A positive electrode material of an electrode, a preparation method thereof, a positive electrode sheet, and an ion battery

Abstract

The present application belongs to the technical field of ion battery positive electrode materials, and particularly relates to a positive electrode material of an electrode, a preparation method of the positive electrode material, a positive electrode sheet and an ion battery. The disclosed positive electrode material comprises long strip-shaped NFPP-based primary particles and a core-shell fiber structure of a flexible adhesive copolymer. The shell layer is closely attached to the core, has high adhesion, and will not crack, peel off or be partially exposed during use. The problems of existing positive electrode materials, such as large intrinsic structure brittleness, low deformation tolerance, weak structure continuity and mechanical properties, and crack and current collector peeling during repeated bending and winding, are solved. The use of the positive electrode material to prepare a positive electrode sheet can significantly reduce or completely replace the amount of existing non-active binders and auxiliary conductive agents, thereby increasing the proportion of active substances in the electrode sheet and improving the performance of the electrode sheet.

Description

Technical Field

[0001] This invention relates to the field of cathode materials technology for ion batteries, and particularly to a cathode material for an electrode, a method for preparing the same, a cathode sheet, and an ion battery. Background Technology

[0002] With the rapid development of lithium-ion and sodium-ion batteries in high-energy-storage portable devices, wearable flexible electronics, curved terminals and rollable energy storage devices, the requirements for high energy density and mechanical flexibility of batteries have been further increased. The mechanical flexibility of the positive electrode sheet of the battery is a key factor restricting the service reliability, electrochemical stability and service life of flexible batteries.

[0003] Currently, battery cathode materials mainly include layered oxides and polyanionic compounds. These materials have inherent defects such as high intrinsic structural brittleness and low deformation tolerance. Furthermore, to improve the conductivity and processability of the battery cathode, a high proportion of conductive agents and organic binders need to be incorporated during the preparation of the cathode sheet. This further weakens the continuity and mechanical properties of the cathode structure, leading to problems such as cracks and current collector delamination during repeated bending and winding, resulting in increased interfacial resistance and reduced cycle life. Summary of the Invention

[0004] The main objective of this invention is to provide a positive electrode material and its preparation method, a positive electrode sheet, and an ion battery. It aims to solve the problems of high intrinsic structural brittleness and low deformation tolerance of existing positive electrode materials, as well as the weak continuity and mechanical properties of existing positive electrode material structures, which lead to cracks and current collector peeling during repeated bending and winding.

[0005] To achieve the above objectives, the present invention provides a positive electrode material, the positive electrode material comprising a core-shell fiber structure, the core-shell fiber structure comprising a shell structure and a core structure, the shell structure covering the surface of the core structure, and the shell thickness of the shell structure being <20 nm; The shell structure includes a shell phase material, and the core structure includes a core phase material and the shell phase material; The core phase material and the shell phase material form elongated sodium iron pyrophosphate-based primary particles; the elongated sodium iron pyrophosphate-based primary particles agglomerate to form secondary agglomerated particles including a core-shell fibrous structure. The shell material includes a flexible adhesive polymer, which is a phosphate-esterified polyacrylic acid-aniline copolymer or a polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer.

[0006] Optionally, the elongated sodium iron pyrophosphate-based primary particles have a diameter of <100 nm and a length of 1 μm-3 μm; the secondary aggregated particles formed by the agglomeration of the elongated sodium iron pyrophosphate-based primary particles, including a core-shell fibrous structure, are quasi-spherical particles, and the particle size of the quasi-spherical particles is 5 μm-10 μm.

[0007] To achieve the above objectives, the present invention also provides a method for preparing a positive electrode material, for preparing the positive electrode material as described above, the preparation method comprising: The sodium iron pyrophosphate precursor, flexible adhesive polymer and solvent are mixed evenly and stirred until completely dissolved to obtain electrospinning solution; Based on preset process parameters, using the electrospinning solution as raw material, electrospinning is assisted by external induced variables to obtain a fiber structure including long strips of sodium iron pyrophosphate. The cathode material is obtained by UV in-situ polymerization of the long strip-shaped sodium iron pyrophosphate fiber structure; the cathode material includes a core-shell fiber structure.

[0008] Optionally, in the electrospinning solution, the mass ratio of the sodium iron pyrophosphate precursor is 25%-35%, the mass ratio of the flexible adhesive polymer is 15%-25%, and the mass ratio of the solvent is 40%-60%.

[0009] Optionally, the method for obtaining a fiber structure comprising long strips of sodium iron pyrophosphate phosphate by using the electrospinning solution as raw material and assisted by an external induced variable based on preset process parameters includes: The receiving device of the electrospinning equipment is an aluminum foil, and a rotating magnetic field auxiliary system is installed on the receiving device to assist electrospinning; the magnetic field strength of the rotating magnetic field auxiliary system is 0.4T-0.6T. The electrospinning voltage was adjusted to 17kV-19kV, the feed speed to 0.35mL / min-0.45mL / min, and the receiving distance to 12cm-15cm to perform electrospinning and obtain the fiber structure comprising long strips of sodium iron pyrophosphate.

[0010] Optionally, the method for obtaining the cathode material by UV in-situ polymerization of the fiber structure comprising elongated sodium iron pyrophosphate includes: When the fiber structure comprising elongated sodium iron pyrophosphate falls onto the receiving device of the electrospinning equipment, it is simultaneously subjected to UV irradiation to obtain the positive electrode material; the wavelength of the UV irradiation is 360nm-370nm, and the light intensity is 22mW / cm². 2 -28mW / cm 2 The irradiation time is 8s-12s.

[0011] Optionally, when the flexible adhesive polymer is a phosphate-esterified polyacrylic acid-aniline copolymer, the molecular formula of the phosphate-esterified polyacrylic acid-aniline copolymer is: [CH2 CH(COOH)] m [CH2 CH(COOCH2CH3)] n [CH2 CH(COOCH2CH2OPO(OH)2)] p [=N C6H4 NH C6H4] k ; In the molecular formula, 10≤m≤30, 50≤n≤100, and 5≤p≤15.

[0012] Optionally, the method for synthesizing the sodium iron pyrophosphate precursor includes: The determination of FePO4, NaH2PO4, Na2CO3, and C6H is based on the molecular weight of sodium iron pyrophosphate. 12 The molar ratio of O6 was determined by weighing out FePO4, NaH2PO4, Na2CO3, and C6H. 12 O6 was used to prepare the sodium iron pyrophosphate precursor.

[0013] To achieve the above objectives, the present invention also provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material being prepared by the preparation method described above.

[0014] To achieve the above objectives, the present invention also provides an ion battery, the ion battery comprising a positive electrode as described above.

[0015] Compared with the prior art, the beneficial effects that the present invention can achieve are as follows: 1. The positive electrode material disclosed in this invention comprises a core-shell fiber structure. The elongated sodium iron pyrophosphate (NFPP)-based primary particles in the core phase material of the core-shell fiber structure can naturally interweave between the fibers to form a continuous network structure, which can provide a continuous, short-range diffusion channel for the ion battery. The shell phase material of the core-shell fiber structure is an acrylate-polyaniline composite conductive copolymer containing phosphate ester functional groups, namely, phosphate-esterified polyacrylic acid-aniline copolymer or polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer. This copolymer contains an aniline conjugated conductive structure, which can construct a continuous electronic conduction pathway on the fiber surface. At the same time, the shell thickness of the shell phase material is controlled within 20 nm, which is a nano-ultra-thin coating. It will not block the core phase pores or block the ion intercalation / deintercalation sites, and there is no additional mass transfer impedance superposition. This can significantly reduce the charge-discharge polarization of the battery, and significantly improve the capacity retention rate of the ion battery at high current rates.

[0016] 2. In the cathode material provided by this invention, the phosphate-modified polyacrylic acid-aniline copolymer or polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer of the shell phase material is a phosphate-modified copolymer. The molecular chain of this polymer has phosphate functional groups, which are homologous and polarly matched with the phosphate groups of the core phase sodium iron pyrophosphate, forming a strong interfacial affinity and intermolecular forces. Unlike the simple physical coating of ordinary polymers, this copolymer shell adheres tightly to the core phase with high adhesion, so that the electrode will not experience shell cracking, peeling, or local exposure during repeated intercalation and deintercalation of charge and discharge, and will always maintain an intact core-shell fiber structure. Moreover, it will not peel off during repeated bending and winding, solving the problems of weak continuity and mechanical properties of existing cathode materials, and cracking and current collector peeling during repeated bending and winding. In the core-shell fiber structure of the cathode material provided by this invention, the lattice of the long strip-shaped NFPP-based primary particles undergoes slight expansion and contraction during charging and discharging. The flexible adhesive polymer shell has elastic deformation capability, which can adaptively buffer the volumetric expansion and contraction stress of the core phase fiber, thereby preventing the long strip fiber from cracking, pulverizing, or breaking. This solves the problems of high intrinsic structural brittleness and low deformation tolerance of existing cathode materials. Under long-term cycling, the microstructure of this cathode material does not collapse or disintegrate, which can effectively slow down the battery capacity decay and significantly improve the battery cycle life.

[0017] 3. In the method for preparing the cathode material disclosed in this invention, exogenous induced variable-assisted electrospinning is used. Unlike ordinary electrospinning, which results in disordered fibers of varying lengths and thicknesses, this method can precisely and directionally generate elongated NFPP-based primary particles with uniform aspect ratio, regular morphology, and continuous integrity by controlling the parameters of the exogenous variable. This naturally forms a three-dimensional interwoven network structure. At the same time, the fiber diameter and pore structure can be precisely controlled, providing a structural basis for the rapid diffusion of ions in the battery. In the subsequent UV curing process, UV in-situ polymerization triggers the directional polymerization and curing of polymers on the fiber surface, allowing the flexible adhesive polymer to be uniformly enriched and coated on the surface of the elongated fiber structure. The shell thickness of the shell phase can be precisely and stably controlled within 20 nm, and the coating material can be locally over-thickened.

[0018] 4. Based on the cathode material of this invention, the prepared cathode sheet features an interwoven three-dimensional network of elongated fiber structures, which, in conjunction with a flexible adhesive polymer, ensures continuous and uninterrupted electron conduction and ion diffusion channels within the electrode. Compared to conventional particle-coated electrodes, this cathode sheet exhibits significantly reduced charge transport resistance, lower polarization, and faster electrochemical response. Furthermore, this cathode material possesses flexible self-adhesive properties, significantly reducing or completely replacing the amount of existing inactive binders and auxiliary conductive agents during electrode preparation. This increases the proportion of active material in the electrode and allows for the production of electrodes with high areal loading and high compaction density. Ion batteries equipped with this cathode sheet, such as lithium-ion and sodium-ion batteries, exhibit rapid ion insertion / extraction kinetics, low polarization during high-current charging and discharging, high capacity retention, and the ability to achieve high-rate fast charging, meeting the demands of high-power charging and discharging. Moreover, the battery's capacity decay rate is significantly reduced during charge-discharge cycles, extending its lifespan. Attached Figure Description

[0019] Figure 1 This is an SE-SEM scan of the cathode material in Example 1.

[0020] Figure 2 This is a TEM scan of the cathode material in Example 1. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] To address the issues of high intrinsic structural brittleness, low deformation tolerance, and weak structural continuity and mechanical properties in existing cathode materials, leading to cracks and current collector delamination during repeated bending and winding, this invention provides a cathode material comprising a core-shell fiber structure. The core-shell fiber structure includes a shell structure and a core structure, with the shell structure covering the surface of the core structure. The shell thickness of the shell structure is <20 nm. The shell structure includes a shell phase material, and the core structure includes a core phase material and the shell phase material; The core phase material and the shell phase material form elongated sodium iron pyrophosphate-based primary particles; the elongated sodium iron pyrophosphate-based primary particles agglomerate to form secondary agglomerated particles including a core-shell fibrous structure. The shell material includes a flexible adhesive polymer, which is a phosphate-esterified polyacrylic acid-aniline copolymer or a polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer.

[0023] It should be understood that the above-mentioned core-shell fiber structure refers to a spherical core-shell structure in which the core phase is a strip-shaped NFPP-based fiber body, and the shell phase is a flexible adhesive polymer with continuous or partial surface coating; the interface between the core phase and the shell phase is combined through physical coating and chemical bonding.

[0024] It should be understood that the shell thickness of the above-mentioned shell phase material <20nm means that the maximum thickness of the shell is <20nm. In the technical solution of the present invention, there may be cases where the shell thickness is around 20nm.

[0025] It should be noted that the above-mentioned flexible adhesive polymers, phosphate-esterified polyacrylic acid-aniline copolymers or polyaniline sulfonic acid-polyethyl acrylate phosphate copolymers, contain carboxyl functional groups ( The bonding target of COOH is the Fe on the surface of NFPP. 3 + The bonding mechanism is a chelate bond (Fe-OOC), with data indicating a binding energy of 210 kJ / mol or higher. This represents a high-strength chemical chelation, significantly higher than the binding energies of van der Waals forces and hydrogen bonds. This allows the flexible adhesive polymer to be firmly anchored to the surface of the elongated NFPP-based primary particles, structurally ensuring a uniform, non-slipping, and non-localized desorption shell structure with a thickness <20 nm. The copolymer contains phosphate ester functional groups (…). The target of PO(OH)2 is the Al2O3 oxide layer and AlPO4 passivation layer on the surface of aluminum foil. The bonding mode includes Al-O bond (bond energy about 500 kJ / mol–600) and PO bond (bond energy about 335 kJ / mol). These are high bond energy covalent bonds, which can achieve chemical bonding between the shell phase polymer and the aluminum foil current collector, thereby significantly improving the adhesion of the positive electrode material on the aluminum foil. This ensures that the material does not delaminate, shed powder, or curl up during the rolling, winding, and stacking processes of electrode preparation. The aniline unit functional groups in the copolymer act on the particles between secondary particles and long fiber particles. The molecules associate with each other through the π-π stacking of aromatic rings, thereby constructing a continuous conductive network, which is beneficial to improving conductivity and bringing the conductivity into the semiconductor conductivity range suitable for the positive electrode of ion batteries. This can make up for the shortcoming of poor intrinsic conductivity of pure NFPP. In addition, through π-π stacking, the aniline units can build a continuous three-dimensional conductive network between 5μm-10μm spherical secondary aggregates and between 1μm-3μm long fibers. This network can replace some of the additional conductive agents, thereby reducing the proportion of non-active additives in the electrode and increasing the positive electrode active material loading and battery energy density. Furthermore, it can shorten the electron transport path, reduce battery charge and discharge polarization, and support high-rate fast charging and high-current discharge performance.

[0026] In some instances, the primary particles of the aforementioned elongated sodium iron pyrophosphate have a diameter of <100 nm and a length of 1 μm-3 μm; the secondary aggregated particles formed by the agglomeration of the elongated sodium iron pyrophosphate primary particles, including core-shell fibrous structures, are quasi-spherical particles with a particle size of 5 μm-10 μm.

[0027] It should be understood that the aforementioned primary particles refer to the smallest single crystal or microcrystalline structural unit of NFPP that can exist independently and cannot be mechanically separated. They are the most basic primary units for the growth of material crystals, possessing a complete crystal lattice and electrochemical activity, and are the smallest building blocks that constitute subsequent agglomeration structures.

[0028] It should be understood that the aforementioned secondary agglomerated particles are formed by the spontaneous aggregation of the aforementioned elongated sodium iron pyrophosphate-based primary particles, which interweave, stack, and agglomerate together through van der Waals forces, intermolecular forces, and the bonding effect of the polymer system, resulting in micron-sized secondary composite particles.

[0029] It should be understood that the diameter of the aforementioned particles refers to the average radial diameter of the particles; the length refers to the axial length of the particles.

[0030] It should be noted that, compared to conventional micron-sized cathode particles, when the diameter of the aforementioned elongated NFPP-based primary particles is <100nm, the solid-phase diffusion distance of ions within the particles can be significantly reduced. This results in a significant reduction in the insertion / extraction resistance of ions, such as lithium ions and sodium ions, during charging and discharging of the ion battery, and a decrease in polarization, making it suitable for high-current fast charging conditions. In addition, compared to particles larger than 100nm, particles with a diameter <100nm have a size effect, which can spontaneously disperse the lattice stress generated during charging and discharging, making it less prone to lattice distortion or microcrack initiation. When the length of the elongated NFPP-based primary particles is 1μm-3μm, each particle has a long-range continuous structure. The particles naturally overlap and interweave to form a continuous ion and electron transport network. Unlike the disordered nanoparticle stacking, this continuous structure can ensure a continuous mass transfer channel and will not bend or break due to excessive particle length. At the same time, the elongated shape within this length range allows the stress to be released along the length direction, thereby avoiding local stress concentration and inhibiting particle breakage and pulverization at the microscopic level.

[0031] When the aforementioned elongated NFPP-based primary particles are agglomerated, the resulting spherical secondary agglomerated particles have a particle size of 5μm-10μm. This allows for close packing, forming a continuous conductive network between the particles and avoiding the problems of large voids and low electrode loading in nanopowder packing. Furthermore, in the industrial coating or rolling processes of ion batteries, if the particle size of the secondary agglomerated particles is <5μm, the powder specific surface area will be too large, potentially leading to problems such as easy agglomeration and clumping, and excessive liquid absorption. Coating may also result in uneven thickness and electrode burrs. If the particle size is >10μm, the large particle size may cause a rough electrode surface and low compaction density.

[0032] When the diameter of the aforementioned elongated NFPP-based primary particles is <100nm, the shell phase material with a shell thickness of <20nm, i.e., the flexible adhesive polymer, can uniformly coat them without causing uneven coating due to excessively coarse particles, or excessive coating of the shell material and increased mass transfer resistance due to excessively fine particles. When the length of the primary particles is 1μm-3μm, the flexible adhesive polymer can easily form a uniform film on its surface during in-situ polymerization, resulting in a strong core-shell interface bond and making it less prone to detachment or peeling during use.

[0033] To address the aforementioned problems, the present invention also provides a method for preparing a positive electrode material, for preparing the aforementioned positive electrode material, the method comprising: The sodium iron pyrophosphate precursor, flexible adhesive polymer and solvent are mixed evenly and stirred until completely dissolved to obtain electrospinning solution; Based on preset process parameters, using the electrospinning solution as raw material, electrospinning is assisted by external induced variables to obtain a fiber structure including long strips of sodium iron pyrophosphate. The cathode material is obtained by UV in-situ polymerization of the long strip-shaped sodium iron pyrophosphate fiber structure; the cathode material includes a core-shell fiber structure.

[0034] It should be understood that the aforementioned sodium iron pyrophosphate (NFPP) precursor refers to the raw material that is transformed into long strip-shaped NFPP crystals during electrospinning and subsequent processes.

[0035] It should be understood that the aforementioned UV in-situ polymerization, also known as ultraviolet light in-situ polymerization, refers to a technology that, without moving or transferring the original matrix material, uses ultraviolet light (UV) of a set wavelength to irradiate and trigger free radical polymerization, cross-linking, and curing reactions of polymer prepolymers, monomers, or macromolecular chains within the system, rapidly forming a cross-linked polymer network or dense polymer film under set conditions. In the technical solution of this invention, UV in-situ polymerization refers to maintaining the original interwoven morphology of the original fibers in the in-situ state after obtaining the precursor fiber structure of sodium iron pyrophosphate by electrospinning, without transferring, dismantling, or secondary coating the fiber structure. Through ultraviolet light irradiation, the polymer chains of the phosphate esterified flexible adhesive copolymers contained in the spinning solution are polymerized, cross-linked, and entangled, causing the polymer to spontaneously and uniformly enrich and solidify into a film on the surface of the sodium iron pyrophosphate fiber structure.

[0036] Optionally, the solvent used in preparing the electrospinning solution can be N,N-dimethylformamide (DMF).

[0037] Optionally, in preparing the electrospinning solution, the solvent can be a mixture of supercritical CO2 and DMF, with a mixing volume ratio of 4:1.

[0038] When using a mixed solvent of supercritical CO2 and DMF as the solvent, the method can be as follows: dissolve the above-mentioned flexible adhesive polymer in supercritical CO2, then add DMF as a co-solvent. In the subsequent classic spinning process, the polymer is rapidly sprayed into a low-pressure environment through a nozzle. The CO2 will vaporize instantly, and the polymer solution will become supersaturated, thereby precipitating nanoparticles or short fiber structures.

[0039] It should be noted that the aforementioned exogenous induced variables refer to controllable external variables introduced in addition to the high-voltage electric field of conventional electrospinning, and are additional induction and control methods. Existing conventional electrospinning polymer jets are prone to whip-like oscillation and disordered drift, resulting in fibers of varying lengths and thicknesses. However, the above-mentioned technical solution, by introducing exogenous induced variables, can constrain the oscillation trajectory of the jet, allowing the jet to stretch and extend uniformly along a fixed direction, and to be oriented and shaped during the flight curing process, providing mechanical guidance for the formation of long strip fiber morphologies.

[0040] In some examples, the mass ratio of sodium iron pyrophosphate precursor in the above electrospinning solution is 25%-35%, the mass ratio of flexible adhesive polymer is 15%-25%, and the mass ratio of solvent is 40%-60%.

[0041] It should be noted that in the aforementioned electrospinning solution, if the mass percentage of sodium iron pyrophosphate (NFPP) precursor is greater than 35%, the solid content and viscosity of the spinning solution will be too high, making it difficult to stretch and refine the electrospinning jet, and easily leading to needle blockage and fiber coarsening. If the mass percentage is less than 25%, insufficient active components may result in a weak inorganic fiber skeleton, making it brittle and unable to stably grow long primary particles of 1μm-3μm. This may lead to secondary agglomeration particles smaller than 5μm, resulting in poor powder packing properties, low electrode compaction density, and decreased energy density. If the mass percentage of flexible bonding polymer is greater than 25%, it will lead to a decrease in the content of active materials, resulting in a decrease in battery energy density. Furthermore, excess polymer is prone to excessive accumulation on the fiber surface, resulting in a shell thickness exceeding 20nm after UV polymerization. If the mass percentage is less than 15%, the polymer may not be sufficient to coat and stretch the precursor, making it difficult to form continuous long fibers and prone to breakage. If the solvent accounts for more than 60% of the total mass, the viscosity of the spinning solution will be too low, and the jet will easily drip or splash, making it impossible to form continuous one-dimensional long fibers. If the solvent accounts for less than 40% of the total mass, the viscosity will be too high, the fluidity will be poor, and the external induced field will be unable to control the jet direction and stretching.

[0042] In some instances, the method described above, based on preset process parameters and using the electrospinning solution as raw material, to obtain a fiber structure comprising long strips of sodium iron pyrophosphate phosphate through exogenous induced variables-assisted electrospinning, includes: The receiving device is an aluminum foil, and a rotating magnetic field auxiliary system is installed on the receiving device to assist electrospinning; the magnetic field strength of the rotating magnetic field auxiliary system is 0.4T-0.6T. The electrospinning voltage was adjusted to 17kV-19kV, the feed speed to 0.35mL / min-0.45mL / min, and the receiving distance to 12cm-15cm to perform electrospinning and obtain a fiber structure including long strips of sodium iron pyrophosphate.

[0043] It should be understood that the aforementioned rotating magnetic field-assisted system is the aforementioned exogenous induced variable.

[0044] It should be noted that in the above electrospinning process, a rotating magnetic field auxiliary system is used as an external variable to assist electrospinning. When the magnetic field strength of the rotating magnetic field auxiliary system is 0.4T-0.6T, the voltage of electrospinning is 17kV-19kV, the propulsion speed is 0.35mL / min-0.45mL / min, and the receiving distance is 12cm-15cm, the combined effect can make the resulting spun fibers uniform in thickness and orientation, with long fibers orderly interwoven into a film structure and uniform pore distribution. At the same time, it will not destroy the integrity of the sodium iron pyrophosphate crystal structure, and the polymer distribution on the fiber surface will be uniform. After subsequent UV in-situ polymerization, a continuous, flexible adhesive polymer shell with a thickness of <20nm can be stably formed.

[0045] Furthermore, when the magnetic field strength of the rotating magnetic field-assisted system is 0.4T-0.6T, it can generate an axial magnetic orientation traction force on the sodium iron pyrophosphate phosphate precursor, thereby restricting the transverse radial growth of particles, forcibly inhibiting transverse coarsening of particles, and confining the primary particle diameter to within 100nm. Simultaneously, it guides the particles to extend directionally along the fiber axis. Under constant magnetic field traction, the particle growth length can be limited to 1μm-3μm, ultimately forming standard elongated one-dimensional microcrystals. When the electrospinning voltage is 17kV-19kV, it can provide a moderate electrostatic stretching force to refine and thin the spinning jet. If the voltage is too high or too low, it may cause the primary particle diameter to exceed 100nm. When the liquid supply propulsion speed is 0.35mL / min-0.45mL / min, it can ensure a stable supply of material to a single fiber, preventing both insufficient material leading to short particle development and excessive material leading to radial coarsening of particles. The resulting elongated primary particles, under the combined action of a rotating magnetic field and an electrostatic field, can be orderly interwoven and uniformly stacked on the aluminum foil receiving substrate.

[0046] In some instances, the method for obtaining the above-mentioned cathode material by UV in-situ polymerization of the aforementioned fibrous structure comprising elongated sodium iron pyrophosphate includes: When a fibrous structure comprising long strips of sodium iron pyrophosphate (NFPP) falls onto a receiving device, it is simultaneously subjected to UV irradiation to obtain a cathode material; the wavelength of the UV irradiation is 360nm-370nm, and the light intensity is 22mW / cm². 2 -28mW / cm 2 The irradiation time is 8s-12s.

[0047] It should be noted that during the aforementioned UV in-situ polymerization process, when the UV irradiation wavelength is 360nm-370nm and the irradiation time is 8s-12s, no temperature rise occurs. Therefore, the structure of the primary particles or the near-spherical secondary agglomerates will not be damaged, and their morphology and size will not be changed. Furthermore, 22mW / cm²... 2-28mW / cm 2 The light intensity and the wavelength of 360nm-370nm can be matched to allow the phosphate esterified aniline copolymer molecular chains to fully cross-link into a network. This not only retains the intrinsic flexible buffering properties and self-adhesive properties of the polymer, but also maintains the electronic conductivity of the polyaniline conjugated structure, without structural failure or conductivity loss.

[0048] During UV in-situ polymerization, the polymer's phosphate functional groups can be triggered to form polar bonds with the core phase sodium iron pyrophosphate, causing the molecular structures of the two to become intertwined. This improves the interfacial bonding force between the shell and core phases of the aforementioned core-shell fiber structure, ensuring that the shell layer does not crack or peel off during charge-discharge volume deformation of the cathode material, thus maintaining the integrity of the core-shell structure for a long time.

[0049] Furthermore, during the aforementioned UV in-situ polymerization process, the 360-370nm wavelength only initiates the photoinitiation of the flexible copolymer on the fiber surface and cannot penetrate the fiber interior to trigger the polymerization reaction. Simultaneously, cross-linking and film formation occur only in the thin surface polymer layer, allowing the pure sodium iron pyrophosphate core phase to be completely retained within the fiber, preventing the formation of internal organic phases to thicken the shell. Meanwhile, 22mW / cm²... 2 -28mW / cm 2 The light intensity is only sufficient to cure and crosslink the polymer layer with a thickness of only nanometers on the surface, thus inhibiting secondary migration and accumulation of polymer molecules; and curing is completed within an irradiation time of 8s-12s; ultimately controlling the shell thickness of the aforementioned shell phase within the range of <20nm. In this UV in-situ polymerization, changing any parameter may cause the shell thickness to exceed the 20nm limit.

[0050] Throughout the electrospinning process described above, the NFPP precursor, flexible adhesive polymer, and solvent are uniformly dispersed in the electrospinning solution. Under the combined action of an applied high-voltage electric field and a rotating magnetic field, the spinning jet is directionally stretched and its tip is constrained to oscillate. The precursor nucleates and grows along the jet axis, initially forming elongated primary particles. As the jet travels towards the aluminum foil receiving device, the solvent gradually evaporates, and the rotating magnetic field forces the elongated primary particles to align in the correct direction. These particles are deposited on the aluminum foil surface along with the fibers. During this process, the flexible adhesive polymer molecules can coat the surface of each primary particle, acting as a bonding bridge. This causes the elongated primary particles to spontaneously aggregate, densely pack, and entangle inward, ultimately self-assembling and shrinking into thermodynamically stable, near-spherical, micron-sized secondary aggregates. Subsequent UV polymerization cross-links and solidifies the surface polymer, causing the primary particles to intertwine and aggregate, forming the secondary particle morphology. The strongest bonding force among these secondary particles is the chemical chelate bond, specifically the bond between -COOH and Fe on the surface of the NFPP primary particles. 3+The Fe-OOC chelate bond formed; also includes covalent bond energy (PO(OH)2 phosphate ester groups in the copolymer, and PO, Al-OP type covalent interactions with hydroxyl groups on the particle surface), π-π stacking interaction energy (intermolecular π-π conjugated stacking between aniline aromatic ring units in the copolymer), hydrogen bond energy, van der Waals forces, and binding energy such as physical entanglement, interweaving and coating of macromolecular chains.

[0051] In some instances, when the aforementioned flexible adhesive polymer is a phosphate-esterified polyacrylic acid-aniline copolymer, the molecular formula of the phosphate-esterified polyacrylic acid-aniline copolymer is: [CH2 CH(COOH)] m [CH2 CH(COOCH2CH3)] n [CH2 CH(COOCH2CH2OPO(OH)2)] p [=N C6H4 NH C6H4] k ; In this molecular formula, 10≤m≤30, 50≤n≤100, and 5≤p≤15.

[0052] Optionally, when the above-mentioned flexible adhesive polymer is polyaniline sulfonic acid-polyethyl acrylate phosphate, the synthesis method of polyaniline sulfonic acid-polyethyl acrylate phosphate can be as follows: Polyaniline sulfonic acid, polyethyl acrylate phosphate and an initiator are added to a solvent and polymerized to obtain polyaniline sulfonic acid-polyethyl acrylate phosphate.

[0053] Among them, polyaniline sulfonic acid (PSA) is a sulfonation modification of polyaniline. This modification can be achieved by reacting polyaniline with chlorosulfonic acid (ClSO3H) in dichloroethane (DCE) solvent for 4 hours, washing with water until the pH reaches approximately 6, and then drying. Polyethyl acrylate phosphate can be polymerized from ethyl acrylate phosphate monomer (EPA). EPA is prepared by reacting acrylic acid and P2O5 in DMF for 6 hours, followed by precipitation with diethyl ether.

[0054] Optionally, the initiator can be azobisisobutyronitrile (AIBN), and the dosage can be 1 mol / L.

[0055] Optionally, the solvent mentioned above can be toluene.

[0056] Optionally, the above-mentioned method for synthesizing phosphate-esterified polyacrylic acid-aniline copolymer can be an existing technical solution.

[0057] Optionally, in the above method for synthesizing polyaniline sulfonic acid-polyethyl acrylate phosphate, the specific method can be as follows: First, a solvent, such as toluene, is added to the reaction vessel, and nitrogen is bubbled to remove oxygen. Then, polyaniline sulfonic acid and polyethyl acrylate phosphate are added sequentially under stirring at room temperature, and stirring is continued until completely dissolved to form a homogeneous transparent reaction liquid. Next, a quantitative free radical initiator, such as AIBN, is slowly added, and the entire process is protected by nitrogen gas. The reaction temperature can be 60℃-80℃, the stirring speed can be 300r / min-500r / min, and the isothermal polymerization reaction can be carried out for 4h-6h. After the reaction is completed, the mixture is naturally cooled to room temperature, and unreacted monomers and small molecule byproducts are removed by dialysis and sedimentation separation. The mixture is then dried under vacuum at a constant temperature to obtain powdered phosphate-esterified polyacrylic acid-aniline copolymer.

[0058] The molecular formula of the above polyaniline sulfonic acid-polyethyl acrylate phosphate is: [C6H3(SO3H) NH C6H4 N=] x [CH2 CH(COOCH2CH2OPO(OH)2)] y It is a binary block copolymer formed by free radical copolymerization of two functional monomers.

[0059] It should be noted that in the molecular formula of the above-mentioned phosphate-esterified polyacrylic acid-aniline copolymer (PAA-ANI-P), [CH2] CH(COOH)] m For acrylic acid segments, when 10 ≤ m ≤ 30, the number of carboxyl groups can form strong hydrogen bonds with the core phase sodium iron pyrophosphate (NFPP), and can also form coordinate bonds and hydrogen bonds with the hydroxyl groups of the Al2O3 oxide layer on the surface of the aluminum foil of the electrospun receiving device, thereby significantly improving the adhesion of the electrospun fiber structure to the aluminum foil substrate. [CH2] CH(COOCH2CH3)] n As a flexible segment of ethyl acrylate, when 50≤n≤100, it can impart moderate flexibility and elasticity to the polymer, buffering the cyclic volume deformation of long strip-shaped particles, regulating the viscoelasticity of the spinning solution, and, in conjunction with exogenously induced electrospinning, controlling the length of the primary particles to 1μm-3μm and the particle size of the near-spherical secondary particles to 5μm-10μm; simultaneously, it can match the surface tension of aluminum foil, ensuring uniform fiber spreading. [CH2] CH(COOCH2CH2OPO(OH)2)] pAs a phosphate esterification functional segment, when 5 ≤ p ≤ 15, the number of phosphate ester groups, on the one hand, matches and strongly bonds with the lattice of the core phase material, inducing the polymer to spontaneously accumulate on the surface of the fiber structure during spinning, providing a structural basis for a shell thickness < 20 nm; on the other hand, it can form a microscopic passivation film on the aluminum foil surface, isolating the aluminum foil from electrolyte corrosion and constructing a stable integrated interface. [C6H4] NH C6H4 N=] k It is a polyaniline conjugated conductive segment, namely a p-phenylenediamine type aniline repeating unit, which can form a large π conjugated system, enabling the polymer to have intrinsic conductivity and reducing the positive electrode interface impedance; at the same time, it participates in molecular chain crosslinking, improving the stability of the shell structure.

[0060] Furthermore, when the value of m in the PAA-ANI-P molecular formula is in the range of 10-30, within this range, the number of carboxyl groups in each chain segment is ≥8. This satisfies the requirement of Fe on the surface of NFPP particles. 3+ The chelation requirement is met, and the excessive hydrophilicity of the positive electrode material can be prevented, thus avoiding electrolyte swelling. The value of N, ranging from 50 to 100, is used to adjust the electrode flexibility, ensuring that the elongation at break of the positive electrode material is >200%, meeting the requirement that the electrode bending radius R <1mm; simultaneously, it prevents excessive swelling in the electrolyte, controlling the swelling rate to <15%. The value of P, ranging from 5 to 15, provides chemical bonding between the phosphate groups and the aluminum foil, ensuring that the aluminum foil peel strength is >35N / m, and preventing hydrolysis of the phosphate ester under acidic conditions, such as pH <4, controlling the hydrolysis rate to <5% / month.

[0061] In some instances, the synthesis methods of the aforementioned sodium iron pyrophosphate precursor include: The determination of FePO4, NaH2PO4, Na2CO3, and C6H is based on the molecular weight of sodium iron pyrophosphate. 12 The molar ratio of O6 was determined by weighing out FePO4, NaH2PO4, Na2CO3, and C6H. 12 O6 was used to prepare sodium iron pyrophosphate precursor.

[0062] Optionally, the specific steps of the above-mentioned method for synthesizing the sodium iron pyrophosphate precursor can be as follows: weigh FePO4, NaH2PO4, Na2CO3 and C6H according to the above molar ratio. 12 O6 is added, and then deionized water is added as a dispersion medium to prepare a mixed slurry with a solid content of 30%-45%. The mixture is placed in a water bath at 60℃-70℃ for 2-3 hours under constant temperature and low speed stirring. After completion, it is spray dried, and then calcined and pulverized to obtain sodium iron pyrophosphate precursor.

[0063] To achieve the above objectives, the present invention also provides a positive electrode sheet comprising a positive electrode material prepared by the above-described preparation method.

[0064] When preparing positive electrode sheets using the aforementioned positive electrode materials, they are less prone to cracking, powdering, and brittle fracture during processes such as rolling. They also do not delaminate or peel during high-speed winding, stacking, and bending. Furthermore, because the positive electrode material contains a flexible, conductive bifunctional polymer, it possesses inherent adhesiveness and conductivity. Therefore, the amount of binders and conductive carbon black used in electrode preparation can be significantly reduced, resulting in a significantly higher proportion of NFPP active material in the electrode sheet. This allows for the preparation of high areal loading and high-density electrode sheets, leading to a simultaneous and significant increase in both the mass energy density and volumetric energy density of the battery under the same volume and weight.

[0065] To achieve the above objectives, the present invention also provides an ion battery comprising a positive electrode as described above.

[0066] In ion batteries containing the aforementioned positive electrode sheets, such as sodium-ion or lithium-ion batteries, their fast-charging rate performance is excellent, and their high-current charge-discharge capability is strong. This is because the diameter of the primary particles is <100nm, which can significantly shorten the solid-phase diffusion distance of ions; and the long fibers of 1μm-3μm can interweave to form a continuous and interconnected ion and electron transport network; while the conductive conjugated structure of the surface polymer shell can significantly reduce the overall internal resistance and polarization of the battery, resulting in high capacity retention at high rates, supporting high-current fast charging, significantly shortening charging time, and no performance degradation under high-power discharge conditions. In addition, the flexible polymer shell with a thickness of <20nm can adaptively buffer the volume deformation of NFPP during charge and discharge, and can isolate the electrolyte from direct contact with the active material, suppressing interfacial side reactions, lattice corrosion, and excessive SEI film growth. This ensures that the battery electrode sheets do not shed powder, delaminate, or collapse during long-term use, thus extending battery life.

[0067] Example 1 A method for preparing a positive electrode material is as follows: S10. Mix the NFPP precursor, flexible adhesive polymer, and solvent thoroughly and stir until completely dissolved to obtain the electrospinning solution, specifically: According to FePO4, NaH2PO4, Na2CO3 and C6H 12 The molar ratio of O6 is 3:1:1.5:0.5. Weigh each raw material component, then add deionized water to prepare a mixed slurry with a solid content of 40%. After stirring evenly, place it in a 65℃ water bath for constant temperature and low-speed stirring and aging for 2.5 hours to form a uniform crystal nucleus precursor slurry. After spray drying, calcining and pulverizing the precursor slurry in sequence, the NFPP precursor is obtained. According to the degree of polymerization of 10≤m≤30, 50≤n≤100, and 5≤p≤15, polyaniline sulfonic acid, polyethyl acrylate phosphate, initiator AIBN, and toluene solvent were weighed. High-purity nitrogen gas was bubbled into the reactor to remove oxygen. Then, polyaniline sulfonic acid and polyethyl acrylate phosphate were added in sequence and stirred until completely dissolved. AIBN initiator was then added. The polymerization reaction was carried out at a constant temperature of 70°C under nitrogen protection for 5 hours. After cooling to room temperature, the product was purified by dialysis and vacuum dried to obtain PAA-ANI-P powder. Weigh the raw material components according to the mass ratio of 30% NFPP precursor, 20% PAA-ANI-P, and 50% DMF solvent, mix them, and stir them at room temperature until uniform to obtain the electrospinning solution. S20. Based on preset process parameters, using the electrospinning solution of S10 as raw material, electrospinning is assisted by external induced variables to obtain a fiber structure including long strip-shaped NFPP, specifically: The receiving device of the electrospinning equipment is set to aluminum foil, and a rotating magnetic field auxiliary system is mounted on the receiving device to assist electrospinning. The magnetic field strength of the rotating magnetic field auxiliary system is adjusted to 0.5T. The electrospinning voltage was adjusted to 18kV, the feed speed to 0.40mL / min, and the receiving distance to 13.5cm. The electrospinning equipment was turned on, and electrospinning was carried out under the assistance of an external rotating magnetic field. During the spinning process, the spinning liquid jet was directionally stretched under the dual induction of electric and magnetic fields. During the stretching process, the solvent evaporated. After the spun fiber structure was deposited on the aluminum foil receiving device, a fiber structure including long strips of NFPP was obtained. S30. The fiber structure of S20, including long strip-shaped NFPP, is subjected to UV in-situ polymerization to obtain the cathode material; the cathode material includes a core-shell fiber structure, specifically: When the NFPP fiber structure, including the long strips, lands on the aluminum foil surface, UV irradiation is simultaneously activated, with the UV irradiation parameters adjusted to a wavelength of 365 nm and a light intensity of 25 mW / cm². 2 The irradiation time is 10s. During the irradiation process, the fiber structure, including the long strip-shaped NFPP, undergoes in-situ polymerization and solidification, and the phosphated polyacrylic acid-aniline copolymer is uniformly filmed on the surface of the fiber structure. After natural cooling, a cathode material with a core-shell fiber structure is obtained.

[0068] Using the positive electrode material obtained from S10-S30 in the preparation of positive electrode sheets can produce flexible and flat positive electrode sheets.

[0069] Using this positive electrode as the positive electrode of an ion battery, and assembling it using existing processes, a high-performance ion battery can be obtained.

[0070] The cathode material prepared in Example 1 was subjected to SE-SEM scanning, and the results are as follows: Figure 1 As shown.

[0071] like Figure 1 The image shown is a SE-SEM scan of the cathode material, magnified at 10.00K×(10000x), with a scale bar of 1μm and an accelerating voltage of 10.00kV. This image visually presents the primary particle hierarchy and secondary agglomeration structure of the material. As shown in the image, multiple spherical micron-sized agglomerates, representing secondary agglomerates, are clearly visible. Using the 1μm scale bar as a reference, the diameter of a single spherical particle is approximately 5μm-8μm. The agglomerates exhibit no cracks, breakage, or abnormal adhesion on their surfaces, displaying a regular overall morphology without structural defects. The secondary particles are composed of numerous elongated primary particles agglomerated in a radial and interwoven arrangement, without disordered scattering or excessive agglomeration. This indicates that the rotating magnetic field-assisted electrospinning effectively induced the oriented growth of the particles, leading to their self-assembly into spherical secondary particles. Furthermore, the axial length of a single primary particle is approximately 1μm-2μm, and the radial width is approximately 1 / 10 of the scale bar, i.e., <100nm.

[0072] To further confirm that the shell thickness of the core-shell structure of the cathode material obtained by the technical solution disclosed in this invention is <20 nm, the cathode material obtained in Example 1 was further measured by electron microscopy. The results are as follows: Figure 2 As shown.

[0073] like Figure 2 The image shows a high-resolution transmission electron microscope (TEM) image of the cathode material obtained in Example 1. The scale bar is 100 nm. The bright white area on the left represents the core structure of the cathode material, corresponding to the agglomeration of elongated NFPP primary particles. The translucent gray thin layer on the upper right represents the shell structure, an organic material easily penetrated by the electron beam, coating the surface of the core structure. Using the 100 nm scale bar as a reference, the polymer shell thickness at the edge of the shell structure is approximately 1 / 5 to 1 / 6 of the scale bar length, i.e., between 15 nm and 20 nm, and is uniformly coated, with the thinnest part approximately 12 nm and the thickest part approximately 18 nm. There is no obvious local thickening or agglomeration of the shell thickness, nor is there any localized excessive thinning or breakage.

[0074] Example 2 Compared to Example 1, in S10 of Example 2, the flexible adhesive polymer is a polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer; the mass percentages of NFPP precursor, polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer, and DMF solvent are 25%, 15%, and 60%, respectively; in S20, the magnetic field strength of the rotating magnetic field assisted system is 0.4T, the electrospinning voltage is 17kV, the feed speed is 0.35mL / min, and the receiving distance is 12cm; in S30, the wavelength of UV irradiation is 360nm, and the light intensity is 28mW / cm². 2 The irradiation time was 12 seconds; the remaining steps and process parameters were the same as in Example 1.

[0075] Example 3 Compared to Example 1, in S10 of Example 3, the flexible adhesive polymer is a polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer; the mass percentages of NFPP precursor, polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer, and DMF solvent are 35%, 25%, and 40%, respectively; in S20, the magnetic field strength of the rotating magnetic field assisted system is 0.6T, the electrospinning voltage is 19kV, the feed speed is 0.45mL / min, and the receiving distance is 15cm; in S30, the wavelength of UV irradiation is 370nm, and the light intensity is 25mW / cm. 2 The irradiation time was 8 seconds; the remaining steps and process parameters were the same as in Example 1.

[0076] Comparative Example 1 Comparative Example 1 was set up under Example 1. The difference between Comparative Example 1 and Example 1 is that the flexible adhesive polymer is a mixed solution of polyacrylonitrile dissolved in N,N-dimethylformamide. The remaining steps and process parameters are the same as those in Example 1.

[0077] Comparative Example 2 Comparative Example 2 was set up under Example 1. Compared with Example 1, the difference of Comparative Example 2 is that the rotating magnetic field auxiliary system is not set on the receiving device of the electrospinning equipment, and the rotating magnetic field auxiliary system is not used to assist electrospinning. The remaining steps and process parameters are the same as those of Example 1.

[0078] Comparative Example 3 Comparative Example 3 was set up under Example 1. Compared with Example 1, the difference of Comparative Example 3 is that in S30, when the long strip-shaped NFPP fiber structure falls onto the aluminum foil surface, it is simultaneously heat-cured. The heat-curing temperature is 80°C and the time is 10 min. The remaining steps and process parameters are the same as those of Example 1.

[0079] The performance of the cathode materials obtained in Examples 2-3 and Comparative Examples 1-3 was measured, and the results are shown in Table 1.

[0080] Table 1

[0081] Analysis of the data in Table 1 shows that, in the technical solution of the embodiment, the bonding effect between the functional groups of the flexible adhesive polymer and the functional groups and ions of the NFPP surface layer can significantly improve the interfacial bonding between the core phase material and the shell phase material of the core-shell fiber structure, and also achieve strong bonding and passivation protection between the material and the aluminum foil. Therefore, the peel strength of the positive electrode material prepared in the embodiment is high. In addition, under the condition of electrospinning assisted by a rotating magnetic field, the spinning is induced into long strip-shaped primary particles, forming a continuous ion and electron transport network, thereby improving the rate performance and long cycle performance of the material; UV in-situ curing does not hinder ion diffusion and can effectively isolate the electrolyte, while enabling the π-π stacking of the aniline units of the polymer to form a conductive network structure, thus enabling the material to have high rate performance and low charge transfer impedance.

[0082] In contrast, Comparative Example 1 used a mixed solution of polyacrylonitrile dissolved in N,N-dimethylformamide (PAN / DMF) as the flexible adhesive polymer. PAN lacks the carboxyl, phosphate, and aniline units of the target polymer, and can only form particle morphology under electrospinning and magnetic field induction. This leads to a significant reduction in the interfacial bonding force of the core-shell structure and a significant decrease in peel strength. Furthermore, PAN is an insulating polymer and cannot form the π-π conductive network of aniline units, resulting in a significant decrease in the material's conductivity, hindered electron transport, and a significant reduction in capacity retention at high rates. Comparative Example 2, without the assistance of a rotating magnetic field during electrospinning, could not control the oriented growth of particles. This resulted in the NFPP precursor particles failing to grow along a one-dimensional orientation, ultimately forming short, coarse particles with insufficient aspect ratio, disordered aggregation of secondary particles, and uneven particle size distribution. The ion solid-phase diffusion distance of these short, coarse particles increases, and they cannot form a continuous fibrous ion transport network, ultimately leading to a significant decrease in the material's rate performance and other properties. In the technical solution of Comparative Example 3, thermosetting replaces in-situ curing. During the thermosetting process, the rapid evaporation of solvent and the shrinkage of polymer chain segments can lead to problems such as microcracks, interfacial voids, and uneven thickness in the shell. Furthermore, thermal stress can disrupt the interfacial bond between the polymer and the NFPP core phase, resulting in a significant reduction in peel strength. At the same time, shell cracking allows electrolyte to seep in and corrodes the core phase material, leading to a decrease in cycle capacity retention. Additionally, shell cracking can damage the π-π stacked conductive network of aniline units, resulting in a decrease in material conductivity, an increase in charge transfer impedance, and an impact on rate performance.

[0083] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A positive electrode material, characterized in that, The cathode material includes a core-shell fiber structure, which includes a shell structure and a core structure. The shell structure covers the surface of the core structure, and the shell thickness of the shell structure is <20nm. The shell structure includes a shell phase material, and the core structure includes a core phase material and the shell phase material; The core phase material and the shell phase material form elongated sodium iron pyrophosphate-based primary particles; the elongated sodium iron pyrophosphate-based primary particles agglomerate to form secondary agglomerated particles including a core-shell fibrous structure. The shell material includes a flexible adhesive polymer, which is a phosphate-esterified polyacrylic acid-aniline copolymer or a polyaniline sulfonic acid-polyethyl acrylate phosphate copolymer.

2. The cathode material according to claim 1, characterized in that, The elongated sodium iron pyrophosphate-based primary particles have a diameter of <100 nm and a length of 1 μm-3 μm; the secondary aggregated particles formed by the agglomeration of the elongated sodium iron pyrophosphate-based primary particles, including core-shell fibrous structures, are quasi-spherical particles with a particle size of 5 μm-10 μm.

3. A method for preparing a positive electrode material, used to prepare the positive electrode material as described in claim 1 or 2, characterized in that, The preparation method includes: The sodium iron pyrophosphate precursor, flexible adhesive polymer and solvent are mixed evenly and stirred until completely dissolved to obtain electrospinning solution; Based on preset process parameters, using the electrospinning solution as raw material, electrospinning is assisted by external induced variables to obtain a fiber structure including long strips of sodium iron pyrophosphate. The cathode material is obtained by UV in-situ polymerization of the long, strip-shaped sodium iron pyrophosphate fiber structure; the cathode material includes a core-shell fiber structure.

4. The preparation method according to claim 3, characterized in that, In the electrospinning solution, the mass ratio of the sodium iron pyrophosphate precursor is 25%-35%, the mass ratio of the flexible adhesive polymer is 15%-25%, and the mass ratio of the solvent is 40%-60%.

5. The preparation method according to claim 3, characterized in that, The method for obtaining a fiber structure comprising long strips of sodium iron pyrophosphate phosphate by using the electrospinning solution as raw material and assisted by an external induced variable based on preset process parameters includes: The receiving device of the electrospinning equipment is an aluminum foil, and a rotating magnetic field auxiliary system is installed on the receiving device to assist electrospinning; the magnetic field strength of the rotating magnetic field auxiliary system is 0.4T-0.6T. The electrospinning voltage was adjusted to 17kV-19kV, the feed speed to 0.35mL / min-0.45mL / min, and the receiving distance to 12cm-15cm to perform electrospinning and obtain the fiber structure comprising long strips of sodium iron pyrophosphate.

6. The preparation method according to claim 3, characterized in that, The method for obtaining the cathode material by UV in-situ polymerization of the fiber structure comprising elongated sodium iron pyrophosphate includes: When the fiber structure comprising elongated sodium iron pyrophosphate falls onto the receiving device of the electrospinning equipment, it is simultaneously subjected to UV irradiation to obtain the positive electrode material; the wavelength of the UV irradiation is 360nm-370nm, and the light intensity is 22mW / cm². 2 -28mW / cm 2 The irradiation time is 8s-12s.

7. The preparation method according to claim 3, characterized in that, When the flexible adhesive polymer is a phosphoric acid esterified polyacrylic acid-aniline copolymer, the molecular formula of the phosphoric acid esterified polyacrylic acid-aniline copolymer is: [CH2 CH(COOH)] m [CH2 CH(COOCH2CH3)] n [CH2 CH(COOCH2CH2OPO(OH)2)] p [=N C6H4 NH C6H4] k ; In the molecular formula, 10≤m≤30, 50≤n≤100, and 5≤p≤15.

8. The preparation method according to claim 3, characterized in that, The method for synthesizing the sodium iron pyrophosphate precursor includes: The determination of FePO4, NaH2PO4, Na2CO3, and C6H is based on the molecular weight of sodium iron pyrophosphate. 12 The molar ratio of O6 was determined by weighing out FePO4, NaH2PO4, Na2CO3, and C6H. 12 O6 was used to prepare the sodium iron pyrophosphate precursor.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes a positive electrode material, which is prepared by the preparation method according to any one of claims 3-8.

10. An ion battery, characterized in that, The ion battery includes a positive electrode, as described in claim 9.

Images