Method for preparing sodium-ion battery negative electrode porous hard carbon

Abstract

The application discloses a preparation method of a sodium ion battery negative electrode porous hard carbon, and comprises the following steps: S1, preparation of a precursor powder: biomass carbonization material powder is uniformly mixed with a carbonate to obtain a mixed material; the mixed material is activated at a low temperature under a protective atmosphere to obtain the precursor powder; S2, preparation of an intermediate powder: the precursor powder obtained in the step S1 is added into a tris buffer solution containing dopamine hydrochloride and an iron source compound, and after sufficient stirring and reaction, the intermediate powder is obtained by separation and drying; and S3, high-temperature carbonization: the intermediate powder obtained in the step S2 is subjected to high-temperature carbonization under a protective atmosphere to obtain the sodium ion battery negative electrode porous hard carbon material. The preparation method of the sodium ion battery negative electrode porous hard carbon has the characteristics of excellent electrochemical performance, good process controllability and low self-discharge.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a method for preparing porous hard carbon for sodium-ion battery negative electrodes. Background Technology

[0002] Lithium-ion batteries are considered one of the most advanced energy storage technologies today, but due to the limited reserves of lithium resources, they will struggle to meet the future demands of the energy storage market. Sodium-ion batteries, on the other hand, have shown great potential in the energy storage field due to their unique advantages, including abundant raw material reserves, low production costs, and excellent high and low temperature performance.

[0003] Since the 1980s, research on sodium-ion batteries has undergone decades of development. In terms of anode materials, various materials have been reported, such as metal sulfides, organic materials, and carbon-based materials. Among them, carbon-based materials have attracted much attention due to their low cost and excellent electrochemical performance.

[0004] Carbon materials can be divided into graphite and amorphous carbon, with amorphous carbon further classified into soft carbon and hard carbon. Hard carbon, in particular, has attracted significant attention due to its superior sodium storage performance. The sodium storage sites in hard carbon materials can be broadly categorized into adsorption on the surfaces of material particles and open pores, adsorption at defects in graphite sheets, insertion / embedding between graphite layers, and pore filling at micropores. The sodium storage capacity of hard carbon anode materials can be improved by controlling graphite-like microregions and constructing porous structures.

[0005] However, the poor conductivity and abundant surface defects of hard carbon materials lead to electrolyte decomposition and continuous formation of the solid electrolyte interphase (SEI), resulting in poor electrochemical performance such as low coulombic level in the first week. Furthermore, the high carbonization temperature and energy consumption required for controlling the graphite-like micro-regions and pore structure of hard carbon materials further exacerbate the problem. In addition, commonly used activators in the chemical activation method for preparing porous carbon materials include KOH, ZnCl2, and H3PO4, which are highly corrosive, require sophisticated production equipment, and are difficult to preserve the original morphology of the material, resulting in poor process controllability. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing porous hard carbon for sodium-ion battery negative electrodes, which has the characteristics of excellent electrochemical performance, good process controllability and low self-discharge.

[0007] This invention can be achieved through the following technical solutions: This invention discloses a method for preparing porous hard carbon for sodium-ion battery negative electrodes, comprising the following steps: S1: Preparation of precursor powder: Biomass carbonized material powder and carbonate are mixed evenly to obtain a mixed material. The mixture is then activated at low temperature under a protective atmosphere to obtain precursor powder; S2. Preparation of intermediate powder: The precursor powder obtained in step S1 is added to a Tris buffer containing dopamine hydrochloride and an iron source compound. After stirring and reacting thoroughly, the intermediate powder is separated and dried. S3. High-temperature carbonization: The intermediate powder obtained in step S2 is placed in a protective atmosphere and carbonized at high temperature to obtain a porous hard carbon material for sodium-ion battery negative electrode.

[0008] Further, in step S2, the mass ratio of dopamine hydrochloride to precursor powder is 0.1-1, and the mass ratio of iron source compound to precursor powder is 0.01-0.05. Within the above ratio range, the electrochemical performance of the obtained material shows a trend of first increasing and then decreasing. Exceeding this ratio, the reversible specific capacity, ICE, and other electrochemical properties decrease. Specifically, the excessive coating of PDA leads to an increase in specific surface area, or the addition of excessive iron element increases side reactions, reducing ICE and thus leading to a decrease in reversible specific capacity.

[0009] Furthermore, in step S2, the conditions for sufficient stirring are: magnetic stirring and a stirring time of 6-24 hours. Regarding stirring time, the material's performance improves with increasing stirring time within this range, specifically because the PDA coating becomes more complete with increasing stirring time. If the stirring time is less than 6 hours, insufficient filling and coating, resulting in a still relatively large specific surface area, lead to poor electrochemical performance such as ICE. If the stirring time is greater than 24 hours, the coating tends to be saturated, thus the electrochemical performance tends to plateau.

[0010] Furthermore, in step S2, the iron source compound is one or more of ferric chloride, ferrocene, and iron oxide.

[0011] Further, in step S1, the mass ratio of carbonate to biomass carbonized powder is 1-5. Within this ratio range, the electrochemical performance of the material first increases and then decreases; exceeding this ratio results in a decline in electrochemical performance, and the trend is related to the degree of activation. Increased activation leads to an increase in sodium-storing active sites, improving electrochemical performance such as reversible specific capacity. However, excessive addition of activator can cause over-activation, leading to pore structure collapse and a significant decrease in electrochemical performance.

[0012] Furthermore, in step S1, the carbonate is one or more of potassium carbonate, sodium carbonate, and calcium carbonate.

[0013] Furthermore, in step S1, the mixing method is liquid phase mixing and / or solid phase mixing, and the mixing time is 1-6 hours.

[0014] Further, in step S1, the protective atmosphere is argon and / or nitrogen, with a gas flow rate ranging from 50 to 150 sccm. Within this flow rate range, the material's performance first increases and then tends to remain constant. When the flow rate is less than 50 sccm, the electrochemical performance decreases, and when it is greater than 150 sccm, the electrochemical performance tends to remain constant. The activation temperature range is 600 to 900℃. Within this activation temperature range, the material's performance first increases and then decreases. When it exceeds this range, the electrochemical performance decreases significantly. The trend of change is related to the degree of activation, and is similar to that described above. The activation time range is 0.5 to 3 hours, and the trend of change in the activation time range is similar to that in the activation temperature range.

[0015] Furthermore, in step S3, the conditions for high-temperature carbonization are a carbonization temperature range of 800-1000℃, within which the material properties show a trend of first increasing and then decreasing, and the electrochemical performance decreases when the temperature exceeds this range; the carbonization time range is 1-6h.

[0016] Further, in step S3, the protective atmosphere is argon and / or nitrogen, and the gas flow rate is in the range of 50-150 sccm. Within this flow rate range, the material properties first increase and then tend to remain unchanged. When the flow rate is less than 50 sccm, the electrochemical performance decreases, and when the flow rate is greater than 150 sccm, the electrochemical performance tends to remain unchanged. The carbonization temperature range is 800-1000℃, and the carbonization time range is 1-6h.

[0017] Furthermore, in step S1, the biomass carbonized material powder is carbon powder obtained by crushing biomass raw materials such as lignin, cellulose, and glucose; its particle size is controlled to be 5-10 μm.

[0018] Furthermore, in step S2, the separation method is centrifugation.

[0019] This invention discloses a method for preparing porous hard carbon for sodium-ion battery negative electrodes, which has the following beneficial effects: First, it exhibits excellent electrochemical performance. Polydopamine forms metal complexes with iron source compounds, and the interaction between polydopamine and carbon materials is strong. Through the bridging effect of dopamine, a large amount of trace iron in the solution can be introduced into the carbon materials, maximizing the catalytic graphitization benefits at a lower iron concentration than traditional catalysis. At the same time, iron also catalyzes the degree of graphitization during the carbonization process of polydopamine, greatly improving the reversible specific capacity and enhancing the capacity retention and lifespan of sodium-ion batteries.

[0020] Secondly, the process is highly controllable. The use of carbonates to form pores through chemical activation yields abundant porosity in carbon materials, providing excellent precursor conditions for subsequent optimization measures such as PDA filling. The use of dopamine self-polymerization for pore filling and coating not only controls the pore structure and constructs an artificial SEI film but also increases the conductivity of hard carbon materials. During the high-temperature carbonization process, PDA partially forms carbon, providing additional sodium storage capacity. Trace amounts of iron catalyze graphitization, enabling the control of graphite-like micro-regions at lower temperatures. The control of the addition amounts of these three elements achieves strong process controllability.

[0021] Third, it has low self-discharge. During the high-temperature carbonization process, some iron elements are burned off and carried out by the continuously flowing protective atmosphere. Therefore, the addition of iron elements has little impact on the ash content of hard carbon materials and little impact on battery performance. There is no need to wash away iron elements afterward, and there will be no problem of excessive self-discharge caused by too much elemental iron. Attached Figure Description

[0022] Figure 1 The adsorption-desorption curves of N2 under different conditions; Figure 2 Pore ​​size distribution diagrams based on N2 adsorption isotherms under different conditions. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0024] This invention discloses a method for preparing porous hard carbon for sodium-ion battery negative electrodes, comprising the following steps: S1: Preparation of precursor powder: Biomass carbonized material powder and carbonate are mixed evenly to obtain a mixed material. The mixture is then activated at low temperature under a protective atmosphere to obtain precursor powder; S2. Preparation of intermediate powder: The precursor powder obtained in step S1 is added to a Tris buffer containing dopamine hydrochloride and an iron source compound. After stirring and reacting thoroughly, the intermediate powder is separated and dried. S3. High-temperature carbonization: The intermediate powder obtained in step S2 is placed in a protective atmosphere and carbonized at high temperature to obtain a porous hard carbon material for sodium-ion battery negative electrode.

[0025] Further, in step S2, the mass ratio of dopamine hydrochloride to precursor powder is 0.1-1, and the mass ratio of iron source compound to precursor powder is 0.01-0.05.

[0026] Furthermore, in step S2, the conditions for fully stirring the reaction are: the stirring method is magnetic stirring, and the stirring time is 6-24 hours.

[0027] Furthermore, in step S2, the iron source compound is one or more of ferric chloride, ferrocene, and iron oxide.

[0028] Furthermore, in step S1, the mass ratio of carbonate to biomass raw material powder is 1-5.

[0029] Furthermore, in step S1, the carbonate is one or more of potassium carbonate, sodium carbonate, and calcium carbonate.

[0030] Furthermore, in step S1, the mixing method is liquid phase mixing and / or solid phase mixing, and the mixing time is 1-6 hours.

[0031] Further, in step S1, the protective atmosphere is argon and / or nitrogen, the gas flow rate is in the range of 50-150 sccm, the activation temperature is in the range of 600-900℃, and the activation time is in the range of 0.5-3h.

[0032] Furthermore, in step S3, the conditions for high-temperature carbonization are: carbonization temperature range of 800-1000℃, and carbonization time range of 1-6h.

[0033] Further, in step S3, the protective atmosphere is argon and / or nitrogen, the gas flow rate is in the range of 50-150 sccm, the carbonization temperature is in the range of 800-1000℃, and the carbonization time is in the range of 1-6h.

[0034] Furthermore, in step S1, the biomass carbonized material powder is carbon powder obtained by crushing biomass raw materials such as lignin, cellulose, and glucose; its particle size is controlled to be 5-10 μm.

[0035] Furthermore, in step S2, the separation method is centrifugation.

[0036] Example 1 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:2 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to nitrogen atmosphere at 5℃ for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0037] (2) Using the dopamine self-polymerization reaction, weigh 0.1 g of dopamine hydrochloride and 0.03 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, and then add 1 g of the precursor powder obtained in step (1) into a round bottom flask. After stirring for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0038] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain porous hard carbon material.

[0039] (4) A sodium-ion battery was assembled using the prepared porous hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0040] Example 2 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0041] (2) Using the dopamine self-polymerization reaction, weigh 0.1 g of dopamine hydrochloride and 0.03 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, and then add 1 g of the precursor powder obtained in step (1) into a round bottom flask. After stirring for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0042] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain porous hard carbon material.

[0043] (4) A sodium-ion battery was assembled using the prepared porous hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0044] Example 3 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:4 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0045] (2) Using the dopamine self-polymerization reaction, weigh 0.1 g of dopamine hydrochloride and 0.03 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, and then add 1 g of the precursor powder obtained in step (1) into a round bottom flask. After stirring for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0046] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain porous hard carbon material.

[0047] (4) A sodium-ion battery was assembled using the prepared porous hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0048] Example 4 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0049] (2) Using the dopamine self-polymerization reaction, weigh 0.3 g of dopamine hydrochloride and 0.03 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, and then add 1 g of the precursor powder obtained in step (1) into a round bottom flask. After stirring for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0050] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0051] (4) A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0052] Example 5 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0053] (2) Using the dopamine self-polymerization reaction, weigh 0.5 g of dopamine hydrochloride and 0.03 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, and then add 1 g of the precursor powder obtained in step (1) into a round bottom flask. After stirring for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0054] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0055] (4) A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0056] Example 6 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0057] (2) Using the dopamine self-polymerization reaction, weigh 0.1 g of dopamine hydrochloride and 0.01 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, then add 1 g of the precursor powder obtained in step (1) into a round bottom flask, stir for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0058] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0059] (4) A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0060] Example 7 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0061] (2) Using the dopamine self-polymerization reaction, weigh 0.1 g of dopamine hydrochloride and 0.05 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, and then add 1 g of the precursor powder obtained in step (1) into a round bottom flask. After stirring for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0062] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0063] A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0064] Comparative Example 1 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0065] (2) The precursor powder obtained in step (1) was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0066] (3) A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0067] Comparative Example 2 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) The biomass carbonization powder was heated in a nitrogen atmosphere at 5°C for 5 min. -1 The temperature was increased to 700℃ and activated for 1 hour to obtain pretreated carbon material.

[0068] (2) Using the dopamine self-polymerization reaction, weigh 0.1 g of dopamine hydrochloride and 0.03 g of FeCl3 powder into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, and then add 1 g of the pretreated carbon material obtained in step (1) into a round bottom flask. After stirring for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0069] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0070] (4) A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0071] Comparative Example 3 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0072] (2) Using the dopamine self-polymerization reaction, weigh 0.1 g of dopamine hydrochloride into 100 ml of Tris buffer (pH=8.5), sonicate for 10 minutes, then add 1 g of the pretreated carbon material obtained in step (1) into a round bottom flask, stir for 24 h, centrifuge and wash, and dry in an oven at 80℃ to obtain intermediate powder.

[0073] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0074] (4) A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0075] Comparative Example 4 This embodiment relates to a porous hard carbon negative electrode for sodium-ion batteries, the preparation method of which includes the following steps: (1) Biomass carbonized material powder and K2CO3 solid were placed in a ball mill jar at a mass ratio of 1:3 and ball milled for 2 hours to obtain a homogeneous mixture. The obtained mixture was then subjected to a nitrogen atmosphere at 5°C for 1 minute. -1 The temperature was increased to 700℃ for 1 h. The mixture was then washed with deionized water, centrifuged and filtered, and dried in an oven at 80℃ to obtain the K2CO3 activated pore-forming precursor powder.

[0076] (2) Using the dopamine self-polymerization reaction, 0.03 g FeCl3 powder was weighed into 100 ml Tris buffer (pH=8.5), sonicated for 10 minutes, and then 1 g of the pretreated carbon material obtained in step (1) was added into a round bottom flask. After stirring for 24 h, the mixture was centrifuged, washed, and dried in an oven at 80℃ to obtain intermediate powder.

[0077] (3) The intermediate powder was treated at 900°C for 2 h under an argon atmosphere to obtain hard carbon material.

[0078] (4) A sodium-ion battery was assembled using the prepared hard carbon material as the negative electrode, sodium sheet as the positive electrode, and sodium hexafluorophosphate-G2 as the electrolyte.

[0079] To evaluate the technical effects of the present invention, the materials obtained in Examples 1-7 and Comparative Examples 1-4 were subjected to electrochemical performance tests, and the results are shown in Table 1: Table 1 Performance Test Results Table 1 shows the battery reversible capacity (the battery's sodium removal capacity at 0.1C, with a voltage range of 0-2V), first-cycle efficiency, rate capability (capacity retention at 0.25C / 0.1C), and cycle performance (capacity retention after 100 charge-discharge cycles at 0.1C / 0.25C), where 1C = 200mAh / g. These parameters were tested using a Newway tester.

[0080] A comparison of the electrochemical data from the examples and comparative examples reveals that the reversible capacity and ICE data of each example are superior to those of the comparative examples. This indicates that the combined optimization effect of pore-forming agent activation, PDA coating, and iron catalysis is better than the optimization results of combining one or two technologies. Specific analysis follows: The results from Example 2 and Comparative Example 2 show that without the action of a pore-forming agent, the reversible capacity of the hard carbon is only 323 mAh / g, which is much smaller than that of Example 2 (396 mAh / g). During the activation process of the pore-forming agent, the porosity of the carbon material is enriched, providing more active sites for sodium storage. Therefore, the pore-forming agent has a significant impact on porous hard carbon.

[0081] The results from Example 2 and Comparative Example 1 show that, with only the pore-forming agent present, the hard carbon electrode exhibits a low reversible capacity (307 mAh / g) due to a low ICE (75%). This is because the pore-forming agent activates the hard carbon material, resulting in a high specific surface area after high-temperature carbonization. The higher specific surface area leads to a larger contact area between the carbon material and the electrolyte, increasing irreversible decomposition of the electrolyte and thus lowering the ICE. Therefore, after pore formation through activator activation, it is crucial to reduce the specific surface area of ​​the hard carbon material and improve its ICE by coating it with PDA. Comparative Examples 1 and 3 demonstrate that the synergistic effect of these two agents can effectively improve the reversible capacity of the hard carbon material.

[0082] The results from Example 2 and Comparative Example 3 show that the reversible capacity of the hard carbon electrode can be further improved under the catalytic effect of iron (Example 2: 396 mAh / g, Comparative Example 3: 339 mAh / g). This is because the carbonization temperature of 900℃ is lower than the optimal temperature for carbon layer rearrangement and the growth of graphite-like microregions, but the optimal carbonization temperature can be reduced under the catalytic effect of iron, thus saving energy.

[0083] The results from Example 2 and Comparative Example 4 show that the electrochemical performance improvement of the hard carbon electrode catalyzed by iron alone is relatively small. This is because in systems containing only iron, the interaction between iron and carbon materials is weak. A large amount of iron remains in the filtrate after washing and centrifugation. Iron can form metal complexes with PDA, resulting in a stronger interaction between PDA and carbon materials. Through the bridging effect of PDA, a large amount of iron remains in the carbon materials, thus the iron content in the treated carbon materials is lower in Comparative Example 4 than in Example 2. Furthermore, PDA also forms carbon during high-temperature carbonization, and the growth of its graphite-like microregions is better regulated under the catalytic effect of iron. For these reasons, the electrochemical performance of Example 2 is superior to that of Comparative Example 4. This also demonstrates that the combined effect of PDA and iron can stimulate better electrochemical performance of the hard carbon electrode.

[0084] In summary, the combined optimization effect of pore-forming agent activation, PDA coating, and iron element catalysis is superior to the optimization results of any one or two technologies combined, and can better enhance the sodium storage performance of hard carbon anodes.

[0085] In this invention, the analysis of the dosage is as follows: The results of Examples 2, 4 and 5 show that excessive coating of polydopamine will reduce the capacity and first-efficiency of hard carbon materials. The results also show that the amount of dopamine used in this patent is relatively small, which is beneficial to controlling the production cost of hard carbon materials.

[0086] The results of Examples 2, 6 and 7 show that only a trace amount of iron is needed for catalysis, and the addition of too much iron does not significantly improve the electrochemical performance of hard carbon materials.

[0087] The results from Examples 2, 3 and Comparative Example 2 show that the addition of activator has a significant impact on the electrochemical performance of hard carbon materials. However, when too much activator is added, over-activation can lead to changes in the number of internal micropores, reducing the capacity of hard carbon materials.

[0088] Further BET tests were conducted on Examples 2, 3, and Comparative Example 2, and the results are as follows: Figure 1 and Figure 2 As shown.

[0089] The adsorption-desorption curve of N2 shows that the activator can activate carbon materials to obtain abundant micropores. This can be further verified by the pore size distribution curve. At the same time, the comparison of pore size distribution in Example 2 and Example 3 shows that over-activation will lead to changes in micropores.

[0090] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing porous hard carbon as a negative electrode for sodium-ion batteries, characterized in that... Includes the following steps: S1. Preparation of precursor powder: Biomass carbonization powder and carbonate are mixed evenly to obtain a mixed material, which is then activated at low temperature under a protective atmosphere to obtain precursor powder. S2. Preparation of intermediate powder: The precursor powder obtained in step S1 is added to a Tris buffer solution containing dopamine hydrochloride and an iron source compound. After stirring and reacting thoroughly, the intermediate powder is separated and dried. The mass ratio of dopamine hydrochloride to precursor powder is 0.1-1, and the mass ratio of iron source compound to precursor powder is 0.01-0.

05. The iron source compound is one or more of ferric chloride, ferrocene, and iron oxide. S3. High-temperature carbonization: The intermediate powder obtained in step S2 is placed in a protective atmosphere and carbonized at high temperature to obtain a porous hard carbon material for sodium-ion battery negative electrode.

2. The method for preparing porous hard carbon for sodium-ion battery negative electrodes according to claim 1, characterized in that: In step S2, the conditions for a fully stirred reaction are: the stirring method is magnetic stirring, and the stirring time is 6-24 hours.

3. The method for preparing porous hard carbon for sodium-ion battery negative electrodes according to claim 1, characterized in that: In step S1, the mass ratio of carbonate to biomass carbonization material is 1-5.

4. The method for preparing porous hard carbon for sodium-ion battery negative electrodes according to claim 1, characterized in that: In step S1, the carbonate is one or more of potassium carbonate, sodium carbonate, and calcium carbonate.

5. The method for preparing porous hard carbon for sodium-ion battery negative electrode according to claim 1, characterized in that: In step S1, the mixing method is liquid phase mixing and / or solid phase mixing, and the mixing time is 1-6 hours.

6. The method for preparing porous hard carbon for sodium-ion battery negative electrodes according to claim 1, characterized in that: In step S1, the protective atmosphere is argon and / or nitrogen, the gas flow rate is 50-150 sccm, the activation temperature is 600-900℃, and the activation time is 0.5-3h.

7. The method for preparing porous hard carbon for sodium-ion battery negative electrodes according to claim 1, characterized in that: In step S3, the conditions for high-temperature carbonization are: carbonization temperature range of 800-1000℃ and carbonization time range of 1-6h.

8. The method for preparing porous hard carbon for sodium-ion battery negative electrode according to claim 1, characterized in that: In step S3, the protective atmosphere is argon and / or nitrogen, and the gas flow rate is in the range of 50-150 sccm.

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