Silicon-carbon negative electrode sheet, preparation method thereof and soft package lithium battery

Abstract

This disclosure provides a silicon-carbon anode sheet, its preparation method, and a soft-pack lithium battery. The preparation method of the silicon-carbon anode sheet involves: dissolving water-soluble conductive polyaniline in an organic solvent, mixing it with CMC adhesive, and then mixing it with silicon-carbon slurry and a multifunctional organophosphonic acid crosslinking agent (mixing temperature: 15℃-25℃) to obtain an anode slurry; coating the anode slurry onto a negative current collector to obtain a silicon-carbon anode sheet semi-finished product; and sequentially subjecting the silicon-carbon anode sheet semi-finished product to pre-baking (90℃-120℃) and vacuum drying (70℃-90℃, time: 2h-5h) to obtain the silicon-carbon anode sheet. This method, by adding multifunctional organophosphonic acid crosslinking agents and water-soluble conductive polyaniline, facilitates the formation of a three-dimensional conductive suppression network with high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing ability. This enhances the constraint on the negative electrode slurry, reduces the volume expansion rate to <15%, inhibits silicon-carbon cracking, and improves the self-healing ability of the three-dimensional conductive suppression network, thus broadening the application of high-capacity silicon-carbon negative electrode sheets in soft-pack lithium batteries.

Description

Technical Field

[0001] This disclosure relates to the field of silicon-carbon anode technology, and in particular to a silicon-carbon anode and its preparation method, and a soft-pack lithium battery. Background Technology

[0002] Silicon-carbon anodes are widely considered one of the most promising anode materials for next-generation high-energy-density lithium-ion batteries due to their ultra-high theoretical capacity, low electrochemical reaction potential, and abundant natural resources. However, silicon particles undergo significant volume changes during repeated lithium insertion / extraction, leading to cracking or even pulverization of the active silicon particles. This results in continuous electrolyte consumption and repeated growth of the SEI film, causing the electrode to exhibit poor cycle life.

[0003] Currently, there are many methods to improve the silicon volume expansion of silicon-carbon anodes, such as nano-sizing, alloying, and porous treatment of silicon materials, all of which can effectively solve the above problems. Although the above methods can suppress the silicon volume expansion problem to a certain extent, the effect of suppressing silicon expansion is not ideal. As a result, even in high-capacity (700mAh / g) silicon-carbon anodes, there is still a 40% expansion rate, which severely restricts the application of high-capacity silicon-carbon anodes in pouch lithium batteries. This is mainly because pouch lithium batteries are limited by the extensibility of the aluminum-plastic film shell, which usually only allows a silicon-carbon volume expansion rate of ≤15%, while an excessively high expansion rate of 40% cannot be well applied in pouch lithium batteries. Summary of the Invention

[0004] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a silicon-carbon anode sheet and its preparation method, as well as a soft-pack lithium battery, by incorporating a multifunctional organophosphonic acid crosslinking agent and water-soluble conductive polyaniline to facilitate the formation of a three-dimensional conductive suppression network with high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing. This enhances the constraint force on the negative electrode slurry, reduces the volume expansion rate to <15%, inhibits silicon-carbon cracking, and improves the self-healing ability of the three-dimensional conductive suppression network, thereby broadening the application of high-capacity silicon-carbon anode sheets in soft-pack lithium batteries.

[0005] The purpose of this disclosure is achieved through the following technical solution: A method for preparing a silicon-carbon anode sheet includes the following steps: A water-soluble conductive polyaniline is dissolved in an organic solvent to form an ultra-long conductive network, resulting in a water-soluble conductive polyaniline adhesive solution; wherein the water-soluble conductive polyaniline is doped with sulfonic acid groups R-sulfonic acid groups; The water-soluble conductive polyaniline adhesive solution is mixed with the CMC adhesive solution to obtain a mixed adhesive solution; The mixed adhesive, silicon carbon slurry, and multifunctional organophosphonic acid crosslinking agent are mixed to obtain a negative electrode slurry; wherein the mixing temperature is controlled at 15℃-25℃; the silicon carbon slurry includes a carboxyl polymer binder. The negative electrode slurry is coated onto the negative current collector to obtain a silicon-carbon negative electrode semi-finished product. The silicon-carbon negative electrode semi-finished product is pre-baked at 90℃-120℃ to remove moisture; The pre-baked silicon-carbon anode semi-finished product is subjected to vacuum drying to obtain silicon-carbon anode sheet; wherein the vacuum drying operation is performed at a temperature of 70℃-90℃ for 2h-5h.

[0006] In one embodiment, the step of mixing the mixed adhesive, silicon carbide slurry, and multifunctional organophosphonic acid crosslinking agent includes the following specific steps: The mixed adhesive and the silicon carbide slurry are mixed and stirred to obtain a premix; A multifunctional organophosphonic acid crosslinking agent is added to the premix and the mixture is stirred at low temperature to obtain the negative electrode slurry.

[0007] In one embodiment, when mixing the mixed adhesive and the silicon carbide slurry, the revolution speed is 10 r / min-30 r / min; the rotation speed is 10 r / min-35 r / min; and the time is 120 min-180 min.

[0008] In one embodiment, when adding a multifunctional organophosphonic acid crosslinking agent to the premix and mixing and stirring at low temperature, the revolution speed is 10 r / min-15 r / min; the time is 20 min-30 min.

[0009] In one embodiment, the water-soluble conductive polyaniline adhesive and the CMC adhesive are mixed at a mass ratio of (3-5):(5-8).

[0010] In one embodiment, the solid content of the water-soluble conductive polyaniline adhesive is 3%-5%; and / or, The solid content of the CMC adhesive is 1%-3%.

[0011] In one embodiment, the multifunctional organophosphonic acid crosslinking agent includes at least one of inositol hexaphosphate, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid; and / or, The organic solvent includes N-methylpyrrolidone.

[0012] In one embodiment, the amount of the multifunctional organophosphonic acid crosslinking agent added is 1 to 5 parts by weight; and / or, The carboxylated polymer adhesive includes at least one of polyacrylic acid and carboxylated styrene-butadiene rubber.

[0013] A silicon-carbon anode sheet is prepared using the silicon-carbon anode sheet preparation method described in any of the above embodiments.

[0014] A pouch lithium battery includes the silicon-carbon anode sheet described in any of the above embodiments.

[0015] Compared with the prior art, this disclosure has at least the following advantages: 1) First, water-soluble conductive polyaniline is dissolved in an organic solvent to form an ultra-long conductive network, resulting in a water-soluble conductive polyaniline solution. Then, the water-soluble conductive polyaniline solution is mixed with a CMC solution. The addition of CMC solution helps improve the dispersibility of the water-soluble conductive polyaniline solution. Furthermore, the linear structure of the CMC solution provides reaction sites for the subsequent crosslinking reaction of the ultra-long conductive network. Next, the mixed solution, silicon carbide slurry, and multifunctional organophosphonic acid crosslinking agent are mixed to ensure uniform crosslinking of the silicon carbide slurry and the multifunctional organophosphonic acid crosslinking agent. The dispersion in the mixed adhesive effectively avoids the agglomeration of silicon-carbon slurry or multifunctional organophosphonic acid crosslinking agents. Simultaneously, by controlling the mixing temperature of the multifunctional organophosphonic acid crosslinking agents to 15℃-25℃, premature crosslinking of the negative electrode slurry is prevented, which could affect subsequent coating operations. This ensures good fluidity of the negative electrode slurry, thereby guaranteeing the normal operation of subsequent coating processes. Subsequently, the coated silicon-carbon negative electrode semi-finished product is pre-baked at 90℃-120℃ to remove moisture, effectively preventing crosslinking during the subsequent crosslinking process. Excessive moisture can cause blistering or cracking in the active layer of the final silicon-carbon anode sheet. Finally, the pre-baked silicon-carbon anode sheet semi-finished product is subjected to vacuum drying (70℃-90℃, 2h-5h). Because the multifunctional organophosphonic acid crosslinking agent contains abundant hydroxyl functional groups, it can react with the CMC adhesive to form ester and hydrogen bonds during vacuum drying, and also react with the carboxyl polymer binder, allowing the CMC to connect with the carboxyl polymer binder to form a three-dimensional conductive suppression network. Furthermore, multifunctional organophosphonic acid crosslinking agents can form hydrogen bonds with the hydroxyl groups on the surface of silicon particles in silicon-carbon slurry, effectively encapsulating the silicon-carbon particles in the slurry and enhancing the constraint on the negative electrode slurry. This not only effectively inhibits the expansion of silicon-carbon but also effectively inhibits silicon-carbon cracking, which is conducive to forming a three-dimensional conductive inhibition network with high conductivity, uniform and continuous conductivity, strong toughness, and strong self-healing properties. This results in a silicon-carbon volume expansion rate of <15%, which broadens the application of high-capacity silicon-carbon negative electrode sheets in pouch lithium batteries, thereby improving the cycle life of high-capacity silicon-carbon negative electrode sheets in pouch lithium batteries.

[0016] 2) Because the added water-soluble conductive polyaniline introduces R-sulfonic acid groups, on the one hand, the doped R-sulfonic acid groups can improve the solubility of the water-soluble conductive polyaniline, ensuring that it can be uniformly dispersed in the organic solvent. This allows the conjugated structure of the water-soluble conductive polyaniline to spontaneously assemble into a continuous ultra-long conductive network, providing an efficient electron conduction path and ensuring the preparation of a uniform and continuous ultra-long conductive network. On the other hand, the doped R-sulfonic acid groups can increase the cross-linking reaction sites of the water-soluble conductive polyaniline, enabling it to form hydrogen bonds with CMC. Ionic or ester bonds significantly enhance the crosslinking density and structural toughness of the three-dimensional conductive suppression network, enabling the strongly crosslinked three-dimensional conductive suppression network to more effectively encapsulate silicon-carbon particles, strengthen the constraint on the volume expansion of silicon-carbon, further reduce the expansion rate of silicon-carbon, and thus improve the toughness of the three-dimensional conductive suppression network, thereby providing better structural support for the three-dimensional conductive suppression network. On the other hand, the doped R-sulfonic acid groups can enhance the interaction between water-soluble conductive polyaniline and the hydroxyl groups on the surface of silicon-carbon particles, improve the uniformity of coating on silicon-carbon particles, thereby reducing silicon-carbon agglomeration and indirectly suppressing cracking caused by local excessive expansion. In addition, the R-sulfonic acid groups of water-soluble conductive polyaniline will form dynamic reversible hydrogen bonds with the carboxyl groups of carboxyl polymer adhesives, ensuring that water-soluble conductive polyaniline can quickly complete bridging repair between cracks when silicon-carbon expands and cracks, thereby achieving rapid hydrogen bond reconstruction. Furthermore, the introduced R-sulfonic acid groups can better guide the polyaniline molecular chains to migrate directionally to the crack, thereby improving the self-healing efficiency of the conductive pathway of the three-dimensional conductive suppression network. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a photograph of the silicon-carbon negative electrode sheet disassembled after 400 cycles in Embodiment 5 of the present invention. Detailed Implementation

[0019] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0020] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] To better understand the technical solution and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments. One embodiment of the method for preparing a silicon-carbon anode sheet includes some or all of the following steps: S101. Dissolve water-soluble conductive polyaniline in an organic solvent to form an ultra-long conductive network, thereby obtaining a water-soluble conductive polyaniline adhesive solution.

[0023] It should be noted that some literature currently uses polyaniline in lithium-ion batteries, such as patent CN115832293A. However, the polyaniline added in this patent is mainly used as an N-type conductive organic material. Through its electronic structure characteristics, it accelerates the migration of lithium ions and reduces interfacial impedance. That is, the polyaniline in this patent mainly plays a conductive role and cannot play a role in inhibiting silicon-carbon expansion.

[0024] Therefore, in this disclosure, by introducing R-sulfonic acid groups into water-soluble conductive polyaniline, on the one hand, the doped R-sulfonic acid groups can improve the solubility of the water-soluble conductive polyaniline, ensuring that the water-soluble conductive polyaniline can be uniformly dispersed in the organic solvent. This allows the conjugated structure of the water-soluble conductive polyaniline to spontaneously assemble into a continuous ultra-long conductive network, which provides an efficient electronic conduction path, thereby ensuring the preparation of a uniform and continuous ultra-long conductive network. On the other hand, the doped R-sulfonic acid groups can increase the cross-linking reaction sites of the water-soluble conductive polyaniline, enabling the water-soluble conductive polyaniline to form hydrogen with CMC. The presence of crosslinks, ionic bonds, or ester bonds significantly enhances the crosslinking density and structural toughness of the three-dimensional conductive suppression network. This allows the strongly crosslinked three-dimensional conductive suppression network to more effectively encapsulate silicon-carbon particles, strengthens the constraint on the volume expansion of silicon-carbon, further reduces the expansion rate of silicon-carbon, and thus improves the toughness of the three-dimensional conductive suppression network, thereby providing better structural support for the three-dimensional conductive suppression network. On the other hand, the doped R-sulfonic acid groups can enhance the interaction between water-soluble conductive polyaniline and the hydroxyl groups on the surface of silicon-carbon particles, improve the uniformity of coating on silicon-carbon particles, thereby reducing silicon-carbon agglomeration and indirectly suppressing cracking caused by local excessive expansion. Furthermore, the R-sulfonic acid groups of water-soluble conductive polyaniline form dynamic and reversible hydrogen bonds with the carboxyl groups of the carboxyl polymer adhesive. This ensures that the water-soluble conductive polyaniline can quickly bridge and repair the cracks when silicon carbon expands and cracks, thereby achieving rapid hydrogen bond reconstruction. The introduced R-sulfonic acid groups can also effectively guide the polyaniline molecular chains to migrate directionally to the cracks, thereby improving the self-healing efficiency of the conductive pathways in the three-dimensional conductive inhibition network. In particular, when used in conjunction with CMC adhesive and multifunctional organophosphonic acid crosslinking agents, the water-soluble conductive polyaniline, carboxyl polymer adhesive, CMC adhesive, and multifunctional organophosphonic acid crosslinking agents undergo a crosslinking reaction during vacuum drying to form a highly conductive, uniformly conductive, continuous, tough, and self-healing three-dimensional conductive inhibition network.

[0025] Therefore, the water-soluble conductive polyaniline disclosed in this invention not only serves a conductive function but also participates in the construction and repair of the three-dimensional conductive suppression network. This ensures that even if the three-dimensional conductive suppression network cracks due to silicon-carbon expansion, it can still quickly complete bridging repair between the cracks, avoiding the deactivation of the conductivity of the three-dimensional conductive suppression network. This achieves the dual effect of the three-dimensional conductive suppression network constraining silicon-carbon expansion and repairing cracks after cracking. Please refer to the following: Figure 1 ,from Figure 1 It can be seen that the high-capacity silicon-carbon anode sheet disclosed herein can still maintain a good structural morphology after 400 cycles, without any obvious expansion, bulging, leakage, or bag breakage. It also improves the uniformity of silicon-carbon particle coating, thereby reducing silicon-carbon agglomeration and thus improving the cycle life of the high-capacity silicon-carbon anode sheet in soft-pack lithium batteries.

[0026] It is worth mentioning that the conjugated structure of water-soluble conductive polyaniline refers to the continuous delocalized π-electron system formed by the π electrons on the benzene ring of water-soluble conductive polyaniline and the lone pair electrons of the adjacent nitrogen atom. Because the molecular chain of water-soluble conductive polyaniline is relatively long and it is a high molecular conductive agent, the water-soluble conductive polyaniline retains a local conjugated structure after cracking. This ensures that the water-soluble conductive polyaniline can still achieve hydrogen bond recombination through the π electron cloud after cracking. In this way, it can still complete bridging repair between cracks even if cracking occurs, ensuring that the conductivity of the three-dimensional conductive suppression network will not be deactivated after cracking.

[0027] It is understandable that if the R in the R-sulfonic acid group is an aliphatic carbon segment group, since aliphatic carbon segment groups, such as polyethylene sulfonic acid and polypropylene sulfonic acid, lack aromatic ring structures, they only bind to conductive polyaniline through electrostatic interactions. This weak interaction makes phase separation easy, leading to low conductivity and poor bonding stability in water-soluble conductive polyaniline. In one embodiment, the R in the R-sulfonic acid group is an aromatic polymer segment group. Because aromatic polymer segment groups have hydrophobic aromatic ring structures, they can bind to the benzene ring-amine group conjugated structure of conductive polyaniline through π−π stacking interactions, ensuring low resistance to charge transport between conjugated chains after doping, thereby improving the conductivity and stability of water-soluble conductive polyaniline.

[0028] It should be noted that although the introduction of aromatic polymer chain segments can improve the conductivity, uniformity, and self-healing strength of the three-dimensional conductive suppression network to some extent, aromatic polymer chain segments with excessively large or small molecular chains will affect the conductivity and toughness of the water-soluble conductive polyaniline. Therefore, in one embodiment, the molecular weight of the aromatic polymer chain segments is 50,000-100,000 to ensure that the molecular weight of the doped R-sulfonic acid groups is suitable. This effectively satisfies the requirements of good dispersibility, assemblability, stable cross-linking network, high conductivity, and good flowability of the water-soluble conductive polyaniline. It effectively avoids the problems of insufficient cross-linking network stability, decreased conductivity, and weakened interfacial compatibility of water-soluble conductive polyaniline caused by too small a molecular weight of R-sulfonic acid groups. It also avoids the problems of decreased dispersibility and assemblability, hindered cross-linking reaction, and poor flowability of negative electrode slurry caused by too large a molecular weight of R-sulfonic acid groups. This is beneficial for preparing a three-dimensional conductive suppression network with high capacity, high conductivity, uniform and continuous conductivity, strong toughness, and strong self-healing.

[0029] In one embodiment, the aromatic polymer segment group is polystyrene.

[0030] In one embodiment, polyaniline is mixed with an aromatic polymer so that R-sulfonic acid groups can be doped onto the polyaniline to obtain water-soluble conductive polyaniline.

[0031] In one embodiment, the organic solvent includes N-methylpyrrolidone.

[0032] In one embodiment, the solid content of the water-soluble conductive polyaniline adhesive is 3%-5% to ensure a suitable distribution of the water-soluble conductive polyaniline. This ensures that sufficient water-soluble conductive polyaniline molecular chains are provided to form a continuous, ultra-long conductive network, while also providing ample cross-linking reaction sites. This facilitates cross-linking with subsequent CMC adhesives, carboxyl polymer adhesives, and multifunctional organophosphonic acid cross-linking agents to form a highly conductive, uniformly conductive, continuous, tough, and self-healing three-dimensional conductive inhibition network, effectively constraining silicon-carbon expansion.

[0033] S102. Mix the water-soluble conductive polyaniline adhesive with the CMC adhesive to obtain a mixed adhesive.

[0034] It should be noted that the current traditional method for preparing negative electrode slurry usually involves mixing the components of the negative electrode slurry in one step. However, this method suffers from the problem of silicon carbon agglomeration due to its high specific surface area, making it impossible to prepare a uniformly dispersed negative electrode slurry and a three-dimensional conductive suppression network with high conductivity, uniform conductivity, and strong toughness.

[0035] Therefore, in this disclosure, water-soluble conductive polyaniline adhesive and CMC adhesive are first prepared separately, and then the water-soluble conductive polyaniline adhesive and CMC adhesive are mixed to enhance the dispersibility of the R-sulfonic acid groups in the water-soluble conductive polyaniline adhesive and the CMC adhesive, so that the water-soluble conductive polyaniline adhesive can be uniformly dispersed in the CMC adhesive, resulting in a uniform and stable mixed adhesive. Furthermore, the linear structure of the CMC adhesive can provide uniform reaction sites for the subsequent crosslinking reaction of the ultra-long conductive network. When the mixed adhesive is mixed with silicon carbon slurry and multifunctional organophosphonic acid crosslinking agent, the stable and uniform mixed adhesive can provide a uniform dispersion basis for the mixing of silicon carbon slurry and multifunctional organophosphonic acid crosslinking agent, avoiding the problem of agglomeration of silicon carbon particles or multifunctional organophosphonic acid crosslinking agent. This is beneficial for preparing a three-dimensional conductive suppression network with high conductivity, uniform conductivity, and strong toughness.

[0036] In one embodiment, the solid content of the CMC adhesive is 1%-3% to ensure a suitable distribution of CMC. This ensures that the CMC adhesive has good dispersibility and that the CMC adhesive and the water-soluble conductive polyaniline adhesive are mixed to form a stable basic network, thereby achieving a more uniform encapsulation of silicon carbon particles and conductive agents.

[0037] In one embodiment, CMC is dissolved in water to prepare a CMC adhesive with a solid content of 1%-3%. Further, the water is deionized water.

[0038] In one embodiment, the water-soluble polyaniline adhesive and the CMC adhesive are mixed at a mass ratio of (3-5):(5-8) to ensure uniform dispersion of the slurry.

[0039] In one embodiment, the water-soluble conductive polyaniline adhesive and the CMC adhesive are in a mass ratio of 3:7.

[0040] S103. The mixed adhesive, silicon carbon slurry, and multifunctional organophosphonic acid crosslinking agent are mixed to ensure that the silicon carbon slurry and multifunctional organophosphonic acid crosslinking agent are uniformly dispersed in the mixed adhesive, effectively avoiding the problem of agglomeration of the silicon carbon slurry or multifunctional organophosphonic acid crosslinking agent, thereby obtaining a negative electrode slurry; wherein, the mixing temperature is controlled at 15℃-25℃; the silicon carbon slurry includes a carboxyl polymer binder.

[0041] It should be noted that when the mixed adhesive, silicon carbide slurry, and multifunctional organophosphonic acid crosslinking agent are mixed at room temperature, a small amount of crosslinking may occur. Premature crosslinking cannot ensure that the mixed adhesive, silicon carbide slurry, and multifunctional organophosphonic acid crosslinking agent are mixed thoroughly and uniformly, and it will affect the subsequent coating operation. As a result, it is impossible to prepare a three-dimensional conductive suppression network with high conductivity, uniform conductivity, and strong toughness.

[0042] Therefore, in this disclosure, by controlling the temperature of the mixed adhesive, silicon carbide slurry and multifunctional organophosphonic acid crosslinking agent to be 15℃-25℃, the crosslinking of the negative electrode slurry is prevented from occurring prematurely. On the one hand, this ensures that the mixed adhesive, silicon carbide slurry and multifunctional organophosphonic acid crosslinking agent are mixed more thoroughly and uniformly, and on the other hand, it ensures that the negative electrode slurry has good fluidity so that the coating operation can be completed subsequently.

[0043] It is understandable that if the multifunctional organophosphonic acid crosslinking agent is added before the silicon carbide slurry, it is impossible to achieve a relatively uniform coating of the silicon carbide particles and conductive agent in the silicon carbide slurry. Therefore, in one embodiment, the step of mixing the mixed adhesive, silicon carbide slurry, and multifunctional organophosphonic acid crosslinking agent includes the following specific steps: First, the mixed adhesive and the silicon carbide slurry are mixed and stirred to obtain a premix, so as to achieve a comprehensive and uniform coating of the silicon carbide particles and conductive agent in the silicon carbide slurry; then, the multifunctional organophosphonic acid crosslinking agent is added to the premix and mixed and stirred at low temperature to ensure that the added multifunctional organophosphonic acid crosslinking agent will not crosslink prematurely at a low temperature, thereby ensuring that the mixed adhesive, silicon carbide slurry, and multifunctional organophosphonic acid crosslinking agent are mixed more comprehensively and uniformly, while also ensuring that the negative electrode slurry has good fluidity, so as to complete the subsequent coating operation, which is beneficial to preparing a silicon carbide negative electrode sheet with uniform thickness.

[0044] In one embodiment, when adding a multifunctional organophosphonic acid crosslinking agent to the premix for low-temperature mixing and stirring, the following specific steps are included: after adding the multifunctional organophosphonic acid crosslinking agent, the cooling system of the stirring vessel is immediately started so that the condensate water introduced keeps the temperature inside the stirring vessel between 15°C and 25°C, and then the stirring operation is started to complete the low-temperature mixing and stirring.

[0045] In one embodiment, the silicon-carbon slurry comprises silicon-carbon, a conductive agent, and a carboxyl polymer binder. Specifically, silicon-carbon, a mixed adhesive, a conductive agent, and a carboxyl polymer binder are sequentially added to a stirred tank and mixed to obtain a premix. Then, a multifunctional organophosphonic acid crosslinking agent is added, and the cooling system of the stirred tank is activated to ensure that the temperature inside the stirred tank is maintained between 15°C and 25°C by the introduced condensate. Finally, the stirring operation is started again to prepare the negative electrode slurry.

[0046] In one embodiment, the conductive agent is a mixture of conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs).

[0047] In one embodiment, during the mixing and stirring of the mixed adhesive and the silicon carbide slurry, the revolution speed is 10 r / min-30 r / min; the rotation speed is 10 r / min-35 r / min; and the time is 30 min-45 min. Through the overall mixing of the revolution and the local shearing effect of the rotation, the carboxyl polymer binder of the water-soluble conductive polyaniline, CMC adhesive, and silicon carbide slurry in the mixed adhesive can uniformly encapsulate the silicon carbide particles and conductive agent, avoiding the agglomeration problem of water-soluble conductive polyaniline, CMC, and silicon carbide slurry.

[0048] In one embodiment, when adding a multifunctional organophosphonic acid crosslinking agent to the premix and performing low-temperature mixing and stirring, the revolution speed is 10 r / min-15 r / min; the time is 20 min-30 min. By using only the low revolution speed, the multifunctional organophosphonic acid crosslinking agent is slowly and uniformly diffused, allowing it to fully react with CMC and carboxyl polymer binders. Furthermore, the low-speed stirring used in low-temperature mixing and stirring avoids disrupting the already formed mixture system, which is beneficial for forming a highly conductive, uniformly conductive, continuous, tough, and self-healing three-dimensional conductive inhibition network, effectively constraining the volume expansion of silicon carbon.

[0049] In one embodiment, the multifunctional organophosphonic acid crosslinking agent includes at least one of inositol hexaphosphate, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid, to ensure that the multifunctional organophosphonic acid crosslinking agent contains abundant hydroxyl functional groups, thereby ensuring that the added multifunctional organophosphonic acid crosslinking agent can crosslink with CMC adhesive, carboxyl polymer adhesive, and multifunctional organophosphonic acid crosslinking agent to form a three-dimensional conductive inhibition network with high conductivity, uniform and continuous conductivity, strong toughness, and strong self-healing properties.

[0050] In one embodiment, the multifunctional organophosphonic acid crosslinking agent is inositol hexaphosphate. Since inositol hexaphosphate contains six phosphate groups, far more than the two phosphonic acid groups of hydroxyethylidene diphosphonic acid and the three phosphonic acid groups of aminotrimethylene phosphonic acid, it helps to form more network-like reactive sites. This allows for better crosslinking with CMC adhesive, carboxyl polymer adhesive, and water-soluble conductive polyaniline, forming richer ester and hydrogen bonds. This significantly increases the crosslinking density of the three-dimensional conductive suppression network, enabling the high-density network to more effectively encapsulate silicon-carbon particles and conductive agents, enhancing the constraint on volume expansion and ensuring that the expansion rate of the pouch battery can be stably controlled within <15% during multiple charge-discharge cycles.

[0051] In one embodiment, inositol hexaphosphate is a 60%-75% inositol hexaphosphate solution.

[0052] In one embodiment, inositol hexaphosphate is dissolved in water to prepare an inositol hexaphosphate solution with a concentration of 60%-75%.

[0053] It should be noted that in order to achieve comprehensive and effective encapsulation of silicon carbon particles and conductive agents, multifunctional organophosphonic acid crosslinking agents with high crosslinking density, such as inositol hexaphosphate, are usually selected. However, excessively high crosslinking density will reduce the toughness of the three-dimensional conductive suppression network, resulting in the three-dimensional conductive suppression network being unable to effectively suppress the expansion of high-capacity silicon carbon anode sheets.

[0054] Therefore, in this disclosure, CMC adhesive, carboxyl polymer binder, and water-soluble conductive polyaniline adhesive are compounded and used to fully utilize the inherent flexible structures of the CMC adhesive, carboxyl polymer binder, and water-soluble conductive polyaniline adhesive to suppress the expansion problem of high-capacity silicon-carbon anode sheets. In other words, the linear molecular chains of the CMC adhesive provide a natural flexible buffer, and the polymer of the carboxyl polymer binder provides a flexible buffer, effectively reducing the crosslinking density while providing elastic buffering. Simultaneously, the use of the linear conjugated chains of the water-soluble conductive polyaniline adhesive for "bridging repair" ensures that the formed three-dimensional conductive suppression network effectively suppresses the expansion of high-capacity silicon-carbon anode sheets.

[0055] It should be noted that although the flexible structure of CMC adhesive, carboxyl polymer adhesive and water-soluble conductive polyaniline adhesive can suppress the expansion of high-capacity silicon-carbon anode sheets to a certain extent, the improvement effect is not ideal.

[0056] Therefore, in this disclosure, by further controlling the solid content of the CMC adhesive to 1%-3%, the solid content of the water-soluble conductive polyaniline adhesive to 3%-5%, and mixing the water-soluble conductive polyaniline adhesive with the CMC adhesive at a mass ratio of (3-5):(5-8), the crosslinking density of CMC, water-soluble conductive polyaniline, and multifunctional organophosphonic acid crosslinking agent is effectively controlled by effectively coordinating the ratio of CMC adhesive and water-soluble conductive polyaniline adhesive. In this way, while reducing excessively high crosslinking density, the toughness of the three-dimensional conductive suppression network is also achieved, and the conductivity of the three-dimensional conductive suppression network is also improved, which is beneficial to preparing a three-dimensional conductive suppression network with high conductivity, uniform conductivity, and strong toughness.

[0057] In one embodiment, the amount of the multifunctional organophosphonic acid crosslinking agent added is 1 to 5 parts by weight.

[0058] In one embodiment, the carboxylated polymer adhesive comprises at least one of polyacrylic acid and carboxylated styrene-butadiene rubber.

[0059] It should be noted that although adjusting the ratio of CMC adhesive to water-soluble conductive polyaniline adhesive can effectively suppress the expansion problem of high-capacity silicon-carbon anode sheets to some extent, the improvement effect is still not ideal. Therefore, some scholars have attempted to improve the adhesive of silicon-carbon anode sheets by introducing styrene-butadiene rubber (SBR) while using polyacrylic acid. However, since traditional SBR only contains carbon-carbon double bonds, its reactivity with multifunctional organophosphonic acid crosslinking agents is low, requiring strong crosslinking agents such as peroxides. This results in low crosslinking efficiency and poor network uniformity, and it cannot buffer stress through dynamic bonds, thus failing to achieve the dynamic repair function of the three-dimensional conductive network.

[0060] Therefore, in one embodiment, the carboxyl polymer adhesive is a mixture of polyacrylic acid and carboxyl styrene-butadiene rubber, so that the carboxyl groups of the added carboxyl styrene-butadiene rubber can form dynamic hydrogen bonds or coordination bonds with the phosphate groups of the multifunctional organophosphonic acid crosslinking agent, polyacrylic acid and CMC. When subjected to force, the water-soluble conductive polyaniline of the three-dimensional conductive inhibition network will break, and the broken three-dimensional conductive inhibition network can be reconstructed through dynamic reversible hydrogen bonds, thereby driving the water-soluble polyaniline molecular chains to migrate to the crack, promoting the reconstruction of the conductive path, and giving the three-dimensional conductive inhibition network a strong self-healing ability, so as to achieve rapid self-healing of the large crack area of ​​the three-dimensional conductive inhibition network, ensuring that the conductivity of the three-dimensional conductive inhibition network after self-healing is high, that is, the broken water-soluble conductive polyaniline can still maintain the conductive path through π electron cloud overlap, ensuring that the three-dimensional conductive inhibition network does not become inactive, thereby improving the dynamic repair ability of the three-dimensional conductive inhibition network.

[0061] It is worth mentioning that, because the carboxyl groups of carboxylated styrene-butadiene rubber can form complementary hydrogen bonds with the R-sulfonic acid groups of polyacrylic acid, CMC, and water-soluble conductive polyaniline, and simultaneously form primary hydrogen bonds with the carboxyl groups of polyacrylic acid and the hydroxyl groups of CMC, the fractured three-dimensional conductive suppression network can form multiple dynamic reversible hydrogen bonds. When silicon carbon expands, under stress, the polyacrylic acid and CMC segments of the three-dimensional conductive suppression network migrate directionally along the stress gradient, so as to drive the water-soluble conductive polyaniline molecular chains to preferentially fill the conductive gaps at the cracks. Moreover, the carboxylated styrene-butadiene rubber segments can provide elastic space for hydrogen bond reconstruction, allowing the molecular chains to move freely within a large crack area, achieving elastic closure repair. This enables the three-dimensional conductive suppression network to rapidly self-repair a large crack area, ensuring a high conductivity recovery rate after self-repair. This ensures that the high-capacity silicon-carbon anode sheet can maintain a volume expansion rate of <15% during multiple charge-discharge cycles of the soft-pack lithium battery, thereby improving the cycle life of the high-capacity silicon-carbon anode sheet in the soft-pack lithium battery.

[0062] It is also understandable that the added carboxylated styrene-butadiene rubber can effectively improve the problem of polyacrylic acid's easy absorption of water and swelling, which affects the bonding strength. This allows the carboxylated styrene-butadiene rubber to form physical cross-linking points with polyacrylic acid through molecular entanglement, thereby more effectively restraining the expansion of silicon carbon.

[0063] It is also understandable that polyacrylic acid provides high-density crosslinking points, while carboxylated styrene-butadiene rubber increases network toughness, effectively improving the overall crosslinking density of the negative electrode slurry. In this way, on the one hand, it can better adapt to the high crosslinking density requirements of multifunctional organophosphonic acid crosslinking agents, and on the other hand, the rubber network of carboxylated styrene-butadiene rubber can better compensate for the poor toughness caused by the high crosslinking density of multifunctional organophosphonic acid crosslinking agents. Moreover, the carboxyl groups of carboxylated styrene-butadiene rubber form hydrogen bonds or ionic bonds with the R-sulfonic acid groups of water-soluble conductive polyaniline, effectively inhibiting the agglomeration of water-soluble conductive polyaniline, silicon carbon particles or multifunctional organophosphonic acid crosslinking agents when the mixed adhesive, silicon carbon slurry and multifunctional organophosphonic acid crosslinking agents are mixed, thereby ensuring the continuous distribution of the conductive network, and thus ensuring the preparation of a three-dimensional conductive suppression network with high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing.

[0064] It can also be understood that the linear molecular chains of CMC adhesive form a main network with polyacrylic acid through hydroxyl groups, while the linear molecular chains of CMC adhesive form hydrogen bonds with the carboxyl groups of carboxylated styrene-butadiene rubber through hydroxyl groups, filling the gaps in the main network. The linear conjugated chains of water-soluble polyaniline form a conductive network through π-π stacking. At the same time, with the use of multifunctional organophosphonic acid crosslinking agents, water-soluble polyaniline can achieve interpenetrating crosslinking with polyacrylic acid, CMC, and carboxylated styrene-butadiene rubber through multifunctional organophosphonic acid crosslinking agents, so as to construct a three-dimensional conductive inhibition network with high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing ability.

[0065] In one embodiment, the weight ratio of polyacrylic acid and carboxylated styrene-butadiene rubber is 1:1.

[0066] In one embodiment, the amount of polyacrylic acid added is 1-3 parts by weight; the amount of carboxylated styrene-butadiene rubber added to the negative electrode slurry is 1-3 parts, so as to ensure that the added carboxylated styrene-butadiene rubber improves the toughness of the three-dimensional conductive suppression network while also ensuring that the three-dimensional conductive suppression network has strong self-healing strength.

[0067] In one embodiment, the negative electrode slurry comprises, by weight, 95-98 parts silicon carbon, 0.5-2 parts mixed adhesive, 0.5-1.5 parts conductive agent, 1-3 parts polyacrylic acid, 1-3 parts carboxylated styrene-butadiene rubber, and 1-5 parts multifunctional organophosphonic acid crosslinking agent, which is beneficial for preparing silicon carbon negative electrode sheets with high capacity, low expansion, high conductivity, uniform and continuous conductivity, strong toughness, and strong self-healing properties.

[0068] S104. The negative electrode slurry is coated onto the negative current collector to obtain a silicon-carbon negative electrode semi-finished product.

[0069] In one embodiment, the coating thickness of the negative electrode slurry when coated on the negative current collector is 50um-100um, which is beneficial for preparing silicon-carbon negative electrode sheets with high capacity, low expansion, high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing.

[0070] S105. The silicon-carbon anode semi-finished product is pre-baked at 90℃-120℃ to remove moisture, effectively avoiding the problem of blistering or cracking of the active layer of the final silicon-carbon anode sheet due to excessive moisture during the subsequent cross-linking reaction.

[0071] In one embodiment, the pre-baking time is 1-10 minutes to effectively remove most of the moisture from the silicon-carbon anode sheet semi-finished product.

[0072] S106. The pre-baked silicon-carbon anode semi-finished product is subjected to vacuum drying to obtain silicon-carbon anode; wherein the temperature of the vacuum drying operation is 70℃-90℃ and the time is 2h-5h.

[0073] It is understandable that when the pre-baked silicon-carbon anode semi-finished product is vacuum dried (70℃-90℃, time 2h-5h), the multifunctional organophosphonic acid crosslinking agent contains abundant hydroxyl functional groups, which can react with CMC adhesive to form ester bonds and hydrogen bonds, and can also react with carboxyl polymer binders, enabling CMC to connect with carboxyl polymer binders to form a three-dimensional conductive suppression network. The multifunctional organophosphonic acid crosslinking agent can also form hydrogen bonds with the hydroxyl groups on the surface of silicon particles in silicon-carbon slurry, effectively wrapping the silicon-carbon particles in silicon-carbon slurry, enhancing the constraint force on the anode slurry, not only effectively suppressing the expansion of silicon-carbon, making the volume expansion rate of silicon-carbon <15%, thus broadening the application of high-capacity silicon-carbon anode sheets in soft-pack lithium batteries; but also effectively suppressing silicon-carbon cracking, which helps to improve the cycle life of soft-pack lithium batteries.

[0074] The above-described method for preparing silicon-carbon anode sheets involves first dissolving water-soluble conductive polyaniline in an organic solvent to form an ultra-long conductive network, resulting in a water-soluble conductive polyaniline solution. Then, the water-soluble conductive polyaniline solution is mixed with a CMC solution. The addition of CMC solution helps improve the dispersibility of the water-soluble conductive polyaniline solution. Furthermore, the linear structure of the CMC solution provides reaction sites for the subsequent crosslinking reaction of the ultra-long conductive network. Next, the mixed solution, silicon-carbon slurry, and a multifunctional organophosphonic acid crosslinking agent are mixed to combine the silicon-carbon slurry and the multifunctional organophosphonic acid crosslinking agent. Acidic crosslinking agents can be uniformly dispersed in the mixed adhesive solution, effectively avoiding the agglomeration problem of silicon-carbon slurry or multifunctional organophosphonic acid crosslinking agents. Simultaneously, by controlling the mixing temperature of the multifunctional organophosphonic acid crosslinking agents to 15℃-25℃, premature crosslinking of the negative electrode slurry is prevented, which could affect subsequent coating operations. This ensures good fluidity of the negative electrode slurry, thereby guaranteeing the normal operation of subsequent coating. Subsequently, the coated silicon-carbon negative electrode semi-finished product is pre-baked at 90℃-120℃ to remove moisture, effectively preventing subsequent agglomeration of the silicon-carbon negative electrode semi-finished product. Excessive moisture during the crosslinking reaction caused blistering or cracking of the active layer in the final silicon-carbon anode sheet. Finally, the pre-baked silicon-carbon anode sheet semi-finished product underwent vacuum drying (70℃-90℃, 2h-5h). Because multifunctional organophosphonic acid crosslinking agents contain abundant hydroxyl functional groups, they can react with CMC adhesive to form ester and hydrogen bonds during vacuum drying, and also react with carboxyl polymer binders, allowing CMC to connect with the carboxyl polymer binders to form a three-dimensional conductive layer. The multifunctional organophosphonic acid crosslinking agent can also form hydrogen bonds with the hydroxyl groups on the surface of silicon particles in the silicon-carbon slurry, effectively encapsulating the silicon-carbon particles and enhancing the constraint on the negative electrode slurry. This not only effectively inhibits the expansion of silicon-carbon but also effectively inhibits silicon-carbon cracking, which is conducive to forming a three-dimensional conductive suppression network with high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing. This makes the volume expansion rate of silicon-carbon <15%, thus broadening the application of high-capacity silicon-carbon negative electrode sheets in soft-pack lithium batteries and improving the cycle life of high-capacity silicon-carbon negative electrode sheets in soft-pack lithium batteries.

[0075] Furthermore, the addition of R-sulfonic acid groups to the water-soluble conductive polyaniline has several advantages. First, the doped R-sulfonic acid groups improve the solubility of the water-soluble conductive polyaniline, ensuring its uniform dispersion in the organic solvent. This allows the conjugated structure of the water-soluble conductive polyaniline to spontaneously assemble into a continuous, ultra-long conductive network, providing an efficient electron conduction path and ensuring the preparation of a uniform and continuous ultra-long conductive network. Second, the doped R-sulfonic acid groups increase the cross-linking reaction sites of the water-soluble conductive polyaniline, enabling it to form hydrogen bonds with CMC. Ionic or ester bonds significantly enhance the crosslinking density and structural toughness of the three-dimensional conductive suppression network, enabling the strongly crosslinked three-dimensional conductive suppression network to more effectively encapsulate silicon-carbon particles, strengthen the constraint on the volume expansion of silicon-carbon, further reduce the expansion rate of silicon-carbon, and thus improve the toughness of the three-dimensional conductive suppression network, thereby providing better structural support for the three-dimensional conductive suppression network. On the other hand, the doped R-sulfonic acid groups can enhance the interaction between water-soluble conductive polyaniline and the hydroxyl groups on the surface of silicon-carbon particles, improve the uniformity of coating on silicon-carbon particles, thereby reducing silicon-carbon agglomeration and indirectly suppressing cracking caused by local excessive expansion. In addition, the R-sulfonic acid groups of water-soluble conductive polyaniline will form dynamic reversible hydrogen bonds with the carboxyl groups of carboxyl polymer adhesives, ensuring that water-soluble conductive polyaniline can quickly complete bridging repair between cracks when silicon-carbon expands and cracks, thereby achieving rapid hydrogen bond reconstruction. Furthermore, the introduced R-sulfonic acid groups can better guide the polyaniline molecular chains to migrate directionally to the crack, thereby improving the self-healing efficiency of the conductive pathway of the three-dimensional conductive suppression network.

[0076] This disclosure also provides a silicon-carbon anode sheet, which is prepared using the silicon-carbon anode sheet preparation method described in any of the above embodiments. The prepared silicon-carbon anode sheet has the characteristics of high capacity, low expansion, high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing. It effectively solves the problems of cracking, pulverization, excessive expansion rate, high internal resistance and poor cycle performance of high-capacity silicon-carbon anode sheets during the charging cycle of soft-pack lithium batteries, thereby ensuring that high-capacity silicon-carbon anode sheets can be better adapted to the application of soft-pack lithium batteries.

[0077] In one embodiment, the capacity of the silicon-carbon anode sheet is 700mAh / g-750mAh / g.

[0078] This disclosure provides a pouch lithium battery, including the silicon-carbon anode sheet described in any of the above embodiments, to ensure that the high-capacity silicon-carbon anode sheet can maintain a volume expansion rate of <15% in the application of pouch lithium batteries, and also reduces the problems of cracking, pulverization and high internal resistance of the high-capacity silicon-carbon anode sheet in the application of pouch lithium batteries, thereby improving the cycle performance of the high-capacity silicon-carbon anode sheet in the charging cycle process of pouch lithium batteries.

[0079] The following are some specific examples. When %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively list all possible scenarios, and unless otherwise specified, the materials used in the examples are commercially available.

[0080] Example 1 1 kg of polyaniline was mixed with 0.5 kg of polystyrene sulfonic acid (the molecular weight of the R-sulfonic acid group is 70,000) to obtain water-soluble conductive polyaniline. Then, the water-soluble conductive polyaniline was dissolved in NMP solvent to prepare a water-soluble conductive polyaniline solution with a solid content of 5%.

[0081] (2) Dissolve CMC in deionized water to prepare a CMC adhesive solution with a solid content of 1.5%.

[0082] (3) Then the water-soluble polyaniline adhesive from step (1) and the CMC adhesive from step (2) are mixed in a mass ratio of 3:7 to obtain a mixed adhesive.

[0083] (4) 96.76 kg of silicon carbide, 1 kg of mixed adhesive, 1 kg of conductive carbon black (SP), 0.05 kg of single-walled carbon nanotubes (SWCNT), 1.5 kg of styrene-butadiene rubber (SBR), and 1.5 kg of polyacrylic acid (PAA) were added to a mixing tank in sequence and mixed (revolution speed 15 r / min, rotation speed 35 r / min, time 180 min) to obtain a premix.

[0084] (5) After adding 1.5 kg of 70% inositol hexaphosphate solution, start the cooling system of the stirred tank to keep the temperature inside the stirred tank at 25°C. Finally, start the stirring operation (stirring speed revolution speed 15 r / min, time 30 min) to obtain the negative electrode slurry.

[0085] (6) Coating the negative electrode slurry onto the negative current collector (coating thickness is 70um) to obtain a silicon-carbon negative electrode semi-finished product. The silicon-carbon negative electrode semi-finished product is pre-baked at 120℃ for 10min to remove moisture; then it is placed in a vacuum drying oven at 85℃ for 5h to promote the completion of the crosslinking reaction.

[0086] Example 2 The difference from Example 1 is that the ratio of 3:7 in step (3) is adjusted to 5:5, while the other steps remain unchanged.

[0087] Example 3 The difference from Example 1 is that the 1.5 kg of 70% inositol hexaphosphate solution in step (5) is changed to 1.0 kg of 70% inositol hexaphosphate solution, while the other steps remain unchanged.

[0088] Example 4 The difference from Example 1 is that the molecular weight of polystyrene sulfonic acid in step (1) is adjusted to 100,000, while the other steps remain unchanged.

[0089] Example 5 The difference from Example 1 is that the 1.5 kg styrene-butadiene rubber in step (4) is directly replaced with 1.5 kg carboxylated styrene-butadiene rubber, while the other steps remain unchanged.

[0090] Comparative Example 1 The difference from Example 5 is that only water-soluble conductive polyaniline is used, and inositol hexaphosphate solution is not added, that is, step (5) is omitted, while the other steps remain unchanged.

[0091] Comparative Example 2 The difference from Example 5 is that water-soluble conductive polyaniline is not added, only inositol hexaphosphate solution is added, that is, step (1) is omitted, while the other steps remain unchanged.

[0092] Comparative Example 3 The difference from Example 5 is that water-soluble conductive polyaniline and inositol hexaphosphate solution are not added, that is, steps (1) and (5) are omitted, while other steps remain unchanged.

[0093] Comparative Example 4 The difference from Example 5 is that the ratio of 3:7 in step (3) is adjusted to 3:9, while the other steps remain unchanged.

[0094] Comparative Example 5 The difference from Example 5 is that the 1.5 kg of 70% inositol hexaphosphate solution in step (5) is adjusted to 5.2 kg of 70% inositol hexaphosphate solution, while the other steps remain unchanged.

[0095] Comparative Example 6 The difference from Example 5 is that the molecular weight of polystyrene sulfonic acid in step (1) is adjusted to 200,000, while the other steps remain unchanged.

[0096] Comparative Example 7 The difference from Example 5 is that the organic acid polystyrene sulfonic acid in step (1) is replaced with dodecylbenzene sulfonic acid, while the other steps remain unchanged.

[0097] The silicon-carbon anode sheets prepared in Examples 1-5 and Comparative Examples 1-7 were assembled with lithium cobalt oxide cathode sheets and double-sided coated separators, and then electrolyte was injected to prepare a 3000mAh soft-pack lithium battery. The performance of the obtained soft-pack lithium battery was then tested, and the experimental data in the table below were obtained: Among them, the internal resistance detection method before 400 revolutions is: measured by an internal resistance tester; Coulomb efficiency testing method: Xinwei Electrochemical Integrated Test Cabinet; Capacity retention testing method: Xinwei Electrochemical Integrated Test Cabinet; Internal resistance testing method after 400 revolutions: Measured using an internal resistance tester; Expansion rate testing method after 400 cycles: Test the battery thickness before cycling and test the battery thickness after 400 cycles; Table 1 As can be seen from the comparison of Examples 1-5 in the table above, since Examples 1-4 all used ordinary styrene-butadiene rubber, while Example 5 used carboxylated styrene-butadiene rubber, the carboxylated styrene-butadiene rubber in Example 5 can exert a better synergistic effect with water-soluble conductive polyaniline and inositol hexaphosphate solution, which is conducive to forming a three-dimensional conductive inhibition network with high conductivity, uniform and continuous conductivity, strong toughness and strong self-healing. Therefore, the comprehensive indicators of Example 5 are significantly better than those of Examples 1-4.

[0098] As can be seen from the comparison between Example 5 and Comparative Examples 1-3 in the table above, since Comparative Examples 1-3 did not use carboxylated styrene-butadiene rubber, water-soluble conductive polyaniline and inositol hexaphosphate solution at the same time, the overall performance of Comparative Examples 1-3 was significantly worse than that of Example 5.

[0099] As can be seen from the comparison between Example 5 and Comparative Example 4 in the table above, since the mass ratio of water-soluble polyaniline adhesive to CMC adhesive in Comparative Example 4 is 3:9 which is not within the range of (3-5):(5-8), the overall performance of Comparative Example 4 is significantly worse than that of Example 5.

[0100] As can be seen from the comparison between Example 5 and Comparative Example 5 in the table above, the overall performance of Comparative Example 5 is significantly worse than that of Example 5 because the amount of inositol hexaphosphate solution added to Comparative Example 5 is not between 1 and 5 parts.

[0101] As can be seen from the comparison between Example 5 and Comparative Examples 6-7 in the table above, since the molecular weight of polystyrene sulfonic acid (R-sulfonic acid group) in Comparative Examples 6-7 is not between 50,000 and 100,000, the overall performance of Comparative Examples 6-7 is significantly worse than that of Example 5.

[0102] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing a silicon-carbon anode sheet, characterized in that, Includes the following steps: A water-soluble conductive polyaniline is dissolved in an organic solvent to form an ultra-long conductive network, resulting in a water-soluble conductive polyaniline adhesive solution; wherein the water-soluble conductive polyaniline is doped with R-sulfonic acid groups; The water-soluble conductive polyaniline adhesive solution is mixed with the CMC adhesive solution to obtain a mixed adhesive solution; The mixed adhesive, silicon carbon slurry, and multifunctional organophosphonic acid crosslinking agent are mixed to obtain a negative electrode slurry; wherein the mixing temperature is controlled at 15℃-25℃; the silicon carbon slurry includes a carboxyl polymer binder. The negative electrode slurry is coated onto the negative current collector to obtain a silicon-carbon negative electrode semi-finished product. The silicon-carbon negative electrode semi-finished product is pre-baked at 90℃-120℃ to remove moisture; The pre-baked silicon-carbon anode semi-finished product is subjected to vacuum drying to obtain silicon-carbon anode sheet; wherein the vacuum drying operation is performed at a temperature of 70℃-90℃ for 2h-5h.

2. The method for preparing a silicon-carbon anode sheet according to claim 1, characterized in that, The step of mixing the mixed adhesive, silicon carbide slurry, and multifunctional organophosphonic acid crosslinking agent includes the following specific steps: The mixed adhesive and the silicon carbide slurry are mixed and stirred to obtain a premix; A multifunctional organophosphonic acid crosslinking agent is added to the premix and the mixture is stirred at low temperature to obtain the negative electrode slurry.

3. The method for preparing a silicon-carbon anode sheet according to claim 2, characterized in that, When mixing the mixed adhesive and the silicon carbide slurry, the revolution speed is 10 r / min-30 r / min; the rotation speed is 10 r / min-35 r / min; and the time is 120 min-180 min.

4. The method for preparing a silicon-carbon anode sheet according to claim 2, characterized in that, When adding a multifunctional organophosphonic acid crosslinking agent to the premix and mixing and stirring at low temperature, the revolution speed is 10 r / min-15 r / min; the time is 20 min-30 min.

5. The method for preparing a silicon-carbon anode sheet according to claim 1, characterized in that, The water-soluble conductive polyaniline adhesive and the CMC adhesive are mixed at a mass ratio of (3-5):(5-8).

6. The method for preparing a silicon-carbon anode sheet according to claim 1, characterized in that, The solid content of the water-soluble conductive polyaniline adhesive is 3%-5%; and / or, The solid content of the CMC adhesive is 1%-3%.

7. The method for preparing a silicon-carbon anode sheet according to claim 1, characterized in that, The multifunctional organophosphonic acid crosslinking agent includes at least one of inositol hexaphosphate, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid; and / or, The organic solvent includes N-methylpyrrolidone.

8. The method for preparing a silicon-carbon anode sheet according to claim 1, characterized in that, The amount of the multifunctional organophosphonic acid crosslinking agent added is 1 to 5 parts by weight; and / or, The carboxylated polymer adhesive includes at least one of polyacrylic acid and carboxylated styrene-butadiene rubber.

9. A silicon-carbon anode sheet, characterized in that, The silicon-carbon anode sheet was prepared using any one of claims 1-8.

10. A soft-pack lithium battery, characterized in that, Including the silicon-carbon anode sheet as described in claim 9.

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