A sulfur-doped hard carbon material, a preparation method and application thereof

Abstract

The application belongs to the technical field of metal battery negative electrode materials, and specifically discloses a sulfur-doped hard carbon material and a preparation method and application thereof. The preparation method of the sulfur-doped hard carbon material comprises the following steps: dissolving chitosan in methanesulfonic acid and mixing uniformly; then adding into diethyl ether until white powder is obtained; then removing residual solvent in the white powder to obtain sulfated chitosan; and finally calcining the sulfated chitosan to obtain the sulfur-doped hard carbon material. The sulfur-oxygen acid radical molecular template method effectively anchors the template on the biomass chain through a chemical reaction between the template and the biomass, in the subsequent high-temperature pyrolysis process, the molecular template is decomposed and sacrificed and leaves sub-nanopores in situ, and further effective heteroatom doping is carried out on the pore surface. When the sulfur-doped hard carbon material is applied as a negative electrode in a sodium ion battery, the occurrence of electrolyte-carbon negative electrode interface side reactions can be effectively inhibited, and the reversible adsorption and desorption of sodium ions in the carbon matrix can be promoted, and the first cycle coulombic efficiency is as high as 100%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal battery negative electrode materials, and particularly relates to a sulfur-doped hard carbon material and a preparation method and application thereof. BACKGROUND

[0002] Carbonaceous materials are considered as the most promising candidate system for SIB negative electrode materials due to their abundant resources, low cost and controllable sodium storage active sites. However, due to the large radius of sodium ions and slow solid-phase diffusion kinetics, the capacity retention rate and cycle stability of carbon-based negative electrodes under high current density still face severe challenges. In recent years, the strategy of constructing hierarchical pore structures (micropore-mesopore-macropore system) to optimize the sodium ion transmission path has been widely studied. Theoretical calculations and experiments show that the high-permeability pore structure can significantly reduce the bulk diffusion energy barrier of sodium ions, thereby improving the rate performance of hard carbon materials. However, such high-porosity structures are often accompanied by a large number of topological defects and exposure of active edge sites, resulting in irreversible sodium loss and a significant reduction in the first-cycle coulombic efficiency. Further application to full-cell systems, the sodium storage imbalance caused by negative electrode interface side reactions (such as electrolyte decomposition and excessive growth of solid-state electrolyte layers) will exacerbate the irreversible consumption of active sodium at the positive electrode, resulting in a decrease in full-cell energy density of more than 20%. Therefore, it is believed that in the carbon-based negative electrode system of sodium-ion batteries, "high rate performance" and "high first-cycle coulombic efficiency" are difficult to achieve simultaneously.

[0003] Studies have shown that the main reason for the reduction of the first-cycle coulombic efficiency is the uncontrollable side reactions at the electrolyte-carbon negative electrode interface and the irreversible consumption of active sodium caused by high-activity defects in the carbon negative electrode. Based on this, researchers have found through experiments that when the pore size of the carbon negative electrode is reduced to sub-nanopores (<1 nm), the electrolyte solvent molecules with large sizes are difficult to infiltrate into the pores, which can greatly reduce the electrolyte-carbon negative electrode interface area and reduce the occurrence of interface side reactions; at the same time, the high-activity defects in the carbon matrix can also be passivated by appropriate surface modification, thereby promoting the reversible adsorption and desorption behavior of sodium ions in the carbon matrix and reducing the irreversible consumption of sodium ions. However, there is currently no effective method to construct a uniform sub-nanoporous carbon matrix while effectively passivating the surface chemical state of carbon; considering the link between pore structure construction and surface chemical regulation, there are few reports on methods that can simultaneously control both in one step to achieve "high rate performance" and "high first-cycle coulombic efficiency". SUMMARY

[0004] The purpose of this invention is to address the above-mentioned shortcomings of the prior art by providing a sulfur-doped hard carbon material, its preparation method, and its application. By utilizing the in-situ activation pore-forming technology of sulfur oxyate molecular templates, abundant and uniform sub-nanopores are introduced into biomass-derived carbon, and heteroatoms are simultaneously in-situ doped onto the pore surface to passivate the pore surface, thereby constructing sulfur-doped sub-nanopore carbon, which simultaneously achieves "high rate performance" and "high first-cycle coulombic efficiency".

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The first objective of this invention is to provide a method for preparing sulfur-doped hard carbon materials, comprising the following steps:

[0007] S1. Chitosan is dissolved in methanesulfonic acid. After the reaction, the sulfonate ions are anchored on the chitosan chains to obtain the first mixed solution.

[0008] S2. Add the first mixed solution to the ether until a white powder is dissolved.

[0009] S3. Remove the residual solvent from the obtained white powder to obtain sulfated chitosan;

[0010] S4. The obtained sulfated chitosan was calcined to obtain sulfur-doped nanoporous carbon;

[0011] The calcination process involves heating from room temperature to 600-1500℃ at a rate of 1-10℃ / min, and holding at that temperature for 60-240 min.

[0012] Further, in step S1, the mass concentration of chitosan in the first mixed solution is 0.05~0.5 g / mL.

[0013] Further, in step S2, the volume ratio of the first mixed solution to diethyl ether is (10~30):65.

[0014] Further, in step S3, the process of removing residual solvent involves placing the obtained white powder in the air for 3-4 hours, and then drying it at 40°C-50°C.

[0015] A second objective of this invention is to provide a sulfur-doped hard carbon material prepared using the above-described preparation method.

[0016] Furthermore, the sulfur-doped hard carbon material d 002 Spacing 0.37~0.42 nm.

[0017] Furthermore, the specific surface area of ​​the sulfur-doped hard carbon material is 800~1400 m². 2 g -1 .

[0018] A third object of the present application is to provide a hard carbon negative electrode material, comprising the above-mentioned sulfur-doped hard carbon material.

[0019] A fourth object of the present application is to provide an electrode sheet, wherein the above-mentioned sulfur-doped hard carbon material is used as the active material, a sodium carboxymethyl cellulose solution is used as the binder, and conductive carbon black is used as the conductive agent, which are mixed in a predetermined ratio, deionized water is added and stirred to form a slurry with suitable viscosity, and then coated on a copper foil and dried, and then cut into a round sheet-shaped electrode sheet.

[0020] A fifth object of the present application is to provide a sodium ion battery, comprising: a shell and an electrode assembly arranged in the shell, the electrode assembly is arranged in the shell, the electrode assembly comprises a negative electrode sheet and a positive electrode sheet, the negative electrode sheet comprises a negative electrode current collector and an active material layer coated on the negative electrode current collector, and the active material layer comprises the above-mentioned sulfur-doped hard carbon material or the hard carbon negative electrode material.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) The sulfur-doped hard carbon material provided by the present application uses a sulfur oxyacid molecular template method, which effectively anchors the template on the biomass chain through a chemical reaction between the template and the biomass. The specific process is as follows: during the dissolution of chitosan in methane sulfonic acid, the amino groups on the chitosan chain undergo an acid-base neutralization reaction with methane sulfonic acid. Due to the electrostatic interaction between the sulfonate and the -NH3 group and the hydrogen bonding effect formed between the sulfonate and the hydroxyl group, the chitosan chain is opened, and at the same time, the sulfonate is uniformly anchored on the chitosan chain to obtain sulfated chitosan. In the subsequent high-temperature pyrolysis process, the molecular template decomposes and sacrifices itself in situ, leaving sub-nanopores, and further effectively doping heteroatoms on the pore surface to obtain a material with uniform pore size and stable surface chemical state. +

[0023] (2) When the sulfur-doped hard carbon material negative electrode of the present application is applied in a sodium ion battery, it can effectively inhibit the occurrence of electrolyte-carbon negative electrode interface side reactions, and promote the reversible adsorption and desorption of sodium ions in the carbon matrix, showing extremely high first-cycle coulombic efficiency, which can reach nearly 100%. The slope area (0.1-1V) accounts for more than 80%, greatly reducing the plating sodium behavior in the low voltage area, reducing the generation of sodium dendrites, and reducing the use risk.

[0024] (3) The present application prepares a sulfur-doped sub-nanoporous carbon negative electrode through a simple in-situ activation pore-forming technology of a sulfur oxyacid molecular template, and the preparation method is simple, the raw materials are widely available, the cost is low, and the safety is high. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 and Figure 2 ​BET plot of the sulfur-doped hard carbon material prepared in Example 1, wherein Figure 1 is a carbon dioxide adsorption-desorption plot, Figure 2 is a pore size distribution plot;

[0026] Figure 3 SEM plot of the sulfur-doped hard carbon material prepared in Example 1;

[0027] Figure 4 TEM plot of the sulfur-doped hard carbon material prepared in Example 1;

[0028] Figure 5 XPS analysis spectrum of the sulfur-doped hard carbon material prepared in Example 1, wherein a) is the full spectrum, b) is the N1s high-resolution spectrum, c) is the O1s high-resolution spectrum, and d) is the S2p high-resolution spectrum;

[0029] Figure 6 XRD analysis spectrum of the sulfur-doped hard carbon material prepared at different temperatures;

[0030] Figure 7 Raman analysis spectrum of the sulfur-doped hard carbon material prepared in Example 1;

[0031] Figure 8 Sodium storage performance characterization of the sulfur-doped hard carbon material prepared in Example 1: rate curves at different current densities;

[0032] Figure 9 Sodium storage performance characterization of the sulfur-doped hard carbon material prepared in Example 1: first three cycle charge-discharge curves;

[0033] Figure 10 Sodium storage performance characterization of the sulfur-doped hard carbon material prepared in Example 1: cycle charge-discharge curves at a low current density (0.05 A g -1 );

[0034] Figure 11 Sodium storage performance characterization of the sulfur-doped hard carbon material prepared at different low-temperature calcination temperatures: rate curves at different current densities;

[0035] Figure 12 Sodium storage performance characterization of the sulfur-doped hard carbon material prepared at different high-temperature calcination temperatures: rate curves at different current densities. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present application clearer, the specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings. The specific techniques or conditions not specified in the examples are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained by purchase.

[0037] The present application provides a preparation method of sulfur-doped hard carbon material, comprising the following steps:

[0038] S1, dissolving chitosan in methane sulfonic acid, after reaction, sulfonate is anchored on the chitosan chain, to obtain a first mixed solution;

[0039] S2, adding the first mixed solution into diethyl ether until white powder is precipitated out;

[0040] S3, removing the residual solvent in the obtained white powder to obtain sulfated chitosan;

[0041] S4, calcining the obtained sulfated chitosan to obtain sulfur-doped sub-nanoporous carbon;

[0042] The program of the calcination is to heat from room temperature to 600-1500℃ at a heating rate of 1-10℃ / min, and to keep the temperature for 60-240 min.

[0043] In specific implementation, the mass concentration of chitosan in the first mixed solution is 0.05-0.5 g / mL; the volume ratio of the first mixed solution to diethyl ether is (10-30):65; in step S3, the process of removing the residual solvent is to place the obtained white powder in air for 3-4 h, and then to dry at 40-50℃.

[0044] The d 002 spacing of the sulfur-doped hard carbon material prepared by the above method is in the range of 0.37-0.42 nm, the specific surface area is 800-1400 m 2 g -1 . It should be noted that the d 002 is the interlayer spacing of the (002) crystal plane of the carbon material.

[0045] In some embodiments, the electrode sheet can be prepared by using conventional methods in the art, for example, the above-mentioned sulfur-doped hard carbon material is used as the active material, a sodium carboxymethyl cellulose solution is used as the binder, and conductive carbon black is used as the conductive agent, which are mixed according to a predetermined ratio, deionized water is added and stirred to form a slurry with appropriate viscosity, then coated onto a copper foil and dried, and then cut into a round sheet-shaped electrode, thereby obtaining the electrode.

[0046] In some embodiments, a sodium-ion battery can also be prepared by methods conventional in the art, for example, a sodium-ion battery includes a housing and an electrode assembly disposed in the housing, wherein the electrode assembly includes a negative electrode sheet and a positive electrode sheet, the negative electrode sheet includes a negative electrode current collector and an active material layer coated on the negative electrode current collector, and the active material layer includes the sulfur-doped hard carbon material or the hard carbon negative electrode material described above.

[0047] The embodiments of the present application have achieved some positive effects during research and development or use, and indeed have great advantages compared with the prior art, which are described below in combination with data, graphs and the like in the test process.

[0048] Example 1

[0049] The embodiments of the present application provide a preparation method of a sulfur-doped hard carbon material, including the following steps:

[0050] (1) 2 g of chitosan is dissolved in 20 mL of methane sulfonic acid, and stirred at room temperature for 3-5 h until completely dissolved;

[0051] (2) The mixed solution obtained above is poured into 65 mL of vigorously stirred ether, and a white powder is dissolved out, and then 300 mL of ether is used to further dissolve the excess methane sulfonic acid;

[0052] (3) The obtained white powder is placed in air for 3-4 h to volatilize most of the ether, and then transferred to a 40℃ vacuum oven for complete drying to obtain sulfated chitosan;

[0053] (4) The obtained sulfated chitosan is transferred to a tube furnace for calcination (room temperature-900℃, 3℃ / min temperature rise, and high temperature holding for 120 min), and finally cooled to room temperature to obtain sulfur-doped sub-nanoporous carbon, named SCSC-900; wherein S represents methane sulfonic acid, CS represents chitosan, and 900 represents the temperature of carbonization of sulfated chitosan.

[0054] The obtained sulfur-doped sub-nanoporous carbon is applied to a sodium-ion battery negative electrode, a metal sodium is used as a counter electrode, a Whatman glass fiber is used as a separator, and 1 M NaPF6 (DME=100 vol.%) is used as an electrolyte to assemble a half-cell system, and charge-discharge test characterization is carried out in a voltage range of 0.01-3 V.

[0055] With reference to Figure 1 and Figure 2 , the sulfur-doped sub-nanoporous carbon SCSC-900 prepared in Example 1 of the present application has a high specific surface area and a high micropore ratio, and the micropore distribution is concentrated at 0.52 nm, and the specific surface area is 1028 m 2 g -1 ; with reference to Figure 3 andFigure 4 , which indicates that the sulfur-doped hard carbon material prepared by the embodiment of the present application has no obvious mesopore structure on the surface; refer to Figure 5 , which indicates that the electrode material prepared by the embodiment of the present application successfully incorporates sulfur (2.02 at.%), and the above indicates that the embodiment of the present application successfully prepares sulfur-doped sub-nanoporous carbon.

[0056] Referring to Figure 6 , it can be known that the d 002 spacing of the sulfur-doped hard carbon material prepared in the embodiment is 0.386; refer to Figure 7 , which is the Raman spectrum of the sulfur-doped hard carbon material prepared in the embodiment, and the ratio of the D peak to the G peak is 0.95; refer to Figure 8 and Figure 9 , which indicates that the sulfur-doped hard carbon material as a carbon negative electrode of a sodium ion battery exhibits high rate performance (160.8 mAh g -1 at 2 A g -1 ) and high first-cycle coulombic efficiency (97%); refer to Figure 10 , which indicates that the sulfur-doped hard carbon material as a carbon negative electrode of a sodium ion battery activates groups and increases active sites during the cycle process, and the capacity is significantly improved.

[0057] Embodiment 2

[0058] The embodiment prepared a sulfur-doped carbon negative electrode at a lower carbonization temperature, and compared the sodium storage performance thereof.

[0059] The detailed experimental steps and processing results are as follows:

[0060] Experimental steps: The sulfur-doped carbon material was obtained by calcining the sulfated chitosan precursor at a lower temperature in a nitrogen atmosphere, and the calcination temperature was 600°C, 700°C and 800°C, and the sulfur-doped carbon material was named SCSC-600, SCSC-700 and SCSC-800, respectively; wherein S represents methane sulfonic acid, CS represents chitosan, and 600, 700 and 800 represent the carbonization temperature of the sulfated chitosan. The obtained sulfur-doped carbon was assembled into a sodium ion half-battery for sodium storage performance testing and characterization, and the sodium ion half-battery was assembled in the same manner as in Embodiment 1.

[0061] Referring to Figure 11 , by comparing the sulfur-doped carbon at different carbonization temperatures, it can be found that as the carbonization temperature increases, the first-cycle coulombic efficiency and the rate performance of the material are both improved. In the sodium ion half-battery, the first-cycle coulombic efficiency of SCSC-600, SCSC-700 and SCSC-800 is 75.2%, 83.5% and 84.4%, respectively, and the capacity at a current density of 2 A g -1 is 70.4, 68.4 and 80.3 mAh g -1 , respectively.

[0062] Example 3

[0063] In this example, sulfur-doped carbon anodes at higher carbonization temperatures were prepared, and their sodium storage performances were compared.

[0064] The detailed experimental procedures and processing results are as follows:

[0065] Experimental procedure: The sulfuric acidified chitosan precursor was calcined at a higher temperature in a nitrogen atmosphere, and the calcination temperature was 1300°C, 1400°C, and 1500°C for carbonization, to obtain sulfur-doped carbon materials, which were named SCSC-1300, SCSC-1400, and SCSC-1500, respectively; wherein S represents methane sulfonic acid, CS represents chitosan, and 1300, 1400, and 1500 represent the carbonization temperature of sulfuric acidified chitosan. The obtained sulfur-doped carbon was assembled into sodium ion half-batteries for sodium storage performance testing and characterization, and the sodium ion half-batteries were assembled as in Example 1.

[0066] Reference Figure 12 By comparing sulfur-doped carbon at different carbonization temperatures, it can be found that as the carbonization temperature increases, the first-cycle coulombic efficiency and rate performance of the material are both decreasing. In the sodium ion half-batteries, the first-cycle coulombic efficiency of SCSC-1300, SCSC-1400, and SCSC-1500 was 72.8%, 90.1%, and 82.5%, respectively, and the capacity at a current density of 2 A g -1 -1

[0067] Comparative Example 1

[0068] In this comparative example, a pure chitosan carbon anode without sulfur oxyanion modification was prepared, and its sodium storage performance was compared.

[0069] The detailed experimental procedures and processing results are as follows:

[0070] Experimental procedure: The pure chitosan was calcined at a high temperature in a nitrogen atmosphere, and the calcination temperature was 900°C for carbonization, to obtain chitosan-derived carbon, which was named CSC; wherein CS represents chitosan, and 900 represents the carbonization temperature of sulfuric acidified chitosan. The obtained pure chitosan carbon anode was assembled into sodium ion half-batteries for sodium storage performance testing and characterization.

[0071] Reference Figure 8 It can be found that CSC exhibits lower rate performance and first-cycle coulombic efficiency. In the sodium ion half-batteries, the first-cycle coulombic efficiency of CSC was 48.5%, and the capacity at a current density of 2 A g -1 -1

[0072] The above not involved, applicable to the prior art.​​​​

[0073] The application is not limited to the particular methods or specific compositions described herein as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, as the scope of the application will be limited only by the appended claims and equivalents thereof.

Claims

1. A method for preparing a sulfur-doped hard carbon material, characterized in that, Includes the following steps: S1. Chitosan is dissolved in methanesulfonic acid. After the reaction, the sulfonate ions are anchored on the chitosan chains to obtain a first mixed solution. The mass concentration of the chitosan is 0.05~0.5 g / mL. S2. Add the first mixed solution to the ether until a white powder is dissolved; the volume ratio of the first mixed solution to the ether is (10~30):

65. S3. Remove the residual solvent from the obtained white powder to obtain sulfated chitosan; S4. The obtained sulfated chitosan is calcined to introduce abundant and uniform sub-nanopores, resulting in sulfur-doped sub-nanopore carbon. The calcination process involves heating from room temperature to 600-1500℃ at a rate of 1-10℃ / min, and holding at that temperature for 60-240 min.

2. The preparation method according to claim 1, characterized in that, In step S3, the process of removing residual solvent involves placing the obtained white powder in the air for 3-4 hours, and then drying it at 40℃-50℃.

3. A sulfur-doped hard carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1-2.

4. The sulfur-doped hard carbon material according to claim 3, characterized in that, The sulfur-doped hard carbon material d 002 Spacing 0.37~0.42 nm.

5. The sulfur-doped hard carbon material according to claim 3, characterized in that, The specific surface area of ​​the sulfur-doped hard carbon material is 800~1400 m². 2 g -1 .

6. A hard carbon anode material, characterized in that, It comprises a sulfur-doped hard carbon material as described in any one of claims 3-5.

7. An electrode sheet, characterized in that, Using the sulfur-doped hard carbon material as described in claim 3 as the active material, sodium carboxymethyl cellulose solution as the binder, and conductive carbon black as the conductive agent, they are mixed in a preset ratio, deionized water is added and stirred into a slurry of suitable viscosity, then coated onto copper foil and dried, and cut into circular electrode sheets to obtain the final product.

8. A sodium-ion battery, characterized in that, The invention comprises: a housing and an electrode assembly disposed within the housing, the electrode assembly comprising a negative electrode and a positive electrode, the negative electrode comprising a negative current collector and an active material layer coated on the negative current collector, the active material layer comprising the sulfur-doped hard carbon material of claim 3 or the hard carbon negative electrode material of claim 6.

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