Low-temperature-resistant sodium-ion battery hard carbon negative electrode material and preparation method thereof

Abstract

The application relates to the technical field of sodium ion battery negative electrode materials, in particular to a low-temperature-resistant hard carbon negative electrode material of a sodium ion battery and a preparation method thereof. The negative electrode material is prepared through the following operations: mixing an expanded carbon-based aqueous solution prepared from a cold-resistant gene plant and a carbon nanotube aqueous solution prepared from carbon nanotubes, adding zinc chloride, drying, high-temperature carbonization, acid pickling and the like. The negative electrode material is applied to a sodium ion battery, and the obtained sodium ion battery not only has excellent total battery capacity and ICE at room temperature, but also can maintain a relatively high total battery capacity and ICE at low temperature.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and in particular to a low-temperature resistant hard carbon anode material for sodium-ion batteries and its preparation method. Background Technology

[0002] In recent years, due to the limitation of lithium resources and the increasing demand for lithium resources, the cost of lithium-ion batteries has become increasingly high. Therefore, people have begun to increase their research on sodium-ion batteries, which have more abundant resources and lower costs.

[0003] The main characteristic of sodium-ion batteries is the use of sodium ions instead of expensive lithium ions. Therefore, the positive electrode material, negative electrode material, and electrolyte within the battery must be adjusted and modified accordingly. Negative electrode materials for sodium-ion batteries mainly include carbon materials, alloy materials, and conversion-type metal compound materials. Among these, hard carbon materials have good overall performance and can meet the requirements for use in ordinary environments. However, when sodium-ion batteries are used in low-temperature environments, the lower operating temperature slows down the electrochemical reaction rate inside the battery, reduces the reactivity of the negative electrode material, causes severe polarization, and leads to the deposition of a large amount of metal on the negative electrode surface. This results in increased charge transfer resistance, decreased ion diffusion coefficient, and unstable interfacial reactions, causing damage or even deterioration of the battery, ultimately reducing the total battery capacity and initial coulombic efficiency. Summary of the Invention

[0004] To address the above technical problems, this invention provides a low-temperature resistant hard carbon anode material for sodium-ion batteries and its preparation method. The low-temperature resistant hard carbon anode material prepared according to this method can be used to create sodium-ion batteries with high total capacity and initial coulombic efficiency even at low temperatures.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] The first aspect of this invention provides a method for preparing a low-temperature resistant hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0007] S1. The powder obtained by washing, drying and grinding the roots and / or stems of plants with cold-resistant genes is used as a carbon source and ground and mixed evenly with potassium hydroxide powder, and pre-carbonized to obtain an expanded carbon-based precursor; the obtained expanded carbon-based precursor is added to a PEG aqueous solution and sonicated until completely dissolved to obtain an expanded carbon-based aqueous solution.

[0008] S2. After soaking the carbon nanotubes in acid and washing them with water until neutral, dry them. Add the dried carbon nanotubes to water, then add sodium dodecylbenzenesulfonate to the water and dissolve them by sonication to obtain an aqueous solution of carbon nanotubes.

[0009] S3. Mix the expanded carbon-based aqueous solution obtained in S1 and the carbon nanotube aqueous solution obtained in S2, then add zinc chloride aqueous solution, stir for 2-4 hours, and dry to obtain the initial sample.

[0010] S4. The initial sample obtained in S3 is subjected to high-temperature carbonization to obtain an activated sample. The activated sample is then subjected to acid washing, water washing and drying to obtain a low-temperature resistant sodium-ion battery hard carbon anode material.

[0011] The inventors unexpectedly discovered that using the roots or stems of plants with cold-resistant genes as the carbon source for preparing hard carbon anode materials significantly improved the performance and stability of sodium-ion batteries made from these materials at low temperatures. This is likely because plants with cold-resistant genes possess unique structures such as cushion-like, creeping, or xerophytic forms, and their tissues contain low starch, high sugar, and extremely low free water content. These characteristics enhance the performance of hard carbon anode materials at low temperatures.

[0012] Specifically, this invention first pre-carbonizes plants with cold-resistant genes by grinding and mixing them with potassium hydroxide powder. During pre-carbonization, potassium hydroxide acts as an activator, causing non-carbon atoms in the roots and / or stems of the cold-resistant plants to react with highly reactive disordered carbon atoms, forming a preliminary microporous structure. Furthermore, potassium hydroxide can also enlarge the micropores by etching the carbon atoms on the walls of the formed micropores, thereby increasing the capacity of the microporous structure. During the dissolution of the expanded carbon-based precursor, PEG can act as a toughening agent, preventing the collapse and stacking of the expanded hard carbon layer. After mixing the expanded carbon-based aqueous solution and the carbon nanotube aqueous solution, a zinc chloride solution is added. During high-temperature carbonization, zinc chloride reacts with oxygen atoms in the roots and / or stems of the cold-resistant plants to generate zinc oxide. Zinc oxide further reacts with carbon atoms to generate CO and Zn. The generated CO and Zn play a pore-forming role during the process of escaping under heat, increasing the number of micropores on the surface of the carbon nanotubes, resulting in multi-walled carbon nanotubes. After high-temperature carbonization, a hard carbon anode material with an expanded hard carbon layer and a multi-walled carbon nanotube composite structure is obtained. The expanded hard carbon layer has a sheet structure, and each hard carbon sheet has mesh-like pores. Meanwhile, the multi-walled carbon nanotube structure is distributed between the hard carbon sheets, which plays a role in supporting and connecting the expanded hard carbon sheets.

[0013] The hard carbon anode material provided by this invention has a composite structure of expanded hard carbon layer and multi-walled carbon nanotubes. The expanded hard carbon layer itself has good electrical and thermal conductivity. Each hard carbon sheet has a large number of unique network micropores that can adsorb and allow a large number of sodium ions to pass through, enabling vertical transport of ions between the sheets through the micropores. This greatly shortens the transport distance of sodium ions, thus giving the hard carbon anode material high rate performance and better low-temperature performance. As for the multi-walled carbon nanotubes, on the one hand, they can act as a conductive agent to accelerate the transport of sodium ions in the electrode, making it easier for sodium ions to be inserted and extracted between the positive and negative electrodes, thereby reducing the polarization of the electrode and improving the discharge platform and discharge capacity of the corresponding battery at low temperatures. On the other hand, the multi-walled carbon nanotubes can also enter between the expanded hard carbon sheets to support the expanded hard carbon sheets, preventing the sheets from collapsing and stacking, thereby enhancing the structural stability of the hard carbon anode material and providing more transport channels for sodium ions.

[0014] In conjunction with the first aspect, the plants with cold-resistant genes mentioned in S1 include at least one of bellflower, weigela, or wild cotton.

[0015] In conjunction with the first aspect, the washing described in S1 uses a mixed solution of water and ethanol; the drying temperature is 80–110°C, and the drying is carried out until the remaining moisture content is below 0.5%. By washing with the above-mentioned mixed solution, dust and impurities on the surface of the plant roots or stems can be removed; the drying process removes moisture from the plant roots or stems, bringing them to a dehydrated state.

[0016] In conjunction with the first aspect, the pre-carbonization temperature described in S1 is 680–720°C, the pre-carbonization time is 3–6 h, and the heating rate during pre-carbonization is 2–5°C / min.

[0017] In conjunction with the first aspect, the PEG mentioned in S1 includes at least one of PEG 400MO, PEG 600MO, or PEG 800MO, preferably PEG 400MO. All of the above-mentioned PEGs can serve a toughening function, preventing the collapse and stacking of the expanded hard carbon layer.

[0018] In conjunction with the first aspect, the acid solution used in S2 acid immersion is at least one of nitric acid aqueous solution, hydrochloric acid aqueous solution, or phosphoric acid aqueous solution. Immersion in the above acid solutions can etch carbon nanotubes and increase their reactivity.

[0019] In conjunction with the first aspect, the concentration of hydrogen ions in the acid solution used in the S2 acid immersion is 0.8–1.2 mol / L.

[0020] In conjunction with the first aspect, the high-temperature carbonization temperature described in S4 is 900–1400°C, the high-temperature carbonization time is 1–3 h, and the heating rate during high-temperature carbonization is 3–6°C / min.

[0021] In conjunction with the first aspect, the mass ratio of the carbon source to the potassium hydroxide powder in S1 is 1:0.2 to 0.6.

[0022] A second aspect of the present invention provides a low-temperature resistant hard carbon anode material for sodium-ion batteries prepared according to the above preparation method. The anode material has a composite structure composed of a layered expanded hard carbon layer and a multi-walled carbon nanotube. This composite structure helps the anode material to enable the battery containing it to have stable low-temperature performance at low temperatures.

[0023] A third aspect of the present invention provides the application of the low-temperature resistant sodium-ion battery hard carbon anode material prepared according to the above preparation method in sodium-ion batteries, wherein the resulting sodium-ion battery still has a high total battery capacity and initial coulombic efficiency (ICE) at low temperatures.

[0024] The beneficial effects of the present invention are as follows: The method for preparing low-temperature resistant sodium-ion battery hard carbon anode material provided by the present invention can prepare hard carbon anode material with an expanded hard carbon layer and a multi-walled carbon nanotube composite structure. The hard carbon anode material has more stable low-temperature performance. Sodium-ion batteries made of the hard carbon anode material not only have excellent total battery capacity and ICE at room temperature, but also maintain high total battery capacity and ICE at low temperatures: the total battery capacity can be maintained above 190 mAh / g at a temperature of -30℃, and the ICE is still maintained above 70%. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope image of the hard carbon anode material obtained in Example 1;

[0026] Figure 2 This is a scanning electron microscope image of the hard carbon anode material obtained in Example 2;

[0027] Figure 3 This is a scanning electron microscope image of the hard carbon anode material obtained in Example 3. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] Example 1

[0030] This embodiment provides a method for preparing a low-temperature resistant hard carbon anode material for sodium-ion batteries, including the following steps:

[0031] S1. The bellflower stems were washed three times with a mixed solution of water and ethanol, dried at 95°C for 12 hours, and then pulverized to obtain a powdered carbon source. The obtained powdered carbon source was mixed with KOH powder at a mass ratio of 1:0.4 and ground to make it uniform. Then, it was pre-carbonized in a tube furnace under argon protection at a heating rate of 3°C / min to 700°C for 4.5 hours to obtain an expanded carbon-based precursor.

[0032] Disperse 2 mL of PEG 400MO in 80 mL of water, add 1.5 g of expanded carbon-based precursor, and sonicate for 30 minutes to completely dissolve it, thus obtaining a homogeneous expanded carbon-based aqueous solution.

[0033] S2. Add 0.5g of carbon nanotube powder to 60mL of nitric acid solution with a hydrogen ion concentration of 1.0mol / L, stir and soak for 24h, then wash the carbon nanotube powder with water until neutral by centrifugation, and then dry it in a vacuum oven at 80℃ for 12h (moisture content is 0.4%).

[0034] Dissolve 2 mg of sodium dodecylbenzenesulfonate in 20 mL of water, add 20 mg of dried carbon nanotubes, disperse ultrasonically for 3 h and then dissolve to obtain an aqueous solution of carbon nanotubes.

[0035] S3. Mix the expanded carbon-based aqueous solution obtained in S1 and the carbon nanotube aqueous solution obtained in S2, and sonicate for 30 min to obtain a homogeneous mixed solution. Then add 18 mL of 0.6 mol / L ZnCl2 solution to the mixture and stir magnetically for 3 h until homogeneous. Dry the homogeneous mixed solution in a 90℃ forced-air drying oven for 9 h to obtain the initial sample.

[0036] S4. After grinding the initial sample obtained in S3 into powder, it is subjected to high-temperature carbonization in a tube furnace under inert gas protection. The temperature is increased to 1200℃ at a heating rate of 4.5℃ / min and held for 2 hours to obtain an activated sample.

[0037] The activated sample was washed with a 5% hydrochloric acid solution, then washed with water until neutral, and dried to obtain a low-temperature resistant hard carbon anode material for sodium-ion batteries.

[0038] Example 2

[0039] This embodiment provides a method for preparing a low-temperature resistant hard carbon anode material for sodium-ion batteries, including the following steps:

[0040] S1. The stems of Weigela flowers were washed three times with a mixed solution of water and ethanol, dried at 110°C for 10 hours, and then pulverized to obtain a powdered carbon source. The obtained powdered carbon source was mixed with KOH powder at a mass ratio of 1:0.2 and ground to make it uniform. Then, it was pre-carbonized in a tube furnace under argon protection at a heating rate of 5°C / min to 720°C for 3 hours to obtain an expanded carbon-based precursor.

[0041] Disperse 2 mL of PEG 600MO in 80 mL of water, add 1.5 g of expanded carbon-based precursor, and sonicate for 30 minutes to completely dissolve it, thus obtaining a homogeneous expanded carbon-based aqueous solution.

[0042] S2. Add 0.5g of carbon nanotube powder to 60mL of hydrochloric acid solution with a hydrogen ion concentration of 1.2mol / L, stir and soak for 24h, then wash the carbon nanotube powder with water until neutral by centrifugation, and then dry it in a vacuum oven at 80℃ for 12h (moisture content is 0.4%).

[0043] Dissolve 2 mg of sodium dodecylbenzenesulfonate in 20 mL of water, add 20 mg of dried carbon nanotubes, disperse ultrasonically for 3 h and then dissolve to obtain an aqueous solution of carbon nanotubes.

[0044] S3. Mix the expanded carbon-based aqueous solution obtained in S1 and the carbon nanotube aqueous solution obtained in S2, and sonicate for 30 min to obtain a homogeneous mixed solution. Then add 20 mL of 0.5 mol / L ZnCl2 solution to the mixture and stir magnetically for 3 h until homogeneous. Dry the homogeneous mixed solution in a 90℃ forced-air drying oven for 9 h to obtain the initial sample.

[0045] S4. After grinding the initial sample obtained in S3 into powder, it is subjected to high-temperature carbonization in a tube furnace under inert gas protection. The temperature is increased to 1400℃ at a heating rate of 6℃ / min and held for 1h to obtain an activated sample.

[0046] The activated sample was washed with a 5% hydrochloric acid solution, then washed with water until neutral, and dried to obtain a low-temperature resistant hard carbon anode material for sodium-ion batteries.

[0047] Example 3

[0048] This embodiment provides a method for preparing a low-temperature resistant hard carbon anode material for sodium-ion batteries, including the following steps:

[0049] S1. The stems of wild cotton were washed three times with a mixed solution of water and ethanol, dried at 80°C for 14 hours, and then pulverized to obtain a powdered carbon source. The obtained powdered carbon source was mixed with KOH powder at a mass ratio of 1:0.6 and ground to make it uniform. Then, it was pre-carbonized in a tube furnace under argon protection at a heating rate of 2°C / min to 680°C for 6 hours to obtain an expanded carbon-based precursor.

[0050] Disperse 2 mL of PEG 800MO in 80 mL of water, add 1.5 g of expanded carbon-based precursor, and sonicate for 30 minutes to completely dissolve it, thus obtaining a homogeneous expanded carbon-based aqueous solution.

[0051] S2. Add 0.5g of carbon nanotube powder to 60mL of phosphoric acid solution with a hydrogen ion concentration of 0.8mol / L, stir and soak for 24h, then wash the carbon nanotube powder with water until neutral by centrifugation, and then dry it in a vacuum oven at 80℃ for 12h (moisture content is 0.4%).

[0052] Dissolve 2 mg of sodium dodecylbenzenesulfonate in 20 mL of water, add 20 mg of dried carbon nanotubes, disperse ultrasonically for 3 h and then dissolve to obtain an aqueous solution of carbon nanotubes.

[0053] S3. Mix the expanded carbon-based aqueous solution obtained in S1 and the carbon nanotube aqueous solution obtained in S2, and sonicate for 30 min to obtain a homogeneous mixed solution. Then add 15 mL of 0.8 mol / L ZnCl2 solution to the mixture and stir magnetically for 2.5 h until homogeneous. Dry the homogeneous mixed solution in a 90℃ forced-air drying oven for 9 h to obtain the initial sample.

[0054] S4. After grinding the initial sample obtained in S3 into powder, it is subjected to high-temperature carbonization in a tube furnace under inert gas protection. The temperature is increased to 900℃ at a heating rate of 3℃ / min and held for 3h to obtain an activated sample.

[0055] The activated sample was washed with a 5% hydrochloric acid solution, then washed with water until neutral, and dried to obtain a low-temperature resistant hard carbon anode material for sodium-ion batteries.

[0056] Comparative Example 1

[0057] This comparative example provides a method for preparing a hard carbon anode material for low-temperature sodium-ion batteries. The specific preparation steps are similar to those in Example 1, except that the carbon source, bellflower stems, used in Example 1 is replaced with corn stalks. The remaining steps are the same as in Example 1.

[0058] Comparative Example 2

[0059] This comparative example provides a method for preparing a hard carbon anode material for low-temperature sodium-ion batteries. The specific preparation steps are similar to those in Example 1, except that potassium hydroxide powder is not added in step S1. All other steps are the same as in Example 1.

[0060] Comparative Example 3

[0061] This comparative example provides a method for preparing a hard carbon anode material for low-temperature sodium-ion batteries. The specific preparation steps are similar to those in Example 1, except that potassium hydroxide powder in step S1 is replaced with sodium hydroxide powder. All other steps are the same as in Example 1.

[0062] Comparative Example 4

[0063] This comparative example provides a method for preparing a low-temperature resistant hard carbon anode material for sodium-ion batteries. The specific preparation steps are similar to those in Example 1, except that the zinc chloride solution in step S3 is replaced with a sodium chloride solution. All other steps are the same as in Example 1.

[0064] Test Example

[0065] The hard carbon anode materials prepared in Examples 1-3 and Comparative Examples 1-4 were applied to sodium-ion batteries, and the total capacity and initial coulombic efficiency (ICE) of the corresponding sodium-ion batteries were tested sequentially at room temperature (25°C), -10°C and -30°C. The test results are shown in Table 1.

[0066] Table 1. Test results of different sodium-ion batteries at different temperatures.

[0067]

[0068]

[0069] As shown in Table 1, the sodium-ion batteries containing the hard carbon anode materials prepared in Examples 1 to 3 can maintain a total battery capacity of over 190 mAh / g and an initial coulombic efficiency of over 70%, regardless of whether the temperature is at room temperature or -30°C, thus broadening the application scenarios of sodium-ion batteries.

[0070] from Figures 1-3 It can be seen that the hard carbon anode material prepared according to the preparation method provided by the present invention has a composite structure of expanded hard carbon layer and multi-walled carbon nanotubes. The expanded hard carbon layer is arranged in a layered structure, and the multi-walled carbon nanotubes are distributed between the expanded hard carbon layers, which have the function of supporting the expanded hard carbon layer.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a low-temperature-resistant sodium-ion battery hard carbon anode material, characterized in that, The method comprises the following steps: S1, after washing, drying and grinding the roots and / or stems of plants with cold-resistant genes to obtain a powder, the powder is mixed with potassium hydroxide powder as a carbon source, and pre-carbonization is performed to obtain an expanded carbon-based precursor; the expanded carbon-based precursor is added to a PEG aqueous solution and ultrasonically dissolved to obtain an expanded carbon-based aqueous solution; S2, after acid immersion, water washing to neutral, drying, adding the dried carbon nanotubes to water, adding sodium dodecyl benzene sulfonate to the water, and ultrasonically dissolving to obtain a carbon nanotube aqueous solution; S3, mixing the expanded carbon-based aqueous solution obtained in S1 and the carbon nanotube aqueous solution obtained in S2, adding a zinc chloride aqueous solution, stirring for 2-4 hours, and drying to obtain an initial sample; S4, high-temperature carbonization of the initial sample obtained in S3 to obtain an activated sample, and acid washing, water washing and drying of the activated sample to obtain a low-temperature-resistant sodium ion battery hard carbon negative electrode material; The plants with cold-resistant genes include at least one of bellflowers, fuchsia or wild cotton.

2. The method for preparing a low-temperature-resistant sodium-ion battery hard carbon anode material according to claim 1, characterized in that, The washing in S1 uses a mixed solution of water and ethanol; the drying is performed at a temperature of 80-110 DEG C, and the residual moisture content is less than 0.5% after drying.

3. The method for preparing a low-temperature-resistant sodium-ion battery hard carbon anode material according to claim 1, characterized in that, The pre-carbonization in S1 is performed at a temperature of 680-720 DEG C for 3-6 hours, and the heating rate is 2-5 DEG C / min.

4. The method for preparing a low-temperature-resistant sodium-ion battery hard carbon anode material according to claim 1, characterized in that, The PEG in S1 includes at least one of PEG 400MO, PEG 600MO or PEG 800MO.

5. The method for preparing a low-temperature-resistant sodium-ion battery hard carbon anode material according to claim 1, characterized in that, The acid solution used in the acid immersion in S2 is at least one of a nitric acid aqueous solution, a hydrochloric acid aqueous solution or a phosphoric acid aqueous solution; and / or The concentration of hydrogen ions in the acid solution used in the acid immersion in S2 is 0.8-1.2 mol / L.

6. The method for preparing a low-temperature-resistant sodium-ion battery hard carbon anode material according to claim 1, characterized in that, The high-temperature carbonization in S4 is performed at a temperature of 900-1400 DEG C for 1-3 hours, and the heating rate is 3-6 DEG C / min.

7. The method for preparing the low-temperature resistant hard carbon anode material for sodium-ion batteries as described in claim 1, characterized in that, The mass ratio of the carbon source to the potassium hydroxide powder in S1 is 1:0.2-0.

6.

8. A low-temperature-resistant sodium ion battery hard carbon negative electrode material prepared by the method according to any one of claims 1-7.

9. Use of the low-temperature-resistant sodium ion battery hard carbon negative electrode material according to claim 8 in a sodium ion battery.

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