A method for preparing a positive electrode of a polymer lithium ion battery
By constructing a three-dimensional interconnected network of sulfurized polyacrylonitrile nanofibers on carbon fiber braids, the problems of low active material capacity and polysulfide shuttle effect in the cathode of structured batteries were solved, achieving high energy density and stable electrochemical performance.
Patent Information
- Application Number
- CN202610592851.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-30
- Publication Date
- 2026-06-26
AI Technical Summary
Existing structural batteries suffer from low capacity of positive electrode active materials, severe polysulfide shuttle effect, and poor bonding between active materials and current collectors, leading to issues with battery cycle life and structural safety.
Polyacrylonitrile nanofibers were deposited on carbon fiber woven fabric using electrospinning technology. After pre-oxidation treatment, they were heat-treated in a sulfur-containing atmosphere to transform them in situ into sulfurized polyacrylonitrile nanofibers, forming a three-dimensional interconnected network structure. This achieved a stable bond between the active material and the current collector, and the sulfur was fixed by covalent bonds to eliminate the polysulfide shuttle effect.
It significantly improves the cycle stability and energy density of the battery, increases the contact area of the active material and the ion diffusion path, and enhances the rate performance and mechanical load-bearing capacity of the battery.
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This application relates to the field of lithium-ion battery technology, specifically to a method for preparing the positive electrode of a polymer lithium-ion battery. Background Technology
[0002] With the rapid development of electric vehicles, drones, and portable electronic devices, higher demands are being placed on the energy density and lightweight design of energy storage systems. Structural batteries, as a multifunctional composite material, aim to integrate energy storage units with load-bearing structures, thereby significantly reducing system weight without sacrificing mechanical strength. Carbon fiber, due to its high specific strength, high specific modulus, and good conductivity, has become an ideal skeleton material for structural battery electrodes. However, existing structural battery cathodes mostly use traditional active materials such as lithium iron phosphate (LFP) coated on the carbon fiber surface. Limited by the relatively low theoretical specific capacity of these active materials, it is difficult to achieve a breakthrough in energy density.
[0003] Lithium-sulfur batteries have attracted much attention due to their extremely high theoretical energy density. However, traditional lithium-sulfur batteries use elemental sulfur as the positive electrode active material, which easily generates soluble polysulfides during charge and discharge, leading to a "shuttle effect" that causes loss of active material and rapid capacity decay. In addition, in positive electrodes prepared by traditional slurry coating processes, the active material and current collector are only physically adhered by a binder. When the battery structure is subjected to mechanical loads, interface delamination is very likely to occur, which seriously affects the cycle life and structural safety of the battery.
[0004] Therefore, how to improve the specific capacity of the cathode while solving the polysulfide shuttle effect and achieving a stable integration of the active material and the carbon fiber structural skeleton is a key technical challenge currently facing the research and development of structural battery cathodes. Summary of the Invention
[0005] To address the technical problems of low capacity of positive electrode active materials, polysulfide shuttle effect, poor bonding force between active material and current collector, and poor high-temperature thermal stability of nanofibers in the prior art, this application provides a method for preparing the positive electrode of a polymer lithium-ion battery.
[0006] The first aspect of this application provides a method for preparing a positive electrode of a polymer lithium-ion battery, comprising the following steps: using a carbon fiber woven fabric as a receiving substrate, electrospinning a polyacrylonitrile solution to deposit polyacrylonitrile nanofibers on the surface and in the interfiber gaps of the carbon fiber woven fabric; pre-oxidizing the carbon fiber woven fabric with the deposited polyacrylonitrile nanofibers; and heat-treating the pre-oxidized composite in a sulfur-containing atmosphere to convert the polyacrylonitrile nanofibers into sulfurized polyacrylonitrile nanofibers in situ, thereby obtaining the positive electrode.
[0007] Preferably, the pre-oxidation treatment is carried out at a temperature of 200-280℃ for 0.5-2 hours in an air atmosphere; the electrospinning uses a high-speed roller as a receiving device to control the polyacrylonitrile nanofibers to be oriented along the warp and weft directions of the carbon fiber woven fabric; the electrospinning process employs a layered deposition process: carbon nanotubes or graphene are added to the spinning solution in the layer closest to the carbon fiber woven fabric, and a pure polyacrylonitrile solution is deposited on the outer layer to form a gradient conductive interface.
[0008] Through the above technical solution, this application utilizes electrospinning technology to directly deposit polyacrylonitrile (PAN) nanofibers onto carbon fiber woven fabric, constructing a three-dimensional interconnected nanofiber network structure. PAN nanofibers not only coat the surface of the carbon fiber monofilaments but also fill the gaps between fiber bundles, forming a microscopic composite structure similar to "reinforced concrete." This in-situ generated network structure significantly increases the contact area between the active material and the current collector, achieving a stable bond through physical interlocking and intermolecular forces, effectively solving the problem of easy peeling of active materials in traditional coating processes.
[0009] The subsequent heat treatment and vulcanization step transforms the insulating PAN nanofibers in situ into vulcanized polyacrylonitrile (SPAN) nanofibers. In SPAN, sulfur is covalently bonded to the carbon skeleton, preventing the formation of soluble polysulfide intermediates during charge and discharge, thus fundamentally eliminating the shuttle effect and significantly improving the battery's cycle stability. Simultaneously, SPAN materials exhibit a high specific capacity (theoretically reaching hundreds of mAh / g), far exceeding that of traditional LFP materials, thereby significantly increasing the energy density of the cathode. Furthermore, the nanofiber morphology provides shorter ion diffusion paths and a larger reaction surface area, which is beneficial for improving rate performance.
[0010] Furthermore, prior to the electrospinning step, a desizing treatment of the carbon fiber woven fabric is included. The desizing treatment removes the commercial epoxy sizing agent from the carbon fiber surface, exposing the intrinsic graphitized surface of the carbon fiber, improving the wettability and conductivity of the carbon fiber surface, and facilitating close contact and electronic conduction between the PAN nanofibers and the carbon fiber.
[0011] Furthermore, the polyacrylonitrile solution is an N,N-dimethylformamide solution of polyacrylonitrile, wherein the concentration of polyacrylonitrile is 8-12 wt%. This concentration range can obtain a suitable spinning solution viscosity, ensuring the stability of the electrospinning process and forming nanofibers with uniform diameter and good continuity.
[0012] Furthermore, the electrospinning process parameters are: voltage 15-20kV, injection rate 0.5-1.0mL / h, and receiving distance 12-15cm. These optimized process parameters ensure the stable formation of the Taylor cone and the full stretching of the jet, allowing the nanofibers to penetrate deeply into the interior of the carbon fiber weave.
[0013] Furthermore, the heat treatment temperature is 300-500℃, and the time is 1-4 hours. This temperature range is a suitable window for the cyclization, dehydrogenation, and sulfurization reactions of PAN, which can achieve efficient conversion of PAN to SPAN, while avoiding the deterioration of the carbon fiber skeleton performance due to excessively high temperatures.
[0014] Furthermore, the sulfur-containing atmosphere is provided by the sublimation of sulfur powder under an inert atmosphere, and the mass ratio of the carbon fiber woven fabric with deposited polyacrylonitrile nanofibers to the sulfur powder is 1:3 to 1:5. Sufficient sulfur source ensures complete vulcanization of the PAN, increasing the loading of the positive electrode active material.
[0015] Furthermore, following the heat treatment step, the process includes treating the material under vacuum at 150-250°C for 20-40 minutes to remove unbonded sulfur. This step removes physically adsorbed elemental sulfur, avoiding the shuttle effect risk caused by the dissolution of free sulfur during battery operation, and further purifying the active material.
[0016] Furthermore, selenide powder is added to the polyacrylonitrile solution, and the heat treatment yields selenium-doped sulfurized polyacrylonitrile nanofibers. The introduction of selenium improves the intrinsic electronic conductivity of the material and alleviates the problem of limited solid-state reaction kinetics in SPAN.
[0017] Furthermore, the selenide powder is SeS2, and its addition amount is 1-10 wt% of the mass of polyacrylonitrile. This doping ratio achieves a good balance between improving conductivity and maintaining high capacity.
[0018] The present invention has the following beneficial effects: This application innovatively introduces a "pre-oxidation treatment" before the vulcanization step. This step transforms the linear PAN molecular chains into a heat-resistant trapezoidal structure, preventing the melting and entanglement of PAN nanofibers during subsequent high-temperature vulcanization (300-500℃), thus fully preserving the three-dimensional network structure of the nanofibers and ensuring high specific surface area and ion transport channels.
[0019] This application utilizes an electrospinning method combined with in-situ vulcanization to prepare an integrated SPAN nanofiber / carbon fiber cathode, achieving a robust bond between the active material and the structural framework at the microscale. This solves the problem of weak interfacial bonding in traditional cathodes and meets the dual requirements of structural batteries for mechanical load-bearing capacity and electrochemical energy storage.
[0020] By using SPAN as the positive electrode active material and taking advantage of its covalently bonded sulfur properties, the polysulfide shuttle effect in lithium-sulfur batteries is completely eliminated, significantly improving the cycle stability and coulombic efficiency of the battery.
[0021] The SPAN nanofiber network provides a three-dimensional electron / ion transport channel, shortening the lithium-ion diffusion path. Combined with a highly conductive carbon fiber skeleton, it achieves a synergy of high specific capacity and excellent rate performance.
[0022] The preparation method provided in this application is simple, highly controllable, and has good compatibility with existing carbon fiber composite material manufacturing processes, making it easy to achieve large-scale production. Detailed Implementation
[0023] To facilitate understanding of this application, a more complete description will be provided below. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.
[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.
[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0026] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.
[0027] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.
[0028] Unless otherwise specified, the percentage content mentioned in this application refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures.
[0029] Unless otherwise specified, all percentage concentrations mentioned in this application refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.
[0030] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.
[0031] The term "particle" as used in this application, or a substance with a defined particle size distribution, is not necessarily spherical in shape; it may be irregular and can be either primary or secondary particles. The particle size of irregular particles is calculated as the average of their maximum and minimum diameters.
[0032] This invention provides a method for preparing a positive electrode for a polymer lithium-ion battery, comprising the following steps: using a carbon fiber woven fabric as a receiving substrate, electrospinning a polyacrylonitrile solution to deposit polyacrylonitrile nanofibers on the surface and interfiber spaces of the carbon fiber woven fabric; pre-oxidizing the carbon fiber woven fabric with the deposited polyacrylonitrile nanofibers; and heat-treating the pre-oxidized composite in a sulfur-containing atmosphere to convert the polyacrylonitrile nanofibers into sulfurized polyacrylonitrile nanofibers in situ, thereby obtaining the positive electrode.
[0033] Existing methods for fabricating composite electrodes using electrospinning technology often neglect the thermal stability of polymer nanofibers during high-temperature processing. For example, if polyacrylonitrile (PAN) nanofibers are directly heated to high temperatures without stabilization treatment, they will melt and fibrous, leading to the collapse of the nanostructure, loss of high specific surface area, and consequently affecting electrochemical performance. Therefore, this application innovatively introduces a "pre-oxidation treatment" before the vulcanization step. This step transforms the linear PAN molecular chains into a heat-resistant trapezoidal structure, preventing the melting and fibrous formation of PAN nanofibers during subsequent high-temperature vulcanization (300-500℃), fully preserving the three-dimensional network structure of the nanofibers, and ensuring high specific surface area and ion transport channels.
[0034] Meanwhile, this invention utilizes electrospinning technology to directly deposit polyacrylonitrile (PAN) nanofibers onto carbon fiber woven fabric, constructing a three-dimensional interconnected nanofiber network structure. PAN nanofibers not only coat the surface of the carbon fiber monofilaments but also fill the gaps between fiber bundles, forming a microscopic composite structure similar to "reinforced concrete." This in-situ generated network structure significantly increases the contact area between the active material and the current collector, achieving a stable bond through physical interlocking and intermolecular forces, effectively solving the problem of easy peeling of active materials in traditional coating processes.
[0035] The subsequent heat treatment and vulcanization step transforms the insulating PAN nanofibers in situ into vulcanized polyacrylonitrile (SPAN) nanofibers. In SPAN, sulfur is covalently bonded to the carbon skeleton, preventing the formation of soluble polysulfide intermediates during charge and discharge, thus fundamentally eliminating the shuttle effect and significantly improving the battery's cycle stability. Simultaneously, SPAN materials exhibit a high specific capacity (theoretically reaching hundreds of mAh / g), far exceeding that of traditional LFP materials, thereby significantly increasing the energy density of the cathode. Furthermore, the nanofiber morphology provides shorter ion diffusion paths and a larger reaction surface area, which is beneficial for improving rate performance.
[0036] In a preferred embodiment, the pre-oxidation treatment is carried out at a temperature of 200-280°C for 0.5-2 hours in an air atmosphere. These process parameters ensure that the PAN is fully cyclized to form a heat-resistant trapezoidal structure while avoiding excessive oxidation that could reduce fiber strength.
[0037] In a preferred embodiment, prior to the electrospinning step, a desizing treatment of the carbon fiber woven fabric is included. The desizing treatment removes the commercial epoxy sizing agent from the carbon fiber surface, exposing the intrinsic graphitized surface of the carbon fiber, improving the wettability and conductivity of the carbon fiber surface, and facilitating close contact and electronic conduction between the PAN nanofibers and the carbon fiber.
[0038] In a preferred embodiment, the polyacrylonitrile solution is an N,N-dimethylformamide solution of polyacrylonitrile, wherein the concentration of polyacrylonitrile is 8-12 wt%. This concentration range can obtain a suitable spinning solution viscosity, ensure the stability of the electrospinning process, and form nanofibers with uniform diameter and good continuity.
[0039] In a preferred embodiment, the electrospinning process parameters are preferably: voltage 15-20kV, injection rate 0.5-1.0mL / h, and receiving distance 12-15cm. These optimized process parameters ensure the stable formation of the Taylor cone and sufficient stretching of the jet, allowing the nanofibers to penetrate deeply into the carbon fiber woven fabric.
[0040] In a preferred embodiment, the heat treatment temperature is 300-500°C, and the time is 1-4 hours. This temperature range is a suitable window for the cyclization, dehydrogenation, and sulfurization reactions of PAN, enabling efficient conversion of PAN to SPAN while avoiding excessively high temperatures that could degrade the performance of the carbon fiber skeleton.
[0041] In a preferred embodiment, the sulfur-containing atmosphere is provided by the sublimation of sulfur powder under an inert atmosphere, and the mass ratio of the carbon fiber woven fabric with deposited polyacrylonitrile nanofibers to the sulfur powder is 1:3 to 1:5. Sufficient sulfur source ensures complete vulcanization of the PAN, increasing the loading of the positive electrode active material.
[0042] In a preferred embodiment, following the heat treatment step, the process further includes treating the material under vacuum at 150-250°C for 20-40 minutes to remove unbonded sulfur. This step removes physically adsorbed elemental sulfur, avoiding the shuttle effect risk caused by the dissolution of free sulfur during battery operation, and further purifying the active material.
[0043] In a preferred embodiment, selenide powder is further added to the polyacrylonitrile solution, and the heat treatment yields selenium-doped sulfurized polyacrylonitrile nanofibers. The introduction of selenium improves the intrinsic electronic conductivity of the material, mitigating the limitation of SPAN solid-state reaction kinetics.
[0044] In a preferred embodiment, the selenide powder is SeS2, and its addition amount is 1-10 wt% of the mass of polyacrylonitrile. This doping ratio achieves a good balance between improving conductivity and maintaining high capacity.
[0045] In another preferred embodiment, a selenium source is further added to the polyacrylonitrile solution, and the heat treatment yields selenium-doped sulfurized polyacrylonitrile nanofibers; the selenium source is selenic acid or selenate, with a concentration of 0.01-0.1 mol / L in the solution. Compared to selenide powder, selenic acid or selenate has better solubility, which can further improve the electronic conductivity of the material.
[0046] In a preferred embodiment, the electrospinning process employs a high-speed roller as a receiving device to control the directional alignment of the polyacrylonitrile nanofibers along the warp and weft directions of the carbon fiber woven fabric. The directionally aligned nanofibers can better withstand tensile loads along the fiber direction, significantly improving the interlaminar shear strength of the composite material. Preferably, the electrospinning process uses a layered deposition process: a layer of spinning solution near the carbon fiber woven fabric contains carbon nanotubes or graphene, while a pure polyacrylonitrile solution is deposited on the outer layer, forming a gradient conductive interface. This gradient structure design utilizes the high conductivity and high modulus of carbon nanotubes to construct "reinforcing ribs" at the interface, enhancing both electronic conduction and further strengthening the interfacial bonding.
[0047] The present invention utilizes a preferred high-speed roller receiving process to achieve the directional alignment of nanofibers, enabling the positive electrode to exhibit excellent mechanical reinforcement in a specific direction, thus meeting the load-bearing requirements of structural batteries. Furthermore, by constructing a gradient conductive interface (such as CNT doping), the interface resistance is further reduced, thereby improving rate performance.
[0048] In some preferred embodiments, the molecular weight of the polyacrylonitrile (PAN) can be selected from any one of 50,000, 100,000, 150,000, and 200,000. The molecular weight directly affects the viscosity of the spinning solution and the final diameter and mechanical strength of the nanofibers, and those skilled in the art can adjust it according to actual spinning requirements.
[0049] In some preferred embodiments, the carbon fiber woven fabric can be selected from any one of plain weave, twill weave, or satin weave. The carbon fiber specifications can be selected from the T300, T700, T800, M40, or IMS65 series. The areal density of the carbon fiber woven fabric can be 150, 200, 250, or 300 g / m³. 2 Choose from among them to meet the different structural load-bearing requirements.
[0050] In some preferred embodiments, the ambient temperature for electrospinning can be controlled at 25-35°C, and the relative humidity at 30-50%. Suitable ambient temperature and humidity help the solvent evaporate and prevent fiber fusion or breakage.
[0051] In some preferred embodiments, the heating rate during the heat treatment process can be selected from 1, 2, 3, and 5 °C / min. A slower heating rate is beneficial for the smooth progress of the PAN cyclization reaction and avoids damage to the fiber structure caused by violent exothermic reactions.
[0052] The following detailed embodiments will further illustrate this aspect: Specific Implementation Example 1 This specific embodiment 1 provides a method for preparing the positive electrode of a polymer lithium-ion battery, and the specific steps are as follows: (a) Preparation of carbon fiber woven fabric Toray T700S 12K plain weave carbon fiber fabric (area density 200g / m²) was selected. 2 It serves as both a current collector and a structural skeleton. The carbon fiber cloth is cut to the appropriate size, placed in a muffle furnace, and heated to 400°C at 5°C / min in an air atmosphere. It is then held at that temperature for 2 hours to remove the epoxy sizing agent from the surface, and then allowed to cool naturally to room temperature for later use.
[0053] (b) Electrospinning deposition of PAN nanofibers Prepare a 10wt% polyacrylonitrile (PAN) / N,N-dimethylformamide (DMF) solution, where the molecular weight of PAN is Mw = 150,000. Pour the solution into a syringe and install a No. 9 needle. Ground the desized carbon fiber cloth as the receiving substrate.
[0054] The electrospinning process parameters were set as follows: voltage 18 kV, injection rate 0.8 mL / h, and receiving distance 15 cm. Spinning was carried out at room temperature (25℃) and humidity 40%, with a deposition time of 3 hours. PAN nanofibers were uniformly deposited on the surface of carbon fiber monofilaments and in the interfiber bundles, forming a three-dimensional network structure with a deposition areal density of approximately 30 g / m³. 2 .
[0055] (c) Pre-oxidation treatment The PAN / carbon fiber composite obtained in the previous step was placed in a forced-air drying oven and heated to 250°C at a rate of 1°C / min under air atmosphere, and held at that temperature for 1 hour. This step causes the PAN molecules to undergo a cyclization reaction, forming a heat-resistant trapezoidal structure to prevent subsequent high-temperature melting.
[0056] (d) In-situ vulcanization treatment The pre-oxidized composite and sulfur powder were placed at both ends of an alumina boat at a mass ratio of 1:4 and then placed in a sealed tube furnace. Under an argon atmosphere, the temperature was increased to 350°C at a rate of 2°C / min and held for 2 hours. During this process, sulfur vapor penetrated into the interior of the PAN nanofibers, causing the PAN to undergo cyclization, dehydrogenation, and cross-linking with sulfur, transforming it into vulcanized polyacrylonitrile (SPAN).
[0057] After the reaction was completed, the mixture was cooled to room temperature and then treated under vacuum at 200°C for 30 minutes to remove unbonded residual sulfur, thus obtaining an integrated SPAN nanofiber / carbon fiber cathode. Specific Implementation Example 2: The difference between this specific embodiment 2 and specific embodiment 1 is as follows: When preparing the spinning solution, add 5 wt% SeS2 powder (relative to the mass of PAN) to a 10 wt% PAN / DMF solution and stir to disperse evenly. The electrospinning and vulcanization process parameters are the same as in Specific Example 1. During vulcanization, Se atoms are doped into the SPAN framework to obtain selenium-doped SPAN nanofiber / carbon fiber cathodes. Specific Implementation Example 3: The difference between this specific embodiment 3 and specific embodiment 1 is as follows: The electrospinning process is carried out in three stages, with each stage depositing approximately 15 g / m³. 2 PAN nanofibers were deposited. After each deposition, the composite was pre-stabilized in an oven at 230°C for 30 minutes to prevent fiber melting and collapse during subsequent deposition. After three cycles, the cumulative PAN deposition areal density reached 90 g / m³. 2 Finally, the cathode was subjected to sulfidation treatment according to the process of Specific Example 1 to obtain a cathode with high active material loading. Specific Implementation Example 4 The difference between this specific embodiment 4 and specific embodiment 1 is as follows: A gradient deposition strategy was employed to enhance interfacial bonding and electronic conduction. First, a PAN / DMF solution containing 0.5 wt% multi-walled carbon nanotubes (CNTs) was prepared and electrospun for 30 minutes to form a CNT-rich conductive underlayer on the carbon fiber surface. Then, the solution was switched to pure PAN / DMF and spinning continued for 2.5 hours. Subsequent pre-oxidation and vulcanization process parameters were the same as in Specific Example 1.
[0061] This embodiment utilizes the excellent conductivity and high modulus of CNTs to construct a high-speed electron transport channel inside the positive electrode and form a "reinforcing rib" structure at the interface, which is expected to further improve rate performance and interface bonding. Specific Implementation Example 5 The difference between this specific embodiment 5 and specific embodiment 1 is as follows: In the electrospinning step, a high-speed rotating roller (1500 r / min) is used instead of a stationary receiving plate to receive the carbon fiber cloth, causing the PAN nanofibers to align tangentially along the roller (i.e., along the carbon fiber axis). Furthermore, 0.05 mol / L selenic acid is added to the PAN spinning solution as a selenium source (replacing solid powder doping). Subsequent pre-oxidation and vulcanization processes are the same as in Example 1, ultimately yielding an oriented and selenium-doped SPAN nanofiber cathode.
[0063] This embodiment utilizes a fiber-oriented structure to enhance the mechanical strength of the cathode in the fiber direction, and selenium doping further improves the electronic conductivity of the material, achieving a dual improvement in mechanical and electrochemical performance. Specific Implementation Example 6 The difference between this specific embodiment 6 and specific embodiment 1 is as follows: When preparing the spinning solution, selenic acid was added as a selenium source to a 10 wt% PAN / DMF solution, achieving a concentration of 0.05 mol / L, and stirred until completely dissolved. The electrospinning and vulcanization process parameters were the same as in Specific Example 1. During vulcanization, selenium atoms were uniformly doped into the SPAN framework, resulting in uniformly doped selenium-doped SPAN nanofiber / carbon fiber cathodes. Compared to powder doping, liquid-phase doping avoids the risk of nozzle clogging and provides a more uniform doping distribution.
[0065] Comparative Example 1: Traditional LFP coated cathode This comparative example uses a traditional slurry coating process.
[0066] Lithium iron phosphate (LFP) powder, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:6:4, and N-methylpyrrolidone (NMP) was added to prepare a slurry. The slurry was uniformly coated onto the surface of the desized carbon fiber cloth, the same as in Example 1, and vacuum dried at 80°C for 12 hours to obtain an LFP-coated cathode. Electrospinning and vulcanization were not performed.
[0067] Comparative Example 2: Traditional elemental sulfur coated cathode This comparative example uses a traditional sulfur / carbon composite slurry coating process.
[0068] Elemental sulfur, conductive carbon black, and PVDF were mixed in a mass ratio of 70:20:10, and NMP was added to prepare a slurry. The slurry was coated onto the surface of the desized carbon fiber cloth, similar to that in Example 1, and dried to obtain an elemental sulfur-coated cathode.
[0069] Comparative Example 3 The difference between this comparative example and specific example 1 is that the pre-oxidation treatment step is omitted, and the electrospun PAN / carbon fiber composite is directly subjected to vulcanization treatment (heated to 350°C).
[0070] The results showed that, because the PAN was not stabilized, it melted and fused when heated above the glass transition temperature, completely destroying the nanofiber structure. A dense and non-porous polymer film was formed on the surface of the carbon fiber, resulting in extremely poor electrochemical performance and almost no ability to charge or discharge.
[0071] To better demonstrate the advantages of the present invention, the electrochemical and mechanical properties of the positive electrodes prepared in each specific embodiment and comparative example were tested. The specific testing methods are as follows: Constant current charge / discharge test: conducted on the LAND battery testing system, with the voltage range set at 1.0-3.0 V (vs. Li / Li). +Charge-discharge cycles were performed at rates of 0.1C, 0.2C, 0.5C, 1C, and 2C, and the initial charge-discharge capacity, coulombic efficiency, and cycle stability were recorded.
[0072] Electrochemical impedance spectroscopy (EIS): using an electrochemical workstation, at 10 6 -10 -2 The electrode interface impedance and charge transfer resistance were analyzed under the condition of 5 mV amplitude within the Hz frequency range.
[0073] Microscopic morphology characterization: Scanning electron microscopy (SEM) was used to observe the uniformity of nanofiber deposition on the carbon fiber surface and the morphological changes before and after vulcanization.
[0074] Tensile property testing: Based on ASTM D3039 standard, the tensile modulus and strength of the cathode composite material were tested to evaluate the impact of the electrospun network on structural integrity.
[0075] Based on the above testing methods, the performance test data of each embodiment and comparative example are shown in Table 1:
[0076] As can be seen from the data in Table 1, all specific examples 1-6 exhibit excellent overall performance. In particular, the data from Comparative Example 3 strongly demonstrates the necessity of the pre-oxidation step: due to the omission of this step, the PAN nanofibers melted and fused at high temperatures, resulting in structural collapse and extremely low initial capacity (120 mAh / g) and inability to cycle normally, essentially rendering the product ineffective. In contrast, Specific Example 1, which incorporated the pre-oxidation step, not only maintained the complete nanofiber structure but also achieved a high capacity of 700 mAh / g and a cycle retention rate of 92%.
[0077] Compared to the traditional LFP-coated cathode (Comparative Example 1), the SPAN nanofiber / carbon fiber integrated cathode prepared in this application achieves an order-of-magnitude improvement in specific capacity (from approximately 130 mAh / g to 680-850 mAh / g). This is mainly attributed to the high theoretical capacity of the SPAN material itself and the effective utilization of active materials by the nanofiber network structure. Meanwhile, the cycle stability of all embodiments is significantly better than that of the traditional elemental sulfur cathode (Comparative Example 2), demonstrating that the in-situ sulfurization process described in this application successfully prepares SPAN with a stable covalent bond structure and effectively suppresses the shuttle effect of polysulfides.
[0078] Regarding doping modification, Specific Example 2 and Specific Example 6 employed solid-state (SeS2) powder doping and liquid-phase selenium source (selenic acid) doping, respectively, significantly improving rate performance. Specifically, Specific Example 2, through doping modification by adding SeS2 to the spinning solution, significantly increased its capacity retention at 1C rate from 60% to 75%. This indicates that the introduction of Se atoms effectively improved the intrinsic electronic conductivity of the SPAN material, improved solid-state reaction kinetics, and made it more suitable for high-power discharge scenarios. Compared to Specific Example 2, the liquid-phase doping in Specific Example 6 enabled the selenium source to achieve molecular-level dispersion in the spinning solution, avoiding the risk of nozzle clogging caused by solid particle agglomeration, and also made the distribution of selenium atoms in the final SPAN framework more uniform. Data shows that the rate performance (78%) and first-cycle coulombic efficiency (74%) of Specific Example 6 were slightly higher than those of Example 2, demonstrating the advantages of the liquid-phase doping strategy in improving the microstructure uniformity and reaction kinetics of the active material.
[0079] Compared to Specific Example 1, Specific Example 3 improves the active material loading through multilayer deposition. Although the areal capacity is improved, the rate performance is slightly reduced (55% vs 60%) due to the increased thickness of the nanofiber layer and the longer ion transport path. In practical applications, the loading thickness needs to be weighed according to the specific energy density and power density requirements.
[0080] To address interface and mechanical issues, specific embodiment 4 employs a gradient CNT interface design, which outperforms specific embodiment 1 in both rate performance (78%) and tensile strength improvement (25%), demonstrating the significant improvement of interface performance by the gradient conductive structure.
[0081] Specific embodiment 5 combines fiber orientation and liquid-phase selenium doping technology, exhibiting the best overall performance. Its tensile strength improvement rate reaches 40%, far exceeding that of other embodiments, indicating that the oriented nanofiber structure endows the composite material with excellent mechanical reinforcement effect, perfectly meeting the load-bearing requirements of structural batteries; at the same time, the high capacity of 880 mAh / g and the rate retention rate of 82% also prove its superior electrochemical performance.
[0082] In Comparative Example 1 (LFP), although the coulombic efficiency was high and the cycle stability was stable, its specific capacity was limited by the low theoretical capacity of the LFP material itself (170 mAh / g), which could not meet the high energy density requirements of the structural battery. In addition, in the bending test, obvious interfacial delamination was found between the coating layer and the carbon fiber substrate, while the electrospun network of Example 1 was tightly bonded to the carbon fiber and no delamination was observed.
[0083] In Comparative Example 2 (elemental sulfur), although the initial capacity was extremely high, the capacity decayed very rapidly, with a capacity retention of less than 40% after 100 cycles. This is because the polysulfides generated by elemental sulfur during charge and discharge dissolve in the electrolyte, leading to the loss of active material and a "shuttle effect." In contrast, Specific Example 1, by fixing sulfur atoms through CS covalent bonds, achieved a capacity retention of over 90%, verifying the superiority of the SPAN structure.
[0084] In summary, the preparation method provided in this application successfully constructs a high-performance integrated cathode structure, solving key problems such as low capacity, weak interfacial bonding, and shuttle effect in traditional battery cathode structures.
[0085] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A method for producing a positive electrode of a polymer lithium ion battery, characterized by, Includes the following steps: Using carbon fiber woven fabric as a receiving substrate, a polyacrylonitrile solution is electrospun to deposit polyacrylonitrile nanofibers on the surface of the carbon fiber woven fabric and in the fiber gaps. The carbon fiber woven fabric with the deposited polyacrylonitrile nanofibers is subjected to pre-oxidation treatment; the pre-oxidized composite is then heat-treated in a sulfur-containing atmosphere to convert the polyacrylonitrile nanofibers into vulcanized polyacrylonitrile nanofibers in situ, thereby obtaining the positive electrode.
2. The production method according to claim 1, characterized by, Prior to the electrospinning step, a desizing process is also included for the carbon fiber woven fabric.
3. The preparation method according to claim 1, characterized in that, The polyacrylonitrile solution is an N,N-dimethylformamide solution of polyacrylonitrile, wherein the concentration of polyacrylonitrile is 8-12 wt%.
4. The preparation method according to claim 1, characterized in that, The electrospinning process parameters are: voltage 15-20 kV, injection rate 0.5-1.0 mL / h, and receiving distance 12-15 cm.
5. The preparation method according to claim 1, characterized in that, The heat treatment is performed at a temperature of 300-500℃ for 1-4 hours.
6. The preparation method according to claim 1, characterized in that, The sulfur-containing atmosphere is provided by the sublimation of sulfur powder under an inert atmosphere, and the mass ratio of the carbon fiber woven fabric with deposited polyacrylonitrile nanofibers to the sulfur powder is 1:3 to 1:
5.
7. The preparation method according to claim 1, characterized in that, Following the heat treatment step, the process further includes treating the sample under vacuum at 150-250°C for 20-40 minutes to remove unbonded sulfur.
8. The preparation method according to claim 1, characterized in that, The polyacrylonitrile solution also contains selenide powder, and the heat treatment yields selenium-doped sulfurized polyacrylonitrile nanofibers; or The polyacrylonitrile solution also contains a selenium source, and the heat treatment yields selenium-doped sulfurized polyacrylonitrile nanofibers; the selenium source is selenic acid or selenate, and its concentration in the solution is 0.01-0.1 mol / L.
9. The preparation method according to claim 8, characterized in that, The selenide powder is SeS2, and its addition amount is 1-10 wt% of the mass of polyacrylonitrile.
10. The application of a positive electrode prepared by any one of claims 1-9 in an all-carbon fiber structure lithium-sulfur battery.