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

Abstract

The present invention discloses a negative electrode active material for sodium ion batteries, a preparation method and an application thereof, and belongs to the field of new energy technology. The negative electrode active material for sodium ion batteries provided by the present invention comprises a network hard carbon, hard carbon particles and active metal particles; the hard carbon particles and active metal particles are distributed in the network hard carbon and fixed by the network hard carbon. The technical solution of the present invention reduces the production cost of the negative electrode active material for sodium ion batteries, and improves its capacity, cycle performance and rate performance. The present invention also provides a preparation method and an application of the above-mentioned negative electrode active material for sodium ion batteries.

Description

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, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely used in people's daily lives. At the same time, facing the growing demand for lithium-ion batteries, the available lithium resources are tight. From the perspective of sustainable development, exploring new types of batteries is necessary.

[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. At present, the positive electrode active materials of sodium-ion batteries include polyanions, Prussian blue, oxides and other materials; the negative electrode active materials include carbon-based materials, titanium-based materials, transition metals and their alloy materials, conversion materials and organic materials; overall, they are similar to lithium-ion batteries, but compared with lithium-ion batteries, the electrochemical performance of sodium-ion batteries needs to be improved.

[0004] To improve the electrochemical performance, we need to start with the electrode active materials. At present, among the optional negative electrode materials for sodium ion batteries, hard carbon in carbon-based materials has the most promising prospects due to its advantages of high sodium storage capacity, good cycle stability, and cheap and easy-to-obtain raw materials. There are also many related studies. For example, there is a technology that uses tamarind shell as a carbon source, and obtains hard carbon materials as negative electrode materials for sodium ion batteries through steps such as cleaning, vacuum drying, pre-carbonization, crushing and granulation, and high-temperature carbonization; there is also a technology that uses camphor wood as a carbon source, and obtains hard carbon materials as negative electrode materials for sodium ion batteries through steps such as ultrasonic cleaning, drying, pre-carbonization, crushing, mixing with organic compounds and ball milling, high-temperature carbonization, washing, and drying.

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

[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 invention also provides a method for preparing the negative electrode active material.

[0008] The invention also provides application 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 increasing the reversible capacity of the negative electrode active material.

[0013] (2) However, during the charge and discharge process, the volume change ratio of the active metal particles is relatively large, and pulverization and other problems are prone to occur, thereby reducing the cycle performance of the negative electrode active material. In the negative electrode active material provided by the present invention, the hard carbon particles and the active metal particles are distributed and fixed in the network hard carbon. The fixing effect of the network hard carbon avoids the influence of the pulverization products of the active metal particles on the electrolyte. The meshes in the network hard carbon can accommodate the volume changes of the active metal particles, and to a certain extent avoid the generation of pulverization and the like.

[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 resulting 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, compared with traditional hard carbon materials, or traditional hard carbon materials embedded with metal particles, 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.

[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 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. The active metal particles of the above materials can better alloy with sodium ions, thereby improving 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, and the inherent pores of the network hard carbon.

[0021] In the process of sodium insertion in 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 + The position of 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, and the preparation method comprises 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 through one-step calcination, 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 react with carbon-based materials and active metal particles, thereby affecting the generation of the negative electrode active material.

[0029] The raw materials used in the preparation method are widely available, low in price, and will not cause pollution to the environment. The preparation process is simple, suitable for mass production, in line with the sustainable development strategy, and can be widely used in the fields of 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 flushing and ultrasound in sequence. The duration of the ultrasound is 0.5 to 1.5 hours, for example, specifically about 1 hour. Thus, the dirt impurities in the hard carbon particle source can be significantly removed.

[0032] According to some embodiments of the present invention, in step S1, the hard carbon particle source can pass through an 800-mesh screen. If the particle size does not meet the requirement, it needs to be crushed 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 stalks, 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, calculated as a 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 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, in the wet mixing, the concentration of the organic flocculant is 0.01-1 g / mL. The 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 of the organic flocculant, a network structure is formed at a low concentration; the hard carbon particle source and the active metal particles are uniformly dispersed in the structural gaps therein; and the above structure is fixed in the subsequent drying step. In the subsequent calcination process, the organic flocculant further fixes the hard carbon particles and the active metal particles and dopes them.

[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, it may be about 25°C.

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

[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, and 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 can protect the equipment used for calcination and avoid cracking caused by sudden cooling of the equipment. Therefore, in actual production, if the equipment can withstand a higher cooling rate, other cooling rates can also 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] Since the sodium ion battery adopts all the technical solutions of the negative electrode active materials of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment. For example, the first coulomb efficiency of the sodium ion battery is ≥90%, and it also has the advantages of high energy density, good cycle stability, good rate performance, high safety factor, etc. Compared with traditional lithium ion batteries, it alleviates the problem of limited and uneven distribution of lithium resources.

[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 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] If there is no special explanation, the actual meaning of “about” in the present invention is 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 apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0073] Figure 1 Schematic diagram of the structure of the negative electrode active material obtained in the embodiment of the present invention.

[0074] Figure 2 This is the morphology of the negative electrode active material obtained in Example 1 of the present invention.

[0075] Figure 3 This is the XRD spectrum of the negative electrode active material obtained in Example 1 of the present invention.

[0076] Figure 4 This is a cycle performance diagram of the negative electrode active material obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0077] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments 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.

[0078] In the description of the present invention, the description with reference to the terms "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 schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0079] Example 1

[0080] In this example, a negative electrode active material for a sodium ion battery is prepared, and the specific steps are as follows:

[0081] S1. Weigh 6 g of bamboo fiber powder sieved through an 800-mesh sieve and 1 g of tin (Sn) metal particles with a diameter of 800 nm, add them to 50 ml of deionized water, and stir at 700 rpm for 1 h at room temperature (about 25°C) until they are evenly dispersed;

[0082] Slowly add 3 g of polyacrylamide during continuous stirring and continue stirring for 3 h until completely dissolved;

[0083] The obtained mixture was freeze-dried for 48 hours to remove moisture; and a precursor was obtained.

[0084] 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 Ar atmosphere, keep the temperature constant for 2 hours, and then cool it to room temperature at the same rate.

[0085] The schematic diagram of the negative electrode active material obtained in this example and other examples is as follows: Figure 1 Specifically, the hard carbon particles and the active metal particles are uniformly dispersed in the network hard carbon and are wrapped by the network hard carbon.

[0086] 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.

[0087] Examples 2 to 23 respectively prepared a negative electrode active material, which differed from Example 1 in that the types of hard carbon particle sources used were different, as shown in Table 1.

[0088] Table 1 Types of hard carbon particle sources in Examples 1 to 23

[0089]

[0090] In order to verify the influence of the type of active metal particles on the obtained negative electrode active material, Examples 24 to 40 were specially designed.

[0091] 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.

[0092] Table 2 Materials of active metal particles used in Examples 1, 24 to 40

[0093]

[0094] 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.

[0095] Examples 41 to 46 respectively prepared a negative electrode active material, which differed from Example 1 in that different types of organic flocculants were used, as shown in Table 3.

[0096] Table 3 Types of organic flocculants used in Examples 1, 41 to 46

[0097]

[0098] 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.

[0099] Examples 46 to 52 respectively prepared a negative electrode active material, and the specific differences from Example 1 are as follows:

[0100] 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.

[0101] Table 4 Mass percentage of active metal particles in the precursor in Example 1 and Examples 46 to 52

[0102]

[0103] 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.

[0104] 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.

[0105] Table 5 Particle size of active metal particles used in Example 1 and Examples 53 to 59

[0106]

[0107] 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.

[0108] Examples 60 to 64 respectively prepared a negative electrode active material, and the specific differences from Example 1 are as follows:

[0109] The mass percentage of the added organic flocculant is different, and the corresponding mass percentage of the active metal particles and the hard carbon particle source changes, 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.

[0110] Table 6 Mass percentage of organic flocculant in the precursor in Example 1 and Examples 60-64

[0111]

[0112] In order to verify the effect of calcination temperature on the obtained negative electrode active material, Examples 65 to 69 were specially designed.

[0113] Examples 65 to 69 respectively prepared a negative electrode active material, and the specific difference from Example 1 is that in step S2, the constant temperature of calcination is different, as shown in Table 7.

[0114] Table 7 Calcination temperature in Example 1 and Examples 65 to 69

[0115]

[0116] In order to verify the effect of calcination time on the obtained negative electrode active material, Examples 70 to 73 were specially prepared.

[0117] Examples 70 to 73 respectively prepared a negative electrode active material, and the specific difference from Example 1 is that in step S2, the constant temperature calcination time is different, as shown in Table 8.

[0118] Table 8 Calcination time in Example 1 and Examples 70 to 73

[0119]

[0120] Comparative Example 1

[0121] This example prepares a negative electrode active material, and the specific steps are different from those of Example 1 in that:

[0122] In step S1, neither tin particles nor 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.

[0123] Comparative Example 2

[0124] This example prepares a negative electrode active material, specifically:

[0125] The negative electrode active material made of hard carbon was prepared according to the steps in Experimental Example 4 in CN108439363A.

[0126] Comparative Example 3

[0127] In this example, a negative electrode active material was prepared, specifically referring to the method of Example 1 in patent CN 114551870 A (adjusting the amount of some preparation raw materials). Among them, the carbon source particle source, the mass ratio of carbon source particles and tin used were the same as those in Example 1.

[0128] Application Examples

[0129] This example provides a sodium ion battery, specifically:

[0130] Preparation of diaphragm: Cut the glass fiber diaphragm into discs with a diameter of 16 mm, dry them and use them as diaphragms.

[0131] Prepare 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 of 1:1:1), and stir until the sodium hexafluorophosphate is completely dissolved as the electrolyte for use (electrolyte concentration is 1 M).

[0132] Preparation of working electrode (negative electrode sheet): 0.8g of the negative electrode active material obtained in the embodiment or comparative example, 0.1g of conductive carbon black, and 0.1g of polytetrafluoroethylene are added to 1.5mL of nitrogen methyl pyrrolidone, and fully ground to obtain a uniform slurry; then the slurry is evenly coated on the surface of aluminum foil and vacuum dried. The dried electrode sheet is cut into discs with a diameter of 10mm, and after compaction, it is used as a working electrode for standby use.

[0133] Assembly: In an inert gas-protected glove box, a sodium sheet with a diameter of 12 mm was used as the counter electrode. The counter electrode, diaphragm, and working electrode were stacked and placed in a button-type battery shell in this order. The electrodes and diaphragm were infiltrated with electrolyte, and the button-type battery shell was encapsulated to prepare a sodium-ion battery (half-cell).

[0134] Test Example 1

[0135] This example tests the morphology, crystal state and composition of the negative electrode active materials obtained in the examples and comparative examples. The specific testing methods include SEM, SEM with an EDS accessory and XRD.

[0136] The test results show that in the negative electrode active material obtained in the embodiment of the present invention, carbon and metal are evenly distributed, and 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, and the results showed that there were 16.72wt% tin, 75.76wt% carbon, 4.48wt% nitrogen, and 3.04wt% oxygen; although, from the perspective of quantitative testing, the accuracy of EDS is not very high, it can still show that the components are evenly distributed. At the same time, in the X-ray powder diffraction pattern of the negative electrode active material obtained in the embodiment, there are 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 obviously moves to a lower angle and becomes wider. It shows that its disorder is higher, the cross-linking interaction between carbon layers is stronger, and it is difficult to form crystallization at high temperature. In addition, other characteristic peaks observed correspond to Sn single substance. It can be seen that the hard carbon particle source and organic flocculant added in the example are indeed converted into hard carbon materials during the calcination process, and the active metal particles are also successfully embedded. However, in the XRD spectrum of the negative electrode activity obtained in Comparative Examples 1-2, only obvious hard carbon peaks are shown, and no other characteristic peaks appear. Some test results are shown in Figure 2. Figure 2~3 As the graphs of different embodiments are highly similar, they are not listed one by one in this example.

[0137] Test Example 2

[0138] This example tests the electrochemical performance of the sodium ion battery obtained in the application example, specifically:

[0139] The test method is: at a voltage of 0-2V, the nominal specific capacity is 300mAh / g. Among them, the test rate of reversible specific capacity and coulombic efficiency is 0.1C, which is the test result of the first week after the battery is assembled; the test rate of cycle performance is 0.1C, and the number of cycles when the capacity decays to about 80% of the initial capacity is recorded; the rate performance is: charge and discharge tests are carried out at current densities of 0.1C, 0.2C and 0.5C respectively, and the percentage of 0.5C capacity to 0.1C capacity is calculated.

[0140] Regarding the role 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 obtained negative electrode active material; however, the traditional use of only active metal particles will sacrifice part of the coulombic efficiency and cycle performance. In the negative electrode active material provided by the present invention, due to the fixing effect of the network hard carbon produced by the organic flocculant on the structure and the buffering effect on stress, after synergizing with the active metal particles, it will significantly improve the coulombic efficiency and cycle performance. Specifically, the coulombic efficiency is ≥93%, and the number of cycles to decay to 80% capacity exceeds 2000. The specific test results are shown in Table 9 and Figure 4 shown.

[0141] Table 9 Electrochemical properties of negative electrode active materials obtained in Example 1 and Comparative Examples 1-2 of the present invention

[0142]

[0143] 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 effect on the performance of the resulting negative electrode active material. Among them, when bamboo fiber powder is selected, the capacity, first effect, 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 may be three reasons for the above results. First, the types and amounts of heteroatoms in different hard carbon particle sources are different. During the calcination process, the doping of heteroatoms with 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 looseness, so the degree of infiltration and retention of electrolyte are different. The distribution structure between hard carbon particles and active metal particles may also be affected due to the different pore structures, which ultimately affects the performance of the resulting negative electrode active material. Third, the combination of hard carbon particle sources, active metal particles and organic flocculants is not optimal. It can be expected that by adjusting the parameters or the combination of raw materials, better electrochemical performance can be obtained when other hard carbon particle sources are used. The specific test results are shown in Table 10.

[0144] Table 10 Effect of hard carbon particle source type on the performance of negative electrode active materials

[0145]

[0146] The influence of the type of active metal particles on the obtained negative electrode active material: When the material of the active metal particles is Sn, the comprehensive electrochemical performance of the obtained negative electrode active material is optimal; when other materials are selected, the electrochemical performance decreases to varying degrees. The reasons for this include: first, the alloying degree and process of different active metal particles and sodium are different; second, the synergistic conditions between the preparation raw materials are not met. If the type and amount of other preparation raw materials are adjusted, when the same active metal particle material is used, it is still expected to obtain a negative electrode active material with better performance. The specific results are shown in Table 11.

[0147] Table 11 Effect of active metal particle material on the performance of the obtained negative electrode active material

[0148]

[0149] Effect of the type of organic flocculant on the performance of the negative electrode active material: The results show that the type of organic flocculant has a significant effect on the performance of the obtained negative electrode active material. When polyacrylamide is selected, the electrochemical performance of the obtained negative electrode active material is optimal. The reason is similar to the possible influence of the hard carbon particle source. The specific test results are shown in Table 12.

[0150] Table 12 Effect of organic flocculant types on the performance of negative electrode active materials

[0151]

[0152] Effect of the proportion of active metal particles on negative electrode active materials: The results show that with the increase in the amount of active metal particles, the electrochemical performance of the obtained negative electrode active materials showed a trend of first rising and then falling, and was optimal at around 10% (it does not mean that the point value of 10% is optimal). The reason is that when the amount of active metal particles is small, pure hard carbon cannot provide a higher capacity. When the amount of active metal particles is large, the volume change during the cycle has a negative impact on various performances. The specific test results are shown in Table 13.

[0153] Table 13 Effect of active metal particle ratio on the performance of negative electrode active materials

[0154]

[0155] Effect of particle size of active metal particles on negative electrode active materials: The results show that when the particle size is small, as the particle size of the active metal particles increases, the electrochemical performance of the obtained negative electrode active materials increases first and then decreases. However, when the particle size continues to increase, the relationship between the particle size and the electrochemical performance is no longer obvious. The reason for the above phenomenon is that when the particle size is small, the active metal particles are easily burned during the calcination process and easily oxidized during the transfer and use process, which 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 will affect the electrochemical performance of all parties. The specific test results are shown in Table 14.

[0156] Table 14 Effect of particle size of active metal particles on negative electrode active materials

[0157]

[0158] Effect of organic flocculant ratio on negative electrode active materials: The results show that with the increase in the amount of organic flocculant, the electrochemical performance of the obtained negative electrode active materials showed a trend of first rising and then falling, and the optimal performance range was obtained at about 30%. The reason for the above phenomenon is that when the amount of organic flocculant is small, it cannot wrap and fix the active metal particles and hard carbon particles well, which easily causes the collapse of the structure of the negative electrode active material, so the electrochemical performance is poor; when the amount of organic flocculant is relatively high, the hard carbon particles and active metal particles in the obtained negative electrode active material are difficult to contact with the electrolyte, so the electrochemical performance is not fully exerted. The specific results are shown in Table 15.

[0159] Table 15 Effect of organic flocculant ratio on the performance of negative electrode active materials

[0160]

[0161] Effect of calcination temperature on negative electrode active materials: The results show that calcination temperature has a great influence on the performance of negative electrode active materials. The performance does not change with temperature in a single linear growth relationship. The performance of negative electrode active materials is best at 1200°C. The reasons for the influence of temperature on performance include: temperature affects the size of active metal particles, temperature affects the degree of carbonization, and high temperature may promote the re-fusion of active metal particles, thereby increasing the particle size of active metal particles in negative electrode active materials. The specific test results are shown in Table 16.

[0162] Table 16 Effect of calcination temperature on the performance of the obtained negative electrode active material

[0163]

[0164] Effect of calcination time on the performance of negative electrode active materials: The results show that calcination time also has a great influence on negative electrode active materials. The performance of negative electrode active materials is best when the calcination time is 2h. The calcination time is similar to the calcination temperature, which affects the electrochemical performance of the obtained negative electrode active materials by affecting the thoroughness of carbonization and the doping of heteroatoms. The specific test results are shown in Table 17.

[0165] Table 17 Effect of calcination temperature on the performance of negative electrode active materials

[0166]

[0167] According to the above results, the negative electrode active material prepared by the present invention, in the process of sodium insertion, the micropores in the negative electrode active material are first filled with metallic Na clusters, and then Na + The interlayers of the embedded hard carbon micro-regions are then occupied by defects and other positions that are easy to capture Na+, 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 material, its comprehensive electrochemical properties such as capacity, first efficiency, cycle and rate are significantly improved, and 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 the fields of energy storage, power, 3C, etc.

[0168] 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. Due to the limitation of the 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.

[0169] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without 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 active metal particles are distributed in the network hard carbon and fixed by the network hard carbon; The hard carbon particles can pass through an 800-mesh screen; The particle size of the active metal particles is 10-5000 nm.

2. 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.

3. A method for preparing the negative electrode active material according to claim 1 or 2, 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.

4. The preparation method according to claim 3, characterized in that: In step S1, the mass percentage of the active metal particles in the precursor is 1-50%.

5. The preparation method according to claim 3, 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.

6. The preparation method according to claim 3, 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.

7. The preparation method according to claim 3, characterized in that: In step S2, the calcination temperature is 500-1600° C.; and / or the calcination time is 1-50 hours.

8. 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 claim 1 or 2.

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