An aqueous composite binder for silicon-based anodes of lithium-ion batteries and a preparation method and application thereof

Abstract

The application discloses a water-based composite binder for a silicon-based negative electrode of a lithium ion battery and a preparation method and application thereof, and belongs to the technical field of lithium batteries. The water-based composite binder for inhibiting volume expansion of the silicon-based negative electrode is prepared by cross-linking fucoidan and gallic acid. The water-based composite binder prepared by the application has the advantages of good dispersibility, self-healing property and strong adhesion. The three-dimensional network structure formed after the binder is cross-linked is beneficial to the transmission of electrons and ions, greatly improves the mechanical property and interface stability of the binder, enables the SiOx electrode to maintain good integrity in a cycle process, effectively inhibits the volume expansion of the SiOx negative electrode material in the charging and discharging process of the electrode, and enables the SiOx negative electrode to exhibit good cycle stability and durability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to an aqueous composite binder for a silicon-based anode of a lithium-ion battery, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries have become the mainstream commercial power supply system in fields such as mobile electronic devices, laptop computers, digital cameras, and new energy vehicles due to their advantages such as high capacity, no memory effect, fast charge and discharge ability, and high Coulomb efficiency. Among many anode materials, silicon-based materials are regarded as an important candidate system for the next-generation high-capacity anode because their theoretical specific capacity of about 4200 mAh / g significantly exceeds the unit capacity of traditional graphite anodes (372 mAh / g). However, silicon undergoes a huge volume expansion (up to 300%) during the process of lithium deintercalation and intercalation, which easily leads to particle breakage, pulverization, and electrode structure failure, severely restricting its cycle life and commercial application. Therefore, SiO x (0 < x < 2) materials have received extensive attention in recent years, but they still have a volume change of 100 - 200% and still face defects such as rapid battery capacity decay and poor rate performance.

[0003] Regarding the volume expansion problem of the SiO x anode, the existing solution strategies mainly include methods such as nanosizing, structuring, and compounding. However, these methods generally have limitations such as complex preparation processes, high costs, and difficulties in large-scale production. Among many solution paths, the optimization of the binder is considered to be one of the effective ways to alleviate volume expansion due to its cost-effectiveness and feasibility. The traditional CMC-SBR binder relies on physical adsorption between the active material and the current collector and lacks chemical bond action, resulting in poor adhesion. In recent years, researchers have been working on developing new high-performance composite binder systems to improve the structural integrity of the electrode during cycling to improve the electrochemical performance of the SiO x anode.

[0004] Fucoidan, as a natural renewable polysaccharide resource derived from brown algae, has good water solubility, dispersibility, and biodegradability, and shows stronger adhesion potential compared to traditional binders (such as CMC-SBR). However, due to the electrostatic repulsion of the charged sulfate ester groups on its molecular chain, the molecules adopt a linear conformation, and the adhesion performance is still insufficient to effectively inhibit the stress damage of the SiO x anode during cycling, and further improvement is still needed. Summary of the Invention

[0005] The purpose of this invention is to provide an aqueous composite binder for silicon-based anodes in lithium-ion batteries, its preparation method, and its application, thereby addressing the aforementioned problems in the background art. The aqueous composite binder prepared by this invention possesses advantages such as good dispersibility, self-healing properties, and strong adhesion. The three-dimensional network structure formed after cross-linking facilitates electron and ion transport and significantly improves the mechanical properties and interfacial stability of the binder. This allows the SiOx electrode to maintain good integrity during cycling and effectively suppresses the volume expansion of the SiOx anode material during charge and discharge, resulting in excellent cycle stability and durability for the SiOx anode.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of the present invention is to provide an aqueous composite binder (abbreviated as FUC-GA) for suppressing the volume expansion of silicon-based negative electrodes, which is prepared by crosslinking fucoidan and gallic acid.

[0008] Preferably, the mass ratio of fucoidan to gallic acid is 1:1 to 2.

[0009] Preferably, the fucoidan has a relative molecular mass range of 1 × 10⁻⁶. 4 ~1×10 5 Da.

[0010] The second technical solution of the present invention provides a method for preparing the above-mentioned aqueous composite binder for suppressing the volume expansion of silicon-based negative electrodes, comprising the following steps:

[0011] Fucoidan and gallic acid were mixed in water and subjected to a hydrogen bond crosslinking reaction to obtain the aqueous composite binder used to suppress the volume expansion of silicon-based anodes.

[0012] Preferably, the mass ratio of fucoidan to water is 1:19-20; and the hydrogen bond cross-linking reaction time is 10-12 h.

[0013] The third technical solution of the present invention provides an application of the above-mentioned water-based composite binder in the field of suppressing volume expansion of silicon-based anodes.

[0014] Fourth technical solution of the present invention: A method for preparing an expansion-suppressing silicon-based anode, using the above-mentioned aqueous composite binder as the binder for the silicon-based anode, the preparation method includes the following steps:

[0015] The aqueous composite binder, electrode active material, and conductive agent are mixed to obtain a uniformly dispersed electrode slurry.

[0016] The electrode paste is coated onto the current collector, and a crosslinking reaction is carried out to obtain the expansion-suppressed silicon-based anode.

[0017] Preferably, the electrode active material is SiO x , where 0 < x < 2; the conductive agent is carbon nanotubes and / or carbon black; the mass ratio of the aqueous composite binder, electrode active material and conductive agent is 5-10:70-80:10-20, more preferably 1:7-8:1-2; the temperature of the crosslinking reaction is 80 °C and the time is 10-12 h.

[0018] More preferably, the carbon black is Super P or acetylene black.

[0019] The present invention promotes the crosslinking reaction between fucoidan and gallic acid by heating to improve the degree of crosslinking.

[0020] The fifth technical solution of the present invention: Provide a silicon-based negative electrode with swelling inhibition obtained according to the above preparation method.

[0021] The sixth technical solution of the present invention: Provide an application of the above silicon-based negative electrode with swelling inhibition in the field of negative electrode materials for lithium-ion batteries.

[0022] The technical principle of the present invention is as follows:

[0023] The present invention uses fucoidan as the main chain and crosslinks it with gallic acid to obtain a composite binder with a three-dimensional network structure. Under certain temperature conditions, the sulfate group of fucoidan will crosslink with the phenolic hydroxyl group of gallic acid to form a composite binder with a three-dimensional network structure. In addition, the formed three-dimensional network structure is beneficial to the transmission of electrons and ions, and also greatly improves the mechanical properties of the binder, making the SiO x electrode maintain good integrity during the cycling process. The binder prepared by this method can significantly improve the electrochemical performance of the SiO x negative electrode of lithium-ion batteries. In addition, the preparation process of this binder is simple, low-cost, environmentally friendly, etc., and it is easy to meet the requirements of industrialization.

[0024] Fucoidan is a high molecular polysaccharide with a long molecular chain and a certain branched structure, which can provide multiple binding sites; while gallic acid, as a small molecule, can bind to the molecular chain of fucoidan through multiple hydrogen bond sites. With the continuous occurrence of hydrogen bond crosslinking, individual molecular chains are connected to multiple surrounding molecular chains through hydrogen bonds, gradually forming an interpenetrating space network. The polar groups of the two can be combined with each other through intermolecular hydrogen bonds (such as between hydroxyl groups and hydroxyl groups, hydroxyl groups and carboxyl groups).

[0025] The beneficial technical effects of the present invention are as follows:

[0026] The aqueous composite binder prepared in this invention for suppressing the volume expansion of silicon-based anodes has advantages such as good dispersibility, self-healing properties, and strong adhesion. The three-dimensional network structure formed after cross-linking facilitates electron and ion transport and greatly improves the mechanical properties and interfacial stability of the binder, enabling SiO2 to... x The electrode maintains good integrity during cycling, effectively suppressing SiO₂ formation during electrode charging and discharging. x The volume expansion of the negative electrode material causes SiO to... x The negative electrode exhibits good cycle stability and durability. The binder is simple to prepare, inexpensive, and environmentally friendly, and can significantly improve the SiO₂ content of lithium-ion batteries. x The electrochemical performance of the negative electrode has great application value.

[0027] The composite binder of this invention selects natural high-molecular-weight fucoidan as the main chain of the binder, and crosslinks it with low-molecular-weight gallic acid to precisely control the formation of a composite binder with a three-dimensional network structure. The water-based composite binder of this invention is combined with SiO₂. x The particles have abundant binding sites, allowing the binder to bind with SiO₂. x The particles have strong interfacial bonding ability, thus enabling SiO2 to... x The negative electrode can better withstand volume changes during the charging and discharging process of the electrode. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The graph shows the cycle performance of the coin cell prepared in Application Example 1.

[0030] Figure 2 The graph shows a comparison of the cycle performance of the coin cells prepared in Application Example 1 and Comparative Example 1. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0032] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0034] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0035] The relative molecular mass of fucoidan used in the following embodiments and comparative examples of this invention is 1 × 10⁻⁶. 4 ~1×10 5 Da.

[0036] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0037] Example 1

[0038] A method for preparing an aqueous composite binder for suppressing volume expansion of silicon-based anodes, comprising the following steps:

[0039] Fucoidan and gallic acid were uniformly dispersed in deionized water at a mass ratio of 2:3 to obtain a mixed solution with a fucoidan concentration of 50 mg / mL. The solution was subjected to hydrogen bond crosslinking reaction at 80 °C for 12 h to obtain an aqueous composite binder solution with a three-dimensional network structure, denoted as FUC-GA.

[0040] Example 2

[0041] A method for preparing an aqueous composite binder for suppressing volume expansion of silicon-based anodes, comprising the following steps:

[0042] Fucoidan and gallic acid were uniformly dispersed in deionized water at a mass ratio of 2:3 to obtain a mixed solution with a fucoidan concentration of 50 mg / mL. The solution was subjected to hydrogen bond crosslinking reaction at 60 °C for 12 h to obtain an aqueous composite binder solution with a three-dimensional network structure.

[0043] Application Example 1

[0044] Electrochemical performance testing:

[0045] (1) The active material SiO x The conductive agent Super P and FUC-GA from Example 1 were mixed at a mass ratio of 8:1:1 and stirred in a degassing mixer to obtain a uniformly dispersed electrode slurry. The electrode slurry was coated onto a copper foil and vacuum dried at 80°C for 12 hours (drying helps stabilize the reaction and promotes cross-linking). The slurry was then cut into a circular silicon-based negative electrode sheet with a diameter of 12 mm.

[0046] (2) The silicon-based negative electrode was transferred into an argon-filled glove box. A lithium sheet was used as the counter electrode. The electrolyte consisted of 1.0 mmol / L LiPF6 as the solute and ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio as the solvent. 10 wt% and 1 wt% of fluoroethylene carbonate (FEC) and ethylene carbonate (VC) were added as additives, respectively, based on the total mass of the electrolyte. CR2032 coin cells were assembled, and the assembled coin cells were left to stand at 28°C for 10 hours. The stood cells (denoted as FUC-GA@SiO) were then... x The electrochemical performance was tested using a constant current test system in the Newway testing system. The test conditions were: current density 500 mA / g.

[0047] Figure 1 The graph shows the cycle performance of the coin cell prepared in Application Example 1.

[0048] Depend on Figure 1 It can be seen that the SiO2 composition using the water-based composite binder (FUC-GA) of Example 1... x At a current density of 500 mA / g, the electrode exhibits an initial discharge specific capacity of approximately 2321 mAh / g and an initial coulombic efficiency of approximately 61%. After 100 cycles, the capacity remains at 1158 mAh / g. These results demonstrate that using the aqueous composite binder from Example 1 as a raw material can produce SiO₂... x The negative electrode exhibits good cycle stability.

[0049] Comparative Example 1

[0050] Electrochemical performance testing:

[0051] (1) Add 0.5g of fucoidan to 9.5g of deionized water to obtain 5wt% binder, denoted as FUC.

[0052] active material SiO x The conductive agent SuperP and the above-mentioned FUC are mixed at a mass ratio of 8:1:1 and stirred in a degassing mixer to obtain a uniformly dispersed electrode slurry. The electrode slurry is coated onto a copper foil, vacuum dried at 80°C for 12 hours, and cut into a circular silicon-based negative electrode sheet with a diameter of 12 mm.

[0053] (2) The silicon-based negative electrode was transferred into an argon-filled glove box. A lithium electrode was used as the counter electrode. The electrolyte consisted of 1.0 mmol / L LiPF6 as the solute and ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio as the solvent, with 10 wt% fluoroethylene carbonate (FEC) and 1 wt% ethylene carbonate (VC) as additives. CR2032 coin cells were assembled, and the assembled coin cells were left to stand at 28°C for 10 hours. The stood cells (denoted as FUC@SiO) were then... x The electrochemical performance was tested using a constant current test system in the Newway testing system. The test conditions were: current density 500 mA / g.

[0054] Figure 2 The graph shows a comparison of the cycle performance of the coin cells prepared in Application Example 1 and Comparative Example 1.

[0055] Figure 2 The results show that the coin cell prepared in Comparative Example 1 exhibits a capacity decay of 287 mAh / g after 100 cycles at a current density of 500 mA / g, while the coin cell prepared in Application Example 1 maintains a capacity of 1158 mAh / g, demonstrating higher discharge capacity and better cycle stability. This proves that the aqueous composite binder (FUC-GA) of Example 1 can effectively bind SiO₂. x The negative electrode exhibits good cycle stability.

[0056] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A water-based composite binder for suppressing volume expansion of silicon-based anodes, characterized in that, It was prepared by cross-linking fucoidan and gallic acid; The mass ratio of fucoidan to gallic acid is 1:1~2; The relative molecular mass range of the fucoidan is 1×10⁻⁶. 4 ~1×10 5 Da; The method for preparing the aqueous composite binder for suppressing volume expansion of silicon-based anodes includes the following steps: Fucoidan and gallic acid were mixed in water and subjected to a hydrogen bond crosslinking reaction to obtain the aqueous composite binder used to suppress the volume expansion of silicon-based anodes.

2. The aqueous composite binder for suppressing volume expansion of silicon-based anodes according to claim 1, characterized in that, The mass ratio of fucoidan to water is 1:19~20; the hydrogen bond cross-linking reaction takes 10~12 h.

3. The application of the water-based composite binder according to any one of claims 1 to 2 in the field of suppressing volume expansion of silicon-based anodes.

4. A method for preparing an expansion-suppressed silicon-based anode, characterized in that, The preparation method of using the water-based composite binder according to any one of claims 1 to 2 as a binder for a silicon-based negative electrode includes the following steps: The aqueous composite binder, electrode active material, and conductive agent are mixed to obtain an electrode slurry; The electrode paste is coated onto the current collector, and a crosslinking reaction is carried out to obtain the expansion-suppressed silicon-based anode.

5. The preparation method according to claim 4, characterized in that, The electrode active material is SiO x , where 0 < x < 2; the conductive agent is carbon nanotubes and / or carbon black; the mass ratio of the aqueous composite binder, electrode active material and conductive agent is 5-10:70-80:10-20; the temperature of the cross-linking reaction is 80 °C and the time is 10-12 h.

6. An expansion-suppressed silicon-based anode obtained by the preparation method according to any one of claims 4-5.

7. The application of the expansion-suppressing silicon-based anode as described in claim 6 in the field of lithium-ion battery anode materials.

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