Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector; and the positive electrode film layer comprises lithium-containing transition metal phosphate particles having different manganese-iron molar ratios, and on the basis of the total number of moles of Mn in the lithium-containing transition metal phosphate particles, the molar fraction of Mn contributed by the lithium-containing transition metal phosphate particles having a primary particle size less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 12% and greater than or equal to 0%. The secondary battery of the present application has both good powder compaction density and excellent storage performance.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application incorporates Chinese Patent Application No. 202411035249.6, filed on July 30, 2024, entitled “Secondary Battery 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 and an electrical device. Background Technology

[0004] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the increasing prevalence of rechargeable battery applications, higher requirements have been placed on their lifespan and other aspects.

[0005] Lithium manganese iron phosphate (LMP) is an emerging cathode material for lithium-ion batteries, which has the advantages of high voltage platform and theoretical energy density. However, it is difficult to balance compaction density and storage performance. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and an electrical device, wherein the secondary battery of this application has both excellent powder compaction density and storage performance.

[0007] The first aspect of this application provides a secondary battery, the secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive electrode film disposed on at least one side of the positive current collector; the positive electrode film comprises lithium-containing transition metal phosphate particles with different manganese-iron molar ratios, and based on the total molar number of Mn in the lithium-containing transition metal phosphate particles, the molar percentage of Mn in lithium-containing transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 12% and greater than or equal to 0%.

[0008] In the positive electrode sheet, lithium transition metal phosphate particles with a primary particle size of 180 nm or less and 50 nm or more can fill the gaps between the positive electrode active material particles, resulting in a tighter packing and improving the compaction density of the positive electrode sheet. Manganese ions have a higher redox potential than iron ions, giving lithium manganese iron phosphate a higher voltage plateau compared to lithium iron phosphate. However, due to the Jan Taylor effect, manganese ions are prone to side reactions with the electrolyte, leading to manganese dissolution. Lithium transition metal phosphate particles with a primary particle size of 180 nm or less and 50 nm or more have a larger specific surface area and significantly increased surface activity, making them more susceptible to contact with the electrolyte and causing side reactions, exacerbating manganese dissolution and thus affecting the battery's storage performance. The secondary battery of this application controls the percentage of manganese moles in lithium transition metal phosphate particles with primary particle sizes of 180 nm to 50 nm within a suitable range in the positive electrode sheet. This ensures that the percentage of manganese moles in these particles relative to the total manganese moles in the positive electrode film is within a suitable range. This reduces the rate of side reactions between these particles and the electrolyte, as well as the rate of manganese dissolution. Consequently, the battery exhibits better powder compaction density while improving storage performance.

[0009] In any embodiment, based on the total number of moles of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 8%.

[0010] In any embodiment, based on the total number of moles of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 6%.

[0011] Further optimization involves ensuring that the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is within a certain range, for example, less than or equal to 8%, and further, less than or equal to 6%. This allows the secondary battery of this application to have better powder compaction density and volumetric energy density, while also further improving the battery's storage performance.

[0012] In any embodiment, based on the total number of moles of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is greater than or equal to 0.02%.

[0013] In any embodiment, based on the total number of moles of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is greater than or equal to 0.2%.

[0014] Compared to primary lithium transition metal phosphate particles with a particle size of 180nm or less and 50nm or greater, which do not contain Mn, this product contains a certain amount of Mn, which helps to improve the voltage platform of the secondary battery while also having a certain specific capacity.

[0015] In any embodiment, the lithium-containing transition metal phosphate particles include P1 segment particles, M segment particles, and P2 segment particles. The primary particle size of the P1 segment particles is less than or equal to 180 nm and greater than or equal to 50 nm. The primary particle size of the M segment particles is greater than 180 nm and less than 900 nm. The primary particle size of the P2 segment particles is greater than or equal to 900 nm and less than or equal to 5 μm.

[0016] Wherein, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 1; and / or,

[0017] The ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 1.

[0018] Furthermore, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles, and the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles, are not both 1.

[0019] The secondary battery of this application features a suitable particle gradation design, where the combination of P1, M, and P2 segment particles is beneficial for further improving the compaction density of the positive electrode. Due to the crystal structure of manganese, lithium manganese iron phosphate has lower electronic conductivity and ion diffusion rate compared to lithium iron phosphate. The larger particle size of the P2 segment particles lengthens the migration path of lithium ions within the P2 segment particles, leading to increased discharge polarization and decreased specific capacity. By controlling the ratio of the average molar content of Mn in the P2 segment particles to that in the M segment particles within a suitable range, the discharge polarization of the P2 segment particles can be mitigated, resulting in a battery with superior specific capacity. Similarly, by controlling the ratio of the average molar content of Mn in the P1 segment particles to that in the M segment particles within a suitable range, the rate of side reactions between the P1 segment particles and the electrolyte, as well as the rate of manganese dissolution, can be further reduced, thus further improving the battery's storage performance.

[0020] In any embodiment, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.8 and greater than or equal to 0.

[0021] In any embodiment, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.5.

[0022] In any embodiment, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.0003.

[0023] In any embodiment, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.002.

[0024] Further controlling the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles within a certain range is beneficial to further improve the specific capacity of the secondary battery of this application, while also having better volumetric energy density and storage performance.

[0025] In any embodiment, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.8 and greater than or equal to 0.

[0026] In any embodiment, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.4.

[0027] In any embodiment, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.0003.

[0028] In any embodiment, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.002.

[0029] By further controlling the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles, the secondary battery of this application has good volumetric energy density and its storage performance is further improved.

[0030] In any embodiment, the average manganese-iron molar ratio of the particles in segment P1 is less than or equal to 6:4 and greater than or equal to 0.

[0031] In any embodiment, the average manganese-iron molar ratio of the P1 segment particles is less than or equal to 4:6.

[0032] In any embodiment, the average manganese-iron molar ratio of the particles in segment P1 is less than or equal to 2:8.

[0033] In any embodiment, the average manganese-iron molar ratio of the P1 segment particles is greater than or equal to 0.02:9.98.

[0034] When the average manganese-iron molar ratio of the P1 segment particles is within a suitable range, it helps to further reduce the side reactions between the P1 segment phosphate particles and the electrolyte, as well as the degree of manganese dissolution. This results in the battery having a good volumetric energy density while further improving its storage performance.

[0035] In any embodiment, the average manganese-iron molar ratio of the M-segment particles is greater than or equal to 4:6 and less than or equal to 9:1.

[0036] In any embodiment, the average manganese-iron molar ratio of the M-segment particles is greater than or equal to 5:5 and less than or equal to 9:1.

[0037] The M-segment particles have a suitable particle size, which can reduce the degree of side reactions with the electrolyte and manganese dissolution, while also mitigating discharge polarization and improving specific capacity. Controlling the average manganese-iron molar ratio of the M-segment particles within a suitable range is beneficial for increasing the total molar amount of manganese in the lithium transition metal phosphate particles in the positive electrode film, resulting in a higher voltage plateau for the battery, thereby improving its volumetric energy density and also exhibiting better storage performance.

[0038] In any embodiment, the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 6:4 and greater than or equal to 0.

[0039] In any embodiment, the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 5:5.

[0040] In any of the methods described, the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 3:7.

[0041] In any embodiment, the average manganese-iron molar ratio of the P2 segment particles is greater than or equal to 0.2:9.8.

[0042] In any embodiment, the average manganese-iron molar ratio of the P2 segment particles is greater than or equal to 1:9.

[0043] When the average manganese-iron molar ratio of the P2 segment particles is within a suitable range, it can alleviate the discharge polarization of the P2 segment phosphate particles, improve the specific capacity, and the battery can have a good volumetric energy density while further improving its storage performance.

[0044] In any implementation, the average manganese-iron molar ratio of the lithium transition metal phosphate particles is greater than or equal to 2:8 and less than or equal to 9:1.

[0045] In any embodiment, the average manganese-iron molar ratio of the lithium transition metal phosphate particles is greater than or equal to 2:8 and less than or equal to 6:4.

[0046] When the average manganese-iron molar ratio of lithium-containing transition metal phosphate particles is within a suitable range, lithium-containing transition metal phosphate particles can exhibit superior specific capacity and a higher voltage platform, further improving the volumetric energy density of the battery, while also providing good storage performance.

[0047] In any embodiment, based on the total area of ​​the lithium transition metal phosphate particles, the area ratio of the P1 segment particles is greater than 0% and less than or equal to 30%; and / or,

[0048] Based on the total area of ​​the lithium-containing transition metal phosphate particles, the area ratio of the M-segment particles is greater than or equal to 20% and less than 100%; and / or,

[0049] Based on the total area of ​​the lithium-containing transition metal phosphate particles, the area ratio of the P2 segment particles is greater than or equal to 0% and less than or equal to 80%.

[0050] In any implementation, based on the total area of ​​the lithium transition metal phosphate particles, the area ratio of the P1 segment particles is greater than or equal to 5% and less than or equal to 15%.

[0051] In any embodiment, based on the total area of ​​the lithium transition metal phosphate particles, the area ratio of the M segment particles is greater than or equal to 40% and less than or equal to 85%.

[0052] In any embodiment, the area ratio of the P2 segment particles is 5%-40% based on the total area of ​​the lithium transition metal phosphate particles.

[0053] When the area ratio of M-segment particles is within a suitable range, the battery exhibits superior volumetric energy density and storage performance. When the area ratio of P1-segment particles is within a suitable range, the battery exhibits superior compaction density, volumetric energy density, and storage performance. When the area ratio of P2-segment particles is within a suitable range, lithium-containing transition metal phosphate particles exhibit superior powder compaction density, specific capacity, and storage life, resulting in superior volumetric energy density and storage performance.

[0054] In any embodiment, the P1 segment particles have the molecular formula Li m1 A1 a1 Fe x1 Mn y1M1 b1 P z1 Q1 c1 O n1 N1 d1 Wherein, A1 includes one or more of Al, Na, K, and Mg; M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q1 includes one or more of B, S, Si, and N; N1 includes one or more of S, F, Cl, and Br; 0.8≤m1≤1.2, x1≥0, y1≥0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, and 0≤d1≤0.1.

[0055] In any embodiment, the M-segment particles have the molecular formula Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 Where A2 includes one or more of Al, Na, K, and Mg; M2 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q2 includes one or more of B, S, Si, and N; N2 includes one or more of S, F, Cl, and Br; 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, and 0≤d2≤0.1.

[0056] In any embodiment, the P2 segment particles have the molecular formula Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N2 d3Wherein, A3 includes one or more of Al, Na, K, and Mg; M3 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q3 includes one or more of B, S, Si, and N; N3 includes one or more of S, F, Cl, and Br; 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, and 0≤d3≤0.1.

[0057] In any embodiment, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises the lithium-containing transition metal phosphate particles, and the powder compaction density of the positive electrode active material at a pressure of 29400N is greater than or equal to 2.3 g / cm³. 3 Less than or equal to 2.65 g / cm³ 3 .

[0058] The higher the powder compaction density, the higher the mass of powder material per unit volume. When the powder compaction density of lithium transition metal phosphate particles is within a suitable range, the positive electrode sheet can have a higher compaction density during cold pressing, which is beneficial to further improving the volumetric energy density of the battery.

[0059] In any embodiment, the specific capacity of the positive electrode active material at 40°C and 1 / 3C discharge rate is greater than or equal to 134 mAh / g and less than or equal to 150 mAh / g.

[0060] In any embodiment, the positive electrode film layer further includes a binder and a conductive agent; optionally, in the positive electrode film layer, the ratio of the total mass of the positive electrode active material, the total mass of the binder, and the total mass of the conductive agent is (92-99):(0.5-3):(0.5-3).

[0061] In any embodiment, the single-sided coating weight of the positive electrode sheet is 300 mg / 1540 mm. 2 -580mg / 1540mm 2 .

[0062] When the coating weight of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0063] In any embodiment, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0064] When the compaction density of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0065] A second aspect of this application provides an electrical device comprising a secondary battery of the first party. Attached Figure Description

[0066] Figure 1 is a longitudinal cross-sectional schematic diagram of the positive electrode sheet according to an embodiment of this application;

[0067] Figure 2 is a schematic diagram of the statistical distinction rules of primary particles in the transmission electron microscope image of particles in this application;

[0068] Figure 3 is a schematic diagram of a secondary battery according to an embodiment of this application;

[0069] Figure 4 is an exploded view of the secondary battery according to an embodiment of this application shown in Figure 3;

[0070] Figure 5 is a schematic diagram of a battery module according to an embodiment of this application;

[0071] Figure 6 is a schematic diagram of a battery pack according to an embodiment of this application;

[0072] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6;

[0073] Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0074] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0075] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode, secondary battery, and 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.

[0076] 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.

[0077] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0078] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0079] 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.

[0080] 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.

[0081] 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).

[0082] Lithium manganese iron phosphate (LMP) is an emerging cathode material for lithium-ion batteries. The addition of manganese gives it a higher voltage platform compared to lithium iron phosphate, which is beneficial for improving the energy density of the battery. However, the addition of manganese also reduces the stability of LMP and deteriorates the battery's storage performance. Therefore, existing LMP materials are difficult to balance compaction density and storage performance.

[0083] [Rechargeable Battery]

[0084] Based on this, this application provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film includes lithium transition metal phosphate particles with different manganese-iron molar ratios. Based on the total molar number of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 12% and greater than or equal to 0%.

[0085] In this article, the term "molar number" refers to the number of specific particles contained in a substance, such as molecules and atoms.

[0086] In this paper, the term "primary particle size" refers to the particle size of a primary particle.

[0087] 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 2 is a schematic diagram of the statistical distinction rules for primary particles in a transmission electron microscope (TEM) image. Figure 2-a is the original TEM image, Figure 2-b is the software-recognized image, and Figure 2-c is an example of software and / or manual identification of independent, adhered, and stacked particles in Figure 2-a. Particles 1 and 2 are distinguishable independent particles, designated as primary particles 1 and 2, respectively. Particles 3 and 4 in Figure 2-c are adhered; particles 5, 6, and 7 are also adhered, and after software or manual identification, they are determined to be primary particles 3, 4, 5, 6, and 7, respectively. Particles 8 and 9, which are stacked together, are ultimately identified as primary particles 8 and 9, rather than being classified as a single particle. Figure 2-d is another example of software and / or manual identification of the stacked particles in Figure 2-a, where the stacked particles 10-14 are ultimately identified as primary particles 10, 11, 12, 13 and primary particle 14, instead of identifying the entire stack of particles as a single particle.When selecting the field of view for transmission electron microscopy, the field of view in which the number of stacked particles accounts for less than 20% of the total number of particles (individual particles, adherent particles, and the total number of stacked particles) can be selected for statistical analysis. Alternatively, the field of view in which the number of stacked particles accounts for less than 15% of the total number of particles (individual particles, adherent particles, and the total number of stacked particles) can be selected for statistical analysis. Furthermore, the field of view in which the number of stacked particles accounts for less than 10% of the total number of particles (individual particles, adherent particles, and the total number of stacked particles) can be selected for statistical analysis.

[0088] In this paper, the primary particle size of lithium transition metal phosphate particles can be measured using methods and equipment known in the art. For example, a battery is disassembled to obtain the positive electrode sheet. The positive electrode film layer of the positive electrode sheet is peeled off, and the positive electrode film layer is thoroughly washed with acetone to remove binders and dispersants, etc. The mixture is then filtered and dried to obtain powder. Take 0.05g of the uniformly mixed powder and dissolve it in 40ml of anhydrous ethanol. Then add an appropriate amount of dispersant and stir until a suspension is obtained. Take 2ml of the suspension and 2ml of anhydrous ethanol and mix them together. Then sonicate the mixture at a power of 480W for 5min. Take an appropriate amount of the middle layer suspension for transmission electron microscopy (TEM). According to the definition of primary particles mentioned above, calculate the projection area of ​​each primary particle in the TEM image, which is the cross-sectional area S of the primary particle. Use the equivalent circle method to obtain the equivalent circle diameter of the primary particle, 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 50nm and greater than 5μm are not included in the statistical range (i.e., primary particles with a primary particle diameter greater than or equal to 50nm and less than or equal to 5μm are considered valid particles).

[0089] In this paper, based on the total molar number of Mn in lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of ≤180 nm and ≥50 nm can be measured using methods and equipment known in the art. An example is shown below, where the primary particle size d is measured using the aforementioned method. Simultaneously, the Mn and Fe content of each effective particle can be measured using EDS point scanning in the transmission electron microscope image, allowing the calculation of the molar percentage X of Mn in each effective particle (the molar percentage or molar content of Mn refers to the number of moles of Mn relative to the total number of moles of Mn and Fe). The test point is the middle of the transmission surface of each primary particle. Multiple transmission electron microscopy (TEM) and EDS tests were performed within the aforementioned different test intervals. At least 500 effective particles were tested, measuring their cross-sectional area S, primary particle size d, and the molar ratio X of Mn. The obtained effective particles were then numbered according to their primary particle size as 1, 2, 3, 4, 5…n, with a total particle count of n. The m-th particle was a lithium transition metal phosphate particle with a primary particle size less than or equal to 180 nm, and the (m+1)-th particle was a lithium transition metal phosphate particle with a primary particle size greater than 180 nm.

[0090] Based on the total molar number of Mn in lithium transition metal phosphate particles, the formula for calculating the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of ≤180nm and ≥50nm is as follows:

[0091] Where Xi and Xj represent the molar percentage of manganese in the i-th and j-th lithium transition metal phosphate particles, respectively, and Si and Sj represent the areas of the i-th and j-th lithium transition metal phosphate particles, respectively.

[0092] In the positive electrode sheet, lithium transition metal phosphate particles with a primary particle size of 180 nm or less and 50 nm or more can fill the gaps between the positive electrode active material particles, resulting in a tighter packing and improving the compaction density of the positive electrode sheet. Manganese ions have a higher redox potential than iron ions, giving lithium manganese iron phosphate a higher voltage plateau compared to lithium iron phosphate. However, due to the Jan Taylor effect, manganese ions are prone to side reactions with the electrolyte, leading to manganese dissolution. Lithium transition metal phosphate particles with a primary particle size of 180 nm or less and 50 nm or more have a larger specific surface area and significantly increased surface activity, making them more susceptible to contact with the electrolyte and causing side reactions, exacerbating manganese dissolution and thus affecting the battery's storage performance. The secondary battery of this application controls the percentage of manganese moles in lithium transition metal phosphate particles with primary particle sizes of 180 nm to 50 nm within a suitable range in the positive electrode sheet. This ensures that the percentage of manganese moles in these particles relative to the total manganese moles in the phosphate particles in the positive electrode film is within a suitable range. This reduces the rate of side reactions between these lithium transition metal phosphate particles and the electrolyte, as well as the rate of manganese dissolution. Consequently, the battery exhibits better compaction density while improving storage performance.

[0093] In some implementations, based on the total molar amount of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 8%.

[0094] In some implementations, based on the total molar amount of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 6%.

[0095] In some embodiments, based on the total number of moles of Mn in lithium transition metal phosphate particles, the molar percentage of Mn in phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm can be 12%, 10%, 9%, 8%, 5%, 3%, 2%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.08%, 0.04%, 0.02%, or a value within a range of any two of the above molar percentages.

[0096] Further optimization involves ensuring that the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is within a certain range, for example, less than or equal to 8%, and further, less than or equal to 6%. This allows the secondary battery of this application to have better powder compaction density and volumetric energy density, while also further improving the battery's storage performance.

[0097] In some implementations, based on the total molar number of Mn in lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is greater than or equal to 0.02%.

[0098] In some implementations, based on the total molar number of Mn in lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is greater than or equal to 0.2%.

[0099] Compared to primary lithium transition metal phosphate particles with a particle size of 180nm or less and 50nm or greater, which do not contain Mn, this product contains a certain amount of Mn, which helps to improve the voltage platform of the secondary battery while also having a certain specific capacity.

[0100] In some embodiments, the lithium transition metal phosphate particles include P1 particles, M-segment particles, and P2-segment particles. The primary particle size of the P1-segment particles is less than or equal to 180 nm and greater than or equal to 50 nm. The primary particle size of the M-segment particles is greater than 180 nm and less than 900 nm. The primary particle size of the P2-segment particles is greater than or equal to 900 nm and less than or equal to 5 μm. The ratio of the average molar content of Mn in the P2-segment particles to the average molar content of Mn in the M-segment particles is less than or equal to 1. And / or, the ratio of the average molar content of Mn in the P1-segment particles to the average molar content of Mn in the M-segment particles is less than or equal to 1. Furthermore, the ratios of the average molar content of Mn in the P2-segment particles to the average molar content of Mn in the M-segment particles and the ratios of the average molar content of Mn in the P1-segment particles to the average molar content of Mn in the M-segment particles are not simultaneously 1.

[0101] Figure 1 is a schematic longitudinal cross-section of a positive electrode sheet as an example. As shown in Figure 1, the positive electrode film layer includes lithium transition metal phosphate particles with different primary particle sizes. In this paper, the segmentation of particles into P1, M, and P2 segments can be performed using methods and equipment known in the art. For example, the primary particle size d of the particles can be measured using the aforementioned method for testing primary particle size. The effective particles obtained from the test are numbered from smallest to largest as 1, 2, 3, 4, 5…n, with a total of n particles. The m-th particle is a lithium transition metal phosphate particle with a primary particle size less than or equal to 180 nm, the (m+1)-th particle is a lithium transition metal phosphate particle with a primary particle size greater than 180 nm, the (k-1)-th particle is a lithium transition metal phosphate particle with a primary particle size less than 900 nm, and the k-th particle is a lithium transition metal phosphate particle with a primary particle size greater than or equal to 900 nm and less than or equal to 5 μm. Therefore, particles 1 to m are classified as P1 particles, particles (m+1) to k-1 are classified as M particles, and particles k to n are classified as P2 particles.

[0102] In this paper, the ratios of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles, and the ratios of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles, can be performed using methods and equipment known in the art. For example, the primary particle size d is measured using the aforementioned method. In the above statistical process of particles and their primary particle sizes, particles with a primary particle size less than 50 nm and greater than 5 μm are not included in the statistical range (i.e., particles with a primary particle size greater than or equal to 50 nm and less than or equal to 5 μm are considered valid particles). Simultaneously, the Mn and Fe content of each valid particle can be measured using EDS point scanning in the transmission electron microscope image, thereby calculating the molar percentage X of Mn in each valid particle (the molar percentage or molar content of Mn refers to the content of the number of moles of Mn element relative to the total number of moles of Mn and Fe). The test point is the middle part of the transmission surface of each particle. The above-mentioned transmission electron microscopy and EDS tests were performed multiple times, measuring the cross-sectional area S, primary particle size d, and molar ratio X of Mn for at least 500 effective particles. The effective particles were then numbered according to their primary particle size as 1, 2, 3, 4, 5…n, with a total of n particles. The m-th particle was a lithium transition metal phosphate particle with a primary particle size less than or equal to 180 nm, and the (m+1)-th particle was a lithium transition metal phosphate particle with a primary particle size greater than 180 nm.

[0103] The formula for calculating the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is as follows:

[0104] The formula for calculating the ratio of the average molar content of Mn in the particles of segment P1 to the average molar content of Mn in the particles of segment M is as follows:

[0105] Where Xi and Xj represent the molar content of manganese in the i-th and j-th lithium transition metal phosphate particles, respectively, and Si and Sj represent the areas of the i-th and j-th lithium transition metal phosphate particles, respectively.

[0106] The secondary battery of this application features a suitable particle gradation design, in which P1, M, and P2 segment particles are matched to further improve the compaction density of the positive electrode. However, due to the crystal structure of manganese, lithium manganese iron phosphate has lower electronic conductivity and ion diffusion rate compared to lithium iron phosphate. The larger particle size of the P2 segment particles lengthens the migration path of lithium ions within the P2 segment particles, leading to increased discharge polarization and decreased specific capacity. By controlling the ratio of the average molar content of Mn in the P2 segment particles to that in the M segment particles within a suitable range, the discharge polarization of the P2 segment particles can be mitigated, resulting in a battery with superior specific capacity. Furthermore, by controlling the ratio of the average molar content of Mn in the P1 segment particles to that in the M segment particles within a suitable range, the rate of side reactions between the P1 segment particles and the electrolyte, as well as the rate of manganese dissolution, can be further reduced, thus further improving the battery's storage performance.

[0107] In some embodiments, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.8 and greater than or equal to 0.

[0108] In some embodiments, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.5.

[0109] In some embodiments, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles can be 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, 0.001, 0.0001, or 0, or a value within the range of the two ratios mentioned above.

[0110] Further controlling the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles within a certain range is beneficial to further improve the specific capacity of the secondary battery of this application, while also having better volumetric energy density and storage performance.

[0111] In some embodiments, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.0003.

[0112] In some embodiments, the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.002.

[0113] By controlling the average molar content of Mn in the P2 segment particles to be greater than 0, and ensuring that the P2 segment particles contain a certain amount of Mn, the P2 segment particles can contribute a certain voltage plateau, which is beneficial to improving the energy density of the battery. At the same time, it can also alleviate the impact of excessive Mn concentration in the relatively small primary P1 segment particles on the battery's cycle performance and storage performance caused by Mn dissolution. This makes the battery more suitable for application scenarios with certain requirements for cycle performance and / or storage performance.

[0114] In some embodiments, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.8 and greater than or equal to 0.

[0115] In some embodiments, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.4.

[0116] In some embodiments, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles can be 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.02, 0.01, 0.001, 0.0001, or 0, or a value within the range of any two of the above ratios.

[0117] By further controlling the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles, the secondary battery of this application has good volumetric energy density and its storage performance is further improved.

[0118] In some embodiments, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.0003.

[0119] In some embodiments, the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is greater than or equal to 0.002.

[0120] By controlling the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles to be greater than 0, the P1 segment particles have a certain amount of Mn content. The P1 segment particles with excellent conductivity can fully exert their specific capacity, which is conducive to further improving the energy density of the battery and making the battery more suitable for application scenarios with certain energy density requirements.

[0121] In some implementations, the average manganese-iron molar ratio of the P1 segment particles is less than or equal to 6:4 and greater than or equal to 0.

[0122] In some implementations, the average manganese-iron molar ratio of the P1 segment particles is less than or equal to 4:6.

[0123] In some implementations, the average manganese-iron molar ratio of the P1 segment particles is less than or equal to 2:8.

[0124] In some embodiments, the average manganese-iron molar ratio of the P1 segment particles can be 6:4, 5.5:4.5, 5:5, 4:6, 3:7, 2:8, 1:9, 0.9:9.1, 0.5:9.5, 0.3:9.7, 0.2:9.8, 0.1:9.9, 0.09:9.91, 0.07:9.93, 0.05:9.95, 0.02:9.98, 0:1, or a value within the range formed by any two of the above average manganese-iron molar ratios.

[0125] When the average manganese-iron molar ratio of the P1 segment particles is within a suitable range, it helps to further reduce the side reactions between the P1 segment phosphate particles and the electrolyte, as well as the degree of manganese dissolution. This results in the battery having a good volumetric energy density while further improving its storage performance.

[0126] In some implementations, the average manganese-iron molar ratio of the P1 segment particles is greater than or equal to 0.02:9.98.

[0127] By controlling the average manganese-iron molar ratio of the P1 segment particles to be greater than 0, the P1 segment particles with excellent conductivity can fully exert their specific capacity, which can further improve the energy density of the battery and make the battery more suitable for application scenarios with certain energy density requirements.

[0128] In some implementations, the average manganese-iron molar ratio of the M-segment particles is greater than or equal to 4:6 and less than or equal to 9:1.

[0129] In some implementations, the average manganese-iron molar ratio of the M-segment particles is greater than or equal to 5:5 and less than or equal to 9:1.

[0130] In some embodiments, the average manganese-iron molar ratio of the M-segment particles can be 9:1, 8:2, 7:3, 6:4, or a value within the range of any two of the above average manganese-iron molar ratios.

[0131] The M-segment particles have a suitable particle size, which can reduce the degree of side reactions with the electrolyte and manganese dissolution, while also mitigating discharge polarization and improving specific capacity. Controlling the average manganese-iron molar ratio of the M-segment particles within a suitable range is beneficial for increasing the total molar amount of manganese in the lithium transition metal phosphate particles in the positive electrode film, resulting in a higher voltage plateau for the battery, thereby improving its volumetric energy density and also exhibiting better storage performance.

[0132] In some implementations, the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 6:4 and greater than or equal to 0.

[0133] In some implementations, the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 5:5.

[0134] In some implementations, the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 3:7.

[0135] In some embodiments, the average manganese-iron molar ratio of the P2 segment particles can be 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, 0.5:9.5, 0.2:9.8, 0.1:9.9, 0.02:9.98, 0, or a value within the range of any two of the above average manganese-iron molar ratios.

[0136] When the average manganese-iron molar ratio of the P2 segment particles is within a suitable range, it can alleviate the discharge polarization of the P2 segment particles, improve the specific capacity, and the battery can have a good volumetric energy density while further improving its storage performance.

[0137] In some implementations, the average manganese-iron molar ratio of the P2 segment particles is greater than or equal to 0.2:9.8.

[0138] In some implementations, the average manganese-iron molar ratio of the P2 segment particles is greater than or equal to 1:9.

[0139] By controlling the average manganese-iron molar ratio of the P2 segment particles to be greater than 0, the P2 segment particles have a certain voltage plateau, which can further improve the energy density of the battery.

[0140] In this paper, the average manganese-iron molar ratio of particles in segments P1, M, and P2, as well as the average manganese-iron molar ratio of lithium transition metal phosphate particles, can be determined using methods and equipment known in the art. For example, following the test methods described above for the ratio of the average molar content of Mn in segment P2 particles to the average molar content of Mn in segment M particles, and the ratio of the average molar content of Mn in segment P1 particles to the average molar content of Mn in segment M particles, the cross-sectional area S, the molar percentage of Mn X, and the molar percentage of Fe (also using EDS, where the molar percentage of Fe refers to the content of the number of moles of Fe relative to the total number of moles of Mn and Fe) of the effective particles in segments P1, M, and P2 are determined.

[0141] The formula for calculating the average manganese-iron molar ratio of particles in segment P1 is:

[0142] The formula for calculating the average manganese-iron molar ratio of particles in segment M is:

[0143] The formula for calculating the average manganese-iron molar ratio of particles in segment P2 is as follows:

[0144] The formula for calculating the average manganese-iron molar ratio of the total lithium-containing transition metal phosphate particles is as follows:

[0145] Where Xi represents the molar content of manganese in the i-th lithium transition metal phosphate particle, Yi represents the molar content of iron in the i-th lithium transition metal phosphate particle, and Si represents the area of ​​the i-th lithium transition metal phosphate particle.

[0146] In some embodiments, the average manganese-iron molar ratio of the lithium transition metal phosphate particles is greater than or equal to 2:8 and less than or equal to 9:1.

[0147] In some embodiments, the average manganese-iron molar ratio of the lithium transition metal phosphate particles is greater than or equal to 2:8 and less than 6:4.

[0148] In some embodiments, the average manganese-iron molar ratio of the lithium transition metal phosphate particles can be 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, or a value within the range of any two of the above-mentioned average manganese-iron molar ratios.

[0149] When the average manganese-iron molar ratio of lithium-containing transition metal phosphate particles is within a suitable range, the lithium-containing transition metal phosphate particles can exhibit superior specific capacity and a higher voltage platform, further improving the volumetric energy density of the battery, while also providing better storage performance.

[0150] In some implementations, the area ratio of P1 segment particles is greater than 0% and less than or equal to 30% based on the total area of ​​lithium transition metal phosphate particles.

[0151] In some implementations, based on the total area of ​​lithium transition metal phosphate particles, the area ratio of M-segment phosphate particles is greater than or equal to 20% and less than 100%.

[0152] In some implementations, the area ratio of P2 segment phosphate particles is greater than or equal to 0% and less than or equal to 80% based on the total area of ​​lithium transition metal phosphate particles.

[0153] In this paper, based on the total area of ​​lithium transition metal phosphate particles, the area ratios of segments P1, M, and P2 can be measured using methods and equipment known in the art. For example, following the test methods described above for the ratios of the average molar content of Mn in segment P2 particles to the average molar content of Mn in segment M particles, and the ratios of the average molar content of Mn in segment P1 particles to the average molar content of Mn in segment M particles, the cross-sectional areas S of the effective particles in segments P1, M, and P2 are measured.

[0154] The formula for calculating the area ratio of particles in segment P1 is:

[0155] The formula for calculating the area ratio of particles in segment M is:

[0156] The formula for calculating the area ratio of particles in segment P2 is:

[0157] Where Si and Sj represent the areas of the i-th and j-th lithium transition metal phosphate particles, respectively.

[0158] In some embodiments, based on the total area of ​​the lithium transition metal phosphate particles, the area percentage of the P1 segment particles is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 17%, 20%, 22%, 24%, 26%, 28%, 30%, or any value between these values.

[0159] In some implementations, the area ratio of P1 segment particles is greater than or equal to 5% and less than or equal to 15% based on the total area of ​​lithium transition metal phosphate particles.

[0160] When the area ratio of P1 segment particles is within a suitable range, the battery exhibits superior compaction density, volumetric energy density, and storage performance.

[0161] In some implementations, based on the total area of ​​the lithium transition metal phosphate particles, the area percentage of the M segment particles is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, or any value between these values.

[0162] In some implementations, based on the total area of ​​lithium transition metal phosphate particles, the area ratio of M-segment particles is greater than or equal to 40% and less than or equal to 85%.

[0163] When the area ratio of M-segment particles is within a suitable range, the battery exhibits superior volumetric energy density and storage performance.

[0164] In some implementations, the area percentage of the P2 segment particles is 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value between these values, based on the total area of ​​the lithium transition metal phosphate particles.

[0165] In some implementations, the area ratio of P2 segment phosphate particles is 5%-40% based on the total area of ​​the phosphate particles.

[0166] When the area ratio of P2 segment particles is within a suitable range, lithium-containing transition metal phosphate particles have superior powder compaction density, specific capacity, and storage life, resulting in batteries with superior volumetric energy density and storage performance.

[0167] In some embodiments, the P1 segment phosphate particles have the molecular formula Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 Wherein, A1 includes one or more of Al, Na, K, and Mg; M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q1 includes one or more of B, S, Si, and N; N1 includes one or more of S, F, Cl, and Br; 0.8≤m1≤1.2, x1≥0, y1≥0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, and 0≤d1≤0.1.

[0168] In some embodiments, the M-segment particles have the molecular formula Lim2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 Where A2 includes one or more of Al, Na, K, and Mg; M2 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q2 includes one or more of B, S, Si, and N; N2 includes one or more of S, F, Cl, and Br; 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, and 0≤d2≤0.1.

[0169] In some embodiments, the P2 segment particles have the molecular formula Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N2 d3 Wherein, A3 includes one or more of Al, Na, K, and Mg; M3 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q3 includes one or more of B, S, Si, and N; N3 includes one or more of S, F, Cl, and Br; 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, and 0≤d3≤0.1.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] Selecting appropriate modifying 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 improve the cycle performance of the material.

[0176] Selecting appropriate modifying 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.

[0177] Choosing appropriate modifying elements A1, A2, and A3 can also improve the lattice change rate of the material and maintain its battery capacity.

[0178] Modifying 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, they can enhance the material's resistance to acid corrosion such as HF, thereby improving its cycle performance and lifespan.

[0179] In this paper, the modifying elements M1, M2, M3, Q1, Q2, Q3, A1, A2, A3, N1, N2, and N3 can exist in the lithium-containing transition metal phosphate material as doping elements, or in the coating layer of the material as coating elements.

[0180] In some embodiments, the positive electrode film layer includes a positive electrode active material, which comprises lithium transition metal phosphate particles, and the powder compaction density of the positive electrode active material at a pressure of 29400 N is greater than or equal to 2.3 g / cm³. 3 Less than or equal to 2.65 g / cm³3 .

[0181] In this article, the term "powder compaction density" refers to the mass of powder particles per unit volume under a given pressure.

[0182] The compaction density of the positive electrode active material powder can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven and left to stand for 2 hours. Once the battery temperature remains at 25°C, it is discharged at a constant current of 1 / 3C to 2.0V. The battery is then disassembled to obtain the positive electrode sheet. The positive electrode film is peeled off, thoroughly washed with acetone to remove the binder, and dried to obtain the powder for subsequent characterization testing. Subsequent characterization can be performed using a compaction density instrument, referring to GB / T 24533-2009. Specifically, a certain amount of the prepared powder is placed on a 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 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. Therefore, the compaction density of the positive electrode active material powder is 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 powder after compaction. The compaction density instrument model is UTM7305; the manufacturer is Sansi Zongheng.

[0183] In some embodiments, the powder compaction density of the positive electrode active material at a pressure of 29400 N can be 2.32 g / cm³. 3 2.34 g / cm 3 2.35g / cm 3 2.36 g / cm 3 2.38g / cm 3 2.40 g / cm 3 , or is a range of any two powder compaction densities mentioned above, or a value within that range.

[0184] The higher the powder compaction density, the higher the mass of powder material per unit volume. When the powder compaction density of lithium transition metal phosphate particles is within a suitable range, the positive electrode sheet has a higher compaction density during cold pressing, which is beneficial to further improve the volumetric energy density of the battery.

[0185] In some embodiments, the specific capacity of the positive electrode active material at 40°C and 1 / 3C discharge rate is greater than or equal to 134 mAh / g and less than or equal to 150 mAh / g.

[0186] The full-cell specific capacity of the positive electrode active material can be tested using methods known in the art. As an example, the specific operation can be referred to as follows: (1) Place the battery in a 40°C oven environment and let it stand for 2 hours until the battery temperature is maintained at 40°C; (2) Discharge the battery at a constant current of 1 / 3C to 2.0V; (3) Pause for 5 minutes; (4) Charge the battery at a constant current of 1 / 3C to 4.1V, and then charge it at a constant voltage of 4.1V until the cutoff current is 0.05C; (5) Pause for 5 minutes; (6) Discharge the battery at a constant current of 1 / 3C to 2.0V. This step is the actual cell test capacity C. Disassemble the battery to obtain a positive electrode sheet with a total area of ​​S1. Cut the positive electrode sheet to obtain a positive electrode sheet with an area of ​​S2. After peeling the positive electrode film layer from the current collector, dissolve it in acetone, thoroughly wash away residual solvent, binder, and dispersant, filter, and dry to obtain powder. Weigh the powder as M2. The total mass M1 of the positive electrode active material of the battery is approximately: M2*(S1 / S2). Combining the mass of the positive electrode active material, the specific capacity of the positive electrode active material can be calculated: Specific capacity = Discharge capacity of the battery C / Mass of positive electrode active material M1.

[0187] In some embodiments, the full-cell specific capacity of the positive electrode active material can be 150mAh / g, 149mAh / g, 148mAh / g, 147mAh / g, 146mAh / g, 145mAh / g, 144mAh / g, 143mAh / g, 142mAh / g, 141mAh / g, 140mAh / g, 139mAh / g, 138mAh / g, 137mAh / g, 136mAh / g, 135mAh / g, 134mAh / g, or a value within the range of any two of the above specific capacities.

[0188] [Preparation of positive electrode active materials]

[0189] This application also provides a method for preparing a positive electrode active material:

[0190] A lithium-containing transition metal phosphate material is obtained by mixing a first lithium-containing transition metal phosphate material and a second lithium-containing transition metal phosphate material, or by mixing a second lithium-containing transition metal phosphate material and a third lithium-containing transition metal phosphate material.

[0191] 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; and 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.

[0192] The first average particle size of the lithium-containing transition metal phosphate material is smaller than that of the second lithium-containing transition metal phosphate material, the first average particle size of the second lithium-containing transition metal phosphate material is smaller than that of the third lithium-containing transition metal phosphate material, and the first average particle size of the lithium-containing transition metal phosphate material is 50nm-200nm.

[0193] Based on the total molar number of Mn in the lithium-containing transition metal phosphate material, the molar percentage of Mn in the first lithium-containing transition metal phosphate particle is less than or equal to 50% and greater than or equal to 0%.

[0194] In some embodiments, the first lithium-containing transition metal phosphate material may include a variety of lithium-containing transition metal phosphate materials with different primary particle sizes.

[0195] In some embodiments, the second lithium-containing transition metal phosphate material may include a variety of lithium-containing transition metal phosphate materials with different primary particle sizes.

[0196] In some embodiments, the third lithium-containing transition metal phosphate material may include a variety of lithium-containing transition metal phosphate materials with different primary particle sizes.

[0197] In this paper, the term "primary average particle size" refers to the average primary particle size of all particles.

[0198] The primary average particle size of lithium transition metal phosphate materials can be measured 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 until a suspension is obtained. 2 ml of the suspension is mixed with 2 ml of anhydrous ethanol and then subjected to ultrasonic treatment at a power of 480 W for 5 min. A uniformly dispersed suspension is obtained. An appropriate amount of the intermediate suspension is 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 primary particle diameters less than 50 nm and greater than 5 μm are not included in the statistical range (i.e., primary particles with a primary particle diameter greater than or equal to 50 nm and less than or equal to 5 μm 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.

[0199] Based on the total molar number of Mn in the lithium-containing transition metal phosphate material, the molar percentage of Mn in the first lithium-containing transition metal phosphate particle can be measured using methods and equipment known in the art. A specific example is as follows: Referring to the national standard GB / T 33822-2017, the molar content of Mn and Fe elements is tested using the chemical analysis method for nano-lithium iron phosphate, and the average molar percentage of Mn in the material can be calculated. Based on the total molar number of Mn in the lithium-containing transition metal phosphate material, the molar percentage of Mn in the first lithium-containing transition metal phosphate particle = (average molar percentage of Mn in the first lithium-containing transition metal phosphate particle × mass of the first lithium-containing transition metal phosphate particle) / (average molar percentage of Mn in the lithium-containing transition metal phosphate particle × mass of the lithium-containing transition metal phosphate particle).

[0200] In some embodiments, based on the total number of moles of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the first lithium transition metal phosphate material can be 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 0%, or a range of any two of the above molar percentages or a value within that range.

[0201] In some embodiments, the primary average particle size of the first lithium-containing transition metal phosphate material can be 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, or a value within the range of any two of the above primary average particle sizes.

[0202] In some embodiments, the primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm to 600 nm.

[0203] In some embodiments, the primary average particle size of the second lithium-containing transition metal phosphate material can be 120nm, 140nm, 160nm, 180nm, 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, 520nm, 540nm, 560nm, 580nm, or 600nm, or a value within the range of any two of the above primary average particle sizes.

[0204] In some embodiments, the primary average particle size of the third lithium-containing transition metal phosphate material is 250 nm to 4000 nm.

[0205] In some embodiments, the primary average particle size of the third lithium-containing transition metal phosphate material can be 250nm, 300nm, 350nm, 400nm, 440nm, 500nm, 550nm, 600nm, 650nm, 700nm, 730nm, 750nm, 780nm, 800nm, 830nm, 850nm, 870nm, 900nm, 950nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 2000nm, 2100nm, 2200nm, 2300nm, 2400nm, 2500nm, 2600nm, 2700nm, 2800nm, 2900nm, 3000nm, 3500nm, or 4000nm, or a value within a range consisting of any two of the above primary average particle sizes.

[0206] In some embodiments, the ratio of the average molar content of Mn in the third lithium-containing transition metal phosphate material to the average molar content of Mn in the second lithium-containing transition metal phosphate material is less than or equal to 1; 1, and / or

[0207] The ratio of the average molar content of Mn in the first lithium-containing transition metal phosphate material to the average molar content of Mn in the second lithium-containing transition metal phosphate material is less than or equal to 1;

[0208] Furthermore, the ratio of the average molar content of Mn in the third lithium-containing transition metal phosphate material to the average molar content of Mn in the second lithium-containing transition metal phosphate material, and the ratio of the average molar content of Mn in the first lithium-containing transition metal phosphate material to the average molar content of Mn in the second lithium-containing transition metal phosphate material, are not all 1.

[0209] In this paper, the ratios of the average molar content of Mn in the third lithium-containing transition metal phosphate material to the average molar content of Mn in the second lithium-containing transition metal phosphate material, and the ratios of the average molar content of Mn in the first lithium-containing transition metal phosphate material to the average molar content of Mn in the second lithium-containing transition metal phosphate material, can be measured using methods and equipment known in the art. For example, by referring to the chemical analysis method for nano-lithium iron phosphate in national standard GB / T 33822-2017 to test the molar content of Mn and Fe elements, the average molar content of Mn in the third, second, and first lithium-containing transition metal phosphate materials can be calculated. Dividing the corresponding average molar content of Mn in each material yields the aforementioned parameter values.

[0210] In some embodiments, the average manganese-iron molar ratio of the first lithium-containing transition metal phosphate material is less than or equal to 6:4 and greater than or equal to 0:1.

[0211] In some embodiments, the average manganese-iron molar ratio of the first lithium-containing transition metal phosphate material is less than or equal to 4:6 and greater than or equal to 0:1.

[0212] In some embodiments, the average manganese-iron molar ratio of the first lithium-containing transition metal phosphate material is greater than or equal to 0.02:9.98. In some embodiments, the average manganese-iron molar ratio of the first lithium-containing transition metal phosphate material is greater than or equal to 0.2:9.8. In some embodiments, the average manganese-iron molar ratio of the first lithium-containing transition metal phosphate material is greater than 0:1.

[0213] In some embodiments, the average manganese-iron molar ratio of the first lithium-containing transition metal phosphate material can be 6:4, 5.5:4.5, 5:5, 4.9:5.1, 4:6, 3:7, 2:8, 1:9, 0.5:9.5, 0.2:9.8, 0.02:9.98, 0:1, 0:1, or a value within the range of any two of the above-mentioned average manganese-iron molar ratios.

[0214] In some embodiments, the average manganese-iron molar ratio of the second lithium-containing transition metal phosphate material is greater than or equal to 4:6 and less than or equal to 9:1. In some embodiments, the average manganese-iron molar ratio of the second lithium-containing transition metal phosphate material is greater than or equal to 5:5 and less than or equal to 9:1. In some embodiments, the average manganese-iron molar ratio of the second lithium-containing transition metal phosphate material can be 9:1, 8:2, 7:3, 6:4, 5:5, 4.5:5.5, 5:5, or a value within the range formed by any two of the above average manganese-iron molar ratios.

[0215] In some embodiments, the average manganese-iron molar ratio of the third lithium-containing transition metal phosphate material is less than or equal to 6:4 and greater than or equal to 0. In some embodiments, the average manganese-iron molar ratio of the third lithium-containing transition metal phosphate material is less than or equal to 5:5. In some embodiments, the average manganese-iron molar ratio of the third lithium-containing transition metal phosphate material is greater than or equal to 0.02:9.98, optionally greater than or equal to 0.2:9.8, and more preferably greater than 0.

[0216] In some embodiments, the average manganese-iron molar ratio of the third lithium-containing transition metal phosphate material can be 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, 0.5:9.5, 0.2:9.8, 0.1:9.9, 0.02:9.98, 0:1, or a value within the range of any two of the above average manganese-iron molar ratios.

[0217] The average manganese-iron molar ratio of lithium-containing transition metal phosphate materials can be determined 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. The average molar percentage of Mn and Fe in the material can then be calculated. Therefore, the average manganese-iron molar ratio of lithium-containing transition metal phosphate materials = the average molar percentage of Mn in lithium-containing transition metal phosphate materials / the average molar percentage of Fe in lithium-containing transition metal phosphate materials.

[0218] In some embodiments, the weight percentage of the first lithium-containing transition metal phosphate material is greater than or equal to 0% and less than or equal to 30% based on the total weight of the lithium-containing transition metal phosphate material.

[0219] In some embodiments, the weight percentage of the first lithium-containing transition metal phosphate material is 3%-15% based on the total weight of the lithium-containing transition metal phosphate material.

[0220] In some embodiments, the weight percentage of the first lithium-containing transition metal phosphate material is 3%-10% based on the total weight of the lithium-containing transition metal phosphate material.

[0221] 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 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or a value within a range of any two of the above weight percentages.

[0222] In some embodiments, the weight percentage of the second lithium-containing transition metal phosphate material is greater than or equal to 15% and less than 100% based on the total weight of the lithium-containing transition metal phosphate material.

[0223] In some embodiments, the weight percentage of the second lithium-containing transition metal phosphate material is 30%-85% based on the total weight of the lithium-containing transition metal phosphate material.

[0224] 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 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or a value within a range of any two of the above weight percentages.

[0225] In some implementations, the weight percentage of the third lithium-containing transition metal phosphate material is 0%-85% based on the total weight of the lithium-containing transition metal phosphate material.

[0226] In some embodiments, the weight percentage of the third lithium-containing transition metal phosphate material is 10%-67% based on the total weight of the lithium-containing transition metal phosphate material.

[0227] In some embodiments, based on the total weight of the lithium transition metal phosphate material, the weight percentage of the third lithium transition metal phosphate material can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or a value within a range of any two of the above weight percentages.

[0228] In some embodiments, the weight percentages of the first lithium-containing transition metal phosphate material and the third lithium-containing transition metal phosphate material are not both 0, based on the total weight of the lithium-containing transition metal phosphate material.

[0229] In some embodiments, the specific surface area (BET) of the third lithium-containing transition metal phosphate material is 3 m². 2 / g-13m 2 / g. In some embodiments, the BET of the third lithium-containing transition metal phosphate material can be 3m. 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g, 4.6m 2 / g、5m 2 / g, 5.5m 2 / g、6m 2 / g, 6.5m 2 / g、7m 2 / g, 7.5m 2 / g、8m 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g, 10.5m 2 / g、11m 2 / g, 11.5m 2 / g、12m 2 / g, 12.3m 2 / g, 12.5m 2 / g、13m 2 / g, or a range of any two of the above values, or a value within that range. In some embodiments, the specific surface area of ​​the third lithium-containing transition metal phosphate material is 3m². 2 / g-8m 2 / g.

[0230] In this document, the term "specific surface area" or "BET" refers to the total area per unit mass of material. In this application, the BET of the third lithium transition metal phosphate material is related to factors such as the primary average particle size, carbon content, density of carbon coating, degree of adhesion between carbon and particles, and porosity of the particles.

[0231] Specific surface area (BET) can be measured using methods and equipment known in the art. For example, it can be tested according to the gas adsorption method, referring to GB / T 19587-2017. As an example, a third lithium-containing transition metal phosphate material is placed in a sample tube, which is then immersed in liquid nitrogen at -196°C. The amount of nitrogen adsorbed on the solid surface at different pressures (0.05-0.30) is measured. Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample is calculated, thereby obtaining the specific surface area of ​​the sample.

[0232] In some embodiments, the carbon content of the third lithium-containing transition metal phosphate material is calculated based on the total weight of the third lithium-containing transition metal phosphate material as Cx wt%, where 0.8 ≤ Cx ≤ 2.0.

[0233] In some embodiments, the carbon content of the third lithium-containing transition metal phosphate material is calculated based on the total weight of the material, and is 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.15 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any range of two of the above carbon contents or values ​​within that range.

[0234] In some embodiments, the carbon contained in the third lithium-containing transition metal phosphate material is coated on the surface of its particles. In some embodiments, the carbon contained in the third lithium-containing transition metal phosphate material is embedded within its particles. In some embodiments, the carbon contained in the third lithium-containing transition metal phosphate material is partially coated on the surface of its particles and partially embedded within its particles.

[0235] The weight content of the carbon coating layer of a material can be determined using 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 standard GB / T 20123-2006 / ISO 15350:2000.

[0236] In some embodiments, the ratio z of the specific surface area of ​​the third lithium-containing transition metal phosphate material to Cx satisfies 3 ≤ z ≤ 10. In some embodiments, the ratio z of the specific surface area of ​​the third lithium-containing transition metal phosphate material to Cx satisfies 3 ≤ z ≤ 9. In some embodiments, the ratio z of the specific surface area of ​​the third lithium-containing transition metal phosphate material to Cx satisfies 3.5 ≤ z ≤ 9. In some embodiments, the ratio z of the specific surface area of ​​the third lithium-containing transition metal phosphate material to Cx satisfies 3.8 ≤ z ≤ 8.6.

[0237] In some implementations, z can be 3, 3.2, 3.5, 3.75, 3.8, 4, 4.2, 4.3, 4.5, 4.58, 4.8, 4.98, 5, 5.3, 5.42, 5.5, 5.71, 5.8, 5.83, 6, 6.3, 6.5, 6.7, 6.8, 7, 7.3, 7.5, 7.8, 7.9, 8, 8.2, 8.3, 8.5, 8.6, 9, 9.5, 10, or a range of any two of the above z values ​​or a value within that range.

[0238] In some embodiments, the third lithium-containing transition metal phosphate material satisfies at least one of (a)-(f):

[0239] (a) The Dv10 of the third lithium-containing transition metal phosphate material is ≥0.2 μm;

[0240] (b) The Dv50 of the third lithium-containing transition metal phosphate material is 0.5-5 μm;

[0241] (c) The Dv90 of the third lithium-containing transition metal phosphate material is ≤10μm;

[0242] (d) The Dv99 of the third lithium-containing transition metal phosphate material is ≤12μm;

[0243] (e) The powder compaction density of the third lithium-containing transition metal phosphate material at a pressure of 29400 N is ≥2.25 g / cm³. 3 ;

[0244] (f) The powder resistivity of the third lithium-containing transition metal phosphate material is less than 60 Ω·cm.

[0245] In this paper, the term "Dv10" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 10%.

[0246] In this paper, the term "Dv90" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 90%.

[0247] In this paper, the term "Dv99" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 99%.

[0248] In some embodiments, the third lithium-containing transition metal phosphate material has a Dv10 < Dv50.

[0249] In some embodiments, the Dv90 of the third lithium-containing transition metal phosphate material is greater than the Dv50.

[0250] In some embodiments, the Dv50 of the third lithium-containing transition metal phosphate material can be 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1700nm, 1900nm, 2000nm, 2300nm, 2500nm, 2700nm, 2900nm, 3000nm, 3200nm, 3400nm, 3600nm, 3800nm, 4000nm, 4200nm, 4400nm, 4600nm, 4800nm, or 5000nm, or a range of the Dv50 of any two of the above-mentioned second-stage pulverized products, or a value within that range.

[0251] The Dv10, Dv50, Dv90, and Dv99 of the third lithium-containing transition metal phosphate 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) according to GB / T19077.1-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0252] The powder resistivity of the third lithium-containing transition metal phosphate 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 the third lithium-containing transition metal phosphate 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 third lithium-containing transition metal phosphate material are measured separately. The average value of the two is taken as the powder resistivity of the third lithium-containing transition metal phosphate material.

[0253] The compacted density of the third lithium-containing transition metal phosphate 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 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; the manufacturer is Sansi Zongheng.

[0254] In some implementations, the general formula for the first kernel includes Li m4 A4 a4 Fe x4 Mn y4 M4 b4 P z4 Q4 c4 O n4 N4 d4 ,

[0255] Where 0.8≤m4≤1.2, x4≥0, y4>0, 0.9≤x4+y4≤1, 0.95≤z4≤1.1, 3.5≤n4≤4, 0≤a4≤0.1, 0≤b4≤0.1, 0≤c4≤0.1, 0≤d4≤0.1, and / or

[0256] The general formula for the composition of the second kernel includes Li m5 A5 a5 Fe x5 Mn y5 M5 b5 P z5 Q5 c5 O n5 N5 d5 , 0.8≤m5≤1.2, x5≥0, y5≥0, 0.9≤x5+y5≤1, 0.95≤z5≤1.1, 3.5≤n5≤4, 0≤a5≤0.1, 0≤b5≤0.1, 0≤c5≤0.1, 0≤d5≤0.1, and / or

[0257] The general formula for the composition of the third kernel includes Li m6 A6 a6 Fe x6 Mn y6 M6 b6 P z6 Q6 c6 O n6 N6 d6 ,

[0258] 0.8≤m6≤1.2, x6≥0, y6≥0, 0.9≤x6+y6≤1, 0.95≤z6≤1.1, 3.5≤n6≤4, 0≤a6≤0.1, 0≤b6≤0.1, 0≤c6≤0.1, 0≤d6≤0.1

[0259] Among them, A4, A5, and A6 each independently include one or more of Al, Na, K, and Mg; M4, M5, and M6 each independently include one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q4, Q5, and Q6 each independently include one or more of B, S, Si, and N; and N4, N5, and N6 each independently include one or more of S, F, Cl, and Br.

[0260] In some implementations, m4, m5 and m6 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 consisting of any two of the above values.

[0261] In some implementations, x4+y4, x5+y5, and x6+y6 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.

[0262] In some implementations, z4, z5, or z6 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.

[0263] In some implementations, n4, n5, and n6 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.

[0264] In some implementations, a4, b4, c4, d4, a5, b5, c5, d5, a6, b6, c6, and d6 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.

[0265] [Positive electrode plate]

[0266] 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.

[0267] 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. In some embodiments, the positive electrode film layer also includes a binder and a conductive agent.

[0268] In some embodiments, the ratio of the total mass of the positive electrode active material, the total mass of the binder, and the total mass of the conductive agent in the positive electrode film layer is (92-99):(0.5-3):(0.5-3).

[0269] In some embodiments, the coating weight on one side of the positive electrode is 300 mg / 1540 mm. 2 -580mg / 1540mm 2 .

[0270] The single-sided coating weight of the positive electrode sheet can be tested using methods known in the art. As an example, the battery is fully discharged, the positive electrode sheet is removed, residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and a cutting area of ​​1540 mm² is obtained. 2 If a small circular piece weighs M, and a current collector of the same area weighs N, then the weight of a single-sided coating is (MN) / 2.

[0271] In some embodiments, the coating weight on one side of the positive electrode is 300 mg / 1540 mm. 2 340mg / 1540mm 2 380mg / 1540mm 2 ,

[0272] 420mg / 1540mm 2 460mg / 1540mm 2 500mg / 1540mm 2 540mg / 1540mm 2 580mg / 1540mm 2 Or any value in between.

[0273] When the coating weight of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0274] In some embodiments, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0275] The compaction density of the positive electrode sheet can be tested using methods known in the art. As an example, a positive electrode sheet test sample with area S is weighed using an electronic balance, and the weight is denoted as W. The thickness T of the positive electrode sheet is measured using a micrometer. Then, the compaction density of the positive electrode sheet is PD = W / (T × S).

[0276] 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.

[0277] When the compaction density of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0278] In some implementations, as an example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0279] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, conductive polymers, metal powders, and carbon nanofibers.

[0280] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0281] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymer substrate may be at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0282] 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.

[0283] In some implementations, a secondary battery typically includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0284] [Negative electrode plate]

[0285] 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.

[0286] 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.

[0287] 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.).

[0288] 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.

[0289] 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).

[0290] 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.

[0291] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0292] 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.

[0293] [Electrolytes]

[0294] 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.

[0295] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0296] 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.

[0297] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0298] 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.

[0299] [Isolation membrane]

[0300] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0301] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0302] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0303] 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.

[0304] 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.

[0305] 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 3 shows a square-structured secondary battery 5 as an example.

[0306] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0307] 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.

[0308] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, 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 arbitrary way. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0309] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0310] 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.

[0311] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, 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 body 2 and a lower body 3, with the upper body 2 covering the lower body 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.

[0312] [Electrical appliances]

[0313] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0314] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0315] Figure 8 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.

[0316] 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.

[0317] Example

[0318] 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.

[0319] I. Preparation Method

[0320] Example 1

[0321] (1) Preparation of positive electrode active material

[0322] Material A was purchased from Guangdong Bangpu Recycling Technology Co., Ltd., model M3-1A. The molar ratio of manganese to iron is 0.05:9.95. Material A mainly consists of particles with a primary diameter of less than or equal to 180 nm and greater than or equal to 50 nm. The presence of particles with a diameter greater than 180 nm cannot be ruled out. The primary average particle size of Material A is 140 nm.

[0323] Material B was purchased from Guangdong Bangpu Recycling Technology Co., Ltd., model M3-1B. The molar ratio of manganese to iron is 6:4. Material B mainly consists of particles with a primary particle size greater than 180nm and less than 900nm. It is possible that there are particles with a primary particle size less than or equal to 180nm and a primary particle size greater than or equal to 900nm. The primary average particle size of Material B is 420nm.

[0324] Material C was purchased from Guangdong Bangpu Recycling Technology Co., Ltd., model M3-1C. The molar ratio of manganese to iron is 2.4:7.6. Material C mainly consists of particles with a primary particle size greater than or equal to 900 nm and less than or equal to 5 μm. The presence of particles with a primary particle size less than 900 nm cannot be ruled out. The primary average particle size of material C is 1200 nm.

[0325] (2) Preparation of positive electrode sheet

[0326] Materials A, B, and C are mixed in a mass ratio of 15:75:10 to obtain a positive electrode active material. The above-mentioned mixed positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride are mixed in 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.

[0327] 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 obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 2.45 g / cm³. 3 .

[0328] (3) Preparation of negative electrode sheet:

[0329] 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.

[0330] (4) Battery fabrication:

[0331] 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.

[0332] Example 2

[0333] The difference between Example 2 and Example 1 is that material C is not present, and the mass ratio of material A to material B is 15:85.

[0334] Examples 3-7

[0335] The difference between Examples 3-7 and Example 1 lies in the different manganese-iron molar ratio of material A and / or the different mass ratios of materials A, B, and C, as shown in the table below:

[0336] Examples 8-11

[0337] The difference between Examples 8-11 and Example 1 is that the molar ratio of manganese to iron in material B is different, as shown in the table below:

[0338] Examples 12-16

[0339] The difference between Examples 12-16 and Example 1 lies in the different manganese-iron molar ratio of material C, as shown in the table below:

[0340] Examples 17-19

[0341] The difference between Examples 17-19 and Example 1 is that the mass ratio of materials A, B, and C was adjusted. Specifically, in Example 17, the mass ratio of materials A, B, and C was 10:80:10; in Example 18, the mass ratio of materials A, B, and C was 15:35:50; and in Example 19, the mass ratio of materials A, B, and C was 0:20:80.

[0342] Comparative Example 1

[0343] The difference between Comparative Example 1 and Example 1 is that the molar ratio of manganese to iron in materials A, B, and C is 6:4, as shown in the table below:

[0344] Comparative Example 2

[0345] The difference between Comparative Example 2 and Example 1 is that the molar ratio of manganese to iron in material A is different. Specifically, material A in Comparative Example 2 was purchased from Guangdong Bangpu Recycling Technology Co., Ltd., with the product number M3-7A. The molar ratio of manganese to iron in material A is 8:2, and the average particle size is 140nm.

[0346] II. Performance Testing

[0347] 1) Capacity

[0348] (1) Place the battery in a 40℃ oven and let it stand for 2 hours until the battery temperature is maintained at 40℃; (2) Discharge the battery at a constant current of 1 / 3C to 2.0V; (3) Pause for 5 minutes; (4) Charge the battery at a constant current of 1 / 3C to 4.1V, and then charge it at a constant voltage of 4.1V until the cutoff current is 0.05C; (5) Pause for 5 minutes; (6) Discharge the battery at a constant current of 1 / 3C to 2.0V. This step is the actual cell test capacity C. Disassemble the battery to obtain a positive electrode sheet with a total area of ​​S1. Cut the positive electrode sheet to obtain a positive electrode sheet with an area of ​​S2. After peeling the positive electrode film layer on the positive electrode sheet from the current collector, solvent it in acetone, wash the residual solvent, binder and dispersant thoroughly, filter and dry it to obtain powder. Weigh the powder as M2. Then the total mass M1 of the positive electrode active material of the battery is approximately: M2*(S1 / S2). By combining the mass of the positive electrode active material, the specific capacity of the positive electrode active material can be calculated. Specific capacity = discharge capacity of the battery C / mass of positive electrode active material M1.

[0349] 2) Storage performance

[0350] Place the battery in a 40℃ oven and let it stand for 2 hours to maintain the battery temperature at 40℃. Then, discharge the battery at a constant current of 1 / 3C to 2.0V; pause for 5 minutes; charge the battery at a constant current of 1 / 3C to 4.1V, then charge it at a constant voltage of 4.1V until the cutoff current is 0.05C; pause for 5 minutes; and then discharge the battery at a constant current of 1 / 3C to 2.0V. This constitutes one charge-discharge cycle. Record the discharge capacity C1 of the first cycle. Then, fully charge the battery and place it in a 60℃ environment. Periodically remove the battery and test its remaining capacity at 40℃ until the discharge capacity of the secondary battery decays to 80%. Record the storage time at this point.

[0351] 3) Test method for volumetric energy density

[0352] The specific testing procedure is briefly described as follows: (1) Place the battery in a 40℃ oven environment and let it stand for 2 hours until the battery temperature is maintained at 40℃; (2) Discharge at 1 / 3C constant current to 2.0V; (3) Pause for 5 minutes; (4) Charge at 1 / 3C constant current to 4.1V, then charge at 4.1V constant voltage until the cutoff current is 0.05C; (5) Pause for 5 minutes; (6) Discharge at 1 / 3C constant current to 2.0V. Record the total discharge energy of the battery cell as E0, and the unit of total discharge energy is Wh.

[0353] 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).

[0354] 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.

[0355] 4) Determination of specific surface area of ​​lithium-containing transition metal phosphate particles

[0356] The active material film layer of the positive electrode sheet is peeled off, dissolved in acetone, thoroughly washed with acetone to remove the binder, and dried to obtain powder for specific surface area characterization. The test can be performed according to GB / T 19587-2017 using the gas adsorption method. The obtained powder is placed in a sample tube, which is then 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 monolayer adsorption amount of the sample is calculated, thus obtaining the specific surface area of ​​the lithium transition metal phosphate particles.

[0357] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0358] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1 and 2.

[0359] Table 2 Performance parameters of positive electrode active materials and secondary batteries

[0360] As can be seen from Examples 1-19, when a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive and negative electrodes, wherein the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector; the positive electrode film layer includes lithium transition metal phosphate particles with different manganese-iron molar ratios, and based on the total molar number of Mn in the lithium transition metal phosphate particles, the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 12% and greater than or equal to 0%, the battery has both good storage performance and powder compaction density.

[0361] As can be seen from Examples 1-19 and Comparative Examples 1 and 2, the positive electrode film layer includes lithium transition metal phosphate particles with different manganese-iron molar ratios. Based on the total molar number of Mn in the lithium transition metal phosphate particles, when the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 12%, the battery has excellent storage performance and also has good volumetric energy density.

[0362] A comparison of Examples 1, 3-4, 7, and 5-6 shows that, based on the total molar number of Mn in lithium transition metal phosphate particles, when the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of 180 nm or less and 50 nm or greater is less than or equal to 8%, the battery's storage performance is further improved. Furthermore, a comparison of Examples 1, 3, 7, and 4 shows that when the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of 180 nm or less and 50 nm or greater is less than or equal to 6%, the battery's storage performance is even better. A comparison of Examples 1 and 7 shows that when the molar percentage of Mn in lithium transition metal phosphate particles with a primary particle size of 180 nm or less and 50 nm or greater is greater than 0.2%, the metal battery has a better volumetric energy density.

[0363] As can be seen from the comparison between Examples 1, 13-16 and Example 12, when the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 1, and the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 6:4, the battery has better storage performance, specific capacity and volumetric energy density.

[0364] As can be seen from the comparison between Examples 1 and 14-16 and Examples 12 and 13, when the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.8, and the average manganese-iron molar ratio of the P2 segment particles is less than or equal to 5:5, it is beneficial to further improve the specific capacity of the positive electrode active material, and the battery has both good volumetric energy density and storage performance.

[0365] As can be seen from the comparison of Examples 1, 15-16 and Examples 12-14, when the ratio of the average molar content of Mn in the P2 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.5, it is beneficial to further improve the specific capacity and storage performance of the positive electrode active material, while the battery also has a better volumetric energy density.

[0366] As can be seen from Examples 1 and 3-7, when the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 1, and the average manganese-iron molar ratio of the P1 segment phosphate particles is less than or equal to 6:4, the battery has better storage performance and volumetric energy density.

[0367] As can be seen from the comparison between Examples 1, 3-5, 7 and Example 6, when the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.8, and the average manganese-iron molar ratio of the P1 segment particles is less than or equal to 4:6, it is beneficial to further improve the specific capacity and storage performance of the positive electrode active material, and the battery also has a better volumetric energy density.

[0368] As can be seen from the comparison of Examples 1, 3-4, 7 and Examples 5-6, when the ratio of the average molar content of Mn in the P1 segment particles to the average molar content of Mn in the M segment particles is less than or equal to 0.5, and the average manganese-iron molar ratio of the P1 segment phosphate particles is less than or equal to 2:8, it is beneficial to further improve the specific capacity and storage performance of the positive electrode active material, and the battery also has a better volumetric energy density.

[0369] As can be seen from the comparison between Examples 1, 9-11 and Example 8, when the average manganese-iron molar ratio of the M-segment particles is greater than or equal to 4:6 and less than or equal to 9:1, it is beneficial to improve the volumetric energy density of the secondary battery and also has good storage performance.

[0370] As can be seen from the comparison between Examples 1, 10-11 and Examples 8-9, when the average manganese-iron molar ratio of the M-segment particles is greater than or equal to 5:5 and less than or equal to 9:1, it is beneficial to further improve the volumetric energy density of the secondary battery, while also having good storage performance.

[0371] As can be seen from Examples 1-19, when the average manganese-iron molar ratio of phosphate particles is greater than or equal to 2:8 and less than or equal to 9:1, the battery has improved storage performance and better volumetric energy density.

[0372] As can be seen from Examples 1-19, when the area ratio of the P1 segment particles is 0%-30%, the area ratio of the M segment particles is 20%-85%, and the area ratio of the P2 segment particles is 0%-80%, and the area ratio of the P1 segment particles is not simultaneously 0%, based on the total area of ​​the lithium transition metal phosphate particles, the battery has improved storage performance and better volumetric energy density.

[0373] As can be seen from the comparison of Examples 1, 3-18 and Examples 2, 19, adding P1 segment particles and / or P2 segment particles to the positive electrode sheet of this application is beneficial to improving the compaction density of the positive electrode sheet.

[0374] 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 secondary battery characterized by comprising: The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector; The positive electrode film layer comprises lithium-containing transition metal phosphate particles with different molar ratios of manganese to iron, the molar proportion of manganese in lithium-containing transition metal phosphate particles with a primary particle size less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 12% based on the total number of moles of Mn in the lithium-containing transition metal phosphate particles.

2. The secondary battery according to claim 1, characterized by The molar proportion of manganese in lithium-containing transition metal phosphate particles with a primary particle size less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 8% based on the total number of moles of Mn in the lithium-containing transition metal phosphate particles.

3. The secondary battery according to claim 1 or 2, characterized by The molar proportion of manganese in lithium-containing transition metal phosphate particles with a primary particle size less than or equal to 180 nm and greater than or equal to 50 nm is less than or equal to 6% based on the total number of moles of Mn in the lithium-containing transition metal phosphate particles.

4. The secondary battery according to any one of claims 1 to 3, characterized by, The molar proportion of manganese in lithium-containing transition metal phosphate particles with a primary particle size less than or equal to 180 nm and greater than or equal to 50 nm is greater than or equal to 0.02% based on the total number of moles of Mn in the lithium-containing transition metal phosphate particles.

5. The secondary battery according to any one of claims 1 to 4, characterized by The molar proportion of manganese in lithium-containing transition metal phosphate particles with a primary particle size less than or equal to 180 nm and greater than or equal to 50 nm is greater than or equal to 0.2% based on the total number of moles of Mn in the lithium-containing transition metal phosphate particles.

6. The secondary battery according to any one of claims 1 to 5, characterized by The lithium-containing transition metal phosphate particles comprise P1 section particles, M section particles and P2 section particles, the primary particle size of the P1 section particles is less than or equal to 180 nm and greater than or equal to 50 nm, the primary particle size of the M section particles is greater than 180 nm and less than 900 nm, and the primary particle size of the P2 section particles is greater than or equal to 900 nm and less than or equal to 5 μm; wherein the ratio of the average value of the molar content of Mn in the P2 section particles to the average value of the molar content of Mn in the M section particles is less than or equal to 1; and / or the ratio of the average value of the molar content of Mn in the P1 section particles to the average value of the molar content of Mn in the M section particles is less than or equal to 1; and the ratio of the average value of the molar content of Mn in the P2 section particles to the average value of the molar content of Mn in the M section particles and the ratio of the average value of the molar content of Mn in the P1 section particles to the average value of the molar content of Mn in the M section particles are not both 1.

7. The secondary battery according to claim 6, characterized by The ratio of the average value of the molar content of Mn in the P2 section particles to the average value of the molar content of Mn in the M section particles is less than or equal to 0.8 and greater than or equal to 0.

8. The secondary battery according to any one of claims 6 or 7, characterized by, The ratio of the average value of the molar content of Mn in the P2 section particles to the average value of the molar content of Mn in the M section particles is less than or equal to 0.

5.

9. The secondary battery according to any one of claims 6 to 8, characterized by, The ratio of the average value of the molar content of Mn in the P2 section particles to the average value of the molar content of Mn in the M section particles is greater than or equal to 0.0003.

10. The secondary battery according to any one of claims 6 to 9, characterized by The ratio of the average value of the molar content of Mn in the P2 section particles to the average value of the molar content of Mn in the M section particles is greater than or equal to 0.

002.

11. The secondary battery according to any one of claims 6 to 10, characterized by The ratio of the average value of the molar content of Mn in the P1 section particles to the average value of the molar content of Mn in the M section particles is less than or equal to 0.8, greater than or equal to 0.

12. The secondary battery according to any one of claims 6 to 11, characterized by The ratio of the average value of the molar content of Mn in the P1 section particles to the average value of the molar content of Mn in the M section particles is less than or equal to 0.

4.

13. The secondary battery according to any one of claims 6 to 12, characterized by The ratio of the average value of the molar content of Mn in the P1 section particles to the average value of the molar content of Mn in the M section particles is greater than or equal to 0.0003.

14. The secondary battery according to any one of claims 6 to 13, characterized by The ratio of the average value of the molar content of Mn in the P1 section particles to the average value of the molar content of Mn in the M section particles is greater than or equal to 0.

002.

15. The secondary battery according to any one of claims 6 to 14, characterized by The average value of the molar ratio of manganese to iron in the P1 section particles is less than or equal to 6:4, greater than or equal to 0.

16. The secondary battery according to any one of claims 6 to 15, characterized by The average value of the molar ratio of manganese to iron in the P1 section particles is less than or equal to 4:6, and optionally, the average value of the molar ratio of manganese to iron in the P1 section particles is less than or equal to 2:

8.

17. The secondary battery according to any one of claims 6 to 16, characterized by The average value of the molar ratio of manganese to iron in the P1 section particles is greater than or equal to 0.02:9.

98.

18. The secondary battery according to any one of claims 6 to 17, characterized by, The average value of the molar ratio of manganese to iron in the M section particles is greater than or equal to 4:6, less than or equal to 9:

1.

19. The secondary battery according to any one of claims 6 to 18, characterized by The average value of the molar ratio of manganese to iron in the M section particles is greater than or equal to 5:5, less than or equal to 9:

1.

20. The secondary battery according to any one of claims 6 to 19, characterized by The average value of the molar ratio of manganese to iron in the P2 section particles is less than or equal to 6:4, greater than or equal to 0, and optionally, the average value of the molar ratio of manganese to iron in the P2 section particles is less than or equal to 5:5, and more optionally, the average value of the molar ratio of manganese to iron in the P2 section particles is less than or equal to 3:

7.

21. The secondary battery according to any one of claims 6 to 20, characterized by The average value of the molar ratio of manganese to iron in the P2 section particles is greater than or equal to 0.2:9.

8.

22. The secondary battery according to any one of claims 6 to 21, characterized by The average value of the molar ratio of manganese to iron in the P2 section particles is greater than or equal to 1:

9.

23. The secondary battery according to any one of claims 1 to 22, characterized by The average value of the molar ratio of manganese to iron in the lithium-containing transition metal phosphate particles is greater than or equal to 2:8, less than or equal to 9:

1.

24. The secondary battery according to any one of claims 1 to 23, characterized by, The average value of the molar ratio of manganese to iron in the lithium-containing transition metal phosphate particles is greater than or equal to 2:8, less than or equal to 6:

4.

25. The secondary battery according to any one of claims 6 to 24, characterized by The area percentage of the P1 section particles based on the total area of the lithium-containing transition metal phosphate particles is greater than 0%, less than or equal to 30%; and / or, The area percentage of the M section particles based on the total area of the lithium-containing transition metal phosphate particles is greater than or equal to 20%, less than 100%; and / or, The area percentage of the P2 section particles based on the total area of the lithium-containing transition metal phosphate particles is greater than or equal to 0%, less than or equal to 80%.

26. The secondary battery according to any one of claims 6 to 25, characterized by The area percentage of the P1 section particles based on the total area of the lithium-containing transition metal phosphate particles is greater than or equal to 5%, less than or equal to 15%.

27. The secondary battery according to any one of claims 6 to 26, characterized by The area percentage of the M section particles based on the total area of the lithium-containing transition metal phosphate particles is greater than or equal to 40%, less than or equal to 85%.

28. The secondary battery according to any one of claims 6 to 27, characterized by, The area percentage of the P2 section particles based on the total area of the lithium-containing transition metal phosphate particles is 5%-40%.

29. The secondary battery according to any one of claims 6 to 28, characterized by, The P1 segment particles have the molecular formula Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 wherein A1 comprises one or more of Al, Na, K, Mg, M1 comprises one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1 comprises one or more of B, S, Si, N, N1 comprises one or more of S, F, Cl, Br, 0.8≤m1≤1.2, x1≥0, y1≥0, 0.9≤x1+y1≤1, 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1; and / or The M segment particles have the formula Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 wherein A2 comprises one or more of Al, Na, K, Mg, M2 comprises one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q2 comprises one or more of B, S, Si, N, N2 comprises one or more of S, F, Cl, Br, 0.8 < m2 < 1.2, x2 > 0, y2 > 0, 0.9 < x2 + y2 < 1, 0.95 < z2 < 1, 3.5 < n2 < 4, 0 < a2 < 0.1, 0 < b2 < 0.1, 0 < c2 < 0.1, 0 < d2 < 0.1; and / or, The P2 segment particles have the formula Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N2 d3 wherein A3 comprises one or more of Al, Na, K, Mg, M3 comprises one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q3 comprises one or more of B, S, Si, N, N3 comprises one or more of S, F, Cl, Br, 0.8 < m3 < 1.2, x3 > 0, y3 > 0, 0.9 < x3 + y3 < 1, 0.95 < z3 < 1, 3.5 < n3 < 4, 0 < a3 < 0.1, 0 < b3 < 0.1, 0 < c3 < 0.1, 0 < d3 < 0.

1.

30. The secondary battery according to any one of claims 1 to 29, characterized by, The positive electrode film layer includes a positive electrode active material, the positive electrode active material including the lithium-containing transition metal phosphate particles, the positive electrode active material having a powder compaction density at 29400 N pressure greater than or equal to 2.3 g / cm 3 and less than or equal to 2.65 g / cm 3 .

31. The secondary battery according to any one of claims 1 to 30, characterized by The gram capacity of the positive electrode active material at 40°C and a discharge rate of 1 / 3C is greater than or equal to 134mAh / g, less than or equal to 150mAh / g.

32. The secondary battery according to any one of claims 1 to 31, characterized by The positive electrode film layer further comprises a binder and a conductive agent; optionally, in the positive electrode film layer, the ratio of the total mass of the positive electrode active material, the total mass of the binder, and the total mass of the conductive agent is (92-99):(0.5-3):(0.5-3).

33. The secondary battery according to any one of claims 1 to 32, characterized by, The single-side coating weight of the positive electrode sheet is 300 mg / 1540 mm 2 - 580 mg / 1540 mm 2 .

34. The secondary battery according to any one of claims 1 to 33, characterized by, The compacted density of the positive electrode plate is 2.25 g / cm 3 - 2.75 g / cm 3 .

35. An electrical device, comprising: The power-using device comprises the secondary battery of any one of claims 1 to 34.

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