A negative electrode material, a preparation method therefor, and an application thereof

Abstract

The application relates to a negative electrode material and a preparation method and application thereof, and relates to the field of composite material preparation. The core of the negative electrode material is at least one of NiS2 and Ni3S4, and the shell is nitrogen-sulfur double-doped carbon. A microspherical nickel disulfide / nickel trisulfide / nitrogen-sulfur double-doped carbon composite material with a similar structure to a precursor is prepared through a template method. The special structure is beneficial to reducing the volume expansion and self-pulverization of the electrode material in the charging and discharging process, can correspondingly improve the cycle stability, the carbon left after calcination can increase the conductivity of the material and improve the rate performance of the material. The nitrogen-sulfur element doping can increase the reaction active sites and improve the specific capacity. The stable structure and the nitrogen-sulfur double-doped carbon jointly act to greatly improve the electrochemical performance of the material.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation, and in particular to a negative electrode material, its preparation method, and its application. Background Technology

[0002] In recent years, the massive consumption of fossil fuels has led to a crisis of reform for traditional energy sources. New energy storage devices have begun to attract significant attention from researchers. Among them, lithium-ion batteries, with their advantages of high energy density, high voltage window, light weight, and no self-discharge, have already found practical application and are widely used in new energy vehicles and some energy storage systems. As lithium-ion batteries are applied in many fields, the demand for lithium is increasing daily; however, the lithium content on Earth's surface is not high, leading to rising costs for lithium-ion batteries. At this point, sodium-ion batteries, being in the same group as lithium and possessing similar chemical properties, have become a possibility for replacing and supplementing lithium-ion batteries. As a key component, electrode materials directly affect the performance of sodium-ion batteries. Developing high-performance electrode materials can make the commercialization of sodium-ion batteries possible. Research on negative electrode materials mainly focuses on intercalation materials based on carbon, conversion reaction materials based on transition metal oxides / sulfides, and alloy reaction materials.

[0003] Transition metal sulfides exhibit higher conductivity than their oxides and possess higher specific capacity due to their conversion reactions, making them promising electrode materials. Nickel sulfides are diverse, possess high theoretical specific capacity, and demonstrate high electrochemical reversibility in sodium-ion battery anode materials. However, nickel sulfides themselves have low conductivity, and the volume expansion and material pulverization caused by the conversion reaction mechanism significantly shorten the long-cycle life of the electrode material.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a negative electrode material to address the problems in related technologies, such as the low conductivity of nickel sulfides and the short cycle life of electrode materials due to volume expansion and material pulverization caused by the conversion reaction mechanism.

[0006] A second objective of this invention is to provide a method for preparing the aforementioned negative electrode material.

[0007] A third objective of this invention is to provide the application of the above-mentioned negative electrode material in the preparation of negative electrode materials for sodium-ion batteries.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A negative electrode material having a core-shell structure, characterized in that: the core is at least one of NiS2 and Ni3S4, and the shell is nitrogen-sulfur dual-doped carbon.

[0009] Preferably, the diameter of the negative electrode material is 0.8-1.2 μm.

[0010] Preferably, the diameter of the core portion accounts for 80%-90%, and the diameter of the shell portion accounts for 10%-20%.

[0011] This invention utilizes a template method to prepare microspherical nickel disulfide / triniyl tetrasulfide / nitrogen-sulfur dual-doped carbon composite materials with structures similar to the precursor. Its unique structure helps mitigate the volume expansion and self-pulverization of the electrode material during charge and discharge, thereby improving its cycle stability. The carbon remaining after calcination increases the material's conductivity and improves its rate performance. Furthermore, the doping of nitrogen and sulfur elements increases the number of reactive sites, enhancing its specific capacity. The stable structure and the combined effect of the nitrogen-sulfur dual-doped carbon significantly improve the material's electrochemical performance.

[0012] The carbon and nitrogen of the nitrogen-sulfur dual-doped carbon are obtained by calcination of carbon-nitrogen organic compounds. The sulfur of the nitrogen-sulfur dual-doped carbon is loaded on the surface of the calcined product of the carbon-nitrogen organic compounds. PVP is calcined under gas protection, thus preserving the surface of the calcined product of the carbon-nitrogen organic compounds.

[0013] According to a second objective of the present invention, a method for preparing the above-mentioned negative electrode material by template method is provided, which includes the following steps: Provides nitrogen-containing organic acid-nickel precipitate; Under gas protection, organic acid-nickel precipitate was calcined to obtain Ni@NC; With a molar ratio of S:Ni > 2, a sulfur source is loaded onto Ni@NC, and the reaction temperature is 160~180℃ to obtain the anode material as described in claim 1.

[0014] Preferably, the provision of the nitrogen-containing organic acid-nickel precipitate comprises: subjecting a nickel salt and an organic acid to a hydrothermal reaction in an aqueous solution containing polyvinylpyrrolidone to obtain the nitrogen-containing organic acid-nickel precipitate.

[0015] Preferably, the aqueous solution containing polyvinylpyrrolidone includes polyvinylpyrrolidone, ethylene glycol, and deionized water, with a polyvinylpyrrolidone concentration of 5-20 g / L and nickel salt and organic acid concentrations of 2-5 times that of polyvinylpyrrolidone.

[0016] Preferably, the calcination temperature is 500~600 ℃.

[0017] Preferably, the sulfur source is elemental sulfur.

[0018] Preferably, the step of loading a sulfur source onto Ni@NC comprises: immersing Ni@NC in a solution containing a sulfur source to obtain Ni@NC loaded with a sulfur source.

[0019] The specific operations for steps S1 to S3 are as follows: S1. In a mixed solution of ethylene glycol and deionized water with an appropriate amount of PVP (K30) added, a nickel source is mixed with trisodium citrate and subjected to a hydrothermal reaction. After washing, separation, and drying, the nickel citrate complex precursor (Ni-CA) is obtained. Specifically, PVP (K30) and nickel chloride hexahydrate are dissolved in a mixed solution of deionized water and ethylene glycol to obtain solution A. Trisodium citrate dihydrate is dissolved in solution A, ultrasonicated and stirred, and then hydrothermally reacted at 160~180 ℃ for 10~12 h. The product is washed, separated, and dried to obtain Ni-CA.

[0020] S2. Under argon gas protection, the Ni-CA obtained in step S1 is calcined at 500~600 ℃ for 2~3 h to obtain Ni@NC.

[0021] S3. The Ni@NC obtained in step S2 is dispersed in ethylene glycol to obtain mixture B. After adding sulfur powder, the mixture is ultrasonicated and stirred, then transferred to a reaction vessel and hydrothermally reacted at 160~180 ℃ for 10~18 h. After washing, separation and drying, the product is obtained as a microspherical NiS2 / Ni3S4@N,S-doped C composite material.

[0022] Preferably, in step S1, the amount of PVP added is 0.2~0.6 g, and the mass ratio of the nickel source to trisodium citrate is 1:1.

[0023] Preferably, in step S1, the nickel source can be nickel chloride, nickel nitrate, nickel sulfate, or other soluble nickel sources.

[0024] Preferably, in step S3, the mass ratio of Ni@NC to S powder is 1:2.

[0025] The composite material of this invention is prepared by a two-step hydrothermal method. In step S1, nickel ions and citrate ions are complexed with each other via a hydrothermal method to generate Ni-CA microspheres. The addition of PVP and ethylene glycol helps to form a spherical morphology, and the addition of deionized water allows the above-mentioned reagents to dissolve more quickly and completely. In step S2, the Ni-CA microspheres are calcined at high temperature under an argon atmosphere to form microspherical Ni@NC. After calcination, citrate ions lose hydrogen, oxygen, and water of crystallization to generate Ni@NC, and the precursor retains its special microspherical structure even under high-temperature calcination. In step S3, Ni@NC and sulfur powder are reacted via a hydrothermal reaction. At high temperature, Ni@NC and sulfur powder undergo a redox reaction to generate NiS2 / Ni3S4, and excess sulfur enters the carbon layer to form nitrogen-sulfur dual-doped carbon.

[0026] According to a third objective of the present invention, the above-described negative electrode material is provided for application in the field of electrochemistry.

[0027] The beneficial effects of the technical solution provided by this invention include: (1) This invention prepares microspherical NiS2 / Ni3S4@N,S-doped C composite material with a similar structure to the precursor by template method. Its special structure helps to mitigate the volume expansion and self-powdering of the electrode material during charge and discharge, and can correspondingly improve its cycle stability. The nitrogen-doped carbon left after calcination can increase the conductivity of the material, improve the rate performance of the material, and further improve the structural stability of the composite material.

[0028] (2) The nitrogen-sulfur dual-doped carbon shell can improve conductivity. By incorporating nitrogen and sulfur elements, carbon materials can acquire more defects, providing more active sites and improving electron / ion conductivity. The stable structure and the combined effect of nitrogen-sulfur dual-doped carbon greatly enhance the electrochemical performance of the material.

[0029] (3) The microspheres NiS2 / Ni3S4@N,S-doped C prepared in this invention exhibit excellent electrochemical performance. After 100 cycles at a current density of 0.1 A / g, it retains a discharge specific capacity of 658.4 mAh / g, with a capacity retention of 90.5% (compared to the third cycle). Furthermore, after 3500 cycles at a high current density of 10 A / g, it still retains a discharge specific capacity of 587.1 mAh / g, reflecting good rate performance and excellent cycle life. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The image shows the XRD pattern of the negative electrode material prepared in Example 1. Figure 2 SEM image of the negative electrode material prepared in Example 1; Figure 3 TEM image of the negative electrode material prepared in Example 1; Figure 4 The graph shows the cycling performance of the negative electrode material prepared in Example 1 at a current density of 0.1 A / g. Figure 5 The graph shows the cycling performance of the negative electrode material prepared in Example 1 at a current density of 10 A / g. Figure 6 SEM image of the negative electrode material prepared in Comparative Example 1; Figure 7 SEM image of the negative electrode material prepared in Comparative Example 2; Figure 8 The graph shows a comparison of the cycling performance of Example 1, Comparative Example 1, and Comparative Example 2 at a current density of 4A / g. Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0033] A method for preparing a microspherical nickel disulfide / trinitrogen tetrasulfide / nitrogen-sulfur dual-doped carbon composite material, specifically including the following steps: S1. Dissolve 0.4 g of PVP (K30) and 1 g of NiCl2·6H2O in a mixed solution A of 20 mL of deionized water and 20 mL of ethylene glycol. Dissolve 1 g of trisodium citrate dihydrate in the above solution A. Place the mixed solution A in a reaction vessel and heat it to 180 °C for hydrothermal reaction for 12 h. Wash the obtained precipitate four times by centrifugation with deionized water and anhydrous ethanol, respectively, and then dry it under vacuum to obtain Ni-CA. S2. The obtained Ni-CA solid was placed in a tube furnace protected by argon gas, heated to 600 ℃ at a heating rate of 3 ℃ / min and held for 3 h to obtain Ni @NC; S3. 50 mg Ni @NC was ultrasonically dispersed in 60 mL of ethylene glycol to obtain mixture B. 100 mg S powder was added to it. After ultrasonic and magnetic stirring, mixture B was transferred to a Teflon reactor and heated to 180 °C for 12 h. The precipitate was washed three times with deionized water and anhydrous ethanol, respectively. After centrifugation and drying, NiS2 / Ni3S4@N,S-doped C composite material was obtained.

[0034] Figure 1 The XRD pattern of the NiS2 / Ni3S4@N,S-doped C composite material prepared in Example 1 is shown. The XRD pattern reveals diffraction peaks at 27.1°, 31.4°, 35.3°, 38.8°, and 45.1°, corresponding to the (1 1 1), (2 0 0), (2 1 0), (2 1 1), and (2 2 0) planes of NiS2 (JCPDS No. 89-7142). The diffraction peaks of Ni3S4 (JCPDS No. 43-1369) are distributed around 26.6°, 31.3°, and 37.9°, corresponding to the (0 2 2), (1 1 3), and (0 0 4) planes, respectively. The XRD results indicate that the NiS2 / Ni3S4@N,S-doped C composite material has been successfully synthesized. Figure 2 The image shows a SEM image of the NiS2 / Ni3S4@N,S-doped C composite material prepared in Example 1. As can be seen from the image, the NiS2 / Ni3S4@N,S-doped C composite material is in the form of microspheres with a diameter of 0.8-1.2 μm. Figure 3 The TEM image of the NiS2 / Ni3S4@N,S-doped C composite material prepared in Example 1 clearly shows that NiS2 / Ni3S4 is coated with a layer of N,S dual-doped carbon.

[0035] Comparative Example 1 This comparative example provides a method for preparing NiS2 / Ni3S4@NC, specifically including the following steps: Steps S1 to S2 are the same as in Example 1, and will not be repeated here; S3. 50 mg Ni @NC was ultrasonically dispersed in 60 mL of ethylene glycol to obtain mixture C. 50 mg S powder and 50 mg thiourea were added to it. After ultrasonic and magnetic stirring, mixture C was transferred to a Teflon reactor and heated to 180 °C for 12 h. The precipitate was washed three times with deionized water and anhydrous ethanol, respectively, and then centrifuged and dried to obtain NiS2 / Ni3S4@NC composite material.

[0036] Figure 6 The image shows a SEM image of the NiS2 / Ni3S4@NC composite material prepared in Comparative Example 1. Figure 8 This is a comparison of the cycling performance of the three samples at a current density of 4 A / g. Figure 8 It can be seen that the cycling performance of Comparative Example 1 is significantly lower than that of Example 1, which may be because Comparative Example 1 lacks S doping.

[0037] Comparative Example 2 This comparative example provides a method for preparing NiS2 / NiS composite material, specifically including the following steps: Step S1 is the same as in Example 1, and will not be repeated here; S2. 150 mg Ni-CA was dispersed in 60 mL ethylene glycol solution, sonicated for 10 minutes, then 300 mg S powder was added, and the mixture was magnetically stirred at room temperature for 30 minutes. The precipitate was washed four times by centrifugation with deionized water and anhydrous ethanol, and then dried under vacuum to obtain NiS2 / NiS. Figure 7 The image shows a SEM image of the NiS2 / NiS composite material prepared in Comparative Example 2. It can be seen from the image that the diameter of the NiS2 / NiS without the carbon layer is smaller compared to Example 1.

[0038] Application examples The composite materials prepared in Examples 1 and Comparative Examples 1-2, the conductive agent (Super P), and carboxymethyl cellulose (CMC) were mixed uniformly at a mass ratio of 7:2:1. An appropriate amount of ultrapure water was added to form a slurry, which was then coated onto copper foil using a doctor blade or a four-sided coating applicator to form a negative electrode. The coated copper foil was placed in a drying oven and dried at 80 °C for 12 h. The coated copper foil was then cut into small circular pieces with a diameter of 12 mm and assembled into button batteries (CR2032) in a glove box. The electrochemical performance was tested using the prepared composite material as the working electrode and a sodium block as the counter electrode. The separator was Whatman GF / A, and the electrolyte system consisted of 1 M NaF6 as the solute and 100% DME as the solvent.

[0039] The assembled button batteries were subjected to electrochemical performance testing. The testing instruments used for the electrochemical performance testing were as follows: LANHE-CT2001A multi-channel battery testing system produced by Wuhan Landian Electronics Co., Ltd., with a resting time of 12 h, a voltage window range of 0.2-2.8 V, a current density range of 2000 mA g-1, and a cycle number range of 100-1000 times.

[0040] Figure 4 The graph shows the cycling performance of the NiS2 / Ni3S4@N,S-doped C composite material prepared in Example 1 at a current density of 0.1 A / g. As can be seen from the graph, the composite material still maintains a discharge specific capacity of 658.4 mAh / g after 100 cycles, with a capacity retention of 90.5% (compared to the third cycle), demonstrating good cycling stability.

[0041] Figure 5 The graph shows the cycling performance of the NiS2 / Ni3S4@N,S-doped C composite material prepared in Example 1 at a current density of 10 A / g. As can be seen from the graph, the composite material still has a discharge specific capacity of 587.1 mAh / g after 3500 cycles. Figure 8 The graph shows a comparison of the cycling performance of Example 1, Comparative Example 1, and Comparative Example 2 at a current density of 4 A / g. It can be seen that Example 1, which has a microsphere structure and a nitrogen-sulfur dual-doped carbon layer, has the best cycling performance.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a negative electrode material using a template method, wherein the negative electrode material has a core-shell structure, characterized in that, The core is at least one of NiS2 and Ni3S4, and the shell is nitrogen-sulfur dual-doped carbon. The method includes: Provides nitrogen-containing organic acid-nickel precipitate; Under gas protection, organic acid-nickel precipitate was calcined to obtain Ni@NC; With a molar ratio of S:Ni > 2, Ni@NC is immersed in ethylene glycol containing sulfur powder to obtain Ni@NC loaded with sulfur powder. The mixture is then heated to a reaction temperature of 160~180℃ to obtain the negative electrode material.

2. The method according to claim 1, characterized in that: The nitrogen-containing organic acid-nickel precipitate includes: A hydrothermal reaction is carried out between nickel salt and organic acid in an aqueous solution containing polyvinylpyrrolidone to obtain a nitrogen-containing organic acid-nickel precipitate.

3. The method according to claim 2, characterized in that: The aqueous solution containing polyvinylpyrrolidone includes polyvinylpyrrolidone, ethylene glycol, and deionized water. The concentration of polyvinylpyrrolidone is 5-20 g / L, and the concentrations of nickel salt and organic acid are 2-5 times that of polyvinylpyrrolidone.

4. The method according to claim 1, characterized in that: The calcination temperature is 500~600 ℃.

5. The method according to claim 1, characterized in that: The diameter of the negative electrode material is 0.8-1.2 μm.

6. The method according to claim 1 or 5, characterized in that: The diameter of the core accounts for 80%-90%, and the diameter of the shell accounts for 10%-20%.

7. The application of the negative electrode material prepared by the template method of claim 1 or 2 in the field of electrochemistry.

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