Secondary battery, preparation method therefor, and electric device

Abstract

The present application provides a method for preparing a lithium-ion secondary battery. The method comprises: the preparation of a positive electrode active material, involving: mixing a first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material to obtain a positive electrode active material, wherein the average primary particle size of the first lithium-containing transition metal phosphate material is 250-4000 nm, the average primary particle size of the second lithium-containing transition metal phosphate material is 120-600 nm, the average primary particle size of the first lithium-containing transition metal phosphate material is greater than that of the second lithium-containing transition metal phosphate material, and the molar ratio of Mn in the first lithium-containing transition metal phosphate material is less than the molar ratio of Mn in the second lithium-containing transition metal phosphate material; the preparation of a positive electrode sheet, involving: coating a positive electrode slurry containing the positive electrode active material at least on one surface of a positive electrode current collector, so as to obtain a positive electrode sheet; and the preparation of a secondary battery, involving: assembling the positive electrode sheet, a negative electrode sheet, and an electrolyte comprising a lithium salt into a secondary battery.

Description

Secondary battery, method for manufacturing the same, and power using device

[0001] Cross-reference to related applications

[0002] This application refers to Chinese Patent Application No. 202411035745.1, filed on July 30, 2024, entitled “Secondary battery, method for manufacturing the same, and power using device”, which is incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, and in particular to a lithium ion secondary battery, a method for manufacturing the same, and a power using device. BACKGROUND

[0004] As a positive active material of lithium ion battery, lithium manganese iron phosphate salt has higher voltage platform, theoretical energy density, theoretical specific capacity and lower cost than lithium iron phosphate salt. However, when using lithium manganese iron phosphate salt as a positive active material, the lithium ion battery has a high manganese dissolution amount, which leads to poor storage performance and other problems.

[0005] Therefore, it is necessary to provide a lithium ion secondary battery which uses a positive active material containing lithium manganese iron phosphate salt while having a low manganese dissolution amount. SUMMARY

[0006] The present application is made in view of the above problem, and aims to provide a lithium ion secondary battery having a low manganese dissolution amount, a method for manufacturing the same, and a power using device.

[0007] The inventors have found that the above object can be achieved by adopting the technical solution of the present application.

[0008] A first aspect of the present application provides a method for manufacturing a lithium ion secondary battery, characterized in that it comprises the following steps:

[0009] Preparation of a positive active material: mixing a first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material to obtain a positive active material,

[0010] The first lithium-containing transition metal phosphate material has a primary average particle size of 250-4000 nm,

[0011] The second lithium-containing transition metal phosphate material has a primary average particle size of 120-600 nm,

[0012] The primary average particle size of the first lithium-containing transition metal phosphate material is greater than that of the second lithium-containing transition metal phosphate material,

[0013] The Mn molar ratio of the first lithium-containing transition metal phosphate material is less than the Mn molar ratio of the second lithium-containing transition metal phosphate material.

[0014] The Mn molar ratio refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

[0015] Preparation of the positive electrode tab: coating the positive electrode slurry containing the positive electrode active material on at least one surface of the positive electrode current collector to obtain a positive electrode tab.

[0016] Preparation of the secondary battery: assembling the positive electrode tab, the negative electrode tab, and the electrolyte containing a lithium salt into a secondary battery.

[0017] The lithium ion secondary battery obtained by the preparation method of the present application has a low manganese elution amount. In addition, the lithium ion secondary battery obtained by the preparation method of the present application also has good high-temperature storage performance, good high-temperature cycle performance, and a high gram capacity.

[0018] In any embodiment, the primary average particle size of the first lithium-containing transition metal phosphate material is 870-4000 nm.

[0019] When the primary average particle size of the first lithium-containing transition metal phosphate material is 870-4000 nm, the lithium ion secondary battery obtained by the preparation method of the present application has a low manganese elution amount, good high-temperature storage performance, good high-temperature cycle performance, and a high positive electrode slurry solid content.

[0020] In any embodiment, the primary average particle size of the second lithium-containing transition metal phosphate material is 210-600 nm.

[0021] When the primary average particle size of the second lithium-containing transition metal phosphate material is 210-600 nm, the lithium ion secondary battery obtained by the preparation method of the present application has a low manganese elution amount, good high-temperature storage performance, good high-temperature cycle performance, and a high positive electrode slurry solid content.

[0022] In any embodiment, the weight percentage of the first lithium-containing transition metal phosphate material based on the total weight of the positive electrode active material is 5%-40%, optionally 10%-35%, and optionally 20%-30%; and the weight percentage of the second lithium-containing transition metal phosphate material is 60%-95%, optionally 65%-90%, and optionally 70%-80%.

[0023] In any embodiment, the Mn molar ratio of the first lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.4, more optionally 0-0.2, and further optionally 0.

[0024] In any embodiment, the first lithium-containing transition metal phosphate material has a Mn molar ratio of 0.02-0.6, optionally 0.02-0.4, more optionally 0.02-0.2, and further optionally 0.02.

[0025] In any embodiment, the first lithium-containing transition metal phosphate material has a Mn molar ratio of 0.2-0.6, optionally 0.2-0.4, and more optionally 0.2.

[0026] In any embodiment, the second lithium-containing transition metal phosphate material has a Mn molar ratio of 0.4-0.9, optionally 0.5-0.9.

[0027] In any embodiment, the step of preparing the positive electrode active material comprises mixing the first lithium-containing transition metal phosphate material, the second lithium-containing transition metal phosphate material, and a third lithium-containing transition metal phosphate material to obtain the positive electrode active material,

[0028] The third lithium-containing transition metal phosphate material has a primary particle size of 50-200 nm.

[0029] The second lithium-containing transition metal phosphate material has a primary particle size greater than that of the third lithium-containing transition metal phosphate material.

[0030] The third lithium-containing transition metal phosphate material has a Mn molar ratio less than that of the second lithium-containing transition metal phosphate material.

[0031] When the positive electrode active material further comprises a third lithium-containing transition metal phosphate material, the third lithium-containing transition metal phosphate material has a primary particle size of 50-200 nm, the second lithium-containing transition metal phosphate material has a primary particle size greater than that of the third lithium-containing transition metal phosphate material, and the third lithium-containing transition metal phosphate material has a Mn molar ratio less than that of the second lithium-containing transition metal phosphate material, the lithium ion secondary battery obtained by the preparation method of the present application has a high volumetric energy density.

[0032] In any embodiment, the third lithium-containing transition metal phosphate material has a primary particle size of 90-200 nm.

[0033] When the third lithium-containing transition metal phosphate material has a primary particle size of 90-200 nm, the lithium ion secondary battery obtained by the preparation method of the present application has a low manganese elution amount, good high-temperature storage performance, good high-temperature cycle performance, and a high positive electrode slurry solid content.

[0034] In any embodiment, the weight percentage of the first lithium-containing transition metal phosphate material is 5-30%, optionally 10-30%, optionally 20-30%, based on the total weight of the positive active material; the weight percentage of the second lithium-containing transition metal phosphate material is 60-90%, optionally 65-80%, optionally 70-80%; and the weight percentage of the third lithium-containing transition metal phosphate material is 1-10%, optionally 2-8%, optionally 3-7%.

[0035] In any embodiment, the third lithium-containing transition metal phosphate material has a Mn molar fraction of 0-0.6, optionally 0-0.5, more optionally 0.

[0036] In any embodiment, the third lithium-containing transition metal phosphate material has a Mn molar fraction of 0.02-0.6, optionally 0.02-0.5, more optionally 0.02.

[0037] In any embodiment, the third lithium-containing transition metal phosphate material has a Mn molar fraction of 0.2-0.6, optionally 0.2-0.5, more optionally 0.2.

[0038] In any embodiment, the first lithium-containing transition metal phosphate material has a molecular formula of Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1 wherein Q1 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m1≤1.15, x1>0, r1≥0, 0.9≤x1+r1≤1, 0.95≤y1≤1, 3.5≤j1≤4, 0≤q1≤0.1, and / or

[0039] The second lithium-containing transition metal phosphate material has a molecular formula of Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2 wherein Q2 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m2≤1.15, x2>0, r2>0, 0.9≤x2+r2≤1, 0.95≤y2≤1, 3.5≤j2≤4, 0≤q2≤0.1, and / or

[0040] The third lithium-containing transition metal phosphate material has a molecular formula Li m3 Fe x3 Mn r3 P y3 O j3 Q3 q3 , wherein Q3 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m3≤1.15, x3>0, r3≥0, 0.9≤x3+r3≤1, 0.95≤y3≤1, 3.5≤j3≤4, 0≤q3≤0.1.

[0041] In any embodiment, in the first lithium-containing transition metal phosphate material, Q1 comprises at least one of Ti, V, Mg, Nb, and the content of Ti, V, Mg and / or Nb is 1000-10000 ppm, calculated with reference to the total weight of the first lithium-containing transition metal phosphate material.

[0042] In any embodiment, the specific surface area of the first lithium-containing transition metal phosphate material is 3m 2 / g-13m 2 / g.

[0043] In any embodiment, the carbon content of the first lithium-containing transition metal phosphate material is Cx wt.%, calculated with reference to the total weight of the first lithium-containing transition metal phosphate material, wherein 0.8≤Cx≤2.0.

[0044] In any embodiment, the first lithium-containing transition metal phosphate material satisfies (a) the Dv10 of the first lithium-containing transition metal phosphate material is 0.2μm-2μm;

[0045] (b) the Dv50 of the first lithium-containing transition metal phosphate material is 0.5-5μm;

[0046] (c) the Dv90 of the first lithium-containing transition metal phosphate material is 1.5μm-10μm;

[0047] (d) the Dv99 of the first lithium-containing transition metal phosphate material is 2μm-12μm;

[0048] (e) the powder compaction density of the first lithium-containing transition metal phosphate material under a pressure of 3 tons is 2.25g / cm 3 -2.60g / cm 3 ;

[0049] (f) the powder resistivity of the first lithium-containing transition metal phosphate material is 0Ω·cm to 59Ω·cm.

[0050] In any embodiment, the first lithium-containing transition metal phosphate material is prepared by a method comprising:

[0051] providing raw materials containing at least a lithium source, an iron source, a phosphorus source, a carbon film former, a carbon source, and a modifier, and performing at least two sintering processes, wherein,

[0052] the first sintering process is performed at a temperature of 500°C to 760°C;

[0053] the second sintering process is performed at a temperature of 700°C to 800°C.

[0054] In any embodiment, the first lithium-containing transition metal phosphate material is prepared by a method comprising:

[0055] providing raw materials containing at least a lithium source, an iron source, a phosphorus source, a carbon source, a carbon film former, and a modifier, and performing at least two sintering processes, wherein,

[0056] the carbon content of the material after the first sintering process is 0.01 wt% to 0.79 wt%;

[0057] the carbon content of the material after the second sintering process is 0.8 wt% to 2.0 wt%.

[0058] In any embodiment, the method of preparing the first lithium-containing transition metal phosphate material comprises the following steps:

[0059] performing a first pulverization after the first sintering process and a second pulverization after the second sintering process, wherein,

[0060] the Dv50 of the product after the first pulverization is 300 nm to 1200 nm;

[0061] the Dv50 of the product after the second pulverization is 500 nm to 5000 nm.

[0062] A second aspect of the present application provides a lithium ion secondary battery obtainable by the method of preparing a lithium ion secondary battery according to the first aspect of the present application.

[0063] A third aspect of the present application provides an electrical device comprising the lithium ion secondary battery according to the second aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0064] FIG. 1 is a schematic view of a secondary battery according to an embodiment of the present application.

[0065] FIG. 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 1.

[0066] FIG. 3 is a schematic view of a battery module according to an embodiment of the present application.

[0067] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0068] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0069] Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0070] Figure 7 is a schematic diagram of the statistical distinction rules for primary particles in the transmission electron microscope image of particles in this application.

[0071] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0072] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium-ion secondary battery obtained by the preparation method of this application, the manufacturing method therein, and the electrical device thereof. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0073] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0074] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0075] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0076] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0077] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0078] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0079] As a positive electrode active material for lithium-ion batteries, lithium manganese iron phosphate (LFP) offers a higher voltage plateau, theoretical energy density, theoretical specific capacity, and lower cost compared to lithium iron phosphate (LFP). However, using LFP as the positive electrode active material results in higher manganese leaching in lithium-ion batteries, leading to poor storage performance. Therefore, there is a need for a lithium-ion secondary battery that uses a positive electrode active material containing LFP while exhibiting lower manganese leaching.

[0080] Based on this, this application proposes a technical solution to solve the above-mentioned technical problems.

[0081] The first aspect of this application provides a method for preparing a lithium-ion secondary battery, characterized by comprising the following steps:

[0082] Preparation of positive electrode active material: A first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material are mixed to obtain the positive electrode active material.

[0083] The primary average particle size of the first lithium-containing transition metal phosphate material is 250-4000 nm.

[0084] The primary average particle size of the second lithium-containing transition metal phosphate material is 120-600 nm.

[0085] The primary average particle size of the first lithium-containing transition metal phosphate material is larger than that of the second lithium-containing transition metal phosphate material.

[0086] The molar percentage of Mn in the first lithium-containing transition metal phosphate material is less than that in the second lithium-containing transition metal phosphate material.

[0087] Wherein, the molar percentage of Mn refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe;

[0088] Preparation of positive electrode sheet: A positive electrode slurry containing the positive electrode active material is coated on at least one surface of the positive electrode current collector to obtain a positive electrode sheet;

[0089] Preparation of secondary battery: The positive electrode, negative electrode and electrolyte including lithium salt are assembled into a secondary battery.

[0090] Lithium manganese iron phosphate (MFP) salts exhibit poor ionic and electronic conductivity, which is significantly affected by particle size. When the material contains MFP salt particles with larger diameters, the solid-phase transport of lithium ions is greatly restricted, and the electron transport path during the electrochemical reaction is long, resulting in a significant reduction in the specific capacity and kinetic properties of the material. Studies have found that the surface of MFP salt materials exhibits strong surface oxidizability in the charged state, and due to the Jan Taylor effect, surface oxygen atoms readily react with protons in the electrolyte, leading to manganese dissolution and electrolyte loss. To address this issue, this application combines a second lithium-containing transition metal phosphate material with a higher Mn molar ratio with a first lithium-containing transition metal phosphate material with a lower Mn molar ratio. Simultaneously, particle size and gradation are optimized for both materials, enabling close packing. Furthermore, since the large particle component is the lithium-containing transition metal phosphate material with a lower Mn molar ratio, its kinetic performance is superior compared to the large particle lithium-containing transition metal phosphate material with a higher Mn molar ratio. Moreover, if the first lithium-containing transition metal phosphate material cracks during cycling, the lower manganese content within the particles mitigates the problems of electrolyte oxidation due to material oxidation and manganese dissolution leading to damage to the negative electrode SEI film. Furthermore, by setting the primary average particle size of the first lithium-containing transition metal phosphate material to 250-4000 nm, the particles can maintain a suitable micron-level size, thus avoiding interfacial side reactions and processing difficulties caused by nano-sizing of particles, and preventing the reduction in kinetic performance due to excessively large particle size. It also facilitates the stirring of the slurry containing the first lithium-containing transition metal phosphate material and increases the solid content, thereby improving cell processing and increasing the volumetric energy density of the battery. Additionally, it avoids the impact of excessively high carbon coating density on the normal insertion and extraction of lithium ions, thus affecting the cell capacity. The combined effect of these factors results in a lithium-ion secondary battery obtained by the preparation method of this application exhibiting low manganese dissolution, good high-temperature storage performance, good high-temperature cycling performance, and high specific capacity.

[0091] In this paper, the term "primary particle size" refers to the particle size of a primary particle.

[0092] Primary particles refer to individual particles that can be distinguished after being identified by general-purpose software (e.g., SpectrumSee; Avizo 3D) in transmission electron microscopy (TEM) images, and / or individual particles that can be distinguished after manual identification or manual-assisted calibration. Specifically, in this paper, to identify primary particles, the particles contained in the positive electrode film were enriched and / or dispersed, and then imaged under a TEM. The resulting images can be directly identified using software (based on parameters such as grayscale and / or contrast / brightness), and the individual particles that are distinguished after identification are primary particles. Alternatively, the images can be directly identified manually, and the individual particles that are distinguished after identification are primary particles. Another method is to directly identify the images using a combination of software and manual calibration, and the individual particles that are identified and confirmed to be distinguishable are primary particles. More specifically, particles that form independent, clearly distinguishable boundaries in the TEM field of view can be directly identified as individual particles through software or manual identification. However, some particles, although dispersed, exhibit a certain degree of adhesion and stacking in the TEM field of view. For particles that are stuck together or stacked, those identified as individual particles by software (based on parameters such as grayscale / contrast / brightness) are counted as first-order particles. For more precise analysis, for particles that are stuck together or stacked to some extent under a transmission electron microscope (TEM) field of view, after being identified as individual particles by software based on parameters such as grayscale / contrast / brightness, potentially misidentified particles are manually calibrated according to certain rules. The calibrated, distinguishable individual particles are then counted as first-order particles. If there are inconsistencies in the manual calibration results, 3, 5, or 7 people, unaware of each other's knowledge of the same imaging result, can individually calibrate according to the rules illustrated below. The results are then statistically calculated, and the result obtained in this way is counted as the number of first-order particles. Figure 7 is a schematic diagram of the statistical distinction rules for primary particles in a transmission electron microscope (TEM) image. Figure 7-a is the original TEM image, Figure 7-b is the software-recognized image, and Figure 7-c is an example of software and / or manual identification of independent particles, adhered particles, and stacked particles in Figure 7-a. Particles 1 and 2 are distinguishable independent particles, designated as primary particles 1 and 2, respectively. Particles 3 and 4 in Figure 7-c are adhered; particles 5, 6, and 7 are also adhered, and after software or manual identification, they are determined to be primary particles 3, 4, 5, 6, and 7, respectively. Particles 8 and 9, which are stacked together, are ultimately identified as primary particles 8 and 9, rather than being classified as a single particle. Figure 7-d is another example of software and / or manual identification of the stacked particles in Figure 7-a, where the stacked particles 10-14 are ultimately identified as primary particles 10, 11, 12, 13 and primary particle 14, rather than identifying the entire stack of particles as a single particle.When selecting the field of view for transmission electron microscopy, the field of view in which the number of stacked particles accounts for less than 20% of the total number of particles (individual particles, adherent particles, and the total number of stacked particles) can be selected for statistical analysis. Alternatively, the field of view in which the number of stacked particles accounts for less than 15% of the total number of particles (individual particles, adherent particles, and the total number of stacked particles) can be selected for statistical analysis. Furthermore, the field of view in which the number of stacked particles accounts for less than 10% of the total number of particles (individual particles, adherent particles, and the total number of stacked particles) can be selected for statistical analysis.

[0093] The method for testing the primary average particle size of the first and second lithium-containing transition metal phosphate materials can be carried out using methods and equipment known in the art, as exemplified below: 0.05 g of the test material is dissolved in 40 ml of anhydrous ethanol, and then an appropriate amount of dispersant is added and stirred evenly to obtain a suspension. 2 ml of the suspension and 2 ml of anhydrous ethanol are mixed and ultrasonically treated with an ultrasonic power of 480 W for 5 min to obtain a uniformly dispersed suspension. An appropriate amount of the intermediate suspension is then subjected to transmission electron microscopy (TEM). Referring to the aforementioned definition of primary particles, the projection area of ​​each primary particle in the TEM image is calculated, which is the cross-sectional area S of the primary particle. The equivalent circle diameter of the primary particle is obtained using the equivalent circle method, which is the primary particle diameter d. In the above statistical process of primary particles and their primary particle diameters, primary particles with a primary particle diameter less than 50 nm are not included in the statistical range (i.e., primary particles with a primary particle diameter greater than or equal to 50 nm are considered valid particles). The cross-sectional area S and primary particle size d of at least 500 effective particles are tested. The average primary particle size of the material under test is equal to the sum of the primary particle sizes of all primary particles and the total number of primary particles.

[0094] In some embodiments, the primary average particle size of the first lithium-containing transition metal phosphate material can be 250 nm, 300 nm, 350 nm, 400 nm, 440 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 730 nm, 750 nm, 780 nm, 800 nm, 830 nm, 850 nm, 870 nm, 900 nm, 950 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 2000 nm, 2100 nm, 2200 nm, 2300 nm, 2400 nm, 2500 nm, 2600 nm, 2700 nm, 2800 nm, 2900 nm, 3000 nm, 3500 nm, 4000 nm, or a range of any two of the above primary average particle sizes or a value within that range.

[0095] In some embodiments, the primary average particle size of the first lithium-containing transition metal phosphate material is 870-4000 nm.

[0096] When the primary average particle size of the first lithium-containing transition metal phosphate material is 870-4000 nm, by further optimizing the particle size of the lithium-containing transition metal phosphate material with a low Mn molar ratio combined with the lithium manganese iron phosphate material, the primary particle size is increased and / or the content of smaller particles is controlled, so that the lithium-ion secondary battery obtained by the preparation method of this application has a lower manganese dissolution, better high-temperature storage performance, better high-temperature cycling performance, and higher solid content of the positive electrode slurry.

[0097] In some embodiments, the primary average particle size of the second lithium-containing transition metal phosphate material is 210-600 nm.

[0098] When the primary average particle size of the second lithium-containing transition metal phosphate material is 210-600 nm, by further optimizing the particle size of the lithium manganese iron phosphate material itself, the primary particle size can be increased and / or the content of smaller particles can be controlled, so that the lithium-ion secondary battery obtained by the preparation method of this application has a lower manganese dissolution, better high-temperature storage performance, better high-temperature cycling performance, and higher positive electrode slurry solid content.

[0099] The test method for the molar content of Mn in the first lithium-containing transition metal phosphate material and the second lithium-containing transition metal phosphate material can be carried out using methods and equipment known in the art. For example, the molar content of Mn and Fe elements can be tested by referring to the chemical analysis method for nano-lithium iron phosphate in national standard GB T33822-2017, and the molar content of Mn can be calculated.

[0100] In this application, the term "Mn molar percentage" refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

[0101] In some embodiments, the molar percentage of Mn in the first lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.4, more preferably 0-0.2, and even more preferably 0.

[0102] In some embodiments, the molar ratio of Mn in the first lithium-containing transition metal phosphate material can be selected as 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range of any two of the above values, or any value within that range.

[0103] By controlling the molar ratio of Mn in the first lithium-containing transition metal phosphate material within a suitable range, the side reactions between small-particle materials and the electrolyte and the degree of manganese dissolution can be further reduced, thereby further improving the cycle performance of the battery.

[0104] In some embodiments, the molar ratio of Mn in the first lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.4, more preferably 0.02-0.2, and even more preferably 0.02.

[0105] In some embodiments, the molar percentage of Mn in the first lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.4, and more preferably 0.2.

[0106] By controlling the average molar ratio of Mn in small-particle-size materials within a suitable range, the cycle stability of small-particle-size materials can be improved, while also enabling them to have high specific capacity. This not only results in excellent cycle performance of the battery but also further increases its energy density.

[0107] In some embodiments, the molar percentage of Mn in the second lithium-containing transition metal phosphate material is 0.4-0.9, and optionally 0.5-0.9.

[0108] In some embodiments, the molar ratio of Mn in the second lithium-containing transition metal phosphate material can be selected as 0.4, 0.45, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or any range of any two of the above values ​​or any value within that range.

[0109] By controlling the average Mn molar ratio of the second lithium-containing transition metal phosphate material within a suitable range, the second lithium-containing transition metal phosphate material can have a high plateau capacity, while also ensuring that the second lithium-containing transition metal phosphate material has a certain conductivity. This is conducive to the second lithium-containing transition metal phosphate material exerting its specific capacity, so as to achieve the goal of the second lithium-containing transition metal phosphate material contributing sufficient capacity, thereby improving the energy density of the battery.

[0110] In some embodiments, based on the total weight of the positive electrode active material, the weight percentage of the first lithium transition metal phosphate material is 5%-40%, optionally 10%-35%, optionally 20%-30%; and the weight percentage of the second lithium transition metal phosphate material is 60%-95%, optionally 65%-90%, optionally 70%-80%.

[0111] In some embodiments, the weight percentage of the first lithium transition metal phosphate material is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any range of any two of the above values, or any value within that range, based on the total weight of the positive electrode active material.

[0112] In some embodiments, the weight percentage of the second lithium-containing transition metal phosphate material is 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any range of any two of the above values, or any value within that range, based on the total weight of the positive electrode active material.

[0113] By controlling the mass ratio of materials with different particle sizes within a suitable range, the contribution of the flat voltage capacity and specific capacity of the high-manganese-content second lithium-containing transition metal phosphate material to the energy density can be achieved. At the same time, the impact of the large-particle-size first lithium-containing transition metal phosphate material on the rate performance of the battery can be reduced, so that the battery can achieve both high energy density and good rate performance.

[0114] In some embodiments, the step of preparing the positive electrode active material includes: mixing the first lithium-containing transition metal phosphate material, the second lithium-containing transition metal phosphate material, and the third lithium-containing transition metal phosphate material to obtain the positive electrode active material.

[0115] The primary average particle size of the third lithium-containing transition metal phosphate material is 50-200 nm.

[0116] The primary average particle size of the second lithium-containing transition metal phosphate material is larger than that of the third lithium-containing transition metal phosphate material.

[0117] The molar percentage of Mn in the third lithium-containing transition metal phosphate material is less than that in the second lithium-containing transition metal phosphate material.

[0118] When the positive electrode active material also includes a third lithium-containing transition metal phosphate material that meets the above conditions, the space utilization rate can be further improved by further incorporating lithium-containing transition metal phosphate material micropowder (ultrafine particles) with a low Mn molar ratio. The ultrafine particles can be adjusted into the gaps between the first lithium-containing transition metal phosphate material (ultra-large particles) and the second lithium-containing transition metal phosphate material (medium particles), further increasing the volumetric energy density, i.e., further increasing the compaction density of the electrode. Compared with ultrafine second lithium-containing transition metal phosphate material, the ultrafine third lithium-containing transition metal phosphate material experiences some voltage plateau loss, but its specific capacity and surface stability are greatly improved. In particular, the surface stability is significantly improved; ultrafine second lithium-containing transition metal phosphate material is difficult to form a good coating, exhibits strong oxidizing properties on the surface during charging, and due to the Jan Taylor effect, the high specific surface energy of small particles exacerbates manganese dissolution, worsening the battery cycle life. The lithium-ion secondary battery obtained by the preparation method of this application exhibits good cycle life and specific capacity by controlling the particle size of the second lithium-containing transition metal phosphate material to be relatively moderate, containing fewer ultrafine powders and ultralarge particles. Furthermore, the secondary battery of this application ensures good compaction density by grading ultralarge, medium, and ultrafine particles in the positive electrode active material. For the positive electrode active material, according to the idealized close-packing model, to achieve good compaction density, the material must contain some large particles and ultrafine powders to form a close packing, thereby achieving both good high-temperature cycle performance and high positive electrode compaction density.

[0119] The test methods for the primary average particle size and Mn molar ratio of the third lithium-containing transition metal phosphate material are the same as those for the first lithium-containing transition metal phosphate material described above.

[0120] In some embodiments, the primary average particle size of the third lithium-containing transition metal phosphate material is 90-200 nm.

[0121] When the primary average particle size of the third lithium-containing transition metal phosphate material is 90-200 nm, by further optimizing the particle size of the ultrafine particles, increasing the primary particle size and / or controlling the content of smaller particles, the lithium-ion secondary battery obtained by the preparation method of this application has lower manganese dissolution, better high-temperature storage performance, better high-temperature cycling performance, and higher solid content of the positive electrode slurry.

[0122] In some embodiments, the primary average particle size of the third lithium-containing transition metal phosphate material may be selected as 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or any range of any two of the above values ​​or any value within that range.

[0123] In some embodiments, the molar percentage of Mn in the third lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.5, and more preferably 0.

[0124] In some embodiments, the molar ratio of Mn in the third lithium-containing transition metal phosphate material can be selected as 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or a range consisting of any two of the above values ​​or any value within that range.

[0125] Controlling the molar ratio of Mn in the third lithium-containing transition metal phosphate material within a suitable range can improve the conductivity of the third lithium-containing transition metal phosphate material, enhance the overall conductivity of the material, and improve the rate performance of the battery.

[0126] In some embodiments, the molar percentage of Mn in the third lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.5, and more preferably 0.02.

[0127] In some embodiments, the molar percentage of Mn in the third lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.5, and more preferably 0.2.

[0128] By controlling the molar ratio of Mn in the third lithium-containing transition metal phosphate material within a suitable range, the conductivity of the third lithium-containing transition metal phosphate material is improved, and the third lithium-containing transition metal phosphate material also has a certain plateau capacity, thereby further improving the energy density of the battery.

[0129] In some embodiments, based on the total weight of the positive electrode active material, the weight percentage of the first lithium transition metal phosphate material is 5%-30%, optionally 10%-30%, optionally 20%-30%; the weight percentage of the second lithium transition metal phosphate material is 60%-90%, optionally 65%-80%, optionally 70%-80%; and the weight percentage of the third lithium transition metal phosphate material is 1%-10%, optionally 2%-8%, optionally 3%-7%.

[0130] In some embodiments, based on the total weight of the lithium transition metal phosphate material, the weight percentage of the first lithium transition metal phosphate material can be selected as 5%, 10%, 15%, 20%, 25%, 30%, or any range of any two of the above values ​​or any value within that range.

[0131] In some embodiments, based on the total weight of the lithium transition metal phosphate material, the weight percentage of the second lithium transition metal phosphate material can be selected as 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any range of any two of the above values ​​or any value within that range.

[0132] In some embodiments, based on the total weight of the lithium transition metal phosphate material, the weight percentage of the third lithium transition metal phosphate material can be selected as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of the above values ​​or any value within that range.

[0133] By controlling the mass ratio of materials with different particle sizes within a suitable range, the contribution of the voltage rating and specific capacity of the high-manganese-content second lithium-containing transition metal phosphate material to the energy density can be achieved. At the same time, the influence of the large-particle-size first lithium-containing transition metal phosphate material on the rate performance of the battery and the influence of the small-particle-size third lithium-containing transition metal phosphate material on the cycle performance of the battery can be reduced. The battery can achieve a balance of high energy density, good cycle performance and rate performance.

[0134] In some embodiments, the first lithium-containing transition metal phosphate material has the molecular formula Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1Q1 includes at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, and has the following properties: 0.95 ≤ m1 ≤ 1.15, x1 > 0, r1 ≥ 0, 0.9 ≤ x1 + r1 ≤ 1, 0.95 ≤ y1 ≤ 1, 3.5 ≤ j1 ≤ 4, 0 ≤ q1 ≤ 0.1, and / or

[0135] The second lithium-containing transition metal phosphate material has the molecular formula Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2 Q2 includes at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.95 ≤ m2 ≤ 1.15, x2 > 0, r2 > 0, 0.9 ≤ x2 + r2 ≤ 1, 0.95 ≤ y2 ≤ 1, 3.5 ≤ j2 ≤ 4, 0 ≤ q2 ≤ 0.1, and / or

[0136] The third lithium-containing transition metal phosphate material has the molecular formula Li m3 Fe x3 Mn r3 P y3 O j3 Q3 q3 Q3 includes at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.95≤m3≤1.15, x3>0, r3≥0, 0.9≤x3+r3≤1, 0.95≤y3≤1, 3.5≤j3≤4, and 0≤q3≤0.1.

[0137] In some embodiments, the first lithium-containing transition metal phosphate material has the molecular formula Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1Where m1 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, or 1.15; x1 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0; and r1 can be 0, 0.05, 0.1, 0.15, 0.2, or 0.25. 0.3, 0.35, 0.4, 0.45, y1 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, j1 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, q1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0138] In some embodiments, the second lithium-containing transition metal phosphate material has the molecular formula Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2 Where m2 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, x2 can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and r2 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0; y2 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00; j2 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4; q2 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0139] In some embodiments, the third lithium-containing transition metal phosphate material has the molecular formula Li m3 Fe x3 Mn r3 P y3 O j3 Q3 q3Where m3 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, or 1.15; x3 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0; and r3 can be 0, 0.05, 0.1, 0.15, 0.2, or 0.25. 0.3, 0.35, 0.4, 0.45, y3 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, j3 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, q3 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0140] Modifying the first lithium-containing transition metal phosphate material with Q1 element helps improve the ion transport capability of the cathode active material. This element can create vacancies or alter interatomic bond lengths in the particle lattice, facilitating the movement of lithium ions within the lattice and effectively improving the conductivity of the particles themselves, thereby enhancing the kinetic performance of the cathode active material. In this application, the modification can specifically manifest as doping and / or coating.

[0141] In some embodiments, Q1 in the first lithium-containing transition metal phosphate material includes at least one of Ti, V, Mg, and Nb, and the content of Ti, V, Mg and / or Nb is 1000-10000 ppm based on the total weight of the first lithium-containing transition metal phosphate material.

[0142] In some embodiments, the content of Q1 in the first lithium-containing transition metal phosphate material is calculated based on the total weight of the first lithium-containing transition metal phosphate material as 1000ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, 5500ppm, 6000ppm, 6500ppm, 7000ppm, 7500ppm, 8000ppm, 8500ppm, 9000ppm, 9500ppm, 10000ppm, or a range consisting of any two of the above-mentioned contents of Q1 or a value within that range.

[0143] The content of Q1 in the first lithium-containing transition metal phosphate material, for example, the content of Ti, can be measured using methods and equipment known in the art. For example, it can be tested according to GB / T33822-2017.

[0144] Existing lithium transition metal phosphate materials generally have low or no modifying element content. Increasing the Q1 element content in lithium transition metal phosphate materials helps to further improve the bulk ion transport capacity and kinetic performance. However, with further increases in the Q1 element content, the bulk ion transport capacity may not continue to increase, and it may even occupy lithium ion positions, affecting the specific capacity. The range of Q1 elements specified in this application helps to obtain better kinetic performance and specific capacity.

[0145] In some embodiments, Q1 in the first lithium-containing transition metal phosphate material includes Ti, and the content of Ti is 1000-10000 ppm based on the total weight of the first lithium-containing transition metal phosphate material.

[0146] In some embodiments, Q1 in the first lithium-containing transition metal phosphate material includes V, and the content of V is 1000-10000 ppm based on the total weight of the first lithium-containing transition metal phosphate material.

[0147] In some embodiments, Q1 in the first lithium-containing transition metal phosphate material includes Nb, and the Nb content is 1000-10000 ppm based on the total weight of the first lithium-containing transition metal phosphate material.

[0148] In some embodiments, the specific surface area of ​​the first lithium-containing transition metal phosphate material is 3 m². 2 / g-13m 2 / g.

[0149] In some embodiments, the specific surface area (BET) of the first lithium-containing transition metal phosphate material can be 3 m². 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g, 4.6m 2 / g、5m 2 / g, 5.5m 2 / g、6m 2 / g, 6.5m 2 / g、7m 2 / g, 7.5m 2 / g、8m 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g, 10.5m 2 / g、11m 2 / g, 11.5m 2 / g、12m 2 / g, 12.3m 2 / g, 12.5m 2 / g、13m 2 / g, or a range of any two of the above values, or a value within that range. In some embodiments, the specific surface area of ​​the first lithium-containing transition metal phosphate material is 3m². 2 / g-8m 2 / g.

[0150] In this application, the term "specific surface area" or "BET" refers to the total area per unit mass of material. In this application, the BET of the first lithium transition metal phosphate material is related to factors such as the primary average particle size, carbon content, density of carbon coating, degree of adhesion between carbon and particles, and porosity of the particles.

[0151] Specific surface area (BET) can be measured using methods and equipment known in the art. For example, it can be tested according to the gas adsorption method, referring to GB / T 19587-2017. As an example, a first lithium-containing transition metal phosphate material is placed in a sample tube, which is then immersed in liquid nitrogen at -196°C. The amount of nitrogen adsorbed on the solid surface at different pressures (0.05-0.30) is measured. Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample is calculated, thereby obtaining the specific surface area of ​​the sample.

[0152] An excessively high BET (Body Equivalent Tolerance) in the first lithium-containing transition metal phosphate material will increase the water absorption capacity of the particles, affecting the processing performance of the mixed cathode slurry. However, an excessively low BET in the first lithium-containing transition metal phosphate material will reduce its specific capacity. The BET of the first lithium-containing transition metal phosphate material should be controlled at 3m. 2 / g-13m 2 Within / g, it is beneficial to further balance the processing performance of the positive electrode slurry and improve the solid content, thereby improving the processing problems of the cell and thus increasing the volumetric energy density of the battery.

[0153] In some embodiments, the carbon content of the first lithium-containing transition metal phosphate material is calculated based on the total weight of the first lithium-containing transition metal phosphate material as Cx wt%, where 0.8 ≤ Cx ≤ 2.0.

[0154] When 0.8 ≤ Cx ≤ 2.0, by controlling the carbon content of the first lithium-containing transition metal phosphate material within a certain range, the conductivity and coating integrity of the first lithium-containing transition metal phosphate material can be adjusted. Higher carbon content results in better kinetic performance, better conductivity, improved coating integrity, and reduced surface side reactions. However, excessively high carbon content leads to a high specific surface area, deteriorating cycle performance. High carbon coating also results in some carbon redundancy, existing as floating carbon or ineffective coating, worsening the material's processing performance, particularly significantly affecting the solids content of the pulp. The carbon content range specified in this application helps to further obtain better kinetic and processing performance.

[0155] In some embodiments, the carbon content of the first lithium-containing transition metal phosphate material is calculated based on the total weight of the first lithium-containing transition metal phosphate material as 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.15 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any range of two of the above carbon contents or values ​​within that range.

[0156] In some embodiments, the carbon content of the first lithium-containing transition metal phosphate material is calculated based on the total weight of the first lithium-containing transition metal phosphate material as Cx wt%, where 0.8 ≤ Cx ≤ 1.5.

[0157] In some embodiments, the carbon contained in the first lithium transition metal phosphate material is coated on the surface of its particles. In some embodiments, the carbon contained in the first lithium transition metal phosphate material is embedded within its particles. In some embodiments, the carbon contained in the first lithium transition metal phosphate material is partially coated on the surface of its particles and partially embedded within its particles.

[0158] In some embodiments, the ratio z of the specific surface area of ​​the first lithium-containing transition metal phosphate material to Cx satisfies 1.5 ≤ z ≤ 10. In some embodiments, the ratio z of the specific surface area of ​​the first lithium-containing transition metal phosphate material to Cx satisfies 2 ≤ z ≤ 10. In some embodiments, the ratio z of the specific surface area of ​​the first lithium-containing transition metal phosphate material to Cx satisfies 3 ≤ z ≤ 10. In some embodiments, the ratio z of the specific surface area of ​​the first lithium-containing transition metal phosphate material to Cx satisfies 3 ≤ z ≤ 9. In some embodiments, the ratio z of the specific surface area of ​​the first lithium-containing transition metal phosphate material to Cx satisfies 3.5 ≤ z ≤ 9. In some embodiments, the ratio z of the specific surface area of ​​the first lithium-containing transition metal phosphate material to Cx satisfies 3.8 ≤ z ≤ 8.6.

[0159] In some implementations, z can be 1.5, 2, 2.5, 3, 3.2, 3.5, 3.75, 3.8, 4, 4.2, 4.3, 4.5, 4.58, 4.8, 4.98, 5, 5.3, 5.42, 5.5, 5.71, 5.8, 5.83, 6, 6.3, 6.5, 6.7, 6.8, 7, 7.3, 7.5, 7.8, 7.9, 8, 8.2, 8.3, 8.5, 8.6, 9, 9.5, 10, or a range of any two of the above z values ​​or a value within that range.

[0160] The ratio z of the specific surface area (BET) to Cx of the first lithium transition metal phosphate material can characterize the uniformity and density of the carbon contained in the first lithium transition metal phosphate material. When the primary average particle size and carbon content of the first lithium transition metal phosphate material remain constant, a lower ratio z indicates a higher carbon coating utilization rate and less floating carbon in the particles, resulting in a more uniform and dense carbon composition. Improving the uniformity and density of the contained carbon is beneficial for further improving the kinetic performance and specific capacity of the first lithium transition metal phosphate material. However, excessively high carbon density may affect lithium-ion insertion / extraction, thus impacting the kinetic performance and specific capacity of the secondary battery to some extent. The ratio z range of this application is conducive to the first lithium transition metal phosphate material having a suitable uniform density of carbon, thereby improving the conductivity of the particle surface and further enhancing the specific capacity and kinetic performance of the secondary battery.

[0161] In some embodiments, the first lithium-containing transition metal phosphate material satisfies (a) the Dv10 of the first lithium-containing transition metal phosphate material is 0.2 μm-2 μm;

[0162] (b) The Dv50 of the first lithium-containing transition metal phosphate material is 0.5-5 μm;

[0163] (c) The Dv90 of the first lithium-containing transition metal phosphate material is 1.5 μm-10 μm;

[0164] (d) The Dv99 of the first lithium-containing transition metal phosphate material is 2μm-12μm;

[0165] (e) The powder compaction density of the first lithium-containing transition metal phosphate material under a pressure of 3 tons is 2.25 g / cm³. 3 -2.60g / cm 3 ;

[0166] (f) The resistivity of the powder of the first lithium-containing transition metal phosphate material is 0 Ω·cm to 59 Ω·cm.

[0167] In this application, the term "Dv10" refers to the particle size at which the cumulative volumetric particle size distribution percentage in the particle reaches 10%.

[0168] In this application, the term "Dv90" refers to the particle size at which the cumulative volumetric particle size distribution percentage in the particle reaches 90%.

[0169] In this application, the term "Dv99" refers to the particle size at which the cumulative volumetric particle size distribution percentage in the particle reaches 99%.

[0170] The Dv10, Dv50, Dv90, and Dv99 of the material can be measured using methods and equipment known in the art. For example, they can be determined using a laser particle size analyzer (Malvern Master Size 3000) with reference to GB / T19077.1-2016.

[0171] The first lithium-containing transition metal phosphate material has a suitable particle size parameter, and the material has good conductivity and high specific capacity, which is beneficial for the preparation of batteries with high energy density and high rate.

[0172] In some embodiments, the first lithium-containing transition metal phosphate material has a Dv10 < Dv50.

[0173] In some embodiments, the Dv90 of the first lithium-containing transition metal phosphate material is greater than the Dv50.

[0174] In some embodiments, the Dv50 of the first lithium transition metal phosphate material can be 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1700nm, 1900nm, 2000nm, 2300nm, 2500nm, 2700nm, 2900nm, 3000nm, 3200nm, 3400nm, 3600nm, 3800nm, 4000nm, 4200nm, 4400nm, 4600nm, 4800nm, or 5000nm, or a range of Dv50 of any two of the above-mentioned products after second pulverization, or a value within that range.

[0175] In some embodiments, the first lithium-containing transition metal phosphate material has a powder compaction density ≥ 2.25 g / cm³ at a pressure of 29400 N. 3 In some embodiments, the first lithium-containing transition metal phosphate material has a powder compaction density of 2.25 g / cm³ at a pressure of 29400 N. 3 -2.60g / cm 3 .

[0176] In some embodiments, the powder compaction density of the first lithium-containing transition metal phosphate material at a pressure of 29400 N can be selected as 2.25 g / cm³. 3 2.30g / cm 3 2.35g / cm 3 2.40 g / cm 3 2.45g / cm 3 2.50g / cm 3 2.55g / cm 3 2.60g / cm 3 , or the range between any two of the above values.

[0177] The compacted powder density of a material can be measured using a compaction density instrument, referring to GB / T 24533-2009. Specifically, a certain amount of material powder is placed on a special compaction mold (the mold diameter is known). The mold is hollow in the middle and has a metal disc at the top and bottom. The powder is placed between the metal discs, and a metal cylinder is placed on top. The mold is placed on the compaction density instrument, and the pressure is set to 29400N. The thickness of the powder under 29400N pressure can be read on the instrument. The compacted powder density is then ρ = m / v, where v = (S × H), m is the mass of the powder, S is the bottom area of ​​the mold, and H is the thickness of the compacted powder. The compaction density instrument model is UTM7305; the manufacturer is Sansi Zongheng.

[0178] The first lithium-containing transition metal phosphate material has a high compaction density, which is beneficial to improving the powder compaction density of the positive electrode active material and the compaction density of the positive electrode film, thus providing a material basis for the preparation of high energy density batteries.

[0179] In some embodiments, the powder resistivity of the first lithium-containing transition metal phosphate material is less than 60 Ω·cm. In some embodiments, the powder resistivity of the first lithium-containing transition metal phosphate material is from 0 Ω·cm to 59 Ω·cm.

[0180] In some embodiments, the powder resistivity of the first lithium-containing transition metal phosphate material may be selected as 0 Ω·cm, 5 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm, 35 Ω·cm, 40 Ω·cm, 45 Ω·cm, 50 Ω·cm, 55 Ω·cm, 59 Ω·cm, or any range between any two of the above values.

[0181] The powder resistivity of a material can be measured using methods and equipment known in the art. For example, it can be measured using a powder resistivity meter (Suzhou Jingge, ST2722 type) according to GB / T 33822-2017. Specifically, a certain amount of material (e.g., 1g) is weighed and added to the feeding chamber of the powder resistivity meter, a pressure of 8MPa is applied, and the forward and reverse resistivity of the material are measured separately. The average value of the two is taken as the powder resistivity of the material.

[0182] The first lithium-containing transition metal phosphate material has low powder resistivity, which gives the material excellent conductivity. This is beneficial for improving the conductivity of the positive electrode active material, allowing the material to exert its specific capacity, and improving the energy density and rate performance of the battery.

[0183] By ensuring that the first lithium-containing transition metal phosphate material satisfies at least one of (a)-(f), the first lithium-containing transition metal phosphate material can better achieve the technical effects of this application.

[0184] The raw materials provided contain at least a lithium source, an iron source, a phosphorus source, an optional carbon film-forming agent, an optional carbon source, and an optional modifier, and are subjected to at least two sintering processes, wherein...

[0185] The temperature for the first sintering is 500℃-760℃, and can be selected as 550℃-720℃;

[0186] The temperature for the second sintering is 700℃-800℃, and can be selected as 720℃-780℃.

[0187] In some embodiments, the temperature of the first sintering can be 500°C, 530°C, 550°C, 580°C, 600°C, 630°C, 650°C, 680°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, or 760°C, or a range or a value within that range consisting of any two of the aforementioned first sintering temperatures; the temperature of the second sintering can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, or 800°C, or a range or a value within that range consisting of any two of the aforementioned second sintering temperatures.

[0188] In some embodiments, the heating rates for the first and second sintering are each independently 2°C / min to 20°C / min.

[0189] In some embodiments, the heating rates in the first and second sintering are each independently 2°C / min, 5°C / min, 7°C / min, 10°C / min, 13°C / min, 15°C / min, 17°C / min, or 20°C / min.

[0190] In some embodiments, the isothermal sintering time for the first sintering is 1-6 hours. In some embodiments, the isothermal sintering time for the first sintering can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours.

[0191] In some embodiments, the isothermal sintering time for the second sintering is 2-12 hours. In some embodiments, the isothermal sintering time for the second sintering can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours.

[0192] Compared to traditional methods that use high temperatures to grow particles, the first lithium-containing transition metal phosphate material in this application undergoes two sintering processes. Controlling the temperatures of the two sintering processes is beneficial for obtaining the first lithium-containing transition metal phosphate material with the first-stage average particle size and specific surface area of ​​this application. Furthermore, controlling the heating rate, sintering temperature, and isothermal sintering time of the first and / or second sintering processes helps reduce side reactions, thereby better preparing the first lithium-containing transition metal phosphate material of this application. Furthermore, in conventional high-temperature sintering processes, the carbon coating layer on the particle surface is prone to cracking, reducing the integrity of the carbon coating. This application synthesizes large particles at low temperatures, which is beneficial for improving the consistency and uniformity of the surface carbon coating.

[0193] In some embodiments, the first lithium-containing transition metal phosphate material is mainly obtained by the following preparation methods:

[0194] The raw materials provided contain at least lithium source, iron source, phosphorus source, carbon source, carbon film-forming agent, and modifier, and are subjected to at least two sintering processes.

[0195] The carbon content of the material after the first sintering is 0.01%-0.79% by weight, and can be selected as 0.05%-0.4% by weight.

[0196] The carbon content of the material after the second sintering is 0.8%-2.0% by weight, and can be selected as 1.0%-1.6% by weight.

[0197] In some embodiments, the carbon content of the material after the first sintering can be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, 0.35 wt%, 0.40 wt%, 0.45 wt%, 0.50 wt%, 0.55 wt%, 0.60 wt%, 0.65 wt%, 0.70 wt%, 0.75 wt%, or 0.79 wt%, or a range consisting of any two of the above carbon contents or a value within that range; the carbon content of the material after the second sintering can be 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%, or a range consisting of any two of the above carbon contents or a value within that range.

[0198] In the preparation method of this application embodiment, adding a carbon source before the first sintering can effectively reduce the trivalent iron in the raw material, improving the purity and stability of the product. Furthermore, by controlling the temperature of the first sintering and the carbon content of the intermediate after the first sintering within the aforementioned range, it helps to increase the primary particle size of the first lithium-containing transition metal phosphate material precursor obtained after the first sintering. Specifically, during the first sintering process, a lower carbon content helps to reduce the barrier effect of the carbon layer on the growth process of the first lithium-containing transition metal phosphate material particles, facilitating the crystallization growth of the first lithium-containing transition metal phosphate material precursor at a lower temperature. Simultaneously, it also facilitates the solid-phase diffusion reaction between any added modifier and the first lithium-containing transition metal phosphate material, thereby facilitating the achievement of a higher concentration of metal ion modification. By controlling the temperature of the second sintering and the carbon content of the sintered material within the aforementioned range, it helps to better coat the surface of the first lithium-containing transition metal phosphate material with carbon, forming a uniform and dense carbon coating layer, which is beneficial for improving the surface conductivity of the first lithium-containing transition metal phosphate material particles, and enhancing their kinetic properties and specific capacity.

[0199] In some embodiments, raw materials containing at least a lithium source, an iron source, a phosphorus source, a carbon source, a modifier, and a carbon film-forming agent are provided, and sintering is performed at least twice.

[0200] In some implementations, the mixing ratios of lithium, iron, and phosphorus sources, based on the atomic molar number of each element, satisfy the following: Fe:P = (0.96-0.985):1 and Li:Fe = (1.0-0.95):1.1.

[0201] In some implementations, the mixing ratio of the iron source and the phosphorus source, based on the atomic molar number of each element, satisfies the following: Fe:P = 0.96:1, Fe:P = 0.965:1, Fe:P = 0.97:1, Fe:P = 0.975:1, Fe:P = 0.98:1, or Fe:P = 0.985:1.

[0202] In some embodiments, the mixing ratio of lithium source and iron source, based on the atomic molar number of each element, satisfies the following: Li:Fe = 1.0:1.1, Li:Fe = 0.99:1.1, Li:Fe = 0.98:1.1, Li:Fe = 0.97:1.1, Li:Fe = 0.96:1.1, or Li:Fe = 0.95:1.1.

[0203] In some embodiments, the weight ratio of carbon source to carbon film-forming agent is (9-0.25):1. In some embodiments, the weight ratio of carbon source to carbon film-forming agent can be 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 0.8:1, 0.5:1 or 0.25:1.

[0204] In some embodiments, the lithium source is a lithium-containing compound. In some embodiments, the lithium source includes at least one selected from lithium dihydrogen phosphate, lithium oxalate, lithium carbonate, lithium oxide, lithium hydroxide, and lithium acetate. In some embodiments, the lithium source includes lithium carbonate.

[0205] In some embodiments, the iron source is an iron-containing compound. In some embodiments, the iron source includes at least one of ferric hydroxide, ferrous chloride, ferric oxide, ferric phosphate, ferric pyrophosphate, ferrous oxalate, iron powder, ferric nitrate, magnetite, and ferric hydroxide. In some embodiments, the iron source includes ferric oxide.

[0206] In some embodiments, the phosphorus source is a phosphoric acid compound. In some embodiments, the phosphorus source includes at least one selected from phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. In some embodiments, the phosphorus source includes phosphoric acid.

[0207] In some embodiments, the carbon source includes at least one selected from citric acid, glucose, sucrose, starch, fructose, and lactose. In some embodiments, the carbon source includes glucose.

[0208] In some embodiments, the carbon film-forming agent includes at least one selected from polyethylene glycol, polyaniline, polyacrylonitrile, polyvinylpyrrolidone, and polyvinyl alcohol. In some embodiments, the carbon film-forming agent includes poly(aniline).

[0209] In some embodiments, the modifier includes at least one selected from titanium dioxide, vanadium pentoxide, n-butyl titanate, ammonium metavanadate, niobium ethoxide, niobium oxalate, niobium pentoxide, magnesium hydroxide, and magnesium nitrate. In some embodiments, the modifier includes titanium dioxide.

[0210] By using raw materials in the above proportions, it is advantageous to form the first lithium-containing transition metal phosphate material of this application.

[0211] In some embodiments, the preparation method of the first lithium-containing transition metal phosphate material includes the following steps:

[0212] After the first sintering, a first pulverization is performed; after the second sintering, a second pulverization is performed.

[0213] The Dv50 of the product after the first pulverization is 300nm-1200nm, and can be selected as 400nm-1100nm;

[0214] The Dv50 of the product after the second pulverization is 500nm-5000nm, and can be selected as 700nm-2500nm.

[0215] In this application, the term "Dv50" refers to the particle size at which the cumulative volumetric particle size distribution percentage in the particle reaches 50%.

[0216] In some embodiments, the Dv50 of the product after the first pulverization can be 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, or a range composed of any two of the above-mentioned Dv50 values ​​of the product after the first pulverization, or a value within that range.

[0217] In some embodiments, the Dv50 of the product after the second pulverization can be 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1700nm, 1900nm, 2000nm, 2300nm, 2500nm, 2700nm, 2900nm, 3000nm, 3200nm, 3400nm, 3600nm, 3800nm, 4000nm, 4200nm, 4400nm, 4600nm, 4800nm, or 5000nm, or a range consisting of any two of the above-mentioned Dv50 values ​​of the product after the second pulverization, or a value within that range.

[0218] In some embodiments, the pulverization includes one or more of mechanical crushing, grinding, sand milling, and air jet milling.

[0219] The Dv50 of particles can be measured using methods and equipment commonly used in the art. As an example, it can be determined using a laser particle size analyzer (Malvern Master Size 3000) according to GB / T19077.1-2016.

[0220] Controlling the Dv50 of the product after the first pulverization within the aforementioned range helps reduce the growth barrier effect of the added carbon source and any potentially added modifying elements on the precursor crystal of the first lithium-containing transition metal phosphate material, thus facilitating the preparation of a micron-sized precursor of the first lithium-containing transition metal phosphate material. Controlling the Dv50 value of the product after the second pulverization within the aforementioned range helps to obtain the first lithium-containing transition metal phosphate material with the average particle size of the first pulverization step described in this application.

[0221] A second aspect of this application provides an electrical device comprising a lithium-ion secondary battery as described in the first aspect of this application.

[0222] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0223] In one embodiment of this application, a secondary battery is provided.

[0224] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0225] [Positive electrode plate]

[0226] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0227] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0228] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0229] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0230] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0231] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0232] [Negative electrode plate]

[0233] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0234] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0235] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0236] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0237] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0238] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0239] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0240] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0241] [Electrolytes]

[0242] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0243] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0244] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0245] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0246] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0247] [Isolation membrane]

[0248] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0249] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0250] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0251] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0252] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0253] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured secondary battery 5 as an example.

[0254] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0255] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0256] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0257] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0258] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0259] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0260] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0261] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0262] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0263] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0264] Example

[0265] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0266] Example 1

[0267] (1) Preparation of positive electrode slurry:

[0268] Preparation of the first lithium-containing transition metal phosphate material:

[0269] Lithium carbonate, ferric oxide, phosphoric acid, glucose, titanium dioxide (based on the total weight of the first lithium-containing transition metal phosphate material, with the amount of titanium dioxide added satisfying that the titanium content in the prepared first lithium-containing transition metal phosphate material is 5000 ppm), and polyaniline were weighed out, respectively. The weight ratios of Li, Fe, and P elements were: Fe∶P=0.968∶1, Li∶Fe=1∶0.98, and the weight ratio of glucose to polyaniline was: glucose∶polyaniline=1∶2. The amount of glucose added was such that after the first sintering, the carbon content accounted for 0.15% of the weight of the lithium iron phosphate precursor. Water was added to the above substances to obtain a slurry mixture.

[0270] The mixture was homogenized using a ball mill and then ground using a sand mill to obtain a slurry with a solid content of 38% and a Dv50 of 0.40 μm. The slurry was then spray-dried (using a high-speed spray dryer with a negative pressure of -650 to -200 Pa, an inlet temperature of 300℃ to 360℃, and an outlet temperature of 100℃ to 140℃). The dried reactants were then loaded into a sintering furnace for the first sintering, with a heating rate controlled at 5℃ / min, a holding temperature of 650℃, and a holding time of 4 hours. After cooling, the material was mechanically ground to obtain powder.

[0271] Glucose as a carbon source and polyaniline as a carbon film-forming agent were added to the obtained powder, and then mixed with water to obtain a material with a solid content of 40%. The amounts of glucose and polyaniline added were such that the carbon content of the product after the second sintering was 1.2% (based on the total weight of the first lithium-containing transition metal phosphate material), and the weight ratio of glucose to polyaniline was 1:2. A slurry was obtained by ball milling and sand milling, and the Dv50 of the insoluble matter in the slurry was 550 nm. Spray drying was performed (high-speed spray dryer with a negative pressure of -650 to -200 Pa, an inlet temperature of 300℃ to 360℃, and an outlet temperature of 100℃ to 140℃). The dried reactants were then loaded into a sintering furnace for a second low-temperature sintering (heating rate controlled at 5℃ / min, sintering temperature at 750℃, and sintering time at 4 h). After the material cools, it is pulverized a second time to an average particle size of 870 nm. After demagnetization, the first lithium-containing transition metal phosphate material is obtained, with a carbon content of 1.2% and a Ti element content of 5000 ppm.

[0272] The second lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., with the product number CPF-M603.

[0273] The first lithium-containing transition metal phosphate material (relevant parameters are shown in Table 1) and the second lithium-containing transition metal phosphate material (relevant parameters are shown in Table 1) were blended according to the weight percentages listed in Table 1 to obtain the positive electrode active material. The above-mentioned blended positive electrode active material, conductive carbon black, binder polyvinylidene fluoride and dispersant PVP were mixed in a weight percentage of 93:4.0:2.5:0.5 and N-methylpyrrolidone was added. After thorough mixing, stirring and dispersion, a positive electrode slurry was prepared.

[0274] (2) Preparation of the positive electrode sheet:

[0275] Adjust the viscosity of the thoroughly mixed slurry to 8000-20000 mPa·s until it no longer separates. Then, use a double-sided, double-control coating machine to apply the slurry at a rate of 420 mg / 1540 mm. 2 The coating is applied to the surface of the Al foil substrate, and then dried, cold-pressed, slit, and sheeted to finally obtain the positive electrode sheet.

[0276] (3) Preparation of negative electrode sheet:

[0277] Artificial graphite, conductive carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in a weight percentage of 95:1.0:2.0:2.0, and deionized water was added. After stirring and dispersing, a negative electrode slurry was obtained. The negative electrode slurry was then mixed at a concentration of 211 mg / 1540 mm. 2 The negative electrode sheet is obtained by coating the substrate Cu foil, drying, cold pressing, slitting, and sheet forming.

[0278] (4) Battery fabrication:

[0279] The positive electrode, separator, and negative electrode are stacked in sequence. The separator must be able to isolate the anode and cathode. The bare cell is obtained by winding. The bare cell is placed in the outer packaging, electrolyte is injected, and after processes such as encapsulation, formation, and degassing, a lithium-ion battery is finally obtained.

[0280] Example 2

[0281] The main difference between Example 2 and Example 1 is that the primary average particle size of the first lithium-containing transition metal phosphate material is 250 nm, and the specific surface area is 9.5 m². 2 / g; The primary average particle size of the second lithium-containing transition metal phosphate material is 120nm (the second lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., product number CPF-M601).

[0282] Example 3

[0283] The main difference between Example 3 and Example 1 is that the primary average particle size of the first lithium-containing transition metal phosphate material is 4000 nm, and the specific surface area is 4.5 m². 2 / g; The primary average particle size of the second lithium-containing transition metal phosphate material is 600nm (the second lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., product number CPF-M606).

[0284] Example 4

[0285] The main difference between Example 4 and Example 1 is that the specific surface area of ​​the first lithium-containing transition metal phosphate material is 3m². 2 / g, with a carbon content of 0.8% by weight.

[0286] Example 5

[0287] The main difference between Example 5 and Example 1 is that the specific surface area of ​​the first lithium-containing transition metal phosphate material is 12 m². 2 / g, with a carbon content of 1.4% by weight.

[0288] Example 6

[0289] The main difference between Example 6 and Example 1 is that vanadium pentoxide is used instead of titanium dioxide, and the specific surface area of ​​the first lithium-containing transition metal phosphate material is 8 m². 2 / g.

[0290] Example 7

[0291] The main difference between Example 7 and Example 1 is that niobium pentoxide is used instead of titanium dioxide.

[0292] Example 8

[0293] The main difference between Example 8 and Example 1 is that the titanium content of the first lithium-containing transition metal phosphate material is 1000 ppm; the primary average particle size of the second lithium-containing transition metal phosphate material is 210 nm (the second lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., product number CPF-M602).

[0294] Example 9

[0295] The main difference between Example 9 and Example 1 is that the titanium content of the first lithium-containing transition metal phosphate material is 10,000 ppm; and the primary average particle size of the second lithium-containing transition metal phosphate material is 210 nm (the second lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., product number CPF-M602).

[0296] Example 10

[0297] The main difference between Example 10 and Example 1 is that the weight percentage of the first lithium-containing transition metal phosphate material is 5%, and the weight percentage of the second lithium-containing transition metal phosphate material is 95%.

[0298] Example 11

[0299] The main difference between Example 11 and Example 1 is that the weight percentage of the first lithium-containing transition metal phosphate material is 30%, and the weight percentage of the second lithium-containing transition metal phosphate material is 70%.

[0300] Example 12

[0301] (1) Preparation of positive electrode slurry:

[0302] The source / preparation methods of the first lithium-containing transition metal phosphate material and the second lithium-containing transition metal phosphate material are exactly the same as those in Example 1.

[0303] The third lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., with the product number CPF-S4009. The relevant parameters are shown in Table 1.

[0304] The first lithium-containing transition metal phosphate material, the second lithium-containing transition metal phosphate material, and the third lithium-containing transition metal phosphate material were blended according to the weight percentages listed in Table 1 to obtain the positive electrode active material. The above-mentioned blended positive electrode active material, conductive carbon black, binder polyvinylidene fluoride, and dispersant PVP were mixed in a weight percentage of 93:4.0:2.5:0.5 and N-methylpyrrolidone was added. After thorough mixing, stirring, and dispersion, a positive electrode slurry was prepared.

[0305] (2) Preparation of the positive electrode sheet:

[0306] It is exactly the same as Example 1.

[0307] (3) Preparation of negative electrode sheet:

[0308] It is exactly the same as Example 1.

[0309] (4) Battery fabrication:

[0310] It is exactly the same as Example 1.

[0311] Example 13

[0312] The main difference between Example 13 and Example 12 is that the primary average particle size of the third lithium-containing transition metal phosphate material is 50 nm (the third lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., item number CPF-S4005).

[0313] Example 14

[0314] The main difference between Example 14 and Example 12 is that the primary average particle size of the third lithium-containing transition metal phosphate material is 200 nm (the third lithium-containing transition metal phosphate material was purchased from Hubei Wanrun New Energy Technology Co., Ltd., CPF-S402).

[0315] Example 15

[0316] The main difference between Example 15 and Example 12 is that the weight percentage of the first lithium-containing transition metal phosphate material is 5%, the weight percentage of the second lithium-containing transition metal phosphate material is 90%, and the weight percentage of the third lithium-containing transition metal phosphate material is 5%.

[0317] Examples 16-21

[0318] The main differences between Examples 16-21 and Example 1 are shown in Table 1 (the third lithium-containing transition metal phosphate material in Example 18 was purchased from Hubei Wanrun New Energy Technology Co., Ltd., with the product number CPF-S401; the third lithium-containing transition metal phosphate material in Example 20 was purchased from Hubei Wanrun New Energy Technology Co., Ltd., with the product number CPF-S021; the third lithium-containing transition metal phosphate material in Example 21 was purchased from Hubei Wanrun New Energy Technology Co., Ltd., with the product number CPF-S0008).

[0319] Comparative Example 1

[0320] The main difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain the first lithium-containing transition metal phosphate material.

[0321] Comparative Example 2

[0322] The main difference between Comparative Example 2 and Example 1 is that the molar percentage of Mn in the first lithium-containing transition metal phosphate material is greater than that in the second lithium-containing transition metal phosphate material.

[0323] Comparative Example 3

[0324] The main difference between Comparative Example 3 and Example 12 is that the molar percentage of Mn in the first lithium-containing transition metal phosphate material is greater than that in the second lithium-containing transition metal phosphate material.

[0325] II. Battery Performance Testing

[0326] 1) Dv50

[0327] Referring to GB / T19077.1-2016, the Dv50 value of the particles was determined using a laser particle size analyzer (Malvern Master Size 3000). Furthermore, the Dv10, Dv90, and Dv99 values ​​described in this application were also determined in the same manner.

[0328] 2) Specific surface area

[0329] The specific surface area was tested using the gas adsorption method, according to the GB / T19587-2017 testing standard. The specific steps were as follows: A first lithium-containing transition metal phosphate material was taken as the sample, and the sample tube was immersed in liquid nitrogen at -196℃. The amount of nitrogen adsorbed on the solid surface under different pressures of 0.05-0.30 was measured. Based on the BET multilayer adsorption theory and its formula, the amount of monolayer adsorption of the sample was obtained, and the specific surface area of ​​the material was calculated.

[0330] 3) Carbon content

[0331] The carbon content of the first lithium-containing transition metal phosphate material was tested by infrared absorption method after combustion in a high-frequency induction furnace. The specific testing procedure was in accordance with standard GB / T 20123-2006 / ISO 15350:2000.

[0332] 4) The content of Q element (e.g., Ti element) in the first lithium-containing transition metal phosphate material

[0333] The content of Q element in the first lithium-containing transition metal phosphate material was tested in accordance with GB / T 33822-2017.

[0334] 5) Manganese leaching amount

[0335] Retrieve the fully charged cell after 100 cycles at 25℃. Disassemble it in a glove box. Remove the anode plate in a drying room and gently scrape 1g of material from the center of the plate using a ceramic knife, ensuring the entire active material layer is scraped off to avoid inconsistent manganese content at different thicknesses. Seal the bag and send it to the laboratory. Prepare an electronic scale, heating plate, 150ml quartz beaker, watch glass, funnel, 100ml volumetric flask, pliers (heat-resistant gloves), weighing spoon, and lint-free paper. Confirm the electronic scale's calibration date is valid; expired scales cannot be used and must be recalibrated. Connect the power supply; the heating plate should heat to 250℃ normally. Weigh 0.2000±0.005g of powder into the beaker. Acidification treatment: Prepare a dilute sulfuric acid solution with a volume ratio of 1:4 (concentrated sulfuric acid: ultrapure water = 1:4). Add 20ml of the prepared dilute sulfuric acid solution to the beaker. First, preheat the heating plate to 250℃, then place the sample in the container for 30 minutes to digest. Place a quartz cap on the mouth of the beaker to reduce acid evaporation. After 30 minutes of digestion, remove the sample and allow it to cool to room temperature. Transfer the digested sample to a 100ml glass volumetric flask and make up to volume. Then, perform the ICP standard test procedure: test equipment temperature 22±2℃, humidity <60%; select the trace element method; run the calibration standard: use the prepared standard solution to establish a standard curve; select Mn as the element; finally, the amount of Mn dissolved can be obtained through testing.

[0336] 6) Solid content of positive electrode slurry

[0337] Prepare an electronic balance (accuracy 0.0001), an oven, and a glass drying tray. Take 8-10g of the positive electrode slurry sample and evenly spread it on the sample tray. Record the slurry mass before drying as A. Close the oven door and heat. As heating progresses, the oven temperature continuously increases, reaching 130℃ for 5 hours. After drying, remove the sample from the oven and record the mass of the dried slurry. Repeat the drying process multiple times until the sample mass reaches a constant weight; record the mass after drying as B. The slurry solid content = (A / B) × 100%.

[0338] 7) Electrode compaction density

[0339] The term "electrode compaction density" used in this application refers to the "ultimate compaction density" of the electrode, and its testing method is as follows:

[0340] The double-coated electrode sheets were cold-pressed using a roller press, and the elongation of the cold-pressed electrode sheets was tested. At the same time, the flexibility of the cold-pressed electrode sheets was evaluated.

[0341] By increasing the pressure of the roller press, electrodes with different compaction densities can be obtained. As the pressure increases, the compaction density of the electrode increases, the elongation of the electrode increases, and the flexibility of the electrode decreases. Excessive elongation of the electrode can easily lead to warping, while insufficient flexibility can easily lead to brittle fracture. Therefore, the lower of the compaction density corresponding to an electrode elongation of 6‰ or an electrode flexibility folding number of 3 times is defined as the limiting compaction density.

[0342] The compaction density is calculated by dividing the weight of a single positive electrode film layer by the volume of the positive electrode film layer.

[0343] 8) Capacity

[0344] The batteries in the examples and comparative examples were placed in a 40°C oven and left to stand for 2 hours to maintain the battery temperature at 40°C. Then, the batteries were discharged at a constant current of 1 / 3C to 2.5V; left to stand for 5 minutes; then, the batteries were charged at a constant current of 1 / 3C to 4.1V, and then charged at a constant voltage of 4.1V until the cutoff current was 0.05C; left to stand for 5 minutes; and finally, the batteries were discharged at a constant current of 1 / 3C to 2.5V to obtain the battery's discharge capacity C.

[0345] The specific capacity of the positive electrode active material = the discharge capacity of the battery C / the mass of the positive electrode active material M.

[0346] 9) High-temperature storage performance

[0347] High-temperature storage performance was characterized by storing the battery at 60°C under full charge (charged to 4.1V) and measuring the time it took for the battery capacity to decay to 80% of its initial value.

[0348] 1. Let stand for 10 minutes, then discharge at a constant current of 0.33Cn (Cn is the battery capacity at 40℃ and 1 / 3C) to 2V.

[0349] 2. Let stand for 10 minutes, charge at a constant current of 0.33Cn to 4.1V, then charge at a constant voltage, with a cutoff current of 0.02Cn.

[0350] 3. Let stand for 2 hours, store at 60℃ for 30 days, and then take out to test the reversible capacity of the battery cell.

[0351] The specific testing procedure is briefly described as follows: (1) Place the battery in a 40℃ oven environment and let it stand for 2 hours until the battery temperature is maintained at 40℃; (2) Discharge at 1 / 3C constant current to 2.0V; (3) Pause for 5 minutes; (4) Charge at 1 / 3C constant current to 4.1V, and then charge at 4.1V constant voltage until the cutoff current is 0.05C; (5) Pause for 5 minutes; (6) Discharge at 1 / 3C constant current to 2.0V. This step is for testing the actual cell capacity.

[0352] 4. Conduct tests regularly until the reversible capacity of the battery cell degrades to 80% of its initial value.

[0353] 10) High-temperature cycling performance

[0354] High-temperature cycling performance is characterized by measuring the number of cycles required when the battery capacity decays to 80% of its initial value using a 1C / 1C cycle at 60°C.

[0355] The specific process is briefly described as follows: Place the battery in a 60℃ oven and let it stand for 2 hours until the battery temperature reaches 60℃. Then, discharge the battery at a constant current of 1 / 3C to 2.0V. After standing for 5 minutes, charge the battery at a constant current of 1C to 4.1V, then charge it at a constant voltage of 4.1V to a current of 0.05C. After standing for 2 minutes, discharge the battery at a constant current of 1C to 2.0V. This completes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. Perform multiple charge-discharge cycles on the battery using the above method until the discharge capacity of the secondary battery decreases to 80%, and record the number of cycles.

[0356] 11) Volumetric energy density of the battery

[0357] Battery cell capacity test: The battery cell was left to stand at 40℃ for 2 hours to ensure the temperature of the battery cell was 40℃. Then the battery was discharged at a constant current of 1 / 3C to 2.0V. After standing for 5 minutes, the battery cell was charged at a constant current of 1 / 3C to 4.1V. The constant voltage charging at 4.1V continued until the current was 0.05C. After standing for 5 minutes, the battery cell was discharged at a constant current of 1 / 3 to 2.0V. The total discharge capacity C0 and the total discharge energy E0 of the battery cell were recorded. The unit of total discharge energy is Wh.

[0358] Battery cell volume measurement: Use calipers to measure the length, width, and height of the battery's outer surface, and calculate the cell volume V0 in liters (L).

[0359] Volumetric energy density calculation: The volumetric energy density of a battery cell is calculated as follows: Discharge energy of a single battery cell E0 / Battery volume V0.

[0360] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0361] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The parameters of the positive electrode active material are shown in Table 1, and the performance test results are shown in Table 2.

[0362] Based on the above results, it can be seen that the lithium-ion secondary batteries in Examples 1-21 were all obtained by a preparation method including the following steps: Preparation of positive electrode active material: mixing a first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material to obtain a positive electrode active material. The primary average particle size of the first lithium-containing transition metal phosphate material is 250-4000 nm, and the primary average particle size of the second lithium-containing transition metal phosphate material is 120-600 nm. The primary average particle size of the first lithium-containing transition metal phosphate material is greater than that of the second lithium-containing transition metal phosphate material, and the molar percentage of Mn in the first lithium-containing transition metal phosphate material is less than that in the second lithium-containing transition metal phosphate material; Preparation of positive electrode sheet: coating a positive electrode slurry containing the positive electrode active material onto at least one surface of the positive electrode current collector to obtain a positive electrode sheet; Preparation of secondary battery: assembling the positive electrode sheet, the negative electrode sheet, and an electrolyte including lithium salt into a secondary battery.

[0363] As can be seen from the comparison between Examples 1-21 and Comparative Examples 1-3, the lithium-ion secondary batteries of this application have a lower manganese leaching amount. Furthermore, the lithium-ion secondary batteries of this application also have better high-temperature storage performance, better high-temperature cycle performance, and higher specific capacity.

[0364] A comparison of Examples 12-15, 18, 20-21 with Examples 1-11, 16-17, 19 shows that when the positive electrode active material further includes a third lithium-containing transition metal phosphate material, the primary average particle size of the third lithium-containing transition metal phosphate material is 50-200 nm, the primary average particle size of the second lithium-containing transition metal phosphate material is greater than that of the third lithium-containing transition metal phosphate material, and the molar percentage of Mn in the third lithium-containing transition metal phosphate material is less than that in the second lithium-containing transition metal phosphate material, the lithium-ion secondary battery of the present application embodiment has a higher volumetric energy density.

[0365] As can be seen from the comparison between Examples 1, 3-21 and Example 2, when the primary average particle size of the first lithium-containing transition metal phosphate material is 870-4000 nm, the lithium-ion secondary battery of this application has a lower manganese dissolution, better high-temperature storage performance, better high-temperature cycling performance, and higher solid content of the positive electrode slurry.

[0366] As can be seen from the comparison between Examples 1, 3-21 and Example 2, when the primary average particle size of the second lithium-containing transition metal phosphate material is 210-600 nm, the lithium-ion secondary battery of this application embodiment has a lower manganese dissolution, better high-temperature storage performance, better high-temperature cycling performance, and higher solid content of the positive electrode slurry.

[0367] As can be seen from the comparison between Examples 12, 14 and Example 13, when the primary average particle size of the third lithium-containing transition metal phosphate material is 90-200 nm, the lithium-ion secondary battery of this application embodiment has a lower manganese dissolution, better high-temperature storage performance, better high-temperature cycling performance, and higher positive electrode slurry solid content.

[0368] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for producing a lithium-ion secondary battery, characterized by, comprising the steps of: preparing a positive electrode active material: mixing a first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material to obtain a positive electrode active material, the first lithium-containing transition metal phosphate material has a primary average particle size of 250-4000 nm, the second lithium-containing transition metal phosphate material has a primary average particle size of 120-600 nm, the primary average particle size of the first lithium-containing transition metal phosphate material is greater than the primary average particle size of the second lithium-containing transition metal phosphate material, wherein the first lithium-containing transition metal phosphate material has a Mn molar ratio less than the Mn molar ratio of the second lithium-containing transition metal phosphate material, wherein the Mn molar ratio refers to the proportion of the number of moles of Mn relative to the total number of moles of Mn and Fe; preparing a positive electrode sheet: coating a positive electrode slurry containing the positive electrode active material on at least one surface of a positive electrode current collector to obtain a positive electrode sheet; preparing a secondary battery: assembling the positive electrode sheet, a negative electrode sheet, and an electrolyte comprising a lithium salt into a secondary battery.

2. The preparation method of the lithium ion secondary battery according to claim 1, wherein the first lithium-containing transition metal phosphate material has a primary average particle size of 870-4000 nm.

3. The preparation method of the lithium ion secondary battery according to claim 1 or 2, wherein the second lithium-containing transition metal phosphate material has a primary average particle size of 210-600 nm.

4. The preparation method of the lithium ion secondary battery according to any one of claims 1-3, wherein the weight percentage of the first lithium-containing transition metal phosphate material is 5%-40%, optionally 10%-35%, and optionally 20%-30%, and the weight percentage of the second lithium-containing transition metal phosphate material is 60%-95%, optionally 65%-90%, and optionally 70%-80%, based on the total weight of the positive electrode active material.

5. The preparation method of the lithium ion secondary battery according to any one of claims 1-4, wherein the Mn molar ratio of the first lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.4, more optionally 0-0.2, and further optionally 0.

6. The preparation method of the lithium ion secondary battery according to any one of claims 1-4, wherein the Mn molar ratio of the first lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.4, more optionally 0.02-0.2, and further optionally 0.

02.

7. The preparation method of the lithium ion secondary battery according to any one of claims 1-4, wherein the Mn molar ratio of the first lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.4, and more optionally 0.

2.

8. The preparation method of the lithium ion secondary battery according to any one of claims 1-7, wherein the Mn molar ratio of the second lithium-containing transition metal phosphate material is 0.4-0.9, and optionally 0.5-0.

9.

9. The production method of a lithium-ion secondary battery according to any one of claims 1 to 8, wherein the step of producing a positive electrode active material includes: mixing the first lithium-containing transition metal phosphate material, the second lithium-containing transition metal phosphate material and a third lithium-containing transition metal phosphate material to obtain a positive electrode active material, a primary average particle size of the third lithium-containing transition metal phosphate material is 50-200 nm, a primary average particle size of the second lithium-containing transition metal phosphate material is greater than a primary average particle size of the third lithium-containing transition metal phosphate material, wherein a Mn molar percentage of the third lithium-containing transition metal phosphate material is less than a Mn molar percentage of the second lithium-containing transition metal phosphate material.

10. The preparation method of the lithium ion secondary battery according to claim 9, wherein the primary average particle size of the third lithium-containing transition metal phosphate material is 90-200 nm.

11. The preparation method of the lithium ion secondary battery according to claim 9 or 10, wherein a weight percentage of the first lithium-containing transition metal phosphate material is 5%-30%, optionally 10%-30%, optionally 20%-30%, based on a total weight of the positive electrode active material; a weight percentage of the second lithium-containing transition metal phosphate material is 60%-90%, optionally 65%-80%, optionally 70%-80%; and a weight percentage of the third lithium-containing transition metal phosphate material is 1%-10%, optionally 2%-8%, optionally 3%-7%.

12. The preparation method of the lithium ion secondary battery according to any one of claims 9-11, wherein a Mn molar percentage of the third lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.5, more optionally 0.

13. The preparation method of the lithium ion secondary battery according to any one of claims 9-11, wherein a Mn molar percentage of the third lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.5, more optionally 0.

02.

14. The preparation method of the lithium ion secondary battery according to any one of claims 9-11, wherein a Mn molar percentage of the third lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.5, more optionally 0.

2.

15. The method for producing a lithium-ion secondary battery according to any one of claims 1 to 14, wherein the first lithium-containing transition metal phosphate material has a molecular formula of Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1 wherein Q1 includes at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95 < ml < 1.15, xl > 0, rl > 0, 0.9 < xl + rl < 1, 0.95 < yl < 1, 3.5 < jl < 4, 0 < ql < 0.1, and / or said second lithium-containing transition metal phosphate material has the formula Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2 wherein Q2 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95 < m2 < 1.15, x2 > 0, r2 > 0, 0.9 < x2 + r2 < 1, 0.95 < y2 < 1, 3.5 < j2 < 4, 0 < q2 < 0.1, and / or the third lithium-containing transition metal phosphate material has the formula Li m3 Fe x3 Mn r3 P y3 O j3 Q3 q3 wherein Q3 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95 < m3 < 1.15, x3 > 0, r3 > 0, 0.9 < x3 + r3 < 1, 0.95 < y3 < 1, 3.5 < j3 < 4, 0 < q3 < 0.

1.

16. The preparation method of the lithium ion secondary battery according to claim 15, wherein in the first lithium-containing transition metal phosphate material, the Q1 comprises at least one of Ti, V, Mg, Nb, and a content of Ti, V, Mg and / or Nb is 1000-10000 ppm, calculated based on a total weight of the first lithium-containing transition metal phosphate material.

17. The method of producing a lithium-ion secondary battery according to any one of claims 1 to 16, wherein the specific surface area of the first lithium-containing transition metal phosphate material is 3 m2 / g to 13 m2 / g. 2 / g to 13 m 2 / g.

18. The method of producing a lithium-ion secondary battery according to any one of claims 1 to 17, wherein the carbon content of the first lithium-containing transition metal phosphate material is Cx wt% based on the total weight of the first lithium-containing transition metal phosphate material, wherein, 0.8≤Cx≤2.

0.

19. The preparation method of the lithium ion secondary battery according to any one of claims 1-18, wherein the first lithium-containing transition metal phosphate material satisfies at least one of (a)-(f): (a) a Dv10 of the first lithium-containing transition metal phosphate material is 0.2-2 μm; (b) a Dv50 of the first lithium-containing transition metal phosphate material is 0.5-5 μm; (c) a Dv90 of the first lithium-containing transition metal phosphate material is 1.5-10 μm; (d) the Dv99 of the first lithium-containing transition metal phosphate material is 2 pm to 12 pm; (e) the first lithium-containing transition metal phosphate material has a powder compaction density of 2.25 g / cm3under 3 tons of pressure 3 - 2.60 g / cm3 3 ; (f) the powder resistivity of the first lithium-containing transition metal phosphate material is 0 W-cm to 59 W-cm.

20. The method of claim 1-19, wherein the first lithium-containing transition metal phosphate material is prepared primarily by a method comprising: providing raw materials comprising at least a lithium source, an iron source, a phosphorous source, a carbon film former, a carbon source, and a modifying agent, and performing at least two sintering processes, wherein the first sintering process is performed at a temperature of 500 °C to 760 °C; the second sintering process is performed at a temperature of 700 °C to 800 °C.

21. The method of claim 20, wherein the first lithium-containing transition metal phosphate material is prepared primarily by a method comprising: providing raw materials comprising at least a lithium source, an iron source, a phosphorous source, a carbon source, a carbon film former, and a modifying agent, and performing at least two sintering processes, wherein the carbon content of the material after the first sintering process is 0.01 wt% to 0.79 wt%; the carbon content of the material after the second sintering process is 0.8 wt% to 2.0 wt%.

22. The method of claim 20 or 21, wherein the method of preparing the first lithium- containing transition metal phosphate material comprises: performing a first pulverization after the first sintering process and a second pulverization after the second sintering process, wherein the Dv50 of the product after the first pulverization is 300 nm to 1200 nm; the Dv50 of the product after the second pulverization is 500 nm to 5000 nm.

23. A lithium ion secondary battery obtainable by the method of any one of claims 1-22.

24. An electrical device comprising the lithium ion secondary battery of claim 23.

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