A high-capacity hard carbon material, and a preparation method and application thereof

Abstract

The application discloses a high-capacity hard carbon material and a preparation method and application thereof. The hard carbon material is obtained through the pore expanding effect of carbon dioxide and water vapor, and further pore expanding and catalysis of zinc oxide, and has rich closed pore structure and large carbon layer spacing. The obtained hard carbon material is used as a negative electrode of a sodium ion battery, and high capacity and high initial coulomb efficiency can be realized. The hard carbon is prepared by using cheap raw materials and a simple method, and has low energy consumption, low cost, short cycle and is beneficial to large-scale production.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of energy storage batteries, in particular to a high-capacity hard carbon material and a preparation method and application thereof. BACKGROUND

[0002] To achieve the "double carbon" goal, sustainable energy such as solar energy and wind energy needs to be developed. Due to the intermittency and instability of sustainable energy, low-cost and reliable energy storage batteries need to be configured. Sodium ion batteries have the advantages of abundant resources, good safety and low cost, and are suitable for large-scale energy storage. Similar to lithium ion batteries, sodium ion batteries are mainly composed of a positive electrode, a negative electrode, a separator and an electrolyte, but the positive and negative electrode material systems are different from those of current lithium ion batteries. Commercial lithium ion batteries generally use graphite as the negative electrode, but the radius of sodium ions is larger and they are not wet with the graphite layer, resulting in very low sodium storage capacity of graphite. Although hard carbon negative electrodes can store sodium, the capacity is low or the cost is high. Therefore, it is crucial to develop a high-capacity, low-cost sodium storage negative electrode. Biomass-based hard carbon has the advantages of low production cost, renewable resources and clean environmental protection, and is expected to be used on a large scale as a negative electrode for sodium ion batteries. The capacity of biomass hard carbon is closely related to its pore structure and carbon layer spacing, and obtaining a suitable closed pore structure and carbon layer spacing is the key to improving the specific capacity and reducing the first irreversible capacity. However, obtaining a controllable pore structure and carbon layer still faces great challenges. Therefore, the technical personnel in the field provide a high-capacity hard carbon material and a preparation method and application thereof to solve the problems raised in the above background. SUMMARY

[0003] The application aims to provide a high-capacity hard carbon material and a preparation method and application thereof to solve the problems raised in the above background.

[0004] To achieve the above-mentioned purpose, the application provides the following technical scheme:

[0005] A high-capacity hard carbon material, the hard carbon material has abundant closed pore structure and large interlayer spacing, the closed pore aperture is greater than 5 nm, and the interlayer spacing is greater than 0.39 nm. When the high-capacity hard carbon material is applied to a sodium ion battery, the sodium ion battery has high specific capacity and high first coulomb efficiency.

[0006] As a further scheme of the application, the basic zinc carbonate Zn5(CO3)2(OH)6 is in-situ grown in the pores of biomass carbon, the CO2 and H2O vapor decomposed by the basic zinc carbonate are expanded, and the ZnO is expanded and catalyzed, so that the pore diameter of the biomass hard carbon is further increased and closed, thereby the high specific capacity and first coulomb efficiency of the product are obtained.

[0007] The preparation method of the high-capacity hard carbon material comprises the following steps:

[0008] 1) dissolving a soluble zinc salt, sodium carbonate and a surfactant in deionized water to obtain a mixed solution;

[0009] 2) dispersing biomass charcoal in the above solution to obtain a dispersion liquid;

[0010] 3) transferring the above dispersion to a reaction kettle to perform hydrothermal reaction, growing basic zinc carbonate in the pore channels of the biomass charcoal;

[0011] 4) centrifuging and drying the biomass charcoal with adsorbed basic zinc carbonate, and then placing the biomass charcoal in a magnetic boat;

[0012] 5) placing the magnetic boat in an atmosphere furnace to perform two-step heat treatment, thereby obtaining the high-capacity hard carbon material.

[0013] As a further scheme of the present application: in step 1), the zinc salt is selected from zinc chloride, zinc nitrate, zinc sulfate or zinc acetate, and the concentration of the soluble zinc salt is 0.1-0.5 mol / L;

[0014] The concentration of the sodium carbonate is 0.1-0.5 mol / L;

[0015] The surfactant is selected from sodium citrate, sodium ethylenediaminetetraacetate, sodium dodecylbenzenesulfonate or sodium succinate sulfonate, and the number of moles of the surfactant is 4-8 times the number of moles of the soluble zinc salt, and more preferably, the surfactant is selected from sodium citrate.

[0016] Under this condition, the fine-grained basic zinc carbonate can be uniformly filled in the pore channels of the biomass charcoal without forming large-size basic zinc carbonate precipitates through hydrothermal reaction.

[0017] As a further scheme of the present application: in step 2), the biomass charcoal is selected from charcoal, coconut shell charcoal, bamboo charcoal, walnut shell charcoal, straw charcoal or corn cob charcoal, and the biomass charcoal has a rich pore structure;

[0018] The weight ratio of the biomass charcoal to the basic zinc carbonate is 10-50:1, and the weight of the basic zinc carbonate is its theoretical weight, and under this condition, the basic zinc carbonate obtained through hydrothermal reaction can be fully filled in the pore channels of the biomass charcoal, thereby fully activating the biomass charcoal through pore expansion during the heat treatment process and forming a closed pore structure.

[0019] As a further scheme of the present application: in step 3), the temperature of the hydrothermal reaction is 120-180°C, and the reaction time is 5-15 hours, and under this condition, the fine-grained basic zinc carbonate can be uniformly filled in the pore channels of the biomass charcoal without forming large-size basic zinc carbonate precipitates in combination with the use of the precursor concentration and the surfactant.

[0020] As a further scheme of the present application: in step 5), the biomass char with basic zinc carbonate deposited in the pore is subjected to heat treatment, on the one hand, the basic zinc carbonate pyrolysis product is used to activate the biomass char, on the other hand, the biomass char is converted into biomass hard carbon by heat treatment, and the carbon layer spacing is expanded and the inner pore is closed.

[0021] Two-step heat treatment is carried out:

[0022] The first step heat treatment has a heating rate of 1-3 ℃ / min, a heat treatment temperature of 750-850 ℃, and a heat treatment time of 1-2 hours. Under the above conditions, the basic zinc carbonate is decomposed into ZnO, carbon dioxide and water vapor. The carbon dioxide and water vapor activate the biomass char, and the mechanism is: CO2+C→2CO, H2O+C→CO+H2. In the process, carbon can be consumed to achieve the purpose of pore expansion. At the same time, H2 and CO can play a reducing role to eliminate the oxygen-containing functional groups on the surface of the biomass char, thereby improving the first specific capacity. As a preferred embodiment, the heat treatment step is carried out in a closed condition.

[0023] The second step heat treatment has a heating rate of 3-6 ℃ / min, a heat treatment temperature of 1200-1400 ℃, and a heat treatment time of 2-4 hours. Under the above conditions, ZnO and hard carbon react to form CO and Zn. In the process, carbon can be consumed to achieve the purpose of further pore expansion. At the same time, Zn plays a catalytic role to facilitate the formation of a closed pore structure. In addition, under the above conditions, Zn is converted into zinc vapor, which can be slowly volatilized and removed without introducing Zn impurities. As a preferred embodiment, the heat treatment step is carried out in an inert atmosphere selected from nitrogen, argon or helium.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1. The present application uses inexpensive biomass char raw materials and a simple method to prepare hard carbon materials, which has low energy consumption, low cost, short cycle, and is conducive to large-scale production.

[0026] 2. The hard carbon material prepared by the present application has a rich closed pore structure, large interlayer spacing, and low oxygen-containing functional groups, which is conducive to achieving high specific capacity, high first coulombic efficiency, and excellent cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The X-ray diffraction pattern (XRD) of the hard carbon material prepared in Example 1 of the present application is shown in the following figure:

[0028] Figure 2 The transmission electron microscope (TEM) photo of the hard carbon material prepared in Example 1 of the present application is shown in the following figure:

[0029] Figure 3 Charge-discharge curve of the hard carbon prepared in the preparation case 1 of the present application;

[0030] Figure 4 TEM photo of the hard carbon prepared in the comparative example 1;

[0031] Figure 5 Charge-discharge curve of the hard carbon material prepared in the comparative example 1. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0033] Please refer to Figures 1 to 5 In the embodiments of the present application, a high-capacity hard carbon material and a preparation method and application thereof are provided. The high-capacity hard carbon material has abundant closed pore structure and large interlayer spacing, and the closed pore size is greater than 5 nm and the interlayer spacing is greater than 0.39 nm.

[0034] The preparation method of the high-capacity hard carbon material includes the following steps:

[0035] 1) Dissolving a soluble zinc salt, sodium carbonate and a surfactant in deionized water to obtain a mixed solution;

[0036] 2) Dispersing biomass charcoal in the above solution to obtain a dispersion;

[0037] 3) Transferring the above dispersion to a reaction kettle to perform hydrothermal reaction, and growing basic zinc carbonate in the pore channel of the biomass charcoal;

[0038] 4) Centrifuging and drying the biomass charcoal adsorbed with the basic zinc carbonate, and then placing the biomass charcoal in a magnetic boat;

[0039] 5) Placing the magnetic boat in an atmosphere furnace to perform two-step heat treatment, and obtaining the high-capacity hard carbon material.

[0040] In step 1), the soluble zinc salt is selected from zinc chloride, zinc nitrate, zinc sulfate or zinc acetate, and the concentration of the zinc salt is 0.1-0.5 mol / L;

[0041] The concentration of the sodium carbonate is 0.1-0.5 mol / L;

[0042] The surfactant is selected from sodium citrate, sodium ethylenediaminetetraacetate, sodium dodecylbenzenesulfonate or sodium succinate sulfonate, and the number of moles of the surfactant is 4-8 times the number of moles of the soluble zinc salt.

[0043] In step 2), the biomass charcoal is selected from charcoal, coconut shell charcoal, bamboo charcoal, walnut shell charcoal, straw charcoal or corn cob charcoal; the weight ratio of the biomass charcoal to zinc carbonate hydroxide is 10-50:1.

[0044] In step 3), the temperature of the hydrothermal reaction is 120-180℃, and the reaction time is 5-15 hours.

[0045] In step 5), in the two-step heat treatment, the first-step heat treatment has a heating rate of 1-3℃ / min, a heat treatment temperature of 750-850℃, and a heat treatment time of 1-2 hours; the second-step heat treatment has a heating rate of 3-6℃ / min, a heat treatment temperature of 1200-1400℃, and a heat treatment time of 2-4 hours.

[0046] The high-capacity hard carbon material is applied to a sodium ion battery.

[0047] Preparation Case 1

[0048] ZnCl2 and Na2CO3 were dissolved in deionized water, with the concentrations of the two being 0.5 mol / L and 0.2 mol / L respectively, and then sodium citrate was added, with the molar amount of the sodium citrate being 4 times that of the ZnCl2, to obtain a mixed solution after sufficient stirring; bamboo charcoal was dispersed in the above solution to obtain a dispersion liquid, with the weight ratio of the bamboo charcoal to the theoretical weight of Zn5(CO3)2(OH)6 being 20:1; the dispersion liquid was transferred to a reaction kettle to perform a hydrothermal reaction, and the reaction was performed at 140℃ for 10 hours to obtain bamboo charcoal with Zn5(CO3)2(OH)6 grown in the pores, and then centrifugal separation, drying and placement in a magnetic boat were performed; the magnetic boat was placed in an atmosphere furnace to perform two-step heat treatment, and the high-capacity hard carbon material was obtained, wherein the heating rate in the first-step heat treatment was 2℃ / min, the heat treatment temperature was 800℃, and the heat treatment time was 1.5 hours; the heating rate in the second-step heat treatment was 4℃ / min, the heat treatment temperature was 1300℃, and the heat treatment time was 3 hours. XRD analysis showed that the product was a low-crystalline hard carbon material, as shown in Figure 1 . TEM analysis showed that the product was rich in closed-pore structure, with an average pore diameter of greater than 5.0 nm and an average interlayer distance of 0.393 nm, as shown in Figure 2 .

[0049] The hard carbon material prepared in this case was used as a working electrode, metal sodium was used as a counter electrode, a glass fiber membrane was used as a separator, and a 1 mol / L NaPF6 solution in diethylene glycol dimethyl ether was used as an electrolyte to perform constant-current charge and discharge tests, with the voltage range being 0.01-2V. The charge and discharge curves at 0.1C (30 mA / g) are shown in Figure 3 . As can be seen from the figure, the initial charge capacity can reach 351.3 mAh / g, and the initial capacity retention is 90.1%.

[0050] Preparation Case 2

[0051] ZnCl2and Na2CO3were dissolved in deionized water, with the concentration of 0.5 mol / L and 0.2 mol / L respectively, and then sodium citrate was added, with the molar amount of sodium citrate being 8 times of that of ZnCl2. After sufficient stirring, a mixed solution was obtained. Charcoal was dispersed in the above solution to obtain a dispersion liquid, with the weight ratio of charcoal to the theoretical weight of Zn5(CO3)2(OH)6being 10:1. The dispersion liquid was transferred to a reaction kettle for hydrothermal reaction at 120°C for 15 hours, and then charcoal with Zn5(CO3)2(OH)6grown in the pores was obtained. Centrifugal separation and drying were performed, and then the charcoal was placed in a magnetic boat. The magnetic boat was placed in an atmosphere furnace, nitrogen was introduced, and two-step heat treatment was performed. The high-capacity hard carbon material was obtained, wherein the heating rate in the first step of heat treatment was 1°C / min, the heat treatment temperature was 750°C, and the heat treatment time was 2 hours. The heating rate in the second step of heat treatment was 3°C / min, the heat treatment temperature was 1200°C, and the heat treatment time was 4 hours. XRD analysis showed that the hard carbon material was low crystalline. TEM analysis showed that the product was rich in closed pore structure, with an average pore diameter of more than 5.0 nm and an average carbon layer spacing of 0.396 nm. According to the same test method as in Example 1, the 0.1C initial charge capacity was 353.8 mAh / g, and the initial coulombic efficiency was 89.5%.

[0052] Preparation Case 3

[0053] ZnCl2 and Na2CO3 were dissolved in deionized water, with concentrations of 0.5 mol / L and 0.2 mol / L, respectively, and then sodium citrate was added, with a molar amount of 6 times that of ZnCl2. After stirring, a mixed solution was obtained. Coconut shell carbon was dispersed in the above solution to obtain a dispersion liquid, with a weight ratio of coconut shell carbon to theoretical weight of Zn5(CO3)2(OH)6 of 50:1. The dispersion liquid was transferred to a reaction kettle for hydrothermal reaction at 180°C for 5 hours. The coconut shell carbon with Zn5(CO3)2(OH)6 grown in the pores was obtained, and then subjected to centrifugal separation, drying, and placement in a magnetic boat. The magnetic boat was placed in an atmosphere furnace, and nitrogen was introduced for two-step heat treatment. The first-step heat treatment was performed at a heating rate of 3°C / min, a heat treatment temperature of 850°C, and a heat treatment time of 2 hours. The second-step heat treatment was performed at a heating rate of 6°C / min, a heat treatment temperature of 1400°C, and a heat treatment time of 2 hours. XRD analysis showed that the product was a low-crystalline hard carbon material. TEM analysis showed that the product was rich in closed pore structure, with an average pore diameter of greater than 5.0 nm and an average carbon layer spacing of 0.391 nm. The same test method as in Example 1 was used, and the 0.1C first charge capacity was 355.6 mAh / g, and the first capacity retention was 90.7%.

[0054] Comparative Example 1

[0055] The hard carbon was prepared according to the preparation method of Example 1, except that no Zn5(CO3)2(OH)6 was grown in the pores of the bamboo carbon. TEM analysis showed that no closed pore structure was formed in the product, and the average carbon layer spacing was 0.373 nm, as shown in FIG. 2. Figure 4 The electrochemical test conditions were the same as in Example 1, and the test results showed that the 0.1C first charge capacity was 288.4 mAh / g, and the first capacity retention was 81.9%, as shown in FIG. 3. Figure 5

[0056] Comparative Example 2

[0057] The hard carbon was prepared according to the preparation method of Example 1, except that no Zn5(CO3)2(OH)6 was grown in the pores of the bamboo carbon, and basic magnesium carbonate Mg2CO3(OH)2 was grown instead, i.e., ZnCl2 in the raw material was replaced by MgCl2. The concentrations of MgCl2 and Na2CO3 were 0.5 mol / L and 0.2 mol / L, respectively. TEM analysis showed that no closed pore structure was formed in the product, and the average carbon layer spacing was 0.381 nm.

[0058] Comparative Example 3

[0059] ​The preparation of the hard carbon is the same as that of the preparation example 1, except that no sodium citrate is added in the hydrothermal process, and Zn5(CO3)1(OH)6 is not grown in the pore of the bamboo charcoal, but is separated from the bamboo charcoal in the form of large particles, and other conditions are not changed. The TEM detection shows that no closed pore structure is formed in the product.

[0060] Comparative example 4

[0061] The preparation of the hard carbon is the same as that of the preparation example 1, except that the first step of heat treatment is at 650℃, and other conditions are not changed. At this time, the bamboo charcoal is not fully activated, and the TEM detection shows that no closed pore structure is formed in the product.

[0062] Comparative example 5

[0063] The preparation of the hard carbon is the same as that of the preparation example 1, except that the first step of heat treatment is at 900℃, and other conditions are not changed. At this time, the bamboo charcoal is over-activated, and the TEM detection shows that no closed pore structure is formed in the product.

[0064] Comparative example 6

[0065] The preparation of the hard carbon is the same as that of the preparation example 1, except that the second step of heat treatment is at 1100℃, and other conditions are not changed. At this time, the bamboo charcoal is not fully carbonized, and the TEM detection shows that no closed pore structure is formed in the product.

[0066] Comparative example 7

[0067] The preparation of the hard carbon is the same as that of the preparation example 1, except that the second step of heat treatment is at 1500℃, and other conditions are not changed. At this time, the bamboo charcoal is contracted at high temperature, and the TEM detection shows that no closed pore structure is formed in the product.

[0068] The above only describes the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes to the technical solutions and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for preparing high-capacity hard carbon materials, characterized in that, 1) Dissolve soluble zinc salt, sodium carbonate, and surfactant in deionized water to obtain a mixed solution; 2) Disperse the biochar in the above solution to obtain a dispersion; 3) The above dispersion is transferred to a reactor for hydrothermal reaction to grow basic zinc carbonate in the biochar channels; 4) The biochar adsorbed with basic zinc carbonate is centrifuged, dried, and then placed in a magnetic boat; 5) The magnetic boat is placed in an atmosphere furnace for two-step heat treatment to obtain the high-capacity hard carbon material. The number of moles of the surfactant is 4 to 8 times the number of moles of the soluble zinc salt; The weight ratio of biochar to basic zinc carbonate is 10~50:1; In step 3), the temperature of the hydrothermal reaction is 120~180℃, and the reaction time is 5~15 hours; In step 5), the two-step heat treatment process is as follows: the first heat treatment has a heating rate of 1~3℃ / min, a heat treatment temperature of 750~850℃, and a heat treatment time of 1~2 hours; the second heat treatment has a heating rate of 3~6℃ / min, a heat treatment temperature of 1200~1400℃, and a heat treatment time of 2~4 hours.

2. The method for preparing high-capacity hard carbon material according to claim 1, characterized in that, In step 1), the soluble zinc salt is selected from zinc chloride, zinc nitrate, zinc sulfate, or zinc acetate, and the concentration of the zinc salt is 0.1~0.5 mol / L; the concentration of the sodium carbonate is 0.1~0.5 mol / L; and the surfactant is selected from sodium citrate, sodium ethylenediaminetetraacetate, sodium dodecylbenzenesulfonate, or sodium succinate sulfonate.

3. The method for preparing high-capacity hard carbon material according to claim 1, characterized in that, In step 2), the biochar is selected from wood charcoal, coconut shell charcoal, bamboo charcoal, walnut shell charcoal, straw charcoal or corn cob charcoal.

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