Phosphate-based positive electrode material, preparation method and application thereof

Abstract

The application relates to the technical field of battery materials, and provides a phosphate-based positive electrode material and a preparation method and application thereof. The phosphate-based positive electrode material provided by the application comprises a plurality of composite particles, and in the composite particles, the number ratio of primary particles with a particle size less than or equal to 150 nm is not less than 80%; raw materials of the phosphate-based positive electrode material include a lithium source, an iron source and an iron-based dispersant; the lithium source includes a main lithium source, the main lithium source includes at least one of lithium dihydrogen phosphate and lithium phosphate; the iron source includes a main iron source, the main iron source includes at least one of ferrous oxalate and diiron trioxide; and the iron-based dispersant includes an iron-multiple amine complex. By adopting specific lithium sources, iron sources and iron-based dispersants as raw materials, the positive electrode material has reasonable particle grading, so that the energy density, the rate performance and the cycle life of the positive electrode material are significantly improved, and the positive electrode material exhibits significant applicability in various scenes such as power batteries and energy storage systems.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and in particular relates to a phosphate-based cathode material, its preparation method and application. Background Technology

[0002] The increasingly severe energy crisis is one of the major challenges facing humanity in the 21st century. Developing new, environmentally friendly, and sustainable energy sources is crucial to meeting humanity's growing energy demands. In the field of rechargeable batteries, lithium-ion batteries stand out due to their advantages such as high operating voltage, high energy density, and long cycle life. Among them, lithium iron phosphate (LFP) has become one of the ideal choices for cathode materials in lithium-ion batteries due to its high capacity, long cycle life, excellent stability, environmental friendliness, and low cost.

[0003] Currently, lithium iron phosphate (LFP) holds a crucial position as a cathode material in both power batteries and energy storage batteries. However, these two types of batteries have different focuses regarding material performance: power batteries prioritize energy density, power density, and safety to meet the device's range, charge / discharge efficiency, and operational safety; while energy storage batteries prioritize battery capacity and cycle life, pursuing long-term stable energy storage and release. Since the performance of cathode materials is closely related to key characteristics such as the size of the primary particles, carbon coating process, and metal doping, research on particle distribution has become a hot topic in the industry. However, limited by existing solid-state production processes, achieving precise control of the primary particle ratio to match design requirements still faces significant challenges. Summary of the Invention

[0004] The purpose of this application is to provide a phosphate-based cathode material, its preparation method, and its application, aiming to improve the ability to control the particle size and proportion of primary particles in the cathode material, thereby optimizing the performance of the cathode material.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, this application provides a salt-based cathode material comprising a plurality of composite particles, wherein the composite particles comprise a lithium phosphate core and a carbon shell coating the outer surface of the lithium phosphate core;

[0007] In the composite particles, the proportion of primary particles with a diameter of less than or equal to 150 nm is not less than 80%.

[0008] The raw materials for the phosphate-based cathode material include a lithium source, an iron source, and an iron-based dispersant.

[0009] The lithium source includes a main lithium source, the main lithium source having a mass ratio of not less than 80% in the lithium source, and the main lithium source includes at least one of lithium dihydrogen phosphate and lithium phosphate.

[0010] The iron source includes a main iron source, the main iron source accounts for no less than 80% of the mass of the iron source, and the main iron source includes at least one of ferrous oxalate and ferric oxide.

[0011] The iron-based dispersant includes an iron-polyamine complex.

[0012] Secondly, this application provides a method for preparing a phosphate-based cathode material, comprising the following steps:

[0013] The raw material components, including lithium source, iron source, phosphorus source and doping source, are obtained according to the stoichiometric ratio of lithium phosphate. The lithium source includes a main lithium source, which includes at least one of lithium dihydrogen phosphate and lithium phosphate. The iron source includes a main iron source, which includes at least one of ferrous oxalate and ferric oxide.

[0014] The raw material components, carbon source, iron-based dispersant, and solvent are mixed to obtain a mixture.

[0015] The mixture is sintered to form a phosphate-based cathode material containing a lithium phosphate core and a carbon shell covering the outer surface of the lithium phosphate core.

[0016] Thirdly, this application provides a lithium-ion battery, including a positive electrode and a negative electrode, wherein the positive electrode includes the phosphate-based positive electrode material provided in the first aspect or the phosphate-based positive electrode material prepared by the preparation method provided in the second aspect.

[0017] The phosphate-based cathode material provided in the first aspect of this application includes composite particles with a core-shell structure, specifically comprising a lithium-containing phosphate core and a carbon shell. The carbon shell can effectively improve the electronic conductivity of the cathode material, and plays an additive role in reducing the interfacial resistance and improving the structural stability of the cathode material. Simultaneously, using specific lithium sources, specific iron sources, and iron-based dispersants as reaction raw materials is beneficial for obtaining phosphate-based cathode materials with suitable particle size distribution. Specifically, the decomposition temperature of the iron source is relatively low; for example, the decomposition temperature of ferrous oxalate is approximately 200℃-300℃, and the reduction temperature of ferric oxide is approximately 500℃-600℃. This means that the iron source can generate lithium-containing phosphate under medium and low temperature conditions, which is more conducive to the formation of smaller primary particles. The decomposition temperature of lithium dihydrogen phosphate in the lithium source is also relatively low, approximately 200℃-400℃, which also promotes the formation of small-diameter primary particles. The polyamine ligands in iron-based dispersants can form complexes with iron ions. These complexes then utilize their steric hindrance or charge repulsion to adjust the particle size of the primary particles. Based on this, by using specific lithium sources, iron sources, and iron-based dispersants as raw materials, the cathode material can achieve a reasonable target particle size distribution, meaning that at least 80% of the primary particles have a diameter less than or equal to 150 nm. Optimizing the particle size distribution of phosphate-based cathode materials can significantly improve their energy density, rate performance, and cycle life, making them highly applicable in various scenarios such as power batteries and energy storage systems.

[0018] The method for preparing phosphate-based cathode materials provided in the second aspect of this application involves mixing the raw material components, carbon source, and iron-based dispersant to achieve uniform mixing. During the sintering process, specific lithium sources, iron sources, and iron-based dispersants are used to precisely control the particle size and quantity ratio of primary particles, thereby obtaining a phosphate-based cathode material with a core-shell structure and excellent particle size distribution. This effectively produces the phosphate-based cathode material with the properties described above. Furthermore, the method for preparing phosphate-based cathode materials in this application is beneficial for obtaining phosphate-based cathode materials with high conductivity and good electrochemical performance. Moreover, this method is simple and can be used for industrial-scale mass production.

[0019] The lithium-ion battery provided in the third aspect of this application contains the phosphate-based cathode material of this application, which has a reasonable particle size distribution and advantages such as high electronic conductivity. Therefore, it helps to improve the energy density, rate performance, cycle life and other electrochemical performance of the lithium-ion battery. Attached Figure Description

[0020] 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.

[0021] Figure 1 This is a SEM image of the phosphate-based cathode material provided in Example 1 of this application.

[0022] Figure 2 This is a SEM image of the phosphate-based cathode material provided in Comparative Example 1 of this application;

[0023] Figure 3 This is a SEM image of the phosphate-based cathode material provided in Example 6 of this application;

[0024] Figure 4 This is a SEM image of the phosphate-based cathode material provided in Comparative Example 3 of this application. Detailed Implementation

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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,” “the,” and “the” 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.

[0030] 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 described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0031] 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.

[0032] The first aspect of this application provides a phosphate-based cathode material, comprising a plurality of composite particles. Specifically, the composite particles include a lithium-containing phosphate core and a carbon shell coating the outer surface of the lithium-containing phosphate core; moreover, in the composite particles, the proportion of primary particles with a particle size less than or equal to 150 nm is not less than 80%. The raw materials of the phosphate-based cathode material include a lithium source, an iron source, and an iron-based dispersant. The lithium source includes a main lithium source, the main lithium source accounting for not less than 80% of the total lithium source by mass, and the main lithium source includes at least one of lithium dihydrogen phosphate and lithium phosphate; the iron source includes a main iron source, the main iron source accounting for not less than 80% of the total iron source by mass, and the main iron source includes at least one of ferrous oxalate and ferric oxide; the iron-based dispersant includes an iron-polyamine complex.

[0033] In the technical solution of this application, by using specific lithium sources, specific iron sources, and iron-based dispersants as raw materials, a reasonable particle size distribution can be achieved in the phosphate-based cathode material, meaning that the proportion of primary particles with a diameter less than or equal to 150 nm is not less than 80%. Specifically:

[0034] In the main iron source, ferrous oxalate has a low decomposition temperature, decomposing into ferrous oxide, carbon monoxide, and carbon dioxide at 200℃-300℃, as shown in the reaction equation (I). The decomposition of ferrous oxalate inhibits the growth of crystal nuclei to some extent. Moreover, due to its low decomposition temperature, lithium-containing phosphates can be generated at low temperatures, which is beneficial for obtaining phosphate cathode materials with primary particle sizes ≤50nm.

[0035] FeC2O4→FeO+CO+CO2(I)

[0036] In the main iron source, the reduction temperature range of ferric oxide is 500℃-600℃. Within this temperature range, ferric oxide carbon is reduced to ferrous oxide and carbon monoxide, as shown in equation (II). This results in a moderate reaction temperature for ferric oxide in the formation of phosphate, which is beneficial for forming primary particles with a particle size ≤100nm. Furthermore, ferric oxide has an adsorption effect on the carbon source, allowing the carbon source to form a more uniform carbon shell after carbonization.

[0037] Fe₂O₃ + C → 2FeO + CO (II)

[0038] In the main lithium source, the decomposition temperature of lithium dihydrogen phosphate is 200℃-400℃. Within this temperature range, lithium dihydrogen phosphate decomposes into lithium phosphate and water, as shown in the reaction equation (III). This means that lithium dihydrogen phosphate can form lithium-containing phosphates at lower temperatures, which is beneficial for generating lithium-containing phosphates with a primary particle size ≤100nm.

[0039] 3LiH₂PO₄→Li₃PO₄+2H₂O (III)

[0040] The polyamine ligands contained in iron-based dispersants can form complexes with iron ions. These complexes, on the one hand, regulate the particle size of primary particles in phosphate cathode materials through their own steric hindrance or charge repulsion, promoting the formation of small-diameter primary particles; on the other hand, they can form lithium iron phosphate crystal carriers (i.e., lithium-containing phosphates) with lithium sources during subsequent sintering, thereby helping to improve the reactivity of phosphate-based cathode materials.

[0041] Specifically, iron-based dispersants include at least one of tri(ethylenediamine)ferro(III) nitrate ([Fe(en)3](NO3)3), triethanolamineferro(III) nitrate ([Fe(TEA)](NO3)3), triethylenetetramineferro(III) nitrate ([Fe(TETA)](NO3)3), and ethylenediaminetetraacetic acidferro(III) nitrate ([Fe(EDTA)](NO3)3). These iron-based dispersants contain carboxylic acid and amine groups. In the preparation of lithium iron phosphate, the organic ligands containing carboxylic acid and amine groups act as carbon sources, coating the surface of nanoparticles, which can improve dispersibility, enhance the carbon coating layer, and reduce floating carbon.

[0042] Based on the synergistic effect between the main lithium source, main iron source, and iron-based dispersant, and by controlling the mass ratio of the main lithium source and main iron source, a reasonable particle size distribution is achieved in the phosphate-based cathode material by effectively regulating the primary particle size: the proportion of primary particles with a diameter ≤150nm is not less than 80%. This reasonable particle size distribution not only helps to shorten the lithium-ion diffusion path and reduce interfacial impedance, significantly improving the rate performance of the cathode material, but also increases the compaction density of the electrode, thereby increasing the energy density of the battery. In addition, the appropriate particle size distribution makes the stress distribution of the cathode material more uniform during charging and discharging, which has an added effect on mitigating volume expansion and reducing the risk of particle breakage. This enhances the structural stability of the cathode material, thereby significantly improving the cycle performance and service life of the battery.

[0043] In one embodiment, the primary particles in the composite particles all have a particle size within the range of ≤150nm, meaning that the proportion of primary particles within this particle size range is 100%. In another embodiment, the composite particles include not only primary particles with a particle size within the range of ≤150nm but also primary particles with a particle size greater than 150nm. In this case, the proportion of primary particles with a particle size within the range of ≤150nm is greater than or equal to 80% but less than 100%.

[0044] As an example, in composite particles, the particle size of the primary particles can be any one of 5nm, 10nm, 20nm, 30nm, 50nm, 70nm, 90nm, 100nm, 120nm, 140nm, 150nm, etc., or fall within the range of any two.

[0045] As an example, the percentage of particles with a diameter of ≤150nm can be typical but not limiting values ​​such as 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%.

[0046] As an example, the mass percentage of the main lithium source in the lithium source can be typical but not limiting values ​​such as 80%, 83%, 85%, 88%, 90%, 93%, 95%, 98%, 100%.

[0047] As an example, the mass percentage of the main iron source in the iron source can be typical but not limiting values ​​such as 80%, 83%, 85%, 88%, 90%, 93%, 95%, 98%, 100%.

[0048] In some embodiments, in the composite particles, the proportion of primary particles with a particle size of 20nm-50nm is not less than 80%, and the main iron source is ferrous oxalate.

[0049] Since ferrous oxalate decomposes at temperatures between 200℃ and 300℃, it can participate in phosphate formation at lower temperatures. The low-temperature environment reduces ion migration rates and inhibits crystal growth kinetics, making it difficult for initial crystal nuclei to rapidly aggregate and grow, thus favoring the formation of primary particles with a diameter of 20nm-50nm.

[0050] In some embodiments, in the composite particles, the proportion of primary particles with a diameter of 50nm-150nm is not less than 80%, and the main iron source is ferric oxide.

[0051] Ferric oxide is reduced to ferrous oxide within a temperature range of 500℃-600℃. Subsequently, ferrous oxide can react with a lithium source, such as lithium phosphate, to form lithium iron phosphate, as shown in equation (IV). Since the temperature at which ferric oxide decomposes into ferrous oxide is appropriate, it can participate in the formation of phosphate under suitable temperature conditions. Furthermore, its decomposition promotes the reduction of particle size, which is beneficial for obtaining primary particles with a particle size of 50nm-150nm.

[0052] FeO + Li3PO4 → LiFePO4 + Li2O (IV)

[0053] In some embodiments, the molecular formula of the lithium phosphate core is LiFe. 1-x M x PO4, wherein M includes at least one of Ti, Mg, Al, and V, and 0 ≤ x ≤ 0.1.

[0054] As an example, the lithium phosphate core can be at least one of lithium iron phosphate, lithium magnesium iron phosphate, lithium aluminum iron phosphate, lithium titanium iron phosphate, and lithium vanadium iron phosphate.

[0055] In some embodiments, the particle morphology of the phosphate-based cathode material is quasi-spherical.

[0056] The spherical particles have a uniform surface curvature and fewer grain boundary defects, which significantly shortens the diffusion path of lithium ions within the particles and reduces electron conduction resistance, thereby improving the rate performance of the cathode material. Furthermore, due to the lower anisotropy of the spherical structure, lithium ion diffusion is more balanced in three dimensions, effectively reducing polarization effects and extending cycle life.

[0057] In some embodiments, the carbon shell in the phosphate-based cathode material accounts for 1%-10% of the total mass.

[0058] For example, the mass percentage of the carbon shell can be typical but not limiting values ​​such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

[0059] The fact that the mass percentage of the carbon shell is within the above range indicates that its thickness is appropriate. This not only enables effective coating of the lithium phosphate core but also keeps lithium ions within a suitable migration path range, thereby improving the ionic and electronic conductivity of the cathode material and thus enhancing the rate performance of the battery.

[0060] In some embodiments, the carbon shell comprises the carbonized product of an organic ligand in an iron-polyamine complex.

[0061] Polyamines, as organic ligands in iron-polyamine complexes, can form complexes with iron ions, thereby controlling the particle size of primary particles. During subsequent sintering, these organic ligands are transformed into carbon materials through carbonization, becoming part of the carbon shell.

[0062] In some embodiments, the 0.1C discharge capacity of the phosphate-based cathode material is greater than or equal to 158 mAh / g.

[0063] The 0.1C discharge capacity of phosphate-based cathode materials falls within the above range, indicating that they have high intrinsic activity, good structural stability, and good conductivity, giving them good electrochemical performance such as high energy density, long cycle life, and fast charging performance. This makes them significantly advantageous in various application scenarios such as power batteries and energy storage batteries.

[0064] In some embodiments, the 1C discharge capacity of the phosphate-based cathode material is greater than or equal to 154 mAh / g.

[0065] The 1C discharge capacity of phosphate-based cathode materials falls within the above range, indicating that the cathode materials can efficiently release energy while also taking into account fast charging capability, structural stability, and cost advantages.

[0066] The second aspect of this application provides a method for preparing a phosphate-based cathode material, comprising the following steps:

[0067] Step S10: Obtain raw material components including lithium source, iron source, phosphorus source and doping source according to the stoichiometric ratio in lithium phosphate. The lithium source includes a main lithium source, which includes at least one of lithium dihydrogen phosphate and lithium phosphate. The iron source includes a main iron source, which includes at least one of ferrous oxalate and ferric oxide.

[0068] Step S20: Mix the raw material components with the carbon source, iron-based dispersant and solvent to obtain a mixture.

[0069] Step S30: The mixture is sintered to form a phosphate-based cathode material containing a lithium phosphate core and a carbon shell coating the outer surface of the lithium phosphate core.

[0070] The method for preparing phosphate-based cathode materials provided in the second aspect of this application involves mixing the raw material components, carbon source, and iron-based dispersant to achieve uniform mixing. During the sintering process, specific lithium source, iron source, and iron-based dispersant are used to control the particle size and quantity ratio of primary particles, thereby obtaining a phosphate-based cathode material with a core-shell structure and excellent particle size distribution. This effectively produces a phosphate-based cathode material with the properties described above. Furthermore, the method for preparing phosphate-based cathode materials in this application is advantageous for obtaining phosphate-based cathode materials with high conductivity and good electrochemical performance. This method is also simple and suitable for industrial-scale mass production.

[0071] In some embodiments, in step S10, the main lithium source accounts for 80%-90% of the mass of the lithium source.

[0072] For example, the mass percentage of the main lithium source in the lithium source can be typical but not limiting values ​​such as 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%.

[0073] By controlling the mass ratio of the main lithium source within the above range, its decomposition temperature characteristics can be used to promote the formation of small-diameter primary particles. Furthermore, by leveraging the temperature consistency and stoichiometric correspondence between the main lithium source and the main iron source during the phosphate formation reaction, quantitative control of the particle size and quantity ratio of primary particles in phosphate-based cathode materials can be achieved. This facilitates obtaining phosphate-based cathode materials with a primary particle size ≤150nm and a quantity ratio of not less than 80%.

[0074] In some embodiments, in step S10, the lithium source further includes a modified lithium source, which includes at least one of lithium carbonate, lithium hydroxide, and lithium phosphate, and the main lithium source is different from the modified lithium source.

[0075] The purpose of adding a modified lithium source in this application is to finely control the particle size of primary particles in phosphate-based cathode materials. Taking lithium carbonate as an example, it has a high decomposition temperature, decomposing into lithium oxide and carbon dioxide at approximately 700°C. This allows lithium carbonate to participate in the formation of lithium-containing phosphates at higher temperatures, and the reaction crystallization temperature range for the formation of lithium-containing phosphates is wide, which is more conducive to the formation of primary particles with a particle size greater than 150 nm. Therefore, by adding a modified lithium source, it is possible to promote the formation of phosphate-based cathode materials with a more reasonable particle size distribution, thereby improving the energy density, cycle performance, and other electrochemical performance of the battery.

[0076] In some embodiments, in step S10, the main iron source accounts for 80%-90% of the mass of the iron source.

[0077] For example, the mass percentage of the main iron source in the iron source can be typical but not limiting values ​​such as 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%.

[0078] By controlling the mass ratio of the main iron source within the above range, and leveraging its own decomposition or reduction temperature characteristics, it can participate in the formation of lithium-containing phosphates under medium and low temperature conditions, promoting the formation of small-diameter primary particles, which is conducive to the quantitative control of the particle size and quantity ratio of primary particles in phosphate-based cathode materials.

[0079] In some embodiments, in step S10, the iron source further includes a modified iron source, which includes at least one of iron phosphate, ferric oxide, and ferrous oxalate, and the main iron source is different from the modified iron source.

[0080] The purpose of adding modified iron sources in this application is to finely control the particle size of primary particles in phosphate-based cathode materials. For example, iron phosphate can participate in the formation of lithium-containing phosphates at high temperatures, which is beneficial for obtaining phosphate-based cathode materials with larger primary particle sizes. For example, ferrous oxalate has a low decomposition temperature, which is beneficial for obtaining phosphate-based cathode materials with primary particle sizes ≤50nm. For example, ferric oxide has a reduction temperature range of 500℃-600℃, which is beneficial for forming primary particles with a particle size ≤100nm. Therefore, by adding the above-mentioned modified iron sources, it is possible to promote the formation of phosphate-based cathode materials with more reasonable particle gradation, thereby improving the energy density, cycle performance, and other electrochemical performance of the battery.

[0081] In some embodiments, in step S10, the doping source includes at least one of a titanium source, a vanadium source, a magnesium source, and an aluminum source.

[0082] By adding doping sources, phosphate-based cathode materials can contain doping elements such as vanadium, titanium, magnesium, and aluminum, making them suitable for various applications such as power batteries and energy storage batteries.

[0083] The doping source includes the oxide or organic compound corresponding to the doping element. For example, the titanium source includes at least one of titanium dioxide, tetrabutyl titanate, etc.; the aluminum source includes at least one of aluminum oxide, aluminum hydroxide, and aluminum nitrate; and the vanadium source includes at least one of ammonium metavanadate, vanadium nitrate, and vanadium pentoxide.

[0084] In some embodiments, in step S10, the amount of dopant source added is 0.6%-1% by mass relative to the theoretical yield of the phosphate-based cathode material.

[0085] Adding dopant sources allows phosphate-based cathode materials to contain dopant elements such as vanadium, titanium, magnesium, and aluminum. In application, the amount of dopant source added can be controlled, thereby controlling the total amount of dopant elements to be equivalent to the mass content in the prepared phosphate-based cathode material of 0.6%-1%, as mentioned above, i.e., 6000ppm-10000ppm.

[0086] In some embodiments, in step S10, the phosphorus source includes at least one of phosphoric acid and ammonium dihydrogen phosphate.

[0087] Of course, if the iron or lithium source contains phosphorus, such as lithium phosphate or iron phosphate, and the phosphorus content meets the stoichiometric requirements for lithium phosphate, then there is no need to add an additional phosphorus source.

[0088] In some embodiments, in step S10, the molar ratio of iron in the iron source to phosphorus in the phosphorus source in the raw material composition is Fe:P = (0.97-0.985):1.

[0089] Specifically, in step S10, when the main iron source is ferrous oxalate, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is Fe:P = (0.975-0.985):1.

[0090] Specifically, in step S10, when the main iron source is ferric oxide, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is Fe:P = (0.97-0.98):1.

[0091] By controlling the molar ratio of iron to phosphorus within the above range, the iron source can be fully combined with the phosphorus source, the formation of iron-enriched impurity phases can be suppressed, and the purity of the phosphate main phase can be improved.

[0092] In some embodiments, in step S10, the molar ratio of lithium in the lithium source to iron in the iron source in the raw material composition is Li:Fe = (1.04-1.06):1.

[0093] Specifically, in step S10, when the main iron source is ferrous oxalate, the molar ratio of lithium in the lithium source to iron in the iron source is Li:Fe = (1.05-1.06):1.

[0094] Specifically, in step S10, when the main iron source is ferric oxide, the molar ratio of lithium in the lithium source to iron in the iron source is Li:Fe = (1.04-1.05):1.

[0095] Controlling the molar ratio of lithium to iron within the above range can not only compensate for lithium loss during subsequent sintering and improve the integrity of the lithium phosphate lattice, but also utilize the lithium-rich environment to suppress primary particle agglomeration and promote the refinement and homogenization of primary particles.

[0096] In some embodiments, in step S20, the iron-based dispersant comprises an iron-polyamine complex. As an example, the iron-based dispersant comprises at least one of tri(ethylenediamine)fer(III) nitrate ([Fe(en)3](NO3)3), triethanolaminefer(III) nitrate ([Fe(TEA)](NO3)3), triethylenetetraminefer(III) nitrate ([Fe(TETA)](NO3)3), and ethylenediaminetetraacetic acidfer(III) nitrate ([Fe(EDTA)](NO3)3).

[0097] The ligands in these iron-based dispersants can form complexes with iron ions, and their effects are manifested in three aspects: First, they can regulate the particle size of primary particles through steric hindrance or charge repulsion effects; second, they can combine with lithium sources in the subsequent sintering process to form lithium iron phosphate crystal carriers (i.e. lithium phosphate), thereby improving the reactivity of phosphate-based cathode materials; third, the ligands in the complexes can act as carbon sources, forming carbon materials that coat the surface of the lithium phosphate core during sintering, while improving the dispersibility of composite particles and reducing floating carbon.

[0098] In some embodiments, in step S20, the amount of iron-based dispersant added is 0.5%-2% by mass relative to the theoretical yield of phosphate-based cathode material.

[0099] For example, the amount of iron-based dispersant added as a percentage by mass relative to the theoretical yield of phosphate-based cathode materials can be a typical but not limiting value among 0.5%, 1%, 1.5%, 1.8%, and 2%.

[0100] In some embodiments, in step S20, the carbon source includes at least one of glucose, sucrose, and white sugar.

[0101] In some embodiments, in step S20, the amount of carbon source added is 15%-25% by mass relative to the theoretical yield of the phosphate-based cathode material.

[0102] When the amount of carbon source added is within the above range, an appropriate amount of carbon material can be formed after sintering, so as to effectively coat the surface of the lithium phosphate core and form a carbon shell layer.

[0103] In some embodiments, step S20, the mixing process includes a grinding process and a spray drying process performed sequentially.

[0104] Specifically, the grinding process is sand milling, and the zirconium balls used in the sand milling are 0.8μm in size.

[0105] The initial agglomerated particles of raw materials such as iron, lithium, and phosphorus sources are broken down by sand milling, and dispersed into submicron or nano-sized particles, thereby increasing the contact area between raw materials and promoting the uniform distribution of each raw material component at the microscale.

[0106] Specifically, the inlet air temperature for spray drying is 150℃-200℃, and the outlet air temperature is 60℃-100℃.

[0107] For example, the inlet air temperature can be a typical but non-limiting value such as 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc., and the outlet air temperature can be a typical but non-limiting value such as 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0108] Spray treatment disperses the ground slurry into droplets, and then the solvent evaporates rapidly in a hot air stream, causing the raw material mixture to form spherical precursor particles inside the droplets, thus resulting in spherical particles in the mixture. By controlling the inlet and outlet air temperatures within the aforementioned range, the particle size and morphological regularity of the mixture can be effectively regulated, resulting in a mixture with high sphericity and suitable particle size.

[0109] In some embodiments, in step S20, the particle size of the mixture is 330nm-370nm.

[0110] For example, the particle size of the mixture can be typical but not limiting values ​​such as 330nm, 340nm, 350nm, 360nm, and 370nm.

[0111] In some embodiments, step S30 includes a first sintering process, a second sintering process, and a third sintering process.

[0112] The conditions for the first sintering treatment are sintering at 180℃-300℃ for 1h-2.5h, the conditions for the second sintering treatment are sintering at 400-600℃ for 2h-3h, and the conditions for the third sintering treatment are sintering at 600℃-750℃ for 3h-7h.

[0113] Specifically, the sintering process is carried out under a protective atmosphere, such as at least one of nitrogen, argon, and helium.

[0114] This application employs a gradient sintering method to effectively control the particle morphology and particle size distribution of phosphate-based cathode materials. The first sintering process can be understood as low-temperature preheating. During this process, the lithium and iron sources begin to undergo localized solid-phase reactions, forming nanoscale initial crystal nuclei. Furthermore, the iron-based dispersant stabilizes the initial crystal nuclei through steric hindrance or charge repulsion, reducing the probability of particle agglomeration. In the second sintering process, the sintering temperature is in the intermediate temperature range, allowing the initial crystal nuclei to grow at a controllable rate. At this stage, the carbon source undergoes carbonization to form an amorphous carbon shell, which adsorbs onto the surface of the lithium-containing phosphate core, promoting the particles to grow towards a near-spherical shape. In the third sintering process, the higher temperature helps accelerate the atomic diffusion coefficient, promoting atomic rearrangement within the crystal lattice and forming primary particles with a particle size within a certain range. The holding time can adjust the particle growth rate, ultimately obtaining a phosphate-based cathode material with a reasonable particle size distribution.

[0115] Specifically, in step S30, when the main iron source is ferrous oxalate, the first sintering treatment includes sintering at 180℃-200℃ for 1h-2h at a heating rate of 1℃ / min-3℃ / min, the second sintering treatment includes sintering at 400-500℃ for 2h-3h at a heating rate of 2℃ / min-4℃ / min, and the third sintering treatment includes sintering at 600℃-680℃ for 3h-5h at a heating rate of 3℃ / min-5℃ / min.

[0116] Since the main iron source is ferrous oxalate, and the decomposition temperature of ferrous oxalate is 200℃-300℃, controlling the heating rate, holding temperature and holding time at each stage is beneficial to forming primary particles with a particle size ≤150nm.

[0117] Specifically, in step S30, when the main iron source is ferric oxide, the first sintering treatment includes sintering at 200℃-300℃ for 1.5h-2.5h at a heating rate of 1℃ / min-3℃ / min; the second sintering treatment includes sintering at 500-600℃ for 2h-3h at a heating rate of 2℃ / min-4℃ / min; and the third sintering treatment includes sintering at 650℃-750℃ for 5h-7h at a heating rate of 2℃ / min-5℃ / min.

[0118] Since the main iron source is ferric oxide, and the reduction temperature of ferric oxide is 500℃-600℃, controlling the heating rate, holding temperature and holding time at each stage is beneficial to forming primary particles with a particle size ≤150nm.

[0119] Thirdly, this application provides a lithium-ion battery, including a positive electrode and a negative electrode. The positive electrode includes the phosphate-based positive electrode material provided in the first aspect or the phosphate-based positive electrode material prepared by the preparation method provided in the second aspect.

[0120] The lithium-ion battery provided in the third aspect of this application contains the phosphate-based cathode material of this application, which has a reasonable particle size distribution and advantages such as high electronic conductivity. Therefore, it helps to improve the energy density, rate performance, cycle life and other electrochemical performance of the lithium-ion battery.

[0121] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, wherein the positive active layer includes the phosphate-based positive electrode material described in any of the above embodiments. In one embodiment of this application, the positive current collector includes, but is not limited to, at least one of aluminum foil, carbon-coated aluminum foil, iron foil, tin foil, zinc foil, nickel foil, titanium foil, and manganese foil. In one embodiment of this application, the positive current collector may be aluminum foil.

[0122] In some embodiments, the preparation of the positive electrode active layer includes the following steps: mixing the above-mentioned phosphate-based positive electrode material, conductive agent and binder to form an electrode slurry, coating the electrode slurry onto the current collector, and preparing a positive electrode sheet by drying, rolling, die cutting and other steps.

[0123] In some embodiments, the mass percentage of phosphate-based cathode material in the cathode active layer is 80%-95%. Specifically, the mass percentage of phosphate-based cathode material in the cathode active material layer can be 80%, 85%, 88%, 90%, 95%, etc.

[0124] In some embodiments, the binder content in the positive electrode active layer is 2wt%-5wt%. In specific embodiments, the binder content can be a typical but not limited content such as 2wt%, 3wt%, 4wt%, 5wt%.

[0125] In some embodiments, the adhesive includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0126] In some embodiments, the content of the conductive agent in the positive electrode active material layer is 1wt%-5wt%. In specific embodiments, the content of the conductive agent can be a typical but not limited content such as 3wt%, 4wt%, or 5wt%.

[0127] In some embodiments, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes.

[0128] This application does not specifically limit the negative electrode, electrolyte, separator, etc. in the lithium-ion battery of the embodiments, and can be applied to any battery system.

[0129] In some embodiments, the negative electrode active material of the lithium-ion battery includes, but is not limited to, carbon materials such as graphite, soft carbon (e.g., coke), and hard carbon, or nitrides, tin-based oxides, tin alloys, and nano-anode materials. The current collector includes, but is not limited to, any one of copper foil and aluminum foil.

[0130] In some embodiments, the steps for preparing the negative electrode sheet include: preparing a negative electrode mixed slurry by mixing the negative electrode active material with conductive agents such as conductive carbon black, binders such as carboxymethyl cellulose and styrene-butadiene rubber, and solvents such as water in a mass ratio of (80-99):(1-5):(2-10):100, degassing under vacuum, discharging the material, coating it on a coating machine, and obtaining the negative electrode sheet after rolling, slitting, and die-cutting.

[0131] In some embodiments, the membrane is capable of blocking electrons while allowing ions to pass through. Exemplary examples include, but are not limited to, at least one material selected from polypropylene fibers, polyacrylonitrile fibers, polyvinyl formal fibers, poly(ethylene glycol terephthalate), polyethylene terephthalate, polyamide fibers, and poly(p-phenylene terephthalamide).

[0132] In some embodiments, the electrolyte comprises at least one soluble metal salt. In some specific embodiments, the metal salt includes LiClO4, LiBF4, LiPF6, LiAsF6, LiCF3SO3, LiTDI, Li[(CF3SO2)2N], and Li[(FSO2)2N].

[0133] In some embodiments, a lithium-ion battery can be a rechargeable battery, which refers to a lithium-ion battery that can be recharged after discharge to activate the active materials and continue to be used. As an example, a lithium-ion battery includes at least one of a battery cell, a battery module, and a battery pack.

[0134] To enable those skilled in the art to clearly understand the above-described implementation details and operations of this application, and to demonstrate the significant improvement in the performance of the phosphate-based cathode material and its preparation method in the embodiments of this application, the above technical solutions are illustrated below through multiple embodiments.

[0135] Example 1

[0136] This embodiment provides a phosphate-based cathode material and its preparation method.

[0137] A phosphate-based cathode material includes several composite particles. Each composite particle comprises a lithium-containing phosphate core and a carbon shell coating the outer surface of the lithium-containing phosphate core. In the composite particles, the proportion of primary particles with a diameter of 20 nm to 50 nm is not less than 80%.

[0138] A method for preparing a phosphoric acid-based cathode material includes the following steps:

[0139] Step 1: Provide lithium source, iron source, carbon source (glucose), titanium source (tetrabutyl titanate) and iron-based dispersant ([Fe(en)3](NO3)3).

[0140] The lithium source includes a main lithium source and a modified lithium source with a mass ratio of 8:2. The main lithium source is lithium dihydrogen phosphate and the modified lithium source is lithium phosphate.

[0141] The iron source includes a main iron source and a modified iron source with a mass ratio of 8:2. The main iron source is ferrous oxalate, and the modified iron source is ferric oxide.

[0142] The molar ratio of iron in the iron source to phosphorus in the phosphorus source is Fe:P = 0.98:1; the molar ratio of lithium in the lithium source to iron in the iron source is Li:Fe = 1.06:1; the mass percentage of titanium in the titanium source relative to the theoretical yield of the phosphate-based cathode material is 0.8% (8000 ppm of titanium is added per kilogram of phosphate-based cathode material); the mass percentage of carbon source added relative to the theoretical yield of the phosphate-based cathode material is 19.14% (30.2 g of carbon source is added per kilogram of lithium-containing phosphate); and the mass percentage of iron-based dispersant added relative to the theoretical yield of the phosphate-based cathode material is 1%.

[0143] Step 2: Place the lithium source, iron source, carbon source, titanium source and iron-based dispersant in a sand mill, use zirconium balls with a diameter of 0.8 μm as the grinding medium, and use anhydrous ethanol and water with a volume ratio of 8:2 as the solvent for grinding treatment until the particle size is 350 nm. Then, spray dry the mixture with an inlet air temperature of 200 °C and an outlet air temperature of 90 °C to obtain the mixture.

[0144] Step 3: Place the mixture in a tube furnace and sinter under high-purity nitrogen protection. The sintering process includes a first sintering process, a second sintering process, and a third sintering process performed sequentially. First sintering process: heat to 200℃ at a heating rate of 3℃ / min and sinter for 1 hour; Second sintering process: heat to 400℃ at a heating rate of 2℃ / min and sinter for 2 hours; Third sintering process: heat to 650℃ at a heating rate of 3℃ / min and sinter for 4 hours. Finally, cool to room temperature to obtain the phosphate-based cathode material.

[0145] Example 2

[0146] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 1 is the amount of iron-based dispersant added, as detailed below:

[0147] The amount of iron-based dispersant added is 2% by mass relative to the theoretical yield of phosphoric acid-based cathode materials.

[0148] Example 3

[0149] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 1 is the lithium source, as detailed below:

[0150] The lithium source includes a main lithium source and a modified lithium source with a mass ratio of 8:2. The main lithium source is lithium dihydrogen phosphate and lithium phosphate with a mass ratio of 2:1, and the modified lithium source is lithium carbonate.

[0151] Example 4

[0152] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 1 is the iron source, as detailed below:

[0153] The iron source includes a main iron source and a modifying iron source with a mass ratio of 8:2. The main iron source is ferrous oxalate, and the modifying iron source is ferric phosphate.

[0154] Example 5

[0155] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 1 is the use of different lithium and iron sources, as detailed below:

[0156] The lithium source includes a main lithium source and a modified lithium source with a mass ratio of 9:1. The main lithium source is lithium dihydrogen phosphate, and the modified lithium source is lithium phosphate.

[0157] The iron source includes a main iron source and a modified iron source with a mass ratio of 9:1. The main iron source is ferrous oxalate, and the modified iron source is ferric oxide.

[0158] Example 6

[0159] This embodiment provides a phosphate-based cathode material and its preparation method.

[0160] A phosphate-based cathode material includes several composite particles. Each composite particle comprises a lithium-containing phosphate core and a carbon shell coating the outer surface of the lithium-containing phosphate core. In the composite particles, the proportion of primary particles with a diameter of 50 nm to 150 nm is not less than 80%.

[0161] A method for preparing a phosphoric acid-based cathode material includes the following steps:

[0162] Step 1: Provide lithium source, iron source, carbon source (glucose), titanium source (tetrabutyl titanate) and iron-based dispersant ([Fe(en)3](NO3)3).

[0163] The lithium source includes a main lithium source and a modified lithium source with a mass ratio of 8:2. The main lithium source is lithium dihydrogen phosphate and the modified lithium source is lithium phosphate.

[0164] The iron source includes a main iron source and a modified iron source with a mass ratio of 8:2. The main iron source is ferric oxide and the modified iron source is ferrous oxalate.

[0165] The molar ratio of iron in the iron source to phosphorus in the phosphorus source is Fe:P = 0.98:1; the molar ratio of lithium in the lithium source to iron in the iron source is Li:Fe = 1.05:1; the mass percentage of titanium in the titanium source relative to the theoretical yield of the phosphate-based cathode material is 0.8% (8000 ppm of titanium is added per kilogram of phosphate-based cathode material); the mass percentage of carbon source added relative to the theoretical yield of the phosphate-based cathode material is 19.14% (30.2 g of carbon source is added per kilogram of lithium-containing phosphate); and the mass percentage of iron-based dispersant added relative to the theoretical yield of the phosphate-based cathode material is 1%.

[0166] Step 2: Place the lithium source, iron source, carbon source, titanium source and iron-based dispersant in a sand mill, use zirconium balls with a diameter of 0.8 μm as the grinding medium, and use anhydrous ethanol and water with a volume ratio of 8:2 as the solvent for grinding treatment until the particle size is 350 nm. Then, spray dry the mixture with an inlet air temperature of 200 °C and an outlet air temperature of 90 °C to obtain the mixture.

[0167] Step 3: Place the mixture in a tube furnace and sinter under high-purity nitrogen protection. The sintering process includes a first sintering process, a second sintering process, and a third sintering process performed sequentially. First sintering process: heat to 180℃ at a heating rate of 3℃ / min and sinter for 1 hour; Second sintering process: heat to 500℃ at a heating rate of 2℃ / min and sinter for 2 hours; Third sintering process: heat to 700℃ at a heating rate of 2℃ / min and sinter for 6 hours. Finally, cool to room temperature to obtain the phosphate-based cathode material.

[0168] Example 7

[0169] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 6 is the amount of iron-based dispersant added, as detailed below:

[0170] The amount of iron-based dispersant added is 2% by mass relative to the theoretical yield of phosphoric acid-based cathode materials.

[0171] Example 8

[0172] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 6 is the lithium source, as detailed below:

[0173] The lithium source includes a main lithium source and a modified lithium source with a mass ratio of 8:2. The main lithium source is lithium dihydrogen phosphate and lithium phosphate with a mass ratio of 2:1, and the modified lithium source is lithium carbonate.

[0174] Example 9

[0175] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 6 is the iron source, as detailed below:

[0176] The iron source includes a main iron source and a modifying iron source with a mass ratio of 8:2. The main iron source is ferric oxide and the modifying iron source is iron phosphate.

[0177] Example 10

[0178] This embodiment provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 6 is the use of different lithium and iron sources, as detailed below:

[0179] The lithium source includes a main lithium source and a modified lithium source with a mass ratio of 9:1. The main lithium source is lithium dihydrogen phosphate, and the modified lithium source is lithium phosphate.

[0180] The iron source includes a main iron source and a modified iron source with a mass ratio of 9:1. The main iron source is ferric oxide and the modified iron source is ferrous oxalate.

[0181] Comparative Example 1

[0182] This comparative example provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 1 is that no iron-based dispersant was added.

[0183] Comparative Example 2

[0184] This comparative example provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 1 is the iron source, as detailed below:

[0185] The iron source includes a main iron source and a modified iron source with a mass ratio of 8:2. The main iron source is iron phosphate and the modified iron source is ferrous oxalate.

[0186] Comparative Example 3

[0187] This comparative example provides a phosphate-based cathode material and its preparation method. The only difference between this example and Example 6 is that no iron-based dispersant was added.

[0188] Comparative Example 4

[0189] This comparative example provides a phosphate-based cathode material and its preparation method. The only difference between this material and Example 6 is the iron source, as detailed below:

[0190] The iron source includes a main iron source and a modifying iron source with a mass ratio of 8:2. The main iron source is iron phosphate, and the modifying iron source is ferric oxide.

[0191] The physicochemical properties of the phosphate-based cathode materials prepared in the above embodiments and comparative examples are shown in Tables 1 and 2 below.

[0192] Table 1

[0193]

[0194] In Table 1: [20nm-50nm] indicates that the particle size of a primary particle satisfies the condition of being greater than or equal to 20nm and less than or equal to 50nm.

[0195] Table 2

[0196]

[0197]

[0198] In Table 2: [50nm-150nm] indicates that the particle size of a primary particle satisfies the condition of being greater than or equal to 50nm and less than or equal to 150nm.

[0199] As can be seen from Tables 1 and 2, the embodiments of this application control the average particle size of the primary particles by controlling the proportion of primary particle size, thereby obtaining a cathode material with reasonable particle size distribution. The smaller the particles of the cathode material, the higher the resistivity, but the resistivity of the embodiments of this application is much less than 100 Ω·cm, which does not affect the electrochemical performance of the cathode material.

[0200] This application embodiment effectively controls the nucleation and growth process of lithium phosphate by using specific lithium sources, specific iron sources and iron-based dispersants as reaction raw materials, so that the phosphate-based cathode material has a reasonable particle size distribution. For example, the average particle size of the phosphate-based cathode material is stabilized within a certain range, the particle size distribution is more concentrated and uniform, and a more compact stacking can be achieved during the electrode preparation process, thereby improving the energy density of the battery.

[0201] Methods for determining the average particle size of primary particles in phosphate-based cathode materials:

[0202] The phosphate-based cathode materials in each of the above embodiments were analyzed by scanning electron microscopy (SEM). The particle size characteristics of the phosphate-based cathode materials were measured based on the SEM images, and the average particle size of the primary particles in each embodiment was statistically calculated based on the SEM data. Simultaneously, the particle size of the primary particles was statistically analyzed, and the proportion of particles with a size ≤150 nm was calculated.

[0203] Figure 1 This is a SEM image of the phosphate-based cathode material provided in Example 1 of this application; Figure 2 SEM image of the phosphate-based cathode material provided in Comparative Example 1 of this application; Figure 3 This is a SEM image of the phosphate-based cathode material provided in Example 6 of this application; Figure 4 This is a SEM image of the phosphate-based cathode material provided in Comparative Example 3 of this application.

[0204] Depend on Figure 1 and Figure 2 contrast, Figure 1 The primary particles are relatively small, mainly concentrated around 40nm. Figure 2 The primary particles are relatively large, concentrated around 90-100 nm; Figure 3 and Figure 4 The comparison shows that Figure 3 The particles are evenly distributed with minimal adhesion. Figure 4 The particles are unevenly distributed and severely adhered.

[0205] Example of a lithium-ion battery:

[0206] The phosphate-based cathode materials prepared in the above embodiments and comparative examples are applied to lithium-ion batteries. The specific preparation steps are as follows:

[0207] Positive electrode sheet: Under the same conditions, positive electrode active material, SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) are mixed in a mass ratio of 95:2:3:100 and stirred in a closed mixer for 2 hours to obtain a uniform positive electrode slurry. The prepared positive electrode slurry is coated onto aluminum foil, evenly smoothed with a scraper, dried at 130°C, and then rolled to obtain a positive electrode sheet. The positive electrode active material is the phosphate-based positive electrode material provided in the above embodiment and the phosphate-based positive electrode material provided in the comparative example.

[0208] Negative electrode: Graphite negative electrode.

[0209] Electrolyte: 1.0 mol / L LiPF6 solution is used as the electrolyte. The solvent of the electrolyte is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1.

[0210] Separator: Celgard 2400 microporous membrane.

[0211] Lithium-ion battery assembly: The positive electrode, separator, electrolyte, and negative electrode are assembled into a button cell in an inert atmosphere glove box.

[0212] The coin cells containing the positive electrode materials provided in Examples 1-10 are respectively referred to as Examples S1-S10, and the coin cells containing the positive electrode materials provided in Comparative Examples 1-4 are referred to as Comparative Examples DS1-DS4.

[0213] Electrochemical performance testing:

[0214] (1) 0.1C discharge capacity

[0215] After the battery formation is completed, at room temperature of 25°C, the charge and discharge voltage window is controlled between 2.0 and 3.75V. The battery is charged at 0.1C (cutoff current 0.025C) and discharged at 0.1C to obtain a discharge capacity of 0.1C.

[0216] (2) 1C discharge capacity

[0217] After the battery formation is completed, at room temperature of 25°C, the charge and discharge voltage window is controlled between 2.0 and 3.75V. The battery is charged at 1C (cutoff current 0.025C) and discharged at 1C to obtain a 1C discharge capacity.

[0218] (3) Energy efficiency of 0.5p per 100 cycles

[0219] A. Charging Process

[0220] Charging: Charge at a constant current of 0.5C to 4.2V, then switch to constant voltage charging until the current is ≤0.05C, and let stand for 1 hour.

[0221] Stand still: Let stand for 2 hours at 25℃ to ensure the battery condition is stable.

[0222] B. Loop Testing Process

[0223] Number of cycles: 100 to 1000.

[0224] Single loop operation:

[0225] Discharge: Discharge at a constant current of 0.5C to 50% SOC (i.e., discharge from 100% SOC to 50% SOC).

[0226] Let stand: 10-30 minutes apart (to eliminate polarization effect).

[0227] Charging: Charge at a constant current of 0.5C to 100% SOC (cutoff voltage 4.2V), then switch to constant voltage charging until the current is ≤0.05C.

[0228] Let stand: Let stand for another 10 to 30 minutes, and record data such as voltage, temperature, and capacity.

[0229] The chemical test results are shown in Table 3 below.

[0230] Table 3

[0231]

[0232] As can be seen from Table 3:

[0233] Compared to comparative examples DS1-DS2, embodiments S1-S5 of this application exhibit significant advantages in electrochemical performance, specifically higher discharge capacity and better energy efficiency. Similarly, compared to comparative examples DS3-DS4, embodiments S6-S10 of this application also exhibit significant advantages in electrochemical performance, specifically higher discharge capacity and better energy efficiency.

[0234] Combining Example S1 and Comparative Example DS1, as well as Example S6 and Comparative Example DS3, it can be seen that by adding an iron-based dispersant, the particle size of the lithium phosphate primary particles can be effectively adjusted, thereby optimizing the particle size distribution of the phosphate cathode material and effectively improving the energy density and cycle performance of the battery.

[0235] Comparing the data from Example S1 and Comparative Example DS1, and Example S6 and Comparative Example DS3, it is evident that the introduction of iron-based dispersants significantly optimizes the performance of lithium phosphate cathode materials. In Comparative Examples DS1 and DS3 without iron-based dispersants, the primary particle size distribution of lithium phosphate is wide and the average particle size is relatively large. However, in Examples S1 and S6, after the addition of iron-based dispersants, the primary particle size is precisely controlled within a specific range, effectively shortening the lithium-ion diffusion path and thus improving the battery capacity and cycle performance.

[0236] By comparing the data of Example S1 with Comparative Example DS2, and Example S6 with Comparative Example DS4, it can be seen that selecting an iron source with a lower decomposition temperature or reduction temperature allows the iron source to participate in the formation of lithium phosphate under medium and low temperature conditions, thereby forming lithium phosphate with a reasonable particle size distribution. This significantly improves the stacking efficiency between particles, thereby improving its energy and cycle performance.

[0237] 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 phosphate-based cathode material, characterized in that, It includes several composite particles, wherein the composite particles include a lithium phosphate core and a carbon shell covering the outer surface of the lithium phosphate core; In the composite particles, the proportion of primary particles with a diameter of 150 nm or less is not less than 80%. The raw materials for the phosphate-based cathode material include a lithium source, an iron source, and an iron-based dispersant. The lithium source includes a main lithium source, the main lithium source having a mass ratio of not less than 80% in the total lithium source, and the main lithium source includes at least one of lithium dihydrogen phosphate and lithium phosphate. The iron source includes a main iron source, the main iron source accounts for no less than 80% of the mass of the iron source, and the main iron source includes at least one of ferrous oxalate and ferric oxide. The iron-based dispersant includes an iron-polyamine complex; the iron-based dispersant includes at least one of [Fe(en)3](NO3)3, [Fe(TEA)](NO3)3, [Fe(TETA)](NO3)3, and [Fe(EDTA)](NO3).

2. The phosphate-based cathode material as described in claim 1, characterized in that, In the composite particles, the proportion of primary particles with a diameter of 20nm-50nm is not less than 80%, and the main iron source is ferrous oxalate; or, In the composite particles, the proportion of primary particles with a particle size of 50nm-150nm is not less than 80%, and the main iron source is ferric oxide.

3. The phosphate-based cathode material as described in claim 1 or 2, characterized in that, The molecular formula of the lithium phosphate core is LiFe. 1-x M x PO4, wherein M includes at least one of Ti, Mg, Al, and V, 0 ≤ x ≤ 0.1; and / or, The phosphate-based cathode material has a spherical particle morphology; and / or, In the phosphate-based cathode material, the carbon shell layer accounts for 1%-10% of the total mass; and / or, The carbon shell includes the carbonization product of the organic ligand in the iron-polyamine complex; and / or The 0.1C discharge capacity of the phosphate-based cathode material is greater than or equal to 158 mAh / g; and / or, The phosphate-based cathode material has a 1C discharge capacity greater than or equal to 154 mAh / g.

4. A method for preparing a phosphate-based cathode material, characterized in that, Includes the following steps: According to the stoichiometric ratio in lithium phosphate, a raw material composition including a lithium source, an iron source, a phosphorus source and a doping source is obtained, wherein the lithium source includes a main lithium source, and the main lithium source includes at least one of lithium dihydrogen phosphate and lithium phosphate. The iron source includes a main iron source, and the main iron source includes at least one of ferrous oxalate and ferric oxide. The raw material components, carbon source, iron-based dispersant, and solvent are mixed to obtain a mixture; the iron-based dispersant includes at least one of [Fe(en)3](NO3)3, [Fe(TEA)](NO3)3, [Fe(TETA)](NO3)3, and [Fe(EDTA)](NO3); The mixture is sintered to form a phosphate-based cathode material containing a lithium phosphate core and a carbon shell covering the outer surface of the lithium phosphate core.

5. The method for preparing the phosphate-based cathode material as described in claim 4, characterized in that, The sintering includes a first sintering process, a second sintering process, and a third sintering process; The first sintering treatment is performed at 180℃-300℃ for 1h-2.5h, the second sintering treatment is performed at 400-600℃ for 2h-3h, and the third sintering treatment is performed at 600℃-750℃ for 3h-7h.

6. The method for preparing the phosphate-based cathode material as described in claim 5, characterized in that, When the main iron source is ferrous oxalate, the conditions for the first sintering treatment include sintering at 180℃-200℃ for 1h-2h at a heating rate of 1℃ / min-3℃ / min; the conditions for the second sintering treatment include sintering at 400-500℃ for 2h-3h at a heating rate of 2℃ / min-4℃ / min; and the conditions for the third sintering treatment include sintering at 600℃-680℃ for 3h-5h at a heating rate of 3℃ / min-5℃ / min. Alternatively, When the main iron source is ferric oxide, the conditions for the first sintering treatment include sintering at 200℃-300℃ for 1.5h-2.5h at a heating rate of 1℃ / min-3℃ / min, the conditions for the second sintering treatment include sintering at 500-600℃ for 2h-3h at a heating rate of 2℃ / min-4℃ / min, and the conditions for the third sintering treatment include sintering at 650℃-750℃ for 5h-7h at a heating rate of 2℃ / min-5℃ / min.

7. The method for preparing the phosphate-based cathode material as described in claim 4, characterized in that, The lithium source further includes a modified lithium source, which includes at least one of lithium carbonate, lithium hydroxide, and lithium phosphate, and the main lithium source is different from the modified lithium source; and / or, The main lithium source accounts for 80%-90% of the total lithium source by mass; and / or, The iron source further includes a modified iron source, which includes at least one of ferric phosphate, ferric oxide, and ferrous oxalate, and the main iron source is different from the modified iron source; and / or, The main iron source accounts for 80%-90% of the mass of the iron source; and / or, The doping source includes at least one of titanium, vanadium, magnesium, and aluminum sources.

8. The method for preparing the phosphate-based cathode material according to any one of claims 4 to 7, characterized in that, The mixing process includes sand milling, where the zirconium balls used in the sand milling have a size of 0.8 μm; and / or, The particle size of the mixture is 330nm-370nm; and / or, The mixing process also includes spray drying, wherein the inlet air temperature of the spray drying is 150℃-200℃ and the outlet air temperature is 60℃-100℃.

9. The method for preparing the phosphate-based cathode material according to any one of claims 4 to 7, characterized in that, The amount of the iron-based dispersant added is 0.5%-2% by mass relative to the theoretical yield of the phosphate-based cathode material; and / or, The amount of the dopant source added is 0.6%-1% by mass relative to the theoretical yield of the phosphate-based cathode material; and / or, The amount of carbon source added is 15%-25% by mass relative to the theoretical yield of the phosphate-based cathode material.

10. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode sheet includes the phosphate-based positive electrode material as described in any one of claims 1-3 or the phosphate-based positive electrode material prepared by the preparation method as described in any one of claims 4-9.

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