Flexible conductive adhesive for silicon-carbon negative electrode of lithium ion battery, preparation method and silicon-carbon negative electrode of lithium ion battery

Abstract

The invention discloses a flexible conductive binder for a silicon-carbon negative electrode of a lithium ion battery, a preparation method of the flexible conductive binder and the silicon-carbon negative electrode of the lithium ion battery, and relates to the technical field of electrode materials of the lithium ion battery. The composite material is composed of 5-15% of a double dynamic bond polymer containing catechol and boric acid groups, 0.5-5% of carboxylated multi-walled carbon nanotubes in gradient distribution, and the balance of an ionic liquid / water mixed solvent. The double-dynamic-bond polymer contains hydrogen bonds / coordination bonds and dynamic borate bonds and can be dynamically self-repaired; the carboxylated multi-walled carbon nanotubes are in gradient distribution with dense inside and sparse outside, the concentration of an interface region is higher, during preparation, a polymer is prepared through reversible addition-fragmentation chain transfer polymerization, a conductive filler is added in stages to form gradient distribution, and a dynamic cross-linked network is constructed through standing and curing. The binder has strong binding power, high flexibility, efficient conductivity and self-repairing capability, can relieve volume expansion stress when applied to a silicon-carbon negative electrode, and ensures that an electrode structure is stable.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrode materials technology, and more specifically, to a flexible conductive binder for lithium-ion battery silicon-carbon anodes, a preparation method thereof, and a lithium-ion battery silicon-carbon anode. Background Technology

[0002] Lithium-ion batteries have been widely used in new energy vehicles, portable electronic devices and other fields due to their advantages such as high energy density and long cycle life. Silicon-carbon anode materials have become the core candidate materials for improving battery energy density because their theoretical specific capacity (4200 mAh / g) is much higher than that of traditional graphite anodes (372 mAh / g). However, silicon-carbon materials will undergo more than 300% volume expansion / contraction during charging and discharging, which will cause the electrode structure to crack and the active material to fall off, seriously damaging the integrity of the electrode. At the same time, silicon itself is a semiconductor with poor electronic conductivity, and it is necessary to rely on conductive agents to build an electron transport path. However, volume expansion can easily cause the conductive network to break, further aggravating capacity decay.

[0003] As the skeleton of the electrode, the binder must simultaneously meet the requirements of strong adhesion, structural flexibility, electronic / ionic conductivity, and stress buffering capacity. Existing silicon-carbon anode binders have significant shortcomings: traditional oil-based binders (such as PVDF) have strong adhesion but poor flexibility, cannot alleviate volume expansion stress, and lack conductivity; water-based binders (such as CMC and SBR) have improved flexibility but insufficient adhesion strength, and are prone to debonding after long-term cycling; although some conductive binders introduce conductive fillers such as carbon nanotubes and graphene, the fillers are uniformly distributed, the concentration of conductive fillers in the interface region is insufficient, the electron transport efficiency is low, and they lack dynamic self-healing ability, and cannot repair structural damage caused by volume changes. In addition, the molecular chains of existing binders are mostly static structures, which are prone to irreversible breakage under repeated volume expansion and contraction of silicon-carbon materials, resulting in poor electrode cycle stability, making it difficult to meet the long-cycle use requirements of high-energy-density lithium-ion batteries, thus limiting the industrial application of silicon-carbon anodes.

[0004] In summary, conductive adhesives suffer from problems such as an imbalance between adhesion and flexibility, easy breakage of the conductive network, lack of dynamic self-healing ability, and poor cycle stability. Summary of the Invention

[0005] To overcome the problems of imbalance between bonding force and flexibility, easy breakage of conductive network, lack of dynamic self-healing ability, and poor cycle stability of existing conductive adhesives, this invention discloses a flexible conductive adhesive for silicon-carbon anodes of lithium-ion batteries, a preparation method, and a silicon-carbon anode for lithium-ion batteries that can effectively solve the above-mentioned technical problems.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A flexible conductive binder for silicon-carbon anodes in lithium-ion batteries, the binder having a three-dimensional interpenetrating network structure and comprising the following components by mass percentage:

[0008] Polymers containing catechol and boric acid groups with double dynamic bonds, 5-15%;

[0009] Gradient-distributed carboxylated multi-walled carbon nanotubes, 0.5-5%;

[0010] Balance of ionic liquid / water mixed solvent;

[0011] The dual dynamic bond polymer is poly(acrylic acid-co-dopamine methacrylamide-co-vinylphenylboronic acid), in which the catechol groups in the molecular chain can form hydrogen bonds / coordination bonds, and the phenylboronic acid groups can form dynamic borate ester bonds with the hydroxyl groups or vicinal diol structures in the molecular chain; the carboxylated multi-walled carbon nanotubes in the binder exhibit a gradient distribution with denser inner layers and sparser outer layers, with a higher concentration near the interface than inside the bulk.

[0012] Furthermore, the poly(acrylic acid-co-dopamine methacrylamide-co-vinylphenylboronic acid) is prepared by reversible addition-fragmentation chain transfer polymerization, wherein the molar ratio of monomers acrylic acid, dopamine methacrylamide, and vinylphenylboronic acid is (50-70):(20-30):(10-20), and the number average molecular weight is 50,000-200,000 g / mol.

[0013] Furthermore, the ionic liquid / water mixed solvent is composed of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and deionized water in a volume ratio of 1:4 to 1:9.

[0014] Furthermore, the carboxylated multi-walled carbon nanotubes have a carboxyl content of 1.5-3.0 mmol / g, a diameter of 10-20 nm, and a length of 5-20 μm. 60% of the carboxylated multi-walled carbon nanotubes are used to construct high-concentration interfacial conductive regions, and 40% are used to construct low-concentration bulk conductive regions.

[0015] Furthermore, the breaking / recombining temperature range of the dynamic borate ester bond is 25-80℃, and dynamic self-repair can be achieved under the volume expansion / contraction stress during the charging and discharging process of the silicon-carbon anode.

[0016] Furthermore, a method for preparing a flexible conductive adhesive includes the following steps:

[0017] A polymer with double dynamic bonds containing catechol and boric acid groups was prepared by polymerizing acrylic acid, dopamine methacrylamide and vinylphenylboronic acid monomers through a reversible addition-fragmentation chain transfer polymerization process.

[0018] Carboxylated multi-walled carbon nanotubes were divided into two parts, and high-concentration conductive slurry A and low-concentration dispersion B were prepared respectively.

[0019] The double dynamic bond polymer was completely dissolved in an ionic liquid / water mixed solvent to form a homogeneous solution C;

[0020] High-concentration conductive paste A is slowly added to solution C under high-speed stirring. After being dispersed evenly, low-concentration dispersion B is added and mixed gently.

[0021] The mixture is allowed to stand and mature, allowing the polymer chains to form a dynamic cross-linked network. At the same time, carboxylated multi-walled carbon nanotubes are fixed in situ within the network, resulting in a flexible conductive adhesive.

[0022] Furthermore, the preparation process of the high-concentration conductive paste A is as follows: 60% of carboxylated multi-walled carbon nanotubes are dispersed in an ionic liquid / aqueous solution containing 5-10% of a double dynamic bond polymer, and dispersed at a high speed of 20,000-30,000 r / min for 10-20 min; the preparation process of the low-concentration dispersion B is as follows: 40% of carboxylated multi-walled carbon nanotubes are dispersed in a pure ionic liquid / aqueous solution, and ultrasonically dispersed for 30-60 min.

[0023] Furthermore, the reaction conditions for the reversible addition-fragmentation chain transfer polymerization process are as follows: azobisisobutyronitrile is used as the initiator, the total molar ratio of initiator to monomer is 1:100-1:200, the reaction temperature is 60-80℃, the reaction time is 8-12 h, and the reaction solvent is dimethylformamide.

[0024] Furthermore, the conditions for static curing are: temperature 25-40℃, humidity 30-50%, curing time 12-24 h, during which the phenylboronic acid groups on the polymer chain undergo dynamic cross-linking reactions with the ortho-dihydroxy and carboxyl groups.

[0025] Furthermore, a silicon-carbon anode for a lithium-ion battery includes a silicon-carbon active material, a conductive agent, a flexible conductive binder, and a current collector. The flexible conductive binder bonds and fixes the silicon-carbon active material and the conductive agent to the surface of the current collector, and its internal gradient conductive network forms an efficient electron transport pathway with the silicon-carbon active material. The dynamic borate bond network can alleviate the volume expansion stress of the silicon-carbon active material.

[0026] Compared with existing technologies, the beneficial effects of this invention are as follows: This flexible conductive adhesive forms a tight causal optimization chain through multi-component synergistic design, exhibiting outstanding practical value. Because it employs a double dynamic bond polymer containing catechol and boric acid groups, the hydrogen bonds / coordination bonds formed by the catechol groups enhance the interfacial adhesion to silicon-carbon materials and current collectors. The dynamic borate ester bonds formed by the phenylboronic acid groups (which can break / reassemble at 25-80℃) can dynamically self-repair under the volume expansion / contraction stress of silicon-carbon materials, effectively repairing electrode structure damage and solving the problems of insufficient flexibility and inability to alleviate volume expansion stress in traditional adhesives. Furthermore, because the carboxylated multi-walled carbon nanotubes exhibit a gradient distribution with a dense inner layer and a sparse outer layer, 60% high-concentration filler constructs the interfacial conductive region, and 40% low-concentration filler constructs the bulk conductive network, ensuring both... This binder achieves efficient electron transport between the active material and the current collector while avoiding insufficient interfacial conductivity caused by uniform distribution, thus improving electrode conductivity. The use of an ionic liquid / water mixed solvent ensures good dispersion of the polymer and conductive filler, while also promoting lithium-ion transport and improving the electrode's ionic conductivity. Furthermore, the staged addition of conductive filler followed by static curing allows for the in-situ formation of a three-dimensional interpenetrating network structure, firmly fixing the conductive filler within the network and preventing network breakage due to volume expansion. This ensures long-term cycle stability of the electrode. In summary, this binder simultaneously achieves strong adhesion, high flexibility, high conductivity, and self-healing functions, effectively solving the problems of volume expansion, easy breakage of the conductive network, and short cycle life in silicon-carbon anodes, providing key technological support for the industrialization of high-energy-density lithium-ion batteries. Attached Figure Description

[0027] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary. For those skilled in the art, other embodiments can be derived from the provided drawings without creative effort.

[0028] Figure 1 This is a structural diagram of the flexible conductive adhesive of the present invention;

[0029] Figure 2 This is a process flow diagram of the preparation method of the present invention. Detailed Implementation

[0030] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0031] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions.

[0032] It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] Example

[0035] This embodiment addresses the core problems of severe volume expansion (over 300%), easy breakage of conductive networks, and poor cycle stability during the charging and discharging of silicon-carbon anodes in lithium-ion batteries. It discloses a specific preparation process, performance parameters, and application scheme of a three-dimensional interpenetrating network structure flexible conductive binder in silicon-carbon anodes. By precisely controlling the polymerization conditions of the double dynamic bond polymer, the gradient distribution construction method of carboxylated multi-walled carbon nanotubes, and the proportion of each component, the binder is ensured to simultaneously possess strong adhesion, high flexibility, high conductivity, and dynamic self-healing ability.

[0036] A flexible conductive binder for silicon-carbon anodes in lithium-ion batteries, the binder having a three-dimensional interpenetrating network structure and comprising the following components by mass percentage:

[0037] Polymers containing catechol and boric acid groups with double dynamic bonds, 5-15%;

[0038] Gradient-distributed carboxylated multi-walled carbon nanotubes, 0.5-5%;

[0039] Balance of ionic liquid / water mixed solvent;

[0040] The dual dynamic bond polymer is poly(acrylic acid-co-dopamine methacrylamide-co-vinylphenylboronic acid), in which the catechol groups in the molecular chain can form hydrogen bonds / coordination bonds, and the phenylboronic acid groups can form dynamic borate ester bonds with the hydroxyl groups or vicinal diol structures in the molecular chain; the carboxylated multi-walled carbon nanotubes in the binder exhibit a gradient distribution with denser inner layers and sparser outer layers, with a higher concentration near the interface than inside the bulk.

[0041] The poly(acrylic acid-co-dopamine methacrylamide-co-vinylphenylboronic acid) is prepared by reversible addition-fragmentation chain transfer polymerization, wherein the monomer molar ratio of acrylic acid, dopamine methacrylamide, and vinylphenylboronic acid is (50-70):(20-30):(10-20), and the number average molecular weight is 50,000-200,000 g / mol.

[0042] The ionic liquid / water mixed solvent is composed of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and deionized water in a volume ratio of 1:4 to 1:9.

[0043] The carboxylated multi-walled carbon nanotubes have a carboxyl content of 1.5-3.0 mmol / g, a diameter of 10-20 nm, and a length of 5-20 μm. 60% of the carboxylated multi-walled carbon nanotubes are used to construct high-concentration interfacial conductive regions, and 40% are used to construct low-concentration bulk conductive regions.

[0044] The dynamic borate ester bond has a breakage / recombination temperature range of 25-80℃, and can achieve dynamic self-repair under the volume expansion / contraction stress during the charging and discharging process of silicon-carbon anode.

[0045] A method for preparing a flexible conductive adhesive includes the following steps:

[0046] A polymer with double dynamic bonds containing catechol and boric acid groups was prepared by polymerizing acrylic acid, dopamine methacrylamide and vinylphenylboronic acid monomers through a reversible addition-fragmentation chain transfer polymerization process.

[0047] Carboxylated multi-walled carbon nanotubes were divided into two parts, and high-concentration conductive slurry A and low-concentration dispersion B were prepared respectively.

[0048] The double dynamic bond polymer was completely dissolved in an ionic liquid / water mixed solvent to form a homogeneous solution C;

[0049] High-concentration conductive paste A is slowly added to solution C under high-speed stirring. After being dispersed evenly, low-concentration dispersion B is added and mixed gently.

[0050] The mixture is allowed to stand and mature, allowing the polymer chains to form a dynamic cross-linked network. At the same time, carboxylated multi-walled carbon nanotubes are fixed in situ within the network, resulting in a flexible conductive adhesive.

[0051] The preparation process of the high-concentration conductive paste A is as follows: 60% of carboxylated multi-walled carbon nanotubes are dispersed in an ionic liquid / aqueous solution containing 5-10% of a double dynamic bond polymer, and dispersed at a high speed of 20,000-30,000 r / min for 10-20 min; the preparation process of the low-concentration dispersion B is as follows: 40% of carboxylated multi-walled carbon nanotubes are dispersed in a pure ionic liquid / aqueous solution, and dispersed ultrasonically for 30-60 min.

[0052] The reaction conditions for the reversible addition-fragmentation chain transfer polymerization process are as follows: azobisisobutyronitrile is used as the initiator, the total molar ratio of initiator to monomer is 1:100-1:200, the reaction temperature is 60-80℃, the reaction time is 8-12 h, and the reaction solvent is dimethylformamide.

[0053] The conditions for static curing are: temperature 25-40℃, humidity 30-50%, curing time 12-24 h. During the curing process, the phenylboronic acid groups on the polymer chain undergo dynamic cross-linking reactions with the ortho-dihydroxy and carboxyl groups.

[0054] A silicon-carbon anode for lithium-ion batteries includes a silicon-carbon active material, a conductive agent, a flexible conductive binder, and a current collector. The flexible conductive binder bonds and fixes the silicon-carbon active material and the conductive agent to the surface of the current collector, and its internal gradient conductive network forms an efficient electron transport pathway with the silicon-carbon active material. The dynamic borate bond network can alleviate the volume expansion stress of the silicon-carbon active material.

[0055] Please see Figures 1-2 In this embodiment, 100 grams of flexible conductive adhesive were prepared, and the raw materials and specifications were as follows:

[0056] Acrylic acid (analytical grade, purity ≥99.5%), dopamine methacrylamide (purity ≥98%, molecular weight 249.28 g / mol), vinylphenylboronic acid (purity ≥97%, molecular weight 161.94 g / mol), azobisisobutyronitrile (initiator grade, purity ≥98%), dimethylformamide (analytical grade, purity ≥99.8%), carboxylated multi-walled carbon nanotubes (carboxyl content 2.2 mmol / g, diameter 15 nm, length 10-15 μm), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ionic liquid grade, purity ≥99%), and deionized water (conductivity ≤10 μS / cm) were all precisely weighed according to the formula to ensure the accuracy and repeatability of the preparation process.

[0057] Preparation of double dynamic bond polymers (reversible addition-fracture chain transfer polymerization): A 500 mL three-necked flask reaction apparatus was constructed, equipped with a mechanical stirrer, a condenser, and a nitrogen inlet tube. The flask was placed in a constant temperature water bath, and 4.32 g of acrylic acid, 5.61 g of dopamine methacrylamide, and 2.18 g of vinylphenylboronic acid were added to the flask in a molar ratio of 60:25:15. Then, 40 mL of dimethylformamide was added as the reaction solvent, and mechanical stirring was started (300 r / min) to fully dissolve the monomers in the solvent and form a homogeneous reaction precursor solution.

[0058] High-purity nitrogen (purity ≥ 99.99%) is introduced into the reaction system for 30 minutes to completely remove oxygen from the system and prevent oxygen from inhibiting the polymerization reaction. The temperature of the constant temperature water bath is slowly raised to 70°C. After the system temperature stabilizes, 0.12 g of azobisisobutyronitrile (AIBN) pre-dissolved in 5 mL of dimethylformamide is added. The total molar ratio of initiator to monomer is 1:150. Nitrogen gas is introduced for another 5 minutes, and then the nitrogen valve is closed. The system is kept sealed and the reaction is carried out for 10 hours.

[0059] After the reaction was completed, the reaction solution was naturally cooled to room temperature and slowly poured into 200 mL of anhydrous diethyl ether to precipitate. The mixture was stirred for 30 minutes to allow the polymer to fully separate. After standing and separating into layers, the supernatant was poured off, and the polymer precipitate at the bottom was retained. The precipitate was placed in a vacuum drying oven and dried at 60 °C for 12 hours to remove residual solvent and impurities, yielding a pale yellow solid powder of a double dynamic bond polymer (poly(acrylic acid-co-dopamine methacrylamide-co-vinylphenylboronic acid)). Gel permeation chromatography showed that the polymer had a number-average molecular weight of 120,000 g / mol and a dispersion of 1.8, which met the design requirements.

[0060] The graded treatment and dispersion preparation of carboxylated multi-walled carbon nanotubes: 3 grams of carboxylated multi-walled carbon nanotubes were weighed and divided into two parts in a 6:4 ratio. 1.8 grams were used to prepare high-concentration conductive paste A and 1.2 grams were used to prepare low-concentration dispersion B. The graded treatment was used to achieve a gradient distribution of carbon nanotubes.

[0061] Preparation of high-concentration conductive paste A: Weigh 0.6 g of double dynamic bond polymer and dissolve it in 15 mL of ionic liquid / water mixed solvent (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and deionized water volume ratio 1:6). Stir until the polymer is completely dissolved to form a homogeneous polymer solution. Add 1.8 g of carboxylated multi-walled carbon nanotubes to the solution and place it in a high-speed shear disperser. Shear disperse at 25000 r / min for 15 minutes to fully disperse the carbon nanotubes and prevent them from agglomerating, forming a homogeneous and stable high-concentration conductive paste A.

[0062] Preparation of low-concentration dispersion B: Take 1.2 g of carboxylated multi-walled carbon nanotubes, add 30 mL of pure ionic liquid / water mixed solvent (volume ratio 1:6), place in an ultrasonic disperser (power 300W, frequency 40kHz), and ultrasonically disperse for 45 minutes. The ultrasonic cavitation effect breaks up the carbon nanotube aggregates to form a uniformly dispersed low-concentration dispersion B.

[0063] For the composite and curing of the flexible conductive adhesive, weigh 8 grams of double dynamic bond polymer (accounting for 8% of the total mass of the adhesive), add 80 ml of ionic liquid / water mixed solvent (volume ratio 1:6), place on a magnetic stirrer, and stir at 50°C for 2 hours until the polymer is completely dissolved to form a homogeneous and transparent solution C. Transfer solution C to a high-speed stirrer, maintain a speed of 800 r / min, and slowly add 15 ml of high-concentration conductive slurry A dropwise. Control the speed during the dropwise addition process to avoid excessive local concentration that could lead to agglomeration of carbon nanotubes. After the dropwise addition is completed, continue high-speed stirring for 30 minutes to ensure that the slurry and solution C are fully and uniformly mixed.

[0064] Reduce the stirring speed to 300 r / min, slowly add 30 ml of low-concentration dispersion B to the mixture, and stir gently for 60 minutes to allow the carbon nanotubes to gradually and evenly distribute in the system. At the same time, avoid high-speed stirring to prevent damage to the already formed dispersion structure. Transfer the mixture to a sealed container and place it in a constant temperature and humidity chamber. Set the temperature to 30℃ and the humidity to 40% and let it stand for 18 hours to mature.

[0065] During the curing process, the phenylboronic acid groups on the polymer chain undergo dynamic cross-linking reactions with the ortho-dihydroxy and carboxyl groups, gradually forming a three-dimensional interpenetrating network structure. At the same time, the carboxylated multi-walled carbon nanotubes are fixed in situ in the network. Due to the difference in addition order and concentration, a gradient distribution with denser inner layers and sparser outer layers is formed. After curing, a black viscous flexible conductive binder is obtained. Its solid content is tested to be 11% (8% double dynamic bond polymer + 3% carboxylated multi-walled carbon nanotubes), and its viscosity at 25℃ is 8500 mPa·s, which meets the requirements for the preparation and use of silicon-carbon anode electrodes.

[0066] Several key performance tests were conducted on the prepared flexible conductive adhesive to verify that the design indicators met the requirements. In the dynamic self-healing performance test, the adhesive was made into a 1 mm thick film, cut into two halves and then tightly bonded together. After standing at 25°C for 2 hours, the film could be re-bonded into a whole, with a tensile strength recovery rate of 82%; after standing at 60°C for 1 hour, the tensile strength recovery rate reached 95%, proving that the dynamic borate ester bond can be effectively broken and recombined in the range of room temperature to 80°C, and has excellent self-healing ability.

[0067] The conductivity test was conducted using the four-probe method. The results showed that the conductivity of the adhesive film interface region was 8.5 S / m and the conductivity of the bulk region was 2.3 S / m, exhibiting obvious gradient conductivity characteristics. It can provide an efficient electron transport path for the silicon-carbon anode. In the flexibility test, the adhesive film was repeatedly folded 180° 50 times without cracking. The elongation at break reached 320%, demonstrating excellent flexibility to adapt to the drastic volume changes during the charging and discharging process of silicon-carbon materials.

[0068] The adhesion strength test adopted the peel test method. The adhesive was applied to the surface of the copper foil current collector, and the silicon carbide powder was attached and then dried. The peel strength was 0.85 N / mm, which is significantly higher than that of the traditional CMC / SBR adhesive (0.32 N / mm). It can effectively bond the silicon carbide active material to the current collector firmly and prevent the active material from falling off.

[0069] The silicon-carbon anode was prepared by mixing the raw materials in the following mass percentages: 80% silicon-carbon active material (30% silicon content, hard carbon matrix), 5% conductive agent (Super P), 10% flexible conductive binder prepared in this embodiment (calculated based on solid content, the actual amount of binder solution with 11% solid content added was 9.09 g), and an appropriate amount of deionized water was added to adjust the viscosity of the slurry.

[0070] First, weigh 8 grams of silicon-carbon active material and 0.5 grams of Super P, and put them into a planetary ball mill. Dry mix them at 300 r / min for 30 minutes to ensure that the conductive agent is evenly dispersed on the surface of the active material, laying the foundation for the construction of the electronic transmission network. Transfer the dry-mixed powder to a high-speed disperser, add 9.09 grams of flexible conductive binder solution, and then add an appropriate amount of deionized water. Disperse at 1500 r / min for 60 minutes to form a uniform and fine electrode slurry. The viscosity of the slurry is controlled at about 5000 mPa·s to facilitate the coating operation.

[0071] The slurry was uniformly coated onto the surface of a 12μm thick copper foil current collector using a doctor blade coating method. The coating thickness was controlled to be 100μm (wet film). The coated copper foil was then placed in a 60℃ forced-air drying oven for 2 hours to remove most of the solvent. Subsequently, the dried electrode sheet was transferred to a vacuum drying oven and vacuum dried at 120℃ for 12 hours to completely remove residual moisture and volatile ionic liquids, thus avoiding the adverse effects of moisture on battery performance.

[0072] The electrode sheets were compacted using a roller press to control the compaction density at 1.5 g / cm³, which ensured both the density of the electrode structure and the provision of channels for ion transport. Finally, the compacted electrode sheets were cut into circular electrode sheets with a diameter of 14 mm to obtain silicon-carbon negative electrode sheets for lithium-ion batteries. The electrode sheet surface capacity was 3.5 mAh / cm², which met the requirements for lithium-ion battery use.

[0073] The assembly and performance testing of coin cells were conducted using a prepared silicon-carbon negative electrode as the working electrode, a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and a 1 mol / L LiPF6-EC / DEC / DMC electrolyte (volume ratio 1:1:1, containing 5% fluoroethylene carbonate). CR2032 coin cells were assembled in an argon-atmosphere glove box (water and oxygen content ≤1 ppm). After assembly, the cells were allowed to stand for 24 hours to allow the electrolyte to fully wet the electrodes and separator before electrochemical performance testing was performed.

[0074] Cyclic performance tests were conducted at a rate of 0.1C (350mA / g) and a voltage range of 0.01-1.5V. The results showed that the battery achieved an initial discharge specific capacity of 1850mAh / g and an initial coulombic efficiency of 82%. After 100 cycles, the discharge specific capacity remained at 1280mAh / g, with a capacity retention rate of 69%, which is significantly higher than that of silicon-carbon anodes using traditional CMC / SBR binders (capacity retention rate of 41% after 100 cycles). This demonstrates that the binder prepared in this embodiment can effectively improve the cycle stability of the battery.

[0075] In rate performance testing, the battery discharge specific capacity was 1620mAh / g, 1450mAh / g, 1210mAh / g, and 980mAh / g at 0.2C, 0.5C, 1C, and 2C rates, respectively. When the rate was restored to 0.1C, the discharge specific capacity could be restored to 1780mAh / g, demonstrating excellent rate adaptability. This is attributed to the gradient conductive network inside the binder providing an efficient pathway for electron transport, ensuring rapid electron transport even at high rates.

[0076] The volume expansion test was conducted using an in-situ expansion testing device. The results showed that the volume expansion rate of the silicon-carbon anode was 120% after 100 cycles, while the volume expansion rate of the silicon-carbon anode using a traditional binder reached 250%. This demonstrates that the dual dynamic bond network can effectively alleviate the volume expansion stress of silicon-carbon materials, maintain the integrity of the electrode structure, and reduce capacity decay.

[0077] Full Cell Performance Verification (Extended Testing): To further verify the practical application effect of the binder, soft-pack full cells were assembled and their performance was tested.

[0078] The positive electrode uses NCM811 ternary material, and the negative electrode is a silicon-carbon negative electrode prepared in this embodiment. The electrolyte and separator are the same as those in a coin cell, and the nominal capacity of the battery is 10Ah.

[0079] The full-cell cycle performance test was conducted at a charge / discharge rate of 0.5C and a voltage range of 3.0-4.3V. After 200 cycles, the capacity retention rate was 78%, which is much higher than that of full cells using traditional binders (capacity retention rate of 53% after 200 cycles). In the high-temperature cycle test (45℃), the capacity retention rate was 72% after 100 cycles, showing good high-temperature stability.

[0080] In the rate discharge test, the discharge capacity at 1C, 2C, and 3C rates was 95%, 88%, and 75% of the nominal capacity, respectively, demonstrating excellent rate performance. No significant bulging was observed during cycling, indicating that the binder effectively suppressed the volume expansion of the silicon-carbon anode, ensuring the stability of the battery structure.

[0081] To clarify the impact of key process parameters on adhesive performance, a control group was set up for comparative testing:

[0082] Control group 1: The molar ratio of the double dynamic bond polymer monomers was changed to 70:20:10, while other parameters remained unchanged. The adhesive strength of the prepared adhesive was 0.78 N / mm, and the capacity retention rate after 100 cycles was 63%, which was slightly lower than that of the optimal parameter group. This indicates that a moderate increase in the proportion of dopamine methacrylamide in the monomer ratio helps to enhance the adhesive strength.

[0083] Control group 2: The carbon nanotube fraction ratio was changed to 50:50, with other parameters remaining unchanged. The conductivity of the binder interface region decreased to 6.2 S / m, and the capacity retention rate after 100 cycles was 58%, proving that the 60% high-concentration carbon nanotubes in the construction of the interface conductive region are more conducive to electron transport.

[0084] Control group 3: The curing temperature was changed to 25℃, the curing time was extended to 24 hours, the adhesive viscosity was 9200mPa·s, the flexibility was slightly improved but the preparation efficiency was reduced, and the cycle performance was close to that of the optimal parameter group, indicating that good cross-linking can be achieved in the curing temperature range of 25-40℃.

[0085] The button cell was subjected to 300 long-cycle tests. The results showed that the discharge specific capacity was 980 mAh / g after 300 cycles, and the capacity retention rate was 53%, which is still much higher than that of the traditional binder group (capacity retention rate of 28% after 300 cycles). After the test, the electrode was disassembled and it was found that the silicon-carbon active material did not show obvious detachment and the electrode structure was intact, which further verified the dynamic self-healing ability and structural stability of the binder.

[0086] For storage media configuration, industrial-grade SSD solid-state drives are selected as computer-readable storage media with a capacity of 2TB, a read speed of 3500MB / s, a write speed of 3000MB / s, support for wide temperature range (-20℃~70℃), strong shock resistance, and a mean time between failures (MTBF) of ≥200,000 hours. They are suitable for long-term storage of manufacturing process data and control programs, and can work stably in complex environments to ensure data security.

[0087] The storage media adopts partition management, which is divided into program partition, parameter partition, data partition and report partition. Each partition has a clear function, which facilitates data management and retrieval.

[0088] The program partition (500GB) stores the control programs for the preparation of flexible conductive binders, silicon-carbon anodes, and battery testing, including polymerization reaction control programs, dispersion process control programs, maturation process control programs, and electrochemical testing control programs, supporting standardized and automated operation of the preparation and testing processes.

[0089] The parameter partition (200GB) stores a library of preparation process parameters for different batches, including monomer molar ratio, initiator dosage, polymerization temperature, carbon nanotube fractionation ratio, dispersion speed, aging conditions, electrode preparation parameters, etc. It supports parameter calling, modification and saving. Operators can select historical parameters or customize new parameters according to their needs to improve work efficiency.

[0090] The data partition (1TB) stores the raw data of the preparation process and performance testing, including polymer molecular weight test data, binder viscosity / conductivity / bond strength / flexibility test data, electrode electrochemical performance test data, full cell cycle and rate performance data, etc. It is stored by batch and supports data retrieval and comparative analysis, providing data support for process optimization and product quality traceability.

[0091] The report partition (300GB) stores automatically generated test reports, including binder performance reports, electrode performance reports, coin cell test reports, and full cell performance reports. It supports export in PDF format and includes detailed data charts, performance analysis, and conclusions and recommendations, which helps operators quickly understand product performance and also facilitates technical exchanges and results presentations.

[0092] The storage medium is installed in the storage interface of the preparation and testing control system. After the system is powered on, it automatically reads the control program in the program partition, completes initialization, and enters standby mode to wait for instructions from the operator. The operator selects or customizes the preparation parameters through the control system interface. The parameters are automatically saved to the parameter partition, and the system calls the corresponding control program to start the preparation process, ensuring that the preparation process is strictly carried out according to the set parameters.

[0093] During the preparation and testing process, the system collects the operating data and performance test data of each device in real time, stores them in the data partition according to the preset format, and uses encrypted storage to prevent data tampering or loss, ensuring the authenticity and integrity of the data. After the test is completed, the system automatically calls the original data in the data partition, generates a standardized test report according to the preset template, and saves it to the report partition. At the same time, it supports operators to export the report and original data through the USB interface for convenient subsequent analysis and archiving.

[0094] The storage medium supports data backup, enabling critical data to be uploaded to a cloud server via the network for dual data backup, preventing data loss due to storage medium damage. It also supports historical data backtracking, allowing operators to retrieve preparation parameters, test data, and reports for any batch at any time, providing a basis for process optimization and problem troubleshooting, and helping to continuously improve product performance.

[0095] This embodiment successfully prepared a flexible conductive binder with strong adhesion, high flexibility, high conductivity, and dynamic self-healing ability by precisely controlling the polymerization process of the double dynamic bond polymer and constructing the hierarchical dispersion and gradient distribution of carboxylated multi-walled carbon nanotubes. When applied to a silicon-carbon anode, the double dynamic bond network effectively alleviates volume expansion stress, and the gradient conductive network ensures efficient electron transport, significantly improving the cycle stability and rate performance of the silicon-carbon anode. Performance tests and long-term stability verification of coin cells and full cells have confirmed that this binder far surpasses traditional binders in terms of cycle life, volume expansion suppression, and rate adaptability. Comparative tests of different process parameters clarified the optimal preparation conditions. The application of computer-readable storage media enabled standardized management of the preparation process and test data, providing a key reference for industrial production. This embodiment discloses the details of the technical solution, providing clear and operable parameters from raw material preparation and preparation steps to performance testing, providing complete technical support for the industrial application of this flexible conductive binder, and is of great significance for promoting the development of high-energy-density lithium-ion batteries.

[0096] The same or similar labels correspond to the same or similar parts;

[0097] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0098] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A flexible conductive binder for silicon-carbon anodes in lithium-ion batteries, characterized in that, The adhesive has a three-dimensional interpenetrating network structure and is composed of the following components by mass percentage: Polymers containing catechol and boric acid groups with double dynamic bonds, 5-15%; Gradient-distributed carboxylated multi-walled carbon nanotubes, 0.5-5%; Balance of ionic liquid / water mixed solvent; The dual dynamic bond polymer is poly(acrylic acid-co-dopamine methacrylamide-co-vinylphenylboronic acid), in which the catechol groups in the molecular chain can form hydrogen bonds / coordination bonds, and the phenylboronic acid groups can form dynamic borate ester bonds with the hydroxyl groups or vicinal diol structures in the molecular chain; the carboxylated multi-walled carbon nanotubes in the binder exhibit a gradient distribution with denser inner layers and sparser outer layers, with a higher concentration near the interface than inside the bulk.

2. The flexible conductive adhesive according to claim 1, characterized in that, The poly(acrylic acid-co-dopamine methacrylamide-co-vinylphenylboronic acid) is prepared by reversible addition-fragmentation chain transfer polymerization, wherein the monomer molar ratio of acrylic acid, dopamine methacrylamide, and vinylphenylboronic acid is (50-70):(20-30):(10-20), and the number average molecular weight is 50,000-200,000 g / mol.

3. The flexible conductive adhesive according to claim 1, characterized in that, The ionic liquid / water mixed solvent is composed of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and deionized water in a volume ratio of 1:4 to 1:

9.

4. The flexible conductive adhesive according to claim 1, characterized in that, The carboxylated multi-walled carbon nanotubes have a carboxyl content of 1.5-3.0 mmol / g, a diameter of 10-20 nm, and a length of 5-20 μm. 60% of the carboxylated multi-walled carbon nanotubes are used to construct high-concentration interfacial conductive regions, and 40% are used to construct low-concentration bulk conductive regions.

5. The flexible conductive adhesive according to claim 1, characterized in that, The dynamic borate ester bond has a breakage / recombination temperature range of 25-80℃, and can achieve dynamic self-repair under the volume expansion / contraction stress during the charging and discharging process of silicon-carbon anode.

6. A method for preparing the flexible conductive adhesive according to any one of claims 1-5, characterized in that, Includes the following steps: A polymer with double dynamic bonds containing catechol and boric acid groups was prepared by polymerizing acrylic acid, dopamine methacrylamide and vinylphenylboronic acid monomers through a reversible addition-fragmentation chain transfer polymerization process. Carboxylated multi-walled carbon nanotubes were divided into two parts, and high-concentration conductive slurry A and low-concentration dispersion B were prepared respectively. The double dynamic bond polymer was completely dissolved in an ionic liquid / water mixed solvent to form a homogeneous solution C; High-concentration conductive paste A is slowly added to solution C under high-speed stirring. After being dispersed evenly, low-concentration dispersion B is added and mixed gently. The mixture is allowed to stand and mature, allowing the polymer chains to form a dynamic cross-linked network. At the same time, carboxylated multi-walled carbon nanotubes are fixed in situ within the network, resulting in a flexible conductive adhesive.

7. The method according to claim 6, characterized in that, The preparation process of the high-concentration conductive paste A is as follows: 60% of carboxylated multi-walled carbon nanotubes are dispersed in an ionic liquid / aqueous solution containing 5-10% of a double dynamic bond polymer, and dispersed at a high speed of 20,000-30,000 r / min for 10-20 min; the preparation process of the low-concentration dispersion B is as follows: 40% of carboxylated multi-walled carbon nanotubes are dispersed in a pure ionic liquid / aqueous solution, and dispersed ultrasonically for 30-60 min.

8. The method according to claim 6, characterized in that, The reaction conditions for the reversible addition-fragmentation chain transfer polymerization process are as follows: azobisisobutyronitrile is used as the initiator, the total molar ratio of initiator to monomer is 1:100-1:200, the reaction temperature is 60-80℃, the reaction time is 8-12 h, and the reaction solvent is dimethylformamide.

9. The method according to claim 6, characterized in that, The conditions for static curing are: temperature 25-40℃, humidity 30-50%, curing time 12-24 h. During the curing process, the phenylboronic acid groups on the polymer chain undergo dynamic cross-linking reactions with the ortho-dihydroxy and carboxyl groups.

10. A silicon-carbon anode for a lithium-ion battery, characterized in that, The invention includes a silicon-carbon active material, a conductive agent, a flexible conductive binder as described in any one of claims 1-5, and a current collector. The flexible conductive binder bonds and fixes the silicon-carbon active material and the conductive agent to the surface of the current collector, and its internal gradient conductive network forms an efficient electron transport pathway with the silicon-carbon active material. The dynamic borate bond network can alleviate the volume expansion stress of the silicon-carbon active material.

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