Hard carbon-based negative electrode material and preparation method and application thereof

Abstract

The application discloses a hard carbon-based negative electrode material and a preparation method and application thereof. The hard carbon-based negative electrode material is composed of hard carbon and at least one layer of soft carbon deposited at a closed pore, and the hard carbon has abundant closed pore structures with large diameters. The hard carbon-based negative electrode material is prepared by using commercialized biomass carbon and aromatic organic acid as precursors and through simple heat treatment. The hard carbon-based negative electrode material can be used for a sodium ion battery negative electrode material, and can realize optimization balance of capacity, coulomb efficiency and cycle life. The hard carbon-based negative electrode material is prepared by using cheap raw materials and a simple method, and has the advantages of low energy consumption, low cost, short cycle and the like, and is beneficial to large-scale production.

Description

TECHNICAL FIELD

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

[0002] With the rapid advancement of the "double carbon" goal, it is necessary to develop clean and sustainable energy such as solar energy and wind energy. In order to solve the shortcomings of unstable clean energy, corresponding energy storage batteries need to be configured. Although lithium ion batteries have the advantages of high energy density and mature technology, they face challenges such as resource shortage, high price, and safety hazards in large-scale energy storage. In contrast, sodium ion batteries have the advantages of abundant resources, low cost, and high safety, and are very suitable for large-scale energy storage applications. At present, sodium ion batteries mainly use hard carbon or soft carbon-based negative electrode materials. This type of negative electrode follows the sodium storage mechanisms of adsorption, intercalation, and pore filling. The pore filling mechanism contributes to storing more sodium and thus contributes to higher capacity. Pore formation on carbon materials is considered an effective method to improve capacity. However, it is still a great challenge to controllably form appropriate pore structures, especially closed pore structures. SUMMARY

[0003] To solve the above-mentioned technical problems, the present application provides a hard carbon-based negative electrode material composed of hard carbon and at least one layer of soft carbon at the closed pores of the hard carbon. The hard carbon-based negative electrode material has a rich closed pore structure, and the average diameter of the closed pores is 4.5-5.5 nm. When used as a negative electrode for sodium ion batteries, it can significantly improve the specific capacity and the first coulombic efficiency. The average diameter is about 5 nm.

[0004] The technical solution adopted by the present application is that aromatic organic acids are thermally decomposed at low temperatures to form water vapor and carbon dioxide, effectively expand the pores and activate the biomass carbon at medium temperatures, and the deposited soft carbon at high temperatures closes the large pores to form a closed pore structure, achieving the dual effects of increasing the pore size of biomass hard carbon and closing the pores, thereby improving the specific capacity and the first coulombic efficiency.

[0005] The present application also discloses a preparation method of the hard carbon-based negative electrode material, which comprises the following steps:

[0006] 1) Dissolve the aromatic acid in an organic solvent to obtain a solution of the aromatic acid;

[0007] 2) Place the biomass carbon in a high-temperature atmosphere reactor;

[0008] 3) Introduce an inert gas into the high-temperature atmosphere reactor through the aromatic acid solution;

[0009] 4) Perform three-step heating and holding treatment on the high-temperature atmosphere reactor, and finally reduce it to room temperature to obtain the hard carbon-based negative electrode material.

[0010] In step 1),

[0011] As a preferred, the aromatic organic acid is selected from, but not limited to, benzoic acid, p-methyl benzoic acid, phenylacetic acid, terephthalic acid, phthalic acid, isophthalic acid, m-benzene diacetic acid, which can produce water vapor, carbon dioxide and benzene ring at low temperature thermal decomposition, wherein water vapor and carbon dioxide can be activated and pore expansion at medium temperature, and benzene ring can be pyrolyzed to form soft carbon at high temperature, which can close the pores and form closed structure.

[0012] As a preferred, the organic solvent is selected from, but not limited to, methanol, ethanol, diethyl ether, chloroform, benzene, which can dissolve aromatic organic acid, and more preferably, ethanol is selected as the solvent, which can reduce cost and reduce environmental pollution.

[0013] The molar concentration of the aromatic acid solution is 0.1-1 mol / L, which can effectively activate and close the pores of the biomass carbon under this condition.

[0014] In step 2),

[0015] As a preferred, the biomass carbon is selected from, but not limited to, walnut shell carbon, straw carbon, coconut shell carbon, corn cob carbon, bamboo carbon, charcoal, which is obtained by carbonizing, washing and other biomass such as walnut shell, straw, coconut shell as precursor, and has rich pore structure, but the pore size is generally small and is open structure.

[0016] The high-temperature atmosphere reactor is selected from, but not limited to, a tube furnace, a box furnace, a roller kiln, a rotary kiln, and a fluidized bed, which has the dual functions of heating and atmosphere protection.

[0017] In step 3),

[0018] As a preferred, the inert gas is argon, nitrogen, helium or a mixture thereof, and the gas flow rate is 50-200 cm 3 / minute. Under this condition, the inert gas can effectively introduce the aromatic organic acid into the high-temperature atmosphere reactor while avoiding the oxygen in the air from entering the reaction container.

[0019] In step 4),

[0020] As a preferred, in the first step of heat treatment, the temperature is raised to 300-400℃ at a rate of 1-3℃ / min, and the temperature is kept for 2-4 hours. Under this condition, the aromatic acid is effectively decomposed to produce water vapor and carbon dioxide, which provides activated gas, but the main benzene ring of the aromatic does not pyrolyze, but is adsorbed by the biomass carbon.

[0021] As preferred, in the second step of heat treatment, first, based on the temperature of the first step of heat preservation, the temperature is raised to 700-900 DEG C at a heating rate of 5-10 DEG C / min, and the temperature is kept for 0.5-2 hours, under this condition, water vapor, carbon dioxide and biomass carbon react as follows: CO2+C→2CO, H2O+C→CO+H2, that is, by consuming biomass carbon, its pore expansion and activation are realized.

[0022] As preferred, in the third step of heat treatment, first, based on the temperature of the second step of heat preservation, the temperature is raised to 1100-1400 DEG C at a heating rate of 2-5 DEG C / min, and the temperature is kept for 1-4 hours, under this condition, the expanded biomass carbon is deeply carbonized, and the benzene ring obtained in the first step of heat treatment is sufficiently pyrolyzed, at least one soft carbon is deposited in the opening of the hard carbon, and a hard carbon-based negative electrode material rich in closed pore structure is formed.

[0023] In the present application, the soft carbon refers to graphitizable carbon, which has the advantages of good conductivity and relatively loose stacking, and can realize the rapid deintercalation of sodium ions, but its own capacity is low; the hard carbon refers to non-graphitizable carbon, which has poor conductivity, and its capacity and pore structure, especially the closed pore structure, are closely related. In the present application, the combination of the two can realize high conductivity and high capacity of the hard carbon-based negative electrode material.

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

[0025] 1. The present application uses cheap biomass carbon and aromatic organic acid raw materials to prepare a hard carbon-based negative electrode material by a simple method, which is low in energy consumption, low in cost, short in cycle, and conducive to large-scale production.

[0026] 2. The hard carbon-based negative electrode material prepared by the present application has a rich porous structure and large pore size, which is conducive to realizing high specific capacity, high initial coulombic efficiency and excellent cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The X-ray diffraction pattern (XRD) of the hard carbon-based negative electrode material prepared in Example 1 of the present application;

[0028] Figure 2 The transmission electron microscope photo (TEM) of the hard carbon-based negative electrode material prepared in Example 1 of the present application;

[0029] Figure 3 The charge-discharge curve of the hard carbon-based negative electrode material prepared in Example 1 of the present application;

[0030] Figure 4 The cycle life graph of the hard carbon-based negative electrode material prepared in Example 1 of the present application;

[0031] Figure 5 Charge-discharge curve of the hard carbon material prepared for Comparative Example 1. DETAILED DESCRIPTION

[0032] The application will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] Benzoic acid was dissolved in ethanol to prepare a 100ml benzoic acid solution with a concentration of 0.1mol / L. 1g of commercial bamboo charcoal was placed in a tube furnace, and Ar gas was passed into the tube furnace through the benzoic acid solution, with an argon flow rate of 100ml / min. After 30 minutes of aeration, the temperature was raised to 300°C at a rate of 2°C / min, and the temperature was maintained at this temperature for 3 hours. Then the temperature was raised to 800°C at a rate of 5°C / min, and the temperature was maintained at this temperature for 1 hour. Finally, the temperature was raised to 1300°C at a rate of 4°C / min, and the temperature was maintained at this temperature for 2 hours, to obtain a hard carbon-based negative electrode material for sodium batteries. The obtained material was analyzed by XRD and was a hard carbon material, as shown in Figure 1 . TEM analysis showed that the product was rich in closed pore structure, and soft carbon participated in the formation of the closed pore structure, with an average pore diameter of 4.5nm-5.5nm, and an average pore diameter of about 5nm, as shown in Figure 2 .

[0035] The hard carbon-based negative electrode material prepared in this example was used as the working electrode, metal sodium was used as the counter electrode, glass fiber membrane was used as the separator, and 1M NaPF6 propylene carbonate (PC) / ethyl methyl carbonate (EMC) solution was used as the electrolyte, to perform charge-discharge tests (current density 30mA / g, voltage range 0.005-2V), and the charge-discharge curve is shown in Figure 3 . As can be seen from the figure, the first charge capacity can reach 353mAh / g, the first library efficiency is 91.3%, and after 50 cycles, the capacity retention rate is 95.7%.

[0036] Example 2

[0037] Phenylacetic acid was dissolved in ethanol to prepare 100 ml of 0.1 mol / L phenylacetic acid solution, 1 g of commercial charcoal was placed in a tube furnace, and Ar gas was passed into the tube furnace through the phenylacetic acid solution, with an argon flow rate of 100 ml / min. After 30 minutes of aeration, the temperature was first raised to 400°C at a rate of 1°C / min, and then kept at this temperature for 2 hours; then the temperature was raised to 700°C at a rate of 8°C / min, and kept at this temperature for 2 hours; finally, the temperature was raised to 1200°C at a rate of 2°C / min, and kept at this temperature for 3 hours, to obtain a hard carbon-based negative electrode material. The obtained material was analyzed by XRD to be a hard carbon material, and by TEM analysis, the product was rich in closed pore structure, and soft carbon participated in the formation of the closed pore structure, with an average pore diameter of about 5 nm. By the same test method as in Example 1, the first charge capacity was 350 mAh / g, the first library efficiency was 90.5%, and after 50 cycles, the capacity retention rate was 94.6%.

[0038] Example 3

[0039] p-Toluic acid was dissolved in ethanol to prepare 100 ml of 0.1 mol / L p-toluic acid solution, 1 g of commercial charcoal was placed in a tube furnace, and Ar gas was passed into the tube furnace through the p-toluic acid solution, with an argon flow rate of 100 ml / min. After 30 minutes of aeration, the temperature was first raised to 350°C at a rate of 3°C / min, and then kept at this temperature for 2 hours; then the temperature was raised to 900°C at a rate of 10°C / min, and kept at this temperature for 0.5 hours; finally, the temperature was raised to 1400°C at a rate of 5°C / min, and kept at this temperature for 1 hour, to obtain a hard carbon-based negative electrode material. The obtained material was analyzed by XRD to be a hard carbon material, and by TEM analysis, the product was rich in closed pore structure and soft carbon participated in the formation of the closed pore structure, with an average pore diameter of about 5 nm. By the same test method as in Example 1, the first charge capacity was 355 mAh / g, the first library efficiency was 90.7%, and after 50 cycles, the capacity retention rate was 93.9%.

[0040] Example 4

[0041] Phthalic acid was dissolved in ethanol to prepare 100 ml phthalic acid solution with concentration of 0.1 mol / L. 1 g commercialized coconut shell charcoal was placed in a tube furnace, and Ar gas was passed into the tube furnace through the phthalic acid solution, with a flow rate of 100 ml / min. After 30 minutes of aeration, the temperature was raised to 300 °C at a rate of 2 °C / min, and the temperature was maintained at 300 °C for 4 hours. Then the temperature was raised to 800 °C at a rate of 7 °C / min, and the temperature was maintained at 800 °C for 1 hour. Finally, the temperature was raised to 1100 °C at a rate of 3 °C / min, and the temperature was maintained at 1100 °C for 4 hours to obtain the hard carbon-based negative electrode material. The obtained material was analyzed by XRD and was a hard carbon material. TEM analysis showed that the product was rich in closed pore structure and soft carbon participated in the formation of the closed pore structure, with an average pore diameter of about 2 nm. The same test method as in Example 1 was used, and the results showed that the first charge capacity was 349 mAh / g, the first library efficiency was 92.0%, and the capacity retention rate was 95.1% after 50 cycles.

[0042] Comparative Example 1

[0043] The preparation process of the hard carbon-based negative electrode material was the same as in Example 1, except that the Ar gas did not pass through the benzoic acid solution. In this case, the bamboo charcoal was not activated, and TEM detection showed that no closed pore structure and soft carbon layer were formed. The electrochemical test conditions were the same as in Example 1, and the test results showed that the first charge capacity was 275 mAh / g, and the first library efficiency was 76.3%.

[0044] Comparative Example 2

[0045] The preparation process of the hard carbon-based negative electrode material was the same as in Example 1, except that the Ar gas passed through the benzene solution instead of the benzoic acid solution. In this case, the bamboo charcoal was not activated, and TEM detection showed that a closed pore structure and soft carbon layer were formed, but the pore diameter was less than 2 nm. The electrochemical test conditions were the same as in Example 1, and the test results showed that the first charge capacity was 290 mAh / g, and the first library efficiency was 79.1%.

[0046] Comparative Example 3

[0047] The preparation process of the hard carbon-based negative electrode material was the same as in Example 1, except that the temperature during the first step of heat treatment was 250 °C. In this case, the benzoic acid was not fully decomposed, and water vapor and carbon dioxide were not fully released, so the bamboo charcoal was not fully activated, and the closed pore structure was not perfect. The electrochemical test conditions were the same as in Example 1, and the test results showed that the first charge capacity was 295 mAh / g, and the first library efficiency was 81.6%.

[0048] Comparative Example 4

[0049] The preparation process of the hard carbon-based negative electrode material is the same as that of Example 1, except that the holding time during the first heat treatment is 1 hour, at which time the benzoic acid does not sufficiently release water vapor and carbon dioxide, and the bamboo charcoal is not sufficiently activated. The electrochemical test conditions are the same as those of Example 1, and the test results show that the first charge capacity is 289 mAh / g, and the first library efficiency is 83.4%.

[0050] Comparative Example 5

[0051] The preparation process of the hard carbon-based negative electrode material is the same as that of Example 1, except that the heating rate during the first heat treatment is 5°C / min, at which time the benzoic acid does not sufficiently release water vapor and carbon dioxide during the holding time, and the bamboo charcoal is not sufficiently activated. The electrochemical test conditions are the same as those of Example 1, and the test results show that the first charge capacity is 300 mAh / g, and the first library efficiency is 85.0%.

[0052] Comparative Example 6

[0053] The preparation process of the hard carbon-based negative electrode material is the same as that of Example 1, except that the holding temperature during the second heat treatment is 600°C, at which time the water vapor and carbon dioxide do not easily react with the biomass charcoal, and the bamboo charcoal is not sufficiently activated. The electrochemical test conditions are the same as those of Example 1, and the test results show that the first charge capacity is 284 mAh / g, and the first library efficiency is 83.5%.

[0054] Comparative Example 7

[0055] The preparation process of the hard carbon-based negative electrode material is the same as that of Example 1, except that the holding time during the second heat treatment is 10 minutes, at which time the water vapor and carbon dioxide do not easily react with the biomass charcoal, and the bamboo charcoal is not sufficiently activated. The electrochemical test conditions are the same as those of Example 1, and the test results show that the first charge capacity is 292 mAh / g, and the first library efficiency is 82.9%.

[0056] Comparative Example 8

[0057] The preparation process of the hard carbon-based negative electrode material is the same as that of Example 1, except that the holding temperature during the third heat treatment is 1000°C, at which time the bamboo charcoal and the benzene ring are not sufficiently carbonized, and no closed pore structure is formed. The electrochemical test conditions are the same as those of Example 1, and the test results show that the first charge capacity is 281 mAh / g, and the first library efficiency is 78.9%.

[0058] Comparative Example 9

[0059] The preparation process of the hard carbon-based negative electrode material is the same as that of Example 1, except that the holding time during the third heat treatment is 0.5 hours, at which time the bamboo charcoal and the benzene ring are not sufficiently carbonized, and no closed pore structure is formed. The electrochemical test conditions are the same as those of Example 1, and the test results show that the first charge capacity is 279 mAh / g, and the first library efficiency is 80.3%.

Claims

1. A method for preparing a hard carbon-based negative electrode material, characterized by, The hard carbon-based negative electrode material is composed of hard carbon with closed pores and at least one layer of soft carbon at the closed pores, the hard carbon has abundant closed pore structure, and the average diameter of the closed pores is 4.5 nm to 5.5 nm; the preparation method comprises the following steps: 1) dissolving an aromatic acid in an organic solvent to obtain an aromatic acid solution; 2) placing biomass charcoal in a high-temperature atmosphere reactor; 3) introducing inert gas into the high-temperature atmosphere reactor through the aromatic acid solution; 4) performing three-step heating and heat treatment on the high-temperature atmosphere reactor, and finally reducing to room temperature to obtain the hard carbon-based negative electrode material; In step 1), the aromatic acid is selected from benzoic acid, p-methylbenzoic acid, phenylacetic acid, isophthalic acid and m-benzene diacetic acid; The organic solvent is selected from methanol, ethanol, diethyl ether, chloroform and benzene; The molar concentration of the aromatic acid solution is 0.1 to 1 mol / L; In step 2), the biomass charcoal is selected from walnut shell charcoal, straw charcoal, coconut shell charcoal, corn cob charcoal, bamboo charcoal and charcoal; In step 4), during the three-step heating and heat treatment process, the first-step heating rate is 1 to 3 ℃ / min, the heat treatment temperature is 300 to 400 ℃, and the heat treatment time is 2 to 4 hours; the second-step heating rate is 5 to 10 ℃ / min, the heat treatment temperature is 700 to 900 ℃, and the heat treatment time is 0.5 to 2 hours; the third-step heating rate is 2 to 5 ℃ / min, the heat treatment temperature is 1100 to 1400 ℃, and the heat treatment time is 1 to 4 hours.

2. The method for preparing the hard carbon-based anode material according to claim 1, characterized in that, In step 3), the inert gas is argon, nitrogen, helium or a mixture of the above gases; The gas flow rate is 50-200 cm 3 / minute.

3. Application of the hard carbon-based negative electrode material prepared by the preparation method of claim 1 in a sodium ion battery.

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