Functionalized nfpp-based composite material, preparation method thereof, positive electrode sheet and sodium-ion battery

Abstract

The application provides a functionalized NFPP-based composite material and a preparation method thereof, a positive electrode sheet and a sodium ion battery, and relates to the field of sodium ion batteries. The functionalized NFPP-based composite material comprises at least two of a power unit A, a bridge unit B and an energy unit C. The power unit A comprises NFPP primary particles with a core and a first carbon layer arranged on the surface of the core. The bridge unit B comprises NFPP secondary particles B with a mesoporous core and a second carbon layer arranged on the surface of the core. The energy unit C comprises NFPP secondary particles C with a core containing a doping element M and a third carbon layer arranged on the surface of the core. By combining different functional units in a targeted manner, the compaction density, the rate performance and the cycle stability of the electrode sheet can be synergistically improved, and different application scenarios such as high-power start-stop power supplies or high-energy-density energy storage batteries can be flexibly adapted, so that the NFPP positive electrode material with excellent comprehensive performance is obtained.

Description

Technical Field

[0001] This application relates to the field of sodium-ion batteries, and more particularly to a functionalized NFPP-based composite material and its preparation method, a positive electrode sheet, and a sodium-ion battery. Background Technology

[0002] Sodium iron pyrophosphate (typically Na4Fe3(PO4)2P2O7, abbreviated as NFPP) is prized for its stable three-dimensional framework structure and suitable operating voltage (~3.1V vs. Na4Fe3(PO4)2P2O7). + NFPP materials have attracted much attention due to their excellent thermal stability and high intrinsic electronic conductivity (e.g., Na₂O₃). However, their low intrinsic electronic conductivity and slow ion diffusion kinetics severely limit their commercial application. Mainstream modification strategies include carbon coating, elemental doping, and nanostructuring. For example, existing technologies attempt to construct three-dimensional conductive networks by compositing NFPP with highly conductive carbon materials such as carbon nanotubes and graphene; or by introducing metal ions (such as Mg, Al, and Ti) doping to broaden ion diffusion channels and stabilize the crystal structure.

[0003] The methods described above often focus only on improving the intrinsic properties of materials or are limited to controlling the morphology of a single particle (such as single crystal or porous). In practical electrode engineering, particles with a single morphology have inherent defects: although nanoscale primary particles can shorten the Na... + While micron-sized secondary particles can improve compaction density, their large surface area leads to numerous side reactions, processing difficulties, and low compaction density. Although micron-sized secondary particles can improve compaction density, their long solid-phase transport path within the particles limits their rate performance.

[0004] Currently, no technical solution has been proposed on how to coordinate the contradiction between high energy density and high power density, while taking into account electrode processing performance, by designing and oriented NFPP particles of different sizes and functions in a "functional modular" manner. Summary of the Invention

[0005] The purpose of this application is to provide a functionalized NFPP-based composite material, its preparation method, a positive electrode sheet, and a sodium-ion battery to solve the above-mentioned problems.

[0006] To achieve the above objectives, the first aspect of this application provides a functionalized NFPP-based composite material, comprising at least two of power units A, bridge units B, and energy units C;

[0007] The power unit A includes NFPP primary particles; the NFPP primary particles include a core and a first carbon layer disposed on the surface of the core.

[0008] The bridge unit B includes NFPP secondary particles B; the NFPP secondary particles B include an NFPP core containing mesoporous structures and a second carbon layer disposed on the surface of the core.

[0009] The energy unit C includes NFPP secondary particles C, which include a core containing a dopant element M and a third carbon layer disposed on the surface of the core, wherein M includes at least one of Mg, Al, Ti, Mn, Zr and Cr.

[0010] The particle size and density of the NFPP secondary particles C are greater than those of the NFPP secondary particles B.

[0011] Optionally, the functionalized NFPP-based composite material satisfies at least one of the following conditions:

[0012] (1) The NFPP primary particles have a D50 of 500-800 nm, a D90 ≤ 1.2 μm, and a specific surface area of ​​15-30 m². 2 / g, carbon content is 3.5-5.0%, powder conductivity ≥10 -4 S / cm;

[0013] (2) The thicknesses of the first carbon layer, the second carbon layer and the third carbon layer are each 2-5 nm independently;

[0014] (3) The D50 of the NFPP secondary particles B is 4-8 μm, and the specific surface area BET is 8-15 m². 2 / g, carbon content is 2.0-3.5%; the mesopore size in the core is 2-50 nm;

[0015] (4) The particle size D50 of the NFPP secondary particles C is 10-25 μm, and the specific surface area BET is 1-8 m². 2 / g, carbon content 0.5-2.0%, powder compaction density ≥2.2 g / cm³ 3 ;

[0016] (5) The general chemical formula of the energy unit C is Na4Fe 3-x M x (PO4)2P2O7, where 0 <x≤0.2。

[0017] Optionally, the functionalized NFPP-based composite material includes a power unit A, a bridge unit B, and an energy unit C; when applied to high-power scenarios, the total mass of the power unit A and the bridge unit B accounts for ≥70% of the functionalized NFPP-based composite material, and the mass ratio of the power unit A to the bridge unit B is 1-2:1-2.

[0018] Optionally, the functionalized NFPP-based composite material includes a power unit A, a bridge unit B, and an energy unit C; when applied to high energy density scenarios, the mass of the bridge unit B accounts for ≥50% of the functionalized NFPP-based composite material, and the mass ratio of the bridge unit B to the energy unit C is 1-4:1.

[0019] A second aspect of this application provides a method for preparing the aforementioned functionalized NFPP-based composite material, comprising:

[0020] The preparation method of power unit A includes: mixing a first sodium source, a first iron source, a first phosphorus source and a first carbon source, performing a first sand milling and spray drying to obtain a first precursor powder; and performing a first sintering of the first precursor powder under an inert atmosphere to obtain the power unit A.

[0021] The preparation method of bridge unit B includes: mixing a second sodium source, a second iron source, a second phosphorus source and a pore-forming agent, performing a second sand milling and spray drying to obtain a second precursor powder; and performing a second sintering of the second precursor powder under an inert gas to obtain the bridge unit B.

[0022] The preparation method of energy unit C includes: mixing a third sodium source, a third iron source, a second carbon source, a third phosphorus source and an M source, performing a third sand milling and spray drying to obtain a third precursor powder; and performing a third sintering of the third precursor powder under an inert atmosphere to obtain the energy unit C.

[0023] When the functionalized NFPP-based composite material includes at least two of the raw materials selected from power unit A, bridge unit B, and energy unit C, the raw materials are mixed to obtain the functionalized NFPP-based composite material.

[0024] Optionally, the method for preparing the functionalized NFPP-based composite material satisfies at least one of the following conditions:

[0025] (1) The first sodium source, the second sodium source and the third sodium source each independently include at least one of sodium nitrate, sodium carbonate and sodium dihydrogen phosphate;

[0026] (2) The first iron source, the second iron source and the third iron source each independently include at least one of ferric nitrate, ferrous oxalate and ferric oxide;

[0027] (3) The first phosphorus source, the second phosphorus source and the third phosphorus source each independently include ammonium dihydrogen phosphate and / or phosphoric acid;

[0028] (4) The first carbon source includes at least one of citric acid, glucose, sucrose and carbon nanotubes;

[0029] (5) The pore-forming agent includes at least one of polyethylene glycol, polyvinylpyrrolidone, polymethyl methacrylate, and starch;

[0030] (6) The second carbon source includes at least one of PEG, sucrose, phenolic resin and carbon nanotubes;

[0031] (7) The M source includes oxides containing M;

[0032] (8) The mass of the first carbon source accounts for 6-10% of the mass of the power unit A;

[0033] (9) The mass of the pore-forming agent accounts for 3-8% of the mass of the bridge unit B;

[0034] (10) The mass of the second carbon source accounts for 1-3% of the mass of the energy unit C.

[0035] Optionally, the preparation method of the functionalized NFPP-based composite material satisfies at least one of the following conditions:

[0036] (1) The material after the first sand mill has a D50 ≤ 400 nm;

[0037] (2) The D50 of the material after the second grinding is 1-2.5μm;

[0038] (3) The material D50 of the third precursor powder is 5-20 μm;

[0039] (4) The temperature of the first sintering is 500-650℃ and the time is 6-12h;

[0040] (5) The second sintering temperature is 600-700℃ and the time is 8-14h;

[0041] (6) The temperature of the third sintering is 650-750℃ and the time is 10-18h.

[0042] A third aspect of this application provides a positive electrode sheet comprising the aforementioned functionalized NFPP-based composite material.

[0043] Optionally, the positive electrode further includes a conductive agent and a binder;

[0044] The mass ratio of the functionalized NFPP-based composite material, the conductive agent, and the binder is 90-96:2-5:2-5;

[0045] The conductive agent includes at least two of conductive carbon black, carbon nanotubes, and graphene.

[0046] The compaction density of the positive electrode sheet is 2.2-2.4 g / cm³. 3 .

[0047] A fourth aspect of this application provides a sodium-ion battery, including the aforementioned positive electrode.

[0048] Compared with the prior art, the beneficial effects of this application include:

[0049] The functionalized NFPP-based composite material provided in this application achieves synergistic function through the directional assembly of power unit A, bridge unit B, and energy unit C. It allows for the flexible design of NFPP cathode materials suitable for various applications such as high-power start-stop power supplies and high-energy-density energy storage batteries, and can be configured according to actual performance requirements. Specifically, the small-particle power unit A provides a fast ion transport channel (small particle size results in short ion transport channels, large BET increases transport channels and electrolyte wetting, and high carbon content ensures good conductivity); the large-particle energy unit C ensures high compaction density (dense large particles, low carbon content, small BET, dense internal structure, acting as a skeleton, significantly improving compaction and energy density after combined filling); and the intermediate-sized bridge unit B, which fills gaps and connects the conductive network, plays a crucial "bridging" role (medium-sized particles with internal mesopores, primary carbon coating, and secondary carbon coating, mainly serving as partial fillers and connecting conductive networks). The combination of two or more unit particles can achieve the complementary functions and synergistic structure of particles of different sizes in the electrode. The mixing of multiple unit particles changes the powder stacking mode of a single unit particle, thereby changing the connectivity of the conductive network and the ion transport path, and improving the synergistic and gain effects that cannot be achieved by a single functional unit.

[0050] The method for preparing functionalized NFPP-based composite materials provided in this application allows for the precise control of the preparation process, enabling the preparation of different functional units without introducing complex equipment and facilitating large-scale production.

[0051] The positive electrode and sodium-ion battery provided in this application exhibit excellent energy density and power density. Through a reasonable gradation design, the composite material can form the densest packing structure in the electrode, significantly improving the electrode compaction density. At the same time, the carbon networks on different functional units interlock to construct a long-range continuous three-dimensional conductive network, which significantly improves the rate performance and cycle stability of the material. Attached Figure Description

[0052] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0053] Figure 1 The particle size distribution curve of power unit A provided in Example 1;

[0054] Figure 2 The particle size distribution curve of bridge unit B provided in Example 1;

[0055] Figure 3 SEM image of the positive electrode sheet provided in Example 1;

[0056] Figure 4 The particle size distribution curve of energy unit C provided in Example 2;

[0057] Figure 5 The image shows a SEM image of the positive electrode sheet provided in Example 3. Detailed Implementation

[0058] First, the solution provided in this application will be explained in more detail as follows:

[0059] The first aspect of this application provides a functionalized NFPP-based composite material, comprising at least two of power units A, bridge units B, and energy units C;

[0060] The power unit A includes NFPP primary particles; the NFPP primary particles include a core and a first carbon layer disposed on the surface of the core.

[0061] The bridge unit B includes NFPP secondary particles B; the NFPP secondary particles B include an NFPP core containing mesoporous structures and a second carbon layer disposed on the surface of the core.

[0062] The energy unit C includes NFPP secondary particles C, which include a core containing a dopant element M and a third carbon layer disposed on the surface of the core, wherein M includes at least one of Mg, Al, Ti, Mn, Zr and Cr.

[0063] The particle size and density of the NFPP secondary particles C are greater than those of the NFPP secondary particles B.

[0064] It is important to note that, among these components, power unit A is a primary small-particle material with high carbon content and a large specific surface area, designed to enhance its kinetic performance (i.e., rate performance) and highlight its single function; bridge unit B is a medium-sized secondary particle with a mesoporous structure designed inside and a carbon coating on the surface. The mesoporous structure is used to mitigate the kinetic disadvantages caused by large particles and promote ion transport, while the carbon coating prevents electrolyte corrosion and improves conductivity; energy unit C is a dense, near-solid spherical secondary large particle, mainly acting as a framework to increase compaction density (and thus energy density). Large particles act as the framework, with medium and small particles filling the gaps. Given its dense internal structure, it is doped with element M to enhance structural stability and kinetic performance.

[0065] For example, the functionalized NFPP-based composite material includes power unit A and bridge unit B.

[0066] It should be noted that when the composite material includes power unit A and bridging unit B: the particle size D50 of power unit A is 500-800 nm, and the particle size D50 of bridging unit B is 4-8 μm. Small particles A can effectively fill the gaps between large particles B, increasing the electrode packing density and reducing porosity, thereby improving electrode compaction. Simultaneously, the small particles of A and the mesopores of B can effectively reduce the sodium ion transport path, improving rate performance. The carbon content of power unit A is 3.5-5.0%, and the specific surface area is 15-30 m². 2 / g, the carbon content of bridge unit B is 2-3.5%. After the two are mixed, particles A are attached to the surface of particles B or fill between particles B, so that the short-range high conductivity network of A and the long-range conductive skeleton of B are linked together to form a more uniform and dense conductive network, which improves conductivity and reduces the internal resistance of the electrode.

[0067] For example, the functionalized NFPP-based composite material includes a bridging unit B and an energy unit C.

[0068] It should be noted that when the composite material includes bridge unit B and energy unit C: the particle size D50 of energy unit C is 10-25μm, which can act as a skeleton to support the composite particles. The particles of bridge unit B are used to fill the composite, forming a particle size distribution, increasing the electrode packing density, reducing porosity, and thus improving electrode compaction. The carbon content of energy unit C particles is low, and the dense large particles result in a long sodium ion diffusion path, leading to poor conductivity when used alone. When used in combination with bridge unit B, the higher carbon content and mesoporous structure of B particles can act as a conductive bridge, connecting the single large particles C to form a continuous conductive path, improving the electrode conductivity, and enhancing the dynamic performance and energy density of the battery cell.

[0069] For example, a functionalized NFPP-based composite material includes a power unit A and an energy unit C.

[0070] It is important to note that when the composite material includes power unit A and energy unit C, the combination of A particles and C particles conforms to the gradation principle of particle size ratio greater than 10 in the closest packing theory. A particles can effectively fill the gaps formed by the stacking of C particles, improving electrode compaction. A particles have a high carbon content and a large specific surface area, which will be adsorbed or coated on the surface of C particles, forming a highly conductive point contact interface, which can effectively reduce the interface contact resistance. A particles themselves have good conductivity, and after being combined with C particles, they can effectively form a penetrating conductive network in the electrode, effectively improving the rate performance of the cell. The composite can improve the low compaction problem caused by using a single power unit and the poor conductivity problem caused by using a single energy unit.

[0071] In some embodiments, the functionalized NFPP-based composite material satisfies at least one of the following conditions:

[0072] (1) The NFPP primary particles have a D50 of 500-800 nm, a D90 ≤ 1.2 μm, and a specific surface area of ​​15-30 m². 2 / g, carbon content is 3.5-5.0%, powder conductivity ≥10 -4 S / cm;

[0073] Optionally, the D50 of the NFPP primary particles can be any value between 500 nm, 600 nm, 700 nm, 800 nm, or 500-800 nm; the D90 can be any value between 1.2 μm, 1.1 μm, 1 μm, 0.9 μm, or ≤1.2 μm; and the specific surface area can be 15 m². 2 / g、20 m 2 / g、25 m 2 / g、30 m 2 / g or 15-30 mg 2 The carbon content can be any value between / g and 3.5%, 4%, 4.5%, 5%, or any value between 3.5% and 5%, and the powder conductivity can be 10. -4 S / cm, 2×10 -4 S / cm, 3×10 -4 S / cm, 4×10 -4 S / cm, 5×10 -4 S / cm or ≥10 -4 Any value of S / cm;

[0074] (2) The thicknesses of the first carbon layer, the second carbon layer and the third carbon layer are each 2-5 nm independently;

[0075] Optionally, the thicknesses of the first carbon layer, the second carbon layer, and the third carbon layer can each be independently 2nm, 3nm, 4nm, 5nm, or any value between 2 and 5nm;

[0076] (3) The D50 of the NFPP secondary particles B is 4-8 μm, and the specific surface area BET is 8-15 m². 2 / g, carbon content is 2.0-3.5%, and the mesopore size in the core is 2-50 nm;

[0077] Optionally, the D50 of the NFPP secondary particles B can be any value between 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or 4-8 μm, and the specific surface area BET can be 8 m². 2 / g、9 m 2 / g、10 m 2 / g、11 m 2 / g、12 m 2 / g、13 m 2 / g、14 m 2 / g、15 m 2 / g or 8-15 mg 2 The carbon content can be any value between / g, 2%, 2.5%, 3%, 3.5% or any value between 2-3.5%, and the mesopore size of the core of the NFPP secondary particles B can be any value between 2nm, 10nm, 20nm, 30nm, 40nm, 50nm or any value between 2-50nm.

[0078] (4) The D50 of the NFPP secondary particles C is 10-25 μm, and the specific surface area is 1-8 m². 2 / g, carbon content 0.5-2.0%, powder compaction density ≥2.2 g / cm³ 3 ;

[0079] Optionally, the D50 of the NFPP secondary particles C can be any value between 10 μm, 15 μm, 20 μm, 25 μm, or 10-25 μm, and the specific surface area can be 1 m². 2 / g、2 m 2 / g、3 m 2 / g、4 m 2 / g、5 m 2 / g、6 m 2 / g、7 m 2 / g、8 m 2 / g or 1-8 mg 2 The carbon content can be any value between 0.5%, 1%, 1.5%, 2%, or any value between 0.5% and 2%, and the powder compaction density can be 2.2 g / cm³. 3 2.3 g / cm 3 2.4 g / cm 3 2.5 g / cm 3 3 g / cm 3 Or ≥2.2 g / cm 3 Any value between;

[0080] (5) The general chemical formula of the energy unit C is Na4Fe 3-x M x (PO4)2P2O7, where 0 <x≤0.2。

[0081] Optionally, x in the chemical general formula of the energy unit C can be 0.001, 0.01, 0.1, 0.2, or any value between 0 < x ≤ 0.2.

[0082] In some embodiments, the functionalized NFPP-based composite material includes a power unit A, a bridge unit B, and an energy unit C; when applied to a high-power scenario, the total mass of the power unit A and the bridge unit B accounts for ≥70% of the functionalized NFPP-based composite material, and the mass ratio of the power unit A to the bridge unit B is 1 - 2:1 - 2.

[0083] Optionally, when applied to a high-power scenario, the total mass of the power unit A and the bridge unit B can account for 70%, 75%, 80%, or any value ≥70% of the functionalized NFPP-based composite material; the mass ratio of the power unit A to the bridge unit B can be 1:1, 1:2, 2:1, or any value between 1 - 2:1 - 2.

[0084] It should be noted that a high-power scenario means that the sodium-ion battery needs to be quickly charged and discharged at a rate of ≥10C, and the discharge capacity retention rate (relative to the 0.1C capacity) is required to be not less than 88% at the 10C rate, and the electrode compaction is not less than 2.1 g / cm 3 , and the scenarios include but are not limited to start-stop power supplies, power tools, drones, primary frequency regulation of power grids, etc.; where the total mass ratio of A + B < 70%, the proportion of C > 30%, and the electrode compaction ≥ 2.2 g / cm 3 , but the capacity retention rate at the 10C rate is low and cannot meet the scenario requirements; when the total mass of A + B is 100%, the compaction and rate can both meet the scenario requirements, but adding a C unit < 30% can further improve the compaction while meeting the rate requirements, enabling the battery cell to have a higher energy density; when the mass ratio of A / B is less than 1:2, there are too few A particles, and the point-to-point connection effect is poor, unable to form a continuous conductive percolation network, resulting in a poor improvement in rate performance; when the mass ratio of A / B is higher than 2:1, there are fewer B particles and more A particles, increasing the difficulty of slurry processing, and lacking a long-range conductive skeleton, resulting in a decline in kinetics and unable to meet the scenario requirements; therefore, the mass ratio of A + B ≥ 70%, and the mass ratio of A to B is 1 - 2:1 - 2, which can meet the rate performance and processing performance. At the same time, adding a C unit < 30% can further improve the energy density of the battery cell while meeting the rate performance, enhancing the product competitiveness;

[0085] In some embodiments, the functionalized NFPP-based composite material includes a power unit A, a bridge unit B, and an energy unit C; when applied to a high-energy density scenario, the mass of the bridge unit B accounts for ≥50% of the functionalized NFPP-based composite material, and the mass ratio of the bridge unit B to the energy unit C is 1 - 4:1.

[0086] Optionally, when applied to high energy density scenarios, the mass of bridge unit B can account for any value of 50%, 60%, 70%, 80% or ≥50% of the functionalized NFPP-based composite material, and the mass ratio of bridge unit B to energy unit C can be any value between 1:1, 2:1, 3:1, 4:1 or 1-4:1.

[0087] Preferably, when applied to high energy density scenarios, the mass of the bridge unit B accounts for 50%-80% of the functionalized NFPP-based composite material.

[0088] It is important to note that high energy density scenarios refer to sodium-ion battery cells with a mass energy density > 110 Wh / kg or a volumetric energy density > 200 Wh / L. Rate capability requirements are not high; typically, meeting 3C continuous discharge requirements is sufficient. However, the electrode compaction requirements are significant, usually ≥ 2.3 g / cm³. 3 The scenarios include, but are not limited to, large-scale energy storage power stations, home energy storage systems, and low-speed electric vehicles. Energy unit C acts as a skeleton to enhance compaction, while bridge unit B performs primary filling to improve electrode compaction. Simultaneously, its own conductive network and mesoporous characteristics can be used as conductive bridges, connecting individual large particles C to form a continuous conductive path. Power unit A performs secondary filling of the gaps after the composite stacking of B and C, resulting in low electrode porosity and further increasing compaction density. At the same time, the point-to-point connection of A particles makes the overall conductive network of the electrode more compact, and the larger BET of A particles results in strong liquid absorption capacity, improving the problem of poor liquid absorption and retention in high-compacted electrodes. If there are too many C unit particles, the overall conductivity of the cell is poor, affecting the cell's cycle life. If there are too many A and B unit particles, the electrode compaction is reduced, failing to meet high energy density requirements. Therefore, setting the mass ratio of bridge unit B to energy unit C to 1-4:1 can meet the needs of high energy density scenarios. Adding power units can further improve the cell's energy density and rate performance, enhancing product competitiveness.

[0089] A second aspect of this application provides a method for preparing the aforementioned functionalized NFPP-based composite material, comprising:

[0090] The preparation method of power unit A includes: mixing a first sodium source, a first iron source, a first phosphorus source and a first carbon source, performing a first sand milling and spray drying to obtain a first precursor powder; and performing a first sintering of the first precursor powder under an inert atmosphere to obtain the power unit A.

[0091] The preparation method of bridge unit B includes: mixing a second sodium source, a second iron source, a second phosphorus source and a pore-forming agent, performing a second sand milling and spray drying to obtain a second precursor powder; and performing a second sintering of the second precursor powder under an inert gas to obtain the bridge unit B.

[0092] The preparation method of energy unit C includes: mixing a third sodium source, a third iron source, a second carbon source, a third phosphorus source and an M source, performing a third sand milling and spray drying to obtain a third precursor powder; and performing a third sintering of the third precursor powder under an inert atmosphere to obtain the energy unit C.

[0093] When the functionalized NFPP-based composite material includes at least two of the following: power unit A, bridge unit B, and energy unit C, they are mixed to obtain the functionalized NFPP-based composite material.

[0094] In some embodiments, the method for preparing the functionalized NFPP-based composite material satisfies at least one of the following conditions:

[0095] (1) The first sodium source, the second sodium source and the third sodium source each independently include at least one of sodium nitrate, sodium carbonate and sodium dihydrogen phosphate;

[0096] (2) The first iron source, the second iron source and the third iron source each independently include at least one of ferric nitrate, ferrous oxalate and ferric oxide;

[0097] (3) The first phosphorus source, the second phosphorus source and the third phosphorus source each independently include ammonium dihydrogen phosphate and / or phosphoric acid;

[0098] (4) The first carbon source includes at least one of citric acid, glucose, sucrose and carbon nanotubes;

[0099] Preferably, the first carbon source includes citric acid and carbon nanotubes;

[0100] It is important to note that individual units can be customized and optimized according to the actual project requirements. For example, if higher power performance is required, the single carbon source can be changed to a composite carbon source (citric acid + carbon nanotubes) when designing power unit A. The particle size can also be further reduced to increase its kinetic performance. Furthermore, the material morphology (block or spherical), doping elements, and conductive network structure can be changed according to actual needs.

[0101] (5) The pore-forming agent includes at least one of polyethylene glycol, polyvinylpyrrolidone, polymethyl methacrylate, and starch;

[0102] (6) The second carbon source includes at least one of PEG, sucrose, phenolic resin and carbon nanotubes;

[0103] (7) The M source includes oxides containing M;

[0104] (8) The mass of the first carbon source accounts for 6-10% of the mass of the power unit A;

[0105] Optionally, the mass of the first carbon source can be any value between 6%, 7%, 8%, 9%, 10% or 6-10% of the mass of power unit A;

[0106] (9) The mass of the pore-forming agent accounts for 3-8% of the mass of the bridge unit B;

[0107] Optionally, the mass of the pore-forming agent can be any value between 3%, 4%, 5%, 6%, 7%, 8% or 3-8% of the mass of bridge unit B;

[0108] (10) The mass of the second carbon source accounts for 1-3% of the mass of the energy unit C.

[0109] Optionally, the mass of the second carbon source can be any value between 1%, 2%, 3%, or 1-3% of the mass of the energy unit C.

[0110] In some embodiments, the method for preparing the functionalized NFPP-based composite material satisfies at least one of the following conditions:

[0111] (1) The material after the first sand mill has a D50 ≤ 400 nm;

[0112] Optionally, the D50 of the material after the first grinding can be any value of 400 nm, 350 nm, 300 nm, 250 nm, 200 nm or ≤400 nm;

[0113] (2) The D50 of the material after the second grinding is 1-2.5μm;

[0114] Optionally, the D50 of the material after the second grinding can be any value between 1μm, 1.5μm, 2μm, 2.5μm, or 1-2.5μm;

[0115] (3) The D50 of the third precursor powder is 5-20 μm;

[0116] Optionally, the D50 of the third precursor powder can be any value between 5 μm, 10 μm, 15 μm, 20 μm, or 5-20 μm;

[0117] (4) The temperature of the first sintering is 500-650℃ and the time is 6-12h;

[0118] Optionally, the temperature of the first sintering can be any value between 500℃, 550℃, 600℃, 650℃ or 500-650℃, and the time can be any value between 6h, 7h, 8h, 9h, 10h, 11h, 12h or 6-12h.

[0119] (5) The second sintering temperature is 600-700℃ and the time is 8-14h;

[0120] Optionally, the temperature of the second sintering can be any value between 600℃, 650℃, 700℃ or 600-700℃, and the time can be any value between 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h or 8-14 h.

[0121] (6) The temperature of the third sintering is 650-750℃ and the time is 10-18h.

[0122] Optionally, the temperature of the third sintering can be any value between 650℃, 700℃, 750℃ or 650-750℃, and the time can be any value between 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h or 10-18 h.

[0123] A third aspect of this application provides a positive electrode sheet comprising the aforementioned functionalized NFPP-based composite material.

[0124] In some embodiments, the slurry solid content is 50-70% during the preparation of the positive electrode sheet.

[0125] In some embodiments, the positive electrode sheet further includes a conductive agent and a binder;

[0126] The mass ratio of the functionalized NFPP-based composite material, the conductive agent, and the binder is 90-96:2-5:2-5;

[0127] Optionally, the mass ratio of the functionalized NFPP-based composite material, the conductive agent, and the binder can be (90:5:5), (92:4:4), (94:3:3), (96:2:2), or any value between 90-96:2-5:2-5;

[0128] The conductive agent includes at least two of conductive carbon black, carbon nanotubes, and graphene.

[0129] The compaction density of the positive electrode sheet is 2.2-2.4 g / cm³. 3 .

[0130] Optionally, the compaction density of the positive electrode sheet can be 2.2 g / cm³. 3 2.3 g / cm 3 2.4 g / cm 3 Or 2.2-2.4 g / cm 3 Any value between.

[0131] A fourth aspect of this application provides a sodium-ion battery, including the aforementioned positive electrode.

[0132] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0133] Example 1

[0134] The first aspect of this application provides a functionalized NFPP-based composite material, wherein the power unit A is a near-spherical primary particle; the NFPP primary particle core and a carbon layer disposed on the surface of the core, the carbon layer having a thickness of 2-5 nm, D50=660 nm, D90=980 nm, and BET=22.5 nm. 2 / g, carbon content = 4.2 wt%, powder conductivity = 2.3 × 10 -4 The S / cm and the initial discharge capacity at 0.1C are 112mAh / g.

[0135] Bridge unit B consists of spherical NFPP secondary particles, sintered from primary nanoparticles. The NFPP secondary particles comprise a mesoporous NFPP core and a carbon layer on the core surface, with D50 = 7.5 μm, D90 = 12.6 μm, and BET = 10.8 μm. 2 / g, packing porosity=22%, carbon layer thickness is 2-5 nm, carbon content=2.8wt%, pore size distribution is mainly concentrated in 5-30nm, and the initial discharge capacity at 0.1C is 107 mAh / g.

[0136] The mass ratio of power unit A to bridge unit B is 45:55.

[0137] The second aspect of this application provides a method for preparing a functionalized NFPP-based composite material, as follows:

[0138] With a molar ratio of Na:Fe:P = 4:3:4, sodium nitrate, ferric nitrate, and ammonium dihydrogen phosphate were weighed out. Citric acid, accounting for 8% of the theoretical NFPP mass, was also weighed out as a carbon source and complexing agent. The above raw materials were dissolved in deionized water and added to a sand mill for wet grinding. The solid content of the slurry was controlled at 30%, and the grinding speed was 2500 r / min until the particle D50 in the slurry reached 350 nm. The slurry was spray-dried (inlet temperature 220℃, outlet temperature 110℃) to obtain precursor powder. The precursor powder was placed in a tube furnace and heated to 350℃ at 2℃ / min and held for 4 h under a nitrogen atmosphere. Then, it was heated to 580℃ at 5℃ / min and sintered for 8 h. After natural cooling, power unit A (core of Na4Fe3(PO4)2P2O7) was obtained.

[0139] Sodium carbonate, ferrous oxalate, and ammonium dihydrogen phosphate were weighed out according to the molar ratio Na:Fe:P = 4:3:4; polyethylene glycol (PEG-2000) accounting for 6% of the theoretical NFPP mass was weighed out as a pore-forming agent and carbon source; after mixing, the mixture was wet-milled to control the slurry D50 to 1.5 μm, and spray-dried (inlet temperature 210℃, outlet temperature 105℃) to obtain a spherical precursor; under a nitrogen atmosphere, it was sintered at 650℃ for 10 h (heating rate 3℃ / min) to obtain bridge unit B (core of Na4Fe3(PO4)2P2O7).

[0140] The particle size distribution curve of power unit A is as follows: Figure 1 As shown.

[0141] The particle size distribution curve of bridge unit B is as follows: Figure 2 As shown.

[0142] A third aspect of this application provides a positive electrode sheet, the specific preparation method of which is as follows:

[0143] Power unit A and bridge unit B were dry-mixed at a mass ratio of 45:55 (V-type mixer, mixing time 30 min) to obtain composite material SP. 93 wt% of composite material SP, 3 wt% PVDF, and 3 wt% SP were added to a planetary mixing tank and stirred (30 rpm / min, 30 min). After stirring, 1 wt% CNT and NMP (mass ratio 1:1) were added and kneaded to control the kneading solid content to 66.5% (50 rpm / min, 60 min). After kneading, NMP was added to adjust the slurry viscosity to 6000 mPa·s. This slurry was then coated on both sides of a 12 μm aluminum foil using an extrusion coating machine. After drying, the foil was rolled and cut to obtain the positive electrode sheet.

[0144] SEM images of the positive electrode are as follows: Figure 3 As shown.

[0145] A fourth aspect of this application also provides a battery cell, the preparation method of which is as follows:

[0146] Negative electrode preparation: The negative electrode slurry is uniformly coated onto a 12μm aluminum foil using a slot extrusion coating machine; the negative electrode is then formed by rolling, slitting, and sheet making; the negative electrode slurry is composed of bio-hard carbon, SP, CNT, CMC, and SBR in proportions of 92 parts, 2.5 parts, 0.5 parts, 2 parts, and 3 parts respectively, and is stirred in a planetary mixer. Deionized water is added to control the slurry viscosity at 2000 mPa·s and the solid content at 36%; the hard carbon has a D50 of 5μm.

[0147] Electrolyte preparation: Sodium hexafluorophosphate (12wt%) with a concentration of 1 mol / L was added to a solvent of 25% EC + 23% PC + 38% DMC, and 2 wt% FEC was also added. The electrolyte was prepared by mixing thoroughly.

[0148] Cell fabrication: The positive electrode, negative electrode, separator, electrolyte, and cell casing are assembled into a sodium-ion battery; the separator is a 12PE+2 ceramic separator, the casing is an aluminum-plastic film, and the electrolyte is as described above.

[0149] Example 2

[0150] The first aspect of this application provides a functionalized NFPP-based composite material, comprising a bridge unit B and an energy unit C as provided in Example 1, wherein the energy unit C is a dense, spherical secondary particle containing a small number of uniformly distributed micropores, with D50 = 17.5 μm, D90 = 24.5 μm, and BET = 3.6 μm. 2 / g, the thickness of the carbon layer is 2-5 nm, the carbon content is 1.5 wt%, and the initial discharge capacity at 0.1C is 105 mAh / g.

[0151] The particle size distribution curve of energy unit C is as follows: Figure 4 As shown.

[0152] The mass ratio of bridge unit B to energy unit C is 70:30.

[0153] The second aspect of this application provides a method for preparing a functionalized NFPP-based composite material, specifically:

[0154] With a molar ratio of Na:(Fe+Mg):P = 4:2.97:4, where Mg / (Fe+Mg) = 1 at%, sodium dihydrogen phosphate, iron oxide, magnesium oxide, and phosphoric acid were weighed out. Sucrose (2% of the theoretical NFPP mass) was weighed out as the carbon source, and carbon nanotubes (0.5% of the carbon nanotubes) were weighed out as the reinforcing conductive network. The raw materials were mixed and subjected to high-energy ball milling, followed by spray granulation to obtain precursor microspheres with a wide particle size distribution (D50 = 12 μm). Sintering was carried out at 720℃ for 12 h under an argon atmosphere (heating rate 2℃ / min) to obtain the energy unit C(Na4Fe). 2.8 Mg 0.2 (PO4)2P2O7).

[0155] Bridge unit B and energy unit C are mixed at a mass ratio of B:C=70:30 to obtain composite material SE.

[0156] A third aspect of this application provides a positive electrode sheet, the specific preparation method of which is as follows:

[0157] 93% of the composite material SE, 3% PVDF, 2% SP, and 1% graphene were added to a planetary mixing tank and stirred (30 rpm / min, 30 min). After stirring, 1% CNT and NMP (mass ratio 1:1) were added and kneaded to control the kneading solid content to 66.5% (50 rpm / min, 60 min). After kneading, NMP was added to adjust the slurry viscosity to 6000 mPa·s. This slurry was then coated on both sides of a 12 μm aluminum foil using an extrusion coating machine. After drying, the foil was rolled and cut to obtain the positive electrode sheet.

[0158] A fourth aspect of this application also provides a battery cell, the preparation method of which is as follows:

[0159] Negative electrode preparation: The negative electrode slurry is uniformly coated onto a 12μm aluminum foil using a slot extrusion coating machine; the negative electrode is then formed by rolling, slitting, and sheet making; the negative electrode slurry is composed of bio-hard carbon, SP, CNT, CMC, and SBR in proportions of 92 parts, 2.5 parts, 0.5 parts, 2 parts, and 3 parts respectively, and is stirred in a planetary mixer. Deionized water is added to control the slurry viscosity at 2000 mPa·s and the solid content at 36%; the hard carbon has a D50 of 5μm.

[0160] Electrolyte preparation: Sodium hexafluorophosphate (12wt%) with a concentration of 1 mol / L was added to a solvent of 25% EC + 23% PC + 38% DMC, and 2 wt% FEC was also added. After mixing evenly, the electrolyte was prepared.

[0161] Cell fabrication: The positive electrode, negative electrode, separator, electrolyte, and cell casing are assembled into a sodium-ion battery; the separator is a 12PE+2 ceramic separator, the casing is an aluminum-plastic film, and the electrolyte is as described above.

[0162] Example 3

[0163] The first aspect of this application provides a functionalized NFPP-based composite material, including power unit A and bridge unit B provided in Example 1 and energy unit C provided in Example 2, wherein the mass ratio of power unit A, bridge unit B and energy unit C is 20:50:30.

[0164] The second aspect of this application provides a method for preparing a functionalized NFPP-based composite material, wherein power unit A, bridge unit B, and energy unit C are mixed at a mass ratio of A:B:C = 20:50:30 to obtain composite material ST. The preparation methods for the positive electrode sheet and the battery cell are the same as in Example 1.

[0165] SEM images of the positive electrode are as follows: Figure 5 As shown.

[0166] Example 4

[0167] The difference from Example 1 is that when preparing power unit A, a carbon nanotube (CNT) aqueous dispersion is used as part of the carbon source (CNT accounts for 20% of the total carbon source), so that the surface of particle A is coated with a highly conductive CNT network.

[0168] Comparative Example 1

[0169] The difference from Example 3 is that the functionalized NFPP-based composite material in this comparative example only includes power unit A.

[0170] Comparative Example 2

[0171] The difference from Example 3 is that the functionalized NFPP-based composite material in this comparative example only includes bridge unit B.

[0172] Comparative Example 3

[0173] The difference from Example 3 is that the functionalized NFPP-based composite material in this comparative example only includes energy unit C.

[0174] Comparative Example 4

[0175] The difference from Example 3 is that the same raw material ratio as in Example 3 is used, but the energy unit C is not Mg-doped and the functional unit is not graded. Conventional NFPP particles with a particle size of D50=12 μm are directly prepared by one-time spray granulation and sintering. The positive electrode sheet and cell fabrication method are the same as in Example 3.

[0176] Comparative Example 5

[0177] Referring to the preparation methods of Examples 1 and 2, nano-NFPP (D50=500nm, carbon content 2.0%, corresponding to the low carbon content of power unit A and no intermediate size-controlled variant) and micro-NFPP (D50=15μm, no element doping, corresponding to the undoped energy unit C and no intermediate size-controlled variant) were prepared respectively. The two were physically mixed in a single dual-particle-size ratio of 45:55 to obtain a composite material. The electrode and cell fabrication methods were the same as in Example 1.

[0178] Comparative Example 6

[0179] The difference from Example 3 is that the total mass of power unit A and bridge unit B accounts for 50% of the functionalized NFPP composite material, the mass of energy unit C accounts for 50% of the functionalized NFPP composite material, and the mass ratio of power unit A, bridge unit B and energy unit C is A:B:C=20:30:50. The manufacturing methods of the positive electrode sheet and the battery cell are the same as those in Example 3.

[0180] Comparative Example 7

[0181] The difference from Example 3 is that the mass of bridge unit B accounts for 30% of the functionalized NFPP-based composite material, and the mass ratio of bridge unit B to energy unit C is 1:2. The mass ratio of power unit A, bridge unit B and energy unit C is A:B:C=10:30:60. The manufacturing methods of positive electrode sheet and battery cell are the same as in Example 3.

[0182] The positive electrode sheet and battery cell provided in the above embodiments and comparative examples were subjected to performance tests. The specific test results are shown in Table 1. The composition (A:B:C) refers to the mass ratio of power unit A, bridge unit B and energy unit C.

[0183] Table 1 Performance Tests

[0184]

[0185] analyze:

[0186] The above tests show that, using power unit material A alone, composed of primary small particles, with high carbon content and large specific surface area, results in low electrode compaction and poor cycle stability due to numerous side reactions. However, its kinetic performance is excellent, and its rate performance is outstanding, as can be seen from Comparative Example 1. Bridge unit material B, with its high carbon content and mesoporous structure, has excellent conductivity. As it consists of secondary graded particles, its electrode compaction is relatively higher than A, its smaller specific surface area results in fewer side reactions, and its cycle stability is relatively better. However, its rate performance is slightly worse than A, as can be seen from Comparative Example 2. Energy unit material C, with its secondary... Large particles with low surface carbon content and dense internal structure, further improved by doping to enhance structural stability and kinetics, result in high electrode compaction, small specific surface area, and fewer side reactions. However, they also exhibit higher internal resistance, leading to poorer rate performance and cycle stability between A and C, as demonstrated in Comparative Example 3. When power unit A is combined with bridge unit B, small particles of A effectively fill the gaps between large particles of B, increasing electrode packing density and reducing porosity, thereby improving electrode compaction. Simultaneously, the small particles of A and the mesopores of B effectively reduce sodium ion transport paths, further enhancing rate performance. Now; after mixing, particle A adheres to the surface of particle B or fills between particles B, so that the short-range high conductivity network of A and the long-range conductive framework of B are interconnected, forming a more uniform and dense conductive network, improving conductivity and reducing electrode internal resistance; therefore, the overall performance is better than using A or B alone; replacing the carbon coating of power unit A with CNT further improves its kinetics, but reduces its compaction and its cycle stability is worse than the original scheme, as can be seen from Example 4; when bridge unit B and energy unit C are used in combination, energy unit C can act as in the composite particles The skeleton provides support, and the particles of bridge unit B are used to fill the gaps, forming a particle size distribution, increasing the electrode packing density, reducing porosity, and thus improving electrode compaction. The energy unit C particles have a low carbon content, and the dense, large particles result in a long sodium ion diffusion path, leading to poor conductivity when used alone. When used in combination with bridge unit B, the high carbon content and mesoporous structure of B particles can be used as a conductive bridge to connect the individual large particles C, forming a continuous conductive path, improving electrode conductivity, and enhancing the cell's dynamic performance and energy density, as can be seen from Example 2.When A+B+C are used in combination, the advantages of each material can be effectively utilized while avoiding its inherent disadvantages by controlling the proportions of each added material. Energy unit C acts as a skeleton to enhance compaction, while bridge unit B performs primary filling to enhance electrode compaction. Simultaneously, its own conductive network and mesoporous properties can act as conductive bridges, connecting the individual large particles C to form a continuous conductive path. Power unit A performs secondary filling of the gaps after the composite stacking of B and C, resulting in low electrode porosity and further increasing compaction density. Simultaneously, the point-to-point connection of A particles makes the overall conductive network of the electrode more compact, and the larger BET of A particles results in strong liquid absorption capacity, improving the problems of poor liquid absorption and retention in high-compact electrodes. If C... Excessive particle size in the cell leads to poor overall conductivity, affecting cycle life and kinetic performance. Too many particles in units A and B reduce electrode compaction, failing to meet high energy density requirements, as demonstrated in Example 3 and Comparative Examples 6 and 7. If energy unit C is not doped, its structural stability and kinetic performance decrease, and without graded particle size control, compaction also decreases, resulting in reduced compaction, rate capability, and cycle stability, as demonstrated in Comparative Example 4. Finally, Comparative Example 5 shows that simply combining conventional materials cannot achieve the desired effect; specialized material fabrication is necessary to achieve functional complementarity and structural synergy in the electrodes, thereby improving the overall performance of the cell.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0188] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A functionalized NFPP-based composite material, characterized in that, Includes at least two of the following: power unit A, bridge unit B, and energy unit C; The power unit A includes NFPP primary particles; the NFPP primary particles include a core and a first carbon layer disposed on the surface of the core. The bridge unit B includes NFPP secondary particles B; the NFPP secondary particles B include an NFPP core containing mesoporous structures and a second carbon layer disposed on the surface of the core. The energy unit C includes NFPP secondary particles C, which include a core containing a dopant element M and a third carbon layer disposed on the surface of the core, wherein M includes at least one of Mg, Al, Ti, Mn, Zr and Cr. The particle size and density of the NFPP secondary particles C are greater than those of the NFPP secondary particles B. The NFPP primary particles have a D50 of 500-800 nm and a carbon content of 3.5-5.0%. The NFPP secondary particles B have a D50 of 4-8 μm and a carbon content of 2.0-3.5%. The NFPP secondary particles C have a D50 of 10-25 μm and a carbon content of 0.5-2.0%.

2. The functionalized NFPP-based composite material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The NFPP primary particles have a D90 ≤ 1.2 μm and a specific surface area of ​​15-30 m². 2 / g, powder conductivity ≥10 -4 S / cm; (2) The thicknesses of the first carbon layer, the second carbon layer and the third carbon layer are each 2-5 nm. (3) The specific surface area of ​​the NFPP secondary particles B is 8-15 m². 2 / g, the mesopore size in the core of the NFPP secondary particles B is 2-50 nm; (4) The specific surface area BET of the NFPP secondary particles C is 1-8 m². 2 / g, powder compaction density ≥2.2 g / cm³ 3 ; (5) The general chemical formula of the energy unit C is Na4Fe 3-x M x (PO4)2P2O7, where 0 <x≤0.2。 3. The functionalized NFPP-based composite material according to claim 1, characterized in that, The functionalized NFPP-based composite material includes a power unit A, a bridge unit B, and an energy unit C; the total mass of the power unit A and the bridge unit B accounts for ≥70% of the functionalized NFPP-based composite material, and the mass ratio of the power unit A to the bridge unit B is 1-2:2-1.

4. The functionalized NFPP-based composite material according to claim 1, characterized in that, The functionalized NFPP-based composite material includes a power unit A, a bridge unit B, and an energy unit C; the mass of the bridge unit B accounts for ≥50% of the functionalized NFPP-based composite material, and the mass ratio of the bridge unit B to the energy unit C is 1-4:

1.

5. A method for preparing a functionalized NFPP-based composite material according to any one of claims 1-4, characterized in that, include: The preparation method of power unit A includes: mixing a first sodium source, a first iron source, a first phosphorus source and a first carbon source, performing a first sand milling and spray drying to obtain a first precursor powder; and performing a first sintering of the first precursor powder under an inert atmosphere to obtain the power unit A. The preparation method of bridge unit B includes: mixing a second sodium source, a second iron source, a second phosphorus source and a pore-forming agent, performing a second sand milling and spray drying to obtain a second precursor powder; and performing a second sintering of the second precursor powder under an inert gas to obtain the bridge unit B. The preparation method of energy unit C includes: mixing a third sodium source, a third iron source, a second carbon source, a third phosphorus source and an M source, performing a third sand milling and spray drying to obtain a third precursor powder; and performing a third sintering of the third precursor powder under an inert atmosphere to obtain the energy unit C. When the functionalized NFPP-based composite material includes at least two of the raw materials selected from power unit A, bridge unit B, and energy unit C, the raw materials are mixed to obtain the functionalized NFPP-based composite material.

6. The method for preparing the functionalized NFPP-based composite material according to claim 5, characterized in that, At least one of the following conditions must be met: (1) The first sodium source, the second sodium source and the third sodium source each independently include at least one of sodium nitrate, sodium carbonate and sodium dihydrogen phosphate; (2) The first iron source, the second iron source and the third iron source each independently include at least one of ferric nitrate, ferrous oxalate and ferric oxide; (3) The first phosphorus source, the second phosphorus source and the third phosphorus source each independently include ammonium dihydrogen phosphate and / or phosphoric acid; (4) The first carbon source includes at least one of citric acid, glucose, sucrose and carbon nanotubes; (5) The pore-forming agent includes at least one of polyethylene glycol, polyvinylpyrrolidone, polymethyl methacrylate, and starch; (6) The second carbon source includes at least one of PEG, sucrose, phenolic resin and carbon nanotubes; (7) The M source includes oxides containing M; (8) The mass of the first carbon source accounts for 6-10% of the mass of the power unit A; (9) The mass of the pore-forming agent accounts for 3-8% of the mass of the bridge unit B; (10) The mass of the second carbon source accounts for 1-3% of the mass of the energy unit C.

7. The method for preparing the functionalized NFPP-based composite material according to claim 5 or 6, characterized in that, At least one of the following conditions must be met: (1) The material after the first sand mill has a D50 ≤ 400 nm; (2) The D50 of the material after the second grinding is 1-2.5μm; (3) The D50 of the third precursor powder is 5-20 μm; (4) The temperature of the first sintering is 500-650℃ and the time is 6-12h; (5) The second sintering temperature is 600-700℃ and the time is 8-14h; (6) The temperature of the third sintering is 650-750℃ and the time is 10-18h.

8. A positive electrode sheet, characterized in that, Including the functionalized NFPP-based composite material as described in any one of claims 1-4.

9. The positive electrode sheet according to claim 8, characterized in that, The positive electrode sheet also includes a conductive agent and a binder; The mass ratio of the functionalized NFPP-based composite material, the conductive agent, and the binder is 90-96:2-5:2-5; The conductive agent includes at least two of conductive carbon black, carbon nanotubes, and graphene. The compaction density of the positive electrode sheet is 2.2-2.4 g / cm³. 3 .

10. A sodium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 8 or 9.

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