Negative electrode aqueous slurry, negative electrode sheet, and manufacturing method, secondary battery, and electric device

Abstract

This application provides an aqueous negative electrode slurry, a negative electrode sheet, a preparation method thereof, a secondary battery, and an electrical device, relating to the field of secondary battery technology. The aqueous negative electrode slurry comprises a mixture of a negative electrode active material, a conductive agent, a solvent, and a dispersing agent. The dispersing agent includes lipophilic and hydrophilic segments. During the preparation of the aqueous negative electrode slurry, the lipophilic segments adsorb onto the surfaces of the negative electrode active material and the conductive agent, while the hydrophilic segments extend into the solvent. The lipophilic segments are also miscible with the electrolyte, which is used to wet the negative electrode sheet made from the aqueous negative electrode slurry. The lipophilic segments can reduce the solid-liquid interfacial tension between the particles and the electrolyte. The dispersing agent added to the aqueous negative electrode slurry in this application has a mechanism of action that goes beyond simple physical dispersion. By using an aqueous negative electrode slurry containing this dispersing agent, a secondary battery with both high energy density and high fast-charging capability can be prepared.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to an aqueous negative electrode slurry, a negative electrode sheet and its preparation method, a secondary battery and an electrical device thereof. Background Technology

[0002] With the rapid development of industries such as electric passenger vehicles, heavy trucks, light trucks, and energy storage, the market demand for rechargeable batteries that combine high energy density and fast charging capabilities is increasing. However, the technical means to improve the energy density and fast charging capability of rechargeable batteries are often contradictory.

[0003] For example, increasing the electrode coating density and compaction density can improve the energy density of a secondary battery. However, these increases can lead to several problems: longer ion transport distances within the battery, increased electrode tortuosity, and poorer electrolyte wettability. These issues often result in reduced ion transport rates, significantly decreasing the battery's fast-charging capability. In severe cases, lithium plating can occur on the electrode surface, accelerating the battery's cycle life degradation.

[0004] Therefore, it is necessary to develop an aqueous negative electrode slurry and a negative electrode sheet prepared using the aqueous negative electrode slurry, so as to improve the energy density of the secondary battery while ensuring the negative electrode ion transport rate, thereby obtaining a secondary battery that combines high energy density and fast charging capability. Summary of the Invention

[0005] This application provides an aqueous negative electrode slurry, a negative electrode sheet and its preparation method, a secondary battery and an electrical device, which can improve the energy density of the secondary battery while also ensuring its fast charging capability.

[0006] In a first aspect, this application provides an aqueous negative electrode slurry for preparing a negative electrode sheet, the aqueous negative electrode slurry comprising: a mixture of a negative electrode active material, a conductive agent, a solvent, and a dispersant.

[0007] The dispersing agent includes lipophilic and hydrophilic segments. During the preparation of the aqueous negative electrode slurry, the lipophilic segments adsorb onto the surface of the negative electrode active material and the conductive agent, while the hydrophilic segments extend into the solvent. The lipophilic segments are also miscible with the electrolyte, which is used to wet the negative electrode sheet.

[0008] Through the above scheme, during the preparation stage of the aqueous negative electrode slurry, the lipophilic segments of this dispersant can adsorb onto the surface of the negative electrode active material and the conductive agent, while the hydrophilic segments can extend into the solvent. Furthermore, the hydrophilic segments possess strong steric hindrance and electrostatic repulsion effects, effectively preventing the agglomeration and sedimentation of particles from the negative electrode active material and the conductive agent. This results in a highly stable and uniform aqueous negative electrode slurry, laying a solid foundation for the subsequent preparation of a uniform thick electrode coating. As is well known, thick electrode coating can improve the energy density of secondary batteries. Therefore, the addition of this dispersant can improve the energy density of secondary batteries.

[0009] Furthermore, during the preparation of the negative electrode sheet using this aqueous slurry and the immersion of the negative electrode sheet in the electrolyte, the lipophilic segments originally adsorbed on the surfaces of the negative electrode active material and conductive agent in the dispersant are exposed and oriented outside the negative electrode sheet after the negative electrode sheet dries and the moisture evaporates. These lipophilic segments have highly similar compatibility and good affinity with the carbonate electrolyte solvents commonly used in lithium-ion batteries. Therefore, they can construct "electrolyte-friendly bridges" in situ on the surface of each negative electrode active material and conductive agent particle, reducing the solid-liquid interfacial tension between the particles and the electrolyte, thus effectively improving the electrolyte wettability of the negative electrode sheet. This increases the negative electrode ion transport rate, significantly improving the fast-charging capability of the secondary battery. Therefore, the addition of this dispersant can improve the fast-charging capability of the secondary battery.

[0010] It is evident that the dispersant added to the aqueous negative electrode slurry in this application has a mechanism of action that goes beyond simple physical dispersion. By using the aqueous negative electrode slurry containing this dispersant, a secondary battery with both high energy density and high fast charging capability can be prepared.

[0011] In one possible design, the hydrophilic segment comprises at least one of a polyoxyethylene segment and an ionized group. And / or, the lipophilic segment comprises at least one of a polyoxypropylene segment and a C8-C22 alkyl group.

[0012] Through the above methods, as long as the hydrophilic segment of the dispersant contains at least one of polyoxyethylene segment and ionized group, the particles in the aqueous negative electrode slurry can remain dispersed in Brownian motion, effectively preventing particle aggregation and sedimentation. This results in a highly stable and uniform aqueous negative electrode slurry, ensuring consistent coating quality of the negative electrode sheet and ultimately improving the performance of the secondary battery. Conversely, as long as the lipophilic segment of the dispersant contains at least one of polyoxypropylene segment and C8-C22 alkyl group, it can be well miscible with carbonate electrolytes, ensuring sufficient electrolyte wetting of the negative electrode sheet and ultimately improving the performance of the secondary battery.

[0013] In one possible design, the dispersing agent is selected from at least one or more of the following: polyoxyethylene ether block copolymers, phosphate ester dispersants, modified polyacrylic acid dispersants, aqueous PVDF emulsions, and amide dispersants.

[0014] In one possible design, the polyoxyethylene ether block copolymer is a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer.

[0015] And / or, the phosphate ester dispersant is a high molecular weight phosphate ester salt.

[0016] And / or, the modified polyacrylic acid dispersant is a polyacrylate containing C8-C22 alkyl chains or polyether segments.

[0017] And / or, the aqueous fluoropolymer emulsion is an aqueous emulsion of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0018] And / or, the amide dispersant is a copolymer of polyvinylpyrrolidone or N-vinylpyrrolidone.

[0019] In one possible design, the amount of dispersant added is 0.05% to 5% of the total solid mass in the negative electrode aqueous slurry.

[0020] By using the above method, the amount of dispersant added is set to 0.05% to 5% of the total solid mass in the aqueous negative electrode slurry. This range can cover particle systems with different particle sizes and specific surface areas, so that the dispersant can fully cover the surface of each particle in the aqueous negative electrode slurry. This facilitates the formation of a monolayer "electrolyte-friendly bridge" on the surface of each negative electrode active material and conductive agent particle, thereby making it easier to prepare a secondary battery with both high energy density and high fast charging capability.

[0021] Secondly, this application provides a negative electrode sheet, comprising: a negative electrode current collector and any of the above-mentioned negative electrode aqueous slurry, wherein the negative electrode aqueous slurry is coated on at least one side of the negative electrode current collector.

[0022] Thirdly, this application provides a method for preparing a negative electrode sheet, the method comprising: A negative electrode active material, a conductive agent, an aqueous binder, a solvent, and a dispersant are provided and mixed to obtain a negative electrode aqueous slurry. The lipophilic segments of the dispersant adsorb onto the surfaces of the negative electrode active material and the conductive agent, while the hydrophilic segments of the dispersant extend into the solvent.

[0023] The aqueous slurry of the negative electrode is coated onto the negative electrode current collector.

[0024] The negative electrode current collector coated with negative electrode aqueous slurry is dried and rolled to obtain a negative electrode sheet.

[0025] Among them, the lipophilic segments are exposed and oriented outside the negative electrode after the negative electrode is dried, so as to establish an electrolyte-loving bridge between the negative electrode active material and the conductive agent.

[0026] Fourthly, this application provides a secondary battery, including a positive electrode, a separator, an electrolyte, and the aforementioned negative electrode, wherein the separator is disposed between the positive electrode and the negative electrode, and the electrolyte wets the positive electrode and the negative electrode.

[0027] The above approach allows for improved energy density and faster charging capabilities in secondary batteries.

[0028] In one possible design, the electrolyte is a carbonate-based electrolyte.

[0029] Fifthly, this application provides an electrical device including the aforementioned secondary battery.

[0030] The beneficial effects of the negative electrode aqueous slurry involved in the second and third aspects above can be found in the beneficial effects brought about by the first aspect and the various possible implementations of the first aspect, and will not be repeated here. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart of a method for preparing a negative electrode sheet according to an embodiment of this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims and drawings of this application are intended to cover non-exclusive inclusion.

[0034] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists, A and B exist simultaneously, or B exists. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0036] The directional terms appearing in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of this application. For example, in the description of this application, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0037] Furthermore, the terms "first," "second," etc., in the specification and claims of this application or in the aforementioned drawings are used to distinguish different objects rather than to describe a specific order, and may explicitly or implicitly include one or more of the features.

[0038] In the description of this application, unless otherwise stated, "multiple" means two or more (including two), and similarly, "multiple groups" means two or more (including two groups).

[0039] Existing technologies often use traditional aqueous slurries when preparing negative electrodes for secondary batteries. The binders used in traditional aqueous slurries are mostly styrene-butadiene rubber (SBR) / sodium carboxymethyl cellulose (CMC), abbreviated as SBR / CMC. SBR is hydrophobic and is a synthetic rubber-based binder, primarily providing flexibility and bond strength. CMC is hydrophilic and is a water-soluble polymer, mainly used as a thickener and dispersant to adjust the viscosity of the aqueous slurry and prevent particle sedimentation.

[0040] Traditional aqueous slurry systems are low-cost, environmentally friendly, and technologically mature, but they suffer from poor electrolyte wettability. Specifically, in aqueous slurries, the SBR / CMC binder tends to coat the surface of graphite and conductive agents, forming a polymer film. This polymer film is essentially an interface layer with poor hydrophobicity or hydrophilicity, resulting in poor compatibility with organic electrolytes.

[0041] When thick electrode coatings or high electrode surface density are used to improve the energy density of secondary batteries, if SBR / CMC binders are still used in the aqueous slurry, it will be more difficult for the electrolyte to quickly and evenly penetrate deep into the negative electrode, forming a "dry zone" deep inside the negative electrode. This results in a long and difficult ion transport path, high ion transport impedance at the solid-liquid interface during rapid charging and discharging, and a sharp deterioration in the dynamic performance of the negative electrode, leading to a decrease in fast charging capability.

[0042] It is evident that existing technologies cannot simultaneously improve the energy density of secondary batteries while maintaining their fast-charging capability.

[0043] In view of this, this application provides an aqueous negative electrode slurry so as to prepare a secondary battery with both high energy density and high fast charging capability.

[0044] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application are described clearly and completely below.

[0045] This application provides an aqueous negative electrode slurry for preparing negative electrode sheets. The aqueous negative electrode slurry includes a mixture of negative electrode active material, conductive agent, solvent and dispersant.

[0046] In addition, the negative electrode aqueous slurry provided in this application may also include SBR / CMC binders found in conventional aqueous slurries. Furthermore, it may also include other additives such as thickeners.

[0047] In the aqueous negative electrode slurry provided in this application, the negative electrode active material can be graphite or silicon-based material, the conductive agent can be carbon black or carbon nanotubes, and the solvent can be deionized water. The slurry system formed by uniformly mixing the negative electrode active material, conductive agent, dispersant, binder, etc., with deionized water as the solvent is the aqueous negative electrode slurry of this application.

[0048] Among them, dispersing aids are a type of dispersant with richer functions. Traditional dispersants mainly play a physical dispersing role to prevent particle agglomeration and sedimentation, while the dispersing aids in this application, in addition to simple physical dispersing, also have chemical functions such as interface modification and wetting regulation, and can play a full-process functional regulation role from different stages of negative electrode aqueous slurry preparation to negative electrode sheet preparation.

[0049] For example, the dispersing agent includes lipophilic and hydrophilic segments. During the preparation stage of the aqueous negative electrode slurry, the lipophilic segments adsorb onto the surface of the negative electrode active material and the conductive agent, while the hydrophilic segments extend into the solvent, effectively preventing particle agglomeration and sedimentation. The particles originate at least from the negative electrode active material and the conductive agent. During the formation and wetting stage of the negative electrode sheet, the lipophilic segments are also miscible with the electrolyte, reducing the solid-liquid interfacial tension between the particles and the electrolyte.

[0050] In the preparation stage of anode aqueous slurry, dispersants primarily function as highly efficient "dispersing stabilizers." Specifically, the lipophilic segments in the dispersant's molecular structure can firmly adsorb onto the surfaces of hydrophobic anode active materials (such as graphite) and conductive agents (such as carbon black). The hydrophilic segments can extend into the aqueous phase, forming a barrier. When two particles with this adsorption layer approach each other, their hydrophilic segments physically overlap and compress, generating a repulsive force that prevents different particles from further approaching and agglomerating. Therefore, the presence of hydrophilic segments allows the dispersant to effectively prevent the aggregation and sedimentation of particles from anode active materials and conductive agents through strong steric hindrance and electrostatic repulsion, thereby forming a highly stable and uniform anode aqueous slurry.

[0051] Therefore, the addition of dispersing agents lays a solid foundation for the subsequent preparation of uniform thick electrode coatings.

[0052] During the formation and impregnation stages of the negative electrode sheet, the dispersant plays a crucial role as an "interface modifier." Specifically, the aqueous negative electrode slurry is coated onto the negative electrode current collector, and after processes such as drying and rolling, the negative electrode sheet is dried. After the water evaporates, the lipophilic segments originally adsorbed on the surface of the negative electrode active material and conductive agent are exposed and oriented to the outside of the negative electrode sheet. Taking lithium-ion batteries as an example, because these lipophilic segments have highly similar compatibility and good affinity with the carbonate electrolyte solvents commonly used in lithium-ion batteries, such as ethylene carbonate (EC) and diethyl carbonate (DEC), it is equivalent to constructing an "electrolyte-friendly bridge" in situ on the surface of each negative electrode active material and conductive agent particle. With a reasonable design of the amount of dispersant added, a monolayer "electrolyte-friendly bridge" can be further constructed.

[0053] This "electrolyte-friendly bridge" molecular layer produces two decisive effects: First, it significantly reduces the solid-liquid interfacial tension, transforming the electrolyte from a "liquid-repellent" state that is difficult to spread into a "wetting" state that is easy to spread. Second, it significantly promotes capillary penetration. Driven by capillary forces, the electrolyte can rapidly and uniformly penetrate into the fine pores inside even thick electrodes, ensuring that all active materials on the negative electrode are fully activated in the early stages of formation.

[0054] Therefore, the addition of dispersing agents reduces the solid-liquid interfacial tension between the particles and the electrolyte, effectively improving the electrolyte wettability of the negative electrode. This, in turn, increases the ion transport rate of the negative electrode, significantly enhancing the fast-charging capability of the secondary battery.

[0055] In summary, the negative electrode aqueous slurry provided in this application creatively introduces a specific type of dispersant into conventional negative electrode aqueous slurries composed of negative electrode active materials, conductive agents, solvents, binders, thickeners, and other substances.

[0056] On the one hand, during the preparation of the aqueous slurry for the negative electrode, the lipophilic segments of this dispersant can adsorb onto the surface of the negative electrode active material and the conductive agent, while the hydrophilic segments can extend into the solvent. Furthermore, the hydrophilic segments possess strong steric hindrance and electrostatic repulsion, effectively preventing the agglomeration and sedimentation of particles from the negative electrode active material and the conductive agent. This results in a highly stable and uniform aqueous negative electrode slurry, laying a solid foundation for the subsequent preparation of a uniform thick electrode coating. As is well known, thick electrode coating can improve the energy density of secondary batteries. Therefore, the addition of this dispersant can improve the energy density of secondary batteries.

[0057] On the other hand, during the preparation of the negative electrode sheet using this aqueous slurry and the immersion of the negative electrode sheet in the electrolyte, the lipophilic segments originally adsorbed on the surfaces of the negative electrode active material and conductive agent in the dispersant are exposed and oriented outside the negative electrode sheet after the negative electrode sheet dries and the moisture evaporates. These lipophilic segments have highly similar compatibility and good affinity with the carbonate electrolyte solvents commonly used in lithium-ion batteries. Therefore, they can construct "electrolyte-friendly bridges" in situ on the surface of each negative electrode active material and conductive agent particle, reducing the solid-liquid interfacial tension between the particles and the electrolyte, thus effectively improving the electrolyte wettability of the negative electrode sheet. This increases the negative electrode ion transport rate, significantly improving the fast-charging capability of the secondary battery. Therefore, the addition of this dispersant can improve the fast-charging capability of the secondary battery.

[0058] It is evident that the dispersant added to the aqueous negative electrode slurry in this application has a mechanism of action that goes beyond simple physical dispersion. By using the aqueous negative electrode slurry containing this dispersant, a secondary battery with both high energy density and high fast charging capability can be prepared.

[0059] In some possible designs, the hydrophilic segment of the dispersing agent may include at least one of a polyoxyethylene segment and an ionized group. And / or, the lipophilic segment of the dispersing agent may include at least one of a polyoxypropylene segment and a C8-C22 alkyl group.

[0060] Polyoxyethylene segments (-O-CH2-CH2-) are strongly hydrophilic; the lone pair electrons on their oxygen atoms can form hydrogen bonds with water molecules, causing the entire segment to be strongly solvated by water molecules. This solvation allows the polyoxyethylene segments to fully extend in the aqueous phase, forming a thick hydration layer. When two particles in the negative electrode aqueous slurry approach each other, these extended polyoxyethylene segments compress against each other, generating a strong steric hindrance effect that prevents the particles from further approaching and agglomerating, facilitating the formation of a negative electrode aqueous slurry with extremely high stability and excellent uniformity.

[0061] Ionized groups (such as -COO) - -SO3 - -N + R3 and other similar compounds ionize in water, causing the dispersant molecules to become charged and form charged groups. These charged groups form a double-layer structure on the particle surface, generating a strong electrostatic repulsion. When two particles with the same charge approach each other, the electrostatic repulsion prevents them from agglomerating, which also facilitates the formation of a highly stable and uniform negative-polar aqueous slurry.

[0062] It is evident that as long as the hydrophilic segment of the dispersant contains at least one of the polyoxyethylene segment and the ionized group, the particles in the negative electrode aqueous slurry can remain dispersed in Brownian motion, effectively preventing particle aggregation and sedimentation, thereby forming a negative electrode aqueous slurry with extremely high stability and excellent uniformity, ensuring consistent coating quality of the negative electrode sheet, and ultimately improving the performance of the secondary battery.

[0063] Polyoxypropylene segments (-O-CH(CH3)-CH2-) exhibit moderate hydrophobicity. Their side-chain methyl groups make them more hydrophobic than polyethylene oxide, but less so than C8-C22 alkyl groups. This moderate hydrophobicity allows them to form strong adsorption bonds with hydrophobic surfaces such as graphite and carbon black through hydrophobic interactions. Furthermore, the polarity of polyoxypropylene segments is similar to that of carbonate solvents, and they exhibit good solubility in carbonate electrolytes.

[0064] Long-chain alkyl groups (e.g., C8-C22 alkyl groups) are strongly hydrophobic, with their hydrocarbon segments having weak interactions with water molecules and tending to escape from the aquatic environment. This strong hydrophobicity allows them to be firmly anchored to hydrophobic surfaces through strong hydrophobic interactions, and the polarity of long-chain alkyl groups is similar to that of carbonate solvents, making them completely miscible in carbonate electrolytes.

[0065] It is evident that as long as the lipophilic segment of the dispersant contains at least one of polyoxypropylene segment or long-chain alkyl group, it can be well miscible with carbonate electrolytes, ensuring that the electrolyte fully wets the negative electrode and ultimately improves the performance of the secondary battery.

[0066] It should be noted that in aqueous negative electrode slurries, the lipophilic (i.e., hydrophobic) segments of the dispersant can be firmly adsorbed onto the surfaces of the negative electrode active material and conductive agent through hydrophobic interactions and van der Waals forces, forming a stable anchoring layer. This adsorption causes the dispersant molecules to align oriented on the aforementioned particle surfaces, allowing the hydrophilic segments of the dispersant to stably extend into the aqueous phase, forming a stable dispersion system. Furthermore, during the stage where the negative electrode sheet is immersed in the electrolyte, the lipophilic segments can also be well miscible with carbonate electrolytes, ensuring that the electrolyte fully wets the negative electrode sheet and improving battery performance.

[0067] This demonstrates that the lipophilic segments in dispersants play a crucial role at every stage. Based on this, the relative strengths of the hydrophilic and lipophilic segments in the dispersant can be rationally designed, i.e., the hydrophilic-lipophilic balance value (HLB value), to allow the dispersant to fully exert its functions of stabilizing dispersion and modifying interfaces. In some examples, the HLB value of the dispersant can range from 0 to 10.

[0068] Based on the preceding description of the functions of hydrophilic and lipophilic segments in dispersants, in some possible designs, the dispersant may be selected from at least one or more of the following: polyoxyethylene ether block copolymers, phosphate ester dispersants, modified polyacrylic acid dispersants, aqueous fluoropolymer emulsions (e.g., aqueous polyvinylidene fluoride PVDF emulsions), and amide dispersants.

[0069] For example, the polyoxyethylene ether block copolymer can be a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer. And / or, the phosphate ester dispersant can be a high molecular weight phosphate salt. And / or, the modified polyacrylic acid dispersant can be a polyacrylate containing C8-C22 alkyl chains or polyether segments. And / or, the aqueous fluoropolymer emulsion can be an aqueous emulsion of polyvinylidene fluoride or a polyvinylidene fluoride-hexafluoropropylene copolymer. And / or, the amide dispersant can be a copolymer of polyvinylpyrrolidone or N-vinylpyrrolidone.

[0070] It should be noted that the above only illustrates the possible substances of various types of dispersing agents, but does not constitute a limitation on the technical solution of this application. Any dispersing agent that can achieve the above-mentioned stable dispersion and interface modification effects is applicable to this application.

[0071] Furthermore, in some possible designs, the amount of dispersant added is 0.05% to 5% of the total solids mass in the negative electrode aqueous slurry.

[0072] The solids in the negative electrode aqueous slurry mainly include active substances, conductive agents, binders, and all other solid particles that are insoluble in water.

[0073] Since the dispersant's role is to adsorb onto the surface of solid particles, ideally it should form a monolayer "electrolyte-friendly bridge" on the surface of each negative electrode active material and conductive agent particle. Therefore, the amount of dispersant added needs to match the total surface area of ​​the solid particles. Furthermore, because the total mass of the solids is directly related to the total surface area of ​​the solid particles, determining the amount of dispersant added based on the total mass of the solids in the negative electrode aqueous slurry ensures that each particle surface is adequately covered by the dispersant. This avoids insufficient dispersant addition leading to incomplete particle surface coverage, or excessive dispersant addition causing the formation of multilayers or micelles, which would affect the ion transport rate.

[0074] In this application, the mass percentage of the dispersing agent in the total mass of all solid particles in the negative electrode aqueous slurry is 0.05% to 5%. For example, this percentage may be 0.05%, 0.1%, 0.2%, 0.5%, 2%, 3%, 4.5%, 5%, etc.

[0075] For example, if the total solid mass in the negative electrode aqueous slurry is 100g, the amount of dispersant added can be any value from 0.05g to 5.0g.

[0076] The amount of dispersant added is set to 0.05% to 5% of the total solid mass in the aqueous negative electrode slurry. This range can cover particle systems with different particle sizes and specific surface areas, allowing the dispersant to fully cover the surface of each particle in the aqueous negative electrode slurry. This facilitates the formation of a monolayer "electrolyte-loving bridge" on the surface of each negative electrode active material and conductive agent particle, thereby making it easier to prepare a secondary battery with both high energy density and fast charging capability. The specific amount of dispersant added can be optimized based on particle characteristics.

[0077] This application also provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode aqueous slurry as described in any of the above embodiments, wherein the negative electrode aqueous slurry is coated on at least one side of the negative electrode current collector.

[0078] The negative electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can be copper foil. The composite current collector can be formed by depositing a metallic material on a polymer substrate.

[0079] The negative electrode current collector has two opposing sides in its thickness direction. The negative electrode aqueous slurry can be coated on either one of the opposing sides of the negative electrode current collector, or it can be coated on both sides of the negative electrode current collector.

[0080] After the negative electrode aqueous slurry is coated on one or both sides of the negative electrode current collector, it can be made into a negative electrode sheet through processes such as drying and rolling.

[0081] This application also provides a method for preparing a negative electrode sheet, which is used to prepare the aforementioned negative electrode sheet, such as... Figure 1 As shown, the preparation method of this negative electrode includes the following steps.

[0082] S100 provides a negative electrode active material, a conductive agent, an aqueous binder, a solvent, and a dispersant, and mixes them to obtain a negative electrode aqueous slurry.

[0083] Among them, the lipophilic segments in the dispersant adsorb onto the surface of the negative electrode active material and the conductive agent, while the hydrophilic segments in the dispersant extend into the solvent, which can effectively prevent the agglomeration and sedimentation of particles from at least the negative electrode active material and the conductive agent.

[0084] S200 involves coating the negative electrode aqueous slurry onto the negative electrode current collector.

[0085] S300 is used to dry and roll a negative electrode current collector coated with a negative electrode aqueous slurry to obtain a negative electrode sheet.

[0086] Among them, the lipophilic segments are exposed and oriented outside the negative electrode after the negative electrode is dried, so as to establish an electrolyte-loving bridge between the negative electrode active material and the conductive agent.

[0087] It should be noted that the composition and dosage of the dispersing agent have been described in detail in the previous embodiments and will not be repeated here. This application does not impose any special limitations on the mixing, coating, drying, rolling, and other processes.

[0088] It is worth noting that the aqueous negative electrode slurry of this application contains a dispersant, which effectively prevents the agglomeration and sedimentation of particles in the aqueous negative electrode slurry, resulting in an aqueous negative electrode slurry with extremely high stability and excellent uniformity. Therefore, this application can prepare a uniform thick electrode, which can improve the energy density of the secondary battery while also improving the fast-charging capability of the secondary battery.

[0089] This application also provides a secondary battery, which can be a lithium-ion battery or the like. The secondary battery includes a positive electrode, a separator, an electrolyte, and the negative electrode as described in the above embodiments. The separator is disposed between the positive and negative electrode, and the electrolyte wets both the positive and negative electrode.

[0090] During the charging and discharging process of a secondary battery, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrode plates. A separator is placed between the positive and negative electrode plates, primarily to prevent short circuits while allowing ions to pass through. The electrolyte wets the positive and negative electrode plates, mainly serving to conduct active ions.

[0091] The electrolyte can be a carbonate-based electrolyte. The electrolyte includes an electrolyte solvent, a lithium salt, and an additive solvent. The electrolyte solvent can be a carbonate compound such as ethylene carbonate (EC) or diethyl carbonate (DEC). The lithium salt can be lithium hexafluorophosphate (LiPF6). The additive can be a film-forming additive. Alternatively, the electrolyte can also be a carboxylic acid ester electrolyte, etc., and this application does not limit this choice.

[0092] This application also provides an electrical device that includes the aforementioned secondary battery.

[0093] Secondary batteries can be used as a power source for electrical devices or as an energy storage unit for those devices. These devices can be, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, and energy storage systems.

[0094] The present application will be described in detail below with reference to the embodiments.

[0095] Example 1 A negative electrode sheet is prepared as follows: graphite, conductive agent, binder, and thickener are mixed with water in a mass ratio of 95%:1%:1%:1.8%:1.2%, and a dispersant of 0.05% of the total solids is added to obtain an aqueous negative electrode slurry. This slurry is coated on both sides of the negative electrode current collector, dried, cold-pressed, and cut to obtain the negative electrode sheet.

[0096] Example 2 and Example 3 Unlike Example 1, in Example 2 the amount of dispersant added was 0.1% of the total solids, and in Example 3 the amount of dispersant added was 0.2% of the total solids. The other steps in Examples 2 and 3 were the same as the corresponding steps in Example 1.

[0097] Comparative Example A negative electrode sheet is prepared as follows: graphite, conductive agent, binder and thickener are mixed with water in a mass ratio of 95%:1%:1%:1.8%:1.2% to obtain an aqueous negative electrode slurry, which is coated on both sides of the negative electrode current collector, dried, cold pressed and cut to obtain the negative electrode sheet.

[0098] The contact angle of the electrolyte on the negative electrode sheet was tested for the negative electrode sheets prepared in Examples 1 to 3 and the comparative example. A contact angle measuring instrument was used for the test, and the results are shown in Table 1.

[0099] In addition, the aforementioned negative electrode sheet was assembled with a lithium iron phosphate positive electrode sheet, electrolyte, separator, and aluminum-plastic film to form a soft-pack lithium-ion battery. Negative electrode potential, DC internal resistance (DCR), and fast-charge cycle life were tested on this lithium-ion battery. The test results are shown in Table 1.

[0100] The DC internal resistance (DCR) test is performed as follows: at 25℃, the system is adjusted to 50% SOC, left to stand for 1 hour, and OCV1 is recorded. After 3C discharge for 10 seconds, OCV2 is recorded. The DCR is then calculated based on (OCV1-OCV2) / 3C×1000.

[0101] The potential test specifically involves charging the lithium electrode at 25°C with a constant current and constant voltage of 2C to 3.65V, cutting off the current at 0.05C, and monitoring the lithium potential at the negative electrode.

[0102] The fast charging cycle life test is as follows: charge at 25℃ with 2C constant current and constant voltage to 3.65V, cut off current at 0.05C, rest for 30 minutes, discharge with 1C constant current, cut off at 2.0V, rest for 30 minutes after discharge, and repeat the charging and discharging steps.

[0103] Table 1

[0104] As can be seen from the data in Table 1, this application creatively introduces a specific type of dispersant into a conventional aqueous negative electrode slurry composed of negative electrode active material, binder, thickener, conductive agent and water. Compared with the lithium-ion battery assembled without the addition of dispersant in the comparative example, the assembled lithium-ion battery has a significantly lower DC internal resistance and a significantly higher fast-charging cycle life.

[0105] Comparing the test results of Examples 1 to 3 and the comparative example, it can be seen that, compared with the comparative example, the contact angle of the electrolyte on the negative electrode prepared by Examples 1 to 3 is significantly reduced, indicating that the wettability of the electrolyte in the negative electrode is significantly improved.

[0106] Furthermore, in the lithium-ion batteries prepared according to Examples 1 to 3, the lowest negative electrode potential was >0mV during 2C direct charging, while the negative electrode potential of the comparative examples was below 0mV, resulting in lithium plating. This application adds a dispersant to the aqueous negative electrode slurry to maintain the negative electrode potential above the lithium plating potential, effectively preventing lithium plating, reducing side reactions, and forming a stable SEI film. This improves the cycle life of the secondary battery while ensuring charging speed.

[0107] In summary, this application adds a small amount of dispersant to existing mature aqueous negative electrode slurry formulations and processes. Through the dual-action mechanism of the dispersant, the problem of poor wettability of graphite negative electrodes prepared by aqueous negative electrode slurry systems to oily electrolytes is fundamentally solved. This reduces the contact angle of the thick-coated negative electrode sheet to the electrolyte from the conventional 25-60° to below 25°, significantly reducing the electrolyte wetting time and greatly improving production efficiency.

[0108] This application also improves the kinetic performance of thick electrodes. Specifically, excellent internal electrolyte wetting ensures rapid lithium-ion transport in the thick electrode, significantly reduces charge transfer resistance, thereby greatly improving the high-rate charging performance (such as 3C / 5C capacity retention) and low-temperature discharge performance of the secondary battery, and improving the stability of the secondary battery in the later stages of cycling.

[0109] In addition, uniform wetting and lithiation suppress local side reactions and lithium deposition, which helps to form a stable solid electrolyte interface film and extend the cycle life of the secondary battery.

[0110] It is worth noting that this application does not require any changes to the existing core equipment for preparing aqueous negative electrode slurry, negative electrode sheet, and secondary battery, and the cost increase is negligible, making it highly valuable for industrialization and promotion.

[0111] The preferred embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this application, various simple modifications can be made to the technical solution of this application, and these simple modifications all fall within the protection scope of this application.

[0112] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not describe the various possible combinations separately.

[0113] Furthermore, various different implementations of this application can be combined in any way, as long as they do not violate the spirit of this application, they should also be regarded as the content disclosed in this application.

Claims

1. A negative electrode aqueous slurry for preparing negative electrode sheets, characterized in that, include: A mixture of negative electrode active material, conductive agent, solvent and dispersant; The dispersing agent includes lipophilic segments and hydrophilic segments. In the preparation stage of the negative electrode aqueous slurry, the lipophilic segments are adsorbed on the surface of the negative electrode active material and the conductive agent, and the hydrophilic segments extend into the solvent. The oleophilic segments are also miscible with the electrolyte, which is used to wet the negative electrode.

2. The negative electrode aqueous slurry according to claim 1, characterized in that, The hydrophilic segment includes at least one of a polyoxyethylene segment and an ionized group. And / or, the lipophilic segment includes at least one of polyoxypropylene segment and C8-C22 alkyl group.

3. The negative electrode aqueous slurry according to claim 1, characterized in that, The dispersing agent is selected from at least one or more of the following: polyoxyethylene ether block copolymers, phosphate ester dispersants, modified polyacrylic acid dispersants, aqueous PVDF emulsions, and amide dispersants.

4. The negative electrode aqueous slurry according to claim 3, characterized in that, The polyoxyethylene ether block copolymer is a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; And / or, the phosphate ester dispersant is a high molecular weight phosphate ester salt; And / or, the modified polyacrylic acid dispersant is a polyacrylate containing C8-C22 alkyl chains or polyether segments; And / or, the aqueous fluoropolymer emulsion is an aqueous emulsion of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer; And / or, the amide dispersant is a copolymer of polyvinylpyrrolidone or N-vinylpyrrolidone.

5. The negative electrode aqueous slurry according to any one of claims 1 to 4, characterized in that, The amount of the dispersing agent added is 0.05% to 5% of the total solid mass in the negative electrode aqueous slurry.

6. A negative electrode sheet, characterized in that, include: The negative electrode current collector and the negative electrode aqueous slurry according to any one of claims 1 to 5, wherein the negative electrode aqueous slurry is coated on at least one side of the negative electrode current collector.

7. A method for preparing a negative electrode sheet, characterized in that, The method for preparing the negative electrode sheet according to claim 6 includes: A negative electrode active material, a conductive agent, an aqueous binder, a solvent, and a dispersant are provided and mixed to obtain a negative electrode aqueous slurry; wherein, the lipophilic segments of the dispersant are adsorbed on the surfaces of the negative electrode active material and the conductive agent, and the hydrophilic segments of the dispersant extend into the solvent; The aqueous slurry of the negative electrode is coated onto the negative electrode current collector; The negative electrode current collector coated with the aforementioned negative electrode aqueous slurry is dried and rolled to obtain a negative electrode sheet; The oleophilic segments are exposed and oriented outside the negative electrode after the negative electrode is dried, so as to establish an electrolyte-loving bridge between the negative electrode active material and the conductive agent.

8. A secondary battery, characterized in that, The device includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in claim 6, wherein the separator is disposed between the positive electrode and the negative electrode, and the electrolyte wets the positive electrode and the negative electrode.

9. The secondary battery according to claim 8, characterized in that, The electrolyte is a carbonate-based electrolyte.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 8 or 9.

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