Negative electrode active material for sodium ion battery, and preparation method for and use of negative electrode active material

Abstract

Provided is a negative electrode active material for a sodium ion battery. The negative electrode active material comprises reticulated hard carbon, hard carbon particles, and active metal particles; and the hard carbon particles and the active metal particles are distributed in the reticulated hard carbon and are fixed by the reticulated hard carbon. The production cost of the negative electrode active material for a sodium ion battery is reduced, and the capacity, the cycle performance and the rate performance of the negative electrode active material are improved. Further provided are a preparation method for and a use of the negative electrode active material for a sodium ion battery.

Description

A negative electrode active material for sodium ion battery and its preparation method and application Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a negative electrode active material for a sodium ion battery, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have become widely used in our daily lives. However, the growing demand for LIBs is leading to a shortage of available lithium ore. From a sustainable development perspective, exploring new battery types is essential.

[0003] Sodium-ion batteries (SIBs) have attracted attention due to their abundant resources and low cost, and are expected to be used for large-scale energy storage. Currently, the cathode active materials of SIBs include polyanions, Prussian blue, and oxides; the anode active materials include carbon-based materials, titanium-based materials, transition metals and their alloys, conversion materials, and organic materials. Overall, SIBs are similar to lithium-ion batteries, but their electrochemical performance needs to be improved compared to lithium-ion batteries.

[0004] Improving electrochemical performance requires improving the electrode active materials. Currently, among the available negative electrode materials for sodium-ion batteries, hard carbon, a carbon-based material, holds the greatest promise due to its high sodium storage capacity, excellent cycle stability, and readily available, inexpensive raw materials. Numerous related studies are underway. For example, some studies have used tamarind shells as a carbon source, followed by cleaning, vacuum drying, pre-carbonization, pulverization, granulation, and high-temperature carbonization to produce hard carbon materials for use as negative electrode materials for sodium-ion batteries. Others have used camphor wood as a carbon source, followed by ultrasonic cleaning, drying, pre-carbonization, pulverization, ball milling with organic compounds, high-temperature carbonization, washing, and drying to produce hard carbon materials for use as negative electrode materials for sodium-ion batteries. Technical issues

[0005] However, when the hard carbon materials currently obtained are used in sodium-ion batteries, they still face problems such as low specific capacity, poor rate performance, and unstable cycles compared to commercial lithium-ion battery graphite negative electrodes. There is still much room for improvement in their various electrochemical properties. Technical Solutions

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a negative electrode active material for a sodium ion battery, which reduces the production cost of the negative electrode active material for a sodium ion battery and improves its capacity, cycle performance, and rate performance.

[0007] The present invention also provides a method for preparing the negative electrode active material.

[0008] The present invention also provides applications of the negative electrode active material.

[0009] According to an embodiment of the first aspect of the present invention, a negative electrode active material for a sodium ion battery is provided, wherein the negative electrode active material comprises network hard carbon, hard carbon particles and active metal particles;

[0010] The hard carbon particles and the active metal particles are distributed in the network-like hard carbon and fixed by the network-like hard carbon.

[0011] The negative electrode active material according to the embodiment of the present invention has at least the following beneficial effects:

[0012] (1) The present invention adds active metal particles to the traditional carbon-based material. The active metal particles can react with sodium to form an alloy, thereby improving the reversible capacity of the negative electrode active material.

[0013] (2) However, the volume change ratio of active metal particles during charge and discharge is large, which can easily lead to problems such as pulverization, thereby reducing the cycle performance of the negative electrode active material. In the negative electrode active material provided by the present invention, hard carbon particles and active metal particles are distributed and fixed in a network of hard carbon. The fixation of the network of hard carbon prevents the impact of the pulverization products of the active metal particles on the electrolyte. The meshes in the network of hard carbon can accommodate the volume changes of the active metal particles, thus preventing the occurrence of pulverization and other problems to a certain extent.

[0014] (3) In the present invention, hard carbon particles, network hard carbon and active metal particles are combined, and through structural design, the electronic conductivity (active metal particles) and ionic conductivity (two types of hard carbon) of the obtained negative electrode active material, as well as the wettability to the electrolyte are significantly improved.

[0015] In summary, through the design of structure and composition, the comprehensive electrochemical properties of the negative electrode active material provided by the present invention, such as reversible capacity, coulombic efficiency, rate performance and cycle performance, are significantly improved compared with traditional hard carbon materials or traditional hard carbon materials embedded with metal particles.

[0016] According to some embodiments of the present invention, the hard carbon particles can pass through an 800 mesh sieve.

[0017] According to some embodiments of the present invention, the particle size of the active metal particles is 10-5000 nm, for example, about 50 nm, 100 nm, 300 nm, 500 nm, 800 nm, 1000 nm, 1200 nm, 1500 nm, 2000 nm, 3000 nm or 4000 nm.

[0018] According to some embodiments of the present invention, the active metal particles are made of at least one of Sn, Sb, Bi, W, Nb, Ta, Pt, Mn, Ni, Ge, Pd, In, Ir, Pb, Mo, Ru, Rh, and Ag. Active metal particles made of the above materials can better alloy with sodium ions, thereby increasing the reversible capacity of the negative electrode active material.

[0019] According to some embodiments of the present invention, the material of the active metal particles includes Sn.

[0020] According to some embodiments of the present invention, the negative electrode active material has pores, which are generated by the stacking of the hard carbon particles and the active metal particles, as well as pores inherent in the networked hard carbon.

[0021] During the sodium embedding process of the negative electrode active material, the pore structure of the negative electrode active material is first filled with metallic Na clusters, and then Na + Embedded between the two hard carbon layers, defects such as Na + The position of the negative electrode is also occupied, forming a sodium storage mechanism of "adsorption-intercalation-pore filling". At the same time, in this process, the active metal particles react with sodium to form an alloy, which greatly increases the sodium storage capacity of the negative electrode material. At the same time, the volume change of the active metal particles during the reaction is reduced by the network hard carbon, so that the negative electrode active material has good cycle stability while effectively improving the reversible capacity.

[0022] According to an embodiment of the second aspect of the present invention, a method for preparing the negative electrode active material is provided, the method comprising the following steps:

[0023] S1. The hard carbon particle source, the active metal particles and the organic flocculant are wet mixed and dried to obtain a precursor;

[0024] S2. calcining the precursor in an environment isolated from water and oxygen.

[0025] The mechanism of the preparation method includes: the organic flocculant entangles the carbon source particle source and the active metal particles during the wet mixing; during the calcination in step S2, the carbon source particle source and the organic flocculant are carbonized to generate corresponding hard carbon particles and network hard carbon.

[0026] The method for preparing the negative electrode active material provided by the present invention has at least the following beneficial effects:

[0027] The present invention adopts a wet mixing method to significantly improve the uniformity of the organic flocculant coating other materials. Through the design of the steps, the hard carbon particles and the network hard carbon can be generated by calcining in one step, and the steps are simple.

[0028] The present invention limits the isolation of water and oxygen during the calcination process because under high temperature conditions, water and oxygen will cause side reactions with carbon-based materials and active metal particles, thereby affecting the formation of the negative electrode active material.

[0029] The raw materials used in the preparation method are widely available, inexpensive, and will not cause pollution to the environment. The preparation process is simple, suitable for batch production, in line with the sustainable development strategy, and can be widely used in fields such as large-scale energy storage.

[0030] According to some embodiments of the present invention, step S1 further includes washing and drying the hard carbon particle source before the wet mixing.

[0031] The cleaning method is water washing. The water washing includes rinsing and ultrasonic treatment in sequence. The ultrasonic treatment lasts for 0.5 to 1.5 hours, for example, about 1 hour. This significantly removes dirt and impurities from the hard carbon particle source.

[0032] According to some embodiments of the present invention, in step S1, the hard carbon particle source can pass through an 800-mesh sieve. If the particle size does not meet the requirement, a pulverization process is required before the wet mixing.

[0033] According to some embodiments of the present invention, in step S1, the hard carbon particle source includes at least one of plant raw materials, small molecule organic matter and polymer.

[0034] According to some embodiments of the present invention, the plant raw material includes at least one of bamboo fiber powder, sawdust, starch, coconut shells, nut shells, straw stalks and sugarcane stalks.

[0035] According to some embodiments of the present invention, the small molecule organic matter includes sucrose or glucose.

[0036] According to some embodiments of the present invention, the polymer includes at least one of cellulose, lignin, chitosan, phenolic resin, epoxy resin, phenol-furfural resin, para-diphenol-polyformaldehyde resin, polyacrylonitrile, polyaniline, polypyrrole, polystyrene, polyimidazole, polythiophene, polytetrafluoroethylene and polyvinyl chloride.

[0037] According to some embodiments of the present invention, the hard carbon particle source includes at least one of bamboo fiber powder, sawdust, starch, cellulose, lignin, chitosan, sucrose, glucose, coconut shells, nut shells, straw, sugarcane stalks, phenolic resin, epoxy resin, phenol-furfural resin, para-diphenol-polyformaldehyde resin, polyacrylonitrile, polyaniline, polypyrrole, polystyrene, polyimidazole, polythiophene, polytetrafluoroethylene and polyvinyl chloride.

[0038] According to some embodiments of the present invention, the hard carbon particle source includes the bamboo fiber powder.

[0039] According to some embodiments of the present invention, in step S1, the mass percentage of the active metal particles in the precursor is 1-50%, for example, about 4%, 7%, 8%, 10%, 12%, 15%, 16%, 19%, or 20%.

[0040] During the calcination process in step S2, the particle size of the active metal particles does not substantially change, that is, the active metal particles in the negative electrode active material inherit the particle size of the negative electrode active material in step S1.

[0041] According to some embodiments of the present invention, in step S1, the mass percentage of the organic flocculant in the precursor is 1-50%, for example, about 5%, 10%, 20%, 25%, 30%, 35% or 40%.

[0042] According to some embodiments of the present invention, in step S1, the organic flocculant includes at least one of polyacrylamide, polyacrylic acid, sodium polyacrylate, sodium polystyrene sulfonate, ammonium polyacrylate, and polyethyleneimine.

[0043] According to some embodiments of the present invention, in step S1, the organic flocculant includes polyacrylamide.

[0044] According to some embodiments of the present invention, in step S1, the sum of the mass percentages of the hard carbon particle source, the active metal particles, and the organic flocculant in terms of mass percentage of the precursor is 100%.

[0045] According to some embodiments of the present invention, in step S1, the amount of the raw material used for preparation is as follows, calculated as a percentage by mass of the precursor:

[0046] Hard carbon particle source 55~65%;

[0047] Active metal particles 5~15%;

[0048] Organic flocculant 25~35%.

[0049] According to some embodiments of the present invention, in step S1, the wet-mixed dispersant includes water.

[0050] According to some embodiments of the present invention, in step S1, during the wet mixing, the concentration of the organic flocculant is 0.01-1 g / mL. This concentration is the ratio of the mass of the organic flocculant to the volume of the dispersant used in the wet mixing. For example, it can be 0.05-0.07 g / mL.

[0051] During wet mixing, the organic flocculant forms a network structure at low concentrations; the hard carbon source particles and active metal particles are evenly dispersed within the interstices within the structure; this structure is then fixed during the subsequent drying step. During the subsequent calcination process, the organic flocculant further fixes and dopes the hard carbon and active metal particles.

[0052] According to some embodiments of the present invention, in step S1, the wet mixing method includes at least one of stirring and ultrasound.

[0053] According to some embodiments of the present invention, in step S1, the temperature of the wet mixing is 15-40°C, for example, about 25°C.

[0054] According to some embodiments of the present invention, in step S1, the wet mixing comprises dispersing the hard carbon particle source and the active metal particles in the dispersant, and then mixing the resulting mixture with the organic flocculant. The wet mixing produces a gel-like or relatively viscous mixture (the state of the mixture depends on the amount of organic flocculant used). The stirring speed is 500-1000 rpm, for example, specifically about 700 rpm. The wet mixing duration is 0.5-5 hours, for example, specifically 1-4 hours.

[0055] According to some embodiments of the present invention, in step S1, the drying method includes freeze drying. Compared with other drying methods, freeze drying does not affect the structure of the precursor and does not require strong crushing after drying.

[0056] According to some embodiments of the present invention, in step S2, the heating rate of the calcination is 3-10°C / min, for example, about 5°C / min.

[0057] According to some embodiments of the present invention, in step S2, the calcination temperature is 500-1600°C, for example, about 800°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or 1500°C.

[0058] According to some embodiments of the present invention, in step S2, the calcination time is 1 to 50 hours.

[0059] According to some embodiments of the present invention, in step S2, the calcination time is 1 to 5 hours, for example, about 1.5 hours, 2 hours, 2.5 hours, 3 hours, or 4 hours.

[0060] According to some embodiments of the present invention, in step S2, the calcination time is 15 to 25 hours, more specifically about 20 hours.

[0061] According to some embodiments of the present invention, in step S2, the calcination atmosphere is at least one of an inert atmosphere and a reducing atmosphere. The inert atmosphere includes at least one of nitrogen, helium, and argon. The reducing atmosphere includes hydrogen. Specifically, the calcination atmosphere is a mixture of the inert atmosphere and the reducing atmosphere.

[0062] According to some embodiments of the present invention, in step S2, the cooling rate after calcination is 3-10°C / min. This protects the calcination equipment and prevents cracking caused by sudden cooling. Therefore, in actual production, if the equipment can withstand a higher cooling rate, other cooling rates may be used, such as cooling at the same rate as the heating rate, followed by natural cooling or air cooling.

[0063] According to an embodiment of the third aspect of the present invention, a sodium ion battery is provided, wherein raw materials for preparing the sodium ion battery include the negative electrode active material.

[0064] Because the sodium-ion battery utilizes all the technical solutions of the negative electrode active materials of the above-mentioned embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above-mentioned embodiments. For example, the sodium-ion battery has an initial coulombic efficiency of ≥90%, and also has advantages such as high energy density, good cycle stability, good rate performance, and a high safety factor. Compared with traditional lithium-ion batteries, it alleviates the problem of limited and uneven lithium resource reserves.

[0065] According to some embodiments of the present invention, the sodium ion battery includes a negative electrode sheet; the negative electrode sheet includes a negative electrode current collector and a negative electrode coating covering a surface of the negative electrode current collector.

[0066] According to some embodiments of the present invention, the negative electrode coating layer includes the negative electrode active material, a conductive agent, and a binder.

[0067] In the negative electrode coating, the mass percentage of the conductive agent is 2-30wt%; the mass percentage of the binder is 3-10wt%, and the balance is the negative electrode active material.

[0068] According to some embodiments of the present invention, the sodium ion battery includes at least one of a half cell and a full cell.

[0069] Unless otherwise specified, the term “about” in the present invention means that the error is allowed to be within the range of ±2%. For example, about 100 is actually 100±2%×100.

[0070] Unless otherwise specified, “between” in the present invention includes the number itself, for example, “between 2 and 3” includes the endpoint values ​​2 and 3.

[0071] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. Modes for Carrying Out the Invention

[0072] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0073] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0074] Example 1

[0075] This example prepares a negative electrode active material for sodium ion batteries. The specific steps are as follows:

[0076] S1. Weigh 6 g of bamboo fiber powder sieved through an 800-mesh sieve and 1 g of 800 nm diameter tin (Sn) metal particles and add them to 50 ml of deionized water at room temperature (approximately 25°C) and stir at 700 rpm for 1 h until uniformly dispersed.

[0077] Slowly add 3 g of polyacrylamide while stirring continuously and continue stirring for 3 h until completely dissolved;

[0078] The resulting mixture was freeze-dried for 48 hours to remove moisture, thereby obtaining a precursor.

[0079] S2. Place the precursor obtained in step S1 in a vacuum tube furnace and heat it to 1200°C at a heating rate of 5°C / min under an Ar atmosphere, keep the temperature constant for 2 hours, and then cool it to room temperature at the same rate.

[0080] The schematic diagram of the negative electrode active materials prepared in this example and other examples is shown in Figure 1. Specifically, the hard carbon particles and the active metal particles are uniformly dispersed in the network-like hard carbon and are wrapped by the network-like hard carbon.

[0081] In order to verify the influence of the type of hard carbon particle source on the obtained negative electrode active material, Examples 2 to 23 were specially designed.

[0082] Examples 2 to 23 respectively prepared a negative electrode active material, which differed from Example 1 in the types of hard carbon particle sources used, as shown in Table 1.

[0083] Table 1 Types of hard carbon particle sources in Examples 1 to 23

[0084]

[0085] In order to verify the effect of the type of active metal particles on the obtained negative electrode active material, Examples 24 to 40 were specially designed.

[0086] Examples 24 to 40 respectively prepared a negative electrode active material, which differed from Example 1 in that the materials of the active metal particles used were different, as shown in Table 2.

[0087] Table 2 Materials of active metal particles used in Examples 1, 24-40

[0088]

[0089] In order to verify the effect of the type of organic flocculant on the obtained negative electrode active material, Examples 41 to 46 were specially designed.

[0090] Examples 41 to 46 respectively prepared a negative electrode active material, which differed from Example 1 in the type of organic flocculant used, as shown in Table 3.

[0091] Table 3 Types of organic flocculants used in Examples 1, 41-46

[0092]

[0093] In order to verify the effect of the mass percentage of active metal particles in the precursor on the obtained negative electrode active material, Examples 46 to 52 were specially designed.

[0094] Examples 46 to 52 each prepared a negative electrode active material, and the specific differences from Example 1 are as follows:

[0095] The mass percentage of the added active metal particles in the precursor is different, and the corresponding percentages of the hard carbon particle source and the organic flocculant also change, but the mass ratio of the hard carbon particle source and the organic flocculant is the same as that in Example 1. The details are shown in Table 4.

[0096] Table 4 Mass percentage of active metal particles in the precursor in Example 1 and Examples 46-52

[0097]

[0098] In order to verify the effect of the active metal particle size on the obtained negative electrode active material, Examples 53 to 59 were specially designed.

[0099] Examples 53 to 59 respectively prepared a negative electrode active material, which differed from Example 1 in that the particle sizes of the added active metal particles were different, as shown in Table 5.

[0100] Table 5 Particle size of active metal particles used in Example 1 and Examples 53 to 59

[0101]

[0102] In order to verify the effect of the mass percentage of the organic flocculant in the precursor on the obtained negative electrode active material, Examples 60 to 64 were specially designed.

[0103] Examples 60 to 64 each prepared a negative electrode active material, and the specific differences from Example 1 are as follows:

[0104] The mass percentages of the active metal particles and the hard carbon particle source change with the different mass percentages of the added organic flocculants, but the mass ratio of the active metal particles to the hard carbon particle source is the same as that in Example 1, as shown in Table 6.

[0105] Table 6 Mass percentage of organic flocculant in precursor in Example 1 and Examples 60-64

[0106]

[0107] In order to verify the effect of calcination temperature on the obtained negative electrode active material, Examples 65 to 69 were specially designed.

[0108] Examples 65 to 69 respectively prepared a negative electrode active material, which differed from Example 1 in that the constant temperature of calcination in step S2 was different, as shown in Table 7.

[0109] Table 7 Calcination temperature in Example 1 and Examples 65 to 69

[0110]

[0111] In order to verify the effect of calcination time on the obtained negative electrode active material, Examples 70 to 73 were specially designed.

[0112] Examples 70 to 73 each prepared a negative electrode active material. The specific difference from Example 1 is that in step S2, the constant temperature calcination time is different, as shown in Table 8.

[0113] Table 8 Calcination time in Example 1 and Examples 70-73

[0114] No. Calcination time h No. Calcination time h Example 12 Example 724 Example 701 Example 735 Example 713

[0115] Comparative Example 1

[0116] This example prepares a negative electrode active material. The specific steps differ from those in Example 1 in that:

[0117] In step S1, no tin particles or polyacrylamide are added; bamboo fiber powder is directly used as a raw material and calcined to obtain a negative electrode active material having a granular hard carbon morphology.

[0118] Comparative Example 2

[0119] This example prepares a negative electrode active material, specifically:

[0120] A negative electrode active material made of hard carbon was prepared by referring to the steps in Experimental Example 4 in CN108439363A.

[0121] Comparative Example 3

[0122] In this example, a negative electrode active material was prepared by referring specifically to the method of Example 1 in patent CN 114551870 A (adjusting the amounts of some raw materials). The carbon source particles and the mass ratio of carbon source particles to tin used were the same as those in Example 1.

[0123] Application Examples

[0124] This example provides a sodium ion battery, specifically:

[0125] Preparation of diaphragm: Cut the glass fiber diaphragm into discs with a diameter of 16 mm, dry them and use them as diaphragms.

[0126] Prepare the electrolyte: weigh 1.68 g of sodium hexafluorophosphate and add it to 10 mL of a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio is 1:1:1). Stir until the sodium hexafluorophosphate is completely dissolved and use it as the electrolyte (electrolyte concentration is 1 M).

[0127] Prepare the working electrode (negative electrode sheet): Add 0.8 g of the negative electrode active material obtained in the Examples or Comparative Examples, 0.1 g of conductive carbon black, and 0.1 g of polytetrafluoroethylene to 1.5 mL of nitrogen-methylpyrrolidone and grind thoroughly to obtain a uniform slurry. Apply the slurry evenly to aluminum foil and vacuum dry. Cut the dried electrode sheet into 10 mm diameter discs, compact them, and use as the working electrode.

[0128] Assembly: In an inert gas-protected glove box, a 12mm diameter sodium sheet was used as the counter electrode. The counter electrode, separator, and working electrode were stacked in this order and placed in a button cell shell. The electrodes and separator were soaked with electrolyte, and the button cell shell was encapsulated to produce a sodium-ion battery (half-cell).

[0129] Test Example 1

[0130] This example tests the morphology, crystal state, and composition of the negative electrode active materials obtained in the examples and comparative examples. Specific testing methods include SEM, SEM with an EDS accessory, and XRD.

[0131] The test results show that the carbon and metal are evenly distributed in the negative electrode active material obtained in the embodiment of the present invention. At the same time, heteroatoms such as N in the hard carbon particle source and organic flocculant are also evenly doped in the obtained negative electrode active material. The elemental composition of the obtained negative electrode active material was tested by EDS. The results showed that there were 16.72wt% tin, 75.76wt% carbon, 4.48wt% nitrogen, and 3.04wt% oxygen. Although the accuracy of EDS is not very high from the perspective of quantitative testing, it can still show that the components are evenly distributed. At the same time, the X-ray powder diffraction pattern of the negative electrode active material obtained in the embodiment shows two obvious hard carbon peaks at 2θ=24° and 44°, corresponding to the (002) and (100) diffraction peaks. Compared with graphite, the (002) peak of this material is significantly shifted to a lower angle and becomes wider. This indicates that its degree of disorder is higher, the cross-linking interaction between carbon layers is stronger, and it is difficult to form crystallization even at high temperatures. In addition, other characteristic peaks observed correspond to Sn elemental. This demonstrates that the hard carbon particle source and organic flocculant added to the examples were indeed converted into hard carbon material during the calcination process, and the active metal particles were successfully embedded. In contrast, the XRD patterns of the negative electrode activity obtained in Comparative Examples 1 and 2 exhibit only a distinct hard carbon peak, with no other characteristic peaks. Some of the test results are shown in Figures 2 and 3. Due to the high degree of similarity between the patterns of the different examples, they are not listed here.

[0132] Test Example 2

[0133] This example tests the electrochemical performance of the sodium ion battery obtained in the application example. Specifically:

[0134] The test method is: at a voltage of 0-2V, with a nominal specific capacity of 300mAh / g. The reversible specific capacity and coulombic efficiency are tested at a rate of 0.1C, which is the test result of the first week after the battery is assembled. The cycle performance is tested at a rate of 0.1C, and the number of cycles when the capacity decays to approximately 80% of the initial capacity is recorded. The rate performance is tested at current densities of 0.1C, 0.2C, and 0.5C, and the percentage of the 0.5C capacity to the 0.1C capacity is calculated.

[0135] Regarding the effects of active metal particles and organic flocculants: The active metal particles added in the present invention can significantly improve the reversible specific capacity of the resulting negative electrode active material. However, the traditional use of active metal particles alone sacrifices some coulombic efficiency and cycle performance. In the negative electrode active material provided by the present invention, the networked hard carbon produced by the organic flocculant has a structural fixation effect and a stress buffering effect. In synergy with the active metal particles, the coulombic efficiency and cycle performance are significantly improved. Specifically, the coulombic efficiency is ≥93%, and the number of cycles to 80% capacity decay exceeds 2000. The specific test results are shown in Table 9 and Figure 4.

[0136] Table 9 Electrochemical properties of negative electrode active materials obtained in Example 1 and Comparative Examples 1-2 of the present invention

[0137]

[0138] The influence of the type of hard carbon particle source on the performance of the negative electrode active material shows that the type of hard carbon particle source has a significant influence on the performance of the obtained negative electrode active material. Among them, when bamboo fiber powder is selected, the capacity, first efficiency, cycle performance and rate performance are the best; secondly, the electrochemical performance of polythiophene is also very excellent; thirdly, the performance of the negative electrode active materials selected from glucose, phenolic resin, para-diphenol-polyformaldehyde resin, polyacrylonitrile, polyaniline and polypyrrole is also relatively excellent. There are three possible reasons for the above results. First, different hard carbon particle sources contain different types and amounts of heteroatoms. During the calcination process, heteroatom doping of the negative electrode active material affects the performance of the resulting negative electrode active material. Second, the hard carbon particles generated by different hard carbon particle sources have different pore structures and porosity, resulting in different degrees of electrolyte wetting and electrolyte retention. The different pore structures may also affect the distribution structure between the hard carbon particles and the active metal particles, ultimately affecting the performance of the resulting negative electrode active material. Third, the combination of the hard carbon particle source, active metal particles, and organic flocculant is not optimal. It is expected that by adjusting the parameters or combining the preparation raw materials, when other hard carbon particle sources are used, better electrochemical performance can be achieved. The specific test results are shown in Table 10.

[0139] Table 10 Effect of hard carbon particle source type on the performance of negative electrode active materials

[0140]

[0141] The influence of active metal particle type on the resulting negative electrode active material: When Sn is used as the active metal particle material, the overall electrochemical performance of the resulting negative electrode active material is optimal. When other materials are used, the electrochemical performance declines to varying degrees. This is due to the following reasons: first, the alloying degree and process between different active metal particles and sodium vary; second, the synergistic effect between the preparation raw materials is not achieved. If the type and amount of other preparation raw materials are adjusted, even with the same active metal particle material, it is still possible to obtain a negative electrode active material with better performance. The specific results are shown in Table 11.

[0142] Table 11 Effect of active metal particle material on the performance of the obtained negative electrode active material

[0143]

[0144] Effect of Organic Flocculant Type on Anode Active Material Performance: Results show that the type of organic flocculant significantly influences the performance of the resulting anode active material. Polyacrylamide exhibits the best electrochemical performance. The reasons for this are similar to those for the potential influence of the hard carbon particle source. Specific test results are shown in Table 12.

[0145] Table 12 Effect of organic flocculant type on the performance of negative electrode active materials

[0146]

[0147] Effect of Active Metal Particle Content on Anode Active Materials: Results show that as the active metal particle content increases, the electrochemical performance of the resulting anode active material initially increases and then decreases, reaching an optimum at around 10% (this does not necessarily mean that 10% is the optimal value). This is because, when the active metal particle content is low, hard carbon alone cannot provide high capacity, while when the active metal particle content is high, the volume change during cycling negatively impacts various performance characteristics. Specific test results are shown in Table 13.

[0148] Table 13 Effect of active metal particle ratio on the performance of negative electrode active materials

[0149]

[0150] Effect of active metal particle size on negative electrode active materials: The results show that when the particle size is small, the electrochemical performance of the resulting negative electrode active material increases first and then decreases as the particle size of the active metal particles increases. However, as the particle size continues to increase, the relationship between particle size and electrochemical performance is no longer obvious. The reason for this phenomenon is that when the particle size is small, the active metal particles are easily burned away during the calcination process and easily oxidized during transfer and use, which in turn affects the electrochemical performance. When the particle size increases, the volume expansion of the active metal particles during the charge and discharge process cannot be ignored, which in turn affects the electrochemical performance of all parties. The specific test results are shown in Table 14.

[0151] Table 14 Effect of particle size of active metal particles on negative electrode active materials

[0152]

[0153] Effect of Organic Flocculant Ratio on Anode Active Materials: Results show that as the amount of organic flocculant increases, the electrochemical performance of the resulting anode active materials increases, then decreases, reaching an optimal performance range around 30%. This phenomenon occurs because, when the organic flocculant dosage is low, it fails to effectively encapsulate and fix the active metal particles and hard carbon particles, easily causing structural collapse of the anode active material and resulting in poor electrochemical performance. When the organic flocculant dosage is high, the hard carbon particles and active metal particles in the resulting anode active material are less likely to come into contact with the electrolyte, resulting in incomplete electrochemical performance. Specific results are shown in Table 15.

[0154] Table 15 Effect of organic flocculant ratio on the performance of negative electrode active materials

[0155]

[0156] Effect of Calcination Temperature on Anode Active Materials: Results show that calcination temperature significantly influences the performance of anode active materials. Performance changes with temperature do not follow a linear relationship, with peak performance achieved at 1200°C. This temperature effect on performance stems from factors including its effect on the size of active metal particles, its effect on the degree of carbonization, and the potential for high temperatures to promote the re-fusion of active metal particles, thereby increasing the particle size of the active metal particles within the anode active material. Specific test results are shown in Table 16.

[0157] Table 16 Effect of calcination temperature on the performance of the obtained negative electrode active material

[0158]

[0159] Effect of Calcination Time on the Performance of Anode Active Materials: Results show that calcination time significantly impacts the performance of the anode active materials, with a calcination time of 2 hours yielding the best performance. Calcination time, like calcination temperature, influences the electrochemical performance of the resulting anode active materials by affecting the thoroughness of carbonization and the level of heteroatom doping. Specific test results are shown in Table 17.

[0160] Table 17 Effect of calcination temperature on the performance of negative electrode active materials

[0161]

[0162] According to the above results, the negative electrode active material prepared by the present invention is filled with metallic Na clusters first during the sodium insertion process, and then Na + The interlayers of the hard carbon micro-domains are then embedded, and then positions such as defects that are easy to capture Na+ are also occupied, forming a sodium storage mechanism of "adsorption-intercalation-pore filling". At the same time, in this process, the active metal particles react with sodium to form an alloy, which greatly increases the sodium storage capacity of the negative electrode active material. At the same time, the network structure hard carbon obtained by adjusting the organic flocculant reduces the volume change of the metal particles during the reaction. Overall, through the design of structure and materials, its comprehensive electrochemical performance such as capacity, first efficiency, cycle and rate has been significantly improved. The raw materials used for preparation are widely available, low cost, green and environmentally friendly, the preparation method is simple, and the equipment used is single. It is expected to be widely used in sodium-ion batteries in energy storage, power, 3C and other fields.

[0163] However, in the preparation method provided by the present invention, there is no one-to-one correspondence between the factors and the performance of the obtained negative electrode active material, but rather a synergistic effect between the parameters. Furthermore, due to the limited scope of the present invention and the difficulty in exhausting the conditions of the invention, it is also expected that better results can be obtained by adjusting the parameters within the scope provided by the present invention.

[0164] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A negative electrode active material for a sodium ion battery, characterized in that: The negative electrode active material includes network hard carbon, hard carbon particles and active metal particles; The hard carbon particles and the active metal particles are distributed in the network-like hard carbon and fixed by the network-like hard carbon.

2. The negative electrode active material according to claim 1, characterized in that The hard carbon particles can pass through an 800 mesh screen.

3. The negative electrode active material according to claim 1, characterized in that The particle size of the active metal particles is 10-5000 nm.

4. The negative electrode active material according to claim 1, characterized in that The material of the active metal particles includes at least one of Sn, Sb, Bi, W, Nb, Ta, Pt, Mn, Ni, Ge, Pd, In, Ir, Pb, Mo, Ru, Rh and Ag.

5. A method for preparing the negative electrode active material according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: S1. The hard carbon particle source, the active metal particles and the organic flocculant are wet mixed and dried to obtain a precursor; S2. calcining the precursor in an environment isolated from water and oxygen.

6. The preparation method according to claim 5, characterized in that: In step S1, the mass percentage of the active metal particles in the precursor is 1-50%.

7. The preparation method according to claim 5, characterized in that: In step S1, the mass percentage of the organic flocculant in the precursor is 1-50%; and / or, in step S1, the organic flocculant includes at least one of polyacrylamide, polyacrylic acid, sodium polyacrylate, sodium polystyrene sulfonate, ammonium polyacrylate and polyethyleneimine.

8. The preparation method according to claim 5, characterized in that: In step S1, the hard carbon particle source includes at least one of plant raw materials, small molecule organic matter and polymers; and / or the hard carbon particle source includes at least one of bamboo fiber powder, sawdust, starch, cellulose, lignin, chitosan, sucrose, glucose, coconut shells, nut shells, straw stalks, sugarcane stalks, phenolic resin, epoxy resin, phenol-furfural resin, para-diphenol-polyformaldehyde resin, polyacrylonitrile, polyaniline, polypyrrole, polystyrene, polyimidazole, polythiophene, polytetrafluoroethylene and polyvinyl chloride.

9. The preparation method according to claim 5, characterized in that: In step S2, the calcination temperature is 500-1600° C.; and / or the calcination time is 1-50 hours.

10. A sodium ion battery, characterized in that: The raw materials for preparing the sodium ion battery include the negative electrode active material as claimed in any one of claims 1 to 4.

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