FeP@MXene nanosheet array composite material, and preparation method and application thereof

Abstract

The application discloses a FeP@Ti3C2T x Nanosheet array hetero-composite material, a preparation method and application thereof, and belongs to the technical field of new energy storage materials. x MXene as a conductive substrate, through the in-situ anti-oxidation of PDDA interface charge regulation and citric acid, the directional nucleation and growth of Fe-based precursor on the surface of MXene is promoted, and Fe2O3@Ti3C2T x Nanosheet array is constructed; then, NaH2PO2 is used as a phosphorus source for low-temperature in-situ phosphorization, Fe2O3 is converted into FeP nanosheet array, and FeP@Ti3C2T x Hetero-composite material is obtained. In the obtained material, FeP nanosheets are uniformly distributed on the surface of MXene, forming a continuous and open ion diffusion channel and a high-efficiency electron transmission network, which significantly improves the interface charge transmission capacity and electrochemical reaction kinetics, and effectively buffers the volume expansion. The material exhibits high specific capacity, excellent rate performance and long cycle stability in lithium ion batteries and sodium ion batteries, and has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of new energy storage materials and electrochemical technology, specifically relating to a FeP@Ti3C2T material with interfacial charge regulation characteristics. x Nanosheet array heterocomposite materials, their preparation methods, and their application in lithium-ion / sodium-ion battery anodes. Background Technology

[0002] With the rapid development of new energy vehicles, intelligent electronic devices, and large-scale energy storage systems, the market demand for energy storage devices with high energy density, long cycle life, and excellent rate performance is constantly increasing. Lithium-ion and sodium-ion batteries, as the most promising rechargeable battery systems, rely heavily on the ion diffusion kinetics and electron transport efficiency of the electrode materials for their electrochemical performance. Therefore, developing anode materials that combine high capacity, high conductivity, and excellent structural stability has become an important research direction in the current energy storage field.

[0003] Transition metal phosphides (TMPs) have attracted widespread attention due to their high theoretical capacity, low electrochemical reaction potential, and excellent electronic conductivity. Among them, iron phosphide (FeP) possesses abundant redox active sites and multi-electron transfer characteristics, enabling it to undergo reversible transformation reactions during lithium-ion and sodium-ion storage, thus exhibiting high theoretical specific capacity and excellent energy storage potential, and is considered a promising next-generation transition anode material. However, FeP still faces several limiting factors in practical applications: (1) Volume expansion and structural failure: During the charging and discharging process, FeP is accompanied by the breaking and reconstruction of Fe-P bonds and the large-scale insertion and extraction of Li⁺ / Na⁺, which will produce significant volume changes, leading to the pulverization of active materials, structural collapse and contact failure between electrodes and current collectors, ultimately resulting in rapid capacity decay. (2) Agglomeration and limited active sites: Most existing FeP materials are obtained by high-temperature phosphating, and the resulting nanoparticles have high surface energy and are prone to agglomeration, resulting in insufficient exposure of active sites and limiting electrolyte wetting and ion diffusion processes. (3) Bottleneck of kinetic performance: Although FeP itself has a certain conductivity, there are still problems of interruption of electron transport path and limited ion diffusion during long-term cycling, especially under high current density, it exhibits obvious polarization phenomenon and rate performance decline.

[0004] In recent years, two-dimensional transition metal carbides MXene (Ti3C2Tx) have been widely used in the construction of high-performance energy storage electrode materials due to their metallic-grade electronic conductivity, abundant surface functional groups, high specific surface area, and excellent mechanical flexibility. Theoretically, by loading FeP onto the surface of Ti3C2Tx, the overall conductivity of the composite material can be effectively controlled, and the volume expansion effect of FeP during cycling can be mitigated. However, existing FeP / MXene composite materials still have significant shortcomings in microstructure design and interface engineering: a. Random growth orientation and disordered structure: Existing studies mostly employ simple physical mixing or direct phosphating strategies, lacking effective induction of crystal growth. As a result, FeP often deposits randomly on the MXene surface in isotropic granular form. This disordered accumulation not only obscures the highly conductive pathways of MXene but also hinders the vertical penetration of electrolyte, making it difficult to form a uniform and ordered nanoarray structure, leading to low utilization of active sites.

[0005] b. Weak interfacial coupling and hindered charge transport: Most FeP and MXene are mainly bound by van der Waals forces or simple physical adsorption, lacking robust chemical bonds and electronic interactions. This weak interfacial coupling makes it difficult to achieve effective charge redistribution and form a built-in electric field that accelerates ion migration, thus limiting the kinetic properties of the composite material at high magnification.

[0006] c. The preparation process damages the MXene framework: During the existing hydrothermal reaction and subsequent high-temperature heat treatment, Ti3C2Tx MXene is prone to irreversible oxidation or destruction of its layered structure, which leads to the failure of its excellent conductive network and thus seriously weakens the long-term cycling stability of the composite material.

[0007] d. Neglecting the regulation of interface electronic structure: Existing technologies mainly focus on the size control of FeP particles, attempting to shorten the ion diffusion path by reducing the particle size, while neglecting the important influence of the regulation of the electronic structure of the heterogeneous interface and charge redistribution on energy storage dynamics. As a result, the materials still cannot meet the practical application requirements in terms of rate performance and long cycle life.

[0008] Therefore, developing a novel FeP / MXene heterocomposite material that can effectively suppress MXene oxidation and deactivation, achieve directional growth of FeP nanostructures, strengthen the interfacial coupling between FeP and Ti3C2Tx, and induce interfacial charge redistribution is of great significance for improving lithium / sodium ion storage kinetics, enhancing structural stability, and realizing high-performance, long-life energy storage devices. Summary of the Invention

[0009] To address the problems of FeP agglomeration, MXene oxidation, weak interfacial bonding, and severe volume expansion during lithium / sodium ion storage in existing FeP / MXene composites, this invention provides a FeP@Ti3C2T composite with interfacial charge regulation characteristics. x Nanosheet array heterogeneous composite materials and their preparation methods.

[0010] This invention utilizes the synergistic effect of PDDA interface charge regulation and citric acid to achieve the development of iron-based precursors in Ti3C2T x In-situ directional growth of MXene on the surface and construction of a strongly coupled heterogeneous interface via vapor-phase phosphating. This method not only effectively inhibits MXene oxidation and FeP aggregation, but also mitigates the volume expansion effect by constructing a continuous electron transport network and open ion diffusion channels, thereby significantly improving the material's structural stability, rate performance, and long cycle life.

[0011] In a first aspect, the present invention provides a FeP@Ti3C2T with interface charge modulation characteristics. x Nanosheet array heterogeneous composite materials: with two-dimensional layered Ti3C2T x MXene serves as the conductive substrate, and iron phosphide (FeP) nanosheets are grown in situ on the Ti3C2T substrate. x MXene surface and edge active sites, and self-assembled to form a three-dimensional open nanosheet array structure; the FeP and Ti3C2T x Strong interfacial coupling heterogeneous interfaces are formed between MXenes to induce electronic structure regulation of Fe active sites and redistribution of interfacial charges, thereby constructing a continuous electron transport network and open ion diffusion channels.

[0012] Preferably, the FeP nanosheets constitute 70 wt% to 95 wt% of the total heterocomposite material, with the balance being Ti3C2T. x MXene. More preferably, the FeP nanosheets have a mass percentage content of 80 wt% to 90 wt%.

[0013] Preferably, the Ti3C2T x The MXene surface contains one or more surface-terminating groups selected from -O, -OH, and -F; the FeP nanosheets preferentially nucleate and grow epitaxially at the active sites of the surface-terminating groups.

[0014] Preferably, the FeP has a two-dimensional ultrathin nanosheet morphology and is cross-linked to form flower-like or array-like micro / nano structures; the structure forms continuous open mesoporous channels to promote electrolyte wetting and ion transport.

[0015] Secondly, the present invention provides the above-mentioned FeP@Ti3C2T x The preparation method of nanosheet array heterocomposite material includes the following steps: (1) Interface charge control: Ti3C2T x MXene was dispersed in an aqueous solution, and the surface was modified by adding cationic polyelectrolyte PDDA and citric acid to obtain an MXene dispersion with regulated interfacial charge. (2) Precursor mixing: Add iron source precursor and precipitant to the MXene dispersion, stir and mix thoroughly to obtain reaction precursor solution; (3) In-situ hydrothermal growth: The precursor solution was placed in a high-pressure reactor for in-situ hydrothermal reaction to obtain Fe2O3@Ti3C2T x Precursor; (4) Heat treatment crystallization: The obtained Fe2O3@Ti3C2T x The precursor is heat-treated; (5) Gas-phase phosphating conversion: Using NaH2PO2 as the phosphorus source, a gas-phase in-situ phosphating reaction is carried out to convert Fe2O3 into FeP in situ, obtaining FeP@Ti3C2T x Nanosheet array heterogeneous composite material.

[0016] Preferably, in step (1), the amount of PDDA added is 10~100 mg, the amount of citric acid added is 20~200 mg, the mass ratio of PDDA to MXene is 1:1~1:10, in step (2), the iron source precursor is FeCl3·6H2O, and the precipitant is urea.

[0017] Preferably, in step (3), the hydrothermal reaction temperature is 130~150℃ and the reaction time is 6~24 h; in step (4), the heat treatment temperature is 250~450℃ and the heat treatment time is 0.5~3 h.

[0018] Preferably, in step (5), the NaH2PO2 is placed upstream of the tubular furnace, and Fe2O3@Ti3C2T x Located downstream of the tube furnace; NaH2PO2 and Fe2O3@Ti3C2T x The mass ratio is 1:5 ~ 1:30; the phosphating temperature is 250~450℃, and the phosphating time is 1~3 h.

[0019] Thirdly, an energy storage electrode includes a current collector and an active material layer coated on the surface of the current collector, the active material layer comprising the aforementioned FeP@Ti3C2T x Nanosheet array heterogeneous composite material.

[0020] Fourthly, the present invention provides the above-mentioned FeP@Ti3C2T x The application of nanosheet array heterocomposite materials is specifically as a negative electrode active material in the preparation of energy storage devices such as lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, or supercapacitors.

[0021] The present invention provides an oxygen-bridge-coupled three-dimensional array NiFeCo-LDH / MXene heterocomposite material, its preparation method, and its application, which have the following significant advantages compared with the prior art: 1. An efficient interfacial charge transport network and continuous ion diffusion channels were constructed. This invention utilizes the electrostatic adsorption of PDDA cationic polyelectrolytes to precisely control the surface charge distribution of MXene, inducing the directional nucleation and epitaxial growth of FeP precursors on the MXene surface. This in-situ growth strategy enables the growth of FeP and Ti3C2T... x A strong interfacial coupling heterostructure with atomically close contact is formed between MXenes. This heterostructure not only effectively reduces the electron transport barrier at the interface and promotes the rapid redistribution of interfacial charge, but also provides abundant electrolyte wetting sites and short-range ion diffusion paths through a three-dimensional open framework constructed using a two-dimensional nanosheet array, thereby significantly improving the rate performance and reaction kinetics of the material.

[0022] 2. A multi-effect synergistic preparation mechanism of "interface regulation, anti-oxidation protection, and in-situ phosphating" was achieved. This invention creatively introduces a dual auxiliary mechanism of PDDA and citric acid: PDDA acts as an "anchoring agent" to regulate interfacial charge and promote uniform deposition, while citric acid acts as a "complexing agent" and "antioxidant," effectively inhibiting the oxidative degradation of MXene during hydrothermal and heat treatment processes, maintaining the integrity of its highly conductive framework. Combined with a low-temperature vapor-phase phosphating strategy, in-situ transformation for lattice matching is achieved while preserving the original array morphology. The entire process is simple and controllable, avoiding particle agglomeration and substrate damage caused by high-temperature sintering, and exhibits good process repeatability and potential for large-scale production.

[0023] 3. Significantly enhanced structural stability and interfacial mechanical toughness. Traditional FeP materials are prone to severe volume expansion, particle pulverization, and electrical contact failure during charge and discharge. This invention utilizes a strong interfacial coupling structure formed by in-situ epitaxial growth to firmly anchor FeP nanosheets onto the surface of an MXene conductive framework, constructing a three-dimensional array network with high elasticity and open pores. This effectively buffers the volume changes caused by repeated lithium-ion or sodium-ion intercalation and deintercalation, fundamentally avoiding active material shedding and interfacial delamination problems, and significantly improving structural integrity during cycling.

[0024] 4. Possesses excellent comprehensive electrochemical energy storage performance. The FeP@Ti3C2Tx nanosheet array heterocomposite material constructed in this invention possesses high conductivity, high exposure of active sites, and excellent structural stability. In energy storage devices such as lithium-ion and sodium-ion batteries, it exhibits higher reversible specific capacity, lower polarization voltage, and superior long-cycle stability. Strong interfacial coupling significantly reduces charge transfer impedance and electrochemical polarization, improving reaction reversibility and energy utilization efficiency, and has broad application prospects in high-performance energy storage devices, new energy vehicle power batteries, and large-scale energy storage systems. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 shows the FeP@Ti3C2T prepared in the embodiment of the present invention. x XRD patterns of heterogeneous composite materials; Figure 2 shows the FeP@Ti3C2T prepared in the embodiment of the present invention. x SEM morphology of the heterogeneous composite material (a) and corresponding EDS mapping diagrams of Ti, Fe, and P elements (bd); Figure 3 shows the FeP@Ti3C2T prepared in the embodiment of the present invention. x Nitrogen adsorption-desorption isotherms and pore size distribution of heterogeneous composite materials; Figure 4 shows the FeP@Ti3C2T prepared in the embodiment of the present invention. x Long-cycle stability test results of heterogeneous composite materials as electrode materials; Figure 5 shows the FeP@Ti3C2T prepared in the embodiment of the present invention. x Electrochemical performance test results of heterogeneous composite materials; Figure 5a shows the lithium storage CV curve, Figure 5b shows the sodium storage CV curve, and Figure 5c shows the long-cycle performance of lithium storage. Figure 5 d represents the sodium storage long-cycle performance diagram. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] In a first aspect, the present invention provides a FeP@Ti3C2T with interface charge modulation characteristics. x Nanosheet array heterogeneous composite materials: with two-dimensional layered Ti3C2T x MXene serves as the conductive substrate, and iron phosphide (FeP) nanosheets are grown in situ on Ti3C2T. x MXene surface and edge active sites, and self-assembled to form a three-dimensional open nanosheet array structure; FeP and Ti3C2T x Strong interfacial coupling heterogeneous interfaces are formed between MXenes to induce electronic structure regulation of Fe active sites and redistribution of interfacial charges, thereby constructing a continuous electron transport network and open ion diffusion channels.

[0032] The FeP nanosheets comprise 70 wt% to 95 wt% of the entire heterocomposite material, with the balance being Ti3C2T. x MXene. Preferably, the FeP nanosheets have a mass percentage content of 80 wt% to 90 wt%.

[0033] Ti3C2T x The MXene surface contains one or more surface-terminating groups selected from -O, -OH, and -F; FeP nanosheets preferentially nucleate and grow epitaxially at the active sites of the surface-terminating groups.

[0034] FeP exhibits a two-dimensional ultrathin nanosheet morphology, with cross-linking to form flower-like or array-like micro-nano structures; continuous open mesoporous channels are formed inside the structure to promote electrolyte wetting and ion transport.

[0035] FeP nanosheets are 5–50 nm thick and 50–500 nm long, interwoven to form abundant mesopores and ion diffusion channels.

[0036] FeP@Ti3C2T x Nanosheet array heterogeneous composite materials utilizing Ti3C2T x The terminating groups (-O, -OH, -F) on the surface of MXene serve as active sites, inducing FeP to undergo directional nucleation and epitaxial growth, forming a heterojunction with strong interfacial coupling.

[0037] This three-dimensional open array structure forms continuous open mesoporous channels. On the one hand, it provides abundant electrolyte wetting sites and shortens the ion diffusion path; on the other hand, the flexible MXene framework can effectively buffer the volume expansion of FeP during charge and discharge, preventing particle pulverization, thereby significantly improving the rate performance and long-cycle stability of the material.

[0038] Secondly, this invention provides FeP@Ti3C2T x The preparation method of nanosheet array heterocomposite material includes the following steps: (1) Interface charge control: Ti3C2T x MXene was dispersed in an aqueous solution, and the surface was modified by adding cationic polyelectrolyte PDDA and citric acid to obtain an MXene dispersion with regulated interfacial charge. The concentration of Ti3C2Tx MXene is 5–15 mg / mL, preferably 10 mg / mL; the amount of PDDA added is 10–100 mg, and the amount of citric acid added is 20–200 mg; the mass ratio of PDDA to MXene is 1:1 to 1:10; and the mass ratio of citric acid to iron source is 1:2 to 1:5.

[0039] PDDA (anchoring agent): Precisely regulates the surface charge distribution of MXene through electrostatic adsorption, increasing positive charge sites and inducing uniform deposition of negatively charged iron-based precursors, thus preventing aggregation. Citric acid (complexing agent / antioxidant): Complexes iron ions to achieve slow release while inhibiting the oxidative degradation of MXene under hydrothermal conditions, maintaining its high conductivity.

[0040] (2) Precursor mixing: Add iron source precursor and precipitant to MXene dispersion, stir and mix thoroughly to obtain reaction precursor solution; wherein, iron source precursor is FeCl3·6H2O; precipitant is urea.

[0041] Urea hydrolyzes slowly at high temperatures, releasing OH⁻ and CO3²⁻, which react with Fe³⁺ to form precursors, ensuring a mild and controllable reaction.

[0042] (3) In-situ hydrothermal growth: The precursor solution was placed in a high-pressure reactor for in-situ hydrothermal reaction to obtain Fe2O3@Ti3C2T x The precursor; wherein the hydrothermal reaction temperature is 130~150℃, preferably 140℃; the reaction time is 6~24 h, preferably 12 h.

[0043] Under the induction of PDDA, Fe2O3 precursors were directionally nucleated and epitaxially grown on the MXene surface to construct Fe2O3@Ti3C2T x The precursor nanoarray heterostructure achieves atomic-level close contact.

[0044] (4) Heat treatment crystallization: The obtained Fe2O3@Ti3C2T x The precursor undergoes heat treatment; the heat treatment temperature is 250~450℃, preferably 350℃; the heat treatment time is 0.5~3 h. This step improves the crystallinity of the crystals, enhances the bonding strength of the heterogeneous interface, removes some impurities, and activates the surface activity of the material.

[0045] (5) Gas-phase phosphating conversion: Using NaH2PO2 as the phosphorus source, a gas-phase in-situ phosphating reaction is carried out to convert Fe2O3 into FeP in situ, obtaining FeP@Ti3C2T x Nanosheet array heterogeneous composite material.

[0046] NaH2PO2 is placed upstream of the tubular furnace, and Fe2O3@Ti3C2T x Located downstream of the tube furnace; NaH2PO2 and Fe2O3@Ti3C2T x The mass ratio is 1:5 to 1:30; the phosphating temperature is 250 to 450°C, preferably 350°C; and the phosphating time is 1 to 3 hours.

[0047] This step utilizes the phosphorus-containing reactive gas (PH3) generated by the thermal decomposition of sodium hypophosphite to convert Fe2O3 into FeP in situ. Because it is a gas-solid reaction, the original array morphology is preserved to the greatest extent, achieving in-situ lattice-matched conversion and avoiding particle agglomeration caused by high-temperature sintering.

[0048] In addition, after the reaction was completed, the product was naturally cooled to room temperature, collected, and washed alternately with anhydrous ethanol and deionized water, followed by vacuum drying to finally obtain pure FeP@Ti3C2T. x Nanosheet array heterogeneous composite material.

[0049] Thirdly, an energy storage electrode includes a current collector and an active material layer coated on the surface of the current collector, the active material layer comprising the aforementioned FeP@Ti3C2T x Nanosheet array heterogeneous composite material.

[0050] Fourthly, the present invention provides FeP@Ti3C2T x The application of nanosheet array heterocomposite materials is specifically as a negative electrode active material in the preparation of energy storage devices such as lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, or supercapacitors.

[0051] This invention provides FeP@Ti3C2T x The nanosheet array heterocomposite material has the following advantages: 1. Highly efficient charge transport: It constructs a strong interfacial coupling of "MXene conductive framework + FeP active sites", reducing the electron transport barrier. 2. Structural stability: The three-dimensional array structure and mesoporous channels effectively alleviate volume expansion and solve the problem of easy pulverization of traditional FeP. 3. Excellent electrochemical performance: It exhibits higher reversible specific capacity, lower polarization voltage, and excellent long-term cycling stability.

[0052] Example 1

[0053] This embodiment provides a FeP@Ti3C2T with interface charge modulation characteristics. x Nanosheet array heterogeneous composite material and its preparation method. The FeP content is 80 wt%, and the Ti3C2T content is... x The MXene content was 20 wt%. The resulting composite material exhibited a three-dimensional ordered self-assembled nanosheet array morphology, with FeP nanosheets uniformly distributed and vertically grown on Ti3C2T. x Active sites on the surface and edges of MXene.

[0054] The preparation method is strictly carried out in accordance with the steps of the foregoing claims, and the specific operation is as follows: (1) Preparation of dispersions with controlled interfacial charge: Weigh 50 mg of cationic polyelectrolyte PDDA and 80 mg of citric acid and add them to 30 mL of deionized water. Stir magnetically at room temperature until completely dissolved. Slowly add 5 mL of 10 mg / mL Ti3C2T to the above solution. x The MXene aqueous solution (containing 50 mg of solid MXene) was magnetically stirred for 2 h to allow PDDA to be fully adsorbed onto the MXene surface and to complete the interfacial charge regulation, thus obtaining the modified MXene dispersion.

[0055] (2) Precursor mixing and in-situ hydrothermal reaction: 0.81 g of iron source precursor (FeCl3·6H2O) and 1 g of precipitant (urea) were added sequentially to the dispersion obtained in step (1), and the mixture was magnetically stirred for 2 h at room temperature to obtain a homogeneous reaction precursor solution A. Precursor solution A was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor and reacted at a constant temperature of 140 ℃ for 12 h. During the reaction, the iron ion release rate was controlled by the complexing and slow-release effect of citric acid, and PDDA was used to induce the directional nucleation and ordered growth of the iron-based precursor on the MXene surface, resulting in Fe2O3@Ti3C2T. x Precursor.

[0056] (3) Product washing and drying (intermediate treatment): The product obtained in step (2) was washed alternately with deionized water and anhydrous ethanol, and then dried under vacuum at 60 °C for 12 h to obtain dried Fe2O3@Ti3C2T x Precursor powder.

[0057] (4) In-situ gas-phase phosphating conversion: Weigh 50 mg of dried Fe2O3@Ti3C2T x The precursor was placed in the central region of a tube furnace, while 1.0 g of phosphorus source (NaH2PO2) was placed in the upstream region. The gas-phase phosphating reaction was carried out by heating to 350 °C and holding for 12 h under argon protection. After cooling, FeP@Ti3C2T was obtained. x Nanosheet array heterogeneous composite material.

[0058] Application test cases This embodiment also provides a method for preparing an energy storage negative electrode and a button half-cell using the above-mentioned composite material: Electrode slurry composition: consisting of 80 mg FeP@Ti3C2T xThe composite material, 10 mg of acetylene black and 10 mg of PVDF were used as solvents to prepare the slurry and uniformly coated on the surface of copper foil.

[0059] Electrode preparation: After vacuum drying at 60 ℃ for 12 h, the electrode is punched into a diameter of 13 mm.

[0060] Battery Assembly and Testing: CR2032 lithium-ion and sodium-ion half-cells were assembled separately. The lithium storage test voltage range was 0.01~3.0 V (vs. Li⁺ / Li); the sodium storage test voltage range was 0.01~3.0 V (vs. Na⁺ / Na). Constant current charge-discharge tests were performed using a battery testing system, and cyclic voltammetry and impedance tests were conducted using an electrochemical workstation.

[0061] Comparative Example 1 This comparative example provides a pure FeP material (without introducing an MXene substrate or an interface charge modulation strategy). Its preparation process is as follows: 0.81 g FeCl3·6H2O and 0.50 g urea were dissolved in 30 mL deionized water and stirred at room temperature for 2 h. The mixture was then transferred to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene (PTFE). The reaction was carried out at a constant temperature of 140 °C for 12 h. After the reaction, the mixture was washed and dried to obtain the Fe2O3 precursor. Subsequently, 50 mg of the obtained Fe2O3 precursor was subjected to gas-phase phosphating treatment with 1.0 g NaH2PO2 at 350 °C for 12 h. After the reaction, the mixture was allowed to cool naturally and then washed and dried to obtain pure FeP powder material. Following the electrode preparation and battery assembly method in Example 1, a negative electrode was prepared using pure FeP as the active material, and its lithium and sodium storage electrochemical performance was compared under the same test conditions. This can be used to verify the contribution of the MXene conductive framework and interface charge regulation strategy to the improvement of the material's electrochemical performance.

[0062] Example 1: Phase crystal structure analysis (XRD) X-ray diffraction (XRD) was performed on the FeP@Ti3C2Tx nanosheet array heterocomposite material with interfacial charge modulation characteristics prepared in Example 1. The spectral results are as follows: Figure 1 As shown.

[0063] Depend on Figure 1The results show that the prepared composite product exhibits clear, sharp, and significantly intense characteristic diffraction peaks at 2 theta of 32.8°, 43.7°, 47.3°, 52.4°, and 57.3°, which strictly correspond to the (020), (111), (121), (210), and (031) crystal planes of orthorhombic iron phosphide (FeP, JCPDS standard card number: 39-0809). This strongly indicates that the in-situ gas-phase chemical transformation reaction between the phosphorus-containing reactive gas generated by the thermal decomposition of sodium hypophosphite (NaH2PO2) and the iron oxide precursor successfully achieved a complete transformation from oxide to the highly crystalline transition metal phosphide FeP crystal phase.

[0064] Meanwhile, a characteristic (002) diffraction peak belonging to the two-dimensional transition metal carbide Ti3C2Tx MXene was clearly observed near a low angle of 5.8°. The presence of this peak confirms that MXene successfully maintained its highly conductive two-dimensional layered topological framework under the in-situ synergistic protection of the cationic polyelectrolyte (PDDA) and citric acid (CA) proposed in this invention, as well as the subsequent low-temperature vapor-phase phosphating process. In addition, the (002) diffraction peak position showed a slight overall shift to a lower angle compared to the original pure MXene material, confirming that the intercalation regulation of the cationic surfactant and the in-situ epitaxial growth of FeP nanosheets in the interlayer during the preparation process effectively and elastically extended the interlayer spacing of MXene.

[0065] The entire spectrum exhibits a stable baseline and extremely high purity. No diffraction peaks attributable to unreacted iron oxide precursors (such as Fe2O3), metallic iron, or oxide impurities like TiO2 were found across the entire spectrum. This irrefutably confirms that the prepared composite material is a pure crystalline phase consisting of a highly crystalline two-dimensional FeP nanosheet array and a Ti3C2Tx MXene two-phase heterogeneous coexistence. This demonstrates the significant technological advancement of the proposed "interface regulation—in-situ growth—gas-phase phosphating" synergistic strategy in controlling phase purity and heterojunction quality.

[0066] Example 2: Microscopic morphology and spatial distribution analysis of components (SEM / EDX-Mapping) The microstructure and surface elemental spatial distribution of the sample from Example 1 were characterized using scanning electron microscopy (SEM) and corresponding elemental mapping (EDS Mapping). The results are as follows: Figure 2 As shown.

[0067] High / low magnification SEM images (Figures a and b) clearly show that the FeP@Ti3C2Tx heterocomposite exhibits a unique three-dimensional self-assembled flower-like array heteromorphic morphology. The two-dimensional ultrathin FeP nanosheets display extremely high areal density, and are longitudinally interwoven and cross-linked, growing in situ vertically on the surface and edges of the two-dimensional layered Ti3C2Tx MXene conductive substrate. This non-tiling, open array growth mode constructs a continuous micro / nano transport network, effectively generating microscopic steric hindrance to prevent the high specific surface energy two-dimensional MXene substrate from overlapping and reconstructing during subsequent drying or deep electrochemical cycling. It also constructs extremely rich mesoporous channels, greatly increasing the exposure density of active sites.

[0068] Figure 2 The elemental mapping spectrum of this heterocomposite material is presented. The results show that the spatial distribution of Ti (titanium) (mainly derived from the Ti3C2Tx MXene conductive framework) highly overlaps with that of Fe (iron) and P (phosphorus) (derived from FeP), and is densely, uniformly, and extensively distributed throughout the entire three-dimensional externally cross-linked nanosheet array structure. This highly homogeneous in-situ integration of elements at the microscale strongly confirms that after the iron-based oxide precursor undergoes a low-temperature in-situ gas-phase phosphating reaction, phosphorus has completely and uniformly penetrated and embedded in the lattice, achieving a complete transformation into the orthorhombic FeP active phase. Simultaneously, this result irrefutably confirms from a morphological perspective that a tight cross-interfacial coupling contact has been established between the FeP nanosheets and Ti3C2Tx MXene, laying a solid micro-engineering foundation for efficient electronic structure control, charge redistribution, and extremely rapid cross-interfacial electron / ion transport.

[0069] Example 3: Quantitative Analysis of Specific Surface Area and Porous Network (BET) The micropore size and specific surface area of ​​the sample from Example 1 were quantitatively analyzed using nitrogen adsorption-desorption tests (BET model and BJH method). The isothermal adsorption-desorption curves and pore size distribution results are shown below. Figure 3 As shown.

[0070] Figure 3The nitrogen isotherm adsorption-desorption curves of the FeP@Ti3C2Tx nanosheet array heterocomposite material with interfacial charge modulation characteristics are presented. According to the IUPAC classification, the curves exhibit a very obvious Type IV isotherm characteristic. At low relative pressures P / P0 ($<0.4$), the adsorption curve rises gently, indicating that abundant micropores were introduced into the material during in-situ epitaxial crystallization and subsequent low-temperature gas-phase phosphating reaction. In the medium-to-high relative pressure range (P / P0 = 0.45-1.0), the curves show a significant H3-type hysteresis loop, which is a typical feature of the three-dimensional open slit-like mesoporous / macroporous framework network formed by the disordered self-assembly of FeP two-dimensional ultrathin nanosheets that are vertically grown in situ on the surface of a two-dimensional Ti3C2Tx MXene conductive substrate and are cross-linked with each other.

[0071] Figure 3 The inset in the figure shows the pore size distribution curve calculated based on the BJH model. As can be seen from the inset, this heterocomposite material exhibits a unique hierarchical mesoporous distribution, with its pore size mainly concentrated in the ultrafine mesoporous region around 3.8 nm and the cross-linked channel mesoporous region between 15-45 nm. This concentrated, stepped distribution of pores confirms that the proposed synergistic strategy of "interface regulation—in-situ growth—vapor phase phosphating" has successfully created a highly open micro / nano porous network in terms of spatial morphology construction.

[0072] Rigorous calculations using the BET model formula revealed that the specific surface area of ​​this three-dimensional nanosheet array heterocomposite material reached 56 m² / g. Compared to conventional bulk FeP materials that are prone to crystallization and aggregation, or pure two-dimensional MXene materials that are prone to tight self-stacking between layers without surface charge modification (typically with a specific surface area <20 m² / g), the hydrothermal in-situ self-assembled flower-like array epitaxial growth mode of the sample in Example 1 resulted in a significant leap in the specific surface area. This large specific surface area, combined with the unique stepped porous channels, can significantly improve the effective exposure density of the transformed FeP active sites in energy storage reactions, greatly reduce the capillary wetting resistance of the interfacial electrolyte, and provide perfect elasticity and free release space for the intense lattice volume expansion generated by the FeP anode during deep charge-discharge conversion reactions (especially the insertion and extraction of large-radius sodium ions).

[0073] Example 4: Cyclic voltammetric electrochemical behavior and kinetic peak position analysis (CV) The Faraday redox behavior of the coin half-cell assembled in Example 1 was analyzed using cyclic voltammetry (CV). Specifically, the lithium storage CV test was performed at a scan rate of 0.2 mV / s and a range of 0.01–3.0 V (vs. Li). + The experiment was conducted within the voltage window of / Li, and the results are as follows: Figure 5As shown in figure a; sodium storage CV test at a scan rate of 0.1 mV / s and 0.01–3.0 V (vs. Na + The experiment was conducted within the voltage window of / Na, and the results are as follows: Figure 5 As shown in c.

[0074] Depend on Figure 5 The lithium storage CV curve behavior of electrode a shows that during the first discharge (cathode scan), the electrode exhibits an extremely strong and broad cathode reduction peak near 0.49V. This main peak corresponds to the complete reduction of the FeP lattice to nano-metallic iron (Fe). 0 The deep transformation reaction process that generates amorphous Li3P in situ (FeP + 3Li) involves the in-situ formation of FeP + 3Li + + 3e- →Fe +Li3P); At the same time, this peak also superimposed the reaction of the electrolyte undergoing irreversible decomposition on the ultra-high specific surface area of ​​the heterogeneous material (such as the 56m2 / g porous framework described in Effect Example 3) and forming a solid electrolyte interphase (SEI) film.

[0075] During the charging (anodic scan) process, the curve exhibits two distinct and continuous broad anodic oxidation peaks near 1.28 V and 2.12 V, which is attributed to metallic Fe. 0 It is reversibly phosphated step by step, and eventually re-converted back to the orthorhombic FeP active phase accompanied by Li + The process involves a multi-step Faraday oxidation conversion. In the subsequent 2nd to 5th cycles, the cathodic reduction peak shifts significantly to a higher potential and stabilizes around 0.78V, with the curve shape, peak current, and integral area showing almost complete overlap.

[0076] Depend on Figure 5 The sodium storage CV curve behavior of c shows that during the first discharge process, due to the large radius Na... + The lattice reconstruction barrier generated by the embedding and the construction of the SEI film show that the discharge cathode peak is located near 0.31V; during the charging anode scan, the reversible sodium deoxidation peak is clearly located near 1.17V. Starting from the second cycle, the cathode reduction peak stabilizes at 0.55V, and the redox peak current intensity and overlap remain at a very high level in subsequent cycles.

[0077] These two sets of CV response characteristics strongly demonstrate that the FeP@Ti3C2Tx three-dimensional nanosheet array heterocomposite material constructed in this invention exhibits excellent electrochemical reversibility and structural volume retention during Faraday transformation reactions involving deep multi-electron transfer. The voltage polarization difference between the oxidation and reduction peaks is strictly suppressed to a low level, which directly confirms at the electrochemical level that the atomic-level cross-interfacial electron migration framework constructed by the redistribution of interfacial charge and the strong coupling of the Fe-P-Ti interface significantly reduces the charge transfer impedance and transformation reaction energy barrier of the heterointerface, endowing the system with an ultrafast electrochemical reaction kinetic response rate.

[0078] Example 5: Long-lasting secondary lithium and sodium storage cycle durability verification (GCD) The button half-cells of Example 1 and Comparative Example 1 were placed under a constant current charge-discharge test system for long-cycle life comparison. The results of the lithium storage long-cycle performance are as follows: Figure 5 As shown in b, the sodium storage long-cycle performance results are as follows: Figure 5 As shown in d.

[0079] Lithium battery long cycle test ( Figure 5 b): The test was conducted at a high current density of 0.5 A / g, and the performance curves after 300 deep charge-discharge cycles are as follows. Figure 5 As shown in b.

[0080] As shown in the figure, the pure FeP material in Comparative Example 1, due to the lack of a conductive substrate and severe particle self-aggregation, experiences rapid pulverization of the active phase and electrical contact deactivation under the enormous volume stress of the Faraday transformation reaction, resulting in a rapid and precipitous drop in its specific capacity. Figure 4 As shown. In contrast, the FeP@Ti3C2Tx nanosheet array heterocomposite material prepared in Example 1 of this invention exhibits high stability: in the initial cycling stage (first 40 cycles), the specific capacity slightly decreases due to the in-situ reconstruction of the conversion-type negative electrode crystal phase and the gradual and robust formation of the SEI film; subsequently, thanks to the electrochemical activation of the three-dimensional self-assembled flower-like array framework and the deep penetration of the electrolyte in the rich multi-level mesoporous network, the electrode exhibits extremely excellent capacity recovery and release characteristics; after undergoing 300 deep constant current charge-discharge cycles, its discharge specific capacity remains stable at around 900 mAh / g, with extremely high capacity retention. More importantly, throughout the long cycling process, the coulombic efficiency of this electrode material rapidly increases after the first cycle and remains strictly maintained between 99.5% and 100%.

[0081] Sodium long-cycle test ( Figure 5 d): Performance curves after 800 cycles of deep constant current charge-discharge at a high current density of 1 A / g are shown below. Figure 5As shown in d. Experimental results show that although the insertion and extraction of sodium ions are accompanied by more severe lattice distortion stress, the capacity curve of the composite electrode of Example 1 of this invention exhibits an excellent stable trend throughout the entire high-frequency deep cycling process of up to 800 cycles. After 800 cycles, it still maintains a high reversible discharge specific capacity of 280 mAh / g without showing obvious kinetic deactivation or a sudden drop in capacity. At the same time, except for a slightly lower coulombic efficiency in the first cycle due to the formation of an irreversible solid electrolyte interphase (SEI) film, from the subsequent cycles onwards, the cyclic coulombic efficiency of the electrode rapidly increases and remains stable at around 99.8%.

[0082] The two sets of long-cycle stability test results constitute a perfect closed loop of structural and electrochemical evidence, thoroughly confirming the core mechanism advantage of this invention: by regulating the charge on the MXene surface through the cationic polyelectrolyte PDDA, combined with the in-situ anti-oxidation and complexation slow release of citric acid, FeP nanosheets are successfully induced to self-assemble in situ at the atomic scale and form strong interfacial coupling. This three-dimensional array cross-linked network with high mechanical toughness and high electronic conductivity fundamentally prevents the "interfacial delamination and detachment" problem that is prone to occur in the active phase of traditional physically compounded anode materials under repeated large-volume expansion / contraction stress, ensuring the integrity of the overall electrical contact while endowing the material with long-term secondary energy storage durability.

[0083] Those skilled in the art can make various modifications and applications without departing from the essential characteristics of the embodiments. For example, each component detailed in the embodiments can be modified and operated, and the differences associated with such modifications and applications can be considered to be included within the scope of protection of the invention as defined in the appended claims.

[0084] The embodiments described in this specification are intended to imply that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. These terms appearing throughout the specification do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is assumed that it falls within the scope of those particular features, structures, or characteristics that could be implemented by one of ordinary skill in the art in conjunction with other embodiments.

Claims

1. A FeP@Ti3C2T composite with interfacial charge modulation characteristics x Nanosheet array heterogeneous composite material, characterized in that: Two-dimensional layered Ti3C2T x MXene serves as the conductive substrate, and iron phosphide (FeP) nanosheets are grown in situ on the Ti3C2T substrate. x MXene surface and edge active sites, and self-assembled to form a three-dimensional open nanosheet array structure; The FeP and Ti3C2T x Strong interfacial coupling heterogeneous interfaces are formed between MXenes to induce electronic structure regulation of Fe active sites and redistribution of interfacial charges, thereby constructing a continuous electron transport network and open ion diffusion channels.

2. The heterogeneous composite material according to claim 1, characterized in that: The FeP nanosheets comprise 70wt%~95wt% of the total mass of the heterocomposite material, with the remainder being Ti3C2T. x MXene.

3. The heterogeneous composite material according to claim 1, characterized in that: The Ti3C2T x The MXene surface contains one or more surface-terminating groups selected from -O, -OH, and -F; the FeP nanosheets preferentially nucleate and grow epitaxially at the active sites of the surface-terminating groups.

4. The heterogeneous composite material according to claim 1, characterized in that: The FeP exhibits a two-dimensional ultrathin nanosheet morphology, with cross-linking to form flower-like or array-like micro / nano structures; continuous open mesoporous channels are formed inside the structure to promote electrolyte wetting and ion transport.

5. A FeP@Ti3C2T as described in any one of claims 1 to 4 x A method for preparing nanosheet array heterogeneous composite materials, characterized in that, Includes the following steps: (1) Ti3C2T x MXene was dispersed in an aqueous solution, and the surface was modified by adding cationic polyelectrolyte PDDA and citric acid to obtain an MXene dispersion with regulated interfacial charge. (2) Add an iron source precursor and a precipitant to the MXene dispersion, and stir thoroughly to obtain a reaction precursor solution; (3) The reaction precursor solution was placed in a high-pressure reactor for in-situ hydrothermal reaction to obtain Fe2O3@Ti3C2T x Precursor; (4) The obtained Fe2O3@Ti3C2T x The precursor is heat-treated; (5) Using NaH2PO2 as the phosphorus source, a gas-phase in-situ phosphating reaction was carried out to convert Fe2O3 into FeP in situ, obtaining FeP@Ti3C2T x Nanosheet array heterogeneous composite material.

6. The preparation method according to claim 5, characterized in that: In step (1), the amount of PDDA added is 10~100mg, and the amount of citric acid added is 20~200mg; the mass ratio of PDDA to MXene is 1:1~1:10; In step (2), the iron source precursor is FeCl3·6H2O; the precipitant is urea.

7. The preparation method according to claim 5, characterized in that: In step (3), the hydrothermal reaction temperature is 130~150℃ and the reaction time is 6~24h; In step (4), the heat treatment temperature is 250~450℃ and the heat treatment time is 0.5~3h.

8. The preparation method according to claim 5, characterized in that: In step (5), the NaH2PO2 is placed upstream of the tubular furnace, and Fe2O3@Ti3C2T x Located downstream of the tube furnace; NaH2PO2 and Fe2O3@Ti3C2T x The mass ratio is 1:5 to 1:30; the phosphating temperature is 250 to 450℃; and the phosphating time is 1 to 3 hours.

9. An energy storage electrode, characterized in that, The current collector includes a current collector and an active material layer coated on the surface of the current collector, the active material layer comprising FeP@Ti3C2T as described in any one of claims 1 to 4. x Nanosheet array heterogeneous composite material.

10. A FeP@Ti3C2T according to any one of claims 1 to 4 x The application of nanosheet array heterocomposite materials in the fabrication of energy storage devices is characterized by, The energy storage device includes lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, or supercapacitors.

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