A method of making a solid electrolytic capacitor paper

Abstract

The application relates to the technical field of pulping and papermaking, and provides a preparation method of solid-state electrolytic capacitor paper, which comprises the following steps: S100, respectively preparing A slurry and B slurry, adopting wet papermaking to perform multi-layer forming on the A slurry and the B slurry, and obtaining a multi-layer wet paper sheet; S200, performing pressing treatment and drying treatment on the multi-layer wet paper sheet, and obtaining the solid-state electrolytic capacitor paper. According to the application, the A slurry and the B slurry are respectively prepared and wet papermaking is performed to form a multi-layer structure with different pore diameters, the layer with a larger pore diameter has better connectivity, the resistance of precursor liquid entering is reduced, and the entering speed is accelerated; the layer structure with a relatively small pore diameter is more uniform, which is beneficial to intercepting burrs and improving pressure safety, and is also beneficial to redistributing and homogenizing the precursor liquid in the thickness direction, and reducing local enrichment or local loss.

Description

Technical Field

[0001] This application relates to the field of pulp and paper technology, and in particular to a method for preparing solid electrolytic capacitor paper. Background Technology

[0002] Solid-state electrolytic capacitors, with their advantages of low ESR, high-frequency resistance, and long lifespan, are widely used in communication power supplies, servers, automotive electronics, and industrial control. Their core uses a conductive polymer or other solid electrolyte as the cathode, and typically contains an anode foil, a dielectric layer, an insulating material (usually capacitor paper), and a cathode layer. The capacitor paper not only serves as insulation and prevents short circuits but also provides adsorption, storage, and transport channels for solid electrolyte precursors (such as monomers and oxidant solutions), thereby ensuring the formation of a uniform and continuous conductive network.

[0003] Currently, capacitor paper is mostly made from natural fibers such as wood pulp and hemp pulp through a wet papermaking process, and sometimes synthetic fibers are added to improve strength. Unlike liquid electrolytic capacitor paper, which focuses on liquid absorption and corrosion resistance, solid electrolytic capacitor paper also needs to ensure the uniformity of precursor penetration and structural stability during the curing process. Therefore, it faces a design contradiction between high porosity and high liquid absorption and high strength, high pressure resistance and low defects.

[0004] If the paper is too loose and has too high porosity, although it is beneficial for precursor wetting and mass transfer, it will lead to a decrease in mechanical strength. This can easily cause problems such as paper breakage and fuzzing during slitting and winding. After winding, burrs or weak points may also cause insufficient pressure resistance and short circuits. Conversely, if the pressure resistance and burr resistance are enhanced by increasing density, thickness, or multilayer composites, it will hinder precursor penetration and loading, easily causing uneven wetting and local discontinuity of the solid electrolyte. This will result in increased ESR of the capacitor, increased leakage current, and poor batch consistency.

[0005] Therefore, balancing the porosity and permeability of paper with its density and toughness is a key challenge in improving the performance and reliability of solid-state electrolytic capacitors. Summary of the Invention

[0006] In view of the above-mentioned shortcomings in the prior art, the purpose of this application is to provide a method for preparing solid electrolytic capacitor paper.

[0007] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: This application provides a method for preparing solid electrolytic capacitor paper, including the following steps: S100. Prepare pulp A and pulp B separately, and use wet papermaking to form multiple layers of pulp A and pulp B to obtain a multi-layer wet paper sheet; S200: Press and dry the multi-layer wet paper sheets to obtain solid electrolytic capacitor paper.

[0008] In one optional implementation, the method for preparing slurry A includes the following steps: S111. After pulping natural fiber pulp A, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion A and synthetic short fiber dispersion A are added sequentially and stirred to obtain pulp A.

[0009] In one alternative embodiment, the mass ratio of natural fiber pulp A, nanocellulose dispersion A, and synthetic short fiber dispersion A is 1:(0.01-0.16):(0.2-0.8).

[0010] In an optional embodiment, the natural fiber pulp A has a freeness of 10-40°SR; and / or the concentration of pulp A is 0.01-0.2 wt.%; and / or the natural fiber pulp A includes at least one or a combination of jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; and / or the synthetic short fiber dispersion A includes at least one of polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and / or the nanocellulose dispersion A includes at least one of cellulose nanocellulose dispersion and cellulose nanocrystal dispersion.

[0011] In an optional implementation, the method for preparing slurry B includes the following steps: S121. After pulping natural fiber pulp B, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion B and synthetic short fiber dispersion B are added sequentially and stirred to obtain pulp B.

[0012] In one alternative embodiment, the mass ratio of natural fiber pulp B, nanocellulose dispersion B, and synthetic short fiber dispersion B is 1:(0.025-0.5):(1-3.75).

[0013] In an optional embodiment, the natural fiber pulp B has a freeness of 65-80°SR; and / or the concentration of pulp B is 0.02-0.1 wt.%; and / or the natural fiber pulp B includes at least one or a combination of jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; and / or the synthetic short fiber dispersion B includes at least one of polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and / or the nanocellulose dispersion B includes at least one of cellulose nanocellulose dispersion and cellulose nanocrystal dispersion.

[0014] In an optional implementation, the pressing process is a staged pressing process; the staged pressing process includes a first stage pressing process and a second stage pressing process; the pressure of the first stage pressing process is 2-3 bar, and the pressure of the second stage pressing process is 4-6 bar.

[0015] In one optional embodiment, the drying process is a segmented drying process; the segmented drying process includes a first stage drying process, a second stage drying process, and a third stage drying process; the temperature of the first stage drying process is 55-65℃, the temperature of the second stage drying process is 85-95℃, and the temperature of the third stage drying process is 100-115℃.

[0016] In an optional embodiment, the preparation method further includes: S300, spray water-based reinforcing agent onto the surface of solid electrolytic capacitor paper; The amount of water-based reinforcing agent applied is less than 3 wt.% of the weight of solid electrolytic capacitor paper.

[0017] The beneficial effects of this application include at least the following: (1) By preparing slurry A and slurry B separately and performing wet papermaking to form a multilayer structure with different pore sizes, a multilayer structure with different pore sizes can be formed. The layer with larger pore size has better connectivity, which reduces the resistance to the entry of the precursor liquid and accelerates the introduction speed. The layer with relatively smaller pore size has a more uniform structure, which is beneficial for intercepting burrs and improving pressure resistance and safety. It is also beneficial for redistributing and homogenizing the precursor liquid in the thickness direction, reducing local enrichment or local loss. (2) A pulp reduces the beating degree of natural fibers, resulting in a lower degree of fiber fineness and fewer inter-fiber bonding points, thereby forming a more open pore structure and better connectivity, so that the precursor liquid can quickly wet and enter the core package along the pores; B pulp increases the beating degree of natural fibers, resulting in fiber surface texturing and enhanced inter-fiber hydrogen bonding, thereby improving strength and tear resistance, and constructs a tough skeleton with a higher proportion of synthetic short fibers, improving stability in the wet state and processing. Detailed Implementation

[0018] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are only for explaining this application, but the implementation of this application is not limited thereto.

[0019] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this application pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; the amounts of experimental reagents used are, unless otherwise specified, the amounts used in conventional experimental operations; and the experimental methods used are, unless otherwise specified, conventional methods.

[0020] Solid electrolytic capacitor paper plays multiple roles in the core-pack structure, going beyond simple electrical isolation. It integrates electrical insulation, burr resistance, and breakdown protection; it serves as a channel for adsorbing and transporting solid electrolyte precursors (such as monomer solutions and oxidant solutions); and it maintains stable mechanical properties during manufacturing processes such as slitting, winding, impregnation, and subsequent drying. In practice, these functional requirements often conflict with each other. High porosity and a loose structure in the paper sheet, while facilitating the wetting of precursor liquids, will correspondingly decrease its mechanical strength, voltage withstand capability, and burr resistance. Conversely, excessively dense, high-strength, and high-voltage-resistant paper sheets can lead to slow and uneven wetting of precursors, resulting in incomplete local solid electrolyte formation and increased dispersion in the capacitor's electrical performance.

[0021] In the preparation method of this application, A pulp and B pulp are prepared separately and then wet-processed into multiple layers. Pulp A and pulp B are not simply two separate pulps, but rather correspond to two different structural objectives: Pulp A is used to form an absorbent layer or induction layer, prioritizing rapid ingress of the precursor liquid and its storage capacity; Pulp B is used to form a pressure-resistant layer or barrier layer, prioritizing mechanical strength, burr resistance, and pressure resistance reliability. By preparing the pulps separately, the two types of structures can be targeted at the source, avoiding the forced compromise in a single paper layer and preventing a situation where a single pulp simultaneously pursues high porosity and high strength, resulting in a compromise between both.

[0022] Embodiments of this application provide a method for preparing solid electrolytic capacitor paper, comprising the following steps: S100. Prepare pulp A and pulp B separately, and use wet papermaking to form multiple layers of pulp A and pulp B to obtain a multi-layer wet paper sheet; S200: Press and dry the multi-layer wet paper sheets to obtain solid electrolytic capacitor paper.

[0023] Preferably, in step S100, after preparing A slurry and B slurry with different beating degrees, a wet papermaking process is used for multi-layer forming. This can form a multi-layer structure with different pore sizes. The layers with larger pore sizes have better connectivity, reducing the resistance to the introduction of the precursor liquid and accelerating the introduction speed. The layers with relatively smaller pore sizes have a more uniform structure, which is beneficial for intercepting burrs, improving pressure resistance, and also for redistributing and homogenizing the precursor liquid in the thickness direction, reducing local enrichment or local loss. Multi-layer wet forming facilitates the interweaving of fibers at the interface, forming mechanical interlocking and hydrogen bond connections. This wet composite interface is usually stronger than that of dry lamination, which can significantly reduce the risk of interlayer delamination caused by subsequent pressing, drying, and impregnation processes.

[0024] Specifically, the design philosophy of pulp A typically involves reducing the freeness of natural fibers, resulting in lower fiber fineness and fewer inter-fiber bonding points. This creates a more open pore structure and better connectivity, allowing the precursor liquid to quickly wet and enter the core pack along the pores. Simultaneously, the addition of synthetic short fibers and nanocellulose should not be too high to avoid excessive pore shrinkage or blockage. Conversely, the design philosophy of pulp B is to increase the freeness of natural fibers, resulting in surface texturing and enhanced inter-fiber hydrogen bonding, thereby improving strength and tear resistance. A higher proportion of synthetic short fibers is used to construct a tough skeleton, improving stability in the wet state and during processing. Furthermore, the appropriate increase in the amount of nanocellulose utilizes its nanoscale bridging and networking reinforcement to enhance the structural stability and defect tolerance of thin paper under low density conditions. This interlayer difference—a looser absorbent layer and a denser, stronger pressure-resistant layer—directly addresses the dual requirements of mass transfer and safety for solid-state capacitor paper.

[0025] Preferably, the freeness of natural fiber pulp A is 10-40°SR. Within this freeness range, the degree of fiber refinement is relatively limited, fiber length and rigidity are largely retained, and the density of interfiber bonding points is low. After papermaking, it is easier to form a larger average pore size and a higher proportion of through-pores. The capillary resistance of the precursor liquid entering the paper is lower, the wetting speed is faster, and the wetting depth is easier to achieve. At the same time, the layer prepared by pulp A needs to avoid pore throat shrinkage and increased pore tortuosity due to excessive fine fibers. Otherwise, although the liquid absorption may not be low, the penetration will be slower, the thickness distribution will be worse, and the formation of solid electrolytes will easily lead to local enrichment and local loss. If the freeness is below 10°SR, the interfiber bonding is too weak, the wet paper strength is insufficient, the bonding is poor, and it is easy to shed powder and break paper during forming, pressing, drying, and slitting and winding. If it is above 40°SR, the refinement is excessive, the pore structure begins to become significantly dense, its function will be weakened, and the gradient pore advantage will not be obvious.

[0026] Furthermore, the freeness of natural fiber pulp B is 65-80°SR. Within this freeness range, the fiber surface is significantly texturized, the fine fiber content is increased, and the hydrogen bonding ability between fibers is enhanced, resulting in improved tensile strength, tear resistance, folding endurance, and wet stability of the paper sheet. Simultaneously, the pore size distribution is more uniform, and the pore throats are finer, which helps suppress the risk of localized breakdown caused by pinhole defects and burr punctures. The layer prepared from pulp B is usually close to the anode foil side and is the safety baseline layer; therefore, it is allowed to be more dense in exchange for burr resistance and compressive strength margin. If the freeness is below 65°SR, the improvement in strength and compressive strength is insufficient, especially under thinner conditions, making processing damage or short-circuit risks more likely. If it is above 80°SR, the pulp's excessive water retention leads to poor drainage, excessively high compactness after pressing, and a significant increase in pore resistance. It is even possible that there is no pore size difference between the different layers formed by pulp A and pulp B, slowing down overall impregnation, affecting ESR, and decreasing stability.

[0027] Preferably, the preparation method of slurry A includes the following steps: S111. After pulping natural fiber pulp A, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion A and synthetic short fiber dispersion A are added sequentially and stirred to obtain pulp A.

[0028] Furthermore, the preparation method of slurry B includes the following steps: S121. After pulping natural fiber pulp B, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion B and synthetic short fiber dispersion B are added sequentially and stirred to obtain pulp B.

[0029] Preferably, in the preparation of pulp A and pulp B, the reinforcing efficiency of nanocellulose depends on the formation of an effective contact and entanglement network with natural fibers. Adding nanocellulose first helps it to preferentially adsorb onto the surface of natural fibers and form bridging at fiber nodes, thereby achieving higher strength with a lower dosage. Then, adding synthetic short fibers with relatively inert surfaces allows the synthetic short fibers to mainly play a supporting role in skeleton and toughness, while reducing the probability of nanocellulose agglomerating in the aqueous phase or around the short fibers, reducing the risk of ineffective thickening and pore clogging, and improving papermaking stability and paper uniformity.

[0030] Preferably, the core objective of the layer obtained from the preparation of pulp A is to allow the solid electrolyte precursor to enter the paper's internal pores faster, deeper, and more uniformly. Therefore, it is essential to maintain large porosity, high connectivity, and low flow resistance. In pulp A, nanocellulose is a nanoscale material with a high specific surface area. Increasing its amount increases the density of effective bonding points between fibers, leading to smaller pore sizes and increased pore tortuosity. It also fills the gaps between pore walls and fibers, weakening the openness of large pores. Furthermore, nanocellulose improves the pulp's water retention and slows down drainage, making it easier to form a higher density after pressing, thus negating the advantages of the gradient pore structure. Therefore, the amount of nanocellulose added must be controlled within a low range to achieve sufficient reinforcement without clogging the pores. Adding an appropriate amount of synthetic short fibers to pulp A can provide cross-scale support and stress dispersion, improve wet strength and processing stability, and is less likely to significantly reduce pore size compared to increasing freeness. Synthetic short fibers are mainly bonded together mechanically. If the amount of natural fibers is less than that of synthetic short fibers, the hydrogen bond network will be weakened, resulting in poor geocompatibility, weaker interlayer bonding, and uneven pore structure, which is detrimental to pressure resistance and consistency. Therefore, a mass ratio of natural fiber slurry A, nanocellulose dispersion A, and synthetic short fiber dispersion A of 1:(0.01-0.16):(0.2-0.8) is more suitable.

[0031] Preferably, the B slurry is mainly used as a pressure-resistant layer or barrier layer, usually close to the anode foil side. Its primary objectives are burr resistance, pressure resistance, and strength stability. It is a safety baseline layer, needing to withstand winding stress and structural disturbances caused by wet impregnation, and suppress the risk of breakdown and short circuits caused by defects such as pinholes and weak points. If strength is gained solely by increasing density, thickening, or excessive compaction, impregnation and mass transfer are often sacrificed, resulting in uneven solid electrolyte formation and discrete electrical properties. Adding an appropriate amount of nanocellulose to the B slurry can enhance the hydrogen bonding between natural fibers, improving tensile, tear, and fatigue resistance; it also improves pore wall stability, reducing the risk of structural drift and collapse caused by swelling and shrinkage during impregnation and subsequent reactions, and to some extent suppressing microcrack propagation and sensitivity to pinhole defects. Synthetic short fibers provide the skeleton and toughness, significantly improving the tensile and wet strength of the paper, and enhancing its resistance to point loads and burr penetration. Simultaneously, the amount of natural fibers must be sufficient to ensure the strength of the hydrogen bond network and interlayer bonding. Therefore, the mass ratio of natural fiber pulp B, nanocellulose dispersion B and synthetic short fiber dispersion B is 1:(0.025-0.5):(1-3.75), which meets the requirements.

[0032] Furthermore, the concentration of pulp A is 0.01-0.2 wt.%, which makes it easier to disperse and more conducive to the formation of open-pore structures, reducing the risk of synthetic short fiber agglomeration and the formation of local dense blocks, and avoiding the occurrence of wetting dead zones; the concentration of pulp B is 0.02-0.1 wt.%, which controls the risks of flocculation and drainage while ensuring consistent strength and compressive strength, making it easier to achieve a stable multilayer structure. When using wet papermaking to form multilayer wet paper sheets, the multilayer forming can be two-layer forming or three-layer forming. In two-layer forming, the wet paper sheet structure is A / B; in three-layer forming, the wet paper sheet structure is A / B / A or B / A / B, where A and B represent the layers formed by pulp A and pulp B, respectively.

[0033] Preferably, the natural fiber pulp A includes at least one or a combination of jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; and / or the synthetic short fiber dispersion A includes at least one of polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and / or the nanocellulose dispersion A includes at least one of cellulose nanocellulose dispersion and cellulose nanocrystal dispersion.

[0034] Preferably, the natural fiber pulp B includes at least one or a combination of jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; and / or the synthetic short fiber dispersion B includes at least one of polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and / or the nanocellulose dispersion B includes at least one of cellulose nanocellulose dispersion and cellulose nanocrystal dispersion.

[0035] Preferably, the above-mentioned types of natural fibers are selected in pulp A and pulp B because hemp fibers are generally longer and stronger, which is more conducive to forming a stable skeleton at a lower density. The wood pulp system is convenient for achieving uniformity of forming and control of pore size distribution. By compounding hemp pulp and wood pulp, it is beneficial to achieve interlayer differentiation and structural gradient. The above-mentioned types of synthetic short fibers are selected because these synthetic fibers can provide the paper sheet with a tough skeleton, wet stability and puncture resistance. The paper sheet structure can be adjusted by fiber length, fineness and surface properties. They also have relatively good stability and manufacturability in an electrochemical environment. The above-mentioned types of nanofibers are selected because cellulose nanofibers (CNF) have a large aspect ratio, are easy to form continuous nanonetworks, and have more significant bridging reinforcement and wet stability improvement. Cellulose nanocrystals (CNC) can improve local modulus and pore wall stability.

[0036] Preferably, in step S200, due to the high moisture content in the wet paper sheet, the fibers are in a relatively loose, suspended, and weakly bonded state. If they are dried directly without proper pressing, the fibers will migrate significantly during the drying shrinkage process, easily leading to poor bonding, uncontrolled pore structure, insufficient interlayer bonding, and internal stress that causes curling, cracking, or delamination. The essence of pressing is to remove free water and bring the fiber spacing closer together, forming sufficient hydrogen bond points, while strengthening the interlayer interface bonding, so that the multilayer structure remains stable during subsequent drying.

[0037] Furthermore, the pressing process is a segmented pressing process; the segmented pressing process includes a first-stage pressing process and a second-stage pressing process; the first-stage pressing process is used to fix the layer structure and reduce interlayer slippage, while preserving as much open pores in the absorbent layer as possible, with a pressure of 2-3 bar; the second-stage medium-pressure process is used to improve overall strength, interfacial bonding, and dimensional stability, ensuring the reliability of subsequent processing and use, with a pressure of 4-6 bar. If only a high pressure is used for a single pressing process, it is easy to cause the pores of the absorbent layer to collapse, uneven local compaction, and the formation of hard spots, which will increase the risk of breakdown and short circuit.

[0038] Furthermore, the drying process is segmented, comprising a first, second, and third stage. The first stage, at 55-65°C, gently removes free water, preventing rapid surface hardening and the formation of a shell that hinders internal moisture removal, thus reducing interlayer shrinkage and minimizing warping and delamination risks. The second stage, at 85-95°C, improves dewatering efficiency and removes most of the bound water; at this point, the paper structure is fixed through pressing, reducing the likelihood of large-scale structural migration. The third stage, at 100-115°C, is used for setting and homogenizing, removing residual moisture and improving dimensional stability, reducing dimensional fluctuations, fuzzing, or strength fluctuations caused by subsequent rewetting. Direct high-temperature drying without segmentation often results in rapid surface shrinkage while the inner layers remain wet, leading to stress accumulation and consequently curling, cracking, interlayer delamination, and collapse of the absorbent layer's pore structure. This weakens or even eliminates the advantages of the multi-layer gradient structure in post-processing stages.

[0039] Preferably, the preparation method further includes: S300: Spray a water-based reinforcing agent onto the surface of solid electrolytic capacitor paper.

[0040] Preferably, common failures of solid electrolytic capacitor paper in mass production, besides insufficient overall strength, often stem from localized surface and edge problems such as slitting burrs, fiber fuzzing and dusting, winding friction abrasion, surface peeling during wet impregnation and handling, and the propagation of surface microcracks after pressing and drying. These problems often occur in the surface layer and edge areas of the paper sheet. Even if the overall tensile strength of the paper sheet meets the standards, surface dusting or fuzzing can cause microparticle contamination in the core pack, increase the risk of local short circuits, or form local blockages and air bubble retention during impregnation, leading to increased dispersion in electrical performance. Therefore, lightly reinforcing the surface without changing the main pore structure is a reinforcement strategy targeting localized problems. Spraying water-based reinforcing agents allows the reinforcing agents to mainly act on the surface fiber bundles and surface pore walls, strengthening the surface abrasion resistance and dusting resistance, while minimizing the intrusion and alteration of the internal pore structure. The spraying amount of water-based reinforcing agents is less than 3 wt.% of the solid electrolytic capacitor paper mass, which can often achieve effective fixation of surface fiber bundles and improved abrasion resistance without significantly sacrificing porosity and permeability. Example 1

[0041] This embodiment provides a method for preparing solid electrolytic capacitor paper, including the following steps: S100. Prepare A pulp and B pulp separately, and use wet papermaking to form a double layer of A pulp and B pulp to obtain a multi-layer wet paper sheet with structure A / B. S200: Press and dry the multi-layer wet paper sheet to obtain solid electrolytic capacitor paper; The preparation method of slurry A includes the following steps: S111. After beating natural fiber pulp A to 10°SR, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion A and synthetic short fiber dispersion A are added sequentially according to the mass ratio of natural fiber pulp A, nanocellulose dispersion A and synthetic short fiber dispersion A of 1:0.01:0.2. After stirring, pulp A with a concentration of 0.01wt.% is obtained. The preparation method of slurry B includes the following steps: S121. After beating the natural fiber pulp B to 65°SR, deionized water is added for dilution and stable dispersion. Then, the nanocellulose dispersion B and the synthetic short fiber dispersion B are added sequentially according to the mass ratio of natural fiber pulp B, nanocellulose dispersion B and synthetic short fiber dispersion B of 1:0.025:1. After stirring, a pulp B with a concentration of 0.02wt.% is obtained. Natural fiber pulp A includes jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; synthetic short fiber dispersion A includes polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and nanocellulose dispersion A is a cellulose nanocellulose dispersion. Natural fiber pulp B includes jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; synthetic short fiber dispersion B includes polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and nanocellulose dispersion B includes cellulose nanocellulose dispersion. The pressing process is a segmented pressing process; the segmented pressing process includes a first-stage pressing process and a second-stage pressing process; the pressure of the first-stage pressing process is 2 bar, and the pressure of the second-stage pressing process is 4 bar; the drying process is a segmented drying process; the segmented drying process includes a first-stage drying process, a second-stage drying process, and a third-stage drying process; the temperature of the first-stage drying process is 55℃, the temperature of the second-stage drying process is 85℃, and the temperature of the third-stage drying process is 100℃. Example 2

[0042] This embodiment provides a method for preparing solid electrolytic capacitor paper, including the following steps: S100. Prepare A pulp and B pulp separately, and use wet papermaking to form three layers of A pulp and B pulp to obtain a multi-layer wet paper sheet with a structure of A / B / A. S200: Press and dry the multi-layer wet paper sheet to obtain solid electrolytic capacitor paper; The preparation method of slurry A includes the following steps: S111. After beating natural fiber pulp A to 40°SR, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion A and synthetic short fiber dispersion A are added sequentially according to the mass ratio of natural fiber pulp A, nanocellulose dispersion A and synthetic short fiber dispersion A of 1:0.16:0.8. After stirring, pulp A with a concentration of 0.2wt.% is obtained. The preparation method of slurry B includes the following steps: S121. After beating the natural fiber pulp B to 80°SR, add deionized water to dilute and stabilize the dispersion. Then, add the nanocellulose dispersion B and the synthetic short fiber dispersion B in sequence according to the mass ratio of natural fiber pulp B, nanocellulose dispersion B and synthetic short fiber dispersion B of 1:0.5:3.75. After stirring, a pulp B with a concentration of 0.1wt.% is obtained. Natural fiber pulp A includes jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; synthetic short fiber dispersion A includes polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and nanocellulose dispersion A is a cellulose nanocrystal dispersion. Natural fiber pulp B includes jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; synthetic short fiber dispersion B includes polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and nanocellulose dispersion B includes cellulose nanocrystal dispersion. The pressing process is a segmented pressing process; the segmented pressing process includes a first-stage pressing process and a second-stage pressing process; the pressure of the first-stage pressing process is 3 bar, and the pressure of the second-stage pressing process is 6 bar; the drying process is a segmented drying process; the segmented drying process includes a first-stage drying process, a second-stage drying process, and a third-stage drying process; the temperature of the first-stage drying process is 65℃, the temperature of the second-stage drying process is 95℃, and the temperature of the third-stage drying process is 115℃. Example 3

[0043] This embodiment provides a method for preparing solid electrolytic capacitor paper, including the following steps: S100. Prepare A pulp and B pulp separately, and use wet papermaking to form three layers of A pulp and B pulp to obtain a multi-layer wet paper sheet with a structure of B / A / B. S200: Press and dry the multi-layer wet paper sheet to obtain solid electrolytic capacitor paper; S300, spray a water-based reinforcing agent onto the surface of solid electrolytic capacitor paper in an amount less than 3 wt.% of the solid electrolytic capacitor paper mass; The preparation method of slurry A includes the following steps: S111. After beating natural fiber pulp A to 30°SR, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion A and synthetic short fiber dispersion A are added sequentially according to the mass ratio of natural fiber pulp A, nanocellulose dispersion A and synthetic short fiber dispersion A of 1:0.1:0.5. After stirring, pulp A with a concentration of 0.1wt.% is obtained. The preparation method of slurry B includes the following steps: S121. After beating the natural fiber pulp B to 65°SR, add deionized water to dilute and stabilize the dispersion. Then, add the nanocellulose dispersion B and the synthetic short fiber dispersion B in sequence according to the mass ratio of natural fiber pulp B, nanocellulose dispersion B and synthetic short fiber dispersion B of 1:0.1:2. After stirring, a pulp with a concentration of 0.05wt.%B is obtained. Natural fiber pulp A includes jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; synthetic short fiber dispersion A includes polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and nanocellulose dispersion A is a cellulose nanocellulose dispersion. Natural fiber pulp B includes jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; synthetic short fiber dispersion B includes polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and nanocellulose dispersion B includes cellulose nanocellulose dispersion. The pressing process is a segmented pressing process; the segmented pressing process includes a first-stage pressing process and a second-stage pressing process; the pressure of the first-stage pressing process is 2 bar, and the pressure of the second-stage pressing process is 5 bar; the drying process is a segmented drying process; the segmented drying process includes a first-stage drying process, a second-stage drying process, and a third-stage drying process; the temperature of the first-stage drying process is 60℃, the temperature of the second-stage drying process is 90℃, and the temperature of the third-stage drying process is 110℃.

[0044] Comparative Example 1 This comparative example provides a method for preparing solid electrolytic capacitor paper. The difference from Example 1 is that only A slurry is provided in step S100 and multi-layer forming is not performed. That is, the wet paper sheet obtained in step S100 has only one layer and there is no step S121.

[0045] Comparative Example 2 This comparative example provides a method for preparing solid electrolytic capacitor paper. The difference from Example 1 is that only B slurry is provided in step S100 and multi-layer forming is not performed. That is, the wet paper sheet obtained in step S100 has only one layer and there is no step S111.

[0046] Comparative Example 3 This comparative example provides a method for preparing solid electrolytic capacitor paper. The difference from Example 1 is that in step S200, the pressing process is carried out only once with a pressure of 4 bar, and the drying process is carried out only once at 100°C.

[0047] This application has undergone multiple experiments, and some of the test results are presented here for reference to further describe the invention in detail. The following is a detailed description in conjunction with specific embodiments.

[0048] Basic physical property tests: The tensile strength and interlaminar peel strength of the solid electrolytic capacitor paper of Examples 1-3 and Comparative Examples 1-3 were measured respectively. The test results are shown in Table 1.

[0049] Table 1 As can be seen from Table 1, the tensile strength and interlayer peel strength of the examples are better than those of the comparative examples, especially Example 3, which shows that surface spraying can further reduce the risk of surface fiber shedding and interface weakening, thus achieving the highest interlayer peel strength and tensile strength. The tensile strength of Comparative Example 1 is low, indicating that although using only A pulp is beneficial to forming an open-pore structure, the fiber node bonding and load-bearing skeleton are insufficient, resulting in low overall paper strength. The tensile strength of Comparative Example 2 is better, indicating that B pulp has a strong load-bearing network and node reinforcement effect, and a single layer can also achieve high tensile strength. The tensile strength and interlayer peel strength of Comparative Example 3 are significantly lower than those of Comparative Example 1, indicating that using only one pressing and one drying cannot effectively lock the interlayer fiber interweaving structure. The drying stress and local shrinkage difference lead to insufficient interface bonding, ultimately resulting in a significant decrease in peel strength.

[0050] Impregnation capacity test: Solid electrolytic capacitor paper from Examples 1-3 and Comparative Examples 1-3 was taken, dried to constant weight, and then immersed in simulated precursor solution under normal pressure. The surface was scraped off at 5 min and 30 min, weighed again, and the weight gain rate was calculated. The results are shown in Table 2.

[0051] Table 2 As shown in Table 2, the weight gain rates of Examples 1-3 are all within a reasonable range compared to Comparative Examples 1-3. Comparative Example 1 has a higher liquid absorption weight gain rate, but this cannot guarantee the performance and consistency of subsequent devices. The weight gain rate of Comparative Example 2 is significantly lower, indicating that the permeation of the precursor liquid is limited. The weight gain rate of Comparative Example 3 is significantly lower than that of Comparative Example 1, indicating that the single pressing and drying process makes the pore structure and interlayer interface more prone to local collapse or non-uniform densification, thus limiting the impregnation capacity. Although the weight gain is not the lowest, Table 1 shows that its interlayer peel strength is significantly insufficient, indicating poor structural stability and a higher likelihood of generating non-uniform regions during the impregnation process.

[0052] Device testing: Using the same capacitor samples, solid electrolytic capacitor paper from Examples 1-3 and Comparative Examples 1-3 was used for testing, with 30 samples in each group. The average value of the test results was taken, and the test results are shown in Table 3.

[0053] Table 3 As can be seen from Table 3, the devices prepared using the solid electrolytic capacitor paper of Examples 1-3 have better performance, indicating that the electrical performance and consistency are significantly improved. At the same time, the short-circuit failure rate of the examples is significantly reduced and the withstand voltage pass rate is significantly improved, especially Example 3, which shows that the multilayer gradient pore structure combined with segmented pressing and segmented drying, as well as surface lightweight reinforcement, can effectively reduce the risk of short circuit / breakdown and improve the reliability of the devices.

[0054] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing solid electrolytic capacitor paper, characterized in that, Includes the following steps: S100. Prepare pulp A and pulp B separately, and use wet papermaking to form multiple layers of pulp A and pulp B to obtain a multi-layer wet paper sheet; S200: The multi-layer wet paper sheet is subjected to pressing and drying treatment to obtain the solid electrolytic capacitor paper.

2. The preparation method according to claim 1, characterized in that, The preparation method of the A slurry includes the following steps: S111. After pulping the natural fiber pulp A, deionized water is added to dilute and stabilize the dispersion. Then, nanocellulose dispersion A and synthetic short fiber dispersion A are added sequentially and stirred to obtain the pulp A.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the natural fiber pulp A, the nanocellulose dispersion A, and the synthetic short fiber dispersion A is 1:(0.01-0.16):(0.2-0.8).

4. The preparation method according to claim 2, characterized in that, The freeness of the natural fiber pulp A is 10-40°SR; and / or The concentration of slurry A is 0.01-0.2 wt.%; and / or The natural fiber pulp A includes at least one or a combination of jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; and / or The synthetic short fiber dispersion A includes at least one of polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and / or The nanocellulose dispersion A includes at least one of cellulose nanocellulose dispersion and cellulose nanocrystal dispersion.

5. The preparation method according to claim 1, characterized in that, The preparation method of the B slurry includes the following steps: S121. After pulping the natural fiber pulp B, deionized water is added for dilution and stable dispersion. Then, nanocellulose dispersion B and synthetic short fiber dispersion B are added sequentially and stirred to obtain the B pulp.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the natural fiber pulp B, the nanocellulose dispersion B, and the synthetic short fiber dispersion B is 1:(0.025-0.5):(1-3.75).

7. The preparation method according to claim 5, characterized in that, The natural fiber pulp B has a freeness of 65-80°SR; and / or The concentration of the slurry is 0.02-0.1 wt.%; and / or The natural fiber pulp B includes at least one or a combination of jute pulp, sisal pulp, ramie pulp, softwood pulp, and hardwood pulp; and / or The synthetic short fiber dispersion B includes at least one of polyester short fiber dispersion, polyamide short fiber dispersion, polypropylene short fiber dispersion, polyvinylidene fluoride short fiber dispersion, and polyacrylonitrile short fiber dispersion; and / or The nanocellulose dispersion B includes at least one of cellulose nanocellulose dispersion and cellulose nanocrystal dispersion.

8. The preparation method according to claim 1, characterized in that, The pressing process is a segmented pressing process; The segmented pressing process includes a first-stage pressing process and a second-stage pressing process; The pressure of the first stage of pressing is 2-3 bar, and the pressure of the second stage of pressing is 4-6 bar.

9. The preparation method according to claim 1, characterized in that, The drying process is a segmented drying process; The segmented drying process includes a first-stage drying process, a second-stage drying process, and a third-stage drying process; The temperature of the first drying stage is 55-65℃, the temperature of the second drying stage is 85-95℃, and the temperature of the third drying stage is 100-115℃.

10. The preparation method according to claim 1, characterized in that, The preparation method further includes: S300, spray an aqueous reinforcing agent onto the surface of the solid electrolytic capacitor paper; the amount of the aqueous reinforcing agent sprayed is less than 3 wt.% of the mass of the solid electrolytic capacitor paper.

Images