A positive electrode sheet containing a graphene composite conductive agent, a preparation method thereof and a lithium ion battery

Abstract

The application discloses a positive electrode sheet containing a graphene composite conductive agent and a preparation method thereof and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The positive electrode sheet containing the graphene composite conductive agent comprises a composite conductive agent, a positive electrode active material and a binder. The composite conductive agent comprises graphene, conductive carbon black and an organic solvent. The composite conductive agent containing graphene, conductive carbon black and an organic solvent is used to form the positive electrode sheet together with the positive electrode active material and the binder, so that the problem of limited conductive path and high overall internal resistance of the existing single conductive agent system is solved. The dimension complementary characteristics of the zero-dimensional carbon black and the two-dimensional graphene are relied on to construct a point-surface collaborative conductive framework in the positive electrode sheet, the electronic transmission efficiency is improved, the stability of the positive electrode sheet structure is enhanced, and core structural support is provided for performance optimization under a low conductive agent dosage.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a positive electrode sheet containing a graphene composite conductive agent, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, due to their advantages such as high energy density, long cycle life, and low self-discharge rate, have been widely used in various fields such as consumer electronics, new energy vehicles, and energy storage power stations. As a core component of lithium-ion batteries, the positive electrode's internal conductive network structure stability and transmission efficiency directly determine the battery's rate charge / discharge performance, cycle life, and overall energy density, making it one of the core research directions in the development of positive electrode material systems.

[0003] Currently, commercially available cathode electrodes generally use zero-dimensional conductive carbon black as a conductive agent, relying on point contacts between particles to fill the gaps between active materials and construct electron transport pathways. However, this type of conductive agent has a high percolation threshold, typically requiring an addition of 3% to 5% to form a continuous conductive network. This not only reduces the proportion of active material in the cathode, limiting further improvements in battery energy density, but also, in high-area-density thick electrode systems, carbon black particles struggle to form uniform, interconnected pathways along the electrode thickness, easily leading to localized agglomeration and the formation of "conductive islands." This results in uneven electron transport resistance within the electrode, severe polarization under high-rate charge-discharge conditions, and accelerated capacity decay during cycling.

[0004] To reduce the amount of conductive agent used and improve conductivity, two-dimensional layered graphene materials, with their excellent in-plane conductivity and structural reinforcement, are being gradually introduced into cathode conductive systems. Existing technologies have developed techniques for combining graphene with conductive carbon black, attempting to create a synergistic conductivity effect through a "point-to-surface" combination. Some of these solutions can reduce the amount of conductive agent used to a certain extent and demonstrate performance improvements in cathode systems such as lithium cobalt oxide and ternary materials. For example, some commercially available graphene conductive slurry products can achieve high-rate capacity retention in lithium iron phosphate cathodes, and have seen initial applications in the power battery field.

[0005] However, existing graphene composite conductive agents and corresponding positive electrode technologies still have many defects and shortcomings, making it difficult to meet the development needs of high-performance lithium-ion batteries: First, there is a lack of cross-scale conductive network designs at the electrode scale. Existing solutions mostly involve simple compounding of raw materials, which leads to easy stacking and agglomeration of graphene and carbon black failing to effectively fill the gaps between the sheets and active particles, making it difficult to form a stable three-dimensional pathway that runs through the electrode and resulting in insufficient synergistic effects.

[0006] Secondly, the evolution of the conductive network throughout the entire preparation process is not controlled. The existing process does not match the entire process of homogenization, coating, drying, and rolling, and cannot achieve the orderly transfer of the conductive network from the dispersed state of the slurry to the solid state of the electrode. As a result, the network has poor continuity and insufficient batch stability of the product.

[0007] Third, the electron percolation capacity is insufficient at low amounts of conductive agent. Existing systems tend to exceed the percolation threshold when the addition amount is reduced to below 2.0%, resulting in a significant increase in the internal resistance of the electrode and a significant decrease in performance. It is impossible to achieve both low dosage and high electrochemical performance in the range of 0.5% to 2.0%.

[0008] Fourth, the uniformity of conductive agent distribution within the electrode is poor, resulting in a significant island effect. Due to limitations in dispersion and coating processes, the conductive agent is prone to local enrichment or absence, failing to form a continuous network across the entire area. This problem is further amplified in high areal density electrodes, leading to poor overall electrode uniformity.

[0009] Fifth, there is a mismatch between electron and ion channel transport. Existing optimized multi-focus electron conduction methods have not achieved decoupling between the two; excessive graphene coverage of the active material surface can block lithium-ion diffusion channels, leading to increased polarization and accelerated capacity decay under high rate and high load conditions.

[0010] Sixth, the adaptability of the preparation process is insufficient. Most existing graphene slurries adopt a single dispersion process. High-intensity shearing can easily damage the graphene sheet structure, while low-intensity shearing results in insufficient dispersion and poor slurry stability. Moreover, some preparation routes are costly and difficult to adapt to large-scale production.

[0011] In summary, the field currently lacks a systematic technical solution covering the entire process from conductive agent formulation design and dispersion preparation to electrode molding. It is impossible to construct a stable and uniform cross-scale three-dimensional conductive network under low conductive agent addition conditions, and it is difficult to simultaneously achieve a synergistic improvement in the rate performance, cycle stability, and energy density of lithium-ion batteries. Therefore, it is urgent to develop novel positive electrode sheets containing graphene composite conductive agents and their preparation technology to solve the above-mentioned problems in the existing technology. Summary of the Invention

[0012] Based on the technical problems existing in the prior art, the present invention provides a positive electrode sheet containing graphene composite conductive agent, a method for preparing the same, and a lithium-ion battery.

[0013] According to a first aspect of the technical solution of the present invention, a positive electrode sheet containing a graphene composite conductive agent is provided, comprising a composite conductive agent, a positive electrode active material and a binder; the composite conductive agent includes graphene, conductive carbon black and an organic solvent.

[0014] A further improvement of the present invention is that: in the composite conductive agent, the mass percentage of graphene is 5% to 15%, the mass percentage of conductive carbon black is 10% to 25%, and the mass percentage of organic solvent is 60% to 85%.

[0015] A further improvement of the present invention is that: the organic solvent is N-methylpyrrolidone, the positive electrode active material is lithium iron phosphate positive electrode material, and the binder is polyvinylidene fluoride.

[0016] A further improvement of the present invention is that the graphene has 1 to 10 layers and a sheet diameter of 1 μm to 20 μm, and the conductive carbon black has a particle size of 20 nm to 80 nm.

[0017] A further improvement of the present invention is that, in the composite conductive agent, the positive electrode active material and the binder, the mass percentage of the composite conductive agent is 0.5% to 2%.

[0018] According to a second aspect of the present invention, a method for preparing a positive electrode sheet containing a graphene composite conductive agent is provided, which is used to prepare the above-mentioned positive electrode sheet containing a graphene composite conductive agent, comprising the following steps: Step S1: Mix the composite conductive agent, positive electrode active material and binder in a preset ratio to obtain a mixed slurry; Step S2: Stir the mixed slurry evenly and then sieve it to obtain the first slurry; Step S3: Coat the first electrode sheet with the first slurry at a preset first temperature and a preset first speed to obtain the first electrode sheet; Step S4: Dry and roll the first electrode sheet to obtain the positive electrode sheet.

[0019] A further improvement of the present invention is that the preparation of the composite conductive agent includes the following steps: Step S11: After mixing graphene powder and organic solvent, pre-disperse the mixture using a shear emulsifier to obtain a graphene pre-dispersion liquid; Step S12: Add conductive carbon black to the graphene pre-dispersion liquid in sequence and disperse it using a grinding mill to obtain a pre-dispersion slurry; Step S13: The prepared slurry is subjected to vacuum degassing treatment to obtain a composite conductive agent.

[0020] A further improvement of the present invention is that the first temperature is 80℃~120℃ and the first speed is 2m / min~10m / min.

[0021] A further improvement of the present invention is that the shear emulsifier operates at 3000~8000 rpm for 20min~60min, the grinding machine operates at 1500rpm~3000rpm for 1h~4h, and the operating temperature is less than 40℃.

[0022] According to a third aspect of the technical solution of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode is the above-mentioned positive electrode containing a graphene composite conductive agent.

[0023] Compared with the prior art, the above-mentioned technical solution of the present invention has the following beneficial technical effects: 1. This invention solves the problems of limited conductive pathways and high overall internal resistance of existing single-conductive agent systems by using a composite conductive agent containing graphene, conductive carbon black, and organic solvent, which together with the positive electrode active material and binder to form the positive electrode sheet. Leveraging the complementary dimensional properties of zero-dimensional carbon black and two-dimensional graphene, a "point-to-surface" synergistic conductive architecture can be constructed within the electrode sheet, improving electron transport efficiency, enhancing electrode structural stability, and providing core structural support for performance optimization with low conductive agent dosage.

[0024] 2. This invention solves the problems of graphene stacking and uneven carbon black dispersion caused by the imbalance of component ratios in existing compound systems by limiting the mass ratio of graphene in the composite conductive agent to 5%~15%, conductive carbon black to 10%~25%, and organic solvent to 60%~85%. The balanced composition allows carbon black to fully fill the gaps between graphene sheets, forming a stable three-dimensional conductive network. This ensures the continuity of the conductive framework, avoids the agglomeration of the conductive agent, and balances the dispersion stability of the slurry with the conductivity of the electrode.

[0025] 3. This invention solves the problems of insufficient compatibility and poor interfacial contact between the composite conductive agent and the positive electrode system by selecting N-methylpyrrolidone (NMP) as an organic solvent, lithium iron phosphate (LFP) as the positive electrode active material, and polyvinylidene fluoride (PVDF) as a binder. NMP ensures uniform dispersion of graphene and carbon black, while PVDF has good compatibility with the conductive agent and active material, improving electrode adhesion and structural integrity, adapting to the industrial production process of lithium iron phosphate positive electrodes, and effectively reducing the risk of interfacial polarization.

[0026] 4. This invention solves the problem of weak synergistic effect and poor network connectivity caused by the mismatch between the morphology and size of the conductive agents by limiting the graphene to 1 to 10 layers with a sheet diameter of 1 μm to 20 μm and the conductive carbon black particle size to 20 nm to 80 nm. The size-matched carbon black can precisely fill the gaps between the graphene sheets and the active particles, while the thin-layer, large-diameter graphene can construct a continuous conductive framework. Both fully leverage their dimensional synergistic advantages to improve the connectivity and structural stability of the conductive network.

[0027] 5. This invention solves the problem of high conductive agent addition and crowding out of active material content in existing technologies by limiting the mass ratio of the composite conductive agent in the positive electrode to 0.5%~2%. Relying on a highly efficient three-dimensional conductive network, the electron percolation threshold can be broken through at low addition levels, which not only reduces the amount of conductive agent and increases the proportion of positive electrode active material to improve battery energy density, but also ensures the conductivity of the electrode, achieving simultaneous improvement in rate performance and cycle stability at low dosage levels.

[0028] 6. This invention prepares positive electrode sheets by employing a process of mixing and adjusting the slurry, sieving, coating, drying, and rolling, thus solving the problems of mismatch between existing electrode preparation processes and composite conductive agents, and poor conductive network formation. Sieving ensures the uniformity of the slurry, while the coating, drying, and rolling processes promote the orderly transfer of the conductive network from a dispersed state in the slurry to a solid state on the electrode sheet, gradually compacting and connecting the electronic pathways, ensuring the continuity of the conductive network inside the electrode sheet, and improving the batch production stability of the electrode sheet.

[0029] 7. This invention employs a three-step process—high-speed shear pre-dispersion, sand milling fine dispersion, and vacuum degassing—to prepare a composite conductive agent, solving the problems of graphene's tendency to agglomerate and stack, and the poor dispersion stability of the slurry. Pre-dispersion initially removes graphene agglomerates, sand milling further refines the dispersion and prevents excessive fragmentation of the sheets, and vacuum degassing eliminates air bubbles in the slurry. This process yields a uniformly dispersed composite conductive slurry with excellent static stability, ensuring the quality of subsequent electrode coating.

[0030] 8. This invention solves the problems of uneven solvent evaporation and conductive agent migration and agglomeration during the coating process by limiting the coating temperature to 80℃~120℃ and the coating speed to 2m / min~10m / min. The appropriate temperature and speed can ensure that the slurry dries and forms at a uniform speed, avoid the local enrichment of conductive agent due to solvent migration, maintain the uniform distribution of the conductive network inside the electrode, and ensure the consistency of electrode surface density and the overall stability of conductivity.

[0031] 9. This invention solves the problem of graphene sheet damage or insufficient dispersion caused by improper dispersion process parameters by limiting the speed of the shear emulsifier to 3000~8000 rpm and the dispersion time to 20~60 min, and the speed of the sand mill to 1500~3000 rpm, the grinding time to 1~4 h, and the working temperature to below 40℃. The mild and controllable dispersion conditions can fully exfoliate graphene aggregates while preserving the complete graphene sheet structure, ensuring the conductive framework performance and batch stability of the composite conductive agent.

[0032] 10. This invention solves the problem of existing batteries' inability to simultaneously achieve high energy density, rate performance, and cycle life by assembling lithium-ion batteries using the aforementioned graphene-containing composite conductive agent as the positive electrode. The highly efficient three-dimensional conductive network reduces battery internal resistance, enhances high-rate charge and discharge capabilities, improves electrode structure stability, significantly increases battery cycle life, and is compatible with various battery forms such as cylindrical and pouch cells, meeting the high-performance application requirements of power batteries and energy storage fields. Attached Figure Description

[0033] The accompanying drawings are provided to better understand the invention and are not intended to unduly limit the scope of the invention. Wherein: Figure 1 This is a graph showing the relationship between the number of cycles and capacity retention rate of the cylindrical battery cell at room temperature (1.0C / 1.0C) in Example 5. Figure 2 This is a graph showing the relationship between the number of cycles and capacity retention rate of the soft-pack battery cell at room temperature (1.0C / 1.0C) in Example 6. Figure 3 This is the charge / discharge curve of the soft-pack battery in Example 6; Figure 4 This is a charge / discharge curve of the cylindrical battery in Example 5. Detailed Implementation

[0034] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0035] This invention discloses a positive electrode sheet containing a graphene composite conductive agent, its preparation method, and a lithium-ion battery, belonging to the field of lithium-ion battery technology. The positive electrode sheet containing the graphene composite conductive agent comprises a composite conductive agent, a positive electrode active material, and a binder. The composite conductive agent includes graphene, conductive carbon black, and an organic solvent. This invention solves the problems of limited conductive pathways and high overall internal resistance of existing single conductive agent systems by using a composite conductive agent containing graphene, conductive carbon black, and an organic solvent, which, together with the positive electrode active material and binder, forms the positive electrode sheet. Furthermore, this invention leverages the complementary dimensional properties of zero-dimensional carbon black and two-dimensional graphene to construct a "point-to-surface" synergistic conductive architecture within the electrode sheet, improving electron transport efficiency, enhancing electrode structural stability, and providing core structural support for performance optimization with low conductive agent dosages.

[0036] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0037] Example 1 This embodiment provides a positive electrode sheet containing a graphene composite conductive agent, which comprises a composite conductive agent, a positive electrode active material, and a binder; the composite conductive agent includes graphene, conductive carbon black, and an organic solvent. The positive electrode active material, as the core carrier for lithium-ion intercalation and deintercalation, determines the theoretical capacity and voltage platform of the battery; the binder is used to bond the active material and the conductive agent into a whole and attach it to the surface of the current collector, maintaining the structural integrity of the electrode sheet; the composite conductive agent provides a core pathway for electron transport, wherein graphene constructs a long-range conductive framework with its two-dimensional sheet structure, conductive carbon black fills the structural gaps in the form of zero-dimensional particles, and the organic solvent is used to disperse the conductive agent components and ensure the uniformity of slurry dispersion. The three work together to form a stable conductive system inside the electrode sheet, effectively reducing the overall internal resistance of the electrode sheet.

[0038] Specifically, in the composite conductive agent, the graphene accounts for 5% to 15% by mass, the conductive carbon black accounts for 10% to 25% by mass, and the organic solvent accounts for 60% to 85% by mass. This ratio provides a suitable proportion of graphene, forming a continuous planar conductive network without causing excessive agglomeration of the sheets. The conductive carbon black effectively fills the gaps between graphene sheets and between graphene and active material particles, achieving an effective connection between point and planar structures. Sufficient organic solvent fully impregnates the conductive agent powder, maintaining appropriate viscosity and dispersion stability of the slurry, preventing agglomeration and sedimentation caused by excessive solid content, and ensuring the composite conductive agent remains homogeneous and stable.

[0039] Specifically, the organic solvent is N-methylpyrrolidone, the positive electrode active material is lithium iron phosphate positive electrode material, and the binder is polyvinylidene fluoride (PVDF). N-methylpyrrolidone is highly polar and has excellent solubility, allowing for good dispersion of graphene and conductive carbon black powder. It also exhibits good compatibility with PVDF binder, forming a uniform and stable positive electrode slurry during homogenization. Lithium iron phosphate positive electrode material has a stable structure, long cycle life, and outstanding safety performance, providing reversible lithium-ion insertion / extraction sites for the battery. PVDF has strong adhesion and good electrochemical stability, firmly bonding the active material and conductive agent to the current collector surface, maintaining the integrity of the electrode structure during cycling and preventing active material detachment and failure.

[0040] Specifically, the graphene has 1 to 10 layers with a sheet diameter of 1 μm to 20 μm, and the conductive carbon black has a particle size of 20 nm to 80 nm. The 1 to 10-layer few-layer graphene combines high conductivity with good dispersibility, avoiding the problem of decreased conductivity in multilayer graphene while weakening van der Waals forces between layers and reducing stacking and agglomeration. The 1 to 20 μm sheet diameter can cover multiple active material particles, constructing a long-range continuous conductive framework. The 20 to 80 nm conductive carbon black particle size matches the spacing between active particles and graphene sheets, effectively filling these gaps, connecting the graphene conductive framework to the surface of the active material particles, eliminating conductive breakpoints, and forming a three-dimensional electronic pathway penetrating the electrode.

[0041] Specifically, in the composite conductive agent, positive electrode active material, and binder, the composite conductive agent accounts for 0.5% to 2% of the total mass. Relying on a point-to-surface synergistic three-dimensional conductive network structure, the composite conductive agent can reach the electron percolation threshold at a low addition amount of 0.5% to 2%, forming a continuous and stable electron transport channel. Compared to the conventional 3% to 5% addition amount of conductive agent, this amount can significantly increase the proportion of the positive electrode active material, thereby improving the volumetric and gravimetric energy density of the battery, while avoiding the ion channel blockage problem caused by high conductive agent dosage, achieving a balance between electron transport and ion diffusion performance.

[0042] Example 2 This embodiment provides a method for preparing a positive electrode sheet containing a graphene composite conductive agent, used to prepare the positive electrode sheet containing a graphene composite conductive agent as described in Example 1, which includes the following steps: Step S1: The composite conductive agent, positive electrode active material, and binder are mixed in a preset ratio to obtain a mixed slurry. During the mixing process, the composite conductive agent is uniformly dispersed in the slurry system, the positive electrode active material particles are in full contact with the conductive agent components, and the binder gradually dissolves and is uniformly distributed among the components, so that the raw materials are initially mixed evenly, laying the foundation for the subsequent formation of a homogeneous slurry and a uniform conductive network, and ensuring the consistency of the distribution of each component in the final electrode.

[0043] Step S2: Stir the mixed slurry evenly and then sieve it to obtain the first slurry. Thorough stirring allows the conductive agent, active material, and binder to be further dispersed and mixed, breaking up local agglomerates and ensuring a uniform distribution of each component at the microscopic level. The sieving process removes large agglomerates and impurities from the slurry, preventing scratches, particle protrusions, and other defects in the subsequent coating process, ensuring a smooth wet film surface, and further improving the uniformity of the slurry, providing a prerequisite for the formation of a uniform conductive network inside the electrode.

[0044] Step S3: Coating with the first slurry at a preset first temperature and a preset first speed to obtain the first electrode. The coating process uniformly coats the slurry onto the surface of the current collector, forming a wet film electrode with a set surface density; a suitable coating temperature allows the solvent in the wet film to evaporate at a uniform rate, avoiding the migration and aggregation of conductive agent caused by rapid solvent evaporation; a matched coating speed ensures that the surface density of the electrode is uniform, so that the conductive agent is uniformly distributed in both the plane and thickness direction of the electrode, initially forming a dispersed structure of the conductive network.

[0045] Step S4: The first electrode sheet is dried and rolled to obtain the positive electrode sheet. The drying process completely removes residual solvent from the electrode sheet, solidifies the binder, and bonds and fixes the components. The conductive network gradually takes shape as the solvent evaporates. The rolling process compacts the electrode sheet to a set thickness, increasing the compaction density of the electrode sheet. At the same time, it further contacts and connects the graphene sheets and carbon black particles, compacting and connecting the conductive network to form a stable three-dimensional electronic pathway that runs through the thickness direction of the electrode sheet. Finally, a dense positive electrode sheet with excellent conductivity is obtained. The density of the positive electrode sheet is 150 g / m²~300 g / m². Specifically, the preparation of the composite conductive agent includes the following steps: Step S11: After mixing graphene powder and organic solvent, pre-dispersion is performed using a shear emulsifier to obtain a graphene pre-dispersion liquid. Graphene powder is prone to forming agglomerates due to van der Waals forces between the sheets. The strong shear force generated by the high-speed shear emulsifier can initially peel off the graphene agglomerates, allowing the graphene sheets to be initially dispersed in the organic solvent. The pre-dispersion process can initially open up the graphene agglomerate structure, avoiding uneven dispersion caused by excessively large agglomerates during subsequent sand milling, providing a foundation for subsequent fine dispersion, and ensuring the initial uniform dispersion of the graphene sheets.

[0046] Step S12: Conductive carbon black is added sequentially to the graphene pre-dispersion liquid and dispersed using a sand mill to obtain a pre-slurry. Sequential addition of conductive carbon black allows the carbon black particles to be gradually dispersed in the graphene dispersion system, avoiding localized agglomeration caused by a single addition. The sand mill, through the collision and shearing action of the grinding media, further removes residual graphene agglomerates, while simultaneously ensuring uniform dispersion of carbon black particles in the gaps between graphene sheets. This achieves microscopic uniform mixing of the two conductive agents, initially forming a point-to-surface synergistic dispersed conductive structure, and avoids excessive shearing that could damage the integrity of the graphene sheets.

[0047] Step S13: The prepared slurry is subjected to vacuum degassing to obtain a composite conductive agent. Vacuum degassing can remove air bubbles mixed in during the dispersion process of the slurry under negative pressure, avoiding defects such as pinholes and pits caused by residual air bubbles in the subsequent coated electrode. The composite conductive slurry after degassing is uniform in texture and stable in state, and is not prone to sedimentation and stratification during standing, which can ensure the uniform dispersion of conductive components in the subsequent positive electrode homogenization process and maintain the uniformity of the final electrode conductive network.

[0048] Specifically, the first temperature is 80℃~120℃, and the first speed is 2m / min~10m / min. The coating temperature of 80℃~120℃ allows the N-methylpyrrolidone solvent to evaporate steadily. If the temperature is too low, the solvent will not evaporate completely, affecting the drying effect of the electrode. If the temperature is too high, the solvent will evaporate rapidly, causing the conductive agent to migrate to the surface of the electrode with the solvent, destroying the uniformity of the internal conductive network. The coating speed of 2m / min~10m / min is suitable for this temperature range, which can ensure that the wet film is fully dried and formed during the coating process, while maintaining the uniformity of the electrode surface density, which meets the efficiency requirements of large-scale production.

[0049] Specifically, the shear emulsifier operates at 3000-8000 rpm for 20-60 minutes, and the sand mill operates at 1500-3000 rpm for 1-4 hours, with an operating temperature below 40℃. The shear speed of 3000-8000 rpm and the 20-60 minute dispersion time effectively break up graphene agglomerates during the pre-dispersion stage, while avoiding graphene sheet breakage caused by excessive speed or time. The sand mill speed of 1500-3000 rpm and the 1-4 hour grinding time achieve fine dispersion of the conductive agent, ensuring uniform mixing of carbon black and graphene. The operating temperature below 40℃ avoids solvent evaporation and changes in slurry properties caused by high temperatures, while preventing structural damage to graphene sheets due to high temperatures, ensuring the conductivity and batch stability of the conductive agent. After the milling process, the particle size range in the slurry is 0.3mm-1mm. The dispersant forms a steric hindrance layer on the graphene surface, inhibiting sheet recombination. The slurry treated in this way has a solid content of 5%~15%, a viscosity of 2000~8000 mPa·s, and an average particle size D50≤5μm.

[0050] Example 3 This embodiment provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is a graphene-containing composite conductive agent positive electrode as described in Embodiment 1. The negative electrode provides sites for lithium-ion insertion, matching the positive electrode to achieve charge-discharge cycles. The separator separates the positive and negative electrodes, preventing internal short circuits and providing a transport channel for lithium ions. The electrolyte, as a medium for lithium-ion transport, fills the pores of the electrode and separator, ensuring smooth lithium-ion migration. The positive electrode using this composite conductive agent can construct a highly efficient and stable electron transport network inside the battery, reducing polarization during charge-discharge processes, improving high-rate charge-discharge performance, maintaining electrode structural stability, and extending the battery's cycle life. This allows the battery to possess both high energy density and high power performance, and is adaptable to various battery forms such as cylindrical and pouch cells. The battery's charge-discharge cutoff voltage is 2.5~4.2V.

[0051] Example 4 This embodiment provides a method for preparing the composite conductive agent in Example 1, comprising the following steps: 1. Weigh the following raw materials by mass percentage: 10g graphene (3-8 layers, 5-15μm diameter), 15g conductive carbon black (30-40nm particle size), and 68.5g N-methylpyrrolidone (NMP).

[0052] 2. Graphene powder was mixed with NMP and polyvinylpyrrolidone (PVP) and pre-dispersed for 30 minutes at 5000 rpm using a high-speed shear emulsifier. Then, conductive carbon black was added, and the mixture was transferred to a sand mill for fine dispersion. Milling conditions: zirconia beads with a particle size of 0.5 mm, milling speed of 2000 rpm, milling time of 8 hours, and temperature controlled below 40℃. After milling, vacuum degassing was performed for 15 minutes, followed by filtration through a 200-mesh sieve to obtain the finished composite conductive agent.

[0053] The resulting slurry had a solid content of approximately 12.5%, a viscosity of 3500 mPa·s, and an average particle size D50 of 2.8 μm. No sedimentation was observed after 30 days of standing, indicating good dispersion stability.

[0054] Example 5 This embodiment provides a method for preparing an 18650 cylindrical battery using the composite conductive agent prepared in Example 4. This agent is mixed with lithium iron phosphate cathode material and PVDF binder at a mass ratio of 3:92:5, and an appropriate amount of NMP is added to adjust the slurry to a suitable viscosity. The mixture is homogenized, sieved through a 200-mesh sieve, coated (coating temperature 100℃, speed 5m / min), dried, and rolled to form a positive electrode sheet. Graphite is used as the negative electrode, and the resulting 18650 cylindrical battery is assembled. Figure 1 and 4As shown, under 1C / 1C charge / discharge conditions, the battery has an initial capacity of 1.52Ah and retains a capacity of 1.48Ah after 500 cycles, which is less than 0.5% of the original capacity, and is superior to commercially available batteries.

[0055] Example 6 This embodiment provides a method for preparing a soft-pack battery. The composite conductive agent prepared in Example 4 is mixed with lithium iron phosphate cathode material and PVDF binder at a mass ratio of 2:93:5. The cathode sheet is fabricated using the same slurry preparation, coating, and rolling process as in Example 2, and then assembled into a 1.5Ah soft-pack battery. Figure 2 and 3 As shown, under 1C / 1C cycling conditions, the battery's capacity decays by no more than 0.5% after 500 cycles, which is superior to commercially available batteries.

[0056] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0057] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A positive electrode sheet containing a graphene composite conductive agent, characterized in that, It comprises a composite conductive agent, a positive electrode active material, and a binder; the composite conductive agent includes graphene, conductive carbon black, and an organic solvent.

2. The positive electrode sheet containing a graphene composite conductive agent according to claim 1, characterized in that, In the composite conductive agent, the graphene accounts for 5% to 15% by mass, the conductive carbon black accounts for 10% to 25% by mass, and the organic solvent accounts for 60% to 85% by mass.

3. The positive electrode sheet containing a graphene composite conductive agent according to claim 1, characterized in that, The organic solvent is N-methylpyrrolidone, the positive electrode active material is lithium iron phosphate positive electrode material, and the binder is polyvinylidene fluoride.

4. The positive electrode sheet containing a graphene composite conductive agent according to claim 1, characterized in that, The graphene has 1 to 10 layers and a sheet diameter of 1 μm to 20 μm, while the conductive carbon black has a particle size of 20 nm to 80 nm.

5. The positive electrode sheet containing a graphene composite conductive agent according to claim 1, characterized in that, In the composite conductive agent, positive electrode active material and binder, the mass percentage of the composite conductive agent is 0.5% to 2%.

6. A method for preparing a positive electrode sheet containing a graphene composite conductive agent, used to prepare a positive electrode sheet containing a graphene composite conductive agent as described in any one of claims 1-5, characterized in that, Includes the following steps: Step S1: Mix the composite conductive agent, positive electrode active material and binder in a preset ratio to obtain a mixed slurry; Step S2: Stir the mixed slurry evenly and then sieve it to obtain the first slurry; Step S3: Coat the first electrode sheet with the first slurry at a preset first temperature and a preset first speed to obtain the first electrode sheet; Step S4: Dry and roll the first electrode sheet to obtain the positive electrode sheet.

7. The method for preparing a positive electrode sheet containing a graphene composite conductive agent according to claim 6, characterized in that, The preparation of the composite conductive agent includes the following steps: Step S11: After mixing graphene powder and organic solvent, pre-disperse the mixture using a shear emulsifier to obtain a graphene pre-dispersion liquid; Step S12: Add conductive carbon black to the graphene pre-dispersion liquid in sequence and disperse it using a grinding mill to obtain a pre-dispersion slurry; Step S13: The prepared slurry is subjected to vacuum degassing treatment to obtain a composite conductive agent.

8. The method for preparing a positive electrode sheet containing a graphene composite conductive agent according to claim 6, characterized in that, The first temperature is 80℃~120℃, and the first speed is 2m / min~10m / min.

9. The method for preparing a positive electrode sheet containing a graphene composite conductive agent according to claim 7, characterized in that, The shear emulsifier operates at 3000~8000 rpm for 20min~60min, the grinding mill operates at 1500rpm~3000rpm for 1h~4h, and the operating temperature is less than 40℃.

10. A lithium-ion battery, characterized in that, Includes positive electrode, negative electrode, separator and electrolyte; The positive electrode sheet is a positive electrode sheet containing a graphene composite conductive agent as described in any one of claims 1-5.

Images