Preparation method and application of porous carbon-based nanocage sodium negative electrode material

Abstract

The present invention relates to the field of electrode materials and electrochemical energy storage technology, and in particular, to a preparation method and application of a porous carbon-based nanocage sodium negative electrode material. The present invention obtains a porous carbon-based nanocage sodium negative electrode material by carbonizing, acid etching, alkaline etching and sulfurization treatment of the prepared Ni-MOF precursor. By adopting etching pore formation and sulfurization treatment methods, the optimized design and precise synthesis of the components and structure of the composite electrode material are achieved, which not only achieves effective control of the structural components of the electrode material, but also further improves the rapid charge and discharge performance and cycle stability of the sodium ion battery through the porosity of the nanocage, thereby improving the energy density and comprehensive performance of the sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the field of electrode materials and electrochemical energy storage technology, and in particular to a preparation method and application of a porous carbon-based nanocage sodium negative electrode material. Background Art

[0002] The rapid development of lithium-ion batteries must take into account the existing lithium resources and their costs. Due to the increasing cost, uneven distribution and scarcity of lithium, it is crucial to seek alternatives to lithium to meet future needs. Sodium is in the same family as lithium in the periodic table. It not only has similar physical and chemical properties and electrochemical reaction mechanisms as lithium, but also has the advantages of abundant reserves and low cost. These characteristics make sodium-ion batteries (SIBs) the preferred alternative to lithium-ion batteries. However, Na + The radius is much larger than Li + The radius, Na + The ion migration kinetics are slow, and there is irreversible volume expansion during the sodiumation / desodiumation process, which leads to the defects of sodium-ion batteries in practical applications such as low coulombic efficiency, poor cycle stability, and low energy density.

[0003] Common negative electrode materials for SIBs include carbon materials, alloy materials, and metal compound materials. Among carbon materials, hard carbon is the most commercially promising negative electrode material, but its commercialization process is hindered by its high cost and low capacity. Although alloy materials have the advantages of good conductivity and high capacity, they usually have low cycle stability. In contrast, transition metal oxides and metal sulfides have the advantages of low price, abundant reserves, and high theoretical specific capacity. Among them, nickel-sulfur compounds in metal sulfides have lower cost and higher theoretical capacity and are considered to be suitable negative electrode materials for SIBs. However, nickel-sulfur compounds have low conductivity and Na + Disadvantages such as slow ion diffusion kinetics and large volume changes limit its further application.

[0004] Metal-organic frameworks (MOFs) are promising precursors for synthesizing heteroatom-doped nanostructures. The advantages of MOFs, such as ultra-high surface area, high porosity, and easily modifiable structures, make their derivatives ideal for electrochemical performance. Nanostructures shorten the electron and ion transport pathways, thereby promoting diffusion kinetics and improving electrochemical performance. Therefore, how to leverage the advantages of MOFs to load NiS nanoparticles onto porous carbon nanostructures, thereby preparing smaller carbon-based nanocages and improving the low conductivity of nickel-sulfur compounds, is a question that researchers in this field should consider. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of porous carbon-based nanocage sodium negative electrode materials. A Ni-MOF precursor is prepared, carbonized, and then acid-etched to control the Ni content. The pore structure is then adjusted by alkaline etching. Finally, a composite electrode material of porous carbon spheres coated with NiS (NiS / C) nanoparticles derived from a metal organic framework material is formed in situ by sulfurization. The composite electrode material is used for electrochemical energy storage in sodium ion batteries to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing a porous carbon-based nanocage sodium negative electrode material, comprising the following steps:

[0008] Ni-MOF precursor was obtained by hydrothermal reaction with Ni(NO3)2·6H2O as metal source, 1,4-diazabicyclo[2,2,2]octane as first ligand, terephthalic acid as second ligand and urea as modifier.

[0009] Carbonizing the Ni-MOF precursor under an inert atmosphere to obtain a Ni / C composite material;

[0010] The Ni / C composite material is subjected to acid etching, alkaline etching and sulfurization treatment to obtain the porous carbon-based nanocage sodium negative electrode material.

[0011] Furthermore, the preparation steps of the Ni-MOF precursor include:

[0012] Ni(NO3)2·6H2O and 1,4-diazabicyclo[2,2,2]octane were dissolved in DMF to obtain solution A;

[0013] Dissolve terephthalic acid and urea in DMF to obtain solution B;

[0014] The solution A and the solution B were mixed evenly, subjected to a hydrothermal reaction at 80° C. for 12 h, and centrifuged and dried to obtain a Ni-MOF precursor.

[0015] Preferably, the mass ratio of Ni(NO3)2·6H2O, 1,4-diazabicyclo[2,2,2]octane, terephthalic acid and urea is 4:1:2:3.

[0016] Furthermore, the temperature of the carbonization treatment is 600-1000° C., and the time is 2-8 hours.

[0017] The Ni / C composite material obtained after carbonization treatment includes Ni metal nanoparticles and porous carbon-based nanocages, wherein the size of the porous carbon-based nanocages is 10-100nm.

[0018] Furthermore, the acid etching is performed by soaking in HCl solution.

[0019] In some specific embodiments, the concentration of the HCl solution is 1 mol / L; the immersion time is 60 min; and the mass / volume ratio of the Ni / C composite material to the HCl solution in the acid etching is 1:150 g / mL.

[0020] Furthermore, the alkaline etching is etching using alkali metal ions.

[0021] In some specific embodiments, the ratio of alkali metal ions to Ni / C composite material in the alkaline etching is 0.02-0.03 mol:0.2 g.

[0022] In some embodiments, the alkali metal ion comprises K + and / or Na + .

[0023] The present invention adopts hydrochloric acid aqueous solution immersion to adjust the Ni content in the Ni / C composite material, and utilizes the alkali metal ion etching effect to adjust the surface interface and pore structure of the carbon nano cage.

[0024] In some specific embodiments, the alkali metal ions are provided by KOH solution, KCl solution, or NaOH solution, and the concentration thereof is 0.5-5M.

[0025] In some embodiments, the alkali metal ions are provided by solid KOH.

[0026] Furthermore, the sulfur source used in the sulfurization treatment includes at least one of elemental sulfur, thiourea and hydrogen sulfide; the temperature of the sulfurization treatment is 550-850° C., and the time is 0.5-4 hours.

[0027] In some specific embodiments, the mass ratio of the sulfur source to the Ni / C composite material is 10:1.

[0028] The present invention obtains a composite material of NiS and porous carbon-based nanocages by sulfurization treatment, wherein the NiS nanoparticles have a size of 10 to 200 nm and form a mixture with the porous carbon-based nanocages or are partially encapsulated inside the porous carbon-based nanocages, with a content of 5 to 50 wt.%.

[0029] In the present invention, the porous carbon-based nanocages are small, at the nanometer scale. This not only increases the contact area between the active material and the electrolyte, promoting the intercalation and extraction of sodium ions, but also reduces the diffusion distance of sodium ions and provides more active sites for redox reactions on their surface. Furthermore, the etching effect of alkali metal ions further modulates the surface interface and pore structure of the carbon nanocages, facilitating the rapid diffusion of sodium ions. This can reduce polarization during battery charge and discharge, improving overall battery performance.

[0030] The second technical solution of the present invention is to provide a porous carbon-based nanocage sodium negative electrode material prepared by the above method.

[0031] The third technical solution of the present invention is to provide an application of the above-mentioned porous carbon-based nanocage sodium negative electrode material in a sodium ion battery.

[0032] Small-sized nanocages not only have a higher specific surface area, but also provide more active sites for sodium ions, thereby increasing the contact area between the electrode and the electrolyte and improving the battery's charge and discharge efficiency. In addition, their volume changes less during charge and discharge, which helps maintain the stability of the electrode structure and thus improve the battery's cycle life. In addition, the pore structure is conducive to the rapid diffusion of sodium ions, which can reduce polarization during the battery's charge and discharge process and improve the battery's overall performance.

[0033] The present invention discloses the following technical effects:

[0034] The present invention uses a nickel-based metal-organic framework (Ni-MOF) as a precursor to prepare a NiS / C composite material with high specific capacity and good stability as a negative electrode material for sodium ion batteries. The porosity of the carbon-based material is utilized to further improve the rapid charge and discharge performance and cycle stability of the sodium ion battery, which is beneficial to improving the energy density and charge and discharge performance of the sodium ion battery.

[0035] The present invention uses Ni-MOF as a precursor to prepare NiS / C electrode materials, which not only can well control the morphology and structure of the electrode material, but also can utilize the heteroatoms in MOF to regulate the carbon-based carrier and optimize its conductivity and sodium storage capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order 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 use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1TEM images of the electrode materials prepared in Comparative Example 1 and Example 1, wherein (a) is C in Comparative Example 1, and (b) is NiS / CK in Example 1;

[0038] Figure 2 SEM images of the electrode materials prepared in Comparative Example 1 and Example 1, wherein (a) is the sodium negative electrode material of Comparative Example 1, (b) is the Ni-MOF precursor in Example 1, (c) is the Ni / C in Example 1, and (d) is the NiS / CK in Example 1;

[0039] Figure 3 is the XRD pattern of the electrode material prepared in Example 1;

[0040] Figure 4 The electrochemical properties of the electrode material prepared in Example 1 are shown in Figure 1, where (a) is a CV curve at a scan rate of 0.5 mV / s, and (b) is a constant current charge-discharge curve at 500 mA / g.

[0041] Figure 5 1 is a comparison chart of the discharge specific capacity-cycle number curves of the electrode materials of Example 1, Example 4 and Comparative Examples 1 to 3 during constant current discharge at 200 mA / g and 500 mA / g, wherein (a) is 200 mA / g and (b) is 500 mA / g. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] The raw materials and reagents used in the specific embodiments of the present invention are all commercially available products.

[0048] Example 1

[0049] Preparation of porous carbon-based nanocage sodium anode materials:

[0050] S1. Dissolve 4 g of Ni(NO3)2·6H2O and 1 g of 1,4-diazabicyclo[2,2,2]octane in 75 mL of DMF as solution A; dissolve 2 g of terephthalic acid and 3 g of urea in 75 mL of DMF by stirring thoroughly as solution B; then mix solution A and solution B evenly, and hydrothermally react at 80°C for 12 h to obtain the Ni-MOF precursor;

[0051] S2. The Ni-MOF precursor was placed in a crucible for carbonization treatment at a heating rate of 5°C / min, a holding temperature of 800°C, and a holding time of 4 h, followed by natural cooling to room temperature to obtain a Ni / C composite material, denoted as Ni / C;

[0052] S3, mixing 0.2 g of Ni / C composite material with 30 mL of HCl solution (concentration of 1 mol / L) and stirring for 60 min, followed by centrifugal drying to obtain Ni / C-HCl;

[0053] S4. Wash Ni / C-HCl with water until neutral, then stir with 30 mL of KOH solution (concentration is 1 mol / L), let it stand for 24 h, pour out the supernatant, and centrifuge to dry to obtain Ni / C-(HCl,KOH);

[0054] S5. Take 0.1g Ni / C-(HCl, KOH) and 1g thiourea, mix them and place them in a crucible. Heat the temperature to 600℃ at a heating rate of 5℃ / min and then perform sulfurization treatment for 2h. After cooling to room temperature, a porous carbon-based nanocage sodium negative electrode material is obtained, which is recorded as NiS / CK.

[0055] Example 2

[0056] Preparation of porous carbon-based nanocage sodium anode materials:

[0057] S1. Dissolve 4 g of Ni(NO3)2·6H2O and 1 g of 1,4-diazabicyclo[2,2,2]octane in 75 mL of DMF as solution A; dissolve 2 g of terephthalic acid and 3 g of urea in 75 mL of DMF by stirring thoroughly as solution B; then mix solution A and solution B evenly, and hydrothermally react at 80°C for 12 h to obtain the Ni-MOF precursor;

[0058] S2. The Ni-MOF precursor was placed in a crucible for carbonization treatment at a heating rate of 5°C / min, a holding temperature of 800°C, and a holding time of 4 h, followed by natural cooling to room temperature to obtain a Ni / C composite material, denoted as Ni / C;

[0059] S3, mixing 0.2 g of Ni / C composite material with 30 mL of HCl solution (concentration of 1 mol / L) and stirring for 60 min, followed by centrifugal drying to obtain Ni / C-HCl;

[0060] S4, wash Ni / C-HCl with water until neutral, then add 5.6g solid KOH (KOH s ) mixed and ground to obtain Ni / C-(HCl,KOH s );

[0061] S5, take 0.1g Ni / C-(HCl,KOH s ) and 1g thiourea were mixed in a crucible, heated to 600℃ at a heating rate of 5℃ / min, and then sulfurized for 2h. After cooling to room temperature, a porous carbon-based nanocage sodium anode material was obtained, which was recorded as NiS / C(HCl,KOH s ).

[0062] Example 3

[0063] Preparation of porous carbon-based nanocage sodium anode materials:

[0064] S1. Dissolve 4 g of Ni(NO3)2·6H2O and 1 g of 1,4-diazabicyclo[2,2,2]octane in 75 mL of DMF as solution A; dissolve 2 g of terephthalic acid and 3 g of urea in 75 mL of DMF by stirring thoroughly as solution B; then mix solution A and solution B evenly, and hydrothermally react at 80°C for 12 h to obtain the Ni-MOF precursor;

[0065] S2. The Ni-MOF precursor was placed in a crucible for carbonization treatment at a heating rate of 5°C / min, a holding temperature of 800°C, and a holding time of 4 h, followed by natural cooling to room temperature to obtain a Ni / C composite material, denoted as Ni / C;

[0066] S3, mixing 0.2 g of Ni / C composite material with 30 mL of HCl solution (concentration of 1 mol / L) and stirring for 60 min, followed by centrifugal drying to obtain Ni / C-HCl;

[0067] S4. Wash Ni / C-HCl with water until neutral, then stir with 30 mL of KCl solution (concentration is 1 mol / L), let it stand for 24 h, pour out the supernatant, and centrifuge to dry to obtain Ni / C-(HCl, KCl);

[0068] S5. Take 0.1g Ni / C-(HCl, KCl) and 1g thiourea, mix them and place them in a crucible. Heat the temperature to 600℃ at a heating rate of 5℃ / min and then perform sulfurization treatment for 2h. After cooling to room temperature, a porous carbon-based nanocage sodium negative electrode material is obtained, which is recorded as NiS / C(HCl, KCl).

[0069] Example 4

[0070] Preparation of porous carbon-based nanocage sodium anode materials:

[0071] S1. Dissolve 4 g of Ni(NO3)2·6H2O and 1 g of 1,4-diazabicyclo[2,2,2]octane in 75 mL of DMF as solution A; dissolve 2 g of terephthalic acid and 3 g of urea in 75 mL of DMF by stirring thoroughly as solution B; then mix solution A and solution B evenly, and hydrothermally react at 80°C for 12 h to obtain the Ni-MOF precursor;

[0072] S2. The Ni-MOF precursor was placed in a crucible for carbonization treatment at a heating rate of 5°C / min, a holding temperature of 800°C, and a holding time of 4 h, followed by natural cooling to room temperature to obtain a Ni / C composite material, denoted as Ni / C;

[0073] S3, mixing 0.2 g of Ni / C composite material with 30 mL of HCl solution (concentration of 1 mol / L) and stirring for 60 min, followed by centrifugal drying to obtain Ni / C-HCl;

[0074] S4. Wash Ni / C-HCl with water until neutral, then stir with 30 mL of NaOH solution (concentration is 1 mol / L), let it stand for 24 h, pour out the supernatant, and centrifuge to dry to obtain Ni / C-(HCl, NaOH);

[0075] S5. Take 0.1g Ni / C-(HCl, NaOH) and 1g thiourea, mix them and place them in a crucible. Heat the temperature to 600℃ at a heating rate of 5℃ / min and then perform sulfurization treatment for 2h. After cooling to room temperature, a porous carbon-based nanocage sodium negative electrode material is obtained, which is recorded as NiS / C-Na.

[0076] Comparative Example 1

[0077] Preparation of sodium battery negative electrode materials:

[0078] S1. Dissolve 4 g of Ni(NO3)2·6H2O and 1 g of 1,4-diazabicyclo[2,2,2]octane in 75 mL of DMF as solution A; dissolve 2 g of terephthalic acid and 3 g of urea in 75 mL of DMF by stirring thoroughly as solution B; then mix solution A and solution B evenly, and hydrothermally react at 80°C for 12 h to obtain the Ni-MOF precursor;

[0079] S2. The Ni-MOF precursor was placed in a crucible for carbonization treatment at a heating rate of 5°C / min, a holding temperature of 800°C, and a holding time of 4 h, followed by natural cooling to room temperature to obtain a Ni / C composite material, denoted as Ni / C;

[0080] S3, taking 0.1g Ni / C and thiourea, mixing them in a crucible, heating them to 600℃ at a heating rate of 5℃ / min, and then sulfiding them for 2h. After cooling to room temperature, the precursor of the sodium negative electrode material was obtained, which was recorded as NiS / C;

[0081] S4. Mix 0.1 g NiS / C and 30 mL HCl solution (concentration of 1 mol / L) and stir for 60 min, let it stand, and centrifuge to dry to obtain a sodium negative electrode material, which is recorded as C.

[0082] Comparative Example 2

[0083] Preparation of porous carbon-based nanocage sodium anode materials:

[0084] S1. Dissolve 4 g of Ni(NO3)2·6H2O and 1 g of 1,4-diazabicyclo[2,2,2]octane in 75 mL of DMF as solution A; dissolve 2 g of terephthalic acid and 3 g of urea in 75 mL of DMF by stirring thoroughly as solution B; then mix solution A and solution B evenly, and hydrothermally react at 80°C for 12 h to obtain the Ni-MOF precursor;

[0085] S2. The Ni-MOF precursor was placed in a crucible for carbonization treatment at a heating rate of 5°C / min, a holding temperature of 800°C, and a holding time of 4 h, followed by natural cooling to room temperature to obtain a Ni / C composite material, denoted as Ni / C;

[0086] S3, mixing 0.2 g of Ni / C composite material with 30 mL of HCl solution (concentration of 1 mol / L) and stirring for 60 min, followed by centrifugal drying to obtain Ni / C-HCl;

[0087] S4. Wash Ni / C-HCl with water until it is neutral, and take 0.1g of it and 1g of thiourea and mix them in a crucible. Heat it to 600℃ at a heating rate of 5℃ / min and then perform sulfurization treatment for 2h. After cooling to room temperature, a porous carbon-based nanocage sodium negative electrode material is obtained, which is recorded as HCl-NiS / C.

[0088] Comparative Example 3

[0089] Preparation of porous carbon-based nanocage sodium anode materials:

[0090] S1. Dissolve 4 g of Ni(NO3)2·6H2O and 1 g of 1,4-diazabicyclo[2,2,2]octane in 75 mL of DMF as solution A; dissolve 2 g of terephthalic acid and 3 g of urea in 75 mL of DMF by stirring thoroughly as solution B; then mix solution A and solution B evenly, and hydrothermally react at 80°C for 12 h to obtain the Ni-MOF precursor;

[0091] S2. The Ni-MOF precursor was placed in a crucible for carbonization treatment at a heating rate of 5°C / min, a holding temperature of 800°C, and a holding time of 4 h, followed by natural cooling to room temperature to obtain a Ni / C composite material, denoted as Ni / C;

[0092] S3, mixing 0.2 g of Ni / C composite material with 30 mL of KOH solution (concentration of 1 mol / L) and stirring for 60 min, followed by centrifugal drying to obtain Ni / C-KOH;

[0093] S4. Take 0.1g Ni / C-NaOH and 1g thiourea, mix them and place them in a crucible. Heat the temperature to 600℃ at a heating rate of 5℃ / min and then perform sulfurization treatment for 2h. After cooling to room temperature, a porous carbon-based nanocage sodium negative electrode material is obtained, which is recorded as KOH-NiS / C.

[0094] Test example

[0095] The electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were used to prepare sodium ion batteries in the following steps:

[0096] The electrode material and PVDF were mixed in a mass ratio of 85:15, and degassed to obtain a slurry; the slurry was coated on an aluminum foil, and the loading amount of the electrode material was 1.5-2.0 mg / cm 2 The electrodes were then dried to obtain electrode plates. The electrodes were assembled into sodium ion batteries in a glove box. A glass fiber diaphragm was used as the diaphragm, and a commercial sodium hexafluorophosphate electrolyte was used as the electrolyte. After the assembly was completed, the batteries were allowed to stand for 6 to 12 hours and then electrochemical tests were performed.

[0097] Figure 1TEM images of the electrode materials prepared in Comparative Example 1 and Example 1, where (a) is C in Comparative Example 1 and (b) is NiS / CK in Example 1. As can be seen from the figure, the carbon sphere size is 20 nm and the thickness of the carbon shell is about 2 nm. The small size of the nanocage can reduce its volume change during the charge and discharge process, which helps to maintain the stability of the electrode structure, thereby improving the cycle life of the battery. In addition, the etching effect of alkali metal ions will further regulate the surface interface and pore structure of the carbon nanocage, which is conducive to the rapid diffusion of sodium ions. The mixing of NiS nanoparticles and carbon nanocages or encapsulation inside the nanocage will improve the overall performance of the battery.

[0098] Figure 2 These are SEM images of the electrode materials prepared in Comparative Example 1 and Example 1, wherein (a) is the sodium negative electrode material of Comparative Example 1, (b) is the Ni-MOF precursor in Example 1, (c) is Ni / C in Example 1, and (d) is NiS / CK in Example 1. It can be seen from the figure that the size of the electrode material after carbonization treatment is about 20 nm. The electrode material in the comparative example that is first sulfurized and then pickled has a carbon ball structure, while the material that is pickled, alkaline treated and then sulfurized, wherein the NiS nanoparticles form a mixture with the carbon nanocage or are partially encapsulated inside the nanocage.

[0099] Figure 3 This is the XRD pattern of the electrode material prepared in Example 1. It can be seen from the figure that the NiS particles mixed on the surface of the carbon nanocage or encapsulated inside play a major role in the overall performance of the battery.

[0100] Figure 4 The electrochemical properties of the electrode material prepared in Example 1 are shown, where (a) is the CV curve at a scan rate of 0.5 mV / s, and (b) is the constant current charge-discharge curve at 500 mA / g. As can be seen from the figure, the cyclic voltammetry (CV) curve and the constant current charge-discharge voltage curve illustrate the conversion mechanism of NiS / CK in the sodium / desodium process, and the initial coulombic efficiency reaches 75%.

[0101] Figure 5 Comparative graphs of the specific discharge capacity versus cycle number curves for the electrode materials of Example 1, Example 4, and Comparative Examples 1-3 at constant current discharges of 200 mA / g and 500 mA / g are shown, with (a) at 200 mA / g and (b) at 500 mA / g. As can be seen from the graphs, the carbon sphere structure in Comparative Example 1 has a certain impact on the stability of the electrode material. The simultaneous treatment of the resulfurized electrode material with HCl treatment and K metal etching in Example 1 further improves the material's stability and capacity.

[0102] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a porous carbon-based nanocage sodium negative electrode material, characterized in that the steps include: Ni-MOF precursor was obtained by hydrothermal reaction with Ni(NO3)2·6H2O as metal source, 1,4-diazabicyclo[2,2,2]octane as first ligand, terephthalic acid as second ligand and urea as modifier. Carbonizing the Ni-MOF precursor under an inert atmosphere to obtain a Ni / C composite material; The Ni / C composite material is subjected to acid etching, alkaline etching, and sulfurization treatment to obtain the porous carbon-based nanocage sodium negative electrode material; The acid etching is performed by soaking in HCl solution; the concentration of the HCl solution is 1 mol / L; the soaking time is 60 min; the mass / volume ratio of the Ni / C composite material to the HCl solution in the acid etching is 1:150 g / mL; The alkaline etching is carried out by using alkali metal ions; the ratio of the amount of alkali metal ions to the Ni / C composite material in the alkaline etching is 0.02-0.03 mol:0.2 g; the alkali metal ions include K + and / or Na + .

2. The preparation method according to claim 1, wherein The preparation steps of the Ni-MOF precursor include: Ni(NO3)2·6H2O and 1,4-diazabicyclo[2,2,2]octane were dissolved in DMF to obtain solution A; Dissolve terephthalic acid and urea in DMF to obtain solution B; The solution A and the solution B were mixed evenly, subjected to a hydrothermal reaction at 80° C. for 12 h, and centrifugally dried to obtain a Ni-MOF precursor.

3. The preparation method according to claim 2, wherein The mass ratio of Ni(NO3)2·6H2O, 1,4-diazabicyclo[2,2,2]octane, terephthalic acid and urea is 4:1:2:

3.

4. The preparation method according to claim 1, wherein The temperature of the carbonization treatment is 600-1000° C., and the time is 2-8 hours.

5. The preparation method according to claim 1, wherein The sulfur source used in the sulfurization treatment includes at least one of elemental sulfur, thiourea and hydrogen sulfide; the temperature of the sulfurization treatment is 550-850° C., and the time is 0.5-4 hours.

6. The preparation method according to claim 5, wherein The mass ratio of the sulfur source to the Ni / C composite material is 10:

1.

7. The porous carbon-based nanocage sodium negative electrode material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the porous carbon-based nanocage sodium negative electrode material as claimed in claim 7 in sodium ion batteries.

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