A silicon-carbon anode material and its preparation method

Abstract

This invention belongs to the field of lithium battery electrode materials, specifically relating to a novel silicon-carbon anode material and its preparation method. The preparation method involves first mixing, kneading, and aging plant starch, nitrogen-boron dopant, and nano-silicon to obtain a silicon-carbon anode precursor, followed by carbonization and vapor-phase coating to obtain a novel cage-like silicon-carbon anode material. This invention uniformly disperses nano-silicon within a high-strength amorphous carbon shell formed by carbonizing plant starch gel, effectively improving the conductivity of the nano-silicon and suppressing its expansion during charge and discharge. Subsequent vapor-phase coating significantly reduces the specific surface area of ​​the material, improving initial efficiency and cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery electrode materials, specifically relating to a silicon-carbon anode material and its preparation method. Background Technology

[0002] With the development of new energy vehicles and the low-altitude economy, lithium batteries are constantly moving towards higher energy density. The main path to this is through the use of positive and negative electrode active materials with higher specific capacity. However, due to the reduced safety of high specific capacity positive electrodes, the trend of high energy density of positive electrodes has encountered some setbacks. At present, improving the energy density of lithium batteries through negative electrodes has regained widespread attention.

[0003] Silicon is considered one of the most promising anode materials for lithium-ion batteries due to its extremely high theoretical capacity and low lithium potential. However, silicon also has some problems. First, the lithium insertion / extraction process is accompanied by severe volume expansion, which leads to cracking and pulverization of the material. Second, as a semiconductor, silicon has low conductivity, resulting in poor battery performance in fast charging and fast discharging.

[0004] To address the volume expansion problem of silicon materials, an effective method is to nanoscale silicon to shorten the lithium-ion diffusion path, reduce internal stress concentration, and suppress material cracking and pulverization. Although nanoscale silicon significantly improves electrochemical performance, it still suffers from problems such as large specific surface area, low initial coulombic efficiency, easy agglomeration, and poor conductivity, making pure silicon unsuitable as an anode material. Currently, silicon-carbon composites (Si / C) based on nanoscale silicon materials show the greatest commercial application potential. Carbon materials can improve the conductivity of silicon-based materials, enhancing rate performance; suppress silicon expansion, improving cycle performance; and isolate the electrolyte from direct contact with nanoscale silicon, improving initial coulombic efficiency.

[0005] Biomass carbon materials have shown significant application potential in the battery field. Their hierarchical porous structure, high specific surface area, and tunable surface chemistry make them a key component of high-performance electrode materials. In lithium-ion batteries, biomass-derived carbon (such as coconut shell carbon and bamboo charcoal) can serve as a buffer framework for silicon-based anodes, effectively mitigating silicon volume expansion and improving conductivity. In sodium / potassium-ion batteries, their disordered hard carbon structure provides stable ion intercalation sites, supporting low-cost energy storage systems. Starch, one of the most abundant renewable resources on Earth, is widely found in various plants. It is a typical polysaccharide with a simple structure and high carbon content, making it an ideal carbon precursor for lithium / sodium-ion battery anode materials. Therefore, developing a novel silicon-carbon anode material using starch as a precursor is of great significance. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a silicon-carbon anode material and its preparation method. The silicon-carbon anode material not only has low volume effect and good conductivity, but also has high initial charge-discharge capacity and initial efficiency, and excellent electrochemical performance.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first objective of this invention is to provide a method for preparing a silicon-carbon anode material, comprising the following steps:

[0009] S1. Plant starch, nitrogen-boron dopant and nano-silicon are added to a double planetary mixer in sequence. After mixing for 2-3 hours, deionized water is added. The mixture is kneaded at 55-100℃ for 4-6 hours and then aged in air for 12-15 hours to obtain silicon-carbon anode precursor.

[0010] Starch is a polysaccharide composed of glucose units linked by α-1,4 and α-1,6 glycosidic bonds. Depending on the type of starch, the gelatinization temperature varies from 55 to 100°C. During starch gelatinization, the insertion of water molecules causes the α-1,4 and α-1,6 glycosidic bonds to break, resulting in a sharp increase in viscosity. The strong shear force of a kneader ensures uniform mixing of the components. During aging, the amylopectin chain structure reorganizes, forming a cage structure that encapsulates nano-silicon. Finally, by introducing nitrogen and boron atoms, the electronic structure of the carbon matrix is ​​altered, increasing the charge carrier concentration and significantly improving the material's conductivity. Furthermore, active sites are formed, providing additional lithium storage centers and increasing reversible capacity.

[0011] S2. The silicon-carbon anode precursor is placed in an atmosphere furnace under nitrogen protection, heated to 260°C, held for 2-4 hours, then heated to 800°C and held for 6-8 hours. The carbonized material is then removed, pulverized by an air jet mill, and passed through a 325-mesh sieve to obtain the intermediate material. In this step, starch reacts violently at 260°C, releasing a large amount of volatiles such as tar and wood vinegar. At 800°C, it can form an amorphous carbon skeleton without causing silicon crystal phase transformation, resulting in excellent electrochemical performance.

[0012] S3. Place the intermediate material in a rotary kiln, heat it to 600°C under a nitrogen atmosphere, introduce acetylene gas, continue heating to 800°C and hold for 2-3 hours, then turn off the acetylene gas and hold for 1-2 hours. After cooling, the silicon-carbon anode material is obtained.

[0013] This invention first gelatinizes starch, breaking down amylopectin and then uniformly mixing it with nano-silicon and nitrogen-boron dopants. During aging, the starch molecules recombine to form a cage structure that traps the nano-silicon, effectively suppressing the volume effect of nano-silicon during cycling. Simultaneously, boron doping enhances the material's conductivity and increases reversible capacity. After carbonization, vapor deposition further reduces the material's specific surface area, suppressing side reactions between the material and the electrolyte. The resulting silicon-carbon anode material exhibits excellent electrochemical and cycling performance.

[0014] Furthermore, in the above technical solution S1, the plant starch is one or more of potato starch, cassava starch, and corn starch.

[0015] Furthermore, in the above technical solution S1, the nitrogen-boron dopant is one or more of ammonium borate, ammonium tetraborate, and ammonium pentaborate, and the amount added is 1% to 2% of the total mass of the plant starch.

[0016] Furthermore, in the above technical solution S1, the amount of nano-silicon added is 10%~15% of the total mass of the plant starch, and the particle size Dv50 is 90nm~150nm.

[0017] Furthermore, in the above technical solution S1, the stirring speed is 80 r / min to 120 r / min.

[0018] Furthermore, in the above technical solution S1, the amount of deionized water added is 100% to 120% of the total mass of the plant starch.

[0019] Furthermore, in the above technical solution S2, the heating rate is 1℃ / min to 5℃ / min.

[0020] Furthermore, in the above technical solution S3, the heating rate is 2℃ / min~5℃ / min, the nitrogen gas introduction rate is 8L / min, and the acetylene gas introduction rate is 2L / min.

[0021] A second objective of this invention is to provide a silicon-carbon anode material prepared by the above-described method, wherein the initial coulombic efficiency of the silicon-carbon anode material is ≥90%.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention utilizes the gelatinization properties of starch to fully gelatinize and break down amylopectin. After thorough mixing with nano-silicon and nitrogen-boron dopants, the aging properties of starch are utilized to allow the amylopectin to recombine and form a cage structure that encapsulates the nano-silicon. After carbonization, the nano-silicon is uniformly dispersed in a high-strength amorphous carbon shell formed by the carbonization of plant starch gel. This effectively improves the conductivity of the nano-silicon and inhibits its expansion during charging and discharging. Further vapor-phase coating significantly reduces the specific surface area of ​​the material, improving its initial efficiency and cycle performance. The resulting silicon-carbon material has the advantages of high energy density, high initial efficiency, and high cycle stability.

[0024] The carbon source raw materials used in the preparation method of this invention are inexpensive and readily available, and the resulting silicon-carbon anode material has excellent performance and high market competitiveness. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a SEM image of the silicon-carbon anode material prepared in Example 1 of the present invention.

[0027] Figure 2 This is a 1C 300-cycle cycling diagram of the silicon-carbon anode material prepared in Example 1 of the present invention. Detailed Implementation

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the raw materials used in the following examples are all commercially available products and can be purchased from the market.

[0029] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions.

[0030] The raw materials involved in the various embodiments of the present invention are either existing commercially available products or can be prepared according to existing methods, and the testing methods are industry-standard methods.

[0031] Example 1

[0032] A method for preparing a silicon-carbon anode material includes the following steps:

[0033] 100g of potato starch, 12g of nano-silicon with a Dv50 of 100nm, and 1g of ammonium borate were added to a double planetary mixer and mixed at 90r / min for 2.5h. Then, 100g of deionized water was added, and the mixture was kneaded at 60℃ for 6h. After aging in air for 12h, precursor 1 was obtained. Precursor 1 was placed in an atmosphere furnace and heated to 260℃ at a heating rate of 2℃ / min under nitrogen protection, and held at that temperature for 2 hours. h, then heat to 800℃ at a heating rate of 2℃ / min, hold for 8h, remove and pulverize with an air jet mill and pass through a 325 mesh sieve to obtain precursor 2; place precursor 2 in a rotary furnace, introduce nitrogen at a flow rate of 8L / min, heat to 800℃ at a heating rate of 5℃ / min, introduce acetylene at a rate of 2L / min for 3h, then turn off the acetylene gas, hold at 800℃ for 1h; after cooling, obtain silicon-carbon anode material.

[0034] Example 2

[0035] A method for preparing a silicon-carbon anode material includes the following steps:

[0036] 100g of corn starch, 12g of nano-silicon with a Dv50 of 100nm, and 1g of ammonium tetraborate were added to a double planetary mixer and mixed at 90r / min for 2.5h. Then, 100g of deionized water was added, and the mixture was kneaded at 65℃ for 4h. After aging in air for 12h, precursor 1 was obtained. Precursor 1 was placed in an atmosphere furnace and heated to 260℃ at a heating rate of 2℃ / min under nitrogen protection, and held at that temperature for 2 hours. h, then heat to 800℃ at a heating rate of 2℃ / min, hold for 8h, remove and pulverize with an air jet mill and pass through a 325 mesh sieve to obtain precursor 2; place precursor 2 in a rotary furnace, introduce nitrogen at a flow rate of 8L / min, heat to 800℃ at a heating rate of 5℃ / min, introduce acetylene at a rate of 2L / min for 3h, then turn off the acetylene gas, hold at 800℃ for 1h; after cooling, obtain silicon-carbon anode material.

[0037] Example 3

[0038] A method for preparing a silicon-carbon anode material includes the following steps:

[0039] 100g of cassava starch, 12g of nano-silicon with a Dv50 of 100nm, and 1g of ammonium pentaborate were added to a double planetary mixer and mixed at 90r / min for 2.5h. Then, 100g of deionized water was added, and the mixture was kneaded at 60℃ for 6h. After aging in air for 12h, precursor 1 was obtained. Precursor 1 was placed in an atmosphere furnace and heated to 260℃ at a heating rate of 2℃ / min under nitrogen protection, and held at that temperature for 2 hours. h, then heat to 800℃ at a heating rate of 2℃ / min, hold for 8h, remove and pulverize with an air jet mill and pass through a 325 mesh sieve to obtain precursor 2; place precursor 2 in a rotary furnace, introduce nitrogen at a flow rate of 8L / min, heat to 800℃ at a heating rate of 5℃ / min, introduce acetylene at a rate of 2L / min for 3h, then turn off the acetylene gas, hold at 800℃ for 1h; after cooling, obtain silicon-carbon anode material.

[0040] Example 4

[0041] A method for preparing a silicon-carbon anode material includes the following steps:

[0042] 100g of potato starch, 12g of nano-silicon with a Dv50 of 150nm, and 1g of ammonium borate were added to a double planetary mixer and mixed at 90r / min for 2.5h. Then, 100g of deionized water was added, and the mixture was kneaded at 60℃ for 6h. After aging in air for 12h, precursor 1 was obtained. Precursor 1 was placed in an atmosphere furnace and heated to 260℃ at a heating rate of 2℃ / min under nitrogen protection, and held at that temperature for 2 hours. h, then heat to 800℃ at a heating rate of 2℃ / min, hold for 8h, remove and pulverize with an air jet mill and pass through a 325 mesh sieve to obtain precursor 2; place precursor 2 in a rotary furnace, introduce nitrogen at a flow rate of 8L / min, heat to 800℃ at a heating rate of 5℃ / min, introduce acetylene at a rate of 2L / min for 3h, then turn off the acetylene gas, hold at 800℃ for 1h; after cooling, obtain silicon-carbon anode material.

[0043] Comparative Example 1

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

[0045] 100g of potato starch, 12g of nano-silicon with a Dv50 of 100nm, and 1g of ammonium borate were added to a double planetary mixer and mixed at 90r / min for 2.5h. Then, 100g of deionized water was added and kneaded at 60℃ for 6h to obtain precursor 1. Precursor 1 was placed in an atmosphere furnace and heated to 260℃ at a heating rate of 2℃ / min under nitrogen protection, and held for 2h. Then, it was heated to 800℃ at a heating rate of 2℃ / min and held for 8h. After removal, it was pulverized by an air jet mill and passed through a 325-mesh sieve to obtain precursor 2. Precursor 2 was placed in a rotary furnace and nitrogen was introduced at a flow rate of 8L / min. The temperature was increased to 800℃ at a heating rate of 5℃ / min, and acetylene was introduced at a rate of 2L / min for 3h. Then, the acetylene gas was turned off and the temperature was held at 800℃ for 1h. After cooling, silicon-carbon anode material was obtained.

[0046] Comparative Example 2

[0047] A method for preparing a silicon-carbon anode material includes the following steps:

[0048] 100g of potato starch, 12g of nano-silicon with a Dv50 of 100nm, and 1g of ammonium borate were added to a double planetary mixer and mixed at 90r / min for 2.5h. Then, 100g of deionized water was added, and the mixture was kneaded at 60℃ for 6h. After aging in air for 12h, precursor 1 was obtained. Precursor 1 was placed in an atmosphere furnace and heated to 260℃ at a heating rate of 2℃ / min under nitrogen protection, and held at that temperature for 2 hours. h, then heat to 800℃ at a heating rate of 2℃ / min, hold for 8h, remove and pulverize with an air jet mill and pass through a 325 mesh sieve to obtain precursor 2; place precursor 2 in a rotary furnace, introduce nitrogen at a flow rate of 8L / min, heat to 900℃ at a heating rate of 5℃ / min, introduce acetylene at a rate of 2L / min for 3h, then turn off the acetylene gas, hold at 800℃ for 1h; after cooling, obtain silicon-carbon anode material.

[0049] Comparative Example 3

[0050] A method for preparing a silicon-carbon anode material includes the following steps:

[0051] 100g of potato starch and 12g of nano-silicon with a Dv50 of 100nm were added to a double planetary mixer and mixed at 90r / min for 2.5h. Then 100g of deionized water was added and kneaded at 60℃ for 6h. After aging in air for 12h, precursor 1 was obtained. Precursor 1 was placed in an atmosphere furnace and heated to 260℃ at a heating rate of 2℃ / min under nitrogen protection, and held for 2h. Then it was heated to 800℃ at a heating rate of 2℃ / min and held for 8h. After removal, it was pulverized by an air jet mill and passed through a 325-mesh sieve to obtain precursor 2. Precursor 2 was placed in a rotary furnace and nitrogen was introduced at a flow rate of 8L / min. The temperature was increased to 800℃ at a heating rate of 5℃ / min. Acetylene was introduced at a rate of 2L / min for 3h. Then the acetylene gas was turned off and the temperature was held at 800℃ for 1h. After cooling, silicon-carbon anode material was obtained.

[0052] Test case

[0053] 1. The silicon-carbon anode material obtained during the preparation process in Example 1 was examined using a scanning electron microscope to observe its microstructure. The results are as follows: Figure 1 As shown, the silicon-carbon anode material exhibits uniform material distribution, with nano-silicon demonstrating good dispersion and material coating integrity. Furthermore, the use of high-strength biomass as a substrate effectively suppresses silicon expansion.

[0054] 2. To test the performance of the silicon-carbon anode materials prepared in Examples 1-4 and Comparative Examples 1-3 for lithium-ion batteries, a half-cell test method was used.

[0055] The half-cell testing method was as follows: Silicon-carbon materials prepared in Examples 1-4 and Comparative Examples 1-3 were used as negative electrode active materials to form a slurry. The slurry ratio was: active material: CNTs (including dispersant): CMC: SBR = 89%: 4.5%: 1.5%: 5%, where CMC was a 1.5% aqueous solution. The slurry was then coated onto copper foil and vacuum dried for 12 hours to form a negative electrode sheet. The electrolyte was commercially available, the separator was a PE film, and the lithium sheet was used as the counter electrode. Half-cells were assembled in a glove box. Constant current charge-discharge experiments were conducted using a LAND battery testing system, with the charge-discharge voltage limited to 0.005V-2V. Data acquisition and control were performed using a computer-controlled charge-discharge cabinet. The physical and electrochemical performance test results of the negative electrode materials in Examples 1-4 and Comparative Examples 1-3 are shown in Table 1 and... Figure 2 As shown.

[0056] Table 1 Test results of physical and electrochemical properties of the anode material

[0057]

[0058] As can be seen from Table 1, the materials in Examples 1 to 4 have a low specific surface area, indicating that the coated carbon layer is uniform and dense. This improves conductivity while avoiding direct contact between silicon and electrolyte, giving the materials good cycling performance. The initial reversible capacity is all >1570mAh / g; the initial coulombic efficiency is all >90%; and the capacity retention rate after 300 cycles is all >91%, demonstrating the advantages of high energy density, high initial efficiency, and high cycling stability. Comparative Example 1 has a larger specific surface area, but lower initial coulombic efficiency and cycle capacity retention. This is because the absence of an aging step means that the starch molecules remain in a broken state, unable to encapsulate silicon, resulting in an increased specific surface area. Furthermore, the exposed nano-silicon reacts violently with the electrolyte, leading to low initial coulombic efficiency and cycle capacity retention. Comparative Example 2 shows a decrease in initial reversible capacity, initial coulombic efficiency, and cycle capacity retention because the carbonization temperature is increased to 900℃, causing a phase transformation in the nano-silicon crystals and a decline in the electrochemical performance of the silicon-based material, resulting in a decrease in initial reversible capacity, initial coulombic efficiency, and cycle capacity retention. Comparative Example 3 shows a decrease in initial reversible capacity because it lacks nitrogen and boron dopants, resulting in a decrease in charge carrier concentration and active sites, leading to decreased conductivity and reversible capacity.

[0059] In summary, this invention uses starch as a carbon precursor and utilizes the gelatinization properties of starch to fully gelatinize and break down amylopectin. After being thoroughly mixed with nano-silicon and nitrogen-boron dopants, the aging properties of starch are utilized to form a cage structure during the recombination of amylopectin, which encapsulates the nano-silicon. This effectively inhibits the expansion of the nano-silicon, and the resulting silicon-carbon material has the advantages of high energy density, high initial efficiency, and high cycle stability.

[0060] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. 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 silicon-carbon anode material, characterized in that, Includes the following steps: S1. Plant starch, nitrogen-boron dopant, and nano-silicon are sequentially added to a dual planetary mixer and stirred for 2-3 hours. Then, deionized water is added, and the mixture is kneaded at 55-100°C for 4-6 hours. The mixture is then aged in air for 12-15 hours to obtain a silicon-carbon anode precursor. The amount of nitrogen-boron dopant added is 1%-2% of the total mass of the plant starch; the amount of nano-silicon added is 10%-15% of the total mass of the plant starch; and the amount of deionized water added is 100%-120% of the total mass of the plant starch. The nitrogen-boron dopant is one or more of ammonium borate, ammonium tetraborate, and ammonium pentaborate. S2. Place the silicon-carbon anode precursor in an atmosphere furnace under nitrogen protection, heat it to 260℃, hold it for 2-4 hours, then heat it to 800℃ and hold it for 6-8 hours. After taking out the carbonized material, crush it with an air jet mill and pass it through a 325-mesh sieve to obtain the intermediate material. S3. Place the intermediate material in a rotary kiln, heat it to 600°C under a nitrogen atmosphere, introduce acetylene gas, continue heating to 800°C and hold for 2-3 hours, then turn off the acetylene gas and hold for 1-2 hours. After cooling, the silicon-carbon anode material is obtained.

2. The preparation method according to claim 1, characterized in that, In S1, the plant starch is one or more of potato starch, cassava starch, and corn starch.

3. The preparation method according to claim 1, characterized in that, In S1, the particle size Dv50 of the nano-silicon is 90nm~150nm.

4. The preparation method according to claim 1, characterized in that, In S1, the stirring speed is 80 r / min to 120 r / min.

5. The preparation method according to claim 1, characterized in that, In S2, the heating rate is 1℃ / min to 5℃ / min.

6. The preparation method according to claim 1, characterized in that, In S3, the heating rate is 2℃ / min to 5℃ / min, the nitrogen gas introduction rate is 8L / min, and the acetylene gas introduction rate is 2L / min.

7. A silicon-carbon anode material prepared by the preparation method according to any one of claims 1-6, characterized in that, The initial coulombic efficiency of the silicon-carbon anode material is ≥90%.

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