Biomass hard carbon negative electrode material for sodium ion battery based on heteroatom modification and preparation method thereof

Abstract

The application discloses a biomass hard carbon negative material for sodium ion batteries based on heteroatom modification and a preparation method thereof, and comprises the following steps: under an air atmosphere, biomass powder is kept at 200-400 DEG C for 1-8 hours, cooled, and a pre-carbonization product is obtained; the pre-carbonization product and a modifier are mixed, ball milled to be uniform, and a first powder is obtained; under a nitrogen or inert gas atmosphere, the first powder is kept at 800-900 DEG C for 1-8 hours, cooled, ground, sieved, and a second powder is obtained; the second powder is washed to be neutral, dried, and a biomass hard carbon negative material for sodium ion batteries based on heteroatom modification is obtained, wherein the modifier is a mixture of a pore-forming agent and an additive. The biomass hard carbon negative material for sodium ion batteries based on heteroatom modification has a suitable interlayer spacing, is beneficial to the embedding and discharging of sodium ions, and a sodium ion half-battery obtained based on the biomass hard carbon negative material has a high initial coulombic efficiency and reversible specific capacity, and simultaneously has excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery electrode material technology, specifically relating to a sodium-ion battery biomass hard carbon anode material based on heteroatom modification and its preparation method. Background Technology

[0002] With increasing global concern about fossil fuel use and the resulting environmental problems, the past few decades have seen a surge in the development of promising energy storage and conversion devices, including fuel cells, solar cells, supercapacitors, and lithium-ion batteries (LIBs). Since their successful commercialization in the 1990s, LIBs have been widely used in powering portable electronic devices due to their advantages such as high voltage, high energy density, and long cycle life. However, the potential shortage and uneven distribution of lithium resources remain a concern, potentially limiting the further development of lithium-ion batteries and increasing their cost. Considering that sodium (Na) is the sixth most abundant element in the Earth's crust, and possesses similar physicochemical properties to lithium and is readily available, it may be a suitable alternative to lithium-ions. Therefore, sodium-ion batteries (SIBs) have attracted attention due to their low cost, safety, and environmental friendliness.

[0003] Carbon, with its advantages of low cost, good conductivity, and stable physicochemical properties, is widely considered one of the most promising electrode active materials for energy storage systems. Currently, several carbonaceous materials, such as hard carbon, carbon spheres, carbon nanofibers, and carbon nanotubes, have been tested as anodes for energy storage batteries (SIBs). Among them, hard carbon is the most promising SIB anode material due to its large interlayer spacing, low graphitization degree, and disordered structure. Generally, hard carbon can be prepared by pyrolyzing various carbonaceous precursors in an inert atmosphere. These precursors mainly include polymers, sugars, biomass, petroleum pitch, and anthracite. Currently, commercially available hard carbon mainly includes industrial activated carbon, pitch-based hard carbon (coal tar pitch, petroleum pitch, natural pitch), resin-based hard carbon (phenolic resin, epoxy resin, polysaccharide alcohol, etc.), and starch-based hard carbon. The cost per ton of phenolic resin-based, starch-based, and pitch-based hard carbon is approximately RMB 44,000, RMB 29,000, and RMB 23,000, respectively, which are relatively high. Biomass, on the other hand, is abundant, easy to obtain, and inexpensive, which can significantly reduce production costs. Furthermore, reusing waste biomass can reduce environmental pollution. In other words, from the perspective of sustainable development, biomass hard carbon is a promising SIB anode material.

[0004] In the research on using hard carbon as the anode in sodium-ion batteries, problems such as low specific capacity and poor cycle stability exist, which need to be improved. To further improve the electrochemical performance of hard carbon materials, researchers in this field have conducted extensive research and confirmed that the electrochemical performance of hard carbon materials can be improved by doping with heteroatoms. In recent years, carbon materials doped with elements such as nitrogen, boron, phosphorus, sulfur, and oxygen have also attracted widespread attention. To date, the methods for preparing heteroatom-doped carbon materials remain very challenging, and there is an urgent need to develop methods that offer high specific capacity, good cycle stability, and simpler preparation methods. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification.

[0006] Another object of the present invention is to provide a sodium-ion battery biomass hard carbon anode material based on heteroatom modification obtained by the above preparation method.

[0007] Another object of the present invention is to provide the application of the above-mentioned heteroatom-modified sodium-ion battery biomass hard carbon anode material in sodium-ion batteries.

[0008] The objective of this invention is achieved through the following technical solution.

[0009] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification includes the following steps:

[0010] Step 1: Under an air atmosphere, the biomass powder is kept at 200-400℃ for 1-8 hours and then cooled to obtain the pre-carbonized product;

[0011] In step 1, the method for obtaining the biomass powder is as follows: waste biomass is ultrasonically washed at 30-80°C for 6-12 hours to remove surface dust and impurities, crushed into powder with a particle size of 200-400 mesh, and dried to obtain the biomass powder.

[0012] In the above technical solution, the waste biomass is washed using one or more of water, anhydrous ethanol, and acetone.

[0013] In the above technical solution, the waste biomass is one or a mixture of several of the following: wheat straw, corn straw, sugarcane bagasse, reed straw, sunflower straw, ivy vine, and sesame straw.

[0014] In step 1, the heating rate to 200–400°C is 1–10°C / min.

[0015] Step 2: Mix the pre-carbonized product and the modifier, ball mill until uniform to obtain a first powder. Under a nitrogen or inert gas atmosphere, keep the first powder at 800-900℃ for 1-8 hours, cool, grind, and sieve to obtain a second powder. Wash the second powder until neutral and dry to obtain a sodium-ion battery biomass hard carbon anode material based on heteroatom modification. The modifier is a mixture of pore-forming agent and additive. By mass, the ratio of pre-carbonized product to modifier is 1:7, and the ratio of pore-forming agent to additive is 40:1.

[0016] In step 2, the additive is one or a mixture of several of Na2S2O3, (NH4)2SO4 and thiourea.

[0017] In step 2, the pore-forming agent is one or a mixture of several of K2C2O4, NaCl, NaOH, KOH and CaCO3.

[0018] In step 2, the ball milling time is 10 to 100 minutes, and the ball milling speed is 100 to 300 r / min.

[0019] In step 2, the heating rate to 600–1000°C is 1–10°C / min.

[0020] In step 2, the particle size of the second powder is 200-400 mesh.

[0021] In step 2, washing to neutrality involves first washing with water to remove metal heteroatoms, and then washing with water and anhydrous ethanol in sequence.

[0022] The above preparation method yields a sodium-ion battery biomass hard carbon anode material based on heteroatom modification.

[0023] A sodium-ion full battery, wherein the negative electrode material includes the aforementioned sodium-ion battery biomass hard carbon negative electrode material based on heteroatom modification.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The biomass hard carbon anode material for sodium-ion batteries based on heteroatom modification has a suitable interlayer spacing, which is conducive to the insertion and extraction of sodium ions. The sodium-ion half-cell obtained based on it has high initial coulombic efficiency and reversible specific capacity. Its charging curve is plateau type with a high plateau capacity ratio, and it also has excellent cycle stability and rate performance.

[0026] 2. The preparation method of the present invention uses waste biomass as raw material, which has the advantages of being green, environmentally friendly, and low-cost.

[0027] 3. This invention modifies the microstructure of hard carbon (pre-carbonized product) through structural regulation by incorporating heteroatoms via pyrolysis. By introducing anions (O, S), it alters the interlayer spacing, ion diffusion coefficient, and conductivity of the biomass hard carbon anode material for sodium-ion batteries, thereby improving cycle stability. The heteroatom-modified biomass hard carbon anode material for sodium-ion batteries obtained by this invention, based on a simple preparation method, outperforms existing anode materials. Attached Figure Description

[0028] Figure 1 The images show the XRD patterns of the heteroatom-modified sodium-ion battery biomass hard carbon anode materials prepared in Examples 1-7.

[0029] Figures 2-22 Sodium-ion half-cells prepared in Examples 8-14 and Comparative Examples 15-28, respectively, were used at a current density of 30 mA g. -1 Charge-discharge curves at the time;

[0030] Figures 23-29 The sodium-ion half-cells prepared in Examples 8-14 are shown in sequence at a current density of 500 mA g. -1 Cyclic performance and coulomb efficiency at that time;

[0031] Figures 30-43 The sodium-ion half-cells prepared in Comparative Examples 15–28 are shown in sequence at a current density of 500 mA g. -1 Cyclic performance and coulomb efficiency at that time;

[0032] Figure 44 The rate performance diagram of the sodium-ion half-cell prepared in Example 8 is shown.

[0033] Figure 45 The rate performance diagram of the sodium-ion half-cell prepared in Comparative Example 15 is shown.

[0034] Figure 46 The image shows a scanning electron microscope (SEM) image of the heteroatom-modified sodium-ion battery biomass hard carbon anode material prepared in Example 1.

[0035] Figure 47 The image shown is a transmission electron microscope image of the heteroatom-modified sodium-ion battery biomass hard carbon anode material prepared in Example 1 (the inset is a SAED image).

[0036] Figure 48 The diffusion coefficient of sodium ions in the sodium-ion half-cell prepared in Example 8;

[0037] Figure 49 The charge transfer resistance of the sodium-ion half-cell prepared in Example 8;

[0038] Figure 50The graph shows the cycle performance of the full cell prepared in Example 15. Detailed Implementation

[0039] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0040] The raw material information involved in the following examples is as follows:

[0041] Anhydrous ethanol: purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd.; pore-forming agents (NaCl, NaOH): purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; additives (Na2S2O3, (NH4)2SO4): purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0042] The instrument information involved in the following embodiments is as follows:

[0043] Muffle furnace: KSL-1100X, Tube furnace: GSL-1500X, Glove box: MIKROUNA Universal, Newway battery testing system: CT-4008Tn-5 V 50mA, X-ray diffractometer: Rigaku SmartLab 9kw, Scanning electron microscope: Verios460 L, Transmission electron microscope: Talos F200x.

[0044] In the following examples, the waste biomass is sunflower straw.

[0045] Examples 1-7

[0046] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification includes the following steps:

[0047] Step 1: Waste biomass was washed alternately with deionized water and anhydrous ethanol at 60°C under ultrasonic conditions for 10 hours (each cycle consisted of washing with deionized water for 30 minutes and then washing with anhydrous ethanol for 30 minutes) to remove surface dust and impurities. The washed waste biomass was then crushed into powder with an average particle size of 300 mesh using a crusher. The powder was dried at 80°C for 10 hours to obtain biomass powder. The biomass powder was then transferred to a muffle furnace and kept at 250°C for 2 hours in an air atmosphere. After natural cooling, the pre-carbonized product was obtained. The heating rate to 250°C was 5°C / min.

[0048] Step 2: Mix the pre-carbonized product and the modifier, and ball mill at 250 r / min for 30 min until uniform to obtain the first powder. Transfer the first powder to a high-temperature tube furnace and keep it at 850℃ for 2 h under a nitrogen atmosphere. Cool (natural cooling), grind, and sieve to obtain the second powder (average particle size of 300 mesh). Wash: first wash with pure water to remove metal heteroatoms, then wash with deionized water and anhydrous ethanol until pH 7. Dry at 80℃ for 8 h to obtain the sodium-ion battery biomass hard carbon anode material based on heteroatom modification. The heating rate to 850℃ is 5℃ / min. The ratio of pre-carbonized product to modifier by mass is 1:7. The modifier is X, which is shown in Table 1.

[0049] Table 1

[0050]

[0051] Figure 1 The XRD patterns of the heteroatom-modified sodium-ion battery biomass hard carbon anode materials prepared in Examples 1-7 are shown below. Figure 1 As shown, the sodium-ion battery biomass hard carbon anode materials based on heteroatom modification prepared in Examples 1 to 7 all exhibited obvious broad (002) diffraction peaks and inconspicuous (101) diffraction peaks, indicating that the sodium-ion battery biomass hard carbon anode materials based on heteroatom modification prepared in Examples 1 to 7 have highly amorphous properties.

[0052] Figure 46 The image shows a scanning electron microscope (SEM) image of the heteroatom-modified sodium-ion battery biomass hard carbon anode material prepared in Example 1. The image shows that the morphological differences of the heteroatom-modified sodium-ion battery biomass hard carbon anode material prepared in Example 1 are very small, with an average particle size of 0.5–5.0 μm.

[0053] Comparative Example 1

[0054] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 1, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 750°C for 2 hours".

[0055] Comparative Example 2

[0056] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 1, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 950°C for 2 hours".

[0057] Comparative Example 3

[0058] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 2, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 750°C for 2 hours".

[0059] Comparative Example 4

[0060] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 2, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 950°C for 2 hours".

[0061] Comparative Example 5

[0062] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 3, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 750°C for 2 hours".

[0063] Comparative Example 6

[0064] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 3, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 950°C for 2 hours".

[0065] Comparative Example 7

[0066] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 4, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 750°C for 2 hours".

[0067] Comparative Example 8

[0068] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 4, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 950°C for 2 hours".

[0069] Comparative Example 9

[0070] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 5, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 750°C for 2 hours".

[0071] Comparative Example 10

[0072] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 5, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 950°C for 2 hours".

[0073] Comparative Example 11

[0074] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 6, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 750°C for 2 hours".

[0075] Comparative Example 12

[0076] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 6, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 950°C for 2 hours".

[0077] Comparative Example 13

[0078] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 7, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 750°C for 2 hours".

[0079] Comparative Example 14

[0080] A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification is basically the same as the method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification in Example 7, except that "the first powder is kept at 850°C for 2 hours" is replaced with "the first powder is kept at 950°C for 2 hours".

[0081] Examples 8-14 and Comparative Examples 15-28

[0082] A sodium-ion half-cell includes a positive electrode, a negative electrode, and a separator. The positive electrode is a sodium metal sheet with a diameter of 12 mm and a thickness of 0.5 mm. The separator is a glass fiber (Whitman, GF / A) disc with a diameter of 19 mm. A standard CR2032 coin cell is assembled in a glove box filled with high-purity argon gas. A mixture of sodium perchlorate and polycarbonate is used as the electrolyte, with a sodium perchlorate concentration of 1 mol / L. The negative electrode is prepared by mixing the negative electrode material, conductive carbon black, and polyvinylidene fluoride, grinding them until homogeneous, and then mixing them with N-methylpyrrolidone until homogeneous to obtain an electrode slurry. The electrode slurry is uniformly coated onto copper foil using a coating machine and vacuum dried in a vacuum drying oven at 80°C for 12 hours. Then, it is processed into a disc with a diameter of 12 mm using a die-cutting machine. The electrode slurry on the disc was loaded with 2 mg and compacted to serve as the negative electrode. The ratio of negative electrode material, conductive carbon black and polyvinylidene fluoride by mass was 8:1:1, and the ratio of N-methylpyrrolidone volume fraction to negative electrode material mass fraction was 1:30. Volume fractions are in mL and mass fractions are in mg. The negative electrode material was one of the heteroatom-modified sodium-ion battery biomass hard carbon negative electrode materials prepared in Examples 1-7 and Comparative Examples 1-14. The sodium-ion half-cells of Examples 8-14 were obtained sequentially from the heteroatom-modified sodium-ion battery biomass hard carbon negative electrode materials prepared in Examples 1-7, and the sodium-ion half-cells of Comparative Examples 15-28 were obtained sequentially from the heteroatom-modified sodium-ion battery biomass hard carbon negative electrode materials prepared in Comparative Examples 1-4.

[0083]

[0084]

[0085] Example 15

[0086] A full cell is assembled in the following order: positive electrode shell, positive electrode sheet, separator, electrolyte, negative electrode sheet, and negative electrode shell. The positive electrode material in the positive electrode sheet is a commercially available layered cathode material (LC) (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.). The positive electrode sheet is prepared by mixing the positive electrode material, conductive carbon black, and polyvinylidene fluoride, grinding them until homogeneous, and then mixing them with N-methylpyrrolidone until homogeneous to obtain an electrode slurry. The electrode slurry is then uniformly coated onto aluminum foil using a coating machine. The electrode was vacuum dried in a vacuum drying oven at 80°C for 12 hours, and then prepared into 10mm diameter discs using a die-casting machine (the electrode slurry loading on the 10mm diameter discs was 2mg). These discs were then compacted to serve as the positive electrode. The ratio of positive electrode material, conductive carbon black, and polyvinylidene fluoride by mass was 8:1:1, and the volume ratio of N-methylpyrrolidone to the mass ratio of positive electrode material was 1:30. Volume parts are expressed in mL, and mass parts are expressed in mg. The negative electrode was the negative electrode of the sodium-ion half-cell in Example 8. The electrolyte was the same as that used in the sodium-ion half-cell, and the separator was 19mm diameter glass fiber (Whitman, GF / A).

[0087] The sodium-ion half-cells prepared in Examples 8-14 and Comparative Examples 15-28 were left to stand for 10 hours, and then tested on a Newway battery testing system (CT-4008Tn-5 V 50mA) using 30mAg. -1 and 500mAg -1 The current density was used to conduct charge-discharge tests and cycle tests on the sodium-ion half-cells prepared in Examples 8-14 and Comparative Examples 15-28.

[0088] Figures 2-22 Sodium-ion half-cells prepared in Examples 8-14 and Comparative Examples 15-28, respectively, were used at a current density of 30 mA g. -1 The charge / discharge curves at that time. Figures 2-22 It can be seen that at a current density of 30 mA g -1 At that time, the sodium-ion half-cell prepared in Example 8 had an initial charge capacity of 285.92 mAh g. -1 The sodium-ion half-cell prepared in Example 9 has an initial charge capacity of 252.67 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Example 10 was 263.70 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Example 11 was 237.01 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Example 12 was 145.91 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Example 13 was 160.08 mAh g. -1The initial charge capacity of the sodium-ion half-cell prepared in Example 14 was 148.82 mAh g. -1 .

[0089] The sodium-ion half-cell prepared in Comparative Example 15 achieved an initial charge capacity of 156.23 mAh g. -1 The sodium-ion half-cell prepared in Comparative Example 16 achieved an initial charge capacity of 220.63 mAh g. -1 The sodium-ion half-cell prepared in Comparative Example 17 achieved an initial charge capacity of 160.55 mAh g. -1 The sodium-ion half-cell prepared in Comparative Example 18 achieved an initial charge capacity of 170.03 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 19 was 116.77 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 20 was 135.58 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 21 was 119.36 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 22 was 131.16 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 23 was 119.32 mAh g. -1 The sodium-ion half-cell prepared in Comparative Example 24 had an initial charge capacity of 134.76 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 25 was 106.12 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 26 was 151.25 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 27 was 71.18 mAh g. -1 The initial charge capacity of the sodium-ion half-cell prepared in Comparative Example 28 was 115.86 mAh g. -1 .

[0090] pass Figures 2-8 As can be seen, the charge and discharge curves both exhibit two regions: a flat plateau below 0.1V and a slope between 0.1V and 3V. This indicates that the curves are plateau-shaped and that the capacity below 0.1V accounts for a relatively large proportion.

[0091] Figures 23-29 The sodium-ion half-cells prepared in Examples 8-14 are shown in sequence at a current density of 500 mA g. -1 Cyclic performance and coulomb efficiency at that time. (From...) Figures 23-29 It can be seen that at a current density of 500 mA g -1At that time, the initial reversible capacity of the sodium-ion half-cell prepared in Example 8 was 151.35 mAh g. -1 The reversible capacity after 500 cycles is 132.35 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Example 9 was 122.29 mAh g. -1 The reversible capacity after 500 cycles is 81.4 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Example 10 was 115.31 mAh g. -1 The reversible capacity after 500 cycles is 101.12 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Example 11 was 127.01 mAh g. -1 The reversible capacity after 500 cycles is 106.4 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Example 12 was 147.72 mAh g. -1 The reversible capacity after 500 cycles is 107.38 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Example 13 was 111.53 mAh g. -1 The reversible capacity after 500 cycles is 77.96 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Example 14 was 127.56 mAh g. -1 The reversible capacity after 500 cycles is 86.76 mAh g. - 1.

[0092] Figures 30-43 The sodium-ion half-cells prepared in Comparative Examples 15–28 are shown in sequence at a current density of 500 mA g. -1 Cyclic performance and coulomb efficiency at that time. (From...) Figures 30-43 It can be seen that at a current density of 500 mA g -1 At that time, the initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 15 was 106.82 mAh g. -1 The reversible capacity after 500 cycles is 90.99 mAhg. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 16 was 113.35 mAh g. -1 The reversible capacity after 500 cycles is 100.15 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 17 was 108.71 mAh g. -1 The reversible capacity after 500 cycles is 80.28 mAhg. -1The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 18 was 101.96 mAh g. -1 The reversible capacity after 500 cycles is 75.58 mAhg. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 19 was 101.88 mAh g. -1 The reversible capacity after 500 cycles is 82.51 mAhg. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 20 was 80.18 mAh g. -1 The reversible capacity after 500 cycles is 79.04 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 21 was 106.85 mAh g. -1 The reversible capacity after 500 cycles is 38.05 mAhg. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 22 was 82.32 mAh g. -1 The reversible capacity after 500 cycles is 45.28 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 23 was 79.17 mAh g. -1 The reversible capacity after 500 cycles is 59.34 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 24 was 108.44 mAh g. -1 The reversible capacity after 500 cycles is 85.56 mAhg. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 25 was 86.12 mAh g. -1 The reversible capacity after 500 cycles is 75.87 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 26 was 94.89 mAh g. -1 The reversible capacity after 500 cycles is 68.45 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 27 was 52.53 mAh g. -1 The reversible capacity after 500 cycles is 32.35 mAh g. -1 The initial reversible capacity of the sodium-ion half-cell prepared in Comparative Example 28 was 91.55 mAh g. -1 The reversible capacity after 500 cycles is 65.64 mAh g. -1 .

[0093] based on Figures 23-43The sodium-ion half-cells prepared in Examples 8-14 and Comparative Examples 15-28 were obtained at a current density of 500 mA g. -1 The capacity retention rate and capacity variation range at that time are as follows:

[0094]

[0095]

[0096] Figure 44 The diagram shows the rate performance of the sodium-ion half-cell prepared in Example 8. Figure 44 It can be seen that the sodium-ion half-cell prepared in Example 8 performs well at 50, 100, 200, 500 and 1000 mA g. -1 The specific reversible capacities at different times were 222.565, 195.25, 171.06, 139.75, and 113.91 mAh g, respectively. -1 When the current density increases from 1000 mA g -1 Reverse to 500mA g -1 50mAg -1 When the capacity is almost completely recovered, it indicates that the sodium-ion half-cell prepared in Example 8 has good capacity reversibility. Figure 45 The rate performance diagram of the sodium-ion half-cell prepared in Comparative Example 15 is shown below. Figure 45 It can be seen that the sodium-ion half-cell prepared in Comparative Example 15 performs well at 50, 100, 200, 500, and 1000 mA g. -1 The specific reversible capacities at different times were 137.416, 116.081, 95.791, 72.975, and 54.165 mAh g, respectively. -1 The value is significantly lower than that of Example 8.

[0097] Figure 47 The inset is a transmission electron microscope image (SAED image) of the heteroatom-modified sodium-ion battery biomass hard carbon anode material prepared in Example 1. Figure 47 It can be seen that the heteroatom-modified sodium-ion battery biomass hard carbon anode material prepared in Example 1 has a disordered structure with many voids, making it a good sodium storage material. XRD and TEM tests revealed that the heteroatom-modified sodium-ion battery biomass hard carbon anode has a larger interlayer spacing, which is more conducive to the insertion and extraction of sodium ions (the interlayer spacing of the heteroatom-modified sodium-ion battery biomass hard carbon anode material prepared in Example 1 was calculated to be 0.3914 nm according to the Bragg equation 2dsinθ=nλ, where d is the interlayer spacing, θ is the angle between the incident X-ray and the corresponding crystal plane, λ is the wavelength of the X-ray, and n is the diffraction order).

[0098] The diffusion coefficient of sodium ions in the sodium-ion half-cell prepared in Example 8 was determined by constant-current intermittent titration. The constant-current intermittent titration test is a cyclic process of pulse-constant current-relaxation. The pulse refers to a brief current flow, and relaxation refers to a period without current flow. The specific steps are as follows: The sodium-ion half-cell prepared in Example 8 is charged with a constant current of 0.1C for 20 minutes, then left to rest for 20 minutes to reach equilibrium. This process is repeated until 3V (the upper limit voltage) is reached. Figure 48 As shown, the measured diffusion coefficient of sodium ions is 10. -10 cm 2 s -1 .

[0099] The conductivity of the sodium-ion half-cell prepared in Example 8 was determined by electrochemical impedance spectroscopy. Testing system: Chenhua electrochemical workstation; testing voltage: 1.8V; testing frequency: 0.01Hz-10000Hz. Test results are as follows: Figure 49 As shown, the charge transfer resistance is 450Ω.

[0100] The working principle of a full battery is as follows Figure 50 As illustrated in the illustration, during charging, sodium ions deintercalate from the positive electrode and migrate to the negative electrode through the solid electrolyte, which is an ion conductor, while electrons migrate through the external circuit; during discharging, sodium ions deintercalate from the negative electrode and migrate to the positive electrode through the solid electrolyte. At 75 mA g -1 The cycling performance of the full cell prepared in Example 15 was studied at a current density. Figure 50 This is the cycle performance diagram of the full cell, with a current density of 75 mA g. -1 At that time, the reversible capacity of the full battery was 118.95 mAh g. -1 After 100 cycles, the capacity remained at 85.9%.

[0101] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery biomass hard carbon anode material based on heteroatom modification, characterized in that, Includes the following steps: Step 1: Under an air atmosphere, the biomass powder is kept at 200~400 ℃ for 1~8h, then cooled to obtain the pre-carbonized product; Step 2: Mix the pre-carbonized product and the modifier, ball mill until uniform to obtain a first powder, keep the first powder at 800~900 ℃ for 1~8 h under a nitrogen or inert gas atmosphere, cool, grind, and sieve to obtain a second powder, wash the second powder until neutral, and dry to obtain a sodium-ion battery biomass hard carbon anode material based on heteroatom modification, wherein the modifier is a mixture of pore-forming agent and additive, and the ratio of pre-carbonized product to modifier by mass is 1:7, and the ratio of pore-forming agent to additive by mass is 40:1; The additive is (NH4)2SO4, and the pore-forming agent is NaCl; The method for obtaining the biomass powder is as follows: waste biomass is ultrasonically washed at 30~80 ℃ for 6~12 hours to remove surface dust and impurities, crushed into powder with a particle size of 200~400 mesh, and dried to obtain the biomass powder. The waste biomass is sunflower straw.

2. The preparation method according to claim 1, characterized in that, In step 2, the particle size of the second powder is 200-400 mesh.

3. The preparation method according to claim 1, characterized in that, In step 1, the heating rate to 200~400 ℃ is 1~10 ℃ / min.

4. The sodium-ion battery biomass hard carbon anode material based on heteroatom modification obtained by any one of the preparation methods of claims 1 to 3.

5. A sodium-ion full battery, wherein the negative electrode material comprises the sodium-ion battery biomass hard carbon negative electrode material based on heteroatom modification as described in claim 4.

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