Composite conductive agent and preparation method thereof, positive plate, battery, battery assembly and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a composite conductive agent, a preparation method of the composite conductive agent, a positive plate, a battery, a battery assembly and an electric device. The liquid metal particles comprise liquid metal oxide shells and liquid metal wrapped in the liquid metal oxide shells. When the composite conductive agent is applied to a battery pole piece, the compaction density of the pole piece can be effectively improved, the energy density of a battery is further improved, meanwhile, the composite conductive agent has excellent conductivity, the liquidity of liquid metal enables the composite conductive agent to play a self-repairing role, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to composite conductive agents and their preparation methods, positive electrode sheets, batteries, battery modules, and electrical devices. Background Technology

[0002] With the increasing demand for volumetric energy density (VED) in batteries, higher requirements are being placed on the development of high areal density and high compaction electrodes. Currently, researchers have adopted various methods to improve electrode compaction density, such as particle size distribution, particle morphology control, and improved electrode rolling methods. However, some problems remain to be solved, such as limited compaction effect, complex manufacturing processes, increased costs, and particle breakage due to excessive rolling pressure. For example, over-compression of the electrode can cause large-area breakage of spherical particles, resulting in many small primary particles detached from the secondary spheres on the newly formed surface. These detached particles deteriorate the local performance of the electrode due to detachment from the binder or conductive agent. The newly formed surface leads to an increase in specific surface area and side reactions, resulting in reduced electrical performance. In over-compressed electrodes, excessive compression between material particles results in low electrode porosity, reduced electrolyte absorption, difficulty for electrolyte to penetrate the electrode interior, low specific capacity, and reduced electrolyte retention.

[0003] Therefore, the relevant technologies for improving the volumetric energy density of batteries still need to be improved. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a composite conductive agent that can improve the volumetric energy density of a battery while also improving cycle performance, its preparation method, a positive electrode, a battery, a battery assembly, and an electrical device.

[0005] In a first aspect, this application provides a composite conductive agent. According to embodiments of this application, the composite conductive agent comprises a physically mixed solid conductive agent and liquid metal particles, wherein the liquid metal particles comprise a liquid metal oxide shell and liquid metal encapsulated within the liquid metal oxide shell. When applied to battery electrodes, this composite conductive agent can effectively increase the compaction density of the electrodes, thereby increasing the volumetric energy density of the battery. It also exhibits excellent conductivity, and the fluidity of the liquid metal enables it to perform self-healing, resulting in better cycle performance of the battery.

[0006] According to an embodiment of this application, the liquid metal particles are attached to the surface of the solid conductive agent.

[0007] According to an embodiment of this application, the surface of the solid conductive agent has oxygen-containing functional groups.

[0008] According to embodiments of this application, the oxygen-containing functional group includes hydroxyl groups.

[0009] According to embodiments of this application, the solid conductive agent includes a carbon-based conductive agent, preferably including at least one of carbon nanotubes, carbon nanofibers, conductive carbon black, acetylene black, superconducting carbon, conductive graphite, carbon black, Ketjen black, carbon dots, and graphene, more preferably carbon nanotubes.

[0010] According to an embodiment of this application, the mass ratio of the solid conductive agent to the liquid metal particles is 1-6:1-6, preferably 3:4.

[0011] According to an embodiment of this application, the total size of the liquid metal particles is no greater than 600 nm, specifically it can be 100 nm to 600 nm.

[0012] According to embodiments of this application, the liquid metal includes Ga, Ga2, and Ga3. x1 In y1 Ga x2 In y2 Sn (1-x2-y2) At least one of the following, wherein x1 is 0.70 to 0.84, y1 is 0.16 to 0.30, x2 is 0.60 to 0.75, and y2 is 0.15 to 0.25.

[0013] A second aspect of this application provides a method for preparing the aforementioned composite conductive agent. According to an embodiment of this application, the method includes mixing a solid conductive agent and a liquid metal to obtain a composite conductive agent. This method is simple and convenient to operate, and the prepared composite conductive agent exhibits excellent conductivity. When applied to electrodes, it can effectively increase the compaction density of the electrodes, thereby improving the energy density and cycle performance of the battery.

[0014] According to an embodiment of this application, the method includes: dispersing the solid conductive agent and the liquid metal in a solvent, and subjecting the resulting mixture to ultrasonic treatment at 0°C to 25°C to obtain a composite conductive agent.

[0015] According to an embodiment of this application, the method further includes: performing a surface treatment on the solid conductive agent to give the surface of the solid conductive agent oxygen-containing functional groups.

[0016] According to an embodiment of this application, the surface treatment includes plasma treatment.

[0017] According to embodiments of this application, the solvent includes N-methylpyrrolidone (NMP).

[0018] According to an embodiment of this application, the ultrasonic treatment is performed under 0°C ice-water bath conditions.

[0019] According to an embodiment of this application, the power of the ultrasonic treatment is 100W to 500W.

[0020] According to an embodiment of this application, the ultrasonic treatment time is 10 min to 2 h.

[0021] A third aspect of this application provides an electrode. According to an embodiment of this application, the electrode includes: a current collector; and an active material layer disposed on at least one surface of the current collector, comprising the aforementioned composite conductive agent. This electrode has high compaction density and good conductivity, thereby enabling batteries using this electrode to have high volumetric energy density and cycle performance.

[0022] According to an embodiment of this application, the active material layer further includes an active material main body, and the mass ratio of the active material main body to the composite conductive agent is 100:3 to 10.

[0023] According to embodiments of this application, the main active material includes at least one of lithium manganese iron phosphate, lithium-rich manganese-based phosphate, and lithium iron phosphate, preferably lithium iron phosphate.

[0024] A fourth aspect of this application provides a battery. According to an embodiment of this application, the battery includes the composite conductive agent or the electrode sheet described above. This battery exhibits high volumetric energy density and excellent cycle performance.

[0025] A fifth aspect of this application provides a battery assembly. According to embodiments of this application, it includes the aforementioned electrodes or the aforementioned battery. This battery assembly combines high energy volume density and long cycle performance.

[0026] In a sixth aspect, this application provides an electrical device. According to embodiments of this application, the electrical device includes the battery or battery assembly described above. This electrical device combines high energy volume density and long cycle life. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the positive electrode active material layer in a positive electrode sheet according to an embodiment of this application. Detailed Implementation

[0028] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] In a first aspect, this application provides a composite conductive agent. According to an embodiment of this application, the composite conductive agent comprises a physically mixed solid conductive agent and liquid metal particles, wherein the liquid metal particles comprise a liquid metal oxide shell and liquid metal encapsulated within the liquid metal oxide shell.

[0030] It should be noted that, since liquid metal is exposed to air, surface oxidation follows the Cabrera-Mott kinetics. The formation of a thin nano-oxide layer leads to self-terminating oxidation, and this thin surface oxide layer is the liquid metal oxide shell.

[0031] This composite conductive agent is applied to battery electrodes. The liquid metal particles can promote the transition from solid-solid interface contact to solid-liquid interface contact between particles, playing a lubricating role and promoting the formation of a compact electrode structure, which can significantly improve the compaction density of the electrode and thus improve the volumetric energy density of the battery. At the same time, the liquid metal particles have high fluidity and high conductivity. Under different operating conditions (such as particle breakage or detachment from the conductive agent interface in the rolling section, and damage to the conductive network during long-term cycling), the composite conductive agent can achieve self-repair of the conductive network, greatly improving the cycle life of the battery.

[0032] Specifically, when composite conductive agents are applied to battery electrodes, liquid metal particles can fill the gaps between electrode material particles. The liquid nature can reduce the friction between electrode material particles, transforming the solid-solid contact interface of the electrode material particles into a solid-liquid contact interface, thus playing a lubricating role. This significantly improves the electron transport efficiency of the line-point conductive network and enhances the electron transport dynamics of the electrode.

[0033] Under normal circumstances, the self-confining oxide layer (i.e., liquid metal oxide shell) on the surface of liquid metal particles maintains and protects their morphology. When the conductive network is damaged (e.g., due to rolling causing the main material particles to detach from the conductive agent, or due to expansion and contraction during charging and discharging causing the main material to peel off), the self-confining oxide layer on the surface of the liquid metal particles, under external force, allows the liquid metal to regain its fluidity and fill the gaps between the main material particles, achieving self-repair of the conductive network. This prevents the local performance of the electrode from deteriorating due to the main material particles not being in contact with the conductive agent, thus avoiding a decrease in cycle performance. In other words, in the electrode rolling section, the composite conductive agent can prevent the conductive network from being damaged by excessive local pressure, thereby extending the battery's cycle life. At the same time, liquid metal particles can also promote the formation of a compact electrode structure, which can significantly improve the battery's volumetric energy density. Furthermore, the self-confining oxide layer on the surface of the liquid metal particles can prevent oxidation at the cathode potential, thus not introducing additional side reactions in the battery.

[0034] Furthermore, the thermal conductivity of liquid metals is typically between 10 W / (mK) and 40 W / (mK), and they have a wide melting range (for example, GaInSn remains liquid from 10.7℃ to 2200℃). These characteristics endow liquid metal particles with excellent convective heat transfer capabilities, as well as superior specific heat capacity, thermal conductivity, and thermal diffusivity. Utilizing these advantages in a composite conductive agent network, rapid heat transfer from the electrode can be achieved, preventing localized overheating and improving the battery's thermal safety.

[0035] According to an embodiment of this application, the liquid metal particles are attached to the surface of the solid conductive agent. Specifically, the liquid metal oxide shell on the surface of the liquid metal particles can easily adhere to the solid conductive agent through van der Waals forces. Based on this, the liquid metal particles can easily and uniformly adhere to the surface of the solid conductive agent, and the liquid metal particles can be more uniformly dispersed. When applied to the electrode, they can locally fill the spaces between the active material, which is more conducive to forming a conductive network when applied to the electrode, further improving conductivity, improving the electron transport dynamics of the electrode, and benefiting the fast charging performance of the battery.

[0036] According to embodiments of this application, by appropriately surface-treating the solid conductive agent, the adhesion between the liquid metal particles and the solid conductive agent can be further enhanced. In some embodiments, the surface of the solid conductive agent has oxygen-containing functional groups. The liquid metal particles can adhere more easily to the surface of the solid conductive agent, and due to hydrogen bonding, the adhesion between the two can be significantly improved, reducing the possibility of liquid metal detachment.

[0037] According to embodiments of this application, the specific type of oxygen-containing functional group is not particularly limited, as long as it can increase the adhesion between the liquid metal particles and the solid conductive agent. In some embodiments, the oxygen-containing photofunctional group may include hydroxyl groups. This can further enhance the adhesion between the liquid metal and the solid conductive agent.

[0038] According to embodiments of this application, the mass ratio of the solid conductive agent to the liquid metal particles can be 1-6:1-6. In some embodiments, the mass ratio of the solid conductive agent to the liquid metal particles can be 3:4. As examples, the specific mass ratio of the solid conductive agent to the liquid metal particles can be 1:6, 2:5, 3:4, 5:1, 6:1, etc. Within the above ratio range, the liquid metal particles can form a continuous conductive network in the electrode, greatly shortening the electron transport path and improving the conductivity of the electrode. In addition, the self-healing property of the liquid metal can improve the detachment of the conductive network caused by the contraction and expansion of the material during charging and discharging, thereby improving the cycle life of the battery. If the proportion of liquid metal particles is too low, the improvement in electrode compaction is not significant, and the effect of improving battery performance is relatively poor; if the proportion of liquid metal particles is too high, the compaction density of the electrode may be too high, and the degree of compression between the electrode material particles may be too great, resulting in low electrode porosity, reduced electrolyte absorption by the electrode, difficulty for the electrolyte to penetrate into the interior of the electrode, reduced liquid retention capacity, and reduced cycle life.

[0039] According to embodiments of this application, the specific type of the solid conductive agent is not particularly limited and can be flexibly selected according to actual needs. In some embodiments, the solid conductive agent may include a carbon-based conductive agent. In some embodiments, the carbon-based conductive agent may include at least one of carbon nanotubes, carbon nanofibers, conductive carbon black, acetylene black, superconducting carbon, conductive graphite, carbon black, Ketjen black, carbon dots, and graphene.

[0040] As a specific example, carbon-based conductive agents can be carbon nanotubes. Carbon nanotubes have extremely high tensile strength (approximately 50 GPa to 200 GPa), flexibility, and conductivity. They can form a continuous, long-range conductive network in the electrode, improving the electrode's conductivity and toughness, and mitigating the peeling caused by volume changes during charge-discharge cycles.

[0041] According to embodiments of this application, the specific type of liquid metal can be selected according to actual needs. In some embodiments, the liquid metal may include Ga, Ga2, etc. x1 In y1 Ga x2 In y2 Sn (1-x2-y2) At least one of the following, wherein x1 is 0.70–0.84, y1 is 0.16–0.30, x2 is 0.60–0.75, and y2 is 0.15–0.25. This is more conducive to forming a eutectic alloy and maintaining the room-temperature liquid properties of the alloy. As an example, the liquid metal may include Ga, Ga... 0.784 In 0.214 Ga 0.685 In 0.215 Sn 0.10 Alloys, etc. The aforementioned liquid metals possess high thermal conductivity, a wide melting range, and excellent electrical conductivity, which can further enhance the overall performance of batteries.

[0042] According to embodiments of this application, the size of the liquid metal particles is no greater than 600 nm. In some embodiments, the size of the liquid metal particles can be 100 nm to 600 nm. As examples, the specific sizes of the liquid metal particles can be 100 nm, 200 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, etc. Within the above size range, the liquid metal particles can be stably maintained during the rolling process of electrode preparation, maintaining a good particle morphology, better forming a conductive network, and obtaining electrodes with higher compaction density and better cycle performance. It is worth noting that when the size of the liquid metal particles is reduced to the nanometer scale, the liquid metal particles exhibit a supercooling effect (e.g., liquid gallium can remain liquid above 150 K when the size of liquid metal particles is reduced to the micrometer or submicrometer scale), and the supercooling temperature of liquid metal in the nanometer size range can even be as low as 90 K. Based on this, the liquid metal can maintain its liquid properties throughout the entire operating temperature range of the battery, so as to better exert the function of the liquid metal. It is worth noting that if the liquid metal particles are too large, their high surface tension may cause them to detach from the electrode, potentially increasing the risk of short circuits. Furthermore, liquid metal particles possess excellent convective heat transfer capabilities, with high specific heat capacity, thermal conductivity, and thermal diffusivity, enabling rapid heat transfer from the electrode and preventing localized overheating, thus significantly improving the battery's heat dissipation and safety.

[0043] In this article, because of the high surface tension of liquid metal, it usually exists as spherical particles. Therefore, the size of liquid metal particles refers to the diameter of the liquid metal particles, which can be detected by SEM images.

[0044] A second aspect of this application provides a method for preparing the aforementioned composite conductive agent. According to embodiments of this application, the method includes mixing a solid conductive agent and a liquid metal to obtain a composite conductive agent. This method is simple and convenient to operate, and the prepared composite conductive agent exhibits excellent conductivity. When applied to electrodes, it can effectively improve the compaction density of the electrodes, thereby contributing to improved volumetric energy density and cycle performance of the battery.

[0045] According to embodiments of this application, the method may include: dispersing the solid conductive agent and the liquid metal in a solvent, and subjecting the resulting mixture to ultrasonic treatment at 0°C to 25°C to obtain a composite conductive agent. Thus, the liquid metal particles can adhere relatively uniformly to the surface of the solid conductive agent, further enhancing the conductivity of the composite conductive agent, and consequently further improving the compaction density and kinetic performance of the electrode.

[0046] According to embodiments of this application, there are no particular limitations on the specific type of solvent; any solvent capable of effectively dispersing the solid conductive agent and liquid metal can be selected. In some embodiments, the solvent includes NMP (N-methylpyrrolidone). As a specific example, NMP is chosen as the solvent because it provides good dispersion and is compatible with the electrode preparation process, allowing it to be directly used in electrode preparation without considering solvent compatibility issues.

[0047] According to an embodiment of this application, the ultrasonic treatment can be performed under 0°C ice-water bath conditions. This mitigates the problem of solution overheating caused by ultrasonic treatment, preventing the liquid metal alloy from undergoing a dealloying reaction due to excessively high temperatures, thus avoiding the formation of solid byproducts from the reaction with the solvent system.

[0048] According to embodiments of this application, the size of liquid metal particles can be controlled by adjusting the parameters (power, time, etc.) of the ultrasonic treatment. In some embodiments, the power of the ultrasonic treatment can be 100W to 500W (specifically, 100W, 150W, 200W, 250W, 300W, 350W, 400W, 450W, 500W, etc.). In some embodiments, the time of the ultrasonic treatment can be 30min to 2h (e.g., 30min, 1h, 2h, etc.). Within the above power and time ranges, liquid metal particles of suitable size can be obtained, thereby further improving the performance of the composite conductive agent.

[0049] According to embodiments of this application, the method further includes: surface-treating the solid conductive agent to give the surface of the solid conductive agent oxygen-containing functional groups. This can improve the adhesion between the solid conductive agent and the liquid metal particles.

[0050] According to embodiments of this application, the surface treatment includes plasma treatment, etc. This allows for the formation of more oxygen-containing functional groups on the surface of the solid conductive agent, further enhancing the adhesion between the solid conductive agent and the liquid metal particles. Furthermore, this surface treatment method is convenient to operate and easy to implement.

[0051] A third aspect of this application provides an electrode. According to an embodiment of this application, the electrode includes: a current collector; and an active material layer disposed on at least one surface of the current collector, comprising the aforementioned composite conductive agent. This electrode has high compaction density and good conductivity, thereby enabling batteries using this electrode to have high volumetric energy density and cycle performance.

[0052] According to embodiments of this application, the active material layer further includes an active material main body, and the mass ratio of the active material main body to the composite conductive agent is 100:3 to 10, specifically 100:3, 100:4, 100:5, 100:6, 100:7, etc. Within the above ratio range, the conductivity and compaction density of the electrode can be effectively improved. If the proportion of the composite conductive agent is too high, the proportion of the active material main body will decrease, which may affect the battery capacity and volumetric energy density. If the proportion of the composite conductive agent is too low, the effect of improving the conductivity and compaction density of the electrode will be relatively worse, and the battery impedance may increase.

[0053] It is understandable that the aforementioned electrode can be either a positive electrode or a negative electrode.

[0054] According to an embodiment of this application, the positive electrode sheet may include a positive current collector and a positive active material layer, wherein the positive active material layer is disposed on at least one surface of the positive current collector.

[0055] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. Composite current collectors can be formed by applying a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) to a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0056] In some embodiments, the positive electrode active material layer may include positive electrode active material (i.e., the main active material in the positive electrode sheet), binder and conductive agent, and may also include additives with specific functions and effects, such as thickeners, sodium supplements, film-forming additives, flame retardants, high-temperature / low-temperature stabilizers, etc., as needed.

[0057] As an example, the positive electrode active material of a lithium-ion battery may include at least one of the following: layered structure positive electrode active materials (e.g., nickel-cobalt-manganese ternary cathode materials, nickel-cobalt-aluminum ternary cathode materials, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich / sodium layered and rock salt phase layered materials), olivine-type phosphate active materials (e.g., lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, etc.), and spinel structure positive electrode active materials (e.g., spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide, and lithium nickel manganese oxide, etc.). It is understood that the above-mentioned positive electrode active materials may further include doping elements and coating layers, etc.

[0058] In some embodiments, the positive electrode active material may include at least one of lithium manganese iron phosphate, lithium-rich manganese-based phosphate, and lithium iron phosphate. As a specific example, the positive electrode active material may include lithium iron phosphate. It is understood that lithium iron phosphate has high safety, low cost, and long cycle life, but its low compaction density limits its application in high volumetric energy density batteries. However, using the composite conductive agent of the first aspect of this application can effectively improve the electrode compaction density while simultaneously possessing high kinetic performance, effectively overcoming the shortcomings of lithium iron phosphate and expanding the application range of lithium iron phosphate materials.

[0059] As an example, the binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0060] As an example, the conductive agent in the positive electrode active material layer may include the composite conductive agent of the first aspect of this application. Specifically, taking lithium iron phosphate as the main active material and carbon nanotubes as the solid conductive agent as an example, the structural schematic diagram of the positive electrode active material layer of the positive electrode sheet of this application can be referred to... Figure 1 .

[0061] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a layer of negative electrode active material disposed on at least one side surface of the negative electrode current collector.

[0062] As an example, the negative electrode active material layer may include a negative electrode active material, a thickener, a conductive agent, and a binder, wherein the negative electrode current collector may be a metal foil, for example, a copper foil.

[0063] According to embodiments of this application, the negative electrode active material may include carbon-based materials, silicon-based materials, tin-based materials, etc.

[0064] According to embodiments of this application, the binder in the negative electrode material layer may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS).

[0065] According to embodiments of this application, the conductive agent in the negative electrode material layer may include the composite conductive agent of the first aspect of this application.

[0066] A fourth aspect of this application provides a battery. According to an embodiment of this application, the battery includes the composite conductive agent or the electrode sheet described above. This battery exhibits high volumetric energy density and excellent cycle performance.

[0067] It is understood that there are no particular restrictions on the specific type of battery; it can be a primary battery, a secondary battery, a lithium-ion battery, a sodium-ion battery, etc. The battery shape can be cylindrical, square, or any other shape. Based on the outer packaging, the battery can be a hard-shell battery, a pouch battery, etc.

[0068] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode, negative electrode, and separator are manufactured into a cell using winding or stacking processes. The cell and electrolyte are then housed in an outer package. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through.

[0069] It can be understood that the positive and negative electrodes can be consistent with the previous description, and will not be repeated here.

[0070] According to embodiments of this application, taking a lithium-ion battery as an example, the electrolyte may include an electrolyte lithium salt, an organic solvent, and optional additives.

[0071] According to embodiments of this application, the type of electrolyte lithium salt is not particularly limited and can be selected according to actual needs. Specifically, the electrolyte lithium salt can be selected from LiN(C) x2 F 2x2+1 SO2)(C y2 F 2y2+1 The lithium salt can be one or more of the following: SO2), LiPF6, LiBF4, LiBOB, LiAsF6, Li(FSO2)2N, LiCF3SO3, and LiClO4, where x2 and y2 are natural numbers. In the electrolyte, the concentration range of the lithium salt can be 0.5M to 2.5M, specifically 0.8M to 2M, for example 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1.0M, 1.2M, 1.5M, 1.8M, 2.0M, 2.2M, 2.5M, etc.

[0072] According to embodiments of this application, the type of organic solvent is not particularly limited and can be selected according to actual needs. Specifically, the organic solvent may include one or more of chain carbonates, cyclic carbonates, and carboxylic acid esters. The types of chain carbonates, cyclic carbonates, and carboxylic acid esters are not specifically limited and can be selected according to actual needs. As an example, the organic solvent may include one or more of diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butenyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl propionate, and tetrahydrofuran.

[0073] According to embodiments of this application, the separator can be any known porous structure separator with good chemical and mechanical stability. As an example, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0074] A fifth aspect of this application provides a battery assembly. According to embodiments of this application, it includes the aforementioned electrodes or the aforementioned battery. This battery assembly combines high energy volume density and long cycle performance.

[0075] It is understood that the battery assembly can be a battery module, a battery pack, etc. Specifically, the specific structure of the battery module and battery pack can be found in conventional technology in this field, and will not be described in detail here.

[0076] In a sixth aspect, this application provides an electrical device. According to embodiments of this application, the electrical device includes the battery or battery assembly described above. This electrical device combines high volumetric energy density and long cycle life.

[0077] According to embodiments of this application, the specific type of the electrical device is not particularly limited and can be any device that uses a battery as a power source or energy storage unit. As examples, the electrical device includes, but is not limited to, electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (e.g., mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc. It is understood that, in addition to the battery mentioned above, the electrical device also includes necessary structures and components, all of which can be implemented with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be elaborated upon here.

[0078] The embodiments of this application are described in detail below.

[0079] Example 1

[0080] Carbon nanotubes (CNTs) and liquid metal GaIn were dispersed in an appropriate amount of NMP at a mass ratio of 3:4 and subjected to constant temperature ultrasonic treatment in an ice-water bath for 30 minutes to prepare a composite solution of CNTs and liquid metal, i.e., a conductive agent solution, containing a composite conductive agent in which liquid metal particles are attached to the surface of CNTs. PVDF was dispersed in NMP and stirred to obtain a binder slurry. The prepared conductive agent solution was added to the binder slurry. Then, lithium iron phosphate cathode material was added to the resulting mixed solution containing the composite conductive agent and binder, and stirred evenly to obtain a cathode slurry. The cathode slurry was uniformly coated onto a cathode current collector aluminum foil, and after drying and rolling, a lithium iron phosphate cathode sheet containing the composite conductive agent was obtained.

[0081] A soft-pack battery can be fabricated by subjecting the lithium iron phosphate positive electrode containing a composite conductive agent, a graphite negative electrode (the foil material is 8μm copper foil; the active material layer and the ratio is graphite: conductive agent: binder = 100:7:2), and a 9μm PP separator to subsequent processes such as die cutting, stacking, assembly, electrolyte injection (lithium salt is LiPF6), formation, and aging.

[0082] Examples 2-16

[0083] Same as Example 1, with specific differences shown in Table 1.

[0084] Comparative Example 1

[0085] Same as Example 1, with specific differences shown in Table 1.

[0086] Table 1: Preparation parameters of composite conductive agent

[0087]

[0088] Performance testing:

[0089] 1. Positive electrode compaction density test

[0090] 1) Electrode compaction density test: Take the rolled electrode, avoiding the thinned area, and use a 15mm punch to take small round pieces. Take 3 groups from left to right (width direction) and take 5 times along the length of the electrode, for a total of 15 small round pieces. Weigh each piece, record the data, and calculate the average mass value.

[0091] 2) Take the rolled electrode sheet, use a Marl thickness gauge to measure 5 points in the width direction, and test 5 times along the length direction of the electrode sheet, for a total of 25 sets, and calculate the average thickness value.

[0092] 3) Electrode compaction density = average mass of small discs / (area of ​​small discs × average thickness of small discs).

[0093] 2. Porosity test of positive electrode sheet:

[0094] Porosity of the positive electrode can be measured using focused ion beam scanning electron microscopy (FIB-SEM). The principle involves coupling a single-beam focused ion beam system with a conventional scanning electron microscope, where the electron beam is mounted vertically and the ion beam is mounted at a specific angle. When the sample is at the same height as both beams during the test, electron beam imaging and ion beam processing can be achieved simultaneously, allowing for three-dimensional cutting of the sample. Porosity information of the positive electrode can then be obtained through imaging analysis.

[0095] 3. Battery cycle life test

[0096] The batteries were placed in a 25°C ambient chamber and cycled 1000 times under a 0.33C / 0.33C strategy. The charge / discharge voltage range for LFP batteries was 2V to 3.8V, and the charge / discharge voltage range for ternary batteries was 2.5V to 4.2V. The cycle performance of the batteries was then tested.

[0097] 4. Liquid metal particle size testing

[0098] The analysis was performed using SEM imaging. First, a well-dispersed liquid metal and CNT composite solution was dropped onto a silicon wafer. After the solvent evaporated, the sample was placed in the SEM chamber for morphological imaging. The size distribution of the liquid metal particles was obtained by measuring the diameter of the dispersed liquid metal nanoparticles from the SEM images.

[0099] 5. Volumetric Energy Density (VED) Test

[0100] Volumetric energy density (Wh / L) = Discharge energy (Wh) / Battery volume (L). The battery is placed in a 25°C ambient chamber and cycled for 3 times under a 0.33C / 0.33C strategy to determine its discharge energy. The volumetric energy density of the battery cell can be calculated based on the cell's design dimensions.

[0101] Table 2: Performance Test Results

[0102]

[0103] The test data above show that using the composite conductive agent of this application can simultaneously achieve high compaction density, volumetric energy density, and capacity retention. The higher the content of the composite conductive agent in the electrode, the higher both the compaction density and capacity retention. However, excessively high composite conductive agent content will reduce the proportion of the active material in the electrode, resulting in a decrease in capacity. Without liquid metal, it is difficult to improve compaction density, and volumetric energy density will also decrease. Therefore, appropriate combination of CNTs and liquid metal is more conducive to forming a three-dimensional conductive network, while simultaneously achieving self-healing, high conductivity, and improved compaction, thus realizing high volumetric energy density and long lifespan.

[0104] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0105] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0106] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A composite conductive agent, characterized in that, It includes a physically mixed solid conductive agent and liquid metal particles, wherein the liquid metal particles comprise a liquid metal oxide shell and liquid metal encapsulated within the liquid metal oxide shell.

2. The composite conductive agent according to claim 1, characterized in that, The liquid metal particles adhere to the surface of the solid conductive agent.

3. The composite conductive agent according to claim 1 or 2, characterized in that, The surface of the solid conductive agent has oxygen-containing functional groups.

4. The composite conductive agent according to claim 3, characterized in that, The oxygen-containing functional group includes hydroxyl groups.

5. The composite conductive agent according to any one of claims 1 to 4, characterized in that, The solid conductive agent includes a carbon-based conductive agent, preferably including at least one of carbon nanotubes, carbon nanofibers, conductive carbon black, acetylene black, superconducting carbon, conductive graphite, carbon black, Ketjen black, carbon dots and graphene, more preferably carbon nanotubes.

6. The composite conductive agent according to any one of claims 1 to 5, characterized in that, The mass ratio of the solid conductive agent to the liquid metal particles is 1-6:1-6, preferably 3:

4.

7. The composite conductive agent according to any one of claims 1 to 6, characterized in that, The size of the liquid metal particles is no greater than 600 nm, preferably 100 nm to 600 nm.

8. The composite conductive agent according to any one of claims 1 to 7, characterized in that, The liquid metal includes Ga and Ga2. x1 In y1 Ga x2 In y2 Sn (1-x2-y2) At least one of the following, wherein x1 is 0.70 to 0.84, y1 is 0.16 to 0.30, x2 is 0.60 to 0.75, and y2 is 0.15 to 0.

25.

9. A method for preparing the composite conductive agent according to any one of claims 1 to 8, characterized in that, include: A composite conductive agent is obtained by mixing a solid conductive agent and a liquid metal.

10. The method according to claim 9, characterized in that, include: The solid conductive agent and the liquid metal are dispersed in a solvent, and the resulting mixture is ultrasonically treated at 0℃~25℃ to obtain the composite conductive agent.

11. The method according to claim 10, characterized in that, Also includes: The solid conductive agent is surface treated to give the surface of the solid conductive agent oxygen-containing functional groups.

12. The method according to claim 11, characterized in that, The surface treatment includes plasma treatment.

13. The method according to any one of claims 10 to 12, characterized in that, At least one of the following conditions must be met: The solvent includes N-methylpyrrolidone; The ultrasonic treatment was performed under 0°C ice-water bath conditions; The power of the ultrasonic treatment is 100W to 500W; The ultrasonic treatment time is 30 min to 2 h.

14. An electrode sheet, characterized in that, include: current collector; An active material layer is disposed on at least one side surface of the current collector, comprising the composite conductive agent according to any one of claims 1 to 8.

15. The electrode sheet according to claim 14, characterized in that, The active material layer also includes an active material main body, and the mass ratio of the active material main body to the composite conductive agent is 100:3 to 10.

16. The electrode sheet according to claim 15, characterized in that, The active material is composed of at least one of lithium manganese iron phosphate, lithium-rich manganese-based phosphate, and lithium iron phosphate, preferably lithium iron phosphate.

17. A battery, characterized in that, It includes the composite conductive agent according to any one of claims 1 to 8 or the electrode according to any one of claims 14 to 16.

18. A battery assembly, characterized in that, Includes the electrode sheet according to any one of claims 14 to 16 or the battery according to claim 17.

19. An electrical appliance, characterized in that, Includes the battery of claim 17 or the battery assembly of claim 18.

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