Nitrogen and sulfur doped hard carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-sulfur-doped hard carbon negative electrode material and a preparation method and application thereof, and relates to the technical field of battery negative electrode materials, and the preparation method of the nitrogen-sulfur-doped hard carbon negative electrode material comprises the following steps: S1, pretreating camellia oleifera shells, drying, and crushing to obtain camellia oleifera shell powder; s2, ball-milling and uniformly mixing the camellia oleifera shell powder obtained in the step S1, molten salt and a mixed element precursor to obtain mixed powder; s3, activating and carbonizing the mixed powder obtained in the step S2 to obtain carbonized powder; s4, carrying out acid pickling, water washing, suction filtration, drying and filtration on the carbonized powder obtained in S3 to obtain the hard carbon negative electrode material; the invention also provides the nitrogen-sulfur-doped hard carbon negative electrode material prepared by the preparation method and application of the nitrogen-sulfur-doped hard carbon negative electrode material in a sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery negative electrode materials, and in particular to a nitrogen-sulfur doped hard carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development of renewable energy and energy storage technology, sodium-ion batteries have become an important supplement to lithium-ion batteries due to their advantages such as abundant sodium resources and low cost. Hard carbon materials are regarded as ideal candidate materials for sodium-ion battery negative electrodes due to their disordered carbon layer structure, high specific surface area and excellent sodium ion insertion / extraction performance. However, traditional hard carbon preparation mostly relies on high-cost precursors such as synthetic resins, and the process is complex and the carbon yield is low, which limits its large-scale application. For this reason, the development of high-performance hard carbon materials using renewable biomass as precursors has become a research hotspot, but how to synergistically improve electrochemical performance through structural design and heteroatom doping remains a technical problem that needs to be overcome.

[0003] In order to solve the above problems, a sulfur-doped biomass hard carbon material, its preparation method and application are disclosed in the Chinese invention patent with publication number CN113912039A. It uses biomass raw materials such as camphor tree and soybean as precursors, and prepares hard carbon materials at a carbonization temperature of 600-800°C through a molten salt method combined with a sulfur doping process. It dopes sulfur atoms into the carbon interlayer to increase the carbon spacing and increase the surface active sites, thereby increasing the sodium ion migration rate and improving the electrochemical performance.

[0004] Although the above methods utilize biomass resources and reduce costs, they still have the following limitations:

[0005] (1) The single sulfur doping strategy has limited control over the carbon layer structure and is difficult to fully activate the surface active sites; (2) The carbonization temperature is low and the degree of graphitization of the material is insufficient, resulting in limited electronic conductivity and cycle stability; (3) No research has been conducted on the efficient utilization and waste resource recovery of specific biomass, and there is a lack of refined design of the components of the molten salt system. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a nitrogen-sulfur doped hard carbon negative electrode material and its preparation method and application, so as to solve the problems that the preparation method of the hard carbon negative electrode material in the prior art is greatly limited and the performance of the prepared hard carbon negative electrode material is not excellent enough.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a nitrogen-sulfur doped hard carbon negative electrode material comprises the following steps:

[0009] S1. The camellia shells are pretreated, dried, and crushed to obtain camellia shell powder;

[0010] S2 S1 obtained camellia shell powder and molten salt and miscellaneous element precursor ball milling mixed uniformly to obtain a mixed powder;

[0011] S3. The mixed powder obtained in S2 is activated and carbonized to carbonized powder;

[0012] S4. The carbonized powder obtained in S3 is acid-washed, water-washed, filtered, dried, and filtered to obtain a hard carbon negative electrode material.

[0013] Preferably, in step S1, the camellia oleifera shells are pretreated by soaking the camellia oleifera shells in pure water for 6 to 24 hours, and drying them at a temperature of 80 to 120° C. for a drying time of 4 to 12 hours.

[0014] Preferably, in step S2, the molten salt is one of NaCl-KCl-MgCl2, FeCl-AlCl3, FeCl-MgCl2, and FeCl3-NaCl, and in terms of molar ratio, NaCl:KCl:MgCl2 in NaCl-KCl-MgCl2 is 1:1:1, FeCl:AlCl3 in FeCl-AlCl3 is 2:1, FeCl:MgCl2 in FeCl-MgCl2 is 1:1, and FeCl3:NaCl in FeCl3-NaCl is 1:2.

[0015] Preferably, in step S2, the heteroelement precursor includes one of thiourea, thioacetamide, cysteine, and benzothiazole.

[0016] Preferably, in step S2, the mass ratio of camellia oleifera shell powder: molten salt: heteroelement precursor is 1:1:0.05 to 1:5:0.15.

[0017] Preferably, in step S2, the ball milling speed is 300-600 r / min, the ball milling time is 8-24 h, and the ball milling atmosphere is one of air, argon, and nitrogen.

[0018] Preferably, in step S3, the activation temperature is 600-800°C, the carbonization temperature is 1100-1500°C, the heating rates of activation and carbonization are both 1-10°C / min, the holding times of activation and carbonization are both 1-3h, and the atmospheres of activation and carbonization are both nitrogen or ammonia.

[0019] Preferably, in step S4, the pickling is performed using one of hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 0.1M to 2M, the soaking time is 12 to 24 hours, and the mesh size of the sieve used for filtration is 100 to 500 meshes.

[0020] The present invention also provides a nitrogen-sulfur doped hard carbon negative electrode material, which is prepared by the preparation method.

[0021] The present invention also provides an application of a nitrogen-sulfur doped hard carbon negative electrode material in a sodium ion battery.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides a nitrogen-sulfur doped hard carbon negative electrode material and a preparation method thereof, and applies them to the field of sodium ion batteries. The preparation method is a method for preparing the hard carbon negative electrode material using camellia oleifera shell as a hard carbon precursor, through the steps of crushing pretreatment, mixing with molten salt, doping with miscellaneous elements, activation and high-temperature carbonization.

[0024] Among them, the high-temperature molten salt medium can not only obtain a more uniform carbon structure and control the micro-nanopore structure during the carbonization process, but also for the molten salt containing iron salt, it can inhibit the carbon volatilization during the carbonization process and increase the carbon yield. It can also play the catalytic graphitization effect of iron on carbon elements to form a hard-soft carbon structure, which is beneficial to improve the ion transport kinetics and interface stability of sodium ion batteries, while reducing preparation costs and environmental risks; and the doping of heteroelements can expand the spacing between hard carbon layers by introducing heteroatoms, which is beneficial to sodium ion storage.

[0025] This preparation method has the characteristics of low cost, high carbon yield, simple preparation, high safety, high reaction efficiency, etc. It meets the environmental requirements of green resources and realizes the efficient utilization of waste resources.

[0026] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0027] In order to make the technical means, creative features, objectives and effects of the present invention clearer and easier to understand, the present invention is further described below in conjunction with specific embodiments:

[0028] Example 1

[0029] S1. The camellia shells were soaked in pure water for 12 hours, impurities and dust were washed off the surface of the camellia shells, and then dried in a vacuum drying oven at 80 ° C for 8 hours. The camellia shells were crushed into powder by a wall-breaking machine and passed through a 100-mesh sieve to obtain camellia shell powder;

[0030] S2. The camellia shell powder obtained in S1 was mixed with NaCl-KCl-MgCl2 and thiourea in a mass ratio of 1:3:0.1 in a planetary ball mill under an air atmosphere at a speed of 500 rpm for 12 h to obtain a mixed powder;

[0031] S3. The mixed powder obtained in S2 was placed in a tube furnace, activated and carbonized, and then cooled to room temperature to obtain a carbonized powder, wherein the activation temperature was 600°C, the holding time was 2h, the heating rate was 5°C / min, the carbonization temperature was 1300°C, the holding time was 2h, the heating rate was 1°C / min, and the activation and carbonization atmosphere was nitrogen;

[0032] S4. The carbonized powder obtained in S3 was soaked in a 1M hydrochloric acid solution for 12 h, and then washed with water, filtered, dried, and passed through a 100-mesh sieve to obtain a hard carbon negative electrode material.

[0033] Example 2

[0034] S1. The camellia shells were soaked in pure water for 24 hours, impurities and dust were washed off the surface of the camellia shells, and then dried in a vacuum drying oven at 100 ° C for 8 hours. The camellia shells were crushed into powder by a wall breaking machine and passed through a 100-mesh sieve to obtain camellia shell powder;

[0035] S2. The camellia shell powder obtained in S1 was mixed with FeCl-AlCl3 and thioacetamide in a mass ratio of 1:5:0.05 in a planetary ball mill under an argon atmosphere at a speed of 600 rpm for 16 h to obtain a mixed powder;

[0036] S3. The mixed powder obtained in S2 was placed in a tube furnace, activated and carbonized, and then cooled to room temperature to obtain a carbonized powder, wherein the activation temperature was 700°C, the holding time was 1h, the heating rate was 10°C / min, the carbonization temperature was 1100°C, the holding time was 3h, the heating rate was 5°C / min, and the activation and carbonization atmosphere was argon;

[0037] S4. The carbonized powder obtained in S3 was soaked in a 0.5 M nitric acid solution for 12 h, and then washed with water, filtered, dried, and passed through a 200-mesh sieve to obtain a hard carbon negative electrode material.

[0038] Example 3

[0039] S1. The camellia shells were soaked in pure water for 16 hours, impurities and dust were washed off the surface of the camellia shells, and then dried in a vacuum drying oven at 120°C for 4 hours. The camellia shells were crushed into powder by a wall-breaking machine and passed through a 100-mesh sieve to obtain camellia shell powder.

[0040] S2. The camellia shell powder obtained in S1 was mixed with FeCl-MgCl2 and cysteine in a mass ratio of 1:1:0.15 in a planetary ball mill under a nitrogen atmosphere at a speed of 400 rpm for 8h to obtain a mixed powder;

[0041] S3. The mixed powder obtained in S2 was placed in a tube furnace, activated and carbonized, and then cooled to room temperature to obtain a carbonized powder, wherein the activation temperature was 800°C, the holding time was 3h, the heating rate was 5°C / min, the carbonization temperature was 1500°C, the holding time was 1h, the heating rate was 5°C / min, and the activation and carbonization atmosphere was nitrogen;

[0042] S4. The carbonized powder obtained in S3 was soaked in a 2M sulfuric acid solution for 24 h, and then washed with water, filtered, dried, and passed through a 500-mesh sieve to obtain a hard carbon negative electrode material.

[0043] Example 4

[0044] S1. The camellia shells were soaked in pure water for 6 hours, impurities and dust were washed off the surface of the camellia shells, and then dried in a vacuum drying oven at 100 ° C for 12 hours. The camellia shells were crushed into powder by a wall breaking machine and passed through a 100-mesh sieve to obtain camellia shell powder;

[0045] S2. The camellia shell powder obtained in S1 was mixed with FeCl3-NaCl and benzothiazole in a mass ratio of 1:3:0.1 in a planetary ball mill under an air atmosphere at a speed of 300 rpm for 24 h to obtain a mixed powder;

[0046] S3. The mixed powder obtained in S2 was placed in a tube furnace, activated and carbonized, and then cooled to room temperature to obtain a carbonized powder, wherein the activation temperature was 600°C, the holding time was 1h, the heating rate was 1°C / min, the carbonization temperature was 1300°C, the holding time was 2h, the heating rate was 10°C / min, and the activation and carbonization atmosphere was nitrogen;

[0047] S4. The carbonized powder obtained in S3 was soaked in a 0.1 M hydrochloric acid solution for 18 h, and then washed with water, filtered, dried, and passed through a 300-mesh sieve to obtain a hard carbon negative electrode material.

[0048] Comparative Example 1

[0049] Compared with Example 1, the mass ratio of camellia oleifera shell powder to NaCl-KCl-MgCl2 and thiourea is 5:3:0.1, and the other steps are the same.

[0050] Comparative Example 2

[0051] Compared with Example 1, the mass ratio of camellia oleifera shell powder, NaCl-KCl-MgCl2 and thiourea is 1:10:0.1, and the other steps are the same.

[0052] Performance Testing

[0053] The hard carbon negative electrode materials prepared in Examples 1-4 and Comparative Examples 1-2 were used as negative electrodes for sodium-ion batteries. The electrode test conditions were as follows: by mass, the electrode consisted of 80% hard and soft carbon active material, 10% Super P, and 10% polyvinylidene fluoride (PVDF), and the diluent was N,N-dimethylformamide (NMP). Constant current charge and discharge performance tests were conducted on a NEWARE charge and discharge instrument using glass fiber as the separator, copper foil as the current collector, and a 1 mol / L NaPF6-DME solution as the electrolyte. The current density was 30 mA / g and the voltage range was 0.01 to 3 V. Super P is a small particle conductive carbon black, and the NaPF6-DME solution is a solution containing pure 1,2-dimethoxyethane as the solvent and sodium hexafluorophosphate as the solute. The final electrochemical performance results are shown in the following table.

[0054]

[0055] As can be seen from Table 1, the hard carbon negative electrode materials prepared in Examples 1-4 all exhibited good electrochemical performance as negative electrodes for sodium ion batteries. The reversible capacity at a current density of 0.1C could reach up to 377.55 mAh / g, and the coulombic efficiency could reach up to 85%. Under appropriate raw material ratios, the reversible capacity at 0.1C exceeded 340 mAh / g, and the coulombic efficiency was greater than 78%. This indicates that the hard carbon negative electrode material prepared by the present invention, which is a process of crushing tea shells for pretreatment, mixing with molten salts, doping with miscellaneous elements, activation, and carbonization, has a good effect and can effectively improve the sodium storage performance of hard carbon.

[0056] In Comparative Example 1, the mass of molten salt added during preparation is less than the mass of camellia oleifera shell powder. Its reversible capacity at a current density of 0.1C is 275.34 mAh / g, and the first coulombic efficiency is 64%. Compared with Example 1, the electrochemical performance is poor. This is because the amount of molten salt added is too small, which makes it unable to fully react with the carbon element in the camellia oleifera shell powder, resulting in uneven crystal structure, underdeveloped micropore structure, insufficient pore volume, and inability to provide more sodium ion active sites. Therefore, the sodium storage performance is slightly poor.

[0057] In Comparative Example 2, an excessive amount of molten salt was added during preparation, and its reversible capacity at a current density of 0.1C was 281.82 mAh / g, and the first coulombic efficiency was 68%. Compared with Example 1, the electrochemical performance was also poor. This was because too much high-temperature molten salt medium was added, resulting in the pore structure of the camellia shell powder after activation and carbonization being too large, resulting in an uneven structure and insufficient pore volume, which could not provide more sodium ion active sites. Therefore, the sodium storage performance was slightly poor, and resources were wasted.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a nitrogen-sulfur doped hard carbon negative electrode material, characterized in that: The following steps are involved: S1. The camellia shells are pretreated, dried, and crushed to obtain camellia shell powder; S2 S1 obtained camellia shell powder and molten salt and miscellaneous element precursor ball milling mixed uniformly to obtain a mixed powder; S3. The mixed powder obtained in S2 is activated and carbonized to carbonized powder; S4. The carbonized powder obtained in S3 is acid-washed, water-washed, filtered, dried, and filtered to obtain a hard carbon negative electrode material.

2. The method for preparing a nitrogen-sulfur doped hard carbon negative electrode material according to claim 1, characterized in that: In step S1, the camellia oleifera shells are pretreated by soaking them in pure water for 6 to 24 hours, and drying them at a temperature of 80 to 120° C. for a drying time of 4 to 12 hours.

3. The method for preparing a nitrogen-sulfur doped hard carbon negative electrode material according to claim 1, characterized in that: In step S2, the molten salt is one of NaCl-KCl-MgCl2, FeCl-AlCl3, FeCl-MgCl2, and FeCl3-NaCl, and in terms of molar ratio, NaCl:KCl:MgCl2 in NaCl-KCl-MgCl2 is 1:1:1, FeCl:AlCl3 in FeCl-AlCl3 is 2:1, FeCl:MgCl2 in FeCl-MgCl2 is 1:1, and FeCl3:NaCl in FeCl3-NaCl is 1:

2.

4. The method for preparing a nitrogen-sulfur doped hard carbon negative electrode material according to claim 1, characterized in that: In step S2, the heteroelement precursor includes one of thiourea, thioacetamide, cysteine, and benzothiazole.

5. The method for preparing a nitrogen-sulfur doped hard carbon negative electrode material according to claim 1, characterized in that: In step S2, the mass ratio of camellia oleifera shell powder: molten salt: heteroelement precursor is 1:1:0.05 to 1:5:0.

15.

6. The method for preparing a nitrogen-sulfur doped hard carbon negative electrode material according to claim 1, characterized in that: In step S2, the ball milling speed is 300-600 r / min, the ball milling time is 8-24 h, and the ball milling atmosphere is one of air, argon, and nitrogen.

7. The method for preparing a nitrogen-sulfur doped hard carbon negative electrode material according to claim 1, characterized in that: In step S3, the activation temperature is 600-800°C, the carbonization temperature is 1100-1500°C, the heating rates of activation and carbonization are both 1-10°C / min, the holding time of activation and carbonization are both 1-3h, and the atmosphere of activation and carbonization are both nitrogen or ammonia.

8. The method for preparing a nitrogen-sulfur doped hard carbon negative electrode material according to claim 1, characterized in that: In step S4, pickling is performed using one of hydrochloric acid, sulfuric acid, and nitric acid with a concentration of 0.1M to 2M, the soaking time is 12 to 24 hours, and the mesh size of the sieve used for filtration is 100 to 500 meshes.

9. A nitrogen-sulfur doped hard carbon negative electrode material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the nitrogen-sulfur doped hard carbon negative electrode material according to claim 9 in sodium ion batteries.

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