Lithium iron phosphate positive electrode material and preparation method and application thereof

Abstract

The invention provides a lithium iron phosphate positive electrode material and a preparation method and application thereof. The provided lithium iron phosphate positive electrode material comprises a body and a coating layer coating at least part of the surface of the body, wherein the body comprises lithium iron phosphate, the lithium iron phosphate is selected from doped lithium iron phosphate, doping elements of the doped lithium iron phosphate comprise one or more of titanium, magnesium and aluminum, and the coating layer comprises nickel cobalt lithium manganate. The lithium iron phosphate positive electrode material provided by the invention has relatively high electronic conductivity and lithium ion diffusion rate.

Description

TECHNICAL FIELD

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

[0002] Lithium iron phosphate (LiFePO4) has become a popular positive electrode material in lithium ion batteries due to its excellent thermal stability, safety, and long cycle life, and is widely used in electric vehicles and energy storage systems. However, the electronic conductivity and lithium ion diffusion rate of LiFePO4 (LFP) are relatively low, which limits its performance in high-rate discharge and fast charging applications. SUMMARY

[0003] In view of the technical problems in the background art, the present application provides a lithium iron phosphate positive electrode material, a preparation method and application thereof. The technical problems of low electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material are solved.

[0004] In a first aspect, the embodiments of the present application provide a lithium iron phosphate positive electrode material, comprising a body and a coating layer coated on at least part of the surface of the body; wherein the body comprises lithium iron phosphate, and the lithium iron phosphate is selected from doped lithium iron phosphate, the doping elements of the doped lithium iron phosphate include one or more of titanium, magnesium and aluminum, and the coating layer comprises lithium nickel cobalt manganese oxide.

[0005] In the technical solution of the embodiments of the present application, a lithium nickel cobalt manganese oxide material with high conductivity is coated on the surface of the lithium iron phosphate as a coating layer. The coating layer provides additional electronic conduction channels and ion diffusion channels, improves the electrical conductivity and ion diffusion rate of the lithium iron phosphate positive electrode material, effectively alleviates the conductivity bottleneck of the lithium iron phosphate under high-rate discharge conditions, and improves the energy output capacity of the lithium iron phosphate positive electrode material. The coating layer effectively isolates the direct contact between the lithium iron phosphate and the electrolyte, reduces the occurrence of side reactions, and delays the aging of the lithium iron phosphate positive electrode material. The doping elements reduce the collapse of the lattice structure of the lithium iron phosphate during charging and discharging, improve the structural stability of the material of the coating layer and the body, and prolong the cycle life of the lithium iron phosphate positive electrode material. In addition, the doping elements help to refine the lithium iron phosphate crystal grains, increase the specific surface area of the lithium iron phosphate body, increase the embedding rate and de-embedding rate of lithium ions in the lithium iron phosphate positive electrode material, and thus improve the rate performance of the lithium iron phosphate positive electrode material.

[0006] In some embodiments, the chemical formula of the lithium iron phosphate positive electrode material is: Li z Fe 0.96 PO4-M x @Li a Ni b Co c Mnd O2, wherein M is a doping element selected from one or more of Ti, Mg and Al, 0.003≤x≤0.005, 0.98≤z≤1.03, 0.97≤a≤1.07, 0.5≤b≤0.8, 0.1≤c≤0.2, 0.1≤d≤0.3;

[0007] In the above embodiments, the doping type lithium iron phosphate represented by the above chemical formula, while maintaining high charge specific capacity and discharge specific capacity of the lithium iron phosphate cathode material, is conducive to improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate cathode material, thereby improving the cycle performance and rate performance of the lithium iron phosphate cathode material.

[0008] In some embodiments, the coating layer has a layered crystal structure in the lithium iron phosphate cathode material.

[0009] In the above embodiments, the layered structure of the coating layer provides a smooth diffusion channel for lithium ions, significantly improving the diffusion rate of lithium ions in the lithium iron phosphate cathode material.

[0010] In some embodiments, the thickness of the coating layer is 3 nm to 25 nm in the lithium iron phosphate cathode material.

[0011] In the above embodiments, the thickness of the coating layer is 3 nm to 25 nm, which is conducive to improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate cathode material.

[0012] In some embodiments, the mass fraction of the coating layer in the lithium iron phosphate cathode material is 0.5% to 5%.

[0013] In the above embodiments, the coating layer has a mass fraction in the above range, which is conducive to improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate cathode material. If the coating layer is too thick, on the one hand, it hinders the diffusion of Li + On the other hand, it is easy to cause the coating layer to crack or peel off due to stress accumulation, resulting in failure of the electrode / electrolyte interface contact, which significantly reduces the rate performance and cycle stability. If the coating layer is too thin, it cannot sufficiently block the direct contact between LFP and electrolyte, and it is also difficult to build a continuous electronic conduction network, which reduces the capacity utilization and limits the improvement of rate performance.

[0014] In some embodiments, the mass fraction of the doping element of the doping type lithium iron phosphate in the lithium iron phosphate cathode material is 0.3% to 0.5%.

[0015] In the above embodiments, by doping an appropriate amount of a doping element in the lithium iron phosphate, while maintaining the high charge specific capacity and discharge specific capacity of the lithium iron phosphate positive electrode material, the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material are improved, thereby improving the cycle performance and rate performance of the lithium iron phosphate positive electrode material.

[0016] In some embodiments, the compaction density of the lithium iron phosphate positive electrode material is 2.45 g / cm 3 to 2.57 g / cm 3 .

[0017] In the above embodiments, the compaction density of the positive electrode material is within the above range, which is beneficial to improving the energy density of the lithium iron phosphate positive electrode material.

[0018] In some embodiments, the lithium iron phosphate positive electrode material has a spacing of 1.1 to 2.8, and the lithium iron phosphate positive electrode material has a D 50 particle size of 1.1 to 1.35 microns.

[0019] In the above embodiments, the spacing and D 50 particle size are within the above range, the particle size of the lithium iron phosphate positive electrode material is more appropriate and the particle size distribution is more concentrated, the electronic transmission and lithium ion diffusion path is shorter, which helps to improve the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material, and the more uniform particle size is beneficial to improving the compaction density of the lithium iron phosphate positive electrode material.

[0020] In some embodiments, the specific surface area of the lithium iron phosphate positive electrode material is 8.5 m 2 / g to 11.6 m 2 / g.

[0021] In the above embodiments, the specific surface area is within the above range, which avoids excessive contact area with the electrolyte while providing more lithium ion diffusion paths, improves the embedding and de-embedding rate of lithium ions, and is beneficial to improving the rate performance of the lithium iron phosphate positive electrode material.

[0022] In some embodiments, the powder resistivity of the lithium iron phosphate positive electrode material is 6 Ω·cm to 20 Ω·cm.

[0023] In the above embodiments, the powder resistivity of the lithium iron phosphate positive electrode material is controlled in the above range, which is beneficial to improve the electrical conductivity of the lithium iron phosphate positive electrode material, improve the charge-discharge rate of the lithium iron phosphate positive electrode material, especially the charge-discharge rate under high-rate charge-discharge conditions, and reduce the heat generated in the lithium iron phosphate positive electrode material during the charge-discharge process, reduce the damage to the structure of the lithium iron phosphate positive electrode material caused by the heat, and prolong the service life of the lithium iron phosphate material.

[0024] In some embodiments, the lithium ion diffusion rate of the lithium iron phosphate positive electrode material is 0.9x10 -12 cm 2 ·s -1 ~4.8x10 -10 cm 2 ·s -1 .

[0025] In the above embodiments, the lithium ion diffusion rate of the lithium iron phosphate positive electrode material is controlled in the above range, which is beneficial to improve the energy output capacity of the lithium iron phosphate positive electrode material, thereby improving the charge-discharge performance of the lithium iron phosphate positive electrode material under high-rate conditions, and improving the rate performance of the lithium iron phosphate positive electrode material.

[0026] In a second aspect, the embodiments of the present application provide a preparation method of a lithium iron phosphate positive electrode material, comprising:

[0027] A first mixture is provided, and the first mixture comprises a nickel source, a cobalt source, a manganese source, and a first lithium source;

[0028] The first mixture is subjected to a first drying treatment and a first calcination treatment to obtain a coating layer material, and the coating layer material comprises lithium nickel cobalt manganese oxide;

[0029] A second mixture is provided, and the second mixture comprises the coating layer material, an iron source, a second lithium source, a dopant, and a phosphorus source;

[0030] The second mixture is subjected to a second drying treatment and a second calcination treatment to obtain the lithium iron phosphate positive electrode material;

[0031] The dopant is selected from one or more of a titanium source, a magnesium source, and an aluminum source.

[0032] In the technical scheme of the embodiment of the present application, by controlling the preparation of the coating layer material and the coating process, a uniform and stable coating layer is formed, and a nickel-cobalt-manganese lithium material with high conductivity is coated on the surface of the lithium iron phosphate as the coating layer. The coating layer provides additional electronic conduction channels and ion diffusion channels, improves the electrical conductivity and ion diffusion rate of the lithium iron phosphate positive electrode material, effectively alleviates the conductivity bottleneck of the lithium iron phosphate under high-rate discharge conditions, and improves the energy output capacity of the lithium iron phosphate positive electrode material. The coating layer effectively isolates the direct contact between the lithium iron phosphate and the electrolyte, reduces the occurrence of side reactions, and delays the aging of the lithium iron phosphate positive electrode material. The doping elements reduce the collapse of the lattice structure of the lithium iron phosphate during the charging and discharging process, improve the structural stability of the coating layer and the bulk material, and prolong the cycle life of the lithium iron phosphate positive electrode material. In addition, the doping elements help to refine the lithium iron phosphate crystal grains, increase the specific surface area of the bulk material, increase the embedding rate and de-embedding rate of lithium ions in the lithium iron phosphate positive electrode material, and thus improve the rate performance of the lithium iron phosphate positive electrode material.

[0033] In some embodiments, the nickel source comprises one or more of nickel nitrate, nickel carbonate.

[0034] In some embodiments, the cobalt source comprises one or more of cobalt nitrate, cobalt carbonate.

[0035] In some embodiments, the manganese source comprises one or more of manganese nitrate, manganese carbonate.

[0036] In some embodiments, the first lithium source and the second lithium source are each independently selected from one or more of lithium carbonate, lithium phosphate, lithium dihydrogen phosphate.

[0037] In some embodiments, the titanium source comprises one or more of titanium white powder, titanium tetranitrate.

[0038] In some embodiments, the magnesium source comprises one or more of magnesium oxide, magnesium nitrate.

[0039] In some embodiments, the aluminum source comprises one or more of aluminum oxide, aluminum nitrate.

[0040] In some embodiments, the iron source comprises one or more of ferrous oxalate, anhydrous iron phosphate.

[0041] In some embodiments, the phosphorus source comprises one or more of ammonium dihydrogen phosphate, lithium phosphate, lithium dihydrogen phosphate.

[0042] In the above embodiments, the above nickel source, cobalt source, manganese source, first lithium source, second lithium source, titanium source, magnesium source, aluminum source, iron source, and phosphorus source are widely available and low in cost, which is conducive to obtaining a lithium iron phosphate positive electrode material with improved cycle performance and rate performance at a lower preparation cost.

[0043] In some embodiments, the method for preparing the lithium iron phosphate cathode material, the step of providing the first mixture comprises:

[0044] mixing the nickel source, the cobalt source, the manganese source, and a first solvent to obtain a first sub-mixture;

[0045] mixing the first sub-mixture and the first lithium source to obtain the first mixture.

[0046] In the above embodiments, the first mixture is obtained by step-by-step mixing, which is conducive to the sufficient and uniform mixing of each raw material in the first mixture, thereby improving the purity of the coating layer material obtained after the first drying treatment and the first calcination treatment of the first mixture.

[0047] In some embodiments, the method for preparing the lithium iron phosphate cathode material, the step of providing the second mixture comprises:

[0048] mixing the iron source, the second lithium source, the phosphorus source, the dopant, the coating layer material, and a second solvent to obtain the second mixture.

[0049] In the above embodiments, the second mixture is obtained by mixing the above raw materials, which is conducive to the further sufficient reaction between each raw material, thereby improving the purity of the lithium iron phosphate cathode material obtained and improving the product quality of the lithium iron phosphate cathode material obtained.

[0050] In some embodiments, the method for preparing the lithium iron phosphate cathode material, the step of mixing the nickel source, the cobalt source, the manganese source, and a first solvent to obtain a first sub-mixture comprises: a first grinding treatment of mixing the nickel source, the cobalt source, the manganese source, and the first solvent; wherein the time of the first grinding treatment is 30 min to 90 min.

[0051] In some embodiments, the method for preparing the lithium iron phosphate cathode material, the step of mixing the first sub-mixture and the first lithium source to obtain the first mixture comprises: a second grinding treatment of mixing the first sub-mixture and the first lithium source, and the time of the second grinding treatment is 20 min to 60 min.

[0052] In the above embodiments, each raw material in the first mixture is mixed by step-by-step grinding treatment, which is conducive to the sufficient and uniform mixing of each raw material in the first mixture, thereby improving the purity of the coating layer material obtained after the first drying treatment and the first calcination treatment of the first mixture.

[0053] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the step of mixing the iron source, the second lithium source, the phosphorus source, the coating layer material and the second solvent to obtain the second mixture comprises: a third grinding treatment of the iron source, the second lithium source, the phosphorus source, the coating layer material, the dopant and the second solvent; the third grinding treatment is performed for 20-40 minutes; or the third grinding treatment is performed until the D50 particle size of the second mixture is 350-400 nm.

[0054] In the above embodiments, the second mixture is obtained by grinding and mixing the raw materials, which is beneficial to the sufficient mixing of the raw materials and the further sufficient reaction, improves the purity of the obtained lithium iron phosphate positive electrode material, and thus improves the product quality of the obtained lithium iron phosphate positive electrode material.

[0055] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the molar ratio of lithium, nickel, cobalt and manganese in the first mixture is (20-22):(10-16):(2-4):(2-6).

[0056] In the above embodiments, the molar ratio of lithium, nickel, cobalt and manganese is controlled to be (20-22):(10-16):(2-4):(2-6), which is beneficial to the sufficient reaction between the raw materials and improves the purity of the obtained coating layer material, thereby improving the product quality of the finally obtained lithium iron phosphate positive electrode material.

[0057] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the molar ratio of lithium, iron and phosphorus in the second mixture is (1.12-1.18):1.10:1.14.

[0058] In the above embodiments, the molar ratio of lithium, iron and phosphorus in the second mixture is controlled to be (1.12-1.18):1.10:1.14, which is beneficial to the sufficient reaction between the raw materials and improves the purity of the lithium iron phosphate positive electrode material, thereby improving the performance stability of the lithium iron phosphate positive electrode material.

[0059] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the first drying treatment and the second drying treatment are independently selected from spray drying.

[0060] In the above embodiments, the first drying treatment is spray drying, which is beneficial to the particle size of the solid particles in the first calcination treatment, so as to obtain a coating layer material with a suitable particle size after the first calcination treatment; the second drying treatment is spray drying, which is beneficial to the particle size of the solid particles in the second calcination treatment, and is beneficial to obtaining a lithium iron phosphate positive electrode material with a concentrated particle size distribution and a suitable particle size after the second calcination treatment, thereby improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material, and improving the compaction density of the lithium iron phosphate positive electrode material.

[0061] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the first calcination treatment comprises a first sub-calcination treatment and a second sub-calcination treatment, the temperature of the first sub-calcination treatment is 700-800 DEG C, and the time of the first sub-calcination treatment is 5-8 h; the temperature of the second sub-calcination treatment is 900-1000 DEG C, and the time of the second sub-calcination treatment is 8-15 h.

[0062] In the above embodiments, the first calcination treatment is performed by step calcination, and the temperature and time of the first sub-calcination treatment and the second sub-calcination treatment are controlled within the above ranges, which is beneficial to the sufficient reaction between the raw materials, improves the purity of the coating layer material, and thus improves the product quality and performance of the lithium iron phosphate positive electrode material.

[0063] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the gas atmosphere for the second calcination treatment is nitrogen, the temperature of the second calcination treatment is 700-900 DEG C, and the time of the second calcination treatment is 10-15 h.

[0064] In the above embodiments, the gas atmosphere, calcination temperature and calcination time of the second calcination treatment are controlled, which is beneficial to the sufficient reaction between the raw materials, improves the purity of the lithium iron phosphate positive electrode material, and thus improves the product quality and performance of the lithium iron phosphate positive electrode material.

[0065] In a third aspect, the embodiments of the present application provide a positive electrode sheet, which comprises at least one of the lithium iron phosphate positive electrode material and the lithium iron phosphate positive electrode material prepared by the preparation method.

[0066] In the above embodiments, the positive electrode sheet comprises the above positive electrode material, and thus has good electrochemical performance.

[0067] In a fourth aspect, the embodiments of the present application provide a secondary battery, which comprises the positive electrode sheet.

[0068] In the above embodiments, the secondary battery comprises the above positive electrode sheet, and thus has comprehensively improved electrochemical performance, so as to be well applied to multiple use scenarios.

[0069] The above description is only a summary of the technical solutions of the present application. In order to make the technical means of the present application more clearly understood, and to be implemented according to the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0070] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings. Figure 1 The flow chart of the preparation method of the lithium iron phosphate positive electrode material provided in some embodiments;

[0071] Figure 2 The scanning electron microscope images of the positive electrode materials of Comparative Example 1 and Example 1, wherein (a) is the scanning electron microscope image of the positive electrode material of Comparative Example 1, and (b) is the scanning electron microscope image of the lithium iron phosphate positive electrode material of Example 1;

[0072] Figure 3 The X-ray diffraction pattern of the lithium iron phosphate positive electrode material of Example 1 and the comparison result with the lithium iron phosphate standard card;

[0073] Figure 4 The electrochemical performance graphs of the positive electrode materials of Comparative Example 1 and Example 1 at 0.1C and 1C rates, wherein (a) is the electrochemical performance graph of the lithium iron phosphate positive electrode material of Comparative Example 1 at 0.1C and 1C rates; (b) is the electrochemical performance graph of the lithium nickel cobalt manganese oxide coated lithium iron phosphate positive electrode material of Example 1 at 0.1C and 1C rates. DETAILED DESCRIPTION

[0074] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0075] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0076] In the description of the embodiments of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0077] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0078] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0079] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0080] In the description of the embodiments of the present application, "the amount of substance" represents the physical quantity of the number of particles contained in the substance, and the unit is mol (mol).

[0081] In the description of the embodiments of the present application, unless otherwise specified, "ppm" means that the mass of the tested element, molecule or ion accounts for one millionth of the mass of the sample.

[0082] In the description of the embodiments of the present application, the solvents such as the first solvent, the second solvent, etc. are selected from at least one of distilled water, deionized water, pure water, and ultrapure water.

[0083] In the context of the present application, "span" is also called span, and its calculation formula is: Span=(D90-D10)÷D50. The smaller the span, the more concentrated the particle size distribution of the particles; the larger the span, the greater the difference in particle size of the particles, and the more dispersed the distribution.

[0084] The provided lithium iron phosphate positive electrode material includes a body and a coating layer coated on at least part of the surface of the body; wherein the body includes lithium iron phosphate, the lithium iron phosphate is selected from doped lithium iron phosphate, the doping elements of the doped lithium iron phosphate include one or more of titanium, magnesium and aluminum, and the coating layer includes lithium nickel cobalt manganese oxide. The provided lithium iron phosphate positive electrode material has high electronic conductivity and lithium ion diffusion rate.

[0085] In a first aspect, the embodiments of the present application provide a lithium iron phosphate positive electrode material, including a body and a coating layer coated on at least part of the surface of the body; wherein the body includes lithium iron phosphate, the lithium iron phosphate is selected from doped lithium iron phosphate, the doping elements of the doped lithium iron phosphate include one or more of titanium, magnesium and aluminum, and the coating layer includes lithium nickel cobalt manganese oxide.

[0086] In the technical solution of the embodiments of the present application, the lithium nickel cobalt manganese oxide material with high conductivity is coated on the surface of the lithium iron phosphate as a coating layer, the coating layer provides additional electronic conduction channels and ion diffusion channels, improves the electrical conductivity and ion diffusion rate of the lithium iron phosphate positive electrode material, especially under high rate discharge conditions, effectively alleviates the conductivity bottleneck of the lithium iron phosphate, and improves the energy output capacity of the lithium iron phosphate positive electrode material; the coating layer effectively isolates the direct contact between the lithium iron phosphate and the electrolyte, reduces the occurrence of side reactions, and delays the aging of the lithium iron phosphate positive electrode material; the doping elements reduce the collapse of the lattice structure of the lithium iron phosphate during charging and discharging, improve the structural stability of the material of the coating layer and the body, and prolong the cycle life of the lithium iron phosphate positive electrode material; in addition, the doping elements help to refine the lithium iron phosphate crystal grains, increase the specific surface area of the body, increase the embedding rate and de-embedding rate of lithium ions in the lithium iron phosphate positive electrode material, and thus improve the rate performance of the lithium iron phosphate positive electrode material.

[0087] In some embodiments, the chemical formula of the lithium iron phosphate positive electrode material is: z Fe 0.96 PO4-M x @Li a Ni b Co c Mn d O2, wherein M is a doping element selected from one or more of Ti, Mg and Al, 0.003≤x≤0.005, 0.98≤z≤1.03, 0.97≤a≤1.07, 0.5≤b≤0.8, 0.1≤c≤0.2, 0.1≤d≤0.3.

[0088] In some embodiments, the doping element M is Ti.

[0089] It should be noted that in the above and below context, the subscript x of the doping element M in the lithium iron phosphate positive electrode material refers to the mass ratio of the doping element M to the mass of LFP.

[0090] In some embodiments, the chemical formula of the lithium iron phosphate cathode material includes:

[0091] LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.01Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.03Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.05Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.005Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,

[0092] LiFe 0.96 PO4-Ti 0.0035 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,LiFe 0.96 PO4-Ti 0.003 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,LiFe 0.96 PO4-Ti 0.0045 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2,LiFe 0.96 PO4-Ti 0.005 @0.02Li 1.02 Ni 0.6 Co0.2 Mr 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mr 0.2 O2,LiFe 0.96 PO4-Mg 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mr 0.2 O2,LiFe 0.96 PO4-Al 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mr 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mr 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.8 Co 0.1 Mr 0.1 O2,LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.5 Co 0.2 Mr 0.3 O2,LiFe 0.96 PO4-Ti 0.004 @0.02Li 0.97 Ni 0.6 Co 0.2 Mr 0.2 O2,LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.07 Ni 0.6 Co 0.2 Mr 0.2 O2,Li 0.98 Feb 0.96 PO4-Ti 0.004 @0.02Li 1.07 Ni 0.6 Co 0.2 Mr 0.2 O2,

[0093] Li 1.03 Fe 0.96 PO4-Ti 0.004 @0.02Li 1.07 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0094] In the above embodiments, the doped lithium iron phosphate represented by the above formula, while maintaining high charge specific capacity and discharge specific capacity of the lithium iron phosphate positive electrode material, is conducive to improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material, thereby improving the cycle performance and rate performance of the lithium iron phosphate positive electrode material.

[0095] In some embodiments, in the lithium iron phosphate positive electrode material, the coating layer has a layered crystal structure.

[0096] In the above embodiments, the layered structure of the coating layer provides a smooth diffusion channel for lithium ions, significantly improving the diffusion rate of lithium ions in the lithium iron phosphate positive electrode material.

[0097] In some embodiments, in the lithium iron phosphate positive electrode material, the thickness of the coating layer can be 3 nm to 25 nm, and further can be 6 nm to 13 nm, which is conducive to improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material. For example, the thickness of the coating layer can be 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, or can also be selected from a range composed of any two of the above values.

[0098] In some embodiments, in the lithium iron phosphate positive electrode material, the mass fraction of the coating layer in the lithium iron phosphate positive electrode material can be 0.5% to 5%, and further can be 1% to 3%. For example, the mass fraction of the coating layer in the lithium iron phosphate positive electrode material can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or can also be selected from a range composed of any two of the above values.

[0099] In the above embodiments, the coating layer in the above mass fraction range is conducive to improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material.

[0100] In some embodiments, in the lithium iron phosphate cathode material, the mass fraction of the doping element of the doped lithium iron phosphate in the lithium iron phosphate cathode material can be 0.3% to 0.5%, further can be 0.3% to 0.45%. For example, the mass fraction of the doping element of the doped lithium iron phosphate in the lithium iron phosphate cathode material can be 0.3%, 0.4%, 0.5%, or can also be selected from the range composed of any two of the above values.

[0101] In the above embodiments, by doping an appropriate amount of a doping element in the lithium iron phosphate, while maintaining the high charge specific capacity and discharge specific capacity of the lithium iron phosphate cathode material, the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate cathode material are improved, thereby improving the cycle performance and rate performance of the lithium iron phosphate cathode material.

[0102] In some embodiments, in the lithium iron phosphate cathode material, the compaction density of the lithium iron phosphate cathode material can be 2.45 g / cm 3 to 2.57 g / cm 3 , further can be 2.47 g / cm 3 to 2.57 g / cm 3 . For example, the compaction density of the lithium iron phosphate cathode material can be 2.45 g / cm 3 , 2.46 g / cm 3 , 2.47 g / cm 3 , 2.48 g / cm 3 , 2.49 g / cm 3 , 2.50 g / cm 3 , 2.51 g / cm 3 , 2.52 g / cm 3 , 2.53 g / cm 3 , 2.54 g / cm 3 , 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , or can also be selected from the range composed of any two of the above values.

[0103] In the above embodiments, the compaction density of the cathode material in the above range is beneficial to improve the energy density of the lithium iron phosphate cathode material.

[0104] In some embodiments, in the lithium iron phosphate cathode material, the spacing of the lithium iron phosphate cathode material can be 1.1 to 2.8, further can be 1.17 to 2.75. The D 50The particle size can be 1.11 μm, 1.12 μm, 1.13 μm, 1.14 μm, 1.15 μm, 1.16 μm, 1.17 μm, 1.18 μm, 1.19 μm, 1.20 μm, 1.21 μm, 1.22 μm, 1.23 μm, 1.24 μm, 1.25 μm, 1.26 μm, 1.27 μm, 1.28 μm, 1.29 μm, 1.30 μm, 1.31 μm, or can also be selected from a range consisting of any two of the above values. 50 The particle size can be 1.11 μm, 1.12 μm, 1.13 μm, 1.14 μm, 1.15 μm, 1.16 μm, 1.17 μm, 1.18 μm, 1.19 μm, 1.20 μm, 1.21 μm, 1.22 μm, 1.23 μm, 1.24 μm, 1.25 μm, 1.26 μm, 1.27 μm, 1.28 μm, 1.29 μm, 1.30 μm, 1.31 μm, or can also be selected from a range consisting of any two of the above values.

[0105] In the above embodiments, the particle size and D 50 When the particle size is within the above range, the particle size of the lithium iron phosphate positive electrode material is more appropriate and the particle size distribution is more concentrated, so that the electron transport and lithium ion diffusion path is shorter, which helps to improve the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material, and a more uniform particle size is beneficial to improving the compaction density of the lithium iron phosphate positive electrode material.

[0106] In some embodiments, the specific surface area of the lithium iron phosphate positive electrode material is 8.5 m 2 / g to 11.6 m 2 / g, and further can be 8.53 m 2 / g to 11.58 m 2 / g. For example, the specific surface area of the lithium iron phosphate positive electrode material can be 8.53 m 2 / g, 9.0 m 2 / g, 9.5 m 2 / g, 10.0 m 2 / g, 10.5 m 2 / g, 11 m 2 / g, 11.58 m 2 / g, or can also be selected from a range consisting of any two of the above values.

[0107] In the above embodiments, the specific surface area is within the above range, which avoids excessive contact area with the electrolyte while providing more lithium ion diffusion paths, improves the embedding and de-embedding rate of lithium ions, and is beneficial to improving the rate performance of the lithium iron phosphate positive electrode material.

[0108] In some embodiments, in the lithium iron phosphate cathode material, the powder resistivity of the lithium iron phosphate cathode material can be 6 Ω·cm-20 Ω·cm, further can be 6 Ω·cm-18 Ω·cm. For example, the powder resistivity of the lithium iron phosphate cathode material can be 10 Ω·cm, 11 Ω·cm, 12 Ω·cm, 14.17 Ω·cm, 15 Ω·cm, 16 Ω·cm, 17 Ω·cm, 18 Ω·cm, 19 Ω·cm, 20 Ω·cm, or can also be selected from the range composed of any two of the above values.

[0109] In the above embodiments, controlling the powder resistivity of the lithium iron phosphate cathode material in the above range is beneficial to improve the electrical conductivity of the lithium iron phosphate cathode material, and is beneficial to improve the charge-discharge rate of the lithium iron phosphate cathode material, especially under high-rate charge-discharge conditions, while reducing the heat generated inside the lithium iron phosphate cathode material during charge-discharge, reducing the damage to the structure of the lithium iron phosphate cathode material caused thereby, and prolonging the service life of the lithium iron phosphate material.

[0110] In some embodiments, in the lithium iron phosphate cathode material, the lithium ion diffusion rate of the lithium iron phosphate cathode material is 0.9×10 -12 cm 2 ·s -1 -4.8×10 -10 cm 2 ·s -1 , further can be 3.3×10 -12 cm 2 ·s -1 -4.8×10 - 10 cm 2 ·s -1 . For example, the lithium ion diffusion rate of the lithium iron phosphate cathode material can be 0.9×10 -13 cm 2 ·s -1 , 1.9×10 -13 cm 2 ·s -1 , 3.9×10 -13 cm 2 ·s -1 , 5.9×10 -13 cm 2 ·s -1 , 6.9×10 -13 cm 2 ·s -1 , 7×10 -13 cm 2 ·s -1 , 8×10 -13 cm 2 ·s-1 , 9 x 10 -13 cm 2 · s -1 , 1 x 10 -12 cm 2 · s -1 , 2 x 10 -12 cm 2 · s -1 , 3 x 10 -12 cm 2 · s -1 , 4 x 10 -12 cm 2 · s -1 , 5 x 10 -12 cm 2 · s -1 , 6 x 10 -12 cm 2 · s -1 , 7 x 10 -12 cm 2 · s -1 , 8 x 10 -12 cm 2 · s -1 , 9 x 10 -12 cm 2 · s -1 , 1 x 10 -11 cm 2 · s -1 , 2 x 10 -11 cm 2 · s -1 , 3 x 10 -11 cm 2 · s -1 , 4 x 10 -11 cm 2 · s -1 , 5 x 10 -11 cm 2 · s -1 , 6 x 10 -11 cm 2 · s -1 , 7 x 10 -11 cm 2 · s -1 , 8 x 10 -11 cm 2 · s -1 , 9 x 10 -11 cm 2 · s -1 , 1 x 10 -10 cm 2 · s -1 , 2 x 10 -10 cm2 · s -1 2.5 x 10 -10 cm 2 · s -1 3.5 x 10 -10 cm 2 · s -1 4.5 x 10 -10 cm 2 · s -1 4.8 x 10 -10 cm 2 · s -1 or can be selected from a range defined by any two of the above values.

[0111] In the above embodiments, the lithium ion diffusion rate of the lithium iron phosphate positive electrode material is controlled to be within the above range, which is beneficial to improve the energy output capability of the lithium iron phosphate positive electrode material, thereby improving the charge-discharge performance of the lithium iron phosphate positive electrode material under high rate conditions, and thereby improving the rate performance of the lithium iron phosphate positive electrode material.

[0112] In some embodiments, the mass fraction of Li element in the lithium iron phosphate positive electrode material is 4.39% to 4.61%. For example, the mass fraction of Li element can be 4.39%, 4.40%, 4.41%, 4.42%, 4.43%, 4.44%, 4.45%, 4.46%, 4.47%, 4.48%, 4.49%, 4.50%, 4.51%, 4.52%, 4.53%, 4.54%, 4.55%, 4.56%, 4.57%, 4.58%, 4.59%, 4.60%, 4.61%, or can be selected from a range defined by any two of the above values.

[0113] In some embodiments, the mass fraction of Fe element in the lithium iron phosphate positive electrode material is 33.3% to 34.23%. For example, the mass fraction of Fe element can be 33.3%, 33.4%, 33.5%, 33.6%, 33.7%, 33.8%, 33.9%, 33.0%, 33.1%, 34.23%, or can be selected from a range defined by any two of the above values.

[0114] In some embodiments, the mass fraction of P element in the lithium iron phosphate positive electrode material is 19.24% to 19.77%. For example, the mass fraction of P element can be 19.24%, 19.25%, 19.26%, 19.27%, 19.28%, 19.29%, 19.30%, 19.31%, 19.32%, 19.33%, 19.34%, 19.35%, 19.36%, 19.37%, 19.38%, 19.39%, 19.40%, 19.41%, 19.42%, 19.43%, 19.44%, 19.45%, 19.46%, 19.47%, 19.48%, 19.49%, 19.50%, 19.51%, 19.52%, 19.53%, 19.54%, 19.55%, 19.56%, 19.57%, 19.58%, 19.59%, 19.60%, 19.61%, 19.62%, 19.63%, 19.64%, 19.65%, 19.66%, 19.67%, 19.68%, 19.69%, 19.70%, 19.77%, or can also be selected from a range composed of any two of the above values.

[0115] In some embodiments, the mass fraction of Ni element in the lithium iron phosphate positive electrode material is 0.11% to 1.09%. For example, the mass fraction of Ni element can be 0.11%, 0.22%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.09%, or can also be selected from a range composed of any two of the above values.

[0116] In some embodiments, the mass fraction of Co element in the lithium iron phosphate positive electrode material is 0.04% to 0.36%. For example, the mass fraction of Co element can be 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, or can also be selected from a range composed of any two of the above values.

[0117] In some embodiments, the mass fraction of Mn element in the lithium iron phosphate positive electrode material is 0.03% to 0.34%. For example, the mass fraction of Mn element can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, or can also be selected from a range composed of any two of the above values.

[0118] In some embodiments, when the lithium iron phosphate positive electrode material is applied to a secondary battery, the initial charge specific capacity at 0.1C rate at 25°C is 157.5 mAh / g to 161.9 mAh / g, and further can be 158 mAh / g to 161.9 mAh / g.

[0119] In some embodiments, when the lithium iron phosphate positive electrode material is applied to a secondary battery, the initial discharge specific capacity at 0.1C rate at 25°C is 155.3 mAh / g to 159.6 mAh / g, and further can be 155.7 mAh / g to 159.6 mAh / g.

[0120] In some embodiments, when the lithium iron phosphate positive electrode material is applied to a secondary battery, the initial charge specific capacity at 1C rate at 25°C is 157 mAh / g to 160.3 mAh / g, and further can be 157.8 mAh / g to 160.3 mAh / g.

[0121] In some embodiments, when the lithium iron phosphate positive electrode material is applied to a secondary battery, the initial discharge specific capacity at 1C rate at 25°C is 143 mAh / g to 149 mAh / g, and further can be 144 mAh / g to 149 mAh / g.

[0122] In some embodiments, when the lithium iron phosphate positive electrode material is applied to a secondary battery, the initial charge-discharge efficiency (initial coulombic efficiency) at 1C rate at 25°C is 90% to 92.7%.

[0123] In some embodiments, when the lithium iron phosphate positive electrode material is applied to a secondary battery, the capacity retention rate after 500 cycles of charge-discharge at 1C rate at 25°C is 89% to 93.5%, and further can be 90% to 93.5%.

[0124] In a second aspect, the embodiments of the present application provide a preparation method of a lithium iron phosphate positive electrode material, comprising:

[0125] a first mixture is provided, the first mixture comprising a nickel source, a cobalt source, a manganese source, and a first lithium source;

[0126] The first mixture is subjected to a first drying treatment and a first calcination treatment to obtain a coating layer material, the coating layer material comprising lithium nickel cobalt manganese oxide;

[0127] a second mixture is provided, the second mixture comprising the coating layer material, an iron source, a second lithium source, a dopant, and a phosphorus source;

[0128] The second mixture is subjected to a second drying treatment and a second calcination treatment to obtain the lithium iron phosphate positive electrode material;

[0129] The dopant is selected from one or more of a titanium source, a magnesium source, and an aluminum source.

[0130] In the technical solutions of the embodiments of the present application, by controlling the preparation and coating process of the coating layer material, a uniform and stable coating layer is formed, and a lithium nickel cobalt manganese oxide material with high conductivity is coated on the surface of the lithium iron phosphate as the coating layer. The coating layer provides additional electronic conduction channels and ion diffusion channels, improves the electrical conductivity and ion diffusion rate of the lithium iron phosphate positive electrode material, effectively alleviates the conductivity bottleneck of the lithium iron phosphate under high-rate discharge conditions, and improves the energy output capacity of the lithium iron phosphate positive electrode material. The coating layer effectively isolates the direct contact between the lithium iron phosphate and the electrolyte, reduces the occurrence of side reactions, and delays the aging of the lithium iron phosphate positive electrode material. The doping elements reduce the collapse of the crystal structure of the lithium iron phosphate during charging and discharging, improve the structural stability of the coating layer and the bulk material, and prolong the cycle life of the lithium iron phosphate positive electrode material. In addition, the doping elements help to refine the lithium iron phosphate crystal grains, increase the specific surface area of the bulk material, increase the embedding rate and de-embedding rate of lithium ions in the lithium iron phosphate positive electrode material, and thus improve the rate performance of the lithium iron phosphate positive electrode material.

[0131] In some embodiments, referring to the flowchart shown in FIG. 1, a preparation method of a lithium iron phosphate positive electrode material is provided, comprising: Figure 1

[0132] S100: a first mixture is provided, the first mixture comprising a nickel source, a cobalt source, a manganese source, and a first lithium source;

[0133] S200: the first mixture is subjected to a first drying treatment and a first calcination treatment to obtain a coating layer material, the coating layer material comprising lithium nickel cobalt manganese oxide;

[0134] S300: a second mixture is provided, the second mixture comprising the coating layer material, an iron source, a second lithium source, a dopant, and a phosphorus source; the dopant is selected from one or more of a titanium source, a magnesium source, and an aluminum source.​

[0135] S400: The second mixture is subjected to a second drying treatment and a second calcination treatment to obtain the lithium iron phosphate positive electrode material.

[0136] In some embodiments, the application provides a preparation method of the lithium iron phosphate positive electrode material, which is used for preparing the lithium iron phosphate positive electrode material as described above.

[0137] In some embodiments, the nickel source comprises one or more of nickel nitrate and nickel carbonate.

[0138] In some embodiments, the cobalt source comprises one or more of cobalt nitrate and cobalt carbonate.

[0139] In some embodiments, the manganese source comprises one or more of manganese nitrate and manganese carbonate.

[0140] In some embodiments, the first lithium source and the second lithium source are each independently selected from one or more of lithium carbonate, lithium phosphate, and lithium dihydrogen phosphate.

[0141] In some embodiments, the titanium source comprises one or more of titanium white and titanium tetranitrate.

[0142] In some embodiments, the magnesium source comprises one or more of magnesium oxide and magnesium nitrate.

[0143] In some embodiments, the aluminum source comprises one or more of aluminum oxide and aluminum nitrate.

[0144] In some embodiments, the iron source comprises one or more of ferrous oxalate and anhydrous iron phosphate.

[0145] In some embodiments, the phosphorus source comprises one or more of ammonium dihydrogen phosphate, lithium phosphate, and lithium dihydrogen phosphate.

[0146] In the above embodiments, the nickel source, the cobalt source, the manganese source, the first lithium source, the second lithium source, the titanium source, the magnesium source, the aluminum source, the iron source, and the phosphorus source are widely available and low in cost, which is conducive to obtaining the lithium iron phosphate positive electrode material with improved cycle performance and rate performance at a low preparation cost.

[0147] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the step of providing the first mixture comprises:

[0148] mixing the nickel source, the cobalt source, the manganese source, and the first solvent to obtain a first sub-mixture;

[0149] mixing the first sub-mixture and the first lithium source to obtain the first mixture.

[0150] In the above embodiment, the first mixture is obtained by step-by-step mixing, which is beneficial to the sufficient and uniform mixing of the raw materials in the first mixture, thereby improving the purity of the coating layer material obtained after the first drying treatment and the first calcination treatment of the first mixture.

[0151] In some embodiments, the method for preparing the lithium iron phosphate positive electrode material, the step of providing the second mixture comprises:

[0152] The iron source, the second lithium source, the phosphorus source, the dopant, the coating layer material, and the second solvent are mixed to obtain the second mixture.

[0153] In the above embodiment, the second mixture is obtained by mixing the above raw materials, which is beneficial to the further sufficient reaction between the raw materials, thereby improving the purity of the lithium iron phosphate positive electrode material obtained, and improving the product quality of the lithium iron phosphate positive electrode material obtained.

[0154] In some embodiments, the method for preparing the lithium iron phosphate positive electrode material, the step of mixing the nickel source, the cobalt source, the manganese source, and the first solvent to obtain the first sub-mixture comprises: a first grinding treatment of mixing the nickel source, the cobalt source, the manganese source, and the first solvent; wherein the time of the first grinding treatment is 0.5h-1.5h, for example, 0.5h, 1h, 1.5h, or can also be selected from the range composed of any two of the above values.

[0155] In some embodiments, the method for preparing the lithium iron phosphate positive electrode material, the step of mixing the first sub-mixture and the first lithium source to obtain the first mixture comprises: a second grinding treatment of mixing the first sub-mixture and the first lithium source, and the time of the second grinding treatment is 20min-60min, for example, 20min, 30min, 40min, 50min, 60min, or can also be selected from the range composed of any two of the above values.

[0156] In the above embodiment, the raw materials in the first mixture are mixed by step-by-step grinding treatment, which is beneficial to the sufficient and uniform mixing of the raw materials in the first mixture, thereby improving the purity of the coating layer material obtained after the first drying treatment and the first calcination treatment of the first mixture.

[0157] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the step of mixing the iron source, the second lithium source, the phosphorus source, the coating layer material, and the second solvent to obtain the second mixture comprises: thirdly grinding the iron source, the second lithium source, the phosphorus source, the coating layer material, the dopant, and the second solvent; the third grinding time is 20-40 min, for example, the third grinding time can be 20 min, 30 min, 40 min, or can also be selected from the range composed of any two of the above values; or, the third grinding is performed until the D50 particle size of the second mixture is 300-400 nm, for example, the third grinding is performed until the D50 particle size of the second mixture can be 300 nm, 350 nm, 400 nm, or can also be selected from the range composed of any two of the above values.

[0158] In the above embodiments, the second mixture is obtained by grinding the mixed raw materials, which is beneficial to the sufficient mixing of the raw materials and thus the further sufficient reaction, improves the purity of the obtained lithium iron phosphate positive electrode material, and thus improves the product quality of the obtained lithium iron phosphate positive electrode material.

[0159] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the molar ratio of lithium element, nickel element, cobalt element, and manganese element in the first mixture is (20-22):(10-16):(2-4):(2-6). For example, the molar ratio of lithium element, nickel element, cobalt element, and manganese element in the first mixture can be 20:10:2:2, 20:10:4:6, 20:16:2:6, 20:16:4:6, 22:10:2:2, 22:16:2:2, 22:16:2:6, 22:16:4:6, or can also be selected from the range composed of any two of the above values.

[0160] In the above embodiments, the molar ratio of lithium element, nickel element, cobalt element, and manganese element in the first mixture is controlled to be (20-22):(10-16):(2-4):(2-6), which is beneficial to the sufficient reaction between the raw materials and thus improves the purity of the obtained coating layer material, and thus improves the product quality of the finally obtained lithium iron phosphate positive electrode material.

[0161] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the molar ratio of lithium element, iron element, and phosphorus element in the second mixture is (1.12-1.18):1.10:1.14. For example, the molar ratio of lithium element, iron element, and phosphorus element in the second mixture can be 1.12:1.10:1.14, 1.14:1.10:1.14, 1.16:1.10:1.14, 1.18:1.10:1.14, or can also be selected from the range composed of any two of the above values.

[0162] In the above embodiment, the molar ratio of lithium element, iron element and phosphorus element in the second mixture is controlled to be (1.12-1.18):1.10:1.14, which is beneficial to the sufficient reaction between the raw materials, improves the purity of the lithium iron phosphate positive electrode material, and thus improves the performance stability of the lithium iron phosphate positive electrode material.

[0163] In some embodiments, in the method for preparing the lithium iron phosphate positive electrode material, the first drying treatment and the second drying treatment are independently selected from spray drying.

[0164] In the above embodiment, the first drying treatment is spray drying, which is beneficial to the particle size of the solid particles in the first calcination treatment, so as to obtain a coating layer material with a suitable particle size after the first calcination treatment. The second drying treatment is spray drying, which is beneficial to the control of the particle size of the solid particles in the second calcination treatment, and is beneficial to obtaining a lithium iron phosphate positive electrode material with a concentrated particle size distribution and a suitable particle size after the second calcination treatment, improves the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material, and improves the compaction density of the lithium iron phosphate positive electrode material.

[0165] In some embodiments, after the first mixture is subjected to the first drying treatment, a first dried material is obtained.

[0166] The first dried material is subjected to the first calcination treatment to obtain a coating layer material.

[0167] In some embodiments, the first drying treatment is selected from spray drying, the inlet air temperature of the first drying treatment is 230-250°C, and the outlet air temperature of the first drying treatment is 145-155°C, so as to obtain a first dried material with a suitable particle size.

[0168] In some embodiments, the D50 particle size of the first dried material is 23-25μm.

[0169] In some embodiments, the preparation method of the lithium iron phosphate cathode material, the first calcination process comprises a first sub-calcination process and a second sub-calcination process, the temperature of the first sub-calcination process is 700-800°C, and the time of the first sub-calcination process is 5-8h; the temperature of the second sub-calcination process is 900-1000°C, and the time of the second sub-calcination process is 8-15h. For example, the temperature of the first sub-calcination process can be 700°C, 750°C, 800°C, or can also be selected from the range consisting of any two of the above values. For example, the time of the first sub-calcination process can be 5h, 6h, 7h, 8h, or can also be selected from the range consisting of any two of the above values. For example, the temperature of the second sub-calcination process is 900°C, 950°C, 1000°C, or can also be selected from the range consisting of any two of the above values. For example, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or can also be selected from the range consisting of any two of the above values.

[0170] In the above embodiments, the first calcination process is carried out by step calcination, and the temperature and time of the first sub-calcination process and the second sub-calcination process are controlled to be within the above ranges, which is beneficial to the full reaction between the raw materials and improves the purity of the coating layer material, thereby improving the product quality and performance of the lithium iron phosphate cathode material.

[0171] In some embodiments, the preparation method of the lithium iron phosphate cathode material further comprises a crushing process after the second sub-calcination process, thereby obtaining the coating layer material.

[0172] In some embodiments, the preparation method of the lithium iron phosphate cathode material, the gas atmosphere during the first sub-calcination process is air; and the gas flow rate during the first sub-calcination process is 1.7-7.0L / min. For example, the gas flow rate can be 1.7L / min, 2.0L / min, 2.5L / min, 3.0L / min, 3.5L / min, 4.0L / min, 4.5L / min, 5.0L / min, 5.5L / min, 6.0L / min, 6.5L / min, 7.0L / min, or can also be selected from the range consisting of any two of the above values.

[0173] In the above embodiments, the gas atmosphere during the first sub-calcination process is controlled to be air, and the gas flow rate is controlled to be 1.7-7.0L / min, which is beneficial to the full reaction between the raw materials and improves the purity of the coating layer material, thereby improving the product quality and performance of the lithium iron phosphate cathode material.

[0174] In some embodiments, the heating rate of the first sub-calcination process in the preparation method of the lithium iron phosphate positive electrode material is 4-8℃ / min, for example, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, or can also be selected from a range consisting of any two of the above values.

[0175] In some embodiments, the gas atmosphere of the second sub-calcination process in the preparation method of the lithium iron phosphate positive electrode material is oxygen; and the second sub-calcination process is performed at an oxygen flow rate of 1.5-6.7L / min. For example, the oxygen flow rate can be 1.5L / min, 2.0L / min, 2.5L / min, 3.0L / min, 3.5L / min, 4.0L / min, 4.5L / min, 5.0L / min, 5.5L / min, 6.0L / min, 6.5L / min, 6.7L / min, or can also be selected from a range consisting of any two of the above values.

[0176] In some embodiments, the heating rate of the second sub-calcination process in the preparation method of the lithium iron phosphate positive electrode material is 4-8℃ / min, for example, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, or can also be selected from a range consisting of any two of the above values.

[0177] In the above embodiments, controlling the oxygen flow rate during the second sub-calcination process is beneficial to the full reaction between the raw materials, improves the purity of the coating layer material, and thus improves the product quality and performance of the lithium iron phosphate positive electrode material.

[0178] In some embodiments, the second mixture is subjected to a second drying process to obtain a second dried material;

[0179] The second dried material is subjected to a second calcination process to obtain the lithium iron phosphate positive electrode material.

[0180] In some embodiments, the second drying process is selected from spray drying, and the inlet air temperature of the second drying process is 220-255℃, and the outlet air temperature of the first drying process is 100-110℃, so as to obtain a second dried material with a suitable particle size.

[0181] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the gas atmosphere for the second calcination treatment is nitrogen, the temperature for the second calcination treatment is 700-900℃, and the time for the second calcination treatment is 10-15h. For example, the temperature for the second calcination treatment can be 700℃, 800℃, 900℃, or can also be selected from a range consisting of any two of the above values. For example, the time for the second calcination treatment can be 10h, 11h, 12h, 13h, 14h, 15h, or can also be selected from a range consisting of any two of the above values.

[0182] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the heating rate for the second calcination treatment is 4-8℃ / min, for example, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, or can also be selected from a range consisting of any two of the above values.

[0183] In the above embodiments, controlling the gas atmosphere, calcination temperature and calcination time of the second calcination treatment is beneficial to improving the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate positive electrode material.

[0184] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material, the second calcination treatment is followed by a crushing treatment.

[0185] In a third aspect, the embodiments of the present application provide a positive electrode sheet, which comprises at least one of the lithium iron phosphate positive electrode material and the lithium iron phosphate positive electrode material prepared by the preparation method.

[0186] In the above embodiments, the positive electrode sheet contains the above positive electrode material, and thus has good electrochemical performance.

[0187] In a fourth aspect, the embodiments of the present application provide a secondary battery, which comprises the positive electrode sheet.

[0188] In the above embodiments, the secondary battery contains the above positive electrode sheet, and thus has comprehensively improved electrochemical performance, and can be well applied to multiple use scenarios.

[0189] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation on the present application. If a specific technology or condition is not specified in the embodiments, it is performed according to the technology or condition described in the literature in the art or according to the product manual. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained from the market.

[0190] I. Preparation method

[0191] Embodiment 1

[0192] Preparation of lithium nickel cobalt manganese oxide (LNCM): First, nickel nitrate, cobalt nitrate and manganese nitrate were weighed according to the molar ratio of Ni:Co:Mn as 6:2:2, and then ball-milled in pure water for 1 h. Subsequently, lithium carbonate was added according to the molar ratio of Li:(Ni+Co+Mn) as 1.05:1, and the mixing was continued for 36 min to obtain a first mixture with uniform mixing. Then, the mixed uniform suspension was dried by spraying, with an inlet air temperature of 230°C and an outlet air temperature of 150°C, to obtain solid particles with a D50 particle size of 24.2 μm after drying. Then, the dried solid particles were placed in a calcination device, and calcined under an air atmosphere with a flow rate of 1.8 L / min, at a heating rate of 5°C / min, and heated to 750°C and then calcined for 6 h. Then, the second stage of sintering was carried out by passing oxygen at a flow rate of 1.6 L / min, at a heating rate of 5°C / min, and heated to 920°C and then calcined for 10 h. After crushing, LNCM was obtained.

[0193] Preparation of LNCM-coated LFP: First, ferrous oxalate, lithium carbonate and ammonium dihydrogen phosphate were weighed according to the molar ratio of Li:Fe:P as 1.15:1.10:1.14. Then, the LNCM obtained in the previous step was weighed according to the amount of LNCM accounting for 2.0% of the mass fraction of the LFP positive electrode material. Titanium dioxide was added according to the mass ratio of titanium element in LFP as 4000 ppm. Then, the mixture was dispersed in pure water and ground for 30 min, and the slurry D50 particle size was controlled to be 350 nm. Subsequently, the ground slurry was dried by spraying, with an inlet air temperature of 250°C and an outlet air temperature of 105°C. Then, the dried intermediate was calcined under N2 atmosphere at a heating rate of 5°C / min, heated to 800°C and then calcined for 12 h. Finally, after crushing, the LNCM-coated LFP positive electrode material was obtained.

[0194] The chemical formula of the obtained LNCM-coated LFP positive electrode material (i.e., lithium iron phosphate positive electrode material) is LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0195] Example 2

[0196] The difference between this example and Example 1 is that:

[0197] The mass fraction of LNCM as the coating layer in the lithium iron phosphate positive electrode material is 1.0%.

[0198] The chemical formula of the obtained LNCM-coated LFP positive electrode material (i.e., lithium iron phosphate positive electrode material) is LiFe 0.96 PO4-Ti0.004 @0.01 Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0199] Example 3

[0200] The difference between this example and Example 1 is that:

[0201] The mass fraction of LNCM as the coating layer in the lithium iron phosphate positive electrode material is 3.0%.

[0202] The chemical formula of the obtained LNCM-coated LFP positive electrode material is LiFe 0.96 PO4-Ti 0.004 @0.03 Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0203] Example 4

[0204] The difference between this example and Example 1 is that:

[0205] The mass fraction of LNCM as the coating layer in the lithium iron phosphate positive electrode material is 5.0%.

[0206] The chemical formula of the obtained LNCM-coated LFP positive electrode material is LiFe 0.96 PO4-Ti 0.004 @0.05 Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0207] Example 5

[0208] The difference between this example and Example 1 is that:

[0209] The mass fraction of LNCM as the coating layer in the lithium iron phosphate positive electrode material is 0.5%.

[0210] The chemical formula of the obtained LNCM-coated LFP positive electrode material is LiFe 0.96 PO4-Ti 0.004 @0.005 Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0211] Example 6

[0212] The difference between this example and Example 1 is that:

[0213] Titanium white powder is added according to the proportion of 3500 ppm of Ti element in LFP by mass fraction.

[0214] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.0035 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0215] Example 7

[0216] This example is similar to Example 1, except that:

[0217] Titanium white powder is added according to the proportion of 3000 ppm of Ti element in LFP by mass fraction.

[0218] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.003 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0219] Example 8

[0220] This example is similar to Example 1, except that:

[0221] Titanium white powder is added according to the proportion of 4500 ppm of Ti element in LFP by mass fraction.

[0222] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.0045 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0223] Example 9

[0224] This example is similar to Example 1, except that:

[0225] Titanium white powder is added according to the proportion of 5000 ppm of Ti element in LFP by mass fraction.

[0226] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.005 @0.02Li 1.02 Ni0.6 Co 0.2 Mn 0.2 O2.

[0227] Example 10

[0228] The difference between this embodiment and Example 1 is that:

[0229] In the preparation of LNCM-coated LFP, the dried intermediate is calcined under N2atmosphere at a temperature rising rate of 5℃ / min to 750℃ and then calcined for 12h.

[0230] The obtained LNCM-coated LFP positive electrode material has the chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0231] Example 11

[0232] The difference between this embodiment and Example 1 is that:

[0233] In the preparation of LNCM-coated LFP, magnesium oxide is added according to the proportion of 4000ppm of the mass of Mg element in LFP.

[0234] The obtained LNCM-coated LFP positive electrode material has the chemical formula of LiFe 0.96 PO4-Mg 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0235] Example 12

[0236] The difference between this embodiment and Example 1 is that:

[0237] In the preparation of LNCM-coated LFP, aluminum oxide is added according to the proportion of 4000ppm of the mass of Al element in LFP.

[0238] The obtained LNCM-coated LFP positive electrode material has the chemical formula of LiFe 0.96 PO4-Al 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0239] Example 13

[0240] The difference between this embodiment and embodiment 1 is that:

[0241] In the preparation of lithium nickel cobalt manganese oxide, nickel carbonate, cobalt carbonate and manganese carbonate are weighed according to the molar ratio of Ni:Co:Mn as 6:2:2, ball-milled and mixed in pure water for 1 h, lithium dihydrogen phosphate is added according to the molar ratio of Li:(Ni+Co+Mn) as 1.05:1 to obtain a first mixture uniformly mixed;

[0242] In the preparation of LNCM-coated LFP, anhydrous iron phosphate + red iron oxide (weighed according to the molar ratio of Fe as 1:1), lithium carbonate and ammonium dihydrogen phosphate are weighed according to the molar ratio of Li:Fe:P as 1.15:1.10:1.14.

[0243] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0244] Example 14

[0245] The difference between this embodiment and embodiment 1 is that:

[0246] In the preparation of lithium nickel cobalt manganese oxide, nickel nitrate, cobalt nitrate and manganese nitrate are weighed according to the molar ratio of Ni:Co:Mn as 8:1:1, ball-milled and mixed in pure water for 1 h.

[0247] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0248] Example 15

[0249] The difference between this embodiment and embodiment 1 is that:

[0250] In the preparation of lithium nickel cobalt manganese oxide, nickel nitrate, cobalt nitrate and manganese nitrate are weighed according to the molar ratio of Ni:Co:Mn as 5:2:3, ball-milled and mixed in pure water for 1 h.

[0251] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.5 Co 0.2 Mn0.3 O2.

[0252] Example 16

[0253] The difference between this embodiment and Example 1 is that:

[0254] In the preparation of the lithium nickel cobalt manganese oxide, lithium carbonate was added in a molar ratio of Li:(Ni+Co+Mn) of 1.00:1.00, and mixing was continued for 36 min to obtain a first mixture that was uniformly mixed.

[0255] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 0.97 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0256] Example 17

[0257] The difference between this embodiment and Example 1 is that:

[0258] In the preparation of the lithium nickel cobalt manganese oxide, lithium carbonate was added in a molar ratio of Li:(Ni+Co+Mn) of 1.10:1.00, and mixing was continued for 36 min to obtain a first mixture that was uniformly mixed.

[0259] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.07 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0260] Example 18

[0261] The difference between this embodiment and Example 1 is that:

[0262] In the preparation of the LNCM-coated LFP, ferrous oxalate, lithium carbonate, and ammonium dihydrogen phosphate were weighed in a molar ratio of Li:Fe:P of 1.12:1.1:1.14.

[0263] The obtained LNCM-coated LFP positive electrode material has a chemical formula of Li 0.98 Fe 0.96 PO4-Ti 0.004 @0.02Li 1.07 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0264] Example 19

[0265] The difference between this example and Example 1 is that:

[0266] In the preparation of LNCM-coated LFP, ferrous oxalate, lithium carbonate, and ammonium dihydrogen phosphate were weighed according to the molar ratio of Li:Fe:P of 1.18:1.1:1.14.

[0267] The obtained LNCM-coated LFP positive electrode material has the chemical formula of Li 1.03 Fe 0.96 PO4-Ti 0.004 @0.02Li 1.07 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0268] Example 20

[0269] The difference between this example and Example 1 is that:

[0270] In the preparation of lithium nickel cobalt manganese oxide (LNCM), first, nickel nitrate, cobalt nitrate, and manganese nitrate were weighed and ball-milled in pure water for 30 min according to the molar ratio of Ni:Co:Mn of 6:2:2. Then, lithium carbonate was added according to the molar ratio of Li:(Ni+Co+Mn) of 1.05:1, and the mixture was continuously mixed uniformly for 60 min. Next, the mixed uniform suspension was dried by spraying, with an inlet temperature of 240°C and an outlet temperature of 150°C. Then, the first stage of sintering was carried out, and the dried solid particles were placed in a calcination device, with an air flow of 1.7 L / min, a heating rate of 4°C / min, and calcination at 700°C for 8 h. Then, the second stage of sintering was carried out, with oxygen flowing at 1.6 L / min, a heating rate of 5°C / min, and calcination at 920°C for 10 h. After crushing, LNCM was obtained.

[0271] The obtained LNCM-coated LFP positive electrode material has the chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0272] Example 21

[0273] The difference between this example and Example 1 is that:

[0274] In the preparation of lithium nickel cobalt manganese oxide (LNCM), first, nickel nitrate, cobalt nitrate and manganese nitrate are weighed according to the molar ratio of Ni:Co:Mn as 6:2:2, and then ball-milled and mixed in pure water for 90 min. Subsequently, lithium carbonate is added according to the molar ratio of Li:(Ni+Co+Mn) as 1.05:1, and the mixture is continuously mixed uniformly for 20 min. Then, the mixed uniform suspension is dried by spraying, with the inlet air temperature being 250℃ and the outlet air temperature being 150℃. Then, the first stage of sintering is carried out, and the dried solid particles are placed in a calcination device, with the air flow being 7L / min, the heating rate being 8℃ / min, and the calcination being carried out at 800℃ for 5h. Then, the second stage of sintering is carried out, with the oxygen flow being 1.6L / min, the heating rate being 5℃ / min, and the calcination being carried out at 920℃ for 10h. After crushing, LNCM is obtained.

[0275] The LNCM-coated LFP positive electrode material obtained has the chemical formula LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0276] Example 22

[0277] The difference between this example and Example 1 is that:

[0278] In the preparation of lithium nickel cobalt manganese oxide (LNCM), the second stage of sintering is carried out, with the oxygen flow being 1.5L / min, the heating rate being 4℃ / min, and the calcination being carried out at 900℃ for 15h.

[0279] The LNCM-coated LFP positive electrode material obtained has the chemical formula LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0280] Example 23

[0281] The difference between this example and Example 1 is that:

[0282] In the preparation of lithium nickel cobalt manganese oxide (LNCM), the second stage of sintering is carried out, with the oxygen flow being 6.7L / min, the heating rate being 8℃ / min, and the calcination being carried out at 1000℃ for 8h.

[0283] The LNCM-coated LFP positive electrode material obtained has the chemical formula LiFe 0.96 PO4-Ti 0.004 @0.02Li1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0284] Example 24

[0285] The difference between this example and Example 1 is that:

[0286] In the preparation of LNCM-coated LFP, the mixture was dispersed in pure water and ground for 20 min. Subsequently, the ground slurry was dried by spraying, with an inlet temperature of 220°C and an exhaust temperature of 105°C. Next, the dried intermediate was calcined under N2atmosphere at a temperature of 700°C for 15 h, with a temperature increase rate of 4°C / min.

[0287] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0288] Example 25

[0289] The difference between this example and Example 1 is that:

[0290] In the preparation of LNCM-coated LFP, the mixture was dispersed in pure water and ground for 40 min. Subsequently, the ground slurry was dried by spraying, with an inlet temperature of 255°C and an exhaust temperature of 105°C. Next, the dried intermediate was calcined under N2atmosphere at a temperature of 900°C for 10 h, with a temperature increase rate of 8°C / min.

[0291] The obtained LNCM-coated LFP positive electrode material has a chemical formula of LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0292] Comparative Example 1

[0293] Ferrous oxalate, lithium carbonate, ammonium dihydrogen phosphate were weighed according to the amount-of-substance ratio of Li:Fe:P as 1.05:1.10:1.14, and titanium dioxide was added according to the mass ratio of Ti element in LFP as 4000ppm. Then, the mixture was dispersed in pure water for grinding, and the slurry D50 was controlled as 350nm. Subsequently, the ground slurry was dried by spraying, with the inlet air temperature as 230℃ and the exhaust air temperature as 105℃. Then, the dried intermediate was calcined at 800℃ for 12h under N2 atmosphere at a heating rate of 5℃ / min. Finally, the LFP positive electrode material was obtained after crushing.

[0294] The chemical formula of the obtained positive electrode material is LiFe 0.96 PO4-Ti 0.004 .

[0295] Comparative Example 2

[0296] Nickel nitrate, cobalt nitrate and manganese nitrate were weighed according to the amount-of-substance ratio of Ni:Co:Mn as 6:2:2, and then ball-milled in pure water. Subsequently, lithium carbonate was added according to the amount-of-substance ratio of Li:(Ni+Co+Mn) as 1.05:1, and then uniformly mixed. Then, the mixed uniform suspension was dried by spraying, with the inlet air temperature as 240℃ and the exhaust air temperature as 150℃. Then, the dried solid particles were placed into a calcination device, and calcined at 750℃ for 6h under an air atmosphere with a flow rate of 1.8L / min and a heating rate of 5℃ / min. Then, the second stage sintering was carried out by passing oxygen at a flow rate of 1.6L / min, and calcining at 920℃ for 10h with a heating rate of 5℃ / min. After crushing, the LNCM was obtained.

[0297] Subsequently, ferrous oxalate, lithium carbonate, ammonium dihydrogen phosphate were weighed according to the amount-of-substance ratio of LFP as a coating layer with a mass fraction of 2.0% in the positive electrode material, and Li:Fe:P as 1.15:1.10:1.14, and titanium dioxide was added according to the mass ratio of Ti element in LFP as 4000ppm. Then, the mixture was dispersed in pure water for grinding, and the slurry D50 particle size was controlled as 350nm. Subsequently, the ground slurry was dried by spraying, with the inlet air temperature as 230℃ and the exhaust air temperature as 105℃. Then, the dried intermediate was calcined at 800℃ for 12h under N2 atmosphere at a heating rate of 5℃ / min. Finally, the LFP-coated LNCM positive electrode material was obtained after crushing.

[0298] The chemical formula of the obtained LFP-coated LNCM positive electrode material is Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2@0.02LiFe 0.96PO4-Ti 0.004 .

[0299] Comparative Example 3

[0300] First, the preparation method of LNCM is the same as Example 1. Then, LFP is prepared using the method of Comparative Example 1, and the fine grinding average particle size D50 is controlled to be 380 nm. Subsequently, LFP and LNCM are dispersed and sand ground in pure water in a mass ratio of 49:1, and the average particle size is controlled to be 350 nm. Then, the ground slurry is dried by spraying, with an inlet air temperature of 260°C and an exhaust air temperature of 105°C. Finally, after crushing, the LFP-LNCM composite positive electrode material is obtained.

[0301] The chemical formula of the obtained positive electrode material is LiFe 0.96 PO4-Ti 0.004 -0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0302] Comparative Example 4

[0303] The difference between this comparative example and Example 1 is that:

[0304] Preparation of LNCM-coated LFMP: ferrous oxalate, lithium carbonate, ammonium dihydrogen phosphate, and manganese carbonate are weighed according to the molar ratio of Li:Fe:P:Mn as 1.15:0.88:1.14:0.22. Then, the LNCM obtained in the previous step is weighed according to the amount of LNCM with a LNCM mass fraction of 2.0% in the lithium iron phosphate positive electrode material. Titanium white is added according to the mass ratio of Ti element in LFP as 4000ppm. Then, the mixture is dispersed and ground in pure water for 30 min, and the slurry D50 particle size is controlled to be 350 nm. Subsequently, the ground slurry is dried by spraying, with an inlet air temperature of 250°C and an exhaust air temperature of 105°C. Then, the dried intermediate is calcined under N2 atmosphere at a heating rate of 5°C / min to 800°C for 12h. Finally, after crushing, the LNCM-coated LFMP positive electrode material is prepared.

[0305] The chemical formula of the obtained positive electrode material is LiFe 0.768 Mn 0.192 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0306] Comparative Example 5

[0307] The present comparative example differs from Example 1 in that:

[0308] Lithium nickel cobalt oxide (LNC) preparation: nickel nitrate and cobalt nitrate were weighed according to the molar ratio of Ni:Co as 6:2, and ball-milled in pure water for 1 h. Then, lithium carbonate was added according to the molar ratio of Li:(Ni+Co) as 1.05:1, and the mixing was continued for 36 min to obtain a first mixture with uniform mixing. Then, the mixed uniform suspension was dried by spraying, with an inlet air temperature of 230°C and an outlet air temperature of 150°C, to obtain solid particles with a D50 particle size of 24.2 pm after drying. Then, the first-stage sintering was performed, and the dried solid particles were placed in a calcination device, with an air flow of 1.8 L / min, a heating rate of 5°C / min, and calcination at 750°C for 6 h. Then, the second-stage sintering was performed, with an oxygen flow of 1.6 L / min, a heating rate of 5°C / min, and calcination at 920°C for 10 h. After crushing, LNC was obtained.

[0309] LNC-coated LFP preparation: First, ferrous oxalate, lithium carbonate, and ammonium dihydrogen phosphate were weighed according to the molar ratio of Li:Fe:P as 1.15:1.10:1.14. Then, the LNC obtained in the previous step was weighed according to the amount of LNC accounting for 2.0% of the mass fraction of the lithium iron phosphate positive electrode material. Titanium white powder was added according to the mass ratio of Ti element in LFP as 4000 ppm. Then, the mixture was dispersed in pure water and ground for 30 min, with the slurry D50 particle size controlled at 350 nm. Then, the ground slurry was dried by spraying, with an inlet air temperature of 250°C and an outlet air temperature of 105°C. Then, the dried intermediate was calcined at 800°C for 12 h under N2 atmosphere, with a heating rate of 5°C / min. Finally, after crushing, the LNC-coated LFP positive electrode material was obtained.

[0310] The chemical formula of the obtained positive electrode material is LiFe 0.96 PO4-Ti 0.004 @0.02Li 1.02 Ni 0.75 Co 0.25 O2.

[0311] Comparative Example 6

[0312] The present comparative example differs from Example 1 in that: in the preparation of LNCM-coated LFP, no doping elements are added.

[0313] The chemical formula of the obtained positive electrode material is LiFe 0.96 PO4@0.02Li 1.02 Ni 0.6 Co 0.2 Mn0.2 O2.

[0314] The performance of the positive electrode materials in the above examples and comparative examples was tested, wherein the elemental composition was detected by ICP-OES; the powder resistivity was measured by a four-probe method, the measurement pressure was 8 MPa; the compaction density was measured by pressure under 3 tons; the specific surface area was determined by gas adsorption BET method; the D 50 The particle size was tested by a laser particle size analyzer; the coating layer thickness was detected by TEM; the lithium ion diffusion rate was measured by cyclic voltammetry.

[0315] The test results are shown in Tables 1-4 below:

[0316] Table 1

[0317]

[0318]

[0319] Table 2

[0320]

[0321] Table 3

[0322]

[0323]

[0324] Table 4

[0325]

[0326] II. Test methods

[0327] 1. Morphology observation

[0328] The morphology of the lithium iron phosphate positive electrode material of Example 1 and the positive electrode material of Comparative Example 1 was observed by a JSM-7900F scanning electron microscope. The results are shown in Figure 2 .

[0329] Figure 2 Among them, (a) is the scanning electron microscope image of the lithium iron phosphate positive electrode material of Comparative Example 1, and (b) is the scanning electron microscope image of the lithium iron phosphate positive electrode material of Example 1.

[0330] As can be seen from Figure 2 , after the lithium nickel-manganese-cobalt oxide coating treatment, the particle size of the lithium iron phosphate positive electrode material is more uniform, and the large particles are significantly reduced. This change is beneficial to increase the specific surface area of the lithium iron phosphate positive electrode material, shorten the diffusion path of lithium ions, and thus improve the charge and discharge efficiency and rate performance of the battery.

[0331] 2. Grain analysis

[0332] The lithium iron phosphate positive electrode material of Example 1 was subjected to XRD detection by using a PAN analytical X'Pert 3X ray diffractometer, the test parameters were Cu Kα radiation and Ni filter, and the X-ray wavelength was Cu Kα The measurement angle was 5-80°. The results are shown in Figure 3 .

[0333] It can be known from Figure 3 that the lithium iron phosphate positive electrode material still corresponds to the standard card of LFP, which indicates that the coating of a small amount of lithium nickel manganese cobalt oxide does not change the crystal structure of LFP.

[0334] 3. Property test of secondary battery

[0335] The positive electrode material prepared in each example and comparative example was mixed with conductive carbon black and a PVDF binder according to a mass ratio of 90:5:5, coated on a 12 μm thick aluminum foil, and then the electrode sheet was dried in an oven at 110°C for 10 h. The dried electrode sheet was punched into a 15 mm diameter positive electrode round sheet, and was roll-pressed at a pressing density of 2.5 g / cm 3 , and a lithium sheet with a diameter of 16 mm was used as a counter electrode. The electrolyte was 1M LiPF6 dissolved in EC:EMC:DEC with a volume ratio of 1:1:1. The battery was assembled in an LG2400 / 1000TS glove box produced by WIGAS Purification Technology (Suzhou) Co., Ltd., to obtain a button cell, and the rate performance test was performed.

[0336] The battery performance test system (model: CT3002A) of Wuhan Blue Electric Technology Co., Ltd. was used for the test, the test temperature was 25°C, the voltage range was 2V-3.75V, and the test was performed at 0.1C rate and 1C rate, respectively. The test results are shown in Table 5 and Figure 4 . Figure 4 Figures of the electrochemical performance of the positive electrode material of Comparative Example 1 and the lithium iron phosphate positive electrode material of Example 1 at 0.1C and 1C rates, wherein (a) is the figure of the electrochemical performance of the positive electrode material of Comparative Example 1 at 0.1C and 1C rates; and (b) is the figure of the electrochemical performance of the lithium iron phosphate positive electrode material of Example 1 at 0.1C and 1C rates.

[0337] Table 5

[0338]

[0339]

[0340] III. Analysis of test results of each example and comparative example

[0341] As can be seen from the data in Tables 1 to 4, the specific surface area of ​​the lithium iron phosphate cathode materials provided in Examples 1 to 25 of this application reaches 8.53 m². 2 / g~11.58m 2 The lithium iron phosphate cathode materials provided in Examples 1 to 25 of this application have a high specific surface area. The powder resistivity of the lithium iron phosphate cathode materials is 6 Ω·cm to 20 Ω·cm, exhibiting high electronic conductivity. The lithium-ion diffusion rate of the lithium iron phosphate cathode materials provided in Examples 1 to 25 of this application is 0.9 x 10⁻⁶ g. - 12 cm 2 ·s -1 ~4.8x10 -10 cm 2 ·s -1 The lithium-ion diffusion rate is relatively high.

[0342] As can be seen from the data in Table 5, a comparison of the data obtained by the coin cells prepared by the lithium iron phosphate cathode materials provided in Examples 1 to 25 of this application with the data obtained by the coin half-cell prepared by the LFP cathode material without the use of lithium nickel cobalt manganese oxide in Comparative Example 1 shows that this application effectively improves the electrochemical performance of lithium iron phosphate cathode materials, such as charging specific capacity, discharging specific capacity, rate performance, and cycle performance, by coating lithium iron phosphate with lithium nickel cobalt manganese oxide.

[0343] A comparison of the data obtained from the coin cells prepared by the lithium iron phosphate cathode material provided in Examples 1 to 25 of this application and the coin cells prepared by the LFP-coated LNCM cathode material in Comparative Example 2 shows that this application effectively improves the electrochemical performance of the lithium iron phosphate cathode material, such as its charge specific capacity, discharge specific capacity, rate performance, and cycle performance, by coating the surface of lithium iron phosphate with lithium nickel cobalt manganese oxide.

[0344] A comparison of the data obtained from the coin cells prepared by the lithium iron phosphate cathode materials provided in Examples 1 to 25 of this application and the coin half-cells prepared by the cathode material without a coating structure but containing both LNCM and LFP in Comparative Example 3 shows that this application effectively improves the electrochemical performance of the lithium iron phosphate cathode material, such as its charge specific capacity, discharge specific capacity, rate performance, and cycle performance, by coating the surface of lithium iron phosphate with lithium nickel cobalt manganese oxide.

[0345] A comparison of the data obtained from the coin cells prepared by the lithium iron phosphate cathode materials provided in Examples 1 to 25 of this application and the coin cells prepared by the LNCM-coated LFMP cathode material in Comparative Example 4 shows that this application effectively improves the electrochemical performance of lithium iron phosphate cathode materials, such as charging specific capacity, discharging specific capacity, rate performance, and cycle performance, by coating lithium nickel cobalt manganese oxide on the surface of lithium iron phosphate.

[0346] The data obtained by the button cell prepared by the lithium iron phosphate cathode material provided in embodiments 1 to 25 and the button cell prepared by the LNC coated LFP cathode material in comparative example 5 can be compared, and it can be known that the application effectively improves the charge specific capacity, discharge specific capacity, rate performance and cycle performance and other electrochemical properties of the lithium iron phosphate cathode material by coating lithium nickel cobalt manganese oxide on the surface of lithium iron phosphate.

[0347] The data obtained by the button cell prepared by the lithium iron phosphate cathode material provided in embodiments 1 to 25 and the button cell prepared by the LNCM coated LFP cathode material in comparative example 6 can be compared, and it can be known that the application effectively improves the charge specific capacity, discharge specific capacity, rate performance and cycle performance and other electrochemical properties of the lithium iron phosphate cathode material by coating lithium nickel cobalt manganese oxide on the surface of lithium iron phosphate containing doping elements.

[0348] It should be noted that the application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having substantially the same technical idea and playing the same role and effect within the scope of the technical solution of the application are all included in the technical scope of the application. In addition, within the scope of the main idea of the application, various modifications of the embodiments that can be thought of by those skilled in the art, other ways constructed by combining part of the constituent elements in the embodiments are also included in the scope of the application.

Claims

1. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate positive electrode material comprises a body and a coating layer covering at least part of the surface of the body; wherein the body comprises lithium iron phosphate selected from doped lithium iron phosphate, the doping elements of the doped lithium iron phosphate include one or more of titanium, magnesium and aluminum, and the coating layer comprises nickel cobalt manganese acid lithium.

2. The lithium iron phosphate cathode material of claim 1, wherein, One or more of the following characteristics are met: (1) the chemical formula of the lithium iron phosphate positive electrode material is: Li z Fe 0.96 PO4-M x @Li a Ni b Co c Mn d O2, wherein M is a doping element, is selected from one or more of Ti, Mg and Al, 0.003≤x≤0.005, 0.98≤z≤1.03, 0.97≤a≤1.07, 0.5≤b≤0.8, 0.1≤c≤0.2, 0.1≤d≤0.3; (2) The coating layer has a layered crystal structure; (3) The thickness of the coating layer is distributed between 3nm and 25nm; (4) The mass fraction of the coating layer in the lithium iron phosphate positive electrode material is 0.5%-5%; (5) The mass fraction of the doping elements of the doped lithium iron phosphate in the lithium iron phosphate positive electrode material is 0.3%-0.5%.

3. The lithium iron phosphate cathode material of claim 2, wherein, One or more of the following characteristics are met: (1) the compaction density of the lithium iron phosphate positive electrode material is 2.45 g / cm 3 ~ 2.57 g / cm 3 ; (2) the diameter of the lithium iron phosphate positive electrode material is 1.1-2.8, and the D 50 The particle size is 1.1-1.35 μm. (3) the specific surface area of the lithium iron phosphate positive electrode material is 8.5 m 2 / g ~ 11.6 m 2 / g; (4) The powder resistivity of the lithium iron phosphate positive electrode material is 6Ω·cm-20Ω·cm; (5) the lithium ion diffusion rate of the lithium iron phosphate positive electrode material is 0.9 x 10 -12 cm 2 ·s -1 ~ 4.8 x 10 -10 cm 2 ·s -1 .

4. A method for preparing a lithium iron phosphate cathode material, characterized in that, The preparation method comprises: Providing a first mixture comprising a nickel source, a cobalt source, a manganese source and a first lithium source; The first mixture is subjected to a first drying treatment and a first calcination treatment to obtain a coating layer material comprising nickel cobalt manganese acid lithium; Providing a second mixture comprising the coating layer material, an iron source, a second lithium source, a dopant and a phosphorus source; The second mixture is subjected to a second drying treatment and a second calcination treatment to obtain a lithium iron phosphate positive electrode material; The dopant is selected from one or more of a titanium source, a magnesium source and an aluminum source.

5. The method of claim 4, wherein the lithium iron phosphate cathode material is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphoric acid; and heating the mixture to a temperature of 600-700°C for 6-8 hours. One or more of the following characteristics are met: (1) The nickel source contains one or more of nickel nitrate and nickel carbonate; (2) The cobalt source contains one or more of cobalt nitrate and cobalt carbonate; (3) The manganese source contains one or more of manganese nitrate and manganese carbonate; (4) The first lithium source and the second lithium source are each independently selected from one or more of lithium carbonate, lithium phosphate and lithium dihydrogen phosphate; (5) The titanium source contains one or more of titanium white and titanium tetranitrate; (6) The magnesium source contains one or more of magnesium oxide and magnesium nitrate; (7) The aluminum source contains one or more of aluminum oxide and aluminum nitrate; (8) The iron source contains one or more of ferrous oxalate and anhydrous iron phosphate; (9) The phosphorus source contains one or more of ammonium dihydrogen phosphate, lithium phosphate and lithium dihydrogen phosphate.

6. The method of producing a lithium iron phosphate cathode material according to claim 4 or 5, characterized in that, The preparation method of the lithium iron phosphate positive electrode material meets one or more of the following conditions: (1) The step of providing a first mixture comprises: Mixing the nickel source, the cobalt source, the manganese source and a first solvent to obtain a first sub-mixture; Mixing the first sub-mixture and the first lithium source to obtain the first mixture; (2) The step of providing a second mixture comprises: Mixing the iron source, the second lithium source, the phosphorus source, the dopant, the coating layer material and a second solvent to obtain the second mixture.

7. The method of claim 6, wherein the lithium iron phosphate cathode material is prepared by the steps of: One or more of the following characteristics are met: ​ (1) The step of mixing the nickel source, the cobalt source, the manganese source and a first solvent to obtain a first sub-mixture comprises: a first grinding treatment of mixing the nickel source, the cobalt source, the manganese source and a first solvent; wherein the time of the first grinding treatment is 30min-90min; (2) The step of mixing the first sub-mixture and the first lithium source to obtain the first mixture comprises: mixing the first sub-mixture and the first lithium source through a second grinding treatment, and the second grinding treatment is performed for 20-60 minutes; (3) The step of mixing the iron source, the second lithium source, the phosphorus source, the coating layer material and the second solvent to obtain the second mixture comprises: mixing the iron source, the second lithium source, the phosphorus source, the coating layer material, the dopant and the second solvent through a third grinding treatment, and the third grinding treatment is performed for 20-40 minutes; or, the third grinding treatment is performed until the D50 particle size of the second mixture is 350-400 nm; (4) In the first mixture, the molar ratio of lithium, nickel, cobalt and manganese is (20-22):(10-16):(2-4):(2-6); (5) In the second mixture, the molar ratio of lithium, iron and phosphorus is (1.12-1.18):1.10:1.

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8. The method of producing a lithium iron phosphate cathode material according to claim 6 or 7, characterized in that, One or more of the following characteristics are met: (1) The first drying treatment and the second drying treatment are independently selected from spray drying; (2) The first calcination treatment comprises a first sub-calcination treatment and a second sub-calcination treatment, the temperature of the first sub-calcination treatment is 700-800 DEG C, and the first sub-calcination treatment is performed for 5-8 hours; the temperature of the second sub-calcination treatment is 900-1000 DEG C, and the second sub-calcination treatment is performed for 8-15 hours; (3) The gas atmosphere of the second calcination treatment is a nitrogen atmosphere, the temperature of the second calcination treatment is 700-900 DEG C, and the second calcination treatment is performed for 10-15 hours.

9. A positive electrode sheet characterized by comprising: At least one of the lithium iron phosphate positive electrode materials prepared by the preparation method of any one of claims 1-4.

10. A secondary battery characterized by comprising: The positive electrode sheet of claim 9.

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