Graphene conductive paste added with free radical quenching agent and preparation method of graphene conductive paste

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to graphene conductive paste added with a free radical quenching agent and a preparation method of the graphene conductive paste. The graphene conductive paste is formed by adding a free radical quenching agent into a graphene conductive paste matrix. According to the invention, 2, 6-di-tert-butyl-4-methylphenol (BHT) is utilized to capture free radicals in the graphene conductive slurry, the cross-linking reaction of a PVDF binder is inhibited, and the gelation reaction of the high-nickel ternary positive electrode material and the graphene conductive slurry is effectively inhibited on the premise of ensuring good conductivity and fluidity of the graphene conductive slurry.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a graphene conductive paste with added free radical quenchers and its preparation method. Background Art

[0002] The core structure of a lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. Its working principle involves charge transfer through the insertion / extraction of lithium ions between the positive and negative electrodes: during charging, lithium ions are extracted from the positive electrode, pass through the electrolyte and separator, and insert into the negative electrode; during discharging, they migrate in the opposite direction, releasing electrical energy. The positive electrode material is a key factor determining the energy density, voltage plateau, and cycle life of a lithium-ion battery. Positive electrode materials can be mainly divided into three categories: ternary materials (NCM / NCA), lithium iron phosphate (LFP), and lithium cobalt oxide (LCO). Ternary materials typically refer to materials with nickel, cobalt, and manganese / aluminum as core transition metals. These materials balance energy density, cost, and stability, making them the mainstream choice for mid-to-high-end lithium-ion battery positive electrode materials, especially in energy density-sensitive applications such as new energy vehicles and high-end consumer electronics.

[0003] Lithium nickel cobalt manganese oxide (NCM), as the most widely used ternary material, possesses comprehensive advantages such as controllable cost, excellent safety, balanced performance, and a mature industrial chain. High-nickel ternary materials, due to their high specific capacity, have become the mainstream direction for ternary material development. However, the cathode slurry system composed of high-nickel ternary materials and polyvinylidene fluoride (PVDF) binder suffers from severe chemical gelation problems. These chemical gelation problems are caused by the cross-linking reaction of PVDF molecular chains in the cathode slurry. In existing technologies, some studies have attempted to reduce side reactions between PVDF and high-nickel ternary materials by chemically modifying PVDF (e.g., introducing acrylate groups or adjusting the molecular chain structure). However, this method not only relies on complex synthesis processes but also leads to a decrease in the cycle performance of lithium-ion batteries due to reduced electrolyte tolerance of the binder after chemical modification. Other studies have used additives such as epoxides and organophosphonates to slow down the gelation process; however, these additives can only partially inhibit the reaction and cannot fundamentally block the reaction caused by the active sites on the surface of high-nickel ternary cathode materials (such as Ni...). 4+The free radical chain cross-linking reaction initiated by the defluorination of PVDF is catalyzed. Meanwhile, traditional carbon-based conductive agents (such as Super P and carbon nanotubes) suffer from defects in cathode slurries, including uneven dispersion, high interfacial impedance with high-nickel ternary cathode materials, and poor mechanical stability. These defects easily lead to the formation of conductive islands during lithium-ion battery charging and discharging, increasing charge transfer resistance, and causing conductive network breakage due to electrode volume changes. Consequently, cathode slurries exhibit drawbacks such as short shelf life, poor coating quality, and low capacity retention after 500 battery cycles, making it difficult to meet the industrial production requirements of high-energy-density lithium-ion batteries. Summary of the Invention

[0004] To address the severe chemical gelation problem in cathode slurry systems composed of high-nickel ternary cathode materials and polyvinylidene fluoride (PVDF) binders, this invention provides a graphene conductive slurry with added free radical quenchers and its preparation method. The free radical quenchers capture free radicals in the graphene conductive slurry and are combined with glycidyl etheroxypropyltrimethoxysilane (GPTMS), an inhibitor of the elimination reaction, to suppress the crosslinking reaction of the PVDF binder. This effectively inhibits the gelation reaction between the high-nickel ternary cathode material and the graphene conductive slurry while ensuring good conductivity and flowability of the graphene conductive slurry.

[0005] The technical solution of this invention is as follows: In a first aspect, the present invention provides a graphene conductive paste with added free radical quenchers, wherein free radical quenchers are added to the graphene conductive paste matrix.

[0006] Furthermore, the graphene conductive paste matrix comprises the following components in parts by weight: 100 parts by weight of active material, 0.6-2.4 parts by weight of graphene or its derivatives, 3-6 parts by weight of conductive agent, 0.2-0.8 parts by weight of dispersant, 16-24 parts by weight of PVDF binder, 1.2-3.6 parts by weight of GPTMS, and 61-78.4 parts by weight of diluent.

[0007] Furthermore, the mass of the free radical quencher is 0.6%-2.2% of the mass of the active material. This invention controls the mass of the free radical quencher to 0.6%-2.2% of the mass of the active material, which is beneficial for regulating the coating viscosity of the graphene conductive paste, significantly reducing the gelation rate of the graphene conductive paste during coating, and avoiding problems such as equipment blockage and uneven coating.

[0008] Furthermore, the free radical quencher is BHT (molecular formula C). 15 H 24The active material is NCM811. BHT (2,6-di-tert-butyl-4-methylphenol) is used to suppress the chemical gelation phenomenon caused by the chemical reaction between the PVDF binder and the high-nickel cathode material, significantly improving the fluidity of the slurry, ensuring the smooth progress of the coating process, maintaining the conductivity of the slurry, and ensuring the overall performance and long-term stability of the battery. As a small molecule organic compound (relative molecular mass of approximately 220 g / mol), BHT has the characteristics of low steric hindrance and excellent dispersibility, which can diffuse rapidly and uniformly in the graphene conductive slurry. It has a high probability of colliding with the PVDF chain free radicals in the graphene conductive slurry, resulting in high free radical capture efficiency. The phenolic hydroxyl group in the BHT molecule has a strong hydrogen donation capacity, which can quench the free radicals generated during the PVDF deHF removal process, form stable new chemical bonds, cut off the PVDF crosslinking reaction chain, and fundamentally inhibit the gelation reaction. Moreover, the steric hindrance effect of the tert-butyl group on the benzene ring can enhance its stability in an alkaline environment, avoiding direct destruction by residual alkali. Furthermore, it can rapidly capture PVDF chain free radicals at low concentrations. The present invention extends the gelation time to 5-8 hours by adding BHT to a graphene conductive slurry containing PVDF binder, and the viscosity change rate is ≤30% after 7 days of storage at 25°C, indicating high storage stability.

[0009] Furthermore, the graphene derivative is graphene oxide, the conductive agent is at least one of carbon black or carbon nanotubes, preferably carbon black, the PVDF binder is PVDF5130, the dispersant is polyvinylpyrrolidone or carboxymethyl cellulose, preferably carboxymethyl cellulose, and the diluent is N-methylpyrrolidone.

[0010] Secondly, the present invention also provides a method for preparing a graphene conductive paste with added free radical quencher as described above, comprising the following steps: Step 1: Prepare the adhesive solution. Add 0.2-0.8 parts by weight of dispersant and 16-24 parts by weight of PVDF binder to 61-78.4 parts by weight of diluent. Heat to 65±2℃ and stir until the dispersant and PVDF binder are completely dissolved to obtain the adhesive solution.

[0011] Step 2: Base material mixing. Add 0.6-2.4 parts by weight of graphene or its derivatives and 3-6 parts by weight of conductive agent to the binder, and stir at a constant temperature of 65±2℃ to obtain conductive slurry.

[0012] Step 3: Adding free radical quencher and GPTMS. After the conductive slurry cools to room temperature, add 0.6-2.2 parts by weight of free radical quencher and 1.2-3.6 parts by weight of GPTMS, and then perform ultrasonic dispersion to obtain the modified slurry. Step 4: Homogenization control. The modified slurry is homogenized, and then the viscosity of the homogenized slurry is adjusted to 3000-5000 mPa·s to obtain a homogenized slurry. The homogenized slurry is stirred for 30 minutes under a vacuum of -0.08 to -0.1 MPa to remove air bubbles. Step 5: Slowly add 100 parts by weight of active material to the homogenized slurry and stir at 300-500 rpm for 1-2 hours to obtain graphene conductive slurry.

[0013] Furthermore, in step one, the stirring speed is 500-600 rpm.

[0014] Furthermore, in step two, the constant temperature stirring speed is 300-800 rpm, and the constant temperature stirring time is 15-20 minutes.

[0015] Furthermore, in step three, the ultrasonic dispersion time is 30 minutes, and the ultrasonic dispersion power is 200W.

[0016] Furthermore, in step four, the homogenized slurry is homogenized for 10 minutes using a high-shear homogenizer at a speed of 10,000-12,000 rpm. The viscosity of the homogenized slurry is monitored in real time using a Brookfield viscometer and adjusted to 3,000-5,000 mPa·s.

[0017] Thirdly, the present invention also provides an application of the above-mentioned graphene conductive paste to further prepare a positive electrode sheet using the above-mentioned graphene conductive paste. The preparation method of the positive electrode sheet includes the following steps: A wet film with a thickness of 100-200 μm is coated on aluminum foil using a slit coating method at a coating speed of 1-5 m / min. After coating, the film is vacuum dried at 60-80℃ for 6-12 hours to obtain the positive electrode sheet. Lithium-ion batteries prepared using the above positive electrode sheet exhibit a capacity retention of ≥85% after 100 cycles at a 1C charge-discharge rate, and a capacity retention of over 80% under 5C high-rate discharge conditions.

[0018] The beneficial effects of the present invention are: This invention introduces 2,6-di-tert-butyl-4-methylphenol (BHT) as a free radical quencher into a graphene conductive slurry containing PVDF binder. With a relatively low addition amount, the slurry gelation time is extended to 5-8 hours. The viscosity change rate of the slurry with added BHT after 7 days of storage at 25°C is only 24%-27%. This fundamentally solves the chemical gelation problem caused by the reaction between high-nickel cathode materials and PVDF binder, ensuring the slurry maintains stable fluidity over a long period. Lithium-ion batteries prepared using the slurry provided by this invention retain 88.6%-97.2% of their capacity after 100 charge-discharge cycles at 1C; 82%-89% of their capacity after 5C high-rate discharge; and only 15%-25% of their internal resistance increase after 30 days of storage at 60°C. This significantly extends the cycle life of lithium-ion batteries and improves their safety. Attached Figure Description

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 This is a photograph of the graphene conductive paste after being sealed and stored for 45 days in Example 1.

[0021] Figure 2 This is a photo of the cathode slurry in Comparative Example 3 after being sealed and stored for 45 days. Detailed Implementation

[0022] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0023] Example 1 A graphene conductive paste with added free radical quencher, wherein 0.78 parts by weight of BHT is added to the graphene conductive paste matrix, wherein the graphene conductive paste matrix comprises the following components in parts by weight: 100 parts by weight of NCM811, 1.94 parts by weight of graphene, 3.88 parts by weight of carbon black, 0.29 parts by weight of carboxymethyl cellulose, 17.41 parts by weight of PVDF binder, 1.95 parts by weight of GPTMS and 74.15 parts by weight of N-methylpyrrolidone.

[0024] A method for preparing the graphene conductive paste as described above includes the following steps: Step 1: Preparation of the binder solution. First, add 74.15 parts by weight of N-methylpyrrolidone to the reactor. Then, add 0.29 parts by weight of carboxymethyl cellulose and 17.41 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. Heat to 65°C and stir at 600 rpm for 30 minutes until the carboxymethyl cellulose and PVDF binder are completely dissolved, resulting in a homogeneous binder solution. The PVDF binder was purchased from KELOD Company, model PVDF5130, with a purity ≥99% and a water content <0.1%.

[0025] Step 2: Base material mixing. Add 1.94 parts by weight of graphene powder and 3.88 parts by weight of carbon black to the binder liquid, and stir at 450 rpm for 20 minutes at 65°C to obtain a conductive paste. The graphene powder has a sheet diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0026] Step 3: Adding free radical quencher and GPTMS. After the conductive slurry cools to 25°C, add 0.78 parts by weight of BHT and 1.95 parts by weight of GPTMS. Then, disperse the mixture using 200W ultrasonic waves for 30 minutes at a frequency of 40kHz to obtain the modified slurry. The purity of BHT is ≥98%.

[0027] Step 4: Homogenization and Adjustment. Homogenize the slurry using a high-shear homogenizer at 11,000 rpm for 10 minutes, monitoring the viscosity of the modified slurry in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized slurry to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 A homogeneous slurry was obtained, and the homogeneous slurry was stirred for 30 minutes under a vacuum of -0.09 MPa to remove air bubbles.

[0028] Step 5: Slowly add 100 parts by weight of NCM811 to the homogenized slurry after removing air bubbles, and stir at 450 rpm for 1 hour to obtain graphene conductive slurry.

[0029] The stability of the graphene conductive paste was tested using the following method: The graphene conductive paste was sealed and stored at 25°C. The viscosity change rates after 48 hours and 7 days of sealed storage were measured using a rotational rheometer and found to be 12% and 24%, respectively. After 45 days of sealed storage, the graphene conductive paste was observed... Figure 1 As shown, the graphene conductive paste did not exhibit gelation.

[0030] A wet film of graphene conductive paste with a thickness of 100 μm was coated on an aluminum foil with a thickness of 12 μm using a slit coating method at a coating speed of 2 m / min. After coating, the film was vacuum dried at 65 °C for 12 hours to obtain the positive electrode of a lithium-ion battery.

[0031] A 2032-type coin cell was assembled using the prepared lithium-ion battery positive electrode sheet, with a 1M LiPF6 / EC+DEC electrolyte (volume ratio 1:1). The battery retained 97.2% of its capacity after 100 cycles at 1C charge-discharge conditions and 93.5% after 500 cycles.

[0032] The battery retains 89% of its capacity at a 5C high-rate discharge and 75% at a 10C discharge. After 30 days of storage at 60℃, the capacity loss is 3.2%, and the internal resistance increases by 15%.

[0033] Example 2 A graphene conductive paste with added free radical quencher, wherein 0.6 parts by weight of BHT is added to the graphene conductive paste matrix, wherein the graphene conductive paste matrix comprises the following components in parts by weight: 100 parts by weight of NCM811, 1.94 parts by weight of graphene, 3.88 parts by weight of carbon black, 0.29 parts by weight of carboxymethyl cellulose, 17.41 parts by weight of PVDF binder, 1.95 parts by weight of GPTMS, and 73.93 parts by weight of N-methylpyrrolidone.

[0034] A method for preparing the graphene conductive paste as described above includes the following steps: Step 1: Preparation of the binder solution. First, add 73.93 parts by weight of N-methylpyrrolidone to the reactor. Then, add 0.29 parts by weight of carboxymethyl cellulose and 17.41 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. Heat to 65°C and stir at 600 rpm for 30 minutes until the carboxymethyl cellulose and PVDF binder are completely dissolved, resulting in a homogeneous binder solution. The PVDF binder was purchased from KELOD Company, model PVDF5130, with a purity ≥99% and a water content <0.1%.

[0035] Step 2: Base material mixing. Add 1.94 parts by weight of graphene powder and 3.88 parts by weight of carbon black to the binder liquid, and stir at 450 rpm at 65°C for 20 minutes to obtain a conductive paste. The graphene powder has a sheet diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0036] Step 3: Adding free radical quencher and GPTMS. After the conductive slurry cools to 25°C, add 0.6 parts by weight of BHT and 1.95 parts by weight of GPTMS. Then, disperse the mixture using 200W ultrasonic waves for 30 minutes at a frequency of 40kHz to obtain the modified slurry. The purity of BHT is ≥98%.

[0037] Step 4: Homogenization and Adjustment. Homogenize the slurry using a high-shear homogenizer at 11,000 rpm for 10 minutes, monitoring the viscosity of the modified slurry in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized slurry to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 A homogeneous slurry was obtained, and the homogeneous slurry was stirred at a vacuum of -0.09 MPa for 30 minutes to remove air bubbles.

[0038] Step 5: Slowly add 100 parts by weight of NCM811 to the homogenized slurry after removing air bubbles, and stir at 450 rpm for 1 hour to obtain graphene conductive slurry.

[0039] The stability of the graphene conductive paste was tested using the following method: the graphene conductive paste was sealed and stored at 25°C. The viscosity change rate of the graphene conductive paste after 48 hours and 7 days of sealed storage was measured using a rotational rheometer, and was 15% and 29%, respectively. After 45 days of sealed storage, the graphene conductive paste was observed, and no gelation phenomenon was observed.

[0040] A wet film of graphene conductive paste with a thickness of 100 μm was coated on an aluminum foil with a thickness of 12 μm using a slit coating method at a coating speed of 2 m / min. After coating, the film was vacuum dried at 65 °C for 12 hours to obtain the positive electrode of a lithium-ion battery.

[0041] A 2032-type coin cell was assembled using the prepared lithium-ion battery positive electrode sheet, with a 1M LiPF6 / EC+DEC electrolyte (volume ratio 1:1). The battery retained 88.6% of its capacity after 100 cycles at 1C charge-discharge conditions; and 82.2% of its capacity after 500 cycles.

[0042] The battery retains 82% of its capacity during 5C high-rate discharge and 68% during 10C discharge. After 30 days of storage at 60℃, the capacity loss rate is 5.8%, and the internal resistance increases by 25%.

[0043] Example 3 A graphene conductive paste with added free radical quencher, wherein 2.2 parts by weight of BHT are added to the graphene conductive paste matrix, wherein the graphene conductive paste matrix comprises the following components in parts by weight: 100 parts by weight of NCM811, 1.94 parts by weight of graphene, 3.88 parts by weight of carbon black, 0.29 parts by weight of carboxymethyl cellulose, 17.41 parts by weight of PVDF binder, 1.95 parts by weight of GPTMS and 72.33 parts by weight of N-methylpyrrolidone.

[0044] A method for preparing the graphene conductive paste as described above includes the following steps: Step 1: Preparation of the binder solution. First, add 72.33 parts by weight of N-methylpyrrolidone to the reactor. Then, add 0.29 parts by weight of carboxymethyl cellulose and 17.41 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. Heat to 65°C and stir at 600 rpm for 30 minutes until the carboxymethyl cellulose and PVDF binder are completely dissolved, resulting in a homogeneous binder solution. The PVDF binder was purchased from KELOD Company, model PVDF5130, with a purity ≥99% and a water content <0.1%.

[0045] Step 2: Base material mixing. Add 1.94 parts by weight of graphene powder and 3.88 parts by weight of carbon black to the binder liquid, and stir at 450 rpm at 65°C for 20 minutes to obtain a conductive paste. The graphene powder has a sheet diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0046] Step 3: Adding free radical quencher and GPTMS. After the conductive slurry cools to 25°C, add 2.2 parts by weight of BHT and 1.95 parts by weight of GPTMS. Then, disperse the mixture using 200W ultrasonic waves for 30 minutes at a frequency of 40kHz to obtain the modified slurry. The purity of BHT is ≥98%.

[0047] Step 4: Homogenization and Adjustment. Homogenize the slurry using a high-shear homogenizer at 11,000 rpm for 10 minutes, monitoring the viscosity of the modified slurry in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized slurry to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 A homogeneous slurry was obtained, and the homogeneous slurry was stirred at a vacuum of -0.09 MPa for 30 minutes to remove air bubbles.

[0048] Step 5: Slowly add 100 parts by weight of NCM811 to the homogenized slurry after removing air bubbles, and stir at 450 rpm for 1 hour to obtain graphene conductive slurry.

[0049] The stability of the graphene conductive paste was tested using the following method: the graphene conductive paste was sealed and stored at 25°C. The viscosity change rate of the graphene conductive paste after 48 hours and 7 days of sealed storage was measured using a rotational rheometer, and was 14% and 27%, respectively. After 45 days of sealed storage, the graphene conductive paste was observed, and no gelation phenomenon was observed.

[0050] A wet film of graphene conductive paste with a thickness of 100 μm was coated on an aluminum foil with a thickness of 12 μm using a slit coating method at a coating speed of 2 m / min. After coating, the film was vacuum dried at 65 °C for 12 hours to obtain the positive electrode of a lithium-ion battery.

[0051] A 2032-type coin cell was assembled using the prepared lithium-ion battery positive electrode sheet, with a 1M LiPF6 / EC+DEC electrolyte (volume ratio 1:1). The battery retained 91.8% of its capacity after 100 cycles at 1C charge-discharge conditions; and 85.4% of its capacity after 500 cycles.

[0052] The battery retains 86% of its capacity at a 5C high-rate discharge and 69% at a 10C discharge. After 30 days of storage at 60℃, the capacity loss rate is 3.1%, and the internal resistance increases by 19%.

[0053] Comparative Example 1 Comparative Example 1 provides a positive electrode slurry, in which 0.78 parts by weight of Irganox 1010 are added to a graphene conductive slurry matrix. The graphene conductive slurry matrix comprises the following components in parts by weight: 100 parts by weight of NCM811, 1.94 parts by weight of graphene, 3.88 parts by weight of carbon black, 0.29 parts by weight of carboxymethyl cellulose, 17.41 parts by weight of PVDF binder, 1.95 parts by weight of GPTMS, and 74.15 parts by weight of N-methylpyrrolidone.

[0054] The preparation method of the positive electrode slurry in Comparative Example 1 is basically the same as that in Example 1, the main difference being the addition of Irganox 1010 as a quenching agent in step three. The preparation method of the positive electrode slurry in Comparative Example 1 is as follows: Step 1: Prepare the adhesive solution. First, add 74.15 parts by weight of N-methylpyrrolidone to the reactor. Then, add 0.29 parts by weight of carboxymethyl cellulose and 17.41 parts by weight of PVDF adhesive to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the carboxymethyl cellulose and PVDF adhesive are completely dissolved to obtain a uniform adhesive solution.

[0055] Step 2: Base material mixing. Add 1.94 parts by weight of graphene powder and 3.88 parts by weight of carbon black to the binder liquid, and stir at 450 rpm for 20 minutes at 65°C to obtain a conductive paste. The graphene powder has a sheet diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0056] Step 3: Addition of quencher and GPTMS. After the conductive slurry cools to 25°C, add 0.78 parts by weight of Irganox 1010 and 1.95 parts by weight of GPTMS. Then, disperse the mixture using 200W ultrasonic waves for 30 minutes at a frequency of 40kHz to obtain the modified slurry. The molecular formula of Irganox 1010 is C2. 73 H 108 O 12 .

[0057] Step 4: Homogenization and Adjustment. Homogenize the slurry using a high-shear homogenizer at 11,000 rpm for 10 minutes, monitoring the viscosity of the modified slurry in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized slurry to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 A homogeneous slurry was obtained, and the homogeneous slurry was stirred at a vacuum of -0.09 MPa for 30 minutes to remove air bubbles.

[0058] Step 5: Slowly add 100 parts by weight of NCM811 to the homogenized slurry after removing air bubbles, and stir at 450 rpm for 1 hour to obtain the positive electrode slurry.

[0059] The stability of the cathode slurry was tested using the following method: the cathode slurry was sealed and stored at 25°C. The viscosity change rate of the cathode slurry after 48 hours and 7 days of sealed storage was measured using a rotational rheometer, and was 29% and 58%, respectively. After 45 days of sealed storage, the cathode slurry was observed, and no gelation was observed.

[0060] A wet film of positive electrode slurry was coated on an aluminum foil with a thickness of 12 μm using a slit coating method. The wet film thickness was 100 μm, and the coating speed was 2 m / min. After coating, the film was vacuum dried at 65 °C for 12 hours to obtain the positive electrode sheet of a lithium-ion battery.

[0061] A 2032-type coin cell was assembled using the prepared lithium-ion battery positive electrode sheet, with a 1M LiPF6 / EC+DEC electrolyte (volume ratio 1:1). The battery retained 81.7% of its capacity after 100 cycles at 1C charge-discharge conditions; and 76.2% of its capacity after 500 cycles.

[0062] The battery retains 68% of its capacity at a 5C high-rate discharge and 52% at a 10C discharge. After 30 days of storage at 60℃, the capacity loss rate is 8.7%, and the internal resistance increases by 45%.

[0063] Comparative Example 2 Comparative Example 2 provides a positive electrode slurry, in which 0.78 parts by weight of poly(2,2,6,6-tetramethylpiperidin-1-oxy)methacrylate (PTMA, molecular weight approximately 5000 Da) is added to a graphene conductive slurry matrix. The graphene conductive slurry matrix comprises the following components in parts by weight: 100 parts by weight of NCM811, 1.94 parts by weight of graphene, 3.88 parts by weight of carbon black, 0.29 parts by weight of carboxymethyl cellulose, 17.41 parts by weight of PVDF binder, 1.95 parts by weight of GPTMS, and 74.15 parts by weight of N-methylpyrrolidone.

[0064] The preparation method of the positive electrode slurry in Comparative Example 2 is basically the same as that in Example 1, the main difference being the addition of PTMA as a quenching agent in step three. The preparation method of the positive electrode slurry in Comparative Example 1 is as follows: Step 1: Prepare the adhesive solution. First, add 74.15 parts by weight of N-methylpyrrolidone to the reactor. Then, add 0.29 parts by weight of carboxymethyl cellulose and 17.41 parts by weight of PVDF adhesive to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the carboxymethyl cellulose and PVDF adhesive are completely dissolved to obtain a uniform adhesive solution.

[0065] Step 2: Base material mixing. Add 1.94 parts by weight of graphene powder and 3.88 parts by weight of carbon black to the binder liquid, and stir at 450 rpm for 20 minutes at 65°C to obtain a conductive paste. The graphene powder has a sheet diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0066] Step 3: Addition of quencher and GPTMS. After the conductive slurry cools to 25°C, add 0.78 parts by weight of PTMA and 1.95 parts by weight of GPTMS. Then, disperse the mixture using 200W ultrasonic waves for 30 minutes at a frequency of 40kHz to obtain the modified slurry. The PTMA was purchased from Shanghai Yuyu New Materials Technology Co., Ltd., model Rhodamine B (PTMA).

[0067] Step 4: Homogenization and Adjustment. Homogenize the slurry using a high-shear homogenizer at 11,000 rpm for 10 minutes, monitoring the viscosity of the modified slurry in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized slurry to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 A homogeneous slurry was obtained, and the homogeneous slurry was stirred at a vacuum of -0.09 MPa for 30 minutes to remove air bubbles.

[0068] Step 5: Slowly add 100 parts by weight of NCM811 to the homogenized slurry after removing air bubbles, and stir at 450 rpm for 1 hour to obtain the positive electrode slurry.

[0069] The stability of the cathode slurry was tested using the following method: the cathode slurry was sealed and stored at 25°C. The viscosity change rate of the cathode slurry after 48 hours and 7 days of sealed storage was measured using a rotational rheometer, and was 27% and 68%, respectively. After 45 days of sealed storage, the cathode slurry was observed, and no gelation phenomenon was observed.

[0070] A wet film of positive electrode slurry was coated on an aluminum foil with a thickness of 12 μm using a slit coating method. The wet film thickness was 100 μm, and the coating speed was 2 m / min. After coating, the film was vacuum dried at 65 °C for 12 hours to obtain the positive electrode sheet of a lithium-ion battery.

[0071] A 2032-type coin cell was assembled using the prepared lithium-ion battery positive electrode sheet, with a 1M LiPF6 / EC+DEC electrolyte (volume ratio 1:1). The battery retained 82% of its capacity after 100 cycles at 1C charge-discharge conditions; and 78% of its capacity after 500 cycles.

[0072] The battery retains 70% of its capacity during 5C high-rate discharge and 58% during 10C discharge. After 30 days of storage at 60℃, the capacity loss rate is 7.9%, and the internal resistance increases by 28%.

[0073] Comparative Example 3 Comparative Example 3 provides a positive electrode slurry comprising a graphene conductive slurry matrix, wherein the graphene conductive slurry matrix comprises the following components in parts by weight: 100 parts by weight of NCM811, 1.94 parts by weight of graphene, 3.88 parts by weight of carbon black, 0.29 parts by weight of carboxymethyl cellulose, 17.41 parts by weight of PVDF binder, 1.95 parts by weight of GPTMS, and 74.93 parts by weight of N-methylpyrrolidone.

[0074] The preparation method of the positive electrode slurry includes the following steps: Step 1: Prepare the adhesive solution. First, add 74.93 parts by weight of N-methylpyrrolidone to the reactor. Then, add 0.29 parts by weight of carboxymethyl cellulose and 17.41 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the carboxymethyl cellulose and PVDF binder are completely dissolved to obtain a uniform adhesive solution.

[0075] Step 2: Base material mixing. Add 1.94 parts by weight of graphene powder and 3.88 parts by weight of carbon black to the binder liquid, along with 1.95 parts by weight of GPTMS. Stir at 450 rpm at 65°C for 20 minutes to obtain a conductive paste. The graphene powder has a sheet diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0076] Step 3: Homogenization and Adjustment. Homogenize the conductive slurry for 10 minutes using a high-shear homogenizer at 11,000 rpm, monitoring the viscosity in real-time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized slurry to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 A homogeneous slurry was obtained, and the homogeneous slurry was stirred at a vacuum of -0.09 MPa for 30 minutes to remove air bubbles.

[0077] Step 4: Slowly add 100 parts by weight of NCM811 to the homogenized slurry after removing air bubbles, and stir at 450 rpm for 1 hour to obtain the positive electrode slurry.

[0078] The stability of the cathode slurry was tested using the following method: The cathode slurry was sealed and stored at 25°C. The viscosity change rates after 48 hours and 7 days of sealed storage were measured using a rotational rheometer; these rates were 29% and 78%, respectively. After 45 days of sealed storage, the cathode slurry was observed. Figure 2 As shown, the positive electrode slurry exhibits obvious gelation.

[0079] A wet film of positive electrode slurry was coated on an aluminum foil with a thickness of 12 μm using a slit coating method. The wet film thickness was 100 μm, and the coating speed was 2 m / min. After coating, the film was vacuum dried at 65 °C for 12 hours to obtain the positive electrode sheet of a lithium-ion battery.

[0080] A 2032 coin cell was assembled using lithium-ion battery positive electrode sheets, with a 1M LiPF6 / EC+DEC electrolyte (volume ratio 1:1). After 100 cycles at 1C charge-discharge conditions, the battery capacity decayed to 78% of its initial value; after 500 cycles, the capacity retention was only 42%.

[0081] The battery retains 62% of its capacity at a 5C high-rate discharge and 36% at a 10C discharge. After 30 days of storage at 60℃, the capacity loss rate is 42%, and the internal resistance increases by 210%.

[0082] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A graphene conductive paste with added free radical quencher, characterized in that, Add a free radical quencher to the graphene conductive paste matrix.

2. The graphene conductive paste with added free radical quencher as described in claim 1, characterized in that, The graphene conductive paste matrix comprises the following components in parts by weight: 100 parts by weight of active material, 0.6-2.4 parts by weight of graphene or its derivatives, 3-6 parts by weight of conductive agent, 0.2-0.8 parts by weight of dispersant, 16-24 parts by weight of PVDF binder, 1.2-3.6 parts by weight of GPTMS, and 61-78.4 parts by weight of diluent.

3. The graphene conductive paste with added free radical quencher as described in claim 2, characterized in that, The mass of the free radical quencher is 0.6%-2.2% of the mass of the active substance.

4. The graphene conductive paste with added free radical quencher as described in claim 3, characterized in that, The free radical quencher is BHT, and the active substance is NCM811.

5. The graphene conductive paste with added free radical quencher as described in claim 2, characterized in that, The graphene derivative is graphene oxide, the conductive agent is at least one of carbon black or carbon nanotubes, the PVDF binder is PVDF5130, the dispersant is polyvinylpyrrolidone or carboxymethyl cellulose, and the diluent is N-methylpyrrolidone.

6. A method for preparing a graphene conductive paste as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Prepare the adhesive solution by adding the dispersant and PVDF binder to the diluent in sequence, heating to 65±2℃, and stirring until the dispersant and PVDF binder are completely dissolved to obtain the adhesive solution. Step 2: Base material mixing. Graphene or its derivatives and conductive agents are added to the binder liquid and stirred at a constant temperature of 65±2℃ to obtain conductive slurry. Step 3: Adding free radical quencher and GPTMS. After the conductive slurry cools to room temperature, add free radical quencher and GPTMS to it, and then perform ultrasonic dispersion to obtain the modified slurry. Step 4: Homogenization control. The modified slurry is homogenized, and then the viscosity of the homogenized slurry is adjusted to 3000-5000 mPa·s to obtain a homogenized slurry. Step 5: Add the active material to the homogeneous slurry and stir to obtain graphene conductive slurry.

7. The preparation method according to claim 6, characterized in that, In step one, the stirring speed is 500-600 rpm.

8. The preparation method according to claim 6, characterized in that, In step two, the constant temperature stirring speed is 300-800 rpm, and the constant temperature stirring time is 15-20 minutes.

9. The preparation method according to claim 6, characterized in that, In step three, the ultrasonic dispersion time is 30 minutes.

10. The preparation method according to claim 6, characterized in that, In step four, the mixture is homogenized for 10 minutes using a high-shear homogenizer at a speed of 10,000-12,000 rpm.

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