Composite phosphate positive electrode precursor and preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a composite phosphate positive electrode precursor and a preparation method and application thereof. The composite phosphate positive electrode precursor comprises at least two mutually mixed precursor sources, each precursor source independently comprises main elements Li and P, and Fe and / or Mn, and each precursor source comprises at least one of the following 1)-4): 1) different types of main elements; 2) different contents of main elements; 3) different types of doping elements; and 4) different doping element contents. The compaction density of the composite phosphate positive electrode material can be effectively improved, and the electrochemical performance of the composite phosphate positive electrode material can be improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to a composite phosphate-based positive electrode precursor and a preparation method and application thereof. Background Art

[0002] Among various lithium-ion battery cathode materials, lithium iron phosphate has attracted extensive attention and research due to its abundant resources, low cost, no heavy metals, high safety, and long life. However, since lithium iron phosphate is a semiconductor material, its own lithium ion diffusion rate (10 -14 cm 2 / S) and electronic conductivity (10 -9 S / cm) is relatively low, and the voltage platform is low, resulting in its electrochemical performance not being able to meet the demand well. On the basis of lithium iron phosphate, a certain proportion of manganese is added according to the proportion (corresponding to a certain proportion of iron is subtracted) to form lithium manganese iron phosphate, which can improve the voltage platform. However, after adding manganese, lithium manganese iron phosphate still has a lithium ion diffusion rate (10 -15 cm 2 / S) and electronic conductivity (10 -13 S / cm) is low.

[0003] To this end, many researchers have improved lithium iron phosphate or lithium iron manganese phosphate by means of doping, carbon coating, particle morphology control, etc., in order to control its electrochemical properties; or try to increase the energy density by increasing the compaction density of lithium iron phosphate or lithium iron manganese phosphate.

[0004] Moreover, the compaction density and electrochemical performance of the material are two closely related aspects. If the compaction density is blindly increased based on the current technology, it will often lead to a degradation of the electrochemical performance. At the same time, in order to improve the electrochemical performance, the particles are often required to be smaller, which will lead to a relatively low compaction density. Summary of the invention

[0005] The purpose of this application is to provide a composite phosphate-based positive electrode precursor and its preparation method and application, aiming to solve the problems of low compaction density and poor electrochemical performance of phosphate-based positive electrode materials, and can effectively increase the compaction density of composite phosphate-based positive electrode materials and improve their electrochemical performance.

[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 composite phosphate-based positive electrode precursor, comprising at least two mutually mixed precursor sources, each of the precursor sources independently comprising mainly Li and P, and Fe and / or Mn;

[0008] And each of the precursor sources comprises at least one of the following 1) to 4):

[0009] 1) Different main element types;

[0010] 2) Different main element contents;

[0011] 3) Different types of doping elements;

[0012] 4) Different doping element contents.

[0013] In the embodiment of the present application, precursor sources having different main element types, and / or different main element contents, and / or different doping element types, and / or different doping element contents are mixed as precursors of phosphate-based positive electrode materials, and the composite phosphate-based positive electrode precursor can be sintered to form a composite phosphate-based positive electrode material. Since different precursor sources contain different element types and / or element contents, these different precursor sources have different properties, have different growth processes during the sintering process, and spontaneously generate particles of different morphologies / particle sizes in situ in the same sintering process. Since it is spontaneously generated, the gradation between large and small particles is relatively ideal, that is, a natural gradation effect is formed, so that in the sintered product, small particles can be fully dispersed between the gaps between large particles, effectively improving the compaction density of the composite phosphate-based positive electrode material. Moreover, the composite phosphate positive electrode material obtained in this way exhibits excellent electrochemical properties, such as high capacity and high rate performance.

[0014] In a second aspect, the present application provides a method for preparing a composite phosphate-based positive electrode precursor, comprising:

[0015] At least two precursor solutions are provided; each of the precursor solutions independently comprises the main elements Li and P, and Fe and / or Mn; and each of the precursor solutions mutually comprises at least one of the following 1) to 4):

[0016] 1) Different types of main elements;

[0017] 2) Different main element contents;

[0018] 3) Different types of doping elements;

[0019] 4) Different doping element contents;

[0020] The precursor solutions are dried and mixed during the drying process to obtain a composite phosphate-based positive electrode precursor comprising at least two mutually mixed precursor sources.

[0021] The preparation method of the embodiment of the present application can effectively improve the compaction density of the composite phosphate positive electrode material. Moreover, the composite phosphate positive electrode material obtained in this way exhibits excellent electrochemical properties, such as high capacity and high rate performance.

[0022] In a third aspect, the present application provides a method for preparing a composite phosphate-based positive electrode material, which comprises calcining the above-mentioned composite phosphate-based positive electrode precursor.

[0023] In a fourth aspect, the present application provides a composite phosphate-based positive electrode material, comprising at least two mutually mixed active components, each of which independently comprises main elements Li and P, and Fe and / or Mn;

[0024] And each of the active components includes at least one of the following 1) to 4):

[0025] 1) Different main element types;

[0026] 2) Different main element contents;

[0027] 3) Different types of doping elements;

[0028] 4) Different doping element contents.

[0029] The composite phosphate-based positive electrode material of the embodiment of the present application has a high compaction density and excellent electrochemical performance.

[0030] In a fifth aspect, the present application provides a secondary battery comprising the above-mentioned composite phosphate-based positive electrode material.

[0031] The composite phosphate-based positive electrode material of the embodiment of the present application has a high compaction density. Applying it to a secondary battery can greatly increase the energy density of the secondary battery and improve the electrochemical performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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.

[0033] Figure 1 This is a scanning electron microscope image of the composite phosphate-based positive electrode material in Example 3 provided in the examples of the present application;

[0034] Figure 2 This is a scanning electron microscope image of the composite phosphate positive electrode material in Comparative Example 2 provided in the embodiments of the present application;

[0035] Figure 3 This is a particle size distribution diagram of the composite phosphate-based positive electrode material in Example 3 provided in the examples of the present application;

[0036] Figure 4 This is a particle size distribution diagram of the composite phosphate-based positive electrode material in Comparative Example 2 provided in the examples of the present application. DETAILED DESCRIPTION

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] In a first aspect, an embodiment of the present application provides a composite phosphate-based positive electrode precursor, comprising at least two mutually mixed precursor sources, each precursor source independently comprising main elements Li and P, and Fe and / or Mn;

[0045] And each precursor source includes at least one of the following 1) to 4) between each other:

[0046] 1) Different types of main elements;

[0047] 2) Different main element contents;

[0048] 3) Different types of doping elements;

[0049] 4) Different doping element contents.

[0050] The "composite phosphate positive electrode precursor" refers to a substance that can be used to prepare a composite phosphate positive electrode material after sintering. The "precursor source" refers to the components included in the composite phosphate positive electrode precursor.

[0051] "Main elements" refer to the elements mainly contained in the precursor source, and their content is usually high. In an embodiment of the present application, the main elements in each precursor source independently include Li and P, as well as Fe and / or Mn. That is, the main elements in any one precursor source include Li, P, Fe, Mn, or include Li, P, Fe, or include Li, P, Mn. The precursor source can be a precursor of positive electrode materials such as lithium manganese iron phosphate, lithium iron phosphate, and lithium manganese phosphate. In some cases, the composite phosphate-based positive electrode precursor includes two precursor sources, and the main elements of the two precursor sources include any one of the following combinations:

[0052] I) LMFP+LFP, i.e., the main elements of the first drive body source include Li, P, Fe, and Mn, and the main elements of the second drive body source include Li, P, and Fe;

[0053] II) LMFP+LMP, i.e. the main elements of the first drive source include Li, P, Fe, and Mn, and the main elements of the second drive source include Li, P, and Mn;

[0054] III) LMP+LFP, i.e. the main elements of the first drive source include Li, P, and Mn, and the main elements of the second drive source include Li, P, and Fe;

[0055] IV) LFP+LFP, i.e., the main elements of the first precursor source and the second precursor source both include Li, P, and Fe;

[0056] V) LMFP+LMFP, i.e., the main elements of the first precursor source and the second precursor source both include Li, P, Fe, and Mn;

[0057] VI) LMP+LMP, that is, the main elements of the first precursor source and the second precursor source include Li, P, and Mn.

[0058] "Different main element types" means that the main element types contained in different precursor sources are different and not completely the same. In some cases, the composite phosphate positive electrode precursor includes two precursor sources. When the precursor sources include 1) with each other, the combination of the main elements in the two precursor sources includes any one of I), II), and III) above.

[0059] A "dopant element" is an element that is present in a lower concentration than the main element. It is understood that the type of doping element is different from the type of the main element.

[0060] "Different types of doping elements" means that the types of doping elements contained in different precursor sources are different and not completely the same. In the case of including doping elements, the types of doping elements in each precursor source may include one or more. In the case where each precursor source includes one doping element, the one doping element included in each precursor source is different. For example, in the case where there are two precursor sources, the first precursor source includes a doping element M1, and the second precursor source includes a doping element M2, and M1 and M2 are different elements.

[0061] In the case where at least one precursor source includes more than one doping element, then at least one of the more than one doping elements included in the precursor source is different from the doping elements of other precursor sources. For example, in the case where there are two precursor sources, the first precursor source includes a doping element m1, and the second precursor source includes more than one, such as two doping elements m2 and m3, then at least one of m2 and m3 is different from m1 (there may be a case where one of m2 and m3 is the same element as m1).

[0062] In this application, "element content" can be the mass content of a certain element in a certain precursor source. "Different main element contents" means that the content of at least one element among Li, P, Fe, and Mn is different between different precursor sources; "different doping element contents" means that the content of doping elements is different between different precursor sources.

[0063] It is understood that each precursor source includes at least one of the above 1) to 4) mutually, that is, each precursor source may include one or more of the situations in 1) to 4) mutually. When each precursor source includes one or several situations mutually, other situations may not be included.

[0064] In the embodiment of the present application, precursor sources having different main element types, and / or different main element contents, and / or different doping element types, and / or different doping element contents are mixed as precursors of phosphate-based positive electrode materials, and a composite phosphate-based positive electrode material can be formed through sintering. During the sintering process, since different precursor sources contain different element types and / or element contents, these different precursor sources have different properties, have different growth processes during the sintering process, and spontaneously generate particles of different morphologies / particle sizes in situ in the same sintering process. Since it is spontaneously generated, the gradation between large and small particles is relatively ideal, that is, a natural gradation effect is formed, so that in the sintered product, small particles can be fully dispersed between the gaps between large particles, effectively improving the compaction density of the composite phosphate-based positive electrode material. Moreover, the composite phosphate positive electrode material obtained in this way exhibits excellent electrochemical properties, such as high capacity and high rate performance.

[0065] In some embodiments, the doping element includes one or more of transition metals, alkaline earth metals, group IIIA metals, group VIA metals, and group VA metals. Among them, transition metals include but are not limited to one or more of Ti, Ni, V, Nb, Zr, Cr, Co, Zn, and Mo; alkaline earth metals include but are not limited to one or more of Mg and Ca; group IIIA metals include one or more of Al and Ga; group VIA metals include but are not limited to one or more of Ge and Sn; and group VA metals include one or more of Sb and Bi.

[0066] In the case of containing doping elements, on the one hand, the difference between different precursor sources can be increased, so that different precursor sources have different elemental compositions and thus exhibit different properties, which is beneficial to the formation of a composite phosphate-based positive electrode material with high compaction density after sintering; on the other hand, these doping elements are beneficial to improving the electrochemical properties of the composite phosphate-based positive electrode material.

[0067] In some embodiments, at least one precursor source includes one or more doping elements of Ti, Ni, and V. Doping of Ti, Ni, and V is beneficial to adjusting the properties of different precursor sources, thereby improving the electrochemical performance of the composite phosphate-based cathode material.

[0068] In some embodiments, the mass content of any one doping element in any one precursor source is 50 to 20,000 ppm, optionally including 100 to 9,000 ppm, such as any one of 50 ppm, 100 ppm, 500 ppm, 1,000 ppm, 5,000 ppm, 10,000 ppm, 15,000 ppm, 20,000 ppm or any range therebetween. At a suitable doping amount, the doping element can improve the structural stability of the composite phosphate-based cathode material, improve the electrochemical properties of the material, etc.

[0069] At the same time, the study found that within a certain range, the greater the content of doping elements in the precursor source, the smaller the particles formed after sintering; and the smaller the content of doping elements in the precursor source, the larger the particles formed after sintering. Therefore, by changing the mass content of doping elements, the particle size and morphology of the precursor source after sintering can be adjusted, which is beneficial to improve the compaction density of the composite phosphate-based positive electrode material.

[0070] In some embodiments, the composite phosphate-based positive electrode precursor includes a first precursor source and a second precursor source; the first precursor source includes a first doping element with a first mass content, and the second precursor source includes a second doping element with a second mass content; wherein the first doping element and the second doping element are of different element types, and / or the first content is different from the second content.

[0071] It should be noted that the amounts of the first doping element and the second doping element are independently one or more, the first content is the total content of all the first doping elements in the first precursor source, and the second content is the total content of all the second doping elements in the second precursor source. By adjusting the element type and / or content of the doping element, two precursor sources with different properties can be obtained, which is helpful for the subsequent formation of a phosphate-based positive electrode material with a high compaction density.

[0072] In some embodiments, the particle sizes of at least two precursor sources are different. The particle size D50 of at least one precursor source is 50nm≤D50≤200nm, and the particle size D50 of another precursor source is 200nm≤D50≤500nm. The mass ratio of the precursor source with a larger particle size to the precursor source with a smaller particle size is (6:4) to (9:1), that is, (6-9): (4-1), for example, any one of 6:4, 7:3, 8:2, 9:1 or the range between any two. D50 represents the median particle size. The particle sizes of at least two precursor sources are different, so that the composite phosphate-based positive electrode precursor can form a composite phosphate-based positive electrode material including large particles and small particles after sintering, and the mass ratio of large particles to small particles is equal to or approximately equal to the mass ratio of the first precursor source to the second precursor source. At this ratio, the compaction density of the composite phosphate-based positive electrode material can be well improved.

[0073] In this case, the first content can be set to 100-1000 ppm, optionally 500-1000 ppm, such as any one of 100 ppm, 500 ppm, 1000 ppm or a range between any two thereof. The second content can be set to 1500-15000 ppm, optionally 1500-13000 ppm, such as any one of 1500 ppm, 5000 ppm, 10000 ppm, 13000 ppm or a range between any two thereof.

[0074] In some embodiments, the composite phosphate-based positive electrode precursor further includes an nth precursor source, which includes an nth doping element having an nth content by mass; wherein n is a positive integer greater than 2, and the element type of the nth doping element is different from at least one of the first doping element to the n-1th doping element, and / or the nth content is different from at least one of the first content to the n-1th content. Similarly, the number of the nth doping elements independently includes one or more.

[0075] In some embodiments, n is 3 to 4, for example, it may include any one of 3 and 4.

[0076] In some embodiments, the first precursor source includes Ti, and the second precursor source includes Ti and V. That is, the first precursor source is a Ti-doped lithium manganese iron phosphate precursor source, and the second precursor source is a precursor source doped with Ti and V. Studies have shown that after the two types of precursor sources are mixed, they can be sintered to form large and small particles with excellent gradation relationship, and the resulting composite phosphate-based positive electrode material has a high compaction density and excellent electrochemical properties.

[0077] In some embodiments, the first precursor source further includes V and / or Ni.

[0078] In some embodiments, the mass content of Ti in the first precursor source and the second precursor source is independently 300-15000 ppm, for example, any one of 300 ppm, 500 ppm, 1000 ppm, 2000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 8000 ppm, 10000 ppm, 15000 ppm or any range between two thereof. Optionally, the mass content of Ti in the first precursor source and the second precursor source in the composite phosphate-based positive electrode precursor is different.

[0079] In some embodiments, when both the first precursor source and the second precursor source include Ni, the mass content of Ni in the first precursor source and the second precursor source is independently 50 to 2000 ppm, for example, any one of 50 ppm, 100 ppm, 500 ppm, 1000 ppm, 2000 ppm or any range between the two. Optionally, the mass content of Ni in the first precursor source and the second precursor source in the composite phosphate-based positive electrode precursor is different.

[0080] In some embodiments, when both the first precursor source and the second precursor source include V, the mass content of V in the first precursor source and the second precursor source is independently 50 to 2000 ppm, for example, any one of 50 ppm, 100 ppm, 500 ppm, 1000 ppm, 2000 ppm or any range between two thereof. Optionally, the mass content of V in the first precursor source and the second precursor source in the composite phosphate-based positive electrode precursor is different.

[0081] In some embodiments, the mass content of any one precursor source in the composite phosphate positive electrode precursor can be set in any proportion as needed, for example, the mass content of any one precursor source in the composite phosphate positive electrode precursor is 5% to 95%, optionally 10% to 90%, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or any point value or any range between two of them. By adjusting the content of various precursor sources, different types of high compaction density phosphate positive electrode materials can be prepared.

[0082] In some embodiments, the main elements of at least one precursor source include Li, Fe, and P, wherein the element molar ratio of Li, Fe, and P includes Li:Fe:P=(0.8~1.2):(0.8~1.2):(0.8~1.5), and optionally includes Li:Fe:P=(1~1.2):(0.9~1):(1~1.3), for example, Li:Fe:P=0.8:0.9:1.2, Li:Fe:P=1:0.9:1, Li:Fe:P=1:0.9:1.2, Li:Fe:P=1.2:0.9:1, Li:Fe:P=1.2:0.9:1.2, any one of the values ​​or the range between any two of them.

[0083] In some embodiments, the main elements of at least one precursor source include Li, Fe, P and Mn, wherein the molar ratio of Li, Fe, Mn and P includes Li:Fe:Mn:P=(0.8-1.2):(0.1-1.2):(0.1-0.9):(0.8-1.5), and the molar ratio of Fe+Mn is 0.8-1.2, for example, Li:Fe:Mn:P=0.8:0.1:0.9:1.2, Li:Fe:Mn: P=0.8:0.2:0.8:1,Li:Fe:Mn:P=0.8:03:0.7:1.2,Li:Fe:Mn:P=1:0.5:0.5:1,Li:Fe:Mn:P=1.2:0.9:0.1:1,Li:Fe:Mn:P=1.2:0.8:0.2:1.2,1,Li:Fe:Mn:P=1:0.4:0.6:1.2,any one of the point values ​​or the range between any two of them.

[0084] The composite phosphate-based positive electrode precursor of the present application can be prepared by the following second method.

[0085] A second aspect of the present application provides a method for preparing a composite phosphate-based positive electrode precursor, comprising:

[0086] S1. Providing at least two precursor solutions; each precursor solution independently comprises the main elements Li and P, and Fe and / or Mn; and the various precursor solutions mutually comprise at least one of the following 1) to 4):

[0087] 1) Different types of main elements;

[0088] 2) Different main element contents;

[0089] 3) Different types of doping elements;

[0090] 4) Different doping element contents;

[0091] S2. Drying various precursor solutions and mixing them during the drying process to obtain a composite phosphate-based positive electrode precursor including at least two mutually mixed precursor sources.

[0092] Regarding the four situations 1) to 4), reference may be made to the composite phosphate-based positive electrode precursor of the first aspect, which will not be elaborated here.

[0093] It can be understood that the precursor liquid corresponds to the precursor source, that is, the precursor liquid is dried to obtain the precursor source, so the precursor liquid and the corresponding precursor source have the same or corresponding characteristics. For example, in step S1, the doping element includes one or more of transition metals, alkaline earth metals, IIIA group metals, VIA group metals, and VA group metals. In step S1, at least one precursor liquid includes one or more doping elements of Ti, Ni, and V.

[0094] In some embodiments, step S1 comprises:

[0095] S11. Providing a first precursor solution, the first precursor solution comprising a first doping element having a first mass content;

[0096] S12. Providing a second precursor solution, the second precursor solution comprising a second doping element having a second mass content;

[0097] The first doping element and the second doping element are of different element types, and / or the first content and the second content are different.

[0098] By adjusting the type and / or content of the doping element, two precursor solutions with different properties can be obtained, which can form different types of precursor particles after drying, which is conducive to the subsequent formation of a phosphate-based positive electrode material with a high compaction density.

[0099] It can be understood that the first precursor liquid corresponds to the first precursor source in the foregoing text, and the second precursor liquid corresponds to the second precursor source in the foregoing text, and has corresponding characteristics. For example, the particle sizes of at least two precursor sources are different. The particle size D50 of at least one precursor source is 50nm≤D50≤200nm, and the particle size D50 of another precursor source is 200nm≤D50≤500nm. The solid mass ratio of the precursor liquid corresponding to the precursor source with a larger particle size to the precursor liquid corresponding to the precursor source with a smaller particle size is (6:4) to (9:1). The setting of the first content and the second content can refer to the foregoing text and will not be repeated here.

[0100] In some embodiments, corresponding to the nth precursor source, step S1 further includes:

[0101] S1n. Providing an nth precursor solution, the nth precursor solution comprising an nth doping element having an nth content by mass;

[0102] Wherein, n is a positive integer greater than 2, the element type of the nth doping element is different from any one of the first to n-1th doping elements, and / or the nth content is different from any one of the first to n-1th contents.

[0103] In some embodiments, in step S11, the first precursor solution includes Ti; in step S12, the second precursor solution includes Ti and V.

[0104] In some embodiments, in step S11, the first precursor solution further includes V and / or Ni.

[0105] It is understandable that the solid content or concentration of the aforementioned various precursor solutions can be flexibly adjusted as needed, as long as the ratio between the relevant elements or the content relationship of the relevant elements in different precursor solutions is met. The various precursor solutions can be solutions or suspensions, and the solvents used in the various precursor solutions include water and / or ethanol.

[0106] At the same time, regarding the ratio between the aforementioned various precursor solutions, the mass content of the solid (precursor source) formed by drying each precursor solution in the composite phosphate positive electrode precursor in step S2 can be set according to any ratio. The mass content of the solid mass of any precursor solution in the composite phosphate positive electrode precursor in step S2 can be set to 5% to 95%, optionally 10% to 90%.

[0107] In some embodiments, in step S2, the drying method includes airflow drying. Airflow drying is a method of making a liquid or slurry into a dry powder using a hot air flow. Various precursor liquids are subjected to airflow drying and mixed during the airflow drying process, that is, various precursor liquids are subjected to airflow drying at the same time, and under the airflow, each precursor liquid is instantly solidified to form a solid precursor source of different types, and each precursor source is uniformly mixed during the airflow drying process.

[0108] In some embodiments, in step S2, the air flow velocity in the air flow drying process is 0.01 to 10 m / s, for example, any one of 0.01 m / s, 0.1 m / s, 0.5 m / s, 1 m / s, 5 m / s, and 10 m / s or any range therebetween. Under a certain air flow velocity, uniform mixing of different precursor solutions and / or different precursor sources formed by drying different precursor solutions can be achieved.

[0109] In some embodiments, in step S2, the air flow temperature in the air flow drying process is 45 to 150° C., for example, any one of 45° C., 50° C., 70° C., 90° C., 100° C., 120° C., and 150° C. or a range between any two thereof. Under the action of the hot air flow, the solvent in the precursor solution evaporates, thereby drying the precursor solution to form a dry powder. The air flow drying process can be carried out at normal pressure (101 kPa) or a pressure close thereto, for example, 90 to 110 kPa.

[0110] In some embodiments, in step S2, the gas used in the airflow drying process includes, but is not limited to, one or more of nitrogen, helium, neon, and argon. Using these inert gases to form a hot air flow can avoid unnecessary side reactions of the raw materials during the drying process.

[0111] In some embodiments, in step S2, the airflow drying process step includes: different precursor liquids are respectively input into the same curing chamber into which the airflow is introduced through different paths, and dried and mixed under the action of the airflow; wherein, the flow rate of each precursor liquid into the curing chamber is independently 0.001 to 10 mL / s, for example, 0.001 mL / s, 0.1 m / Ls, 0.5 mL / s, 1 mL / s, 5 mL / s, 10 mL / s, any one point value or any range between the two, and the flow rate here represents the amount of the precursor liquid pumped out per unit time. It is understandable that in order to make each precursor liquid mix evenly with each other, in the airflow drying process, the time for each precursor liquid to be airflow dried should be the same. That is, each precursor liquid enters the curing chamber at the same or similar time, and stops input at the same or similar time.

[0112] In the curing chamber, the inflow directions of any two precursor liquids can be combined in any direction, for example, the inflow directions of any two precursor liquids can form an acute angle, an obtuse angle, a right angle, or flow into each other at 180°. At the same time, the inflow direction of any one precursor liquid and the airflow direction can be set to be perpendicular to each other or inclined to each other to form an acute angle or an obtuse angle; optionally, the inflow direction of any one precursor liquid and the airflow direction can be set to be perpendicular to each other, for example, the airflow direction is vertical, and the inflow direction of any one precursor is horizontal, so as to facilitate bringing the mixed material to the outlet position of the curing chamber.

[0113] Regarding the preparation method of the composite phosphate-based positive electrode precursor of the second aspect, the types of related substances involved can be selected as follows:

[0114] The Li element is provided by a lithium source, and the lithium source includes one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium acetate, lithium dihydrogen phosphate, and lithium nitrate;

[0115] The Fe element is provided by an iron source, and the iron source includes one or more of ferric sulfate, ferric chloride, ferric phosphate, ferric acetate, ferric nitrate, ferrous oxalate, ferrous chloride, and ferric oxide;

[0116] The P element is provided by a phosphorus source, and the phosphorus source includes one or more of diammonium phosphate, ammonium phosphate, iron phosphate, lithium dihydrogen phosphate, and phosphoric acid;

[0117] The Mn element is provided by a manganese source, and the manganese source includes one or more of manganese sulfate, manganese chloride, manganese phosphate, manganese acetate, manganese nitrate, and manganese oxide;

[0118] The doping element is provided by a doping element source, and the doping element source includes one or more of a hydroxide containing the doping element, a carbonate containing the doping element, a sulfate containing the doping element, a nitrate containing the doping element, a phosphate containing the doping element, a chloride containing the doping element, and an oxide containing the doping element.

[0119] The aforementioned composite phosphate-based positive electrode precursor can be used to make positive electrode materials for positive electrode sheets.

[0120] Specifically, the third aspect of the embodiment of the present application further provides a composite phosphate-based positive electrode material, which is obtained by sintering the composite phosphate-based positive electrode precursor of the first aspect mentioned above.

[0121] In some embodiments, the sintering temperature is 300-800°C, for example, any one of 300°C, 400°C, 500°C, 600°C, 700°C, 800°C or a range between any two of them; the sintering time is 1-30h, for example, any one of 1h, 5h, 10h, 15h, 20h, 25h, 30h or a range between any two of them.

[0122] In some embodiments, the sintering treatment includes m stages, the temperature of each stage of the sintering treatment is independently 300-800°C, and the time of each stage of the sintering treatment is independently 1-30h; wherein m is a positive integer greater than or equal to 1 (for example, m is 1-4, which can include any one of 1, 2, 3, and 4; preferably, m is 2). Through multiple stages of sintering treatment, it is beneficial to improve the crystallinity of the composite phosphate positive electrode material and improve the structural stability of the material. After any stage of sintering treatment is completed, the material can be cooled before the next stage of sintering treatment. After each stage of sintering treatment, a crushing treatment step can be set.

[0123] In some embodiments, the sintering process is performed under a protective atmosphere, and the protective atmosphere includes one or more of nitrogen, helium, neon, and argon.

[0124] In some embodiments, a carbon source may be introduced into the sintering process. In the case of containing a carbon source, these carbon sources may form a carbon material coating layer on the surface of the composite phosphate-based cathode material during the sintering process, which is beneficial to improve the conductivity of the composite phosphate-based cathode material. The carbon source may be in the form of one or more of a gaseous state and a liquid state. Different amounts of carbon sources may be selected according to the different contents of the desired carbon material coating layer or the different coating thicknesses. For example, in the case of using a gaseous carbon source, the gaseous carbon source may be introduced into the sintering process at a flow rate of 0.01 to 10 m / s (e.g., any one of 0.01 m / s, 0.05 m / s, 0.1 m / s, 0.5 m / s, 1 m / s, 3 m / s, 5 m / s, 10 m / s or any range between the two).

[0125] In some embodiments, the carbon source includes one or more of alcohols (e.g., ethanol), methane, and acetylene. These carbon sources can decompose to form carbon materials under high temperature and protective atmosphere, and deposit on the surface of the phosphate-based cathode material. At the same time, these carbon sources can also form a reducing atmosphere, reduce the oxidation reaction of the precursor, and improve the purity of the composite phosphate-based cathode material.

[0126] Corresponding to the composition of the composite phosphate-based positive electrode precursor, the composite phosphate-based positive electrode material includes at least two different active components.

[0127] Specifically, the composite phosphate-based positive electrode material of the embodiment of the present application includes at least two active components mixed with each other, each active component independently includes the main elements Li and P, and Fe and / or Mn;

[0128] And the active components mutually include at least one of the following 1) to 4):

[0129] 1) Different main element types;

[0130] 2) Different main element contents;

[0131] 3) Different types of doping elements;

[0132] 4) Different doping element contents.

[0133] Overall, in terms of active components, composite phosphate-based positive electrode materials include one or more of lithium iron manganese phosphate, doped lithium iron manganese phosphate, lithium iron phosphate, and doped lithium iron phosphate. The doping elements in doped lithium iron manganese phosphate or doped lithium iron phosphate include one or more of transition metals, alkaline earth metals, IIIA group metals, VIA group metals, and VA group metals, such as Ti, Ni, V, etc.

[0134] The phosphate-based positive electrode material also includes a carbon material coating layer, which is coated on the surface of one or more of lithium iron manganese phosphate, lithium iron phosphate, and lithium manganese phosphate, and forms a partial coating or a complete coating. Through the effect of the carbon material coating layer, the conductivity of the composite phosphate-based positive electrode material can be improved, the side reaction of the electrolyte can be reduced, and it is more conducive to the use of capacity and other aspects.

[0135] The carbon material includes one or more of amorphous carbon, graphene, graphite, and carbon nanotubes. These carbon materials have good electrical conductivity and can improve the conductivity of the composite phosphate cathode material, thereby improving the electrochemical performance of the composite phosphate cathode material.

[0136] The composite phosphate-based positive electrode material of the embodiment of the present application includes large and small particles with different particle sizes. The gradation between the large and small particles is relatively ideal, and the small particles are fully dispersed between the gaps between the large particles.

[0137] Specifically, the composite phosphate-based positive electrode material has at least two levels of particle grading, including at least first-level particles (large particles) and second-level particles (small particles). The particle size range D1 of the first-level particles is 50nm≤D1≤500nm, and the particle size range D2 of the second-level particles is 500nm<D2≤1000nm. The mass ratio of the first-level particles to the second-level particles is (4:6) to (1:9). The particle sizes D1 and D2 here refer to the actual particle sizes of the particles, that is, the actual particle sizes of a single particle. At the same time, it should be understood that particles of different particle sizes do not correspond one to one to different active components, and any first-level particle can include two active components.

[0138] The particle size distribution index SPAN of the composite phosphate positive electrode material is ≥ 2, and optionally SPAN is 2 to 5. Wherein SPAN = (D90-D10) / D50, and the larger the SPAN value, the wider the particle size distribution.

[0139] The compaction density of the composite phosphate cathode material is greater than 2.4g / cm 3 , optionally 2.41 to 2.8 g / cm 3 .

[0140] The phosphate-based cathode material of the present invention has a high compaction density, which is higher than that of the existing phosphate-based cathode materials, especially the compaction density of lithium manganese iron phosphate (2.1-2.2 g / cm 3 ) is significantly improved. The increase in the compaction density of composite phosphate-based cathode materials will help to increase their energy density and thus improve their electrochemical performance.

[0141] The discharge capacity of the composite phosphate positive electrode material at 25°C and 0.1C rate is greater than or equal to 145 mAh / g, optionally 145-162 mAh / g; the discharge capacity at 25°C and 1C rate is greater than or equal to 130 mAh / g, optionally 130-155 mAh / g.

[0142] A fourth aspect of an embodiment of the present application provides a secondary battery, comprising the above-mentioned composite phosphate-based positive electrode material.

[0143] The composite phosphate-based positive electrode material of the embodiment of the present application has a high compaction density. Applying it to a secondary battery can greatly increase the energy density of the secondary battery and improve the electrochemical performance of the secondary battery.

[0144] In some embodiments, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a current collector and a positive electrode active layer, the positive electrode active layer is disposed on at least one side of the current collector, and the positive electrode active layer includes the above-mentioned composite phosphate positive electrode material. The positive electrode active layer may also include a conductive agent, a binder, etc. The conductive agent, the binder and the composite material are mixed under the action of a solvent to form a positive electrode slurry, which is coated on at least one side of the current collector and dried to obtain the positive electrode active layer.

[0145] In some embodiments, the secondary battery further includes a negative electrode plate, and during the charge and discharge process of the secondary battery, the positive electrode plate and the negative electrode plate form a loop.

[0146] In some embodiments, the secondary battery further includes an electrolyte and a separator stacked between the positive electrode sheet and the negative electrode sheet.

[0147] The following describes the invention in conjunction with specific embodiments.

[0148] Example 1

[0149] This embodiment provides a composite phosphate-based positive electrode material, and the preparation method thereof includes:

[0150] (1) Prepare the precursor solution

[0151] 1) Prepare the first precursor solution

[0152] The first precursor solution is a Ti- and V-doped lithium manganese iron phosphate precursor solution, and the preparation method is:

[0153] Lithium hydroxide, ferric nitrate, manganese nitrate and phosphoric acid were dissolved in water according to the element molar ratio of Li:Fe:Mn:P=1:0.3:0.7:1, and appropriate amounts of titanium tetrachloride and vanadium pentoxide were added so that the Ti doping amount was 500ppm and the V doping amount was 500ppm, thereby obtaining a first precursor solution.

[0154] 2) Prepare the second precursor solution

[0155] The second precursor solution is a Ti- and Ni-doped lithium manganese iron phosphate precursor solution, and the preparation method is as follows:

[0156] Lithium hydroxide, ferric nitrate, manganese nitrate and phosphoric acid were dissolved in water according to the element molar ratio of Li:Fe:Mn:P=1:0.3:0.7:1, and appropriate amounts of titanium tetrachloride and nickel hydroxide were added so that the Ti doping amount was 15000 ppm and the Ni doping amount was 2000 ppm, thereby obtaining a second precursor solution.

[0157] (2) Airflow drying treatment

[0158] Nitrogen is introduced into the curing chamber at a flow rate of 0.5 m / s, and the temperature in the curing chamber is controlled to be 100°C. According to a solid mass ratio of 9:1, the first precursor liquid and the second precursor liquid are respectively introduced into the same curing chamber through different fine pipes, wherein the flow rate of the first precursor liquid is 0.9 mL / s, and the flow rate of the second precursor liquid is 0.1 mL / s. The inflow direction of the first precursor liquid and the second precursor liquid is set at 180° in the curing chamber, and the nitrogen gas flow is perpendicular to the inflow direction of the first precursor liquid and the second precursor liquid. After the first precursor liquid and the second precursor liquid are cured (dried) and mixed in the curing chamber, a composite phosphate-based positive electrode precursor containing different precursor sources is obtained.

[0159] (3) Sintering

[0160] The composite phosphate positive electrode precursor obtained in step (2) is placed in a sintering furnace and sintered once and twice in sequence. First sintering: nitrogen (flow rate of 0.3 m / s) and methane (flow rate of 10 m / s) are introduced, and the temperature is increased to 560°C at a rate of 5°C / min, and the temperature is kept constant for 7 hours. After the material is cooled to room temperature, it is taken out and crushed to obtain a semi-finished product. Second sintering: Under the same nitrogen and methane conditions as the first sintering, the semi-finished product is heated to 790°C at a rate of 3°C / min and kept constant for 10 hours. After cooling, it is crushed by air jet mill to obtain the finished product.

[0161] It should be noted that the Ti doping amount, V doping amount, and Ni doping amount in step (1) refer to the mass content of the corresponding elements in the corresponding precursor source after drying in step (2).

[0162] The element doping amounts in the following embodiments and comparative examples have the same meaning as the element doping amounts in this embodiment.

[0163] Example 2

[0164] This embodiment provides a composite phosphate-based positive electrode material, and the preparation method thereof is different from that of Embodiment 1 in that: in step (2), the solid mass ratio of the first precursor solution to the second precursor solution is 8:2.

[0165] Example 3

[0166] This embodiment provides a composite phosphate-based positive electrode material, and the preparation method thereof is different from that of Embodiment 1 in that: in step (2), the solid mass ratio of the first precursor solution to the second precursor solution is 7:3.

[0167] Example 4

[0168] This embodiment provides a composite phosphate-based positive electrode material, and the preparation method thereof is different from that of Embodiment 1 in that: in step (2), the solid mass ratio of the first precursor solution to the second precursor solution is 6:4.

[0169] Example 5

[0170] This embodiment provides a composite phosphate-based positive electrode material, and its preparation method is different from that of Embodiment 1 in that: in step (1), the molar ratio of elements in the first precursor solution is Li:Fe:Mn:P=1.2:0.3:0.7:1.3.

[0171] Example 6

[0172] This embodiment provides a composite phosphate-based positive electrode material, and its preparation method is different from that of Embodiment 1 in that: in step (1), only nickel hydroxide is added so that the Ni doping amount is 2000 ppm, thereby obtaining a second precursor solution.

[0173] Example 7

[0174] The difference between this embodiment and embodiment 1 is that in step (1), the first precursor solution does not contain Mn, and the molar ratio of elements in the first precursor solution is Li:Fe:P=1.2:1:1.

[0175] Comparative Example 1

[0176] This comparative example provides a phosphate-based positive electrode material, and its preparation method is different from that of Example 1 in that it does not contain a second precursor solution.

[0177] Comparative Example 2

[0178] This comparative example provides a phosphate-based positive electrode material, and its preparation method is different from that of Example 1 in that it does not contain the first precursor solution.

[0179] Comparative Example 3

[0180] This comparative example provides a composite phosphate-based positive electrode material, and its preparation method is different from that of Example 1 in that: in step (2), the first precursor liquid and the second precursor liquid are air-dried separately to obtain two different precursor sources, and then the two precursor sources are mixed.

[0181] Specifically, step (2) of the preparation method of this comparative example comprises:

[0182] Nitrogen was introduced into the curing chamber at a flow rate of 0.5 m / s, and the temperature in the curing chamber was controlled to be 100° C. The first precursor liquid was introduced into the curing chamber through a thin pipe at a flow rate of 0.5 mL / s. After the first precursor liquid was cured (dried) in the curing chamber, a solid first precursor source was obtained.

[0183] Nitrogen was introduced into the curing chamber at a flow rate of 0.5 m / s, and the temperature in the curing chamber was controlled to be 100° C. The second precursor liquid was introduced into the curing chamber through a thin pipe at a flow rate of 0.5 mL / s. After the second precursor liquid was cured (dried) in the curing chamber, a solid second precursor source was obtained.

[0184] The obtained first precursor source and the second precursor source are mixed in a solid mass ratio of 9:1.

[0185] The compositions of the precursor solutions of the embodiments and comparative examples are shown in the following table.

[0186] Table 1. Precursor liquid composition

[0187]

[0188] Test example:

[0189] Structural characterization and performance testing:

[0190] (1) The morphology of the composite phosphate-based positive electrode materials prepared in each example and comparative example was observed by scanning electron microscopy, wherein the scanning electron microscopy images of Example 3 and Comparative Example 2 are shown in FIG. Figure 1 and Figure 2 As shown, the particle size distribution diagrams of Example 3 and Comparative Example 2 are respectively as shown in Figure 3 and Figure 4 As shown. It can be seen from the figure that the composite phosphate-based positive electrode material of Example 3 includes particles with significantly different particle sizes, with an average particle size of D = 124 ± 105.11nm, D99 = 587.76nm, D90 = 221.56nm, D50 = 81.03nm, D10 = 46.98nm, SPAN = (D90-D10) / D50 = 2.15, and the particle size distribution range of the particles is wide, and there is almost no agglomeration between small particles, but they are evenly filled between large particles. In contrast, in the phosphate-based positive electrode material of Comparative Example 2, there is no obvious difference in particle size between particles, the particle size distribution is narrow, and there is more serious agglomeration between particles, and no morphology of small particles filling between large particles is formed.

[0191] (2) The compaction density of the material powder of the composite phosphate-based positive electrode material prepared in each embodiment and comparative example was tested. The compaction density was obtained by using a compaction density meter with reference to Appendix L "Test method for compaction density of powder" in GB / T 24533-2019. The test results are shown in Table 2 below.

[0192] (3) The composite phosphate positive electrode materials prepared in each embodiment and comparative example are applied to lithium ion batteries to prepare button batteries. The specific steps are as follows:

[0193] ① Preparation of slurry: The composite phosphate positive electrode materials prepared in each embodiment and comparative example were respectively mixed with SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) in a mass ratio of 93.5:2.5:4:100, and ball-milled at a speed of 360 r / min for 4 h to obtain positive electrode slurry.

[0194] ② Coating of slurry: adjust the scale of the scraper of the coating machine, evenly coat the milled positive electrode slurry on the aluminum foil, place it in a vacuum drying oven at 130°C and bake for 3 hours;

[0195] ③ Rolling and punching: Place the aluminum foil coated with slurry flatly in the middle of the roller and roll the positive electrode sheet; place the front of the rolled positive electrode sheet close to the punched area and punch the sheet in sequence; the compaction density of the positive electrode sheet is controlled at 2.0-2.4g / cm 3 , with a diameter of 14 mm and a thickness of 0.05-0.10 mm; the punched positive electrode sheet is placed in a vacuum drying oven at a temperature of 130°C and baked for 3 hours;

[0196] ④ Assemble button batteries. In a glove box, assemble the negative electrode shell, spring sheet, steel sheet, lithium sheet, diaphragm, positive electrode sheet and positive electrode shell in this order. In the process, inject 10 μL of electrolyte, and then use a sealing machine to seal the button batteries to obtain lithium-ion button batteries corresponding to the composite phosphate positive electrode materials provided in the embodiment and the comparative example.

[0197] The charge and discharge tests were conducted at room temperature 25°C with different current densities of 0.1C and 1.0C. The test results are shown in Table 2 below.

[0198] Table 2. Test results

[0199]

[0200] The test results show that Examples 1 to 6 respectively use two precursor solutions with the same main elements and different doping elements / contents to perform airflow drying and mixing to form two different LMFP precursor particles. The composite phosphate-based cathode materials obtained by sintering have a high compaction density of 2.41 g / cm 3And above, while showing high capacity. At the same time, in Examples 1 to 4, when the solid mass ratio corresponding to the first precursor solution and the second precursor solution changes, within a certain range, as the solid mass ratio of the second precursor solution increases, the compaction density and discharge capacity of the resulting composite phosphate-based positive electrode material also gradually increase. This is because the doping amount of the doping element in the second precursor solution in Examples 1 to 4 is high, and it forms small particles after airflow drying and sintering. Within a certain range, the increase of small particles is conducive to improving the compaction density of the material, that is, to improve the electrochemical performance. Example 5 adjusts Li and P relative to Example 1, and the corresponding compaction density and electrochemical performance are relatively improved. This is because the increase in the amount of Li corresponds to the increase in the total amount of mobile lithium, and the increase in the P element corresponds to the increase in the size of the particles, and the corresponding compaction and electrochemical performance are improved. In Example 6, the Ti doping in the second precursor solution is removed relative to Example 1, and the corresponding electrochemical performance is lower than that of Example 1, and the corresponding particle size will be reduced, resulting in the corresponding compaction density and electrochemical performance being lower than that of Example 1. However, overall, the balance between high compaction density and electrochemical performance can also be achieved. Similarly, it can be seen from Example 7 that this method is also suitable for precursors containing different main elements, and a composite phosphate-based positive electrode material with high chemical properties is obtained after compounding.

[0201] In comparison, the composite phosphate positive electrode materials in Comparative Examples 1 and 2 are obtained by sintering a single precursor source of lithium iron manganese phosphate. In Comparative Example 3, two precursor sources of lithium iron manganese phosphate and lithium iron manganese phosphate are dried separately and then mixed and sintered. Although their electrochemical properties are slightly increased, the compaction density is reduced.

[0202] On the whole, through the technical scheme of the present invention, two or more different precursor sources are mixed into the composite phosphate-based positive electrode precursor. Due to the regulatory effect of the types and contents of elements in different precursor sources, the compaction density of the sintered composite phosphate composite positive electrode material is generally relatively improved, and the electrochemical performance is improved. At the same time, it can also be seen that within a certain range, when the proportion of precursor sources that can be sintered to form small particles is increased, the grading effect of the generated finished product is better, and the corresponding compaction density and electrochemical performance are relatively improved.

[0203] 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 composite phosphate positive electrode precursor, characterized in that: At least two mutually mixed precursor sources are included, each of which independently includes the main elements Li and P, and Fe and / or Mn; and each of the precursor sources mutually includes at least one of the following 1) to 4): 1) Different main element types; 2) Different main element contents; 3) Different types of doping elements; 4) Different doping element contents.

2. The composite phosphate positive electrode precursor according to claim 1, characterized in that: The doping element includes one or more of transition metals, alkaline earth metals, Group IIIA metals, Group VIA metals, and Group VA metals; and / or, The mass content of any one of the doping elements in any one of the precursor sources is 50 to 20,000 ppm; and / or, The mass content of any one of the precursor sources in the composite phosphate-based positive electrode precursor is 5% to 95%.

3. The composite phosphate positive electrode precursor according to claim 2, characterized in that: The transition metal includes one or more of Ti, Ni, V, Nb, Zr, Cr, Co, Zn, and Mo; and / or, The alkaline earth metal includes one or more of Mg and Ca; and / or, The IIIA group metal includes one or more of Al and Ga; and / or, The VIA Group metal includes one or more of Ge and Sn; and / or, The VA group metal includes one or more of Sb and Bi; and / or, The mass content of any one of the doping elements in any one of the precursor sources is 100 to 9000 ppm; and / or, The mass content of any one of the precursor sources in the composite phosphate-based positive electrode precursor is 10% to 90%.

4. The composite phosphate positive electrode precursor according to any one of claims 1 to 3, characterized in that: The particle sizes of at least two of the precursor sources are different; and / or, The particle size D50 of at least one of the precursor sources is 50nm≤D50≤200nm, and the particle size D50 of another of the precursor sources is 200nm≤D50≤500nm; and / or, At least one of the precursor sources comprises one or more doping elements selected from the group consisting of Ti, Ni, and V; and / or, The composite phosphate positive electrode precursor includes a first precursor source and a second precursor source; the first precursor source includes a first doping element having a first mass content, and the second precursor source includes a second doping element having a second mass content; The first doping element and the second doping element are of different element types, and / or the first content and the second content are different.

5. The composite phosphate positive electrode precursor according to claim 4, characterized in that: The composite phosphate-based positive electrode precursor further includes an nth precursor source, and the nth precursor source includes an nth doping element having an nth content by mass; n is a positive integer greater than 2, the element type of the nth doping element is different from at least one of the first to n-1th doping elements, and / or the nth content is different from at least one of the first to n-1th contents.

6. A method for preparing a composite phosphate positive electrode precursor, characterized in that: include: At least two precursor solutions are provided; each of the precursor solutions independently comprises the main elements Li and P, and Fe and / or Mn; and each of the precursor solutions mutually comprises at least one of the following 1) to 4): 1) Different main element types; 2) Different main element contents; 3) Different types of doping elements; 4) Different doping element contents; The precursor solutions are dried and mixed during the drying process to obtain a composite phosphate-based positive electrode precursor comprising at least two mutually mixed precursor sources.

7. The method for preparing the composite phosphate positive electrode precursor according to claim 6, characterized in that: The step of providing at least two of the precursor solutions comprises: Providing a first precursor solution, wherein the first precursor solution includes a first doping element having a first mass content; providing a second precursor solution, wherein the second precursor solution includes a second doping element having a second mass content; The first doping element and the second doping element are of different element types, and / or the first content and the second content are different; and / or, The drying method includes air flow drying; and / or, At least two of the precursor sources have different particle sizes.

8. The method for preparing the composite phosphate positive electrode precursor according to claim 7, characterized in that: The solid mass ratio of the precursor liquid corresponding to the precursor source with a larger particle size to the precursor liquid corresponding to the precursor source with a smaller particle size is (6:4) to (9:1); and / or, The air flow speed in the air flow drying process is 0.01 to 10 m / s; and / or, The air flow temperature in the air flow drying process is 45 to 150° C.; and / or, The airflow drying treatment step includes: inputting different precursor liquids into the same curing chamber into which airflow is introduced through different paths, and drying and mixing them under the action of the airflow.

9. A method for preparing a composite phosphate positive electrode material, characterized in that: The composite phosphate-based positive electrode precursor according to any one of claims 1 to 5 is subjected to a calcination treatment.

10. A composite phosphate positive electrode material, characterized in that: The invention comprises at least two active components mixed with each other, each of which independently comprises the main elements Li and P, and Fe and / or Mn; and each of the active components mutually comprises at least one of the following 1) to 4): 1) Different main element types; 2) Different main element contents; 3) Different types of doping elements; 4) Different doping element contents.

11. The composite phosphate positive electrode material according to claim 10, characterized in that: The composite phosphate-based positive electrode material comprises first-stage particles and second-stage particles, the particle size range D1 of the first-stage particles is 50nm≤D1≤500nm, the particle size range D2 of the second-stage particles is 500nm<D2≤1000nm, and the mass ratio of the first-stage particles to the second-stage particles is (4:6) to (1:9); and / or, The particle size distribution index SPAN of the composite phosphate positive electrode material is ≥ 2; and / or, The compaction density of the composite phosphate positive electrode material is greater than 2.4 g / cm 3 .

12. A secondary battery, characterized in that: It comprises the composite phosphate positive electrode material as described in any one of claims 10 to 11.

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