Negative plate, negative plate preparation method and battery

Abstract

The invention provides a negative electrode plate, a negative electrode plate preparation method and a battery, the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material and a modified binder, the negative electrode active material comprises a silicon carbon material and a polar coating, and the polar coating coats the silicon carbon material; the modified binder comprises a binder precursor, and an epoxy compound is grafted on the binder precursor. According to the negative plate provided by the invention, the silicon-carbon material is coated with the polar coating, the negative plate can be tightly attached to the silicon-carbon surface by utilizing polar interaction, the volume expansion of the silicon-carbon material is inhibited in the cyclic charging and discharging process, and meanwhile, the modified binder grafted with the epoxy compound can be used for inhibiting the volume expansion of the silicon-carbon material through the strong interaction among the epoxy compound, the silicon-carbon material and the polar coating. According to the present invention, the structure loosening caused by expansion is inhibited, and the flexibility of the binder is optimized, such that the binder can adapt to the expansion and shrinkage of silicon carbon, and the shedding of the active material and the side reaction of the electrolyte during the circulation process are reduced so as to effectively alleviate the capacity fading and improve the cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet, a negative electrode sheet preparation method and a battery. BACKGROUND

[0002] In the process of iteration of consumer lithium ion battery technology, silicon-carbon negative electrode has become the core direction gradually turned to by the industry due to its higher theoretical capacity advantage, but there are still some defects in silicon-carbon negative electrode material, one is that the volume expansion phenomenon is significant in the process of cyclic charging and discharging, which is easy to cause the damage of electrode structure, and the other is that the capacity attenuation is fast after long-term cycle, and the cycle life is difficult to meet the demand of high-end application. The main improvement scheme in the industry at present is to increase the amount of binder to alleviate the expansion and life problems by enhancing the binding force between materials, but excessive binder will greatly reduce the kinetic performance of the battery, leading to the decrease of ion and electron transmission efficiency, and also cause uneven dispersion of electrode material particles, further affecting the overall electrical performance of the battery. SUMMARY

[0003] In view of the problems of volume expansion and rapid cycle capacity reduction in the application of silicon-carbon negative electrode in the prior art, a negative electrode sheet, a negative electrode sheet preparation method and a battery are provided.

[0004] The technical solution adopted by the present application to solve the above technical problems is as follows: On the one hand, the present application provides a negative electrode sheet, comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material and a modified binder, the negative electrode active material comprising a silicon-carbon material and a polar coating, the polar coating coating the silicon-carbon material. The modified binder comprises a binder precursor, and the binder precursor is grafted with an epoxy compound.

[0005] Optionally, the polar coating comprises one or more of an anhydride group-containing compound and a double bond-containing carboxylic acid compound.

[0006] Optionally, the anhydride group-containing compound comprises one or more of maleic anhydride, glutaric anhydride, chloroacetic anhydride and allyl succinic anhydride; and / or, The double bond-containing carboxylic acid compound comprises one or more of acrylic acid, methacrylic acid, maleic acid and fumaric acid.

[0007] Optionally, the epoxy compound comprises one or more of oxirane, oxetane and epoxy-terminated polyurethane.

[0008] Optionally, the binder precursor comprises one or more of sodium alginate and lithium alginate.

[0009] Optionally, the molecular weight of the modified binder is 50-150W.

[0010] Optionally, the elongation at break of the modified binder is 5% to 30%.

[0011] Optionally, the mass percentage of silicon in the negative electrode sheet is 5% to 50%.

[0012] Optionally, the mass percentage of the modified binder in the negative electrode sheet is 1% to 5%.

[0013] Optionally, the mass ratio of the negative electrode active material to the modified binder is 10: (0.1 to 0.5).

[0014] In another aspect, the application provides a method for preparing the negative electrode sheet as described above, comprising the following operations: placing the polar coating in an initial solvent to obtain a mixed solution; placing the silicon-carbon material in the mixed solution and stirring in a high-temperature environment, and obtaining a silicon-carbon material precursor after the solution is completely dried; calcining the silicon-carbon material precursor to obtain a negative electrode active material; dispersing the binder precursor in a third solvent, adding a catalyst, performing etherification, then adding an epoxide compound, and stirring at a high temperature to perform grafting reaction, and obtaining a modified binder after the reaction is completed; mixing the negative electrode active material, the modified binder, and a conductive agent to prepare a negative electrode slurry, coating and drying to obtain a negative electrode sheet.

[0015] Optionally, in the operation of "placing the polar coating in an initial solvent", the initial solvent is obtained by mixing a first solvent and a second solvent.

[0016] Optionally, the mass ratio of the first solvent to the second solvent is 1:0.1 to 1:1.

[0017] Optionally, the first solvent and the third solvent are both water, and the second solvent is an organic solvent.

[0018] Optionally, in the mixed solution, the solid content of the polar coating is 0.1% to 30%.

[0019] Optionally, in the silicon-carbon material precursor, the mass ratio of the polar coating to the silicon-carbon material is 0.01:1 to 0.1:1.

[0020] Optionally, the pH value for the grafting reaction of the binder precursor and the epoxide compound is 7 to 9.

[0021] Optionally, the calcination temperature is 400-450℃, and the calcination time is 3-3.5h.

[0022] In another aspect, the present application provides a battery comprising the negative electrode sheet or the negative electrode sheet prepared by the preparation method of the negative electrode sheet.

[0023] The present application has the following beneficial effects: The negative electrode sheet provided by the present application has the following advantages: the polar coating covers the silicon-carbon material and tightly adheres to the surface of the silicon-carbon material by utilizing the polar interaction, thereby inhibiting the volume expansion of the silicon-carbon material and reducing the structural damage of the electrode during the cyclic charging and discharging process; meanwhile, the modified binder grafted with the epoxy compound can further enhance the binding stability of the electrode by the strong interaction between the epoxy compound and the silicon-carbon material and the polar coating, thereby inhibiting the structural loosening caused by the expansion; in addition, the modified binder can optimize the flexibility of the binder, so that the binder can adapt to the expansion and contraction of the silicon-carbon material, thereby avoiding the intensification of the electrolyte side reaction caused by the interface cracking, reducing the shedding of the active material and the side reaction of the electrolyte during the cyclic process, and effectively alleviating the capacity attenuation and improving the cycle life. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] The present application provides a negative electrode sheet comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material and a modified binder, the negative electrode active material comprises a silicon-carbon material and a polar coating, and the polar coating covers the silicon-carbon material. The modified binder comprises a binder precursor, and the binder precursor is grafted with an epoxy compound.

[0026] Specifically, the negative electrode sheet provided by the present application has the following advantages: the polar coating covers the silicon-carbon material and tightly adheres to the surface of the silicon-carbon material by utilizing the polar interaction, thereby inhibiting the volume expansion of the silicon-carbon material and reducing the structural damage of the electrode during the cyclic charging and discharging process; meanwhile, the modified binder grafted with the epoxy compound can further enhance the binding stability of the electrode by the strong interaction between the epoxy compound and the silicon-carbon material and the polar coating, thereby inhibiting the structural loosening caused by the expansion; in addition, the modified binder can optimize the flexibility of the binder, so that the binder can adapt to the expansion and contraction of the silicon-carbon material, thereby avoiding the intensification of the electrolyte side reaction caused by the interface cracking, reducing the shedding of the active material and the side reaction of the electrolyte during the cyclic process, and effectively alleviating the capacity attenuation and improving the cycle life.

[0027] In some embodiments, the polar coating comprises one or more compounds containing anhydride groups and carboxylic acid compounds containing double bonds.

[0028] Specifically, when compounds containing anhydride groups and carboxylic acid compounds containing double bonds are used as polar coatings, their strong polarity allows them to form a stable interfacial bond with silicon-carbon materials, effectively constraining the volume expansion of silicon-carbon during cyclic charging and discharging. They also provide abundant active binding sites for modified binders grafted with epoxy compounds. Through polar interactions and chemical bonding, the adsorption effect of the binder is synergistically enhanced, strengthening the adhesion and structural integrity of the electrode. At the same time, these polar coatings can also optimize the surface properties of silicon-carbon materials, reduce side reactions between active materials and electrolytes, and, combined with the flexibility of modified binders, further suppress the shedding of active materials and interfacial damage during cycling. Ultimately, this alleviates electrode cyclic expansion while significantly improving the cycle life of the battery cell. Furthermore, when any one or more of the above-mentioned polar coatings are selected in this application, they can effectively suppress the volume expansion of silicon carbon during cyclic charging and discharging.

[0029] In some embodiments, the compound containing anhydride groups includes one or more of maleic anhydride, glutaric anhydride, chloroacetic anhydride, and allyl succinic anhydride; and / or, The carboxylic acid compounds containing double bonds include one or more of acrylic acid, methacrylic acid, maleic acid, and fumaric acid.

[0030] Specifically, compounds containing anhydride groups, such as maleic anhydride, glutaric anhydride, chloroacetic anhydride, and allyl succinic anhydride, as well as carboxylic acid compounds containing double bonds, such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid, all possess strong polarity and abundant active functional groups. On the one hand, they can form a stable bond with the surface of silicon-carbon materials, effectively constraining their volume expansion during cyclic charging and discharging. On the other hand, they can synergistically interact with modified binders grafted with epoxy compounds. Through the chemical bonding and polar interaction of active groups, they can improve the adsorption efficiency of the binder and the adhesion between materials, thereby strengthening the integrity of the electrode structure. At the same time, these compounds can optimize the surface properties of silicon-carbon, reduce the side reactions between active materials and electrolytes, and, combined with the flexibility of modified binders, further suppress the shedding of active materials and interface damage during cycling. Ultimately, by alleviating the cyclic expansion of the electrode, they can significantly improve the cycle life of the battery cell.

[0031] In some embodiments, the epoxy compound includes one or more of ethylene oxide, propylene oxide, and epoxy-terminated polyurethane.

[0032] Specifically, epoxy compounds such as ethylene oxide, propylene oxide, and epoxy-terminated polyurethane contain highly active epoxy groups that can chemically bond with the active functional groups on the surface of silicon-carbon materials and polar coatings. At the same time, they enhance the interfacial bonding with each component through polar interactions, significantly improving the adsorption force of modified binders on silicon-carbon materials and the adhesion force inside the electrode. This effectively constrains the volume expansion of silicon-carbon materials during cyclic charging and discharging. Furthermore, these epoxy compounds can optimize the flexibility and structural stability of binders, better adapting to the expansion and contraction deformation of silicon-carbon materials.

[0033] Furthermore, when any one or more of the above-mentioned epoxy compounds are grafted onto the adhesive precursor, the flexibility of the adhesive can be optimized while maintaining the adhesive strength.

[0034] In some embodiments, the binder precursor includes one or more of sodium alginate and lithium alginate.

[0035] Specifically, the binder precursor is selected from materials with strong polarity and high adhesion, such as sodium alginate and lithium alginate. On the one hand, through its excellent adhesion and hydrophilicity, it forms a stable interfacial bond with silicon-carbon materials and polar coatings. On the other hand, the rich active groups contained in its molecular structure can react synergistically with the grafted epoxy compounds. While retaining its original bonding strength, it further improves the flexibility and interfacial compatibility of the modified binder. It can effectively constrain the volume expansion of silicon-carbon during cyclic charging and discharging, inhibit the shedding of active materials during cycling, reduce electrolyte side reactions, and synergistically improve the cycle stability of the electrode and the cycle life of the cell.

[0036] In some embodiments, the molecular weight of the modified binder is 50-150W.

[0037] Specifically, this molecular weight range ensures that the modified binder has sufficient molecular chain length to strengthen the interfacial bonding with silicon-carbon materials and polar coatings, and improve the internal adhesion of the electrode to constrain the cyclic expansion of silicon-carbon. It also avoids problems such as abnormal binder viscosity and hindered particle dispersion caused by excessively high molecular weight, while ensuring that the molecular chain has good flexibility to adapt to the expansion and contraction deformation of silicon-carbon, reducing electrode structure damage and active material shedding during cycling. In addition, this molecular weight range can balance the film-forming properties of the binder and the wettability of the electrolyte, and suppress the occurrence of side reactions.

[0038] In some embodiments, the modified adhesive has an elongation at break of 5% to 30%.

[0039] Specifically, when the elongation at break is in the range of 5% to 30%, the binder has sufficient flexibility to adapt to the volume expansion and contraction deformation of silicon-carbon materials during cyclic charging and discharging, alleviate the stress concentration caused by deformation of the electrode structure, avoid interface cracking and structural damage, and prevent the binder from being too strong due to excessive elongation at break, thereby maintaining the stable bonding of the components inside the electrode and inhibiting the shedding of active materials.

[0040] In some embodiments, the mass percentage of silicon in the negative electrode is 5% to 50%.

[0041] Specifically, when the mass percentage of silicon in the negative electrode is in the range of 5% to 50%, the capacity advantage of silicon materials can be fully utilized to improve the energy density of the battery. At the same time, it can avoid the problems of increased cycle volume expansion and easy damage to the electrode structure caused by excessive silicon content, thus reducing the impact on electrode stability. In addition, this content range can form a highly efficient synergy with polar coatings and modified binders. Under the premise of ensuring the core performance of silicon-carbon negative electrodes, the combination of various components can further suppress expansion and reduce capacity decay, thus balancing battery energy density and cycle life.

[0042] Furthermore, the mass percentage of silicon in the negative electrode can be 5%, 10%, 15%, 20%, 25%, 30%, 45%, or 50%.

[0043] In some embodiments, the modified binder in the negative electrode sheet has a mass percentage content of 1% to 5%.

[0044] Specifically, when the mass percentage of the modified binder in the negative electrode sheet is 1% to 5%, it can ensure that the binder provides sufficient interfacial bonding force, forming a stable synergy with the polar coating and silicon-carbon material, effectively constraining the cyclic expansion of silicon-carbon and inhibiting the shedding of active materials; it can also avoid the loss of cell dynamic performance and uneven particle dispersion caused by excessive binder dosage, ensuring the transmission efficiency of ions and electrons inside the electrode, while balancing the bonding effect and the energy density of the battery.

[0045] In some embodiments, the mass ratio of the negative electrode active material to the modified binder is 10:(0.1~0.5).

[0046] When the mass ratio of the negative electrode active material to the modified binder is in the range of 10:(0.1~0.5), it ensures the proportion of the negative electrode active material (silicon-carbon material coated by the polar coating), fully utilizes the high capacity characteristics of silicon-carbon material, and guarantees the energy density of the battery. At the same time, the modified binder in the above-mentioned ratio range provides sufficient adhesion to stabilize and maintain the internal structure of the electrode, effectively constrains the cyclic expansion of silicon-carbon and inhibits the shedding of active material. This ratio can also avoid problems such as decreased kinetic performance and energy density loss due to an excessively high proportion of modified binder, or insufficient adhesion and easy electrode breakage due to an excessively low proportion. On the basis of balancing battery energy density and cycle stability, the polar coating and the modified binder can fully exert their synergistic effect.

[0047] In some embodiments, the method for preparing the negative electrode sheet includes the following operations: The polar coating was placed in the initial solvent to obtain a mixture; Silicon-carbon material is placed in a mixture and stirred at high temperature. After the solution is completely dried, a silicon-carbon material precursor is obtained. The silicon-carbon material precursor was calcined to obtain the negative electrode active material. The binder precursor was dispersed in a third solvent, a catalyst was added, and etherification was carried out. Then an epoxy compound was added, and the mixture was stirred at high temperature to carry out a grafting reaction. After the reaction was completed, the modified binder was obtained. A negative electrode active material, a modified binder, and a conductive agent are mixed to form a negative electrode slurry, which is then coated and dried to obtain a negative electrode sheet.

[0048] Specifically, in the above operation, the polar coating material and silicon-carbon material are first stirred and calcined at high temperature to form a stable coating structure, ensuring the uniformity and bonding stability of the silicon-carbon material coating; then, through etherification pretreatment and high-temperature grafting reaction, the epoxy compound is efficiently grafted onto the binder precursor, ensuring the structural integrity and performance consistency of the obtained modified binder; finally, the coated silicon-carbon material, modified binder and conductive agent are mixed and coated to achieve uniform dispersion and synergistic effect of each component, and a silicon-carbon anode sheet with stable structure and excellent cycle performance is prepared.

[0049] In some embodiments, in the operation of "placing the polar coating in the initial solvent", the initial solvent is obtained by mixing a first solvent and a second solvent, wherein the mass ratio of the first solvent to the second solvent is 1:0.1 to 1:1.

[0050] Specifically, the initial solvent is prepared by mixing the first solvent and the second solvent in a mass ratio of 1:0.1 to 1:1. This ratio range can balance the synergistic effect of the two solvents, ensuring that the polar coating is fully dissolved and uniformly dispersed, while also optimizing the interfacial bonding between the silicon-carbon material and the polar coating. This provides a guarantee for the formation of a stable and uniform coating structure during subsequent high-temperature stirring and calcination, ensuring that the polar coating effectively plays its core role in constraining the volume expansion of silicon-carbon.

[0051] In some embodiments, both the first solvent and the third solvent are water, and the second solvent is an organic solvent.

[0052] Specifically, water, as the first solvent, ensures the efficient dissolution and uniform dispersion of the polar coating; organic solvent, as the second solvent, can further optimize the interfacial compatibility between silicon-carbon materials and polar coatings, forming a stable and uniform coating structure and ensuring the effect of constraining silicon-carbon expansion; water is selected as the third solvent, which can facilitate the dispersion, etherification, and grafting reactions of the binder precursor, ensuring the preparation efficiency and performance stability of the modified binder.

[0053] In some embodiments, the solid content of the polar coating in the mixture is 0.1% to 30%.

[0054] Specifically, the solid content range of the aforementioned polar coating can ensure sufficient contact and reaction between the polar coating and the silicon-carbon material, guaranteeing the formation of a uniform and dense coating layer and effectively constraining the volume expansion of silicon-carbon cycling; it can also avoid problems such as abnormal viscosity of the mixture and coating agglomeration caused by excessively high solid content, or incomplete coating and insufficient bonding caused by excessively low solid content.

[0055] In some embodiments, the mass ratio of the polar coating to the silicon-carbon material precursor is 0.01:1 to 0.1:1.

[0056] In some embodiments, the pH of the grafting reaction between the adhesive precursor and the epoxy compound is 7 to 9.

[0057] Specifically, the grafting reaction between the binder precursor and the epoxy compound is controlled within a weakly alkaline range of 7 to 9. This range provides a suitable reaction environment for the epoxy groups and the active functional groups of the binder precursor, promoting efficient grafting and ensuring the structural integrity and performance stability of the modified binder. It avoids excessive acidity leading to over-opening of the epoxy groups and runaway reaction, and also prevents excessive alkalinity from causing degradation of the binder precursor or failure of the epoxy compound, ensuring grafting efficiency and product consistency.

[0058] In some embodiments, the calcination temperature is 400-450℃ and the calcination time is 3-3.5h.

[0059] Specifically, this calcination temperature range can promote the chemical bonding reaction between the polar coating and the surface of the silicon-carbon material, forming a stable and dense coating layer, ensuring that the coating structure is not easy to fall off and fully exerting its role in restraining the cyclic expansion of silicon-carbon. At the same time, it can avoid the problems of excessively high temperature causing damage to the structure of silicon-carbon material itself and performance degradation, or excessively low temperature causing insufficient coating reaction and weak bonding force. In addition, the calcination time of 3-3.5 hours can ensure that the reaction is fully carried out, while avoiding excessive time causing energy waste and excessive sintering of materials. Through the coordinated control of temperature and time, the overall improvement of battery structural stability and battery cycle performance can be achieved.

[0060] In another embodiment of the present invention, a battery is provided, including the aforementioned negative electrode sheet, or a negative electrode sheet prepared by the method for preparing the aforementioned negative electrode sheet.

[0061] Specifically, the battery includes the negative electrode sheet provided in this application, which comprises a negative electrode active material layer and a modified binder. The polar coating material coats the silicon-carbon material and can be tightly bonded to the silicon-carbon surface using polar interactions. This suppresses the volume expansion of the silicon-carbon material during cyclic charging and discharging, reducing electrode structure damage. Simultaneously, the modified binder grafted with epoxy compounds enhances the internal bonding stability of the electrode through strong interactions between the epoxy compound, the silicon-carbon material, and the polar coating material, suppressing structural loosening caused by expansion. Furthermore, it optimizes the binder's flexibility, allowing it to adapt to the expansion and contraction of the silicon-carbon material, preventing interface cracking that exacerbates electrolyte side reactions, reducing active material shedding and electrolyte side reactions during cycling, thereby effectively mitigating capacity decay and improving cycle life.

[0062] The present invention will be further illustrated by the following examples.

[0063] Table 1 Example 1 Preparation of negative electrode sheet This embodiment illustrates the negative electrode sheet, negative electrode sheet preparation method, and battery disclosed in this invention, and includes the following operational steps: The first solvent (water) and the second solvent (ethanol) are mixed in a ratio of 1:0.5 to obtain the initial solvent. Maleic anhydride is dissolved in the initial solvent to prepare a 2% maleic anhydride mixture. The silicon-carbon material was placed in the mixture and stirred at 75°C with a speed of 500 r / min until the solution was completely dried to obtain the silicon-carbon material precursor. The silicon-carbon material precursor was placed in a tube furnace and calcined in an argon atmosphere at a temperature of 400°C for 3 hours to obtain the negative electrode active material. Sodium alginate was evenly dispersed in water, NaOH was added, the pH was adjusted to 8.5 to etherify it, and then ethylene oxide was added. Under an argon atmosphere, the temperature was adjusted to 70°C and the reaction was carried out for 2 hours to carry out the grafting reaction. After the reaction was completed, the modified binder was obtained. The negative electrode active material, modified binder, and conductive agent are stirred in a ratio of 95:4:1 for 15 minutes. Then, water is added to adjust the solid content to 45%, and a second dispersion is carried out for 60 minutes to prepare a negative electrode slurry. The slurry is then coated and dried to obtain a negative electrode sheet.

[0064] Preparation of positive electrode sheet Ternary materials 811, PVDF, and CNT were stirred in a ratio of 98:1:1 for 15 minutes. Then, NMP was added to adjust the solid content to 75%, followed by secondary dispersion for 60 minutes. The mixture was then coated, dried, and rolled to obtain the positive electrode sheet.

[0065] The negative electrode, positive electrode, and separator are assembled, and electrolyte is injected to obtain the battery.

[0066] Examples 2-10 Examples 2-10 illustrate the negative electrode sheet, negative electrode sheet preparation method, and battery disclosed in this invention, and include most of the operations in Example 1, except that: The types of polar coatings, the ratio of polar coatings to silicon-carbon materials, the mass percentage of modified binders, the ratio of negative electrode active materials to modified binders, and the solid content of polar coatings in Examples 2-10 are all based on Table 2.

[0067] Comparative Example 1 This comparative example is used to illustrate the negative electrode sheet, negative electrode sheet preparation method, and battery disclosed in this invention, and includes the following sub-operations: The first solvent (water) and the second solvent (ethanol) are mixed in a ratio of 1:0.5 to obtain the initial solvent. Maleic anhydride is dissolved in the initial solvent to prepare a 2% maleic anhydride mixture. The silicon-carbon material was placed in the mixture and stirred at 75°C with a speed of 500 r / min until the solution was completely dried to obtain the silicon-carbon material precursor. The silicon-carbon material precursor was placed in a tube furnace and calcined in an argon atmosphere at a temperature of 400°C for 3 hours to obtain the negative electrode active material. The negative electrode active material, binder (sodium alginate), and conductive agent are stirred in a ratio of 95:4:1 for 15 minutes. Then, water is added to adjust the solid content to 45%, and a second dispersion is carried out for 60 minutes to prepare a negative electrode slurry. The slurry is then coated and dried to obtain a negative electrode sheet.

[0068] Preparation of positive electrode sheet Ternary materials 811, PVDF, and CNT were stirred in a ratio of 98:1:1 for 15 minutes. Then, NMP was added to adjust the solid content to 75%, followed by secondary dispersion for 60 minutes. The mixture was then coated, dried, and rolled to obtain the positive electrode sheet.

[0069] The negative electrode, positive electrode, and separator are assembled, and electrolyte is injected to obtain the battery.

[0070] Comparative Example 2 This comparative example is used to illustrate the negative electrode sheet, negative electrode sheet preparation method, and battery disclosed in this invention, and includes the following sub-operations: Sodium alginate was evenly dispersed in water, NaOH was added, the pH was adjusted to 8.5 to etherify it, and then ethylene oxide was added. Under an argon atmosphere, the temperature was adjusted to 70°C and the reaction was carried out for 2 hours to carry out the grafting reaction. After the reaction was completed, the modified binder was obtained. The negative electrode active material (silicon-carbon material), modified binder, and conductive agent are stirred in a ratio of 95:4:1 for 15 minutes. Then, water is added to adjust the solid content to 45%, and a second dispersion is carried out for 60 minutes to prepare a negative electrode slurry. The slurry is then coated and dried to obtain a negative electrode sheet.

[0071] Preparation of positive electrode sheet Ternary materials 811, PVDF, and CNT were stirred in a ratio of 98:1:1 for 15 minutes. Then, NMP was added to adjust the solid content to 75%, followed by secondary dispersion for 60 minutes. The mixture was then coated, dried, and rolled to obtain the positive electrode sheet.

[0072] The negative electrode, positive electrode, and separator are assembled, and electrolyte is injected to obtain the battery.

[0073] Comparative Example 3 This comparative example is used to illustrate the negative electrode sheet, negative electrode sheet preparation method and battery disclosed in this invention, including most of the operations in Example 1, with the following differences: In the preparation of modified adhesives, ethylenediamine (a non-epoxy compound) is grafted onto the adhesive precursor.

[0074] Comparative Example 4 The negative electrode active material (silicon-carbon material), binder (sodium alginate), and conductive agent are stirred in a ratio of 95:4:1 for 15 minutes. Then, water is added to adjust the solid content to 45%, and a second dispersion is carried out for 60 minutes to prepare a negative electrode slurry. The slurry is then coated and dried to obtain a negative electrode sheet. In Comparative Example 4, the silicon-carbon material was not coated with a polar coating, and the sodium alginate was not modified with grafted epoxy compounds.

[0075] Preparation of positive electrode sheet Ternary materials 811, PVDF, and CNT were stirred in a ratio of 98:1:1 for 15 minutes. Then, NMP was added to adjust the solid content to 75%, followed by secondary dispersion for 60 minutes. The mixture was then coated, dried, and rolled to obtain the positive electrode sheet.

[0076] The negative electrode, positive electrode, and separator are assembled, and electrolyte is injected to obtain the battery.

[0077] Performance testing The following performance tests were performed on Examples 1-10 and Comparative Examples 1-4 prepared above: Cyclic performance test The test temperature was 25℃. The battery was charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 0.005C. After standing for 5 minutes, it was discharged at 1C to 3.0V. The capacity obtained by this process was taken as the initial discharge capacity C1. The thickness H1 of the fully charged battery was measured using a micrometer.

[0078] Cyclic testing was conducted using 1C charge / 1C discharge. After 600 cycles, the discharge capacity C2 was obtained, and the cycle capacity retention rate was calculated. The thickness H2 of the fully charged battery after the cycle was measured using a micrometer.

[0079] Cyclic thickness expansion rate = (H2-H1) / H1*100%.

[0080] Cyclic capacity retention rate = C2 / C1 * 100%.

[0081] The test results are entered into Table 2.

[0082] Table 2 As can be seen from the test results in Table 2, the batteries of Examples 1-10 prepared using the modified binder with polar coating on silicon-carbon material and grafted epoxy compound as described in this application have a high capacity retention rate of 85%-94% after 600 cycles at 25°C, and a thickness expansion rate of only 4%-12%. In contrast, the capacity retention rate of Comparative Examples 1-4, which lack modified binder, have no polar coating, have binder grafted with non-epoxy compound, or use conventional commercially available negative electrode sheets, is only 60%-70%, while the thickness expansion rate is as high as 18%-28%. This fully verifies that the negative electrode sheet provided in this application plays a key role in suppressing the volume expansion of silicon-carbon material and alleviating battery capacity decay.

[0083] Specifically, Example 1 exhibits the best overall performance. It uses maleic anhydride as the polar coating material, with a mass ratio of polar coating material to silicon-carbon material of 0.05:1. Combined with a modified binder of 50W molecular weight and 1% by mass, it achieves a capacity retention rate of 94% and a thickness expansion rate of 4%. The test data from Example 1 show that when appropriate amounts of polar coating material, molecular weight, and modified binder are combined, a better synergistic effect can be achieved. The polar coating material's pre-constraint suppresses the initial expansion of silicon-carbon material, while the strong interaction and flexibility of the modified binder enhance the stability of the electrode structure, reducing active material shedding and electrolyte side reactions. In Examples 2-3, the mass ratio of polar coating material to silicon-carbon material was adjusted to 0.1:1 and 0.15:1, respectively. Correspondingly, compared with Example 1, the capacity retention rate of Examples 2-3 decreased to 90% and 88%, and the thickness expansion rate increased to 8% and 10%, respectively. It is speculated that the reason may be that too much polar coating material may slightly weaken the electrical performance. Examples 4-5 used glutaric anhydride and acrylic acid as polar coatings, respectively, and their performance was similar to that of Example 2, indicating that the polar coatings within the scope of this application can all play their corresponding roles. In Examples 6-8, the molecular weight of the modified binder was increased to 100W, 130W, and 150W, respectively, and the capacity retention rate gradually decreased to 88%, 87%, and 86%, while the thickness expansion rate increased to 10%, 11%, and 12%. This indicates that the excessively high molecular weight affected the migration and transport of lithium ions inside the electrode, but the overall performance was better than that of the comparative example. In Examples 9-10, the mass percentage of the modified binder was increased to 4% and 5%, respectively, the capacity retention rate decreased to 88% and 85%, and the thickness expansion rate increased to 10% and 10.5%. Compared with other examples, this also shows that excessive binder has a certain impact on the kinetic performance of the battery. However, the overall performance of Examples 9-10 is better than that of the comparative examples.

[0084] Analysis of the specific test data above shows that the negative electrode provided by this invention, by utilizing polar interactions to tightly adhere to the silicon-carbon surface, suppresses the volume expansion of the silicon-carbon material during cyclic charging and discharging. Simultaneously, a modified binder grafted with epoxy compounds, through the strong interaction between the epoxy compounds and the silicon-carbon material and polar coatings, suppresses structural loosening caused by expansion, and optimizes the binder's flexibility to adapt to the expansion and contraction of silicon-carbon, reducing the shedding of active materials and side reactions of the electrolyte during cycling, thereby effectively alleviating capacity decay and improving cycle life. Furthermore, further optimization of various parameters contributes to further improving overall performance.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material and a modified binder, the negative electrode active material includes silicon carbon material and a polar coating, the polar coating coating the silicon carbon material; The modified adhesive includes an adhesive precursor grafted with an epoxy compound.

2. The negative electrode sheet according to claim 1, characterized in that, The polar coating includes one or more compounds containing anhydride groups and carboxylic acid compounds containing double bonds.

3. A negative electrode sheet according to claim 2, characterized in that, The compounds containing anhydride groups include one or more of maleic anhydride, glutaric anhydride, chloroacetic anhydride, and allyl succinic anhydride; and / or, The carboxylic acid compounds containing double bonds include one or more of acrylic acid, methacrylic acid, maleic acid, and fumaric acid.

4. The negative electrode sheet according to claim 1, characterized in that, The binder precursor includes one or more of sodium alginate and lithium alginate; and / or, The epoxy compound includes one or more of ethylene oxide, propylene oxide, and epoxy-terminated polyurethane.

5. A negative electrode sheet according to claim 1, characterized in that, The modified binder has a molecular weight of 50-150W; and / or, The modified adhesive has an elongation at break of 5% to 30%.

6. A negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet contains 5% to 50% silicon by mass; and / or, The modified binder in the negative electrode sheet has a mass percentage content of 1% to 5%.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, The mass ratio of the negative electrode active material to the modified binder is 10:(0.1~0.5).

8. The method for preparing the negative electrode sheet according to any one of claims 1-6, characterized in that, Includes the following operations: The polar coating was placed in the initial solvent to obtain a mixture; Silicon-carbon material is placed in a mixture and stirred at high temperature. After the solution is completely dried, a silicon-carbon material precursor is obtained. The silicon-carbon material precursor was calcined to obtain the negative electrode active material. The binder precursor was dispersed in a third solvent, a catalyst was added, and etherification was carried out. Then an epoxy compound was added, and the mixture was stirred at high temperature to carry out a grafting reaction. After the reaction was completed, the modified binder was obtained. A negative electrode active material, a modified binder, and a conductive agent are mixed to form a negative electrode slurry, which is then coated and dried to obtain a negative electrode sheet.

9. The method for preparing the negative electrode sheet according to claim 8, characterized in that, In the operation of "placing the polar coating in the initial solvent", the initial solvent is obtained by mixing a first solvent and a second solvent.

10. The method for preparing the negative electrode sheet according to claim 9, characterized in that, The mass ratio of the first solvent to the second solvent is 1:0.1 to 1:1; Both the first solvent and the third solvent are water, and the second solvent is an organic solvent.

11. The method for preparing the negative electrode sheet according to claim 8, characterized in that, In the mixture, the solid content of the polar coating is 0.1% to 30%.

12. The method for preparing the negative electrode sheet according to claim 8, characterized in that, In the silicon-carbon material precursor, the mass ratio of the polar coating to the silicon-carbon material is 0.01:1 to 0.1:

1.

13. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The pH of the grafting reaction between the adhesive precursor and the epoxy compound is 7-9.

14. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The calcination temperature is 400-450℃, and the calcination time is 3-3.5h.

15. A battery, characterized in that, This includes the negative electrode sheet as described in any one of claims 1 to 7, or the negative electrode sheet prepared by the method described in any one of claims 8 to 14.

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