Secondary battery and manufacturing method therefor, and electric device

Abstract

The present application provides a secondary battery and a manufacturing method therefor, and an electric device. The manufacturing method for the secondary battery comprises: preparation of a positive electrode active material: mixing a first lithium-containing transition metal phosphate material with a second lithium-containing transition metal phosphate material to obtain the positive electrode active material, wherein the first lithium-containing transition metal phosphate material comprises a first core and a first carbon coating layer covering the outer surface of the first core; the second lithium-containing transition metal phosphate material comprises a second core and a second carbon coating layer covering the outer surface of the second core; the primary average particle size of the first lithium-containing transition metal phosphate material is smaller than that of the second lithium-containing transition metal phosphate material; a molar ratio of Mn in the first lithium-containing transition metal phosphate material is less than a molar ratio of Mn in the second lithium-containing transition metal phosphate material; the primary average particle size of the first lithium-containing transition metal phosphate material is 50 nm-200 nm; and the primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm-600 nm.

Description

Secondary batteries, their preparation methods and electrical devices

[0001] Cross-referencing

[0002] This application incorporates Chinese Patent Application No. 202411035681.5, filed on July 30, 2024, entitled “Secondary Battery, Method of Preparation Thereof and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology, and in particular to a secondary battery, its preparation method and power supply device. Background Technology

[0004] Secondary batteries have advantages such as high energy density, high operating voltage, low self-discharge rate, small size, and light weight, and have a wide range of applications.

[0005] With the rapid development of electric vehicles and mobile electronic devices, the requirements for energy density and cycle performance of rechargeable batteries are becoming increasingly stringent. How to improve battery energy density while simultaneously ensuring good cycle performance is a pressing technical problem that needs to be solved in the current application of rechargeable batteries. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its object is to provide a secondary battery, a method for preparing the same, and an electrical device thereof. The secondary battery obtained by this preparation method has both high energy density and excellent cycle performance.

[0007] The first aspect of this application provides a method for preparing a secondary battery, comprising the following steps:

[0008] 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.

[0009] The first lithium-containing transition metal phosphate material includes a first core and a first carbon coating layer covering the outer surface of the first core; the second lithium-containing transition metal phosphate material includes a second core and a second carbon coating layer covering the outer surface of the second core.

[0010] The primary average particle size of the first lithium-containing transition metal phosphate material is smaller than that of the second lithium-containing transition metal phosphate material.

[0011] 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.

[0012] The primary average particle size of the first lithium-containing transition metal phosphate material is 50 nm-200 nm.

[0013] The primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm-600 nm.

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

[0015] Preparation of positive electrode sheet: A positive electrode slurry containing positive electrode active material is coated on at least one surface of the positive electrode current collector to obtain a positive electrode sheet;

[0016] Preparation of secondary batteries: Assemble an electrode assembly containing a positive electrode, a negative electrode, and an electrolyte into a secondary battery.

[0017] The positive electrode active material comprises two materials with different primary average particle size ranges. This allows for the complementary size distribution of the materials to fill gaps, resulting in a denser packing of the positive electrode active material, increasing the powder compaction density and electrode compaction density, thereby improving the battery's energy density. However, the first lithium-containing transition metal phosphate material has a smaller primary average particle size and a larger specific surface area, leading to higher surface activity and making it more susceptible to side reactions in the electrolyte, exacerbating manganese ion dissolution and affecting the battery's cycle performance. This application reduces the molar Mn content of the smaller-particle-size, higher-specific-surface-area first lithium-containing transition metal phosphate material compared to the second lithium-containing transition metal phosphate material. This reduces the likelihood of manganese dissolution during cycling in the highly reactive first lithium-containing transition metal phosphate material, improving both the powder compaction density and battery energy density, while also enhancing the material's cycle stability and overall battery cycle performance.

[0018] In any embodiment, 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.

[0019] 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 electrolytes and the degree of manganese dissolution can be further reduced, thereby further improving the cycle performance and storage performance of the battery. The battery is more suitable for application scenarios with high requirements for cycle life and / or storage life.

[0020] In any embodiment, 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.

[0021] In any embodiment, 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.

[0022] 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 allowing the highly conductive small-particle-size materials to fully utilize their specific capacity. This results in excellent cycle performance of the battery and further increases its energy density, making the battery more suitable for scenarios with high energy density requirements.

[0023] In any embodiment, the molar percentage of Mn in the second lithium-containing transition metal phosphate material is 0.4-0.9, and can be optionally 0.5-0.9.

[0024] 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.

[0025] In any embodiment, based on the total weight of the positive electrode active material, the weight percentage of the first lithium transition metal phosphate material is greater than 0% and less than or equal to 20%, optionally 5%-20%; and / or, the weight percentage of the second lithium transition metal phosphate material is greater than or equal to 80% and less than 100%, optionally 80%-95%.

[0026] By controlling the mass ratio of materials with different particle sizes within a suitable range, the contribution of the high-manganese content second lithium-containing transition metal phosphate material to the energy density in terms of voltage rating and specific capacity can be achieved. At the same time, the impact of the small-particle-size first lithium-containing transition metal phosphate material on the battery's cycle performance can be reduced. In addition, by keeping the mass content of the other two materials within a suitable range, the molar ratio of Mn in the positive electrode active material can be kept within a suitable range, thereby improving the battery's energy density and cycle performance.

[0027] In any embodiment, the steps for preparing the positive electrode active material include:

[0028] 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 are mixed to obtain the positive electrode active material.

[0029] The third lithium-containing transition metal phosphate material includes a third core and a third carbon coating layer covering the outer surface of the third core.

[0030] The primary average particle size of the third lithium-containing transition metal phosphate material is greater than that of the second lithium-containing transition metal phosphate material.

[0031] 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.

[0032] Among them, the primary average particle size of the third lithium-containing transition metal phosphate material is 250nm-4000nm.

[0033] Compared to the first and second lithium-containing transition metal phosphate materials, the third lithium-containing transition metal phosphate material has a larger primary average particle size. During cycling or storage, the third lithium-containing transition metal phosphate material is less likely to undergo side reactions with the electrolyte or experience manganese dissolution. The inclusion of the third lithium-containing transition metal phosphate material, which has excellent cycle stability and storage stability, in the positive electrode active material can further improve the cycle stability and storage stability of the positive electrode active material, thereby enhancing the cycle performance and storage performance of the battery. Meanwhile, the third lithium-containing transition metal phosphate material with a larger primary average particle size has a high powder compaction density, which can further improve the compaction density of the material and the electrode. At the same time, the positive electrode film layer contains a variety of materials with different primary particle sizes, which can form a large, medium and small particle size distribution system. The filling between the materials is more compact, which can further improve the powder compaction density of the material and the compaction density of the electrode, which is conducive to obtaining a high energy density battery. In addition, by controlling the Mn molar ratio of the third lithium-containing transition metal phosphate material with a relatively large primary average particle size to be less than the Mn molar ratio of the second lithium-containing transition metal phosphate material with a relatively small primary average particle size, this application can improve the conductivity of the third lithium-containing transition metal phosphate material with a relatively large primary average particle size, alleviate the discharge polarization of the third lithium-containing transition metal phosphate material, and facilitate the utilization of the material's specific capacity and kinetic performance, thereby achieving the goal of improving the battery's energy density.

[0034] In any embodiment, the molar percentage of Mn in the third lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.5, more preferably 0-0.1, and even more preferably 0.

[0035] Controlling the molar ratio of Mn in the third lithium-containing transition metal phosphate material within a suitable range can improve the cycle stability and conductivity of the third lithium-containing transition metal phosphate material, which is conducive to further exerting its specific capacity and improving the energy density and cycle life of the battery.

[0036] In any embodiment, the molar percentage of Mn in the third lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.5, more preferably 0.02-0.1, and even more preferably 0.02.

[0037] In any embodiment, 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.

[0038] 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.

[0039] In any embodiment, based on the total weight of the lithium transition metal phosphate material, the weight percentage of the first lithium transition metal phosphate material is 1%-10%, and / or the weight percentage of the second lithium transition metal phosphate material is 60%-90%, and / or the weight percentage of the third lithium transition metal phosphate material is 5%-30%.

[0040] Controlling the mass ratio of materials with different particle sizes within a suitable range is beneficial for achieving the goal of increasing the contribution of the high-manganese content second lithium-containing transition metal phosphate material to the energy density through its voltage rating and specific capacity. Simultaneously, it reduces the impact of the large-particle-size third lithium-containing transition metal phosphate material on the battery's rate performance and the small-particle-size first lithium-containing transition metal phosphate material on the battery's cycle performance. Furthermore, maintaining the appropriate mass ratio of the three materials also ensures that the molar ratio of Mn in the positive electrode active material is within a suitable range, which is conducive to obtaining a battery with high energy density, excellent rate performance, and good cycle performance.

[0041] In any embodiment, the third lithium-containing transition metal phosphate material satisfies the following relationship:

[0042] 1.5≤A / B≤10

[0043] Where A is the specific surface area of ​​the third lithium-containing transition metal phosphate material; B% is the mass content of the third carbon coating layer in the third lithium-containing transition metal phosphate material.

[0044] The third lithium-containing transition metal phosphate material has a suitable A / B value range. The carbon coating layer contains less floating carbon and is more uniform and dense, which is beneficial to improving the conductivity and specific capacity of the material and provides a material basis for the preparation of high energy density and high rate batteries.

[0045] In any embodiment, the specific surface area of ​​the third lithium-containing transition metal phosphate material is 3m². 2 / g-13m 2 / g.

[0046] The third lithium-containing transition metal phosphate material has a specific surface area within a suitable range, and the material has a relatively high specific capacity. At the same time, it avoids the high water absorption caused by an excessively large specific surface area, which may affect the processing performance of the cathode slurry. This balances the material's performance in both use and processing.

[0047] In any embodiment, based on the mass of the third lithium-containing transition metal phosphate material, the mass content of the third carbon coating layer is 0.8%-2.0%.

[0048] When the carbon content of the material's coating layer is within a suitable range, it can improve the material's conductivity and facilitate the formation of a complete and dense coating layer, reducing the possibility of side reactions on the material surface and improving the material's cycle stability and conductivity. On the other hand, it can also prevent excessive carbon content from affecting the material's specific capacity and avoid the impact of floating carbon caused by excessive carbon content on the material's processing performance.

[0049] In any embodiment, the third lithium-containing transition metal phosphate material satisfies at least one of (a1)-(f1):

[0050] (a1) The Dv10 of the third lithium-containing transition metal phosphate material is 0.2 μm-2 μm;

[0051] (b1) The Dv50 of the third lithium-containing transition metal phosphate material is 0.5 μm-5 μm;

[0052] (c1) The Dv90 of the third lithium-containing transition metal phosphate material is 1.5μm-10μm;

[0053] (d1) The Dv99 of the third lithium-containing transition metal phosphate material is 2μm-12μm;

[0054] (e1) The compacted density of the third lithium-containing transition metal phosphate material at a pressure of 29400 N is 2.25 g / cm³. 3 -2.60g / cm 3 ;

[0055] (f1) The powder resistivity of the third lithium-containing transition metal phosphate material is 0 Ω·cm to 59 Ω·cm.

[0056] In any implementation, the general formula for the first kernel includes Li m1 A1 a1 Fe x1 Mn y1 M4 b1 P z1 Q1 c1 O n1 N4 d1 ,

[0057] Where 0.8≤m1≤1.2, x1≥0, y1≥0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n4≤4, 0≤a4≤0.1, 0≤b4≤0.1, 0≤c4≤0.1, 0≤d4≤0.1,

[0058] The general formula for the composition of the second kernel includes Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 , 0.8≤m2≤1.2, x2≥0, y2>0, 0.9≤x2+y2≤1, 0.95≤z2≤1.1, 3.5≤n2≤4, 0≤a2≤0.1, 0≤b2≤0.1, 0≤c2≤0.1, 0≤d2≤0.1,

[0059] The general formula for the composition of the third kernel includes Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N3 d3 ,

[0060] 0.8≤m³≤1.2, x³≥0, y³≥0, 0.9≤x³+y³≤1, 0.95≤z³≤1.1, 3.5≤n³≤4, 0≤a³≤0.1, 0≤b³≤0.1, 0≤c³≤0.1, 0≤d³≤0.1

[0061] Among them, A1, A2, and A3 each independently include one or more of Al, Na, K, and Mg; M1, M2, and M3 each independently include one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q1, Q2, and Q3 each independently include one or more of B, S, Si, and N; and N1, N1, and N3 each independently include one or more of S, F, Cl, and Br.

[0062] In any embodiment, the compacted density of the positive electrode active material powder at a pressure of 29400 N is 2.25 g / cm³. 3 -2.60g / cm 3 .

[0063] In any embodiment, the specific capacity of the positive electrode active material at 40°C and 1 / 3C is 135mAh / g-150mAh / g.

[0064] In any embodiment, the positive electrode film layer further includes a binder and a conductive agent, wherein the mass ratio of the positive electrode active material, the binder and the conductive agent in the positive electrode film layer is (92-99):(0.5-3):(0.5-3).

[0065] In any embodiment, the areal density of the positive electrode sheet is 300 mg / 1540 mm². 2 -580mg / 1540mm 2 .

[0066] In any embodiment, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0067] The second aspect of this application provides a secondary battery prepared by the preparation method of the first aspect.

[0068] A third aspect of this application provides an electrical device comprising a secondary battery prepared by the method of the first aspect or a secondary battery of the second aspect. Attached Figure Description

[0069] Figure 1 is a schematic diagram of the statistical distinction rules of primary particles in the transmission electron microscope image of particles in this application;

[0070] Figure 2 is a schematic diagram of a secondary battery according to an embodiment of this application;

[0071] Figure 3 is an exploded view of the secondary battery according to an embodiment of this application shown in Figure 2;

[0072] Figure 4 is a schematic diagram of a battery module according to an embodiment of this application;

[0073] Figure 5 is a schematic diagram of a battery pack according to an embodiment of this application;

[0074] Figure 6 is an exploded view of the battery pack of one embodiment of this application shown in Figure 5;

[0075] Figure 7 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0076] Reference numerals: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0077] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, and the power-consuming device of this application. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0078] 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.

[0079] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0080] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0081] 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.

[0082] 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.

[0083] 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).

[0084] The cathode active material is one of the decisive factors in the performance of secondary batteries. Currently, common cathode active materials mainly include lithium cobalt oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, and lithium iron phosphate. Each of these materials has its advantages and disadvantages. For example, lithium cobalt oxide has high energy density and voltage plateau, but its cost is high and its safety is poor; lithium manganese oxide has lower cost and better safety, but its energy density and voltage plateau are lower; nickel-cobalt-manganese ternary materials combine the advantages of the former two, but their cost is still high. Lithium iron phosphate, on the other hand, has advantages such as low cost, high safety, and long lifespan, which can better meet the requirements of the new energy vehicle market for high safety and low cost of lithium-ion batteries. However, lithium iron phosphate also has some disadvantages, such as low compaction density and low discharge capacity, which limit its application in high-energy-density batteries. Lithium manganese iron phosphate, as a new material for the further development of lithium iron phosphate, combines the advantages of manganese and iron, and has two voltage plateaus at 4.1V and 3.4V respectively, which can provide a certain plateau capacity and is expected to improve the shortcomings of lithium iron phosphate materials. However, in current research and applications, lithium manganese iron phosphate (LFP) still suffers from low compaction density and has not yet demonstrated the potential advantage of high energy density. Furthermore, the trivalent manganese ions in LFP exhibit the Jan Taylor effect, transforming into tetravalent manganese ions. These highly reactive tetravalent manganese ions readily react with the electrolyte to become divalent manganese ions. These divalent manganese ions further dissolve in the electrolyte and are reduced and precipitated at the negative electrode, damaging the SEI film. This results in more active lithium being consumed during SEI film repair, thus affecting the battery's cycle life. Therefore, how to improve the compaction density of LFP to obtain high-energy-density batteries while simultaneously maintaining good cycle performance has become a key research focus.

[0085] [Preparation methods for secondary batteries]

[0086] Based on this, this application provides a method for preparing a secondary battery, comprising the following steps:

[0087] 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.

[0088] The first lithium-containing transition metal phosphate material comprises a first core and a first carbon coating layer covering the outer surface of the first core, and the second lithium-containing transition metal phosphate material comprises a second core and a second carbon coating layer covering the outer surface of the second core.

[0089] The primary average particle size of the first lithium-containing transition metal phosphate material is smaller than that of the second lithium-containing transition metal phosphate material.

[0090] 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.

[0091] The primary average particle size of the first lithium-containing transition metal phosphate material is 50 nm to 200 nm.

[0092] The primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm-600 nm.

[0093] 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.

[0094] 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;

[0095] Preparation of secondary battery: Assemble the electrode assembly containing the positive electrode, negative electrode and electrolyte into a secondary battery.

[0096] 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.

[0097] In this paper, the term "primary particle size" refers to the particle size of a primary particle.

[0098] 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 1 is a schematic diagram of the statistical distinction rules for primary particles in a transmission electron microscope (TEM) image. 1-a is the original TEM image, 1-b is the software-recognized image, and 1-c are examples of software and / or manual identification of independent, adhered, and stacked particles in 1-a. Particles 1 and 2 are distinguishable independent particles, designated as primary particles 1 and 2, respectively. Particles 3 and 4 in 1-c are adhered; particles 5, 6, and 7 are also adhered, and after software or manual identification, they are identified as 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. 1-d is another example of software and / or manual identification of stacked particles in 1-a, where stacked particles 10-14 are ultimately identified as primary particles 10, 11, 12, 13, and 14, rather than classifying the entire stack 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.

[0099] 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.

[0100] In some embodiments, the primary average particle size of the first 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 between any two of the above values.

[0101] In some embodiments, the primary average particle size of the second lithium-containing transition metal phosphate material may be selected as 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, or any range between any two of the above values.

[0102] The positive electrode active material comprises two materials with different primary average particle sizes. This allows the particles of varying sizes to complement each other and fill gaps, resulting in a denser particle packing within the positive electrode active material. This increases the powder compaction density and electrode compaction density, thereby improving the battery's energy density. However, the first lithium-containing transition metal phosphate material has a smaller primary average particle size and a larger specific surface area. Its high surface activity makes it more susceptible to side reactions in the electrolyte, exacerbating manganese ion dissolution and affecting the battery's cycle performance. This application reduces the molar Mn content of the smaller-particle-size, higher-specific-surface-area first lithium-containing transition metal phosphate material compared to the second lithium-containing transition metal phosphate material. This reduces the likelihood of manganese dissolution during cycling in the highly reactive first lithium-containing transition metal phosphate material. This not only improves the powder compaction density and battery energy density but also enhances the material's cycle stability and overall battery cycle performance.

[0103] 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.

[0104] 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 between any two of the above values.

[0105] 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 electrolytes and the degree of manganese dissolution can be further reduced, thereby further improving the cycle performance and storage performance of the battery. The battery is more suitable for application scenarios with high requirements for cycle life and / or storage life.

[0106] 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.

[0107] In some embodiments, the molar ratio of Mn in the first lithium-containing transition metal phosphate material can be selected as 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 between any two of the above values.

[0108] 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 allowing the highly conductive small-particle-size materials to fully utilize their specific capacity. This results in excellent cycle performance of the battery and further increases its energy density, making the battery more suitable for scenarios with certain energy density requirements.

[0109] 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.

[0110] In some embodiments, the molar ratio of Mn in the first lithium-containing transition metal phosphate material can be selected as 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range between any two of the above values.

[0111] 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 allowing the highly conductive small-particle-size materials to fully utilize their specific capacity. This results in excellent cycle performance of the battery and further increases its energy density, making the battery more suitable for scenarios with high energy density requirements.

[0112] 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.

[0113] 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 between any two of the above values.

[0114] 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.

[0115] 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 greater than 0% and less than or equal to 20%, and can be selected as 5%-20%. 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 can be selected as 1%, 3%, 5%, 10%, 15%, 20%, or any range between any two of the above values.

[0116] In some embodiments, based on the total weight of the positive electrode active material, the weight percentage of the second lithium transition metal phosphate material is greater than or equal to 80% and less than 100%, and can be selected as 80%-95%. In some embodiments, based on the total weight of the positive electrode active material, the weight percentage of the second lithium transition metal phosphate material can be selected as 80%, 85%, 90%, 95%, 97%, 99%, or a range between any two of the above values.

[0117] By controlling the mass ratio of materials with different particle sizes within a suitable range, the contribution of the high-manganese content second lithium-containing transition metal phosphate material to the energy density in terms of voltage rating and specific capacity can be achieved. At the same time, the impact of the small-particle-size first lithium-containing transition metal phosphate material on the battery's cycle performance can be reduced. In addition, by keeping the mass content of the other two materials within a suitable range, the molar ratio of Mn in the positive electrode active material can be kept within a suitable range, thereby improving the battery's energy density and cycle performance.

[0118] In some embodiments, the step of preparing the positive electrode active material includes:

[0119] 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 are mixed to obtain the positive electrode active material.

[0120] The third lithium-containing transition metal phosphate material comprises a third core and a third carbon coating layer covering the outer surface of the third core.

[0121] The primary average particle size of the third lithium-containing transition metal phosphate material is greater than that of the second lithium-containing transition metal phosphate material.

[0122] 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.

[0123] The primary average particle size of the third lithium-containing transition metal phosphate material is 250 nm to 4000 nm.

[0124] In some embodiments, the primary average particle size of the third lithium-containing transition metal phosphate material is selected as 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1200 nm, 1300 nm, 1500 nm, 2000 nm, 2500 nm, 3000 nm, 3500 nm, 4000 nm, or a range between any two of the above values.

[0125] 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.

[0126] Compared to the first and second lithium-containing transition metal phosphate materials, the third lithium-containing transition metal phosphate material has a larger primary average particle size. During cycling or storage, the third lithium-containing transition metal phosphate material is less likely to undergo side reactions with the electrolyte or experience manganese dissolution. The inclusion of the third lithium-containing transition metal phosphate material, which has excellent cycle stability and storage stability, in the positive electrode active material can further improve the cycle stability and storage stability of the positive electrode active material, thereby enhancing the cycle performance and storage performance of the battery. Meanwhile, the third lithium-containing transition metal phosphate material with a larger primary average particle size has a high powder compaction density, which can further improve the compaction density of the material and the electrode. At the same time, the positive electrode film layer contains a variety of materials with different primary particle sizes, which can form a large, medium and small particle size distribution system. The filling between the materials is more compact, which can further improve the powder compaction density of the material and the compaction density of the electrode, which is conducive to obtaining a high energy density battery. In addition, by controlling the Mn molar ratio of the third lithium-containing transition metal phosphate material with a relatively large primary average particle size to be less than the Mn molar ratio of the second lithium-containing transition metal phosphate material with a relatively small primary average particle size, this application can improve the conductivity of the third lithium-containing transition metal phosphate material with a relatively large primary average particle size, alleviate the discharge polarization of the third lithium-containing transition metal phosphate material, and facilitate the utilization of the material's specific capacity and kinetic performance, thereby achieving the goal of improving the battery's energy density.

[0127] 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, more preferably 0-0.1, and even more preferably 0.

[0128] 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, 0.007, 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 between any two of the above values.

[0129] Controlling the molar ratio of Mn in the third lithium-containing transition metal phosphate material within a suitable range can improve the cycle stability of the third lithium-containing transition metal phosphate material and increase the cycle life of the battery.

[0130] In some embodiments, the molar ratio 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.

[0131] In some embodiments, the molar ratio of Mn in the third lithium-containing transition metal phosphate material can be selected as 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 between any two of the above values.

[0132] 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, while also enabling the third lithium-containing transition metal phosphate material to have a certain plateau capacity, thereby increasing the energy density of the battery.

[0133] 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.

[0134] In some embodiments, the molar ratio of Mn in the third lithium-containing transition metal phosphate material can be selected as 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range between any two of the above values.

[0135] 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, while also enabling the third lithium-containing transition metal phosphate material to have a relatively high plateau voltage and plateau capacity, thereby further improving the energy density of the battery.

[0136] In some embodiments, the weight percentage of the first lithium-containing transition metal phosphate material is 1%-10% based on the total weight of the lithium-containing transition metal phosphate material.

[0137] 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 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two of the above values.

[0138] In some embodiments, the weight percentage of the second lithium-containing transition metal phosphate material is 60%-90% based on the total weight of the lithium-containing transition metal phosphate material.

[0139] 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 between any two of the above values.

[0140] In some embodiments, the third lithium-containing transition metal phosphate material accounts for 5%-30% of the total weight of the lithium-containing transition metal phosphate material.

[0141] In some embodiments, the weight percentage of the third lithium-containing transition metal phosphate material may be selected as 5%, 10%, 15%, 20%, 25%, 30%, or any range between any two of the above values, based on the total weight of the lithium-containing transition metal phosphate material.

[0142] Controlling the mass ratio of materials with different particle sizes within a suitable range is beneficial for achieving the goal of increasing the contribution of the high-manganese content second lithium-containing transition metal phosphate material to the energy density through its voltage rating and specific capacity. Simultaneously, it reduces the impact of the large-particle-size third lithium-containing transition metal phosphate material on the specific capacity and rate performance of the battery, and reduces the impact of the small-particle-size first lithium-containing transition metal phosphate material on the battery's cycle performance. Furthermore, maintaining the appropriate mass ratio of the three materials within a suitable range also ensures that the molar ratio of Mn in the positive electrode active material is within a suitable range, which is beneficial for obtaining a battery with high energy density, excellent rate performance, and good cycle performance.

[0143] In some embodiments, the third lithium-containing transition metal phosphate material satisfies the following relationship:

[0144] 1.5≤A / B≤10

[0145] Where A is the specific surface area of ​​the third lithium-containing transition metal phosphate material; B% is the mass content of the third carbon coating layer in the third lithium-containing transition metal phosphate material.

[0146] In some implementations, A / B can be selected as 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 between any two of the above values.

[0147] The mass content of the carbon coating layer of a material can be determined by methods and equipment known in the art, for example as follows: the carbon content is tested by infrared absorption method after the material is burned in a high-frequency induction furnace, and the specific testing procedure is in accordance with the standard GB / T 20123-2006 / ISO 15350:2000.

[0148] The specific surface area of ​​a material can be determined using methods and equipment known in the art, as exemplified below: The specific surface area is tested using the gas adsorption method, according to the GB / T19587-2017 testing standard. Specifically, the material is taken as a sample, and the sample tube is immersed in liquid nitrogen at -196℃. 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 amount of monolayer adsorption of the sample is calculated, thereby determining the specific surface area of ​​the material.

[0149] The ratio A / B, which is the specific surface area A of the material to the mass content B% of the third carbon coating layer in the third lithium-containing transition metal phosphate material, can characterize the uniformity and density of the carbon coating layer. A high degree of uniformity and density of the carbon coating layer is beneficial to improving the conductivity and specific capacity of the material. At the same time, it avoids the carbon coating layer being too dense, which would affect the insertion and extraction of active ions and thus affect the specific capacity of the material. This provides a material basis for the preparation of high energy density and high rate batteries.

[0150] In some embodiments, the specific surface area of ​​the third lithium-containing transition metal phosphate material is 3 m². 2 / g-13m 2 / g. In some embodiments, the specific surface area of ​​the third lithium-containing transition metal phosphate material may be selected as 3m². 2 / g, 3.5m2 / 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 the range between any two of the above values.

[0151] The third lithium-containing transition metal phosphate material has a specific surface area within a suitable range, and the material has a relatively high specific capacity. At the same time, it avoids the high water absorption caused by an excessively large specific surface area, which may affect the processing performance of the cathode slurry. This balances the material's performance in both use and processing.

[0152] In some embodiments, the mass content of the third carbon coating layer is 0.8%-2.0% based on the mass of the third lithium transition metal phosphate material. In some embodiments, the mass content of the third carbon coating layer may be selected from 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, or any range between any two of the above values, based on the mass of the third lithium transition metal phosphate material.

[0153] When the carbon content of the material's coating layer is within a suitable range, it can improve the material's conductivity and facilitate the formation of a complete and dense coating layer, reducing the possibility of side reactions on the material surface and improving the material's cycle stability and conductivity. On the other hand, it can also prevent excessive carbon content from affecting the material's specific capacity and avoid the impact of floating carbon caused by excessive carbon content on the material's processing performance.

[0154] In some embodiments, the Dv10 of the third lithium-containing transition metal phosphate material is 0.2 μm-2 μm. In some embodiments, the Dv10 of the third lithium-containing transition metal phosphate material may be selected as 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, or any range between two of the above values.

[0155] In some embodiments, the Dv50 of the third lithium-containing transition metal phosphate material is 0.5 μm-5 μm. In some embodiments, the Dv50 of the third lithium-containing transition metal phosphate material can be selected as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range between any two of the above values.

[0156] In some embodiments, the Dv90 of the third lithium-containing transition metal phosphate material is 1.5 μm-10 μm. In some embodiments, the Dv90 of the third lithium-containing transition metal phosphate material can be selected as 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range between any two of the above values.

[0157] In some embodiments, the Dv99 of the third lithium-containing transition metal phosphate material is 2 μm-12 μm. In some embodiments, the Dv99 of the third lithium-containing transition metal phosphate material can be selected as 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or a range between any two of the above values.

[0158] In this paper, the term "Dv10" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 10%.

[0159] In this paper, the term "Dv50" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 10%.

[0160] In this paper, the term "Dv90" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 90%.

[0161] In this paper, the term "Dv99" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 99%.

[0162] 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.

[0163] The third lithium-containing transition metal phosphate material has good conductivity and high specific capacity when the particle size parameters are within a suitable range, which is beneficial for the preparation of batteries with high energy density and high rate.

[0164] In some embodiments, the third 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 .

[0165] In some embodiments, the powder compaction density of the third 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.

[0166] 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.

[0167] The third 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.

[0168] In some embodiments, the powder resistivity of the third lithium-containing transition metal phosphate material is from 0 Ω·cm to 59 Ω·cm.

[0169] In some embodiments, the powder resistivity of the third 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.

[0170] 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.

[0171] The third lithium-containing transition metal phosphate material has low powder resistivity, which makes the material have excellent conductivity. This is beneficial to 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.

[0172] This application also provides a method for preparing a third lithium-containing transition metal phosphate material, wherein the third lithium-containing transition metal phosphate material is lithium iron phosphate, specifically as follows: providing raw materials containing at least a lithium source, an iron source, a phosphorus source, optionally a carbon film-forming agent, optionally a carbon source, and optionally a modifier, and performing at least two sintering processes, wherein...

[0173] The temperature for the first sintering is 500℃-760℃, and can be selected as 550℃-720℃;

[0174] The temperature for the second sintering is 700℃-800℃, and can be selected as 720℃-780℃.

[0175] 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.

[0176] In some embodiments, the heating rates for the first and second sintering are each independently 2°C / min to 20°C / min.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] Compared to traditional methods that use high temperatures to grow particles, the third 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 third 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 third 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.

[0181] In some embodiments, the third lithium-containing transition metal phosphate material is mainly obtained by the following preparation methods:

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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 third 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 third lithium-containing transition metal phosphate material particles, facilitating the crystallization growth of the third 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 third lithium-containing transition metal phosphate material, thereby enabling 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 third 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 third lithium-containing transition metal phosphate material particles, and enhancing their kinetic properties and specific capacity.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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).

[0197] 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.

[0198] By using raw materials in the above proportions, it is beneficial to form the third lithium-containing transition metal phosphate material of this application.

[0199] In some embodiments, the preparation method of the third lithium-containing transition metal phosphate material includes the following steps:

[0200] After the first sintering, a first pulverization is performed; after the second sintering, a second pulverization is performed.

[0201] The Dv50 of the product after the first pulverization is 300nm-1200nm, and can be selected as 400nm-1100nm;

[0202] The Dv50 of the product after the second pulverization is 500nm-5000nm, and can be selected as 700nm-2500nm.

[0203] 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%.

[0204] 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.

[0205] 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.

[0206] In some embodiments, the pulverization includes one or more of mechanical crushing, grinding, sand milling, and air jet milling.

[0207] 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.

[0208] 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 potentially added modifying elements on the precursor crystal of the third lithium-containing transition metal phosphate material, thus facilitating the preparation of micron-sized precursors of the third 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 third lithium-containing transition metal phosphate material with the average particle size of the first pulverization step as described in this application.

[0209] In some implementations, the general formula for the first kernel includes Li m1 A1 a1 Fe x1 Mn y1 M4 b1 P z1 Q1 c1 O n1 N4 d1 ,

[0210] Where 0.8≤m1≤1.2, x1≥0, y1≥0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n4≤4, 0≤a4≤0.1, 0≤b4≤0.1, 0≤c4≤0.1, 0≤d4≤0.1,

[0211] The general formula for the composition of the second kernel includes Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 , 0.8≤m2≤1.2, x2≥0, y2>0, 0.9≤x2+y2≤1, 0.95≤z2≤1.1, 3.5≤n2≤4, 0≤a2≤0.1, 0≤b2≤0.1, 0≤c2≤0.1, 0≤d2≤0.1,

[0212] The general formula for the composition of the third kernel includes Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 On3 N3 d3 ,

[0213] 0.8≤m³≤1.2, x³≥0, y³≥0, 0.9≤x³+y³≤1, 0.95≤z³≤1.1, 3.5≤n³≤4, 0≤a³≤0.1, 0≤b³≤0.1, 0≤c³≤0.1, 0≤d³≤0.1

[0214] Among them, A1, A2, and A3 each independently include one or more of Al, Na, K, and Mg; M1, M2, and M3 each independently include one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q1, Q2, and Q3 each independently include one or more of B, S, Si, and N; and N1, N1, and N3 each independently include one or more of S, F, Cl, and Br.

[0215] In some implementations, m1, m2 and m3 can each independently be 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, 1.17, 1.2, or a value within a range of any two of the above values.

[0216] In some implementations, x1+y1, x2+y2, and x3+y3 can each independently be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or a value within a range consisting of any two of the above values.

[0217] In some implementations, z1, z2, or z3 can each independently be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, or a value within a range of any two of the above values.

[0218] In some implementations, n1, n2, and n3 can each independently be 3.5, 3.6, 3.7, 3.8, 3.9, 4, or a value within a range consisting of any two of the above values.

[0219] In some implementations, a1, b1, c1, d1, a2, b2, c2, d2, a3, b3, c3, and d3 can each independently be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within a range of any two of the above values.

[0220] Selecting appropriate doping elements M1, M2, and M3 can improve the lattice change rate of the material during lithium insertion / extraction, enhance the structural stability of the material, reduce manganese dissolution, and decrease oxygen activity on the particle surface. This can improve the specific capacity of the material, reduce interfacial side reactions between the material and the electrolyte during use, and thus enhance the cycle performance of the material and the battery.

[0221] Choosing appropriate doping elements Q1, Q2, and Q3 can help change the ease with which the Mn-O bond length changes, thereby improving electronic conductivity, reducing the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance of secondary batteries.

[0222] Selecting appropriate element doping with Al, A2, and A3 can also improve the lattice change rate of the material and maintain its battery capacity.

[0223] Doping with elements N1, N2, and N3 can help improve interfacial side reactions between the material and the electrolyte, reduce interfacial activity, and thus improve the cycle performance of the positive electrode active material. Furthermore, doping at the O sites can enhance the material's resistance to acid corrosion such as HF, thereby improving cycle performance and lifespan, and extending battery life.

[0224] In some embodiments, the compacted density of the positive electrode active material at a pressure of 29400 N is 2.25 g / cm³. 3 -2.65g / cm 3 .

[0225] The compaction density of positive electrode active material powder under 29400N pressure can be determined using methods and equipment known in the art, as exemplified below: Referring to GB / T 24533-2009, the compaction density is measured using a compaction density instrument. Specifically, a certain amount of sample powder is placed on a compaction mold (mold diameter 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 a 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 compaction density of the material 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; manufacturer: Sansi Zongheng.

[0226] In some embodiments, the compacted density of the positive electrode active material at a pressure of 29400 N is 2.25 g / cm³. 3 2.30g / cm 3 2.31 g / cm 3 2.32 g / cm 32.33 g / cm 3 2.34 g / cm 3 2.35g / cm 3 2.36 g / cm 3 2.37 g / cm 3 2.38g / cm 3 2.39 g / cm 3 2.40 g / cm 3 2.41 g / cm 3 2.42 g / cm 3 2.43 g / cm 3 2.44 g / cm 3 2.45g / cm 3 2.46 g / cm 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.50g / cm 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 3 2.54 g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 2.60g / cm 3 2.61 g / cm 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 , or the range between any two of the above values.

[0227] In some embodiments, the specific capacity of the positive electrode active material at 40°C and 1 / 3C is 135mAh / g-150mAh / g. In some embodiments, the specific capacity of the positive electrode active material at 40°C and 1 / 3C can be selected as 135mAh / g, 140mAh / g, 145mAh / g, 150mAh / g, or a range between any two of the above values.

[0228] The specific capacity of the positive electrode active material at 40°C and 1 / 3C can be determined using methods and equipment known in the art, as exemplified below: The battery is placed in a 40°C oven and left to stand for 2 hours to maintain the battery temperature at 40°C; then the battery is discharged at a constant current of 1 / 3C to 2.0V; left to stand for 5 minutes; the battery is then charged at a constant current of 1 / 3C to 4.1V, followed by constant voltage charging at 4.1V until the cutoff current is 0.05C; left to stand for 5 minutes; and finally discharged at a constant current of 1 / 3C to 2.0V to obtain the discharge capacity C of the battery. The specific capacity of the positive electrode active material at 40°C and 1 / 3C = the discharge capacity C of the battery / the mass M of the positive electrode active material.

[0229] [Preparation of positive electrode sheet]

[0230] 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.

[0231] In some embodiments, the positive electrode slurry further includes a binder and a conductive agent.

[0232] In some embodiments, the mass ratio of positive electrode active material, binder and conductive agent in the positive electrode slurry is (92-99):(0.5-3):(0.5-3).

[0233] In some embodiments, the adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0234] In some embodiments, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0235] 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.).

[0236] 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.

[0237] [Positive electrode plate]

[0238] 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.

[0239] 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.

[0240] In some embodiments, the areal density of the positive electrode sheet on one side is 300 mg / 1540 mm². 2 -580mg / 1540mm 2 .

[0241] In some embodiments, the areal density of the positive electrode sheet on one side is 300 mg / 1540 mm². 2 340mg / 1540mm 2 380mg / 1540mm 2 420mg / 1540mm 2 460mg / 1540mm 2 500mg / 1540mm 2 540mg / 1540mm 2 580mg / 1540mm 2 , or the range between any two of the above values.

[0242] The areal density of the positive electrode sheet can be tested using methods known in the art. An example is shown below: the positive electrode sheet is cut into pieces with an area of ​​1540 mm². 2 The small circular sheet is weighed as M. Then, the positive electrode film layer of the weighed electrode sheet is wiped off, and the weight of the current collector is weighed and recorded as N. Then, the weight of the single-sided coating is (MN) / 2.

[0243] In some embodiments, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0244] The "compacted density of the positive electrode sheet" mentioned in this application refers to the "limited compacted density" of the positive electrode sheet, and its test method is as follows:

[0245] 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.

[0246] 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.

[0247] The compaction density of the positive electrode sheet is calculated as the weight of a single positive electrode sheet divided by the volume of a single positive electrode sheet.

[0248] In some embodiments, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 2.35g / cm 3 2.45g / cm 3 2.55g / cm 3 2.65g / cm 3 2.75g / cm 3 Or any value in between.

[0249] When the compaction density of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0250] [Negative electrode plate]

[0251] 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.

[0252] 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.

[0253] 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.).

[0254] 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.

[0255] 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).

[0256] 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.

[0257] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0258] 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.

[0259] [Electrolytes]

[0260] 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.

[0261] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0262] 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.

[0263] 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.

[0264] [Isolation membrane]

[0265] The separator used in this application is the separator described above. Furthermore, the separator used in this application can be used in combination with other separators commonly used in the art, as needed.

[0266] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0267] 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.

[0268] 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.

[0269] [Rechargeable Battery]

[0270] In one embodiment of this application, a secondary battery is provided, including a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the binder in the active material layer of the positive electrode includes polymers according to any embodiment of this application.

[0271] In some embodiments, the secondary battery is a lithium-ion battery or a sodium-ion battery. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. A separator is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0272] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0273] 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.

[0274] 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.

[0275] 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 2 shows a square-structured secondary battery 5 as an example.

[0276] In some embodiments, referring to FIG3, 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. The positive electrode, negative electrode, and separator may 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.

[0277] 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.

[0278] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, 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.

[0279] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0280] 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.

[0281] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, 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.

[0282] 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 the power source of the electrical device or as the energy storage unit of 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.

[0283] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0284] Figure 7 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.

[0285] 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.

[0286] Example

[0287] 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.

[0288] The performance parameters of the first lithium-containing transition metal phosphate material are shown in Table 1.

[0289] Table 1

[0290] The performance parameters of the second lithium-containing transition metal phosphate material are shown in Table 2.

[0291] Table 2

[0292] The performance parameters of the third lithium-containing transition metal phosphate material are shown in Table 3.

[0293] Table 3

[0294] I. Preparation Method

[0295] Example 1

[0296] (1) Preparation of the positive electrode sheet:

[0297] The first lithium-containing transition metal phosphate material A1 and the second lithium-containing transition metal phosphate material B1 are mixed at a mass ratio of 15%:85% to obtain a positive electrode active material. The above-mentioned mixed positive electrode active material, conductive agent conductive carbon black, and binder polyvinylidene fluoride are mixed at a weight percentage of 96:1.5:2.5 and N-methylpyrrolidone is added. After thorough mixing, stirring, and dispersion, a positive electrode slurry is prepared.

[0298] 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 substrate aluminum foil, and then dried, cold-pressed, slit, and sheeted to finally obtain the positive electrode sheet.

[0299] (2) Preparation of negative electrode sheet:

[0300] 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 copper foil substrate, drying, cold pressing, slitting, and sheet forming.

[0301] (3) Diaphragm

[0302] Polypropylene film is used as the separator.

[0303] (4) Electrolyte

[0304] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) were mixed evenly in a volume ratio of 1:1:1:1. LiPF6 was then added and dissolved in the organic solvent and stirred evenly to achieve an electrolyte concentration of 1 mol / L, thus obtaining the electrolyte of Example 1.

[0305] (5) Battery fabrication:

[0306] 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.

[0307] Examples 2-11 and Comparative Examples 1-2 are prepared in a similar manner to Example 1, except that the types or mass contents of the first lithium-containing transition metal phosphate material, the second lithium-containing transition metal phosphate material and / or the third lithium-containing transition metal phosphate material in the positive electrode active material are adjusted, as shown in Table 4.

[0308] II. Testing Methods

[0309] 1. Number of high-temperature cycles of the battery

[0310] 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.

[0311] 2. Volumetric energy density of the battery

[0312] 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.

[0313] 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).

[0314] 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.

[0315] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0316] Secondary batteries for each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in the table below.

[0317] Table 4

[0318] As shown in the table above, the preparation method of the secondary battery in Examples 1-11 of this application includes the following method for preparing the positive electrode active material: mixing a first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material to obtain the positive electrode active material. The first lithium-containing transition metal phosphate material includes a first core and a first carbon coating layer covering the outer surface of the first core. The second lithium-containing transition metal phosphate material includes a second core and a second carbon coating layer covering the outer surface of the second core. The primary average particle size of the first lithium-containing transition metal phosphate material is smaller than that of the second lithium-containing transition metal phosphate material. The molar ratio of Mn in the first lithium-containing transition metal phosphate material is smaller than that in the second lithium-containing transition metal phosphate material. The primary average particle size of the first lithium-containing transition metal phosphate material is 50 nm-200 nm, and the primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm-600 nm.

[0319] As can be seen from the comparison between Examples 1-11 and Comparative Example 1, compared with the positive electrode active material containing only a single second lithium-containing transition metal phosphate material, the positive electrode active material of this application contains a first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material, which can improve the powder compaction density of the positive electrode active material and improve the energy density and cycle number of the battery.

[0320] As can be seen from the comparison between Examples 1-11 and Comparative Example 2, controlling the molar ratio of Mn in the first lithium-containing transition metal phosphate material to be less than that in the second lithium-containing transition metal phosphate material can improve the specific capacity of the positive electrode active material, increase the energy density of the battery, increase the cycle number of the battery, and extend the battery's service life.

[0321] As shown in Examples 1-2, controlling the molar ratio of Mn in the first lithium-containing transition metal phosphate material to be 0-0.6 results in a positive electrode active material with high powder compaction density and specific capacity, leading to a battery with high energy density and long cycle life. A comparison between Examples 1 and 2 shows that controlling the molar ratio of Mn in the first lithium-containing transition metal phosphate material to 0 can further increase the number of battery cycles and improve the battery's cycle performance.

[0322] As can be seen from the comparison between Example 2 and Example 1, controlling the molar ratio of Mn in the first lithium-containing transition metal phosphate material to be 0.2-0.6 can improve the volumetric energy density of the battery.

[0323] As can be seen from Examples 1 and 3, the Mn molar ratio of the second lithium-containing transition metal phosphate material is 0.4-0.9, the positive electrode active material has high powder compaction density and specific capacity, and the battery has high energy density and long cycle life.

[0324] As shown in Examples 1 and 4-5, the first lithium-containing transition metal phosphate material has a primary average particle size of 50nm-200nm, and the positive electrode active material has high powder compaction density and specific capacity, resulting in a battery with high energy density and long cycle life. As shown in Examples 1 and 6-7, the second lithium-containing transition metal phosphate material has a primary average particle size of 120nm-600nm, and the positive electrode active material has high powder compaction density and specific capacity, resulting in a battery with high energy density and long cycle life.

[0325] As can be seen from Examples 1 and 8-9, based on the mass of the positive electrode active material, the weight percentage of the first lithium transition metal phosphate material is greater than 0% and less than or equal to 20%, and the weight percentage of the second lithium transition metal phosphate material is greater than or equal to 80% and less than 100%. This results in a positive electrode active material with high powder compaction density and specific capacity, and a battery with high energy density and long cycle life. Comparing Examples 1 and 8 with Example 9, it is evident that, based on the mass of the positive electrode active material, a weight percentage of 5%-20% for the first lithium transition metal phosphate material and a weight percentage of 80%-95% for the second lithium transition metal phosphate material can further improve the powder compaction density and specific capacity of the positive electrode active material, thereby increasing the battery's energy density and cycle life.

[0326] The steps for preparing the positive electrode active material in Examples 10-11 include: mixing a first lithium-containing transition metal phosphate material, a second lithium-containing transition metal phosphate material, and a third lithium-containing transition metal phosphate material to obtain a positive electrode active material. The third lithium-containing transition metal phosphate material includes a third core and a third carbon coating layer covering the outer surface of the third core. The primary average particle size of the third lithium-containing transition metal phosphate material is larger than that of the second lithium-containing transition metal phosphate material. The molar percentage of Mn in the third lithium-containing transition metal phosphate material is smaller than that in the second lithium-containing transition metal phosphate material. The primary average particle size of the third lithium-containing transition metal phosphate material is 250 nm-4000 nm.

[0327] As can be seen from the comparison between Examples 10-11 and Example 1, the positive electrode active material also includes a third lithium-containing transition metal phosphate material, which can further improve the powder compaction density of the positive electrode active material, improve the energy density of the battery, and extend the cycle life of the battery.

[0328] As can be seen from Examples 10 and 11, controlling the Mn molar ratio of the third lithium-containing transition metal phosphate material to 0-0.1 can further increase the number of battery cycles and improve the battery's cycle performance.

[0329] A comparison of Example 11 and Example 10 shows that controlling the Mn molar ratio of the third lithium-containing transition metal phosphate material to 0.2-0.6 can improve the energy density of the battery.

[0330] 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 secondary battery, characterized by, The method comprises the following steps: Preparation of 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, wherein the first lithium-containing transition metal phosphate material comprises a first inner core and a first carbon coating layer coated on the outer surface of the first inner core, and the second lithium-containing transition metal phosphate material comprises a second inner core and a second carbon coating layer coated on the outer surface of the second inner core, the primary average particle size of the first lithium-containing transition metal phosphate material is smaller than the primary average particle size of the second lithium-containing transition metal phosphate material, the Mn molar ratio of the first lithium-containing transition metal phosphate material is smaller than the Mn molar ratio of the second lithium-containing transition metal phosphate material, wherein the primary average particle size of the first lithium-containing transition metal phosphate material is 50 nm-200 nm, the primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm-600 nm, the Mn molar ratio refers to the proportion of the number of moles of Mn to the total number of moles of Mn and Fe, Preparation of a positive electrode plate: 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 plate; Preparation of a secondary battery: assembling an electrode assembly containing the positive electrode plate, a negative electrode plate, and an electrolyte into a secondary battery.

2. The production method according to claim 1, characterized by, 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.

3. The preparation method according to claim 1, characterized in that, 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.

4. The method of claim 1, 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.

5. The production method according to any one of claims 1 to 4, characterized by, The Mn molar ratio of the second lithium-containing transition metal phosphate material is 0.4-0.9, optionally 0.5-0.

9.

6. The production method according to any one of claims 1 to 5, characterized by, The weight percentage of the first lithium-containing transition metal phosphate material is greater than 0% and less than or equal to 20%, optionally 5%-20%, based on the total weight of the positive electrode active material; and / or, the weight percentage of the second lithium-containing transition metal phosphate material is greater than or equal to 80% and less than 100%, optionally 80%-95%.

7. The production method according to any one of claims 1 to 5, characterized by, 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, wherein the third lithium-containing transition metal phosphate material comprises a third inner core and a third carbon coating layer coated on the outer surface of the third inner core, the primary average particle size of the third lithium-containing transition metal phosphate material is greater than the primary average particle size of the second lithium-containing transition metal phosphate material, the Mn molar ratio of the third lithium-containing transition metal phosphate material is smaller than the Mn molar ratio of the second lithium-containing transition metal phosphate material, The first lithium-containing transition metal phosphate material has a primary average particle size of 250 nm-4000 nm.

8. The preparation method according to claim 7, characterized in that, The Mn molar percentage of the third lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.5, more optionally 0-0.1, and further optionally 0.

9. The preparation method according to claim 7, characterized in that, The Mn molar percentage of the third lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.5, more optionally 0.02-0.1, and further optionally 0.

02.

10. The preparation method according to claim 7, characterized in that, The Mn molar percentage of the third lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.5, and more optionally 0.

2.

11. The production method according to any one of claims 7 to 10, characterized by, The weight percentage of the first lithium-containing transition metal phosphate material is 1%-10%, and / or the weight percentage of the second lithium-containing transition metal phosphate material is 60%-90%, and / or the weight percentage of the third lithium-containing transition metal phosphate material is 5%-30%, based on the total weight of the lithium-containing transition metal phosphate material.

12. The production method according to any one of claims 7 to 11, characterized by, The third lithium-containing transition metal phosphate material satisfies the following relationship: 1.5≤A / B≤10, A is the specific surface area of the third lithium-containing transition metal phosphate material; and B% is the mass content of the third carbon coating layer in the third lithium-containing transition metal phosphate material.

13. The production method according to any one of claims 7 to 12, characterized by, The third lithium-containing transition metal phosphate material has a specific surface area of 3 m 2 / g-13 m 2 / g.

14. The production method according to any one of claims 7 to 13, characterized by, The mass content of the third carbon coating layer is 0.8%-2.0%, based on the mass of the third lithium-containing transition metal phosphate material.

15. The production method according to any one of claims 7 to 14, characterized by, The third lithium-containing transition metal phosphate material satisfies at least one of (a1)-(f1): (a1) the Dv10 of the third lithium-containing transition metal phosphate material is 0.2 μm-2 μm; (b1) the Dv50 of the third lithium-containing transition metal phosphate material is 0.5 μm-5 μm; (c1) the Dv90 of the third lithium-containing transition metal phosphate material is 1.5 μm-10 μm; (d1) the Dv99 of the third lithium-containing transition metal phosphate material is 2 μm-12 μm; (e1 ) the powder compaction density of the third lithium-containing transition metal phosphate material at 29400 N pressure is 2.25 g / cm3 3 - 2.60 g / cm3 3 ; (f1) the powder resistivity of the third lithium-containing transition metal phosphate material is 0 Ω·cm-59 Ω·cm.

16. The production method according to any one of claims 7 to 15, characterized by, The general formula of the first inner core comprises Li m1 A1 a1 Fe x1 Mn y1 M4 b1 P z1 Q1 c1 O n1 N4 d1 , 0.8≤m1≤1.2, x1≥0, y1≥0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n4≤4, 0≤a4≤0.1, 0≤b4≤0.1, 0≤c4≤0.1, 0≤d4≤0.1, The general formula of the second core comprises Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 , 0.8≤m2≤1.2, x2≥0, y2>0, 0.9≤x2+y2≤1, 0.95≤z2≤1.1, 3.5≤n2≤4, 0≤a2≤0.1, 0≤b2≤0.1, 0≤c2≤0.1, 0≤d2≤0.1, The general formula of the third core comprises Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N3 d3 , 0.8≤m3≤1.2, x3≥0, y3≥0, 0.9≤x3+y3≤1, 0.95≤z3≤1.1, 3.5≤n3≤4, 0≤a3≤0.1, 0≤b3≤0.1, 0≤c3≤0.1, 0≤d3≤0.1, A1, A2, A3 each independently include one or more of Al, Na, K, Mg, M1, M2, M3 each independently include one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1, Q2, Q3 each independently include one or more of B, S, Si, N, N1, N1, N3 each independently include one or more of S, F, Cl, Br.

17. The production method according to any one of claims 1 to 16, characterized by, The powder compaction density of the positive electrode active material under 29400N pressure is 2.25g / cm 3 - 2.60g / cm 3 .

18. The production method according to any one of claims 1 to 17, characterized by, The positive electrode active material has a specific capacity of 135 mAh / g-150 mAh / g at 40℃, 1 / 3C.

19. The production method according to any one of claims 1 to 18, characterized by, The positive electrode slurry further includes a binder and a conductive agent, and the mass ratio of the positive electrode active material, the binder and the conductive agent in the positive electrode slurry is (92-99):(0.5-3):(0.5-3).

20. The production method according to any one of claims 1 to 19, characterized by, The single surface area density of the positive electrode tab is 300 mg / 1540 mm 2 - 580 mg / 1540 mm 2 .

21. The production method according to any one of claims 1 to 20, characterized by, The compacted density of the positive electrode plate is 2.25 g / cm 3 - 2.75 g / cm 3 .

22. A secondary battery prepared by the preparation method of any one of claims 1 to 21.

23. An electrical device, comprising: A secondary battery prepared by the preparation method of any one of claims 1 to 21 or the secondary battery of claim 22.

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