Binder and method for producing the same, secondary battery

Abstract

The application discloses a binder, a preparation method thereof and a secondary battery. The binder comprises sodium alginate, polyether thiourea and metal ions, the sodium alginate is coordinated with the metal ions, and a double network structure is formed between the sodium alginate and the polyether thiourea. The binder has good mechanical properties and stable rheological properties, and can realize rapid self-healing at room temperature. The battery adopting the binder has good cycle stability and excellent rate performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a binder and its preparation method, and a secondary battery. Background Technology

[0002] Currently, commercially available lithium-ion batteries primarily use graphite as the anode material. Graphite's theoretical specific capacity is 372 mAh / g, and even high-end graphite materials on the market only achieve 360-365 mAh / g, offering limited improvement to the energy density of lithium-ion batteries. However, silicon boasts a higher theoretical specific capacity of 4200 mAh / g, a lower lithium removal potential (<0.5V), and advantages such as environmental friendliness and abundance. Silicon-based anode materials are considered the preferred choice for next-generation high-capacity lithium-ion battery anode materials. However, in Li... + During the insertion and deinsertion process, the volume of Si particles changes dramatically (about 300%), leading to problems such as the silicon particles squeezing and crushing each other, damage to the electrode structure, and instability of the solid electrolyte interface (SEI). These issues severely affect the cycle life of the battery and limit its development and application in lithium batteries.

[0003] The concept of binders is one of the core aspects of the entire silicon anode field. They play a crucial role in bonding active materials, conductive agents, and current collectors, shortening the lithium-ion transport path, and stabilizing the structure of electrode materials. Among them, PVDF, as a commercial binder, has been widely used in battery systems. However, its low adhesion strength, poor stability, and poor conductivity prevent it from meeting the development and application requirements of high-capacity batteries. Summary of the Invention

[0004] This application provides an adhesive and its preparation method, as well as a secondary battery, which solves the problems of low adhesion strength and poor stability of current adhesives.

[0005] According to the adhesive in the first embodiment of this application, the adhesive includes sodium alginate, polyether thiourea and metal ions, wherein sodium alginate coordinates with the metal ions and forms a double network structure with polyether thiourea.

[0006] Optionally, in other embodiments of this application, the metal ions include at least one of aluminum ions, barium ions, zinc ions, calcium ions, or manganese ions.

[0007] Optionally, in other embodiments of this application, metal ions form coordination bonds with the guluronic acid units of sodium alginate.

[0008] Optionally, in other embodiments of this application, the relative molecular mass of sodium alginate is 30-50 kg / mol, and the relative molecular mass of polyether thiourea is 20-30 kg / mol.

[0009] Optionally, in other embodiments of this application, the mass ratio of sodium alginate to polyether thiourea can be (3-5):1, (3.5-4.5):1, or 4:1.

[0010] The method for preparing the adhesive according to the second embodiment of this application includes:

[0011] Dissolve sodium alginate and polyether thiourea in a solvent and mix well;

[0012] Add metal salts, mix well, and you will get a binder.

[0013] Optionally, in other embodiments of this application, the metal salt includes at least one of AlCl3, Al2(SO4)3, CaCl2, BaCl2, MnCl2 or ZnCl2.

[0014] The secondary battery according to the third embodiment of this application includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector, the negative active material layer includes a negative active material, a conductive agent, a binder and a solvent, and the binder is the binder described above or the binder prepared by the preparation method described above.

[0015] Optionally, in other embodiments of this application, the negative electrode active material includes one or more of silicon materials, silicon-carbon materials, or silicon-oxygen materials.

[0016] The adhesive according to the embodiments of this application has at least the following technical effects:

[0017] (1) The adhesive of this application is a mixture of sodium alginate and polyether thiourea, which forms an interpenetrating double network structure, thereby improving the adhesion and mechanical properties of sodium alginate.

[0018] (2) This application introduces metal ions into the adhesive, which further enhances the intermolecular forces, giving the adhesive good mechanical properties and stable rheological properties, and enabling it to achieve rapid self-healing at room temperature. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0020] Figure 1 This is a schematic diagram of the dual-network structure of an embodiment of this application;

[0021] Figure 2 This is an embodiment of the present application, A1. 3+Infrared spectra of coordinated sodium alginate-polyether thiourea, sodium alginate-polyether thiourea, polyether thiourea and sodium alginate;

[0022] Figure 3A This is a state diagram of the adhesive provided in Embodiment 1 of this application;

[0023] Figure 3B This is a state diagram of the adhesive provided in Comparative Example 1 of this application;

[0024] Figure 4A , Figure 4B and Figure 4C This is the viscoelastic-time scan curve of the adhesive provided in Example 1 of this application;

[0025] Figure 5 This is the peeling force-displacement curve of the negative electrode sheet provided in Embodiment 1 of this application;

[0026] Figure 6 This is a surface change diagram of the electrode sheet after peeling off in Embodiment 1 of this application;

[0027] Figure 7 This is a swelling performance diagram of the adhesive provided in Example 1 of this application;

[0028] Figure 8 This is an SEM elemental distribution scan of the negative electrode sheet provided in Embodiment 1 of this application;

[0029] Figure 9 This is a battery long-cycle test diagram provided in Embodiment 1 of this application;

[0030] Figure 10 This is the battery coulombic efficiency diagram provided in Embodiment 1 of this application;

[0031] Figure 11 This is the battery cyclic voltammogram provided in Embodiment 1 of this application;

[0032] Figure 12 This is a battery rate performance diagram provided in Embodiment 1 of this application;

[0033] Figure 13 This is the battery impedance diagram provided in Embodiment 1 of this application;

[0034] Figure 14 This is Example 1A1 of this application. 3+ Figures showing the morphological changes of the coordinated sodium alginate-polyether thiourea electrode and the sodium alginate electrode before and after 100 cycles.

[0035] Figure 15 This is a cycle performance diagram of a full-cell lithium iron phosphate battery provided in Embodiment 2 of this application;

[0036] Figure 16This is a diagram showing the rate cycling performance of a full-cell nickel-cobalt-manganese battery provided in Example 3 of this application. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] This application provides an adhesive, a method for preparing the same, and a secondary battery. These are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments.

[0039] In this specification, the range of values ​​indicated by “~” represents the range containing the minimum and maximum values ​​recorded before and after “~”, respectively.

[0040] This application provides an adhesive comprising sodium alginate (Alg), polyether thiourea (TEUG), and metal ions. Sodium alginate coordinates with the metal ions and forms a dual-network structure with the polyether thiourea. Sodium alginate is a natural polyanionic polysaccharide with high viscosity in its aqueous solution. The abundant guluronic acid units in its molecular structure can interact with the hydroxyl groups on the surface of the silicon negative electrode material, enhancing the connection between silicon and the adhesive and current collector. This invention improves the adhesion and mechanical properties of sodium alginate by mixing sodium alginate and polyether thiourea, which has abundant hydrogen bonds, to form an interpenetrating dual-network structure. Simultaneously, Al is added to the dual-network structure... 3+ An adhesive with dual self-healing properties was prepared.

[0041] In some embodiments of this application, the metal ion includes at least one selected from aluminum ions, barium ions, zinc ions, calcium ions, or manganese ions. Preferably, the metal ion is aluminum ion, which is more beneficial for improving battery performance.

[0042] In some embodiments of this application, such as Figure 1 As shown, metal ions form coordination bonds with the guluronic acid units of sodium alginate. In this application, TUEG can achieve self-healing through hydrogen bond rearrangement. As a recoverable first network, the guluronic acid units in different alginate chains can interact with dissociated Al... 3+ Ions form coordination bonds, acting as a sacrificial but recoverable second network. The introduction of metal ions (Al) into the dual-network structure... 3+ This further enhances the intermolecular forces, giving the adhesive good mechanical properties and stable rheological properties, and enabling it to achieve rapid self-healing at room temperature.

[0043] In some embodiments of this application, the relative molecular mass of sodium alginate is 30-50 kg / mol, for example, the relative molecular mass of sodium alginate can be 43.2 kg / mol; the relative molecular mass of polyether thiourea is 20-30 kg / mol, for example, the relative molecular mass of polyether thiourea can be 25.5 kg / mol.

[0044] In some embodiments of this application, the mass ratio of sodium alginate to polyether thiourea can be (3-5):1, (3.5-4.5):1, or 4:1. Within this range, the binder exhibits good adhesion, rheological properties, and appropriate swelling properties, demonstrating excellent cycle stability and rate performance when applied to lithium-ion battery silicon anodes, as well as good cycle stability and rate performance in full-cell applications.

[0045] Accordingly, this application also provides a method for preparing an adhesive, comprising: dissolving sodium alginate and polyether thiourea in a solvent and mixing them; adding a metal salt and mixing them to obtain an adhesive.

[0046] In some embodiments of this application, the metal salt includes at least one of AlCl3, Al2(SO4)3, CaCl2, BaCl2, MnCl2 or ZnCl2.

[0047] Specifically, the solvent includes at least one of deionized water or N-methylpyrrolidone.

[0048] In specific implementation, the preparation methods of the adhesive include:

[0049] 1) Dissolve sodium alginate and polyether thiourea in a mixture of deionized water and N-methylpyrrolidone, and stir the solution vigorously at room temperature for a certain period of time to obtain a homogeneous solution.

[0050] 2) Add an appropriate amount of AlCl3 aqueous solution to the above solution and continue stirring for a certain period of time to form a transparent and uniform gel, thus obtaining the adhesive.

[0051] Furthermore, this application also provides a secondary battery, including a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a solvent. The binder is the binder described above or a binder prepared by the above-described preparation method. Using the binder of this application on the negative electrode sheet is more conducive to ensuring the integrity of the electrode and also demonstrates that the binder has strong peeling force. The secondary battery prepared using this method exhibits good cycle stability and excellent rate performance.

[0052] In some embodiments of this application, the negative electrode active material includes one or more of silicon, silicon-carbon, or silicon-oxygen materials. Silicon-based negative electrode materials have high theoretical specific capacity, low lithium removal potential, and are environmentally friendly and relatively abundant in resources.

[0053] Specifically, the secondary battery also includes a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, a conductive agent, a binder, and a solvent. The positive active material includes at least one of lithium iron phosphate, lithium manganese oxide, nickel-cobalt-manganese ternary material, or nickel-cobalt-aluminum ternary material.

[0054] Accordingly, embodiments of this application also provide a method for preparing a negative electrode sheet, comprising:

[0055] Mix the negative electrode active material and the conductive agent evenly;

[0056] Add binder and solvent, stir evenly to obtain negative electrode slurry;

[0057] The negative electrode slurry is coated onto the current collector and dried to obtain the negative electrode sheet;

[0058] The adhesive is the adhesive described above or the adhesive prepared by the above preparation method.

[0059] The following description is based on specific embodiments.

[0060] Example 1

[0061] This application provides a method for preparing a binder and a negative electrode sheet, the specific steps of which are as follows:

[0062] 1) Preparation of the adhesive: 0.8 g of sodium alginate and 0.2 g of polyether thiourea were dissolved in a mixture of deionized water and N-methylpyrrolidone, and the solution was vigorously stirred at room temperature for 12 h to obtain a homogeneous solution. Then, 10 ml of 1 M AlCl3 aqueous solution was added to the above solution and stirring was continued for 1 h to form a transparent and homogeneous gel, thus obtaining the adhesive.

[0063] 2) Preparation of the negative electrode sheet: First, weigh 0.8g of thoroughly dehydrated and dried nano-silicon powder and 0.1g of conductive carbon, add them to a special quartz mortar and grind for 30-45 minutes to ensure uniform mixing. Then, add the prepared binder solution and an appropriate amount of solvent, and stir thoroughly. Use a four-sided coating tool to evenly coat the uniformly stirred electrode slurry onto a clean copper foil (current collector), and place it in a vacuum oven to dry thoroughly to obtain the negative electrode sheet.

[0064] 3) Assembly of coin cell half-cells: Cut the negative electrode sheet into 9mm diameter circular pieces using a slicer. Weigh and record the weight of the cut negative electrode sheets, and then assemble the C2025 coin cells in a glove box. Use Celgaed 2400 polypropylene as the separator and lithium foil as the counter electrode when assembling the coin cells.

[0065] Example 2

[0066] This application provides a method for preparing a negative electrode sheet and a battery, the specific steps of which are as follows:

[0067] 1) Preparation of negative electrode sheet: The negative electrode sheet is the same as in Example 1, except that the negative electrode sheet is cut into 12mm pieces using a slicer;

[0068] 2) Preparation of Lithium Iron Phosphate Cathode: The pharmaceutical materials were thoroughly dried in a vacuum drying oven. 0.8g LiFePO4, 0.1g conductive carbon, and 0.1g PVDF binder were weighed and ground thoroughly in a quartz mortar until homogeneous. The mixture was then transferred to a glass container. An appropriate amount of N-methylpyrrolidone solvent was added to the glass container and stirred for a certain period to form a uniform electrode slurry. The electrode slurry was then evenly coated onto an aluminum foil (positive electrode current collector) using a four-sided coating tool and thoroughly dried in a vacuum oven. Finally, the electrode was cut into 9mm pieces using a slicer.

[0069] 3) Full Cell Assembly: First, using a 12mm electrode as the negative electrode and a lithium sheet as the counter electrode, assemble the C2025 coin cell as described above. After assembly, let it stand for 6-12 hours. Then, pre-lithiate the electrode and discharge the half-cell at a constant current (1.5mA) for 5 hours. Finally, disassemble the half-cell in a glove box, remove the pre-lithiated electrode as the negative electrode of the full cell, and assemble the full cell using a lithium iron phosphate electrode as the positive electrode, following the same method as assembling the half-cell.

[0070] Example 3

[0071] Similar to Example 2, except that the positive electrode active material is replaced with a ternary nickel-cobalt-manganese material.

[0072] Comparative Example 1

[0073] Similar to Example 1, except that the adhesive component contains only sodium alginate.

[0074] The adhesive of Comparative Example 1 was prepared by adding sodium alginate, using deionized water as a solvent, and stirring the solution vigorously at room temperature for 12 hours to prepare a 35% solution.

[0075] Test method:

[0076] 1) Swelling performance test: Cut the dried adhesive sample film into the same shape and weigh it (w0). Then, immerse the sample in the electrolyte at room temperature for 40-60 hours, remove the sample, wipe off the solvent, and weigh and record its mass (w1). Each sample is tested three times. The swelling coefficient is calculated using the following formula:

[0077]

[0078] 2) Peel performance test: The mechanical properties of the prepared adhesive were tested using a universal material tester. The peel performance test was conducted at a constant speed of 180° with a peel rate between 10 and 40 mm / min.

[0079] 3) Use a rheometer to characterize the self-healing properties of the adhesive (the changes in storage modulus (G') and loss modulus (G") of the sample at room temperature are tested over time or with changes in shear stress).

[0080] 4) The cycle performance of the electrodes was studied through constant current charge-discharge testing. A lithium-ion symmetric battery was used, at 0.1 mA / cm². -2 Tested at current density.

[0081] 5) The important electrochemical properties of the electrodes, such as cycle life, rate performance, discharge specific capacity, and coulombic efficiency, were studied through charge-discharge tests. All batteries underwent constant current charge-discharge cycle tests at room temperature.

[0082] 6) The cycle life and rate performance of the lithium iron phosphate electrode in the full battery were studied through charge-discharge tests.

[0083] 7) The cycle life and rate performance of the nickel-cobalt-manganese electrode of the full cell were studied through charge-discharge tests. The full cell test voltage range was adjusted to 2.5-4.3V.

[0084] The test results are as follows:

[0085] like Figure 2 As shown, Figure 2 Al of Example 1 3+ The infrared spectrum of coordinated sodium alginate-polyether thiourea was compared with that of pure Alg and TUEG in Fourier transform infrared spectroscopy by physically mixing Alg and TUEG. The NH and C vibrations were in the range of 3600–2750 cm⁻¹. -1 and 1026cm -1 Sodium alginate-polyether thiourea and Al were found at the site. 3+ The coordination of sodium alginate-polyether thiourea O-1 further confirms the physical mixing. Additionally, another adsorption at 812 cm⁻¹... -1 Discover Al 3+The coordination of sodium alginate-polyether thiourea Al-O groups indicates that the guluronic acid units in different sodium alginate chains react with free Al in AlCl3 aqueous solution. 3+ The ions successfully coordinated with each other.

[0086] Figure 3A This is a state diagram of the adhesive provided in Embodiment 1 of this application. Figure 3B This is a state diagram of the adhesive provided in Comparative Example 1 of this application. It can be seen that the addition of polyether thiourea and Al... 3+ The solution then forms a stable emulsion gel, while the sodium alginate aqueous solution remains in a solution state.

[0087] Figure 4A , Figure 4B and Figure 4C Al of Example 1 3+ The viscoelastic-time scan curve of the coordinated sodium alginate-polyether thiourea gel shows that when the shear strain is less than 600%, Al 3+ The storage modulus (G') of the coordinated sodium alginate-polyether thiourea gel remains consistently higher than its loss modulus (G"). However, as shear stress continues to increase, both G' and G" values ​​decrease sharply and cross over. After experiencing a shear force of 1000, the modulus recovers to the value under low shear force.

[0088] Figure 5 These are peel test images of the negative electrode sheets prepared in Example 1 and Comparative Example 1. Al 3+ The peeling force of coordinated sodium alginate-polyether thiourea is significantly increased.

[0089] Figure 6 The changes on the electrode surface after peeling in Example 1 show that Al... 3+ The sodium alginate-polyether thiourea silicon anode sheet is uniform and has less material detached after peeling.

[0090] Figure 7 Al for Example 1 and Comparative Example 1 3+ Swelling properties of coordinated sodium alginate-polyether thiourea membrane and sodium alginate membrane, Al 3+ Coordinated sodium alginate-polyether thiourea membranes have appropriate swelling properties.

[0091] Figure 8 Al of Example 1 3+ SEM elemental distribution scan of the coordinated sodium alginate-polyether thiourea electrode sheet proves that the electrode sheet contains the corresponding Si, C, N, O, S, and Al elements.

[0092] Figure 9 Al for Example 1 and Comparative Example 1 3+ Comparison of cycling performance between sodium alginate-polyether thiourea electrode and sodium alginate electrode, Al 3+The coordinated sodium alginate-polyether thiourea silicon anode sheet retains a reversible capacity of 2480 mAh g after 300 charge-discharge cycles. -1 The capacity retention rate was 77.4%, while sodium alginate's capacity rapidly decreased to 1172 mAh g after 300 cycles. -1 The capacity retention rate was 37.3%.

[0093] Figure 10 The coulombic efficiency of the electrodes of Example 1 and Comparative Example 1 was tested during a constant current charge-discharge process. 3+ The initial coulombic efficiencies of the coordinated sodium alginate-polyether thiourea electrode and the sodium alginate electrode were 87.1% and 79.3%, respectively.

[0094] Figure 11 The cyclic voltammogram of the battery provided in Embodiment 1 of this application shows a reduction peak observed at approximately 1.6V in the first cyclic voltammogram. This reduction peak is primarily due to the decomposition of the electrolyte at this voltage. The electrolyte decomposition consumes some lithium ions and active materials, forming a dense SEI layer on the electrode surface. The formation of the SEI layer helps suppress the reaction between the electrolyte and the active materials, reducing subsequent capacity loss. Simultaneously, the SEI layer possesses electronic insulation but good ion-conducting properties, effectively preventing battery short circuits while promoting lithium-ion transport between the positive and negative electrodes.

[0095] Figure 12 This is a comparison chart of the rate performance of electrodes in Example 1 and Comparative Example 1. The sodium alginate electrode experiences almost zero capacity reduction under high current density, indicating irreversible damage. Under the same conditions, Al... 3+ The coordinated sodium alginate-polyether thiourea electrode remains intact.

[0096] Figure 13 The graph shows a comparison of the AC impedance of the electrode variations in Example 1 and Comparative Example 1. It can be seen that Al... 3+ The slope of the coordinated sodium alginate-polyether thiourea electrode is greater than that of the sodium alginate electrode, representing Al 3+ The coordinated sodium alginate-polyether thiourea electrode exhibits better lithium-ion diffusion. Al can also be observed... 3+ The semicircle of the coordinated sodium alginate-polyether thiourea electrode is smaller than that of the sodium alginate electrode, indicating a lower SEI layer interfacial impedance. This suggests that Al... 3+ The coordinated sodium alginate-polyether thiourea electrode exhibits good ionic conductivity.

[0097] Figure 14Figures show the electrode morphology changes before and after 50 cycles for Examples 1 and Comparative Example 1. Figures (a), (c), and (e) show the electrode morphology changes for Example 1; Figures (b), (d), and (f) show the electrode morphology changes for Comparative Example 1. Before cycling, Al... 3+ Both the coordinated sodium alginate-polyether thiourea silicon electrode and the sodium alginate electrode have relatively intact surfaces with many uniform micropores. These micropores facilitate electrolyte wetting and lithium ion diffusion between the electrodes. As shown in Figures (c) and (e), after 50 cycles, Al... 3+ Only a few tiny cracks were found on the surface of the coordinated sodium alginate-polyether thiourea silicon electrode, and a dense and stable SEI layer was formed on the electrode surface. This is mainly due to Al 3+ The sodium alginate-polyether thiourea silica binder can promptly repair mechanical damage to the electrode. However, after charge-discharge testing under the same conditions, an uneven SEI layer appeared on the surface of the sodium alginate electrode, and deep and obvious cracks appeared on the electrode surface. This indicates that the sodium alginate binder has weak adhesion and lacks self-healing properties. During cycling, it cannot effectively inhibit silicon volume expansion and cannot promptly repair mechanical damage to the electrode, leading to electrode breakage and large cracks.

[0098] Figure 15 The full-cell lithium iron phosphate cycle performance diagram provided in Example 2, and the long-term cycle performance diagram of the LiPO4 full-cell (0.5C) show that the full cell also has stable cycle performance.

[0099] Figure 16 The diagram shows the rate cycling performance of the full cell nickel-cobalt-manganese provided in Example 3, and the long-term cycling performance of the NCM full cell (0.5C). The full cell also has stable cycling performance.

[0100] This application provides an adhesive with excellent mechanical properties and stable rheological properties, enabling rapid self-healing at room temperature. Batteries using this adhesive exhibit good cycle stability and excellent rate performance.

[0101] The above provides a detailed description of the adhesive, its preparation method, and the secondary battery provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A binder, characterized by The binder comprises sodium alginate, polyether thiourea and metal ions, the metal ions comprising aluminum ions; The polyether thiourea realizes self-healing through rearrangement of hydrogen bonds, as a first network; The sodium alginate is coordinated with the metal ions, wherein the aluminum ions form coordination bonds with guluronic acid units of the sodium alginate, as a second network; the sodium alginate and the polyether thiourea with hydrogen bonds form a double network structure interpenetrating each other; The relative molecular mass of the sodium alginate is 30-50 kg / mol, and the relative molecular mass of the polyether thiourea is 20-30 kg / mol.

2. The binder of claim 1, wherein, The metal ions further comprise at least one of barium ions, zinc ions, calcium ions or manganese ions.

3. The binder of claim 1, wherein, The mass ratio of the sodium alginate to the polyether thiourea is (3-5):

1.

4. A method of producing the binder as claimed in any one of claims 1 to 3, characterized in that, The method comprises: dissolving sodium alginate and polyether thiourea in a solvent and mixing uniformly; adding a metal salt and mixing uniformly to obtain the binder.

5. The method of claim 4, wherein the binder is prepared by mixing the components in the following order: the polyol, the polyisocyanate, the chain extender, the crosslinker, the catalyst, and the surfactant. The metal salt comprises at least one of AlCl3, Al2(SO4)3, CaCl2, BaCl2, MnCl2 or ZnCl2.

6. A secondary battery characterized by comprising: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a conductive agent, a binder and a solvent, the binder being the binder according to any one of claims 1-3 or prepared by the method according to claim 4 or 5.

7. The secondary battery according to claim 6, characterized by The negative electrode active material comprises one or more of a silicon material, a silicon-carbon material or a silicon-oxygen material. The negative electrode active material comprises one or more of a silicon material, a silicon-carbon material or a silicon-oxygen material.

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