Negative electrode self-repairing binder as well as preparation method and application thereof

Abstract

The invention provides a negative electrode self-repairing binder as well as a preparation method and application thereof. The negative electrode self-repairing binder is a chemical cross-linking product, and cross-linking raw materials comprise guar gum, an acrylic polymer and a flexible chain segment polymer. The negative electrode self-repairing binder is a three-dimensional network binder which is hard and soft and has self-repairing performance, the binder is rich in hydrogen bonds and has self-repairing performance at room temperature, volume expansion of a silicon-based negative electrode in the charging and discharging process can be effectively relieved, electrode internal stress accumulation and crack generation caused by the volume expansion are reduced, and the service life of the negative electrode is prolonged. Therefore, the stability of the electrode structure is remarkably improved, the cycle performance of the battery is improved, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular, to a negative electrode self-healing binder, a preparation method thereof, and an application thereof. Background Art

[0002] High-energy density lithium-ion secondary batteries are of great significance for alleviating energy and environmental crises. Traditional graphite negative electrodes cannot meet the existing requirements. Silicon-based materials such as silicon-carbon negative electrodes have a theoretical specific capacity far exceeding that of graphite and are currently recognized as the next-generation negative electrode materials for lithium-ion batteries. However, the huge volume change of silicon-based negative electrodes during charge and discharge cycles seriously hinders their large-scale commercial application.

[0003] Currently, commercially available silicon-based negative electrode binders such as sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, polyacrylic acid, etc. are all linear structures, with a small number and variety of functional groups. The hydrogen bond strength formed is insufficient to cope with the stress generated by the volume expansion of silicon-based negative electrodes during charge and discharge cycles. Moreover, these binders have insufficient viscosity and no self-healing property. After the electrode expands and ruptures, they are prone to pulverization and peeling, ultimately leading to a rapid decline in battery capacity.

[0004] Patent CN117820984A discloses a self-healing binder, which is a copolymer formed by polymerizing a self-healing monomer, styrene, an acrylic monomer, and an acrylate monomer. Patent CN117080449A discloses a self-healing binder for batteries, including a binder, an auxiliary agent, a solvent, and a self-healing agent. The self-healing agent includes polymer microcapsules, and the polymer microcapsules include a capsule wall material and a repair liquid core material. The repair liquid core material includes a repair solvent and a repair binder, and the repair binder includes one or more of polyacrylic acid, acrylate copolymer, polyamide, acrylate-acrylamide copolymer, polyurethane; the binder includes one or more of polyacrylic acid, acrylate copolymer, polyamide, acrylate-acrylamide copolymer, polyurethane. However, due to the unstable structure of the binder and limited self-healing effect in the above solutions, the performance of the binder still has relatively large defects, and the effect of alleviating the volume expansion of silicon-based negative electrodes is limited. Summary of the Invention

[0005] The main object of the present invention is to provide a negative electrode self-healing binder, a preparation method thereof, and an application thereof, so as to solve the problem that the improvement effect of the binder in the prior art on the phenomena of electrode pulverization, peeling, and battery performance attenuation caused by serious volume expansion of silicon-based negative electrodes is limited.

[0006] To achieve the above object, according to one aspect of the present invention, a negative electrode self-healing binder is provided. The negative electrode self-healing binder is a chemical cross-linking product, and the cross-linking raw materials include guar gum, an acrylic polymer, and a flexible chain segment polymer.

[0007] Furthermore, the molar ratio of guar gum, acrylic polymer, and flexible segment polymer is (0.1 - 5):(0.5 - 2):(0.5 - 5).

[0008] Furthermore, the acrylic polymer includes one or more of polyacrylic acid, polymethacrylic acid, sodium polyacrylate, and polyacrylate, and the weight-average molecular weight is 1,000 - 450,000; and / or the flexible segment polymer includes one or more of polyethylene oxide, polycaprolactone, polyethylene glycol, and polysiloxane, and the weight-average molecular weight is 1,000 - 1,000,000.

[0009] According to another aspect of the present invention, there is provided a method for preparing the above-mentioned negative electrode self-healing binder of the present invention, including the following steps: Step S1, dispersing guar gum in water to obtain a guar gum solution; Step S2, sequentially adding an acrylic polymer and a flexible segment polymer to the guar gum solution to obtain a cross-linking raw material solution; Step S3, dissolving an initiator in water to obtain an initiator solution, and dissolving a cross-linking agent in water to obtain a cross-linking agent solution; Step S4, under an inert atmosphere, adding the initiator solution and the cross-linking agent solution to the cross-linking raw material solution simultaneously, and performing water bath stirring, and after freeze-drying, a negative electrode self-healing binder is obtained.

[0010] Furthermore, the initiator includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; and / or the weight ratio of the initiator to guar gum is (0.01 - 0.30):1.

[0011] Furthermore, the cross-linking agent includes one or more of N,N-methylenebisacrylamide, glutaraldehyde, and tetraethyl orthosilicate; and / or the weight ratio of the cross-linking agent to guar gum is (0.002 - 0.060):1.

[0012] Furthermore, the inert atmosphere is one or more of a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere; and / or the temperature of the water bath stirring is 40 - 70 °C, and the time is 2 - 8 h.

[0013] According to another aspect of the present invention, there is provided a negative electrode plate, including a current collector and a negative electrode paste loaded on at least one surface of the current collector, the negative electrode paste including a negative electrode active material, a conductive additive, and a binder, and the binder is the above-mentioned negative electrode self-healing binder of the present invention.

[0014] Furthermore, the negative electrode active material is a silicon-based material, and the weight percentage of the negative electrode self-healing binder in the negative electrode paste is 5 - 10%.

[0015] According to another aspect of the present invention, there is provided a secondary battery, including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, and the negative electrode plate is the above-mentioned negative electrode plate of the present invention.

[0016] The negative electrode self-healing binder of the present invention is a three-dimensional network binder that combines rigidity and flexibility and has self-healing properties. This binder is rich in hydrogen bonds and has self-healing properties at room temperature, which can effectively relieve the volume expansion of the silicon-based negative electrode during charge and discharge, reduce the accumulation of internal stress and crack generation in the electrode caused by volume expansion, prevent electrode pulverization and the exfoliation of active materials from the current collector, thereby significantly improving the stability of the electrode structure, enhancing the cycling performance of the battery and extending the cycle life. Detailed implementation manners

[0017] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0018] As described in the background art of the present invention, there is a problem in the prior art that the improvement effect of the binder on the electrode pulverization and exfoliation and the battery performance attenuation caused by the serious volume expansion of the silicon-based negative electrode is limited. To solve the above problems, in a typical implementation manner of the present invention, a negative electrode self-healing binder is provided. The negative electrode self-healing binder is a chemical cross-linking product, and the cross-linking raw materials include guar gum, acrylic polymer and flexible segment polymer.

[0019] In view of the huge volume change of the silicon-based negative electrode during charge and discharge, which induces the accumulation of internal stress in the electrode, generates cracks, causes electrode pulverization, separates the active material from the current collector, and finally results in the attenuation of battery performance and other problems, the present invention adopts a self-healing three-dimensional network binder that combines rigidity and flexibility. This silicon-based negative electrode binder is chemically cross-linked by guar gum (GG), acrylic polymer and flexible segment polymer under the action of an initiator and a cross-linking agent. Among them, the guar gum molecule contains a large number of hydroxyl groups, and the acrylic polymer is rich in strongly polar functional groups of carboxyl groups. An esterification reaction can occur between the hydroxyl group and the carboxyl group to form an ester bond. In addition, the cross-linking agent commonly used in the cross-linking process can undergo a free radical polymerization reaction with the ester bond of the polymer molecular chain through double bonds to link different molecular chains and form a three-dimensional network structure.

[0020] The flexible segment polymer has flexible segments that can penetrate into the three-dimensional network structure. During the charge and discharge process of the silicon-based negative electrode material, silicon will undergo large volume expansion and contraction. The flexible segments can adapt to this volume change and buffer the expansion stress of silicon particles through their own stretching and compression, reducing the stress concentration between silicon particles and between silicon particles and the current collector, thereby alleviating the damage of volume expansion to the electrode structure.

[0021] Some hydroxyl and carboxyl groups that can form hydrogen bonds are still retained on the polymers finally formed by the above three cross-linking raw materials. When the volume of the silicon-based anode material changes or structural damage occurs due to external stress, the hydrogen bonds will break. However, due to their dynamic reversibility, the broken hydrogen bonds can reform, restoring the three-dimensional network structure of the binder, thus achieving the self-healing function.

[0022] The anode self-healing binder of the present invention is rich in hydrogen bonds, has strong adhesiveness and self-healing properties. The rigid guar gum and the flexible segment polymer can form a new self-healing binder with a rigid-flexible balance through cross-linking with acrylic polymers. Based on the good elasticity, stretchability and hydrogen bond self-healing ability of the binder, it can effectively alleviate the volume expansion and electrode delamination and peeling problems of the silicon-based anode during charge and discharge, which is beneficial to improving the cycle performance of the silicon-based anode and extending the cycle life of the battery. The anode self-healing binder is preferably a silicon-based anode self-healing binder.

[0023] In a preferred embodiment, the molar ratio of guar gum, acrylic polymer and flexible segment polymer is (0.1-5):(0.5-2):(0.5-5). Within the above ratio range, GG can provide more sufficient rigid support, while the acrylic polymer and the flexible segment polymer respectively contribute better adhesiveness and flexibility. The synergistic effect of the three is conducive to constructing a self-healing binder with both rigidity and flexibility. Beyond this range, too much GG may lead to too high hardness of the binder and loss of flexibility, while too much flexible segment polymer or acrylic polymer may weaken the rigidity and adhesiveness of the binder, and the effect of the binder in resisting the volume expansion of the silicon-based anode and maintaining the stability of the electrode structure cannot reach the best.

[0024] Preferably, the molar ratio of guar gum, acrylic polymer and flexible segment polymer is 1:(0.2-1):(0.2-1). The ratio within this molar ratio range can more effectively combine the rigidity of GG, the adhesiveness of the acrylic polymer and the flexibility of the flexible segment polymer to form a three-dimensional network structure binder with excellent self-healing ability and good adhesiveness to cope with the volume change of the silicon-based anode material during charge and discharge, so as to more effectively solve the problems of electrode pulverization and peeling and battery performance decay caused by the volume expansion of the silicon-based anode, and improve the cycle performance and service life of the battery.

[0025] In a lithium-ion battery, the molecular weight of the binder has a direct impact on its viscosity, mechanical strength, and self-healing ability. Based on the relationship between the molecular structure and properties of the binder, the weight-average molecular weight of the self-healing binder for the negative electrode can be further defined. Preferably, the weight-average molecular weight of the self-healing binder for the negative electrode is 10,000 to 1,000,000. For silicon-based negative electrode materials, since significant volume changes occur during charge and discharge processes, the binder needs to have certain mechanical strength and flexibility to resist and relieve the stress caused by such changes. At the same time, it also needs to have good self-healing ability to restore the structural integrity and conductivity of the electrode, prevent the pulverization and exfoliation of the active material, and thus avoid the attenuation of battery performance. A binder with too low a weight-average molecular weight has short molecular chains, and the formed network structure may not be firm enough, with insufficient viscosity, and is not sufficient to provide enough support when the silicon-based negative electrode material expands, easily leading to the destruction of the electrode structure. On the contrary, a binder with too high a weight-average molecular weight, although improving the mechanical strength, has overly rigid molecular chains, lacks flexibility and self-healing ability, and cannot effectively adapt to and buffer the volume changes of the silicon-based negative electrode material, which will also cause stress concentration inside the electrode, resulting in cracks and pulverization.

[0026] Therefore, defining the weight-average molecular weight of the binder within a certain range can enable the binder molecules to have sufficient mechanical strength while also maintaining appropriate flexibility and self-healing ability. Such a binder can form a stable three-dimensional network when the silicon-based material expands to resist stress, and when the material contracts, the flexibility of the molecular chains allows the binder network to reconnect and repair, maintaining the structural stability and conductivity of the electrode, thereby improving the cycle performance of the battery and extending its service life. The above molecular weight range can achieve the best balance among viscosity, mechanical strength, and self-healing ability, enabling the binder to have the best performance during the charge and discharge cycles of the battery.

[0027] Defining the specific types and weight-average molecular weights of the acrylic polymer and the flexible segment polymer can further optimize the performance of the binder. In a preferred embodiment, the acrylic polymer includes one or more of polyacrylic acid, polymethacrylic acid, sodium polyacrylate, and polyacrylate, with a weight-average molecular weight of 1,000 to 450,000; and / or the flexible segment polymer includes one or more of polyethylene oxide, polycaprolactone, polyethylene glycol, and polysiloxane, with a weight-average molecular weight of 1,000 to 1,000,000.

[0028] Acrylic polymers, especially their carboxyl functional groups, can form hydrogen bonds with the hydroxyl groups on the surface of silicon-based materials, enhancing the binding force between the binder and the active material of the electrode and preventing the separation of the active material from the current collector during volume expansion. Different types of acrylic polymers may have different viscosities and chemical activities, and the above types of acrylic polymers can further optimize the bonding performance. The weight-average molecular weight range of the above acrylic polymers can better balance their viscosity and diffusivity. Excessively high molecular weight will increase the viscosity but reduce its penetration ability between electrode materials, and vice versa.

[0029] The above flexible segment polymers are more conducive to relieving the volume expansion of the silicon-based negative electrode through their own elastic deformation in the binder system of the present invention. The flexible segments of the flexible segment polymers can effectively absorb and buffer the stress generated by the volume change of the silicon-based material during the battery cycle, reducing the generation of cracks. At the same time, after cracks appear, the high molecular weight segments of the flexible segment polymers can be stretched and compressed flexibly, assisting the hydrogen bonds on the polymer surface to achieve self-healing. When the weight-average molecular weight of the flexible segment polymer is within the above range, it is beneficial to make it have sufficient flexibility while also having a certain molecular chain length to promote the stretching and compression during the self-healing process.

[0030] Through the above limitations, acrylic polymers, flexible segment polymers, and GG form a more stable dynamic equilibrium system in the binder. The viscosity of the acrylic polymer, the flexibility of the flexible segment polymer, and the rigidity of GG complement each other, jointly constructing a self-healing binder network that can effectively respond to the volume change of the silicon-based negative electrode. This binder can not only resist external stress and prevent electrode pulverization but also self-heal when internal cracks appear, maintaining the integrity and conductivity of the electrode structure, thereby significantly improving the cycle performance of the battery and extending its service life.

[0031] In another typical embodiment of the present invention, a method for preparing the above negative electrode self-healing binder of the present invention is also provided, including the following steps: Step S1, dispersing guar gum in water to obtain a guar gum solution; Step S2, sequentially adding an acrylic polymer and a flexible segment polymer to the guar gum solution to obtain a cross-linking raw material solution; Step S3, dissolving an initiator in water to obtain an initiator solution, and dissolving a cross-linking agent in water to obtain a cross-linking agent solution; Step S4, under an inert atmosphere, adding the initiator solution and the cross-linking agent solution to the cross-linking raw material solution simultaneously, and performing water bath stirring. After freeze-drying, a negative electrode self-healing binder is obtained.

[0032] Specifically, in the present invention, guar gum, acrylic polymer, and flexible segment polymer are first dispersed in water in sequence to obtain a cross-linking raw material solution; then, under an inert atmosphere, an initiator solution and a cross-linking agent solution are simultaneously added to the cross-linking raw material solution, and water bath stirring is carried out. During this process, the initiator can decompose to generate highly active free radicals, which can initiate the polymerization reaction of monomer molecules in the cross-linking raw materials. The cross-linking agent can form covalent bonds with polymer molecular chains through chemical cross-linking reactions to connect different molecular chains together, thereby transforming the polymer from a linear or branched structure into a three-dimensional network structure. The inert atmosphere can prevent the highly active free radicals from being oxidized and play a protective role. After the liquid material is cooled to room temperature, freeze-drying is carried out to obtain a negative electrode self-healing binder. The above preparation process is simple and easy for large-scale production. The obtained binder can effectively improve the electrode pulverization and exfoliation and battery performance attenuation caused by the serious volume expansion of the silicon-based negative electrode, and is a negative electrode self-healing binder with development potential.

[0033] By precisely controlling the types and proportions of the initiator and the cross-linking agent, the cross-linking degree and network structure of the binder can be further adjusted. In a preferred embodiment, the initiator includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; and / or the weight ratio of the initiator to guar gum is (0.01 - 0.30):1, preferably (0.01 - 0.15):1; and / or the cross-linking agent includes one or more of N,N'-methylenebisacrylamide, glutaraldehyde, and tetraethyl orthosilicate; and / or the weight ratio of the cross-linking agent to guar gum is (0.002 - 0.060):1, preferably (0.003 - 0.060):1.

[0034] The above initiator has better water solubility and stable initiation activity, and can effectively promote polymerization at a lower temperature. The limitation of the addition amount is beneficial to achieving a moderate reaction rate and a moderate cross-linking degree of the binder network. Excessive initiator may lead to over-polymerization, forming a too rigid structure and reducing the self-healing ability; too little may not be able to fully initiate the reaction, resulting in an incomplete binder network and affecting the viscosity and mechanical strength.

[0035] When the weight ratio of the above cross-linking agent to guar gum is within the above range, it is more conducive to forming an appropriate amount of cross-linking points in the binder network, which not only improves the stability and rigidity of the structure but also retains the necessary flexibility and self-healing mechanism. Too high a proportion of the cross-linking agent may form an overly dense network, restricting the movement of molecular chains and reducing the self-healing efficiency; too low may result in an overly loose network structure, affecting the mechanical properties and stability of the binder.

[0036] Therefore, when the types and proportions of the initiator and the cross-linking agent are within the above ranges, it is beneficial to provide sufficient mechanical strength when the silicon-based anode material expands in volume, and at the same time achieve rapid and effective self-repair after electrode damage, maintaining the integrity of the electrode structure and the stability of the battery performance, thereby improving the cycling performance of the battery and extending its service life.

[0037] In the polymerization reaction, oxygen can act as a terminator of free radicals, affecting the progress of the polymerization reaction, resulting in uneven molecular weight distribution of the product and affecting the performance of the binder. In a preferred embodiment, the inert atmosphere is one or more of a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere; and / or the temperature of the water bath stirring is 40-70 °C, and the time is 2-8 h. Creating an inert atmosphere using inert gases such as nitrogen can effectively isolate oxygen in the air, avoid its interference with the polymerization reaction, and make the formation process of the binder molecules more stable and controlled. The binder synthesized under the above conditions has a more uniform molecular weight distribution and a more optimized network structure, and can provide a more stable and effective self-repairing ability to resist the stress generated when the silicon-based anode expands in volume.

[0038] Within the above temperature and time ranges, it is beneficial to carry out the polymerization reaction under mild conditions to achieve the effects of sufficient cross-linking and uniform dispersion. Too high a temperature will accelerate the reaction, which may lead to out-of-control polymerization reaction, forming an overly rigid binder network and reducing its self-repair ability; too low a temperature will result in a slow reaction rate, which may prolong the polymerization time and affect the production efficiency. Within the above ranges, the reaction rate is moderate, and a binder with a stable structure and excellent performance can be generated. At the same time, the control of the stirring time is beneficial to make all reactants fully mixed, promote the uniform progress of the polymerization reaction, and obtain a binder material with consistent performance.

[0039] In yet another typical embodiment of the present invention, a negative electrode sheet is further provided, which includes a current collector and a negative electrode paste loaded on at least one surface of the current collector. The negative electrode paste includes a negative electrode active material, a conductive additive, and a binder, and the binder is the negative electrode self-repairing binder of the present invention. Due to the use of the self-repairing binder of the present invention, it can effectively buffer and cope with the volume expansion during the cycling process, reduce pulverization and peeling, and maintain the integrity of the electrode structure.

[0040] The proportion of the binder in the anode slurry affects its effect inside the electrode. If the proportion is too low, the density of the binder network is insufficient to effectively resist the volume change of the silicon-based material during charge and discharge, resulting in a weakened connection between the active material particles and prone to pulverization and exfoliation. If the proportion is too high, it may lead to poor rheology of the slurry, affecting the coating process. At the same time, there are too many inactive components, the effective loading of the active material is reduced, and the energy density of the battery decreases. In a preferred embodiment, the anode active material is a silicon-based material, and the weight percentage of the self-healing binder for the anode in the anode slurry is 5-10%. The above addition amount can enable the binder to form a dense enough network to resist the stress caused by volume change without overly affecting the processability of the slurry and the overall performance of the battery.

[0041] Preferably, the silicon-based material includes one or more of silicon-carbon materials, pure silicon materials, and silicon-oxygen materials. The silicon-based material has a high theoretical specific capacity because it can store more lithium ions during charge and discharge. However, during the lithiation / delithiation process, it is accompanied by significant volume expansion, which easily leads to stress accumulation inside the electrode and mechanical damage to the active material. Selecting a suitable silicon-based material and combining it with the use of the self-healing binder of the present invention can effectively alleviate this problem. The self-healing binder of the present invention can not only enhance the adhesion between the above-mentioned active material and the current collector, but also restore the structural integrity and conductivity of the electrode through its own repair mechanism after the electrode is damaged, reduce pulverization and exfoliation, which is beneficial to maintaining a high energy density while extending the service life of the battery.

[0042] In another typical embodiment of the present invention, a secondary battery is further provided, including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet is the negative electrode sheet of the present invention as described above, and it has significantly improved structural stability and cycle life.

[0043] Typical but non-limiting, by weight, when guar gum is 0.1-5 parts, the acrylic polymer is 0.5-2 parts, and the flexible chain segment polymer is 0.5-5 parts. Specifically, when guar gum is 0.1 part, 0.5 part, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts or the range value composed of any two of these values, the acrylic polymer is 0.5 part, 1 part, 1.5 parts, 2 parts or the range value composed of any two of these values, and the flexible chain segment polymer is 0.5 part, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts or the range value composed of any two of these values.

[0044] Typical but non-limiting, the weight average molecular weight of the acrylic polymer is 1000, 10000, 100000, 200000, 300000, 400000, 450000 or the range value composed of any two of these values.

[0045] Typically but not limited to, the weight-average molecular weight of the flexible segment polymer is 1000, 10000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000 or a range value composed of any two of these numerical values.

[0046] Typically but not limited to, the weight-average molecular weight of the negative electrode self-healing binder is 10000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000 or a range value composed of any two of these numerical values.

[0047] Typically but not limited to, the weight ratio of the initiator to guar gum is 0.01:1, 0.05:1, 0.10:1, 0.15:1, 0.20:1, 0.25:1, 0.30:1 or a range value composed of any two of these numerical values.

[0048] Typically but not limited to, the weight ratio of the crosslinking agent to guar gum is 0.002:1, 0.005:1, 0.010:1, 0.020:1, 0.030:1, 0.040:1, 0.050:1, 0.060:1 or a range value composed of any two of these numerical values.

[0049] Typically but not limited to, the weight percentage of the negative electrode self-healing binder in the negative electrode slurry is 5%, 6%, 7%, 8%, 9%, 10% or a range value composed of any two of these numerical values.

[0050] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed in the present application.

[0051] Example 1

[0052] Step S1, weigh 100 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Subsequently, weigh guar gum (1.0 g) and disperse it in the water to obtain a guar gum solution.

[0053] Step S2, sequentially add polyacrylic acid (high molecular weight, weight-average molecular weight 450000, 1.0 g) and polyethylene oxide (low molecular weight, weight-average molecular weight 10000, 1.0 g) to the guar gum solution. Place the above flask in a 50 °C constant temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a cross-linking raw material solution (mass concentration 0.029 g / mL).

[0054] Step S3: Weigh 0.03 g of initiator (ammonium persulfate), dissolve it in water to obtain an initiator solution (mass concentration: 0.0015 g / mL), weigh 0.003 g of crosslinking agent (N,N'-methylenebisacrylamide), dissolve it in water to obtain a crosslinking agent solution (mass concentration: 0.0003 g / mL), transfer them to a constant pressure funnel respectively, and place the constant pressure funnel on a four-necked flask.

[0055] Step S4: Pass high-purity N₂ into the above solution to remove the air in the flask. Open the stopcock of the constant pressure funnel, add the initiator and the crosslinking agent into the above flask respectively, and carry out water bath stirring (50 °C, 4 h) to obtain a self-healing binder for the negative electrode.

[0056] Example 2

[0057] Step S1: Weigh 100 g of deionized water, place it in a 250 mL three-necked round-bottom flask, and then weigh 5.0 g of guar gum and disperse it in water to obtain a guar gum solution.

[0058] Step S2: Add polyacrylic acid (high molecular weight, weight average molecular weight 450000, 1.0 g) and polyethylene oxide (low molecular weight, weight average molecular weight 10000, 1.0 g) to the guar gum solution in sequence. Place the above flask in a constant temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a crosslinking raw material solution (mass concentration: 0.065 g / mL).

[0059] Step S3: Weigh 0.03 g of initiator (ammonium persulfate), dissolve it in water to obtain an initiator solution (mass concentration: 0.0015 g / mL), weigh 0.003 g of crosslinking agent (N,N'-methylenebisacrylamide), dissolve it in water to obtain a crosslinking agent solution (mass concentration: 0.0003 g / mL), transfer them to a constant pressure funnel respectively, and place the constant pressure funnel on a four-necked flask.

[0060] Step S4: Pass high-purity N₂ into the above solution to remove the air in the flask. Open the stopcock of the constant pressure funnel, add the initiator and the crosslinking agent into the above flask respectively, and carry out water bath stirring (50 °C, 4 h) to obtain a self-healing binder for the negative electrode.

[0061] Example 3

[0062] Step S1: Weigh 100 g of deionized water, place it in a 250 mL three-necked round-bottom flask, and then weigh 1.0 g of guar gum and disperse it in water to obtain a guar gum solution.

[0063] Step S2, successively add polyacrylic acid (high molecular weight, weight average molecular weight 450,000, 1.0 g) and polyethylene oxide (low molecular weight, weight average molecular weight 10,000, 5.0 g) into the guar gum solution. Place the above flask in a constant temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a cross-linking raw material solution (mass concentration 0.065 g / mL);

[0064] Step S3, weigh the initiator (ammonium persulfate 0.03 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.0015 g / mL). Weigh the cross-linking agent (N,N'-methylenebisacrylamide 0.003 g) and dissolve it in water to obtain a cross-linking agent solution (mass concentration 0.0003 g / mL). Transfer them to dropping funnels respectively and place the dropping funnels on the four-necked flask;

[0065] Step S4, introduce high-purity N2 into the above solution to remove the air in the flask. Open the stopcock of the dropping funnel, add the initiator and the cross-linking agent into the above flask respectively, and carry out water bath stirring (50 °C, 4 h) to obtain a negative electrode self-healing binder.

[0066] Example 4

[0067] Step S1, weigh 100 g of deionized water and place it in a 250 mL three-necked round bottom flask. Then weigh guar gum (1.0 g) and disperse it in water to obtain a guar gum solution;

[0068] Step S2, successively add polyacrylic acid (high molecular weight, weight average molecular weight 450,000, 1.0 g) and polyethylene oxide (low molecular weight, weight average molecular weight 10,000, 1.0 g) into the guar gum solution. Place the above flask in a constant temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a cross-linking raw material solution (mass concentration 0.029 g / mL);

[0069] Step S3, weigh the initiator (ammonium persulfate 0.15 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.0075 g / mL). Weigh the cross-linking agent (N,N'-methylenebisacrylamide 0.06 g) and dissolve it in water to obtain a cross-linking agent solution (mass concentration 0.006 g / mL). Transfer them to dropping funnels respectively and place the dropping funnels on the four-necked flask;

[0070] Step S4, introduce high-purity N2 into the above solution to remove the air in the flask. Open the stopcock of the dropping funnel, add the initiator and the cross-linking agent into the above flask respectively, and carry out water bath stirring (50 °C, 4 h) to obtain a negative electrode self-healing binder.

[0071] Example 5

[0072] Step S1: Weigh 100 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Subsequently, weigh guar gum (1.0 g) and disperse it in the water to obtain a guar gum solution.

[0073] Step S2: Sequentially add polyacrylic acid (high molecular weight, weight-average molecular weight 450,000, 1.0 g) and polyethylene oxide (low molecular weight, weight-average molecular weight 10,000, 1.0 g) to the guar gum solution. Place the above flask in a constant temperature water bath and rapidly stir for half an hour to make it homogeneous, obtaining a cross-linking raw material solution (mass concentration 0.029 g / mL).

[0074] Step S3: Weigh the initiator (ammonium persulfate 0.03 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.0015 g / mL). Weigh the cross-linking agent (N,N'-methylenebisacrylamide 0.003 g) and dissolve it in water to obtain a cross-linking agent solution (mass concentration 0.0003 g / mL). Transfer them to dropping funnels respectively and place the dropping funnels on a four-necked flask.

[0075] Step S4: Pass high-purity N2 into the above solution to remove the air in the flask. Open the stopcock of the dropping funnel, add the initiator and the cross-linking agent to the above flask respectively, and perform water bath stirring (60 °C, 4 h) to obtain a negative electrode self-healing binder.

[0076] Example 6

[0077] Step S1: Weigh 100 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Subsequently, weigh guar gum (0.1 g) and disperse it in the water to obtain a guar gum solution.

[0078] Step S2: Sequentially add polyacrylic acid (high molecular weight, weight-average molecular weight 450,000, 0.5 g) and polyethylene oxide (low molecular weight, weight-average molecular weight 10,000, 5.0 g) to the guar gum solution. Place the above flask in a constant temperature water bath and rapidly stir for half an hour to make it homogeneous, obtaining a cross-linking raw material solution (mass concentration 0.061 g / mL).

[0079] Step S3: Weigh the initiator (ammonium persulfate 0.03 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.0015 g / mL). Weigh the cross-linking agent (N,N'-methylenebisacrylamide 0.003 g) and dissolve it in water to obtain a cross-linking agent solution (mass concentration 0.0003 g / mL). Transfer them to dropping funnels respectively and place the dropping funnels on a four-necked flask.

[0080] Step S4: Pass high-purity N2 into the above solution to remove the air in the flask. Open the stopcock of the dropping funnel, add the initiator and the cross-linking agent to the above flask respectively, and perform water bath stirring (50 °C, 4 h) to obtain a negative electrode self-healing binder.

[0081] Example 7

[0082] Step S1: Weigh 100 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Then weigh guar gum (5 g) and disperse it in the water to obtain a guar gum solution.

[0083] Step S2: Sequentially add polyacrylic acid (high molecular weight, weight-average molecular weight 450000, 2 g) and polyethylene oxide (low molecular weight, weight-average molecular weight 10000, 0.5 g) to the guar gum solution. Place the above flask in a constant temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a cross-linking raw material solution (mass concentration 0.070 g / mL).

[0084] Step S3: Weigh the initiator (ammonium persulfate 0.03 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.0015 g / mL). Weigh the cross-linking agent (N,N'-methylenebisacrylamide 0.003 g) and dissolve it in water to obtain a cross-linking agent solution (mass concentration 0.0003 g / mL). Transfer them to dropping funnels respectively and place the dropping funnels on a four-necked flask.

[0085] Step S4: Pass high-purity N2 into the above solution to remove the air in the flask. Open the stopcock of the dropping funnel, add the initiator and the cross-linking agent into the above flask respectively, and carry out water bath stirring (50 °C, 4 h) to obtain a self-healing binder for the negative electrode.

[0086] Example 8

[0087] Step S1: Weigh 27 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Then weigh guar gum (1.0 g) and disperse it in the water to obtain a guar gum solution.

[0088] Step S2: Sequentially add polyacrylic acid (medium molecular weight, weight-average molecular weight 10000, 1.0 g) and polyethylene oxide (high molecular weight, weight-average molecular weight 500000, 1.0 g) to the guar gum solution. Place the above flask in a constant temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a cross-linking raw material solution (mass concentration 0.10 g / mL).

[0089] Step S3: Weigh the initiator (sodium persulfate 0.03 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.001 g / mL). Weigh the cross-linking agent (glutaraldehyde 0.003 g) and dissolve it in water to obtain a cross-linking agent solution (mass concentration 0.0002 g / mL). Transfer them to dropping funnels respectively and place the dropping funnels on a four-necked flask.

[0090] Step S4: Introduce high-purity N₂ into the above solution to remove the air in the flask. Open the stopcock of the constant-pressure funnel, add the initiator and the crosslinking agent into the above flask respectively, and carry out water-bath stirring (50 °C, 4 h) to obtain the self-healing binder for the negative electrode.

[0091] Example 9

[0092] Step S1: Weigh 147 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Then weigh guar gum (1.0 g) and disperse it in the water to obtain a guar gum solution.

[0093] Step S2: Sequentially add polyacrylic acid (medium molecular weight, weight-average molecular weight 10,000, 1.0 g) and polyethylene oxide (high molecular weight, weight-average molecular weight 500,000, 1.0 g) into the guar gum solution. Place the above flask in a constant-temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a crosslinking raw material solution (mass concentration 0.02 g / mL).

[0094] Step S3: Weigh the initiator (potassium persulfate 0.03 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.002 g / mL). Weigh the crosslinking agent (N,N'-methylenebisacrylamide 0.003 g) and dissolve it in water to obtain a crosslinking agent solution (mass concentration 0.0003 g / mL). Transfer them to the constant-pressure funnel respectively and place the constant-pressure funnel on the four-necked flask.

[0095] Step S4: Introduce high-purity N₂ into the above solution to remove the air in the flask. Open the stopcock of the constant-pressure funnel, add the initiator and the crosslinking agent into the above flask respectively, and carry out water-bath stirring (50 °C, 4 h) to obtain the self-healing binder for the negative electrode.

[0096] Example 10

[0097] Step S1: Weigh 100 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Then weigh guar gum (1.0 g) and disperse it in the water to obtain a guar gum solution.

[0098] Step S2: Sequentially add polyacrylic acid (high molecular weight, weight-average molecular weight 450,000, 1.0 g) and polyethylene oxide (low molecular weight, weight-average molecular weight 10,000, 1.0 g) into the guar gum solution. Place the above flask in a constant-temperature water bath and stir rapidly for half an hour to make it homogeneous, obtaining a crosslinking raw material solution (mass concentration 0.029 g / mL).

[0099] Step S3: Weigh 0.03 g of initiator (ammonium persulfate), dissolve it in water to obtain an initiator solution (mass concentration: 0.0015 g / mL), weigh 0.003 g of crosslinking agent (N,N - methylenebisacrylamide), dissolve it in water to obtain a crosslinking agent solution (mass concentration: 0.0003 g / mL), transfer them to dropping funnels respectively, and place the dropping funnels on a four - necked flask.

[0100] Step S4: Pass high - purity N₂ into the above - mentioned solution to remove the air in the flask. Open the stopcock of the dropping funnel, add the initiator and the crosslinking agent into the above - mentioned flask respectively, and carry out water - bath stirring (40 °C, 8 h) to obtain the self - healing binder for the negative electrode.

[0101] Example 11

[0102] Step S1: Weigh 100 g of deionized water, place it in a 250 - mL three - necked round - bottom flask, then weigh 1.0 g of guar gum and disperse it in water to obtain a guar gum solution.

[0103] Step S2: Sequentially add 1.0 g of polyacrylic acid (high molecular weight, weight - average molecular weight 450000) and 1.0 g of polyethylene oxide (low molecular weight, weight - average molecular weight 10000) into the guar gum solution. Place the above - mentioned flask in a constant - temperature water - bath, stir rapidly for half an hour to make it homogeneous, and obtain a cross - linking raw material solution (mass concentration: 0.029 g / mL).

[0104] Step S3: Weigh 0.03 g of initiator (ammonium persulfate), dissolve it in water to obtain an initiator solution (mass concentration: 0.0015 g / mL), weigh 0.003 g of crosslinking agent (N,N - methylenebisacrylamide), dissolve it in water to obtain a crosslinking agent solution (mass concentration: 0.0003 g / mL), transfer them to dropping funnels respectively, and place the dropping funnels on a four - necked flask.

[0105] Step S4: Pass high - purity N₂ into the above - mentioned solution to remove the air in the flask. Open the stopcock of the dropping funnel, add the initiator and the crosslinking agent into the above - mentioned flask respectively, and carry out water - bath stirring (70 °C, 2 h) to obtain the self - healing binder for the negative electrode.

[0106] Example 12

[0107] The difference from Example 1 is that in Step S2, 1.0 g of polymethacrylic acid (weight - average molecular weight 100000) and 1.0 g of polycaprolactone (weight - average molecular weight 800000) are sequentially added into the guar gum solution. Place the above - mentioned flask in a 50 °C constant - temperature water - bath, stir rapidly for half an hour to make it homogeneous, and obtain a cross - linking raw material solution.

[0108] Example 13

[0109] The difference from Example 1 is that in step S2, sodium polyacrylate (weight-average molecular weight 200,000, 1.0 g) and polysiloxane (weight-average molecular weight 600,000, 1.0 g) are successively added to the guar gum solution. The above flask is placed in a constant temperature water bath at 50 °C and rapidly stirred for half an hour to make it uniform, obtaining a cross-linked raw material solution.

[0110] Comparative Example 1

[0111] Step S1, weigh 100 g of deionized water and place it in a 250 mL three-necked round-bottom flask. Subsequently, weigh guar gum (1.0 g) and disperse it in water to obtain a guar gum solution;

[0112] Step S2, place the above flask in a constant temperature water bath and rapidly stir for half an hour to make it uniform, obtaining a raw material solution (mass concentration 1 g / mL);

[0113] Step S3, weigh an initiator (ammonium persulfate 0.03 g) and dissolve it in water to obtain an initiator solution (mass concentration 0.0015 g / mL), weigh a cross-linking agent (N,N-methylenebisacrylamide 0.003 g) and dissolve it in water to obtain a cross-linking agent solution (mass concentration 0.0003 g / mL), transfer them to a constant pressure funnel respectively, and place the constant pressure funnel on a four-necked flask;

[0114] Step S4, introduce high-purity N2 into the above solution to remove the air in the flask, open the stopcock of the constant pressure funnel, add the initiator and the cross-linking agent to the above flask respectively, and carry out water bath stirring (50 °C, 4 h) to obtain a self-healing negative electrode binder.

[0115] Comparative Example 2

[0116] The difference from Example 1 is that guar gum is not used.

[0117] Comparative Example 3

[0118] The difference from Example 1 is that polyacrylic acid is not used.

[0119] Comparative Example 4

[0120] The difference from Example 1 is that polyethylene oxide is not used.

[0121] Performance test:

[0122] The binders obtained from the above-mentioned examples and comparative examples were used to prepare silicon-based anode sheets, which were assembled into coin-type half-cells. The specific operations were as follows: They were mixed according to the weight ratio of silicon-carbon active material (theoretical specific capacity is about 600 mAh / g): conductive carbon black: binder = 80:10:10, and slurried with deionized water as the solvent. Subsequently, the above-mentioned slurry was coated on copper foil. After vacuum drying at 80 °C for 12 h, the anode sheet was taken out, cut into pieces, and assembled into a coin-type battery. Among them, the electrolyte used was a silicon-carbon electrolyte, and the separator used was a PP separator.

[0123] The obtained coin-type batteries were left standing for 12 h at 25 ± 2 °C, and then charge-discharge tests were carried out on a NEWARE BTS-5V / 10mA type charge-discharge tester produced by Shenzhen Neware Electronic Co., Ltd. The charge-discharge voltage range was 0.005 - 2.0 V, and the current density was 0.1 C. The first-cycle charge specific capacity, the first-cycle Coulombic efficiency, and the 50-cycle performance were tested respectively.

[0124] The compositions of the binders in the above-mentioned examples and comparative examples are shown in Table 1, and the electrochemical test results are shown in Table 2.

[0125] Table 1

[0126]

[0127]

[0128] Table 2

[0129] Sample Initial Coulombic efficiency (%) Initial charge specific capacity (mAh / g) Capacity retention rate after 50 cycles (%) Example 1 89.6 533.5 93.2 Example 2 89.3 533.9 92.3 Example 3 88.7 564.7 91.6 Example 4 86.2 532.8 86.7 Example 5 85.9 534.9 85.3 Example 6 85.3 545.6 84.9 Example 7 84.8 537.2 84.5 Example 8 84.6 541.6 83.4 Example 9 83.2 553.8 83.1 Example 10 83.3 539.7 82.6 Example 11 82.6 536.1 82.3 Example 12 89.7 533.4 93.4 Example 13 89.5 533.1 93.0 Comparative Example 1 70.9 513.7 71.8 Comparative Example 2 71.8 532.1 78.6 Comparative Example 3 72.5 528.7 75.5 Comparative Example 4 71.4 522.8 78.3

[0130] It can be seen that in Comparative Example 1, acrylic polymers and flexible-chain polymers were not used. Therefore, the flexibility of the binder was insufficient, and the anode expanded and cracked after charge-discharge, resulting in the exfoliation of the active material and a decrease in the first-cycle Coulombic efficiency. In Comparative Example 2, guar gum was not used. Therefore, the rigidity of the binder was insufficient, causing the structure of the anode to collapse after charge-discharge and a decrease in the first-cycle Coulombic efficiency. In Comparative Example 3, acrylic polymers were not used. Therefore, the binder lacked carboxyl groups, the hydrogen bond interaction was weakened, the self-healing performance was poor, and the cycle stability of the anode decreased. In Comparative Example 4, flexible-chain polymers were not used. Therefore, the flexibility of the binder was insufficient, and the active material pulverized and exfoliated after charge-discharge of the anode, resulting in a decrease in the first-cycle Coulombic efficiency and the cycle performance. The self-healing binder of the present invention can significantly alleviate the volume expansion problem of the silicon-based anode during charge-discharge through its unique three-dimensional network structure and the abundance of hydrogen bonds, reduce anode pulverization and the exfoliation of the active material, thereby improving the cycle performance and rate performance of the silicon-based anode and extending the cycle life of the battery. Experimental data show that the silicon-based anode battery prepared with this binder is superior to the traditional binder system in terms of the first-cycle Coulombic efficiency, the first-cycle charge specific capacity, and the capacity retention rate after 50 cycles.

[0131] As can be seen from the above, compared with the comparative example, the negative electrode self-healing binder of the present invention is a three-dimensional network binder that combines rigidity and flexibility and has self-healing properties. This binder is rich in hydrogen bonds and has self-healing properties at room temperature, which can effectively alleviate the volume expansion of the silicon-based negative electrode during charge and discharge, and reduce the accumulation of internal stress and crack generation in the electrode caused by volume expansion, preventing electrode pulverization and the exfoliation of active materials from the current collector, thereby significantly improving the stability of the electrode structure, enhancing the cycle performance of the battery and prolonging the cycle life.

[0132] In addition, it can be seen that when each process parameter is within the preferred range of the present invention, the comprehensive effect is better.

[0133] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A negative electrode self-repairing binder, characterized in that, The negative electrode self-healing binder is a chemical cross-linked product, and the cross-linking raw materials include guar gum, acrylic polymer, and flexible segment polymer.

2. The negative electrode self-repairing binder according to claim 1, wherein The molar ratio of the guar gum, the acrylic polymer, and the flexible segment polymer is (0.1 - 5):(0.5 - 2):(0.5 - 5).

3. The negative electrode self-healing binder according to claim 1 or 2, wherein the acrylic polymer includes one or more of polyacrylic acid, polymethacrylic acid, sodium polyacrylate, and polyacrylate, and the weight-average molecular weight is 1000 - 450000; and / or the flexible segment polymer includes one or more of polyethylene oxide, polycaprolactone, polyethylene glycol, and polysiloxane, and the weight-average molecular weight is 1000 - 1000000.

4. The preparation method of the negative electrode self-repairing binder according to any one of claims 1 to 3, characterized in that, It includes the following steps: Step S1: Disperse the guar gum in water to obtain a guar gum solution. Step S2: Sequentially add the acrylic polymer and the flexible segment polymer to the guar gum solution to obtain a cross-linking raw material solution. Step S3: Dissolve the initiator in water to obtain an initiator solution, and dissolve the cross-linking agent in water to obtain a cross-linking agent solution. Step S4: Under an inert atmosphere, simultaneously add the initiator solution and the cross-linking agent solution to the cross-linking raw material solution, and perform water bath stirring. After freeze-drying, the negative electrode self-healing binder is obtained.

5. The preparation method of the negative electrode self-healing binder according to claim 4, wherein the initiator includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; and / or the weight ratio of the initiator to the guar gum is (0.01 - 0.30):

1.

6. The preparation method of the negative electrode self-healing binder according to claim 4 or 5, wherein the cross-linking agent includes one or more of N,N-methylenebisacrylamide, glutaraldehyde, and tetraethyl orthosilicate; and / or the weight ratio of the cross-linking agent to the guar gum is (0.002 - 0.060):

1.

7. The preparation method of the negative electrode self-healing binder according to any one of claims 4 to 6, wherein the inert atmosphere is one or more of a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere; and / or the temperature of the water bath stirring is 40 - 70°C, and the time is 2 - 8 h.

8. A negative electrode sheet, comprising a current collector and a negative electrode paste loaded on at least one surface of the current collector, the negative electrode paste comprising a negative electrode active material, a conductive additive, and a binder, characterized in that, The binder is the negative electrode self-healing binder according to any one of claims 1 to 3.

9. The negative electrode sheet according to claim 8, wherein The negative electrode active material is a silicon-based material, and the weight percentage of the negative electrode self-healing binder in the negative electrode slurry is 5 - 10%.

10. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that, The negative electrode sheet is the negative electrode sheet according to claim 8 or 9.

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