Core-shell type composite carbon material, method for preparing same, carbon-coated aluminum foil, electrode sheet, and secondary battery

Abstract

The application provides a core-shell type composite carbon material, a preparation method thereof, a carbon-coated aluminum foil, an electrode sheet and a secondary battery. The core-shell type composite carbon material comprises carbon particles and a polymer composite layer coated on the surface of the carbon particles; along a direction away from the carbon particles, the polymer composite layer comprises a first composite layer and a second composite layer arranged in sequence; the first composite layer comprises a first conductive polymer and a first functional additive; and the second composite layer comprises a second conductive polymer and a second functional additive. The application is based on a core-shell structure design, and a double-layer polymer composite layer with gradient functions is constructed on the surface of the carbon particles, wherein the first conductive polymer and the first functional additive are introduced into the first composite layer to enhance the electronic conduction path, and the second conductive polymer and the second functional additive are loaded in the second composite layer to improve the water phase dispersion stability, so that the technical effects of high conductivity, excellent water system dispersion and structural stability are achieved.

Description

Technical Field

[0001] This invention relates to the field of secondary batteries, and more specifically, to a core-shell composite carbon material and its preparation method, carbon-coated aluminum foil, electrode sheets, and a secondary battery. Background Technology

[0002] In layered oxides (such as Na) x Fe x Mn y In high-energy-density sodium-ion batteries using O2, Prussian blue compounds, or polyanionic compounds (such as Na3V2(PO4)3) as cathode materials, aluminum foil is widely used as the current collector for both the positive and negative electrodes because sodium ions do not alloy with aluminum. With the development of sodium-ion battery technology, its operating voltage has been continuously increasing (layered oxides and polyanionic compounds typically operate above 4.0 V vs. Na / Na+). Furthermore, to reduce costs, aqueous binders and electrolytes of different systems (such as ether-based or ester-based electrolytes like NaPF6 and NaFSI) have been widely explored. However, traditional pure aluminum foil as a current collector for sodium-ion batteries still faces several challenges to interfacial stability under long-term cycling and complex operating conditions. First, under high-potential operating conditions, the aluminum foil surface is prone to electrochemical oxidation, which, together with electrolyte decomposition products, forms a passivation layer rich in alumina or fluorides. When trace amounts of moisture or acidic impurities are present in the electrolyte, the aforementioned interfacial reactions are further intensified, leading to a continuous thickening of the surface insulating film. This significantly increases the charge transport impedance at the positive electrode / current collector interface, thereby affecting the battery's rate performance and cycle stability. Secondly, under overcharge or high-voltage abuse conditions, the electrolyte is prone to oxidative decomposition accompanied by gas generation. Enhanced interfacial side reactions not only damage the integrity of the electrode structure but may also induce increased internal battery pressure, posing potential safety risks. Furthermore, although aluminum foil exhibits good electrochemical stability at low potentials on the negative electrode side, the interfacial contact state, adhesion strength, and conductive network construction between it and negative electrode active materials such as hard carbon can still be limiting factors. During cycling, the solid electrolyte interphase (SEI) film formed by the electrolyte reduction reaction is continuously reconstructed. If the interfacial bonding is unstable, it can easily lead to increased contact impedance and decreased electron / ion transport efficiency.

[0003] To address the aforementioned issues, pre-coating the aluminum foil surface with a conductive carbon coating (i.e., carbon-coated aluminum foil) has become an industry standard practice. This carbon coating can significantly reduce interfacial resistance, improve the adhesion between the active material and the current collector, and provide a certain degree of physical barrier to the aluminum foil substrate, thereby inhibiting corrosion and side reactions to some extent. However, existing carbon-coated aluminum foil technologies, whether employing environmentally friendly water-based processes or traditional oil-based processes, inherently consist of electrochemically inert passive conductive layers. These coatings conduct electrons during normal battery operation, but they lack any active protection function when the battery is overcharged or the voltage abnormally rises above the safety threshold. Conversely, the high specific surface area of ​​the carbon coating can become a catalytic center for side reactions, accelerating electrolyte decomposition, while the aluminum foil substrate will still corrode at high potentials, ultimately leading to battery swelling, failure, and even serious safety issues such as thermal runaway.

[0004] To further address the overcharge safety issue of high-voltage batteries, current solutions attempt to physically blend electrochemically active conductive polymers as conductive agents into conventional carbon black or graphite slurries. This utilizes the oxidation reaction of the conductive polymer under high voltage to provide overcharge protection. However, this approach has the following drawbacks:

[0005] First, the structure is inefficient and unstable. In the physical blending system, conductive polymer particles, carbon black particles, and graphite particles are all independent phases, and they are merely random physical stacks in the slurry and the final coating. The first drawback of this structure is that it leads to extremely high interfacial contact resistance: the transfer of electrons between different types of particles (such as from carbon black to polymer, and then to graphite) requires crossing a large number of physical potential barriers, resulting in low overall conductivity of the coating and violating the original intention of carbon coating to reduce resistance. The second drawback is functional instability. Since the conductive polymer particles are only "stuck" in the coating by the binder and are not firmly anchored, these polymer particles are prone to migration, detachment from the coating, or slow dissolution in the electrolyte during long-term immersion in the electrolyte and electrochemical cycling. This causes the preset response potential to "drift" or the protective function to completely fail, resulting in poor durability of the structure and function.

[0006] Secondly, the manufacturing process is complex and contradictory. The "physical blending" approach does not solve the hydrophobicity problem of one of its key components, particularly the conductive carbon black. To disperse this hydrophobic carbon black in an aqueous binder, this approach still relies on adding a large amount of surfactant, which is itself an insulator. This leads to a contradiction: to achieve the coating process (dispersion), electrochemical performance (high resistance) is sacrificed. This complex (multi-component), costly (reliant on expensive surfactants), and performance-compromising process does not meet the requirements for low-cost, high-performance mass production.

[0007] Third, its functionality is limited. Simply mixing conductive polymers and conductive agents results in a crude superposition of functions, with poor synergy between the components. The distribution of conductive polymers is extremely uneven, making it impossible to form a uniform and complete protective layer on the aluminum foil surface. As a result, during overcharging, the current bypasses these isolated polymer points and continues to cause side reactions on the exposed carbon black surface and aluminum foil substrate, greatly limiting its protective efficiency and response speed.

[0008] Therefore, how to provide a carbon-coated aluminum foil that balances high conductivity and excellent structural stability, so that it can maintain low interfacial impedance under high voltage conditions and have passive response capability under abnormal overcharge conditions, thereby comprehensively improving the electrochemical performance and intrinsic safety of sodium-ion batteries under high energy density conditions, is a technical problem that needs to be solved in this field. Summary of the Invention

[0009] The main objective of this invention is to provide a core-shell composite carbon material and its preparation method, carbon-coated aluminum foil, electrode sheet, and secondary battery, in order to solve the problem that in the prior art, the carbon layer on the carbon-coated aluminum foil is difficult to provide effective protection, resulting in severe corrosion of the aluminum foil and severe oxidation and decomposition of the electrolyte, which in turn leads to poor cycle performance and safety of the battery.

[0010] To achieve the above objectives, a first aspect of the present invention provides a core-shell composite carbon material comprising carbon particles and a polymer composite layer coated on the surface of the carbon particles; the polymer composite layer comprises a first composite layer and a second composite layer disposed sequentially along a direction away from the carbon particles; the first composite layer comprises a first conductive polymer and a first functional additive; the first functional additive is used to regulate the voltage response characteristics of the first conductive polymer; the second composite layer comprises a second conductive polymer and a second functional additive, the second functional additive being used to improve the hydrophilicity of the second conductive polymer; the weight ratio of the carbon particles, the first composite layer, and the second composite layer is (70~100):(5~12):(2~6).

[0011] Furthermore, in the first composite layer, the weight ratio of the first conductive polymer to the first functional additive is 100:(20~30); and / or, the weight-average molecular weight of the first conductive polymer is 3×10⁻⁶. 4 ~5×10 4 ; and / or, the degree of crosslinking of the first conductive polymer is 5% to 8%; and / or, the first conductive polymer is selected from one or more of polyaniline, polythiophene, polypyrrole and poly(3,4-ethylenedioxythiophene); and / or, the first functional additive is selected from one or more of small molecule sulfonic acid compounds, fluorosulfonyl imide salt compounds, fluorinated complex anionic compounds and low molecular weight polyelectrolytes.

[0012] Further, the small molecule sulfonic acid compound is selected from one or more of p-toluenesulfonic acid, camphorsulfonic acid, and methanesulfonic acid; and / or, the fluorosulfonyl imide salt compound is sodium bis(trifluoromethylsulfonyl)imide and / or sodium bisfluorosulfonylimide; and / or, the fluorinated complex anion compound is selected from one or more of fluoroboric acid, sodium fluoroborate, hexafluorophosphate, and sodium hexafluorophosphate; and / or, the number average molecular weight of the low molecular weight polyelectrolyte is 1×10⁻⁶. 3 ~2×10 4 The low molecular weight polyelectrolyte is polystyrene sulfonic acid and / or poly(2-acrylamide-2-methyl-1-propanesulfonic acid).

[0013] Furthermore, in the second composite layer, the weight ratio of the second conductive polymer to the second functional additive is 100:(10~20); and / or, the weight-average molecular weight of the second conductive polymer is 1×10⁻⁶. 4 ~4×10 4 ; and / or, the degree of crosslinking of the second conductive polymer is 3% to 5%; and / or, the second conductive polymer is selected from one or more of polyaniline, polythiophene, polypyrrole and poly(3,4-ethylenedioxythiophene); and / or, the second functional additive is selected from one or more of polystyrene sulfonic acid, polystyrene sulfonate, poly(2-acrylamide-2-methylpropanesulfonic acid), poly(2-acrylamide-2-methylpropanesulfonic acid) salt, polyacrylic acid, polyacrylate, carboxymethyl cellulose, and carboxymethyl cellulose salt.

[0014] Furthermore, the carbon particles have a particle size of 50 nm to 2 μm; and / or the total thickness of the polymer composite layer is 10 nm to 500 nm, and the thickness ratio of the first composite layer to the second composite layer in the polymer composite layer is 1:(0.2 to 2.5).

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned core-shell composite carbon material, comprising: step R1, preparing a first slurry containing carbon particles and a first functional additive, and adding a first monomer to the first slurry, and dispersing it first to allow the first monomer and the first functional additive to be adsorbed on the surface of the carbon particles, thereby obtaining a second slurry; the weight ratio of carbon particles, the first functional additive, and the first monomer is 1:(0.3~2.5):(0.3~3.0); step R2, adding a first oxidant solution dropwise to the second slurry to carry out a first polymerization reaction, and forming a first oxidant solution on the surface of the carbon particles. A composite layer is formed to obtain the first product; in step R3, the first product is dispersed in a solvent, and a second functional additive and a second monomer are added thereto. After a second dispersion, the second monomer and the second functional additive are adsorbed on the surface of the first product to obtain a third slurry; the weight ratio of the first product, the second functional additive and the second monomer is 1:(0.03~0.530):(0.10~1.00); in step R4, a second oxidant solution is added dropwise to the third slurry to carry out a second polymerization reaction and form a second composite layer on the surface of the first product to obtain a core-shell composite carbon material.

[0016] Further, in step R1, the concentration of the first functional additive in the first slurry is 0.2wt%~3.0wt%; and / or, the first monomer is added at 0℃~10℃; and / or, step R1 further includes a standing treatment of the second slurry for 5min~30min.

[0017] Further, in step R2, the molar ratio of the first monomer to the first oxidant in the first oxidant solution is 1:(0.8~1.5); and / or, the mass concentration of the first oxidant solution is 5%~10%, and the total dripping time is 4h~10h; and / or, step R2 is carried out at 0℃~5℃; and / or, after the dripping is completed, step R2 also includes stirring the second slurry for 4h~24h.

[0018] Further, in step R3, the solid-liquid ratio of the first product to the solvent is 1:(5~20); and / or, in the third slurry, the concentration of the second functional additive is 0.1wt%~0.3wt%; and / or, the second dispersion is carried out at 0℃~5℃.

[0019] Further, in step R4, the molar ratio of the second monomer to the second oxidant in the second oxidant solution is 1:(1~5); and / or, the mass concentration of the second oxidant solution is 8%~15%, and the total dripping time is 0.5h~1.5h; and / or, step R4 is carried out at 0℃~5℃; and / or, after the dripping is completed, step R4 also includes stirring the second slurry for 2h~4h.

[0020] Furthermore, the first monomer and the second monomer are each independently selected from one or more of aniline, thiophene, pyrrole, and 3,4-ethylenedioxythiophene; and / or, the first oxidant in the first oxidant solution is selected from one or more of ammonium persulfate, potassium persulfate, and sodium persulfate; and / or, the second oxidant in the second oxidant solution is selected from one or more of ferric chloride, ferric p-toluenesulfonate, and hydrogen peroxide.

[0021] A third aspect of the present invention provides a carbon-coated aluminum foil, comprising an aluminum foil and a carbon layer disposed on at least one surface of the aluminum foil, the carbon layer comprising the aforementioned core-shell composite carbon material.

[0022] Furthermore, based on the total weight of the carbon layers (100%), the content of the core-shell composite carbon material is 85%–95%; and / or, the thickness of the carbon layers is 0.2 μm–2.0 μm, and the areal density is 0.10 mg·cm³. -2 ~0.60mg·cm -2 ; and / or, the peel strength between the carbon layer and the aluminum foil at 180±5° is ≥1.0 N·cm. -1 ; and / or, the initial sheet resistance of the carbon-coated aluminum foil is ≤10 Ω / □.

[0023] Furthermore, the carbon layer is obtained by sequentially coating and drying a slurry containing a core-shell composite carbon material, and the pH value of the slurry is 7~9.

[0024] A fourth aspect of the present invention provides an electrode sheet comprising the aforementioned carbon-coated aluminum foil.

[0025] A fifth aspect of the present invention provides a secondary battery comprising at least one of the aforementioned electrode plates.

[0026] The technical solution of this invention is based on a core-shell structure design and involves constructing a gradient functional bilayer polymer composite layer on the surface of carbon particles. The first composite layer incorporates a first conductive polymer and a first functional additive to enhance electron conduction pathways, while the second composite layer loads a second conductive polymer and a second functional additive to improve aqueous dispersion stability. By utilizing the properties and synergistic effects of the two polymer composite layers, the overall conductivity and process compatibility of the material are improved, achieving a balance between high conductivity, excellent aqueous dispersibility, and structural stability. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1The results are shown in the scanning electron microscope (SEM) characterization of the core-shell composite carbon material provided in Example 1 of this invention. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0030] As described in the background art, the conductive coatings used in existing electrochemical energy storage devices are essentially "electrochemically inert" passive conductive layers. When the battery encounters abuse conditions such as overcharging, this inert coating cannot provide any active protection and can only passively conduct current, allowing the current collector substrate (such as aluminum foil) to undergo severe anodic corrosion and catalyze the oxidative decomposition of the electrolyte, thereby causing major safety hazards such as battery swelling, failure, and even thermal runaway. To solve the above technical problems, the first aspect of the present invention provides a core-shell composite carbon material, including carbon particles and a polymer composite layer coated on the surface of the carbon particles; along the direction away from the carbon particles, the polymer composite layer includes a first composite layer and a second composite layer arranged sequentially; the first composite layer includes a first conductive polymer and a first functional additive; the first functional additive is used to regulate the voltage response characteristics of the first conductive polymer; the second composite layer includes a second conductive polymer and a second functional additive, the second functional additive being used to improve the hydrophilicity of the second conductive polymer; the weight ratio of carbon particles, the first composite layer, and the second composite layer is (70~100):(5~12):(2~6).

[0031] Specifically, the first functional additive enables the first composite layer to change from a conductive state to a low-conductivity state or an insulating state when the voltage reaches or exceeds a preset threshold, thereby reducing the continuous conductivity under overcharge conditions and inhibiting anodic corrosion of the current collector substrate and oxidative decomposition of the electrolyte. The second functional additive improves the wetting properties of the material surface, thereby enhancing slurry dispersibility, coating processability, and interface compatibility.

[0032] This invention achieves a layered configuration of conductivity, overvoltage protection, and aqueous dispersion functions within the material through a dual-layer polymer structure. The first composite layer is disposed on the surface of the carbon core, primarily responsible for normal conductivity and overvoltage response protection; the second composite layer is disposed outside the first composite layer, primarily responsible for surface wetting and aqueous dispersion. The two layers work synergistically, resulting in a core-shell composite carbon material that possesses excellent normal conductivity, active protection under overvoltage conditions, and uniform dispersion in aqueous slurries. Specifically:

[0033] The first composite layer is directly coated on the surface of the carbon particles. Its components include a first conductive polymer and a first functional additive, which are used to construct the electron transport interface between the carbon core and the outer structure, and to regulate the voltage response characteristics of the first composite layer. Due to its intrinsic conductivity, the first conductive polymer can form a tight heterogeneous interface with the carbon particles, achieving efficient charge transfer through π-π interactions or in-situ grafting. The first functional additive is not simply used to improve conductivity, but to regulate the conductivity threshold or voltage response behavior of the first conductive polymer, so that the first composite layer maintains a conductive state within the normal operating voltage range, and undergoes a transition from a conductive state to a low conductivity state or a high resistance state when the voltage reaches or exceeds a preset threshold.

[0034] Therefore, the first composite layer maintains high conductivity within the normal operating voltage range of the battery to ensure low interfacial impedance and good electron transport efficiency. However, when the potential exceeds the peroxidation threshold or preset voltage response threshold of the first conductive polymer, the first conductive polymer undergoes excessive oxidation, dedoping, or structural degradation, thereby causing the first composite layer to transform in situ into a low conductivity or insulating state and forming an interfacial barrier that blocks electron transport and / or material contact.

[0035] This interface barrier can reduce the continuous electron transport capability and block the direct contact between the electrolyte and the current collector substrate, thereby inhibiting side reactions such as aluminum foil corrosion and electrolyte oxidation decomposition under high potential conditions, and thus delaying the occurrence of battery gas generation, swelling, performance degradation and thermal runaway.

[0036] The second composite layer is located outside the first composite layer. Its components include a second conductive polymer and a second functional additive, and its core function is to improve the dispersibility of the material in aqueous systems. The second functional additive imparts or enhances the hydrophilicity of the second conductive polymer, improving the wettability and interfacial compatibility of the second composite layer surface. The hydrophilic functional component can form hydrogen bonds or other intermolecular interactions with water molecules through polar groups, reducing the solid-liquid interfacial tension, enhancing the wettability of the particle surface to the aqueous phase, and enabling the entire core-shell particle to achieve stable suspension in the aqueous phase.

[0037] In summary, in existing technologies, the polymer particles in the carbon layer of carbon-coated aluminum foil are not anchored, making them highly susceptible to migration and dissolution in the electrolyte, leading to changes in the safety response window or functional failure. This invention, however, firmly anchors the functional shell to the carbon particle core through in-situ polymerization, ensuring absolute stability and reliability of the safety protection function throughout the entire battery lifespan. Secondly, the physical mixing structure of existing technologies forces electrons to cross numerous high-resistance particle interfaces, while the core-shell integrated structure of this invention achieves tight bonding at the nanoscale, fundamentally eliminating interfacial resistance and resulting in coating conductivity far superior to the former. Most importantly, this invention resolves the fundamental contradiction of aqueous processes: existing technologies disperse hydrophobic carbon black, relying on insulating surfactants that significantly sacrifice conductivity; while this invention, by designing the outermost shell layer (i.e., the second composite layer) to be hydrophilic, allows the entire composite material to disperse in aqueous slurries, completely eliminating dependence on insulating dispersants, while simultaneously achieving excellent process compatibility and high conductivity.

[0038] In the first composite layer, the weight ratio of the first conductive polymer to the first functional additive is further preferably 100:(20~30), so that the amount of the first functional additive is sufficient to effectively regulate the voltage response characteristics of the first conductive polymer, while taking into account both the conductivity of the first composite layer under normal operating conditions and its ability to switch to high resistance under overvoltage conditions. Within this ratio range, the first functional additive can form a stable composite with the first conductive polymer, improving the electron transport efficiency of the first composite layer within the normal operating voltage range, and can also more effectively promote or induce the first conductive polymer to switch from a conductive state to a low-conductivity state or a high-resistivity state when the voltage reaches or exceeds a preset threshold. At the same time, an appropriate amount of the first functional additive also helps to maintain the uniformity of the coating of the first conductive polymer on the surface of the carbon particles and the continuity of the interface, thereby improving the overall electrochemical performance and cycle stability of the obtained core-shell composite carbon material.

[0039] Furthermore, the weight-average molecular weight of the first conductive polymer is preferably 3 × 10⁻⁶. 4 ~5×10 4 To ensure that the first conductive polymer possesses suitable film-forming properties, chain segment fluidity, and interfacial coating capabilities, it is easier to form a continuous and dense first composite layer on the surface of carbon particles, reducing interfacial defects and improving electron transport continuity. Furthermore, to form a more suitable network structure or interchain bonding degree, thereby significantly enhancing the mechanical stability and structural integrity of the first composite layer and reducing the risk of interlayer delamination, cracking, or localized failure caused by volume changes, swelling, or stress during electrochemical cycling, the crosslinking degree of the first conductive polymer is preferably 5% to 8%.

[0040] In several preferred embodiments, the first functional additive is selected from one or more of small-molecule sulfonic acid compounds, fluorosulfonyl imide salt compounds, fluorinated complex anion compounds, and low-molecular-weight polyelectrolytes. These first functional additives can regulate the charge carrier state, conductivity, and voltage response characteristics of the first conductive polymer through doping, ion coordination, electrostatic interactions, and / or interface modulation. Specifically, small-molecule sulfonic acid compounds help improve the doping level and conductivity of the first conductive polymer under normal operating conditions; fluorosulfonyl imide salt compounds help improve the ionic environment, charge transport characteristics, and electrochemical stability of the polymer system; fluorinated complex anion compounds help stabilize the charge distribution on the polymer chain and regulate its redox response behavior; and low-molecular-weight polyelectrolytes have both doping regulation and structural stabilization effects, improving the electrical properties of the first composite layer while also helping to inhibit excessive polymer chain aggregation and improve interface stability during cycling. Based on these effects, the first functional additive enables the first composite layer to maintain good conductivity within the normal operating voltage range and promotes the transition of the first conductive polymer from a conductive state to a low-conductivity or high-resistivity state when the voltage reaches or exceeds a preset threshold.

[0041] Furthermore, regarding the specific type of the aforementioned first functional additive, preferably: Small molecule sulfonic acid compounds are selected from one or more of p-toluenesulfonic acid, camphorsulfonic acid, and methanesulfonic acid. The sulfonic acid groups contained in their molecules facilitate entry into the polymer chains and form a doping effect with the first conductive polymer, thereby helping to improve the conductivity of the first composite layer under normal operating conditions and improve its structural density. Fluorosulfonyl imide salts are sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) and / or sodium bis(fluorosulfonyl)imide (NaFSI), which have good electrochemical stability and help improve the ionic environment and voltage response stability of the polymer system. Fluoro-containing complex anionic compounds are selected from one or more of fluoroboric acid, sodium fluoroborate, hexafluorophosphate, and sodium hexafluorophosphate. The anions contained therein can improve the stability of the polymer doped state through interaction with the positive charge centers of the polymer and help to regulate its response behavior during the transition from a conductive state to a high-resistivity state. The number average molecular weight of the low molecular weight polyelectrolyte is 1×10⁻⁶. 3 ~2×10 4 Furthermore, the low molecular weight polyelectrolyte is polystyrene sulfonic acid (PSS) and / or poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS). The low molecular weight polyelectrolyte possessing the aforementioned molecular weight characteristics can be distributed within the polymer network without significantly disrupting the continuity of the first composite layer, thereby simultaneously achieving doping regulation, dispersion, and interfacial stabilization effects, and further enhancing the bonding stability between the first composite layer and carbon particles.

[0042] In the second composite layer, the preferred weight ratio of the second conductive polymer to the second functional additive is 100:(10~20). This allows the second functional additive to be distributed in an appropriate amount within the outer structure formed by the second conductive polymer, thereby imparting or improving the surface hydrophilicity, wettability, and water dispersibility of the second composite layer. Within this ratio range, the second functional additive helps to form a relatively uniform and continuous hydrophilic interface on the surface of the second composite layer, reducing the interfacial tension of the core-shell composite carbon material in the aqueous system and improving its dispersion stability in aqueous slurries. Furthermore, during the aqueous coating process, the core-shell composite carbon material can possess both good rheological properties and coating uniformity, while improving water dispersibility and minimizing significant damage to the overall conductive network, thus facilitating the formation of a conductive carbon layer with both high safety and long-term cycling stability.

[0043] Furthermore, the weight-average molecular weight of the second conductive polymer is preferably 1 × 10⁻⁶. 4 ~4×10 4 This design aims to ensure that the second conductive polymer possesses suitable segmental flexibility, film-forming ability, and outer layer coating capability. This facilitates the formation of a continuous, dense, and resilient second composite layer on the outer side of the first composite layer. It also promotes the uniform distribution of the second functional additive within the second composite layer, reducing the risk of phase separation or localized enrichment, thereby improving the dispersion stability of the resulting core-shell composite carbon material in an aqueous system. Simultaneously, a crosslinking degree of 3% to 5% is preferred for the second conductive polymer to form a suitable network structure in the second composite layer, thereby improving the coating's mechanical strength, structural stability, and water resistance. Furthermore, a moderate degree of crosslinking helps retain some segmental mobility, allowing the hydrophilic groups in the second functional additive to be more effectively distributed or exposed on the surface of the second composite layer, further enhancing its wetting and dispersing effects.

[0044] Furthermore, the hydrophilic additive is selected from one or more of polystyrene sulfonic acid, polystyrene sulfonate (specifically sodium / potassium salt), poly(2-acrylamide-2-methylpropanesulfonic acid), poly(2-acrylamide-2-methylpropanesulfonic acid) salt (specifically sodium / potassium salt), polyacrylic acid, polyacrylate (specifically sodium / potassium salt), carboxymethyl cellulose, and carboxymethyl cellulose salt (specifically sodium / potassium salt).

[0045] In several preferred embodiments, the first conductive polymer and the second conductive polymer are each independently selected from one or more of polyaniline, polythiophene, polypyrrole, and poly(3,4-ethylenedioxythiophene). These polymers are all dopable conductive polymers, possessing good conductivity, environmental stability, and tunable redox response characteristics. In the first composite layer, any one or a combination of these polymers can form a good interfacial bond with the carbon particle surface and construct a relatively stable electron transport channel. Simultaneously, under the action of the first functional additive, the doping state, voltage response characteristics, and transition behavior from a conductive state to a low-conductivity or high-resistivity state of the first conductive polymer can be tunable. In the second composite layer, any one or a combination of the same or different types of conductive polymers can serve as an outer conductive framework. While maintaining a certain conductive pathway, the second functional additive, in combination with the second composite polymer, imparts better surface wettability, water dispersibility, and interfacial compatibility to the second composite layer, thereby further improving the dispersion stability and processing adaptability of the core-shell composite carbon material in aqueous slurries.

[0046] In several more preferred embodiments, the first conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT), and the first functional additive is polystyrene sulfonic acid (PSS); and / or, the second conductive polymer is polypyrrole (Ppy), and the second functional additive is sodium polyacrylate (PAA-Na). In this preferred embodiment, PEDOT and PSS are a classic conductive composite pair. PSS not only acts as a dopant to enhance the conductivity of PEDOT, but its benzene ring structure can also form π-π interactions with the carbon core, enhancing interfacial bonding and achieving precise voltage protection response. The second conductive polymer Ppy has high electrochemical activity and rapid oxidation response characteristics. When combined with PAA-Na, the sodium carboxylate groups of PAA-Na have extremely strong hydrophilicity, which can significantly reduce surface tension and form a more continuous hydrophilic film without disrupting the conductive pathway. In general, the above-mentioned combination system has good thermal stability and, while maintaining high performance, is also better compatible with existing waterborne coating processes.

[0047] To promote the formation of a denser, less defective core-shell interface between the carbon particles and the first composite layer, thus improving electron transport continuity and uniform coating of the conductive polymer; and to further balance the structural stability and functional compatibility between the composite layer as a whole and the carbon particles, as well as between the first and second composite layers, the particle size of the carbon particles is preferably 50 nm to 2 μm; and / or, the total thickness of the polymer composite layer is preferably 10 nm to 500 nm (more preferably 40 nm to 60 nm), and the thickness ratio of the first composite layer to the second composite layer in the polymer composite layer is 1:(0.2 to 2.5) (more preferably (1 to 2):1). Within the above parameter range, the carbon particles can serve as a stable conductive core, the first composite layer is beneficial for providing normal conductivity and voltage response regulation, and the second composite layer is beneficial for providing surface hydrophilicity and aqueous phase dispersion, thereby achieving synergistic optimization between conductivity, overvoltage response capability, and adaptability to aqueous processing, and is more conducive to obtaining a core-shell composite carbon material with both good dispersibility and low interfacial impedance.

[0048] In practical applications, the carbon particles are conductive carbon black and / or conductive graphite. Conductive carbon black, with its high branching degree and nanoscale primary particles, possesses abundant active sites on its surface, which facilitates the in-situ adsorption and polymerization of the first conductive polymer, promoting dense coating and becoming a more ideal core for core-shell coating. In some embodiments, the aforementioned carbon particles can be used alone or in combination of two or more types to balance conductivity, coating compatibility, dispersibility, and structural stability.

[0049] A second aspect of the present invention provides a method for preparing the above-mentioned core-shell composite carbon material, comprising: step R1, preparing a first slurry containing carbon particles and a first functional additive, and adding a first monomer to the first slurry, and dispersing it first to allow the first monomer and the first functional additive to be adsorbed on the surface of the carbon particles, thereby obtaining a second slurry; the weight ratio of carbon particles, the first functional additive, and the first monomer is 1:(0.3~2.5):(0.3~3.0); step R2, adding a first oxidant solution dropwise to the second slurry to carry out a first polymerization reaction, and forming a first oxidant solution on the surface of the carbon particles. A composite layer is formed to obtain the first product; in step R3, the first product is dispersed in a solvent, and a second functional additive and a second monomer are added thereto. After a second dispersion, the second monomer and the second functional additive are adsorbed on the surface of the first product to obtain a third slurry; the weight ratio of the first product, the second functional additive and the second monomer is 1:(0.03~0.30):(0.10~1.00); in step R4, a second oxidant solution is added dropwise to the third slurry to carry out a second polymerization reaction and form a second composite layer on the surface of the first product to obtain a core-shell composite carbon material.

[0050] The above preparation method constructs a gradient functional structure through stepwise adsorption and in-situ polymerization. Its core advantage lies in achieving precise sequential coating and interfacial synergy between the first and second composite layers. In step R1, carbon particles, the first functional additive, and the first monomer work synergistically in a specific weight ratio, causing the first functional additive to form a concentration gradient adsorption layer on the carbon surface. This provides electrostatic or hydrogen bond anchoring sites for the first monomer, significantly improving the adsorption density and distribution uniformity of the monomer on the carbon core surface. This ensures that the subsequent polymerization reaction forms a complete and dense first composite layer on the carbon surface, avoiding local exposure or uneven coating. In step R3, the first product, the second functional additive, and the second monomer are mixed in a specific ratio to ensure that the second functional additive is uniformly dispersed at a moderate concentration on the surface of the first product, without agglomeration or precipitation. At the same time, the second monomer can be fully adsorbed on the outer edge of the first composite layer, providing a homogeneous reaction environment for the controllable growth of the second composite layer. Meanwhile, the above preparation method also overcomes the defects of random distribution of conductive polymers and high interfacial resistance in traditional physical mixing. Through in-situ polymerization with chemical bonding, the first composite layer forms a π-π conjugated electron transport network with the carbon core, while the second composite layer forms a hydrogen bond network with water molecules through the polar groups of hydrophilic additives, significantly improving the dispersion stability of the aqueous phase. Finally, a core-shell composite carbon material with superior performance is obtained.

[0051] In step R1, the concentration of the first functional additive in the first slurry is preferably 0.2wt% to 3.0wt%, thereby more effectively ensuring both uniform dispersion and complete coating. Preferably, the first monomer is added at 0℃ to 10℃, which more effectively inhibits the free diffusion and bulk polymerization of the monomer in the solution, causing the monomer to preferentially adsorb onto the carbon core surface rather than self-polymerize in the solution, thereby further improving surface coating efficiency and core-shell structure regularity. Furthermore, to ensure the adsorption process reaches a quasi-equilibrium state, promoting the formation of a more stable and dense prepolymer layer on the carbon core surface by the first monomer and the first functional additive, providing a uniform reaction template for subsequent oxidative polymerization, step R1 preferably also includes a settling treatment of the second slurry for 5 min to 30 min.

[0052] In step R2, preferably: the molar ratio of the first monomer to the first oxidant in the first oxidant solution is 1:(0.8~1.5); and / or, the mass concentration of the first oxidant solution is 5%~10%, and the total dropping time is 4h~10h; and / or, step R2 is carried out at 0℃~5℃; and / or, after the dropping is completed, step R2 further includes stirring the second slurry for 4h~24h. The amount of the first oxidant used is sufficient to initiate polymerization while reducing over-oxidation or polymer chain breakage, resulting in a higher doping degree and higher conductivity of the first conductive polymer. The slow dropping over 4~10h makes the polymerization reaction more controllable, thereby promoting the slow growth of the first conductive polymer chains on the carbon core surface, forming a denser, non-porous coating layer. Reaction at 0℃~5℃ can more effectively suppress free radical chain transfer and side reactions, improving the uniformity of polymer molecular weight and crosslinking. Continuing stirring for 4–24 hours after dropwise addition allows unreacted monomers and oxidants to diffuse more fully into the coating layer, further densifying the internal structure of the first composite layer and reducing internal porosity and chain-end defects. The optimized conditions achieved above enable more controllable, uniform, and defect-free polymerization of the first conductive polymer on the carbon core surface, ultimately yielding a core-shell composite carbon material with superior electrochemical performance.

[0053] Further, in step R3, the solid-liquid ratio of the first product to the solvent is preferably 1:(5~20) to facilitate more thorough dispersion of the first product in the solvent, allowing the second monomer and the second functional additive to more uniformly contact the surface of the first composite layer. In the third slurry, to promote better adsorption of the second functional additive in a monomolecular or oligomeric state onto the surface of the first composite layer, and to more fully expose its hydrophilic groups, the concentration of the second functional additive is preferably 0.1wt%~0.3wt%. Also, the second dispersion is preferably carried out at 0℃~5℃ to more effectively suppress the self-aggregation of the second functional additive, promoting better molecular-level uniform distribution on the surface of the first composite layer, while delaying the bulk polymerization of the second monomer, allowing it to preferentially adsorb onto the first composite layer, ultimately forming a more stable second conductive composite layer.

[0054] In step R4, the molar ratio of the second monomer to the second oxidant in the second oxidant solution is preferably 1:(1~5) to facilitate more complete oxidation of the second monomer on the surface of the first composite layer, forming a highly conductive polymer network, while also reducing over-oxidation of the polymer chains. In practical applications, it is preferred that the mass concentration of the second oxidant solution is 8%~15%, the total dropping time is 0.5h~1.5h, and / or step R4 is carried out at 0℃~5℃. Thus, the dropping process within 0.5~1.5h, combined with the low temperature environment of 0℃~5℃, allows the second polymerization reaction to nucleate more rapidly at a localized high concentration, followed by more uniform growth, forming a denser and more continuous outer film, further optimizing the performance of the obtained core-shell composite carbon material.

[0055] In addition, in order to passivate the polymer chain ends by the residual oxidant, enhance the interfacial bonding force between the second composite layer and the first composite layer, and further reduce the risk of peeling, after the drop addition is completed, step R4 preferably includes stirring the second slurry for 2 to 4 hours.

[0056] In several typical embodiments, preferably: the first monomer and the second monomer are each independently selected from one or more of aniline, thiophene, pyrrole, and 3,4-ethylenedioxythiophene; and / or, the first oxidant in the first oxidant solution is selected from one or more of ammonium persulfate, potassium persulfate, and sodium persulfate; and / or, the second oxidant in the second oxidant solution is selected from one or more of ferric chloride, ferric p-toluenesulfonate, and hydrogen peroxide.

[0057] A third aspect of the present invention provides a carbon-coated aluminum foil, comprising an aluminum foil and a carbon layer disposed on at least one surface of the aluminum foil, the carbon layer comprising the aforementioned core-shell composite carbon material. In the core-shell composite carbon material provided by the present invention, the first composite layer maintains good conductivity within the normal operating voltage range and undergoes a transition from a conductive state to a low-conductivity state or a high-resistivity state when the voltage reaches or exceeds a preset threshold; the second composite layer imparts or improves the surface hydrophilicity, water dispersibility, and interfacial compatibility of the material. Based on the above structural design, the core-shell composite carbon material can be used as the main conductive component in the carbon-coated aluminum foil system, thereby giving the resulting carbon layer both good conductive network construction capability and water-based process adaptability. Because the core-shell composite carbon material itself has good aqueous wettability and dispersion stability, it can be stably dispersed in aqueous slurries without or with minimal dependence on additional insulating dispersants, thereby helping to reduce the introduction of high-resistivity non-conductive components and lower the interfacial resistance and sheet resistance of the coating. Meanwhile, the core-shell structure also helps improve the bonding tightness between particles within the carbon layer and between the carbon layer and the aluminum foil substrate, thereby improving the coating's density, adhesion, and structural stability. Furthermore, when carbon-coated aluminum foil is applied to electrochemical energy storage devices, the decrease in conductivity or high-resistivity transition of the first composite layer under overvoltage conditions helps suppress continuous electron transport and further side reactions between the aluminum foil substrate and the electrolyte, thus reducing the risk of aluminum corrosion and electrolyte oxidative decomposition under high-potential conditions, and contributing to improved battery safety and cycle stability.

[0058] Further, preferably, the content of the core-shell composite carbon material is 85%~95% based on the total weight of the carbon layer; and / or, the thickness of the carbon layer is 0.2μm~2.0μm, and the areal density is 0.10mg·cm³. -2 ~0.60mg·cm -2 Within the aforementioned range, it is beneficial to achieve a better balance between electrical conductivity, interfacial impedance, coating density, and mechanical stability, and to fully leverage the comprehensive advantages of the core-shell composite carbon material in terms of normal conductivity, aqueous dispersion, and interface construction, thereby further optimizing the processing performance and electrochemical performance of the obtained carbon-coated aluminum foil.

[0059] In several preferred embodiments, the peel strength between the carbon layer and the aluminum foil at 180±5° is ≥1.0 N·cm. -1 And / or, the initial sheet resistance of the carbon-coated aluminum foil is ≤10 Ω / □. That is to say, in the carbon-coated aluminum foil obtained by this invention, the carbon layer and the aluminum foil substrate have excellent interfacial bonding force, sufficient to resist the mechanical stress generated during electrode winding, rolling, and cycling, reducing local contact failures or sudden increases in internal resistance due to delamination. At the same time, the aforementioned carbon-coated aluminum foil also possesses extremely low electron transport resistance, which can well meet the low resistance requirements of current collectors for high-rate charging and discharging of batteries.

[0060] To further enhance adhesion and carbon layer stability, the carbon layer preferably includes 2% to 15% binder and 0% to 0.5 wt% functional additives, based on 100% of the total weight of the carbon layer. The binder is a water-soluble binder, specifically selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, and sodium alginate. The functional additives may be defoamers (exemplarily, BYK's BYK-012 or BYK-035) and / or pH adjusters (exemplarily, Advancion's AMP-95™ or DMAMP-80™).

[0061] In practical applications, the carbon layer is obtained by sequentially coating and drying a slurry containing a core-shell composite carbon material. Simultaneously, the pH value of the slurry is preferably 7-9 to more effectively maintain the stability of the doped state of the conductive polymer in the core-shell composite material, reducing the adverse effects of strong acid or alkali environments on the doped state of the conductive polymer, the interfacial bonding state, and the structural stability of the composite layer. This results in a more stable and dense carbon layer, further optimizing the electrochemical performance of the carbon-coated aluminum foil. In several preferred embodiments, the drying process includes a first stage at a temperature of 70℃-90℃ for 2-5 minutes, and a second stage at a temperature of 100℃-130℃ for 10-30 minutes. In this preferred embodiment, the first stage uses a relatively low temperature for pre-drying, which helps to gradually remove moisture from the slurry, reducing blistering, cracking, surface defects, or local structural collapse of the coating caused by rapid moisture evaporation. This helps maintain the uniform distribution and particle structure integrity of the core-shell composite carbon material in the coating. The second stage involves further drying and heat setting at higher temperatures, which promotes adhesive film formation and coating structure stabilization, and further removes residual moisture, thereby improving the density, mechanical stability, and interfacial adhesion between the resulting carbon layer and the aluminum foil substrate. Simultaneously, this stage also helps maintain the structural integrity and functional stability of the polymer composite layer, further enhancing the conductivity, interfacial stability, and durability of the resulting carbon-coated aluminum foil.

[0062] A fourth aspect of the present invention provides an electrode sheet comprising the aforementioned carbon-coated aluminum foil. The carbon-coated aluminum foil provided by the present invention exhibits good conductivity, interfacial adhesion, and compatibility with aqueous processing. When used as an electrode current collector, the core-shell composite carbon material in the carbon layer can construct a relatively continuous electron transport pathway and improve the interfacial bonding stability between the carbon layer and the aluminum foil substrate, thereby reducing impedance increases caused by local delamination, interfacial deterioration, or contact failure during electrode fabrication and cycling. Simultaneously, the first composite layer in the core-shell composite carbon material maintains good conductivity within the normal operating voltage range and undergoes a transition from a conductive state to a low-conductivity state or a high-resistivity state under overvoltage conditions; the second composite layer imparts or enhances the surface hydrophilicity and water dispersibility of the material, thus resulting in an electrode sheet with good conductivity, processing stability, interfacial stability, and safety.

[0063] A fifth aspect of the present invention provides a secondary battery comprising at least one of the aforementioned electrode sheets. Because the electrode sheets obtained by the present invention have a simple structure and compatible manufacturing process, they can be directly used in high-voltage cathode systems such as layered oxides and polyanions, and the corresponding batteries exhibit superior overall performance, possessing advantages such as high safety, long lifespan, and low cost.

[0064] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0065] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0066] Example 1

[0067] Preparation of a core-shell composite carbon material:

[0068] (R1-1) Weigh 5.0 g of conductive carbon black (Ketjen Black, ECP-600JD) and add it to 800 mL of deionized water. Add 7.5 g of polystyrene sulfonic acid (PSS, i.e., the first functional additive) to the suspension. Place the mixture in an ice-water bath at 0~5℃ and treat it with a high-power ultrasonic probe for 15 minutes. Then transfer it to a high-speed shear disperser and continue to disperse it at 1000 rpm for 30 minutes to obtain a uniform and stable black suspension, i.e., the first slurry. The concentration of the first functional additive is 0.94 wt%.

[0069] (R1-2) Add 2.5 g of 3,4-ethylenedioxythiophene (EDOT) monomer to the above suspension. Continue mechanical stirring at 0-5°C for 5 minutes to allow the EDOT monomer to preferentially adsorb onto the surface of the conductive carbon core under the action of PSS anions, and let stand for 20 minutes to achieve quasi-equilibrium coverage. This yields the second slurry. The weight ratio of carbon particles, the first functional additive, and the first monomer is 1:1.5:0.5.

[0070] (R2) Weigh 4.0 g of ammonium persulfate (APS) as the oxidant and dissolve it in 50 mL of deionized water to obtain an 8% (w / w) APS oxidant solution. Using a peristaltic pump, add the corresponding volume of APS solution dropwise to the above reaction solution over 4 hours, according to a 1:1 molar ratio of the first monomer to APS, to initiate the polymerization of EDOT on the carbon core surface. After the addition is complete, continue stirring the reaction at 0–5 °C for 4 hours. Filter the reaction product and wash it with 500 mL of ethanol, followed by repeated washing with plenty of deionized water until the conductivity of the filtrate is ≤ 80 μS·cm. -1 .

[0071] (R3) The product obtained in step (R2) was redispersed in 300 mL of deionized water at a solid-liquid ratio of 1 g: 20 mL. 0.45 g of sodium polyacrylate (PAA-Na) was added as a second functional additive, and the mixture was stirred at room temperature for 30 minutes to obtain a third slurry, wherein the mass concentration of the second functional additive was 0.15%. 0.60 g of pyrrole monomer was added to the third slurry as a second monomer, and the mixture was stirred at 0–5 °C for 10 minutes. The weight ratio of the first product, the second functional additive, and the second monomer was 1:0.12:0.18.

[0072] (R4) Take 1.90 g of ferric chloride (FeCl3) and dissolve it in 20 mL of deionized water to obtain an oxidant solution with a mass concentration of 9.5%. Add the solution slowly dropwise to the third slurry over 1 hour (the molar ratio of the second monomer pyrrole to FeCl3 is 1:1.307) to initiate the in-situ polymerization of pyrrole on the outside of the first composite layer. Continue stirring at 0~5℃ for 3 hours to form the second composite layer.

[0073] (R5) The reaction product was filtered and washed repeatedly with deionized water and ethanol until the filtrate was nearly neutral. Then it was vacuum dried at 60°C for 12 h to obtain the core-shell composite carbon material.

[0074] The SEM characterization results of the obtained core-shell composite carbon material are shown in the figure. Figure 1This includes carbon particles with a diameter of 150 nm, each coated with a first composite layer of 30 nm thickness and a second composite layer of 20 nm thickness (i.e., first composite layer: second composite layer = 1.5:1, total thickness 50 nm). The weight ratio of carbon particles:first composite layer:second composite layer is 88:8:4.

[0075] In the first composite layer, the weight ratio of the first conductive polymer to the conductive additive is 100:25. According to gel permeation chromatography, the weight-average molecular weight of the first conductive polymer is 4.2 × 10⁻⁶. 4 According to the gel content method, the degree of crosslinking of the first conductive polymer is 6.8%.

[0076] In the second composite layer, the weight ratio of the second conductive polymer to the hydrophilic additive is 100:15. The weight-average molecular weight of the second conductive polymer, as determined by gel permeation chromatography, is 2.8 × 10⁻⁶. 4 According to the gel content method, the degree of crosslinking of the second conductive polymer is 4.5%.

[0077] Preparation of a carbon-coated aluminum foil:

[0078] (S1) Take a 12μm thick battery-grade aluminum foil roll, perform physical cleaning and phosphate corrosion-resistant primer treatment, wash and dry for later use.

[0079] (S2) In 80.0 g of deionized water, 2 g of sodium carboxymethyl cellulose (CMC) was slowly added as a binder, and stirred at room temperature to allow it to swell for 60 minutes to obtain a CMC solution. 18 g of the core-shell composite powder prepared above was added to the CMC solution. The mixture was dispersed at 1200 rpm for 30 minutes using a planetary vacuum mixer. The pH of the slurry was adjusted to 8.0 using a small amount of ammonia, and the mixture was degassed under vacuum for 15 minutes to obtain a solid content of 20 wt% and a viscosity of 1550 mPa·s (10⁻⁶ s⁻¹). -1 ) stabilized slurry.

[0080] (S3) Using a micro-gravure coating process, the slurry from step (S2) is uniformly coated on both sides of the aluminum foil after the treatment in step (S1), and the wet film thickness is controlled to be 8μm.

[0081] (S4) The coated aluminum foil is passed through a segmented drying oven in sequence: the first stage is drying at 80°C for 3 minutes; the second stage is heat setting at 110°C for 10 minutes. After winding, active safety carbon-coated aluminum foil is obtained.

[0082] The resulting carbon-coated aluminum foil has a dry film thickness of 0.8 μm / sided and an areal density of 0.16 mg·cm³ on both sides. -2 (That is, the total areal density of both sides is 0.32 mg·cm³) -2The carbon layer consists of a core-shell composite carbon material with a content of 90% and a binder content of 10%.

[0083] Example 2

[0084] A method for preparing a core-shell composite carbon material:

[0085] The only difference between this embodiment and Embodiment 1 is that in step (R1-2), the weight ratio of carbon particles, the first functional additive, and the first monomer is changed to 1:0.9:0.5, so that in the resulting first composite layer, the weight ratio of the first conductive polymer to the conductive additive is changed to 100:15.

[0086] Example 3

[0087] A method for preparing a core-shell composite carbon material:

[0088] The only difference between this embodiment and Embodiment 1 is that in step (R1-2), the weight ratio of carbon particles, the first functional additive, and the first monomer is changed to 1:2.4:0.5, so that in the resulting first composite layer, the weight ratio of the first conductive polymer to the conductive additive is changed to 100:40.

[0089] Example 4

[0090] A method for preparing a core-shell composite carbon material:

[0091] The only difference between this embodiment and Embodiment 1 is that in step (R3), the weight ratio of the first product, the second functional additive and the second monomer is changed to 1:0.04:0.18, so that in the resulting second composite layer, the weight ratio of the second conductive polymer and the hydrophilic additive is changed to 100:5.

[0092] Example 5

[0093] A method for preparing a core-shell composite carbon material:

[0094] The only difference between this embodiment and Embodiment 1 is that in step (R3), the weight ratio of the first product, the second functional additive and the second monomer is changed to 1:0.3:0.18, so that in the resulting second composite layer, the weight ratio of the second conductive polymer and the hydrophilic additive is changed to 100:25.

[0095] Example 6

[0096] A method for preparing a core-shell composite carbon material:

[0097] The only difference between this embodiment and Embodiment 1 is that in step (R1-2), the weight ratio of carbon particles, the first functional additive, and the first monomer is changed to 1:1.0:0.5; and in step (R3), the weight ratio of the first product, the second functional additive, and the second monomer is changed to 1:0.06:0.18.

[0098] Furthermore, the thickness of the first composite layer is changed to 25nm, and the thickness of the second composite layer is changed to 5nm. At this time, the ratio of the first composite layer to the second composite layer is 1:0.1, and the total thickness is 30nm.

[0099] Example 7

[0100] A method for preparing a core-shell composite carbon material:

[0101] The only difference between this embodiment and Embodiment 1 is that in step (R1-2), the weight ratio of carbon particles, the first functional additive, and the first monomer is changed to 1:1.5:0.5; and in step (R3), the weight ratio of the first product, the second functional additive, and the second monomer is changed to 1:0.45:0.9.

[0102] Furthermore, the thickness of the first composite layer is changed to 20nm, and the thickness of the second composite layer is changed to 50nm. At this time, the ratio of the first composite layer to the second composite layer is 1:2.5, and the total thickness is 70nm.

[0103] Example 8

[0104] A method for preparing a core-shell composite carbon material:

[0105] The only difference between this embodiment and Embodiment 1 is that in step (R2), the molar ratio of the first monomer to APS (i.e., the molar ratio of the first monomer to the first oxidant in the first oxidant solution) is changed to 1:0.5.

[0106] Example 9

[0107] A method for preparing a core-shell composite carbon material:

[0108] The only difference between this embodiment and Embodiment 1 is that in step (R2), the molar ratio of the first monomer to APS (i.e., the molar ratio of the first monomer to the first oxidant in the first oxidant solution) is changed to 1:2.

[0109] Example 10

[0110] A method for preparing a core-shell composite carbon material:

[0111] The only difference between this embodiment and Embodiment 1 is that in step (R2), the total amount of the first oxidant remains unchanged, while the mass concentration of the first oxidant solution is changed to 4%, and the total dripping time is changed to 3 hours.

[0112] Example 11

[0113] A method for preparing a core-shell composite carbon material:

[0114] The only difference between this embodiment and Embodiment 1 is that in step (R2), the total amount of the first oxidant remains unchanged, while the mass concentration of the first oxidant solution is changed to 12%, and the total dripping time is changed to 12h.

[0115] Example 12

[0116] A method for preparing a core-shell composite carbon material:

[0117] The only difference between this embodiment and Embodiment 1 is that in step (R4), the molar ratio of the second monomer pyrrole to FeCl3 (i.e., the molar ratio of the second monomer to the second oxidant in the second oxidant solution) is changed to 1:0.8.

[0118] Example 13

[0119] A method for preparing a core-shell composite carbon material:

[0120] The only difference between this embodiment and Embodiment 1 is that in step (R4), the molar ratio of the second monomer pyrrole to FeCl3 (i.e., the molar ratio of the second monomer to the second oxidant in the second oxidant solution) is changed to 1:4.

[0121] Example 14

[0122] A method for preparing a core-shell composite carbon material:

[0123] The only difference between this embodiment and Embodiment 1 is that in step (R4), the total amount of the second oxidant remains unchanged, while the mass concentration of the second oxidant solution is changed to 5%, and the total dripping time is changed to 0.3h.

[0124] Example 15

[0125] A method for preparing a core-shell composite carbon material:

[0126] The only difference between this embodiment and Embodiment 1 is that in step (R4), the total amount of the second oxidant remains unchanged, while the mass concentration of the second oxidant solution is changed to 20%, and the total dripping time is changed to 2 hours.

[0127] Comparative Example 1

[0128] A method for preparing composite carbon materials:

[0129] The only difference between this comparative example and Example 1 is that the first product obtained in step (R2) is directly used as the composite carbon material sample.

[0130] Comparative Example 2

[0131] A method for preparing composite carbon materials:

[0132] The only difference between this comparative example and Example 1 is that steps (R1) and (R2) were not performed, and the carbon particle raw material was directly used as the product obtained in step (R2) for steps (R3) and (R4).

[0133] Comparative Example 3

[0134] A method for preparing composite carbon materials:

[0135] The only difference between this comparative example and Example 1 is that: carbon particles are used as raw materials, and a second composite layer is coated onto them according to steps (R3) and (R4) to obtain the first product; then, a first composite layer is coated onto them according to steps (R1) and (R2). Thus, a composite carbon material sample is obtained.

[0136] Comparative Example 4

[0137] The only difference between this comparative example and Example 1 is that in step (R1-2), the weight ratio of carbon particles, the first functional additive, and the first monomer is changed to 1:0.6:0.5; and in step (R3), the weight ratio of the first product, the second functional additive, and the second monomer is changed to 1:0.32:0.36.

[0138] Furthermore, the weight ratio of carbon particles to the first composite layer to the second composite layer in the resulting composite carbon material is 60:4:8.

[0139] Comparative Example 5

[0140] The only difference between this comparative example and Example 1 is that in step (R1-2), the weight ratio of carbon particles, the first functional additive, and the first monomer is changed to 1:1.8:0.5; and in step (R3), the weight ratio of the first product, the second functional additive, and the second monomer is changed to 1:0.03:0.06.

[0141] Furthermore, the resulting composite carbon material has a carbon particle : first composite layer : second composite layer ratio of 120 : 15 : 1 by weight.

[0142] Test methods

[0143] The initial sheet resistance of the carbon-coated aluminum foil is obtained by testing using the four-probe method. The unit is “Ω / □”, where “□” means square. The sheet resistance remains unchanged regardless of the size.

[0144] The 180° peel strength between the carbon layer and the aluminum foil on the carbon-coated aluminum foil was obtained according to GB / T 2792-2014 "Test Method for 180° Peel Strength of Pressure-Sensitive Adhesive Tapes".

[0145] Battery sample preparation and performance testing: The carbon-coated aluminum foil obtained in each example and comparative example was used as the positive electrode current collector, coated with sodium-ion battery positive electrode slurry (where the ratio of positive electrode active material: binder: conductive agent = 96:2:2, and the solvent is deionized water) to prepare the positive electrode sheet. A metallic sodium sheet was used as the negative electrode sheet, and a glass fiber membrane was used as the separator. A 1 mol·L⁻¹ solution was applied. -1 NaPF6 / EC:DEC (volume ratio 1:1) was used as the electrolyte to assemble CR2032 coin cells.

[0146] The assembled battery sample, after being left to stand for 12 hours, was placed in a battery testing system and tested at 25°C as follows: It was charged at a constant current of 0.1 C to 4.3 V; once the voltage reached 4.3 V, it was then subjected to a constant voltage holding step for 10 hours; the current-time curve during the constant voltage holding process was recorded; the average current during the last 30 minutes of constant voltage holding was taken and converted into current density based on the effective coating area of ​​the positive electrode, and recorded as the 4.3 V constant voltage holding current density of the sample, in μA·cm. -2 4.3 The lower the constant voltage current density, the lower the degree of side reactions in the battery under high voltage conditions, and the more obvious the inhibitory effect of carbon-coated aluminum foil on interfacial reactions under high voltage conditions.

[0147] Table 1

[0148]

[0149] As can be seen from the above description, compared with the various comparative examples, the above embodiments of the present invention are based on a core-shell structure design and achieve the purpose of improving the overall conductivity and process compatibility of the material by constructing a gradient functional bilayer polymer composite layer on the surface of carbon particles. This achieves the technical effect of balancing high conductivity, excellent water dispersibility and structural stability.

[0150] In the various embodiments:

[0151] Comparing Examples 2 and 3 with Example 1, it can be seen that by optimizing the weight ratio of the first conductive polymer to the first functional additive in the first composite layer, the amount of the first functional additive added can be sufficient to effectively regulate the voltage response characteristics of the first conductive polymer, while taking into account both the conductivity of the first composite layer under normal operating conditions and its high resistance switching capability under overvoltage conditions.

[0152] Comparing Examples 4 and 5 with Example 1, it can be seen that by optimizing the weight ratio of the second conductive polymer to the second functional additive in the second composite layer, the second functional additive can be distributed in an appropriate amount in the outer layer structure formed by the second conductive polymer, thereby imparting or improving the surface hydrophilicity, wettability and water dispersibility of the second composite layer.

[0153] Comparing Examples 6 and 7 with Example 1, it can be seen that by optimizing the thickness ratio of the first composite layer to the second composite layer, synergistic optimization of conductivity, overvoltage response capability and water system processing adaptability can be achieved, which is more conducive to obtaining core-shell composite carbon materials with both good dispersibility and low interfacial impedance.

[0154] Comparing Examples 8 and 9 with Example 1, it can be seen that by optimizing the molar ratio of the first monomer to the first oxidant in the first oxidant solution, the oxidant can be used to initiate polymerization in sufficient quantity, while reducing over-oxidation or polymer chain breakage, so that the first conductive polymer exhibits higher doping degree and higher conductivity.

[0155] Comparing Examples 10 and 11 with Example 1, it can be seen that by adding the first oxidant solution, the polymerization of the first conductive polymer on the carbon core surface can be more controllable, more uniform, and with fewer defects, ultimately resulting in a core-shell composite carbon material with superior electrochemical performance.

[0156] Comparing Examples 12 and 13 with Example 1, it can be seen that by optimizing the molar ratio of the second monomer to the second oxidant in the second oxidant solution, the second monomer can be more fully oxidized on the surface of the first composite layer, forming a highly conductive polymer network.

[0157] Comparing Examples 14 and 15 with Example 1, it can be seen that by adding the second oxidant solution, the second polymerization reaction can nucleate more rapidly under local high concentration, and then grow more uniformly to form a denser and more continuous outer film, further optimizing the performance of the obtained core-shell composite carbon material.

[0158] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0159] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A core-shell composite carbon material, characterized in that, Includes carbon particles and a polymer composite layer coating the surface of the carbon particles; Along a direction away from the carbon particles, the polymer composite layer includes a first composite layer and a second composite layer disposed sequentially. The first composite layer comprises a first conductive polymer and a first functional additive; the first functional additive is used to regulate the voltage response characteristics of the first conductive polymer; the first functional additive is selected from one or more of small molecule sulfonic acid compounds, fluorosulfonyl imide salt compounds, fluorinated complex anionic compounds, and low molecular weight polyelectrolytes; the low molecular weight polyelectrolytes have a number average molecular weight of 1×10⁻⁶. 3 ~2×10 4 The low molecular weight polyelectrolyte is polystyrene sulfonic acid and / or poly(2-acrylamide-2-methyl-1-propanesulfonic acid); The second composite layer includes a second conductive polymer and a second functional additive. The second functional additive is used to improve the hydrophilicity of the second conductive polymer. The second functional additive is selected from one or more of polystyrene sulfonic acid, polystyrene sulfonate, poly(2-acrylamide-2-methylpropanesulfonic acid), poly(2-acrylamide-2-methylpropanesulfonic acid) salt, polyacrylic acid, polyacrylate, carboxymethyl cellulose, and carboxymethyl cellulose salt. The weight ratio of the carbon particles, the first composite layer, and the second composite layer is (70~100):(5~12):(2~6).

2. The core-shell composite carbon material according to claim 1, characterized in that, In the first composite layer, The weight ratio of the first conductive polymer to the first functional additive is 100:(20~30); and / or, The weight-average molecular weight of the first conductive polymer is 3 × 10⁻⁶. 4 ~5×10 4 ; and / or, The degree of crosslinking of the first conductive polymer is 5%~8%; and / or, The first conductive polymer is selected from one or more of polyaniline, polythiophene, polypyrrole, and poly(3,4-ethylenedioxythiophene).

3. The core-shell composite carbon material according to claim 2, characterized in that, The small molecule sulfonic acid compound is selected from one or more of p-toluenesulfonic acid, camphorsulfonic acid, and methanesulfonic acid; and / or, The fluorosulfonyl imide salt compound is sodium bis(trifluoromethylsulfonyl)imide and / or sodium bisfluorosulfonylimide; and / or, The fluorinated complex anionic compound is selected from one or more of fluoroboric acid, sodium fluoroborate, hexafluorophosphate, and sodium hexafluorophosphate.

4. The core-shell composite carbon material according to claim 1, characterized in that, In the second composite layer, The weight ratio of the second conductive polymer to the second functional additive is 100:(10~20); and / or, The weight-average molecular weight of the second conductive polymer is 1×10⁻⁶. 4 ~4×10 4 ; and / or, The degree of crosslinking of the second conductive polymer is 3% to 5%; and / or, The second conductive polymer is selected from one or more of polyaniline, polythiophene, polypyrrole, and poly(3,4-ethylenedioxythiophene).

5. The core-shell composite carbon material according to any one of claims 1 to 4, characterized in that, The carbon particles have a particle size of 50 nm to 2 μm; and / or, The total thickness of the polymer composite layer is 10nm~500nm, and the thickness ratio of the first composite layer to the second composite layer in the polymer composite layer is 1:(0.2~2.5).

6. A method for preparing a core-shell composite carbon material according to any one of claims 1 to 5, characterized in that, include: Step R1: Prepare a first slurry containing the carbon particles and the first functional additive, and add the first monomer to the first slurry. After first dispersion, the first monomer and the first functional additive are adsorbed onto the surface of the carbon particles to obtain a second slurry; the weight ratio of the carbon particles, the first functional additive, and the first monomer is 1:(0.3~2.5):(0.3~3.0). Step R2: A first oxidant solution is added dropwise to the second slurry to carry out a first polymerization reaction and form the first composite layer on the surface of the carbon particles, thereby obtaining the first product; Step R3: The first product is dispersed in a solvent, and the second functional additive and the second monomer are added thereto. After a second dispersion, the second monomer and the second functional additive are adsorbed onto the surface of the first product to obtain a third slurry; the weight ratio of the first product, the second functional additive and the second monomer is 1:(0.03~0.30):(0.10~1.00). Step R4: A second oxidant solution is added dropwise to the third slurry to carry out a second polymerization reaction and form a second composite layer on the surface of the first product, thereby obtaining the core-shell composite carbon material.

7. The method for preparing the core-shell composite carbon material according to claim 6, characterized in that, In step R1, In the first slurry, the concentration of the first functional additive is 0.2wt%~3.0wt%; and / or, The first monomer is added at 0°C to 10°C; and / or, Step R1 further includes allowing the second slurry to stand for 5 to 30 minutes.

8. The method for preparing the core-shell composite carbon material according to claim 6, characterized in that, In step R2 The molar ratio of the first monomer to the first oxidant in the first oxidant solution is 1:(0.8~1.5); and / or, The mass concentration of the first oxidant solution is 5%~10%, and the total dripping time is 4h~10h; and / or, Step R2 is performed at 0℃~5℃; and / or, After the dripping is completed, step R2 further includes stirring the second slurry for 4 to 24 hours.

9. The method for preparing the core-shell composite carbon material according to any one of claims 6 to 8, characterized in that, In step R3 The solid-liquid ratio of the first product to the solvent is 1:(5~20); and / or, In the third slurry, the concentration of the second functional additive is 0.1wt%~0.3wt%; and / or, The second dispersion was carried out at 0℃~5℃.

10. The method for preparing the core-shell composite carbon material according to any one of claims 6 to 8, characterized in that, In step R4 The molar ratio of the second monomer to the second oxidant in the second oxidant solution is 1:(1~5); and / or, The mass concentration of the second oxidant solution is 8%~15%, and the total dropping time is 0.5h~1.5h; and / or, Step R4 is performed at 0℃~5℃; and / or, After the dripping is completed, step R4 further includes stirring the third slurry for 2 to 4 hours.

11. The method for preparing the core-shell composite carbon material according to any one of claims 6 to 8, characterized in that, The first monomer and the second monomer are each independently selected from one or more of aniline, thiophene, pyrrole, and 3,4-ethylenedioxythiophene; and / or, The first oxidant in the first oxidant solution is selected from one or more of ammonium persulfate, potassium persulfate, and sodium persulfate; and / or, The second oxidant in the second oxidant solution is selected from one or more of ferric chloride, ferric p-toluenesulfonate, and hydrogen peroxide.

12. A carbon-coated aluminum foil, comprising an aluminum foil and a carbon layer disposed on at least one surface of the aluminum foil, characterized in that, The carbon layer includes any one of the core-shell composite carbon materials according to claims 1 to 5.

13. The carbon-coated aluminum foil according to claim 12, characterized in that, Based on the total weight of the carbon layers as 100%, the content of the core-shell composite carbon material is 85%~95%; and / or, The carbon layer has a thickness of 0.2 μm to 2.0 μm and an areal density of 0.10 mg·cm³. -2 ~0.60mg·cm -2 ; and / or, The peel strength between the carbon layer and the aluminum foil at 180±5° is ≥1.0 N·cm. -1 ; and / or, The initial sheet resistance of the carbon-coated aluminum foil is ≤10 Ω / □.

14. The carbon-coated aluminum foil according to claim 12 or 13, characterized in that, The carbon layer is obtained by sequentially coating and drying a slurry containing the core-shell composite carbon material, and the pH value of the slurry is 7-9.

15. An electrode sheet, characterized in that, The electrode sheet includes the carbon-coated aluminum foil as described in any one of claims 12 to 14.

16. A secondary battery, characterized in that, The secondary battery includes at least one electrode sheet as described in claim 15.

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