Preparation method and application of PET (Polyethylene Terephthalate)-based hard carbon negative electrode material of sodium-ion battery

Abstract

The invention discloses a preparation method and application of a polyethylene glycol terephthalate (PET)-based hard carbon negative electrode material of a sodium ion battery. The method comprises the following steps: taking waste PET as a raw material, performing a pretreatment process, and drying to obtain a precursor; and physically mixing the precursor with an additive, and carrying out low-temperature and high-temperature carbonization treatment to obtain the PET-based hard carbon material. The method is simple in technological process and low in raw material cost, and meets the requirements of large-scale industrial production. The obtained sodium-ion battery hard carbon negative electrode material has excellent reversible specific capacity when being applied to a sodium-ion battery, and has certain competitive advantages and good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion batteries and relates to a preparation method and application of a polyethylene terephthalate (PET)-based hard carbon negative electrode material for a sodium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic products and new energy vehicles due to their high energy density and long cycle life. However, due to the limited lithium resources, the cost of lithium-ion batteries is relatively high. At the same time, the increasing consumption of lithium resources will lead to the risk of lithium resource depletion. Therefore, finding alternatives to lithium-ion batteries or backup energy storage technologies has become a current research hotspot. Among energy storage devices other than lithium-ion batteries, sodium-ion batteries have the advantages of low cost, high reserves of raw materials, high safety, and similar working principles to lithium-ion batteries, making them a research hotspot.

[0003] Among the negative electrode materials of sodium ion batteries, hard carbon materials in carbon-based materials have become the main materials for commercial negative electrodes due to their advantages such as wide sources of precursors, low volume expansion, high reversible capacity, and simple preparation process. At present, the types of commercial hard carbon mainly include biomass-based hard carbon and resin-based hard carbon. Biomass-based materials have low cost, abundant sources and are renewable, but biomass hard carbon has a lot of ash, and the pre- and post-processing processes are complicated. In addition, due to the different types and sources of biomass materials, the structure of the obtained hard carbon materials is unstable and there are large differences in performance. Although the hard carbon prepared with resin-based materials as precursors has good performance, the resin preparation process is complicated, requiring multi-step organic synthesis processes, and the cost is high, which is not conducive to commercial application. At present, polymer plastics represented by PET occupy the primary position for beverage packaging bottles. Due to its non-biodegradable characteristics, a large number of discarded PET packaging bottles accumulate in the environment after use. At present, the main treatment methods for discarded PET are incineration and landfill, which has caused serious environmental problems. Therefore, it is of great significance to recycle waste PET and improve the economic value of its recycled materials. PET is a thermoplastic polyester resin with a carbon content of 61.92%, and is an effective precursor for preparing carbon materials. Based on this, it is necessary to provide a method for preparing PET-based hard carbon materials, which is simple, low-cost, and can enable the obtained hard carbon materials to have high reversible specific capacity and cycle stability in sodium ion batteries.

[0004] The Chinese patent application with application number 202311725591.4 discloses a method for preparing hard carbon materials using PET plastics and the application of hard carbon materials; the method comprises the following steps: subjecting the PET plastics to a first heat treatment (200-350°C, 1-8h, heating rate of 1-10°C / min) to obtain homogenized PET plastics; subjecting the homogenized PET plastics to a carbonization treatment (350-600°C, 1-8h, heating rate of 1-10°C / min) to obtain a hard carbon precursor; subjecting the hard carbon precursor to a second heat treatment (600-1800°C, 1-8h, heating rate of 1-10°C / min) to obtain a hard carbon material. This technical solution can make full use of waste PET plastics, realize the recycling and reuse of resources, and the obtained hard carbon material has excellent physical and chemical properties. However, the heat treatment process includes three steps, namely the first heat treatment, carbonization treatment and the second heat treatment. The heat treatment process is relatively complicated, which greatly increases the production energy consumption. In addition, the capacity of the prepared hard carbon material used in sodium ion batteries only gives the initial charge and discharge capacity, and its long-term cycle stability and rate performance are still unclear. On the other hand, the existing heat treatment process is difficult to regulate the microstructure of the obtained hard carbon material, and the microstructure of the hard carbon material, especially the closed-pore structure, will have an important impact on the sodium storage capacity.

[0005] The present invention adds a suitable proportion of zinc-containing pore-forming agent and directly heats in one step, which not only simplifies the heat treatment process and reduces energy consumption, but also effectively improves the structure of the hard carbon material by introducing the zinc-containing pore-forming agent: the zinc oxide produced during the pyrolysis process has a catalytic carbonization effect, and the zinc oxide containing Lewis acid sites can catalyze the dehydration and decarboxylation reactions of PET, which is conducive to the occurrence of cross-linking reactions. When the carbonization temperature rises, some open pores gradually close as the carbon layer grows, constructing many closed-pore structures that can store sodium, so that the obtained sodium ion battery hard carbon negative electrode material has more excellent performance. Summary of the invention

[0006] The present invention aims to provide a method for preparing a high-capacity hard carbon negative electrode material for a sodium ion battery. Polyethylene terephthalate (PET) is used as a precursor material, and a high-capacity hard carbon negative electrode material for a sodium ion battery is obtained by high-temperature carbonization with an additive. The method has the advantages of low cost and simple process, and is easy to achieve large-scale production. The reversible specific capacity of the negative electrode material for a sodium ion battery reaches 300.28 mAh / g to 616.42 mAh / g.

[0007] In order to achieve the above invention object, the present invention adopts the following technical solution:

[0008] <First aspect>

[0009] The present invention provides a method for preparing a polyethylene terephthalate-based sodium ion battery hard carbon negative electrode material, the method comprising the following steps:

[0010] Pre-treating polyethylene terephthalate to obtain a precursor material;

[0011] The precursor material and the additive are ball-milled and mixed in a certain proportion to obtain a mixed material;

[0012] The mixed material is carbonized in a protective environment to obtain a hard carbon negative electrode material for a sodium ion battery.

[0013] As an embodiment of the present invention, the pretreatment is pulverization, ultrasonic washing with an alcohol solution, water washing, and drying.

[0014] As an embodiment of the present invention, the polyethylene terephthalate is a sheet sample cut from a commercially available mineral water bottle, and the size is a fragment with a side length of 2 to 10 mm.

[0015] As an embodiment of the present invention, the additive is one or more of zinc oxide, zinc gluconate and zinc acetate.

[0016] As an embodiment of the present invention, the mass ratio of PET to the additive is 8 to 150:1.

[0017] As an embodiment of the present invention, in the pretreatment method, the alcohol solution is one of ethanol and isopropanol.

[0018] As an embodiment of the present invention, in the ultrasonic treatment, the ultrasonic frequency is 53 kHz and the ultrasonic time is 10 to 30 minutes.

[0019] As an embodiment of the present invention, the drying temperature of the drying treatment is 80-100° C., and the drying time is 5-8 hours.

[0020] As an embodiment of the present invention, during the ball milling mixing process, the ball milling speed is 100 to 300 r / min.

[0021] As an embodiment of the present invention, during the ball milling mixing process, the ball milling time is 20 to 60 minutes.

[0022] As an embodiment of the present invention, during the carbonization process, the protective gas is one of nitrogen and argon.

[0023] As an embodiment of the present invention, the obtained carbonized product is ground and sieved, and the sieve size is 100-500 meshes.

[0024] As an embodiment of the present invention, the carbonization treatment method is to first perform low-temperature carbonization (using a tubular furnace for heating), and then perform high-temperature carbonization after keeping the temperature for a certain period of time.

[0025] As an embodiment of the present invention, the low-temperature carbonization temperature is 500-700°C.

[0026] As an embodiment of the present invention, during the low-temperature carbonization process, the heating rate is 2-10°C / min.

[0027] As an embodiment of the present invention, during the low-temperature carbonization process, the heat preservation time is 30 to 60 minutes.

[0028] As an embodiment of the present invention, the high temperature carbonization temperature is 1400-1600°C.

[0029] As an embodiment of the present invention, during the high temperature carbonization process, the heating rate is 2-10° C. / min.

[0030] As an embodiment of the present invention, during the high-temperature carbonization process, the heat preservation time is 30 to 60 minutes.

[0031] <Second Aspect>

[0032] The present invention also provides a sodium ion battery hard carbon negative electrode material prepared by the above method.

[0033] As an embodiment of the present invention, the interlayer distance of the hard carbon negative electrode material is 0.373nm to 0.392nm.

[0034] The present invention provides the structure and performance parameters of the hard carbon negative electrode material for a sodium ion battery. The particle size of the hard carbon negative electrode material is about 50 μm.

[0035] <Third Aspect>

[0036] The present invention also provides an application of the sodium ion battery hard carbon negative electrode material prepared by the aforementioned method in preparing a negative electrode for a sodium ion battery.

[0037] Compared with the prior art, the sodium ion battery hard carbon negative electrode material of the present invention has the following advantages:

[0038] 1) The present invention uses polyethylene terephthalate as a raw material, especially waste polyethylene terephthalate plastic bottles as a raw material, which can effectively solve the problem of plastic bottle recycling and convert them into high value-added sodium ion battery hard carbon negative electrode materials. The raw material is easy to obtain, the production cost is low, and it is easy to achieve large-scale production.

[0039] 2) The additive used in the present invention is zinc oxide, zinc gluconate or zinc acetate, which plays a role in promoting the pyrolysis of raw materials, the formation of hard carbon and pore formation during the reaction process. It is converted into metallic zinc in the high-temperature carbonization stage. Zinc has a relatively low sublimation temperature (906°C). Therefore, in the high-temperature carbonization stage, zinc diffuses out of the hard carbon in the form of gas to obtain hard carbon materials. No post-treatment process of pickling is required, which simplifies the process flow and reduces production costs. Compared with other hard carbon preparation methods, it avoids the generation of waste pollutants and is beneficial to environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0041] Figure 1 XRD spectra of samples ZHC and GHC obtained in Examples 1 to 6;

[0042] Figure 2 The SEM photos of the samples ZHC obtained in Examples 1 to 3;

[0043] Figure 3 The constant current charge and discharge curves of the first cycle of the sample ZHC obtained in Examples 1 to 3;

[0044] Figure 4 The long cycle curve and rate curve of sample ZHC5-14 (100:1) obtained in Example 2;

[0045] Figure 5 The constant current charge and discharge curves of the first cycle of the samples GHC obtained in Examples 4 to 7;

[0046] Figure 6 This is the first cycle constant current charge and discharge curve of sample AHC7-14 (12:1) obtained in Example 8. DETAILED DESCRIPTION

[0047] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0048] Example 1

[0049] The present embodiment provides a method for preparing a PET-based hard carbon negative electrode material for a sodium ion battery, comprising the following steps:

[0050] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 10 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 80° C. for 5 h;

[0051] (2) Weighing the dried polyethylene terephthalate precursor and zinc oxide in a mass ratio of 30:1, placing them in a ball mill and mixing them for 60 minutes at a rotation speed of 100 r / min to obtain a mixed material;

[0052] (3) The mixed material obtained in (2) is placed in a tube furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 500°C, the heating rate is 2°C / min, and the holding time is 30min; then the high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1400°C, the heating rate is 2°C / min, and the holding time is 30min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, which is marked as ZHC5-14 (30:1).

[0053] The prepared sodium ion battery hard carbon negative electrode material is mixed with a conductive agent and a binder in a mass ratio of 8:1:1, wherein the conductive agent is Super P and the binder is PVDF (polyvinylidene fluoride). A certain amount of NMP (N-methylpyrrolidone, analytical grade, content>99%) is added, and the mass of PVDF accounts for 3% of the mass of NMP. A slurry mixer is used to mix the mixture to prepare a mixed slurry, which is evenly coated on a copper foil, dried overnight at 120°C in a vacuum oven, and cut into hard carbon negative electrode sheets for sodium ion batteries with a diameter of 12 mm.

[0054] The sodium ion half-cell was assembled in a glove box, and the oxygen value and water value of the glove box were required to be <0.01ppm and <0.01ppm, respectively. Metallic sodium was used as the counter electrode, GF / C (Whatman) was used as the diaphragm, 1M NaPF6+EC:DEC:EMC (1:1:1) was used as the electrolyte, and the battery shell was CR2025 battery shell. The half-cell was assembled in the order of [positive electrode shell / hard carbon electrode sheet / diaphragm / electrolyte / sodium sheet / gasket / shrapnel / negative electrode shell], sealed with a battery sealer and removed from the glove box for 12 hours.

[0055] The stationary battery was subjected to constant current charge and discharge test, and the test instrument was CT4008 Shenzhen Xinwei Battery Tester. The specific test method was: the test current density was 20mA / g, and the voltage range was 0.01~2.5V. The test obtained the reversible specific capacity (unit: mAh / g) of the hard carbon negative electrode material of the sodium ion battery.

[0056] Figure 1Figure a is the XRD spectrum of sample ZHC5-14 (30:1) obtained in Example 1. Through data analysis and processing, the carbon layer spacing of the sample is 0.392 nm.

[0057] Figure 2 Figures a and b are SEM photos of the sample ZHC5-14 (30:1) obtained in Example 1. It can be seen that there are a large number of pore structures on the surface of the sample, which is attributed to the role of zinc oxide in forming pores during the carbonization process.

[0058] Figure 3 This is the first cycle constant current charge-discharge curve of the sample ZHC5-14 (30:1) obtained in Example 1. The sample has a reversible specific capacity of 321.96 mAh / g at a current density of 20 mA / g.

[0059] Example 2

[0060] The present embodiment provides a method for preparing a PET-based hard carbon negative electrode material for a sodium ion battery, comprising the following steps:

[0061] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 10 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 80° C. for 5 h;

[0062] (2) Weighing the dried polyethylene terephthalate precursor and zinc oxide in a mass ratio of 100:1, placing them in a ball mill and mixing them for 60 minutes at a rotation speed of 100 r / min to obtain a mixed material;

[0063] (3) The mixed material obtained in (2) is placed in a tube furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 500°C, the heating rate is 2°C / min, and the holding time is 30min; then the high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1400°C, the heating rate is 2°C / min, and the holding time is 30min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, which is marked as ZHC5-14 (100:1).

[0064] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0065] Figure 1 Figure a is the XRD spectrum of sample ZHC5-14 (100:1) obtained in Example 2. Through data analysis and processing, the carbon layer spacing of the sample is 0.386 nm.

[0066] Figure 2 Figures c and d are SEM photos of sample ZHC5-14 (100:1) obtained in Example 2. Compared with ZHC5-14 (30:1), as the amount of zinc oxide decreases, the number of surface open pore structures decreases significantly, but the performance is greatly improved, indicating that the open pore structure is not the factor that causes the high battery capacity.

[0067] Figure 3 This is the first cycle constant current charge-discharge curve of sample ZHC5-14 (100:1) obtained in Example 2. The sample has a reversible specific capacity of 616.42 mAh / g at a current density of 20 mA / g.

[0068] Figure 4 Figures a and b are respectively the long cycle curve and rate curve of the sample ZHC5-14 (100:1) obtained in Example 2. It can be seen that the sample has no obvious capacity decay after 40 cycles at a current density of 20 mA / g, and the capacity retention rate is 93.42%, with good stability. It still has a reversible specific capacity of more than 300 mAh / g at a current density of 100 mA / g, and after charging and discharging at different current densities, it can recover to a capacity of about 600 mAh / g, indicating that its rate performance is good.

[0069] Example 3

[0070] The present embodiment provides a method for preparing a PET-based hard carbon negative electrode material for a sodium ion battery, comprising the following steps:

[0071] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 10 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 80° C. for 5 h;

[0072] (2) Weighing the dried polyethylene terephthalate precursor and zinc oxide at a mass ratio of 150:1, placing them in a ball mill and mixing them for 60 minutes at a rotation speed of 100 r / min to obtain a mixed material;

[0073] (3) The mixed material obtained in (2) is placed in a tube furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 500°C, the heating rate is 2°C / min, and the holding time is 30min; then the high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1400°C, the heating rate is 2°C / min, and the holding time is 30min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, which is marked as ZHC5-14 (150:1).

[0074] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0075] Figure 1 Figure a is the XRD spectrum of sample ZHC5-14 (150:1) obtained in Example 3. Through data analysis and processing, the carbon layer spacing of the sample is 0.388 nm.

[0076] Figure 2 Figures e and f are SEM photos of sample ZHC5-14 (150:1) obtained in Example 3. Compared with the samples in Examples 1 and 2, the sample surface is smoother and the number of openings is reduced.

[0077] Figure 3 This is the first cycle constant current charge-discharge curve of sample ZHC5-14 (150:1) obtained in Example 3. The sample has a reversible specific capacity of 333.11 mAh / g at a current density of 20 mA / g.

[0078] Example 4

[0079] A method for preparing a hard carbon negative electrode material for a sodium ion battery provided in this embodiment comprises the following steps:

[0080] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 20 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 90° C. for 6 h;

[0081] (2) Weighing the dried polyethylene terephthalate precursor and zinc gluconate in a mass ratio of 8:1, placing them in a ball mill and mixing them for 40 minutes at a speed of 200 r / min to obtain a mixed material;

[0082] (3) The mixed material obtained in (2) is placed in a tubular furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 600°C, the heating rate is 5°C / min, and the insulation time is 40min; then high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1400°C, the heating rate is 5°C / min, and the insulation time is 40min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, which is labeled GHC6-14 (8:1).

[0083] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0084] Figure 1 Figure b is the XRD spectrum of sample GHC6-14 (8:1) obtained in Example 4. Through data analysis and processing, the carbon layer spacing of the sample is 0.379 nm.

[0085] Figure 5 This is the first cycle constant current charge-discharge curve of the sample GHC6-14 (8:1) obtained in Example 4. The sample has a reversible specific capacity of 323.77 mAh / g at a current density of 20 mA / g.

[0086] Example 5

[0087] The present embodiment provides a method for preparing a PET-based hard carbon negative electrode material for a sodium ion battery, comprising the following steps:

[0088] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 20 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 90° C. for 6 h;

[0089] (2) Weighing the dried polyethylene terephthalate precursor and zinc gluconate in a mass ratio of 16:1, placing them in a ball mill and mixing them for 40 minutes at a speed of 200 r / min to obtain a mixed material;

[0090] (3) The mixed material obtained in (2) is placed in a tubular furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 600°C, the heating rate is 5°C / min, and the holding time is 40min; then high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1400°C, the heating rate is 5°C / min, and the holding time is 40min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, which is labeled GHC6-14 (16:1).

[0091] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0092] Figure 1 Figure b is the XRD spectrum of sample GHC6-14 (16:1) obtained in Example 5. Through data analysis and processing, the carbon layer spacing of the sample is 0.373 nm.

[0093] Figure 5This is the first cycle constant current charge-discharge curve of the sample GHC6-14 (16:1) obtained in Example 5. The sample has a reversible specific capacity of 343.13 mAh / g at a current density of 20 mA / g.

[0094] Example 6

[0095] The present embodiment provides a method for preparing a PET-based hard carbon negative electrode material for a sodium ion battery, comprising the following steps:

[0096] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 20 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 90° C. for 6 h;

[0097] (2) Weighing the dried polyethylene terephthalate precursor and zinc gluconate at a mass ratio of 50:1, placing them in a ball mill and mixing them for 40 minutes at a rotation speed of 200 r / min to obtain a mixed material;

[0098] (3) The mixed material obtained in (2) is placed in a tubular furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 600°C, the heating rate is 5°C / min, and the holding time is 40min; then high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1400°C, the heating rate is 5°C / min, and the holding time is 40min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, labeled GHC6-14 (50:1).

[0099] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0100] Figure 1 Figure b is the XRD spectrum of sample GHC6-14 (50:1) obtained in Example 6. Through data analysis and processing, the carbon layer spacing of the sample is 0.376 nm.

[0101] Figure 5 This is the first cycle constant current charge-discharge curve of the sample GHC6-14 (50:1) obtained in Example 6. The sample has a reversible specific capacity of 317.46 mAh / g at a current density of 20 mA / g.

[0102] Example 7

[0103] The present embodiment provides a method for preparing a PET-based hard carbon negative electrode material for a sodium ion battery, comprising the following steps:

[0104] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 20 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 90° C. for 6 h;

[0105] (2) Weighing the dried polyethylene terephthalate precursor and zinc gluconate at a mass ratio of 50:1, placing them in a ball mill and mixing them for 40 minutes at a rotation speed of 200 r / min to obtain a mixed material;

[0106] (3) The mixed material obtained in (2) is placed in a tubular furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 600°C, the heating rate is 5°C / min, and the holding time is 40min; then high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1600°C, the heating rate is 5°C / min, and the holding time is 40min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, labeled GHC6-16 (50:1).

[0107] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0108] Figure 5 This is the first cycle constant current charge-discharge curve of the sample GHC6-16 (50:1) obtained in Example 7. The sample has a reversible specific capacity of 300.28 mAh / g at a current density of 20 mA / g.

[0109] Example 8

[0110] A method for preparing a hard carbon negative electrode material for a sodium ion battery provided in this embodiment comprises the following steps:

[0111] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 30 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 100° C. for 8 h;

[0112] (2) Weighing the dried polyethylene terephthalate precursor and zinc acetate in a mass ratio of 12:1, placing them in a ball mill and mixing them for 20 minutes at a speed of 300 r / min to obtain a mixed material;

[0113] (3) The mixed material obtained in (2) is placed in a tubular furnace, vacuumed, and then carbonized by introducing nitrogen. The low-temperature carbonization temperature is 700°C, the heating rate is 10°C / min, and the holding time is 60min; then high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 1400°C, the heating rate is 10°C / min, and the holding time is 60min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, labeled AHC7-14 (12:1).

[0114] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0115] Figure 6 This is the first cycle constant current charge-discharge curve of sample AHC7-14 (12:1) obtained in Example 8. The sample has a reversible specific capacity of 335.37 mAh / g at a current density of 20 mA / g.

[0116] Comparative Example 1

[0117] This comparative example is the same as the preparation scheme of Example 1, except that the additive zinc oxide is not added in this comparative example, and comprises the following steps:

[0118] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 10 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 80° C. for 5 h;

[0119] (2) Weigh the dried polyethylene terephthalate precursor and put it into a tube furnace for vacuum treatment, and then introduce nitrogen gas for heating and carbonization treatment. The low-temperature carbonization temperature is 500°C, the heating rate is 2°C / min, and the insulation time is 30min; then directly carry out high-temperature carbonization, the high-temperature carbonization temperature is 1400°C, the heating rate is 2°C / min, and the insulation time is 30min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, which is marked as HC500-1400.

[0120] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 h, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g.

[0121] Table 1 shows the constant current charge-discharge capacity data of the first cycle of Examples 1 to 3 and Comparative Example 1. The sample of Comparative Example 1 has a reversible capacity of 250.10 mAh / g at a current density of 20 mA / g. Compared with Examples 1 to 3, the sample with zinc oxide added has a higher reversible capacity.

[0122] Table 1

[0123]

[0124] Comparative Example 2

[0125] The purpose of this comparative example is to prepare hard carbon with a final carbonization temperature of 600°C, comprising the following steps:

[0126] (1) The selected polyethylene terephthalate raw material is crushed to a size of 2 to 10 mm; then an ethanol solution is added to perform ultrasonic cleaning at a frequency of 53 kHz for 10 min, filtered, washed three times with water, and then placed in a drying oven for drying at a drying temperature of 80° C. for 5 h;

[0127] (2) Weighing the dried polyethylene terephthalate precursor and zinc oxide in a mass ratio of 100:1, placing them in a ball mill and mixing them for 60 minutes at a rotation speed of 100 r / min to obtain a mixed material;

[0128] (3) The mixed material obtained in (2) is placed in a tubular furnace, vacuumed, and then heated by nitrogen for carbonization. The low-temperature carbonization temperature is 350°C, the heating rate is 2°C / min, and the holding time is 30min; then the high-temperature carbonization is directly performed, the high-temperature carbonization temperature is 600°C, the heating rate is 2°C / min, and the holding time is 30min. The carbonized product is ground and passed through a 300-mesh sieve to obtain a sodium ion battery hard carbon negative electrode material, which is marked as ZHC3.5-6 (100:1).

[0129] Finally, the sodium ion half-cell was assembled using the method described in Example 1. After standing for 12 hours, a voltage range of 0.01 to 2.5 V was selected, and a constant current charge and discharge test was performed at a current density of 20 mA / g. The reversible specific capacity of the ZHC3.5-6 (100:1) sample was 102.38 mAh / g. This was because the carbonization temperature was too low, the carbonization degree was low, and the zinc oxide could not be removed at 600°C, so that a carbon layer and closed pores conducive to sodium storage could not be formed, resulting in poor sodium storage performance.

[0130] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a polyethylene terephthalate-based sodium ion battery hard carbon negative electrode material, It is characterized in that The method comprises the following steps: Pre-treating polyethylene terephthalate to obtain a precursor material; The precursor material and the additive are ball-milled and mixed in a certain proportion to obtain a mixed material; The mixed material is carbonized in a protective environment to obtain a hard carbon negative electrode material for a sodium ion battery.

2. The preparation method according to claim 1, It is characterized in that The pretreatment includes crushing, ultrasonic washing with alcohol solution, washing with water, and drying. After crushing, the fragments have a side length of 2 to 10 mm; and / or, the alcohol solution comprises ethanol or isopropanol; And / or, the drying temperature of the drying treatment is 80-100° C., and the drying time is 5-8 hours.

3. The preparation method according to claim 1, It is characterized in that The additive is one or more of zinc oxide, zinc acetate and zinc gluconate; the mass ratio of polyethylene terephthalate to the additive is 8 to 150:

1.

4. The preparation method according to claim 1, It is characterized in that During ball milling mixing, the ball milling speed is 100-300 r / min, and the ball milling time is 20-60 min.

5. The preparation method according to claim 1, It is characterized in that The protective gas is one of nitrogen and argon.

6. The preparation method according to claim 1, It is characterized in that The obtained carbonized product is ground and sieved, and the sieve size is 100-500 mesh.

7. The preparation method according to claim 1, It is characterized in that The carbonization treatment method is to first perform low-temperature carbonization, keep the temperature for a certain period of time, and then perform high-temperature carbonization.

8. The preparation method according to claim 7, It is characterized in that The treatment temperature of the low-temperature carbonization is 500-700°C, the heating rate is 2-10°C / min, and the insulation time is 30-60min; the treatment temperature of the high-temperature carbonization is 1400-1600°C, the heating rate is 2-10°C / min, and the insulation time is 30-60min.

9. A hard carbon negative electrode material for a sodium ion battery prepared according to the method according to any one of claims 1 to 8, It is characterized in that The interlayer distance of the hard carbon negative electrode material is 0.373nm to 0.392nm.

10. Use of a sodium ion battery hard carbon negative electrode material prepared according to the method of any one of claims 1 to 8 in preparing a negative electrode for a sodium ion battery.

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