Nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material and its preparation method

Abstract

This invention relates to a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, its preparation method, anode sheet, and lithium battery, belonging to the field of electrode material technology. It solves the problem of poor cycle stability and discharge specific capacity caused by severe volume expansion in existing bimetallic selenide anode materials. The anode material comprises carbon nanotubes and cubic secondary particles composed of primary nickel-iron selenide particles; the primary nickel-iron selenide particles are carbon-coated particles, and the carbon is N-doped; the nickel selenide and iron selenide in the primary nickel-iron selenide particles form a heterostructure; the carbon nanotubes connect adjacent cubic secondary particles by penetrating them. This anode material exhibits good cycle stability, discharge specific capacity, and conductivity.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, its preparation method, anode sheet, and lithium battery. Background Technology

[0002] Selenides, as compounds of chalcogens, have attracted widespread attention due to their high electrical conductivity. Iron, a transition metal, is abundant in the Earth's crust and possesses low cost and environmental friendliness, making it widely used in daily production and life. Therefore, combining iron and selenides to prepare iron selenide as a negative electrode material for lithium-ion batteries has significant advantages, such as high specific capacity, simple preparation process, energy saving and environmental protection, and excellent cycle stability. However, the low electronic conductivity of monometallic selenide negative electrode materials limits their further development. Studies have shown that bimetallic selenides have higher conductivity and more electrochemical reaction active sites than monometallic selenides. Different metals, due to their different valence bands, can form an internal electric field, thereby enabling charge redistribution during charge and discharge, effectively improving the reaction kinetics of the negative electrode material. However, bimetallic selenide negative electrode materials also have problems; during lithium-ion cycling, severe volume expansion leads to poor cycle stability and low discharge specific capacity. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to provide a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material and its preparation method, anode sheet and lithium battery, in order to solve the problem of poor cycle stability and discharge specific capacity caused by severe volume expansion of existing bimetallic selenide anode materials.

[0004] On one hand, embodiments of the present invention provide a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, the anode material comprising carbon nanotubes and cubic secondary particles composed of primary nickel-iron selenide particles;

[0005] The nickel-iron selenide primary particles are carbon-coated particles, and the carbon is N-doped; the nickel selenide and iron selenide in the nickel-iron selenide primary particles form a heterostructure.

[0006] The carbon nanotubes connect adjacent cubic secondary particles by penetrating them.

[0007] Preferably, the side length of the cubic secondary particles is 350-550 nm.

[0008] Secondly, the present invention also provides a method for preparing a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, which includes the following steps:

[0009] (1) Preparation of nickel-iron Prussian blue precursor

[0010] Nickel source, carbon nanotubes, and chelating agent are dissolved in a solvent to obtain solution A; iron source and chelating agent are dissolved in a solvent to obtain solution B; solution A and solution B are mixed to obtain nickel-iron Prussian blue precursor;

[0011] (2) Preparation of nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material

[0012] The nickel-iron Prussian blue precursor obtained in step (1) and the selenium source were placed at both ends of a ceramic boat. The ceramic boat was then moved into a tube furnace filled with argon gas. The selenium powder was placed in an upward gas flow and calcined to obtain a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material.

[0013] Preferably, in step (1), the nickel source is at least one of nickel chloride, nickel sulfate, and nickel nitrate.

[0014] Preferably, in step (1), the iron source is at least one of potassium ferricyanide and sodium ferricyanide.

[0015] Preferably, in step (1), the chelating agents in solution A and solution B are at least one of citric acid, oxalic acid, and ascorbic acid.

[0016] Preferably, in step (1) and step (2), the mass of the selenium source is 5-8 times the mass of the nickel-iron Prussian blue precursor.

[0017] Preferably, in step (2), the calcination process includes: first raising the temperature to 350-400℃ at a heating rate of 2-10℃ / min and calcining for 2-4 hours, and then raising the temperature to 450-600℃ at a heating rate of 2-10℃ / min and calcining for 1-3 hours.

[0018] Thirdly, the present invention also provides a negative electrode sheet, wherein the negative electrode sheet comprises the above-mentioned nickel-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material or the nickel-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material obtained by the above preparation method.

[0019] Fourthly, the present invention also provides a lithium battery, the lithium battery comprising the above-mentioned negative electrode sheet.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material of the present invention has high discharge specific capacity for both nickel selenide (NiSe) and iron selenide (FeSe2), and the combination of the two can improve the discharge specific capacity of the electrode material.

[0022] 2. By connecting cubic secondary particles through carbon nanotubes, gaps are created between the cubic secondary particles, preventing them from agglomerating. This provides a buffer space when nickel-iron selenide undergoes volume changes during charging and discharging, ensuring the structural integrity of the electrode material and thus improving the battery's cycle performance and rate performance.

[0023] 3. The gaps between the cubic secondary particles facilitate the full wetting of nickel iron selenide by the electrolyte. Ions shuttle back and forth between the positive and negative electrodes of the battery, requiring the electrolyte as a medium to fully wet the electrode materials, ensuring that the battery has a high discharge specific capacity and good rate performance.

[0024] 4. The primary nickel-iron selenide particles have a carbon coating layer, and the nitrogen-doped carbon can create defects in the carbon, thereby increasing the graphitization degree and conductivity of the carbon, thus improving electronic conductivity. Furthermore, the carbon nanotubes shuttling within the cubic secondary particles can further enhance electronic conductivity. The heterostructure formed by the composite of nickel selenide and iron selenide generates defects, which in turn promote electron conduction, further enhancing electronic conductivity. The negative electrode material of this invention achieves a conductivity of 3.21 × 10⁻⁶. - 11 cm 2 / s.

[0025] 5. The negative electrode material of the present invention is a three-dimensional network structure composed of cubic secondary particles and carbon nanotubes, which can ensure sufficient space for volume change of electrode material, avoid stress concentration, and prevent material structure damage caused by large volume change of electrode material; in addition, the three-dimensional network structure can ensure that the material is fully wetted by electrolyte, shorten the ion transport path, reduce ion shuttle resistance, enable ion free transport, improve material reaction kinetics, and thus improve the rate performance of battery.

[0026] 6. The preparation method of the present invention uses a co-precipitation method to synthesize a uniform cubic nickel-iron Prussian blue precursor, and then synthesizes a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material by calcination. The resulting anode material has a uniform cubic structure of nickel-iron selenide, a rich carbon coating layer, a heterogeneous structure between nickel-iron selenide, and carbon nanotubes, which gives the anode material good cycle stability, discharge specific capacity and conductivity.

[0027] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0028] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0029] Figure 1 This is a schematic diagram of the structure of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material of the present invention;

[0030] Figure 2 SEM image of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in Example 2;

[0031] Figure 3 The image shows the XRD pattern of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in Example 2.

[0032] Figure 4 The constant current charge-discharge curve of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in Example 2 is shown.

[0033] Figure 5 The rate performance diagram is shown for the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in Example 2.

[0034] Figure 6 The graph shows the cycling performance of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in Example 2.

[0035] Figure 7 The conductivity test diagram is shown for the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in Example 2.

[0036] Figure 8 SEM image of the negative electrode material in Comparative Example 1;

[0037] Figure 9 The constant current charge-discharge curve of the negative electrode material in Comparative Example 1 is shown.

[0038] Figure 10 SEM image of the negative electrode material in Comparative Example 2;

[0039] Figure 11 The constant current charge-discharge curves are for the negative electrode material of Comparative Example 2.

[0040] Figure label:

[0041] 1- Cubic secondary particles; 2- Carbon nanotubes. Detailed Implementation

[0042] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0043] On the one hand, this invention provides a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, such as... Figure 1 As shown, the negative electrode material includes carbon nanotubes 2 and cubic secondary particles 2 composed of primary nickel-iron selenide particles;

[0044] The nickel-iron selenide primary particles are carbon-coated particles, and the carbon is N-doped; the nickel selenide and iron selenide in the nickel-iron selenide primary particles form a heterostructure.

[0045] The carbon nanotubes 2 connect adjacent cubic secondary particles 2 by penetrating them.

[0046] Compared with existing technologies, the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material of the present invention utilizes both nickel selenide (NiSe) and iron selenide (FeSe2) to achieve high discharge specific capacity. The combination of these two components enhances the discharge specific capacity of the electrode material. Furthermore, the interconnection of cubic secondary particles via carbon nanotubes creates gaps between these particles, preventing agglomeration and providing a buffer space for volume changes in nickel-iron selenide during charging and discharging. This ensures the structural integrity of the electrode material, thereby improving the battery's cycle performance and rate performance. The gaps between the cubic secondary particles facilitate thorough wetting of the nickel-iron selenide by the electrolyte. Ions shuttle between the positive and negative electrodes, requiring the electrolyte as a medium. Thorough wetting of the electrode material ensures the battery exhibits high discharge specific capacity and good rate performance. The primary nickel-iron selenide particles have a carbon coating layer, and the nitrogen-doped carbon can create defects in the carbon, thereby increasing the graphitization degree and conductivity of the carbon, thus improving electronic conductivity. Furthermore, the carbon nanotubes shuttling within the cubic secondary particles can enhance electronic conductivity. The heterostructure formed by the composite of nickel selenide and iron selenide generates defects, further promoting electron conduction. The negative electrode material of this invention achieves a conductivity of 3.21 × 10⁻⁶. -11 cm 2 / s.

[0047] It should be noted that nickel iron selenide refers to NiSe and FeSe2, and the nickel iron selenide / carbon-nitrogen composite carbon nanotube anode material of the present invention can be represented as NiSe / FeSe2@NC-CNT.

[0048] Furthermore, the negative electrode material is a three-dimensional network structure composed of cubic secondary particles and carbon nanotubes.

[0049] The three-dimensional mesh structure can ensure sufficient space for changes in the volume of the electrode material, avoid stress concentration, and prevent material structure damage caused by large volume changes in the electrode material. Furthermore, the three-dimensional mesh structure can ensure that the material is fully wetted by the electrolyte, shorten the ion transport path, reduce ion shuttle resistance, enable free ion transport, improve the material reaction kinetics, and thus improve the rate performance of the battery.

[0050] Furthermore, the three-dimensional mesh structure is a three-dimensional multi-level layered structure, which is composed of multiple three-dimensional mesh structure units, and each three-dimensional mesh structure unit has micropores, mesopores, mesopores, or macropores. The three-dimensional multi-level layered structure is beneficial for mitigating the volume change of the negative electrode material during charging and discharging.

[0051] Furthermore, the side length of the cubic secondary particles is 350-550 nm.

[0052] Secondly, the present invention also provides a method for preparing a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, which includes the following steps:

[0053] (1) Preparation of nickel-iron Prussian blue precursor

[0054] Nickel source, carbon nanotubes, and chelating agent are dissolved in a solvent to obtain solution A; iron source and chelating agent are dissolved in a solvent to obtain solution B; solution A and solution B are mixed to obtain nickel-iron Prussian blue precursor;

[0055] (2) Preparation of nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material

[0056] The nickel-iron Prussian blue precursor obtained in step (1) and the selenium source were placed at both ends of a ceramic boat. The ceramic boat was then moved into a tube furnace filled with argon gas. The selenium powder was placed in an upflow gas stream and calcined to obtain the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material (NiSe / FeSe2@NC-CNT).

[0057] For example, in step (1), the nickel source is at least one of nickel chloride, nickel sulfate, and nickel nitrate.

[0058] For example, in step (1), the iron source is at least one of potassium ferricyanide and sodium ferricyanide.

[0059] For example, in step (1), the chelating agents in solution A and solution B are at least one of citric acid, oxalic acid, and ascorbic acid. Preferably, the chelating agents in solution A and solution B are at least two of citric acid, oxalic acid, and ascorbic acid.

[0060] For example, in step (1), the solvents in solution A and solution B are both mixed solutions of ethanol, deionized water and ethylene glycol.

[0061] For example, in solution A, there are 4-8 mmol of nickel source, 3-7 g of chelating agent, 20-40 mg of carbon nanotubes, 20-50 mL of ethylene glycol, 30-70 mL of ethanol, and 60-110 mL of deionized water, with a total volume of 150 mL for ethylene glycol, ethanol, and deionized water.

[0062] For example, in step (1), after dissolving the nickel source, carbon nanotubes and chelating agent in a solvent, the mixture is stirred. The stirring speed is 180-240 r / min and the stirring time is 20-60 min.

[0063] For example, in solution B, there are 3-6 mmol of iron source, 3-7 g of chelating agent, 20-50 mL of ethylene glycol, 30-70 mL of ethanol, and 60-110 mL of deionized water, with a total volume of 150 mL for ethylene glycol, ethanol, and deionized water.

[0064] For example, in step (1), after dissolving the iron source and chelating agent in the solvent, the mixture is stirred. The stirring speed is 180-240 r / min and the stirring time is 20-60 min.

[0065] For example, in step (1), solution A and solution B are mixed and precipitated. The precipitate is then centrifuged, washed, and dried to obtain the target product, nickel-iron Prussian blue precursor. The centrifugation process uses a centrifuge with a speed of 7000-8000 r / min. The product is washed 3-4 times with deionized water and 2-3 times with ethanol, and then dried in a vacuum drying oven at 60-70℃ for 10-12 h to obtain the target product, nickel-iron Prussian blue precursor.

[0066] For example, in step (2), the selenium source is selenium powder. The particle size of the selenium powder is preferably 200 mesh or more.

[0067] For example, the mass of the selenium source is 5-8 times the mass of the nickel-iron Prussian blue precursor.

[0068] In order to obtain a material with better crystallinity and purer phase, the calcination process in step (2) includes: first raising the temperature to 350-400℃ at a heating rate of 2-10℃ / min (more preferably 3-5℃ / min) and calcining for 2-4h, and then raising the temperature to 450-600℃ at a heating rate of 2-10℃ / min (more preferably 5-8℃ / min) and calcining for 1-3h.

[0069] Thirdly, the present invention also provides a negative electrode sheet, wherein the negative electrode sheet comprises the above-mentioned nickel-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material or the nickel-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material obtained by the above preparation method.

[0070] For example, the negative electrode sheet further includes a conductive agent and a binder, wherein the conductive agent is acetylene black and the binder is polyvinylidene fluoride.

[0071] For example, in the negative electrode sheet, the active material NiSe / FeSe2@NC-CNT is 320 mg, the conductive agent is 40 mg, and the binder is 40 mg.

[0072] For example, the preparation method of the negative electrode sheet includes: mixing the active material NiSe / FeSe2@NC-CNT, the conductive agent, and the binder evenly, using N-methylpyrrolidone as the solvent, stirring the slurry in a wide-mouth bottle until a metallic luster appears, uniformly coating the prepared electrode slurry onto a 10cm×10cm copper foil, vacuum drying at 60℃ for 12 hours, and then pressing it into an electrode sheet with a diameter of 8mm using a press.

[0073] Fourthly, the present invention also provides a lithium battery, the lithium battery comprising the above-mentioned negative electrode sheet.

[0074] For example, the lithium battery further includes a counter electrode, a reference electrode, and an electrolyte. The counter electrode and the reference electrode are both lithium metal sheets, and the electrolyte is a LiPF6 solution. The electrolyte solvent is a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1.

[0075] For example, the method for preparing the lithium battery includes: using NiSe / FeSe2@NC-CNT electrode material as the negative electrode, lithium metal sheet as the counter electrode and reference electrode, and assembling a coin cell in a glove box, wherein the water and oxygen content of the glove box is less than 0.01 ppm.

[0076] The lithium battery of the present invention has good cycle performance, rate performance, discharge specific capacity and conductivity.

[0077] The following specific embodiments further illustrate the present invention's nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, its preparation method, anode sheet, and lithium battery.

[0078] Example 1

[0079] A nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, the anode material comprising carbon nanotubes and cubic secondary particles (side length 400 nm) composed of primary nickel-iron selenide particles.

[0080] The primary nickel-iron selenide particles are N-doped carbon-coated particles, and the nickel selenide and iron selenide in the primary nickel-iron selenide particles form a heterostructure.

[0081] The carbon nanotubes connect adjacent cubic secondary particles by penetrating them.

[0082] The negative electrode material is a three-dimensional network structure composed of the cubic secondary particles and the carbon nanotubes.

[0083] The three-dimensional mesh structure is a three-dimensional multi-level layered structure, which is composed of multiple three-dimensional mesh structure units. Each three-dimensional mesh structure unit has micropores, mesopores, mesopores or macropores.

[0084] Example 2

[0085] This embodiment provides a method for preparing the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material of Example 1, an anode sheet, and a lithium battery.

[0086] 1. Preparation of nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material

[0087] Weigh out 2 mmol of NiSO4·5H2O, 2 mmol of NiCl2·2H2O, and 2 mmol of Ni(NO3)2·3H2O, 25 mg of CNT, 2.4 g of ascorbic acid, 1 g of citric acid, and 2 g of oxalic acid using a balance. Measure out 30 mL of ethanol, 75 mL of deionized water, and 45 mL of ethylene glycol using a graduated cylinder and mix them. Simultaneously add the weighed nickel source, CNT, and chelating agent to the above solvents and stir at 200 rpm for 20 min to form solution A. Weigh out 3 mmol of K3[Fe(CN)6] and 1 mmol of Na4Fe(CN)6, 2.4 g of ascorbic acid, 1 g of citric acid, and 2 g of oxalic acid using a balance. Measure out 30 mL of ethanol, 75 mL of deionized water, and 45 mL of ethylene glycol using a graduated cylinder and mix them. Simultaneously, the weighed iron source and chelating agent were added to the above solvent, and stirred at 200 r / min for 20 min to form solution B. Solution A was poured into solution B, stirred for 22 h, and then washed three times with deionized water and twice with ethanol using a centrifuge at 7500 r / min. Subsequently, it was dried in a vacuum drying oven at 60 °C for 12 h to obtain the nickel-iron Prussian blue precursor.

[0088] 200 mg of the obtained nickel-iron Prussian blue precursor product and 1.4 g of selenium powder were placed at opposite ends of a ceramic boat. The ceramic boat was then transferred to a tube furnace filled with argon gas, ensuring that the selenium powder was in an upflow. The heating rate was set to 3 °C / min in an argon gas flow of 60 mL / min. After high-temperature calcination at 350 °C for 3 h, the heating rate was set to 5 °C / min. The temperature was then increased to 550 °C and held for 1 h. The furnace was then allowed to cool slowly to room temperature to obtain the target product NiSe / FeSe2@NC-CNT.

[0089] 2. Preparation of negative electrode sheet

[0090] 320 mg of the active material NiSe / FeSe2@NC-CNT, 40 mg of the conductive agent acetylene black, and 40 mg of PVDF were mixed evenly in a wide-mouth bottle with N-methylpyrrolidone (NMP) as the solvent. The mixture was stirred until a metallic luster appeared. The prepared electrode paste was then evenly coated onto a 10 cm × 15 cm copper foil and vacuum dried at 60 °C for 12 h. The dried foil was then pressed into an electrode sheet with a diameter of 8 mm using a press.

[0091] 3. Preparation of lithium batteries

[0092] The prepared negative electrode sheet was used as the negative electrode, and the lithium metal sheet was used as the counter electrode and reference electrode. The electrolyte was 1.0 mol / L LiPF6, and the solvent was a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1. The coin cell was assembled in a glove box, wherein the water and oxygen content of the glove box was less than 0.01 ppm.

[0093] Figure 2 The image shows a SEM image of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in this embodiment. Figure 2 The morphology of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material of the present invention can be seen, wherein the carbon nanotubes shuttle through the copper-iron selenide / carbon-nitrogen nanoblocks, connecting them into a three-dimensional network structure.

[0094] Figure 3 The image shows the XRD pattern of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in this embodiment. Figure 3 The sharp peak shape indicates that a well-crystallized electrode material has been obtained.

[0095] The electrochemical performance of the lithium battery was tested using a Blue Electric charge-discharge tester between 0.1 and 3V. Figure 4 The constant current charge-discharge curve of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in this embodiment (charge-discharge performance of the electrode material in the first three weeks) shows that it has a very high discharge specific capacity in the first week, reaching 1300 mAh / g.

[0096] Figure 5The diagram shows the rate performance of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in this embodiment. The current density varies from 50 to 10000 mA / g. When the current density returns to 50 mA / g, it can still release a discharge specific capacity of about 200 mA / g.

[0097] Figure 6 The graph shows the cycling performance of the nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in this embodiment. It can be seen that the material maintains good cycling stability at a current density of 200 mA / g.

[0098] The conductivity of the copper-iron selenide / carbon-nitrogen composite carbon nanotube anode material prepared in this embodiment can be obtained by impedance calculation, such as... Figure 7 As shown, the conductivity is 3.21 × 10⁻⁶. -11 cm 2 / s.

[0099] Example 3

[0100] This embodiment provides a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, its preparation method, anode sheet, and lithium battery.

[0101] 1. Preparation of nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material

[0102] Weigh out 4 mmol of NiSO4·5H2O, 3.5 mmol of Ni(NO3)2·3H2O, 30 mg of CNT, 1.8 g of ascorbic acid, 1.8 g of citric acid, and 1.8 g of oxalic acid using a balance. Measure out 50 mL of ethanol, 60 mL of deionized water, and 40 mL of ethylene glycol using a graduated cylinder and mix them. Simultaneously, add the weighed nickel source, CNT, and chelating agent to the above solvent and stir at 220 rpm for 25 min to form solution A. Weigh out 4 mmol of K3[Fe(CN)6] and 1 mmol of Na4Fe(CN)6, 1.8 g of ascorbic acid, 1.8 g of citric acid, and 1.8 g of oxalic acid using a balance. Measure out 50 mL of ethanol, 60 mL of deionized water, and 40 mL of ethylene glycol using a graduated cylinder and mix them. Simultaneously, the weighed iron source and chelating agent were added to the above solvent, and the mixture was stirred at 220 r / min for 25 min to form solution B. Solution A was poured into solution B, and the mixture was stirred for 24 h. The solution was then centrifuged at 7500 r / min, washed three times with deionized water, and twice with ethanol. Finally, it was dried in a vacuum drying oven at 60 °C for 12 h to obtain the nickel-iron Prussian blue precursor.

[0103] 200 mg of the obtained nickel-iron Prussian blue precursor and 1.5 g of selenium powder were placed at opposite ends of a ceramic boat. The ceramic boat was then transferred to a tube furnace filled with argon gas, ensuring that the selenium powder was in an upflow. The heating rate was set to 3 °C / min in an argon gas flow of 70 mL / min. After high-temperature calcination at 350 °C for 2 h, the heating rate was set to 5 °C / min. The temperature was then increased to 500 °C and held for 2 h. The furnace was then allowed to cool slowly to room temperature to obtain the target product NiSe / FeSe2@NC-CNT.

[0104] 2. Preparation of negative electrode sheet

[0105] 320 mg of the active material NiSe / FeSe2@NC-CNT, 40 mg of the conductive agent acetylene black, and 40 mg of PVDF were mixed evenly in a wide-mouth bottle with N-methylpyrrolidone (NMP) as the solvent. The mixture was stirred until a metallic luster appeared. The prepared electrode paste was then evenly coated onto a 10 cm × 15 cm nickel foil and vacuum dried at 60 °C for 12 h. The resulting material was then pressed into an electrode sheet with a diameter of 8 mm using a press.

[0106] 3. Preparation of lithium batteries

[0107] The prepared negative electrode sheet was used as the negative electrode, and the lithium metal sheet was used as the counter electrode and reference electrode. The electrolyte was 1.0 mol / L LiPF6, and the solvent was a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1. The coin cell was assembled in a glove box, where the water and oxygen content of the glove box was less than 0.01 ppm.

[0108] Example 4

[0109] This embodiment provides a nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material, its preparation method, anode sheet, and lithium battery.

[0110] 1. Preparation of nickel-iron selenide / carbon-nitrogen composite carbon nanotube anode material

[0111] Weigh out 3 mmol of NiSO4·5H2O, 1.5 mmol of NiCl2·2H2O, 40 mg of CNT, 2.4 g of ascorbic acid, and 3 g of citric acid using a balance. Measure out 50 mL of ethanol, 70 mL of deionized water, and 30 mL of ethylene glycol using a graduated cylinder and mix them. Simultaneously add the weighed nickel source, CNT, and chelating agent to the above solvent and stir at 200 rpm for 10 min to form solution A. Weigh out 4 mmol of K3[Fe(CN)6] and 1 mmol of Na4Fe(CN)6, 2.4 g of ascorbic acid, and 3 g of citric acid using a balance. Measure out 50 mL of ethanol, 70 mL of deionized water, and 30 mL of ethylene glycol using a graduated cylinder and mix them. Simultaneously add the weighed iron source and chelating agent to the above solvent and stir at 200 rpm for 10 min to form solution B. Solution A was poured into solution B and stirred for 20 hours. The mixture was then washed three times with deionized water and twice with ethanol at a centrifuge speed of 7500 r / min. Finally, it was dried in a vacuum drying oven at 60℃ for 12 hours to obtain the nickel-iron Prussian blue precursor.

[0112] 200 mg of the obtained nickel-iron Prussian blue precursor and 1.2 g of selenium powder were placed at opposite ends of a ceramic boat. The ceramic boat was then transferred to a tube furnace filled with argon gas, ensuring that the selenium powder was in an upflow. The heating rate was set to 3 °C / min in an argon gas flow of 50 mL / min. After high-temperature calcination at 360 °C for 2 h, the heating rate was set to 5 °C / min. The temperature was then increased to 520 °C and held for 2 h. The furnace was then slowly cooled to room temperature to obtain the target product NiSe / FeSe2@NC-CNT.

[0113] 2. Preparation of negative electrode sheet

[0114] 320 mg of the active material NiSe / FeSe2@NC-CNT, 40 mg of the conductive agent acetylene black, and 40 mg of PVDF were mixed evenly in a wide-mouth bottle with N-methylpyrrolidone (NMP) as the solvent. The mixture was stirred until a metallic luster appeared. The prepared electrode paste was then evenly coated onto a 10 cm × 15 cm copper foil and vacuum dried at 60 °C for 12 h. The coated foil was then pressed into an electrode sheet with a diameter of 8 mm using a press.

[0115] 3. Preparation of lithium batteries

[0116] The prepared negative electrode sheet was used as the negative electrode, and the lithium metal sheet was used as the counter electrode and reference electrode. The electrolyte was 1.0 mol / L LiPF6, and the solvent was a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1. The coin cell was assembled in a glove box, where the water and oxygen content of the glove box was less than 0.01 ppm.

[0117] Comparative Example 1

[0118] This comparative example provides a negative electrode material similar to that of Example 1, except that it does not contain carbon nanotubes. Instead, it consists of cubical secondary particles composed of primary nickel-iron selenide particles aggregated together.

[0119] like Figure 8 As shown, the negative electrode material particles have varying morphologies and are relatively large, exhibiting severe agglomeration. This structure results in poor kinetic properties, leading to a low initial discharge specific capacity of approximately 360 mAh / g. Figure 9 As shown in the figure. Meanwhile, the material exhibits poor cycle stability and rate performance.

[0120] Comparative Example 2

[0121] This comparative example provides a negative electrode material similar to that of Example 1, except that the primary particles contain only iron selenide and no nickel selenide.

[0122] like Figure 10 As shown, the negative electrode material particles are relatively large and vary in size, and exhibit varying degrees of agglomeration. This structure is detrimental to lithium-ion transport and the wetting of the electrode material by the electrolyte. Electrochemical performance testing revealed a low first-cycle discharge specific capacity of approximately 250 mAh / g. Figure 11 As shown in the figure. Meanwhile, the material exhibits poor cycle stability and rate performance.

[0123] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A nickel iron selenide / carbon nitride composite carbon nanotube negative electrode material, characterized in that, The negative electrode material comprises carbon nanotubes and cubic secondary particles composed of nickel selenide nickel-iron primary particles; The nickel selenide iron primary particles are carbon-coated particles, and the carbon is N-doped; the nickel selenide and the iron selenide in the nickel selenide iron primary particles are combined to form a heterostructure; The carbon nanotubes connect adjacent cubic secondary particles by penetrating through the cubic secondary particles.

2. The negative electrode material according to claim 1, characterized in that, The edge length of the cubic secondary particles is 350-550 nm.

3. A preparation method of a nickel-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material, characterized in that, A method for preparing the nickel selenide iron / carbon-nitrogen composite carbon nanotube negative electrode material of claim 1 or 2 comprises the following steps: (1) preparing a nickel-iron Prussian blue precursor A nickel source, carbon nanotubes, and a chelating agent are dissolved in a solvent to obtain solution A; an iron source and a chelating agent are dissolved in a solvent to obtain solution B; solution A and solution B are mixed to obtain a nickel-iron Prussian blue precursor; (2) preparing a nickel selenide iron / carbon-nitrogen composite carbon nanotube negative electrode material The nickel-iron Prussian blue precursor obtained in step (1) and a selenium source are placed at both ends of a porcelain boat, the porcelain boat is moved to a tube furnace with argon flowing through, ensuring that the selenium powder is in the upper gas flow, and calcination is performed to obtain a nickel selenide iron / carbon-nitrogen composite carbon nanotube negative electrode material.

4. The production method according to claim 3, characterized by, In step (1), the nickel source is at least one of nickel chloride, nickel sulfate, and nickel nitrate.

5. The preparation method according to claim 3, characterized in that, In step (1), the iron source is at least one of potassium ferricyanide and sodium ferricyanide.

6. The preparation method according to claim 3, characterized in that, In step (1), the chelating agent in solution A and solution B is at least one of citric acid, oxalic acid, and ascorbic acid.

7. The preparation method according to claim 3, characterized in that, In step (2), the mass of the selenium source is 5-8 times the mass of the nickel-iron Prussian blue precursor.

8. The preparation method according to claim 3, characterized in that, In step (2), the calcination process comprises: first increasing the temperature to 350-400°C at a temperature increase rate of 2-10°C / min, calcining for 2-4h, and then increasing the temperature to 450-600°C at a temperature increase rate of 2-10°C / min, calcining for 1-3h.

9. A negative electrode sheet characterized by comprising: The negative electrode material comprises carbon nanotubes and cubic secondary particles composed of nickel selenide nickel-iron primary particles; 10. A lithium battery, characterized by, The lithium battery comprises the negative electrode tab of claim 9. The lithium battery comprises the negative electrode tab of claim 9.

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