Modified binder and method for producing the same, secondary battery

Abstract

This application relates to the field of lithium-ion battery technology, and particularly to modified binders and their preparation methods, and secondary batteries. The modified binder comprises the following raw material components: a carboxyl-containing polymer binder; polyurethane, wherein nitrogen-containing heterocyclic groups are grafted into the molecular chain of the polyurethane, and these nitrogen-containing heterocyclic groups contain hydrogen bond acceptor groups and hydrogen bond donor groups; and a crosslinking agent, which contains hydrogen bond donor groups, hydrogen bond acceptor groups, and positively charged groups. The carboxyl-containing polymer binder provides basic bonding properties; the polyurethane provides flexibility and elasticity. Based on this, the polyurethane and the crosslinking agent form a complementary pairing pattern similar to hydrogen bonds in DNA and RNA, allowing the crosslinking agent to accurately recognize the nitrogen-containing heterocyclic groups on the polyurethane, resulting in high bonding strength. The crosslinking agent and the carboxyl-containing polymer binder exhibit electrostatic adsorption. The modified binder possesses high flexibility, elasticity, and adhesive properties, effectively mitigating the impact caused by the volume expansion of silicon-based anode materials.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to modified binders and their preparation methods, and secondary batteries. Background Technology

[0002] The negative electrode of lithium-ion batteries is gradually shifting from traditional graphite systems to high-capacity silicon-based materials. However, silicon-based negative electrodes undergo significant volume expansion during charge and discharge, impacting the bonding system in the film layer and leading to problems such as electrode structure cracking and poor cycle stability. To address this, existing technologies have begun to modify traditional negative electrode binders by incorporating polyurethane and small-molecule crosslinking agents. The small-molecule crosslinking agents provide crosslinking sites, while the flexibility and elasticity of polyurethane synergistically improve the overall mechanical properties of the binder, thereby buffering the volume changes of the silicon-based material.

[0003] However, this modified binder still has many problems. First, the degree of crosslinking between the small molecule crosslinking agent and the binder substrate, polyurethane, and silicon-based materials is limited. After charge-discharge cycles, the bonding strength between the binder substrate and the polyurethane decreases significantly, allowing each to perform only its own function, resulting in a substantial reduction in the modification effect. Furthermore, the bonding strength between the modified binder and the silicon-based materials also decreases, making them prone to detachment. Second, its applicability is limited. This modified binder is often only suitable for a single negative electrode, such as one of the products made of nano-silicon materials, micron-silicon materials, or silicon-carbon materials. Third, the crosslinking reaction it induces is difficult to control in terms of binding sites and reaction rate, resulting in complex reaction kinetics and uncontrollable product structure and mechanism of action, which is not conducive to scaling up to industrial production. Therefore, the improvement effect of introducing polyurethane in this method is limited.

[0004] Therefore, this polyurethane-introduced negative electrode binder system needs further optimization. Summary of the Invention

[0005] The purpose of this application is to provide a modified binder and its preparation method, and a secondary battery, aiming to solve the technical problem that the modification effect of introducing polyurethane into the negative electrode binder in the prior art is not good.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a modified adhesive comprising the following raw material components:

[0008] Carboxyl-containing polymer adhesives;

[0009] Polyurethane has nitrogen-containing heterocyclic groups grafted into its molecular chain. These nitrogen-containing heterocyclic groups contain one hydrogen bond acceptor group and one hydrogen bond donor group.

[0010] Crosslinking agents contain hydrogen bond donor groups, hydrogen bond acceptor groups, and positively charged groups.

[0011] The modified adhesive of this application includes a carboxyl-containing polymer adhesive commonly used in negative electrodes, which provides basic bonding properties; it also includes polyurethane, which can leverage its flexibility and elasticity to improve the mechanical properties of the modified adhesive. Based on this, firstly, the nitrogen-containing heterocyclic groups grafted into the polyurethane molecular chain can provide strong hydrogen bond acceptor and hydrogen bond donor groups, and the crosslinking agent also contains hydrogen bond donor and hydrogen bond acceptor groups. On the one hand, at least two pairs of complementary hydrogen bonds are formed between the two, similar to the pairing pattern in DNA and RNA, allowing the crosslinking agent to accurately recognize the nitrogen-containing heterocyclic groups on the polyurethane, i.e., to bind the crosslinking agent to a specific position in the polyurethane, which is beneficial for controlling the structure of the modified adhesive; on the other hand, the crosslinking agent can form multiple hydrogen bond interactions with the polyurethane, increasing the bonding strength between the two. Secondly, the crosslinking agent contains positively charged groups, and the carboxyl groups in the carboxyl-containing polymer adhesive are negatively charged, resulting in electrostatic adsorption between the two, further increasing the bonding strength. Therefore, polyurethane and carboxyl-containing polymer binders can achieve a tight bond through the crosslinking agent, spontaneously assembling to form a stable and controllable three-dimensional crosslinked network. This allows for long-term synergistic performance of both, significantly improving the modification effect of polyurethane on carboxyl-containing polymer binders, enhancing the flexibility and elasticity of the modified binders, and effectively mitigating the impact of volume expansion of silicon-based anode materials.

[0012] Secondly, this application provides a method for preparing the modified adhesive described above, comprising the following steps:

[0013] A modified adhesive is obtained by mixing components including a carboxyl-containing polymer binder, polyurethane, and a crosslinking agent.

[0014] The preparation method of this application involves mixing components including polyurethane with nitrogen-containing heterocyclic groups grafted onto its molecular chain, a carboxyl-containing polymer binder, and a crosslinking agent. Both the nitrogen-containing heterocyclic groups and the crosslinking agent contain hydrogen bond donor and acceptor groups, enabling the formation of at least two pairs of complementary hydrogen bonds. This results in precise recognition and high bonding strength. The crosslinking agent also contains positively charged groups, which can electrostatically adsorb onto the carboxyl groups in the carboxyl-containing polymer binder. This preparation method offers controllable processing, allowing these components to form a three-dimensional crosslinked network. The resulting modified binder exhibits excellent adhesion, flexibility, and elasticity, effectively mitigating the impact of volume expansion in silicon-based anode materials.

[0015] Thirdly, this application provides a secondary battery, wherein the negative electrode film layer of the secondary battery includes the modified binder of this application described above, or includes the modified binder prepared by the preparation method of this application described above.

[0016] Because the modified binder has high viscosity, elasticity, and flexibility, it can be applied to various negative electrode active materials, especially various silicon-based materials. It can buffer the stress impact caused by the volume expansion of silicon-based materials and stabilize the capacity performance and charge-discharge life of the negative electrode made of silicon-based materials during battery cycling. Therefore, the negative electrode film layer of the secondary battery of this application has good structural stability and is not prone to cracking or detachment. The secondary battery has high cycle stability, rate performance, and service life. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is the infrared spectrum of the polyurethane synthesized in Example AS1 of this application;

[0019] Figure 2 This is a stress-strain tensile test curve of the polyurethane synthesized by AS2 in embodiment AS of this application;

[0020] Figure 3 This is a graph showing the results of a 10-cycle tensile-rebound cycle test on the AS3 synthetic polyurethane of this application embodiment;

[0021] Figure 4 This is a graph showing the results of a 10-cycle tensile-rebound cycle test on the AS4 synthetic polyurethane of this application embodiment;

[0022] Figure 5 This is a comparison chart of the coin cells of embodiment BS1 and blank group BK1 of this application after 300 charge-discharge cycle tests;

[0023] Figure 6 This is a comparison chart of the 100 charge-discharge cycle test of the button cells of embodiment BS2 and blank group BK2 in this application;

[0024] Figure 7 This is a comparison chart of the rate performance test results of coin cells of embodiment BS3 and blank group BK3 in this application;

[0025] Figure 8 This is a comparison chart of the peel strength test results of the negative electrode sheet in the coin cell of embodiment BS4 and blank group BK4 of this application;

[0026] Figure 9 This is a SEM image of the negative electrode plate of the blank group BK5 button cell after 70 cycles.

[0027] Figure 10 This is a SEM image of the negative electrode sheet of the coin cell of embodiment BS5 of this application after 70 cycles.

[0028] Figure 11 This is a schematic diagram illustrating the mechanism of interaction between the modified binder and the silicon-based material surface before the negative electrode film layer is heated.

[0029] Figure 12 This is a schematic diagram illustrating the mechanism of interaction between the modified binder and the silicon-based material surface after the negative electrode film layer is heated. Detailed Implementation

[0030] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0032] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions mean any combination of these items, including any combination of single or multiple items.

[0033] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0034] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0035] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, a first feature may also be referred to as a second feature, and similarly, a second feature may also be referred to as a first feature. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0036] The first aspect of this application provides a modified adhesive, comprising the following raw material components:

[0037] Carboxyl-containing polymer adhesives;

[0038] Polyurethane has nitrogen-containing heterocyclic groups grafted into its molecular chain. These nitrogen-containing heterocyclic groups contain one hydrogen bond acceptor group and one hydrogen bond donor group.

[0039] Crosslinking agents contain hydrogen bond donor groups, hydrogen bond acceptor groups, and positively charged groups.

[0040] The term "raw material components" as used above refers to modified adhesives made from at least the carboxyl-containing polymer adhesives, polyurethanes and crosslinking agents listed above. Specifically, modified adhesives may include physical mixtures of these raw material components, chemical products formed by chemical reactions or chemical bonding of these raw material components, or both physical mixtures and chemical products.

[0041] The modified adhesive in this application includes a carboxyl-containing polymer adhesive commonly used in negative electrodes, which provides basic bonding properties; it also includes polyurethane, which leverages its flexibility and elasticity to improve the mechanical properties of the modified adhesive. Based on this, firstly, the nitrogen-containing heterocyclic groups grafted into the polyurethane molecular chain provide strong hydrogen bond acceptor and hydrogen bond donor groups, and the crosslinking agent also contains hydrogen bond donor and hydrogen bond acceptor groups. On one hand, at least two pairs of complementary hydrogen bonds are formed between them, similar to the pairing pattern in DNA and RNA, allowing the crosslinking agent to accurately recognize the nitrogen-containing heterocyclic groups on the polyurethane, i.e., to bind the crosslinking agent to a specific position in the polyurethane, which is beneficial for controlling the structure of the modified adhesive; on the other hand, the crosslinking agent can form multiple hydrogen bond interactions with the polyurethane, increasing the bonding strength between the two. Secondly, the crosslinking agent contains positively charged groups, and the carboxyl groups in the carboxyl-containing polymer adhesive are negatively charged, resulting in electrostatic adsorption between the two, further increasing their bonding strength. Therefore, polyurethane and carboxyl-containing polymer binders can achieve a tight bond through a crosslinking agent, spontaneously assembling into a stable and controllable three-dimensional crosslinked network. This allows for long-term synergistic performance enhancement, significantly improving the modification effect of polyurethane on carboxyl-containing polymer binders, improving the flexibility and elasticity of the modified binders, and effectively mitigating the impact of volume expansion in silicon-based anode materials. The following will detail the components of the modified binder.

[0042] Regarding carboxyl-containing polymer adhesives.

[0043] Carboxyl-containing polymers are commonly used anode binders. Rich in carboxyl groups, they exhibit strong hydrogen bonding, resulting in strong adhesion to both the anode active material and the current collector. They also possess certain elasticity, flexibility, self-healing properties, and water-processability. In some embodiments, carboxyl-containing polymer binders may include at least one of polyacrylic acid (PAA) and its salts, carboxymethyl cellulose and its salts, alginate and its salts, polyacrylamide and its salts, polyacrylonitrile, and guar gum and its salts. The aforementioned salt binders may include at least one of lithium, sodium, potassium, magnesium, zinc, or calcium salts. These binders are suitable for most anode material systems, such as those containing silicon-based materials. Formulating salt binders can balance solubility, processing performance, and stability in aqueous slurries.

[0044] In some embodiments, the carboxyl-containing polymer binder has a carboxyl group content of 20% to 80% by mass, including but not limited to any value or any two values ​​between 20%, 40%, 50%, 60%, and 80%, which can be determined by nuclear magnetic resonance hydrogen spectroscopy. In some embodiments, the carboxyl-containing polymer binder has a weight-average molecular weight of 100,000 to 3,000,000, including but not limited to any value or any two values ​​between 100,000, 500,000, 1,000,000, 2,000,000, and 3,000,000. These carboxyl-containing polymer binders with varying carboxyl group content or molecular weight can balance various properties such as adhesion, stability of the formulated negative electrode slurry, flexibility, and elasticity.

[0045] About polyurethane.

[0046] Existing technologies introduce polyurethane as a modifying component in adhesives primarily due to its excellent flexibility and elastic recovery capabilities. However, these technologies often treat it merely as an independent elastomer, using only conventional crosslinking agents for simple linkage. This results in random crosslinking sites and poor crosslinking stability, limiting the effectiveness of the introduced polyurethane. In contrast, the polyurethane in this application is grafted with nitrogen-containing heterocyclic groups, which possess strong hydrogen bonding interactions. These groups contain both hydrogen bond acceptor and hydrogen bond donor groups, enabling them to form strong complementary hydrogen bond interactions with the hydrogen bond donor and acceptor groups in the crosslinking agent. Specifically, the polyurethane and crosslinking agent correspond their respective hydrogen bond donor groups to each other's hydrogen bond acceptor groups, or vice versa, achieving a specific recognition mechanism similar to two-point or three-point hydrogen bond recognition in DNA and RNA base pairing.

[0047] Based on this, crosslinking agents are generally small molecules, and a single crosslinking agent molecule typically only crosslinks to one region on the polyurethane molecule. Therefore, by designing the distribution region of nitrogen-containing heterocyclic groups within the polyurethane molecular chain, the region of the crosslinking site of the crosslinking agent in the polyurethane molecular chain can be precisely controlled, achieving ordered self-assembly between the polyurethane and the crosslinking agent. Furthermore, this hydrogen bond interaction also exhibits high bonding strength, making it difficult for the crosslinking agent to detach from the polyurethane molecular chain, thus significantly improving the stability of the crosslinked structure.

[0048] Ideally, because the crosslinking agent is a small molecule, the distance between a polyurethane molecular chain and a carboxyl-containing polymer binder molecular chain that has already been crosslinked is very close in the crosslinking region. Other polymer molecular chains are difficult to penetrate between them, which allows the polyurethane molecular chain and the carboxyl-containing polymer binder molecular chain to guide each other's extension, improve the synergistic effect between the two, and thus enhance the modification effect of introducing polyurethane.

[0049] In some embodiments, the number of hydrogen bond acceptor groups in the nitrogen-containing heterocyclic group is equal to the number of hydrogen bond donor groups in the crosslinking agent, and the number of hydrogen bond donor groups in the nitrogen-containing heterocyclic group is equal to the number of hydrogen bond acceptor groups in the crosslinking agent. This matching of numbers further facilitates precise hydrogen bond complementary pairing between the polyurethane and the crosslinking agent, improving the specificity and accuracy of recognition. In an exemplary embodiment, each may contain one hydrogen bond donor and one acceptor group, forming two pairs of complementary hydrogen bonds, mimicking the two-point hydrogen bond recognition pattern in DNA; in another exemplary embodiment, three pairs of complementary hydrogen bonds may be formed, mimicking the three-point hydrogen bond recognition pattern in DNA. If the number is further increased, there are higher requirements for the spatial positional relationship and order between the hydrogen bond acceptors and hydrogen bond donors in their respective structures, in order to improve the accuracy of matching.

[0050] In some embodiments, the nitrogen-containing heterocyclic group includes at least one of pyrimidine groups, pyridine groups, and purine groups. This statement should be interpreted broadly; the nitrogen-containing heterocyclic group can refer to the collection of all nitrogen-containing heterocyclic groups in the polyurethane molecular chain, which may include one or more of the aforementioned groups; it can also refer to a specific side chain group grafted into the polyurethane molecular chain, which may contain one or more of the aforementioned groups. Base pairing in DNA and RNA follows this pattern: adenine (A) pairs with thymine (T) or uracil (U) through two hydrogen bonds, and guanine (G) pairs with cytosine (C) through three hydrogen bonds. Due to the high specificity of their group structure and hydrogen bond binding mode, base pairing has extremely high recognition accuracy and binding stability. Referring to the above recognition mechanism, when the nitrogen-containing heterocyclic group includes at least one of the aforementioned pyrimidine groups, pyridine groups, and purine groups, it can mimic the specific hydrogen bond recognition between bases with the crosslinking agent, achieving precise and orderly assembly between the polyurethane and the crosslinking agent.

[0051] In some embodiments, the grafting rate of nitrogen-containing heterocyclic groups in the polyurethane is 2% to 15%, including but not limited to any value or any two values ​​between 2%, 5%, 8%, 12%, and 15%. This grafting rate is a mass percentage. Such a grafting rate range is beneficial for the polyurethane to contain a larger number of nitrogen-containing heterocyclic groups, enabling hydrogen bond recognition and bonding with a larger number of crosslinking agents. It also avoids affecting the flexibility and elasticity of the polyurethane molecular chain due to an excessively high grafting rate, and prevents excessive crosslinking at too many positions in the molecular chain, thus limiting the spatial conformation of the polyurethane. Therefore, these grafting rates are beneficial for improving the uniformity and stability of the crosslinked structure formed in the modified binder.

[0052] In some embodiments, the nitrogen-containing heterocyclic group is located between the hard and soft segments of the polyurethane molecular chain. In existing technologies, the crosslinking sites between polyurethane and the crosslinking agent are relatively random. The middle of the soft and hard segments often crosslinks with external molecular chains, causing the soft and hard segments to be frequently affected by external molecular chains. This makes it difficult for each segment to fully exert its performance advantages, such as the mobility and elasticity of the soft segments. However, in the embodiments of this application, the nitrogen-containing heterocyclic group is located between the hard and soft segments. Its specific hydrogen bond recognition with the crosslinking agent can accurately anchor the crosslinking sites, so that the crosslinking region between the polyurethane molecular chain and the outside world is concentrated between the hard and soft segments. Therefore, in complex three-dimensional crosslinking structures, this structure can effectively reduce the influence of external molecular chains on the soft and hard segments of the polyurethane molecular chain, allowing each segment to fully exert its performance advantages and macroscopically improving the modification effect of introducing polyurethane into the modified binder.

[0053] In some embodiments, the weight-average molecular weight of polyurethane is 20,000 to 200,000, which may include, but is not limited to, any value or any range between two values ​​of 20,000, 50,000, 100,000, 150,000 and 200,000. Polyurethanes with these molecular weights can possess various properties such as flexibility and elasticity.

[0054] Regarding crosslinking agents.

[0055] Crosslinking agents are used to crosslink the molecular chains of polyurethane and carboxyl-containing polymer binders, enabling the main chains of both to work synergistically. The hydrogen bond donor and acceptor groups in the crosslinking agent form complementary hydrogen bond pairs with the polyurethane molecules, allowing for precise identification of the polyurethane molecules and improving the bonding strength. Simultaneously, the positively charged groups in the crosslinking agent can electrostatically adsorb the carboxyl groups in the carboxyl-containing polymer binder, further enhancing the bonding strength. Thus, the crosslinking agent can spontaneously assemble with both the polyurethane and the carboxyl-containing polymer binder, crosslinking them together. In some embodiments, some positively charged groups in the crosslinking agent can also act as hydrogen bond donor groups; the specific role they play depends on the structure of the crosslinking agent and the structure of the nitrogen-containing heterocyclic groups.

[0056] In some embodiments, the crosslinking agent includes at least one selected from guanidinoacetic acid, guanidinourea, serine, malonamide, barbituric acid, and cyanuric acid, and may be selected from at least one selected from guanidinoacetic acid and guanidinourea. These crosslinking agents contain both hydrogen bond donor groups and hydrogen bond acceptor groups, as well as positively charged groups, which can achieve efficient crosslinking with polyurethane and carboxyl-containing polymer adhesives through complementary hydrogen bond pairing and electrostatic adsorption, respectively, significantly improving the degree of crosslinking between polyurethane and carboxyl-containing polymer adhesives.

[0057] In some embodiments, the mass ratio of the carboxyl-containing polymer binder, polyurethane, and crosslinking agent is (1-30):(1-3):1, which may include, but is not limited to, any ratio or any range between two of the ratios of (1 or 5 or 10 or 20 or 30):(1 or 2 or 3):1. These ratios facilitate efficient crosslinking between polyurethane and the carboxyl-containing polymer binder, taking into account both the processing performance and bonding performance of the binder system, while giving full play to the elasticity and toughness advantages of the introduced polyurethane, thereby improving the overall performance of the modified binder. In particular, when used for silicone-based materials, it can buffer the impact caused by volume expansion.

[0058] In some embodiments, the modified binder contains a pH adjuster, which includes at least one selected from sulfuric acid, citric acid, maleic acid, malonic acid, phytic acid, arginine, and lysine. On the one hand, the introduction of a pH adjuster can effectively regulate the acid-base environment of the system, promote cross-linking reactions, enhance the stability of hydrogen bonding and electrostatic interactions, and improve the processing performance of the formulated slurry. On the other hand, these types of pH adjusters facilitate interaction with the silanol groups on the surface of the negative electrode active material, such as silicon-based materials, including but not limited to hydrogen bonding or further formation of ester groups or other chemical bonds at certain temperatures, further improving the bonding strength between the modified binder and the negative electrode active material. Therefore, the pH adjuster can further optimize the overall performance of the modified binder.

[0059] Existing adhesives function as bonds, such as carboxyl-containing polymer adhesives and silicon-based materials, primarily through the bonding of carboxyl groups with hydroxyl groups on the silicon surface, which can form chemical bonds during subsequent heating. In some embodiments, the modified adhesive contains metal ions with a positive charge. These metal ions can not only electrostatically adsorb onto the carboxyl groups in the carboxyl-containing polymer adhesive, but also, in an example, further electrostatically adsorb onto the aforementioned pH adjuster. This provides a further bonding pathway—negative electrode active material-pH adjuster-metal ions-carboxyl-containing polymer adhesive—on top of the bonding between the carboxyl groups of the carboxyl-containing polymer adhesive and the surface groups of the negative electrode active material, thereby further improving the bonding strength between the modified adhesive and the negative electrode active material. Figure 11 , Figure 12 As shown. These metal ions may include, but are not limited to, at least one of lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, and calcium ions. These metal ions may be provided by at least one of carboxyl-containing polymer binders, the aforementioned pH adjusters, and additional metal compounds. For example, carboxyl-containing polymer binders are often highly acidic, and therefore are often used as raw materials in the form of their salts; the same applies to pH adjusters.

[0060] In some embodiments, the modified binder contains water, has a solid content of 5% to 50%, and a pH value of 5 to 8. The modified binder of this application embodiment is suitable for aqueous systems. The modified binder solution with the above-mentioned solid content and pH value can be better used for the preparation of negative electrode slurries. It can be used with components such as negative electrode active materials to prepare slurries, and has good processing performance and film-forming performance.

[0061] A second aspect of this application provides a method for preparing the modified adhesive described in the above-described embodiments, comprising the following step S10:

[0062] S10. The components, including a carboxyl-containing polymer binder, polyurethane, and a crosslinking agent, are mixed to obtain a modified binder.

[0063] The preparation method of this application involves mixing components including polyurethane with nitrogen-containing heterocyclic groups grafted onto its molecular chain, a carboxyl-containing polymer binder, and a crosslinking agent. Both the nitrogen-containing heterocyclic groups and the crosslinking agent contain hydrogen bond donor and acceptor groups, enabling the formation of at least two pairs of complementary hydrogen bonds. This results in precise identification and high bonding strength. The crosslinking agent also contains positively charged groups, which can electrostatically adsorb onto the carboxyl groups in the carboxyl-containing polymer binder. This preparation method offers process control, allowing these components to form a three-dimensional crosslinked network. The resulting modified binder exhibits excellent adhesion, flexibility, and elasticity, effectively mitigating the impact of volume expansion in silicon-based anode materials.

[0064] In some embodiments, step S10 can be further divided into the following steps S11 to S14:

[0065] S11. Prepolymerize raw materials including polyols and polyisocyanates to obtain a first prepolymer;

[0066] S12. The raw materials including the first prepolymer and the functional organic compound are subjected to a first chain extension treatment to obtain a second prepolymer, wherein the functional organic compound includes nitrogen-containing heterocyclic groups;

[0067] S13. The raw materials, including the second prepolymer and the chain extension agent, are subjected to a second chain extension treatment to obtain polyurethane;

[0068] S14. The synthesized polyurethane is mixed with components including a carboxyl-containing polymer binder and a crosslinking agent.

[0069] Step S11 involves prepolymerizing polyols and polyisocyanates, where hydroxyl and isocyanate groups undergo addition reactions to form urethane bonds, generating a low-molecular-weight first prepolymer containing NCO-terminated end groups. This forms soft segments and provides reaction sites for subsequent steps. Step S12 introduces nitrogen-containing heterocyclic groups into the first prepolymer, resulting in a second prepolymer as the molecular chain lengthens. Step S13 further extends the chain segments using a chain extender to obtain polyurethane. Through steps S11 to S13, nitrogen-containing heterocyclic groups can be grafted into the molecular chain of this polyurethane, which is then combined with other components to prepare a modified binder.

[0070] Specifically, step S11 involves an addition reaction between polyols and polyisocyanates to form soft segments. The main function of hydrophilic polyols is to provide multiple hydroxyl groups as reactive groups, and their weight-average molecular weight ranges from 400 to 4000, with slightly higher molecular weights offering better flexibility. In some embodiments, the polyols may include hydrophilic polyols and / or hydrophobic polyols. Hydrophilic polyols, as raw materials, are beneficial for improving the hydrophilicity of the subsequently produced polyurethane. They may include at least one of polyethylene glycol (PEG), polyethylene glycol monomethyl ether (MPEG), polyethylene oxide-propylene oxide copolymer (PEO-PPO, EO / PO ratio > 2:1 to ensure hydrophilicity), polytrimethylene ether glycol (PO3G), and polycarbonate glycol (PCD). Hydrophobic polyols, used as raw materials, help balance hydrophilicity and hydrophobicity, reducing the risk of swelling or dissolution of polyurethane due to excessive hydrophilicity. These polyols can include at least one of polypropylene glycol (PPG), polytetrahydrofuran (PTMEG), polycaprolactone diol (PCL), polyhexyl carbonate (PCDL), polybutadiene glycol (PBD), castor oil-based polyols, and soybean oil-based polyols. The mass ratio of the hydrophilic to hydrophobic polyol can be (1.5–4):1, including but not limited to any ratio or range between two of 1.5:1, 2:1, 3:1, and 4:1. These ratios help to produce polyurethanes that balance hydrophilicity and structural stability. In an example, various polyols can be mixed and thoroughly stirred before reacting with polyisocyanates.

[0071] The main function of polyisocyanates is to provide multiple isocyanate groups as reactive groups, which may include at least one of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), butyl diisocyanate (BDI, 1,4-butanediisocyanate), pentyl diisocyanate (PDI, 1,5-pentanediisocyanate), dicyclohexylmethane 4,4'-diisocyanate (H12MDI), cyclohexane 1,3-diisocyanate (CHDI), norbornane diisocyanate (NBDI), cyclohexane 1,4-diisocyanate (1,4-CHDI), diphenylmethane 4,4'-diisocyanate (MDI), toluene diisocyanate (TDI, 2,4- / 2,6-isomer), lysine diisocyanate (LDI), and isocyanurate ring (HDI trimer). These polyisocyanate raw materials can provide multiple isocyanate groups, which can undergo addition reactions with hydroxyl groups to form the first prepolymer of the desired end-capped NCO with polyols.

[0072] In some embodiments, the molar ratio of polyols to polyisocyanates is 1:(0.6–2.4), and may include, but is not limited to, any ratio or any range between two of 1:0.6, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2.0, and 1:2.4. When the polyols contain both hydrophilic and hydrophobic polyols, they can be formulated at a molar ratio of 1:(1–3) for both hydrophilic and polyisocyanates. These molar ratios of polyols reacting with polyisocyanates can control the degree of prepolymerization and the length of the soft segments formed.

[0073] In some embodiments, the raw materials for prepolymerization further include carboxyl-containing polyols and / or catalysts. The multiple hydroxyl groups in the carboxyl-containing polyol can undergo addition reactions with polyisocyanates, thereby introducing carboxyl groups into the main chain of the first prepolymer. If a neutralization treatment is subsequently performed, the carboxyl groups can generate carboxylate salts. The resulting ionic groups can improve the hydrophilicity of the subsequently produced polyurethane and facilitate the formation of stable micelles in water, improving its dispersion stability in water while preventing excessive hydrophilicity that could lead to swelling or dissolution. In exemplary cases, the carboxyl-containing polyol may include, but is not limited to, materials such as dimethylolpropionic acid (DMPA). The amount of carboxyl-containing polyol can be proportioned according to a mass ratio of hydrophilic polyol to carboxyl-containing polyol of (10-20):1. It can be added simultaneously and mixed evenly during the mixing of various polyols to ensure uniform distribution of carboxyl groups in the prepolymer.

[0074] Catalysts can lower the activation energy of the reaction, catalyze the addition reaction of polyols and polyisocyanates, improve reaction efficiency and selectivity, reduce side reactions, and facilitate the preparation of a first prepolymer with a uniform molecular weight distribution. Catalysts can include organotin catalysts, such as dibutyltin dilaurate (DBTDL) and stannous octoate. The amount of catalyst can be formulated according to a mass ratio of polyisocyanate to catalyst of (50–200):1. This range effectively promotes the reaction to form the first prepolymer without causing the reaction to be too rapid and difficult to control due to excessive dosage. These catalysts will continue to play a catalytic role in subsequent steps S12 and S13.

[0075] In some embodiments, the temperature of the prepolymerization treatment is 65°C to 85°C, which may include, but is not limited to, any value or any two of 65°C, 70°C, 75°C, 80°C, and 85°C. These temperature ranges are conducive to promoting the addition reaction between polyols and isocyanates to generate the first prepolymer, while reducing side reactions.

[0076] The prepolymerization process in step S11 can be achieved by first thoroughly mixing polyols and carboxyl-containing polyols, then adding polyisocyanates dropwise, adding the catalyst all at once, and stirring at 400 rpm to 800 rpm for 1 to 4 hours to ensure thorough mixing and the addition reaction. Referring to step S11 above, the weight-average molecular weight of the prepolymer can be 5000 to 10000, with a uniform molecular weight distribution among the prepolymer molecules.

[0077] Step S12 is a further step of subjecting the first prepolymer and the functional organic compound to a second chain extension treatment, in order to graft nitrogen-containing heterocyclic groups onto the molecular chain of the first prepolymer to achieve functional modification. In some embodiments, the functional organic compound may include 5-(hydroxymethyl)uracil, 6-amino-1,3-dimethyluracil, 5,6-diamino-2,4-dihydroxypyrimidine, 4,5-diamino-6-hydroxy-2-mercaptopyrimidine, 5-aminouracil, 5-hydroxyuracil, 5-(hydroxymethyl)thymidine, 5-aminothymidine, 5-aminocytosine, 5-(hydroxymethyl)cytosine, 1,3,5- At least one of the following functionalized organic compounds: tris(hydroxymethyl)isocyanuric acid, 5,5-dimethylisocyanuric acid, 2-amino-4,6-dihydroxypyrimidine, 4-amino-2,6-dichloropyrimidine, 2-hydroxypyridine, 3-hydroxypyridine, 4-hydroxypyridine, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 3,5-dichloro-2-hydroxypyridine, 5-amino-2-methylpyridine, 2,6-dihydroxypyridine, and 2,6-diaminopyridine. These functionalized organic compounds contain groups, such as hydroxyl and amino groups, that can undergo nucleophilic addition reactions with polyisocyanates to form urethane (-NHCOO-) or urea bonds (-NHCONH-). Grafting these into the first prepolymer yields the second prepolymer. Furthermore, the selected functionalized organic compounds possess unique structures that allow hydroxyl and amino groups to preferentially react with isocyanate groups during nucleophilic addition reactions, as these groups exhibit higher reactivity than those on nitrogen-containing heterocyclic groups, thus minimizing their impact on the nitrogen-containing heterocyclic groups. These nitrogen-containing heterocyclic groups contain hydrogen bond donor and acceptor groups, and some groups (such as uracil and thymine) also have complementary base pairings with DNA or RNA bases, enabling the final polyurethane to form precise recognition and strong bonds with the crosslinking agent.

[0078] In some embodiments, the functional organic compound can be added at a molar ratio of (2-10):1 between the polyisocyanate in step S11 and the functional organic compound in step S12. This ratio can include, but is not limited to, any value or a range between any two values ​​from 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1. This ratio allows the functional organic compound to be grafted into the first prepolymer as much as possible to obtain the desired second prepolymer, while reserving a portion of the polyisocyanate for subsequent second chain extension treatment. In an exemplary embodiment, these functional organic compounds can first be dissolved in a solvent, such as N,N-dimethylformamide (DMF). This solvent has good compatibility with aqueous systems, effectively promoting uniform reaction and reducing side reactions. Then, the functional organic compound solution is added to the first prepolymer, and the mixture is stirred at a stirring rate of 400 rpm to 800 rpm for 1 h to 3 h to ensure thorough mixing. The first chain extension treatment is then performed at a certain temperature. In some embodiments, the reaction temperature for the first chain elongation treatment can be 50°C to 65°C. After the reaction is complete, a second prepolymer is obtained.

[0079] Step S13 involves adding a chain extender to perform a second chain extension treatment to obtain polyurethane. In some embodiments, prior to the second chain extension treatment in step S13, the second prepolymer may be subjected to a neutralization treatment and a water dispersion treatment in sequence.

[0080] The neutralization treatment mainly neutralizes the carboxyl groups in the carboxyl-containing polyols added during the prepolymerization process in step S11, generating carboxylates. On one hand, carboxylates are ionic groups, which facilitates the formation of an aqueous dispersion. On the other hand, the pH of the reaction system can be adjusted to neutral, and the electrostatic repulsion and hydrogen bonding of the carboxylates stabilize the entire reaction system, reducing side reactions during the subsequent second-chain elongation process. Furthermore, it improves the swelling resistance of the resulting polyurethane, allowing it to fully utilize its flexibility and resilience. In the example, the neutralizing agent used in the neutralization treatment may include, but is not limited to, at least one of triethylamine (TEA), trimethylamine (TMA), N,N-dimethylethylamine (DMEA), tripropylamine (TPA), N-methyldiethanolamine (MDEA), diethylamine (DEA), ammonia (NH3·H2O), hydroxides (lithium, sodium, potassium, and calcium hydroxides), 2-amino-2-methyl-1-propanol (AMP), and N,N-dimethylethanolamine (DMAE). During neutralization, the neutralizing agent can be directly added to the second prepolymer mentioned above. The amount added can be adjusted according to the mass ratio of carboxyl polyol to neutralizing agent as (1-3):1, and the pH value of the entire solution system can be adjusted to 6-8.

[0081] After the neutralization reaction, an appropriate amount of deionized water can be added for water dispersion treatment, followed by stirring at 800 rpm to 1500 rpm for 1 to 2 hours to ensure uniform dispersion. This water dispersion treatment forms an aqueous dispersion, which facilitates the formation of the -COO- generated during neutralization. - The ionic groups impart good hydrophilicity to the second prepolymer, and deionized water disperses the ionized prepolymer into stable micelles, giving the subsequently prepared polyurethane water-based properties. Furthermore, adding water after neutralization helps reduce side reactions between the remaining polyisocyanates and water. Additionally, the combination of -COO groups... - The hydrophilic / hydrophobic balance of the ionic groups and the raw materials selected in step S11 ensures that the dispersion of the second prepolymer remains stable and has high film anti-swelling properties. On the other hand, water dispersion treatment can also improve dispersion efficiency, prevent particle aggregation, and meet the standards for industrial production of polyurethane.

[0082] A second chain extension process is then performed, the main step of which involves adding a chain transfer agent to the second prepolymer to continue the addition reaction with the remaining polyisocyanates, increasing the molecular weight of the resulting polyurethane, and introducing hard segments to increase the chain length. In some embodiments, the chain extension agent (chain transfer agent) may include at least one of ethylenediamine (EDA), 1,4-butanediol (BDO), 1,6-ethylenediol (HDO), 1,3-propanediamine (PDA), 1,6-hexanediamine (HDA), isophorone diamine (IPDA), diethylenetriamine (DETA), ethylene glycol (EG), 1,3-propanediol (PDO), 1,5-pentanediol (PeDO), diethylene glycol (DEG), trimethylolpropane (TMP), 1,4-cyclohexanediethanolamine (CHDM), m-phenylenediamine (MXDA), and polyetheramine (weight-average molecular weight of 200-400). On the one hand, these chain extenders contain hydroxyl and amino groups that can react with polyisocyanates, and each contains more than two reactive groups, which can effectively extend the molecular chain of the polyurethane and increase its molecular weight. On the other hand, they can also increase the proportion of hard segments (urethane, urea bonds), balance the flexibility of soft segments, regulate the ratio of the two, and improve the tensile strength, toughness, and resilience of polyurethane. Furthermore, they are also beneficial to improving the chemical stability of the system. Since the remaining -NCO groups will react with water to generate amines and release carbon dioxide, and will continue to generate urea bonds, they are prone to uncontrolled crosslinking or bubble generation. The timely consumption of the remaining -NCO groups by the chain extender helps to reduce the occurrence of side reactions and obtain polyurethane with suitable viscosity.

[0083] Steps S11 to S13 above also help to combine nitrogen-containing heterocyclic groups between the soft and hard segments of polyurethane, so that each segment can give full play to its own performance advantages and improve the modification effect of introducing polyurethane into the modified adhesive from a macroscopic perspective.

[0084] Finally, the product after reaction can be dialyzed in pure water for at least 96 hours. Then, it can be rotary evaporated for 1 to 3 hours at 40℃ to 50℃ and a vacuum of 5 mbar to 10 mbar to remove some of the solvent water, resulting in a concentrated polyurethane dispersion with a solid content of 20% to 55%, which is convenient for storage, transportation and subsequent application.

[0085] Step S14 is a step of further preparing the synthesized polyurethane into a modified adhesive. In this step, the raw materials including the above-mentioned carboxyl-containing polymer adhesive, polyurethane, and crosslinking agent are mixed. The crosslinking agent will spontaneously and accurately identify and bind to the nitrogen-containing heterocyclic groups in the polyurethane, so that the crosslinking agent binds to the preset position in the polyurethane molecule. The positively charged groups in the crosslinking agent will also generate electrostatic adsorption with the carboxyl groups in the carboxyl-containing polymer adhesive, thereby effectively bridging the carboxyl-containing polymer adhesive and the polyurethane to form a stable three-dimensional network structure.

[0086] In the example, the mixing process may involve first dispersing the carboxyl-containing polymer binder in water, then adding a crosslinking agent, and finally adding the polyurethane synthesized in step S13 above. In some embodiments, the mass ratio of the carboxyl-containing polymer binder, polyurethane, and crosslinking agent used in the mixing process may be (1-30):(1-3):1, where the ratio includes only the effective components and excludes the solvent.

[0087] In some embodiments, the mixing process in step S14 may further include the following steps S141 to S143:

[0088] S141. A first solution is prepared by mixing a carboxyl-containing polymer binder, a metal hydroxide, and water, wherein the pH value of the first solution is 5 to 8.5;

[0089] S142. Prepare a second solution by mixing the first solution, crosslinking agent, and pH adjuster. The pH value of the second solution is 5 to 7.5.

[0090] S143. The second solution is prepared with polyurethane to form a solution containing a modified adhesive.

[0091] The addition of metal hydroxides in step S141 is primarily to neutralize the carboxyl-containing polymer binder and generate carboxylates, thereby improving its solubility. When subsequently used in the anode material system, the metal ions can also form electrostatic adsorption interactions with the pH adjuster and the carboxyl-containing polymer binder, further enhancing the bonding strength between the modified binder and the anode active material, especially the silicon-based material, and fully utilizing the viscosity, elasticity, and flexibility of the modified binder. These hydroxides may include at least one of lithium, sodium, potassium, magnesium, zinc, or calcium hydroxides.

[0092] Step S142 involves adding a crosslinking agent and a pH adjuster. The types of crosslinking agents and pH adjusters can be found in the description of the modified binder in the first aspect above. The added crosslinking agent combines with the carboxyl-containing polymer binder through electrostatic adsorption. The added pH adjuster is mainly a carboxyl-containing substance. On one hand, it can further adjust the pH value of the system; on the other hand, it also forms an electrostatic adsorption effect with metal ions, helping to establish an electrostatic adsorption network in the solution system; furthermore, it can undergo esterification reactions with the hydroxyl groups on the surface of the negative electrode active material, such as silicon-based materials, during the subsequent preparation of the negative electrode. Based on the combination of the carboxyl-containing polymer binder and the silicon-based material, this adds another binding pathway: negative electrode active material - pH adjuster - metal ions - carboxyl-containing polymer binder, further improving the bonding strength between the modified binder and the negative electrode active material.

[0093] In step S143, polyurethane is added, allowing the crosslinking agent and polyurethane to accurately recognize and bind through complementary hydrogen bonding. The crosslinking agent enables efficient bridging between the polyurethane and the carboxyl-containing polymer binder, leading to the spontaneous assembly of the entire modified binder into a three-dimensional crosslinked network structure. The resulting modified binder exhibits high viscosity, flexibility, and elasticity. When used in silicon-based anode materials, it can significantly buffer the impact of volume expansion, improving structural stability and electrical performance. The resulting solution can be directly used for subsequent anode slurry preparation, or, as needed, a suitable amount of water can be removed for storage and transportation.

[0094] A third aspect of this application provides a secondary battery, wherein the negative electrode film layer of the secondary battery includes the modified binder described in the embodiments of this application, or includes the modified binder prepared by the preparation method described in the embodiments of this application.

[0095] Because the modified binder has high viscosity, elasticity, and flexibility, it can be applied to various negative electrode active materials, especially various silicon-based materials. It can buffer the stress impact caused by the volume expansion of silicon-based materials and stabilize the capacity performance and charge-discharge life of the negative electrode made of silicon-based materials during battery cycling. Therefore, the negative electrode film layer of the secondary battery in the embodiments of this application has good structural stability and is not prone to cracking or peeling. The secondary battery has high cycle stability, rate performance, and service life.

[0096] In this embodiment, the negative electrode preparation process can be as follows: mixing the negative electrode active material, conductive agent, modified binder, and solvent to obtain a negative electrode slurry; coating the negative electrode slurry onto a current collector; and preparing the negative electrode sheet through steps such as drying, rolling, and die-cutting. Specific material types and amounts can refer to commonly used parameters for existing negative electrode sheets. The relationship between the modified binder and the silicon-based negative electrode active material can be as follows: Figure 11 , Figure 12 As shown, Figure 11 , Figure 12 The “polymer backbone” refers to carboxyl-containing polymer binders, the “small molecules” refer to crosslinking agents, and the “small molecule regulators” refer to pH regulators. Figure 11 The display shows the state before high-temperature heating. It can be seen that the crosslinking agent and polyurethane form complementary hydrogen bonds, and also form electrostatic adsorption with the carboxyl-containing polymer binder. In addition to direct bonding, the carboxyl-containing polymer binder can also bind to the silicon surface through an electrostatic adsorption network of carboxyl-metal ions-pH adjuster-silicon surface. Therefore, the raw material components in the entire system can spontaneously assemble. Figure 12 The image shows the state after high-temperature heating, where the binder forms chemical bonds such as ester groups with the silicon surface, resulting in high bonding strength. Figure 11 , Figure 12 The diagram illustrates the mechanism of modified binders during application. The functional groups shown are for illustrative purposes only, reflecting the relationships between the components.

[0097] The following description is based on specific examples. The abbreviations of the substances in each example are detailed in the above specification. For example, PEG-2000, where PEG stands for polyethylene glycol, as mentioned above, refers to PEG products with an average molecular weight of around 2000. Such expressions in the following text can be used as a reference.

[0098] Polyurethane Example AS1.

[0099] This embodiment provides a polyurethane and its preparation method. The polyurethane has extremely high flexibility. The preparation method includes the following steps S1 to S7:

[0100] S1. Polyol mixing: Add PEG-2000 (10 g), PTMEG-1000 (5 g), and DMPA (0.5 g) all at once at 80℃, and stir at 500 rpm for 1 h.

[0101] S2. Prepolymer formation: IPDI (4.44 g) was added dropwise at a uniform rate over 30 min, followed by DBTDL (0.05 g), and the mixture was stirred at 80°C and 600 rpm for 2 h.

[0102] S3. Chain extension: Cool to 60℃, add 5-(hydroxymethyl)uracil (1 g, dissolved in 5 mL DMF), stir at 400 rpm for 1 h. The -NH (amide group of uracil) on the pyrimidine ring has low reactivity (conjugation effect reduces nucleophilicity), so -OH will preferentially react with -NCO to bind the pyrimidine ring in the above prepolymer and reduce the influence on the pyrimidine ring.

[0103] S4. Neutralization: Keep at 60°C, add TEA (0.35 g), and stir at 300 rpm for 30 min.

[0104] S5. Water dispersion: At room temperature, add 50 mL of deionized water at 1000 rpm and disperse for 1 h.

[0105] S6. Secondary chain extension: Add EDA (0.5 g) at room temperature and stir at 400 rpm for 30 min.

[0106] S7. Removal and Concentration: After dialyzing in pure water for 96 h, the solution is rotary evaporated for 1 h at 40 °C and a vacuum of 10 mbar to remove some of the solvent water, resulting in a polyurethane aqueous solution concentrated to a solid content of 30%.

[0107] Infrared spectroscopy was performed on the sample obtained from the polyurethane aqueous solution in step S7 above after thorough drying. The results are as follows: Figure 1 As shown. Figure 1 Middle, 3200-3500 cm -1 : NH and OH stretching, corresponding to carbamates, urea bonds, and pyrimidine amides.

[0108] 2937 cm -1 -CH3 asymmetric stretching corresponds to DMPA, IPDI, and TEA.

[0109] 2861: -CH2- Symmetric stretching, corresponding to PTMEG, IPDI, EDA, BDO, and 5-(hydroxymethyl)uracil.

[0110] 1716: C=O (carbamate), corresponding to IPDI+PTMEG / 5-(hydroxymethyl)uracil / BDO.

[0111] 1580: C=N / C=C (pyrimidine ring), corresponding to 5-(hydroxymethyl)uracil.

[0112] 1275: CO (carbamate), corresponding to IPDI+PTMEG / 5-(hydroxymethyl)uracil / BDO.

[0113] 1122: COC (ether bond), corresponding to PTMEG. Infrared spectroscopy confirmed the successful synthesis of the flexible polyurethane in Example AS1.

[0114] Polyurethane Example AS2.

[0115] This embodiment provides a polyurethane and its preparation method. The polyurethane has extremely high flexibility. The preparation method includes the following steps S1 to S7:

[0116] S1. Polyol mixing: Add PEG-2000 (8 g), PPG-1000 (7 g), and DMPA (0.6 g) at 85℃ in one go, and stir at 600 rpm for 1.5 h.

[0117] S2. Prepolymer formation: Keep at 85℃, add HDI (5 g) dropwise at a uniform rate over 40 min, add DBTDL (0.06 g), and stir at 600 rpm for 2.5 h.

[0118] S3. Chain extension: Cool to 65°C, add 6-amino-1,3-dimethyluracil (1.2 g, dissolved in 6 mL DMF), stir at 500 rpm for 1 h. The -N(CH3) group (amide nitrogen) on the pyrimidine ring is not reactive, so the -NH2 in the 6-amino group preferentially reacts with -NCO due to its high nucleophilicity, thus binding the pyrimidine ring in the prepolymer and reducing the influence on the pyrimidine ring.

[0119] S4. Neutralization: Keep at 65°C, add TEA (0.4 g), and stir at 300 rpm for 40 minutes.

[0120] S5. Water dispersion: At room temperature, add 60 mL of water dropwise and disperse at 1200 rpm for 1.5 h.

[0121] S6. Secondary chain extension: Add BDO (0.6 g) and stir at 400 rpm for 45 min.

[0122] S7. Impurity removal and concentration: After dialyzing in pure water for 100 h, the solution is rotary evaporated for 1.5 h at 40 °C and a vacuum of 10 mbar to remove part of the solvent water, resulting in a polyurethane aqueous solution concentrated to a solid content of 35%.

[0123] The sample obtained from the polyurethane aqueous solution in step S7 above was thoroughly dried and subjected to stress-strain tensile testing. The test results are as follows: Figure 2 As shown. From Figure 2 As can be seen, this polyurethane has extremely high flexibility and high tensile strength, with an elongation of up to 1060.70% and a Young's modulus of 31.5 MPa in the elastic region.

[0124] Polyurethane Example AS3.

[0125] This embodiment provides a polyurethane and its preparation method. The polyurethane has extremely high resilience. The preparation method includes the following steps S1 to S7:

[0126] S1. Polyol mixing: Add PEG-1000 (12 g) and DMPA (0.7 g) at 75℃ in one go, and stir at 550 rpm for 1 h.

[0127] S2. Prepolymer formation: IPDI (4.5 g) was added dropwise at a constant rate for 30 min while maintaining 75℃. Then DBTDL (0.05 g) was added, and the reaction was carried out at 550 rpm for 2 h.

[0128] S3. Chain extension: Cool to 55℃, add 5,6-diamino-2,4-dihydroxypyrimidine (1.5 g, dissolved in 6 mL DMF), stir at 450 rpm for 1.5 h. Due to the low activity of the -OH (phenolic hydroxyl group) on the pyrimidine ring due to the conjugation effect, at 55℃, the -NH2 in the 5,6-diamino group preferentially reacts with -NCO to bind the pyrimidine ring in the above prepolymer, reducing the influence on the pyrimidine ring.

[0129] S4. Neutralization: Keep at 55°C, add TEA (0.5 g), and stir at 400 rpm for 30 min.

[0130] S5. Water dispersion: At room temperature, add 55 mL of water and stir at 1200 rpm for 1 h.

[0131] S6. Secondary chain extension: Add BDO (1 g) at room temperature and stir at 400 rpm for 1 h.

[0132] S7. Impurity removal and concentration: After dialyzing in pure water for 120 h, the solution is rotary evaporated for 1.5 h at 40 °C and a vacuum of 10 mbar to remove part of the solvent water, resulting in a polyurethane aqueous solution concentrated to a solid content of 50%.

[0133] The polyurethane aqueous solution obtained in step S7 was thoroughly dried, and a continuous tensile-springback cycle test was performed. The stress-strain curve was measured for each cycle, and a total of 10 tensile tests were conducted. The test results are as follows: Figure 3 As shown. From Figure 3 As can be seen, when stretched to a fixed elongation of 440%, the residual strain from the first to the tenth stretch only increases by 29.35%, proving that it has high resilience.

[0134] Polyurethane Example AS4.

[0135] This embodiment provides polyurethane and its preparation method. The modified adhesive has extremely high resilience. The preparation method includes the following steps S1 to S7:

[0136] S1. Polyol mixing: Add PEG-2000 (9 g) and DMPA (0.5 g) at 80℃ in one go, and stir at 600 rpm for 1 h.

[0137] S2. Prepolymer formation: HDI (4 g) was added dropwise at a constant rate for 30 min while maintaining 80℃. Then DBTDL (0.04 g) was added and stirred at 500 rpm for 2 h.

[0138] S3. Chain extension: Cool to 60℃, add 4,5-diamino-6-hydroxy-2-mercaptopyrimidine (1 g, dissolved in 5 mL DMF), stir at 500 rpm for 1 h. The nitrogen atom in the amino group attacks the carbon atom in -NCO to form a urea bond. Therefore, compared with -OH or -SH, -NH2 will preferentially react with -NCO to bind the pyrimidine ring in the above prepolymer, reducing the influence on the pyrimidine ring.

[0139] S4. Neutralization: Keep at 60°C, add TEA (0.35 g), and stir at 400 rpm for 30 min.

[0140] S5. Water dispersion: At room temperature, add 50 mL of water and stir at 1000 rpm for 1 h.

[0141] S6. Secondary chain extension: At room temperature, add HDO (0.8 g) and stir at 400 rpm for 40 minutes.

[0142] S7. Impurity removal and concentration: After dialyzing in pure water for 120 h, the solution is rotary evaporated for 1.5 h at 40 °C and a vacuum of 10 mbar to remove part of the solvent water, resulting in a polyurethane aqueous solution concentrated to a solid content of 40%.

[0143] The polyurethane aqueous solution obtained in step S7 was thoroughly dried, and a continuous tensile-springback cycle test was performed. The stress-strain curve was measured for each cycle, and a total of 10 tensile tests were conducted. The test results are as follows: Figure 4 As shown. From Figure 4 As can be seen, when stretched to an elongation of 330%, the residual strain increases by only 18.46% from the first to the tenth stretch, proving that it has high resilience.

[0144] Example BS1 (Polyacrylic acid-guanidinoacetic acid-phytic acid-polyurethane modified binder and the battery made therefrom).

[0145] This embodiment provides a button cell battery, further modifying the polyurethane of the above embodiment AS1 into a binder, and obtaining a lithium-ion battery, including the following steps G1 to G3:

[0146] G1. Preparation of modified binder: At 50°C and with a stirring speed of 400 rpm, 0.5 g of polyacrylic acid was dissolved in 9.5 g of deionized water over 4 h, and the pH was adjusted to 6.5 with 0.26 g of sodium hydroxide to obtain a polymer aqueous solution. 0.03 g of guanidinoacetic acid and 0.05 g of phytic acid were added to the polymer aqueous solution, and the pH was adjusted to 6.3. The solution was stirred at 50°C and with a stirring speed of 400 rpm for 60 min to ensure homogeneity. 1.67 g of the flexible polyurethane aqueous solution obtained in step S7 of Example AS1 was added, and the solution was stirred at 50°C and with a stirring speed of 400 rpm for 60 min to ensure homogeneity, resulting in an aqueous solution containing the modified binder.

[0147] G2. Preparation of negative electrode sheet: BTR silicon carbon (120 mg), the above-mentioned aqueous solution containing modified binder (150 mg), conductive agent (300 mg, 5% concentration of multi-walled carbon nanotube aqueous solution) and 300 μL of water are mixed and homogenized in a homogenizer at a speed of 400 r / min for 180 s to obtain a mixture slurry. The mixture slurry is coated on copper foil, dried at 60℃ for 60 min, and then cured at 110℃ for 16 h. The negative electrode sheet is then cut into sheets.

[0148] G3. Preparation of lithium-ion batteries: The above negative electrode sheet is transferred to a glove box, and a 2016 coin cell is assembled using a lithium sheet as the counter electrode.

[0149] Polyurethane comparative example AD1 and button cell comparative example BD1.

[0150] Compared to Example AS1, in the synthesis of polyurethane in Comparative Example AD1, the step of adding 5-(hydroxymethyl)uracil for chain extension in S3 is omitted, while the remaining steps remain unchanged. Compared to the coin cell of Example BS1, the coin cell comparative example BD1 uses the binder of Comparative Example AD1 instead.

[0151] Blank group AK1 and button cell blank group BK1.

[0152] Compared to Example AS1, blank group AK1 does not contain polyurethane, but is a solution obtained by dissolving 0.5 g of polyacrylic acid in 9.5 g of deionized water, which undergoes the same sodium hydroxide pH adjustment step. Step S7 is replaced with drying at 110°C for 16 h, while the remaining steps remain unchanged, and this solution serves as the binder. Compared to coin cell Example BS1, coin cell blank group BK1 uses the binder from blank group AK1, while the remaining steps remain unchanged.

[0153] Performance tests were conducted on the aforementioned batteries, including constant current charge-discharge tests on the coin cells assembled in the third step. The activation current density was 5000 mA / g to 1000 mA / g, with activation proceeding from high to low rate. The long-cycle current density was 500 mA / g, with a voltage window of 0.01 V to 1.5 V. All current densities mentioned in this application refer to the current per unit mass of the film layer on the current collector in the electrode. The test results for Example BS1 and the blank group BK1 are as follows... Figure 5 As shown.

[0154] When polyacrylic acid-guanidinoacetic acid-phytic acid-polyurethane is used as the modified binder and BTR silicon carbide is used as the active material, it can achieve 500 mA g -1 Stable at a current density of 800 mAh g -1 ~900 mAh g -1 After 300 cycles, the capacity retention rate of the BTR silicon-carbon anode was 88.8%. In contrast, the lithium-ion battery using polyacrylic acid as a binder only retained 66.7% of its capacity after 300 cycles at the same rate. This indicates that the electrostatic adsorption and multiple hydrogen bonding introduced by guanidinoacetic acid, phytic acid, and polyurethane significantly improve the cycle stability of the BTR silicon-carbon anode. Meanwhile, the capacity retention rate of comparative example BD1 after 300 cycles was 73.7%, falling between that of example BS1 and the blank group BK1. Therefore, while the introduction of conventional polyurethane does improve the performance of the binder, the lack of precise hydrogen bond complementary coordination recognition between polyurethane and the crosslinking agent, coupled with weak bonding strength, limits its improvement effect, significantly less than that of example BS1.

[0155] Example BS2 (Sodium alginate-polyacrylic acid-barbituric acid-maleic acid-polyurethane modified binder and the battery made therefrom).

[0156] This embodiment provides a button cell battery, further modifying the polyurethane of the above embodiment AS2 into a binder, and obtaining a lithium-ion battery, including the following steps G1 to G3:

[0157] G1. Preparation of modified binder: At 50°C, with a stirring speed of 600 rpm, 0.25 g of sodium alginate and 0.25 g of polyacrylic acid were dissolved in 9.5 g of deionized water over 4 h, and the pH was adjusted to 7.3 with 0.12 g of sodium hydroxide to obtain a polymer aqueous solution. 0.05 g of barbituric acid and 0.1 g of maleic acid were added to the polymer aqueous solution, and the pH was adjusted to 6.0. The solution was stirred at 50°C with a stirring speed of 400 rpm for 60 min to ensure homogeneity. 1.42 g of the flexible polyurethane aqueous solution obtained in step S7 of Example AS2 was added, and the solution was stirred at 50°C with a stirring speed of 400 rpm for 60 min to ensure homogeneity, resulting in an aqueous solution containing the modified binder.

[0158] G2. Preparation of negative electrode sheet: 30 nm silicon (120 mg), the above-mentioned aqueous solution containing modified binder (150 mg), conductive agent (300 mg, 5% concentration of multi-walled carbon nanotube aqueous solution) and 300 μL water are mixed and homogenized in a homogenizer at a speed of 400 r / min for 180 s to obtain a mixture slurry. The mixture slurry is coated on copper foil, dried at 60℃ for 60 min, and then cured at 120℃ for 12 h. The negative electrode sheet is then cut into sheets.

[0159] G3. Preparation of lithium-ion batteries: The above negative electrode sheet is transferred to a glove box, and a 2016 coin cell is assembled using a lithium sheet as the counter electrode.

[0160] Polyurethane comparative example AD2 and button cell comparative example BD2.

[0161] Compared to Example AS2, in the synthesis of polyurethane in Comparative Example AD2, the step of adding 6-amino-1,3-dimethyluracil for chain extension in S3 is omitted, while the remaining steps remain unchanged. Compared to the coin cell of Example BS2, the coin cell comparative example BD2 uses the binder of Comparative Example AD2 instead.

[0162] Blank group AK2 and button cell blank group BK2.

[0163] Compared to Example AS2, blank group AK2 does not contain polyurethane. It is a solution obtained by dissolving 0.25 g of sodium alginate and 0.25 g of polyacrylic acid in 9.5 g of deionized water, which has undergone the same sodium hydroxide pH adjustment step. Step S7 is replaced with drying at 120°C for 12 h, while the other steps remain unchanged. This solution serves as the binder. Compared to coin cell Example BS2, coin cell blank group BK2 uses the binder of blank group AK2, while the other steps remain unchanged.

[0164] Performance tests were performed on the above-mentioned batteries, including constant current charge-discharge tests on the coin cells assembled in the third step. The current density during activation was 178.95 mA / g, the current density during long-cycle testing was 715.8 mA / g, and the voltage window was 0.01 V to 1.5 V. The test results for Example BS2 and the blank group BK2 are as follows. Figure 6 As shown.

[0165] When sodium alginate-polyacrylic acid-barbituric acid-maleic acid-polyurethane is used as a modified binder and 30 nm silicon is used as the active material, the battery can be stabilized at approximately 3400 mAh g at a current density of 715.8 mA / g. -1 The capacity retention rate of the nano-silicon anode was 84.5% after 100 cycles at the specified capacity. In contrast, the lithium-ion battery using sodium alginate-polyacrylic acid as a binder only retained 28.6% of its capacity after 100 cycles at the same rate. This indicates that the electrostatic adsorption and multiple hydrogen bonding introduced by barbituric acid, maleic acid, and polyurethane significantly improve the cycle stability of the nano-silicon anode. Meanwhile, the capacity retention rate of comparative example BD2 after 100 cycles was 40.2%, falling between that of example BS2 and the blank group BK2. Therefore, while the introduction of conventional polyurethane does improve the performance of the binder, the lack of precise hydrogen bond complementary coordination recognition between polyurethane and the crosslinking agent, coupled with weak bonding strength, limits its improvement effect, significantly less than that of example BS2.

[0166] Example BS3 (Sodium carboxymethyl cellulose-polyacrylic acid-guanidinium urea-citric acid-polyurethane modified binder and the battery made therefrom).

[0167] This embodiment provides a button cell battery, further modifying the polyurethane of the above embodiment AS3 into a binder, and obtaining a lithium-ion battery, including the following steps G1 to G3:

[0168] G1. Preparation of modified binder: At 50°C and with a stirring speed of 600 rpm, 0.25 g of sodium carboxymethyl cellulose and 0.25 g of polyacrylic acid were dissolved in 9.5 g of deionized water over 4 h, and the pH was adjusted to 8.0 with 0.14 g of sodium hydroxide to obtain a polymer aqueous solution. 0.05 g of guanidinium urea and 0.1 g of citric acid were added to the polymer aqueous solution, and the pH was adjusted to 6.0. The solution was stirred at 50°C and with a stirring speed of 400 rpm for 60 min to achieve homogeneity. 1 g of the resilient polyurethane aqueous solution prepared in step S7 of Example AS3 was added, and the solution was stirred at 50°C and with a stirring speed of 400 rpm for 60 min to achieve homogeneity, resulting in an aqueous solution containing the modified binder.

[0169] G2. Preparation of negative electrode sheet: G14 CVD silicon carbon (120 mg), the above-mentioned aqueous solution containing modified binder (150 mg), conductive agent (300 mg, 5% concentration of multi-walled carbon nanotube aqueous solution) and 300 μL of water are mixed and homogenized in a homogenizer at a speed of 400 r / min for 180 s to obtain a mixture slurry. The mixture slurry is coated on copper foil, dried at 60℃ for 60 min, and then cured at 150℃ for 24 h. The negative electrode sheet is then cut into sheets.

[0170] G3. Preparation of lithium-ion batteries: The above negative electrode sheet is transferred to a glove box, and a 2016 coin cell is assembled using a lithium sheet as the counter electrode.

[0171] Polyurethane comparative example AD3 and button cell comparative example BD3.

[0172] Compared to Example AS3, in the synthesis of polyurethane in Comparative Example AD3, the step of adding 6-amino-1,3-dimethyluracil for chain extension in S3 is omitted, while the remaining steps remain unchanged. Compared to the coin cell of Example BS3, the coin cell comparative example BD3 uses the binder of Comparative Example AD3 instead.

[0173] Blank group AK3 and blank button battery group BK3.

[0174] Compared to Example AS3, blank group AK3 does not contain polyurethane. It is a solution obtained by dissolving 0.25 g of sodium carboxymethyl cellulose and 0.25 g of polyacrylic acid in 9.5 g of deionized water, which has undergone the same sodium hydroxide pH adjustment step. Step S7 is replaced with drying at 150°C for 24 h, while the other steps remain unchanged. This solution serves as the binder. Compared to coin cell Example BS3, coin cell blank group BK3 uses the binder of blank group AK3, while the other steps remain unchanged.

[0175] Performance tests were performed on the above-mentioned batteries, including constant current charge-discharge tests on the coin cells assembled in the third step. The activation current density was 50 mA / g, and the current density for each rate test ranged from 100 mA / g to 5000 mA / g, with a voltage window of 0.01 V to 1.5 V. The test results for Example BS3 and the blank group BK3 are as follows: Figure 7 As shown.

[0176] Sodium carboxymethyl cellulose-polyacrylic acid When guanidinourea-citric acid-polyurethane is used as a modified binder and G14 CVD silicon carbide is used as the active material, it can achieve 5000 mA g 1 (2C) Maintains approximately 920 mAh g at a high current density. 1Its specific capacity far exceeds that of lithium-ion batteries using sodium carboxymethyl cellulose-polyacrylic acid as a binder, which only have about 260 mAh g⁻¹ at the same rate. 1 The specific capacity indicates that guanidinyl urea, citric acid, and polyurethane introduce electrostatic adsorption and multiple hydrogen bonding interactions, significantly improving the conductivity and rate performance of the G14CVD silicon-carbon anode. Meanwhile, the comparative example BD3 exhibits a specific capacity of approximately 380 mAhg at the same rate. 1 The performance of this component falls between that of Example BS3 and the blank group BK3. Therefore, while introducing conventional polyurethane does improve the performance of the binder, the lack of precise hydrogen bond complementary coordination recognition between the polyurethane and the crosslinking agent, coupled with weak bonding strength, limits its effectiveness, making it significantly less effective than Example BS3.

[0177] Example BS4 (Polyacrylic acid-guanidinium urea-sulfuric acid-polyurethane modified binder and the battery made therefrom).

[0178] This embodiment provides a button cell battery, further modifying the polyurethane of the above embodiment AS4 into a binder, and obtaining a lithium-ion battery, including the following steps G1 to G3:

[0179] G1. Preparation of modified binder: At 50°C and with a stirring speed of 400 rpm, 0.5 g of polyacrylic acid was dissolved in 9.5 g of deionized water over 4 h, and the pH was adjusted to 8.0 with 0.17 g of lithium hydroxide to obtain a polymer aqueous solution. 0.03 g of guanidinium urea and 0.01 g of sulfuric acid were added to the polymer aqueous solution to adjust the pH to 6.5. The solution was stirred at 50°C and with a stirring speed of 400 rpm for 60 min to achieve homogeneity. 1.25 g of the resilient polyurethane aqueous solution prepared in step S7 of Example AS4 was added, and the solution was stirred at 50°C and with a stirring speed of 400 rpm for 60 min to achieve homogeneity, resulting in an aqueous solution containing the modified binder.

[0180] G2. Preparation of negative electrode sheet: G14 CVD silicon carbon (120 mg), the above-mentioned aqueous solution containing modified binder (150 mg), conductive agent (300 mg, 5% concentration of multi-walled carbon nanotube aqueous solution) and 300 μL of water are mixed and homogenized in a homogenizer at a speed of 400 r / min for 180 s to obtain a mixture slurry. The mixture slurry is coated on copper foil, dried at 60℃ for 60 min, and then cured at 130℃ for 12 h. The negative electrode sheet is then cut into sheets.

[0181] G3. Preparation of lithium-ion batteries: The above negative electrode sheet is transferred to a glove box, and a 2016 coin cell is assembled using a lithium sheet as the counter electrode.

[0182] Polyurethane comparative example AD4 and button cell comparative example BD4.

[0183] Compared to Example AS4, in the synthesis of polyurethane in Comparative Example AD4, the step of adding 5,6-diamino-2,4-dihydroxypyrimidine for chain extension in S3 is omitted; the remaining steps remain unchanged. Compared to the coin cell of Example BS4, the coin cell comparative example BD4 uses the same binder as comparative example AD4.

[0184] Blank group AK4 and blank button battery group BK4.

[0185] Compared to Example AS4, blank group AK4 does not contain polyurethane. It is a solution obtained by dissolving 0.5 g of polyacrylic acid in 9.5 g of deionized water, which undergoes the same lithium hydroxide pH adjustment step. Step S7 is replaced with drying at 130°C for 12 h, while the other steps remain unchanged. This solution serves as the binder. Compared to coin cell Example BS4, coin cell blank group BK4 uses the binder of blank group AK4, while the other steps remain unchanged.

[0186] The negative electrode sheet in the above battery was subjected to a 180° peel strength test, including: cutting the negative electrode sheet prepared in step G2 into a rectangular sheet with a width of 2 cm and a length of 7.5 cm, rolling it, and then attaching it to a glass slide. A 1.8 cm wide adhesive tape was used to tightly adhere the tape to the electrode surface. One end of the tape was held by the lower clamp of a universal tensile testing machine, and the glass slide was held by the upper clamp. The instrument's movement speed was 30 mm / min. The relationship between the instrument's displacement and the force was recorded. The test results are as follows: Figure 8 As shown.

[0187] The negative electrode sheet modified with polyacrylic acid-guanidinium urea-sulfuric acid-polyurethane as the binder exhibits a peel strength approximately 3.5 times that of the polyacrylic acid binder without polyurethane. This indicates that the introduction of guanidinium urea and sulfuric acid as crosslinking agents and pH adjusters, as well as the introduction of polyurethane, significantly enhances the bonding forces between the binder components, thereby strengthening the adhesive performance and resulting in stronger electrode structural stability for the G14 CVD silicon-carbon negative electrode. Meanwhile, the peel strength of comparative example BD4 is approximately 1.6 times that of the polyacrylic acid binder without polyurethane, falling between that of example BS4 and the blank group BK4. Therefore, while the introduction of conventional polyurethane does improve binder performance, the lack of precise hydrogen bond complementary coordination recognition between polyurethane and the crosslinking agent, coupled with weaker bonding strength, limits its improvement effect, significantly less than that of example BS4.

[0188] Example BS5 (Polyacrylic acid-tricyanate-arginine-polyurethane modified binder and the battery made therefrom).

[0189] This embodiment provides a button cell battery, further modifying the polyurethane of the above embodiment AS4 into a binder, and obtaining a lithium-ion battery, including the following steps G1 to G3:

[0190] G1. Preparation of modified binder: At 50°C, with a stirring speed of 400 rpm, 0.5 g of polyacrylic acid was dissolved in 9.5 g of deionized water over 4 h, and the pH was adjusted to 8.0 with 0.38 g of potassium hydroxide to obtain a polymer aqueous solution. 0.03 g of tricyanic acid and 0.03 g of arginine were added to the polymer aqueous solution, and the pH was adjusted to 6.3. The solution was stirred at 50°C and 400 rpm for 60 min to ensure homogeneity. 1.25 g of the resilient polyurethane aqueous solution prepared in step S7 of Example AS4 was added, and the solution was stirred at 50°C and 400 rpm for 60 min to ensure homogeneity, resulting in an aqueous solution containing the modified binder.

[0191] G2. Preparation of negative electrode sheet: BTR silicon carbon (120 mg), the above-mentioned aqueous solution containing modified binder (125 mg), conductive agent (300 mg, 5% concentration of multi-walled carbon nanotube aqueous solution) and 300 μL of water are mixed and homogenized in a homogenizer at a speed of 400 r / min for 180 s to obtain a mixture slurry. The mixture slurry is coated on copper foil, dried at 60℃ for 60 min, and then cured at 150℃ for 20 h. The negative electrode sheet is then cut into sheets.

[0192] G3. Preparation of lithium-ion batteries: The above negative electrode sheet is transferred to a glove box, and a 2016 coin cell is assembled using a lithium sheet as the counter electrode.

[0193] Polyurethane comparative example AD5 and button cell comparative example BD5.

[0194] Compared to Example AS4, in the synthesis of polyurethane in Comparative Example AD5, the step of adding 5,6-diamino-2,4-dihydroxypyrimidine for chain extension in S3 is omitted; the remaining steps remain unchanged. Compared to the coin cell in Example BS5, the coin cell in Comparative Example BD5 uses the same binder as Comparative Example AD5.

[0195] Blank group AK5 and button battery blank group BK5.

[0196] Compared to Example AS4, blank group AK5 does not contain polyurethane, but is a solution obtained by dissolving 0.5 g of polyacrylic acid in 9.5 g of deionized water, which undergoes the same potassium hydroxide pH adjustment step. Step S7 is replaced with drying at 150°C for 20 h, while the remaining steps remain unchanged, serving as the binder. Compared to coin cell Example BS5, coin cell blank group BK5 uses the binder of blank group AK5, while the remaining steps remain unchanged.

[0197] The above-mentioned batteries underwent charge-discharge cycling and SEM morphology testing, including: constant current charge-discharge testing of the coin cells, where the activation current density was 1000 mA / g to 5000 mA / g, the long-cycle current density was 500 mA / g, and the voltage window was 0.01 V to 1.5 V. After 70 cycles, the electrode was removed from the battery, and its surface morphology was observed using SEM at an accelerating voltage of 15 kV. The test results for the blank group BK5 are as follows: Figure 9 As shown, the test results of Example BS5 are as follows: Figure 10 As shown.

[0198] When polyacrylic acid-tricyanate-arginine-polyurethane is used as a modified binder and BTR silicon-carbon is used as the negative electrode active material, the negative electrode structure remains intact after 70 cycles, and the negative electrode particles are tightly bonded. However, lithium-ion batteries using polyacrylic acid as a binder show more surface cracks and multiple separations between particles after 70 cycles under the same cycling conditions. This indicates that the tricyanate-arginine-polyurethane introduces electrostatic adsorption and multiple hydrogen bonding, and polyurethane effectively induces the formation of a more chemically and mechanically stable and uniform SEI film, significantly improving the adhesion between BTR silicon-carbon negative electrode particles and the integrity of the negative electrode structure. Meanwhile, the comparative example BD5 electrode also shows some cracks on its surface, with the number falling between that of example BS5 and the blank group BK5. Therefore, while introducing conventional polyurethane does improve binder performance, the lack of precise hydrogen bond complementary coordination recognition between polyurethane and the crosslinking agent, coupled with weaker bonding strength, limits its improvement effect, significantly less than that of example BS5.

[0199] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A modified binder characterized by, It includes the following raw material components: Carboxyl-containing polymer binders; said carboxyl-containing polymer binders include at least one of polyacrylic acid and its salts, carboxymethyl cellulose and its salts, and alginate and its salts; Polyurethane, wherein nitrogen-containing heterocyclic groups are grafted into the molecular chain of the polyurethane, and the nitrogen-containing heterocyclic groups contain hydrogen bond acceptor groups and hydrogen bond donor groups; A crosslinking agent, wherein the crosslinking agent contains hydrogen bond donor groups, hydrogen bond acceptor groups, and positively charged groups; The number of hydrogen bond acceptor groups in the nitrogen-containing heterocyclic group is equal to the number of hydrogen bond donor groups in the crosslinking agent, and the number of hydrogen bond donor groups in the nitrogen-containing heterocyclic group is equal to the number of hydrogen bond acceptor groups in the crosslinking agent; the nitrogen-containing heterocyclic group includes pyrimidine groups; The nitrogen-containing heterocyclic group is located between the hard and soft segments in the molecular chain of the polyurethane; The crosslinking agent includes at least one of guanidinoacetic acid and guanidinourea; The modified binder contains a pH adjuster, which includes at least one of sulfuric acid, citric acid, maleic acid, malonic acid, phytic acid, arginine, and lysine; the modified binder also contains metal ions.

2. The modified binder of claim 1, wherein: The grafting rate of the nitrogen-containing heterocyclic group in the polyurethane is 2% to 15%; and / or, The carboxyl-containing polymer adhesive has a carboxyl group content of 20% to 80% by mass.

3. The modified binder of claim 1 or 2, wherein: The polyurethane has a weight-average molecular weight of 20,000 to 200,000; and / or, The carboxyl-containing polymer binder has a weight-average molecular weight of 100,000 to 3,000,000; and / or, The mass ratio of the carboxyl-containing polymer adhesive, the polyurethane, and the crosslinking agent is (1-30):(1-3):

1.

4. The modified adhesive according to claim 1 or 2, characterized in that: The modified adhesive contains water, has a solid content of 5% to 50%, and a pH value of 5 to 8.

5. A method for preparing the modified adhesive as described in any one of claims 1 to 4, characterized in that, Includes the following steps: The modified adhesive is obtained by mixing the components comprising the carboxyl-containing polymer adhesive, the polyurethane, and the crosslinking agent.

6. The preparation method according to claim 5, characterized in that, The method for preparing the polyurethane includes the following steps: The raw materials, including polyols and polyisocyanates, are prepolymerized to obtain the first prepolymer. The raw materials, including the first prepolymer and the functional organic compound, are subjected to a first chain extension treatment to obtain a second prepolymer, wherein the functional organic compound includes the nitrogen-containing heterocyclic group; The raw materials, including the second prepolymer and the chain extender, are subjected to a second chain extension treatment to obtain the polyurethane.

7. The preparation method according to claim 6, characterized in that: The functional organic compound includes at least one of 5-(hydroxymethyl)uracil, 6-amino-1,3-dimethyluracil, 5,6-diamino-2,4-dihydroxypyrimidine, 4,5-diamino-6-hydroxy-2-mercaptopyrimidine, 5-aminouracil, 5-hydroxyuracil, 5-(hydroxymethyl)thymidine, 5-aminothymidine, 5-aminocytosine, and 5-(hydroxymethyl)cytosine; and / or, The molar ratio of the polyisocyanate to the functional organic compound is (2-10):1; and / or, The reaction temperature for the first chain elongation treatment is 50℃~65℃.

8. The preparation method according to claim 6 or 7, characterized in that: The polyols include hydrophilic polyols and hydrophobic polyols, wherein the mass ratio of the hydrophilic polyol to the hydrophobic polyol is (1.5–4):1; and / or, The molar ratio of the polyol to the polyisocyanate is 1:(0.6–2.4); and / or, The prepolymerization treatment temperature is 65℃~85℃; and / or, The raw materials for the prepolymer treatment include carboxyl-containing polyols and / or catalysts; and / or, The chain extender comprises at least one of ethylenediamine, 1,4-butanediol, 1,3-propanediamine, 1,6-hexanediamine, isophorone diamine, diethylenetriamine, ethylene glycol, 1,3-propanediol, 1,5-pentanediol, diethylene glycol, trimethylolpropane, 1,4-cyclohexanediol, m-phenylenediamine, and polyetheramine; and / or, Prior to the second chain extension treatment, the process further includes the steps of neutralizing and dispersing the second prepolymer sequentially.

9. The preparation method according to any one of claims 5 to 7, characterized in that: The mass ratio of the carboxyl-containing polymer binder, the polyurethane, and the crosslinking agent is (1-30):(1-3):1; and / or, The mixing process includes the following steps: The carboxyl-containing polymer binder, metal hydroxide, and water are formulated into a first solution, the pH of which is 5 to 8.

5. The first solution, the crosslinking agent, and the pH adjuster are used to prepare a second solution, the pH value of which is 5 to 7.

5. The second solution is formulated with the polyurethane to form a solution containing the modified adhesive.

10. A secondary battery, characterized in that: The negative electrode film layer of the secondary battery includes the modified binder as described in any one of claims 1 to 4, or includes the modified binder prepared by the preparation method described in any one of claims 5 to 9.

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