Water-based composite conductive paste for silicon-based negative electrode of lithium battery and preparation method of water-based composite conductive paste

Abstract

The invention relates to the technical field of conductive agents, and particularly discloses water-based composite conductive paste for a silicon-based negative electrode of a lithium battery and a preparation method of the water-based composite conductive paste. The water-based composite conductive paste is prepared from the following raw materials in parts by weight: 5 to 7 parts of carbon nanotube powder, 2 to 4 parts of graphene powder, 0.5 to 1.5 parts of conductive carbon black, 0.6 to 0.8 part of sulfonated polythiophene-cellulose nanocrystalline composite dispersing agent, 0.2 to 0.4 part of hydroxy propyl cellulose, 0.1 to 0.3 part of boric acid ester coupling agent, 0.6 to 0.8 part of glycerol, 0.3 to 0.5 part of carboxymethyl cellulose and 80 to 100 parts of deionized water. According to the water-based composite conductive paste for the silicon-based negative electrode of the lithium battery and the preparation method of the water-based composite conductive paste, the storage time of the conductive paste can be effectively prolonged, sedimentation of the conductive paste is delayed, meanwhile, silicon expansion failure energy can be converted into reversible deformation energy, meanwhile, continuous smoothness of an electron-ion channel is guaranteed, and the cycle life of the silicon-based negative electrode is prolonged.

Description

Technical Field

[0001] This invention relates to the field of conductive agent technology, and more specifically, to an aqueous composite conductive slurry for silicon-based anodes of lithium batteries and its preparation method. Background Technology

[0002] With the surge in demand for high-energy-density lithium batteries, silicon-based anode materials, with their theoretical specific capacity ≥4200mAh / g, have become a key alternative to traditional graphite. However, silicon materials suffer from drastic volume changes and poor intrinsic conductivity during charge and discharge, leading to the pulverization and deactivation of active materials and the collapse of the conductive network.

[0003] Currently, the industry commonly uses aqueous conductive pastes to construct the negative electrode conductive network, but existing technologies have significant drawbacks. While metal-based pastes improve conductivity, residual metal ions catalyze the decomposition of the electrolyte, resulting in a high-temperature gas generation rate >0.25 mL / Ah (stored at 60℃ for 7 days), posing a safety hazard. Carbon-based compound pastes rely on graphene / carbon nanotubes, but physical mixing makes it difficult to form a stable three-dimensional network. Therefore, dispersants are needed to promote powder dispersion. However, traditional anionic dispersants form an insulating adsorption layer on the silicon surface, increasing interfacial impedance. Polymer dispersants (such as polyaniline), although conductive, accelerate silicon oxidation in an acidic environment to form a SiO2 passivation layer, causing an initial efficiency loss >15%.

[0004] Meanwhile, the weak interfacial bonding between silicon particles and conductive agents leads to point contact failure due to volume expansion. Metallic impurities (Fe / Ni > 30 ppm) migrate into the silicon lattice, forming the brittle FeSi2 phase, which induces particle crack propagation. Therefore, there is an urgent need to develop a non-metallic, highly interfacially stable aqueous conductive paste to overcome the cycle life limitations of silicon-based anodes while ensuring environmental friendliness. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an aqueous composite conductive slurry for silicon-based anodes in lithium batteries and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A water-based composite conductive slurry for silicon-based anodes in lithium-ion batteries comprises, by weight, 5-7 parts carbon nanotube powder, 2-4 parts graphene powder, 0.5-1.5 parts conductive carbon black, 0.6-0.8 parts sulfonated polythiophene-cellulose nanocrystal composite dispersant, 0.2-0.4 parts hydroxypropyl cellulose, 0.1-0.3 parts borate coupling agent, 0.6-0.8 parts glycerol, 0.3-0.5 parts carboxymethyl cellulose, and 80-100 parts deionized water.

[0007] Furthermore, the carbon nanotube powder includes at least one of multi-walled carbon nanotube powder, oligo-walled carbon nanotube powder, and single-walled carbon nanotube powder.

[0008] Furthermore, the graphene powder has a sheet diameter of 0.6~1.2μm and 2~5 layers.

[0009] Furthermore, the conductive carbon black has a particle size of 30~60nm.

[0010] Furthermore, the preparation method of the sulfonated polythiophene-cellulose nanocrystal composite dispersant includes the following steps: S1. By weight, weigh out 10-20 parts of 3,4-ethylenedioxythiophene, 20-24 parts of ammonium persulfate, 15-18 parts of fuming sulfuric acid with an SO3 content of 20%-30%, 3-5 parts of cellulose nanocrystals with a diameter of 10-20 nm, 0.01-0.02 parts of 2,2,6,6-tetramethylpiperidine-1-oxy free radical, 0.2-0.4 parts of ammonium bicarbonate, 30-50 parts of oxalic acid, 10-12 parts of hydrogen peroxide solution with a mass fraction of 20%-30%, and 180-200 parts of deionized water. S2. Add ammonium persulfate to 3 / 5 of the deionized water and add 3,4-ethylenedioxythiophene dropwise. In an ice bath reactor at 0~5℃, nitrogen gas is introduced for protection. The mixture is stirred at 200~300 rpm for 4~6 hours. After filtration, polythiophene precipitate is obtained. S3. Add the polythiophene precipitate to fuming sulfuric acid, heat to 50-60℃ and react for 2-3 hours. After the product precipitates, wash it with anhydrous ethanol 3-5 times to obtain sulfonated polythiophene. S4. Add cellulose nanocrystals to oxalic acid, reflux in an oil bath at 100~110℃ for 2~3 hours, centrifuge, wash the lower solid with deionized water until neutral, and dry to obtain acid-heat activated cellulose nanocrystals. S5. Add acid-heat activated cellulose nanocrystals to 1 / 5 deionized water, and add 2,2,6,6-tetramethylpiperidine-1-oxy free radical, ammonium bicarbonate and hydrogen peroxide solution. Heat to 50~60℃ and stir for 6~8h. Filter and wash the product with anhydrous ethanol 3~5 times to obtain carboxylated cellulose nanocrystals. S6. Add sulfonated polythiophene and carboxylated cellulose nanocrystals to the remaining 1 / 5 of deionized water, and ultrasonically disperse at 200-300W for 20-30 minutes. Add acetic acid dropwise to adjust the pH to 3.0-3.5, heat to 50-60℃ and stir to react for 2-4 hours. After the reactants are rapidly frozen in liquid nitrogen, they are placed at -50--40℃ for vacuum freeze-drying for 20-24 hours, and then pulverized to obtain sulfonated polythiophene-cellulose nanocrystal composite dispersant.

[0011] Furthermore, the borate coupling agent includes at least one of alkyl borate diethanolamine ester, glyceryl borate ester, sorbitol borate ester, and mannitol borate ester.

[0012] Furthermore, the preparation method of the aqueous composite conductive slurry for the silicon-based negative electrode of a lithium battery includes the following steps: (1) Weigh the raw materials according to the weight percentages; (2) Add carbon nanotube powder, graphene powder and conductive carbon black to 3 / 5 deionized water, add sulfonated polythiophene-cellulose nanocrystal composite dispersant, place in a high shear disperser and shear disperse at a speed of 14000~18000rpm for 30~40min, and then use an ultrasonic generator to ultrasonic disperse for 30~40min to obtain a pre-dispersion liquid. (3) Add hydroxypropyl cellulose, borate coupling agent, glycerol, carboxymethyl cellulose and the remaining 2 / 5 of deionized water to the pre-dispersion liquid, stir at 500~600 rpm at room temperature for 20~30 min, add ammonia water to adjust the pH to 8.5~9.5, then place in a homogenizer for homogenization for 1~2 h, and vacuum degas for 20~30 min to obtain an aqueous composite conductive slurry for silicon-based negative electrodes of lithium batteries.

[0013] Furthermore, the ultrasonic dispersion conditions in step (2) are a temperature of 30~40℃ and a power of 300~400W.

[0014] Furthermore, the vacuum degassing pressure in step (3) is -0.08 to -0.06 MPa.

[0015] In summary, this application includes at least the following beneficial effects: (1) This invention uses carbon nanotube powder, graphene powder and conductive carbon black as raw materials to construct a ternary conductive phase. The one-dimensional linear structure of carbon nanotubes can construct a long-range conductive network, and 2-5 layers of graphene provide large-area contact conductivity through a two-dimensional planar structure. Carbon black particles fill the nano gaps to form an efficient three-dimensional conductive pathway, which synergistically reduces the interfacial resistance, thereby effectively improving the conductivity of the conductive paste.

[0016] (2) In this invention, sulfonated polythiophene with fuming sulfuric acid enhances hydrophilicity. Simultaneously, cellulose nanocrystals are activated by oxalic acid and then oxidized to introduce carboxyl groups, which are then combined with sulfonated polythiophene. This results in a composite dispersant that possesses the conductivity and water solubility of sulfonated polythiophene while also improving dispersibility and mechanical strength. The combination of the two materials provides both conductivity enhancement and steric stabilization. Sulfonated polythiophene provides an intrinsic conductive pathway, which works synergistically with carbon materials to reduce slurry resistance. Sulfonated polythiophene can provide electrostatic repulsion to buffer expansion stress through sulfonic acid groups. The polythiophene main chain is ductile and absorbs deformation energy, which can convert the silicon expansion failure energy into reversible deformation energy. At the silicon expansion cracking site, sulfonated polythiophene re-adheresizes carbon nanotubes / graphene through π-π interactions, rebuilding the conductive pathway and ensuring the continuous unobstructed electron-ion channels. Carboxylated cellulose nanocrystals prevent filler sedimentation and extend slurry storage life through a dual mechanism of electrostatic repulsion and steric hindrance. Simultaneously, the carboxylated cellulose nanocrystals embed themselves in the gaps between silicon particles, constraining silicon expansion through mechanical modulus, thus forming a 3D network framework that buffers the volume expansion of silicon particles during charge and discharge. This results in extended cycle life of silicon-based anodes. Furthermore, borate ester coupling agents can improve the compatibility between inorganic fillers and organic polymer interfaces. Borate ester coupling agents can also be activated in alkaline slurries (pH 8.5-9.5) to form reversible bonds with -OH groups on the silicon surface. After the bonds are broken by charge and discharge stress, the borate ester can quickly combine with the newly exposed silanol groups to continuously repair cracks. During charge and discharge, the reversible breakage and recombination can continuously maintain the integrity of the electrode. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0018] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] This invention provides a method for preparing an aqueous composite conductive paste for a silicon-based negative electrode in lithium batteries, comprising the following steps: (1) Weigh out the following by weight: 10-20 parts of 3,4-ethylenedioxythiophene, 20-24 parts of ammonium persulfate, 15-18 parts of fuming sulfuric acid with SO3 content of 20%-30%, 3-5 parts of cellulose nanocrystals with a diameter of 10-20 nm, 0.01-0.02 parts of 2,2,6,6-tetramethylpiperidine-1-oxy free radical, 0.2-0.4 parts of ammonium bicarbonate, 30-50 parts of oxalic acid, 10-12 parts of hydrogen peroxide solution with a mass fraction of 20%-30%, and 180-200 parts of deionized water.

[0020] (2) Add ammonium persulfate to 3 / 5 of deionized water and add 3,4-ethylenedioxythiophene dropwise. In an ice bath reactor at 0~5℃, nitrogen gas is introduced for protection. The mixture is stirred at 200~300 rpm for 4~6 hours. After filtration, polythiophene precipitate is obtained.

[0021] (3) Add the polythiophene precipitate to fuming sulfuric acid, heat to 50-60℃ and react for 2-3 hours. After the product precipitates, wash with anhydrous ethanol 3-5 times to obtain sulfonated polythiophene.

[0022] (4) Add cellulose nanocrystals to oxalic acid, reflux in an oil bath at 100~110℃ for 2~3h, centrifuge to separate, wash the lower solid with deionized water until neutral, dry to obtain acid-heat activated cellulose nanocrystals.

[0023] (5) Add acid-heat activated cellulose nanocrystals to 1 / 5 deionized water, and add 2,2,6,6-tetramethylpiperidine-1-oxy free radical, ammonium bicarbonate and hydrogen peroxide solution. Heat to 50~60℃ and stir for 6~8h. Filter and wash the product with anhydrous ethanol 3~5 times to obtain carboxylated cellulose nanocrystals.

[0024] (6) Add sulfonated polythiophene and carboxylated cellulose nanocrystals to the remaining 1 / 5 of deionized water, and ultrasonically disperse them at a power of 200-300W for 20-30 minutes. Add acetic acid dropwise to adjust the pH to 3.0-3.5, heat to 50-60℃ and stir to react for 2-4 hours. After the reactants are rapidly frozen in liquid nitrogen, they are placed at -50--40℃ for vacuum freeze-drying for 20-24 hours, and then pulverized to obtain sulfonated polythiophene-cellulose nanocrystal composite dispersant.

[0025] (7) Weigh out 5-7 parts of carbon nanotube powder, 2-4 parts of graphene powder with a sheet diameter of 0.6-1.2 μm and 2-5 layers, 0.5-1.5 parts of conductive carbon black with a particle size of 30-60 nm, 0.6-0.8 parts of sulfonated polythiophene-cellulose nanocrystal composite dispersant, 0.2-0.4 parts of hydroxypropyl cellulose, 0.1-0.3 parts of borate coupling agent, 0.6-0.8 parts of glycerol, 0.3-0.5 parts of carboxymethyl cellulose, and 80-100 parts of deionized water by weight.

[0026] (8) Add carbon nanotube powder, graphene powder, and conductive carbon black to 3 / 5 of deionized water, add sulfonated polythiophene-cellulose nanocrystal composite dispersant, place in a high shear disperser and shear disperse at a speed of 14000~18000rpm for 30~40min, and then use an ultrasonic generator to ultrasonic disperse at a temperature of 30~40℃ and a power of 300~400W for 30~40min to obtain a pre-dispersion liquid.

[0027] (9) Add hydroxypropyl cellulose, borate coupling agent, glycerol, carboxymethyl cellulose and the remaining 2 / 5 of deionized water to the pre-dispersion liquid, stir at 500~600 rpm at room temperature for 20~30 min, add ammonia water dropwise to adjust the pH to 8.5~9.5, then place it in a homogenizer for homogenization for 1~2 h, and degas under vacuum at a pressure of -0.08~-0.06 MPa for 20~30 min to obtain an aqueous composite conductive slurry for silicon-based negative electrodes of lithium batteries.

[0028] The carbon nanotube powder includes at least one of multi-walled carbon nanotube powder, oligo-walled carbon nanotube powder, and single-walled carbon nanotube powder; the borate ester coupling agent includes at least one of alkyl borate diethanolamine ester, borate glycerol ester, sorbitol borate ester, and mannitol borate ester.

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1 The method for preparing the aqueous composite conductive paste for the silicon-based negative electrode of lithium battery in this embodiment includes the following steps: (1) Weigh out the following components by weight: 10 parts of 3,4-ethylenedioxythiophene, 20 parts of ammonium persulfate, 15 parts of fuming sulfuric acid with 20% SO3 content, 3 parts of cellulose nanocrystals with a diameter of 10 nm, 0.01 parts of 2,2,6,6-tetramethylpiperidine-1-oxy free radical, 0.2 parts of ammonium bicarbonate, 30 parts of oxalic acid, 10 parts of hydrogen peroxide solution with a mass fraction of 20% to 30%, and 180 parts of deionized water.

[0031] (2) Add ammonium persulfate to 3 / 5 of deionized water and add 3,4-ethylenedioxythiophene dropwise. In an ice bath reactor at 0°C, nitrogen gas is introduced for protection. The mixture is stirred at 200 rpm for 4 hours. After filtration, polythiophene precipitate is obtained.

[0032] (3) Add the polythiophene precipitate to fuming sulfuric acid, heat to 50°C and react for 2 hours. After the product precipitates, wash it three times with anhydrous ethanol to obtain sulfonated polythiophene.

[0033] (4) Add cellulose nanocrystals to oxalic acid, reflux in an oil bath at 100°C for 2 hours, centrifuge to separate, wash the lower solid with deionized water until neutral, and dry to obtain acid-heat activated cellulose nanocrystals.

[0034] (5) Add acid-heat activated cellulose nanocrystals to 1 / 5 deionized water, and add 2,2,6,6-tetramethylpiperidine-1-oxy free radical, ammonium bicarbonate and hydrogen peroxide solution. Heat to 50°C and stir for 6 hours. Filter and wash the product three times with anhydrous ethanol to obtain carboxylated cellulose nanocrystals.

[0035] (6) Sulfonated polythiophene and carboxylated cellulose nanocrystals were added to the remaining 1 / 5 of deionized water and ultrasonically dispersed at 200W for 20min. Acetic acid was added dropwise to adjust the pH to 3.0. The mixture was heated to 50℃ and stirred for 2h. After the reactants were rapidly frozen in liquid nitrogen, they were placed at -50℃ for vacuum freeze-drying for 20h and then pulverized to obtain sulfonated polythiophene-cellulose nanocrystal composite dispersant.

[0036] (7) Weigh out 5 parts by weight of multi-walled carbon nanotube powder, 2 parts of graphene powder with a sheet diameter of 0.6 μm and 2 layers, 0.5 parts of conductive carbon black with a particle size of 30 nm, 0.6 parts of sulfonated polythiophene-cellulose nanocrystal composite dispersant, 0.2 parts of hydroxypropyl cellulose, 0.1 parts of alkyl borate diethanolamine ester, 0.6 parts of glycerol, 0.3 parts of carboxymethyl cellulose, and 80 parts of deionized water.

[0037] (8) Add multi-walled carbon nanotube powder, graphene powder, and conductive carbon black to 3 / 5 of deionized water, add sulfonated polythiophene-cellulose nanocrystal composite dispersant, place in a high shear disperser and shear disperse at 14000 rpm for 30 min, and then use an ultrasonic generator to ultrasonic disperse at 30℃ and 300W for 30 min to obtain a pre-dispersed liquid.

[0038] (9) Add hydroxypropyl cellulose, diethanolamine alkyl borate, glycerol, carboxymethyl cellulose and the remaining 2 / 5 of deionized water to the pre-dispersion liquid, stir at 500 rpm at room temperature for 20 min, add ammonia water to adjust the pH to 8.5, then place it in a homogenizer for homogenization for 1 h, and degas under vacuum at -0.08 MPa for 20 min to obtain an aqueous composite conductive slurry for silicon-based negative electrodes of lithium batteries.

[0039] Example 2 This embodiment describes a method for preparing an aqueous composite conductive paste for a silicon-based negative electrode in lithium-ion batteries, comprising the following steps: (1) Weigh out the following components by weight: 15 parts of 3,4-ethylenedioxythiophene, 22 parts of ammonium persulfate, 16 parts of fuming sulfuric acid with 25% SO3 content, 4 parts of cellulose nanocrystals with a diameter of 15 nm, 0.015 parts of 2,2,6,6-tetramethylpiperidine-1-oxy free radical, 0.3 parts of ammonium bicarbonate, 40 parts of oxalic acid, 11 parts of hydrogen peroxide solution with a mass fraction of 25%, and 190 parts of deionized water.

[0040] (2) Add ammonium persulfate to 3 / 5 of deionized water and add 3,4-ethylenedioxythiophene dropwise. In an ice bath reactor at 3°C, nitrogen gas is introduced for protection. The mixture is stirred at 250 rpm for 5 hours. After filtration, polythiophene precipitate is obtained.

[0041] (3) Add the polythiophene precipitate to fuming sulfuric acid, heat to 55°C and react for 2.5 h. After the product precipitates, wash it 4 times with anhydrous ethanol to obtain sulfonated polythiophene.

[0042] (4) Add cellulose nanocrystals to oxalic acid, reflux in an oil bath at 105°C for 2.5 h, centrifuge to separate, wash the lower solid with deionized water until neutral, and dry to obtain acid-heat activated cellulose nanocrystals.

[0043] (5) Add acid-heat activated cellulose nanocrystals to 1 / 5 deionized water, and add 2,2,6,6-tetramethylpiperidine-1-oxy free radical, ammonium bicarbonate and hydrogen peroxide solution. Heat to 55°C and stir for 7 hours. Filter and wash the product with anhydrous ethanol 4 times to obtain carboxylated cellulose nanocrystals.

[0044] (6) Sulfonated polythiophene and carboxylated cellulose nanocrystals were added to the remaining 1 / 5 of deionized water and ultrasonically dispersed at 250W for 25min. Acetic acid was added dropwise to adjust the pH to 3.3. The mixture was heated to 55℃ and stirred for 3h. After the reactants were rapidly frozen in liquid nitrogen, they were placed at -45℃ for vacuum freeze-drying for 22h and then pulverized to obtain sulfonated polythiophene-cellulose nanocrystal composite dispersant.

[0045] (7) Weigh out 6 parts by weight of oligowalled carbon nanotube powder, 3 parts of graphene powder with a diameter of 0.9 μm and 4 layers, 1 part of conductive carbon black with a particle size of 45 nm, 0.7 parts of sulfonated polythiophene-cellulose nanocrystal composite dispersant, 0.3 parts of hydroxypropyl cellulose, 0.2 parts of borate glyceride, 0.7 parts of glycerol, 0.4 parts of carboxymethyl cellulose, and 90 parts of deionized water.

[0046] (8) Add oligowalled carbon nanotube powder, graphene powder, and conductive carbon black to 3 / 5 of deionized water, add sulfonated polythiophene-cellulose nanocrystal composite dispersant, place in a high shear disperser and shear disperse at 16000 rpm for 35 min, and then use an ultrasonic generator to ultrasonic disperse at 35℃ and 350W for 35 min to obtain a pre-dispersed liquid.

[0047] (9) Add hydroxypropyl cellulose, glyceryl borate, glycerol, carboxymethyl cellulose and the remaining 2 / 5 of deionized water to the pre-dispersion liquid, stir at 550 rpm at room temperature for 25 min, add ammonia water to adjust the pH to 9, then place it in a homogenizer for homogenization for 1.5 h, and degas under vacuum at -0.07 MPa for 25 min to obtain an aqueous composite conductive slurry for silicon-based negative electrodes of lithium batteries.

[0048] Example 3 This embodiment describes a method for preparing an aqueous composite conductive paste for a silicon-based negative electrode in lithium-ion batteries, comprising the following steps: (1) Weigh out the following components by weight: 20 parts of 3,4-ethylenedioxythiophene, 24 parts of ammonium persulfate, 18 parts of fuming sulfuric acid with 30% SO3 content, 5 parts of cellulose nanocrystals with a diameter of 20 nm, 0.02 parts of 2,2,6,6-tetramethylpiperidine-1-oxy free radical, 0.4 parts of ammonium bicarbonate, 50 parts of oxalic acid, 12 parts of hydrogen peroxide solution with a mass fraction of 30%, and 200 parts of deionized water.

[0049] (2) Add ammonium persulfate to 3 / 5 of deionized water and add 3,4-ethylenedioxythiophene dropwise. In an ice bath reactor at 5°C, nitrogen gas is introduced for protection. The mixture is stirred at 300 rpm for 6 hours. After filtration, polythiophene precipitate is obtained.

[0050] (3) Add the polythiophene precipitate to fuming sulfuric acid, heat to 60°C and react for 3 hours. After the product precipitates, wash it 5 times with anhydrous ethanol to obtain sulfonated polythiophene.

[0051] (4) Add cellulose nanocrystals to oxalic acid, reflux in an oil bath at 110°C for 3 hours, centrifuge to separate, wash the lower solid with deionized water until neutral, and dry to obtain acid-heat activated cellulose nanocrystals.

[0052] (5) Add acid-heat activated cellulose nanocrystals to 1 / 5 deionized water, and add 2,2,6,6-tetramethylpiperidine-1-oxy free radical, ammonium bicarbonate and hydrogen peroxide solution. Heat to 60°C and stir for 8 hours. Filter and wash the product with anhydrous ethanol 5 times to obtain carboxylated cellulose nanocrystals.

[0053] (6) Sulfonated polythiophene and carboxylated cellulose nanocrystals were added to the remaining 1 / 5 of deionized water and ultrasonically dispersed at 300W for 30min. Acetic acid was added dropwise to adjust the pH to 3.5. The mixture was heated to 60℃ and stirred for 4h. After the reactants were rapidly frozen in liquid nitrogen, they were placed at -40℃ for vacuum freeze-drying for 24h and then pulverized to obtain sulfonated polythiophene-cellulose nanocrystal composite dispersant.

[0054] (7) Weigh out 7 parts by weight of single-walled carbon nanotube powder, 4 parts of graphene powder with a diameter of 1.2 μm and 5 layers, 1.5 parts of conductive carbon black with a particle size of 60 nm, 0.8 parts of sulfonated polythiophene-cellulose nanocrystal composite dispersant, 0.4 parts of hydroxypropyl cellulose, 0.3 parts of sorbitol borate, 0.8 parts of glycerol, 0.5 parts of carboxymethyl cellulose, and 100 parts of deionized water.

[0055] (8) Add single-walled carbon nanotube powder, graphene powder, and conductive carbon black to 3 / 5 of deionized water, add sulfonated polythiophene-cellulose nanocrystal composite dispersant, place in a high-shear disperser and shear disperse at 18000 rpm for 40 min, and then use an ultrasonic generator to ultrasonic disperse at 40℃ and 400W for 40 min to obtain a pre-dispersion liquid.

[0056] (9) Add hydroxypropyl cellulose, sorbitol borate, glycerol, carboxymethyl cellulose and the remaining 2 / 5 of deionized water to the pre-dispersion liquid, stir at 600 rpm at room temperature for 30 min, add ammonia water to adjust the pH to 9.5, then place it in a homogenizer for homogenization for 2 h, and degas under vacuum at -0.06 MPa for 30 min to obtain an aqueous composite conductive slurry for silicon-based negative electrodes of lithium batteries.

[0057] Comparative Example 1 The preparation method of the aqueous composite conductive slurry for the silicon-based negative electrode of lithium battery in this comparative example is basically the same as that in Example 1. The difference is that sulfonated polythiophene-cellulose nanocrystal composite dispersant was not added in this comparative example.

[0058] Comparative Example 2 The preparation method of the aqueous composite conductive slurry for the silicon-based negative electrode of lithium battery in this comparative example is basically the same as that in Example 1, except that alkylboronic acid diethanolamine ester is not added in this comparative example.

[0059] Experimental Example Conductive paste samples from Examples 1-3 and Comparative Examples 1-2 were selected for various performance tests, including: Slurry sedimentation rate: According to GB / T19077-2016 Particle Size Analysis by Laser Diffraction, a Malvern Mastersizer 3000 laser particle size analyzer was used. 50 mL of slurry sample was placed in a graduated centrifuge tube and kept at a constant temperature of 25℃. At 0h, 24h, and 7 days, 5 mL samples were taken from a depth of 2 / 3 of the liquid surface using a pipette. The change rate of D50 of solid particles in the sample was measured: Sedimentation rate (%) = [(Initial D50 - D50 at test) / Initial D50] × 100% Note: If D50 increases by more than 15% or a sediment layer of more than 3 mm appears at the bottom, the sedimentation is considered to have failed.

[0060] Slurry viscosity change rate: Following the ASTM D2196-20 rotational viscometer method, a Brookfield DV2T viscometer (SC4-21 rotor) was used. First, the initial viscosity η0 of the slurry sample was measured. The slurry sample was sealed and stored at 25°C for 24 hours. Then, at 25°C ± 0.5°C, the viscosity was measured at 10s⁻¹. -1 After re-stirring at the shear rate for 5 minutes, the viscosity η after storage was measured. t Viscosity change rate (%) = [(η) t -η0) / η0]×100%.

[0061] First charge / discharge efficiency (initial efficiency): Based on GB / T37201-2018 Lithium-ion Battery Anode Materials, using the Blue Electric Testing System (CT-4008T), and according to the active material (SiO2). x / C): Conductive agent: binder = 80:10:10, areal density 10±0.5mg / cm³ 2 Compacted density 1.6 g / cm³ 3 Electrodes for coin cell (CR2032) were prepared. During testing, the cells were charged at a constant current of 0.1C (1C = 2000mA / g) to 0.01V, charged at a constant voltage until the current ≤0.005C, and discharged at 0.1C to 1.5V. Initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100%.

[0062] 100-cycle capacity retention: Test standard 《IEC62660-1:2018 Power Battery Cycle Life》. Full cell assembly: Negative electrode is a silicon-based electrode with an areal density of 120 g / m³. 2 The positive electrode is NCM811, with a surface density of 180 g / m³. 2 The lithium battery electrolyte formulation is 1M LiPF6 in EC:EMC:DMC=1:1:1+10%FEC; Cycling conditions: 0.5C constant current charging to 4.2V → constant voltage to 0.05C, 0.5C constant current discharging to 3.0V, with 0.1C capacity calibration performed every 10 weeks; Capacity retention rate (%) = (discharge capacity at week 100 / discharge capacity at week 5) × 100%.

[0063] Electrode expansion rate test: The initial thickness T0 of the new electrode was measured under 1 MPa pressure (average of 9 points). After 100 battery cycles, the electrode was disassembled, cleaned by DMC, and vacuum dried. The drying temperature was 60℃, and the thickness T1 was measured under the same pressure. Expansion rate (%) = [(T1-T0) / T0]×100%. The specific results are shown in Table 1.

[0064] Table 1: Performance Test Results of Conductive Paste Samples from Examples and Comparative Examples

[0065] As shown in Table 1, comparing Example 1 with Comparative Example 1, since no sulfonated polythiophene-cellulose nanocrystal composite dispersant was added in Comparative Example 1, there was no effective component in the slurry sample of Comparative Example 1 to inhibit the expansion of the silicon-based negative electrode, which resulted in a significant increase in the slurry sedimentation rate and electrode expansion rate. This is because the sulfonated polythiophene-cellulose nanocrystal composite dispersant can effectively disperse the conductive phase, while sulfonated polythiophene provides an intrinsic conductive path, which works synergistically with carbon materials to reduce the slurry resistance. The carboxylated cellulose nanocrystals are embedded in the gaps between silicon particles, and the expansion of silicon is constrained by the mechanical modulus, so that the nanocellulose forms a 3D network skeleton to buffer the volume expansion of silicon particles during charging and discharging.

[0066] Comparing Example 1 with Comparative Example 2, the viscosity change rate of the slurry sample in Comparative Example 2 was significantly higher during storage because alkyl borate diethanolamine ester (boronate coupling agent) was not added. This is because the borate coupling agent can improve the compatibility between the inorganic filler and the organic polymer interface, maintain the stability of the slurry, and effectively prevent changes in slurry viscosity. At the same time, the borate coupling agent can also be activated in alkaline slurries (pH 8.5-9.5) to form reversible bonds with -OH on the silicon surface. After the bond breaks due to charge and discharge stress, the borate can quickly combine with the newly exposed silanol groups to continuously repair the cracks. The reversible breakage and recombination during charge and discharge continuously maintain the integrity of the electrode.

[0067] Therefore, the aqueous composite conductive slurry for silicon-based anodes of lithium batteries and its preparation method provided by the present invention can effectively improve the storage time of conductive slurry and delay the sedimentation of conductive slurry. At the same time, when applied to silicon-based anodes, it can convert the silicon expansion and destruction energy into reversible deformation energy, while ensuring the continuous unobstructed electron-ion channels, and ultimately extending the cycle life of silicon-based anodes. It has good performance and broad application prospects.

[0068] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An aqueous composite conductive paste for silicon-based anodes in lithium-ion batteries, characterized in that, The raw materials, by weight, include: 5-7 parts carbon nanotube powder, 2-4 parts graphene powder, 0.5-1.5 parts conductive carbon black, 0.6-0.8 parts sulfonated polythiophene-cellulose nanocrystal composite dispersant, 0.2-0.4 parts hydroxypropyl cellulose, 0.1-0.3 parts borate coupling agent, 0.6-0.8 parts glycerol, 0.3-0.5 parts carboxymethyl cellulose, and 80-100 parts deionized water.

2. The aqueous composite conductive paste for a silicon-based negative electrode of a lithium battery according to claim 1, characterized in that, The carbon nanotube powder includes at least one of multi-walled carbon nanotube powder, oligo-walled carbon nanotube powder, and single-walled carbon nanotube powder.

3. The aqueous composite conductive paste for a silicon-based negative electrode of a lithium battery according to claim 1, characterized in that, The graphene powder has a sheet diameter of 0.6~1.2μm and 2~5 layers.

4. The aqueous composite conductive paste for a silicon-based negative electrode of a lithium battery according to claim 1, characterized in that, The conductive carbon black has a particle size of 30~60nm.

5. The aqueous composite conductive slurry for a silicon-based negative electrode of a lithium battery according to claim 1, characterized in that, The preparation method of the sulfonated polythiophene-cellulose nanocrystal composite dispersant includes the following steps: S1. By weight, weigh out 10-20 parts of 3,4-ethylenedioxythiophene, 20-24 parts of ammonium persulfate, 15-18 parts of fuming sulfuric acid with an SO3 content of 20%-30%, 3-5 parts of cellulose nanocrystals with a diameter of 10-20 nm, 0.01-0.02 parts of 2,2,6,6-tetramethylpiperidine-1-oxy free radical, 0.2-0.4 parts of ammonium bicarbonate, 30-50 parts of oxalic acid, 10-12 parts of hydrogen peroxide solution with a mass fraction of 20%-30%, and 180-200 parts of deionized water. S2. Add ammonium persulfate to 3 / 5 of the deionized water and add 3,4-ethylenedioxythiophene dropwise. In an ice bath reactor at 0~5℃, nitrogen gas is introduced for protection. The mixture is stirred at 200~300 rpm for 4~6 hours. After filtration, polythiophene precipitate is obtained. S3. Add the polythiophene precipitate to fuming sulfuric acid, heat to 50-60℃ and react for 2-3 hours. After the product precipitates, wash it with anhydrous ethanol 3-5 times to obtain sulfonated polythiophene. S4. Add cellulose nanocrystals to oxalic acid, reflux in an oil bath at 100~110℃ for 2~3 hours, centrifuge, wash the lower solid with deionized water until neutral, and dry to obtain acid-heat activated cellulose nanocrystals. S5. Add acid-heat activated cellulose nanocrystals to 1 / 5 deionized water, and add 2,2,6,6-tetramethylpiperidine-1-oxy free radical, ammonium bicarbonate and hydrogen peroxide solution. Heat to 50~60℃ and stir for 6~8h. Filter and wash the product with anhydrous ethanol 3~5 times to obtain carboxylated cellulose nanocrystals. S6. Add sulfonated polythiophene and carboxylated cellulose nanocrystals to the remaining 1 / 5 of deionized water, and ultrasonically disperse at 200-300W for 20-30 minutes. Add acetic acid dropwise to adjust the pH to 3.0-3.5, heat to 50-60℃ and stir to react for 2-4 hours. After the reactants are rapidly frozen in liquid nitrogen, they are placed at -50--40℃ for vacuum freeze-drying for 20-24 hours, and then pulverized to obtain sulfonated polythiophene-cellulose nanocrystal composite dispersant.

6. The aqueous composite conductive paste for a silicon-based negative electrode of a lithium battery according to claim 1, characterized in that, The borate ester coupling agent includes at least one of alkyl borate diethanolamine ester, glyceryl borate ester, sorbitol borate ester, and mannitol borate ester.

7. A method for preparing an aqueous composite conductive paste for a silicon-based negative electrode of a lithium battery as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Weigh the raw materials according to the weight percentages; (2) Add carbon nanotube powder, graphene powder and conductive carbon black to 3 / 5 deionized water, add sulfonated polythiophene-cellulose nanocrystal composite dispersant, place in a high shear disperser and shear disperse at a speed of 14000~18000rpm for 30~40min, and then use an ultrasonic generator to ultrasonic disperse for 30~40min to obtain a pre-dispersion liquid. (3) Add hydroxypropyl cellulose, borate coupling agent, glycerol, carboxymethyl cellulose and the remaining 2 / 5 of deionized water to the pre-dispersion liquid, stir at 500~600 rpm at room temperature for 20~30 min, add ammonia water to adjust the pH to 8.5~9.5, then place in a homogenizer for homogenization for 1~2 h, and vacuum degas for 20~30 min to obtain an aqueous composite conductive slurry for silicon-based negative electrodes of lithium batteries.

8. The method for preparing an aqueous composite conductive paste for a silicon-based negative electrode of a lithium battery according to claim 7, characterized in that, The ultrasonic dispersion conditions in step (2) are a temperature of 30~40℃ and a power of 300~400W.

9. The method for preparing an aqueous composite conductive paste for a silicon-based negative electrode of a lithium battery according to claim 7, characterized in that, The vacuum degassing pressure in step (3) is -0.08 to -0.06 MPa.

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