A method for preparing a phosphorus-metal alloy co-doped hard carbon composite material

Abstract

This invention discloses a method for preparing a phosphorus-metal alloy co-doped hard carbon composite material. The method involves adding red phosphorus and a crosslinking agent to a solid resin and mixing them uniformly using a ball mill. The mixture is then heated and cured at 300-500℃ to obtain a porous intermediate. This porous intermediate is then mixed uniformly with metal alloy powder and sodium carboxymethyl cellulose, followed by carbonization at 1200-1500℃ for 1-6 hours, and finally pulverized to obtain the phosphorus-metal co-doped hard carbon composite material. This composite material utilizes the porous hard carbon generated during the carbonization of the solid resin, and incorporates a high-specific-capacity metal alloy within its pores to increase specific capacity and reduce expansion. Furthermore, the pore-forming effect of phosphorus doping enhances sodium storage capacity, and the bonding function of sodium carboxymethyl cellulose, along with the formation of inorganic sodium salts after carbonization, improves the initial efficiency of the material. The resulting material exhibits high specific capacity, high initial efficiency, and excellent cycling performance when applied to sodium ions.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery material preparation, specifically a method for preparing a phosphorus-metal alloy co-doped hard carbon composite material. Background Technology

[0002] As market demands for the energy density and fast-charging performance of sodium-ion batteries increase, the fast-charging performance of hard carbon materials used in sodium-ion batteries must also be improved in addition to high energy density. The main factors affecting the energy density of hard carbon are specific capacity, compaction density, and initial efficiency. Currently, the most effective measures are to improve the specific capacity and initial efficiency of the material while also considering its charging capability. Current measures to improve the specific capacity and initial efficiency include selecting raw materials with more nanopores to enhance sodium storage performance, doping with non-metals such as phosphorus to create pores and improve specific capacity, and reducing surface defects to improve initial efficiency. However, these measures have limited effect on improving specific capacity or initial efficiency. For example, patent application 202210339329.5 discloses a sulfur-phosphorus co-doped hard carbon composite material and its preparation method. The preparation method is as follows: take hydrocarbons, sulfur-phosphorus organics and nitrogen-containing polymers, add them to an organic solvent to prepare an organic solution, and prepare a porous hard carbon precursor through hydrothermal reaction. Carbonize to obtain a hard carbon composite material. However, the preparation process is complicated, and the sulfur-phosphorus doping has a small effect on improving the specific capacity of the material and does not improve the first efficiency of the material. At the same time, since sulfur and phosphorus are non-metallic elements, their own electronic impedance is large, which reduces the rate performance of the material. Summary of the Invention

[0003] To improve the specific capacity and initial efficiency of hard carbon, this invention creates pores by doping with high-specific-capacity sodium compounds and non-metallic phosphorus, leveraging their synergistic effect to enhance the specific capacity and initial efficiency of the material; simultaneously, it provides a method for preparing phosphorus-metal alloy co-doped hard carbon composite materials.

[0004] A method for preparing a phosphorus-metal alloy co-doped hard carbon composite material includes the following steps:

[0005] Step (1):

[0006] According to the mass ratio of red phosphorus: crosslinking agent: solid resin = 1-10: 10-30: 100, red phosphorus and crosslinking agent were added to the solid resin and ball-milled at a speed of 400-500 r / min for 1-6 h. Then, the mixture was heated and cured at a temperature of 300-500℃ to obtain a porous intermediate.

[0007] Step (2):

[0008] The porous intermediate, metal alloy powder, and sodium carboxymethyl cellulose were mixed evenly according to a mass ratio of porous intermediate: metal alloy powder: sodium carboxymethyl cellulose = 100:1-10:1-5. Then, the mixture was carbonized at 1200-1500℃ for 1-6 hours and pulverized to obtain a phosphorus-metal alloy co-doped hard carbon composite material.

[0009] The red phosphorus in step (1) has a particle size of 100-1000 μm.

[0010] In step (1), the crosslinking agent is one of m-hydroxybenzaldehyde, 4-ethoxybenzaldehyde, p-dimethylaminobenzaldehyde, p-aminobenzaldehyde, 3-ethoxyo-hydroxybenzaldehyde, and 3,5-bis(trifluoromethylbenzaldehyde).

[0011] The solid resin in step (1) is one of melamine-formaldehyde resin, furan resin, polyester resin, vinyl resin, bismaleimide, or thermosetting polyimide.

[0012] In step (2), the metal alloy powder is Na. 15 Sn4, Na3Sb, Na 15 One of the Pb4 particles, with a particle size of 100-500 nm.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] 1) Utilize the porous hard carbon generated by solid-phase resin carbonization, and dope the pores with high specific capacity metal alloys to increase specific capacity and reduce expansion. Utilize the pore-forming effect during phosphorus doping to enhance sodium storage capacity, the adhesive function of sodium carboxymethyl cellulose, and the inorganic sodium salt formed after carbonization to enhance the initial efficiency of the material.

[0015] 2) Doping the material with metal alloy powder (Na15Sn4, Na3Sb, Na15Pb4) forms sodium salt compounds after carbonization. Sn, Sb, and Pb themselves have high specific capacity, which improves the sodium storage function of the material. At the same time, the sodium salt compounds doped in the material increase the number of sodium ions during charging and discharging, reduce the loss caused by the formation of SEI film, improve the first efficiency and rate performance. Attached Figure Description

[0016] Figure 1 The image shows a SEM image of the phosphorus-metal co-doped hard carbon composite material prepared in Example 1. Detailed Implementation Example 1

[0017] Step (1):

[0018] 5g of red phosphorus (particle size 500µm) and 20g of m-hydroxybenzaldehyde were added to 100g of melamine-formaldehyde resin and ball-milled at 500r / min for 3h. Then, the mixture was heated and cured at 400℃ for 3h to obtain a porous hard carbon intermediate.

[0019] Step (2):

[0020] 100g of porous hard carbon intermediate was mixed with 5g of Na 15 Sn4 and 3g of sodium carboxymethyl cellulose were mixed evenly, then carbonized at 1400℃ for 3 hours, and pulverized to obtain a phosphorus-metal alloy co-doped hard carbon composite material. Example 2

[0021] Step (1):

[0022] 1g of red phosphorus (particle size 100µm) and 10g of 4-ethoxybenzaldehyde were added to 100g of furan resin and ball-milled at 400r / min for 6h. Then, the mixture was heated and cured at 300℃ for 6h to obtain a porous hard carbon intermediate.

[0023] Step (2):

[0024] 100g of porous hard carbon intermediate was mixed with 1g of Na3Sb and 1g of sodium carboxymethyl cellulose, and then carbonized at 1200℃ for 6h. After pulverization, phosphorus-metal alloy co-doped hard carbon composite material was obtained. Example 3

[0025] Step (1):

[0026] 10g of red phosphorus (particle size 1000µm) and 30g of p-dimethylaminobenzaldehyde were added to 100g of polyester resin and ball-milled at 500r / min for 1h. Then, the mixture was heated and cured at 500℃ for 1h to obtain a porous hard carbon intermediate.

[0027] Step (2):

[0028] 100g of porous hard carbon intermediate was mixed with 10g of Na 15 Pb4 and 5g of sodium carboxymethyl cellulose were mixed evenly, then carbonized at 1500℃ for 1 hour, and pulverized to obtain a phosphorus-metal alloy co-doped hard carbon composite material. Comparative Example 1:

[0029] Unlike Example 1, step S(1) does not involve the addition of red phosphorus, but the rest is the same as in Example 1. Comparative Example 2:

[0030] Unlike Example 1, no Na was added. 15Sn4 and sodium carboxymethyl cellulose, otherwise the same as in Example 1.

[0031] Performance testing of the materials prepared in the above embodiments and comparative examples:

[0032] (1) SEM test

[0033] The phosphorus-metal alloy co-doped hard carbon composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. By Figure 1 As can be seen from the above, the hard carbon composite material prepared in Example 1 has a granular structure, and the white substance on the surface is a metal compound with a particle size D50 between (3-8) μm.

[0034] (2) Physical and chemical properties and button cell testing

[0035] The interlayer spacing (D002), specific surface area, tap density, particle size D50, and powder conductivity of the phosphorus-metal alloy co-doped hard carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were measured. The tests were conducted according to the methods specified in the national standard GB / T-24533-2019, "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0036] The phosphorus-metal alloy co-doped hard carbon composite materials from Examples 1-3 and Comparative Examples 1-2 were used as negative electrode materials for lithium-ion batteries to assemble coin cells. The specific preparation method for the negative electrode material was as follows: a negative electrode sheet was prepared by mixing hard carbon composite material, CMC, SBR, SP, and H2O in a mass ratio of 95:2.5:1.5:1:150; a sodium sheet was used as the counter electrode; the electrolyte was NaPF6 / EC+DEC, where NaPF6 was the electrolyte, and a 1:1 volume ratio mixture of EC and DEC was used as the solvent, with an electrolyte concentration of 1.3 mol / L; the separator was a composite membrane of polyethylene (PE), polypropylene (PP), and polyethylene propylene (PEP). The coin cells were assembled in an argon-filled glove box. Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The initial discharge capacity and initial efficiency of the coin cells were tested. The test results are shown in Table 1.

[0037] Table 1

[0038] Example D002 (nm) <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Tap density (g / cm 3 )]]> Particle size (D50, μm) Powder conductivity (S / cm) Initial discharge capacity (mAh / g) First-time efficiency (%) Example 1 0.376 6.5 0.89 6.8 64 357.2 91.5 Example 2 0.375 6.3 0.84 6.5 62 351.7 90.8 Example 3 0.379 7.2 0.85 6.6 69 362.8 92.3 Comparative Example 1 0.372 4.3 0.62 7.5 43 321.5 85.4 Comparative Example 2 0.374 5.4 0.64 7.6 47 332.4 89.2

[0039] As can be seen from Table 1, the phosphorus-metal alloy co-doped hard carbon composite material of the example is superior to Comparative Examples 1-2 in terms of specific surface area and initial discharge capacity. This is because the specific capacity is increased by doping a high-specific-capacity metal alloy into the pores of hard carbon, and the pore-forming effect of phosphorus doping process is used to improve the sodium storage performance, the bonding function of sodium carboxymethyl cellulose, and the inorganic sodium salt formed after carbonization to improve the initial efficiency of the material. At the same time, the doping of sodium compounds reduces impedance and improves the conductivity of the powder material.

[0040] (3) Soft-pack battery test:

[0041] The phosphorus-metal alloy co-doped hard carbon composite materials from Examples 1-3 and Comparative Examples 1-2 were slurried and coated to prepare negative electrode sheets, using layered oxides (NaFe) 1 / 3 Mn 1 / 3 Ni 1 / 3 A 5Ah soft-pack battery was prepared using NaPF6 (solvent: EC:DEC:PC:propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3mol / L) as electrolyte.

[0042] To test the liquid absorption capacity of the negative electrode: Using a 1 mL burette, draw V mL of electrolyte and add one drop to the surface of the negative electrode. Timing is maintained until the electrolyte is completely absorbed. Record the time t and calculate the liquid absorption rate V / t of the electrode.

[0043] Cyclic performance test: charge / discharge current 1.0C / 1.0C, voltage range 2.8-4.2V, number of cycles 500.

[0044] Test rate performance: constant current ratio under 2C charging conditions, i.e. constant current capacity / (constant current capacity + constant voltage capacity).

[0045] Table 2

[0046] project Liquid absorption rate Cycle retention rate (%) Cyclic charging DCR (mΩ) 2C constant current ratio (%) Example 1 6.8 95.3 47.4 93.3 Example 2 7.2 95.9 52.3 91.7 Example 3 6.3 94.6 43.3 92.5 Comparative Example 1 2.4 88.8 78.4 87.3 Comparative Example 2 3.4 90.4 67.8 88.4

[0047] As shown in Table 2, compared with the comparative example, the liquid absorption and retention capacity of the phosphorus-metal alloy co-doped hard carbon composite materials in Examples 1-3 are significantly better than those in the comparative example. The reason for this is that the materials in the examples have a high specific surface area, which increases the liquid absorption rate of the materials; at the same time, the materials in the examples have excellent powder conductivity, which improves the fast charging performance.

[0048] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a phosphorus-metal alloy co-doped hard carbon composite material, characterized in that, Includes the following steps: Step (1): Red phosphorus and crosslinking agent are added to solid resin according to the mass ratio of red phosphorus: crosslinking agent: solid resin = 1-10: 10-30: 100 and ball milled for 16 hours at a speed of 400-500 r / min. Then, it is heated and cured at a temperature of 300-500℃ to obtain a porous intermediate. Step (2): The porous intermediate, metal alloy powder, and sodium carboxymethyl cellulose are mixed evenly according to a mass ratio of porous intermediate: metal alloy powder: sodium carboxymethyl cellulose = 100:1-10:1-5. Then, the mixture is carbonized at 1200-1500℃ for 1-6 hours and pulverized to obtain a phosphorus-metal alloy co-doped hard carbon composite material. In step (2), the metal alloy powder is Na. 15 Sn4, Na3Sb, Na 15 One of the Pb4 particles, with a particle size of 100-500 nm.

2. The method for preparing a phosphorus-metal alloy co-doped hard carbon composite material according to claim 1, characterized in that, The red phosphorus in step (1) has a particle size of 100-1000 μm.

3. The method for preparing a phosphorus-metal alloy co-doped hard carbon composite material according to claim 1, characterized in that, In step (1), the crosslinking agent is one of m-hydroxybenzaldehyde, 4-ethoxybenzaldehyde, p-dimethylaminobenzaldehyde, p-aminobenzaldehyde, 3-ethoxyo-hydroxybenzaldehyde, and 3,5-bis(trifluoromethylbenzaldehyde).

4. The method for preparing a phosphorus-metal alloy co-doped hard carbon composite material according to claim 1, characterized in that, The solid resin in step (1) is one of melamine-formaldehyde resin, furan resin, polyester resin, vinyl resin, bismaleimide, or thermosetting polyimide.

Images