Modified chitosan-modified carbon nanotube covalent binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of positive electrode materials and lithium-sulfur batteries, and discloses a modified chitosan-modified carbon nanotube covalent binder and a preparation method and application thereof.The preparation method comprises the steps that modified chitosan and modified carbon nanotubes are placed in deionized water, and heating, stirring and concentration are performed to obtain the modified chitosan-modified carbon nanotube covalent binder. The modified chitosan and the modified carbon nano tube covalent binder are prepared; the modified chitosan is 3, 4-dihydroxyphenyl propionic acid grafted chitosan, and the modified carbon nano tube is a carboxylation modified carbon nano tube. According to the invention, the strong adhesiveness and excellent polysulfide adsorption capacity of CCS are utilized, and the MWCNTs have electronic conductivity and excellent mechanical properties. A composite material formed by covalent binding of the two is used as a binder, so that positive electrode materials can be tightly bonded together, the loss of positive electrode active substances in the battery circulation process is reduced, and meanwhile, a formed complete electron conduction network can also enhance electron exchange on an electrochemical interface and improve the charge-discharge efficiency of the battery.

Description

Technical Field

[0001] The invention relates to the technical field of positive electrode materials and lithium-sulfur batteries, and in particular to a modified chitosan-modified carbon nanotube covalent binder and a preparation method and application thereof. Background Art

[0002] As society gradually gets rid of its dependence on fossil fuels, the demand for the development of high energy density and low-cost battery technology is growing. Lithium-sulfur batteries (LSBs) have attracted much attention due to their high theoretical specific energy density (2600Wh / kg) and the natural abundance of sulfur. However, the main challenges facing lithium-sulfur batteries include the insulating properties of sulfur and its discharge products, the "shuttle effect" of polysulfides, and significant volume changes during lithiation-delithiation, which limit their commercial application. The binder system suitable for sulfur cathode is one of the important directions to alleviate the above problems.

[0003] Traditional binders such as polyvinylidene fluoride (PVDF) and carboxymethyl cellulose / styrene butadiene rubber (CMC / SBR) are mainly designed for lithium-ion batteries. They have poor electronic and ionic conductivity, weak adsorption capacity for polysulfides, and cannot effectively prevent the migration of polysulfides. In addition, the preparation of PVDF requires the use of toxic and expensive solvent N-methylpyrrolidone (NMP). In view of this, the development of green, safe and sustainable binder materials for lithium-sulfur batteries has become a research hotspot, such as renewable bio-based organic materials.

[0004] Chitosan (CS) has received extensive attention in the field of lithium-sulfur battery binder research because it contains a large number of amino and hydroxyl groups, which can effectively fix polysulfides and reduce the shuttle effect. In addition, its flexible ether bond is conducive to lithium ion transmission and improves electrochemical performance. However, chitosan-based binders still need to be improved in terms of mechanical properties and conductivity. Summary of the invention

[0005] In view of the shortcomings and defects of the prior art, the present invention aims to provide a modified chitosan-modified carbon nanotube covalent binder and a preparation method and application thereof. A polysaccharide-based conductive composite binder material having modified chitosan grown in situ on the surface of the modified carbon nanotube is obtained by heating and blending the modified carbon nanotubes and modified chitosan. The modified chitosan in the binder provides adhesion and adsorption capacity for polysulfides, and the modified carbon nanotubes can provide excellent conductivity and further improve the overall mechanical properties of the binder by forming covalent bonds with chitosan. The polysaccharide-based conductive binder finally formed is applied to the positive electrode of a lithium-sulfur battery to simultaneously improve the battery cycle performance, rate performance and kinetic performance.

[0006] To achieve the above object, the present invention provides a method for preparing a modified chitosan-modified carbon nanotube covalent binder, comprising the following steps:

[0007] The modified chitosan and the modified carbon nanotubes are placed in deionized water, and concentrated by heating and stirring to cause a chemical esterification reaction on the surface of the modified carbon nanotubes, so as to prepare a modified chitosan-modified carbon nanotube covalent binder (CCS-MWCNTs) in which the modified chitosan is in situ grown on the surface of the modified carbon nanotubes;

[0008] Wherein, the modified chitosan is 3,4-dihydroxyphenylpropionic acid grafted chitosan (CCS), and the modified carbon nanotubes are carboxyl modified carbon nanotubes (MWCNTs).

[0009] In the present invention, carboxyl modified carbon nanotubes are obtained by acidifying carbon nanotubes, so that a large number of carboxyl groups exist on the surface of the carbon nanotubes, providing reaction sites for the growth of modified chitosan, thereby enabling the modified chitosan to grow in situ on the surface of the carbon nanotubes, so that the final composite binder material and the positive electrode slurry using the composite binder have better consistency.

[0010] As a further preferred technical solution of the present invention, the modified chitosan is obtained by amination reaction of 3,4-dihydroxyphenylpropionic acid (hydrogenated caffeic acid) on the chitosan molecular chain, that is, hydrogenated caffeic acid is grafted onto the side chain of the chitosan molecule based on an amination reaction to obtain the modified chitosan.

[0011] As a further preferred technical solution of the present invention, a mixed solution of 3,4-dihydroxyphenylpropionic acid and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride dissolved in a water-ethanol mixed solvent is added dropwise to a chitosan solution dissolved in an acidic medium to carry out an amination reaction, followed by dialysis treatment to remove unreacted components and small molecular impurities, thereby obtaining a modified chitosan solution; wherein: the mass ratio of the chitosan to the 3,4-dihydroxyphenylpropionic acid is 1.5:1; and / or, the acidic medium is dilute acetic acid; the volume ratio of the chitosan to the acidic medium is 1g:100mL; and / or, the water-alcohol mixed solvent consists of equal volumes of deionized water and anhydrous ethanol; and / or, the pH value of the amination reaction is controlled between 4.6-4.8, the temperature is room temperature, and the time is 12 hours.

[0012] As a further preferred technical solution, the dialysis treatment includes:

[0013] A lithium nitrate solution is used as a dialysis medium, the concentration of the lithium nitrate solution is 0.2 g / L, and the pH value is adjusted to 4.6-4.8; and / or, the dialysis medium is replaced every 4-6 hours during the dialysis process, and the total dialysis time is 2-3 days; and / or, after the dialysis is completed, the product is dialyzed for a second time using a dilute nitric acid solution with a pH value of 4.6-4.8 to completely remove residual impurities; and / or, the 3,4-dihydroxyphenylpropionic acid grafted chitosan solid product is recovered from the dialyzed solution by freeze-drying technology.

[0014] As a further preferred technical solution of the present invention, the modified carbon nanotubes are obtained by adding carbon nanotubes to a strong acid solution for modification, and then washing and freeze-drying. Furthermore, the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; and / or, the diameter of the carbon nanotubes is less than 10nm, and the tube length is 1-15μm; and / or, the strong acid solution is 65% concentrated nitric acid, and the ratio of the mass g of the carbon nanotubes to the volume mL of the strong acid solution is 1:500; and / or, the temperature of the modification treatment is 110-120℃, and the time is 12-36h.

[0015] The modified chitosan and the modified carbon nanotubes are subjected to chemical esterification reaction in deionized water, and the ratio of the modified chitosan and the modified carbon nanotubes can meet the requirements as long as the dispersion effect is not affected. As a further preferred technical solution of the present invention, in terms of mass percentage, relative to the total mass of the modified chitosan material and the modified carbon nanotubes, the modified chitosan material accounts for 94%-97%, and the modified carbon nanotubes account for 3%-6%;

[0016] And / or, the temperature of the chemical esterification reaction is 60-120° C., and the reaction time is 4-6 hours.

[0017] According to another aspect of the present invention, the present invention also provides a modified chitosan-modified carbon nanotube covalent binder, which is prepared by the above method.

[0018] According to another aspect of the present invention, the present invention also provides an application of a modified chitosan-modified carbon nanotube covalent binder in the preparation of an electrode, wherein the positive electrode comprises: a current collector and an active material layer attached to at least one surface of the current collector; the raw materials of the active material layer comprise a positive electrode material, a conductive additive and the modified chitosan-modified carbon nanotube covalent binder.

[0019] According to another aspect of the present invention, the present invention also provides a use of the above-mentioned positive electrode in a lithium-sulfur battery.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0021] 1) A small amount of carbon nanotubes can be used to prepare a composite material by simply mixing and heating. The preparation method is simple, low-cost, and easy to industrialize;

[0022] 2) Natural materials are used, which are cheap, and the water-based adhesive is environmentally friendly and meets the requirements of sustainable development;

[0023] 3) The introduction of carbon nanotubes can simultaneously improve the mechanical properties and conductive properties of the binder. It is a multifunctional binder that can be used in lithium-sulfur batteries to simultaneously improve the battery cycle performance, rate performance and kinetic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 is the molecular structural formula of the CCS-MWCNTs (B1) binder prepared in Example 1;

[0026] Figure 2 Transmission electron microscope (TEM) images of carbon nanotubes used in the present invention before and after modification;

[0027] Figure 3 Fourier transform infrared spectroscopy (FT-IR) characterization of unmodified chitosan (B0), CCS (B2) and CCS-MWCNTs (B1);

[0028] Figure 4 This is a photo taken after adding 10 mg of B1-B4 binder to 1 mM Li2S6 solution and letting it stand for 4 hours;

[0029] Figure 5 The sulfur loading of 1 mg cm was prepared by four binders B1-B4. -2 Scanning electron microscope (SEM) images of the sulfur cathode before and after 100 cycles at 0.2C, where: Figure 5 (a, c, e, g) are SEM images of sulfur cathodes prepared with different binders before cycling. Figure 5 (b, d, f, h) are SEM images of sulfur positive electrodes prepared with different binders after cycling.

[0030] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0032] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0033] Embodiment 1:

[0034] The preparation method of the lithium-sulfur battery based on the modified chitosan-modified carbon nanotube covalent binder provided in this embodiment is as follows:

[0035] 1) Preparation of modified chitosan-modified carbon nanotube covalent binder

[0036] S101: 100 mg of carbon nanotube powder was placed in a three-necked flask, 50 mL of 65% concentrated nitric acid was added, and the mixture was refluxed at 110 degrees Celsius for 24 hours. After cooling and settling, the supernatant was sucked out with a pipette, and the mixture was rinsed with a large amount of deionized water until the washing liquid was neutral. Then, the carbon nanotubes were dispersed in 100 ml of deionized water, ultrasonicated for 1 hour, and frozen in liquid nitrogen and then freeze-dried.

[0037] S102: 2.500 g of chitosan was dissolved in 250 mL of dilute acetic acid, and the pH was adjusted to about 5.2. 1.783 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and about 1.695 g of 3,4-dihydroxyhydrocinnamic acid were dissolved in a mixed solution of 125 mL of deionized water and 125 mL of anhydrous ethanol, and the pH was adjusted to about 4.8 with 0.01 mol L-1 acetic acid. After sufficient stirring and mixing, it was added dropwise to the chitosan solution and reacted for 12 hours. Afterwards, 5 L of lithium nitrate solution with a concentration of 0.2 g L-1 was prepared as a dialysis medium, and the pH was adjusted to 4.6-4.8 with nitric acid. The modified chitosan solution was placed in a dialysis bag and dialyzed in a lithium nitrate solution for 3 days, during which the dialysate was replaced every 4-6 hours. Then, the chitosan was further dialyzed twice with a dilute nitric acid solution with a pH of 4.6-4.8 to wash the chitosan. Finally, CCS was obtained by freeze-drying the purified solution.

[0038] S103: 500 mg of 3,4-dihydroxyphenylpropionic acid grafted chitosan (CCS) was dissolved in 50 mL of water to prepare a CCS aqueous binder solution with a concentration of 10 mg mL-1.

[0039] S104: Dispersing the freeze-dried multi-walled carbon nanotubes in water and ultrasonically treating for 1 hour to form a uniform dispersion with a concentration of 0.15 mg / mL.

[0040] 100 mL of MWCNTs dispersion was taken, stirred at 1000 rpm, and 48.5 mL of 10 mg / mL chitosan (CCS) aqueous solution was added dropwise. After addition, the mixture was ultrasonically treated for 1 hour, heated to 60 °C and stirred for 4 hours to obtain a structure of Figure 1 The CCS-MWCNTs binder shown is denoted as B1.

[0041] 2) Battery assembly

[0042] S201: The positive electrode is prepared by conventional process: the positive electrode active material (S / KB), conductive agent (super-p), and binder (B1) are mixed evenly in a mass ratio of 7:2:1 and coated on the positive electrode collector (carbon-coated aluminum foil). After drying at room temperature, it is rolled with a roller press, dried at 60 degrees Celsius, and cut into pieces to make positive electrode sheets with a diameter of 12 mm.

[0043] S202: A lithium metal sheet with a diameter of 15.6 mm is used as the negative electrode.

[0044] S203: The electrolyte is prepared by conventional process: 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) are uniformly mixed in a volume ratio of 1:1, and then lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) is added thereto to prepare a 1 mol / L electrolyte, and 2% of the electrolyte mass of lithium nitrate is added as an additive to prepare a final electrolyte.

[0045] S204: Assemble the positive electrode sheet, the negative electrode sheet, the separator (16 mm polypropylene film) and the electrolyte in a conventional manner, place them in an aluminum-plastic film and pressurize them to obtain a 2032 button-type lithium-sulfur battery.

[0046] It should be noted that the rolling, cutting, drying and pressing used in the present invention are all conventional operations in the art.

[0047] Comparative Example 1:

[0048] The difference between this comparative example and Example 1 is that 3,4-dihydroxyphenylpropionic acid grafted chitosan (CCS) is used as the positive electrode binder. The specific method is as follows:

[0049] 1) Preparation of 3,4-dihydroxyphenylpropionic acid grafted chitosan water-based binder

[0050] D101: 2.500 g chitosan was dissolved in 250 mL dilute acetic acid and the pH was adjusted to about 5.2. 1.783 g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and about 1.695 g 3,4-dihydroxyhydrocinnamic acid were dissolved in a mixed solution of 125 mL deionized water and 125 mL anhydrous ethanol, and the pH was adjusted to about 4.8 with 0.01 mol L-1 acetic acid. After sufficient stirring and mixing, it was added dropwise to the chitosan solution and reacted for 12 hours. After that, 5 L of lithium nitrate solution with a concentration of 0.2 g L-1 was prepared as a dialysis medium, and the pH was adjusted to 4.6-4.8 with nitric acid. The modified chitosan solution was placed in a dialysis bag and dialyzed in a lithium nitrate solution for 3 days, during which the dialysate was replaced every 4-6 hours. Then, the chitosan was further dialyzed twice with a dilute nitric acid solution with a pH of 4.6-4.8 to wash the chitosan. Finally, CCS was obtained by freeze-drying the purified solution.

[0051] D102: 500 mg of 3,4-dihydroxyphenylpropionic acid grafted chitosan (CCS) was dissolved in 50 mL of water to prepare a CCS aqueous binder solution with a concentration of 10 mg mL-1. This binder was recorded as B2.

[0052] 2) Battery assembly

[0053] The specific operation method of assembling the battery is the same as that of Example 1, except that the binder used to prepare the positive electrode sheet is B2.

[0054] Comparative Example 2:

[0055] The difference between this comparative example and Example 1 is that the positive electrode binder adopts a polyvinylidene fluoride (PVDF) binder known to those skilled in the art, and the binder is denoted as B3.

[0056] Comparative Example 3:

[0057] The difference between this comparative example and Example 1 is that the positive electrode binder uses styrene-butadiene rubber SBR and sodium carboxymethyl cellulose CMC, which are well known to those skilled in the art, and SBR:CMC are mixed in a mass ratio of 4:6. This binder is recorded as B4.

[0058] Figure 2Transmission electron microscopy (TEM) images of carbon nanotubes before and after modification in Example 1 show that the original MWCNTs (M1) present a dense and aggregated structure with limited separation between individual carbon nanotubes. In contrast, the modified MWCNTs (M2) form a more dispersed and loose network, with individual nanotubes clearly visible and significantly reduced aggregation. This enhanced dispersion promotes uniform mixing of carbon nanotubes and modified chitosan, promotes stable interactions, and can significantly improve the mechanical and conductive properties of the formed composite adhesive. These improvements are critical to accommodating volume changes that occur during charge and discharge cycles while maintaining conductivity.

[0059] Figure 3 Fourier transform infrared spectroscopy (FT-IR) was used to characterize pure chitosan (B0), chitosan grafted with 3,4-dihydroxyphenylpropionic acid (B2), and CCS-MWCNTs (B1). The absorption peaks of chitosan at 1650 cm-1 and 1591 cm-1 correspond to the stretching vibration of N-acetyl (amide I) and bending vibration of NH (amide II) of chitosan, respectively. After grafting with 3,4-dihydroxyphenylpropionic acid (HCA), these peaks shifted to lower wavenumbers, which may be due to the formation of denser hydrogen bonds and the introduction of aromatic ring structures, resulting in steric hindrance that limits molecular rotation. In addition, a new C=O peak appeared at 1740 cm-1, and the amino peak at 1320 cm-1 weakened, indicating that a covalent bond was formed between the carboxyl group of HCA and the amino group of chitosan, further confirming the successful grafting modification. Furthermore, in the infrared data of CCS–MWCNTs, the broadened C=O peak at 1740 cm-1 and the enhanced CO peak at 1250 cm-1 indicated that ester bonds were successfully formed between the modified chitosan and the functionalized carbon nanotubes.

[0060] Figure 4 The following are photos of 10 mg of different binders (B1-B4) in 1 mM Li2S6 solution. It can be seen that the different binders exhibit different characteristics in their adsorption capacity for polysulfides, reflecting their different interaction abilities with polysulfides. The result of CMC / SBR (B4) showed a lighter yellow color, which was significantly lighter than the dark yellow color of the control group (1 mM Li2S6) and PVDF binder (B3). It is worth noting that the Li2S6 solution treated with CCS (B2) and CCS-MWCNTs (B1) was almost colorless because almost all the polysulfides were adsorbed by the binder, indicating that the polysulfide adsorption capacity of CCS and CCS-MWCNTs was stronger than that of CMC / SBR and PVDF binders. This is because chitosan is rich in amino / acetylamino and secondary hydroxyl groups, providing a stronger polysulfide chemical adsorption capacity than CMC / SBR binder.

[0061] Figure 5The following are scanning electron microscope (SEM) images of positive electrodes with a sulfur loading of 1 mg cm-2 prepared using four different binders B1-B4, corresponding to the positive electrodes before and after 0.2C cycling: Figure 5 (a,c,e,g), the positive electrode after cycling is shown in Figure 5 (b, d, f, h). For the positive electrode before cycling, a large number of microcracks appeared on the surface of the PVDF (B3) and CMC / SBR (B4) positive electrodes, while the positive electrodes prepared by CCS (B2) and CCS-MWCNTs (B1) binders were almost crack-free and had uniform coatings, showing excellent structural integrity and great potential as binders. The reason is that chitosan is a natural hydrophobic linear polymer. The introduction of catechol groups makes its molecular chain soluble in water. The uniform binder solution helps to evenly distribute the active materials and conductive particles during the electrode preparation process. At the same time, the chitosan main chain remains hydrophobic and can be adsorbed on similar sulfur-carbon particles through hydrophobic interactions, thereby preventing the active materials from agglomerating. The addition of MWCNTs further enhances the mechanical toughness of the binder, enabling it to withstand volume shrinkage during electrode drying. Such excellent uniformity is crucial for optimizing electrochemical performance, helping to improve the overall conductivity and mechanical stability of the electrode, thereby improving rate performance and extending the cycle life of the battery. SEM analysis of the positive electrode after 100 cycles at 0.2C revealed that the electrode based on CCS-MWCNTs (B1) maintained the best structural integrity after cycling. In contrast, the electrode based on PVDF (B3) showed deepening cracks and an increase in fine cracks. The electrode based on CMC / SBR (B4) also showed a certain degree of crack extension. Although the electrode based on CCS (B2) showed microcracks, these cracks were shallower than those of the CMC / SBR (B4) electrode, and the quality of the surrounding area was uniform, indicating that the CCS binder promoted a more uniform dispersion of the electrode material. Figure 5 (h) shows that the electrode based on CCS-MWCNTs (B1) contains only a shallow crack and maintains a dense surface, showing good cycling stability.

[0062] The tensile test results of the four adhesives in Example 1 and Comparative Examples 1-3 after film formation are shown in Table 1.

[0063] Table 1

[0064] Binder B1 B2 B3 B4 Breaking strength(Mpa) 38.0 28.4 3.3 28.8 Elongation at break (%) 14.7 3.3 64.9 10.6

[0065] From Table 1, PVDF (B3) showed the highest toughness (tensile strain up to 64.9%), but its fracture stress was only 3.3MPa, indicating that its bearing capacity was limited. In contrast, CCS (B2) showed the lowest toughness (3.3%), but the fracture strength was 28.4MPa, showing potential application value under high load conditions. The fracture strength of CMC / SBR (B4) was slightly higher than that of CCS (B2), and due to the addition of SBR, its tensile strain increased, thereby improving flexibility. It is worth noting that by covalently bonding 3wt.% of MWCNTs to CCS, the CCS-MWCNTs (B1) binder exhibited the greatest tensile strength (38.0MPa), indicating that the introduction of carbon nanotubes significantly enhanced the mechanical properties of CCS while showing good interfacial compatibility. Therefore, this modification endows the CCS-MWCNTs binder with superior sulfur volume change tolerance in Li-S batteries compared with PVDF and CMC / SBR binders, which improves the cycling stability and minimizes the structural damage during the charge-discharge cycles.

[0066] The comparison results of the electrochemical performance of the batteries using the four binders B1-B4 in the above-mentioned Example 1 and Comparative Examples 1-3 are shown in Table 2.

[0067] Table 2

[0068]

[0069] From Table 2, compared with PVDF (B3) and CMC / SBR (B4) binders, the Li-S battery using CCS-MWCNTs (B1) binder exhibited the highest initial capacity of 1470 mAh g-1 at 0.2C, corresponding to 88% of the theoretical capacity of sulfur (1672 mAh g-1). In the rate performance test, the cathode performance of CMC / SBR (B4) binder at 1C was similar to that of PVDF (B3). In contrast, the chitosan-based CCS-MWCNTs (B1) cathode can maintain a reversible specific capacity of 720 mAh g-1, which is higher than that of the cathodes with other binders. The excellent rate performance of CCS-MWCNTs (B1) binder indicates that the rich functional groups of MWCNTs and chitosan improve the discharge / charge kinetics. High uniformity and structural integrity of the positive electrode are crucial for long-term stable battery operation. In order to evaluate the stability of the positive electrode using different binders, a long-term constant current discharge-charge cycle test of 100 cycles at 0.2C was further carried out. The test results showed that the CCS-MWCNTs (B1) positive electrode can still maintain a capacity of 830mAh g-1 after 100 cycles at 0.2C, which is much higher than the positive electrodes with PVDF (B3), CMC / SBR (B4) and CCS (B2) binders. In addition, increasing the sulfur surface loading is crucial to obtain higher practical energy density. Therefore, the cycle stability of the positive electrode prepared with different binders at a higher sulfur loading (2.0mg cm-2) was studied. It was found that after 100 cycles at 0.2C, the reversible capacity was still 687mAh g-1, surpassing the use of commercial PVDF (B3), CMC / SBR (B4) binders and CCS (B2) binders, showing the highest capacity and stability. These results fully demonstrate that the CCS-MWCNTs (B1) binder is very efficient in chemically absorbing polysulfides and improving the kinetics.

[0070] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a modified chitosan-modified carbon nanotube covalent binder, characterized in that: The following steps are involved: The modified chitosan and the modified carbon nanotubes are placed in deionized water, and concentrated by heating and stirring to cause a chemical esterification reaction on the surface of the modified carbon nanotubes, so as to prepare a modified chitosan-modified carbon nanotube covalent binder having modified chitosan in situ grown on the surface of the modified carbon nanotubes; Wherein, the modified chitosan is 3,4-dihydroxyphenylpropionic acid grafted chitosan, and the modified carbon nanotube is carboxyl modified carbon nanotube.

2. The method for preparing the modified chitosan-modified carbon nanotube covalent binder according to claim 1, characterized in that: The modified chitosan is prepared by an amination reaction of 3,4-dihydroxyphenylpropionic acid on a chitosan molecular chain.

3. The method for preparing the modified chitosan-modified carbon nanotube covalent binder according to claim 2, characterized in that: A mixed solution of 3,4-dihydroxyphenylpropionic acid and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride dissolved in a water-ethanol mixed solvent is added dropwise to a chitosan solution dissolved in an acidic medium to cause an amination reaction, followed by dialysis treatment to remove unreacted components and small molecular impurities, thereby obtaining a modified chitosan solution; Wherein: the mass ratio of the chitosan to the 3,4-dihydroxyphenylpropionic acid is 1.5:1; And / or, the acidic medium is dilute acetic acid; the volume ratio of the chitosan to the acidic medium is 1 g:100 mL; and / or, the water-alcohol mixed solvent consists of equal volumes of deionized water and anhydrous ethanol; And / or, the pH value of the amination reaction is controlled between 4.6 and 4.8, the temperature is room temperature, and the time is 12 hours.

4. The method for preparing the modified chitosan-modified carbon nanotube covalent binder according to claim 3, characterized in that: The dialysis treatment comprises: Lithium nitrate solution was used as the dialysis medium, the concentration of lithium nitrate solution was 0.2 g / L, and the pH value was adjusted to 4.6-4.8; and / or, the dialysis medium is replaced every 4-6 hours during dialysis, with a total dialysis time of 2-3 days; And / or, after the dialysis is completed, the product is dialyzed a second time using a dilute nitric acid solution with a pH value of 4.6-4.8 to remove residual impurities.

5. The method for preparing the modified chitosan-modified carbon nanotube covalent binder according to claim 1, characterized in that: The modified carbon nanotubes are obtained by adding carbon nanotubes into a strong acid solution for modification, followed by washing and freeze-drying.

6. The method for preparing the modified chitosan-modified carbon nanotube covalent binder according to claim 5, characterized in that: The carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; And / or, the strong acid solution is 65% concentrated nitric acid, and the ratio of the mass g of the carbon nanotubes to the volume mL of the strong acid solution is 1:500; And / or, the temperature of the modification treatment is 110-120° C. and the time is 12-36 hours.

7. The method for preparing the modified chitosan-modified carbon nanotube covalent binder according to any one of claims 1 to 6, characterized in that: In terms of mass percentage, relative to the total mass of the modified chitosan material and the modified carbon nanotubes, the modified chitosan material accounts for 94%-97%, and the modified carbon nanotubes account for 3%-6%; And / or, the temperature of the chemical esterification reaction is 60-120° C., and the reaction time is 4-6 hours.

8. A modified chitosan-modified carbon nanotube covalent binder, characterized in that: The method is prepared by any one of claims 1 to 7.

9. Use of the modified chitosan-modified carbon nanotube covalent binder according to claim 8 in preparing an electrode, characterized in that: The positive electrode comprises: a current collector and an active material layer attached to at least one surface of the current collector; the raw materials of the active material layer comprise positive electrode materials, conductive additives and the modified chitosan-modified carbon nanotube covalent binder.

10. Use of the positive electrode as claimed in claim 9 in a lithium-sulfur battery.

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