High-strength positive electrode graphene composite fiber, its preparation method, and the structured battery prepared therefrom

Abstract

This invention discloses a high-strength positive electrode graphene composite fiber, its preparation method, and the resulting structural battery. Belonging to the field of structural battery technology, the method involves mixing nano-positive electrode materials with graphene fiber precursor slurry, followed by liquid-phase solidification into filaments. The graphene oxide filaments containing the positive electrode material undergo reduction crystallization treatment to obtain graphene composite fibers containing the positive electrode material. A structural battery is assembled using high-strength positive electrode graphene composite fibers, a high-strength insulating fiber separator, and a carbon fiber negative electrode layer, along with a structural electrolyte, thereby improving the mechanical properties of the structural battery.

Description

Technical Field

[0001] This invention belongs to the field of structural battery fiber cathode materials and their preparation technology, and specifically relates to a high-strength cathode graphene composite fiber, its preparation method, and the structural battery prepared therefrom. Background Technology

[0002] A structural battery refers to a multifunctional material or structure that can act as an electrochemical energy storage system (i.e., a battery) while possessing mechanical integrity. It is a composite energy storage device capable of bearing structural mechanical loads (sufficient stiffness and strength) and storing electrochemical energy (sufficient capacity). Typically, structural batteries are based on the concept of carbon fiber reinforced polymers, where carbon fiber serves as both the electrode and structural reinforcement material. This reduces the overall system volume / mass, addressing the fundamental size and weight issues of batteries and improving system efficiency.

[0003] Structural batteries can be used in consumer electronics such as smartphones and laptops, as well as small electric devices like electric bicycles, potentially halving the weight while achieving a more compact structure. Furthermore, in transportation applications such as electric vehicles and drones, when structural batteries become part of the vehicle or drone structure, bearing impact and torsional loads, this can reduce the need for fastening processes and additional structural reinforcements required by traditional battery packs, thereby reducing space requirements, lightening weight, and increasing driving range.

[0004] More than 20 years ago, some scholars proposed the basic concept of structured batteries, and began attempting to manufacture them in 2007. However, due to limitations in carbon fiber performance and experimental conditions, research progress on structured batteries has been relatively slow. With the continuous improvement of carbon fiber performance, research on the fabrication of structured batteries using T800 carbon fiber as electrodes has attracted widespread attention from scholars both domestically and internationally, and related basic research has also developed rapidly. Currently, structured batteries still have a significant gap to bridge in terms of overall performance compared to practical applications. In particular, fiber-structured cathodes typically use carbon fiber as both current collector and support layer, with the cathode material grown or coated onto the carbon fiber surface. Therefore, the bonding strength between the cathode layer and the carbon fiber is limited, and weak interlayer bonding affects the overall mechanical strength of the energy storage composite material.

[0005] Existing technologies, including CN202310026879.6 (a high-toughness, low-resistivity structural energy storage component and its molding method), CN202211545130.4 (an integrated structural energy storage composite material and its preparation method), and CN202210579702.4 (a biomimetic multifunctional fiber composite material and its component multi-point flexible molding manufacturing method), all utilize carbon fiber as the current collector and support layer in the fiber structure cathode of the aforementioned patented structural batteries. The cathode material is grown or coated onto the carbon fiber surface. The aforementioned patented structural cathodes actually consist of two layers: a cathode material layer and a carbon fiber layer. The cathode material is attached to the carbon fiber surface, thus limiting the bonding strength. Weak interlayer bonding affects the overall mechanical strength of the energy storage composite material. Summary of the Invention

[0006] The purpose of this invention is to address the problem that existing structural cathodes use a high-strength matrix as a support layer, with the cathode material layer adhering to the surface of the support layer, which affects the overall mechanical performance of the structural battery. This invention provides a high-strength cathode graphene composite fiber, its preparation method, and the resulting structural battery. By preparing graphene fibers containing cathode material, a continuous, high-strength fibrous cathode is obtained, which can effectively improve the mechanical strength of the battery when applied to structural batteries.

[0007] To achieve this objective, the high-strength cathode graphene composite fiber preparation method of this invention employs the following technical solution: Nano-cathode material is added to a graphene oxide dispersion, stirred to obtain a slurry, and then the slurry is extruded through a spinneret into a coagulation bath to form a slurry. Further, high-strength cathode graphene composite fibers are obtained through low-temperature reduction. Specifically, the method includes the following steps:

[0008] 1) Add the nano-positive electrode material to the graphene oxide dispersion and stir to obtain a slurry;

[0009] 2) The slurry is extruded through a spinneret into a coagulation bath to form graphene oxide fibers containing nano-positive electrode materials;

[0010] 3) The graphene oxide fiber containing nano-positive electrode material is reduced at low temperature to obtain high-strength positive electrode graphene composite fiber.

[0011] Furthermore, the nano-cathode material mentioned in step 1) is LiNi. x Co y Al 1-x-y O2, LiNi x Co y Mn 1-x-y One or more of O2, LiMPO4 (M = Fe, Mn), and LiCoO2, with a particle size of 20 nm to 1000 nm.

[0012] Furthermore, the graphene oxide dispersion mentioned in step 1) is one or a mixture of two or more of the following: an aqueous dispersion of graphene oxide, a DMF dispersion, an NMP dispersion, or a DMSO dispersion.

[0013] Furthermore, the coagulation bath mentioned in step 2) is one or a mixture of two or more of ethyl acetate, dichloromethane, acetic acid, ethanol, water, isopropanol, chloroform, and acetone.

[0014] Furthermore, the reagents used in the low-temperature reduction in step 3) are one or a mixture of two or more of lithium aluminum hydride, potassium borohydride (sodium, lithium), sodium thioborohydride, trisec-butyl borohydride, and hydrazine hydrate, and the low-temperature reduction temperature is 80℃~150℃.

[0015] Furthermore, the weight percentage of nano-positive electrode material in the high-strength positive electrode graphene composite fiber is 10% to 50%.

[0016] A high-strength positive electrode graphene composite fiber is prepared by the above-described preparation method.

[0017] A structural battery includes a carbon fiber negative electrode, an insulating fiber separator, a structural electrolyte, and a fiber positive electrode, wherein the fiber positive electrode is the aforementioned high-strength graphene composite fiber positive electrode.

[0018] The advantages of this invention are as follows: This invention achieves continuous fiberization of the cathode material by combining nano-cathode material with graphene fiber, and low-temperature reduction avoids damage to the cathode material structure and affect the cathode electrical performance during the reduction process. The high-strength cathode graphene composite fiber is woven into a fabric that can be directly used as the cathode of the structural battery. Compared with the traditional cathode material attached to a high-strength fiber fabric support, this high-strength cathode graphene composite fiber avoids the disadvantage of weak interlayer bonding strength of the traditional structural cathode, thereby improving the overall mechanical strength of the structural battery. Attached Figure Description

[0019] Figure 1 This example compares the tensile strength of LiCoO2-graphene composite fiber in Example 1 with that of graphene fiber with LiCoO2 attached to its surface in Comparative Example 1.

[0020] Figure 2 The XRD patterns of the LiCoO2 material used in Example 1 before and after the reduction process prepared by graphene fiber are shown below. Detailed Implementation

[0021] To further illustrate the present invention more clearly, specific embodiments will be described in more detail below.

[0022] Example 1

[0023] 1) Add 1g of LiCoO2 material with an average particle size of 500nm to 100g of monolayer graphene oxide NMP phase dispersion (the content of monolayer graphene oxide is 1g), mechanically stir for 3h, and ultrasonically disperse for 12h to mix evenly.

[0024] 2) The slurry obtained in 1) is extruded through a spinneret with a diameter of 5 μm into an isopropanol coagulation bath at an extrusion speed of 5 mm / s, and then solidified in the liquid phase to form graphene oxide fiber filaments containing positive electrode material.

[0025] 3) The graphene oxide fibers containing LiCoO2 material obtained in 2) were dried at 80°C for 12 hours. Then, the fibers were immersed in hydrazine hydrate and reduced at 110°C for 1 hour. After being washed with deionized water, they were dried at 60°C for 6 hours and then dried under vacuum at 110°C for 24 hours to obtain LiCoO2 graphene composite fibers.

[0026] Comparative Example 1

[0027] 1) Add 100g of monolayer graphene oxide NMP phase dispersion (the content of monolayer graphene oxide is 1g)

[0028] As a spinning solution, it is extruded into an isopropanol coagulation bath through a spinneret with a diameter of 5μm at an extrusion speed of 5mm / s, and then solidified in the liquid phase to form graphene oxide fiber filaments.

[0029] 2) The graphene oxide fiber obtained in 2) was dried at 80°C for 12 hours. Then the fiber was immersed in hydrazine hydrate and reduced at 110°C for 1 hour. After being washed with deionized water, it was dried at 60°C for 6 hours and then dried under vacuum at 110°C for 24 hours to obtain graphene fiber.

[0030] 3) Weigh 2.7g LiCoO2, 0.15g SP, and 0.15g PVDF, mix them, add 11g NMP, and mechanically ball mill for 2h to obtain a positive electrode slurry. After homogenizing the slurry with a 200μm scraper, coat it onto the surface of the graphene fiber obtained in 2). Dry it at 100℃ for 1h, and then dry it under vacuum at 110℃ for 24h to obtain graphene fiber with LiCoO2 attached to its surface.

[0031] Figure 1 The tensile strength of the LiCoO2 graphene composite fiber in Example 1 is compared with that of the graphene fiber with LiCoO2 attached to the surface in Comparative Example 1. The tensile strength of Example 1 is 654.9 MPa, while that of the fiber in Comparative Example 1 is 283.0 MPa. The composite fiber prepared by the method of the present invention improves the strength of the cathode.

[0032] Figure 2The XRD patterns of the LiCoO2 material used in Example 1 before and after the reduction process using graphene fibers are shown. As can be seen from the patterns, the characteristic peaks of the LiCoO2 material did not change before and after the reduction process, and the low-temperature reduction did not damage the structure of the cathode material.

[0033] Example 2

[0034] 1) Add 0.5g of LiFeO4 material with an average particle size of 50nm to 100g of monolayer graphene oxide DMF phase dispersion (the content of monolayer graphene oxide is 1g), mechanically stir for 6h, and ultrasonically disperse for 48h to mix evenly.

[0035] 2) The slurry obtained in 1) is extruded into an ethyl acetate coagulation bath through a spinneret with a diameter of 10 μm at an extrusion speed of 1 mm / s, and then solidified in the liquid phase to form graphene oxide fibers containing LiFeO4 material.

[0036] 3) The graphene oxide fibers containing LiFeO4 material obtained in 2) were dried at 80°C for 6 hours. Then, the fibers were immersed in hydroiodic acid and reduced at 140°C for 0.5 hours. After being washed with deionized water, they were dried at 60°C for 4 hours and then dried under vacuum at 100°C for 12 hours to obtain LiFeO4 graphene composite fibers.

[0037] Comparative Example 2

[0038] 1) 100g of monolayer graphene oxide DMF phase dispersion (monolayer graphene oxide content is 1g) was used as spinning solution and extruded into an ethyl acetate coagulation bath through a spinneret with a diameter of 10μm. The extrusion speed was 1mm / s, and the solution was solidified into graphene oxide fiber filaments through liquid phase.

[0039] 2) The graphene oxide fiber obtained in 2) was dried at 80°C for 6 hours, then the fiber was immersed in hydroiodic acid and reduced at 140°C for 0.5 hours. After being washed with deionized water, it was dried at 60°C for 4 hours and then dried under vacuum at 100°C for 12 hours to obtain graphene composite fiber.

[0040] 3) Weigh 2.4g LiFeO4, 0.3g SP, and 0.3g PVDF, mix them, add 12g NMP, and mechanically ball mill for 3h to obtain a positive electrode slurry. Coat the slurry onto the surface of graphene composite fibers using a 150μm scraper, dry at 100℃ for 1h, and then dry under vacuum at 110℃ for 24h to prepare graphene fibers with LiFeO4 attached to the surface.

[0041] Tensile tests were conducted on the fibers of Example 2 and Comparative Example 2. The tensile strength of the fiber of Example 2 was 1074.9 MPa, and the tensile strength of the fiber of Comparative Example 2 was 253.3 MPa.

[0042] Example 3

[0043] A positive electrode graphene composite fiber prepared using any combination of Examples 1-2 or other embodiments is used as the structural positive electrode. It is stacked with a glass fiber separator and a PAN-based carbon fiber negative electrode to assemble a structural battery. The battery is then immersed in a structural electrolyte (bisphenol A dimethacrylate and EMIM-TFSI (6:4, by weight)) and cured.

[0044] Example 4

[0045] A positive electrode graphene composite fiber prepared using any combination of Examples 1-2 or other embodiments is used as the structural positive electrode. It is stacked with Kevlar fiber separator and pitch-based carbon fiber negative electrode to assemble a structural battery. The battery is then immersed in a structural electrolyte (bisphenol A dimethacrylate and solid electrolyte (3:7, weight ratio)) and cured.

[0046] The embodiments described above are only used to illustrate the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The patent scope of the present invention should not be limited by these embodiments. That is, any equivalent changes or modifications made in accordance with the spirit disclosed in the present invention still fall within the patent scope of the present invention.

Claims

1. A method for preparing high-strength positive electrode graphene composite fibers, characterized in that, Includes the following steps: (1) The nano-cathode material is composited with a graphene oxide dispersion, and graphene oxide fibers containing the cathode material are obtained by liquid-phase solidification; the nano-cathode material is LiNi. x Co y Al 1-x-y O2, LiNi x Co y Mn 1-x-y One or more of O2, LiMPO4 (M=Fe, Mn), and LiCoO2, with a particle size of 20nm to 1000nm; (2) High-strength positive electrode graphene composite fiber is obtained by low-temperature reduction of graphene oxide fiber containing nano-positive electrode material. The weight ratio of nano-positive electrode material in the high-strength positive electrode graphene composite fiber is 10% to 50%, and the low-temperature reduction temperature is 80℃ to 150℃.

2. The method for preparing high-strength positive electrode graphene composite fiber according to claim 1, characterized in that, Step (1) is as follows: add the nano cathode material to the graphene oxide dispersion and stir to obtain a slurry; then extrude the slurry through the spinneret hole into the coagulation bath to form a solid.

3. The method for preparing high-strength positive electrode graphene composite fibers according to claim 1 or 2, characterized in that, The graphene oxide dispersion is one or a mixture of two or more of the following: an aqueous dispersion of graphene oxide, a DMF dispersion, an NMP dispersion, or a DMSO dispersion.

4. The method for preparing high-strength positive electrode graphene composite fiber according to claim 2, characterized in that, The coagulation bath is one or a mixture of two or more of the following: ethyl acetate, dichloromethane, acetic acid, ethanol, water, isopropanol, chloroform, and acetone.

5. The method for preparing high-strength positive electrode graphene composite fiber according to claim 1, characterized in that, The reagents used in the low-temperature reduction are one or a mixture of two or more of the following: lithium aluminum hydride, potassium borohydride, sodium borohydride, lithium borohydride, sodium thioborohydride, trisec-butyl borohydride, and hydrazine hydrate.

6. A high-strength positive electrode graphene composite fiber, characterized in that, Using as claimed in claim 1 It is prepared by any one of the preparation methods described in item 5.

7. A structural battery, comprising a carbon fiber negative electrode, an insulating fiber separator, a structural electrolyte, and a fiber positive electrode, characterized in that, The fiber positive electrode is the high-strength positive electrode graphene composite fiber according to claim 6.

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