Alkali metal salt doped carbon-coated hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention discloses an alkali metal salt doped carbon-coated hard carbon negative electrode material and a preparation method and application thereof. The preparation method comprises the following steps: (1) uniformly dispersing glucose, alkali metal salt and activated carbon into deionized water, and then putting a mixed solution into a reaction kettle for hydrothermal treatment; (2) carrying out vacuum filtration on the hydrothermal product obtained in the step (1), and then drying to obtain a hard carbon precursor; and transferring the hard carbon precursor into a tubular furnace, and carrying out high-temperature carbonization treatment in a nitrogen atmosphere to prepare the alkali metal salt doped carbon-coated hard carbon negative electrode material. The alkali metal salt doped carbon coated hard carbon negative electrode material has a low specific surface area and a large interlayer spacing, so that the irreversible consumption of an electrolyte is reduced, and the intercalation kinetics of sodium ions is improved. Therefore, the negative electrode material shows relatively high reversible capacity (310mAh / g) and first coulombic efficiency (82.3%) under low current density, and the capacity is still kept at about 75% after 1000 cycles under high current density.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials for sodium-ion batteries, and specifically relates to an alkali metal salt-doped carbon-coated hard carbon negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) dominate in the fields of portable devices and electric vehicles. However, due to the uneven geographical distribution and rising prices of lithium resources, they cannot meet the requirements of grid-scale energy storage. Sodium-ion batteries (SIBs) have received extensive attention in recent years because they have a working principle similar to that of lithium-ion batteries (LIBs). Sodium-ion batteries have advantages such as low cost and rich resources, and can be used as an effective supplement to lithium-ion batteries in applications such as electric vehicles, power energy storage, and other large-scale energy storage systems. From the perspective of the SIBs system, developing negative electrode materials with low cost and excellent performance is the key to realizing the commercial application of SIBs. However, due to inherent thermodynamic and kinetic limitations, commercial graphite anodes in LIBs cannot be used as anodes for SIBs. In contrast, hard carbon materials (HCs) are expected to become negative electrode materials for industrialized SIBs due to their unique microscopic morphology structure and stable electrochemical performance.

[0003] So far, researchers have made many attempts to improve the electrochemical performance of HCs, especially the capacity in the low-voltage plateau region and the initial Coulomb efficiency (ICE). The low-voltage discharge plateau of the hard carbon negative electrode is very important for achieving a high output voltage of the entire battery. In addition, sodium ion storage in the plateau region is considered to contribute more reversible specific capacity, resulting in a higher ICE value. Researchers generally believe that the plateau region is mainly affected by the closed pore structure or the layer spacing. Therefore, many studies mainly focus on the closed pore engineering of hard carbon materials and the layer spacing in the pseudo-graphite region. Although many research methods reported recently can produce a closed pore structure or expand the layer spacing, the process costs are relatively high. In particular, the separate optimization of the pore structure and layer spacing can indeed improve the sodium storage performance of carbonaceous negative electrodes, but the improvement is limited. Against this background, developing an effective method to simultaneously optimize the closed pore structure and layer spacing of carbonaceous negative electrodes is expected to further improve the reversible capacity and initial Coulomb efficiency of hard carbon materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of an alkali metal salt-doped carbon-coated hard carbon negative electrode material. The hard carbon negative electrode material prepared by using this method has a low specific surface area and a large layer spacing, and the prepared sodium-ion battery has a high reversible capacity and an initial Coulomb efficiency.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A preparation method of an alkali metal salt-doped carbon-coated hard carbon negative electrode material, comprising the following steps:

[0007] (1) Glucose, an alkali metal salt, and activated carbon are uniformly dispersed in deionized water, and then the mixed solution is placed in a reaction kettle for hydrothermal treatment;

[0008] (2) The hydrothermal product obtained in step (1) is subjected to vacuum filtration and then dried to obtain a hard carbon precursor; the hard carbon precursor is transferred to a tubular furnace and subjected to high-temperature carbonization treatment under a nitrogen atmosphere to obtain an alkali metal salt-doped carbon-coated hard carbon negative electrode material.

[0009] Preferably, the alkali metal salt in step (1) is any one of sodium acetate, zinc acetate, manganese acetate, and iron sulfate.

[0010] Preferably, the mass ratio of glucose, the alkali metal salt, and activated carbon in step (1) is 0.1-0.5:0.1-0.3:1.

[0011] Preferably, the temperature of the hydrothermal treatment in step (1) is 180 °C and the treatment time is 12 hours.

[0012] Preferably, during the high-temperature carbonization treatment in step (2), the heating rate is 3 °C / min between room temperature and 900 °C, and the heating rate is 2 °C / min between 900 °C and 1100 °C.

[0013] A sodium-ion battery, comprising a negative electrode material, and the negative electrode material comprises the alkali metal salt-doped carbon-coated hard carbon negative electrode material described above.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The surface of the hard carbon is carbon-coated by using the esterification reaction of the oxygen-containing functional groups on the surfaces of glucose and activated carbon, which can close some of the open pore structures on the surface of the hard carbon, thereby reducing the specific surface area of the material, reducing the irreversible consumption of the electrolyte to a certain extent, reducing the loss of irreversible capacity, and improving the initial Coulomb efficiency and plateau capacity of the sodium-ion battery.

[0016] (2) The hard carbon material is carbon-coated by using a simple hydrothermal reaction, and at the same time, metal elements are introduced to dope the hard carbon material. The liquid-phase mixing of the hydrothermal reaction can make the metal elements uniformly distributed on the hard carbon material, effectively expanding the interlayer spacing of the hard carbon material, which promotes the insertion / extraction of sodium ions and is conducive to the rapid transfer of ions and electrons, further improving the rate performance of the hard carbon material. Therefore, the doping of metal elements can significantly improve the reversible capacity and rate performance of the sodium-ion battery.

[0017] (3) The raw materials used in this preparation method are abundant, and the preparation process is simple, easy to operate, and suitable for large-scale production. The alkali metal salt-doped carbon-coated hard carbon anode material prepared by this method has a disordered hard carbon structure inside, a carbon-coated structure on the outer layer, a large interlayer spacing, and a high initial Coulomb efficiency of specific capacity, and can be applied to fields such as electric vehicles and energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the preparation method of the alkali metal salt-doped carbon-coated hard carbon anode material provided by the present invention.

[0019] Figure 2 It is a scanning electron microscope image of the hard carbon material prepared in Example 2.

[0020] Figure 3 It is the first charge-discharge curve of the hard carbon material prepared in Example 2 as the anode of a sodium-ion battery.

[0021] Figure 4 It is the cycle performance graph of the hard carbon material prepared in Example 2 as the anode of a sodium-ion battery at a high current density.

[0022] Figure 5 It is the rate performance graph of the hard carbon material prepared in Example 2 as the anode of a sodium-ion battery. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The present invention will be further described in detail below with reference to the embodiments and the drawings. The described embodiments are only a part of the embodiments of the present invention, not all of them. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0024] Example 1:

[0025] (1) Add 0.75 g of glucose and 0.25 g of manganese acetate to 30 ml of deionized water, stir and dissolve until the solution is clear and transparent, then weigh 2.5 g of activated carbon powder and pour it into the solution, and continue to stir until there is no activated carbon powder floating on the surface of the solution. Subsequently, the mixture solution is placed in a reaction kettle and hydrothermally treated at 180 °C for 12 h to obtain a hydrothermal product.

[0026] (2) Vacuum filter the hydrothermal product obtained in step (1), and then dry it to obtain a hard carbon precursor; transfer the hard carbon precursor to a tube furnace and perform high-temperature carbonization treatment at 1100 °C for 2 hours in a nitrogen atmosphere to obtain an alkali metal salt-doped carbon-coated hard carbon anode material. During the high-temperature carbonization process, the heating rate is 3 °C / min between room temperature and 900 °C, and 2 °C / min between 900 °C and 1100 °C.

[0027] (3) 90 mg of the hard carbon negative electrode material prepared in this example, 5 mg of Ketjen black, 5 mg of PVDF, and an appropriate amount of NMP solution were uniformly mixed to prepare an electrode slurry. Then, the slurry was evenly coated on a copper foil, and subsequently, the electrode was placed in a vacuum oven at 105 °C and dried for 12 hours. A sodium metal foil was used as the working electrode in a glove box filled with argon (H2O, O2 < 0.1 ppm). A CR2032 button cell was assembled to perform electrochemical measurements on the hard carbon negative electrode material.

[0028] Example 2:

[0029] (1) 0.75 g of glucose and 0.25 g of sodium acetate were added to 30 ml of deionized water, stirred and dissolved until the solution was clear and transparent. Then, 2.5 g of activated carbon powder was weighed and poured into it, and stirring was continued until no activated carbon powder floated on the surface of the solution. Subsequently, the mixture solution was placed in a reaction kettle and hydrothermally treated at 180 °C for 12 h to obtain a hydrothermal product.

[0030] (2) The hydrothermal product obtained in step (1) was subjected to vacuum filtration and then dried to obtain a hard carbon precursor; the hard carbon precursor was transferred to a tube furnace and heat-treated at 1100 °C for 2 hours under a nitrogen atmosphere to obtain an alkali metal salt-doped carbon-coated hard carbon negative electrode material. During the high-temperature carbonization process, the heating rate was 3 °C / min between room temperature and 900 °C, and 2 °C / min between 900 °C and 1100 °C.

[0031] (3) The method for assembling a CR2032 button cell using this material was the same as that in Example 1.

[0032] Example 3:

[0033] (1) 0.75 g of glucose and 0.25 g of zinc acetate were added to 30 ml of deionized water, stirred and dissolved until the solution was clear and transparent. Then, 2.5 g of activated carbon powder was weighed and poured into it, and stirring was continued until no activated carbon powder floated on the surface of the solution. Subsequently, the mixture solution was placed in a reaction kettle and hydrothermally treated at 180 °C for 12 h to obtain a hydrothermal product.

[0034] (2) The hydrothermal product obtained in step (1) was subjected to vacuum filtration and then dried to obtain a hard carbon precursor; the hard carbon precursor was transferred to a tube furnace and heat-treated at 1100 °C for 2 hours under a nitrogen atmosphere to obtain an alkali metal salt-doped carbon-coated hard carbon negative electrode material. During the high-temperature carbonization process, the heating rate was 3 °C / min between room temperature and 900 °C, and 2 °C / min between 900 °C and 1100 °C.

[0035] (3) The method for assembling a CR2032 button cell using this material was the same as that in Example 1.

[0036] Example 4:

[0037] (1) Add 0.75 g of glucose and 0.25 g of ferric sulfate to 30 ml of deionized water, stir and dissolve until the solution is transparent and clear, then weigh 2.5 g of activated carbon powder and pour it into the solution, and continue to stir until there is no activated carbon powder floating on the surface of the solution. Subsequently, transfer the mixture solution to a reaction kettle and hydrothermally treat it at 180 °C for 12 h to obtain a hydrothermal product.

[0038] (2) Vacuum filter the hydrothermal product obtained in step (1), and then dry it to obtain a hard carbon precursor; transfer the hard carbon precursor to a tube furnace and perform high-temperature carbonization treatment at 1100 °C for 2 hours in a nitrogen atmosphere to obtain an alkali metal salt-doped carbon-coated hard carbon negative electrode material. During the high-temperature carbonization process, the heating rate is 3 °C / min between room temperature and 900 °C, and 2 °C / min between 900 °C and 1100 °C.

[0039] (3) The method for assembling a CR2032-type button battery using this material is the same as that in Example 1.

[0040] Comparative Example 1:

[0041] Prepare a hard carbon negative electrode using an existing common method:

[0042] (1) First, prepare a 0.1 mol / L hydrochloric acid solution, then weigh 2.5 g of activated carbon powder and pour it into the solution, and continue to stir until there is no activated carbon powder floating on the surface of the solution, and perform acid solution impregnation for 2 hours.

[0043] (2) Vacuum filter the solid-liquid mixture obtained in step (1), wash it with deionized water multiple times, and then dry it to obtain a hard carbon precursor; transfer the hard carbon precursor to a tube furnace and perform high-temperature carbonization treatment at 1100 °C for 2 hours in a nitrogen atmosphere to obtain a hard carbon negative electrode material. During the high-temperature carbonization process, the heating rate is 3 °C / min.

[0044] (3) The method for assembling a CR2032-type button battery using this material is the same as that in Example 1.

[0045] Performance Test

[0046] Perform performance tests on the alkali metal salt-doped carbon-coated hard carbon negative electrode materials prepared in Examples 1-4 above. The specific method is as follows:

[0047] (1) Use characterization methods such as X-ray diffraction technology (XRD), Raman spectroscopy (Raman), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET specific surface area test on the materials prepared in Examples 1-4 above. Analyze their morphology, structure, and specific surface area.

[0048] (2) Electrochemical performance test of sodium-ion battery: After assembling the prepared hard carbon material into a button battery, a Neware battery test system was used to conduct constant current charge and discharge tests at room temperature. The current density for the first charge and discharge test was 30 mA / g, the current density for the cycle performance test was 300 mA / g, and the current densities for the rate performance test were 30 mA / g, 60 mA / g, 150 mA / g, 300 mA / g, 600 mA / g, and 1500 mA / g, respectively.

[0049] Table 1

[0050]

[0051]

[0052] It can be seen by comparison that all 4 examples have a significant improvement compared to Comparative Example 1. Among them, the hard carbon material prepared with sodium acetate as the alkali metal salt in Example 2 has the best electrochemical performance as the negative electrode material of the sodium-ion battery. Its first charge specific capacity and initial Coulomb efficiency are 310 mAh / g and 82.3%, respectively. The capacity retention rate after 1000 cycles at a current density of 300 mA / g is 75%, and the reversible capacity at a current density of 1500 mA / g is as high as 235 mAh / g.

Claims

1. A method for preparing an alkali metal salt-doped carbon-coated hard carbon negative electrode material, characterized in that: The steps include: (1) Glucose, alkali metal salt and activated carbon are uniformly dispersed in deionized water, and the mixed solution is placed in a reactor for hydrothermal treatment; (2) The hydrothermal product obtained in step (1) is vacuum filtered and then dried to obtain a hard carbon precursor; the hard carbon precursor is transferred to a tubular furnace and subjected to high-temperature carbonization treatment under a nitrogen atmosphere to obtain an alkali metal salt-doped carbon-coated hard carbon negative electrode material.

2. The method for preparing the alkali metal salt-doped carbon-coated hard carbon negative electrode material according to claim 1, characterized in that: The alkali metal salt in step (1) is any one of sodium acetate, zinc acetate, manganese acetate and ferric sulfate.

3. The method for preparing the alkali metal salt-doped carbon-coated hard carbon negative electrode material according to claim 1, characterized in that: The mass ratio of glucose, alkali metal salt and activated carbon in step (1) is 0.1-0.5:0.1-0.3:

1.

4. The method for preparing the alkali metal salt-doped carbon-coated hard carbon negative electrode material according to claim 1, characterized in that: The temperature of the hydrothermal treatment in step (1) is 180° C. and the treatment time is 12 hours.

5. The method for preparing the alkali metal salt-doped carbon-coated hard carbon negative electrode material according to claim 1, characterized in that: During the high-temperature carbonization treatment in step (2), the heating rate between room temperature and 900°C is 3°C / min, and the heating rate between 900°C and 1100°C is 2°C / min.

6. An alkali metal salt doped carbon coated hard carbon negative electrode material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 5.

7. A sodium ion battery comprising a negative electrode material, characterized in that The negative electrode material comprises the alkali metal salt-doped carbon-coated hard carbon negative electrode material according to claim 6.

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