A chitosan-based polyethylene glycol diglycidyl ether modified water-based adhesive, and a preparation method and application thereof

Abstract

The application discloses a kind of polyethylene glycol diglycidyl ether modified water-based binder based on chitosan and its preparation method and application, it is related to lithium ion battery technical field.The application effectively solves the problems of poor water solubility, large film brittleness and other problems of high degree of polymerization chitosan, successfully prepares low degree of polymerization chitosan with good water solubility and processing performance;And on this basis, it is grafted with polyethylene glycol diglycidyl ether in aqueous phase Copolymerization, constructs a kind of water-based binder system.Lithium ion battery prepared by using the water-based binder of the application exhibits excellent cycle stability and low-temperature discharge performance, at the same time, due to its good water dispersibility and processing adaptability, electrode preparation process can be simplified, production cost is reduced, and has broad industrialization application prospect.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a chitosan-based polyethylene glycol diglycidyl ether modified aqueous binder, its preparation method, and its application. Background Technology

[0002] Binders are a crucial component of lithium-ion batteries, directly determining their overall performance. In the industrial-scale production of lithium-ion batteries, organic solvent-based polyvinylidene fluoride (PVDF) is commonly used as a binder, paired with N-methylpyrrolidone (NMP) as a dispersant. While PVDF possesses excellent binding properties, it suffers from poor electronic and ionic conductivity; and while NMP provides good dispersion, it is volatile, flammable, explosive, and highly toxic. This not only necessitates strict sealing in the electrode coating process using PVDF, significantly increasing production costs, but also leads to a continuous performance degradation of lithium-ion batteries due to the fluorine-containing groups in PVDF readily reacting with lithium-intercalated graphite.

[0003] In contrast, aqueous binders, due to their solvent-free nature, possess core advantages such as being environmentally friendly, low-cost, non-flammable, and highly safe, making them a key development direction in the current lithium-ion battery binder field. Currently, there are numerous literature reports on the application of aqueous binders in anode materials, and aqueous binders for graphite anodes have been commercialized. The mainstream aqueous anode binder is a mixture of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), but this system has significant limitations: firstly, it requires the synergistic use of both components, resulting in higher overall costs; secondly, SBR has poor shear resistance, necessitating low-speed stirring and dispersion in the final stage, placing higher demands on production processes and equipment precision, further increasing production costs. Therefore, various natural polymer materials are gradually being explored as binders, such as cellulose, chitosan, gelatin, starch, and sodium alginate. Among them, chitosan (CTS), as a natural polymer compound containing bipolar hydroxyl and amino groups, not only has a wide range of raw material sources and low cost but also possesses environmentally friendly and pollution-free characteristics. Due to its bipolar groups, chitosan, when used as a binder, can enhance bonding with active materials, improve the coating effect on active materials, and thus increase the adhesion strength between active materials, conductive agents, and current collectors. Simultaneously, it can maintain the relative stability of the electrolyte and improve the electrochemical performance of the battery. However, chitosan itself suffers from poor water solubility and high brittleness, which greatly limits its large-scale application in aqueous processing of lithium-ion battery anodes.

[0004] It is worth noting that silicon-based materials, as the next generation of high-energy-density anode materials, have a theoretical specific capacity that is about 10 times that of existing graphite materials, and have broad application prospects. However, silicon undergoes drastic volume changes (expansion rate can reach about 400%) during the lithium delithiation-lithiation process, which places extremely high demands on the elasticity of the binder, requiring it to adapt to and buffer such drastic volume fluctuations. The existing CMC+SBR system is difficult to meet this requirement.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive, its preparation method, and its application, in order to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] One of the technical solutions of this invention is to provide a method for degrading high-polymerization-degree chitosan, comprising the following steps:

[0009] Highly polymerized chitosan is dissolved in an aqueous solution containing peroxy acid to form a homogeneous reaction system;

[0010] The homogeneous reaction system is kept at 40-60℃ for 10-20h to allow the chitosan to undergo controlled oxidative degradation. After the oxidative degradation is completed, the pH of the system is adjusted to neutral, and the insoluble matter is removed by filtration to obtain a low degree of polymerization chitosan solution.

[0011] The low-polymerization-degree chitosan solution was subjected to alcohol precipitation (preferably ethanol), the precipitate was collected and freeze-dried to obtain low-polymerization-degree chitosan;

[0012] The high degree of polymerization chitosan has a degree of deacetylation greater than 90% and a number-average molecular weight greater than 100,000.

[0013] The resulting low-polymerization degree chitosan has a deacetylation degree greater than 90% and a number-average molecular weight of 0.8-10,000; its solubility in water at 25°C is greater than 30 g / L.

[0014] Furthermore, the peroxy acid is selected from at least one of peroxy organic acids or peroxy inorganic acids. Examples include peroxyformic acid, peroxyacetic acid, peroxytrifluoroacetic acid, peroxypropionic acid, peroxybutyric acid, peroxyisovaleric acid, long-chain peroxy fatty acids, peroxybenzoic acid, m-chloroperoxybenzoic acid, nitroperoxybenzoic acid, monoperoxyphthalic acid, persulfuric acid, persulfuric acid, persulfuric acid, pernitric acid, perphosphoric acid, perphosphoric acid, percarbonic acid, and perboric acid, etc.

[0015] Furthermore, the concentration of the peroxy acid aqueous solution is 0.5-10 wt%; the solid-liquid ratio of the highly polymerized chitosan and the peroxy acid aqueous solution is 10 g:1L-50 g:1L.

[0016] Furthermore, an alkaline solution is used to adjust the pH, wherein the alkaline solution is an aqueous solution of LiOH, NaOH, or KOH; preferably a 10 wt% LiOH solution.

[0017] The second technical solution of this invention provides a chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive, wherein the raw materials comprise the following components by mass percentage: 10-90% low-polymerization-degree chitosan and 10-90% polyethylene glycol diglycidyl ether; the total of the two is 100%.

[0018] The low-polymerization degree chitosan was prepared by the above-described degradation method;

[0019] The number-average molecular weight of the polyethylene glycol diglycidyl ether is Mn=500-6000.

[0020] At 40℃, the solid content of the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive is 15.0%, the pH value is 6.0-8.0, and the viscosity is 11.0-18.5 Pa·s.

[0021] Structurally, polyethylene glycol diglycidyl ether (PEGDGE) contains PEG elastic segments, which possess strong flexibility, exhibiting higher tensile strength and elongation at break than other carbon-chain polymers. Therefore, introducing PEG elastic segments into binders can significantly improve their flexibility, thus meeting the requirements of highly flexible binders for silicon-carbon anodes during large volume changes during charging and discharging. However, PEGDGE contains relatively few free polar groups, resulting in weak adhesion provided by pure PEGDGE polymers. In view of this, this invention combines PEGDGE with chitosan, forming a polymer network through polymerization. This polymer network simultaneously provides high adhesion and high flexibility to meet the high standards of binders required by silicon-carbon anodes.

[0022] From a synthetic perspective, polyethylene glycol diglycidyl ether contains two reactive epoxy groups, which can react efficiently with the hydroxyl groups on chitosan to form a reasonable polymer network, which is beneficial to improving the overall mechanical properties of the adhesive, including flexibility and elastic modulus.

[0023] From the perspective of battery performance, the polyethylene glycol diglycidyl ether segment contains uniformly distributed O atoms. This oxygen-containing polymer segment can assist in the high-speed transport of lithium ions and can perfectly act as a medium for the transport of lithium ions at the interface between active materials (such as silicon carbon materials) and conductive agents, current collectors, etc., greatly improving the transport efficiency of lithium ions at different material interfaces, thereby improving the battery's charge and discharge performance, high-rate charge and discharge performance, and low-temperature rate performance.

[0024] From the processing of silicon-carbon anode sheets, the polymer network formed by polyethylene glycol diglycidyl ether and chitosan has a high density of polar groups that can fully contact the active material and conductive agent, thereby forming a good coating and preparing an electrode slurry with good suspension properties. This is one of the important indicators in the electrode sheet processing process.

[0025] The third technical solution of the present invention provides a method for preparing the above-mentioned chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive, comprising the following steps:

[0026] (1) Dissolve the low-polymerization degree chitosan and polyethylene glycol diglycidyl ether in deionized water to form a mixture;

[0027] (2) The mixture is stirred at 50-70°C for 12-24 hours, and then subjected to aqueous graft copolymerization to obtain a transparent viscous solution.

[0028] (3) Cool the transparent viscous solution, dilute it with water and filter it. Collect the filtrate to obtain the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive.

[0029] Furthermore, the total mass ratio of the low-polymerization-degree chitosan and polyethylene glycol diglycidyl ether to deionized water is 1:10-1:5.

[0030] The fourth technical solution of the present invention provides the application of the above-mentioned chitosan-based polyethylene glycol diglycidyl ether modified aqueous binder in the silicon-carbon anode of lithium-ion batteries.

[0031] This invention does not use any organic solvents or low-boiling-point reactants, and no low-boiling-point substances are generated during the reaction process, thus avoiding the risk of VOC residues from the source. The related products were tested by the standard test method for VOC residues (GB / T 6618-2011: Determination of Volatile Organic Compounds by Gas Chromatography), and no VOC residues were found.

[0032] The present invention discloses the following technical effects:

[0033] This invention effectively solves the problems of poor water solubility and high film brittleness of high-polymerization-degree chitosan through controlled degradation technology, and successfully prepares low-polymerization-degree chitosan with good water solubility and processing performance. While retaining the advantage of high deacetylation degree of chitosan, this degradation method significantly improves its solubility and film flexibility, laying the foundation for subsequent functional modification to prepare water-based binders for silicon-carbon anodes of lithium-ion batteries.

[0034] This invention employs low-polymerization-degree chitosan and polyethylene glycol diglycidyl ether in an aqueous phase to construct an aqueous binder system. This binder is free of organic solvents and volatile components, making it environmentally friendly. Its molecular structure combines polar groups and flexible segments, enabling it to form strong interactions with silicon-carbon anode materials, effectively buffering structural damage caused by drastic volume changes during charging and discharging. It also significantly enhances the interfacial bonding between the active material, conductive agent, and current collector, thereby improving the overall mechanical stability of the electrode.

[0035] Lithium-ion batteries prepared using the binder of this invention exhibit excellent cycle stability and low-temperature discharge performance. Furthermore, due to its good water dispersibility and processing adaptability, it simplifies electrode fabrication processes, reduces production costs, and has broad prospects for industrial application. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart illustrating the preparation process of the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive of this invention.

[0038] Figure 2 This is a schematic diagram of the aqueous phase polymerization reaction of low-polymerization degree chitosan and polyethylene glycol diglycidyl ether according to the present invention.

[0039] Figure 3 This is a schematic diagram of the structural model of the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive of the present invention.

[0040] Figure 4 This is a scanning electron microscope (SEM) image of the film made from the chitosan-based polyethylene glycol diglycidyl ether modified aqueous binder in Example 9 of the present invention. The scale bar is 10 μm.

[0041] Figure 5The infrared spectrum of the powder obtained after drying the chitosan-based polyethylene glycol diglycidyl ether modified waterborne binder in Example 9.

[0042] Figure 6 The test results show the cycle performance of lithium-ion batteries with negative electrodes prepared using the binders of Example 9, Comparative Example 1, and Comparative Example 2 of this invention (test conditions: 1C rate charging to 4.35V (constant voltage), 1C rate discharging to 3.0V).

[0043] Figure 7 The low-temperature (-20℃) discharge performance test charts of lithium-ion batteries with negative electrodes prepared using the binders of Example 9, Comparative Example 1, and Comparative Example 2 of this invention are shown. (Test conditions: pretreatment by charging at 0.2C rate to 4.35V (constant voltage) at room temperature, and discharging at 1C rate to 2.5V at -20℃). Detailed Implementation

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0050] While high-polymerization-degree chitosan (degree of deacetylation greater than 90%, molecular weight 100,000) can dissolve in acetic acid aqueous solution, its solubility does not meet the performance requirements of water-based adhesives. Therefore, this invention achieves its controlled degradation through peroxyacid degradation in a weakly acidic aqueous solution. The preferred specific operating steps are as follows:

[0051] (1) Dissolve high-polymerization-degree chitosan powder (degree of deacetylation greater than 90%, molecular weight > 100,000) in a peroxy acid aqueous solution (preferably 1 wt.%) according to a solid-liquid ratio of 10 g: 1 L, and continue stirring until a transparent viscous solution is formed;

[0052] (2) The solution system of step (1) is placed in an environment of 40-60℃ for 10-20 hours to complete the degradation and obtain a diluted chitosan solution;

[0053] (3) Neutralize the chitosan solution diluted in step (2) with LiOH solution (preferably 10wt%), and filter to remove insoluble chitosan;

[0054] (4) Take the clear low-polymerization degree chitosan solution filtered in step (3), mix it with excess ethanol to form a turbid liquid, and freeze-dry it to obtain a white powder of low-polymerization degree chitosan.

[0055] Among them, peroxy acids are one or more of peroxy organic acids or peroxy inorganic acids; such as peroxyformic acid, peroxyacetic acid, peroxytrifluoroacetic acid, peroxypropionic acid, peroxybutyric acid, peroxyisovaleric acid, long-chain peroxy fatty acids, peroxybenzoic acid, m-chloroperoxybenzoic acid, nitroperoxybenzoic acid, monoperoxyphthalic acid, peroxymonosulfuric acid, peroxydisulfuric acid, pernitric acid, peroxymonophosphate, peroxydiphosphate, percarbonic acid, perboric acid, etc.

[0056] The low-polymerization degree chitosan prepared by the degradation process of this invention has a degree of deacetylation > 90% and a molecular weight controlled between 8,000 and 10,000; at 25°C, its solubility in water is > 30 g / L, which meets the requirements of subsequent processes.

[0057] The high degree of polymerization chitosan powder used in this embodiment was purchased from Sigma Aldrich, product number 419419.

[0058] The preparation process of the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive of this invention is as follows: Figure 1 As shown; Figure 2 This invention describes the aqueous phase polymerization process of low-polymerization-degree chitosan and polyethylene glycol diglycidyl ether. Figure 3 The molecular structure model of the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive of this invention is presented.

[0059] Example 1

[0060] This embodiment provides a chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive. By mass percentage, the raw materials include the following components: 40% low-polymerization degree chitosan; 60% polyethylene glycol diglycidyl ether (Mn=500).

[0061] The preparation steps are as follows:

[0062] (1) Preparation of low-polymerization-degree chitosan:

[0063] a. Take 10 grams of high-polymerization-degree chitosan powder (degree of deacetylation greater than 90%, molecular weight > 100,000), dissolve it in 1 liter of 1 wt% peracetic acid aqueous solution, and stir continuously until a transparent viscous solution is formed;

[0064] b. The solution system of step a is placed in an environment of 40°C for 10 hours to complete the degradation and obtain a diluted chitosan solution;

[0065] c. Add a 10wt% LiOH solution to the chitosan solution diluted in step b to neutralize it until neutral, and filter to remove insoluble chitosan;

[0066] d. Take the clear, low-polymerization-degree chitosan solution filtered in step c, mix it with excess ethanol to form a turbid liquid, and freeze-dry it to obtain low-polymerization-degree chitosan.

[0067] The resulting low-polymerization degree chitosan was a white powder with a degree of deacetylation > 90%; GPC analysis showed that its number-average molecular weight was 9116 and its PDI was 1.6; at 25℃, its solubility in water was 38.7 g / L.

[0068] (2) Preparation of water-based adhesives:

[0069] The low-polymerization degree chitosan and polyethylene glycol diglycidyl ether (Mn=500) were mixed according to the mass percentage, and 100g of the mixture was dissolved in 1L of deionized water and stirred continuously. The resulting mixture was reacted at 60°C for 12 hours to obtain a transparent and viscous solution. After cooling the solution system to room temperature, it was diluted with water and filtered to obtain the target product, the water-based adhesive.

[0070] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content 15.0%, pH value 7.1, and viscosity 16.2 Pa·s.

[0071] Example 2

[0072] This embodiment provides a chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive. By mass percentage, the raw materials include the following components: 40% low-polymerization degree chitosan; 60% polyethylene glycol diglycidyl ether (Mn=2000).

[0073] The preparation steps are as follows:

[0074] (1) Preparation of low-polymerization-degree chitosan:

[0075] a. Take 10 grams of high-polymerization-degree chitosan powder (degree of deacetylation greater than 90%, molecular weight > 100,000), dissolve it in 1 liter of 1 wt% m-chloroperoxybenzoic acid aqueous solution, and stir continuously until a transparent viscous solution is formed;

[0076] b. The solution system of step a is placed at 50°C for 20 hours to complete the degradation and obtain a diluted chitosan solution;

[0077] c. Add a 10wt% LiOH solution to the chitosan solution diluted in step b to neutralize it, and filter to remove insoluble chitosan;

[0078] d. Take the clear, low-polymerization-degree chitosan solution filtered in step c, mix it with excess ethanol to form a turbid liquid, and freeze-dry it to obtain low-polymerization-degree chitosan.

[0079] The resulting low-polymerization degree chitosan was a white powder with a degree of deacetylation > 90%; GPC analysis showed that its number-average molecular weight was 9736 and its PDI was 1.7; at 25℃, its solubility in water was 38.6 g / L.

[0080] (2) Preparation of water-based adhesives:

[0081] The above-mentioned low-polymerization degree chitosan and polyethylene glycol diglycidyl ether (Mn=2000) were mixed according to the mass percentage, and 100g of the mixture was dissolved in 1L of deionized water and stirred continuously. The resulting mixture was reacted at 50°C for 24 hours to obtain a transparent and viscous solution. After cooling the solution system to room temperature, it was diluted with water and filtered to obtain the target product, the water-based adhesive.

[0082] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content 15.0%, pH value 7.1, and viscosity 16.5 Pa·s.

[0083] Example 3

[0084] This embodiment provides a chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive. By mass percentage, the raw materials include the following components: 40% low-polymerization degree chitosan; 60% polyethylene glycol diglycidyl ether (Mn=6000).

[0085] The preparation steps are as follows:

[0086] (1) Preparation of low-polymerization-degree chitosan:

[0087] a. Take 10 grams of high-polymerization-degree chitosan powder (degree of deacetylation greater than 90%, molecular weight > 100,000), dissolve it in 1 liter of 1 wt% peroxyformic acid aqueous solution, and stir continuously until a transparent viscous solution is formed;

[0088] b. The solution system of step a is placed in an environment of 60°C for 16 hours to complete the degradation and obtain a diluted chitosan solution;

[0089] c. Add a 10wt% LiOH solution to the chitosan solution diluted in step b to neutralize it, and filter to remove insoluble chitosan;

[0090] d. Take the clear, low-polymerization-degree chitosan solution filtered in step c, mix it with excess ethanol to form a turbid liquid, and freeze-dry it to obtain low-polymerization-degree chitosan.

[0091] The resulting low-polymerization degree chitosan was a white powder with a degree of deacetylation > 90%; GPC analysis showed that its number-average molecular weight was 9077 and its PDI was 1.4; at 25℃, its solubility in water was 38.5 g / L.

[0092] (2) Preparation of water-based adhesives:

[0093] The low-polymerization degree chitosan and polyethylene glycol diglycidyl ether (Mn=6000) were mixed according to the mass percentage, and 100g of the mixture was dissolved in 1L of deionized water and stirred continuously. The resulting mixture was reacted at 70°C for 20 hours to obtain a transparent and viscous solution. After cooling the solution system to room temperature, it was diluted with water and filtered to obtain the target product, the water-based adhesive.

[0094] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.1, and viscosity is 16.1 Pa·s.

[0095] Example 4

[0096] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 10% low-polymerization-degree chitosan; 90% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0097] The preparation method of the water-based adhesive is the same as in Example 1.

[0098] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.0, and viscosity is 15.0 Pa·s.

[0099] Example 5

[0100] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 20% low-polymerization-degree chitosan; 80% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0101] The preparation method of the water-based adhesive is the same as in Example 1.

[0102] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.0, and viscosity is 15.9 Pa·s.

[0103] Example 6

[0104] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 30% low-polymerization-degree chitosan; 70% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0105] The preparation method of the water-based adhesive is the same as in Example 1.

[0106] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.0, and viscosity is 16.1 Pa·s.

[0107] Example 7

[0108] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 45% low-polymerization-degree chitosan; 55% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0109] The preparation method of the water-based adhesive is the same as in Example 1.

[0110] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content 15.0%, pH value 7.0, and viscosity 16.6 Pa·s.

[0111] Example 8

[0112] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 50% low-polymerization-degree chitosan; 50% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0113] The preparation method of the water-based adhesive is the same as in Example 1.

[0114] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.1, and viscosity is 17.5 Pa·s.

[0115] Example 9

[0116] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 60% low-polymerization degree chitosan; 40% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization degree chitosan was prepared using the degradation method described in Example 2.

[0117] The preparation method of the water-based adhesive is the same as in Example 1.

[0118] Figure 4 This is a scanning electron microscope (SEM) image of the film made from the chitosan-based polyethylene glycol diglycidyl ether modified aqueous binder in Example 9 of the present invention. The scale bar is 10 μm.

[0119] The SEM sample preparation process is as follows: The chitosan-based polyethylene glycol diglycidyl ether modified waterborne binder prepared in Example 9 is dropped into a polytetrafluoroethylene mold, and the water is evaporated at room temperature to form a film. After drying, SEM testing is performed.

[0120] from Figure 4It can be seen that the microstructure of the membrane material is uniform, dense, non-porous, and continuous, with no obvious particles, cracks, or phase separation. This indicates that the low-polymerization degree chitosan and polyethylene glycol diglycidyl ether graft copolymerization reaction is sufficient, forming a uniform polymer network.

[0121] Figure 5 The infrared spectrum of the powder obtained after drying the chitosan-based polyethylene glycol diglycidyl ether modified waterborne binder in Example 9.

[0122] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.1, and viscosity is 17.6 Pa·s.

[0123] Example 10

[0124] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 70% low-polymerization-degree chitosan; 30% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0125] The preparation method of the water-based adhesive is the same as in Example 1.

[0126] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content 15.0%, pH value 7.2, and viscosity 18.0 Pa·s.

[0127] Example 11

[0128] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 80% low-polymerization-degree chitosan; 20% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0129] The preparation method of the water-based adhesive is the same as in Example 1.

[0130] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.2, and viscosity is 18.3 Pa·s.

[0131] Example 12

[0132] The only difference from Example 2 is that, by mass percentage, the raw materials include the following components: 90% low-polymerization-degree chitosan; 10% polyethylene glycol diglycidyl ether (Mn=2000). The low-polymerization-degree chitosan was prepared using the degradation method described in Example 2.

[0133] The preparation method of the water-based adhesive is the same as in Example 1.

[0134] The resulting water-based adhesive is a pale yellow transparent solution. At 40℃, its performance parameters are as follows: solid content is 15.0%, pH value is 7.2, and viscosity is 18.5 Pa·s.

[0135] Comparative Example 1

[0136] This comparative example provides an adhesive composed of CMC (sodium carboxymethyl cellulose) and SBR (styrene-butadiene rubber), with CMC:SBR = 1:2 (ratio based on solid weight).

[0137] Comparative Example 2

[0138] This comparative example provides an aqueous binder for lithium-ion batteries, which, by mass percentage, comprises: 5% chitosan, 45% methacrylic acid, 15% acrylamide, 5% butyl acrylate, and 30% acrylonitrile.

[0139] This lithium-ion battery is prepared by copolymerizing the above components in an aqueous phase using an aqueous binder. The specific preparation method is as follows:

[0140] (1) Chitosan (5%), a portion of methacrylic acid (5%), and 4-dimethylaminopyridine (1% of the mass of chitosan) were added to water, mixed evenly, and heated to 50°C and stirred continuously for 3 hours to prepare a partially acrylated chitosan aqueous solution. After the reaction solution cooled to room temperature, the remaining methacrylic acid (40%) and sodium hydroxide (11.6% of the mass of the added methacrylic acid) were added and neutralized to neutral. After neutralization was completed and cooled to room temperature, acrylamide (15%), butyl acrylate (5%), acrylonitrile (30%), and surfactant NP14 (1% of the total mass of butyl acrylate) were added in sequence and stirred vigorously at 300 rpm for 30 minutes to form an emulsion for polymerization reaction.

[0141] (2) Nitrogen gas was introduced into the emulsion system for 30 minutes to remove dissolved oxygen. The stirring speed was reduced to 100 rpm, and the temperature was raised to 60°C. Under these conditions, an aqueous solution of ammonium persulfate (0.1% of the total mass of the monomers, including methacrylic acid, acrylamide, acrylonitrile, and butyl acrylate) was slowly added dropwise, and the reaction temperature was controlled within the range of 60-76°C. The reaction was continued with stirring for 10 hours. After the reaction was completed, the mixture was cooled to room temperature. After removing unreacted monomers, diluting with water, and filtering, the target water-based binder was obtained.

[0142] The resulting adhesive was a white latex-like liquid with a solid content of 15.0% at 40°C, a pH of 6.8, and a viscosity of 15.8 Pa·s.

[0143] Example of effect verification:

[0144] To verify the performance of the aqueous binder prepared in this invention in lithium-ion batteries, the mechanical properties of the binder film, electrode peel strength, and battery electrochemical performance were tested respectively:

[0145] 1. Tensile modulus of elasticity and elongation at break test

[0146] Tensile specimens of the adhesive film were prepared according to ASTM D638 standard. Five parallel specimens were tested at each strain rate, and the average value was taken. All tensile tests were conducted in a constant temperature and humidity environment, with conditions set at 25°C and 40% RH.

[0147] The test results are shown in Table 1.

[0148] Table 1

[0149]

[0150] 2. 180° peel force test

[0151] The binders used in Examples 1-12 and Comparative Examples 1-2 of this invention were used to prepare negative electrode sheets, and their 180° peel strength was measured. The specific method is as follows: silicon carbon graphite (GS45 product of Ningbo Shanshan Co., Ltd.), binder (the binders prepared in Examples 1-12 and Comparative Examples 1-2 of this invention), and conductive carbon black (super-p) were added to deionized water according to the proportions in Table 2, and a negative electrode mixture slurry was prepared by a wet process. Then, the negative electrode mixture slurry was coated onto a 6-micron thick copper (Cu) foil current collector, and then dried and rolled to achieve an areal density of 20 mg / cm³. 2 The compacted density is 1.70 g / cm³. 3 .

[0152] The adhesion strength of the negative electrode sheet was tested according to ASTM D3330. The equipment and tools used were: YISIDA mechanical testing instrument (DS2-50N); 3M tape (Scotch 600 / 20mm wide). The test results are shown in Table 2.

[0153] Table 2

[0154]

[0155] Note: The above ratios are the mass ratios of the solid components.

[0156] 3. Battery performance testing

[0157] Batteries were fabricated using the binders prepared in some embodiments of this invention and Comparative Examples 1-2, and their performance was measured. The positive electrode sheet, battery assembly, electrolyte, and processing procedures were all completed using publicly available standard preparation methods and processes.

[0158] a. Preparation of the negative electrode sheet:

[0159] Same as the "180° peel force test" section.

[0160] b. Preparation of the positive electrode sheet:

[0161] Using a publicly available standard cathode preparation method, lithium iron phosphate compound (94 wt.%) as the cathode active material, carbon black (super-p, 2 wt.%) as the conductive material, and polyvinylidene 1,1-difluoroethylene (PVDF, 4 wt.%) as the binder were added to an N-methyl-2-pyrrolidone (NMP) solvent to prepare a cathode mixture slurry. This cathode mixture slurry was then coated onto a 12-micron-thick aluminum (Al) foil current collector, dried, and rolled to form an areal density of 39 mg / cm². 2 Compacted density 4.1 g / cm³ 3 The positive electrode sheet.

[0162] c. Battery winding and electrolyte injection:

[0163] A battery with specification 406379 was prepared using the electrodes described above. The battery was fabricated by winding the positive electrode, separator, and negative electrode, and packaged using an aluminum-plastic composite. An electrolyte of lithium hexafluorophosphate (LiPF6) with a concentration of 1 mol / L (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1 / 2 (volume ratio)) was injected into the assembled battery, and the battery was vacuum-sealed to obtain a battery ready for activation.

[0164] d. Battery formation

[0165] The obtained cells were left to stand at 45°C for 20 hours, then shaped by hot pressing at 95°C for 1 minute. The cells were then placed directly on a formation device without clamping, and formed at 30±2°C with a formation current of 1C for 100 minutes, achieving a formation cutoff potential of 4.35V. They were then subjected to a charge / discharge / charge cycle in a charge / discharge testing machine, with a cutoff potential of 3.8V. Finally, the cells were degassed and the gas bags were removed to obtain the battery. This process required only 8 minutes of hot and cold pressing, without the need for clamping each battery for formation, and the entire formation and capacity testing time was 270 minutes.

[0166] e. Battery performance testing

[0167] Cycle performance: The battery was charged to 4.35V at a 1C rate and then kept at a constant voltage of 4.35V. It was then discharged at a 1C rate with a cutoff voltage of 3.0V, completing one cycle. The results are shown in [link to results]. Figure 6 From Table 3 and Figure 6 As can be seen from the results, the product of Embodiment 9 of the present invention has good cycle performance.

[0168] Low-temperature discharge test: Under normal temperature conditions, the battery is charged to 4.35V at a 0.2C rate and then kept at a constant voltage of 4.35V. The cell is then placed at a set temperature for 16 hours and discharged at the corresponding temperature using a 1.0C rate current. The cutoff voltage is 2.5V. See details... Figure 7 And Table 3.

[0169] Table 3

[0170]

[0171] Note: Generally, a battery is considered to be in failure if its capacity retention rate is below 80%. In Comparative Example 1, the battery capacity was below 80% after 700 charge-discharge cycles, so the test was stopped after 700 cycles.

[0172] The battery performance test results above clearly show that the battery prepared using the binder of this invention has better performance.

[0173] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive, characterized in that, By mass percentage, the raw materials consist of the following components: 10-90% low-polymerization degree chitosan and 10-90% polyethylene glycol diglycidyl ether, totaling 100%; The low-polymerization-degree chitosan was obtained by the following degradation method: Highly polymerized chitosan is dissolved in an aqueous solution containing peroxy acid to form a homogeneous reaction system; The homogeneous reaction system is kept at 40-60℃ for 10-20h to allow chitosan to undergo oxidative degradation. After the oxidative degradation is completed, the pH of the system is adjusted to neutral, and the insoluble matter is removed by filtration to obtain a low degree of polymerization chitosan solution. The low-polymerization-degree chitosan solution was subjected to alcohol precipitation, the precipitate was collected and freeze-dried to obtain low-polymerization-degree chitosan. The high degree of polymerization chitosan has a degree of deacetylation greater than 90% and a number-average molecular weight greater than 100,000. The resulting low-polymerization degree chitosan has a deacetylation degree greater than 90% and a number-average molecular weight of 0.8-10,000; its solubility in water at 25°C is greater than 30 g / L. The peroxy acid is selected from at least one of peroxy organic acid or peroxy inorganic acid; The concentration of the aqueous solution of the peroxy acid is 0.5-10 wt%. The pH is adjusted using an alkaline solution, wherein the alkaline solution is an aqueous solution of LiOH, NaOH, or KOH. The number-average molecular weight of the polyethylene glycol diglycidyl ether is Mn = 500-6000.

2. The preparation method of the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive as described in claim 1, characterized in that, Includes the following steps: (1) Dissolve the low-polymerization degree chitosan and polyethylene glycol diglycidyl ether in deionized water to form a mixture; (2) The mixture is stirred at 50-70°C for 12-24 hours, and then subjected to aqueous graft copolymerization to obtain a transparent viscous solution. (3) Cool the transparent viscous solution, dilute it with water and filter it, collect the filtrate to obtain the chitosan-based polyethylene glycol diglycidyl ether modified waterborne adhesive.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the total mass of the low-polymerization degree chitosan and polyethylene glycol diglycidyl ether to the mass of deionized water is 1:10-1:

5.

4. The application of the chitosan-based polyethylene glycol diglycidyl ether modified aqueous binder as described in claim 1 in the silicon-carbon anode of lithium-ion batteries.

Images