Copper-Iron Selenide / C-N Composite Carbon Nanotube Anode Material and Preparation Method Thereof

Abstract

The present invention relates to a copper-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material, its preparation method, negative electrode plate, and lithium battery. These materials belong to the technical field of electrode materials and address the problem of poor cycle and rate performance in prior art bimetallic selenide negative electrode materials due to severe volume expansion. The negative electrode material comprises carbon nanotubes and cubic secondary particles composed of copper-iron selenide primary particles; the copper-iron selenide primary particles are carbon-coated particles doped with nitrogen; the copper selenide and iron selenide in the copper-iron selenide primary particles form a heterogeneous structure; and the carbon nanotubes penetrate the cubic secondary particles to connect adjacent cubic secondary particles. This negative electrode material exhibits excellent cycle performance, rate performance, and electrical conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material and a preparation method thereof, a negative electrode plate and a lithium battery. Background Art

[0002] Currently, graphite remains the most widely used anode material for lithium-ion batteries, both in experimental research and commercial applications. However, its low theoretical specific capacity (372 mAh / g) can affect lithium-ion battery performance. Although doping graphite with silicon can significantly increase its specific capacity, the large volume changes during charge and discharge severely impact the stability of the material's overall structure. Excessive volume changes can even lead to detachment of the active material from the current collector, causing the electrode to lose functionality. Transition metal selenides offer significant advantages as anode materials for lithium-ion batteries, such as high specific capacity, ease of preparation, energy conservation and environmental protection, and excellent cycling stability. However, the low electronic conductivity of single-metal selenide anode materials has limited their further development. Research has shown that bimetallic selenides offer higher conductivity and more electrochemically active sites than single-metal selenides, effectively improving the reaction kinetics of the anode materials. However, bimetallic selenide anode materials also present challenges. During lithium-ion intercalation and deintercalation, they experience significant volume expansion, resulting in poor cycling and rate performance. Summary of the Invention

[0003] In view of the above analysis, the embodiments of the present invention aim to provide a copper-iron-selenide / carbon-nitrogen composite carbon nanotube negative electrode material and its preparation method, negative electrode plate and lithium battery, so as to solve the problem that the existing bimetallic selenide negative electrode material has poor cycle performance and rate performance due to severe volume expansion.

[0004] On the one hand, an embodiment of the present invention provides a copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material, wherein the negative electrode material comprises carbon nanotubes and cubic secondary particles composed of copper iron selenide primary particles;

[0005] The copper-iron selenide primary particles are carbon-coated particles, and the carbon is N-doped; the copper selenide and iron selenide in the copper-iron selenide primary particles are composited to form a heterogeneous structure;

[0006] The carbon nanotubes penetrate the cubic secondary particles to connect adjacent cubic secondary particles.

[0007] Preferably, the negative electrode material is a three-dimensional network structure composed of the cubic secondary particles and the carbon nanotubes.

[0008] In a second aspect, the present invention further provides a method for preparing a copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material, which is used to prepare the above-mentioned copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material, comprising the following steps:

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

[0010] Dissolving a copper source, carbon nanotubes, and a chelating agent in a solvent to obtain a solution A; dissolving an iron source and a chelating agent in a solvent to obtain a solution B; mixing solution A with solution B to obtain a copper-iron Prussian blue precursor;

[0011] (2) Preparation of copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material

[0012] The copper-iron Prussian blue precursor obtained in step (1) is mixed with a selenium source and calcined to obtain a copper-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material.

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

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

[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), the solvents in solution A and solution B are both mixed solutions of ethanol, deionized water and ethylene glycol.

[0017] Preferably, in step (2), the calcination process comprises: firstly raising the temperature to 300-350°C at a heating rate of 2-10°C / min, calcining for 1-3h, and then raising the temperature to 450-650°C at a heating rate of 2-10°C / min, and calcining for 1-3h.

[0018] In a third aspect, the present invention further provides a negative electrode plate, which comprises the above-mentioned copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material or the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material obtained by the above-mentioned preparation method.

[0019] In a fourth aspect, the present invention further provides a lithium battery comprising the above-mentioned negative electrode plate.

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

[0021] 1. The copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material of the present invention has good cycle stability and iron selenide (FeSe2) has a high discharge specific capacity. The combination of the two can stabilize the performance of the electrode material.

[0022] 2. The cubic secondary particles are connected through carbon nanotubes so that there are gaps between the cubic secondary particles to prevent the cubic secondary particles from agglomerating. This provides buffer space when the volume of copper iron selenide changes during charging and discharging, thereby ensuring the structural integrity of the electrode material and improving the cycle performance and rate performance of the battery.

[0023] 3. 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 the volume change of the electrode material, avoid stress concentration, and prevent the material structure from being destroyed due to large volume changes of the electrode material; and the three-dimensional network structure can ensure that the material is fully infiltrated by the electrolyte, shorten the ion transmission path, reduce the ion shuttle resistance, allow the ions to be transmitted freely, improve the material reaction kinetics conditions, and thereby improve the battery's rate performance.

[0024] 4. The gaps between the cubic secondary particles are conducive to the full infiltration of the electrolyte into the copper iron selenide, ensuring that the battery has a high discharge capacity and good rate performance.

[0025] 5. Copper iron selenide has a carbon coating layer, and N doping of carbon can create some defects in the carbon, which can improve the degree of graphitization and carbon conductivity, thereby improving electronic conductivity. In addition, carbon nanotubes shuttle through the cubic secondary particles, which can also improve electronic conductivity. The heterogeneous structure formed by the composite of copper selenide and iron selenide will produce defects, thereby promoting the conduction of electrons, further promoting electronic conduction. The conductivity of the negative electrode material of the present invention can reach 1.76×10 -11 cm 2 / s.

[0026] 6. The preparation method of the present invention adopts a co-precipitation method to synthesize a uniform cubic copper-iron Prussian blue precursor, and then synthesizes a copper-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material by calcination. The obtained negative electrode material has a uniform copper-iron selenide cubic structure, a rich carbon coating layer, and a heterogeneous structure between copper-iron selenide, and is combined with carbon nanotubes, so that the negative electrode material has good cycle performance, rate performance and conductivity.

[0027] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

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

[0030] Figure 2 This is an SEM image of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in Example 2;

[0031] Figure 3 This is the XRD pattern of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in Example 2;

[0032] Figure 4 This is a constant current charge-discharge curve of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in Example 2;

[0033] Figure 5 This is a rate performance diagram of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in Example 2;

[0034] Figure 6 This is a cycle performance diagram of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in Example 2;

[0035] Figure 7 This is a conductivity test graph of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in Example 2;

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

[0037] Figure 9 This is a constant current charge and discharge curve diagram of the negative electrode material of Comparative Example 1;

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

[0039] Figure 11 This is a constant current charge and discharge curve diagram of the negative electrode material of Comparative Example 2.

[0040] Reference numerals:

[0041] 1-cubic secondary particles; 2-carbon nanotubes. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

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

[0044] The copper-iron selenide primary particles are carbon-coated particles, and the carbon is N-doped; the copper selenide and iron selenide in the copper-iron selenide primary particles are composited to form a heterogeneous structure;

[0045] The carbon nanotubes 2 penetrate the cubic secondary particles 2 to connect adjacent cubic secondary particles 2 .

[0046] Compared with the prior art, the copper-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material of the present invention has good cycle stability for copper selenide and high discharge specific capacity for iron selenide. The combination of the two can stabilize the performance of the electrode material. In addition, the cubic secondary particles are connected through the carbon nanotubes, so that there are gaps between the cubic secondary particles, which prevents the cubic secondary particles from agglomerating. This provides a buffer space when the copper-iron selenide undergoes volume changes during charging and discharging, thereby ensuring the structural integrity of the electrode material and improving the cycle performance and rate performance of the battery. The gaps between the cubic secondary particles are conducive to the electrolyte fully infiltrating the copper-iron selenide, ensuring that the battery has a high discharge specific capacity and good rate performance. The copper-iron selenide has a C coating layer and N doped carbon, which can create some defects in the carbon, thereby increasing the degree of graphitization of the carbon and the conductivity of the carbon, thereby improving the electronic conductivity. In addition, the carbon nanotubes shuttle through the cubic secondary particles, which can improve the electronic conductivity. The heterogeneous structure formed by the composite between copper selenide and iron selenide will produce defects, thereby promoting the conduction of electrons, further promoting electronic conduction. The conductivity of the negative electrode material of the present invention can reach 1.76×10 -11 cm 2 / s.

[0047] It should be noted that copper iron selenide refers to CuSe and FeSe2, and the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material of the present invention can be expressed as CuSe / FeSe2@NC-CNT.

[0048] Furthermore, the negative electrode material is a three-dimensional network structure composed of the cubic secondary particles and the carbon nanotubes, which can ensure sufficient space for the volume change of the electrode material, avoid stress concentration, and prevent the material structure from being damaged due to large volume changes of the electrode material; and the three-dimensional network structure can ensure that the material is fully infiltrated by the electrolyte, shorten the ion transmission path, reduce the ion shuttle resistance, allow the ions to be transmitted freely, improve the material reaction kinetics conditions, and thereby improve the battery's rate performance.

[0049] Furthermore, the three-dimensional network structure is a three-dimensional multi-level hierarchical structure, which is composed of multiple three-dimensional network structure units, and each three-dimensional network structure unit has a micropore, mesopore, mesopore, or macropore structure. The three-dimensional multi-level hierarchical structure is conducive to alleviating the volume change of the negative electrode material during charge and discharge.

[0050] Furthermore, the side length of the cubic secondary particles is 150-350 nm.

[0051] In a second aspect, the present invention further provides a method for preparing a copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material, which is used to prepare the above-mentioned copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material, comprising the following steps:

[0052] (1) Preparation of copper iron Prussian blue precursor

[0053] Dissolving a copper source, carbon nanotubes, and a chelating agent in a solvent to obtain a solution A; dissolving an iron source and a chelating agent in a solvent to obtain a solution B; mixing solution A with solution B to obtain a copper-iron Prussian blue precursor;

[0054] (2) Preparation of copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material

[0055] The copper-iron Prussian blue precursor obtained in step (1) is mixed with a selenium source and calcined to obtain a copper-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material (CuSe / FeSe2@NC-CNT).

[0056] Illustratively, in step (1), the copper source is at least one of copper chloride, copper sulfate, and copper nitrate.

[0057] Illustratively, in step (1), the iron source is at least one of potassium ferrocyanide and sodium ferrocyanide.

[0058] Illustratively, in step (1), the chelating agents in solution A and solution B are at least one of citric acid, oxalic acid, and ascorbic acid, and more preferably at least two of citric acid, oxalic acid, and ascorbic acid.

[0059] Illustratively, in step (1), the solvents in solution A and solution B are both mixed solutions of ethanol, deionized water, and ethylene glycol.

[0060] For example, solution A contains 5-10 mmol of copper source, 4-9 g of chelating agent, 30-60 mg of carbon nanotubes, 10-40 mL of ethylene glycol, 40-80 mL of ethanol, and 50-100 mL of deionized water, and the total volume of ethylene glycol, ethanol, and deionized water is 150 mL.

[0061] Illustratively, in step (1), after the copper source, carbon nanotubes, and chelating agent are dissolved in a solvent, stirring is performed, the speed of the stirring bar is 170-260 r / min, and the stirring time is 30-120 min.

[0062] For example, in solution B, the iron source is 4-6 mmol, the chelating agent is 4-9 g, ethylene glycol is 10-40 mL, ethanol is 40-80 mL, and deionized water is 50-100 mL. The total volume of ethylene glycol, ethanol, and deionized water is 150 mL.

[0063] Illustratively, in step (1), after the iron source and the chelating agent are dissolved in the solvent, stirring is performed, the speed of the stirring bar is 170-260 r / min, and the stirring time is 30-120 min.

[0064] For example, in step (1), solution A and solution B are mixed and precipitated, and the precipitated product is centrifuged, washed, and dried to obtain the target product, copper-iron Prussian blue precursor. The speed of the centrifuge used in the centrifugation process is 7000-8000 r / min, and the product is washed with deionized water 3-4 times, washed with ethanol 2-3 times, and then dried in a vacuum drying oven at 80-90°C for 8-10 hours to obtain the target product, copper-iron Prussian blue precursor.

[0065] For example, in step (2), the selenium source is selenium powder, and the particle size of the selenium powder is preferably above 200 mesh.

[0066] Illustratively, the mass of the selenium source is 4-10 times the mass of the copper-iron-Prussian blue precursor.

[0067] In order to mix the selenium source and the copper-iron-Prussian blue precursor evenly, the copper-iron-Prussian blue precursor and the selenium source were mixed and then ground in a clockwise direction in an agate mortar for 10-15 minutes.

[0068] Illustratively, in step (2), the calcination process includes: first raising the temperature to 300-350°C at a heating rate of 2-10°C / min (more preferably 2-4°C / min), calcining for 1-3 hours, and then raising the temperature to 450-650°C at a heating rate of 2-10°C / min (more preferably 5-8°C / min), calcining for 1-3 hours.

[0069] In a third aspect, the present invention further provides a negative electrode plate, which comprises the above-mentioned copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material or the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material obtained by the above-mentioned preparation method.

[0070] Exemplarily, the negative electrode plate 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 CuSe / FeSe2@NC-CNT is 400 mg, the conductive agent is 50 mg, and the binder is 50 mg.

[0072] Exemplarily, the negative electrode sheet preparation method includes: uniformly mixing the active material CuSe / FeSe2@NC-CNT, a conductive agent, and a binder using N-methylpyrrolidone as the solvent; stirring the slurry in a wide-mouth bottle until a metallic luster develops; evenly coating the prepared electrode slurry on a 10 cm x 10 cm copper foil; and vacuum drying at 60°C for 12 hours before removing the foil. The electrode sheet is then punched out using a press to form an 8 mm diameter electrode sheet.

[0073] In a fourth aspect, the present invention further provides a lithium battery comprising the above-mentioned negative electrode plate.

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

[0075] Illustratively, the lithium battery preparation method includes: using CuSe / FeSe2@NC-CNT electrode material as the negative electrode, metal lithium sheet as the counter electrode and reference electrode, and forming a button battery 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 and electrical conductivity.

[0077] The copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material and its preparation method, negative electrode plate and lithium battery of the present invention are further described below through specific examples.

[0078] Example 1

[0079] A copper-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material, comprising carbon nanotubes and cubic secondary particles (with a side length of 200 nm) composed of copper-iron selenide primary particles;

[0080] The copper-iron selenide primary particles are particles coated with N-doped carbon, and the copper selenide and iron selenide in the copper-iron selenide primary particles are composited to form a heterogeneous structure;

[0081] The carbon nanotubes penetrate the cubic secondary particles to connect adjacent cubic secondary particles.

[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 network structure is a three-dimensional multi-level hierarchical structure, which is composed of a plurality of three-dimensional network structure units. Micropores, mesopores, mesopores or macropores exist between each three-dimensional network structure unit.

[0084] Example 2

[0085] This embodiment provides a method for preparing the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material of Example 1, a negative electrode plate, and a lithium battery.

[0086] 1. Preparation of copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material

[0087] Using a balance, weigh 9 mmol of CuSO4·5H2O, 50 mg of CNTs, 3.4 g of oxalic acid, and 2 g of citric acid. Using a graduated cylinder, measure and mix 75 mL of ethanol, 25 mL of deionized water, and 50 mL of ethylene glycol. Simultaneously, add the weighed CuSO4·5H2O, CNTs, oxalic acid, and citric acid to the above solvents and stir at 200 rpm for 10 minutes to form Solution A. Using a balance, weigh 3 mmol of K3[Fe(CN)6] and 3 mmol of Na4Fe(CN)6, 3.4 g of oxalic acid, and 2 g of citric acid. Using a graduated cylinder, measure and mix 75 mL of ethanol, 25 mL of deionized water, and 50 mL of ethylene glycol. Simultaneously, add the weighed K3[Fe(CN)6] and Na4Fe(CN)6, oxalic acid, and citric acid to the above solvents and stir at 200 rpm for 10 minutes to form Solution B. Solution A was poured into solution B, stirred for 24 h, washed with deionized water 3 times and ethanol 2 times using a centrifuge at a speed of 8000 r / min, and then dried in a vacuum drying oven at 80° C. for 10 h to obtain a copper-iron Prussian blue precursor.

[0088] 200 mg of the obtained copper-iron Prussian blue precursor product and 1 g of selenium powder were thoroughly ground in an agate mortar, mixed evenly, and placed in a corundum ark. In an argon flow at a flow rate of 60 mL / min, the heating rate was set to 2°C / min. After high-temperature calcination at 350°C for 3 h, the heating rate was set to 5°C / min, and the temperature was continued to rise to 500°C and kept at this temperature for 1 h. The temperature was slowly cooled to room temperature as the furnace cooled to obtain the target product CuSe / FeSe2@NC-CNT.

[0089] 2. Preparation of negative electrode sheet

[0090] 320 mg of active material CuSe / FeSe2@NC-CNT, 40 mg of conductive agent acetylene black, and 40 mg of PVDF were mixed evenly in N-methylpyrrolidone (NMP) as the solvent. The mixture was stirred in a wide-mouth bottle until a metallic luster appeared. The prepared electrode slurry was evenly coated on a 10 cm × 10 cm copper foil and vacuum-dried at 60°C for 12 hours before removal. Electrode pieces with a diameter of 8 mm were punched out using a press.

[0091] 3. Preparation of lithium batteries

[0092] The prepared negative electrode sheet was used as the negative electrode, the metal lithium 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. A button battery was formed in a glove box, where the water and oxygen content in the glove box was less than 0.01 ppm.

[0093] Figure 2 This is the SEM image of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in this example. Figure 2 It can be seen that the morphology of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material of the present invention is that the carbon nanotubes shuttle through the copper iron selenide / carbon nitrogen nanoblocks, connecting them into a three-dimensional network structure.

[0094] Figure 3 The XRD pattern of the copper iron selenide / carbon nitrogen nanoblocks prepared in this example shows that the peaks are sharp, indicating that an electrode material with good crystallinity is obtained.

[0095] Use the Blue Electric charge and discharge tester to test the electrochemical performance of lithium batteries between 0.1-3V. Figure 4 This is the constant current charge and discharge curve of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in this embodiment (charge and discharge performance diagram of the electrode material in the first three weeks). Figure 4 It can be seen that it has a high first-week discharge capacity, reaching 450mAh / g;

[0096] Figure 5This is the rate performance diagram of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in this embodiment, from Figure 5 It can be seen that when the current density changes from 50-10000mA / g, when the current density returns to 50mA / g, it can still release a discharge capacity of about 200mA / g, which has good rate performance;

[0097] Figure 6 This is the cycle performance diagram of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in this embodiment. Figure 6 It can be seen that at a current density of 200 mA / g, the material maintains good cycle stability.

[0098] The conductivity of the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material prepared in this embodiment can be obtained by impedance calculation, such as Figure 7 As shown, the conductivity is 1.76×10 -11 cm 2 / s.

[0099] Example 3

[0100] This embodiment provides a copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material and a preparation method thereof, a negative electrode plate and a lithium battery.

[0101] 1. Preparation of copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material

[0102] Using a balance, weigh 4 mmol of CuSO4·5H2O, 5 mmol of CuCl2·2H2O, 50 mg of CNTs, 2.4 g of ascorbic acid, and 3 g of citric acid. Using a graduated cylinder, measure and mix 50 mL of ethanol, 50 mL of deionized water, and 50 mL of ethylene glycol. Simultaneously, add the weighed CuSO4·5H2O, CuCl2·2H2O, CNTs, ascorbic acid, and citric acid to the above solvents and stir at 200 rpm for 10 minutes to form Solution A. Using a balance, weigh 2 mmol of K3[Fe(CN)6] and 4 mmol of Na4Fe(CN)6, 2.4 g of ascorbic acid, and 3 g of citric acid. Using a graduated cylinder, measure and mix 50 mL of ethanol, 50 mL of deionized water, and 50 mL of ethylene glycol. At the same time, weighed K3[Fe(CN)6] and Na4Fe(CN)6 were added to the above solvent and stirred at 200 r / min for 15 minutes to form solution B. Solution A was poured into solution B and stirred for 20 hours. The mixture was washed with deionized water three times and ethanol twice using a centrifuge at 7000 r / min, and then dried in a vacuum drying oven at 80°C for 8 hours to obtain a copper-iron Prussian blue precursor.

[0103] 200 mg of the obtained copper-iron Prussian blue precursor and 1.2 g of selenium powder were thoroughly ground in an agate mortar, mixed evenly, and placed in a corundum ark. In an argon flow at a flow rate of 50 mL / min, the heating rate was set to 2°C / min. After high-temperature calcination at 300°C for 2 h, the heating rate was set to 5°C / min, and the temperature was continued to rise to 500°C and kept warm for 2 h. The temperature was slowly cooled to room temperature as the furnace cooled to obtain the target product CuSe / FeSe2@NC-CNT.

[0104] 2. Preparation of negative electrode sheet

[0105] 400 mg of active material CuSe / FeSe2@NC-CNT, 50 mg of conductive agent acetylene black, and 50 mg of PVDF were mixed evenly in N-methylpyrrolidone (NMP) as the solvent. The mixture was stirred in a wide-mouth bottle until a metallic luster appeared. The prepared electrode slurry was evenly coated on a 10 cm × 10 cm copper foil and vacuum-dried at 60°C for 12 hours before removal. Electrode pieces with a diameter of 8 mm were punched out using a press.

[0106] 3. Preparation of lithium batteries

[0107] The prepared negative electrode sheet was used as the negative electrode, the metal lithium 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. A button battery was formed in a glove box, where the water and oxygen content in the glove box was less than 0.01 ppm.

[0108] Example 4

[0109] This embodiment provides a copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material and a preparation method thereof, a negative electrode plate and a lithium battery.

[0110] 1. Preparation of copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material

[0111] Using a balance, weigh 3 mmol of CuSO4·5H2O, 3 mmol of CuCl2·2H2O, and 3 mmol of Cu(NO3)2·3H2O, 50 mg of CNTs, 2.4 g of ascorbic acid, 1 g of citric acid, and 2 g of oxalic acid. Using a graduated cylinder, measure 25 mL of ethanol, 75 mL of deionized water, and 50 mL of ethylene glycol and mix them. Simultaneously, add the weighed CuSO4·5H2O, CuCl2·2H2O, Cu(NO3)2·3H2O, CNTs, ascorbic acid, citric acid, and oxalic acid to the above solvents and stir at 200 rpm for 10 minutes to form Solution A. Using a balance, weigh 4 mmol of K3[Fe(CN)6] and 2 mmol of Na4Fe(CN)6, 2.4 g of ascorbic acid, 1 g of citric acid, and 2 g of oxalic acid. Use a graduated cylinder to measure and mix 25 mL of ethanol, 75 mL of deionized water, and 50 mL of ethylene glycol. Simultaneously, weighed K3[Fe(CN)6], Na4Fe(CN)6, ascorbic acid, citric acid, and oxalic acid are added to the above solvents and stirred at 200 rpm for 10 minutes to form Solution B. Solution A is poured into Solution B and stirred for 22 hours. The mixture is then centrifuged at 7500 rpm, washed three times with deionized water and twice with ethanol, and then dried in a vacuum oven at 80°C for 9 hours to obtain the copper-iron Prussian blue precursor.

[0112] 200 mg of the obtained copper-iron Prussian blue precursor and 1.4 g of selenium powder were thoroughly ground in an agate mortar, mixed evenly, and placed in a corundum ark. In an argon flow at a flow rate of 70 mL / min, the heating rate was set to 2°C / min. After high-temperature calcination at 300°C for 3 h, the heating rate was set to 5°C / min, and the temperature was continued to rise to 550°C and kept at this temperature for 1 h. The temperature was slowly cooled to room temperature as the furnace cooled to obtain the target product CuSe / FeSe2@NC-CNT.

[0113] 2. Preparation of negative electrode sheet

[0114] 400 mg of the active material CuSe / FeSe2@NC-CNT, 50 mg of the conductive agent acetylene black, and 50 mg of PVDF were mixed evenly in N-methylpyrrolidone (NMP) as the solvent. The slurry was stirred in a wide-mouth bottle until a metallic luster appeared. The prepared electrode slurry was evenly coated on a 10 cm × 10 cm copper foil and vacuum-dried at 60°C for 12 hours before removal. Electrode pieces with a diameter of 8 mm were punched out using a press.

[0115] 3. Preparation of lithium batteries

[0116] The prepared negative electrode sheet was used as the negative electrode, the metal lithium 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. A button battery was formed in a glove box, where the water and oxygen content in 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, that is, cubic secondary particles composed of copper iron selenide primary particles are agglomerated together.

[0119] like Figure 8 As shown in FIG, the particle morphology of the negative electrode material is different in size, and the size is large and the agglomeration is serious; the electrode material with this structure has poor kinetic properties, resulting in a low first-cycle discharge capacity of about 280 mAh / g. Figure 9 At the same time, the material's cycle stability and rate performance are poor.

[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 copper selenide.

[0122] like Figure 10 As shown in the figure, the negative electrode material has large particles of varying sizes and varying degrees of agglomeration. This structure is not conducive to the transport of lithium ions and the infiltration of the electrode material by the electrolyte. After electrochemical performance testing, it has a low first-cycle discharge capacity of about 250mAh / g. Figure 11 At the same time, the material's cycle stability and rate performance are poor.

[0123] The above description is only a preferred specific 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 thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material, characterized in that: The negative electrode material includes carbon nanotubes and cubic secondary particles composed of copper iron selenide primary particles; The copper-iron selenide primary particles are carbon-coated particles, and the carbon is N-doped; the copper selenide and iron selenide in the copper-iron selenide primary particles are composited to form a heterogeneous structure; The carbon nanotubes penetrate the cubic secondary particles to connect adjacent cubic secondary particles.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material is a three-dimensional network structure composed of the cubic secondary particles and the carbon nanotubes.

3. A method for preparing a copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material, characterized in that: The method for preparing the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material according to claim 1 or 2 comprises the following steps: (1) Preparation of copper-iron Prussian blue precursor Dissolving a copper source, carbon nanotubes, and a chelating agent in a solvent to obtain a solution A; dissolving an iron source and a chelating agent in a solvent to obtain a solution B; mixing solution A with solution B to obtain a copper-iron Prussian blue precursor; (2) Preparation of copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material The copper-iron Prussian blue precursor obtained in step (1) is mixed with a selenium source and calcined to obtain a copper-iron selenide / carbon-nitrogen composite carbon nanotube negative electrode material.

4. The preparation method according to claim 3, characterized in that In step (1), the copper source is at least one of copper chloride, copper sulfate, and copper nitrate.

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

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 (1), the solvents in solution A and solution B are both mixed solutions of ethanol, deionized water and ethylene glycol.

8. The preparation method according to claim 3, characterized in that In step (2), the calcination process includes: firstly raising the temperature to 300-350°C at a heating rate of 2-10°C / min, calcining for 1-3 hours, and then raising the temperature to 450-650°C at a heating rate of 2-10°C / min, and calcining for 1-3 hours.

9. A negative electrode plate, characterized in that: The negative electrode plate comprises the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material according to any one of claims 1-2 or the copper iron selenide / carbon nitrogen composite carbon nanotube negative electrode material obtained by the preparation method according to any one of claims 3-8.

10. A lithium battery, characterized in that: The lithium battery comprises the negative electrode sheet according to claim 9.

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