Starch-based hard carbon negative electrode material, preparation method thereof and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and particularly relates to a starch-based hard carbon negative electrode material, a preparation method thereof and a lithium ion battery, the preparation method comprising the following steps: mixing a polyvinyl alcohol solution and a lithium hydroxide solution, adding starch, stirring, adding a halogenated acid to react, and obtaining a reaction mixture; dropping the reaction mixture into a liquid nitrogen bath to obtain a spherical precursor; and calcining the spherical precursor in an inert gas atmosphere to obtain the starch-based hard carbon negative electrode material. The present application uses polyvinyl alcohol as a self-sacrificial template, reduces the subsequent step of removing the template, reduces the process and energy consumption, and helps to generate a porous structure in the hard carbon negative electrode material and helps to realize the regulation of the pore structure. At the same time, in combination with lithium halide generated in situ inside the starch as a lithium supplement salt, the preparation steps are simplified, and a porous carbon negative electrode material with excellent electrochemical performance is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a starch-based hard carbon negative electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] The negative electrode material is one of the important factors determining the comprehensive performance of the lithium ion battery. At present, the negative electrode materials of the lithium ion battery mainly include graphite, hard carbon, soft carbon and the like. The hard carbon has dispersed crystallization, stable structure, easy lithium ion deintercalation, high output power of the battery, long charge and discharge cycle life and good safety performance, and thus becomes the focus of the research on the negative electrode materials.

[0003] The raw materials for preparing the conventional hard carbon negative electrode material mainly include non-renewable mineral resources such as coal, resin and pitch. In recent years, due to the shortage of mineral resources, the development and application of the conventional hard carbon negative electrode material have been limited. Under this premise, the biomass resources have become the focus of the research and attention of people for preparing the hard carbon negative electrode material due to the advantages of rich carbon elements, renewability, low pollution and wide distribution.

[0004] The starch is a raw material belonging to the biomass resources, has the advantages of low price, wide source and rich carbon elements, and has strong potential in the preparation of carbon materials. For the electrode material, the introduction of the porous structure usually has great influence on the electrochemical performance. At present, in the preparation process of the hard carbon negative electrode material, the porous structure is usually prepared by the fixed template method. This preparation method needs to remove the fixed template subsequently, and thus the cleaning process is added in the process, the process is complicated, and the energy consumption is high.

[0005] Therefore, it is a technical problem to be solved at present to provide a preparation method of the starch-based hard carbon negative electrode material with simple process. SUMMARY

[0006] In order to solve the problem of the complex preparation process of the porous hard carbon negative electrode material in the prior art, the present application provides a preparation method of the starch-based hard carbon negative electrode material. The preparation method uses polyvinyl alcohol as a self-sacrificial template to synthesize the starch-based hard carbon negative electrode material with a porous structure, and the template does not need to be removed subsequently, so that the preparation process is simplified, and the problem of the complex preparation process of the porous hard carbon negative electrode material in the prior art is solved.

[0007] The technical scheme adopted by the present application to solve the technical problems is as follows:

[0008] A preparation method of a starch-based hard carbon negative electrode material, comprising the following steps:

[0009] S1: mixing a polyvinyl alcohol solution and a lithium hydroxide solution, adding starch, stirring, and then adding a halogenated acid to react to obtain a reaction mixture;

[0010] S2: drop the reaction mixture into a liquid nitrogen bath to obtain a spherical precursor;

[0011] S3: calcining the spherical precursor under an inert gas atmosphere to obtain the starch-based hard carbon negative electrode material.

[0012] Optionally, the mass ratio of the starch to the polyvinyl alcohol is (8-10): 1.

[0013] Optionally, the mass ratio of the lithium hydroxide to the polyvinyl alcohol is 1:5.

[0014] Optionally, the starch is selected from at least one of cereal starch, potato starch, and bean starch.

[0015] Optionally, step S3 comprises: under an inert gas atmosphere, heating the spherical precursor from room temperature to 200℃, heating from 200℃ to 400℃, and then heating from 400℃ to 900-1000℃ to obtain the starch-based hard carbon negative electrode material.

[0016] Optionally, when the spherical precursor is heated from room temperature to 200℃, the heating rate is 5℃ / min.

[0017] Optionally, when the spherical precursor is heated from 200℃ to 400℃, the heating rate is 1℃ / min.

[0018] Optionally, when the spherical precursor is heated from 400℃ to 900-1000℃, the heating rate is 5℃ / min.

[0019] Another object of the present application is to provide a starch-based hard carbon negative electrode material prepared by the preparation method of the starch-based hard carbon negative electrode material as described above.

[0020] Still another object of the present application is to provide a lithium ion battery comprising the starch-based hard carbon negative electrode material as described above.

[0021] The present application has the following advantages:

[0022] The preparation method of the starch-based hard carbon negative electrode material provided by the present application uses polyvinyl alcohol as a self-sacrificial template, which not only acts as a template during the preparation process and is carbonized into an active material at high temperature, but also reduces the subsequent step of removing the template, reduces the process and energy consumption, and helps to generate a porous structure in the hard carbon negative electrode material and to control the pore structure. At the same time, in combination with the in-situ generated lithium halide inside the starch as a lithium supplement salt, the preparation steps are simplified, and a porous carbon negative electrode material with excellent electrochemical performance is prepared. DETAILED DESCRIPTION

[0023] The application will now be described in further detail. The examples described below are illustrative and are not meant to limit the application to their details. All other examples that a person of ordinary skill in the art obtains based on the examples of the application, without having to make creative efforts, are within the scope of the application.

[0024] To solve the problem of complex preparation process of the porous hard carbon negative electrode material in the prior art, the application provides a preparation method of a starch-based hard carbon negative electrode material, which comprises the following steps:

[0025] S1: mixing a polyvinyl alcohol solution with a lithium hydroxide solution, adding starch, stirring, preferably stirring at 40-50 DEG C for 3-6 h, then adding a halogenated acid for reaction to obtain a reaction mixture;

[0026] Preferably, the polyvinyl alcohol solution is prepared by the following method:

[0027] According to the formula amount, polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 10-50 minutes to prevent caking, then stirred at 80-100 DEG C for 20-50 minutes to obtain a transparent solution, and cooled to room temperature to obtain a polyvinyl alcohol solution;

[0028] In this step, the polyvinyl alcohol solution is fully mixed with the lithium hydroxide solution, then the starch is added, which helps the lithium hydroxide to penetrate into the starch; then the halogenated acid is added, so that the lithium hydroxide reacts with the halogenated acid to generate lithium halide; since the lithium hydroxide has penetrated into the starch, the lithium halide can be generated in situ in the starch; the lithium halide is used as a prelithiated salt here, which is beneficial to improve the first efficiency of the porous carbon; the application preferably uses the halogenated acid in an amount equal to that of the lithium hydroxide;

[0029] S2: dropping the reaction mixture into a liquid nitrogen bath for rapid freezing to obtain spherical precursors;

[0030] In this step, the liquid nitrogen bath miniaturizes the precursor into small balls, which is beneficial to the shaping of the precursor carbonization material in the subsequent step;

[0031] S3: calcining the spherical precursors in an inert gas atmosphere, preferably washing the carbonized sample with deionized water to eliminate any potential impurities, then drying at 85 DEG C for 12 hours, so that the lithium halide is partially left in the pore structure of the porous carbon to obtain the starch-based hard carbon negative electrode material.

[0032] The present application is based on the fact that both polyvinyl alcohol and starch contain a large number of hydroxyl groups, and mixing starch with a polyvinyl alcohol solution can form a physical crosslinking network through hydrogen bonds. This interaction can enhance the uniformity of the mixed system and provide a stable precursor structure for subsequent carbonization. At the same time, by first mixing lithium hydroxide with polyvinyl alcohol and then adding starch, the lithium hydroxide can be wrapped in the physical crosslinking network formed by polyvinyl alcohol and starch. Then, by adding a halogenated acid to react with lithium hydroxide, lithium halide is introduced as a lithium supplement salt. The generated lithium halide is located in the crosslinking network, thereby ensuring the electrochemical performance of the negative electrode material. Compared with the direct addition of lithium halide, the lithium halide located in the crosslinking network is more stable and can achieve prelithiation for a long time.

[0033] During subsequent calcination, the hydroxyl groups of polyvinyl alcohol and starch can undergo condensation reactions at high temperatures, which helps to further enhance the crosslinking degree of the carbon skeleton and form a three-dimensional network structure. This crosslinking effect can inhibit the generation of disordered structures during carbonization and improve the mechanical strength and electrical conductivity of the hard carbon. During carbonization, the decomposition of starch produces gases such as CO2 and H2O, thereby generating pores in the material. The presence of polyvinyl alcohol helps to form a uniform carbon matrix, and the synergistic effect of the two controls the specific surface area and pore size distribution of the hard carbon. At the same time, the carbonization of polyvinyl alcohol tends to form short-range ordered graphite microcrystalline structures, which helps to improve the electrical conductivity, while the carbonization products of starch are usually amorphous carbon. The mixture of the two can optimize the lithium storage performance of the hard carbon by adjusting the microcrystalline size and defect density.

[0034] The preparation method of the starch-based hard carbon negative electrode material provided by the present application uses polyvinyl alcohol as a self-sacrificial template. During the preparation process, it not only acts as a template but also carbonizes into an active material at high temperatures. This not only reduces the subsequent steps of removing the template and reduces the process and energy consumption, but also helps to generate a porous structure in the hard carbon negative electrode material and helps to control the pore structure. At the same time, by combining the in-situ generated lithium halide inside the starch as a lithium supplement salt, the preparation steps are simplified, and a porous carbon negative electrode material with excellent electrochemical performance is prepared.

[0035] When the content of polyvinyl alcohol in the system is too high, it will inhibit the porosity of the carbon material. When the content of polyvinyl alcohol is too low, it will cause the mechanical properties and electrical conductivity of the carbon material to deteriorate. In order to balance the porosity, mechanical properties, and electrical conductivity of the starch-based hard carbon negative electrode material, the present application preferably uses a mass ratio of starch to polyvinyl alcohol of (8-10):1.

[0036] The polyvinyl alcohol solution in the present application is an aqueous solution of polyvinyl alcohol, and the lithium hydroxide solution is an aqueous solution of lithium hydroxide. Preferably, the mass concentration of the polyvinyl alcohol solution in step S1 is 10%, and the mass concentration of the lithium hydroxide solution is 10%. Further preferably, the mass ratio of lithium hydroxide to polyvinyl alcohol is 1:5.

[0037] The starch of the present application is preferably selected from at least one of cereal starch, potato starch, and legume starch.

[0038] To ensure the mechanical properties and electrochemical properties of the starch-based hard carbon negative electrode material, the step S3 preferably comprises: under an inert gas atmosphere, the spherical precursor is heated from room temperature to 200℃, heated from 200℃ to 400℃, and then heated from 400℃ to 900-1000℃ for calcination, to obtain the starch-based hard carbon negative electrode material.

[0039] During the calcination process, at 200-400℃, the starch first undergoes dehydration and chain scission to generate small molecule organic substances such as glucose, and then further decomposes into tar and carbon black, which is the tar removal stage of the starch; at the same time, the polyvinyl alcohol undergoes dehydration reaction to generate conjugated double bond structure, while releasing small molecules such as water and acetic acid, and the condensation reaction of the molecular chain can form stable aromatic ring structure to promote the generation of graphite microcrystals; and the crosslinking and condensation reaction of the hydroxyl groups of the starch and the polyvinyl alcohol forms a three-dimensional carbon skeleton; and further calcination and carbonization at 900-1000℃ forms the starch-based hard carbon negative electrode material with a porous structure.

[0040] In the step S3, the spherical precursor is heated from room temperature to 200℃ at a heating rate of 5℃ / min; the spherical precursor is heated from 200℃ to 400℃ at a heating rate of 1℃ / min to avoid the collapse of the pore structure; and the spherical precursor is heated from 400℃ to 900-1000℃ at a heating rate of 5℃ / min.

[0041] Another object of the present application is to provide a starch-based hard carbon negative electrode material prepared by the preparation method of the starch-based hard carbon negative electrode material as described above.

[0042] The starch-based hard carbon negative electrode material provided by the present application uses polyvinyl alcohol as a self-sacrificial template during the preparation process. The polyvinyl alcohol not only acts as a template, but also can be carbonized into an active substance at high temperature, which not only reduces the subsequent step of removing the template and reduces the process and energy consumption, but also helps to generate a porous structure in the hard carbon negative electrode material and helps to realize the regulation of the pore structure. At the same time, the in-situ generated lithium halide inside the starch is used as a lithium supplement salt, which simplifies the preparation steps and prepares a porous carbon negative electrode material with excellent electrochemical performance.

[0043] Another object of the present application is to provide a lithium ion battery comprising the starch-based hard carbon negative electrode material as described above.

[0044] The lithium ion battery provided by the application adopts the starch-based hard carbon negative electrode material, and polyvinyl alcohol is used as a self-sacrificial template in the preparation process. The polyvinyl alcohol not only plays the role of a template, but also can be carbonized into an active substance at high temperature. Therefore, the process of removing the template is reduced, the process and energy consumption are reduced, the generation of the porous structure in the hard carbon negative electrode material is facilitated, and the regulation of the pore structure is facilitated. Meanwhile, lithium halide generated in situ in the starch is used as a lithium supplement salt. The preparation steps are simplified, the porous carbon negative electrode material with excellent electrochemical performance is prepared, and the electrochemical performance of the lithium ion battery is improved.

[0045] In order to make the above-mentioned purposes, characteristics and advantages of the application more obvious and easy to understand, the specific embodiments of the application are described in detail below.

[0046] Embodiment 1

[0047] The embodiment provides a preparation method of a starch-based hard carbon negative electrode material, and the preparation method comprises the following steps:

[0048] S1: polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 30 minutes to prevent caking, and then stirred at 95 DEG C for 30 minutes to obtain a 10% mass concentration polyvinyl alcohol transparent solution, and then cooled to room temperature; then 500g of the polyvinyl alcohol solution is carefully mixed with 100g of a 10% mass concentration LiOH solution, 450g of corn starch is then added, stirred at 45 DEG C for 5h, and then an amount of dilute hydrochloric acid equal to that of lithium hydroxide is added to react lithium hydroxide with hydrochloric acid to generate lithium chloride, thereby obtaining a reaction mixture;

[0049] S2: the prepared reaction mixture is added dropwise into a liquid nitrogen bath to quickly freeze the solution to obtain a small spherical precursor;

[0050] S3: the precursor is heated from room temperature to 200 DEG C at a heating rate of 5 DEG C / min under an argon atmosphere using a tube furnace; between 200 DEG C and 400 DEG C, the process is a corn starch tar removal stage, and a very slow heating rate of 1 DEG C / min is required to avoid the collapse of the pore structure; then, the heating rate is 5 DEG C / min, and the temperature is increased from 400 DEG C to 900 DEG C, and the temperature is kept at 900 DEG C for 3h to complete the carbonization process; the solid mixture after the reaction is ultrasonically cleaned in deionized water for 4 hours to remove excess lithium chloride, and then dried at 85 DEG C for 12 hours; the residual lithium chloride is left in the pore structure of the porous carbon and participates in the prelithiation effect in the subsequent charging and discharging process, thereby obtaining the target product, the starch-based hard carbon negative electrode material.

[0051] The specific surface area of the negative electrode material is tested by using a specific surface area tester, and the specific surface area is 164m 2 / g.

[0052] Example 2

[0053] The present embodiment provides a preparation method of a starch-based hard carbon negative electrode material, which comprises the following steps:

[0054] S1: polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 30 minutes to prevent caking, then stirred at 95°C for 30 minutes to obtain a 10% mass concentration of polyvinyl alcohol transparent solution, and cooled to room temperature; then 500g of polyvinyl alcohol solution is carefully mixed with 100g of 10% mass concentration LiOH solution, 450g of wheat starch is added, stirred at 45°C for 5h, and then an amount of dilute hydrochloric acid equal to that of lithium hydroxide is added to react lithium hydroxide with hydrochloric acid to generate lithium chloride, thereby obtaining a reaction mixture;

[0055] S2: the prepared reaction mixture is added dropwise into a liquid nitrogen bath to quickly freeze the solution to obtain a small spherical precursor;

[0056] S3: the precursor is heated from room temperature to 200°C at a heating rate of 5°C / min in a tube furnace under an argon atmosphere; between 200°C and 400°C, the process is a wheat starch tar removal stage, which requires a very slow heating rate of 1°C / min to avoid the collapse of the pore structure; then, the heating rate is 5°C / min from 400°C to 950°C, and the solid mixture after reaction is washed in deionized water for 4 hours to remove excess lithium chloride, and then dried at 85°C for 12 hours, and the residual lithium chloride remains in the pore structure of the porous carbon to participate in the prelithiation effect in the subsequent charging and discharging process, thereby obtaining the target product of the starch-based hard carbon negative electrode material.

[0057] The specific surface area of the negative electrode material is tested by a specific surface area tester, and the specific surface area is 142m 2 / g.

[0058] Example 3

[0059] The present embodiment provides a preparation method of a starch-based hard carbon negative electrode material, which comprises the following steps:

[0060] S1: polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 30 minutes to prevent caking, then stirred at 95°C for 30 minutes to obtain a 10% mass concentration of polyvinyl alcohol transparent solution, and cooled to room temperature; then 500g of polyvinyl alcohol solution is carefully mixed with 100g of 10% mass concentration LiOH solution, 450g of wheat starch is added, stirred at 45°C for 5h, and then an amount of dilute hydrochloric acid equal to that of lithium hydroxide is added to react lithium hydroxide with hydrochloric acid to generate lithium chloride, thereby obtaining a reaction mixture;

[0061] S2: The prepared reaction mixture is added dropwise into a liquid nitrogen bath, and the solution is rapidly frozen to obtain small spherical precursors;

[0062] S3: The precursors are heated from room temperature to 200℃ at a rate of 5℃ / min in a tube furnace under an argon atmosphere; between 200℃ and 400℃, the process is a tar removal stage of wheat starch, and a very slow heating rate of 1℃ / min is required to avoid the collapse of the pore structure; then, the heating rate is 5℃ / min from 400℃ to 950℃, and the reaction is kept at 950℃ for 2.5h to complete the carbonization process; the solid mixture after reaction is ultrasonically cleaned in deionized water for 4h to remove excess lithium fluoride, and then dried at 85℃ for 12h; the residual lithium fluoride remains in the pore structure of the porous carbon and participates in the prelithiation effect of the subsequent charge and discharge process, and the target product of the starch-based hard carbon negative electrode material is obtained.

[0063] The specific surface area of the negative electrode material is tested by a specific surface area tester, and the specific surface area is 152m 2 / g.

[0064] Example 4

[0065] The present embodiment provides a preparation method of a starch-based hard carbon negative electrode material, which comprises the following steps:

[0066] S1: Polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 30 minutes to prevent caking, and then stirred at 95℃ for 30 minutes to obtain a 10% mass concentration of polyvinyl alcohol transparent solution, which is cooled to room temperature; then 500g of polyvinyl alcohol solution is carefully mixed with 100g of 10% mass concentration LiOH solution, and then 400g of potato starch is added, stirred at 45℃ for 5h, and then an amount of hydrobromic acid equal to that of lithium hydroxide is added to react lithium hydroxide with hydrobromic acid to generate lithium bromide, and a reaction mixture is obtained;

[0067] S2: The prepared reaction mixture is added dropwise into a liquid nitrogen bath, and the solution is rapidly frozen to obtain small spherical precursors;

[0068] S3: the precursor is heated from room temperature to 200 DEG C under argon atmosphere by using a tube furnace, the heating rate is 5 DEG C / min; between 200 DEG C and 400 DEG C, the process is a potato starch tar removal stage, a very slow heating rate 1 DEG C / min needs to be adopted to avoid the collapse of the pore structure; then, the heating rate is 5 DEG C / min, from 400 DEG C to 950 DEG C, and 2.5h is kept at 950 DEG C to complete the carbonization process; the solid mixture after reaction is cleaned in deionized water for 4h by ultrasonic cleaning to clean the excess lithium bromide, and then dried at 85 DEG C for 12h; the residual lithium bromide remains in the pore structure of the porous carbon and participates in the prelithiation of the subsequent charging and discharging process, and the target product of the starch-based hard carbon negative electrode material is obtained.

[0069] The specific surface area of the negative electrode material is tested by using a specific surface area tester, and the specific surface area is 157m 2 / g.

[0070] The various comparative examples in the application are used for comparison with example 1.

[0071] Comparative example 1

[0072] The preparation method of the starch-based hard carbon negative electrode material provided by the comparative example comprises the following steps:

[0073] S1: 450g of corn starch is added into 100g of a lithium hydroxide solution with a mass concentration of 10%, and stirred at 45 DEG C for 5h; then, lithium hydroxide is reacted with hydrochloric acid to generate lithium chloride, and a reaction mixture is obtained;

[0074] S2: the prepared reaction mixture is added dropwise into a liquid nitrogen bath to quickly freeze the solution to obtain a small spherical precursor;

[0075] S3: the precursor is heated from room temperature to 200 DEG C under argon atmosphere by using a tube furnace, the heating rate is 5 DEG C / min; between 200 DEG C and 400 DEG C, the process is a potato starch tar removal stage, a very slow heating rate 1 DEG C / min needs to be adopted to avoid the collapse of the pore structure; then, the heating rate is 5 DEG C / min, from 400 DEG C to 900 DEG C, and 3h is kept at 900 DEG C to complete the carbonization process; the solid mixture after reaction is cleaned in deionized water for 4h by ultrasonic cleaning to clean the excess lithium bromide, and then dried at 85 DEG C for 12h; the residual lithium bromide remains in the pore structure of the porous carbon and participates in the prelithiation of the subsequent charging and discharging process, and the target product of the starch-based hard carbon negative electrode material is obtained.

[0076] The specific surface area of the negative electrode material is tested by using a specific surface area tester, and the specific surface area is 101m 2 / g.

[0077] Comparative example 2

[0078] The present comparative example provides a preparation method of a starch-based hard carbon negative electrode material, which comprises the following steps:

[0079] S1: polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 30 minutes to prevent caking, and then stirred at 95°C for 30 minutes to obtain a 10% mass concentration of polyvinyl alcohol transparent solution, which is cooled to room temperature; then 450g of corn starch is added and stirred at 45°C for 5h to obtain a reaction mixture;

[0080] S2: the prepared reaction mixture is added dropwise into a liquid nitrogen bath, and the solution is quickly frozen to obtain a small spherical precursor;

[0081] S3: the precursor is heated from room temperature to 200°C at a heating rate of 5°C / min in a tube furnace under an argon atmosphere; between 200°C and 400°C, the process is a corn starch tar removal stage, which requires a very slow heating rate of 1°C / min to avoid the collapse of the pore structure; then, the heating rate is 5°C / min from 400°C to 900°C, and the reaction is kept at 900°C for 3h to complete the carbonization process; the solid mixture after reaction is ultrasonically cleaned in deionized water for 4 hours, and then dried at 85°C for 12 hours to obtain the target product, a starch-based hard carbon negative electrode material.

[0082] The specific surface area of the negative electrode material is tested by a specific surface area tester, and the specific surface area is 161m 2 / g.

[0083] Comparative Example 3

[0084] The present comparative example provides a preparation method of a starch-based hard carbon negative electrode material, which comprises the following steps:

[0085] S1: polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 30 minutes to prevent caking, and then stirred at 95°C for 30 minutes to obtain a 10% mass concentration of polyvinyl alcohol transparent solution, which is cooled to room temperature; then 450g of corn starch is added and stirred at 45°C for 5h to obtain a reaction mixture;

[0086] S2: the prepared reaction mixture is added dropwise into a liquid nitrogen bath, and the solution is quickly frozen to obtain a small spherical precursor;

[0087] S3: The precursor is heated from room temperature to 200℃ at a heating rate of 5℃ / min under argon atmosphere using a tube furnace; between 200℃ and 400℃, the process is a toasting stage of the corn starch, a very slow heating rate of 1℃ / min is used to avoid the collapse of the pore structure; then, the heating rate is 5℃ / min from 400℃ to 900℃, and the reaction is kept at 900℃ for 3h to complete the carbonization process; the solid mixture after the reaction is cleaned in deionized water for 4 hours by ultrasonic cleaning to remove excess lithium chloride, and then dried at 85℃ for 12 hours; the residual lithium chloride remains in the pore structure of the porous carbon and participates in the pre-lithiation of the subsequent charging and discharging process, and the target product of the starch-based hard carbon negative electrode material is obtained.

[0088] The specific surface area of the negative electrode material is tested by a specific surface area tester, and the specific surface area is 126m 2 / g

[0089] Comparative Example 4

[0090] The present comparative example provides a preparation method of a starch-based hard carbon negative electrode material, which comprises the following steps:

[0091] S1: Polyvinyl alcohol (PVA) powder is added to deionized water, stirred at room temperature for 30 minutes to prevent caking, and then stirred at 95℃ for 30 minutes to obtain a 10% mass concentration of polyvinyl alcohol transparent solution, which is cooled to room temperature; then 500g of polyvinyl alcohol solution is carefully mixed with 178g of lithium chloride solution with a mass concentration of 10%, and 450g of corn starch is added, and stirred at 45℃ for 5h to obtain a reaction mixture;

[0092] S2: The prepared reaction mixture is added dropwise into a liquid nitrogen bath to quickly freeze the solution to obtain a small spherical precursor;

[0093] S3: The precursor is heated from room temperature to 200℃ at a heating rate of 5℃ / min under argon atmosphere using a tube furnace; between 200℃ and 400℃, the process is a toasting stage of the corn starch, a very slow heating rate of 1℃ / min is used to avoid the collapse of the pore structure; then, the heating rate is 5℃ / min from 400℃ to 900℃, and the reaction is kept at 900℃ for 3h to complete the carbonization process; the solid mixture after the reaction is cleaned in deionized water for 4 hours by ultrasonic cleaning to remove excess lithium chloride, and then dried at 85℃ for 12 hours; the residual lithium chloride remains in the pore structure of the porous carbon and participates in the pre-lithiation of the subsequent charging and discharging process, and the target product of the starch-based hard carbon negative electrode material is obtained.

[0094] The specific surface area of the negative electrode material is tested by a specific surface area tester, and the specific surface area is 153m 2 / g.

[0095] The negative electrode materials prepared in each of the above examples and the comparative examples were prepared into button cells according to a button cell process, and were tested, and the test results are shown in Table 1.

[0096] The preparation process of the button cell is as follows:

[0097] The negative electrode materials prepared in each of the above examples and the comparative examples were prepared into button cells according to a button cell process, and were tested, and the test results are shown in Table 1.

[0098] Table 1

[0099]

[0100] From the data in the above table, it can be seen that the negative electrode materials prepared in each of the examples of the application all have excellent electrochemical performance.

[0101] Comparative Example 1 is a material prepared without a template, and the first efficiency is not affected, but the gram capacity is significantly decreased; Comparative Example 2 has a template, but lacks a pre-lithiated salt, and the gram capacity is higher, but the first efficiency is greatly reduced; in Comparative Example 3, the polyvinyl alcohol solution is mixed with starch before lithium hydroxide and hydrochloric acid are added in sequence, and the starch blocks the pores of the polyvinyl alcohol template, so that less pre-lithiated salt enters the pores, resulting in that both the first efficiency and the gram capacity are affected; in Comparative Example 4, lithium chloride solution is directly added, and the hydroxyl group of lithium hydroxide in Example 1 has similar solubility with the hydroxyl group of polyvinyl alcohol, so that lithium hydroxide can better enter the pores of the template, and if lithium chloride salt is directly added, the presence of hydroxyl group will result in that less pre-lithiated salt enters the pores, affecting the first efficiency.

[0102] Based on the above ideal examples according to the application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the application. The technical scope of the application is not limited to the content in the specification, and the technical scope must be determined according to the scope of claims.

Claims

1. A method for preparing a starch-based hard carbon anode material, characterized in that, Includes the following steps: S1: Mix polyvinyl alcohol solution and lithium hydroxide solution, add starch, stir, add haloacid to react, and obtain reaction mixture; S2: The reaction mixture is added dropwise into a liquid nitrogen bath to obtain a spherical precursor; S3: The spherical precursor is calcined under an inert gas atmosphere to obtain a starch-based hard carbon anode material.

2. The method for preparing the starch-based hard carbon anode material as described in claim 1, characterized in that, The mass ratio of starch to polyvinyl alcohol is (8-10):

1.

3. The method for preparing the starch-based hard carbon anode material as described in claim 1, characterized in that, The mass ratio of lithium hydroxide to polyvinyl alcohol is 1:

5.

4. The method for preparing the starch-based hard carbon anode material according to any one of claims 1-3, characterized in that, The starch is selected from at least one of cereal starch, potato starch, and legume starch.

5. The method for preparing the starch-based hard carbon anode material according to any one of claims 1-3, characterized in that, Step S3 includes: calcining the spherical precursor in an inert gas atmosphere by heating it from room temperature to 200°C, from 200°C to 400°C, and then from 400°C to 900-1000°C to obtain a starch-based hard carbon anode material.

6. The method for preparing the starch-based hard carbon anode material as described in claim 5, characterized in that, When the spherical precursor is heated from room temperature to 200°C, the heating rate is 5°C / min.

7. The method for preparing the starch-based hard carbon anode material as described in claim 5, characterized in that, When the spherical precursor is heated from 200°C to 400°C, the heating rate is 1°C / min.

8. The method for preparing the starch-based hard carbon anode material as described in claim 5, characterized in that, When the spherical precursor is heated from 400°C to 900-1000°C, the heating rate is 5°C / min.

9. A starch-based hard carbon anode material, characterized in that, The starch-based hard carbon anode material is prepared by the method described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that, Including the starch-based hard carbon anode material as described in claim 9.

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