A phenolic resin-based hard carbon material and its preparation method and application

Abstract

The invention belongs to the technical field of hard carbon materials, and proposes a phenolic resin-based hard carbon material and a preparation method and application thereof, comprising: ball-milling a phenolic resin, zinc acrylate, and potassium tripolyphosphate in a mass ratio of 2-10:0.5-5:1-8, and then carbonizing at 1300-1500°C in an inert gas atmosphere, and keeping the temperature for 1-5 hours to obtain a phenolic resin-based hard carbon material. The preparation process provided by the invention is simple, easy to operate, and has good application value. The prepared hard carbon material has higher battery specific capacity and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of hard carbon materials and relates to a phenolic resin-based hard carbon material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have attracted widespread attention due to their high energy density, long service life and environmental friendliness. However, with the large-scale application of electric vehicles and energy storage power stations, the demand for lithium resources has also greatly increased. The shortage and uneven distribution of lithium resources have also begun to emerge, becoming a bottleneck problem restricting the development of lithium-ion batteries. In contrast, sodium and lithium in sodium-ion batteries, which store energy as charge carriers, are in the same main group, and have both cost and resource advantages, making them the best alternative to lithium-ion batteries. Among the many negative electrode materials available for sodium-ion batteries, carbon negative electrodes have lower potential, higher capacity, stable physicochemical properties and low cost, making them the preferred negative electrode materials for the commercial development of sodium-ion batteries. However, the current commercial graphite negative electrode materials cannot be used in sodium-ion batteries. Their sodium storage capacity is too low and their energy density is far from that of existing commercial lithium-ion batteries. Therefore, it is necessary to develop new carbon negative electrode materials.

[0003] Among various carbon materials, amorphous carbon materials show better performance. Amorphous carbon materials include soft carbon and hard carbon. Hard carbon, as the negative electrode of sodium ion batteries, has a higher specific capacity. At the same time, hard carbon materials have a larger interlayer spacing and porous structure, which can alleviate the volume expansion during the reaction process, which is conducive to the commercialization of sodium ion batteries. However, there are also some problems with hard carbon materials as negative electrodes for sodium ion batteries, such as low specific capacity and poor stability. These factors seriously hinder the industrial application of hard carbon-based negative electrode materials.

[0004] Therefore, it is of great value to research and develop a hard carbon material for sodium ion batteries with rich pore structure, excellent sodium storage performance, high specific capacity, good stability and simple preparation process. Summary of the invention

[0005] The present invention provides a phenolic resin-based hard carbon material and a preparation method and application thereof, wherein the preparation process is simple, easy to operate, and has good application value; the prepared hard carbon material has higher specific capacity and stability.

[0006] The technical solution of the present invention is achieved in this way:

[0007] Technical Theme 1

[0008] The invention provides a method for preparing phenolic resin-based hard carbon, comprising the following steps: ball-milling a phenolic resin, zinc acrylate and potassium tripolyphosphate in a mass ratio of 2-10:0.5-5:1-8, and then carbonizing at 1300-1500°C in an inert gas atmosphere, and keeping the temperature for 1-5 hours to obtain a phenolic resin-based hard carbon material.

[0009] Preferably, the mass ratio of the phenolic resin, zinc acrylate and potassium tripolyphosphate is 5:1.5:2.

[0010] Preferably, the preparation method of the phenolic resin comprises the following steps: adding phenol, formaldehyde, cashew nut oil, melamine and hydrochloric acid in a mass ratio of 100:75-90:0-38:0-1.5:0.5-1 into a reaction kettle, heating to 65-75°C, stopping heating, naturally heating to boiling, boiling reaction for 1.5-2.5 hours, starting decompression dehydration, the pressure is -0.08~-0.03MPa, and the dehydration is stopped when the temperature returns to 140-180°C, discharging the material to obtain the resin, and crushing the resin to obtain the phenolic resin.

[0011] Preferably, the preparation method of the phenolic resin comprises the following steps: putting bisphenol A, aniline, formaldehyde and hydrochloric acid in a mass ratio of 100:15-25:75-95:0.5-1.5 into a reaction kettle, heating to 65-75°C, stopping heating, naturally heating to boiling, boiling reaction for 1.5-2.5 hours, starting decompression dehydration, the pressure is -0.08~-0.03MPa, and stopping dehydration when the temperature returns to 140-180°C, discharging the material to obtain resin, and crushing the resin to obtain phenolic resin.

[0012] Preferably, the resin crushing step comprises: mixing the resin and hexamethylenetetramine in a mass ratio of 100:5-10 and crushing them to 80-200 meshes to obtain a phenolic resin;

[0013] The formaldehyde is liquid formaldehyde with a mass fraction of 37%, and the hydrochloric acid is a hydrochloric acid solution with a mass fraction of 37%.

[0014] Preferably, the rotation speed of the ball mill is 350-450 rpm, and the ball mill is milled to 80-200 mesh.

[0015] Preferably, the inert gas is selected from one of nitrogen, helium or argon.

[0016] Preferably, the carbonization process specifically includes: continuously introducing inert gas at a rate of 6-10 mL / min, heating to 1300-1500° C. at a rate of 2-5° C. / min, maintaining for 1-5 hours, and naturally cooling to room temperature.

[0017] Technical Theme 2

[0018] The present invention also provides a phenolic resin-based hard carbon material prepared by the preparation method of the phenolic resin-based hard carbon.

[0019] Technical Theme 3

[0020] The present invention also provides application of the phenolic resin-based hard carbon material in a sodium ion battery.

[0021] The working principle and beneficial effects of the present invention are:

[0022] 1. The preparation method provided by the present invention is simple and suitable for large-scale promotion. When the phenolic resin-based hard carbon material prepared by the present invention is used as the negative electrode of a sodium ion battery, it has good electrochemical performance: at a high current of 10A / g, the battery specific capacity is as high as 345mAh / g, and the specific capacity after 10,000 cycles can still be as high as 95%.

[0023] 2. In the present invention, the phenolic resin, zinc acrylate and potassium tripolyphosphate are an interactive mechanism to form a battery negative electrode material with high specific capacity, and the interaction is as follows: the role of zinc acrylate is to be able to polymerize with the phenolic resin to generate macromolecular organic matter, thereby increasing the carbon residue, and zinc can be used as an activator to etch and activate the hard carbon structure, thereby increasing the defect sites; the role of potassium tripolyphosphate is to enable the material to withstand high temperatures, thereby avoiding the loss of phosphorus at high temperatures, thereby increasing the phosphorus residue, and potassium can form potassium vapor to further activate the material, thereby increasing the sodium storage sites of the material;

[0024] The different preparation processes used for the phenolic resin result in different degrees of polycondensation of the material during carbonization and different carbon residues. The phenolic resin prepared by aniline and bisphenol A, because aniline is added during the preparation process, forms hexagonal graphite carbon during carbonization, which is more conducive to the storage of sodium ions and significantly improves the battery specific capacity and stability. In addition, the phenolic resin prepared by aniline contains a large amount of amino groups, which can polymerize with the double bonds in zinc acrylate at high temperatures to form a cross-linked structure. At the same time, the phosphoric acid produced by the decomposition of potassium tripolyphosphate at high temperatures can react with the alkaline amino groups to increase the phosphorus doping amount. These effects together improve the battery specific capacity and stability of the hard carbon material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0026] Figure 1 This is a nitrogen adsorption-desorption curve diagram of the hard carbon material obtained in Example 5 of the present invention.

[0027] Figure 2 This is a pore size distribution diagram of the hard carbon material obtained in Example 5 of the present invention.

[0028] Figure 3This is a SEM image of the hard carbon material obtained in Example 5 of the present invention.

[0029] Figure 4 This is the XPS graph of phosphorus element in the hard carbon material obtained in Example 5 of the present invention.

[0030] Figure 5 This is the XPS graph of the zinc element in the hard carbon material obtained in Example 5 of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased on the market or prepared by existing methods. Among them:

[0032] Zinc acrylate was purchased from Aladdin Reagents, catalog number Z472262-250g;

[0033] Potassium tripolyphosphate was purchased from Aladdin Reagent, catalog number P165312-100g;

[0034] Formaldehyde: 37wt% liquid formaldehyde (McLean's reagent);

[0035] Hydrochloric acid was purchased from Aladdin Reagent, 37% mass fraction;

[0036] Cashew nut oil was purchased from Wuhan Kamik Technology Co., Ltd., industrial grade.

[0037] Preparation Example 1

[0038] Raw materials: prepare 100g phenol; 75g formaldehyde; 0.5g hydrochloric acid;

[0039] Preparation method: Phenol, formaldehyde and hydrochloric acid are put into a reaction kettle in sequence, heated to 70°C, and then the heating is stopped. The temperature is naturally raised to boiling, and the boiling reaction is carried out for 2 hours. The decompression dehydration is started, and the pressure is -0.06MPa. When the temperature rises back to 140°C, the dehydration is stopped, and the material is discharged to obtain resin a.

[0040] The resin A prepared above was crushed to 100 meshes to obtain phenolic resin A.

[0041] Preparation Example 2

[0042] Raw materials: prepare 100g phenol; 75g formaldehyde; 0.5g hydrochloric acid;

[0043] Preparation method: Phenol, formaldehyde and hydrochloric acid are put into a reaction kettle in sequence, heated to 70°C, and then the heating is stopped. The temperature is naturally raised to boiling, and the boiling reaction is carried out for 2 hours. The decompression dehydration is started, and the pressure is -0.06MPa. When the temperature rises back to 140°C, the dehydration is stopped, and the material is discharged to obtain resin a.

[0044] The resin A prepared above was mixed with urotropine in a ratio of 100 g:10 g and ground into 80 meshes to obtain phenolic resin B.

[0045] Preparation Example 3

[0046] Raw materials: prepare 100g phenol; 90g formaldehyde; 38g cashew oil; 1.5g melamine; 0.8g hydrochloric acid;

[0047] Preparation method: Phenol, formaldehyde, cashew nut oil, melamine and hydrochloric acid are put into a reaction kettle in sequence, heated to 70°C, stopped heating, naturally heated to boiling, boiled for 2 hours, started decompression dehydration, pressure -0.06MPa, stopped dehydration when the temperature returned to 140°C, discharged, and obtained resin c;

[0048] The resin C prepared above and urotropine were mixed in a ratio of 100 g:10 g and ground into 200 meshes to obtain phenolic resin C.

[0049] Preparation Example 4

[0050] Raw materials: prepare 100g phenol; 87g formaldehyde; 20g cashew oil; 0.8g hydrochloric acid;

[0051] Preparation method: Phenol, formaldehyde, cashew nut oil and hydrochloric acid are put into a reaction kettle in sequence, heated to 70°C, stopped heating, naturally heated to boiling, boiled for 2 hours, started decompression dehydration, pressure -0.06MPa, stopped dehydration when the temperature returned to 140°C, discharged the material, and obtained resin d;

[0052] The resin D prepared above was mixed with urotropine in a ratio of 100 g:10 g and ground into 100 meshes to obtain phenolic resin D.

[0053] Preparation Example 5

[0054] Raw materials: prepare 100g bisphenol A; 20g aniline; 90g formaldehyde; 1g hydrochloric acid;

[0055] Preparation method: bisphenol A, formaldehyde, aniline and hydrochloric acid are put into a reaction kettle in sequence, heated to 70°C, stopped heating, naturally heated to boiling, boiled for 2 hours, started decompression dehydration, pressure -0.06MPa, stopped dehydration when the temperature returned to 140°C, discharged, and obtained resin e-1;

[0056] The resin e-1 prepared above and urotropine were mixed in a ratio of 100 g:5 g and ground into 100 mesh to obtain phenolic resin E-1.

[0057] Preparation Example 6

[0058] Raw materials: prepare 100g bisphenol A; 15g aniline; 95g formaldehyde; 0.5g hydrochloric acid;

[0059] Preparation method: bisphenol A, formaldehyde, aniline and hydrochloric acid are put into a reaction kettle in sequence, heated to 75°C, stopped heating, naturally heated to boiling, boiled for 1.5 hours, and decompressed to dehydrate, the pressure was -0.08MPa, and the dehydration was stopped when the temperature returned to 140°C, and the material was discharged to obtain resin e-2;

[0060] The resin e-2 prepared above and urotropine were mixed in a ratio of 100 g:6 g and ground into 200 meshes to obtain phenolic resin E-2.

[0061] Preparation Example 7

[0062] Raw materials: prepare 100g bisphenol A; 25g aniline; 75g formaldehyde; 1.5g hydrochloric acid;

[0063] Preparation method: bisphenol A, formaldehyde, aniline and hydrochloric acid are put into a reaction kettle in sequence, heated to 65°C, stopped heating, naturally heated to boiling, boiled for 2.5 hours, started decompression dehydration, pressure -0.03MPa, stopped dehydration when the temperature returned to 180°C, discharged, and obtained resin e-3;

[0064] The resin E-3 prepared above was mixed with urotropine in a ratio of 100 g:10 g and ground into 80 meshes to obtain phenolic resin E-3.

[0065] Example 1

[0066] Weigh 2.0g of the above-mentioned phenolic resin A, 0.5g of zinc acrylate, and 1.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 6mL / min in a carbonization furnace, increase the temperature to 1300°C at a rate of 5°C / min, maintain it for 5h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 350 rpm, and the ball milling is to 200 mesh.

[0067] Example 2

[0068] Weigh 10.0g of the above-mentioned phenolic resin B, 5g of zinc acrylate, and 8.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 10mL / min in a carbonization furnace, increase the temperature to 1500°C at a rate of 2°C / min, maintain it for 1h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 450 rpm, and the ball milling is to 80 mesh.

[0069] Example 3

[0070] Weigh 5.0g of the above-mentioned phenolic resin C, 1.5g of zinc acrylate, and 2.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 8mL / min in a carbonization furnace, increase the temperature to 1400°C at a rate of 3°C / min, maintain it for 2h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 400 rpm, and the ball milling is to 200 mesh.

[0071] Example 4

[0072] Weigh 5.0g of the above-mentioned phenolic resin D, 1.5g of zinc acrylate, and 2.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 8mL / min in a carbonization furnace, increase the temperature to 1400°C at a rate of 3°C / min, maintain it for 2h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 400 rpm, and the ball milling is to 100 mesh.

[0073] Example 5

[0074] Weigh 5.0g of the above-mentioned phenolic resin E-1, 1.5g of zinc acrylate, and 2.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 8mL / min in a carbonization furnace, increase the temperature to 1400°C at a rate of 3°C / min, maintain it for 2h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 400 rpm, and the ball milling is to 100 mesh.

[0075] The hard carbon material obtained in Example 5 was characterized by specific surface area, pore size distribution, SEM and XPS, as shown in Figure 1-Figure 4 As shown by Figure 1 It can be seen that there are mesopores, macropores and micropores in hard carbon materials, indicating that the material has a multi-level pore structure. Figure 2 It can be seen that the pore size of hard carbon materials is mainly concentrated around 2nm; Figure 3 It can be seen that hard carbon materials have rich pore structures; Figure 4 It can be seen that hard carbon materials contain phosphorus, of which the phosphorus content is 8.1at%; Figure 5 It can be seen that the hard carbon material contains zinc element, and the phosphorus content is 5.63at%.

[0076] Example 6

[0077] Weigh 5.0g of the above-mentioned phenolic resin E-2, 1.5g of zinc acrylate, and 2.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 8mL / min in a carbonization furnace, increase the temperature to 1400°C at a rate of 3°C / min, maintain it for 2h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 400 rpm, and the ball milling is to 200 mesh.

[0078] Example 7

[0079] Weigh 5.0g of the above-mentioned phenolic resin E-3, 1.5g of zinc acrylate, and 2.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 8mL / min in a carbonization furnace, increase the temperature to 1400°C at a rate of 3°C / min, maintain it for 2h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 400 rpm, and the ball milling is to 100 mesh.

[0080] Comparative Example 1

[0081] After weighing 5.0g of the above-mentioned phenolic resin E-1 and 2.0g of potassium tripolyphosphate, the mixture was ball-milled, and nitrogen was introduced into the carbonization furnace at a rate of 8mL / min. The temperature was raised to 1400°C at a rate of 3°C / min and maintained for 2h. The mixture was naturally cooled to room temperature to obtain a hard carbon material co-doped with zinc, phosphorus and nitrogen. The ball milling speed was 400 rpm and the mixture was ball-milled to 100 mesh.

[0082] Comparative Example 2

[0083] After weighing 5.0g of the above-mentioned phenolic resin E-1 and 1.5g of zinc acrylate, the mixture was ball-milled, and nitrogen was introduced into the carbonization furnace at a rate of 8mL / min. The temperature was raised to 1400°C at a rate of 3°C / min and maintained for 2h. The mixture was naturally cooled to room temperature to obtain a hard carbon material co-doped with zinc, phosphorus and nitrogen. The ball milling speed was 400 rpm and the mixture was ball-milled to 100 mesh.

[0084] Comparative Example 3

[0085] Weigh 5.0g of the above-mentioned phenolic resin E-1, 0.76g of zinc chloride, 1.03g of acrylic acid, and 2.0g of potassium tripolyphosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 8mL / min in a carbonization furnace, increase the temperature to 1400°C at a rate of 3°C / min, maintain it for 2h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 400 rpm, and the ball milling is to 100 mesh.

[0086] Comparative Example 4

[0087] Weigh 5.0g of the above-mentioned phenolic resin E-1, 1.5g of zinc acrylate, and 1.7g of potassium phosphate, and ball-mill the mixture. Then, introduce nitrogen at a rate of 8mL / min in a carbonization furnace, increase the temperature to 1400°C at a rate of 3°C / min, maintain it for 2h, and naturally cool it to room temperature to obtain a zinc, phosphorus, and nitrogen co-doped hard carbon material; wherein, the ball milling speed is 400 rpm, and the ball milling is to 100 mesh.

[0088] Performance Testing

[0089] (1) Nitrogen adsorption and desorption experiment

[0090] The specific surface areas of the hard carbon materials obtained in the above examples and comparative examples were characterized using a nitrogen adsorption-desorption analyzer (ASAP2420), and the results are shown in Table 1.

[0091] (2) Battery charge and discharge cycle test

[0092] Preparation of working electrode: The hard carbon material prepared in the embodiment and the comparative example was mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1 and ground respectively, and then N-methylpyrrolidone was added dropwise while grinding to prepare a slurry. The slurry was evenly applied on a copper box, and heated and dried to obtain a working electrode.

[0093] Preparation of electrolyte: The electrolyte was a mixed solution of EC:DMC:EMC in a volume ratio of 1:2:2 prepared in a glove box, and the concentration of solute NaPF6 was 1.5M.

[0094] Test: The glass microfiber separator, sodium metal sheet as reference electrode, working electrode, CR2032 battery shell and gasket were assembled into a half-cell in a glove box filled with argon. The specific capacity and stability of the assembled button cell were tested with the LAND CT2001A battery test system at a high current of 10A / g, where stability refers to the battery capacity retention rate after 1000 cycles. The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing phenolic resin-based hard carbon, characterized in that: The method comprises the following steps: mixing phenolic resin, zinc acrylate and potassium tripolyphosphate in a mass ratio of 2-10:0.5-5:1-8 by ball milling, then carbonizing at 1300-1500 DEG C in an inert gas atmosphere, and keeping the temperature for 1-5 hours to obtain a phenolic resin-based hard carbon material.

2. The method for preparing a phenolic resin-based hard carbon according to claim 1, characterized in that: The mass ratio of the phenolic resin, zinc acrylate and potassium tripolyphosphate is 5:1.5:

2.

3. The method for preparing a phenolic resin-based hard carbon according to claim 1, characterized in that: The preparation method of the phenolic resin comprises the following steps: adding phenol, formaldehyde, cashew nut oil, melamine and hydrochloric acid in a mass ratio of 100:75-90:0-38:0-1.5:0.5-1 into a reaction kettle, heating to 65-75°C, stopping heating, naturally heating to boiling, boiling reaction for 1.5-2.5 hours, starting decompression dehydration, the pressure is -0.08~-0.03MPa, and when the temperature returns to 140-180°C, stopping dehydration, discharging materials, obtaining resin, and crushing the resin to obtain phenolic resin.

4. The method for preparing a phenolic resin-based hard carbon according to claim 1, characterized in that: The preparation method of the phenolic resin comprises the following steps: putting bisphenol A, aniline, formaldehyde and hydrochloric acid in a mass ratio of 100:15-25:75-95:0.5-1.5 into a reaction kettle, heating to 65-75°C, stopping heating, naturally heating to boiling, boiling reaction for 1.5-2.5 hours, starting decompression dehydration with a pressure of -0.08 to -0.03MPa, stopping dehydration when the temperature returns to 140-180°C, discharging materials to obtain resin, and crushing the resin to obtain phenolic resin.

5. The method for preparing a phenolic resin-based hard carbon according to claim 3 or 4, characterized in that: The resin crushing step comprises: mixing the resin and hexamethylenetetramine in a mass ratio of 100:5-10 and crushing them to 80-200 meshes to obtain a phenolic resin; The formaldehyde is liquid formaldehyde with a mass fraction of 37%, and the hydrochloric acid is a hydrochloric acid solution with a mass fraction of 37%.

6. The method for preparing a phenolic resin-based hard carbon according to claim 1, characterized in that: The rotation speed of the ball mill is 350-450 rpm, and the ball mill is milled to 80-200 meshes.

7. The method for preparing a phenolic resin-based hard carbon according to claim 1, characterized in that: The inert gas is selected from nitrogen, helium or argon.

8. The method for preparing a phenolic resin-based hard carbon according to claim 1, characterized in that: The carbonization process specifically includes: continuously introducing inert gas at a rate of 6-10 mL / min, heating to 1300-1500° C. at a rate of 2-5° C. / min, maintaining for 1-5 hours, and naturally cooling to room temperature.

9. A phenolic resin-based hard carbon material obtained by the method for preparing phenolic resin-based hard carbon according to any one of claims 1 to 8.

10. Use of the phenolic resin-based hard carbon material according to claim 9 in a sodium ion battery.

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