nanofibers. The electrospinning voltage is 20 kV, the flow rate is 0.6 mL / h, and the collection distance between the syringe needle and the collector is 15 cm.

[0058] S4. The lignin sulfonate-silicon nanofibers obtained in S3 are first kept at 200℃ for 6 hours, then carbonized at 700℃ under nitrogen atmosphere, cooled to room temperature, and then ground uniformly to obtain carbon silicon nanofiber anode material.

[0059] Example 3

[0060] A method for preparing a silicon-carbon nanofiber anode material includes the following steps:

[0061] S1. Mix 2g sodium lignosulfonate powder and 2g polyvinyl alcohol powder and grind them evenly. Then add 15mL of deionized water and heat and stir at 50℃ until completely dissolved. Then cool for 18h to obtain lignosulfonate-polyvinyl alcohol solution.

[0062] S2. 10g of silicon-aluminum alloy was added to 500mL of 0.2mol / L hydrochloric acid solution and stirred at room temperature for 18h. The mixture was then vacuum filtered, washed with deionized water, and vacuum dried to obtain porous silicon micropowder with a specific surface area of ​​220m². 2 / g, with a pore size of 2–15 nm;

[0063] Add 0.5g of the porous silica powder obtained above to the lignin sulfonate-polyvinyl alcohol solution obtained in S1, stir for 2 hours, and then ultrasonically disperse for 2 hours to obtain the precursor solution.

[0064] S3. Transfer the precursor solution obtained in S2 to a 20 mL syringe and perform electrospinning to obtain lignin sulfonate-silicon nanofibers. The electrospinning voltage is 20 kV, the flow rate is 1 mL / h, and the collection distance between the syringe needle and the collector is 15 cm.

[0065] S4. The lignin sulfonate-silicon nanofibers obtained in S3 are first kept at 300℃ for 4 hours, then carbonized at 900℃ under nitrogen atmosphere, cooled to room temperature, and then ground uniformly to obtain carbon silicon nanofiber anode material.

[0066] Example 4

[0067] The only difference between Example 4 and Example 1 is that porous silica powder coated with polydiallyldimethylammonium chloride is used instead of porous silica powder.

[0068] The specific preparation method of porous silica powder coated with polydiallyldimethylammonium chloride is as follows:

[0069] 10g of silicon-aluminum alloy was added to 500mL of 0.8mol / L hydrochloric acid solution and stirred at room temperature for 6h. Then, the mixture was vacuum filtered, washed with deionized water, and vacuum dried to obtain porous silicon micropowder.

[0070] Porous silica powder was dispersed in water to obtain an aqueous dispersion of porous silica powder with a solid content of 2%.

[0071] Polydiallyldimethylammonium chloride (10% of the mass of porous silica powder) was added to an aqueous dispersion of porous silica powder. The mixture was stirred and reacted at room temperature for 2 hours. The mixture was then vacuum filtered, washed with deionized water, and vacuum dried to obtain porous silica powder coated with polydiallyldimethylammonium chloride.

[0072] Comparative Example 1

[0073] A method for preparing a silicon-carbon nanofiber anode material includes the following steps:

[0074] S1. Add 4g of polyvinyl alcohol powder to 15mL of deionized water and heat and stir at 50℃ until completely dissolved, then cool for 18h to obtain a polyvinyl alcohol solution.

[0075] S2. 10g of silicon-aluminum alloy was added to 500mL of 0.5mol / L hydrochloric acid solution and stirred at room temperature for 9h. The mixture was then vacuum filtered, washed with deionized water, and vacuum dried to obtain porous silicon micropowder with a specific surface area of ​​132m². 2 / g, with a pore size of 2–15 nm;

[0076] Add 1.5g of the porous silica powder obtained above to the polyvinyl alcohol solution obtained in S1, stir for 2 hours, and then ultrasonically disperse for 2 hours to obtain the precursor solution;

[0077] S3. Transfer the precursor solution obtained in S2 into a 20 mL syringe and perform electrospinning to obtain silicon-containing nanofibers. The electrospinning voltage is 20 kV, the flow rate is 0.8 mL / h, and the collection distance between the syringe needle and the collector is 15 cm.

[0078] S4. The silicon-containing nanofibers obtained in S3 are first kept at 260℃ for 5 hours, then carbonized at 800℃ under nitrogen atmosphere, cooled to room temperature, and then ground uniformly to obtain the silicon-carbon nanofiber anode material.

[0079] Lithium-ion batteries were prepared using the negative electrode materials obtained in Examples 1-4 and Comparative Example 1, and their electrochemical performance was tested. The test results are shown in Table 1.

[0080] Table 1

[0081]

[0082]

[0083] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-silicon nanofiber anode material, characterized in that, Includes the following steps: S1. After mixing water-soluble lignin sulfonate powder and polyvinyl alcohol powder, add deionized water to dissolve completely to obtain lignin sulfonate-polyvinyl alcohol solution. S2. Add the porous silica powder coated with polydiallyldimethylammonium chloride to the lignin sulfonate-polyvinyl alcohol solution and disperse it evenly to obtain a precursor solution. The method for preparing the polydiallyldimethylammonium chloride-coated porous silica powder includes: A silicon-aluminum alloy is added to an acid solution and stirred at room temperature to obtain porous silicon micropowder; the porous silicon micropowder is dispersed in water to obtain an aqueous dispersion of porous silicon micropowder; polydiallyldimethylammonium chloride is added to the aqueous dispersion of porous silicon micropowder and stirred at room temperature to obtain porous silicon micropowder coated with polydiallyldimethylammonium chloride. S3. The precursor solution is electrospinned to obtain lignin sulfonate-silicon nanofibers. S4. The lignin sulfonate-silicon nanofibers are first pre-carbonized by heating, and then carbonized at high temperature under an inert atmosphere to obtain carbon silicon nanofiber anode material.

2. The method for preparing the silicon-carbon nanofiber anode material according to claim 1, characterized in that, The mass ratio of the water-soluble lignin sulfonate powder to the polyvinyl alcohol powder is 0.8~1.2:

1.

3. The method for preparing the carbon-silicon nanofiber anode material according to claim 1, characterized in that, The ratio of the total mass of the water-soluble lignin sulfonate powder and polyvinyl alcohol powder to the mass of the porous silica powder is 8:1~3.

4. The method for preparing the carbon-silicon nanofiber anode material according to claim 1, characterized in that, The specific surface area of ​​the porous silica powder is 50~320m². 2 / g, with a pore size of 2~15nm.

5. The method for preparing the silicon-carbon nanofiber anode material according to claim 1, characterized in that, In S3, the conditions for electrospinning include: a voltage of 20 kV, a flow rate of 0.6~1 mL / h, and a collection distance of 14~16 cm.

6. The method for preparing the carbon-silicon nanofiber anode material according to claim 1, characterized in that, In S4, the pre-carbonization temperature is 200~300℃ and the time is 4~6h; in S4, the high-temperature carbonization temperature is 700~900℃ and the time is 1~3h.

7. A carbon-silicon nanofiber anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

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