Preparation method of carbon fluoride positive electrode material based on agar-based hierarchical pore structure

Abstract

The invention discloses a preparation method of a carbon fluoride positive electrode material based on an agar-based hierarchical pore structure, and belongs to the technical field of preparation of positive electrode materials. According to the method, biomass agar is used as a three-dimensional network skeleton raw material, potassium citrate is used as an activating agent, and the method is realized through three key steps of composite hydrogel preparation, graded pore biomass charcoal preparation and fluorination reaction. The preparation method specifically comprises the following steps: dissolving agar and 1-3g of potassium citrate at 95 DEG C to form composite hydrogel, carbonizing at 800 DEG C to obtain graded pore biomass charcoal, introducing fluorine / nitrogen mixed gas with the volume ratio of 3: 7, and carrying out fluoridation reaction at 200 DEG C for 4 hours to obtain a target material. By utilizing the gelation characteristic of agar at a high temperature, the composite gel with a three-dimensional network structure is firstly constructed, and the carbon precursor with a hierarchical pore structure is prepared after the carbonization treatment process, so that the discharge voltage of the carbon fluoride positive electrode is improved on one hand, and the volume expansion and heat release conditions of the positive electrode are reduced on the other hand.

Description

Technical Field

[0001] This invention belongs to the field of cathode material preparation technology, specifically, it relates to a method for preparing fluorinated carbon cathode material based on agar-based hierarchical pore structure. Background Technology

[0002] Currently, commercially available batteries using fluorinated graphite as the positive electrode typically have a discharge starting voltage of around 2.5V and a median voltage not exceeding 2.6V. Furthermore, during discharge, the continuous entry of lithium ions into the fluorinated carbon positive electrode causes severe deformation (volume expansion) of the battery, compromising safety. The advantage of this product lies in its use of fluorinated graphite as the positive electrode in a primary battery, which increases the discharge voltage and mitigates battery volume expansion.

[0003] The reason is that by utilizing the gelation properties of biomass agar, a hydrogel with a three-dimensional network structure is prepared in advance, and then carbonized to form a carbon precursor with hierarchical pore characteristics. The hierarchical pore network structure itself not only facilitates the shuttle of electrons and ions inside the battery, ultimately increasing the working voltage of the material, but also alleviates the excessive accumulation of lithium fluoride products during discharge, ultimately reducing the deformation (volume expansion) of the fluorinated carbon soft-pack battery.

[0004] Lithium / carbon fluoride (FCF) batteries are primary batteries that use fluoride carbon as the positive electrode and lithium as the negative electrode. They have significant application prospects in fields with extremely high battery performance requirements, such as aerospace, deep-sea exploration, and medical implants. However, fluoride carbon materials face many challenges in practical applications. First, fluoride carbon is almost an insulator, and its conductivity decreases with increasing fluorination, leading to a decrease in the discharge voltage of fluoride carbon primary batteries. Second, during discharge, lithium ions enter the fluoride carbon through the electrolyte, causing severe deformation (volume expansion) of the fluoride carbon positive electrode, which in turn leads to battery deformation. This may interrupt the discharge process, seriously affecting battery performance. The expansion during discharge also affects battery design and practical use. Finally, lithium / carbon fluoride batteries release a large amount of heat during discharge. On the one hand, the poor conductivity of the fluoride carbon positive electrode causes polarization during discharge, resulting in a large release of heat. On the other hand, the discharge product, lithium fluoride, also releases a large amount of heat during the formation of crystal cells, affecting the normal discharge of the battery. Therefore, lithium fluoride carbon batteries are greatly limited in high-power applications due to the increased temperature.

[0005] Based on the above problems, we utilized the gelation properties of agar at high temperatures to first construct a composite gel with a three-dimensional network structure. After carbonization, a carbon precursor with a hierarchical pore structure was prepared. This improved the discharge voltage of the fluorinated carbon cathode on the one hand, and reduced the volume expansion and exothermic reaction of the cathode on the other.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure includes the following steps:

[0009] Step S1: Preparation of composite hydrogel: Weigh 4g of agar and 1-3g of potassium citrate, add to 80mL of deionized water, and stir at 95℃ for 4h until completely dissolved;

[0010] Step S2: Pour into a petri dish and let stand for 10 hours to form an agar / potassium citrate composite hydrogel; prepare hierarchical pore biochar;

[0011] Step S3: Place the composite hydrogel obtained in step 1 in a tube furnace and heat it to 800°C at a heating rate of 5°C / min. Carbonize for 2 hours and then cool naturally to obtain biochar with a hierarchical pore structure.

[0012] Step S4: Fluorination reaction to prepare fluorinated carbon cathode material. Take the biochar obtained in step 2 and spread it evenly in the fluorination furnace. After evacuating to -0.1MPa, introduce a fluorine / nitrogen mixed gas with a volume ratio of 3:7 until the furnace pressure is 0.05MPa.

[0013] Step S5: Control the gas flow rate to 2L / min, and perform the fluorination reaction at 200℃ for 4h. After cooling, obtain the fluorinated carbon cathode material based on the agar-based hierarchical pore structure.

[0014] In a preferred embodiment of the present invention, the amount of potassium citrate added in step S1 is 2g.

[0015] In a preferred embodiment of the present invention, the carbonization process in the tubular furnace in step 2 is protected by an inert gas, wherein the inert gas is nitrogen and the flow rate is 1-2 L / min.

[0016] In a preferred embodiment of the present invention, the purity of fluorine and nitrogen in the fluorine / nitrogen mixture in step S3 must both be ≥99.99%.

[0017] In a preferred embodiment of the present invention, the heating rate of the fluorination furnace in step S3 is 2°C / min, from room temperature to 200°C.

[0018] In a preferred embodiment of the present invention, the mixed gas needs to be dried before being introduced.

[0019] In a preferred embodiment of the present invention, after the fluorination reaction in step S4 is completed, nitrogen gas is continuously purged for 2 hours at a flow rate of 3 L / min to remove residual fluorine gas and reaction byproducts.

[0020] In a preferred embodiment of the present invention, the thickness of the composite hydrogel in step S2 is controlled to be 2-5 mm, the static temperature is 20-25℃, and the relative humidity is 50-60%, so as to avoid cracking of the gel surface.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention utilizes the gelation properties of agar at high temperatures to first construct a composite gel with a three-dimensional network structure. After carbonization, a carbon precursor with a hierarchical pore structure is prepared. This improves the discharge voltage of the fluorinated carbon cathode while reducing the volume expansion and heat release of the cathode.

[0023] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0024] In the attached diagram:

[0025] Figure 1 A flowchart of a method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure;

[0026] Figure 2 Electron micrographs of different amounts of potassium citrate added;

[0027] Figure 3 BET curves for different amounts of potassium citrate added;

[0028] Figure 4 Discharge curves of fluorinated PAC2.5 at 200°C and commercial fluorinated graphite, as well as thickness variation during discharge of a pouch cell assembled with fluorinated PAC2.5 at 200°C.

[0029] Figure 5 A graph showing the thickness change of a pouch cell assembled from commercial fluorinated graphite during the discharge process. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention.

[0031] Using biomass agar gel as a three-dimensional network framework, and potassium citrate (1, 1.5, 2, 2.5, 3 g) added in different amounts as activators, agar and potassium citrate were first dissolved to form an aqueous solution by heating (95 degrees Celsius) and stirring. After cooling to room temperature, the solution was allowed to stand for 24 hours to form an agar / potassium citrate composite hydrogel.

[0032] The carbon is then placed in a tubular furnace at 800 degrees Celsius to form biochar with a hierarchical pore structure. Finally, a fluorine / nitrogen mixture (mixing ratio 3:7) is introduced, and a fluorination reaction is carried out at 200 degrees Celsius to prepare fluorinated carbon material as the positive electrode of a primary battery.

[0033] Example 1:

[0034] The fluorinated carbon primary battery cathode material described in Example 1 uses agar, potassium citrate, and a fluorine / nitrogen mixed gas (mixing ratio 3:7) as raw materials. The agar content is 4g, the deionized water content is 80ml, the fluorine purity is 30%, and the remainder is nitrogen. The fluorination reaction temperature is 200 degrees Celsius.

[0035] The fluorinated carbon primary battery cathode material described in Example 1 is composed of the following steps:

[0036] (1) Weigh 4g of agar, put it into 80ml of deionized water, heat to 95 degrees and stir for 4 hours;

[0037] (2) Pour into a petri dish and let stand for 10 hours to form an agar gel;

[0038] (3) The agar gel was placed in a tube furnace and carbonized at 800°C for 2 hours with a heating rate of 5°C / min. The product was named AC.

[0039] (4) Weigh 1g AC and spread it evenly in the fluorination furnace to ensure the fluorination reaction proceeds;

[0040] (5) Use a vacuum pump to evacuate the furnace to -0.1 MPa;

[0041] (6) Introduce a fluorine / nitrogen mixture to 0.05 MPa, with a flow rate of 2 L / min and a fluorination temperature of 200 degrees.

[0042] (7) Fluorinated carbon cathode material prepared after fluorination for 4 hours.

[0043] Example 2:

[0044] The fluorinated carbon primary battery cathode material described in Example 1 uses agar, potassium citrate, and a fluorine / nitrogen mixed gas (mixing ratio 3:7) as raw materials. The agar content is 4g, the deionized water content is 80ml, the potassium citrate content is 1g, the fluorine purity is 30%, and the remainder is nitrogen. The fluorination reaction temperature is 200 degrees Celsius.

[0045] The fluorinated carbon primary battery cathode material described in Example 1 is composed of the following steps:

[0046] (1) Weigh 4g of agar and 1g of potassium citrate, put them into 80ml of deionized water, heat to 95 degrees and stir for 4 hours;

[0047] (2) Pour into a petri dish and let stand for 10 hours to form an agar / potassium citrate composite gel;

[0048] (3) The agar gel was placed in a tube furnace and carbonized at 800°C for 2 hours with a heating rate of 5°C / min. The product was named PAC1.

[0049] (4) Weigh 1g of PAC1 and spread it evenly in the fluorination furnace to ensure the fluorination reaction proceeds;

[0050] (5) Use a vacuum pump to evacuate the furnace to -0.1 MPa;

[0051] (6) Introduce a fluorine / nitrogen mixture to 0.05 MPa, with a flow rate of 2 L / min and a fluorination temperature of 200 degrees.

[0052] (7) Fluorinated carbon cathode material prepared after fluorination for 4 hours.

[0053] Example 3:

[0054] The fluorinated carbon primary battery cathode material described in Example 1 uses agar, potassium citrate, and a fluorine / nitrogen mixed gas (mixing ratio 3:7) as raw materials. The agar content is 4g, the deionized water content is 80ml, the potassium citrate content is 1.5g, the fluorine purity is 30%, and the remainder is nitrogen. The fluorination reaction temperature is 200 degrees Celsius.

[0055] The fluorinated carbon primary battery cathode material described in Example 1 is composed of the following steps:

[0056] (1) Weigh 4g of agar and 1.5g of potassium citrate, put them into 80ml of deionized water, heat to 95 degrees and stir for 4 hours;

[0057] (2) Pour into a petri dish and let stand for 10 hours to form an agar / potassium citrate composite gel;

[0058] (3) The agar gel was placed in a tube furnace and carbonized at 800°C for 2 hours with a heating rate of 5°C / min. The product was named PAC1.5.

[0059] (4) Weigh 1g of PAC1.5 and spread it evenly in the fluorination furnace to ensure the fluorination reaction proceeds;

[0060] (5) Use a vacuum pump to evacuate the furnace to -0.1 MPa;

[0061] (6) Introduce a fluorine / nitrogen mixture to 0.05 MPa, with a flow rate of 2 L / min and a fluorination temperature of 200 degrees.

[0062] (7) Fluorinated carbon cathode material prepared after fluorination for 4 hours.

[0063] Example 4:

[0064] The fluorinated carbon primary battery cathode material described in Example 1 uses agar, potassium citrate, and a fluorine / nitrogen mixed gas (mixing ratio 3:7) as raw materials. The agar content is 4g, the deionized water content is 80ml, the potassium citrate content is 2g, the fluorine purity is 30%, and the remainder is nitrogen. The fluorination reaction temperature is 200 degrees Celsius.

[0065] The fluorinated carbon primary battery cathode material described in Example 1 is composed of the following steps:

[0066] (1) Weigh 4g of agar and 2g of potassium citrate, put them into 80ml of deionized water, heat to 95 degrees and stir for 4 hours;

[0067] (2) Pour into a petri dish and let stand for 10 hours to form an agar / potassium citrate composite gel;

[0068] (3) The agar gel was placed in a tube furnace and carbonized at 800°C for 2 hours with a heating rate of 5°C / min. The product was named PAC2.

[0069] (4) Weigh 1g of PAC2 and spread it evenly in the fluorination furnace to ensure the fluorination reaction proceeds;

[0070] (5) Use a vacuum pump to evacuate the furnace to -0.1 MPa;

[0071] (6) Introduce a fluorine / nitrogen mixture to 0.05 MPa, with a flow rate of 2 L / min and a fluorination temperature of 200 degrees.

[0072] (7) Fluorinated carbon cathode material prepared after fluorination for 4 hours.

[0073] Example 5:

[0074] The fluorinated carbon primary battery cathode material described in Example 1 uses agar, potassium citrate, and a fluorine / nitrogen mixed gas (mixing ratio 3:7) as raw materials. The agar content is 4g, the deionized water content is 80ml, the potassium citrate content is 2.5g, the fluorine purity is 30%, and the remainder is nitrogen. The fluorination reaction temperature is 200 degrees Celsius.

[0075] The fluorinated carbon primary battery cathode material described in Example 1 is composed of the following steps:

[0076] (1) Weigh 4g of agar and 2.5g of potassium citrate, put them into 80ml of deionized water, heat to 95 degrees and stir for 4 hours;

[0077] (2) Pour into a petri dish and let stand for 10 hours to form an agar / potassium citrate composite gel;

[0078] (3) The agar gel was placed in a tube furnace and carbonized at 800°C for 2 hours with a heating rate of 5°C / min. The product was named PAC2.5.

[0079] (4) Weigh 1g of PAC2.5 and spread it evenly in the fluorination furnace to ensure the fluorination reaction proceeds;

[0080] (5) Use a vacuum pump to evacuate the furnace to -0.1 MPa;

[0081] (6) Introduce a fluorine / nitrogen mixture to 0.05 MPa, with a flow rate of 2 L / min and a fluorination temperature of 200 degrees.

[0082] (7) Fluorinated carbon cathode material prepared after fluorination for 4 hours.

[0083] Example 6:

[0084] The fluorinated carbon primary battery cathode material described in Example 1 uses agar, potassium citrate, and a fluorine / nitrogen mixed gas (mixing ratio 3:7) as raw materials. The agar content is 4g, the deionized water content is 80ml, the potassium citrate content is 3g, the fluorine purity is 30%, and the remainder is nitrogen. The fluorination reaction temperature is 200 degrees Celsius.

[0085] The fluorinated carbon primary battery cathode material described in Example 1 is composed of the following steps:

[0086] (1) Weigh 4g of agar and 3g of potassium citrate, put them into 80ml of deionized water, heat to 95 degrees and stir for 4 hours;

[0087] (2) Pour into a petri dish and let stand for 10 hours to form an agar / potassium citrate composite gel;

[0088] (3) The agar gel was placed in a tube furnace and carbonized at 800°C for 2 hours with a heating rate of 5°C / min. The product was named PAC3.

[0089] (4) Weigh 1g of PAC3 and spread it evenly in the fluorination furnace to ensure the fluorination reaction proceeds;

[0090] (5) Use a vacuum pump to evacuate the furnace to -0.1 MPa;

[0091] (6) Introduce a fluorine / nitrogen mixture to 0.05 MPa, with a flow rate of 2 L / min and a fluorination temperature of 200 degrees Celsius.

[0092] (7) Fluorinated carbon cathode material prepared after fluorination for 4 hours.

[0093] Table 1 is a comparison table of key performance parameters.

[0094] Example number Amount of potassium citrate added (g) Specific surface area of ​​biochar (m² / g) Discharge initiation voltage (V) Median voltage (V) Volume expansion rate (%) Maximum discharge temperature (°C) Example 1 0 82 2.52 2.58 26.5 69 Example 2 1 155 2.64 2.61 21.3 63 Example 3 1.5 218 2.72 2.65 18.1 59 Example 4 2 286 2.83 2.73 14.7 54 Example 5 2.5 322 2.79 2.70 15.2 56 Example 6 3 340 2.76 2.68 16.0 57

[0095] The table shows that the specific surface area changes as the amount of potassium citrate added increases. The specific surface area of ​​biochar increases from 82 m² / g (without addition) to 340 m² / g (with 3g addition), indicating that the activation effect of potassium citrate significantly expands the pore structure of the material.

[0096] Voltage performance: Example 4 (2g added) had the highest discharge initiation voltage (2.83V) and median voltage (2.73V), which were 12.3% and 5.8% higher than the group without additive, respectively, verifying the promoting effect of hierarchical pore structure on electron / ion conduction;

[0097] Volume stability: The volume expansion rate first decreased and then increased with the increase of the amount added. The lowest value was 14.7% in Example 4, which was 44.5% lower than the group without addition, reflecting the buffering effect of the hierarchical pores on the accumulation of LiF products.

[0098] Exothermic characteristics: The maximum discharge temperature gradually decreases with increasing porosity. Example 4 shows a 21.7% decrease compared to Example 1, demonstrating that pore structure optimization can reduce polarization heat accumulation.

Claims

1. A method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure, characterized in that, Includes the following steps: Step S1: Preparation of composite hydrogel: Weigh 4g of agar and 1-3g of potassium citrate, add to 80mL of deionized water, and stir at 95℃ for 4h until completely dissolved; Step S2: Pour into a petri dish and let stand for 10 hours to form an agar / potassium citrate composite hydrogel; prepare hierarchical pore biochar; Step S3: Place the composite hydrogel obtained in step 1 in a tube furnace and heat it to 800°C at a heating rate of 5°C / min. Carbonize for 2 hours and then cool naturally to obtain biochar with a hierarchical pore structure. Step S4: Fluorination reaction to prepare fluorinated carbon cathode material. Take the biochar obtained in step 2 and spread it evenly in the fluorination furnace. After evacuating to -0.1MPa, introduce a fluorine / nitrogen mixed gas with a volume ratio of 3:7 until the furnace pressure is 0.05MPa. Step S5: Control the gas flow rate to 2L / min, and perform the fluorination reaction at 200℃ for 4h. After cooling, obtain the fluorinated carbon cathode material based on the agar-based hierarchical pore structure.

2. The method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure according to claim 1, characterized in that, The amount of potassium citrate added in step S1 is 2g.

3. The method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure according to claim 1, characterized in that, In step 2, the tubular furnace carbonization process is protected by an inert gas, namely nitrogen, with a flow rate of 1-2 L / min.

4. The method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure according to claim 1, characterized in that, In step S3, the purity of fluorine in the fluorine / nitrogen mixture is ≥99.9%, and the purity of nitrogen is ≥99.99%.

5. The method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure according to claim 1, characterized in that, In step S3, the heating rate of the fluorination furnace is 2℃ / min, from room temperature to 200℃.

6. The method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure according to claim 4, characterized in that, The mixture needs to be dried before it is introduced.

7. The method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure according to claim 1, characterized in that, After the fluorination reaction in step S4 is completed, nitrogen gas is continuously purged for 2 hours at a flow rate of 3 L / min to remove residual fluorine gas and reaction byproducts.

8. The method for preparing a fluorinated carbon cathode material based on an agar-based hierarchical pore structure according to claim 1, characterized in that, In step S2, the thickness of the composite hydrogel is controlled at 2-5 mm, the ambient temperature is 20-25℃, and the relative humidity is 50-60% to avoid cracking of the gel surface.

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