A lignin-derived carbon-coated NiS / TiO 2 Composite materials, their preparation methods and applications

Abstract

This invention discloses a lignin-derived carbon-coated NiS / TiO 2 Composite materials, their preparation methods, and applications. This invention uses sodium lignosulfonate as a carbon precursor and introduces TiO2, a substance with strong adsorption properties for sodium polysulfide. 2 NiS / TiO₂ with high specific capacity and good cycle stability was prepared by hydrothermal and calcination treatment. 2 / C composite material has a simple preparation process and low cost. As a high-energy-density and high-stability sodium-ion battery anode material, it is of great significance to the development of sodium-ion battery anode materials.

Description

A lignin-derived carbon-coated NiS / TiO2 composite material, its preparation method and application Technical Field

[0001] This invention belongs to the fields of high-value utilization of lignin and sodium-ion battery anode materials, specifically relating to a lignin-derived carbon-coated NiS / TiO2 composite material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are currently the most widely used and technologically mature power battery technology. They are widely used in portable power sources such as mobile phones and toys, as well as power batteries for electric vehicles. However, the lack of lithium resources and the relatively low safety of these batteries have hindered their further development.

[0003] Compared to lithium-ion batteries, sodium-ion batteries, as an emerging energy storage device, have many advantages. Sodium resources are abundant and widely distributed, very inexpensive, and belong to the same group as lithium, possessing similar physical and chemical properties. Therefore, sodium-ion batteries have great development potential and are a good complement and alternative to lithium-ion batteries. Sodium-ion batteries have relatively low operating voltages, and the electrolyte is less prone to decomposition at high voltages, resulting in better battery safety and stability. However, sodium... + Larger ionic radii inevitably cause structural deformation and slow kinetic processes during charge and discharge, leading to capacity decay and poor cycle stability. Therefore, finding suitable sodium-ion battery anode materials with high sodium storage capacity and excellent cycle performance is a critical problem that urgently needs to be solved.

[0004] Transition metal sulfides possess high theoretical specific capacity and excellent electrochemical reversibility, making them ideal candidates for efficient sodium storage anode materials. Among various metal sulfides, nickel sulfide (NiS) boasts a high theoretical capacity of 590 mAh / g, is relatively easy to synthesize, and exhibits higher electrochemical activity and conductivity than other nickel sulfide systems and metal sulfides. However, NiS anodes share similar drawbacks with other metal sulfides, such as low electronic conductivity and large volume changes during charge and discharge. Furthermore, the sodium polysulfides generated during cycling dissolve in the electrolyte, causing sodium polysulfide shuttle, leading to poor cycle stability and a series of problems such as battery undervoltage failure.

[0005] To address the above problems, researchers have proposed many methods to improve the sodium storage performance of NiS. For the problems of poor conductivity and volume expansion, there are two main solutions: (1) By designing nanostructures, constructing multi-shell hollow structures, core-shell structures, etc., can effectively alleviate the volume expansion during cycling. At the same time, smaller nanoparticles can accelerate ion transport and electron transfer. Fan et al. prepared hierarchical urchin-shaped multi-shell hollow NiS@NCNT microspheres by chemical vapor deposition (CVD) and subsequent sulfidation strategy. This unique multi-shell hollow structure greatly improves the cycling stability, but the rate performance of this material is not excellent. -1 At a current density of only 282.1 mAh·g -1 The specific capacity is high, and this unique structural design is usually more complex in process and the morphology is difficult to control. (2) When combined with carbon materials, it can effectively improve the conductivity during cycling and alleviate volume change. Song et al. prepared a double-layer carbon-coated NiS@C / rGO composite material by using a simple hydrothermal reaction, PDA coating process and subsequent heat treatment, at 0.1 A·g -1 After 500 cycles at the current density, it exhibits a strength of 240.2 mAh·g. -1 While the capacity is maintained, the overall capacity of this material is low, resulting in poor rate performance. Furthermore, the relatively high cost of polydopamine and graphene oxide increases the material's manufacturing cost, hindering practical production and application. Regarding the dissolution and shuttle problem of sodium polysulfides generated during cycling, some researchers have proposed introducing highly electronegative elements such as N and S to construct polar CS bonds and anchor dissolved sodium polysulfide intermediates. However, due to the less-than-ideal overall adsorption effect, sodium polysulfide shuttle inevitably occurs during cycling, damaging the separator and causing sodium metal corrosion, potentially leading to battery failure.

[0006] Therefore, designing and preparing a NiS-carbon composite material with excellent electrochemical performance to address the issues of low conductivity, volume expansion during cycling, and the dissolution and shuttle problems of sodium polysulfides generated by NiS is of great significance to the development of anode materials for sodium-ion batteries. Summary of the Invention

[0007] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing lignin-derived carbon-coated NiS / TiO2 composite materials.

[0008] This invention utilizes sodium lignosulfonate, an ideal carbon precursor, and introduces TiO2, a substance with strong adsorption properties for sodium polysulfide, to prepare a NiS / TiO2 / C composite material with high specific capacity and good cycle stability as a negative electrode material for sodium-ion batteries through hydrothermal and calcination treatment. The preparation process is simple and low-cost, which is of great significance to the development of sodium-ion battery negative electrode materials.

[0009] Another object of the present invention is to provide a lignin-derived carbon-coated NiS / TiO2 composite material prepared by the above preparation method.

[0010] Another object of the present invention is to provide the application of the above-mentioned lignin-derived carbon-coated NiS / TiO2 composite material.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A method for preparing a lignin-derived carbon-coated NiS / TiO2 composite material includes the following steps:

[0013] Using water as a solvent, nickel salt, sulfur source, carbon source, small molecule diol and nano TiO2 or TiO2 precursor are mixed evenly and hydrothermally reacted in a reactor at 80-250 °C for 4-20 h. After washing and drying, the mixture is calcined under a protective gas atmosphere to obtain lignin-derived carbon-coated NiS / TiO2 composite material.

[0014] Preferably, the preparation method of the lignin-derived carbon-coated NiS / TiO2 composite material includes the following steps:

[0015] (1) Dissolve nickel salt and sulfur source in water, then add carbon source and disperse evenly, add small molecule diol and mix evenly, and finally add nano TiO2 or TiO2 precursor and mix evenly to obtain mixed reaction solution.

[0016] (2) The mixed reaction solution was hydrothermally reacted in a reactor at 80-250 °C for 4-20 h, washed, and dried to obtain a carbon-coated NiS / TiO2 composite material precursor;

[0017] (3) The carbon-coated NiS / TiO2 composite material precursor was calcined in a protective gas atmosphere to obtain the carbon-coated NiS / TiO2 composite material.

[0018] Preferably, the nickel salt is at least one of nickel chloride hexahydrate and nickel nitrate hexahydrate.

[0019] Preferably, the sulfur source is at least one of thiourea and sodium thiosulfate pentahydrate.

[0020] Preferably, the carbon source is at least one of alkali lignin, lignin sulfonate, ammoniated lignin, and enzymatically hydrolyzed lignin; more preferably, it is at least one of sodium lignin sulfonate and ammoniated lignin.

[0021] More preferably, the ammonia-oxidized lignin is prepared by the following method:

[0022] (10-30) g of alkali lignin, (250-350) mL of water, (10-30) g of hydrogen peroxide solution with a concentration of (20-40) wt% and (5-15) g of ammonia solution with a concentration of (15-35) wt% were mixed evenly and then hydrothermally reacted in a hydrothermal reactor at (100-180) ℃ for (8-15) h. After removing the water, ammonia-oxidized lignin was obtained.

[0023] Preferably, the small molecule diol is at least one of ethylene glycol, propylene glycol, and butanediol.

[0024] Preferably, the nano-TiO2 is anatase TiO2 with an average particle size of 30-200 nm; the TiO2 precursor is at least one of tetrabutyl titanate and titanium isopropoxide.

[0025] Preferably, the ratio of nickel salt, sulfur source, carbon source, small molecule diol and nano TiO2 is 0.9 g: (1.0~4.0) g: (0.1~3.0) g: (10~40) mL: (0.3~2.0) g; more preferably, it is 0.9 g: 2.5 g: 0.6 g: (10~25) mL: (0.3~0.5) g.

[0026] Preferably, the ratio of nickel salt, sulfur source, carbon source, small molecule diol and TiO2 precursor is 0.9 g: (1.0-4.0) g: (0.1-3.0) g: (10-40) mL: (1.0-3.0) g; more preferably, it is 0.9 g: 2.5 g: 0.6 g: (10-25) mL: 1.5 g.

[0027] Preferably, the volume ratio of the small molecule diol to water is (1-4):(1-4); more preferably, it is (1-2.5):2.5.

[0028] Preferably, the hydrothermal reaction is carried out at a temperature of 100–180 °C for 8–15 h. More preferably, the hydrothermal reaction is carried out at a temperature of 150 °C for 12 h.

[0029] Preferably, the washing refers to centrifugal washing with water and anhydrous ethanol.

[0030] Preferably, the protective gas is at least one of nitrogen and rare gases, more preferably at least one of nitrogen, argon and helium.

[0031] Preferably, the calcination temperature is 300–900 °C and the time is 2–5 h; more preferably, the calcination temperature is 500–700 °C and the time is 3–5 h.

[0032] Preferably, the heating rate of the calcination is 1 to 10 °C / min.

[0033] A lignin-derived carbon-coated NiS / TiO2 composite material was prepared by the above method.

[0034] The above-mentioned application of a lignin-derived carbon-coated NiS / TiO2 composite material.

[0035] Preferably, the lignin-derived carbon-coated NiS / TiO2 composite material is used in sodium-ion batteries.

[0036] This patent will now be described in more detail.

[0037] (1) Mix 0.9 g of nickel salt with 10–40 mL of ultrapure water evenly;

[0038] (2) Add 1.0 to 4.0 g of sulfur source to the solution obtained in step (1) and stir until it is evenly dispersed;

[0039] (3) Add 0.1–3.0 g of carbon source to the solution obtained in step (2) and stir to dissolve;

[0040] In this step, adding different amounts of carbon source can act as a carbon layer coating material after calcination. The amount of carbon source added needs to be further determined through experiments. If too little carbon source is added, the resulting carbon layer will be thin and unable to effectively alleviate the volume expansion caused by cycling. If too much carbon source is added, more gas will be released and foaming will occur during pyrolysis, resulting in reduced contact between the carbon layer and the material, greatly reducing the coating effect. Moreover, excessive carbon content will reduce the relative content of NiS, leading to a decrease in the specific capacity of the prepared anode material.

[0041] (4) Add 10-40 mL of small molecule diol to the solution obtained in step (3); stir and mix thoroughly;

[0042] In this step, the use of a large amount of water as a solvent will cause the material prepared after hydrothermal treatment to agglomerate, resulting in poor cycle stability. However, adding an appropriate amount of small molecule diol can adjust the solution viscosity, which is beneficial for controlling the growth of crystal nuclei diffusion and preparing uniformly dispersed nanoparticles. At the same time, it can also maintain the solubility of the carbon source in the solution, so that the lignin carbon source can more uniformly coat the nickel salt and sulfur source, thereby improving the uniformity of lignin-derived carbon coating NiS / TiO2 and increasing the long-term cycle stability of the electrode material.

[0043] (5) Add 0.3-2.0 g nano TiO2 or 1.0-3.0 g TiO2 precursor to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 100-180 °C for 8-15 h;

[0044] In this step, directly adding nano-TiO2 or adding TiO2 precursors of varying amounts and then hydrothermally generating TiO2 can effectively incorporate TiO2 into the electrode material, achieving adsorption of sodium polysulfides, alleviating sodium polysulfide dissolution and shuttle behavior, and improving battery cycle stability. If the amount of nano-TiO2 or TiO2 precursor added is too small, the TiO2 generated in the reaction will be insufficient to adsorb the sodium polysulfides produced during cycling, leading to poor stability and battery failure. However, due to the low theoretical specific capacity of TiO2, adding too much nano-TiO2 or TiO2 precursor will result in a lower overall battery specific capacity.

[0045] (6) The substance obtained in step (5) was washed three times each by centrifugation with water and anhydrous ethanol, and then dried to obtain NiS2 / TiO2 / LS;

[0046] This step mainly involves washing away incompletely reacted lignin and excess sulfur sources to improve the purity of the material.

[0047] (7) The powder obtained in step (6) is calcined at 300-900 °C for 2-5 h under a protective atmosphere to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0048] In this step, calcination was carried out at temperatures ranging from 300 to 900 °C. Due to the inherent characteristics of nickel sulfide and the reducing properties of lignin carbon sources, if the temperature is too low, the lignin carbonization will be incomplete, and nickel chloride will be difficult to convert into highly crystalline NiS, making it impossible to prepare NiS / TiO2 / C composite anode materials with high purity and crystallinity. If the temperature is too high, it may lead to material loss, while increasing energy consumption, making it less green and energy-efficient, and significantly increasing costs.

[0049] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0050] (1) This invention uses industrial lignin as a carbon precursor. The reducing gas generated during the calcination process reduces NiS2 to NiS. There is no need to add H2 / Ar mixed gas as a reducing agent, which reduces energy consumption and cost and has high safety. At the same time, it realizes the high-value utilization of industrial lignin.

[0051] (2) The present invention prepares NiS / TiO2 / C sodium ion battery anode material in only two steps: hydrothermal method and calcination treatment. The calcination temperature is low, which greatly reduces energy consumption and cost. The preparation process is simple and easy to operate, highly controllable, low in energy consumption and high in production efficiency.

[0052] (3) The composite material prepared by the present invention consists of uniformly dispersed nanoparticles coated with a carbon layer, which is beneficial for ion and electron transport and can also prevent polysulfides from escaping to a certain extent.

[0053] (4) In the NiS / TiO2 / C composite material of the present invention, the coated carbon layer can effectively alleviate the volume change of the electrode material during charging and discharging, while TiO2 can achieve strong adsorption of sodium polysulfides, preventing polysulfides from escaping into the electrolyte, thereby solving the undervoltage failure problem caused by polysulfides penetrating the membrane. The resulting material has high specific capacity and good cycle stability at high current density, making it an ideal anode material for sodium-ion batteries. Attached Figure Description

[0054] Figure 1 shows the XRD patterns of the composite material prepared in Example 1 after calcination at different temperatures.

[0055] Figure 2 is the EDX spectrum of the NiS / TiO2 / C composite material prepared in Example 1.

[0056] Figure 3 is the EDX spectrum of the NiS / TiO2 / C composite material prepared in Example 4.

[0057] Figure 4 shows the NiS / TiO2 / C composite material prepared in Example 1 assembled into a coin cell at a current density of 0.1 A·g. -1 The first charge-discharge curve at that time.

[0058] Figure 5 shows the rate performance of the NiS / TiO2 / C composite material prepared in Example 1 assembled into a coin cell at different current densities.

[0059] Figure 6 shows the assembly of the NiS / TiO2 / C composite material prepared in Example 1 into a coin cell at 10 A·g. -1 Cyclic performance at current density.

[0060] Figure 7 shows the assembly of the NiS / TiO2 / C composite material prepared in Example 2 into a coin cell at 10 A·g. -1 Cyclic performance at current density.

[0061] Figure 8 shows the assembly of the NiS / TiO2 / C composite material prepared in Example 4 into a coin cell at 10 A·g. -1 Cyclic performance at current density.

[0062] Figure 9 shows the assembly of the NiS / C composite material prepared in Example 1 into a coin cell at 10 A·g. -1 Cyclic performance at current density.

[0063] Figure 10 shows the assembly of the NiS / TiO2 / C composite material prepared in Comparative Example 2 into a coin cell at 10 A·g. -1 Cyclic performance at current density. Detailed Implementation

[0064] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0065] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0066] The nano-TiO2 described in this embodiment of the invention is anatase TiO2 with an average particle size of 100 nm, purchased from Maclean, catalog number: T861555-500g.

[0067] The ammonia-oxidized lignin described in this embodiment of the invention is prepared by the following method:

[0068] Add 20 g of alkali lignin (Al) to 160 mL of ultrapure water, then add 20 g of H2O2 (30 wt%) and 10 g of NH3•H2O (25 wt%), stir well, and hydrothermally react at 120 ℃ for 12 h in a hydrothermal reactor.

[0069] Then, it was rotary evaporated. First, ice was added and it was rotary evaporated for 3 hours to remove air bubbles. Then, it was rotary evaporated at room temperature for 3 hours. Then, the temperature was raised to 60 ℃ and rotary evaporated for 5 hours to dry it. It was then placed in a vacuum drying oven to dry overnight. After drying, it was ground.

[0070] Example 1

[0071] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0072] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0073] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0074] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0075] (5) Add 0.3 g of nano TiO2 to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0076] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0077] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0078] Repeat steps (1)-(6), only changing the calcination temperature in step (7) to 500 ℃ and 700 ℃, to investigate the effect of different calcination temperatures on NiS / TiO2 / C composite materials.

[0079] Example 2

[0080] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0081] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0082] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0083] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0084] (5) Add 0.5 g of nano TiO2 to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0085] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0086] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0087] Example 3

[0088] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0089] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0090] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0091] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0092] (5) Add 1.5 g of titanium isopropoxide to the solution obtained in step (4), stir continuously until it is evenly dispersed, then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0093] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0094] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0095] Example 4

[0096] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0097] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0098] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0099] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0100] (5) Add 1.5 g of tetrabutyl titanate (TBOT) to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0101] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0102] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0103] Example 5

[0104] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0105] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0106] (3) Add 0.6 g of ammonia-oxidized lignin to the solution obtained in step (2) and stir to dissolve;

[0107] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0108] (5) Add 0.3 g of nano TiO2 to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0109] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0110] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0111] Example 6

[0112] (1) Add 0.9 g of nickel chloride hexahydrate to 40 mL of ultrapure water;

[0113] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0114] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0115] (4) Add 10 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0116] (5) Add 0.3 g of nano TiO2 to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0117] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0118] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0119] Example 7

[0120] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0121] (2) Add 1.0 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0122] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0123] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0124] (5) Add 0.3 g of nano TiO2 to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0125] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0126] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0127] Example 8

[0128] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0129] (2) Add 4.0 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0130] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0131] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0132] (5) Add 0.3 g of nano TiO2 to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0133] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0134] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0135] Comparative Example 1

[0136] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0137] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0138] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0139] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3), stir and mix evenly, then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0140] (5) Wash the substance obtained in step (4) three times each with water and anhydrous ethanol by centrifugation, and dry it for later use;

[0141] (6) The powder obtained in step (5) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / C composite material.

[0142] Comparative Example 2

[0143] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0144] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0145] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0146] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3) and stir to mix evenly;

[0147] (5) Add 0.2 g of nano TiO2 to the solution obtained in step (4), stir continuously until it is evenly dispersed, and then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0148] (6) The substance obtained in step (5) is washed three times each by centrifugation with water and anhydrous ethanol, and then dried for later use;

[0149] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0150] Comparative Example 3

[0151] (1) Add 0.9 g of nickel chloride hexahydrate to 25 mL of ultrapure water;

[0152] (2) Add 2.5 g of sodium thiosulfate pentahydrate to the solution obtained in step (1) and stir until it is evenly dispersed;

[0153] (3) Add 0.6 g of sodium lignosulfonate to the solution obtained in step (2) and stir to dissolve;

[0154] (4) Add 25 mL of ethylene glycol to the solution obtained in step (3), stir and mix evenly, then transfer it to a reaction vessel and react at 150 °C for 12 h;

[0155] (5) The substance obtained in step (4) is washed three times each by centrifugation with water and anhydrous ethanol, and the resulting powder is dried for later use.

[0156] (6) Add 0.3 g of nano TiO2 to the powder obtained in step (5) and grind and mix evenly;

[0157] (7) The powder obtained in step (6) is heated to 600 °C for 4 h under a nitrogen protective atmosphere at a heating rate of 5 °C / min to obtain the sodium-ion battery negative electrode NiS / TiO2 / C composite material.

[0158] The morphology and size of the samples of this invention were tested using a field emission scanning electron microscope (SEM, Hitach SU8220). The battery assembly used was a half-cell assembly, model CR2032. The negative electrode material consisted of 70 wt% active material, 15 wt% carbon black, and 15 wt% carboxymethyl cellulose (CMC), wherein the active material was the NiS / TiO2 / C or NiS / C composite material prepared in the above examples and comparative examples. A sodium sheet was used as the counter electrode, and the electrolyte was prepared using 1 mol / L NaPF6 as the solute and dimethyl ethylene glycol (DME) as the solvent. The entire assembly process of the sodium-ion half-cell was completed in an argon-protected glove box. The performance was tested using a Neware battery performance testing system at 0.1 A·g within a voltage range of 0.01 V to 3.0 V. -1 and 10 A·g -1 The battery's constant current charge / discharge performance was tested at a current density of 0.5 A·g. -1 1 A·g -1 2 A·g -1 5 A·g -1 10 A·g -1 20 A·g -1 30 A g -1 The test was completed at a current density of 10 A·g, and the long-term cycling stability test was performed. -1 Performed at high current density.

[0159] Table 1 shows the NiS / TiO2 / C composite electrode material prepared in the examples and the sample prepared in the comparative example at 10 A·g. -1 Comparison table of cycling performance under high current density.

[0160] Table 1

[0161]

[0162] Table 1 shows that the NiS / TiO2 / C anode material prepared in Example 1 has a performance of 10 A·g -1 At the specified current density, the initial capacity was 483.88 mAh / g, and after 1000 cycles, it retained 82.41% of its capacity without exhibiting undervoltage failure. This is mainly attributed to the adsorption of sodium polysulfide by TiO2, effectively preventing its dissolution and shuttle effect, thus achieving excellent cycle stability, significantly superior to similar materials. In Example 2, the addition of 0.5 g of nano-TiO2 achieved good cycle stability, but the capacity was relatively low. The materials prepared in Examples 3 and 4, using titanium isopropoxide and tetrabutyl titanate as titanium sources respectively, also exhibited excellent cycle performance. Example 5 demonstrates that the material prepared using ammoniated lignin as a carbon source also exhibits excellent stability. In Example 6, using a smaller amount of ethylene glycol, the prepared material showed some agglomeration, resulting in a lower capacity retention after 1000 cycles compared to Example 1. In Comparative Example 1, without the addition of nano-TiO2, charge-discharge mismatch began to appear after 350 cycles, followed by undervoltage failure, indicating that simple lignin carbon cannot effectively alleviate the sodium polysulfide shuttle effect. In Comparative Example 2, the addition of 0.2 g of nano-TiO2 improved the initial capacity compared to Example 1, but the cycle stability was poor, with undervoltage failure occurring at 575 cycles. In Comparative Example 3, nano-TiO2 was added only during calcination, which may have resulted in uneven TiO2 distribution in the final sample. The small amount of TiO2 was insufficient to adsorb the generated polysulfides, and undervoltage failure still occurred.

[0163] Figure 1 shows the XRD patterns of the composite material calcined at different temperatures in Example 1 of this invention. As can be seen from the figure, at temperatures above 600°C, NiS2 is successfully reduced by the pyrolysis products of lignin along with the pyrolysis of lignin. 600°C is a dividing point for obtaining NiS material with high purity and good crystallinity.

[0164] Figure 2 is the EDX spectrum of the NiS / TiO2 / C composite material prepared in Example 1. It can be seen that the material is uniformly distributed overall, and the NiS / TiO2 composite material is uniformly coated with the outer carbon layer.

[0165] Figure 3 is the EDX spectrum of the NiS / TiO2 / C composite material prepared in Example 4. It can be seen that the material is uniformly distributed, but the particle size is relatively large, and some areas are not wrapped by the outer carbon layer.

[0166] Figure 4 shows the composite material in Example 1 at a current density of 0.1 A·g. -1 The initial charge-discharge curves show that the material has high initial capacity and initial coulombic efficiency.

[0167] Figure 5 shows the rate performance of the NiS / TiO2 / C composite material in Example 1 at different current densities. It can be seen that it still maintains a high specific capacity at high current densities. When the current returns to a low current, the capacity is not significantly reduced compared with the initial capacity, indicating that the composite material has good reversibility.

[0168] Figure 6 shows the assembly of the NiS / TiO2 / C composite material prepared in Example 1 into a coin cell at a high current density of 10 A·g. -1 The long-term cycling performance graph shows that adding an appropriate amount of nano-TiO2 can effectively alleviate the dissolution and shuttle of sodium polysulfide, achieving excellent cycling stability.

[0169] Figure 7 shows the material prepared by adding more nano-TiO2 in Example 2. It can be seen that the prepared material also has excellent stability, but the overall capacity is reduced due to the excessive addition of TiO2.

[0170] Figure 8 shows the NiS / TiO2 / C composite material prepared in Example 4 using tetrabutyl titanate as a TiO2 precursor at 10 A·g. -1 The cycling performance diagram at current density shows that the material also has good cycling stability. However, due to the low purity and large particle size of TiO2 prepared by tetrabutyl titanate, more tetrabutyl titanate needs to be added, which will reduce the capacity accordingly.

[0171] Figure 9 shows the NiS / C composites with different lignin contents prepared in Comparative Example 1 at 10 A·g -1 The cycling performance diagram at current density shows that the physical adsorption of lignin carbon alone is insufficient to alleviate the dissolution and shuttle of polysulfides, which may cause potential battery undervoltage failure.

[0172] Figure 10 shows the NiS / TiO2 / C composite material prepared in Comparative Example 2 at 10 A·g -1 The cycling performance graph at current density shows that the addition of nano-TiO2 has a certain adsorption effect on polysulfides, which improves the cycling stability to a certain extent. However, due to the small amount used, there is still a problem of undervoltage failure.

[0173] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-coated NiS / TiO2 battery anode composite material, characterized in that, The process includes the following steps: (1) dissolving nickel salt and sulfur source in water, then adding carbon source and dispersing evenly, adding small molecule diol and mixing evenly, and finally adding nano-TiO2 or TiO2 precursor and mixing evenly to obtain a mixed reaction solution; (2) hydrothermally reacting the mixed reaction solution in a reactor at 80-250 °C for 4-20 h, washing, and drying to obtain a carbon-coated NiS / TiO2 composite material precursor; (3) calcining the carbon-coated NiS / TiO2 composite material precursor under a protective gas atmosphere to obtain a carbon-coated NiS / TiO2 battery anode composite material; the carbon source is at least one of alkali lignin, lignin sulfonate, ammonia-oxidized lignin, and enzymatically hydrolyzed lignin; the ratio of nickel salt, sulfur source, carbon source, small molecule diol, and nano-TiO2 is 0.

9. g: (1.0~4.0)g: (0.1~3.0)g: (10~40)mL: (0.3~2.0)g; the ratio of nickel salt, sulfur source, carbon source, small molecule diol and TiO2 precursor is 0.9 g: (1.0~4.0)g: (0.1~3.0)g: (10~40)mL: (1.0~3.0)g; the volume ratio of small molecule diol and water is (1~4): (1~4).

2. The method for preparing a carbon-coated NiS / TiO2 battery anode composite material according to claim 1, characterized in that, The nano-TiO2 is anatase-type TiO2 with an average particle size of 30–200 nm; the TiO2 precursor is at least one of tetrabutyl titanate and titanium isopropoxide; the ammonia-oxidized lignin is prepared by the following method: 10–30 g of alkali lignin, 250–350 mL of water, 10–30 g of hydrogen peroxide solution with a concentration of 20–40 wt% and 5–15 g of ammonia solution with a concentration of 15–35 wt% are mixed evenly, and then hydrothermally reacted in a hydrothermal reactor at 100–180 °C for 8–15 h. After removing the water, ammonia-oxidized lignin is obtained; the small molecule diol is at least one of ethylene glycol, propylene glycol and butanediol; the nickel salt is at least one of nickel chloride hexahydrate and nickel nitrate hexahydrate; the sulfur source is at least one of thiourea and sodium thiosulfate pentahydrate.

3. The method for preparing a carbon-coated NiS / TiO2 battery anode composite material according to claim 1, characterized in that, The calcination temperature is 300–900 °C, and the time is 2–5 h; the protective gas is at least one of nitrogen and rare gases.

4. The method for preparing a carbon-coated NiS / TiO2 battery anode composite material according to claim 1, characterized in that, The ratio of nickel salt, sulfur source, carbon source, small molecule diol and nano TiO2 is 0.9 g: 2.5 g: 0.6 g: (10-25) mL: (0.3-0.5) g; the ratio of nickel salt, sulfur source, carbon source, small molecule diol and TiO2 precursor is 0.9 g: 2.5 g: 0.6 g: (10-25) mL: 1.5 g; the volume ratio of small molecule diol and water is (1-2.5): 2.

5.

5. The method for preparing a carbon-coated NiS / TiO2 battery anode composite material according to claim 2, characterized in that, The carbon source is at least one of sodium lignin sulfonate and ammoniated lignin.

6. The method for preparing a carbon-coated NiS / TiO2 battery anode composite material according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 100–180 °C for 8–15 h; the calcination is carried out at a temperature of 500–700 °C for 3–5 h; and the calcination heating rate is 1–10 °C / min.

7. A carbon-coated NiS / TiO2 battery anode composite material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the carbon-coated NiS / TiO2 battery anode composite material as described in claim 7 in sodium-ion batteries.

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