A silicon-carbon negative electrode material based on spherical starch porous carbon and its preparation method

Abstract

The present invention belongs to the field of lithium battery electrode materials, and specifically relates to a silicon-carbon negative electrode material based on spherical starch porous carbon and a preparation method thereof. The preparation method first esterifies plant starch with an esterifying agent, then carbonizes it, activates it with potassium hydroxide after crushing, and then uses vapor deposition silane technology to further prepare the silicon-carbon negative electrode material after acid washing. The present invention uses starch after esterification as a precursor, prepares porous carbon through carbonization and activation, and then prepares the silicon-carbon negative electrode material through vapor deposition silane technology. The silicon-carbon negative electrode material not only has a spherical porous carbon skeleton, low volume effect, good conductivity, but also has high first charge and discharge capacity and first efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of lithium battery electrode materials, and in particular relates to a silicon-carbon negative electrode material based on spherical starch porous carbon and a preparation method thereof. Background Art

[0002] As the energy industry pursues high-capacity batteries, the insufficient energy density of lithium batteries has limited the further development of energy storage batteries. Silicon, due to its extremely high theoretical capacity and low potential for lithium, is considered a promising anode material for lithium-ion batteries. However, silicon undergoes severe volume expansion during lithium insertion and extraction, significantly reducing the anode capacity and, as a result, the cycle life of silicon as an anode material is very short. Furthermore, as a semiconductor, silicon has low electrical conductivity, which results in low battery output power, thus reducing the efficiency of silicon in lithium-ion batteries.

[0003] In order to solve the impact of silicon material on lithium-ion batteries due to volume expansion, an effective method is to use gas-phase silicon to deposit on the surface of porous carbon to form a coated silicon-carbon material. Among them, porous carbon is used as a carrier, and silicon source gas is deposited in its pores to form a silicon-carbon negative electrode material. The pores of porous carbon are mainly micropores and mesopores, and its pores are highly ordered. It is widely used in adsorption purification, energy storage, catalysis and other fields. Porous carbon is the core of CVD preparation of silicon-carbon negative electrode materials. The morphology, components and pore structure of porous carbon have a significant impact on the performance of porous silicon-carbon negative electrode materials.

[0004] Biomass has attracted widespread attention in recent years as a low-cost, environmentally friendly, and sustainable resource. Due to its diverse morphology and structure, a wide range of biomass precursors have been used to manufacture carbon materials, which have been applied in numerous fields, such as alkali metal ion batteries, supercapacitors, and catalysis. Starch, one of the most abundant renewable resources on Earth and found in a wide variety of plants, is a typical polysaccharide with a simple structure and high carbon content, making it an ideal carbon precursor for lithium- and sodium-ion battery anode materials. Furthermore, starch's inherent spherical structure makes it a highly competitive candidate for the preparation of spherical carbon materials. However, starch chains linked by glycosidic bonds exhibit poor thermal stability. During pyrolysis, the thermal cleavage of glycosidic bonds releases a large number of volatile products, particularly levoglucosan. Furthermore, the rapid release of volatiles disrupts the spherical morphology, leading to structural melting and blistering, resulting in low carbon yields. Therefore, the development of a silicon-carbon anode material that can utilize starch as a carbon source and effectively overcome these challenges is of great significance. Summary of the Invention

[0005] In response to the above defects or improvement needs of the prior art, the present invention provides a silicon-carbon negative electrode material based on spherical starch porous carbon and a preparation method thereof. The silicon-carbon negative electrode material not only has a spherical porous carbon skeleton, low volume effect, and good conductivity, but also has high first charge and discharge capacity and first efficiency, and excellent charge-withdrawal performance.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The first object of the present invention is to provide a method for preparing a silicon-carbon negative electrode material based on spherical starch porous carbon, comprising the following steps:

[0008] S1. Add plant starch and esterifying agent to a high-speed mixer in sequence, stir and mix evenly, then heat to 70-100°C for esterification reaction, and continue the reaction for 2-6 hours. Plant starch is a polysaccharide composed of glucose units connected by α-1,4 and α-1,6 glycosidic bonds. Each glucose unit has 3 free hydroxyl groups (C2, C3, and C6 positions). In this step, through the esterification reaction, these hydroxyl groups undergo nucleophilic substitution reaction or ester exchange reaction with the esterifying agent. As the ester group is gradually generated, the activation energy of the reaction will gradually increase. In this technical solution, acid anhydride is selected as the esterifying agent. The alcoholysis activity of acid anhydride is higher than that of the corresponding carboxylic acid, and its alcoholysis temperature is usually lower, which is more suitable for the process requirements of the present invention. Taking succinic anhydride as an example, the reaction formula is as follows:

[0009] (CH2CO)2O + Starch-OH → Starch-O-COCH2CH2COO - + H + ,

[0010] Starch-O-COCH2CH2COO - + Starch-OH → Starch-O-COCH2CH2OC-O-Starch + OH - .

[0011] S2. Placing the starch after the esterification reaction in S1 in an atmosphere furnace and heating it to 800°C-950°C under a nitrogen atmosphere for carbonization. The carbonization of the esterified starch is essentially a high-temperature pyrolysis reaction, which converts organic matter into a carbon skeleton at high temperature in an inert atmosphere while retaining or enhancing its specific functions, such as pore structure and conductivity.

[0012] S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray the potassium hydroxide solution dissolved in water onto the carbonized material under the sieve, let it stand for 24 hours, and then dry it;

[0013] S4. The carbonized material dried in S3 is placed in a rotary kiln and heated to 800-950°C for activation. A series of reactions occur during the carbonization process, as shown below:

[0014] 2KOH → K2O +H2O formula (1-1),

[0015] H2O + C → H2 + CO (1-2),

[0016] H2O + CO → H2+ CO2 (1-3),

[0017] K2O + CO2→ K2CO3 formula (1-4),

[0018] When the activation temperature is higher than 700℃, the K2CO3 formed in formula 1-4 decomposes into CO2 and K2O, and is further reduced by carbon to form CO and K. The specific reaction process is as follows:

[0019] K2O + C → 2K + CO (1-5),

[0020] K2CO3 + 2C → 2K + 3CO formula (1-6),

[0021] CO2+ C → 2CO formula (1-7).

[0022] K2CO3 potassium carbonate begins to decompose, producing CO2 and K2O, and decomposition is complete at 800°C. At higher temperatures, the physical activation effects of CO2 and water vapor are significantly enhanced, significantly improving the overall activation effect. Furthermore, potassium vapor produced during the reaction of K2O with carbon can intercalate and activate the carbon, traveling between carbon microcrystal layers to create and expand pores.

[0023] S5. The carbon material activated in S4 is washed with acid for 3-5 times, then washed with deionized water until neutral, and then placed in a drying oven at 100±5°C to a constant weight. The obtained carbon material is a spherical porous carbon;

[0024] S6. The carbon material obtained in S5 is placed in a fluidized bed, nitrogen is introduced, the temperature is raised to 450°C-550°C, silane gas is introduced to deposit silicon. After deposition for 3-6 hours, the silane gas is stopped, acetylene gas is introduced, and the temperature is maintained for 1-2 hours. The material is then cooled to obtain a silicon-carbon negative electrode material. The porous carbon obtained after esterification and carbonization activation has a large specific surface area and developed porosity, and can adsorb silane gas SiH4 in its pores. When heated, SiH4 generates Si element and H2, thereby forming a silicon-carbon negative electrode material.

[0025] The present invention can effectively prevent the starch from foaming and expanding during the pyrolysis process by first subjecting it to an esterification reaction and then to carbonization. Not only is the carbon yield high, but the original spherical morphology can also be effectively maintained. Potassium hydroxide is then used for activation treatment to obtain spherical porous carbon with a high specific surface area. Finally, silicon is adsorbed on the surface and in the pores of the carbon material through vapor deposition silane technology to further prepare a silicon-carbon negative electrode material. The obtained silicon-carbon negative electrode material has a higher compaction density, good conductivity, and excellent charge-discharge performance.

[0026] Furthermore, in the above technical solution S1, the plant starch is one or more of potato starch, corn starch, and sweet potato starch; the esterifying agent is one or more of succinic anhydride, maleic anhydride, and phthalic anhydride; the amount of the esterifying agent added is 10%-20% of the total mass of the plant starch; and the stirring speed is 100rpm-200rpm. Since when a polybasic organic acid undergoes an esterification reaction with a hydroxyl group, the activation energy of the reaction gradually increases with the gradual generation of ester groups, and the esterification temperature of polybasic carboxylic acids is usually high, the present invention selects anhydrides as esterifying agents. The alcoholysis activity of anhydrides is higher than that of the corresponding carboxylic acids, and their alcoholysis temperature is usually lower, which is more suitable for the process requirements of the present invention. The anhydrides are crushed in advance before use.

[0027] Furthermore, in the above technical solution S1, the plant starch is dried to a moisture content between 4% and 5% before the esterification reaction.

[0028] Furthermore, in the above technical solution S2, the heating rate is 2°C / min-5°C / min, and when the temperature reaches 500°C, it is kept at this temperature for 2 hours before further heating for carbonization. In this technical solution, the heating at 500°C for 2 hours can promote the increase of the degree of polymerization of the starch carbon material, improve the conductivity of the starch carbon, and improve the initial efficiency of the subsequent negative electrode material.

[0029] Furthermore, in the above technical solution S3, the mass ratio of potassium hydroxide to carbonized material is 1:1-5, and the drying temperature is 80°C-100°C.

[0030] Furthermore, in the above technical solution S5, the acid is 5 mol / L hydrochloric acid. In this technical solution, the use of high-concentration acid for washing can remove excess potassium hydroxide and activate the generated potassium carbonate.

[0031] Furthermore, in the above technical solution S6, the heating rate is 5°C / min, the rate of introducing silane gas is 3 L / min, and the rate of introducing acetylene gas is 3 L / min.

[0032] Furthermore, in the above technical solution S6, the silane gas is monosilane or disilane.

[0033] Furthermore, in the above technical solution S6, the pipeline needs to be purged with high-purity nitrogen gas before and after the silane gas is passed.

[0034] A second object of the present invention is to provide a silicon-carbon negative electrode material prepared by the above-mentioned preparation method, wherein the silicon-carbon negative electrode material is spherical in shape and has a first coulombic efficiency between 88% and 92%.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention performs an esterification reaction on starch so that the starch will not bubble and expand during the carbonization process, thereby providing the silicon-carbon material with higher conductivity. At the same time, the carbonization of the starch after esterification can maintain the spherical morphology of the starch, providing a larger specific surface area for the porous carbon. The obtained silicon-carbon material is also spherical, has a higher compaction density, first effect, etc., and has excellent electrical conductivity.

[0037] The carbon source raw materials used in the preparation method of the present invention are abundant, extensive and inexpensive. After pretreatment, they can maintain their original morphology. After activation, they have the advantages of larger specific surface area, good physical and chemical stability, excellent conductivity, and controllable pore structure. The obtained silicon-carbon negative electrode material has excellent performance and good market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 This is the SEM image of the porous carbon prepared in Example 1 of the present invention.

[0040] Figure 2 This is the SEM image of the porous carbon prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials involved in the following examples are common commercial products and can be purchased from the market unless otherwise specified.

[0042] The above-mentioned technical features of the present invention and the technical features specifically described below (such as embodiments) can be combined with each other to form new or preferred technical solutions.

[0043] The raw materials involved in the 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 methods.

[0044] The plant starch is dried to a moisture content between 4% and 5% before the esterification reaction.

[0045] Example 1

[0046] A method for preparing a silicon-carbon negative electrode material based on spherical starch porous carbon comprises the following steps:

[0047] S1. Add 10 kg of potato starch and 2 kg of succinic anhydride into a high-speed mixer in sequence, stir and mix at 100 rpm, then heat to 70°C for esterification reaction, and continue the reaction for 2 hours;

[0048] S2. Place the starch after esterification reaction in S1 in an atmosphere furnace, heat it to 500°C at a rate of 2°C / min under a nitrogen atmosphere, keep it at that temperature for 2 hours, and then continue to heat it to 800°C for carbonization;

[0049] S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray the potassium hydroxide solution dissolved in water onto the carbonized material under the sieve (the mass ratio of KOH to carbonized material is 1:3), let it stand for 24 hours, and then dry it in a drying oven at 80°C;

[0050] S4, placing the carbonized material dried in S3 in a rotary kiln and heating it to 800°C for activation;

[0051] S5. Wash the carbon material activated in S4 with 5 mol / L hydrochloric acid five times (to remove excess KOH and K2CO3 generated by activation), then wash with deionized water until neutral, and then place in a drying oven at 100±5°C to a constant weight to obtain porous carbon;

[0052] S6. Place 1 kg of the carbon material obtained in S5 in a fluidized bed, introduce nitrogen and raise the temperature to 450°C at a rate of 5°C / min, introduce 3 L / min of monosilane and disilane gas to carry out silicon deposition. After deposition for 3 hours, stop the silane gas, introduce nitrogen to drain the silane gas, and then introduce 3 L / min of acetylene gas. After maintaining for 1 hour, cool down to obtain the silicon-carbon negative electrode material.

[0053] Example 2

[0054] A method for preparing a silicon-carbon negative electrode material based on spherical starch porous carbon comprises the following steps:

[0055] S1. Add 10 kg corn starch and 2 kg succinic anhydride into a high-speed mixer in sequence, stir and mix at 150 rpm, then heat to 80°C for esterification reaction, and continue the reaction for 3 hours;

[0056] S2. Place the starch after esterification reaction in S1 in an atmosphere furnace, heat it to 500°C at a rate of 4°C / min under a nitrogen atmosphere, keep it at that temperature for 2 hours, and then continue to heat it to 800°C for carbonization;

[0057] S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray the potassium hydroxide solution dissolved in water onto the carbonized material under the sieve (the mass ratio of KOH to carbonized material is 1:4), let it stand for 24 hours, and then dry it in a drying oven at 90°C;

[0058] S4, placing the carbonized material dried in S3 in a rotary kiln and heating it to 850°C for activation;

[0059] S5. Wash the carbon material activated in S4 with 5 mol / L hydrochloric acid 4 times (to remove excess KOH and K2CO3 generated by activation), then wash with deionized water until neutral, and then place in a drying oven at 100±5℃ to constant weight to obtain porous carbon;

[0060] S6. Place 1 kg of the carbon material obtained in S5 in a fluidized bed, introduce nitrogen and raise the temperature to 500°C at a rate of 5°C / min, introduce 3 L / min of monosilane and disilane gas to carry out silicon deposition. After deposition for 4 hours, stop the silane gas, introduce nitrogen to drain the silane gas, and then introduce 3 L / min of acetylene gas. After maintaining for 1.5 hours, cool and obtain the silicon-carbon negative electrode material.

[0061] Example 3

[0062] A method for preparing a silicon-carbon negative electrode material based on spherical starch porous carbon comprises the following steps:

[0063] S1. Add 10 kg of potato starch, corn starch, and sweet potato starch and 2 kg of succinic anhydride, maleic anhydride, and phthalic anhydride into a high-speed mixer in sequence, stir and mix at 200 rpm, then heat to 100°C for esterification reaction, and continue the reaction for 2 hours;

[0064] S2. Place the starch after esterification reaction in S1 in an atmosphere furnace, heat it to 500°C at a rate of 5°C / min under a nitrogen atmosphere, keep it at that temperature for 2 hours, and then continue to heat it to 950°C for carbonization;

[0065] S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray the potassium hydroxide solution dissolved in water onto the carbonized material under the sieve (the mass ratio of KOH to carbonized material is 1:5), let it stand for 24 hours, and then dry it in a drying oven at 80°C;

[0066] S4, placing the carbonized material dried in S3 in a rotary kiln and heating it to 950°C for activation;

[0067] S5. Wash the carbon material activated in S4 with 5 mol / L hydrochloric acid three times (to remove excess KOH and K2CO3 generated by activation), then wash with deionized water until neutral, and then place in a drying oven at 100±5°C to a constant weight to obtain porous carbon;

[0068] S6. Place 1 kg of the carbon material obtained in S5 in a fluidized bed, introduce nitrogen and raise the temperature to 550°C at a rate of 5°C / min, introduce 3 L / min of monosilane and disilane gas to carry out silicon deposition. After deposition for 6 hours, stop the silane gas, introduce nitrogen to drain the silane gas, and then introduce 3 L / min of acetylene gas. After maintaining for 2 hours, cool to obtain the silicon-carbon negative electrode material.

[0069] Comparative Example 1

[0070] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0071] S1. Add 10 kg of potato starch and 0.5 kg of succinic anhydride into a high-speed mixer in sequence, stir and mix at 100 rpm, then heat to 70°C for esterification reaction, and continue the reaction for 2 hours;

[0072] S2. Place the starch after esterification reaction in S1 in an atmosphere furnace, heat it to 500°C at a rate of 2°C / min under a nitrogen atmosphere, keep it at that temperature for 2 hours, and then continue to heat it to 800°C for carbonization;

[0073] S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray the potassium hydroxide solution dissolved in water onto the carbonized material under the sieve (the mass ratio of KOH to carbonized material is 1:3), let it stand for 24 hours, and then dry it in a drying oven at 80°C;

[0074] S4, placing the carbonized material dried in S3 in a rotary kiln and heating it to 800°C for activation;

[0075] S5. Wash the carbon material activated in S4 with 5 mol / L hydrochloric acid five times (to remove excess KOH and K2CO3 generated by activation), then wash with deionized water until neutral, and then place in a drying oven at 100±5°C to a constant weight to obtain porous carbon;

[0076] S6. Place 1 kg of the carbon material obtained in S5 in a fluidized bed, introduce nitrogen and raise the temperature to 450°C at a rate of 5°C / min, introduce 3 L / min of monosilane and disilane gas to carry out silicon deposition. After deposition for 3 hours, stop the silane gas, introduce nitrogen to drain the silane gas, and then introduce 3 L / min of acetylene gas. After maintaining for 1 hour, cool down to obtain the silicon-carbon negative electrode material.

[0077] Comparative Example 2

[0078] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0079] S1. Add 10 kg of potato starch and 2.5 kg of succinic anhydride into a high-speed mixer in sequence, stir and mix at 100 rpm, then heat to 70°C for esterification reaction, and continue the reaction for 2 hours;

[0080] S2. Place the starch after esterification reaction in S1 in an atmosphere furnace, heat it to 500°C at a rate of 2°C / min under a nitrogen atmosphere, keep it at that temperature for 2 hours, and then continue to heat it to 800°C for carbonization;

[0081] S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray the potassium hydroxide solution dissolved in water onto the carbonized material under the sieve (the mass ratio of KOH to carbonized material is 1:3), let it stand for 24 hours, and then dry it in a drying oven at 80°C;

[0082] S4, placing the carbonized material dried in S3 in a rotary kiln and heating it to 800°C for activation;

[0083] S5. Wash the carbon material activated in S4 with 5 mol / L hydrochloric acid five times (to remove excess KOH and K2CO3 generated by activation), then wash with deionized water until neutral, and then place in a drying oven at 100±5°C to a constant weight to obtain porous carbon;

[0084] S6. Place 1 kg of the carbon material obtained in S5 in a fluidized bed, introduce nitrogen and raise the temperature to 450°C at a rate of 5°C / min, introduce 3 L / min of monosilane and disilane gas to carry out silicon deposition. After deposition for 3 hours, stop the silane gas, introduce nitrogen to drain the silane gas, and then introduce 3 L / min of acetylene gas. After maintaining for 1 hour, cool down to obtain the silicon-carbon negative electrode material.

[0085] Comparative Example 3

[0086] A method for preparing a silicon-carbon negative electrode material based on spherical starch porous carbon comprises the following steps:

[0087] S1. Add 10 kg of potato starch and 2 kg of succinic anhydride into a high-speed mixer in sequence, stir and mix at 100 rpm, then heat to 70°C for esterification reaction, and continue the reaction for 2 hours;

[0088] S2, placing the starch after esterification reaction in S1 in an atmosphere furnace, and heating it to 800°C at a rate of 2°C / min under a nitrogen atmosphere for carbonization;

[0089] S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray the potassium hydroxide solution dissolved in water onto the carbonized material under the sieve (the mass ratio of KOH to carbonized material is 1:3), let it stand for 24 hours, and then dry it in a drying oven at 80°C;

[0090] S4, placing the carbonized material dried in S3 in a rotary kiln and heating it to 800°C for activation;

[0091] S5. Wash the carbon material activated in S4 with 5 mol / L hydrochloric acid five times (to remove excess KOH and K2CO3 generated by activation), then wash with deionized water until neutral, and then place in a drying oven at 100±5°C to a constant weight to obtain porous carbon;

[0092] S6. Place 1 kg of the carbon material obtained in S5 in a fluidized bed, introduce nitrogen and raise the temperature to 450°C at a rate of 5°C / min, introduce 3 L / min of monosilane and disilane gas to carry out silicon deposition. After deposition for 3 hours, stop the silane gas, introduce nitrogen to drain the silane gas, and then introduce 3 L / min of acetylene gas. After maintaining for 1 hour, cool down to obtain the silicon-carbon negative electrode material.

[0093] Test example

[0094] 1. The specific surface area and porosity of the porous carbon obtained in the preparation process of Examples 1 to 3 and Comparative Examples 1 to 3 were measured, and the micromorphology was observed. The results were tested using a scanning electron microscope, a specific surface area analyzer, and a porosity analyzer. The results are shown in Table 1. The micromorphology of the porous carbon obtained in Example 1 and Comparative Example 1 is as follows: Figure 1 and Figure 2 shown.

[0095] Table 1 Test results of specific surface area and porosity of porous carbon

[0096]

[0097] As can be seen from Table 1, the specific surface areas of Examples 1 to 3 are all > 1750 m 2 / g, and a microporosity >85%, indicating that the porous carbon prepared by the present invention meets the requirements for preparing silicon carbon using vapor-deposited silane. Comparative Example 1 exhibits lower specific surface area and microporosity due to insufficient esterifying agent, incomplete starch esterification, and foaming and expansion during starch carbonization, generating mesopores and macropores, which impairs the ability to vapor-deposit silane. Comparative Example 2 exhibits similar specific surface area and microporosity to those of Examples 1-3, due to an excess of esterifying agent. Therefore, the amount of esterifying agent used in the present invention is sufficient to allow for a sufficient esterification reaction with starch and prevent starch expansion during carbonization.

[0098] In addition, from Figure 1 It can be seen from the figure that the morphology of the porous carbon of Example 1 basically maintains a relatively uniform spherical shape, which indicates that the carbonization and activation process has no significant impact on the spherical morphology of starch; Figure 2It can be seen that the spherical morphology of starch carbon has been completely broken. This is probably because the starch is not completely esterified due to the low content of esterification agent, so that the starch foams and expands during the carbonization process, causing the spherical shape to be destroyed.

[0099] 2. To test the performance of the silicon-carbon negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 for lithium-ion batteries, a half-cell test method and 18650 steel shell full batteries were used.

[0100] (1) The half-cell test method is to use the silicon-carbon materials prepared in Examples 1-3 and Comparative Examples 1-3 as the negative electrode active material to prepare a slurry. The slurry ratio is active material: CNTs (including dispersant): CMC: SBR = 89%: 4.5%: 1.5%: 5%. The slurry is then coated on copper foil and vacuum dried for 12 hours to form a negative electrode sheet. The electrolyte is commercially purchased, the separator is a PE film, and the lithium sheet is the counter electrode. The half-cell is assembled in a glove box. Constant current charge and discharge experiments are conducted in a LAND battery test system. The charge and discharge voltage is limited to 0.005V-2V. A computer-controlled charge and discharge cabinet is used for data acquisition and control. The comparison results of the buckling performance of Examples 1-3 and Comparative Examples 1-3 are shown in Table 2.

[0101] Table 2 Test results of power-on performance

[0102]

[0103] From the results in Table 2, it can be seen that from the perspective of first charge and first discharge, the buckle test of Examples 1 to 3 is relatively excellent. This is mainly because the starch carbon generated after the starch is completely esterified by the esterifying agent has excellent conductivity. At the same time, after being activated into porous carbon, the specific surface area is large and the microporosity is high, so that the capacity of silicon can be fully released after silane deposition; while the first charge and first discharge of Comparative Example 1 are poor. This is because the content of the esterifying agent is reduced, and the incomplete esterification causes the starch to foam and dissolve during the carbonization process, resulting in more mesopores and macropores, and the conductivity is also poor, and the silicon content cannot be fully released. In Comparative Example 2, there is no obvious difference between its first charge and first discharge and that of Example 1. This is because the esterifying agent is already in excess, which is sufficient to undergo a sufficient esterification reaction with the starch to avoid starch expansion during carbonization. Therefore, it was further determined that the amount of esterifying agent used was 10%-20% of the starch mass, which was sufficient to fully esterify the starch, and no higher ratio was required; in Comparative Example 3, the temperature was directly raised to 800°C during the activation process, which affected the initial effect due to the poor degree of polymerization.

[0104] In summary, the present invention uses starch as the carbon source and, after pretreatment and esterification reaction, can effectively overcome the foaming during the carbonization process that affects the morphology and conductivity. The obtained silicon-carbon negative electrode material not only has a spherical porous carbon skeleton, low volume effect, and good conductivity, but also has a high first charge and discharge capacity and first efficiency.

[0105] Finally, it should be emphasized that the above 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 may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material based on spherical starch porous carbon, characterized in that: The steps include: S1. Add plant starch and esterifying agent into a high-speed mixer in sequence, stir and mix evenly, then heat to 70-80°C for esterification reaction, and continue the reaction for 2-6 hours; wherein the amount of the esterifying agent added is 20% of the total mass of the plant starch; S2. Placing the starch after esterification reaction in S1 in an atmosphere furnace, heating to 800°C-950°C under a nitrogen atmosphere for carbonization; wherein, the heating rate is 2°C / min-5°C / min, and when the temperature reaches 500°C, it is kept at this temperature for 2 hours and then further heated for carbonization; S3, crush the carbonized material after carbonization in S2 and pass it through a 325-mesh sieve, then evenly spray potassium hydroxide dissolved in water onto the carbonized material under the sieve, let it stand for 24 hours, and then dry it; S4, placing the carbonized material dried in S3 in a rotary kiln and heating it to 800°C-950°C for activation; S5. Wash the carbon material activated in S4 with acid for 3-5 times, then wash with deionized water until neutral, and then dry in a drying oven at 100±5℃ until constant weight; S6. Place the carbon material obtained in S5 in a fluidized bed, introduce nitrogen and raise the temperature to 450-550°C at a rate of 5°C / min, introduce 3L / min of silane gas for silicon deposition. After deposition for 3h-6h, stop the silane gas and introduce 3L / min of acetylene gas, maintain for 1h-2h, and then cool to obtain a silicon-carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that In S1, the plant starch is one or more of potato starch, corn starch, and sweet potato starch; the esterifying agent is one or more of succinic anhydride, maleic anhydride, and phthalic anhydride; and the stirring speed is 100 rpm-200 rpm.

3. The preparation method according to claim 1, characterized in that In S1, the plant starch is dried to a moisture content of 4%-5% before the esterification reaction.

4. The preparation method according to claim 1, characterized in that In S3, the mass ratio of potassium hydroxide to carbonized material is 1:1-5, and the drying temperature is 80°C-100°C.

5. The preparation method according to claim 1, characterized in that In S5, the acid is 5 mol / L hydrochloric acid.

6. The preparation method according to claim 1, characterized in that In S6, the silane gas is monosilane or disilane.

7. The preparation method according to claim 1, characterized in that In S6, the pipeline needs to be purged with high-purity nitrogen before and after the silane gas is passed.

8. A silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The silicon-carbon negative electrode material is spherical in shape, and the first coulombic efficiency is between 88% and 92%.

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