A kind of waste biomass fruit core derived hard carbon material and its preparation method and application

Abstract

The present invention belongs to the technical field of new secondary battery electrode materials, and discloses a hard carbon material derived from a waste biomass fruit core, and a preparation method and application thereof. The preparation method of the hard carbon material comprises the following steps: washing and crushing the waste biomass fruit core to obtain a carbon precursor; sequentially soaking the carbon precursor in water and alkaline extraction to obtain a suspension, and performing solid-liquid separation on the suspension to obtain a precipitate; pre-carbonizing the precipitate at 200-350°C to obtain a hard carbon precursor; in a protective atmosphere, performing high-temperature pyrolysis treatment on the hard carbon precursor at 1000-1500°C to prepare a hard carbon material. The hard carbon material prepared by the present invention is used as an active material for the negative electrode of a sodium ion battery. The first cycle coulomb efficiency of the sodium ion battery reaches more than 86%, and the capacity retention rate exceeds 80% after 400 cycles at a current density of 0.5A / g. It can effectively solve the problem of too low first efficiency of the sodium ion battery, and at the same time realize the resource utilization of waste biomass fruit cores, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel secondary battery electrode materials, and in particular relates to a hard carbon material derived from a waste biomass fruit core, and a preparation method and application thereof. Background Art

[0002] The development of high-performance positive and negative electrode materials is the premise and key to promoting the large-scale application of sodium-ion batteries. Among all materials, hard carbon is an ideal negative electrode material for sodium-ion batteries because of its large interlayer spacing and abundant defects, which are conducive to the storage and deintercalation of sodium ions and its low cost. A large number of studies have shown that biomass-based hard carbon is the most promising negative electrode material for sodium-ion batteries.

[0003] At present, hard carbon materials prepared with starch as raw material show excellent sodium storage performance. In the prior art, there is a technical solution that obtains hard carbon negative electrode materials by sintering at least one of corn starch, mung bean starch, potato starch, wheat starch, cassava starch or lotus root starch four times at different temperatures. There is also a technical solution that mixes at least one of corn starch, potato starch, rice starch and wheat starch with yeast to make dough or Newtonian fluid, pre-carbonizes it to obtain a precursor powder, and then ball-mills the precursor powder and calcines it to obtain biomass hard carbon. However, the above technical solution directly uses edible starch as raw material to prepare hard carbon, which not only has a cumbersome process, but also has low product added value and an unreasonable process route, which is not conducive to large-scale industrial production and limits its application. Summary of the invention

[0004] In view of the current situation that the preparation of existing starch-based hard carbon has complicated procedures, low product added value and unreasonable process routes, the inventors have found through extensive and in-depth research that, compared with other biomass raw materials, the structure of the hard carbon material prepared using waste biomass fruit cores as raw materials is more suitable for sodium storage, and the sodium ion battery negative electrode prepared using this hard carbon material as the active component has a higher specific capacity density and excellent cycle stability. In addition, waste biomass fruit cores are widely available, sustainably renewable, low-pollution and inexpensive. While obtaining hard carbon materials with excellent sodium storage performance, it is also possible to realize the resource utilization of waste biomass, which has great application prospects.

[0005] The inventors have come up with the basic idea of ​​preparing hard carbon materials using waste biomass fruit cores as raw materials. While considering the influence of the structure of hard carbon materials on their sodium storage performance, they have also comprehensively considered the influence of impurities in waste biomass fruit cores on the cyclic stability of the negative electrode of sodium ion batteries, and have studied and obtained the technical solution for preparing hard carbon materials in the present invention.

[0006] In the preparation process of hard carbon materials, the waste biomass fruit cores are treated with water immersion, alkaline extraction, etc. to destroy the secondary bonds such as hydrogen bonds between protein molecules in the waste biomass fruit cores, and dissociate certain polar groups so that the surfaces of protein molecules have the same charge, thereby solubilizing the protein molecules and reducing the residual amount of protein. The protein content in the precipitate can be reduced, which is conducive to the formation of a good sodium storage structure in the subsequent preparation process; then, before the high-temperature pyrolysis treatment at 1000-1500°C, the precipitate needs to be pre-carbonized at a lower temperature of 200-350°C. chemistry, which can make the precipitate dehydrated and cross-linked during the pre-carbonization process, which is more conducive to the formation of the final structure of the hard carbon material, can not only improve the carbon yield of the subsequent high-temperature pyrolysis treatment, but also maintain the original microstructure of the starch, so that the hard carbon material finally prepared has a three-dimensional spherical structure with an average particle size of 3 to 12 μm, and the average spacing of the carbon layers in the three-dimensional spherical structure is 0.37-0.42 nm, with a good sodium storage structure, which solves the problem of the low first efficiency of sodium ion batteries, and the sodium ion battery negative electrode with the carbon electrode as the active component also has good cycle stability performance.

[0007] One of the objects of the present invention is to provide a method for preparing a hard carbon material.

[0008] A second object of the present invention is to provide a hard carbon material.

[0009] A third object of the present invention is to provide a negative electrode for a sodium ion battery.

[0010] A fourth object of the present invention is to provide a method for preparing a negative electrode of a sodium ion battery.

[0011] A fifth object of the present invention is to provide a sodium ion battery.

[0012] The present invention provides a method for preparing a hard carbon material, the method comprising the following steps:

[0013] S1, washing and crushing the waste biomass fruit core to prepare a carbon precursor;

[0014] S2, sequentially soaking the carbon precursor in water and performing alkaline extraction to obtain a suspension; and performing solid-liquid separation on the suspension to obtain a precipitate;

[0015] S3, pre-carbonizing the precipitate at 200-350° C. to obtain a hard carbon precursor;

[0016] S4. In a protective atmosphere, subjecting the hard carbon precursor to high-temperature pyrolysis treatment at 1000-1500° C. to obtain the hard carbon material.

[0017] In some preferred embodiments, the waste biomass fruit core is selected from one or more of longan core, loquat seed, jackfruit seed and litchi core;

[0018] In other preferred embodiments, the particle size of the carbon precursor is 1 to 100 μm.

[0019] In some preferred embodiments, during the water soaking process of S2, the carbon precursor and water are mixed and soaked in a mass ratio of 1:(10-50);

[0020] Furthermore, the water soaking time is 24 to 48 hours.

[0021] In some preferred embodiments, during the alkaline extraction process of S2, an alkaline solution is used for the alkaline extraction, and the alkaline solution is selected from one or more of a sodium hydroxide solution, a potassium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution, a potassium carbonate solution or a potassium bicarbonate solution;

[0022] In some other preferred embodiments, in the turbid liquid system extracted with alkaline, OH - The concentration is 0.1~10.0mol / L;

[0023] In some preferred embodiments, the alkaline extraction is carried out at a temperature of 30 to 60° C. and for a time of 12 to 48 hours.

[0024] In some preferred embodiments, the pre-carbonization time is 2 to 12 hours.

[0025] In some preferred embodiments, the high temperature pyrolysis treatment is carried out by heating the temperature to 1000-1500° C. at a heating rate of 0.1-5° C. / min and keeping the temperature at 1000-1500° C. for 1-5 hours.

[0026] The hard carbon material provided by the invention has a three-dimensional spherical structure and an average particle size of 3 to 12 μm.

[0027] The sodium ion battery negative electrode provided by the present invention uses the above-mentioned hard carbon material as an active component.

[0028] The method for preparing the negative electrode of the sodium ion battery is as follows: mixing at least one of a conductive agent, a binder, a thickener and a solvent with a hard carbon material, and then coating the resulting mixture on a current collector to prepare the negative electrode of the sodium ion battery.

[0029] The sodium ion battery provided by the present invention comprises the above-mentioned sodium ion battery negative electrode or the sodium ion battery negative electrode prepared by the above-mentioned method. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1This is a SEM image of the hard carbon material provided in Example 1 of the present invention;

[0031] Figure 2 This is the XRD pattern of the hard carbon material provided in Example 1 of the present invention;

[0032] Figure 3 The cycle curve of the hard carbon material provided in Example 1 of the present invention at 0.5 A / g;

[0033] Figure 4 This is the Coulombic efficiency of the hard carbon material provided in Example 1 of the present invention when cycled at 0.5 A / g. DETAILED DESCRIPTION

[0034] The present application provides a method for preparing a hard carbon material, which uses one or more of waste biomass fruit cores - longan cores, loquat seeds, jackfruit seeds and lychee cores as raw materials, and is prepared through water soaking, alkaline extraction, pre-carbonization and high-temperature pyrolysis treatment. The hard carbon material has a three-dimensional spherical structure, and the average spacing of the carbon layers in the three-dimensional spherical structure is 0.37-0.42nm. It has a good sodium storage structure and can effectively solve the problem of too low first efficiency of sodium ion batteries in the prior art. At the same time, the sodium ion negative electrode prepared with the hard carbon material as the active component has good cycle stability performance.

[0035] In the present invention, in order to increase the contact area between the waste biomass fruit core and the liquid during water immersion and alkaline extraction and improve the extraction efficiency, after the waste biomass fruit core is washed and dried, a pulverizer is used to pulverize the waste biomass fruit core for 10 to 20 minutes to obtain a carbon precursor with a smaller particle size. For comprehensive consideration of production cost and extraction effect, the waste biomass fruit core is pulverized to a particle size of 1 to 100 μm, and then water immersion, alkaline extraction and other treatments are carried out to obtain a precipitate.

[0036] In some specific embodiments, the carbon precursor is mixed with water in a mass ratio of 1: (10-50), and the waste biomass fruit core is soaked and softened with water for 24-48 hours, which is beneficial to the subsequent alkaline extraction and can also remove water-soluble impurities. The specific mass ratio of the carbon precursor to water can be 1:10, 1:20, 1:30, 1:40, 1:50 and any value therebetween. The specific water soaking time is adjusted according to the state of the waste biomass fruit core, and the specific water soaking time can be 24h, 30h, 35h, 40h, 45h, 48h and any value therebetween.

[0037] After the water soaking treatment is completed, an alkaline solution is directly added to the turbid liquid to adjust the OH- concentration to 0.1-10.0 mol / L, and the carbon precursor is subjected to alkaline extraction to obtain a suspension.

[0038] In some specific embodiments, the added alkaline solution is a solution that provides OH-; further, the ions or compounds contained in the alkaline solution are: even if a large amount of them remain in the hard carbon material, they will not have an adverse effect on its related properties; specifically, the solute in the alkaline solution can be but is not limited to one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate.

[0039] Furthermore, the temperature of alkaline extraction is 30-60°C, and the time is 12-48h. The specific temperature can be 30°C, 34°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C and any value therebetween, and the time can be but is not limited to 12h, 15h, 18h, 20h, 24h, 28h, 30h, 34h, 36h, 40h, 44h, 48h and any value therebetween. Under the above temperature and time conditions, the extraction efficiency is guaranteed while the production efficiency is also improved.

[0040] In order to further improve the performance of hard carbon materials as negative electrode materials for sodium ion batteries, in some preferred embodiments, after the suspension is centrifuged, the supernatant is removed to obtain a precipitate, which is then washed with clean water until the upper clear layer is neutral, and the precipitate is washed again with ethanol, and the water and ethanol in the precipitate are removed by drying for subsequent pre-carbonization treatment.

[0041] In the present invention, the precipitate obtained above is placed in a muffle furnace for pre-carbonization to obtain a hard carbon precursor. There are no particularly strict requirements for the atmosphere during pre-carbonization. It can be air, or it can be nitrogen, argon and other protective gases with similar properties. In practice, it is found that pre-carbonization under air atmosphere has better effects than other atmospheres, and the processing cost is also lower.

[0042] The inventors ingeniously adopt a lower temperature than conventional pre-carbonization in the present invention, that is, pre-carbonization is carried out at 200-350°C, which can cause the precipitate to be dehydrated and cross-linked during the pre-carbonization process. The hard carbon material finally obtained by high-temperature pyrolysis treatment has a structure that is more suitable for sodium storage, achieving an unexpected effect.

[0043] In some specific embodiments, the specific temperature of pre-carbonization can be 210°C, 250°C, 280°C, 300°C, 320°C, 340°C, 350°C and any value therebetween, and the specific pre-carbonization time needs to be determined according to the temperature, and can be 2h, 5h, 7h, 9h, 10h, 12h and any value therebetween.

[0044] In the present invention, the high-temperature pyrolysis treatment of the hard carbon precursor includes a heating stage and a heat preservation stage, and the hard carbon precursor is converted into a hard carbon material with a three-dimensional spherical structure.

[0045] In some specific embodiments, the heating rate in the heating stage is controlled within the range of 0.1 to 5°C / min. The specific heating rate can be 0.1°C / min, 0.2°C / min, 0.5°C / min, 1.0°C / min, 2.5°C / min, 3.0°C / min, 5.0°C / min and any value therebetween to avoid adverse effects on the formation of three-dimensional spherical structures in hard carbon materials due to excessively fast heating rates.

[0046] In some specific embodiments, the temperature in the insulation stage should be maintained at 1000-1500°C, specifically 1000°C, 1105°C, 1200°C, 1350°C, 1400°C, 1500°C and any value therebetween. Within this temperature range, the hard carbon precursor can better form a three-dimensional spherical structure.

[0047] The present application also provides a hard carbon material having a three-dimensional spherical structure. The hard carbon material can be prepared by one of the above-mentioned specific embodiments, or can be a mixture of hard carbon materials prepared by multiple specific embodiments. Specifically, the hard carbon material can be selected according to the desired performance of the sodium ion battery negative electrode.

[0048] The present application also provides a sodium ion battery negative electrode. According to performance requirements, a corresponding conductive agent, adhesive, thickener and solvent are selected and mixed with at least the above-mentioned hard carbon material, and the electrode is prepared by direct solidification and molding, or a composite negative electrode is formed by coating on a current collector.

[0049] The present application further provides a sodium ion battery, which uses the above-mentioned sodium ion battery negative electrode as the negative electrode, has an initial charge and discharge efficiency of more than 80%, and has a charge and discharge efficiency of more than 100% at 0.5A g -1 After 400 cycles at the current density, the capacity retention rate is about 80%. It has a high specific capacity density and excellent cycle stability.

[0050] Embodiments of the present invention are described in detail below, and the examples of the embodiments are intended to be used to explain the present invention, but should not be construed as limiting the present invention. In the embodiments, if specific techniques or conditions are not specified, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not specified for reagents or instruments used, they are all conventional products that can be obtained commercially.

[0051] Example 1. Hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0052] This embodiment provides a hard carbon material, which is prepared by using longan kernel as a raw material through the following steps:

[0053] S1, washing the longan core with water and placing it in an oven, drying it at 80°C to constant weight, and crushing the washed longan core with a grinder to prepare a carbon precursor with a particle size of 3 to 10 μm;

[0054] S2, mixing the carbon precursor with water in a mass ratio of 1:10 to obtain a turbid solution, and immersing the mixture for 24 hours;

[0055] S3, add sodium hydroxide to the turbid liquid of S2, adjust the OH- in the suspension to 0.1 mol / L, and place it in a constant temperature oil bath at 45°C and stir for 24 hours for alkaline extraction to obtain a suspension;

[0056] S4, centrifuging the suspension to remove the supernatant to obtain a precipitate, washing with water until neutral, then washing with anhydrous ethanol three times, and finally drying the precipitate in an oven at 40°C for 48 hours;

[0057] S5, placing the precipitate in an alumina crucible, and pre-carbonizing it in a muffle furnace at 210° C. for 8 h under air atmosphere to prepare a hard carbon precursor;

[0058] S6. The hard carbon precursor is heated to 1300°C at a rate of 2°C / min in a high-purity N2 atmosphere and kept at this temperature for 2 hours for high-temperature pyrolysis treatment. The hard carbon material is prepared after cooling and grinding.

[0059] The microstructure and XRD of the hard carbon material of this embodiment are shown in Figure 1 and Figure 2 As shown in the figure, the hard carbon material prepared with longan core as raw material has a spherical structure. At the same time, according to the XRD diagram, it can be calculated that the average interlayer spacing within the three-dimensional spherical structure of the hard carbon material is 0.378nm, and there are many defects on the surface and inside of the hard carbon material particles, which makes the hard carbon material have good sodium embedding ability.

[0060] This embodiment also provides a sodium ion battery negative electrode, using the hard carbon material prepared by the above method as an active component; the specific preparation method is: the hard carbon material, conductive carbon black and sodium alginate are evenly mixed in a mass ratio of 70:20:10, and water is added to grind into a paste, which is coated on the surface of the copper foil current collector and dried at 80°C for 12 hours to prepare the sodium ion battery negative electrode.

[0061] This embodiment also provides a sodium ion half-cell, comprising the above-mentioned sodium ion battery negative electrode, and using a metal sodium sheet as a counter electrode, a glass fiber as a diaphragm, and a 1 mol / L NaPF6 / DME solution as an electrolyte, and assembling the sodium ion half-cell in an argon protection glove box.

[0062] The long cycle test and coulombic efficiency test results of the hard carbon material of this embodiment at 0.5A / g are as follows: Figure 3 and Figure 4 As shown in the figure, the hard carbon material prepared with longan core as raw material has a spherical structure. At the same time, according to the XRD diagram, it can be calculated that the average interlayer spacing within the three-dimensional spherical structure of the hard carbon material is 0.378nm, and there are many defects on the surface and inside of the hard carbon material particles, which makes the hard carbon material have good cycle stability.

[0063] Example 2. Hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0064] A hard carbon material is prepared according to the method provided in Example 1, except that in S2, the carbon precursor is mixed with water at a mass ratio of 1:20 and immersed, and in S3, the OH- in the suspension is adjusted to 0.5 mol / L using sodium hydroxide, and the suspension is placed in a constant temperature oil bath at 40°C and stirred for 24 h for alkaline extraction. The remaining conditions are the same as in Example 1 to prepare a hard carbon material.

[0065] The sodium ion battery negative electrode provided in this embodiment uses the hard carbon material prepared by the above method as an active component.

[0066] Furthermore, the sodium ion half-cell provided in this embodiment includes the sodium ion battery negative electrode provided in this embodiment.

[0067] Example 3. Hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0068] In this embodiment, loquat seeds are used as raw materials for preparing hard carbon materials. The hard carbon materials are prepared according to the method provided in Example 1, except that in S2, the carbon precursor is mixed with water at a mass ratio of 1:30 and soaked for 48 hours, in S3, the OH- in the suspension is adjusted to 1.0 mol / L using sodium hydroxide, in S5, pre-carbonization is carried out at 300°C for 2 hours, and in S6, the temperature is increased to 1200°C at a rate of 0.1°C / min. The remaining conditions are the same as in Example 1 to prepare the hard carbon material.

[0069] The sodium ion battery negative electrode provided in this embodiment uses the hard carbon material prepared by the above method as an active component.

[0070] Furthermore, the sodium ion half-cell provided in this embodiment includes the sodium ion battery negative electrode provided in this embodiment.

[0071] Example 4. Hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0072] In this embodiment, jackfruit seeds are used as raw materials for preparing hard carbon materials. The hard carbon materials are prepared according to the method provided in Example 1, except that in S2, the carbon precursor is mixed and soaked with water at a mass ratio of 1:50, in S3, the OH- in the suspension is adjusted to 5.0 mol / L using sodium hydroxide, and placed in a constant temperature oil bath at 50°C and stirred for 24 hours for alkaline extraction, in S5, pre-carbonized at 350°C for 2 hours, and in S6, the temperature is raised to 1400°C at a rate of 0.2°C / min, and the remaining conditions are the same as in Example 1 to prepare the hard carbon material.

[0073] The sodium ion battery negative electrode provided in this embodiment uses the hard carbon material prepared by the above method as an active component.

[0074] Furthermore, the sodium ion half-cell provided in this embodiment includes the sodium ion battery negative electrode provided in this embodiment.

[0075] Example 5. Hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0076] In this embodiment, litchi kernels are used as raw materials for preparing hard carbon materials. The hard carbon materials are prepared according to the method provided in Example 1, except that in S2, the carbon precursor is mixed with water at a mass ratio of 1:20 and soaked, in S3, the OH- in the suspension is adjusted to 10.0 mol / L using sodium hydroxide, and placed in a constant temperature oil bath at 35°C and stirred for 24 h for alkaline extraction, in S4, the precipitate after washing with anhydrous ethanol is placed in an oven at 50°C and dried for 24 h, in S5, it is pre-carbonized at 280°C for 2 h, and in S6, it is heated to 1500°C at a rate of 5°C / min, and the remaining conditions are the same as in Example 1 to prepare the hard carbon material.

[0077] The sodium ion battery negative electrode provided in this embodiment uses the hard carbon material prepared by the above method as an active component.

[0078] The sodium ion half-cell provided in this embodiment includes the sodium ion battery negative electrode provided in this embodiment.

[0079] Comparative Example 1. Reference hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0080] A reference hard carbon material was prepared according to the method of Example 1, except that longan kernels were replaced with corn starch in the same weight portion. Other conditions were the same as in Example 1 to prepare a reference hard carbon material.

[0081] The sodium ion battery negative electrode provided in this comparative example uses the reference hard carbon material prepared by the above method as an active component.

[0082] The sodium ion half-cell provided in this comparative example includes the sodium ion battery negative electrode provided in this comparative example.

[0083] Comparative Example 2. Reference hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0084] A reference hard carbon material was prepared according to the method of Example 1, except that the carbon precursor was not subjected to alkaline extraction but was directly subjected to pre-carbonization treatment. The remaining conditions were the same as those of Example 1 to prepare a reference hard carbon material.

[0085] The sodium ion battery negative electrode provided in this comparative example uses the reference hard carbon material prepared by the above method as an active component.

[0086] The sodium ion half-cell provided in this comparative example includes the sodium ion battery negative electrode provided in this comparative example.

[0087] Comparative Example 3. Reference hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0088] A reference hard carbon material was prepared according to the method of Example 1, except that the carbon precursor was not pre-carbonized but directly subjected to high-temperature pyrolysis. The remaining conditions were the same as those of Example 1 to prepare a reference hard carbon material.

[0089] The sodium ion battery negative electrode provided in this comparative example uses the reference hard carbon material prepared by the above method as an active component.

[0090] The sodium ion half-cell provided in this comparative example includes the sodium ion battery negative electrode provided in this comparative example.

[0091] Comparative Example 4. Reference hard carbon material, sodium ion battery negative electrode and sodium ion half-cell

[0092] A reference hard carbon material was prepared according to the method of Example 1, except that the pre-carbonization temperature was 400° C., so that the pre-carbonization temperature was higher than the range of the present invention. The remaining conditions were the same as those of Example 1, and a reference hard carbon material was prepared.

[0093] The sodium ion battery negative electrode provided in this comparative example uses the reference hard carbon material prepared by the above method as an active component.

[0094] The sodium ion half-cell provided in this comparative example includes the sodium ion battery negative electrode provided in this comparative example.

[0095] Test example.

[0096] In the constant current charge and discharge mode, the sodium ion half-cells provided in Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to charge and discharge tests. The current density range of the charge and discharge tests was 0.02 to 2 A / g, and the voltage range was 0 to 2.5 V. The test results are shown in Table 1.

[0097] Table 1.

[0098]

[0099]

[0100] It can be seen from Table 1 that compared with the comparative example 1 in which corn starch is directly used to prepare the hard carbon material, the sodium ion half-cells prepared by the hard carbon materials provided by Examples 1 to 5 of the present invention have shown excellent performance in terms of first coulombic efficiency, specific capacity density, etc., indicating that compared with the use of starch materials to prepare hard carbon materials in the prior art, the hard carbon materials prepared by using waste biomass fruit cores as raw materials in the present invention have a structure that is more suitable for sodium storage. Using it as the active component of the negative electrode of the sodium ion battery solves the problem of too low first efficiency of the sodium ion battery.

[0101] Compared with Comparative Examples 2 to 4, the lack of one or more steps such as alkaline extraction, pre-carbonization or water immersion in the preparation process of hard carbon will affect the microstructure of the prepared hard carbon material, and further affect its sodium storage performance. In the preparation method provided by the present invention, each step works synergistically, and the structure of the hard carbon material is gradually formed during alkaline extraction, pre-carbonization and high-temperature pyrolysis treatment. If one or more steps are changed, replaced or omitted, the final hard carbon structure will change, affecting the sodium storage performance of the hard carbon material, and ultimately affecting the first coulombic efficiency, specific capacity density and other properties of the battery including the negative electrode using it as the active material.

[0102] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for preparing a sodium ion battery negative electrode hard carbon material, characterized in that: The method comprises the following steps: S1, washing and crushing the waste biomass core to obtain a carbon precursor; S2, sequentially soaking the carbon precursor in water and extracting it with alkaline to obtain a suspension, and performing solid-liquid separation on the suspension to obtain a precipitate, wherein in the turbid liquid system extracted with alkaline, OH - The concentration is 0.1-10.0 mol / L, the temperature of the alkaline extraction is 30-60°C, and the time is 12-48h; S3, pre-carbonizing the precipitate at 200-350° C. for 2-12 hours to obtain a hard carbon precursor; S4. In a protective atmosphere, subjecting the hard carbon precursor to a high-temperature pyrolysis treatment at 1000-1500° C. to obtain the sodium ion battery negative electrode hard carbon material, wherein the high-temperature pyrolysis treatment is performed by heating the temperature to 1000-1500° C. at a heating rate of 0.1-5° C. / min, and keeping the temperature at 1000-1500° C. for 1-5 hours; The sodium ion battery negative electrode hard carbon material has a three-dimensional spherical structure, an average particle size of 3 to 12 μm, and an average spacing between carbon layers in the three-dimensional spherical structure of 0.37 to 0.42 nm; The waste biomass fruit cores are selected from one or more of longan cores, loquat seeds, jackfruit seeds and litchi cores.

2. The method for preparing the hard carbon material for the negative electrode of a sodium ion battery according to claim 1, characterized in that: The particle size of the carbon precursor is 1-100 μm.

3. The method for preparing the hard carbon material for the negative electrode of a sodium ion battery according to claim 1, characterized in that: During the water soaking process of S2, the carbon precursor and water are mixed and soaked in a mass ratio of 1:(10-50).

4. The method for preparing the hard carbon material for the negative electrode of a sodium ion battery according to claim 1, characterized in that: The water soaking time is 24 to 48 hours.

5. The method for preparing the hard carbon material for the negative electrode of a sodium ion battery according to claim 1, characterized in that: During the alkaline extraction process of S2, an alkaline solution is used for the alkaline extraction, and the alkaline solution is selected from one or more of a sodium hydroxide solution, a potassium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution, a potassium carbonate solution or a potassium bicarbonate solution.

6. A sodium ion battery negative electrode hard carbon material prepared by the method for preparing a sodium ion battery negative electrode hard carbon material according to any one of claims 1 to 5, characterized in that: The sodium ion battery negative electrode hard carbon material has a three-dimensional spherical structure and an average particle size of 3 to 12 μm.

7. A sodium ion battery negative electrode, characterized in that: The sodium ion battery negative electrode hard carbon material according to claim 6 is used as an active component.

8. A method for preparing a negative electrode for a sodium ion battery, characterized in that: A conductive agent, a binder, a thickener and a solvent are mixed with the sodium ion battery negative electrode hard carbon material according to claim 6, and then the obtained mixture is coated on a current collector to obtain the sodium ion battery negative electrode.

9. A sodium ion battery, characterized in that: The invention comprises the sodium ion battery negative electrode as claimed in claim 7 or the sodium ion battery negative electrode prepared by the preparation method provided in claim 8.

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