A highly fluorinated polyamide acid-based silicon-based pole piece functional adhesive, preparation method and application

Abstract

The application provides a highly fluorinated polyamide acid silicon-based cathode functional adhesive and application, which is synthesized by reaction of fluorinated diamine-based small molecules, fluorinated dianhydride-based small molecules and amine-based cross-linking agents at room temperature, and has a highly fluorinated three-dimensional cross-linking network structure. The high content of fluorine atoms in the adhesive can help generate a LiF-based stable SEI phase inside the silicon-based cathode, the abundant carbonyl and carboxylic acid groups can form strong interactions with the silicon-based active particles and copper current collectors, and the adhesive has the characteristics of dynamic self-adaptive volume change, thereby solving the core problem of volume expansion of the silicon-based cathode from the aspects of structural buffering and interface stabilization. The preparation process of the application is simple, the yield is high, the prepared lithium ion battery has a capacity retention rate of 86% or more after 80 cycles at a rate of 0.5C, the coulombic efficiency is continuously higher than 99%, and the lithium ion battery exhibits excellent cycle stability and reliable adhesion.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a highly fluorinated polyamic acid-based silicon-based electrode functional binder, its preparation method, and its application in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and energy storage power stations due to their advantages such as high energy density, long cycle life, and environmental friendliness. To further improve battery energy density, silicon-based anode materials have attracted much attention due to their ultra-high theoretical specific capacity (approximately 3579 mAh / g).

[0003] However, silicon undergoes volume expansion and contraction of over 300% during lithium insertion / extraction, leading to problems such as silicon particle pulverization, severe damage to the electrode structure, and separation of the current collector from the active material. This results in a sharp decline in capacity and coulombic efficiency. Therefore, how to buffer the huge volume changes of silicon-based active materials at the electrode level is one of the core challenges restricting the practical application of silicon-based anodes.

[0004] As a key functional component in silicon-based electrodes, the binder plays a crucial role in organically connecting silicon particles, conductive agents, and current collectors, and has a decisive impact on the mechanical integrity, interfacial stability, and long cycle life of the electrode. In the existing technology, polyacrylic acid (PAA), due to its abundant carboxyl groups and excellent adhesion to copper current collectors and silicon surfaces, has become one of the most commonly used water-based binders for silicon anodes.

[0005] However, PAA is a linear polymer with strong hydrogen bonding between its chain segments, resulting in high modulus and significant brittleness in its bulk material. Under the cyclic stress generated by the repeated expansion and contraction of silicon particles, PAA binder is prone to irreversible plastic deformation, brittle fracture, and bonding failure, making it difficult to adapt to the large volume changes of silicon-based anodes over long periods.

[0006] To address the aforementioned problems in PAAs and improve the flexibility and adaptability of binders, existing technologies have attempted to enhance the fatigue resistance of binders through chemical crosslinking, the introduction of functional monomers, or the construction of dynamic bonds. Other technologies utilize highly flexible frameworks such as polyvinyl alcohol (PVA) combined with hydrogen bonds or coordination bonds to construct three-dimensional networks, thereby achieving a certain degree of self-healing capability. However, these systems often require additional complex synthesis steps, and some matrix polymers do not significantly promote lithium-ion transport. Furthermore, they lack functional groups that can assist in the formation of a stable solid electrolyte interphase (SEI) phase in silicon-based anodes, failing to address the volume expansion problem of silicon-based anodes from both interface and structural perspectives.

[0007] Furthermore, PAA molecules contain only C, H, and O elements, lacking fluorine. Fluorine is a core element of lithium fluoride (LiF), a key component in the solid electrolyte interphase (SEI) of the electrode interface. LiF, as one of the most stable and ionicly conductive components in the SEI film, directly affects the film's density and cycle stability. Therefore, PAA binders contribute very little to the formation of LiF in the SEI film, making it difficult to optimize and control the SEI film through binder molecule design. Summary of the Invention

[0008] The first objective of this invention is to provide a highly fluorinated polyamic acid-based silicon-based electrode functional binder.

[0009] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution: A highly fluorinated polyamic acid-based silicon-based electrode functional binder, wherein the binder is a cross-linked polyamic acid-based binder, and its synthetic raw materials include at least: fluorinated diamine small molecules, fluorinated dianhydride small molecules, and anamine cross-linking agent; the binder is synthesized at room temperature and has a highly fluorinated three-dimensional network structure, with a fluorine element mass ratio of not less than 20%. The stoichiometric ratio of the fluorinated diamine small molecule, the fluorinated dianhydride small molecule, and the amine crosslinking agent is 1:x:(x-1)×2 / 3, where 1<x≤1.1.

[0010] The aforementioned highly fluorinated polyamic acid-based silicon-based electrode functional binder has abundant carbonyl and carboxyl groups and a high content of fluorine atoms. Its thermal decomposition temperature is higher than 300°C. During the charging and discharging process of lithium-ion batteries, it can form dynamic molecular interactions with silicon-based active particles, achieving dynamic self-adaptation to changes in the volume of silicon-based active particles.

[0011] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred technical solution of the present invention, the preferred value of x is 1.02.

[0012] As a preferred embodiment of the present invention, the fluorinated diamine small molecule is at least one of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2′-bis(trifluoromethyl)diaminobiphenyl, and 4,4′-diaminooctafluorobiphenyl.

[0013] As a preferred embodiment of the present invention, the fluorinated dianhydride small molecule is at least one of 4,4′-(hexafluoroisopropylidene) phthalic anhydride, 2,3,5,6-tetrafluorophthalic anhydride, and hexafluorodianhydride.

[0014] As a preferred embodiment of the present invention, the amine crosslinking agent is at least one of 1,3,5-tris(4-aminophenyl)benzene, tris(4-aminophenyl)amine, and 1,3,5-triaminobenzene.

[0015] The second objective of this invention is to provide a method for preparing a highly fluorinated polyamic acid-based silicon-based electrode functional binder.

[0016] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution: A method for preparing a highly fluorinated polyamic acid-based silicon-based electrode functional binder includes the following steps: S1. Add a small molecule of fluorinated diamine to an anhydrous aprotic polar solvent and stir until completely dissolved under nitrogen protection and at room temperature to obtain an amine solution. S2. Add fluorinated dianhydride small molecules to the amine solution in step S1, and stir continuously at room temperature for 8-16 h to obtain polyamic acid prepolymer solution; S3. Add an amine crosslinking agent to the polyamic acid prepolymer solution in step S2, and continue stirring at room temperature for 8-16 h to allow a crosslinking reaction to occur, thereby obtaining a highly fluorinated crosslinked polyamic acid viscous solution, which is the silicon-based electrode adhesive. The amount of the anhydrous aprotic polar solvent added, calculated as the amount of fluorinated diamine small molecules, is 5-10 mL / mmol.

[0017] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred embodiment of the present invention: the anhydrous aprotic polar solvent is N,N -Dimethylacetamide, N,N -Dimethylformamide, N At least one of methylpyrrolidone.

[0018] As a preferred embodiment of the present invention, the fluorinated diamine small molecule is at least one of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2′-bis(trifluoromethyl)diaminobiphenyl, and 4,4′-diaminooctafluorobiphenyl.

[0019] As a preferred embodiment of the present invention, the fluorinated dianhydride small molecule is at least one of 4,4′-(hexafluoroisopropylidene) phthalic anhydride, 2,3,5,6-tetrafluorophthalic anhydride, and hexafluorodianhydride.

[0020] As a preferred embodiment of the present invention, the amine crosslinking agent is at least one of 1,3,5-tris(4-aminophenyl)benzene, tris(4-aminophenyl)amine, and 1,3,5-triaminobenzene.

[0021] The third objective of this invention is to provide a silicon-based electrode.

[0022] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution: A silicon-based electrode, the electrode comprising a silicon-based active material, a conductive agent, and a highly fluorinated polyamic acid-based silicon-based electrode functional binder as described above, wherein the three are in the following mass ratio: silicon-based active material: conductive agent: highly fluorinated polyamic acid-based silicon-based electrode functional binder (6~8): (1~2): (1~2).

[0023] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred embodiment of the present invention: the silicon-based active material is a silicon / carbon composite with a theoretical specific capacity of 1800 mAh / g; the conductive agent is Super P.

[0024] As a preferred embodiment of the present invention, the method for preparing the silicon-based electrode includes the following steps: (1) Dissolve 0.1 g of silicon-based electrode binder in 3 mL of DMAC solvent and stir until homogeneous to obtain slurry A; (2) Grind 0.8 g of silicon-based active material and 0.1 g of conductive agent in a mortar and pestle to obtain mixed powder B; (3) Pour the mixed powder B into the slurry A and stir for 12 h to obtain the mixed slurry C; (4) The mixed slurry C is uniformly coated on copper foil and dried at 100°C for 12 h to obtain silicon-based electrode sheets.

[0025] The fourth objective of this invention is to provide a lithium-ion battery.

[0026] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution: A lithium-ion battery includes a lithium metal negative electrode, a positive electrode, a separator, and an electrolyte, wherein the positive electrode is a silicon-based electrode as described above; and the electrolyte is a fluorinated lithium salt electrolyte.

[0027] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred embodiment of the present invention, the electrolyte is 1.0 M lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, and contains 10 vol% fluoroethylene carbonate (FEC) as an additive.

[0028] As a preferred embodiment of the present invention, the lithium-ion battery is a button cell. The assembly steps of the button half-cell include: in an argon-protected glove box, using a silicon-based electrode as the working electrode, a lithium metal sheet as the counter electrode and reference electrode, and Celgard 2400 as the separator, the above electrolyte is added, and then packaged by a button cell packaging machine to obtain a CR2032 type lithium-ion button half-cell.

[0029] During battery charging and discharging, due to the intermolecular interaction between polyamic acid and silicon-based active particles in the electrode, the silicon-based particles preferentially break to release stress when the volume of the silicon-based particles expands, and can spontaneously recover after delithiation and shrinkage, thus achieving dynamic self-adaptation to changes in the volume of silicon-based active particles.

[0030] This invention addresses the technical shortcomings of existing silicon-based electrode binders, including complex synthesis, high brittleness, inability to dynamically adapt to changes in silicon particle volume, and difficulty in assisting the formation of a stable SEI phase. It provides a highly fluorinated polyamic acid-based functional binder for silicon-based electrodes and its preparation method, along with silicon-based electrodes and lithium-ion batteries prepared using this binder. The binder of this invention can be efficiently synthesized at room temperature, with a simple and high-yield preparation process. Furthermore, it solves the core problem of volume expansion in silicon-based electrodes from both structural buffering and interface stability perspectives, significantly improving the cycle stability and bonding reliability of lithium-ion batteries.

[0031] Specifically, compared with the prior art, the present invention has the following beneficial effects: (1) The binder of the present invention uses fluorinated diamine small molecules, fluorinated dianhydride small molecules and amine crosslinking agent as raw materials. It can be synthesized and crosslinked at room temperature without the need for harsh reaction conditions such as high temperature and high pressure. The preparation process is simple and efficient, and the yield can reach more than 95%, which is suitable for large-scale industrial production. (2) The binder of the present invention is a highly fluorinated three-dimensional cross-linked network structure with a high fluorine content, which can assist in the generation of a stable SEI phase with LiF-based material inside the silicon electrode. LiF has high mechanical strength and good lithium-ion transport performance, which can effectively suppress the repeated breakage and reconstruction of the SEI phase, reduce the continuous consumption of electrolyte, and improve the coulombic efficiency and cycle stability of the battery. (3) The binder molecules contain abundant carbonyl and carboxylic acid groups, which can form strong hydrogen bonds and coordination interactions with silicon-based active particles and copper current collectors, enhance the bonding strength between the components of the electrode, effectively suppress the shedding of active particles and the peeling of current collectors during charging and discharging, and maintain the integrity of the electrode structure. (4) The cross-linked polyamic acid binder of the present invention has the characteristic of dynamic adaptive volume change. When the volume of silicon-based particles expands, the molecular interaction between the binder and silicon particles breaks preferentially to release stress and avoid the electrode structure from being cracked. After delithiation and shrinkage, the molecular interaction can spontaneously recover and re-encapsulate and bond the silicon particles, thus buffering the volume change of the silicon-based electrode from the structure and solving the problems of brittle fracture and irreversible deformation of traditional linear PAA binders. (5) The binder of the present invention has extremely high thermal and chemical stability, with a thermal decomposition temperature higher than 300°C. It does not degrade significantly within a wide temperature range of battery charging and discharging (-20°C to 60°C) and does not react with electrolyte or silicon-based active materials. It can maintain bonding performance and structural stability for a long time. (6) The silicon-based electrode of the present invention has optimized the proportion of each component. The three-dimensional network structure of the binder can form a continuous lithium-ion transport channel in the electrode. Combined with the LiF-based SEI phase, it can improve the transport efficiency of lithium ions inside the electrode. At the same time, the bonding strength of the electrode can reach more than 1.2 N / cm, which is much higher than that of the electrode prepared by traditional PAA binder. (7) The lithium-ion battery prepared using the binder of the present invention exhibits excellent cycle stability. After 80 cycles at a 0.5C rate, the capacity retention rate can still reach more than 86%, and the coulombic efficiency remains higher than 99%, which solves the core problem of short cycle life of silicon-based anode batteries. Attached Figure Description

[0032] Figure 1 The graph shows the cycling performance of the silicon-carbon negative electrode lithium-ion battery prepared using the binder of this invention at a rate of 0.5C. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0034] All raw materials used in this invention are commercially available conventional raw materials, and unless otherwise specified, the experimental methods are conventional methods.

[0035] Example 1: Preparation of a highly fluorinated polyamic acid-based silicon electrode binder Add 5 mL of anhydrous DMAC solvent to a three-necked flask, and under nitrogen protection and at room temperature (25℃), add 320 mg (1.0 mmol) of 2,2′-bis(trifluoromethyl)diaminobiphenyl (TFMB), and stir for 5 min until completely dissolved to obtain a TFMB solution; 453 mg (1.02 mmol) of 4,4′-(hexafluoroisopropene) phthalic anhydride (6FDA) was added to the above TFMB solution, and the mixture was stirred continuously at room temperature for 12 h to obtain a polyamic acid prepolymer solution. 4.6 mg (0.013 mmol) of 1,3,5-tris(4-aminophenyl)benzene (TAPB) was added to the above polyamic acid prepolymer solution, and the mixture was stirred at room temperature for 12 h to induce a crosslinking reaction, resulting in a viscous, highly fluorinated crosslinked polyamic acid solution, which is a silicon-based electrode binder with a yield of 98% and a fluorine content of approximately 27%.

[0036] Example 2: Preparation of silicon-based electrode sheets Take 0.1 g of the crosslinked polyamic acid binder prepared in Example 1, dissolve it in 3 mL of DMAC solvent, and stir at room temperature for 2 h until completely dissolved to obtain slurry A; Take 0.8 g of silicon / carbon composite with a theoretical specific capacity of 1800 mAh / g and 0.1 g of Super P conductive agent, grind them in a mortar for 30 min until they are mixed to obtain mixed powder B; The mixed powder B was slowly poured into slurry A and magnetically stirred at room temperature for 12 hours to obtain a uniform mixed slurry C. The mixed slurry C was uniformly coated onto a 10 μm thick copper foil using a doctor blade, with a coating surface density of 1.05~1.34 mg / cm³. 2 The coated copper foil was placed in a vacuum drying oven and dried at 100°C for 12 h to remove the solvent, thus obtaining a silicon-based electrode.

[0037] Example 3 Assembly of a lithium-ion button half-cell In an argon-protected glove box (water and oxygen content <0.1 ppm), using the silicon-based electrode prepared in Example 2 as the working electrode, a 1 mm thick lithium metal sheet as the counter electrode and reference electrode, and Celgard 2400 as the separator, 1.0 M LiPF6 in EC:DEC=1:1 vol% with 10% FEC electrolyte was added dropwise, with 80 μL added per electrode. The cells were then packaged using a CR2032 button cell packaging machine to obtain lithium-ion button half-cells.

[0038] Comparative Example 1 Commercial linear polyacrylic acid (PAA) was used as a binder. Silicon-based electrodes were prepared according to the raw material ratio (silicon / carbon composite: Super P: PAA = 8:1:1) and preparation method of Example 2. Lithium-ion button half-cells were then assembled according to the method of Example 3, with the remaining conditions being the same as in Example 3.

[0039] Electrochemical performance tests were conducted on the lithium-ion button half-cells of Example 3 and Comparative Example 1. The test conditions were: room temperature (25°C), 0.5C rate constant current charge-discharge, and a voltage window of 0.01~1.5V. The test results are as follows: Cyclic performance: such as Figure 1 As shown, Figure 1 The graph shows the cycle performance of the silicon-carbon anode lithium-ion battery prepared using the binder of this invention at a 0.5C rate. The horizontal axis represents the number of cycles (0-80), and the vertical axis represents the battery's discharge specific capacity (mAh / g) (0-3000). The curve label is: Li-SiC -1.05 -1.34 mg / cm³. 2 -0.5C represents a surface density of 1.05~1.34 mg / cm³. 2 The cycling performance of the silicon / carbon anode at 0.5C rate was observed. The battery in Example 3 retained 86.2% of its capacity after 80 cycles at 0.5C, with an initial discharge specific capacity of 2850 mAh / g, and maintained a discharge specific capacity of 2457 mAh / g after 80 cycles. Coulombic efficiency: The battery of Example 3 maintained a coulombic efficiency above 99.2% throughout the entire cycle, with no significant capacity decay; the battery of Comparative Example 1 had a larger fluctuation in coulombic efficiency, which dropped below 95% after 20 cycles.

[0040] Electrode bonding strength: The bonding strength between the silicon-based electrode and the copper current collector in Example 2 was 1.32 N / cm, and after 50 charge-discharge cycles, the bonding strength remained at 1.05 N / cm; the initial bonding strength of the electrode in Comparative Example 1 was 0.85 N / cm, and after 20 cycles, the bonding strength dropped to 0.2 N / cm, with obvious active particle detachment.

[0041] Thermal stability: The binder of Example 1, when heated at 300°C for 2 hours, showed a mass loss of only 3.5% and still maintained a three-dimensional cross-linked structure; the commercial PAA, when heated at 200°C for 2 hours, showed a mass loss of 25% and underwent melt deformation.

[0042] The above test results show that the highly fluorinated polyamic acid-based silicon electrode binder of the present invention can significantly improve the bonding strength and thermal stability of silicon electrode, effectively solve the problem of volume expansion of silicon electrode, and greatly improve the cycle stability and coulombic efficiency of lithium-ion batteries.

[0043] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A highly fluorinated polyamic acid-based silicon-based electrode functional binder, characterized in that, The binder is a cross-linked polyamic acid-based binder, and its synthetic raw materials include at least: fluorinated diamine-based small molecules, fluorinated dianhydride-based small molecules, and anamine-based cross-linking agent; the binder is synthesized at room temperature and has a highly fluorinated three-dimensional network structure, with a fluorine element mass ratio of not less than 20%. The stoichiometric ratio of the fluorinated diamine small molecule, the fluorinated dianhydride small molecule, and the amine crosslinking agent is 1:x:(x-1)×2 / 3, where 1<x≤1.

1.

2. The silicon-based electrode functional binder according to claim 1, characterized in that, The preferred value for x is 1.

02.

3. The silicon-based electrode functional binder according to claim 1, characterized in that, The fluorinated diamine small molecule is at least one of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2′-bis(trifluoromethyl)diaminobiphenyl, and 4,4′-diaminooctafluorobiphenyl.

4. The silicon-based electrode functional binder according to claim 1, characterized in that, The fluorinated dianhydride small molecule is at least one of 4,4′-(hexafluoroisopropylidene) phthalic anhydride, 2,3,5,6-tetrafluorophthalic anhydride, and hexafluorodianhydride.

5. The silicon-based electrode functional binder according to claim 1, characterized in that, The amine crosslinking agent is at least one of 1,3,5-tris(4-aminophenyl)benzene, tris(4-aminophenyl)amine, and 1,3,5-triaminobenzene.

6. A method for preparing a highly fluorinated polyamic acid-based silicon-based electrode functional binder, characterized in that, Includes the following steps: S1. Add a small molecule of fluorinated diamine to an anhydrous aprotic polar solvent and stir until completely dissolved under nitrogen protection and at room temperature to obtain an amine solution. S2. Add fluorinated dianhydride small molecules to the amine solution in step S1, and stir continuously at room temperature for 8-16 h to obtain polyamic acid prepolymer solution; S3. Add an amine crosslinking agent to the polyamic acid prepolymer solution in step S2, and continue stirring at room temperature for 8-16 h to allow a crosslinking reaction to occur, thereby obtaining a highly fluorinated crosslinked polyamic acid viscous solution, which is the silicon-based electrode adhesive. The amount of the anhydrous aprotic polar solvent added, calculated as the amount of fluorinated diamine small molecules, is 5~10 mL / mmol.

7. A silicon-based electrode, characterized in that, The electrode comprises a silicon-based active material, a conductive agent, and a highly fluorinated polyamic acid-based silicon-based electrode functional binder as described in any one of claims 1 to 5, wherein the three are in the following mass ratio: silicon-based active material: conductive agent: highly fluorinated polyamic acid-based silicon-based electrode functional binder = (6 to 8): (1 to 2): (1 to 2).

8. A lithium-ion battery, characterized in that, It includes a lithium metal anode, a cathode, a separator, and an electrolyte, wherein the cathode is a silicon-based electrode as described in claim 7; and the electrolyte is a fluorinated lithium salt electrolyte.

9. The lithium-ion battery according to claim 8, characterized in that, The electrolyte is 1.0 M lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, and contains 10 vol% fluoroethylene carbonate (FEC) as an additive.

10. The lithium-ion battery according to claim 8, characterized in that, The lithium-ion battery is a button cell.

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