A synthesis method of carbon cross-linked network phosphide material and its sodium negative electrode application

Abstract

The present invention discloses a method for synthesizing a carbon cross-linked network phosphide material and its application as a sodium negative electrode. The material is used as a negative electrode material in the performance test of sodium ion batteries and obtains relatively excellent sodium storage performance. The present invention mainly forms a carbon cross-linked network during heat treatment in a phosphine atmosphere by directionally binding iron ions in a metal salt solution to attach to a precursor through polyvinyl pyrrolidone in a liquid phase atmosphere. After the nickel hydroxide nanosheet precursor is initially hydrothermally synthesized, it is impregnated with an aqueous solution of uniformly mixed polyvinyl pyrrolidone and ferric nitrate, and the phosphating treatment and the construction of a carbon cross-linked network are simultaneously achieved by heat treatment in a tubular furnace. This carbon cross-linked network is not only beneficial to the stability of the nanostructure during the charge and discharge process of the battery, but also beneficial to intercalation conversion.

Description

Technical Field

[0001] The present invention belongs to the field of clean and sustainable new energy preparation and application, in particular to a carbon cross-linked network phosphide material, a synthesis method thereof and a sodium ion battery negative electrode application thereof. Background Art

[0002] Sodium-ion batteries are poised to become the primary power source for a new generation of portable electronics, electric vehicles, and smart grids, and are also crucial for the development of renewable and sustainable energy. To meet the demands of these massive energy storage applications, the development of high-energy-density lithium-ion batteries based on advanced materials is particularly urgent. As an important family of functional materials, transition metal phosphides (TMPs) can, in principle, possess higher theoretical capacities based on their conversion reaction mechanisms. Furthermore, compared with transition metal oxides and sulfides, TMPs exhibit relatively superior potential for sodium storage. Furthermore, due to their high theoretical capacity and superior electronic conductivity compared to their oxide counterparts, TMPs are also emerging candidates for anodes in lithium-ion batteries and potassium-ion batteries (PIBs). However, TMPs appear to be underexplored, likely due to a lack of suitable and feasible preparation methods. Despite their high theoretical capacity and low redox voltage, their large volume changes during charge and discharge lead to rapid capacity decay. Furthermore, their inherently low electrical conductivity cannot keep pace with the kinetics of the electrochemical reactions, resulting in poor rate performance. Therefore, some efforts should be devoted to designing efficient synthetic routes to engineer the morphology and composition of TMPs considering the significant impact on the electrochemical performance while maintaining the structural integrity. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention provides a method for synthesizing a carbon cross-linked network phosphide material and its sodium negative electrode application.

[0004] In one aspect, the present invention provides a carbon cross-linked network phosphide material comprising a nanosheet array and a carbon cross-linked network coating the nanosheet array, wherein the carbon cross-linked network is doped with iron; the nanosheets are Ni2P nanosheets. The phosphide nanosheets facilitate sodium intercalation conversion, and the nanosheet structure has a large specific surface area, increasing the number of active sites. The outer iron-containing carbon cross-linked network provides abundant pores, and the coating network structure is crucial for regulating volume changes during cycling, facilitating cyclic charge and discharge.

[0005] In the present invention, the Ni2P nanosheets are vertically constructed on the nickel foam substrate, and the outer side is coated by the carbon cross-linked network doped with iron.

[0006] On the other hand, the present invention also provides a method for preparing the above-mentioned carbon cross-linked network phosphide material, which can prepare a multi-level nanostructure with efficient charge transfer and has the characteristics of mild conditions, easy implementation and high yield.

[0007] Specifically, the method includes the following steps:

[0008] (1) A 2 cm*3 cm substrate was placed in an autoclave liner containing a precursor solution, wherein the precursor solution was a mixed aqueous solution of 0.02-0.05 M Ni(NO3)2·6H2O, 0.12-0.25 M NH4F, and 0.1-0.4 M urea; after hydrothermal reaction at 100-130°C for 10 hours, the substrate was washed with deionized water and ethanol to remove surface adsorbed impurities, thereby obtaining a Ni(OH)2 precursor on the substrate;

[0009] (2) The Ni(OH)2 precursor was placed in a 30 ml aqueous solution containing 0.5-2.0 g polyvinylpyrrolidone (PVP) and 0.5-3.0 g Fe(NO3)3·9H2O, where the molecular weight of the polyvinylpyrrolidone was between 56,000 and 68,000. The solution was allowed to stand at room temperature for 10 minutes, then removed and rinsed with deionized water to obtain a PVP / Fe@Ni(OH)2 intermediate.

[0010] (3) The PVP / Fe@Ni(OH)2 intermediate was placed in the downstream of a tube furnace, with 0.4 g NaH2PO2·H2O in the upstream, and argon as the carrier gas. The mixture was heat treated at 500 °C for 2 hours, and then naturally cooled to room temperature and taken out to obtain a carbon cross-linked network sodium negative electrode material C. Fe @Ni2P.

[0011] The beneficial effect of the present invention is that the present invention constructs an iron-doped carbon cross-linked network around the phosphide nanosheet array, which is not only beneficial to the stability of the nanostructure, but also beneficial to the intercalation conversion. -1 Under the condition that after 100 cycles, the battery can still reach 317mAh g -1 High performance and stability.

[0012] The present invention also directionally binds iron ions in a metal salt solution to attach to a precursor through polyvinyl pyrrolidone in a liquid phase atmosphere, and forms a carbon cross-linked network during heat treatment in an atmosphere containing phosphine. The method has the characteristics of mild conditions, easy implementation and high yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The carbon cross-linked network material C prepared by the present invention Fe @SEM image of Ni2P (Example);

[0014] Figure 2 is a scanning electron microscope image of the comparative material Fe@Ni2P (Comparative Example 1);

[0015] Figure 3 is a scanning electron microscope image of the comparative material C@Ni2P (Comparative Example 2);

[0016] Figure 4 The carbon cross-linked network material C prepared by the present invention Fe @Energy dispersive X-ray spectroscopy analysis of Ni2P (Example);

[0017] Figure 5 The carbon cross-linked network material C prepared by the present invention Fe X-ray diffraction spectra of Fe@Ni2P (Example) and comparative material Fe@Ni2P (Comparative Example 1);

[0018] Figure 6 This is the constant current cycle specific capacity curve of the negative electrode battery of the carbon cross-linked network material CFe@Ni2P (Example) prepared by the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be further described below with reference to the embodiments. These embodiments should not be construed as limiting the technical solution.

[0020] Example 1:

[0021] (1) 2 cm x 3 cm nickel foam (NF) was first pretreated to remove surface oil and oxide layers. The surface was ultrasonically cleaned with 4 M hydrochloric acid, acetone, ethanol, and distilled water, and then dried with a high-speed stream of Ar gas.

[0022] (2) Synthesis of Ni(OH)2 / NF precursor: 0.29g Ni(NO3)2.6H2O, 0.15g NH4F and 0.30g urea were dissolved in 30mL deionized water and stirred vigorously for 20min, and then the mixture was transferred to an autoclave. A nickel foam with a size of 3cm×3cm was immersed in the lining of the autoclave used for hydrothermal synthesis. The autoclave was treated at 120℃ for 10 hours. After cooling to room temperature, a clear light green substance appeared on the surface of the nickel foam. It was taken out and washed with deionized water and ethanol to remove the adsorbed impurities on the surface. Finally, it was dried under vacuum at 60℃ for 15 hours to obtain Ni(OH)2 nanosheet arrays on the surface of the nickel foam substrate, and the Ni(OH)2 nanosheets were perpendicular to the substrate.

[0023] (3) The Ni(OH)2 precursor was placed in a 30 mL aqueous solution containing 1.0 g polyvinylpyrrolidone (PVP) (molecular weight 58,000) and 1.5 g Fe(NO3)3·9H2O. The solution was allowed to stand at room temperature for 10 minutes, then removed and rinsed with deionized water to obtain the PVP / Fe@Ni(OH)2 intermediate.

[0024] (4) The PVP / Fe@Ni(OH)2 intermediate was placed in the downstream of a tube furnace, with 0.4 g NaH2PO2·H2O in the upstream, and nitrogen as the carrier gas. The mixture was heat treated at 500 °C for 2 hours, and then naturally cooled to room temperature and taken out to obtain a carbon cross-linked network sodium negative electrode material C. Fe @Ni2P.

[0025] Comparative Example 1:

[0026] (1) 2 cm*3 cm nickel foam was first pretreated according to the above-mentioned method to remove the oil and oxide layer on the surface;

[0027] (2) synthesizing a Ni(OH)2 precursor on nickel foam according to the method of the above embodiment;

[0028] (3) The above Ni(OH)2 precursor was placed in 30 ml of an aqueous solution of 1.5 g of Fe(NO3)3·9H2O, allowed to stand at room temperature for 10 minutes, then taken out and washed with deionized water to obtain a Fe@Ni(OH)2 intermediate.

[0029] (4) The Fe@Ni(OH)2 intermediate was placed in the downstream of a tube furnace with 0.4 g NaH2PO2·H2O in the upstream. The carrier gas was nitrogen. The intermediate was heat treated at 500 °C for 2 h and naturally cooled to room temperature to obtain Fe@Ni2P.

[0030] Comparative Example 2:

[0031] (1) A 2 cm*3 cm nickel foam was first pretreated according to the above-mentioned method to remove the oil and oxide layer on the surface;

[0032] (2) synthesizing a Ni(OH)2 precursor on nickel foam according to the method of the above embodiment;

[0033] (3) The Ni(OH)2 precursor was placed in a 30 ml aqueous solution containing 1.0 g of polyvinylpyrrolidone (PVP) (molecular weight 58,000). The solution was allowed to stand at room temperature for 10 minutes, then removed and rinsed with deionized water to obtain the PVP@Ni(OH)2 intermediate.

[0034] (4) The PVP@Ni(OH)2 intermediate was placed in the downstream of a tube furnace with 0.4 g NaH2PO2·H2O in the upstream. The carrier gas was nitrogen. The intermediate was heat treated at 500 °C for 2 h and naturally cooled to room temperature to obtain C@Ni2P.

[0035] Figure 1 The carbon cross-linked network material C prepared by the present invention Fe SEM image of @Ni2P (Example). The cross-linked network formed outside the nanosheet array can be clearly observed. This structure plays an important role in the cycling stability of sodium-ion batteries.

[0036] Figure 2 The scanning electron microscope image of the comparative material Fe@Ni2P (Comparative Example 1) is shown in FIG. Fe Compared with @Ni2P (Example), there is no carbon cross-linked network. The attachment of a small amount of Fe element maintains the morphology of the original nanosheet precursor.

[0037] Figure 3 This is a scanning electron microscope image of the comparative material C@Ni2P (Comparative Example 2). Fe Compared with Ni2P (Example), there is no carbon cross-linked network. A single PVP coating on the surface, without the adhesive action of Fe ions, cannot form a large-scale cross-linked network, and the nanosheets are attached to the surface as scattered particles.

[0038] Figure 4 The carbon cross-linked network material C prepared by the present invention Fe Energy dispersive X-ray spectroscopy analysis of @Ni2P (Example). Observing the overall elemental distribution at a relatively small magnification, we can clearly see the uniform distribution of the four elements Ni, P, Fe, and C. This proves that the Fe element is successfully mixed with the carbon cross-linked network, maintaining the stability of the cyclic structure while increasing sustainable intercalation conversion.

[0039] Figure 5 The carbon cross-linked network material C prepared by the present invention Fe X-ray diffraction spectra of @Ni2P (Example) and comparative material Fe@Ni2P (Comparative Example 1). Among them, 44.5°, 51.8° and 76.4° correspond to the characteristic peaks of the foam nickel of the substrate, which are (111), (200) and (220) crystal planes respectively. In the X-ray diffraction spectrum of Fe@Ni2P (Comparative Example 1), the (111), (300) and (211) crystal planes of the Ni2P structure can be observed. The carbon cross-linked network material C prepared by the present invention Fe @Ni2P (Example) After successful carbon cross-linking coating, the characteristic peak of Ni2P decreases, and an amorphous carbon peak appears near 23 degrees, proving the presence of carbon during the heat treatment process.

[0040] Figure 6This is the constant current cycle specific capacity curve of the negative electrode battery of the carbon cross-linked network material CFe@Ni2P (Example) prepared by the present invention; 1.0M NaClO4, ethylene carbonate (EC): dimethyl carbonate (DMC) (volume ratio of 1:1) and 5% fluoroethylene carbonate (FEC) are used as the electrolyte. Sodium metal is used as the counter electrode. The test conditions are 2Ag -1 , it can be seen that after 100 cycles, the battery can still reach 317mAh g -1 High performance and stability.

[0041] Example 2:

[0042] (1) 2 cm x 3 cm nickel foam (NF) was first pretreated to remove surface oil and oxide layers. The surface was ultrasonically cleaned with 4 M hydrochloric acid, acetone, ethanol, and distilled water, and then dried with a high-speed stream of Ar gas.

[0043] (2) NF was placed in an autoclave liner containing a precursor solution consisting of a mixed aqueous solution of 0.02 M Ni(NO3)2·6H2O, 0.12 M NH4F, and 0.1 M urea; after hydrothermal reaction at 130°C for 10 h, the NF was washed with deionized water and ethanol to remove surface adsorbed impurities, resulting in a Ni(OH)2 precursor on the substrate;

[0044] (3) The Ni(OH)2 precursor was placed in a 30 mL aqueous solution containing 1.0 g polyvinylpyrrolidone (PVP) (molecular weight 58,000) and 1.5 g Fe(NO3)3·9H2O. The solution was allowed to stand at room temperature for 10 minutes, then removed and rinsed with deionized water to obtain the PVP / Fe@Ni(OH)2 intermediate.

[0045] (4) The PVP / Fe@Ni(OH)2 intermediate was placed in the downstream of a tube furnace, with 0.4 g NaH2PO2·H2O in the upstream, and nitrogen as the carrier gas. The mixture was heat treated at 500 °C for 2 hours, and then naturally cooled to room temperature and taken out to obtain a carbon cross-linked network sodium negative electrode material C. Fe @Ni2P.

[0046] Scanning electron microscopy revealed that the cross-linked network formed outside the nanosheet array had a clear morphology. XRD revealed that an amorphous carbon peak appeared near 23 degrees in the cross-linked network. X-ray spectroscopy revealed that the cross-linked network was uniformly doped with Fe.

[0047] 1.0M NaClO4, ethylene carbonate (EC): dimethyl carbonate (DMC) (volume ratio of 1:1) and 5% fluoroethylene carbonate (FEC) were used as electrolytes. Sodium metal was used as the counter electrode. -1The cycle test was carried out under the same conditions. It can be seen that after 100 cycles, the battery can still reach 278mAh g -1 High performance and stability.

[0048] Example 3:

[0049] (1) 2 cm x 3 cm nickel foam (NF) was first pretreated to remove surface oil and oxide layers. The surface was ultrasonically cleaned with 4 M hydrochloric acid, acetone, ethanol, and distilled water, and then dried with a high-speed stream of Ar gas.

[0050] (2) NF was placed in an autoclave liner containing a precursor solution consisting of a mixed aqueous solution of 0.05 M Ni(NO3)2·6H2O, 0.25 M NH4F, and 0.4 M urea; after hydrothermal reaction at 130°C for 10 h, the NF was washed with deionized water and ethanol to remove surface adsorbed impurities, resulting in a Ni(OH)2 precursor on the substrate;

[0051] (3) The Ni(OH)2 precursor was placed in a 30 mL aqueous solution containing 1.0 g polyvinylpyrrolidone (PVP) (molecular weight 58,000) and 1.5 g Fe(NO3)3·9H2O. The solution was allowed to stand at room temperature for 10 minutes, then removed and rinsed with deionized water to obtain the PVP / Fe@Ni(OH)2 intermediate.

[0052] (4) The PVP / Fe@Ni(OH)2 intermediate was placed in the downstream of a tube furnace, with 0.4 g NaH2PO2·H2O in the upstream, and nitrogen as the carrier gas. The mixture was heat treated at 500 °C for 2 hours, and then naturally cooled to room temperature and taken out to obtain a carbon cross-linked network sodium negative electrode material C. Fe @Ni2P.

[0053] Scanning electron microscopy revealed that the cross-linked network formed outside the nanosheet array had a clear morphology. XRD revealed that an amorphous carbon peak appeared near 23 degrees in the cross-linked network. X-ray spectroscopy revealed that the cross-linked network was uniformly doped with Fe.

[0054] 1.0M NaClO4, ethylene carbonate (EC): dimethyl carbonate (DMC) (volume ratio of 1:1) and 5% fluoroethylene carbonate (FEC) were used as electrolytes. Sodium metal was used as the counter electrode. -1 The cycle test was carried out under the same conditions. It can be seen that after 100 cycles, the battery can still reach 265mAh g -1 High performance and stability.

[0055] In summary, the present invention discloses a method for synthesizing a carbon cross-linked network phosphide material and its application as a sodium negative electrode. The material was used as a negative electrode material in the performance test of sodium ion batteries and achieved relatively excellent sodium storage performance. -1 The battery can still reach 317 mAh g after 100 cycles at a high current density. -1 High performance and stability. The present invention mainly forms a carbon cross-linked network during heat treatment in a phosphine atmosphere by directionally binding the iron ions in the metal salt solution through polyvinyl pyrrolidone in a liquid atmosphere. After the preliminary hydrothermal synthesis of the nickel hydroxide nanosheet precursor, it is immersed in an aqueous solution of uniformly mixed polyvinyl pyrrolidone and ferric nitrate, and the phosphating treatment and the construction of the carbon cross-linked network are simultaneously achieved by heat treatment in a tubular furnace. This carbon cross-linked network is not only beneficial to the stability of the nanostructure during the charge and discharge process of the battery, but also beneficial to the intercalation conversion, which is of great significance for the innovative application and development of transition metal-based materials in sodium ion batteries.

Claims

1. A method for preparing a carbon cross-linked network sodium negative electrode material, characterized in that: The steps include: (1) placing a substrate in an autoclave liner containing a precursor solution, wherein the precursor solution is a mixed aqueous solution of 0.02-0.05M Ni(NO3)2·6H2O, 0.12-0.25M NH4F, and 0.1-0.4M urea; after hydrothermal reaction at 100-130°C for 10 hours, washing with deionized water and ethanol to remove surface adsorbed impurities, thereby obtaining a Ni(OH)2 precursor on the substrate; (2) The Ni(OH)2 precursor was placed in a 30 ml aqueous solution containing 0.5-2.0 g of polyvinyl pyrrolidone and 0.5-3.0 g of Fe(NO3)3·9H2O, wherein the molecular weight of the polyvinyl pyrrolidone was between 56,000 and 68,000; the mixture was allowed to stand at room temperature for 10 minutes, then taken out and washed with deionized water to obtain a PVP / Fe@Ni(OH)2 intermediate; (3) The PVP / Fe@Ni(OH)2 intermediate was placed downstream of a tubular furnace, with 0.4 g NaH2PO2×H2O upstream, and the carrier gas was argon. The mixture was heat treated at 500°C for 2 hours, cooled naturally to room temperature, and then taken out to obtain a carbon cross-linked network sodium negative electrode material; the carbon cross-linked network sodium negative electrode material included a nanosheet array and a carbon cross-linked network coating the nanosheet array, and the carbon cross-linked network was doped with iron; the nanosheet was a Ni2P nanosheet.

2. The carbon cross-linked network sodium negative electrode material prepared by the preparation method as claimed in claim 1.

3. Application of the carbon cross-linked network sodium negative electrode material as claimed in claim 2 in sodium batteries.

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