A method for controllable preparation of sodium polysulfide heterostructures anchored to hard carbon through grafting synergy, its products and applications

Abstract

This invention discloses a method for controllably preparing sodium polysulfide heterostructures anchored to hard carbon through grafting synergy. The method includes the following steps: S1, dissolving sucrose and performing a hydrothermal reaction to obtain hydrothermal carbon microspheres; S2, mixing the hydrothermal carbon microspheres and sodium thiosulfate (Na2S2O3) and ball milling them at high energy followed by high-temperature treatment to obtain covalently coupled Na2S... x / HC heterostructure. This invention also discloses a Na2S obtained by the above preparation method. x / HC heterostructure and its application in sodium-ion battery anode. The Na2S provided by this invention... x / HC heterostructure, as the negative electrode of sodium-ion batteries, features high sodium storage capacity, high initial efficiency, and ultra-high rate sodium storage.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery energy storage, specifically relating to a method for controllably preparing sodium polysulfide heterostructures anchored to hard carbon through grafting synergy, as well as its products and applications. Background Technology

[0002] Lithium-ion batteries have achieved significant success in portable electronics and automobiles. However, concerns about the scarcity and uneven distribution of raw lithium minerals have driven the exploration of alternative technologies for lithium-ion batteries. Sodium-ion batteries (SIBs), due to their abundant sources and favorable electrochemical properties, are becoming a sustainable technology for next-generation grid-scale energy storage systems. Developing high-performance anode materials is a key technology for realizing high-performance sodium-ion batteries. However, graphite anodes, widely used in lithium-ion batteries, cannot effectively store sodium ions due to the thermodynamic instability of intercalation compounds. To date, a large number of advanced anode materials have been studied, among which hard carbon (HC) is considered a practical candidate for sodium-ion storage due to its abundant sodium storage sites, stable electrode structure, and low cost. However, hard carbon derived from various precursors (such as biomass, sugars, resins, etc.) typically exhibits insufficient specific capacity (~300 mAh g⁻¹). -1 Poor initial coulombic efficiency (ICE, ~50–75%) and unsatisfactory rate performance (<5Ag). -1 This inevitably hinders its further application.

[0003] It is a generally accepted fact that sodium ion transport is determined by the presence and characteristics of active sites and ion channels within nanoscale spaces. However, the random orientation of graphene layers in hard carbon makes elucidating specific sodium storage mechanisms challenging. Typically, the specific capacity of energy storage includes contributions from diffusion and surface-controlled behavior. The former is based on the insertion / extraction of sodium ions in the bulk phase, while the latter includes surface adsorption and pseudocapacitive processes, corresponding to the plateau region (0.01–0.1 V) and ramp region (>0.1 V) in typical charge-discharge characteristics, respectively. Various methods have been proposed to achieve surface-dominated sodium ion storage behavior with rapid charge transfer, including heteroatom doping, nanostructure construction, and the introduction of porous or defective structures. However, these methods often lead to insufficient first-effect, and some even impair it in an attempt to improve rate performance. For example, the high specific surface area resulting from abundant porous structures and defects often leads to excessive solid electrolyte interphase (SEI) formation and side reactions, which inevitably consume large amounts of sodium ions, resulting in ultra-low ICE (electrolyte efficiency). In contrast, pre-sodium anodes can achieve approximately 100% high ICE, where the additional sodium ions compensate for the irreversible capacity loss caused by the trapping of sodium ions from numerous structural defects by the five- or seven-membered carbon rings. However, its improvement in rate performance is negligible, and its complex operation makes it unsuitable for widespread use. Therefore, balancing high ICE and excellent rate performance is challenging for hard carbon anodes in sodium-ion storage devices.

[0004] For example, Chinese Patent Publication No. 116632211A discloses sodium-ion modified hard carbon materials, sodium-ion batteries, and their preparation methods. By using a sodium-ion solid electrolyte to coat the hard carbon material as an artificial SEI film, improvements in the rate performance, initial coulombic efficiency, and long-cycle stability of the hard carbon battery are achieved. However, the relatively complex preparation method still offers limited performance improvements, with a maximum current density of only 0.2 Ag. -1 Furthermore, the initial coulombic efficiency is only 75%. And, as disclosed in Chinese Patent Publication No. CN 115417398 A, a high-efficiency hard carbon anode for sodium-ion batteries achieves efficiency in 0.05Ag... -1 It boasts an ultra-high first-efficiency of 94.3% at current density, but its reversible sodium storage capacity needs further improvement.

[0005] Optimizing electrolyte composition and the electrode / electrolyte interface is another effective strategy for addressing the aforementioned challenges. Recently, ether-based electrolytes have attracted significant attention due to their excellent resistance to reduction and their ability to produce a thinner SEI film on the anode compared to ester-based electrolytes. Therefore, considering that solid-phase diffusion of ions within the electrode material is a decisive step in charge transfer kinetics, adjusting the inherent properties of hard carbon materials while using ether-based electrolytes may be an effective solution to achieve high capacity, high ICE (electrical conductivity), and rapid sodium ion storage rates. Summary of the Invention

[0006] The purpose of this invention is to provide a method for controllably preparing sodium polysulfide heterostructures anchored to hard carbon through grafting synergy. When the prepared sodium polysulfide heterostructures anchored to hard carbon are applied to the anode of sodium-ion batteries, they can achieve high initial efficiency, high capacity, and high-rate sodium storage.

[0007] This invention provides the following technical solution:

[0008] A method for controllably preparing sodium polysulfide heterostructures anchored to hard carbon through grafting synergy, the preparation method comprising the following steps:

[0009] S1. After dissolving sucrose, hydrothermal reaction is carried out to obtain hydrothermal carbon microspheres;

[0010] S2. Hydrothermal carbon microspheres and sodium thiosulfate (Na2S2O3) are mixed, ball-milled at high energy, and then subjected to high-temperature treatment to obtain covalently coupled Na2S... x / HC (sodium polysulfide / hard carbon) heterostructure.

[0011] The technical concept of the preparation method provided by this invention is as follows: sodium thiosulfate and hydrothermal carbon spheres undergo a reduction reaction at high temperature, resulting in sodium polysulfide and hard carbon composites. Simultaneously, sulfur dioxide and carbon dioxide are generated, which disrupt the carbon matrix structure. Then, based on the synergistic grafting effect of sodium polysulfide, CSSC covalent bonds are formed on the subsurface of hard carbon, creating Na2S. x / HC heterostructure.

[0012] In step S1, the temperature of the hydrothermal reaction is 170–190°C.

[0013] In step S2, the feeding ratio of hydrothermal carbon ball powder to sodium thiosulfate powder is 1:1-3.

[0014] In step S2, the high-temperature treatment method is as follows: heating to 800-900°C in an argon atmosphere (such as a tube furnace filled with argon) at a heating rate of 3-5°C per minute, and maintaining it for 3-4 hours.

[0015] The present invention also provides a sodium polysulfide heterostructure anchored to hard carbon / Na2S obtained according to the above method. x / HC heterostructure. In this structure, sodium polysulfide is anchored on the subsurface of the hard carbon material, increasing the subsurface interlayer spacing of the hard carbon, repairing carbon ring defects, and is uniformly distributed.

[0016] The hard carbon subsurface composite sodium polysulfide (Na2S) prepared by this invention x / HC) heterostructures with catalytically active disulfide bonds can increase the interlayer spacing of hard carbon. Preferably, the Na2S xThe carbon interlayer spacing of hard carbon in the / HC heterostructure is 0.36-0.38 nm.

[0017] The present invention also provides an application of the above-mentioned sodium polysulfide heterostructure anchoring hard carbon in the negative electrode of a sodium-ion battery.

[0018] When the sodium polysulfide heterostructure anchored hard carbon provided by this invention is applied to the negative electrode of a sodium-ion battery, it can catalyze the formation of a thinner solid electrolyte membrane, promoting the diffusion kinetics of sodium ions. Preferably, the thickness of the SEI film catalyzed by the sodium polysulfide heterostructure anchored hard carbon is 7-10 nm.

[0019] Compared with the prior art, the Na2S formed on the hard carbon subsurface by covalent bonding provided by the present invention x The advantages of the / HC heterostructure are as follows: The hard carbon subsurface composite sodium polysulfide heterostructure utilizes CSSC covalent bonds to increase the carbon interlayer spacing, promoting ion phase diffusion; the sodium-sulfur alloying reaction increases the number of active sites for sodium storage, thereby improving the sodium storage capacity; simultaneously, the disulfide bonds within the structure catalyze the formation of a thinner solid electrolyte film, promoting charge transfer; and the pre-embedded sodium ions repair carbon ring defects, reducing irreversible adsorption of sodium ions in the electrolyte, thus achieving high capacity and high-rate sodium storage in the electrode. These advantages work together to enable this composite material to possess high sodium storage capacity, high initial efficiency, and ultra-high rate sodium storage characteristics when used as the negative electrode of a sodium-ion battery. Attached Figure Description

[0020] Figure 1 In the diagram, 'a' represents the SEM image of NASHC-2; 'bc' represents the HRTEM image and structural interlayer spacing analysis of NASHC-2; and 'd' represents the TEM image and mapping spectrum of different elements of NASHC-2.

[0021] Figure 2 This is an HRTEM image of the original hard carbon PHC.

[0022] Figure 3 In the figure, 'a' represents the total XPS spectrum of four samples: PHC, NASHC-1, NASHC-2, and NASHC-3; 'be' represents the XPS spectra of C1s, O 1s, S2p, and Na 1s of sample NASHC-2.

[0023] Figure 4 X-ray diffraction patterns of four samples: PHC, NASHC-1, NASHC-2, and NASHC-3.

[0024] Figure 5 Raman spectra of four samples: PHC, NASHC-1, NASHC-2, and NASHC-3.

[0025] Figure 6 Figure a shows the nitrogen adsorption-desorption test results of four samples: PHC, NASHC-1, NASHC-2, and NASHC-3; Figure b shows the pore size distribution of the four samples.

[0026] Figure 7 The ad diagrams in the figure are galvanostatic charge-discharge diagrams for four samples: PHC, NASHC-1, NASHC-2, and NASHC-3.

[0027] Figure 8 The graphs show the rate performance of four samples: PHC, NASHC-1, NASHC-2, and NASHC-3.

[0028] Figure 9 In the figure, a represents the cyclic voltammetric curves of the NASHC-2 sample at different scan rates; b represents the normalized contribution rate of its surface control process.

[0029] Figure 10 In the image, a is the SEI membrane HRTEM image of NASHC-2; b is the SEI membrane HRTEM image of PHC. Detailed Implementation

[0030] To make the present invention more apparent and understandable, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The embodiments described below are only for explaining the present invention and are not intended to limit the present invention in any form or substance.

[0031] Example 1

[0032] This embodiment prepares Na2S according to the following steps. x / HC(NASHC-2) heterostructure composite material.

[0033] Material preparation steps:

[0034] S1. Hydrothermal preparation of sucrose precursor yields hydrothermal carbon microspheres:

[0035] (1) Weigh 4g of sucrose powder, dissolve it in a small beaker containing 70ml of deionized water, and stir for 30min.

[0036] (2) Place the mixed solution obtained in step (1) into a stainless steel reactor lined with Teflon and place it in a forced-air drying oven at a temperature of 180°C for 12 hours.

[0037] (3) After the brown suspension obtained in step (2) is cooled to room temperature, the lower layer of sediment is taken out, washed three times with deionized water by centrifugation, and then placed in a vacuum drying oven and dried at 60°C for 24 hours.

[0038] S2. The obtained hydrothermal carbon microsphere powder was mixed with sodium thiosulfate (Na2S2O3), then wet-milled using high-energy ball milling, followed by high-temperature annealing to prepare Na2S. x / HC heterostructure materials:

[0039] (1) Take 150mg of hydrothermal carbon microspheres and 300mg of Na2S2O3 powder obtained in step S1 and place them in a ball mill jar. Add anhydrous ethanol solvent into the ball mill jar in a glove box, then seal it and use a planetary ball mill to ball mill at a speed of 800rpm for 4h.

[0040] (2) After taking out the mixture obtained in step (1), wash it three times with anhydrous ethanol and place it in a vacuum drying oven to dry for 12 hours. Then, heat it to 800°C in a tube furnace under an argon atmosphere at a heating rate of 3-5°C / min and maintain it for 3 hours. After it cools down to room temperature naturally, Na2S is obtained. x / HC(NASHC-2) heterostructure composite material.

[0041] The Na2S prepared in this embodiment x The / HC heterostructure (NASHC-2) was characterized using tests. Figure 1 As shown in Figure a, scanning electron microscopy (SEM) reveals that the composite material exhibits surface damage due to high-energy impact, with the diameter remaining around 500 nm. Meanwhile, as... Figure 1 High-power transmission electron microscopy (HRTEM) observations of samples b and c reveal clearly visible lattice fringes of sodium polysulfide and hard carbon, exhibiting different interlayer spacings. Figure 1 Transmission electron microscopy and energy dispersive spectroscopy analysis of d in the image show that C, O, S and Na elements are uniformly distributed.

[0042] In addition, such as Figure 3 As shown, the NASHC-2 sample also exhibited S and Na peaks in XPS photoelectron spectroscopy, and the elemental spectra also indicated the presence of CS, SS, and CO-Na bonds in the material.

[0043] like Figure 4 As shown in the XRD pattern, the NASHC-2 sample exhibits characteristic peaks for both sulfur and sodium sulfide, confirming the presence of Na2S. x Successful synthesis of the / HC heterostructure.

[0044] like Figure 5 As shown, Raman spectroscopy reveals that the NASHC-2 sample exhibits the lowest Ig. D / I G This indicates that a large number of sodium ions occupy defect sites in hard carbon, while the Raman peak signal of disulfide bonds also indicates the existence of a heterostructure.

[0045] like Figure 6 As shown, BET testing revealed that the specific surface area of ​​the NASHC-2 sample decreased sharply compared to the original hard carbon material (PHC), while the number of micropores decreased and the average pore size increased, indicating that the microporous structure was filled with sodium polysulfide.

[0046] Negative electrode coating and electrochemical testing:

[0047] The first step involved mixing the active material (80 wt%), Super P (10 wt%), and PVDF (10 wt%) in an N-methylpyrrolidone solution and grinding for 10 minutes to obtain an electrode slurry. The slurry was then coated onto an aluminum foil surface using a spatula and subsequently dried in a vacuum drying oven at 60°C for 24 hours. Afterward, the electrode was perforated into 11 mm small discs, with an active material loading of 1.5 mg / cm³. 2 Left and right. Half-cell tests were conducted using CR2032 button cell casings, with 16 mm diameter sodium foil as the counter electrode. The electrode solution was 1 M NaPF6 dissolved in DEGDME organic solvent. Whatman GF / D glass fiber was used as the separator. The entire assembly process was carried out in an argon-filled glove box with water and oxygen concentrations both less than 0.1 ppm and at room temperature.

[0048] Constant current charge-discharge experiments were conducted on a LAND CT2001A battery testing system, with a voltage range of 0.01–3V. Example 1 showed an initial coulombic efficiency of 84.1% and a reversible capacity of 514.8 mAh g⁻¹ at a current density of 0.05 A g⁻¹. -1 The capacity below 1V is 354.31mAh g. -1 The proportion was 71%. Rate performance testing showed that at 40Ag... -1 It still has 87.5 mAh g at current density. -1 .

[0049] Using an electrochemical workstation, model PGSTAT302N (Metrohm Autolab BV), the range was 0.2–1.5 mVs. -1 Cyclic voltammetry tests were performed on it at a scan rate, such as... Figure 9 As shown, the voltage range is 0.01–3V, and through fitting, its voltage values ​​at 0.2, 0.5, 0.75, 1.0, and 1.5 mV s are obtained. -1 The percentages of surface control processes at different scanning speeds were 63.3%, 66.9%, 71.5%, 75.4%, and 81.9%, respectively.

[0050] like Figure 10As shown, HRTEM observation of the electrode interface after cycling stability revealed the formation of a thin and dense SEI film on the electrode surface, with a thickness of approximately 7.1 nm, indicating a faster sodium ion kinetic migration process.

[0051] Example 2

[0052] In this embodiment, composite samples with different reactant ratios (hydrothermal carbon spheres: Na2S2O3 = 1:1, NASHC-1) were prepared according to the following steps.

[0053] Material preparation steps:

[0054] S1. Hydrothermal preparation of sucrose precursor yields hydrothermal carbon microspheres:

[0055] (1) Weigh 4g of sucrose powder, dissolve it in a small beaker containing 70ml of deionized water, and stir for 30min.

[0056] (2) Place the mixed solution obtained in step (1) into a stainless steel reactor lined with Teflon and place it in a forced-air drying oven at a temperature of 180°C for 12 hours.

[0057] (3) After the brown suspension obtained in step (2) is cooled to room temperature, the lower layer of sediment is taken out, washed three times with deionized water by centrifugation, and then placed in a vacuum drying oven and dried at 60°C for 24 hours.

[0058] S2. The obtained hydrothermal carbon microsphere powder was mixed with sodium thiosulfate (Na2S2O3), then wet-milled using high-energy ball milling, followed by high-temperature annealing to prepare Na2S. x / HC heterostructure materials:

[0059] (1) Take 150 mg of hydrothermal carbon microspheres and 150 mg of Na2S2O3 powder obtained in step S1 and place them in a ball mill jar. Add anhydrous ethanol solvent into the ball mill jar in a glove box, then seal it and use a planetary ball mill to ball mill at a speed of 800 rpm for 4 hours.

[0060] (2) After taking out the mixture obtained in step (1), wash it three times with anhydrous ethanol and place it in a vacuum drying oven to dry for 12 hours. Then, heat it to 800°C in a tube furnace under an argon atmosphere at a heating rate of 3-5°C / min and maintain it for 3 hours. After it cools down to room temperature naturally, the NASHC-1 composite material is obtained.

[0061] The NASHC-1 sample prepared in Example 2 was characterized.

[0062] like Figure 3As shown, in XPS photoelectron spectroscopy, the NASHC-1 sample exhibited S and Na peaks, and the ratio of S to Na elements was 0.69, which was greater than that of NASHC-2 (0.56). This indicates that as the proportion of sodium thiosulfate increased, the proportion of sodium in the composite sample gradually increased, which also led to different balances between the initial sodium storage efficiency and the multiplier of the sample.

[0063] like Figure 4 As shown in the XRD spectrum, the NASHC-1 sample has characteristic peaks including sulfur and sodium sulfide, but the peak intensity is weaker than that of NASHC-2, and the position of the (002) peak is similar to that of the PHC sample. The interlayer spacing calculated by Bragg equation is about 0.362 nm, which is slightly larger than that of PHC.

[0064] like Figure 5 As shown, Raman spectroscopy reveals the I of the NASHC-1 sample. D / I G The ratio of 2.41 indicates that the material is more disordered after heteroatomic doping, and the high S / Na ratio indicates that the amount of sodium ions is insufficient to repair the defect sites in hard carbon.

[0065] like Figure 6 As shown, BET testing revealed that the specific surface area of ​​the NASHC-1 sample decreased sharply compared to the original hard carbon material (PHC), while the number of micropores decreased and the number of mesopores and macropores increased, forming a hierarchical porous structure.

[0066] Negative electrode coating and electrochemical testing:

[0067] The first step involved mixing the active material (80 wt%), Super P (10 wt%), and PVDF (10 wt%) in an N-methylpyrrolidone solution and grinding for 10 minutes to obtain an electrode slurry. The slurry was then coated onto an aluminum foil surface using a spatula and subsequently dried in a vacuum drying oven at 60°C for 24 hours. Afterward, the electrode was perforated into 11 mm small discs, with an active material loading of 1.5 mg / cm³. 2 Left and right. Half-cell tests were conducted using CR2032 button cell casings, with 16 mm diameter sodium foil as the counter electrode. The electrode solution was 1 M NaPF6 dissolved in DEGDME organic solvent. Whatman GF / D glass fiber was used as the separator. The entire assembly process was carried out in an argon-filled glove box with water and oxygen concentrations both less than 0.1 ppm and at room temperature.

[0068] Constant current charge-discharge experiments were conducted on a LAND CT2001A battery testing system, with a voltage range of 0.01–3V. Example 2 involved a 0.05Ag... -1The initial coulombic efficiency at the given current density is 80.3%, and the reversible capacity is 420.8 mAh g. -1 The capacity below 1V is 279.1mAh g. -1 Rate performance testing showed that at 40Ag... -1 At current density, it is 35.1 mAh g. -1 .

[0069] Example 3

[0070] In this embodiment, composite samples with different reactant ratios (hydrothermal carbon spheres: Na2S2O3 = 1:3, NASHC-3) were prepared according to the following steps.

[0071] Material preparation steps:

[0072] S1. Hydrothermal preparation of sucrose precursor yields hydrothermal carbon microspheres:

[0073] (1) Weigh 4g of sucrose powder, dissolve it in a small beaker containing 70ml of deionized water, and stir for 30min.

[0074] (2) Place the mixed solution obtained in step (1) into a stainless steel reactor lined with Teflon and place it in a forced-air drying oven at a temperature of 180°C for 12 hours.

[0075] (3) After the brown suspension obtained in step (2) is cooled to room temperature, the lower layer of sediment is taken out, washed three times with deionized water by centrifugation, and then placed in a vacuum drying oven and dried at 60°C for 24 hours.

[0076] S2. The obtained hydrothermal carbon microsphere powder was mixed with sodium thiosulfate (Na2S2O3), then wet-milled using high-energy ball milling, followed by high-temperature annealing to prepare Na2S. x / HC heterostructure materials:

[0077] (1) Take 150 mg of hydrothermal carbon microspheres and 450 mg of Na2S2O3 powder obtained in step S1 and place them in a ball mill jar. Add anhydrous ethanol solvent into the ball mill jar in a glove box, then seal it and use a planetary ball mill to ball mill at a speed of 800 rpm for 4 hours.

[0078] (2) After taking out the mixture obtained in step (1), wash it three times with anhydrous ethanol and place it in a vacuum drying oven to dry for 12 hours. Then, heat it to 800°C in a tube furnace under an argon atmosphere at a heating rate of 3-5°C / min and maintain it for 3 hours. After it cools down to room temperature naturally, the NASHC-3 composite material is obtained.

[0079] The NASHC-3 sample prepared in Example 3 was characterized.

[0080] like Figure 3 As shown, in XPS photoelectron spectroscopy, the NASHC-3 sample exhibited S and Na peaks, and the ratio of S to Na elements was 0.47, which was less than 0.56 for NASHC-2. This indicates that as the proportion of sodium thiosulfate increases, the proportion of sodium in the composite sample gradually increases, which also leads to different balances between the initial sodium storage efficiency and the rate performance of the sample. That is, it exhibits a higher initial efficiency, but the rate performance decreases.

[0081] like Figure 4 As shown in the XRD spectrum, the NASHC-3 sample has characteristic peaks of both sulfur and sodium sulfide, but the peak intensity is much higher than that of NASHC-2. However, the position of its (002) peak is comparable to that of the NASHC-1 and PHC samples. The interlayer spacing can be calculated to be about 0.37 nm by Bragg equation. The comparison shows that the NASHC-3 sample generates more sodium polysulfide during the synthesis process to fill the interlayer, which reduces the interlayer spacing.

[0082] like Figure 5 As shown, Raman spectroscopy reveals the I of the NASHC-3 sample. D / I G The value was 2.41, which is much higher than that of NASHC-2, NASHC-1 and PHC, indicating that the large amount of amorphous sodium polysulfide makes the material exhibit a higher degree of disorder.

[0083] like Figure 6 As shown, the NASHC-3 sample exhibited the smallest specific surface area and a single pore structure, as indicated by the BET test, suggesting the formation of excessive sodium polysulfides.

[0084] Negative electrode coating and electrochemical testing:

[0085] The first step involved mixing the active material (80 wt%), Super P (10 wt%), and PVDF (10 wt%) in an N-methylpyrrolidone solution and grinding for 10 minutes to obtain an electrode slurry. The slurry was then coated onto an aluminum foil surface using a spatula and subsequently dried in a vacuum drying oven at 60°C for 24 hours. Afterward, the electrode was perforated into 11 mm small discs, with an active material loading of 1.5 mg / cm³. 2 Left and right. Half-cell tests were conducted using CR2032 button cell casings, with 16 mm diameter sodium foil as the counter electrode. The electrode solution was 1 M NaPF6 dissolved in DEGDME organic solvent. Whatman GF / D glass fiber was used as the separator. The entire assembly process was carried out in an argon-filled glove box with water and oxygen concentrations both less than 0.1 ppm and at room temperature.

[0086] Constant current charge-discharge experiments were conducted on a LAND CT2001A battery testing system, with a voltage range of 0.01–3V. Example 3 involved a 0.05Ag... -1 The initial coulombic efficiency at the given current density was 96.4%, however, the reversible capacity subsequently dropped rapidly to 362.2 mAh g. -1 The capacity below 1V is 240.1mAh g. -1 Rate performance testing showed that at 40Ag... -1 The current density is 75.4 mAh g. -1 .

[0087] Comparative Example 1

[0088] The original hard carbon material was prepared according to the following steps in this comparative example.

[0089] Material preparation steps:

[0090] Hard carbon materials were synthesized using a hydrothermal carbonization reaction with sucrose powder as a precursor.

[0091] (1) Weigh 4g of sucrose powder, dissolve it in a small beaker containing 70ml of deionized water, and stir for 30min.

[0092] (2) Place the mixed solution obtained in step (1) into a stainless steel reactor lined with Teflon and place it in a forced-air drying oven at a temperature of 180°C for 12 hours.

[0093] (3) After the brown suspension obtained in step (2) is cooled to room temperature, the lower layer of sediment is taken out, washed three times with deionized water by centrifugation, and then placed in a vacuum drying oven and dried at 60°C for 24 hours.

[0094] (4) Place the dried powder obtained in step (3) in a quartz boat and place it in a tube furnace filled with argon atmosphere. Heat it to 800°C at a heating rate of 3-5° / min and keep it for 3 hours.

[0095] The original hard carbon material (PHC) prepared in Comparative Example 1 was characterized.

[0096] like Figure 2 As shown, the HRTEM image of the original hard carbon material reveals a microstructure of disordered, randomly oriented graphene sheets, and the interlayer spacing is measured to be 0.355 nm, which is consistent with the basic characteristics of hard carbon.

[0097] like Figure 3 The XPS spectrum of PHC is shown in (a), which has a good carbon-oxygen ratio.

[0098] like Figure 4 The presence of broad peaks of PHC in the XRD pattern also indicates the characteristic amorphous structure of hard carbon.

[0099] like Figure 5 PHC I in Raman spectra D / I G A value of 2.22 indicates that the original hard carbon has a high degree of disorder, while Figure 6 BET testing showed that the original hard carbon had a high micropore content and a high specific surface area, which is consistent with the characteristics of hard carbon samples synthesized at this temperature.

[0100] Negative electrode coating and electrochemical testing:

[0101] The first step involved mixing the active material (80 wt%), Super P (10 wt%), and PVDF (10 wt%) in an N-methylpyrrolidone solution and grinding for 10 minutes to obtain an electrode slurry. The slurry was then coated onto an aluminum foil surface using a spatula and subsequently dried in a vacuum drying oven at 60°C for 24 hours. Afterward, the electrode was perforated into 11 mm small discs, with an active material loading of 1.5 mg / cm³. 2 The half-cell test was conducted using a CR2032 button cell casing. A 16mm diameter sodium foil was used as the counter electrode, and the electrode solution was 1M NaPF6 dissolved in DEGDME organic solvent. Whatman GF / D glass fiber was used as the separator. The entire assembly process was carried out in an argon-filled glove box with water and oxygen concentrations of less than 0.1ppm at room temperature.

[0102] A constant current charge-discharge experiment was conducted on the LAND CT2001A battery testing system, with a voltage range of 0.01–3V. Comparative Example 1 was performed at 0.05Ag. -1 The initial coulombic efficiency at the given current density is 71.5%, and the reversible capacity is 298.2 mAh g. -1 The capacity below 1V is 280.4mAh g. -1 Rate performance testing showed that at 10Ag... -1 The reversible capacity at current density is only 68.1 mAh g. -1 .

[0103] like Figure 10 As shown in b, HRTEM observation of the SEI on the stabilized electrode surface revealed a relatively thick SEI film of approximately 16.2 nm, corresponding to relatively slow kinetic performance.

[0104] Further analysis of the electrochemical performance of Examples 1-3 and Comparative Example 1

[0105] For details regarding the coating and electrochemical testing results of NASHC-2 prepared in Example 1, PHC prepared in Comparative Example 1, NASHC-1 prepared in Example 2, and NASHC-3 prepared in Example 3 as negative electrodes, please refer to [link / reference needed]. Figures 7-10 :

[0106] Figure 7 The figures in the diagrams are the galvanostatic charge-discharge performance graphs of Example 1, Comparative Examples 1, and Examples 2-3 at a current density of 0.05 A g⁻¹, respectively. It can be seen that the initial coulombic efficiency (84.1%) and reversible capacity (514.8 mAh g⁻¹) of NASHC-2 (Example 1) are... -1 The capacity below 1V is 354.31mAh g. -1 The proportion of sodium polysulfide in Example 3 (71%) was significantly higher than that in Comparative Example 1 and Example 2. However, the higher sodium content in Example 3 promoted an improvement in the initial coulombic efficiency. The subsequent rapid capacity decay also indicated that the excessive sodium polysulfide dissolved in the electrolyte led to the irreversible loss of active material.

[0107] from Figure 8 It can be seen that the electrochemical sodium storage performance at different expansion rates (0.05~40Ag) is... -1 ), that is, at ultra-high current density (40Ag) -1 Example 1 (NASHC-2) still has 87.5 mAh g. -1 Far exceeding Example 2 (NASHC-1, 35.1 mAh g) -1 Example 1 and Example 2 (NASHC-3, 75.4 mAh g) -1 ), and Comparative Example 1 (PHC) at 10 Ag -1 At a current density of only 68.1 mAh g -1 Reversible capacity. Therefore, Examples 1-3, as negative electrodes for sodium-ion batteries, exhibit excellent sodium storage kinetics, especially Example 1.

[0108] Figure 9 In the figures, (a) and (b) represent the normalized contribution rates of the cyclic voltammetry curves and the surface control process of Example 1 at different scan rates, respectively. It can be seen that the surface control process of NASHC-2 (Example 1) is dominant, at 1.5 mV / s. -1 The high percentage of sodium storage at the scan rate of 81.9% further illustrates its rapid sodium storage kinetics.

[0109] Figure 10In the figures, a and b correspond to the HRTEM images of the SEI films on the electrode surfaces of Example 1 (NASHC-2) and Comparative Example 1 (PHC) after cycling stabilization, respectively. The SEI film on the surface of the NASHC-2 electrode is dense and thin (approximately 7.1 nm), and is dominated by inorganic components, while the SEI film on the surface of the PHC electrode is thicker (approximately 16.2 nm), and its layered structure of inorganic inner layer and organic outer layer also hinders the rapid diffusion of ions, thus exhibiting slower kinetic performance compared to Example 1.

[0110] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for controllable preparation of sodium polysulfide heterostructure anchored hard carbon by grafting synergy, characterized in that, The preparation method comprises the following steps: S1, dissolving sucrose and then performing a hydrothermal reaction to obtain hydrothermal carbon microspheres; S2, hydrothermal carbon microspheres and sodium thiosulfate Na2S2O3 are mixed and high-energy ball-milled, and then high-temperature treated to obtain covalently coupled Na2S x / HC heterostructure.

2. The method for controllable preparation of sodium polysulfide heterostructure anchored hard carbon by branch grafting synergy according to claim 1, characterized in that, In the step S1, the temperature of the hydrothermal reaction is 170-190 DEG C.

3. The method of controllably preparing sodium polysulfide heterostructure-anchored hard carbon by dendritic synergistic effect according to claim 1, wherein, In the step S2, the feeding ratio of the hydrothermal carbon microspheres to sodium thiosulfate is 1:1-3.

4. The method for controllable preparation of sodium polysulfide heterostructure anchored hard carbon by branch grafting synergy according to claim 1, characterized in that, In the step S2, the high-temperature treatment method is: heating to 800-900 DEG C at a temperature increasing rate of 3-5 DEG C per minute in an argon atmosphere, and maintaining for 3-4 h.

5. A hard carbon anchored by sodium polysulfide heterostructure obtained by the method of any one of claims 1-4.

6. The sodium polysulfide heterostructure anchor hard carbon of claim 5, wherein, The Na2S x The carbon layer spacing of the hard carbon in the / HC heterostructure is 0.36-0.38 nm.

7. Application of the hard carbon anchored by sodium polysulfide heterostructure of claim 5 to a negative electrode of a sodium ion battery.

8. Use according to claim 7, characterized in that, The SEI film formed by the catalysis of the hard carbon anchored by sodium polysulfide heterostructure has a thickness of 7-10 nm.

Images