Multidimensional heterostructured anode materials for sodium-ion batteries

Abstract

A multi-dimensional heterogeneous structure negative electrode material for a sodium ion battery, the preparation method of which includes: mixing selenium powder and a metal nickel salt and dissolving them in an ethanol solution of citric acid, then adding a hydrazine hydrate solution dropwise and stirring evenly, subjecting the mixed solution to a solvothermal reaction; centrifugally washing the solvothermal reaction product to obtain a bulk metal selenide material; placing the dried metal selenide in a muffle furnace for calcination for a period of time, and rapidly annealing to room temperature to obtain a multi-dimensional NiSe / NiO heterogeneous structure composite material. The present invention can in-situ construct a heterojunction and a metal oxide protective layer by calcining a bulk metal selenide with a multi-dimensional hierarchical structure, and the prepared multi-dimensional heterogeneous structure composite material exhibits excellent rate performance and cycle performance as a negative electrode material for a sodium ion battery.

Description

Technical Field

[0001] The present invention relates to a sodium ion battery, and in particular to a multi-dimensional heterostructure negative electrode thereof. Background Art

[0002] With the rapid development of social economy, traditional fossil energy can hardly meet the current energy demand and will also cause serious environmental pollution. Therefore, various new types of renewable energy, such as wind energy, hydropower, tidal energy, etc., have become the focus of attention. However, this type of energy is usually intermittent and has regional limitations, which limits the continuous output and universal application of clean energy. In this context, it is of great significance to develop stable energy storage devices. Thanks to its abundant resources and low prices, sodium-ion batteries are considered to be an ideal choice in the field of large-scale energy storage.

[0003] However, Na + The larger size makes the reversibility of sodium-ion batteries relatively poor, and the reaction kinetics and cycle performance also need to be improved. Seeking high-performance sodium storage electrode materials and continuously improving them to enhance the sodium ion diffusion performance of the materials has always been the focus of this field. Among the many sodium-ion battery negative electrode materials, two-dimensional layered transition metal sulfide compounds (including metal sulfides and selenides) can provide higher theoretical specific capacity based on the multi-electron reaction mechanism and have been successfully applied in lithium / sodium-ion batteries. However, this type of material also has problems such as poor reversibility and loss of active substances.

[0004] Among various chalcogenides, many two-dimensional layered metal selenides outperform metal sulfides in many fields, mainly due to their narrower band gap, line width and better electronic conductivity. However, selenides have problems such as decomposition of active substances and large volume changes during the charge and discharge process. Although many modification methods such as carbon coating and element doping are also commonly used to modify selenides such as nickel selenide and cobalt selenide, they still have problems such as poor rate performance and low capacity retention. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-dimensional heterostructure negative electrode material for sodium ion batteries, which has excellent cycle stability and fast electrochemical reaction kinetics.

[0006] According to a first aspect of the present invention, a method for preparing a multi-dimensional heterostructure negative electrode material for a sodium ion battery is provided, comprising:

[0007] Dissolve citric acid in ethanol to form an organic solution, wherein the mass fraction of citric acid is 12% to 16%;

[0008] Provide selenium powder;

[0009] Providing a metal nickel salt, wherein the nickel salt is selected from at least one of nickel acetate tetrahydrate, nickel nitrate, nickel sulfate, nickel carbonate, nickel chloride, nickel bromide and nickel oxalate;

[0010] Adding selenium powder and nickel salt to the formed organic solution to form a mixed solution, wherein the mass concentration of the selenium powder is 0.0065-0.0075 g / ml, and the molar ratio of the selenium powder to the metal nickel salt is 1:0.8-1:1.2;

[0011] Adding hydrazine hydrate dropwise to the formed mixed solution to form a reaction solution, wherein the volume ratio of hydrazine hydrate to ethanol is 1:2-1:5;

[0012] The reaction solution is subjected to a solvothermal reaction to obtain a solvothermal reaction product, wherein the reaction temperature is 150-250° C. and the reaction time is 20-28 h;

[0013] The solvothermal reaction product is separated by centrifugation and washed and dried to obtain the NiSe bulk;

[0014] In an air atmosphere or other oxygen-containing atmosphere, the obtained body is calcined to form a NiSe / NiO multi-dimensional heterostructure composite electrode material, wherein the calcination temperature is 300-500°C and the calcination time is 5-15 min.

[0015] According to the preparation method of the present invention, the metal nickel salt may preferably be nickel acetate tetrahydrate.

[0016] According to the preparation method of the present invention, the mass concentration of selenium powder is preferably about 0.0071 g / ml.

[0017] According to the preparation method of the present invention, the molar ratio of selenium powder to metal nickel salt is preferably about 1:1.

[0018] According to the preparation method of the present invention, the volume ratio of hydrazine hydrate to ethanol is preferably about 1:3.

[0019] According to the preparation method of the present invention, the solvent thermal reaction temperature is preferably about 180° C. and the reaction time is about 24 h.

[0020] According to the preparation method of the present invention, the calcination temperature is preferably about 400°C, and the calcination time is about 10 min. In addition, the heating rate during the calcination process can be 1-10°C / min, preferably about 10°C / min.

[0021] The preparation method according to the present invention may further include: rapid annealing to room temperature after calcination.

[0022] According to the preparation method of the present invention, the mass fraction of citric acid is preferably about 14%.

[0023] According to the preparation method of the present invention, the rotation speed of the centrifugal separation can be 2000~8000 rpm.

[0024] According to another aspect of the present invention, a sodium ion battery negative electrode material prepared according to the above method is provided.

[0025] According to another aspect of the present invention, a sodium ion battery is provided, comprising the above-mentioned negative electrode material and an electrolyte, wherein the electrolyte comprises a sodium salt selected from NaClO4, NaPF6, NaTFSI and NaBF4 and a non-aqueous solvent selected from ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate, diethylene glycol dimethyl ether and ethylene glycol dimethyl ether.

[0026] The electrolyte is preferably a diglyme solvent containing 1M NaPF6.

[0027] The present invention has at least the following advantages:

[0028] The present invention can construct a heterojunction in situ only by placing the bulk material in the air for a short period of calcination, thereby being able to achieve in-situ coating of the NiSe bulk material and inhibit the Se dissolution phenomenon of the material, thereby ensuring the structural stability of the material.

[0029] By constructing a heterostructure, a built-in electric field effect can be induced at the material interface, thereby significantly improving the material's kinetic properties and improving electrochemical reactions.

[0030] The prepared composite material is a three-dimensional micron-shaped spherical particle composed of two-dimensional nanosheets, and has uniform one-dimensional nanofibers interspersed to form a network structure. This special multi-dimensional, micro-nano composite material can effectively coordinate the advantages of micron and nano materials, significantly improving the material's cycle stability and rate performance.

[0031] The preparation process is simple and the energy consumption is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the SEM image of the NiSe / NiO composite material prepared in Example 1.

[0033] Figure 2 3 is a comparison diagram of XRD of bulk NiSe and NiSe / NiO composite material prepared in Example 1.

[0034] Figure 3 This is the HRTEM image of the NiSe / NiO composite material prepared in Example 1.

[0035] Figure 4 This is a graph showing the cycling performance of a sodium ion battery assembled with the NiSe / NiO composite material prepared in Example 1 at a current density of 10 A / g.

[0036] Figure 5 Capacitance contribution of the sodium ion battery assembled with the NiSe / NiO composite material prepared in Example 1 under a scan rate of 1 mV / s. Implementation

[0037] In order to better understand the present invention, the present invention is further described below through embodiments, comparative examples and test examples; those skilled in the art should understand that they are used to explain rather than limit the present invention.

[0038] Example 1: Preparation of multi-dimensional heterostructure negative electrode materials for sodium ion batteries

[0039] Dissolve 0.32 g of selenium powder and 1.01 g of nickel acetate tetrahydrate in a molar ratio of 1:1 in 45 ml of ethanol solution containing 4 g of citric acid, and stir thoroughly until the mixture is well mixed.

[0040] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 24 h.

[0041] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0042] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 10 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0043] Figure 1 This is a SEM image of the multi-dimensional heterogeneous structure NiSe / NiO composite material prepared in this example. It is obvious that the obtained material has a uniform morphology and generates nanofibers with a length of about 10 μm, which are evenly distributed in the spherical particles. The overall morphology is a multi-dimensional material, the main body is a three-dimensional micron cluster spherical particle composed of two-dimensional nanosheets, and uniform one-dimensional nanofibers are interspersed to form a network structure.

[0044] Figure 2 This is the XRD comparison diagram of the bulk material NiSe and the NiSe / NiO composite material prepared in this embodiment. After a short heat treatment, the diffraction peak of NiO is clearly visible, but a small amount of SeO phase is inevitably detected. In general, the material maintains the two-phase crystal structure of the bulk material and generates a NiO heterogeneous phase.

[0045] Figure 3 : is a high-resolution transmission electron microscope diffraction pattern of the NiSe / NiO composite material prepared in this example. Figure 3In the figure, the lattice spacing of 2.63 Å corresponds to the (021) crystal plane of the NiSe R3m space group, and the lattice spacing of 2.73 Å and 1.83 Å correspond to the (101) crystal plane and (110) crystal plane of the P63 / mmc space group, respectively. There is an obvious heterogeneous lattice spacing in the main material. After measurement, the lattice spacing is 2.1 Å, corresponding to the (200) crystal plane of NiO, indicating that the prepared composite material is indeed composed of two components, NiSe and NiO.

[0046] Comparative Example 2

[0047] Dissolve 0.32 g of selenium powder and 0.504 g of nickel acetate tetrahydrate in a molar ratio of 1:0.5 in 45 ml of ethanol solution containing 4 g of citric acid, and stir thoroughly until the mixture is uniform.

[0048] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 24 h.

[0049] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0050] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 10 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0051] Comparative Example 3

[0052] Dissolve 0.32 g of selenium powder and 1.51 g of nickel acetate tetrahydrate in a molar ratio of 1:1.5 in 45 ml of ethanol solution containing 4 g of citric acid, and stir thoroughly until the mixture is well mixed.

[0053] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 150 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 24 h.

[0054] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0055] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 10 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0056] Comparative Example 4

[0057] 0.32 g of selenium powder and 1.01 g of nickel acetate tetrahydrate in a molar ratio of 1:1 were dissolved in a mixed solution consisting of 22.5 ml of water and 22.5 ml of ethanol, 4 g of citric acid was added, and the mixture was stirred thoroughly until the mixture was uniform.

[0058] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 24 h.

[0059] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0060] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 10 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0061] Comparative Example 5

[0062] Dissolve 0.32 g of selenium powder and 1.01 g of nickel acetate tetrahydrate in a molar ratio of 1:1 in a mixed solution consisting of 30 ml of water and 15 ml of ethanol, add 4 g of citric acid, and stir thoroughly until the mixture is uniform.

[0063] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 24 h.

[0064] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0065] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 10 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0066] Comparative Example 6

[0067] Dissolve 0.32 g of selenium powder and 1.01 g of nickel acetate tetrahydrate in a molar ratio of 1:1 in 45 ml of ethanol solution containing 4 g of citric acid, and stir thoroughly until the mixture is well mixed.

[0068] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 16 h.

[0069] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0070] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 10 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0071] Comparative Example 7

[0072] Dissolve 0.32 g of selenium powder and 1.01 g of nickel acetate tetrahydrate in a molar ratio of 1:1 in 45 ml of ethanol solution containing 4 g of citric acid, and stir thoroughly until the mixture is well mixed.

[0073] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 32 h.

[0074] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0075] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 10 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0076] Comparative Example 8

[0077] Dissolve 0.32 g of selenium powder and 1.01 g of nickel acetate tetrahydrate in a molar ratio of 1:1 in 45 ml of ethanol solution containing 4 g of citric acid, and stir thoroughly until the mixture is well mixed.

[0078] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 24 h.

[0079] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0080] The NiSe bulk material was calcined in a muffle furnace at 400 ℃ for 40 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0081] Comparative Example 9

[0082] Dissolve 0.32 g of selenium powder and 1.01 g of nickel acetate tetrahydrate in a molar ratio of 1:1 in 45 ml of ethanol solution containing 4 g of citric acid, and stir thoroughly until the mixture is well mixed.

[0083] 15 ml of hydrazine hydrate (98%) solution was added dropwise to the solution, and the mixed solution was transferred to a 100 ml solvothermal reactor and subjected to solvothermal reaction at 180 °C for 24 h.

[0084] After the reaction was completed, the reactor was cooled to room temperature, and the sample was centrifuged and washed several times with ethanol. The sample was vacuum dried at 60 °C for 24 h to obtain the bulk NiSe negative electrode material.

[0085] The NiSe bulk material was calcined in a muffle furnace at 400 °C for 1 min and rapidly annealed to room temperature to obtain a heterogeneous NiSe / NiO composite material.

[0086] Test example

[0087] Sodium ion battery assembly and electrochemical performance testing

[0088] (1) Coating method: The NiSe / NiO composite material prepared in Example 1, acetylene black, and a binder were uniformly mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1, and ground evenly for 1 hour to prepare a negative electrode slurry, which was coated on a copper foil current collector and dried in a vacuum drying oven at 80°C for 12 h; then rolled and cut to obtain a negative electrode sheet.

[0089] (2) Select some of the cut, uniform and complete electrode sheets, weigh them using a precision balance, and calculate the mass of the active material ((mtotal-mcopper)*0.8); use the sodium sheet as the counter electrode and reference electrode, and assemble them into a CR2032 button cell in a glove box under an argon atmosphere according to the correct operating steps together with the positive electrode shell, negative electrode shell, glass fiber diaphragm, sodium sheet (diameter 12 mm*thickness 1 mm), and electrolyte. The electrolyte used is diethylene glycol dimethyl ether dissolved with 1M NaPF6. Use a button cell sealer to seal the assembled battery, take it out of the glove box, and let it stand at room temperature for 24 hours.

[0090] The electrochemical performance of the prepared sodium ion battery was tested using a LAND CT2001A tester (Landian Electronics Co., Ltd., Wuhan City). The test cycle was set to 500 and 2000 cycles (voltage 0-3 V). At a current density of 10 A / g, the battery was charged and discharged for 2000 cycles; at a current density of 500 mA / g, the battery was charged and discharged for 500 cycles. The charge capacity (mAh / g) of the button battery in the first week and the charge capacity (mAh / g) after 500 and 2000 cycles of charge and discharge were tested respectively.

[0091] Figure 4The figure is a cycle performance diagram of a sodium ion battery assembled with the NiSe / NiO composite material prepared in Example 1 at a current density of 10 A / g. As can be seen from the figure, the NiSe / NiO composite material exhibits excellent electrochemical performance, and can still maintain a reversible capacity of 310.9 mAh / g after 2000 cycles, and the coulombic efficiency remains stable, indicating that the micro-nanostructure of the material has high stability and provides strong sodium ion transport kinetics.

[0092] Figure 5 The capacitance contribution of the sodium ion battery assembled with the NiSe / NiO composite material prepared in Example 1 under a scan rate of 1 mV / s. The contribution rate of the capacitance charge storage to the total sodium storage is 77%, indicating that the special micromorphology and built-in electric field effect in the NiSe / NiO composite material promote the capacitance behavior of the material, thereby presenting excellent high-rate cycling stability.

[0093] The NiSe / NiO composite materials prepared in Examples / Comparative Examples 1-9 were assembled into sodium ion batteries and then subjected to electrochemical performance tests. The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] Comparison of Example 1 with Comparative Examples 2 and 3 shows that the molar ratio of selenium powder to nickel salt in the raw material significantly affects the electrochemical properties of the material. When the nickel salt content is too little, the presence of a large amount of elemental selenium seriously affects the electrochemical performance; when there is too much nickel salt, the excess nickel salt cannot form a heterostructure to provide stable cycle performance and battery capacity, and the specific capacity is low. When the selenium powder concentration is 0.0071 g / ml and the molar ratio of selenium powder to nickel salt is 1:1, the product has the best first-week charging capacity and the best charging capacity after 500 weeks.

[0097] It can be seen from the comparison between Example 1 and Comparative Examples 4 and 5 that when the solvent is a single alcohol phase, the cycle stability and charge specific capacity of the material obtained by solvothermal reaction are higher. Mixing water and alcohol as solvent will affect the formation of stable morphology of the bulk material, thereby reducing the electrochemical performance of the material.

[0098] Comparison of Example 1 with Comparative Examples 6 and 7 shows that the solvothermal reaction time of the material has an impact on the performance of the product. When the solvothermal time is too short, the particles are just clustered and the nanofibers are unevenly distributed; when the solvothermal time is too long, the material matures with the crystals, and the nanofibers break and gradually disappear, which will reduce the material's cycle stability and charge capacity. When the solvothermal time is about 24 h, three-dimensional micron cluster spherical particles composed mainly of two-dimensional nanosheets can be generated, and uniform one-dimensional nanofibers are interspersed to form a network structure with good electrochemical performance.

[0099] Comparison of Example 1 with Comparative Examples 8 and 9 shows that the calcination time of the NiSe bulk material has a significant effect on the performance of the resulting material. If the calcination time is too long, NiSe is over-oxidized, the oxide layer is thick, and the material specific capacity decreases; if the calcination time is too short, it is difficult to generate a multi-dimensional heterogeneous structure NiSe / NiO composite material, and the electrochemical performance is not significantly improved.

Claims

1. A method for preparing a negative electrode material for a sodium ion battery, comprising: Dissolve citric acid in ethanol to form an organic solution, wherein the mass fraction of citric acid is 12% to 16%; Provide selenium powder; Providing a metal nickel salt, wherein the nickel salt is selected from at least one of nickel acetate tetrahydrate, nickel nitrate, nickel sulfate, nickel carbonate, nickel chloride, nickel bromide and nickel oxalate; Adding selenium powder and nickel salt to the formed organic solution to form a mixed solution, wherein the mass concentration of selenium powder is 0.0065-0.0075 g / ml, and the molar ratio of selenium powder to metal nickel salt is 1:0.8-1:1.2; Adding hydrazine hydrate dropwise to the formed mixed solution to form a reaction solution, wherein the volume ratio of hydrazine hydrate to ethanol is 1:2-1:5; The reaction solution is subjected to a solvothermal reaction to obtain a solvothermal reaction product, wherein the reaction temperature is 150-250°C and the reaction time is 20-28 hours; The solvothermal reaction product is separated by centrifugation and washed and dried to obtain the NiSe bulk; In an air atmosphere or other oxygen-containing atmosphere, the obtained body is calcined to form a NiSe / NiO multi-dimensional heterostructure composite electrode material, wherein the calcination temperature is 300-500°C and the calcination time is 5-15 min.

2. The preparation method according to claim 1, wherein the metal nickel salt is nickel acetate tetrahydrate.

3. The preparation method according to claim 1, further comprising: After calcination, the alloy was rapidly annealed to room temperature.

4. A sodium ion battery negative electrode material, prepared according to the method of any one of claims 1-3.

5. A sodium ion battery comprising the negative electrode material according to claim 4 and an electrolyte, wherein the electrolyte comprises a sodium salt selected from the group consisting of NaClO4, NaPF6, NaTFSI and NaBF4 and a non-aqueous solvent selected from the group consisting of ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate, diethylene glycol dimethyl ether and ethylene glycol dimethyl ether.

6. The sodium ion battery according to claim 5, wherein the electrolyte is diethylene glycol dimethyl ether containing 1M NaPF6.

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