Hybrid phenolic resin-based amorphous carbon@C composites and their preparation and application in sodium secondary batteries

Abstract

The present invention belongs to the field of electrode material preparation and secondary battery, and specifically relates to a hybrid phenolic resin-based amorphous carbon@C composite material having a core-shell structure, wherein the core is a heteroatom-hybridized phenolic resin-based amorphous carbon material having a sub-nanometer pore structure, and the heteroatom includes N atoms; the shell is a thin layer of amorphous carbon with a thickness of 1 to 10 nm. The present invention also provides the preparation of the material and the application in sodium ion batteries. The material of the present invention has excellent sodium ion battery performance.

Description

Technical Field

[0001] The invention belongs to the field of negative electrode materials, and in particular to the field of negative electrode materials for sodium secondary batteries. Background Art

[0002] The rising demand for lithium-ion batteries has caused lithium prices to soar, and the competition for limited lithium resources has also entered a white-hot stage. Sodium-ion batteries are considered to be a game-changer in solving this situation. Because it not only has an operating mechanism similar to that of lithium-ion batteries, but also has huge reserves and good dispersion compared to lithium. However, negative electrode materials with good electrochemical properties are crucial to the commercialization of sodium-ion batteries, because the common graphite negative electrode materials of lithium ions cannot be embedded in sodium ions due to some thermodynamic reasons, and are therefore incompatible with sodium-ion batteries. Among the negative electrode candidate materials for sodium-ion batteries, hard carbon is currently considered to be one of the most balanced negative electrode materials in terms of electrochemical performance (such as operating voltage, cycle stability, reversible capacity, etc.), cost, etc. However, the sodium storage capacity of hard carbon is still lower than the capacity required for its commercial development. At the same time, the structure of hard carbon makes it unlike graphite, which can provide sufficient delocalized π electrons to obtain good conductivity. Therefore, improving its internal electron transport is very important for improving the rate performance and fast charging characteristics of the material. In addition, if the surface reactivity of hard carbon materials used in sodium-ion batteries is too high, the first-cycle coulombic efficiency of the battery will be low, resulting in higher irreversible sodium loss during the first charge and discharge process.

[0003] Some studies have found that the capacity of sodium-ion batteries can be improved by heteroatom doping or specific surface area control. However, these strategies will significantly affect the first-cycle coulomb efficiency of the battery while improving the capacity, which leads to many problems in the application of materials in sodium-ion batteries. In order to solve this problem, it is worth paying attention to how to maintain a high first-cycle coulomb efficiency while improving the sodium storage capacity of the material. Studies generally show that elements such as B, N, and P can be used to adjust the microstructure or crystal structure of hard carbon, thereby helping to improve the reversible capacity of hard carbon. The first-cycle coulomb efficiency of hard carbon has a great correlation with the surface composition and structure of hard carbon materials, and heteroatom doping will increase its reactivity with the electrolyte, which will restrict the first-cycle coulomb efficiency of hard carbon materials used in sodium-ion batteries. Therefore, how to obtain sodium-ion battery negative electrode materials that take into account excellent energy density, fast charging performance and high first-cycle coulomb efficiency is still the main difficulty hindering the development of sodium secondary batteries. Summary of the invention

[0004] In view of the problem that it is difficult for the negative electrode of sodium secondary batteries to have a high energy density, rate, first-cycle coulombic efficiency and cycle stability, the first purpose of the present invention is to provide a hybrid phenolic resin-based amorphous carbon@C composite material, aiming to provide a negative electrode active material suitable for sodium secondary batteries that has excellent capacity, rate, first efficiency and stability.

[0005] The second purpose of the present invention is to provide a method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material, aiming to successfully prepare the new material with the special physical and chemical structure and excellent electrochemical properties.

[0006] The third object of the present invention is to provide the use of the hybrid phenolic resin-based amorphous carbon@C composite material in sodium secondary batteries.

[0007] The fourth object of the present invention is to provide a sodium secondary battery and a negative electrode thereof comprising the hybrid phenolic resin-based amorphous carbon@C composite material.

[0008] In view of the unsatisfactory adaptability of the negative electrode active material of the sodium secondary battery to sodium ions, and the difficulty in taking into account the problems of capacity, rate, first efficiency and cycle stability, the present invention provides the following improvement scheme:

[0009] A hybrid phenolic resin-based amorphous carbon@C composite material having a core-shell structure, wherein the core is a heteroatom-hybridized phenolic resin-based amorphous carbon material having a sub-nanometer pore structure, and the heteroatom comprises a N atom;

[0010] The shell is a thin layer of amorphous carbon with a thickness of 1 to 10 nm.

[0011] The present invention provides a new material having an ultra-thin amorphous carbon shell layer, and a phenolic resin cross-linked amorphous carbon material with a sub-nanoporous structure and a heteroatom cross-linked doped carbon shell layer. The present invention has found that the special core and shell materials and the combination of physical properties can achieve synergy, can provide a large amount of space suitable for sodium ion storage, and can provide abundant sodium ion-adapted embedding-de-embedding sites. In addition, it also has low surface activity, which can synergistically improve its electrochemical performance in sodium secondary batteries, so that it can take into account excellent capacity, rate, first effect and long-range cycle stability.

[0012] In the present invention, the heteroatoms further include at least one of P and B. The present invention has found that on the basis of the main N hybridization, further coordination with the auxiliary hybridization of P and B helps to synergize and further improve the electrochemical performance of the material in the sodium secondary battery.

[0013] Preferably, among the heteroatoms, the content of N element is greater than or equal to 20 atm%;

[0014] Preferably, in the core, the pore size is 0.2-0.8 nm; the porosity is 20-70%;

[0015] Preferably, the hybrid phenolic resin-based amorphous carbon@C composite material has a porosity of 40-60% and a specific surface area of ​​less than or equal to 10m2 / g; preferably 2 to 4 m 2 / g; tap density ≥0.5g / cm 3 ; preferably ≥0.7g / cm 3 .

[0016] The present invention also provides a method for preparing the hybrid phenolic resin amorphous carbon@C composite material, characterized in that the steps include:

[0017] Step (1):

[0018] The phenolic resin and the heteroatom source are subjected to a hybrid crosslinking reaction at a temperature of 200 to 400° C. in advance, and then subjected to a first stage of calcination at a temperature of 500 to 800° C., and then subjected to a second stage of calcination at a temperature of 1000 to 1800° C. to obtain a hybrid material; the heteroatom source comprises a N source;

[0019] Step (2):

[0020] The calcined material is thermally modified in an organic atmosphere at a temperature of 750-950° C. to obtain the hybrid phenolic resin amorphous carbon@C composite material.

[0021] How to successfully construct the sub-nanopores of the core suitable for sodium ion storage and de-embedding and how to construct a uniform ultra-thin amorphous carbon layer are the difficulties and key points in preparing the material described in the present invention. To this end, the present invention has been found through in-depth research that it innovatively adopts phenolic resin as the main body, and hybridizes and crosslinks it with N-containing heteroatoms in advance, and creates a suitable crosslinking and hybrid network for sodium ions through the control of conditions, and then cooperates with the subsequent two-stage roasting, such as creating a pore network for storage and de-embedding adapted to sodium ions, and further cooperates with the subsequent thermal modification in the organic atmosphere, which helps to block the surface through-holes and regulate the surface pore structure and active sites. In the present invention, the innovative chemical crosslinking-two-stage roasting and calcination in an organic atmosphere with phenolic resin and heteroatom sources can achieve synergy, which can significantly improve the adaptability of the prepared material to sodium ions, significantly improve its electrochemical performance, and allow it to take into account excellent capacity, rate, first effect and cycle stability.

[0022] In the present invention, the combination of the phenolic resin, the N-containing heteroatom source, the hybrid crosslinking, the two-stage calcination and the thermal modification process under an organic atmosphere and the parameters thereof is the key to synergistically improving the material's adaptability to sodium ions and improving its electrochemical performance.

[0023] In the present invention, chemical crosslinking is performed in the heteroatom containing at least N by using phenolic resin, which helps to construct pore properties suitable for sodium ions and helps to synergistically improve the electrochemical performance of sodium secondary batteries.

[0024] Preferably, the phenolic resin is a condensation product of aromatic phenol and formaldehyde, preferably a condensation product of phenol or substituted phenol and formaldehyde. The substituted phenol is a substituted phenol with C1-C6 alkyl or C1-C6 alkoxy substituents on the benzene ring.

[0025] Preferably, the phenolic resin is a phenol-formaldehyde polycondensate and a substituted phenol-formaldehyde polycondensate. The present invention unexpectedly found that the phenolic resins with different configurations can be combined with other processes unexpectedly, which helps to further improve the compatibility of the material to sodium ions and further improve the electrochemical performance of sodium secondary batteries.

[0026] Preferably, the phenolic resin is a phenol-formaldehyde condensation product and a substituted phenol-formaldehyde condensation product in a weight ratio of 1-9:9-1.

[0027] Preferably, the N source is at least one of urea, melamine and dicyandiamide;

[0028] Preferably, at least one of a boron source and a phosphorus source is also added to the heteroatom source; in the present invention, the use of combined heteroatoms in N- and (B / P) can unexpectedly achieve synergy, which helps to further improve the compatibility of sodium ions and the electrochemical performance of sodium secondary batteries.

[0029] Preferably, the boron source is at least one of boric acid, boron oxide, and tetraphenylboric acid;

[0030] Preferably, the phosphorus source is at least one of hypophosphorous acid, phosphorous acid, phosphoric acid, metaphosphoric acid, pyrophosphoric acid, and polyphosphoric acid;

[0031] Preferably, in the heteroatom source, the content of the N source is greater than or equal to 20 atm%;

[0032] Preferably, the weight ratio of the heteroatom source to the phenolic resin is 0.01-0.2:1; more preferably 0.01-0.1:1;

[0033] Preferably, the heteroatom source and the phenolic resin are mixed in a solid phase or a liquid phase.

[0034] In the present invention, the combination of the phenolic resin and the heteroatom source, and further coordination of the hybrid crosslinking reaction and the two-stage roasting process are helpful to improve the adaptability of the prepared material to sodium ions, which is beneficial to improving the electrochemical performance of the sodium secondary battery.

[0035] Preferably, the atmosphere during the hybrid cross-linking reaction is a protective atmosphere or an oxygen-containing atmosphere;

[0036] Preferably, the protective atmosphere is at least one of nitrogen and an inert gas;

[0037] Preferably, the oxygen-containing atmosphere is oxygen, a mixture of oxygen and protective gas, or air;

[0038] Preferably, the hybrid crosslinking reaction is carried out in an oxygen-containing atmosphere. The present invention unexpectedly found that the combined hybrid crosslinking of phenolic resin and heteroatom source under the assistance of an oxygen-containing atmosphere helps to further synergize and further improve the adaptability of the prepared material to sodium ions, and can further improve the electrochemical performance of sodium secondary batteries.

[0039] Preferably, the temperature of the hybrid cross-linking reaction is 300-350°C;

[0040] Preferably, the hybrid cross-linking time is 1 to 3 hours;

[0041] Preferably, the first stage calcination and the second stage calcination process are carried out under a protective atmosphere;

[0042] Preferably, the temperature of the first stage calcination is 600-800°C.

[0043] Preferably, the first stage of roasting takes 1 to 5 hours;

[0044] Preferably, after the first stage of roasting, the powder is crushed, air-milled, and sieved to select a powder with a particle size of 3-15 μm and then the second stage of roasting is performed;

[0045] Preferably, the temperature of the second stage calcination is 1000-1600°C.

[0046] Preferably, the second calcination time is 1 to 3 hours.

[0047] In the present invention, the organic atmosphere is a mixed gas containing an organic gas and a protective gas;

[0048] Preferably, the organic gas includes at least one of C1-C6 alkanes, C2-C6 olefins, C2-C6 alkynes, and C1-C4 alcohols; preferably, it is a combination gas of C1-C6 alkanes and C2-C6 olefins.

[0049] Preferably, in the organic atmosphere, the content of the organic gas is 5 to 20 V%;

[0050] Preferably, the flow rate of the organic atmosphere is 20 to 200 L / min;

[0051] Preferably, the calcination temperature is 850-900°C;

[0052] Preferably, the calcination time is 1 to 5 hours.

[0053] In the present invention, there is no particular requirement for the heating rate in the heating stage, and it may be, for example, 1-10° C. / min.

[0054] The present invention also provides a hybrid phenolic resin amorphous carbon@C composite material prepared by the preparation method.

[0055] The present invention also provides an application of the hybrid phenolic resin amorphous carbon@C composite material, which is used as a negative electrode active material for preparing a sodium secondary battery;

[0056] Preferably, it is used as a negative electrode active material to prepare a negative electrode of a sodium secondary battery;

[0057] Preferably, it is used as a negative electrode active material to prepare a negative electrode material for a sodium secondary battery;

[0058] Preferably, the sodium secondary battery is a sodium ion battery.

[0059] In the present invention, the hybrid phenolic resin amorphous carbon@C composite material of the present invention can be prepared into the required sodium secondary battery and its components based on existing means.

[0060] The present invention also provides a sodium secondary battery negative electrode, comprising the hybrid phenolic resin amorphous carbon@C composite material of the present invention.

[0061] Preferably, it comprises a current collector and a negative electrode material composited on the surface of the current collector; the negative electrode material comprises the hybrid phenolic resin amorphous carbon@C composite material;

[0062] Preferably, the negative electrode material further comprises a conductive agent and a binder.

[0063] The present invention also provides a sodium secondary battery, comprising the negative electrode of the present invention.

[0064] In the present invention, the sodium thiophene secondary battery and its negative electrode and negative electrode material, except for the active material of the hybrid phenolic resin amorphous carbon@C composite material described in the present invention, other materials, components and structures can be well-known.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (1) The present invention provides a new material having an ultra-thin amorphous carbon shell layer, and a phenolic resin cross-linked amorphous carbon material with a sub-nanoporous structure and a heteroatom cross-linked doped carbon shell layer. The present invention has found that the special core and shell materials and the combination of physical properties can achieve synergy, can provide a large amount of space suitable for sodium ion storage, and can provide abundant sodium ion-compatible embedding-de-embedding sites. In addition, it also has low surface activity, which can synergistically improve its electrochemical performance in sodium secondary batteries, so that it can take into account excellent capacity, rate, first effect and long-range cycle stability.

[0067] (2) In order to successfully prepare the material and improve the electrochemical performance of the material in a sodium secondary battery, the present invention innovatively adopts phenolic resin as the main body, and pre-hybridizes and crosslinks it with N-containing heteroatoms, and creates a suitable crosslinking and hybrid network for sodium ions by controlling the conditions, and then cooperates with the subsequent two-stage roasting, such as creating a pore network suitable for storage and de-embedding of sodium ions, and further cooperates with the subsequent thermal modification in an organic atmosphere, which helps to block the surface through-holes and regulate the surface pore structure and active sites. In the present invention, the innovative combination of chemical crosslinking with phenolic resin and heteroatom source-two-stage roasting and calcination in an organic atmosphere can achieve synergy, can significantly improve the adaptability of the prepared material to sodium ions, significantly improve its electrochemical performance, and can make it have excellent capacity, rate, first effect and cycle stability.

[0068] (3) In the present invention, the combined control of the molecular weight of the phenolic resin, the hybridization mode of the heteroatoms, the atmosphere of the hybridization crosslinking, the two-stage roasting process and the organic atmosphere in the calcination stage can unexpectedly achieve better performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 Schematic diagram of high first efficiency and high capacity hard carbon composite material;

[0070] Figure 2 SEM image of the prepared hard carbon composite material; DETAILED DESCRIPTION

[0071] The present invention will be further described in detail below in conjunction with the embodiments, but the invention is not limited to its protection scope.

[0072] Example 1

[0073] Step (1) Preparation of kernel:

[0074] The carbon source (50 g 2123 phenolic resin; phenol-formaldehyde condensation resin) and the heteroatom source (0.5 g urea) were mixed and dispersed uniformly, dried, and then heated to 300 °C (T1) at a rate of 1 °C / min under an argon atmosphere and kept warm for 2 h, and then heated to 600 °C (T2) at a rate of 5 °C / min and kept warm for 2 h.

[0075] The T2 insulation product is added to a powder machine for preliminary crushing, and then the crushed carbon material is added to an air flow cutting machine and sieved into powder with a particle size of 3-15um. It is kept at 1400℃ (T3) for 2 hours in a nitrogen atmosphere with a heating rate of 5℃ / min to obtain the inner core.

[0076] Step (2) modification:

[0077] The core was added into a CVD deposition furnace, nitrogen and methane mixed gas (methane volume content was 10%) was introduced, and heat treated at 850° C. for 2 h to obtain a hard carbon composite material with a core-shell structure.

[0078] The hard carbon composite material, conductive carbon black and sodium carboxymethyl cellulose (CMC) obtained in Example 1 were uniformly mixed in a mass ratio of 90:5:5, and dispersed in a certain mass of deionized water to make a slurry, which was then coated on an aluminum foil current collector and vacuum dried at 60°C to obtain a sodium ion battery negative electrode sheet. The battery assembly and test were as follows: the negative electrode sheet was punched into an electrode sheet with a diameter of 10 mm, metallic sodium was used as the counter electrode, the electrolyte was 1M NaPF6 / EC:DEC (1:1), and a CR2032 button cell was assembled in an argon-filled glove box. Constant current charge and discharge tests were carried out at room temperature (25°C) with a current density of 30 mA / g, and the charge and discharge cut-off voltage was 0 to 3 V. The first discharge specific capacity was 442 mAh / g, the first cycle coulomb efficiency was 92.28%, and the specific capacity remained 403 mAh / g after 100 cycles.

[0079] Example 2

[0080] Compared with Example 1, the only difference is that the type of phenolic resin carbon source is changed, specifically, respectively:

[0081] Group A: Phenolic resin 2402# (tert-butylphenol-formaldehyde condensation resin) was used as the carbon source, and the total amount was the same as in Example 1.

[0082] Group B: Replace 50g of phenolic resin 2123# with 90% phenolic resin 2123# mixed with 10% phenolic resin

[0083] Fat 2402#;

[0084] Group C: 50g of phenolic resin 2123# was replaced with 10% phenolic resin 2123# mixed with 90% phenolic resin 2402#;

[0085] The results were as follows:

[0086] The electrochemical test results of group A: the first discharge specific capacity is 420mAh / g, the first cycle coulombic efficiency is 91.40%, and the specific capacity remains at 369mAh / g after 100 cycles.

[0087] The electrochemical test results of group B: the first discharge specific capacity is 458 mAh / g, the first cycle coulombic efficiency is 92.24%, and the specific capacity remains at 418 mAh / g after 100 cycles.

[0088] The electrochemical test results of group C: the first discharge specific capacity was 459 mAh / g, the first cycle coulombic efficiency was 92.13%, and the specific capacity remained at 419 mAh / g after 100 cycles.

[0089] It can be seen from Examples 2 and 1 that the use of a combined phenolic resin as a carbon source can further synergistically improve the compatibility of the prepared material in a sodium ion battery, and contribute to further improving the performance of the sodium ion battery.

[0090] Example 3

[0091] Compared with Example 1, the only difference is that the type and ratio of heteroatoms are changed, respectively:

[0092] Group A: The heteroatom source was replaced from 0.5 g urea to a mixture of 0.4 g urea and 0.1 g boric acid.

[0093] Group B: The heteroatom source was replaced from 0.5 g urea to a mixture of 0.4 g urea and 0.1 g phosphoric acid.

[0094] Group C: The heteroatom source was replaced from 0.5 g urea to 5 g urea.

[0095] The results were as follows:

[0096] The electrochemical test results of group A: the first discharge specific capacity is 462mAh / g, the first cycle coulombic efficiency is 92.28%, and the specific capacity remains at 421mAh / g after 100 cycles.

[0097] The electrochemical test results of group B: the first discharge specific capacity was 468 mAh / g, the first cycle coulombic efficiency was 93.16%, and the specific capacity remained at 432 mAh / g after 100 cycles.

[0098] The electrochemical test results of Group C: the first discharge specific capacity was 454 mAh / g, the first cycle coulombic efficiency was 92.72%, and the specific capacity remained at 412 mAh / g after 100 cycles.

[0099] It can be seen from Examples 3 and 1 that the combination of N and other heteroatoms can further synergistically improve the adaptability of the prepared material in sodium ion batteries, which helps to further improve the performance of sodium ion batteries.

[0100] Example 4

[0101] Compared with Example 1, the only difference is that the conditions of the T1 segment are changed to:

[0102] Group A: treated in air atmosphere; after stage T1, the atmosphere was changed to Ar, and continued with subsequent stages T2 and T3;

[0103] Group B: treated in oxygen atmosphere; after stage T1, the atmosphere was changed to Ar, and continued with subsequent stages T2 and T3;

[0104] Group C: temperature 200℃, time 3h;

[0105] Group D: temperature is 400℃, time is 1h.

[0106] The results were as follows:

[0107] The electrochemical test results of group A: the first discharge specific capacity is 462mAh / g, the first cycle coulombic efficiency is 91.66%, and the specific capacity remains at 424mAh / g after 100 cycles.

[0108] The electrochemical test results of group B: the first discharge specific capacity was 468 mAh / g, the first cycle coulombic efficiency was 92.28%, and the specific capacity remained at 426 mAh / g after 100 cycles.

[0109] The electrochemical test results of group C: the first discharge specific capacity was 432mAh / g, the first cycle coulombic efficiency was 93.31%, and the specific capacity remained at 392mAh / g after 100 cycles.

[0110] The electrochemical test results of group D: the first discharge specific capacity was 436 mAh / g, the first cycle coulombic efficiency was 92.68%, and the specific capacity remained at 398 mAh / g after 100 cycles.

[0111] Example 5

[0112] Compared with Example 1, the only difference is that the conditions of the T2 and T3 segments are changed to:

[0113] Group A: T2 stage temperature is 500℃, roasting time is 3h, and heating rate is 5℃ / min; T3 stage temperature is 1600℃, roasting time is 1h, and heating rate is 5℃ / min.

[0114] Group B: T2 stage temperature is 500℃, roasting time is 1h, heating rate is 10℃ / min; T3 stage temperature is 1800℃, roasting time is 1h, heating rate is 10℃ / min.

[0115] Group C: T2 stage temperature is 800℃, roasting time is 3h, heating rate is 10℃ / min; T3 stage temperature is 1000℃, roasting time is 3h, heating rate is 1℃ / min.

[0116] The results were as follows:

[0117] The electrochemical test results of group A: the first discharge specific capacity is 458 mAh / g, the first cycle coulombic efficiency is 91.29%, and the specific capacity remains at 415 mAh / g after 100 cycles.

[0118] The electrochemical test results of group B: the first discharge specific capacity was 432 mAh / g, the first cycle coulombic efficiency was 92.36%, and the specific capacity remained at 386 mAh / g after 100 cycles.

[0119] Electrochemical test results of Group C: The first discharge specific capacity was 446 mAh / g, the first cycle coulombic efficiency was 90.33%, and the specific capacity remained at 400 mAh / g after 100 cycles.

[0120] Example 6

[0121] Compared with Example 1, the only difference is that the gas phase carbon source in step (2) is changed to:

[0122] Group A: The methane content in the nitrogen-methane mixed gas (methane content is 10% by volume) is adjusted to 20%;

[0123] Group B: The nitrogen-methane mixed gas (methane content is 10% by volume) was replaced with a nitrogen-acetylene mixed gas (acetylene content is 10% by volume);

[0124] Group C: The nitrogen-methane mixed gas (the volume content of methane is 10%) is replaced with a nitrogen-methane and acetylene mixed gas (the volume content of methane and acetylene are both 10%).

[0125] The results were as follows:

[0126] The electrochemical test results of group A: the first discharge specific capacity is 453mAh / g, the first cycle coulombic efficiency is 92.29%, and the specific capacity remains at 417mAh / g after 100 cycles.

[0127] The electrochemical test results of group B: the first discharge specific capacity is 448 mAh / g, the first cycle coulombic efficiency is 93.38%, and the specific capacity remains at 410 mAh / g after 100 cycles.

[0128] The electrochemical test results of group C: the first discharge specific capacity was 459 mAh / g, the first cycle coulombic efficiency was 93.45%, and the specific capacity remained at 422 mAh / g after 100 cycles.

[0129] By comparing Example 6 with Example 1, the use of a combined gas source can further synergistically improve the compatibility of the prepared material and the sodium ion battery, which helps to further improve the performance of the sodium ion battery.

[0130] Example 7

[0131] Compared with Example 1, the only difference is that the temperature and time of step (2) are changed to:

[0132] Group A: heat treatment temperature is 750℃, heat treatment time is 5h;

[0133] Group B: heat treatment temperature is 950℃, heat treatment time is 1h;

[0134] The results were as follows:

[0135] The electrochemical test results of group A: the first discharge specific capacity is 432mAh / g, the first cycle coulombic efficiency is 92.31%, and the specific capacity remains at 381mAh / g after 100 cycles.

[0136] The electrochemical test results of group B: the first discharge specific capacity is 438 mAh / g, the first cycle coulombic efficiency is 93.89%, and the specific capacity remains at 391 mAh / g after 100 cycles.

[0137] Comparative Example 1

[0138] Compared with Example 1, the only difference is that the phenolic resin is replaced by

[0139] A: Replace phenolic resin with furfural resin;

[0140] B: Replace phenolic resin with urea-formaldehyde resin;

[0141] The results were as follows:

[0142] The electrochemical test results of group A: the first discharge specific capacity is 371mAh / g, the first cycle coulombic efficiency is 91.18%, and the specific capacity remains at 321mAh / g after 100 cycles.

[0143] The electrochemical test results of group B: the first discharge specific capacity is 362mAh / g, the first cycle coulombic efficiency is 91.22%, and the specific capacity remains at 318mAh / g after 100 cycles.

[0144] Comparative Example 2

[0145] Compared with Example 1, the only difference is that only phenolic resin carbon source is added to the raw material without adding heteroatom source, which are

[0146] The results were as follows:

[0147] The first discharge specific capacity is 409 mAh / g, the first cycle coulombic efficiency is 90.28%, and the specific capacity remains at 348 mAh / g after 100 cycles.

[0148] Comparative Example 3

[0149] Compared with Example 1, the only difference is that the heteroatom source in the raw material is replaced by boric acid from urea.

[0150] The results were as follows:

[0151] The first discharge specific capacity is 402mAh / g, the first cycle coulombic efficiency is 90.33%, and the specific capacity remains at 352mAh / g after 100 cycles.

[0152] Comparative Example 4

[0153] Compared with Example 1, the only difference is that the raw material is not subjected to cross-linking treatment in the T1 temperature range, but is directly heated to the T2 range and subjected to subsequent treatment.

[0154] The results were as follows:

[0155] The first discharge specific capacity is 386 mAh / g, the first cycle coulombic efficiency is 89.27%, and the specific capacity remains at 312 mAh / g after 100 cycles.

[0156] Comparative Example 5

[0157] Compared with Example 1, the only difference is that the temperature of the cross-linking treatment is 150° C. (T1).

[0158] The results were as follows:

[0159] The first discharge specific capacity is 392mAh / g, the first cycle coulombic efficiency is 90.28%, and the specific capacity remains at 342mAh / g after 100 cycles.

[0160] Comparative Example 6

[0161] Compared with Example 1, the only difference is that the temperature of the cross-linking treatment is 450°C.

[0162] The results were as follows:

[0163] The first discharge specific capacity is 388mAh / g, the first cycle coulombic efficiency is 91.26%, and the specific capacity remains at 343mAh / g after 100 cycles.

[0164] Comparative Example 7

[0165] Compared with Example 1, the only difference is that the cross-linked product is not subjected to the heat preservation treatment in the T2 temperature section, and is directly subjected to the T3 section treatment after the T1 section.

[0166] The results were as follows:

[0167] The first discharge specific capacity is 412 mAh / g, the first cycle coulombic efficiency is 90.33%, and the specific capacity remains at 351 mAh / g after 100 cycles.

[0168] Comparative Example 8

[0169] Compared with Example 1, the only difference is that the calcination temperature of stage T2 is 450°C.

[0170] The results were as follows:

[0171] The first discharge specific capacity is 379 mAh / g, the first cycle coulombic efficiency is 90.18%, and the specific capacity remains at 336 mAh / g after 100 cycles.

[0172] Comparative Example 9

[0173] Compared with Example 1, the only difference is that the calcination temperature of stage T2 is 850°C.

[0174] The results were as follows:

[0175] The first discharge specific capacity is 323mAh / g, the first cycle coulombic efficiency is 90.28%, and the specific capacity remains at 282mAh / g after 100 cycles.

[0176] Comparative Example 10

[0177] Compared with Example 1, the only difference is that the roasting temperature of stage T3 is 900°C.

[0178] The results were as follows:

[0179] The first discharge specific capacity is 346 mAh / g, the first cycle coulombic efficiency is 87.63%, and the specific capacity remains at 256 mAh / g after 100 cycles.

[0180] Comparative Example 11

[0181] Compared with Example 1, the only difference is that the roasting temperature of stage T3 is 2000°C.

[0182] The results were as follows:

[0183] The first discharge specific capacity is 341 mAh / g, the first cycle coulombic efficiency is 88.43%, and the specific capacity remains at 265 mAh / g after 100 cycles.

[0184] Comparative Example 12

[0185] Compared with Example 1, the only difference is that the material obtained in step (1) is not subjected to the thermal modification treatment of step (2).

[0186] The results were as follows:

[0187] The first discharge specific capacity is 406 mAh / g, the first cycle coulombic efficiency is 78.85%, and the specific capacity remains at 292 mAh / g after 100 cycles.

[0188] Comparative Example 13

[0189] Compared with Example 1, the only difference is that the material obtained in step (1) and asphalt are mixed in a ratio of 97:3, ball-milled evenly, and then heat-treated at 850° C. for 2 h.

[0190] The results were as follows:

[0191] The first discharge specific capacity is 408 mAh / g, the first cycle coulombic efficiency is 87.85%, and the specific capacity remains at 312 mAh / g after 100 cycles.

[0192] Comparative Example 14

[0193] Compared with Example 1, the only difference is that the heat treatment temperature in the modification step in step (2) is adjusted from 850° C. to 700° C., and other parameters remain the same.

[0194] The results were as follows:

[0195] The first discharge specific capacity is 432mAh / g, the first cycle coulombic efficiency is 82.14%, and the specific capacity is maintained at 224mAh / g after 100 cycles.

Claims

1. A hybrid phenolic resin-based amorphous carbon@C composite material, characterized in that: It has a core-shell structure, wherein the core is a phenolic resin-based amorphous carbon material hybridized with heteroatoms, which has a sub-nanometer pore structure, and the heteroatoms include N atoms; The shell is a thin layer of amorphous carbon with a thickness of 1 to 10 nm; The hybrid phenolic resin-based amorphous carbon@C composite material is prepared by the following steps: Step (1): The phenolic resin and the heteroatom source are subjected to a hybrid crosslinking reaction at a temperature of 200-400°C in advance, and then subjected to a first stage of calcination at a temperature of 500-800°C, and then subjected to a second stage of calcination at a temperature of 1000-1800°C to obtain a hybrid material; the heteroatom source comprises a N source; Step (2): The hybrid material is thermally modified in an organic atmosphere at a temperature of 750-950° C. to obtain the hybrid phenolic resin-based amorphous carbon@C composite material.

2. The hybrid phenolic resin-based amorphous carbon@C composite material according to claim 1, characterized in that: The heteroatoms also include at least one of P and B.

3. The hybrid phenolic resin-based amorphous carbon@C composite material according to claim 2, characterized in that: Among the heteroatoms, the content of N element is greater than or equal to 20 at%.

4. The hybrid phenolic resin-based amorphous carbon@C composite material according to claim 1, characterized in that: In the core, the pore size is 0.2-0.8 nm; the porosity is 20-70%; The specific surface area is less than or equal to 10 m 2 / g; tap density ≥0.5 g / cm 3 .

5. The hybrid phenolic resin-based amorphous carbon@C composite material according to claim 4, characterized in that: The core has a specific surface area of ​​2 to 4 m 2 / g; tap density ≥0.7 g / cm 3 .

6. A method for preparing a hybrid phenolic resin-based amorphous carbon@C composite material according to any one of claims 1 to 5, characterized in that the steps include: Step (1): The phenolic resin and the heteroatom source are subjected to a hybrid crosslinking reaction at a temperature of 200-400°C in advance, and then subjected to a first stage of calcination at a temperature of 500-800°C, and then subjected to a second stage of calcination at a temperature of 1000-1800°C to obtain a hybrid material; the heteroatom source comprises a N source; Step (2): The hybrid material is thermally modified in an organic atmosphere at a temperature of 750-950° C. to obtain the hybrid phenolic resin-based amorphous carbon@C composite material.

7. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The phenolic resin is a condensation product of aromatic phenol and formaldehyde.

8. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 7, characterized in that: The aromatic phenol is phenol or substituted phenol; the substituted phenol is a substituted phenol with a C1-C6 alkyl or alkoxy substituent on the benzene ring.

9. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The N source is at least one of urea, melamine and dicyandiamide.

10. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The heteroatom source further includes at least one of a boron source and a phosphorus source; The boron source is at least one of boric acid, boron oxide and tetraphenylboric acid; The phosphorus source is at least one of hypophosphorous acid, phosphorous acid, phosphoric acid, metaphosphoric acid, pyrophosphoric acid and polyphosphoric acid; In the heteroatom source, the content of the N source is greater than or equal to 20 at%.

11. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The weight ratio of the heteroatom source to the phenolic resin is 0.01-0.2:

1.

12. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The heteroatom source and the phenolic resin are mixed in a solid phase or a liquid phase.

13. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The atmosphere during the hybrid cross-linking reaction is a protective atmosphere or an oxygen-containing atmosphere; Wherein, the protective atmosphere is at least one of nitrogen and inert gas; The oxygen-containing atmosphere is oxygen, a mixture of oxygen and protective gas or air.

14. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The temperature of the hybrid cross-linking reaction is 300~350℃.

15. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The hybrid cross-linking time is 1~3 h.

16. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The first and second calcination processes are carried out under a protective atmosphere; The first roasting time is 1~5 h.

17. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: After the first stage of roasting, the powder is crushed, air-milled and sieved, and the powder with a particle size of 3-15 μm is selected and then the second stage of roasting is carried out.

18. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The second roasting time is 1~3 h.

19. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The organic atmosphere is a mixed gas containing organic gas and protective gas; The organic gas includes at least one of C1-C6 alkanes, C2-C6 alkenes, C2-C6 alkynes, and C1-C4 alcohols.

20. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 19, characterized in that: In the organic atmosphere, the volume content of the organic gas is 5-20%; The flow rate of organic atmosphere is 20~200 L / min.

21. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The temperature of thermal modification is 850~900℃.

22. The method for preparing the hybrid phenolic resin-based amorphous carbon@C composite material according to claim 6, characterized in that: The thermal modification time is 1~5 h.

23. Use of the hybrid phenolic resin-based amorphous carbon@C composite material according to any one of claims 1 to 5 or the hybrid phenolic resin-based amorphous carbon@C composite material prepared by the preparation method according to any one of claims 6 to 22, characterized in that: It is used as negative electrode active material to prepare sodium secondary batteries.

24. The use according to claim 23, characterized in that It is used as negative electrode active material to prepare the negative electrode of sodium secondary battery.

25. The use according to claim 23, characterized in that The sodium secondary battery is a sodium ion battery.

26. A negative electrode for a sodium secondary battery, characterized in that: The hybrid phenolic resin-based amorphous carbon@C composite material comprises the hybrid phenolic resin-based amorphous carbon@C composite material according to any one of claims 1 to 5 or the hybrid phenolic resin-based amorphous carbon@C composite material prepared by the preparation method according to any one of claims 6 to 22.

27. The negative electrode for a sodium secondary battery according to claim 26, characterized in that: It comprises a current collector and a negative electrode material compounded on the surface of the current collector; the negative electrode material comprises the hybrid phenolic resin-based amorphous carbon@C composite material.

28. The negative electrode for a sodium secondary battery according to claim 27, characterized in that: The negative electrode material also includes a conductive agent and a binder.

29. A sodium secondary battery, characterized in that: A negative electrode comprising the negative electrode according to any one of claims 26 to 28.

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