Lithium ion battery porous silicon / carbon nanotube composite negative electrode material, preparation method and lithium ion battery

Abstract

This application provides a porous silicon / carbon nanotube composite anode material for lithium-ion batteries, comprising a nanoporous silicon framework with three-dimensional through-holes and hierarchical channels, within which villous carbon nanotubes are distributed and grown in situ. The preparation method involves: dealloying silicon alloy particles to create pores by generating oxide or nitride particles during the dealloying process; removing the oxides / nitrides with acid to form a nanoporous silicon framework structure with hierarchical channels; mixing this with a catalyst and a carbon source solution to obtain a silicon-carbon precursor powder; and then rapidly heating the powder in an inert atmosphere for 0.1-3 minutes to allow the catalyzed carbon source to grow in situ on the nanoporous silicon framework, forming villous carbon nanotubes, which react with the porous silicon to generate SiC and metal silicides, resulting in a porous silicon / carbon nanotube composite anode material with carbon nanotubes grown in situ within the channels. This material exhibits good cycle performance and rate performance. This application also provides a lithium battery using the above-mentioned composite anode material.

Description

Technical Field

[0001] This application relates to the field of new energy materials technology, and in particular to a porous silicon / carbon nanotube composite anode material from waste lithium-ion batteries, its preparation method, and the lithium battery thereof. Background Technology

[0002] With the growth of the portable electronics and electric vehicle markets, the demand for high-energy-density lithium-ion batteries is increasing. As a key material in lithium-ion batteries, the anode material plays a crucial role in improving battery performance.

[0003] Currently, the specific capacity of commercial graphite anodes (approximately 360 mAh / g) is almost close to the theoretical value (372 mAh / g), so there is an urgent need to develop an anode material with high specific capacity.

[0004] Silicon anodes have a theoretical specific capacity (4200 mAh / g) approximately ten times that of commercial graphite anodes, and their operating voltage (0.4 V) is suitable, making them a very promising anode material. Furthermore, silicon is abundant in the Earth's crust, inexpensive, and environmentally friendly. Therefore, silicon-based anode materials are increasingly favored by researchers. However, although silicon-based anodes possess high theoretical specific capacity, they undergo volume expansion of up to 300% during charge and discharge. This severe expansion leads to the fragmentation and shedding of battery materials, a continuous increase in the SEI (Sediment Interval), a rapid decrease in specific capacity, and ultimately, the loss of battery activity.

[0005] The key to preparing high-performance silicon-carbon anode materials lies in the rational structural design of the materials. A porous structure can provide the necessary space for the volume expansion of silicon, preventing subsequent pulverization and ensuring the integrity of the electrode material. The coated carbon structure can buffer the enormous stress during silicon expansion and improve the poor intrinsic conductivity of silicon. However, currently prepared silicon-carbon composite anode materials struggle to effectively limit the volume expansion of silicon during charge and discharge, making material pulverization unavoidable. This results in poor cycle and rate performance, limiting the application of silicon-carbon composite anode materials. Summary of the Invention

[0006] The purpose of this application is to overcome the shortcomings of the prior art and to provide a porous silicon / carbon nanotube composite anode material for lithium-ion batteries.

[0007] The lithium-ion battery porous silicon / carbon nanotube composite anode material provided in this application includes a nanoporous silicon framework, wherein the nanoporous silicon framework has three-dimensional through-holes in a multi-level channel, and carbon nanotubes are distributed in the multi-level channel. The carbon nanotubes grow in situ in a villous manner within the channel, forming a porous silicon composite anode material with villous carbon nanotubes.

[0008] This application also provides a method for preparing the above-mentioned porous silicon / carbon nanotube composite anode material for lithium-ion batteries, comprising the following steps: S1 Silicon alloy particles are placed in an air, nitrogen, or oxygen atmosphere and de-alloyed at a heating rate of 1-10℃ / min at 700~1000℃. Pores are formed by generating oxide or nitride particles during the de-alloying process. Then, the oxides or nitrides are removed by acid washing to form multi-level channels. After filtration and drying, nanoporous silicon powder with a framework structure is obtained. S2 The nanoporous silicon powder particles prepared in step S1 are mixed with the catalyst and carbon source solution, ultrasonically dispersed for 5-30 min, and the mixture is dried to obtain silicon-carbon precursor powder. S3 is rapidly heated by Joule for 0.1-30 min under an inert atmosphere and at a temperature of 700-1200℃, so that the catalyzed carbon source grows in situ on the nanoporous silicon framework to form villous carbon nanotubes, which react with porous silicon to generate SiC and metal silicides. After acid washing and drying, a porous silicon / carbon nanotube composite anode material with carbon nanotubes grown in situ in the pores is obtained.

[0009] This application also provides a lithium battery, including the above-described recycled lithium iron phosphate cathode material.

[0010] The porous silicon / carbon nanotube composite anode material for lithium-ion batteries provided in this application is composed of a nanoporous silicon framework with three-dimensionally continuous hierarchical channels containing villous carbon nanotubes. The nanoporous silicon framework structure disperses stress during lithiation, promotes lithium-ion migration, and maintains high electrochemical stability of the electrode. Its continuous pore structure provides space for silicon expansion during lithiation, achieving a self-adaptive volume effect and low electrode film swelling. The in-situ grown villous carbon nanotubes possess excellent mechanical properties, further mitigating silicon volume expansion. Furthermore, the carbon nanotubes exhibit good electrical conductivity, thereby improving the cycle performance and rate performance of silicon.

[0011] The present invention provides a method for preparing porous silicon / carbon nanotube composite anode materials for lithium-ion batteries. The method involves dealloying a silicon alloy at high temperature in an air, nitrogen, or oxygen atmosphere to construct three-dimensional interconnected channels within the silicon alloy, forming nanoporous silicon powder with a framework structure. The nanoporous silicon powder is then ultrasonically mixed with a carbon source and catalyst, ensuring uniform dispersion of the nanoporous silicon powder, carbon source, and catalyst, providing favorable conditions for the subsequent uniform growth of carbon nanotubes. The use of Joule heating for rapid heating ensures in-situ growth of carbon nanotubes on the silicon framework, overcoming the problems of agglomeration and poor dispersion associated with traditional physical mixing methods. Furthermore, the use of Joule heating technology to prepare silicon-carbon composite anode materials significantly shortens the production cycle, saves production costs, and is environmentally friendly and energy-saving.

[0012] The porous silicon / carbon nanotube composite anode material prepared by the method of this application exhibits good electrochemical performance when applied to lithium-ion batteries, providing a promising application prospect for silicon-carbon anode materials in lithium-ion batteries, with significant economic and social benefits. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of Example 1 of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application; Figure 2 This is a scanning electron microscope (SEM) image of porous silicon in Example 1 of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application. Figure 3 Scanning electron microscopy (SEM) of Example 1 of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application. Figure 1 ; Figure 4 Scanning electron microscopy (SEM) of Example 1 of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application. Figure 2 ; Figure 5 This is the X-ray diffraction (XRD) pattern of Example 1 of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application; Figure 6 The graph shows the cycle performance of lithium-ion batteries prepared in Example 1 and Comparative Example 1 using the porous silicon / carbon nanotube composite anode material for lithium-ion batteries according to this application. Figure 7 The graphs show the rate performance of lithium-ion batteries prepared in Example 1 and Comparative Example 1 using the porous silicon / carbon nanotube composite anode material for lithium-ion batteries according to this application. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0015] See Figure 1This application first provides a porous silicon / carbon nanotube composite anode material for lithium-ion batteries. The porous silicon is composed of a three-dimensional interconnected nanoframework with hierarchical channels (meaning it has macropores and mesopores). The macropores provide sufficient buffer space for the volume expansion of silicon particles during charging and discharging, allowing for the directional release of expansion stress. The mesopores ensure sufficient electrolyte wetting and significantly reduce lithium-ion transport resistance, providing efficient channels for lithium-ion diffusion within the electrode and improving the battery's rate performance and fast-charging capability. The hierarchical channels are interconnected and interpenetrating within the three-dimensional space of the nanoporous silicon framework, effectively dispersing the catalyst and carbon source. During the subsequent growth of carbon nanotubes catalyzed by the catalyst particles, they act as nano-confined spaces, preventing excessively large catalyst particles from causing decreased catalytic efficiency and material waste. Within the channels, carbon nanotubes grow in situ in a villous manner and are evenly distributed within the channels, forming a porous silicon composite anode material with villous carbon nanotubes.

[0016] The composite anode material with the above structure has a porous silicon nanoframework with three-dimensional through-holes that are interconnected internally and externally. This helps prevent the silicon anode from breaking during the lithiation process, disperses the stress during lithiation, promotes lithium-ion migration, and maintains high electrochemical stability of the electrode. The continuous through-hole structure, while introducing carbon nanotubes, provides space for silicon expansion during lithiation, achieving a self-adaptive effect and low electrode film swelling. This gives the in-situ grown carbon nanotubes excellent mechanical properties, which can alleviate and accommodate the volume expansion of silicon, avoiding particle breakage caused by volume expansion during lithiation and improving the cycle performance of the lithium battery. At the same time, the villous carbon nanotubes can provide fast channels for lithium-ion and electron transport. The addition of carbon nanotubes also has good conductivity, improving the electronic and ionic conductivity of the silicon-carbon composite anode material, thereby enhancing the cycle performance and rate performance of the composite anode material.

[0017] As one embodiment of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application, such as Figure 1 As shown, the nanoporous silicon framework has a spherical structure, and the surface of the framework has multi-level interconnected channels from the outside to the inside. The fluffy carbon nanotubes grow in situ in the channels, making the composite anode material an overall porous silicon spherical structure with fluffy carbon nanotubes.

[0018] As one embodiment of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application, the porous silicon composite anode material with villous carbon nanotubes has a particle size of 1-10 μm and a pore size of 5-500 nm.

[0019] The fluffy carbon nanotubes have a length of 100-800 nm and a diameter of 5-20 nm, which are compatible with the pore size of the nanoporous silicon framework. This allows the pores to have appropriate expansion space when the carbon nanotubes are placed in the nanoporous silicon framework, ensuring that the in-situ grown carbon nanotube structure is not destroyed and that there is a certain bonding force between the carbon nanotubes and the nanoporous silicon framework pores, thereby improving the stability of the overall structure.

[0020] As one embodiment of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries in this application, the weight percentage of porous silicon in the composite anode material is 20-90%.

[0021] This application also provides a method for preparing the above-mentioned porous silicon / carbon nanotube composite anode material for lithium-ion batteries, comprising the following steps: S1 Silicon alloy particles are placed in an air, nitrogen, or oxygen atmosphere and de-alloyed at a heating rate of 1-10℃ / min at 700~1000℃. Pores are created in the silicon alloy by generating oxide or nitride particles during the de-alloying process. Then, the oxides / nitrides are removed by acid washing to form a nanoporous silicon framework with multi-level channels. After filtration and drying, nanoporous silicon powder is obtained.

[0022] In this step, the silicon alloy selected is either a silicon-magnesium alloy or a silicon-calcium alloy. Magnesium and calcium in the alloy are relatively reactive; during the dealloying process, they react with nitrogen and oxygen at high temperatures of 700-1000℃ to form nitrides or oxides bonded to magnesium and calcium. These nitrides or oxides are in a molten state and flow and converge within the three-dimensional space of the silicon alloy. Then, acid washing is used to remove these nitrides or oxides formed during the dealloying process, clearing the nitrides or oxides from the three-dimensional space and creating interconnected channels within the three-dimensional space. This constructs a nanoporous silicon framework structure, resulting in nanoporous silicon powder with a framework structure.

[0023] The reaction time for this dealloying step is 3-5 hours.

[0024] During pickling, hydrochloric acid with a concentration of 0.1M to 1M is used for about 1 hour, which can remove nitrides or oxides as well as metals other than silicon.

[0025] S2 Mix the nanoporous silicon powder particles prepared in step S1 with the catalyst and carbon source solution, ultrasonically disperse for 5-30 min, and evaporate and dry the mixture to obtain silicon-carbon precursor powder.

[0026] In this step, the catalyst is one of ferrocene, ferric nitrate, ferric sulfate, ferric chloride, nickel nitrate, or nickel chloride. Using transition metals such as iron and nickel as catalysts can effectively catalyze the growth of carbon nanotubes, accelerate the reaction rate, and these catalysts are relatively safe, readily available, and inexpensive.

[0027] The carbon source is at least one of ferrocene, fructose, sucrose, glucose, and starch, which is inexpensive and has low cost.

[0028] The mass ratio of nanoporous silicon particles, catalyst, and carbon source is 40–50: 1–2: 20–30.

[0029] By ultrasonically mixing nanoporous silicon powder with carbon source and catalyst, the nanoporous silicon powder, carbon source and catalyst can be uniformly dispersed, and the carbon source and catalyst are uniformly distributed in the channels and on the surface.

[0030] This step can be performed by using a rotary evaporator to evaporate and dry the solids under vacuum conditions at 40-60℃, thus achieving solid-liquid separation.

[0031] S3 is rapidly heated by Joule for 0.1-3 minutes in an inert atmosphere at a temperature of 700-1200℃, causing the catalyzed carbon source to grow in situ on a nanoporous silicon framework to form villous carbon nanotubes. These nanotubes then react with porous silicon to generate SiC and metal silicides. After acid washing and drying, a porous silicon / carbon nanotube composite anode material with carbon nanotubes growing in situ in the pores is obtained.

[0032] In an inert atmosphere, rapid Joule heating at 700-1200℃ accelerates carbon nanotube growth while preventing the sublimation of the catalytic material, which would negatively impact the catalytic effect. Simultaneously, using transition metals as catalysts generates iron, nickel atoms, and hydrocarbon gases at high temperatures. These hydrocarbons, catalyzed by iron and nickel atoms, form carbon nanotubes. When nanoporous silicon powder particles are mixed with the catalyst and carbon source solution, ultrasonic dispersion ensures that the catalytically generated carbon nanotubes are uniformly distributed within the pores and surface of the nanoporous silicon framework. Rapid heating at high temperatures causes the decomposed carbon nanotubes to grow perpendicular to the porous silicon during rapid temperature changes, exhibiting a villous appearance, forming in-situ grown villous carbon nanotubes. Furthermore, the in-situ grown carbon nanotubes react with porous silicon to generate SiC and metal silicides, which can act as solder joints, preventing detachment during subsequent silicon expansion and thus avoiding performance degradation. This method overcomes the problems of easy agglomeration and poor dispersion associated with traditional physical mixing, resulting in excellent mechanical properties. The pores between the carbon nanotubes and the porous silicon framework effectively resist expansion and contraction during charging and discharging, mitigating and accommodating the volume expansion of silicon and ensuring the excellent cycle stability of the silicon-carbon anode material. The in-situ grown carbon nanotubes not only ensure that their structure is not damaged, but also have a strong interfacial bond with the porous silicon, thereby improving structural stability. Furthermore, the carbon nanotubes also possess good electrical conductivity, thus enhancing the cycle performance and rate performance of silicon.

[0033] This Joule heating device utilizes high-current resistance heating, resulting in rapid heating, high energy efficiency, and minimal energy loss. It enables ultra-rapid heating within an extremely short time, allowing for the rapid decomposition of the carbon source into carbon nanotubes. Furthermore, it prevents the sublimation of transition metals in the catalyst under prolonged high temperatures, which could lead to catalyst failure and ultimately prevent the formation of carbon nanotubes. Moreover, using a Joule heating device to prepare composite anode materials significantly shortens the production cycle, saves production costs, and is environmentally friendly and energy-efficient.

[0034] This step involves rapid Joule heating at 700-1200℃ to ensure the SiC content and graphitization degree of carbon nanotubes, while avoiding the impact of prolonged high-temperature heating on the crystal structure and material properties.

[0035] This application also provides a lithium-ion battery in which the porous silicon / carbon nanotube composite anode material obtained by the above preparation method has good cycle performance and rate performance.

[0036] The preparation method of the above-mentioned porous silicon / carbon nanotube composite anode material for lithium-ion batteries will be further described in detail below with reference to specific embodiments.

[0037] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0038] Example 1: The preparation method of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries provided in Example 1 includes the following steps: S1 will use 2g of median particle size D 50 Mg₂Si powder with a density of approximately 3 μm was calcined at 700 °C under a nitrogen atmosphere at a heating rate of 5 °C / min for 5 h. After cooling, a porous silicon precursor material was obtained. This precursor material was then stirred with 1 M dilute hydrochloric acid for 1 h, filtered, and washed repeatedly with deionized water until the solution reached neutral pH. Finally, it was filtered again, vacuum dried, and cooled to obtain nanoporous silicon powder material. (See attached image.) Figure 2 .

[0039] from Figure 2 As can be seen, porous silicon is composed of a three-dimensional interconnected nanoframework, with a spherical structure and a particle size of approximately 3 μm. It has a three-dimensional through-hole multi-level channel, with macropores having a diameter of approximately 300 nm and mesopores having a diameter of approximately 30 nm. S2 Select 0.5g of nanoporous silicon powder obtained in step S1 and 0.2g of ferrocene powder (which also serves as a catalyst and carbon source) and sonicate them in an ethanol solution for 5 minutes. Transfer the homogenized liquid into a rotary evaporator and perform solid-liquid separation under vacuum at 50°C to obtain silicon-carbon precursor powder.

[0040] S3 involves rapidly heating the silicon-carbon precursor powder at 1000°C for 1 minute under an Ar atmosphere, removing iron atoms with 1M dilute hydrochloric acid, washing with deionized water, and drying to obtain a porous silicon / carbon nanotube composite anode material. (See...) Figure 3 , Figure 4 and Figure 5 .

[0041] Figure 3 As can be seen, the three-dimensional structure of the nanoporous silicon is well preserved, and uniformly distributed villous tubes can be seen in both the framework and the channels.

[0042] Figure 4 The fluffy carbon nanotubes are clearly visible, with a diameter of approximately 16 nm and a length of approximately 600 nm.

[0043] Figure 5 As can be seen, in addition to silicon and graphite (carbon nanotubes), new phases of SiC and FeSi were also formed.

[0044] The above negative electrode materials were prepared into negative electrode sheets according to the ratio of active material: binder (paa): conductive agent (super P) of 8:1:1. Then, they were assembled with positive electrode sheet (metallic Li sheet), separator (Celgard 2500) and electrolyte (1M LiPF6 and 5wt% FEC added to a mixed solution of EC / DMC / EMC in a volume ratio of 1:1:1) to obtain a 2032 coin cell half cell for charge and discharge testing.

[0045] The cycle test method is as follows: activate at 0.05C for 5 cycles, and then conduct battery charge and discharge tests at a rate of 0.1C (1C=3580mAh / g), with the discharge and charge voltage range being 0.01-1.5V; The rate test method is as follows: the battery is charged and discharged at rates of 0.1C, 0.2C, 0.5C, 1C, and 0.1C (1C=3580mAh / g), with 5 cycles at each rate. The discharge and charge voltage range is 0.01-1.5V.

[0046] Test results are available Figure 6 , Figure 7 See Table 1.

[0047] Depend on Figure 6 , Figure 7 As can be seen from the cycle performance diagram, the carbon nanotubes grown in situ in Example 1 have a buffering effect during the contraction and expansion of silicon material. The generated SiC and FeSi new phases act as solder joints, thereby preventing the carbon nanotubes from falling off during the contraction and expansion of silicon material, improving the first-efficiency and cycle performance of the lithium-ion battery. At the same time, the carbon nanotubes increase the migration speed of lithium ions and electrons, increasing the rate performance of the material. Because the carbon nanotubes are grown in situ on the porous silicon framework, the problems of easy agglomeration and poor dispersion of traditional physical mixing are overcome, thus improving the cycle stability of the silicon-carbon anode material during charge and discharge.

[0048] As can be seen from Table 1, when the porous silicon / carbon nanotube composite anode material prepared in Example 1 is applied to lithium-ion battery products, the initial reversible specific capacity is 2032.5 mAh / g, the initial coulombic efficiency is 83.5%, and the capacity retention rate after 50 cycles is 74.2%, which shows high specific capacity and initial coulombic efficiency, as well as good charge-discharge cycle stability.

[0049] Comparative Example 1: The preparation method of the negative electrode material in Comparative Example 1 includes the following specific steps: 2g of median particle size D 50Mg2Si powder of about 3 μm was calcined at 700 °C for 5 h under a nitrogen atmosphere at a heating rate of 5 °C / min. After cooling, a porous silicon precursor material was obtained. Then, it was stirred with 1 M dilute hydrochloric acid for 1 h, filtered, and washed repeatedly with deionized water until the solution was neutral. Finally, it was filtered, vacuum dried, and cooled to obtain micron-sized porous silicon powder material.

[0050] Combination Figure 6 As shown in Table 1, the coin cell assembled from the materials prepared in Comparative Example 1 has an initial reversible specific capacity of 2797.2 mAh / g (Note: this refers to the reversible specific capacity, not the actual capacity). Figure 6 The discharge specific capacity (vertical axis) rapidly decayed to 891.88 mAh / g after 25 cycles, while the initial reversible specific capacity of Example 1 was 2032.5 mAh / g, and the specific capacity still remained at 1414.7 mAh / g after 25 cycles, demonstrating better cycle stability; from Figure 7 As can be seen, the coin cells assembled from the materials prepared in Example 1 have higher specific capacity and better stability than those in Comparative Example 1 at different charging rates.

[0051] The above-mentioned micron-porous silicon anode material was prepared into anode sheets according to the ratio of active material: binder (paa): conductive agent (super P) of 8:1:1. Then, it was assembled with anode sheet (metallic Li sheet), separator (Celgard 2500) and electrolyte (1M LiPF6 and 5wt% FEC added to a mixed solution of EC / DMC / EMC in a volume ratio of 1:1:1) to obtain a 2032 coin cell half cell for charge and discharge testing.

[0052] The cyclic testing method and the rate testing method are the same as in Example 1.

[0053] The test results are shown in Table 1.

[0054] As can be seen from Table 1, the lithium-ion battery prepared using the negative electrode material of Comparative Example 1 has an initial reversible specific capacity of 2797.2 mAh / g, an initial coulombic efficiency of 74.3%, and a capacity retention rate of only 37.1% after 50 cycles. Although the specific capacity and initial coulombic efficiency are good, the charge-discharge cycle stability is very low.

[0055] Comparative Example 2: The difference from Example 1 is that the carbon nanotubes are physically mixed, that is, the conductive agent (super P) in the coin cell is replaced with commercial multi-walled carbon nanotubes (SWCNTs).

[0056] The specific steps of the preparation method of the negative electrode material in Comparative Example 2 are as follows: 2g of median particle size D50 Mg2Si powder with a density of approximately 3 μm was calcined at 700 °C for 5 h under a nitrogen atmosphere at a heating rate of 5 °C / min. After cooling, a porous silicon precursor material was obtained. Subsequently, it was stirred with 1 M dilute hydrochloric acid for 1 h, filtered, and washed repeatedly with deionized water until the solution was neutral. Finally, it was filtered, vacuum dried, and cooled to obtain micron-sized porous silicon powder material.

[0057] The above-mentioned micron-porous silicon anode material was prepared into anode sheets according to the ratio of active material: binder (paa): conductive agent (SWCNT) of 8:1:1. Then, it was assembled with anode sheet (metallic Li sheet), separator (Celgard 2500) and electrolyte (1M LiPF6 and 5wt% FEC added to a mixed solution of EC / DMC / EMC in a volume ratio of 1:1:1) to obtain a 2032 coin cell half cell for charge and discharge testing.

[0058] The cyclic testing method and the rate testing method are the same as in Example 1.

[0059] The test results are shown in Table 1.

[0060] As can be seen from Table 1, the lithium-ion battery prepared using the negative electrode material of Comparative Example 2 has an initial reversible specific capacity of 2716.9 mAh / g, an initial coulombic efficiency of 76.2%, and a capacity retention rate of only 50.2% after 50 cycles. Although the specific capacity and initial coulombic efficiency are good, the charge-discharge cycle stability is low.

[0061] Example 2: The preparation method of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries provided in Example 2 includes the following steps: S1 will use 2g of median particle size D 50 Ca2Si powder of approximately 3 μm was calcined at 800 °C under a nitrogen atmosphere for 3 h at a heating rate of 8 °C / min. After cooling, a porous silicon precursor material was obtained. Subsequently, it was stirred with 0.5 M dilute hydrochloric acid for 2 h, filtered, and washed repeatedly with deionized water until the solution was neutral. Finally, it was filtered, vacuum dried, and cooled to obtain a nanoporous silicon powder material with three-dimensional through-holes.

[0062] S2 Select 0.5g of nanoporous silicon powder obtained in step S1 and 0.2g of ferrocene powder, and sonicate them in an ethanol solution for 6 minutes. Transfer the homogenized liquid into a rotary evaporator and perform solid-liquid separation under vacuum at 50℃ to obtain silicon-carbon precursor powder.

[0063] S3 The silicon-carbon precursor powder was rapidly heated to 800°C for 3 min in an Ar atmosphere, then acid-washed with 1M dilute hydrochloric acid to remove iron atoms, washed with deionized water, and dried to obtain a porous silicon / carbon nanotube composite anode material. The porous silicon had a particle size of 6 μm, a macropore diameter of approximately 450 nm, a mesopore diameter of approximately 20 nm, and a villous carbon nanotube length of 500 nm and a tube diameter of 16 nm.

[0064] The above-mentioned porous silicon / carbon nanotube composite anode material was used to prepare 2032 coin cells according to the method in Example 1, and charge-discharge tests were performed.

[0065] The cyclic testing method and the rate testing method are the same as in Example 1.

[0066] The test results are shown in Table 1.

[0067] As can be seen from Table 1, the lithium-ion battery prepared using the porous silicon / carbon nanotube composite anode material of Example 2 has an initial reversible specific capacity of 2082.9 mAh / g, an initial coulombic efficiency of 81.9%, and a capacity retention rate of only 71.3% after 50 cycles. It has high specific capacity and initial coulombic efficiency, and good charge-discharge cycle stability.

[0068] Example 3: The preparation method of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries provided in Example 3 includes the following steps: S1 will use 2g of median particle size D 50 Mg2Si powder of about 5 μm was calcined at 900 °C under nitrogen atmosphere at a heating rate of 10 °C / min for 4 h. After cooling, a porous silicon precursor material was obtained. Then, it was stirred with 0.5 M dilute hydrochloric acid for 2 h, filtered, and washed repeatedly with deionized water until the solution was neutral. Finally, it was filtered, vacuum dried, and cooled to obtain nanoporous silicon powder material.

[0069] S2 Select 0.4g of nanoporous silicon powder obtained in step S1 and 0.2g of nickel nitrate powder, and sonicate them in fructose solution for 10min. Transfer the homogenized liquid into a rotary evaporator and perform solid-liquid separation under vacuum at 60℃ to obtain silicon-carbon precursor powder.

[0070] S3 subjected silicon-carbon precursor powder to rapid heating at 900°C for 1 min in an Ar atmosphere, removed iron atoms by acid washing with 1M dilute hydrochloric acid, washed with deionized water, and dried to obtain a porous silicon / carbon nanotube composite anode material. The porous silicon has a particle size of 6 μm, a macropore diameter of approximately 100 nm, a mesopore diameter of approximately 10 nm, and a villous carbon nanotube length of 600 nm and a tube diameter of 20 nm.

[0071] The above-mentioned porous silicon / carbon nanotube composite anode material was used to prepare 2032 coin cells according to the method in Example 1, and charge-discharge tests were performed.

[0072] The cyclic testing method and the rate testing method are the same as in Example 1.

[0073] The test results are shown in Table 1.

[0074] As can be seen from Table 1, the lithium-ion battery prepared using the porous silicon / carbon nanotube composite anode material of Example 3 has an initial reversible specific capacity of 2131.8 mAh / g, an initial coulombic efficiency of 82.4%, and a capacity retention rate of only 70.5% after 50 cycles. It has high specific capacity and initial coulombic efficiency, and good charge-discharge cycle stability.

[0075] Example 4: The preparation method of the porous silicon / carbon nanotube composite anode material for lithium-ion batteries provided in Example 4 includes the following steps: S1 will use 2g of median particle size D 50 Ca2Si powder of about 3 μm was calcined at 1000 °C in an oxygen atmosphere for 2 h at a heating rate of 10 °C / min. After cooling, a porous silicon precursor material was obtained. Then, it was stirred with 1 M dilute hydrochloric acid for 1 h, filtered, and washed repeatedly with deionized water until the solution was neutral. Finally, it was filtered, vacuum dried, and cooled to obtain nanoporous silicon powder material.

[0076] S2 Select 0.5g of nanoporous silicon powder obtained in step S1, 0.01g of ferric nitrate powder, and 0.2g of glucose, and sonicate them in a deionized aqueous solution for 5 minutes. Transfer the homogenized liquid into a rotary evaporator and perform solid-liquid separation under vacuum at 50 degrees Celsius to obtain silicon-carbon precursor powder.

[0077] 3) The silicon-carbon precursor powder was rapidly heated to 800°C for 1 min in an Ar atmosphere, iron atoms were removed by acid washing with 1M dilute hydrochloric acid, and the powder was washed with deionized water and dried to obtain a porous silicon / carbon nanotube composite anode material. The porous silicon had a particle size of 5 μm, a macropore diameter of approximately 150 nm, a mesopore diameter of approximately 40 nm, and a villous carbon nanotube length of 700 nm and a tube diameter of 15 nm.

[0078] The above-mentioned porous silicon / carbon nanotube composite anode material was used to prepare 2032 coin cells according to the method in Example 1, and charge-discharge tests were performed.

[0079] The cyclic testing method and the rate testing method are the same as in Example 1.

[0080] The test results are shown in Table 1.

[0081] As can be seen from Table 1, the lithium-ion battery prepared using the porous silicon / carbon nanotube composite anode material of Example 4 has an initial reversible specific capacity of 1930.1 mAh / g, an initial coulombic efficiency of 80.3%, and a capacity retention rate of only 68.3% after 50 cycles. It has high specific capacity and initial coulombic efficiency, and good charge-discharge cycle stability.

[0082] Example 5: S1 will use 2g of median particle size D 50 Mg2Si powder of about 3 μm was calcined at 700 °C in an oxygen atmosphere for 5 h at a heating rate of 5 °C / min. After cooling, a porous silicon precursor material was obtained. Then, it was stirred with 1 M dilute hydrochloric acid for 1 h, filtered, and washed repeatedly with deionized water until the solution was neutral. Finally, it was filtered, vacuum dried, and cooled to obtain nanoporous silicon powder material.

[0083] S2 Select 0.5g of nanoporous silicon powder obtained in step S1, 0.01g of ferric sulfate powder, and 0.2g of sucrose and sonicate them in a deionized aqueous solution for 5 minutes. Transfer the homogenized liquid into a rotary evaporator and perform solid-liquid separation under vacuum at 50℃ to obtain silicon-carbon precursor powder.

[0084] S3 The silicon-carbon precursor powder was rapidly heated to 1200°C for 1 min in an Ar atmosphere, iron atoms were removed by acid washing with 1M dilute hydrochloric acid, and the powder was washed with deionized water and dried to obtain a porous silicon / carbon nanotube composite anode material. The porous silicon had a particle size of 10 μm, a macropore diameter of approximately 500 nm, a mesopore diameter of approximately 50 nm, and a villous carbon nanotube length of 800 nm and a tube diameter of 20 nm.

[0085] The above-mentioned porous silicon / carbon nanotube composite anode material was used to prepare 2032 coin cells according to the method in Example 1, and charge-discharge tests were performed.

[0086] The cyclic testing method and the rate testing method are the same as in Example 1.

[0087] The test results are shown in Table 1.

[0088] As can be seen from Table 1, the lithium-ion battery prepared using the porous silicon / carbon nanotube composite anode material of Example 5 has an initial reversible specific capacity of 1825.7 mAh / g, an initial coulombic efficiency of 81.5%, and a capacity retention rate of only 72.9% after 50 cycles. It has high specific capacity and initial coulombic efficiency, and good charge-discharge cycle stability.

[0089] Table 1

[0090] The above embodiments shown in this application are only part of the preferred embodiments of this application and should not be construed as limiting this application. Any modifications, equivalent substitutions and improvements made by those skilled in the art without departing from the spirit of this application shall be within the protection scope of this application.

Claims

1. A porous silicon / carbon nanotube composite anode material for lithium ion batteries, characterized in that, The material includes a nanoporous silicon framework having three-dimensional through-holes in a multi-level channel, in which carbon nanotubes are distributed. The carbon nanotubes grow in situ in a villous manner within the channel, forming a porous silicon composite anode material with villous carbon nanotubes.

2. The porous silicon / carbon nanotube composite anode material for lithium-ion batteries as described in claim 1, characterized in that, The composite negative electrode material has a spherical structure.

3. The porous silicon / carbon nanotube composite anode material for lithium-ion batteries as described in claim 2, characterized in that, The composite negative electrode material has a particle size of 1-10 μm, the pore size of the channel is 5-500 nm, and the carbon nanotubes have a length of 100-800 nm and a diameter of 5-20 nm.

4. The porous silicon / carbon nanotube composite anode material for lithium-ion batteries as described in claim 1, characterized in that, The weight percentage of porous silicon in the composite anode material is 20-90%.

5. A method for preparing a porous silicon / carbon nanotube composite anode material for lithium-ion batteries according to any one of claims 1-4, characterized in that, Includes the following steps: S1 Silicon alloy particles are placed in an air, nitrogen, or oxygen atmosphere and de-alloyed at a heating rate of 1-10℃ / min at 700~1000℃. Pores are formed by generating oxide or nitride particles during the de-alloying process. Then, the oxides or nitrides are removed by acid washing to form multi-level channels. After filtration and drying, nanoporous silicon powder with a framework structure is obtained. S2 The nanoporous silicon powder particles prepared in step S1 are mixed with the catalyst and carbon source solution, ultrasonically dispersed for 5-30 min, and the mixture is dried to obtain silicon-carbon precursor powder. S3 is rapidly heated by Joule for 0.1-3 minutes in an inert atmosphere at a temperature of 700-1200℃ to allow the catalyzed carbon source to grow in situ on a nanoporous silicon framework to form villous carbon nanotubes. These nanotubes then react with porous silicon to generate SiC and metal silicides. After acid washing and drying, a porous silicon / carbon nanotube composite anode material with carbon nanotubes growing in situ in the pores is obtained.

6. The method for preparing the porous silicon / carbon nanotube composite anode material for lithium-ion batteries according to claim 5, characterized in that, The silicon alloy in step S1 is either a silicon-magnesium alloy or a silicon-calcium alloy.

7. The method for preparing the porous silicon / carbon nanotube composite anode material for lithium-ion batteries according to claim 5, characterized in that, In step S2, the catalyst is one of ferrocene, ferric nitrate, ferric sulfate, ferric chloride, nickel nitrate, and nickel chloride.

8. The method for preparing the porous silicon / carbon nanotube composite anode material for lithium-ion batteries according to claim 5 or 7, characterized in that, In step S2, the carbon source is at least one of ferrocene, fructose, sucrose, glucose, and starch.

9. The method for preparing the porous silicon / carbon nanotube composite anode material for lithium-ion batteries according to claim 5 or 7, characterized in that, The mass ratio of the nanoporous silicon powder particles, the catalyst, and the carbon source solution is 40-50: 1-2: 20-30.

10. A lithium-ion battery, characterized in that, The composite anode material for lithium-ion batteries comprising porous silicon / carbon nanotubes as described in any one of claims 5-9.

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