A concave-convex composite carbon-based material, its preparation method and application

Abstract

This invention relates to an uneven composite carbon-based material, its preparation method, and its application. The preparation method includes: uniformly mixing a first type of carbon source precursor and a second type of carbon source precursor in a specific ratio, or uniformly mixing a first type of carbon source precursor and a carbonized second type of carbon source precursor in a specific ratio; and subjecting the mixture to high-temperature heat treatment under an inert atmosphere to obtain the uneven composite carbon-based material; wherein the first type of carbon source precursor is a carbon-based precursor that has foamed and / or expanded during the high-temperature heat treatment; and the second type of carbon source precursor has an open porous structure and a porosity of not less than 300 μm. 2 Porous carbon materials with a specific surface area of ​​ / g or those with an open pore structure and a specific surface area of ​​not less than 100m after low-temperature carbonization treatment at 600℃-800℃. 2 Carbon-based biomass materials with a specific surface area of ​​ / g.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a concave-convex composite carbon-based material, its preparation method, and its application. Background Technology

[0002] Amorphous carbon materials are considered to be the most commercially promising anode materials for sodium-ion batteries and have received widespread attention and research. Improving the reversible specific capacity of carbon materials has always been a key focus and challenge in this field.

[0003] Some reported technologies have demonstrated that by constructing and controlling closed-cell structures, the reversible specific capacity of amorphous carbon anodes can approach or even exceed that of graphite anodes in lithium-ion batteries. However, the reported technical routes involve complex synthesis methods, which increases the material preparation cost and hinders large-scale manufacturing and utilization. Furthermore, the precursors used in most cases are themselves expensive and have low carbon yields, which also limits the large-scale practical application of carbon materials.

[0004] Therefore, developing practical high-capacity amorphous carbon anode materials for sodium-ion batteries that are low-cost, easy to synthesize, and readily available for large-scale fabrication is one of the core challenges of next-generation high-energy sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a concave-convex composite carbon-based material, its preparation method, and its applications. This material can be obtained by using low-cost precursors and through simple composite processing. It is a high-capacity, low-cost carbon-based composite anode material that can be used as a high-capacity carbon-based anode for sodium-ion batteries and is conducive to large-scale commercial preparation and application.

[0006] Therefore, in a first aspect, embodiments of the present invention provide a method for preparing an uneven composite carbon-based material, the method comprising:

[0007] The first type of carbon source precursor and the second type of carbon source precursor are mixed evenly in a certain proportion, or the first type of carbon source precursor and the carbonized second type of carbon source precursor are mixed evenly in a certain proportion, and the mixture is subjected to high-temperature heat treatment under an inert atmosphere to obtain the concave-convex composite carbon-based material.

[0008] Wherein, the first type of carbon source precursor is a carbon-based precursor that foams and / or expands during the high-temperature heat treatment; the second type of carbon source precursor has an open porous structure and a porosity of not less than 300 μm. 2 Porous carbon materials with a specific surface area of ​​ / g or those with an open pore structure and a surface area of ​​not less than 100m² after low-temperature carbonization treatment at 600℃-800℃. 2 Carbon-based biomass materials with a specific surface area of ​​ / g.

[0009] Preferably, the first type of carbon source precursor includes one or more of glucose, fructose, sucrose, maltose, starch, and pitch; the porous carbon material includes activated carbon; and the carbon-based biomass material includes one or more of cellulose, lignin, and straw.

[0010] Preferably, the high-temperature heat treatment is performed at a temperature of 1000℃-2800℃, with a heating rate of 0.5℃ / min-30℃ / min and a holding time of 0.5 hours-72 hours, and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0011] Preferably, the mixing mass ratio of the first type of carbon source precursor and the second type of carbon source precursor is 1:4 to 4:1.

[0012] Secondly, embodiments of the present invention provide an convex-concave composite carbon-based material prepared by the preparation method described in the first aspect above.

[0013] Preferably, the concave-convex composite carbon-based material is used as a carbon-based anode material for sodium-ion batteries, and has a reversible specific capacity of more than 280 mAh / g through the synergistic effect of the first type of carbon source precursor and the second type of carbon source precursor.

[0014] Preferably, the synergistic effect specifically includes:

[0015] The specific surface area is reduced by blocking the open pore structure of the second type of carbon source precursor, either present in the first type of carbon source precursor or formed during the heating process of the second type of carbon source precursor in high-temperature heat treatment; and,

[0016] The foaming and / or expansion of the first type of carbon source precursor during the high-temperature heat treatment process is suppressed by the second type of carbon source precursor.

[0017] Thirdly, embodiments of the present invention provide a sodium-ion battery. The negative electrode of the sodium-ion battery is the concave-convex composite carbon-based material described in the second aspect above.

[0018] The method for preparing the concave-convex composite carbon-based material provided in this invention combines a convex carbon source precursor (a first type of carbon source precursor that expands and foams during heat treatment) with a concave carbon source precursor (a second type of carbon source precursor) that has a porous structure or can form a porous structure. The convex precursor blocks the open pores of the concave precursor, reducing its specific surface area and thus solving the problem of low first-cycle coulombic efficiency caused by a large specific surface area. Meanwhile, the concave precursor suppresses the expansion and foaming problem during the pyrolysis of the convex precursor, thus achieving a synergistic effect and yielding a sodium-ion battery carbon-based anode material with a reversible specific capacity of over 280 mAh / g. Furthermore, by adjusting and optimizing the selection and ratio of the convex and concave precursors, the specific capacity can be further increased to over 400 mAh / g. The "convex" and "concave" precursors used in this invention are inexpensive and significantly improve carbon yield compared to the traditional strategy of using biomass precursors alone for pyrolysis. The two precursors can be simply mixed and then subjected to high-temperature heat treatment to prepare the material. The processing method is simple and easy to apply to large-scale industrial production. Attached Figure Description

[0019] Figure 1 The charge-discharge curves of the concave-convex composite carbon-based anode material prepared in Example 1 are shown below.

[0020] Figure 2 This is a photograph of the concave-convex composite carbon-based anode material prepared in Example 3;

[0021] Figure 3 This is a photograph of the concave-convex composite carbon-based anode material prepared in Example 5;

[0022] Figure 4 The charge-discharge curves of the concave-convex composite carbon-based anode material prepared in Example 5 are shown.

[0023] Figure 5 Charge-discharge curves of the concave-convex composite carbon-based anode material prepared in Example 8;

[0024] Figure 6 Charge-discharge curves of the concave-convex composite carbon-based anode material prepared in Example 9;

[0025] Figure 7 A physical image of the "convex" carbon-based anode material prepared for Comparative Example 1;

[0026] Figure 8 Charge-discharge curves of the "convex" carbon-based anode material prepared for Comparative Example 1;

[0027] Figure 9 Charge-discharge curves of the "concave" carbon-based anode material prepared in Comparative Example 2;

[0028] Figure 10 Charge-discharge curves of the "concave" carbon-based anode material prepared in Comparative Example 3;

[0029] Figure 11 A physical image of the "convex" carbon-based anode material prepared in Comparative Example 4;

[0030] Figure 12 Charge-discharge curves of the "convex" carbon-based anode material prepared in Comparative Example 4;

[0031] Figure 13 A physical image of the "convex" carbon-based anode material prepared in Comparative Example 6;

[0032] Figure 14 Charge-discharge curves of the "convex" carbon-based anode material prepared for Comparative Example 6. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] This invention provides a simple and easy method for preparing concave-convex composite carbon-based materials.

[0035] The carbon-based precursor that foams and / or expands during heat treatment is designated as a "convex" precursor, also known as a type I carbon source precursor, which has an open porous structure and a porosity of not less than 300 μm. 2 Carbon-based materials with a specific surface area of ​​ / g or forming an open porous structure of not less than 100m during the heating process of heat treatment. 2 The precursor with a specific surface area of ​​ / g is a "concave" precursor, which is a second type of carbon source precursor. The two precursors are mixed uniformly in a mass ratio of 1:4 to 4:1, or the first type of carbon source precursor and the carbonized second type of carbon source precursor are mixed uniformly in a mass ratio of 1:4 to 4:1. The mixture is then subjected to high-temperature heat treatment in an inert atmosphere to obtain a concave-convex composite carbon-based material. The high-temperature heat treatment temperature is 1000℃-2800℃, the heating rate is 0.5℃ / min-30℃ / min, the holding time is 0.5 hours-72 hours, and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0036] In a preferred embodiment, the high-temperature heat treatment temperature is 1200℃-2000℃; the heating rate is 1℃ / min-10℃ / min; and the holding time is 0.5-6 hours.

[0037] The first type of carbon source precursors mentioned above include one or more of glucose, fructose, sucrose, maltose, starch, and pitch; the second type of carbon source precursors mentioned above include those with a specific surface area ≥ 300 m². 2Porous carbon materials with a specific surface area ≥100m² / g, such as activated carbon, or carbonized at low temperature. 2 / g of carbon-based biomass materials, such as cellulose, lignin, straw, etc., one or more of these. The low-temperature carbonization process is carried out at a temperature of 600℃-800℃. During the process of heating to the high-temperature heat treatment temperature mentioned above in this invention, the carbon-based biomass materials will pass through the low-temperature carbonization process, thus achieving low-temperature carbonization of the carbon-based biomass materials during the heating process.

[0038] Accordingly, the aforementioned mixing of the first type of carbon source precursor and the carbonized second type of carbon source precursor at a mass ratio of 1:4 to 4:1 is divided into two cases. One is the mixing of the first type of carbon source precursor and the carbonized porous carbon material, where the carbonization temperature can be between 600℃ and 1500℃ for porous carbon materials; the second is the mixing of the first type of carbon source precursor and the carbonized carbon-based biomass material, where the carbonization temperature is between 600℃ and 800℃ for carbon-based biomass materials.

[0039] The concave-convex composite carbon-based material prepared by the above method can be used as a carbon-based anode material for sodium-ion batteries. It has a reversible specific capacity of more than 280 mAh / g through the synergistic effect of the first type of carbon source precursor and the second type of carbon source precursor.

[0040] In the concave-convex composite carbon-based material, the first type of carbon source precursor blocks the open pore structure of the second type of carbon source precursor or the second type of carbon source precursor during the heating process of high temperature heat treatment, so as to reduce the specific surface area; while the second type of carbon source precursor can inhibit the foaming and / or expansion of the first type of carbon source precursor during the high temperature heat treatment process.

[0041] The proposed preparation method of this invention addresses two main issues. First, some promising and inexpensive biomass hard carbon precursors, such as sugars, expand and foam during heating and carbonization, which is extremely detrimental to material preparation and processing. Furthermore, these precursors have very low carbon yields, thus increasing material costs. Second, while some porous carbon materials and precursors have relatively high carbon yields, their excessively large specific surface area results in extremely low first-cycle coulombic efficiency in the prepared carbon-based anode materials, hindering practical applications. Therefore, combining expansion and foaming with a porous structure creates a synergistic effect, resulting in high-capacity carbon-based anode materials that are inexpensive, easy to synthesize, and suitable for large-scale production.

[0042] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the specific process of obtaining the concave-convex composite carbon-based material by applying the method provided by the present invention, and compares the proportions to illustrate the characteristics of the concave-convex composite carbon-based material obtained by the method of the present invention.

[0043] Example 1

[0044] 1g of pitch and 2g of cellulose were placed in a beaker, and 100mL of ethanol was added. The mixture was stirred at 300r / min for 1 hour, then transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was then placed in a crucible and heated to 1000℃ at a rate of 2℃ / min under N2 protection for 1 hour to carbonize the precursor. During the heating process to 1000℃, the cellulose first carbonized at a low temperature, thus exhibiting a high specific surface area.

[0045] After high-temperature heat treatment and natural cooling, the concave-convex composite carbon-based material of Example 1 was obtained. This material did not exhibit significant foaming and expansion after carbonization. The specific surface area was measured to be 50 m². 2 / g, which is far smaller than the specific surface area of ​​540m² of the carbon-based material prepared by using cellulose alone under the same conditions in Comparative Example 2. 2 / g.

[0046] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode, and a coin cell was assembled using 1M NaPF6-ethylene carbonate (EC) / diethyl carbonate (DEC) as the electrolyte. A reversible specific capacity of 280 mAh / g was obtained in the 0-2V voltage range, with a first-cycle coulombic efficiency of 86%. Figure 1 As shown.

[0047] Example 2

[0048] 2g of asphalt and 1g of activated carbon were placed in a beaker, 100mL of ethanol was added, and the mixture was stirred at 300r / min for 1 hour. Then, it was transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1550℃ at a heating rate of 2℃ / min under Ar protection and held for 2 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 2 was obtained. The material did not show obvious foaming and expansion after carbonization.

[0049] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 291mAh / g and the coulombic efficiency in the first week was 75% in the 0-2V voltage range.

[0050] Example 3

[0051] 2g of glucose and 1g of activated carbon were placed in a beaker, and 100mL of ethanol was added. The mixture was stirred at 300r / min for 1 hour, then transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1400℃ at a rate of 2℃ / min under Ar protection, and held at that temperature for 2 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 3 was obtained. Figure 2 As shown, the material does not exhibit significant expansion or foaming after carbonization.

[0052] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 304 mAh / g and the coulombic efficiency in the first week was 78% in the 0-2V voltage range.

[0053] Example 4

[0054] 2g of fructose and 1g of activated carbon were placed in a beaker, 100mL of ethanol was added, and the mixture was stirred at 300r / min for 1 hour. Then, it was transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection and held for 6 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 4 was obtained. The material did not show obvious expansion and foaming after carbonization.

[0055] The carbon-based material was used to make an electrode, and a coin cell was assembled with sodium metal as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 300 mAh / g and the coulombic efficiency was 70% in the first week within the 0-2V voltage range.

[0056] Example 5

[0057] 2g of sucrose and 1g of activated carbon were placed in a beaker, and 100mL of ethanol was added. The mixture was stirred at 300r / min for 1 hour, then transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1400℃ at a rate of 2℃ / min under Ar protection, and held at that temperature for 2 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 5 was obtained. Figure 3 As shown, the material did not exhibit significant expansion or foaming after carbonization. Its specific surface area was measured to be 40 m². 2 / g, which is far smaller than the specific surface area of ​​672m² of the carbon-based material prepared by using sucrose alone under the same conditions in Comparative Example 6. 2 / g.

[0058] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. A reversible specific capacity of 417 mAh / g was obtained in the 0-2V voltage range, with a first-cycle coulombic efficiency of 75%. Figure 4 .

[0059] Example 6

[0060] 2g of maltose and 1g of activated carbon were placed in a beaker, and 100mL of ethanol was added. The mixture was stirred at 300r / min for 1 hour, and then transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection and held for 2 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 6 was obtained. The material did not show obvious expansion and foaming after carbonization.

[0061] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 353 mAh / g and the coulombic efficiency in the first week was 77% in the 0-2V voltage range.

[0062] Example 7

[0063] 2g of potato starch and 1g of activated carbon were placed in a beaker, 100mL of ethanol was added, and the mixture was stirred at 300r / min for 1 hour. Then, it was transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection and held for 0.5 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 7 was obtained. The material did not show obvious expansion and foaming after carbonization.

[0064] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 287 mAh / g and the coulombic efficiency in the first week was 71% in the 0-2V voltage range.

[0065] Example 8

[0066] 0.8g of sucrose, 0.2g of pitch and 1g of activated carbon were placed in a beaker, and 100mL of ethanol was added. The mixture was stirred at 300r / min for 1 hour, and then transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection and held for 2 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 8 was obtained. The material did not show obvious expansion and foaming after carbonization.

[0067] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. A reversible specific capacity of 327 mAh / g was obtained in the 0-2V voltage range, with a first-cycle coulombic efficiency of 75%. Figure 5 .

[0068] Example 9

[0069] 4g of sucrose and 1g of activated carbon were placed in a beaker, and 100mL of ethanol was added. The mixture was stirred at 300r / min for 1 hour, and then transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1600℃ at a heating rate of 2℃ / min under Ar protection and held for 2 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 1 was obtained. The material did not show obvious expansion and foaming after carbonization.

[0070] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. A reversible specific capacity of 343 mAh / g was obtained in the 0-2V voltage range, with a first-cycle coulombic efficiency of 75%. Figure 6 .

[0071] Example 10

[0072] 1g of sucrose and 4g of activated carbon were placed in a beaker, and 100mL of ethanol was added. The mixture was stirred at 300r / min for 1 hour, and then transferred to an oven and dried at 80℃ for 9 hours to obtain the mixed precursor. The precursor was placed in a crucible and heated to 1600℃ at a heating rate of 2℃ / min under Ar protection and held for 2 hours to carbonize the precursor. After natural cooling, the concave-convex composite carbon-based material of Example 1 was obtained. The material did not show obvious expansion and foaming after carbonization.

[0073] The carbon-based material was used to make an electrode, and a coin cell was assembled with sodium metal as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 284 mAh / g and the coulombic efficiency was 70% in the first week within the 0-2V voltage range.

[0074] Comparative Example 1

[0075] 1g of asphalt was placed in a crucible and heated to 1000℃ at a rate of 2℃ / min under Ar protection. The temperature was held for 2 hours, and after carbonization, it was allowed to cool naturally to obtain the "convex" carbon-based material of Comparative Example 1. Figure 7 As shown, the material exhibits obvious foaming and expansion.

[0076] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. The reversible specific capacity was only 182 mAh / g in the 0-2V voltage range, and the first-cycle coulombic efficiency was 80%. Figure 8 Its performance is far lower than that of Example 1.

[0077] Comparative Example 2

[0078] 1g of cellulose was placed in a crucible and heated to 1000℃ at a rate of 2℃ / min under Ar protection, held at that temperature for 2 hours, and then allowed to cool naturally after carbonization to obtain the "concave" carbon-based material of Comparative Example 2, which has a specific surface area as high as 540m². 2 / g.

[0079] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. The reversible specific capacity was only 145 mAh / g in the 0-2V voltage range, and the first-cycle coulombic efficiency was 35%. Figure 9 Its performance is far lower than that of Example 1.

[0080] Comparative Example 3

[0081] 1g of activated carbon was placed in a crucible and heated to 1400℃ at a rate of 2℃ / min under Ar protection, held at that temperature for 2 hours, and then allowed to cool naturally after carbonization to obtain the "concave" carbon-based material of Comparative Example 3. This material had a specific surface area as high as 1400m² before carbonization. 2 / g / , still 672m after carbonization 2 / g, which is much higher than in Examples 2-9.

[0082] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. The reversible specific capacity was only 126 mAh / g in the 0-2V voltage range, and the first-cycle coulombic efficiency was 26%. Figure 10 The performance is far lower than that of Examples 2-9.

[0083] Comparative Example 4

[0084] 1g of glucose was placed in a crucible and heated to 1400℃ at a rate of 2℃ / min under Ar protection. The temperature was maintained for 2 hours, followed by carbonization treatment and natural cooling to obtain the "convex" carbon-based material of Comparative Example 4. Figure 11 As shown, the material exhibits obvious foaming and expansion.

[0085] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. A reversible specific capacity of 211 mAh / g was obtained in the 0-2V voltage range, with a first-cycle coulombic efficiency of 77%. Figure 12 Its performance is far lower than that of Example 3.

[0086] Comparative Example 5

[0087] 1g of fructose was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection. The temperature was maintained for 2 hours and then naturally cooled after carbonization to obtain the “convex” carbon-based material of Comparative Example 5. This material exhibited obvious foaming and expansion.

[0088] The carbon-based material was used to make an electrode, and a coin cell was assembled with sodium metal as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 240mAh / g and the coulombic efficiency was 65% in the first week within the 0-2V voltage range.

[0089] Comparative Example 6

[0090] 1g of sucrose was placed in a crucible and heated to 1400℃ at a rate of 2℃ / min under Ar protection. The temperature was maintained for 2 hours, followed by carbonization treatment and natural cooling to obtain the "convex" carbon-based material described in Comparative Example 6. Figure 13 The material exhibits obvious foaming and expansion.

[0091] The carbon-based material was used to fabricate the electrode, with metallic sodium as the counter electrode and 1M NaPF6-EC / DEC as the electrolyte to assemble a coin cell. A reversible specific capacity of 246 mAh / g was obtained in the 0-2V voltage range, with a first-cycle coulombic efficiency of 69%. Figure 14 Its performance is far lower than that of Examples 5, 8, and 9.

[0092] Comparative Example 7

[0093] 1g of maltose was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection. The temperature was maintained for 2 hours and then naturally cooled after carbonization to obtain the “convex” carbon-based material of Comparative Example 7. This material exhibited obvious foaming and expansion.

[0094] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 216 mAh / g in the 0-2V voltage range, and the first-cycle coulombic efficiency was 54%, which was much lower than that of Example 6.

[0095] Comparative Example 8

[0096] 1g of potato starch was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection. The temperature was maintained for 2 hours and then naturally cooled after carbonization to obtain the "convex" carbon-based material of Comparative Example 8. This material exhibited obvious foaming and expansion.

[0097] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 238 mAh / g in the 0-2V voltage range, and the first-cycle coulombic efficiency was 74%, which is much lower than that of Example 7.

[0098] Comparative Example 9

[0099] 2g of sucrose and 1g of commercial hard carbon were placed in a beaker, 100mL of ethanol was added, and the mixture was stirred at 300r / min for 1 hour. Then, it was transferred to an oven and dried at 80℃ for 9 hours to obtain a composite carbon source precursor. The precursor was placed in a crucible and heated to 1400℃ at a heating rate of 2℃ / min under Ar protection. The temperature was held for 2 hours and then naturally cooled after carbonization to obtain the carbon-based composite material of Comparative Example 9. The material showed obvious foaming and expansion, indicating that the composite of "convex" carbon source precursor and non-"concave" precursor could not achieve the expected effect.

[0100] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 242 mAh / g in the 0-2V voltage range, and the first-cycle coulombic efficiency was 72%, which is much lower than that of Examples 5, 8 and 9.

[0101] Comparative Example 10

[0102] 2g of microcrystalline cellulose (MCC) and 1g of activated carbon were placed in a beaker, 100mL of ethanol was added, and the mixture was stirred at 300r / min for 1 hour. Then, the mixture was transferred to an oven and dried at 80℃ for 9 hours to obtain the composite carbon source precursor. The precursor was placed in a crucible and carbonized to 1400℃ at a heating rate of 2℃ / min under Ar protection. The temperature was held for 2 hours, and after natural cooling, the carbon-based composite material of Comparative Example 10 was obtained.

[0103] The material has a specific surface area of ​​up to 599m².2 / g indicates that using a combination of a non-convex carbon source precursor and a concave carbon source precursor cannot effectively block open pores and reduce specific surface area.

[0104] The carbon-based material was used to make an electrode, and sodium metal was used as the counter electrode. A coin cell was assembled using 1M NaPF6-EC / DEC as the electrolyte. The reversible specific capacity was 148 mAh / g in the 0-2V voltage range, and the first-cycle coulombic efficiency was 34%, which is much lower than that of Examples 2-9.

[0105] The method for preparing the concave-convex composite carbon-based material provided in this invention combines a convex carbon source precursor (a first type of carbon source precursor that expands and foams during heat treatment) with a concave carbon source precursor (a second type of carbon source precursor) that has a porous structure or can form a porous structure. The convex precursor blocks the open pores of the concave precursor, reducing its specific surface area and thus solving the problem of low first-cycle coulombic efficiency caused by a large specific surface area. Meanwhile, the concave precursor suppresses the expansion and foaming problem during the pyrolysis of the convex precursor, thus achieving a synergistic effect and yielding a sodium-ion battery carbon-based anode material with a reversible specific capacity of over 280 mAh / g. Furthermore, by adjusting and optimizing the selection and ratio of the convex and concave precursors, the specific capacity can be increased to over 400 mAh / g. The "convex" and "concave" precursors used in this invention are inexpensive and significantly improve carbon yield compared to the traditional strategy of using biomass precursors alone for pyrolysis. The material can be prepared by simply mixing and carbonizing the two precursors. Furthermore, optimizing the mixing ratio and carbonization conditions can control the specific surface area and microstructure, thereby improving sodium storage performance. The preparation method proposed in this invention is simple and easily applicable to large-scale industrial production.

[0106] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a concavo-convex composite carbon-based material, characterized by comprising: a step of mixing a carbon-based material and a binder to prepare a mixture; a step of molding the mixture; and a step of baking the mixture. The preparation method comprises: mixing the first type of carbon source precursor and the second type of carbon source precursor in proportion, or mixing the first type of carbon source precursor and the second type of carbon source precursor after carbonization in proportion, and uniformly mixing the mixture, and then performing high-temperature heat treatment on the mixture in an inert atmosphere to obtain the concave-convex composite carbon-based material; The first type of carbon source precursor is a carbon-based precursor that foams and / or expands during the high-temperature heat treatment process; the second type of carbon source precursor is a porous carbon material having an open pore structure and a specific surface area of not less than 300 m 2 / g, or a carbon-based biomass material having an open pore structure and a specific surface area of not less than 100 m 2 / g after being subjected to a low-temperature carbonization treatment at 600-800°C. The first type of carbon source precursor and the second type of carbon source precursor have a synergistic effect, the first type of carbon source precursor is used to block the open pore structure of the second type of carbon source precursor or formed in the heating process of the high-temperature heat treatment process of the second type of carbon source precursor, so as to reduce the specific surface area; the second type of carbon source precursor is used to inhibit the foaming and / or expansion of the first type of carbon source precursor in the high-temperature heat treatment process; The first type of carbon source precursor comprises one or more of glucose, fructose, sucrose, maltose and starch; the porous carbon material comprises activated carbon; and the carbon-based biomass material comprises one or more of cellulose, lignin and straw.

2. The production method according to claim 1, characterized by, The high-temperature heat treatment is performed at a temperature of 1000-2800°C, a heating rate of 0.5-30°C / min and a holding time of 0.5-72 hours, and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

3. The preparation method according to claim 1, characterized in that, The mixing mass ratio of the first type of carbon source precursor and the second type of carbon source precursor is 1:4-4:

1.

4. A concave-convex composite carbon-based material prepared by the preparation method of any one of claims 1-3. The concave-convex composite carbon-based material is used as a carbon-based negative electrode material for a sodium ion battery and has a reversible specific capacity of 280 mAh / g or more through the synergistic effect of the first type of carbon source precursor and the second type of carbon source precursor. wherein, The synergistic effect specifically comprises: blocking the open pore structure of the second type of carbon source precursor or formed in the heating process of the high-temperature heat treatment process of the second type of carbon source precursor by the first type of carbon source precursor to reduce the specific surface area; and, inhibiting the foaming and / or expansion of the first type of carbon source precursor in the high-temperature heat treatment process by the second type of carbon source precursor.

5. A sodium-ion battery, characterized in that, The negative electrode of the sodium ion battery is the concave-convex composite carbon-based material of claim 4.

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