Preparation method of porous hard carbon negative electrode material and application of porous hard carbon negative electrode material in sodium-ion battery

Abstract

The invention relates to a preparation method of a porous hard carbon negative electrode material, which comprises the following steps: 1) uniformly mixing a carbon source and an activating agent in proportion, and then pre-sintering in an inert atmosphere to obtain a precursor material; the invention discloses a porous hard carbon negative electrode material.The porous hard carbon negative electrode material is prepared through the steps of 1, preparing a precursor material, 2, washing and drying the precursor material to obtain a purified material.The method is simple in process, and the prepared porous hard carbon negative electrode material is low in impurity content, rich in pore structure and excellent in product performance.

Description

Technical Field

[0001] This invention belongs to the field of anode material preparation technology, specifically relating to a method for preparing a porous hard carbon anode material and its application in sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries have attracted widespread attention due to their advantages such as abundant raw materials, low cost, and good low-temperature performance. In sodium-ion batteries, sodium ions are embedded in hard carbon through adsorption, intercalation, and pore filling to provide charging capacity, with pore filling accounting for the majority of the capacity. Therefore, developing hard carbon anode materials with rich porosity is of great significance for the application of sodium-ion batteries.

[0003] Currently, hard carbon anode materials are mainly based on biomass and coal, but these materials suffer from problems such as complex preparation processes, high impurity content, and limited pore structure. For example, application number CN202510386074.1 discloses a method for preparing a hard carbon anode material coated for sodium-ion batteries; application number CN202510372021.4 discloses a method for preparing a biomass-derived hard carbon anode material and a sodium-ion battery; application number CN202510275093.7 discloses a method for preparing hard carbon based on sugarcane bagasse and its application in sodium batteries; application number CN202510422390.X discloses a method for preparing a composite material rich in closed-pore soft and hard carbon from silk fibers and coal liquefaction pitch and its application in sodium batteries, etc. However, the above-mentioned patent applications often have the following defects: 1) Existing preparation methods involve complex pretreatment processes: raw materials need to undergo soaking, impurity removal, drying, crushing, and other processes; 2) Existing pore-forming methods are corrosive: For example, using KOH for chemical activation to form pores will cause alkaline corrosion to the equipment, and the material needs to be washed multiple times. The activation process is violent and there is a risk of combustion. 3) The existing preparation methods involve a single carbonization and sintering step, a fast heating rate, and a fixed heating program, resulting in a large number of graphite microcrystals in the material, fewer pore structures, and unstable structures.

[0004] Therefore, there is an urgent need to develop a hard carbon anode material with a simple preparation process, low impurity content, rich pore structure, and excellent product performance. Based on this, this application was developed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing porous hard carbon anode materials. This method is simple, and the prepared porous hard carbon anode materials have low impurity content, rich pore structure, and excellent product performance.

[0006] This invention also provides the application of the above-mentioned porous hard carbon anode material in sodium-ion batteries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a porous hard carbon anode material includes the following steps: 1) Mix the carbon source and activator in a certain proportion, and then perform low-temperature pre-sintering under an inert atmosphere to obtain the precursor material; 2) The precursor material is washed with water and dried to remove unreacted activators and other impurities, and the purified material is obtained. 3) The purified material is subjected to multi-step temperature-controlled sintering under an inert atmosphere to obtain the porous hard carbon anode material.

[0008] Specifically, in step 1), the carbon source can be a compound containing multiple hydroxyl groups, all of which can participate in the carbonization reaction. For example, the carbon source can be at least one of cellulose, carbohydrate compounds (glucose, starch), etc.; the activator is ZnCl2. The principle of this step is as follows: under the action of the activator ZnCl2, dehydration condensation reactions occur between hydroxyl groups to form products with higher polymerization degrees (such as polysaccharides or carbon-like structures). As the temperature increases, these polymerized products will further undergo dehydration, cyclization, aromatization, and other reactions, ultimately forming carbonaceous materials.

[0009] Specifically, in step 1), the mass ratio of the activator to the carbon source is 0.2-0.4:1.

[0010] Furthermore, in step 1), the low-temperature pre-sintering is performed by holding at 250-350℃ for 3-5 hours.

[0011] Specifically, in step 3), the multi-step programmed temperature sintering is divided into three stages: the first stage is dehydration sintering at a temperature of 20-300℃, the purpose of which is to remove moisture and low-boiling-point compounds from the material; the second stage is medium-temperature sintering at a temperature of 300-600℃, the purpose of which is to allow unstable groups in the carbon skeleton to gradually escape and form a stable carbon skeleton; the third stage is carbonization sintering at a temperature of 600-1300℃, the purpose of which is to generate partially graphitized hard carbon with good electrical conductivity.

[0012] Furthermore, the first stage of heat preservation time is 20-40 min, and the heating rate is 4-6℃ / min; the second stage of heat preservation time is 20-40 min, and the heating rate is 1-2℃ / min; the third stage of heat preservation time is 1.5-2.5 h, and the heating rate is 4-6℃ / min.

[0013] This invention provides a porous hard carbon anode material prepared by the above-described preparation method.

[0014] This invention also provides the application of the above-mentioned porous hard carbon anode material in the preparation of sodium-ion batteries.

[0015] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1) By utilizing the dehydrating ability of the activator ZnCl2, dehydrogenation and dehydroxylation reactions of cellulose compounds are catalyzed, accelerating the polymerization of samples to form a rigid structure, providing structural support for subsequent porous structures. Furthermore, the introduction of ZnCl2 can also inhibit the loss of small molecule gases due to insufficient dehydration of cellulose, thus improving the yield of carbon materials.

[0016] 2) The activator ZnCl2 will vaporize during the high-temperature sintering of hard carbon. The method of the present invention can generate a rich pore structure in hard carbon materials, increase the specific surface area of ​​the materials, and thus improve the sodium storage capacity.

[0017] 3) By adopting a segmented heating program, graphitized microcrystals can be avoided during the high-temperature calcination of carbon materials, and unstable groups in the material can be fully released, thus obtaining structurally stable carbon materials. Attached Figure Description

[0018] Figure 1 XRD patterns of the porous hard carbon anode materials prepared in Examples 1 and 2; Figure 2 Cyclic performance of sodium-ion coin cells prepared using the porous hard carbon anode materials prepared in Examples 1, 2 and 5 during the first charge-discharge cycle; Figure 3 Rate performance diagram of sodium-ion coin cells fabricated from the porous hard carbon anode materials prepared in Examples 2 and 5. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0020] In the following examples, all raw materials used are common commercially available products that can be purchased directly, or can be prepared using conventional techniques in the art.

[0021] I. Comparison with and without activator Example 1: No activator 100.0 g of cellulose powder was placed in a graphite crucible, and the crucible containing the sample was transferred to a high-temperature sintering furnace for activation pre-sintering (sintering conditions: 20-300℃, 5℃ / min, 4h, N2 atmosphere, N2 flow rate: 0.5L / min). After pre-sintering, the sintered powder was washed multiple times with deionized water to remove soluble impurities. The washed material was filtered to obtain a precursor filter cake, which was then dried overnight in an oven at 120℃ to obtain purified precursor powder with a yield of approximately 15.4%.

[0022] The precursor powder was placed in a graphite crucible and transferred to a high-temperature sintering furnace. A multi-stage gradient heating program was set (Stage 1: 20-300℃, 5℃ / min, 30min; Stage 2: 300-600℃, 1℃ / min, 30min; Stage 3: 600-1300℃, 5℃ / min, 2h; N2 atmosphere, N2 flow rate: 0.5L / min). After sintering, the high-temperature sintering furnace was allowed to cool to room temperature to obtain the porous hard carbon anode material.

[0023] Example 2 contains an activator 100.0 g of cellulose powder and 20.0 g of zinc chloride powder (activator:cellulose = 0.2:1) were thoroughly mixed in a stirrer for 10 min. The mixture was then transferred to a graphite crucible, which was then placed in a high-temperature sintering furnace for activation pre-sintering (sintering conditions: 20-300℃, 5℃ / min, 4h, N2 atmosphere, N2 flow rate: 0.5 L / min). After pre-sintering, the sintered powder was washed repeatedly with deionized water to remove unreacted zinc chloride and other soluble impurities. The washed material was then filtered to obtain a precursor filter cake, which was subsequently dried overnight in a 120℃ oven to obtain purified precursor powder with a yield of approximately 31.2%.

[0024] The precursor powder was placed in a graphite crucible and transferred to a high-temperature calcination furnace. A multi-stage gradient heating program was set (Stage 1: 20-300℃, 5℃ / min, 30min; Stage 2: 300-600℃, 1℃ / min, 30min; Stage 3: 600-1300℃, 5℃ / min, 2h; N2 atmosphere, N2 flow rate: 0.5L / min). After sintering, the high-temperature sintering furnace was allowed to cool to room temperature to obtain the porous hard carbon anode material.

[0025] II. Optimization of Activator (Zinc Chloride) Addition Amount Example 3: Activator:Cellulose = 0.1:1 (mass ratio) 100.0 g of cellulose powder and 10.0 g of zinc chloride powder (activator:cellulose = 0.1:1) were thoroughly mixed in a stirrer for 10 min. The mixture was then transferred to a graphite crucible, which was then placed in a high-temperature sintering furnace for activation pre-sintering (sintering conditions: 20-300℃, 5℃ / min, 4h, N2 atmosphere, N2 flow rate: 0.5 L / min). After pre-sintering, the sintered powder was washed repeatedly with deionized water to remove unreacted zinc chloride and other soluble impurities. The washed material was then filtered to obtain a precursor filter cake, which was subsequently dried overnight in a 120℃ oven to obtain the purified precursor powder.

[0026] The precursor powder was placed in a graphite crucible and transferred to a high-temperature calcination furnace. A multi-stage gradient heating program was set (Stage 1: 20-300℃, 5℃ / min, 30min; Stage 2: 300-600℃, 1℃ / min, 30min; Stage 3: 600-1300℃, 5℃ / min, 2h; N2 atmosphere, N2 flow rate: 0.5L / min). After sintering, the high-temperature sintering furnace was allowed to cool to room temperature to obtain the porous hard carbon anode material.

[0027] Example 4: Activator: Carbon = 0.3:1 (mass ratio) Take 100.0g of cellulose powder and 30.0g of zinc chloride powder (activator: cellulose = 0.3: 1) and stir them thoroughly in a stirrer. The remaining steps are the same as the experimental steps in Example 3 above.

[0028] III. Comparison of Sintering Processes Example 5: Direct heating without gradient (20-1300℃, 5℃ / min) 100.0 g of cellulose powder and 20.0 g of zinc chloride powder (activator:cellulose = 0.2:1) were thoroughly mixed in a stirrer for 10 min. The mixture was then transferred to a graphite crucible, which was then placed in a high-temperature sintering furnace for activation pre-sintering (sintering conditions: 20-300℃, 5℃ / min, 4h, N2 atmosphere, N2 flow rate: 0.5 L / min). After pre-sintering, the sintered powder was washed repeatedly with deionized water to remove unreacted zinc chloride and other soluble impurities. The washed material was then filtered to obtain a precursor filter cake, which was subsequently dried overnight in a 120℃ oven to obtain the purified precursor powder.

[0029] The precursor powder was placed in a graphite sagger and transferred to a high-temperature calcination furnace. A single gradient heating program was set (20-1300℃, 5℃ / min, 2h, N2 atmosphere, N2 flow rate: 0.5L / min). After sintering, the high-temperature sintering furnace was cooled to room temperature to obtain the porous hard carbon anode material.

[0030] Performance testing Table 1 presents a comparison of the specific surface area and ash content data of the porous hard carbon anode materials prepared in different embodiments. By comparing the physicochemical information of hard carbon anode materials obtained by sintering with different amounts of activator, it can be seen that the addition of zinc chloride activator can effectively increase the specific surface area of ​​the material, but it also increases the ash content. The increase in specific surface area can effectively improve the sodium storage capacity of the sample, but the higher ash content will affect the active sites of the material.

[0031] Table 1. Comparison of physicochemical information of porous hard carbon anode materials prepared in different embodiments Figure 1 XRD patterns of the porous hard carbon anode materials prepared in Examples 1 and 2 are given. By comparing the XRD patterns of Examples 1 and 2, it can be seen that the sample of Example 1 (without activator) has a slight peak at 2θ=26.5° (002 crystal plane of graphite), while the sample of Example 2 has no peak trace at this position. Therefore, the addition of zinc chloride activator can improve the disorder of the microenvironment of hard carbon, which helps to generate a long-range disordered hard carbon structure during high-temperature sintering.

[0032] The hard carbon anode material prepared in the example is the main component of the anode. The hard carbon anode material, conductive carbon black and polyvinylidene fluoride binder (PVDF) are mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is uniformly coated on copper foil and dried to obtain the anode sheet. A 1 mol / L sodium hexafluorophosphate solution is used as the electrolyte (the solvent of the electrolyte is composed of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1). A sodium sheet is used as the counter electrode. The battery is assembled in a glove box to obtain a coin cell.

[0033] Figure 2 The following graphs (specific capacity comparison graphs) show the first-cycle charge-discharge performance of sodium-ion coin cells prepared from the porous hard carbon anode materials of Examples 1, 2, and 5. By comparing the first-cycle charge-discharge performance graphs of the sodium-ion coin cells from Examples 1, 2, and 5, it can be seen that the sample from Example 1 (without activator) has the lowest specific capacity at 273.6 mAh / g; Example 5 (with activator, no gradient temperature increase) is second at 294.7 mAh / g; and Example 2 (with activator, with gradient temperature increase) has the highest specific capacity. Therefore, by adding an activator and using gradient temperature increase, the sodium storage capacity of the sample can be synergistically improved to 314.8 mAh / g.

[0034] Figure 3Rate performance graphs of sodium-ion coin cells fabricated using the porous hard carbon anode materials prepared in Examples 2 and 5 are provided. The graphs show that the specific capacities of the sample from Example 2 are: 0.1C: 313.4, 316.9 mAh / g; 0.2C: 304.3, 304.0, 303.7 mAh / g; 1C: 296.8, 295.8, 295.7, 297.7, 297.9 mAh / g; and the specific capacities of the sample from Example 5 are: 0.1C: 297.6, 296.9 mAh / g; 0.2C: 279.1, 278.6, 275.1 mAh / g; 1C: 268.6, 265.5, 263.5, 263.6, 262.4 mAh / g. By comparing the rate performance of sodium-ion button batteries in Examples 2 and 5, it can be seen that the rate performance of the sample in Example 2 (with activator and gradient temperature) is better than that in Example 5 (with activator and no gradient temperature), and it still has a good capacity retention rate after multiple cycles at 1C rate.

Claims

1. A method for preparing a porous hard carbon anode material, characterized in that, Includes the following steps: 1) Mix the carbon source and activator in a certain proportion, and then pre-sinter them under an inert atmosphere to obtain the precursor material; 2) The precursor material is washed with water and dried to obtain the purified material; 3) The purified material is sintered under a programmed temperature rise under an inert atmosphere to obtain the porous hard carbon anode material.

2. The method for preparing the porous hard carbon anode material as described in claim 1, characterized in that, In step 1), the carbon source is at least one of cellulose, glucose, and starch; the activator is ZnCl2.

3. The method for preparing the porous hard carbon anode material as described in claim 1, characterized in that, In step 1), the mass ratio of the activator to the carbon source is 0.2-0.4:

1.

4. The method for preparing the porous hard carbon anode material as described in claim 1, characterized in that, In step 1), the pre-sintering is carried out at 250-350℃ for 3-5 hours.

5. The method for preparing the porous hard carbon anode material as described in claim 1, characterized in that, In step 3), the programmed temperature sintering is specifically divided into three stages: the first stage is dehydration sintering at a temperature of 20-300℃; the second stage is medium-temperature sintering at a temperature of 300-600℃; and the third stage is carbonization sintering at a temperature of 600-1300℃.

6. The method for preparing the porous hard carbon anode material as described in claim 5, characterized in that, The first stage of heat preservation lasts for 20-40 minutes, with a heating rate of 4-6℃ / min; the second stage of heat preservation lasts for 20-40 minutes, with a heating rate of 1-2℃ / min; the third stage of heat preservation lasts for 1.5-2.5 hours, with a heating rate of 4-6℃ / min.

7. A porous hard carbon anode material prepared by any one of the preparation methods described in claims 1 to 6.

8. The application of the porous hard carbon anode material according to claim 7 in the preparation of sodium-ion batteries.

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