An activated hemp powder material and its use in the preparation of lithium-sulfur battery separators

Abstract

The application belongs to the field of nanometer materials and lithium-sulfur batteries, and discloses application of activated hemp powder in preparation of lithium-sulfur battery diaphragm. The application first removes impurities from hemp core powder with hydrochloric acid, then activates the hemp core powder with potassium salt in a muffle furnace, and carbonizes the activated material, potassium salt and melamine in the previous step under the protection of inert gas. In this process, the potassium salt can effectively activate the hemp core powder, etch the surface of the hemp core powder to form a rich porous structure, and the melamine forms nitrogen-doped biomass hemp powder through high-temperature carbonization. After the reaction is completed, the target product is obtained. The nitrogen-doped hemp powder material is used as a diaphragm modification material and is coated on a commercial diaphragm by a doctor blade method, and can effectively improve the electrochemical performance of lithium-sulfur batteries when applied in lithium-sulfur batteries.

Description

Technical Field

[0001] This invention belongs to the fields of nanomaterials and lithium-sulfur batteries, and specifically relates to an activated hemp powder material and its application in the preparation of lithium-sulfur battery separators. Background Technology

[0002] The rapid development of high technology relies heavily on energy consumption and use. However, limited fossil fuel resources cannot meet the ever-growing demands of the population. Therefore, the development of renewable and clean energy is imperative, making the research of efficient and safe energy storage systems crucial. Compared to the widely used fuel cells and lithium-ion battery energy storage systems, lithium-sulfur batteries possess a high specific energy (2600 Wh / kg). -1 With its advantages such as low cost of raw materials and environmental friendliness, it is considered a high-capacity energy storage system with great development potential.

[0003] However, lithium-sulfur batteries have not yet achieved large-scale practical application, mainly due to the following reasons: 1. The insulation properties of sulfur and lithium sulfide during charging and discharging, as well as their significant volume expansion (~80%); 2. During the electrochemical reaction process, the intermediate product lithium polysulfide is soluble in organic electrolytes, thus easily migrating between the positive and negative electrodes, forming a "shuttle effect" that reduces the utilization efficiency of active materials, leading to battery capacity loss and decreased cycle performance; 3. The high chemical reactivity of lithium metal results in unstable dendrite formation on its surface, which also limits the application of lithium-sulfur batteries.

[0004] In recent years, much research has focused on improving the performance of lithium-sulfur batteries to realize their practical application. Among these efforts, the performance of the separator, a crucial component of the lithium-sulfur battery system, directly impacts its electrochemical performance, making it a key research area. The main research methods involve designing novel separators and modifying commercially available separators. Compared to novel separator design, modifying commercially available separators offers advantages in terms of simplicity and ease of use, leading to more extensive research in this area. Nanocarbon materials, as excellent separator modification materials, possess good conductivity and superior physical adsorption capabilities during charge and discharge, effectively enhancing the electrochemical stability of lithium-sulfur batteries. However, the poor chemical affinity between nonpolar carbon materials and polar lithium polysulfides is insufficient to effectively limit the "shuttle effect" during charge and discharge. Therefore, researching modified separators with excellent conductivity, strong chemical adsorption, and the ability to accelerate sulfur oxidation / reduction reactions is an effective way to improve the electrochemical performance and cycle stability of lithium-sulfur batteries. Biomass materials, as naturally occurring carbon materials, can be rationally processed and applied to the modification of commercial separators to improve the performance of lithium-sulfur batteries. This not only enables the practical application of lithium-sulfur batteries but also provides a scientific approach for the reuse of biomass materials. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing activated hemp powder material.

[0006] Another object of the present invention is to provide an activated hemp powder material prepared by the above method.

[0007] Another objective of this invention is to provide the application of the above-mentioned activated hemp powder material in the preparation of lithium-sulfur battery separators.

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

[0009] A method for preparing activated hemp powder material includes the following steps:

[0010] (1) Preparation of first activated hemp powder: Hemp stalk core powder and potassium salt are mixed and placed in a crucible, then activated in a muffle furnace, and then washed and dried to obtain first activated hemp powder;

[0011] (2) Preparation of activated hemp powder material: The first activated hemp powder obtained in step (1) is mixed with potassium salt and melamine and placed in a porcelain boat. Then, it is carbonized under an inert atmosphere (such as N2), and then washed and dried to obtain activated hemp powder material.

[0012] The hemp stalk core powder mentioned in step (1) includes a purification step before mixing with potassium salt, as follows: the hemp stalk core powder is purified in a heated hydrochloric acid solution, then washed and dried; wherein the concentration of the hydrochloric acid solution is 1-3 mol / L, preferably 3 mol / L, the heating and drying are carried out for 8-16 hours, the temperature is 60-80℃, preferably 60℃, and the heating and drying time is 8-16 hours, preferably 12 hours.

[0013] The potassium salt mentioned in step (1) is at least one of KCl, KNO3, KHCO3, and K3C6H5O7, preferably K3C6H5O7.

[0014] The mass ratio of hemp stalk core powder to potassium salt in step (1) is 1:0.5-3, preferably 1:2.

[0015] The activation mentioned in step (1) refers to keeping the temperature at 250-350℃ for 1-3 hours, preferably at 300℃ for 2 hours.

[0016] The potassium salt mentioned in step (2) is at least one of KCl, KNO3, KHCO3, and K3C6H5O7, preferably K3C6H5O7.

[0017] The mass ratio of activated hemp powder to potassium salt and melamine in step (2) is 1:0-2:0-2, preferably 1:0-1:0-1.

[0018] The carbonization mentioned in step (2) refers to holding at 600-800℃ for 2-4 hours, preferably at 700℃ for 3 hours.

[0019] The mass ratio of activated hemp powder to potassium salt and melamine mentioned in step (2) will affect the composition of the product.

[0020] Preferably, when the potassium salt and melamine mentioned in step (2) are not both 0, especially when the mass ratio of activated hemp powder to potassium salt and melamine is 1:1:1, the product obtained is nitrogen-doped activated hemp powder material, denoted as NHPC;

[0021] Preferably, when the melamine in step (2) is 0 and the potassium salt is not 0, especially when the mass ratio of activated hemp powder to potassium salt is 1:1, the product obtained is a secondary activated hemp powder material, denoted as HPC;

[0022] Preferably, when the melamine in step (2) is not 0 and the potassium salt is 0, especially when the mass ratio of activated hemp powder to melamine is 1:1, the product obtained is nitrogen-doped hemp powder material, denoted as NPC;

[0023] An activated hemp powder material prepared by the above method.

[0024] The above-mentioned activated hemp powder material is used in the preparation of lithium-sulfur battery separators.

[0025] A lithium-sulfur battery separator is prepared by the following method: activated hemp powder, a conductive agent, and a binder are mixed evenly in a solvent; the resulting slurry is then uniformly coated onto a commercial separator using a doctor blade method; and vacuum drying completes the lithium-sulfur battery separator. Compared to ordinary commercial separators, this modified separator significantly improves the cycle stability of lithium-sulfur batteries.

[0026] The conductive agent is preferably Super P Li; the binder is preferably PVDF; and the solvent is preferably N-methylpyrrolidone.

[0027] The preferred mass ratio of the biomass hemp powder material, conductive agent, and binder is 8:1:1.

[0028] This invention first removes impurities from hemp stalk core powder using hydrochloric acid, then activates it with potassium salt in a muffle furnace, and finally carbonizes the activated material, potassium salt, and melamine together at high temperature under N2 protection. During this process, the potassium salt effectively activates the hemp stalk core powder, etching its surface to form a rich porous structure, while the melamine, through high-temperature carbonization, causes the biomass hemp powder to become nitrogen-rich doped. After the reaction is complete, the target product is obtained. Using this nitrogen-doped hemp powder material as a membrane modification material, it is coated onto commercially available membranes using a doctor blade method. Its application in lithium-sulfur batteries can effectively improve the electrochemical performance of lithium-sulfur batteries.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] (1) The biomass hemp powder materials (NHPC, HPC and NPC) of the present invention have a simple synthesis process. The porous structure of the material can be achieved by activating the hemp stalk core powder with potassium salt, and nitrogen-rich doping can be formed by annealing with melamine, which can realize large-scale industrial production.

[0031] (2) The biomass hemp powder materials (NHPC, HPC and NPC) of the present invention, as metal-free porous nitrogen-carbon materials, can greatly improve the electrochemical performance of lithium-sulfur batteries as membrane modification materials. Attached Figure Description

[0032] Figure 1 The X-ray diffraction (XRD) spectra of NHPC, HPC, and NPC prepared in Examples 1, 2, and 3 are shown.

[0033] Figure 2 The image shows a scanning electron microscope (SEM) image of the NHPC material prepared in Example 1.

[0034] Figure 3 The image shows a scanning electron microscope (SEM) image of the NHPC material prepared in Example 1.

[0035] Figure 4 The specific capacity-voltage diagrams of the NHPC / PP, HPC / PP, NPC / PP, and PP lithium-sulfur batteries prepared in Examples 1, 2, and 3 at 0.1C are shown.

[0036] Figure 5 The specific capacity-voltage diagrams of the NHPC / PP, HPC / PP, NPC / PP, and PP lithium-sulfur batteries prepared in Examples 1, 2, and 3 at 0.5C are shown.

[0037] Figure 6The graphs show the cycle performance of NHPC / PP, HPC / PP, NPC / PP, PC / PP, and PP lithium-sulfur batteries prepared in Examples 1, 2, 3, and Comparative Example 1 at 0.5C. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0039] Unless otherwise specified, all reagents used in the examples are commercially available.

[0040] The assembly and testing methods for the lithium-sulfur battery described in the examples are as follows:

[0041] (1) Preparation of NHPC / PP, HPC / PP, NPC / PP and PC / PP modified separators: Biomass hemp powder materials (NHPC, HPC, NPC, PC), conductive agent Super P Li and binder PVDF were mixed in a mass ratio of 8:1:1, with N-methylpyrrolidone (NMP) as solvent and magnetically stirred for 12 h to achieve uniform mixing. The resulting slurry was then uniformly coated onto commercial separator Celgard2500 (PP) using a doctor blade method. After vacuum drying, the resulting separators were cut into discs with a diameter of 19 mm.

[0042] (2) Preparation of the positive electrode: Ketjen Black ECP-200L and sublimed sulfur were thoroughly ground and mixed in an agate mortar at a mass ratio of 1:3 for 15 min, then placed in a porcelain boat. The mixture was then kept at 155℃ for 12 h under N2 atmosphere, followed by a further warming at 200℃ for 30 min until the reaction was complete, yielding a C / S composite material. 80 wt% C / S, 10 wt% Super P Li, and 10 wt% La133 (5 wt% in water) were mixed uniformly with deionized water as the solvent using magnetic stirring for 12 h. The resulting slurry was then uniformly coated onto the carbon coating layer of a carbon-coated aluminum foil using a scraper method. After vacuum drying, the resulting electrode was cut into round pieces with a diameter of 12 mm.

[0043] (3) Assembly of coin cells: The following operations are all performed in a glove box filled with argon gas. The CR2032 coin cells are assembled with lithium foil as the negative electrode, C / S electrode as the positive electrode, modified membrane as the separator, and LiTFSI electrolyte (1.0 mol / L LiTFSI in DME / DOL=1:1 vol% with 1.0 wt% LiNO3, Suzhou Zhongyan Chemical Technology Co., Ltd.) as the electrolyte, and the amount of electrolyte used is 30 μL for each cell.

[0044] (4) Testing the cycle stability of lithium-sulfur batteries: After the assembled button batteries were left to stand for 12 hours, constant current charge and discharge tests were performed on them at different current densities using the Newwell battery testing system. The working voltage range of the batteries was 1.7-2.8V.

[0045] Example 1

[0046] The preparation method of nitrogen-doped activated hemp powder material (NHPC) in this embodiment includes the following specific steps:

[0047] 10g of hemp stalk core powder was dispersed in 100mL of 3mol / L HCl solution, then magnetically stirred in an oil bath at 60℃ for 12h. After filtration, washing, and drying at 60℃, it was mixed with K3C6H5O7 at a mass ratio of 1:2 and kept at 300℃ for 2h in a muffle furnace with a heating rate of 5℃ / min. -1 Activated hemp powder was obtained. Then, the activated hemp powder was mixed evenly with K3C6H5O7 and melamine at a mass ratio of 1:1:1, and placed in a tube furnace. Under a nitrogen atmosphere, the mixture was heated at 3°C ​​for [time missing]. -1 The sample obtained after heating at a rate of 700℃ and high-temperature carbonization for 3 hours is NHPC.

[0048] The XRD pattern of NHPC in this embodiment is as follows: Figure 1 As shown, the diffraction pattern of NHPC material has two main peaks, located at 26.5° and 44.0°, respectively. The characteristic peak located at 2θ = 26.5° corresponds to the (0 0 2) crystal plane of nitrogen-doped carbon, indicating the successful synthesis of NHPC. Furthermore, the SEM image of NHPC is shown below. Figure 2 and Figure 3 As shown, it can be clearly observed that the surface of NHPC material has a rich porous structure with a large pore size.

[0049] The synthesized NHPC was used to modify commercial PP separators, which were then assembled into NHPC / PP lithium-sulfur batteries. The specific capacity-voltage diagram of the first charge-discharge cycle of this lithium-sulfur battery at 0.1C is shown in the figure below. Figure 4 As shown in the figure, the initial discharge specific capacity of the NHPC / PP battery is as high as 1568.0 mA hg. -1 ; and from Figure 5 The lithium-sulfur battery exhibits an initial discharge specific capacity of 1129.2 mA hg at 0.5C. -1 ; and from Figure 6 The cycling performance graph at 0.5C shows that after 100 cycles, its discharge specific capacity remains at 1011.8 mA hg. -1 The capacity retention rate is as high as 89.6%, far exceeding that of unmodified commercial membrane batteries (391.3 mA hg). -1(61.6%).

[0050] Example 2

[0051] The preparation method of the secondary activated hemp powder material (HPC) in this embodiment includes the following specific steps:

[0052] 10g of hemp stalk core powder was dispersed in 100mL of 3mol / L HCl solution, then magnetically stirred in an oil bath at 60℃ for 12h. After filtration, washing, and drying at 60℃, it was mixed with K3C6H5O7 at a mass ratio of 1:2 and kept at 300℃ for 2h in a muffle furnace with a heating rate of 5℃ / min. -1 Activated hemp powder was obtained. Then, the activated hemp powder was mixed evenly with K3C6H5O7 at a mass ratio of 1:1, placed in a tube furnace, and heated at 3℃ for 1 minute under a N2 atmosphere. -1 The sample obtained after heating at a rate of 700℃ and high-temperature carbonization for 3 hours is HPC.

[0053] The XRD pattern of HPC in this embodiment is as follows: Figure 1 As shown, the diffraction pattern of NHPC material has two main peaks, at 21.6° and 44.0° respectively. The characteristic peak located at 2θ=21.6° corresponds to the (0 0 2) crystal plane of carbon, indicating that HPC was successfully synthesized.

[0054] The synthesized HPC was used to modify commercial PP separators, which were then assembled into HPC / PP lithium-sulfur batteries. The specific capacity-voltage diagram of the lithium-sulfur battery at 0.1C during the first charge-discharge cycle is shown in the figure. Figure 4 As shown in the figure, the initial discharge specific capacity of the HPC / PP battery is as high as 1289.3 mA hg. -1 ; and from Figure 5 The lithium-sulfur battery exhibits an initial discharge specific capacity of 1034.0 mAh g at 0.5C. -1 ; and from Figure 6 The cycling performance graph at 0.5C shows that after 100 cycles, its discharge specific capacity remains at 886.7 mA hg. -1 The capacity retention rate is as high as 85.7%, far exceeding that of unmodified commercial membrane batteries (391.3 mA hg). -1 (61.6%).

[0055] Example 3

[0056] The specific steps of the preparation method of nitrogen-doped hemp powder material (NPC) in this embodiment are as follows:

[0057] 10g of hemp stalk core powder was dispersed in 100mL of 3mol / L HCl solution, then magnetically stirred in an oil bath at 60℃ for 12h. After filtration, washing, and drying at 60℃, it was mixed with K3C6H5O7 at a mass ratio of 1:2 and kept at 300℃ for 2h in a muffle furnace with a heating rate of 5℃ / min. -1 Activated hemp powder was obtained. Then, the activated hemp powder was mixed with melamine at a mass ratio of 1:1, and placed in a tube furnace. Under a nitrogen atmosphere, the mixture was heated at 3°C ​​for [time missing]. -1 The sample obtained after heating at a rate of 700℃ and high-temperature carbonization for 3 hours is NHPC.

[0058] The XRD pattern of the NPC in this embodiment is as follows: Figure 1 As shown, the diffraction pattern of NHPC material has two main peaks, at 26.5° and 44.0° respectively. The characteristic peak located at 2θ = 26.5° corresponds to the (0 0 2) crystal plane of nitrogen-doped carbon, indicating that NPC was successfully synthesized.

[0059] The synthesized NPC was used to modify a commercial PP separator, which was then assembled into an NPC / PP lithium-sulfur battery. The specific capacity-voltage diagram of the lithium-sulfur battery at 0.1C during the first charge-discharge cycle is shown in the figure. Figure 4 As shown in the figure, the initial discharge specific capacity of the NPC / PP battery is as high as 1373.4 mA hg. -1 ; and from Figure 5 The lithium-sulfur battery exhibits an initial discharge specific capacity of 972.2 mA hg at 0.5C. -1 ; and from Figure 6 The cycling performance graph at 0.5C shows that after 100 cycles, its discharge specific capacity remains at 865.8 mA hg. -1 The capacity retention rate is as high as 89.1%, far exceeding that of unmodified commercial membrane batteries (391.3 mA hg). -1 (61.6%).

[0060] Comparative Example 1

[0061] The preparation method of the hemp powder material (PC) in this comparative example is as follows:

[0062] 10g of hemp stalk core powder was dispersed in 100mL of 3mol / L HCl solution, and then magnetically stirred in an oil bath at 60℃ for 12h. After filtration, washing, and drying at 60℃, hemp powder, i.e., PC, was obtained.

[0063] The synthesized PC was used to modify commercially available PP separators, which were then assembled into PC / PP lithium-sulfur batteries. Figure 6 The cycling performance graph at 0.5C shows that the initial discharge specific capacity is 852.1 mA hg. -1After 100 cycles, its discharge specific capacity remained at 712.5 mA hg. -1 The capacity retention rate was relatively low (83.6%), but still higher than that of unmodified commercial membrane batteries (391.3 mA hg). -1 (61.6%), slightly lower than nitrogen-doped activated hemp powder materials.

[0064] The electrochemical performance comparison above shows that the NHPC material obtained in Example 1 is the best candidate as a modification layer for lithium-sulfur battery separators.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing activated hemp powder material, characterized in that... Includes the following steps: (1) Preparation of first activated hemp powder: Hemp stalk core powder and potassium salt are mixed and placed in a crucible, then activated in a muffle furnace, and then washed and dried to obtain first activated hemp powder; (2) Preparation of activated hemp powder material: The first activated hemp powder obtained in step (1) is mixed with potassium salt and melamine and placed in a porcelain boat. Then, it is carbonized under an inert atmosphere, and then washed and dried to obtain activated hemp powder material; The potassium salt mentioned in step (1) is at least one of KCl, KNO3, KHCO3, and K3C6H5O7; The activation mentioned in step (1) refers to incubation at 250-350°C for 1-3 hours; The potassium salt mentioned in step (2) is K3C6H5O7; The carbonization mentioned in step (2) refers to holding at 600-700°C for 2-4 hours.

2. The method for preparing activated hemp powder material according to claim 1, characterized in that: The hemp stalk core powder mentioned in step (1) includes a purification step before mixing with potassium salt, as follows: the hemp stalk core powder is purified in a heated hydrochloric acid solution, and then washed and dried; wherein the concentration of the hydrochloric acid solution is 1-3 mol / L, the heating temperature is 60-80℃, and the heating time is 8-16 h.

3. The method for preparing activated hemp powder material according to claim 1, characterized in that: The potassium salt mentioned in step (1) is K3C6H5O7.

4. The method for preparing activated hemp powder material according to claim 1, characterized in that: The mass ratio of hemp stalk core powder to potassium salt in step (1) is 1:0.5-3; The activation mentioned in step (1) refers to keeping the temperature at 300°C for 2 hours.

5. The method for preparing activated hemp powder material according to claim 4, characterized in that: The mass ratio of hemp stalk core powder to potassium salt in step (1) is 1:

2.

6. The method for preparing activated hemp powder material according to claim 1, characterized in that: The mass ratio of activated hemp powder to potassium salt and melamine in step (2) is 1:1:

1.

7. The method for preparing activated hemp powder material according to claim 1, characterized in that: The carbonization mentioned in step (2) refers to holding at 700°C for 3 hours.

8. An activated hemp powder material prepared by the method according to any one of claims 1-7.

9. The application of the activated hemp powder material according to claim 8 in the preparation of lithium-sulfur battery separators.

10. A lithium-sulfur battery separator, characterized in that... The lithium-sulfur battery separator is prepared by the following method: the activated hemp powder material, conductive agent and binder described in claim 8 are stirred and mixed evenly in a solvent, and then the resulting slurry is uniformly coated on a commercial separator by a scraper method. After vacuum drying, the lithium-sulfur battery separator is formed.

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