Positive electrode material, preparation method thereof and secondary battery

Abstract

The invention relates to a positive electrode material, a preparation method thereof and a secondary battery, the positive electrode material comprises a phosphate core and a carbon coating layer, the phosphate core is coated by the carbon coating layer, the particle size of primary particles of the positive electrode material is 250-450 nm, and the particle size variance of the positive electrode material is 1-10. The particle granularity of the positive electrode material is in normal distribution, the finished product particles are relatively large and uniform in size, and the compaction density and the capacity are remarkably improved; moreover, the surface of the phosphate core is uniformly coated with the carbon coating layer, and the thickness of the carbon coating layer is moderate, so that not only can the electronic conductivity of the positive electrode material be improved, but also the discharge capacity, coulombic efficiency and other electrochemical properties of the composite phosphate positive electrode material can be improved.

Description

Technical Field

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

[0002] Phosphate-based positive electrode materials commonly use lithium iron phosphate and lithium manganese iron phosphate. Both materials have an olivine structure and have the same theoretical specific capacity and good safety performance. With the continuous deepening of the application and development of phosphate-based positive electrode materials, people have put forward higher and higher requirements on the material's compaction density, processing performance and other indicators. Generally speaking, the compaction density of the powder is affected by its particle size, morphology and consistency. For phosphate-based positive electrode materials, the size and morphology of the precursor have a key and direct impact on the finished particles. Currently, phosphate-based positive electrode materials are mainly prepared by high-temperature solid-phase sintering methods. However, the particle size and particle distribution of the phosphate-based positive electrode materials obtained by conventional high-temperature solid-phase sintering methods are uneven, and the carbon coating uniformity is poor, resulting in poor carbon coating quality, low compaction density, and small specific capacity of the phosphate-based positive electrode materials, which is not conducive to widespread application. Summary of the Invention

[0003] The purpose of the present invention is to provide a positive electrode material and a preparation method thereof, and a secondary battery, so as to solve the problems of uneven particle size and particle distribution of phosphate-based positive electrode materials and poor carbon coating uniformity in the prior art.

[0004] To achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0005] In a first aspect, the present invention provides a positive electrode material comprising a phosphate core and a carbon coating layer, wherein the carbon coating layer coats the phosphate core, the primary particles of the positive electrode material have a particle size of 250 nm to 450 nm, and the particle size variance of the positive electrode material is 0 to 10.

[0006] In some embodiments, the precursor of the carbon coating layer includes an amphiphilic bottle brush polymer, and the amphiphilic bottle brush polymer includes a main chain segment, a hydrophilic segment, and a hydrophobic segment, wherein the hydrophilic segment and the hydrophobic segment are both connected to the main chain segment.

[0007] In some embodiments, the molecular chain of the amphiphilic bottle brush polymer is in the shape of a bottle brush, and the hydrophilic segment and the hydrophobic segment are respectively distributed on opposite sides of the main chain segment.

[0008] In some embodiments, the hydrophilic segment contains one or more of a hydroxyl group, an amino group, a carboxyl group, a phosphate group, a sulfonic acid group, and an ether bond.

[0009] In some embodiments, the hydrophobic segment contains one or more of a siloxy group, an ester group, an aromatic group, and an alkane group.

[0010] In some embodiments, the main chain segment includes one or more of polyethylene, polyethylene glycol, polydimethylsiloxane, polyurethane, polymethyl methacrylate, polystyrene, polyimide, and polyphenylene ether.

[0011] In some embodiments, the molecular weight of the amphiphilic bottle brush polymer is 10,000 to 50,000.

[0012] In some embodiments, the molecular weight of the hydrophilic segment is 500 to 5000.

[0013] In some embodiments, the molecular weight of the hydrophobic segment is 500 to 5000.

[0014] In some embodiments, the molar ratio of the hydrophilic segment to the hydrophobic segment is 1:(0.1-10).

[0015] In some embodiments, the thickness of the carbon coating layer is 0.5 nm to 5.0 nm, and the thickness variance of the carbon coating layer is 0.1 to 4.0.

[0016] In some embodiments, the carbon coating layer contains organic functional groups, and the organic functional groups include one or more of carboxyl groups, hydroxyl groups, and carbon-carbon double bonds.

[0017] In some embodiments, in the Raman spectrum curve of the positive electrode material, the integrated intensity ratio of the D peak to the G peak is D / I G It is 0.70~0.99.

[0018] In a second aspect, the present invention provides a method for preparing a positive electrode material, which is used to prepare the positive electrode material as described in the first aspect. The preparation method comprises: mixing raw materials comprising at least a lithium source, an iron source, and a phosphorus source to obtain a mixture, adding the mixture and an amphiphilic bottle brush polymer to an organic solvent in a mass ratio, removing the organic solvent after sufficient mixing to obtain a solid material; and calcining the solid material to obtain a positive electrode material.

[0019] In some embodiments, the mixture and the amphiphilic bottle brush polymer are added to an organic solvent in a mass ratio, and the organic solvent is removed after sufficient mixing to obtain a solid material, including: adding the mixture and the amphiphilic bottle brush polymer A to an organic solvent A in a mass ratio, and removing the organic solvent A after sufficient mixing to obtain a solid precursor; calcining the solid precursor to obtain an intermediate; adding the intermediate and the amphiphilic bottle brush polymer B to an organic solvent B in a mass ratio, and removing the organic solvent B after sufficient mixing to obtain the solid material.

[0020] In some embodiments, the mass ratio of the mixture to the amphiphilic bottle brush polymer A is 100:(40-60); the mass ratio of the intermediate to the amphiphilic bottle brush polymer B is 100:(5-10).

[0021] In a third aspect, the present invention provides a positive electrode plate, which includes the positive electrode material as described in the first aspect, or the positive electrode plate includes the positive electrode material prepared by the preparation method of the positive electrode material as described in the second aspect.

[0022] In a fourth aspect, the present invention provides a secondary battery, wherein the secondary battery comprises the positive electrode material as described in the first aspect, or the secondary battery comprises the positive electrode material prepared by the preparation method of the positive electrode material as described in the second aspect.

[0023] The positive electrode material provided by the present invention includes a phosphate core and a carbon coating layer, wherein the particle size and particle size variance of the primary particles of the positive electrode material meet the above-mentioned ranges, so that the particle size of the positive electrode material is normally distributed, the finished particles are large and the particle size is uniform, and the compaction density and capacity are significantly improved; and the carbon coating layer is uniformly coated on the surface of the phosphate core, and the thickness of the carbon coating layer is moderate, which can not only improve the electronic conductivity of the positive electrode material, but also improve the electrochemical properties such as the discharge capacity and coulombic efficiency of the composite phosphate-based positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 is a schematic cross-sectional view of a positive electrode material in one embodiment;

[0026] Figure 2 is a schematic cross-sectional view of a precursor of a positive electrode material in one embodiment;

[0027] Figure 3 is a diagram of the molecular structure of an amphiphilic bottlebrush polymer in one embodiment;

[0028] Figure 4 is a flow chart for preparing a positive electrode material in one embodiment;

[0029] Figure 5 is a flow chart for preparing a secondary coating of a positive electrode material in one embodiment;

[0030] Figure 6 is a scanning electron microscope image (SEM) of the positive electrode material provided in Example 1;

[0031] Figure 7 is a transmission electron micrograph (TEM) of the positive electrode material provided in Example 1;

[0032] Figure 8 This is the electrochemical curve of the secondary battery prepared with the positive electrode material provided in Example 1 at 0.1C. DETAILED DESCRIPTION

[0033] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0035] It should be noted that the "ranges" disclosed herein are defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values ​​listed are 1 and 2, and if the maximum range values ​​listed are 3, 4, and 5, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present invention, unless otherwise specified, the numerical range "a to b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] All steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, a statement that a method includes steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a statement that a method may also include step (c) indicates that step (c) may be added to the method in any order, e.g., the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0037] The following embodiments of the present invention are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0038] The present invention provides a positive electrode material 100, please refer to Figure 1 The positive electrode material 100 has a core-shell structure, including a phosphate core 10 and a carbon coating layer 20, wherein the carbon coating layer 20 covers the phosphate core 10, and the particle size of the primary particles of the positive electrode material 100 is 250 nm to 450 nm, and the particle size variance of the positive electrode material 100 is 1 to 10.

[0039] In some embodiments, the phosphate core 10 comprises phosphate, the chemical formula of which comprises Li x Mn y Fe 1-y- z Mz PO4, wherein 0.9≤x≤1, 0≤y<0.85, 0≤z<0.01, and M includes one or more of Mg, Al, Ti, V, Mo, Nb, La, Zn, Zr, and Ce. It should be noted that the phosphate core 10 may also be lithium iron phosphate, i.e., it does not include Mn and M elements. The purpose of adding the doping element M is to introduce certain defects within the lattice of the phosphate core 10, broadening the lithium ion transmission channel, thereby improving the lithium ion mobility of the material, and further improving the material's performance such as discharge specific capacity.

[0040] In some embodiments, the carbon coating layer 20 comprises a carbon material obtained by carbonizing an organic polymer. In a specific embodiment, the carbon coating layer 20 is obtained by carbonizing an amphiphilic bottlebrush polymer. It should be noted that amphiphilic bottlebrush polymers are a class of polymers that possess both hydrophilic (polar) and hydrophobic (non-polar) groups. The unique structure of amphiphilic bottlebrush polymers enables them to exhibit unique self-assembly behaviors in different solvents or at interfaces.

[0041] In some embodiments, the particle size of the primary particles of the positive electrode material 100 can be understood as the average particle size of the primary particles of the positive electrode material 100, that is, the average value of the particle sizes of the primary particles of the positive electrode material 100. In specific embodiments, the particle size of the primary particles of the positive electrode material 100 can be 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm, 400 nm, 430 nm, or 450 nm.

[0042] In some embodiments, the particle size variance of the positive electrode material 100 refers to the variance calculated from the standard deviation of the particle size of each (primary) particle in the positive electrode material 100 after fitting it to a lognormal distribution. The particle size variance of the positive electrode material 100 reflects the degree of particle size dispersion of the primary particles of the positive electrode material 100. The larger the variance, the more dispersed the particle size of the primary particles; the smaller the variance, the more concentrated the particle size of the primary particles. In specific embodiments, the particle size variance of the positive electrode material 100 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0043] The positive electrode material 100 provided by the present invention includes a phosphate core 10 and a carbon coating layer 20, wherein the particle size and particle size variance of the primary particles of the positive electrode material 100 satisfy the above-mentioned range, so that the particle size of the positive electrode material 100 is normally distributed, the finished particles are large and the particle size is uniform, and the compaction density and capacity are significantly improved; and the carbon coating layer 20 is uniformly coated on the surface of the phosphate core 10, and the thickness of the carbon coating layer 20 is moderate, which can not only improve the electronic conductivity of the positive electrode material 100, but also improve the electrochemical properties of the composite phosphate-based positive electrode material 100, such as the discharge capacity and coulombic efficiency.

[0044] At the same time, the carbon coating layer 20 provided by the present invention is also obtained by carbonizing an amphiphilic bottle brush polymer. By utilizing the hydrophilic and hydrophobic effects of the amphiphilic bottle brush polymer in the solution, the precursor of the phosphate core 10 is evenly wrapped in the amphiphilic bottle brush polymer formed by self-assembly, and the size and morphology of the amphiphilic bottle brush polymer are controlled to achieve the effect of controlling the particle size of the core; at the same time, the coated amphiphilic bottle brush polymer can act as a carbon source to play a reducing role, avoiding the introduction of additional carbon sources, and achieving carbon coating while limiting the particle size.

[0045] In some implementations, please refer to Figure 2 The precursor of the carbon coating layer includes an amphiphilic bottle brush polymer 40, which includes a main chain segment 41, a hydrophilic chain segment 42, and a hydrophobic chain segment 43. The hydrophilic chain segment 42 and the hydrophobic chain segment 43 are both connected to the main chain segment 41. Specifically, in the amphiphilic bottle brush polymer 40 provided by the present invention, the hydrophilic chain segment 42 and the hydrophobic chain segment 43 are respectively distributed on opposite sides of the main chain segment. The molecular chain of the amphiphilic bottle brush polymer is "bottle brush shaped". The main chain segment 41 is similar to the handle of a bottle brush, and the hydrophilic chain segment 42 and the hydrophobic chain segment 43 are similar to the bristles of the bottle brush. Therefore, the hydrophilic segment 42 and the hydrophobic segment 43 are connected to the main chain segment 41 to form a "bottle brush shaped" structure.

[0046] In some implementations, please refer to Figure 2 The precursor of the positive electrode material includes an amphiphilic bottle brush polymer 40 and a precursor raw material 30 (i.e., a precursor of the aforementioned phosphate core 10). The amphiphilic bottle brush polymer 40 coats the precursor raw material 30. The precursor raw material 30 includes raw materials such as a lithium source, an iron source, and a phosphorus source for generating a lithium-containing phosphate active material precursor. The precursor raw material 30 is used to convert into the phosphate core 10, and the amphiphilic bottle brush polymer 40 is used to convert into the carbon coating layer 20. For convenience of description, the precursor of the positive electrode material is referred to as the precursor below.

[0047] In a specific embodiment, the structure of the precursor is a core-shell structure, which can be understood as a "capsule"-like structure, in which the amphiphilic bottle brush polymer 40 encapsulates the precursor raw material 30. In addition, the hydrophilic segment 42 of the amphiphilic bottle brush polymer 40 is used to connect the precursor raw material 30, and the hydrophobic segment 43 of the amphiphilic bottle brush polymer 40 is located on the side of the main segment 41 facing away from the precursor raw material 30, that is, the hydrophobic segment 43 is used to contact the organic solvent. In this way, the precursor particles form an independent shell, which not only prevents self-agglomeration between the precursors, but also limits the particle size of the encapsulated precursor raw material 30.

[0048] In a specific embodiment, the amphiphilic bottlebrush polymer 40 self-assembles on the outer surface of the precursor material 30. It should be noted that due to its "bottlebrush" structure, the amphiphilic bottlebrush polymer 40 can be assembled into a spherical or quasi-spherical shape based on the precursor material 30 after application in an organic solvent. The hydrophilic segments 42 can form hydrogen bonds with the precursor material 30, thereby connecting and coating the surface of the precursor material 30. Furthermore, the outermost surface of the precursor is a hydrophobic segment 43, which is used to repel other uncoated precursor materials 30, preventing the precursors from bonding with each other and avoiding particle self-agglomeration.

[0049] In a specific embodiment, the present invention's solution of coating the precursor material 30 with an amphiphilic bottle brush polymer 40 differs from the prior art solution of mixing a dispersant with the precursor material 30. In the prior art, an organic dispersant (e.g., sodium dodecylbenzenesulfonate) is added to the precursor material 30 to disperse the precursor material 30. The dispersant modifies the properties of the liquid-solid interface, thereby achieving sufficient dispersion of the precursor material 30.

[0050] It should be noted that the amphiphilic bottle brush polymer 40 provided by the present invention differs from the organic dispersants used in the prior art. It has a larger molecular weight, exhibits both hydrophilic and hydrophobic properties, and possesses a "bottle brush" structure. Furthermore, the amphiphilic bottle brush polymer 40 can firmly coat the outer surface of the precursor material 30 to form a coating layer, while also providing a stable carbon source. Organic dispersants are mostly small molecules that can achieve surface modification, but they cannot achieve the same coating effect as larger organic molecules.

[0051] Furthermore, due to the encapsulation properties of the amphiphilic bottlebrush polymer 40, the phosphate is firmly confined within the "capsule" space formed after coating the precursor material 30. This limits the particle size of the precursor material 30, thereby achieving a confinement effect. Furthermore, the hydrophobic segments 43 of the amphiphilic bottlebrush polymer 40 prevent self-agglomeration of the precursor particles. In contrast, organic dispersants, while providing a dispersion effect through surface modification, lack the ability to confine and control particle size. Furthermore, due to their low molecular weight and poor carbon yield, organic dispersants cannot be used as carbon sources.

[0052] At the same time, compared to the amphiphilic organic compounds in the prior art, the amphiphilic bottle brush polymer 40 has a "bottle brush shape" structure on the basis of its hydrophilic and hydrophobic properties. Therefore, the hydrophilic segment 42 and the hydrophobic segment 43 can be evenly distributed on both sides of the main segment 41, so that the amphiphilic bottle brush polymer 40 forms a special structure with one side hydrophilic and the other side hydrophobic, with the main segment 41 as the dividing line. Based on the bendable deformation of the main segment 41, the amphiphilic bottle brush polymer 40 can surround the precursor raw material 30, and the hydrophilic segment 42 is connected to the precursor raw material 30. In contrast, due to the small molecular weight of the organic dispersant, its hydrophilic and hydrophobic groups are mostly connected together, or the hydrophilic and hydrophobic groups are too close, resulting in it only providing a dispersion effect. The organic dispersant does not have a large steric hindrance to provide a confining effect.

[0053] In some embodiments, the amphiphilic bottle brush polymer 40 includes a plurality of repeating units A and a plurality of repeating units B, wherein the repeating units A and B are linked to form the amphiphilic bottle brush polymer 40. It is understood that the amphiphilic bottle brush polymer 40 is formed by polymerization of monomer A and monomer B, wherein monomer A constitutes the repeating unit A in the amphiphilic bottle brush polymer 40, and monomer B constitutes the repeating unit B in the amphiphilic bottle brush polymer 40.

[0054] In some embodiments, the repeating unit A includes a main chain group A and a hydrophilic segment 42, and the hydrophilic segment 42 is connected to the main chain group A; the repeating unit B includes a main chain group B and a hydrophobic segment 43, and the hydrophobic segment 43 is connected to the main chain group B. Multiple main chain groups A and multiple main chain groups B are polymerized and connected to form a main chain segment 41.

[0055] In some embodiments, the atomic compositions of multiple repeating units A are not identical, and the atomic compositions of multiple repeating units B are not identical. Specifically, repeating unit A can be understood as a hydrophilic unit, and repeating unit B can be understood as a hydrophobic unit. The amphiphilic bottlebrush polymer 40 can include multiple different hydrophilic units, i.e., multiple hydrophilic segments 42, so the atomic compositions of the multiple hydrophilic repeating units A can be different. Similarly, the amphiphilic bottlebrush polymer 40 can include multiple different hydrophobic units, i.e., multiple hydrophobic segments 43, so the atomic compositions of the multiple hydrophobic repeating units B can be different.

[0056] In some implementations, please refer to Figure 3 , Figure 3 Part 1) in FIG. 1 shows a main chain segment 41, which is a rigid chain segment. A rigid chain segment refers to a polymer having a rigid molecular chain structure that is difficult to bend or deform. A rigid chain segment typically has a high glass transition temperature, a high modulus, and low flexibility. Main chain segment 41 may contain a benzene ring, a conjugated double bond, or a rigid heterocycle (such as polyimide or polyphenylene ether).

[0057] The amphiphilic bottle-brush polymer 40 provided by the present invention has rigid chain segments, which not only enhance the mechanical strength of the coating formed after the amphiphilic bottle-brush polymer 40 coats the precursor material 30, but also further improve the confinement effect. Because the rigid chain segments possess stronger mechanical properties, the encapsulated precursor material 30 is less likely to break through the coating of the amphiphilic bottle-brush polymer 40, thereby stabilizing the precursor material 30 within the coating formed by the amphiphilic bottle-brush polymer 40 and enhancing the confinement effect of the amphiphilic bottle-brush polymer 40.

[0058] In some implementations, please refer to Figure 3 , Figure 3 Part 2) shows a hydrophilic segment 42, which includes one or more of a polyvinyl pyrrolidone segment (PVP), a polyethylene glycol segment (PEG), a polyvinyl alcohol segment (PVA), a polyacrylamide segment (PAM), and a polyalkyl sulfonate segment. It should be noted that the hydrophilic segment 42 itself is a polymer, such as Figure 3 As shown in parts 1) and 2), one end of the hydrophilic segment 42 is connected to the main chain group A mentioned above through a chemical bond.

[0059] In some implementations, please refer to Figure 3 , Figure 3Part 3) shows a hydrophobic segment 43, which includes one or more of a polyethylene segment (PE), a polystyrene segment (PS), a polyvinyl chloride segment (PVC), a polymethyl methacrylate segment (PMMA), a polycarbonate (PC), and a polysiloxane segment. It should be noted that the hydrophobic segment 43 itself is a polymer, such as Figure 3 As shown in parts 1) and 3), one end of the hydrophobic segment 43 is connected to the main chain group B in the above-mentioned structure through a chemical bond.

[0060] In some embodiments, the hydrophilic segment 42 includes one or more of a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, a phosphate group, a carbonyl group (aldehyde, ketone), an ether bond, a quaternary ammonium salt, and an amide group. Specifically, all of the above functional groups are hydrophilic functional groups. Hydrophilic organic functional groups typically contain polar bonds or are capable of forming hydrogen bonds, and may even dissociate into charged groups.

[0061] In a specific embodiment, the hydrophilic segment 42 may contain alcoholic hydroxyl groups and / or phenolic hydroxyl groups, both of which can form hydrogen bonds; amino groups can also form hydrogen bonds. The carboxyl group can dissociate protons to become negatively charged carboxyl groups with strong polarity. The phosphate group and sulfonic acid group can easily dissociate to form sulfonate groups (-SO3 - ) and phosphate (-PO4 3- ), negatively charged and extremely hydrophilic.

[0062] In some embodiments, the hydrophobic segment 43 includes one or more of a siloxy group, an ester group, an aryl group, an alkane group, and a halogenated hydrocarbon. Specifically, the above functional groups are all hydrophobic functional groups. Hydrophobic organic functional groups are generally composed of non-polar or weakly polar structures and are unable to form strong interactions with water molecules (such as hydrogen bonds or ion-dipole interactions).

[0063] In a specific embodiment, the low electronegativity and flexible Si-O-Si chain connected to the silicon atom in the siloxy group have low surface energy and repel water molecules. The alkyl group (-R) has a non-polar C-H bond and lacks the ability to form hydrogen bonds or dipole interactions with water. The aromatic group (such as a benzene ring, a naphthalene ring, etc.) has a non-polar π electron cloud distribution, with extremely low polarity, making it difficult to interact with water molecules. The alkoxy group (-OR') of the ester group hinders the formation of hydrogen bonds with water, and the overall polarity is low.

[0064] In some embodiments, the main chain segment 41 includes one or more of polystyrene (PS), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), polyamide (nylon), and ladder polymer.

[0065] In some embodiments, the molecular weight of the amphiphilic bottle brush polymer 40 is between 10,000 and 50,000. This molecular weight range ensures that the amphiphilic bottle brush polymer 40 can better coat the precursor material 30 to form a confinement effect. Furthermore, the amphiphilic bottle brush polymer 40 exhibits stable mechanical properties, enhanced entanglement between polymer chains, increased molecular chain slip resistance, and improved tensile strength and toughness, thereby enhancing the confinement effect and achieving particle size control. Furthermore, the amphiphilic bottle brush polymer 40 exhibits a high carbonization yield, reduced defects in the coating layer, a stable coating layer, and improved conductivity.

[0066] When the molecular weight of the amphiphilic bottle brush polymer 40 is too low, its mechanical properties deteriorate, and its ability to confine the precursor material 30 decreases, leading to an increase in the particle size of the phosphate core 10. Furthermore, the coating layer formed by the amphiphilic bottle brush polymer 40 exhibits increased defects, resulting in decreased stability and conductivity. When the molecular weight of the amphiphilic bottle brush polymer 40 is too high, its rheological properties deteriorate, making it more difficult to process and unable to disperse the precursor material 30.

[0067] Optionally, the molecular weight of the amphiphilic bottle brush polymer 40 may be 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, or 50,000.

[0068] In some embodiments, the molecular weight of the hydrophilic segment 42 is 500 to 5000. Satisfying the molecular weight of the hydrophilic segment 42 within the above range can ensure the length of the hydrophilic segment 42 and the content of the hydrophilic functional groups on the hydrophilic segment 42, thereby ensuring the connection stability between the amphiphilic bottle brush polymer 40 and the precursor material 30.

[0069] If the molecular weight of the hydrophilic chain segment 42 is too low, the bonding strength between the hydrophilic side of the amphiphilic bottlebrush polymer 40 and the precursor material 30 decreases, resulting in poor encapsulation of the amphiphilic bottlebrush polymer 40 and difficulty in forming core particles of uniform size and morphology. If the molecular weight of the hydrophilic chain segment 42 is too high, the chain complexity of the hydrophilic side of the amphiphilic bottlebrush polymer 40 increases, leading to entanglement between the polymer chains, poor dispersibility of the amphiphilic bottlebrush polymer 40, and increased difficulty in self-assembly.

[0070] Optionally, the molecular weight of the hydrophilic segment 42 can be 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000.

[0071] In some embodiments, the molecular weight of the hydrophobic segment 43 is 500 to 5000. Satisfying the molecular weight of the hydrophobic segment 43 within the above range can ensure the length of the hydrophobic segment 43 and the content of the hydrophobic functional groups on the hydrophobic segment 43, thereby ensuring that the hydrophobic segment 43 can repel uncoated precursor material 30 and avoid particle self-agglomeration.

[0072] When the molecular weight of the hydrophobic segment 43 is too low, the hydrophobic side of the amphiphilic bottlebrush polymer 40 exhibits poor solvent affinity, resulting in poor dispersion and confinement of the amphiphilic bottlebrush polymer 40, making it difficult to form core particles of uniform size and morphology. When the molecular weight of the hydrophobic segment 43 is too high, the segment complexity on the hydrophobic side of the amphiphilic bottlebrush polymer 40 increases, leading to entanglement between the polymer chains, poor dispersibility of the amphiphilic bottlebrush polymer 40, and increased difficulty in self-assembly.

[0073] Optionally, the molecular weight of the hydrophobic segment 43 may be 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000.

[0074] In some embodiments, the molar ratio of the hydrophilic segment 42 to the hydrophobic segment 43 is 1:(0.1-10). Satisfying the molar ratio of the hydrophilic segment 42 to the hydrophobic segment 43 within this range ensures uniform distribution of the hydrophilic and hydrophobic segments 42, 43, thereby adjusting the surface energy and surface tension of the hydrophilic and hydrophobic sides of the amphiphilic bottle brush polymer 40. This ensures that the hydrophilic side of the amphiphilic bottle brush polymer 40 has strong binding properties with the precursor material 30, while the hydrophobic side has strong affinity with the solvent.

[0075] When the proportion of hydrophilic segments 42 is too low, the bonding strength between the hydrophilic side of the amphiphilic bottle brush polymer 40 and the precursor material 30 decreases, resulting in a poorer coating effect of the amphiphilic bottle brush polymer 40. This weakens the bonding strength between the hydrophilic side of the amphiphilic bottle brush polymer 40 and the precursor material 30, and the coated structure is easily broken, thus affecting the confinement effect. When the proportion of hydrophilic segments 42 is too high, the hydrophobic side of the amphiphilic bottle brush polymer 40 has a reduced affinity for the solvent, resulting in poor wettability and dispersibility of the amphiphilic bottle brush polymer 40 in the solvent, making self-assembly more difficult.

[0076] Optionally, the molar ratio of the hydrophilic segment 42 to the hydrophobic segment 43 can be 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10.

[0077] In some embodiments, the thickness of the carbon coating layer 20 is 0.5 nm to 5.0 nm. Satisfying the thickness of the carbon coating layer 20 within this range ensures uniform coating and a moderate thickness, which helps improve the overall capacity of the composite phosphate-based positive electrode material 100. Furthermore, the better the uniformity of the carbon coating layer 20, the more uniform the overall particle size of the positive electrode material, which helps improve the compaction density of the positive electrode material.

[0078] When the thickness of the carbon coating layer 20 is too thin, the electrolyte will directly contact the phosphate core 10, increasing side reactions and causing capacity loss. When the thickness of the carbon coating layer 20 is too thick, the transmission of lithium ions will be hindered to a certain extent.

[0079] Optionally, the thickness of the carbon coating layer 20 may be 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, or 5.0 nm.

[0080] In some embodiments, the thickness variance of the carbon coating layer 20 is 0.1 to 4.0. The thickness variance of the carbon coating layer 20 refers to the average of the squared deviations of the coating layer thickness of each particle in the positive electrode material 100 from its mean, reflecting the dispersion of the coating layer thickness. The larger the variance, the more uneven the coating layer thickness; the smaller the variance, the more uniform the coating layer thickness. When the thickness variance of the carbon coating layer 20 falls within the above range, the thickness of the carbon coating layer 20 is normally distributed, ensuring uniform particle size and facilitating improved overall compaction density and capacity of the material.

[0081] When the thickness variance of the carbon coating layer 20 is too large, the thickness uniformity of the coating layer is poor, which will cause direct contact between the electrolyte and the phosphate core 10, increase side reactions and cause capacity loss; and it is easy for particles to agglomerate severely and the boundaries to be unclear, which is not conducive to improving the compaction density of the material.

[0082] Optionally, the thickness variance of the carbon coating layer 20 may be 0.1, 0.4, 0.8, 1.2, 1.6, 2, 2.4, 2.8, 3.2, 3.6, or 4.0.

[0083] In some embodiments, the carbon coating layer 20 contains organic functional groups, including one or more of carboxyl groups, hydroxyl groups, and carbon-carbon double bonds. It is understood that the precursor of the carbon coating layer 20 is an amphiphilic bottlebrush polymer 40, which includes both hydrophobic and hydrophilic groups. During the carbonization process of the amphiphilic bottlebrush polymer 40, some organic functional groups are not fully carbonized and remain in the coating layer. The organic functional groups in the coating layer can improve the ionic conductivity of the coating layer, thereby increasing the energy density of the material.

[0084] In some embodiments, in the Raman spectrum curve of the positive electrode material 100, the integrated intensity ratio of the D peak to the G peak is D / I G 0.70~0.99. Optionally, the integrated intensity ratio of peak D and peak G is I D / I G It can be 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or 0.99.

[0085] The present invention provides a method for preparing a positive electrode material. Figure 4 The preparation method is used to prepare the positive electrode material provided in the above embodiment, and the preparation method specifically comprises the following steps:

[0086] In step S100 , raw materials comprising at least a lithium source, an iron source, and a phosphorus source are mixed to obtain a mixture, the mixture and an amphiphilic bottle brush polymer are added to an organic solvent according to a mass ratio, and the organic solvent is removed after sufficient mixing to obtain a solid material.

[0087] Step S200: calcining the solid material to obtain a positive electrode material.

[0088] This invention coats the precursor of a phosphate cathode material with an amphiphilic bottlebrush polymer, leveraging the hydrophilic and hydrophobic properties of the amphiphilic bottlebrush polymer to achieve localized coating, resulting in a cathode material with uniform particle size and morphology. The primary particles of this cathode material have a particle size of 250 to 450 nm, with a particle size variance of 1 to 10. This material also exhibits good processability during slurrying.

[0089] In a specific embodiment, in step S100, raw materials of a lithium source, an iron source, and a phosphorus source are mixed by ball milling to obtain a powdered mixture. The iron source includes at least one of ferric nitrate, ferric phosphate, ferric sulfate, and ferrous oxalate dihydrate. The lithium source includes at least one of lithium nitrate, lithium hydroxide, lithium carbonate, and lithium acetate. The phosphorus source includes at least one of phosphoric acid, ferric phosphate, ammonium hydrogen phosphate, and diammonium hydrogen phosphate.

[0090] In a specific embodiment, in step S100, the raw materials of the phosphate positive electrode material (phosphate core) may further include at least one of a manganese source, a titanium source, and a vanadium source. The manganese source, titanium source, and vanadium source are metal element sources doped in the lithium iron phosphate. The titanium source includes at least one of titanium chloride, titanate, titanate ester, and titanium oxide. Optionally, the vanadium source includes at least one of vanadium chloride, vanadium oxide, and vanadate. The manganese source includes at least one of manganese nitrate, manganese oxide, manganese sulfate, manganese dioxide, manganese tetraoxide, and manganese oxalate.

[0091] In a specific embodiment, in step S100, the amphiphilic bottle brush polymer includes a main chain segment, a hydrophilic segment, and a hydrophobic segment. The main chain segment includes one or more of polystyrene, polymethyl methacrylate, polyethylene terephthalate, polycarbonate, polyamide, and a ladder polymer. The hydrophilic segment includes one or more of polyvinyl pyrrolidone segment, polyethylene glycol segment, polyvinyl alcohol segment, polyacrylamide segment, and polyalkyl sulfonate segment. The hydrophobic segment includes one or more of polyethylene segment, polystyrene segment, polyvinyl chloride segment, polymethyl methacrylate segment, polycarbonate, and polysiloxane segment.

[0092] In a specific embodiment, in step S100, the organic solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethylacetamide (DMAc), and tetrahydrofuran (THF). It should be noted that the above organic solvents are good solvents for hydrophobic segments, which facilitates the formation of a hydrophilic inner side and hydrophobic outer side structure when the amphiphilic bottle brush polymer is mixed with the precursor raw material.

[0093] In some implementations, please refer to Figure 5 In step S100, the mixture and the amphiphilic bottle brush polymer are added to an organic solvent according to a mass ratio, and the organic solvent is removed after being fully mixed to obtain a solid material, which specifically includes the following steps:

[0094] Step S110 , adding the mixture and the amphiphilic bottle brush polymer A into the organic solvent A according to a mass ratio, and removing the organic solvent A after thorough mixing to obtain a solid precursor.

[0095] Step S120: calcining the solid precursor to obtain an intermediate.

[0096] Step S130 , adding the intermediate and the amphiphilic bottle brush polymer B into the organic solvent B according to the mass ratio, removing the organic solvent B after thorough mixing, and obtaining a solid material.

[0097] The present invention prepares cathode materials through a double coating process, leveraging the hydrophilic and hydrophobic properties of amphiphilic bottlebrush polymers to achieve particle size reduction. Furthermore, the double coating process improves the uniformity of the carbon coating layer, specifically controlling the thickness and thickness variance of the carbon coating layer. Compared to a single coating process, the double coating process results in a more uniform primary particle size of the cathode material, conforming to a normal distribution, and exhibiting a smaller particle size variance.

[0098] In a specific embodiment, in step S110, the mixture is the powdered mixture material in the above embodiment. The amphiphilic bottle brush polymer A is one or more of the above embodiments. The organic solvent A is one or more of the above embodiments.

[0099] Optionally, in step S120, the heating rate of calcination is 3°C / min to 8°C / min; in a specific embodiment, the heating rate of calcination can be 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, or 8°C / min.

[0100] Optionally, in step S120, the calcination temperature is 520°C to 560°C; in a specific embodiment, the calcination temperature can be 520°C, 525°C, 530°C, 535°C, 540°C, 545°C, 550°C, 555°C, or 560°C.

[0101] Optionally, in step S120, the constant temperature calcination time is 2h to 4h; in a specific embodiment, the constant temperature calcination time can be 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h, or 4h.

[0102] In a specific embodiment, in step S130, the mixture is the powdered mixture material described in the above-mentioned embodiment. The amphiphilic bottle brush polymer B is one or more of the materials described in the above-mentioned embodiment. The organic solvent B is one or more of the materials described in the above-mentioned embodiment. It should be noted that the amphiphilic bottle brush polymer A and the amphiphilic bottle brush polymer B may be the same or different, and the organic solvent A and the organic solvent B may be the same or different.

[0103] Optionally, in step S200, the heating rate of calcination is 3°C / min to 8°C / min; in a specific embodiment, the heating rate of calcination can be 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, or 8°C / min.

[0104] Optionally, in step S200, the calcination temperature is 720℃~780℃; in a specific embodiment, the calcination temperature can be 720℃, 725℃, 730℃, 735℃, 740℃, 745℃, 750℃, 755℃, 760℃, 765℃, 770℃, 775℃, or 780℃.

[0105] Optionally, in step S200, the constant temperature calcination time is 8 hours to 12 hours; in a specific embodiment, the constant temperature calcination time can be 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours.

[0106] It should be noted that in the above embodiment, step S120 is the first calcination after the first coating, and step S200 is the second calcination after the second coating. Therefore, the heating rate, temperature and holding time of the calcination may be different.

[0107] In some embodiments, in step S110, the mass ratio of the mixture to the amphiphilic bottle brush polymer A is 100:(40-60). Alternatively, the mass ratio of the mixture to the amphiphilic bottle brush polymer A can be 100:40, 100:42, 100:44, 100:46, 100:48, 100:50, 100:52, 100:54, 100:56, 100:58, or 100:60.

[0108] In some embodiments, in step S130, the mass ratio of the intermediate to the amphiphilic bottle brush polymer B is 100:(5-10). Optionally, the mass ratio of the intermediate to the amphiphilic bottle brush polymer B can be 100:5, 100:6, 100:7, 100:8, 100:9, or 100:10.

[0109] The present invention also provides a positive electrode plate.

[0110] In one embodiment, the positive electrode plate comprises the positive electrode material provided in the above embodiment, or the positive electrode plate comprises the positive electrode material prepared by the method for preparing the positive electrode material provided in the above embodiment. In a specific embodiment, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode material obtained by the above preparation method or the above positive electrode material. Optionally, the positive electrode current collector has two surfaces opposing each other in the thickness direction thereof, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0111] In one embodiment, the positive electrode film layer optionally includes a positive electrode conductive agent. The present invention does not particularly limit the type of the positive electrode conductive agent. By way of example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene oxide, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent based on the total mass of the positive electrode film layer is ≤5%.

[0112] In one embodiment, the positive electrode film layer may further optionally include a positive electrode binder. The present invention has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride, tetrafluoroethylene, propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and at least one of fluorine-containing acrylic resins. In some embodiments, the mass percentage of the positive electrode binder is ≤5% based on the total mass of the positive electrode film layer.

[0113] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0114] In one embodiment, the positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0115] The present invention also provides a secondary battery.

[0116] In one embodiment, the secondary battery includes a positive electrode, a negative electrode, an electrolyte, etc., wherein the positive electrode is the positive electrode plate provided in the above embodiment; or, the secondary battery includes the positive electrode material provided in the above embodiment; or the secondary battery includes the positive electrode material obtained by the above preparation method.

[0117] The technical solutions of the present invention are described in detail below through specific embodiments.

[0118] Example 1

[0119] This embodiment provides a positive electrode material, the positive electrode material includes a phosphate core and a carbon coating layer, the phosphate core includes lithium manganese iron phosphate. The particle size of the primary particles of the positive electrode material is 343 nm, the particle size variance of the positive electrode material is 3.24, the thickness of the carbon coating layer is 2.829 nm, the thickness variance of the carbon coating layer is 0.282, and the primary particles of the positive electrode material are 343 nm and 3.24, respectively. D / I G It is 0.904.

[0120] The precursor for the carbon coating is an amphiphilic bottlebrush polymer, consisting of a backbone segment composed of polymethyl methacrylate (PMMA), a hydrophilic segment composed of polyethylene glycol (PEG), and a hydrophobic segment composed of polyethylene (PE). The molecular weight of the amphiphilic bottlebrush polymer is 23,500, while the molecular weight of the hydrophilic segment is 1,000 and the molecular weight of the hydrophobic segment is 1,000. The molar ratio of the hydrophilic to hydrophobic segments is 1:1.

[0121] This embodiment also provides a method for preparing a positive electrode material:

[0122] 1) 37.0 g of lithium carbonate, 26.1 g of manganese dioxide, 27.9 g of iron phosphate, 36.2 g of ammonium dihydrogen phosphate, and 1.2 g of titanium dioxide were mixed and ball-milled. After drying, a powdered mixture was obtained. The above mixture was mixed with 64.2 g of amphiphilic bottle brush polymer (50% by mass of the mixture) and added to 500 mL of DMF. The solution was heated to 80° C. and kept warm for 3 h. The solvent was then evaporated under vacuum to obtain a solid precursor.

[0123] 2) Under an argon atmosphere, the solid precursor was heated to 550° C. at a heating rate of 5° C. / min and calcined at a constant temperature for 4 hours to obtain 114.2 g of a primary sintered intermediate.

[0124] 3) The primary sintered intermediate was ball-milled and dried, then mixed with 9.1 g of an amphiphilic bottle-brush polymer (8% by mass) and added to 500 mL of DMF. The solution was heated to 80°C for 3 h, and then the solvent was evaporated under vacuum to obtain a secondary coated solid material.

[0125] 4) In a nitrogen or argon atmosphere, the solid material was heated to 750° C. at a heating rate of 5° C. / min and calcined at a constant temperature for 10 hours. After cooling, 118.0 g of positive electrode material was obtained.

[0126] Figure 6 is a scanning electron microscope image (SEM) of the positive electrode material provided in Example 1, Figure 7 is a transmission electron micrograph (TEM) of the cathode material provided in Example 1, wherein A) and B) show the thickness of the carbon coating layer; Figure 6 and Figure 7 It can be clearly seen that the prepared positive electrode material particles are uniform and the thickness of the carbon coating layer is uniform.

[0127] Example 2

[0128] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the hydrophilic segment is polyacrylamide (PAM) and the hydrophobic segment is polystyrene (PS), that is, the polymer types of the hydrophilic segment and the hydrophobic segment in this embodiment and Example 1 are different.

[0129] The method for preparing the positive electrode material provided in this embodiment is the same as that in Example 1.

[0130] Example 3

[0131] This embodiment provides a positive electrode material. The difference between this embodiment and embodiment 1 is that the main chain segment is polyethylene glycol (PEG), that is, the main chain segment of this embodiment is different from that of embodiment 1, and this embodiment is a flexible chain segment.

[0132] The method for preparing the positive electrode material provided in this embodiment is the same as that in Example 1.

[0133] Example 4

[0134] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the molecular weight of the amphiphilic bottle brush polymer is 10300, the molecular weight of the hydrophilic segment is 500, and the molecular weight of the hydrophobic segment is 500, that is, the molecular weight of the hydrophobic segment in this embodiment is smaller.

[0135] The method for preparing the positive electrode material provided in this embodiment is the same as that in Example 1.

[0136] Example 5

[0137] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the molecular weight of the amphiphilic bottle brush polymer is 32600, the molecular weight of the hydrophilic segment is 5000, and the molecular weight of the hydrophobic segment is 5000, that is, the molecular weight of the hydrophobic segment in this embodiment is larger.

[0138] The method for preparing the positive electrode material provided in this embodiment is the same as that in Example 1.

[0139] Example 6

[0140] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the molar ratio of the hydrophilic segment to the hydrophobic segment is 1:10, that is, the hydrophobic segment in this embodiment accounts for a larger proportion.

[0141] The method for preparing the positive electrode material provided in this embodiment is the same as that in Example 1.

[0142] Example 7

[0143] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the molar ratio of the hydrophilic segment to the hydrophobic segment is 1:0.1, that is, the proportion of the hydrophobic segment in this embodiment is relatively small.

[0144] The method for preparing the positive electrode material provided in this embodiment is the same as that in Example 1.

[0145] Example 8

[0146] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the particle size of the primary particles of the positive electrode material is 253 nm, and the particle size variance of the positive electrode material is 4.68.

[0147] The difference between the positive electrode material preparation method provided in this embodiment and that in Example 1 is that in step 1), the amount of amphiphilic bottle brush polymer added is 38.52 g (30% of the mass fraction of the mixture); in step 2), the primary sintering temperature is 520°C; and in step 4), the secondary sintering temperature is 720°C.

[0148] Example 9

[0149] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the particle size of the primary particles of the positive electrode material is 445 nm, and the particle size variance of the positive electrode material is 3.76.

[0150] The difference between the positive electrode material preparation method provided in this embodiment and that in Example 1 is that in step 1), the amount of amphiphilic bottle brush polymer added is 89.74 g (70% of the mass fraction of the mixture); in step 2), the primary sintering temperature is 580°C; and in step 4), the secondary sintering temperature is 780°C.

[0151] Example 10

[0152] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the thickness of the carbon coating layer is 0.532 nm, and the thickness variance of the carbon coating layer is 0.324.

[0153] The difference between the positive electrode material preparation method provided in this embodiment and that in embodiment 1 is that in step 3), the amount of amphiphilic bottle brush polymer added is 6.85 g (6% of the mass fraction of the mixture); in step 4), the secondary sintering temperature is 740°C.

[0154] Example 11

[0155] This embodiment provides a positive electrode material. The difference between this embodiment and Example 1 is that the thickness of the carbon coating layer is 4.346 nm, and the thickness variance of the carbon coating layer is 3.213.

[0156] The difference between the positive electrode material preparation method provided in this embodiment and that in embodiment 1 is that in step 3), the amount of amphiphilic bottle brush polymer added is 11.42 g (10% of the mass fraction of the mixture); in step 4), the secondary sintering temperature is 760°C.

[0157] Comparative Example 1

[0158] This comparative example provides a positive electrode material, the positive electrode material comprising a phosphate core and a carbon coating layer, the phosphate core comprising lithium manganese iron phosphate. The particle size of the primary particles of the positive electrode material is 329 nm, the particle size variance of the positive electrode material is 30.5, the thickness of the carbon coating layer is 4.39 nm, the thickness variance of the carbon coating layer is 7.62, and the primary particles of the positive electrode material are 329 nm and 30.5, respectively. D / I G It is 0.986.

[0159] This comparative example also provides a method for preparing a positive electrode material: 1) 37.0 g of lithium carbonate, 26.1 g of manganese dioxide, 27.9 g of iron phosphate, 36.2 g of ammonium dihydrogen phosphate, and 1.2 g of titanium dioxide were mixed and ball-milled, and dried to obtain a powdery mixture. The above mixture was mixed with 64.2 g of glucose (50% of the mass fraction of the mixture) and added to 500 mL of DMF. The solution was heated to 80°C and kept warm for 3 hours. The solvent was then evaporated under vacuum to obtain a solid precursor.

[0160] 2) Under an argon atmosphere, the solid precursor was heated to 550° C. at a heating rate of 5° C. / min and calcined at a constant temperature for 4 hours to obtain 114.2 g of a primary sintered intermediate.

[0161] 3) The primary sintered intermediate was ball-milled and dried, mixed with 9.1 g of glucose (8% by mass of the mixture), and added to 500 mL of DMF. The solution was heated to 80° C. and kept warm for 3 h. The solvent was then evaporated under vacuum to obtain a secondary coated solid material.

[0162] 4) Under nitrogen or argon atmosphere, the solid material was heated to 780° C. at a heating rate of 5° C. / min and calcined at a constant temperature for 10 hours. After cooling, 118.0 g of positive electrode material was obtained.

[0163] Comparative Example 2

[0164] This comparative example provides a positive electrode material, the positive electrode material comprising a phosphate core and a carbon coating layer, the phosphate core comprising lithium manganese iron phosphate. The particle size of the primary particles of the positive electrode material is 336 nm, the particle size variance of the positive electrode material is 13.7, the thickness of the carbon coating layer is 4.69 nm, the thickness variance of the carbon coating layer is 3.24, and the primary particles of the positive electrode material are 336 nm and 13.7, respectively. D / I G It is 0.952.

[0165] This comparative example also provides a method for preparing a positive electrode material: 1) 37.0 g of lithium carbonate, 26.1 g of manganese dioxide, 27.9 g of iron phosphate, 36.2 g of ammonium dihydrogen phosphate, and 1.2 g of titanium dioxide were mixed and ball-milled, and dried to obtain a powdery mixture. The above mixture was mixed with 64.2 g of glucose (50% of the mass fraction of the mixture) and 1.9 g of sodium dodecylbenzenesulfonate (1% of the total mass of the mixture and glucose), and then added to 500 mL of DMF. The solution was heated to 80°C and kept warm for 3 hours. The solvent was then evaporated under vacuum to obtain a solid precursor.

[0166] 2) Under an argon atmosphere, the solid precursor was heated to 550° C. at a heating rate of 5° C. / min and calcined at a constant temperature for 4 hours to obtain 114.2 g of a primary sintered intermediate.

[0167] 3) The primary sintered intermediate was ball-milled and dried, then mixed with 9.1 g of glucose (8% by mass of the mixture) and 0.12 g of sodium dodecylbenzenesulfonate (0.1% of the total mass of the mixture and glucose), and then added to 500 mL of DMF. The solution was heated to 80° C. and kept warm for 3 h. The solvent was then evaporated under vacuum to obtain a secondary coated solid material.

[0168] 4) Under nitrogen or argon atmosphere, the solid material was heated to 780° C. at a heating rate of 5° C. / min and calcined at a constant temperature for 10 hours. After cooling, 118.0 g of positive electrode material was obtained.

[0169] The parameters of the positive electrode materials provided by Examples 1 to 11 and Comparative Examples 1 and 2 are shown in Tables 1-1 and 1-2:

[0170] Table 1-1 Parameters of positive electrode materials provided in Examples and Comparative Examples 1

[0171]

[0172] Table 1-2 Parameters of positive electrode materials provided in Examples and Comparative Examples 2

[0173]

[0174]

[0175] It can be seen from the positive electrode material parameters in Table 1-1 and Table 1-2 that the positive electrode materials prepared by the preparation method provided by the present invention have smaller particle size variance and carbon coating layer thickness variance, indicating that the particle size of the positive electrode material provided by the present invention is more uniform and the carbon coating layer thickness is also more uniform.

[0176] It can be seen from Examples 1 to 3 that the solution provided by the present invention can be applied to different hydrophilic segments, hydrophobic segments and main segments; it can be seen from Example 3 that the particle size of the positive electrode material and the uniformity of the carbon coating (particle size variance and thickness variance) are affected by the physical properties of the main segment, among which the rigid segment has a higher strength, so the coated positive electrode material is more stable.

[0177] It can be seen from Examples 1, 4 and 5 that the molecular weight of the amphiphilic bottle brush polymer affects the uniformity of the particle size of the positive electrode material and the thickness of the carbon coating layer; it can be seen from Example 5 that, under the same mass, the higher the molecular weight, the higher the decomposition temperature of the amphiphilic bottle brush polymer, the higher the residual carbon rate after sintering, and therefore the thicker the carbon coating layer.

[0178] It can be seen from Examples 1, 6 and 7 that the molar ratio of the hydrophilic segment to the hydrophobic segment in the amphiphilic bottle brush polymer affects the particle size of the positive electrode material and the uniformity of the carbon coating layer; it can be seen from Example 7 that because the hydrophilic segment has more polar groups, the polar groups are more easily removed during the sintering process, so the more hydrophilic segments there are, the easier it is for the amphiphilic bottle brush polymer to decompose, resulting in a lower residual carbon rate, so the thickness of the carbon coating layer will be reduced.

[0179] Examples 1, 8, and 11 demonstrate that the particle size of the cathode material and the uniformity of the carbon coating are affected by the sintering temperature and the ratio of the amphiphilic bottle brush polymer. By decreasing or increasing the amount of amphiphilic bottle brush polymer and adjusting the temperatures of the two sintering stages, the particle size of the cathode material can be controlled. However, the use of amphiphilic bottle brush polymer consistently yields cathode material particles with uniform particle size and carbon coating thickness.

[0180] As can be seen from Example 1, Comparative Examples 1, and 2, the use of conventional glucose as a carbon source instead of an amphiphilic bottlebrush polymer resulted in poor cathode material uniformity and poor uniformity in carbon coating thickness. Even with the addition of a small molecule dispersant, which improves the dispersibility of the carbon source, the poor coating stability of the glucose carbon source still leads to poor cathode material particle size uniformity and large variance.

[0181] Test Case

[0182] Battery preparation:

[0183] The lithium iron manganese phosphate positive electrode materials provided in Examples 1 to 11 and Comparative Examples 1 and 2 were prepared into positive electrode sheets. The positive electrode sheet preparation method includes: mixing the lithium iron manganese phosphate positive electrode material, polyvinylidene fluoride, and carbon black in proportions of 96.5%, 2.2%, and 1.3% by mass, respectively, and then mixing and thoroughly stirring with a certain amount of N-methylpyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is dried on the surface of the positive electrode current collector at a temperature of 120°C on a coater to form a film, and then rolled on a roller press to obtain a positive electrode sheet.

[0184] The positive electrode sheets provided in the above-mentioned Examples 1 to 11 and Comparative Examples 1 to 2 are prepared as secondary batteries. The preparation method of the secondary battery comprises: cutting the above-mentioned positive electrode sheets into pieces, fixing the positive electrode sheets on the positive electrode shell, and moving the fixed positive electrode shell into an oven for drying. The prepared positive electrode shell, gasket, spring, diaphragm, electrolyte, negative electrode sheet and negative electrode shell are placed in a glove box for assembly. The assembled button half-cell is placed in the center of the tablet press with the negative electrode facing up and the positive electrode facing down for tableting. When the tableting is completed, the battery assembly is completed. The choice of electrolyte can be based on any electrolyte suitable for lithium-ion batteries in this industry, and the type of electrolyte is not limited here.

[0185] The secondary batteries provided in Examples 1 to 11 and Comparative Examples 1 and 2 were subjected to electrochemical performance tests under the following test conditions:

[0186] Conventional charge and discharge test:

[0187] The electrochemical performance test was carried out on an electrochemical test cabinet at room temperature of 25°C, and the charge and discharge test was carried out using 0.1C and 1C constant currents.

[0188] The results of the secondary battery are shown in Table 2 below:

[0189] Table 2. Test results of secondary batteries assembled in Examples and Comparative Examples

[0190]

[0191] From the test results of Examples 1 to 11 and Comparative Examples 1 to 2 in Table 2, it can be seen that the secondary battery produced by the positive electrode material provided by the present invention has a higher discharge specific capacity and efficiency, and the average voltage of the secondary battery of the embodiment is similar to that of the secondary battery of the comparative example, and can be applied to the existing battery system. At the same time, the positive electrode slurry produced by the positive electrode material provided by the present invention has a higher solid content and viscosity, which is more conducive to the production of high energy density batteries. At the same time, from Figure 8 It can be seen from the electrochemical performance of the secondary battery prepared by the positive electrode material provided in Example 1 at 0.1C that the secondary battery has a higher 0.1C discharge specific capacity and the average voltage is not increased.

[0192] In the test results of Example 5, because the hydrophilic and hydrophobic segments of the amphiphilic bottle brush polymer have higher molecular weights, more residual groups are left in the carbon coating after carbonization. These residual groups are more conducive to binding with the organic solvent in the positive electrode slurry, resulting in better dispersion of the positive electrode material in the slurry. Therefore, compared with Example 4, the positive electrode slurry of Example 5 has a higher solid content. Therefore, controlling the amphiphilic bottle brush polymer is also beneficial for adjusting the solid content and viscosity of the positive electrode slurry.

[0193] In the test results of Example 7, because the proportion of hydrophilic segments in the amphiphilic bottle brush polymer increases, there are more residual groups on the hydrophilic segments, and the residual groups on the hydrophilic segments are beneficial to combining with the organic solvent in the positive electrode slurry, thereby increasing the solid content of the positive electrode slurry.

[0194] In the test results of Example 8, the particle size of the primary particles of the positive electrode material is reduced, which shortens the lithium ion transmission path, thereby improving the electrochemical performance of the positive electrode material, thereby obtaining a secondary battery with higher discharge specific capacity and efficiency.

[0195] In the test results of Example 10, by reducing the amount of amphiphilic bottle brush polymer added to reduce the thickness of the carbon coating layer in the positive electrode material, the proportion of carbon material in the positive electrode material can be reduced. In this way, in the positive electrode slurry, the free amount of carbon material in the positive electrode material becomes less, that is, the floating carbon is reduced, thereby reducing the impact of the floating carbon on the positive electrode material, which is beneficial to increase the solid content of the positive electrode slurry.

[0196] In the description of the embodiments of the present invention, it should be noted that the orientations or positional relationships of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are based on the orientations or positional relationships of the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0197] The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of the rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material comprises a phosphate core and a carbon coating layer, wherein the carbon coating layer covers the phosphate core, the primary particles of the positive electrode material have a particle size of 250nm to 450nm, and the particle size variance of the positive electrode material is 1 to 10.

2. The positive electrode material according to claim 1, characterized in that The precursor of the carbon coating layer includes an amphiphilic bottle brush polymer, which includes a main chain segment, a hydrophilic segment and a hydrophobic segment. The hydrophilic segment and the hydrophobic segment are both connected to the main chain segment.

3. The positive electrode material according to claim 2, characterized in that The molecular chain of the amphiphilic bottle brush polymer is in the shape of a bottle brush, and the hydrophilic segment and the hydrophobic segment are respectively distributed on opposite sides of the main chain segment.

4. The positive electrode material according to claim 2, characterized in that The hydrophilic segment contains one or more of hydroxyl, amino, carboxyl, phosphoric acid, sulfonic acid, and ether bond; and / or The hydrophobic segment contains one or more of siloxy, ester, aryl, and alkane groups; and / or The main chain segment includes one or more of polyethylene, polyethylene glycol, polydimethylsiloxane, polyurethane, polymethyl methacrylate, polystyrene, polyimide, and polyphenylene ether.

5. The positive electrode material according to claim 2, characterized in that The molecular weight of the amphiphilic bottle brush polymer is 10,000 to 50,000; and / or The molecular weight of the hydrophilic segment is 500 to 5000; and / or The molecular weight of the hydrophobic segment is 500 to 5000.

6. The positive electrode material according to claim 2, characterized in that The molar ratio of the hydrophilic segment to the hydrophobic segment is 1:(0.1-10).

7. The positive electrode material according to claim 1, characterized in that The thickness of the carbon coating layer is 0.5 nm to 5.0 nm, and the thickness variance of the carbon coating layer is 0.1 to 4.

0.

8. The positive electrode material according to claim 1, characterized in that The carbon coating layer contains organic functional groups, and the organic functional groups include one or more of carboxyl groups, hydroxyl groups, and carbon-carbon double bonds.

9. The positive electrode material according to claim 1, characterized in that In the Raman spectrum curve of the positive electrode material, the integrated intensity ratio of the D peak to the G peak is D / I G It is 0.70~0.

99.

10. A method for preparing a positive electrode material, characterized in that: The preparation method is used to prepare the positive electrode material according to any one of claims 1 to 9, and the preparation method comprises: Mixing raw materials comprising at least a lithium source, an iron source, and a phosphorus source to obtain a mixture, adding the mixture and an amphiphilic bottle brush polymer to an organic solvent according to a mass ratio, and removing the organic solvent after thorough mixing to obtain a solid material; The solid material is calcined to obtain a positive electrode material.

11. The preparation method according to claim 10, characterized in that: The method comprises adding the mixture and the amphiphilic bottle brush polymer to an organic solvent in a mass ratio, and removing the organic solvent after sufficient mixing to obtain a solid material, comprising: adding the mixture and the amphiphilic bottle brush polymer A to an organic solvent A according to a mass ratio, and removing the organic solvent A after thorough mixing to obtain a solid precursor; calcining the solid precursor to obtain an intermediate; The intermediate and the amphiphilic bottle brush polymer B are added to the organic solvent B according to a mass ratio, and after being fully mixed, the organic solvent B is removed to obtain the solid material.

12. The preparation method according to claim 11, characterized in that The mass ratio of the mixture to the amphiphilic bottle brush polymer A is 100:(40-60); the mass ratio of the intermediate to the amphiphilic bottle brush polymer B is 100:(5-10).

13. A secondary battery, characterized in that: The secondary battery comprises the positive electrode material according to any one of claims 1 to 9, or the secondary battery comprises the positive electrode material prepared by the method for preparing the positive electrode material according to any one of claims 10 to 12.

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