A method for preparing a zinc salt assisted epoxy resin based hard carbon material and application as a negative electrode material for sodium ion batteries

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a preparation method of a zinc salt-assisted epoxy resin-based hard carbon material and application of the hard carbon material as a negative electrode material of a sodium ion battery. A zinc salt and a phenolic epoxy resin are uniformly mixed, pre-burning and high-temperature pyrolysis are carried out to obtain a hard carbon material. In the application, inorganic zinc salt is introduced, ring-opening cross-linking reaction of epoxy groups occurs under the catalysis of zinc ions in the pre-burning process, complex reaction of zinc ions and epoxy groups and hydroxyl functional groups in the resin, promotion of uniform dispersion of zinc ion atoms and subsequent uniform dispersion of superfine zinc oxide nanoparticles, effective regulation of mesostructure of intermediates and improvement of structure thermal stability. In the high-temperature pyrolysis process, elemental zinc generated by carbon thermal reduction is used for activation and catalysis of carbon intermediates, and the microstructure of the hard carbon is effectively regulated. The hard carbon as the negative electrode material of the sodium ion battery, the prepared sodium ion battery shows excellent initial coulombic efficiency, charge-discharge capacity and long cycle stability.

Description

Technical fields:

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a method for preparing a zinc salt-assisted epoxy resin-based hard carbon material and its application as a negative electrode material for sodium-ion batteries. Background technology:

[0002] Sodium-ion batteries (SIBs), due to their abundant sodium resources and highly promising charge storage capacity, have become the next generation of large-scale energy storage systems supporting the sustainable development of renewable energy. Hard carbon (HC) is an amorphous carbon composed of internal micropores existing between pseudo-graphite domains. It possesses advantages such as large interlayer spacing, complex microstructure, good structural stability, and strong reversibility, and its abundant availability makes it the preferred material for SIB anodes, attracting widespread attention.

[0003] To date, numerous attempts have been made to improve the electrochemical performance of HC, including increasing the interlayer distance to achieve Na+. + While rapid insertion and extraction of sodium ions are possible, they inevitably introduce defects such as irreversible sodium ion pores, leading to low initial coulombic efficiency and poor cycle performance. Optimizing porous systems, such as closing the pores on activated carbon, can improve sodium ion absorption. + The storage of Na clusters in suitable pores and the introduction of heteroatoms (such as N, F, etc.) or defects to provide more charge adsorption sites are all ways to achieve higher specific capacity. However, traditional methods for controlling the microstructure of HC have encountered bottlenecks. The trade-off between rate performance, initial coulombic efficiency (ICE), or specific capacity remains a challenge hindering the practical application of hard carbon anode materials.

[0004] The microstructure of hard carbon is primarily influenced by its precursors, which largely determine the anode's performance. Currently, precursors for hard carbon materials can be broadly categorized into three types: biomass-based, resin-based, and petroleum-based. Although biomass-based and petroleum-based hard carbon materials are widely available and low-cost, their low carbon yield and reproducibility make them unsuitable for large-scale industrial production. Resin-based hard carbon preparation technology is mature, with high consistency and reproducibility, thus resin-based hard carbon materials have gained favor among researchers in recent years. However, the low yield, low reversible capacity, and poor cycling performance of traditional resin-derived hard carbon limit its further development. Therefore, we designed a pore structure suitable for Na storage and adjusted the volume and surface structure to achieve a high-performance hard carbon anode material. Summary of the Invention:

[0005] Based on the above analysis, the purpose of this invention is to provide a method for preparing zinc salt-assisted epoxy resin-based hard carbon materials and their application as a negative electrode material for sodium-ion batteries. By utilizing the controllable generation of ultrafine zinc oxide templates from inorganic zinc salts to regulate the microstructure of resin-based hard carbon, a hard carbon negative electrode material with simple process, high specific capacity, high rate capability, and excellent cycle stability is prepared.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing a zinc salt-assisted epoxy resin-based hard carbon material includes the following steps:

[0008] S1: By using phenolic epoxy resin as a precursor, inorganic zinc salt and phenolic epoxy resin are mixed evenly in a mass ratio of 10:(0.5~2) to obtain intermediate A;

[0009] S2: Under an inert atmosphere, at 200℃~600℃, intermediate A is placed in the first heating furnace for pre-calcination to obtain intermediate B;

[0010] During the pre-calcination process, under the catalysis of zinc ions, the epoxy groups of phenolic epoxy resin undergo ring-opening cross-linking reaction. The complexation reaction between zinc ions and the epoxy and hydroxyl functional groups in phenolic epoxy resin promotes the atomic-level uniform dispersion of zinc ions and the uniform dispersion of subsequent ultrafine zinc oxide nanoparticles, effectively regulating the mesoscopic structure of intermediate B and improving the structural thermal stability.

[0011] S3: Intermediate B is placed in a second heating furnace for high-temperature pyrolysis. Gas is introduced at 900℃~1600℃ to obtain hard carbon material.

[0012] During high-temperature pyrolysis, ultrafine zinc oxide nanoparticles and elemental zinc generated by carbothermic reduction effectively regulate the microstructure of hard carbon by activating and catalyzing the graphitization of carbon intermediates.

[0013] In the method for preparing zinc salt-assisted epoxy resin-based hard carbon materials, in step S1, the inorganic zinc salt is one or more of zinc acetate, zinc sulfate, zinc nitrate, and zinc chloride.

[0014] In the method for preparing zinc salt-assisted epoxy resin-based hard carbon material, in step S1, the phenolic epoxy resin is one or more of o-cresol-type phenolic epoxy resin, bisphenol A-type phenolic epoxy resin, and biphenol-type phenolic epoxy resin.

[0015] In the method for preparing zinc salt-assisted epoxy resin-based hard carbon material, in step S2, the inert atmosphere is selected from one of argon atmosphere, nitrogen atmosphere, and helium atmosphere.

[0016] In the method for preparing the zinc salt-assisted epoxy resin-based hard carbon material, step S2, the pre-calcination includes: heating to 200℃ to 600℃ at a rate of 1 to 5℃ / min and holding at that temperature for 30 min to 4 h.

[0017] In the preparation method of the zinc salt-assisted epoxy resin-based hard carbon material, step S3, the high-temperature pyrolysis includes: heating to 900℃~1600℃ at a rate of 5~10℃ / min and holding at that temperature for 30min~4h.

[0018] The method for preparing the zinc salt-assisted epoxy resin-based hard carbon material describes a method for preparing ultrafine zinc oxide nanoparticles with a particle size of 5–8 nm.

[0019] Application of the zinc salt-assisted epoxy resin-based hard carbon material as a negative electrode material for sodium-ion batteries.

[0020] The technical mechanism and beneficial effects of this invention are as follows:

[0021] 1. This invention involves uniformly mixing zinc salt and phenolic epoxy resin, followed by pre-calcination and high-temperature pyrolysis to prepare a high-performance hard carbon anode material for sodium-ion batteries. The method uses phenolic epoxy resin as a precursor, a readily available raw material containing numerous epoxy functional groups. In the first pre-calcination step, under the catalysis of zinc ions, the epoxy groups undergo ring-opening cross-linking. The complexation reaction between zinc ions and the epoxy and hydroxyl functional groups in the resin promotes atomic-level uniform dispersion of zinc ions and subsequent uniform dispersion of ultrafine zinc oxide nanoparticles, effectively controlling the mesoscopic structure of the intermediate and improving its structural thermal stability, thereby increasing the yield of hard carbon. In the second high-temperature pyrolysis step, the zinc element generated from the carbothermic reduction of zinc oxide activates and catalyzes the graphitization of the carbon intermediate, effectively controlling the microstructure of the hard carbon.

[0022] 2. When the hard carbon material prepared using this invention is applied to the anode of a sodium-ion battery, it can reach 405 mAh / g at a current density of 30 mA / g. Even when the current density increases to 1 A / g, the capacity of the sodium-ion battery can still be maintained at 317 mAh / g, and after 500 cycles, the capacity retention rate can still reach 97.4%. Compared with other resin-based anode materials, its initial coulombic efficiency, charge-discharge specific capacity, and long-term cycle stability are all improved.

[0023] 3. The preparation process of the present invention is simple, environmentally friendly, and suitable for large-scale production. Attached image description:

[0024] Figure 1 This is a comparison chart of thermogravimetric analysis (TG) of the precursors in Example 1 and Comparative Example 1 of the present invention. In the chart, the horizontal axis Temperature represents temperature (°C), and the vertical axis Mass represents mass percentage (%).

[0025] Figure 2 This is a charge-discharge curve of the hard carbon anode material obtained in Example 1 of the present invention. In the figure, the horizontal axis, Specific Capacity, represents the specific capacity (mAh g). -1 The vertical axis represents voltage (V).

[0026] Figure 3 This is a comparison graph of Example 1 and Comparative Example 1 under 1C cycling conditions. In the graph, the horizontal axis represents the number of cycles (n), and the vertical axis represents the specific capacity (mAh g). -1 ). Detailed implementation method:

[0027] The present invention will now be further described with reference to the embodiments. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0028] In its specific implementation, this invention provides a method for preparing a zinc salt-assisted epoxy resin-based hard carbon material and its application as a negative electrode material for sodium-ion batteries. The preparation method includes the following steps:

[0029] S1: By using phenolic epoxy resin as a precursor, a certain proportion of inorganic zinc salt is mixed evenly with phenolic epoxy resin to obtain intermediate A.

[0030] S2: Under an inert atmosphere, at 200℃~600℃, intermediate A is placed in the first heating furnace for pre-calcination to obtain intermediate B.

[0031] S3: The intermediate B is placed in a second heating furnace for high-temperature pyrolysis. Gas is introduced at 900℃~1600℃ to obtain a hard carbon anode material.

[0032] The phenolic epoxy resin (EPN) of this invention, also known as F-type epoxy resin, is different from both epoxy resin and phenolic resin. It is formed by the reaction of phenolic resin and epoxy resin under certain conditions, resulting in a compound with unique properties. F-type epoxy resin contains both epoxy functional groups and active phenolic hydroxyl functional groups, thus possessing the dual characteristics of both epoxy and phenolic resins. This dual characteristic makes it possible to develop novel high-performance hard carbon materials.

[0033] In the following embodiments, the half-cell testing method is as follows: The negative electrode material samples prepared in each embodiment are mixed evenly with conductive agent acetylene black and binder sodium polyacrylate emulsion at a mass ratio of 70:20:10 in deionized water, and then pressed onto aluminum foil to obtain negative electrode sheets. The negative electrode sheets are then placed in a vacuum drying oven at 80°C for 8 hours for later use. Using metallic sodium sheets as positive electrodes, CR2025 type button sodium-ion batteries are assembled and charged and discharged.

[0034] Example 1

[0035] In this embodiment, a method for preparing a zinc salt-assisted o-cresol-type phenolic epoxy resin-based hard carbon material includes the following steps:

[0036] S1: Anhydrous zinc acetate and o-cresol type phenolic epoxy resin were mixed evenly at a mass ratio of 10:1 to obtain intermediate 1.

[0037] S2: Place intermediate 1 into a tube furnace, heat it to 400℃ at 4℃ / min, and hold it for 2 hours to obtain intermediate 2, and obtain ultrafine zinc oxide nanoparticles with a particle size of 5-8nm.

[0038] S3: Grind the obtained intermediate 2, put the intermediate 2 into a high temperature furnace, heat it to 1300℃ at 10℃ / min, and keep it at that temperature for 1h to obtain hard carbon anode material.

[0039] like Figure 1 As shown, the obtained precursor was subjected to TG-DSC testing. After adding zinc salt, the zinc salt decomposed at a certain temperature to controllably generate zinc oxide template, thereby regulating the microstructure of the hard carbon anode material and improving the hard carbon yield.

[0040] like Figure 2 As shown, the performance of the hard carbon anode material prepared in this embodiment was tested. The specific capacity of this anode material reached 405 mAh / g, and the initial efficiency reached 89%. Compared with hard carbon prepared from pure o-cresol phenolic epoxy resin, the specific capacity is increased by about 20%, and it has high rate capability and long cycle stability, which can meet the requirements of power sodium-ion batteries.

[0041] Example 2

[0042] In this embodiment, a method for preparing a zinc salt-assisted bisphenol A type phenolic epoxy resin-based hard carbon material includes the following steps:

[0043] S1: Anhydrous zinc acetate and bisphenol A phenolic epoxy resin were mixed evenly at a mass ratio of 10:1.5 to obtain intermediate 3.

[0044] S2: Place intermediate 3 into a tube furnace, heat it to 300℃ at 3℃ / min, and hold it for 3h to obtain intermediate 4, and obtain ultrafine zinc oxide nanoparticles with a particle size of 5-10nm.

[0045] S3: Grind the obtained intermediate 4, put the intermediate 4 into a high-temperature furnace, heat it to 1200℃ at 6℃ / min, and keep it at that temperature for 2 hours to obtain hard carbon anode material.

[0046] The testing and inspection process for this sodium-ion battery hard carbon anode material is described in Example 1. The specific capacity of this anode material reaches over 396 mAh / g, the initial coulombic efficiency is 91%, and the cycle performance is stable.

[0047] Example 3

[0048] In this embodiment, a method for preparing a zinc salt-assisted biphenol-type phenolic epoxy resin-based hard carbon material includes the following steps:

[0049] S1: Take anhydrous zinc acetate and biphenol-type phenolic epoxy resin in a mass ratio of 10:1, mix them evenly to obtain intermediate 5.

[0050] S2: Place intermediate 5 into a tube furnace, heat it to 500℃ at 5℃ / min, and hold it for 1 hour to obtain intermediate 6, and obtain ultrafine zinc oxide nanoparticles with a particle size of 4-10nm.

[0051] S3: Grind the obtained intermediate 6, put the intermediate 6 into a high-temperature furnace, heat it to 1600℃ at 8℃ / min, and hold it for 0.5h to obtain hard carbon anode material.

[0052] For the detection and testing process of this sodium-ion battery hard carbon anode material, please refer to the relevant content in Example 1. The specific capacity of this anode material can reach 401 mAh / g, the initial coulombic efficiency is 89%, and it has high rate capability and cycle stability.

[0053] Comparative Example 1

[0054] In this comparative example, a method for preparing an o-cresol-type phenolic epoxy resin hard carbon material includes the following steps:

[0055] S1: Take a certain mass of o-cresol-type phenolic epoxy resin as precursor 7.

[0056] S2: Place precursor 7 into a tube furnace, heat it to 400℃ at 4℃ / min, and hold it for 2 hours to obtain intermediate 8.

[0057] S3: Grind the obtained intermediate 8, put the intermediate 8 into a high-temperature furnace, heat it to 1300℃ at 10℃ / min, and keep it at that temperature for 1h to obtain hard carbon anode material.

[0058] The testing and analysis process for this sodium-ion battery hard carbon anode material is described in Example 1. The initial charge-discharge efficiency was 88%, but the charge capacity dropped to 343 mAh / g. However, the rate capability and cycle stability were excellent. Furthermore, compared to Example 1, the absence of zinc salt catalytic crosslinking resulted in reduced intermediate thermal stability and a significantly lower yield of hard carbon.

[0059] like Figure 3 As shown in the comparison graph of cycling at 1C between Example 1 and Comparative Example 1, it can be seen that after 1000 cycles at 1C, the o-crestyrene epoxy resin, regulated by zinc ions, still retains a capacity of 344 mAh / g, with a capacity retention rate of 93.5%. In contrast, the o-crestyrene epoxy resin-based hard carbon without zinc ion regulation has a capacity of only 252 mAh / g after 1000 cycles, with a capacity retention rate of only 79.7%. Therefore, the phenolic epoxy resin-based hard carbon regulated by zinc ions exhibits excellent long-term cycling stability.

[0060] Comparative Example 2

[0061] In this comparative example, a method for preparing a bisphenol A type phenolic epoxy resin-based hard carbon material includes the following steps:

[0062] S1: Take a certain mass of bisphenol A type phenolic epoxy resin as precursor 9.

[0063] S2: Place precursor 2 into a tube furnace, heat it to 300℃ at 3℃ / min, and hold it for 3h to obtain intermediate 10.

[0064] S3: Grind the obtained intermediate 10, put the intermediate 10 into a high-temperature furnace, heat it to 1200℃ at 6℃ / min, and keep it at that temperature for 2 hours to obtain hard carbon anode material.

[0065] The testing and evaluation process for this sodium-ion battery hard carbon anode material is described in Example 1. The initial charge-discharge efficiency reached over 86%, and the charge specific capacity reached 320 mAh / g. Compared to Example 2, which did not add zinc salt and proceeded directly with carbonization, the yield was significantly lower than that of Example 3.

[0066] Comparative Example 3

[0067] In this comparative example, a method for preparing a bisphenol A type epoxy resin-based hard carbon material includes the following steps:

[0068] S1: Anhydrous zinc acetate and bisphenol A epoxy resin are mixed evenly at a mass ratio of 10:1 to obtain intermediate 11.

[0069] S2: Place intermediate 11 into a tube furnace, heat it to 400℃ at 4℃ / min, and hold it for 2 hours to obtain intermediate 12.

[0070] S3: Grind the obtained intermediate 12, put the intermediate 12 into a high-temperature furnace, heat it to 1300℃ at 10℃ / min, and keep it at that temperature for 1h to obtain hard carbon anode material.

[0071] The testing and analysis process for this sodium-ion battery hard carbon anode material is described in Example 1, except that a different resin was used compared to Example 1. Adding zinc salt increased the yield by more than 10% compared to pure bisphenol A resin, and the initial charge-discharge efficiency reached 89%. The charge capacity reached 352 mAh / g. Different heating ratios were used in the tests, and the performance was excellent.

[0072] The test results are shown in the table below:

[0073]

[0074] The results show that the preparation method of this invention overcomes the shortcomings of existing hard carbon anode material preparation processes, such as complexity, environmental unfriendliness, low initial efficiency, and difficulty in commercialization. The hard carbon anode material prepared by this invention exhibits good electrochemical performance, excellent high-current charge-discharge performance and long-cycle performance, and good stability. In the preparation process of the hard carbon material of this invention, the zinc salt content is low and uniformly distributed, the preparation method is simple, the process is short, energy consumption is low, safety is good, and it is easy to achieve mass production with no batch-to-batch variation. As a sodium-ion battery anode material, the sodium-ion battery prepared with this hard carbon material exhibits excellent initial coulombic efficiency, charge-discharge capacity, and long-cycle stability.

[0075] The above description is merely a basic explanation of the concept of this invention, and any equivalent modifications made based on the technical solution of this invention shall fall within the protection scope of this invention.

Claims

1. A method for preparing a zinc salt-assisted epoxy resin-based hard carbon material, characterized in that, Includes the following steps: S1: By using phenolic epoxy resin as a precursor, inorganic zinc salt and phenolic epoxy resin are mixed evenly in a mass ratio of 10:(0.5~2) to obtain intermediate A; S2: Under an inert atmosphere, intermediate A is placed in the first heating furnace for pre-calcination, and the temperature is increased to 400℃~600℃ at a rate of 1~5℃ / min and held for 30min~4h to obtain intermediate B; During the pre-calcination process, under the catalysis of zinc ions, the epoxy groups of phenolic epoxy resin undergo ring-opening cross-linking reaction. The complexation reaction between zinc ions and the epoxy and hydroxyl functional groups in phenolic epoxy resin promotes the atomic-level uniform dispersion of zinc ions and the uniform dispersion of subsequent ultrafine zinc oxide nanoparticles, effectively controlling the mesoscopic structure of intermediate B and improving the thermal stability of the structure. The particle size of the ultrafine zinc oxide nanoparticles is 4~10nm. S3: Place intermediate B in a second heating furnace for high-temperature pyrolysis, raise the temperature to 900℃~1300℃ at a rate of 5~10℃ / min, and hold for 30min~4h to obtain hard carbon material; During high-temperature pyrolysis, ultrafine zinc oxide nanoparticles and elemental zinc generated by carbothermic reduction effectively regulate the microstructure of hard carbon by activating and catalyzing the graphitization of carbon intermediates.

2. The method for preparing zinc salt-assisted epoxy resin-based hard carbon material according to claim 1, characterized in that, In step S1, the inorganic zinc salt is one or more of zinc acetate, zinc sulfate, zinc nitrate, and zinc chloride.

3. The method for preparing zinc salt-assisted epoxy resin-based hard carbon material according to claim 1, characterized in that, In step S1, the phenolic epoxy resin is one or more of o-cresol phenolic epoxy resin, bisphenol A phenolic epoxy resin, and biphenol phenolic epoxy resin.

4. The method for preparing zinc salt-assisted epoxy resin-based hard carbon material according to claim 1, characterized in that, In step S2, the inert atmosphere is selected from one of argon atmosphere, nitrogen atmosphere, and helium atmosphere.

5. The application of the zinc salt-assisted epoxy resin-based hard carbon material as described in any one of claims 1 to 4 as a negative electrode material for sodium-ion batteries.

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