Current collector for high-performance lithium battery, conductive slurry, and method for producing the same

Abstract

A current collector for a high-performance lithium battery, a conductive slurry, and a method for manufacturing the same, belonging to the technical field of producing lithium batteries. The functional coating of the current collector is a functional layer-like coating structure with a thickness of 800 nm or less formed by applying a conductive slurry onto the surface of a metal foil and drying it. The functional coating contains a plurality of strip-shaped modified conductive agents. After curing and forming, the modified conductive agents are parallel to each other within the functional coating. In the thickness direction of the coating, the axes of the modified conductive agents form an angle of 15 to 45° with the surface of the metal foil respectively and are arranged obliquely. The modified nanofibers, binders, and conductive agents in the coating are intertwined to form an oriented three-dimensional network connection structure that enhances adhesion, conductivity, and thermal conductivity and is uniformly deformable and automatically recoverable. The functional coating can automatically adapt to the volume and offset them. During the expansion and contraction of the active material due to charge and discharge, it can maintain the relative stability of the connection network and the electrical connection strength, and improve the overall performance of the lithium battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of producing lithium batteries, and particularly relates to a current collector for high-performance lithium batteries, a conductive slurry, and a manufacturing method thereof.

Background Art

[0002] Lithium-ion batteries for driving, etc. are widely used in industrial fields such as new energy vehicles and large-scale energy storage, and the market demand is increasing. The current collector of a secondary battery such as a lithium-ion battery refers to a structure or component that collects current, and in a lithium-ion battery, it mainly refers to a metal foil such as a copper foil or an aluminum foil. The general term may also include tabs. Its main function is to collect the current generated by the active material of the battery in order to form a large current for external output. Therefore, the current collector needs to be in sufficient contact with the active material and have as small an internal resistance as possible.

[0003] In the prior art, using a functional coating for the surface treatment of the conductive base material of the battery is an important technological innovation. Carbon-coated aluminum foil / copper foil uniformly and finely coats conductive materials such as dispersed nano-conductive graphite, carbon-coated particles, and carbon nanotubes on the aluminum foil / copper foil. This exhibits excellent static conductivity and collects the minute current from the active material, thereby greatly reducing the contact resistance between the positive / negative electrode material and the current collector, improving the adhesion ability between the two, reducing the usage amount of the binder, and further significantly improving the overall performance of the battery.

[0004] Currently, LiFePO4 is a promising cathode material that is safer and cheaper. However, due to its low electronic conductivity and ionic conductivity, as well as relatively low mass density and tap density, it has main defects such as poor conductivity and adhesion (stickiness) during use, and is prone to powder shedding. Carbon-coated aluminum foil is used as the cathode current collector, which can reduce the contact resistance at the interface, reduce the internal resistance of the battery, reduce the internal partial polarization of the battery, lighten the internal design of the battery, and increase the discharge rate of the battery to a certain extent. In the anode of a lithium-ion battery, by using carbon-coated copper foil, a battery electrode plate with high surface density and high adhesion and high energy density can be provided, and even in a silicon-carbon material system that is prone to expansion, powder shedding during punching of the laminated battery can be avoided.

[0005] Existing carbon-coated foil materials are prepared by coating a conductive slurry, which is a mixture of conductive materials such as graphite, carbon black, and multi-walled carbon nanotubes, and dispersants and binders with various ratios uniformly dispersed, on aluminum foil or copper foil. The carbon coating is about 2 to 50 μm thick and has poor peel resistance due to repeated charging. Also, depending on the blending ratio of the conductive agent, although there are slight differences in the appearance of the carbon coating, it is generally black or gray in various shades. When using different lithium battery material systems, the coating machine cannot use monitoring methods such as observation and machine vision to judge the coating rate and thickness of the electrode plate coating based on color and color differences, so as to improve the quality stability of the current collector product. In high-speed production quality control, the coating rate of the coating cannot be accurately monitored, which limits the improvement of production efficiency.

[0006] Among the existing technologies, in order to improve the performance of the conductive coating of the current collector, Chinese Invention Patent Application No.: 201610410998.1 discloses a carbon nanotube conductive coating current collector including a metal current collector and a carbon nanotube conductive coating, and its manufacturing process. The carbon nanotube conductive coating is applied to the surface of the metal current collector. The carbon nanotube conductive coating has a thickness of 1 to 50 μm, and a mesh-like microcrack structure and a rough porous structure are provided on the surface. The carbon nanotube conductive coating of the present invention provides a good conductive mesh for the electrode. By manufacturing conductive slurries with different dispersion effects, the carbon nanotube conductive coating forms dense microcracks on the surface after drying, improves the bonding force with the current collector, and reduces the internal resistance of the battery. However, since the conductive coating of this technical solution needs to use two or more types of conductive materials, its thickness is relatively thick at the micron level. After multiple charge and discharge cycles, its adhesion (indicating the durability of the coating) rapidly decreases, and the coating is easily peeled off. When the coating peels off, the metal layer of the current collector is directly exposed to the active material, so failures due to corrosion and oxidation of the current collecting electrode are likely to occur, and the battery life is shortened. Also, when this material is applied, this conductive coating has poor recoverability and looks black or gray. During the coating operation, it is impossible to judge the situation such as the thickness and coverage rate of the coating based on the color difference of the coating. There is no effective method to monitor the coating quality during coating. Also, in the subsequent coating and welding processes of the battery electrode plate, since the color of the coating cannot be accurately judged, it has an adverse effect.

[0007] The Chinese invention patent application No. 201610522526.5 discloses a conductive slurry and a method for forming a network-shaped carbon current collector having thermal conductivity and conductivity using this conductive slurry. This conductive slurry is manufactured with 4 to 6 parts by weight of carbon nanotubes, 8 to 12 parts by weight of conductive carbon black, 1 to 3 parts by weight of flaky graphite, and 15 to 25 parts by weight of polyvinyl alcohol as raw materials. In the present invention, a network-shaped material can be formed using a carbon material having high thermal conductivity and conductivity of one-dimensional or higher. For example, by adding a high thermal conductivity material such as carbon nanotubes or graphene to general conductive carbon black, a continuous network coating having thermal conductivity and conductivity is formed on the current collector, whereby not only can the heat dissipation effect be improved when charging and discharging at a high rate, but also the conductivity requirements are considered, the problem of aging deterioration of the system due to heat is avoided, and the life of the system can be extended. However, in the above technical solution, it is necessary to use two or more types of conductive materials, the thickness of the formed conductive network coating is still large, the coating has poor recoverability, and the color is gray or black that cannot be monitored. The spatial structure of the network-shaped material is randomly distributed, without orientation, and the effect of reducing the internal resistance of the interface and enhancing conductivity, thermal conductivity, and adhesion is also limited.

[0008] During charge and discharge, in a lithium battery, based on electrochemical reactions and physical volume changes, the relative positions, contact surfaces, and contact points among the components of the internal substances (especially between the active material, conductive material, and current collector) all change periodically. In the change process, especially during the volume expansion process, the distance between components increases, the contact points decrease, and the contact resistance increases. As a result, the internal resistance of the battery increases, and the efficiency rapidly decreases. And it is difficult to guarantee that after each cycle, each substance returns exactly to its original position and can recover its original connection network and strength. Gradually, the spatial distribution among the components becomes disordered, and the connection (electrical conductivity and thermal conductivity) performance decreases. As a result, after multiple cycles, the battery's various performances decline. To overcome this defect, it is necessary to consider maintaining a strong connection network and strength among the components of the internal substances of the lithium battery during charge and discharge and after multiple cycles, and reducing the loss of the connection network due to physicochemical effects, the increase in internal resistance, and the decrease in capacity.

[0009] In the above prior art, randomly and irregularly arranged carbon nanotubes are used, so the excellent mechanical properties, electrical properties, and thermal conduction properties of a single carbon nanotube and its array cannot be fully exerted. Furthermore, due to the irregular distribution, aggregation of carbon nanotubes is likely to occur, and the contact resistance between carbon nanotubes is likely to increase. As a result, the performance of the negative electrode material of a lithium-ion battery manufactured using this type of conductive coating material is far below the expected value. However, arranging carbon nanotubes regularly in the existing technology is not easy to control or achieve in constructing a three-dimensional skeleton of a specific three-dimensional structure. Therefore, to significantly improve the comprehensive performance of the current collector, it is necessary to simultaneously improve the manufacturing processes of carbon nanotubes, conductive slurry, coating structure, and current collector.

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention provides a current collector for a high-performance lithium battery in view of the above-mentioned drawbacks of the prior art. The functional coating uses a modified conductive agent as a conductive material. Based on the dumbbell-shaped structure of the modified conductive agent, within the coating, a bridge-island structure with both ends fixed is formed, which can automatically adapt to changes and deformations such as volume and offset them, and under the action of an external magnetic field, the modified conductive agent is arranged obliquely and parallel at a specific angle of 15-45° along the thickness direction, enhancing adhesion, conductivity, and heat conductivity, and forming a three-dimensional network structure with high recovery characteristics, thereby solving the problem in the prior art that the network structure is irregularly arranged and it is impossible to simultaneously consider enhancing the adhesion, conductivity, and heat conductivity of the coating. When the current collector of the present invention is applied to a lithium battery, a spatial network structure and a reliable connection can be well established with the active components. Also, during the expansion and contraction of the battery coating and the active material due to charge and discharge, the modified conductive agent maintains the regularity of the spatial distribution of the conductive substances inside the lithium battery through changes in its angle and fixing action, etc., and maintains the relative stability of the connection network and the electrical connection strength. Thereby, after multiple charge and discharge cycles during the use of the lithium battery, the problem in the prior art that the adhesion of the coating rapidly decreases and the coating is easily peeled off is solved.

[0011] The present invention also provides a method for manufacturing the modified conductive agent with the dumbbell-shaped structure. Oxidation and chemical modification of both ends are performed on multi-walled carbon nanotubes, and by pre-connecting larger conductive agent particles of other sizes to both ends thereof, a dumbbell-shaped structure is formed, which can automatically adapt to a regular arrangement within the coating, automatically adjust the inclination angle, and offset changes and deformations such as volume, and form a bridge-island structure with both ends fixed. In the oxidation process, there are pore defects formed by the oxidation of local C-C bonds in single-walled carbon nanotubes. Due to the existence of the defects, there are magnetic moments near the defects, whereby weak magnetism is imparted to the carbon nanotube modified conductive agent.

[0012] The present invention also provides a conductive slurry for manufacturing the above functional coating and a method for manufacturing the same. By simultaneously improving the formulation and manufacturing process of the coating, the addition amount of the modified conductive agent is reduced, and the average thickness of the dried coating is made 800 nm or less. By using a modified conductive agent with weak magnetism, a structure arranged obliquely at a specific 15 to 45° along the thickness direction is formed within the coating, further increasing the contact specific surface area between the coating and the active material, thereby greatly enhancing the adhesion of this coating after multiple charge and discharge cycles, solving problems such as the conventional coating being thick and having poor adhesion, extending the life of secondary batteries such as lithium-ion batteries, and improving the high-rate characteristics.

[0013] The present invention also provides a method for manufacturing the above current collector, solving the problems that it is difficult to form a self-adaptive three-dimensional network connection structure within the coating and the process is complex, realizing an oriented array of the magnetic modified conductive agent by a constant magnetic field, enhancing the conductivity and adhesion of the functional coating, and reducing the usage amount of the modified conductive agent and the thickness of the functional coating. In the process of applying the conductive slurry, a three-dimensional structure of the modified conductive agent and the substrate is constructed, facilitating shaping and control. The structure is constructed simultaneously with the coating and drying processes, thereby saving steps and obtaining a coating structure in which the oriented modified conductive agent and the substrate are intertwined.

Means for Solving the Problems

[0014] To achieve the above object, the present invention provides the following technical solutions.

[0015] A current collector for a high-performance lithium battery including a metal foil and a functional coating, The functional coating is a functional layered coating structure with a thickness of 800 nm or less formed by applying a conductive slurry onto one or two surfaces of a metal foil and drying it. The functional coating contains a plurality of strip-shaped modified conductive agents, and the modified conductive agent is a magnetically oriented modified multi-walled carbon nanotube. After curing and forming, the modified conductive agents are parallel to each other within the functional coating. In the thickness direction of the coating, the axes of the modified conductive agents form an angle of 15° to 45° with the surface of the metal foil respectively and are arranged obliquely. The modified nanofibers, binders, and modified conductive agents in the coating are intertwined to form an oriented three-dimensional network connection structure that enhances adhesion, conductivity, and heat conductivity and uniformly deforms and recovers.

[0016] The magnetically oriented modified multi-walled carbon nanotubes in the functional coating are modified multi-walled carbon nanotubes having a dumbbell structure, with an inner diameter of the tube of 5 nm or more, an outer diameter of the tube of 20 nm or less, and a length of 1200 nm or less. The modified multi-walled carbon nanotubes become a dumbbell-shaped fiber structure with thick ends and a thin central part due to oxidation and chemical modification. After orientation arrangement, the thick lower ends are respectively connected to the surface of the metal foil, and the upper ends are connected to each other. Using a binder, other nano-conductive agent particles and modified nanofibers of different sizes are sandwiched between the fiber parts with a thin central part. As a result, after each part is connected to each other, both ends are fixed, and an oriented three-dimensional network of a bridge-island structure is formed. The deformation and displacement of the modified multi-walled carbon nanotubes and nano-conductive agent particles during battery operation are restricted by the elastic three-dimensional network, automatically adapting to the change in internal volume during charge and discharge of the lithium battery and the deformation and displacement of the conductive particles, offsetting them, and maintaining the reliability of the functional coating for the connection between the surface of the metal foil and the active material.

[0017] A conductive slurry for manufacturing the current collector for the high-performance lithium battery, wherein the conductive slurry is an aqueous slurry produced by dispersing and mixing modified multi-walled carbon nanotubes, nano conductive agents, modified nanofibers, dispersants, binders, and solvents, and the slurry is characterized in that the solid content is 0.1 to 5%, the viscosity is 200 to 1000 mPa·s (25 °C), and the pH is 8 to 11.

[0018] The weight ratio of each raw material component of the conductive slurry is: modified multi-walled carbon nanotubes:nano conductive agents:modified nanofibers:dispersants:binders: solvents = (0.01 to 1.8):(0.01 to 0.2):(0.02 to 2):(0.02 to 20):(0.05 to 20):(56 to 99.89).

[0019] A method for manufacturing the conductive slurry of the current collector for the high-performance lithium battery, Manufacturing materials, that is, step S1 of manufacturing modified multi-walled carbon nanotubes, nano conductive agents, modified nanofibers, dispersants, binders, and solvents respectively according to the ratio; Manufacturing a high-concentration modified conductive agent suspension, that is, weighing modified nanofibers and dispersants according to the ratio, adding them to 1 / 3 of the amount of the solvent, mechanically stirring until completely dissolved, then weighing the required modified conductive agent and adding it to the mixed solution, and performing ultrasonic treatment for more than 30 min to obtain a modified conductive agent suspension, specifically, a modified multi-walled carbon nanotube suspension, step S2; Performing magnetization, that is, placing the modified conductive agent suspension in a strong external magnetic field for magnetization to further excite the magnetic anisotropy of the magnetic modified multi-walled carbon nanotubes to obtain a high-concentration magnetic modified multi-walled carbon nanotube suspension, step S3; Pre-disperse, that is, add a binder in a proportion corresponding to the above high-concentration magnetic-modified multi-walled carbon nanotube suspension, replenish the solvent until the desired usage amount is reached, and pre-disperse in the order of a high-speed vacuum disperser and a sand mill. The shear rate during dispersion by the vacuum disperser is 10 - 25 m / s, the vacuum degree is 0.085 MPa or more, and the vacuum dispersion time is 1 - 5 h. In the sand mill, the diameter of the sand milling beads is 0.2 - 2 mm, the proportion of the sand milling beads is 30 - 90%, the sand milling rotation speed is 600 - 10,000 r / min, and the sand milling time is 0.1 - 5 h in step S4, Perform secondary dispersion, that is, re-disperse by ultrasonic resonance using an ultrasonic treatment device, and apply an alternating magnetic field to both sides to further uniformly disperse the modified multi-walled carbon nanotubes and nano-conductive agent particles, and arrange them in the same direction by the induction of the magnetic field to obtain a conductive slurry with magnetic orientation in step S5. It is characterized by including this.

[0020] A method for manufacturing the current collector for a high-performance lithium battery, Manufacture a current collector metal foil and a dispersed conductive slurry respectively, and perform step (A1) of installing a coating device, an ultrasonic device, a constant magnetic field generating device, and a drying device. Apply the dispersed conductive slurry onto the surface of the metal foil to form a liquid colloidal coating with a viscosity of 200 - 1000 mPa·s (25 °C) and a thickness of 500 - 1200 nm on the surface in step (A2). Continuously apply a constant magnetic field perpendicular to the surface of the metal foil to the liquid colloidal coating, regularly arrange the orientation-modified conductive agent in the coating by the induction of the external magnetic field, gradually stretch it straight from the original spiral state, form a parallel array, and entangle it with the substrate in step (A3). Dry the coating, evaporate the solvent and volatile components, continuously apply a static magnetic field, and as the viscosity of the coating rapidly increases, the modified conductive agent is quickly molded while maintaining its arrangement position and posture. In the thickness direction, it is arranged obliquely and parallel at 15 - 45°, and the cured component of the conductive slurry to be coated is fixed on the surface of the metal foil to form a dense functional coating structure with a thickness of 800 nm or less. That is, on the surface of the metal foil, a step (A4) of forming a three-dimensional network structure with enhanced adhesion, conductivity, and thermal conductivity and having high recovery characteristics is included, and it is characterized by this.

Advantages of the Invention

[0021] Compared with the prior art, the present invention has the following advantages.

[0022] (1) The functional coating and conductive slurry of the present invention use a modified conductive agent as the conductive substance. The unique dumbbell-shaped structure of this modified conductive agent forms a bridge-island structure with both ends fixed, which can automatically adapt to changes and deformations such as volume in the coating and offset them. Also, this modified conductive agent has magnetic anisotropy and is arranged in a specific direction by the induction of a magnetic field. When applied to a lithium battery, it can automatically adjust the inclination angle according to the change in the internal volume of the battery, and can well establish a spatial network structure and reliable connection with the active component. Also, during the expansion and contraction of the battery coating and active material during charge and discharge, the regularity of the spatial distribution is maintained to maintain the relative stability of the connection network and electrical connection strength. Thereby, after multiple charge and discharge cycles during the use of the lithium battery, the problem of the prior art that the adhesion of the coating rapidly decreases and the coating is easily peeled off is solved.

[0023] (2) The conductive slurry according to the present invention realizes the combined use of a modified conductive agent, modified nanocellulose, and a dispersant in the manufacturing process. The dispersant can non-covalently modify the surface of the modified conductive agent, weaken the intermolecular van der Waals force, reduce their surface energy, and enable better dispersion in an aqueous solution. The modified nanocellulose provides a three-dimensional porous network structure for components such as the modified conductive agent in the functional coating, generates an electrostatic repulsive force between fibers due to negatively charged groups, forms a stable colloid, stably confines the modified conductive agent within its developed pores, and plays a role in assisting dispersion. Due to the combined action of both, the magnetic modified conductive agent is well dispersed in the conductive slurry, aggregation is avoided, and it is convenient for the modified conductive agent to be oriented and arranged by the induction of a magnetic field in subsequent processes.

[0024] (3) The functional coating of the present invention continuously applies an external magnetic field during the manufacturing and coating processes of the conductive slurry, so that the magnetic modified conductive agent therein is induced to form an induced magnetic moment under the action of a strong magnetic field, thereby realizing the regularization of the magnetic modified conductive agent, and finally being obliquely and parallelly arranged at a specific angle of 15 to 45° along the thickness direction within the coating.

[0025] (4) The modified conductive agent in the functional coating of the present invention is a modified carbon nanotube. The relatively large inner diameter size of the carbon nanotube can be used as an ion diffusion channel that exhibits a channel effect. As a result, Li + ions can quickly penetrate into the coating along the internal cavity of the carbon nanotube, increase the diffusion rate of Li + ions, shorten the migration path of Li + ions, enhance the electron transfer efficiency, reduce the impedance, and when applied to a lithium battery, it plays a role in improving the rate performance and low-temperature performance of the battery.

[0026] (5) Due to the oriented parallel array of the magnetic variable conductive agent in the functional coating of the present invention, the functional coating can have magnetic orientation. Since a combination of magnetic current collectors with a positive electrode and a negative electrode is used as a battery, a stable magnetic field is formed between the positive electrode current collector and the negative electrode current collector of the battery. That is, the movement of lithium ions is regularly carried out due to the restriction of the magnetic field. On the other hand, when lithium ions pass through the separator of the lithium-ion battery, the permeation efficiency of the separator is also improved by the movement pattern of lithium ions, and thereby, the impedance of the separator can be reduced. The lithium battery assembled using magnetic current collectors of different polarities manufactured according to the present invention can significantly increase the battery capacity, reduce the battery impedance, and improve the cycle characteristics of the battery. In addition, by self-adapting to and offsetting the volume change and maintaining a reliable connection, the safety of the lithium battery during high-power discharge is improved, the energy utilization rate and the charging efficiency during charge and discharge are improved, and the charging time is shortened.

[0027] (6) The functional coating of the present invention constructs a three-dimensional network structure in which a modified conductive agent and a flexible binder matrix material are intertwined, providing a connection layer with high strength, conductive efficiency, and good flexibility. Thereby, the contact area between the rigid metal current collector and the conductive slurry is effectively increased, the adhesion of the coating is improved, the interfacial resistance between the current collector and the battery active material is effectively reduced, the electrochemical stability of the current collector material is improved, an increase in the internal resistance of the battery is avoided, and the adverse effects on the battery performance, especially the performance under high-current charge and discharge conditions, can be reduced. In addition, a three-dimensional intertwined network fixed at both ends of the modified conductive agent is used to buffer the volume change during charge and discharge, improve the reliability of the electrical connection, avoid the expansion and peeling between the conductive slurry and the current collector, enhance the continuous adhesion between the current collector metal foil substrate and the battery active material when charge and discharge are repeated multiple times, improve the stability of the electrode plate, avoid cycle failures, and thereby improve the specific capacity, cycle stability, and rate characteristics of the electrode. Therefore, the functional coating according to the present invention and the lithium battery manufactured thereby have advantages such as high capacity, long cycle life, and good rate characteristics.

[0028] (7) In the present invention, the introduction of modified carbon nanotubes and the effective structure of the three-dimensional network provide more contact sites for active particles, increase the specific surface area in contact with the active material, and greatly improve the adhesion of the current collector of the positive / negative electrode material. Therefore, the current collector of the present invention can appropriately reduce the proportion of the binder in the positive / negative electrode slurry of the battery, further reduce the internal resistance, and is beneficial to improving the energy density of the battery. When manufacturing a positive electrode plate using the current collector of the present invention, the resistance is only 1 / 3 of that of a pure shiny foil, but the peel strength exceeds 4 times that of a pure shiny foil. The manufactured lithium-ion battery has an AC internal resistance that is reduced by 42% or more compared to the battery manufactured with a shiny foil current collector.

[0029] (8) The current collector according to the present invention can significantly increase the energy density of the battery and improve the cycle life and rate characteristics. Under the system of 1C charging and 2C discharging, after 2000 cycles at room temperature, the capacity retention rate of the lithium-ion battery manufactured using the current collector of the present invention can reach 93%, which is much higher than 80% of the capacity of the shiny foil current collector. Also, the consistency of the battery cycles is significantly better than that of a pure shiny foil current collector.

[0030] (9) The method for manufacturing the current collector and conductive slurry for high-performance lithium batteries according to the present invention has easily available materials, simple steps, high controllability, and low manufacturing costs. The functional coating of the manufactured current collector has a unique upper and lower two-layer internal aggregation structure and excellent mechanical properties, and development potential and application value can be expected in fields such as the manufacture of driving lithium batteries.

Embodiments for Carrying Out the Invention

[0031] Hereinafter, the present invention will be described in more detail with reference to a plurality of embodiments.

Examples

[0032] The current collector for high-performance lithium batteries, the conductive slurry, and the method for manufacturing the same according to the present invention can be applied to the manufacture of lithium batteries through technical routes such as lithium cobaltate (LCO), lithium manganate (LMO), lithium iron phosphate (LFP), and ternary materials (such as lithium nickel cobalt manganate (NCM) and lithium nickel cobalt aluminate (NCA)). Moreover, various separators and electrolytes can be used, and the applicable range is wide.

[0033] The current collector for high-performance lithium batteries includes a metal foil and a functional coating. The functional coating is a functional layer-like coating structure with a thickness of 800 nm or less formed by applying a conductive slurry on one or two surfaces of the metal foil and drying it. The functional coating includes a plurality of strip-shaped modified conductive agents, and the modified conductive agent is a magnetically oriented modified multi-walled carbon nanotube. After curing and forming, the modified conductive agents are parallel to each other within the functional coating. In the thickness direction of the coating, the axis of each modified conductive agent forms an angle of 15 to 45° with the surface of the metal foil and is arranged obliquely, intertwining with the modified nanofibers, binders, and conductive agents in the coating to form an oriented three-dimensional network connection structure that enhances adhesion, conductivity, and thermal conductivity and uniformly deforms and recovers.

[0034] The modified conductive agent in the functional coating, namely, the magnetically oriented modified multi-walled carbon nanotube, is a modified multi-walled carbon nanotube having a dumbbell structure, with an inner diameter of the tube of 5 nm or more, an outer diameter of the tube of 20 nm or less, and a length of 1200 nm or less. The modified multi-walled carbon nanotube forms a dumbbell-shaped fiber structure with thick ends and a thin central part through oxidation and chemical modification. After orientation and alignment, the thick lower ends are respectively connected to the surface of the metal foil, and the upper ends are connected to each other. Using a binder, conductive agent particles and modified nanofibers of other different sizes are sandwiched between the fiber parts with a thin central part. Thereby, after each part is connected to each other, both ends are fixed, and a three-dimensional network of a bridge-island structure with orientation and alignment is formed. The deformation and displacement of the modified multi-walled carbon nanotubes and conductive agent particles during battery operation are restricted by the elastic three-dimensional network, automatically adapting to the change in internal volume and the deformation and displacement of conductive particles during charge and discharge of the lithium battery, offsetting them, and maintaining the reliability of the functional coating for the connection between the surface of the metal foil and the active material.

[0035] A conductive slurry for manufacturing the current collector for the high-performance lithium battery, wherein the conductive slurry is an aqueous slurry prepared by dispersing and mixing a modified conductive agent (modified multi-walled carbon nanotube), a nano conductive agent, a modified nanofiber, a dispersant, a binder, and a solvent. The slurry is characterized in that the solid content is 0.1 to 5%, the viscosity is 200 to 1000 mPa·s (25 °C), and the pH is 8 to 11.

[0036] The weight ratio of each raw material component of the conductive slurry is: modified conductive agent (i.e., modified multi-walled carbon nanotube): nano conductive agent: modified nanofiber: dispersant: binder: solvent = (0.01 to 1.8):(0.01 to 0.2):(0.02 to 2):(0.02 to 20):(0.05 to 20):(56 to 99.89).

[0037] A method for manufacturing the conductive slurry of the current collector for the high-performance lithium battery, Manufacture the materials, that is, step S1 of manufacturing a modified conductive agent (modified multi-walled carbon nanotubes), a nano conductive agent, modified nanofibers, a dispersant, a binder, and a solvent according to the ratio respectively; Manufacture a high-concentration modified conductive agent suspension, that is, weigh the modified nanofibers and the dispersant according to the ratio, add them to 1 / 3 of the amount of the solvent, mechanically stir to completely dissolve, then weigh the required modified conductive agent and add it to the mixed solution, perform ultrasonic treatment for more than 30 min to obtain a modified conductive agent suspension, specifically, a high-concentration modified multi-walled carbon nanotube suspension, step S2; Perform magnetization, that is, place the modified conductive agent suspension in a strong external magnetic field for magnetization to further excite the magnetic anisotropy of the magnetic modified multi-walled carbon nanotubes to obtain a high-concentration magnetic modified multi-walled carbon nanotube suspension, step S3; Pre-disperse, that is, add a binder in a ratio corresponding to the above high-concentration magnetic modified multi-walled carbon nanotube suspension, replenish the solvent until the desired usage amount is reached, and pre-disperse in the order of a high-speed vacuum disperser and a sand mill. The shear rate during dispersion by the vacuum disperser is 10 - 25 m / s, the vacuum degree is 0.085 MPa or more, and the vacuum dispersion time is 1 - 5 h. In the sand mill, the diameter of the sand milling beads is 0.2 - 2 mm, the ratio of the sand milling beads is 30 - 90%, the sand milling rotation speed is 600 - 10000 r / min, and the sand milling time is 0.1 - 5 h, step S4; Perform secondary dispersion, that is, re-disperse by ultrasonic resonance using an ultrasonic treatment device, and apply an alternating magnetic field to both sides to further uniformly disperse the modified multi-walled carbon nanotubes and the nano conductive agent particles, and arrange them in the same direction by magnetic field induction to obtain a conductive slurry with magnetic orientation, step S5, characterized by including the above steps.

[0038] A method for manufacturing the current collector for a high-performance lithium battery, Manufacture a current collector metal foil and a dispersed conductive slurry respectively, and step (A1) of installing a coating device, an ultrasonic device, a constant magnetic field generating device, and a drying device; Applying the dispersed conductive slurry onto the surface of the metal foil to form a liquid colloid coating with a viscosity of 200 to 1000 mPa·s and a thickness of 500 to 1200 nm at 25°C on the surface (step A2); Continuously applying a static magnetic field perpendicular to the surface of the metal foil to the liquid colloid coating, regularly arranging the orientation-modified conductive agent in the coating by the induction of the external magnetic field, gradually stretching it straight from the original spiral state, arranging it in a parallel array, and intertwining with the substrate (step A3); Drying the coating, evaporating the solvent and volatile components, continuously applying a static magnetic field, and quickly molding the modified conductive agent while maintaining its arrangement position and posture as the viscosity of the coating rapidly increases. In the thickness direction, it is obliquely arranged in parallel at 15 to 45°, and the cured component of the conductive slurry to be applied is fixed on the surface of the metal foil to form a dense functional coating structure with a thickness of 800 nm or less. That is, a three-dimensional network structure with enhanced adhesion, conductivity, and heat conductivity and high recovery characteristics is formed on the surface of the metal foil (step A4), which is characterized by including the above steps.

[0039] Example 1 This example is a specific application example. In this example, an aluminum foil with a thickness of 10 to 15 μm is used as the metal foil substrate.

[0040] The current collector for a high-performance lithium battery according to the present invention includes a metal aluminum foil and a functional coating. The functional coating is a functional coating structure with a thickness of 700 nm formed by applying a conductive slurry on two surfaces of the metal aluminum foil and drying it. The functional coating has magnetic orientation.

[0041] In this example, the axes of the modified conductive agents and each modified multi-walled carbon nanotube in the functional coating form a specific 45° angle with the surface of the metal aluminum foil along the thickness direction, are obliquely arranged, and intertwine with the matrix material such as a binder to form a three-dimensional network structure with enhanced adhesion, conductivity, and heat conductivity.

[0042] The magnetic modified conductive agent used in the present invention forms an array distributed in parallel, enables carriers to move along the direction of the modified conductive agent array, increases the propagation speed of the carriers, and can avoid the recombination of carriers during transportation. It has good orientation conductivity and can quickly transport carriers to the metal foil.

[0043] In this embodiment, the production of the modified conductive agent specifically includes the following steps.

[0044] (1) Oxidation of carbon nanotubes: Put 2 g of multi-walled carbon nanotubes and 200 mL of a mixture of concentrated sulfuric acid and concentrated nitric acid [V (濃HNO3) :V (濃H2SO4) = 1:3] into a 500 mL Erlenmeyer flask, perform ultrasonic treatment for 2 h to disperse the carbon nanotubes in the acid solution. Put the mixture into a constant temperature magnetic stirrer and stir at 55 °C for 6 h to oxidize the carbon nanotubes and cut them into short tubes of 150 - 400 nm (in this embodiment, the specific length is 150 - 300 nm). Then, dilute with deionized water and perform vacuum suction filtration through a 0.22 μm filter membrane. Next, repeatedly wash with deionized water and perform suction filtration until the pH of the filtrate reaches about 7. Collect the black solid on the filter membrane, dry it in a vacuum drying oven at 60 °C for 24 h, pulverize it, and sieve it through a 200-mesh sieve, thereby realizing the cutting, oxidation, and purification of single-walled carbon nanotubes. In the oxidation process, pore defects are formed between the internal meshes of the short carbon nanotubes, a local magnetic moment is imparted to this carbon nanotube, and weak magnetism is imparted to the short multi-walled nanocarbon tubes.

[0045] (2) Ammoniation of carbon nanotubes: Weigh 1 g of oxidized carbon nanotubes and 6 g of 1,6 - hexanediamine into 30 mL of acetone, perform ultrasonic treatment for over 1 h, add 0.4 g of condensing agent DCC (dicyclohexylcarbodiimide), mix uniformly, and reflux and heat at 70 °C for 32 h. Use absolute ethanol to ultrasonically wash and remove excess 1,3 - hexanediamine, DCC, and reaction by - products, perform vacuum suction filtration with a 0.22 - μm filter membrane and a membrane filter, repeatedly wash with absolute ethanol, collect the black substance on the filter membrane, then dry it in a vacuum drying oven at 65 °C for 24 h, pulverize it, sieve it through a 200 - mesh sieve to obtain amino - modified magnetic carbon nanotubes.

[0046] (3) Construction of dumbbell - shaped structure: Weigh 0.5 g of amino - modified magnetic carbon nanotubes and 0.7 g of nano - conductive carbon black, add them to 30 mL of acetone, perform ultrasonic dispersion for 1 h, add condensing agent DCC, and reflux and heat at 70 °C for 24 h. Use absolute ethanol to ultrasonically wash and remove DCC and reaction by - products, perform vacuum suction filtration with a 0.45 - μm filter membrane and a membrane filter, repeatedly wash with absolute ethanol, collect the black substance on the filter membrane, then dry it in a vacuum drying oven at 65 °C for 24 h, pulverize it, sieve it through a 200 - mesh sieve for separation, and obtain a modified conductive agent with a dumbbell - shaped structure where both ends are thick and the central part is thin.

[0047] The multi - wall carbon nanotubes used in the examples of the present invention have an inner diameter of the tube of 5 nm or more, an outer diameter of the tube of 20 nm or less, and a length before cutting of 1200 nm or less.

[0048] In the oxidation step of the embodiment of the present invention, due to the oxidation action of the mixed acid, unstable five-membered carbon rings and seven-membered carbon rings at the helically twisted portions with a large aspect ratio in the carbon nanotubes are broken, and the carbon nanotubes are cut into short carbon nanotubes with both ends open, obtaining processed carbon nanotubes that are shorter and have their top ends opened. Further, through continuous oxidation, the C atoms at the end portions are oxidized to carboxyl groups, providing many contact sites for grafting reactions at the end portions. Also, in the short-cut carbon nanotubes, there are pore defects formed by the oxidation and opening of local C-C bonds. Due to the presence of the defects, there are magnetic moments near the defects, thereby imparting weak magnetism to the carbon nanotubes. Additionally, by utilizing the high reactivity due to the structural defects and local high curvature of carbon nanoparticles, amorphous carbon, and graphite fragments, impurities are oxidized with concentrated acid to selectively remove these impurities.

[0049] In the embodiment of the present invention, as the diamine-based compound, one of diamine-based compounds such as 1,6-hexanediamine, 1,4-butylenediamine, and p-phenylenediamine can be used. Its functional characteristics are that it reacts with the carboxyl at the end of the single-walled carbon nanotube through the contained amino group to form an amide bond, exposing another amino group to perform amino modification on the carbon nanotube. The grafted diamine expands the closely adjacent carbon nanotubes, increases the gap between the carbon nanotubes. Also, due to the presence of diamine steric hindrance, the hydrogen bonds formed between the multi-walled carbon nanotubes in the oxidation process are weakened, improving the dispersibility of the amino-functionalized carbon nanotubes, which is advantageous for grafting a large amount of nano-conductive particles containing carboxyl later. In Example 1, specifically, 1,6-hexanediamine is used.

[0050] In the examples of the present invention, the condensing agent can be one of dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), or 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDCI). Its functional characteristic is that it acts as a dehydrating agent that promotes the reaction between amino and carboxy to form an amide bond and binds them. In this example, specifically, dicyclohexylcarbodiimide DCC is used.

[0051] In the examples of the present invention, the inert solvent can be one of acetone and xylene, etc. In this example, specifically, acetone is used.

[0052] The nano conductive agent particles of the present invention can be one of carbon black and graphite oxide, with a particle size of 20 to 250 nm. A large number of carboxy groups present on its surface can react with amino-modified carbon nanotubes to form an amide bond and bind them. In Example 1 of the present invention, specifically, nano conductive carbon black with an average particle size of 120 nm is used.

[0053] The conductive slurry for manufacturing the current collector for the aforementioned high-performance lithium battery is an aqueous slurry produced by dispersing and mixing a modified conductive agent, modified nanofibers, a dispersant, a binder, and a solvent. The solid content of the slurry is 0.1 to 10%, the viscosity is 200 to 1000 mPa·s (25 °C), and the pH is 8 to 10. Specifically, those skilled in the art may select according to specific needs. In this example, the solid content of the slurry is 8.5%, the viscosity is 500 mPa·s (25 °C), and the pH is 9.

[0054] The functional coating has a thickness of about 800 - 1200 nm when it is undried after coating, providing sufficient space for the modified conductive agent to unwind and stretch straight, arranging with directionality. By controlling the viscosity within a specific range, the modified conductive agent unwinds and stretches straight under the induction of a magnetic field, arranging with directionality, and it helps prevent the agent from sliding and rising to the surface. As the volatile components in the slurry evaporate, the agent is captured within the lattice structure of the substrate, intertwining with the substrate to form a three-dimensional network structure.

[0055] In Example 1 of the present invention, the weight ratio of each raw material component of the conductive slurry is: modified multi-walled carbon nanotubes: nano conductive agent: modified nanofibers: dispersant: binder: solvent = 0.3: 0.05: 5: 20: 20: 54.65.

[0056] In the embodiments of the present invention, the modified nanofibers can be one of cellulose nanofibers and chitin (ChNF) nanofibers modified by carboxylation, sulfonation, phosphorylation, and quaternization reactions. They are dispersed in a deionized water medium so that the solid content is 0.1 - 3.0 wt%. The modified nanofibers are suitable for use in an aqueous medium. As its functional characteristics, it provides a three-dimensional porous network structure, generates an electrostatic repulsive force between fibers due to negatively charged groups, forms a stable colloid, stably confines the magnetic modified conductive agent within its developed pores, plays a role in assisting dispersion, and also intertwines with carbon nanotubes in the functional coating to form a three-dimensional network structure, improving the overall performance of the current collector. In Example 1, specifically, carboxylated cellulose nanofibers are used.

[0057] In the embodiments of the present invention, the dispersant can be a mixture of one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), or poly-N-vinylacetamide (PNVA) and a resin for binder. The usage amount of the dispersant (including single-component or multi-component mixtures) is generally 20 to 1000 times the weight of the carbon nanotube dry powder. The dispersant is suitable for use in an aqueous medium, and its functional feature is to uniformly disperse the conductive agent in the conductive slurry system. In Example 1 of the present embodiment, specifically, polyvinylpyrrolidone (PVP) is used.

[0058] In the embodiments of the present invention, the binder can be a resin having resistance to lithium-ion battery electrolytes and high voltage resistance. The resin is polyacrylic acid (PAA) and its salts with a wide molecular weight distribution, isopropyl alcohol, modified acrylic resin, or modified polyacrylonitrile (PAN) resin. It is dispersed in a deionized water medium so that the solid content is 5 to 30 wt%. The binder is suitable for use in an aqueous medium, and its functional feature is to adhere the conductive slurry between the current collector body and the positive / negative electrode materials and enhance the fixing ability of both. In Example 1 of the present embodiment, specifically, isopropyl alcohol is used.

[0059] In Example 1 of the present invention, deionized water is used as the solvent.

[0060] The method for manufacturing the conductive slurry of the current collector for the high-performance lithium battery described above includes the following steps.

[0061] (1) Material production: Modified conductive agent, modified nanocellulose, dispersant, binder, and solvent were respectively produced according to the ratio of modified multi-walled carbon nanotubes: nano conductive agent: modified nanofiber: dispersant: binder: solvent = 0.3: 0.05: 5: 20: 20: 56.45.

[0062] (2) Preparation of a high-concentration modified conductive agent suspension: The modified nanofibers and the dispersant were weighed according to the ratio, added to 1 / 3 of the amount of the solvent, and mechanically stirred until completely dissolved. Then, the required modified conductive agent was weighed and added to the mixed solution, followed by ultrasonic treatment for 30 min to obtain a modified conductive agent suspension, specifically, a high-concentration modified multi-walled carbon nanotube suspension.

[0063] (3) Magnetization: The modified conductive agent suspension was placed in a strong external magnetic field for magnetization so that the vacancy defects in the carbon nanotube part of the modified conductive agent formed an induced magnetic moment, thereby further exciting the magnetic anisotropy of the magnetic modified conductive agent to obtain a high-concentration magnetic modified multi-walled carbon nanotube suspension.

[0064] (4) Preliminary dispersion: A binder in a ratio corresponding to the above high-concentration modified conductive agent suspension was added, and the solvent was replenished until the desired usage amount was reached. Preliminary dispersion was carried out in the order of a high-speed vacuum disperser and a sand mill. The shear rate during dispersion by the vacuum disperser was 10 - 25 m / s, the vacuum degree was 0.085 MPa or more, and the vacuum dispersion time was 1 - 5 h. In the sand mill, the diameter of the sand milling beads was 0.2 - 2 mm, the ratio of the sand milling beads was 30 - 90%, the sand milling rotation speed was 600 - 10000 r / min, and the sand milling time was 0.1 - 5 h.

[0065] (5) Secondary dispersion: Using an ultrasonic treatment device, dispersion was carried out again by ultrasonic resonance, and by applying an alternating magnetic field to both sides, the magnetic modified conductive agent was dispersed more uniformly and oriented in the same direction by the induction of the magnetic field to obtain a conductive slurry with magnetic orientation. Here, the ultrasonic treatment device is an ultrasonic generator arranged in the liquid, the ultrasonic frequency of each power unit is 20 kHz - 40 kHz, and the power is 1 kW - 3 kW. The magnetic field has an intensity of 0.1 - 5 T and a frequency of 40 - 60 Hz.

[0066] Steps (4) and (5) further include maintaining the stability of the slurry by adjusting the pH value of the conductive slurry to 8 - 11 with ammonia water during the dispersion process.

[0067] In Example 1 of the present invention, the specific component mixing ratio of the conductive slurry and some manufacturing steps are as follows. 20 g of a 10% polyvinylpyrrolidone (PVP K30) solution and 5 g of a 1% carboxylated nanocellulose solution were added to 13 g of deionized water and mixed well. Then, 0.3 g of modified multi-walled carbon nanotubes and 0.05 g of a nano conductive agent were added to the mixed solution, and ultrasonic treatment was performed for 30 min to obtain a magnetic modified conductive agent suspension. The magnetic modified conductive agent suspension was magnetized by placing it in a strong external magnetic field. 20 g of isopropyl alcohol and 43.45 g of deionized water were added to the magnetized magnetic modified conductive agent suspension, and pre-dispersed with a high-speed disperser for 30 minutes (first stirred at a low speed and then accelerated). After the slurry was stirred almost uniformly, it was vacuum-dispersed at 2400 RPM for 120 minutes (the vacuum degree needs to exceed 0.08 MPa), and then sand milling was performed at 3000 revolutions per minute for 10 minutes. The slurry treated as described above was ultrasonically dispersed again, and an alternating magnetic field was applied to both sides to obtain an oriented aqueous conductive slurry with a solid content of 2.1%. By adjusting the usage amounts of the magnetic modified conductive agent, modified nanocellulose, dispersant, and binder in the above formulation, an aqueous conductive slurry with a solid content of 0.1 to 6% can also be obtained.

[0068] The method for manufacturing the aforementioned current collector for high-performance lithium batteries includes the following steps.

[0069] (1) The current collector metal foil and the dispersed conductive slurry were each manufactured, and a coating device, an ultrasonic device, a constant magnetic field generating device, and a drying device were installed.

[0070] (2) The dispersed conductive slurry was applied onto the surface of the current collector metal foil to form a liquid colloidal coating with a viscosity of 200 - 1000 mPa·s (25°C) and a thickness of 800 - 1000 nm on the surface. The coating had a thickness of about 800 - 1200 nm when it was not yet dried after application, providing sufficient space for the magnetically modified conductive agent to unwind under the induction of a magnetic field, stretch straight, and align directionally. By controlling the viscosity within a specific range, the conditions necessary for the orientation effect induced by the magnetic field were provided, and the modified conductive agent did not slide to the surface. As the volatile components in the slurry evaporated, it was captured within the lattice structure of the substrate, intertwined with the substrate, and formed a three-dimensional network structure.

[0071] (3) A stable magnetic field perpendicular to the surface of the metal foil was continuously applied to the liquid colloidal coating, causing the magnetically oriented modified conductive agent in the coating to generate an induced magnetic moment under the induction of the magnetic field, and forming an array arranged directionally under the induction of the magnetic field.

[0072] The specific steps of the orientation induced by an external magnetic field are as follows. In the first 1 / 3 process of the coating production line, an orientation magnetic field with a strength of 200 mT - 1000 mT and forming an angle of 45 degrees with the surface of the metal foil was applied to complete the first orientation and positioning for the magnetically modified conductive agent, and reorient the magnetically single-layer carbon nanotubes with a regular arrangement disrupted during coating. Next, in the remaining 2 / 3 process of the coating production line, a uniform orientation magnetic field with a strength of 500 mT - 1000 mT and forming an angle of 45 - 90 degrees with the surface of the metal foil was applied to complete the second orientation and positioning. Since the viscosity of the coating continued to increase, the magnetically modified conductive agent finally formed an oblique array with a specific angle of 15 - 45° along the thickness direction within the coating and was molded.

[0073] (4) Dry the coating to sufficiently evaporate the solvent and volatile components, continuously apply a static magnetic field, and quickly mold while maintaining the arrangement position and posture as the viscosity of the coating rapidly increases. The solid content of the conductive slurry component of the coating adheres to the surface of the metal foil to form a dense functional coating structure with a thickness of 800 nm or less. This structure forms a three-dimensional network structure layer on the surface of the metal foil that enhances adhesion, conductivity, and heat conductivity.

[0074] Step (3) further includes the following steps.

[0075] (31) In the first 1 / 3 process of the coating production line, raise the temperature of the conductive slurry or the applied coating to 45 - 65 °C for preliminary drying to extend the condensation time, thereby reducing the viscosity of the liquid colloidal coating, increasing the kinetic energy for the single-walled carbon nanotubes to unwind and straighten and align directionally.

[0076] The current collector for high-performance lithium batteries manufactured in Example 1 was used in the manufacture of lithium-ion batteries for performance testing. Here, the electrodes were manufactured using the following parameters. The positive electrode plate includes a current collector and a positive electrode active material layer coated on the current collector. The current collector is the current collector for high-performance lithium batteries manufactured in this example. The positive electrode active material layer consists of 93 parts by weight of a positive electrode material (LFP), 4 parts by weight of a positive electrode conductive agent (SP), and 3 parts by weight of a positive electrode binder (PVDF - 5130) as raw materials.

[0077] The negative electrode plate includes a current collector and a negative electrode active material layer coated on the current collector. The current collector is a shiny copper foil. The negative electrode active material layer consists of 96 parts by weight of a negative electrode material (artificial graphite), 1 part by weight of a negative electrode conductive agent (SP), 1 part by weight of a negative electrode binder 1 (sodium carboxymethyl cellulose CMC), and 2 parts by weight of a negative electrode binder 2 (styrene-butadiene rubber SBR) as raw materials.

[0078] The positive and negative plates, 20-μm polypropylene (PP) separator, and LiPF6 electrolyte were used to assemble 18650 batteries, and the performance of the plates and the batteries are shown in Tables 1 and 2.

[0079] Comparative Example 1 In Comparative Example 1, the positive current collector was manufactured under the same manufacturing conditions as above, except that shiny aluminum foil was used.

[0080] Using the current collector for high-performance lithium batteries manufactured in Example 1 and directly using shiny aluminum foil as the positive current collector, 18650 batteries were manufactured according to the same formulations and processes for the positive and negative electrodes of the same lithium battery, and the performance of the plates and the batteries was tested. The performance of the tested plates and the batteries are shown in Tables 1 and 2, respectively.

[0081] [Table 1]

[0082] [Table 2]

[0083] Based on the test results, it is easy to draw the following conclusions. When the current collector for high-performance lithium batteries according to the present invention is used in the manufacture of lithium batteries, all performances from the plates to the batteries are superior to those of Comparative Example 1 using shiny foil as the current collector. Among them, the resistance of the positive plate manufactured in Example 1 is only 1 / 3 of that of Comparative Example 1, which is a scheme using pure shiny foil as the current collector, and the peel strength exceeds 4 times that of Comparative Example 1. For the battery of Example 1, as a result of testing the AC internal resistance, it is 42% lower than that in the case of shiny foil. At room temperature, the lithium-ion battery manufactured in Example 1 can reach a capacity retention rate of 93% after 2000 cycles of 1C charge and 2C discharge, which is much higher than the 80% capacity retention rate of Comparative Example 1, which is a scheme using shiny foil as the current collector. Also, the consistency of the battery cycles is clearly superior to that of the scheme using pure shiny foil as the current collector.

[0084] Example 2 The current collector for high-performance lithium batteries, the conductive slurry, and the manufacturing method thereof according to this example were basically the same as those in Example 1, except for the following points.

[0085] The modified conductive agent for manufacturing the aforementioned high-performance battery current collector is formed by oxidizing and chemically modifying multi-walled carbon nanotubes, and then connecting them to nano-conductive agent particles of other sizes to form a dumbbell-shaped bridge-island structure with both ends fixed. In this Example 2, 1,4-butanediamine was used as the modifier, and diisopropylcarbodiimide (DIC) was used as the condensing agent.

[0086] The conductive slurry for manufacturing the aforementioned high-performance lithium battery current collector is an aqueous slurry produced by dispersing and mixing a modified conductive agent, modified nanofibers, a dispersant, a binder, and a solvent. The solid content of the slurry is 4 - 6%, the viscosity is 300 - 1000 mPa·s (25 °C), and the pH is 8 - 9.

[0087] In this Example 2, the weight ratio of each raw material component of the conductive slurry is: modified multi-walled carbon nanotubes:nano-conductive agent:modified nanofibers:dispersant:binder:solvent = 0.6:0.1:6:20:20:53.3.

[0088] In this Example 2, the modified nanocellulose is carboxylated chitin nanofibers, the binder is a modified acrylic resin, and polyvinyl alcohol (PVA) was used as the dispersant.

[0089] The conductive slurry of this Example 2 was coated on a copper foil to manufacture a current collector for high-performance lithium batteries.

[0090] The manufacturing parameters of the negative electrode plate of the lithium-ion battery for the comparative test of the current collector manufactured in Example 2 are as follows. The negative electrode plate includes a current collector and a negative electrode active material layer coated on the current collector. The current collector is the current collector for high-performance lithium batteries manufactured in Example 2. The negative electrode active material layer is composed of, as raw materials, 96 parts by weight of a negative electrode material (artificial graphite), 1 part by weight of a negative electrode conductive agent (SP), 1 part by weight of a negative electrode binder 1 (carboxymethyl cellulose sodium CMC), and 2 parts by weight of a negative electrode binder 2 (styrene butadiene rubber SBR). The peeling strength of the electrode plate was tested using an electronic tensile tester, and the resistance of the electrode plate was tested by pressing with upper and lower double probes. The performance of the tested electrode plates is shown in Table 3.

[0091] Example 3 The current collector for high-performance lithium batteries, the conductive slurry, and the manufacturing method thereof according to this example were basically the same as those in Examples 1 and 2, except for the following points.

[0092] In this Example 3, for the modified conductive agent used to manufacture the aforementioned high-performance battery current collector, 1,6-hexanediamine was used as the modifier and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDCI) was used as the condensing agent.

[0093] The conductive slurry used to manufacture the aforementioned current collector for high-performance lithium batteries is an aqueous slurry manufactured by dispersing and mixing a modified conductive agent, modified nanofibers, a dispersant, a binder, and a solvent. The slurry has a solid content of 3 - 4%, a viscosity of 200 - 800 mPa·s (25°C), and a pH of 9 - 10.

[0094] In this Example 3, the weight ratio of each raw material component of the conductive slurry is modified multi-walled carbon nanotubes:nano conductive agent:modified nanofibers:dispersant:binder:solvent = 0.3:0.1:4:12:14:69.6.

[0095] In Example 3, the modified nanocellulose is carboxylated chitin nanofibers, the binder is modified polyacrylonitrile (PAN), and poly-N-vinylacetamide (PNVA) is used as the dispersant.

[0096] The conductive slurry of Example 3 was applied onto a copper foil to fabricate a current collector for high-performance lithium batteries.

[0097] The manufacturing parameters of the negative electrode plate of the lithium-ion battery for the comparative test of the current collector manufactured in Example 3 are as follows. The negative electrode plate includes a current collector and a negative electrode active material layer coated on the current collector. The current collector is the current collector for high-performance lithium batteries manufactured in Example 2. The negative electrode active material layer is composed of, as raw materials, 97 parts by weight of a negative electrode material (artificial graphite), 1 part by weight of a negative electrode conductive agent (SP), 1 part by weight of a negative electrode binder 1 (sodium carboxymethyl cellulose CMC), and 1 part by weight of a negative electrode binder 2 (styrene-butadiene rubber SBR). The peel strength of the electrode plate was tested using an electronic tensile tester, and the resistance of the electrode plate was tested by pressing with upper and lower double probes. The performance of the tested electrode plates is shown in Table 3 (comparative test data when the current collector for high-performance lithium batteries of the present invention is used for the negative electrode plate).

[0098] Comparative Example 2 The parameters of the manufacturing process of the negative electrode plate of the lithium-ion battery are the same as those in Example 2. Specifically, the ratio of the negative electrode material (artificial graphite): conductive agent (SP): binder 1 (CMC): binder 2 (SBR) is 96:1:1:2. However, it is different in that a shiny copper foil is used for the current collector. The performance of the tested electrode plates is shown in Table 3.

[0099] Comparative Example 3 The parameters of the manufacturing process of the negative electrode plate of the lithium-ion battery are the same as those in Example 3. Specifically, the ratio of the negative electrode material (artificial graphite): conductive agent (SP): binder 1 (CMC): binder 2 (SBR) is 97:1:1:1. However, it is different in that a shiny copper foil is used for the current collector. The performance of the tested electrode plates is shown in Table 3.

[0100]

Table 3

[0101] Based on the test results, it is easy to draw the following conclusion. When the usage amount of the binder for the negative electrode is the same, the negative electrode plate manufactured using the current collector for high-performance lithium batteries of the present invention has a higher adhesion to the electrode plate, and the resistance of the electrode plate is also lower than that of a purely shiny foil. As can be seen from this, the current collector for high-performance lithium batteries of the present invention can appropriately reduce the proportion of the binder in the positive / negative electrode slurry of the battery and further reduce the internal resistance, which is advantageous for improving the energy density of the battery.

[0102] As can be seen from the above, in the current collector for high-performance lithium batteries of the present invention, the magnetic modified conductive agents used form an array that is parallelly distributed within the functional coating, constructing a three-dimensional network structure in which the modified conductive agent and the flexible substrate are intertwined, providing a connection layer with high strength, conductive efficiency, and good flexibility. Thereby, the contact area between the rigid metal current collector and the conductive slurry can be effectively increased, the adhesion of the coating can be improved, and the interfacial resistance between the current collector and the battery active material can be effectively reduced. In addition, by using the intertwined network, the volume change during charge and discharge can be buffered and automatically recovered, avoiding the expansion and peeling between the conductive slurry and the current collector, enhancing the continuous adhesion between the current collector metal foil substrate and the battery active material when repeating charge and discharge multiple times, improving the stability of the electrode plate, avoiding cycle failures, thereby improving the specific capacity, cycle stability, and rate characteristics of the electrode, and significantly improving the overall performance of the lithium battery.

[0103] In other embodiments of the present invention, metal foils such as copper foils, iron foils or stainless steel foils can also be used as the metal base material of the current collector. Further, under the mixing ratios of the above-described respective components and the operating conditions of the process steps according to the present invention, those skilled in the art can select by themselves the desired specific components, ratios and processes, and the values of the operating conditions according to ordinary techniques, and all can achieve the technical effects described in the present invention, and it is not necessary to list one by one the embodiments of the present invention.

[0104] The above are only preferred embodiments of the present invention and do not limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the technical solution of the present invention without departing from the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A current collector for a high-performance lithium battery comprising a metal foil and a functional coating, wherein the functional coating is a functional layer coating structure with a thickness of 800 nm or less formed by applying a conductive slurry onto one or two surfaces of the metal foil and drying it. The functional coating contains a plurality of strip-shaped modified conductive agents, and the modified conductive agent is a magnetically oriented modified multi-walled carbon nanotube. After curing and forming, the modified conductive agents are parallel to each other within the functional coating. In the thickness direction of the coating, the axes of the modified conductive agents form an angle of 15 to 45° with the surface of the metal foil respectively and are arranged obliquely, and are intertwined with the modified nanofibers, binders, and modified conductive agents within the coating to form an oriented three-dimensional network connection structure that enhances adhesion, conductivity, and heat conductivity and uniformly deforms and recovers. The magnetically oriented modified multi-walled carbon nanotubes in the functional coating are modified multi-walled carbon nanotubes having a dumbbell structure, with an inner diameter of the tube of 5 nm or more, an outer diameter of the tube of 20 nm or less, and a length of 1200 nm or less. The modified multi-walled carbon nanotubes have a dumbbell-shaped fiber structure with thick ends and a thin central part due to oxidation and chemical modification. After orientation arrangement, the thick lower ends are respectively connected to the surface of the metal foil, and the upper ends are connected to each other. Using a binder, other nano-conductive agent particles and modified nanofibers of different sizes are sandwiched between the fiber parts with a thin central part. Thereby, after each part is connected to each other, both ends are fixed, and a three-dimensional network of a bridge-island structure with an oriented arrangement is formed. The deformation and displacement of the modified multi-walled carbon nanotubes and nano-conductive agent particles during battery operation are restricted by the elastic three-dimensional network, automatically adapting to the change in the internal volume during charge and discharge of the lithium battery and the deformation and displacement of the conductive particles, offsetting them, and maintaining the reliability of the connection of the functional coating to the surface of the metal foil and the active material. A current collector for a high-performance lithium battery, characterized in that.

2. The modified multi-walled carbon nanotubes are Oxidize the carbon nanotubes, that is, put an appropriate amount of multi-walled carbon nanotubes into a mixed solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 1:3 and perform ultrasonic treatment for 2 h to uniformly disperse the multi-walled carbon nanotubes in the acid solution to obtain a dispersion. Put the dispersion into a constant-temperature magnetic stirrer and stir at 55 °C for 6 h to oxidize the carbon nanotubes and cut them into short tubes with a length of 150-400 nm. Then, dilute with deionized water and perform vacuum suction filtration with a 0.22 μm filter membrane and a membrane filter. Next, repeatedly wash with deionized water and perform suction filtration. When the pH of the filtrate reaches about 7, collect the black solid on the filter membrane, dry it in a vacuum drying oven at 60 °C for 24 h, pulverize it, and sieve it through a 100-mesh sieve to obtain short-cut and purified oxidized multi-walled carbon nanotubes in step (1); Ammonify the carbon nanotubes, that is, add the oxidized multi-walled carbon nanotubes and an excessive amount of diamine-based compound to an inert solvent, perform ultrasonic treatment for 1 h, add a condensing agent, mix uniformly, reflux and heat at 70 °C for 32 h, and use absolute ethanol to ultrasonically wash away the excess amine, dicyclohexylcarbodiimide (DCC), and reaction by-products. Perform vacuum suction filtration with a 0.22 μm filter membrane and a membrane filter, repeatedly wash with absolute ethanol, collect the black substance on the filter membrane, then dry it in a vacuum drying oven at 65 °C for 24 h, pulverize it, and sieve it through a 200-mesh sieve to obtain amino-modified magnetic multi-walled carbon nanotubes in step (2); Construct a dumbbell-shaped structure, that is, add the amino-modified magnetic multi-walled carbon nanotubes and nano-conductive agent particles to an inert solvent, perform ultrasonic dispersion for 1 h, add a condensing agent, and reflux and heat at 70 °C for 24 h. Use absolute ethanol to ultrasonically wash away the excess condensing agent and reaction by-products. Perform vacuum suction filtration with a 0.45 μm filter membrane and a membrane filter, repeatedly wash with absolute ethanol, collect the black substance on the filter membrane, then dry it in a vacuum drying oven at 65 °C for 24 h, pulverize it, and sieve it through a 200-mesh sieve to obtain modified multi-walled carbon nanotubes with a dumbbell-shaped structure having thick ends and a thin central part in step (3). The current collector for a high-performance lithium battery according to claim 1, characterized in that it is manufactured by the above steps.

3. In the step (1) of oxidizing the carbon nanotubes, due to the oxidation by the mixed acid, the unstable five-membered carbon rings and seven-membered carbon rings at the helically twisted portions with a large aspect ratio among the carbon nanotubes are broken, and the carbon nanotubes are cut into short carbon nanotubes with both ends open, obtaining processed carbon nanotubes that are shorter and have their top ends opened. Further, by continuous oxidation, the C atoms at the end portions are oxidized to carboxyl groups, providing many contact sites for graft reaction at the end portions. Also, in the short-cut carbon nanotubes, there are pore defects formed by the oxidation and opening of local C-C bonds. Due to the presence of the defects, there are magnetic moments near the defects, thereby imparting weak magnetism to the carbon nanotubes. The current collector for a high-performance lithium battery according to claim 2, characterized in that.

4. In the step (3) of constructing the dumbbell-type structure, the nano-conductive agent particles are one of carbon black and graphite oxide, with a particle size of 20 to 250 nm. A large amount of carboxyl groups present on their surfaces react with the amino-modified carbon nanotubes to form amide bonds, stably bonding them, and thick fixing portions are formed at both ends of the modified multi-walled carbon nanotubes. The current collector for a high-performance lithium battery according to claim 2, characterized in that.

5. In the step (2), the diamine-based compound is one of 1,6-hexanediamine, 1,4-butanediamine, and p-phenylenediamine. It reacts with the carboxyl group at the end of the carbon nanotube through the contained amino group to form an amide bond, and by exposing another amino group, amino modification of the carbon nanotubes is performed. The grafted diamine expands the closely adjacent carbon nanotubes, increasing the gap between the carbon nanotubes. Also, due to the presence of diamine steric hindrance, the hydrogen bonds formed between the multi-walled carbon nanotubes in the oxidation process are weakened, improving the dispersibility of the amino-modified carbon nanotubes, which is advantageous for grafting nano-conductive agent particles containing a large amount of carboxyl groups later. In the step (2), the condensing agent is dicyclohexylcarbodiimide (DCC), which acts as a dehydrating agent to promote the reaction between the amino group and the carboxyl group to form an amide bond and stably bond them. In the step (3), the inert solvent is one of acetone and xylene, and the current collector for a high-performance lithium battery according to claim 2 is characterized in that.

6. A conductive slurry for manufacturing the current collector for a high-performance lithium battery according to any one of claims 1 to 5, The conductive slurry is an aqueous slurry produced by dispersing and mixing modified multi-walled carbon nanotubes, a nano conductive agent, modified nanofibers, a dispersant, a binder, and a solvent. The slurry has a solid content of 0.1 to 5%, a viscosity of 200 to 1000 mPa·s, and a pH of 8 to 11. The weight ratio of each raw material component of the conductive slurry is modified multi-walled carbon nanotubes: nano conductive agent: modified nanofibers: dispersant: binder: solvent = (0.01 to 1.8): (0.01 to 0.2): (0.02 to 2): (0.02 to 20): (0.05 to 20): (56 to 99.89), and the conductive slurry is characterized in that.

7. The modified nanofibers are one of cellulose nanofibers and chitin ChNF nanofibers modified by carboxylation, sulfonation, phosphorylation, and quaternization reactions, and are dispersed in a deionized water medium so that the solid content is 0.1 to 3.0 wt%. The modified nanofibers are suitable for use in an aqueous medium, provide a three-dimensional porous network structure, generate an electrostatic repulsive force between fibers by negatively charged groups, form a stable colloid, stably confine the modified conductive agent in its developed pores, and also entangle with the modified conductive agent in a functional coating to form a three-dimensional network structure, improving the overall performance of the current collector. The dispersant is one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), or poly-N-vinylacetamide (PNVA). The amount of the dispersant used is 20 to 1000 times the weight of the dry powder of the modified conductive agent. The dispersant is suitable for use in an aqueous medium and uniformly disperses the modified conductive agent in the conductive slurry system. The binder is a resin having resistance to a lithium-ion battery electrolyte and high-voltage resistance, and the resin is one kind or a mixture of polyacrylic acid (PAA) having a wide molecular weight distribution and its salts, modified acrylic resin, and modified polyacrylonitrile (PAN) resin, and is dispersed in a deionized water medium so that the solid content is 5 to 30 wt%. The binder is suitable for use in an aqueous medium, adheres a conductive slurry between the current collector body and the positive / negative electrode material, and enhances the fixing ability of both. The conductive slurry of the current collector for a high-performance lithium battery according to claim 6, wherein the solvent is deionized water.

8. A method for manufacturing the conductive slurry of the current collector for a high-performance lithium battery according to claim 6 or 7, comprising: Manufacturing materials, that is, step S1 of manufacturing modified multi-walled carbon nanotubes, nano conductive agents, modified nanofibers, dispersants, binders, and solvents according to the ratio respectively; Manufacturing a high-concentration modified conductive agent suspension, that is, weighing modified nanofibers and dispersants according to the ratio, adding them to 1 / 3 of the amount of the solvent, mechanically stirring until completely dissolved, then weighing the required modified conductive agent and adding it to the mixed solution, and performing ultrasonic treatment for more than 30 min to obtain a modified conductive agent suspension, specifically, a high-concentration modified multi-walled carbon nanotube suspension, step S2; Performing magnetization, that is, placing the modified conductive agent suspension in a strong external magnetic field for magnetization to further excite the magnetic anisotropy of the magnetic modified multi-walled carbon nanotubes to obtain a high-concentration magnetic modified multi-walled carbon nanotube suspension, step S3; Pre-dispersing, that is, adding a binder in a ratio corresponding to the above high-concentration magnetic modified multi-walled carbon nanotube suspension, replenishing the solvent until the desired usage amount is reached, and pre-dispersing in the order of a high-speed vacuum disperser and a sand mill. When dispersing with the vacuum disperser, the shear rate is 10 to 25 m / s, the vacuum degree is 0.085 MPa or more, and the vacuum dispersion time is 1 to 5 h. In the sand mill, the diameter of the sand milling beads is 0.2 to 2 mm, the ratio of the sand milling beads is 30 to 90%, the sand milling rotation speed is 600 to 10,000 r / min, and the sand milling time is 0.1 to 5 h, step S4. Step S5 of performing secondary dispersion, that is, redispersing by ultrasonic resonance using an ultrasonic treatment device and applying an alternating magnetic field to both sides to further uniformly disperse the modified multi-walled carbon nanotubes and nano conductive agent particles, arranging them in the same direction by magnetic field induction, and obtaining a conductive slurry with magnetic orientation. The method is characterized by including this step.

9. In the above steps S2 and S5, the ultrasonic treatment device is an ultrasonic generator disposed in a liquid, the ultrasonic frequency of each power unit is 20 kHz to 40 kHz, and the power is 1 kW to 3 kW. In the above steps S3 and S5, the alternating magnetic field has an intensity of 0.1 to 5 T and a frequency of 40 to 60 Hz. The method according to claim 8 is characterized by this.

10. A method for manufacturing a current collector for a high-performance lithium battery according to any one of claims 1 to 5, Step (A1) of manufacturing a current collector metal foil and a dispersed conductive slurry respectively, and installing a coating device, an ultrasonic device, a constant magnetic field generating device, and a drying device; Step (A2) of applying the dispersed conductive slurry onto the surface of the metal foil to form a liquid colloidal coating with a viscosity of 200 to 1000 mPa·s and a thickness of 500 to 1200 nm at 25°C on the surface; Step (A3) of continuously applying a constant magnetic field perpendicular to the surface of the metal foil to the liquid colloidal coating, regularly arranging the orientation-modified conductive agent in the coating by the induction of an external magnetic field, gradually stretching it straight from the original helical state, making it into a parallel array, and intertwining with the substrate; Step (A4) of drying the coating, evaporating the solvent and volatile components, continuously applying a constant magnetic field, and quickly molding the modified conductive agent while maintaining the arrangement position and posture as the viscosity of the coating rapidly increases. In the thickness direction, it is obliquely and parallelly arranged at 15 to 45°, and the cured component of the conductive slurry to be applied is fixed on the surface of the metal foil to form a dense functional coating structure with a thickness of 800 nm or less. That is, on the surface of the metal foil, a three-dimensional network structure with enhanced adhesion, conductivity, heat conductivity, and high recovery characteristics is formed. The manufacturing method is characterized by including this step.

11. The above step (A3) Raise the temperature of the conductive slurry or the applied coating to 45 to 65 °C for preliminary drying to extend the condensation time, thereby reducing the viscosity of the liquid colloidal coating, allowing the modified conductive agent to unwind and stretch straight, increasing the kinetic energy for directional alignment, and / or simultaneously applying ultrasonic waves to the liquid colloidal coating to further increase the kinetic energy for the modified conductive agent to unwind and stretch straight and align directionally, accelerating the formation of an array in which the modified conductive agent is arranged in parallel, increasing the density of the three-dimensional connection structure formed between the modified conductive agent and the substrate, and forming a three-dimensional network structure on the surface of the metal foil that enhances adhesion, conductivity, and heat conductivity, suppresses deformation, and automatically recovers, further comprising step (A3-1). The manufacturing method according to claim 10, characterized in that it further comprises the above steps.

Images