A binder for lithium ion battery negative electrode and its preparation method and application

Abstract

The present application relates to a kind of binder for lithium ion battery negative electrode and its preparation method and application.The binder includes polyacrylamide as rigid component and aqueous polyurethane as flexible component, the polyacrylamide is combined with the aqueous polyurethane by intermolecular interaction and forms three-dimensional network structure.Compared with prior art, the binder obtained by the present application can effectively inhibit the volume expansion of silicon-based negative electrode while having excellent interfacial adhesion and electrochemical stability.

Description

Technical Field

[0001] This invention relates to the fields of new energy materials and electrochemical energy storage technology, and in particular to a binder for the negative electrode of lithium-ion batteries, its preparation method and application. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage grids, the market demand for energy storage devices with high energy density and long cycle life is becoming increasingly urgent. Lithium-ion batteries, with their high specific energy and long cycle performance, have become the dominant technology in the current energy storage field. Among many anode materials, silicon, due to its extremely high theoretical specific capacity, suitable lithium intercalation potential, and abundant natural reserves, is considered an important development direction for next-generation high-energy-density lithium-ion battery anode materials.

[0003] However, silicon anodes still face significant challenges in practical applications. During cycling, silicon materials undergo dramatic volume expansion, leading to particle breakage, electrode structure damage, and continuous reconstruction of the solid electrolyte interface film, resulting in rapid capacity decay and a decrease in coulombic efficiency. To alleviate these problems, various material modification strategies such as silicon-carbon composites and nanostructure design have been proposed in existing technologies, but these methods are often complex in preparation and costly, limiting their large-scale application.

[0004] In comparison, using high-performance binders is considered one of the feasible ways to solve the volume expansion problem of silicon anodes. An ideal binder needs to possess sufficient bonding strength to maintain electrode integrity while also being able to adapt to the significant volume changes of silicon materials during charging and discharging. Currently, while binders such as polyacrylamide (PAM) can coat silicon particles through hydrogen bonding, their high brittleness and insufficient toughness are detrimental to the long-term stability of the electrode. Waterborne polyurethane (WPU), although possessing both rigid and flexible segments and attracting attention due to its good elasticity, has a low modulus, limiting its ability to constrain the volume expansion of silicon particles, and its interfacial compatibility with hydrophobic silicon-carbon composite materials is often unsatisfactory. In recent years, although some research has focused on developing composite or cross-linked binder systems, such as the waterborne binder based on sodium carboxymethyl cellulose (CMC-Na) and its applications disclosed in patent publication CN118256171A, a composite binder based on CMC-Na and WPU has been reported. However, balancing "rigidity" and "toughness" in water-based systems, so that the binder can firmly bind the active particles and effectively buffer cyclic stress, while also taking into account environmental protection and economy, remains a technical challenge that urgently needs to be overcome.

[0005] Therefore, developing an environmentally friendly, cost-effective, and high-modulus and high-toughness waterborne composite binder is of great value for promoting the practical application of silicon-carbon anodes. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by providing a binder for lithium-ion battery anodes, its preparation method and application, so that the obtained binder can effectively suppress the volume expansion of silicon-based anodes while possessing excellent interfacial adhesion and electrochemical stability.

[0007] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide a binder for the negative electrode of a lithium-ion battery, comprising PAM as a rigid component and WPU as a flexible component, wherein the PAM and the WPU are bonded together through intermolecular interactions to form a three-dimensional network structure.

[0008] Furthermore, the three-dimensional network structure is an interpenetrating network structure formed through intermolecular hydrogen bonding. The rigid and flexible components are tightly bound together at the molecular level through hydrogen self-assembly, with no obvious macroscopic phase separation regions, and the macromolecular chains are intertwined. The amide groups (-CONH2) on the PAM molecular chain and the urethane esters (-NHCOO-) on the WPU molecular chain form intermolecular hydrogen bonds. This structure is beneficial for providing high modulus to resist mechanical deformation, while also providing high toughness to dissipate stress. Simultaneously, due to the abundance of polar groups on the molecular chains, adhesion occurs through intermolecular hydrogen bonding and mechanical interlocking mechanisms, resulting in excellent adhesion to both silicon-based active materials and copper foil current collectors, and significantly improved peel strength after adhesion.

[0009] Furthermore, the mass ratio of PAM to WPU is 0.5 to 5:1.

[0010] Furthermore, the mass ratio of PAM to WPU is 2:1, which ensures sufficient rigid frame support while retaining excellent flexible cushioning capabilities.

[0011] The second technical solution of the present invention provides a method for preparing a binder for a lithium-ion battery negative electrode, comprising the following steps: The PAM aqueous solution and WPU dispersion were mixed to obtain a mixture; The mixture is stirred to allow PAM and WPU to self-assemble in situ through physical entanglement and hydrogen bonding during the mixing process, forming the binder.

[0012] Furthermore, the concentration of the polyacrylamide aqueous solution is 0.5wt%~10wt%, and the solid content of the aqueous polyurethane dispersion is 0.5wt%~10wt%. The mass ratio of PAM in the PAM aqueous solution to WPU in the WPU dispersion is 0.5~5:1.

[0013] Furthermore, the in-situ self-assembly is performed at room temperature for 0.5–5 hours. The preparation process is a pure water system with no organic solvent evaporation and requires no complex high-temperature chemical synthesis steps.

[0014] Further, the preparation method of the PAM aqueous solution is as follows: under the protection of an inert atmosphere, acrylamide monomer is polymerized in an aqueous solution containing an initiator to obtain a PAM solution; the PAM solution is diluted to obtain a PAM aqueous solution with a predetermined mass fraction.

[0015] Furthermore, the initiator is ammonium persulfate.

[0016] Furthermore, the polymerization reaction is carried out at a temperature range of 60-85°C for a reaction time of 4-8 hours.

[0017] The third technical solution of the present invention is to provide an application of a binder for a lithium-ion battery anode, wherein the binder is used to prepare a silicon-based anode for a lithium-ion battery.

[0018] Furthermore, the binder is used to prepare slurries, electrode sheets, and / or batteries for silicon-based anodes of lithium-ion batteries.

[0019] Furthermore, the silicon-based anode comprises a silicon-carbon composite material, Si / C.

[0020] Furthermore, the binder is a water-based binder, used to replace binder systems using organic solvents as dispersion media in the preparation of slurries for silicon-based anode materials. Based on the binder's excellent adhesion and dispersibility, the binder, as a binder for silicon-based anode materials, replaces traditional PVDF, PAA, or single WPU systems, and is mixed with active and conductive materials, using deionized water as a solvent to prepare a uniform electrode slurry.

[0021] Furthermore, a multi-hydrogen bond network is formed between the amide groups on the PAM molecular chain and the polar groups on the WPU molecular chain, as well as between the composite binder and the surface of the silicon-based anode active material.

[0022] Furthermore, based on the binder's combined rigidity and flexibility, the binder is used to prepare silicon-based negative electrode sheets capable of withstanding significant volume expansion. During charging and discharging, the PAM component provides rigidity to constrain the macroscopic deformation of the electrode, while the flexible segments in the WPU component provide elasticity to dissipate local stress. When silicon particles expand in volume, the rigid PAM framework restricts the macroscopic deformation of the electrode, while the flexible WPU segments absorb local stress, thereby maintaining the integrity of the electrode structure and preventing the active material from pulverizing and detaching.

[0023] Furthermore, the preparation process of the silicon-based anode slurry is as follows: mixing silicon-based anode active material, conductive material and binder, and ball milling to obtain silicon-based anode material slurry.

[0024] Furthermore, the mass ratio of the silicon-based negative electrode active material to the conductive material is 5~10:1, and the dry weight of the binder accounts for 5%~20% of the total solids.

[0025] Furthermore, the slurry is evenly coated onto the copper foil current collector, dried, and then punched to obtain the electrode sheet.

[0026] Furthermore, the coating thickness of the slurry is 20~30μm, the drying temperature is 50~80℃, and the drying time is 5~20h.

[0027] Furthermore, the electrodes are assembled to form a battery.

[0028] Compared with the prior art, the present invention has the following advantages: (1) Adjustable mechanical properties and a balance between rigidity and toughness: By adjusting the ratio of rigid component PAM to flexible component WPU, the modulus and toughness of the composite adhesive can be adjusted within a wide range. For example, under a specific preferred ratio (especially 2:1), the obtained three-dimensional network structure can effectively combine the high modulus of polyacrylamide with the high elasticity of waterborne polyurethane, thereby enabling the adhesive material to simultaneously resist deformation and dissipate stress on a macroscopic level, overcoming the shortcomings of single-component materials that are too rigid and brittle or too flexible and weak.

[0029] (2) Strong interfacial bonding: The amide groups abundant in the PAM molecular chain synergistically interact with various polar groups (such as urethane) on the WPU molecular chain, making the composite binder not only stable in its own network structure, but also capable of generating strong polar interactions (including hydrogen bonds) with the polar functional groups (such as hydroxyl groups) on the surface of silicon-based anode active materials (such as silicon-carbon composite materials) and the surface of copper foil current collectors. This multi-bonding effect significantly enhances the adhesion between active materials and between the active material layer and the current collector. Experiments show that the electrode prepared using this composite binder has a high peel strength (up to 3.69 N), effectively suppressing the problem of electrode material peeling off from the current collector due to drastic volume changes during cycling of the silicon anode.

[0030] (3) Excellent stress dissipation and structural maintenance capabilities: The three-dimensional interpenetrating network structure has unique biomimetic mechanical properties. Among them, the rigid PAM network forms a spider web-like support skeleton, providing overall strength to constrain the macroscopic deformation of the electrode; while the WPU flexible chain segments are interspersed among them, which can effectively buffer local stress. This structure that combines rigidity and flexibility can disperse the concentrated stress generated during cycling and transform large cracks that may cause the conductive network to break into a large number of small, harmless microcracks, thereby better maintaining the integrity of the overall electrode structure and the continuity of the conductive path during long cycles.

[0031] (4) Facilitates the formation of a stable electrode interface: Since the binder can effectively maintain the structural integrity of the electrode during cycling, it reduces cracks and exposure of fresh surfaces caused by repeated volume expansion and contraction of the active material. Therefore, it is beneficial to form a thinner, more stable, and more uniform solid electrolyte interface (SEI) film on the silicon particle surface. This reduces the continuous decomposition of the electrolyte and the irreversible consumption of active lithium during cycling, thus enabling batteries using this binder to typically exhibit higher initial coulombic efficiency (up to 93%) and excellent long-cycle capacity retention (89.33%).

[0032] (5) The preparation process is simple, environmentally friendly, and has significant cost advantages: The preparation method of the binder does not require complex chemical reactions, such as chemical grafting or copolymerization. It mainly forms a stable structure through physical blending and in-situ self-assembly driven by intermolecular forces. The entire preparation process uses water as a solvent, avoiding the use of organic solvents. It is environmentally friendly, the production process is simple, it is easy to scale up, and it has significant potential for industrial application. Attached Figure Description

[0033] Figure 1 The following is a comparison of the infrared spectra (FTIR) of Example 1 (P2W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU); Figure 2 The stress-strain curves of Example 1 (P2W1), Example 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU) are compared, as are the stress-strain curves of their individual components, to compare the mechanical properties of the adhesives under different formulations. Figure 3 The electrochemical cycling performance of the electrodes prepared in Example 1 (P2W1), Example 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU) is compared, showing (a) cycling capacity retention, (b) coulombic efficiency, and (c) initial coulombic efficiency. Figure 4The results of the 180° peel strength test of the electrodes prepared in Example 1 (P2W1), Example 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU) are shown. (a) 180° peel strength test, (b) average peel strength, and (c) electrolyte absorption rate. Figure 5 The electrochemical performance comparison diagrams of the electrodes prepared in Example 1 (P2W1), Example 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU) are shown. (a) is the cyclic voltammetry (CV) curve at a scan rate of 0.1 mV / s, and (b) is the CV curve at different scan rates. Figure 6 The following are Nyquist plots of electrochemical impedance spectroscopy (EIS) of electrodes after different number of cycles: (a) Electrochemical impedance spectra of three cyclic anodes, (b) Impedance spectrum of P2W1 after 200 cycles, and (c) Equivalent circuit diagram. Figure 7 The following are Nyquist plots of electrochemical impedance spectroscopy (EIS) before and after cycling of four electrodes: (a) EIS spectrum of P2W1, (b) EIS spectrum of P1W1, (c) EIS spectrum of PAM, and (d) EIS spectrum of WPU. Figure 8 The images show the scanning electron microscope (SEM) morphology of the electrode surfaces with different binders before and after 50 cycles, and the crack situation is compared. (a) shows the surface cracking of four electrodes, P2W1, P1W1, PAM, and WPU, before and after the cycles. (b) shows the volume expansion of four electrodes, P2W1, P1W1, PAM, and WPU, before and after the cycles. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without creative effort are within the scope of protection of this application.

[0035] Unless otherwise specified, the reagents, methods, instruments and equipment used in this invention are conventional reagents, methods, instruments and equipment in the art.

[0036] In the following examples, acrylamide (AM) and GCS were purchased from Shanghai Titan Technology Co., Ltd.; WPU with a solid content of 40±1% was purchased from Wanhua Chemical Group Co., Ltd.; silicon-carbon anode material (Si / C, model 950K) was purchased from Guangdong Zhuguangxin Energy Technology Co., Ltd.; and conductive carbon black (Super P) was purchased from Guangdong Zhuguangxin Energy Technology Co., Ltd.

[0037] The preparation process of 5 wt% PAM aqueous solution is as follows: A three-necked flask reaction apparatus was constructed, and 40 mL of deionized water was added. The water bath heating device and condenser were turned on, and nitrogen gas was introduced to purge air from the reaction system. 0.15 g of ammonium persulfate initiator was weighed and dissolved in 10 mL of deionized water for later use. 7.5 g of acrylamide monomer was weighed and dissolved in 40 mL of deionized water for later use. The total volume of deionized water solvent was 100 mL throughout the synthesis experiment. After the water bath reached 75 °C, 5 mL of the initiator solution was added to the three-necked flask and allowed to stabilize for 15 min. The total reaction time was 6 h. After 3 h of reaction time, the remaining 5 mL of the initiator aqueous solution was added to the reaction apparatus. After the reaction was complete, the water bath heating device was turned off, and the condenser and nitrogen gas supply were stopped after the product cooled. The obtained polyacrylamide solution was added to deionized water to prepare a 5 wt% PAM aqueous solution.

[0038] The preparation process of 5 wt% WPU dispersion is as follows: Take an appropriate amount of WPU dispersion and dilute it with deionized water to a mass fraction of 5 wt%.

[0039] Example 1 A binder for a lithium-ion battery anode includes PAM as a rigid component and WPU as a flexible component, wherein the PAM and WPU are bonded together through intermolecular interactions to form a three-dimensional network structure.

[0040] In this embodiment, the three-dimensional network structure is an interpenetrating network structure formed by intermolecular hydrogen bonding. The rigid and flexible components are tightly bound together at the molecular level through hydrogen self-assembly, with no obvious macroscopic phase separation regions. The macromolecular chains intertwine to form a continuous, integrated structure. The amide groups (-CONH2) on the PAM molecular chain and the urethane esters (-NHCOO-) on the WPU molecular chain form intermolecular hydrogen bonds. This structure is beneficial for providing high modulus to resist mechanical deformation and high toughness to dissipate stress. Furthermore, due to the abundance of polar groups on the molecular chains, adhesion occurs through intermolecular hydrogen bonding and mechanical interlocking mechanisms, resulting in excellent adhesion to both silicon-based active materials and copper foil current collectors. The peel strength after adhesion is significantly improved.

[0041] In this embodiment, the mass ratio of PAM to WPU is 2:1. This ensures the system provides sufficient rigid support while retaining excellent flexible cushioning capabilities.

[0042] A method for preparing a binder for the negative electrode of a lithium-ion battery includes the following steps: (1) Mix 5 wt% PAM aqueous solution and 5 wt% WPU dispersion to obtain a mixture, wherein the mass ratio of PAM in the PAM aqueous solution and WPU in the WPU dispersion is 2:1.

[0043] (2) The mixture is stirred for 2 hours to allow PAM and WPU to self-assemble in situ through physical entanglement and hydrogen bonding during the mixing process, forming a uniform emulsion and obtaining a rigid-flexible three-dimensional network composite adhesive, named P2W1.

[0044] Example 2 A binder for the negative electrode of a lithium-ion battery is largely the same as that in Example 1, except that the mass ratio of PAM to WPU is 1:1.

[0045] A method for preparing a binder for the negative electrode of a lithium-ion battery is largely the same as that in Example 1, except that the mass ratio of PAM in the PAM aqueous solution to WPU in the WPU dispersion is 1:1, and it is named P1W1.

[0046] Comparative Example 1 A single-component adhesive comprising only PAM, without the addition of WPU compared to Example 1.

[0047] In this embodiment, the adhesive has a linear polymer structure, and the molecular chains are mainly connected by van der Waals forces or intramolecular hydrogen bonds, lacking flexible buffer units.

[0048] Comparative Example 2 A single-component adhesive comprising only WPU, without the addition of PAM compared to Example 1.

[0049] In this embodiment, the adhesive has a micelle particle structure, which has good elasticity but low modulus and lacks rigid skeleton support.

[0050] Performance testing: Silicon-based anode slurry was prepared using the binders from Examples 1 and 2 and Comparative Examples 1 and 2: active material Si / C and conductive material Super P were weighed at a mass ratio of 8:1 and added to the binder solution (the dry weight of the binder accounted for 10% of the total solids). The solid content was adjusted to a suitable viscosity. The mixture was then placed in a ball mill jar and ball-milled at 300 r / min for 30 min to obtain a uniform silicon-based anode slurry.

[0051] Silicon-based anode sheets and batteries were prepared by uniformly coating the silicon-based anode slurry onto a copper foil current collector to a thickness of 25 μm. The slurry was then transferred to a vacuum oven at 70 °C and dried for 12 h, before being punched into circular electrodes with a diameter of 12 mm. These electrodes can be used to assemble 2032-type coin cells.

[0052] Figure 1 The image shows a comparison of the Fourier Transmission Infrared (FTIR) spectra of Example 1 (P2W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU). It can be seen that pure PAM at 3343 cm⁻¹... -1 The peak at 1729 cm⁻¹ shows the characteristic peak of amide groups. Pure WPU shows the peak at 1729 cm⁻¹. -1 The carbonyl characteristic peak is displayed at [location missing]. In the P2W1 composite binder, the carbonyl peak and the NH peak show a certain frequency shift (shifted to 1726 cm⁻¹, respectively). -1 and 3335 cm -1 This is due to the significant intermolecular hydrogen bonding between the amide groups on the PAM molecular chain and the polar groups on the WPU molecular chain. This physical cross-linking network is the microscopic basis for achieving the "rigid-flexible" performance, indicating that the two components achieve good compatibility and compositeness at the molecular level, rather than a simple macroscopic mixing.

[0053] Figure 2 The stress-strain curves of Example 1 (P2W1), Example 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU) are compared to illustrate the mechanical properties of the binder under different formulation ratios. Uniaxial tensile tests were performed on each sample at room temperature according to ASTM D638 to evaluate the modulating effect of different component ratios on the mechanical properties of the materials. The test results show that pure PAM exhibits typical high strength and brittleness (strength ~64 MPa), while pure WPU exhibits excellent elastomer characteristics (elongation at break >650%). The stress-strain curves of the composite materials (P2W1, P1W1) show obvious yielding, necking, and subsequent strain hardening phenomena, confirming the good interfacial interaction and synergistic effect between the rigid PAM phase and the flexible WPU phase. Among them, the P2W1 sample achieved the best balance between rigidity and toughness, with a tensile strength of 45 MPa (approximately 4 times that of pure WPU) while maintaining an elongation at break of approximately 250%. In summary, PAM provides skeletal support as a rigid segment, while the flexible segments in WPU dissipate energy through segment movement. The combination of the two effectively overcomes the performance defects of a single component and optimizes the overall mechanical properties of the material.

[0054] Figure 3The graph shows a comparison of the electrochemical cycling performance of the electrodes prepared in Example 1 (P2W1), Example 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU), with (a) cycling capacity retention, (b) coulombic efficiency, and (c) initial coulombic efficiency. The results show that Comparative Example 1 (single PAM) exhibits a sharp capacity decay after 150 cycles, while Comparative Example 2 (single WPU) shows a low initial capacity. Example 1 (P2W1) demonstrates the best cycling stability, maintaining a capacity retention of 82.4% after 200 cycles, and achieving an initial coulombic efficiency (ICE) of 93%. This is because while single PAM is rigid, it is too brittle to withstand the significant volume expansion of silicon and thus fractures; while single WPU has good toughness, its low modulus fails to limit excessive electrode deformation. In this invention, P2W1, by controlling the rigidity-flexibility ratio, effectively maintains the integrity of the electrode structure by both limiting deformation and dissipating stress. During charging and discharging, as silicon particles expand in volume, the rigid PAM framework restricts the macroscopic deformation of the electrodes, while the flexible WPU segments absorb local stress, thus maintaining the integrity of the electrode structure. During cycling, the three-dimensional network structure effectively dissipates mechanical energy and prevents the active material from pulverizing and detaching.

[0055] Figure 4 The 180° peel strength test results are shown for electrodes prepared in Examples 1 (P2W1), 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU). (a) 180° peel strength test, (b) average peel strength, and (c) electrolyte absorption rate. The adhesion strength of the binders to the copper foil current collector differs significantly among the different examples. The measurement results show that the peel strength of the P2W1 electrode is as high as 3.69 N, significantly better than that of single PAM (approximately 1.2 N) and single WPU (approximately 0.8 N). This is because PAM provides a large number of polar functional groups (such as -CONH2) to form hydrogen bonds with the hydroxyl groups on the copper foil and silicon surface, while the flexible segments of WPU provide good interfacial wettability and cohesive force. When the two are combined, the rigid framework and the flexible matrix work synergistically, enhancing van der Waals forces and mechanical interlocking, thereby significantly improving the overall adhesion strength of the electrode.

[0056] Figure 5 This is a comparison chart of the electrochemical performance of the electrodes prepared in Example 1 (P2W1), Example 2 (P1W1), Comparative Example 1 (PAM), and Comparative Example 2 (WPU). Figure 5 (a) shows the cyclic voltammetry (CV) curves at a scan rate of 0.1 mV / s. Figure 5 (b) shows the CV curves at different scan rates. To further evaluate the electrochemical activity and energy storage mechanism of the material, the CV curves were obtained at 0-2.5 V (vs. Li / Li). +Cyclic voltammetry (CV) tests were performed on each sample within a voltage window. Figure 5 As shown in (a), at a low scan rate of 0.1 mV / s, the composite material P2W1 exhibits the largest closed integral area of ​​the CV curve and the highest redox peak current density, significantly outperforming pure PAM, WPU, and P1W1 samples. This indicates that a synergistic network favorable for ion transport is formed among the components of P2W1, endowing the material with the highest specific capacity and charge storage capacity. Figure 5 (b) Further analysis revealed the kinetic behavior of P2W1. As the scan rate gradually increased from 0.1 mV / s to 0.5 mV / s, the peak current increased accordingly, and the CV curve shape remained highly stable, exhibiting only slight polarization. This result strongly demonstrates that P2W1 possesses excellent rate performance and electrochemical stability, and its internal structure effectively supports the rapid insertion and extraction of lithium ions, making it suitable for high-energy-density applications.

[0057] Figure 6 The Nyquist plots of the electrochemical impedance spectroscopy (EIS) of the electrodes after different number of cycles are shown. Figure 6 The comparison results in (a) show that the P2W1 composite material exhibits the smallest high-frequency semicircle in diameter, which means that it has the lowest charge transfer resistance, significantly better than the high-impedance single PAM and other samples; this confirms that the unique component network of P2W1 effectively constructs a fast ion transport channel and greatly improves the reaction kinetics. Figure 6 (b) illustrates the dynamic evolution of the P2W1 impedance with the number of cycles. Notably, in the initial stage of cycling, the semicircle diameter of the impedance spectrum shows a decreasing trend. This is attributed to the "electrochemical activation" process of the electrode; that is, as cycling progresses, the electrolyte fully wets the porous structure of the composite material, increasing the effective reaction area and optimizing the ion transport channels. After long-term cycling (e.g., 200 cycles), the semicircle diameter slightly increases, which is consistent with the general pattern of gradual growth and thickening of the SEI film. Nevertheless, it still maintains good diffusion characteristics in the low-frequency region, indicating that after undergoing activation and film formation, the overall structure of P2W1 maintains excellent tolerance and interfacial stability. The equivalent circuit model shown in Figure (c) is used to fit and analyze the electrochemical impedance spectroscopy (EIS).

[0058] Figure 7 The following are Nyquist plots of electrochemical impedance spectroscopy (EIS) before and after cycling for four electrodes: (a) EIS of P2W1, (b) EIS of P1W1, (c) EIS of PAM, and (d) EIS of WPU. To further evaluate the interfacial kinetic stability of the materials during long-term electrochemical cycling, the impedance evolution of the four samples at different cycle numbers (0, 50, 200 cycles) was compared. Lateral comparison shows that pure PAM (… Figure 7 (c) and WPU ( Figure 7 (d) exhibits extremely high interfacial impedance, indicating that the single component has extremely poor conductivity; while the composite materials P1W1 and P2W1 ( Figure 7 The impedance of (a) and (b) decreased significantly, confirming that the synergistic effect between components effectively constructed the lithium-ion transport channel. Longitudinal observation revealed that, with cycling, the impedance semicircles of all samples showed varying degrees of expansion due to SEI film growth and interface aging. However, P2W1 ( Figure 7 (a) It maintains the minimum charge transfer resistance throughout its entire life cycle (initially <50 Ω, only 180 Ω after 200 cycles). Its excellent resistance growth capability indicates that the microstructure under this ratio is most conducive to maintaining electrolyte wetting and rapid ion shuttle, exhibiting the best electrochemical reaction kinetics and interface stability.

[0059] Figure 8 The images show the scanning electron microscope (SEM) morphology of the electrode surfaces with different binders before and after 50 cycles, comparing the crack conditions. (a) shows the surface cracking of the four electrodes (P2W1, P1W1, PAM, and WPU) before and after cycling, and (b) shows the volume expansion of the four electrodes (P2W1, P1W1, PAM, and WPU) before and after cycling. It can be seen that the surface of Comparative Example 1 (PAM) electrode developed severe, wide, penetrating cracks, causing the active material to lose electrical contact with the current collector, becoming "dead silicon." Although Comparative Example 2 (WPU) electrode had fewer cracks, it exhibited significant swelling and deformation. In contrast, the surface of Example 1 (P2W1) electrode maintained better integrity, with only minor microcracks observed. The formation of these microcracks helps release internal stress during cycling, preventing damage from large cracks, and directly demonstrates that the "rigid skeleton constraint + flexible buffer energy dissipation" mechanism of the composite binder of this invention effectively adapts to the volume changes of the silicon-carbon anode.

[0060] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A binder for the negative electrode of a lithium-ion battery, characterized in that, It includes polyacrylamide as a rigid component and waterborne polyurethane as a flexible component, wherein the polyacrylamide and the waterborne polyurethane are bonded together through intermolecular interactions to form a three-dimensional network structure.

2. The binder for the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The three-dimensional network structure is an interpenetrating network structure formed through intermolecular hydrogen bonding.

3. The binder for the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The mass ratio of the polyacrylamide to the waterborne polyurethane is 0.5~5:

1.

4. A method for preparing a binder for a lithium-ion battery negative electrode as described in any one of claims 1 to 3, characterized in that, Includes the following steps: An aqueous solution of polyacrylamide and an aqueous polyurethane dispersion were mixed to obtain a mixture. The mixture is stirred to allow the polyacrylamide and the waterborne polyurethane to self-assemble in situ through physical entanglement and hydrogen bonding during the mixing process, forming the binder.

5. A method for preparing a binder for a lithium-ion battery negative electrode according to claim 4, characterized in that, The concentration of the polyacrylamide aqueous solution is 0.5wt%~10wt%, and the solid content of the aqueous polyurethane dispersion is 0.5wt%~10wt%. The mass ratio of polyacrylamide in the aqueous polyacrylamide solution to waterborne polyurethane in the aqueous polyurethane dispersion is 0.5~5:

1.

6. A method for preparing a binder for a lithium-ion battery negative electrode according to claim 4, characterized in that, The in-situ self-assembly was performed at room temperature for 0.5 to 5 hours.

7. A method for preparing a binder for a lithium-ion battery negative electrode according to claim 4, characterized in that, The method for preparing the polyacrylamide aqueous solution is as follows: under the protection of an inert atmosphere, acrylamide monomer is polymerized in an aqueous solution containing an initiator to obtain a polyacrylamide solution; the polyacrylamide solution is diluted to obtain a polyacrylamide aqueous solution with a predetermined mass fraction.

8. A method for preparing a binder for a lithium-ion battery negative electrode according to claim 7, characterized in that, The initiator is ammonium persulfate.

9. A method for preparing a binder for a lithium-ion battery negative electrode according to claim 7, characterized in that, The polymerization reaction is carried out at a temperature range of 60-85°C for 4-8 hours.

10. The application of the binder for the negative electrode of a lithium-ion battery as described in any one of claims 1 to 3, characterized in that, The binder is used to prepare slurries, electrode sheets, and / or batteries for silicon-based anodes of lithium-ion batteries.

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