NiSe2-coated C composite material for negative electrode of sodium-ion battery and preparation method of NiSe2-coated C composite material

Abstract

The invention relates to the technical field of lithium batteries, in particular to a NiSe2 (at) C composite material for a negative electrode of a sodium ion battery and a preparation method of the NiSe2 (at) C composite material. The preparation method comprises the following steps: by taking NiC2O4 as a precursor, sequentially carrying out in-situ polymerization coating and high-temperature selenylation to obtain the three-dimensional flower-shaped NiSe2 (at) C composite material. The microstructure of the composite material is of a three-dimensional flower-shaped structure, and the surface of the composite material is covered with a carbon layer, so that the volume expansion of NiSe2 in the charging and discharging process can be effectively inhibited, and the structural stability of the composite material is maintained. The three-dimensional flower-shaped NiSe2 (at) C composite material shows high sodium storage capacity, excellent rate capability and long cycle stability when being used as a sodium ion battery negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly relates to a NiSe 2 @C composite material for the negative electrode of a sodium-ion battery and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long cycle life, low self-discharge rate, low pollution, no memory effect, and high safety, enabling them to develop rapidly in various fields such as portable power supplies and electric vehicles. However, with the wide application of lithium-ion batteries, the shortage of lithium resources and the increase in their prices have become the primary factors restricting the development of lithium-ion batteries. Therefore, it is particularly important to develop new secondary batteries with excellent comprehensive performance, low cost, and high safety. Sodium and lithium are alkali metal elements in the same main group, and they have similar physical and chemical properties. Compared with lithium, sodium resources are abundant and the cost is low, making sodium-ion batteries promising to replace lithium-ion batteries and be widely used in large-scale energy storage such as smart grids and renewable energy. However, the sodium ion radius is larger than that of the lithium ion, making it difficult for it to be embedded and extracted in layered graphite. When graphite is used as the negative electrode of a sodium-ion battery, its capacity is much smaller than that when used as the negative electrode of a lithium-ion battery. Therefore, developing a negative electrode material with high capacity, high rate performance, and good cycle stability is crucial for the development of sodium-ion batteries. Nickel selenide has a relatively high theoretical specific capacity as the negative electrode of a sodium-ion battery and is considered a promising negative electrode material for sodium-ion batteries. However, nickel selenide will undergo serious volume expansion during charge and discharge, resulting in material pulverization and shedding, and causing a decline in the cycle stability of the electrode. Summary of the Invention

[0003] The object of the present invention is to provide a NiSe 2 @C composite material for the negative electrode of a sodium-ion battery with high specific capacity, excellent rate performance, and good cycle stability, as well as a preparation method for this material. The NiSe 2 @C composite material prepared by this method is in the shape of a 3D micron flower, has a high tap density, excellent performance, and at the same time, this method is simple and easy to operate, has a low cost, and is easy to industrialize.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A preparation method for a NiSe 2 @C composite material for the negative electrode of a sodium-ion battery, characterized by comprising the following steps:

[0006] 1) Weigh a nickel source and dissolve it in a mixed solvent A composed of deionized water and ethylene glycol, add oxalic acid, and stir to obtain a mixed solution;

[0007] 2) Place the mixed solution obtained in step 1) in a high-pressure reactor for hydrothermal treatment to obtain NiC 2 O 4 micrometer flower precursor; NiC 2 O 4 The precursor has a flower-like structure with a lateral size of 2.5 - 3 μm;

[0008] 3) By in-situ polymerization coating, coat the carbon source on the surface of the NiC 2 O 4 micrometer flower precursor to obtain an intermediate;

[0009] 4) Calcinate the intermediate and selenium powder in an inert atmosphere according to a certain mass ratio to obtain the NiSe 2 @C composite material.

[0010] Preferably, in the above preparation method, the nickel source in step 1) is one or more of nickel sulfate, nickel chloride, nickel nitrate, and nickel carbonate.

[0011] Preferably, in the above preparation method, the mixed solvent A in step 1) is composed of deionized water and ethylene glycol mixed at a volume ratio of 1:1 - 1:5.

[0012] Preferably, in the above preparation method, the nickel source and oxalic acid in step 1) are weighed according to the molar ratio of NiC 2 O 4 in the material chemical formula of Ni 2+ to C 2 O 4 2- to be 1:1.

[0013] Preferably, in the above preparation method, the stirring temperature in step 1) is 20 - 80 °C, and the stirring time is 10 - 20 min.

[0014] Preferably, in the above preparation method, in step 2), the specific operation of the hydrothermal treatment is to increase the temperature to 100 - 200 °C at a heating rate of 1 - 5 °C / min and keep it warm for 10 - 36 hours.

[0015] Preferably, in the above preparation method, in step 2), after the hydrothermal reaction ends, wait for the reactor to cool to room temperature, filter the reaction solution, wash the obtained black powder material 2 - 5 times with a mixed solvent B composed of deionized water and ethanol, and then dry the washed black solid product at 80 - 120 °C for 4 - 12 hours to obtain NiC 2 O 4 micrometer flower precursor; wherein, the mixed solvent B is deionized water and ethanol mixed at a volume ratio of 1:3 - 9.

[0016] Preferably, in the above preparation method, the carbon source in step 3) is resorcinol, N-methylpyrrole monomer, dopamine hydrochloride, starch or glucose.

[0017] When the carbon source is resorcinol, the specific operation of in-situ polymerization coating is as follows: Disperse the NiC 2 O 4 precursor in a mixed solution of ethanol and deionized water, ultrasonically disperse for 0.1 - 1 hour, then add resorcinol and 1 - 5 mL of ammonia water and continue stirring for 10 - 50 min, add formaldehyde solution, continue ultrasonic stirring for 5 - 30 h, centrifuge, wash and filter to obtain a powder, dry the powder to obtain the intermediate NiC 2 O 4 @RF; wherein, the volume ratio of ethanol to deionized water is 5 - 10:1; the mass ratio of the NiC 2 O 4 precursor to resorcinol is 1:1 - 5; the mass ratio of the formaldehyde solution to the precursor is 1 - 5:1;

[0018] When the carbon source is N-methylpyrrole monomer, the specific operation of in-situ polymerization coating is as follows: Add the NiC 2 O 4 precursor to a mixed solution composed of deionized water and ethylene glycol in a volume ratio of 1:5, ultrasonically stir, then add sodium dodecyl sulfate and deionized water and continue stirring; after 30 min, add N-methylpyrrole monomer and ammonium persulfate, continuously stir for 1 hour, collect NiSe 2 @ppy and dry overnight to obtain the intermediate NiSe 2 @ppy;

[0019] When the carbon source is dopamine hydrochloride, the specific operation of in-situ polymerization coating is as follows: Add the NiC 2 O 4 precursor to a mixed solution composed of deionized water and ethylene glycol in a volume ratio of 1:5, ultrasonically stir, then add tris(hydroxymethyl)aminomethane and deionized water and continue stirring; after 30 min, add dopamine hydrochloride, continuously stir for 1 hour, collect NiSe 2 @PDA and dry overnight to obtain the intermediate NiSe 2 @PDA;

[0020] When the carbon source is starch, the specific operation of in-situ polymerization coating is as follows: Dissolve tin tetrachloride in deionized water to prepare a tin salt solution with a concentration of 1.2 mol / L, add the NiC 2 O 4The precursor and Tween 80 were ultrasonically stirred at 65 °C for 0.7 h. The obtained mixture was added into a high-pressure reactor and kept at 150 °C for 14.5 h. After the reactor was naturally cooled to room temperature, the reaction solution was filtered to obtain a black powder material, which was washed three times with deionized water and ethanol respectively. Then the washed black solid product was dried at 100 °C for 8 h. The prepared black solid product was dispersed in a mixed solvent composed of deionized water and ethanol in a volume ratio of 1:3, starch was added, and after ultrasonically stirring at 65 °C for 0.7 h, the obtained mixture was added into a high-pressure reactor and kept at 150 °C for 17 h. After the reactor was naturally cooled to room temperature, the reaction solution was filtered to obtain a black powder material, which was washed three times with deionized water and ethanol respectively. Then the washed black solid product was dried at 100 °C for 8 h to obtain an intermediate.

[0021] When the carbon source is glucose, the specific operation of in-situ polymerization coating is as follows: NiC 2 O 4 The precursor was dispersed in a mixed solvent composed of deionized water and ethanol, and the volume ratio of deionized water to ethanol in the mixed solvent was 1:5. Then glucose was added, and after ultrasonically stirring at 80 °C for 1 h, the obtained mixture was added into a high-pressure reactor and kept at 200 °C for 24 h. After the reactor was naturally cooled to room temperature, the reaction solution was filtered to obtain a black powder material, which was washed five times with deionized water and ethanol respectively. Then the washed black solid product was dried at 120 °C for 12 h to obtain an intermediate.

[0022] Preferably, in the above preparation method, in step 4), the mass ratio of the intermediate to selenium powder is 1:1 - 10, the calcination temperature is 300 - 900 °C, the time is 2 - 12 h, and the inert atmosphere is a nitrogen atmosphere.

[0023] The present invention also provides a NiSe 2 @C composite material for the negative electrode of a sodium-ion battery. In the composite material, NiSe 2 @C has a three-dimensional flower-like structure, and each nanorod in the NiSe 2 @C microflowers is uniformly coated with a carbon layer with a thickness of 15 nm, and the carbon content is about 9.19 wt%.

[0024] In summary, due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0025] 1. The present invention provides a NiSe 2 @C composite material for the negative electrode of a sodium-ion battery and its preparation method. First, a flower-like NiC 2 O 4 precursor is prepared; then a three-dimensional flower-like NiSe is obtained through in-situ polymerization coating and high-temperature selenization2 @C composite material, and the NiSe prepared by this method 2 @C composite material is in the shape of 3D micron-sized flowers, with a high tap density and excellent performance. At the same time, this method is simple and easy to operate, with low cost and easy industrialization.

[0026] 2. The NiSe 2 @C composite material prepared by the present invention has a three-dimensional flower-like microstructure, with a carbon layer covering its surface, which can effectively inhibit the volume expansion of NiSe during charge and discharge 2 and maintain its structural stability. The three-dimensional flower-like NiSe 2 @C composite material exhibits high sodium storage capacity, excellent rate performance and long cycle stability when used as the anode material of sodium-ion batteries.

[0027] 3. The three-dimensional micron-sized flower-like NiSe 2 @C composite material prepared by the present invention has a carbon (C) film coated on its surface; the 3D micron-sized flower-like NiSe 2 @C composite material is carefully designed and assembled from one-dimensional nanorods and a carbon framework. The three-dimensional flower-like structure can not only balance the structural stress and avoid the concentration of local stress, but also achieve fast sodium ion storage kinetics during the repeated sodiation / desodiation process, ensuring its outstanding structural integrity during cycling. In addition, this attractive multi-dimensional structure can provide more Na + storage sites, multi-directional migration pathways, and fast interfacial ion migration during sodiation / desodiation. Research shows that the NiSe2@C composite material has high rate performance and excellent cycle performance when used as the anode material of sodium-ion batteries.

[0028] 4. Experimental data show that the first discharge capacity of the NiSe 2 @C composite material is 803.3 mAh / g, the charge capacity is 755 mAh / g, and the first Coulombic efficiency is 94%; the battery made of the NiC 2 O 4 @C composite material can still provide a reversible capacity of 454 mAh / g at a high current density of 5 A·g -1 . In addition, as can be seen from Figure 3 c, after 100 cycles at a current density of 0.2 A·g -1 , its discharge specific capacity is 603 mAh·g -1 . It can be seen that the obtained NiSe 2 @C sodium-ion battery composite anode material has high specific capacity and excellent cycle performance. Description of the Drawings

[0029] Figure 1 For the flower-like NiSe 2SEM images, TEM images, and HAADF-STEM images of @C.

[0030] Figure 2 is flower-like NiSe 2 XRD patterns of @C and its comparative samples.

[0031] Figure 3 is flower-like NiSe 2 Electrochemical performance diagrams of @C and its comparative samples. Detailed implementation manners

[0032] To more clearly express the present invention, the following further illustrates the present invention through specific embodiments.

[0033] Example 1

[0034] 1) Weigh 2 mmol of nickel sulfate and dissolve it in a mixed solvent A composed of deionized water and ethylene glycol in a volume ratio of 1:1 to prepare a salt solution with a concentration of 0.01 mol / L; add 2 mmol of oxalic acid and stir at 25 °C for 15 min to obtain a mixed solution;

[0035] 2) Place the mixed solution obtained in step 1) in a high-pressure reaction kettle, heat it to 120 °C at a heating rate of 1 °C / min, and keep it at 120 °C for 24 hours; after the hydrothermal reaction is completed, wait for the reaction kettle to cool to room temperature, filter the reaction solution to obtain a black powder material, wash it 3 times with a mixed solvent B composed of deionized water and ethanol in a volume ratio of 1:3, and then dry the washed black solid product at 80 °C for 12 hours to obtain NiC 2 O 4 micron flower precursor;

[0036] 3) Add 0.1 g of NiC 2 O 4 precursor to a mixed solution prepared from ethanol and deionized water in a volume ratio of 7:1, ultrasonically stir for 0.5 hour, then add 0.1 g of resorcinol and 1.2 mL of ammonia water and continue stirring. After 10 min, add 0.25 mL of formaldehyde solution, continuously stir for 24 hours, and collect NiSe 2 @RF and dry overnight.

[0037] 4) Place the obtained NiSe 2 @RF and selenium powder at both ends of a boat respectively, and calcine at 450 °C for 2.5 hours under a nitrogen atmosphere to obtain NiSe 2 @C composite material.

[0038] The NiC prepared in Example 1 2 O 4SEM images, TEM images, HAADF-STEM images, XRD patterns of the precursor, NiSe 2 The electrochemical performance diagrams of @C and its comparative samples are as follows Figure 1 , Figure 2 , Figure 3 shown Figure 1 The SEM images of a and b Figure 1 The TEM images of d and e show the three-dimensional flower-like structure of NiSe 2 @C, Figure 1 c shows that each nanorod in NiSe 2 @C is uniformly coated with a 15-nm-thick carbon layer and has a hollow structure, which can provide a buffer space for NiSe2 Figure 1 The HRTEM of f detected a lattice fringe of 0.264 nm, which is attributed to the (210) crystal plane of NiSe2. At the same time, the clear crystal plane boundaries of amorphous carbon and NiSe2 were also detected, confirming the carbon layer coated on each nanorod. From Figure 1 The EDS mapping of g shows that there are three elements, Ni, Se, and C, in the NiSe 2 @C composite material and they are uniformly distributed. The XRD pattern of the NiSe 2 @C composite material obtained in this example is as follows Figure 2 shown. It can be seen that all the characteristic peaks of the sample correspond one by one to the standard card 11-0552, proving the successful preparation of the sample

[0039] The NiSe 2 @C composite material prepared in Example 1, conductive carbon black superP, and binder PVDF were added to 0.4 g of N-methylpyrrolidone and mixed and stirred. Then the slurry was coated on the current collector copper foil, dried and cut into a negative electrode sheet with a diameter of 12 mm. Using a sodium metal sheet as the counter electrode, polypropylene as the separator, and NaPF 6 in DME as the electrolyte, a CR2032-type button experimental battery was assembled in a glove box filled with argon

[0040] From Figure 3 the charge-discharge curve of a, the initial discharge capacity of the NiSe 2 @C composite material is 803.3 mAh / g, the charge capacity is 755 mAh / g, corresponding to an initial Coulomb efficiency of 94%. From Figure 3 the rate performance of b, the battery made of the NiC 2 O 4 @C composite material obtained in Example 1 can still provide a reversible capacity of 454 mAh / g at a large current density of 5 A·g -1 . In addition, from Figure 3It can be seen that after 100 cycles at a current density of 0.2 A·g -1 , its discharge specific capacity is 603 mAh·g -1 . From the above results, it can be seen that the obtained NiSe 2 @C sodium-ion battery composite anode material has a high specific capacity and excellent cycling performance.

[0041] Example 2

[0042] The difference between this example and Example 1 is only in step 3), and the other steps are the same as those in Example 1. The specific operation of step 3) in this example is as follows:

[0043] 3) Add 0.1 g of NiC 2 O 4 precursor to a mixed solution prepared from ethanol and deionized water in a volume ratio of 5:1, ultrasonically stir for 0.1 hour, then add 0.5 g of resorcinol and 5 mL of ammonia water and continue stirring. After 30 min, add 0.5 g of formaldehyde solution and continue ultrasonically stirring for 5 hours. Then collect the NiSe 2 @RF powder and dry it overnight to obtain the intermediate NiC 2 O 4 @RF.

[0044] Example 3

[0045] The difference between this example and Example 1 is only in step 3), and the other steps are the same as those in Example 1. The specific operation of step 3) in this example is as follows:

[0046] 3) Add 0.1 g of NiC 2 O 4 precursor to a mixed solution prepared from ethanol and deionized water in a volume ratio of 10:1, ultrasonically stir for 0.1 hour, then add 0.1 g of resorcinol and 5 mL of ammonia water and continue stirring. After 50 min, add 0.1 g of formaldehyde solution and continue ultrasonically stirring for 30 hours. Then collect the NiSe 2 @RF powder and dry it overnight to obtain the intermediate NiC 2 O 4 @RF.

[0047] The SEM images, TEM images, and HAADF-STEM images of the samples obtained in Examples 2 and 3 are basically consistent with the patterns of the above Example 1, and the corresponding images are omitted here.

[0048] Example 4

[0049] 1) Weigh 2 mmol of nickel chloride and dissolve it in a mixed solvent A composed of ionized water and ethylene glycol in a volume ratio of 1:5 to prepare a salt solution with a concentration of 0.01 mol / L; add 2 mmol of oxalic acid and stir at 20°C for 10 min to obtain a mixed solution.

[0050] 2) placing the mixed solution obtained in step 1) in a high-pressure reactor, heating it to 100°C at a heating rate of 5°C / min, and keeping it at 100°C for 36 hours; after the hydrothermal reaction is completed, the reactor is cooled to room temperature, the reaction liquid is filtered to obtain a black powder material, and the black powder material is washed three times with a mixed solvent B composed of deionized water and ethanol in a volume ratio of 1:6, and then the washed black solid product is dried at 100°C for 6 hours to obtain NiC 2 O 4 Micron flower precursor.

[0051] 3) 0.1g NiC 2 O 4 The precursor was added to a mixed solution consisting of deionized water and ethylene glycol in a volume ratio of 1:5, and ultrasonic stirring was performed for 0.5 hours. Then 10 mg of sodium dodecyl sulfate and 80 mL of deionized water were added and stirring continued. After 30 minutes, 40 μl of methylpyrrole monomer and 10 mL of ammonium persulfate were added. After continuous stirring for 1 hour, NiSe 2 @ppy Dry overnight to obtain the intermediate NiSe 2 @ppy;

[0052] 4) The obtained NiSe 2 @ppy and selenium powder were placed at both ends of the calcination boat in a mass ratio of 1:1, and calcined at 300℃ for 10 hours in a nitrogen atmosphere to obtain NiSe 2 @CComposite materials.

[0053] The SEM, TEM and HAADF-STEM images of the sample obtained in Example 4 are basically consistent with the pattern of the above-mentioned Example 1, and the corresponding patterns are omitted here.

[0054] The NiSe obtained in Example 4 2 Preparation and electrochemical performance analysis of @C composite negative electrode: Weigh 0.4g of NiSe 2 @C, add 0.05g of acetylene black as a conductive agent and 0.05g of PVDF (HSV900) as a binder, grind thoroughly, add 0.4g of NMP to disperse and mix, slurry is evenly mixed, and then the slurry is drawn on copper foil to make sheets. After drying, the metal sodium sheet is used as the counter electrode in an anaerobic glove box to assemble into a CR2025 button battery. At 25°C, 200 charge and discharge cycles are carried out at a rate of 100mA / g and 500mA / g between 0.01-2.5V. NiSe 2The @C anode material exhibits excellent electrochemical performance.

[0055] Example 5

[0056] 1) Weigh 2 mmol of nickel nitrate and dissolve it in a mixed solvent A composed of deionized water and ethylene glycol in a volume ratio of 1:1 to prepare a salt solution with a concentration of 0.01 mol / L; add 2 mmol of oxalic acid and stir at 40 °C for 20 min to obtain a mixed solution.

[0057] 2) Place the mixed solution obtained in step 1) in a high-pressure reaction kettle, heat it to 200 °C at a heating rate of 1 °C / min, and keep it at 200 °C for 10 hours; after the hydrothermal reaction is completed, wait for the reaction kettle to cool to room temperature, filter the reaction solution to obtain a black powder material, wash it 3 times with a mixed solvent B composed of deionized water and ethanol in a volume ratio of 1:9, and then dry the washed black solid product at 80 °C for 12 hours to obtain NiC 2 O 4 micron flower precursor;

[0058] 3) Add 0.1 g of NiC 2 O 4 precursor to a mixed solution composed of deionized water and ethylene glycol in a volume ratio of 1:5, ultrasonically stir for 0.5 hour, then add 0.133 g of tris(hydroxymethyl)aminomethane and 110 mL of deionized water and continue to stir. After 30 min, add 0.1 g of dopamine hydrochloride, continuously stir for 1 hour, and collect NiSe 2 @PDA and dry it overnight to obtain the intermediate NiSe 2 @PDA;

[0059] 4) Place NiSe 2 @PDA and selenium powder at both ends of a boat, and calcine it at 600 °C for 2 hours in a nitrogen atmosphere to prepare the NiSe 2 @C composite material.

[0060] The SEM image, TEM image, and HAADF-STEM image of the sample obtained in Example 5 are basically the same as the patterns of the above Example 1, and the corresponding images are omitted here.

[0061] Preparation and electrochemical performance analysis of the NiSe 2 @C composite anode: Weigh 0.4 g of the obtained NiSe 2@C, 0.05 g of acetylene black was added as a conductive agent and 0.05 g of PVDF (HSV900) was added as a binder. After thorough grinding, 0.4 g of NMP was added for dispersion and mixing. After the slurry was evenly adjusted, it was coated on a copper foil to make a film. After drying, it was assembled into a CR2025 coin cell with a sodium metal sheet as the counter electrode in an anaerobic glove box. At 25 °C, it was charged and discharged 200 times at a rate of 100 mA / g and between 0.01 - 2.5 V at 500 mA / g, NiSe 2 @C The anode material showed excellent electrochemical performance.

[0062] Example 6

[0063] 1) Weigh 2 mmol of nickel carbonate and dissolve it in a mixed solvent A composed of deionized water and ethylene glycol in a volume ratio of 1:1 to prepare a salt solution with a concentration of 0.01 mol / L; add 2 mmol of oxalic acid and stir at 80 °C for 20 min to obtain a mixed solution;

[0064] 2) Place the mixed solution obtained in step 1) in a high-pressure reaction kettle and heat it to 200 °C at a heating rate of 1 °C / min, and keep it at 200 °C for 10 hours; after the hydrothermal reaction is completed, wait for the reaction kettle to cool to room temperature, filter the reaction solution to obtain a black powder material, wash it 3 times with a mixed solvent B composed of deionized water and ethanol in a volume ratio of 1:6, and then dry the washed black solid product at 80 °C for 12 hours to obtain NiC 2 O 4 micrometer flower precursor;

[0065] 3) Dissolve 0.24 mol of tin tetrachloride in deionized water to prepare a tin salt solution with a concentration of 1.2 mol / L. Add 0.72 mol of NiC 2 O 4 precursor and 0.12 mol of Tween80, and ultrasonically stir at 65 °C for 0.7 hours. Add the obtained mixture to a high-pressure reaction kettle and keep it at 150 °C for 14.5 hours; wait for the reaction kettle to cool naturally to room temperature, filter the reaction solution to obtain a black powder material, and wash it 3 times with deionized water and ethanol respectively; then dry the washed black solid product at 100 °C for 8 hours; disperse the above-prepared black solid product in a mixed solvent composed of deionized water and ethanol in a volume ratio of 1:3, and then add 5 g of starch and ultrasonically stir at 65 °C for 0.7 hours. Then add the obtained mixture to a high-pressure reaction kettle and keep it at 150 °C for 17 hours. Wait for the reaction kettle to cool naturally to room temperature, filter the reaction solution to obtain a black powder material, wash it 3 times with deionized water and ethanol respectively, and then dry the washed black solid product at 100 °C for 8 h to obtain an intermediate; then add selenium powder and calcine it at 750 °C for 8.5 hours in an argon environment to obtain NiSe 2@CComposite materials.

[0066] The SEM, TEM and HAADF-STEM images of the sample obtained in Example 6 are basically consistent with the pattern of the above-mentioned Example 1, and the corresponding patterns are omitted here.

[0067] The NiSe obtained in Example 6 2 Preparation and electrochemical performance analysis of @C composite negative electrode: Weigh 0.4g of NiSe 2 @C, add 0.05g of acetylene black as a conductive agent and 0.05g of PVDF (HSV900) as a binder, grind thoroughly, add 0.4g of NMP to disperse and mix, slurry is evenly mixed, and then the slurry is drawn on copper foil to make sheets. After drying, the metal sodium sheet is used as the counter electrode in an anaerobic glove box to assemble into a CR2025 button battery. At 25°C, 200 charge and discharge cycles are carried out at a rate of 100mA / g and 500mA / g between 0.01-2.5V. NiSe 2 @C negative electrode material shows excellent electrochemical performance.

[0068] Example 7

[0069] NiC was prepared by the same method as in Example 1. 2 O 4 Precursor;

[0070] Then, NiC 2 O 4 The precursor was dispersed in 200 mL of a mixed solvent of ionized water and ethanol in a volume ratio of 1:5, and then 8 g of glucose was added. After ultrasonic stirring at 80 ° C for 1 hour, the resulting mixture was added to a high-pressure reactor and kept at 200 ° C for 24 hours. The reactor was naturally cooled to room temperature, and the reaction liquid was filtered to obtain a black powder material, which was washed with deionized water and ethanol for 5 times respectively. The washed black solid product was then dried at 120 ° C for 12 hours to obtain an intermediate. Then, selenium powder was added under argon and calcined at 900 ° C for 12 hours to obtain NiSe. 2 @CComposite materials.

[0071] The SEM, TEM and HAADF-STEM images of the sample obtained in Example 7 are basically consistent with the pattern of the above-mentioned Example 1, and the corresponding patterns are omitted here.

[0072] The NiSe obtained in Example 7 2 Preparation and electrochemical performance analysis of @C composite negative electrode: Weigh 0.4g of NiSe 2@C, 0.05 g of acetylene black was added as a conductive agent and 0.05 g of PVDF (HSV900) was added as a binder. After thorough grinding, 0.4 g of NMP was added for dispersion and mixing. After the slurry was evenly adjusted, it was pasted and made into a film on a copper foil. After drying, it was assembled into a CR2025 button cell with a sodium metal sheet as the counter electrode in an anaerobic glove box. At 25 °C, charge and discharge cycles were carried out 200 times at a rate of 100 mA / g and between 0.01 - 2.5 V at 500 mA / g, NiSe 2 @C The anode material exhibited excellent electrochemical performance.

[0073] The above description is a detailed description of the preferred and feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications made under the technical spirit prompted by the present invention shall fall within the scope of the patent covered by the present invention.

Claims

1. A method for preparing a NiSe2@C composite material for a negative electrode of a sodium ion battery, characterized in that: The following steps are involved: 1) weighing a nickel source and dissolving it in a mixed solvent A consisting of ionized water and ethylene glycol, adding oxalic acid, and stirring to obtain a mixed solution; 2) placing the mixed solution obtained in step 1) in a high pressure reactor and performing hydrothermal treatment to obtain a NiC2O4 micron flower precursor; 3) coating the carbon source on the surface of the NiC2O4 micron flower precursor by in-situ polymerization coating to obtain an intermediate; 4) calcining the intermediate and selenium powder in a certain mass ratio under an inert atmosphere to obtain a NiSe2@C composite material.

2. The preparation method according to claim 1, characterized in that: The nickel source in step 1) is one or more of nickel sulfate, nickel chloride, nickel nitrate and nickel carbonate.

3. The preparation method according to claim 1, characterized in that: In step 1), the volume ratio of deionized water to ethylene glycol is 1:1 to 1:

5.

4. The preparation method according to claim 1, characterized in that: In step 1), the nickel source and oxalic acid are prepared according to the chemical formula of NiC2O4. 2+ With C2O4 2- Weigh out the molar ratio of 1:

1.

5. The preparation method according to claim 1, characterized in that: The stirring temperature in step 1) is 20-80° C. and the stirring time is 10-20 min.

6. The preparation method according to claim 1, characterized in that: The specific operation of step 2) hydrothermal treatment is to keep the temperature at 100-200° C. for 10-36 hours.

7. The preparation method according to claim 1, characterized in that: In step 2), after the hydrothermal reaction is completed, the reactor is cooled to room temperature, the reaction liquid is filtered to obtain a black powder material, and the black powder material is washed 2-5 times with a mixed solvent B composed of deionized water and ethanol, and then the washed black solid product is dried at 80-120°C for 4-12 hours to obtain a NiC2O4 micron flower precursor; wherein the mixed solvent B is a mixture of deionized water and ethanol in a volume ratio of 1:3-9.

8. The preparation method according to claim 1, characterized in that: The carbon source in step 3) is resorcinol, methylpyrrole monomer, dopamine hydrochloride, starch or glucose.

9. The preparation method according to claim 1, characterized in that: In step 4), the mass ratio of the intermediate to selenium powder is 1:1-10, the calcination temperature is 300-900° C., the time is 2-12 hours, and the inert atmosphere is nitrogen or argon atmosphere.

10. A NiSe2@C composite material for a negative electrode of a sodium ion battery prepared by the preparation method according to any one of claims 1 to 9.

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