Preparation of a carbon-coated nickel trisulfide composite and its application as a negative electrode material for lithium-ion batteries

Abstract

The invention discloses a preparation method of a carbon-coated nickel trisulfide composite material, which uses peach gum as a carbon source, thioacetamide or sodium thioacetate as a sulfur source, and metal nickel salt as a nickel source. First, a hydrothermal reaction is carried out in deionized water to obtain a composite material precursor; the composite material precursor is then subjected to high-temperature carbonization to obtain a carbon-coated nickel trisulfide composite material. The carbon-coated nickel trisulfide composite material prepared by the invention has a spherical nanoscale structure and uniform particle size. The existence of the nanospherical structure enables the carbon-coated nickel trisulfide composite material to relieve the volume expansion of nickel trisulfide during the charge and discharge process when used as the anode material of a lithium-ion battery, thereby being beneficial to the overall structural stability of the material, and ultimately showing good long-cycle stability. Electrochemical performance tests show that the nanocomposite material exhibits excellent cycle stability when used as the anode material of a lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to a preparation method of a carbon-coated nickel trisulfide composite material, which is mainly used as a negative electrode material for lithium-ion batteries, belonging to the technical fields of composite materials and new energy technologies. Background Art

[0002] Lithium-ion batteries are increasingly used in many fields such as mobile phones, laptop computers, digital cameras, electric vehicles, aerospace, and military equipment due to their advantages of high energy density, low self-discharge current, high safety, large current charge and discharge, many cycle times, and long life. However, with the further growth of people's demand for lithium-ion batteries, coupled with restrictive factors such as the relative scarcity and high cost of lithium compared to sodium, it is difficult to meet the needs of large-scale energy storage brought about by market changes. In the field of new energy materials, carbon coating is one of the most common material modification methods. Carbon coating of materials can, on the one hand, improve the electrical conductivity of the materials, and on the other hand, provide a stable chemical and electrochemical reaction interface. Therefore, how to achieve effective carbon coating becomes particularly important.

[0003] CN112018344A discloses a carbon-coated nickel sulfide electrode material and its preparation method, which uses glucose as a carbon source, thiosulfate as a sulfur source, and nickel salts such as nickel acetate tetrahydrate, nickel acetate, nickel nitrate, nickel sulfate, and nickel chloride as nickel sources. In an ethylene glycol aqueous solution, a hydrothermal reaction is carried out at 160°C to 240°C for 6 to 24 hours, and then calcined at 300°C to 600°C for 1 to 5 hours in a protective atmosphere to obtain a flower-like nanostructured carbon-coated nickel sulfide electrode material. The flower-like nanostructure of this method is formed by bonding nickel sulfide to each other through glucose as an adhesive. Low-cost glucose is used as both an adhesive and a carbon source. On the one hand, after nickel source and sulfur source react to form nickel disulfide particles, glucose as an adhesive can bond the nickel disulfide particles together to form a flower-like nanostructure, and the flower-like nanostructure provides an effective path for the diffusion of sodium ions in the electrochemical reaction; on the other hand, glucose can evenly adhere to the surface of the nickel disulfide material, and after calcination treatment, a uniform amorphous carbon coating layer can be formed on the surface of the nickel disulfide material, and the amorphous carbon coating layer can improve the conductivity of the electrode material and buffer the sharp volume change of the material during the sodium ion insertion and extraction process to ensure its structure and electrochemical stability. However, in this process, using thiosulfate as a sulfur source is prone to deliquescence and is not conducive to storage; using an ethylene glycol aqueous solution as a solvent not only has a high cost but also is not conducive to environmental protection. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method of a carbon-coated nickel trisulfide composite material;

[0005] Another object of the present invention is to study the performance of the carbon-coated nickel trisulfide composite material prepared above as an anode material for lithium-ion batteries.

[0006] I. Preparation of carbon-coated nickel sulfide composite material

[0007] A preparation method of a carbon-coated nickel trisulfide composite material of the present invention uses peach gum as a carbon source, thioacetamide or sodium thioacetate as a sulfur source, and metal nickel salt as a nickel source, and performs a hydrothermal reaction in deionized water to obtain a composite material precursor; the composite material precursor is then subjected to high-temperature carbonization to obtain a carbon-coated nickel trisulfide composite material; the specific process is as follows: first, peach gum is prepared into an aqueous solution with a mass concentration of 10% to 80%, then the metal nickel salt and the sulfur source are dispersed in the peach gum solution under stirring, and then hydrothermal reaction is carried out in an industrial reaction kettle with a stirring function at 150 to 300 °C for 6 to 8 hours. The solid product is washed and dried with deionized water to obtain a composite material precursor; finally, the composite material precursor is calcined in a pre-carbonization tunnel kiln at 400 to 1000 °C for 1 to 3 h to obtain a carbon-coated nickel trisulfide composite material.

[0008] Peach gum is a reddish-brown or yellowish-brown colloidal substance secreted by the bark of peach trees. Generally speaking, the colloidal substances secreted by Rosaceae plants such as apricot trees and cherry trees can also be called peach gum. Peeling these secretions from the bark and drying them is the original peach gum, which can be used in traditional Chinese medicine or eaten after simple processing. The main component of the original peach gum is macromolecular polysaccharide, which is not easily soluble in water but has good water absorption, and its volume can be swollen more than 10 times. After the original peach gum is removed of impurities and undergoes hydrolysis, decolorization and other treatments, it becomes a small-molecule polysaccharide, which is commercial peach gum. The purpose of hydrolysis is to turn the insoluble macromolecular polysaccharide into a soluble small-molecule polysaccharide for convenient industrial use. Commercial peach gum can play the roles of thickening, emulsifying, solidifying, etc. in food, and its function is similar to that of another common gum (arabic gum), but in some properties, peach gum is better than arabic gum, such as greater light transmittance and viscosity. As a carbon source, it can be dissolved in water, and no large environmental pollution will be generated; at the same time, since it is a natural polymer, in addition to carbon, oxygen, and hydrogen, there are also heteroatoms such as nitrogen and sulfur in its composition, and the presence of heteroatoms is beneficial to increasing the structural active sites and conductivity of the material.

[0009] Thioacetamide and sodium thioacetate as sulfur sources have the advantage of being easy to store compared with sodium thiosulfate, and sodium thiosulfate is easily oxidized. The reaction mechanism of the carbon source peach gum and the sulfur source to prepare nickel trisulfide is as follows: the carbon source peach gum has a certain viscosity when dissolved in water. The nickel source and the sulfur source are dispersed in the carbon source solution, and during the hydrothermal reaction, due to external heating, the chemical reaction is accelerated, and nickel trisulfide is rapidly generated. Since this reaction is carried out in a viscous solution, nickel trisulfide nanoparticles are used as the core in the reaction system, and the carbon source is gradually dispersed on the surface of the core in the later stage of the reaction, forming carbon-coated nickel trisulfide.

[0010] The amount of carbon source (tremella gum) added will affect the particle size of nickel sulfide coated with carbon formed by nickel salt and sulfur source (thioacetamide or sodium thioacetate). Since the mass of carbon after carbonization of the carbon source at a certain temperature is constant, excessive carbon source will cause the carbon coating layer of the final product to thicken. Such a thick structure is not conducive to the cycle stability of nickel trisulfide as a lithium battery anode material (the lithium ion shuttle distance becomes longer). Experiments show that when the mass ratio of carbon source (tremella gum) to sulfur source (thioacetamide or sodium thioacetate) is 1:4 - 1:12, the obtained carbon-coated nickel sulfide composite material is a regular spherical shape and a nanomaterial, which has excellent cycle stability when used as the anode material of a lithium ion battery.

[0011] The metal nickel salt is one of nickel acetate tetrahydrate, nickel acetate, nickel nitrate, nickel sulfate and nickel chloride. The ratio of carbon source (tremella gum) to metal nickel salt will have a certain impact on the morphology of the carbon-coated nickel sulfide composite material (affecting the particle size of nickel sulfide coated with carbon). Excessive carbon source will cause the carbon layer of the composite material to be too thick, and there will also be independent carbon blocks (caused by excessive carbon source). Experiments show that the mass ratio of carbon source (tremella gum) to metal nickel salt is preferably in the range of 1:1 - 4:1.

[0012] The carbonization temperature and time have little effect on the morphology of the carbon-coated nickel trisulfide composite material, but only affect the performance of the carbon-coated nickel trisulfide composite material when used as a lithium battery anode material. Because the carbon source is not completely carbonized at a lower temperature and the conductivity is poor, too high a carbonization temperature will cause a change in the structure of nickel trisulfide in the carbon-coated nickel trisulfide composite material. This change is mainly that high temperature will cause the sulfur in the compound to volatilize, thus affecting the composition, and different compositions will result in different electrochemical performances when used as a lithium battery anode. Experiments show that when the carbonization temperature is controlled within 400°C - 1000°C and the carbonization time is controlled within 1 - 3 h, the obtained carbon-coated nickel trisulfide composite material shows high long-cycle stability when used as the anode material of a lithium ion battery. This is due to the strong conductivity of the carbon layer after carbonization.

[0013] II. Structure Characterization of Carbon-Coated Nickel Trisulfide Composite Material

[0014] The morphology of the prepared carbon-coated nickel trisulfide composite material was characterized by scanning electron microscopy (SEM), and the components of the prepared carbon-coated nickel trisulfide composite material were characterized by X-ray diffraction pattern (XRD).

[0015] Figure 1Scanning electron microscope (SEM) image of the carbon-coated nickel trisulfide composite prepared for this invention. The image shows that the prepared carbon-coated nickel trisulfide composite exists in spherical shape. The spherical structure has uniform particle size and is nanoscale (80 - 150 nm). The existence of the nanostructure is beneficial to the long cycle performance of the carbon-coated nickel trisulfide composite as the anode material of lithium-ion batteries because the nanostructure can slow down the volume expansion of nickel trisulfide during charge and discharge, thus contributing to the overall structural stability of the material and ultimately showing good long cycle stability.

[0016] Figure 2 XRD spectrum of the carbon-coated nickel trisulfide composite prepared for this invention. It can be seen from Figure 2 that the diffraction peaks of nickel trisulfide exist, and the large peak around 25° in the figure is the existence of amorphous carbon.

[0017] III. Performance of the carbon-coated nickel trisulfide composite as a lithium-ion battery material

[0018] The above-prepared carbon-coated nickel trisulfide composite was assembled into a lithium-ion battery and its electrochemical performance was measured.

[0019] The assembly process is as follows: The prepared active material (carbon-coated nickel trisulfide composite) was mixed and ground with a binder (PVDF) and conductive carbon black at a mass ratio of 7.0:2.0:1.0. Then the above-ground mixture was dispersed in a 5 mL small beaker containing N-methylpyrrolidone (NMP) solvent and stirred magnetically for 6 - 8 hours. Subsequently, the slurry with appropriate viscosity was evenly coated on a clean and flat copper foil (anode) using a coater. The above-coated sample was placed in a blast drying oven at 60 °C for 12 h. Finally, the dried copper foil was cut into 12 mm circular pieces and used as electrode sheets for standby. The battery assembly was carried out in a glove box filled with argon atmosphere. The assembly sequence of the button battery was as follows: negative (positive) electrode shell, electrode sheet, polypropylene separator, electrolyte, lithium sheet, steel sheet, spring sheet, positive (negative) electrode shell, and finally it was quickly sealed by a press.

[0020] Test conditions: At 25 °C, cycle at a current density of 200 mA g -1 : Charge and discharge range: 0.01V - 3.0V. Figure 3 Cycling performance graph of the carbon-coated nickel trisulfide composite prepared for this invention (Example 1) as the anode material of a lithium-ion battery. It can be seen from Figure 3 that when the carbon-coated nickel trisulfide composite prepared for this invention is used as the anode material of a lithium-ion battery and cycled at a current density of 200 mA g -1 its initial reversible specific capacity is 995.1 mAh g -1, the reversible specific capacity is 990.7 mAh g after 88 cycles -1 , and the capacity retention rate is 99.6%. It shows excellent cycle stability, indicating that the carbon-coated nickel trisulfide composite material prepared by the present invention has excellent cycle stability when used as the anode material of a lithium-ion battery.

[0021] In summary, the present invention uses peach gum as the carbon source and thioacetamide or sodium thioacetate as the sulfur source, and performs a hydrothermal reaction with metal nickel salt in deionized water to generate an incompletely carbonized carbon-coated nickel trisulfide precursor product. The precursor product is washed with deionized water, dried, and then calcined in an oxygen-free atmosphere to obtain a carbon-coated nickel trisulfide composite material. The carbon-coated nickel trisulfide composite material is a spherical nano-structure with uniform particle size. The existence of the nano-spherical structure enables the carbon-coated nickel trisulfide composite material to relieve the volume expansion of nickel trisulfide during the charge and discharge process when used as the anode material of a lithium-ion battery, thereby facilitating the overall structural stability of the material, and ultimately showing good long-term cycle stability. Electrochemical performance tests show that the nano-composite material exhibits excellent cycle stability when used as the anode material of a lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a scanning electron microscope (SEM) image of the carbon-coated nickel trisulfide composite material prepared in Example 1.

[0023] Figure 2 It is an X-ray diffraction pattern (XRD) of the carbon-coated nickel trisulfide composite material prepared in Example 1.

[0024] Figure 3 It is a cycle performance graph of the carbon-coated nickel trisulfide composite material prepared in Example 1 as the anode material of a lithium-ion battery.

[0025] Figure 4 It is a cycle performance graph of the carbon-coated nickel trisulfide composite material prepared in Example 2 as the anode material of a lithium-ion battery.

[0026] Figure 5 It is a cycle performance graph of the carbon-coated nickel trisulfide composite material prepared in Example 3 as the anode material of a lithium-ion battery. DETAILED DESCRIPTION OF THE INVENTION

[0027] The preparation, structure and cycle performance of the carbon-coated nickel trisulfide of the present invention as the anode material of a lithium-ion battery will be further described below through specific examples.

[0028] Example 1

[0029] Weigh 3 g of peach gum and disperse it evenly in 100 ml of deionized water under stirring to obtain a peach gum solution; take 1 g of metal nickel salt (nickel nitrate) and 12 g of thioacetamide, and disperse them in the peach gum solution under stirring; then place the mixed solution in an oven and carry out hydrothermal reaction at 150 °C for 8 h; after the reaction is completed, perform solid-liquid separation, wash the obtained solid product with deionized water, dry it, place it in a silicon carbide crucible, and calcine it at 600 °C for 2 h in an oxygen-free atmosphere to obtain a composite material of carbon-coated nickel trisulfide (the structure is shown in Figure 1 , 2 ).

[0030] Use the prepared carbon-coated nickel trisulfide material as the active ingredient to make the anode material of a lithium-ion battery and carry out long-term cycling at a current density of 200 mA g -1 . The results show that its initial reversible specific capacity is 995.1 mAh g -1 , and the reversible specific capacity is 990.7 mAh g -1 after 88 cycles (see Figure 3 ), showing excellent cycling stability. The increase in specific capacity after cycling is mainly due to the activation of transition metals.

[0031] Example 2

[0032] Weigh 3 g of peach gum and disperse it evenly in 100 ml of deionized water under stirring to obtain a peach gum solution; take 1 g of metal nickel salt (nickel nitrate) and 12 g of thioacetamide, and disperse them in the peach gum solution under stirring; then place the mixed solution in an oven and carry out hydrothermal reaction at 200 °C for 8 h; after the reaction is completed, perform solid-liquid separation, wash the obtained solid product with deionized water, dry it, place it in a silicon carbide crucible, and calcine it at 600 °C for 2 h in an oxygen-free atmosphere to obtain a composite material of carbon-coated nickel trisulfide.

[0033] Use the prepared carbon-coated nickel trisulfide material as the active ingredient to make the anode material of a lithium-ion battery and carry out long-term cycling at a current density of 200 mA g -1 . The results show that its initial reversible specific capacity is 666.4 mAh g -1 , and the reversible specific capacity is 529.3 mAh g -1 after 88 cycles (see Figure 4 ), showing good cycling stability.

[0034] Example 3

[0035] Weigh 4 g of peach gum and disperse it evenly in 100 ml of deionized water under stirring to obtain a peach gum solution; take 1 g of metal nickel salt (nickel nitrate) and 12 g of thioacetamide, and disperse them in the peach gum solution under stirring; then place the mixed solution in an oven and carry out a hydrothermal reaction at 180 °C for 6 h; after the reaction is completed, perform solid-liquid separation, wash the obtained solid product with deionized water, dry it, place it in a silicon carbide crucible, and calcine it at 800 °C for 2 h in an oxygen-free atmosphere to obtain a carbon-coated nickel trisulfide composite material.

[0036] Using the prepared carbon-coated nickel trisulfide material as the active ingredient, fabricate the anode material of a lithium-ion battery and perform long-term cycling at a current density of 200 mA g -1 . The results show that its initial reversible specific capacity is 833.1 mAh g -1 , and the reversible specific capacity is 787.6 mAh g -1 after 88 cycles (see Figure 5 ), showing excellent cycling stability.

Claims

1. A preparation method of a carbon-coated nickel trisulfide composite material uses peach gum as a carbon source, thioacetamide or sodium thioacetate as a sulfur source, and a metal nickel salt as a nickel source. A hydrothermal reaction is carried out in deionized water to obtain a composite material precursor; the composite material precursor is then subjected to high-temperature carbonization to obtain the carbon-coated nickel trisulfide composite material. The specific process is as follows: First, peach gum is prepared into an aqueous solution with a mass concentration of 10% - 80%. Then, the metal nickel salt and the sulfur source are dispersed in the peach gum solution under stirring. Then, a hydrothermal reaction is carried out in an industrial reaction kettle with a stirring function at 150 - 300 °C for 6 - 8 hours. The solid product is washed and dried with deionized water to obtain the composite material precursor. Finally, the composite material precursor is calcined in a pre-carbonization tunnel kiln at 400 - 1000 °C for 1 - 3 h to obtain the carbon-coated nickel trisulfide composite material.

2. The preparation method of a carbon-coated nickel trisulfide composite material according to claim 1, characterized in that: The metal nickel salt is one of nickel acetate tetrahydrate, nickel acetate, nickel nitrate, nickel sulfate, and nickel chloride.

3. The preparation method of a carbon-coated nickel trisulfide composite material according to claim 1, wherein: The mass ratio of the metal nickel salt to the sulfur source is 1:4 - 1:

12.

4. The preparation method of a carbon-coated nickel trisulfide composite material according to claim 1, characterized in that: The mass ratio of the carbon source peach gum to the metal nickel salt is 1:1 - 4:

1.

5. Application of the carbon-coated nickel trisulfide composite material prepared by the method according to claim 1 as a negative electrode material for a lithium-ion battery.

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