Phosphate positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a phosphate-based positive electrode material and a preparation method and application thereof.The phosphate-based positive electrode material has the characteristic of large and small particle grading and is prepared by at least mixing first phosphate-based semi-finished product particles and second phosphate-based semi-finished product particles, the D50 of the first phosphate series semi-finished product particles is smaller than that of the second phosphate series semi-finished product particles; the outer surface of the first phosphate-based semi-finished product particle is provided with a first carbon layer, the outer surface of the second phosphate-based semi-finished product particle is provided with a second carbon layer, and the mass ratio of the first carbon layer in the first phosphate-based semi-finished product particle is smaller than the mass ratio of the second carbon layer in the second phosphate-based semi-finished product particle. The phosphate positive electrode material is prepared by mixing the two semi-finished product particles with different particle sizes and different carbon contents, so that the compaction density of the phosphate positive electrode material can be remarkably improved, and the discharge capacity of the phosphate positive electrode material can be effectively improved.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium-ion batteries, and in particular relates to a phosphate-based positive electrode material and a preparation method and application thereof. Background Art

[0002] Among the positive electrode materials of lithium-ion batteries, lithium iron phosphate (LiFePO 4 ) has become one of the mainstream positive electrode materials because of its good thermal stability and safety. It also has the advantages of long cycle life, environmental protection and low cost.

[0003] Currently, lithium iron phosphate has been used in commercial batteries, but there are still some performance issues, such as low energy density of lithium iron phosphate materials and poor electronic and ionic conductivity, which limit the application of lithium iron phosphate in the next generation of lithium-ion batteries. Although nano-sizing and doping coating can be used to improve the electronic and ionic conductivity of lithium iron phosphate, the uniform and fine particles make the compaction density of lithium iron phosphate low, which directly leads to its poor volume energy density and is difficult to meet the energy density requirements of power batteries.

[0004] In terms of improving compaction density, the commonly used method at this stage is the grading method, that is, mixing particles of different sizes in a certain proportion to reduce the porosity generated when the material is piled up, so as to achieve the purpose of improving the compaction density. However, this method also has obvious defects. On the one hand, although the introduction of large particles is beneficial to the improvement of compaction density, it will have a negative impact on the electrochemical properties of the material, which is specifically manifested in the decline of discharge capacity, weakening of rate performance, and deterioration of low-temperature performance; on the other hand, even after grading treatment to form a finished mixture, it still faces the problem of difficult to ensure mixing uniformity. Once the mixing is uneven, it is easy to cause instability and inconsistency of material performance, which brings many uncertainties to subsequent applications. Summary of the invention

[0005] The purpose of the present application is to provide a phosphate-based positive electrode material and a preparation method and application thereof, aiming to increase the compaction density of the phosphate-based positive electrode material while making it have a higher discharge capacity.

[0006] In order to achieve the above application purpose, the technical solution adopted in this application is as follows:

[0007] In a first aspect, the present application provides a phosphate-based positive electrode material, which has the characteristics of large and small particle grading, and is prepared by mixing at least first phosphate-based semi-finished particles and second phosphate-based semi-finished particles, wherein the D50 of the first phosphate-based semi-finished particles is smaller than the D50 of the second phosphate-based semi-finished particles; the outer surface of the first phosphate-based semi-finished particles has a first carbon layer, and the outer surface of the second phosphate-based semi-finished particles has a second carbon layer, and the mass proportion of the first carbon layer in the first phosphate-based semi-finished particles is smaller than the mass proportion of the second carbon layer in the second phosphate-based semi-finished particles.

[0008] In a second aspect, the present application provides a method for preparing a phosphate-based positive electrode material, comprising the following steps:

[0009] Mixing raw materials including at least an iron source, a phosphorus source, a lithium source and a carbon source to obtain a precursor material;

[0010] The precursor material is divided into two parts, and a first sintering treatment and a second sintering treatment are respectively performed in an atmosphere containing a gaseous carbon material to obtain first phosphate-based semi-finished particles and second phosphate-based semi-finished particles of different particle sizes; wherein the sintering temperature of the first sintering treatment is lower than the sintering temperature of the second sintering treatment, and the rotation frequency of the first sintering treatment is higher than the rotation frequency of the second sintering treatment;

[0011] The first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles are mixed and calcined in an atmosphere containing a gaseous carbon material to obtain a phosphate-based positive electrode material.

[0012] In a third aspect, the present application provides a lithium-ion battery, comprising a negative electrode plate and a positive electrode plate, wherein the positive electrode plate comprises the phosphate-based positive electrode material provided in the first aspect and / or the phosphate-based positive electrode material prepared by the preparation method provided in the second aspect.

[0013] The phosphate-based positive electrode material provided in the first aspect of the present application has the characteristic of large and small particle gradation. In this way, the phosphate-based particles with smaller particle sizes are filled in the gaps between the phosphate-based particles with larger particle sizes, thereby effectively improving the compaction density of the phosphate-based positive electrode material; at the same time, since the phosphate-based positive electrode material is prepared by mixing at least the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles with different particle sizes, the first phosphate-based semi-finished particles with smaller particle sizes have a lower carbon content, which means that the first carbon layer is thinner, and the carbon layer of the corresponding positive electrode material particles formed is also relatively thin. During the charge and discharge process, the active ions can relatively easily penetrate the carbon layer to reach the surface of the core, providing a better transmission channel for the embedding and extraction of ions; the second phosphate-based semi-finished particles with larger particle sizes have a higher carbon content, and the carbon layer of the corresponding positive electrode material particles formed is also relatively thick, which can significantly improve its electronic conductivity, thereby accelerating the redox rate of the transition metal sites on the surface of the positive electrode material particles, and optimizing the embedding and extraction kinetics of lithium ions in the positive electrode material particles. Based on this, a phosphate-based positive electrode material is prepared by synergistically matching and mixing two phosphate-based semi-finished particles with different particle sizes and carbon contents. While significantly improving the compaction density of the phosphate-based positive electrode material, the diffusion channels of active ions in the entire phosphate-based positive electrode material are also optimized, so that the ions can move more efficiently inside the phosphate-based positive electrode material, thereby significantly improving the discharge capacity of the phosphate-based positive electrode material.

[0014] The preparation method of the phosphate-based positive electrode material provided in the second aspect of the present application is to divide the prepared solid-phase precursor material into two parts, and respectively sinter them in a gaseous carbon material atmosphere at different sintering temperatures and different rotation frequencies. At different sintering temperatures, the degree of adhesion growth between the sintered particles is different, and at different rotation frequencies, the speed of relative movement between the sintered particles is different, thereby adjusting the chance of adhesion growth between the sintered particles, and adjusting the carbon layer content on the surface of the sintered particles at the same time, thereby preparing primary sintered particles with different particle sizes and different carbon contents. After mixing the primary sintered particles with different particle sizes and different carbon contents, they are calcined in a gaseous carbon material atmosphere, so that the precursor material is converted into a uniform carbon-coated phosphate-based active material, and then effectively prepare the performance of the phosphate-based positive electrode material of the present application as described above. In addition, the preparation method of the phosphate-based positive electrode material of the present application is conducive to obtaining a phosphate-based positive electrode material with high compaction density and good electrochemical performance, and this method is simple in process and can be industrialized and mass-produced.

[0015] The lithium-ion battery provided in the third aspect of the present application comprises the phosphate-based positive electrode material of the present application, and the phosphate-based positive electrode material has a high compaction density. Therefore, the lithium-ion battery of the present application has a high energy density and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 This is a scanning electron microscope photograph of the phosphate-based positive electrode material provided in Example 1 of the present application;

[0018] Figure 2 This is a scanning electron microscope photograph of the phosphate-based positive electrode material provided in Comparative Example 5 of the present application;

[0019] Figure 3 This is a scanning electron microscope photograph of the phosphate-based positive electrode material provided in Comparative Example 6 of the present application. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0022] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0023] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and 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 the present application.

[0024] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0025] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0026] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0027] In this article, D50 particle size, i.e., the particle size value when the cumulative distribution percentage reaches 50%, is also called median diameter or median particle size.

[0028] In this article, the powder compaction density refers to the mass of the phosphate cathode material per unit volume after compaction under a pressure of 3 T. The powder compaction density can be measured by any known means, and the powder compaction density method of GB / T 24533-2009 can be referred to.

[0029] According to a first aspect of an embodiment of the present application, there is provided a phosphate-based positive electrode material, which has the characteristics of large and small particle grading, and is prepared by mixing at least first phosphate-based semi-finished particles and second phosphate-based semi-finished particles, wherein the D50 of the first phosphate-based semi-finished particles is smaller than the D50 of the second phosphate-based semi-finished particles; the outer surface of the first phosphate-based semi-finished particles has a first carbon layer, and the outer surface of the second phosphate-based semi-finished particles has a second carbon layer, and the mass proportion of the first carbon layer in the first phosphate-based semi-finished particles is smaller than the mass proportion of the second carbon layer in the second phosphate-based semi-finished particles.

[0030] In the technical solution of the present application, the phosphate-based positive electrode material has the characteristic of large and small particle grading, which allows the phosphate-based particles with smaller particle sizes to fill the gaps between the phosphate-based particles with larger particle sizes, thereby effectively improving the compaction density of the phosphate-based positive electrode material.

[0031] The phosphate-based positive electrode material is prepared by mixing the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles, wherein the first phosphate-based semi-finished particles with a smaller particle size have a lower carbon content, which means that the first carbon layer is thinner, and the carbon layer of the corresponding positive electrode material particles is also relatively thin. During the charge and discharge process, active ions can more easily penetrate the first carbon layer to reach the surface of the core, providing a better transmission channel for the embedding and extraction of ions. The second phosphate-based semi-finished particles with a larger particle size have a higher carbon content, and the carbon layer of the corresponding positive electrode material particles is also relatively thick, which can significantly improve their electronic conductivity, thereby accelerating the redox rate of the transition metal sites on the surface of the positive electrode material particles and optimizing the kinetics of lithium ion embedding and extraction in the positive electrode material particles.

[0032] Therefore, the particles of the phosphate semi-finished particles with different carbon contents cooperate with each other. The semi-finished particles with small particle size provide a channel for quickly reaching the nucleus, and the semi-finished particles with large particle size have higher lithium ion deintercalation kinetics. This synergistic effect enables ions to move more efficiently inside the lithium iron phosphate material, thereby improving the utilization rate of the active substances and ultimately increasing the discharge capacity of the battery.

[0033] Based on this, the phosphate positive electrode material is prepared by the coordinated combination of two phosphate-based semi-finished particles with different particle sizes and carbon contents. While significantly improving the compaction density of the phosphate-based positive electrode material, the diffusion channels of the active ions in the entire phosphate-based positive electrode material are also optimized, so that the ions can move more efficiently inside the phosphate-based positive electrode material, thereby significantly improving the discharge capacity of the phosphate-based positive electrode material.

[0034] In some embodiments, the mass proportion of the first carbon layer in the first phosphate-based semi-finished particle is 0.2%-0.35% less than the mass proportion of the second carbon layer in the second phosphate-based semi-finished particle. This means that the difference between the mass proportion of the second carbon layer in the second phosphate-based semi-finished particle and the mass proportion of the first carbon layer in the first phosphate-based semi-finished particle is 0.2%-0.35%. Exemplarily, the difference between the mass proportion of the second carbon layer in the second phosphate-based semi-finished particle and the mass proportion of the first carbon layer in the first phosphate-based semi-finished particle can be 0.2%, 0.25%, 0.28%, 0.3%, 0.35%, etc., which are typical but non-limiting values.

[0035] When the carbon layer content is low, its thickness is relatively thin, which can reduce the path length and obstacles of electron transmission, allowing electrons to be transmitted more quickly between particles; and the thinner carbon coating allows lithium ions to pass through the carbon layer interface more easily, thereby increasing the rate of lithium ion insertion and extraction, which helps to increase the diffusion rate of lithium ions; when the carbon layer content is high, it can significantly increase its electronic conductivity, thereby accelerating the redox rate of transition metal sites on the surface of the positive electrode material particles and optimizing the kinetics of lithium ion extraction and insertion in the positive electrode material particles. Therefore, the absolute value of the difference in carbon layer content optimizes the ion transmission rate of the positive electrode material particles to a certain extent, allowing ions to move more efficiently inside the phosphate-based positive electrode material, thereby significantly improving the discharge capacity of the phosphate-based positive electrode material.

[0036] In some embodiments, the mass proportion of the first carbon layer in the first phosphate-based semi-finished particle is 0.8-1.0%wt, and the mass proportion of the second carbon layer in the second phosphate-based semi-finished particle is 1.1-1.3%wt. Exemplarily, the mass proportion of the first carbon layer in the first phosphate-based semi-finished particle can be 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, etc., which are typical but non-limiting values. Exemplarily, the mass proportion of the second carbon layer in the second phosphate-based semi-finished particle can be 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, etc., which are typical but non-limiting values.

[0037] The content of the first carbon layer is within the above range, which can effectively improve the electronic conductivity of the phosphate-based positive electrode material, and can build an effective conductive network between the positive electrode material particles, so that electrons can be transmitted more quickly within the positive electrode material, thereby reducing the polarization of the electrode, improving the battery's charge and discharge efficiency and rate performance, and enabling the phosphate-based positive electrode material to have a higher gram capacity.

[0038] The content of the second carbon layer is within the above range, which can significantly enhance the conductivity of the phosphate-based positive electrode material, allowing electrons to be transmitted more quickly within the positive electrode material, and enhance the ability of ion migration, thereby activating more active sites, which helps to promote the phosphate-based positive electrode material to have a higher gram capacity.

[0039] In some embodiments, the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles are the same lithium-containing phosphate.

[0040] Since the core materials are the same, that is, the types and contents of the main elements and doping elements in the core are the same, during the charge and discharge process, the performance change trends of the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles are basically consistent, making the electrochemical properties of the battery such as voltage and capacity more stable during the cycle use, thereby improving the overall reliability and consistency of the battery.

[0041] Exemplarily, the lithium-containing phosphate includes, but is not limited to, at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium manganese phosphate, lithium titanium iron phosphate, lithium magnesium iron phosphate, lithium vanadium phosphate, and lithium nickel phosphate.

[0042] Phosphate-based positive electrode materials containing lithium phosphate as the core have abundant lithium ion storage sites, can provide higher specific capacity, and have good chemical stability. They can still maintain good structural stability after multiple charge and discharge cycles, thereby improving the cycle performance and reliability of the battery.

[0043] In some embodiments, the particle size D50 of the phosphate-based cathode material is 0.8-1.2 μm. For example, the particle size D50 of the phosphate-based cathode material can be 0.8 μm, 0.85 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, and other typical but non-limiting values.

[0044] Within the above range, the contact area between the phosphate-based positive electrode material particles is moderate, which can generate strong interaction forces such as van der Waals force and electrostatic force, so that the particles are more closely combined together, thereby increasing the compaction density.

[0045] In some embodiments, when the phosphate-based cathode material is lithium iron phosphate, the powder compaction density of the phosphate-based cathode material is 2.55 g / cm 3 -2.7g / cm 3 For example, the compacted density of the phosphate cathode material powder can be 2.55 g / cm 3 , 2.6g / cm 3 , 2.62g / cm 3 , 2.65g / cm 3 , 2.68g / cm 3 etc. are typical but not limiting values.

[0046] In lithium-ion batteries, the higher the compaction density, the more active materials can be packed into the same volume of electrode, thus increasing the energy density of the battery. Therefore, when the compaction density of the phosphate cathode material powder is controlled within the above range, the battery can store more electrical energy in a limited space, improve the battery's endurance and output power, and meet application scenarios with higher energy density requirements.

[0047] The higher powder compaction density makes the contact between the positive electrode material particles closer, reduces the gaps and contact resistance between the particles, and thus reduces the internal resistance of the battery. The reduction of internal resistance is conducive to improving the charge and discharge efficiency and rate performance of the battery. At the same time, the tightly compacted material structure helps to enhance the structural stability of the phosphate-based positive electrode material during the charge and discharge process, reduce the shedding and pulverization of active substances, and thus improve the cycle life of the battery.

[0048] A second aspect of the present application provides a method for preparing a phosphate-based positive electrode material, comprising the following steps:

[0049] Step S10, mixing raw materials including at least an iron source, a phosphorus source, a lithium source and a carbon source to obtain a precursor material;

[0050] Step S20, dividing the precursor material into two parts, performing a first sintering treatment and a second sintering treatment in an atmosphere containing a gaseous carbon material, respectively, to obtain first phosphate-based semi-finished particles and second phosphate-based semi-finished particles of different particle sizes, respectively; wherein the sintering temperature of the first sintering treatment is lower than the sintering temperature of the second sintering treatment, and the rotation frequency of the first sintering treatment is higher than the rotation frequency of the second sintering treatment;

[0051] Step S30: Mix the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles, and perform calcination treatment in an atmosphere containing a gaseous carbon material to obtain a phosphate-based positive electrode material.

[0052] The preparation method of the phosphate-based positive electrode material provided in the second aspect of the embodiment of the present application is to divide the prepared solid-phase precursor material into two parts, and respectively sinter the solid-phase precursor material in a gaseous carbon material atmosphere at different sintering temperatures and different rotation frequencies. At different sintering temperatures, the degree of adhesion growth between the sintered particles is different, and at different rotation frequencies, the relative movement speed between the sintered particles is different, thereby adjusting the chance of adhesion growth between the sintered particles, and adjusting the carbon layer content on the surface of the sintered particles at the same time, thereby preparing primary sintered particles with different particle sizes and different carbon contents. After mixing the primary sintered particles with different particle sizes and different carbon contents, they are calcined in a gaseous carbon material atmosphere, so that the precursor material is converted into a uniform carbon-coated phosphate-based active material, and then effectively prepare the performance of the phosphate-based positive electrode material of the present application as described above. In addition, the preparation method of the phosphate-based positive electrode material of the present application is conducive to obtaining a phosphate-based positive electrode material with high compaction density and good electrochemical performance, and this method is simple in process and can be industrialized and mass-produced.

[0053] In some embodiments, in step S10, the precursor material can be prepared by a liquid phase method, a solid phase method, or a gel method well known in the art.

[0054] As an example, the specific process of preparing the precursor material by liquid phase method is as follows:

[0055] Step S11, adding an iron source, a phosphorus source and a lithium source into a solvent, and heat treating at 60° C.-90° C. until each component is fully dissolved, to obtain a mixed solution A;

[0056] Step S12, adding a doping source and a carbon source to the mixed solution A, and after fully dissolving, heating and stirring at 120° C.-140° C. for 3 h-5 h until evaporated to dryness and then crushed to obtain a precursor material.

[0057] Specifically, in step S11, the iron source includes a soluble iron salt. Exemplarily, the iron source includes but is not limited to at least one of ferric nitrate, ferric nitrite, ferric sulfate, ferric chloride, ferric bromide and ferric oxalate.

[0058] Specifically, in step S11, the phosphorus source includes a soluble phosphorus salt and / or phosphoric acid. Exemplarily, the phosphorus source includes but is not limited to at least one of phosphoric acid, monoammonium hydrogen phosphate, diammonium phosphate, ammonium phosphate, ammonium polyphosphate, ammonium hexafluorophosphate, and pyrophosphoric acid.

[0059] Specifically, in step S11, the lithium source includes a soluble lithium salt. Exemplarily, the lithium source includes but is not limited to at least one of lithium chloride, lithium acetate, lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide, lithium nitrate, lithium formate, lithium silicate, lithium sulfate, lithium phosphate, lithium oxalate, lithium octanoate, lithium citrate, lithium salicylate, lithium orthosilicate, lithium permanganate, lithium trifluoroacetate, lithium acetoacetate, lithium difluorophosphate, lithium hexafluorophosphate, lithium benzoate, lithium metaphosphate, lithium pyruvate, lithium fluoride, lithium bromide, lithium methoxide, lithium ethoxide, lithium oxide, lithium nitride, and lithium sulfide.

[0060] Specifically, in step S11, the solvent includes but is not limited to at least one of deionized water, ethanol, isopropanol, and acetone. These solvents have good solubility and dispersibility for raw material components such as carbon source, phosphorus source, iron source, and lithium source, which is conducive to uniform dispersion of each raw material component and subsequent formation of a uniformly mixed precursor material.

[0061] Specifically, in step S12, the carbon source includes but is not limited to at least one of glucose, fructose, sucrose, starch, citric acid, lactic acid, oxalic acid, tannic acid, ascorbic acid, polyvinyl alcohol, and polyethylene glycol. These carbon sources can be converted into carbon materials such as amorphous carbon at high temperature during the subsequent sintering process, and coated on the surface of the phosphate-based positive electrode material to form a carbon layer, thereby improving the stability and electrochemical performance of the phosphate-based positive electrode material.

[0062] Specifically, in step S12, the crushing equipment used for crushing includes but is not limited to at least one of a jet mill, a sand mill and a ball mill.

[0063] In some embodiments, in step S10, the molar ratio of iron, phosphorus and lithium in the raw material is Fe:P:Li=(0.97-1.02):(1.00-1.04):(1.02-1.05); or, the raw material also includes a manganese source, and the molar ratio of manganese, iron, phosphorus and lithium in the raw material is (Fe+Mn):P:Li=(0.97-1.02):(0.98-1.04):(0.98-1.05).

[0064] By obtaining the iron source, phosphorus source and lithium source according to the above-mentioned stoichiometric ratio, phosphate-based positive electrode materials can be obtained. These phosphate-based positive electrode materials have abundant lithium ion storage sites and can provide higher specific capacity.

[0065] In some embodiments, in step S10, the carbon source accounts for 10%-20% of the total weight of the raw material. Exemplarily, the mass proportion of the carbon source can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., which are typical but non-limiting values.

[0066] The amount of carbon source added is controlled within the above range so that the carbon source can form carbon material to coat the surface of the phosphate semi-finished product particles during the sintering process, thereby improving the electronic conductivity of the phosphate positive electrode material.

[0067] In some embodiments, in step S10, the raw material further includes a doping source, and the molar ratio of the doping element in the doping source to the iron element in the raw material is (0.005-0.008): 1. Exemplarily, the molar ratio of the doping element to the iron element can be 0.005: 1, 0.006: 1, 0.007: 1, 0.008: 1, and other typical but non-limiting values.

[0068] By controlling the content of the doping source within the above range, that is, introducing an appropriate amount of doping elements into the phosphate-based positive electrode material, the conductivity and structural stability of the phosphate-based positive electrode material can be effectively improved, thereby significantly improving its electronic conductivity, lithium ion migration rate, structural stability, etc.

[0069] Specifically, the doping source includes at least one of a magnesium source, a titanium source, a vanadium source, and a nickel source. The doping source includes a soluble salt corresponding to the doping element, including but not limited to at least one of chloride, oxalate, carbonate, nitrate, sulfate, and acetate.

[0070] Exemplarily, the magnesium source includes, but is not limited to, at least one of magnesium nitrate, magnesium chloride, and magnesium oxalate.

[0071] Exemplarily, the titanium source includes, but is not limited to, at least one of titanium tetrachloride, tetrabutyl titanate, and ammonium titanium oxalate.

[0072] In some embodiments, in step S20, the conditions of the first sintering treatment include: a sintering temperature of 400°C-500°C, a rotation frequency of 2.5rpm-4rpm, and a gas flow rate of the gaseous carbon material atmosphere of 0.8-1.2L / min. Exemplarily, the sintering temperature can be 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, and other typical but non-limiting values. The rotation frequency can be 2.5rpm, 3rpm, 3.5rpm, 4rpm, and other typical but non-limiting values. The gas flow rate of the gaseous carbon material atmosphere can be 0.8L / min, 0.9L / min, 1L / min, 1.1L / min, 1.2L / min, and other typical but non-limiting values.

[0073] In the first sintering process, a lower temperature is selected for sintering, and the specific range of the sintering temperature is as described above, which makes the thermal motion energy of atoms or molecules on the surface of the primary sintered particles lower, and thus, the driving force for mutual diffusion and adhesion growth between the primary sintered particles is also smaller, so that the primary sintered particles can maintain a relatively independent state, reducing the phenomenon of adhesion growth between particles, which is conducive to retaining the number of small particles. Therefore, controlling the sintering temperature in the first sintering process within the above range can effectively reduce the adhesion growth between the primary sintered particles, thereby obtaining the first phosphate-based semi-finished particles with a smaller particle size.

[0074] During the first sintering process, a higher rotation frequency is selected, and the specific range of the rotation frequency is as described above. At this time, the first sintered particles are in a state of relative movement, and the degree of relative movement is relatively high. This relative movement makes it difficult for the first sintered particles to maintain contact for a long time, and they are easy to separate quickly after colliding with each other. This rapid relative movement does not allow enough time for material diffusion and adhesion growth between the first sintered particles, thereby reducing the chance of adhesion growth between particles. In this way, the number of small particles is retained, and the first phosphate-based semi-finished particles with a smaller particle size are obtained.

[0075] Since the first sintering treatment is carried out in an atmosphere containing gaseous carbon material, that is, the gaseous carbon material forms a carbon layer through vapor deposition during the sintering process, choosing a shorter sintering time means that the vapor deposition time is shorter. The carbon atoms generated by the decomposition of the gaseous carbon material have a limited deposition time on the surface of the lithium phosphate core, and a thinner carbon layer is easily formed, that is, the carbon content on the surface of the first phosphate-based semi-finished product particles is lower.

[0076] During the first sintering process, since the sintering is carried out in an atmosphere containing gaseous carbon material, that is, the gaseous carbon material can form a carbon layer on the surface of the lithium phosphate core through chemical vapor deposition (CVD) during the sintering process, and an appropriate rotation frequency is set during the first sintering process, that is, the material is rotated during the vapor deposition process, as the rotation continues, each particle can obtain the same coating opportunity at different times, so that the distribution of the deposited carbon layer coating in the entire material is more uniform, thereby reducing the difference in carbon coating and obtaining a more uniform carbon layer, thereby improving the conductivity and stability of the phosphate-based positive electrode material.

[0077] In some embodiments, in step S20, the conditions of the second sintering treatment include: a sintering temperature of 600°C-700°C, a rotation frequency of 1rpm-1.5rpm, and a gas flow rate of the gaseous carbon material atmosphere of 1.5-2.5L / min. Exemplarily, the sintering temperature can be 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, and other typical but non-limiting values. The rotation frequency can be 1rpm, 1.1rpm, 1.2rpm, 1.3rpm, 1.4rpm, 1.5rpm, and other typical but non-limiting values. The gas flow rate of the gaseous carbon material atmosphere can be 1.5L / min, 1.8L / min, 2L / min, 2.2L / min, 2.5L / min, and other typical but non-limiting values.

[0078] In the second sintering process, a higher temperature is selected for sintering. The specific range of the sintering temperature is as described above. A higher sintering temperature can provide more energy, so that the atoms on the surface of the once sintered particles have enough energy to cross the interface between the particles, diffuse with each other at the contact points and form new chemical bonds, thereby promoting the adhesion growth between the particles. This adhesion growth will cause small particles to gradually merge into large particles, thereby obtaining a second phosphate-based semi-finished particle with a larger particle size.

[0079] During the second sintering process, a lower rotation frequency is selected. The specific range of the rotation frequency is as described above. By using a lower rotation frequency, the relative movement between the particles of the first sintering becomes slow. In this way, after the particles come into contact, the relatively static state is conducive to the diffusion of atoms at the contact points, thereby increasing the chances of adhesion and growth. At the same time, since the material is flipped during the sintering process, the contact between the particles is more uniform, so that the growth of the particles is more uniform, and it is not easy for some particles to continue to adhere to form oversized particles, thereby obtaining larger and uniform second phosphate-based semi-finished particles, which is beneficial to improving the discharge capacity of the phosphate-based positive electrode material.

[0080] During the second sintering process, since the sintering is carried out in an atmosphere containing gaseous carbon material, that is, the gaseous carbon material can form a carbon layer on the surface of the lithium phosphate core through vapor deposition during the sintering process, and an appropriate rotation frequency is set during the second sintering process, that is, the material is rotated during the vapor deposition process, this dynamic process allows each surface of each particle to contact the gaseous carbon material more evenly, thereby making the carbon coating more uniform, reducing the difference in the carbon coating layer at different positions, and making the growth of the particles more balanced, thereby obtaining a second phosphate-based semi-finished particle with a continuous and uniform carbon layer.

[0081] Based on this, through the second sintering treatment, a second phosphate-based semi-finished particle with a large particle size, good particle size distribution uniformity and a continuous and uniform carbon layer can be obtained, which is beneficial to improving the electrochemical reaction activity of the phosphate-based positive electrode material, thereby improving its discharge capacity.

[0082] In some embodiments, in step S20, the sintering time of the first sintering process is lower than the sintering time of the second sintering process.

[0083] During the first sintering process, a shorter sintering time is selected, which means that there is not enough time for sufficient material exchange and fusion between particles, and the atomic diffusion distance is limited, so it is difficult for the particles to grow, which is conducive to obtaining smaller-sized first phosphate semi-finished particles.

[0084] In the second sintering process, a longer sintering time is selected, which provides sufficient time for the diffusion and migration of substances between particles, so that small particles are continuously fused together, thereby increasing the particle size, which is conducive to obtaining the second phosphate-based semi-finished particles with relatively large particle sizes. Moreover, the selection of a longer sintering time means that the time of the first sintered particles in the gaseous carbon material is increased, which allows more gaseous carbon materials to have enough time to decompose and deposit carbon atoms on the surface of the lithium-containing phosphate core, and it is easy to form a thicker carbon layer, that is, the carbon content on the surface of the second phosphate-based semi-finished particles is higher.

[0085] In some embodiments, in step S20, the sintering time of the first sintering process is 4 hours to 6 hours. For example, the first sintering time can be 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, and other typical but non-limiting values.

[0086] In some embodiments, in step S20, the sintering time of the second sintering process is 8 hours to 10 hours. For example, the second sintering time can be 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, and other typical but non-limiting values.

[0087] In some embodiments, in step S20, the sintering furnace used in the first sintering process and the second sintering process is a sintering device with a material turning function and capable of controlling the turning frequency or speed, such as a rotary kiln, a large sintering cup, etc.

[0088] In some embodiments, in step S20, the D50 particle size of the first phosphate-based semi-finished particles is 0.35 μm-0.55 μm, and the D50 particle size of the second phosphate-based semi-finished particles is 0.8 μm-1.2 μm. Exemplarily, the D50 particle size of the first phosphate-based semi-finished particles can be 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, etc., which are typical but non-limiting values. The D50 particle size of the second phosphate-based semi-finished particles can be 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.1 μm, 1.2 μm, etc., which are typical but non-limiting values.

[0089] By using primary particles of different particle sizes and mixing them in a reasonable ratio, the first phosphate-based semi-finished product particles with smaller particle sizes can be filled in the gaps between the second phosphate-based semi-finished product particles with larger particle sizes. In this way, after calcining the primary sintered particles, a phosphate-based positive electrode material with dense packing, low porosity, and large and small particle grading can be obtained, thereby effectively improving the powder compaction density of the phosphate-based positive electrode material.

[0090] In some embodiments, in step S30, the content of the first phosphate-based semi-finished particles is 45%-70%, based on the total weight of the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles as 100%. The content of the second phosphate-based semi-finished particles is 30%-55%. Exemplarily, the content of the first phosphate-based semi-finished particles can be 45%, 50%, 55%, 60%, 65%, 70%, etc., which are typical but non-limiting values; the content of the second phosphate-based semi-finished particles can be 30%, 35%, 40%, 45%, 50%, 55%, etc., which are typical but non-limiting values.

[0091] In this case, a gradation can be formed by the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles of different particle sizes, and a phosphate-based positive electrode material with a particle coordinated particle gradation can be obtained through subsequent calcination treatment. Among them, the positive electrode material particles with smaller particle sizes can be embedded in the pores between the positive electrode material particles with larger particle sizes, thereby increasing the compaction density of the phosphate-based positive electrode material. However, considering that excessively increasing the proportion of large particles will lead to a decrease in the capacity of the positive electrode material, the present application controls the content ratio of the first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles within the above range, so that the prepared positive electrode material particles with smaller particle sizes can fully fill the voids of the positive electrode material particles with larger particle sizes, thereby increasing the compaction density, and the capacity of the phosphate-based positive electrode material will not be too low due to the excessive proportion of large particles, thereby achieving a good balance between compaction density and capacity.

[0092] In some embodiments, in step S30, the conditions of the calcination treatment include: a calcination temperature of 760°C-820°C, a rotation frequency of 2rpm-3rpm; and a gas flow rate of the gaseous carbon material atmosphere of 0.6-1L / min. Exemplarily, the calcination temperature can be 760°C, 780°C, 800°C, 820°C, and other typical but non-limiting values, the rotation frequency can be 2.1rpm, 2.2rpm, 2.3rpm, 2.4rpm, 2.5rpm, 2.6rpm, 2.7rpm, 2.8rpm, 2.9rpm, 3rpm, and other typical but non-limiting values, and the gas flow rate of the gaseous carbon material atmosphere can be 0.6L / min, 0.7L / min, 0.8L / min, 0.9L / min, 1L / min, and other typical but non-limiting values.

[0093] The first phosphate series semi-finished particles with different particle sizes and carbon contents are mixed with the second phosphate series semi-finished particles and calcined. During the calcination process, due to the high temperature, the primary particles soften and flow to a certain extent, so that the first phosphate series semi-finished particles with smaller particle sizes can move and redistribute more easily in the gaps between the second phosphate series semi-finished particles with larger particle sizes. At the same time, as the calcination process proceeds, the first phosphate series semi-finished particles with smaller particle sizes continuously optimize the filling position, making the stacking of the entire material system more compact and orderly, thereby improving the material grading effect, making the stacking density of the entire system higher, and thus improving the discharge capacity.

[0094] In addition, under high-temperature calcination environment, the thermal motion of atoms intensifies, and the atoms on the surface of the calcined particles diffuse with each other, making the boundaries between particles of different sizes gradually blurred. This not only helps the adhesion of particles, but also makes the combination between large and small particles tighter and more uniform.

[0095] The calcination treatment is carried out in an atmosphere containing gaseous carbon materials, that is, in the process of vapor deposition, it mainly depends on the contact between the gaseous carbon materials and the particle surface. Therefore, by setting an appropriate rotation frequency, that is, utilizing the material flipping, the blind area of ​​vapor deposition is reduced, thereby achieving uniform carbon coating; moreover, on the basis of the carbon source already premixed in the precursor material and the initial formation of carbon through sintering treatment, vapor deposition further supplements the carbon source to fill the tiny defects and gaps in the pre-deposited carbon material, so that the carbon layer on the surface of the lithium phosphate core body is more continuous, complete and uniform.

[0096] In some embodiments, the calcination time of the calcination treatment is 6 hours to 10 hours. For example, the calcination time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, and other typical but non-limiting values.

[0097] In some embodiments, the gaseous carbon material in the gaseous carbon material-containing atmosphere includes at least one of methane, ethane, propane, and ethylene.

[0098] In some embodiments, the gaseous carbon material-containing atmosphere further includes a protective gas.

[0099] Exemplarily, the protective gas includes at least one of nitrogen, argon, and helium.

[0100] In the atmosphere containing the gaseous carbon material, the protective gas is used as a carrier gas to bring the gaseous carbon material into the sintering device. In some embodiments, the gaseous carbon material can be diluted by the carrier gas and brought into the sintering device. At the same time, these protective gases can provide a protective atmosphere for the sintering process and the calcining process to prevent the raw material components from being oxidized under high temperature sintering conditions.

[0101] Controlling the volume ratio of the gaseous carbon material and the protective gas within the above range can not only provide sufficient carbon source to form a uniform, complete and continuous carbon layer, but also maintain a good reaction environment so that the deposited carbon layer has a higher purity.

[0102] A third aspect of an embodiment of the present application provides a lithium-ion battery, comprising a negative electrode plate and a positive electrode plate, wherein the positive electrode plate comprises the phosphate-based positive electrode material provided in the first aspect and / or the phosphate-based positive electrode material prepared by the preparation method provided in the second aspect.

[0103] The secondary battery provided in the third aspect of the embodiment of the present application contains the phosphate-based positive electrode material of the present application, and the phosphate-based positive electrode material has a high compaction density. Therefore, the lithium-ion battery of the present application has a high energy density and cycle performance.

[0104] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active layer includes the phosphate-based positive electrode material described in any of the above embodiments. In one embodiment of the present application, the positive electrode 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 the present application, the positive electrode current collector can be aluminum foil.

[0105] In some embodiments, in the positive electrode active layer, the mass percentage of the phosphate-based positive electrode material is 70%-95%, which can improve the charge-discharge specific capacity and cycle life of the positive electrode sheet. Specifically, the mass percentage of the phosphate-based positive electrode material can be 70%, 73%, 75%, 80%, 85%, 88%, 90%, 95% and other typical but non-limiting values. In one embodiment of the present application, the mass percentage of the phosphate-based positive electrode material can be 75%-86%. In another embodiment of the present application, the mass percentage of the phosphate-based positive electrode material can be 80%-95%.

[0106] In some embodiments, the positive electrode active layer may further include a binder, which may improve the binding ability of the components in the positive electrode active layer and improve the binding ability between the positive electrode active layer and the positive electrode current collector. Specifically, the binder may be a commonly used electrode binder, such as but not limited to polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and one or more of chitosan derivatives.

[0107] In some embodiments, the positive electrode active layer may further include a conductive agent, which can increase the conductivity of the phosphate-based positive electrode material and improve the electronic conductivity. Specifically, the conductive agent may include, but is not limited to, at least one of graphite, carbon black, acetylene black, carbon fiber, carbon nanotubes, and graphene.

[0108] In some embodiments, the preparation process of the positive electrode plate can be: mixing the positive electrode active material, the conductive agent and the binder to obtain an electrode slurry, coating the electrode slurry on the positive electrode collector, and preparing the positive electrode plate through drying, rolling, die cutting and other steps, wherein the positive electrode active material includes the phosphate-based positive electrode material of the present application.

[0109] In some embodiments, the negative electrode plate includes a positive electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active layer includes a negative electrode active material. Specifically, the negative electrode current collector may be, but is not limited to, at least one of copper, aluminum, nickel, and stainless steel; the negative electrode active material may be, but is not limited to, at least one of graphite, soft carbon, hard carbon, lithium metal, nitride, and tin metal.

[0110] The following uses a number of specific embodiments to illustrate the phosphate-based positive electrode material, preparation method, and application of the present application.

[0111] Example 1

[0112] A method for preparing a phosphate-based positive electrode material comprises the following steps:

[0113] Step 1, weigh ferric nitrate, ammonium dihydrogen phosphate, and lithium nitrate in a molar ratio of 0.98:1.00:1.02 among iron atoms, phosphorus atoms, and lithium atoms, mix, add 200% by weight of deionized water, heat to 90° C. to fully dissolve, and obtain a mixed solution A.

[0114] Step 2: Add tetrabutyl titanate and glucose to mixed solution A, heat and stir at 90° C. to obtain mixed solution B, then heat and stir mixed solution B at 120° C. for 3 hours, and evaporate to obtain a precursor material, wherein, based on the total mass of ferric nitrate, ammonium monohydrogen phosphate and lithium nitrate, the mass proportion of tetrabutyl titanate is 3%, and the mass proportion of glucose is 10%.

[0115] Step 3, breaking the precursor material into two parts;

[0116] A portion of the precursor material is placed in a rotary kiln for a first sintering treatment, specifically, in an atmosphere of nitrogen and methane, at a rotation frequency of 4 rpm and a sintering temperature of 400° C. for 4 hours, and after the material is cooled, it is crushed to obtain a first phosphate-based semi-finished particle, wherein methane and nitrogen are mixed and introduced into the rotary kiln at a gas flow rate of 0.8 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9;

[0117] Another portion of the precursor material is placed in a rotary kiln for a second sintering treatment, specifically, in an atmosphere of nitrogen and methane, at a rotation frequency of 1 rpm and a sintering temperature of 600°C for 8 hours. After the material is cooled, it is crushed to obtain a second phosphate-based semi-finished particle; wherein, after methane and nitrogen are mixed, they are introduced into the rotary kiln at a flow rate of 1.5 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0118] Step 4. Mix the first phosphate semi-finished particles and the second phosphate semi-finished particles in a mass ratio of 45:55, place them in a rotary kiln, and keep them warm for 6 hours at a rotation frequency of 2 rpm and a calcination temperature of 760°C in an atmosphere of nitrogen and methane. After cooling, grind them by air flow mill to obtain a phosphate positive electrode material; wherein, after methane and nitrogen are mixed, they are introduced into the rotary kiln at a gas flow rate of 0.6 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0119] Example 2

[0120] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that, in step 4, the mass ratio of the first phosphate-based semi-finished particles to the second phosphate-based semi-finished particles is 55:45.

[0121] Example 3

[0122] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that, in step 4, the mass ratio of the first phosphate-based semi-finished particles to the second phosphate-based semi-finished particles is 70:30.

[0123] Example 4

[0124] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that, in step 3, the conditions for the first sintering treatment are: keeping warm for 6 hours at a rotation frequency of 2.5 rpm and a sintering temperature of 500°C, and after methane and nitrogen are mixed, they are introduced into a rotary furnace at a gas flow rate of 1.2 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0125] Example 5

[0126] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that, in step 3, the conditions for the second sintering treatment are: keeping warm for 10 hours at a rotation frequency of 1.5 rpm and a sintering temperature of 700°C, and crushing the material after it is cooled to obtain a second phosphate-based semi-finished particle; wherein, after methane and nitrogen are mixed, they are introduced into a rotary furnace at a gas flow rate of 2.5 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0127] Example 6

[0128] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that, in step 4, the calcination treatment conditions are: keeping warm for 10 hours at a rotation frequency of 3 rpm and a calcination temperature of 820°C, and then cooling and grinding by air flow mill to obtain a phosphate-based positive electrode material; wherein, after methane and nitrogen are mixed, they are introduced into a rotary furnace at a gas flow rate of 1 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0129] Example 7

[0130] A method for preparing a phosphate-based positive electrode material, which is different from Example 1 in that step 1 is different, specifically comprising:

[0131] Step 1, weigh manganese carbonate, manganese nitrate, ferric nitrate, ammonium hydrogen phosphate, and lithium nitrate according to the molar ratio of manganese atom + iron atom, phosphorus atom and lithium atom of (0.6 + 0.4): 1.00: 1.02, mix, add 200% by weight of deionized water, heat to 90°C to fully dissolve, and obtain a mixed solution A.

[0132] Comparative Example 1

[0133] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that, in step 4, the mass ratio of the first phosphate-based semi-finished particles to the second phosphate-based semi-finished particles is 30:70.

[0134] Comparative Example 2

[0135] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that, in step 4, the mass ratio of the first phosphate-based semi-finished particles to the second phosphate-based semi-finished particles is 80:20.

[0136] Comparative Example 3

[0137] A method for preparing a phosphate-based positive electrode material, which differs from Example 2 in that: the rotation frequency of the first sintering treatment in step 3 is 1 rpm.

[0138] Comparative Example 4

[0139] A method for preparing a phosphate-based positive electrode material, which differs from Example 2 in that:

[0140] Step 3, breaking the precursor material into two parts;

[0141] A portion of the precursor material is placed in a rotary kiln for a first sintering treatment, specifically, in an atmosphere of nitrogen and methane, at a rotation frequency of 3 rpm and a sintering temperature of 400° C. for 5 hours, and after the material is cooled, it is crushed to obtain a first phosphate-based semi-finished particle, wherein methane and nitrogen are mixed and introduced into the rotary kiln at a gas flow rate of 1 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9;

[0142] Another portion of the precursor material is placed in a rotary kiln for a second sintering treatment, specifically, in an atmosphere of nitrogen and methane, at a rotation frequency of 3 rpm and a sintering temperature of 600°C for 8 hours. After the material is cooled, it is crushed to obtain a second phosphate-based semi-finished particle; wherein, after methane and nitrogen are mixed, they are introduced into the rotary kiln at a flow rate of 1.5 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0143] Comparative Example 5

[0144] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that:

[0145] Step 3, placing the precursor material in a rotary furnace for the first sintering treatment, specifically, in an atmosphere of nitrogen and methane, at a rotation frequency of 3 rpm and a sintering temperature of 400°C for 4 hours. After the material is cooled, it is crushed to obtain the first phosphate-based semi-finished particles, wherein methane and nitrogen are mixed and then introduced into the rotary furnace at a gas flow rate of 0.8 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0146] Step 4: Place the first phosphate-based semi-finished particles in a rotary kiln, in an atmosphere of nitrogen and methane, keep warm for 6 hours at a rotation frequency of 2 rpm and a calcination temperature of 760°C, and grind them by air flow grinding after cooling to obtain a phosphate-based positive electrode material; wherein, after methane and nitrogen are mixed, they are introduced into the rotary kiln at a gas flow rate of 0.6 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0147] Comparative Example 6

[0148] A method for preparing a phosphate-based positive electrode material, which differs from Example 1 in that:

[0149] Step 3, the precursor material is crushed and placed in a rotary furnace for a second sintering treatment, specifically, in an atmosphere of nitrogen and methane, at a rotation frequency of 1 rpm and a sintering temperature of 600°C for 8 hours, and after the material is cooled, it is crushed to obtain a second phosphate-based semi-finished particle; wherein, after methane and nitrogen are mixed, they are introduced into a rotary furnace at a flow rate of 1.5 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0150] Step 4: Place the second phosphate-based semi-finished particles in a rotary kiln, in an atmosphere of nitrogen and methane, keep warm for 6 hours at a rotation frequency of 2 rpm and a calcination temperature of 760°C, and then grind them by air flow grinding after cooling to obtain a phosphate-based positive electrode material; wherein, after methane and nitrogen are mixed, they are introduced into the rotary kiln at a gas flow rate of 0.6 L / min for vapor deposition, and the volume ratio of methane to nitrogen is 1:9.

[0151] Lithium-ion battery example:

[0152] The phosphate-based positive electrode materials provided in the above-mentioned Examples 1 to 7 and the phosphate-based positive electrode materials provided in Comparative Examples 1 to 6 are respectively assembled into positive electrodes and lithium-ion batteries according to the following methods:

[0153] Positive electrode: Under the same conditions, (positive electrode active material): SuperP-Li: PVDF, the three are mixed in a ratio of 95:2:3 by mass, and N-methylpyrrolidone (NMP) is used as a solvent to mix the materials evenly to form a slurry, and then evenly coated on the surface of the aluminum foil, rolled to a certain thickness, and vacuum dried at 110°C for 12 hours to form a positive electrode sheet; wherein the positive electrode active materials are the phosphate-based positive electrode materials provided in the above embodiments and the phosphate-based positive electrode materials provided in the comparative example.

[0154] Counter electrode: Lithium metal sheet.

[0155] Electrolyte: The electrolyte is 1 mol / L LiPF 6 / ethylene carbonate:ethyl methyl carbonate (volume ratio) = 1:1 solution.

[0156] Diaphragm: Polypropylene microporous membrane.

[0157] Lithium-ion battery assembly: The assembly sequence of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet is assembled into button cells in an inert atmosphere glove box.

[0158] Performance Testing

[0159] (1) Physical property characterization

[0160] The phosphate-based positive electrode material prepared in Example 1 was subjected to scanning electron microscopy (SEM) analysis, and the results were as follows: Figure 1 As shown. Figure 1 It can be seen that the phosphate-based positive electrode material includes multiple phosphate-based particles with smaller particle sizes and multiple phosphate-based particles with larger particle sizes. These large particles are intertwined with small particles, that is, the small particles fill the gaps between the large particles, and there is no obvious agglomeration area or component segregation, which makes the entire phosphate-based positive electrode material present a highly dense, uniform and orderly organizational structure at the microscopic level.

[0161] The phosphate-based positive electrode material prepared in Comparative Example 5 was subjected to scanning electron microscopy (SEM) analysis, and the results were as follows: Figure 2 As shown. Figure 2 It can be seen that phosphate-based positive electrode materials contain more phosphate-based particles with smaller particle sizes. Due to the small size and relatively single size of the small particles, it is difficult to form a compact and multi-level stacking structure during the stacking process.

[0162] The phosphate-based positive electrode material prepared in Comparative Example 6 was subjected to scanning electron microscopy (SEM) analysis, and the results were as follows: Figure 3 As shown. Figure 3It can be seen that the phosphate-based positive electrode materials contain more phosphate-based particles with larger particle sizes. Due to their large size and irregular shape, these large particles are difficult to fit tightly together when stacked, and there are obvious gaps between them.

[0163] The phosphate-based cathode materials prepared in the above-mentioned Examples 1-7 and Comparative Examples 1-6 were tested for powder compaction density using an electronic pressure testing machine UTM7305. The results are shown in Table 1.

[0164] (2) Electrochemical performance test

[0165] The button cells provided in the above embodiments and comparative examples were subjected to electrochemical performance tests, and the results are shown in Table 1. The button cells provided in the above embodiments and comparative examples were subjected to electrochemical performance tests using a LAND electrochemical tester, with a test temperature of 25°C and a charge and discharge voltage window of 2.0V-4.2V.

[0166] The performance test results are shown in Table 1 below.

[0167] Table 1 Test results

[0168]

[0169]

[0170] It can be seen from Table 1 that, compared with Comparative Examples 1-6, the phosphate-based positive electrode material provided in the embodiments of the present application can maintain a relatively high capacity while increasing the compaction density of the powder.

[0171] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A phosphate-based positive electrode material, characterized in that: The phosphate-based positive electrode material has the characteristics of large and small particle grading, and is prepared by mixing at least first phosphate-based semi-finished particles and second phosphate-based semi-finished particles, wherein the D50 of the first phosphate-based semi-finished particles is smaller than the D50 of the second phosphate-based semi-finished particles; the outer surface of the first phosphate-based semi-finished particles has a first carbon layer, and the outer surface of the second phosphate-based semi-finished particles has a second carbon layer, and the mass proportion of the first carbon layer in the first phosphate-based semi-finished particles is smaller than the mass proportion of the second carbon layer in the second phosphate-based semi-finished particles.

2. The phosphate-based positive electrode material according to claim 1, characterized in that: The mass proportion of the first carbon layer in the first phosphate-based semi-finished particle is 0.2% to 0.35% less than the mass proportion of the second carbon layer in the second phosphate-based semi-finished particle; and / or, The mass proportion of the first carbon layer in the first phosphate-based semi-finished particle is 0.8-1.0%wt, and the mass proportion of the second carbon layer in the second phosphate-based semi-finished particle is 1.1-1.3%wt.

3. The phosphate-based positive electrode material according to claim 1 or 2, characterized in that: The first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles are the same lithium-containing phosphate; and / or, The particle size D50 of the phosphate-based positive electrode material is 0.8 to 1.2 μm; and / or, When the phosphate-based cathode material is lithium iron phosphate, the powder compaction density is 2.55 g / cm 3 -2.7g / cm 3 .

4. A method for preparing a phosphate-based positive electrode material, characterized in that: The following steps are involved: Mixing raw materials including at least an iron source, a phosphorus source, a lithium source and a carbon source to obtain a precursor material; The precursor material is divided into two parts, and a first sintering treatment and a second sintering treatment are respectively performed in an atmosphere containing a gaseous carbon material to obtain first phosphate-based semi-finished particles and second phosphate-based semi-finished particles of different particle sizes; wherein the sintering temperature of the first sintering treatment is lower than the sintering temperature of the second sintering treatment, and the rotation frequency of the first sintering treatment is higher than the rotation frequency of the second sintering treatment; The first phosphate-based semi-finished particles and the second phosphate-based semi-finished particles are mixed and calcined in an atmosphere containing a gaseous carbon material to obtain a phosphate-based positive electrode material.

5. The method for preparing a phosphate-based positive electrode material according to claim 4, characterized in that: The conditions of the first sintering treatment include: a sintering temperature of 400° C.-500° C., a rotation frequency of 2.5 rpm-4 rpm, and a gas flow rate of the gaseous carbon material-containing atmosphere of 0.8-1.2 L / min; and / or, The conditions of the second sintering treatment include: a sintering temperature of 600° C.-700° C., a rotation frequency of 1 rpm-1.5 rpm, and a gas flow rate of the gaseous carbon material-containing atmosphere of 1.5-2.5 L / min; and / or, The calcination treatment conditions include: a calcination temperature of 760° C.-820° C., a rotation frequency of 2 rpm-3 rpm, and a gas flow rate of the gaseous carbon material-containing atmosphere of 0.6-1 L / min.

6. The method for preparing a phosphate-based positive electrode material according to claim 4, characterized in that: The sintering time of the first sintering process is lower than the sintering time of the second sintering process; and / or, The sintering time of the first sintering treatment is 4h-6h; and / or, The sintering time of the second sintering treatment is 8h-10h; and / or, The calcination time of the calcination treatment is 6h-10h.

7. The method for preparing a phosphate-based positive electrode material according to claim 4, characterized in that: The D50 particle size of the first phosphate-based semi-finished particles is 0.35 μm-0.55 μm; the D50 particle size of the second phosphate-based semi-finished particles is 0.8 μm-1.2 μm; and / or, Taking the total weight of the first phosphate semi-finished particles and the second phosphate semi-finished particles as 100%, the content of the first phosphate semi-finished particles is 45%-70%, and the content of the second phosphate semi-finished particles is 30%-55%.

8. The method for preparing a phosphate-based positive electrode material according to claim 4, characterized in that: The gaseous carbon material in the gaseous carbon material-containing atmosphere comprises at least one of methane, ethane, propane and ethylene; and / or The gaseous carbon material-containing atmosphere also includes a protective gas.

9. The method for preparing a phosphate-based positive electrode material according to any one of claims 4 to 8, characterized in that: The molar ratio of iron, phosphorus and lithium in the raw material is Fe:P:Li=(0.97-1.02):(1.00-1.04):(1.02-1.05); or, the raw material further includes a manganese source, and the molar ratio of manganese, iron, phosphorus and lithium in the raw material is (Fe+Mn):P:Li=(0.97-1.02):(0.98-1.04):(0.98-1.05), and / or The carbon source accounts for 10%-20% of the total weight of the raw material; and / or The raw material also includes a doping source, and the molar ratio of the doping element in the doping source to the iron element in the raw material is (0.005-0.008):

1.

10. A lithium ion battery, characterized in that: It comprises a negative electrode sheet and a positive electrode sheet, wherein the positive electrode sheet comprises the phosphate-based positive electrode material according to any one of claims 1 to 3 and / or the phosphate-based positive electrode material prepared by the preparation method according to any one of claims 4 to 9.

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