High-rate starch-based hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a high-rate starch-based hard carbon negative electrode material and a preparation method thereof, and the preparation method comprises the following steps: S1, firstly performing stabilization treatment on pre-modified starch at a low temperature of 300-500 DEG C, and crushing the material for later use; s2, carbonization: performing high-temperature carbonization on the powder in the step S1 in an inert atmosphere, and cooling to obtain a starch-based hard carbon material; s3, coating treatment: mixing the hard carbon material in the step S2 with soft carbon; and S4, heat treatment: carrying out heat treatment on the mixture in the step S3 to obtain the hard carbon negative electrode material with the soft carbon coating. According to the preparation method, the first coulombic efficiency can be remarkably improved. The formed soft carbon coating has good electronic conductivity, the transmission rate of electrons among particles is greatly improved, the impedance of an electrode is reduced, and direct and repeated contact between electrolyte and a hard carbon core is reduced, so that continuous side reaction is inhibited, the cycle life of the battery is prolonged, and the capacity retention rate of the battery is increased.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a high-rate starch-based hard carbon anode material and its preparation method. Background Technology

[0002] Sodium-ion batteries are considered an ideal alternative or supplement to lithium-ion batteries in large-scale energy storage, low-speed electric vehicles, and backup power applications due to the abundant, low-cost, and widely distributed sodium resources, as well as their similar working principle to lithium-ion batteries. Among various anode materials for sodium-ion batteries, hard carbon, with its unique crystal structure and excellent electrochemical performance, has become one of the most promising anode materials for commercial application. However, its practical application still faces severe challenges, especially in high-rate (fast charge / discharge) scenarios. The migration rate of sodium ions in the solid phase cannot match the rapid conduction of electrons in the external circuit, leading to severe concentration polarization and electrochemical polarization. Therefore, how to prepare hard carbon materials with high capacity, high initial efficiency, and excellent rate performance has become an important research direction in this field.

[0003] Biomass-based hard carbon production technology stands out due to its advantages of renewable raw materials, low cost, and environmental friendliness. Its natural structure easily forms defects and channels suitable for sodium ion storage. Starch, as a precursor, holds unique value, with its high purity ensuring extremely low ash content in hard carbon products. However, during starch carbonization, its long molecular chains and strong hydrogen bonding lead to inconsistent rates of dehydration, polymerization, and aromatization reactions during high-temperature pyrolysis. This results in significant inhomogeneities in the pore size distribution and surface chemical state of the hard carbon product. This phenomenon not only exacerbates the degradation of battery performance, such as cycle stability, initial coulombic efficiency, and rate performance, but also causes batch instability, hindering the large-scale production of hard carbon.

[0004] Existing technologies typically employ chemical modifications such as cross-linking and oxidation, or optimize reaction equipment to control the uniformity of starch pyrolysis. However, these methods cannot guarantee a complete chemical reaction and may require more research time and increase costs, which is detrimental to the industrialization of hard carbon. Summary of the Invention

[0005] This invention employs a coating post-treatment method to modify the surface of starch-based hard carbon materials. By constructing a soft carbon coating on the surface of the hard carbon, a new composite carbon layer structure is formed. This structure can effectively promote the electron and ion transport rate and reduce side reactions between the electrolyte and the material, thereby significantly improving the first coulombic efficiency, rate performance, and yield of the final product of the starch-based hard carbon material.

[0006] A high-rate starch-based hard carbon anode material and its preparation method include the following steps: S1. First, the pre-modified starch is stabilized at a low temperature of 300-500℃, and the material is crushed for later use.

[0007] S2, Carbonization: The powder from step S1 is carbonized at high temperature under an inert atmosphere, and after cooling, starch-based hard carbon material is obtained.

[0008] S3. Coating treatment: Mix the hard carbon material and soft carbon from step S2.

[0009] S4. Heat treatment: The mixture from step S3 is heat treated to obtain a hard carbon anode material with a soft carbon coating.

[0010] Furthermore, the starch in step S1 includes acetylated distarch phosphate, acetate starch, corn starch, wheat starch, potato starch, tapioca starch, water chestnut starch, and lotus root starch.

[0011] Furthermore, in step S1, the modified starch is modified by heating the starch to 200-300℃ in air at a rate of 0.5-5℃ / min and holding it at that temperature for 1-2 hours to perform oxidative crosslinking, thereby obtaining crosslinked modified starch.

[0012] Furthermore, in step S1, the stabilization treatment first raises the temperature to 300-500℃ at a rate of 5-10℃ / min and holds it at that temperature for 1-2 hours, then allows it to cool naturally to room temperature before removing it.

[0013] Further, the pulverization step in step S1 is as follows: the carbonized precursor is pulverized to 200-400 mesh using an air jet mill.

[0014] Furthermore, in the carbonization process of step S2, the protective atmosphere is nitrogen or argon, the heating rate is 0.5℃ / min-10℃ / min, the temperature is raised to 1200-1400℃, and the temperature is maintained for 2-5 hours, and the material is pulverized to 300-500 mesh.

[0015] Furthermore, in step S3, the raw material for the soft carbon coating is one or more of low-temperature petroleum asphalt, high-temperature petroleum asphalt, coal tar pitch, starch, graphite, toluene, tetrahydrofuran, and propylene glycol. The mixing method is liquid phase coating or ball milling coating.

[0016] Further, in step S3, when a liquid phase coating is used, the steps are as follows: hard carbon powder and soft carbon coating raw material are mixed in a tetrahydrofuran solution, the amount of soft carbon coating raw material added is 3-10% of the mass of hard carbon powder, and then dried after thorough stirring.

[0017] Further, in step S3, when ball milling coating is used, the steps are as follows: put hard carbon powder and soft carbon coating raw material into a ball mill jar, the amount of soft carbon coating raw material added is 3-10% of the mass of hard carbon powder, the ball-to-material ratio is 10-15:1, the rotation speed is 500 r / min, and the ball milling is carried out for 1-3 hours.

[0018] Furthermore, in step S3, the coating amount is 3-15 wt% of starch-based hard carbon.

[0019] Furthermore, in step S4, the heat treatment conditions are as follows: heating rate of 1-20℃ / min, carbonization temperature of 500-1000℃, carbonization time of 1-4h, and protective gas of nitrogen or argon.

[0020] According to another aspect of the invention, another object of the invention is to provide a negative electrode material for a sodium-ion battery, said negative electrode material being formed from the hard carbon according to the invention.

[0021] This invention provides a high-ratio starch-based hard carbon anode material and its preparation method, which has the following beneficial effects: 1. Soft carbon coating can effectively cover defects and active sites on the surface of hard carbon materials, reduce irreversible decomposition of electrolyte on the surface during the first charge and discharge process, and significantly improve the first coulombic efficiency.

[0022] 2. The formed soft carbon coating has good electronic conductivity, which greatly improves the electron transport rate between particles, reduces the electrode impedance, and meets the needs of fast charging application scenarios.

[0023] 3. The uniform and dense soft carbon layer acts as a physical barrier, reducing direct and repeated contact between the electrolyte and the hard carbon core, thereby suppressing the occurrence of continuous side reactions and improving the cycle life and capacity retention of the battery.

[0024] 4. Coating treatment can improve the microscopic inhomogeneities (such as pores and defects) on the surface of the original hard carbon material particles, enhancing the structural consistency of the final product. This reduces intra-batch and inter-batch product quality differences, significantly increases the yield rate, and decreases the scrap and defective product rates, thereby lowering overall production costs. Attached Figure Description

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

[0026] Figure 1 The image shows the nitrogen adsorption of the hard carbon material prepared in Example 1.

[0027] Figure 2 The first 0.1C specific capacity diagram of the hard carbon material prepared in Example 1.

[0028] Figure 3 The specific capacity diagrams for the hard carbon materials prepared in Example 1 and Comparative Example 1 at different expansion rates are shown.

[0029] Figure 4 The image shows the long-cycle stability of the hard carbon material prepared in Example 1.

[0030] Figure 5 The first 0.1C specific capacity diagram of the hard carbon material prepared in Example 4.

[0031] Figure 6 This is a specific capacity graph for different batches at 0.1C and 5C in Example 1. Detailed Implementation

[0032] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0033] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0034] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Before description, it should be understood that the terminology used in the specification and appended claims should not be construed as limited to its general and dictionary meaning, but rather should be interpreted based on the principle of allowing the inventors to appropriately define the terminology for the best interpretation, and based on its meaning and concept corresponding to the technical level of the invention. Therefore, the description herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention; thus, it should be understood that other equivalent implementations and modifications can be made without departing from the spirit and scope of the invention.

[0035] In this document, the terms “comprising,” “including,” “having,” “containing,” or any similar terms are open-ended transitional phrases intended to encompass non-exclusive inclusions. For example, a composition or article containing a plural element is not limited to the elements listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated otherwise, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously encompassing closed or semi-closed transitional phrases such as “composed of” and “substantially composed of.”

[0036] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual values ​​within those ranges, particularly integer values. For example, a range description of "1 to 8" should be considered as specifically disclosing all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., particularly secondary ranges defined by all integer values, and should be considered as specifically disclosing individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc. Unless otherwise specified, the foregoing interpretation applies to all content throughout this invention, regardless of its scope.

[0037] If a quantity or other numerical value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any upper or preferred value of that range and the lower or preferred value of that range, regardless of whether such ranges are separately disclosed. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range shall include its endpoints and all integers and fractions within the range.

[0038] In this document, numerical values ​​are to be understood as having a precision with significant digits, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover the range from 39.50 to 40.49.

[0039] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0040] The experimental methods, production processes, instruments, and equipment involved in the embodiments and comparative examples of this invention are all conventional names in the art, and are very clear and distinct in their respective fields of application. Those skilled in the art can understand the conventional process steps and apply the corresponding equipment based on these names, and implement them according to conventional conditions or conditions recommended by the manufacturer.

[0041] Furthermore, unless otherwise stated, the reagents and solvents disclosed below were purchased from Sigma-Aldrich Korea, and IR measurements were performed using a Jasco FT-IR 4100 series; HPLC measurements were performed using an Agilent Technoliges 1200 series; and 1 ¹H NMR was measured using an Oxford NMR 300MHz spectrometer from Varian Mercury Instruments. Purity was calculated as area % by HPLC.

[0042] In addition, unless otherwise stated, the reagents and solvents disclosed below were purchased from Maclean's Reagents, tetrahydrofuran solution CAS No. 109-99-9, AR≥99%; corn starch was purchased from Shandong Fuyang Corn Starch, and the BET test was performed using a Micromeritics ASAP 2460 (USA); battery testing was performed using a LAND CT2001A battery testing system (Wuhan Landian Electronics Co., Ltd.).

[0043] Button cell manufacturing and testing The hard carbon material prepared above is mixed with sodium carboxymethyl cellulose (CMC) binder and styrene-butadiene rubber (SBR) conductive carbon black in a mass ratio of 94:2:2:2 to form a slurry. The slurry is then uniformly coated onto the surface of copper foil, dried, and cut into electrode sheets with a diameter of 14 cm.

[0044] Using a sodium metal sheet as the counter electrode and an EC / DMC (1:1) solution of 1 mol / L NaClO4 or NaPF6 as the electrolyte, the CR2016 button cell was assembled in an argon-filled glove box.

[0045] The battery charge and discharge tests were conducted on the LAND CT2001A battery testing system (Wuhan Landian Electronics Co., Ltd.). The test voltage range was 0-2.5V, the test ambient temperature was 25℃, and the first charge and discharge test, rate test, and cycle test were performed.

[0046] The rate testing current densities are 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 5C. Example 1

[0047] Corn starch was subjected to oxidative crosslinking by heating to 250℃ at a rate of 2℃ / min and holding for 2 hours in air to obtain crosslinked modified corn starch. The modified corn starch was then stabilized at 300℃ for 1 hour in an inert atmosphere with a heating rate of 5℃ / min. The material was then pulverized to 200 mesh using an air jet mill.

[0048] High-temperature carbonization and calcination were carried out. The calcination process was as follows: the temperature was increased to 1400℃ at 5℃ / min and held for 3 hours; after cooling to room temperature, hard carbon material was obtained and pulverized to 400 mesh using an air jet mill.

[0049] Hard carbon powder and medium-temperature petroleum asphalt are mixed in a tetrahydrofuran solution. The amount of medium-temperature petroleum asphalt added is 5% of the mass of hard carbon powder. After thorough stirring, the mixture is dried.

[0050] The coated hard carbon powder was heat-treated at a heating rate of 10℃ / min, a treatment temperature of 700℃, and held at that temperature for 1 hour. Argon was used as the protective gas. After cooling to room temperature, the starch-based hard carbon with a soft carbon coating was obtained. Example 2

[0051] The only difference between this embodiment and Embodiment 1 is that the amount of medium-temperature petroleum asphalt added is 3% of the mass of hard carbon powder; the rest of the preparation process steps are the same as in Embodiment 1. Example 3

[0052] The only difference between this embodiment and Embodiment 1 is that the amount of medium-temperature petroleum asphalt added is 10% of the mass of hard carbon powder; the rest of the preparation process steps are the same as in Embodiment 1. Example 4

[0053] The gelatinized starch was stabilized at a low temperature of 300℃ with a heating rate of 5℃ / min, and the material was then pulverized for later use.

[0054] High-temperature carbonization and calcination were carried out. The calcination process was as follows: the temperature was increased to 1400℃ at 5℃ / min and held for 3 hours; after cooling to room temperature, hard carbon material was obtained and then ball-milled.

[0055] Hard carbon powder and low-temperature petroleum asphalt are mixed in a tetrahydrofuran solution, with the amount of low-temperature petroleum asphalt added being 5% of the mass of hard carbon powder. After thorough stirring, the mixture is dried.

[0056] The coated hard carbon powder was heat-treated at a heating rate of 10℃ / min, a treatment temperature of 900℃, and held for 1 hour under argon as the protective gas. After cooling to room temperature, the starch-based hard carbon with a soft carbon coating was obtained. Example 5

[0057] The modified starch was transferred to a hydrothermal reactor and stabilized at 180°C. All other preparation steps were the same as in Example 1.

[0058] Comparative Example 1 The difference between this embodiment and Embodiment 1 is that no coating treatment or heat treatment was performed; all other preparation process steps are the same as in Embodiment 1.

[0059] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that no coating treatment was performed, but heat treatment was performed. All other preparation process steps are the same as in Embodiment 1.

[0060] Comparative Example 3 The difference between this embodiment and Example 1 is that no stabilization reaction was performed; all other preparation process steps are the same as in Example 1.

[0061] The specific testing methods are explained below. The test results of the above embodiments and comparative examples are detailed in Table 1.

[0062]

[0063] Table 1 Figure 1 The hard carbon material prepared in Example 1 was tested using a fully automated specific surface area and porosity analyzer, and its specific surface area was found to be 5.5 m². 2 / g.

[0064] Figure 2 The first charge-discharge curve of the hard carbon material prepared in Example 1 at a current density of 0.1C is given. It can be seen from the figure that the initial specific capacity of the material is as high as 344.32mAh / g, and the first efficiency reaches 93.49%.

[0065] Figure 3The specific capacity performance of the hard carbon materials prepared in Example 1 and Comparative Example 1 at different rate powers is shown in the graphs. As can be seen from the graphs, the rate performance of the starch-based hard carbon is significantly improved after surface coating treatment. At a 5C current density, Example 1 retains a reversible specific capacity of 277 mAh / g, while Comparative Example 1 only has 180.33 mAh / g. The capacity retention at 0.1C / 5C increases from 53.23% to 80.60%.

[0066] Figure 4 This is a cycling performance graph for Example 1. The capacity retention after 500 cycles at 1C reaches 93.46%, demonstrating excellent cycling performance. The coating treatment significantly alleviates the problem of rapid capacity decay of the hard carbon anode during cycling.

[0067] Figure 5 The first charge-discharge curve of the hard carbon material prepared in Example 4 at a current density of 0.1C is given. It can be seen from the figure that the initial specific capacity of the material is as high as 332.10 mAh / g, and the first efficiency reaches 90.64%.

[0068] Figure 6 Repeated experiments of Example 1 are presented. The specific capacity at 0.1C, the rate performance at 5C, and the initial coulombic efficiency are stable. The hard carbon material prepared by this method has good consistency and shows good prospects for industrial application.

[0069] The electrochemical test results from Examples 1-5 and Comparative Examples 1-3 show that by adjusting and controlling parameters such as starch type, stabilization reaction temperature, heating rate, and time, a uniformly reacted modified starch can be obtained. The carbonization process of the modified starch forms a more disordered structure. The disordered carbon layer structure and abundant closed pores within the hard carbon can improve the plateau region capacity, thereby increasing the specific capacity of the electrode material.

[0070] By applying a soft carbon coating to the surface of hard carbon materials, the position occupied by the coating is fixed during the carbonization process, forming new carbon layers. These carbon layers modify the surface of the hard carbon materials, improving the cycle stability of the hard carbon anode material, enhancing electron and ion transport rates, and reducing irreversible capacity loss. The coating also helps form a more uniform and stable SEI film on the material surface, avoiding Na⁺ loss and capacity decay caused by repeated film rupture and regeneration. Simultaneously, the coating acts as a mechanical support layer, effectively suppressing volume changes of the active material during cycling and preventing electrode pulverization or structural breakage.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-ratio starch-based hard carbon anode material and its preparation method, characterized in that, Includes the following steps: S1. First, the pre-modified starch is stabilized at a low temperature of 300-500℃, and the material is crushed for later use. S2, Carbonization: The powder from step S1 is carbonized at high temperature under an inert atmosphere, and after cooling, starch-based hard carbon material is obtained. S3, Coating treatment: Mix the hard carbon material and soft carbon from step S2; S4. Heat treatment: The mixture from step S3 is heat treated to obtain a hard carbon anode material with a soft carbon coating.

2. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, The starch in step S1 includes acetylated distarch phosphate, acetate starch, corn starch, wheat starch, potato starch, tapioca starch, water chestnut starch, and lotus root starch.

3. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, The modification method of the modified starch in step S1 is as follows: the starch is heated to 200-300℃ in air at a rate of 0.5-5℃ / min and kept at that temperature for 1-2 hours to carry out oxidative crosslinking, thereby obtaining crosslinked modified starch.

4. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, The stabilization process in step S1 is as follows: heat the temperature to 300-500℃ at a rate of 5-10℃ / min and keep it at that temperature for 1-2 hours, then let it cool naturally to room temperature before removing it. Further, the pulverization step in step S1 is as follows: the carbonized precursor is pulverized to 200-400 mesh using an air jet mill.

5. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, In step S2, the protective atmosphere for carbonization is nitrogen or argon, the heating rate is 0.5℃ / min-10℃ / min, the temperature is raised to 1200-1400℃ and maintained at a constant temperature for 2-5 hours, and the material is pulverized to 300-500 mesh.

6. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, In step S3, the raw materials for the soft carbon coating are one or more of low-temperature petroleum asphalt, high-temperature petroleum asphalt, coal tar pitch, starch, graphite, toluene, tetrahydrofuran, and propylene glycol; the mixing method is liquid phase coating or ball milling coating.

7. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, In step S3, when a liquid phase coating is used, the steps are as follows: hard carbon powder and soft carbon coating raw material are mixed in a tetrahydrofuran solution, the amount of soft carbon coating raw material added is 3-10% of the mass of hard carbon powder, and after thorough stirring, it is dried.

8. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, In step S3, when ball milling coating is used, the steps are as follows: put hard carbon powder and soft carbon coating raw material into a ball mill jar, the amount of soft carbon coating raw material added is 3-10% of the mass of hard carbon powder, the ball-to-material ratio is 10-15:1, the rotation speed is 500 r / min, and the ball milling is carried out for 1-3 hours; Furthermore, in step S3, the coating amount is 3-15 wt% of starch-based hard carbon.

9. The high-ratio starch-based hard carbon anode material and its preparation method according to claim 1, characterized in that, In step S4, the heat treatment conditions are as follows: heating rate is 1-20℃ / min, carbonization temperature is 500-1000℃, carbonization time is 1-4h, and the protective gas is nitrogen or argon.

10. The hard carbon anode material prepared according to the method described in claims 1-9 is used as an anode material for sodium-ion batteries.

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