Preparation method and application of high-load stable PMAAC-I composite positive electrode

Abstract

The application belongs to the technical field of water-based zinc-iodine battery electrode materials, and discloses a preparation method and application of a high-load stable PMAAC-I composite positive electrode. A MXene dispersion liquid and a polyethylene imine solution are stirred to perform electrostatic self-assembly, then an ANF water dispersion liquid and an activated carbon dispersion liquid are sequentially added and stirred to obtain a composite electrode slurry, the composite electrode slurry is subjected to suction filtration and drying to obtain a PMAAC composite electrode sheet, then an iodine-containing positive electrolyte is loaded on the surface of the PMAAC composite electrode sheet, and the PMAAC-I composite positive electrode is obtained after drying. The prepared PMAAC-I composite positive electrode successfully integrates physical confinement, chemical anchoring and rapid electron transmission, and effectively alleviates the problems of loss of iodine species and limited transmission of iodine species under high load conditions.

Description

Technical Field

[0001] This invention belongs to the technical field of aqueous zinc-iodine battery electrode materials, specifically relating to a method for preparing and applying a high-load stable PMAAC-I composite cathode. Background Technology

[0002] With the rapid development of renewable energy grid connection and portable and flexible electronic devices, safe, low-cost, and long-life electrochemical energy storage technology has become a research hotspot in the industry. Aqueous zinc-iodine batteries, relying on the high theoretical capacity of the zinc anode, the inherent safety of the aqueous electrolyte, and the conversion-type energy storage mechanism of the iodine cathode, do not suffer from the lattice distortion and metal dissolution problems of traditional manganese-based and vanadium cathodes, making them ideal energy storage devices for next-generation large-scale energy storage and flexible wearable devices. However, the industrialization of zinc-iodine batteries still faces two major technological bottlenecks: First, during charging and discharging, elemental iodine and iodide ions easily combine to form I3. - I5 - Soluble polyiodides can migrate across the separator to the zinc anode and cause side reactions, triggering a shuttle effect that leads to loss of active materials, increased battery self-discharge, and a significant reduction in cycle life. Secondly, to improve battery energy density, the iodine loading needs to be increased. However, traditional cathodes are prone to problems such as loose structure, obstructed ion transport, and slow kinetics under high iodine loading conditions, making it difficult to achieve both energy density and rate performance.

[0003] The current mainstream solution in the industry is to prepare a high-iodine-loading cathode by combining MXene with carbon materials and a polymer bonding framework, with patent CN202411624044.1 being a typical example. This solution uses MXene as the electrochemical functional component, activated carbon as the physical carrier, and cellulose as the bonding framework, and prepares the composite iodine cathode through a combination of vacuum filtration and electrolyte dripping. The iodine loading range of this solution is 10~23 mg. cm -1 Maximum iodine loading 23.0 mg cm -1 The corresponding area-specific capacity is 4.0 mAh. cm -1 ; at 0.1 A g -1 At low current density, the mainstream sample MX-AB-I retains 95.65% of its capacity after 260 cycles. Even with these fundamental properties, this technology still has several significant drawbacks: First, MXene sheets are prone to agglomeration and stacking due to van der Waals forces, which not only block ion transport channels and reduce effective active sites, but also increase electrode interface impedance, causing deterioration of electrochemical reaction kinetics and making them unsuitable for high-current, fast-charging and other application scenarios. Second, this system relies solely on the two-stage passive adsorption structure formed by activated carbon and pristine MXene, without introducing strongly polar functional groups to enhance the anchoring effect on polyiodides. After being fully charged and left to stand at room temperature for 24 hours, the capacity retention rate was only 74.2%, while the capacity retention rate of the pure carbon control group AB-I was even lower at 63.1%. Polyiodides readily dissolve and migrate in the electrolyte, and the shuttle effect is difficult to suppress effectively, resulting in poor battery storage performance and failing to meet the requirements for long-term energy storage. Third, the active material in this composite system will be continuously lost during long-term operation. The capacity of MX-AB-I shows a significant decay after 260 cycles, and the 0.5MX-AB-I sample with reduced doping level completely fails after 160 cycles. The overall service life is difficult to meet the requirements of commercial energy storage devices. Fourth, this technology uses cellulose as the skeleton material, which has relatively low mechanical strength. Under the repeated volumetric deformation stress caused by charging and discharging, the electrode is prone to cracking and material shedding. Furthermore, cellulose is easily swollen and degraded in aqueous electrolyte environments, and its bonding with MXene and carbon materials relies solely on physical entanglement, resulting in weak interfacial adhesion. The highest iodine loading in this system can reach 23.0 mg. cm -1 However, under high load conditions, the electrode structure will gradually loosen and collapse, significantly limiting the improvement of load capacity.

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing a high-load stable PMAAC-I composite cathode. This invention modifies MXene with polyethyleneimine and replaces the traditional cellulose skeleton with aramid nanofibers to construct a multi-level synergistic composite structure. This effectively improves problems such as MXene layer stacking, polyiodide shuttle, electrode structure damage, and poor reaction kinetics, comprehensively enhancing the overall performance of aqueous zinc-iodine batteries. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing a high-load stable PMAAC-I composite cathode and its application. The high-load stable PMAAC-I composite cathode provided by this invention has high iodine loading capacity, strong adsorption anchoring, fast ion transport and excellent structural integrity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] A method for preparing a high-load stable PMAAC-I composite cathode includes the following steps: (1) preparing a PEI-MXene composite dispersion: adding a polyethyleneimine solution to the MXene dispersion, wherein the solid mass ratio of the MXene dispersion to the polyethyleneimine solution is 1:(0.01-0.05), stirring to perform electrostatic self-assembly, and obtaining a PEI-MXene composite dispersion; (2) preparing a composite electrode slurry: adding an ANF aqueous dispersion to the PEI-MXene composite dispersion in step (1), and stirring to perform electrostatic self-assembly. After the first stirring, an activated carbon dispersion is added, and a second stirring is performed to obtain a composite electrode slurry; the solid mass ratio of the PEI-MXene composite dispersion to the ANF aqueous dispersion and the activated carbon dispersion is 1:(0.6~0.7):(6~7); (3) Preparation of composite electrode sheet: The composite electrode slurry of step (2) is filtered and dried to obtain a PMAAC composite electrode sheet; (4) Iodine loading: Iodine-containing positive electrode electrolyte is loaded onto the surface of the PMAAC composite electrode sheet, and after drying, a PMAAC-I composite positive electrode is obtained. The above solid mass ratio refers to the solid matter (converted to dry weight) in each dispersion / solution, such as 500 μL of the MXene dispersion (30 mg) After diluting the MXene dispersion with 25 mL of deionized water and stirring, a 3 wt% polyethyleneimine solution is added. The dry weight of solids in the MXene dispersion is 15 mg, and the dry weight of solids in the polyethyleneimine solution is 0.45 mg. The mass ratio of solids in the MXene dispersion to the polyethyleneimine solution is 15 mg: 0.45 mg, or 1:0.03.

[0008] This invention uses polyethyleneimine (PEI) to pre-modify MXene to construct PEI-MXene synergistic functional units. The PEI-MXene complex is constructed through an electrostatic self-assembly strategy, in which positively charged PEI aqueous solution is added dropwise to negatively charged MXene dispersion, and in-situ composite is achieved by electrostatic interaction. PEI not only effectively blocks the interlayer stacking of MXene nanosheets through steric hindrance and electrostatic repulsion, but its rich amino functional groups can also form strong chemical interactions with polyiodides, significantly enhancing the chemical anchoring ability of active substances. Building upon this foundation, aramid nanofibers (ANF) were further introduced as a flexible three-dimensional framework. ANF can form a stable, high-porosity mechanical network in the composite cathode, effectively buffering volume changes during cycling. Its excellent mechanical strength and thermal stability provide ideal support for constructing high-load electrodes. PEI-MXene functional units were bridged and integrated with wood-based activated carbon (AC) microparticles. Through steps such as filtration to form a film, drying, and drying with iodine-loaded solution, a multi-level composite cathode material—PEI-MXene / ANF / AC-I (abbreviated as PMAAC-I)—was successfully prepared. In this material, the PEI-MXene functional units play a crucial role in inhibiting polyiodide shuttle and accelerating iodine conversion reactions, constructing fast electron transport channels, and enhancing chemisorption. The main roles of activated carbon and aramid nanofibers in the cathode are to provide physical confinement sites and mechanical framework support, respectively.

[0009] Preferably, in step (1), the stirring time is 20-60 min; in step (2), the first stirring time is 20-60 min, and the second stirring time is 12-36 h. The stirring speed for all three stirring operations is 400-600 rpm.

[0010] Preferably, in step (1), the preparation method of the MXene dispersion includes the following steps: S1: Etching reaction: Add HCl to LiF, stir until the solution is clear, add Ti3AlC2, and stir at 30-40℃ until the solution is dark green to obtain multilayer Ti3C2T X The solution contains LiF, HCl, and Ti3AlC2 in a ratio of (1-2) g: (14-16) mL: (0.5-1) g, wherein the concentration of HCl is 11-12 mol. L -1 The first stirring speed is 600-800 rpm, and the stirring time is 5-10 min; the second stirring speed is 600-800 rpm, and the stirring time is 24-48 h; S2: Washing and centrifugation: Add the multilayer Ti3C2T from step S1... XThe solution was washed with deionized water and centrifuged until the pH of the supernatant reached 6.0. The lower part of the liquid was then collected and resuspended in water to obtain the multilayer Ti3C2T. X Washing solution; the parameters for each centrifugation are: rotation speed 3500-4500 rpm, time 2-5 min; S3: ultrasonic exfoliation: the multilayer Ti3C2T from step S2 is removed. X The washing solution is sonicated for 60-80 min, centrifuged after sonication, and the supernatant is taken to obtain the MXene dispersion. In step S3, the sonication power is 250-350 W, argon gas is continuously introduced during sonication, and the sonication time is 45-75 min; the centrifugation speed is 3500-4000 rpm and the time is 0.5-5 min.

[0011] Preferably, in step (2), the preparation method of the ANF aqueous dispersion includes the following steps: P1: Preparation of ANF / DMSO dispersion: First, dimethyl sulfoxide, KOH and deionized water are mixed evenly to obtain a mixture, then poly(p-phenylene terephthalamide) is dispersed in the mixture, and after stirring, an ANF / DMSO dispersion is formed, wherein: the mass ratio of dimethyl sulfoxide, KOH and deionized water is (540-560):(1.4-1.6):(19-21); the mass ratio of poly(p-phenylene terephthalamide) to the mixture is 1:(560-580); the stirring speed is 400-600 rpm, the temperature is 30-60℃, and the time is 4-12 minutes. P2: Preparation of the mixed gel: Deionized water is added to the ANF / DMSO dispersion obtained in step P1 as a proton donor, and stirring is continued to complete the deprotonation reaction. After the reaction is completed, the mixture is filtered to obtain the mixed gel. The stirring speed is 400-600 rpm, the temperature is 25-30 ℃, and the time is 1-2 h. P3: Purification: Ethanol and deionized water are added to the mixed gel obtained in step P2 for washing and filtration. Then, the mixture is dispersed in deionized water by stirring to obtain an ANF aqueous dispersion. The stirring speed is 400-600 rpm, the temperature is 25-30 ℃, and the time is 0.5-1 h.

[0012] Preferably, in step (2), the solid content of the activated carbon dispersion is 4-5 mg / mL; the activated carbon in the activated carbon dispersion is wood-based activated carbon.

[0013] Preferably, in step (3), the filtration is vacuum filtration, and the filtration time is 20-40 min; the drying is vacuum drying, and the drying temperature is 50-70℃ and the drying time is 8-24 h.

[0014] Preferably, in step (4), the iodine-containing positive electrode electrolyte is an aqueous solution containing 0.1 M I₂ and 0.5 M ZnI₂. The iodine-containing positive electrode electrolyte is an aqueous system, and the solutes include 0.1 mol / L I₂ and 0.5 mol / L ZnI₂. This electrolyte ratio provides sufficient I₂. - / I3 - Redox active materials, adapted to the cyclic testing conditions of ultra-high iodine-loaded composite cathodes. The high-load stable PMAAC-I composite cathode prepared by the above-described method comprises: a PEI-MXene functional unit assembled from MXene and polyethyleneimine, a flexible three-dimensional framework composed of aramid nanofibers, a multi-level confined support composed of activated carbon, and a loaded iodine active material; the iodine loading of the high-load stable PMAAC-I composite cathode is 6.8-26.9 mg. cm -2 .

[0015] Application of high-load stable PMAAC-I composite cathode in the assembly of zinc-iodine batteries.

[0016] Beneficial Effects: This invention provides a method for preparing a high-load stable PMAAC-I composite cathode. Polyethylene imine is modified onto an MXene dispersion via electrostatic self-assembly to obtain a PEI-MXene functional unit that combines anti-stabilization stacking, enhanced conductivity, and strong chemisorption properties. This is further enhanced by a three-dimensional mechanical framework of aramid nanofibers and physical confinement by high-porosity wood-based activated carbon, successfully integrating physical confinement, chemical anchoring, and rapid electron transport. Batteries assembled based on the prepared composite cathode further demonstrate its promising application prospects at the device level. The PMAAC-I composite cathode prepared by this method provides an effective solution to simultaneously address the shuttle effect and kinetic limitations of high-load zinc-iodine batteries, specifically offering the following advantages: (1) This invention introduces polyethyleneimine (PEI) to intercalate MXene, which effectively suppresses van der Waals aggregation between MXene sheets and alleviates the stacking phenomenon of MXene sheets, enabling it to form a smooth and uniform porous conductive network together with ANF, thereby increasing the BET specific surface area to 108.757 m². 2 g -1 This significantly shortens the ion transport path, providing a solid physical basis for achieving excellent rate performance and fast charge and discharge.

[0017] (2) This invention constructs a synergistic adsorption mechanism of "amino electron-donating-titanium center redox-hydroxyl proton coupling". The electron-rich amino groups in PEI synergistically interact with the Ti active centers on the MXene surface to adsorb soluble polyiodides (such as I3) - The iodine content on the zinc anode surface is reduced and chemically anchored at the positive electrode. Experiments have shown that this mechanism significantly reduces the iodine content on the zinc anode surface, effectively inhibiting zinc corrosion and dendrite growth caused by the shuttle effect, achieving a coulombic efficiency of nearly 99% and excellent interfacial stability.

[0018] (3) The introduction of PEI significantly optimized the charge transfer kinetics at the electrode / electrolyte interface. The PMAAC-I composite cathode exhibited a low redox peak potential difference (ΔEp) and high symmetry in its CV curve. This indicates that the PEI-MXene functional unit significantly reduced the activation energy of the reaction and accelerated the I2 / I2 / I2 reaction. - The conversion reaction rate allows the electrode to maintain a small polarization even with a high areal loading, achieving a high utilization rate of active materials (90.4% in the first cycle).

[0019] (4) By combining aramid nanofibers (ANF) with PEI-MXene and activated carbon, the three-dimensional framework constructed in this invention possesses both high mechanical strength and high porosity, effectively inhibiting the swelling and degradation of cellulose-based frameworks in aqueous environments. At 13.4 mg cm -2 With ultra-high iodine areal loading, the PMAAC-I cathode maintained a capacity retention of 93.9% after 200 cycles at 3 A. g -1 After 10,000 long cycles at high current density, the single-cycle capacity decay is less than 0.0012%, achieving compatibility between high load and long cycle life. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 Preparation process of PMAAC-I composite cathode.

[0022] Figure 2 Optical photographs and microscopic structural diagrams of the intermediate component dispersion during the preparation of PMAAC composite electrode slurry.

[0023] Figure 3Characterization results of MXene dispersion and PEI-MXene dispersion, where: (a) TEM image of MXene dispersion, with the inset showing the Tyndall effect of MXene dispersion; (b) TEM image of PEI-MXene composite dispersion, with the inset showing the Tyndall effect of PEI-MXene composite dispersion.

[0024] Figure 4 : Elemental map surface scan of PEI-MXene.

[0025] Figure 5 XRD patterns of Ti3AlC2(MAX), MXene, and PEI-MXene.

[0026] Figure 6 EDS elemental distribution diagram of PMAAC-I composite cathode.

[0027] Figure 7 Electrochemical impedance spectroscopy (EIS) of MAAC-I composite cathodes with different MXene contents: (a) EIS; (b) EIS at 0.1 A. g -1 (c) Cycle count-specific capacity curve at current density for 50 cycles; (d) Comparison of capacity retention and average coulombic efficiency.

[0028] Figure 8 (a) Optical photographs of PEI-MXene composite dispersions with different PEI mass fractions; (b) Zeta potential.

[0029] Figure 9 (a) Electrochemical impedance spectroscopy; (b) Rate performance at different current densities (current density range: 0.2-3 A) of PMAAC-I composite cathodes constructed based on PEI-MXene composite dispersions with different PEI mass fractions. g -1 ).

[0030] Figure 10 SEM surface morphology of AAC, MAAC and PMAAC electrode sheets at (a) 10 μm and (b) 1 μm; (c) SEM cross-sectional morphology of AAC-I, MAAC-I and PMAAC-I composite cathodes.

[0031] Figure 11: Specific surface area and pore size distribution of AAC, MAAC and PMAAC; where: (a) nitrogen adsorption-desorption curve of AC; (b) nitrogen adsorption-desorption curve of MXene nanosheets; (c) nitrogen adsorption-desorption curve of PEI-MXene unit; (d) pore size distribution curves of AC, MXene and PEI-MXene; (e) nitrogen adsorption-desorption curves of AAC, MAAC and PMAAC electrodes; (f) pore size distribution curves of AAC, MAAC and PMAAC electrodes.

[0032] Figure 12 The adsorption results of iodine solution and iodine solutions with added activated carbon, MXene, and PEI-MXene respectively; where: (a) physical image of iodine adsorbed after 24 h; (b) UV-Vis absorption spectrum of the corresponding solution after 24 h adsorption; (c) the adsorption of I3 by the three adsorbents. - The adsorption capacity and corresponding specific surface area are shown in the figure. In the figure, "original" refers to the untreated iodine solution, "AC" refers to the iodine solution after adding activated carbon, "MXene" refers to the iodine solution after adding MXene, and "PEI-MXene" refers to the iodine solution after adding PEI-MXene.

[0033] Figure 13 Thermogravimetric analysis curves of iodine-loaded electrodes (AAC-I, MAAC-I and PMAAC-I).

[0034] Figure 14 The shift of the (002) peak in the XRD patterns of MXene and PEI-MXene before and after adsorption of iodine solution; in the figure, MXene / I catholyte and PEI-MXene / I catholyte refer to MXene and PEI-MXene after adsorption of iodine solution, respectively.

[0035] Figure 15 XPS spectra of MXene and PEI-MXene before and after adsorption of iodine solution.

[0036] Figure 16 High-resolution fine spectra of Ti 2p before and after iodine adsorption by MXene and PEI-MXene: (a) and (b) PEI-MXene.

[0037] Figure 17 (a) High-resolution fine N 1s spectra of PEI-MXene before and after adsorption of iodine solution; (b) High-resolution fine I 3d spectra of MXene and PEI-MXene after adsorption of iodine solution.

[0038] Figure 18 High-resolution fine spectra of O 1s before and after 1-s adsorption of MXene and PEI-MXene into iodine solution (a) and (b).

[0039] Figure 19 (a) High-resolution fine spectrum of I after AC adsorption of iodine solution 3d; (b) C 1s spectrum and (c) O 1s spectrum before and after AC adsorption of iodine solution.

[0040] Figure 20 : Schematic diagram of a battery structure based on composite cathode assembly; where (a) is a coin cell and (b) is a pouch cell.

[0041] Figure 21 (a) Electrochemical impedance spectroscopy analysis of AAC-I, MAAC-I, and PMAAC-I, and (b) Electrochemical impedance spectroscopy analysis at 0.2 mV. s -1 Cyclic voltammetry curves at scan rate.

[0042] Figure 22 Cyclic voltammetry curves (a, c, e) and CV contour plots (b, d, f) at different scan rates: (a, b) AAC-I; (c, d) MAAC-I; (e, f) PMAAC-I.

[0043] Figure 23 Capacitance contribution percentage of AAC-I, MAAC-I, and PMAAC-I at different scan rates.

[0044] Figure 24 : PMAAC-I, MAAC-I and AAC-I at 0.1 A g -1 (Corresponding area current 1.34 mA) cm -2 (a) Charge-discharge cycle capacity curves and corresponding coulombic efficiencies at current density; (b) Iodine utilization and average coulombic efficiency.

[0045] Figure 25 First-cycle charge-discharge GCD curves of PMAAC-I, MAAC-I, and AAC-I.

[0046] Figure 26 : PMAAC-I, MAAC-I and AAC-I at 3 A g -1 (Corresponding area current 40.2 mA) cm -2 Long-term cycling stability test at high rates.

[0047] Figure 27 PMAAC-I, MAAC-I, and AAC-I are suitable for current densities starting from 0.2 A. g -1 Gradually rise to 3A g -1It then dropped back to 0.2 A. g -1 Specific capacity change curve during the process Figure 28 Performance of zinc-iodine batteries AAC-I (a, b), MAAC-I (c, d), and PMAAC-I (e, f) after 24 hours of rest; where (a, c, e) represents capacity retention and (b, d, f) represents the corresponding voltage-capacity curves.

[0048] Figure 29 (a) PMAAC-I at iodine loadings of 6.8, 20.2, and 26.9 mg, respectively. cm -2 (a) Cyclic capacity retention rate under the given conditions; (b) Average coulombic efficiency under the corresponding cyclic conditions.

[0049] Figure 30 : Mass specific capacity and area specific capacity of PMAAC-I under different iodine loading.

[0050] Figure 31 PMAAC-I-Zn pouch cell at 0.1 A g -1 Long-cycle curves at current density. Detailed Implementation

[0051] The present invention will be further described in detail below through embodiments.

[0052] Example 1: Preparation of MXene Dispersion The steps for preparing MXene dispersions via liquid-phase exfoliation are as follows: (1) Etching reaction: 1.6 g of LiF was added to 15 mL of 12 mol solution in one go. L -1 In HCl, the solution was magnetically stirred (5 min at 700 rpm) to form a clear solution (HF was generated in situ). 1 g of Ti3AlC2(MAX) powder was slowly added, and the mixture was stirred in a 35°C water bath (48 h at 700 rpm). During the reaction, the solution gradually changed from gray to dark green, indicating that the Al layer was selectively removed, resulting in the formation of multilayer Ti3C2T. x .

[0053] (2) Washing and centrifugation: After 48 h, the obtained solution was transferred to a centrifuge tube, and deionized water was added for multiple washing and centrifugation until the pH of the supernatant reached 6.0, thus obtaining the multilayer Ti3C2T after washing and centrifugation. x The parameters for each centrifugation were: rotation speed 3500 rpm, time 2 min.

[0054] (3) Peeling and dispersion: The resulting washed and centrifuged multilayer Ti3C2T x Pour the solution into a gas washing bottle and place it in an ice-water bath for sonication; the sonication power is 280 W and the sonication duration is 1 h (argon gas is continuously introduced during the process). Then, centrifuge at 3500 rpm for 1 min and collect the supernatant to obtain monolayer / few-layer Ti3C2T. X (MXene) dispersion, i.e., MXene dispersion.

[0055] The obtained MXene dispersion was characterized by transmission electron microscopy (TEM). The results are as follows: Figure 3 As shown in (a), the typical two-dimensional sheet structure of MXene can be clearly observed. At the same time, the aqueous dispersion of MXene exhibits a significant Tyndall effect, indicating that the dispersion system has excellent colloidal stability.

[0056] Example 2: Preparation of ANF Aqueous Dispersion An aqueous dispersion of ANF was prepared by donor-assisted deprotonation, comprising the following steps: 1 g of poly(p-phenylene terephthalamide) (PPTA) was dispersed in a mixture containing 500 mL of dimethyl sulfoxide (DMSO), 1.5 g of KOH, and 20 mL of deionized water. The mixture was stirred at 50 °C for 4 h (500 rpm, 50 °C) to form a uniform, deep red ANF / DMSO dispersion. Subsequently, 250 mL of deionized water was added to the ANF / DMSO dispersion as a proton donor, and stirring was continued for 1 h (500 rpm, 30 °C) to complete the reprotonation treatment. The resulting mixture was filtered under vacuum to obtain a gel. The gel was then repeatedly washed and filtered with ethanol and deionized water to thoroughly remove residual DMSO and potassium hydroxide impurities. Finally, the purified ANF was redispersed in deionized water under stirring conditions (stirring speed 500 rpm, temperature 30℃, time 0.5 h), and the volume was adjusted to 500 mL to obtain a stable ANF aqueous dispersion (ANF concentration 2 mg). mL -1 ), used for the subsequent preparation of composite cathodes.

[0057] Example 3: Preparation of activated carbon dispersion Because activated carbon is insoluble in water and has relatively large particles, it cannot be pre-dispersed into a large-scale suspension for storage. Therefore, the activated carbon dispersion needs to be stirred and dispersed each time it is used. When using, 100 mg of activated carbon (preferably 425 mesh wood-based activated carbon in this embodiment) is placed in 25 mL of deionized water and pre-dispersed by magnetic stirring for 30 min at a stirring speed of 500 rpm, resulting in a solid content of 4 mg. mL-1 Activated carbon dispersion.

[0058] Example 4: Preparation of PMAAC-I composite cathode The preparation steps of the PMAAC-I composite cathode are as follows: Figure 1 As shown, it includes: 500 μL of MXene dispersion (30 mg) mL -1 After diluting with 25 mL of deionized water and stirring for 2 min, add 45 μL of polyethyleneimine aqueous solution (hereinafter referred to as PEI solution) (10 mg). mL -1 In this embodiment, the PEI solution contained 0.45 mg of polyethyleneimine. Electrostatic self-assembly was then performed by stirring (stirring for 30 min at 500 rpm) to obtain a PEI-MXene composite dispersion. Subsequently, 5 mL of ANF aqueous dispersion (2 mg) was added. mL -1 Continue stirring for 30 min (500 rpm) to form a PEI-MXene / ANFs composite network, then add 25 mL of activated charcoal dispersion (4 mg). mL -1 The mixture was stirred for another 24 hours (500 rpm) to obtain a composite electrode slurry. The composite electrode slurry was then vacuum-filtered for 30 minutes to form a film, and vacuum-dried at 60°C for 12 hours to obtain a PEI-MXene / ANF / AC composite electrode sheet (denoted as PMAAC). Iodine was quantitatively added to the surface of the PMAAC composite electrode sheet (in this embodiment, if used for assembling a coin cell, iodine was added at 1.13 cm intervals). 2 100 μL of iodine-containing positive electrolyte was dropped onto the surface of the electrode sheet, corresponding to an iodine loading of 13.4 mg per square meter; if used for assembling a pouch battery, 100 μL of iodine-containing positive electrolyte was dropped onto the surface of the electrode sheet, corresponding to an iodine loading of 13.4 mg per square meter. 2 530-550 μL of iodine-containing positive electrode electrolyte was dropped onto the surface of the electrode sheet, corresponding to an iodine loading of 13.4 mg per square meter; the iodine-containing positive electrode electrolyte was an aqueous solution containing 0.1 M I2 and 0.5 M ZnI2. After vacuum drying at 60 °C for 12 h, the PMAAC-I composite positive electrode was obtained.

[0059] The colloidal stability of the intermediate component dispersion is as follows: Figure 2As shown, all systems exhibit a significant Tyndall effect, with no obvious aggregation or sedimentation, and can form stable aqueous colloids, providing a basis for the preparation of composite electrodes with uniform structures. During the preparation process, positively charged PEI and negatively charged MXene achieve in-situ composite through electrostatic self-assembly; high aspect ratio ANF fibers effectively connect PEI-MXene sheets and activated carbon particles through physical winding bridging, constructing a three-dimensional interpenetrating network structure, achieving uniform mixing of each component at the nanoscale, and obtaining a PMAAC composite electrode slurry with excellent stability.

[0060] The microstructure and elemental distribution of the PEI-MXene composite material are as follows: Figure 3 , Figure 4 As shown, compared to pure MXene, the edge contours of the PEI-MXene sheets are blurred, proving that the PEI polymer film was successfully coated onto the MXene surface, and the modified dispersion still exhibits good colloidal stability. Elemental surface scanning results show that nitrogen is uniformly distributed on the MXene sheet surface, further confirming the successful modification of MXene by PEI.

[0061] XRD test results of MXene and PEI-MXene are as follows Figure 5 As shown. The etched MXene exhibits a sharp (002) characteristic peak at 2θ=6.5°, a low-angle shift compared to the original MAX phase peak, and the aluminum layer-related impurity peaks completely disappear, proving that the aluminum layer was effectively etched and a few-layer MXene was successfully prepared. After PEI modification, the spectrum shows an amorphous broad diffuse peak corresponding to PEI, and the MXene (002) peak is further shifted to a low angle of 2θ≈6.4°, confirming that PEI intercalation can effectively expand the interlayer spacing, suppress layer stacking, and optimize the orderliness of layer stacking, forming a stable PEI-MXene composite structure. The uniformity of PMAAC-I electrode composition distribution was characterized by EDS surface scanning. Figure 6 Test results show that iodine is continuously distributed and the signal is uniform within the electrode, proving that active iodine can be uniformly loaded and stably retained inside the electrode. Simultaneously, the distributions of N and Ti elements highly overlap, directly confirming that PEI-MXene is tightly integrated with ANF and AC components, forming a continuous and uniform three-dimensional conductive network. This structure enables rapid electron and ion transport throughout the electrode domain, and the uniformly distributed chemisorption sites effectively mitigate polyiodide concentration gradients and suppress shuttle side reactions, providing structural assurance for the electrode's excellent rate performance and long-cycle stability.

[0062] Example 5: Preparation of PMAAC-I composite cathode The preparation steps of the PMAAC-I composite cathode are generally the same as in Example 4, except that only 15 μL (10 mg) of PEI solution is added. mL -1The self-assembly process was carried out by stirring for 20 minutes at a speed of 600 rpm; only 3.8 mL (2 mg) of ANF aqueous dispersion was added. mL -1 The stirring time after adding ANF aqueous dispersion was 20 min; only 19 mL (4 mg) of activated carbon dispersion was added. mL -1 The stirring time after adding activated carbon dispersion was 12 h; the vacuum-assisted filtration time was 20 min; the temperature of the two vacuum drying processes was 70℃ and the time was 8 h, resulting in a PMAAC-I composite cathode.

[0063] Example 6: Preparation of PMAAC-I composite cathode The preparation steps of the PMAAC-I composite cathode are generally the same as in Example 4, except that 75 μL (10 mg) of PEI solution is added. mL -1 The self-assembly process was carried out by stirring for 60 min at a speed of 400 rpm; 7.8 mL (2 mg) of ANF aqueous dispersion was added. mL -1 The stirring time after adding ANF aqueous dispersion was 60 min; 39 mL (4 mg) of activated carbon dispersion was added. mL -1 The stirring time after adding activated carbon dispersion was 36 h; the vacuum-assisted filtration time was 40 min; the temperature of the two vacuum drying processes was 50℃ and the time was 24 h, to obtain a PMAAC-I composite cathode.

[0064] Comparative Example 1: Preparation of AAC-I composite cathode Add 5 mL of ANF aqueous dispersion (2 mg) mL -1 Add 25 mL of activated carbon dispersion to the AAC composite electrode (ensuring the activated carbon content in the prepared AAC composite electrode sheet is the same as that in the PMAAC composite electrode sheet), stir for 24 h to obtain a composite electrode slurry. The composite electrode slurry is then vacuum-filtered to form a film, and vacuum-dried at 60 °C for 12 h to obtain an ANF / AC composite electrode sheet (denoted as AAC). Iodine is quantitatively added to the surface of the AAC electrode sheet, and after vacuum drying again at 60 °C for 12 h, the AAC-I composite cathode is obtained.

[0065] Comparative Example 2: Preparation of MAAC-I composite cathode 500 μL of MXene dispersion (30 mg) mL -1The solution was diluted with 25 mL of deionized water and stirred for 2 min. Then, 5 mL of ANF aqueous dispersion (2 mg) was added. mL -1 Continue stirring for 30 min, then add 25 mL of activated carbon dispersion (ensuring the activated carbon content in the prepared AAC composite electrode sheet is the same as that in the PMAAC composite electrode sheet), and continue stirring for 24 h to obtain the composite electrode slurry. The composite electrode slurry is then vacuum-filtered to form a film, and vacuum-dried at 60℃ for 12 h to obtain the MXene / ANF / AC composite electrode sheet (denoted as MAAC). Iodine is quantitatively added to the surface of the MAAC electrode sheet, and after vacuum drying again at 60℃ for 12 h, the MAAC-I composite cathode is obtained. The MAAC-I composite cathode contains 15 mg of MXene, 100 mg of activated carbon, and 10 mg of ANF.

[0066] Example 7: Regulation of PEI-MXene component ratio In the PMAAC-I composite cathode, the PEI-MXene functional units work together to play a key role in suppressing polyiodide shuttle and accelerating iodine conversion. To fully utilize this key role, this embodiment explores the optimal ratio of MXene to PEI, and then systematically analyzes its impact on the battery's electrochemical performance.

[0067] 1. Regulation of MXene content The amount of MXene introduced significantly affects the iodine conversion kinetics, specific capacity, cycle stability, and coulombic efficiency of the composite cathode. To optimize its dosage, MAAC-I composite cathodes with MXene contents of 5, 10, 15, 20, and 25 mg were prepared according to the steps of Comparative Example 2, while keeping the mass of wood-based activated carbon (AC) and aramid nanofibers (ANF) constant (other components remained unchanged). These were denoted as M5AAC-I, M... 10 AAC-I, M 15 AAC-I, M 20 AAC-I, M 25 AAC-I was tested, and its electrochemical performance was evaluated.

[0068] like Figure 7 As shown: In the electrochemical impedance spectroscopy, the semicircle diameter in the mid-to-high frequency region reflects the charge transfer impedance (Ro) at the electrode / electrolyte interface. ct ), where M 15 The AAC-I composite cathode exhibits the smallest semi-circular diameter, indicating that it possesses the lowest electrochemical impedance and the best interfacial reaction kinetics; at 0.1 A·g -1 After 50 constant current charge-discharge cycles at a current density, M 15The AAC-I composite cathode exhibits the highest average reversible specific capacity and best cycle stability; the corresponding capacity retention is 96.8%, and the average coulombic efficiency is 98.4%, both significantly better than other MXene content groups. This indicates that at this content, the electrode achieves an optimal balance between its anchoring ability for soluble polyiodides and the reversibility of redox reactions. These performance differences demonstrate the regulatory effect of MXene content on the electrode's microstructure and interfacial chemistry. When the MXene content is low (5-10 mg), it cannot form a continuous conductive network in the composite cathode, resulting in poor kinetics (manifested as a larger semicircle diameter in the electrochemical impedance spectroscopy), insufficient chemisorption sites, and difficulty in effectively adsorbing and catalyzing polyiodides (such as I3). - I5 - The rapid conversion of MXene to iodine leads to low utilization of active iodine species and limited reversible specific capacity. Increasing the MXene content to 15 mg resulted in uniform dispersion of the two-dimensional dispersion in the AC / ANF matrix, constructing an efficient three-dimensional electron conduction pathway and providing numerous electrochemical active sites, significantly improving the kinetic rate of the iodine redox reaction, thus achieving high specific capacity and excellent cycle stability. However, when the MXene content was further increased to 25 mg, the enhanced van der Waals forces caused irreversible stacking of the MXene dispersion, leading to reduced interlayer spacing and decreased effective specific surface area. Excessive MXene sheets may block the ion transport channels inside the composite cathode, hindering the flow of I- in the electrolyte. - / I3 - The free diffusion of plasma exacerbates concentration polarization, ultimately leading to accelerated capacity decay and reduced coulombic efficiency.

[0069] In summary, the introduction of 15 mg MXene in this experimental system achieved the best synergy between electronic conductivity, active site density and ion transport, exhibiting the best comprehensive electrochemical performance. Therefore, it was determined as the benchmark ratio for constructing the PMAAC composite cathode.

[0070] 2. Regulation of PEI content (1) Effect of PEI addition amount on the colloidal stability of MXene aqueous dispersion Following the method of Example 4, PEI-MXene composite dispersions with different PEI mass fractions were prepared: using MXene as a baseline, six groups were set with PEI mass fractions of 0%, 1%, 2%, 3%, 4%, and 5% (other components remained unchanged), i.e., the overall process was the same as in Example 4. The volumes of PEI solution added to the six groups were 0, 15, 30, 45, 60, and 75 μL (10 mg) respectively. mL -1 ).

[0071] Figure 8The results show that the pure MXene dispersion (0%) exhibits a typical homogeneous colloidal state with a Zeta potential of -28.16 mV, demonstrating good electrostatic stability. When the PEI addition is no higher than 2%, the absolute value of the Zeta potential is between 10 and 30 mV, and the system is in the metastable dispersion region. Low molecular weight PEI molecular chains penetrate into the MXene interlayers, achieving partial intercalation through weak physical adsorption, resulting in a moderate increase in interlayer spacing. However, the surface negative charge still dominates (Zeta potential below -20 mV), and the electrostatic repulsion is sufficient to counteract van der Waals forces. The dispersion maintains good dispersibility and fluidity, with no obvious aggregation. When the addition is increased to 3%, the Zeta potential drops to -7.63 mV. At mV, the electrostatic repulsion is significantly weakened, and the steric hindrance effect is insufficient to completely suppress the approach of the sheets. At this point, visible flocculent aggregates begin to appear in the system, but they can still be uniformly suspended. When the concentration is increased to 4% and 5%, the Zeta potential undergoes charge reversal. Excess PEI forms a supersaturated adsorption layer on the MXene surface, which not only neutralizes the initial negative charge but also introduces a net positive charge, inducing charge flocculation. At the same time, excess free PEI may bridge adjacent sheets, and the dispersion rapidly undergoes macroscopic stratification with obvious sedimentation at the bottom, indicating that the colloidal system has become severely unstable and cannot maintain a uniform dispersion state.

[0072] (2) Effect of PEI modification degree on electrode kinetic behavior and rate performance Following the method in Example 4, PMAAC-I composite cathodes with different PEI mass fractions (six groups of 0%, 1%, 2%, 3%, 4%, and 5% based on MXene) were prepared at 0.2–3 A·g. -1 Its electrochemical impedance and rate capacity were tested within the current density range.

[0073] like Figure 9 As shown, charge transfer resistance (R) ct The change in PEI content with increasing PEI concentration first showed a decreasing trend followed by an increasing trend: when the PEI content was ≤3%, R... ct The percentage of samples with PEI content significantly lower than the unmodified control group (0%) was 3%, with 3% of samples exhibiting the lowest interfacial charge transfer impedance, indicating that moderate PEI modification effectively improved the interfacial compatibility and electronic transport capacity between MXene and the active material; while when the PEI content was ≥4%, R... ct The increase is likely due to the agglomeration caused by excessive PEI, which prolongs the ion diffusion path and disrupts the continuity of the conductive network. Rate performance test results further validate the above analysis: under low current density conditions (≤0.4 A·g), -1 All electrodes with added PEI exhibited higher specific capacity than the unmodified electrodes, indicating that the introduction of PEI indeed optimized the electrode's microstructure and improved charge transport efficiency. However, at higher rate current densities (e.g., 3 A·g),...-1 (corresponding to approximately 14.2 C), the performance differences between PEI-modified electrodes with different mass fractions significantly increased. When the PEI content was ≤4%, the specific capacity at high rates was improved compared to the 0% sample, with the 3% PEI-modified PMAAC-I composite cathode exhibiting the best performance and a reversible specific capacity of 114 mAh·g. -1 However, when the PEI addition amount increased to 5%, the rate performance of the battery dropped sharply. This was mainly due to the excessive adsorption of PEI on the surface of the MXene sheets, which increased the polarization of the electrode at high current densities and slowed down the electrochemical reaction kinetics, ultimately resulting in a rapid decrease in specific capacity and a significant deterioration in rate performance.

[0074] In summary, the introduction of PEI needs to be strictly controlled within a moderate range. Therefore, this invention ultimately determined 3% as the optimal addition amount. Under this condition, PEI can enhance the chemical anchoring effect on polyiodides through its abundant amino functional groups, and maintain the good dispersibility and conductive network integrity of MXene, thereby achieving synergistic optimization of interface functionalization and transport dynamics.

[0075] Example 8: Electrode Morphology Comparison The AAC, MAAC, and PMAAC composite electrode sheets prepared in Comparative Examples 1, 2, and 4, as well as the AAC-I, MAAC-I, and PMAAC-I composite cathodes, were analyzed by scanning electron microscopy. The results are as follows: Figure 10 As shown, the AAC composite electrode sheet exhibits disordered particle packing, relying on the ANF fiber network to bind the activated carbon. Iodine adsorption is limited to physical channels, failing to inhibit the loss of active materials. Adding MXene to obtain the MAAC composite electrode sheet results in a smoother surface. MXene is uniformly dispersed and forms a continuous conductive network with ANF (MXene / ANF conductive network), adding chemisorption sites. However, this reduces surface porosity, hindering ion transport. The PEI-modified PMAAC composite electrode sheet exhibits a uniform structure. PEI intercalation alleviates MXene layer stacking and forms a continuous porous conductive network with ANF (PEI-MXene / ANF porous conductive network), significantly accelerating ion migration.

[0076] The cross-sectional morphology of the iodine-loaded electrode is shown in Figure 10 (c) AAC-I and MAAC-I have loose structures and large interfacial gaps, making them prone to collapse under cyclic stress. PMAAC-I, on the other hand, has tightly bonded components and a dense structure, and its excellent structural integrity ensures long-term cyclic stability.

[0077] Example 9: Comparison of iodine loading capacity of electrodes 1. Pre-experiment An aqueous solution containing 0.1 M I2 and 0.5 M ZnI2 was used as the positive electrode electrolyte. The solution was added quantitatively to the surface of the PMAAC composite electrode sheet, AAC composite electrode sheet, and MAAC composite electrode sheet prepared in Example 4, Comparative Example 1, and Comparative Example 2, respectively. After vacuum drying at 60°C for 12 h, iodine-loaded composite positive electrodes were obtained and were denoted as PMAAC-I, MAAC-I, and AAC-I, respectively.

[0078] To ensure the reliability of electrochemical performance comparisons, the actual iodine loading needs to be precisely controlled and verified. Taking typical loading conditions (addition of 100 μL of positive electrolyte) as an example, the relative error between the actual iodine loading mass of the electrode sheet and the theoretical value of iodine in the positive electrolyte was calculated through experiments on the mass difference of the electrode sheet before and after drying. This indicates that the loading method has good accuracy and repeatability. To further investigate the effect of iodine loading on the electrode specific capacity, 50, 100, 150, and 200 μL of positive electrolyte were added, respectively, yielding iodine surface loadings of 6.8, 13.4, 20.2, and 26.9 mg, respectively. cm -2 A series of composite cathodes (with other components increased proportionally. For example, when 50 μL was added, the electrode components were reduced by 0.5 times: activated carbon was reduced to 50 mg, MXene to 7.5 mg (PEI was 3% of the mass of MXene), and ANF to 5 mg) were used for subsequent comparative studies of electrochemical performance.

[0079] Considering that differences in electrode wettability might affect the uniformity of iodine loading and thus interfere with the accuracy of electrochemical performance comparisons, the contact angles of PMAAC-I, MAAC-I, and AAC-I with the electrolyte were measured to be 14.4°, 15.2°, and 15.7°, respectively. All three electrodes exhibited good wettability with the cathode electrolyte, allowing droplets to spread rapidly on the surface. This excellent interfacial wetting characteristic ensures that when using the same solution impregnation process for iodine loading, the electrolyte can fully penetrate into the internal pore structure of the electrode, thereby achieving efficient, uniform, and repeatable iodine loading. This confirms that subsequent differences in electrochemical performance originate from the electrode's own composition and microstructure, eliminating external interference caused by uneven wettability and loading.

[0080] 2. Study on specific surface area and pore size distribution The specific surface area and pore structure of a material directly determine its physical confinement and adsorption capacity for iodine species. Therefore, the pore structure characteristics of activated carbon (AC), MXene, PEI-MXene dispersion, and composite cathode were characterized by nitrogen adsorption-desorption tests. Figure 11The AC exhibits type I / IV isotherms and a type H3 hysteresis loop, possessing both abundant microporous and mesoporous structures, with a BET specific surface area reaching 670.432 m². 2 g -1 This provides ample physical sites for iodine adsorption. MXene is predominantly mesoporous with extremely low micropore content; its layered stacking results in a specific surface area of ​​only 19.768 m². 2 g -1 After modification with PEI, PEI intercalation effectively suppressed MXene sheet stacking, optimized the pore structure, and increased the specific surface area to 108.757 m². 2 g -1 Aperture distribution results ( Figure 11 d) indicates that AC is mainly composed of 2 nm micropores and 4–6 nm mesopores, while MXene only has 4–5 nm mesopores. In contrast, PEI-MXene simultaneously introduces 0–2 nm micropores while retaining the original mesopore structure, successfully constructing a micropore-mesopore multi-level pore system.

[0081] Further analysis was conducted on the pore structure of the AAC, MAAC, and PMAAC composite electrodes. Figure 11 The AAC electrode experienced partial pore blockage due to disordered particle accumulation, resulting in a decrease in specific surface area to 557.275 m². 2 g -1 In the MAAC electrode, MXene covers and blocks the micropores of the AC portion, further reducing the specific surface area to 501.372 m². 2 g -1 In contrast, the PMAAC electrode, supported by an ANF framework, achieves uniform composite of AC and PEI-MXene, effectively avoiding pore blockage and significantly increasing the specific surface area to 749.504 m². 2 g -1 This is superior to single AC and other composite electrodes. The pore sizes of all three types of electrodes are concentrated in the 2.10–4.48 nm mesoporous range, which is much larger than I... - I2, I3 - The isoiodine species kinetic diameter can achieve both efficient physical confinement of polyiodides and reduce ion transport resistance, thus balancing high iodine loading capacity with excellent reaction kinetic performance.

[0082] 3. Experiment on the adsorption mechanism of key components on polyiodides Take equal amounts of AC, MXene and PEI-MXene powders, and immerse them in iodine solution (containing 50 mM I2 and 250 mM ZnI2) and let them stand for 24 h.

[0083] The results are as follows Figure 12 As shown, compared to the unadsorbed iodine solution (Original), the colors of all sample solutions were significantly lighter, indicating that all three adsorbents have the ability to adsorb iodine. Among them, the sample solutions treated with MXene and PEI-MXene showed higher transparency, reflecting their stronger adsorption efficiency. The original solution exhibited the strongest I3 adsorption at 288 nm and 350 nm. - Characteristic absorption peaks were observed, but the corresponding absorption peak intensities significantly decreased after treatment with adsorbents (AC, MXene, PEI-MXene). The absorption peak intensity of the adsorbent-treated group containing MXene was significantly lower than that of the AC group, indicating that the addition of MXene significantly improves the adsorption effect of the adsorbent for iodine. The I3 in the PEI-MXene treated group... - The lowest absorption peak indicates that PEI modification further enhances the adsorption capacity of MXene for iodine. Based on UV-vis data, the adsorption capacity of iodine in three adsorbents—AC, MXene, and PEI-MXene—was quantitatively calculated: AC has a high specific surface area (670.4 m²). 2 ·g -1 Its abundant porous structure provides numerous physical adsorption sites for polyiodine substances, but its iodine adsorption capacity is only 0.73 g·g. -1 In contrast, the MXene dispersion had a significantly lower specific surface area (19.8 m²). 2 ·g -1 However, it exhibited a higher iodine adsorption capacity (1.27 g·g). -1 After modification with PEI, the specific surface area of ​​PEI-MXene increased to 108.7 m². 2 ·g -1 Meanwhile, the adsorption capacity further increased to 1.33 g·g -1 This indicates that the introduction of amino (-NH2) not only enhances the chemical anchoring ability, but also improves the physical adsorption performance by regulating the pore structure.

[0084] Thermogravimetric analysis was performed on AAC, MAAC, and PMAAC composite electrodes before iodine loading, as well as AAC-I, MAAC-I, and PMAAC-I composite cathodes after iodine loading, further revealing the iodine loading state and thermal stability of each composite material. Figure 13As shown, within the temperature range of room temperature to 600℃, all samples exhibited two distinct weight loss processes. Weight loss in the low-temperature region below 300℃ mainly corresponds to the sublimation and volatilization of physically loaded iodine, while weight loss in the high-temperature region above 400℃ originates from the thermal decomposition of chemically adsorbed iodine. Quantitative analysis indicates that with the introduction of non-volatile functional components (MXene and PEI), the iodine mass fraction of the composite cathode decreased sequentially from 67.4% in AAC-I to 53.9% in MAAC-I and 49.2% in PMAAC-I. This "dilution" of content at the same iodine adsorption capacity is a necessary mass sacrifice to achieve strong chemical anchoring capability. Although the absolute iodine content of PMAAC-I is slightly lower, its iodine volatilization initiation temperature is significantly delayed, and the weight loss process is more gradual, further confirming that the PEI-MXene functional unit effectively locks in iodine through strong chemical interactions. This strategy successfully transforms a simple high loading into a high stable loading, sacrificing a slight theoretical specific capacity for a qualitative improvement in the battery's long-cycle stability and rate performance.

[0085] 4. Analysis of the iodine adsorption mechanism of PEI-MXene unit Unlike activated carbon that relies solely on high specific surface area for physical adsorption, MXene and its composite materials achieve efficient capture of iodine species primarily through the synergistic effect of chemical adsorption by surface functional groups, tunable electron transfer of Ti elements, and interlayer confinement effect. Figure 14 The (002) peak of MXene shifted to a smaller angle after iodine adsorption, indicating that the interlayer spacing of MXene was significantly expanded due to iodine intercalation. This not only confirms that iodine entered the interlayer rather than remaining only on the surface, but also demonstrates that intercalation is an important component of its adsorption mechanism, essentially stemming from the chemical bonding between titanium atoms and iodine species. After PEI modification, the (002) peak of PEI-MXene showed an even greater shift to a smaller angle after iodine adsorption, indicating that the introduction of PEI further promoted the intercalation and adsorption of iodine in the interlayer, thereby increasing the overall adsorption capacity of the material for iodine.

[0086] To reveal the differentiated chemical capture mechanisms of iodine species by MXene and PEI-MXene at the atomic scale, XPS was used to systematically characterize the two adsorbents before and after adsorption. All spectra were charged to C 1s (284.8 eV) standard. Full spectrum ( Figure 15 The results showed that characteristic elemental signals of MXene, such as C 1s, Ti 2p, O 1s, and F 1s, were detected in all samples. The N 1s signal that appeared after the introduction of PEI confirmed the successful recombination of PEI and MXene. Meanwhile, a significant I 3d signal was observed only in samples impregnated with iodine solution, indicating that iodine was effectively adsorbed onto the material surface. (Ti 2p fine spectrum...) Figure 16This visually reflects the change in the electronic state of the active sites of titanium during the adsorption of iodine. After pure MXene adsorbs iodine, its Ti 2p binding energy shifts significantly positively in eV, indicating that titanium undergoes oxidation (Ti 2p binding energy shifts to the positive value). n+ → Ti (n+δ)+ This is for I - / I3 - Coordination and charge transfer with titanium sites provide strong evidence. Meanwhile, PEI-MXene, in the absence of iodine adsorption, exhibits Ti 2p... 3 / 2 The binding energy (454.65 eV) shifts negatively compared to pure MXene, indicating that the electron-rich amino groups of PEI form a strong coupling with the MXene surface, leading to an increase in the electron cloud density around the titanium interface, placing it in an electron-rich state. When PEI-MXene adsorbs iodine, the Ti 2p binding energy shifts back, indicating that these enriched electrons are consumed during adsorption. Figure 17 As shown in (a), after iodine adsorption, the N 1s high-resolution XPS spectrum of PEI-MXene shifts overall towards the direction of higher binding energy, indicating a decrease in the electron cloud density of nitrogen atoms, suggesting that the amino groups (-NH2 / -NH3) in PEI... + As an electron donor, it underwent a strong chemical interaction with the iodine species, resulting in the partial loss of electrons from the nitrogen atom. This result is consistent with... Figure 17 (b) The I3d spectra are highly consistent, jointly confirming that nitrogen atoms in PEI play a crucial role in enhancing the iodine chemisorption process. The high-resolution I3d spectra reveal the differentiated capture behavior of different adsorbents in the complex iodine system (I2 / ZnI2 solution) at the chemical state level. The main peaks at 618.83 eV and 630.45 eV in the MXene spectrum are attributed to iodide ions (I... - The peaks at 620.50 eV and 631.74 eV correspond to I3. - The presence of iodine species or weakly bound iodine on the surface indicates that MXene has a good chemical affinity for iodine species in solution. The I3d peak of PEI-MXene shifts overall towards lower binding energies, and its I... - The characteristic peak binding energy decreases, which is attributed to I3. - The / I2 peak also decreased synchronously. This shift indicates that the adsorbed iodine is in a chemical environment with a higher electron density, stemming from the modulation of the electronic structure of the MXene interface by the electron-rich amino groups of PEI. This further confirms that the introduction of PEI significantly enhances the chemical anchoring ability of the composite material for polyiodides and the interfacial bonding stability.

[0087] The change in Ti 2p binding energy, the electron loss behavior of nitrogen atoms reflected in the 0.56 eV shift of N 1s towards higher binding energy directions, and the I 3d... -The significantly enhanced signal reflects the electron-gaining process of iodine, and the trends of these three factors are highly consistent, forming a complete chain of mutually corroborating evidence. When PEI-MXene interacts with iodine species, electrons tend to be transferred directionally along the N→Ti→I pathway. The electron-rich amino groups in PEI first donate electrons to the Ti active sites of MXene, and then the Ti sites transfer electrons to the adsorbed polyiodides (such as I3). - ), to restore it to I - And it is stably anchored. This cascaded electron transfer not only enhances the fixation effect of iodine at the interface, but also because of I... - The generation of these compounds further increases the local negative charge density, promoting the adsorption and transformation of more iodine species, thus creating a positive promoting effect. In contrast, unmodified MXene mainly relies on the direct chemisorption of iodine by surface oxygen-containing functional groups (such as -O and -OH) and Ti sites. Although it has a certain capture capacity, it lacks efficient electron supply channels, making it difficult to achieve deep reduction and high-density anchoring of polyiodides.

[0088] O 1s high-resolution fine spectrum ( Figure 18 This indicates that for pure MXene, after adsorption, Ti-(OH) x The signal strength decreased significantly and the binding energy shifted to a higher level, indicating that I - / I3 - It competes with surface titanium sites for coordination, weakening the original Ti-(OH) group. x Bond. In contrast, PEI-MXene under the same conditions exhibits Ti-(OH) bonds. x The peak intensity increased instead of decreased, accompanied by a positive shift. This phenomenon can be explained by the reaction of the protonated amine group of PEI with the I group generated by the reduction of iodine. - Formation (N) + -I - After ion pairing, the released protons rapidly migrate to the MXene surface and react with Ti-O. - The combination generates new Ti-OH; simultaneously, the interfacial electric field caused by the loss of electrons from nitrogen atoms enhances the electron cloud density of the hydroxyl oxygen, resulting in an increase in binding energy. Therefore, the changes in the O 1s spectrum, from the perspective of proton transfer, confirm the synergistic adsorption mechanism of "amino electron donation - titanium center redox - hydroxyl proton coupling".

[0089] As a control, the I 3d spectrum of activated carbon (AC) adsorbent ( Figure 19 a) Only broad peaks (619.7 eV and 631.13 eV) belonging to physically adsorbed iodine species were observed. The peak shape and position indicate their affinity for I3 in solution. - There is no clear distinction or chemical interaction between it and I2; adsorption depends entirely on physical processes. Furthermore, the high-resolution fine spectra of C 1s and O 1s of the AC adsorbent before and after adsorption of iodine cathode solution show almost no change. Figure 19 bc), further verifying that the fixation effect of AC on iodine mainly relies on the physical confinement brought about by the high specific surface area and porous structure.

[0090] The above experimental results confirm that PEI-MXene, relying on the synergistic effect of physical confinement and chemical anchoring of pores, has a significantly better capture effect on polyiodides than activated carbon and pure MXene, and can firmly bind iodine active substances and inhibit the loss of active components.

[0091] Example 10: Battery Assembly 1. Button cell assembly The entire battery is assembled using a standard CR2032 coin cell structure. For example... Figure 20 (a) The positive electrode is an iodine-loaded composite positive electrode with a diameter of 12 mm (PMAAC-I of Example 4, AAC-I of Comparative Example 1 and MAAC-I of Comparative Example 2), the separator is a glass fiber separator GF / B with a diameter of 16 mm, the negative electrode is a zinc foil with a thickness of 30 μm (diameter of 14 mm), and the electrolyte is a 2M Zn(CF3SO3)2 aqueous solution.

[0092] 2. Assembly of pouch batteries The PMAAC-I positive electrode and zinc foil negative electrode from Example 4 were cut into rectangles with dimensions of 2 cm × 3 cm. Figure 20 (b) Take a glass fiber separator slightly larger than the electrode sheet (pre-wetted with 2 M Zn(CF3SO3)2 electrolyte), stack them in the order of positive electrode-separator-negative electrode, and heat-seal them with aluminum-plastic film to prepare a soft-pack battery simulating actual application conditions. The electrolyte injection volume is 500 μL, and after sealing, it is allowed to stand at room temperature for 10 h for activation.

[0093] Example 11: Battery Performance Test Following the method of Example 10, a coin cell was assembled using a composite cathode of AAC-I, MAAC-I, and PMAAC-I, and then characterized and analyzed.

[0094] 1. Electrode conversion kinetics analysis Figure 21 (a) Nyquist impedance spectra of different composite cathodes. Fitting results show that the charge transfer impedances of AAC-I, MAAC-I, and PMAAC-I are 18.79 Ω, 8.56 Ω, and 3.50 Ω, respectively. The introduction of MXene effectively reduces the interfacial charge transfer impedance, and PEI modification can further optimize the conductive network structure and significantly improve the interfacial charge transport efficiency. Different electrodes at 0.2 mV... s -1 Cyclic voltammetry (CV) curves at scan rate are as follows: Figure 21As shown in (b), all three groups of samples exhibit the corresponding I2 / I - The reversible redox peaks of the redox couple. The peak potential differences of AAC-I, MAAC-I, and PMAAC-I decrease sequentially, to 274 mV, 192 mV, and 143 mV, respectively. PMAAC-I has the largest peak current, indicating that the PEI-MXene modified structure can effectively reduce electrode polarization and improve the reversibility and reaction rate of the redox reaction.

[0095] CV tests and contour maps at different scan rates Figure 22 The results show that PMAAC-I exhibits the best current response and the smallest peak separation at all scan rates, demonstrating excellent charge transport capability and reversibility.

[0096] To quantitatively analyze the contribution ratio of surface-dominated processes to diffusion-controlled processes in the electrode reaction, the formula i = k1v + k2v is used. 1 / 2 The capacitance contribution (k1v) and diffusion confinement contribution (k2v) of the electrode 1 / 2 Separate calculations were performed, and the results are as follows: Figure 23 As shown, the capacitance contribution ratios of both MAAC-I and PMAAC-I composite cathodes are significantly higher than those of the AAC-I composite cathode. Furthermore, the gap between the three gradually narrows with increasing scan rate, indicating that the introduction of MXene significantly enhances the surface control behavior of the electrode, while PEI modification further improves the interfacial charge storage and transfer efficiency. Since the PMAAC-I composite cathode already exhibits near-limiting capacitance control characteristics at low scan rates, the gap with PMAAC-I decreases relatively as the capacitance contribution ratios of other electrodes increase with increasing scan rate. In other words, the PMAAC-I composite cathode possesses superior surface reactivity and faster charge transfer kinetics, enabling it to maintain efficient and stable capacitance-dominated behavior across a wide scan rate range, thus providing a kinetic basis for its excellent rate performance.

[0097] 2. Battery cycle life test Existing zinc-iodine batteries generally suffer from low active material loading and difficulty in balancing high loading capacity with fast reaction kinetics; the conventional iodine cathode surface loading is only 1-5 mg. cm -2 This invention increases the iodine loading of the electrode to 6.8-26.9 mg. cm -2 and at 13.4 mg cm -2 Electrochemical performance evaluation was conducted using high-load systems as a representative example. For instance... Figure 24 As shown in (a), at 0.1 A g -1Under the given conditions, the PMAAC-I electrode can achieve 190.8 mAh. g -1 The high reversible specific capacity, close to the theoretical capacity of iodine, achieves a capacity retention of 93.9% after 200 cycles, demonstrating excellent cycling stability. Under the same testing conditions, the MAAC-I electrode retains 90.3% of its capacity after 200 cycles, but its reversible capacity is significantly lower than that of PMAAC-I; while the AAC-I electrode's capacity decays to 79.5% after only 50 cycles, indicating poor cycling stability. Figure 24 As shown in (b), PMAAC-I achieves an initial iodine utilization rate of 90.4% and an average coulombic efficiency of 92.8%, significantly superior to MAAC-I (78.2%, 87.3%) and AAC-I (70.4%, 75.9%), demonstrating higher utilization of active materials and electrochemical reversibility. The initial GCD curve is shown below. Figure 25 As shown, the calculated first-cycle coulombic efficiency of PMAAC-I is 89.7%, which is much higher than that of MAAC-I (66.6%) and AAC-I (56.7%). This indicates that PEI modification significantly inhibits the dissolution and shuttle of polyiodine species, reduces interfacial side reactions, and provides a stable interfacial basis for maintaining high capacity in subsequent long cycles.

[0098] High-rate long-cycle test results are as follows Figure 26 As shown. In 3A g -1 At high current densities, PMAAC-I can maintain 110.8 mAh. g -1 The reversible capacity of the MAAC-I remains high even after 10,000 cycles, with an average capacity decay of less than 0.0012% per cycle, demonstrating excellent structural stability and ultra-long cycle life. The MAAC-I retains 81.4% of its capacity after 10,000 cycles, showing good stability but low reversible capacity. The AAC-I electrode kinetics and anchoring ability are insufficient, and it experiences a precipitous capacity decay and essentially fails after only 3,400 cycles.

[0099] Rate performance at different current densities, such as Figure 27 As shown. PMAAC-I at 0.2-3 A g -1 It exhibits stable discharge capacity over a wide rate range, 3 A g -1 At high rates, it retains 61.6% of its initial capacity, and the capacity is fully recovered after switching back to low rates, demonstrating excellent reversibility. (1 A) g -1 At high rates, the PMAAC-I composite cathode not only maintained the highest reversible capacity (151.4 mAh·g), but also... -1Furthermore, it achieves a coulombic efficiency of nearly 99%, highlighting the interface confinement advantage of its PEI-MXene functional unit under fast charging conditions. At all rates, PMAAC-I outperforms MAAC-I and AAC-I, demonstrating that the composite structure of this invention can significantly improve the reaction kinetics and rate adaptability of high-load electrodes.

[0100] 3. Inhibition of polyiodine shuttle during battery cycling Polyiodine substances (mainly I3) - and I - Through the synergistic effect of electrostatic adsorption of PEI and surface coordination of MXene, it is effectively anchored to the positive electrode side, thereby confining its redox reaction within the positive electrode region; zinc ions (Zn 2+ Reversible deposition / stripping occurs independently on the negative electrode side. Self-discharge test results provide direct evidence for this. Figure 28 After 24 hours of rest following charging, PMAAC-I exhibited a capacity retention of 90.1%, significantly higher than AAC-I (63.1%) and MAAC-I (74.2%). Electrodes with weaker shuttle suppression capabilities (such as AAC-I) showed more pronounced dendrite growth, surface corrosion, and XRD impurity peaks in their zinc anodes, and also exhibited faster self-discharge rates. These results demonstrate that the PMAAC structure achieves the most effective suppression of polyiodide shuttle through the synergistic confinement effect of PEI and MXene, which is key to the electrode's low self-discharge rate and high cycle stability.

[0101] 4. Analysis and practical application of the effect of different iodine loading on the performance of PMAAC-I like Figure 29 As shown, at 0.1 A g -1 At different current densities, the iodine loadings were 6.8, 20.2, and 26.9 mg, respectively. cm -2 The volume retention rates of PMAAC-I after 200 cycles were 93.8%, 90.9%, and 93.3%, respectively, compared to 13.4 mg. cm -2 Retention rate under load (93.9%, see...) Figure 24 The difference was not significant, indicating that PMAAC-I maintains highly stable cycling performance over a wide load range, and its structure demonstrates excellent applicability and reliability in high-load systems. The loading was 6.8 mg. cm -2 The highest average coulombic efficiency (98.6%) was observed, decreasing with increasing load. This is mainly due to the intensified dissolution and shuttle movement of polyiodine species under high load, and the increased interfacial side reactions caused by reduced electrolyte wetting and ion transport uniformity. Although the coulombic efficiency needs further improvement, it is still possible to achieve optimal efficiency at ultra-high loads (26.9 mg / L). cm -2 The PMAAC structure still achieved a capacity retention of >93%, demonstrating that it plays an effective role in physically confining polyiodides and maintaining structural stability.

[0102] Depend on Figure 30 It can be seen that the electrode specific capacity decreases slightly with increasing iodine loading, due to a slight increase in electrode polarization under high loading. However, even at 26.9 mg... cm -2 Despite its ultra-high areal capacity, the specific capacity can still reach the theoretical value (211mAh). g -1 The capacity retention rate is approximately 85% of the active material loading, and it is above 90% under all loading conditions. Furthermore, the electrode area specific capacity increases significantly with increasing active material loading, reaching a maximum of 4.82 mAh. cm -2 This indicates that the PMAAC composite cathode of the present invention can be adapted to high-load conditions and has the potential to be used in high-energy-density zinc-iodine batteries. To verify the practical value of the PMAAC-I composite cathode, a cathode with an areal loading of 13.4 mg was assembled according to the method of Example 10. cm -2 The zinc-iodine pouch cell battery. Due to the influence of cell interface contact, the specific capacity of the pouch cell battery is slightly lower than that of the button cell battery; after 300 cycles, the capacity retention rate of this battery can reach 86.4%. Figure 31 It has excellent anti-attenuation performance and can adapt to the interface impedance problems caused by actual packaging.

[0103] The above are preferred embodiments of the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-load stable PMAAC-I composite cathode, characterized in that, It includes the following steps: (1) Preparation of PEI-MXene composite dispersion: Add polyethyleneimine solution to MXene dispersion and stir to perform electrostatic self-assembly to obtain PEI-MXene composite dispersion; the solid mass ratio of MXene dispersion to polyethyleneimine solution is 1:(0.01-0.05). (2) Preparation of composite electrode slurry: Add aramid nanofiber aqueous dispersion to the PEI-MXene composite dispersion in step (1), stir for the first time, add activated carbon dispersion, stir for the second time, and obtain composite electrode slurry; the solid mass ratio of the PEI-MXene composite dispersion to the aramid nanofiber aqueous dispersion and the activated carbon dispersion is 1:(0.6~0.7):(6~7); (3) Preparation of composite electrode sheet: The composite electrode slurry from step (2) is filtered and dried to obtain PMAAC composite electrode sheet; (4) Iodine loading: Iodine-containing positive electrode electrolyte is loaded onto the surface of the PMAAC composite electrode sheet, and after drying, a PMAAC-I composite positive electrode is obtained; The high-load stable PMAAC-I composite cathode prepared by the method comprises: a PEI-MXene functional unit assembled from MXene and polyethyleneimine, a flexible three-dimensional framework composed of aramid nanofibers, a multi-level confined support composed of activated carbon, and iodine-loaded active material; the iodine loading of the high-load stable PMAAC-I composite cathode is 6.8-26.9 mg. cm -2 .

2. The method for preparing a high-load stable PMAAC-I composite cathode according to claim 1, characterized in that, In step (1), the stirring time is 20-60 min; in step (2), the first stirring time is 20-60 min, and the second stirring time is 12-36 h.

3. The method for preparing a high-load stable PMAAC-I composite cathode according to claim 1, characterized in that, In step (1), the preparation method of the MXene dispersion includes the following steps: S1: Etching reaction: Add HCl to LiF and stir until the solution is clear. Then add Ti3AlC2 and stir at 30-40℃ until the solution turns dark green to obtain multilayer Ti3C2T. X The solution contains LiF, HCl, and Ti3AlC2 in a ratio of (1-2) g: (14-16) mL: (0.5-1) g, wherein the concentration of HCl is 11-12 mol. L -1 ; S2: Washing and centrifugation: Add the multilayer Ti3C2T from step S1... X The solution was washed with deionized water and centrifuged until the pH of the supernatant reached 6.0, yielding multilayer Ti3C2T. X Detergent; S3: Ultrasonic ablation: The multilayer Ti3C2T from step S2 is then ablated. X The washing solution is sonicated, then centrifuged, and the supernatant is collected to obtain the MXene dispersion.

4. The method for preparing a high-load stable PMAAC-I composite cathode according to claim 1, characterized in that, In step (2), the preparation method of the aramid nanofiber aqueous dispersion includes the following steps: P1: Preparation of aramid nanofiber / DMSO dispersion: First, dimethyl sulfoxide, KOH, and deionized water are mixed evenly in a mass ratio of (540-560):(1.4-1.6):(19-21) to obtain a mixture. Then, poly(p-phenylene terephthalamide) is dispersed in the mixture and stirred to form an aramid nanofiber / DMSO dispersion. The mass ratio of poly(p-phenylene terephthalamide) to the mixture is 1:(560-580). P2: Preparation of the mixture gel: Deionized water was added to the aramid nanofiber / DMSO dispersion obtained in step P1 as a proton donor, and stirring was continued to complete the reprotonation treatment. After the reaction was completed, the mixture gel was obtained by filtration. P3: Purification: Ethanol and deionized water are added to the mixture gel obtained in step P2 for washing and filtration, and then the mixture is dispersed in deionized water by stirring to obtain an aqueous dispersion of aramid nanofibers.

5. The method for preparing a high-load stable PMAAC-I composite cathode according to claim 1, characterized in that, In step (2), the activated carbon in the activated carbon dispersion is wood-based activated carbon.

6. The method for preparing a high-load stable PMAAC-I composite cathode according to claim 1, characterized in that, In step (3), the filtration is vacuum filtration, and the filtration time is 20-40 min; the drying is vacuum drying, and the drying temperature is 50-70℃ and the drying time is 8-24 h.

7. The method for preparing a high-load stable PMAAC-I composite cathode according to claim 1, characterized in that, In step (4), the iodine-containing positive electrode electrolyte is an aqueous solution containing 0.1 M I2 and 0.5 M ZnI2.

8. The application of the high-load stable PMAAC-I composite cathode prepared by the preparation method according to claim 1 in the assembly of zinc-iodine batteries.

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