High-performance nitrogen-doped hard carbon negative electrode material prepared based on waste graphite as well as preparation method and application of high-performance nitrogen-doped hard carbon negative electrode material

Abstract

The invention relates to the technical field of electrochemical energy storage materials, in particular to a high-performance nitrogen-doped hard carbon negative electrode material prepared on the basis of waste graphite and a preparation method and application of the high-performance nitrogen-doped hard carbon negative electrode material. The preparation method comprises the following steps: crushing and screening graphite, mixing graphite powder with glucose, adding ammonia water, stirring, then adding urea as a nitrogen source, and preserving heat at 1000 + / -50 DEG C to obtain the high-performance nitrogen-doped hard carbon negative electrode material. According to the preparation method provided by the invention, the interlayer spacing of the hard carbon material can be increased, the nitrogen content is increased, the quick charge performance of the material is improved, and the preparation method has relatively high practical value and application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage materials, and in particular to a high-performance nitrogen-doped hard carbon negative electrode material prepared based on waste graphite, and a preparation method and application thereof. Background Art

[0002] With the rapid growth of the lithium-ion battery market, the treatment and recycling of waste batteries has become an urgent problem to be solved. During the long-term use of waste graphite negative electrode materials, the distance between graphite layers will expand to a certain extent due to the repeated insertion / extraction process of lithium ions. The existing technology is difficult to ensure the purity and integrity of the recycled graphite, which affects the reuse value of the recycled graphite. In the process of reprocessing graphite negative electrode materials, although the expansion of the distance between graphite layers provides the possibility of performance improvement, the immaturity of technology limits the full realization of this potential. Secondly, a large amount of waste and harmful gases may be generated during the recycling process. How to achieve green recycling is a major technical bottleneck currently faced. Although the doping of nitrogen can improve the electrochemical performance, the energy consumption and environmental protection problems in the doping process still need to be solved. Summary of the invention

[0003] To solve the above problems, the present invention provides a method for preparing high-performance nitrogen-doped hard carbon negative electrode materials based on waste graphite, using waste graphite negative electrode materials and glucose as raw materials, and adding urea as a nitrogen source, and carbonizing treatment at different temperatures in a sealed graphite crucible to prepare a porous hard carbon negative electrode material rich in edge nitrogen, which significantly improves the electrochemical performance.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for preparing a high-performance nitrogen-doped hard carbon negative electrode material based on waste graphite, characterized in that it comprises the following steps:

[0006] S1, crushing and sieving waste graphite to obtain graphite powder;

[0007] S2, mixing graphite powder and glucose in a mass ratio of (8-12):1, adding ammonia water and stirring;

[0008] S3. Wash the graphite powder and glucose until they are neutral, add (8-10) wt% urea, and keep warm at 1000±50° C. to obtain a high-performance nitrogen-doped hard carbon negative electrode material.

[0009] Preferably, the concentration of the ammonia water in S2 is 0.1-2 mol / L.

[0010] Preferably, after adding ammonia water to S2, stirring is carried out at 0°C for 12 h, and then stirring at 25°C for 12 h.

[0011] Preferably, the insulation time of S3 is 5 to 10 hours, and the insulation process is carried out under a nitrogen atmosphere.

[0012] Preferably, the mass ratio of graphite powder to glucose in S2 is 10:1; and the amount of urea added in S3 is 9±0.5wt%.

[0013] The high-performance nitrogen-doped hard carbon negative electrode material is prepared by the method of the present invention.

[0014] Preferably, the nitrogen content of the negative electrode material is 1.5% to 2.5%.

[0015] Application of the high-performance nitrogen-doped hard carbon negative electrode material of the present invention in sodium ion batteries and / or lithium ion batteries.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. Recycling of waste resources: Different from directly discarding or recycling waste graphite at low value, the present invention gives waste graphite new electrochemical properties by mixing it with low-cost carbon sources such as glucose and carbonizing it at high temperature, thereby converting it into high-performance hard carbon negative electrode materials, achieving effective recycling of waste graphite negative electrode materials, reducing environmental pollution, and lowering raw material costs.

[0018] 2. Significant expansion of interlayer spacing: The expansion of interlayer spacing facilitates the rapid embedding and extraction of large-sized ions such as sodium ions, thereby improving the sodium storage capacity and rate performance of the material. The present invention promotes the expansion of the interlayer spacing of carbon materials through the interaction between glucose and waste graphite during high-temperature carbonization, as well as the gas expansion effect produced by possible pyrolysis reactions. In addition, trace nitrogen elements in glucose and optional additional nitrogen sources (such as urea) are doped at high temperatures, further increasing the interlayer spacing.

[0019] 3. Effective doping of nitrogen: The doping of nitrogen not only increases the active sites of the material, but also improves the conductivity and electrochemical stability of the material, which helps to improve the overall electrochemical performance of the material. The present invention utilizes the trace nitrogen naturally contained in glucose, and introduces an additional nitrogen source (such as urea) when necessary to achieve effective doping of nitrogen during the high-temperature carbonization process. In particular, the dual role of glucose as a carbon source and a nitrogen source makes the nitrogen doping process simpler and more efficient.

[0020] 4. Formation of porous structure: The existence of porous structure increases the specific surface area of ​​the material, shortens the diffusion path of sodium ions, and further improves the rate performance and cycle stability of the material. Glucose will undergo pyrolysis reaction at high temperature, generate gas products and escape, leaving a rich porous structure in the material. These pores are combined with the original interlayer voids of waste graphite to form a porous hard carbon structure.

[0021] 5. Simple preparation process and low cost: The preparation method of the present invention is simple and easy to implement, and the required raw materials are cheap and easily available, which is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a flow chart of a method for preparing a high-performance nitrogen-doped hard carbon negative electrode material based on waste graphite. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below through specific implementation cases. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of protection of the present invention. After reading the present invention, the modifications of various equivalent forms of the present invention by those skilled in the art are all limited by the claims attached to this application. Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents that can be purchased in the conventional market.

[0024] The waste graphite used in the present invention comes from recycled graphite produced by battery recycling, and the original interlayer spacing is 0.335nm.

[0025] Example 1

[0026] 1. Pretreatment of waste graphite: crush and screen the waste graphite negative electrode material to remove impurities and obtain pretreated graphite powder.

[0027] 2. The pretreated graphite powder and glucose were mixed evenly in a mass ratio of 10:1, stirred with 1 mol / L ammonia water at 0°C for 12 h, then stirred at 25°C for 12 h, and then washed to neutrality.

[0028] 3. Mix the graphite powder and glucose evenly, add 7 wt % of urea, fill into a sealed graphite crucible, and perform carbonization treatment under a nitrogen atmosphere at a carbonization temperature of 1100° C. for 4 hours.

[0029] Results: As shown in Table 1, the interlayer spacing of the prepared hard carbon material was expanded from 0.335 nm of the original graphite to 0.374 nm, the nitrogen content was about 1.2%, and the first discharge capacity reached 321.3 mAh / g.

[0030] Example 2

[0031] 1. Pretreatment of waste graphite: crush and screen the waste graphite negative electrode material to remove impurities and obtain pretreated graphite powder.

[0032] 2. The pretreated graphite powder and glucose were mixed evenly in a mass ratio of 10:1, stirred with 1 mol / L ammonia water at 0°C for 12 h, then stirred at 25°C for 12 h, and then washed to neutrality.

[0033] 3. Mix the graphite powder and glucose evenly, add 2 wt % urea, fill into a sealed graphite crucible, and perform carbonization treatment under a nitrogen atmosphere at a carbonization temperature of 900° C. for 6 hours.

[0034] Results: As shown in Table 1, the interlayer spacing of the hard carbon material further increased to 0.383 nm, the nitrogen content increased to 1.5%, the first discharge capacity increased to 350.1 mAh / g, and the fast charging performance was significantly improved.

[0035] Example 3

[0036] 1. Pretreatment of waste graphite: crush and screen the waste graphite negative electrode material to remove impurities and obtain pretreated graphite powder.

[0037] 2. The pretreated graphite powder and glucose were mixed evenly in a mass ratio of 10:1, stirred with 1 mol / L ammonia water at 0°C for 12 h, then stirred at 25°C for 12 h, and then washed to neutrality.

[0038] 3. The graphite powder and glucose were mixed evenly, 9 wt % of urea was added, and the mixture was filled into a sealed graphite crucible. The mixture was carbonized in a nitrogen atmosphere at a temperature of 1000° C. for 8 hours.

[0039] Results: As shown in Table 1, the hard carbon material exhibits the best electrochemical performance, with an interlayer spacing of 0.394nm, a nitrogen content of up to 2.0%, and a significant increase in the proportion of edge nitrogen. The first discharge capacity is as high as about 380mAh / g, and the capacity retention rate remains above 85% after 500 cycles, and the fast charging performance is excellent, showing good application prospects.

[0040] Comparative Example 1

[0041] 1. Pretreatment of waste graphite: crush and screen the waste graphite negative electrode material to remove impurities and obtain pretreated graphite powder.

[0042] 2. The pretreated graphite powder and glucose were mixed evenly in a mass ratio of 5:1, stirred with 1 mol / L ammonia water at 0°C for 12 h, then stirred at 25°C for 12 h, and then washed to neutrality.

[0043] 3. Fill graphite powder and glucose into a sealed graphite crucible and perform carbonization treatment in a nitrogen atmosphere at a carbonization temperature of 1100°C for 8 hours.

[0044] Comparative Example 2

[0045] 1. Pretreatment of waste graphite: crush and screen the waste graphite negative electrode material to remove impurities and obtain pretreated graphite powder.

[0046] 2. The pretreated graphite powder and glucose were mixed evenly in a mass ratio of 20:1, stirred with 1 mol / L ammonia water at 0°C for 12 h, then stirred at 25°C for 12 h, and then washed to neutrality.

[0047] 3. Fill graphite powder and glucose into a sealed graphite crucible and perform carbonization treatment in a nitrogen atmosphere at a carbonization temperature of 1100°C for 8 hours.

[0048] Comparative Example 3

[0049] 1. Pretreatment of waste graphite: crush and screen the waste graphite negative electrode material to remove impurities and obtain pretreated graphite powder.

[0050] 2. The pretreated graphite powder and glucose were mixed evenly in a mass ratio of 10:1, stirred with 1 mol / L ammonia water at 0°C for 12 h, then stirred at 25°C for 12 h, and then washed to neutrality.

[0051] 3. Fill graphite powder and glucose into a sealed graphite crucible and perform carbonization treatment in a nitrogen atmosphere at a carbonization temperature of 1000°C for 8 hours.

[0052] Test Case

[0053] The samples prepared in the embodiment and the comparative example were used as negative electrode materials to prepare sodium ion button batteries:

[0054] 1: The mixing ratio is sample: CMC: SP: SBR = 94: 1.96: 1.74: 2.3, add a small amount of deionized water to make the solid content 30-50%, stir in a degassing machine for 10 minutes and then coat on the copper foil;

[0055] The electrode in step 1 was dried in a forced air drying oven at 105°C for 4 hours, then cut into small discs with a diameter of 16 mm and weighed;

[0056] The electrode in step 2 was dried in a vacuum drying oven at 110°C for 6 h and then quickly transferred to a glove box;

[0057] Assemble the above-mentioned negative electrode plate and the metal sodium plate into a button battery using a 2430-type battery shell;

[0058] The button cell assembled in step 4 is tested using the following steps:

[0059] (1) Charging capacity and initial efficiency test:

[0060] Step 1: Let stand for 12 hours;

[0061] Step 2: rate discharge: 0.02A / g (cut-off condition: voltage ≤ 0V), constant voltage discharge: 0V (cut-off condition: current → 10uA);

[0062] Step 3: Let stand for 10 minutes;

[0063] Step 4: Charge rate: 0.02A / g (cut-off condition: voltage ≥ 2V);

[0064] (2) Cycle retention rate test:

[0065] Step 1: Let stand for 12 hours;

[0066] Step 2: rate discharge: 0.02A / g (cut-off condition: voltage ≤ 0V), constant voltage discharge: 0V (cut-off condition: current → 10uA);

[0067] Step 3: Let stand for 10 minutes;

[0068] Step 4: Charge rate: 0.02A / g (cut-off condition: voltage ≥ 2V);

[0069] Step 5: Let stand for 10 minutes;

[0070] Step 6: Step 2 to Step 5 are cycled 500 times

[0071] Table 1

[0072]

[0073] The experimental results show that with the increase of carbonization temperature and the introduction of urea nitrogen source, the interlayer spacing of hard carbon materials gradually increases, the nitrogen content increases, and the electrochemical performance is significantly improved. In particular, the improvement of fast charging performance provides strong material support for applications such as sodium ion batteries that require fast charging and discharging.

[0074] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a high-performance nitrogen-doped hard carbon negative electrode material based on waste graphite, characterized in that: The following steps are involved: S1, crushing and sieving waste graphite to obtain graphite powder; S2, mixing graphite powder and glucose in a mass ratio of (8-12):1, adding ammonia water and stirring; S3. Wash the graphite powder and glucose until they are neutral, add (8-10) wt% urea, and keep warm at 1000±50° C. to obtain a high-performance nitrogen-doped hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that: The concentration of the ammonia water in S2 is 0.1-2 mol / L.

3. The preparation method according to claim 2, characterized in that: After adding ammonia water to S2, the mixture was stirred at 0°C for 12 h, and then at 25°C for 12 h.

4. The preparation method according to claim 3, characterized in that: The insulation time of S3 is 5 to 10 hours, and the insulation process is carried out under a nitrogen atmosphere.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The mass ratio of graphite powder to glucose in S2 is 10:1; the amount of urea added in S3 is 9±0.5wt%.

6. A high performance nitrogen-doped hard carbon negative electrode material prepared by the method according to any one of claims 1 to 5.

7. The high performance nitrogen-doped hard carbon negative electrode material according to claim 1, characterized in that: The nitrogen content of the negative electrode material is 1.5% to 2.5%.

8. Use of the high-performance nitrogen-doped hard carbon negative electrode material according to claim 6 or 7 in sodium ion batteries and / or lithium ion batteries.

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