Method for improving reversible capacity of sodium ion battery

Abstract

The invention provides a method for improving the reversible capacity of a sodium-ion battery, application of the method to a negative electrode of the sodium-ion battery and the sodium-ion battery, and relates to the field of sodium-ion batteries. The preparation method comprises the following steps: crushing the sugarcane by using a powder grinding machine, immersing the crushed sugarcane into an acid solution, then heating at 80 DEG C for 120 minutes, and then washing, filtering and drying. And carrying out high-temperature treatment on the obtained sugarcane powder in a protective atmosphere. And after calcination is completed, sequentially adding acid and deionized water to clean the obtained carbon material, regulating the acid-base until the pH value is 7, and then drying. And finally, carrying out high-temperature treatment on the carbon material in a protective atmosphere to obtain the hard carbon. The raw material of the sodium ion battery negative electrode comprises hard carbon prepared from sugarcane powder. The sodium-ion battery comprises the sodium-ion battery negative electrode. According to the invention, the sugarcane powder is used as a precursor, the closed pore volume of hard carbon is effectively increased by using the preparation method, the reversible capacity of the sodium-ion battery is enhanced, and the sodium-ion battery has long cycle stability and huge application potential.

Description

(1) Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials for sodium-ion batteries, and specifically relates to a method for improving the reversible capacity of sodium-ion batteries, a negative electrode for sodium-ion batteries, and a sodium-ion battery. (2) Background Art

[0002] With the rapid development of industries such as electric vehicles, electronic products, and renewable energy storage, the demand for lithium-ion batteries (LIBs) has increased sharply. However, the reserves of lithium element in the earth's crust are limited, its availability cannot be guaranteed when the demand surges, and it will cause a substantial price increase. These problems lead to risks in the sustainable supply of LIBs. Compared with lithium, sodium element has rich reserves and wide distribution, and sodium-ion batteries (SIBs) have also attracted attention due to their low cost and high safety, and are expected to become a complement or substitute for LIBs. Graphite is the main negative electrode material for LIBs. However, since sodium ions cannot be effectively inserted and extracted in graphite, graphite performs poorly in SIBs. Therefore, exploring negative electrode materials with high energy density and good rate performance is one of the research focuses of SIBs.

[0003] Biomass hard carbon is widely regarded as the most promising negative electrode material for sodium-ion batteries due to its high capacity, low potential, sustainability, cost-effectiveness, and environmental friendliness. Hard carbon consists of a turbostratic graphene structure and internal pores surrounded by it. The larger interlayer spacing and hierarchical pore structure can solve the problem of sodium ion insertion and extraction. And increasing the closed pore volume in hard carbon is considered the most effective method to improve the electrochemical performance of sodium-ion batteries. It is found that modifying the precursor of hard carbon is an effective method to regulate the closed pore structure. Moreover, most of the biomass precursors available on the market are low-cost and easy to obtain.

[0004] Based on the above discussion, we choose sugarcane powder as the precursor, perform delignification treatment on it, so as to regulate the closed pore volume of hard carbon and effectively improve the reversible capacity of sodium-ion batteries. For this purpose, a brand-new hard carbon negative electrode material for sodium-ion batteries and its preparation method are provided, with low-cost and easily available raw materials. (3) Summary of the Invention

[0005] The purpose of this application is to provide a hard carbon material and its preparation method, a negative electrode for sodium-ion batteries, and a sodium-ion battery to solve the above problems.

[0006] To achieve the above purpose, this application adopts the following technical solutions:

[0007] A method for preparing a hard carbon material using sugarcane powder as a precursor, comprising:

[0008] Step 1: Grind sugarcane with a powder grinder and filter through a 50-mesh sieve;

[0009] Step 2: Immerse 6 g of sugarcane powder in 450 ml of acidic NaClO2 solution (the mass ratio of H2O:CH3COOH:NaClO2 is 450:12:6);

[0010] Step 3: Perform a water bath on the mixed solution obtained in Step 2;

[0011] Step 4: Wash, filter, and freeze-dry to remove residual NaClO2 and CH3COOH;

[0012] Step 5: Pyrolyze the obtained sugarcane powder under argon;

[0013] Step 6: After completing the high-temperature treatment, perform pickling to remove inorganic impurities;

[0014] Step 7: Wash with deionized water and then dry;

[0015] Step 8: Pyrolyze the above carbon material again under an argon atmosphere;

[0016] Preferably, the water bath temperature is 80 °C and the time is 120 min;

[0017] Preferably, the cold trap temperature of the freeze-drying treatment is -100 °C, the vacuum degree is 15 Pa, and the time is 72 h;

[0018] Preferably, the high-temperature treatment temperatures are 380 °C and 1300 °C respectively, and the heating rate is 2 °C / min;

[0019] Preferably, the gas flow rate under the argon atmosphere is 50 - 200 mL / min;

[0020] Preferably, the acid solution used for pickling is hydrochloric acid, the concentration is 2 mol / L, and the soaking time is 6 h;

[0021] Preferably, the drying temperature is 80 °C and the time is 10 h;

[0022] This application also provides a hard carbon material prepared by using the preparation method of the hard carbon material;

[0023] This application also provides a negative electrode of a sodium-ion battery, the raw materials of which include the above hard carbon material and a binder;

[0024] Preferably, the binder includes one or more of CMC, sodium alginate, and SBR;

[0025] Preferably, the mass ratio of the hard carbon material to the binder is 9:1;

[0026] Preferably, the current collector material of the negative electrode of the sodium-ion battery is selected from any one of pure copper foil and carbon-coated copper foil.

[0027] The present application also provides a sodium-ion battery, including the negative electrode of the sodium-ion battery described above;

[0028] Preferably, the preparation method of the sodium-ion battery includes:

[0029] Mix the hard carbon material, the binder and deionized water to obtain a slurry, then coat it on the current collector and dry it to obtain the negative electrode of the sodium-ion battery. Then, under an argon atmosphere, assemble the sodium-ion battery using a sodium-based ether electrolyte;

[0030] Preferably, in the argon atmosphere, the oxygen content is less than 1 ppm and the water content is less than 1 ppm;

[0031] Preferably, the sodium salt in the sodium-based ether electrolyte includes one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium tetrafluoroborate;

[0032] Preferably, the concentration of the sodium salt in the sodium-based ether electrolyte is 0.5 - 2 mol / L.

[0033] Compared with the prior art, the beneficial effects of the present invention include the following aspects:

[0034] The hard carbon material provided by the present application innovatively uses sugarcane powder as the raw material, with low cost.

[0035] The preparation method of the hard carbon material for the negative electrode of the sodium-ion battery provided by the present application exposes the free radicals in the sugarcane powder through delignification treatment, enhancing the activity of the carbonization reaction. A sufficient amount of free radicals promotes the utilization of precursor fragments in the carbonization reaction, thereby forming a well-developed carbon layer and abundant closed pores, making the hard carbon exhibit a high closed pore volume and a high reversible capacity. (IV) BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope of the present application itself.

[0037] Figure 1 It is the process flow chart of the production of the hard carbon material;

[0038] Figure 2 It is the 100 mA g -1 cycling curve and Coulomb efficiency graph of the hard carbon material in Example 1;

[0039] Figure 3 It is the XRD graph of the hard carbon material prepared in Example 1;

[0040] Figure 4 、 Figure 5SEM images of the hard carbon materials prepared in Example 1 at different magnifications;

[0041] Figure 6 The galvanostatic charge-discharge curve of the hard carbon material in Example 1. (V) Specific implementation manners

[0042] Example 1

[0043] Step 1: Grind sugarcane with a powder grinder and filter through a 50-mesh sieve;

[0044] Step 2: Immerse 6 g of sugarcane powder in 450 ml of acidic NaClO2 solution (mass ratio of H2O:CH3COOH:NaClO2 is 450:12:6);

[0045] Step 3: Heat the mixed solution obtained in Step 2 at 80 °C for 120 min;

[0046] Step 4: Wash and filter with deionized water until pH = 7. After freezing overnight in the refrigerator to set the shape, transfer it to a freeze dryer. The cold trap temperature for freeze-drying treatment is -100 °C, the vacuum degree is 15 Pa, and the time is 72 h to obtain a pretreated biomass hard carbon material;

[0047] Step 5: Heat the material described in Step 4 under the protection of an argon atmosphere at a heating rate of 2 °C / min to 380 °C, pyrolyze for 2 h, then heat up to 1300 °C and pyrolyze for 2 h;

[0048] Step 6: After completion of calcination, take out the active substance, add hydrochloric acid with a concentration of 2 mol / L and wash for about 6 h until the organic impurities are washed away;

[0049] Step 7: Wash the obtained carbon with deionized water until pH = 7; then place the obtained product in a constant temperature drying oven and dry at 80 °C for 10 h;

[0050] Step 8: Calcinate the above carbon material under the protection of an argon atmosphere at a heating rate of 2 °C / min at 1300 °C for 2 h;

[0051] Figure 3 The XRD pattern of the hard carbon material synthesized by the above steps, Figure 4 、 Figure 5 The scanning electron microscope image of the hard carbon material synthesized by the above steps.

[0052] Based on the synthesized hard carbon material, it is mixed and ground with CMC at a ratio of 9:1. The ground powder is added with an appropriate amount of deionized water and SBR, and the obtained slurry is uniformly coated on a copper current collector by a doctor blade method or a spraying method and dried to obtain an electrode. The battery is assembled under an argon atmosphere, where the oxygen content in the argon atmosphere is less than 1 ppm and the water content is less than 1 ppm. The electrolyte is 1 M NaPF6 dissolved in diethylene glycol methyl ether.

[0053] In a sodium-ion battery, the obtained hard carbon material has a first specific capacity of 248 mAh g -1 at a current density of 100 mA g -1 , and a specific capacity of 228 mAh g after 100 cycles -1 .

[0054] Comparative Example 1

[0055] The preparation of the hard carbon and the assembly process of the sodium-ion battery in this example are the same as those in Example 1, except that the precursor used in this example is rice.

[0056] Comparative Example 2

[0057] The preparation of the hard carbon and the assembly process of the sodium-ion battery in this example are the same as those in Example 1, except that 1 mol / L nickel chloride is added after centrifugation in step 4 of Example 1. Based on the synthesized sugarcane bagasse-derived hard carbon in a sodium-ion battery, at a current density of 100 mA / g, the first Coulombic efficiency is as high as 84%, and its first reversible specific capacity is 248 mAh g -1 , and the capacity retention rate after 50 cycles is greater than 98%.

[0058] The above are only the embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the art are not described in detail again. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can still be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners in the specification can be used to interpret the content of the claims.

Claims

1. A method for improving the reversible capacity of a sodium ion battery, wherein the preparation method is characterized in that: include: The precursor used is sugarcane. The specific steps are as follows: Step 1: crush the sugarcane with a powder grinder and filter through a 50-mesh sieve; Step 2: Pre-treat the sugarcane powder by immersing it in an acidic NaClO2 solution; Step 3: placing the mixed solution obtained in step 2 in a water bath; Step 4: washing, filtering and freeze drying to remove residual NaClO2 and CH3COOH; Step 5: pyrolyzing the obtained sugarcane powder under protective gas; Step 6: After the high temperature treatment, pickling is performed to remove inorganic impurities; Step 7: washing with deionized water and then drying; Step 8: Pyrolyze the carbon material again under an argon atmosphere.

2. The preparation method according to claim 1, characterized in that: The concentration range of the acidic NaClO2 solution is 2-4%; Preferably, the acidic NaClO2 solution has a solubility of 3%.

3. The preparation method according to claim 1, characterized in that: The water bath time range is 65 to 120 minutes, and the water bath temperature range is 80 to 100°C; Preferably, the water bath time is 120 min and the temperature is 80°C.

4. The preparation method according to claim 1, characterized in that: The temperature range of the cold trap for freeze drying is -20 to 200°C, the vacuum range is 10 to 20 Pa, and the time range is 10 to 96 hours; Preferably, the cold trap temperature of the freeze-drying treatment is -100°C, the vacuum degree is 15 Pa, and the time is 36 hours.

5. The preparation method according to claim 1, characterized in that: The high temperature treatment temperature range is 380-1300°C, and the heating rate range is 2-5°C / min; the gas in the protective atmosphere includes one or more of nitrogen and argon, and the gas flow rate range is 50-200mL / min; Preferably, the high temperature treatment temperature is 380°C or 1300°C, and the heating rate is 3°C / min. Preferably, the protective atmosphere is argon, and the gas flow rate is 80 mL / min.

6. The preparation method according to claim 1, characterized in that: The acid solution used for pickling includes at least one of hydrochloric acid, sulfuric acid, nitric acid and acetic acid, and the concentration range of the acid solution is 1-2 mol / L; Preferably, the acid solution used in the pickling is hydrochloric acid with a concentration of 2 mol / L.

7. The preparation method according to claim 1, characterized in that: The drying temperature range is 60-100°C and the drying time range is 5-24h; Preferably, the drying temperature is 80° C. and the drying time is 10 h.

8. A hard carbon material, characterized in that: The method for improving the reversible capacity of a sodium ion battery according to any one of claims 1 to 7 is used to prepare the sodium ion battery.

9. A sodium ion battery negative electrode, characterized in that: The raw materials include the hard carbon material as claimed in claim 8 and a binder; Preferably, the binder includes one or more of CMC, sodium alginate, and SBR; Preferably, the mass ratio of the hard carbon material to the binder is 9:1; Preferably, the current collector material of the negative electrode of the sodium ion battery is selected from any one of pure copper foil and carbon-coated copper foil.

10. A sodium ion battery, characterized in that: A sodium ion battery negative electrode comprising the sodium ion battery negative electrode according to claim 9; Preferably, the method for preparing the sodium ion battery comprises: The hard carbon material, the binder and deionized water are mixed to obtain a slurry, which is then coated on a current collector and dried to obtain a negative electrode of a sodium ion battery, and then assembled using a sodium ether electrolyte under an argon atmosphere to obtain a sodium ion battery; Preferably, in the argon atmosphere, the oxygen content is less than 1 ppm and the water content is less than 1 ppm; Preferably, the sodium salt in the sodium-ether electrolyte includes one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium tetrafluoroborate; Preferably, the concentration of the sodium salt in the sodium-ether electrolyte is 0.5-2 mol / L.

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