Preparation method and application of organic zinc modified starch-based hard carbon negative electrode material

Abstract

The invention belongs to the technical field of ion battery negative electrode materials, and particularly relates to a preparation method and application of an organic zinc modified starch-based hard carbon negative electrode material. The method comprises the following steps: mixing an organic zinc source and starch, and then carrying out ball milling treatment to obtain a mixture; activating the mixture in air to obtain a precursor, and crushing the precursor to obtain precursor powder; pre-carbonizing the precursor powder to obtain a pre-carbonized material; and performing high-temperature carbonization on the pre-carbonized material, and cooling to room temperature to obtain the organic zinc modified starch-based hard carbon negative electrode material. The material is applied to a sodium ion battery as a negative electrode. The starch is adopted as a raw material, an organic zinc source and the starch are fully mixed through ball milling, the zinc source is uniformly distributed in a precursor by adopting an activation method in air, and the zinc source serves as a pore-forming agent in a high-temperature carbonization process, so that rich sodium storage sites are given to hard carbon, and the capacity of the hard carbon serving as a sodium ion negative electrode material is improved; and the electrochemical performance of the material as a sodium ion negative electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion battery negative electrode materials, and more specifically, relates to a preparation method and application of an organic zinc-modified starch-based hard carbon negative electrode material. Background Art

[0002] Since the Industrial Revolution, the exploitation and use of non-renewable resources has led to increasing global environmental degradation, necessitating the development of green, renewable energy. However, renewable energy sources like solar and wind power suffer from intermittent nature, requiring energy storage technologies to address this issue. Lithium-ion batteries, a key electrochemical energy storage technology, are a promising option. However, the low abundance and uneven distribution of lithium resources in the Earth's crust make lithium-ion batteries unsuitable for large-scale energy storage.

[0003] Sodium-ion batteries (SIBs) share similar principles and physical structures with lithium-ion batteries. Based on technological experience and production practices, large-scale SIB production is highly feasible. Like lithium-ion batteries, SIBs primarily consist of a positive electrode, a negative electrode, and an electrolyte. While both positive electrode materials and electrolytes have advanced rapidly in recent years, the development of negative electrode materials has not kept pace. Therefore, developing a negative electrode material that matches the positive electrode is crucial for the commercialization of SIBs.

[0004] Currently, anode materials suitable for sodium-ion batteries mainly include titanium-based, alloy-based, organic compound, and carbon-based materials. Hard carbon, as a representative carbon-based material, is expected to be the first to achieve large-scale commercial application due to its advantages such as good cycle stability, small volume change during cycling, abundant raw materials, and low cost. However, existing hard carbon materials suffer from lower-than-expected capacity and poor rate performance, which seriously hinders the commercial application of hard carbon materials as anode materials for sodium-ion batteries. Therefore, the development and preparation of hard carbon materials with high capacity and good rate performance is of great significance for sodium-ion batteries.

[0005] For the existing technology, it is still a big challenge to prepare hard carbon with high capacity and good rate performance using relatively low-cost biomass as raw material. Current research believes that porous structure design can solve the above-mentioned problems of biomass hard carbon. For example, the patent with publication number CN115571867B discloses a method for preparing hard carbon materials using sugar compounds and organic zinc pore-forming agents. The sugar compounds and organic zinc pore-forming agents are combined by hydrothermal reaction, and then high-temperature carbonization is used to obtain a hard carbon material with a porous structure. The patent with publication number CN114524425B discloses a hard carbon material, a preparation method thereof, and its use in sodium ion batteries. An organic carbon source, a solvent, and a template are mixed, and a hard carbon material with a porous structure is prepared through pre-carbonization, acidification, high-temperature carbonization and plasma etching. Although the above two schemes successfully constructed hard carbon materials with a porous structure, they adopted an overly complicated process route, and the actual production energy consumption was large and the cost was high, which is not conducive to industrial production and needs further improvement. Summary of the Invention

[0006] (1) Technical problems solved

[0007] In view of the problems of complex process and high production cost in the above-mentioned technology, the present invention intends to provide a preparation method and application of an organic zinc-modified starch-based hard carbon negative electrode material. The organic zinc-modified starch-based hard carbon negative electrode material has the advantages of a wide source of raw materials, simple process and low energy consumption, which is convenient for industrial production.

[0008] (2) Technical solution

[0009] To achieve the above-mentioned and other related purposes, the present invention provides the following technical solutions:

[0010] In a first aspect, a method for preparing an organic zinc-modified starch-based hard carbon negative electrode material is provided, comprising the following steps:

[0011] The organic zinc source and starch are mixed and then ball-milled to obtain a mixture;

[0012] activating the mixture in air to obtain a precursor, and crushing the precursor to obtain precursor powder;

[0013] Pre-carbonizing the precursor powder to obtain a pre-carbonized material;

[0014] The pre-carbonized material is carbonized at high temperature and cooled to room temperature to obtain an organic zinc-modified starch-based hard carbon negative electrode material.

[0015] In detail or preferably, the organic zinc source includes at least one of zinc gluconate, zinc lactate, licorice zinc, zinc acetate, zinc citrate, and zinc glycinate.

[0016] In detail or preferably, the starch includes at least one of corn starch, potato starch, sweet potato starch, wheat starch, tapioca starch, mung bean starch, pea starch, kudzu root starch, lotus root starch, and water chestnut starch.

[0017] In detail or preferably, when the organic zinc source and starch are mixed, the mixing ratio of the organic zinc source to the starch is 2:1-1:15.

[0018] In detail or preferably, during the ball milling treatment, the ball milling speed is 500-1000 rpm, the material of the ball milling beads includes one of agate, stainless steel and zirconia, and the ball milling time is 2-12 hours.

[0019] Specifically or preferably, the activation temperature in air is 110-280° C., the activation time is 4-16 h, and the stirring speed is 100-400 rpm.

[0020] In detail or preferably, the D50 of the precursor powder is 5-50 μm.

[0021] In detail or preferably, the pre-carbonization is carried out in an inert gas, and the inert gas includes at least one of nitrogen, helium, and argon.

[0022] In detail or preferably, the pre-carbonization treatment method includes first heating the temperature to 500-600°C at a heating rate of 1-8°C / min and keeping the temperature for 1-3 hours; then heating the temperature to 800-1000°C and keeping the temperature for 2-5 hours.

[0023] In detail or preferably, the high-temperature carbonization is carried out in an inert gas, and the inert gas includes at least one of nitrogen, helium, and argon.

[0024] In detail or preferably, the high temperature carbonization treatment method includes first heating the temperature to 800-1000° C. at a heating rate of 1-6° C. / min and keeping the temperature for 1-3 hours; then heating the temperature to 1200-1600° C. and keeping the temperature for 4-8 hours.

[0025] In the second aspect, an application of an organic zinc-modified starch-based hard carbon negative electrode material in a sodium ion battery is provided. The organic zinc-modified starch-based hard carbon negative electrode material is prepared according to the aforementioned preparation method of an organic zinc-modified starch-based hard carbon negative electrode material.

[0026] In detail or preferably, the main components of the sodium ion battery are a positive electrode, a negative electrode, a separator, an electrolyte, and a current collector. The organic zinc-modified starch-based hard carbon negative electrode material is used as the negative electrode in the sodium ion battery.

[0027] In detail or preferably, the sodium ion battery is charged and discharged under the conditions of 0.1C current density and 0.0-2.5V voltage, and the first discharge capacity is 370-400mAh / g, the first charge capacity is 330-370mAh / g, and the first charge and discharge efficiency is 88-92%.

[0028] It should be noted that the present invention uses starch as raw material, fully mixes the organic zinc source and starch through ball milling, and adopts the method of activation in air to make the organic zinc source evenly distributed inside the precursor. During the high-temperature carbonization process, the organic zinc source acts as a pore-forming agent, and the pores created are further transformed into a closed-pore structure, which enriches the sodium storage sites of the hard carbon material, increases the capacity of the hard carbon as a sodium ion negative electrode material, and improves its electrochemical performance as a sodium ion negative electrode material.

[0029] (3) Beneficial technical effects

[0030] Advantages of the present invention:

[0031] (1) The present invention uses starch, which is widely available and green and renewable, as the carbon source of the hard carbon material. Ball milling and air activation are used to wrap organic zinc in the precursor. During carbonization, the oxidation, reduction, and sublimation of the organic zinc will produce a large number of porous structures in the hard carbon material. After high-temperature carbonization, some of the porous structures can still be retained, thereby serving as an effective sodium ion storage site, greatly improving the capacity of the hard carbon material.

[0032] (2) The process route of the present invention is simple. The present invention does not require the use of a hydrothermal reaction. The present invention only requires the following steps: mixing the raw materials with organic zinc, ball milling, activation in air, crushing, pre-carbonization, and high-temperature carbonization to prepare a high-capacity hard carbon negative electrode material.

[0033] (3) The present invention uses an organic zinc source as a pore-forming agent, which has the following advantages over traditional alkali or basic salt pore-forming agents: less impact on the environment, milder reaction conditions, and lower loss of equipment and instruments; in addition, compared with enzyme preparation activators, organic zinc pore-forming agents have lower costs and are more suitable for large-scale production.

[0034] (4) The technical principles of the present invention include:

[0035] Ball milling: Physical and mechanical forces are used to achieve uniform dispersion of the organic zinc source and starch, enhancing interfacial bonding and laying the foundation for subsequent doping. During this process, the organic zinc source and starch do not undergo esterification or hydrothermal reactions. Ball milling can refine the material, increase the specific surface area, and improve electrochemical performance in subsequent applications. However, ball milling is prone to problems such as material agglomeration. The present invention addresses the shortcomings of existing technologies by limiting specific mixing ratios, milling media (balls), and milling conditions.

[0036] Activation: Heating in an oxidizing atmosphere promotes partial oxidation and cross-linking of starch to form stable oxygen-containing functional groups (such as carboxyl and carbonyl), enhance the thermal stability of the precursor, and avoid excessive shrinkage or structural collapse during carbonization.

[0037] Crushing: Improve the uniformity of the precursor powder after crushing. The uniformity will directly affect the pore distribution of the carbonized product and the electrode processing performance.

[0038] Pre-carbonization: The initial decomposition of organic matter and the formation of a carbon skeleton are completed by staged temperature increase, and the inert atmosphere prevents the oxidation of the carbon material.

[0039] High-temperature carbonization: Promotes carbon layer rearrangement and pore formation through staged temperature increase. At the same time, the catalytic effect of zinc reduces the carbonization temperature requirement and increases the carbon yield. The inert atmosphere prevents the oxidation of the carbon material and ensures the formation of a hard carbon structure.

[0040] In summary, during activation in air, the starch undergoes oxidative cross-linking, encapsulating the organic zinc source. During high-temperature carbonization, the organic zinc is converted into oxides, which are then reduced and sublimated, forming numerous pores. Ultimately, at temperatures exceeding 1000°C, these pores rearrange and transform into the closed-pore structure of the hard carbon material, enabling excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 This is a SEM image of the hard carbon material prepared in Example 5, where the magnification is 500;

[0043] Figure 2 This is a SEM image of the hard carbon material prepared in Example 5, where the magnification is 2000. DETAILED DESCRIPTION

[0044] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified as manufacturers are conventional products that can be purchased commercially.

[0045] The present invention provides a method for preparing and applying an organozinc-modified starch-based hard carbon anode material, with specific implementations provided below. The battery assembly reagents used in the application and testing are battery-grade, which is not a critical factor affecting the present invention and is therefore not described in detail.

[0046] In particular, some of the raw materials involved are as follows:

[0047] Zinc gluconate: Purchased from Zhengzhou Ruipu Bioengineering Co., Ltd., its main ingredient is zinc gluconate dihydrate, with an active ingredient content of not less than 97% and a zinc content of not less than 12.89%.

[0048] Zinc lactate: purchased from Zhengzhou Ruipu Bioengineering Co., Ltd., its main component is zinc lactate dihydrate, the active ingredient content is not less than 98%, and the zinc content is not less than 22.69%.

[0049] Zinc acetate: purchased from Guangzhou Deli Chemical Co., Ltd., its main component is zinc acetate dihydrate, the active ingredient content is not less than 98%, and the zinc content is not less than 29.18%.

[0050] Zinc citrate: purchased from Zhengzhou Ruipu Bioengineering Co., Ltd., its main ingredient is zinc citrate dihydrate, the active ingredient content is not less than 98%, and the zinc content is not less than 31.50%.

[0051] Corn starch: purchased from Henan Fengwei Biotechnology Co., Ltd., with an amylose content of no less than 50%, which is a high-amylose starch.

[0052] Cassava starch: purchased from Dongguan Jinguanhua Food Co., Ltd., with a straight chain content of 15 to 20%, which is a high-branched starch.

[0053] Sweet potato starch: purchased from Jinan Xingjian Biotechnology Co., Ltd., with a straight chain content of 18 to 25%, which is a high-branched starch.

[0054] Pea starch: Purchased from Jinan Xingjian Biotechnology Co., Ltd., it has a linear content of 25 to 35%, and is a highly branched starch.

[0055] Example 1

[0056] A method for preparing an organic zinc-modified starch-based hard carbon negative electrode material, comprising the following steps:

[0057] (1) Zinc gluconate and corn starch were added to a ball mill in a mass ratio of 1:4 and subjected to ball milling to obtain a mixture. The ball milling conditions were as follows: the volume of zinc gluconate and corn starch and the volume of ball milling beads each occupied 1 / 3 of the inner cavity of the ball mill, the ball milling beads were stainless steel ball milling beads, the ball milling speed was 500 rpm, and the ball milling time was 8.0 h.

[0058] It should be noted that the amount of raw materials added is limited by mass ratio and volume ratio in the present invention. Those skilled in the art can clearly know the implementation conditions and can add specific mass of raw materials according to the aforementioned restrictions and actual test scale. The same is true for the other embodiments and comparative examples, which will not be described in detail later.

[0059] (2) The mixture obtained in step (1) was placed in an electric heating mantle and stirred, and air-activated to obtain a precursor, wherein the activation temperature was 120° C., the activation time was 12.0 h, and the activation stirring rate was 300 rpm.

[0060] (3) The precursor obtained in step (2) is placed in a jet mill for pulverization to obtain a precursor powder, wherein the particle size of the precursor powder is: D50 is 25 μm.

[0061] (4) The precursor powder obtained in step (3) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 500°C at a rate of 2.4°C / min and kept warm for 1 hour; then raised to 850°C, kept warm for 3 hours, and then naturally cooled to room temperature to obtain a pre-carbonized material.

[0062] (5) The pre-carbonized material obtained in step (4) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 800°C at a rate of 1.6°C / min and kept warm for 1 hour; then the temperature was raised to 1400°C at a rate of 2.1°C / min, kept warm for 3.0 hours, and then naturally cooled to room temperature to obtain a hard carbon material.

[0063] Example 2

[0064] A method for preparing an organic zinc-modified starch-based hard carbon negative electrode material, comprising the following steps:

[0065] (1) Zinc lactate and cassava starch were added to a ball mill in a mass ratio of 1:5 and subjected to ball milling to obtain a mixture. The ball milling conditions were as follows: the volume of zinc lactate and cassava starch and the volume of ball milling beads each occupied 1 / 3 of the inner cavity of the ball mill, stainless steel ball milling beads were used, the ball milling speed was 550 rpm, and the ball milling time was 6.5 h.

[0066] (2) The mixture obtained in step (1) was placed in an electric heating mantle and stirred, and air-activated to obtain a precursor. The activation temperature was 140° C., the activation time was 10.0 h, and the activation stirring rate was 300 rpm.

[0067] (3) The precursor obtained in step (2) is placed in a jet mill for pulverization to obtain a precursor powder, wherein the particle size of the precursor powder is: D50 is 25 μm.

[0068] (4) The precursor powder obtained in step (3) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 520°C at a rate of 2.6°C / min and kept warm for 1 hour; then the temperature was raised to 900°C, kept warm for 2.5 hours, and then naturally cooled to room temperature to obtain a pre-carbonized material.

[0069] (5) The pre-carbonized material obtained in step (4) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 850°C at a rate of 1.8°C / min and kept warm for 1 hour; then the temperature was raised to 1500°C at a rate of 2.3°C / min, kept warm for 4.0 hours, and then naturally cooled to room temperature to obtain a hard carbon material.

[0070] Example 3

[0071] A method for preparing an organic zinc-modified starch-based hard carbon negative electrode material, comprising the following steps:

[0072] (1) Zinc acetate and sweet potato starch were added to a ball mill in a mass ratio of 1:6 and subjected to ball milling to obtain a mixture. The ball milling conditions were as follows: the volume of zinc acetate and sweet potato starch and the volume of ball milling beads each occupied 1 / 3 of the inner cavity of the ball mill, stainless steel ball milling beads were used, the ball milling speed was 600 rpm, and the ball milling time was 5.0 h.

[0073] (2) The mixture obtained in step (1) was placed in an electric heating mantle and stirred, and air-activated to obtain a precursor. The activation temperature was 160° C., the activation time was 8.0 h, and the activation stirring rate was 300 rpm.

[0074] (3) The precursor obtained in step (2) is placed in a jet mill for pulverization to obtain a precursor powder, wherein the particle size of the precursor powder is: D50 is 25 μm.

[0075] (4) The precursor powder obtained in step (3) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 560°C at a rate of 2.8°C / min and kept warm for 1 hour; then the temperature was raised to 950°C, kept warm for 2.0 hours, and then naturally cooled to room temperature to obtain a pre-carbonized material.

[0076] (5) The pre-carbonized material obtained in step (4) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 900°C at 2.0°C / min and kept warm for 1 hour; then the temperature was raised to 1500°C at 2.5°C / min, kept warm for 5.0 hours, and then naturally cooled to room temperature to obtain a hard carbon material.

[0077] Example 4

[0078] A method for preparing an organic zinc-modified starch-based hard carbon negative electrode material, comprising the following steps:

[0079] (1) Zinc citrate and pea starch were added to a ball mill in a mass ratio of 1:7 and ball milled to obtain a mixture. The ball milling conditions were as follows: the mass ratio of the total amount of zinc lactate and cassava starch to the ball milling beads was 1:10, stainless steel ball milling beads were used, the ball milling speed was 700 rpm, and the ball milling time was 3.5 h.

[0080] (2) The mixture obtained in step (1) was placed in an electric heating mantle and stirred, and air-activated to obtain a precursor. The activation temperature was 190° C., the activation time was 6.0 h, and the activation stirring rate was 300 rpm.

[0081] (3) The precursor obtained in step (2) is placed in a jet mill and pulverized to obtain a precursor powder. The particle size of the precursor powder is: D50 is 25 μm.

[0082] (4) The precursor powder obtained in step (3) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 600°C at 3.0°C / min and kept warm for 1 hour; then the temperature was raised to 1000°C, kept warm for 1.5 hours, and then naturally cooled to room temperature to obtain a pre-carbonized material.

[0083] (5) The pre-carbonized material obtained in step (4) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 1000°C at 2.2°C / min and kept warm for 1 hour; then the temperature was raised to 1600°C at 2.7°C / min, kept warm for 4 hours, and then naturally cooled to room temperature to obtain a hard carbon material.

[0084] Example 5

[0085] Different from Example 1, in step (1) of the preparation method of this embodiment, zinc gluconate and corn starch are added into a ball mill in a mass ratio of 2:1 and ball milled to obtain a mixture.

[0086] The rest are the same as in Example 1.

[0087] The hard carbon material prepared in this example can be referred to Figure 1 and Figure 2 .

[0088] Example 6

[0089] Different from Example 1, in step (1) of the preparation method of this embodiment, zinc gluconate and corn starch are added into a ball mill in a mass ratio of 1:1 and ball milled to obtain a mixture.

[0090] The rest are the same as in Example 1.

[0091] Example 7

[0092] Different from Example 1, in step (1) of the preparation method of this embodiment, zinc gluconate and corn starch are added into a ball mill in a mass ratio of 1:2 and ball milled to obtain a mixture.

[0093] The rest are the same as in Example 1.

[0094] It should be noted that the hard carbon materials prepared in Examples 1 to 7 are organic zinc-modified starch-based hard carbon negative electrode materials.

[0095] Comparative Example 1

[0096] In this comparative example, unlike Example 1, zinc gluconate was not added, and the specific steps were as follows:

[0097] (1) Add corn starch to a ball mill and perform ball milling to obtain a mixture. The ball milling conditions are as follows: the volume of the corn starch and the volume of the ball milling beads each occupy 1 / 3 of the inner cavity of the ball mill, the ball milling beads are stainless steel ball milling beads, the ball milling speed is 500 rpm, and the ball milling time is 8.0 h.

[0098] (2) The mixture obtained in step (1) was placed in an electric heating mantle and stirred, and air-activated to obtain a precursor. The activation temperature was 120° C., the activation time was 12.0 h, and the activation stirring rate was 300 rpm.

[0099] (3) The precursor obtained in step (2) is placed in a jet mill for pulverization to obtain a precursor powder, wherein the particle size of the precursor powder is: D50 is 25 μm.

[0100] (4) The precursor powder obtained in step (3) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 500°C at a rate of 2.4°C / min and kept warm for 1 hour; then raised to 850°C, kept warm for 3 hours, and then naturally cooled to room temperature to obtain a pre-carbonized material.

[0101] (5) The pre-carbonized material obtained in step (4) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 800°C at a rate of 1.6°C / min and kept warm for 1 hour; then the temperature was raised to 1400°C at a rate of 2.1°C / min, kept warm for 3.0 hours, and then naturally cooled to room temperature to obtain a hard carbon material.

[0102] Comparative Example 2

[0103] In this comparative example, unlike Example 1, no activation was performed, and the specific steps were as follows:

[0104] (1) Zinc gluconate and corn starch were added to a ball mill in a mass ratio of 1:1 and ball milled to obtain a mixture. The ball milling conditions were as follows: the volume of zinc gluconate and corn starch and the volume of ball milling beads each occupied 1 / 3 of the inner cavity of the ball mill, the ball milling beads were stainless steel ball milling beads, the ball milling speed was 500 rpm, and the ball milling time was 8.0 h.

[0105] (2) The mixture obtained in step (1) is placed in a jet mill as a precursor and pulverized to obtain a precursor powder. The particle size of the precursor powder is: D50 is 25 μm.

[0106] (3) The precursor powder obtained in step (2) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 500°C at 2.4°C / min and kept warm for 1 hour; then raised to 850°C, kept warm for 3 hours, and then naturally cooled to room temperature to obtain a pre-carbonized material.

[0107] (4) The pre-carbonized material obtained in step (3) was placed in a box-type atmosphere furnace, and in a nitrogen atmosphere, the temperature was raised to 800°C at a rate of 1.6°C / min and kept warm for 1 hour; then the temperature was raised to 1400°C at a rate of 2.1°C / min, kept warm for 3.0 hours, and then naturally cooled to room temperature to obtain a hard carbon material.

[0108] Application and testing: The hard carbon materials prepared in Examples 1-7 and Comparative Examples 1-2 were prepared into button batteries and subjected to electrochemical performance testing. The specific methods are as follows:

[0109] The hard carbon materials, conductive agent (conductive carbon black Super P) and binder (sodium carboxymethyl cellulose (CMC)) prepared in Examples 1-7 and Comparative Examples 1-2 were weighed separately, and the three were mixed in a ratio of 95:2:3. A small amount of deionized water was added while grinding in an agate mortar to form a black paste slurry after uniform grinding. The slurry was then coated on a copper foil current collector, vacuum dried, and cut to prepare a test electrode.

[0110] The prepared test electrode was used as the negative electrode, the sodium sheet as the counter electrode, the glass fiber as the separator, and the electrolyte was 1 M sodium hexafluorophosphate dissolved in a mixed solution of dimethyl carbonate (DMC) and ethylene carbonate (EC) with a volume ratio of 1:1. 2 wt% of fluoroethylene carbonate (FEC) was added as an additive. CR2032 stainless steel was used as the battery casing, and the button cell was assembled in an argon-protected glove box. The charge and discharge test rate was 0.1C (1C = 300 mA / g), and the voltage range was 0.0-2.5V. The first discharge capacity and first charge efficiency obtained from the test are listed in Table 1. Among them, the calculation method of the first charge and discharge efficiency refers to the determination method of the first discharge specific capacity and the first coulombic efficiency in the national standard GB / T 43114-2023, that is, the first charge and discharge efficiency = (first charge capacity ÷ first discharge capacity) × 100%; the capacity retention rate after 100 cycles of 1C / 1C cycling at room temperature is calculated as: (discharge capacity after the current cycle ÷ first discharge capacity) × 100%.

[0111] Table 1 Electrochemical performance test results of prepared hard carbon negative electrode materials

[0112]

[0113]

[0114] From the above table we can see that:

[0115] (1) The present invention uses starch as a raw material, organic zinc as a pore-forming agent, and activates the material in air to prepare a hard carbon negative electrode material with excellent performance. During the activation process in air, the starch undergoes oxidative cross-linking and coats the organic zinc source inside it. During carbonization, the organic zinc is converted into zinc oxide, which is then reduced to zinc elemental substance by carbon. Subsequently, it sublimates at high temperature to form a large number of pores, forming a porous structure, and finally forming a large number of closed-pore structures at high temperature, thereby achieving a hard carbon material with excellent electrochemical performance, such as Figure 1 shown.

[0116] (2) As can be seen from Example 1 and Examples 5-7, there is an optimal addition ratio when organic zinc is used as an activator. Excessive organic zinc will cause a sharp increase in pores and specific surface area, thereby hindering the pore-forming effect of organic zinc and reducing electrochemical performance. When the amount of organic zinc added is small, the pore-forming effect of organic zinc cannot be manifested, and the gain in electrochemical performance is not obvious. As can be seen from Example 1 and Comparative Examples 1-2, when organic zinc is not introduced to form pores, the closed-pore content in the hard carbon material does not change, and the electrochemical performance is average. When air activation is not performed, starch does not undergo oxidative cross-linking, and thus fails to cover the organic zinc. The starch and organic zinc are simply dispersed evenly, and the pore-forming effect is also poor, and excellent electrochemical performance cannot be achieved.

[0117] (3) In summary, the present invention provides a preparation method and application of an organic zinc-modified starch-based hard carbon negative electrode material, which uses biomass raw material starch as a carbon source, organic zinc as a pore-forming agent, and is combined with air activation and other preparation methods to give the hard carbon material the characteristics of higher first charge and discharge capacity, first charge and discharge efficiency and energy density.

[0118] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing an organic zinc-modified starch-based hard carbon negative electrode material, characterized in that: The steps include: An organic zinc source and starch are mixed and then ball-milled to obtain a mixture; the mixture is activated in air to obtain a precursor; the precursor is crushed to obtain a precursor powder; and the precursor powder is pre-carbonized to obtain a pre-carbonized material; The pre-carbonized material is carbonized at high temperature and cooled to room temperature to obtain an organic zinc-modified starch-based hard carbon negative electrode material.

2. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: When the organic zinc source and starch are mixed, the mixing ratio of the organic zinc source to the starch is 2:1-1:

15.

3. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: The activation temperature in air is 110-280°C, the activation time is 4-16 hours, and the stirring speed is 100-400 rpm.

4. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: The organic zinc source includes at least one of zinc gluconate, zinc lactate, licorice zinc, zinc acetate, zinc citrate, and zinc glycinate; the starch includes at least one of corn starch, potato starch, sweet potato starch, wheat starch, cassava starch, mung bean starch, pea starch, kudzu starch, lotus root starch, and water chestnut starch.

5. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: During the ball milling process, the ball milling speed is 500-1000 rpm, the ball milling beads are made of one of agate, stainless steel and zirconia, and the ball milling time is 2-12 hours.

6. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: The D50 of the precursor powder is 5-50 μm.

7. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: Both the pre-carbonization and the high-temperature carbonization are carried out in an inert gas, and the inert gas includes at least one of nitrogen, helium and argon.

8. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: The pre-carbonization treatment method includes first heating the temperature to 500-600°C at a heating rate of 1-8°C / min and keeping the temperature for 1-3 hours; then heating the temperature to 800-1000°C and keeping the temperature for 2-5 hours.

9. The method for preparing an organic zinc-modified starch-based hard carbon negative electrode material according to claim 1, characterized in that: The high-temperature carbonization treatment method includes first heating the temperature to 800-1000°C at a heating rate of 1-6°C / min and keeping the temperature for 1-3 hours; then heating the temperature to 1200-1600°C and keeping the temperature for 4-8 hours.

10. An organic zinc-modified starch-based hard carbon negative electrode material is used as a negative electrode in a sodium ion battery, characterized in that: Organic zinc-modified starch-based hard carbon anode material It is obtained by the preparation method of an organic zinc-modified starch-based hard carbon negative electrode material according to any one of claims 1 to 9.

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