A multilayer separator based on an active material coating and an organic flame retardant material coating, a method of preparation and use thereof

Abstract

This invention discloses a multilayer separator based on an active material coating and an organic flame-retardant material coating, its preparation method, and its application. The preparation method of the multilayer separator includes the following steps: A. Preparation of Moringa flame-retardant powder; B. Preparation of the multilayer separator. The multilayer separator is a three-layer separator. The first layer slurry is prepared from Moringa powder and PVDF-HFP copolymer, the second layer is made of PVDF-HFP copolymer, and the third layer contains the active material. The use of the multilayer separator of this invention can improve thermal stability, reduce the risk of short circuits and thermal runaway, thereby significantly improving battery safety.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials, focusing on the separator design for lithium-ion batteries (LIBs). Its purpose is to improve the capacity and safety performance of lithium-ion batteries by designing multi-layer separators and coating them with organic materials and positive electrode active materials. Technical Background

[0002] The separator is a key component of lithium-ion batteries (LIBs). It enables the rapid transport of lithium ions while isolating the positive and negative electrode materials, preventing electrical short circuits, and plays a crucial role in the safety, lifespan, and energy density of lithium-ion batteries. Extensive research has been conducted in academia and industry on the design and development of separators to ensure battery safety. However, separator puncture and significant thermal shrinkage pose threats to battery safety. Two major breakthroughs in separator technology are Celgard's multilayer polyolefin separator with a thermal shutdown mechanism and heat-resistant ceramic-coated polyolefin separators developed by companies such as Hitachi Maxell and Degussa. However, coating polyolefin separators with inert ceramics can have a "dead weight" effect on battery capacity, and the ultra-thin inert ceramic layer may collapse after the polyolefin film melts upon heating, leading to short circuits and thermal runaway.

[0003] Developing separators with high mechanical strength, high temperature resistance, and flame retardancy is crucial for battery performance and safety. Many high-strength polymer materials, such as polyimide (PI), polybenzimidazole (PBI), polyetherimide (PEI), polyetheretherketone (PEEK), and poly(m-phenylene isophthalamide) (PMIA), have been used in battery separators; however, these materials are difficult to process into thin films (sheets) and are costly, limiting their large-scale application. Flame-retardant polymers and coating materials, such as PI and PBI, have also been used to prepare separators, but processing technology and cost remain challenges. Traditional single-polymer separators often fail to meet the requirements of battery performance and safety. Surface modification, mixing of inorganic and organic materials, and designing multilayer structures are effective methods for improving commercial polyolefin separators, PVDF-based separators, and other polymer separators. Furthermore, replacing liquid electrolytes and separators with solid-state electrolytes can eliminate safety hazards such as toxicity, leakage, and flammability; however, the low ionic conductivity of solid-state batteries at room temperature and poor electrode / electrolyte interface stability are major obstacles. Therefore, improving liquid battery separators remains of great significance. Summary of the Invention

[0004] This invention aims to address the shortcomings of traditional inert ceramic separators by introducing a multi-layered structural design, coating a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) separator with a positive electrode active material and a flame-retardant organic material. This method eliminates the need for expensive and complex polymer materials and allows for the coating of lithium-ion battery positive electrode active materials such as lithium iron phosphate (LFP), ternary NMC, and lithium cobalt oxide (LiCoO2); as well as flame-retardant natural (organic) materials such as moringa leaf powder. The active material coating not only exhibits excellent heat resistance but also creates electrical conductivity pathways and undergoes electrochemical reactions with the positive electrode, thereby providing additional capacity.

[0005] The key scientific problem of this invention:

[0006] 1. The relationship between the composition, structure, and performance of multilayer separators in lithium-ion batteries:

[0007] The separator is one of the most critical components in a lithium-ion battery. Although it doesn't directly participate in the electrochemical reactions within the battery, the separator prevents contact between electrodes, avoids internal short circuits, stores liquid electrolyte, and enables efficient ion transport during charge and discharge. The traditional battery structure is "positive electrode || separator || negative electrode." In this concept, by adding two additional components to the battery—"positive electrode || positive electrode active material layer / separator substrate layer / moringa flame retardant layer || negative electrode"—the number of components and interfaces increases significantly. By controlling the composition and structure of the separator and studying battery performance, the relationship between the composition, structure, and performance (capacity, rate capability, safety) of multilayer separators can be established. This will help in the rational design of lithium-ion battery separators and provide guidance for the development of high-performance lithium-ion battery separators.

[0008] 2. Charging and ion transport mechanisms of multilayer separators in lithium-ion batteries:

[0009] The complex porous structure of the multilayer membrane design establishes a new system for studying ion diffusion and lithium deposition behavior in porous media. A complex charge and ion transport mechanism exists at the interface between the active ceramic layer of the membrane and the electrode. Investigating the mass and charge transport characteristics of this interface, as well as the flame-retardant properties of organic materials, through experimental and theoretical methods can enrich the electrochemical research system and provide a theoretical basis for developing high-capacity, high-safety chemical power sources with similar structures.

[0010] The objective of this invention is to address the safety and performance challenges of lithium-ion batteries (LIBs) through an innovative multilayer separator design. Specific objectives include:

[0011] 1. Improve the capacity and safety of lithium-ion batteries:

[0012] Develop multilayer separators coated with organic materials and positive electrode active materials to improve the capacity and safety of lithium-ion batteries.

[0013] Battery capacity is increased by involving the separator in the electrochemical reaction process.

[0014] 2. Flame-retardant and explosion-proof design:

[0015] A flame-retardant layer made from natural moringa material is introduced to prevent fire and explosion risks, thereby improving the safety of lithium-ion batteries.

[0016] Improving the battery's resistance to thermal shrinkage and high-temperature conditions is key to preventing internal short circuits and thermal runaway.

[0017] 3. Mass and charge transport mechanisms:

[0018] Investigating the mass and charge transport mechanisms at the electrode / active ceramic coating separator interface to enhance the understanding and control of lithium-ion battery performance.

[0019] To investigate the flame-retardant and dendrite-resistant mechanisms of Moringa coatings in order to guide improvements in battery performance and safety.

[0020] 4. Cost-effective and sustainable solutions:

[0021] By avoiding the use of expensive polymer materials, a cost-effective membrane alternative is provided, which also has environmental advantages by utilizing natural organic materials such as moringa.

[0022] 5. Improves thermal stability and mechanical strength:

[0023] The separator is designed with high thermal stability and mechanical strength to ensure that the battery remains safe and functional under extreme conditions.

[0024] 6. Structural innovations in lithium-ion batteries:

[0025] By introducing a multi-layered separator that incorporates layers of active materials and flame-retardant organic materials, the traditional "positive electrode|| separator|| negative electrode" battery structure is broken. This design aims to enhance thermal stability and mechanical strength, thereby improving overall battery performance.

[0026] To achieve the technical objective of this invention, the following technical solution is adopted:

[0027] A method for preparing a multilayer membrane based on an active material coating and an organic flame-retardant material coating includes the following steps:

[0028] A. Preparation of Moringa flame retardant powder;

[0029] B. Preparation of multilayer diaphragms.

[0030] Furthermore, the preparation method of Moringa flame retardant powder in step A includes the following steps:

[0031] Moringa leaves are dried in an oven at 80°C for 24 hours to obtain dried moringa leaves. They are then manually ground to obtain leaf powder. The leaf powder is then ball-milled at 500 rpm for 4-8 hours to make fine leaf powder particles. The ball-milled suspension is then centrifuged three times at 5000 rpm for 15 minutes each time to separate the particles. Finally, it is dried at 80°C for 12 hours to obtain dried moringa powder.

[0032] Furthermore, the multilayer diaphragm mentioned in step B is a three-layer diaphragm.

[0033] Furthermore, the slurry for the first layer will be prepared from Moringa powder and PVDF-HFP copolymer.

[0034] Further, the preparation method of the first layer includes the following steps: dissolving PVDF-HFP in acetone at room temperature for 5 to 10 minutes, then stirring at 50°C until transparent; after preparing the PVDF-HFP matrix, adding Moringa powder and acetone and stirring for 2 hours; then, coating the prepared solution with a thickness of 10 micrometers on the substrate using a doctor blade and drying at room temperature to obtain a PVDF-HFP / Moringa particle composite coating based on a paper substrate.

[0035] Furthermore, the second layer is made of PVDF-HFP copolymer.

[0036] Furthermore, the preparation method of the second layer includes the following steps: dissolving PVDF-HFP in acetone at room temperature for 5 to 10 minutes, then stirring at 50°C until transparent; after preparing the PVDF-HFP matrix, stirring for 2 hours; then, coating the prepared solution with a thickness of 10 micrometers on the substrate using a doctor blade, and drying at room temperature to obtain the second coating.

[0037] Furthermore, the third layer contains active materials.

[0038] Furthermore, the choice of the active material will depend on the type of cathode used, such as LFP, NMC, or LiCoO2.

[0039] Furthermore, the preparation method of the third layer includes the following steps: dissolving PVDF in NMP, then adding active materials and carbon, stirring at room temperature for 6 hours, coating a thickness of 10 micrometers on a substrate that has already been coated with the first and second layers, and then drying at 60°C for 12 hours.

[0040] This invention improves the capacity and safety performance of lithium-ion batteries by developing a multilayer separator design with a complex porous structure, coating the positive electrode side with active materials, and using flame-retardant Moringa (an organic material) powder. The proposed lithium-ion battery separator will have the following characteristics:

[0041] 1. The multilayer membrane design with a complex porous structure will improve the wettability and retention of the electrolyte, thereby increasing the ionic conductivity; in addition, this structure helps to prevent dendritic structures from penetrating from the negative electrode to the positive electrode.

[0042] 2. The active layer coated on the positive electrode side will ensure the compatibility between the separator and the positive electrode interface and improve chemical stability.

[0043] 3. Coating the active layer will enhance electrochemical performance because the active layer of the membrane participates in the charge and discharge process.

[0044] 4. The moringa layer coated on the negative electrode side will inhibit the growth of lithium dendrites and has good flame retardant ability, avoiding serious problems caused by internal short circuits.

[0045] 5. The proposed diaphragm will have high thermal and mechanical stability and be able to resist diaphragm shrinkage at high temperatures.

[0046] 6. The proposed separator thickness is less than 25μm or thinner, which will not affect the overall energy density of the lithium-ion battery.

[0047] The innovative aspects of this invention are as follows:

[0048] 1. Technological Innovation: Traditional battery structures consist of "positive electrode || separator || negative electrode". This work breaks away from the traditional sandwich structure by adding two additional components: "positive electrode || positive electrode active material layer / separator substrate layer / moringa layer || negative electrode". The multilayer design and the thermodynamic and mechanical stability of the positive electrode material improve the thermal stability and mechanical strength of the separator, reducing thermal shrinkage and preventing internal short circuits. Furthermore, the flame-retardant layer of the separator uses moringa, which possesses a "natural flame-retardant" effect due to its antioxidant properties, thus reducing the possibility of fire / explosion under any severe conditions. The proposed multilayer separator exhibits strong thermomechanical stability and flame-retardant properties, significantly improving the safety of lithium-ion batteries. On the other hand, the positive electrode material coating of the separator maintains physical contact with the electrode, enabling it to participate in the battery's electrochemical reaction, increasing capacity and achieving "capacity enhancement".

[0049] 2. Theoretical Innovation: The separator employs a complex porous structure and multilayer design, with active materials coated on the positive electrode side and flame-retardant materials coated on the negative electrode side, establishing a novel system for studying ion diffusion and lithium deposition behavior in porous media. Traditional lithium-ion battery designs provide an inert / active interface between the separator and the positive electrode, while the proposed separator design provides an active / active interface (positive electrode / separator active layer), namely, positive electrode || positive electrode active material layer / separator substrate layer / moringa flame-retardant layer. Studying the mass and charge transport characteristics of this interface, as well as the flame-retardant capability of the moringa layer, through experimental and theoretical methods, can enrich the electrochemical research system and provide a theoretical basis for developing high-capacity, high-safety chemical power sources with similar structures.

[0050] Compared with the prior art, the present invention has the following technical advantages:

[0051] 1. Enhanced Battery Safety: Lithium-ion batteries (LIBs) are notorious for safety issues such as overheating and fire risks. The use of a multi-layer separator in this invention improves thermal stability and reduces the risk of short circuits and thermal runaway, thereby significantly enhancing battery safety.

[0052] 2. Improved Capacity and Lifespan: This invention aims to explore strategies to enhance the capacity and lifespan of lithium-ion batteries. The separator will participate in the electrochemical reaction, increasing battery capacity and maintaining stability under extreme conditions, thereby improving stability during long-term use.

[0053] 3. Flame Retardant Properties: The organic material coating exhibits excellent thermal stability and flame retardant properties. This is a significant improvement for applications requiring high safety standards, especially electric vehicles or other high-power energy storage systems.

[0054] 4. Enhanced performance under extreme conditions: High-temperature performance is critical in many applications. Separators coated with active ceramics and organic materials can maintain battery performance under harsh conditions, potentially making them more suitable for extreme environments.

[0055] 5. Wider application in energy storage systems: This research could open up new possibilities for the application of lithium-ion batteries in large-scale energy storage systems where capacity and safety are equally important.

[0056] 6. Environmental and economic benefits: Improving the performance and safety of lithium-ion batteries can lead to more sustainable energy storage solutions, reducing the need for frequent replacements and thus reducing waste. This also has the potential for long-term cost savings.

[0057] These advantages demonstrate that this invention has enormous potential for technological innovation in the fields of energy storage and lithium-ion battery safety. Attached Figure Description

[0058] Figure 1 A schematic diagram illustrating the failure mechanism of the membrane's high-temperature stability;

[0059] Figure 2 This is a diagram illustrating the overall technical solution of the present invention;

[0060] Figure 3 A schematic diagram illustrating the preparation of Moringa flame retardant powder;

[0061] Figure 4 This is a schematic diagram of the fabrication of the first layer of a multilayer membrane;

[0062] Figure 5 A schematic diagram illustrating the fabrication of the second layer of a multilayer membrane;

[0063] Figure 6 A schematic diagram illustrating the fabrication of the third layer of a multilayer membrane;

[0064] Figure 7 This is a schematic diagram showing the placement of the separator in a lithium-ion battery.

[0065] Figure 8 This is a schematic diagram of the cell fabrication process used for in-situ Raman analysis. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Rather, this invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined by the claims. Furthermore, to provide the public with a better understanding of this invention, certain specific details are described in detail below. Those skilled in the art will fully understand this invention even without these detailed descriptions.

[0067] like Figure 1 , 2As shown, in this embodiment of the invention, a simple and cost-effective blade coating method will be used to prepare a multilayer lithium-ion battery separator. The proposed separator consists of three layers: (a) a positive electrode active material layer, (b) a base separator, and (c) a Moringa granule layer. The active material layer coated onto the separator from the positive electrode side will participate in the electrochemical reaction of the lithium-ion battery and contribute to the battery capacity (capacity enhancement). In addition, the complex multilayer design of the separator has a significant impact on thermal stability, mechanical strength, and ionic conductivity. These properties will be optimized through the relationship between material composition and structure. Moringa is a natural flame retardant due to its antioxidant properties. After determining the material composition and structure of the proposed separator, lithium-ion batteries will be assembled, and the capacity, rate performance, and cycle performance of the lithium battery based on this separator will be studied and observed. Furthermore, the thermodynamic and mechanical properties of the battery under thermal runaway conditions and its explosion characteristics will be studied. Further in-situ experimental techniques, such as in-situ Raman spectroscopy and finite element analysis based on mass transport and charge transport models, will be used to study the capacity enhancement mechanism and flame retardant mechanism of this separator.

[0068] 1. Construction of a multilayer membrane based on active material coating and organic flame-retardant material (moringa material) coating:

[0069] A. Preparation of Moringa Flame Retardant Powder: In the proposed multi-layer membrane concept, Moringa leaves will serve as a "natural flame retardant" material within the membrane, helping to prevent fires, explosions, or thermal runaway. For example... Figure 3 As shown, firstly, moringa leaves are dried in an oven at 80℃ for 24 hours to obtain dried moringa leaves, which are then manually ground to obtain leaf powder. Next, the leaf powder is ball-milled at 500 rpm for 4-8 hours to produce fine leaf powder particles. The ball-milled suspension is then centrifuged three times at 5000 rpm for 15 minutes each time. Finally, it is dried at 80℃ for 12 hours to obtain dried moringa powder.

[0070] B. Preparation of multilayer membranes: The preparation of multilayer membranes (three layers) involves three steps, such as... Figure 4-6 As shown. The detailed preparation process is as follows:

[0071] First layer: The slurry for this layer will be prepared from Moringa powder and PVDF-HFP copolymer. First, PVDF-HFP is dissolved in acetone at room temperature for 5 to 10 minutes, and then stirred at 50°C until transparent. After preparing the PVDF-HFP matrix, Moringa powder and acetone are added and stirred for 2 hours. Then, the prepared solution is coated onto the substrate with a thickness of 10 micrometers using a doctor blade and dried at room temperature to obtain a PVDF-HFP / Moringa particle composite coating based on a paper substrate.

[0072] The second layer: This layer will be made of PVDF-HFP copolymer. The preparation method of the PVDF-HFP solution is the same as that of the first layer, except that moringa powder and acetone are not added. The PVDF-HFP solution is coated on the substrate with the same thickness as the first layer, which is 10 micrometers.

[0073] The third layer: This layer will contain active materials (the choice of active materials will depend on the type of cathode used, such as LFP, NMC, or LiCoO2). The slurry will be prepared in NMP by mixing active materials, carbon, and PVDF binder in a specific ratio. First, PVDF is dissolved in NMP, then the active materials and carbon are added, stirred at room temperature for 6 hours, and coated to a thickness of 10 micrometers on a substrate that has already been coated with the first and second layers. Then, it is dried at 60°C for 12 hours.

[0074] 2. Characterization methods and analysis:

[0075] Different characterization techniques were employed to observe the properties and behavior of the multilayer membrane. Details of the characterization and related analyses to be performed during the process are provided below:

[0076]

[0077] 3. Study on the electrochemical performance of lithium-ion batteries based on multilayer separators:

[0078] like Figure 7 As shown, lithium-ion batteries employing multilayer separators will be assembled in an argon-filled glove box for electrochemical performance testing. During battery assembly, it is ensured that the active material coated on the separator corresponds to the type of positive electrode material (e.g., when LFP is coated on the separator, the positive electrode must be LFP). The moringa flame-retardant layer of the separator should face the negative electrode side. The following are details of the electrochemical characterization and related analyses:

[0079]

[0080] 4. Research on the safety performance of lithium-ion batteries based on multilayer separators:

[0081] To conduct safety analysis of lithium-ion batteries, flexible lithium-ion batteries will be assembled using multilayer active flame-retardant separators and conventional separators. Two different tests will be performed, using varying temperatures to examine the battery's safety during charge and discharge processes.

[0082]

[0083]

[0084] 5. In-situ Raman analysis of the membrane-electrode interface:

[0085] To perform in-situ Raman analysis of the separator / electrode interface, lithium-ion coin cells will be assembled in a specified manner. For example... Figure 8 As shown, this analysis will reveal in detail the impact of membrane coating materials or membrane design on the performance of lithium-ion batteries.

[0086] A. Focusing the laser beam from the positive electrode side: To analyze the interface between the battery's active layer and the positive electrode, a laser beam will be continuously focused on the separator coated with the active material layer during the charging and discharging process of the lithium-ion battery. The in-situ Raman spectral changes of lithium-ion batteries based on the proposed separator and conventional separators will be observed, and final conclusions will be drawn.

[0087] B. Focusing the laser beam from the negative electrode side: To analyze the interface between the moringa coating and the battery negative electrode, a laser beam will be continuously focused on the moringa coating of the separator during the charging and discharging process of the lithium-ion battery. The in-situ Raman spectral changes of lithium-ion batteries based on the proposed separator and conventional separators will be observed, and final conclusions will be drawn.

[0088] Material details:

[0089]

[0090]

Claims

1. A method for preparing a multilayer membrane based on an active material coating and an organic flame-retardant material coating, characterized in that, Includes the following steps: A. Preparation of Moringa flame retardant powder; B. Preparation of multilayer membranes; The preparation method of Moringa flame retardant powder in step A includes the following steps: Moringa leaves are dried in an oven at 80°C for 24 hours to obtain dried moringa leaves. They are then manually ground to obtain leaf powder. The leaf powder is then ball-milled at 500 rpm for 4-8 hours to make fine leaf powder particles. The ball-milled suspension is then centrifuged three times at 5000 rpm for 15 minutes each time. Finally, it is dried at 80°C for 12 hours to obtain dried moringa powder. The multilayer membrane mentioned in step B is a three-layer membrane, namely the first layer, the second layer, and the third layer. The slurry of the first layer will be prepared from Moringa powder and PVDF-HFP copolymer. The second layer is made of PVDF-HFP copolymer; The preparation method of the second layer includes the following steps: dissolving PVDF-HFP in acetone at room temperature for 5 to 10 minutes, then stirring at 50°C until transparent; after preparing the PVDF-HFP matrix, stirring for 2 hours; then, coating the prepared solution with a thickness of 10 micrometers on the substrate with a doctor blade and drying at room temperature to obtain the second coating. The third layer contains active materials.

2. The method for preparing a multilayer membrane based on an active material coating and an organic flame-retardant material coating according to claim 1, characterized in that, The preparation method of the first layer includes the following steps: dissolving PVDF-HFP in acetone at room temperature for 5 to 10 minutes, then stirring at 50°C until transparent; after preparing the PVDF-HFP matrix, adding Moringa powder and acetone and stirring for 2 hours; then, coating the prepared solution with a thickness of 10 micrometers on the substrate using a doctor blade and drying at room temperature to obtain a PVDF-HFP / Moringa particle composite coating based on a paper substrate.

3. The method for preparing a multilayer membrane based on an active material coating and an organic flame-retardant material coating according to claim 1, characterized in that, The preparation method of the third layer includes the following steps: dissolving PVDF in NMP, then adding active materials and carbon, stirring at room temperature for 6 hours, coating a thickness of 10 micrometers on a substrate that has been coated with the first and second layers, and then drying at 60°C for 12 hours.

4. A multilayer membrane based on an active material coating and an organic flame-retardant material coating, prepared by the method according to any one of claims 1-3.

5. The application of a multilayer separator based on an active material coating and an organic flame-retardant material coating as described in claim 4 in the preparation of lithium-ion batteries.

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