Coated modified phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of positive electrode materials, in particular to a coated modified phosphate positive electrode material as well as a preparation method and application thereof. The coated modified phosphate positive electrode material provided by the invention is of a double-coating-layer core-shell structure and comprises a phosphate positive electrode material core body, the first coating layer is arranged on the surface of the phosphate positive electrode material core body and comprises a first carbon layer formed by carbonizing thiophene substances and doped with sulfur and bromine elements; the second coating layer is arranged on the surface of the first coating layer, and the second coating layer is a second carbon layer formed by carbonizing a metal organic framework material. Through organic combination of the inner compact conductive carbon layer and the outer porous metal carbon skeleton, a three-dimensional mixed conductive network is constructed on the surfaces of lithium iron phosphate particles, and the electron conduction and ion diffusion processes are synchronously optimized, so that the comprehensive electrochemical performance of the material in high-rate charge and discharge and low-temperature environments is remarkably improved.

Description

Technical Field

[0001] This application belongs to the field of cathode material technology, and particularly relates to a coated modified phosphate-based cathode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, as the core of modern electrochemical energy storage, have successfully expanded from consumer electronics to key areas such as electric vehicles, renewable energy storage, and smart grids due to their high energy density, long cycle life, and relatively environmentally friendly characteristics. Their overall performance, safety, and cost largely depend on the properties of the cathode material. Therefore, developing cathode materials with excellent comprehensive performance is a crucial issue for driving the continuous advancement of lithium-ion battery technology.

[0003] Among numerous cathode materials, phosphate-based cathode materials exhibit significant advantages due to their unique olivine structure: abundant iron and phosphorus reserves, controllable cost; strong covalent bonds in the structure provide excellent thermal stability and safety, with virtually no risk of thermal runaway; and high structural stability during charge and discharge, resulting in extremely long cycle life. However, this robust structure also brings inherent drawbacks: firstly, its crystal structure restricts the free migration of electrons, leading to extremely low intrinsic electronic conductivity; secondly, the one-dimensional diffusion channels for lithium ions in the crystal are relatively narrow, resulting in a low ion diffusion coefficient. These two defects together cause severe polarization of phosphate-based materials during high-current charge and discharge, resulting in insufficient capacity utilization, and performance degradation is particularly pronounced at low temperatures, limiting their potential in high-end power batteries and wide-temperature-range applications.

[0004] Therefore, modifying phosphate-based cathode materials has become an important way to improve their performance. Through targeted optimization, the aim is to improve the electronic conductivity and lithium-ion diffusion rate of the material, thereby effectively improving the rate performance and low-temperature performance of the battery and promoting its wider application. Summary of the Invention

[0005] The purpose of this application is to provide a coated modified phosphate-based cathode material, its preparation method and application, aiming to solve the problem that the low electronic conductivity and lithium-ion diffusion rate of phosphate-based cathode materials in the prior art cannot improve the rate performance and low-temperature performance of batteries.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a coated modified phosphate-based cathode material, wherein the coated modified phosphate-based cathode material has a double-coated core-shell structure, comprising: Phosphate-based cathode material core; The first coating layer disposed on the surface of the core of the phosphate-based cathode material includes a first carbon layer doped with sulfur and bromine elements, formed by carbonization of thiophene-like substances. A second coating layer is disposed on the surface of the first coating layer, the second coating layer being a second carbon layer formed by carbonization of a metal-organic framework material.

[0007] In some embodiments, the thickness of the first coating layer is 2-3 nm.

[0008] In some embodiments, the mass percentage of sulfur is 1 wt%-10 wt% and the mass percentage of bromine is 1 wt%-10 wt% based on the total mass of the first coating layer being 100%.

[0009] In some embodiments, the second coating layer is a porous carbon layer containing metal nanoparticles, wherein the metal nanoparticles include at least one of elemental metals, metal alloys, metal oxides, or metal carbides. In some embodiments, the thickness of the second coating layer is 2-3 nm.

[0010] In some embodiments, the mass percentage of metal nanoparticles is 1 wt%-10 wt%, based on the total mass of the second coating layer being 100%.

[0011] In some embodiments, the porous carbon layer includes at least one pore structure selected from micropores, mesopores, and macropores.

[0012] In some embodiments, a portion of the second coating layer and a portion of the first coating layer interweave through covalent bonds or π-π interactions to form a three-dimensional hybrid conductive network.

[0013] In some embodiments, the raw material for the first coating layer is a mixed carbon source comprising thiophene component A and bromine-containing organic component B, wherein the mass ratio of thiophene component A to bromine-containing organic component B is (4-6):(6-4).

[0014] In some embodiments, the metal-organic framework material includes at least one of zinc-containing metal-organic framework materials, titanium-containing metal-organic framework materials, iron-containing metal-organic framework materials, copper-containing metal-organic framework materials, magnesium-containing metal-organic framework materials, and manganese-containing metal-organic framework materials.

[0015] In some embodiments, the phosphate-based cathode material core includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium manganese phosphate, lithium titanium phosphate, and lithium cobalt phosphate.

[0016] Secondly, embodiments of this application provide a method for preparing the above-mentioned coated modified phosphate-based cathode material, comprising the following steps: The first carbon source raw material containing thiophene-like substances and the phosphate-based cathode material raw material are mixed and dried to obtain a solid-phase phosphate-based cathode material precursor. A first sintering treatment is performed on the solid-phase phosphate-based cathode material precursor to obtain a phosphate-based cathode material intermediate. Phosphate-based cathode material intermediates are mixed with metal-organic framework materials and subjected to a second sintering process to obtain coated modified phosphate-based cathode materials.

[0017] In some embodiments, the first carbon source material includes a mixed carbon source of thiophene component A and bromine-containing organic component B, wherein the mass ratio of thiophene component A to bromine-containing organic component B is (4-6):(6-4).

[0018] In some embodiments, the metal-organic framework material includes at least one of zinc-containing metal-organic framework materials, titanium-containing metal-organic framework materials, iron-containing metal-organic framework materials, copper-containing metal-organic framework materials, magnesium-containing metal-organic framework materials, and manganese-containing metal-organic framework materials.

[0019] In some embodiments, thiophene component A is selected from at least one of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) complex, poly(3,4-ethylenedioxythiophene)-p-toluenesulfonate, and poly(3,4-ethylenedioxythiophene)-trifluoromethanesulfonate.

[0020] In some embodiments, the bromine-containing organic component B is selected from at least one of methyl α-bromoacrylate, 6,6'-dibromoindigo, N-bromophthalimide, and hexadecyltrimethylammonium bromide.

[0021] In some embodiments, the zinc-containing metal-organic framework material includes at least one of ZIF-8 and ZIF-68; the titanium-containing metal-organic framework material includes at least one of NTU-9, MIL-125(Ti), and NH2-MIL-125(Ti); the iron-containing metal-organic framework material includes at least one of MIL-100(Fe), MIL-101(Fe), and PCN-250(Fe); the copper-containing metal-organic framework material includes at least one of HKUST-1 and SIFSIX-1-Cu; the magnesium-containing metal-organic framework material includes at least one of MOF-74(Mg) and Basosiv™ M050; and the manganese-containing metal-organic framework material includes at least one of MOF-74(Mn) and TPP-Mn.

[0022] In some embodiments, the temperature of the first sintering treatment is 400℃~600℃, the heating rate is 3℃ / min~10℃ / min, and the holding time is 10h~14h.

[0023] In some embodiments, the temperature of the second sintering treatment is 400℃~700℃, the heating rate is 3℃ / min~10℃ / min, and the holding time is 6h~10h.

[0024] In some embodiments, the metal-organic framework material undergoes the second sintering treatment to form a porous carbon layer containing metal nanoparticles, wherein the porous carbon layer includes at least one pore structure selected from micropores, mesopores, and macropores.

[0025] In some embodiments, the amount of the first carbon source material added is 1wt%-5wt%, based on the total mass of the solid phosphate-based cathode material precursor as 100%.

[0026] In some embodiments, the amount of metal-organic framework material added is 1wt%-5wt%, based on the total mass of the phosphate-based cathode material intermediate as 100%.

[0027] In some embodiments, the raw materials for phosphate-based cathode materials include a lithium source, an iron source, and a phosphorus source, wherein the molar ratio of the lithium source, the iron source, and the phosphorus source is (1.01-1.06):(0.93-0.98):(0.98-1.00).

[0028] Thirdly, embodiments of this application provide a lithium-ion battery comprising a positive electrode sheet, wherein the positive electrode sheet comprises the aforementioned coated modified phosphate-based positive electrode material.

[0029] In some embodiments, at 25°C, the 1C discharge specific capacity of the lithium-ion battery is greater than 147 mAh / g, the 5C discharge specific capacity is greater than 132 mAh / g, and the 10C discharge specific capacity is greater than 120 mAh / g.

[0030] In some embodiments, at -20°C, the lithium-ion battery has a 0.2C discharge specific capacity greater than 96 mAh / g and a 1C discharge specific capacity greater than 60 mAh / g.

[0031] The first aspect of this application provides a coated modified phosphate-based cathode material, which constructs a double-layer coated core-shell structure. The first coating layer comprises a first carbon layer doped with sulfur and bromine, formed by carbonizing thiophene-based materials. In this first carbon layer, sulfur doping enhances the electron delocalization and surface activity of the carbon layer, while the introduction of bromine further improves the conductivity of the carbon layer by forming C-Br bonds and effectively suppresses interfacial side reactions between the electrolyte and the cathode material. The first coating layer is in close contact with the phosphate-based cathode material core, significantly improving electron transport efficiency and providing physical isolation, reducing direct contact between the active material and the electrolyte at low temperatures, and inhibiting the growth of harmful SEI films. The second coating layer is a second carbon layer formed by carbonizing a metal-organic framework material. This structure provides abundant and continuous transport channels for lithium ion migration, greatly reducing ion diffusion resistance. Simultaneously, the nano-metal particles are uniformly dispersed within the carbon framework, further enhancing the overall conductivity of the material. This dual-coating structure synergistically optimizes both electron conduction and ion diffusion, giving the material low resistance, high interfacial stability, and excellent porous ion channels, resulting in a phosphate-based cathode material with superior overall performance.

[0032] The second aspect of this application provides a method for preparing a coated modified phosphate-based cathode material. This method involves mixing a first carbon source material with a phosphate-based cathode material raw material, performing a first sintering to obtain an intermediate containing a first coating layer; then mixing this intermediate with a metal-organic framework material and performing a second sintering to prepare a second coating layer, thus obtaining the coated modified phosphate-based cathode material. This preparation method is simple, convenient, and does not require large-scale equipment. It can prepare a double-coated structure, synergistically optimizing both electron conduction and ion diffusion, resulting in a material with low resistance, high interfacial stability, and excellent porous ion channels, thus obtaining a phosphate-based cathode material with excellent comprehensive performance; this is beneficial for industrial applications.

[0033] The lithium-ion battery provided in the third aspect of this application has excellent rate performance and low-temperature performance because the lithium-ion battery uses the above-mentioned coated modified phosphate-based positive electrode material as the positive electrode active material of the positive electrode sheet, which is beneficial for its wide application. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1These are SEM images of Comparative Example 1 and Example 2 provided in this application; Figure 2 This is a TEM image of Embodiment 2 provided in this application; Figure 3 This is a pore size-pore volume adsorption diagram for Comparative Example 1 and Example 2 of this application; Figure 4 These are EIS diagrams of Comparative Example 1 and Example 2 of this application; Figure 5 These are charge-discharge curves of Comparative Example 1 and Example 2 provided in this application at a 10C rate. Detailed Implementation To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0036] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0037] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0038] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0039] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0040] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0041] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0042] The first aspect of this application provides a coated modified phosphate-based cathode material, wherein the coated modified phosphate-based cathode material has a double-coated core-shell structure, comprising: Phosphate-based cathode material core; The first coating layer is disposed on the surface of the core of the phosphate-based cathode material. The first coating layer includes a first carbon layer doped with sulfur and bromine elements, which is formed by carbonization of thiophene-like substances. A second coating layer is disposed on the surface of the first coating layer, the second coating layer being a second carbon layer formed by carbonization of a metal-organic framework material.

[0043] The first aspect of this application provides a coated modified phosphate-based cathode material. This material constructs a double-layered core-shell structure. The first coating layer comprises a first carbon layer doped with sulfur and bromine, formed by carbonizing a thiophene-based substance. In this first carbon layer, sulfur doping enhances the electron delocalization and surface activity of the carbon layer, while the introduction of bromine further improves the conductivity of the carbon layer by forming C-Br bonds and effectively suppresses interfacial side reactions between the electrolyte and the cathode material. The first coating layer is in close contact with the phosphate-based cathode material core, significantly improving electron transport efficiency and providing physical isolation, reducing direct contact between the active material and the electrolyte at low temperatures, and inhibiting the growth of harmful SEI films. The second coating layer is a second carbon layer formed by carbonizing a metal-organic framework material. This structure provides abundant and continuous transport channels for lithium ions, greatly reducing ion diffusion resistance. Simultaneously, the nano-metal particles are uniformly dispersed within the carbon framework, further enhancing the overall conductivity of the material. This dual-coating structure synergistically optimizes both electron conduction and ion diffusion, giving the material low resistance, high interfacial stability, and excellent porous ion channels, resulting in a phosphate-based cathode material with superior overall performance.

[0044] In some embodiments, the coated modified phosphate-based cathode material includes a phosphate-based cathode material core.

[0045] In some embodiments, the phosphate-based cathode material core includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium manganese phosphate, lithium titanium phosphate, and lithium cobalt phosphate.

[0046] In some embodiments, the resistivity of the coated modified phosphate-based cathode material is less than 20 Ω·cm. Further, the resistivity includes, but is not limited to, typical but not limiting values ​​such as 19 Ω·cm, 17 Ω·cm, 15 Ω·cm, 12 Ω·cm, 10 Ω·cm, 8 Ω·cm, 7 Ω·cm, 5 Ω·cm, 4 Ω·cm, and 2 Ω·cm.

[0047] Furthermore, the coated modified phosphate-based cathode material has a double-coated core-shell structure, including: a first coating layer disposed on the surface of the core of the phosphate-based cathode material, the first coating layer including a first carbon layer doped with sulfur and bromine elements formed by carbonization of thiophene-like substances.

[0048] In some embodiments, the raw material for the first coating layer is a mixed carbon source comprising thiophene component A and bromine-containing organic component B, wherein the mass ratio of thiophene component A to bromine-containing organic component B is (4-6):(6-4).

[0049] Specifically, the thiophene ring of thiophene component A undergoes pyrolysis to form a continuous carbon chain, resulting in a dense graphitized carbon layer that adheres tightly to the particle surface of the phosphate-based cathode material. Furthermore, it retains some sulfur atoms; sulfur doping in the carbon layer enhances its electron delocalization and surface activity. Subsequently, when bromine in bromine-containing organic component B is carbonized and attached to the carbon framework, it attracts electrons from the carbon, generating hole carriers in the carbon valence band, significantly improving the electronic conductivity of the carbon coating layer. In addition, Br may form stable chemical bonds (such as C-Br bonds) with carbon or surface functional groups. These chemical bonds help to suppress side reactions to some extent and improve the stability of the material-electrolyte interface.

[0050] A mixed carbon source consisting of thiophene-based component A and bromine-containing organic component B is sintered to obtain a first carbon layer containing sulfur and bromine elements. This first carbon layer is graphitized carbon. This type of carbon has a dense structure, providing a large number of charge carriers and significantly improving electronic conductivity. As the first layer in direct contact with the phosphate cathode material, it provides good interfacial contact and basic electronic conduction. Furthermore, the dense graphitized carbon layer can more effectively isolate the active material from direct contact with the electrolyte, suppressing harmful side reactions at low temperatures and the excessive growth of harmful SEI films.

[0051] In some embodiments, the mass ratio of thiophene component A to bromine-containing organic component B is (4-6):(6-4). In some specific embodiments, the mass ratio of thiophene component A to bromine-containing organic component B includes, but is not limited to, typical but non-limiting values ​​such as 4:6, 5:5, and 6:4.

[0052] In some embodiments, the thickness of the first coating layer is 2-3 nm. If the thickness of the first coating layer is too thin, a complete coating layer cannot be formed, which will affect the improvement of electronic conductivity; if the thickness of the first coating layer is too thick, it will make lithium ion diffusion difficult and reduce the ion transport rate.

[0053] In some specific implementations, the thickness of the first coating layer includes, but is not limited to, typical but non-limiting values ​​such as 2nm, 2.1nm, 2.2nm, 2.3nm, 2.4nm, 2.5nm, 2.6nm, 2.7nm, 2.8nm, 2.9nm, and 3.0nm.

[0054] In some embodiments, based on the total mass of the first coating layer being 100%, the mass percentage content of sulfur is 1wt%-10wt%, and the mass percentage content of bromine is 1wt%-10wt%. By limiting the doping content of sulfur and bromine, the electronic structure and surface chemistry of the carbon layer can be effectively controlled, thereby improving electronic conductivity, enhancing interface stability, suppressing side reactions, and thus improving the initial efficiency and cycle life of the battery.

[0055] In some specific embodiments, the mass percentage of sulfur element, based on the total mass of the first coating layer as 100%, includes, but is not limited to, typical but non-limiting values ​​such as 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, and 10wt%.

[0056] In some specific embodiments, the mass percentage of bromine, based on the total mass of the first coating layer as 100%, includes, but is not limited to, typical but non-limiting values ​​such as 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, and 10wt%.

[0057] Furthermore, it also includes a second coating layer disposed on the surface of the first coating layer. The second coating layer is a second carbon layer formed by carbonizing a metal-organic framework (MOF) material. The ordered porous structure inherent in the MOF material is partially retained after carbonization, generating a porous carbon framework and creating abundant micron / nanoscale channels in the double coating layer. These channels, together with the dense layer formed by the thiophene polymer in the first coating layer, constitute a hierarchical pore system, greatly facilitating the rapid insertion and extraction of lithium ions. In addition, metal particles are uniformly dispersed in the porous carbon framework formed by the carbonized MOF material. These metal particles and the inherent porous carbon framework work synergistically with the first coating layer to construct a three-dimensional conductive network on the material surface, allowing electrons to be rapidly transported through multiple paths via the carbonized framework of the first coating layer, the metal particles in the second coating layer, and the MOF material framework, significantly reducing the overall impedance of the electrode. At the same time, this hierarchical pore structure, which facilitates lithium ion migration, achieves a dual enhancement of electron transport and ion diffusion, laying the foundation for improving the rate performance and low-temperature performance of the material.

[0058] In some embodiments, the metal-organic framework material includes at least one selected from zinc-containing metal-organic framework materials, titanium-containing metal-organic framework materials, iron-containing metal-organic framework materials, copper-containing metal-organic framework materials, magnesium-containing metal-organic framework materials, and manganese-containing metal-organic framework materials. Different types of metal-organic framework materials are defined, which can be carbonized to form a conductive network with specific pore structures and metallic activity.

[0059] In some embodiments, the second coating layer is a porous carbon layer containing metal nanoparticles, wherein the metal nanoparticles include at least one of elemental metals, metal alloys, metal oxides, or metal carbides.

[0060] The second coating layer has a porous structure, providing abundant channels for electrolyte wetting and rapid lithium ion migration; the uniformly dispersed metal nanoparticles, acting as "conductive islands," greatly enhance the overall electron transport capability.

[0061] In some embodiments, the thickness of the second coating layer is 2-3 nm. By limiting the thickness of the second coating layer, it is beneficial to ensure a balance between the unobstructed flow of ion channels and the mechanical strength of the coating layer.

[0062] In some embodiments, the mass percentage of metal nanoparticles is 1 wt%-10 wt%, based on the total mass of the second coating layer being 100%. By controlling the metal particle content, it is beneficial to improve the overall single-particle transport capability.

[0063] In some embodiments, by controlling the metal particles to be nanoparticles, the electron conduction gain is maximized without clogging the pores.

[0064] In some embodiments, the porous carbon layer includes at least one pore structure selected from micropores, mesopores, and macropores. dV / dlog(w) is the differential expression of pore volume (V) with respect to the logarithmic form of pore diameter (w), characterizing the change in pore volume as the pore diameter increases by one logarithmic unit. Based on pore size, pores are classified as micropores (<2nm), mesopores (2-50nm), and macropores (>50nm). Constructing a multi-level pore system containing micropores, mesopores, and even macropores can synergistically optimize the diffusion dynamics of ions at different scales, which is particularly beneficial for improving the fast-charging performance of batteries.

[0065] In some embodiments, a portion of the second coating layer interweaves with a portion of the first coating layer through covalent bonds or π-π interactions to form a three-dimensional hybrid conductive network. This integrates the inner and outer coating layers into a single, robust conductive framework, preventing coating layer detachment and ensuring the long-term integrity of the electron and ion transport network. Consequently, this significantly improves the structural stability and performance retention of the electrode during long-term cycling.

[0066] The second aspect of this application provides a method for preparing the above-mentioned coated modified phosphate-based cathode material, comprising the following steps: S01. Mix and dry the first carbon source raw material containing thiophene-like substances and the phosphate-based cathode material raw material to obtain a solid-phase phosphate-based cathode material precursor. S02. The solid-phase phosphate-based cathode material precursor is subjected to a first sintering treatment to obtain a phosphate-based cathode material intermediate. S03. The phosphate-based cathode material intermediate is mixed with the metal-organic framework material and subjected to a second sintering treatment to obtain the coated modified phosphate-based cathode material.

[0067] The second aspect of this application provides a method for preparing a coated modified phosphate-based cathode material. This method involves mixing a first carbon source material with a phosphate-based cathode material raw material, performing a first sintering to obtain an intermediate containing a first coating layer; then mixing this intermediate with a metal-organic framework material and performing a second sintering to prepare a second coating layer, thus obtaining the coated modified phosphate-based cathode material. This preparation method is simple, convenient, and does not require large-scale equipment. It can prepare a double-coated structure, synergistically optimizing both electron conduction and ion diffusion, resulting in a material with low resistance, high interfacial stability, and excellent porous ion channels, thus obtaining a phosphate-based cathode material with excellent comprehensive performance; this is beneficial for industrial applications.

[0068] In step S01, the first carbon source raw material containing thiophene-like substances and the phosphate-based cathode material raw material are mixed and dried to obtain a solid-phase phosphate-based cathode material precursor.

[0069] In some embodiments, the raw materials for phosphate-based cathode materials include a lithium source, an iron source, and a phosphorus source, wherein the molar ratio of the lithium source, the iron source, and the phosphorus source is (1.01-1.06):(0.93-0.98):(0.98-1.00).

[0070] The lithium source can be one or more of the following materials: lithium oxide, lithium carbonate, lithium hydroxide, lithium acetate, lithium phosphate, lithium citrate, etc.; the iron source includes one or more of the following: ferrous nitrate, ferrous sulfate, ferrous citrate, ferrous oxalate, ferrous oxide, and ferrous phosphate; the phosphorus source is selected from one or more of the following: phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, and ferric phosphate.

[0071] In some embodiments, the first carbon source material includes a mixed carbon source of thiophene component A and bromine-containing organic component B, wherein the mass ratio of thiophene component A to bromine-containing organic component B is (4-6):(6-4).

[0072] In some embodiments, thiophene component A is selected from at least one of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) complex, poly(3,4-ethylenedioxythiophene)-p-toluenesulfonate, and poly(3,4-ethylenedioxythiophene)-trifluoromethanesulfonate.

[0073] In some embodiments, the bromine-containing organic component B is selected from at least one of methyl α-bromoacrylate, 6,6'-dibromoindigo, N-bromophthalimide, and hexadecyltrimethylammonium bromide.

[0074] In some embodiments, the amount of the first carbon source material added is 1 wt%-5 wt%, based on the total mass of the solid-phase phosphate-based cathode material precursor as 100%. In some specific embodiments, the amount of the first carbon source material added is, but is not limited to, typical but non-limiting values ​​such as 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, and 5 wt%, based on the total mass of the solid-phase phosphate-based cathode material precursor as 100%.

[0075] In some embodiments, lithium source, iron source, phosphorus source, first carbon source raw material and deionized water are mixed evenly, and then the mixed solution is dried by heating treatment to obtain solid-phase lithium iron phosphate precursor.

[0076] In step S02, the solid-phase phosphate-based cathode material precursor undergoes a first sintering treatment to obtain a phosphate-based cathode material intermediate. The first sintering treatment is an in-situ carbonization and simultaneous doping process of the first carbon source. By organically combining the carbon framework and sulfur source provided by thiophene-based substances with the bromine doping source provided by bromine-containing organic compounds during pyrolysis, a sulfur / bromine co-doped carbon coating layer with high conductivity, dense structure, and interfacial stability is constructed on the cathode material surface in a one-step manner, laying a crucial electron transport foundation for the subsequent construction of a double-layer coating structure.

[0077] In some embodiments, the temperature of the first sintering treatment is 400℃~600℃, the heating rate is 3℃ / min~10℃ / min, and the holding time is 10h~14h.

[0078] In some specific embodiments, the temperature of the first sintering treatment includes, but is not limited to, typical but non-limiting values ​​such as 400°C, 450°C, 500°C, 550°C, and 600°C; the heating rate includes, but is not limited to, typical but non-limiting values ​​such as 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, and 10°C / min; and the holding time includes, but is not limited to, typical but non-limiting values ​​such as 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, and 14h.

[0079] In step S03, the phosphate-based cathode material intermediate is mixed with the metal-organic framework material and subjected to a second sintering treatment to obtain the coated modified phosphate-based cathode material.

[0080] The second sintering process involves constructing a second coating layer that combines a porous structure, metal nanoparticles, and a carbon skeleton by in-situ pyrolysis and carbonization of metal-organic framework materials (MOFs) on the basis of the first coating layer (sulfur / bromine co-doped carbon layer). This second coating layer forms a stable three-dimensional conductive network with the first coating layer, thus constructing an electron / ion conductive network.

[0081] Furthermore, the metal-organic framework material undergoes the second sintering treatment to form a porous carbon layer containing metal nanoparticles, wherein the porous carbon layer includes at least one pore structure selected from micropores, mesopores, and macropores.

[0082] In some embodiments, the metal-organic framework material includes at least one of zinc-containing metal-organic framework materials, titanium-containing metal-organic framework materials, iron-containing metal-organic framework materials, copper-containing metal-organic framework materials, magnesium-containing metal-organic framework materials, and manganese-containing metal-organic framework materials.

[0083] In some embodiments, the zinc-containing metal-organic framework material includes at least one of ZIF-8 and ZIF-68; the titanium-containing metal-organic framework material includes at least one of NTU-9, MIL-125(Ti), and NH2-MIL-125(Ti); the iron-containing metal-organic framework material includes at least one of MIL-100(Fe), MIL-101(Fe), and PCN-250(Fe); the copper-containing metal-organic framework material includes at least one of HKUST-1 and SIFSIX-1-Cu; the magnesium-containing metal-organic framework material includes at least one of MOF-74(Mg) and Basosiv™ M050; and the manganese-containing metal-organic framework material includes at least one of MOF-74(Mn) and TPP-Mn.

[0084] In some embodiments, the amount of metal-organic framework material added is 1 wt%-5 wt%, based on 100% of the total mass of the phosphate-based cathode material intermediate. In some specific embodiments, the amount of metal-organic framework material added is, but is not limited to, typical but non-limiting values ​​such as 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, and 5 wt%, based on 100% of the total mass of the phosphate-based cathode material intermediate.

[0085] In some embodiments, the temperature of the second sintering treatment is 400℃~700℃, the heating rate is 3℃ / min~10℃ / min, and the holding time is 6h~10h.

[0086] In some specific embodiments, the temperature of the second sintering treatment includes, but is not limited to, typical but non-limiting values ​​such as 400°C, 450°C, 500°C, 550°C, and 600°C; the heating rate includes, but is not limited to, typical but non-limiting values ​​such as 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, and 10°C / min; and the holding time includes, but is not limited to, typical but non-limiting values ​​such as 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, and 10 h.

[0087] In some embodiments, the entire reaction is carried out under an inert atmosphere, which includes, but is not limited to, at least one of nitrogen, argon, and helium.

[0088] A third aspect of this application provides a lithium-ion battery comprising a positive electrode sheet, the positive electrode sheet comprising the aforementioned coated modified phosphate-based positive electrode material.

[0089] The lithium-ion battery provided in the third aspect of this application has excellent rate performance and low-temperature performance because the modified phosphate-based cathode material is used as the cathode active material of the cathode sheet. This makes it suitable for wide application.

[0090] In some embodiments, at 25°C, the 1C discharge specific capacity of the lithium-ion battery is greater than 147 mAh / g, the 5C discharge specific capacity is greater than 132 mAh / g, and the 10C discharge specific capacity is greater than 120 mAh / g.

[0091] In some embodiments, at -20°C, the lithium-ion battery has a 0.2C discharge specific capacity greater than 96 mAh / g and a 1C discharge specific capacity greater than 60 mAh / g.

[0092] The following description is based on specific embodiments.

[0093] Example A1 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I includes PEDOT component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) The zinc MOF material ZIF-8 is uniformly mixed into the first sintered body. The amount of ZIF-8 added is 3wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700℃ at a heating rate of 3℃ / min under a nitrogen atmosphere. It is held for 8 hours and then cooled and pulverized by air jet mill to obtain the final product lithium iron phosphate material.

[0094] Example A2 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) The zinc MOF material ZIF-8 is uniformly mixed into the first sintered body. The amount of ZIF-8 added is 3wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700℃ at a heating rate of 3℃ / min under a nitrogen atmosphere. It is held for 8 hours and then cooled and pulverized by air jet mill to obtain the final product lithium iron phosphate material.

[0095] Example A3 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) The titanium MOF material NTU-9 is uniformly mixed into the first sintered body at a rate of 3 wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700°C at a rate of 3°C / min under a nitrogen atmosphere. The temperature is held for 8 hours and then cooled. After cooling, the final product lithium iron phosphate material is obtained by air jet milling.

[0096] Example A4 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) MIL-100(Fe) containing iron MOFs is uniformly mixed into the first sintered body. The amount of the addition is 3wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700℃ at a heating rate of 3℃ / min under a nitrogen atmosphere. The temperature is held for 8h and then cooled. After cooling, the final product lithium iron phosphate material is obtained by air jet milling.

[0097] Example A5 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) The copper MOF material HKUST-1 is uniformly mixed into the first sintered body at a rate of 3 wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700°C at a rate of 3°C / min under a nitrogen atmosphere. The temperature is held for 8 hours and then cooled. After cooling, the final product lithium iron phosphate material is obtained by air jet milling.

[0098] Example A6 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) The magnesium MOF material MOF-74(Mg) is uniformly mixed into the first sintered body at a rate of 3wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700℃ at a rate of 3℃ / min under a nitrogen atmosphere. The temperature is held for 8 hours and then cooled and pulverized by air jet mill to obtain the final product lithium iron phosphate material.

[0099] Example A7 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) MOF-74 (Mn) containing manganese MOFs is uniformly mixed into the first sintered body. The amount of MOF-74 (Mn) added is 3 wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700°C at a heating rate of 3°C / min under a nitrogen atmosphere. The temperature is held for 8 hours. After cooling, the material is pulverized by air jet mill to obtain the final product lithium iron phosphate material.

[0100] Example A8 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) Zinc-containing MOF material ZIF-8 and manganese-containing MOF material MOF-74(Mn) are uniformly mixed into the first sintered body. The total amount of the two added is 3wt% of the mass of the first sintered body. The mass ratio of ZIF-8 to MOF-74(Mn) is 5:5. The first sintered body after mixing is placed in a tube furnace and heated to 700℃ at a heating rate of 3℃ / min under a nitrogen atmosphere. It is held for 8h and then cooled and pulverized by air jet mill to obtain the final product lithium iron phosphate material.

[0101] Example A9 A coated modified phosphate-based cathode material, the preparation of which includes the following steps: (1) Ferric nitrate, manganese nitrate, ammonium dihydrogen phosphate, and lithium hydroxide were mixed in a ratio of 0.6:0.4:1.00:1.04, and 12% by weight of deionized water was added as a dispersant. At the same time, 3% of mixed carbon source I was added to prepare a mixed solution. Mixed carbon source I included PEDOT:PSS component and methyl α-bromoacrylate component. The two components were mixed uniformly in a mass ratio of 5:5 beforehand. After drying the solution, a solid phase lithium manganese iron phosphate precursor was obtained. (2) The solid phase lithium manganese iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) The zinc MOF material ZIF-8 is uniformly mixed into the first sintered body. The amount of ZIF-8 added is 3wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700℃ at a heating rate of 3℃ / min under a nitrogen atmosphere. It is held for 8 hours and then cooled and pulverized by air jet mill to obtain the final product lithium manganese iron phosphate material.

[0102] Comparative Example A1 Using the uncoated modification as a comparative example, its preparation includes the following steps: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant; at the same time, 3% glucose was added as carbon source I to prepare a mixed solution. After drying the solution, a solid-phase lithium iron phosphate precursor was obtained. (2) The solid lithium iron phosphate precursor was placed in a tube furnace and kept at 500℃ for 12 hours under a nitrogen atmosphere with a heating rate of 3℃ / min. After the material cooled to room temperature, it was taken out and crushed to obtain a primary sintered body. (3) Glucose is uniformly mixed into the first sintered body. The amount of glucose added is 3wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700℃ at a rate of 3℃ / min under a nitrogen atmosphere. It is held for 8 hours and then cooled and pulverized by air jet mill to obtain the final product lithium iron phosphate material.

[0103] The key process differences between Examples A1-A8 and Comparative Example A1 are summarized in Table 1, as follows.

[0104] Comparative Example A2 A single-coated modified phosphate-based cathode material, the preparation steps of which differ from those in Example 1 in step (3), while the other steps are the same: (3) Glucose is uniformly mixed into the first sintered body. The amount of glucose added is 3wt% of the mass of the first sintered body. The first sintered body is placed in a tube furnace and heated to 700℃ at a rate of 3℃ / min under a nitrogen atmosphere. It is held for 8 hours and then cooled and pulverized by air jet mill to obtain the final product lithium iron phosphate material.

[0105] Comparative Example A3 A single-coated modified phosphate-based cathode material, the preparation steps of which differ from those in Example 1 in step (1), while the other steps are the same: (1) Ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide were mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water was added as a dispersant; at the same time, 3% glucose was added as carbon source I to prepare a mixed solution. After drying the solution, a solid-phase lithium iron phosphate precursor was obtained. Examples B1-B9 and Comparative Examples B1-B3 Preparation of secondary batteries: The prepared lithium iron phosphate materials, PVDF, and conductive carbon black from Examples A1-A9 and Comparative Examples A1-A3 were taken at mass percentages of 93.5%, 4.2%, and 2.3%, respectively. These were mixed with a certain amount of NMP and thoroughly stirred. The slurry was then dried on a coating machine at 100°C to form a film, followed by rolling. After rolling, the film was cut into 14 mm diameter discs using a punching machine to obtain the positive electrode. A lithium metal sheet (16.5 mm in diameter and 0.4 mm in thickness) was used as the negative electrode, and a polypropylene separator was used. 80 μL of electrolyte was added to both ends of the separator. The cells were then assembled into CR2032 button batteries in an argon-atmosphere glove box. Assemble the following components in the following order: negative electrode shell, spring sheet, add 100 μL of electrolyte, gasket, lithium sheet, add 50 μL of electrolyte, separator, add 50 μL of electrolyte, electrode sheet, and positive electrode shell. After inverting them, seal them on a hydraulic sealing machine and let them stand at room temperature for 12 hours to prepare a lithium-ion battery.

[0106] Table 1

[0107] Performance testing Cathode material resistivity test: Place a 1g sample in an ST2742B automated powder resistivity tester, maintain at 8±0.1 MPa for 10s, and obtain the resistivity data.

[0108] Battery rate performance test: The battery was tested at different rates of 0.1 C, 0.5 C, 1 C, 5 C and 10 C under the conditions of temperature 25℃±2℃ and humidity <2%RH using the Blue Electric (CT2001) test system and according to the battery charge and discharge tester operation procedure. The test results are shown in Table 2 below.

[0109] Low temperature performance test: The battery was tested at a temperature of -20℃±2℃ and a humidity of <2%RH using the Blue Electric (CT2001) test system, and the discharge specific capacity data of the battery at 0.2 C and 1 C current were tested according to the tester's operating procedures. The test results are shown in Table 3 below.

[0110] Table 2

[0111] Table 3

[0112] Results Analysis As shown in Tables 2 and 3, compared with the uncoated Comparative Example B1, all embodiments employing the double-layer coating design exhibited significantly improved rate performance and low-temperature performance. Specifically, in terms of rate performance, Example B2 achieved a discharge specific capacity of 131.7 mAh / g at 10C, the highest among all samples, representing an improvement of 24.9 mAh / g over Comparative Example B1 (106.8 mAh / g), a relative improvement of 23.3%. Besides Example B2, other double-layer coated samples also demonstrated good high-rate discharge capabilities. For example, Examples B3, B6, and B8 all exceeded 128 mAh / g at 10C, while Examples B5, B7, and B9 reached 127.3 mAh / g, 125.8 mAh / g, and 130.2 mAh / g, respectively, all significantly better than Comparative Examples B1-B3 (106.8–114.7 mAh / g). In particular, the lithium manganese iron phosphate battery of Example B9 still maintains 130.2 mAh / g at 10C, demonstrating excellent fast charging capability.

[0113] In terms of low-temperature performance, Example B7 exhibited the best discharge specific capacity of 70.2 mAh / g at -20°C and 1C, an improvement of 22.0 mAh / g compared to Comparative Example B1 (48.2 mAh / g). Other double-layer coated examples also showed significantly improved low-temperature discharge characteristics. For example, Examples B6 and B3 reached 68.4 mAh / g and 66.8 mAh / g, respectively, while Examples B8, B5, and B2 all exceeded 63.9 mAh / g, outperforming Comparative Examples B1–B3 (48.2–55.7 mAh / g) overall. Notably, the lithium manganese iron phosphate battery of Example B9 achieved a capacity as high as 119.4 mAh / g at -20°C and 0.2C, and maintained 86.5 mAh / g at 1C, indicating lower resistance to ion migration and charge transfer at low temperatures, demonstrating the outstanding advantages of its structural design.

[0114] The resistivity data shows that the resistivity of the double-layer coated materials is generally significantly lower than that of the comparative examples. Examples B2, B5, and B6 have resistivities of only 5.6 Ω·cm, 4.8 Ω·cm, and 5.3 Ω·cm, respectively, far lower than the 41.9 Ω·cm of comparative example B1, indicating that the coating layer effectively improves electronic conductivity. Resistivity shows a clear correlation with rate capability and low-temperature performance: examples with lower resistivity tend to have higher discharge capacity at high rates and low temperatures.

[0115] As can be seen, by using carbonized thiophene-like substances and bromine-containing organic compounds as the first coating layer, and then forming a second coating layer by carbonizing metal ion-containing MOFs, a bilayer synergistic coating structure with both high electronic conductivity and porous ion channels was successfully constructed on the surface of lithium iron phosphate. This design not only significantly reduces the resistivity of the material, but also provides an efficient lithium-ion transport pathway through the porous carbon framework derived from MOFs, resulting in a comprehensive improvement in the electrochemical performance of the material under high-rate and low-temperature conditions.

[0116] like Figure 1 As shown, the double-layer coating makes the material particles more rounded, dispersed, and uniform in morphology, which is beneficial to structural stability and rapid lithium-ion insertion / extraction. Figure 2 The TEM image shown clearly shows that the inner layer is a dense sulfur / bromine co-doped carbon layer, which provides an efficient electron transport path and suppresses interfacial side reactions; the outer layer is a loose porous carbon framework derived from MOFs, whose regular arrangement creates abundant micron / nano-scale pores, which greatly promotes electrolyte wetting and lithium-ion migration.

[0117] like Figure 3 As shown, dV / dlog(w) is the differential expression of pore volume (V) with respect to the logarithmic form of pore diameter (w), characterizing the change in pore volume for each logarithmic increase in pore diameter. Pore structure analysis shows that Example 2, while retaining micropores and mesopores, introduced more macropore structures, forming a micro-meso-macropore hierarchical pore system. This structure not only provides more spacious ion diffusion channels but also optimizes bulk electrolyte transport, thereby significantly improving ion migration kinetics at high rates and low temperatures.

[0118] like Figure 4 As shown in the electrochemical impedance spectroscopy, the ohmic impedance (4.6 Ω) and interfacial transfer impedance (60.9 Ω) of Example 2 are significantly lower than those of Comparative Example 1 (24.1 Ω and 250.6 Ω, respectively). This result directly confirms that the double-layer coating structure effectively improves the overall electronic conductivity of the material and significantly enhances the transport kinetics of lithium ions at the electrode / electrolyte interface, providing a key basis for improving rate capability and low-temperature performance.

[0119] Depend on Figure 5It can be seen that the discharge capacity of Example 2 at a high rate of 10C (131.7 mAh / g) is higher than that of Comparative Example 1 (106.8 mAh / g), with a capacity increase of 24.9 mAh / g, representing an increase of 23.3%.

[0120] In summary, the modified phosphate-based cathode material provided in this application constructs a double-layer core-shell structure. The first coating layer consists of a carbon layer containing sulfur and bromine. Sulfur doping enhances the electron delocalization and surface activity of the carbon layer, while the introduction of bromine further improves the conductivity of the carbon layer by forming C-Br bonds and effectively suppresses interfacial side reactions between the electrolyte and the cathode material. The first coating layer is in close contact with the phosphate-based cathode material core, significantly improving electron transport efficiency and providing physical isolation, reducing direct contact between the active material and the electrolyte at low temperatures and inhibiting the growth of harmful SEI films. The second coating layer is a second carbon layer formed by carbonization of a metal-organic framework material. This structure provides abundant and continuous transport channels for lithium ion migration, greatly reducing ion diffusion resistance. Simultaneously, the nano-metal particles are uniformly dispersed within the carbon framework, further enhancing the overall conductivity of the material. This dual-coating structure synergistically optimizes both electron conduction and ion diffusion, giving the material low resistance, high interfacial stability, and excellent porous ion channels, resulting in a phosphate-based cathode material with superior overall performance.

[0121] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A coated modified phosphate-based cathode material, characterized in that, The coated modified phosphate-based cathode material has a double-coated core-shell structure, comprising: Phosphate-based cathode material core; The first coating layer disposed on the surface of the phosphate-based cathode material core includes a first carbon layer doped with sulfur and bromine elements, formed by carbonization of thiophene-like substances. A second coating layer is disposed on the surface of the first coating layer, wherein the second coating layer is a second carbon layer formed by carbonization of a metal-organic framework material.

2. The coated modified phosphate-based cathode material according to claim 1, characterized in that, The thickness of the first coating layer is 2-3 nm; and / or, Based on the total mass of the first coating layer as 100%, the mass percentage of sulfur is 1 wt%-10 wt%, and the mass percentage of bromine is 1 wt%-10 wt%.

3. The coated modified phosphate-based cathode material according to claim 1, characterized in that, The second coating layer is a porous carbon layer containing metal nanoparticles, wherein the metal nanoparticles include at least one of elemental metals, metal alloys, metal oxides, or metal carbides; and / or, The thickness of the second coating layer is 2-3 nm.

4. The coated modified phosphate-based cathode material according to claim 3, characterized in that, With the total mass of the second coating layer being 100%, the mass percentage content of the metal nanoparticles is 1 wt%-10 wt%; and / or, The porous carbon layer includes at least one pore structure selected from micropores, mesopores, and macropores.

5. The coated modified phosphate-based cathode material according to claim 1, characterized in that, A portion of the second coating layer interweaves with a portion of the first coating layer through covalent bonds or π-π interactions, forming a three-dimensional hybrid conductive network.

6. The coated modified phosphate-based cathode material according to any one of claims 1-5, characterized in that, The raw material for the first coating layer is a mixed carbon source comprising a thiophene component A and a bromine-containing organic component B, wherein the mass ratio of the thiophene component A to the bromine-containing organic component B is (4-6):(6-4); and / or, The metal-organic framework material includes at least one of zinc-containing metal-organic framework materials, titanium-containing metal-organic framework materials, iron-containing metal-organic framework materials, copper-containing metal-organic framework materials, magnesium-containing metal-organic framework materials, and manganese-containing metal-organic framework materials; and / or, The phosphate-based cathode material core includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium manganese phosphate, lithium titanium phosphate, and lithium cobalt phosphate.

7. A method for preparing a coated modified phosphate-based cathode material, characterized in that, Includes the following steps: The first carbon source raw material containing thiophene-like substances and the phosphate-based cathode material raw material are mixed and dried to obtain a solid-phase phosphate-based cathode material precursor. The solid-phase phosphate-based cathode material precursor is subjected to a first sintering treatment to obtain a phosphate-based cathode material intermediate. The phosphate-based cathode material intermediate is mixed with a metal-organic framework material and subjected to a second sintering treatment to obtain a coated modified phosphate-based cathode material.

8. The method for preparing the coated modified phosphate-based cathode material according to claim 7, characterized in that, The first carbon source material comprises a mixed carbon source of thiophene component A and bromine-containing organic component B, wherein the mass ratio of thiophene component A to bromine-containing organic component B is (4-6):(6-4); and / or, The metal-organic framework material includes at least one of zinc-containing metal-organic framework materials, titanium-containing metal-organic framework materials, iron-containing metal-organic framework materials, copper-containing metal-organic framework materials, magnesium-containing metal-organic framework materials, and manganese-containing metal-organic framework materials.

9. The method for preparing the coated modified phosphate-based cathode material according to claim 8, characterized in that, The thiophene component A is selected from at least one of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) complex, poly(3,4-ethylenedioxythiophene)-p-toluenesulfonate, and poly(3,4-ethylenedioxythiophene)-trifluoromethanesulfonate; and / or, The bromine-containing organic component B is selected from at least one of methyl α-bromoacrylate, 6,6'-dibromoindigo, N-bromophthalimide, and hexadecyltrimethylammonium bromide; and / or The zinc-containing metal-organic framework material includes at least one of ZIF-8 and ZIF-68; the titanium-containing metal-organic framework material includes at least one of NTU-9, MIL-125(Ti), and NH2-MIL-125(Ti); the iron-containing metal-organic framework material includes at least one of MIL-100(Fe), MIL-101(Fe), and PCN-250(Fe); the copper-containing metal-organic framework material includes at least one of HKUST-1 and SIFSIX-1-Cu; the magnesium-containing metal-organic framework material includes at least one of MOF-74(Mg) and Basosiv™ M050; and the manganese-containing metal-organic framework material includes at least one of MOF-74(Mn) and TPP-Mn.

10. The method for preparing the coated modified phosphate-based cathode material according to claim 7, characterized in that, The first sintering treatment is performed at a temperature of 400℃~600℃, a heating rate of 3℃ / min~10℃ / min, and a holding time of 10h~14h; and / or, The second sintering treatment is performed at a temperature of 400℃~700℃, a heating rate of 3℃ / min~10℃ / min, and a holding time of 6h~10h; and / or, The metal-organic framework material undergoes the second sintering treatment to form a porous carbon layer containing metal nanoparticles, wherein the porous carbon layer includes at least one pore structure selected from micropores, mesopores, and macropores.

11. The method for preparing the coated modified phosphate-based cathode material according to claim 7, characterized in that, Based on the total mass of the solid-phase phosphate-based cathode material precursor being 100%, the amount of the first carbon source material added is 1wt%-5wt%; and / or, Based on the total mass of the phosphate-based cathode material intermediates as 100%, the amount of the metal-organic framework material added is 1wt%-5wt%; and / or, The phosphate-based cathode material raw materials include lithium source, iron source and phosphorus source, wherein the molar ratio of lithium source, iron source and phosphorus source is (1.01-1.06):(0.93-0.98):(0.98-1.00).

12. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, wherein the positive electrode sheet comprises the coated modified phosphate-based positive electrode material according to any one of claims 1-6.

13. The lithium-ion battery according to claim 12, characterized in that, At 25°C, the lithium-ion battery exhibits a 1C discharge specific capacity greater than 147 mAh / g, a 5C discharge specific capacity greater than 132 mAh / g, and a 10C discharge specific capacity greater than 120 mAh / g; and / or, At -20℃, the lithium-ion battery has a 0.2C discharge specific capacity greater than 96 mAh / g and a 1C discharge specific capacity greater than 60 mAh / g.

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