Sodium ion battery hard carbon negative electrode material and preparation method and application thereof

Abstract

The application relates to the field of battery material manufacturing, and discloses a sodium ion battery hard carbon negative material and a preparation method and application thereof. The method comprises the following steps: (1) first contacting a plastic component with concentrated H2SO4 to obtain a mixture I; (2) carrying out a first reaction on the mixture I under microwave conditions and / or in the presence of hydrogen peroxide, and filtering and drying to obtain a mixture II; and (3) calcining the mixture II in an inert or reducing atmosphere to obtain a sodium ion battery hard carbon negative material. The method provided by the application is simple, and can convert waste lithium battery separators into valuable sodium ion battery hard carbon negative materials with stable and excellent electrical properties.

Description

Technical Field

[0001] This invention relates to the field of battery material manufacturing, specifically to a hard carbon anode material for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] Under pressure from lithium resource shortages, sodium-ion batteries (SIBs) have developed rapidly in recent years, accelerating their transition from laboratory to mass production. Compared to lithium-ion batteries (LIBs), SIBs have significant advantages in cost and certain performance aspects. For example, sodium resources are abundant, there is a wide selection of elements for cathode materials, and there are abundant sources of precursors for anode materials such as soft and hard carbon. Aluminum foil can be used for the anode current collector to further reduce costs and improve safety. The higher interfacial ion diffusion capacity and ionic conductivity of sodium ions give SIBs excellent rate performance. In addition, SIBs have better adaptability to a wider temperature range than LIBs, especially their low-temperature performance, which is outstanding, with a capacity retention of over 70% at -40℃.

[0003] However, the research and industrialization of cathode materials for SIBs have clearly outpaced those for anode materials. Regarding anode materials, carbon-based materials, especially hard carbon, have become the mainstream in current industrialization due to their abundant raw materials, low sodium storage potential, high specific capacity, and non-toxic and environmentally friendly properties. However, the lagging preparation technology of hard carbon anode materials leads to high prices for high-quality materials. The import price of industry benchmark hard carbon materials used for SIBs (Kuraray, Japan) is as high as approximately 200,000 RMB / ton, while the average price of graphite anode materials used for LIBs is only about 50,000 RMB / ton. Therefore, the high cost of anode materials for SIBs reduces their competitive advantage. Developing low-cost, high-performance hard carbon anode materials has become crucial for the development of the SIB industry.

[0004] Currently, hard carbon anode materials are usually prepared by carbonizing carbon source precursors at high temperatures. The main carbon sources include three categories: biomass (coconut shells, starch, etc.), resins (phenolic resins, etc.) and asphalt.

[0005] However, the large-scale production of high-quality hard carbon using biomass precursors presents a challenge in balancing cost and structural consistency. Resin-based precursors offer high purity and good consistency, but are costly. Asphalt (petroleum asphalt, coal tar)-based precursors are widely available and inexpensive, but their preparation process is complex, generates significant amounts of pollutants, and results in lower product volume.

[0006] Therefore, finding abundant, inexpensive, and consistent carbon source precursors and studying suitable carbonization processes are of great significance for the industrialization of SIBs.

[0007] Waste plastics and recycled lithium battery separators offer significant advantages as carbon source precursors for preparing SIBs carbon anode materials, including abundant sources, good consistency, and high theoretical yield. However, the main components of waste plastics and recycled lithium battery separators, PP and PE, are both "non-carbon-forming polymers." When directly heated, they first melt and then undergo thermal decomposition, gradually breaking down the long carbon chains of the macromolecules and ultimately converting them all into small molecule volatile products. The carbonization rate is almost zero. Therefore, direct carbonization of PP and PE cannot yield solid carbon materials in high yield.

[0008] Furthermore, to improve the thermal stability and mechanical strength of the separator, prevent large-area contact between positive and negative surfaces caused by separator shrinkage, and enhance puncture resistance and safety performance, lithium battery separators undergo coating treatment. Inorganic coatings, primarily composed of boehmite (AlOOH) and alumina, account for approximately 90% of these coatings. While the use of inorganic coatings improves separator performance, it has also become a major obstacle to separator recycling. This is because inorganic coatings are difficult to separate from the separator, and there is currently no direct recycling method. A large number of separators generated from the recycling of retired lithium batteries, especially inorganically coated separators, are primarily incinerated.

[0009] Therefore, in response to the ever-expanding market demand for carbon-based anode materials for sodium-ion batteries and the growing problem of unmanageable waste separator materials generated from retired lithium-ion batteries, a method has been developed that is both economical and engineering-feasible to convert waste plastics containing PP, PE, and other substances and waste lithium-ion battery separators into valuable hard carbon anode materials for sodium-ion batteries. This method is of great significance for achieving high-value utilization of waste and for the green and sustainable development of the new energy industry. Summary of the Invention

[0010] The purpose of this invention is to overcome the problems of high cost of carbon-based anode materials for sodium-ion batteries and difficulty in removing inorganic coating materials from lithium battery recycled separators during the conversion into SIBs anode materials.

[0011] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a hard carbon anode material for sodium-ion batteries, the method comprising the following steps:

[0012] (1) The plastic component is brought into first contact with concentrated H2SO4 to obtain mixture I;

[0013] (2) Mixture I is subjected to a first reaction under microwave conditions and / or in the presence of hydrogen peroxide, and then filtered and dried to obtain mixture II;

[0014] (3) Under an inert or reducing atmosphere, the mixture II is calcined to obtain a hard carbon anode material for sodium-ion batteries;

[0015] The sodium-ion battery hard carbon anode material is used in a process with a density of 0.1 A g. -1 The initial discharge specific capacity is 250-480 mAh g. -1 0.5 A g -1 After 500 cycles, the capacity retention rate is 82-95%;

[0016] The plastic component is composed of waste plastic and recycled lithium battery separator, and the content of the recycled lithium battery separator in the plastic component is 10-100 wt%.

[0017] The second aspect of the present invention provides a sodium-ion battery hard carbon anode material prepared by the method described in the first aspect above.

[0018] The third aspect of this invention provides the application of the sodium-ion battery hard carbon anode material described in the second aspect above in the preparation of sodium-ion batteries.

[0019] Compared with existing technologies, the method provided by this invention has at least the following advantages:

[0020] (1) The method provided by the present invention uses lithium-ion battery recycling membrane with regular molecular structure and low content of inorganic impurity elements as one of the carbon sources, so the hard carbon anode material prepared has high purity and good consistency; sulfuric acid is used as a dehydrogenation crosslinking agent and also acts as a sulfur source, so sulfur element is simultaneously doped in the hard carbon preparation process, which significantly improves the specific capacity and rate performance of the hard carbon anode material.

[0021] (2) The lithium-ion battery waste ceramic coating separator used in the method provided by the present invention is one of the raw materials. The ceramic coating material on the separator can act as a pore-forming agent in the process of hard carbon formation, enriching the pore structure of hard carbon, increasing the internal surface area, providing more active sites for sodium ion storage, and providing channels for electrolyte transport, significantly improving the specific capacity and rate performance of the material.

[0022] (3) The method provided by the present invention has a simple preparation process, fast reaction rate, high carbonization rate, and is easy to industrialize;

[0023] (4) The waste plastics and membranes used in the method provided by the present invention are widely available and low in cost. This solves both the source of precursors for SIBs carbon anode materials and the problem of recycling waste membranes, turning waste into treasure and achieving two goals at once. This is of great significance for both the sustainable use of resources and the protection of the environment. Attached Figure Description

[0024] Figure 1 These are high-resolution transmission images and EDS diagrams of the preferred sodium-ion battery hard carbon anode material provided by this invention.

[0025] Figure 2These are low-resolution and high-resolution transmission images of another preferred sodium-ion battery hard carbon anode material provided by the present invention.

[0026] Figure 3 The first three charge-discharge curves of the preferred sodium-ion battery hard carbon anode material provided by this invention;

[0027] Figure 4 This is the first three charge-discharge curve of another preferred sodium-ion battery hard carbon anode material provided by the present invention;

[0028] Figure 5 This is a rate performance diagram of the preferred sodium-ion battery hard carbon anode material provided by the present invention;

[0029] Figure 6 This is a rate performance diagram of another preferred sodium-ion battery hard carbon anode material provided by the present invention;

[0030] Figure 7 The cyclic voltammetry curves of the preferred sodium-ion battery hard carbon anode material provided by this invention are shown.

[0031] Figure 8 This is the cyclic voltammetry curve of another preferred sodium-ion battery hard carbon anode material provided by the present invention;

[0032] Figure 9 This is the electrochemical impedance curve of the preferred sodium-ion battery hard carbon anode material provided by the present invention before cycling;

[0033] Figure 10 This is the electrochemical impedance curve of another preferred sodium-ion battery hard carbon anode material provided by the present invention before cycling. Detailed Implementation

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] As mentioned above, this invention provides a method for preparing hard carbon anode materials for sodium-ion batteries, the method comprising the following steps:

[0036] (1) The plastic component is brought into first contact with concentrated H2SO4 to obtain mixture I;

[0037] (2) Mixture I is subjected to a first reaction under microwave conditions and / or in the presence of hydrogen peroxide, and then filtered and dried to obtain mixture II;

[0038] (3) Under an inert or reducing atmosphere, the mixture II is calcined to obtain a hard carbon anode material for sodium-ion batteries;

[0039] The sodium-ion battery hard carbon anode material is used in a process with a density of 0.1 A g. -1 The initial discharge specific capacity is 250-480 mAh g. -1 0.5 A g -1 After 500 cycles, the capacity retention rate is 82-95%;

[0040] The plastic component is composed of waste plastic and recycled lithium battery separator, and the content of the recycled lithium battery separator in the plastic component is 10-100 wt%.

[0041] Preferably, the waste plastic is selected from at least one of polyethylene terephthalate plastic, polyethylene plastic, polypropylene plastic, polyacrylonitrile plastic, and polystyrene plastic.

[0042] Preferably, the lithium battery recycling separator is selected from at least one of polypropylene separator, polyethylene separator, polyethylene-polypropylene composite separator, and ceramic-coated composite separator.

[0043] More preferably, the lithium battery recycling separator is a ceramic-coated composite separator. Studies have found that in this preferred configuration, the ceramic coating material acts as a pore-forming template during the hard carbon formation process, resulting in hard carbon with a richer pore structure and a larger internal surface area. This provides more active sites for sodium ion storage and channels for electrolyte transport, thereby improving the material's specific capacity and rate performance.

[0044] Preferably, in step (1), the waste plastic is the product obtained by sequentially crushing, washing, and dehydrating recycled plastic; and

[0045] The average volume diameter of the waste plastic is no greater than 2 mm, and the moisture content is no higher than 3 wt%.

[0046] More preferably, the waste plastic has an average volume diameter of less than 0.5 mm and a moisture content of 0.5-1 wt%.

[0047] Preferably, the method of the present invention further includes, in step (1), first washing the lithium battery recycling membrane with water, then drying it to a moisture content of 0.5-1 wt%, and then crushing it to a size not exceeding 5 cm². 2 The size is then applied to the first contact.

[0048] In a preferred embodiment, in step (1), the weight ratio of the plastic component to the volume ratio of the concentrated H2SO4 is 1:2.5-25.

[0049] More preferably, in step (1), the weight ratio of the plastic component to the volume ratio of the concentrated H2SO4 is 1:3-6.

[0050] It should be noted that, in this invention, the unit of weight of the plasticizing component is g, and the unit of volume of the concentrated H2SO4 is mL.

[0051] In a preferred embodiment, the method of the present invention further includes, in step (2), carrying out a first reaction under microwave conditions, and obtaining mixture II after filtration and drying;

[0052] The conditions for the first reaction must at least be met: microwave power of 500-2500W and time of 30-150s.

[0053] More preferably, in step (2), under microwave conditions, the conditions of the first reaction are at least satisfied as follows: microwave power is 800-1200W and time is 50-80s.

[0054] Preferably, the method of the present invention further includes, in step (2), under microwave conditions, the first reaction is repeated 3-10 times before the drying is performed.

[0055] More preferably, the method of the present invention further includes, in step (2), under microwave conditions, repeating the first reaction 6-9 times before performing the drying. Studies have found that this preferred condition is more conducive to improving the crosslinking degree of waste plastics, increasing the carbonization rate and the yield of hard carbon anode materials, while obtaining a suitable amount of S doping.

[0056] Preferably, in step (2), the first reaction is carried out in a microwave-heated vertical tube solid-liquid reactor.

[0057] In a preferred embodiment, the method of the present invention further includes, in step (2), the first reaction is carried out in the presence of hydrogen peroxide, and after filtration and drying, mixture II is obtained;

[0058] The volume ratio of hydrogen peroxide to concentrated H2SO4 is 1:2-10.

[0059] More preferably, in step (2), the first reaction is carried out in the presence of hydrogen peroxide, and the volume ratio of hydrogen peroxide to concentrated H2SO4 is 1:5-8. Studies have found that under this preferred condition, the carbon formation rate of the prepared sodium-ion battery hard carbon anode material can be improved, which is more conducive to the industrial application of the method of the present invention.

[0060] Preferably, the concentration of hydrogen peroxide is 20-30 wt%.

[0061] In a preferred embodiment, the first reaction is carried out in the presence of hydrogen peroxide, and the conditions for the first reaction are at least: temperature not exceeding 80°C and time of 3-6 minutes. Studies have found that under this preferred embodiment, the hard carbon anode material has a larger internal surface area and a suitable pore structure, while simultaneously improving the carbonization rate of waste plastics, reducing preparation costs, and making it more conducive to the industrial application of the method of this invention.

[0062] In a preferred embodiment, the method of the present invention further includes, in step (2), before the drying, cooling the product of the first reaction to 25-60°C and then performing vacuum filtration and washing until the pH of the washing water is 6-8, and then drying the filter cake.

[0063] Preferably, the method of the present invention further includes, in step (3), before calcination, raising the temperature at a rate of 5°C / min and then performing the calcination.

[0064] According to a preferred embodiment, in step (3), the calcination conditions must at least satisfy: a temperature of 800-1800℃ and a time of 2-24h.

[0065] More preferably, in step (3), the calcination conditions must at least satisfy: a temperature of 1300-1500℃ and a time of 8-10h. Studies have found that this preferred condition is more conducive to controlling the pore structure of the hard carbon anode material for sodium-ion batteries.

[0066] Preferably, in step (3), the calcination is carried out under an argon atmosphere.

[0067] Preferably, in step (3), the calcination is carried out in a high-temperature tubular rotary furnace.

[0068] Preferably, in step (1), the concentration of the concentrated H2SO4 is 95-98 wt%.

[0069] As previously stated, the second aspect of the present invention provides a sodium-ion battery hard carbon anode material prepared by the method described in the first aspect.

[0070] As previously stated, the third aspect of this invention provides the application of the sodium-ion battery hard carbon anode material described in the second aspect above in the preparation of sodium-ion batteries.

[0071] The present invention will be described in detail below through examples. Unless otherwise specified, the raw materials used are all commercially available products.

[0072] Waste plastics:

[0073] Waste Plastic I: This is the product obtained by sequentially cutting, washing, and dehydrating recycled polypropylene (PP) plastic; its dimensions are 10*1*0.2mm, and its moisture content is 1wt%.

[0074] Lithium battery recycling separator: It is a ceramic-coated composite separator with polypropylene as the substrate;

[0075] Plasticizing components:

[0076] Plastic component I: Wash 2g of the recycled lithium battery separator with deionized water, then dry it until the moisture content is less than 1wt%, cut it to a size of 2.5*2.5cm, and then mix it with waste plastic I at a weight ratio of 1:0.2;

[0077] Concentrated H2SO4: concentration is 98 wt%.

[0078] Example 1:

[0079] This embodiment illustrates that the method for preparing hard carbon anode material for sodium-ion batteries provided by the present invention is carried out according to the following steps:

[0080] (1) First, wash 2g of lithium battery recycled separator with deionized water, then dry it until the water content is less than 1wt%, cut it to a size of 2.5*2.5cm, and then add it to 50mL of concentrated H2SO4 for the first contact to obtain mixture I;

[0081] (2) In a microwave-heated vertical tube solid-liquid reactor with a microwave power of 800W, the mixture I was subjected to a first reaction for 60s under microwave conditions, and the first reaction was repeated 3 times. After cooling to 25°C, it was diluted with 300mL of distilled water, and then filtered and washed until the pH of the washing water was 7.0. The filter cake was then dried to obtain mixture II.

[0082] (3) In a high-temperature tubular rotary furnace under an argon atmosphere, the mixture II was heated at a rate of 5°C / min and then calcined at a temperature of 1300°C for 5 hours to obtain a sodium-ion battery hard carbon anode material named HC3-1300-5.

[0083] Example 2:

[0084] This embodiment uses a method similar to that of Embodiment 1, except that in step (3), the calcination time is 8 hours;

[0085] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HC3-1300-8.

[0086] Example 3:

[0087] This embodiment uses a method similar to that of Embodiment 1, except that in step (3), the calcination time is 10 hours.

[0088] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HC3-1300-10.

[0089] Example 4:

[0090] This embodiment uses a method similar to that of Example 1, except that in step (2), the first reaction is repeated 5 times, and in step (3), the calcination time is 8 hours.

[0091] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HC5-1300-8.

[0092] Example 5:

[0093] This embodiment uses a method similar to that of Embodiment 1, except that in step (3), the calcination temperature is 1500℃ and the time is 8h;

[0094] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HC3-1500-8.

[0095] Example 6:

[0096] This embodiment uses a method similar to that of Embodiment 1, except that step (2) is different, specifically including:

[0097] (2) Under the stirring conditions of 120 rpm and the temperature controlled below 80°C, 5 mL of hydrogen peroxide (concentration of 30 wt%) was added dropwise to mixture I for the first reaction for 3 min. After cooling to 25°C, it was diluted with 300 mL of distilled water, and then filtered and washed until the pH of the washing water was 7.0. The filter cake was then dried at 120°C for 2 h to obtain mixture II.

[0098] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HCPP1300-5.

[0099] Example 7:

[0100] This embodiment uses a method similar to that of Embodiment 6, except that in step (3), the calcination time is 3 hours;

[0101] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HCPP1300-3.

[0102] Example 8:

[0103] This embodiment uses a method similar to that of Embodiment 6, except that in step (3), the calcination time is 8 hours;

[0104] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HCPP1300-8.

[0105] Example 9:

[0106] This embodiment uses a method similar to that of Example 1, except that in step (1), an equal weight (2g) of plastic component I is used to replace the lithium battery recycling membrane and make the first contact with concentrated H2SO4 to obtain mixture I;

[0107] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named HH3-1300-5.

[0108] Comparative Example 1:

[0109] This comparative example was conducted using a method similar to that of Example 1, except that the microwave conditions for the first reaction in step (2) were replaced with hydrothermal conditions, specifically including:

[0110] (2) Place the mixture I obtained in step (1) into a hydrothermal reactor lined with polytetrafluoroethylene, heat the hydrothermal reactor in an oven at 160°C for 4 hours, cool it to 25°C and dilute it with 300 mL of distilled water, then filter and wash it until the pH of the washing water is 7.0, and then dry the filter cake to obtain mixture II.

[0111] Ultimately, a hard carbon anode material for sodium-ion batteries was obtained and named DP1.

[0112] Comparative Example 2:

[0113] This comparative example uses the existing technology (G. Lee, M. Eui Lee, Sung-Soo Kim et al. Efficient upcycling of polypropylene-based waste disposable masks into hardcarbons for anodes in sodium ion batteries[J]. Journal of Industrial and Engineering Chemistry, 105(2022)268-277) to prepare hard carbon anode materials for sodium-ion batteries. The difference is that the material used is the lithium battery recycled separator from Example 1, specifically including:

[0114] S1. Immerse 4g of lithium battery recycled separator in 40 mL of concentrated H2SO4 and react continuously at 120℃ for 4h to obtain intermediate product I.

[0115] S2. After cooling intermediate product I to 25°C, dilute it with 300 mL of distilled water, then filter and wash it until the pH of the washing water is 7.0. Dry the filter cake under vacuum at 80°C for 12 h; then grind it with a planetary ball mill for 12 h to obtain powder.

[0116] S3. Load the powder into a graphite boat and heat it to 1600°C at a heating rate of 5°C / min under an argon atmosphere, then stop heating.

[0117] The resulting hard carbon anode material for sodium-ion batteries was named DP2.

[0118] Test Example 1

[0119] Electrochemical performance tests were performed on the sodium-ion battery hard carbon anode materials prepared in the above examples, including:

[0120] The prepared sodium-ion battery hard carbon anode material, polyvinylidene fluoride (PVDF), and conductive carbon black (SP) were mixed in a mass ratio of 8:1:1 and added to N-methylpyrrolidone and stirred into a slurry. The slurry was coated on copper foil, dried under vacuum at 100°C for 12 h, and then transferred to an anhydrous and oxygen-free glove box. Using a sodium metal sheet as a reference electrode, glass fiber as a separator, and NP-035 as an electrolyte, a 2032 coin cell was assembled, and its electrochemical performance was tested. The results are shown in Table 1 and Figure 1.

[0121] Figure 1 High-resolution transmission images of HC3-1300-5, HC3-1300-8, HC3-1300-10, HC5-1300-8 and HC3-1500-8 are shown. Figure 1 (a)-(e)) and EDS plots of HC3-1300-8 ( Figure 1 (f));

[0122] Figure 2 Low-resolution transmission images of HCPP1300-3, HCPP1300-5, and HCPP1300-8 are shown. Figure 2 (a)-(c)) and high-resolution transmission images ( Figure 2 (d)-(f));

[0123] As can be seen from the figure, the sodium-ion battery hard carbon anode material provided by the present invention has a disordered layered turbine graphite structure, without clear lattice stripes, and exhibits obvious hard carbon characteristics.

[0124] Except for DP1 and DP2, the charge-discharge cycle curves of the sodium-ion battery hard carbon anode materials prepared in the embodiments of the present invention all show a charge-discharge plateau below 0.1 V, indicating that the sodium-ion battery hard carbon anode material prepared by the improved method of the present invention has a hard carbon structure.

[0125] Table 1:

[0126] Initial discharge specific capacity at 0.1 A g⁻¹ / mAh g⁻¹ Capacity retention after 500 cycles at 0.5 A g⁻¹ HC3-1300-5 270 92% HC3-1300-8 289 95% HC3-1300-10 265 91% HC5-1300-8 275 93% HC3-1500-8 258 92% HCPP1300-5 260 92% HCPP1300-3 233 88% HCPP1300-8 250 90% HH3-1300-5 348 94% DP1 220 82% DP2 225 84%

[0127] Figure 3 The results show that HC3-1300-5, HC3-1300-8, HC3-1300-10, HC5-1300-8, and HC3-1500-8 are present at 0.1 A g. -1 The first three charge / discharge curves below;

[0128] Figure 4 The results show that HCPP1300-3, HCPP1300-5, and HCPP1300-8 are present at 0.1 A g. -1 The first three charge / discharge curves below;

[0129] from Figure 3 and Figure 4 As can be seen, the hard carbon anode material for sodium-ion batteries exhibits varying degrees of capacity decay after the first charge-discharge cycle. This is because during the first charge-discharge cycle (1st), some sodium ions are used to form the SEI film, resulting in an irreversible decrease in capacity. The specific capacity changes in the second (2nd) and third (3rd) charge-discharge cycles are relatively small, indicating that the formed SEI film is relatively stable. Furthermore, the charge-discharge curves after the second cycle show almost identical specific capacities, indicating that the sodium ion insertion and extraction amounts are nearly consistent each time. This means that the hard carbon anode material for sodium-ion batteries provided by this invention has a coulombic efficiency of nearly 100%.

[0130] In addition, from Figure 3 It can also be seen that the sodium-ion battery hard carbon anode material provided by this invention has obvious plateau regions and slope regions. The plateau region is conducive to the insertion-deposition of sodium ions, while the slope region can increase the adsorption of sodium ions on the material surface.

[0131] Figure 5 The rate performance diagrams for HC3-1300-5, HC3-1300-8, HC3-1300-10, HC5-1300-8 and HC3-1500-8 are shown.

[0132] Figure 6 The rate performance diagrams for HCPP1300-3, HCPP1300-5, and HCPP1300-8 are shown.

[0133] from Figure 5 and 6 As can be seen, the hard carbon anode material for sodium-ion batteries provided by this invention exhibits excellent rate performance. (2 A g) -1 Even at high current densities, the specific capacity can still reach 200 mAh g. -1 This is closely related to the pore-forming effect of the ceramic material in the diaphragm.

[0134] The inventors discovered that the relationship between calcination temperature, calcination time, microwave cycles, and the electrochemical performance of the prepared sodium-ion battery hard carbon anode material is complex:

[0135] Reducing the number of microwave cycles can improve the adsorption capacity of the material; appropriately extending the calcination time or increasing the calcination temperature is beneficial to improving the stability of the material, but it will lead to a decrease in its specific capacity; suitable calcination temperature, calcination time, and number of microwave cycles are more conducive to improving the specific capacity of the material at different ratios.

[0136] Figure 7 The results show that HC3-1300-5, HC3-1300-8, HC3-1300-10, HC5-1300-8 and HC3-1500-8 are at 0.5 mV s. -1 0.8 mV s -1 1 mV s -1 2 mV s -1 and 5 mV s -1 Cyclic voltammetry curves;

[0137] Figure 8 The results show that HCPP1300-3, HCPP1300-5, and HCPP1300-8 are at 0.5 mV s. -1 0.8 mV s -1 1 mVs -1 2 mV s -1 and 5 mV s -1 Cyclic voltammetry curves;

[0138] from Figure 7 and Figure 8 As can be seen from the data, the redox peaks of the sodium-ion battery hard carbon anode material provided by this invention are almost symmetrical, indicating that the polarization phenomenon of the material is weak, and also indicating that the material has good reversibility.

[0139] Figure 9 Electrochemical impedance spectroscopy curves of HC3-1300-5, HC3-1300-8, HC3-1300-10, HC5-1300-8 and HC3-1500-8 before cycling are shown. Figure 10The electrochemical impedance spectroscopy curves of HCPP1300-3, HCPP1300-5, and HCPP1300-8 before cycling are shown, and the corresponding equivalent circuit diagrams are as follows: The fitting data are shown in Table 2. As can be seen from the figure, the electrochemical impedance of the materials consists of a semicircle in the high-frequency region and a sloping line in the low-frequency region. Among them, the semicircle of HC3-1300-8 is smaller, indicating that its charge transfer impedance is smaller and more conducive to charge transfer. Furthermore, the slope of the sloping line in the low-frequency region is larger, indicating that the hard carbon anode material of the sodium-ion battery of the present invention has low Warbug impedance and high sodium ion diffusion coefficient.

[0140] Table 2:

[0141] HC3-1300-5 HC3-1300-8 HC3-1300-10 HC5-1300-8 HC3-1500-8 Rct 3.51 1.51 4.13 13.2 2.11 HCPP1300-3 HCPP1300-5 HCPP1300-8 Rct 4.05 1.51 3.11

[0142] The results above show that the method provided by this invention is simple and easy to operate, and can convert waste lithium battery separators into valuable, electrically stable and excellent sodium-ion battery hard carbon anode materials, which has broad practical application value.

[0143] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing hard carbon anode material for sodium-ion batteries, characterized in that, The method includes the following steps: (1) The plastic component is brought into first contact with concentrated H2SO4 to obtain mixture I; (2) Mixture I is subjected to a first reaction under microwave conditions and / or in the presence of hydrogen peroxide, and then filtered and dried to obtain mixture II; (3) Under an inert or reducing atmosphere, the mixture II is calcined to obtain a hard carbon anode material for sodium-ion batteries; The sodium-ion battery hard carbon anode material is used in a process with a density of 0.1 A g. -1 The initial discharge specific capacity is 250-480 mAh g. -1 0.5A g -1 After 500 cycles, the capacity retention rate is 82-95%; The plastic-containing component is composed of waste plastics and recycled lithium battery separators, wherein the content of the recycled lithium battery separator in the plastic-containing component is 10-100 wt%, the waste plastics are selected from at least one of polyethylene terephthalate plastics, polyethylene plastics, polypropylene plastics, polyacrylonitrile plastics, and polystyrene plastics, and the recycled lithium battery separators are selected from at least one of polypropylene separators, polyethylene separators, polyethylene-polypropylene composite separators, and ceramic-coated composite separators.

2. The method according to claim 1, characterized in that, In step (1), the waste plastic is the product obtained by sequentially crushing, washing, and dehydrating recycled plastic; and The average volume diameter of the waste plastic is no greater than 2 mm, and the moisture content is no higher than 3 wt%.

3. The method according to claim 1, characterized in that, In step (1), the weight ratio of the plastic component to the volume ratio of the concentrated H2SO4 is 1:2.5-25.

4. The method according to claim 1, characterized in that, The method further includes, in step (2), carrying out a first reaction under microwave conditions, and obtaining mixture II after filtration and drying; The conditions for the first reaction must at least be met: microwave power of 500-2500W and time of 30-150s.

5. The method according to claim 4, characterized in that, The method further includes, in step (2), under microwave conditions, repeating the first reaction 3-10 times before performing the drying.

6. The method according to claim 1, characterized in that, The method further includes, in step (2), the first reaction is carried out in the presence of hydrogen peroxide, and after filtration and drying, mixture II is obtained; The volume ratio of hydrogen peroxide to concentrated H2SO4 is 1:2-10.

7. The method according to claim 6, characterized in that, The conditions for the first reaction must at least be met: the temperature is not higher than 80℃ and the time is 3-6 min.

8. The method according to claim 1, characterized in that, In step (3), the calcination conditions must at least meet the following requirements: temperature of 800-1800℃ and time of 2-24h.

9. The sodium-ion battery hard carbon anode material prepared by the method according to any one of claims 1-8.

10. The application of the sodium-ion battery hard carbon anode material according to claim 9 in the preparation of sodium-ion batteries.

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