Multi-element gradient step-by-step doped hard carbon composite negative electrode material and preparation method thereof

Abstract

The invention discloses a multi-element gradient step-by-step doped hard carbon composite negative electrode material and a preparation method thereof, and the multi-element gradient step-by-step doped hard carbon composite negative electrode material is characterized in that the hard carbon composite negative electrode material comprises a hard carbon matrix, 0.5-5 wt% of Zn, 0.3-3 wt% of Ni, 2-8 wt% of N and 1-6 wt% of S, the atomic ratio of Zn to Ni is 1: 1-3: 1, and the atomic ratio of N to S is 1: 0.5-1: 2; the preparation method comprises the steps of hard carbon preparation, mixed gel preparation and gradient doping heat treatment. Four elements of zinc, nickel, nitrogen and sulfur are doped in hard carbon to form a core-shell hierarchical pore structure, a core layer is crystalline hard carbon, a shell layer is amorphous carbon, Zn-Ni alloy nanoparticles are coated with the core-shell hierarchical pore structure, N-S co-doped functional groups are enriched on the surface of the core-shell hierarchical pore structure, and sodium embedding energy, high conductivity and high catalytic activity of the hard carbon composite negative electrode material are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery negative electrode materials, and in particular to a multi-element gradient step-by-step doping hard carbon composite negative electrode material and a preparation method thereof. Background Art

[0002] Existing hard carbon doping technologies mostly focus on single or double element modification (such as nitrogen doping and single metal doping), which has the following problems: 1. Metal doping is unevenly distributed, and particles are prone to agglomeration, reducing the utilization rate of active sites; 2. Non-metallic doping has a high loss rate during the heat treatment process, and the doping effect is relatively poor; 3. The multi-element doping process is complex and difficult to achieve uniform distribution; 4. Traditional one-step high-temperature carbonization can easily destroy the original short-range order and porous structure of hard carbon; and the use of biomass carbon sources (such as pine cones, coconut shells, sugarcane bagasse, bamboo shells, etc.) as hard carbon precursors has the advantages of environmental protection and low cost. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a multi-element gradient step-by-step doped hard carbon composite negative electrode material and a preparation method thereof, which has the advantages of high conductivity and catalytic activity, effectively improving the sodium insertion capacity of hard carbon, and is conducive to overcoming the shortcomings of the existing technology.

[0004] In order to solve the above technical problems, the technical solution of the present invention is:

[0005] A multi-element gradient step-by-step doped hard carbon composite negative electrode material, characterized by comprising a hard carbon matrix, four elements: Zn, Ni, N, and S, wherein the Zn content is 0.5-5wt%, the Ni content is 0.3-3wt%, the N content is 2-8wt%, the S content is 1-6wt%, and the balance is the hard carbon matrix; the Zn / Ni atomic ratio is 1:1-3:1, and the N / S atomic ratio is 1:0.5-1:2; the hard carbon composite negative electrode material is used as a negative electrode material for lithium ion or sodium ion batteries.

[0006] Furthermore, a method for preparing a multi-element gradient step-by-step doped hard carbon composite negative electrode material comprises the following steps:

[0007] S1: Grind the biomass carbon source to less than 200 mesh.

[0008] S2: The crushed biomass carbon source is placed in a nitrogen atmosphere for heat treatment at a constant temperature of 400-600° C. for 2-5 hours, or at a constant temperature of 800-1200° C. for 2-5 hours.

[0009] S3: After cooling naturally, the hard carbon matrix is ​​soaked in hydrochloric acid and potassium hydroxide to remove ash. After soaking, it is fully washed with deionized water and then placed in a sand mill for ball milling to form a hard carbon matrix.

[0010] S4: mixing the prepared hard carbon matrix with zinc salt, nickel salt, sulfur source, and nitrogen source according to the mass ratio of the material elements, and performing a hydrothermal reaction to form a gel.

[0011] S5: Treat at 300-500° C. for 2-5 hours under an inert atmosphere to form a primary carbon skeleton anchored by metal ions.

[0012] S6: In a H2S / NH3 mixed atmosphere, treat at 800-1200°C for 1-3 hours to achieve S / N doping and in-situ reduction of metal particles.

[0013] Furthermore, the biomass carbon source includes one or more of pine cones, coconut shells, bagasse, and bamboo shells, and the specific surface area of ​​the hard carbon matrix is ​​300-800m 2 / g, among the pores of the hard carbon matrix, mesopores with a pore diameter of 2-5nm account for more than 50%.

[0014] Furthermore, the concentration of hydrochloric acid and potassium hydroxide used to soak the biomass carbon source is 0.5-3 mol / L; and the particle size D50 of the hard carbon matrix after ball milling is 500-900 nm.

[0015] Furthermore, the reaction temperature for preparing the gel is 130°C-250°C, and the pressure is 1-60MPa; the zinc salt is ZnSO4, the nickel salt is Ni(NO3)2, the sulfur source is one or more of thiourea, ammonium thiocyanate, and ammonium persulfate, and the nitrogen source is one or more of urea and melamine.

[0016] The above technical solution has the following beneficial effects: the present invention adopts a gradient distribution doping process to dope zinc, nickel, nitrogen and sulfur into hard carbon to form a core-shell multi-level porous structure, the core layer is crystalline hard carbon, and the shell layer is amorphous carbon, which is coated with Zn-Ni alloy nanoparticles and enriched with NS co-doped functional groups on the surface. It has high conductivity and catalytic activity, effectively improves the sodium embedding energy of hard carbon, and has the advantages of environmental protection and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other implementation drawings based on the provided drawings without inventive effort.

[0018] The structures, proportions, sizes, etc. illustrated in this specification are intended only to complement the contents disclosed herein and to facilitate understanding and reading by persons familiar with the art. They are not intended to limit the conditions under which the present invention may be implemented and therefore have no substantive technical significance. Any structural modifications, changes in proportions, or adjustments in sizes, without affecting the efficacy and objectives of the present invention, shall still fall within the scope of the technical contents disclosed herein.

[0019] Figure 1 This is a scanning electron microscope (SEM) image of the hard carbon composite negative electrode material of the present invention. DETAILED DESCRIPTION

[0020] The following is a further description of specific embodiments of the present invention in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0021] The present invention discloses a multi-element gradient step-by-step doping hard carbon composite negative electrode material and a preparation method thereof. The present invention is further described in conjunction with specific embodiments:

[0022] 1. Grind 10g of pine cones to less than 200 mesh, and heat treat them under nitrogen atmosphere at a constant temperature of 600℃ for 2 hours and 1200℃ for 2 hours; after natural cooling, soak them in hydrochloric acid and potassium hydroxide to remove ash from the hard carbon. The concentration of hydrochloric acid and potassium hydroxide is 2mol / L. After soaking, rinse them thoroughly with deionized water, then put them into a sand mill and ball mill them to a particle size D50 of 800nm.

[0023] 2. The above hard carbon was dissolved in 50 mL of water with 0.5 g of ZnSO4·7H2O, 0.3 g of Ni(NO3)2·6H2O, 2 g of thiourea, and 3 g of urea. The mixture was heated at 180°C for 12 h and freeze-dried to obtain a gel.

[0024] 3. Pre-carbonize at 400℃ in Ar atmosphere for 3 hours.

[0025] 4. Treat in H2S / NH3 (volume ratio 1:2) mixed gas at 1000℃ for 2 hours.

[0026] 5. Wash with 1M HCl and then dry to obtain quaternary doped hard carbon material.

[0027] Performance testing:

[0028] The first discharge specific capacity at 0.2C reaches 750mAh / g (sodium ion battery), and the capacity retention rate after 300 cycles is 99%. The test results are shown in Table 1.

[0029]

[0030]

[0031] Table 1

[0032] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations to these embodiments may be made without departing from the principles and spirit of the present invention, and these changes and modifications still fall within the scope of protection of the present invention.

Claims

1. A multi-element gradient step-by-step doping hard carbon composite negative electrode material, characterized by: It includes four elements: hard carbon matrix, Zn, Ni, N and S, wherein the Zn content is 0.5-5wt%, the Ni content is 0.3-3wt%, the N content is 2-8wt%, the S content is 1-6wt%, and the balance is the hard carbon matrix; the Zn / Ni atomic ratio is 1:1-3:1, and the N / S atomic ratio is 1:0.5-1:2; the hard carbon composite negative electrode material is used for lithium ion or sodium ion battery negative electrode materials.

2. The method for preparing a multi-element gradient step-by-step doping hard carbon composite negative electrode material according to claim 1, characterized in that The steps include: S1: Grind the biomass carbon source to less than 200 mesh. S2: The crushed biomass carbon source is placed in a nitrogen atmosphere for heat treatment at a constant temperature of 400-600° C. for 2-5 hours, or at a constant temperature of 800-1200° C. for 2-5 hours. S3: After cooling naturally, the hard carbon matrix is ​​soaked in hydrochloric acid and potassium hydroxide to remove ash. After soaking, it is fully washed with deionized water and then placed in a sand mill for ball milling to form a hard carbon matrix. S4: mixing the prepared hard carbon matrix with zinc salt, nickel salt, sulfur source, and nitrogen source according to the mass ratio of the material elements, and performing a hydrothermal reaction to form a gel. S5: treating at 300-500° C. for 2-5 hours under an inert atmosphere to form a primary hard carbon material anchored by metal ions. S6: In a H2S / NH3 mixed atmosphere, treat at 800-1200°C for 1-3 hours to achieve S / N doping and in-situ reduction of metal particles.

3. The method for preparing a multi-element gradient step-by-step doped hard carbon composite negative electrode material according to claim 2, characterized in that: The biomass carbon source includes one or more of pine cones, coconut shells, bagasse, and bamboo shells; the specific surface area of ​​the hard carbon matrix is ​​300-800m 2 / g, among the pores of the hard carbon matrix, mesopores with a pore diameter of 2-5nm account for more than 50%.

4. The method for preparing a multi-element gradient step-by-step doped hard carbon composite negative electrode material according to claim 2, characterized in that: The concentration of hydrochloric acid and potassium hydroxide used to soak the biomass carbon source is 0.5-3 mol / L.

5. The method for preparing a multi-element gradient step-by-step doped hard carbon composite negative electrode material according to claim 2, characterized in that: The particle size D50 of the hard carbon matrix after ball milling is 500-900 nm.

6. The method for preparing a multi-element gradient step-by-step doped hard carbon composite negative electrode material according to claim 2, characterized in that: The reaction temperature for preparing the gel is 130° C.-250° C., and the pressure is 1-60 MPa.

7. The method for preparing a multi-element gradient step-by-step doped hard carbon composite negative electrode material according to claim 2, characterized in that: The zinc salt is ZnSO4, the nickel salt is Ni(NO3)2, the sulfur source is one or more of thiourea, ammonium thiocyanate, and ammonium persulfate, and the nitrogen source is one or more of urea and melamine.

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