Biomass hard carbon material, preparation method thereof, sodium ion battery negative electrode plate containing biomass hard carbon material, and sodium ion battery

Abstract

The invention discloses a biomass hard carbon material and a preparation method thereof as well as a sodium ion battery negative pole piece containing the biomass hard carbon material and a sodium ion battery. The preparation method comprises the following steps: primary carbonization: firstly, treating a coconut shell biomass precursor with a phosphoric acid solution, and then performing primary carbonization on biomass to obtain a coconut shell biomass precursor; the temperature of the primary carbonization is higher than the boiling point of the phosphoric acid; and performing high-temperature pyrolysis: performing high-temperature pyrolysis on the precursor subjected to primary carbonization at 1200-1500 DEG C to prepare the biomass hard carbon material. Through a simple carbonization treatment process, a large number of oxygen-containing functional groups are modified on the surface of coconut shell hard carbon. Through phosphoric acid activation, P atoms are doped in a carbon skeleton of coconut shell hard carbon. The coconut shell hard carbon negative electrode rich in oxygen functional groups and doped with P atoms has higher sodium ion adsorption capacity, so that the negative electrode obtains larger sodium storage capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of new negative electrode materials, and in particular to a biomass hard carbon material, a preparation method thereof, and a sodium ion battery negative electrode sheet and a sodium ion battery containing the same. Background Art

[0002] Lithium-ion batteries, with their high specific capacity, long cycle life, and stable operation, have garnered significant attention in recent decades. However, due to limited lithium resources, lithium-ion batteries struggle to meet the growing demand for electric vehicles and energy storage. Because sodium is abundant in the Earth's crust, sodium-ion batteries are considered the most promising alternative to lithium-ion batteries.

[0003] The negative electrode material is one of the most important components of the battery. The most commonly used graphite negative electrode material for lithium-ion batteries is not suitable for sodium-ion batteries. Hard carbon is currently the negative electrode material with the best comprehensive electrochemical performance for sodium-ion batteries and has been widely used in sodium-ion batteries.

[0004] Hard carbon, as a sodium-ion anode material, offers advantages such as abundant raw materials, stable structure, low voltage platform, and excellent safety performance. Biomass is the most commonly used precursor for hard carbon anode materials, but biomass raw materials contain many impurities, making stability difficult to ensure, and the sodium storage capacity needs to be further improved. Summary of the Invention

[0005] In order to overcome the above shortcomings, the purpose of the present invention is to provide a biomass hard carbon material and a preparation method thereof, which can improve the sodium storage capacity.

[0006] In order to achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a biomass hard carbon material, comprising the following steps:

[0007] Preliminary carbonization: first treating the coconut shell biomass precursor with a phosphoric acid solution, and then performing preliminary carbonization on the biomass, wherein the temperature of the preliminary carbonization is higher than the boiling point of the phosphoric acid;

[0008] Sodium hydroxide treatment: The pre-carbonized precursor is treated with sodium hydroxide solution, washed and dried, and sodium hydroxide is used to remove impurities (mainly silicon) in the carbonized biomass;

[0009] High-temperature pyrolysis: The precursor after preliminary carbonization is pyrolyzed at 1200-1500°C to produce biomass hard carbon material.

[0010] Phosphoric acid, an oxygen-containing acid, fully reacts with the coconut shell biomass precursor during boiling and vaporization, generating a large number of oxygen-containing functional groups on its surface and incorporating phosphorus atoms into the carbon skeleton. The oxygen-containing functional groups and phosphorus atom doping facilitate the adsorption of sodium ions on the hard carbon surface, increasing the sodium storage capacity of the hard carbon anode material.

[0011] Furthermore, the phosphoric acid is concentrated phosphoric acid with a mass concentration of 85%, and the volume mass ratio of the phosphoric acid to the coconut shell biomass is (2-4):1.

[0012] Furthermore, the temperature of the preliminary carbonization is 270-280°C, the time is 3-5 hours, and the heating rate is 2-5°C / min. Exemplarily, the temperatures of the preliminary carbonization are 270°C, 271°C, 272°C, 273°C, 274°C, 275°C, 276°C, 277°C, 278°C, 279°C, and 280°C.

[0013] In this solution, phosphoric acid, an oxygen-containing acid, fully reacts with the coconut shell biomass precursor during the boiling and vaporization process, generating a large number of oxygen-containing functional groups on its surface and incorporating phosphorus atoms into the carbon skeleton. Ensuring full reaction with the coconut shell biomass precursor during the boiling and vaporization process is a key technical aspect of this solution.

[0014] Phosphoric acid has a boiling point of 261°C. The initial carbonization temperature needs to be above 261°C to ensure boiling and vaporization of the phosphoric acid. However, the higher the temperature, the more complete the reaction between the phosphoric acid and the coconut shell biomass precursor. Research has found that the initial carbonization temperature should be slightly above the boiling point of phosphoric acid. The temperature should not be too high, as excessively high temperatures can lead to excessive vaporization and volatilization of phosphoric acid, resulting in incomplete subsequent reactions and ultimately reduced sodium-ion battery performance. The temperature should also not be too low, as temperatures below the boiling point of phosphoric acid reduce the reactivity of the precursor with phosphoric acid, similarly leading to a significant decrease in sodium-ion battery performance. Ultimately, the research found that a temperature between 270 and 280°C is suitable, with 280°C being the optimal temperature.

[0015] Furthermore, the method for treating the coconut shell biomass precursor with the phosphoric acid solution is as follows: mixing the phosphoric acid and the coconut shell biomass with a stirrer for 20 to 40 minutes.

[0016] Furthermore, preliminary carbonization is performed under air atmosphere.

[0017] Furthermore, the high-temperature pyrolysis is carried out under an inert gas atmosphere.

[0018] Furthermore, the heating rate of the high-temperature pyrolysis is 3 to 5°C / min, and the reaction time is 2 to 6 hours.

[0019] Furthermore, the preliminary carbonization comprises the following steps:

[0020] S11, mixing 100-200 mL of 85% concentrated phosphoric acid with 50 g of coconut shell biomass under the action of a magnetic stirrer for 30 minutes;

[0021] S12, transferring the mixed suspension into a crucible, then placing the crucible in a muffle furnace, heating the temperature to 280°C at a rate of 2-5°C / min in an air atmosphere and keeping the temperature for 3-5 hours, then cooling the temperature to room temperature naturally;

[0022] S13, after the initial carbonization is completed, the precursor is washed with deionized water in a vacuum filter until the filtrate is neutral;

[0023] S14. After the above steps are completed, the preliminarily carbonized precursor is placed in a forced air drying oven and dried at 80°C.

[0024] Furthermore, the high temperature pyrolysis comprises the following steps:

[0025] S21, placing the preliminarily carbonized precursor in a corundum crucible;

[0026] S22, transferring the corundum crucible to a tube furnace;

[0027] S23, the reaction temperature of the heat treatment process is 1200-1500°C, the heating rate is 3-5°C / min, the reaction time is 2-6h, and then the temperature is naturally lowered to room temperature;

[0028] During the high-temperature pyrolysis reaction, nitrogen or argon is used as a protective gas throughout the entire process.

[0029] The present invention provides a biomass hard carbon material, which is prepared by the above-mentioned method for preparing the biomass hard carbon material.

[0030] The present invention provides a sodium ion battery negative electrode plate, comprising the biomass hard carbon material as described above.

[0031] The present invention provides a sodium ion battery, comprising the sodium ion battery negative electrode sheet as described above.

[0032] The specific preparation steps of sodium ion batteries are:

[0033] Step 1: The obtained hard carbon negative electrode material is mixed with a conductive additive and a binder to prepare a slurry, and water is used as a dispersant. When preparing the slurry, in order to ensure uniform mixing of the components, a mixer is preferably used for thorough mixing.

[0034] Furthermore, the conductive additive is selected from one or more of carbon black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0035] Furthermore, the mass ratio of the conductive additive to the negative electrode active material is 1 to 10 wt. %. The negative electrode active material includes a biomass hard carbon negative electrode material, a conductive additive, and a binder.

[0036] Furthermore, the binder is selected from at least one of sodium alginate, polyacrylic acid PAA, lithium polyacrylate LiPAA, sodium polyacrylate NaPAA, and sodium carboxymethyl cellulose CMC / styrene-butadiene rubber SBR.

[0037] Furthermore, the mass ratio of the binder to the negative electrode active material is 1 to 10 w.t.%.

[0038] Step 2: Use a coating machine to apply the obtained slurry onto a copper foil current collector with a thickness of 4 to 15 μm, dry it, roll it, and then cut it into appropriate sizes for later use.

[0039] Step 3: The positive electrode is prepared using a slurry coating process similar to that of the negative electrode. The positive electrode material includes one or more of the following substances:

[0040] a. sodium-containing transition metal oxides, such as NaMO2 (M is one or more transition metal elements);

[0041] b. Polyanion cathode materials, such as Na x M y (X a O b ) z Z w (M is a transition metal atom, X is phosphorus, sulfur, tungsten, etc., and Z is F or OH), which is composed of polyanion polyhedrons and transition metal ion polyhedrons connected by strong covalent bonds and has a strong and open three-dimensional network structure;

[0042] c. Prussian blue / white, its chemical formula is Na x M1[M2(CN)6] (M is a transition metal atom, such as Mn, Ni, Co, Zn, Cu and Fe, 0<x≤2). It is divided into two materials according to the sodium ion content: Prussian white (high) and Prussian blue (low). It is a new technology route for sodium ion batteries. The positive electrode current collector is generally made of aluminum, nickel, stainless steel, titanium, etc. or a composite foil formed by metal and non-metal. The coating dispersion solvent generally uses a non-aqueous solvent, and the adhesive generally uses a fluorine-containing polymer, such as polyvinylidene fluoride (PVDF).

[0043] Step 4: Assemble the negative electrode, separator and positive electrode into a battery.

[0044] Step 5: Add electrolyte and then seal to obtain a sodium ion battery.

[0045] The electrolyte system is a non-aqueous electrolyte solution containing salts that is liquid at room temperature. The aprotic solvent used in the electrolyte includes at least one of dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (VC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC), as well as at least one sodium-containing electrolyte salt soluble in the above solvents, such as sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), and sodium perchlorate (NaClO4). The concentration of the electrolyte solution is preferably 0.8 to 2.0 M (mole per liter). In addition, 0.1 to 3 wt.% of a compound containing a carboxylic anhydride group, a compound containing sulfur such as sultones (e.g., propylene sultone and propane sultone), or a compound containing boron may be added to the electrolyte. This improves the chemical stability of the electrolyte and inhibits its decomposition on the surface of the negative electrode material.

[0046] The electrolyte system may also contain some or all solid electrolyte components, such as organic solid electrolytes, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, etc.

[0047] The present invention has the following beneficial effects: Through a simple carbonization process, a large number of oxygen-containing functional groups are modified on the surface of coconut shell hard carbon. Furthermore, phosphorus atoms are doped into the carbon skeleton of the coconut shell hard carbon through phosphoric acid activation. The coconut shell hard carbon anode, enriched with oxygen functional groups and doped with phosphorus atoms, exhibits a stronger sodium ion adsorption capacity, resulting in a greater sodium storage capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of 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.

[0050] Figure 1 1 is a comparison chart of the cycle curves of half-cells prepared using the hard carbon materials prepared in Example 1, Comparative Examples 1 and 2;

[0051] Figure 2 Comparison of cycle curves of half-cells prepared using the hard carbon materials prepared in Examples 1 to 8;

[0052] Figure 31 is a comparison chart of rate curves of half-cells prepared using the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2;

[0053] Figure 4 A comparison of rate curves of half-cells prepared using the hard carbon materials prepared in Examples 1 to 8;

[0054] Figure 5 This is a SEM image of the precursor after preliminary carbonization in Example 1 of the present invention;

[0055] Figure 6 This is the EDS image of the precursor after preliminary carbonization in Example 1 of the present invention;

[0056] Figure 7 This is the EDS graph of the C element of the precursor after preliminary carbonization in Example 1 of the present invention;

[0057] Figure 8 This is the O element EDS graph of the precursor after preliminary carbonization in Example 1 of the present invention;

[0058] Figure 9 This is the P element EDS graph of the precursor after preliminary carbonization in Example 1 of the present invention;

[0059] Figure 10 This is the N element EDS graph of the precursor after preliminary carbonization in Example 1 of the present invention;

[0060] Figure 11 This is an SEM image of the biomass hard carbon material of Example 1 of the present invention;

[0061] Figure 12 This is the EDS image of the biomass hard carbon material of Example 1 of the present invention;

[0062] Figure 13 This is the EDS graph of the C element of the biomass hard carbon material of Example 1 of the present invention;

[0063] Figure 14 This is the O element EDS diagram of the biomass hard carbon material of Example 1 of the present invention;

[0064] Figure 15 This is the EDS graph of the P element of the biomass hard carbon material of Example 1 of the present invention;

[0065] Figure 16 This is the EDS diagram of the N element of the biomass hard carbon material in Example 1 of the present invention. DETAILED DESCRIPTION

[0066] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0067] The following examples more particularly describe the present disclosure, and these examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0068] Example 1

[0069] Mix 50g of coconut shell biomass precursor with 120mL of 85% phosphoric acid in a 500mL beaker. Add a magnet and place the beaker on a magnetic stirrer. Stir at room temperature for 30 minutes. After stirring, transfer the suspension to a crucible. Place the crucible in a muffle furnace and heat it to 280°C at a rate of 5°C / min in an air atmosphere. Hold the temperature for 5 hours, then cool it to room temperature. After preliminary carbonization, wash the coconut shell biomass with deionized water in a vacuum filter until the filtrate is neutral. After these steps, dry the precursor in a forced-air drying oven at 80°C.

[0070] The dried precursor was then mixed with 200 mL of 1 mol / L sodium hydroxide solution in a 500 mL beaker. A magnet was then added and the beaker was placed on a magnetic stirrer. Stirring was continued at room temperature for 2 hours. The mixture was then washed with deionized water in a vacuum filter until the filtrate was neutral. After these steps, the precursor was dried in a forced air drying oven at 80°C.

[0071] The treated precursor was placed in a corundum crucible, and then the corundum crucible was transferred to a tubular furnace. Nitrogen was used as a protective gas throughout the process, and the temperature was increased to 1400°C at a heating rate of 5°C / min and kept at this temperature for 2 hours, and then naturally cooled to room temperature to obtain a hard carbon negative electrode material.

[0072] According to calculation, the volume-to-mass ratio of the phosphoric acid to the coconut shell biomass is 120:50=12:5.

[0073] Example 2

[0074] The preparation methods of Example 2 and Example 1 are essentially the same, with the primary difference being that the volume of phosphoric acid in Example 2 was changed from 120 mL to 200 mL during the precursor treatment process. All other experimental conditions remained unchanged. Calculations indicate that the volume-to-mass ratio of the phosphoric acid to the coconut shell biomass is 200:50 = 4:1.

[0075] Example 3

[0076] The preparation methods of Example 3 and Example 1 are essentially the same, with the primary difference being that the volume of phosphoric acid in Example 3 was changed from 120 mL to 100 mL during the precursor treatment process. All other experimental conditions remained unchanged. Calculations indicate that the volume-to-mass ratio of the phosphoric acid to the coconut shell biomass is 100:50 = 2:1.

[0077] Example 4

[0078] The preparation methods of Example 4 and Example 1 are basically the same, the main difference being that the processing temperature of the precursor in Example 4 is changed from 280° C. to 300° C. The other experimental conditions remain unchanged.

[0079] Example 5

[0080] The preparation methods of Example 5 and Example 1 are basically the same, the main difference being that the precursor treatment time in Example 5 is changed from 5 h to 3 h compared to Example 1. The other experimental conditions remain unchanged.

[0081] Example 6

[0082] The preparation methods of Example 6 and Example 1 are basically the same, the main difference being that, compared to Example 1, the pyrolysis temperature of the precursor during pyrolysis in Example 6 is changed from 1400°C to 1500°C. The other experimental conditions remain unchanged.

[0083] Example 7

[0084] The preparation methods of Example 7 and Example 1 are basically the same, the main difference being that, compared with Example 1, in Example 7, the pyrolysis temperature during the pyrolysis of the precursor is changed from 1400° C. to 1200° C.

[0085] Example 8

[0086] The preparation methods of Example 8 and Example 1 are basically the same, the main difference being that, compared with Example 1, in Example 8, the holding time during the precursor pyrolysis process is changed from 2 h to 5 h.

[0087] Comparative Example 1

[0088] The preparation methods of Comparative Example 1 and Example 1 are basically the same, the main difference being that the phosphoric acid treatment of the precursor is omitted in Comparative Example 1 compared to Example 1. The other experimental conditions remain unchanged.

[0089] Specifically, the initial carbonization process for the coconut shell biomass precursor is as follows: 50g of the coconut shell biomass precursor is placed in a crucible. The crucible is then placed in a muffle furnace and heated to 280°C at a rate of 5°C / min under a nitrogen atmosphere. The temperature is then maintained for 5 hours, followed by a natural cooling to room temperature. The initially carbonized coconut shell biomass is then washed with deionized water in a vacuum filter until the filtrate is neutral. After these steps, the precursor is dried in a forced air drying oven at 80°C.

[0090] Comparative Example 2

[0091] The preparation methods of Comparative Example 2 and Example 1 are basically the same, the main difference being that the processing temperature of the precursor in Comparative Example 2 is changed from 280°C to 250°C compared to Example 1. The other experimental conditions remain unchanged.

[0092] Experimental Example 1

[0093] The physical and chemical properties of the biomass hard carbon negative electrode materials prepared in Examples 1 to 8 and Comparative Examples 1 to 2 were tested, and the test results are shown in Table 1.

[0094] Specific surface area test method: measure the amount of gas adsorbed on the solid surface at different relative pressures, and then calculate the monolayer adsorption amount of the sample based on the Brunaue-Emmett-Teller (BET formula).

[0095] Material tap density test method: The tap density is tested using a Quantachrome AutoTap tap density meter.

[0096] Table 1 Physical and chemical properties of phenolic resin hard carbon negative electrode materials of Examples 1 to 8 and Comparative Examples 1 to 2

[0097] <![CDATA[Apparent density of the material / g / cm 3 > <![CDATA[Specific surface area of material / m 2 / g]]> Example 1 0.86 6.4 Example 2 0.82 7.3 Example 3 0.88 5.2 Example 4 0.85 6.3 Example 5 0.85 7.1 Example 6 0.88 5.4 Example 7 0.82 6.8 Example 8 0.84 5.9 Comparative Example 1 0.92 4.9 Comparative Example 2 0.81 6.2

[0098] Experimental Example 2

[0099] Half-cells were prepared using the biomass hard carbon negative electrode materials prepared in Examples 1 to 8 and Comparative Examples 1 to 2 using the following method, and the electrochemical performance of the half-cells was tested. The test results are shown in Table 2.

[0100] Half-cell preparation: The biomass hard carbon anode material, conductive carbon black SP, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 90:2:2:6 using water as a dispersant to prepare a slurry. The resulting slurry was coated onto a copper foil current collector and dried, rolled, and cut to produce the negative electrode sheet.

[0101] The half-cell uses metallic sodium as the negative electrode, with a voltage range of 0.005 to 1.5 V. During discharge, the current density is first 0.05C constant current discharge to 0.05V, then 0.2C constant current discharge to 0.005V, and then stand for 20 minutes, and then charge to 1.5V at 0.05C constant current. Table 2: Electrochemical performance of the half-cell

[0102]

[0103] As can be seen from the data in Tables 1 and 2 above, during the preparation of the biomass hard carbon provided in Comparative Examples 1-2, one or more of the various parameters were outside the range of the present invention, resulting in poor electrochemical performance of the half-cells prepared using these biomass hard carbon materials. In contrast, the half-cells prepared using the biomass hard carbon negative electrode materials provided in Examples 1-8 of the present invention exhibited good electrochemical performance and excellent sodium storage capacity.

[0104] From the experimental data of Example 1 and Comparative Example 1, it can be seen that the performance of sodium ion batteries can be improved by treating the biomass precursor with phosphorus. The reason is that phosphoric acid treatment can modify a large number of oxygen-containing functional groups on the hard carbon surface and incorporate P atoms into the carbon skeleton to improve material performance.

[0105] From the experimental data of Example 1, Example 4 and Comparative Example 2, it can be seen that during the initial carbonization, the carbonization temperature needs to be strictly controlled, and the carbonization temperature needs to be slightly higher than the boiling point of phosphoric acid to fully react the solid-liquid-gas three-phase. The boiling point of phosphoric acid is 261°C, and the lower limit of the suitable temperature is 270°C, but the effect of 280°C is better. In Example 4, if the temperature is higher, phosphoric acid will be excessively vaporized and volatilized in large quantities, resulting in incomplete subsequent reactions and ultimately a decrease in the performance of the sodium ion battery. In Comparative Example 2, the initial carbonization temperature is 250°C. Since 250°C is below the boiling point of phosphoric acid, the reactivity of the precursor and phosphoric acid at this temperature is reduced, which leads to a significant decrease in the performance of the sodium ion battery.

[0106] It can be seen from the experimental data of Example 1 and Example 5 that when the initial carbonization time is reduced, the degree of reaction is insufficient, resulting in a decrease in the capacity of the prepared sodium ion battery.

[0107] From the attached Figure 1 It can be seen that the cycle performance of the half-cell prepared by the biomass hard carbon negative electrode material prepared in Example 1 is much better than the cycle performance of the half-cell prepared by the biomass hard carbon negative electrode material prepared in Comparative Examples 1 to 2.

[0108] From the attached Figure 2 It can be seen that by changing the conditions for preparing the biomass hard carbon anode material, the cycling performance of the half-cell can be changed. Specifically, from the three curves of Examples 1 to 3, it can be seen that when the volume-to-mass ratio of phosphoric acid to coconut shell biomass reaches 4:1, the performance of the prepared half-cell decreases.

[0109] From the attached Figure 3 It can be seen that the rate performance of the half-cell prepared by the biomass hard carbon negative electrode material prepared in Example 1 is much better than the rate performance of the half-cell prepared by the biomass hard carbon negative electrode material prepared in Comparative Examples 1 to 2.

[0110] From the attached Figure 4 It can be seen that by changing the conditions for preparing biomass hard carbon negative electrode materials, the rate performance of the half-cell can be changed.

[0111] From the attached Figures 5-10 It can be seen that the surface of the biomass precursor after initial carbonization is rich in oxygen elements under the action of phosphoric acid, and P heteroatoms are evenly doped in the carbon skeleton.

[0112] From the attached Figures 11-16 It can be seen that biomass hard carbon materials are rich in oxygen functional groups, and P heteroatoms are evenly doped in the carbon skeleton.

[0113] The present invention uses the above-described embodiments to illustrate the detailed process equipment and process flow of the present invention. However, the present invention is not limited to the above-described detailed process equipment and process flow, and does not mean that the present invention must rely on the above-described detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacement of raw materials of the present invention, changes in structural form, addition of auxiliary ingredients, selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

[0114] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0115] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0116] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

[0117] The above embodiments are only for illustrating the technical concept and features of the present invention. Its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a biomass hard carbon material, characterized in that: The following steps are involved: Preliminary carbonization: first treating the coconut shell biomass precursor with a phosphoric acid solution, and then performing preliminary carbonization on the biomass, wherein the temperature of the preliminary carbonization is higher than the boiling point of the phosphoric acid; High-temperature pyrolysis: The precursor after preliminary carbonization is pyrolyzed at 1200-1500°C to produce biomass hard carbon material.

2. The method for preparing biomass hard carbon material according to claim 1, characterized in that: The phosphoric acid is concentrated phosphoric acid with a mass concentration of 85%, and the volume mass ratio of the phosphoric acid to the coconut shell biomass is (2-4):

1.

3. The method for preparing biomass hard carbon material according to claim 1, characterized in that: The temperature of the initial carbonization is 270-280°C, the time is 3-5h, and the heating rate is 2-5°C / min.

4. The method for preparing biomass hard carbon material according to claim 1, characterized in that: The method for treating the coconut shell biomass precursor with phosphoric acid solution is as follows: mixing phosphoric acid and coconut shell biomass under the action of a stirrer for 20 to 40 minutes, and then performing preliminary carbonization with the biomass under air atmosphere after mixing.

5. The method for preparing biomass hard carbon material according to claim 1, characterized in that: The initial carbonization was carried out in air atmosphere.

6. The method for preparing biomass hard carbon material according to claim 1, characterized in that: The high-temperature pyrolysis is carried out under an inert gas atmosphere.

7. The method for preparing biomass hard carbon material according to claim 1, characterized in that: The heating rate of high-temperature pyrolysis is 3 to 5°C / min, and the reaction time is 2 to 6 hours.

8. A biomass hard carbon material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. A negative electrode plate for a sodium ion battery, characterized in that: Including the biomass hard carbon material according to claim 8.

10. A sodium ion battery, characterized in that: Including the sodium ion battery negative electrode plate according to claim 9.

Images