Preparation method and application of high-capacity activated carbon-based electrode material

Abstract

The present invention relates to the technical field of lithium-ion batteries, and discloses a preparation method and application of a high-capacity activated carbon-based electrode material. Hyperbranched polycarbonate polyurethane and potassium hydroxide are ground and blended, calcined in a tubular furnace, washed with water after cooling, and dried to obtain the high-capacity activated carbon-based electrode material. The hyperbranched polycarbonate polyurethane of the present invention contains a large amount of nitrogen and sulfur elements. After high-temperature carbonization, nitrogen-sulfur co-doped porous activated carbon is formed, generating active sites such as pyrrolic nitrogen, pyridinic nitrogen, and thiophene sulfur, which are beneficial to improving electrical conductivity, improving pore structure, and increasing lithium storage sites. The porous structure is beneficial to promoting the transmission of lithium ions and electrons, thereby improving the charge and discharge specific capacity and capacity retention rate of the electrode material, and having better specific capacity and cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a preparation method and application of a high-capacity activated carbon-based electrode material. Background Art

[0002] As the global energy crisis intensifies, the development of green energy conversion and storage devices is urgent. Lithium-ion batteries, with their advantages of high charge and discharge efficiency, high output voltage, good environmental performance, and wide operating temperature range, have been widely used in new energy vehicles, laptops, mobile phones, and other equipment. The current commercial anode material for lithium-ion batteries is graphite carbon, which has a theoretical capacity of only 372 mA·h / g, severely limiting the energy density of lithium-ion batteries. The development of new high-capacity activated carbon anode materials for lithium-ion batteries is a research hotspot.

[0003] Current activated carbon materials are primarily formed through high-temperature carbonization using biomass precursors such as fruit shells and wood powder, as well as polymers. Polymers offer a wide variety of advantages, including the ability to adjust the pore size and specific surface area of ​​the carbon matrix and facilitate the introduction of active heteroatoms such as nitrogen, phosphorus, and sulfur. These polymers are widely used as electrode materials in lithium-ion batteries and supercapacitors. Summary of the Invention

[0004] Technical problem to be solved: The present invention provides a method for preparing an activated carbon-based electrode material for lithium-ion batteries with high specific surface area and high capacitance.

[0005] Technical solution: A method for preparing a high-capacity activated carbon-based electrode material, comprising the following steps:

[0006] Step A: Add dry polycarbonate diol and diisocyanate to a reaction vessel, carry out a prepolymerization reaction at 65-75° C. in a nitrogen atmosphere for 2-3 hours, then add acetone and a hyperbranched chain extender, carry out a hyperbranching reaction at 40-45° C. for 1.5-2 hours, and after the reaction, rotary evaporate the solution, wash with ethanol, and dry to obtain a hyperbranched polycarbonate polyurethane.

[0007] Step B: Grind and blend the hyperbranched polycarbonate polyurethane and potassium hydroxide, calcine in a tube furnace, cool, wash with water, and dry to obtain a high-capacity activated carbon-based electrode material.

[0008] In step A, the ratio of polycarbonate diol, diisocyanate, and hyperbranched chain extender is 1 mol: (2.4-2.8) mol: (1.6-1.9) mol. The diisocyanate is toluene-2,4-diisocyanate or 4,4'-methylenebis(phenyl isocyanate).

[0009] Wherein, the preparation method of hyperbranched chain extender is:

[0010] Step (1), add 1,4-dioxane, water, tris(2-aminoethyl)amine, 1,4-butanesulfonic acid lactone, and sodium hydroxide to a reaction vessel, heat to 70-80°C, react for 5-8h, then add 1,4-butanesulfonic acid lactone, wherein the ratio of tris(2-aminoethyl)amine, 1,4-butanesulfonic acid lactone, and sodium hydroxide is 1 mol: (3-3.3) mol: (3-3.3) mol, continue to react for 3-5h, cool, add hydrochloric acid solution dropwise to adjust the pH to 5-6, precipitate, filter, and dry to obtain a chain extender precursor.

[0011] Step (2): Add ethanol, a chain extender precursor in a ratio of 1 mol: (3-3.3) mol: (3-3.6) mol, 2-bromoethanol, and sodium hydroxide to a reaction vessel, heat to 40-60°C, react for 12-18 hours, distill under reduced pressure, wash with acetone, add the product to water, heat and evaporate, cool and crystallize to obtain a hyperbranched chain extender. The reaction formula is:

[0012] .

[0013] Wherein, in step B, the ratio of hyperbranched polycarbonate polyurethane to potassium hydroxide is 1 g:(2-3) g.

[0014] The heating rate during calcination in step B is 4-6°C / min, the temperature is raised to 700-800°C, and the temperature is kept for 2-3 hours.

[0015] (3) Technical effect: The present invention utilizes a hyperbranched chain extender containing sulfonate to react with polycarbonate and diisocyanate to obtain a hyperbranched polycarbonate polyurethane, which has a large molecular chain cross-linking density and good carbonization property. After carbonization, it can form a three-dimensional porous structure with richer pores, which is beneficial to improving the specific carbonization rate, pore volume and surface area. At the same time, the molecular chain contains a large amount of sulfonate structure, which can accelerate the thermal decomposition of polycarbonate in the molecular chain, promote the isomerization and cross-linking of polycarbonate to form carbon, further improve the carbonization rate, and thus carbonize to form a porous activated carbon material with better electrochemical properties.

[0016] The hyperbranched polycarbonate polyurethane of the present invention contains a large amount of nitrogen and sulfur elements. After high-temperature carbonization, nitrogen-sulfur co-doped porous activated carbon is formed, generating active sites such as pyrrolic nitrogen, pyridinic nitrogen, and thiophene sulfur, which are beneficial to improving electrical conductivity, improving pore structure, and increasing lithium storage sites. The porous structure is beneficial to promoting the transmission of lithium ions and electrons, thereby improving the charge and discharge specific capacity and capacity retention rate of the electrode material, and having better specific capacity and cycle stability. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present disclosure clearer, the technical solutions of the present disclosure will be clearly and completely described below in combination with the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments.

[0018] Example 1:

[0019] (1) Add 120 mL of 1,4-dioxane, 20 mL of water, 40 mmol of tris(2-aminoethyl)amine, 80 mmol of 1,4-butanesulfonate, and 120 mmol of sodium hydroxide to a reaction vessel, heat to 70 °C, and react for 8 h. Then add 46 mmol of 1,4-butanesulfonate and continue to react for 5 h. After cooling, add hydrochloric acid solution dropwise to adjust the pH to 5, precipitate, filter, and dry to obtain a chain extender precursor.

[0020] (2) Add 200 mL of ethanol, 40 mmol of chain extender precursor, 120 mmol of 2-bromoethanol, and 132 mmol of sodium hydroxide to a reaction vessel, heat to 50 °C, react for 18 h, distill under reduced pressure, wash with acetone, add the product to water, heat to evaporate, cool and crystallize to obtain a hyperbranched chain extender.

[0021] (3) Add 30 mmol of dry polycarbonate diol (molecular weight 1000) and 78 mmol of 4,4'-methylenebis(phenyl isocyanate) into the reaction vessel, and carry out prepolymerization at 65 °C in a nitrogen atmosphere for 3 h. Then, add 40 mL of acetone and 48 mmol of hyperbranched chain extender, and carry out hyperbranching reaction at 40 °C for 2 h. After the reaction, the solution is rotary evaporated, washed with ethanol, and dried to obtain hyperbranched polycarbonate polyurethane.

[0022] (4) 10 g of hyperbranched polycarbonate polyurethane and 25 g of potassium hydroxide were ground and blended. The mixture was heated to 700°C in a tube furnace at a heating rate of 5°C / min and calcined for 3 h. After cooling, the mixture was washed with water and dried to obtain a high-capacity activated carbon-based electrode material. The material was weighed and the carbonization rate was calculated. Carbonization rate = (mass before carbonization - mass after carbonization) ÷ mass before carbonization × 100%.

[0023] Example 2:

[0024] (1) Add 150 mL of 1,4-dioxane, 30 mL of water, 40 mmol of tris(2-aminoethyl)amine, 80 mmol of 1,4-butanesulfonate, and 132 mmol of sodium hydroxide to a reaction vessel, heat to 75 °C, and react for 5 h. Then add 40 mmol of 1,4-butanesulfonate and continue to react for 5 h. After cooling, add hydrochloric acid solution dropwise to adjust the pH to 6, precipitate, filter, and dry to obtain a chain extender precursor.

[0025] (2) Add 300 mL of ethanol, 40 mmol of chain extender precursor, 132 mmol of 2-bromoethanol, and 144 mmol of sodium hydroxide to a reaction vessel, heat to 40 °C, react for 18 h, distill under reduced pressure, wash with acetone, add the product to water, heat to evaporate, cool and crystallize to obtain a hyperbranched chain extender.

[0026] (3) Add 30 mmol of dry polycarbonate diol (molecular weight 1000) and 84 mmol of 4,4'-methylenebis(phenyl isocyanate) into the reaction vessel, and carry out prepolymerization at 70 °C in a nitrogen atmosphere for 3 h. Then, add 40 mL of acetone and 57 mmol of hyperbranched chain extender, and carry out hyperbranching reaction at 45 °C for 1.5 h. After the reaction, the solution is rotary evaporated, washed with ethanol, and dried to obtain hyperbranched polycarbonate polyurethane.

[0027] (4) 10 g of hyperbranched polycarbonate polyurethane and 20 g of potassium hydroxide were ground and blended, and then heated to 750 °C in a tubular furnace at a heating rate of 5 °C / min. The mixture was kept warm and calcined for 3 h. After cooling, it was washed with water and dried to obtain a high-capacity activated carbon-based electrode material. The material was weighed and the carbonization rate was calculated.

[0028] Example 3:

[0029] (1) Add 120 mL of 1,4-dioxane, 20 mL of water, 40 mmol of tris(2-aminoethyl)amine, 80 mmol of 1,4-butanesulfonate, and 132 mmol of sodium hydroxide to a reaction vessel, heat to 80 °C, and react for 5 h. Then add 52 mmol of 1,4-butanesulfonate and continue to react for 3 h. After cooling, add hydrochloric acid solution dropwise to adjust the pH to 6, precipitate, filter, and dry to obtain a chain extender precursor.

[0030] (2) Add 300 mL of ethanol, 40 mmol of chain extender precursor, 120 mmol of 2-bromoethanol, and 120 mmol of sodium hydroxide to a reaction vessel, heat to 60 °C, react for 12 h, distill under reduced pressure, wash with acetone, add the product to water, heat to evaporate, cool and crystallize to obtain a hyperbranched chain extender.

[0031] (3) Add 30 mmol of dry polycarbonate diol (molecular weight 1000) and 72 mmol of toluene-2,4-diisocyanate into the reaction vessel, and carry out prepolymerization at 75 °C for 2 h in a nitrogen atmosphere. Then, add 30 mL of acetone and 48 mmol of hyperbranched chain extender, and carry out hyperbranching reaction at 40 °C for 2 h. After the reaction, the solution is rotary evaporated, washed with ethanol, and dried to obtain hyperbranched polycarbonate polyurethane.

[0032] (4) 10 g of hyperbranched polycarbonate polyurethane and 30 g of potassium hydroxide were ground and blended, and then heated to 800 °C at a heating rate of 5 °C / min in a tubular furnace. The mixture was kept warm and calcined for 2 h. After cooling, it was washed with water and dried to obtain a high-capacity activated carbon-based electrode material. The material was weighed and the carbonization rate was calculated.

[0033] Comparative Example 1:

[0034] (1) Add 30 mmol of dry polycarbonate diol (molecular weight 1000) and 78 mmol of 4,4'-methylenebis(phenyl isocyanate) into a reaction vessel, and carry out a prepolymerization reaction at 65°C in a nitrogen atmosphere for 3 hours. Then, add 40 mL of acetone and 48 mmol of 1,4-butanediol, and carry out a hyperbranching reaction at 40°C for 2 hours. After the reaction, the solution is rotary evaporated, washed with ethanol, and dried to obtain a hyperbranched polycarbonate polyurethane.

[0035] (2) 10 g of hyperbranched polycarbonate polyurethane and 25 g of potassium hydroxide were ground and blended, and then heated to 700 °C in a tubular furnace at a heating rate of 5 °C / min. The mixture was kept warm and calcined for 3 h. After cooling, it was washed with water and dried to obtain an activated carbon-based electrode material. The material was weighed and the carbon yield was calculated.

[0036] Comparative Example 2:

[0037] (1) Add 30 mmol of dry polycarbonate diol (molecular weight 1000) and 78 mmol of 4,4'-methylenebis(phenyl isocyanate) into the reaction vessel, and carry out prepolymerization at 65 °C for 3 h in a nitrogen atmosphere. Then add 40 mL of acetone and 48 mmol of trimethylolpropane ( ), and a hyperbranched reaction was carried out at 40° C. for 2 h. After the reaction, the solution was rotary evaporated, washed with ethanol, and dried to obtain a hyperbranched polycarbonate polyurethane.

[0038] (2) 10 g of hyperbranched polycarbonate polyurethane and 25 g of potassium hydroxide were ground and blended, and then heated to 700 °C in a tubular furnace at a heating rate of 5 °C / min. The mixture was kept warm and calcined for 3 h. After cooling, it was washed with water and dried to obtain an activated carbon-based electrode material. The material was weighed and the carbon yield was calculated.

[0039] Comparative Example 3:

[0040] (1) Add 30 mmol of dry polycarbonate diol (molecular weight 1000) and 78 mmol of 4,4'-methylenebis(phenyl isocyanate) into a reaction vessel, and carry out prepolymerization at 65°C for 3 h in a nitrogen atmosphere. Then, add 40 mL of acetone and 48 mmol of sodium 1,2-dihydroxy-3-propanesulfonate ( ), a hyperbranching reaction was carried out at 40°C for 2h, and after the reaction, the solution was rotary evaporated, washed with ethanol, and dried to obtain polycarbonate polyurethane.

[0041] (2) 10 g of polycarbonate polyurethane and 25 g of potassium hydroxide were ground and blended, and then heated to 700 °C in a tube furnace at a heating rate of 5 °C / min. The mixture was kept warm and calcined for 3 h. After cooling, it was washed with water and dried to obtain an activated carbon-based electrode material. The material was weighed and the carbonization rate was calculated.

[0042] The pore volume and specific surface area of ​​the carbon-based electrode material were determined by nitrogen adsorption-desorption method using a specific surface and porosity analyzer. Before the test, the electrode material was vacuum degassed at 150°C for 12 h.

[0043] Table 1 Carbonization rate, pore volume and specific surface area test

[0044] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Carbonization rate (%) 11.4 16.7 14.9 4.2 6.4 7.5 Pore ​​volume (cm3 / g) 0.732 0.581 0.836 0.407 0.680 0.436 Specific surface area (m2 / g) 985.8 824.9 1135.2 585.7 913.6 604.5

[0045] Activated carbon-based electrode material, conductive carbon black, and polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 8:1:1. After mixing, the slurry was evenly coated on the surface of copper foil and dried to form a working electrode. Metal lithium sheet was used as the negative electrode, and a 1 mol / L LiPF6 solution was used as the electrolyte (the solvent was ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1). A button cell was assembled with a glass fiber membrane in an argon glove box, and the constant current discharge and charge performance test was carried out using a battery testing system with a voltage range of 0.1-3 V and a current density of 0.1 A / g.

[0046] Table 2 Charge and discharge performance test

[0047] First cycle discharge capacity (mA·h / g) Discharge capacity after 100 cycles (mA·h / g) Capacity retention rate (%) Example 1 804.5 712.9 88.6 Example 2 627.8 579.0 92.2 Example 3 955.4 836.7 87.6 Comparative Example 1 512.6 376.9 73.5 Comparative Example 2 667.2 542.3 81.3 Comparative Example 3 585.0 451.7 77.2

[0048] After testing, the high-capacity activated carbon-based electrode materials prepared in each embodiment have a higher carbonization rate, pore volume and specific surface area. This is because the hyperbranched polycarbonate polyurethane has a hyperbranched cross-linked network structure with a large cross-linking density, better carbonization, and can form a three-dimensional porous structure with richer pores after carbonization, which is beneficial to improving the specific carbonization rate, pore volume and surface area. At the same time, the molecular chain contains a large amount of sulfonate structure, which can accelerate the thermal decomposition of polycarbonate in the molecular chain, promote isomerization and cross-linking of polycarbonate into carbon, thereby further improving the carbonization rate, and can be carbonized to form a porous activated carbon material with better electrochemical performance. At the same time, the hyperbranched polycarbonate polyurethane contains a large amount of nitrogen and sulfur elements, which form nitrogen-sulfur co-doped porous activated carbon after high-temperature carbonization, generating active sites such as pyrrole nitrogen, pyridine nitrogen, and thiophene sulfur, which is beneficial to improving electrical conductivity, improving pore structure, increasing lithium storage sites, improving the specific capacity and cycle stability of the electrode material, and showing higher charge and discharge specific capacity and capacity retention rate.

[0049] Compared with Example 1, Comparative Examples 1 and 3 use 1,4-butanediol and sodium 1,2-dihydroxy-3-propanesulfonate as chain extenders, and the obtained polycarbonate polyurethanes are linear molecular chains without hyperbranched three-dimensional cross-linked structures. The polycarbonate polyurethane of Comparative Example 1 also does not contain a sulfonate structure, resulting in small pore volume and specific surface area of ​​the activated carbon after carbonization of the two, and low carbonization rate, and low charge and discharge specific capacity and capacity retention rate of the electrode material, and poor electrochemical performance.

[0050] Comparative Example 2 uses trimethylolpropane as a chain extender, and the obtained polycarbonate polyurethane does not contain sulfonate groups, has poor carbonization properties, and has a low carbonization rate. In addition, the charge and discharge specific capacity and capacity retention rate of the electrode material are low, and the electrochemical performance is poor.

Claims

1. A method for preparing a high-capacity activated carbon-based electrode material, characterized in that: The preparation method is as follows: Step A: Add dry polycarbonate diol and diisocyanate into a reaction vessel, perform prepolymerization in a nitrogen atmosphere, and then add acetone. The structural formula is A hyperbranched chain extender is added to carry out a hyperbranching reaction, and after the reaction, the solution is rotary evaporated, washed with ethanol, and dried to obtain a hyperbranched polycarbonate polyurethane; Step B: Grind and blend the hyperbranched polycarbonate polyurethane and potassium hydroxide, calcine in a tube furnace, cool, wash with water, and dry to obtain a high-capacity activated carbon-based electrode material.

2. The method for preparing a high-capacity activated carbon-based electrode material according to claim 1, characterized in that: In the step A, the ratio of polycarbonate diol, diisocyanate, and hyperbranched chain extender is 1 mol: (2.4-2.8) mol: (1.6-1.9) mol.

3. The method for preparing a high-capacity activated carbon-based electrode material according to claim 1, characterized in that: The diisocyanate is toluene-2,4-diisocyanate or 4,4'-methylenebis(phenyl isocyanate).

4. The method for preparing a high-capacity activated carbon-based electrode material according to claim 1, wherein: The preparation method of the hyperbranched chain extender is: Step (1), adding 1,4-dioxane, water, tris(2-aminoethyl)amine, 1,4-butane sultone, and sodium hydroxide to a reaction vessel, heating to 70-80°C, reacting for 5-8 hours, then adding 1,4-butane sultone, continuing the reaction for 3-5 hours, cooling, adding hydrochloric acid solution dropwise to adjust the pH to 5-6, precipitating the precipitate, filtering, and drying to obtain a chain extender precursor; Step (2): add ethanol, a chain extender precursor in a ratio of 1 mol: (3-3.3) mol: (3-3.6) mol, 2-bromoethanol, and sodium hydroxide to a reaction vessel, heat to 40-60° C., react for 12-18 hours, distill under reduced pressure, wash with acetone, add the product to water, heat to evaporate, cool and crystallize to obtain a hyperbranched chain extender.

5. The method for preparing a high-capacity activated carbon-based electrode material according to claim 4, characterized in that: In the step (1), the ratio of tris(2-aminoethyl)amine, 1,4-butanesulfonate, and sodium hydroxide is 1 mol: (3-3.3) mol: (3-3.3) mol.

6. The method for preparing a high-capacity activated carbon-based electrode material according to claim 1, characterized in that: In the step A, the prepolymerization reaction is carried out at 65-75° C. for 2-3 hours, and the hyperbranching reaction is carried out at 40-45° C. for 1.5-2 hours.

7. The method for preparing a high-capacity activated carbon-based electrode material according to claim 1, wherein: In the step B, the ratio of the hyperbranched polycarbonate polyurethane to potassium hydroxide is 1 g:(2-3) g.

8. The method for preparing a high-capacity activated carbon-based electrode material according to claim 1, wherein: The heating rate during calcination in step B is 4-6°C / min, the temperature is raised to 700-800°C, and the temperature is kept for 2-3 hours.

9. Use of a high-capacity activated carbon-based electrode material obtained by the preparation method according to any one of claims 1 to 8 in a lithium-ion battery.

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