Positive electrode material, and preparation method therefor and use thereof

Abstract

A positive electrode material, and a preparation method therefor and the use thereof. The positive electrode material comprises secondary particles formed by the agglomeration of primary particles, wherein the primary particles comprise an active material having a chemical formula of LiMz(MnxFe1-x)1-z(BO3)y(PO4)1-y, where M comprises at least one of Mg, Ti, Nb, Al, Ni and rare earth elements, 0.4≤x≤0.7, 0.0025≤y≤0.01, and 0≤z≤0.003; the mass percent of boron in the primary particles is 0.5-1%; and B-O bonds are present between adjacent primary particles. In the positive electrode material, an excess of boron is introduced into the active material, thereby resulting in the presence of B-O bonds between adjacent primary particles in the positive electrode material; and the fluxing effect of the B-O bonds can improve the compactness between the primary particles and reduce the distance between adjacent primary particles, which is beneficial for improving the compaction density of a positive electrode active layer prepared from the positive electrode material and enables the positive electrode material to have relatively high discharge capacity.

Description

Positive electrode materials, preparation methods and applications

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 21, 2023, with application number 202311781702.3 and application name “Positive Electrode Materials, Preparation Methods and Applications”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a positive electrode material, a preparation method and an application thereof. Background Art

[0003] Lithium iron phosphate materials have good structural stability and are not prone to structural collapse during use. However, when lithium iron phosphate is used as the positive electrode active material, the compaction density of the positive electrode active layer is low. Summary of the Invention

[0004] Based on this, it is necessary to provide a positive electrode material, a preparation method and an application that can improve the compaction density of the positive electrode active layer.

[0005] A positive electrode material, comprising secondary particles agglomerated from primary particles, wherein the primary particles comprise a chemical formula of LiM z (Mn x Fe 1-x ) 1-z (BO3) y (PO4) 1-y active material, wherein M includes at least one of Mg, Ti, Nb, Al, Ni and rare earth elements, 0.4≤x≤0.7, 0.0025≤y≤0.01, 0≤z≤0.003, the mass percentage of boron element in the primary particles is 0.5% to 1%, and adjacent primary particles have BO bonds.

[0006] In the above cathode materials, by introducing boron into the active material, and in the primary particles, compared with LiM z (Mn x Fe 1-x ) 1-z (BO3) y (PO4) 1-y The mass percentage of boron element in the positive electrode material is large, and the mass percentage of boron element in the primary particles is large, which can make the adjacent primary particles in the positive electrode material have BO bonds. The fluxing effect of the BO bond can increase the compactness between the primary particles and reduce the distance between adjacent primary particles, which is beneficial to improve the compaction density of the positive electrode active layer prepared by the positive electrode material, and at the same time can make the positive electrode material have a higher discharge capacity.

[0007] In some embodiments, the primary particle further includes a coating layer, the coating layer is located on the surface of the active material, and the coating layer includes a boron-doped carbon material.

[0008] In some embodiments, the boron-doped carbon material has the chemical formula B m C 1-m , where 0.005≤m≤0.01.

[0009] In some embodiments, the D50 particle size of the primary particles is 0.3 μm to 0.5 μm.

[0010] In some embodiments, the D50 particle size of the secondary particles is 7 μm to 10 μm.

[0011] A method for preparing the positive electrode material comprises the following steps:

[0012] Mixing raw materials with a solvent to prepare a dispersion liquid, wherein the raw materials include a lithium source, an iron source, a phosphorus source, and a boron source; or the raw materials include a lithium source, an M source, an iron source, a phosphorus source, and a boron source, and M includes at least one of Mg, Ti, Nb, Al, Ni, and a rare earth element; and the molar ratio of the boron element in the boron source to the lithium element in the lithium source is (0.025-0.038):1;

[0013] performing drying and granulation treatment on the dispersion to prepare a powder;

[0014] The powder is sintered in a protective gas atmosphere.

[0015] In some embodiments, the feedstock further comprises a carbon source.

[0016] In some embodiments, the boron source includes at least one of boric acid and boron oxide.

[0017] In some embodiments, the D50 particle size of the solid dispersoid in the dispersion is 80 nm to 150 nm.

[0018] In some embodiments, the sintering process is a constant temperature sintering process.

[0019] In some embodiments, the sintering temperature of the sintering process is 500°C to 700°C.

[0020] In some embodiments, the sintering time of the sintering process is 6 hours to 10 hours.

[0021] A positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector, wherein the positive electrode active layer contains the positive electrode material or the positive electrode material prepared by the preparation method.

[0022] A battery comprises the positive electrode plate.

[0023] An electrical device comprises the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG1 is a scanning electron microscope (SEM) image of a positive electrode material in one embodiment of the present application.

[0025] FIG2 is a transmission electron microscope (TEM) image of the positive electrode material corresponding to FIG1 .

[0026] FIG3 is a scanning tunneling microscope (STM) image of the positive electrode material corresponding to FIG1 . DETAILED DESCRIPTION

[0027] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0028] In this application, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] One embodiment of the present application provides a positive electrode material. The positive electrode material includes secondary particles formed by agglomeration of primary particles, wherein the primary particles include a chemical formula of LiM z (Mn x Fe 1-x ) 1-z (BO3) y (PO4) 1- y active material, wherein M includes at least one of Mg, Ti, Nb, Al, Ni and rare earth elements, 0.4≤x≤0.7, 0.003≤y≤0.01, 0≤z≤0.003, the mass percentage of boron element in the primary particles is 0.5% to 1%, and adjacent primary particles have BO bonds.

[0032] In the positive electrode material of this embodiment, by introducing boron into the active material, and in the primary particles, compared with LiM z (Mn x Fe 1-x ) 1-z (BO3) y (PO4) 1-y The mass percentage of boron element in the positive electrode material is large, and the mass percentage of boron element in the primary particles is large, which can make the adjacent primary particles in the positive electrode material have BO bonds. The fluxing effect of the BO bond can increase the compactness between the primary particles and reduce the distance between adjacent primary particles, which is beneficial to improve the compaction density of the positive electrode active layer prepared by the positive electrode material, and at the same time can make the positive electrode material have a higher discharge capacity.

[0033] It is understood that the mass percentage of boron in the primary particles may be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc. Further optionally, the mass percentage of boron in the primary particles may be other values ​​within the range of 0.5% to 1%.

[0034] It is understood that y can represent the amount of boron doped in the active material. Optionally, y can be 0.0025, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc. When y is small, the effect of boron doping may be difficult to achieve. When y is large, it may cause significant changes to the intrinsic structure of lithium iron phosphate, which may restrict the full realization of the intrinsic advantages of lithium iron phosphate materials. Optionally, y can also be other values ​​within the range of 0.0025 to 0.01.

[0035] Optionally, x can be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc. A larger x may significantly change the intrinsic structure of lithium iron phosphate, which may restrict the full utilization of the intrinsic advantages of lithium iron phosphate materials. Optionally, x can also be other values ​​within the range of 0.4 to 0.7.

[0036] It is understood that z can represent the doping amount of element M in the active material. Alternatively, z can be 0, 0.001, 0.0015, 0.002, 0.0025, 0.003, and so on. It is also understood that when z is 0, it indicates that the active material does not contain element M. Alternatively, z can be another value within the range of 0 to 0.003. Furthermore, 0.001 ≤ z ≤ 0.003.

[0037] It is understood that among the active materials, LiMn x Fe 1-x PO4 is the basic material, boron is doped in LiMn x Fe 1-x In the lattice of PO4. During the doping process of boron, boron can replace LiMn x Fe 1-x Part of the phosphorus in PO4, thereby achieving boron doping in LiMn x Fe 1-x In the PO4 lattice.

[0038] In some embodiments, the primary particles further include a coating layer, located on the surface of the active material, comprising a boron-doped carbon material. Excess boron can enter the coating layer, resulting in the coating layer comprising a boron-doped carbon material. The coating layer can, on the one hand, provide a degree of protection for the active material and improve its stability during use; on the other hand, it can provide improved electrical conductivity, increasing the electronic conductivity of the positive electrode material, thereby improving the rate capability of the battery. Alternatively, the coating layer can be located on a portion of the active material's surface, or on the entire surface of the active material.

[0039] In some embodiments, the coating layers of adjacent primary particles have BO bonds, which can increase the compactness between the primary particles and reduce the spacing between adjacent primary particles, thereby increasing the compaction density of the positive electrode active layer prepared from the positive electrode material.

[0040] It is understood that when the primary particle further includes a coating layer, the primary particle has a core-shell structure. The core-shell structure includes a core and a shell coated on the surface of the core. The core includes a chemical formula of LiM z (Mn x Fe 1-x )1-z (BO3) y (PO4) 1-y An active material, wherein M comprises at least one of Mg, Ti, Nb, Al, Ni, and a rare earth element, 0.4 ≤ x ≤ 0.7, 0.0025 ≤ y ≤ 0.01, and 0 ≤ z ≤ 0.003. The shell comprises a boron-doped carbon material. Optionally, the shell coats a portion of the surface of the core, or the shell coats the entire surface of the core. Further optionally, x can be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc. y can be 0.0025, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc. z can be 0, 0.001, 0.0015, 0.002, 0.0025, 0.003, etc.

[0041] In some embodiments, the boron-doped carbon material has the formula B m C 1-m , where 0.005≤m≤0.01. It is understood that m can represent the amount of boron doping in the carbon material. Optionally, m can be 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc. When m is small, the effect of boron doping may be difficult to achieve. When m is large, it may cause significant changes to the intrinsic structure of the carbon material, which may restrict the full realization of the intrinsic advantages of the carbon material. Optionally, m can also be other values ​​within the range of 0.005 to 0.01.

[0042] In some embodiments, boron is doped into the carbon lattice of the carbon material in the coating layer. Boron replaces trigonal positions in carbon atoms. Because boron atoms have three valence electrons and can act as electron acceptors, this shifts the Fermi level toward the conduction band, altering the electronic structure of the coating layer. Boron atoms can act as electron acceptors in the electronic structure, further improving the conductivity and high-rate discharge performance of the positive electrode material.

[0043] In some embodiments, the thickness of the coating layer is 5nm to 10nm. The thickness of the coating layer in this range can better exert the effect of the coating layer. When the thickness of the coating layer is small, the protective effect and the improvement effect of the conductive performance of the coating layer may be small, and it is difficult to fully exert the effect of the coating layer. When the thickness of the coating layer is large, it may restrict the reduction of the distance between adjacent primary particles, and thus restrict the improvement of the compaction density of the positive electrode active layer prepared by the positive electrode material. Optionally, the thickness of the coating layer can be 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, etc. Further optionally, the thickness of the coating layer can also be other values ​​within the range of 5nm to 10nm.

[0044] In some embodiments, the mass percentage of the boron element gradually decreases along the direction from the inside to the outside of the primary particle. The mass percentage of the boron element gradually decreases along the direction from the inside to the outside of the primary particle, and the conductive properties of the primary particles can be adjusted accordingly, so that the conductive properties of the primary particles gradually decrease from the inside to the outside, thereby reducing the resistance to the transmission of lithium ions and electrons in the primary particles, thereby improving the electrochemical properties of the positive electrode material. Optionally, the mass percentage of the boron element in the active material is greater than the mass percentage of the boron element in the boron-doped carbon material. It is understandable that the mass percentage of the boron element gradually decreases along the direction from the inside to the outside of the primary particle, which may cause the volume of the primary particle to gradually decrease in the direction from the inside to the outside of the primary particle, thereby forming a primary particle in the shape of an American football.

[0045] As some examples of the primary particle size, the D50 particle size of the primary particles is 0.3 μm to 0.5 μm. Smaller and more uniform primary particle sizes can improve the lithium ion conductivity of the active material and facilitate lithium ion transport. Alternatively, the D50 particle size of the primary particles can be 0.3 μm, 0.35 μm, 0.4 μm, 0.5 μm, etc.

[0046] As some optional examples of the particle size of the secondary particles, the D50 particle size of the secondary particles is 7μm to 10μm. The D50 particle size of the secondary particles within this range can enable the positive electrode active layer prepared from the positive electrode material to have a higher compaction density. Alternatively, the D50 particle size of the secondary particles can be 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, etc. It is understandable that the D50 particle size of the secondary particles can also be other values ​​within the range of 7μm to 10μm.

[0047] As some optional examples of the specific surface area of ​​the positive electrode material, the specific surface area of ​​the positive electrode material is 10m 2 / g~22m 2 / g. The specific surface area of ​​the positive electrode material within this range can provide more transmission channels for the transmission of lithium ions and improve the transmission performance of lithium ions. At the same time, when the positive electrode material is used in a battery, the specific surface area of ​​the positive electrode material within this range is conducive to the infiltration of the electrolyte into the positive electrode material and promotes the transmission of lithium ions inside the battery. Optionally, the specific surface area of ​​the positive electrode material can be 10m 2 / g、12m 2 / g、15m 2 / g、18m 2 / g, 20m 2 / g、22m 2 / g, etc. It is understandable that the specific surface area of ​​the positive electrode material can also be 10m 2 / g~22m 2 Other values ​​within the range of / g.

[0048] Another embodiment of the present application provides a method for preparing the above-mentioned positive electrode material. The method for preparing the positive electrode material comprises the following steps: mixing raw materials with a solvent to prepare a dispersion liquid, wherein the raw materials include a lithium source, an iron source, a phosphorus source, and a boron source; or the raw materials include a lithium source, an M source, an iron source, a phosphorus source, and a boron source, wherein M includes at least one of Mg, Ti, Nb, Al, Ni, and a rare earth element, and the molar ratio of the boron element in the boron source to the lithium element in the lithium source is (0.025-0.038):1. The dispersion liquid is dried and granulated to prepare a powder. The powder is sintered under a protective gas atmosphere.

[0049] In the preparation method of the positive electrode material of this embodiment, the boron element is made excessive by adjusting the element ratio, and through drying granulation and sintering treatment, a positive electrode material with BO bonds between adjacent primary particles and a higher compaction density can be obtained.

[0050] Optionally, the molar ratio of the boron element in the boron source to the lithium element in the lithium source is 0.025:1, 0.026:1, 0.027:1, 0.028:1, 0.029:1, 0.03:1, 0.031:1, 0.032:1, 0.033:1, 0.034:1, 0.035:1, 0.036:1, 0.037:1, 0.038:1, etc. It will be appreciated that the molar ratio of the boron element in the boron source to the lithium element in the lithium source may also be other values ​​within the range of (0.025 to 0.038):1.

[0051] In some embodiments, the raw material further comprises a carbon source. By introducing the carbon source, a coating layer comprising a boron-doped carbon material can be prepared by a corresponding preparation method, thereby further improving the performance of the positive electrode material.

[0052] In some embodiments, the boron source includes at least one of boric acid and boron oxide. In the preparation process of the positive electrode material, boric acid, as a weak acid, can react with LiFePO4, LiM x Fe 1-x Lithium iron phosphate materials such as PO4 undergo chemical reactions, making the BO bonds generated during the preparation process more uniform, which is beneficial to further improve the compactness between adjacent primary particles, further reduce the distance between adjacent primary particles, and thus increase the compaction density of the positive electrode active layer prepared from the positive electrode material.

[0053] In some embodiments, the carbon source comprises at least one of glucose, sucrose and polyethylene glycol. Alternatively, the carbon source comprises glucose, or sucrose, or a mixture of glucose and sucrose, or a mixture of glucose and polyethylene glycol, or a mixture of sucrose and polyethylene glycol, or a mixture of glucose, sucrose and polyethylene glycol.

[0054] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide, and lithium oxalate.

[0055] In some embodiments, the M source includes at least one of magnesium oxide, titanium dioxide, niobium oxide, aluminum oxide, nickel oxide, and rare earth oxides. Optionally, the titanium dioxide is nano-titanium dioxide.

[0056] In some embodiments, the manganese source includes at least one of manganese dioxide, trimanganese tetraoxide, manganese carbonate, manganese oxalate, and manganese iron oxide.

[0057] In some embodiments, the iron source includes at least one of ferric phosphate, ferrous oxalate, ferroferric oxide, ferrous oxide, and ferromanganese oxide.

[0058] In some embodiments, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate.

[0059] In some embodiments, the solvent comprises water.

[0060] In some embodiments, the D50 particle size of the solid dispersoid in the dispersion is 80 nm to 150 nm. The particle size of the solid dispersoid in the dispersion within this range helps to obtain a powder of appropriate particle size during the drying and granulation process. Alternatively, the D50 particle size of the solid dispersoid in the dispersion can be 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, etc. Further optionally, the D50 particle size of the solid dispersoid in the dispersion can also be other values ​​within the range of 80 nm to 150 nm.

[0061] It is understood that when preparing the dispersion, stirring, grinding, etc. can be used to promote the mixing of the raw materials and the solvent, and the D50 particle size of the solid dispersoid in the dispersion can be adjusted.

[0062] In some embodiments, the drying and granulation process is performed using a spray drying and granulation process. Optionally, during the spray drying and granulation process, the air inlet temperature is 220°C, the air outlet temperature is 100°C, the atomizing disk speed is 30,000 rpm, and the feed rate is 40 L / h. Furthermore, optionally, the spray drying and granulation process is performed using a centrifugal spray dryer.

[0063] In some embodiments, the powder obtained by the dry granulation process has a D50 particle size of 4 μm to 7 μm.

[0064] In some embodiments, the sintering process is performed at a constant temperature. This is advantageous for obtaining a positive electrode material with stable performance. It is understood that the term "constant temperature sintering" means that the temperature during the holding phase of the sintering process is kept constant.

[0065] Furthermore, the sintering temperature of the sintering process is 500°C to 700°C. A sintering temperature within this range is conducive to promoting the doping of boron elements in the positive electrode material. Alternatively, the sintering temperature can be 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 700°C, etc. Further optionally, the sintering temperature can also be other values ​​within the range of 500°C to 700°C. It is understood that the sintering temperature refers to the holding temperature during the sintering process.

[0066] Furthermore, the sintering time of the sintering process is 6 hours to 10 hours. Alternatively, the sintering time of the sintering process can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc. Further, the sintering time of the sintering process can also be other values ​​within the range of 6 hours to 10 hours. It is understood that the sintering time of the sintering process refers to the holding time during the sintering process.

[0067] In some embodiments, during the sintering process, the temperature is increased to the sintering temperature at a heating rate of 3° C. / min.

[0068] In some embodiments, the protective gas includes at least one of nitrogen and a rare gas. Alternatively, the rare gas includes at least one of helium, neon, and argon. Further, during the sintering process, the protective gas has a flow rate of 0.5 L / min.

[0069] Another embodiment of the present application provides a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector. The positive electrode active layer contains the aforementioned positive electrode material or a positive electrode material prepared by the aforementioned preparation method. In this embodiment, the use of the aforementioned positive electrode material or a positive electrode material prepared by the aforementioned preparation method can result in the positive electrode active layer having a higher compaction density, thereby helping to improve the energy density of the battery.

[0070] In some embodiments, the compacted density of the positive electrode active layer is 2.2 g / cm 3 ~2.45g / cm 3 For example, the compaction density of the positive electrode active layer can be 2.2g / cm 3 , 2.25g / cm 3 , 2.3g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 , 2.45g / cm 3 Optionally, the compaction density of the positive electrode active layer can also be 2.2 g / cm 3 ~2.45g / cm 3 Other values ​​within the range.

[0071] Another embodiment of the present application provides a battery comprising the above-mentioned positive electrode plate.

[0072] Another embodiment of the present application provides an electrical device comprising the above-mentioned battery.

[0073] Example 1

[0074] The preparation method of the positive electrode material in this embodiment includes:

[0075] S101: Lithium carbonate, manganese carbonate, iron phosphate, ammonium dihydrogen phosphate, and boric acid are mixed with deionized water in a molar ratio of boron in the boric acid to lithium in the lithium carbonate of 0.025:1. The mixture is stirred and then ground in a sand mill to obtain a dispersion. The D50 particle size of the solid dispersoid in the dispersion is 100 nm.

[0076] S102: Dry and granulate the dispersion using a centrifugal spray dryer to obtain a powder. The powder has a D50 particle size of 4 μm. The centrifugal spray dryer has an air inlet temperature of 220°C, an air outlet temperature of 100°C, an atomizing disk speed of 30,000 rpm, and a feed rate of 40 L / h.

[0077] S103: Sintering the powder and glucose under a nitrogen atmosphere. The sintering conditions are: a nitrogen gas flow rate of 0.5 L / min, heating to 650°C at a rate of 3 min / °C, and sintering at 650°C for 8 hours.

[0078] S104: After sintering, the mixture is cooled to room temperature to obtain a positive electrode material.

[0079] The chemical composition and parameter indicators of the positive electrode material prepared in this example are shown in Table 1.

[0080] Example 2

[0081] The preparation method of the positive electrode material in this embodiment includes:

[0082] S101: Lithium dihydrogen phosphate, manganese oxalate, ferrous oxalate, glucose, and boric acid are mixed with deionized water in a molar ratio of boron in the boric acid to lithium in the lithium dihydrogen phosphate of 0.034:1. The mixture is stirred and then ground in a sand mill to obtain a dispersion. The D50 particle size of the solid dispersoid in the dispersion is 100 nm.

[0083] S102: Dry and granulate the dispersion using a centrifugal spray dryer to obtain a powder. The powder has a D50 particle size of 4 μm. The centrifugal spray dryer has an air inlet temperature of 220°C, an air outlet temperature of 100°C, an atomizing disk speed of 30,000 rpm, and a feed rate of 40 L / h.

[0084] S103: Sintering the powder in a nitrogen atmosphere. Sintering conditions are: nitrogen gas flow rate of 0.5 L / min. Raise the temperature to 650°C at a rate of 3 min / °C and sinter at 650°C for 8 hours.

[0085] S104: After sintering, the mixture is cooled to room temperature to obtain a positive electrode material.

[0086] The chemical composition and parameter indicators of the positive electrode material prepared in this example are shown in Table 1.

[0087] The SEM image of the positive electrode material prepared in this embodiment is shown in Figure 1. As can be seen from Figure 1, in the positive electrode material, the boundaries between adjacent primary particles are blurred, which shows that the primary particles have a certain compatibility, so that the distance between the primary particles is small. Furthermore, the TEM image of the positive electrode material is shown in Figure 2. As can be seen from Figure 2, a connecting layer is formed on the surface of the primary particles. It can be measured by Raman spectroscopy that the connecting layer has a BO bond, and the connecting layer includes BO3 substance. The connecting layer can make the connection between adjacent primary particles more tightly. Furthermore, the STM image of the positive electrode material is shown in Figure 3. In Figure 3, the circles represent boron atoms, and the vertices of the hexagons are carbon atoms. As can be seen from Figure 3, the boron element in the coating layer is doped in the carbon lattice of the carbon material.

[0088] Example 3

[0089] Compared with Example 2, Example 3 is different in that the partial ratios in the raw materials are different, wherein the molar ratio of the boron element in boric acid to the lithium element in lithium dihydrogen phosphate is 0.038:1.

[0090] Example 4

[0091] Compared with Example 2, Example 4 is different in that the partial ratios in the raw materials are different, wherein the molar ratio of the boron element in boric acid to the lithium element in lithium dihydrogen phosphate is 0.035:1.

[0092] Example 5

[0093] Compared with Example 2, the difference of this embodiment is that the raw materials further include magnesium oxide.

[0094] Example 6

[0095] Compared with Example 2, the difference of this embodiment is that the raw materials further include nano-titanium dioxide.

[0096] Example 7

[0097] Compared with Example 2, the difference of this embodiment is that the raw material further includes niobium oxide.

[0098] Comparative Example 1

[0099] The positive electrode material of this comparative example is carbon-coated LiMn 0.4 Fe 0.6 PO4.

[0100] Comparative Example 2

[0101] Compared with Example 1, the difference of this embodiment is that the partial ratios in the raw materials are different, wherein the molar ratio of the boron element in boric acid to the lithium element in lithium dihydrogen phosphate is 0.015:1.

[0102] Comparative Example 3

[0103] Compared with Example 1, the difference of this embodiment is that the partial ratios in the raw materials are different, wherein the molar ratio of the boron element in boric acid to the lithium element in lithium dihydrogen phosphate is 0.020:1.

[0104] The positive electrode sheet was prepared by adding an appropriate amount of organic solvent NMP to the positive electrode material: PVDF: acetylene black in a ratio of 8:1:1 to obtain a slurry, and coating the slurry on a carbon-coated aluminum foil.

[0105] A button cell was prepared using the positive electrode sheet as the positive electrode, a metal lithium sheet as the negative electrode, a microporous polypropylene membrane as the separator, and 1M LiPF6 (a mixture of EC and EMC with a volume ratio of 3:7 as the solvent) as the electrolyte.

[0106] Test Case

[0107] (1) The compaction density of the positive electrode active layer was tested, and the results are shown in Table 1.

[0108] Use a compaction density meter to test compaction density. At 25°C ± 2°C, place a clean, empty mold (including upper and lower test electrodes / gaskets) into the test equipment. Use the accompanying test software to reset the thickness. After resetting, weigh an appropriate amount of the sample to be tested and place it into the mold. Shake the sample properly to level it, install the test electrodes / gaskets, place the mold into the test equipment, and start the software test.

[0109] (2) The discharge capacity of the positive electrode material was tested, and the results are shown in Table 1.

[0110] Place the prepared battery in a battery testing system to test its electrochemical performance. Set the charge / discharge current and cycle number for each rate (discharge cutoff voltage 2.0V, charge cutoff voltage 4.3V), start the battery testing system, and input the mass of the positive electrode material. After the test is complete, read the data.

[0111] Table 1

[0112] It can be seen from Example 1 and Comparative Examples 1 to 3 that in Examples 1 to 7, by introducing boron into the positive electrode active material and when the mass percentage of the boron element in the primary particles is within an appropriate range, the obtained positive electrode material can have both a larger positive electrode active layer compaction density and a higher discharge capacity.

[0113] It can be seen from Examples 2 to 7 and Example 1 that when the coating layer is B m C 1-m , that is, introducing boron into the coating layer can further improve the discharge capacity of the positive electrode active material.

[0114] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] The above-described embodiments merely represent several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make a number of variations and improvements without departing from the concept of the present application, and these variations and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the patent application shall be based on the appended claims, and the description and drawings may be used to interpret the content of the claims.

Claims

1. A positive electrode material, wherein: The secondary particles are formed by agglomerating primary particles, wherein the primary particles include a chemical formula of LiM z (Mn x Fe 1-x ) 1-z (BO3) y (PO4) 1-y active material, wherein M includes at least one of Mg, Ti, Nb, Al, Ni and rare earth elements, 0.4≤x≤0.7, 0.0025≤y≤0.01, 0≤z≤0.003, the mass percentage of boron element in the primary particles is 0.5% to 1%, and there are BO bonds between adjacent primary particles.

2. The positive electrode material according to claim 1, wherein The primary particle further includes a coating layer, the coating layer is located on the surface of the active material, and the coating layer includes a boron-doped carbon material.

3. The positive electrode material according to claim 2, wherein The chemical formula of the boron-doped carbon material is B m C 1-m , where 0.005≤m≤0.

01.

4. The positive electrode material according to any one of claims 1 to 3, wherein The D50 particle size of the primary particles is 0.3 μm to 0.5 μm.

5. The positive electrode material according to any one of claims 1 to 3, wherein The D50 particle size of the secondary particles is 7 μm to 10 μm.

6. A method for preparing the positive electrode material according to any one of claims 1 to 5, wherein: The steps include: Mixing raw materials with a solvent to prepare a dispersion, wherein the raw materials include a lithium source, an iron source, a phosphorus source and a boron source; or the raw materials include a lithium source, an M source, an iron source, a phosphorus source and a boron source, and M includes at least one of Mg, Ti, Nb, Al, Ni and a rare earth element; the molar ratio of the boron element in the boron source to the lithium element in the lithium source is (0.025-0.038):1; Drying and granulating the dispersion to prepare a powder; The powder is sintered in a protective gas atmosphere.

7. The method for preparing the positive electrode material according to claim 6, wherein: The feedstock also includes a carbon source.

8. The method for preparing the positive electrode material according to claim 6, wherein: The boron source includes at least one of boric acid and boron oxide.

9. The method for preparing a positive electrode material according to any one of claims 6 to 8, wherein: The D50 particle size of the solid dispersoid in the dispersion is 80nm to 150nm.

10. The method for preparing a positive electrode material according to any one of claims 6 to 9, wherein: The sintering process adopts a constant temperature sintering process.

11. The method for preparing a positive electrode material according to any one of claims 6 to 10, wherein: The sintering temperature of the sintering treatment is 500°C to 700°C.

12. The method for preparing a positive electrode material according to any one of claims 6 to 11, wherein: The sintering time of the sintering treatment is 6 hours to 10 hours.

13. A positive electrode sheet, wherein: The invention comprises a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector, wherein the positive electrode active layer contains the positive electrode material according to any one of claims 1 to 5 or the positive electrode material prepared by the preparation method according to any one of claims 6 to 12.

14. A battery, wherein: Including the positive electrode sheet as described in claim 13.

15. An electrical device, wherein: Comprising the battery of claim 14.

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