Conductive polymer composite, preparation method and flexible direct current transmission grounding electrode

Abstract

The present application relates to the technical field of flexible direct current transmission equipment, and discloses a conductive polymer composite material, a preparation method and a flexible direct current transmission grounding electrode. The conductive polymer composite material provided by the present application has excellent conductive temperature regulation, heat conduction and heat dissipation, and environmental aging resistance, and provides a material basis for long-term stable service of the flexible direct current transmission grounding electrode. The flexible direct current transmission grounding electrode provided by the present application realizes temperature-sensitive self-adaptive resistance adjustment and efficient heat dissipation through a coating layer, effectively balances the current and temperature distribution inside the grounding electrode, avoids the risk of local overheating failure, and inhibits direct current anode corrosion of the metal core material by using the dense barrier effect of the polymer. The interface between the composite material and the metal core material is firmly combined, and cracking and peeling problems are less likely to occur. The resistance change is small under long-term direct current current-carrying conditions, the soil and seawater corrosion resistance is outstanding, the service life of the grounding electrode can be significantly prolonged, and the use requirements of large-capacity new energy flexible direct current transmission projects can be met.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission equipment technology, and in particular to a conductive polymer composite material, its preparation method, and a flexible DC transmission grounding electrode. Background Technology

[0002] With the large-scale development of new energy sources and the continued growth in demand for long-distance, high-capacity power transmission, traditional AC power transmission suffers from high losses, limited reactive power regulation, and weak system stability in long-distance transmission and multi-grid interconnection scenarios. Flexible DC transmission technology based on voltage source converters has become a core power transmission solution for new power systems due to its advantages such as independent active and reactive power control, adaptability to weak grids, multi-terminal networking, and friendly grid connection with new energy sources. Flexible DC systems generally adopt a bipolar transmission architecture. Under normal operating conditions, the positive and negative lines form a current loop; when a single pole fails or equipment is under maintenance, the system switches to single-pole operation. The DC grounding electrode serves as the core channel for earth return current, and its service performance directly determines the safety and service life of the entire power transmission system, requiring it to meet the requirements of decades of continuous DC operation.

[0003] Unlike AC grounding systems, which withstand long-term unidirectional direct current, flexible grounding electrodes experience continuous electron transfer, leading to severe electrochemical polarization, electrode corrosion, and Joule heat accumulation. Existing grounding electrode material systems all suffer from irreconcilable defects. Metal grounding electrodes, including steel, copper, and titanium alloys, offer excellent conductivity and machinability, but under long-term anodic conditions, continuous metal dissolution and loss occur, resulting in a reduction in grounding cross-sectional area and a gradual increase in grounding resistance. Copper-based materials have higher conductivity, but the anodic dissolution rate is faster, and the connection of dissimilar metals is prone to galvanic corrosion, making large-scale engineering applications prohibitively expensive. Carbon-based grounding electrodes, such as graphite and calcined petroleum coke, have good resistance to soil corrosion, but the materials are brittle and prone to cracking and damage during transportation, burial, and settling. Graphite anodes experience oxidation and gas generation losses during long-term operation, and connecting graphite to metal leads is difficult, leading to a surge in contact resistance and localized overheating failure at the connection point.

[0004] Metal oxide coating (MMO) electrodes, widely used in the industry, rely on noble metal oxides (such as RuO2 and IrO2) for electrochemical stability. However, the high cost of noble metal raw materials and the complex preparation process make them difficult to implement on a large scale in land-based flexible direct current engineering projects. The coating is extremely thin, making it prone to cracking and peeling under soil friction and current impact. After the coating is damaged, the substrate corrodes rapidly and locally. Furthermore, there is no targeted heat dissipation design, which cannot solve the problem of DC Joule heat accumulation. Ordinary conductive polymer-coated grounding electrodes rely on carbon fillers to improve conductivity and polymers to block corrosive media. However, the polymer matrix has extremely low thermal conductivity, and Joule heat cannot be dissipated under high current conditions, resulting in severe thermal aging of the material. Moreover, conventional conductive polymers lack temperature self-regulation capabilities. After local high-resistance areas heat up, the resistance further increases, forming a vicious cycle of current concentration and accelerated temperature rise. After long-term energization, the conductive network is reconstructed, the resistance drift is large, and the coating layer is prone to blistering, microcracks, or even interface peeling, leading to the failure of the metal core material's protection.

[0005] In summary, existing single-metal, carbon-based, precious metal-coated, and ordinary conductive polymer grounding electrodes cannot simultaneously achieve low resistivity, high thermal conductivity, electrothermal adaptive regulation, long-term corrosion resistance, high interfacial bonding strength, and low engineering cost. They are difficult to adapt to the operational requirements of high-capacity, long-service-cycle flexible DC transmission systems. Therefore, there is an urgent need to develop multifunctional integrated composite grounding electrode structures and manufacturing processes. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a conductive polymer composite material.

[0007] The second objective of this invention is to provide a method for preparing this conductive polymer composite material.

[0008] The third objective of this invention is to provide a flexible DC transmission grounding electrode.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a conductive polymer composite material, comprising, by mass percentage: a polymer matrix of 29%-64%; a negative temperature coefficient thermosensitive conductive filler of 8%-18%; a conjugated conductive polymer filler of 10%-22%; a graphene-hexagonal boron nitride thermally and electrically conductive filler of 15%-28%; and additives of 2%-4%. The negative temperature coefficient thermosensitive conductive filler enables the conductive polymer composite material to have a negative temperature coefficient of resistance in the range of 25-90℃.

[0010] In some embodiments of the present invention, the conductive polymer composite material comprises, by weight percentage, the following components: polymer matrix 35%-56%; negative temperature coefficient thermosensitive conductive filler 10%-16%; conjugated conductive polymer filler 13%-20%; graphene-hexagonal boron nitride thermally and electrically conductive filler 18%-25%; and additives 2%-4%.

[0011] In some embodiments of the present invention, the polymer matrix comprises, by weight percentage: 50%-80% polypropylene and 20%-50% thermoplastic elastomer.

[0012] In some preferred embodiments of the present invention, the polymer matrix comprises, by weight percentage: 55%-75% polypropylene and 25%-45% thermoplastic elastomer.

[0013] In some embodiments of the present invention, the thermoplastic elastomer includes at least one of styrene-based thermoplastic elastomers, thermoplastic polyurethane elastomers, and thermoplastic polyolefin elastomers.

[0014] Specifically, in the polymer matrix used in this invention, polypropylene is a non-polar polyolefin resin with saturated molecular chains and no active groups. It is chemically inert and not easily hydrolyzed or oxidized in acidic, alkaline, or saline-alkali soil environments. It has long-lasting weather resistance and corrosion resistance. Its melting temperature range matches the processing window of various functional fillers and is suitable for extrusion coating processes. The thermoplastic elastomer molecular chains contain hard segments and flexible soft segments. The microphase separation structure of the hard and soft segments gives the matrix both rigidity and high elasticity. It can rebound after being deformed under force, offsetting the interfacial stress generated by the thermal expansion and contraction of the conductive core and the coating layer, and preventing interfacial peeling and microcracks in the coating layer. In the molten state, the resin molecular chains wet the surface of various inorganic and organic fillers. After cooling and solidification, they form a continuous three-dimensional organic barrier, making it difficult for corrosive ions and water molecules to penetrate the dense polyolefin layer to reach the inner conductive core.

[0015] It should be noted that, in addition to the polypropylene + thermoplastic elastomer compound system, polypropylene, polyvinylidene fluoride, ethylene-vinyl acetate copolymer, polyamide, polyphenylene sulfide, thermoplastic polyurethane, polyolefin elastomer, EPDM rubber, silicone rubber, epoxy resin, polyurethane, and fluorosilicone resin can be used alone or in combination as polymer matrix. The replaced resin system must meet the requirements of fixing various functional fillers, blocking water and corrosive ions, adapting to the mechanical strength required for grounding electrode construction and service, and aging resistance and environmental stability. Thermoplastic resins can use melt blending + extrusion coating process, while thermosetting resins and general elastomers can be coated on the surface of conductive core material using processes such as dip coating, spraying, molding, winding, potting, and in-situ curing.

[0016] In some embodiments of the present invention, the negative temperature coefficient thermosensitive conductive filler comprises the following components by mass percentage: 55%-75% negative temperature coefficient thermosensitive semiconductor material, 24%-40% carbon-based conductive material, and 1%-7% interface modifier.

[0017] In some preferred embodiments of the present invention, the negative temperature coefficient thermosensitive conductive filler comprises the following components by mass percentage: 55%-65% negative temperature coefficient thermosensitive semiconductor material, 30%-40% carbon-based conductive material, and 3%-5% interface modifier.

[0018] In some embodiments of the present invention, the negative temperature coefficient thermosensitive semiconductor material is selected from at least one of manganese nickel oxide, manganese nickel cobalt oxide, manganese nickel copper oxide, manganese cobalt oxide, manganese oxide, nickel oxide, cobalt oxide, and copper oxide.

[0019] In some embodiments of the present invention, the carbon-based conductive material includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene.

[0020] In some preferred embodiments of the present invention, the carbon-based conductive material comprises the following components by mass percentage: 50%-60% conductive carbon black, 40%-50% conductive graphite, and 0%-10% carbon nanotubes.

[0021] In some embodiments of the present invention, the interface modifier includes at least one of silane coupling agents, titanate coupling agents, aluminate coupling agents, and zirconate coupling agents.

[0022] In some embodiments of the present invention, the concentration of the interface modifier is 1wt%-10wt%.

[0023] In some embodiments of the present invention, the negative temperature coefficient thermosensitive conductive filler is prepared by a method comprising the following steps: The negative temperature coefficient thermosensitive semiconductor material and the carbon-based conductive material are dried to remove moisture. Then, the negative temperature coefficient thermosensitive semiconductor material and the carbon-based conductive material are premixed. Then, the interface modifier is added in the form of spray. After stirring and mixing, the mixture is dried, crushed, and sieved to obtain the negative temperature coefficient thermosensitive conductive filler.

[0024] In some embodiments of the present invention, the drying temperature for the negative temperature coefficient thermosensitive semiconductor material and the carbon-based conductive material is selected from 80-120°C, and the drying time is selected from 2-6h.

[0025] In some embodiments of the present invention, the premixing speed is 500-1500 r / min and the time is 10-30 min.

[0026] In some embodiments of the present invention, the stirring and mixing temperature is 60-100°C and the time is 30-120 min.

[0027] In some embodiments of the present invention, the drying temperature is 80-110°C and the time is 4-10 hours.

[0028] Specifically, in the negative temperature coefficient thermosensitive conductive filler used in this invention, the negative temperature coefficient thermosensitive semiconductor material belongs to the variable valence transition metal oxide semiconductor category. As the temperature increases, lattice thermal vibration intensifies, and Mn... 2+ / Mn 3+ Co 2+ / Co 3+ Ni 2+ / Ni 3+ The migration rate and concentration of variable-valence ion carriers are simultaneously increased, and the macroscopic resistivity decreases significantly with increasing temperature, giving the filler a negative temperature coefficient characteristic. The carbon-based conductive material itself has stable conductivity and is interspersed between the negative temperature coefficient thermosensitive semiconductor materials to build a continuous conductive framework, which makes up for the high room temperature resistivity of the pure negative temperature coefficient thermosensitive semiconductor materials and ensures the conductivity of the grounding electrode at room temperature. The carbon nanotubes are used to connect adjacent conductive particles and reduce the percolation threshold of the conductive network. The interface modifier has a bifunctional structure of inorganic active end + organic compatibility end. The inorganic end (hydroxyl / alkoxy) can dehydrate and bond with the hydroxyl groups on the surface of the negative temperature coefficient thermosensitive semiconductor material and the carbon-based conductive material, while the organic end (alkyl, olefin long chain) can be entangled and compatible with the polymer matrix resin molecular chain, building a molecular-level transition layer between the inorganic filler and the organic matrix, realizing the transformation of the two phases from incompatible separation to a tightly integrated system, thereby eliminating the interfacial gap between the inorganic filler and the organic resin, achieving uniform dispersion of the filler and reducing interfacial contact resistance.

[0029] Negative temperature coefficient (NTC) thermosensitive conductive fillers form temperature-sensitive conductive channels in conductive polymer composites. When the local temperature of the composite increases, the migration ability of charge carriers is enhanced, which reduces the local resistance of the composite, thereby reducing the resistance loss in the corresponding area and promoting the redistribution of current and heat to adjacent areas. By adjusting the ratio of negative temperature coefficient thermosensitive semiconductor materials to carbon-based conductive materials, the composite material can exhibit a negative temperature coefficient of resistance in the range of 25-90℃, that is, the resistance value of the composite material at 90℃ is less than its resistance value at 25℃.

[0030] It should be noted that, in addition to the above-listed examples, negative temperature coefficient thermosensitive semiconductor materials may also include titanate semiconductors, and carbon-based conductive materials may also be composites of any negative temperature coefficient ceramic particles with conductive carbon black, conductive graphite, carbon nanotubes, graphene, and carbon fibers. As long as the composite powder can reduce the resistivity of the conductive polymer composite material after heating, thereby alleviating resistance drift and local heat accumulation under long-term DC current carrying, the technical effect of this invention can be achieved.

[0031] In some embodiments of the present invention, the conjugated conductive polymer filler comprises, by weight percentage, the following components: 20%-40% polyaniline, 40%-50% poly3,4-ethylenedioxythiophene:polystyrene sulfonate, and 15%-30% polybenzodifurandione.

[0032] In some preferred embodiments of the present invention, the conjugated conductive polymer filler comprises, by weight percentage: 25%-35% polyaniline, 42%-50% poly3,4-ethylenedioxythiophene: polystyrene sulfonate, and 20%-28% polybenzodifurandione.

[0033] In some embodiments of the present invention, the polyaniline (PANI) is doped polyaniline, and its form is selected from solid powder or polyaniline masterbatch; the dopant is selected from organic / inorganic protic acids such as hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, camphorsulfonic acid, and dodecylbenzenesulfonic acid; the dopant accounts for 15%-40% of the total mass of the doped polyaniline.

[0034] In some embodiments of the present invention, the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT: PSS) is selected from dried powder, concentrated slurry or polymer masterbatch.

[0035] In some embodiments of the present invention, the polybenzodifurandione (PBFDO) is selected from dried powder, concentrated slurry or polymer masterbatch.

[0036] In some embodiments of the present invention, the conjugated conductive polymer filler is prepared by a method comprising the following steps: Polyaniline, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, and polybenzodifuran dione were dried to remove water, and then the three were mixed evenly to obtain a conjugated conductive polymer filler.

[0037] In some embodiments of the present invention, the drying temperatures of the polyaniline, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, and polybenzodifuran dione are selected from 50-90°C, and the drying times are selected from 6-24h.

[0038] In some embodiments of the present invention, the mixing speed is 300-1000 r / min and the time is 10-30 min.

[0039] In some embodiments of the present invention, the volatile content of the conjugated conductive polymer filler is ≤2wt%.

[0040] Specifically, in the conjugated conductive polymer fillers used in this invention, all three types of materials are intrinsically conjugated conductive polymers with a continuous delocalized π-electron system in their molecular backbone. Under an applied DC electric field, π-electrons can migrate freely along the molecular chain, possessing inherent conductivity. Among them, the doped polyaniline molecules contain a large number of mobile proton carriers, which can be adsorbed onto the metal surface to form a passivation film, inhibiting metal oxidation and corrosion. PEDOT:PSS is a water-soluble conjugated polymer with excellent dispersibility, which can form long-range continuous conductive channels inside the resin. The large conjugated planar structure of polybenzodifuran diketone has a high carrier mobility, which can improve the conductivity stability in high-temperature environments. The conjugated conductive polymer filler forms molecular-level contact with the conductive core material surface, which can fill the microscopic gaps in the metal, eliminate the interfacial air insulation layer, and reduce the interfacial contact resistance. At the same time, it can also capture metal ions generated by metal ionization, reduce the outward diffusion of metal ions, and slow down the corrosion rate.

[0041] It should be noted that, in addition to the components listed above, the conjugated conductive polymer filler can also be selected from any single component or combination of conjugated intrinsic conductive polymers such as polypyrrole, polythiophene, PEDOT derivatives, poly(p-phenylene), poly(p-phenyleneacetylene), and polyacetylene. As long as such materials can form a continuous / quasi-continuous electron transport channel and have stable conductivity under long-term DC conditions, equivalent replacement can be achieved.

[0042] In some embodiments of the present invention, the graphene-hexagonal boron nitride thermally and electrically conductive filler comprises the following components by mass percentage: 25%-45% graphene, 40%-70% hexagonal boron nitride, and 5%-15% carbon nanotubes.

[0043] In some preferred embodiments of the present invention, the graphene-hexagonal boron nitride thermally and electrically conductive filler comprises the following components by mass percentage: 30%-40% graphene, 48%-62% hexagonal boron nitride, and 8%-12% carbon nanotubes.

[0044] In some embodiments of the present invention, the average sheet diameter of the graphene is 0.5-30 μm.

[0045] In some preferred embodiments of the present invention, the average sheet diameter of the graphene is 1-15 μm.

[0046] In some embodiments of the present invention, the average particle size of the hexagonal boron nitride is 0.5-50 μm.

[0047] In some preferred embodiments of the present invention, the average particle size of the hexagonal boron nitride is 2-20 μm.

[0048] In some embodiments of the present invention, the average length of the carbon nanotubes is 1-100 μm.

[0049] In some preferred embodiments of the present invention, the average length of the carbon nanotubes is 5-50 μm.

[0050] In some embodiments of the present invention, the graphene-hexagonal boron nitride thermally and electrically conductive filler is prepared by a method comprising the following steps: Graphene, hexagonal boron nitride, and carbon nanotubes are mixed with a dispersion medium. The resulting suspension is then subjected to high-speed shearing and ultrasonic dispersion in sequence. The resulting mixture is then subjected to solid-liquid separation and drying in sequence to obtain the graphene-hexagonal boron nitride thermally and electrically conductive filler.

[0051] In some embodiments of the present invention, the dispersion medium is selected from at least one of water, ethanol, and isopropanol.

[0052] In some embodiments of the present invention, the concentrations of graphene, hexagonal boron nitride, and carbon nanotubes in the suspension are 1wt%-8wt%.

[0053] In some embodiments of the present invention, the high-speed shearing rotation speed is 3000-8000 r / min and the time is 20-60 min.

[0054] In some embodiments of the present invention, the ultrasonic dispersion time is 30-120 min.

[0055] In some embodiments of the present invention, the drying method is selected from spray drying, vacuum drying or freeze drying.

[0056] Specifically, this invention first pre-assembles graphene, hexagonal boron nitride, and carbon nanotubes to form a three-dimensional thermally and electrically conductive synergistic network, which is then used in the preparation of conductive polymer composite materials. The graphene sheets possess ultra-high electron mobility and in-plane thermal conductivity, responsible for building the main electron conduction channels. Hexagonal boron nitride is a highly thermally conductive insulating sheet-like inorganic filler that does not interfere with the conductive pathway and is specifically used to transfer lattice vibration heat, achieving electrothermal separation and synergistic transmission. Carbon nanotubes act as a one-dimensional bridge, connecting the dispersed graphene and boron nitride sheets to form a continuous and interconnected three-dimensional network within the resin. This three-dimensional network penetrates the conductive polymer composite material, allowing the heat generated at local heating points to diffuse rapidly laterally and longitudinally along the boron nitride and graphene network, preventing heat from being trapped in local areas and forming high-temperature hotspots. In other words, the network structure interconnects the discrete conductive fillers, significantly increasing the density of the conductive pathway, reducing the overall resistance, and reducing the amount of Joule heat generated, forming a dual thermal management mechanism of low heat generation and rapid heat dissipation.

[0057] It should be noted that graphene can be replaced by one or more of expanded graphite, graphite nanosheets, reduced graphene oxide, carbon nanotubes, carbon fibers, carbon nanofibers, and conductive graphite. Hexagonal boron nitride can be replaced by one or more of corrosion-resistant and thermally conductive inorganic fillers such as aluminum nitride, silicon nitride, silicon carbide, alumina, magnesium oxide, and diamond micropowder. Graphene-hexagonal boron nitride thermally and electrically conductive fillers can be made into sheet, particle, fiber, or three-dimensional porous framework morphologies, achieving mutual bridging through carbon nanotubes, carbon fibers, and conductive polymers. As long as the filler system can simultaneously construct thermally and electrically conductive channels within the resin matrix and reduce local temperature rise, it possesses equivalent functions. The preparation methods of graphene-hexagonal boron nitride thermally and electrically conductive fillers are not limited to wet pre-assembly processes. Mechanical ball milling, dry high-speed mixing, electrostatic self-assembly, in-situ polymerization, spray drying, freeze drying, chemical vapor deposition, and three-dimensional framework impregnation methods can also be used to build continuous networks. As long as the process can improve the uniformity of filler dispersion and ensure the continuity and integrity of the conductive and thermally conductive network, it can be substituted.

[0058] In some embodiments of the present invention, the additives include at least one of compatibilizers, antioxidants, and lubricants.

[0059] In some embodiments of the present invention, the compatibilizer includes at least one of maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride-grafted elastomer.

[0060] In some embodiments of the present invention, the antioxidant includes at least one of hindered phenolic antioxidants and phosphite antioxidants.

[0061] In some embodiments of the present invention, the lubricant includes at least one of polyethylene wax, stearate, and silicone processing aid.

[0062] A second aspect of the present invention provides a method for preparing the conductive polymer composite material described in the first aspect of the present invention, comprising the following steps: First, the polymer matrix, the negative temperature coefficient thermosensitive conductive filler, and the additives are melt-blended in a first-stage process. Then, the conjugated conductive polymer filler and the graphene-hexagonal boron nitride thermally and electrically conductive filler are added for a second-stage melt-blending process. The mixture is then extruded and granulated to obtain the conductive polymer composite material.

[0063] In some embodiments of the present invention, the temperature of the first-order melt blending is 145-185°C, the rotation speed is 80-200 r / min, and the time is 2-6 min.

[0064] In some preferred embodiments of the present invention, the temperature of the first-order melt blending is 150-170°C, the rotation speed is 80-140 r / min, and the time is 2-4 min.

[0065] In some embodiments of the present invention, the temperature of the second-order melt blending is 145-200°C, the rotation speed is 50-180 r / min, and the time is 1-5 min.

[0066] In some preferred embodiments of the present invention, the temperature of the second-stage melt blending is 155-175°C, the rotation speed is 50-110 r / min, and the time is 1-3 min.

[0067] In some embodiments of the present invention, the first-stage melt blending and the second-stage melt blending are carried out in a mixer or a twin-screw extruder.

[0068] In some embodiments of the present invention, the extrusion process further includes a cooling operation; the granulation process further includes a drying operation; the drying temperature is 60-90°C, and the drying time is 2-8 hours.

[0069] Specifically, this invention employs a segmented melt blending method to prepare conductive polymer composite materials. By step-by-step feeding and differentiated temperature and shear control, on the one hand, the negative temperature coefficient thermosensitive conductive filler and the polymer matrix can be fully impregnated and dispersed in advance. On the other hand, the conjugated conductive polymer filler with poor heat resistance and the easily broken graphene-hexagonal boron nitride thermally and electrically conductive filler are added at a later, slower rate. This helps to completely preserve the original molecular / microscopic network structure of each functional component and prevent the degradation of conductivity, temperature sensitivity, and thermal conductivity. At the same time, it improves the dispersion uniformity of multiphase fillers, reduces local high-resistance hot spots, reduces long-term DC operation resistance drift, broadens the processing window, and improves the performance stability and molding quality of the grounding electrode product.

[0070] A third aspect of the present invention provides a flexible DC transmission grounding electrode, the flexible DC transmission grounding electrode comprising a conductive core material and a coating layer covering the outer surface of the conductive core material; wherein the coating layer is prepared from the conductive polymer composite material described in the first aspect of the present invention.

[0071] Specifically, the flexible DC transmission grounding electrode provided by the present invention has a coating layer that is continuously distributed along the circumference of the conductive core material and is tightly bonded to the outer surface of the conductive core material.

[0072] It should be noted that the coating layer is not limited to a single-layer homogeneous structure. A radial gradient structure can be designed, that is, the content of conjugated conductive polymer filler and compatibilizer is increased on the side closer to the conductive core material to enhance interfacial conductivity and adhesion; the content of negative temperature coefficient thermosensitive conductive filler, graphene-hexagonal boron nitride thermally conductive filler and polymer matrix is ​​increased on the outer side closer to the soil to enhance temperature control, heat dissipation and dielectric barrier capabilities; and segmented functional areas can also be set along the length of the grounding electrode. The filling amount of graphene-hexagonal boron nitride thermally conductive filler and negative temperature coefficient thermosensitive conductive filler is increased in the high current density section to balance the current distribution and temperature field of the entire grounding electrode.

[0073] In addition, a conductive bonding transition layer can be added between the conductive core material and the coating layer. The raw materials of the transition layer can be selected from conductive polymers, conductive carbon black, graphene, metal powder, epoxy resin, polyurethane, silane coupling agent, or single components or compounded materials. This transition layer is only used to improve the interfacial bonding force between the core material and the coating layer and reduce the interfacial contact resistance. It does not serve as an independent anti-corrosion protection layer and does not change the overall core structure of the outer coating layer of the conductive core material. It belongs to the extended alternative structure of this invention.

[0074] In some embodiments of the present invention, the outer diameter of the conductive core material is 4-30 mm.

[0075] In some preferred embodiments of the present invention, the outer diameter of the conductive core material is 8-24 mm.

[0076] In some more preferred embodiments of the present invention, the outer diameter of the conductive core material is 12-20 mm.

[0077] In some embodiments of the present invention, the thickness of the coating layer is 0.5-8 mm.

[0078] In some preferred embodiments of the present invention, the thickness of the coating layer is 1-5 mm.

[0079] In some preferred embodiments of the present invention, the thickness of the coating layer is 2-4 mm.

[0080] In some embodiments of the present invention, the conductive core material includes one of steel strand, low carbon steel rod, copper-clad steel rod, copper-clad steel strand, and titanium-based conductor.

[0081] In some preferred embodiments of the present invention, the conductive core material is selected from steel strand or copper-clad steel strand.

[0082] It should be noted that, in addition to the above-listed materials, conductive core materials can also be selected from stainless steel, pure copper, aluminum alloy, titanium-based conductors, galvanized steel, or composite conductive core materials of two or more metals; the cross-section of the conductive core material can be designed as circular, elliptical, polygonal, or other irregular shapes; the overall structure can be selected from solid rods, stranded wires, metal mesh, strips, or hollow tubes; to improve the interfacial bonding strength, roughening textures, grooves, and embossing can be processed on the surface of the core material, or metal mesh or bonding transition layer can be added.

[0083] In some embodiments of the present invention, the flexible DC transmission grounding electrode is prepared by a method comprising the following steps: The conductive core material is sequentially subjected to degreasing, acid pickling and activation, water washing and drying; The conductive polymer composite material is fed into an extrusion coating equipment, and the conductive core material is drawn through the coating die at a uniform speed, so that the molten conductive polymer composite material continuously and tightly coats the outer periphery of the conductive core material to form a coating layer. After cooling, shaping and winding, the flexible DC transmission grounding electrode is obtained.

[0084] In some embodiments of the present invention, the degreasing includes using an alkaline degreasing agent or an organic solvent, and the degreasing time is 5-20 minutes.

[0085] In some embodiments of the present invention, the acid washing activation includes using a 5wt%-15wt% hydrochloric acid solution, sulfuric acid solution, or phosphoric acid solution for a time of 2-10 minutes.

[0086] In some embodiments of the present invention, the cleaning includes using deionized water.

[0087] In some embodiments of the present invention, the drying temperature is 60-120°C and the time is 10-60 min.

[0088] In some embodiments of the present invention, after the drying process is completed, a silane coupling agent is coated on the surface of the conductive core material to improve the interfacial adhesion strength between the conductive core material and the coating layer.

[0089] In some embodiments of the present invention, the concentration of the silane coupling agent is 0.5wt%-2wt%.

[0090] In some embodiments of the present invention, the coating of the silane coupling agent further includes a drying process at 80-120°C for 10-30 minutes.

[0091] In some embodiments of the present invention, the extrusion coating temperature is 150-200°C and the screw speed is 30-150 r / min.

[0092] In some embodiments of the present invention, the traction speed of the conductive core material is 0.5-8 m / min.

[0093] In some embodiments of the present invention, the cooling and shaping temperature is 15-35°C.

[0094] Compared with the prior art, the beneficial effects of the present invention are: The conductive polymer composite material provided by this invention, through the synergistic combination of negative temperature coefficient thermosensitive conductive filler, conjugated conductive polymer filler, and graphene-hexagonal boron nitride thermally and electrically conductive filler, and relying on the resin matrix to support each functional component, can achieve an electrothermal self-regulating effect in the operating temperature range, where resistivity decreases with increasing temperature, suppressing local heat accumulation. It can also construct a continuous conductive-thermal dual channel to quickly dissipate Joule heat and reduce the overall resistivity. At the same time, through interface modification, the dispersion and interfacial bonding of each filler in the matrix are improved, reducing resistance drift under DC current. The resin matrix also provides excellent barrier protection capabilities, giving the composite material excellent conductive temperature regulation, thermal conductivity and heat dissipation, and environmental aging resistance, providing a material basis for the long-term stable service of flexible DC transmission grounding electrodes.

[0095] The flexible DC transmission grounding electrode provided by this invention uses a conductive core material as the main conductive component, and is covered with a coating layer formed by the aforementioned conductive polymer composite material. On the one hand, the coating layer enables temperature-sensitive adaptive resistance adjustment and efficient heat dissipation, effectively balancing the current and temperature distribution inside the grounding electrode and avoiding the risk of local overheating failure. On the other hand, the dense barrier effect of the polymer inhibits DC anodic corrosion of the metal core material. The interface between the composite material and the metal core material is firmly bonded, making it less prone to cracking and peeling. Under long-term DC current-carrying conditions, the resistance change is small, and the resistance to soil and seawater corrosion is outstanding, which can significantly extend the service life of the grounding electrode and meet the application requirements of large-capacity new energy flexible DC transmission projects. Attached Figure Description

[0096] Figure 1 The diagram shows the structure of the flexible DC transmission grounding electrode in Application Example 2, where 1-steel strand, 2-cladding layer, 3-negative temperature coefficient thermosensitive conductive filler, 4-graphene-hexagonal boron nitride thermally and electrically conductive filler, 5-polymer matrix, 6-direction of DC current transmission, and 7-direction of heat diffusion. Detailed Implementation

[0097] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0098] Note: 1. In Tables 1-3 corresponding to Examples 1-3, dosage 1 refers to the percentage content of each specific substance in the raw material, such as 80wt% polypropylene in Table 1, which means that the percentage content of polypropylene in the polymer matrix is ​​80%; dosage 2 refers to the percentage content of each raw material in the conductive polymer composite material, such as 64wt% polymer matrix in Table 1, which means that the percentage content of the polymer matrix in the conductive polymer composite material is 64%. 2. The average sheet diameter of the graphene used in the examples and comparative examples is 1-15 μm, the average particle size of the hexagonal boron nitride is 2-20 μm, and the average length of the carbon nanotubes is 5-50 μm. 3. The polyaniline used in the examples and comparative examples is dodecylbenzenesulfonic acid-doped polyaniline, and the amount of dodecylbenzenesulfonic acid used is 20% of the total mass of the dodecylbenzenesulfonic acid-doped polyaniline.

[0099] Example 1 This embodiment provides a conductive polymer composite material, and the raw materials and dosages are shown in Table 1 below: Table 1. Raw materials and dosages used in the preparation of the conductive polymer composite material in Example 1

[0100] The preparation steps of the conductive polymer composite material are as follows: Manganese nickel cobalt oxide, conductive carbon black and conductive graphite were dried at 80℃ for 2 hours, then placed in a high-speed mixer and premixed at 500 r / min for 10 minutes. Then, 5 wt% silane coupling agent solution was added in the form of spray, and stirring was continued at 60℃ for 30 minutes. After drying at 80℃ for 4 hours, the mixture was pulverized and sieved to obtain a negative temperature coefficient thermosensitive conductive filler. Polyaniline, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and polybenzodifurandione were vacuum dried at 50°C for 6 h, and then the three were mixed at 300 r / min for 10 min to obtain a conjugated conductive polymer filler. Graphene, hexagonal boron nitride, and carbon nanotubes were mixed with an ethanol / water solution (7:3, v / v) to obtain a suspension with a concentration of 2wt% of graphene, hexagonal boron nitride, and carbon nanotubes. The suspension was then dispersed for 20 min at 3000 r / min using a high-speed shearing device, followed by ultrasonic treatment for 30 min. The resulting mixture was filtered to collect the solid phase and then vacuum dried at 60 °C for 8 h to obtain a graphene-hexagonal boron nitride thermally and electrically conductive filler. First, the polymer matrix, negative temperature coefficient thermosensitive conductive filler, and additives are melt-blended at 150℃, with a screw speed of 80 r / min and a melt-blending time of 2 min. Then, conjugated conductive polymer filler and graphene-hexagonal boron nitride thermally and electrically conductive filler are added for a second-stage melt-blending at 155℃, with a screw speed of 50 r / min and a melt-blending time of 1 min. The resulting melt is extruded, cooled, pelletized, and dried at 60℃ for 3 h to obtain a conductive polymer composite material.

[0101] Example 2 This embodiment provides a conductive polymer composite material. The raw materials and dosages used in its preparation are shown in Table 2 below. Table 2. Raw materials and dosages used in the preparation of the conductive polymer composite material in Example 2

[0102] The preparation steps of the conductive polymer composite material are as follows: Manganese nickel cobalt oxide, conductive carbon black and conductive graphite were dried at 100℃ for 4 hours, then placed in a high-speed mixer and premixed at 1000 r / min for 20 minutes. Then, 5 wt% silane coupling agent solution was added in the form of spray, and stirring was continued at 80℃ for 75 minutes. After drying at 95℃ for 7 hours, the mixture was pulverized and sieved to obtain a negative temperature coefficient thermosensitive conductive filler. Polyaniline, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and polybenzodifurandione were vacuum dried at 70°C for 15 h, and then the three were mixed at 650 r / min for 20 min to obtain a conjugated conductive polymer filler. Graphene, hexagonal boron nitride, and carbon nanotubes were mixed with an ethanol / water solution (8:2, v / v) to obtain a suspension with a concentration of 5 wt% of graphene, hexagonal boron nitride, and carbon nanotubes. The suspension was then dispersed at 5500 r / min for 40 min using a high-speed shearing device, followed by ultrasonic treatment for 75 min. The resulting mixture was filtered to collect the solid phase and then vacuum dried at 80 °C for 10 h to obtain a graphene-hexagonal boron nitride thermally and electrically conductive filler. First, the polymer matrix, negative temperature coefficient thermosensitive conductive filler, and additives are melt-blended at 170℃, with a screw speed of 140 r / min and a melt-blending time of 4 min. Then, conjugated conductive polymer filler and graphene-hexagonal boron nitride thermally and electrically conductive filler are added for a second-stage melt-blending at 175℃, with a screw speed of 110 r / min and a melt-blending time of 3 min. The resulting melt is extruded, cooled, pelletized, and dried at 60℃ for 3 h to obtain a conductive polymer composite material.

[0103] Example 3 This embodiment provides a conductive polymer composite material. The raw materials and dosages used in its preparation are shown in Table 3 below. Table 3. Raw materials and dosages used in the preparation of the conductive polymer composite material in Example 3

[0104] The preparation steps of the conductive polymer composite material are as follows: Manganese nickel cobalt oxide, conductive carbon black and conductive graphite were dried at 90℃ for 6 hours, then placed in a high-speed mixer and premixed at 1300 r / min for 15 minutes. Then, 5 wt% silane coupling agent solution was added in the form of spray, and stirring was continued at 90℃ for 90 minutes. After drying at 100℃ for 5 hours, the mixture was pulverized and sieved to obtain a negative temperature coefficient thermosensitive conductive filler. Polyaniline, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and polybenzodifurandione were vacuum dried at 60 °C for 18 h, and then the three were mixed at 800 r / min for 15 min to obtain a conjugated conductive polymer filler. Graphene, hexagonal boron nitride, and carbon nanotubes were mixed with an ethanol / water solution (8:2, v / v) to obtain a suspension with a concentration of 5 wt% of graphene, hexagonal boron nitride, and carbon nanotubes. The suspension was then dispersed for 30 min at 7500 r / min using a high-speed shearing device, followed by ultrasonic treatment for 90 min. The resulting mixture was filtered to collect the solid phase and then vacuum dried at 80 °C for 10 h to obtain a graphene-hexagonal boron nitride thermally and electrically conductive filler. First, the polymer matrix, negative temperature coefficient thermosensitive conductive filler, and additives are melt-blended at 190℃, with a screw speed of 100 r / min and a melt-blending time of 5 min. Then, conjugated conductive polymer filler and graphene-hexagonal boron nitride thermally and electrically conductive filler are added for a second-stage melt-blending at 160℃, with a screw speed of 80 r / min and a melt-blending time of 3 min. The resulting melt is extruded, cooled, pelletized, and dried at 60℃ for 3 h to obtain a conductive polymer composite material.

[0105] Comparative Example 1 This comparative example provides a conductive polymer composite material, which differs from Example 2 only in that: No negative temperature coefficient thermosensitive conductive filler is added, and the filler is made up with an equal mass of polymer matrix.

[0106] Comparative Example 2 This comparative example provides a conductive polymer composite material, which differs from Example 2 only in that: No graphene-hexagonal boron nitride thermally and electrically conductive filler is added, and the remainder is made up with an equal mass of polymer matrix.

[0107] Comparative Example 3 This comparative example provides a conductive polymer composite material. The raw materials and their amounts are shown in Table 4 below: Table 4. Raw materials and dosages used in the preparation of the conductive polymer composite material in Comparative Example 3

[0108] The preparation steps of the conductive polymer composite material are as follows: First, polypropylene, thermoplastic polyolefin elastomer, conductive carbon black, conductive graphite, and additives are melt-blended at 190℃, with a screw speed of 100 r / min and a melt blending time of 5 min. Then, polyaniline is added for a second-stage melt blending at 160℃, with a screw speed of 80 r / min and a melt blending time of 3 min. The resulting melt is extruded, cooled, pelletized, and dried at 60℃ for 3 h to obtain a conductive polymer composite material.

[0109] Application Example 1 This application example provides a flexible DC transmission grounding electrode, and the preparation steps are as follows: The steel strand with an outer diameter of 4mm was first degreased with an alkaline degreasing agent, then activated by acid washing with 5wt% hydrochloric acid solution for 2 minutes, rinsed with deionized water and dried at 80℃ for 20 minutes. The conductive polymer composite material prepared in Example 1 was fed into an extrusion coating equipment. The extrusion coating temperature was set to 150°C and the screw speed was set to 100 r / min. The steel strand was pulled through the coating die at a uniform traction speed of 0.5 m / min, so that the molten conductive polymer composite material continuously and tightly coated the outer periphery of the steel strand to form a 0.5 mm thick coating layer. The coating layer was then water-cooled and shaped at 15°C and wound up to obtain a flexible DC transmission grounding electrode.

[0110] Application Example 2 This application example provides a flexible DC transmission grounding electrode, and the preparation steps are as follows: The steel strand with an outer diameter of 17mm was first degreased with an alkaline degreasing agent, then acid-washed and activated with a 10wt% hydrochloric acid solution for 6 minutes, cleaned with deionized water and dried at 80℃ for 20 minutes, and then coated with a 1wt% silane coupling agent solution and dried at 100℃ for 20 minutes. The conductive polymer composite material prepared in Example 2 was fed into an extrusion coating equipment. The extrusion coating temperature was set to 175°C and the screw speed was set to 100 r / min. The steel strand was pulled through the coating die at a uniform traction speed of 4 m / min, so that the molten conductive polymer composite material continuously and tightly coated the outer periphery of the steel strand, forming a 4.25 mm thick coating layer. The coating layer was then water-cooled and shaped at 25°C and wound up to obtain a flexible DC transmission grounding electrode.

[0111] Figure 1 This is a schematic diagram of the flexible DC transmission grounding electrode in Application Example 2.

[0112] Application Example 3 This application example provides a flexible DC transmission grounding electrode, and the preparation steps are as follows: The steel strand with an outer diameter of 12mm was first degreased with an alkaline degreasing agent, then acid-washed and activated with a 12wt% hydrochloric acid solution for 65 minutes, rinsed with deionized water, and dried at 80℃ for 20 minutes. The conductive polymer composite material prepared in Example 3 was fed into an extrusion coating equipment. The extrusion coating temperature was set to 200°C and the screw speed was set to 130 r / min. The steel strand was pulled through the coating die at a uniform traction speed of 6 m / min, so that the molten conductive polymer composite material continuously and tightly coated the outer periphery of the steel strand to form a 2.5 mm thick coating layer. The coating layer was then water-cooled and shaped at 18°C ​​and wound up to obtain a flexible DC transmission grounding electrode.

[0113] Application Comparative Example 1 This application provides a flexible DC transmission grounding electrode, and the preparation steps are as follows: The steel strand with an outer diameter of 17mm was first degreased with an alkaline degreasing agent, then acid-washed and activated with a 10wt% hydrochloric acid solution for 6 minutes, cleaned with deionized water and dried at 80℃ for 20 minutes, and then coated with a 1wt% silane coupling agent solution and dried at 100℃ for 20 minutes. The conductive polymer composite material prepared in Comparative Example 1 was fed into an extrusion coating equipment. The extrusion coating temperature was set to 175℃ and the screw speed was set to 100r / min. The steel strand was pulled through the coating die at a uniform traction speed of 4m / min, so that the molten conductive polymer composite material continuously and tightly coated the outer periphery of the steel strand to form a 4.25mm thick coating layer. The coating layer was then water-cooled and shaped at 25℃ and wound up to obtain a flexible DC transmission grounding electrode.

[0114] Application Comparative Example 2 This application provides a flexible DC transmission grounding electrode, and the preparation steps are as follows: The steel strand with an outer diameter of 17mm was first degreased with an alkaline degreasing agent, then acid-washed and activated with a 10wt% hydrochloric acid solution for 6 minutes, cleaned with deionized water and dried at 80℃ for 20 minutes, and then coated with a 1wt% silane coupling agent solution and dried at 100℃ for 20 minutes. The conductive polymer composite material prepared in Comparative Example 3 was fed into an extrusion coating equipment. The extrusion coating temperature was set to 175℃ and the screw speed was set to 100r / min. The steel strand was pulled through the coating die at a uniform traction speed of 4m / min, so that the molten conductive polymer composite material continuously and tightly coated the outer periphery of the steel strand, forming a coating layer with a thickness of 4.25mm. The coating layer was then water-cooled and shaped at 25℃ and wound up to obtain a flexible DC transmission grounding electrode.

[0115] Application Comparative Example 3 This application provides a flexible DC transmission grounding electrode, and the preparation steps are as follows: The steel strand with an outer diameter of 17mm was first degreased with an alkaline degreasing agent, then acid-washed and activated with a 10wt% hydrochloric acid solution for 6 minutes, cleaned with deionized water and dried at 80℃ for 20 minutes, and then coated with a 1wt% silane coupling agent solution and dried at 100℃ for 20 minutes. The conductive polymer composite material prepared in Comparative Example 3 was fed into an extrusion coating equipment. The extrusion coating temperature was set to 175℃ and the screw speed was set to 100r / min. The steel strand was pulled through the coating die at a uniform traction speed of 4m / min, so that the molten conductive polymer composite material continuously and tightly coated the outer periphery of the steel strand, forming a coating layer with a thickness of 4.25mm. The coating layer was then water-cooled and shaped at 25℃ and wound up to obtain a flexible DC transmission grounding electrode.

[0116] Performance testing 1. The conductive polymer composite materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. The test items and reference standards are as follows: 1) Volume resistivity at 25℃ / 60℃ / 90℃: Tested according to GB / T 15662-1995 "Test Method for Volume Resistivity of Conductive and Antistatic Plastics"; 2) Resistivity reduction rate at 25-90℃: The volume resistivity was measured in accordance with GB / T 15662-1995, and the resistance-temperature characteristic evaluation method was carried out in accordance with the resistance-temperature characteristic evaluation approach of GB / T 6663.1-2007 "Directly heated negative temperature coefficient thermistors Part 1: General Specification". 3) Thermal conductivity: The test was conducted in accordance with GB / T 42919.2-2025 "Determination of thermal conductivity and thermal diffusivity of plastics - Part 2: Transient planar heat source (heat plate) method"; 4) Maximum surface temperature during continuous power-on: Tested in accordance with GB / T 28706-2012 "Infrared thermal imaging testing method for nondestructive testing of mechanical and electrical equipment".

[0117] Table 5 Performance test results of conductive polymer composite materials in Examples 1-3 and Comparative Examples 1-3

[0118] Table 5 shows the performance test results of the conductive polymer composites in Examples 1-3 and Comparative Examples 1-3. As can be seen from Table 5, the conductive polymer composites obtained in Examples 1-3 all exhibited significant negative temperature coefficient resistivity characteristics in the temperature range of 25-90℃. Specifically, the volume resistivity of the composites in Examples 2 and 3 decreased from 2.8 × 10⁻⁶ at 25℃. -2 Ω·cm and 2.9×10 -2 Ω·cm decreased to 1.3 × 10 at 90℃ -2 The resistivity decreased by 53.6% and 55.2% respectively in Ω·cm; in Comparative Example 1, without the addition of a negative temperature coefficient thermosensitive conductive filler, the resistivity did not decrease with increasing temperature, but instead decreased from 3.0 × 10⁻⁶ Ω·cm at 25℃. -2 3.2 × 10 Ω·cm at 90℃ -2 The value of Ω·cm indicates that the negative temperature coefficient thermosensitive conductive filler enables the conductive polymer composite material to possess negative temperature coefficient of resistance characteristics within the range of 25-90℃; the thermal conductivity of the composite material in Example 2 is 2.31 W·(m·K). -1 The value was significantly higher than that of Comparative Example 2 (0.62 W·(m·K) without the addition of graphene-hexagonal boron nitride thermally and electrically conductive filler. -1 The results show that the three-dimensional network formed by the graphene-hexagonal boron nitride thermally and electrically conductive filler can construct continuous heat transfer channels in the polymer matrix, significantly improving the thermal diffusion capability of the composite material. Under the same DC current carrying conditions, the highest surface temperature of the composite material in Example 2 was 44.2℃, while the highest surface temperatures of Comparative Examples 1, 2, and 3 were 62.3℃, 73.9℃, and 79.6℃, respectively. This indicates that the negative temperature coefficient thermosensitive conductive filler and the graphene-hexagonal boron nitride thermally and electrically conductive filler can produce a synergistic effect. On the one hand, it reduces resistance loss by reducing the material resistance when the temperature rises. On the other hand, it rapidly diffuses the heat generated inside the composite material through the three-dimensional heat transfer network, thereby reducing local heat accumulation.

[0119] 2. Performance tests were conducted on the flexible DC transmission grounding electrodes corresponding to Case 1-3 and Application Comparison Example 1-3. Uncoated 17mm outer diameter steel strand, commercially available MMO electrodes, and commercially available graphite grounding electrodes were used for comparison. The test items and reference standards are as follows: 1) Corrosion rate after 4000h seawater immersion: Seawater exposure was tested according to JB / T 8424-1996 "Test method for corrosion of metal coatings and organic coatings in natural seawater", and the removal of corrosion products was carried out according to GB / T 16545-2025 "Corrosion of metals and alloys, removal of corrosion products on corrosion specimens". 2) Corrosion rate after 4000h burial in soil: The artificial soil burial test was conducted in accordance with SY / T 0029-2024 "Technical Specification for Application of Buried Steel Inspection Plates", and the removal of corrosion products was carried out in accordance with GB / T 16545-2025 "Corrosion of Metals and Alloys - Removal of Corrosion Products from Corrosion Specimens". 3) Resistance change rate after continuous energization for 10 hours: The test was conducted in accordance with GB / T 15662-1995 "Test Method for Volume Resistivity of Conductive and Antistatic Plastics". 4) Peel strength of the coating layer: The test shall be conducted in accordance with GB / T 7760-2003 "Determination of the bond strength between vulcanized rubber or thermoplastic rubber and rigid sheet material - 90° peel method". 5) Appearance after continuous power-on: Tested according to GB / T 1766-2008 "Rating Method for Aging of Paint and Varnish Coatings"; among which, The corrosion rate refers to the equivalent annual corrosion rate calculated based on the mass loss of the conductive core material after the coating layer is removed and the corrosion products on the surface of the conductive core material are cleared after the test. That is, the corrosion rate is calculated using the weight loss method. Each group has no less than 3 parallel samples, and the test results are expressed as the arithmetic mean. The resistance change rate after continuous DC energization for 10 hours is calculated based on the resistance measured before and after the test under the same temperature and humidity conditions, and the high temperature resistance value at the moment of power-on end is not used. Commercially available MMO electrodes and commercially available graphite grounding electrodes do not have the coating layer described in this invention, so the 90° peel strength test is not performed.

[0120] Table 6 Performance test results of flexible DC transmission grounding electrodes in Application Examples 1-3 and Comparative Application Examples 1-3

[0121] Table 6 shows the performance test results of the flexible DC transmission grounding electrodes in Application Examples 1-3 and Comparative Examples 1-3. As shown in Table 6, the corrosion rates of the grounding electrodes in Application Examples 1-3 and Comparative Examples 1-3 are both 0.001-0.003 mm / a, significantly lower than that of the uncoated steel strand. The corrosion rate of the steel strand in seawater is 0.13 mm / a, and in soil it is 0.5 mm / a, with obvious corrosion products appearing on the metal surface. This indicates that the coating layer formed by the conductive polymer composite material can effectively reduce the direct contact between the corrosive medium and the conductive metal core, inhibiting the corrosion of the metal core in the simulated service environment. The small difference in corrosion rates between Application Examples 1-3 and Comparative Examples 1-3 indicates that under the experimental conditions, each polymer coating system has a good medium barrier effect. Given that the seawater corrosion rates of Comparative Examples 2 and 3 are both 0.001 mm / a, slightly lower than those of Application Examples 1-3, this data is mainly used to demonstrate the anti-corrosion effectiveness of the coating layer relative to the exposed metal core, and not to demonstrate the negative temperature coefficient. Thermosensitive conductive fillers or graphene-hexagonal boron nitride thermally and electrically conductive fillers can further reduce the corrosion rate of the metal core material. After 10 hours of continuous DC energization, the resistance change rates of Application Examples 1-3 were 8.4%, 3.1%, and 3.4%, respectively, all lower than those of Comparative Examples 1-3. Among them, Application Example 2 had the lowest resistance change rate, at only 3.1%, which was approximately 77.2%, 84.0%, and 88.4% lower than that of Comparative Examples 1, 2, and 3, respectively. This result indicates that the negative temperature coefficient thermosensitive... The conductive filler, conjugated conductive polymer filler, and graphene-hexagonal boron nitride thermally and electrically conductive filler have a synergistic effect. The negative temperature coefficient thermosensitive conductive filler can adjust the conductivity state of the material with the temperature rise during energization. The graphene-hexagonal boron nitride thermally and electrically conductive filler can improve the continuity of electron transport and heat dissipation within the coating layer, thereby reducing local heat accumulation and conductive path failure, and reducing the change in material resistance during continuous DC current carrying. The peel strength of the coating layer of the grounding electrode in Application Examples 2 and 3 is 9.2 N·mm. -1 and 9.0 N·mm -1 The peel strength was higher than that of Application Example 1 and the comparative examples of each application, and no bubbling, cracking or peeling was observed after continuous power-on; the peel strength of the grounding electrode in Example 1 was 6.4 N·mm. -1 After continuous energization, no obvious cracking was observed, only slight surface discoloration, indicating that even at a low level of functional filler content, the resulting coating still possesses a certain degree of DC current-carrying stability. However, its interfacial bonding performance and resistance stability are lower than those of Application Examples 2 and 3. The resistance change rate of the grounding electrode in Comparative Example 1 after 10 hours of continuous energization was 13.6%, and localized hardening occurred. The resistance change rate of the grounding electrode in Comparative Example 2 was 19.4%, and microcracks appeared locally in the coating. The resistance change rate of the grounding electrode in Comparative Example 3 reached 26.7%, with a peel strength of only 5.1 N·mm.-1 The presence of cracks and localized interface separation indicates that while the corrosion barrier effect of the polymer matrix can reduce the corrosion rate of the metal core, it cannot fully guarantee the resistance stability and structural integrity of the material under continuous DC current conditions. When the composite material lacks negative temperature coefficient thermosensitive conductive fillers or graphene-hexagonal boron nitride thermally and electrically conductive fillers, it is more prone to increased resistance, hardening, microcracks, and interface separation due to localized temperature rise, conductive network reconstruction, or interface stress accumulation.

[0122] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A conductive polymer composite material, characterized in that, By weight percentage, it comprises the following components: polymer matrix 29%-64%; negative temperature coefficient thermosensitive conductive filler 8%-18%; conjugated conductive polymer filler 10%-22%; graphene-hexagonal boron nitride thermally and electrically conductive filler 15%-28%; additives 2%-4%; wherein... The negative temperature coefficient thermosensitive conductive filler enables the conductive polymer composite material to have a negative temperature coefficient of resistance in the range of 25-90℃.

2. The conductive polymer composite material according to claim 1, characterized in that, The polymer matrix comprises, by weight percentage, the following components: 50%-80% polypropylene and 20%-50% thermoplastic elastomer.

3. The conductive polymer composite material according to claim 1, characterized in that, By mass percentage, the negative temperature coefficient thermosensitive conductive filler comprises the following components: 55%-75% negative temperature coefficient thermosensitive semiconductor material, 24%-40% carbon-based conductive material, and 1%-7% interface modifier.

4. The conductive polymer composite material according to claim 3, characterized in that, The negative temperature coefficient thermosensitive semiconductor material includes at least one of manganese nickel oxide, manganese nickel cobalt oxide, manganese nickel copper oxide, manganese cobalt oxide, manganese oxide, nickel oxide, cobalt oxide, and copper oxide. And / or, the carbon-based conductive material includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene; And / or, the interface modifier includes at least one of silane coupling agents, titanate coupling agents, aluminate coupling agents, and zirconate coupling agents.

5. The conductive polymer composite material according to claim 1, characterized in that, The conjugated conductive polymer filler comprises, by weight percentage, the following components: 20%-40% polyaniline, 40%-50% poly3,4-ethylenedioxythiophene: polystyrene sulfonate, and 15%-30% polybenzodifurandione.

6. The conductive polymer composite material according to claim 1, characterized in that, The graphene-hexagonal boron nitride thermal and electrical conductive filler comprises the following components by mass percentage: 25%-45% graphene, 40%-70% hexagonal boron nitride, and 5%-15% carbon nanotubes.

7. The method for preparing the conductive polymer composite material according to any one of claims 1-6, characterized in that, Includes the following steps: First, the polymer matrix, the negative temperature coefficient thermosensitive conductive filler, and the additives are melt-blended in a first-stage process. Then, the conjugated conductive polymer filler and the graphene-hexagonal boron nitride thermally and electrically conductive filler are added for a second-stage melt-blending process. The mixture is then extruded and granulated to obtain the conductive polymer composite material.

8. A flexible DC transmission grounding electrode, characterized in that, It includes a conductive core material and a coating layer covering the outer surface of the conductive core material; wherein the coating layer is prepared from the conductive polymer composite material according to any one of claims 1-6.

9. The conductive polymer composite material according to claim 8, characterized in that, The outer diameter of the metal conductive core is 4-30 mm; And / or, the thickness of the coating layer is 0.5-8 mm.

10. The conductive polymer composite material according to claim 8, characterized in that, The conductive core material includes one of the following: steel strand, low carbon steel rod, copper-clad steel rod, copper-clad steel strand, and titanium-based conductor.

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