A P,O co-doped hard carbon anode material for sodium-ion batteries and its preparation method

Abstract

This invention discloses a P,O co-doped hard carbon anode material for sodium-ion batteries and its preparation method. The method includes: pulverizing raw material asphalt through a high-energy ball mill and then sieving it; removing impurities by acid / alkali washing, then washing with deionized water and drying to obtain pure asphalt powder; mixing the asphalt powder, organophosphorus source, and alcohol in a certain proportion, transferring the mixture to a crucible, and then transferring it to a tube furnace; heating at a certain heating rate, holding at that temperature, and then cooling to room temperature at a certain cooling rate; after the tube furnace has completely cooled down, removing the crucible, grinding the material, and sieving it to obtain the P,O co-doped asphalt-based carbon anode material. The novel P,O co-doped asphalt-based hard carbon anode material for sodium-ion batteries prepared by this invention greatly improves the sodium storage performance of asphalt cracking carbon, possessing high specific capacity, high initial coulombic efficiency, and long cycle life, and can be used in low-speed electric vehicles and distributed energy storage fields.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and in particular to a P,O co-doped pitch-based hard carbon anode material for sodium-ion batteries and its preparation method. Background Technology

[0002] With the "dual carbon" approach becoming a global consensus, energy storage has experienced explosive growth. However, lithium-ion batteries, constrained by limited lithium reserves and rising prices, cannot meet market demand. Compared to lithium, sodium is abundant in nature and inexpensive, thus sodium-ion batteries have received widespread attention in recent years.

[0003] Sodium-ion batteries have yet to achieve industrialization, primarily due to the lack of suitable anode materials. Currently, considering both energy storage performance and raw material costs, amorphous carbon (including hard carbon and soft carbon) anodes offer the best overall performance. Among them, hard carbon anodes have a relatively high sodium storage capacity, reaching up to 300 mAh g⁻¹. -1 However, the precursor is expensive and has a low carbon yield. In contrast, soft carbon precursors are widely available, inexpensive, and have a high carbon yield, but soft carbon has a low sodium storage capacity and no sodium storage platform, which limits its development in the field of sodium-ion batteries.

[0004] Generally, the typical charge-discharge curve of carbon-based anode materials used in sodium-ion batteries consists of a slope controlled by surface diffusion in a high-voltage range (≥0.5V) and a plateau controlled by embedding in a low-voltage range (≤0.1V). The sodium-ion kinetics in the plateau region are relatively slow, while the capacity in the slope region exhibits faster reaction kinetics.

[0005] Currently, there is limited research on the modification of soft carbon anodes for sodium batteries, with the focus mainly on pitch-based carbon anode materials. Existing modification techniques can be broadly categorized into four types:

[0006] 1. Soft and hard carbon composite: Adding hard carbon precursors (such as phenolic resin and lignin) improves the disorder of pitch pyrolysis carbon materials, resulting in higher reversible capacity and ICE, but lower rate performance and higher cost.

[0007] 2. Pre-oxidation: The carbonyl functional groups generated during the process cross-link with the asphalt molecules, slowing down the liquid phase carbonization process of asphalt and generating a large number of disordered structures. At the same time, the CO and CO2 released during the high-temperature carbonization process will generate nanopores in the amorphous carbon, resulting in higher sodium storage capacity and ICE, but lower rate performance.

[0008] 3. Low-temperature carbonization yields amorphous carbon materials with randomly arranged short carbon layers and high defect concentration, resulting in slope-dominated carbon materials with a sodium storage capacity of up to 263 mAh g⁻¹, good rate performance, and an ICE of up to 80%. However, the low-temperature carbonization rate is slow, the reaction time is long, and the efficiency is low. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a P, O co-doped sodium-ion battery hard carbon anode material and its preparation method, which addresses the shortcomings of the prior art.

[0010] The technical solution of the present invention is as follows:

[0011] A method for preparing a P,O co-doped sodium-ion battery hard carbon anode material includes the following steps:

[0012] A1. The raw material asphalt is pulverized by a high-energy ball mill and then sieved.

[0013] A2. After sieving, the material is acid-washed / alkali-washed to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder.

[0014] A3. Mix the asphalt powder, organophosphorus source and alcohol evenly according to a certain ratio, then transfer the mixture into a crucible and then into a tube furnace.

[0015] A4. In an inert gas atmosphere, turn on the tube furnace, heat it at a certain heating rate, hold it at that temperature for a period of time, and then cool it down to room temperature at a certain cooling rate.

[0016] A5. After the tube furnace has completely cooled down, remove the crucible, grind the material and sieve it to obtain P and O co-doped pitch-based carbon anode material.

[0017] In the preparation method described above, the sieve mesh size is 50-300 mesh, and in the acid washing / alkali washing, the acid is one or more of hydrochloric acid, nitric acid, hydrofluoric acid, and oxalic acid, with a molar fraction of 0.05-2 mol / L, and the alkali is one or more of sodium hydroxide, potassium hydroxide, ammonia, ammonium bicarbonate, and ammonium bicarbonate, with a molar fraction of 0.05-2 mol / L.

[0018] In the preparation method described above, the mass ratio of asphalt powder, organophosphorus source and alcohol in step A3 is 1:0.05-2:0.05-2.

[0019] In the preparation method described above, the organophosphorus source in step A3 is one or more of phytic acid (PA), hydroxyethylidene diphosphonic acid (HEDP), and methylene diphosphonic acid (MDP), and the polyol is one or more of ethylene glycol, propylene glycol, hexanediol, glycerol, and polyoxypropylene glycol.

[0020] The preparation method described herein involves a tubular furnace with a heating rate of 1-10℃ / min, a holding temperature of 500-1400℃, a holding time of 2-20h, and a cooling rate of 1-10℃ / min.

[0021] The preparation method described above states that the negative electrode material obtained in step A4 is a pitch cracking carbon material with high amorphity and numerous microporous structures.

[0022] P,O co-doped sodium-ion battery hard carbon anode material prepared according to any of the methods described.

[0023] This invention primarily addresses the problems of low sodium storage capacity and difficulty in simultaneously improving slope capacity and initial coulombic efficiency in existing asphalt-based carbon materials. Simultaneously, it responds to the demand for novel sodium-ion battery anode materials driven by the development of low-speed electric vehicles and energy storage, providing a method for preparing a novel P,O co-doped sodium-ion battery hard carbon anode material.

[0024] This invention is the first to utilize an organophosphorus source (such as phytic acid) as a P and O precursor, achieving a comprehensive modification effect that inhibits the ordered transformation and doping of asphalt. This is mainly reflected in: 1. During heating, the multifunctional organophosphorus source indirectly induces the cross-linking reaction of aromatic molecules in the asphalt through its own cross-linking reaction and emulsification effect on the asphalt, forming suitable closed pores after carbonization and introducing plateau capacity; 2. The organophosphorus source contains abundant P and O atoms, which, when doped into carbon materials during heating, can effectively increase the sodium storage sites of carbon-based composite materials, while also increasing the defect density in the carbon materials, significantly improving slope capacity. By utilizing the synergistic effect of the organophosphorus source inducing disordered transformation of asphalt and controllable in-situ doping, the sodium storage performance of amorphous carbon materials is comprehensively improved.

[0025] The present invention has the following beneficial effects:

[0026] (1) Multifunctional organophosphorus sources indirectly induce cross-linking between aromatic molecules in asphalt through their own cross-linking reaction and emulsification of asphalt, forming closed pores with suitable pore size. Based on improving slope capacity through doping, plateau capacity is introduced.

[0027] (2) Although NaH2PO4 is an inorganic phosphorus source with low cost, the residual Na-containing compounds after the reaction need to be removed by an additional water washing process. The remaining pores will also increase the new electrode / electrolyte interface, which limits the further improvement of the first coulombic efficiency of the carbon anode. This invention can avoid the porosity caused by the removal of Na-containing compounds. At the same time, it is expected to utilize the designability of its molecular structure to increase more reversible heteroatom configurations, thereby further improving the ramp capacity and first efficiency. Attached Figure Description

[0028] Figure 1 XRD pattern of pyrolysis carbon after carbonization of asphalt and phytic acid mixture at 1400℃.

[0029] Figure 2 Raman spectrum (a) and constant current charge-discharge curve (b) of pyrolysis carbon after carbonization at 1000℃ of a mixture of asphalt, phytic acid and propylene glycol;

[0030] Figure 3 Raman spectroscopy of pyrolysis carbon after carbonization of a mixture of asphalt, phytic acid and ethanol at 1000℃.

[0031] Figure 4 XRD pattern (a) and charge-discharge curve (b) of pyrolysis carbon after carbonization at 800℃ of a mixture of asphalt, phytic acid and propylene glycol;

[0032] Figure 5 Raman spectroscopy (a), SEM image (b), and magnification (c) of the cracked carbon after carbonization at 800℃ of a mixture of asphalt, phytic acid, and ethanol.

[0033] Figure 6 Raman spectroscopy and SEM image of pyrolysis carbon after asphalt carbonization at 800℃ (a) and (b); Detailed Implementation

[0034] The present invention will be described in detail below with reference to specific embodiments.

[0035] The preparation method of P, O co-doped sodium-ion battery hard carbon anode material is carried out according to the following steps:

[0036] 1. The raw material asphalt is pulverized by high-energy ball milling and then passed through a 100-300 mesh sieve.

[0037] 2. Removal of ash from asphalt: The sieved material is acid-washed / alkali-washed to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder.

[0038] 3. After mixing the asphalt powder, organophosphorus source and alcohol evenly according to a certain ratio, transfer the mixture into a crucible and then into a tube furnace.

[0039] 4. Under N2 atmosphere, turn on the tube furnace and heat at a heating rate of 3℃ / min until it reaches 700~1400℃. Hold the temperature for 1~12h and then cool it down to room temperature at a rate of 2℃ / min.

[0040] 5. After the tube furnace has completely cooled down, remove the crucible, grind the material and pass it through a 200-mesh sieve to obtain a novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material.

[0041] Accordingly, based on the above-described method for preparing the novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material, this invention also provides a P,O co-doped pitch-based carbon anode material. Naturally, this novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material can be prepared by the above method. If this novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material is prepared by other methods, it is also within the scope of disclosure and protection of this invention.

[0042] Example 1: The preparation method of the novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material of this embodiment is carried out according to the following steps:

[0043] 1. The raw material asphalt is pulverized by high-energy ball milling and then passed through a 200-mesh sieve.

[0044] 2. Removal of ash from asphalt: The sieved material is acid-washed with hydrochloric acid and hydrofluoric acid to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder.

[0045] 3. Mix 1.5g of asphalt powder, 0.1g of phytic acid and 10ml of ethanol, evaporate to dryness and then transfer to a crucible and transfer to a tube furnace.

[0046] 4. Under N2 atmosphere, turn on the tube furnace and heat at a rate of 3℃ / min until it reaches 1400℃. Hold at this temperature for 5 hours and then cool to room temperature at a rate of 2℃ / min.

[0047] 5. After the tube furnace has completely cooled down, remove the crucible, grind the material and pass it through a 200-mesh sieve to obtain a novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material.

[0048] like Figure 1 As shown, asphalt and phytic acid are uniformly mixed, and ethanol is used as a dispersant. After the ethanol is evaporated, carbonization is carried out at 1400℃. It can be seen that the (003) peak is relatively sharp, indicating that the material has relatively good crystallinity, high degree of graphitization, and correspondingly weak sodium storage capacity.

[0049] Example 2: The preparation method of the novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material of this embodiment is carried out according to the following steps:

[0050] 1. The raw material asphalt is pulverized by high-energy ball milling and then passed through a 200-mesh sieve.

[0051] 2. Removal of ash from asphalt: The sieved material is acid-washed with hydrochloric acid and hydrofluoric acid to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder.

[0052] 3. Mix 1.5g of asphalt powder, 0.2g of phytic acid and 10ml of ethanol evenly, evaporate to dryness and place in a crucible to transfer to a tube furnace.

[0053] 4. Under N2 atmosphere, turn on the tube furnace and heat at a rate of 5℃ / min until it reaches 1000℃. Hold at this temperature for 2 hours and then cool to room temperature at a rate of 3℃ / min.

[0054] 5. After the tube furnace has completely cooled down, remove the crucible, grind the material and pass it through a 200-mesh sieve to obtain a novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material.

[0055] like Figure 2 As shown, the Raman spectrum at 1340 cm⁻¹ -1 and 1580cm -1 The appearance of peaks D and G at the edge of the graphene layer represents the A peaks of the edge defects. 1g Symmetric vibrational modes and E of an ideal graphite lattice 2g Symmetric vibrational modes. The Raman spectrum of a mixture of asphalt and phytic acid carbonized at 1000℃ exhibits I-mode vibration. D / I G The significant increase indicates a substantial decrease in the degree of graphitization of the material, resulting in an increase in reversible specific capacity and an increase in ICE.

[0056] Example 3: The preparation method of the novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material of this embodiment is carried out according to the following steps:

[0057] 1. The raw material asphalt is pulverized by high-energy ball milling and then passed through a 200-mesh sieve.

[0058] 2. Removal of ash from asphalt: The sieved material is acid-washed with hydrochloric acid and hydrofluoric acid to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder.

[0059] 3. Mix 2g of asphalt powder, 0.2g of phytic acid and 10ml of propylene glycol evenly and place them in a crucible to transfer to a tube furnace.

[0060] 4. In an N2 atmosphere, turn on the tube furnace and heat at a rate of 3℃ / min until it reaches 1000℃. Hold at this temperature for 2 hours and then cool to room temperature at a rate of 2℃ / min.

[0061] 5. After the tube furnace has completely cooled down, remove the crucible, grind the material and pass it through a 200-mesh sieve to obtain a novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material.

[0062] like Figure 3 As shown, when asphalt, phytic acid, and propylene glycol are mixed and carbonized at 1000℃, the Raman spectrum shows I... D / I GThe significant increase indicates that the graphitization degree of the material has decreased significantly and the disorder has increased. This is related to the following reasons: (1) Phytic acid contains abundant P and O elements. A large amount of P and O enters the cracked carbon, which inhibits the orderly arrangement of carbon atoms in the asphalt cracking process and provides a large number of sodium storage sites, increasing the defect density in the composite material. While providing slope capacity, it reduces irreversible capacity loss; (2) Phytic acid has abundant organic functional groups that cross-link with the hydroxyl groups in propylene glycol and the aromatic molecules in asphalt, forming closed pores with suitable pore size during carbonization and introducing plateau capacity.

[0063] Example 4: The preparation method of the novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material of this embodiment is carried out according to the following steps:

[0064] 1. The raw material asphalt is pulverized by high-energy ball milling and then passed through a 200-mesh sieve.

[0065] 2. Removal of ash from asphalt: The sieved material is acid-washed with hydrochloric acid and hydrofluoric acid to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder.

[0066] 3. Mix 1.5g of asphalt powder, 0.5g of phytic acid and 10ml of propylene glycol evenly, then transfer the mixture to a crucible and transfer it to a tube furnace.

[0067] 4. Under N2 atmosphere, turn on the tube furnace and heat at a rate of 3℃ / min until it reaches 800℃. Hold at this temperature for 2 hours and then cool to room temperature at a rate of 2℃ / min.

[0068] 5. After the tube furnace has completely cooled down, remove the crucible, grind the material and pass it through a 200-mesh sieve to obtain a novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material.

[0069] like Figure 4-5 As shown, when asphalt, phytic acid, and propylene glycol are mixed and carbonized at 1000℃, the (003) peak in the XRD becomes coarser and lower, and the I peak in the Raman spectrum becomes... D / I G The significant increase indicates that the graphitization degree of the material is significantly reduced, the disorder degree is increased, and the capacity is greatly improved, with ICE reaching as high as 84.6%. This is related to the following reasons: (1) Phytic acid contains abundant P and O elements. A large amount of P and O enters the cracked carbon, which inhibits the orderly arrangement of carbon atoms in the asphalt cracking process and provides a large number of sodium storage sites, increasing the defect density in the composite material. While providing slope capacity, it reduces irreversible capacity loss; (2) Phytic acid has abundant organic functional groups that cross-link with the hydroxyl groups in propylene glycol and the aromatic molecules in asphalt, forming closed pores with suitable pore size during carbonization and introducing plateau capacity.

[0070] The modified SEM images show that the asphalt doped with phytic acid exhibits a typical flaky shape with relatively fine particles and a high degree of disorder. The rate performance graph shows a capacity of 151.9 mAh / g at a high current of 2 A / g, and the capacity recovers to the initial value when the current is reduced to 0.1 A / g, indicating good rate performance.

[0071] Example 5: The preparation method of the novel P,O co-doped pitch-based sodium-ion battery hard carbon anode material of this embodiment is carried out according to the following steps:

[0072] 1. The raw material asphalt is pulverized by high-energy ball milling and then passed through a 200-mesh sieve.

[0073] 2. Removal of ash from asphalt: The sieved material is acid-washed with hydrochloric acid and hydrofluoric acid to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder.

[0074] 3. Place 1.5g of asphalt powder into a crucible and transfer it to a tube furnace.

[0075] 4. Under N2 atmosphere, turn on the tube furnace and heat at a rate of 3℃ / min until it reaches 800℃. Hold at this temperature for 2 hours and then cool to room temperature at a rate of 2℃ / min.

[0076] 5. After the tube furnace has completely cooled down, remove the crucible, grind the material and pass it through a 200-mesh sieve to obtain the asphalt cracking sodium-carbon ion battery anode material.

[0077] Compared to Example 4, the pure asphalt without phytic acid modification, when carbonized at 800°C, showed a significant decrease in its Raman spectrum ID / IG ratio. Figure 6 Without the P and O doping and cross-linking reaction in the organophosphorus source, the graphitization degree of the asphalt increases, and SEM shows that the particle size is large, indicating that the sodium storage performance of the material is not ideal.

[0078] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a P,O co-doped hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: A1. The raw material asphalt is pulverized by a high-energy ball mill and then sieved. A2. After sieving, the material is acid-washed / alkali-washed to remove impurities, then washed with deionized water and dried to obtain pure asphalt powder. A3. Mix asphalt powder, organophosphorus source, and alcohol evenly according to a certain ratio, then transfer the mixture to a crucible and transfer it to a tube furnace; the mass ratio of asphalt powder, organophosphorus source, and alcohol is 1:0.05-2:0.05-2; the organophosphorus source is one or more of phytic acid (PA), hydroxyethylidene diphosphonic acid (HEDP), and methylene diphosphonic acid (MDP), and the polyol is one or more of ethylene glycol, propylene glycol, hexanediol, glycerol, and polyoxypropylene glycol; A4. In an inert gas atmosphere, turn on the tube furnace, heat it at a certain heating rate, hold it at that temperature for a period of time, and then cool it down to room temperature at a certain cooling rate. A5. After the tube furnace has completely cooled down, remove the crucible, grind the material and sieve it to obtain P and O co-doped pitch-based carbon anode material. The sieve mesh size is 50-300 mesh. In the acid washing / alkali washing, the acid is one or more of hydrochloric acid, nitric acid, hydrofluoric acid, and oxalic acid, with a molar fraction of 0.05-2 mol / L. The alkali is one or more of sodium hydroxide, potassium hydroxide, ammonia, ammonium bicarbonate, and ammonium bicarbonate, with a molar fraction of 0.05-2 mol / L.

2. The preparation method according to claim 1, characterized in that, The heating rate of the tubular furnace is 1-10℃ / min, the holding temperature is 500-1400℃, the holding time is 2-20h, and the cooling rate is 1-10℃ / min.

3. The preparation method according to claim 1, characterized in that, The negative electrode material obtained in step A4 is a pitch cracking carbon material with high amorphity and a large number of micropores.

4. The P, O co-doped sodium-ion battery hard carbon anode material prepared by any one of the methods described in claims 1-3.

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