A high-temperature-resistant conjugated skeleton electrode material and a preparation method thereof

Abstract

This invention belongs to the field of lithium-ion battery electrode material technology, and discloses a high-temperature resistant polyimide covalent organic framework (PI-COF) cathode material and its preparation method. The cathode material uses melamine and 1,4,5,8-naphthalenetetracarboxylic anhydride as monomers, and prepares a polyamic acid precursor through hydrothermal polymerization. This precursor is then subjected to a high-temperature imidization reaction to form a polyimide covalent organic framework material with a highly ordered covalent organic framework structure. Further, it is composited with reduced graphene oxide, conductive carbon black, and a binder to obtain the high-temperature resistant lithium-ion battery cathode material. The PI-COF material possesses a highly ordered two-dimensional conjugated framework structure and regular nanopores, providing continuous lithium-ion transport channels. It also has abundant carbonyl and triazine active sites, enabling multi-electron reversible lithium storage reactions. Due to the stable imide conjugated framework and high crystallinity, the material exhibits excellent thermal stability, structural stability, and cycle stability. The preparation method of this invention is simple, uses widely available raw materials, does not require high-temperature sintering, and has advantages such as low cost, environmental friendliness, and ease of large-scale preparation. The prepared cathode material exhibits excellent cycle stability and high specific capacity under both room temperature and high temperature conditions, making it particularly suitable for applications such as high-temperature lithium-ion batteries at 100 ℃ and above, special power supplies, and energy storage systems in extreme environments.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode material technology, specifically relating to a high-temperature resistant polyimide covalent organic framework (PI-COF) cathode material and its preparation method, and more specifically to a method for constructing a polyimide covalent organic framework material with an ordered conjugated framework structure using melamine and 1,4,5,8-naphthalenetetracarboxylic anhydride, and applying it to the cathode of a high-temperature resistant lithium-ion battery. Background Technology

[0002] With the rapid development of new energy vehicles, aerospace, oil and gas drilling, deep well logging, military equipment, and extreme environment energy storage systems, lithium-ion batteries are gradually shifting from room temperature applications to high-temperature, high-power, and high-safety applications. In particular, power batteries and special power supplies operating in environments of 80–200 °C place higher demands on the thermal stability, structural stability, and cycle life of electrode materials.

[0003] Currently, commercially available lithium-ion batteries mainly use inorganic cathode materials such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), and ternary layered oxides. Although these materials have high energy densities, they generally suffer from insufficient thermal stability at high temperatures. Specifically, lithium cobalt oxide easily releases lattice oxygen at high temperatures, inducing thermal runaway; lithium manganese oxide is prone to manganese ion dissolution and Jahn-Teller distortion at high temperatures, leading to rapid capacity decay; while lithium iron phosphate has good safety, its low ion diffusion rate and severe polarization at high temperatures and high rates limit its further application. Furthermore, these inorganic cathode materials typically require high-temperature sintering at 600–1000 °C, which is not only energy-intensive but also heavily reliant on scarce metal resources such as cobalt and nickel, hindering green and sustainable development.

[0004] In recent years, organic electrode materials have gradually become an important research direction in the field of lithium-ion batteries due to their wide availability, environmental friendliness, designable structure, and excellent thermal stability. Among them, polyimide (PI) materials, with their rigid aromatic rings and stable imide structure in the main chain, typically have thermal decomposition temperatures above 500 °C, exhibiting excellent heat resistance. Furthermore, the carbonyl groups in polyimide molecules can act as reversible redox active sites in lithium storage reactions, resulting in a theoretically high capacity, thus demonstrating potential as cathode materials for high-temperature lithium-ion batteries.

[0005] However, most traditional polyimide materials are amorphous polymers, lacking regular and ordered ion transport channels, resulting in low lithium-ion diffusion rates. Simultaneously, their limited specific surface area leads to low utilization of active sites, making them prone to molecular chain rearrangement and structural degradation during long-term cycling, resulting in capacity decay. Furthermore, traditional polyimide materials have poor electronic conductivity, typically requiring the addition of large amounts of conductive agents to meet electrode conductivity requirements, thus limiting their further applications.

[0006] Polyimide covalent organic frameworks (PI-COFs) are a class of highly ordered crystalline porous materials constructed from organic monomers through covalent bonds. They combine the excellent heat resistance of polyimide with the regular pore structure of covalent organic frameworks. PI-COFs exhibit high crystallinity, a regular two-dimensional layered structure, and periodically ordered pores, providing continuous lithium-ion migration channels and effectively shortening lithium-ion diffusion paths. This improves the utilization rate of active sites and significantly enhances the rate performance and cycle stability of electrode materials. Furthermore, their stable conjugated framework effectively suppresses structural collapse under high-temperature conditions, thus endowing the material with excellent high-temperature electrochemical stability.

[0007] While some research reports have documented the application of PI-COF materials in lithium-ion batteries, problems remain, including insufficient crystallinity, low conductivity, limited high-temperature cycle stability, and complex preparation processes. These limitations prevent them from meeting the requirements for long-term stable operation of high-temperature lithium-ion batteries. Therefore, developing a PI-COF cathode material with high crystallinity, high conductivity, high thermal stability, and excellent high-temperature cycle performance, along with a simple and controllable preparation method, is of great significance for promoting the development of high-temperature resistant lithium-ion batteries. Summary of the Invention

[0008] To address the shortcomings of existing inorganic cathode materials in terms of high-temperature safety, poor conductivity, slow ion transport, and insufficient cycle stability of traditional polyimide materials, as well as the need to improve the high-temperature performance of existing PI-COF materials, this invention provides a high-temperature resistant polyimide covalent organic framework cathode material and its preparation method. This invention constructs a PI-COF with a highly ordered two-dimensional conjugated framework and a regular nanoporous structure, and introduces reduced graphene oxide to build a continuous conductive network. While ensuring excellent thermal stability, it improves electron transport capability and lithium-ion diffusion rate, thereby significantly enhancing the material's cycle stability, rate performance, and specific capacity under both room temperature and high-temperature conditions. To achieve the above objectives, this invention adopts the following technical solution:

[0009] This invention provides a high-temperature resistant polyimide covalent organic framework cathode material, characterized in that the cathode material comprises a polyimide covalent organic framework material, a conductive agent, and a binder, wherein the polyimide covalent organic framework material is formed by polymerization of melamine and 1,4,5,8-naphthalenetetracarboxylic anhydride and high-temperature imidization reaction.

[0010] The polyimide covalent organic framework material possesses a two-dimensional layered conjugated structure and a periodic ordered pore structure. Its framework simultaneously contains imide carbonyl active sites and triazine nitrogen active sites, enabling reversible multi-electron lithium storage reactions. Preferably, the molar ratio of melamine to 1,4,5,8-naphthalenetetracarboxylic anhydride is 1:1.5; other ratios cannot synthesize this PI-COF.

[0011] Preferably, the polyimide covalent organic framework material is prepared by the following steps:

[0012] (1) Melamine and 1,4,5,8-naphthalenetetracarboxylic anhydride were dispersed in acetic anhydride, and after ultrasonic dispersion, they were placed in a closed reaction vessel and subjected to hydrothermal reaction at 140-180 °C for 12-36 h to obtain polyamic acid precursor;

[0013] (2) The obtained polyamic acid precursor was washed with DMF, ethanol and deionized water in sequence, freeze-dried and then imidized at 320-400 °C under an inert atmosphere to obtain polyimide covalent organic framework material.

[0014] (3) The obtained polyimide covalent organic framework material is combined with reduced graphene oxide to form a conductive network. Then, conductive carbon black and polyvinylidene fluoride binder are added to prepare an electrode slurry, which is then coated onto the current collector and dried to obtain a high-temperature resistant polyimide covalent organic framework cathode material.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) A highly ordered two-dimensional conjugated structure and regular channels are constructed using a polyimide covalent organic framework, which significantly improves lithium-ion transport efficiency and active site utilization.

[0017] (2) By introducing reduced graphene oxide to construct a continuous electronic conductive network, the charge transfer impedance at the electrode interface is effectively reduced and the electrode conductivity is improved.

[0018] (3) The material has a stable imide conjugated skeleton and high crystallinity, and can maintain excellent structural stability and electrochemical stability under high temperature conditions.

[0019] (4) The prepared electrode material has excellent cycle stability and high specific capacity at room temperature and 100 °C, and is suitable for extreme environment energy storage fields such as high temperature lithium-ion batteries, aerospace, oil and gas drilling and military special power supply. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments are described below. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0021] Figure 1 This is a process flow diagram for the preparation of the PI-COF cathode material of the present invention.

[0022] Figure 2 This is the X-ray diffraction (XRD) spectrum of the PI-COF material of this invention.

[0023] Figure 3 The Fourier transform infrared (FT-IR) spectrum of the PI-COF material of the present invention is shown, wherein: (a) polyamic acid (PAA) precursor; (b) PI-COF material.

[0024] Figure 4 The images show the morphology and pore structure characterization of the PI-COF material of this invention, including: (a) scanning electron microscope (SEM) image; (b) nitrogen adsorption-desorption isotherm; and (c) pore size distribution curve.

[0025] Figure 5 The results of room temperature electrochemical performance tests for PI-COF cathode materials include: (a) cycle performance curves; (b) charge-discharge curves for different cycle numbers; (c) electrochemical impedance spectroscopy (EIS); (d) CV curves for different scan rates; and (e) pseudocapacitance contribution ratio.

[0026] Figure 6 The high-temperature cycling performance of PI-COF cathode material at 100 ℃ is shown in the figures: (a) cycling performance; (b) charge-discharge curves for different number of cycles. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0028] Any appropriate adjustments made by those skilled in the art to the process conditions, raw material ratios, and testing methods without departing from the spirit of this invention are within the scope of protection of this invention.

[0029] Unless otherwise specified, all raw materials used in the embodiments of this invention are commercially available. See Table 1 for details.

[0030] Table 1

[0031] 1,4,5,8-Naphthalenetetracarboxylic dianhydride NTCDA AR Aladdin Reagent Co., Ltd. 81-30-1 melamine MA AR Anaiji Reagent Co., Ltd. 108-78-1 Acetic anhydride — AR Aladdin Reagent Co., Ltd. 108-24-7 N,N-Dimethylformamide DMF AR Aladdin Reagent Co., Ltd. 68-12-2 Deionized water — RO / 7732-18-5 N-methyl-2-pyrrolidone NMP AR Aladdin Reagent Co., Ltd. 872-50-4. Super P (Conductive Carbon Black) Super P AR Cyber ​​Electrochemical Materials Co., Ltd. 1333-86-4 polyvinylidene fluoride PVDF AR Shenzhen Kejing Co., Ltd. 24937-79-9

[0032] Example 1

[0033] This embodiment provides a method for preparing PI-COF material, specifically:

[0034] Melamine (1 mmol, 0.126 g) and 1,4,5,8-naphthalenetetracarboxylic anhydride (1.5 mmol, 0.262 g) were dissolved in 20 mL of acetic anhydride at a molar ratio of 1:1.5. The solutions were ultrasonically dispersed and then transferred to a 40 mL hydrothermal reactor. The reactor was placed in an oven at 160 °C for 24 h. After the reaction, the product was centrifuged with DMF, ethanol, and deionized water until the liquid was colorless. The precipitate was then dispersed in 50 mL of deionized water and freeze-dried. A polyamic acid precursor was obtained after drying. This precursor was then subjected to an imidization reaction at 355 °C for 5 h under nitrogen protection. After imidization, a polyimide conjugated backbone material was obtained.

[0035] Example 2

[0036] This embodiment provides a method for preparing a PI-COF positive electrode, specifically as follows:

[0037] 0.03 g of reduced graphene oxide was ultrasonically dispersed in 5 mL of NMP solution for 30 min. After uniform dispersion, a reduced graphene oxide conductive agent dispersion was obtained. 0.05 g of PI-COF was added to the reduced graphene oxide conductive agent dispersion, and the mixture was heated and stirred at 60 °C for 12 h. After uniform dispersion, Super P (0.02 g) and HSV900-PVDF (0.01 g) were added. After stirring at room temperature, a PI-COF electrode material slurry was obtained. The mass ratio of polyimide conjugated framework reduced graphene oxide, Super P, and HSV900-PVDF in the slurry was 5:3:2:1. The slurry was coated onto aluminum foil using a 200 μm scraper and baked in a vacuum oven at 100 °C for 12 h. After drying, a polyimide conjugated framework electrode material was obtained.

[0038] Example 3

[0039] Battery assembly

[0040] CR2032 coin cells were assembled in an argon-protected glove box. The negative electrode was a lithium metal sheet. The separator was Celgard 2400. The electrolyte for room temperature testing was 1 mol·L⁻¹ LiPF₆ / EC:DMC:EMC (1:1:1). The electrolyte for high-temperature testing was 1 mol·L⁻¹ LiTFSI / EMIMTFSI ionic liquid electrolyte. After assembly, the cells were allowed to stand for 12 h before testing.

[0041] Example 4

[0042] Material structure characterization

[0043] The crystal structure was analyzed using Bruker D8 Advance XRD. Scan range: 5°–80°. Cu Kα rays. Scan rate: 5° / min. Chemical bonds were analyzed using FT-IR. Scan range: 4000–400 cm⁻¹. The microstructure was observed using SEM. Specific surface area and pore size distribution were determined using BET. The results showed that the obtained PI-COF material exhibited obvious crystal diffraction peaks, indicating high crystallinity. The characteristic peaks of imide were clearly visible in the FT-IR, while the amino and carboxyl peaks disappeared, indicating that the imidization reaction was basically completed. SEM observation showed that the material has a two-dimensional nanosheet structure with a thickness of approximately 50–100 nm and a length of approximately 0.5–1 μm. BET results showed that the specific surface area of ​​the material was approximately 332 m²·g⁻¹, and the pore size was mainly concentrated at approximately 1.2 nm.

[0044] Example 5

[0045] Electrochemical performance testing

[0046] Constant current charge-discharge tests were conducted using a LAND battery testing system. Voltage range: 0–3 V (vs Li / Li⁺). Room temperature test temperature: 30 ℃. High temperature test temperature: 100 ℃. Temperature control accuracy of the constant temperature chamber: ±0.5 ℃. Cyclic voltammetry tests were performed using an electrochemical workstation. AC impedance was measured within a frequency range of 100 kHz to 0.01 Hz. Combined with XRD, FT-IR, CV, and EIS test results, it is evident that the PI-COF material of this invention possesses a dual-active-site lithium storage mechanism. Specifically, the imide carbonyl group serves as the main redox active site, capable of undergoing reversible lithiation / delithiation reactions; the triazine ring nitrogen atoms introduced by melamine further provide reversible lithium storage sites, achieving multi-electron synergistic lithium storage. Two-dimensional ordered channels shorten the lithium-ion diffusion path and improve ion transport efficiency; reduced graphene oxide forms a continuous conductive network, reducing electron transport impedance, enabling the material to exhibit excellent rate performance and cycle stability under both room temperature and high temperature conditions.

[0047] Example 6

[0048] Room temperature cycling performance

[0049] Cyclic testing was conducted at 30 °C and 1 A·g⁻¹. The initial discharge specific capacity of the PI-COF cathode material was approximately 764.2 mAh·g⁻¹. After cyclic activation, the specific capacity increased to 821.5 mAh·g⁻¹. After 1500 consecutive cycles, the specific capacity remained at approximately 698.3 mAh·g⁻¹, exhibiting a capacity retention greater than 85%. The coulombic efficiency remained consistently at approximately 99%.

[0050] Example 7

[0051] High temperature cycling performance

[0052] Cyclic testing was conducted at 100 °C. The initial discharge capacity was approximately 324.7 mAh·g⁻¹, and the initial coulombic efficiency was approximately 91.9%. The capacity stabilized after 50 cycles. After 120 cycles, the capacity retention was approximately 77%. The coulombic efficiency remained above 98% throughout the cycling process. These results demonstrate that the PI-COF material of this invention exhibits good cycling stability and structural stability even at high temperatures.

[0053] Comparison Column 1

[0054] 0.03 g of reduced graphene oxide was ultrasonically dispersed in 5 mL of NMP solution for 30 min. After uniform dispersion, a reduced graphene oxide conductive agent dispersion was obtained. Super P (0.02 g) and HSV900-PVDF (0.01 g) were added, and the mixture was stirred at room temperature to obtain an rGO electrode material slurry. The mass ratio of reduced graphene oxide, Super P, and HSV900-PVDF in the slurry was 8:2:1. The slurry was coated onto aluminum foil using a 200 μm scraper and baked in a vacuum oven at 100 ℃ for 12 h. After drying, the reduced graphene oxide electrode material was obtained. CR2032 coin cells were assembled in an argon-protected glove box. A lithium metal sheet was used as the negative electrode. A Celgard 2400 separator was used. The electrolyte for room temperature testing was 1 mol·L⁻¹ LiPF₆ / EC:DMC:EMC (1:1:1). Charge-discharge cycle tests were conducted on the battery, revealing extremely low capacity—only 30 mAh / g in the first cycle—making it unsuitable for application. This indicates that rGO only functions as a conductive load for PI-COF in the battery and has no actual lithium storage performance.

Claims

1. A high-temperature resistant lithium-ion battery cathode material, characterized in that... The electrode material is a polyimide conjugated framework electrode material, which is polymerized from melamine and 1,4,5,8-naphthalenetetracarboxylic anhydride in a molar ratio of 1:1.

5.

2. A method for preparing the lithium-ion battery electrode material according to claim 1, comprising the following steps: (1) Melamine 1 mmol (0.126 g) and 1,4,5,8-naphthalenetetracarboxylic anhydride 1.5 mmol (0.262 g) were taken at a molar ratio of 1:1.

5. Melamine and 1,4,5,8-naphthalenetetracarboxylic anhydride were dissolved in 20 mL of acetic anhydride and ultrasonically dispersed evenly. The above dispersion was placed in a 40 mL hydrothermal reactor and placed in an oven at 160 °C for 24 h. After the reaction was completed, the product was centrifuged with DMF, ethanol and deionized water until the centrifuged liquid was colorless. After centrifugation, the precipitate was dispersed with 50 mL of deionized water and then freeze-dried. After drying, polyamic acid precursor was obtained. (2) The polyamic acid precursor was subjected to a heating imidization reaction at a temperature of 355 °C for 5 h under nitrogen protection during the heating process. After the imidization was completed, a polyimide conjugated skeleton material was obtained. (3) 0.03 g of reduced graphene oxide was ultrasonically dispersed in 5 mL of NMP solution for 30 min. After uniform dispersion, a reduced graphene oxide conductive agent dispersion was obtained. 0.05 g of PI-COF was added to the reduced graphene oxide conductive agent dispersion. The mixture was heated and stirred at 60 °C for 12 h. After uniform dispersion, Super P (0.02 g) and HSV900-PVDF (0.01 g) were added. After uniform stirring at room temperature, a PI-COF electrode material slurry was obtained. The mass ratio of polyimide conjugated framework reduced graphene oxide, Super P, and HSV900-PVDF in the slurry was 5:3:2:

1. The slurry was coated onto aluminum foil with a 200 μm scraper. The vacuum oven temperature was 100 °C and the baking time was 12 h. After drying, a polyimide conjugated framework electrode material was obtained.

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