Negative electrode material for sodium ion battery as well as preparation method and application of negative electrode material

Abstract

The invention provides a negative electrode material for a sodium-ion battery as well as a preparation method and application of the negative electrode material, and relates to the technical field of battery materials. The preparation method of the negative electrode material comprises the following steps: dissolving an amine compound and an aldehyde compound in water, heating, adding an acrylic monomer aqueous solution and an initiator, carrying out heat preservation, continuously adding a chain transfer agent under a stirring condition, mixing, cooling, adjusting the pH value of the mixed solution to 7-8, adding a curing agent, carrying out hydrothermal treatment, drying, and grinding a hydrothermal product, so as to obtain the negative electrode material. And calcining in an inert gas atmosphere to obtain the negative electrode material for the sodium-ion battery. The prepared negative electrode material solves the problems of extremely poor thermal stability, relatively large volume expansion and blockage of an internal porous structure during UF carbonization, the carbonized negative electrode material is applied to SIBs, active sites of Na < + > are greatly increased by the porous structure, meanwhile, relatively wide interlayer spacing is also convenient for intercalation and deintercalation of Na < + >, and the specific capacity and cycling stability of the SIBs are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly to a negative electrode material for sodium-ion batteries, a preparation method thereof, and an application thereof. Background Art

[0002] In the past few decades, the development of lithium-ion batteries (LIBs) has been remarkable. However, due to resource, cost, and environmental issues, researchers have been motivated to find alternatives. Due to the high abundance of sodium in nature, low acquisition cost, and similar electrochemical properties to lithium, sodium-ion batteries (SIBs) have received much attention. However, traditional graphite electrodes, due to their inherent interlayer spacing (0.334 nm), prevent Na + from being effectively inserted and extracted like Li + and sodium cannot form a stable compound with graphite. Therefore, it is necessary to find a negative electrode material that can stably exist in SIBs.

[0003] Amorphous carbon materials, especially those obtained by carbonizing urea-formaldehyde resin (UF), exhibit good structural stability and cycling stability due to their large interlayer spacing and disordered microcrystalline structure. In addition, the porous structure after UF carbonization is beneficial for the transport of ions in the electrolyte and provides more active sites, thereby improving the rate performance and cycling stability of sodium-ion batteries.

[0004] Although UF, as an amino resin, has the advantages of low price, easy availability of raw materials, simple operation, and rich nitrogen content, its poor thermal stability during the high-temperature carbonization process still remains the main obstacle restricting its application in the field of battery energy storage.

[0005] Therefore, there is an urgent need to develop a method to improve the thermal stability of UF carbonized materials to prepare negative electrode materials suitable for sodium-ion batteries and further enhance their electrochemical performance in sodium-ion batteries. Summary of the Invention

[0006] In view of this, the present invention provides a negative electrode material for sodium-ion batteries, a preparation method thereof, and an application thereof, which improve the specific capacity and cycling stability in the application of sodium-ion batteries by forming an interpenetrating three-dimensional network structure at the molecular level of UF.

[0007] In a first aspect, the present invention provides a preparation method of a negative electrode material for sodium-ion batteries, comprising the following steps: S1. Dissolve an amine compound and an aldehyde compound in water, heat it up, add an aqueous solution of acrylic acid monomer and an initiator, and keep warm to obtain Material I; S2. Under stirring conditions, add a chain transfer agent to Material I obtained in step S1, mix, then cool, and add an alkali solution dropwise to the mixed solution until the pH value is 7-8 to obtain Material II; S3. Add a curing agent to Material II in Step S2, and obtain Material III after hydrothermal treatment; S4. After drying and grinding Material III in Step S3, calcine it in an inert gas atmosphere to obtain the negative electrode material for the sodium-ion battery.

[0008] In one or some possible embodiments, in Step S1, the mass ratio of the amine compound to the aldehyde compound is 1:1.5 - 2.0; the mass ratio of the amine compound to the acrylic acid monomer is 1:2.5 - 3.2.

[0009] Further, before adding it to the mixed solution prepared in the previous step of Step S1, the acrylic acid monomer needs to be dissolved in water to prepare an aqueous solution of acrylic acid monomer with a mass concentration of 40 - 60%.

[0010] Further, the amine compound is selected from one or more of urea, dicyandiamide, p-phenylenediamine, o-phenylenediamine or melamine; the aldehyde compound is selected from one or more of formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde or furfural.

[0011] In one or some possible embodiments, the addition amount of the initiator is 6.0% of the mass of the acrylic acid monomer, and the initiator is selected from one or more of water-soluble initiators such as ammonium persulfate ((NH 4 ) 2 S 2 O 8 , APS), sodium sulfite, sodium persulfate or 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBI).

[0012] Further, the initiator is ammonium persulfate.

[0013] In one or some possible embodiments, control the addition time of the aqueous solution of acrylic acid monomer and the initiator to be 20 - 40 min.

[0014] In one or some possible embodiments, in Step S1, the heat preservation temperature is 70 - 75 °C, and the heat preservation time is 1 - 2 h.

[0015] In one or some possible embodiments, in Step S2, the addition amount of the chain transfer agent is 0.52 times the mass of the acrylic acid monomer, and the chain transfer agent is selected from one or more of isopropyl alcohol, acetone, carbon tetrachloride, acetic acid or triethylamine; the alkali solution is selected from a 30% NaOH solution and / or a KOH solution by mass fraction.

[0016] Further, the chain transfer agent is isopropyl alcohol.

[0017] In one or some possible embodiments, in Step S2, cool the temperature to 30 - 40 °C.

[0018] In one or some possible embodiments, in step S3, the curing agent is selected from benzenesulfonyl chloride which accounts for 12% - 15% of the mass of Material II.

[0019] In one or some possible embodiments, in step S4, the drying temperature is 90 °C, and the particle size of the ground Material III is ground to 12 - 20 mesh.

[0020] In one or some possible embodiments, in step S4, the flow rate of the inert gas is 30 mL / min - 50 mL / min; the calcination temperature is 700 - 1200 °C, and the time is 2 - 3 h.

[0021] In one or some possible embodiments, when performing the calcination, the heating rate is 5 - 7 °C / min.

[0022] In a second aspect, the present invention relates to a negative electrode material for a sodium - ion battery prepared by the above - mentioned preparation method.

[0023] In a third aspect, the present invention relates to the application of the negative electrode material for a sodium - ion battery in a negative electrode of a sodium - ion battery.

[0024] In a fourth aspect, the present invention provides a sodium - ion battery, including a negative electrode sheet, and the negative electrode sheet includes the above - mentioned negative electrode material for a sodium - ion battery.

[0025] The negative electrode material for a sodium - ion battery, its preparation method and application provided by the present invention have the following beneficial effects compared with the prior art: (1) The negative electrode material for a sodium - ion battery prepared by the present invention not only forms a highly complex three - dimensional network structure, but also has a certain specific surface area and porosity. In addition, the negative electrode material for a sodium - ion battery of the present invention has excellent hardness and chemical stability, and can effectively inhibit problems such as volume expansion, pore collapse or over - sintering during the high - temperature carbonization process of resin materials.

[0026] (2) The negative electrode material for a sodium - ion battery prepared by the present invention has high strength and is rich in a porous structure. When used as an electrode material, it is beneficial to the transmission of ions in the electrolyte, thereby improving its electrochemical performance in sodium - ion batteries (SIBs).

[0027] (3) The method for preparing the negative electrode material for a sodium - ion battery of the present invention has a simple process, convenient operation, low production cost, and can be applied to large - scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0029] Figure 1 Process flow chart for preparing the negative electrode material of the sodium-ion battery provided in Embodiment 1 of the present invention; Figure 2 XRD patterns of the negative electrode materials of the sodium-ion battery provided in Embodiment 1 and Comparative Example 1 of the present invention; Figure 3 XRD patterns of the negative electrode materials of the sodium-ion battery provided in Embodiment 1, Embodiment 3 and Comparative Example 4 of the present invention; Figure 4 SEM images of the negative electrode materials of the sodium-ion battery provided in Embodiment 1 and Comparative Examples 1 and 2 of the present invention. In the figure, a is the SEM image of the negative electrode material of the sodium-ion battery provided in Comparative Example 2, b is the SEM image of the negative electrode material of the sodium-ion battery provided in Comparative Example 1, and c is the SEM image of the negative electrode material of the sodium-ion battery provided in Embodiment 1; Figure 5 Physical images of the carbonized matrix materials of the sodium-ion battery provided in Comparative Example 1 and Embodiment 1 of the present invention. In the figure, a is the physical image of the carbonized matrix material of the sodium-ion battery provided in Comparative Example 1, and b is the physical image of the carbonized matrix material of the sodium-ion battery provided in Embodiment 1; Figure 6 Physical images of the carbonized matrix materials of the sodium-ion battery provided in Comparative Example 5 and Embodiment 2 of the present invention. In the figure, a is the physical image of the carbonized matrix material of the sodium-ion battery provided in Comparative Example 5, and b is the physical image of the carbonized matrix material of the sodium-ion battery provided in Embodiment 2; Figure 7 Rate performance comparison chart of the sodium-ion half-cells provided in Embodiment 1 and Comparative Examples 1 and 2 of the present invention; Figure 8 Long cycle performance comparison chart of the sodium-ion half-cells provided in Embodiment 1 and Comparative Examples 1 and 2 of the present invention; Figure 9 Long cycle performance comparison chart of the sodium-ion half-cells provided in Embodiment 1 and Comparative Examples 3 and 4 of the present invention; Figure 10 Rate performance comparison chart of the sodium-ion half-cells provided in Embodiment 1 and Comparative Examples 3 and 4 of the present invention; Figure 11 For the sodium-ion half-cell provided in Embodiment 1 of the present invention at a current density of 10 A g -1Lower specific capacity and capacity-voltage test diagrams. In the diagrams, a is the specific capacity test diagram, and b is the capacity-voltage test diagram; Figure 12 For the sodium-ion half-cell provided in Example 1 of the present invention at a current density of 2 A g -1 Lower specific capacity and capacity-voltage test diagrams. In the diagrams, c is the specific capacity test diagram, and d is the capacity-voltage test diagram; Figure 13 For the sodium-ion half-cell provided in Example 1 of the present invention at a current density of 0.5 A g -1 Lower specific capacity and capacity-voltage test diagrams. In the diagrams, e is the specific capacity test diagram, and f is the capacity-voltage test diagram; Figure 14 For the sodium-ion half-cell reaction kinetics test diagram provided in Comparative Example 1 of the present invention. In the diagram, a is the capacitance contribution at 1.0 mVs -1 ; b is the percentage of capacitance contribution at different scanning rates; Figure 15 For the sodium-ion half-cell reaction kinetics test diagram provided in Comparative Example 2 of the present invention. In the diagram, a is the capacitance contribution at 1.0 mVs -1 ; b is the percentage of capacitance contribution at different scanning rates; Figure 16 For the sodium-ion half-cell reaction kinetics test diagram provided in Example 1 of the present invention. In the diagram, a is the capacitance contribution at 1.0 mVs -1 ; b is the percentage of capacitance contribution at different scanning rates. Detailed implementation manners

[0030] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only a part of the implementation manners of the present invention, rather than all of the implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0031] The inventors found in practice that: under high-temperature conditions, the polymer segments of UF are prone to melting, resulting in volume expansion and destruction of the original structure and morphology. More seriously, this process will form a dense carbon layer on the surface of the sample, blocking the internal porous structure, and thus affecting its performance as an electrode material. Therefore, based on the above problems, the inventors made the present invention through further exploration and research.

[0032] The technical solution of the present invention is achieved as follows: A preparation method of a negative electrode material for a sodium-ion battery, comprising the following steps: S1. Dissolve amine compound (U) and aldehyde compound (F) in water. After heating, add aqueous acrylic acid monomer solution and initiator, and keep warm to obtain Material I. S2. Under stirring conditions, heat Material I obtained in Step S1, add a chain transfer agent, mix, and then cool. Dropwise add an alkali solution to the mixed solution until the pH value is 7 - 8 to obtain Material II. S3. Add a curing agent to Material II obtained in Step S2 to obtain Material III. S4. After drying and grinding Material III obtained in Step S3, calcine it under an inert gas atmosphere. After cooling to room temperature, perform pickling on the carbide to remove metal ions, and then dry to obtain the negative electrode material for sodium - ion batteries.

[0033] First, the inventor forms a highly complex three - dimensional network structure by interpenetrating the UF prepolymer, that is, the UF prepolymer swells into the molecular pores of the polyacrylic acid metal salt, enabling the UF prepolymer to further polymerize and cross - link to form an interpenetrating polymer (IPN) that is only intertwined at the molecular level. At the same time, the addition of the polyacrylic acid metal salt plays an etching role in the subsequent carbonization process, which can initially optimize the specific surface area and porosity of the carbonized product and improve the electrochemical performance of the negative electrode material in sodium - ion batteries. Second, during the carbonization process, the interpenetrated UF prepolymer serves as the matrix (carbonized matrix) of the negative electrode material (negative electrode carbonized material). Due to the decomposition of the polyacrylic acid metal salt, the etching effect of metal ions, and carbothermal reduction, the negative electrode material is again endowed with foam - like mesopores and abundant sub - nanometer micropores. Its porous structure is conducive to the transport of ions in the electrolyte, further improving the electrochemical performance of the negative electrode material. Finally, by adding a curing agent to the interpenetrated UF prepolymer and adjusting the content of the curing agent, the apparent porosity of the porous carbon is further controlled, avoiding the generation of cracks in the porous carbon, making the cured substance reach an ideal state, and greatly improving the hardness and chemical stability of the negative electrode material.

[0034] Therefore, due to its excellent structural stability, large specific surface area, large interlayer spacing, and porous structure, the negative electrode material prepared by the present invention is applicable to the energy storage field, especially for application in sodium - ion batteries.

[0035] The following further describes the present invention in combination with specific embodiments. The protection scope of the present invention is not limited by the following embodiments. Unless otherwise specified, the main materials involved in the following examples are all conventional commercially available products.

[0036] Example 1 As Figure 1 shown, the preparation method of the negative electrode material for sodium - ion batteries in this example includes the following steps: S1. Dissolve 2.785 g of urea (H 2 N - CO - NH2 ), and 5.705 g of formaldehyde (HCHO) were mixed and dissolved in water. The temperature was raised to 70 °C under stirring, and within 30 min, 15 ml of an aqueous solution with a concentration of 50% prepared from 8.93 g of acrylic acid (C 2 and 20 ml of an aqueous solution prepared from 0.6623 g of ammonium persulfate (APS) were added dropwise to the mixed solution (H-[NH-CO-NH-CH 3 H 4 O 2 ). After keeping warm for 1 h, Material I (UF-ASAP) was obtained; S2. Under stirring conditions, 4.713 g of isopropyl alcohol (IPA) was added to Material I, and it was kept warm for another 1 h. Subsequently, it was cooled to 30 °C, and a 30% NaOH solution by mass was added dropwise to the mixed solution until the pH value reached 7, obtaining Material II; S3. 2.76 g of benzenesulfonyl chloride (C 6 H 5 ClO 2 S) was added to Material II, and then hydrothermal treatment was carried out at 180 °C for 6 h to obtain Material III (precursor); S4. After drying Material III at 90 °C, the particle size of Material III was ground to 12 - 20 mesh. Nitrogen with a flow rate of 40 ml / min was introduced into a tubular furnace. Under nitrogen protection, the furnace temperature was raised from room temperature to 800 °C at a rate of 6 °C / min and kept for 2 h. Subsequently, the material was taken out and cooled to room temperature. The carbide was pickled to remove metal ions, and after drying, the negative electrode material for sodium-ion batteries was obtained.

[0037] Example 2 The preparation method of the negative electrode material for sodium-ion batteries in this example includes the following steps: S1. 2.785 g of urea and 4.178 g of formaldehyde were mixed and dissolved in water. The temperature was raised to 70 °C under stirring, and within 30 min, 15 ml of an aqueous solution with a concentration of 40% prepared from 8.93 g of acrylic acid monomer and 20 ml of an aqueous solution prepared from 0.6623 g of ammonium persulfate were added dropwise to the mixed solution. After keeping warm for 1 h, Material I was obtained; S2. Under stirring conditions, 4.713 g of isopropyl alcohol was added to Material I, and it was kept warm for another 1 h. Subsequently, it was cooled to 30 °C, and a 30% NaOH solution by mass was added dropwise to the mixed solution until the pH value reached 7, obtaining Material II; S3. 2.76 g of benzenesulfonyl chloride was added to Material II, and then hydrothermal treatment was carried out at 180 °C for 6 h to obtain Material III; S4. After drying Material III at 90°C, grind the particle size of Material III to 12 - 20 mesh. Pass nitrogen with a flow rate of 30 ml / min in a tube furnace. Under its protection, raise the furnace temperature from room temperature to 700°C at a rate of 5°C / min and hold for 2 h. Then take out the material and cool it to room temperature. After cooling to room temperature, pickle the carbide to remove metal ions, and obtain the negative electrode material for sodium-ion batteries after drying.

[0038] Example 3 The preparation method of the negative electrode material for sodium-ion batteries in this example includes the following steps: S1. Mix 2.785 g of urea and 5.018 g of formaldehyde and dissolve them in water. Raise the temperature to 75°C under stirring. Drop 15 ml of an aqueous solution with a concentration of 40% prepared from 8.93 g of acrylic acid monomer and 20 ml of an aqueous solution prepared from 0.6623 g of ammonium persulfate into the mixed solution within 30 min, and keep warm for 1 h to obtain Material I; S2. Under stirring conditions, add 4.713 g of acetone to Material I, continue to keep warm for 1 h, then cool to 40°C, and drop a 30% KOH solution by mass fraction into the mixed solution until the pH value reaches 8 to obtain Material II; S3. After adding 2.76 g of benzenesulfonyl chloride to Material II, perform hydrothermal treatment at 180°C for 6 h to obtain Material III; S4. After drying Material III at 90°C, grind the particle size of Material III to 12 - 20 mesh. Pass nitrogen with a flow rate of 50 ml / min in a tube furnace. Under its protection, raise the furnace temperature from room temperature to 1000°C at a rate of 6°C / min and hold for 2 h. Then take out the material and cool it to room temperature. After cooling to room temperature, pickle the carbide to remove metal ions, and obtain the negative electrode material for sodium-ion batteries after drying.

[0039] Example 4 The preparation method of the negative electrode material for sodium-ion batteries in this example includes the following steps: S1. Mix 2.785 g of urea and 5.705 g of formaldehyde and dissolve them in water. Raise the temperature to 75°C under stirring. Drop 15 ml of an aqueous solution with a concentration of 40% prepared from 6.96 g of acrylic acid monomer and 20 ml of an aqueous solution prepared from 0.6623 g of ammonium persulfate into the mixed solution within 30 min, and keep warm for 1 h to obtain Material I; S2. Under stirring conditions, add a mixture of 4.713 g of acetic acid and triethylamine to Material I, continue to keep warm for 1 h, then cool to 40°C, and drop a 30% KOH solution by mass fraction into the mixed solution until the pH value reaches 8 to obtain Material II; S3. After adding 2.76 g of benzenesulfonyl chloride to Material II, perform hydrothermal treatment at 180°C for 6 h to obtain Material III; S4. After drying Material III at 90°C, grind the particle size of Material III to 12 - 20 mesh. Introduce nitrogen with a flow rate of 50 ml / min into a tube furnace. Under its protection, raise the furnace temperature from room temperature to 1200°C at a rate of 7°C / min and hold for 2 h. Then take out the material and cool it to room temperature. After cooling to room temperature, perform pickling on the carbide to remove metal ions, and obtain the negative electrode material for sodium-ion batteries after drying.

[0040] Example 5 The preparation method of the negative electrode material for sodium-ion batteries in this example includes the following steps: S1. Mix 2.785 g of urea and 5.018 g of formaldehyde and dissolve them in water. Raise the temperature to 75°C under stirring conditions. Within 30 min, add 15 ml of an aqueous solution with a concentration of 40% prepared from 8.93 g of acrylic acid monomer and 20 ml of an aqueous solution prepared from 0.6623 g of ammonium persulfate to the mixed solution, and keep warm for 2 h to obtain Material I; S2. Under stirring conditions, add 4.713 g of acetone to Material I, continue to keep warm for 1 h, then cool to 40°C, and add a 30% by mass KOH solution to the mixed solution until the pH value reaches 8 to obtain Material II; S3. After adding 2.76 g of benzenesulfonyl chloride to Material II, perform hydrothermal treatment at 180°C for 6 h to obtain Material III; S4. After drying Material III at 90°C, grind the particle size of Material III to 12 - 20 mesh. Introduce nitrogen with a flow rate of 50 ml / min into a tube furnace. Under its protection, raise the furnace temperature from room temperature to 800°C at a rate of 6°C / min and hold for 3 h. Then take out the material and cool it to room temperature. After cooling to room temperature, perform pickling on the carbide to remove metal ions, and obtain the negative electrode material for sodium-ion batteries after drying.

[0041] Example 6 The preparation method of the negative electrode material for sodium-ion batteries in this example includes the following steps: S1. Mix 2.785 g of urea and 5.018 g of formaldehyde and dissolve them in water. Raise the temperature to 75°C under stirring conditions. Within 30 min, add 15 ml of an aqueous solution with a concentration of 40% prepared from 8.93 g of acrylic acid monomer and 20 ml of an aqueous solution prepared from 0.6623 g of ammonium persulfate to the mixed solution, and keep warm for 2 h to obtain Material I; S2. Under stirring conditions, add 4.713 g of acetone to Material I, continue to keep warm for 1 h, then cool to 40°C, and add a 30% by mass KOH solution to the mixed solution until the pH value reaches 8 to obtain Material II; S3. After adding 2.76 g of benzenesulfonyl chloride to Material II, perform hydrothermal treatment at 180°C for 6 h to obtain Material III; S4. After drying Material III at 90°C, grind the particle size of Material III to 12 - 20 mesh. Pass nitrogen with a flow rate of 50 ml / min in a tube furnace. Under its protection, raise the furnace temperature from room temperature to 800°C at a rate of 6°C / min and hold for 3 h. Then take out the material and cool it to room temperature. After cooling to room temperature, pickle the carbide to remove metal ions, and obtain the negative electrode material for sodium-ion batteries after drying.

[0042] Comparative Example 1 The difference from Example 1 is that: step S3 is missing, and the remaining conditions and steps remain unchanged.

[0043] Comparative Example 2 The preparation of the negative electrode material for sodium-ion batteries in this comparative example includes the following steps: Dissolve 2.785 g of urea and 5.705 g of formaldehyde in water, raise the temperature to 70°C under stirring, add a 30% NaOH solution by mass fraction to the mixed solution until the pH value is 7, keep warm for 2 h to obtain a polymer; after drying the polymer at 90°C, grind its particle size to 12 - 20 mesh. Pass nitrogen with a flow rate of 40 ml / min in a tube furnace. Under nitrogen protection, raise the furnace temperature from room temperature to 800°C at a rate of 6°C / min and hold for 2 h. Then take out the material and cool it to room temperature. After cooling to room temperature, pickle the carbide to remove metal ions, and obtain the negative electrode material for sodium-ion batteries after drying.

[0044] Comparative Example 3 The difference from Example 1 is that: in step S4, the furnace temperature is raised from room temperature to 600°C, and the remaining conditions and steps remain unchanged.

[0045] Comparative Example 4 The difference from Example 1 is that: in step S4, the furnace temperature is raised from room temperature to 1300°C, and the remaining conditions and steps remain unchanged.

[0046] Comparative Example 5 The difference from Example 2 is that: in step S1, the temperature is raised to 80°C under stirring, and the remaining conditions and steps remain unchanged.

[0047] Comparative Example 6 The difference from Example 2 is that: in step S1, the mass ratio of the urea to the aqueous solution of acrylic acid monomer is 1:2.4, and the remaining conditions and steps remain unchanged.

[0048] Comparative Example 7 The difference from Example 2 is that: in step S1, the mass ratio of the urea to the aqueous solution of acrylic acid monomer is 1:3.2, and the remaining conditions and steps remain unchanged.

[0049] Combining the experimental results of Example 2 and Comparative Examples 6 and 7, it was found that: in Comparative Example 6, due to the insufficient amount of acrylic monomer, the molecular weight of the polymer chain decreased, resulting in a decline in the performance of the product; while in Comparative Example 7, due to the use of an excessive amount of acrylic monomer, on the one hand, the probability of chain transfer increased, reducing the monomer conversion rate and causing a decline in the product performance; on the other hand, it also increased the production cost, that is, with an excess of acrylic acid, more alkali was needed for neutralization, which affected the final pH value of the polymer solution, and under acidic conditions, side reactions (such as esterification crosslinking) might be aggravated, resulting in a decrease in product gelation. Therefore, subsequent performance tests were not required.

[0050] Taking Example 1 and Comparative Example 1 as examples, the inventors used an X-ray diffractometer to conduct XRD tests on the negative electrode materials for sodium-ion batteries they prepared respectively, and the test results are as Figure 2 shown.

[0051] It can be Figure 2 seen from: both diffraction peaks of 2θ≈23 0 and 43 0 are included in the figure, corresponding to the (002) diffraction peak and the (100) diffraction peak respectively, which are typical characteristic peaks of amorphous carbon. After calculation, the interlayer spacing of the solidified negative electrode material (UF-ASAP-solid) in Example 1 was 3.81 Å, and the interlayer spacing of the non-solidified negative electrode material (UF-ASAP) in Comparative Example 1 was 3.76 Å, both of which were larger than the interlayer spacing of graphite (3.35 Å). Therefore, it can be shown that the negative electrode materials prepared by the method of the present invention, whether solidified or not, have a relatively large interlayer spacing, and a larger interlayer spacing can better promote the diffusion of Na + , which is helpful for the rapid insertion / extraction of Na + , thereby improving the electrochemical performance of sodium-ion batteries.

[0052] Taking Example 1, Example 3 and Comparative Example 4 as examples, the inventors used an X-ray diffractometer to conduct XRD tests on the negative electrode materials for sodium-ion batteries they prepared respectively, and the test results are as Figure 3 shown.

[0053] It can be Figure 3 seen from: when the carbonization temperature is as high as 1300 °C, the (002) diffraction peak is sharper compared to the (002) diffraction peaks at 800 °C and 1000 °C, and the peak position shifts towards the direction of increasing 2θ, increasing the order degree of the amorphous carbon structure and reducing the interlayer spacing (d002), indicating that the graphitization degree will be improved with the increase of the carbonization temperature. As the graphitization degree of the carbonized material gradually increases, the long-range order inside the carbonized material increases, resulting in a further reduction in the electrochemical performance of the material.

[0054] Taking the anode materials for sodium-ion batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2 as examples, scanning electron microscopy (SEM) tests were carried out, and the test results are as follows: Figure 4 as shown.

[0055] It can be seen from Figure 4 that for the anode material for sodium-ion batteries prepared in Comparative Example 2, after simple UF carbonization only, it showed the morphological characteristics of uneven particle size with a particle size of about 5-10 μm, a flat surface and no pores ( Figure 4 a); for the anode material for sodium-ion batteries prepared in Comparative Example 1, since no curing agent was added during preparation, it showed that some or all of the originally open pores were closed ( Figure 4 b), which was caused by partial collapse of the pore structure during the high-temperature carbonization process of the material; while for the anode material for sodium-ion batteries prepared in Example 1, due to the addition of acrylic monomer and curing agent during preparation, it showed larger pore diameters ( Figure 4 c), indicating that the anode material prepared by the present invention has undergone etching of metal ions, realizing the optimization of the specific surface area and porosity of the anode material, which is helpful to improve the electrochemical performance of the anode carbonized material in sodium-ion batteries.

[0056] Taking Example 2 and Comparative Example 1 as examples, the carbonized matrix materials for sodium-ion batteries prepared by each of them are as follows: Figure 5 as shown.

[0057] It can be seen from Figure 5 that the color of the carbonized anode material prepared without adding a curing agent in Comparative Example 1 is lighter, as shown in Figure 5 a, because when preparing the carbonized anode material, since the interpenetrated UF prepolymer was not cured, some monomers may not react completely, resulting in a decrease in yield; after adding a curing agent in Example 2, the color of the carbonized anode material further deepened, as shown in Figure 5 b, because adding a curing agent and then performing hydrothermal treatment will introduce oxygen atoms into the interpenetrated UF prepolymer, thereby introducing carbonyl groups. The addition of carbonyl groups effectively restricts the movement of carbon atoms during the subsequent carbonization process, thus hindering the graphitization of the carbon layer and preventing the carbon layer from shrinking. However, when the addition amount of the curing agent is too much, that is, more than 15% of the mass of Material II, the excessive curing agent will remain in the system, reducing the effective resin yield. In addition, excessive curing agent may cause side reactions (such as self-polymerization or degradation), consuming resin monomers, and at the same time, the interpenetrated UF prepolymer will crack during curing, so that a solid material cannot be formed.

[0058] Taking Example 2 and Comparative Example 5 as examples, the carbonized matrix materials for sodium-ion batteries prepared by each of them are as follows: Figure 6 as shown.

[0059] It can be seen from Figure 6It can be seen that the temperature was too high during the preparation of the prepolymer in Comparative Example 5, resulting in an intensified reaction and a phenomenon of explosive polymerization, so that a large amount of bubbles or sponge-like porous solids were generated, showing a phenomenon of being relatively white in color. As Figure 6 shown in a, this is because part of the resin decomposed into low-molecular-weight carbon slag and could not be used. From this, it can be inferred that the preparation of the prepolymer in Comparative Example 5 is not conducive to the later carbonization reaction. The sodium-ion battery carbonized matrix material prepared in Example 2, as Figure 6 shown in b, retained more nitrogen elements during the subsequent drying process of the matrix material. When drying, the material did not undergo a large volume expansion, and the matrix material had relatively high thermosetting and mechanical properties. Therefore, the inventor suggests that when the polymerization temperature of the UF prepolymer is set at 70-75 °C, the performance of the finally prepared negative carbonized material is the best.

[0060] The negative electrode materials for sodium-ion batteries prepared in the above Examples 1-6 and Comparative Examples 1-5 were assembled into negative electrode plates for sodium-ion batteries, including the following steps: The negative electrode materials for sodium-ion batteries prepared in each group were mixed with a conductive agent Super P and a binder sodium carboxymethyl cellulose (CMC-Na) at a mass ratio of 8:1:1 in water and stirred at a rotation speed of 950 rpm for 5 h to obtain a slurry; the slurry was scraped onto a current collector aluminum foil using a scraper and dried in a blast oven at 80 °C for 9 h, and then the electrode was punched into a pole piece with a diameter of 12 mm using a punching machine as the negative electrode plate for the sodium-ion battery.

[0061] The inventor further assembled the negative electrode plates for sodium-ion batteries prepared in each group, a glass fiber GF-D membrane, and an electrolyte solution of 1 M NaPF 6 in ethylene glycol dimethyl ether (DME) into a CR2023 type button battery and conducted charge and discharge tests on it. The test method was as follows: After the sodium-ion half-cells assembled in each group were left standing for 12 h, cyclic charge and discharge tests were carried out at a current density of 2 A / g under a voltage of 0-3 V, and rate charge and discharge tests were carried out at current densities of 0.02 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.4 A / g, 0.8 A / g, 1.0 A / g, 2.0 A / g, and 0.02 A / g.

[0062] (1) The performance test results of the sodium-ion half-cells assembled in Example 1 and Comparative Examples 1 and 2 at different cycle numbers are as Figure 7 、 8 shown.

[0063] From Figure 7It can be seen that the negative electrode carbon materials prepared in Comparative Examples 1 and 2 were subjected to rate charge-discharge tests at different current densities. The capacity of the battery decayed relatively fast at low current densities and very slowly at high current densities, with little difference between them. However, the carbonized material prepared in Example 1 after interpenetrating curing had excellent rate performance at different current densities. When the current density was 20 mA g -1 the specific capacity could reach 419 mAh / g. When it increased to 2 A g -1 the specific capacity could be stabilized at 271 mAh / g. Moreover, when the carbonized material of Example 1 was tested at a relatively high current density, its specific capacity hardly decreased, further indicating that the carbonized material of the present invention after interpenetrating curing has excellent application prospects as a negative electrode in sodium-ion batteries.

[0064] It is known from Figure 8 that the sodium-ion half-cell assembled in Example 1 showed good cycle stability at a current density of 2 A / g and had an advantage of a high cycle specific capacity of up to 217 mAh / g. This shows that the negative electrode material of the present invention after interpenetrating curing can be applied to large energy storage devices and / or high-power demand equipment.

[0065] (2) The performance test results of the sodium-ion half-cells assembled in Example 1 and Comparative Examples 3 and 4 at different cycle numbers are as shown in Figure 9 and 10 .

[0066] Combined with Figure 9 and Figure 10 it can be seen that when the negative electrode material prepared based on Comparative Example 2 was used in the sodium-ion half-cell, both the specific capacity and rate performance of the battery were poor. Analyzing the reasons, it may be that at the calcination temperature of 600 °C, the negative electrode material itself was not completely carbonized, resulting in incomplete development of the carbon layer and a large atomic spacing between C-C bonds. Therefore, irreversible capacity loss occurred in the negative electrode material itself. When the negative electrode material prepared based on Comparative Example 3 was used in the sodium-ion half-cell, both the specific capacity and rate performance of the battery were poor. Analyzing the reasons, it may be that at the calcination temperature of 1300 °C, the micropores and mesopores in the negative electrode material further grew, some micropores collapsed to form macropores, and some micropores closed and buried to form a closed pore structure, resulting in excessive graphitization of the negative electrode material and indirectly causing a sharp decrease in the specific capacity of this material.

[0067] The inventor placed the sodium-ion half-cell assembled in Example 1 under different current densities to test its specific capacity and capacity voltage. The test methods were cyclic voltammetry (CV) and constant current charge-discharge test methods. The test conditions included: voltage 0 - 3 V, current densities 10 A g -1 , 2 A g -1 and 0.5 A g -1 .

[0068] The test results are as Figures 11 - 13 shown.

[0069] It can be seen from Figures 11 - 13 that: (1) The sodium-ion half-cell assembled in Example 1, as Figure 11 shown in a, at a current density of 10 A g -1 , after 1200 cycles, the specific capacity can still reach 166 mAh / g. As Figure 11 shown in b, based on the constant current discharge-charge curve at a current density of 10 A / g, the sodium storage behavior of the carbon material was studied. The capacity-voltage curve of the battery changed after 20 cycles, and the capacity increased compared with the previous few cycles.

[0070] (2) The sodium-ion half-cell assembled in Example 1, as Figure 12 shown in c, at a current density of 2 A g -1 , after 800 cycles, the specific capacity can still reach 217 mAh / g. As Figure 12 shown in d, based on the constant current discharge-charge curve at a current density of 2 A / g, the sodium storage behavior of the carbon material was studied. The capacity-voltage curve of the battery did not change after 20 cycles, and the cycle stability was relatively high.

[0071] (3) The sodium-ion half-cell assembled in Example 1, as Figure 13 shown in e, at a current density of 0.5 A g -1 , after 500 cycles, the specific capacity can still reach 230 mAh / g. As Figure 13 shown in f, based on the constant current discharge-charge curve at a current density of 0.5 A / g, the sodium storage behavior of the carbon material at low current was studied. The capacity-voltage curve of the battery had a small increase after 150 cycles.

[0072] Therefore, it can be inferred that the sodium-ion battery prepared with the negative electrode material of the present invention has good stability regardless of the current density; at the same time, this negative electrode material can exhibit an adsorptive sodium storage method from the cyclic voltammetry characteristic curve at any current density.

[0073] The inventors carried out reaction kinetics tests on the sodium-ion half-cells prepared in Example 1 and Comparative Examples 1 and 2 by cyclic voltammetry at different scanning rates. The test results are as Figures 14 - 16 shown. Among them, a is the capacitance contribution at 1.0 mV s -1 , and b is the percentage of the capacitance contribution at different scanning rates.

[0074] It can be seen from Figure 14 that: For the sodium-ion half-cell directly prepared with the non-interpenetrating cured UF resin carbonized material in Comparative Example 2, as Figure 14As shown in a, when scanning UF at a relatively high rate (1 mV s -1 ), 36% of the capacity is contributed by capacitive behavior. At the same time, the relatively narrow shape of the latter half of its curve may be due to the presence of a soft carbon layer. As Figure 14 shown in b, as the scanning rate increases, the capacitive contribution gradually decreases, indicating that diffusion behavior dominates the electrochemical reaction at high scanning rates. In this case, a part of the capacitance of the capacitance-controlled reaction inevitably loses.

[0075] It can be seen from Figure 15 that: as Figure 15 shown in a, although the UF prepolymer in the negative electrode carbonized material prepared in Comparative Example 1 is not cured, its CV morphology does not change compared with the negative electrode carbonized material prepared in Example 1. However, as Figure 15 shown in b, at high scanning rates, the capacitance ratio of the negative electrode carbonized material prepared in Comparative Example 1 is still decreased compared with the cured negative electrode carbonized material prepared in Example 1.

[0076] It can be seen from Figure 16 that: the sodium-ion half-cell assembled in Example 1 exhibits ultra-high rate performance. As Figure 16 shown in a, after the prepared UF prepolymer is cured, its electrochemical behavior is mainly controlled by capacitance, and this characteristic corresponds to the relatively high micropore / mesopore ratio and special ion channels in the finally prepared negative electrode carbonized material, enabling Na + to be reversibly inserted and extracted in the carbon layer. As Figure 16 shown in b, even at high scanning rates, the capacitance ratio can still reach 89.81%, indicating that the porosity of the material is relatively rich and the pore size is relatively uniform. Therefore, it can be shown that the negative electrode material prepared by the method of the present invention has excellent performance in high-current SIBs.

[0077] Therefore, it can be inferred that when the negative electrode material applied to SIBs selects the interpenetrating and cured negative electrode carbonized material prepared by the present invention, SIBs can exhibit excellent electrochemical performance.

[0078] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode material for a sodium ion battery, characterized in that: The following steps are involved: S1, dissolving an amine compound and an aldehyde compound in water, heating, adding an acrylic acid monomer aqueous solution and an initiator, and keeping the temperature to obtain material I; S2. Add a chain transfer agent to the material I of step S1 under stirring, mix, and then cool, and add alkali solution dropwise to the mixture until the pH value is 7-8 to obtain material II; S3, adding a curing agent to the material II of step S2, and obtaining material III after hydrothermal treatment; S4, drying and grinding the material III of step S3, and then calcining it under an inert gas atmosphere to obtain the negative electrode material for the sodium ion battery.

2. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S1, the mass ratio of the amine compound to the aldehyde compound is 1:1.5-2.0; the mass ratio of the amine compound to the acrylic acid monomer is 1:2.5-3.2; and the mass concentration of the acrylic acid monomer aqueous solution is 40-60%.

3. The method for preparing a negative electrode material for a sodium ion battery according to claim 2, characterized in that: In step S1, the insulation temperature is 70-75° C., and the insulation time is 1-2 hours.

4. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S2, the added amount of the chain transfer agent is 0.52 times the mass of the acrylic acid monomer, and the chain transfer agent is selected from one or more of isopropanol, acetone, carbon tetrachloride, acetic acid or triethylamine; the alkali solution is selected from a NaOH solution and / or a KOH solution with a mass fraction of 30%.

5. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, characterized in that: The cooling temperature is to 30-40°C.

6. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S3, the curing agent is selected from benzenesulfonyl chloride accounting for 12% to 15% by mass of the material II.

7. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S4, the flow rate of the inert gas is 30 mL / min-50 mL / min; the calcination temperature is 700-1200° C., and the time is 2-3 h.

8. A negative electrode material for a sodium ion battery, characterized in that: The negative electrode material for sodium ion battery is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the negative electrode material for sodium ion battery as claimed in claim 8 in the negative electrode of a sodium ion battery.

10. A sodium ion battery, comprising a negative electrode plate, characterized in that: The negative electrode plate comprises a negative electrode material for a sodium ion battery as described in claim 8.

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