Method for inhibiting shuttle effect of lithium polysulfide by introducing activated sludge-based biomass charcoal and application

Abstract

The invention relates to the technical field of lithium-sulfur batteries, in particular to a method for inhibiting a shuttle effect of lithium polysulfide by introducing activated sludge-based biomass charcoal and application. The invention aims to solve the problems of capacity fading and short cycle life caused by the shuttle effect of lithium polysulfide in the lithium-sulfur battery. According to the main scheme, the method comprises the following steps: by taking activated sludge generated in an urban domestic sewage treatment process as a carbon sequestration precursor, drying the activated sludge, grinding into powder, etching silicon dioxide with hydrofluoric acid, washing to be neutral, drying, adding potassium carbonate, grinding, pyrolyzing for 2 hours at 800 DEG C in a nitrogen atmosphere, pickling, washing and drying to obtain SC; the SC and sublimed sulfur are mixed according to the mass ratio of 1: 4, heat preservation is conducted for 24 hours at the temperature of 155 DEG C in the nitrogen atmosphere to form a carbon-sulfur mixture, the carbon-sulfur mixture, conductive carbon black and polyvinylidene fluoride are subjected to size mixing according to the mass ratio of 8: 1: 1, and an aluminum foil is coated with the mixture to prepare a positive electrode; an SC sulfur positive electrode, a metal lithium sheet as a negative electrode, a polypropylene film as a diaphragm and a DOL / DME solution containing 1.0 M of LiTFSI and 1wt% of LiNO3 are assembled into the CR2032 type button cell.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery cathode material design technology, and to a method and application for achieving physical confinement and chemical anchoring of polysulfides by introducing activated sludge-based biomass. Background Technology

[0002] Developing energy storage technologies that combine high energy density and environmental friendliness has become a key direction in the energy transition. Lithium-sulfur batteries, with their theoretical energy density of up to 2600 Wh·kg⁻¹, the low cost of sulfur cathodes, and eco-friendliness, are considered important candidates for next-generation high-energy battery systems. However, their commercialization is still limited by issues such as the "shuttle effect" of polysulfides, the insulating properties of sulfur, and volume expansion during charge and discharge, leading to significant degradation in battery cycle life and capacity loss.

[0003] Biochar materials, due to their renewability, high specific surface area, abundant porous structure, and heterogeneous element doping characteristics, have become an ideal carrier for solving the above problems. Carbon materials derived from natural biomass can inhibit the dissolution and migration of polysulfides in electrolytes through physical confinement and chemical adsorption, while improving the conductivity of sulfur.

[0004] Activated sludge, a typical byproduct of wastewater treatment processes, originates from the metabolic processes of microorganisms on organic pollutants (such as carbohydrates, proteins, and lipids) in wastewater. In the activated sludge process, heterotrophic microorganisms convert organic matter into their own cellular components through aerobic / anaerobic reactions, while simultaneously adsorbing metal ions, ultimately forming flocculent sludge rich in organic matter and metal elements. After pyrolysis, the organic components in the activated sludge carbonize into a graphitized framework, while metal elements (such as Fe and Al) form hierarchical pores through in-situ doping or etching, thus transforming into biochar with hierarchical porosity and self-doping characteristics. This strategy not only achieves carbon sequestration and emission reduction but also reduces material preparation costs, aligning with the sustainable development concept of "resource utilization."

[0005] The unique structure of activated sludge-based carbon materials (such as three-dimensional conductive networks and surface functional groups) can effectively anchor lithium polysulfides and accelerate their kinetic conversion through catalytic redox reactions, thereby mitigating the shuttle effect and improving battery cycle stability. However, the electrochemical performance of biochar prepared from activated sludge from different regions and seasons varies due to wastewater quality characteristics (including inorganic suspended solids (ISS) content, organic composition, heavy metal content, etc.) and processing methods (aerobic or anaerobic processes). Sludge from municipal wastewater treatment plants with low ISS and low heavy metal content, and which has been operating stably for a long time, should be selected whenever possible. This can effectively reduce the ash content after pyrolysis, increase the specific surface area, and reduce HF usage and secondary pollution. Furthermore, municipal sludge has a relatively high organic content, allowing for the incorporation of more nitrogen and the formation of more surface functional groups in the prepared biochar.

[0006] In recent years, strategies for suppressing polysulfides have evolved from single physical confinement to composite functional designs. For example, the introduction of heterojunction structures can induce an internal electric field, accelerating charge transfer; while the synergistic effect of metal atoms (such as V and Co) with the carbon matrix can enhance the adsorption-catalytic bifunctional effect on polysulfides. Furthermore, breakthroughs in electrolyte engineering and novel solid-state electrolytes have further propelled the practical application of lithium-sulfur batteries. However, designing high-performance cathode materials using green, low-cost biomass precursors remains a significant research challenge. Summary of the Invention

[0007] The purpose of this invention is to address the problem of capacity decay and short cycle life caused by the shuttle effect of lithium polysulfides in lithium-sulfur batteries. It proposes to achieve dual regulation of physical confinement and chemical adsorption of polysulfides through the multi-level porous structure of activated sludge-based biochar materials and surface polar groups (such as oxygen / nitrogen doping), thereby suppressing the shuttle effect and improving battery performance.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A method for preparing activated sludge-based biochar that suppresses the lithium polysulfide shuttle effect includes the following steps: Step 1: Select activated sludge produced by municipal wastewater treatment plant as raw material. The activated sludge contains organic components and inorganic suspended solids generated by microbial metabolism. The inorganic suspended solids include SiO2. Dry and grind the dewatered activated sludge into powder and label it as DS. Step 2: Weigh DS powder at a solid-liquid ratio of 1:15 (g / mL), add hydrofluoric acid for etching to remove silica, wash with water until pH 6, and then dry to obtain etched powder. Step 3: Mix the etched powder with potassium carbonate at a mass ratio of 1:2 and then ball mill it. Pyrolyze it at 800°C for 2 hours in a nitrogen atmosphere to obtain the pyrolyzed powder. Step 4: The pyrolyzed powder is acid-washed, water-washed and dried to obtain activated sludge-based biochar SC.

[0009] In the above scheme, in step 1, the activated sludge is dried at 80 ℃ for 24 h, ground into powder using a ball mill, and labeled as DS.

[0010] In the above scheme, the concentration range of hydrofluoric acid in step 2 is 40 wt%, the etching time is 6 hours, the solid is collected by centrifugation after reaction, washed with water until pH=6, and vacuum dried at 80℃ for 12 h.

[0011] In the above scheme, step 3 uses 5 ℃·min -1 Heat to 800℃.

[0012] In the above scheme, the powder after pyrolysis in step 3 is acid-washed with 1 M HCl solution for 12 h, washed with deionized water until neutral, and dried at 60℃ for 24 h to finally obtain activated sludge-based biochar SC.

[0013] The present invention also provides a lithium-sulfur battery cathode comprising a composite of activated sludge-based biochar SC and sulfur in a mass ratio of 1:4. The composite is heat-treated at 155°C under a nitrogen atmosphere for 24 hours to obtain a carbon-sulfur mixture. The carbon-sulfur mixture, conductive carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1, and polyvinylpyrrolidone is added to form a slurry. The slurry is coated onto aluminum foil, dried, and cut into sheets to obtain a sulfur cathode.

[0014] The present invention also provides a lithium-sulfur battery, which uses a prepared sulfur positive electrode, a lithium metal sheet as the negative electrode, and a polypropylene membrane as the separator, and is assembled into a battery in an argon atmosphere. The present invention also provides a lithium-sulfur battery, wherein the electrolyte is a solution of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1, with the addition of 1.0 M lithium bis(trifluoromethanesulfonyl)imide and 1 wt% LiNO3.

[0015] This invention also provides a method for suppressing the lithium polysulfide shuttle effect by introducing activated sludge-based biochar, comprising the following steps: Step (1) The activated sludge is sequentially subjected to acid etching treatment, alkaline activator mixing, and inert atmosphere pyrolysis to obtain activated sludge-based biochar SC with multi-level porous structure and oxygen / nitrogen doping. Step (2) The SC is combined with sulfur to form a positive electrode material and then assembled into a lithium-sulfur battery.

[0016] In the above scheme, the acid etching treatment in step (1) uses hydrofluoric acid, the alkaline activator is potassium carbonate, the pyrolysis temperature is 800℃, and the time is 2 hours.

[0017] To achieve the above objectives, the present invention adopts the following technical solution: Because the present invention employs the above-mentioned technical means, it has the following beneficial effects: This invention prepares a biochar material with a hierarchical porous structure based on activated sludge. Its surface is rich in oxygen / nitrogen polar groups, enabling dual regulation of physical confinement and chemical adsorption of polysulfides. The SC battery exhibits low internal resistance, rapid lithium-ion diffusion, and excellent reaction kinetics, effectively suppressing the lithium polysulfide shuttle effect, achieving an initial capacity of 1165.5 mAh·g at 0.1 C. -1 The cyclic decay rate after 1000 cycles is only 0.05%. Furthermore, at 8 mg·cm⁻¹... -2It operates stably even with high sulfur loading, and retains 55.0% of its capacity after 500 cycles at 0.5 C. This provides a green path for the development of cathode materials for lithium-sulfur batteries. Attached Figure Description

[0018] Figure 1 These are scanning electron microscope (SEM) images of the present invention, wherein a is dehydrated activated sludge, b is unactivated biochar, and c and d are SEM images of activated sludge-based biochar. Figure 2 In the image, a is a magnified view of the nitrogen adsorption-desorption isotherm, and b is the XPS full spectrum. Figure 3 This is a comparison diagram of dewatered activated sludge, unactivated activated sludge-based biochar, and activated sludge-based biochar of the present invention, wherein a is an XRD spectrum, b is an ultraviolet-visible absorption spectrum of the supernatant of the polysulfide adsorption experiment (the built-in image is a photograph of the polysulfide adsorption experiment), c is a nitrogen adsorption-desorption isotherm curve, and d is the pore size distribution. Figure 4 These are comparative images of the present invention, where a is the FT-IR spectrum of dewatered activated sludge, unactivated activated sludge-based biochar, and activated sludge-based biochar; the high resolution of activated sludge-based biochar is shown; b is the C 1s spectrum, c is the O 1s spectrum, and d is the N 1s spectrum. Figure 5 The diagram shows a comparison of three types of lithium-sulfur batteries according to the present invention, where a is the performance of 50 charge-discharge cycles under a constant current of 0.1 C, b is the first charge-discharge cycle curve at 0.1 C, c is the cycle performance under a rate current of 0.1 C to 2 C, d is the AC impedance diagram, e is the CV curve at different scan rates, and f is the ion diffusion rate curve. Figure 6 The SC lithium-sulfur battery of the present invention exhibits 1000 charge-discharge cycle performance under 0.1 C constant current conditions. Figure 7 These are the charge-discharge curves of the SC lithium-sulfur battery of the present invention, where a is the charge-discharge curve after 1000 cycles under a constant current of 0.1 C, and b is the charge-discharge curve under a rate current of 0.1 C to 2 C. Figure 8 The performance of SC lithium-sulfur batteries with different loading capacities under 500 charge-discharge cycles at a constant current of 0.5 C according to the present invention; Figure 9 This is a comparison of the CV curves of the present invention, where 'a' represents the CV curves of three lithium-sulfur batteries at 0.1 mV·s. -1 Comparison of CV curves in the first week under sweep rate conditions; b represents the SC lithium-sulfur battery at 0.1 mV·s. -1 CV curves under sweep rate conditions; Figure 10This is a comparison of the CV curves of the present invention, where a is the CV curve of the USC lithium-sulfur battery under different scan rates and b is the CV curve of the DS lithium-sulfur battery under different scan rates. Figure 11 These are the ion diffusion rate curves of the three lithium-sulfur batteries of the present invention at peaks A, B, and C, where a corresponds to peak A, b corresponds to peak B, and c corresponds to peak C. Detailed Implementation

[0019] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, any modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0020] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without these specific details.

[0021] This paper focuses on the preparation of activated sludge-based biochar and its application in the cathode of lithium-sulfur batteries. Activated sludge (DS) was prepared by etching, activation, and pyrolysis to obtain activated sludge-based biochar (SC). This was compared with unactivated biochar (USC) to systematically explore the correlation mechanism between the structural regulation of carbon materials (such as porosity and surface chemical states) and their electrochemical performance (such as capacity retention and cycle life) in lithium-sulfur batteries. The aim is to provide theoretical and technical support for the development of cost-effective lithium-sulfur batteries, while promoting the high-value utilization of waste biomass resources.

[0022] A method for preparing activated sludge-based biochar that suppresses the lithium polysulfide shuttle effect includes the following steps: Step 1: Select activated sludge produced by municipal wastewater treatment plant as raw material. The activated sludge contains organic components and inorganic suspended solids generated by microbial metabolism. The inorganic suspended solids include SiO2. Dry and grind the dewatered activated sludge into powder and label it as DS. Step 2: Weigh DS powder at a solid-liquid ratio of 1:15 (g / mL), add hydrofluoric acid for etching to remove silica, wash with water until pH 6, and then dry to obtain etched powder. Step 3: Mix the etched powder with potassium carbonate at a mass ratio of 1:2 and then ball mill it. Pyrolyze it at 800°C for 2 hours in a nitrogen atmosphere to obtain the pyrolyzed powder. Step 4: The pyrolyzed powder is acid-washed, water-washed and dried to obtain activated sludge-based biochar SC.

[0023] In the above scheme, in step 1, the activated sludge is dried at 80 ℃ for 24 h, ground into powder using a ball mill, and labeled as DS.

[0024] In the above scheme, the concentration range of hydrofluoric acid in step 2 is 40 wt%, the etching time is 6 hours, the solid is collected by centrifugation after reaction, washed with water until pH=6, and vacuum dried at 80℃ for 12 h.

[0025] In the above scheme, step 3 uses 5 ℃·min -1 Heat to 800℃.

[0026] In the above scheme, the powder after pyrolysis in step 3 is acid-washed with 1 M HCl solution for 12 h, washed with deionized water until neutral, and dried at 60℃ for 24 h to finally obtain activated sludge-based biochar SC.

[0027] The present invention also provides a lithium-sulfur battery cathode comprising a composite of activated sludge-based biochar SC as described in any one of claims 1 or 5 and sulfur in a mass ratio of 1:4. The composite is heat-treated at 155°C under a nitrogen atmosphere for 24 hours to obtain a carbon-sulfur mixture. The carbon-sulfur mixture, conductive carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1, and polyvinylpyrrolidone is added to form a slurry. The slurry is coated onto aluminum foil, dried, and cut into sheets to obtain a sulfur cathode.

[0028] The present invention also provides a lithium-sulfur battery, which uses a prepared sulfur positive electrode, a lithium metal sheet as the negative electrode, and a polypropylene membrane as the separator, and is assembled into a battery in an argon atmosphere. The present invention also provides a lithium-sulfur battery, wherein the electrolyte is a solution of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1, with the addition of 1.0 M lithium bis(trifluoromethanesulfonyl)imide and 1 wt% LiNO3.

[0029] This invention also provides a method for suppressing the lithium polysulfide shuttle effect by introducing activated sludge-based biochar, comprising the following steps: Step (1) The activated sludge is sequentially subjected to acid etching treatment, alkaline activator mixing, and inert atmosphere pyrolysis to obtain activated sludge-based biochar SC with multi-level porous structure and oxygen / nitrogen doping. Step (2) The SC is combined with sulfur to form a positive electrode material and then assembled into a lithium-sulfur battery.

[0030] In the above scheme, the acid etching treatment in step (1) uses hydrofluoric acid, the alkaline activator is potassium carbonate, the pyrolysis temperature is 800℃, and the time is 2 hours.

[0031] The following example illustrates the application of this method, including the following steps: Step 1. After thoroughly drying the activated sludge (DS), grind it into powder using a ball mill. Slowly add a certain mass of the activated sludge powder to hydrofluoric acid to etch the silica. Wash with water until the pH reaches 6, then dry. Add potassium carbonate and grind evenly. Pyrolyze at 800℃ for 2 hours under a nitrogen atmosphere. The pyrolyzed powder is then acid-washed, water-washed, and dried to obtain activated sludge-based biochar, labeled SC. The product obtained by directly pyrolyzing without adding potassium carbonate after etching is unactivated biochar (USC).

[0032] Step 2. The microstructure of the samples was investigated using field emission scanning electron microscopy (FE-SEM, Hitachi S-4800). X-ray powder diffraction (XRD) was recorded using a Rigaku D / max 2200 pc diffractometer with Cu target Kα radiation at a wavelength of 0.15418 nm, voltage of 40 kV, and current of 40 mA. The specific surface area and pore structure of the samples were determined using a nitrogen adsorption-desorption apparatus (ASAP2460, micromeritics Inc., USA). After degassing in vacuum at 120 °C for 4 h, the samples were tested at 77 K. The specific surface area was calculated using the Brunauere-Emmette-Teller (BET) method, and the pore size distribution was obtained using the Barrette-Joynere-Halenda (BJH) model.

[0033] Step 3. Prepare a DOL / DME solvent with a volume ratio of 1:1. Mix S and Li2S in the above solvent at a molar ratio of 1:5 in an argon-filled glove box to prepare a Li2S6 solution. After vacuum drying SC, USC and DS at 60 °C for 24 h, take 10 mg of each and immerse them in the above Li2S6 solution for 12 h. Take the supernatant and perform ultraviolet-visible (UV-Vis) spectroscopy testing using a Shimadzu UV-2550 spectrometer.

[0034] Step 4. Mix SC and sublimed sulfur at a mass ratio of 1:4 and heat at 155°C for 24 hours under a nitrogen atmosphere to obtain a carbon-sulfur mixture. Mix the carbon-sulfur mixture, conductive carbon black, and polyvinylidene fluoride at a mass ratio of 8:1:1, add polyvinylpyrrolidone to form a slurry, coat the slurry onto aluminum foil, dry, and cut into sheets to obtain a sulfur cathode.

[0035] Step 5. Using a lithium metal sheet as the negative electrode and a Celgard 2325 polypropylene membrane as the separator, the obtained sulfur positive electrode was assembled into a CR2032 button cell in an argon-atmosphere glove box. The electrolyte used was a 1:1 volume ratio solution of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) with the addition of 1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt% LiNO3.

[0036] Experimental verification: The structural characterization of the samples was performed using field emission scanning electron microscopy, a Rigaku D / max 2200 pc diffractometer, a nitrogen adsorption-desorption spectrometer, an X-ray energy dispersive spectroscopy (EDS) spectrometer, a Fourier transform infrared spectroscopy (FTIR) spectrometer, and a Shimadzu UV-2550 spectrometer. Constant current charge-discharge tests were conducted in the blue battery testing system within a voltage window of 1.6–2.8 V, with discharge times ranging from 0.1 to 0.5 mV∙s. -1 Cyclic voltammetry was performed using a scanning speed of 1.6–2.8 V and a scanning range of 1.6–2.8 V. Electrochemical impedance spectroscopy was performed using a high-voltage impedance analyzer with an AC voltage amplitude of 5 mV and a test frequency range of 10 mV. 3 Electrochemical performance tests were performed on the sample at frequencies ranging from kHz to 10 mHz, and the results are as follows: 1. After dewatering and grinding (DS), the activated sludge appears as granular blocks (~5 μm). Figure 1 (a), while the morphology of unactivated biochar (USC) is similar to that of DS (a). Figure 1 (b) indicates that the pretreatment did not significantly alter its microstructure. Activated biochar (SC) prepared through etching, activation, pyrolysis, and acid washing processes exhibits a hierarchical porous structure. Figure 1 The coexistence of micron-sized macropores (~2 μm) and mesopores (2-5 nm) in the cd: reveals the regulatory role of the activation process on the pore structure. Combined with nitrogen adsorption results ( Figure 3 The specific surface area of ​​SC (cd) is 1643.3 m². 2 ·g⁻¹) compared to DS (260.8 m 2 ·g⁻¹) and USC (400.5 m 2 The ·g⁻¹) was significantly improved, and the pore volume increased by nearly 7 times (1.18 cm⁻¹). 3 ·g⁻¹), and the pore size distribution is concentrated (2-5 nm), confirming its H4 type hysteresis loop characteristics ( Figure 2 a). The hierarchical porous structure provides dual protection for the physical confinement and chemisorption of polysulfides.

[0037] 2. XRD analysis ( Figure 3(a) indicates that SiO2 is the main crystalline phase in DS, which is also a major characteristic of activated sludge. Hydrofluoric acid etching effectively removes SiO2, causing USC and SC to exhibit graphitized characteristics (broad diffraction peaks). In the polysulfide adsorption experiment ( Figure 3 (b) UV-Vis adsorption analysis of the supernatant from the mixture of the analyte and Li₂S₆ showed that DS and USC exhibited some adsorption activity for polysulfides because their porous structure provides a degree of confinement for the polysulfides. However, the supernatant from the mixture of SC and polysulfides showed virtually no characteristic peaks (350 nm) for polysulfides, and the SC and polysulfide solutions were almost transparent in the adsorption photographs. This indicates that SC has a strong adsorption effect on polysulfides, suggesting that the hierarchical pores and polar surface synergistically suppress the shuttle effect, rather than simply providing physical confinement.

[0038] 3. Activated sludge, as a biomass, may contain a large number of oxygen- and nitrogen-containing groups, and its high-temperature carbonization can form oxygen- and nitrogen-doped biochar. FTIR and XPS were used to further reveal the surface chemical advantages of SC (Sludge Carbon). Figure 4 ).exist Figure 4 In a, 3420 cm -1 The peak at this point is related to the stretching vibrations of OH and NH. DS is at 2360 cm⁻¹. -1 There is only a very small absorption peak at this point, while the absorption peaks of USC and SC are significantly enhanced after carbonization, which is related to C≡N. Furthermore, at 1637 cm⁻¹... -1 The absorption peak at 1400 cm⁻¹ is caused by the C=O stretching vibration, while the absorption peak at 1400 cm⁻¹ is caused by the C=O stretching vibration. -1 This is related to the NH stretching vibration. Combined with XPS test results, it can be seen that the SC surface contains oxygen doping (8.7 at% O) and nitrogen doping (3.2 at% N). Figure 2 In b), it is represented by CO (286.0 eV) and C=O bonds (288.5 eV). Figure 4 (b and c in the text), as well as graphitic nitrogen (400.5 eV), pyrrole nitrogen (401.8 eV) and pyridine nitrogen (398.5 eV, Figure 4 (d) This means that SC is not a nonpolar carbon material, but a hierarchical porous biochar with multiple polar groups on its surface and nitrogen and oxygen doping.

[0039] 4. Cyclic performance tests were conducted on SC, USC, and DS under a constant current of 0.1 C. During the first charge-discharge cycle, the SC battery discharged 1165.5 mAh·g. -1 The specific capacity of the USC and DS batteries is higher than that of the USC and DS batteries, which can only discharge 540.6 mAh·g. -1 and 413.7 mAh·g -1 Specific capacity, such as Figure 5 a. The plateau voltage differences for the three batteries are 210.5 mV (SC), 437.0 mV (USC), and 566.7 mV (DS), respectively. The SC battery has a smaller plateau voltage difference and a longer discharge plateau (e.g., Figure 5 (b) indicates that SC effectively limits the dissolution of lithium polysulfides in the electrolyte, thereby releasing more charge. The cycle retention rates of the three batteries after 50 cycles were 92.8% (SC), 25.4% (USC), and 49.4% (DS), respectively. The SC battery, after 1000 cycles under a constant current of 0.1 C (…),… Figure 6 It can also release 581.1 mAh·g -1 The specific capacity is [value missing], and the cycle decay rate is 0.05%. The three lithium-sulfur batteries perform as follows under rate current conditions of 0.1 C to 2 C: [details missing]. Figure 5 c and Figure 7 As shown, the SC lithium-sulfur battery can maintain its previous discharge level after undergoing a high-current charge-discharge cycle followed by a low-current charge-discharge cycle. The other two electrode types, however, cannot return to their original discharge levels. Furthermore, tests were conducted on different sulfur areal loadings, such as... Figure 8 After 500 cycles under a constant current of 0.5 C, 66.8% (2 mg·cm⁻¹) remained. -2 ), 56.9% (4 mg·cm -2 ) and 55.0% (8 mg·cm -2 ) capacity retention rate.

[0040] 5. Electrochemical impedance spectroscopy (EIS) diagrams for three types of lithium-sulfur batteries are shown below. Figure 5 As shown in d, all three types of lithium-sulfur batteries exhibit a semicircle in the mid-to-high frequency range, with the SC battery having the smallest radius and corresponding to the lowest charge transfer impedance (R0). ct =177.9 Ω), which is the fastest electron transfer rate. The SC battery also has the lowest internal resistance at 20.71 Ω, and the activation and pyrolysis processes effectively reduce the internal resistance of the biochar. The DS battery has the highest internal resistance (64.45 Ω), and the USC battery also has a relatively large charge transfer impedance (217.1 Ω), which is consistent with the lower initial discharge capacity and higher decay rate of these two batteries in the constant current charge-discharge test.

[0041] 6. Figure 9 The reduction peaks at 2.34 V and 2.04 V of the SC battery correspond to two discharge plateaus during constant current discharge. The reduction peaks of the other two lithium-sulfur batteries shifted to the left, while the oxidation peaks shifted to the right, indicating significant battery polarization and poor reaction kinetics. At 0.1 mV·s -1 Under constant scan rate conditions, the SC battery showed good overlap in its three CV curves, indicating that its charge-discharge reaction was stable and reversible. Figure 5e and Figure 10 The CV curves of SC batteries under different scan rates show that as the scan rate increases, the reduction peak shifts significantly to the left, while the oxidation peak shifts to the right to some extent. The oxidation and reduction peaks of SC batteries are significantly sharper, indicating that the reaction kinetics are faster and the reaction is easier to carry out during the charge and discharge process. Figure 5 f and Figure 11 The peak current exhibits a linear relationship with the square root of the scan rate, indicating that the reaction in the battery is controlled by lithium-ion diffusion. SC demonstrates a higher current response and a larger peak area, and the Iv of the ABCD peak is... 0.5 The slope is much higher than that of USC and DS, which means that the addition of SC is beneficial to improving the lithium-ion transfer rate, promoting reaction kinetics, and effectively suppressing the shuttle effect.

[0042] Compared with the prior art, the present invention has the following advantages: This study prepared a biochar material with a hierarchical porous structure based on activated sludge. Its surface is rich in oxygen / nitrogen polar groups, enabling dual regulation of physical confinement and chemical adsorption of polysulfides. The SC battery exhibits low internal resistance, rapid lithium-ion diffusion, and excellent reaction kinetics, effectively suppressing the lithium polysulfide shuttle effect, achieving an initial capacity of 1165.5 mAh·g at 0.1 C. -1 The cycle decay rate after 1000 cycles is only 0.05%. Furthermore, at 8 mg·cm⁻¹... -2 It operates stably even with high sulfur loading, and retains 55.0% of its capacity after 500 cycles at 0.5 C. This provides a green path for the development of cathode materials for lithium-sulfur batteries.

[0043] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for preparing activated sludge-based biochar that suppresses the lithium polysulfide shuttle effect, characterized in that, Includes the following steps: Step 1: Select activated sludge produced by municipal wastewater treatment plant as raw material. The activated sludge contains organic components and inorganic suspended solids generated by microbial metabolism. The inorganic suspended solids include SiO2. Dry and grind the dewatered activated sludge into powder and label it as DS. Step 2: Weigh DS powder at a solid-liquid ratio of 1:15 (g / mL), add hydrofluoric acid for etching to remove silica, wash with water until pH 6, and then dry to obtain etched powder. Step 3: Mix the etched powder with potassium carbonate at a mass ratio of 1:2 and then ball mill it. Pyrolyze it at 800°C for 2 hours in a nitrogen atmosphere to obtain the pyrolyzed powder. Step 4: The pyrolyzed powder is acid-washed, water-washed and dried to obtain activated sludge-based biochar SC.

2. The method according to claim 1, characterized in that, In step 1, the activated sludge is dried at 80°C for 24 hours and then ground into powder using a ball mill, which is labeled as DS.

3. The method according to claim 1, characterized in that, In step 2, the concentration of hydrofluoric acid is 40 wt%, the etching time is 6 hours, the solid is collected by centrifugation after the reaction, washed with water until pH=6, and vacuum dried at 80℃ for 12 hours.

4. The method according to claim 1, characterized in that, In step 3, the temperature is 5℃·min -1 Heat to 800℃.

5. The method according to claim 1, characterized in that, The powder after pyrolysis in step 3 was acid-washed with 1M HCl solution for 12 hours, washed with deionized water until neutral, and dried at 60℃ for 24 hours to finally obtain activated sludge-based biochar SC.

6. A lithium-sulfur battery cathode, characterized in that, A composite containing activated sludge-based biochar SC as described in any one of claims 1 or 5 and sulfur in a mass ratio of 1:4 is obtained by heat-treating the composite under a nitrogen atmosphere at 155°C for 24 hours to obtain a carbon-sulfur mixture. The carbon-sulfur mixture, conductive carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1, and polyvinylpyrrolidone is added to form a slurry. The slurry is coated onto aluminum foil, dried, and cut into sheets to obtain a sulfur cathode.

7. A lithium-sulfur battery, characterized in that, Using the sulfur cathode prepared according to claim 6, a battery is assembled in an argon atmosphere using the sulfur cathode, a lithium metal sheet as the negative electrode, and a polypropylene membrane as the separator.

8. A lithium-sulfur battery according to claim 7, characterized in that, The electrolyte was a 1,3-dioxolane and ethylene glycol dimethyl ether solution in a volume ratio of 1:1, with the addition of 1.0 M lithium bis(trifluoromethanesulfonyl)imide and 1 wt% LiNO3.

9. A method for suppressing the lithium polysulfide shuttle effect by introducing activated sludge-based biochar, characterized in that... Includes the following steps: Step (1) The activated sludge is subjected to acid etching treatment, alkaline activator mixing and inert atmosphere pyrolysis in sequence to obtain activated sludge-based biochar SC with multi-level porous structure and oxygen / nitrogen doping. Step (2) The SC is combined with sulfur to form a positive electrode material and then assembled into a lithium-sulfur battery.

10. The method according to claim 9, characterized in that, The acid etching process in step (1) uses hydrofluoric acid, the alkaline activator is potassium carbonate, the pyrolysis temperature is 800℃, and the time is 2 hours.

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