Preparation method of high-capacity high-cycle sodium ion battery negative electrode material

Abstract

The invention discloses a preparation method of a high-capacity and high-cycle sodium ion battery negative electrode material, which explores and optimizes the deviation degree of a 002 peak by regulating and controlling the nitrogen doping content and matching with a proper pre-carbonization system, thereby regulating and controlling the change of the interlayer spacing of the negative electrode material. When the nitrogen doping content and the pre-carbonization temperature meet the condition that 3 * (10 * W + 0.0001 * T) is larger than or equal to 1.65 and smaller than or equal to 2.75, appropriate interlayer spacing change can be obtained, stable existence of the layer structure of the carbon material can be maintained, an appropriate amount of nitrogen doping active sites can be obtained, uniform distribution of the nitrogen doping active sites on the microcrystal surface and between layers of the carbon material can be maintained, high ion diffusion efficiency can be obtained, and rapid transmission of Na < + > can be promoted; and the negative electrode material has relatively high reversible specific capacity and first coulombic efficiency, so that the assembled sodium ion battery has excellent use performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a method for preparing a high-capacity, high-cycle sodium-ion battery anode material. Background Technology

[0002] With the transformation of the global energy structure and the demand for sustainable development, electrochemical energy storage technology has become a research hotspot. Among the many electrochemical energy storage systems, sodium-ion batteries have attracted much attention due to their low cost, abundant resources, and similar working principle to lithium-ion batteries. Because sodium resources are abundant on Earth and inexpensive, they are gradually becoming an effective supplement to lithium-ion batteries and are regarded as a promising large-scale energy storage technology.

[0003] Hard carbon materials have been widely studied as anode materials for sodium-ion batteries due to their structural characteristics and sodium storage potential. Their high specific capacity, long cycle stability, and low raw material cost make them a focus of sodium-ion energy storage research. However, hard carbon materials still have some drawbacks in practical applications, such as low initial coulombic efficiency, slow electrochemical reaction kinetics, and instability during cycling. These problems limit the electrochemical performance of hard carbon materials; in particular, the small interlayer spacing of carbon in hard carbon materials restricts the diffusion rate of sodium ions, resulting in limited rate performance and low cycle life of the battery.

[0004] To address these issues, researchers have conducted extensive explorations and experiments; among them, elemental doping to improve the electrochemical performance of hard carbon materials is an effective method; N-doped carbon materials increase Na... + The adsorption of active sites and the expansion of interlayer distance enable Na… + Rapid ion transport leads to excellent electrochemical performance. However, improper nitrogen doping can easily introduce excessive structural defects, causing instability or damage to the carbon material structure, reducing the diffusion rate of ions in the carbon layer, resulting in decreased structural stability, and consequently affecting the cycle life and coulombic efficiency of the battery.

[0005] X-ray diffraction (XRD), a commonly used material structure characterization technique, plays a crucial role in studying structural changes in carbon materials. Through XRD patterns, researchers can quantitatively analyze layer parameters and interplanar spacing. For nitrogen-doped carbon materials, the shift of the 002 peak in the XRD pattern can serve as direct evidence of changes in interplanar spacing. Appropriately increasing the interplanar spacing facilitates the diffusion of sodium ions within the carbon layers, thereby improving the material's electrochemical performance.

[0006] Therefore, exploring the relationship between the doping method, content, and interlayer spacing of carbon materials, and further optimizing the nitrogen doping strategy to achieve precise control over interlayer spacing and nitrogen content, is of great significance for improving the performance of hard carbon materials. Summary of the Invention

[0007] This invention addresses the problems in existing technologies by disclosing a method for preparing high-capacity, high-cycle sodium-ion battery anode materials. This invention explores and optimizes the shift of the 002 peak by controlling the nitrogen doping content and using a suitable pre-carbonization process, thereby controlling the interlayer spacing of the anode material. Appropriate interlayer spacing variations can maintain the stable layer structure of the carbon material, preserve high ion diffusion efficiency, and promote Na+ diffusion. + The rapid transport of energy enables the negative electrode material to have a high reversible specific capacity and initial coulombic efficiency, thereby giving the assembled sodium-ion battery excellent performance.

[0008] This invention is achieved through the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a high-capacity, high-cycle sodium-ion battery anode material, the specific steps of which include:

[0010] S1: Pre-carbonize the carbon source for the first time to prepare precursor materials;

[0011] S2: Purify the precursor material using an acid solution;

[0012] S3: Mix the purified powder with a urea-containing nitrogen source and perform a second pre-carbonization of the mixture;

[0013] S4: Completely carbonize the material after the second pre-carbonization;

[0014] In step S3, the following values ​​are controlled: 1.65 ≤ 3*(10*W + 0.0001*T) ≤ 2.75, where 4% ≤ W ≤ 9%, 400℃ ≤ T ≤ 1000℃; W is the content of nitrogen source in terms of nitrogen as a percentage of the total mass of the mixed materials in step S3, and T is the temperature of the second pre-carbonization in step S3.

[0015] In the material design scheme of the present invention, the urea-containing nitrogen source can provide sufficient nitrogen doping kinetics under the material system (specifically, a purified carbon material system) and carbonization regime (specifically, primary carbonization, secondary carbonization, and complete carbonization), and its doping degree is synergistically correlated with the nitrogen content (W) and the pre-carbonization temperature (T). This allows for a suitable change in the interlayer spacing of the carbon material microcrystals after nitrogen doping, while maintaining a good balance between the amount of nitrogen-doped active sites and interlayer diffusion, which is beneficial for the adsorption and intercalation of sodium ions and promotes their rapid migration; thus, the battery achieves good coulombic efficiency, high capacity, and high cycle performance.

[0016] Therefore, this invention optimizes the nitrogen content of urea-based nitrogen sources and the pre-carbonization temperature. When the optimized W and T satisfy the above relationship, nitrogen doping can introduce an appropriate amount of doping active sites and cause appropriate changes in interlayer spacing, so that the battery material has better battery capacity, coulombic efficiency and better cycle performance.

[0017] Through extensive experimental research, the inventors discovered that when the values ​​of W and T satisfy the above-mentioned relationship, the electrochemical performance of the material is optimal, and better doping effects can be obtained.

[0018] As a further option, W in S3 is preferably 6.5% ≤ W ≤ 7%.

[0019] As a further option, the pre-carbonization temperature T in S3 is preferably 550℃≤T≤650℃.

[0020] When the nitrogen content and pre-carbonization temperature T within the control range meet the above-mentioned preferred range, the diffusion of nitrogen doping active sites on the surface and between layers of carbon material microcrystals can be better balanced; a more stable interlayer spacing can be formed, promoting the diffusion of Na+. + The rapid adsorption and diffusion rate results in better battery capacity, coulombic efficiency, and cycle performance.

[0021] As a further option, the urea-containing nitrogen source may be selected from one of urea, melamine, ethyl carbamate, thiourea, isothiourea, urea-formaldehyde resin, or cyanuric acid triamide.

[0022] Urea-containing nitrogen sources have a high nitrogen content, which reduces the influence of other impurities on nitrogen doping. During the doping process, more nitrogen atoms can be introduced into the carbon material, thereby improving the nitrogen doping effect. In addition, urea-containing substances have multiple active sites and higher reactivity, which helps to improve the doping efficiency. Urea-containing nitrogen sources usually also have a stable structure and better thermal stability, which helps to maintain the integrity of the structure during high-temperature carbonization and makes it less volatile, thus ensuring the effective incorporation of nitrogen atoms.

[0023] Furthermore, the urea-containing nitrogen source is preferably urea; when performing nitrogen doping, urea not only has the advantages of high nitrogen content and stable structure of urea-containing structures, but also low cost, which helps to reduce the production cost of hard carbon materials; the doping process of urea is relatively simple, it is not easy to introduce other impurities, the side reaction during the doping process is very low, and the doping effect is good; in addition, urea is also an environmentally friendly nitrogen source, and its use is not likely to produce harmful by-products, which is beneficial to environmental protection.

[0024] As a further option, the carbon source in S1 can be selected from one of the following: biomass-based, resin-based, pitch-based, sugars, polyacrylonitrile, or anthracite. As some specific examples: biomass-based includes coconut shell charcoal, apricot shell, bamboo charcoal, starch, peanut shell, etc.; resin-based includes phenolic resin, epoxy resin, polyfurfuryl alcohol, etc.; pitch-based includes coal tar pitch, petroleum pitch, natural pitch, etc.; sugars include glucose, sucrose, etc.

[0025] As a further option, the acid solution in S2 can be selected from any one or two of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid.

[0026] Furthermore, the acid solution is preferably composed of hydrochloric acid and nitric acid, with a preferred mass ratio of hydrochloric acid:nitric acid = 2:1.

[0027] Hydrochloric acid and nitric acid have high solubility. In particular, the strong oxidizing property of nitric acid can better dissolve metal impurities and inorganic salts introduced during the preparation of hard carbon. It can also promote some impurities to undergo chemical reactions and be converted into soluble impurities. In addition to its strong solubility, the chloride ions of hydrochloric acid also have a small size and high mobility. This allows them to penetrate the pore structure of the hard carbon material precursor, achieve deep cleaning, and form a more open and interconnected pore network structure, thereby achieving better purification effect and facilitating the uniform doping of nitrogen.

[0028] As a further option, the temperature T1 of the first pre-carbonization in S1 is selected from 500℃≤T1≤700℃. This range of pre-carbonization temperature can effectively promote the cracking and transformation of the carbon source during the first pre-carbonization treatment, so as to facilitate the subsequent doping of nitrogen elements more smoothly.

[0029] As a further option, the complete carbonization temperature T3 in S3 is selected from 1100℃≤T3≤1500℃. The complete carbonization temperature in this range can effectively remove volatiles and other impurities in the material, avoiding affecting the electrochemical performance and adsorption capacity of the material.

[0030] Secondly, the present invention provides a high-capacity, high-cycle sodium-ion battery anode material; the material is obtained by the preparation method of the first aspect.

[0031] Thirdly, the present invention provides a high-capacity, high-cycle sodium-ion battery negative electrode sheet, which comprises the high-capacity, high-cycle sodium-ion battery negative electrode material, conductive agent, and binder described in the second aspect of the present invention.

[0032] This negative electrode exhibits excellent electrochemical characteristics, possessing outstanding energy storage capacity, high coulombic efficiency, and good cycle retention, indicating its enormous application potential in the sodium-ion battery industry.

[0033] This invention does not impose any particular limitation on the type of conductive agent, as long as it enhances the conductivity of the negative electrode and does not adversely affect the performance of the sodium-ion battery negative electrode material. Those skilled in the art can select conductive agents commonly used in the field according to actual needs. As some specific examples, the conductive agent used to prepare the negative electrode sheet can be selected from carbon blacks such as acetylene black and conductive carbon black, conductive polymers such as carbon nanotubes, graphene, graphite, polyaniline, and polythiophene, metal oxide conductive agents such as tin oxide and zinc oxide, and carbon nanofiber conductive agents, etc.

[0034] This invention does not impose any particular limitation on the type of binder, as long as it enhances the adhesion between the particles of the negative electrode active material and does not adversely affect the performance of the sodium-ion battery negative electrode material. Those skilled in the art can select the appropriate binder according to actual needs. As some specific examples, binders used to prepare the negative electrode sheet include polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyimide, polystyrene sulfonic acid, polyacrylonitrile, polycarbonate, or polyetherimide ketone, etc.

[0035] Fourthly, the present invention provides a sodium-ion battery comprising the negative electrode, positive electrode, electrolyte, and separator described in the third aspect.

[0036] The high-capacity, high-cycle sodium-ion battery provided by this invention possesses significantly high energy density, high coulombic efficiency, and excellent cycle life, making it highly promising for applications in multiple key fields. Whether in energy storage systems for solar and wind power generation, or in critical infrastructure such as aerospace, distributed power stations, emergency backup power supplies, military equipment, and communication base stations, the battery of this invention can play a vital role.

[0037] The features and beneficial effects of this invention are as follows:

[0038] (1) By controlling the relationship between nitrogen content (W) and pre-carbonization temperature (T) and the degree of interlayer offset in XRD, the present invention can obtain the appropriate change in interlayer spacing of carbon material after nitrogen doping. At the same time, the retention of nitrogen doping active sites and interlayer diffusion are well balanced, which is conducive to the adsorption and insertion of sodium ions and promotes the rapid migration of sodium ions. Thus, the battery can obtain good coulombic efficiency, high capacity and high cycle performance.

[0039] (2) The nitrogen source optimized by the present invention is a urea-containing nitrogen source, preferably urea, which not only has a high nitrogen content, but also a stable structure. Furthermore, the doping process is simple, environmentally friendly, low in production cost, and has a good doping effect.

[0040] (3) Before nitrogen doping, the present invention uses a mixed solution of hydrochloric acid and nitric acid to purify the precursor material, which not only effectively removes impurities, but also helps to deeply clean the pore structure of the hard carbon material precursor, forming a more open and interconnected pore network structure, thereby achieving a better purification effect and facilitating uniform doping of nitrogen. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a SEM image of the product after doping and carbonization.

[0043] Figure 2 These are the XRD patterns of Examples 1, 5, 6, and 7. Detailed Implementation

[0044] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0045] Research has found that when doping carbon materials, nitrogen can enhance the tilt capacity of the battery by binding sodium ions at the material's edges and defects. Simultaneously, lower nitrogen content helps form a broader carbon layer, which can increase the battery's plateau capacity and provide more stable discharge performance. The reason nitrogen-doped carbon materials exhibit better electrochemical properties is that they not only provide active sites for sodium ion adsorption but also promote rapid sodium ion migration by expanding the interlayer spacing. Therefore, exploring the relationship between the doping method, content, and changes in the lattice spacing of carbon materials is crucial for improving the performance of hard carbon materials. Based on this, this invention explores and optimizes the shift of the 002 peak by controlling the nitrogen doping content and using a suitable pre-carbonization regime, providing a method for preparing a high-capacity, high-cycle sodium-ion battery anode material, thereby achieving control over the interlayer spacing of the anode material.

[0046] In a first aspect, the present invention provides a method for preparing a high-capacity, high-cycle sodium-ion battery anode material, the specific steps of which include:

[0047] S1: Pre-carbonize the carbon source for the first time to prepare precursor materials;

[0048] S2: Purify the precursor material using an acid solution;

[0049] S3: Mix the purified powder with a urea-containing nitrogen source and perform a second pre-carbonization of the mixture;

[0050] S4: Completely carbonize the material after the second pre-carbonization;

[0051] In step S3, the following values ​​are controlled: 1.65 ≤ 3*(10*W + 0.0001*T) ≤ 2.75, where 4% ≤ W ≤ 9%, 400℃ ≤ T ≤ 1000℃; W is the content of nitrogen source in terms of nitrogen as a percentage of the total mass of the mixed materials in step S3, and T is the temperature of the second pre-carbonization in step S3.

[0052] In the material design scheme of the present invention, the urea-containing nitrogen source can provide sufficient nitrogen doping kinetics under the material system (specifically, a purified carbon material system) and carbonization regime (specifically, primary carbonization, secondary carbonization, and complete carbonization) of the present invention, and its doping degree is synergistically correlated with the nitrogen content (W) and the pre-carbonization temperature (T). Therefore, on the one hand, by jointly regulating the type of nitrogen source, the carbonization regime, and the nitrogen doping content, suitable nitrogen doping active sites can be introduced, which can combine sodium ions at the edges and defects of the material to improve the tilt capacity of the battery; on the other hand, by regulating the synergistic relationship between W and T, an appropriate change in the interlayer spacing of the carbon material after nitrogen doping can be obtained, while the retention of nitrogen doping active sites and interlayer diffusion are well balanced, which is conducive to the adsorption and intercalation of sodium ions and promotes the rapid migration of sodium ions; thereby enabling the battery to obtain good coulombic efficiency, high capacity, and high cycle performance.

[0053] In the design scheme of this invention, the precursor material is purified by acid solution before nitrogen doping. Acid washing of the precursor material can remove any residual metallic impurities, alkaline substances, or other soluble impurities that may interfere with the subsequent nitrogen doping process or affect the performance of the final material. Acid washing can also cause slight etching on the surface of the carbon material, which to some extent increases the reaction interface of the material and the number of active sites required for nitrogen doping, thus improving the doping efficiency of nitrogen atoms in the carbon material. Acid washing can also partially remove closed pores, forming a more open and interconnected pore network structure, which helps the urea-containing nitrogen source to be more uniformly distributed in the precursor material, thereby achieving more uniform nitrogen doping.

[0054] By adjusting the data ranges of W and T, the shift of the 002 peak can be reflected in XRD. This shift reflects the change in interlayer spacing of the hard carbon material after nitrogen doping. Increased interlayer spacing facilitates the diffusion of sodium ions within the carbon layers, achieving a good balance between nitrogen-doped active sites on the carbon microcrystal surface and between layers, thus promoting Na... +The rapid progress of the adsorption reaction enables the battery to have higher discharge capacity, cycle capability and initial coulombic efficiency; however, excessive changes in interlayer spacing may also damage the layer structure of carbon materials, reduce the diffusion rate of ions in the carbon layer, and lead to reduced structural stability, thereby affecting the cycle life and coulombic efficiency of the battery.

[0055] Therefore, this invention optimizes the nitrogen content and pre-carbonization temperature of the urea-based nitrogen source. When the optimized W and T satisfy the above relationship, nitrogen doping can introduce a suitable amount of doped active sites and cause appropriate changes in interlayer spacing, resulting in better battery capacity, coulombic efficiency, and superior cycle performance. When the nitrogen content exceeds this range, excessive doping may damage the pore structure of the hard carbon material, leading to a reduction in active sites for sodium ion adsorption, thereby reducing its sodium storage capacity; it is also detrimental to the uniform diffusion of nitrogen-doped active sites, affecting the sodium ion transport channels, increasing the internal resistance of the battery material, and thus affecting the rate performance and cycle stability of the battery; in addition, excessively high nitrogen content may lead to excessive expansion of the interlayer spacing, which is not conducive to maintaining the stability of the layer structure, increasing structural defects, and making it more difficult for sodium ions to insert and extract into the material, thereby affecting the cycle stability and capacity retention of the battery. However, excessively low nitrogen content may not achieve the effect of improving electrochemical performance, making it difficult to control and obtain a suitable interlayer spacing, limiting the diffusion rate of sodium ions, and thus failing to obtain higher coulombic efficiency and cycle performance.

[0056] Nitrogen content and pre-carbonization temperature are synergistically correlated. When selecting a nitrogen content within the optimized range, if the pre-carbonization temperature is too low, nitrogen-doped active sites cannot diffuse uniformly on the surface and between layers of the carbon material microcrystals, resulting in insignificant interlayer spacing changes and low nitrogen diffusion efficiency. This leads to insufficient doping, failing to fully utilize the modification effect of nitrogen, and may also cause structural defects in the material, affecting the rate performance and coulombic efficiency of the battery. If the pre-carbonization temperature is too high, it may cause lattice anomalies, damaging the material structure and affecting the adsorption capacity and diffusion rate of sodium ions. High temperatures may also lead to uneven nitrogen doping, forming localized enrichment regions, which is not conducive to forming a uniform and stable interlayer spacing, affecting the overall electrochemical performance of the material. In addition, high temperatures can also cause nitrogen to volatilize from the material, thereby reducing the nitrogen content and decreasing the doping effect.

[0057] Therefore, through extensive experimental research, the inventors discovered that when the values ​​of W and T satisfy the above-mentioned relationship, the coulombic efficiency, battery capacity, and cycle performance of the material are optimal, resulting in better doping effects.

[0058] As a further option, W in S3 is preferably 6.5% ≤ W ≤ 7%.

[0059] As a further option, the pre-carbonization temperature T in S3 is preferably 550℃≤T≤650℃.

[0060] When the nitrogen content and pre-carbonization temperature T within the control range meet the above-mentioned preferred range, the diffusion of nitrogen doping active sites on the surface and between layers of carbon material microcrystals can be better balanced; a more stable interlayer spacing can be formed, promoting the diffusion of Na+. + The rapid adsorption and diffusion rate results in better battery capacity, coulombic efficiency, and cycle performance.

[0061] As a further option, the urea-containing nitrogen source may be selected from one of urea, melamine, ethyl carbamate, thiourea, isothiourea, urea-formaldehyde resin, or cyanuric acid triamide.

[0062] Urea-containing nitrogen sources have a high nitrogen content, which reduces the influence of other impurities on nitrogen doping. During the doping process, more nitrogen atoms can be introduced into the carbon material, thereby improving the nitrogen doping effect. In addition, urea-containing substances have multiple active sites and higher reactivity, which helps to improve the doping efficiency. Urea-containing nitrogen sources usually also have a stable structure and better thermal stability, which helps to maintain the integrity of the structure during high-temperature carbonization and makes it less volatile, thus ensuring the effective incorporation of nitrogen atoms.

[0063] Furthermore, the urea-containing nitrogen source is preferably urea; when performing nitrogen doping, urea not only has the advantages of high nitrogen content and stable structure of urea-containing structures, but also low cost, which helps to reduce the production cost of hard carbon materials; the doping process of urea is relatively simple, it is not easy to introduce other impurities, the side reaction during the doping process is very low, and the doping effect is good; in addition, urea is also an environmentally friendly nitrogen source, and its use is not likely to produce harmful by-products, which is beneficial to environmental protection.

[0064] As a further option, the carbon source in S1 can be selected from one of the following: biomass-based, resin-based, pitch-based, sugars, polyacrylonitrile, or anthracite. As some specific examples: biomass-based includes coconut shell charcoal, apricot shell, bamboo charcoal, starch, peanut shell, etc.; resin-based includes phenolic resin, epoxy resin, polyfurfuryl alcohol, etc.; pitch-based includes coal tar pitch, petroleum pitch, natural pitch, etc.; sugars include glucose, sucrose, etc.

[0065] As a further option, the acid solution in S2 can be selected from any one or two of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid.

[0066] Furthermore, the acid solution is preferably composed of hydrochloric acid and nitric acid, with a preferred mass ratio of hydrochloric acid:nitric acid = 2:1.

[0067] Hydrochloric acid and nitric acid have high solubility. In particular, the strong oxidizing property of nitric acid can better dissolve metal impurities and inorganic salts introduced during the preparation of hard carbon. It can also promote some impurities to undergo chemical reactions and be converted into soluble impurities. In addition to its strong solubility, the chloride ions of hydrochloric acid also have a small size and high mobility. This allows them to penetrate the pore structure of the hard carbon material precursor, achieve deep cleaning, and form a more open and interconnected pore network structure, thereby achieving better purification effect and facilitating the uniform doping of nitrogen.

[0068] As a further option, the temperature T1 of the first pre-carbonization in S1 is selected from 500℃≤T1≤700℃. This range of pre-carbonization temperature can effectively promote the cracking and transformation of the carbon source during the first pre-carbonization treatment, so as to facilitate the subsequent doping of nitrogen elements more smoothly.

[0069] As a further option, the complete carbonization temperature T3 in S3 is selected from 1100℃≤T3≤1500℃. The complete carbonization temperature in this range can effectively remove volatiles and other impurities in the material, avoiding affecting the electrochemical performance and adsorption capacity of the material.

[0070] Secondly, the present invention provides a high-capacity, high-cycle sodium-ion battery anode material; the material is obtained by the preparation method of the first aspect.

[0071] Thirdly, the present invention provides a high-capacity, high-cycle sodium-ion battery negative electrode sheet, which comprises the high-capacity, high-cycle sodium-ion battery negative electrode material, conductive agent, and binder described in the second aspect of the present invention.

[0072] This type of negative electrode exhibits superior electrochemical characteristics, possessing excellent energy storage capacity, high coulombic efficiency, and good cycle retention, indicating its enormous application potential in the sodium-ion battery industry. Therefore, it can significantly improve the overall performance of sodium-ion batteries, meeting the ever-increasing energy demands.

[0073] This invention does not impose any particular limitation on the type of conductive agent, as long as it enhances the conductivity of the negative electrode and does not adversely affect the performance of the sodium-ion battery negative electrode material. Those skilled in the art can select conductive agents commonly used in the field according to actual needs. As some specific examples, the conductive agent used to prepare the negative electrode sheet can be selected from carbon blacks such as acetylene black and conductive carbon black, conductive polymers such as carbon nanotubes, graphene, graphite, polyaniline, and polythiophene, metal oxide conductive agents such as tin oxide and zinc oxide, and carbon nanofiber conductive agents, etc.

[0074] This invention does not impose any particular limitation on the type of binder, as long as it enhances the adhesion between the particles of the negative electrode active material and does not adversely affect the performance of the sodium-ion battery negative electrode material. Those skilled in the art can select the appropriate binder according to actual needs. As some specific examples, binders used to prepare the negative electrode sheet include polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyimide, polystyrene sulfonic acid, polyacrylonitrile, polycarbonate, or polyetherimide ketone, etc.

[0075] Fourthly, the present invention provides a sodium-ion battery comprising the negative electrode, positive electrode, electrolyte, and separator described in the third aspect.

[0076] The high-capacity, high-cycle sodium-ion battery provided by this invention possesses significantly high energy density, high coulombic efficiency, and excellent cycle life, making it widely applicable in several key fields. Whether in energy storage systems for solar and wind power generation, or in critical infrastructure such as aerospace, distributed power stations, emergency backup power, military equipment, and communication base stations, the battery of this invention can play a vital role. This technological advancement not only opens up new possibilities for the battery manufacturing industry but also propels sodium-ion battery technology forward significantly, providing an efficient, reliable, and economical energy storage option, thus securing a favorable position in the fiercely competitive market.

[0077] As a specific example of the implementation of this invention, detailed cases are provided below:

[0078] Example 1

[0079] 1) 30g of clean apricot shells were coarsely crushed by a small mechanical mill, collected and sieved to a particle size of 10mm. The particles were loaded into a sufficiently large graphite crucible and sent into a tube furnace. The temperature was increased to 600℃ at 5℃ per minute for pre-carbonization for 2h. Then the temperature was decreased to room temperature at 3℃ per minute and the precursor material was obtained.

[0080] 2) The black granules were crushed to a particle size of 5μm using an air crusher. 50g of pure water, 10g of hydrochloric acid, and 5g of nitric acid were mixed to form solution A. The pre-carbonized powder was immersed in solution A and stirred for 2 hours. After filtration and drying, the powder was ground and mixed with urea to obtain a uniform mixture. The urea content was calculated as nitrogen, so that the nitrogen content of the urea accounted for 5.57% of the total mass of the mixture.

[0081] 3) The mixed material is placed into a sufficiently large graphite crucible and sent to a tube furnace. The temperature is increased at 5°C per minute to 600°C for a second pre-carbonization for 2 hours. Then, the temperature is decreased at 3°C ​​per minute to room temperature, and the resulting black powder is removed. The black powder is then placed into a sufficiently large graphite crucible and sent to a tube furnace. The temperature is increased at 5°C per minute to 1250°C for high-temperature carbonization for 2 hours. Then, the temperature is decreased at 3°C ​​per minute to room temperature, and the resulting final product material is obtained. Its SEM image is shown below. Figure 1 As shown.

[0082] Example 2

[0083] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 6.80% of the total mass of the powder.

[0084] Example 3

[0085] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 7.10% of the total mass of the powder.

[0086] Example 4

[0087] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 7.70% of the total mass of the powder.

[0088] Example 5

[0089] The specific process is the same as in Example 1, except that the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 450°C.

[0090] Example 6

[0091] The specific process is the same as in Example 1, except that the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 500°C.

[0092] Example 7

[0093] The specific process is the same as in Example 1, except that the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 700°C.

[0094] Example 8

[0095] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 4.50% of the total mass of the powder, and the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 1000℃.

[0096] Example 9

[0097] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 8.70% of the total mass of the powder, and the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 400°C.

[0098] Comparative Example 1

[0099] The specific process is the same as in Example 1, except that no dopant is added in this process.

[0100] Comparative Example 2

[0101] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 3.70% of the total mass of the powder.

[0102] Comparative Example 3

[0103] The specific process is the same as in Example 1, except that the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 300°C.

[0104] Comparative Example 4

[0105] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 4.70% of the total mass of the powder, and the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 650°C.

[0106] Comparative Example 5

[0107] The specific process is the same as in Example 1, except that the total mass of nitrogen in the mixture accounts for 8.50% of the total mass of the powder, and the secondary pre-carbonization temperature after mixing the pre-carbonized powder with urea is 900℃.

[0108] Specific testing conditions and methods:

[0109] Performance testing

[0110] The negative electrode material, polyvinylidene fluoride (PVDF), and conductive agent (SP) provided in the above examples and comparative examples were dispersed and dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5. The mixture was stirred and dispersed to obtain a slurry with a solid content of 55%. After coating, drying, and rolling, the slurry was punched into button cell sheets. A small amount of sodium ion battery electrolyte was added to prepare a button cell with a negative electrode material, using a sodium metal sheet as the counter electrode and polypropylene (PP) as the separator material. The electrolyte solute was 1M NaPF6 and the solvent was an ethylene carbonate-dimethyl carbonate (EC-DMC) system.

[0111] Within the 0-2V voltage range, the following tests were performed: 1) rest for 2 hours; 2) rate discharge (0.1C, 0V); 3) rest for 10 minutes; 4) rate discharge (0.02C, 0V); 5) rest for 30 seconds; 6) rate charge (0.1C, 2.0V). The initial reversible specific capacity, initial coulombic efficiency, and capacity after 100 cycles were recorded. The test results are shown in Table 1.

[0112] Table 1

[0113]

[0114]

[0115] As shown in Table 1, Examples 1-9 and Comparative Examples 1-5 exhibit higher battery capacity, first-cycle coulombic efficiency, and cycle retention. This indicates that by controlling the nitrogen doping content and pre-carbonization temperature, and satisfying the formula 1.65≤3*(10*W+0.0001*T)≤2.75 proposed in this invention, the interlayer spacing can be controlled by nitrogen doping, resulting in a suitable interlayer spacing and an appropriate number of sodium ion adsorption sites, thus enhancing the electrochemical performance of the material.

[0116] Figure 1 The SEM images show that the morphology exhibits typical characteristics of hard carbon materials, with the main body consisting of large, irregularly shaped blocky particles and obvious adhesion of small particles.

[0117] Depend on Figure 2 It can be seen that the XRD curves of Examples 1, 5, 6, and 7 show that the peak position corresponding to amorphous carbon in the material shifted to a smaller angle, indicating that the interlayer spacing of the finished material changed, which is beneficial to improving the adsorption and diffusion rate of sodium ions and obtaining better electrochemical performance.

[0118] Examples 1 and 1 (Comparative Example 1) show that introducing nitrogen with urea at a suitable pre-carbonization temperature can achieve higher coulombic efficiency, rate capability, and cycle performance. This is because the introduction of nitrogen with an appropriate doping content can increase the active sites for sodium ion adsorption, causing changes in interlayer spacing within a certain range, promoting the adsorption and diffusion rate of sodium ions, and improving the electrochemical performance of the material. Examples 1, 2, and 3 (Comparative Example 3) show that the nitrogen doping content and pre-carbonization temperature need to be synergistically controlled to improve battery cycle performance, capacity, and coulombic efficiency. When the pre-carbonization temperature is suitable but the urea doping content is too low, a significant change in interlayer spacing cannot be obtained, which is insufficient to provide enough nitrogen-doped active sites, affecting their uniformity on the surface and between layers of the carbon material microcrystals, limiting the adsorption and insertion rate of sodium ions, and resulting in lower coulombic efficiency and capacity. Conversely, when the pre-carbonization temperature is too low, although the nitrogen doping ratio is suitable, it cannot provide sufficient nitrogen doping motive force to promote uniform diffusion of active sites, resulting in insignificant changes in interlayer spacing, hindering the transport of sodium ions between layers, and negatively impacting electrochemical performance.

[0119] Examples 8 and 9 and Comparative Examples 4 and 5 show that although the nitrogen content and pre-carbonization temperature meet the optimization range, the electrochemical performance is still lower than that of the examples. This indicates that the nitrogen content and pre-carbonization temperature range need to be further controlled. By controlling the limited diffusion of nitrogen doping sites, a uniform distribution on the surface and between layers of carbon material microcrystals can be achieved, and a good balance can be reached with the interlayer offset to obtain a suitable interlayer change, thereby effectively improving the electrochemical performance.

[0120] As can be seen from Examples 2 and 1, 3, 4, 5, 6, 7, 8, and 9, the optimal battery cycle retention, capacity, and coulombic efficiency can be obtained under appropriate urea doping content and pre-carbonization temperature.

[0121] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a high-capacity, high-cycle sodium-ion battery anode material, the method comprising the following steps: S1: Pre-carbonize the carbon source for the first time to prepare precursor materials; S2: Purify the precursor material using an acid solution; S3: Mix the purified powder with a urea-containing nitrogen source and perform a second pre-carbonization of the mixture; S4: Completely carbonize the material after the second pre-carbonization; In step S3, the following values ​​are controlled: 1.65 ≤ 3*(10*W + 0.0001*T) ≤ 2.75, where 4% ≤ W ≤ 9%, 400℃ ≤ T ≤ 1000℃; W is the content of nitrogen source in terms of nitrogen as a percentage of the total mass of the mixed materials in step S3, and T is the temperature of the second pre-carbonization in step S3.

2. The method for preparing the high-capacity, high-cycle sodium-ion battery anode material according to claim 1, characterized in that, In S3, W is preferably 6.5% ≤ W ≤ 7%.

3. The method for preparing the high-capacity, high-cycle sodium-ion battery anode material according to claim 1, characterized in that, In S3, T is preferably 550℃≤T≤650℃.

4. The method for preparing the high-capacity, high-cycle sodium-ion battery anode material according to claim 1, characterized in that, The urea nitrogen source in S3 can be selected from one of urea, melamine, ethyl carbamate, thiourea, isothiourea, urea-formaldehyde resin, or cyanuric acid triamide. More preferably, the urea-containing nitrogen source is urea.

5. The method for preparing the high-capacity, high-cycle sodium-ion battery anode material according to claim 1, characterized in that, The carbon source in S1 can be selected from one of the following: biomass-based, resin-based, pitch-based, sugar, polyacrylonitrile, or anthracite.

6. The method for preparing the high-capacity, high-cycle sodium-ion battery anode material according to claim 1, characterized in that, The acid solution in S2 can be selected from any one or two of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid; More preferably, the acid solution is selected from hydrochloric acid and nitric acid, with a preferred mass ratio of hydrochloric acid:nitric acid = 2:

1.

7. The method for preparing the high-capacity, high-cycle sodium-ion battery anode material according to claim 1, characterized in that, The temperature T1 for the first pre-carbonization in S1 is selected from 500℃≤T1≤700℃.

8. The method for preparing the high-capacity, high-cycle sodium-ion battery anode material according to claim 1, characterized in that, The temperature T3 for complete carbonization in S3 is selected from 1100℃≤T3≤1500℃.

9. A high-capacity, high-cycle sodium-ion battery anode material, characterized in that, The material is obtained by any one of the preparation methods according to claims 1-8.

10. A sodium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The active material of the negative electrode includes the high-capacity, high-cycle sodium-ion battery negative electrode material as described in claim 9.

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