Sisal hard carbon anode material for sodium ion battery and preparation method and application thereof

Abstract

The application provides a preparation method of a hard carbon negative electrode material of a sisal for a sodium ion battery, and comprises the following steps: cutting the dried sisal into small pieces; putting a proper amount of the sisal into an acid-containing reaction kettle to perform a hydrothermal reaction, then washing to neutral, and drying to obtain a first black plant fiber; putting the black plant fiber of step S2 into an alkali-containing reaction kettle to perform a hydrothermal reaction, then washing to neutral, and drying to obtain a second black plant fiber; performing high-temperature carbonization of the second black plant fiber of step S3 in an inert gas atmosphere, then cooling to room temperature to obtain the hard carbon negative electrode material of the sisal; wherein the carbonization temperature is 1100-1500 DEG C, the holding time is 0.5-3h, and the heating / cooling rate is 1-10 DEG C / min. The preparation method of the hard carbon negative electrode material of the sisal for the sodium ion battery has high platform capacity and excellent long cycle stability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, specifically to a sisal hard carbon anode material for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] Currently, the increasing global energy demand and global warming are driving the development of clean and renewable energy storage devices. Lithium-ion batteries have dominated the commercial market for decades, but due to rising costs and uneven distribution of lithium resources, they are unlikely to meet the growing demand for grid-scale energy storage. Therefore, there is an urgent need to explore low-cost, high-efficiency alternatives for practical applications. In recent years, sodium-ion batteries have attracted widespread attention due to the abundance of sodium resources in the Earth's crust. Simultaneously, the "rocking chair" working mechanism of lithium-ion batteries is a perfect fit for sodium-ion battery energy storage systems, making sodium-ion batteries a potential candidate for next-generation energy storage devices.

[0003] One of the biggest obstacles hindering the development of sodium-ion batteries is the lack of suitable anode materials. Currently available anode materials include intercalated, alloyed, and conversion-type materials. While metals / alloys and metal compounds exhibit high capacity in both lithium-ion and sodium-ion batteries, they suffer from significant volume expansion and poor cycle performance during charge-discharge cycles. Carbon-based materials, on the other hand, are abundant, have high conductivity, are non-toxic, and possess stable physicochemical properties, making them highly promising anode materials. However, due to the small interlayer spacing of graphite, and the limited availability of Na... + Its large radius prevents it from being used directly as the negative electrode in sodium-ion batteries.

[0004] Hard carbon (HC) materials are generally considered a collective term for carbon materials that are difficult to graphitize. Their microstructure consists of short-range ordered micro-regions formed by the stacking of curved, graphite-like sheets, with the random, disordered stacking of these micro-regions leaving numerous nanopores. Due to their often large interlayer spacing, numerous nanopores, and many defect sites, they can store a large number of sodium ions, resulting in high specific capacity. Therefore, hard carbon is one of the most promising anode materials for sodium-ion batteries. Sisal hard carbon is widely available and inexpensive; using it as a sodium-ion anode can significantly reduce battery costs and advance the industrialization of sodium-ion batteries.

[0005] Chinese patent (CN107732177A) discloses the preparation of a sulfur / sisal carbon lithium-ion battery composite anode material. It uses sisal as a biomass raw material to prepare hard carbon, and then combines it with sulfur to prepare the lithium-ion battery anode material. This technical solution discloses the application of sisal hard carbon material in lithium batteries. The composite material incorporates sulfur (S), whose atom radius is much larger than that of carbon atoms. Therefore, the introduction of S can expand the interlayer spacing. When the interlayer spacing is greater than 0.4 nm, the carbon material mainly stores lithium ions through surface adsorption. Furthermore, the introduction of S can increase surface defects and activation sites, improving the material's adsorption capacity for lithium ions, resulting in a high sodium storage capacity in the slope region. In full-cell matching, a high capacity in the plateau region is more beneficial for improving the battery's voltage window and energy density. However, the introduction of S also causes significant lattice distortion, leading to irreversible collapse of the material structure during cycling, thus affecting cycle stability and capacity retention.

[0006] Therefore, it is necessary to provide a sisal hard carbon material with excellent sodium storage performance to solve the above-mentioned technical problems. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing sisal hard carbon anode material for sodium-ion batteries. The prepared sisal hard carbon material has high plateau capacity and excellent long-cycle stability.

[0008] To solve the above problems, the technical solution of the present invention is as follows:

[0009] A method for preparing a sisal hard carbon anode material for sodium-ion batteries includes the following steps:

[0010] Step S1: Cut the washed and dried sisal into small pieces;

[0011] Step S2: Place an appropriate amount of sisal into an acidic reaction vessel for hydrothermal reaction, then wash until neutral, and dry to obtain the first black plant fiber.

[0012] Step S3: The black plant fiber from step S2 is placed in an alkaline reaction vessel for hydrothermal reaction, then washed until neutral, and dried to obtain the second black plant fiber.

[0013] Step S4: The second black plant fiber from step S3 is carbonized at high temperature in an inert gas atmosphere and then cooled to room temperature to obtain sisal hard carbon anode material; wherein the carbonization temperature is 1100-1500℃, the holding time is 0.5-3h, and the heating / cooling rate is 1-10℃ / min.

[0014] Furthermore, in step S2, the acid used is one or more of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid; the hydrothermal reaction temperature is 100-200℃; the drying temperature is 60-80℃; and the drying time is 12-24h.

[0015] Furthermore, in the hydrothermal reaction of step S2, the concentration of the acid solution is 0.5-2 mol / L.

[0016] Furthermore, in step S3, the alkali used is one or more of potassium hydroxide, sodium hydroxide, and hydrazine hydrate, the hydrothermal reaction temperature is 100-200℃, the drying temperature is 60-80℃, and the drying time is 12-24h.

[0017] Furthermore, in the hydrothermal reaction of step S3, the concentration of the alkaline solution is 0.5-2 mol / L.

[0018] Furthermore, in step S4, the carbonization temperature is 1300℃.

[0019] Furthermore, in step S4, the inert gas is argon or nitrogen.

[0020] The present invention also provides a sisal hard carbon anode material for sodium-ion batteries, which is prepared by the above preparation method.

[0021] This invention also provides an application of sisal hard carbon anode material in sodium-ion batteries.

[0022] A sodium-ion secondary battery negative electrode sheet includes a current collector and a negative electrode material layer coated on the current collector. The negative electrode material layer is made of the above-mentioned sisal hard carbon negative electrode material, conductive additives, and binders.

[0023] Furthermore, the mass ratio of the sisal hard carbon anode material, conductive additives, and binders is 80:10:10.

[0024] Compared with the prior art, the sisal hard carbon anode material for sodium-ion batteries and its preparation method provided by the present invention have the following advantages:

[0025] The present invention provides a method for preparing sisal hard carbon anode material for sodium-ion batteries, which combines a hydrothermal method with a high-temperature carbonization process. At a high-temperature carbonization temperature of 1100-1500℃, the sisal hard carbon material exhibits a moderate degree of graphitization, possessing relatively suitable carbon interlayer spacing and pores for storing Na ions. The carbon interlayer spacing is approximately 0.36-0.4 nm. Within this spacing, sodium storage in hard carbon primarily occurs through an intercalation mechanism, with sodium ions mainly intercalating and deintercalating between carbon layers, resulting in a high sodium storage capacity at a low voltage plateau. Therefore, using the sisal hard carbon anode material of the present invention as a sodium-ion battery anode offers advantages such as high capacity, low voltage plateau, and good stability. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a SEM image of the sisal hard carbon material in Embodiment 2 of the present invention;

[0028] Figure 2 These are the XRD patterns of the sisal hard carbon materials in Examples 1-3 of this invention;

[0029] Figure 3 These are the laser Raman spectra of the sisal hard carbon materials in Examples 1-3 of this invention;

[0030] Figure 4 These are the charge-discharge curves of the batteries assembled from sisal hard carbon materials in Examples 1-3 and Comparative Example 1 of this invention for the first two cycles, with a current density of 0.1C (1C = 300 mA g). -1 );

[0031] Figure 5 This is a long-cycle diagram of the battery assembled with sisal hard carbon material in Examples 1-3 of the present invention, with a current density of 1C;

[0032] Figure 6 This is a schematic diagram of the microstructure of the sisal hard carbon material in Comparative Example 2 and Example 2 of the present invention;

[0033] Figure 7 These are the XRD patterns of the sisal hard carbon materials in Comparative Example 2 and Example 2 of this invention, and the fitting results of their 002 peaks.

[0034] Figure 8 These are the discharge curves of the batteries assembled from sisal hard carbon materials in Comparative Example 2 and Example 2 of this invention at a current density of 0.1C.

[0035] Figure 9 This refers to the plateau capacity of the batteries assembled from sisal hard carbon materials in Comparative Examples 1-2 and Examples 1-3 of this invention at a current density of 0.1C. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below.

[0037] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] The present invention provides a method for preparing sisal hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0039] Step S1: Cut the washed and dried sisal into small pieces;

[0040] Specifically, wash the sisal several times with dish soap and dry it in an 80℃ forced-air drying oven for 48 hours; then cut the dried sisal into appropriately sized small pieces, such as 2-5mm segments.

[0041] Step S2: Place an appropriate amount of sisal into an acidic reaction vessel for hydrothermal reaction, then wash until neutral, and dry to obtain the first black plant fiber.

[0042] Specifically, the acid used is one or more of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid; the hydrothermal reaction temperature is 100-200℃; the drying temperature is 60-80℃; and the drying time is 12-24 hours. Specifically, the hydrothermal reaction temperature under acidic conditions can be 100℃, 120℃, 140℃, 150℃, 180℃, or 200℃, or other temperatures within this range; the drying temperature can be 60℃, 65℃, 70℃, 75℃, or 80℃, or other temperatures within this range; the drying time can be 12 hours, 18 hours, or 24 hours, or other times within this range; and the acid solution concentration is 0.5-2 mol / L, such as 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L, or other values ​​within this range.

[0043] Step S3: The black plant fiber from step S2 is placed in an alkaline reaction vessel for hydrothermal reaction, then washed until neutral, and dried to obtain the second black plant fiber.

[0044] Specifically, the alkali used is one or more of potassium hydroxide, sodium hydroxide, and hydrazine hydrate; the hydrothermal reaction temperature is 100-200℃; the drying temperature is 60-80℃; and the drying time is 12-24 hours. Specifically, the hydrothermal reaction temperature under alkaline conditions can be 100℃, 120℃, 140℃, 150℃, 180℃, or 200℃, or other temperatures within this range; the drying temperature can be 60℃, 65℃, 70℃, 75℃, or 80℃, or other temperatures within this range; the drying time can be 12 hours, 18 hours, or 24 hours, or other times within this range; and the concentration of the alkali solution is 0.5-2 mol / L, such as 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L, or other values ​​within this range.

[0045] Step S4: The second black plant fiber from step S3 is carbonized at high temperature in an inert gas atmosphere and then cooled to room temperature to obtain sisal hard carbon anode material; wherein the carbonization temperature is 1100-1500℃, the holding time is 0.5-3h, and the heating / cooling rate is 1-10℃ / min.

[0046] Specifically, the carbonization temperature can be 1100℃, 1200℃, 1300℃, 1400℃, or 1500℃, or other temperatures within this range; the holding time can be 0.5h, 1h, 1.5h, 2h, 2.5h, or 3h, or other times within this range; the heating / cooling rate can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, or other values ​​within this range; the inert gas can be nitrogen or argon.

[0047] The sisal hard carbon material prepared by the preparation method of the present invention can be used as the negative electrode sheet of sodium-ion secondary batteries.

[0048] A sodium-ion secondary battery negative electrode sheet includes a current collector and a negative electrode material layer coated on the current collector. The materials used in the negative electrode material layer include the aforementioned sisal hard carbon negative electrode material, conductive additives, and binders.

[0049] The mass ratio of the sisal hard carbon anode material, conductive additives, and binders is 80:10:10.

[0050] The conductive additive is one or more of acetylene black, Super P, and Ketjen black;

[0051] The binders are polyvinylidene fluoride and sodium carboxymethyl cellulose.

[0052] The assembly process for sodium-ion batteries can refer to existing technologies.

[0053] The following specific embodiments illustrate in detail the sisal hard carbon anode material for sodium-ion batteries and its preparation method provided by the present invention.

[0054] Example 1

[0055] A method for preparing a sisal hard carbon anode material for sodium-ion batteries includes the following steps:

[0056] Step S1: Wash the sisal several times with dish soap and dry it in an 80℃ forced-air drying oven for 48 hours; cut the dried sisal into small pieces of appropriate size.

[0057] Step S2: Place an appropriate amount of sisal into a reaction vessel containing 1 mol / L hydrochloric acid for hydrothermal reaction at a temperature of 160°C for 12 hours. Then, filter and wash the sisal until pH=7, and dry to obtain the first black plant fiber.

[0058] Step S3: The first black plant fiber from step S2 is placed in a reactor containing 1 mol / L hydrazine hydrate for another hydrothermal reaction at a temperature of 120°C for 12 hours. Then, it is filtered and washed until pH=7, and finally dried to obtain the second black plant fiber.

[0059] In step S4, the second black plant fiber from step S3 is placed into a tube furnace under an Ar atmosphere for high-temperature carbonization. The carbonization temperature is 1100℃, the heating rate is 5° / min, and the holding time is 2h, to obtain sisal hard carbon anode material, denoted as HC-1100.

[0060] Example 2

[0061] A method for preparing a sisal hard carbon anode material for sodium-ion batteries includes the following steps:

[0062] Step S1: Wash the sisal several times with dish soap and dry it in an 80℃ forced-air drying oven for 48 hours; cut the dried sisal into small pieces of appropriate size.

[0063] Step S2: Place an appropriate amount of sisal into a reaction vessel containing 1 mol / L hydrochloric acid for hydrothermal reaction at a temperature of 160°C for 12 hours. Then, filter and wash the sisal until pH=7, and dry to obtain the first black plant fiber.

[0064] Step S3: The first black plant fiber from step S2 is placed in a reactor containing 1 mol / L hydrazine hydrate for another hydrothermal reaction at a temperature of 120°C for 12 hours. Then, it is filtered and washed until pH=7, and finally dried to obtain the second black plant fiber.

[0065] In step S4, the second black plant fiber from step S3 is placed into a tube furnace under an Ar atmosphere for high-temperature carbonization. The carbonization temperature is 1300℃, the heating rate is 5° / min, and the holding time is 2h, to obtain sisal hard carbon anode material, denoted as HC-1300.

[0066] Example 3

[0067] A method for preparing a sisal hard carbon anode material for sodium-ion batteries includes the following steps:

[0068] Step S1: Wash the sisal several times with dish soap and dry it in an 80℃ forced-air drying oven for 48 hours; cut the dried sisal into small pieces of appropriate size.

[0069] Step S2: Place an appropriate amount of sisal into a reaction vessel containing 1 mol / L hydrochloric acid for hydrothermal reaction at a temperature of 160°C for 12 hours. Then, filter and wash the sisal until pH=7, and dry to obtain the first black plant fiber.

[0070] Step S3: The first black plant fiber from step S2 is placed in a reactor containing 1 mol / L hydrazine hydrate for another hydrothermal reaction at a temperature of 120°C for 12 hours. Then, it is filtered and washed until pH=7, and finally dried to obtain the second black plant fiber.

[0071] In step S4, the second black plant fiber from step S3 is placed into a tube furnace under an Ar atmosphere for high-temperature carbonization. The carbonization temperature is 1500℃, the heating rate is 5° / min, and the holding time is 2h, to obtain sisal hard carbon anode material, denoted as HC-1500.

[0072] Comparative Example 1

[0073] A method for preparing a sisal hard carbon anode material for sodium-ion batteries includes the following steps:

[0074] Step S1: Wash the sisal several times with dish soap and dry it in an 80℃ forced-air drying oven for 48 hours; cut the dried sisal into small pieces of appropriate size.

[0075] Step S2: Place an appropriate amount of sisal into a reaction vessel containing 1 mol / L hydrochloric acid for hydrothermal reaction at a temperature of 160°C for 12 hours. Then, filter and wash the sisal until pH=7, and dry to obtain the first black plant fiber.

[0076] Step S3: The first black plant fiber from step S2 is placed in a reactor containing 1 mol / L hydrazine hydrate for another hydrothermal reaction at a temperature of 120°C for 12 hours. Then, it is filtered and washed until pH=7, and finally dried to obtain the second black plant fiber.

[0077] In step S4, the second black plant fiber from step S3 is placed into a tube furnace under an Ar atmosphere for high-temperature carbonization. The carbonization temperature is 1000℃, the heating rate is 5° / min, and the holding time is 2h, to obtain sisal hard carbon anode material, denoted as HC-1000.

[0078] Comparison document 2

[0079] A method for preparing a sisal hard carbon anode material for sodium-ion batteries includes the following steps:

[0080] Step S1: Wash the sisal several times with dish soap and dry it in an 80℃ forced-air drying oven for 48 hours; cut the dried sisal into small pieces of appropriate size.

[0081] Step S2: Place an appropriate amount of sisal into a reaction vessel containing 1 mol / L hydrochloric acid for hydrothermal reaction at a temperature of 160°C for 12 hours. Then, filter and wash the sisal until pH=7, and dry to obtain the first black plant fiber.

[0082] Step S3: The first black plant fiber from step S2 is placed in a reactor containing 1 mol / L hydrazine hydrate for another hydrothermal reaction at a temperature of 120°C for 12 hours. Then, it is filtered and washed until pH=7, and finally dried to obtain the second black plant fiber.

[0083] Step S4: The second black plant fiber from step S3 is placed into a tube furnace under an Ar atmosphere for high-temperature carbonization. The carbonization temperature is 800°C, the heating rate is 5° / min, and the holding time is 2h to obtain the sisal anode material, denoted as AC-800 (AC stands for Amorphous carbon).

[0084] Please refer to the following: Figures 1 to 3 ,in Figure 1 This is a SEM image of the sisal hard carbon material in Embodiment 2 of the present invention; Figure 2 These are the XRD patterns of the sisal hard carbon materials in Examples 1-3 of this invention; Figure 3 These are the laser Raman spectra of the sisal hard carbon materials in Examples 1-3 of this invention.

[0085] Sodium ion electron assembly and electrochemical performance testing:

[0086] (1) Sisal hard carbon material powder, Super P, and polyvinylidene fluoride are mixed in a mass ratio of 80:10:10. An appropriate amount of N-methylpyrrolidone is added. The mixture is ground in a dry environment at room temperature to obtain a black slurry. The slurry is then uniformly coated onto the current collector copper foil. After that, it is placed in a vacuum drying oven and dried at 80°C for 12 hours. The electrode is then cut into a circular electrode sheet with a radius of 6 mm. The electrode sheet is weighed using a five-position balance and the corresponding mass of active material is calculated. The electrode sheet is then transferred to a glove box for later use.

[0087] (2) Using a sodium sheet as the counter electrode, and under conditions where both water and oxygen content are less than 0.01 ppm, assemble the positive electrode shell, negative electrode shell, glass fiber separator, sodium sheet, electrolyte, gasket, spring sheet, and negative electrode sheet together according to the correct assembly steps. The electrolyte used is 1M NaClO4 with EC / DEC (v:v = 1:1):FEC = 95%:5%. Finally, seal the assembled battery with a button cell sealing machine, then remove it from the glove box and let it stand for 8 hours.

[0088] (3) The assembled sodium-ion battery was subjected to electrochemical testing using a LANDCT2001A instrument.

[0089] Please refer to the following: Figure 4 and Figure 5 ,in Figure 4 These are the charge-discharge curves of the batteries assembled from sisal hard carbon materials in Examples 1-3 and Comparative Example 1 of this invention for the first two cycles, with a current density of 0.1C (1C = 300 mA g). -1 ); Figure 5 This is a long-cycle diagram of the battery assembled from sisal hard carbon material in Examples 1-3 of this invention, with a current density of 1C. Figure 4 It can be seen that the specific capacity of the battery's first discharge and charge cycles corresponding to the HC-1300 sisal hard carbon material is 559.1 mA hg. -1 and 298.8mA hg -1 Its battery performance is superior to other embodiments. Figure 5 It can be seen that the battery corresponding to the HC-1300 sisal hard carbon material still has 242.7 mA hg after 500 cycles. -1 The high reversible specific capacity indicates that the sisal hard carbon material of the present invention has excellent long-cycle stability when applied to sodium-ion batteries.

[0090] The following further explains the effect of high-temperature carbonization temperature on the structure of sisal hard carbon materials, including interlayer spacing and sodium storage mechanism.

[0091] Please see Figure 6 This is a schematic diagram of the microstructure of the sisal hard carbon material in Comparative Example 2 and Example 2 of the present invention, wherein... Figure 6a represents a schematic diagram of the material microstructure in Comparative Example 2. Figure 6 b represents a schematic diagram of the material microstructure in Example 2. (From...) Figure 6 It can be seen that when the carbonization temperature is 800℃, the degree of structural ordering of carbon materials is low. As the carbonization temperature increases, the degree of graphitization of carbon materials increases, while the interlayer spacing decreases.

[0092] Please see Figure 7 Figure 1 shows the XRD patterns of the sisal hard carbon materials in Comparative Example 2 and Example 2 of this invention, along with the fitting results of their 002 peaks. Figure 7 'a' represents the XRD patterns of AC-800 and HC-1300. Figure 7 b and 7c represent the fitting results of the 002 peak for AC-800 and HC-1300. Figure 7 As can be seen, the 002 peak shifts to the right and the interlayer spacing decreases as the temperature increases. To further analyze the XRD results, the 002 peaks of the samples from Examples 1-3 and Comparative Examples 1-2 were subjected to peak fitting, and the specific structural parameters are shown in Table 1.

[0093]

[0094] Table 1: XRD analysis results of different samples

[0095] As shown in Table 1, the portion of carbon interlayer spacing greater than 0.4 nm in AC-800 accounts for 60.45%, while the portion of carbon interlayer spacing greater than 0.4 nm in HC-1300 accounts for only 38.27%. This indicates that carbonization temperature has a significant impact on the structure of hard carbon materials and will further affect their sodium storage performance.

[0096] Please see Figure 8 The figures show the discharge curves of the batteries assembled from sisal hard carbon materials in Comparative Example 2 and Example 2 of this invention at a current density of 0.1C. When the interlayer spacing is greater than 0.4 nm, the carbon material mainly stores sodium ions through surface adsorption, corresponding to the high sodium storage capacity in the slope region of the charge-discharge curve, such as... Figure 8 a. When the interlayer spacing is between 0.36 and 0.4 nm, sodium ions can intercalate and deintercalate between carbon layers, corresponding to a high sodium storage capacity in the low-voltage (<0.1 V) plateau region, such as... Figure 8 b.

[0097] Please see Figure 9 This represents the plateau capacity of the batteries assembled from sisal hard carbon materials in Comparative Examples 1-2 and Examples 1-3 of this invention at a current density of 0.1C. The interlayer spacing has a significant impact on the plateau capacity; in AC-800, the portion with an interlayer spacing between 0.36-0.4 nm occupies 39.55%, resulting in a plateau capacity of only 28.2 mA hg. -1The portion of HC-1300 with a carbon interlayer spacing between 0.36 and 0.4 nm accounts for 61.73%, and the platform capacity is as high as 169 mA hg. -1 .

[0098] In summary, this invention optimizes the high-temperature carbonization temperature of the material and adjusts the interlayer spacing of the hard carbon material, making it mainly located in the range of 0.36-0.4 nm. At this distance, the hard carbon material primarily stores sodium through an interlayer intercalation mechanism, thus exhibiting a high capacity with a low voltage platform. When matched with full cells, the high-capacity battery with a low voltage platform exhibits superior electrochemical performance, improving the battery's voltage window and energy density.

[0099] The sodium-ion secondary battery of the present invention can be applied to large-scale energy storage devices for solar power generation, wind power generation, tidal power generation, smart grid peak shaving, or distributed power stations.

[0100] The present invention provides a method for preparing sisal hard carbon anode material for sodium-ion batteries, which combines a hydrothermal method with a high-temperature carbonization process. At a high-temperature carbonization temperature of 1100-1500℃, the sisal hard carbon material exhibits a moderate degree of graphitization, possessing relatively suitable carbon interlayer spacing and pores for storing Na ions. The carbon interlayer spacing is approximately 0.36-0.4 nm. Within this spacing, sodium storage in hard carbon primarily occurs through an intercalation mechanism, with sodium ions mainly intercalating and deintercalating between carbon layers, resulting in a high sodium storage capacity at a low voltage plateau. Therefore, using the sisal hard carbon anode material of the present invention as a sodium-ion battery anode offers advantages such as high capacity, low voltage plateau, and good stability.

[0101] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations made to these embodiments without departing from the principles and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for preparing a sisal hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: Step S1: Cut the washed and dried sisal into small pieces; Step S2: Place an appropriate amount of sisal into an acidic reaction vessel for hydrothermal reaction, then wash until neutral, and dry to obtain the first black plant fiber. Step S3: The black plant fiber from step S2 is placed in an alkaline reaction vessel for hydrothermal reaction, then washed until neutral, and dried to obtain the second black plant fiber. Step S4: The second black plant fiber from step S3 is carbonized at high temperature in an inert gas atmosphere and then cooled to room temperature to obtain sisal hard carbon anode material; wherein the carbonization temperature is 1100-1300℃, the holding time is 0.5-3h, and the heating / cooling rate is 1-10℃ / min. In step S2, the acid used is one or more of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid. The hydrothermal reaction temperature is 100-200℃, the drying temperature is 60-80℃, and the drying time is 12-24h. In the hydrothermal reaction of step S2, the concentration of the acid solution is 0.5-2 mol / L; In step S3, the alkali used is one or more of potassium hydroxide and sodium hydroxide, the hydrothermal reaction temperature is 100-200℃, the drying temperature is 60-80℃, and the drying time is 12-24h. In the hydrothermal reaction of step S3, the concentration of the alkaline solution is 0.5-2 mol / L.

2. The method for preparing sisal hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that, In step S4, the inert gas is argon or nitrogen.

3. A sisal hard carbon anode material for sodium-ion batteries, characterized in that, It is prepared by the preparation method according to any one of claims 1-2.

4. The application of the sisal hard carbon anode material as described in claim 3 in a sodium-ion battery.

5. A negative electrode sheet for a sodium-ion secondary battery, characterized in that, It includes a current collector and a negative electrode material layer coated on the current collector, wherein the negative electrode material layer is made of materials including the sisal hard carbon negative electrode material as described in claim 3, conductive additives and binders.

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