Low-temperature fast-charging lithium iron phosphate positive electrode material, preparation method and application thereof

Abstract

The application provides a low-temperature fast-charging type lithium iron phosphate positive electrode material and a preparation method and application thereof, and belongs to the field of lithium ion batteries. The iron source, the phosphorus source and the first dopant are mixed to prepare a composite precursor through reaction; the composite precursor is uniformly mixed with a lithium source, a carbon source, a second dopant and a third dopant to obtain a mixture, and the mixture is ground and spray-dried to obtain an intermediate product; and the intermediate product is subjected to calcination treatment to obtain the low-temperature fast-charging type lithium iron phosphate positive electrode material. The first dopant is introduced into the composite precursor to construct a biomimetic ion channel, and a synergistic strategy of multi-element composite doping and calcination treatment is combined, so that the diffusion path of lithium ions is significantly widened, the migration resistance of lithium ions at low temperature is reduced, the comprehensive electrochemical performance of the lithium iron phosphate positive electrode material is improved, and the defects of poor low-temperature performance and insufficient fast-charging capacity of traditional materials are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a low-temperature fast-charging lithium iron phosphate cathode material, its preparation method, and its application. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has become one of the most widely used cathode materials in the fields of power batteries and consumer electronics due to its advantages such as high safety, long cycle life and low cost. However, its inherent defects such as poor low temperature performance (severe capacity decay at -20℃) and insufficient fast charging capability (only supports 1-3C charging) have seriously restricted its application in high-end fields.

[0003] In traditional preparation methods, modifications such as carbon coating, metal ion doping, or nanostructuring can improve conductivity or optimize ion transport pathways to some extent, but a significant bottleneck remains: while the carbon coating improves electronic conductivity, it physically hinders the formation of Li. + Rapid diffusion; however, metal ion doping and nano-sizing face problems such as decreased structural stability and limited performance improvement, making it difficult to simultaneously achieve low-temperature performance and fast charging capability. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a low-temperature fast-charging lithium iron phosphate cathode material, its preparation method and application, aiming to solve the technical problem that traditional preparation methods are difficult to simultaneously achieve low-temperature performance and fast-charging capability.

[0005] In a first aspect, embodiments of this application provide a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material, comprising the following steps: A composite precursor was prepared by mixing an iron source, a phosphorus source and a first dopant, and then reacting the mixture. The composite precursor is mixed uniformly with a lithium source, a carbon source, a second dopant, and a third dopant to obtain a mixture, which is then ground and spray-dried to obtain an intermediate product. The intermediate product was calcined to obtain a low-temperature fast-charging lithium iron phosphate cathode material.

[0006] In the technical solution of this application embodiment, by introducing a first dopant into the composite precursor to construct a biomimetic ion channel, and combining a synergistic strategy of multi-element composite doping and calcination treatment, the diffusion path of lithium ions is significantly broadened, the migration resistance of lithium ions at low temperatures is reduced, and the comprehensive electrochemical performance of lithium iron phosphate cathode material is improved, effectively solving the defects of poor low-temperature performance and insufficient fast charging capability of traditional materials.

[0007] In some embodiments, the molar ratio of the composite precursor, the lithium source, and the carbon source is 1:(1.05~1.15):(0.09~0.15); and / or, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, and lithium acetate; and / or, the carbon source is selected from one or more of glucose, sucrose, citric acid, and polyethylene glycol.

[0008] In this embodiment, the molar ratio of the composite precursor, lithium source, and carbon source ensures a moderate excess of lithium source to compensate for volatilization losses during high-temperature calcination, thereby obtaining lithium iron phosphate with accurate stoichiometry and high crystallinity. At the same time, the precise carbon source ratio is the basis for the subsequent formation of gradient carbon coating, which can form a continuous conductive network to improve rate performance, while avoiding the obstruction of lithium-ion diffusion due to excessive carbon content. Selecting a suitable lithium source can ensure high reactivity and good product purity. Selecting a suitable organic carbon source can form a carbon layer with good conductivity after pyrolysis.

[0009] In some embodiments, the first dopant is a MOF or COF material, wherein the MOF is selected from one or more of ZIF-8, MIL-101, and MOF-5, and the COF is selected from one or more of COF-1, COF-5, and COF-LZU1; and / or, the amount of the first dopant added is 1 to 3‰ of the mass of the iron source; and / or, the iron source is selected from one or more of ferric sulfate, ferric oxide, ferric chloride, and ferric nitrate; and / or, the phosphorus source is selected from one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate; and / or, the molar ratio of the iron source to the phosphorus source is 1:(1 to 1.05).

[0010] In this embodiment, MOFs or COFs materials are composited into lithium iron phosphate as a physical structural support, providing a framework for constructing biomimetic ion channels and broadening the diffusion channels of lithium ions. Controlling the amount added can effectively construct three-dimensional ion channels without affecting the energy density and main crystal structure of the material. Selecting appropriate iron and phosphorus sources and controlling the iron-phosphorus ratio helps to ensure the regularity of the precursor structure and avoid the generation of impurities.

[0011] In some embodiments, the step of mixing the iron source, phosphorus source, and first dopant, and preparing the composite precursor by reaction, includes: The iron source and the phosphorus source are added to a solvent, and the solid content is controlled to be 40-45%. Then, the first dopant is added, and the pH value of the reaction system is adjusted to 2.5-3.5 by ammonia water. The reaction is carried out hydrothermally at 140-190℃ for 6-12 hours to obtain the composite precursor. The solvent is one or more of water, methanol, ethanol, and glycerol.

[0012] In this embodiment, by controlling the solid content and using a specific solvent, the uniformity of the reaction system was ensured, which is beneficial to the uniform dispersion of the first dopant. The pH value was adjusted to a weakly acidic range by using ammonia water, which provided a suitable chemical environment for the stable existence of MOFs / COFs and their recombination with FePO4. Controlling the hydrothermal reaction temperature and time can effectively synthesize FePO4 nanosheets with uniform morphology and good crystallinity, which is helpful for the subsequent construction of efficient biomimetic ion channels and the achievement of excellent low-temperature fast charging performance.

[0013] In some embodiments, the second dopant is one or more of TiOSO4, TiO2, Mn(CH3COO)2, MnSO4, MnO, and ZrO2; and / or, the amount of the second dopant added is 1 to 5‰ of the mass of the mixture; and / or, the third dopant is one or more of Nb3Sn, Nb-Ti, V3Si, and Nb3Al; and / or, the amount of the third dopant added is 1 to 3‰ of the mass of the mixture.

[0014] In this embodiment, a second dopant is introduced to optimize the lattice and broaden the lithium-ion diffusion channels. A third dopant is then used to construct a low-temperature superconducting electron transport network, synergistically addressing the performance bottleneck of lithium iron phosphate from both ionic and electronic perspectives. Precise control of the amounts of the second and third dopants facilitates effective regulation of the material's microstructure and conductivity, avoiding the negative impact of excessive doping on the material's intrinsic properties. Ultimately, this achieves high capacity retention and fast-charging performance at low temperatures.

[0015] In some embodiments, the particle size of the mixture after grinding is 0.2~1.8μm.

[0016] In this embodiment, reducing the particle size to the micrometer to submicrometer level through liquid-phase milling facilitates more complete and rapid solid-phase reactions during subsequent calcination. It also promotes uniform coating of dopants and carbon sources on the particle surface, ensuring consistent final material properties. Smaller particles help reduce the migration distance of lithium ions within the material, thereby improving the material's rate performance.

[0017] In some embodiments, the calcination treatment includes low-temperature pyrolysis treatment and high-temperature crystallization treatment, wherein the pyrolysis temperature of the low-temperature pyrolysis treatment is 350~450℃ and the time is 2~4h; the crystallization temperature of the high-temperature crystallization treatment is 700~800℃ and the time is 4~8h; and the carbon coating amount of the obtained low-temperature fast-charging lithium iron phosphate cathode material is 1~2wt%.

[0018] In this embodiment, the carbon source is first uniformly and gently decomposed and coated onto the particle surface through low-temperature pyrolysis. Then, high-temperature crystallization is carried out to promote the growth of the LiFePO4 crystal phase and further graphitize the carbon layer, thereby forming a continuous and highly conductive gradient carbon network, which effectively improves the electronic conductivity of the material. By precisely controlling the process, the final carbon coating amount is optimized to 1~2wt%, which not only provides the electronic channels required for fast charging, but also avoids the problem of excessive carbon layer hindering lithium ion diffusion, thus achieving a balance between high electronic conductivity and high ion diffusion rate.

[0019] Secondly, embodiments of this application provide a low-temperature fast-charging lithium iron phosphate cathode material, prepared by the method described in the first aspect, wherein the chemical formula of the low-temperature fast-charging lithium iron phosphate cathode material is Li. 1+x+y M y FePO4 / C, wherein M is at least one of Ti, Mn, Mg, and Zr, 0.03≤x≤0.2, and 0.001≤y≤0.01.

[0020] In the technical solution of this application embodiment, the low-temperature fast-charging lithium iron phosphate cathode material ensures high performance from the intrinsic structure of the material by precisely controlling the stoichiometric ratio of lithium, iron and doping elements.

[0021] Thirdly, embodiments of this application provide a positive electrode sheet, including the low-temperature fast-charging lithium iron phosphate positive electrode material described in the second aspect.

[0022] In this embodiment, the positive electrode sheet contains the aforementioned low-temperature fast-charging lithium iron phosphate positive electrode material, thus possessing excellent low-temperature discharge performance and ultra-fast charging capability, extremely high electronic conductivity and ion diffusion rate, as well as good structural stability and cycle life under harsh charging and discharging conditions.

[0023] Fourthly, embodiments of this application provide a lithium-ion battery, including the positive electrode sheet described in the third aspect.

[0024] In this embodiment, the lithium-ion battery includes the aforementioned positive electrode, thus possessing advantages such as excellent low-temperature endurance, charging efficiency, safety performance, and cycle life.

[0025] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0027] Figure 1 This is a flowchart illustrating the preparation method of the low-temperature fast-charging lithium iron phosphate cathode material provided in the embodiments of this application. Figure 2 The biomimetic ion channel construction mechanism in the embodiments of this application; Figure 3 This is a SEM image of the low-temperature fast-charging lithium iron phosphate cathode material provided in Embodiment 1 of this application; Figure 4 The image shows the XRD pattern of the low-temperature fast-charging lithium iron phosphate cathode material provided in Example 1 of this application. Detailed Implementation

[0028] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0030] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] In the description of the embodiments in this application, the term "and / or" is merely a description of 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, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0033] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0034] Lithium iron phosphate (LFP) has become a mainstream cathode material due to its high safety and low cost. However, its inherent poor low-temperature performance and insufficient fast-charging capability severely restrict its application in high-end fields. Traditional modification methods such as carbon coating, metal ion doping, and nano-sizing can improve conductivity, but they suffer from problems such as carbon layers hindering lithium-ion diffusion, reduced structural stability, and limited performance improvement, making it difficult to simultaneously meet the dual requirements of low-temperature performance and fast-charging capability.

[0035] To address the inherent poor low-temperature performance and insufficient fast-charging capability of lithium iron phosphate cathode materials, as well as the technical problems of traditional carbon coating hindering lithium-ion diffusion and existing modification methods failing to achieve both performance goals, this application provides a low-temperature fast-charging lithium iron phosphate cathode material, its preparation method, and its application. Specifically, by introducing MOFs / COFs precursors to construct biomimetic ion channels, adding low-temperature superconducting materials and specific dopants for multi-dimensional modification, and employing a two-step calcination process combining low-temperature pyrolysis and high-temperature crystallization to form a gradient carbon coating layer, a balance between high electronic conductivity and lithium-ion diffusion rate can be achieved with low carbon coating amount. This significantly improves the material's low-temperature capacity retention and rate performance, thereby enhancing the charging efficiency and cycle life of the cathode sheet and lithium-ion battery.

[0036] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material, comprising the following steps: S1. Iron source, phosphorus source and first dopant are mixed and reacted to prepare composite precursor; S2. The composite precursor is mixed evenly with lithium source, carbon source, second dopant and third dopant to obtain a mixture, which is then ground and spray dried to obtain an intermediate product; S3. The intermediate product is calcined to obtain a low-temperature fast-charging lithium iron phosphate cathode material.

[0037] In this application, a porous composite precursor was prepared by using a first dopant as a biomimetic template, thereby constructing an internally interconnected ion rapid migration channel. Secondly, lithium source, carbon source and composite dopant were precisely introduced during the mixing stage. Nanoscale uniform mixing and structure locking were achieved through grinding and spray drying. Carbon layer formation, crystal growth and doping solid solution were completed simultaneously through calcination treatment, thereby obtaining a lithium iron phosphate cathode material that simultaneously possesses a high-speed ion diffusion path, an efficient electronic conductivity network and ultra-low temperature interface impedance. This achieved a breakthrough in the core performance of high capacity retention and ultra-high rate fast charging under low temperature conditions.

[0038] Furthermore, in some embodiments, the molar ratio of the composite precursor, lithium source, and carbon source is 1:(1.05~1.15):(0.09~0.15); and / or, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, and lithium acetate; and / or, the carbon source is selected from one or more of glucose, sucrose, citric acid, and polyethylene glycol.

[0039] In this application, a moderate excess of lithium source relative to the precursor helps to compensate for sintering losses and fill lithium vacancies, thereby reducing the ion migration barrier and improving transport efficiency. The carbon source is controlled within a suitable range to ensure the formation of a continuous and dense conductive network while avoiding excessive carbon dilution of the active material, achieving an optimal balance between electronic conductivity and volumetric energy density. The selected lithium sources are all commonly used lithium salts with moderate reactivity and easy uniform dispersion, ensuring the sufficiency and consistency of the solid-phase reaction. The selected carbon source can be stably pyrolyzed and carbonized at a suitable temperature to form a uniformly coated, highly conductive carbon layer, thereby synergistically constructing an efficient electron transport path and ensuring the material's low-temperature fast-charging performance and structural stability. Specifically, the molar ratio of the composite precursor, lithium source, and carbon source can be any value within the range of 1:1.05:0.09, 1:1.1:0.10, 1:1.15:0.15, or 1:(1.05~1.15):(0.09~0.15).

[0040] Further, in some embodiments, the first dopant is a MOF or COF material, wherein the MOF is selected from one or more of ZIF-8, MIL-101, and MOF-5, and the COF is selected from one or more of COF-1, COF-5, and COF-LZU1; and / or, the amount of the first dopant added is 1 to 3‰ of the iron source mass; and / or, the iron source is selected from one or more of ferric sulfate, ferric oxide, ferric chloride, and ferric nitrate; and / or, the phosphorus source is selected from one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate; and / or, the molar ratio of the iron source to the phosphorus source is 1:(1 to 1.05).

[0041] In this application, specific MOFs or COFs materials are selected as the first dopant. Their inherent high specific surface area and regular nanopores serve as structural templates, facilitating the directional growth of the iron phosphate precursor during the hydrothermal reaction. This allows for the precise replication of the template's pore structure into the product, forming biomimetic ion transport channels. Furthermore, during subsequent sintering, the carbon framework of the MOFs / COFs can be transformed into a portion of the coated carbon, forming a continuous electronically conductive network, further enhancing electron conduction efficiency. In addition, the porous structure of the MOFs / COFs allows lithium sources and dopants to more easily penetrate into the precursor during subsequent sintering, reducing "solid-state reaction dead zones" and lowering the crystallization temperature required (compared to the traditional lithium iron phosphate crystallization temperature). The temperature is typically 800-850℃, but this scheme lowers it to 700-800℃, while avoiding excessive particle growth caused by high temperatures and further shortening the ion diffusion distance. Controlling the amount of the first dopant ensures the formation of an effective porous network while avoiding the excessive introduction of impurities or damage to the main structure. The selection of iron and phosphorus sources is based on their high reactivity and solubility in the hydrothermal system to ensure the sufficiency and uniformity of precursor synthesis. Setting the molar ratio of iron to phosphorus sources to 1:(1~1.05), i.e., a slight excess of phosphorus, helps ensure that iron is completely converted into the target precursor phase, preventing the formation of electrochemically inert iron oxide impurities due to excess iron, thereby ensuring the purity and electrochemical activity of the final cathode material from the source. Specifically, the molar ratio of iron to phosphorus sources can be any value within the range of 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, or 1:(1~1.05).

[0042] Furthermore, in some embodiments, the step of mixing the iron source, phosphorus source and the first dopant and preparing the composite precursor by reaction includes: adding the iron source and phosphorus source to a solvent, controlling the solid content to be 40-45%, then adding the first dopant, adjusting the pH of the reaction system to 2.5-3.5 with ammonia water, and hydrothermally reacting at 140-190°C for 6-12 hours to obtain the composite precursor; The solvent is one or more of water, methanol, ethanol, and glycerol.

[0043] In this application, controlling the solid content helps ensure sufficient concentration of reactants to promote efficient nucleation and growth, while maintaining good fluidity and mass and heat transfer efficiency of the system, avoiding agglomeration due to excessive concentration or reduced yield due to excessive dilution; precisely adjusting the pH to a weakly acidic range of 2.5-3.5 with ammonia helps ensure sufficient dissolution of iron and phosphorus sources and reaction to generate the target iron phosphate precursor, while providing a suitable environment for the structural stability of MOFs / COFs, enabling them to effectively function as templates; the hydrothermal reaction temperature and time provide the necessary energy and time for the directional adhesion and crystallization of the precursor on the template surface, ensuring the formation of a composite structure with regular porous channels; the selected solvent helps provide good solubility and reaction medium, and its polarity and boiling point characteristics also help to regulate the chemical environment and crystallization kinetics of the reaction system, thereby synergistically achieving the controllable preparation of composite precursors with ideal ion channel structures.

[0044] Further, in some embodiments, the second dopant is one or more of TiOSO4, TiO2, Mn(CH3COO)2, MnSO4, MnO, and ZrO2; and / or, the amount of the second dopant added is 1 to 5‰ of the mass of the mixture; and / or, the third dopant is one or more of Nb3Sn, Nb-Ti, V3Si, and Nb3Al; and / or, the amount of the third dopant added is 1 to 3‰ of the mass of the mixture.

[0045] In this application, the main function of the second dopant is to enter the lithium iron phosphate lattice, stabilize the crystal structure through ion doping, and introduce electronic defects to improve intrinsic electronic conductivity. Its addition amount ensures significant doping effects while avoiding excessive damage to the olivine backbone. The third dopant is a low-temperature superconducting material with zero resistance at low temperatures. Its addition can form superconducting conductive pathways between lithium iron phosphate particles, significantly reducing interfacial impedance at low temperatures (charge transfer impedance can be reduced by 30-50% at -20℃). This avoids the sharp drop in charge and discharge efficiency caused by impedance surges at low temperatures in traditional materials (e.g., traditional LFP fast charging efficiency is <50% at -20℃, while this solution can improve it to over 70%). Its extremely low addition amount can form an effective conductive network at key interfaces, thus overcoming the low-temperature performance bottleneck without sacrificing the content of active materials. The combined use of these two dopants at trace levels achieves a complementary dual mechanism of enhanced bulk conductivity and reduced interfacial impedance, endowing the material with excellent low-temperature fast charging capabilities.

[0046] Furthermore, in some embodiments, the particle size of the mixture after grinding is 0.2~1.8μm.

[0047] In this application, a suitable particle size range can significantly shorten the diffusion path of lithium ions within the solid particles, providing a kinetic basis for high-rate fast charging. This helps maintain high material tap density and electrode volumetric energy density, while ensuring sufficient and uniform solid-state reactions between the lithium source, dopant, and porous precursor during subsequent calcination, promoting complete lattice development and uniform solid solution of dopant elements. Furthermore, the fine particles allow additives such as carbon sources and low-temperature superconducting materials to be more effectively coated or distributed on the surface of the active material, thereby constructing a more continuous and efficient composite conductive network.

[0048] Furthermore, in some embodiments, the calcination treatment includes low-temperature pyrolysis treatment and high-temperature crystallization treatment, wherein the pyrolysis temperature of the low-temperature pyrolysis treatment is 350~450℃ and the time is 2~4h; the crystallization temperature of the high-temperature crystallization treatment is 700~800℃ and the time is 4~8h; and the carbon coating amount of the obtained low-temperature fast-charging lithium iron phosphate cathode material is 1~2wt%.

[0049] In this application, the low-temperature pyrolysis stage provides mild and sufficient decomposition conditions for the carbon source, enabling it to slowly and uniformly transform into amorphous carbon, forming a continuous and dense initial carbon layer, while avoiding violent combustion and carbon loss caused by rapid heating. The high-temperature crystallization stage is carried out under the protection of the formed carbon layer. This combination of temperature and duration ensures that the lithium iron phosphate olivine structure is fully developed and crystallized completely, while effectively inhibiting excessive grain growth, thereby obtaining active particles of moderate size and stable structure. Precisely controlling the carbon coating amount to 1~2wt% helps to construct an efficient electron transport pathway and ensures that the effective capacity of the material is not excessively diluted.

[0050] Secondly, embodiments of this application provide a low-temperature fast-charging lithium iron phosphate cathode material, prepared by the above-described method, with the chemical formula Li. 1+x+y M y FePO4 / C, wherein M is at least one of Ti, Mn, Mg, and Zr, 0.03≤x≤0.2, and 0.001≤y≤0.01.

[0051] Specifically, by providing excess lithium to fill lattice vacancies, the lithium-ion migration barrier is lowered, providing intrinsically high ionic conductivity for fast charging. Simultaneously, at least one of Ti, Mn, Mg, and Zr is selected for trace doping, utilizing the interaction between these elements and Fe... 2+Similar ionic radii enable lattice solid solution, effectively stabilizing the crystal structure and suppressing volume changes. Furthermore, the multi-valence characteristics of Ti / Zr introduce electronic defects, significantly enhancing the intrinsic electronic conductivity of the material. The conductive carbon coating layer on the material surface, in synergy with lattice doping, jointly constructs a highly efficient electron transport network spanning the bulk phase and interfaces of the material. This lithium iron phosphate cathode material maintains excellent electrochemical performance even at -20℃, with significantly improved 5C fast charging capability. The material exhibits the core characteristics of low temperature and low resistance, effectively addressing the technical pain points of low charge-discharge efficiency and poor cycle stability in lithium-ion batteries at low temperatures. It can be widely applied in fields with high demands for low-temperature performance and fast charging, such as new energy vehicles and energy storage devices, and has significant industrial application value.

[0052] Thirdly, embodiments of this application provide a positive electrode sheet, including the aforementioned low-temperature fast-charging lithium iron phosphate positive electrode material.

[0053] In this application, because the provided positive electrode includes the aforementioned lithium iron phosphate positive electrode material, the electrochemical performance of the obtained positive electrode is improved.

[0054] Fourthly, embodiments of this application provide a lithium-ion battery, including the aforementioned positive electrode sheet.

[0055] In this application, because the provided lithium-ion battery includes the aforementioned positive electrode, the electrochemical performance of the lithium-ion battery is also improved.

[0056] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0057] I. Preparation Method Example 1 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material, including the following steps: S1. Ferric chloride and phosphoric acid were added to ethanol at a molar ratio of 1:1.02, and the solid content was controlled at 42%. Then, 2‰ of the mass of ferric chloride ZIF-8 was added, and the pH of the reaction system was adjusted to 3 by ammonia. The reaction was carried out hydrothermally at 160℃ for 8 hours to obtain the composite precursor. S2. The composite precursor is mixed evenly with lithium hydroxide, glucose, TiOSO4 and Nb-Ti to obtain a mixture, wherein the molar ratio of the composite precursor to lithium hydroxide and glucose is 1:1.1:0.12, the amount of TiOSO4 added is 3‰ of the mass of the mixture, and the amount of Nb-Ti added is 2‰ of the mass of the mixture. The mixture is then liquid-phase ground to a particle size range of 0.2~1.8μm and spray-dried to obtain an intermediate product. S3. The obtained intermediate product is subjected to two-step sintering: the pyrolysis temperature is 400℃ and the time is 3h; the crystallization temperature is 750℃ and the time is 6h; the carbon coating amount is 1.5wt%, to obtain a low-temperature fast-charging lithium iron phosphate cathode material.

[0058] Example 2 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the amount of the first dopant added is 1‰ of the iron source mass.

[0059] Example 3 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the amount of the first dopant added is 3‰ of the iron source mass.

[0060] Example 4 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the first dopant is changed to COF-1.

[0061] Example 5 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the amount of the second dopant added is 1‰ of the mass of the mixture.

[0062] Example 6 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the amount of the second dopant added is 5‰ of the mass of the mixture.

[0063] Example 7 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the second dopant is 1‰TiOSO4 and 2‰MnSO4.

[0064] Example 8 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the amount of the third dopant added is 1‰ of the mass of the mixture.

[0065] Example 9 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the amount of the third dopant added is 3‰ of the mass of the mixture.

[0066] Example 10 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the third dopant is Nb3Al.

[0067] Example 11 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. Compared with Example 1, the only difference is that the pH value of the reaction system is adjusted to 2.5 by ammonia water, and the hydrothermal reaction is carried out at 140°C for 8 hours to obtain a composite precursor.

[0068] Example 12 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that the pH value of the reaction system is adjusted to 3.5 by ammonia water, and the hydrothermal reaction is carried out at 190°C for 8 hours to obtain a composite precursor.

[0069] Example 13 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the pyrolysis temperature is 350°C and the crystallization temperature is 700°C.

[0070] Example 14 This embodiment provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Embodiment 1 is that the pyrolysis temperature is 450°C and the crystallization temperature is 800°C.

[0071] Comparative Example 1 Comparative Example 1 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that no first dopant is added.

[0072] Comparative Example 2 Comparative Example 2 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that the amount of the first dopant added is 5‰ of the mass of the iron source.

[0073] Comparative Example 3 Comparative Example 3 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that no second dopant is added.

[0074] Comparative Example 4 Comparative Example 4 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that the amount of the second dopant added is 7‰ of the mass of the mixture.

[0075] Comparative Example 5 Comparative Example 5 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that no third dopant is added.

[0076] Comparative Example 6 Comparative Example 6 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that the amount of the third dopant added is 5‰ of the mass of the mixture.

[0077] Comparative Example 7 Comparative Example 7 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that the pH value of the reaction system is adjusted to 2 by ammonia water, and the hydrothermal reaction is carried out at 120°C for 8 hours to obtain a composite precursor.

[0078] Comparative Example 8 Comparative Example 8 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that the pH value of the reaction system is adjusted to 4 by ammonia water, and the hydrothermal reaction is carried out at 200°C for 8 hours to obtain a composite precursor.

[0079] Comparative Example 9 Comparative Example 9 provides a method for preparing a low-temperature fast-charging lithium iron phosphate cathode material. The only difference from Example 1 is that the two-step calcination is not performed, but a single high-temperature calcination at 750°C for 9 hours is used instead.

[0080] II. Testing Methods 1. SEM testing The low-temperature fast-charging lithium iron phosphate cathode material prepared in Example 1 was examined using a scanning electron microscope; 2. XRD test The low-temperature fast-charging lithium iron phosphate cathode material prepared in Example 1 was analyzed using X-ray diffraction. 3. Powder resistivity test The low-temperature fast-charging lithium iron phosphate cathode materials prepared in the examples and comparative examples were tested using a four-probe powder resistivity tester. 4. Capacity test The lithium iron phosphate cathode material was mixed with conductive agent Super-P, binder PVDF and NMP to form a slurry. The slurry was uniformly coated on an aluminum foil to form an electrode sheet. The negative electrode sheet was made of lithium metal. A simulated battery was assembled with 1 mol / L LiPF6 / (EC+DEC) mass ratio (1:1) as the electrolyte and charge-discharge tests were conducted.

[0081] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 1 Performance data of lithium iron phosphate materials As can be seen from Table 1, this application successfully prepared a lithium iron phosphate cathode material with both excellent low-temperature performance and fast charging capability by introducing MOFs / COFs into the composite precursor to construct a biomimetic ion channel and by using multi-element composite doping and a two-step calcination process.

[0082] Specifically, based on the data from Examples 1-4 and Comparative Examples 1-2, it can be seen that both excessive and insufficient amounts of the first dopant will affect the ion channel construction effect. In Comparative Example 1, without the addition of the first dopant, the capacity retention rate at -20℃ was only 43.26%, indicating that the appropriate addition of the first dopant helps to construct a biomimetic ion channel and improve the lithium-ion diffusion rate and conductivity.

[0083] Specifically, based on the data from Examples 1, 5-7 and Comparative Examples 3-4, it can be seen that the absence or excessive addition of the second dopant leads to a decrease in material performance. In Comparative Example 3, without the addition of the second dopant, the powder resistivity is as high as 34.1 Ω·cm, and the low-temperature performance is significantly reduced, indicating that the second dopant helps to improve electronic conductivity and structural stability.

[0084] Specifically, based on the data from Examples 1, 8-10, and Comparative Examples 5-6, it can be seen that Comparative Example 5, without the addition of a third dopant, had a capacity retention rate of only 40.87% at -20℃. Comparative Example 6, with the addition of an excessive amount of the third dopant, affected the proportion of active material and reduced the material capacity. This indicates that adding an appropriate amount of the third dopant can effectively reduce the interfacial impedance and improve the low-temperature performance.

[0085] Specifically, based on the data from Examples 1, 11, 12 and Comparative Examples 7-8, it can be seen that excessively low or high pH values, as well as excessively low or high hydrothermal reaction temperatures, will lead to a significant decrease in material performance. This is because extreme conditions damage the precursor structure, affect the template function of MOFs / COFs, and cause a decrease in dopant solubility or decomposition. This indicates that appropriate pH values ​​and hydrothermal reaction temperatures are crucial to the performance of low-temperature fast-charging lithium iron phosphate cathode materials.

[0086] Specifically, based on the data from Examples 1, 13, 14 and Comparative Example 9, it can be seen that the resistivity of the powder obtained by Comparative Example 9 through a one-time high-temperature calcination is as high as 39.3 Ω·cm, and its low-temperature performance is significantly inferior to that of Example 1. This indicates that the two-step process of low-temperature pyrolysis + high-temperature crystallization is beneficial to the formation of a gradient carbon coating layer, thereby improving conductivity and structural integrity.

[0087] Figure 2 To illustrate the construction mechanism of the biomimetic ion channel, the blue sphere represents zinc, which is the core metal node of this MOF. It exists in the structure in the form of ions or clusters and is responsible for forming coordination bonds with organic ligands. The yellow sphere, green triangle and pink triangle represent C, N and H respectively, and together they form the organic ligand, namely 2-methylimidazole.

[0088] Figure 3 This is a SEM image of the low-temperature fast-charging lithium iron phosphate cathode material provided in Example 1. Figure 4 The XRD pattern shows that the preparation method of this application successfully obtained a lithium iron phosphate cathode material with a porous structure, high phase purity, and uniform lattice doping.

[0089] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a low-temperature fast-charging lithium iron phosphate cathode material, characterized in that, Includes the following steps: A composite precursor was prepared by mixing an iron source, a phosphorus source and a first dopant, and then reacting the mixture. The composite precursor is mixed uniformly with a lithium source, a carbon source, a second dopant, and a third dopant to obtain a mixture, which is then ground and spray-dried to obtain an intermediate product. The intermediate product was calcined to obtain a low-temperature fast-charging lithium iron phosphate cathode material.

2. The preparation method of the low-temperature fast-charging lithium iron phosphate cathode material according to claim 1, characterized in that, The molar ratio of the composite precursor, the lithium source, and the carbon source is 1:(1.05~1.15):(0.09~0.15); and / or, The lithium source is selected from one or more of lithium hydroxide, lithium carbonate, and lithium acetate; and / or, The carbon source is selected from one or more of glucose, sucrose, citric acid, and polyethylene glycol.

3. The preparation method of the low-temperature fast-charging lithium iron phosphate cathode material according to claim 1, characterized in that, The first dopant is a MOF or COF material, wherein the MOF is selected from one or more of ZIF-8, MIL-101, and MOF-5, and the COF is selected from one or more of COF-1, COF-5, and COF-LZU1; and / or, The amount of the first dopant added is 1-3‰ of the mass of the iron source; and / or, The iron source is selected from one or more of ferric sulfate, ferric oxide, ferric chloride, and ferric nitrate; and / or, The phosphorus source is selected from one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate; and / or, The molar ratio of the iron source to the phosphorus source is 1:(1~1.05).

4. The preparation method of the low-temperature fast-charging lithium iron phosphate cathode material according to claim 1, characterized in that, The step of mixing the iron source, phosphorus source, and first dopant, and preparing the composite precursor by reaction, includes: The iron source and the phosphorus source are added to a solvent, and the solid content is controlled to be 40-45%. Then, the first dopant is added, and the pH value of the reaction system is adjusted to 2.5-3.5 by ammonia water. The reaction is carried out hydrothermally at 140-190℃ for 6-12 hours to obtain the composite precursor. The solvent is one or more of water, methanol, ethanol, and glycerol.

5. The method for preparing the low-temperature fast-charging lithium iron phosphate cathode material according to claim 1, characterized in that, The second dopant is one or more of TiOSO4, TiO2, Mn(CH3COO)2, MnSO4, MnO, and ZrO2; and / or, The amount of the second dopant added is 1-5‰ of the mass of the mixture; and / or, The third dopant is one or more of Nb3Sn, Nb-Ti, V3Si, and Nb3Al; and / or, The amount of the third dopant added is 1 to 3‰ of the mass of the mixture.

6. The method for preparing the low-temperature fast-charging lithium iron phosphate cathode material according to claim 1, characterized in that, The mixture has a particle size of 0.2~1.8μm after grinding.

7. The preparation method of the low-temperature fast-charging lithium iron phosphate cathode material according to claim 1, characterized in that, The calcination treatment includes low-temperature pyrolysis and high-temperature crystallization. The pyrolysis temperature of the low-temperature pyrolysis treatment is 350~450℃ and the time is 2~4h. The crystallization temperature of the high-temperature crystallization treatment is 700~800℃ and the time is 4~8h. The carbon coating of the obtained low-temperature fast-charging lithium iron phosphate cathode material is 1~2wt%.

8. A low-temperature fast-charging lithium iron phosphate cathode material, characterized in that, The low-temperature fast-charging lithium iron phosphate cathode material is prepared by the preparation method according to any one of claims 1-7, and its chemical formula is Li. 1+x+y M y FePO4 / C, wherein M is at least one of Ti, Mn, Mg, and Zr, 0.03≤x≤0.2, and 0.001≤y≤0.

01.

9. A positive electrode sheet, characterized in that, Including the low-temperature fast-charging lithium iron phosphate cathode material as described in claim 8.

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

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