Hard carbon material with high-crosslinking closed-pore structure as well as preparation method and application of hard carbon material

Abstract

The invention belongs to the technical field of battery materials, and relates to a high-crosslinking closed-pore structure hard carbon material and a preparation method and application thereof, and the preparation method comprises the steps of solution preparation, pre-crosslinking, curing, oxidation and pyrolysis which are carried out in sequence; wherein the solution is prepared into a precursor solution, a solute in the precursor solution comprises a carbon precursor and a cross-linking agent, and functional groups of the carbon precursor at least comprise hydroxyl and carboxyl. According to the prepared hard carbon material, accurate construction of short-distance pseudo carbon crystals in the opening and closing process is achieved, high sodium storage capacity, high initial coulombic efficiency and good rate capability are well considered, and application and popularization in sodium ion batteries are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to a hard carbon material, in particular to a hard carbon material with a highly cross-linked closed-pore structure and a preparation method and application thereof. Background Art

[0002] As a potential alternative to lithium-ion batteries, sodium-ion batteries (Na-ion batteries) hold broad application prospects in areas such as stationary energy storage and low-speed electric vehicles. This is due to the abundance of sodium resources on Earth and their cost-effectiveness. As a core component of Na-ion batteries, the performance of the anode material directly determines the battery's energy density, cycle life, and rate characteristics.

[0003] Among numerous anode materials, hard carbon has become a research focus due to its unique structural advantages: its random graphite structure, expanded interlayer spacing, and tunable pore structure enable it to achieve electrochemical storage of sodium ions through various means, including surface adsorption, interlayer insertion, and pore filling. However, hard carbon materials still face many challenges in practical application.

[0004] In order to improve the sodium storage capacity and reaction kinetics of hard carbon, researchers usually adopt strategies such as constructing porous structures or performing heteroatom doping, but these methods often lead to a large loss of active sodium, significantly reducing the initial Coulombic efficiency (ICE) of the battery. To alleviate this problem, the industry generally believes that constructing pseudo-graphite domains and closed pore structures is an effective way, and strategies such as chemical cross-linking, chemical vapor deposition, and pore templates / activation have also been developed and applied. Among them, although increasing the carbonization temperature can promote carbon layer rearrangement and local bending, and help form pseudo-graphite domains and closed pore structures, long-term high-temperature carbon layer rearrangement will lead to a decrease in carbon layer spacing and thickening of the pore wall, which in turn hinders the rapid diffusion of sodium ions and affects sodium storage kinetics.

[0005] It can be seen that how to achieve the precise construction of short-distance pseudo-carbon crystals in the process of pore closure in hard carbon materials to take into account high sodium storage capacity, high initial Coulomb efficiency and good rate performance has become a key technical problem restricting the promotion and application of hard carbon materials in sodium ion batteries. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a highly cross-linked closed-pore structure hard carbon material and its preparation method and application, to achieve the precise construction of short-distance pseudo-carbon crystals in the process of pore closing in the hard carbon material, taking into account high sodium storage capacity, high initial Coulomb efficiency and good rate capability, and promote the promotion and application of hard carbon materials in sodium ion batteries.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present application provides a preparation method of a high-crosslinking closed-pore structure hard carbon material, comprising solution preparation, pre-crosslinking, solidification, oxidation and pyrolysis in sequence.

[0009] The solution preparation obtains a precursor solution, and the solute in the precursor solution comprises a carbon precursor and a crosslinking agent, and the functional groups of the carbon precursor at least include hydroxyl and carboxyl.

[0010] The precursor solution provided by the present application is crosslinked and esterified by the crosslinking agent and the hydroxyl and carboxyl in the carbon precursor, to construct a pre-crosslinking precursor rich in C-(O)-O (carboxyl or ester group). The C-O-C structure can effectively inhibit the graphitization degree of the material in the early stage of the traditional carbonization crosslinking reaction in the subsequent oxidation process, and increase the interlayer spacing of the graphite domain. Compared with the traditional low-temperature carbonization, the solidified precursor is crosslinked between molecules by oxygen as a bridge, which can release unreacted and easily decomposed functional groups, avoid the decomposition of the unreacted functional groups in the pyrolysis process to produce more open pores, and thus fully induce the formation of closed pores in the carbonization process, reduce the irreversible consumption of active sodium, increase the capacity of the platform area, and thus improve the first coulombic efficiency of the obtained hard carbon material.

[0011] Specifically, the present application uses a carbon precursor with oxygen-containing functional groups (hydroxyl and carboxyl) as a raw material, and cooperates with a crosslinking agent to sequentially perform pre-crosslinking, solidification, oxidation and pyrolysis. The hydroxyl and carboxyl on the edge / flat end of the carbon precursor are further crosslinked by the hydrogen bond between the carboxyl groups in the crosslinking agent to obtain a pre-crosslinking product, which is reconfigured as ester, carbonyl and carboxylate functional groups. This unique pre-crosslinking method uses the spatial steric hindrance effect to form closed pores in the polymer-derived hard carbon material by grafting functional groups in the main chain and between the branched chains of the crosslinking agent. The spatial steric hindrance effect of the crosslinking agent can increase the rigidity of the main chain and the internal free volume of the polymer precursor, thereby preventing excessive graphitization and promoting the formation of closed pores in the carbonization process, effectively promoting the bending of the carbon layer, and thus constructing an ideal pseudo-graphite structure with expanded carbon layer spacing and rich super-micropores / closed pores. The pre-crosslinked material is then sequentially subjected to oxidation and pyrolysis, to obtain a high-crosslinking closed-pore structure derived hard carbon material. The oxidation process produces a rich microporous structure in the hard carbon material, and the pyrolysis process further evolves the micropores into a closed-pore structure. This closed-pore structure exhibits higher platform capacity for sodium ion battery hard carbon anodes, and can effectively improve the first coulombic efficiency of the hard carbon material due to the conversion of more open pores into closed pores.

[0012] Preferably, the solution preparation comprises mixing the carbon precursor, the crosslinking agent and deionized water to obtain the precursor solution.

[0013] Preferably, the carbon precursor includes any one or a combination of at least two of cyclodextrin, phenolic resin, chitosan, bamboo charcoal powder or oxidized asphalt. Typical but non-limiting combinations include a combination of cyclodextrin and phenolic resin, a combination of phenolic resin and chitosan, a combination of chitosan and bamboo charcoal powder, or a combination of bamboo charcoal powder and oxidized asphalt. Cyclodextrin and / or phenolic resin are further preferred.

[0014] The carbon precursors used in the present invention are low-cost, widely available, and easily modifiable, enabling large-scale industrial production. Cyclodextrin and / or phenolic resin are preferred carbon precursors because they possess more reactive oxygen-containing functional groups than other carbon precursors, thus facilitating crosslinking reactions with crosslinking agents.

[0015] Preferably, the cyclodextrin includes any one of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin, or a combination of at least two of them. Typical but non-limiting combinations include a combination of α-cyclodextrin and β-cyclodextrin, a combination of β-cyclodextrin and γ-cyclodextrin, a combination of α-cyclodextrin and γ-cyclodextrin, or a combination of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin.

[0016] Preferably, the cross-linking agent comprises any one of tannic acid, citric acid, oxalic acid, gallic acid, ascorbic acid, cyanuric acid, caffeic acid, succinic acid, humic acid or starch, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of tannic acid and citric acid, a combination of citric acid and oxalic acid, a combination of oxalic acid and gallic acid, a combination of gallic acid and ascorbic acid, a combination of ascorbic acid and cyanuric acid, a combination of cyanuric acid and caffeic acid, a combination of caffeic acid and succinic acid, a combination of succinic acid and humic acid, or a combination of humic acid and starch, preferably tannic acid.

[0017] The crosslinking agent used in the present invention can regulate the pores and interfacial functional groups of the hard carbon material. This type of polycarboxylic acid is easily converted into a gaseous state under high temperature and high pressure, and there are active carboxyl groups on the two terminal carbon atoms of the molecular chain. It can undergo esterification reaction through the hydroxyl groups on the carboxyl carbon precursor, thereby achieving crosslinking between the two molecules.

[0018] Among them, since the macromolecule formed by tannic acid when cross-linked with cyclodextrin is not a planar structure but a three-dimensional structure, it can prevent the formation of a linear structure after cross-linking. The linear structure is prone to graphitization, resulting in fewer closed-pore structures and narrower interlayer spacing. Therefore, tannic acid is preferably used as the cross-linking agent in the present invention.

[0019] Preferably, the mixing molar ratio of the carbon precursor and the crosslinker is (1-9):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0020] In the present invention, the molar ratio of the carbon precursor to the cross-linking agent needs to be limited to a reasonable range. If the molar ratio is too large, that is, when there is too much carbon precursor, the self-cross-linking reaction of the carbon precursor will be more dominant, and a full reaction between the carbon precursor and the cross-linking agent cannot be achieved; if the molar ratio is too small, that is, when there is too much cross-linking agent, some cross-linking agent will be in excess and will not participate in the cross-linking reaction. As a result, during the subsequent pyrolysis process, the cross-linking agent decomposes to produce a macroporous structure without sodium storage activity, leading to irreversible decomposition and consumption of the electrolyte during the electrochemical reaction, and thus causing a decrease in the first-cycle coulombic efficiency.

[0021] Preferably, the total concentration of the solute in the precursor solution is 1-10 mol / L, for example, it can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0022] In the present invention, the total concentration of solutes in the precursor solution specifically refers to the sum of the concentrations of the carbon precursor and the crosslinker, and needs to be limited to a reasonable range. If the total concentration is too low, the crosslinking molecular angle will be too small, the resulting carbon layer will have a low degree of torsion, and the closed-pore diameter will be too small, failing to increase the sodium storage capacity. If the total concentration is too high, the precursors that do not participate in the crosslinking reaction will aggregate, preventing the crosslinking reaction from completing uniformly between the carbon precursor and the crosslinker.

[0023] Preferably, the pre-crosslinking comprises: subjecting the precursor solution to a reflux reaction and cooling the solution to obtain a pre-crosslinking solution.

[0024] Preferably, the temperature of the reflux reaction is 80-85°C, for example, it can be 80°C, 80.5°C, 81°C, 81.5°C, 82°C, 82.5°C, 83°C, 83.5°C, 84°C, 84.5°C or 85°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0025] Preferably, the reflux reaction time is 6-12 h, for example, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the curing comprises: curing the pre-crosslinking solution to obtain a cured precursor.

[0027] Preferably, the solidification treatment method includes any one of air drying, vacuum drying, freeze drying or spray drying, or a combination of at least two of them. Typical but non-limiting combinations include a combination of air drying and vacuum drying, a combination of vacuum drying and freeze drying, or a combination of freeze drying and spray drying.

[0028] Preferably, the temperature of the curing treatment is 180-200°C, for example, it can be 180°C, 182°C, 184°C, 186°C, 188°C, 190°C, 192°C, 194°C, 196°C, 198°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0029] Preferably, the curing treatment time is 20-24 hours, for example, it can be 20 hours, 20.5 hours, 21 hours, 21.5 hours, 22 hours, 22.5 hours, 23 hours, 23.5 hours or 24 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the oxidation comprises placing the curing precursor in an oxygen-containing atmosphere for cross-linking and partial carbonization to obtain an oxidation product.

[0031] Preferably, the oxygen-containing atmosphere comprises oxygen and / or ozone.

[0032] Preferably, the temperature of the crosslinking and partial carbonization is 150-360°C, for example, 150°C, 200°C, 250°C, 300°C, 350°C or 360°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0033] In the present invention, the temperature range for crosslinking and partial carbonization is crucial for the crosslinking reaction to proceed fully. If the temperature is too low, the crosslinking reaction is not favorable and further crosslinking cannot be achieved; if the temperature is too high, complete carbonization is likely to occur, and the crosslinking reaction cannot continue.

[0034] Preferably, the heating rate of the crosslinking and partial carbonization is 0.5-10°C / min, for example, it can be 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0035] In the present invention, if the heating rate is too high, the gas production will be too large and the ultra-microporous structure with sodium storage activity cannot be obtained; if the heating rate is too low, the time required is too long and the cost is high.

[0036] Preferably, the cross-linking and partial carbonization is performed for 0.5-24 hours, such as 0.5 hours, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours, but not limited to the listed values, other values not listed within the range are also applicable.

[0037] In the present application, if the holding time is too short, the cross-linking reaction degree will be low; if the holding time is too long, the unstable oxygen-containing functional groups will be decomposed, which will adversely affect the closed pore structure and the interlayer spacing.

[0038] Preferably, the pyrolysis comprises: placing the oxidation product in an inert atmosphere for high-temperature pyrolysis to obtain a hard carbon material.

[0039] Preferably, the inert atmosphere comprises any one or a combination of at least two of nitrogen, argon, or helium, and a typical but non-limiting combination includes a combination of nitrogen and argon, a combination of argon and helium, a combination of nitrogen and helium, or a combination of nitrogen, argon, and helium.

[0040] Preferably, the high-temperature pyrolysis is performed at a temperature of 1000-1600°C, such as 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C, or 1600°C, but not limited to the listed values, other values not listed within the range are also applicable.

[0041] In the present application, the temperature range of the high-temperature pyrolysis is crucial for the formation of the closed pore structure. If the temperature is too low, more short-range ordered and long-range disordered structures cannot be obtained; if the temperature is too high, graphitization will occur due to the accumulation of carbon layers.

[0042] Preferably, the high-temperature pyrolysis is performed at a temperature of 1000-1600°C, such as 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C, or 1600°C, but not limited to the listed values, other values not listed within the range are also applicable.

[0043] Preferably, the high-temperature pyrolysis is performed for 0.5-24 hours, such as 0.5 hours, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours, but not limited to the listed values, other values not listed within the range are also applicable.

[0044] In the present invention, the holding time of the high-temperature pyrolysis also affects the closed-pore structure of the hard carbon material. If the holding time is too short, the carbon layers cannot rearrange, preventing the formation of a further closed-pore structure. If the holding time is too long, the carbon layers will become severely graphitized, preventing the formation of a hard carbon material with a suitable interlayer spacing.

[0045] As a preferred technical solution of the first aspect of the present invention, the preparation method comprises the following steps:

[0046] (1) Solution preparation: mixing a carbon precursor, a crosslinking agent, and deionized water to obtain a precursor solution with a total concentration of 1-10 mol / L; wherein the carbon precursor is cyclodextrin and / or phenolic resin, the crosslinking agent is tannic acid, and the mixing molar ratio of the carbon precursor to the crosslinking agent is (1-9):1;

[0047] (2) Pre-crosslinking: reflux the precursor solution at 80-85°C for 6-12 hours, and then cool it to obtain a pre-crosslinking solution;

[0048] (3) Curing: Curing the pre-crosslinked solution at 180-200° C. for 20-24 hours to obtain a cured precursor; wherein the curing treatment method includes any one of forced air drying, vacuum drying, freeze drying or spray drying, or a combination of at least two thereof;

[0049] (4) Oxidation: placing the curing precursor in an oxygen-containing atmosphere, heating it to 150-360°C at a rate of 0.5-10°C / min for crosslinking and partial carbonization for 0.5-24 hours to obtain an oxidized product; wherein the oxygen-containing atmosphere includes oxygen and / or ozone;

[0050] (5) Pyrolysis: The oxidation product is placed in an inert atmosphere, heated to 1000-1600°C at a rate of 0.5-10°C / min, and subjected to high-temperature pyrolysis for 0.5-24 hours to obtain a hard carbon material; wherein the inert atmosphere comprises any one of nitrogen, argon, or helium, or a combination of at least two of them.

[0051] In a second aspect, the present invention provides a highly cross-linked closed-cell hard carbon material prepared by the preparation method described in the first aspect, wherein the carbon layer spacing of the highly cross-linked closed-cell hard carbon material is greater than 0.37nm, for example, it can be 0.375nm, 0.376nm, 0.377nm, 0.378nm, 0.379nm, 0.38nm, 0.381nm, 0.382nm, 0.383nm, 0.384nm, 0.385nm m, 0.386nm or 0.387nm, the average pore size is 0.9-1.2nm, for example, it can be 0.9nm, 0.92nm, 0.94nm, 0.96nm, 0.98nm, 1nm, 1.02nm, 1.04nm, 1.06nm, 1.08nm, 1.1nm, 1.12nm, 1.14nm, 1.16nm, 1.18nm or 1.2nm, and the specific surface area is 78-435m 2 / g, for example, it can be 78m 2 / g、80m 2 / g、100m 2 / g, 150m 2 / g, 200m 2 / g, 250m 2 / g、300m 2 / g、350m 2 / g, 400m 2 / g or 435m 2 / g, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] In a third aspect, the present invention provides an application of the highly cross-linked closed-pore structure hard carbon material as described in the second aspect, wherein the highly cross-linked closed-pore structure hard carbon material is used as a negative electrode material for a sodium ion battery.

[0053] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The precursor solution provided by the application is crosslinked with the hydroxyl and carboxyl in the carbon precursor by a crosslinking agent to generate a pre-crosslinking precursor rich in C-(O)-O (carboxyl or ester group), and the C-O-C structure can effectively inhibit the graphitization degree of the early-stage material of the traditional carbonization crosslinking reaction and increase the interlayer spacing of the graphite domain through the steric hindrance effect of the oxygen-containing functional group in the subsequent oxidation process. Compared with the traditional low-temperature carbonization, the solidified precursor is crosslinked between molecules by oxygen as a bridge, which can release unreacted and easily decomposed functional groups, avoid the decomposition of the unreacted oxygen-containing functional groups in the pyrolysis process to generate more open pores, thereby fully inducing the formation of closed pores in the carbonization process, reducing the irreversible consumption of active sodium, increasing the capacity of the platform region, and further improving the initial coulombic efficiency of the obtained hard carbon material. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is a preparation method flowchart of the high-crosslinking closed-pore structure hard carbon material provided by the application;

[0057] Figure 2 is an SEM photo of the high-crosslinking closed-pore structure hard carbon material provided in Example 1;

[0058] Figure 3 is an XRD spectrum of the high-crosslinking closed-pore structure hard carbon material provided in Example 1;

[0059] Figure 4 is an N2-adsorption / desorption curve of the high-crosslinking closed-pore structure hard carbon material provided in Example 1;

[0060] Figure 5 is a charge-discharge curve of the high-crosslinking closed-pore structure hard carbon material provided in Example 1;

[0061] Figure 6 is an SEM photo of the high-crosslinking closed-pore structure hard carbon material provided in Example 2;

[0062] Figure 7 is an XRD spectrum of the high-crosslinking closed-pore structure hard carbon material provided in Example 2;

[0063] Figure 8 is an N2-adsorption / desorption curve of the high-crosslinking closed-pore structure hard carbon material provided in Example 2;

[0064] Figure 9 is a charge-discharge curve of the high-crosslinking closed-pore structure hard carbon material provided in Example 2;

[0065] Figure 10 is an SEM photo of the high-crosslinking closed-pore structure hard carbon material provided in Example 3;

[0066] Figure 11is the XRD spectrum of the highly cross-linked closed-pore hard carbon material provided in Example 3;

[0067] Figure 12 This is the N2-adsorption / desorption curve of the highly cross-linked closed-pore hard carbon material provided in Example 3;

[0068] Figure 13 This is the charge and discharge curve of the highly cross-linked closed-pore hard carbon material provided in Example 3. DETAILED DESCRIPTION

[0069] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0070] Example 1

[0071] This embodiment provides a highly cross-linked closed-cell hard carbon material and a preparation method thereof, such as Figure 1 As shown, the preparation method comprises the following steps:

[0072] (1) Solution preparation: 10 g of β-cyclodextrin and 3 g of tannic acid were weighed and placed in a reactor. 30 mL of deionized water was added and ultrasonically dispersed for 30 min to obtain a colorless and transparent precursor solution.

[0073] (2) Pre-crosslinking: The precursor solution was transferred to a reflux reactor and refluxed at 80°C for 12 h, and then cooled to obtain a pre-crosslinking solution;

[0074] (3) Curing: The pre-crosslinked solution was placed in a forced air oven and cured at 180°C for 24 hours to obtain a cured precursor;

[0075] (4) Oxidation: The cured precursor was placed in a muffle furnace and heated to 275°C in an air atmosphere at a rate of 5°C / min for 12 h to perform crosslinking and partial carbonization to obtain an oxidized product;

[0076] (5) Pyrolysis: 3 g of the oxidation product was placed in a high-temperature furnace. In a nitrogen atmosphere with a flow rate of 80 sccm, the temperature was raised to 1300 °C at a rate of 2 °C / min for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0077] Figure 2 This is the microscopic morphology of the hard carbon material obtained in this example, which has irregular shapes, uneven sizes, and a relatively rough surface.

[0078] Figure 3This is the XRD spectrum of the hard carbon material obtained in this example. It can be seen that the 002 peak and the 100 peak appear at 23.5° and 44° respectively, which are the characteristic diffraction peaks of the hard carbon material. The 002 peak can be used to calculate that the carbon layer spacing is 0.385nm, which is conducive to the embedding and deintercalation of sodium ions.

[0079] Figure 4 The N2-adsorption-desorption curve of the hard carbon material obtained in this example shows that its specific surface area is 126m 2 / g, the pore volume is 0.11cc / g, and the average pore diameter is 1.0nm, which is micropore and can effectively increase the capacity of the platform area.

[0080] PAA was used as a binder and SP as a conductive carbon, with a ratio of 8:1:1 used for coating. After drying, the film was sliced ​​and assembled into 2032 button batteries in a glove box. The charge and discharge performance tests were performed using Neware software. The results are as follows: Figure 5 As shown, when the hard carbon material obtained in this embodiment is used as the negative electrode of a sodium ion battery, the reversible capacity is 385 mAh / g at 0.1 C (1 C = 200 mA / g), and the first-week coulombic efficiency is 85%.

[0081] Example 2

[0082] This embodiment provides a highly cross-linked closed-cell hard carbon material and a preparation method thereof, such as Figure 1 As shown, the preparation method comprises the following steps:

[0083] (1) Solution preparation: 10 g of β-cyclodextrin and 3 g of humic acid were weighed and placed in a reactor. 50 mL of deionized water was added and ultrasonically dispersed for 15 min to obtain a colorless and transparent precursor solution.

[0084] (2) Pre-crosslinking: The precursor solution was transferred to a reflux reactor and refluxed at 85°C for 12 h, and then cooled to obtain a pre-crosslinking solution;

[0085] (3) Curing: The pre-crosslinked solution was placed in a forced air oven and cured at 190°C for 20 h to obtain a cured precursor;

[0086] (4) Oxidation: The cured precursor was placed in a muffle furnace and heated to 300°C in an air atmosphere at a rate of 5°C / min for 8 h to perform crosslinking and partial carbonization to obtain an oxidized product;

[0087] (5) Pyrolysis: 4 g of the oxidation product was placed in a high-temperature furnace. In a nitrogen atmosphere with a flow rate of 80 sccm, the temperature was raised to 1300 °C at a rate of 2 °C / min for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0088] Figure 6The micro-morphology of the hard carbon material obtained in the embodiment is irregular in shape and uneven in size, and the surface is relatively rough.

[0089] Figure 7 The XRD spectrum of the hard carbon material obtained in the embodiment shows that the 002 peak and 100 peak at 23.2° and 44° respectively, which are characteristic peaks of the hard carbon material. The carbon layer spacing can be calculated from the 002 peak, which is 0.387 nm, and is conducive to the embedding and extraction of sodium ions.

[0090] Figure 8 The N2-adsorption and desorption curve of the hard carbon material obtained in the embodiment shows that the specific surface area is 176 m 2 / g, the pore volume is 0.13 cc / g, and the average pore size is 0.9 nm, which is microporous and can effectively improve the capacity of the platform region.

[0091] PAA was used as the binder, SP was used as the conductive carbon, and a film was coated with a ratio of 8:1:1. After drying, the slices were cut and assembled into 2032 type button cells in a glove box. The Neware software was used for charge and discharge energy test, and the results are shown in Figure 9 It can be seen that the hard carbon material obtained in the embodiment has a reversible capacity of 409 mAh / g at 0.1C (1C = 200 mA / g) when used as the negative electrode of a sodium ion battery, and the first week coulombic efficiency is 84%.

[0092] Example 3

[0093] The embodiment provides a high-crosslinking closed-pore structure hard carbon material and a preparation method thereof, as shown in Figure 1 The preparation method comprises the following steps:

[0094] (1) Solution preparation: 10 g of α-cyclodextrin and 4 g of ascorbic acid were weighed into a reactor, 30 mL of deionized water was added, and ultrasonic dispersion was performed for 20 min to obtain a colorless transparent precursor solution;

[0095] (2) Pre-crosslinking: The precursor solution was transferred to a reflux reactor and refluxed at 80°C for 8 h. After cooling, a pre-crosslinking solution was obtained;

[0096] (3) Solidification: The pre-crosslinking solution was placed in a blast drying oven and subjected to solidification treatment at 200°C for 24 h to obtain a solidified precursor;

[0097] (4) Oxidation: The solidified precursor was placed in a muffle furnace and subjected to crosslinking and partial carbonization at 250°C for 10 h in an air atmosphere at a rate of 5°C / min to obtain an oxidation product;

[0098] (5) Pyrolysis: 4 g of the oxidation product was placed in a high-temperature furnace, and high-temperature pyrolysis was performed at a rate of 2 °C / min to 1300 °C for 2 h in a nitrogen atmosphere with a flow rate of 80 sccm to obtain a hard carbon material.

[0099] Figure 10 The micro-morphology of the hard carbon material obtained in this example was irregular in shape and uneven in size, and the surface was relatively rough.

[0100] Figure 11 The XRD spectrum of the hard carbon material obtained in this example showed that the 002 peak and 100 peak appeared at 23.3° and 44°, respectively, which were characteristic peaks of the hard carbon material. The interlayer spacing of the carbon layer was calculated to be 0.382 nm from the 002 peak, which was helpful for the insertion and extraction of sodium ions.

[0101] Figure 12 The N2-adsorption / desorption curve of the hard carbon material obtained in this example showed that the specific surface area was 435 m 2 / g, the pore volume was 0.18 cc / g, and the average pore size was 1.1 nm, which belonged to micropores and could effectively improve the capacity of the platform region.

[0102] PAA was used as the binder, SP was used as the conductive carbon, and a film was coated with a ratio of 8:1:1. After drying, the slices were cut and assembled into 2032 type button cells in a glove box. The Neware software was used for charge and discharge energy test, and the results are shown in Figure 13 It can be seen that the hard carbon material obtained in this example has a reversible capacity of 426 mAh / g at 0.1C (1C = 200 mA / g) when used as the negative electrode of a sodium ion battery, and the first cycle coulombic efficiency is 83%.

[0103] Example 4

[0104] This example provides a high-crosslinking closed-pore structure hard carbon material and a preparation method thereof, as shown in Figure 1 The preparation method comprises the following steps:

[0105] (1) Solution preparation: 10 g of phenolic resin and 5 g of tannic acid were weighed into a reactor, 60 mL of deionized water was added, and ultrasonic dispersion was performed for 20 min to obtain a colorless transparent precursor solution;

[0106] (2) Pre-crosslinking: The precursor solution was transferred to a reflux reactor and refluxed at 80 °C for 8 h to obtain a pre-crosslinked solution;

[0107] (3) Solidification: The pre-crosslinked solution was placed in a forced air oven and subjected to solidification treatment at 200 °C for 24 h to obtain a solidified precursor;

[0108] (4) Oxidation: The cured precursor was placed in a muffle furnace and heated to 300°C at a rate of 5°C / min in an air atmosphere for crosslinking and partial carbonization for 6 h to obtain an oxidized product;

[0109] (5) Pyrolysis: 4 g of the oxidation product was placed in a high-temperature furnace. In a nitrogen atmosphere with a flow rate of 80 sccm, the temperature was raised to 1300 °C at a rate of 2 °C / min for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0110] The carbon interlayer spacing of the hard carbon material obtained in this embodiment is 0.378 nm, which is conducive to the insertion and extraction of sodium ions, and the specific surface area is 78 m 2 / g, the pore volume is 0.09cc / g, and the average pore diameter is 1.2nm, which is micropore and can effectively increase the capacity of the platform area.

[0111] PAA was used as a binder and SP as a conductive carbon, with a coating ratio of 8:1:1 selected. After drying, the film was sliced ​​and assembled into 2032 button batteries in a glove box. Charge and discharge energy tests were performed using Neware software. When the hard carbon material obtained in this example was used as the negative electrode of a sodium ion battery, the reversible capacity was 365 mAh / g at 0.1C (1C = 200 mA / g), and the coulombic efficiency in the first week was 78%.

[0112] Example 5

[0113] This embodiment provides a highly cross-linked closed-cell hard carbon material and a preparation method thereof, such as Figure 1 As shown, the preparation method comprises the following steps:

[0114] (1) Solution preparation: 8 g of β-cyclodextrin and 4 g of cyanuric acid were weighed and placed in a reactor. 40 mL of deionized water was added and ultrasonically dispersed for 20 min to obtain a colorless and transparent precursor solution.

[0115] (2) Pre-crosslinking: The precursor solution was transferred to a reflux reactor and refluxed at 80°C for 8 h, and then cooled to obtain a pre-crosslinked solution;

[0116] (3) Curing: The pre-crosslinked solution was placed in a forced air oven and cured at 180°C for 24 hours to obtain a cured precursor;

[0117] (4) Oxidation: The cured precursor was placed in a muffle furnace and heated to 275°C in an air atmosphere at a rate of 5°C / min for 8 h to perform crosslinking and partial carbonization to obtain an oxidized product;

[0118] (5) Pyrolysis: 4 g of the oxidation product was placed in a high-temperature furnace. In a nitrogen atmosphere with a flow rate of 80 sccm, the temperature was raised to 1300 °C at a rate of 2 °C / min for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0119] The carbon interlayer spacing of the hard carbon material obtained in this embodiment is 0.375 nm, which is conducive to the insertion and extraction of sodium ions, and the specific surface area is 128 m 2 / g, the pore volume is 0.18cc / g, and the average pore diameter is 1.1nm, which is micropore and can effectively increase the capacity of the platform area.

[0120] PAA was used as a binder and SP as a conductive carbon, with a coating ratio of 8:1:1 selected. After drying, the film was sliced ​​and assembled into 2032 button batteries in a glove box. Charge and discharge energy tests were performed using Neware software. When the hard carbon material obtained in this example was used as the negative electrode of a sodium ion battery, the reversible capacity was 381 mAh / g at 0.1C (1C = 200 mA / g), and the coulombic efficiency in the first week was 78%.

[0121] Example 6

[0122] This embodiment provides a highly cross-linked closed-cell hard carbon material and a preparation method thereof, such as Figure 1 As shown, the preparation method comprises the following steps:

[0123] (1) Solution preparation: 10 g of β-cyclodextrin and 2 g of succinic acid were weighed and placed in a reactor. 40 mL of deionized water was added and ultrasonically dispersed for 20 min to obtain a colorless and transparent precursor solution.

[0124] (2) Pre-crosslinking: The precursor solution was transferred to a reflux reactor and refluxed at 80°C for 6 h, and then cooled to obtain a pre-crosslinking solution;

[0125] (3) Curing: The pre-crosslinked solution was placed in a forced air oven and cured at 200°C for 24 hours to obtain a cured precursor;

[0126] (4) Oxidation: The cured precursor was placed in a muffle furnace and heated to 300°C at a rate of 5°C / min in an air atmosphere for crosslinking and partial carbonization for 10 h to obtain an oxidized product;

[0127] (5) Pyrolysis: 4 g of the oxidation product was placed in a high-temperature furnace. In a nitrogen atmosphere with a flow rate of 80 sccm, the temperature was raised to 1300 °C at a rate of 2 °C / min for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0128] The carbon interlayer spacing of the hard carbon material obtained in this embodiment is 0.381 nm, which is conducive to the insertion and extraction of sodium ions, and the specific surface area is 115 m 2 / g, the pore volume is 0.11cc / g, and the average pore diameter is 1.1nm, which is micropore and can effectively increase the capacity of the platform area.

[0129] PAA was used as a binder and SP as a conductive carbon, with a coating ratio of 8:1:1 selected. After drying, the film was sliced ​​and assembled into 2032 button batteries in a glove box. Charge and discharge performance tests were performed using Neware software. When the hard carbon material obtained in this example was used as the negative electrode of a sodium ion battery, the reversible capacity was 372 mAh / g at 0.1C (1C = 200 mA / g), and the coulombic efficiency in the first week was 78%.

[0130] Comparative Example 1

[0131] This comparative example provides a hard carbon material and a preparation method thereof, wherein the preparation method comprises the following steps:

[0132] (1) Weigh 10 g of β-cyclodextrin and place it in a porcelain boat. Pre-oxidize it at 200°C for 6 h to obtain a pre-oxidized product.

[0133] (2) 4 g of the pre-oxidation product was placed in a high-temperature furnace, and the temperature was raised to 1300 °C at a rate of 5 °C / min in a nitrogen atmosphere with a flow rate of 80 sccm for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0134] After testing, the carbon interlayer spacing of the hard carbon material obtained in this comparative example is 0.37nm, and the specific surface area is 12m 2 / g, the pore volume is 0.01cc / g, and the average pore diameter is 1.5nm, which is micropore.

[0135] PAA was used as a binder and SP as a conductive carbon, with a coating ratio of 8:1:1 selected. After drying, the film was sliced ​​and assembled into 2032 button batteries in a glove box. Charge and discharge energy tests were performed using Neware software. When the hard carbon material obtained in this example was used as the negative electrode of a sodium ion battery, the reversible capacity was 278 mAh / g at 0.1C (1C = 200 mA / g), and the coulombic efficiency in the first week was 76%.

[0136] Comparative Example 2

[0137] This comparative example provides a hard carbon material and a preparation method thereof, wherein the preparation method comprises the following steps:

[0138] (1) Weigh 10 g of phenolic resin and place it in a porcelain boat. Pre-oxidize it at 200°C for 6 h to obtain a pre-oxidized product.

[0139] (2) 4 g of the pre-oxidation product was placed in a high-temperature furnace, and the temperature was raised to 1300 °C at a rate of 5 °C / min in a nitrogen atmosphere with a flow rate of 80 sccm for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0140] After testing, the carbon interlayer spacing of the hard carbon material obtained in this comparative example is 0.375nm, and the specific surface area is 4m 2 / g, the pore volume is 0.005cc / g, and the average pore diameter is 1.2nm, which is micropore.

[0141] PAA was used as a binder and SP as a conductive carbon, with a coating ratio of 8:1:1 selected. After drying, the film was sliced ​​and assembled into 2032 button batteries in a glove box. Charge and discharge performance tests were performed using Neware software. When the hard carbon material obtained in this example was used as the negative electrode of a sodium ion battery, the reversible capacity was 305 mAh / g at 0.1C (1C = 200 mA / g), and the coulombic efficiency in the first week was 74%.

[0142] Comparative Example 3

[0143] This comparative example provides a hard carbon material and a preparation method thereof, wherein the preparation method comprises the following steps:

[0144] (1) Weigh 10 g of α-cyclodextrin and place it in a porcelain boat. Pre-oxidize it at 200°C for 6 h to obtain a pre-oxidized product.

[0145] (2) 4 g of the pre-oxidation product was placed in a high-temperature furnace, and the temperature was raised to 1300 °C at a rate of 5 °C / min in a nitrogen atmosphere with a flow rate of 80 sccm for high-temperature pyrolysis for 2 h to obtain a hard carbon material.

[0146] The carbon interlayer spacing of the hard carbon material obtained in this comparative example is 0.372nm and the specific surface area is 11m 2 / g, the pore volume is 0.01cc / g, and the average pore diameter is 1.2nm, which is micropore.

[0147] PAA was used as a binder and SP as a conductive carbon, with a coating ratio of 8:1:1 selected. After drying, the film was sliced ​​and assembled into 2032 button batteries in a glove box. Charge and discharge energy tests were performed using Neware software. When the hard carbon material obtained in this example was used as the negative electrode of a sodium ion battery, the reversible capacity was 315 mAh / g at 0.1C (1C = 200 mA / g), and the coulombic efficiency in the first week was 76%.

[0148] For the convenience of comparison, the raw materials of the hard carbon materials obtained in Examples 1-6 and Comparative Examples 1-3, as well as the reversible capacity and first-cycle coulombic efficiency of the corresponding batteries are summarized in Table 1 below.

[0149] Table 1

[0150]

[0151] As shown in Table 1, the reversible capacity and first-cycle coulombic efficiency of the hard carbon materials obtained in Examples 1-6 are significantly higher than those in Comparative Examples 1-3. This is due to the pre-crosslinking effect. The hydroxyl and carboxyl groups at the edges / planar ends of the carbon precursor are further cross-linked through hydrogen bonding between the carboxyl groups in the cross-linker, resulting in a pre-cross-linked product with ester, carbonyl, and carboxylate functional groups. This unique pre-cross-linking method effectively promotes the curvature of the carbon layers through cross-linking between oxygen-containing functional groups, thereby constructing an ideal pseudo-graphite hard carbon with expanded carbon interlayer spacing and abundant ultramicropores / closed pores, ultimately improving the battery's sodium storage performance.

[0152] It can be seen that the precursor solution provided by the present invention undergoes cross-linking reaction and esterification reaction with the hydroxyl and carboxyl groups in the carbon precursor through the cross-linking agent to construct a pre-cross-linked precursor rich in C-(O)-O (carboxyl or ester group). In the subsequent oxidation process, the COC structure can effectively suppress the degree of graphitization of the material in the early stage of the traditional carbonization cross-linking reaction through the steric hindrance effect of the oxygen-containing functional group, thereby increasing the interlayer spacing of the graphite domain. Compared with traditional low-temperature carbonization, the solidified precursor uses oxygen as a bridge to cross-link molecules, which can release unreacted and easily decomposed functional groups, avoiding the decomposition and gas production of such oxygen-containing functional groups that do not participate in cross-linking during the pyrolysis process to cause more open pores, thereby fully inducing the formation of closed pores during the carbonization process, reducing the irreversible consumption of active sodium, increasing the platform area capacity, and thereby improving the first coulombic efficiency of the obtained hard carbon material.

[0153] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a highly cross-linked closed-cell hard carbon material, characterized in that: The preparation method comprises solution preparation, pre-crosslinking, curing, oxidation and pyrolysis performed in sequence; The solution is prepared to obtain a precursor solution, the solute in the precursor solution includes a carbon precursor and a cross-linking agent, and the functional groups of the carbon precursor include at least hydroxyl groups and carboxyl groups.

2. The preparation method according to claim 1, characterized in that The solution preparation comprises: mixing a carbon precursor, a cross-linking agent and deionized water to obtain a precursor solution; Wherein, the carbon precursor comprises any one or a combination of at least two of cyclodextrin, phenolic resin, chitosan, bamboo charcoal powder or oxidized asphalt, preferably cyclodextrin and / or phenolic resin; And / or, the cyclodextrin includes any one of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin, or a combination of at least two thereof; And / or, the cross-linking agent includes any one or a combination of at least two of tannic acid, citric acid, oxalic acid, gallic acid, ascorbic acid, cyanuric acid, caffeic acid, succinic acid, humic acid or starch, preferably tannic acid.

3. The preparation method according to claim 2, characterized in that The mixing molar ratio of the carbon precursor and the cross-linking agent is (1-9):1; And / or, the total concentration of solutes in the precursor solution is 1-10 mol / L.

4. The preparation method according to claim 3, characterized in that The pre-crosslinking comprises: subjecting the precursor solution to a reflux reaction and cooling the solution to obtain a pre-crosslinking solution; Wherein, the temperature of the reflux reaction is 80-85°C; And / or, the reflux reaction time is 6-12 hours.

5. The preparation method according to claim 4, characterized in that The curing comprises: curing the pre-crosslinking solution to obtain a cured precursor; Wherein, the curing treatment method includes any one of air drying, vacuum drying, freeze drying or spray drying, or a combination of at least two thereof; And / or, the curing temperature is 180-200°C; And / or, the curing treatment time is 20-24 hours.

6. The preparation method according to claim 5, characterized in that The oxidation comprises: placing the curing precursor in an oxygen-containing atmosphere for crosslinking and partial carbonization to obtain an oxidation product; Wherein, the oxygen-containing atmosphere includes oxygen and / or ozone; and / or, the temperature of the cross-linking and partial carbonization is 150-360° C.; and / or, the heating rate of the cross-linking and partial carbonization is 0.5-10° C. / min; And / or, the heat preservation time of the cross-linking and partial carbonization is 0.5-24h.

7. The preparation method according to claim 6, characterized in that The pyrolysis comprises: placing the oxidation product in an inert atmosphere for high-temperature pyrolysis to obtain a hard carbon material; Wherein, the inert atmosphere includes any one of nitrogen, argon or helium, or a combination of at least two; and / or, the temperature of the high temperature pyrolysis is 1000-1600° C.; and / or, the heating rate of the high temperature pyrolysis is 0.5-10° C. / min; And / or, the holding time of the high-temperature pyrolysis is 0.5-24h.

8. The preparation method according to any one of claims 1 to 7, characterized in that The preparation method comprises the following steps: (1) Solution preparation: mixing a carbon precursor, a crosslinking agent, and deionized water to obtain a precursor solution with a total concentration of 1-10 mol / L; wherein the carbon precursor is cyclodextrin and / or phenolic resin, the crosslinking agent is tannic acid, and the mixing molar ratio of the carbon precursor to the crosslinking agent is (1-9):1; (2) Pre-crosslinking: reflux the precursor solution at 80-85°C for 6-12 hours, and then cool it to obtain a pre-crosslinking solution; (3) Curing: Curing the pre-crosslinked solution at 180-200° C. for 20-24 hours to obtain a cured precursor; wherein the curing treatment method includes any one of forced air drying, vacuum drying, freeze drying or spray drying, or a combination of at least two thereof; (4) Oxidation: placing the curing precursor in an oxygen-containing atmosphere, heating it to 150-360°C at a rate of 0.5-10°C / min for crosslinking and partial carbonization for 0.5-24 hours to obtain an oxidized product; wherein the oxygen-containing atmosphere includes oxygen and / or ozone; (5) Pyrolysis: The oxidation product is placed in an inert atmosphere, heated to 1000-1600°C at a rate of 0.5-10°C / min, and subjected to high-temperature pyrolysis for 0.5-24 hours to obtain a hard carbon material; wherein the inert atmosphere comprises any one of nitrogen, argon, or helium, or a combination of at least two of them.

9. A highly cross-linked closed-cell hard carbon material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The carbon layer spacing of the highly cross-linked closed-pore hard carbon material is greater than 0.37 nm, the average pore diameter is 0.9-1.2 nm, and the specific surface area is 78-435 m 2 / g.

10. An application of the highly cross-linked closed-cell hard carbon material according to claim 9, characterized in that: The highly cross-linked closed-pore hard carbon material is used as a negative electrode material for sodium ion batteries.

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