Phosphate-series high-compaction positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of secondary battery materials, and particularly relates to a phosphate-series high-compaction positive electrode material as well as a preparation method and application thereof. According to the phosphate-based high-compaction positive electrode material, a precursor, a lithium source, a carbon source and a doping source are mixed, and particle materials with different particle size gradients are formed through carbon source selection and sanding parameter control. According to the phosphate-series high-compaction positive electrode material, the bowls are arranged in the center of the sagger in sequence to form a large-small-large particle sandwich structure, so that the filling rate of the material is improved, meanwhile, central particles are prevented from being fused in the calcining process, and the application performance of the positive electrode material is effectively guaranteed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary battery materials, and particularly relates to a phosphate-based high-compaction positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] A lithium ion battery is a high-energy-density secondary battery, which has the advantages of long service life, no memory effect, environmental friendliness, etc. Since its commercialization, it has been widely used in various portable electronic devices such as mobile phones, notebook computers, etc. At present, the commercialized lithium ion battery generally comprises four main parts: a positive electrode, a negative electrode, an electrolyte and a separator. The positive electrode material acts as a lithium source in the lithium ion battery, and its main structure usually contains lithium ions that can be freely deintercalated.

[0003] In recent years, with the progress of battery cell PACK technology and the continuous upgrading and iteration of battery materials, phosphate-based positive electrode materials such as lithium iron phosphate and lithium manganese iron phosphate have become the mainstream choice of lithium ion battery positive electrode materials. At present, although the lithium iron phosphate positive electrode material has realized mass production supply of the fourth-generation high-compaction product (powder compaction > 2.60 g / cm 3 However, the traditional process usually uses a one-time sintering process to prepare high-compaction materials, which is easy to cause excessive growth or fusion of particles, thereby affecting the specific capacity of the material. Therefore, the fourth-generation high-compaction product often uses a two-time sintering method, i.e. crushing and two-time coating calcination of the material after one-time sintering, and optimizing the finished particle, but there are problems of complex synthesis route, high energy consumption of the two-time sintering process, which seriously affects the production capacity. For example, the power-type high-rate lithium iron phosphate positive electrode material disclosed in Chinese patent CN118373400A uses an organic carbon source for one-time coating calcination, and then uses functionalized graphene coating to further improve the dispersibility and rate performance of the material. The two-time coating and two-time sintering process makes the synthesis energy consumption high and the cost high.

[0004] Therefore, it is expected in the art to develop a phosphate-based positive electrode material with high compaction through only one calcination process, which has a positive significance for the development of secondary battery materials. SUMMARY

[0005] The first object of the present application is to provide a phosphate-based high-compaction positive electrode material, which is prepared by mixing gradient particle materials with different particle sizes and arranging them in the order of large-small-large to form a particle sandwich structure material. The positive electrode material can achieve superior application performance through only one calcination process. The second object of the present application is to provide a preparation method of the above-mentioned phosphate-based high-compaction positive electrode material. The third object of the present application is to provide the application of the above-mentioned phosphate-based high-compaction positive electrode material in the field of secondary batteries, especially lithium ion batteries.

[0006] To address the aforementioned technical problems, this invention provides a phosphate-based high-pressure positive electrode material, wherein the positive electrode material comprises a first particle, a second particle, and a third particle; wherein... The first particle includes a first precursor, a first lithium source, a first carbon source, and a first dopant source; The second particle includes a second precursor, a second lithium source, a second carbon source, and a second doping source; The third particle includes a third precursor, a third lithium source, a third carbon source, and a third doping source; The relationship between the particle size D50 value D1 of the first particle, the particle size D50 value D2 of the second particle, and the particle size D50 value D3 of the third particle is: D1≥D3>D2.

[0007] Specifically, in the phosphate-based high-pressure positive electrode material, the particle size D50 value D1 of the first particle, the particle size D50 value D2 of the second particle, and the particle size D50 value D3 of the third particle are related as follows: D1:D2:D3 = (5-1):1:(5-1); Preferably, the particle size D50 value D2 of the second particle is 0.4-1.0 μm.

[0008] Specifically, in the phosphate-based high-pressure positive electrode material, the mass ratio of the first particle, the second particle, and the third particle is (10-1):1:(10-1).

[0009] Specifically, the phosphate-based high-pressure positive electrode material: The first precursor, the second precursor, and the third precursor independently include ferric phosphate or ferric manganese phosphate; and / or, The first, second, and third lithium sources independently include at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, lithium oxalate, lithium acetate, lithium sulfate, lithium nitrate, or lithium chloride; and / or, The doping elements of the first, second, and third doping sources are independent of each other and include at least one of the following elements: aluminum, magnesium, nickel, cobalt, titanium, copper, calcium, niobium, chromium, zinc, lanthanum, antimony, tellurium, strontium, tungsten, indium, or yttrium; and / or, The first and third carbon sources are independent of each other and include organic carbon sources; and / or, The second carbon source includes a composite carbon source mixture of organic and inorganic carbon sources; Preferably, the organic carbon source includes at least one of glucose, starch, citric acid, sucrose, chitosan, or polyethylene glycol; Preferably, the inorganic carbon source includes at least one of carbon black, graphene, or carbon nanotubes.

[0010] Specifically, the phosphate-based high-pressure positive electrode material: The molar ratio of the first lithium source to the first precursor, the molar ratio of the second lithium source to the second precursor, and the molar ratio of the third lithium source to the third precursor are independently 1-1.05:1; and / or, In the first carbon source and the third carbon source, the mass of carbon element is controlled to be 5-20 wt% of the first precursor and the third precursor, respectively; and / or, In the second carbon source, the mass of carbon element is controlled to be 0-25 wt% of the second precursor. Since the second particle accounts for a small proportion in the whole system, and during the calcination process, the carbon source in the first and third particles is liquefied / gasified and transferred to the second particle, therefore, under certain conditions, the second particle may not contain carbon element. The amount of the first doping source, the second doping source, and the third doping source added is independent of each other and is 0-1 wt% of the first precursor, the second precursor, and the third precursor.

[0011] The present invention also discloses a method for preparing the phosphate-based high-pressure positive electrode material, comprising the steps of mixing and calcining the first particle, the second particle and the third particle according to a selected mass ratio.

[0012] Specifically, the preparation method of the phosphate-based high-pressure positive electrode material is as follows: The mixing step includes the step of uniformly loading the first particle, the second particle, and the third particle into the sagger in the order of the first particle, the second particle, and the third particle; and / or, The calcination step includes calcining at 550-1000℃ for 4-20 hours under a protective atmosphere.

[0013] Specifically, the method for preparing the phosphate-based high-pressure positive electrode material further includes the steps of preparing the first particle, the second particle, and / or the third particle respectively; wherein, The preparation steps of the first particle include taking a selected amount of the first precursor, the first lithium source, the first carbon source, and the first dopant source, mixing them, and grinding them to a selected particle size. The preparation steps of the second particle include taking a selected amount of the second precursor, the second lithium source, the second carbon source, and the second dopant source, mixing them, and grinding them to a selected particle size; The preparation steps of the third particle include mixing selected amounts of the third precursor, the third lithium source, the third carbon source, and the third dopant source, and grinding them to a selected particle size.

[0014] The present invention also discloses the application of the phosphate-based high-pressure positive electrode material or the phosphate-based high-pressure positive electrode material prepared by the method in the field of secondary batteries; Preferably, the secondary battery includes a lithium-ion secondary battery.

[0015] The present invention also discloses a secondary battery positive electrode sheet, a secondary battery, a secondary battery module, a secondary battery pack, or an electrical device comprising the phosphate-based high-pressure positive electrode material or the phosphate-based high-pressure positive electrode material prepared by the method.

[0016] Specifically, the positive electrode sheet of the lithium-ion battery improved by the present invention comprises a positive electrode material including the phosphate-based high-pressure positive electrode material.

[0017] Specifically, the lithium-ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode; the positive electrode is the positive electrode of the lithium-ion battery.

[0018] Specifically, the secondary battery module includes the lithium-ion secondary battery.

[0019] Specifically, the secondary battery pack includes the secondary battery module.

[0020] Specifically, the electrical device includes at least one selected from the lithium-ion secondary battery, the battery module, or the secondary battery pack.

[0021] The phosphate-based high-pressure positive electrode material of this invention is formed by mixing a precursor, a lithium source, a carbon source, and a dopant source, and by controlling the selection of the carbon source and the milling parameters to create particulate materials with different particle size gradients. In the phosphate-based high-pressure positive electrode material of this invention, the particle size of the particulate material coated with the composite carbon source is controlled to be smaller than that of the particulate material coated only with the organic carbon source. These particles are arranged in a specific order in the center of the crucible to form a large-small-large particle sandwich structure, which improves the material filling rate and avoids the melting and coalescence of the central particles during calcination, effectively ensuring the application performance of the positive electrode material.

[0022] The method for preparing the phosphate-based high-pressure positive electrode material of this invention involves first filling a crucible with a certain proportion of large-sized particles coated with an organic carbon source, then filling it with small-sized particles coated with a composite carbon source, and finally filling it with a certain proportion of large-sized particles coated with an organic carbon source. Under gravity, the small particles naturally descend and fill the pores of the larger particles below, improving the powder filling rate. On the other hand, the central part of the crucible has poor heat dissipation, and during calcination, the actual temperature of the particles in the central part of the crucible is high, and the holding time is long, making the particles prone to excessive growth or fusion, thus improving the compaction and electrochemical performance of the material powder.

[0023] The carbon source coated in the phosphate-based high-compact cathode material of the present invention, especially the inorganic carbon source in the composite carbon source, can play a role in inhibiting particle growth and isolating particle contact and melting. The present invention adopts a large-small-large particle sandwich structure, and a high-compact phosphate-based cathode material can be obtained through one calcination. Attached Figure Description

[0024] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 Microscopic characterization diagram of the phosphate-based high-pressure positive electrode material prepared in Example 1; Figure 2 Microscopic characterization diagram of the phosphate-based cathode material prepared for Comparative Example 1. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0027] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0028] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0029] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0031] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0032] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0033] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0034] The following describes the lithium-ion secondary battery of this application.

[0035] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode material of this application.

[0036] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0037] The positive electrode film includes a positive electrode active material. The positive electrode active material can be selected from materials capable of absorbing and releasing lithium. As an example, the positive electrode active material can include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese iron phosphate (LiFeMnPO4), and lithium manganese phosphate (LiMnPO4). These materials can be used alone or in combination.

[0038] The modified compounds for the above-mentioned positive electrode active materials can be modified by doping, surface coating, or both doping and coating.

[0039] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0040] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0041] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0042] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0043] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0044] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0045] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0046] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0047] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0048] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0049] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0050] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0051] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0052] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0053] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0054] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0055] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0056] [Isolation membrane] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0057] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0058] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0059] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0060] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0061] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0062] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0063] Example 1 The preparation method of the phosphate-based high-pressure positive electrode material described in this embodiment includes the following steps: S1. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 6g of glucose and 0.1g of titanium dioxide until D50=300-350nm, and then spray dry to prepare the first particle; S2. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 5g of glucose, 0.1g of graphene and 0.1g of titanium dioxide until D50=200-250nm, and then spray dry to prepare the second particle. S3. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 5g of glucose, and 0.1g of titanium dioxide until D50=250-300nm, and then spray dry to prepare the third particle. S4. Weigh the first particle, the second particle, and the third particle according to a mass ratio of 4:2:4, and spread them evenly into a crucible in sequence. Sinter them at 800°C for 10 hours under a nitrogen atmosphere. After sintering, crush them to obtain the desired positive electrode material.

[0064] The microstructure characterization diagram of the phosphate-based high-pressure positive electrode material prepared in this embodiment is attached. Figure 1 As shown, the cathode material exhibits a uniform distribution of small and large particles, with small particles concentrated in the 200-400nm range and large particles in the 800-1200nm range, resulting in a particle size distribution effect that is beneficial for compaction and electrical performance improvement.

[0065] Example 2 The preparation method of the phosphate-based high-voltage positive electrode material in this embodiment is the same as that in Embodiment 1, except that the first particle, the second particle, and the third particle are weighed in a mass ratio of 9:2:9 and loaded into a crucible in sequence.

[0066] Example 3 The preparation method of the phosphate-based high-pressure positive electrode material in this embodiment is the same as that in Embodiment 1, except that the first particle, the second particle, and the third particle are weighed in a mass ratio of 7:6:7 and loaded into a crucible in sequence.

[0067] Example 4 The preparation method of the phosphate-based high-pressure positive electrode material in this embodiment is the same as that in Embodiment 1, except that the first particle is ground to D50=300-350nm; and the third particle is ground to D50=300-350nm. Example 5 The preparation method of the phosphate-based high-pressure positive electrode material in this embodiment is the same as that in Embodiment 1, except that the first particle is ground to D50=250-300nm and the third particle is ground to D50=300-350nm. Example 6 The preparation method of the phosphate-based high-pressure positive electrode material in this embodiment is the same as that in Embodiment 1, except that the carbon source of the second particle is 5g of glucose and 0.1g of conductive carbon black. Example 7 The preparation method of the phosphate-based high-pressure positive electrode material in this embodiment is the same as that in Embodiment 1, except that the amount of titanium dioxide added in the first particle, the second particle, and the third particle is 0.15g.

[0068] Example 8 The preparation method of the phosphate-based high-pressure positive electrode material in this embodiment is the same as that in Embodiment 1, except that the doping source is 0.1g of titanium dioxide and 0.015g of niobium pentoxide; Comparative Example 1 The method for preparing the cathode material described in this comparative example includes the following steps: 50g of iron phosphate, 12.5g of lithium carbonate, 6g of glucose, and 0.1g of titanium dioxide were ground in a sand mill until D50 < 350nm. After spray drying, the mixture was sent to a sintering furnace and sintered at 800℃ for 10 hours in a nitrogen atmosphere. After sintering, the mixture was crushed to obtain the cathode material.

[0069] The microstructure of the phosphate-based high-pressure cathode material prepared in this comparative example is shown in the attached figure. Figure 2 As shown, in the cathode material, some particles excessively grow / merge, forming primary particles >5µm, which severely restricts the material's electrical properties.

[0070] Comparative Example 2 The method for preparing the cathode material described in this comparative example includes the following steps: S1. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 6g of glucose and 0.1g of titanium dioxide until D50=250-300nm, and then spray dry to prepare the first particle; S2. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 5g of glucose, 0.1g of graphene and 0.1g of titanium dioxide until D50=200-250nm, and then spray dry to prepare the second particle. S3. Weigh the first and second particles at a mass ratio of 8:2 and mix them. Sinter them at 800℃ for 10 hours in a nitrogen atmosphere. After sintering, crush them to obtain the cathode material.

[0071] Comparative Example 3 The preparation method of the phosphate-based high-pressure positive electrode material described in this comparative example is the same as that in comparative example 2, except that the mass ratio of the first particle to the second particle is 9:1. Comparative Example 4 The preparation method of the phosphate-based high-pressure positive electrode material described in this comparative example is the same as that in comparative example 2, except that the mass ratio of the first particle to the second particle is 7:3. Comparative Example 5 S1. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 6g of glucose and 0.1g of titanium dioxide until D50=300-350nm, and then spray dry to prepare the first particle; S2. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 5g of glucose, 0.1g of graphene and 0.1g of titanium dioxide until D50=200-250nm, and then spray dry to prepare the second particle. S3. Grind and mix 50g of iron phosphate, 12.5g of lithium carbonate, 6g of glucose and 0.1g of titanium dioxide until D50=250-300nm, and then spray dry to prepare the third particle; S5. Weigh the first and second particles according to a mass ratio of 4:2:4 and mix them. Sinter them at 800℃ for 10 hours in a nitrogen atmosphere. After sintering, crush them to obtain the positive electrode material.

[0072] Experimental Example 1. Performance Testing The high-compaction cathode materials obtained under the above-mentioned Examples 1-8 and Comparative Examples 1-5 were subjected to relevant performance tests. The tests were conducted using a powder compaction density tester (3T pressure) and a battery testing system (2.0-3.65V). The data results are shown in Table 1 below.

[0073] Table 1 Performance Test Results

[0074] The data from Examples 1-8 show that by controlling the ratio, particle size, carbon source, and doping source of the first, second, and third particles, high-pressure compaction phosphate-based cathode materials suitable for different application scenarios can be prepared. Although particle gradation was carried out during the preparation process of materials in Comparative Examples 1-5, the mixing of materials before plating resulted in lower powder compaction density and discharge capacity. This indicates that the cathode material described in this invention effectively improves the powder compaction density and electrochemical performance through the directional and orderly arrangement of particles of different sizes.

[0075] In summary, the phosphate-based high-compact cathode material of this invention avoids excessive particle growth / fusion during calcination by grinding particles of different sizes separately, compounding and oriented calcination, and preparing cathode materials with high powder compaction and excellent electrochemical performance through a one-time sintering process. This solves the problem of poor electrochemical performance caused by excessive particle growth / fusion in the prior art, optimizes particle gradation, and improves the powder compaction density and electrochemical performance of the material.

[0076] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A phosphate-based high-pressure positive electrode material, characterized in that, The positive electrode material comprises a first particle, a second particle, and a third particle; wherein, The first particle includes a first precursor, a first lithium source, a first carbon source, and a first dopant source; The second particle includes a second precursor, a second lithium source, a second carbon source, and a second doping source; The third particle includes a third precursor, a third lithium source, a third carbon source, and a third doping source; The relationship between the particle size D50 value D1 of the first particle, the particle size D50 value D2 of the second particle, and the particle size D50 value D3 of the third particle is: D1≥D3>D2.

2. The phosphate-based high-pressure positive electrode material according to claim 1, characterized in that, The relationship between the particle size D50 value D1 of the first particle, the particle size D2 of the second particle, and the particle size D50 value D3 of the third particle is: D1:D2:D3 = (5-1):1:(5-1); Preferably, the particle size D50 value D2 of the second particle is 0.4-1.0 μm.

3. The phosphate-based high-pressure positive electrode material according to claim 2, characterized in that, The mass ratio of the first particle, the second particle, and the third particle is (10-1):1:(10-1).

4. The phosphate-based high-pressure positive electrode material according to any one of claims 1-3, characterized in that: The first precursor, the second precursor, and the third precursor independently include ferric phosphate or ferric manganese phosphate; and / or, The first, second, and third lithium sources independently include at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, lithium oxalate, lithium acetate, lithium sulfate, lithium nitrate, or lithium chloride; and / or, The doping elements of the first, second, and third doping sources are independent of each other and include at least one of the following elements: aluminum, magnesium, nickel, cobalt, titanium, copper, calcium, niobium, chromium, zinc, lanthanum, antimony, tellurium, strontium, tungsten, indium, or yttrium; and / or, The first and third carbon sources are independent of each other and include organic carbon sources; and / or, The second carbon source includes a composite carbon source mixture of organic and inorganic carbon sources; Preferably, the organic carbon source includes at least one of glucose, starch, citric acid, sucrose, chitosan, or polyethylene glycol; Preferably, the inorganic carbon source includes at least one of carbon black, graphene, or carbon nanotubes.

5. The phosphate-based high-pressure positive electrode material according to claim 4, characterized in that: The molar ratio of the first lithium source to the first precursor, the molar ratio of the second lithium source to the second precursor, and the molar ratio of the third lithium source to the third precursor are independently 1-1.05:1; and / or, In the first carbon source and the third carbon source, the mass of carbon element is controlled to be 5-20 wt% of the first precursor and the third precursor, respectively; and / or, In the second carbon source, the mass of carbon is controlled to be 0-25 wt% of the second precursor. The amount of the first doping source, the second doping source, and the third doping source added is independent of each other and is 0-1 wt% of the first precursor, the second precursor, and the third precursor.

6. A method for preparing a phosphate-based high-pressure positive electrode material as described in any one of claims 1-5, characterized in that, The process includes the steps of mixing and calcining the first, second, and third particles according to the selected mass ratio.

7. The method for preparing the phosphate-based high-pressure positive electrode material according to claim 6, characterized in that: The mixing step includes the step of uniformly loading the first particle, the second particle, and the third particle into the sagger in the order of the first particle, the second particle, and the third particle; and / or, The calcination step includes calcining at 550-1000℃ for 4-20 hours under a protective atmosphere.

8. The method for preparing the phosphate-based high-pressure positive electrode material according to claim 6 or 7, characterized in that, The method further includes the steps of preparing the first particle, the second particle, and / or the third particle respectively; wherein... The preparation steps of the first particle include taking a selected amount of the first precursor, the first lithium source, the first carbon source, and the first dopant source, mixing them, and grinding them to a selected particle size. The preparation steps of the second particle include taking a selected amount of the second precursor, the second lithium source, the second carbon source, and the second dopant source, mixing them, and grinding them to a selected particle size; The preparation steps of the third particle include mixing selected amounts of the third precursor, the third lithium source, the third carbon source, and the third dopant source, and grinding them to a selected particle size.

9. The application of the phosphate-based high-pressure positive electrode material according to any one of claims 1-5 or the phosphate-based high-pressure positive electrode material prepared by the method according to any one of claims 6-8 in the field of secondary batteries; Preferably, the secondary battery includes a lithium-ion secondary battery.

10. A secondary battery positive electrode sheet, a secondary battery, a secondary battery module, a secondary battery pack, or an electrical device comprising the phosphate-based high-pressure positive electrode material according to any one of claims 1-5 or the phosphate-based high-pressure positive electrode material prepared by the method according to any one of claims 6-8.

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