Preparation and application of organic acid potassium derived hard carbon material

Abstract

The invention relates to the technical field of carbon materials and sodium-ion battery negative electrode materials, and provides a preparation method of an organic acid potassium derived hard carbon material and application of the organic acid potassium derived hard carbon material in a sodium-ion battery, and the preparation method comprises the following steps: carrying out high-temperature pre-carbonization treatment on organic acid potassium, and forming pores by utilizing a K2CO3 template formed in the pre-carbonization process and an activation effect, a graded pore structure is formed after washing and impurity removal, and then open pores are directly converted into closed pores through high-temperature carbonization treatment, so that the hard carbon negative electrode material with rich closed pore structures is obtained. According to the preparation method, pores are formed through a template of K2CO3 and an activation effect, and high-temperature secondary carbonization treatment is further combined, so that construction of a closed-pore structure can be effectively realized, and high platform sodium storage capacity is shown. The method disclosed by the invention is simple in preparation process and low in cost, does not need to add an additional activating agent, and has a good application and development prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrode materials, and in particular to a method for preparing a hard carbon material derived from an organic potassium acid and its application in a negative electrode of a sodium ion battery. Background Art

[0002] Sodium-ion batteries have the advantages of abundant resources, low cost, excellent low-temperature performance and fast charging capabilities, and show broad application potential in the field of large-scale energy storage. Hard carbon materials are widely available and have good structural stability. They are considered to be the most promising negative electrode materials for sodium-ion batteries for large-scale energy storage. Constructing a porous structure is the most commonly used method to regulate the structure of carbon materials. In hard carbon structures, nanopores usually exist in open or closed forms. Closed pores can effectively increase sodium storage sites, improve the sodium storage capacity and first coulombic efficiency of the platform area, and enhance cycle stability. Therefore, constructing carbon materials with a uniform and developed closed-pore structure is the core competitive technology for realizing the large-scale commercialization of sodium-ion batteries.

[0003] The existing methods for constructing closed-pore structures mainly involve first preparing open pores through alkali activation, chemical activation, CO2 activation, etc., and then converting the open pores into closed pores through vapor deposition coating (National Science Review, 2022, 9, nwac084) or high-temperature treatment (Advanced Energy Materials, 2024, 14, 2303064). However, disadvantages such as uneven coating, expensive activator cost, and complex post-activation treatment process have greatly limited large-scale applications.

[0004] Organic acid salts are compounds formed by ionic bonds between organic acid anions and metal cations. The organic acid can be pyrolyzed at high temperatures to form a carbon matrix. During this pyrolysis, the metal cations are in situ converted into metal oxide and carbonate nanoparticles, which are uniformly embedded in the carbon matrix and serve as a template. After the template is removed, a porous structure is formed. K2CO3 reacts with the carbon matrix at high temperatures, etching and activating it, forming a large number of micropores and mesopores.

[0005] Therefore, this patent utilizes the characteristics of high-temperature pyrolysis of organic potassium acid. First, K2CO3 generated during high-temperature pre-carbonization is used as a template and activator to form pores. After washing and removing impurities, high-temperature carbonization is performed to obtain a carbon negative electrode material with a rich closed-pore structure. Since closed pores can effectively increase the platform sodium storage capacity, the reversible specific capacity of the prepared carbon negative electrode material reaches 291.84 mAh g -1 The platform capacity is significantly increased to 177.06 mAh g -1 In addition, this method eliminates the step of adding an external activator, and the water washing waste liquid only contains K2CO3, which can be directly recycled and reused, has significant cost advantages, and shows good application prospects. Summary of the Invention

[0006] The present invention aims to provide a method for preparing a hard carbon material derived from an organic acid potassium and its application. The method has a simple process flow and low cost, and prepares a sodium ion battery negative electrode material with excellent sodium storage performance.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a hard carbon material derived from an organic acid potassium and its application, comprising the following steps:

[0009] (1) The organic acid potassium is subjected to high-temperature pre-carbonization treatment and water washing to remove impurities to form a hierarchical porous structure;

[0010] (2) The above product is subjected to a secondary high-temperature carbonization treatment to obtain a carbon material with a uniform and developed closed-pore structure.

[0011] The organic acid potassium salt can be selected from any one of potassium acetate, potassium citrate, potassium benzoate, and potassium stearate;

[0012] The temperature of the high temperature activation pretreatment is 500-800°C and the time is 0-2h;

[0013] Preferably, the heating rate for the high temperature activation pretreatment is 2-10°C / min;

[0014] The washing conditions are as follows: using deionized water, stirring mechanically at 200-400 rpm at 80-100°C for 4-6 hours, and then washing with deionized water until neutral;

[0015] The carbonization temperature of the product after water washing and impurity removal under inert atmosphere is 1300-1800° C., preferably 1500-1700° C., and the holding time is 1-3 hours.

[0016] The (002) interlayer spacing of the organic acid potassium derived hard carbon material is 0.35-0.38 nm, and the specific surface area is 5-50 m 2 g -1 .

[0017] The organic potassium acid-derived hard carbon material is applied to the negative electrode material of sodium ion batteries.

[0018] The present invention provides a method for preparing a hard carbon material derived from potassium organic acid, comprising the following steps: performing a high-temperature pre-carbonization treatment on potassium organic acid under an inert atmosphere, during which the K2CO3 generated by pyrolysis simultaneously acts as a template and an activation agent to form mesopores and micropores, followed by a subsequent water washing treatment to remove K2CO3 to construct a hierarchical pore structure, and further undergoing a secondary high-temperature carbonization to form a hard carbon material with a uniform and developed closed-pore structure. Traditional organic acid salts, as hard carbon precursors, tend to form a pore structure dominated by mesopores and macropores during the pyrolysis process, while there is almost no closed-pore structure. This pore distribution is not conducive to the storage of sodium ions, resulting in low reversible specific capacity and initial coulombic efficiency of the material, as well as complex impurity removal processes during post-processing.

[0019] To address the problems of organic acid salt-based hard carbon materials, the present invention firstly significantly improves the disorder and specific surface area of the carbon material by using K2CO3 generated in the pre-carbonization treatment stage. After secondary high-temperature carbonization, the hard carbon material with a unique closed-pore structure has a reversible specific capacity of 291.84 mAh g at a current density of 0.1C. -1 , the platform capacity is increased to 177.06mAhg -1 .

[0020] The method of the present invention has a simple preparation process, realizes the development and utilization of low-cost organic acid potassium, and has good application development prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron microscope (SEM) image of the organic acid potassium derived hard carbon material prepared in Example 1 of the present invention;

[0022] Figure 2 This is an X-ray diffraction (XRD) pattern of the organic acid potassium derived hard carbon material prepared in Example 1 of the present invention;

[0023] Figure 3 This is a high-resolution transmission electron microscopy (HRTEM) image of the organic acid potassium-derived hard carbon material prepared in Example 1 of the present invention;

[0024] Figure 4 This is a scanning electron microscope (SEM) image of the organic acid potassium-derived activated carbon prepared in a comparative example of the present invention;

[0025] Figure 5 This is a high-resolution transmission electron microscopy (HRTEM) image of the organic acid potassium-derived activated carbon prepared in the comparative example of the present invention;

[0026] Figure 6 Isothermal adsorption curves of organic acid potassium derived activated carbon and organic acid potassium derived hard carbon material prepared in Comparative Example and Example 1 of the present invention;

[0027] Figure 7 The charge and discharge curves of the sodium ion battery prepared in Example 1 of the present invention in the 1st, 2nd and 3rd cycles are shown;

[0028] Figure 8 The charge and discharge curves of the sodium ion battery prepared in Example 2 of the present invention in the 1st, 2nd and 3rd cycles are shown;

[0029] Figure 9 The charge and discharge curves of the sodium ion battery prepared in Example 3 of the present invention in the 1st, 2nd and 3rd cycles are shown;

[0030] Figure 10 These are the charge and discharge curves of the 1st, 2nd and 3rd cycles of the sodium ion battery prepared in Example 4 of the present invention.

[0031] Figure 11 The charge and discharge curves of the sodium ion battery prepared in the comparative example of the present invention in the 1st, 2nd and 3rd cycles are shown; DETAILED DESCRIPTION

[0032] The technical solution provided by the present invention is further clearly and completely described below by way of specific embodiments.

[0033] The present invention provides a method for preparing a hard carbon material derived from an organic acid potassium, comprising the following steps:

[0034] (1) The organic acid potassium is subjected to high-temperature pre-carbonization treatment and water washing to remove impurities to obtain a hierarchical pore structure;

[0035] (2) The above materials are subjected to a secondary high-temperature carbonization treatment to obtain a hard carbon material with a uniform and developed closed-pore structure.

[0036] In the present invention, the organic acid potassium can be selected from any one of potassium acetate, potassium citrate, potassium benzoate and potassium stearate.

[0037] In the present invention, K2CO3 generated by the organic acid potassium during the high-temperature activation process activates the pyrolytic carbon to form a rich pore structure, thereby increasing the specific surface area and disorder of the material; the pre-carbonization temperature is preferably 500-1000°C, more preferably 600-800°C; the heating rate for heating to the pre-carbonization treatment is preferably 2-10°C / min; the time is preferably 0-2h; the high-temperature pre-carbonization treatment is carried out under an inert atmosphere; the high-temperature pre-carbonized product should be first washed with water and then washed to neutrality before drying; the washing conditions are to use deionized water and mechanically stir at 200-400rpm at 80-100°C for 4-6h; the secondary carbonization temperature is preferably 1300-1800°C, more preferably 1500-1700°C, and the holding time is 1-3h; the heating rate for heating to the high-temperature carbonization treatment temperature is 2-10°C / min; the atmosphere of the high-temperature carbonization treatment is an inert atmosphere. In the present invention, when the carbonization temperature and time are within the above ranges, a hard carbon material with a uniform, well-developed closed-pore structure can be obtained. The cooling, washing, filtration, and drying steps involved in the present invention are not particularly limited and can be performed using processes well known to those skilled in the art.

[0038] The present invention has no particular limitation on the application method of the organic acid potassium-derived hard carbon material, and any method for applying carbon materials in sodium ion battery negative electrode materials well known to those skilled in the art can be used.

[0039] The following detailed description of the method for preparing a potassium organic acid-derived hard carbon material provided by the present invention is provided in conjunction with examples. The examples described herein are merely partial embodiments of the present invention and do not encompass all embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on these partial embodiments without inventive effort are considered within the scope of protection of the present invention.

[0040] Example 1

[0041] (1) 5 g of potassium citrate was heated to 600°C at a heating rate of 5°C / min under argon atmosphere, kept at this temperature for 0 h, and cooled to obtain a mixed product;

[0042] (2) The mixed product in (1) was boiled and stirred in 150 mL of deionized water for 4-6 h. After cooling to room temperature, the mixed solution was vacuum filtered and then washed with deionized water until the solution was neutral. The product was dried in a conventional oven at 80°C for 12 h.

[0043] (3) The product obtained in (2) was subjected to secondary high-temperature carbonization under argon atmosphere protection, and the temperature was raised to 1500°C at a heating rate of 5°C / min, kept at this temperature for 2 hours, and cooled to obtain the potassium citrate-derived hard carbon material of Example 1;

[0044] The potassium citrate-derived hard carbon material in Example 1 was subjected to an electron microscope scanning test. The test results are as follows: Figure 1 The microstructure of the potassium citrate-derived hard carbon in Example 1 is composed of irregular block-shaped particles with a particle size of 2 to 10 μm.

[0045] The closed-cell hard carbon material in Example 1 was tested using an X-ray diffractometer to obtain an XRD pattern. Figure 2 The XRD pattern shows that the angle corresponding to the (002) peak is 24.79°, and the interplanar spacing calculated according to the Bragg formula is 0.3589 nm.

[0046] The hard carbon material prepared in Example 1 was subjected to high-resolution transmission electron microscopy scanning test, and the test results are as follows: Figure 3 As shown, the graphite lattice stripes of Example 1 are disordered and a large number of closed-pore structures are distributed.

[0047] Example 2

[0048] The pre-carbonization temperature in Example 1 was changed to 800° C., the secondary high-temperature carbonization temperature was changed to 1700° C., and the remaining technical features were the same as in Example 1 to obtain an organic acid potassium-derived hard carbon material.

[0049] Example 3

[0050] The potassium citrate in Example 1 was replaced by potassium benzoate, the pre-carbonization temperature was changed to 800° C., and the remaining technical features were the same as in Example 1 to obtain a potassium benzoate-derived hard carbon material.

[0051] Example 4

[0052] The potassium citrate in Example 1 was replaced by potassium stearate, and the remaining technical features were the same as those in Example 1 to obtain a potassium stearate-derived hard carbon material.

[0053] Comparative Example

[0054] (1) 5 g of potassium citrate was heated to 1500°C at a heating rate of 5°C / min under argon atmosphere, kept at this temperature for 2 h, and cooled to obtain a mixed product;

[0055] (2) The mixed product in (1) was boiled and stirred in 150 mL of deionized water for 4-6 h. After cooling to room temperature, the mixed solution was vacuum filtered and then washed with deionized water until the solution was neutral. The product was dried in a conventional oven at 80° C. for 12 h to obtain a potassium citrate-derived activated carbon material.

[0056] The potassium citrate-derived activated carbon in the comparative example was subjected to an electron microscope scanning test, and the test results are as follows: Figure 4The microscopic morphology of the potassium citrate activated carbon in Example 1 is composed of irregular block-shaped particles with a particle size of 1 to 2 μm, and a cavity structure formed by removing a large amount of K2CO3 on the surface.

[0057] The potassium citrate-derived activated carbon of the comparative example was subjected to high-resolution transmission electron microscopy scanning test, and the test results are as follows: Figure 5 As shown, the graphite lattice stripes of the comparative example are disordered, and a large number of micropores are distributed in the material, and most of the micropores are open-pore structures with a high degree of disorder.

[0058] The potassium citrate-derived activated carbon of the comparative example and the potassium citrate-derived hard carbon material of Example 1 were subjected to isothermal nitrogen adsorption tests. The test results are as follows: Figure 6 The specific surface area of the potassium citrate-derived activated carbon in the comparative example is 464.0 m 2 g -1 , the pore volume reaches 0.2794cm 3 g -1 , while the specific surface area of potassium citrate-derived hard carbon material is 36.7 m 2 g -1 , the pore volume is 0.0894cm 3 g -1 .

[0059] Test Example 1

[0060] The potassium organic acid-derived hard carbon materials prepared in the comparative example and Examples 1-4 were mixed with sodium carboxymethyl cellulose at a mass ratio of 95:5 to form a slurry. The slurry was evenly coated onto a current collector copper foil and dried in a 60°C oven for 2 hours before being cut into circular electrode pieces with a diameter of 8 mm. The electrode pieces were dried in a vacuum oven at 120°C for 10 hours, and the active material mass of the electrode pieces was weighed. The cells were then transferred to a glove box and assembled into CR2025 button cells using sodium metal as the counter electrode and a 1M NaClO₄ solution in ethylene carbonate and diethyl carbonate as the electrolyte.

[0061] The assembled CR2025 button battery was subjected to charge and discharge performance tests under the following conditions: the current density was set to 0.1C (1C = 300mA g -1 ); discharge to a cut-off voltage of 0.001V, and charge to a cut-off voltage of 3V.

[0062] Figure 7 The charge-discharge curves of the potassium citrate-derived hard carbon material prepared in Example 1 at the 1st, 2nd and 3rd cycles; Figure 7 It can be seen that the sodium storage capacity of the material described in Example 1 in the first week is 291.84 mA g -1 , the platform capacity is increased to 177.06mAh g -1 ;

[0063] Figure 8 The charge-discharge curves of the potassium citrate-derived hard carbon material prepared in Example 2 at the 1st, 2nd and 3rd cycles; Figure 8 It can be seen that the reversible specific capacity of the material described in Example 2 is 274.44 mAh g -1 , the platform capacity is 146.27mAh g -1 ;

[0064] Figure 9 The charge-discharge curves of the potassium benzoate-derived hard carbon material prepared in Example 3 at the 1st, 2nd and 3rd cycles; Figure 9 It can be seen that the reversible specific capacity of the material described in Example 3 is 278.04 mAh g -1 , the platform capacity is 167.38mAh g -1 ;

[0065] Figure 10 The charge-discharge curves of the potassium stearate-derived hard carbon material prepared in Example 4 at the 1st, 2nd and 3rd cycles; Figure 10 It can be seen that the reversible specific capacity of the material described in Example 4 is 258.08 mAh g -1 , the platform capacity is 155.84mAh g -1 ;

[0066] Figure 11 The charge-discharge curves of the material prepared in the comparative example at the 1st, 2nd and 3rd cycles; Figure 11 It can be seen that the reversible specific capacity of the material in the comparative example is 129.52 mAh g -1 , the first coulombic efficiency is 16.74%, and there is no platform capacity.

[0067] The electrochemical test performances of the organic acid potassium carbon materials of Examples 1-4 and the comparative example are summarized in Table 1 below.

[0068] Table 1 Electrochemical test performance of organic acid potassium carbon materials of implementation (comparison) examples 1-4

[0069]

[0070] The above experimental test results show that the organic acid potassium derived hard carbon material prepared by the present invention has excellent sodium storage capacity and platform capacity.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material derived from an organic acid potassium, characterized in that: The following steps are involved: (1) The organic acid potassium is pre-carbonized at high temperature under an inert atmosphere, and the K2CO3 formed during the pre-carbonization process is used as a template and activation to form pores, and then the K2CO3 is removed by water washing to construct a hierarchical pore structure; (2) The above product is subjected to a secondary high-temperature carbonization treatment to obtain an organic acid potassium-derived hard carbon material with a rich closed-pore structure.

2. The method according to claim 1, wherein The organic acid potassium in step (1) can be selected from any one of potassium acetate, potassium citrate, potassium benzoate and potassium stearate.

3. The method according to claim 1, wherein The pre-carbonization treatment in step (1) is carried out under an inert atmosphere with a heating rate of 2-10°C / min, a high-temperature pretreatment temperature of 500-800°C, and a constant temperature time of 0-2h. The gas of the inert atmosphere is any one of nitrogen, helium or argon, or a mixture of several thereof.

4. The method according to claim 1, wherein The conditions for washing in step (1) are to use deionized water, stir mechanically at 200-400 rpm at 80-100° C. for 4-6 hours, and then wash with deionized water until neutral.

5. The method according to claim 1, wherein In step (2), the high-temperature carbonization temperature is 1300-1800° C. under an inert atmosphere, and the constant temperature time is 1-3 hours. The gas of the inert atmosphere is any one of nitrogen, helium or argon, or a mixture of several of them.

6. The organic acid potassium derived hard carbon material prepared according to any one of claims 1 to 5, characterized in that The (002) interlayer spacing is 0.35-0.38 nm, and the specific surface area is 5-50 m 2 g -1 .

7. An application of a sodium ion battery, characterized in that: The organic potassium acid-derived hard carbon material according to claim 1 is used as a negative electrode material for sodium ion batteries.

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