A conductive composite modified coating and a conductive composite modified separator comprising the same

Abstract

This invention discloses a conductive composite modified coating and a conductive composite modified membrane containing the same. The conductive composite modified coating includes an active material, a conductive agent, and a binder. The active material is micron-shaped WO3 and / or a micron-shaped WO3-based heterojunction. This application constructs an active regulating layer by combining micron-shaped WO3 or its heterojunction with conductive carbon. The micron-shaped structure provides active sites and buffers volume stress. Combined with the conductive agent, it effectively overcomes the insulation or semiconductor defects of the extremely poor intrinsic electronic conductivity of pure metal oxides. The conductive network support allows WO3 to fully participate in electrochemical reactions as an active component, thus improving K... + The deposition behavior is actively regulated and induced to avoid the problem of dendrites piercing the separator caused by disordered deposition. Through a strategy that combines morphology engineering and conductive network construction, the conductive composite modified coating can achieve long-term stable interface regulation of the conductive composite modified separator, thereby improving the long-term cycle stability and safety of alkali metal batteries.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a conductive composite modified coating and a conductive composite modified membrane comprising the same. Background Technology

[0002] With the rapid development of electric vehicles and large-scale energy storage systems, the demand for high-performance, low-cost rechargeable batteries is becoming increasingly urgent. While lithium-ion batteries have achieved widespread application, their uneven resource distribution and cost issues are becoming increasingly prominent. Potassium metal batteries not only possess extremely low standard electrode potential (-2.93 V vs. SHE) and high theoretical specific capacity (687 mAh g⁻¹), but also... -1 Potassium metal batteries (KMBs) offer significant cost advantages and are ideal next-generation anode materials for energy storage batteries. However, the practical application of KMBs still faces severe challenges. Potassium metal itself has extremely high intrinsic chemical reactivity, and during cycling, it undergoes continuous side reactions with organic electrolytes, making it difficult to form a uniform and stable solid electrolyte interphase (SEI) film on the anode surface. This not only causes a decrease in battery coulombic efficiency and rapid capacity decay, but also induces uneven potassium ion deposition, leading to uncontrolled dendrite growth. Continuous dendrite growth can even puncture the separator, causing internal short circuits and posing serious safety hazards.

[0003] To address these bottlenecks, existing research has proposed various modification strategies, including three-dimensional host structure design, electrolyte component regulation, and artificial SEI membrane construction. However, most of these strategies suffer from complex preparation processes, high production costs, and poor compatibility with existing battery industrial production lines, making large-scale promotion difficult. The separator, as a key core component inside the battery, plays a crucial role in physically isolating the positive and negative electrodes to prevent internal short circuits and providing a continuous transport channel for ions. It is in direct contact with the potassium metal negative electrode, and the interfacial physicochemical properties of the separator directly determine the deposition behavior of potassium ions and the long-term cycle stability of the battery. Currently, GF separators are mostly used in KMB laboratory research. While these separators have good electrolyte affinity, their thickness is typically hundreds of micrometers, resulting in low mechanical strength and high brittleness. This not only severely compromises the battery's energy density but also makes them unsuitable for industrial winding production processes, failing to meet the basic requirements for large-scale applications. Commercial polyolefin separators, such as PP and PE, offer numerous advantages, including thinness, high mechanical strength, low cost, and compatibility with automated winding production processes, making them the mainstream separator substrate for large-scale energy storage battery applications. However, these types of separators have non-polar surfaces, resulting in poor wettability with electrolytes commonly used in KMBs. Furthermore, their internal pore distribution is not uniform, easily leading to localized ion concentrations during cycling, further exacerbating the uneven growth of potassium dendrites, making them unsuitable for direct KMB applications. To address the bottlenecks in the application of polyolefin separators in KMB systems, existing research often modifies them by coating the surface with inorganic ceramic particles (such as Al2O3). However, this modification method only initially improves wettability and provides basic passive physical barrier functions, failing to fundamentally solve the problem of interfacial chemical instability. Existing metal oxide coatings mostly exhibit conventional nano / micron particle structures, lacking internal stress release space. During battery cycling, the drastic volume changes of the metal anode easily cause them to peel off, thus completely losing their protective function. Furthermore, pure metal oxides have extremely poor intrinsic electronic conductivity. Single metal oxides typically possess semiconductor or insulating properties. If they are directly coated onto the surface of the separator, due to the lack of an electronic conductive network, they not only cannot actively intervene in and optimize the electrochemical environment of the interface, but will also greatly increase the interfacial internal resistance of the battery, making it difficult for the battery to maintain normal charge and discharge cycles.

[0004] Therefore, developing a novel composite modified membrane that can actively participate in and regulate interfacial chemical reactions, possess both structural stability and conductive network support, and can operate stably for a long time is a key technical problem that urgently needs to be solved in the current KMBs field. Providing a suitable conductive composite modified coating is the key to achieving long-term stable interfacial regulation of conductive composite modified membranes. Summary of the Invention

[0005] In view of this, this application provides a conductive composite modified coating and a conductive composite modified diaphragm containing the same, to solve the problem of how to achieve long-term stable interface control of the conductive composite modified diaphragm.

[0006] To achieve the above technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a conductive composite modified coating, comprising an active material, a conductive agent, and a binder; the active material is micron-shaped WO3 and / or micron-shaped WO3-based heterojunctions.

[0007] Preferably, the micron-shaped WO3 is a three-dimensional open flower-like structure formed by the self-assembly of two-dimensional nanosheets; the micron-shaped WO3-based heterostructure is one or more of Bi2O3 / WO3 heterostructure and WS2 / WO3 heterostructure.

[0008] Preferably, the mass ratio of active material, conductive agent and binder is (5~9):(0.5~2.5):(0.5~2.5); the dry thickness of the conductive composite modified coating is 5~20 μm.

[0009] A preferred method for preparing micron-sized flower-shaped WO3 is as follows: Ammonium metatungstate is dissolved in deionized water, nitric acid solution is added, and a hydrothermal reaction is carried out to obtain micron-sized flower-shaped WO3 powder.

[0010] The preferred method for preparing micron-shaped WO3-based heterojunctions is as follows: micron-shaped WO3 powder is dispersed in a nitric acid solution of bismuth salt or an aqueous solution of a sulfur-containing compound, and a hydrothermal reaction is carried out to obtain micron-shaped WO3-based heterojunctions.

[0011] Preferably, the hydrothermal reaction temperature is 110~220 ℃ and the reaction time is 6~48 h.

[0012] Preferably, the bismuth salt is one or more of bismuth nitrate pentahydrate and bismuth chloride; the sulfur-containing compound is one or more of thioacetamide, thiourea, and sodium sulfide.

[0013] Secondly, this application provides a conductive composite modified membrane with a conductive composite modified coating, comprising a porous substrate membrane and a conductive composite modified coating coated on at least one surface thereon.

[0014] Thirdly, this application provides a method for preparing a conductive composite modified membrane, comprising mixing an active substance, a conductive agent, and a binder, adding an organic solvent to mix, and obtaining a slurry; coating the slurry onto the surface of a porous substrate membrane, and drying it to obtain the conductive composite modified membrane.

[0015] Fourthly, this application provides an application of a conductive composite modified separator in alkali metal secondary batteries.

[0016] The beneficial effects of this application are as follows: This application constructs an active regulation layer by combining micron-shaped WO3 or its heterojunction with conductive carbon. The micron-shaped structure provides active sites and buffers volumetric stress. Combined with conductive agents, it effectively overcomes the insulation or semiconductor defects of the extremely poor intrinsic electronic conductivity of pure metal oxides. The conductive network support allows WO3 to fully participate in electrochemical reactions as an active component, thus improving the performance of K+. + The deposition behavior is actively regulated and induced to avoid the problem of dendrites piercing the separator caused by disordered deposition. Through a strategy that combines morphology engineering and conductive network construction, the conductive composite modified coating can achieve long-term stable interface regulation of the conductive composite modified separator, thereby improving the long-term cycle stability and safety of alkali metal batteries. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0018] Figure 1 The images show SEM images of the micron-shaped WO3 prepared in Examples 1-3 and the different heterojunction composite materials based on micron-shaped WO3, and the granular WO3 and rod-shaped WO3 prepared in Comparative Examples 4-5.

[0019] Figure 2 The images show the XRD patterns of the micron-shaped WO3 and different heterojunction composite materials based on micron-shaped WO3 prepared in Examples 1-3, and the granular WO3 and rod-shaped WO3 prepared in Comparative Examples 4-5.

[0020] Figure 3 The graphs show a comparison of the long-cycle performance of potassium metal full cells assembled with the membranes of Examples 1-3 and Comparative Examples 1-5, respectively. Detailed Implementation

[0021] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0022] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0025] Unless otherwise explicitly defined and specified herein, all technical and scientific terms used in this application shall have the generally accepted meanings understood by one of ordinary skill in the field of chemical and chemical materials technology (including but not limited to polymer chemistry, inorganic chemistry, organic synthesis, catalysis chemistry, materials processing, and chemical unit operations) based on their professional knowledge and conventional practice. The use of any terminology herein is intended to describe the specific embodiments of this application in the clearest and most accurate manner, so as to fully disclose the technical solution. Such use shall not in any way be construed as a limitation on the scope of the claims, nor does it imply the exclusion of equivalent technical solutions that could be reasonably known by one of skill in the art based on the concept of this application.

[0026] The terms "comprising," "including," "having," "containing," and any grammatical variations or similar expressions used in the specification, claims, and drawings of this application are all open-ended and non-exhaustive descriptive terms. Their purpose is to clearly describe the existence of technical features, components, steps, or parts, while explicitly allowing and covering the possibility that other features, components, steps, parts, or any combinations thereof not explicitly listed may exist or be added to the technical solution, as long as such additions do not destroy the integrity and inventiveness of the original technical solution.

[0027] When the terms "embodiments," "some embodiments," or "specific embodiments" are mentioned in the specification, they refer to examples that, in conjunction with the specific parameters, materials, steps, and results described in that section, constitute one or a group of examples for implementing the technical solutions of this application. These embodiments are used for full disclosure and illustrative purposes, not for exhaustive enumeration. Those skilled in the art should understand that, without departing from the overall inventive concept of this application, the various technical features disclosed in different embodiments can be combined, substituted, modified, or deleted to form other implementation methods that are not listed one by one in the specification but also fall within the protection scope of this application.

[0028] Unless otherwise expressly specified and limited, all terms related to chemical process operations, material preparation, processing and analytical testing involved in this application shall be interpreted in the broadest sense based on the conventional understanding of those skilled in the art.

[0029] Regarding performance testing and structural characterization, all testing and characterization methods involved in this application, unless otherwise specified, refer to conventional methods known in the art. Specific testing conditions may be selected and adjusted according to the sample properties and relevant national standards, international standards, or industry-standard methods. Test items may include mechanical properties (such as tensile, bending, and impact strength), thermal properties (such as DSC and TGA analysis), and chemical stability (such as solvent resistance and acid / alkali corrosion resistance). Structural characterization methods may include FT-IR, NMR, XRD, SEM, TEM, and BET. All test results should be understood to be within the allowable range of conventional experimental errors.

[0030] Regarding numerical values ​​and ranges, all parameter ranges expressed in this application in the form of "from a certain value to a certain value" should be understood as explicitly disclosing the endpoints of the range, every specific numerical point between the endpoints, and all sub-ranges formed by any two numerical points within the range. For example, "30 ℃ to 80 ℃" discloses 30, 31, ..., 80 ℃, as well as sub-ranges such as 30-50 ℃, 45-70 ℃, etc. When a numerical value is preceded by "about," "approximately," or similar words, it indicates that the numerical value is allowed to have reasonable errors recognized in the art under the measurement or control conditions, which can generally be understood as the deviation allowed by relevant standards or a normal fluctuation range of ±5% or ±10%.

[0031] This application provides a conductive composite modified coating, comprising an active material, a conductive agent, and a binder; the active material is micron-shaped WO3 and / or micron-shaped WO3-based heterojunctions.

[0032] This invention constructs an active regulating layer by combining micron-sized flower-like WO3 or its heterojunction with conductive carbon, effectively overcoming the insulation or semiconductor defects of pure metal oxides with extremely poor intrinsic electronic conductivity. The conductive network support allows WO3 to fully participate in electrochemical reactions as an active component, thus improving the performance of K+. + The deposition behavior is actively regulated and induced to avoid the problem of dendrites piercing the separator caused by disordered deposition. Through a strategy that combines morphology engineering and conductive network construction, the conductive composite modified coating can achieve long-term stable interface regulation of the conductive composite modified separator, thereby improving the long-term cycle stability and safety of alkali metal batteries.

[0033] In some embodiments, the micron-shaped WO3 is a three-dimensional open flower-like structure formed by the self-assembly of two-dimensional nanosheets; the micron-shaped WO3-based heterostructure is one or more of Bi2O3 / WO3 heterostructure and WS2 / WO3 heterostructure.

[0034] In this embodiment, the micron-sized flower-like WO3 is formed by the self-assembly of two-dimensional nanosheets into a three-dimensional open flower-like hierarchical structure. This hierarchical structure possesses the advantages of nanosheet materials, such as large specific surface area and abundant active sites, enabling uniform adsorption and flux control of alkali metal ions. It also possesses the mechanical stability of a micron-scale structure, effectively buffering the drastic volume changes of the metal anode during battery cycling and preventing coating collapse and peeling. The micron-sized flower-like WO3, formed by the self-assembly of two-dimensional nanosheets into a three-dimensional open configuration, provides both a large specific surface area and abundant K+. + By embedding active sites, a uniform ion flux distribution is achieved, avoiding excessively high local current density and overpotential accumulation during cycling. At the same time, the three-dimensional flower-like structure effectively buffers the volumetric stress during cycling and provides stress release space, completely overcoming the defect that conventional particulate or rod-shaped oxide coatings are prone to peeling and loss of protective function.

[0035] In this embodiment, the further constructed micron-shaped Bi₂O₃ / WO₃ or WS₂ / WO₃ heterojunction can form a built-in electric field at the heterojunction interface, accelerating K2. + Transport dynamics, lowering the nucleation energy barrier, guiding K + This achieves more uniform deposition, further improving the electrochemical performance of the battery.

[0036] In some embodiments, the mass ratio of active material, conductive agent and binder is (5~9):(0.5~2.5):(0.5~2.5); the dry thickness of the conductive composite modified coating is 5~20 μm.

[0037] In this embodiment, the formulation can ensure that the active material fully exerts its interface regulation function, while constructing a continuous and stable electronic conductive network and ensuring excellent adhesion between the coating and the substrate separator, thus preventing the coating from falling off and failing during battery cycling. The dry thickness, within a limited range, can fully exert the dual functions of the coating's interface regulation and physical barrier without significantly sacrificing the battery's energy density.

[0038] In some embodiments, the mass ratio of active material, conductive agent, and binder is 8:1:1; the dry thickness of the conductive composite modified coating is 10 μm.

[0039] In some embodiments, the conductive agent is used to construct a continuous electronic conductive network inside the coating, overcoming the core defects of low intrinsic conductivity and high interfacial resistance of pure metal oxides. The conductive agent is at least one of acetylene black, Super P, Ketjen black, carbon nanotubes, and graphene, preferably acetylene black. The binder is used to ensure the bonding stability between the components inside the coating and between the coating and the substrate membrane. The binder is at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), preferably PVDF.

[0040] In some embodiments, the preparation method of micron-shaped WO3 is as follows: Ammonium metatungstate is dissolved in deionized water, nitric acid solution is added, the mixture is stirred evenly and then placed in a hydrothermal reactor. After high-temperature hydrothermal reaction, micron-shaped WO3 powder is obtained.

[0041] In this embodiment, the active material is synthesized by hydrothermal method and modified separator is prepared by mature coating process. The preparation process is simple and controllable, the raw material cost is low, and it is fully compatible with commercial polyolefin separator substrate and existing battery industrial winding production process.

[0042] In some embodiments, the ratio of ammonium metatungstate to deionized water is (1~5 g):40 mL, preferably 2.26 g:40 mL; the nitric acid solution is nitric acid with a mass fraction of 10~65 wt%, preferably 65 wt%, and the added volume is 1~20 mL, preferably 10 mL; the hydrothermal reaction temperature is 110~220 ℃, the reaction time is 6~48 h, and the hydrothermal reaction conditions for preparing micron-shaped WO3 are preferably 24 h at 180 ℃.

[0043] In some embodiments, the preparation method of micron-shaped WO3-based heterojunction is as follows: micron-shaped WO3 powder is dispersed in a nitric acid solution containing bismuth salt or an aqueous solution containing sulfur compound, and then subjected to a high-temperature hydrothermal reaction to obtain micron-shaped WO3-based heterojunction.

[0044] In this embodiment, both heterojunctions are prepared by growing a second phase material on the surface of micron-shaped WO3 using an in-situ hydrothermal process. This process can retain the original micron-shaped hierarchical structure while forming a built-in electric field at the heterojunction interface, accelerating the alkali metal ion transport dynamics and further optimizing the ion deposition behavior.

[0045] In some embodiments, the hydrothermal reaction temperature is 110~220 °C, the reaction time is 6~48 h, and the hydrothermal reaction conditions for preparing micron-shaped Bi2O3 / WO3 heterojunctions are preferably 24 h at 180 °C; the hydrothermal reaction conditions for preparing micron-shaped WS2 / WO3 heterojunctions are preferably 24 h at 160 °C.

[0046] In some embodiments, the hydrothermal reaction temperature is 110~220 °C and the reaction time is 6~48 h.

[0047] In some embodiments, the bismuth salt is one or more of bismuth nitrate pentahydrate and bismuth chloride, preferably bismuth nitrate pentahydrate; the sulfur-containing compound is one or more of thioacetamide, thiourea, and sodium sulfide, preferably thioacetamide.

[0048] This application provides a conductive composite modified membrane with a conductive composite modified coating, comprising a porous substrate membrane and a conductive composite modified coating coated on at least one surface thereon.

[0049] The conductive composite modified coating of this application transforms the traditional inert membrane into an electrochemical regulator with active interface control capability, so as to achieve long cycle life and high safety of KMBs. It solves the problems of interfacial chemical instability, uncontrollable dendrite growth and oxide coating easy peeling, poor conductivity and difficulty in actively controlling interfacial reaction in existing polyolefin membrane modification strategies.

[0050] In some embodiments, a conductive composite modified coating is applied to the surface opposite the metal anode during battery assembly to achieve direct control and long-term protection of the metal anode / electrolyte interface.

[0051] In some embodiments, the porous substrate membrane is a commercially available porous polyolefin membrane for secondary batteries, which can be any one of PP membrane, PE membrane, or PP / PE composite membrane, and has the characteristics of thin thickness, high mechanical strength, controllable porosity, and suitability for industrial winding production. Those skilled in the art can also select other porous membranes for batteries, such as GF membranes or non-woven membranes, as the substrate according to actual application requirements, all of which fall within the scope of protection of this invention.

[0052] This application provides a method for preparing a conductive composite modified diaphragm, including the preparation of active material, preparation of composite slurry, diaphragm coating and post-treatment: the active material, conductive agent and binder are mixed and mixed with an organic solvent to obtain a slurry; the slurry is coated on at least one surface of a porous substrate diaphragm and dried to obtain a conductive composite modified diaphragm.

[0053] In some embodiments, the organic solvent is at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and deionized water, preferably NMP.

[0054] Specifically, the preparation method of the conductive composite modified separator is as follows: The first part, the preparation of active substances, consists of two steps: the preparation of micron-sized flower-like WO3 and the construction of optional heterostructures.

[0055] Preparation of micron-sized flower-like WO3: A one-step hydrothermal method was used for synthesis, with ammonium metatungstate as the tungsten source, nitric acid as the morphology modifier, and deionized water as the solvent. Specifically: Ammonium metatungstate is dissolved in deionized water and stirred until completely dissolved. Then, concentrated nitric acid solution is added, and the mixture is continuously stirred magnetically for 30–90 min to obtain a homogeneous and transparent precursor solution. The ratio of ammonium metatungstate to deionized water is controlled at (1–5 g):40 mL, preferably 2.26 g:40 mL. The concentrated nitric acid used is a 10–65 wt% aqueous solution, preferably 65 wt%, with an added volume of 1–20 mL, preferably 10 mL. The addition of nitric acid allows for precise control of the hydrolysis and crystallization process of the precursor, which is crucial for forming a three-dimensional micron-like hierarchical structure. The precursor solution is transferred to a stainless steel high-pressure reactor with a polytetrafluoroethylene substrate, sealed, and placed in a forced-air drying oven. The reactor is then reacted at a constant temperature of 110–220 °C for 6–48 h, preferably 180 °C for 24 h. During the hydrothermal reaction, the precursor completes crystallization, directional growth, and self-assembly under high temperature and pressure, forming a stable micron-like flower structure. After the reactor has cooled to room temperature, the bottom precipitate is collected by high-speed centrifugation. It is then washed 3-5 times with deionized water and anhydrous ethanol to remove residual unreacted raw materials and impurities. Finally, the washed product is dried in a vacuum oven at 40-80 ℃ for 6-24 h and then ground to obtain micron-sized flower-shaped WO3 powder.

[0056] Preparation of micron-shaped WO3-based heterojunctions: A two-stage in-situ hydrothermal method was used to construct the heterojunctions. Using pre-prepared micron-shaped WO3 as the matrix, Bi2O3 was grown by bismuth salt hydrolysis and WS2 was grown by sulfurization with sulfur-containing compounds, respectively, while preserving the original micron-shaped structure. When preparing the Bi2O3 / WO3 heterojunction, bismuth pentahydrate was used as the bismuth source, concentrated nitric acid as the co-solvent, and deionized water as the solvent. The bismuth salt was dissolved in concentrated nitric acid solution, diluted with deionized water, and stirred until homogeneous. Then, the pre-prepared micron-shaped WO3 powder was added, and the mixture was continuously magnetically stirred for 30–90 min to ensure uniform dispersion of the WO3 powder, obtaining a precursor dispersion. The precursor dispersion was transferred to a high-pressure reactor and hydrothermally reacted at 110–220 °C for 6–48 h, preferably at 180 °C for 24 h. After the reaction, the mixture was centrifuged, washed, and vacuum dried to obtain the micron-shaped Bi2O3 / WO3 heterojunction powder. When preparing WS2 / WO3 heterojunctions, thioacetamide is used as the sulfur source and deionized water is used as the solvent. Thioacetamide is dissolved in deionized water and stirred until completely dissolved. Then, pre-prepared micron-shaped WO3 powder is added and continuously magnetically stirred for 30-90 min to obtain a uniformly dispersed precursor dispersion. The precursor dispersion is transferred to a high-pressure reactor and hydrothermally reacted at 110-220 °C for 6-48 h, preferably at 160 °C for 24 h. During the reaction, thioacetamide decomposes to release sulfur ions, which react with tungsten atoms on the WO3 surface to grow WS2 in situ. Finally, after centrifugation, washing, and vacuum drying, micron-shaped WS2 / WO3 heterojunction powder is obtained.

[0057] Part Two: Preparation of the Composite Slurry. The micron-sized flower-shaped WO3 powder or its heterojunction powder prepared above is weighed together with the conductive agent and binder at a predetermined mass ratio and added to a container. An appropriate amount of organic solvent is added, and the mixture is dispersed uniformly using any one of the following methods: micro-vibration ball milling, high-speed shear dispersion, or ultrasonic dispersion, to obtain a viscous composite slurry with a viscosity suitable for the coating process. The organic solvent can be one or a combination of NMP, DMF, and deionized water, with NMP being preferred. The solid content of the slurry can be controlled within the range of 10% to 30%, and can be flexibly adjusted according to the actual needs of the coating process.

[0058] Part Three: Membrane Coating and Post-treatment. Any coating process among blade coating, slot coating, dip coating, and spray coating is used, with blade coating being the preferred method as it is suitable for both laboratory research and industrial mass production. The prepared composite slurry is uniformly coated onto at least one surface of the porous substrate membrane. The coating thickness is controlled by adjusting the coating parameters, ensuring that the dry coating thickness is within the range of 5–20 μm. After coating, the wet membrane is dried in a vacuum oven at 40–80 °C for 6–48 h to completely remove organic solvents while ensuring a tight bond between the coating and the substrate membrane. After drying, the modified membrane is cut into circular or square pieces of the corresponding size according to the specifications of the target battery and stored in a dry environment for later use, thus obtaining the conductive composite modified membrane based on micron-shaped tungsten oxide and its heterojunctions of this invention.

[0059] This application provides an application of a conductive composite modified separator in alkali metal secondary batteries.

[0060] When the modified separator of this invention is applied to potassium metal batteries, it can completely suppress the soft short circuit phenomenon during cycling. The battery still maintains a high discharge capacity in 500 long cycles, and the coulombic efficiency is stably maintained at around 100% without significant fluctuations. At the same time, it solves the problem of internal short circuit caused by dendrites piercing the separator, and greatly improves the long cycle life and safety of alkali metal batteries.

[0061] In some embodiments, alkali metal secondary batteries include potassium metal batteries, lithium metal batteries, and sodium metal batteries.

[0062] In some embodiments, the alkali metal secondary battery is a potassium metal battery, which mainly consists of a positive electrode, a negative electrode, an electrolyte, and the aforementioned conductive composite modified separator. The negative electrode is preferably potassium foil, but potassium alloys, potassium-carbon composite negative electrodes, etc., can also be used. The positive electrode can be selected from mainstream potassium battery positive electrode materials such as potassium Prussian blue, polyanionic positive electrode materials, layered oxide positive electrode materials, and organic positive electrode materials, with potassium Prussian blue (KPB) being the preferred choice. The electrolyte is an organic electrolyte containing dissolved potassium salts. Potassium salts can be selected from potassium hexafluorophosphate (KPF6), potassium bis(fluorosulfonyl)imide (KFSI), potassium bis(trifluoromethanesulfonyl)imide (KTFSI), etc., and the organic solvent can be selected from one or more combinations of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. Battery assembly must be completed in an argon atmosphere glove box with water and oxygen content both below 0.1 ppm. During assembly, the side of the modified separator with the composite modified coating should be placed facing the metal negative electrode to achieve the best interface control effect.

[0063] The following specific embodiments further illustrate this solution.

[0064] Example 1 A micron-shaped WO3 conductive composite modified separator is prepared by the following steps: (1) Dissolve 2.26 g of ammonium metatungstate in 40 mL of deionized water, stir well, and then add 10 mL of 65 wt% nitric acid solution. Stir the resulting mixture magnetically for 60 min to obtain a precursor solution. Then, transfer the solution to a 100 mL stainless steel high-pressure reactor with a polytetrafluoroethylene substrate, seal it, and place it in a forced-air drying oven for hydrothermal reaction at 180°C for 24 h. After the reactor cools naturally to room temperature, collect the bottom precipitate by centrifugation, wash it three times with deionized water and anhydrous ethanol, and finally vacuum dry it at 60°C for 12 h to obtain micron-sized flower-shaped WO3 powder; (2) The micron-shaped WO3 powder prepared in step (1) is mixed with conductive carbon (acetylene black) and binder (PVDF) at a mass ratio of 8:1:1, and an appropriate amount of NMP solvent is added. The mixture is then mixed evenly using a micro-vibration ball mill to obtain a viscous slurry. (3) Using a doctor blade coating method, the slurry prepared in step (2) is uniformly coated onto the surface of the PP separator. The doctor blade gap is adjusted so that the coating thickness after drying is controlled at 10 μm. The coated separator is then placed in a vacuum oven at 50 °C and dried for 18 h. After drying, it is cut into circular pieces with a diameter of 16 mm according to the battery specifications to obtain a micron-shaped WO3 conductive composite modified separator.

[0065] Example 2 A conductive composite modified separator based on a micron-sized flower-like Bi2O3 / WO3 heterojunction is prepared by the following steps: (1) 0.97 g of bismuth nitrate pentahydrate was dissolved in 10 mL of 65 wt% nitric acid solution, and then 40 mL of deionized water was added and stirred evenly. Then, 2.32 g of the micron-shaped WO3 powder prepared in Example 1 was added and the mixture was continuously magnetically stirred for 60 min to disperse it. Subsequently, the precursor was transferred to a 100 mL stainless steel high-pressure reactor with a polytetrafluoroethylene substrate, sealed, and placed in a forced-air drying oven for hydrothermal reaction at 180 °C for 24 h. After the reactor cooled naturally to room temperature, the bottom precipitate was collected by centrifugation, washed three times with deionized water and anhydrous ethanol, and finally vacuum dried at 60 °C for 12 h to obtain micron-shaped Bi2O3 / WO3 heterojunction powder.

[0066] (2) Using the same coating process as in Example 1, the slurry was coated on the surface of the PP separator. After drying, it was cut into round pieces with a diameter of 16 mm according to the battery specifications to obtain a micron-shaped Bi2O3 / WO3 heterojunction conductive composite modified separator.

[0067] Example 3 A conductive composite modified separator based on a micron-shaped flower-like WS2 / WO3 heterojunction is prepared by the following steps: (1) 0.75 g of thioacetamide was dissolved in 60 ml of deionized water, and then 2.32 g of the micron-shaped WO3 powder prepared in Example 1 was added and dispersed by continuous magnetic stirring for 60 min. Subsequently, the precursor was transferred to a stainless steel high-pressure reactor with a 100 mL polytetrafluoroethylene substrate, sealed, and placed in a forced-air drying oven for hydrothermal reaction at 160 °C for 24 h. After the reactor cooled naturally to room temperature, the bottom precipitate was collected by centrifugation, washed three times by centrifugation with deionized water and anhydrous ethanol, and finally vacuum dried at 60 °C for 12 h to obtain micron-shaped WS2 / WO3 heterojunction powder.

[0068] (2) Using the same coating process as in Example 1, the slurry was coated on the surface of the PP separator. After drying, it was cut into round pieces with a diameter of 16 mm according to the battery specifications to obtain a micron-shaped WS2 / WO3 heterojunction conductive composite modified separator.

[0069] Example 4 A conductive composite modified coating includes an active substance, a conductive agent, and a binder; the types and proportions of the active substance, conductive agent, and binder are the same as in Example 1.

[0070] Example 5 A conductive composite modified coating includes an active material, a conductive agent, and a binder; the types and proportions of the active material, conductive agent, and binder are the same as in Example 2.

[0071] Comparative Example 1 A blank PP separator is obtained by cutting a PP separator without any surface coating or chemical modification into circular pieces with a diameter of 16mm according to the battery specifications.

[0072] Comparative Example 2 A micron-shaped WO3-modified membrane without conductive carbon is prepared by the following steps: The micron-shaped WO3 powder prepared in Example 1 was mixed with a binder (PVDF) at a mass ratio of 9:1, and an appropriate amount of NMP solvent was added. The mixture was then thoroughly mixed using a micro-vibrating ball mill to obtain a viscous slurry. The slurry was coated onto the surface of a PP separator using the same coating process as in Example 1. After drying, the slurry was cut into discs with a diameter of 16 mm according to the battery specifications to obtain a simple micron-shaped WO3 modified separator.

[0073] Comparative Example 3 A conductive carbon-modified separator free of micron-sized flower-like WO3 is prepared by the following steps: Conductive carbon (acetylene black) and binder (PVDF) were mixed at a mass ratio of 9:1, and an appropriate amount of NMP solvent was added. The mixture was then thoroughly mixed using a micro-vibrating ball mill to obtain a viscous slurry. The slurry was coated onto the surface of a PP separator using the same coating process as in Example 1. After drying, the slurry was cut into 16 mm diameter discs according to the battery specifications to obtain a simple conductive carbon modified separator.

[0074] Comparative Example 4 A conductive composite modified separator based on granular WO3 is prepared by the following steps: (1) 2.26 g of ammonium metatungstate was placed in a muffle furnace and calcined at 650 °C for 3 h in an air atmosphere at a heating rate of 5 °C / min. After cooling naturally to room temperature, granular WO3 powder was obtained.

[0075] (2) Using the same coating process as in Example 1, the slurry was coated onto the surface of the PP separator. After drying, it was cut into round pieces with a diameter of 16 mm according to the battery specifications to obtain a granular WO3 conductive composite modified separator.

[0076] Comparative Example 5 A rod-shaped WO3 conductive composite modified separator is prepared by the following steps: (1) Dissolve 1.48 g of sodium tungstate dihydrate in 40 mL of deionized water and adjust the pH to 1.5 using nitric acid solution. Transfer the solution to a 50 mL hydrothermal reactor and react hydrothermally at 180 °C for 24 h. Collect the reaction product by centrifugation, wash it three times with deionized water and anhydrous ethanol, and dry it at 60 °C for 12 h. Place the dried powder in a muffle furnace and calcine it at 350 °C for 2 h in an air atmosphere at a heating rate of 2 °C / min. After cooling naturally to room temperature, rod-shaped WO3 powder is obtained.

[0077] (2) Using the same coating process as in Example 1, the slurry was coated onto the surface of the PP separator. After drying, it was cut into round pieces with a diameter of 16 mm according to the battery specifications to obtain a rod-shaped WO3 conductive composite modified separator.

[0078] Testing and Evaluation SEM analysis was performed on the active substance powders prepared in Examples 1 to 3 and Comparative Examples 4 to 5. The test results are shown in [Figure number missing]. Figure 1 .

[0079] Figure 1SEM images of WO3 with different morphologies and heterojunction composites are shown. The test results show that the WO3 prepared in Example 1 exhibits a typical micron-shaped flower morphology, formed by the self-assembly of two-dimensional nanosheets, with a flower structure diameter of approximately 5 μm. The WO3 prepared in Comparative Example 4 is an irregular particle with a smooth surface and no obvious pore structure. The WO3 prepared in Comparative Example 5 exhibits a one-dimensional rod-like morphology, with a length of approximately 2-5 μm and a large aspect ratio. The Bi2O3 / WO3 heterojunction prepared in Example 2 retains the original micron-shaped flower pattern, but the overall particle size is larger, and the surface of the nanosheets forming the flower pattern becomes rougher and denser, indicating successful uniform loading of Bi2O3. The WS2 / WO3 heterojunction prepared in Example 3 also maintains the micron-shaped flower pattern, with no significant change in overall particle size, and it is clearly observable that finer sheet-like WS2 is densely grown on the original WO3 surface.

[0080] XRD tests were performed on the active substance powders prepared in Examples 1 to 3 and Comparative Examples 4 to 5. The test results are shown in the figure. Figure 2 .

[0081] Figure 2 The XRD patterns of WO3 with different morphologies and heterojunction composites are shown. The test results show that the micron-shaped flower-like WO3 prepared in Example 1, the granular WO3 prepared in Comparative Example 4, and the rod-shaped WO3 prepared in Comparative Example 5 all exhibit the characteristic diffraction peaks of WO3, with no obvious impurity peaks, confirming the successful synthesis of pure-phase WO3 with different microstructures. In the spectrum of Example 2, in addition to the characteristic peaks of WO3, the standard diffraction peaks of Bi2O3 are clearly visible; in the spectrum of Example 3, the characteristic diffraction peaks of WS2 are visible. These results fully confirm the successful construction of micron-shaped flower-like Bi2O3 / WO3 and micron-shaped flower-like WS2 / WO3 heterojunctions.

[0082] KPB was mixed with acetylene black and PVDF at a mass ratio of 60:30:10 and uniformly dispersed in NMP to form a slurry. The slurry was coated onto aluminum foil and vacuum dried at 110 °C for 10 h, then cut into 10 mm diameter positive electrode sheets to obtain KPB positive electrodes. Subsequently, CR2032 coin cells were assembled in an argon-filled glove box, using the conductive composite modified separators obtained in Examples 1-3 and Comparative Examples 1-5 as separators, and potassium metal foil as negative electrodes, respectively. An electrolyte was added, wherein the electrolyte was 0.8 M KPF6 dissolved in EC / DEC (volume ratio 1:1), and after encapsulation, different KMBs were obtained.

[0083] The KMBs assembled in Examples 1-3 and Comparative Examples 1-5 were subjected to constant current charge-discharge tests. The test results are shown in […]. Figure 3 .

[0084] Figure 3Cyclic performance curves of KMBs assembled with different modified separators. As can be seen from Example 1 and Comparative Examples 1-3, the battery using the blank PP separator of Comparative Example 1 lacks the modified KMBs. + The battery exhibited severe soft short circuits during the second charge-discharge cycle due to its inability to actively control the deposition and extremely poor electrolyte wettability. The coulombic efficiency plummeted to around 10%, indicating that the unmodified polyolefin separator could not effectively suppress potassium dendrite growth. The battery using the simple micron-sized WO3-modified separator (without conductive carbon) in Comparative Example 2 had a low initial discharge capacity. This was due to the high interfacial resistance caused by the lack of an electronic conductive network, preventing WO3 from fully participating in the electrochemical reaction as an active component. This battery could only maintain normal operation for about ten cycles before intermittently experiencing soft short circuits and completely failing within 30 cycles. This demonstrates that while the simple oxide coating provides some physical barrier effect, the lack of conductive support prevents long-term stability. The battery using the simple conductive carbon-modified separator (without WO3) in Comparative Example 3 also exhibited severe soft short circuit characteristics, due to the lack of WO3 to inhibit potassium dendrite growth. + Active induced deposition, K + Disordered deposition within the conductive network prevents the formation of a uniform deposition layer, leading to continuous dendrite growth and penetration of the separator. The battery using the micron-sized flower-shaped WO3 conductive composite modified separator from Example 1 maintained a high discharge capacity throughout 500 cycles, with the coulombic efficiency closely distributed around 100% without significant fluctuations. This comparative result indicates that neither a simple WO3 coating nor a simple conductive carbon coating can achieve long-term interface stability. Only by constructing an activity regulation layer by combining micron-sized flower-shaped WO3 with conductive carbon can the intercalation reaction characteristics of WO3 and the electronic conduction advantages of the conductive network be fully utilized to achieve K... + Active regulation of sedimentation behavior.

[0085] A comparison of Example 1 and Comparative Examples 4-5 shows that while the batteries using the granular WO3 conductive composite modified separator of Comparative Example 4 and the rod-shaped WO3 conductive composite modified separator of Comparative Example 5 can delay dendrite penetration to some extent, soft short circuits occur intermittently during the early cycling stages, resulting in fluctuating coulombic efficiency and significantly lower discharge capacity than in Example 1. This result indicates that the microstructure of WO3 has a decisive influence on its interface control capability. Due to their limited specific surface area, insufficient active sites, and lack of stress release space, granular and rod-shaped structures are prone to excessively high local current densities during cycling, leading to preferential dendrite nucleation and growth in weak areas. In contrast, the micron-shaped flower structure, with its three-dimensional open configuration and nanosheet assembly characteristics, provides abundant ion insertion sites and a uniform ion flux distribution, effectively avoiding the accumulation of local overpotential and thus achieving long-term stable interface control.

[0086] A comparison of Examples 1-3 shows that, based on the excellent performance of Example 1, the batteries using the micron-sized flower-shaped Bi₂O₃ / WO₃ heterojunction conductive composite modified separator of Example 2 and the micron-sized flower-shaped WS₂ / WO₃ heterojunction conductive composite modified separator of Example 3 exhibit even more superior cycle performance. Both maintain high capacity retention and stable coulombic efficiency after 500 cycles, demonstrating further performance improvement. This is mainly attributed to the built-in electric field formed at the heterojunction interface, which accelerates K... + Transport dynamics, lowering the nucleation energy barrier, guiding K + Uniform deposition is achieved, resulting in better battery performance.

[0087] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A conductive composite modified coating, characterized in that, It includes an active material, a conductive agent, and a binder; the active material is micron-shaped WO3 and / or micron-shaped WO3-based heterojunctions.

2. The conductive composite modified coating according to claim 1, characterized in that, The micron-shaped WO3 is a three-dimensional open flower-like structure formed by the self-assembly of two-dimensional nanosheets; the micron-shaped WO3-based heterojunction is one or more of Bi2O3 / WO3 heterojunction and WS2 / WO3 heterojunction.

3. The conductive composite modified coating according to claim 1, characterized in that, The mass ratio of the active material, conductive agent, and binder is (5~9):(0.5~2.5):(0.5~2.5); the dry thickness of the conductive composite modified coating is 5~20μm.

4. The conductive composite modified coating according to claim 1, characterized in that, The preparation method of the micron-shaped WO3 is as follows: Ammonium metatungstate is dissolved in deionized water, nitric acid solution is added, and a hydrothermal reaction is carried out to obtain micron-shaped WO3 powder.

5. The conductive composite modified coating according to claim 1, characterized in that, The preparation method of the micron-shaped WO3-based heterojunction is as follows: the micron-shaped WO3 powder is dispersed in a nitric acid solution of bismuth salt or an aqueous solution of a sulfur-containing compound, and a hydrothermal reaction is carried out to obtain the micron-shaped WO3-based heterojunction.

6. The conductive composite modified coating according to claim 4 or 5, characterized in that, The hydrothermal reaction is carried out at a temperature of 110~220 ℃ for a reaction time of 6~48 h.

7. The conductive composite modified coating according to claim 5, characterized in that, The bismuth salt is one or more of bismuth nitrate pentahydrate and bismuth chloride; the sulfur-containing compound is one or more of thioacetamide, thiourea, and sodium sulfide.

8. A conductive composite modified separator comprising the conductive composite modified coating as described in any one of claims 1-7, characterized in that, It includes a porous substrate membrane and a conductive composite modified coating applied to at least one surface thereon.

9. A method for preparing the conductive composite modified separator as described in claim 8, characterized in that, The process includes mixing the active material, conductive agent, and binder, adding an organic solvent to mix, and obtaining a slurry; coating the slurry onto the surface of the porous substrate membrane, and drying it to obtain the conductive composite modified membrane.

10. The application of the conductive composite modified separator as described in claim 8 in alkali metal secondary batteries.

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