Preparation method and application of nitrogen-sulfur co-doped resin-based porous hard carbon material

Abstract

The embodiment of the invention relates to a preparation method and application of a nitrogen-sulfur co-doped resin-based porous hard carbon material, and belongs to the field of carbon material preparation. The preparation method comprises the following steps: taking resin as a carbon source, taking trithiocyanuric acid as a double doping agent and a pore forming agent, mixing through an ethanol solvent to form a uniform and dry precursor, performing high-temperature carbonization in an inert atmosphere to realize nitrogen-sulfur co-doping and porous structure construction in one step, and cooling to room temperature to obtain the nitrogen-sulfur co-doped resin-based porous hard carbon material. The prepared hard carbon material has an amorphous structure, the doping amounts of nitrogen and sulfur are respectively 1-5at%, and the specific surface area is less than 5m < 2 > g <-1 >. When the material is used as an active material of a negative electrode of a potassium ion battery, the electrochemical properties such as specific capacity, rate capability and cycling stability are excellent. The method has the characteristics of simple process and low cost, is easy to realize large-scale production, and provides a new strategy for the development of high-performance potassium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon material preparation, and in particular relates to a method for preparing a porous carbon and sulfur composite material. Background Art

[0002] The information disclosed in this background section is intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that this information constitutes the prior art already known to those skilled in the art.

[0003] The development of efficient, low-cost and environmentally friendly electrochemical energy storage systems has become an urgent need. Although lithium-ion batteries dominate the market, their sustainable development is limited by the scarcity and high cost of lithium resources, which has promoted the exploration of new battery systems based on abundant elements (such as potassium). Potassium-ion batteries are regarded as a very promising alternative due to their abundant potassium resources, low redox potential and fast ion transport properties. However, potassium ions have a large radius, and traditional graphite negative electrode materials are difficult to adapt to the storage and diffusion requirements of large-sized potassium ions, resulting in limited capacity and slow kinetics. In addition, volume expansion and structural stress are easily caused when potassium ions are inserted / extracted, resulting in rapid capacity decay and insufficient cycle stability, which seriously restricts its commercialization process.

[0004] Amorphous carbon materials (such as hard carbon) can effectively alleviate volume strain and provide more potassium storage sites due to their enlarged interlayer spacing (0.38-0.42 nm) and rich pore structure. Heteroatom doping engineering is an effective strategy to optimize the potassium storage performance of carbon materials. Specifically, nitrogen doping can enhance the polarity of the carbon layer and increase the electron density, while sulfur doping induces lattice distortion through the difference in atomic radius, synergistically expanding the carbon interlayer spacing and increasing defective active sites. However, the existing nitrogen-sulfur co-doping process mostly uses precursors such as thiourea or ammonium sulfide, which has problems such as low doping efficiency and insufficient pore structure control. In addition, although resin-based hard carbon has the advantage of structural uniformity over biomass, there is little research on the one-step method to achieve doping and pore formation. Summary of the Invention

[0005] The present invention aims to provide a method for preparing nitrogen-sulfur co-doped resin-based porous hard carbon materials based on thiocyanate-assisted preparation. The method has the advantages of simple process, low cost, and suitability for large-scale production. The prepared nitrogen-sulfur co-doped resin-based porous hard carbon materials have a porous amorphous structure, with nitrogen and sulfur doping amounts of 1 to 5 at% each and a specific surface area of ​​less than 5 m 2 g -1 , which can be used as the active material for the negative electrode of high-performance potassium ion batteries.

[0006] To achieve the above object, in a first aspect, the preparation method adopted by the present invention comprises the following steps:

[0007] (1) mixing a resin carbon source and an auxiliary agent in a solvent to form a uniform precursor, wherein the mass ratio of the resin carbon source to the auxiliary agent is 1 g:(1-2) g;

[0008] (2) Place the above precursor in a tube furnace and perform high-temperature carbonization treatment under an inert atmosphere at a heating rate of 3-10 °C min -1 The carbonization temperature is 900-1300°C and the holding time is 2-4h to obtain nitrogen-sulfur co-doped resin-based porous hard carbon material.

[0009] In a preferred embodiment of the present invention, the resin carbon source in step (1) is an organic carbon source such as phenolic resin, epoxy resin, polyamide resin, polyester resin, etc., and the auxiliary agent is thiocyanate.

[0010] In a preferred embodiment of the present invention, the solvent in step (1) is ethanol, and the mass volume ratio of the resin carbon source to ethanol is 1 g: (2-4) mL. After sufficient stirring, the solvent is evaporated to obtain a uniformly dried precursor.

[0011] In a preferred embodiment of the present invention, the inert atmosphere in step (2) is any one of nitrogen, argon, and hydrogen, or a combination of more than one of them, with nitrogen being preferred in terms of cost.

[0012] In a second aspect, an embodiment of the present invention provides a nitrogen-sulfur co-doped porous hard carbon negative electrode material obtained by the preparation method according to the first aspect, characterized in that the negative electrode material is a porous amorphous structure, the nitrogen and sulfur doping amounts are 1 to 5 at%, and the specific surface area is less than 5 m 2 g -1 .

[0013] Preferably, the material is used as an active material for the negative electrode of a potassium ion battery.

[0014] In a third aspect, an embodiment of the present invention provides a potassium ion full battery, comprising the negative electrode material described in the second aspect above.

[0015] Compared with the prior art, the present invention has the following significant advantages:

[0016] 1) The present invention adopts a simple and efficient process with low equipment requirements. By using a low-cost resinous organic carbon source and utilizing thiocyanate as a bifunctional dopant and pore-forming agent, the conventional acid-washing step to remove the pore-forming agent is avoided, significantly reducing preparation costs and enabling the large-scale preparation of nitrogen-sulfur co-doped porous hard carbon materials.

[0017] 2) The nitrogen-sulfur co-doped porous hard carbon material prepared by the present invention not only achieves the nitrogen-sulfur synergistic doping effect (nitrogen enhances electronic conductivity, sulfur expands the interlayer spacing) and porous structure optimization, but also constructs micron-scale pores for ion transport and buffering volume expansion. When used as the active material for the negative electrode of potassium ion battery, at 10Ag -1 Achieve 100mAh g -1 The specific capacity at 5A g -1 The capacity retention rate is 82.9% after 2500 cycles at high rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 These are the microstructural characterization results of the nitrogen-sulfur co-doped porous hard carbon material prepared in Example 1 of the present invention, where (a) is a scanning electron microscope photograph and (b) is a transmission electron microscope photograph.

[0019] Figure 2 This is a scanning electron microscope photograph of the hard carbon material prepared in Comparative Example 1 of the present invention without adding thiocyanate auxiliary agent.

[0020] Figure 3 These are the X-ray diffraction spectra of the hard carbon materials prepared in Example 1 and Comparative Example 1 of the present invention.

[0021] Figure 4 These are nitrogen adsorption and desorption curves of the hard carbon materials prepared in Example 1 of the present invention and Comparative Example 1.

[0022] Figure 5 These are EDS spectra of the hard carbon materials prepared in Example 1 and Comparative Example 1 of the present invention.

[0023] Figure 6 When the hard carbon materials prepared in Example 1 and Comparative Example 1 of the present invention are used as negative electrode materials for potassium ion batteries, the discharge capacities of the assembled half-cells at different rates.

[0024] Figure 7 When the hard carbon materials prepared in Example 1 and Comparative Example 1 of the present invention are used as negative electrode materials for potassium ion batteries, the assembled half-cells are -1 Capacity change curve after 1000 cycles.

[0025] Figure 8 When the hard carbon materials prepared in Example 1 and Comparative Example 1 of the present invention are used as negative electrode materials for potassium ion batteries, the assembled half-cells have a -1 Capacity change curve after 2500 cycles.

[0026] Figure 9When the nitrogen-sulfur co-doped porous hard carbon material prepared in Example 1 of the present invention is used as the negative electrode material of potassium ion battery, it is matched with the Prussian blue KPB positive electrode. The assembled full battery has a current density of 0.5A g -1 Capacity change curve after 500 cycles. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to the accompanying drawings and through specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0028] Example 1:

[0029] (1) Weigh 5g of phenolic resin and 5g of trithiocyanate in a beaker, add 20mL of anhydrous ethanol, ensure that the mass ratio of phenolic resin to trithiocyanate is 1:1, and the mass volume ratio of phenolic resin to ethanol is 1g:4mL. Place the mixed solution on a magnetic stirrer and stir continuously at 500rpm for 2h, then ultrasonicate for 30min to form a uniform suspension; (2) Transfer the above suspension to a heating table, stir and evaporate the ethanol until completely dry, and then grind it thoroughly to obtain a powder precursor with uniform particle size; (3) Spread the above precursor powder in a corundum crucible, place it in the reaction chamber of a tubular furnace, introduce nitrogen as a protective gas, and heat at 5℃min -1 The mixture is heated to 900-1300°C at a heating rate, kept at this temperature for 2 hours, and naturally cooled to room temperature to obtain a nitrogen-sulfur co-doped porous hard carbon material; (4) the hard carbon material prepared above is mixed with a binder and a conductive agent to prepare a slurry, coated, and a circular negative electrode sheet is cut to be used as a negative electrode of a potassium ion battery.

[0030] Comparative Example 1:

[0031] Except for not adding thiocyanate as an auxiliary agent, the remaining operations were the same as those in Example 1 to obtain a nitrogen- and sulfur-free hard carbon material.

[0032] The nitrogen-sulfur co-doped porous hard carbon material obtained in Example 1 exhibits a microporous structure ( Figure 1 ), the scanning electron microscope photo shows that the material has micron-sized macropores, and the transmission electron microscope photo proves the amorphous structure; while the electron microscope photo of Comparative Example 1 shows a smooth solid block ( Figure 2 ); grind the sample and perform X-ray diffraction analysis ( Figure 3 ), the characteristic peaks of the samples of Example 1 and Comparative Example 1 correspond to the characteristic peaks of graphite, wherein the angle corresponding to the (002) peak of Example 1 shifts to the left relative to that of Comparative Example 1, proving the increase in the carbon interlayer spacing of the sample of Example 1; the nitrogen adsorption-desorption curve shows that the specific surface area of ​​the hard carbon material is increased by 3.67 times with the assistance of trithiocyanate, but only increases to 2.2m 2 g -1 ( Figure 4), which is conducive to the infiltration and diffusion of electrolyte ions and will not cause a decrease in the initial coulombic efficiency of potassium storage; EDS energy spectrum analysis proves that nitrogen and sulfur elements are successfully incorporated into the hard carbon material ( Figure 5 ).

[0033] The prepared nitrogen-sulfur co-doped porous hard carbon material was used as the negative electrode material of potassium ion battery. The material was pulped, coated, cut into circular pole pieces, and assembled into potassium ion half-cells for performance testing. The results showed that the material had excellent rate capacity ( Figure 6 ), low current cycle stability ( Figure 7 ), and high current long cycle stability ( Figure 8 ). Specifically: at 10A g -1 The discharge capacity at the highest rate reaches 100 mAh g -1 ; in 1A g -1 After 1000 cycles at the same rate, the capacity remains at 284 mAh g -1 ; in 5A g -1 The capacity retention rate was 82.9% after 2500 cycles at a high rate. In addition, the assembled potassium ion full battery had good cycle stability when the negative electrode was matched with the Prussian blue KPB positive electrode. -1 Cycle 500 times at a rate of Figure 9 ).

[0034] Example 2:

[0035] The 5 g of phenolic resin in step (1) of Example 1 was replaced with 10 g of phenolic resin, and the remaining operations were the same as in Example 1. The resulting nitrogen-sulfur co-doped porous hard carbon material also exhibited micron-sized macropores and an amorphous structure, with slightly reduced nitrogen and sulfur doping levels and specific surface area, and its potassium storage performance was similar to that of Example 1.

[0036] Example 3:

[0037] In step (1) of Example 1, 5 g of thiocyanate was replaced with 10 g of thiocyanate, and the remaining operations were the same as in Example 1. The resulting nitrogen-sulfur co-doped porous hard carbon material also exhibited an amorphous structure, with slightly increased nitrogen-sulfur doping amount, pore size, and specific surface area, and the potassium storage performance was similar to that of Example 1.

[0038] Example 4:

[0039] In step (1) of Example 1, 5 g of phenolic resin was replaced with 5 g of epoxy resin, and the remaining operations were the same as in Example 1. The resulting nitrogen-sulfur co-doped porous hard carbon material also exhibited micron-sized macropores and an amorphous structure, and its specific surface area and hierarchical pore structure were comparable to those of Example 1, and its potassium storage performance was similar to that of Example 1.

[0040] Example 5:

[0041] In step (1) of Example 1, 5 g of phenolic resin was replaced with 5 g of polyamide resin, and the remaining operations were the same as those of Example 1. The resulting porous carbon material had similar micron-sized macropores and amorphous structure as those of Example 1, and its specific surface area, hierarchical pore structure, and potassium ion battery performance were comparable to those of Example 1.

[0042] Example 6:

[0043] In step (1) of Example 1, 5 g of phenolic resin was replaced with 5 g of polyester resin, and the remaining operations were the same as those of Example 1. The resulting porous carbon material had similar micron-sized macropores and amorphous structure as those of Example 1, and its specific surface area, hierarchical pore structure, and potassium ion battery performance were comparable to those of Example 1.

[0044] It should be noted that the present invention is not limited to the methods and materials described in the above specific embodiments, and those skilled in the art may make appropriate adjustments and modifications based on actual needs. The terms used herein are only used to describe specific embodiments and are not intended to limit the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing nitrogen-sulfur co-doped resin-based porous hard carbon material, characterized in that: The following steps are involved: (1) mixing a resin carbon source and an auxiliary agent in a solvent to form a precursor, wherein the mass ratio of the resin carbon source to the auxiliary agent is 1 g:(1-2) g; (2) Place the above precursor in a tube furnace and perform high-temperature carbonization treatment under an inert atmosphere at a heating rate of 3-10 °C min -1 The carbonization temperature is 900-1300°C and the holding time is 2-4h to obtain nitrogen-sulfur co-doped resin-based porous hard carbon material.

2. The preparation method according to claim 1, characterized in that The resin carbon source is one or more of phenolic resin, epoxy resin, polyamide resin, polyester resin, etc., and the auxiliary agent is thiocyanate.

3. The preparation method according to claim 1, characterized in that The solvent is ethanol, and the mass volume ratio of the resin carbon source to the ethanol is 1 g: (2-4) mL. After sufficient stirring, the solvent is evaporated to obtain a uniformly dried precursor.

4. The preparation method according to claim 1, characterized in that The inert atmosphere is any one of argon, nitrogen, and helium, or a combination of more than one.

5. The nitrogen-sulfur co-doped porous hard carbon negative electrode material prepared by the method according to claims 1 to 4, characterized in that: The negative electrode material has a porous amorphous structure, the nitrogen and sulfur doping amounts are 1 to 5 at%, and the specific surface area is less than 5m 2 g -1 .

6. The nitrogen-sulfur co-doped porous hard carbon negative electrode material according to claim 5, characterized in that: The material is used as a negative electrode active material for potassium ion batteries.

7. A potassium ion full battery, characterized in that The nitrogen-sulfur co-doped porous hard carbon material according to claim 5 is used as a negative electrode.

Images