Metal-doped hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a metal-doped hard carbon negative electrode material and a preparation method thereof, and relates to the technical field of sodium ion batteries. The method comprises the following steps: 1) mixing a zinc salt activator and a carbon source according to a certain proportion, and stirring to obtain a zinc-doped hard carbon precursor; and 2) performing high-temperature carbonization on the mixture in an inert gas environment to obtain the negative electrode material. The preparation method disclosed by the invention is simple to operate and relatively low in cost, the obtained zinc-doped hard carbon negative electrode material contains rich microporous and mesoporous structures, more sodium storage sites are provided, the diffusion rate of sodium ions is increased by zinc ions through interlayer spacing regulation and control, a charge shielding effect and improvement of interface dynamics, and the performance of the zinc-doped hard carbon negative electrode material is improved. The first-circle coulombic efficiency and the circulation rate capability are promoted to be obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of secondary battery negative electrode materials, and in particular to hard carbon negative electrode materials and a preparation method thereof. Background Art

[0002] With the rapid development of modern society, the global demand for energy is intensifying, necessitating the development of new, efficient energy storage devices. As a crucial component of batteries, anode materials significantly impact their performance. Currently, most commercially available anode materials are graphite, which exhibits excellent cycling, rate performance, and safety. However, the interlayer spacing of graphite is only approximately 0.335 nm. For lithium-ion batteries, this small interlayer spacing limits the diffusion rate of lithium ions, making charge and discharge difficult. Compared to graphite, hard carbon materials have a larger interlayer spacing (0.37-0.42 nm), providing ample ion channels for lithium ion diffusion. Since sodium and lithium are elements of the same family and share similar physicochemical properties, sodium-ion batteries offer low cost, high rate performance, and long lifespan. When using graphite as the anode of sodium-ion batteries, sodium ions, due to their large ionic radius, cannot intercalate into the graphite interlayers to form a stable Na-C compound. However, hard carbon materials, with their larger interlayer spacing, fully accommodate sodium ions. Therefore, hard carbon materials are promising negative electrode materials for both sodium-ion batteries and lithium-ion batteries.

[0003] Current research cannot effectively solve the problems of low first cycle efficiency, large specific surface area, and poor cycle stability of hard carbon materials. Therefore, it is of great significance to develop a new type of hard carbon material. Summary of the Invention

[0004] In response to the problems raised in the background technology, the purpose of the present invention is to provide a hard carbon negative electrode material and a preparation method thereof. The present invention achieves the regulation and optimization of the surface defects and internal structure of the carbon material by adding a certain proportion of zinc source to the carbon source. This method can improve the first coulombic efficiency and theoretical specific capacity of the battery.

[0005] The present invention is specifically achieved by the following method:

[0006] In a first aspect, the present invention provides a method for preparing a hard carbon negative electrode material, comprising the following steps:

[0007] 1) Mixing a zinc salt activator and a carbon source in a certain proportion and stirring to obtain a zinc-doped hard carbon precursor;

[0008] 2) The mixture is carbonized at high temperature in an inert gas environment to obtain a hard carbon negative electrode material.

[0009] Furthermore, in step 1), the zinc source is any one or a combination of at least two of zinc gluconate, zinc acetate, zinc ethoxide, zinc oxalate, zinc acetate dihydrate, and zinc malate, more preferably zinc acetate or zinc acetate dihydrate. The use of an organic zinc salt as the zinc source creates pores during high-temperature carbonization, increasing the specific surface area of the material and providing more active sites. Furthermore, the zinc salt is relatively mild and does not completely etch the hard carbon material. The resulting hard carbon negative electrode material contains a rich microporous and mesoporous structure. The micropores provide more sodium storage sites, while the mesopores improve the material's rate performance.

[0010] Furthermore, in step 1), the carbon source is any one or a combination of two of glucose, carbon nanotubes, starch, carbon cloth and polyester fibers, and is further preferably one of glucose and starch; compared with preparing hard carbon materials with expensive raw materials such as high molecular polymers, preparing hard carbon materials with simple sugar compounds greatly reduces the preparation cost.

[0011] Furthermore, the mass ratio of the zinc source to the carbon source is 0.01:1 to 0.1:1, more preferably 0.03:1 to 0.1:1, and most preferably 0.05:1 to 0.1:1.

[0012] Furthermore, in step 2), the carbonization process is carried out in an inert atmosphere at a carbonization temperature of 500-2000°C, more preferably 500-1500°C, and most preferably 500-1000°C.

[0013] Furthermore, in step 2), the heating rate is 1 to 10°C / min, more preferably 1 to 7°C / min, and most preferably 3 to 7°C / min.

[0014] In step 2), the holding time is 1 to 10 hours, more preferably 1 to 8 hours, and most preferably 1 to 5 hours.

[0015] In a second aspect, the present invention provides a hard carbon negative electrode material prepared by the method described in the first aspect. The hard carbon negative electrode material has a rich pore structure and can provide a relatively spacious channel for the embedding of ions, thereby improving the first coulombic efficiency and cycle performance.

[0016] In a third aspect, the present invention provides a negative electrode for a sodium ion battery, wherein the hard carbon negative electrode material described in the second aspect is mixed with a conductive agent and a binder in proportion, a solvent is added to obtain a slurry, which is coated on a current collector and dried to obtain a zinc-doped hard carbon negative electrode.

[0017] Furthermore, the conductive agent is any one of Super P, acetylene black, Ketjen black, and graphene, or a combination of two thereof, and is more preferably one of Super P and Ketjen black.

[0018] Furthermore, the binder is any one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, and water-based polyacrylate, or a combination of two thereof, and is more preferably one of polytetrafluoroethylene and polyvinylidene fluoride.

[0019] Furthermore, in terms of negative electrode mass percentage, the mass proportion of the hard carbon negative electrode material is 50% to 90%, preferably 70% to 90%, the mass proportion of the conductive agent is 1% to 20%, preferably 5% to 15%, and the mass proportion of the binder is 1% to 20%, preferably 5% to 15%.

[0020] Furthermore, the solvent is N-methylpyrrolidone (NMP); and the current collector is carbon-coated aluminum foil.

[0021] In a fourth aspect, the present invention provides a sodium ion battery, wherein the negative electrode thereof comprises the hard carbon negative electrode material described in the second aspect.

[0022] Compared with the prior art, the present invention has the following advantages and outstanding effects:

[0023] (1) The present invention uses a carbohydrate compound as a carbon source and an organic zinc salt as a zinc source. During the high-temperature carbonization process, these compounds create pores, increasing the specific surface area of the material and providing more active sites. Furthermore, the zinc salt is relatively mild and does not completely etch the hard carbon material. The resulting hard carbon anode material contains abundant micropores and mesoporous structures. The micropores provide more sodium storage sites, while the mesopores enhance the material's rate capability. When sodium-ion batteries are assembled using this hard carbon anode material, the electrochemical performance is significantly improved.

[0024] (2) The introduction of zinc ions can act as "pillars" during the carbonization process, slightly expanding the disordered layered structure of hard carbon and increasing the interlayer spacing. The diffusion resistance of sodium ions in the larger interlayer channels is reduced, thereby improving the ion transport kinetics. In addition, zinc doping may introduce more structural defects, which can serve as preferential adsorption sites for sodium ions, enhancing the contribution of surface-driven pseudocapacitance and further improving the capacity.

[0025] (3) Zinc ions have a high charge density and can be adsorbed on the hard carbon surface in the electrolyte. The electrostatic shielding effect weakens the Coulomb repulsion between sodium ions and the carbon matrix, promoting the Na + The presence of zinc ions can optimize the electrode / electrolyte interface, reduce the desolvation energy barrier of sodium ions, and thus increase the interfacial reaction rate.

[0026] (4) By controlling the ratio of zinc source to carbon source and adopting a suitable carbonization temperature, a hard carbon material with a rich porous structure is obtained, and the first-cycle coulombic efficiency and cycle performance are significantly improved. In addition, the preparation method is simple, low-cost, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the hard carbon negative electrode material synthesized in Example 1.

[0028] Figure 2 This is the X-ray diffraction pattern of the hard carbon negative electrode material synthesized in Example 1.

[0029] Figure 3 Graph showing the cycle performance of a sodium ion battery made with the hard carbon negative electrode material synthesized in Examples 1-5. DETAILED DESCRIPTION

[0030] The present application is further described below with reference to specific embodiments.

[0031] It should be noted that the terms such as "upper", "lower", "left", "right", and "middle" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of this application without substantially changing the technical content.

[0032] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0033] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0034] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement, or value. One skilled in the art can readily determine the degree of flexibility for a particular variable.

[0035] As used herein, the term "at least one of" is intended to be synonymous with "one or more of." For example, "at least one of A, B, and C" explicitly includes only A, only B, only C, and combinations of each thereof.

[0036] Concentration, amount and other numerical data can be presented in range format in this article.Should be understood that such range format is only used for convenience and brevity, and should be flexibly interpreted as not only including the numerical value clearly described as range limit, but also including all independent numerical values or subranges encompassed within the scope, just as each numerical value and subrange are clearly described.For example, the numerical range of about 1 to about 4.5 should be interpreted as not only including the limit value of 1 to about 4.5 clearly described, but also including independent numerals (such as 2,3,4) and subranges (such as 1 to 3,2 to 4 etc.).The same principle is applicable to the scope of only narrating a numerical value, such as "less than about 4.5", which should be interpreted as including all above-mentioned values and scopes.In addition, no matter how the breadth of described scope or feature is, this explanation should be applicable.

[0037] Example 1

[0038] (1) Add 1g zinc acetate dihydrate to 20ml deionized water, stir thoroughly, then add 12.7g starch to obtain a zinc acetate starch mixed solution, stir continuously until zinc acetate and starch are evenly mixed, and freeze-dry the solution. Then, carbonize at high temperature under the protection of argon at a temperature of 800℃ and a heating rate of 5℃ / min for 2h to obtain a hard carbon negative electrode material. The scanning electron microscopy and X-ray diffraction of the hard carbon negative electrode material are shown as follows: Figure 1 and Figure 2 As shown. Scanning electron microscopy images show that the material has a more porous structure, which is more conducive to the storage of sodium ions. From the X-ray diffraction pattern, two broad diffraction peaks appear at 22.5° and 43.6°, corresponding to the (002) and (100) planes of graphite, confirming that the obtained carbon material is disordered or amorphous carbon.

[0039] (2) The hard carbon negative electrode material, Super P, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, N-methylpyrrolidone (NMP) was added dropwise, and the mixture was stirred into a slurry, which was then coated on a carbon-coated aluminum foil and dried to obtain a zinc-doped hard carbon negative electrode.

[0040] (3) Assemble in a glove box, stack the positive electrode shell, hard carbon electrode, diaphragm, electrolyte, sodium sheet, gasket, spring, and negative electrode shell in sequence, and compact them to obtain a sodium ion battery. The cycle performance of the sodium ion battery is as follows: Figure 3 It can be seen that the hard carbon material prepared in this embodiment has a cycle stability and specific capacity far exceeding that of other embodiments.

[0041] Example 2

[0042] The remaining procedures were the same as in Example 1, except that 0.5 g of zinc acetate dihydrate was added to 20 ml of deionized water, thoroughly stirred, and then 12.7 g of starch was added to obtain a zinc acetate-starch mixed solution. The solution was stirred continuously until the zinc acetate and starch were uniformly mixed, and then freeze-dried. The solution was then carbonized under argon at a temperature of 800°C, a heating rate of 5°C / min, and maintained for 2 hours to obtain a hard carbon anode material.

[0043] Example 3

[0044] The remaining procedures were the same as in Example 1, except that 1.5 g of zinc acetate dihydrate was added to 20 ml of deionized water, thoroughly stirred, and then 12.7 g of starch was added to obtain a zinc acetate-starch mixed solution. The solution was stirred continuously until the zinc acetate and starch were uniformly mixed, and then freeze-dried. The solution was then carbonized under argon at a temperature of 800°C, a heating rate of 5°C / min, and maintained for 2 hours to obtain a hard carbon anode material.

[0045] Example 4

[0046] The remaining procedures were the same as in Example 1, except that 1 g of zinc acetate dihydrate was added to 20 ml of deionized water, thoroughly stirred, and then 12.7 g of starch was added to obtain a zinc acetate-starch mixed solution. The solution was stirred continuously until the zinc acetate and starch were uniformly mixed, and then freeze-dried. The solution was then carbonized under argon at a temperature of 1000°C, a heating rate of 5°C / min, and maintained for 2 hours to obtain a hard carbon anode material.

[0047] Example 5

[0048] The remaining steps were the same as in Example 1, except that 12.7 g of starch was added to 20 ml of deionized water and stirred thoroughly until the starch was completely dissolved to obtain a starch solution, which was then freeze-dried. High-temperature carbonization was then performed under argon at a temperature of 800°C, a heating rate of 5°C / min, and a holding time of 2 h to obtain a hard carbon anode material.

[0049] Performance Testing

[0050] The metal-doped hard carbon electrode materials prepared in Examples 1-5 were combined with sodium sheets to form counter electrodes, and non-woven fabrics were used as separators. They were assembled into button cells for electrochemical testing. Long-term cycle tests were conducted at a current density of 1C = 372 mAh / g and a voltage range of 0.01-3 V. The cycle performance was as follows: Figure 3 shown.

Claims

1. A method for preparing a hard carbon negative electrode material, characterized in that: The steps include: 1) Mixing a zinc salt activator and a carbon source in a certain proportion and stirring to obtain a zinc-doped hard carbon precursor; 2) The mixture is carbonized at high temperature in an inert gas environment to obtain a hard carbon negative electrode material.

2. The method according to claim 1, wherein The zinc source is any one of zinc gluconate, zinc acetate, zinc ethoxide, zinc oxalate, zinc acetate dihydrate and zinc malate, or a combination of at least two thereof, and is more preferably zinc acetate or zinc acetate dihydrate.

3. The method according to claim 1, wherein The carbon source is any one of glucose, carbon nanotubes, starch, carbon cloth and polyester fiber or a combination of two thereof, and is more preferably one of glucose and starch.

4. The method according to claim 1, wherein The mass ratio of the zinc source to the carbon source is 0.01:1 to 0.1:1, more preferably 0.03:1 to 0.1:1, and most preferably 0.05:1 to 0.1:

1.

5. The method according to claim 1, wherein In step 2), the carbonization process is carried out in an inert atmosphere at a carbonization temperature of 500-2000°C, more preferably 500-1500°C, and most preferably 500-1000°C.

6. The method according to claim 1, wherein In step 2), the heating rate is 1-10°C / min, more preferably 1-7°C / min, and most preferably 3-7°C / min.

7. The method according to claim 1, wherein In step 2), the holding time is 1 to 10 hours, more preferably 1 to 8 hours, and most preferably 1 to 5 hours.

8. A hard carbon negative electrode material prepared by the method according to any one of claims 1 to 7, characterized in that: The hard carbon negative electrode material has a rich pore structure.

9. A negative electrode for a sodium ion battery, characterized in that The hard carbon negative electrode material according to claim 8 is mixed with a conductive agent and a binder in proportion, a solvent is added to obtain a slurry, and the slurry is coated on a current collector and dried to obtain a zinc-doped hard carbon negative electrode.

10. A sodium ion battery, characterized in that: The negative electrode thereof comprises the hard carbon negative electrode material as claimed in claim 8.

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